JP6308396B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  Non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries are lighter and have higher energy density than existing batteries, and have recently been used as so-called portable power sources for vehicles and personal computers and power sources for vehicle driving. ing. In particular, lithium-ion secondary batteries that are lightweight and provide high energy density will become increasingly popular as high-output power sources for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). It is expected to do.

  Lithium ion secondary batteries used for high output power sources for driving vehicles are required to have higher performance, and higher energy density is being achieved as part of higher performance. One way to increase the energy density of a lithium ion secondary battery is to use a positive electrode active material having a high operating potential (high potential positive electrode active material).

  As a positive electrode active material having a high operating potential, a lithium nickel manganese composite oxide having a spinel crystal structure (hereinafter also referred to as “NiMn spinel structure oxide”) is known. This NiMn-based spinel structure oxide can exhibit an operating potential of 4.5 V or higher.

  In order to improve the characteristics of the NiMn-based spinel structure oxide, a part of the transition metal site of the NiMn-based spinel structure oxide is replaced with a different element. For example, in Patent Document 1, when a NiMn-based spinel structure oxide in which part of a transition metal site is substituted with Fe and Ti is used as a positive electrode active material of a secondary battery, the cycle life of the secondary battery is increased. It is described.

JP 2013-143262 A

  However, according to the study by the present inventors, in the secondary battery using the NiMn spinel structure oxide in which part of the transition metal site described in Patent Document 1 is substituted with Fe and Ti, the cycle life of the secondary battery is It has been found that there is still room for improvement. In addition, it has been found that there is room for improvement in the thermal safety of the positive electrode active material.

  Accordingly, an object of the present invention is to provide a secondary battery using a NiMn-based spinel structure oxide and having improved cycle life and thermal safety of a positive electrode active material.

The non-aqueous electrolyte secondary battery disclosed herein includes a positive electrode having a positive electrode active material layer on a positive electrode current collector, a negative electrode having a negative electrode active material layer on a negative electrode current collector, a non-aqueous electrolyte, Is provided. The positive electrode active material layer is a lithium transition metal composite oxide having a spinel structure containing Li as a positive electrode active material and Ni and Mn as transition metal elements, wherein the transition metal site of the lithium transition metal composite oxide A part is characterized by having a lithium transition metal composite oxide substituted with Ti, Fe and Al.
The present inventor has disclosed a NiMn-based spinel structure oxide in which a part of transition metal sites in a NiMn-based spinel structure oxide is substituted by a trimetallic element of Ti, Fe and Al as a positive electrode active material. As a result, it was found that capacity deterioration and heat generation at a high temperature of the non-aqueous electrolyte secondary battery were suppressed, and the present invention was completed.
Therefore, according to the configuration in which the NiMn spinel structure oxide containing the three metal elements of Ti, Fe and Al is used as the positive electrode active material, the non-aqueous electrolyte with improved cycle life and thermal safety of the positive electrode active material layer A secondary battery is provided.

It is a perspective view which shows typically the external shape of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is sectional drawing which follows the II-II line | wire in FIG.

  Embodiments according to the present invention will be described below with reference to the drawings. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, a general configuration and manufacturing process of a battery that does not characterize the present invention) It can be grasped as a design matter of those skilled in the art based on the prior art. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Moreover, in the following drawings, the same code | symbol is attached | subjected and demonstrated to the member and site | part which show | plays the same effect | action. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

  In the present specification, the “secondary battery” refers to a general power storage device that can be repeatedly charged and discharged, and is a term including a so-called storage battery such as a lithium ion secondary battery and a power storage element such as an electric double layer capacitor. The “non-aqueous electrolyte secondary battery” refers to a secondary battery provided with a non-aqueous electrolyte (that is, an electrolyte containing a supporting electrolyte in a non-aqueous solvent). The “lithium ion secondary battery” refers to a non-aqueous electrolyte secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by the movement of lithium ions between the positive and negative electrodes. Hereinafter, the present invention will be described in detail by taking a flat rectangular lithium ion secondary battery as an example. It should be noted that the present invention is not intended to be limited to that described in the embodiment.

  As shown in FIGS. 1 and 2, the lithium ion secondary battery 10 of this embodiment includes a battery case 15. The battery case 15 of the present embodiment may be made of metal (eg, aluminum, stainless steel, nickel-plated steel, etc.) or resin (eg, polyphenylene sulfide resin, polyimide resin, etc.). Here, Made of aluminum or aluminum alloy.

  The battery case 15 includes a case main body (exterior case) 30 having a flat bottomed box shape (typically a rectangular parallelepiped shape) with an open upper end, and a lid body 25 that closes an opening of the case main body 30. I have. The battery case 15 is electrically connected to the upper surface (that is, the lid body 25) of the positive electrode terminal 60 electrically connected to the positive electrode sheet 64 of the wound electrode body 100 and the negative electrode sheet 84 of the wound electrode body 100. A negative electrode terminal 80 is provided. Further, the lid body 25 is formed with an inlet (not shown) for injecting a non-aqueous electrolyte described later into the case body 30 (battery case 15) in which the wound electrode body 100 is accommodated. . The inlet is sealed with a sealing plug after the nonaqueous electrolyte is injected.

As the nonaqueous electrolytic solution, typically, an organic solvent (nonaqueous solvent) containing a supporting salt is used. As the supporting salt, a lithium salt, a sodium salt or the like can be used, and among them, a lithium salt such as LiPF ₆ or LiBF ₄ can be preferably used. As the organic solvent, aprotic solvents such as carbonates, esters and ethers can be used. Of these, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) can be preferably used. Alternatively, a fluorine-based solvent such as fluorinated carbonate such as monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), or trifluorodimethyl carbonate (TFDMC) is preferably used. be able to.

  Similar to the case of the conventional lithium ion secondary battery, the lid 25 is provided with a safety valve 40 for discharging the gas generated inside the battery case 15 to the outside of the battery case 15 when the battery is abnormal. . The wound electrode body 100 is in a case main body in a posture in which the wound axis of the wound electrode body 100 is laid down (that is, the opening is formed in the normal direction of the wound axis of the wound electrode body 100). 30. The opening of the case body 30 and the lid body 25 are joined and sealed by welding or the like.

  The wound electrode body 100 is in a state in which a positive electrode (long positive electrode sheet) 64 and a negative electrode (long negative electrode sheet) 84 are stacked with a total of two separators (long separator sheets) 90 interposed. It is wound in the longitudinal direction. At the time of the above lamination, the positive electrode active material layer non-formed portion of the positive electrode sheet 64 (that is, the portion where the positive electrode current collector 62 is exposed without forming the positive electrode active material layer 66) 63 and the negative electrode active material of the negative electrode sheet 84 The positive electrode sheet 64 and the negative electrode sheet are so formed that the non-layer-forming part (that is, the part where the negative electrode current collector 82 is exposed without forming the negative electrode active material layer 86) 83 protrudes from both sides in the width direction of the separator sheet 90. 84 are slightly shifted in the width direction and overlapped. As a result, a laminated portion in which the positive electrode sheet 64, the negative electrode sheet 84, and the separator sheet 90 are laminated and wound is formed in the central portion of the wound electrode body 100 in the winding axis direction.

  The positive electrode sheet 64 includes a positive electrode current collector 62 and a positive electrode active material layer 66 formed on the positive electrode current collector 62. The positive electrode active material layer 66 is formed on one side or both sides of the positive electrode current collector 62. As the positive electrode current collector 62, a conductive material made of a metal having good conductivity (for example, aluminum or aluminum alloy) can be preferably used. The positive electrode active material layer 66 typically includes a positive electrode active material, a conductive material, a binder (binder), and the like. The positive electrode active material used in this embodiment will be described later. As the conductive material, a carbon material such as carbon black (for example, acetylene black or ketjen black) can be adopted. As the binder, various polymer materials such as polyvinylidene fluoride (PVdF) and polyethylene oxide (PEO) can be employed.

  The negative electrode sheet 84 includes a negative electrode current collector 82 and a negative electrode active material layer 86 formed on the negative electrode current collector 82. The negative electrode active material layer 86 is formed on one side or both sides of the negative electrode current collector 82. As the negative electrode current collector 82, a conductive material made of a metal having good conductivity (for example, copper) can be preferably used. The negative electrode active material layer 86 typically includes a negative electrode active material, a binder, a thickener, and the like. As the negative electrode active material, a carbon material such as graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), or the like can be used, and among them, graphite can be preferably used. As the binder, various polymer materials such as styrene butadiene rubber (SBR) can be adopted. As the thickener, various polymer materials such as carboxymethyl cellulose (CMC) can be employed.

  As the separator sheet 90, a conventionally known one can be used without any particular limitation. For example, a porous sheet made of resin (a microporous resin sheet) can be preferably used. Among these, porous polyolefin resin sheets such as polyethylene (PE) and polypropylene (PP) are preferable. For example, a PE single layer sheet, a PP single layer sheet, a two layer structure (PE / PP structure) in which a PE layer and a PP layer are laminated, and a three layer structure in which a PP layer is laminated on both sides of the PE layer. A sheet of (PP / PE / PP structure) or the like can be preferably used.

  As shown in FIG. 2, a positive electrode terminal 60 (for example, made of aluminum) is joined to the positive electrode active material layer non-formation portion 63 of the wound electrode body 100 via a positive current collector plate 61. The positive electrode sheet 64 and the positive electrode terminal 60 are electrically connected. Similarly, a negative electrode terminal 80 (for example, made of nickel) is joined to the negative electrode active material layer non-forming portion 83 via a negative electrode current collector plate 81, and the negative electrode sheet 84 and the negative electrode terminal 80 are electrically connected. The positive and negative electrode terminals 60 and 80 and the positive and negative electrode active material layer non-forming portions 63 and 83 (typically, the positive and negative electrode current collectors 62 and 82) are joined by, for example, ultrasonic welding or resistance welding. be able to. In this way, the lithium ion secondary battery 10 is configured.

[Positive electrode active material]
In the present embodiment, the positive electrode active material is a lithium transition metal composite oxide having a spinel structure containing Li and Ni and Mn as transition metal elements, and part of the transition metal sites of the lithium transition metal composite oxide However, a lithium transition metal complex oxide substituted with Ti, Fe and Al is used. In other words, a NiMn spinel structure oxide in which a part of the transition metal site is substituted with Fe, Ti, and Al is used. If a lithium ion secondary battery is manufactured using such a NiMn-based spinel structure oxide as a positive electrode active material, a lithium ion secondary battery with improved cycle life and thermal safety of the positive electrode active material layer can be obtained. it can. This is because the NiMn spinel structure oxidation is performed by substituting a part of Ni, Mn (typically part of the Ni site), which is a main transition metal in the NiMn spinel structure oxide, with Fe, Ti and Al. This is thought to be because the bonding force between the transition metal and oxygen in the material increases, thereby improving the stability (durability) of the NiMn-based spinel structure oxide and suppressing the reaction with the electrolyte. .

  In the NiMn-based spinel structure oxide used as the positive electrode active material in this embodiment, a part of the transition metal site may be further substituted with an element other than Fe, Ti, and Al.

The NiMn-based spinel structure oxide used in the present embodiment preferably has an average composition represented by the following general formula (I).
_{Li x Mn 2-a-b} -c-d-e Ni a Ti b Fe c Al d M e O 4-y X y (I)
Here, in the above formula (I), M is Si, Mg, Ca, Ba, Sr, Sc, V, Cr, Co, Cu, Zn, Ga, Y, Ru, Rh, Pd, In, Sn, Sb. And at least one element selected from the group consisting of La, Ce, Sm, Zr, Nb, Ta, Mo, W, B, C, P, and S. X is at least one element selected from the group consisting of F and Cl. In a preferred embodiment, a, b, c, d and e in the above formula (1) are 0.3 <a <0.6, 0 <b <0.2, 0 <c <0.2, respectively. The values satisfy 0 <d <0.3 and 0 ≦ e <0.2. x is a value satisfying 0.9 <x <1.3. y is a value satisfying 0 ≦ y <0.1.

  X in the above formula (I) indicates the Li content in the NiMn spinel structure oxide, and is a value determined so as to satisfy the charge neutrality condition. Typically, x = 1 ± 0.25 (especially x = 1).

  In the above formula (I), a represents the Ni content ratio in the NiMn-based spinel structure oxide. In the NiMn-based spinel structure oxide, the cycle characteristics and the energy density can be improved by replacing part of the Mn site with Ni. Therefore, from the viewpoint of exhibiting the effect of such Ni substitution at a high level, it is more preferable that 0.35 ≦ a. Further, from the viewpoint of stably maintaining a stable spinel structure, it is more preferable that a ≦ 0.4.

In the above formula (I), b represents the Ti content ratio in the NiMn spinel structure oxide, c represents the Fe content ratio in the NiMn spinel structure oxide, and d represents the Al content ratio in the NiMn spinel structure oxide. Show.
When the Ti content in the NiMn-based spinel structure oxide is too large (typically, b in the above formula (I) is too larger than 0.2), the electron conductivity of the positive electrode active material decreases. In addition, battery resistance may increase in a lithium ion secondary battery in which the operating upper limit potential of the positive electrode is 4.5 V or more based on metallic lithium. Therefore, from the viewpoint of suppressing an increase in battery resistance while exhibiting a high level of Mn elution suppression effect by substituting part of Ni and Mn in the NiMn-based spinel structure oxide with Ti, Fe and Al. The above b is preferably 0 <b ≦ 0.15 (more preferably 0 <b ≦ 0.1, still more preferably 0.01 ≦ b ≦ 0.1).
Further, when the Fe content in the NiMn-based spinel structure oxide is too large (typically c in the above formula (I) is too larger than 0.2), the upper limit operating potential of the positive electrode is based on the metallic lithium Therefore, there is a possibility that the battery capacity that operates stably at 4.5V or more and 5V or less may decrease. Therefore, from the viewpoint of suppressing a decrease in battery capacity while exhibiting a high level of Mn elution suppression effect by substituting part of Ni and Mn in the NiMn-based spinel structure oxide with Ti, Fe and Al. The above c is preferably 0 <c ≦ 0.15 (more preferably 0 <c ≦ 0.1, and still more preferably 0.01 ≦ c ≦ 0.1).

  In addition, even when the Al content in the NiMn-based spinel structure oxide is too large (typically, d in the above formula (I) is excessively larger than 0.3), the battery capacity decreases, Battery resistance may increase. Therefore, while lowering the battery capacity and increasing the battery resistance while exhibiting a high level of Mn elution suppression effect by substituting part of Ni and Mn in the NiMn-based spinel structure oxide with Ti, Fe and Al. From the viewpoint of suppression, d is preferably 0 <d ≦ 0.2 (more preferably 0 <d ≦ 0.15, and still more preferably 0.01 ≦ d ≦ 0.1).

  M in the above formula (I) does not exist or is Si, Mg, Ca, Ba, Sr, Sc, V, Cr, Co, Cu, Zn, Ga, Y, Ru, Rh, Pd, In, Sn , Sb, La, Ce, Sm, Zr, Nb, Ta, Mo, W, B, C, P and S. At least one element selected from the group consisting of S and S. That is, as the NiMn spinel structure oxide, an oxide having only Li, Mn, Ni, Ti, Fe, and Al as constituent metal elements, or the above constituent metal elements (Li, Mn, Ni, Ti, Fe, Al, etc.) And an oxide containing one or more additional elements (M). The NiMn spinel structure oxide used in the present embodiment may be one in which M does not exist, but the battery performance is improved (for example, the energy density is increased, the durability (cycle characteristics) is improved, the input / output characteristics are improved, etc.) For the purpose, one or more elements selected from the elements listed above may be contained as M. M is preferably at least one element selected from the group consisting of Si, Co, La, Zr, Nb, Ta, W, and B. On the other hand, from the viewpoint of stably maintaining the spinel crystal structure, a NiMn-based spinel structure oxide in which M is not present in the general formula (I) is preferable.

  The composition of the elements constituting the NiMn-based spinel structure oxide is confirmed by a conventionally known inductively coupled plasma-atomic emission spectrometry (ICP-AES) or lanthanum-alizarin complexone spectrophotometry method. (Measurement).

In the above general formula (I), O _4-y can be described as O _4-y-δ strictly speaking. Here, δ represents the amount of oxygen vacancies in the above spinel crystal structure, and since it may vary depending on the type of substitution atom and the substitution ratio in the crystal structure, as well as environmental conditions, it is difficult to display accurately. Therefore, δ, which is a variable for determining the number of oxygen atoms, is typically a positive number not exceeding 1 or zero, and for example, 0 ≦ δ ≦ 1 can be adopted. However, in this specification, δ is omitted for the sake of convenience as illustrated in the preferred composite oxide. Therefore, the description of O _4-y in the general formula (I) is not intended to exclude the oxygen-deficient NiMn spinel structure oxide from the technical scope of the present invention.

  Hereinafter, the preferable manufacturing method of the said NiMn type | system | group spinel structure oxide which is a positive electrode active material is demonstrated. The manufacturing method includes a step of preparing a precursor of a NiMn-based spinel structure oxide and a firing step. The NiMn-based spinel structure oxide used in this embodiment is not limited to the one manufactured by the following manufacturing method.

<Precursor preparation step>
In the precursor preparation step, an element other than lithium and oxygen constituting the target NiMn-based spinel structure oxide, for example, a salt containing each constituent element other than lithium and oxygen in the above formula (I) alone (or 2 A basic aqueous solution having a pH of about 11 to 14 is added to an aqueous solution containing a salt containing at least a constituent element) and stirred, and a liquid phase reaction in the aqueous solution causes a general formula: Mn _2-a- bcd (where, m is a positive number not exceeding zero or 1, typically _{0 ≦ m ≦ 0.5.) -e} Ni a Ti b Fe c Al d M e (OH) 4 + m are represented by A precursor is prepared. The meanings of a, b, c, d, e and M are the same as in the above formula (I).
Examples of the basic aqueous solution include an aqueous solution of either a strong base (such as an alkali metal hydroxide) and a weak base (such as ammonia) or a mixed aqueous solution of a strong base and a weak base, and a pH at a liquid temperature of 25 ° C. Can be preferably used that is maintained at about 11 to 14 and does not inhibit the formation of the precursor. For example, a sodium hydroxide aqueous solution alone or a mixed solution of a sodium hydroxide aqueous solution and ammonia water is used.

  The aqueous solution in the precursor preparation step can be prepared, for example, by dissolving a predetermined amount of a desired nickel salt, manganese salt, titanium salt, iron salt, aluminum salt or the like in an aqueous solvent. The order in which these salts are added to the aqueous solvent is not particularly limited. Moreover, you may prepare by mixing the aqueous solution of each salt. What is necessary is just to select the anion of these metal salts (the said nickel salt, manganese salt, etc.) so that each said salt may become desired water solubility. For example, it may be sulfate ion, nitrate ion, chloride ion, carbonate ion and the like. That is, the metal salts may be sulfates such as nickel and manganese, nitrates, hydrochlorides, carbonates, and the like. All or part of these metal salt anions may be the same or different from each other. For example, nickel sulfate and manganese carbonate can be used in combination. These salts may be solvates such as hydrates. The order of addition of these metal salts is not particularly limited.

  A lithium salt as a Li source is further added to the precursor and mixed to obtain a raw material before firing for producing the target NiMn-based spinel structure oxide. As a lithium salt, the general lithium salt used for formation of the conventional lithium composite oxide can be especially used without a restriction | limiting. Specific examples of such a general lithium salt include lithium carbonate and lithium hydroxide. Further, when a part of O is substituted with F, lithium fluoride can be used as the lithium salt. These lithium salts can be used alone or in combination of two or more. By adjusting the addition amount of the lithium salt to be added, a NiMn-based spinel structure oxide having a desired composition can be obtained.

  The amount of the lithium salt (for example, lithium carbonate, lithium hydroxide, lithium fluoride, etc.) added is the composition ratio of the element constituting the synthesized positive electrode active material (NiMn-based spinel structure oxide), for example, the above formula It can be set to be in the range shown in (I). For example, when the total amount of Mn, Ni, Ti, Fe, Al and M in the precursor is 2 mol, the ratio of Li is about 1.0 mol (typically about 1.0 to 1.3 mol). The amount of the lithium salt (for example, lithium carbonate, lithium hydroxide, etc.) added can be set so that

<Baking process>
In the firing step, the raw material before firing is fired to synthesize the target NiMn-based spinel structure oxide. The firing temperature is preferably in the range of about 700 to 1000 ° C. Firing may be performed at the same temperature at a time, or may be performed stepwise at different temperatures. The firing time can be appropriately selected. For example, it may be baked at about 800 to 1000 ° C. for about 2 to 24 hours, or after baking at about 700 to 800 ° C. for about 1 to 12 hours and then at about 800 to 1000 ° C. for about 2 to 24 hours. Also good. For the purpose of controlling the amount of oxygen vacancies, the temperature may be maintained in the temperature range of 500 to 700 ° C. for 3 to 40 hours during the temperature decrease, and the temperature decrease rate may be appropriately adjusted. Further, an additional heat treatment may be performed within the range of the temperature and time after firing.

  After firing, an appropriate pulverization process (for example, pulverization process in a ball mill) or sieving is applied to obtain a NiMn-based spinel structure oxide having a desired property (for example, an average particle diameter) as a positive electrode active material. Can be obtained. Although not particularly limited, a cumulative 50% particle size (median diameter: D50) in a volume-based particle size distribution obtained by a general laser diffraction particle size distribution analyzer is 1 μm to 25 μm (typically 2 μm to 20 μm). For example, a powder substantially composed of secondary particles in the range of 5 μm to 15 μm can be preferably used as the positive electrode active material. Hereinafter, the “average particle diameter of the positive electrode active material” means the median diameter of the secondary particles of the positive electrode active material (particle size distribution measurement based on a general laser diffraction / light scattering method) unless otherwise specified. In the volume-based particle size distribution measured by the above, the particle diameter corresponding to the cumulative 50% from the fine particle side, D50).

  The lithium ion secondary battery 10 of the present embodiment using the positive electrode active material described above can be used as a portable power source or a vehicle driving power source. Here, in the lithium ion secondary battery 10 of the present embodiment, a NiMn-based spinel structure oxide having a high operating potential is used. Therefore, the lithium ion secondary battery 10 has a high energy density. Furthermore, in the lithium ion secondary battery 10, the cycle life is long and the thermal safety of the positive electrode active material layer is high. Therefore, the lithium ion secondary battery 10 of the present embodiment can be suitably used as a power source for driving a vehicle such as an electric vehicle (EV), a hybrid vehicle (HV), and a plug-in hybrid vehicle (PHV).

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

<Example 1>
[Preparation of positive electrode active material]
Manganese sulfate and nickel sulfate were dissolved in water so that the molar ratio Mn: Ni of the metal element was 1.5: 0.5, and the precursor was obtained by stirring while adding sodium hydroxide. This precursor and lithium carbonate are mixed so that the total amount of Mn and Ni in the precursor and Li in the lithium carbonate are in a molar ratio of 2: 1, and calcined at 900 ° C. for 15 hours in an air atmosphere. did. Thereafter, the resultant was pulverized by a ball mill to obtain a LiMn _1.5 Ni _0.5 O ₄ having a spinel crystal structure having an average particle diameter of 10 μm as a positive electrode active material. The composition of the positive electrode active material was confirmed by a normal ICP emission analysis method or an absorptiometric method (lanthanum-alizarin complexone method).

[Production of lithium ion secondary battery]
The positive electrode active material obtained above, acetylene black as a conductive material, PVdF as a binder, and N-methyl-2-pyrrolidone (NMP) so that the mass ratio of these materials is 87: 10: 3. ) To prepare a slurry-like (paste-like) positive electrode active material layer forming composition. This composition was applied to an aluminum foil (positive electrode current collector). The coated material was dried and pressed to produce a positive electrode sheet in which a positive electrode active material layer was formed on the positive electrode current collector.

  Natural graphite having an average particle size of 20 μm as a negative electrode active material, SBR as a binder, and CMC as a thickener are mixed in water so that the mass ratio of these materials is 98: 1: 1. A paste-like composition for forming a negative electrode active material layer was prepared. This composition was applied to a copper foil (negative electrode current collector). The coated material was dried and pressed to prepare a negative electrode sheet in which a negative electrode active material layer was formed on the negative electrode current collector.

The positive electrode sheet and the negative electrode sheet prepared above were wound with the separator sheet (polypropylene / polyethylene composite porous membrane) sandwiched therebetween (laminated) to produce an electrode body. The lithium ion secondary battery which concerns on Example 1 was produced by accommodating this in a lamination type case (laminate film) with a non-aqueous electrolyte. As non-aqueous electrolyte, LiPF ₆ is dissolved at a concentration of 1 mol / L in a mixed solvent of 50:50 volume ratio of monofluoroethylene carbonate (MFEC) and monofluoromethyldifluoromethyl carbonate (F-DMC). It was used.

<Example 2>
Manganese sulfate, nickel sulfate, iron sulfate and titanium sulfate were dissolved in water so that the molar ratio of metal elements Mn: Ni: Fe: Ti was 1.45: 0.45: 0.05: 0.05, The precursor was obtained by stirring while adding sodium hydroxide. This precursor and lithium carbonate were mixed so that the total amount of Mn, Ni, Fe, and Ti in the precursor and Li in the lithium carbonate were in a molar ratio of 2: 1, and 900 ° C. in an air atmosphere. And calcined for 15 hours. Thereafter, by grinding in a ball mill, the average particle diameter as a positive electrode active material was obtained _{LiMn 1.45 Ni 0.45 Fe 0.05 Ti 0.05} O 4 of a spinel type crystal structure of 10 [mu] m. The composition of the positive electrode active material was confirmed by a normal ICP emission analysis method or an absorptiometric method (lanthanum-alizarin complexone method).
A lithium ion secondary battery of Example 2 was produced in the same manner as Example 1 using the obtained positive electrode active material.

<Example 3>
Manganese sulfate, nickel sulfate and aluminum sulfate are dissolved in water so that the molar ratio of metal elements Mn: Ni: Al is 1.475: 0.475: 0.05, and stirred while adding sodium hydroxide. The precursor was obtained by this. This precursor and lithium carbonate were mixed so that the total amount of Mn, Ni and Al in the precursor and Li in the lithium carbonate were in a molar ratio of 2: 1, and the mixture was mixed at 15 ° C. at 900 ° C. in an air atmosphere. Baked for hours. Thereafter, by grinding in a ball mill, the average particle diameter as a positive electrode active material was obtained _LiMn 1.475 _Ni 0.475 _{Al 0.05} O ₄ of spinel crystalline structure of 10 [mu] m. The composition of the positive electrode active material was confirmed by a normal ICP emission analysis method or an absorptiometric method (lanthanum-alizarin complexone method).
A lithium ion secondary battery of Example 3 was produced in the same manner as Example 1 using the obtained positive electrode active material.

<Example 4>
Manganese sulfate, nickel sulfate, iron sulfate, titanium sulfate, and aluminum sulfate are mixed at a metal element molar ratio of Mn: Ni: Fe: Ti: Al of 1.425: 0.425: 0.05: 0.05: 0.05. The precursor was obtained by dissolving in water and stirring while adding sodium hydroxide. This precursor and lithium carbonate were mixed so that the total amount of Mn, Ni, Fe, Ti, and Al in the precursor and Li in the lithium carbonate were in a molar ratio of 2: 1. Firing was performed at 900 ° C. for 15 hours. Thereafter, the mixture was pulverized by a ball mill to obtain a LiMn _1.425 Ni _0.425 Fe _0.05 Ti _0.05 Al _0.05 O ₄ having a spinel crystal structure having an average particle diameter of 10 μm as a positive electrode active material. . The composition of the positive electrode active material was confirmed by a normal ICP emission analysis method or an absorptiometric method (lanthanum-alizarin complexone method).
Using the obtained positive electrode active material, a lithium ion secondary battery of Example 4 was produced in the same manner as in Example 1.

[Initial capacity measurement]
Initial charging was performed on each of the lithium ion secondary batteries of Examples 1 to 4 prepared above. That is, after charging at a constant current up to 4.9 V at a current value (charge rate) of 1/5 C, the battery is fully charged by performing constant voltage charging until the current value at constant voltage charging is 1/50 C. State (SOC 100%). Then, the discharge capacity (initial capacity) when discharging at a constant current up to 3.5 V at a current value of 1/5 C under a temperature condition of 25 ° C. was measured. Here, 1C means a current value that can charge the battery capacity (Ah) predicted from the theoretical capacity of the positive electrode in one hour.

[Charge / discharge cycle test]
For each of the lithium ion secondary batteries of Examples 1 to 4 after the initial capacity measurement, a charge / discharge cycle test was repeated for 200 cycles of charge / discharge, and the discharge capacity after the test was measured.
First, the charge / discharge cycle test is a charge / discharge in which a constant current charge is performed up to a voltage of 4.9 V at a charge rate of 2 C under a temperature condition of 60 ° C., and then a constant current discharge is performed up to a voltage of 3.5 V at a discharge rate of 2 C. The charge / discharge cycle was repeated 200 cycles.
For each battery after completion of the charge / discharge cycle test, the discharge capacity after the charge / discharge cycle test (discharge capacity after 200 cycles) was measured in the same manner as the initial capacity measurement. And the capacity | capacitance fall rate after 200 cycles with respect to an initial capacity ((initial capacity-discharge capacity after 200 cycles) / initial capacity x100 (%)) was computed. Table 1 shows the relative ratio (capacity reduction ratio) of the capacity reduction ratio of each battery when the capacity reduction ratio of the lithium ion secondary battery of Example 1 is 100 (reference).

[Evaluation of thermal stability]
The lithium ion secondary batteries of Examples 1 to 4 after the initial capacity measurement were again fully charged (SOC 100%). Thereafter, the battery was disassembled. A positive electrode active material layer (a mixture of a positive electrode active material, a conductive material, and a binder) was peeled from the disassembled positive electrode of the battery and pulverized to prepare a powder sample. 50 mg of this powdery sample and 80 μL of the non-aqueous electrolyte used for battery preparation were weighed and sealed in a calorimetric container. The work after the dismantling was performed in a probe box in an Ar atmosphere. The container enclosing the sample was set in a Kalbe large-capacity calorimeter (C80), and the calorific value was measured in the temperature range of 70 ° C. to 250 ° C. while raising the temperature at a rate of temperature rise of 0.7 ° C./min. Table 1 shows the relative ratio of the calorific values (calorific value ratio) of each battery when the calorific value of the lithium ion secondary battery of Example 1 is 100 (reference).

  As shown in Table 1, the lithium ion secondary battery of Example 4 using a NiMn spinel structure oxide in which a part of the transition metal site is substituted with Fe, Ti, and Al is a normal NiMn spinel structure oxide. It can be seen that the decrease in capacity is significantly suppressed as compared with the lithium ion secondary battery of Example 1 used, and the cycle life is significantly improved. Moreover, it can be seen that the calorific value of the positive electrode active material is significantly reduced, and the thermal safety is remarkably improved. In addition, the lithium ion secondary battery of Example 4 uses a NiMn spinel structure oxide corresponding to the NiMn spinel structure oxide described in Patent Document 1, in which a part of the transition metal site is substituted with Fe and Ti. Even when compared with the lithium ion secondary battery of Example 2, it can be seen that the cycle life and the thermal stability are improved. Example 3 is a lithium ion secondary battery using a NiMn-based spinel structure oxide in which a part of the transition metal site is substituted with Al. Therefore, by comparing Example 1 and Example 2, the effect of substituting with Fe and Ti, by comparing Example 1 and Example 3, the effect of substituting with Al, by comparing Example 1 and Example 4, The effect of substituting with Fe, Ti, and Al can be grasped. Regarding the result of the calorific value ratio, the calorific value reduction amount of Example 4 is larger than the sum of the calorific value reduction amount of Example 2 and the calorific value reduction amount of Example 3. Therefore, it can be said that a synergistic effect is obtained when the element substituting the transition metal site of the NiMn-based spinel structure oxide is a combination of Fe, Ti and Al.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 10 Lithium ion secondary battery 15 Battery case 25 Cover body 30 Case main body 40 Safety valve 60 Positive electrode terminal 62 Positive electrode current collector 64 Positive electrode sheet (positive electrode)
66 Positive electrode active material layer 80 Negative electrode terminal 82 Negative electrode current collector 84 Negative electrode sheet (negative electrode)
86 Negative electrode active material layer 90 Separator sheet 100 Winding electrode body

Claims (1)

A nonaqueous electrolyte secondary battery comprising a positive electrode having a positive electrode active material layer on a positive electrode current collector, a negative electrode having a negative electrode active material layer on a negative electrode current collector, and a nonaqueous electrolyte solution,
The positive electrode active material layer includes a positive electrode active material,
The positive electrode active material is a lithium transition metal composite oxide having a spinel structure containing Li and Ni and Mn as transition metal elements, wherein a part of the transition metal site of the lithium transition metal composite oxide is Ti, Substituted with Fe and Al,
Non-aqueous electrolyte secondary battery.

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