JP2018063920A - Negative electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery arranged by use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide means in a nonaqueous electrolyte secondary battery, which can achieve adequate charge and discharge cycle characteristics while retaining a high capacity (especially, a negative electrode for a nonaqueous electrolyte secondary battery).SOLUTION: The invention is achieved by a negative electrode for a nonaqueous electrolyte secondary battery, which comprises a current collector; and a negative electrode active material layer disposed on a surface of the current collector and including a negative electrode active material. In the negative electrode, the negative electrode active material layer includes a negative electrode active material represented by the following formula (1): α(Si material)+β(carbon material)(where the Si material comprises a Si-containing alloy, α and β represent mass percentages of respective components in the negative electrode active material layer, 80≤α+β≤98, 0.1≤α≤40, and 58≤β≤97.9). When at an arbitrary location selected in a plane of the negative electrode active material layer, a cross section of the negative electrode active material layer in a thickness direction of the electrode is divided into three equal parts, an area of the Si material in an area of the equal part increases by 1-12% from one equal part to another, from the current collector side toward a surface opposed to a positive electrode.SELECTED DRAWING: None

Description

  The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the same. The negative electrode for a non-aqueous electrolyte secondary battery and the non-aqueous electrolyte secondary battery using the same according to the present invention include, for example, an electric vehicle (EV), a fuel cell vehicle (FCV), an ethanol FCV, and a plug-in that are next-generation eco cars. It is used as a driving power source or auxiliary power source for motors of vehicles such as FCV, plug-in hybrid vehicle (PHV), hybrid electric vehicle (HEV), plug-in hybrid electric vehicle (PHEV).

  In recent years, it has been required to reduce the amount of carbon dioxide in order to cope with global warming. Therefore, non-aqueous electrolyte secondary batteries with a low environmental load are being used not only for portable devices but also for power supply devices for electric vehicles such as EV, FCV, ethanol FCV, plug-in FCV, PHV, HEV, and PHEV. . A lithium ion secondary battery directed to application to an electric vehicle is required to have a large capacity and a large area.

  In recent years, it has been required to reduce the amount of carbon dioxide in order to cope with global warming. Thus, non-aqueous electrolyte secondary batteries with a low environmental load are being used not only for portable devices, but also for power supply devices for electric vehicles such as hybrid vehicles (HEV), electric vehicles (EV), and fuel cell vehicles. . Lithium ion secondary batteries intended for application to electric vehicles are required to have a large capacity (high capacity) and a large area.

Conventionally, carbon materials such as graphite, which are advantageous in terms of charge / discharge cycle life and cost, have been used as negative electrode active materials for negative electrodes of lithium ion secondary batteries. However, in a negative electrode active material using a carbon material such as graphite, charging and discharging are performed by occlusion / release of lithium ions into a graphite crystal. Therefore, a theoretical capacity of 372 mAh / g or more obtained from LiC ₆ which is the maximum lithium introduction compound There is a disadvantage that the charge / discharge capacity cannot be obtained. For this reason, it is difficult to obtain a capacity and an energy density that satisfy a practical level for vehicle use only with a negative electrode active material using a carbon material such as graphite.

In contrast, a battery using a material that is alloyed with Li as a negative electrode active material has higher energy density than a battery using a carbon material such as conventional graphite, and thus is expected as a negative electrode active material for vehicle applications. Has been. For example, the Si material occludes and releases _3.75 mol of lithium ions per mol in charge and discharge, and has a theoretical capacity of 3600 mAh / g in Li ₁₅ Si ₄ (= Li _3.75 Si).

  However, a lithium ion secondary battery using a material that is alloyed with Li for the negative electrode, particularly a Si material, has a large expansion and contraction in the negative electrode during charge and discharge. For example, when Li ions are occluded, the volume expansion is about 1.2 times in the case of graphite material, whereas in the case of Si material, when Si and Li are alloyed, the transition from the amorphous state to the crystalline state is about 4 times. Therefore, there is a problem in that the cycle life of the electrode is reduced. In the case of a negative electrode active material using Si material, the capacity and cycle durability are in a trade-off relationship, and there is a problem that it is difficult to improve the cycle durability while exhibiting a high capacity.

In order to solve these problems, for example, a negative electrode active material for a lithium ion secondary battery has been proposed, which includes an amorphous Si alloy having the formula: Si _x M _y Al _z . Here, x, y, and z in the formula represent atomic percentage values, and x + y + z = 100, x ≧ 55, y <22, z> 0, M represents Mn, Mo, Nb, W, Ta, Fe, Cu, It is a metal composed of at least one of Ti, V, Cr, Ni, Co, Zr, and Y. It is described that the negative electrode active material for a lithium ion secondary battery containing such an amorphous Si alloy exhibits a good cycle life in addition to a high capacity by minimizing the content of the metal M. Further, it is described that a good cycle life is exhibited by mixing a graphite material having a small expansion.

  However, it has been found that sufficient charge / discharge cycle characteristics cannot be achieved even by the technique using the above-described alloy containing Si (Si alloy), and also by the technique of mixing the Si alloy and the graphite material. That is, in the technique described above, due to the large volume change of the Si alloy material, the negative electrode active material layer containing the Si alloy also causes a large volume change, causing separation at the interface between the active material layer and the current collector, and There was a problem of losing the network and reducing cycle durability.

  In order to solve this problem, for example, a graphite layer having a small volume change is disposed near the current collector, and a composite material layer containing Si is disposed on the graphite layer, thereby peeling at the interface between the active material layer and the current collector. A suppression method has been proposed (see, for example, Patent Document 1).

JP 2002-358594 A Special table 2009-517850

  According to the study by the present inventors, it has been found that sufficient charge / discharge cycle characteristics cannot be achieved even by the technique described in Patent Document 2. In this method, peeling at the interface between the active material layer and the current collector can be suppressed, but the volume change of the graphite layer and the composite layer containing Si is greatly different. It was found that peeling occurred at the interface and the cycle durability was lowered.

  Accordingly, an object of the present invention is to provide means (particularly, a negative electrode for a non-aqueous electrolyte secondary battery) capable of achieving sufficient charge / discharge cycle characteristics while maintaining a high capacity in a non-aqueous electrolyte secondary battery. To do.

  In the negative electrode for a non-aqueous electrolyte secondary battery containing an Si material and a carbon material as active materials, the present inventors control the mixing ratio of the carbon material and the Si material, and the amount of the Si material from the current collector side to the positive electrode facing side. It has been found that the above-mentioned problem can be solved by using an active material layer in which the number of particles is gradually increased. This knowledge has led to the completion of the present invention.

  In the present invention, the Si material and the carbon material are included as the active material, and when the Si material content α and the carbon material content β (mass%) of the active material layer are set, the mixing ratio of the carbon material and the Si material is 80 ≦ α + β. The negative electrode is controlled to satisfy ≦ 98, 0.1 ≦ α ≦ 40, and 58 ≦ β ≦ 97.9. In addition to the above requirements, when the active material layer cross section is equally divided into three in the thickness direction, the area of the Si material within each divided area increases by 1% or more and 12% or less from the current collector side to the positive electrode facing surface side. A negative electrode is provided.

  In the present invention, by using an inclined electrode in which the mixing ratio of the Si material increases by an appropriate amount from the current collector side to the positive electrode facing surface side, since there is little Si material having a large volume change in the vicinity of the current collector, Damage and active material layer peeling are reduced. As a result, by maintaining the electronic conductivity in the charge / discharge process, the high capacity can be maintained, the discharge capacity maintenance rate can be greatly improved, and both capacity and cycle durability can be achieved.

1 is a schematic cross-sectional view showing a basic configuration of a lithium ion secondary battery that is not a flat type (stacked type) bipolar type, which is an embodiment of a nonaqueous electrolyte secondary battery according to the present invention. 1 is a perspective view illustrating an appearance of a flat lithium ion secondary battery that is a typical embodiment of a nonaqueous electrolyte secondary battery according to the present invention. FIG. 3 (a) shows the collection of a negative electrode active material slurry with an adjusted solid content ratio in order to manufacture a negative electrode having an inclined electrode structure in which the mixing ratio of the Si material is increased by an appropriate amount from the current collector side to the positive electrode facing surface side. It is sectional drawing which represented a mode that it apply | coated to the electric body typically. FIG. 3 (b) shows the coated surface formed in FIG. 3 (a) in order to manufacture a negative electrode having an inclined electrode structure in which the mixing ratio of the Si material increases by an appropriate amount from the current collector side to the positive electrode facing surface side. FIG. 6 is a cross-sectional view schematically showing a state facing (turned over). FIG. 3 (c) shows a negative electrode having an inclined electrode structure in which the mixing ratio of the Si material is increased by an appropriate amount from the current collector side to the positive electrode facing surface side. It is sectional drawing which represented typically a mode that the drying temperature was adjusted in the state (turned over) and dried at low temperature, and the negative electrode was formed. FIG. 3D schematically shows a negative electrode having an inclined electrode structure in which the mixing ratio of the Si material is increased by an appropriate amount from the current collector side to the positive electrode facing surface side, which is an embodiment of the negative electrode according to the present invention. It is sectional drawing. Fig.4 (a) is drawing which shows the reflected-electron image (measurement image) imaged with the electron microscope (SEM) of the negative electrode of the comparative example 1-1. FIG. 4B is a process obtained by converting the measurement image of FIG. 4A to gray scale by binarization processing and setting a threshold between the gray scale values of the Si material part and parts other than the Si material part. It is drawing which shows an image (the white site | part in a figure corresponds to Si material site | part). 4B shows the processed image, the negative electrode active material layer cross section is equally divided into three in the electrode thickness direction, and the three divided cross sections (divided sections) from the positive electrode facing surface (surface; separator) side. A, B, and C are attached in order toward the current collector side.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

According to one aspect of the present invention, a negative electrode for a non-aqueous electrolyte secondary battery having a current collector and a negative electrode active material layer including a negative electrode active material disposed on a surface of the current collector,
The negative electrode active material layer has the following formula (1)

(In the formula, the Si material is a material made of an alloy containing Si, α and β represent mass% of each component in the negative electrode active material layer, and 80 ≦ α + β ≦ 98, 0.1 ≦ α ≦ 40, 58 ≦ β ≦ 97.9)), and when an arbitrary place in the negative electrode surface is selected, the cross section of the negative electrode active material layer is equally divided into three in the electrode thickness direction. The non-aqueous electrolyte is characterized in that the area of the Si material in each divided area increases from 1% to 12% from the current collector side to the positive electrode facing surface (surface) side. A negative electrode for a secondary battery is provided. Moreover, according to one form of this invention, the positive electrode which has (a) the said negative electrode, (b) current collector, and the positive electrode active material layer containing the positive electrode active material arrange | positioned on the surface of the said current collector, And (c) a non-aqueous electrolyte secondary battery comprising a power generation element including a separator. In this embodiment, by having such a configuration, the effects of the above invention can be effectively expressed.

  The details of the reason why the above effect can be obtained by the negative electrode for a non-aqueous electrolyte secondary battery of the present invention and the non-aqueous electrolyte secondary battery using the same are unknown, but the following action mechanism (mechanism of action) is as follows. Can be considered. The following mechanism of action is speculated, and the present invention is not limited to the following mechanism of action.

  In the negative electrode of this embodiment, a high capacity can be maintained and sufficient charge / discharge cycle characteristics can be exhibited by using an inclined electrode in which the mixing ratio of the Si material is increased by an appropriate amount from the current collector to the positive electrode facing side. As a result, both capacity and cycle durability can be achieved. The mechanism of its action is not clear, but the tilted electrode of this embodiment is not tilted (the Si material mixing ratio does not increase or decrease from the current collector to the side facing the positive electrode) compared to an electrode (existing normal electrode). Thus, the structure (structure) is small in the amount of Si alloy material having a large volume change near the current collector. As a result, damage to the current collector and separation of the active material layer are reduced, and by maintaining electronic conductivity during the charge / discharge process, the discharge capacity maintenance rate can be significantly improved while maintaining high capacity. It is done. In contrast, an inclined electrode (reverse inclined electrode) in which the mixing ratio of the Si alloy decreases from the current collector to the positive electrode facing side has a configuration (structure) with a large volume of Si alloy material having a large volume change near the current collector. . Therefore, it is considered that the active material layer is peeled off or the current collector is deformed in the vicinity of the current collector, the active material is largely removed, and the cycle durability is lowered. In addition, in an inclined electrode (inclined excessive electrode) in which the mixing ratio of the Si material exceeds 12% from the current collector to the positive electrode facing side, the increase rate of the mixing ratio of the Si material is too high (structure). Therefore, since the volume change rate in each block divided into three in the electrode thickness direction is too large, separation occurs between the blocks (especially, near the boundary between regions where the increase rate is greatly different), resulting in reduced cycle durability. it is conceivable that.

  Hereinafter, a basic configuration of a non-aqueous electrolyte secondary battery using the negative electrode for a non-aqueous electrolyte secondary battery according to the present invention will be described. In the present embodiment, a lithium ion secondary battery will be described as an example.

  First, in the lithium ion secondary battery of this embodiment, the voltage of the cell (single cell layer) is large, and high energy density and high output density can be achieved. Therefore, the lithium ion secondary battery of the present embodiment is excellent as a vehicle driving power source or an auxiliary power source. As a result, it can be suitably used as a lithium ion secondary battery for a vehicle driving power source or the like. In addition to this, the present invention can be sufficiently applied to lithium ion secondary batteries for portable devices such as mobile phones.

  When the lithium ion secondary battery is distinguished by its form / structure, it can be applied to any conventionally known form / structure such as a stacked (flat) battery or a wound (cylindrical) battery. Is. By adopting a stacked (flat) battery structure, long-term reliability can be secured by a sealing technique such as simple thermocompression bonding, which is advantageous in terms of cost and workability.

  Moreover, when viewed in terms of electrical connection form (electrode structure) in a lithium ion secondary battery, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries. Is.

  When distinguished by the type of electrolyte layer in the lithium ion secondary battery, a solution electrolyte type battery using a solution electrolyte such as a nonaqueous electrolyte solution for the electrolyte layer, a polymer battery using a polymer electrolyte for the electrolyte layer, etc. It can be applied to any conventionally known electrolyte layer type. The polymer battery is further divided into a gel electrolyte type battery using a polymer gel electrolyte (also simply referred to as gel electrolyte) and a solid polymer (all solid) type battery using a polymer solid electrolyte (also simply referred to as polymer electrolyte). It is done.

  Therefore, in the following description, a non-bipolar (internal parallel connection type) lithium ion secondary battery will be described with reference to the drawings as an example of the lithium ion secondary battery of the present embodiment. However, the technical scope of the nonaqueous electrolyte secondary battery according to the present invention and the lithium ion secondary battery according to the present embodiment should not be limited to these.

<Overall battery structure>
FIG. 1 shows an overall structure of a flat (stacked) lithium ion secondary battery (hereinafter also simply referred to as “stacked battery”), which is a typical embodiment of the nonaqueous electrolyte secondary battery of the present invention. It is the cross-sectional schematic diagram which represented typically.

  As shown in FIG. 1, the stacked battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate sheet 29 that is an exterior body. . Here, the power generation element 21 includes a positive electrode in which the positive electrode active material layer 15 is disposed on both surfaces of the positive electrode current collector 12, an electrolyte layer (separator) 17, and a negative electrode active material layer 13 on both surfaces of the negative electrode current collector 11. It has the structure which laminated | stacked the formed negative electrode. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are laminated in this order so that one positive electrode active material layer 15 and the negative electrode active material layer 13 adjacent thereto face each other with the electrolyte layer 17 therebetween. .

  Thereby, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10 shown in FIG. 1 has a configuration in which a plurality of single battery layers 19 are stacked and electrically connected in parallel. Note that the negative electrode current collector 13 on the outermost layer located on both outermost layers of the power generation element 21 is provided with the negative electrode active material layer 13 only on one side, but the active material layer may be provided on both sides. . That is, instead of using a current collector dedicated to the outermost layer provided with an active material layer only on one side, a current collector having an active material layer on both sides may be used as it is as an outermost current collector. Further, by reversing the arrangement of the positive electrode and the negative electrode as compared with FIG. 1, the outermost positive electrode current collector is positioned on both outermost layers of the power generation element 21, and one side of the outermost positive electrode current collector or A positive electrode active material layer may be disposed on both sides.

  The positive electrode current collector 12 and the negative electrode current collector 11 are attached to the positive electrode current collector plate 27 and the negative electrode current collector plate 25 that are electrically connected to the respective electrodes (positive electrode and negative electrode), and are sandwiched between the end portions of the laminate sheet 29. Thus, it has a structure led out of the laminate sheet 29. The positive electrode current collector 27 and the negative electrode current collector 25 are ultrasonically welded to the positive electrode current collector 12 and the negative electrode current collector 11 of each electrode via a positive electrode lead and a negative electrode lead (not shown), respectively, as necessary. Or resistance welding or the like.

  Hereinafter, main components of the battery will be described.

<Active material layer>
The active material layers (13, 15) contain an active material, and further contain other additives as necessary.

[Positive electrode active material layer]
The positive electrode active material layer 15 includes a positive electrode active material. In this embodiment, the positive electrode active material is not particularly limited, but preferably includes a lithium nickel composite oxide or a spinel lithium manganese composite oxide, and more preferably includes a lithium nickel composite oxide. The ratio of the total amount of the lithium nickel composite oxide and the spinel lithium manganese composite oxide in the total amount of 100% by mass of the positive electrode active material contained in the positive electrode active material layer is preferably 50% by mass or more. Preferably it is 70 mass% or more, More preferably, it is 85 mass% or more, More preferably, it is 90 mass% or more, Most preferably, it is 95 mass% or more, Most preferably, it is 100 mass%.

(Lithium nickel composite oxide)
The composition of the lithium nickel composite oxide is not specifically limited as long as it is a composite oxide containing lithium and nickel. A typical example of a composite oxide containing lithium and nickel is lithium nickel composite oxide (LiNiO ₂ ). However, a composite oxide in which some of the nickel atoms of the lithium nickel composite oxide are substituted with other metal atoms is more preferable. As a preferable example, a lithium-nickel-manganese-cobalt composite oxide (hereinafter simply referred to as “NMC composite”) is preferable. (Also referred to as “oxide”) has a layered crystal structure in which a lithium atomic layer and a transition metal (Mn, Ni, and Co are arranged in order) are alternately stacked via an oxygen atomic layer. One Li atom is contained per atom, and the amount of Li that can be taken out is twice that of the spinel-type lithium manganese oxide, that is, the supply capacity is doubled, so that a high capacity can be obtained. In addition, since it has higher thermal stability than LiNiO ₂ , it is particularly advantageous among the nickel-based composite oxides used as the positive electrode active material.

  In the present specification, the NMC composite oxide includes a composite oxide in which a part of the transition metal element is substituted with another metal element. Other elements in that case include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu , Ag, Zn, etc., preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, more preferably Ti, Zr, P, Al, Mg, From the viewpoint of improving cycle characteristics, Ti, Zr, Al, Mg, and Cr are more preferable.

Since the NMC composite oxide has a high theoretical discharge capacity, it is preferable that the general formula (1): Li _a Ni _b Mn _c Co _d M _x O ₂ (where a, b, c, d, x Satisfies 0.9 ≦ a ≦ 1.2, 0 <b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3, and b + c + d = 1. And at least one element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr. Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Mn, d represents the atomic ratio of Co, and x represents the atomic ratio of M. Represents. From the viewpoint of cycle characteristics, it is preferable that 0.4 ≦ b ≦ 0.6 in the general formula (1). The composition of each element can be measured by, for example, inductively coupled plasma (ICP) emission spectrometry.

  In general, nickel (Ni), cobalt (Co), and manganese (Mn) are known to contribute to capacity and output characteristics from the viewpoint of improving the purity of materials and improving electronic conductivity. Ti or the like partially replaces the transition metal in the crystal lattice. From the viewpoint of cycle characteristics, it is preferable that a part of the transition element is substituted with another metal element, and it is particularly preferable that 0 <x ≦ 0.3 in the general formula (1). Since at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr is dissolved, the crystal structure is stabilized. It is considered that the battery capacity can be prevented from decreasing even if the above is repeated, and that excellent cycle characteristics can be realized.

  As a more preferable embodiment, in the general formula (1), b, c and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31, 0.19 ≦ d ≦ 0.26. It is preferable that it is excellent in balance between capacity and durability.

  Lithium nickel composite oxides such as NMC composite oxides can be prepared by selecting various known methods such as coprecipitation method and spray drying method. The coprecipitation method is preferably used because the complex oxide according to this embodiment is easy to prepare. Specifically, as a method for synthesizing the NMC composite oxide, for example, a nickel-cobalt-manganese composite oxide is manufactured by a coprecipitation method as in the method described in JP2011-105588A, and then nickel- It can be obtained by mixing and baking a cobalt-manganese composite oxide and a lithium compound. This will be specifically described below.

  A raw material compound of the composite oxide, for example, a Ni compound, a Mn compound, and a Co compound is dissolved in an appropriate solvent such as water so as to have a desired composition of the active material. Examples of the Ni compound, Mn compound, and Co compound include sulfates, nitrates, carbonates, acetates, oxalates, oxides, hydroxides, and halides of the metal elements. Specific examples of the Ni compound, Mn compound, and Co compound include, but are not limited to, nickel sulfate, cobalt sulfate, manganese sulfate, nickel acetate, cobalt acetate, and manganese acetate. In this process, as necessary, for example, Ti, Zr, Nb as a metal element that substitutes a part of the layered lithium metal composite oxide constituting the active material so as to have a desired active material composition. , W, P, Al, Mg, V, Ca, Sr, and a compound containing at least one metal element such as Cr may be further mixed.

  A coprecipitation reaction can be performed by a neutralization and precipitation reaction using the raw material compound and an alkaline solution. Thereby, the metal composite hydroxide and metal composite carbonate containing the metal contained in the said raw material compound are obtained. As the alkaline solution, for example, an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate, ammonia or the like can be used, but sodium hydroxide, sodium carbonate or a mixed solution thereof is preferably used for the neutralization reaction. . In addition, an aqueous ammonia solution or an ammonium salt is preferably used for the complex reaction.

  The addition amount of the alkaline solution used for the neutralization reaction may be an equivalent ratio of 1.0 with respect to the neutralized amount of all the metal salts contained, but it is preferable to add the alkali excess together for pH adjustment.

  As for the addition amount of the aqueous ammonia solution or ammonium salt used for the complex reaction, the ammonia concentration in the reaction solution is preferably added in the range of 0.01 to 2.00 mol / l. The pH of the reaction solution is preferably controlled in the range of 10.0 to 13.0. The reaction temperature is preferably 30 ° C. or higher, more preferably 30 to 60 ° C.

  The composite hydroxide obtained by the coprecipitation reaction is then preferably suction filtered, washed with water and dried. The particle size of the composite hydroxide can be controlled by adjusting the conditions (stirring time, alkali concentration, etc.) for carrying out the coprecipitation reaction, which is the secondary electrode of the positive electrode active material finally obtained. It affects the average particle size (D50) of the particles.

  Next, the nickel-cobalt-manganese composite hydroxide is mixed with a lithium compound and fired to obtain a lithium-nickel-manganese-cobalt composite oxide. Examples of the Li compound include lithium hydroxide or a hydrate thereof, lithium peroxide, lithium nitrate, and lithium carbonate.

  The firing process may be performed in one stage, but is preferably performed in two stages (temporary firing and main firing). A composite oxide can be obtained efficiently by two-stage firing. The pre-baking conditions are not particularly limited, and differ depending on the lithium raw material, so that it is difficult to uniquely define them. Here, the factors for controlling the average primary particle size and crystallite size are particularly important as the firing temperature and firing time during firing (temporary firing and main firing in the case of two stages). By adjusting based on the following tendency, the average primary particle diameter and crystallite diameter can be controlled. That is, when the firing time is lengthened, the average primary particle diameter and crystallite diameter increase. Further, when the firing temperature is increased, the average primary particle size and crystallite size are increased. In addition, it is preferable that a temperature increase rate is 1-20 degrees C / min from room temperature. The atmosphere is preferably in air or in an oxygen atmosphere. Here, in the case of synthesizing the NMC composite oxide using lithium carbonate as the Li raw material, the pre-baking temperature is preferably 500 to 900 ° C, more preferably 600 to 800 ° C, and further preferably 650. ~ 750 ° C. Furthermore, the pre-baking time is preferably 0.5 to 10 hours, and more preferably 4 to 6 hours. On the other hand, the conditions for the main firing are not particularly limited, but the rate of temperature rise is preferably from room temperature to 1 to 20 ° C./min. The atmosphere is preferably in air or in an oxygen atmosphere. In the case of synthesizing an NMC composite oxide using lithium carbonate as a Li raw material, the firing temperature is preferably 800 to 1200 ° C, more preferably 850 to 1100 ° C, and still more preferably 900 to 1050. ° C. Furthermore, pre-baking time becomes like this. Preferably it is 1 to 20 hours, More preferably, it is 8 to 12 hours.

  If necessary, when adding a trace amount of a metal element that replaces a part of the layered lithium metal composite oxide constituting the active material, as the method, a method of previously mixing with nickel, cobalt, manganate, Any means such as a method of adding nickel, cobalt and manganate simultaneously, a method of adding to the reaction solution during the reaction, a method of adding to the nickel-cobalt-manganese composite oxide together with the Li compound may be used.

  The lithium nickel composite oxide can be produced by appropriately adjusting reaction conditions such as pH of the reaction solution, reaction temperature, reaction concentration, addition rate, and stirring time.

(Spinel type lithium manganese oxide)
A spinel-based lithium manganese composite oxide is a composite oxide that typically has a composition of LiMn ₂ O ₄ and has a spinel structure and essentially contains lithium and manganese, and its specific configuration and manufacturing method For the above, conventionally known findings such as JP-A-2000-77071 can be appropriately referred.

  Of course, a positive electrode active material other than the above-described lithium nickel composite oxide or spinel lithium manganese composite oxide may be used. When two or more kinds of positive electrode active materials are used in combination, if the optimum particle size is different for expressing the unique effect of each active material, the optimum particle size for expressing each unique effect is determined. What is necessary is just to blend and use, and it is not necessary to make the particle diameter of all the active materials uniform.

  The average particle size of the positive electrode active material contained in the positive electrode active material layer 15 is not particularly limited, but is preferably 6 to 11 μm, more preferably 7 to 10 μm in terms of secondary particle size from the viewpoint of increasing the output. Moreover, the average particle diameter of a primary particle is 0.4-0.65 micrometer, More preferably, it is 0.45-0.55 micrometer. The “particle diameter” in the present specification means the maximum distance L among the distances between any two points on the particle outline. Moreover, as the value of “average particle diameter”, the average particle diameter of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). A value calculated as a value is adopted. As the secondary particle diameter (average particle diameter D50), a value obtained by a laser diffraction method may be used.

  Moreover, it is preferable that a positive electrode active material layer contains a binder and a conductive support agent other than the positive electrode active material mentioned above. Further, if necessary, it further contains other additives such as an electrolyte (polymer matrix, ion-conductive polymer, electrolyte solution, etc.) and a lithium salt for increasing the ion conductivity.

  In the positive electrode active material layer, the content of the positive electrode active material that can function as an active material is preferably 85 to 99.5% by mass.

(Binder)
Although it does not specifically limit as a binder used for a positive electrode active material layer, For example, the following materials are mentioned. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile, polyacrylonitrile, polyimide, polyamide, cellulose, carboxymethyl cellulose (CMC) and its salts, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR) ), Isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and hydrogenated product thereof, styrene / isoprene / styrene block copolymer and hydrogenated product thereof Thermoplastic polymers such as products, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (F P), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE) ), Fluororesin such as polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP) -TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene Fluorine rubber (VDF-PFP-TFE fluorine rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluorine rubber (VDF-PFMVE-TFE fluorine rubber), vinylidene fluoride-chlorotrifluoroethylene fluorine Examples thereof include vinylidene fluoride fluorine rubber such as rubber (VDF-CTFE fluorine rubber), epoxy resin, and the like. These binders may be used independently and may use 2 or more types together.

  The binder content in the positive electrode active material layer is preferably 1 to 10% by mass, and more preferably 1 to 8% by mass.

(Conductive aid)
The conductive assistant refers to an additive that is blended in order to improve the conductivity of the positive electrode active material layer or the negative electrode active material layer. Conductive aids include carbon blacks such as acetylene black, ketjen black, and furnace black, carbon powders such as channel black, thermal black, and graphite, and various carbon fibers such as vapor grown carbon fiber (VGCF). And carbon materials such as expanded graphite. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

  The content of the conductive additive in the positive electrode active material layer is preferably 1 to 10% by mass, more preferably 1 to 8% by mass. By defining the blending ratio (content) of the conductive assistant within the above range, the following effects are exhibited. That is, the electron conductivity can be sufficiently ensured without hindering the electrode reaction, the decrease in the energy density due to the decrease in the electrode density can be suppressed, and as a result, the energy density can be improved due to the increase in the electrode density. It is.

(Other ingredients)
Examples of the electrolyte salt (lithium salt) include Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _{3 and the} like.

  Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

  The compounding ratio of the components contained in the positive electrode active material layer is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries.

  The positive electrode (positive electrode active material layer) can be applied by any one of a kneading method, a sputtering method, a vapor deposition method, a CVD method, a PVD method, an ion plating method, and a thermal spraying method in addition to a method of applying (coating) a normal slurry. Can be formed.

[Negative electrode active material layer]
The negative electrode active material layer 13 has the following formula (1)

(In the formula, the Si material is a material made of an alloy containing Si (Si alloy), and α and β represent mass% of each component of the negative electrode active material in the negative electrode active material layer, and 80 ≦ α + β ≦ 98, 0.1 ≦ α ≦ 40, 58 ≦ β ≦ 97.9)) is included.

  That is, the negative electrode active material layer 13 essentially includes a Si alloy that is a Si material and a carbon material as a negative electrode active material. Hereinafter, these negative electrode active materials will be described in detail.

(Si alloy)
An alloy (Si alloy) containing Si, which is one kind of negative electrode active material, is not particularly limited as long as it is an alloy with another metal containing Si, and conventionally known knowledge can be appropriately referred to. Here, as preferred embodiments of the Si alloy, Si _x Ti _y Ge _za , Si _x Ti _y Zn _z A _a , Si _x Ti _y Sn _z A _a , Si _x Sn _y Al _z A _a , Si _x Sn _y V _z A _a , Si _x Sn _y C _z A _a , Si _x Zn _y V _z A _a , Si _x Zn _y Sn _z A _a , Si _x Zn _y Al _z A _a , Si _x Zn _y C _{zA a} , Si _x Al _y C _{z a a} and _{Si x Al y Nb z a a} ( wherein, a is unavoidable impurities. further, x, y, z, and a represent the value of mass%, 0 < x <100, 0 <y <100, 0 ≦ z <100, and 0 ≦ a <0.5, and x + y + z + a = 100) or the like (for example, Si—Ti alloy) or 3 For example, ternary alloys. By using these Si alloys as the negative electrode active material, by appropriately selecting a predetermined first additive element (binary alloy) and a predetermined second additive element (ternary alloy), it is possible to form an Li alloy. In this case, the cycle life can be improved by suppressing the amorphous-crystal phase transition. This also makes the capacity higher than that of a conventional negative electrode active material, for example, a carbon-based negative electrode active material.

(Average particle diameter of Si alloy (secondary particle diameter) D50)
The average particle diameter of Si alloy should just be comparable with the average particle diameter of the negative electrode active material contained in the existing negative electrode active material layer 13, and is not restrict | limited in particular. From the viewpoint of durability and high output, the average particle diameter (secondary particle diameter) D50 of the Si alloy is preferably in the range of 1 to 20 μm, more preferably 1 to 15 μm, and still more preferably 1 to 10 μm. . Preferably, the average particle diameter (secondary particle diameter) D90 of the Si alloy is in the range of 5 to 100 μm. Here, the value obtained by the laser diffraction method is used as the secondary particle diameter of the Si alloy. However, it is not limited at all to the above range, and it goes without saying that it may be outside the above range as long as the effects of the present embodiment can be effectively expressed. Further, the shape of the Si alloy is not particularly limited, and may be spherical, elliptical, cylindrical, polygonal, scaly, indeterminate, or the like. In the present embodiment, the D50 value is calculated based on the particle size distribution data calculated by a laser particle size distribution meter, and D50; median diameter, that is, an intermediate particle diameter is calculated. In the present embodiment, the laser particle size distribution meter is a laser diffraction / scattering particle size distribution measuring device (manufactured by HORIBA, Ltd., model: LA-920). A scattering type particle size distribution measuring apparatus can be used. The measurement method can be widely applied to other particles, for example, positive electrode active material particles, negative electrode active material particles (Si alloy powder, carbon material powder), conductive assistants, and the like.

(Support (coating) of carbon-based material on Si alloy surface)
In this embodiment, it is preferable that the Si alloy is carbon-coated. A negative electrode active material containing a Si alloy (hereinafter, also simply referred to as “carbon-supported Si alloy” or “carbon-coated Si alloy”) in which a Si alloy is carbon-coated and a carbon-based material is supported (coated) on the surface is used. Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries are excellent in that they have high cycle durability. Note that the carbon-based material used here is a carbon material that is not an active material because it cannot be repeatedly charged and discharged (conductive), that is, an active material that has low crystallinity that is unlikely to cause insertion or desorption of Li ions. (Conductive) carbon materials that do not fit the definition of

  In this specification, “support” or “coating” means that the carbon-based material is chemically or physically bonded to at least a part of the surface of the Si alloy. Whether or not the carbon-based material is supported (coated) on the surface of the Si alloy is observed in the carbon-supported Si alloy manufactured or collected (separated) from the electrode in a state where the carbon-based material adheres to the Si alloy particles. Can be confirmed. In this embodiment, the case where the coverage of the Si alloy particles with the carbon-based material is 15 mol% or more is assumed to be a state in which the carbon-based material is supported (coated) on the surface of the Si alloy. For this reason, the conventional negative electrode active material, conductive auxiliary agent (carbon-based material; this conductive auxiliary agent usually does not correspond to the active material (conductive) carbon material is used) and the binder. Depending on simple mixing, the conductive auxiliary agent is not supported on the negative electrode active material or is supported only when the coverage of the Si alloy with the carbon-based material is less than 15 mol%. In addition, the carrying | support (coating) state to the Si alloy surface of a carbonaceous material can be confirmed easily by well-known means, such as a scanning electron microscope (SEM).

  The reason why the cycle durability of a lithium ion secondary battery or the like using a carbon-supported Si alloy in which the above Si alloy is carbon-coated is improved is unknown, but the following reason Conceivable.

As described above, the Si alloy, which is a Si material, has a greater expansion and contraction during charge / discharge than a carbon material (such as graphite), which is an active material. Deterioration of cycle durability is a problem due to (oxidation) and the like. Further, in the lithium ion secondary battery using the negative electrode having the amorphous alloy having the formula: Si _x M _y Al _z described in the “background art”, the amorphous alloy having the formula: Si _x M _y Al _z is used. However, the expansion and contraction cannot be sufficiently suppressed as in the case of the high purity Si active material. For this reason, the active material (particles) is refined due to expansion and contraction during charge and discharge, the specific surface area of the active material is increased, decomposition of the electrolyte is promoted, and side reactions are generated due to electrolyte depletion and electrolyte decomposition. An object is formed, which hinders conductivity.

  Moreover, since said amorphous alloy contains Si (semiconductor), sufficient electroconductivity is not ensured. For this reason, when the amorphous alloy is used as an active material, it is necessary to add a conductive additive. However, it is difficult to uniformly disperse the conventional conductive additive, and locally highly conductive. In many cases, the active material and the low active material are mixed. For these reasons, it has been difficult for conventional techniques to maintain high cycle characteristics.

  On the other hand, in the present embodiment, as the negative electrode active material, a carbon-rich carbon material and a Si alloy that is a Si material are used in combination, and further, the carbon-based material is supported (coated) on the Si alloy surface. The effect of this form can be expressed more notably. That is, the presence of the carbon-based material on the surface of the Si alloy can further suppress the reactivity between the surface of the Si alloy (particles) and the electrolytic solution. For this reason, it is possible to further suppress the decomposition reaction of the excess electrolyte and the accompanying generation of by-products. Further, unlike the conventional method in which only a conductive auxiliary agent is added, the carbon-based material having high conductivity exists on the surface of the Si alloy (particles), so that the conductivity of the Si alloy (particles) is ensured, and Si High conductivity can be imparted to the entire alloy. Thereby, for example, when applied to a lithium ion secondary battery, when Li ions are inserted, the effect of further promoting uniform charge depth of the Si alloy particles is brought about, and excessive deterioration of Li ions is inserted. Si alloy particles that are easy to be removed can be further eliminated.

  That is, when the carbon material and the above-mentioned carbon-supported Si alloy are used as the negative electrode active material, the carbon-based material, not the Si alloy particles, comes into contact with the electrolytic solution, so that the decomposition reaction of the electrolytic solution (particularly due to silicon) is further enhanced. The conductivity can be further improved by the presence of the carbon-based material on the outermost surface. Therefore, when the carbon material and the above-described carbon-supported Si alloy are used as the negative electrode active material, the cycle characteristics, and further, the initial capacity and the cycle characteristics can be further improved.

  In addition, the said action mechanism is based on estimation, and this form is not restrict | limited to the said action mechanism at all.

  As described above, in this embodiment, it is desirable that the carbon-based material is supported (coated) on the surface of the Si alloy (particles). Here, the coverage (support rate) of the Si alloy with the carbon-based material is not particularly limited as long as it is 15 mol% or more as described above. In consideration of a further improvement effect of cycle characteristics (cycle durability) and a further improvement effect of conductivity, the coverage of the Si alloy with the carbon-based material is preferably 50 to 400 mol%, more preferably. Is 100 to 400 mol%, and more preferably 250 to 400 mol%.

  In this specification, a value measured and calculated by the following method is adopted as the “coverage (support rate) of the Si alloy with the carbon-based material”. In the present specification, “the coverage ratio (support rate) (mol%) of a Si alloy with a carbon-based material” is also simply referred to as “carbon coverage (mol%)”.

<Measurement of Si alloy carbon coverage (support rate)>
The carbon coverage of the Si alloy on which the carbon-based material is supported is determined by measuring the molar ratio of silicon and the molar ratio of carbon using Auger electron spectroscopy under the following measurement conditions.

  Next, using the mole ratio of silicon and the mole ratio of carbon measured above, the mole ratio of carbon to the mole ratio of silicon is calculated according to the following formula, and the obtained value is the carbon coverage (mol%). And

  Here, the method for controlling the coverage (support rate) of the Si alloy with the carbon-based material within the above preferable range is not particularly limited. Specifically, after mixing the Si alloy and the carbon-based material in an appropriate ratio, the carbon-based material is chemically or physically bonded (supported) to the surface of the Si alloy by physical or chemical treatment. Can be used.

  In the above method, the mixing ratio of the Si alloy and the carbon-based material is not particularly limited. Specifically, when the total amount of the Si alloy and the carbon-based material is 100 parts by weight, the carbon-based material is preferably 1 to 25 parts by weight, more preferably 5 to 25 parts by weight. In particular, it is preferably mixed with the Si alloy at a ratio of 10 to 25 parts by weight. According to such a mixing ratio, the coverage (support rate) of the Si alloy with the carbon-based material can be easily controlled within the preferable range as described above. Further, according to such a mixing ratio, the carbon-based material can be uniformly supported (coated) on the surface of the Si alloy.

  The carbon-based material is not particularly limited, and a carbon-based material that is usually used as a conductive additive can be used. Specifically, acetylene black, furnace black, carbon black, channel black, graphite (pulverized to the same extent as the conductive additive, and the carbon material as the active material is clearly from the viewpoint of particle size. For example). Among these, from the viewpoint of supporting maintenance, the carbon-based material cannot be repeatedly charged and discharged as described above, and therefore, the conductive carbon material that does not correspond to the active material, that is, the insertion or desorption of Li ions hardly occurs or does not occur. A conductive carbon material having low crystallinity is preferable. Specifically, it is preferable to use acetylene black or carbon fiber. Further, the shape of the carbon-based material is not particularly limited, and may be in a particle form or a fiber form. From the viewpoint of easy loading, a particle form is preferable, and from a conductive point, a fiber form is preferable. The size of the carbon-based material is not particularly limited as long as it is finely divided to the same degree as the conductive additive and can be clearly distinguished from the carbon material as the active material from the viewpoint of the particle size. . For example, when the carbonaceous material is in the form of particles, the average particle size (secondary particle size) is preferably 10 to 200 nm, more preferably 20 to 150 nm. Moreover, when the said carbonaceous material is a fiber form, a diameter becomes like this. Preferably it is 20-500 nm, More preferably, it is 50-300 nm, Length is preferably 5-20 micrometers, More preferably, it is 8 ~ 15 μm. With such a size, the carbon-based material can be easily supported on the Si alloy surface. Moreover, if it is such a magnitude | size, the said carbonaceous material can carry | support uniformly on the Si alloy surface.

  In the above method, the physical or chemical treatment method for chemically or physically bonding (supporting) the carbon-based material to the Si alloy surface is not particularly limited. For example, a method of embedding at least a part of the carbon-based material in the Si alloy by shearing, a method of chemically bonding the Si alloy and a functional group on the surface of the carbon-based material, and the like can be given. More specifically, a mechanochemical method, a liquid phase method, a sintering method, a vapor deposition (CVD) method, and the like can be given.

  The physical or chemical treatment conditions for chemically or physically bonding (supporting) the carbon-based material to the Si alloy surface are not particularly limited, and can be appropriately selected depending on the method used. For example, when the mechanochemical method is used, the rotation speed (processing rotation speed) is preferably 3000 to 8000 rpm, more preferably 4000 to 7000 rpm. Further, the load power is preferably 200 to 400 W, more preferably 250 to 300 W. The treatment time is preferably 10 to 60 minutes, more preferably 20 to 50 minutes. Under such conditions, the carbon-based material can be supported (coated) on the surface of the Si alloy at the preferable coverage (supporting rate). Further, the carbon-based material can be uniformly supported on the surface of the Si alloy.

(Si alloy production method)
The method for producing the Si alloy according to the present embodiment is not particularly limited, and can be produced using various conventionally known production methods. Examples of the Si alloy production method include the following production methods, but are not limited thereto.

  First, a step of obtaining a mixed powder by mixing raw materials of Si alloy is performed. In this step, the raw material of the alloy is mixed in consideration of the composition of the obtained Si alloy. The form of the alloy is not particularly limited as long as the ratio of elements necessary for the Si alloy can be realized. For example, the element simple substance which comprises Si alloy can be mixed with the target ratio, the alloy which has the target element ratio, a solid solution, or an intermetallic compound can be used. Usually, raw materials in a powder state are mixed. Thereby, the mixed powder which consists of a raw material is obtained.

  Subsequently, an alloying process is performed on the mixed powder obtained above. Thereby, Si alloy which can be used as a negative electrode active material for nonaqueous electrolyte secondary batteries is obtained.

  Examples of alloying methods include a solid phase method, a liquid phase method, and a gas phase method. For example, a mechanical alloy method, an arc plasma melting method, a casting method, a gas atomizing method, a liquid quenching method, an ion beam sputtering method, a vacuum method, and the like. Examples include vapor deposition, plating, and gas phase chemical reaction. Especially, it is preferable to perform an alloying process using a mechanical alloy method. The alloying process is preferably performed by a mechanical alloy method because the phase state can be easily controlled. Further, before the alloying treatment, a step of melting the raw material and a step of rapidly cooling and solidifying the molten material may be included.

  By performing the alloying process described above, a structure composed of a parent phase / silicide phase can be obtained. In particular, when the alloying time is 12 hours or longer, a nonaqueous electrolyte secondary battery capable of exhibiting desired cycle durability can be obtained. The alloying treatment time is preferably 24 hours or more, more preferably 30 hours or more, still more preferably 36 hours or more, still more preferably 42 hours or more, and particularly preferably 48 hours. That's it. In addition, although the upper limit of the time for alloying process is not set in particular, it may usually be 72 hours or less. Moreover, in the case of the alloying process by the mechanical alloying method among the alloying processes mentioned above, it can carry out using a conventionally well-known method. For example, by using a ball mill device (for example, a planetary ball mill device), a pulverized ball and an alloy raw material powder are put into a pulverizing pot, and a high energy is applied by increasing the number of rotations, thereby achieving alloying. The rotation speed (rotation speed) of the ball mill device is, for example, 500 rpm or more, preferably 600 rpm or more.

  The alloying treatment by the above-described method is usually performed in a dry atmosphere, but the particle size distribution after the alloying treatment may have a very large or small width. For this reason, it is preferable to perform the grinding | pulverization process and / or classification process for adjusting a particle size.

  The particle diameter can be controlled by appropriately subjecting the particles obtained by the alloying treatment to classification, pulverization and the like. Examples of classification methods include wind classification, mesh filtration, and sedimentation. The pulverization conditions are not particularly limited, and the pulverization time, rotation speed, and the like using an appropriate pulverizer (for example, a device that can be used in a mechanical alloy method, such as a planetary ball mill) may be set as appropriate. An example of pulverization conditions is an example in which pulverization is performed at a rotational speed of 200 to 400 rpm for 30 minutes to 4 hours using a pulverizer such as a planetary ball mill.

  In addition, the negative electrode active material layer can be formed by applying a negative electrode active material slurry containing a negative electrode active material, a binder, a conductive additive, a solvent, and the like on a current collector. Further, pulverization may be performed. The pulverizing means is not particularly limited, and known means can be appropriately employed. The pulverization conditions are not particularly limited, and pulverization time, rotation speed, and the like may be set as appropriate. An example of pulverization conditions is an example in which pulverization is performed at a rotational speed of 200 to 400 rpm for 30 minutes to 4 hours using a pulverizer such as a planetary ball mill. Further, the pulverization treatment may be performed in several times with a cooling time in between for the purpose of preventing the solvent from being heated and denatured by the pulverization treatment.

(Carbon material)
The carbon material that is one kind of the negative electrode active material is not particularly limited, but is graphite (graphite) that is highly crystalline carbon such as natural graphite or artificial graphite; soft carbon (graphitizable carbon), hard carbon (non-graphitizable) Low crystalline carbon such as carbon); carbon black (amorphous carbon) such as ketjen black, acetylene black, channel black, lamp black, oil furnace black, thermal black; fullerene, carbon nanotube, carbon nanofiber, carbon nanohorn, Examples thereof include carbon materials such as carbon fibrils. Among these, it is preferable to use graphite (graphite) which is highly crystalline carbon such as natural graphite and artificial graphite. These carbon materials may be used individually by 1 type, and may use 2 or more types together. In order for the carbon material to be used as the active material of the secondary battery, any carbon material may be used as long as insertion and desorption of Li ions easily occur (can be repeatedly charged and discharged).

  In the present embodiment, as a negative electrode active material, together with the Si alloy, a carbon material is used so as to be rich in carbon, so that a high capacity can be maintained and higher charge / discharge cycle characteristics can be exhibited, and the capacity and cycle durability can be achieved. Can be achieved.

  There is no restriction | limiting in particular as a shape of a carbon material, A spherical shape, an ellipse shape, a column shape, a polygonal column shape, a scale shape, an indefinite shape etc. may be sufficient.

(Average particle diameter of carbon material (secondary particle diameter) D50)
The average particle size of the carbon material is not particularly limited, but the average particle size (secondary particle size) D50 is preferably 5 to 50 μm, more preferably 5 to 25 μm, and 12 to 25 μm. More preferably it is. Here, the value obtained by the laser diffraction method is used as the average particle size (secondary particle size) of the carbon material. In the present embodiment, the D50 value is calculated based on the particle size distribution data calculated by a laser particle size distribution meter, and D50; median diameter, that is, an intermediate particle diameter is calculated. In the present embodiment, the laser particle size distribution meter is a laser diffraction / scattering particle size distribution measuring device (manufactured by HORIBA, Ltd., model: LA-920). A scattering type particle size distribution measuring apparatus can be used. At this time, regarding the comparison with the average particle diameter of the Si alloy described above, the average particle diameter of the carbon material may be the same as or different from the average particle diameter of the Si alloy, but is preferably different. . In particular, it is more preferable that the average particle diameter of the Si alloy as the Si material is smaller than the average particle diameter of the carbon material. Furthermore, the ratio (A / C) of the average particle diameter (secondary particle diameter) D50 (A) of the Si alloy as the Si material to the average particle diameter (secondary particle diameter) D50 (C) of the carbon material is 0. It is preferably less than 5, more preferably 0.3 or less, and even more preferably 0.1 or less. If the average particle diameter (secondary particle diameter) D50 (C) of the carbon material is relatively larger than the average particle diameter (secondary particle diameter) D50 (A) of the Si alloy that is the Si material, the carbon material is uniformly distributed. The particles are arranged, and the Si alloy particles are arranged in the gaps between the carbon material particles. Further, in this embodiment, when the cross section of the negative electrode active material layer is equally divided into three in the electrode (negative electrode active material layer) thickness direction, the area of the Si alloy as the Si material within each divided area is the current collector side. To the positive electrode facing surface (front surface) side, the structure is arranged so as to increase by 1% or more and 12% or less. That is, it has a configuration in which more Si alloys are arranged in the gaps between the carbon material particles on the positive electrode facing surface (front surface) side than on the current collector side. In such a configuration, for example, as shown in the examples, the solid content concentration of the negative electrode active material (aqueous) slurry is adjusted to a predetermined (narrow) range, and the subsequent drying temperature is also adjusted to a predetermined (narrow) range. Can be achieved (see Examples). In addition to the above, when the particle diameter of the Si alloy, which is a Si material having a relatively large capacity, is equivalent to the particle diameter of the carbon material having a small capacity, even if it can be dispersed evenly in appearance, the negative electrode active material The capacity distribution in the layer plane (direction) tends to vary slightly. Therefore, by reducing the particle diameter of the Si alloy, which is a Si material having a relatively large capacity, the capacity variation in the negative electrode active material layer plane (direction) can be further reduced. The lower limit of the ratio (A / C) of the average particle diameter (secondary particle diameter) D50 (A) of the Si alloy to the average particle diameter (secondary particle diameter) D50 (C) of the carbon material is not particularly limited. For example, it is 0.01 or more. From the above, by making the particle size of the Si alloy, which is a Si material having a relatively large capacity, smaller than the particle size of the carbon material, a more uniform charge / discharge reaction can be promoted, and the performance (capacity and durability) Property) can be further improved. In addition, variation in capacity within the negative electrode active material layer surface can be further reduced, and performance (capacity and durability) can be further improved.

As described above, the Si alloy, which is a Si material, has a slight variation in the negative electrode active material layer surface (direction) (all Si alloy particles are evenly arranged in the gaps between all the carbon material particles in the negative electrode active material layer surface). May not be evenly arranged due to slight variations that may occur if not. In such a case, the potentials and capacities expressed by the respective SiO _x and Si alloys are individually different. As a result, in the SiO _x and Si alloy of the anode active material layer includes a SiO _x and Si alloy that reacts with excessive lithium ion, SiO _x and Si alloy that does not react with lithium ions occur. That is, non-uniformity of reaction between the SiO _x in the negative electrode active material layer and the lithium ions of the Si alloy occurs. Then, the negative electrode active of SiO _x and Si alloy material layer, by SiO _x and Si alloy acts excessively react excessively lithium ion, significant decomposition reaction and excess electrolyte by the electrolyte The structure of the SiO _x and Si alloy can be destroyed due to proper expansion. As a result, excellent even when using SiO _x and Si alloys has a characteristic, uniform in the case of such SiO _x and Si alloy is not disposed, the cycle characteristics as the non-aqueous electrolyte secondary battery Can be reduced.

However, the above problem can be solved by mixing the SiO _x and Si alloy with a carbon material. More specifically, by mixing SiO _x and Si alloy with a carbon material, it is possible to arrange the SiO _x and Si alloy in a balanced manner (with relatively uniform distribution (dispersion)) in the negative electrode active material layer. It can be. As a result, it is considered that both SiO _x and the Si alloy in the negative electrode active material layer exhibit the same reactivity and can prevent deterioration of cycle characteristics. This is because the SiO _x particles and Si alloy particles can enter the gaps between the carbon material particles having a high content, and thereby the SiO _x and Si alloy are well balanced (relatively uniformly dispersed (dispersed)). It can be arranged. As a result, the contact area between each particle increases, electrical conductivity can be ensured, and furthermore, both SiO _x and Si alloy can exhibit the same reactivity (prevent reaction non-uniformity). It is thought that deterioration of characteristics can be prevented. That is, in this embodiment, however, a concentration gradient is positively provided in the Si alloy in the negative electrode active material layer thickness direction so that the above-described effects of the invention can be obtained. ) Is preferably free of variation.

  In addition, as a result of mixing the carbon material so as to be carbon-rich, the initial capacity can be reduced by relatively reducing the content of the Si alloy in the negative electrode active material layer. However, since the carbon material itself is an active material and has reactivity with lithium ions (Li ion insertion / desorption tends to occur), the degree of decrease in the initial capacity is relatively small. That is, the negative electrode active material according to the present embodiment has a large effect of improving the cycle characteristics as compared with the effect of reducing the initial capacity.

  Further, the carbon material is unlikely to undergo a volume change when reacting with lithium ions, as compared with a Si alloy that is a Si material. Therefore, even when the volume change of the Si alloy that is the Si material is large, the carbon material is mixed so as to be carbon-rich. The influence of the volume change can be made relatively minor. Such an effect can also be understood from the results of Examples in which the cycle characteristics increase as the carbon material content increases (the Si material content decreases).

  Moreover, the amount of electricity consumed (Wh) can be improved by containing a carbon material. More specifically, the carbon material has a relatively low potential compared to the Si material (Si alloy). As a result, the relatively high potential of the Si material can be reduced. Then, since the electric potential of the whole negative electrode falls, power consumption (Wh) can be improved. Such an action is particularly advantageous when used for a vehicle application, for example.

A negative electrode active material other than the above-described two types of negative electrode active materials may be used in combination as long as it does not affect (does not damage) the operational effects of this embodiment. Examples of the negative electrode active material that can be used in combination include lithium-transition metal composite oxides (for example, Li ₄ Ti ₅ O ₁₂ ), metal materials, lithium alloy negative electrode materials, and the like. Of course, other negative electrode active materials may be used.

  The negative electrode active material layer contains a negative electrode active material represented by the following formula (1).

  In the formula (1), the Si material and the carbon material in parentheses indicate essential components of the negative electrode active material. Here, the Si material is a material made of an alloy containing Si (Si alloy). Α and β represent the contents (mass%) of the Si material and the carbon material in the negative electrode active material layer, and 80 ≦ α + β ≦ 98, 0.1 ≦ α ≦ 40, 58 ≦ β ≦ 97.9. is there.

  As apparent from the formula (1), the content (α) of the Si material in the negative electrode active material layer is 0.1 to 40% by mass. Moreover, content ((beta)) of a carbon material is 58-97.9 mass%. Furthermore, these total content ((alpha) + (beta)) is 80-98 mass%.

  In addition, the mixing ratio of the Si material and the carbon material of the negative electrode active material is not particularly limited as long as the content specification is satisfied, and can be appropriately selected according to a desired use. In this embodiment, as the mixing ratio of the Si material and the carbon material, the content of the Si material is relatively small, and the content of the carbon material is relatively large (further, a specific concentration of the Si material in the thickness direction). By forming a gradient), the effect of this embodiment can be effectively expressed. Especially, content of Si material ((alpha)) in the said negative electrode active material becomes like this. Preferably it is 0.5-40 mass%, More preferably, it is 1-30 mass%, More preferably, it is the range of 1-20 mass%. . When the content of the Si material in the negative electrode active material layer is less than 0.1% by mass, it is difficult to obtain a high initial capacity. On the other hand, when the content of the Si material exceeds 40% by mass, high cycle characteristics cannot be obtained. In addition, the content of the carbon material (β) in the negative electrode active material is preferably in the range of 58 to 97.5% by mass, more preferably 68 to 97% by mass, and still more preferably 78 to 97% by mass. When the content of the carbon material in the negative electrode active material layer is less than 58% by mass, high cycle characteristics cannot be obtained. On the other hand, when the content of the carbon material exceeds 97.9% by mass, it is difficult to obtain a high initial capacity.

  The total content (α + β) of the Si material and the carbon material in the negative electrode active material layer is not particularly limited as long as it satisfies the above specifications of the content (α and β) of each component, and is appropriately selected according to the desired application. it can. Especially, the total content (α + β) of the Si material and the carbon material in the negative electrode active material layer is preferably in the range of 80 to 98% by mass, more preferably 85 to 97% by mass, and still more preferably 90 to 97% by mass. is there. When the total content (α + β) of the Si material and the carbon material in the negative electrode active material layer is less than 80% by mass, the weight energy density is lowered, which is not preferable. On the other hand, when the total content (α + β) of the Si material and the carbon material in the negative electrode active material layer exceeds 98% by mass, the binder and the conductive auxiliary agent are insufficient, which causes a decrease in battery performance.

(Binder)
In this embodiment, the negative electrode active material layer preferably contains a binder. The binder contained in the negative electrode active material layer preferably contains an aqueous binder. In addition to the easy procurement of water as a raw material, water-based binders can be greatly reduced in capital investment on the production line and can reduce the environmental burden because water is generated during drying. There is an advantage.

  The water-based binder refers to a binder using water as a solvent or a dispersion medium, and specifically includes a thermoplastic resin, a polymer having rubber elasticity, a water-soluble polymer, or a mixture thereof. Here, the binder containing water as a dispersion medium refers to a polymer that includes all expressed as latex or emulsion and is emulsified or suspended in water. For example, a polymer latex that is emulsion-polymerized in a system that self-emulsifies. Kind.

  Specific examples of water-based binders include styrene polymers (styrene-butadiene rubber (SBR), styrene-vinyl acetate copolymer, styrene-acrylic copolymer, etc.), acrylonitrile-butadiene rubber, and methyl methacrylate-butadiene rubber. , (Meth) acrylic polymers (polyethyl acrylate, polyethyl methacrylate, polypropyl acrylate, polymethyl methacrylate (methyl methacrylate rubber), polypropyl methacrylate, polyisopropyl acrylate, polyisopropyl methacrylate, polybutyl acrylate, polybutyl methacrylate, Polyhexyl acrylate, polyhexyl methacrylate, polyethylhexyl acrylate, polyethylhexyl methacrylate, polylauryl acrylate, polylaur Methacrylate), polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polybutadiene, butyl rubber, fluororubber, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer Examples include coalescence, polyvinyl pyridine, chlorosulfonated polyethylene, polyester resin, phenol resin, and epoxy resin. These aqueous binders may be used alone or in combination of two or more.

  The water-based binder includes at least one rubber-based binder selected from the group consisting of styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, and methyl methacrylate rubber from the viewpoint of binding properties. It is preferable to include. Furthermore, since the binding property is good, the aqueous binder preferably contains styrene-butadiene rubber (SBR).

  When using a water-based binder, it is preferable to use a thickener together. This is because the water-based binder has a strong binding property (binding effect), but the thickening is not sufficient. Therefore, a sufficient thickening effect cannot be obtained simply by adding an aqueous binder to the aqueous slurry during electrode production. Therefore, thickening is imparted to the aqueous binder by using a thickener that is excellent in thickening. The thickener is not particularly limited. For example, polyvinyl alcohol (average polymerization degree is preferably 200 to 4000, more preferably 1000 to 3000, and saponification degree is preferably 80 mol%. More preferably, it is 90 mol% or more) and a modified product thereof (ethylene / vinyl acetate = (2/98) to (30/70) molar ratio of 1 to 80 mol% of vinyl acetate units of the copolymer). Saponified products, polyvinyl alcohol 1 to 50 mol% partially acetalized products), starch and modified products thereof (oxidized starch, phosphate esterified starch, cationized starch, etc.), cellulose derivatives (carboxymethylcellulose (CMC), methylcellulose, hydroxy) Propyl cellulose, hydroxyethyl cellulose, and their salts), polyvinylpyrrolidone Polyacrylic acid (salt), polyethylene glycol, (meth) acrylamide and / or (meth) acrylate copolymer [(meth) acrylamide polymer, (meth) acrylamide- (meth) acrylate copolymer, Alkyl (meth) acrylate (C1-4) ester- (meth) acrylate copolymer, etc.], styrene-maleate copolymer, Mannich modified polyacrylamide, formalin condensation type resin (urea- (Formalin resin, melamine-formalin resin, etc.), polyamide polyamine or dialkylamine-epichlorohydrin copolymer, polyethyleneimine, casein, soybean protein, synthetic protein, galactomannan derivative and the like. These thickeners may be used alone or in combination of two or more.

  When using styrene-butadiene rubber (SBR) suitable as an aqueous binder, it is preferable to use the following thickeners together from the viewpoint of improving coatability. Thickeners suitable for use in combination with styrene-butadiene rubber (SBR) include polyvinyl alcohol and modified products thereof, starch and modified products thereof, cellulose derivatives (carboxymethylcellulose (CMC), methylcellulose, hydroxyethylcellulose, and these Salt), polyvinylpyrrolidone, polyacrylic acid (salt), or polyethylene glycol. Among them, it is preferable to combine styrene-butadiene rubber (SBR) with carboxymethyl cellulose (CMC) or a salt thereof (CMC (salt)). The mass ratio of SBR (aqueous binder) and the thickener is not particularly limited, but SBR (aqueous binder): thickener = 1: (0.3 to 0.7). Is preferred.

  When a negative electrode active material layer contains a binder, it is preferable that content of an aqueous binder is 80-100 mass% among the binders used for a negative electrode active material layer, It is preferable that it is 90-100 mass%, 100 It is preferable that it is mass%. Examples of the binder other than the water-based binder include a binder (organic solvent-based binder) used for the positive electrode active material layer.

  The amount of the binder contained in the negative electrode active material layer is not particularly limited as long as it can bind the active material, but is preferably 0 with respect to 100% by mass of the total amount of the negative electrode active material layer. 0.5 to 15% by mass, more preferably 1 to 10% by mass, further preferably 1 to 8% by mass, particularly preferably 2 to 4% by mass, and most preferably 2.5 to 3%. 0.5% by mass. Since the water-based binder has a high binding force, the active material layer can be formed with a small amount of addition as compared with the organic solvent-based binder. The amount of the thickener contained in the negative electrode active material layer includes the content ratio of the aqueous binder (SBR) and the thickener, the amount of binder contained in the negative electrode active material layer, and the negative electrode active material layer. It is calculated | required from content of the aqueous binder in the binder contained.

(Conductive aid)
The conductive assistant refers to an additive that is blended in order to improve the conductivity of the positive electrode active material layer or the negative electrode active material layer. Although not particularly limited, carbon black such as acetylene black, ketjen black and furnace black, carbon powder such as channel black, thermal black and graphite, various carbon fibers such as vapor grown carbon fiber (VGCF; registered trademark), Examples thereof include carbon materials such as expanded graphite. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

  When the conductive additive is carbon powder, the average particle size is not particularly limited, but from the viewpoint of improving conductivity, the secondary particle size is preferably 100 to 500 nm, more preferably 100 to 300 nm. Moreover, the average particle diameter of a primary particle is 10-100 nm, More preferably, it is 20-80 nm. Moreover, when a conductive support agent is carbon fiber, the average fiber diameter in particular is although it does not restrict | limit, From a viewpoint of an intensity | strength and electroconductivity improvement, Preferably it is 10-80 nm, More preferably, it is 10-50 nm. Moreover, from a viewpoint of electronic network formation, the average fiber length of carbon fiber is 5-20 micrometers, More preferably, it is 10-15 micrometers. The “fiber diameter” in this specification means the maximum distance L among the distances between any two points on the contour line of the cross section perpendicular to the longitudinal direction of the carbon fiber. In addition, as the value of “average fiber diameter”, an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) is used, and the longitudinal direction of the carbon fibers observed in several to several tens of fields is used. The value calculated as the average value of the fiber diameters of the vertical cross section shall be adopted. The “fiber length” in this specification means the length (distance) in the longitudinal direction of the carbon fiber. In addition, as the value of “average fiber length”, using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM), the longitudinal direction of the carbon fibers observed in several to several tens of fields is used. The value calculated as the average value of the length (fiber length) shall be adopted. In addition, the positive electrode side conductive assistant can be of the same size (average particle diameter) as the negative electrode side conductive assistant.

  The content of the conductive additive in the negative electrode active material layer is preferably 1 to 10% by mass, more preferably 1 to 8% by mass. By defining the blending ratio (content) of the conductive assistant within the above range, the following effects are exhibited. That is, the electron conductivity can be sufficiently ensured without hindering the electrode reaction, the decrease in the energy density due to the decrease in the electrode density can be suppressed, and as a result, the energy density can be improved due to the increase in the electrode density. It is.

(Lithium salt)
The lithium salt is contained in the negative electrode active material layer when the electrolyte described above penetrates into the negative electrode active material layer. Therefore, the specific form of the lithium salt that can be contained in the negative electrode active material layer is the same as the lithium salt that constitutes the electrolyte. Examples of the lithium salt include Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _{3 and the} like.

(Ion conductive polymer)
Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

  The compounding ratio of the components contained in the negative electrode active material layer is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries.

  The negative electrode (negative electrode active material layer) can be applied by any one of a kneading method, a sputtering method, a vapor deposition method, a CVD method, a PVD method, an ion plating method, and a thermal spraying method in addition to a method of applying (coating) a normal slurry. Can be formed.

  There is no particular limitation on the thickness of each active material layer (active material layer on one side of the current collector), and conventionally known knowledge about the battery can be referred to as appropriate. For example, the thickness of each active material layer is usually about 1 to 500 μm, preferably 2 to 100 μm in consideration of the intended use of the battery (emphasis on output, energy, etc.) and ion conductivity.

The porosity of each active material layer (positive electrode active material layer and negative electrode active material layer) is 10 to 45% by volume, preferably 15 to 40% by volume, more preferably 20 to 35%, based on the total volume of the active material layer. It is in the range of volume%. If the porosity is within the above range, the pores of each active material layer are impregnated with the electrolyte solution inside each active material layer without damaging the characteristics and strength such as battery capacity, and the electrode reaction is promoted. This is because it can effectively function as a path for supplying the electrolytic solution (Li ⁺ ions).

(Configuration of the negative electrode active material layer having an inclined electrode structure)
In this embodiment, when an arbitrary place in the negative electrode active material layer surface is selected, when the cross section of the negative electrode active material layer is equally divided into three in the electrode thickness direction, the area of the Si material within each divided area is collected. It increases by 1% or more and 12% or less from the body side to the positive electrode facing surface side. By adopting such a configuration (inclined electrode structure in which the mixing ratio of the Si material increases by an appropriate amount from the current collector to the side facing the positive electrode), since there is little Si material having a large volume change in the vicinity of the current collector, Damage and active material layer peeling are reduced. As a result, by maintaining the electronic conductivity in the charge / discharge process, the high capacity can be maintained, the discharge capacity maintenance rate can be greatly improved, and both capacity and cycle durability can be achieved.

  When an arbitrary place in the negative electrode active material layer surface is selected, when the negative electrode active material layer cross section is equally divided into three in the electrode thickness direction, the area of the Si material in each divided area is the current collector side From 1% to 10%, more preferably from 3% to 10%, even more preferably from 5% to 10%, particularly preferably from 6% to 10% from the positive electrode facing surface side to the positive electrode facing surface side. It is good to have. By making the tilted electrode structure (the increase rate of the area of the Si material in each of the divided areas) within the above-described preferable range, the cycle durability (discharge capacity maintenance rate, etc.) of the battery is further improved. be able to.

  FIG. 3 (a) shows the collection of a negative electrode active material slurry with an adjusted solid content ratio in order to manufacture a negative electrode having an inclined electrode structure in which the mixing ratio of the Si material is increased by an appropriate amount from the current collector side to the positive electrode facing surface side. It is sectional drawing which represented a mode that it apply | coated to the electric body typically. FIG. 3 (b) shows the coated surface formed in FIG. 3 (a) in order to manufacture a negative electrode having an inclined electrode structure in which the mixing ratio of the Si material increases by an appropriate amount from the current collector side to the positive electrode facing surface side. FIG. 6 is a cross-sectional view schematically showing a state facing (turned over). FIG. 3 (c) shows a negative electrode having an inclined electrode structure in which the mixing ratio of the Si material is increased by an appropriate amount from the current collector side to the positive electrode facing surface side. It is sectional drawing which represented typically a mode that the drying temperature was adjusted in the state (turned over) and dried at low temperature, and the negative electrode was formed. FIG. 3D can be said to be a cross-sectional view schematically showing a negative electrode having an inclined electrode structure in which the mixing ratio of the Si material is increased by an appropriate amount from the current collector side to the positive electrode facing surface side.

  As a method for increasing the area of the Si material in each of the divided areas, the coating surface is mainly adjusted after adjusting the solid content ratio in the negative electrode active material slurry and applying the slurry to the current collector. What is necessary is just to perform drying downward and adjustment of drying temperature (low-temperature drying). Specifically, when preparing the negative electrode active material slurry, the solid content ratio in the slurry (total weight of the solid content such as active material weight + conducting agent weight + thickener weight + binder powder weight / slurry weight) Is 35 to 45 mass%. By doing so, it becomes easy to lower the slurry viscosity and to incline it. As shown in FIG. 3A, the slurry is applied (applied) onto a current collector (current collector foil) 31 to form a coating film (coated film) 31, and then the slurry shown in FIG. As shown in FIG. 3, the coating film (coating film) 31 is directed downward and dried in a low temperature environment of 40 to 90 ° C. as shown in FIG. In this way, due to the specific gravity relationship between the Si material (Si alloy) active material particles 35 and the carbon material active material particles 37, the Si material (Si alloy) 35 moves closer to the positive electrode facing surface side, and the negative electrode active material having an inclined electrode structure. The material layer 33 (negative electrode 30) can be manufactured. That is, as shown in FIG. 3D, in the negative electrode 30 of this embodiment, the negative electrode active material layer 33 on the current collector 31 is formed by the above method, so that the Si material active material particles 35 and the carbon material active material are formed. Due to the specific gravity of the particles 37, the Si material active material particles 35 have an inclined electrode structure with the positive electrode facing surface side approaching. In order to further increase the inclination, it is preferable that the solid content ratio in the slurry is 36 to 43% by mass and the drying temperature is in the range of 40 to 70 ° C. In addition, in addition to the above method, adjustment may be made by further changing the drying time. Specifically, it may be dried at the above drying temperature for 6 to 18 hours, preferably 12 to 18 hours. Alternatively, three or more types having different solid content ratios in the negative electrode active material slurry may be prepared and applied in that order and dried to form a negative electrode active material layer having a laminated structure of three or more layers. It is not something. In a mass production process, a roll-to-roll system is used to collect a slurry on the back surface of a current collector using a die coater on a belt-shaped (ribbon-shaped) current collector that is drawn from a roll-shaped current collector and conveyed. May be applied (coated) and dried while being conveyed. Alternatively, after applying (coating) a slurry to the surface of the current collector using a die coater on a belt-shaped (ribbon-shaped) current collector that is drawn out and conveyed from the current collector wound in a roll, You may dry, conveying a collector in the state twisted (inverted) 180 degreeC.

  As an arbitrary place in the negative electrode active material layer surface, the negative electrode active material is used from the viewpoint of measuring a gradient electrode structure (area ratio of Si material in each divided area) in the electrode thickness direction of the negative electrode active material layer. Any location in the layer surface may be used, and is not particularly limited. For example, the vicinity of the end in the negative electrode active material layer surface, the vicinity of the center, or the vicinity of the middle between the end and the center may be selected as appropriate.

(Method for calculating the ratio of the area of the Si material in each of the divided areas)
The method for calculating the area ratio (%) of the Si material (Si alloy) in each of the divided areas in the negative electrode active material layer is not limited. For example, the following cross section of the negative electrode active material layer There is a method by image processing. That is, after the negative electrode is subjected to cross-section processing by an arbitrary cross-section processing method so that an arbitrary measurement location in the negative electrode active material layer surface is included, a secondary electron image or reflection is observed with an electron microscope for the negative electrode cross-section of the measurement location. An electronic image is taken (see FIG. 4A). Image processing software is used for the image (reflected electron image). The image processing software is not limited. For example, Carl Zeiss AxioVision, Mitani Shoji WinROOF, Media Cybernetics Image-Pro, or the like can be used. In binarization processing (image processing) using image processing software, the measurement image (reflected electron image) is converted to gray scale, and then it is suitable between the gray scale values of the Si material part and parts other than the Si material part. A processed image is obtained by setting an appropriate threshold value. For the obtained processed image, the negative electrode active material layer cross section is equally divided into three in the electrode thickness direction, and Si in the area of the divided processed image (negative electrode active material layer cross section) is divided into three divided cross sections (divided sections). Obtain the area of the material part. Thereafter, the area ratio of the Si material portion occupying the area of the entire divided processed image (the area of the Si material / the area of the entire divided measurement image × 100 (%)) is calculated. In addition, as a method of setting an appropriate threshold value, in addition to setting the value of either Si material or a material other than the Si material part (carbon material, etc.) itself as a threshold value, a method of setting an intermediate value between both values as a threshold value For example, several methods can be applied depending on the difference between the gray scale values. Preferably, an intermediate value between both values is set as a threshold value.

  Specifically, the secondary electron image or reflected electron image (see FIG. 4 (a)) imaged with an electron microscope is binarized and grayscaled for the negative electrode cross section of the measurement location, and the threshold value is set. To obtain a processed image (see FIG. 4B). For this processed image, the cross section of the negative electrode active material layer not including the current collector on one side is equally divided into three in the thickness direction (see FIG. 4B). Thereafter, the ratio (%) of the area of the Si material (Si alloy) within each divided area is calculated (using the image processing software). For example, in the case where the thickness of the negative electrode active material layer (one side) is 60 μm, the processed image (see FIG. 4B) is divided every 20 μm in the thickness direction, and within each divided (image) area. The area ratio (%) of the Si material (Si alloy) is calculated.

  The field area of the secondary electron image or the backscattered electron image captured by the electron microscope with respect to the negative electrode cross section at the measurement location is not particularly limited. For example, the negative electrode active material layer whose longitudinal (thickness direction) is one side is used. It is sufficient if it includes all the thicknesses (see FIG. 4A), and the width (direction perpendicular to the thickness direction) may be in the range of about 50 to 200 μm. In the example, as shown in FIG. 4 (a), the field area of the reflected electron image of the negative electrode cross section is 70 μm including the entire thickness of the negative electrode active material layer on one side in the vertical direction (thickness direction). Images were taken so that the rectangular viewing area was 100 μm in the direction perpendicular to the vertical direction.

  The arbitrary location (measurement location) in the negative electrode active material layer plane may be selected from one location or a plurality of locations (two or more locations), but the inclined electrode structure in the electrode thickness direction in the negative electrode active material layer plane is: Since there is almost no variation depending on the measurement location in the negative electrode active material layer surface, it can be said that one location (for example, the vicinity of the central portion in the negative electrode active material layer surface) may be measured. That is, the negative electrode active material layer cross section may be calculated from one piece of image data. Also in the example, one location in the vicinity of the central portion in the negative electrode active material layer surface was selected (calculated from one piece of image data). In the case where the electrode area is large as in a large battery described later, it is preferably 2 in consideration of a slight non-uniformity of the electrode structure in the manufacturing process (acceptable variation error of the composition in the active material layer surface). It is preferable to take an average value of image data of two (two) or more, more preferably five (5) or more. However, other than a large battery, the average value of two (two) or more image data may be taken similarly.

<Current collector>
The current collectors (11, 12) are made of a conductive material. The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used.

  There is no particular limitation on the thickness of the current collector. The thickness of the current collector is usually about 1 to 100 μm.

  The shape of the current collector is not particularly limited. In the laminated battery 10 shown in FIG. 1, in addition to the current collector foil, a mesh shape (such as an expanded grid) can be used.

  In the case where the negative electrode active material is directly formed on the negative electrode current collector 11 by sputtering or the like, it is preferable to use a current collector foil.

  There is no particular limitation on the material constituting the current collector. For example, a metal or a resin in which a conductive filler is added to a conductive polymer material or a non-conductive polymer material can be employed.

  Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum, stainless steel, copper, and nickel are preferable from the viewpoints of electronic conductivity, battery operating potential, and adhesion of the negative electrode active material by sputtering to the current collector.

  Examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole. Since such a conductive polymer material has sufficient conductivity without adding a conductive filler, it is advantageous in terms of facilitating the manufacturing process or reducing the weight of the current collector.

  Non-conductive polymer materials include, for example, polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA) , Polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or polystyrene (PS). Such a non-conductive polymer material may have excellent potential resistance or solvent resistance.

  A conductive filler may be added to the conductive polymer material or the non-conductive polymer material as necessary. In particular, when the resin used as the base material of the current collector is made of only a non-conductive polymer, a conductive filler is inevitably necessary to impart conductivity to the resin.

  The conductive filler can be used without particular limitation as long as it is a substance having conductivity. For example, metals, conductive carbon, etc. are mentioned as a material excellent in electroconductivity, electric potential resistance, or lithium ion barrier | blocking property. The metal is not particularly limited, but at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K, or these metals It is preferable to contain an alloy or metal oxide containing. Moreover, there is no restriction | limiting in particular as electroconductive carbon. Preferably, it includes at least one selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene.

  The amount of the conductive filler added is not particularly limited as long as it is an amount capable of imparting sufficient conductivity to the current collector, and is generally about 5 to 35% by mass.

<Separator (electrolyte layer)>
The separator has a function of holding an electrolyte and ensuring lithium ion conductivity between the positive electrode and the negative electrode, and a function as a partition wall between the positive electrode and the negative electrode.

  Examples of the separator include a porous sheet separator or a nonwoven fabric separator made of a polymer or fiber that absorbs and holds the electrolyte.

  As a separator for a porous sheet made of a polymer or fiber, for example, a microporous (microporous film) can be used. Specific examples of the porous sheet made of the polymer or fiber include polyolefins such as polyethylene (PE) and polypropylene (PP); a laminate in which a plurality of these are laminated (for example, three layers of PP / PE / PP) And a microporous (microporous membrane) separator made of a hydrocarbon resin such as polyimide, aramid, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), glass fiber, and the like.

  The thickness of the microporous (microporous membrane) separator cannot be uniquely defined because it varies depending on the intended use. For example, in applications such as secondary batteries for driving motors such as electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell vehicles (FCV), it is 4 to 60 μm in a single layer or multiple layers. Is desirable. The fine pore diameter of the microporous (microporous membrane) separator is desirably 1 μm or less (usually a pore diameter of about several tens of nm).

  As the nonwoven fabric separator, cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; conventionally known ones such as polyimide and aramid are used alone or in combination. The bulk density of the nonwoven fabric is not particularly limited as long as sufficient battery characteristics can be obtained by the impregnated electrolyte. Furthermore, the thickness of the nonwoven fabric separator may be the same as that of the electrolyte layer, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

  In addition, as described above, the separator includes an electrolyte. The electrolyte is not particularly limited as long as it can exhibit such a function, but a liquid electrolyte or a gel polymer electrolyte is used. By using the gel polymer electrolyte, the distance between the electrodes is stabilized, the occurrence of polarization is suppressed, and the durability (cycle characteristics) is improved.

The liquid electrolyte functions as a lithium ion carrier. The liquid electrolyte constituting the electrolytic solution layer has a form in which a lithium salt as a supporting salt is dissolved in an organic solvent as a plasticizer. Examples of the organic solvent used include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate. As the lithium _{salt, Li (CF 3 SO 2)} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiClO 4, LiAsF 6, LiTaF such 6, LiCF ₃ SO ₃ A compound that can be added to the active material layer of the electrode can be similarly employed. The liquid electrolyte may further contain additives other than the components described above. Specific examples of such compounds include, for example, vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate, phenyl vinylene carbonate, diphenyl vinylene carbonate, ethyl vinylene carbonate, diethyl vinylene carbonate, vinyl ethylene carbonate, 1,2-divinyl ethylene carbonate. 1-methyl-1-vinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1-ethyl-1-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate, vinylvinylene carbonate, allylethylene carbonate, vinyl Oxymethyl ethylene carbonate, allyloxymethyl ethylene carbonate, acryloxymethyl ethylene carbonate, methacrylate Oxy methylethylene carbonate, ethynyl ethylene carbonate, propargyl carbonate, ethynyloxy methylethylene carbonate, propargyloxy ethylene carbonate, methylene carbonate, etc. 1,1-dimethyl-2-methylene-ethylene carbonate. Among these, vinylene carbonate, methyl vinylene carbonate, and vinyl ethylene carbonate are preferable, and vinylene carbonate and vinyl ethylene carbonate are more preferable. These cyclic carbonates may be used alone or in combination of two or more.

  The gel polymer electrolyte has a configuration in which the liquid electrolyte is injected into a matrix polymer (host polymer) made of an ion conductive polymer. The use of a gel polymer electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost and the ion conductivity between the layers is easily cut off. Examples of the ion conductive polymer used as the matrix polymer (host polymer) include polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene ( PVdF-HEP), poly (methyl methacrylate (PMMA), and copolymers thereof.

  The matrix polymer of gel electrolyte can express excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be performed.

(Separator with heat-resistant insulating layer)
The separator is preferably a separator (a separator with a heat resistant insulating layer) in which a heat resistant insulating layer is laminated on a porous substrate such as a porous sheet separator or a nonwoven fabric separator. The heat resistant insulating layer is a ceramic layer containing inorganic particles and a binder. As the separator with a heat-resistant insulating layer, a highly heat-resistant separator having a melting point or a heat softening point of 150 ° C. or higher, preferably 200 ° C. or higher is used. By having the heat-resistant insulating layer, the internal stress of the separator that increases when the temperature rises is relieved, so that the effect of suppressing thermal shrinkage can be obtained. As a result, it is possible to prevent the induction of a short circuit between the electrodes of the battery, so that the battery configuration is unlikely to deteriorate in performance due to temperature rise. Moreover, by having a heat-resistant insulating layer, the mechanical strength of the separator with a heat-resistant insulating layer is improved, and it is difficult for the separator to break. Furthermore, the separator is less likely to curl in the battery manufacturing process due to the effect of suppressing thermal shrinkage and high mechanical strength.

The inorganic particles in the heat resistant insulating layer contribute to the mechanical strength and heat shrinkage suppressing effect of the heat resistant insulating layer. The material used as the inorganic particles is not particularly limited. Examples thereof include silicon, aluminum, zirconium, titanium oxides (SiO ₂ , Al ₂ O ₃ , ZrO ₂ , TiO ₂ ), hydroxides and nitrides, and composites thereof. These inorganic particles may be derived from mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine and mica, or may be artificially produced. Moreover, only 1 type may be used individually for these inorganic particles, and 2 or more types may be used together. Of these, silica (SiO ₂ ) or alumina (Al ₂ O ₃ ) is preferably used, and alumina (Al ₂ O ₃ ) is more preferably used from the viewpoint of cost.

The basis weight of the heat-resistant particles is not particularly limited, but is preferably 5 to 15 g / m ² . If it is this range, sufficient ion conductivity will be acquired and it is preferable at the point which maintains heat resistant strength.

  The binder in the heat-resistant insulating layer has a role of adhering the inorganic particles to each other or between the inorganic particles and the porous substrate (resin porous substrate layer). With the binder, the heat-resistant insulating layer is stably formed, and peeling between the porous substrate (porous substrate layer) and the heat-resistant insulating layer is prevented.

  The binder used for the heat-resistant insulating layer is not particularly limited. For example, carboxymethyl cellulose (CMC), polyacrylonitrile, cellulose, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), isoprene rubber A compound such as butadiene rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), or methyl acrylate can be used as the binder. Of these, carboxymethylcellulose (CMC), methyl acrylate, or polyvinylidene fluoride (PVDF) is preferably used. As for these compounds, only 1 type may be used independently and 2 or more types may be used together.

  The content of the binder in the heat resistant insulating layer is preferably 2 to 20% by mass with respect to 100% by mass of the heat resistant insulating layer. When the binder content is 2% by mass or more, the peel strength between the heat-resistant insulating layer and the porous substrate (porous substrate layer) can be increased, and the vibration resistance of the separator can be improved. On the other hand, when the binder content is 20% by mass or less, the gaps between the inorganic particles are appropriately maintained, so that sufficient lithium ion conductivity can be ensured.

The thermal contraction rate of the separator with a heat-resistant insulating layer is preferably 10% or less for both MD and TD after holding for 1 hour at 150 ° C. and ² gf / cm ² . By using such a material having high heat resistance, it is possible to effectively prevent the separator from contracting even if the positive electrode heat generation amount increases and the battery internal temperature reaches 150 ° C. As a result, it is possible to prevent the induction of a short circuit between the electrodes of the battery, so that the battery configuration is unlikely to deteriorate in performance due to temperature rise.

<Current collector plate (tab)>
In a lithium ion secondary battery, a current collector plate (tab) electrically connected to a current collector is taken out of a laminate film as an exterior material for the purpose of taking out current outside the battery.

  The material which comprises a current collector plate is not specifically limited, The well-known highly electroconductive material conventionally used as a current collector plate for lithium ion secondary batteries can be used. As a constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. Note that the same material may be used for the positive electrode current collector plate (positive electrode tab) and the negative electrode current collector plate (negative electrode tab), or different materials may be used.

  Further, the removal of the tabs 58 and 59 shown in FIG. 2 is not particularly limited. The positive electrode tab 58 and the negative electrode tab 59 may be drawn out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be divided into a plurality of parts and taken out from each side, as shown in FIG. It is not limited to. Further, in a wound type lithium ion battery, instead of a tab, for example, a terminal may be formed using a cylindrical can (metal can).

<Seal part>
The seal portion is a member unique to the serially stacked battery and has a function of preventing leakage of the electrolyte layer. In addition to this, it is possible to prevent current collectors adjacent in the battery from coming into contact with each other and a short circuit due to a slight unevenness at the end of the laminated electrode.

  The constituent material of the seal portion is not particularly limited, but polyolefin resin such as polyethylene and polypropylene, epoxy resin, rubber, polyimide and the like can be used. Among these, it is preferable to use a polyolefin resin from the viewpoints of corrosion resistance, chemical resistance, film-forming property, economy, and the like.

<Positive terminal lead and negative terminal lead>
As a material for the negative electrode and the positive electrode terminal lead, a lead used in a known laminated secondary battery can be used. In addition, the parts removed from the battery exterior material should be heat-insulating so that they do not affect products (for example, automobile parts, especially electronic devices) by touching peripheral devices or wiring and causing leakage. It is preferable to coat with a heat shrinkable tube or the like.

<Battery exterior>
A conventionally known metal can case can be used as the battery outer package. In addition, the power generation element 21 may be packed using a laminate film 29 as shown in FIG. The laminate film can be configured as a three-layer structure in which, for example, polypropylene, aluminum, and nylon are laminated in this order. By using such a laminate film, it is possible to easily open the exterior material, add the capacity recovery material, and reseal the exterior material. A laminate film is desirable from the viewpoint that it is excellent in high output and cooling performance, and can be suitably used for a battery for large equipment for EV and HEV. Moreover, since the group pressure to the power generation element applied from the outside can be easily adjusted and can be easily adjusted to a desired electrolyte layer thickness, the exterior body is made of a laminate film containing aluminum (for example, Aluminum laminate sheet bags; see examples) are more preferred. As the laminate film containing aluminum, an aluminum laminate film in which the above-described polypropylene, aluminum, and nylon are laminated in this order can be used.

[Cell size]
FIG. 2 is a perspective view showing the appearance of a flat lithium ion secondary battery which is a typical embodiment of the secondary battery. Like this lithium ion secondary battery, according to a preferred embodiment of the present invention, there is provided a flat laminated battery having a structure in which the power generation element is enclosed in a battery outer package made of a laminate film containing aluminum. The

  As shown in FIG. 2, the flat lithium ion secondary battery 50 has a rectangular flat shape, and a positive electrode tab 58 and a negative electrode tab 59 for taking out electric power are drawn out from both sides thereof. Yes. The power generation element 57 is encased by the battery outer packaging material 52 of the lithium ion secondary battery 50, and its periphery is heat-sealed. The power generation element 57 is sealed with the positive electrode tab 58 and the negative electrode tab 59 pulled out to the outside. Has been. Here, the power generation element 57 corresponds to the power generation element 21 of the lithium ion secondary battery 10 shown in FIG. 1 described above. The power generation element 57 is formed by laminating a plurality of single battery layers (single cells) 19 composed of a positive electrode (positive electrode active material layer) 15, an electrolyte layer 17, and a negative electrode (negative electrode active material layer) 13.

  The lithium ion secondary battery is not limited to a stacked flat shape. The wound lithium ion secondary battery may have a cylindrical shape, or may have a shape that is a flattened rectangular shape by deforming such a cylindrical shape. There is no particular limitation. In the said cylindrical shape thing, a laminate film may be used for the exterior material, and the conventional cylindrical can (metal can) may be used, for example, It does not restrict | limit. Preferably, the power generation element is covered with an aluminum laminate film. With this configuration, weight reduction can be achieved.

  Further, the removal of the tabs 58 and 59 shown in FIG. 2 is not particularly limited. The positive electrode tab 58 and the negative electrode tab 59 may be drawn out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be divided into a plurality of parts and taken out from each side, as shown in FIG. It is not limited to. Further, in a wound type lithium ion battery, instead of a tab, for example, a terminal may be formed using a cylindrical can (metal can).

  In a general electric vehicle, the battery storage space is about 170L. Since auxiliary devices such as batteries and charge / discharge control devices are stored in this space, the storage space efficiency of the battery is usually about 50%. The efficiency of battery loading in this space is a factor that governs the cruising range of electric vehicles. If the size of the battery is reduced, the loading efficiency is impaired, and the cruising distance cannot be secured.

  Therefore, in this embodiment, the battery structure in which the power generation element is covered with the exterior body is preferably large. Specifically, the negative electrode active material layer is preferably rectangular (rectangular), and the length of the short side of the rectangle is preferably 100 mm or more. Such a large battery can be used for vehicle applications. Here, the length of the short side of the negative electrode active material layer refers to the side having the shortest length among the electrodes. The upper limit of the short side length is not particularly limited, but is usually 400 mm or less.

[Volume energy density and rated (discharge) capacity]
Considering the travel distance (cruising distance) by one charge of the electric vehicle, the volume energy density of the battery is preferably 157 Wh / L or more, and the rated capacity is preferably 20 Ah or more.

Here, as a viewpoint of a large-sized battery different from the viewpoint of the physical size of the electrode, an increase in the size of the battery is defined from the relationship between the battery volume and the battery capacity (rated capacity). Specifically, the nonaqueous electrolyte secondary battery according to this embodiment has a ratio of battery volume (product of the projected area and thickness of the battery including the battery outer casing) to the rated capacity of 10 cm ³ / Ah or less. And the rated capacity is preferably 3 Ah or more. This large-sized battery has a large battery capacity per unit volume (10 Ah / cm ³ or more), in other words, a small battery volume per unit capacity (ratio of the battery volume to the rated capacity) (10 cm ³ / Ah or less), In addition, the battery capacity (rated capacity) is defined as being large (3 Ah or more). It can be said that this can be applied to a large-capacity battery that has a large capacity and expands more than ever by using a Si material and a carbon material in combination with the negative electrode active material.

The upper limit of the ratio of the battery volume (product of the projected area and thickness of the battery including the battery outer package) to the rated capacity is preferably 8 cm ³ / Ah or less. On the other hand, the lower limit of the value of the ratio of the battery volume to the rated capacity (product of the projected area and thickness of the battery including the battery outer package) is not particularly limited, but is preferably 2 cm ³ / Ah or more, More preferably, it is 3 cm ³ / Ah or more. The rated capacity is preferably 5 Ah or more, more preferably 10 Ah or more, further preferably 15 Ah or more, particularly preferably 20 Ah or more, and particularly preferably 25 Ah or more. Thus, for the first time, it is possible to achieve both vehicle required performance (high capacity and excellent cycle durability) and mounting space by making a battery with a large area (large volume) and a large capacity within the above range of battery volume and rated capacity. There are advantages. On the other hand, even a battery having a large area (large volume) and not having a large capacity as described above, such as a conventional consumer battery, can satisfy the required vehicle performance (high capacity and excellent cycle durability).

  The rated capacity of the battery is determined as follows.

≪Measurement of rated capacity≫
The rated capacity is about 10 hours after injecting the electrolyte solution for the test battery, and then the temperature is 25 ° C. (in the range of ± 2.5 ° C .; ambient temperature), 3.0V to 4.15V. It is measured in the voltage range by the following procedures 1-5.

  Procedure 1: After reaching 4.15 V with a constant current charge of 0.1 C, pause for 5 minutes.

  Procedure 2: After Procedure 1, charge for 1.5 hours by constant voltage charging and rest for 5 minutes.

  Procedure 3: After reaching 3.0 V by constant current discharge of 0.1 C, discharge at constant voltage discharge for 2 hours, and then rest for 10 seconds.

  Procedure 4: After reaching 4.1V by constant current charging at 0.1 C, charge for 2.5 hours by constant voltage charging, and then rest for 10 seconds.

  Procedure 5: After reaching 3.0 V by 0.1 C constant current discharge, discharge by constant voltage discharge for 2 hours, and then stop for 10 seconds.

  Rated capacity: The discharge capacity (CCCV discharge capacity) in the discharge from the constant current discharge to the constant voltage discharge in the procedure 5 is defined as the rated capacity.

  The battery volume is determined by the product of the projected area and thickness of the battery including the battery outer package. Among these, regarding the projected area of the battery including the battery outer casing, the projected area of the six batteries of the front, back, right side, left side, plane, and bottom can be obtained. Usually, this is the projected area of the battery on the flat or bottom surface when the battery is placed in the most stable state on the flat plate. Moreover, the thickness of the battery including the battery outer package is measured at the time of full charge. In addition, since the thickness of the battery including the battery outer package is a large area, eight or more places are measured in consideration of variation depending on the measurement place, and these are averaged. For example, it is possible to use a value obtained by measuring the thickness of the battery including the battery outer package at or near the location represented by the numbers 1 to 9 shown in FIG. However, the measurement location is not limited to the example of FIG.

  Furthermore, the aspect ratio of the rectangular electrode is preferably 1 to 4, and more preferably 1 to 2. The electrode aspect ratio is defined as the aspect ratio of the rectangular positive electrode active material layer. By setting the aspect ratio in such a range, there is an advantage that both required vehicle performance and mounting space can be achieved.

<Method for producing lithium ion secondary battery>
The manufacturing method in particular of a lithium ion secondary battery is not restrict | limited, It can manufacture by a well-known method. Specifically, it includes (1) production of electrodes, (2) production of single cell layers, (3) production of power generation elements, and (4) production of stacked batteries. Hereinafter, although an example is given and demonstrated about the manufacturing method of a lithium ion secondary battery, it is not limited to this. In addition, in the preparation of the inclined electrode in which the mixing ratio of the Si material (Si alloy) is increased by an appropriate amount from the current collector to the positive electrode facing side as in the case of the negative electrode of this embodiment, It can be produced by means (conditions) described.

(1) Production of electrodes (positive electrode and negative electrode) The electrode (positive electrode or negative electrode) is prepared, for example, by preparing an active material slurry (positive electrode active material slurry or negative electrode active material slurry) and applying the active material slurry onto a current collector. It can be made by drying, then pressing. The active material slurry includes the above-described active material (positive electrode active material or negative electrode active material), a binder (in the case where an aqueous binder is used on the negative electrode side, it is desirable to use a thickener together), a conductive auxiliary agent, and a solvent. In addition, in order to control the dispersion of the dispersibility of the binder in the electrode active material layer surface (further, an additive such as a conductive auxiliary agent), mainly when stirring using the ultrasonic vibration at the time of preparing the electrode active material slurry What is necessary is just to change and change vibration time, an ultrasonic wavelength, etc. In addition to this, it may be adjusted mainly by changing the dispersion (stirring mixing) time at the time of preparing the electrode active material slurry. Specifically, it may be dried at the above drying temperature for 6 to 18 hours, preferably 12 to 18 hours. Alternatively, three or more types having different solid content ratios in the negative electrode active material slurry may be prepared and applied in that order and dried to form a negative electrode active material layer having a laminated structure of three or more layers. It is not something. In a mass production process, a roll-to-roll system is used to collect a slurry on the back surface of a current collector using a die coater on a belt-shaped (ribbon-shaped) current collector that is drawn from a roll-shaped current collector and conveyed. May be applied (coated) and dried while being conveyed. Alternatively, after applying (coating) a slurry to the surface of the current collector using a die coater on a belt-shaped (ribbon-shaped) current collector that is drawn out and conveyed from the current collector wound in a roll, You may dry, conveying a collector in the state twisted (inverted) 180 degreeC.

  As a method for producing a gradient electrode having a Si material (Si alloy) ratio in the negative electrode, when preparing the negative electrode active material slurry, the solid content ratio in the slurry (active material weight + conducting agent weight + thickening agent) Weight + total solid content such as binder powder weight / slurry weight) is 35 to 45 mass%. By doing so, it becomes easy to lower the slurry viscosity and to incline it. After applying (applying) this slurry onto a current collector (current collector foil), the slurry is dried in a low temperature environment of 40 to 90 ° C. with the coated surface facing down. By doing so, the Si material (Si alloy) is closer to the positive electrode facing surface side due to the specific gravity relationship between the Si material (Si alloy) active material particles and the carbon material active material particles, and an inclined electrode can be produced. In order to further increase the inclination, it is preferable that the solid content ratio in the slurry is 36 to 43% by mass and the drying temperature is in the range of 40 to 70 ° C. In addition, in addition to the above method, adjustment may be made by further changing the drying time. Alternatively, three or more types having different solid content ratios in the negative electrode active material slurry may be prepared and applied in that order and dried to form a negative electrode active material layer having a laminated structure of three or more layers. It is not something.

  The solvent is not particularly limited, and N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide, cyclohexane, hexane, water and the like can be used.

  A method for applying the active material slurry to the current collector is not particularly limited, and examples thereof include a screen printing method, a spray coating method, an electrostatic spray coating method, an ink jet method, and a doctor blade method.

  The method for drying the coating film formed on the surface of the current collector is not particularly limited as long as at least a part of the solvent in the coating film is removed. An example of the drying method is heating. Drying conditions (drying time, drying temperature, etc.) can be appropriately set according to the volatilization rate of the solvent contained in the applied active material slurry, the coating amount of the active material slurry, and the like. A part of the solvent may remain. The remaining solvent can be removed by a press process described later.

  The pressing means is not particularly limited, and for example, a calendar roll, a flat plate press or the like can be used.

(2) Production of single cell layer The single cell layer can be produced by laminating the electrodes (positive electrode and negative electrode) produced in (1) via a separator (electrolyte layer).

(3) Production of power generation element The power generation element can be produced by laminating the single battery layer produced in the above (2) in consideration of the output and capacity of the single battery layer, the output and capacity required for the battery, and the like. .

(4) Manufacture of laminated battery As the structure of the battery, various shapes such as a rectangular shape, a paper shape, a laminated shape, a cylindrical shape, and a coin shape can be adopted. Further, the current collector and insulating plate of the component parts are not particularly limited, and may be selected according to the above shape. However, in the present embodiment, a stacked battery is preferable. In the stacked battery, a lead is joined to the current collector of the power generation element obtained above, and the positive electrode lead or the negative electrode lead is joined to the positive electrode tab or the negative electrode tab. A power generation element is placed in a laminate sheet so that the positive electrode tab and the negative electrode tab are exposed to the outside of the battery, and an electrolytic solution is injected with a liquid injector and then sealed in a vacuum to produce a stacked battery. sell.

(5) Activation treatment, etc. In the present embodiment, from the viewpoint of enhancing the performance and durability of the laminated battery obtained as described above, initial charge treatment, gas removal treatment, activation treatment, etc. are further required under the following conditions. Depending on In this case, the three sides of the laminate sheet (exterior material) are completely sealed in a rectangular shape by thermocompression when sealing in the production of the laminated battery of (4) so that the gas removal treatment can be performed. Stop (main sealing), and the remaining one side is temporarily sealed by thermocompression bonding. The remaining one side may be freely opened and closed by, for example, clip fastening, but from the viewpoint of mass production (production efficiency), it is preferable to temporarily seal the side by thermocompression bonding. In this case, it is only necessary to adjust the temperature and pressure for pressure bonding. When temporarily sealed by thermocompression, it can be opened by lightly applying force, and after degassing, it may be sealed again by thermocompression, or finally completely sealed by thermocompression ( Main sealing).

(First charging process)
The battery aging process (initial charging process) is preferably performed as follows. At 25 ° C. (within ± 2.5 ° C .; ambient temperature; the same applies hereinafter), 0.05 C and 4 hours of charging (SOC approximately 20%) are performed by the constant current charging method. Next, after charging to 4.45 V at a 0.1 C rate at 25 ° C., the charging is stopped, and the state (SOC is about 70%) is maintained for about 2 days (48 hours).

(First (first) gas removal process)
Next, the following process is performed as the first (first) gas removal process. First, one side temporarily sealed by thermocompression bonding is opened, gas is removed at 10 ± 3 hPa for 5 minutes, and then thermocompression bonding is performed again to perform temporary sealing. Further, pressurization with a roller (surface pressure 0.5 ± 0.1 MPa) is performed, and the electrode and the separator are sufficiently adhered.

(Activation process)
Next, the following electrochemical pretreatment method is performed as an activation treatment method.

  First, the battery is charged at 25 ° C. by a constant current charging method until the voltage reaches 4.45 V at 0.1 C, and then discharged twice to 2.0 V at 0.1 C. Similarly, after charging at 25 ° C. to 4.55 V at 0.1 C by the constant current charging method, a cycle of discharging to 2.0 V at 0.1 C once is 4.65 V at 0.1 C. The battery is charged until it reaches 0, and then discharged once at 0.1 C to 2.0 V. Furthermore, a cycle of charging at 0.1 C to 4.75 V by a constant current charging method at 25 ° C. and then discharging to 0.1 V at 0.1 C may be performed once.

  In this example, the constant current charging method is used as the activation processing method, and the electrochemical pretreatment method when the voltage is set as the termination condition is described as an example, but the charging method is a constant current constant voltage charging method. You may use. Further, as the termination condition, a charge amount or time may be used in addition to the voltage.

(Last (second) gas removal process)
Next, the following process is performed as the last (second) gas removal process. First, one side temporarily sealed by thermocompression bonding is opened, gas is removed at 10 ± 3 hPa for 5 minutes, and then thermocompression bonding is performed again to perform main sealing. Further, pressurization with a roller (surface pressure 0.5 ± 0.1 MPa) is performed, and the electrode and the separator are sufficiently adhered.

  In the present embodiment, the performance and durability of the obtained battery can be enhanced by performing the initial charging process, the gas removal process, and the activation process described above.

[Battery]
The assembled battery is configured by connecting a plurality of batteries. Specifically, it is constituted by serialization and / or parallelization using at least two batteries. Capacitance and voltage can be freely adjusted by paralleling in series.

  A plurality of batteries can be connected in series or in parallel to form a small assembled battery that can be attached and detached. Then, a plurality of small assembled batteries that can be attached and detached are connected in series or in parallel to provide a large capacity and large capacity suitable for vehicle drive power supplies and auxiliary power supplies that require high volume energy density and high volume output density. An assembled battery having an output can also be formed. How many batteries are connected to make an assembled battery, and how many small assembled batteries are stacked to make a large-capacity assembled battery depends on the battery capacity of the mounted vehicle (electric vehicle) It may be determined according to the output.

[vehicle]
The nonaqueous electrolyte secondary battery of the present invention including the lithium ion secondary battery according to the present embodiment maintains a discharge capacity even when used for a long period of time, and has good cycle characteristics. Furthermore, the volume energy density is high. Vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles require higher capacity, larger size, and longer life than electric and portable electronic devices. . Therefore, the lithium ion secondary battery (non-aqueous electrolyte secondary battery) can be suitably used as a vehicle power source, for example, a vehicle driving power source or an auxiliary power source.

  Specifically, a battery or an assembled battery formed by combining a plurality of these batteries can be mounted on a vehicle. In the present invention, since a battery having a long life with excellent long-term reliability and output characteristics can be configured, a plug-in hybrid electric vehicle having a long EV mileage or an electric vehicle having a long charge mileage can be formed by mounting such a battery. . For example, in the case of a car, a hybrid car, a fuel cell car, an electric car (four-wheeled vehicles (passenger cars, trucks, buses, commercial vehicles, light cars, etc.) This is because it can be used for motorcycles (including motorcycles) and tricycles) to provide a long-life and highly reliable automobile. However, the application is not limited to automobiles. For example, it can be applied to various power sources for moving vehicles such as other vehicles, for example, trains, and power sources for mounting such as uninterruptible power supplies. It is also possible to use as.

  Hereinafter, although it demonstrates still in detail using an Example and a comparative example, this invention is not necessarily limited to the following Examples at all.

1. Production of Positive Electrode 94% by mass of NMC composite oxide as a positive electrode active material, 3% by mass of acetylene black as a conductive additive, 3% by mass of polyvinylidene fluoride (PVDF) as a binder, and N-methyl- which is a slurry viscosity adjusting solvent An appropriate amount of 2-pyrrolidone (NMP) was mixed to prepare a positive electrode active material slurry. The obtained positive electrode active material slurry is applied to the surface of an aluminum foil (thickness: 20 μm) as a positive electrode current collector, dried at 120 ° C. for 3 minutes, and then compression-molded with a roll press to form a positive electrode with a rectangular planar shape An active material layer was produced. Similarly, a positive electrode active material layer was formed on the back surface to produce a positive electrode in which a positive electrode active material layer was formed on both surfaces of a positive electrode current collector (aluminum foil). In addition, the single-sided coating amount of the positive electrode active material layer was 21 mg / cm ² (not including the foil). Further, the density of the positive electrode active material layer was 3.0 g / cm ³ (excluding the foil). Further, the aspect ratio of the electrode (the aspect ratio of the rectangular positive electrode active material layer) was 1.3.

The PVDF includes Kureha Battery Materials Japan Co., Ltd., Kureha KF Polymer, powder type, grade no. W # 7200 was used. Further, as the NMC composite oxide, one having a composition represented by LiNi _0.5 Mn _0.3 Co _0.2 O ₂ (average particle diameter of 15 μm) was used. When this is applied to the general formula (1) described above: Li _a Ni _b Mn _c Co _d M _x O ₂ , a = 1, b = 0.5, c = 0.3, d = 0.2, x = 0 and b + c + d = 1, and those satisfying the requirements of the general formula (1) were used. This NMC composite oxide was prepared by the following preparation method.

(Preparation of NMC complex oxide)
To an aqueous solution (1 mol / L) in which nickel sulfate, cobalt sulfate, and manganese sulfate are dissolved, sodium hydroxide and ammonia are continuously supplied at 60 ° C. to adjust the pH to 11.3. And a metal composite hydroxide in which manganese and cobalt were dissolved in a molar ratio of 50:30:20.

This metal composite hydroxide and lithium carbonate were weighed so that the ratio of the total number of moles of metals other than Li (Ni, Mn, Co) and the number of moles of Li was 1: 1, and then mixed well. The temperature was raised at a rate of temperature increase of 5 ° C./min, calcined at 900 ° C. for 2 hours in an air atmosphere, then heated at a rate of temperature increase of 3 ° C./min, main baked at 920 ° C. for 10 hours, and cooled to room temperature. Thus, an NMC composite oxide which is a positive electrode active material having a composition of LiNi _0.5 Mn _0.3 Co _0.2 O ₂ was obtained. The secondary particle diameter (average particle diameter D50) of the obtained NMC composite oxide was 10 μm. The secondary particle size (average particle size D50) used was a value obtained by a laser diffraction method (the same applies hereinafter).

2. Production of Negative Electrode Production of Negative Electrode of Comparative Example 1-1 As negative electrode active material, 76.8% by mass of natural graphite and 19.2% by mass of Si—Ti alloy, 1% by mass of carbon black as a conductive additive, 2% by mass of SBR as binder, and As a thickener, 1% by mass of an ammonium salt of CMC was prepared. These were added to purified water and stirred for 4 minutes using a stirring deaerator to prepare a negative electrode active material (aqueous) slurry sufficiently dispersed. The solid content ratio of the negative electrode active material (aqueous) slurry was adjusted to 46% by mass. The solid content ratio is obtained by dividing the total weight (solid content) of the negative electrode active material Si-Ti alloy (Si material) and natural graphite (carbon material), binder powder, conductive additive and thickener by the slurry weight. Percentage (mass%) is shown. Further, Super-P (registered trademark) (with an average particle size (secondary particle size) D50 of 40 nm) manufactured by IMERYS was used as the carbon black. Also, a styrene-butadiene rubber latex was used as the binder, and the content of styrene-butadiene rubber (SBR) in the solid content was 2 mass%. The ammonium salt of CMC as a thickener is an abbreviation for ammonium salt of carboxymethyl cellulose. In addition, the natural graphite which is a carbon material of a negative electrode active material used that whose average particle diameter (secondary particle diameter) D50 is 20 micrometers. Moreover, what was obtained with the following synthetic | combination methods was used for Si-Ti alloy which is Si material (Si alloy) of a negative electrode active material.

(Synthesis of Si-Ti alloy)
As the Si—Ti alloy, an alloy having a composition represented by Si ₉₀ Ti ₁₀ (unit: mass%) was used. This Si-Ti alloy was manufactured (prepared) by a mechanical alloy method. Specifically, using a planetary ball mill device P-6 manufactured by Fricht, Germany, zirconia pulverized balls and alloy raw material powders were put into a zirconia pulverized pot and alloyed at 450 rpm for 48 hours (alloying treatment). ), And then pulverization was performed at 400 rpm for 1 hour. Si and Ti metal powders were used as alloy raw material powders. In addition, the average particle diameter (secondary particle diameter) D50 of the obtained Si—Ti alloy powder was 2 μm. Here, the alloying treatment is performed by applying high energy to the alloy raw material powder at high rotation (450 rpm). On the other hand, the pulverization process is a process of loosening secondary particles at a low rotation (400 rpm) (not alloyed in this process). Moreover, the average particle diameter D50 of the obtained Si—Ti alloy powder was 2 μm.

The negative electrode active material (aqueous) slurry is applied to a copper foil (thickness 10 μm) serving as a negative electrode current collector, dried at 120 ° C. for 10 minutes, and then compression-molded with a roll press to form a negative electrode active material having a rectangular planar shape. A layer was made. In the same manner, a negative electrode active material layer was formed on the back surface to prepare a negative electrode in which a negative electrode active material layer was formed on both sides of a negative electrode current collector (copper foil). In addition, the single-sided coating amount of the negative electrode active material layer was 7.6 mg / cm ² (excluding the foil). That is, the coating amount on one side of the negative electrode active material layer was adjusted so that the A / C ratio was 1.20 with the positive electrode facing when the battery described later was manufactured. The thickness of the negative electrode active material layer (one side) was 55 μm. Moreover, the density of the negative electrode active material layer was 1.6 g / cm ³ (not including the foil). Here, the A / C ratio refers to a capacity ratio of a negative electrode (Anode) capacity (Li reception amount) and a positive electrode (Cathode) capacity (Li discharge amount). That is, the A / C ratio is a ratio of the amount of Li received (capacity) of the negative electrode to the amount of Li discharge (capacity) of the positive electrode. Moreover, what was designed based on the measured capacity measured by the half cell was used for these capacity ratios. Moreover, the density of the negative electrode active material layer was 1.6 g / cm ³ (not including the foil). Furthermore, when the negative electrode active material layer is applied to Formula (1), which is α (Si material) + β (carbon material), the Si material is a Si—Ti alloy, the carbon material is natural graphite, α + β = 96, α = 19.2 and β = 76.8, which satisfy the requirement of the expression (1).

Production of Negative Electrode of Comparative Example 1-2 In Comparative Example 1-1, the same as Comparative Example 1-1 except that the solid content ratio of the slurry was 43 mass% and the drying temperature after coating was 30 ° C. A negative electrode was produced. The density of the negative electrode active material layer was 1.6 g / cm ³ (excluding the foil).

Production of negative electrode of Comparative Example 1-3 In Comparative Example 1-1, except that the solid content ratio of the slurry was 38% by mass, the coated surface was down after coating, and drying was performed at 60 ° C. A negative electrode was produced in the same manner as in Example 1-1. The density of the negative electrode active material layer was 1.6 g / cm ³ (excluding the foil).

Preparation of negative electrode of Example 1-1 In Comparative Example 1-1, except that the solid content ratio of the slurry was 43% by mass, the coated surface was down after coating, and drying was performed at 60 ° C. A negative electrode was produced in the same manner as in Example 1-1. The density of the negative electrode active material layer was 1.6 g / cm ³ (excluding the foil).

Preparation of negative electrode of Example 1-2 In Comparative Example 1-1, except that the solid content ratio of the slurry was 41% by mass, the coated surface was down after coating, and drying was performed at 40 ° C. A negative electrode was produced in the same manner as in Example 1-1. The density of the negative electrode active material layer was 1.6 g / cm ³ (excluding the foil).

3. Production of Battery The positive electrode obtained in 1 above and the negative electrode obtained in 2 above were cut out to have an active material layer area: 4 cm long × 3 cm wide, and a porous polypropylene separator (thickness 25 μm, porosity 55%) ) (One positive electrode and two negative electrodes) to produce a power generation element. A positive electrode lead and a negative electrode lead were joined to each current collector of the obtained power generation element, and these positive electrode lead or negative electrode lead were joined to a positive electrode current collector plate or a negative electrode current collector plate. Then, the power generation element is inserted into a bag made of aluminum laminate sheet (length 4.5 cm × width 3.5 cm) as a battery exterior material so that the positive electrode collector plate and the negative electrode collector plate are exposed to the outside of the battery. The electrolytic solution was injected from the opening by a machine. This aluminum laminate sheet bag is made by stacking two aluminum laminate sheets (a film sheet obtained by laminating aluminum with a film containing polypropylene) and sealing three of the four outer peripheries (outer edges) by thermocompression bonding. (Seal) and the remaining one side is unsealed (opening). As the electrolyte solution, 3 of 1.0 M LiPF ₆ ethylene carbonate (EC) and diethyl carbonate (DEC): with respect to: (a volume ratio of DEC EC) mixed and dissolved in the solvent solution 100 parts by weight, 7 What added 1 mass part of vinylene carbonate which is an additive was used. Here, the injection amount of the electrolytic solution was set to an amount that is 1.50 times the total pore volume (calculated by calculation) of the positive electrode active material layer, the negative electrode active material layer, and the separator. Next, under vacuum conditions, the opening of the aluminum laminate sheet bag is sealed by thermocompression bonding so that the positive and negative current collectors connected to both electrodes (current collectors) via leads Thus, a test cell which is a laminated lithium ion secondary battery was completed. The rated capacity of the battery at this time is the following 4.2. From the measurement result of the rated capacity, it was 80 mAh (0.080 Ah).

4). Evaluation of battery 4.1. Evaluation of battery characteristics Each battery (test cell) obtained above was subjected to a charge / discharge test under the following conditions to measure the rated capacity and further evaluate cycle durability.

4.2. Measurement of rated capacity The rated capacity of a battery (test cell) was determined as follows.

  The rated capacity is about 10 hours after injecting the electrolyte solution for the battery (test cell), and then the temperature is 25 ° C. (within ± 2.5 ° C .; ambient temperature), 3.0 V to 4 Measured by the following procedures 1 to 5 in the voltage range of 15V.

  Procedure 1: After reaching 4.15 V with a constant current charge of 0.1 C, it was rested for 5 minutes.

  Procedure 2: After Procedure 1, the battery was charged with constant voltage charging for 1.5 hours and rested for 5 minutes.

  Procedure 3: After reaching 3.0 V by constant current discharge of 0.1 C, the battery was discharged by constant voltage discharge for 2 hours and then rested for 10 seconds.

  Procedure 4: After reaching 4.1 V by constant current charging at 0.1 C, charging was performed for 2.5 hours by constant voltage charging, and then paused for 10 seconds.

  Procedure 5: After reaching 3.0 V by 0.1 C constant current discharge, it was discharged by constant voltage discharge for 2 hours, and then stopped for 10 seconds.

  Rated capacity: The discharge capacity (CCCV discharge capacity) in the discharge from the constant current discharge to the constant voltage discharge in the procedure 5 was defined as the rated capacity.

4.3. Evaluation of cycle durability In the evaluation of cycle durability, the above 3. For each battery (test cell) obtained in the production of the battery, charging / discharging at a rate of 0.5 C was repeated 100 cycles at 25 ° C. (within ± 2.5 ° C .; the same applies hereinafter). When the battery was evaluated, charging was performed by a constant current and constant voltage charging method until the current value reached 0.01 C after charging at a 0.5 C rate until the maximum voltage reached 4.2 V. Moreover, the discharge conditions were performed by the constant current discharge method which discharges at a 0.5C rate until the minimum voltage of a battery will be 3.0V. All were performed under normal temperature and normal pressure (25 ° C., atmospheric pressure). The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle was evaluated as “capacity maintenance ratio (%)”. The obtained results are shown in the column “Maintenance rate (%) @ 100cyc” in Table 1 below.

4.4. Measurement of the gradient electrode structure of the negative electrode active material layer (When the in-plane central portion (one location) is selected as the measurement location in the negative electrode active material layer surface, when the cross section of the negative electrode active material layer is equally divided into three in the electrode thickness direction. In addition, the calculation method of the ratio of the area of the Si material within each divided area)
3. above. A negative electrode (4 cm long × 3 cm wide) was prepared in the same manner as the battery. Using this cross-section polisher method as a cross-section polishing method, this negative electrode is irradiated with an argon ion beam to the sample, and the sample is cut using a sputtering phenomenon that blows off sample atoms, thereby passing an axis passing through the center in the plane. The cross section was processed along the direction. Then, for one location (one piece of image data) of the negative electrode cross section; central portion (image size; horizontal (in-plane direction) 100 μm × vertical (thickness direction) 70 μm; including negative electrode active material layer portion on one side) A backscattered electron image was taken with an electron microscope (SEM) (see FIG. 4A). The SEM image (reflected electron image) is binarized using image processing software (WinROOF manufactured by Mitani Corp.) to make the image gray scale, and then the Si material portion and the gray scale of the portion other than the Si material portion. A processed image (see FIG. 4B) in which a threshold was set between the values was obtained. For this processed image, the negative electrode active material layer cross section was equally divided into three in the electrode thickness direction, and the area amount of the Si material portion in each divided area was determined. Thereafter, the ratio of the area of the Si material portion to the total area of each divided image (the area of the Si material / the area of the entire image × 100 (%)) was calculated. As a method of setting the threshold value, an intermediate value between numerical values of the Si material and the material other than the Si material portion was set as the threshold value. 4A is a view showing a reflected electron image (measurement image) taken by an electron microscope (SEM) of the negative electrode of Comparative Example 1-1, and FIG. 4B is a view showing FIG. 4A. Is a drawing obtained by converting the measurement image into a gray scale by binarization processing (a white portion in the drawing corresponds to a Si material portion). In FIG. 4B, the negative electrode active material layer cross section is equally divided into three in the thickness direction for the processed image, and the three divided cross sections (divided sections) are collected from the positive electrode facing surface (surface; separator) side. A, B, and C are attached in order toward the electric body. In addition, when the negative electrode active material layer cross section is equally divided into three in the thickness direction, when the entire negative electrode active material layer cross section in the electrode thickness direction is 100%, the ratio (division ratio) of each divided cross section is 33.3. % ± 0.3% (preferably ± 0.1%), and the total may be 100%.

  Specifically, the result of the negative electrode cross section SEM (the SEM image (see FIG. 4A)) is binarized and grayscaled, the threshold value is set, and the processed image (see FIG. 4B). In this processed image, the cross section of the negative electrode active material layer (one side thickness: 55 μm) not including the current collector on one side was equally divided into three in the thickness direction. The ratio (%) of the area of the Si material was calculated (using the above-described image processing software) in Table 1. In Table 1, the cross-section (divided section) divided into three sections from the positive electrode facing surface (surface) side to the current collector side A, B, and C in this order (corresponding to A, B, and C attached to a three-divided cross section (division section) in FIG. 4B).

  From the results in Table 1, as shown in Example 1-1, in the inclined electrode in which the mixing ratio of the Si material increases from the current collector side (section C) to the positive electrode facing surface side (section A), Comparative Example 1- Compared with the electrode having no inclination shown in FIG. 1, a significant improvement effect in the discharge capacity retention rate was confirmed. This is because there is little Si material with a large volume change near the current collector, so damage to the current collector and peeling of the negative electrode active material layer are reduced, and electronic conductivity is maintained during the charge / discharge process. Seem. Furthermore, as shown in Example 1-2, when the rate of increase in the slope (the rate at which the area (ratio) of the Si material increases between the sections A to C) is as large as 5% or more, the durability is high. The further improvement of the property can be confirmed, and it is considered that the above effect is further exhibited.

  Further, as shown in Comparative Example 1-2, the durability of the inclined electrode in which the mixing ratio of the Si material decreases from the current collector side (divided section C) to the positive electrode facing surface side (divided section A) is observed. It was. This is because there are many Si materials with a large volume change near the current collector, causing peeling of the negative electrode active material layer and deformation of the current collector in the vicinity of the current collector. It seems to have done.

  Moreover, as shown in Comparative Example 1-3, when the rate of increase in the slope was as high as 15 to 16% (exceeding 12%), a decrease in durability was observed. This is probably because the rate of change is too high and the rate of volume change in the ABC divisions (blocks) is too large, causing delamination between the blocks.

  From the above, the volume change in the vicinity of the current collector is achieved by using an inclined electrode in which the mixing ratio of the Si material increases by an appropriate amount (1 to 12%) from the current collector side to the positive electrode facing surface side as in this embodiment. Since there are few large Si materials, the damage to an electrical power collector and peeling of an active material layer are reduced. As a result, it is confirmed that the electronic conductivity is maintained during the charge / discharge process, so that the high capacity can be maintained, the discharge capacity maintenance rate can be greatly improved, and both the capacity and the cycle durability can be achieved. did it.

10, 50 lithium ion secondary battery,
11, 31 Negative electrode current collector,
12 positive electrode current collector,
13, 33 negative electrode active material layer,
15 positive electrode active material layer,
17 electrolyte layer (separator),
19 cell layer,
21, 57 power generation element,
25 negative current collector,
27 positive current collector,
29, 52 Battery exterior material,
30 negative electrode,
33a Coating film (coating film),
35 Si material (Si alloy) active material particles,
37 carbon material active material particles,
58 positive electrode tab,
59 Negative electrode tab.

Claims (8)

A negative electrode for a non-aqueous electrolyte secondary battery, comprising: a current collector; and a negative electrode active material layer including a negative electrode active material disposed on a surface of the current collector,
The negative electrode active material layer has the following formula (1)
(In the formula, the Si material is a material made of an alloy containing Si, α and β represent mass% of each component in the negative electrode active material layer, and 80 ≦ α + β ≦ 98, 0.1 ≦ α ≦ 40, 58 ≦ β ≦ 97.9)).
When an arbitrary place in the negative electrode active material layer plane is selected, when the negative electrode active material layer cross section is equally divided into three in the electrode thickness direction, the area of the Si material in each divided area is the current collector. A negative electrode for a nonaqueous electrolyte secondary battery, characterized by increasing from 1% to 12% from the body side to the positive electrode facing surface side.   2. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the area of the Si material increases by 5% or more and 10% or less from the current collector side to the positive electrode facing surface side. The negative electrode according to claim 1 or 2,
A positive electrode having a current collector and a positive electrode active material layer including a positive electrode active material disposed on a surface of the current collector;
A separator;
A non-aqueous electrolyte secondary battery comprising: a power generation element including: The positive electrode active material has the general formula (1): Li _a Ni _b Mn _c Co _d M _x O ₂ (where a, b, c, d, and x are 0.9 ≦ a ≦ 1.2, 0 < b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3, b + c + d = 1, M is Ti, Zr, Nb, W, P, Al, Mg 4. The non-aqueous electrolyte secondary battery according to claim 3, wherein the non-aqueous electrolyte secondary battery includes a lithium nickel-based composite oxide represented by at least one selected from the group consisting of V, Ca, Sr, and Cr.   The nonaqueous electrolyte secondary battery according to claim 3 or 4, wherein the separator is a separator in which a heat-resistant insulating layer is laminated on a porous substrate. The value of the ratio of the battery volume to the rated capacity (product of the projected area and thickness of the battery including the battery outer package) is 10 cm ³ / Ah or less, and the rated capacity is 3 Ah or more. The nonaqueous electrolyte secondary battery according to any one of the above.   The electrode shape is rectangular, and the aspect ratio of the electrode defined as the aspect ratio of the rectangular electrode active material layer is 1 to 4, wherein the electrode has an aspect ratio of 1 to 6. Non-aqueous electrolyte secondary battery.   The nonaqueous electrolyte according to any one of claims 3 to 7, wherein the nonaqueous electrolyte has a configuration in which the power generation element is enclosed in a battery outer package made of a laminate film containing aluminum. Secondary battery.