JP2014022328A - Method for manufacturing nonaqueous electrolyte secondary battery - Google Patents

Abstract

A method of manufacturing a non-aqueous electrolyte secondary battery having reduced internal resistance and excellent durability (cycle characteristics) is provided.
A method for producing a non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an electrolyte for pretreatment that does not contain a fluorinated non-aqueous solvent. And oxalato complex compound in a pretreatment cell (step S110); pretreatment for applying current between the positive electrode and the negative electrode is performed to form a film derived from the oxalato complex compound on the surface of the negative electrode active material (Step S120); constructing a non-aqueous electrolyte secondary battery using a negative electrode having a negative electrode active material on which the coating film is formed, a positive electrode, and a battery electrolyte containing a fluorine-containing non-aqueous solvent. (Step S130).
[Selection] Figure 1

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. In more detail, it is related with the manufacturing method of this battery.

  Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries are smaller, lighter, and have higher energy density than conventional batteries, and are excellent in output density. For this reason, it is preferably used as a so-called portable power source such as a personal computer or a portable terminal, or an in-vehicle power source (vehicle power source).

  By the way, in a non-aqueous electrolyte secondary battery used for a power source for driving a vehicle or the like, further energy density is being studied as part of performance improvement. Such high energy density can be realized, for example, by increasing the operating voltage of the battery (for example, 4.5 V or more). However, when the operating voltage of the battery is increased, the potential of the positive electrode becomes higher than in the conventional case, so that oxidative decomposition of the electrolytic solution is likely to occur in the positive electrode, and thereby durability (cycle characteristics) is likely to deteriorate. Therefore, in order to prevent such oxidative decomposition, it has been studied to use a material having higher oxidation resistance (that is, having a higher oxidative decomposition potential) as a constituent component of the electrolytic solution. For example, in Patent Document 1, by using a fluorine-containing non-aqueous solvent as the electrolyte component, even when the upper limit of the operating voltage of the lithium ion secondary battery is set to 4.9 V or more, it accompanies decomposition of the electrolyte. It is described that gas generation can be suppressed.

JP 2003-168480 A

  However, since oxidation resistance and reduction resistance are generally contradictory properties, an electrolyte component having high oxidation resistance (for example, the fluorine-containing non-aqueous solvent) has a low reduction resistance as a contradiction. It tends to be reductively decomposed. According to the study of the present inventor, lithium is immobilized on the surface of the negative electrode active material by reductive decomposition of the electrolytic solution and a high resistance passive film (for example, LiF) is formed. Battery characteristics (for example, initial capacity) may be deteriorated. The present invention has been made in view of such a point, and the object thereof is to manufacture a nonaqueous electrolyte secondary battery that is suitably suppressed in reductive decomposition of an electrolyte solution in a negative electrode and has excellent oxidation resistance and reduction resistance. Is to provide a method. Another object is to provide a non-aqueous electrolyte secondary battery obtained by such a manufacturing method.

  In order to solve the above-mentioned problems, the present inventor considered to stabilize the interface with the electrolytic solution by covering the surface of the negative electrode active material with a stable coating and to suppress the reductive decomposition of the electrolytic solution. Then, as a result of intensive studies, a negative active material having a stable and low resistance film on the surface of the negative electrode active material and having such a film having excellent resistance to reduction, and an electrolyte having excellent oxidation resistance are used. Thus, the inventors have conceived of constructing a non-aqueous electrolyte secondary battery and completed the present invention.

  In the method for producing a non-aqueous electrolyte secondary battery provided by the present invention, a pretreatment cell is first constructed. Such a pretreatment cell includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, a pretreatment electrolyte substantially free of a fluorine-containing nonaqueous solvent, and an oxalato complex compound. . In the manufacturing method, next, pretreatment for applying a current between the positive electrode and the negative electrode is performed to form a film derived from the oxalato complex compound on the surface of the negative electrode active material. That is, the pretreatment can also be grasped as a process for producing a negative electrode active material (or a negative electrode having a negative electrode active material with a film) on which a film derived from an oxalato complex compound is formed. In the manufacturing method, next, a non-aqueous electrolyte secondary battery is constructed using the negative electrode active material on which the coating film is formed. The electrolytic solution used in this case (hereinafter sometimes referred to as “battery electrolytic solution”) contains a fluorine-containing nonaqueous solvent.

  According to the production method disclosed herein, the oxalate complex compound is decomposed by the pretreatment, and a low-resistance and stable film is formed on the surface of the negative electrode active material. In the negative electrode active material having such a coating formed, the property of reducing and decomposing the electrolytic solution is suppressed. Therefore, a battery is constructed using an electrolytic solution having a low reduction resistance (for example, a fluorine-containing nonaqueous solvent). However, the electrolytic solution is hardly reduced and decomposed on the negative electrode. Therefore, in a non-aqueous electrolyte secondary battery using a negative electrode active material having a coating excellent in reduction resistance and a fluorine-containing non-aqueous solvent excellent in oxidation resistance, decomposition of the electrolyte is highly suppressed. Therefore, excellent battery performance (for example, high battery capacity and durability) can be realized.

  In the present specification, the “non-aqueous electrolyte secondary battery” refers to a battery provided with a non-aqueous electrolyte (typically, an electrolyte containing a supporting salt in a non-aqueous solvent). The “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by movement of lithium ions between the positive and negative electrodes. In the present specification, the “fluorine-containing nonaqueous solvent” refers to an organic solvent containing fluorine as a constituent atom. In other words, the organic solvent has a chemical structure in which at least one hydrogen atom of an organic solvent not containing fluorine as a constituent element is substituted with a fluorine atom.

  As the pretreatment electrolytic solution, it is preferable to use one having a reduction potential based on metal lithium as compared with the oxalato complex compound. Thereby, the oxalato complex compound can be preferentially reduced and decomposed, and a low-resistance film derived from the oxalato complex compound can be suitably formed on the surface of the negative electrode active material.

The oxalato complex compound preferably contains a boron (B) atom or a phosphorus (P) atom. As a suitable example, lithium bis (oxalato) borate (hereinafter referred to as “LiBOB”) represented by the following formula (I): May be abbreviated).
LiBOB can form a dense and highly stable film on the surface of the negative electrode active material. Therefore, the decomposition reaction of the non-aqueous electrolyte accompanying charging / discharging after that can be suppressed suitably, and the application effect of this invention can be exhibited at a higher level.

In the pretreatment, the negative potential of the pretreatment cell is a reduction potential based on metal lithium of an oxalato complex compound (or at least one when two or more oxalato complex compounds are used). It is preferable to carry out until it becomes equivalent to or lower than “vs. Li ^/ Li ⁺ ”. More specifically, when LiBOB is used as the oxalato complex compound, the oxalato complex compound is used in a state where the potential of the negative electrode is lower than the reduction potential of LiBOB (that is, a state of 1.73 V (vs. Li / Li ⁺ ) or less). Can be preferably carried out in a mode of decomposing. Thereby, the oxalato complex compound is suitably reduced and decomposed in the negative electrode of the pretreatment cell, and a film containing the decomposition product can be stably formed on the surface of the negative electrode active material. Further, this charging is preferably performed so that the negative electrode potential of the pretreatment cell is equal to or higher than the reduction potential of the pretreatment electrolyte based on the metal lithium. That is, in a pretreatment cell in a charged state (for example, a state where the SOC is approximately 100%), it is preferably carried out in such a manner that the potential based on the metal lithium is the reduction potential of the oxalato complex compound> the negative electrode potential> the reduction potential of the electrolyte. obtain. In other words, the negative electrode potential (vs. Li ^/ Li ⁺ ) can be preferably implemented in a mode in which 1.73 V> negative electrode potential> 1.7 V. Thereby, the low resistance film derived from an oxalato complex compound can be densely formed on the surface of the negative electrode active material. Therefore, according to such an embodiment, a film excellent in electrolytic solution decomposition preventing property can be more suitably formed on the surface of the negative electrode active material. In other words, it is possible to obtain a negative electrode active material that is further excellent in electrolytic solution decomposition prevention.

  As the fluorine-containing nonaqueous solvent contained in the battery electrolyte, one or more of fluorinated carbonates can be preferably employed. Here, “carbonate” refers to an organic compound having at least one carbonate structure (—O— (C═O) —O—) in the molecule, and includes both cyclic carbonates and chain carbonates. In the present specification, “chain” means to include both linear and branched chains. More preferably, the fluorine-containing non-aqueous solvent contained in the battery electrolyte contains at least one fluorinated cyclic carbonate. As a preferred example, an electrolytic solution for a battery containing one or both of monofluoroethylene carbonate (hereinafter sometimes referred to as “MFEC”) and difluoroethylene carbonate (hereinafter sometimes referred to as “DFEC”). Is mentioned. The battery electrolyte having such a composition has a wide potential window on the oxidation side (that is, high oxidation resistance). Therefore, in the non-aqueous electrolyte secondary battery constructed using the electrolyte, even when the operating voltage of the battery is set higher, oxidative decomposition hardly occurs at the positive electrode, and the energy density and durability are high. Can be compatible.

The technique disclosed here is a non-aqueous solution in which the positive electrode is set to a potential of 4.5 V (vs. Li ^/ Li ⁺ ) or higher (more preferably, a potential of 4.6 V (vs. Li ^/ Li ⁺ ) or higher). The present invention can be preferably applied to the production of an electrolyte secondary battery (for example, a lithium ion secondary battery). Here, the “non-aqueous electrolyte secondary battery in which the positive electrode operates at a potential of 4.5 V (vs. Li ^/ Li ⁺ ) or higher” means a SOC (State of Charge) range of 0% to 100%. A non-aqueous electrolyte secondary battery having a region where the redox potential (operating potential) of the positive electrode active material is 4.5 V (vs. Li ^/ Li ⁺ ) or higher. Such a battery can also be grasped as a non-aqueous electrolyte secondary battery in which the potential of the positive electrode is 4.5 V (vs. Li ^/ Li ⁺ ) or more in at least a partial range of SOC 0% to 100%.

  In the present specification, “SOC” refers to the state of charge of a battery based on a voltage range in which the battery is normally used. Rated capacity (typically described later) in which the voltage between terminals (open circuit voltage (OCV)) is measured under the condition of an upper limit voltage (for example, 4.9 V) to a lower limit voltage (for example, 3.5 V) The rated capacity specified under the same conditions as the rated capacity measurement of the evaluation battery to be used).

As a preferable example of the positive electrode active material having a region where the operating potential is 4.5 V or more, a lithium transition metal composite oxide having a layered structure or a spinel structure including a lithium element and at least one transition metal element as constituent metal elements is used. Can be mentioned. The positive electrode active material may be a spinel-structure lithium nickel manganese composite oxide.
The non-aqueous electrolyte secondary battery disclosed here is used in combination with the positive electrode active material having a high operating potential because both the oxidative decomposition and the reductive decomposition of the battery electrolyte are suitably suppressed. Thus, a non-aqueous electrolyte secondary battery having a higher voltage between positive and negative electrodes (high voltage), that is, a high energy density can be constructed. Therefore, higher battery performance can be realized.

  As another aspect of the technology disclosed herein, a nonaqueous electrolyte secondary battery including a negative electrode active material on which a film derived from an oxalato complex compound is formed is provided. Such a non-aqueous electrolyte secondary battery includes a negative electrode having a negative electrode active material on which the coating film is formed, a positive electrode having a positive electrode active material, and a non-aqueous electrolyte. Such a nonaqueous electrolyte secondary battery can be a nonaqueous electrolyte secondary battery in which both oxidative decomposition and reductive decomposition of the battery electrolyte are highly suppressed. According to such a nonaqueous electrolyte secondary battery, the internal resistance (typically, the resistance of the negative electrode) is reduced, and excellent durability (cycle characteristics) can be realized.

  The non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) disclosed herein can have reduced internal resistance and excellent durability. For example, the initial capacity is high, and even when charging and discharging are repeated, the capacity can be reduced little. Therefore, taking advantage of this feature, for example, it can be suitably used as a power source (drive power source) of a hybrid vehicle or an electric vehicle.

It is a flowchart which shows the nonaqueous secondary battery manufacturing method which concerns on one Embodiment. It is a perspective view which shows typically the external shape of the nonaqueous electrolyte secondary battery which concerns on one Embodiment. It is a figure which shows typically the cross-sectional structure in the III-III line of the non-aqueous-electrolyte secondary battery of FIG. It is a schematic diagram which shows the structure of the winding electrode body of the nonaqueous electrolyte secondary battery which concerns on one Embodiment. It is a graph showing the initial IV resistance value (Ω) and the capacity retention rate (%) after the cycle test. It is a side view which shows typically the vehicle (automobile) provided with the nonaqueous electrolyte secondary battery which concerns on one Embodiment.

  Hereinafter, a preferred embodiment according to a method for manufacturing a non-aqueous electrolyte secondary battery disclosed herein will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

<Method for producing non-aqueous electrolyte secondary battery>
The manufacturing method of the non-aqueous electrolyte secondary battery disclosed herein is as shown in the flowchart of FIG.
(S110) A positive electrode having a positive electrode active material, a negative electrode containing a negative electrode active material without a film (negative electrode active material before film formation), and a pretreatment electrolyte substantially free of a fluorine-containing nonaqueous solvent And an oxalato complex compound in a pretreatment cell;
(S120) decomposing the oxalato complex compound by charging the pretreatment cell to form a film derived from the oxalato complex compound on the surface of the negative electrode active material;
(S130) constructing a lithium ion secondary battery disclosed herein using the pretreated negative electrode and a battery electrolyte containing a fluorine-containing nonaqueous solvent;
Is included. In addition, (S110) and (S120) can also be grasped as a method for producing a coated negative electrode active material (or a negative electrode having the coated negative electrode active material).

In general, fluorine-containing non-aqueous solvents tend to have higher oxidation resistance and lower reduction resistance than the corresponding non-aqueous solvents not containing fluorine. It is possible to solve the above problems (low reduction resistance) when using an aqueous solvent and to effectively draw out the advantages of using the solvent.
That is, as described above, by using an electrolyte for pretreatment that does not contain a fluorine-containing non-aqueous solvent, reductive decomposition of the oxalato complex compound on the surface of the negative electrode active material (typically, decomposition thereof) Low resistance films (including products) can be formed. Since the negative electrode active material on which such a coating is formed has a property of reducing and decomposing the electrolytic solution, a battery including the negative electrode active material is excellent in reduction resistance. Moreover, high oxidation resistance can be implement | achieved by using what contains a fluorine-containing non-aqueous solvent as electrolyte solution for batteries. Therefore, according to the manufacturing method, a nonaqueous electrolyte secondary battery in which oxidative decomposition and reductive decomposition of the electrolytic solution are suppressed can be realized. In such a non-aqueous electrolyte secondary battery in which the decomposition of the electrolyte is highly suppressed, the internal resistance (typically, the resistance of the negative electrode) is reduced, and higher battery performance (eg, high battery capacity and durability) is achieved. Can be realized.

  Although not intended to be particularly limited, a lithium ion secondary battery is taken as an example of the non-aqueous electrolyte secondary battery according to an embodiment of the present invention with reference to the flowchart shown in FIG. 1 as appropriate. The present invention will be described in detail below. In the following description, the negative electrode active material before the pretreatment is referred to as “untreated negative electrode active material”, and the negative electrode having the untreated negative electrode active material may be referred to as “untreated negative electrode”. . In addition, the negative electrode active material after being subjected to pretreatment may be referred to as a “coated negative electrode active material”, and a negative electrode having a coated negative electrode active material may be referred to as “pretreated negative electrode”.

<Preparation of constituent materials>
The pretreatment cell is a pretreatment substantially free of a positive electrode having a positive electrode active material, a negative electrode active material having no film formed thereon (negative electrode active material before film formation), and a fluorine-containing nonaqueous solvent. And an oxalato complex compound. Here, each material contained in the pretreatment cell will be described first.

<Positive electrode>
The positive electrode is not particularly limited as long as it has a positive electrode active material capable of suitably occluding and releasing charge carriers (here, lithium ions). Typically, the positive electrode is formed on the positive electrode current collector and the positive electrode current collector. And a positive electrode active material layer containing at least a positive electrode active material.
Such a positive electrode includes a paste-like or slurry-like composition (dispersion for forming a positive electrode active material layer) in which a positive electrode active material and a conductive material or a binder used as necessary are dispersed in an appropriate solvent. It can be preferably prepared by applying to a sheet-like positive electrode current collector and drying the composition. As the solvent, any of an aqueous solvent and an organic solvent can be used. For example, N-methyl-2-pyrrolidone (NMP) can be used.

  As the positive electrode current collector, a conductive member made of a metal having good conductivity (for example, aluminum, nickel, titanium, stainless steel, etc.) is preferably used. The shape of the current collector may be different depending on the shape of the battery to be constructed, and is not particularly limited. For example, a rod-like body, a plate-like body, a foil-like body, a net-like body, or the like can be used. In the battery provided with the wound electrode body, a foil-like body is mainly used. The thickness of the foil-like current collector is not particularly limited, but a thickness of about 5 μm to 50 μm (more preferably 8 μm to 30 μm) can be used in consideration of the capacity density of the battery and the strength of the current collector.

  As the positive electrode active material, one kind or two or more kinds of various materials known to be usable as a positive electrode active material of a lithium ion secondary battery can be used without particular limitation. For example, a lithium transition metal compound such as a layered structure or a spinel structure containing lithium and at least one transition metal element as a constituent metal element, a polyanion type (for example, olivine type) lithium transition metal compound, or the like can be used. More specifically, for example, the following compounds (1) to (6) can be used.

(1) General _formula: Li _{x Mn 2-p} represented by _{M p O 4 + α A q} , typically lithium transition metal compound of spinel structure (oxide). Where x is 0.8 ≦ x ≦ 1.2; p is 0 ≦ p <2, typically 0 ≦ p ≦ 1 (eg, 0 ≦ p ≦ 0.5). Α is a value determined so as to satisfy the charge neutrality condition with −0.2 ≦ α ≦ 0.2; q is 0 ≦ q ≦ 1. When p is greater than 0, M can be any metallic or non-metallic element other than Mn. A composition in which M contains at least one transition metal element is preferred. Also, when q is greater than 0, A can be F or Cl. Specific examples include LiNi _0.5 Mn _1.5 O ₄ and LiCrMnO ₄ .
As one preferred embodiment, the compound M comprises at least Ni in the above general formula, for example, the general _{formula: Li x (Ni y Mn 2} -y-z M 1 z) O 4 + α A lithium transition metal of the spinel structure represented by _q Oxides. Here, M ¹ may be any transition metal element or typical metal element other than Ni and Mn (for example, one or more selected from Fe, Co, Cu, Cr, Zn, and Al). It is preferable to contain at least one of valence Fe and Co. Alternatively, it may be a metalloid element (for example, one or more selected from B, Si and Ge) and a non-metallic element. A, x, q, α may be the same as above; y is 0 <y; z is 0 ≦ z; y + z <2 (typically y + z ≦ 1). . In a more preferred embodiment, y is 0.2 ≦ y ≦ 1.0; z is 0 ≦ z <1.0 (eg, 0 <z ≦ 0.3).

(2) A lithium transition metal compound (oxide) typically represented by a general formula: LiMO ₂ and having a layered structure. Here, M includes at least one transition metal element such as Ni, Co, and Mn, and may further include another metal element or a non-metal element. Specific examples include LiNiO ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ .
(3) A lithium transition metal compound (oxide) represented by the general formula: Li ₂ MO ₃ . Here, M includes at least one transition metal element such as Mn, Fe, Co, and may further include another metal element or a nonmetal element. Specific examples include Li ₂ MnO ₃ and Li ₂ PtO ₃ .
(4) A solid solution of LiMO ₂ and Li ₂ MO ₃ . Here, LiMO ₂ refers to the composition represented by the general formula described in (2) above, and Li ₂ MO ₃ refers to the composition represented by the general formula described in (3) above. As a specific example, a solid solution represented by 0.5LiNiMnCoO ₂ —0.5Li ₂ MnO ₃ can be given.
(5) A polyanion type lithium transition metal compound (phosphate) represented by the general formula: LiMPO ₄ A _q . Here, M includes at least one transition metal element such as Mn, Fe, Ni, and Co, and may further include another metal element or a non-metal element. q is 0 ≦ q ≦ 1, and when q is greater than 0, A can be F or Cl. Specific examples include LiMnPO ₄ , LiFePO ₄ , LiMnPO ₄ F, and the like.

In a preferred embodiment, the positive electrode active material is a lithium ion secondary battery having a general operating potential (vs. Li ^/ Li ⁺ ) in a partial range of at least SOC 0% to 100% (the upper limit of the operating potential is 4. 1V to 4.2V) or more is used. For example, a positive electrode active material having an operating potential of 4.5 V (vs. Li ^/ Li ⁺ ) or more can be preferably used. In other words, a positive electrode active material having a maximum operating potential of 4.5 V (vs. Li ^/ Li ⁺ ) or more at SOC ⁰ % to 100% can be preferably used. By using such a positive electrode active material, a lithium ion secondary battery in which the positive electrode operates at a potential of 4.5 V (vs. Li ^/ Li ⁺ ) or higher can be realized. As a suitable example of such a positive electrode active material, the above LiNi _P Mn _{2 -P} O ₄ (0.2 ≦ P ≦ 0.6; for example, LiNi _0.5 Mn _1.5 O ₄ ), LiNiPO ₄ , LiCoPO ₄ , 0 .5LiNiMnCoO ₂ -0.5Li ₂ MnO ₃ , and the like. In particular, it is more preferable to use a positive electrode active material having an operating potential (vs. Li ^/ Li ⁺ ) exceeding 4.5 V (further, 4.6 V or higher, for example, 4.7 V or higher).

Here, the working potential of the positive electrode active material can be measured, for example, as follows. That is, a positive electrode containing a positive electrode active material to be measured is used as a working electrode (WE), the working electrode, metallic lithium as a counter electrode (CE), metallic lithium as a reference electrode (RE), and non-aqueous used. A tripolar cell is constructed using an electrolytic solution (for example, an electrolytic solution containing LiPF ₆ at a concentration of 1 M in a mixed solvent of EC: EMC = 30: 70 (volume basis)). The SOC value of this cell is adjusted in increments of 5% from 0% to 100% SOC based on the theoretical capacity of the cell. Such SOC adjustment can be performed by constant current charging between WE and CE using, for example, a general charging / discharging device or a potentiostat. Then, the potential between WE and RE after the cells adjusted to the respective SOC values are left for 1 hour is measured, and the potential is determined based on the operating potential (vs. Li ^/ Li ⁺ ) of the positive electrode active material at the SOC value. And

In general, the operating potential of the positive electrode active material is highest in a range between SOC 0% and 100% in a range including SOC 100%. Therefore, normally, the operating potential of the positive electrode active material at SOC 100% (that is, fully charged state) is normal. Thus, the upper limit (for example, whether it is 4.5 V or more) of the operating potential of the positive electrode active material can be grasped. The operating potential (vs. Li ^/ Li ⁺ ) of the positive electrode active material at SOC 100% is more preferably higher than 4.4V, and even more preferably 4.5V or higher. In the technique disclosed herein, typically, the operating potential (vs. Li ^/ Li ⁺ ) of the positive electrode active material at 100% SOC is 7.0 V or less (typically 6.0 V or less, for example, 5.5 V or less. It is preferably applied to a lithium ion secondary battery.

The shape of the positive electrode active material is preferably in the form of particles usually having an average particle size of about 0.5 μm to 20 μm (typically 1 μm to 15 μm, for example, 2 μm to 10 μm). In the present specification, the “average particle diameter” means a particle diameter corresponding to 50% cumulative from the fine particle side in a volume-based particle size distribution measured by particle size distribution measurement based on a laser diffraction / light scattering method (that is, , 50% volume average particle diameter, sometimes referred to as “median diameter”). Further, BET specific surface area of the positive electrode active material, ^typically, 0.1m ² / ^g~30m 2 / g approximately are suitable, typically 0.2m ² / g~10m ² / g, for example 0.5m those of about ² / ^{g~3m 2} / g can be preferably used. In the present specification, “specific surface area” indicates a surface area (BET specific surface area) measured by a BET method (BET three-point method) using nitrogen gas.
When the properties of the positive electrode active material are in the above range, a dense and highly conductive positive electrode active material layer can be produced. Moreover, since a moderate space | gap can be hold | maintained in this positive electrode active material layer, a non-aqueous electrolyte can be easily immersed and internal resistance can be reduced.

  Typically, a carbon material can be used as the conductive material. More specifically, for example, various carbon blacks (for example, acetylene black, furnace black, ketjen black, channel black, lamp black, thermal black), coke, activated carbon, graphite (natural graphite, artificial graphite), carbon fiber It may be one or more selected from carbon materials such as (PAN-based carbon fiber, pitch-based carbon fiber), carbon nanotube, fullerene, graphene and the like. Among these, carbon black (typically acetylene black) having a relatively small particle size and a large specific surface area can be preferably used.

  As the binder, a polymer that can be dissolved or dispersed in a solvent to be used can be used. For example, in a positive electrode mixture composition using an aqueous solvent, cellulosic polymers such as carboxymethylcellulose (CMC; typically sodium salt), hydroxypropylmethylcellulose (HPMC); polyvinyl alcohol (PVA), polytetrafluoroethylene Fluorine resins such as (PTFE); rubbers such as styrene butadiene rubber (SBR) can be preferably used. In the positive electrode mixture composition using a nonaqueous solvent, polyvinylidene fluoride (PVdF), polyvinylidene chloride (PVdC), or the like can be preferably used.

  The proportion of the positive electrode active material in the entire positive electrode active material layer is suitably about 50% by mass or more (typically 50% to 95% by mass), and usually about 70% to 95% by mass. It is preferable that When the conductive material is used, the ratio of the conductive material in the entire positive electrode active material layer can be, for example, approximately 2% by mass to 20% by mass, and is generally preferably approximately 2% by mass to 15% by mass. . When using a binder, the ratio of the binder to the whole positive electrode active material layer can be, for example, about 0.5% by mass to 10% by mass, and usually about 1% by mass to 5% by mass is preferable. .

The mass of the positive electrode active material layer provided per unit area of the positive electrode current collector (the total mass on both sides in the configuration having the positive electrode active material layer on both surfaces of the positive electrode current collector) is, for example, 5 mg / cm ^{2 to} 40 mg / cm ^2. (typically ^{10mg / cm 2 ~20mg / cm 2} ) it is appropriate to the degree. In the configuration having the positive electrode active material layers on both surfaces of the positive electrode current collector, the mass of the positive electrode active material layers provided on each surface of the positive electrode current collector is usually preferably approximately the same. Further, the density of the positive electrode active material layer can be, for example, about 1.5 g / cm ^{3 to} 4 g / cm ³ (typically 1.8 g / cm ^{3 to 3} g / cm ³ ). By setting the density of the positive electrode active material layer within the above range, the diffusion resistance of lithium ions can be kept low while maintaining a desired capacity. For this reason, the output characteristics and energy density of the lithium ion secondary battery can be made compatible at a higher level.

<Untreated negative electrode>
The untreated negative electrode includes a negative electrode current collector and a negative electrode active material layer including at least (untreated) negative electrode active material formed on the negative electrode current collector. Such an untreated negative electrode is a paste-like or slurry-like composition (negative electrode active material layer formation) in which an untreated negative electrode active material and a binder (binder) used as necessary are dispersed in an appropriate solvent. Is applied to a sheet-like negative electrode current collector, and the composition is dried to form a negative electrode active material layer (untreated negative electrode active material layer). As the solvent, any of an aqueous solvent and an organic solvent can be used. For example, water can be used.
As the negative electrode current collector, a conductive material made of a metal having good conductivity (for example, copper, nickel, titanium, stainless steel, etc.) is preferably used. The shape of the negative electrode current collector can be the same as that of the positive electrode current collector.

As the negative electrode active material, one type or two or more types of materials conventionally used in non-aqueous electrolyte secondary batteries can be used without any particular limitation. Although not particularly limited, for example, carbon materials such as natural graphite (graphite), artificial graphite, hard carbon (non-graphitizable carbon), soft carbon (graphitizable carbon), carbon nanotubes; silicon oxide, titanium oxide , Vanadium oxide, iron oxide, cobalt oxide, nickel oxide, niobium oxide, tin oxide, lithium silicon composite oxide, lithium titanium composite oxide (LTO, for example, Li ₄ Ti ₅ O ₁₂ , LiTi ₂ O ₄ , Li ₂ Ti ₃ O ₇ ), metal oxide materials such as lithium vanadium composite oxide, lithium manganese composite oxide, lithium tin composite oxide; metals such as lithium nitride, lithium cobalt composite nitride, lithium nickel composite nitride Nitride materials; metals such as tin, silicon, aluminum, zinc, lithium, or these Metal material comprising a metal alloy mainly comprising the metal element; and the like can be used. Particularly, a negative electrode active material having a reduction potential (vs. Li ^/ Li ⁺ ) of about 0.5 V or less, more preferably 0.2 V or less (for example, 0.1 V or less) can realize a high energy density. preferable. Examples of the material that can be at such a low potential include graphite-based carbon materials (typically graphite particles).
Or the particle | grains of the form by which the graphite particle was coat | covered with the amorphous | non-crystalline (amorphous) carbon material may be sufficient. Since such particles are coated on the surface with an amorphous carbon material, the reactivity with the non-aqueous electrolyte is relatively low. Therefore, in a lithium ion secondary battery using such particles as a negative electrode active material, irreversible capacity is suppressed and high durability can be exhibited.

The shape of the negative electrode active material is usually preferably in the form of particles having an average particle size of about 0.5 μm to 20 μm (typically 1 μm to 15 μm, for example, 4 μm to 10 μm). Further, BET specific surface area of the negative electrode active material, ^typically, 0.1m ² / ^g~30m 2 / g approximately are suitable, typically 0.2m ² / g~10m ² / g, for example 0.5m those of about ² / ^{g~3m 2} / g can be preferably used. When the property of the negative electrode active material is in the above range, the reductive decomposition of the nonaqueous electrolytic solution can be suitably suppressed. Moreover, since an appropriate space | gap can be hold | maintained in this negative electrode active material layer, a non-aqueous electrolyte can be easily immersed and internal resistance can be reduced.

The affinity between the negative electrode active material and the non-aqueous electrolyte can be grasped to some extent by, for example, the amount of oil absorption and the ratio of oxygen atoms (O) to carbon atoms (C) (O / C).
The oil absorption amount of the negative electrode active material is typically 40 (ml / 100 g) to 70 (ml / 100 g), and preferably 50 (ml / 100 g) to 60 (ml / 100 g). When satisfy | filling this range, affinity with a nonaqueous electrolyte solution can improve and interface resistance can be restrained low. Furthermore, the negative electrode active material layer which is excellent in coating property and binding property (binding property to the negative electrode current collector) and has little unevenness can be formed. The “oil absorption amount (mL / 100 g)” can be determined in accordance with JIS K6217-4 (2008) “Carbon black for rubber—Basic characteristics—Part 4: Determination of DBP oil absorption amount”. Here, as the reagent liquid, a value using linseed oil instead of DBP (dibutyl phthalate) can be adopted.

O / C of a negative electrode active material can be 0.05 or more and 1 or less (typically 0.1 or more and 1 or less, for example, 0.2 or more and 0.5 or less). When satisfy | filling this range, it is excellent in affinity with electrolyte solution, an excessive reaction with electrolyte solution can be suppressed, and an irreversible capacity | capacitance can be reduced. Note that the value of “O / C” can be calculated using a value obtained by measuring a measurement object by a technique of X-ray photoelectron spectroscopy (XPS). More specifically, oxygen atoms (O) and carbon atoms (C) existing in the vicinity of the surface of the negative electrode active material particles are measured by XPS, and O atoms are determined from the peak areas of the obtained C _1S and O _1S spectra. Calculate the concentration of C atoms. The atomic ratio (O / C) can be obtained by dividing the O atom concentration by the C atom concentration.

  As the binder, an appropriate material can be selected from the polymer materials exemplified as the binder for the positive electrode active material layer. Specifically, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE) and the like are exemplified. In addition, various additives such as a dispersant and a conductive material can be used as appropriate.

  The proportion of the negative electrode active material in the entire negative electrode active material layer is suitably about 50% by mass or more, and preferably 90% by mass to 99% by mass (for example, 95% by mass to 99% by mass). When a binder is used, the proportion of the binder in the entire negative electrode active material layer can be set to, for example, approximately 1% by mass to 10% by mass, and usually approximately 1% by mass to 5% by mass is appropriate. is there.

The mass of the negative electrode active material layer provided per unit area of the negative electrode current collector (the total mass of both surfaces in the case of having a negative electrode active material layer on both surfaces of the negative electrode current collector) is, for example, 5 mg / cm ^{2 to} 20 mg / cm ^2. (typically ^{5mg / cm 2 ~10mg / cm 2} ) it is appropriate to the degree. In the configuration having the negative electrode active material layers on both surfaces of the negative electrode current collector, the mass of the negative electrode active material layers provided on each surface of the negative electrode current collector is usually preferably approximately the same. The density of the negative electrode active material layer, for example, (typically ^{1g / cm 3 ~1.5g / cm 3} ) 0.5g / cm 3 ~2g / cm 3 may be of the order. By setting the density of the negative electrode active material layer in the above range, the interface with the non-aqueous electrolyte can be suitably maintained, and both durability (cycle characteristics) and output characteristics can be achieved at a high level.

<Electrode body>
The produced positive electrode and the untreated negative electrode are laminated to produce an electrode body. In the typical configuration disclosed here, a separator is interposed between the positive electrode and the negative electrode. As this separator, the same separator as that for a general non-aqueous electrolyte secondary battery (for example, lithium ion secondary battery) separator can be used without particular limitation. For example, a porous sheet made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide, a nonwoven fabric, or the like can be used. Preferable examples include a single layer or multilayer structure porous sheet (microporous resin sheet) mainly composed of one or more kinds of polyolefin resins. For example, a PE sheet, a PP sheet, a sheet having a three-layer structure (PP / PE / PP structure) in which PP layers are laminated on both sides of the PE layer, and the like can be suitably used. The thickness of the separator is preferably set within a range of approximately 10 μm to 40 μm, for example.

<Capacitance ratio between positive electrode and negative electrode>
Although not particularly limited, the positive electrode capacity (C _c (mAh)) calculated by the product of the theoretical capacity (mAh / g) per unit mass of the positive electrode active material and the mass (g) of the positive electrode active material. And the negative electrode capacity (C _a (mAh)) calculated by the product of the theoretical capacity per unit mass of the negative electrode active material (mAh / g) and the mass of the negative electrode active material (g) (C _a / C _c ) is usually suitably 1.0 to 2.0, for example, and preferably 1.2 to 1.9 (eg 1.7 to 1.9). The ratio of the positive electrode capacity and the negative electrode capacity facing each other directly affects the battery capacity (or irreversible capacity) and the energy density, and lithium is likely to be precipitated depending on the use conditions of the battery (for example, rapid charging). By setting the capacity ratio of the opposing positive and negative electrodes in the above range, it is possible to favorably suppress lithium deposition while maintaining good battery characteristics such as battery capacity and energy density.

<Pretreatment electrolyte>
The pretreatment electrolytic solution contains a lithium salt as a supporting salt (supporting electrolyte) in a non-aqueous solvent substantially free of a fluorinated solvent.
As the supporting salt, the same supporting salt as that of a general lithium ion secondary battery can be appropriately selected and used. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO _{3 and the} like. Such a supporting salt can be used singly or in combination of two or more. LiPF ₆ may be mentioned as particularly preferred support salt. Moreover, it is preferable to prepare the electrolytic solution for pretreatment so that the concentration of the supporting salt is within a range of 0.7 to 1.3 mol / L, for example. Furthermore, it is preferable to use a pretreatment electrolyte that is liquid at room temperature (for example, 25 ° C.).

  In the technology disclosed herein, the non-aqueous solvent substantially does not contain a fluorine-containing non-aqueous solvent. Here, “substantially does not contain” means that a fluorine-containing non-aqueous solvent is not at least intentionally contained, and does not mean, for example, that it is brought in as an unavoidable impurity. The nonaqueous solvent contained in the pretreatment electrolytic solution can be used without particular limitation as long as it does not contain a fluorine atom as a constituent element. For example, in various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, lactones, etc. used in the electrolyte of general non-aqueous electrolyte secondary batteries, fluorine atoms are substantially eliminated. Those not included can be used. Specific examples include ethylene carbonate (EC), propylene carbonate, diethyl carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, Examples include 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, and γ-butyrolactone. The carbonates mean to include cyclic carbonates and chain carbonates, and the ethers mean to include cyclic ethers and chain ethers. Such a non-aqueous solvent can be used individually by 1 type or in combination of 2 or more types as appropriate.

  As a preferred embodiment, a non-aqueous solvent mainly composed of carbonates can be mentioned. The inclusion of such a non-aqueous solvent as the pretreatment electrolyte is preferable because a good-quality film can be formed on the surface of the negative electrode active material when the cell described later is charged (step S122). Among them, EC having a high relative dielectric constant, DMC, EMC, or the like having a high oxidation potential (wide potential window) can be preferably used. For example, the nonaqueous solvent contains one or more carbonates, and the total volume of these carbonates is 60% by volume or more (more preferably 75% by volume or more, and further preferably 90% by volume) of the total volume of the nonaqueous solvent. That is, it may be substantially 100% by volume.) A non-aqueous solvent can be preferably used.

In another preferred embodiment, the reduction potential (vs. Li ^/ Li ⁺ ) of the pretreatment electrolyte is lower than the reduction potential (vs. Li ^/ Li ⁺ ) of the oxalato complex compound. Thereby, the oxalato complex compound can be preferentially reduced and decomposed, and a low-resistance film derived from the oxalato complex compound can be suitably formed on the surface of the negative electrode active material.
The reduction potential (vs. Li ^/ Li ⁺ ) of the electrolytic solution can be measured by the following method. First, a tripolar cell was created using glassy carbon as the working electrode (WE), metallic lithium as the counter electrode (CE), metallic lithium as the reference electrode (RE), and the electrolyte to be measured. Measure linear sweep voltammetry. Specifically, at a temperature of 20 ° C., the potential of the working electrode is swept from the open circuit voltage (OCV) after cell formation to 0.05V. The sweep speed is 1 mV / sec. The differential value dI / dV is calculated from the current I and the potential V of the measurement result. A graph is created with dI / dV as the vertical axis and the potential V as the horizontal axis. In this graph, the potential V corresponding to the peak of dI / dV that first appears from the start of measurement is taken as the reduction potential (reduction decomposition potential). For example, the reduction potential of the pretreatment electrolytic solution (nonaqueous electrolytic solution containing LiPF ₆ at a concentration of 1 mol / L in a mixed solvent having an EC: DMC volume ratio of 30:70) used in Examples described later is about 1.7 V (vs. Li ^/ Li ⁺ ).

<Oxalato complex compound>
As an oxalato complex compound, what was produced by the well-known method or what was obtained by purchase of a commercial item etc. is not specifically limited, 1 type, or 2 or more types can be used. For example, as represented by the following formula (II) or (III), an oxalato complex compound having a structural portion in which at least one oxalate ion (C ₂ O ₄ ²⁻ ) is coordinated to a boron (B) atom ( B atom-containing oxalate salt) is exemplified. Such an oxalato complex compound can form a good-quality film on the surface of the negative electrode active material when the pretreatment cell is charged (step S122). For example, it is possible to form a dense film having a high reductive decomposition prevention property. By using the negative electrode active material covered with such a film, a lithium ion secondary battery having excellent durability can be constructed.

Here, R ₁ and R ₂ in the formula (II) are a halogen atom (for example, F, Cl, Br, preferably F) and a perfluoroalkyl group having 1 to 10 (preferably 1 to 3) carbon atoms. Are independently selected. A ^{+ in} formulas (II) and (III) may be either an inorganic cation or an organic cation. Specific examples of the inorganic cation include alkali metal cations such as Li, Na, and K; alkaline earth metal cations such as Be, Mg, and Ca; other, Ag, Zn, Cu, Co, Fe, Ni, Mn, And metal cations such as Ti, Pb, Cr, V, Ru, Y, lanthanoids and actinoids; protons; and the like. Specific examples of organic cations include tetraalkylammonium ions such as tetrabutylammonium ion, tetraethylammonium ion and tetramethylammonium ion; trialkylammonium ions such as triethylmethylammonium ion and triethylammonium ion; other pyridinium ions and imidazolium ions Ion, tetraethylphosphonium ion, tetramethylphosphonium ion, tetraphenylphosphonium ion, triphenylsulfonium ion, triethylsulfonium ion; and the like. Examples of preferred cations include lithium ions, tetraalkylammonium ions and protons.

  In a preferred embodiment disclosed herein, a compound represented by the formula (III) is used as the oxalato complex compound. Among them, a preferable example is lithium bis (oxalato) borate (LiBOB) represented by the formula (I). LiBOB can form a dense and highly stable film on the surface of the negative electrode active material. Therefore, the decomposition reaction of the non-aqueous electrolyte accompanying charging / discharging after that can be suppressed suitably, and the application effect of this invention can be exhibited at a higher level.

As another example, a structural portion in which at least one oxalate ion (C ₂ O ₄ ²⁻ ) is coordinated to a phosphorus (P) atom as represented by the following formula (IV) or (V): The oxalato complex compound (P atom containing oxalate salt) which has is illustrated. Specific examples include lithium difluorobis (oxalato) phosphate, lithium tris (oxalato) phosphate, and the like.

In the above formulas (IV) and (V), an example in which the cation is a lithium ion is shown, but other cations may be used in the same manner as A ⁺ in formulas (II) and (III). Further, F in the above formulas (IV) and (V) is independently F and other halogen atoms (for example, F, Cl, Br. Preferably, F is the same as R ₁ and R ₂ in formula (II). ) And perfluoroalkyl groups having 1 to 10 (preferably 1 to 3) carbon atoms.

In a preferred embodiment, the oxalato complex compound exhibits the highest reduction potential among the components contained in the pretreatment electrolyte. By using the pretreatment electrolytic solution having such a composition, a film more suitable for the surface of the negative electrode active material can be formed by the pretreatment (step S120). For example, since the reduction potential of LiBOB used in the examples described later is approximately 1.73 V (vs. Li / Li ⁺ ), other components (typically nonaqueous solvents) contained in the pretreatment electrolyte solution The reduction potential is preferably approximately equal to or lower than 1.73 V (vs. Li / Li ⁺ ). The reduction potential can be measured in the same manner as the above-described reduction potential measurement of the electrolytic solution.

  The oxalato complex compound is typically added to the battery case in a state of being contained in the non-aqueous electrolyte (or the non-aqueous solvent used in the non-aqueous electrolyte). Alternatively, it can be directly added (for example, applied) to a battery component other than the non-aqueous electrolyte such as an electrode (for example, a negative electrode) or a separator.

  A suitable addition amount of the oxalato complex compound may vary depending on, for example, the type and properties of the negative electrode active material (for example, particle size and specific surface area), particle structure, surface state, and the like. In general, if the other conditions (type of active material, particle structure, etc.) are the same, the smaller the particle size and / or the larger the specific surface area, the more the amount of suitable oxalato complex compound added tends to increase. is there. Therefore, the amount of addition is not particularly limited, but if it is too small, the coating formed on the surface of the negative electrode active material becomes thin, and the durability (storage characteristics and cycle characteristics) of the battery may be reduced. On the other hand, when the addition amount is too large, the film formed on the surface of the negative electrode active material becomes thick, and there is a concern that the resistance accompanying charge / discharge increases. For this reason, the addition amount is, for example, 1 μmol / g or more (typically 3 μmol / g or more, for example, 5 μmol / g or more) to 500 μmol / g or less (typical) per unit mass of the negative electrode active material. 200 μmol / g or less, for example, 100 μmol / g or less). When the above addition amount is satisfied, a desired amount of film can be stably formed on the entire surface of the negative electrode active material.

<S110: Construction of pre-processing cell>
Then, the electrode body in which the positive electrode and the negative electrode face each other, the pretreatment electrolytic solution, and the oxalato complex compound are housed in an appropriate battery case to construct a pretreatment cell. In the example shown in FIG. 1, LiNi _0.5 Mn _1.5 O ₄ is exemplified as the positive electrode active material, and graphite is exemplified as the untreated negative electrode active material. Also it illustrates the electrolytic solution of the composition containing LiPF ₆ as a supporting salt in a mixed solvent of EC and DMC as preconditioning electrolyte solution. The mixing ratio of EC and DMC can be, for example, about 30:70 by volume. The concentration of LiPF ₆ can be, for example, about 1 mol / L.
As the battery case, materials and shapes conventionally used for non-aqueous electrolyte secondary batteries can be used. Examples of the material of the case include metal materials such as aluminum and steel; resin materials such as polyphenylene sulfide resin and polyimide resin. Among them, a relatively light metal (for example, aluminum or aluminum alloy) can be preferably employed for the purpose of improving heat dissipation and increasing energy density. The shape of the case (outer shape of the container) is, for example, circular (cylindrical shape, coin shape, button shape), hexahedron shape (rectangular shape, cubic shape), bag shape, and a shape obtained by processing and deforming them. It can be.

<S122: Charging of pretreatment cell>
Next, a pretreatment for applying a current between the positive electrode and the negative electrode is performed (step S122). In this charging, the potential of the negative electrode of the pretreatment cell (vs. Li ^/ Li ⁺ ) is at least one reduction potential (vs. Li ^/ Li ⁺ ) of the oxalato complex compound (included in the pretreatment electrolyte). It is preferable to carry out until approximately equal to or less than the above. For example, the negative electrode potential of the pretreatment cell is 0.05 V or more (preferably 0.1 V) than at least one oxidation potential (vs. Li ^/ Li ⁺ ) of the oxalato complex compound contained in the pretreatment electrolyte. It is preferable to carry out the above charging until it becomes low. More specifically, for example, the oxalate complex compound can be preferably decomposed in a state where the potential of the negative electrode is lower than 1.7 V (vs. Li ^/ Li ⁺ ). Thereby, the oxalato complex compound (for example, LiBOB) can be reduced and decomposed in the negative electrode of the pretreatment cell, and a coating film containing the decomposition product can be stably formed on the surface of the negative electrode active material.
As another preferred embodiment, this charging is preferably performed such that the negative electrode potential of the pretreatment cell is equal to or higher than the reduction potential of the pretreatment electrolyte (nonaqueous solvent containing a supporting salt). That is, in a pretreatment cell in a charged state (for example, a state where the SOC is approximately 100%), it can be preferably carried out in such a manner that the reduction potential of the oxalato complex compound> the negative electrode potential> the reduction potential of the electrolytic solution. More specifically, for example, the negative electrode potential (vs. Li ^/ Li ⁺ ) can be preferably carried out in an aspect in which 1.7 V> negative electrode potential> 1.5 V. Thereby, a high-quality film derived from the oxalato complex compound can be densely formed on the surface of the untreated negative electrode active material. Therefore, according to such an embodiment, a film excellent in electrolytic solution decomposition preventing property can be more suitably formed on the surface of the negative electrode active material. In other words, it is possible to obtain a negative electrode active material that is further excellent in electrolytic solution decomposition prevention.

  The pretreatment cell may be charged by, for example, a method of charging with a constant current (CC charging) until the pretreatment cell reaches the voltage, and after charging with a constant current up to the upper limit voltage, You may carry out by the system (CCCV charge) charged by. Usually, the CCCV charging method can be preferably adopted. The charge rate at the time of CC charge (it may be at the time of CC charge in a CCCV charge system) is not specifically limited, For example, it shall be about 1 / 50C-5C (1C is the electric current value which can be fully charged and discharged in 1 hour). Can do. Usually, it is appropriate to set the charging rate to about 1/30 C to 2 C (for example, 1/20 C to 1 C). If the charge rate is too low, the processing efficiency tends to decrease. On the other hand, if the charging rate is too high, the positive electrode active material may deteriorate, the uniformity of the formed film may decrease, or the reductive degradation prevention performance of the film may tend to decrease.

The time for holding the pretreatment cell at the above-mentioned potential (vs. Li ^/ Li ⁺ ) can be, for example, 90 minutes or less, and is usually 5 minutes to 60 minutes. If the time for maintaining the potential is too short, the formation of the film may be insufficient or non-uniform, and the electrolytic solution decomposition preventing effect may be easily lowered. If the time for maintaining the potential is too long, the formation of a film may proceed excessively depending on the pretreatment conditions, and the internal resistance (for example, initial resistance) of the battery using the coated negative electrode active material may easily increase. possible.

<S124: Discharge of Pretreatment Cell>
In the manufacturing method according to a preferred embodiment, the pretreatment cell thus charged (step S122) is discharged (step S124). By this discharge, it is possible to appropriately manage the time during which the negative electrode of the pretreatment cell is held at the above potential after charging, so that the amount of the coating film formed can be accurately controlled. Further, by avoiding a situation in which the time for which the negative electrode is held at the above potential becomes too long, it is possible to more suitably prevent the formation of the film from proceeding excessively and becoming high resistance. Furthermore, discharging the pretreatment cell before taking out the negative electrode (pretreated negative electrode) from the pretreatment cell is preferable from the viewpoint of workability and safety when taking out the negative electrode.

  The pretreatment (S120) may be performed once. For example, two or more charging (S122) and discharging (S124) operations may be repeated. In order to make the formation amount of a film into a suitable range, it is typically preferable to repeat charging and discharging about 2 to 10 times (for example, 2 to 5 times). Thereby, a low resistance and high reduction-resistant film can be obtained. It should be noted that an operation that can promote the formation of the coating (for example, pressure load due to heating, restraint, etc., irradiation with ultrasonic waves) can be used in combination as long as the battery performance is not greatly adversely affected.

<S130: Construction of Nonaqueous Electrolyte Secondary Battery>
Next, after removing the electrolyte contained in the pretreatment cell, the battery is constructed by injecting the battery electrolyte into the cell (step S130). According to the above method, the effect of the present invention can be obtained only by a simple operation of discharging the pretreatment electrolyte, which is convenient, and is preferable from the viewpoint of workability, efficiency, and operation cost. The removal of the pretreatment electrolyte can be performed, for example, by an operation such as centrifugation of the pretreatment cell.

<Battery electrolyte>
As the battery electrolyte, a solution in which a supporting salt (supporting electrolyte) is dissolved or dispersed in a nonaqueous solvent containing at least a fluorine-containing nonaqueous solvent is used. The kind and density | concentration of the said support salt can be equivalent to the electrolyte solution (pretreatment electrolyte solution) of the cell for a pretreatment mentioned above.

<Fluorine-containing non-aqueous solvent>
The battery electrolyte also contains a fluorine-containing nonaqueous solvent. This fluorine-containing non-aqueous solvent can be, for example, a fluorinated product of an organic solvent (organic compound) that is known to be usable for an electrolyte solution of a lithium ion secondary battery. In other words, it may be an organic solvent having a chemical structure in which at least one hydrogen atom of an organic solvent not containing fluorine as a constituent element is substituted with a fluorine atom. The “non-aqueous solvent containing no fluorine as a constituent element” may be various carbonates, ethers, esters, nitriles, sulfones, lactones and the like. The carbonates mean to include cyclic carbonates and chain carbonates, and the ethers mean to include cyclic ethers and chain ethers. Such fluorine-containing non-aqueous solvents can be used singly or in appropriate combination of two or more.

  The degree of fluorination in the fluorine-containing non-aqueous solvent is usually suitably 10% or more, preferably 20% or more, more preferably 30% or more (for example, 40% or more). Here, the “degree of fluorination” refers to a ratio of [(number of fluorine atoms of fluorine-containing nonaqueous solvent) / (number of hydrogen atoms of corresponding non-fluorine-containing nonaqueous solvent)] (hereinafter, This is also referred to as “fluorine substitution rate”). The upper limit of the fluorine substitution rate is not particularly defined, and may be 100% (that is, a compound in which all of the hydrogen atoms are replaced with fluorine atoms). Further, from the viewpoint of lowering the viscosity of the battery electrolyte and improving ion conductivity, a fluorine-containing non-aqueous solvent having a fluorine substitution rate of 90% or less (typically 80% or less, for example 70% or less) is preferable. Can be adopted.

The oxidation potential (vs. Li ^/ Li ⁺ ) of the battery electrolyte is desirably equal to or higher than the operating upper limit potential (vs. Li ^/ Li ⁺ ) of the positive electrode active material. For example, the difference from the operating potential (vs. Li ^/ Li ⁺ ) of the positive electrode active material is larger than 0 V (typically about 0.1 V to 3.0 V, preferably about 0.2 V to 2.0 V, for example, 0 An electrolytic solution of about 3 V to 1.0 V) can be preferably used.
The oxidation potential (vs. Li ^/ Li ⁺ ) of the electrolytic solution can be measured by the following method. First, a working electrode (WE) is produced using LiNi _0.5 Mn _1.5 O ₄ in the same manner as the positive electrode of the example described later. A tripolar cell is constructed using the produced WE, metallic lithium as the counter electrode (CE), metallic lithium as the reference electrode (RE), and the electrolyte solution to be measured. The triode cell is completely desorbed from WE. Specifically, at a temperature of 25 ° C., constant current charging is performed up to 4.2 V with a current value that is 1/5 of the battery capacity (Ah) predicted from the theoretical capacity of the WE. The constant voltage charging is performed until it becomes 1/50 of the value (that is, the current value of 1/5 of the battery capacity). Next, constant voltage charging is performed for a predetermined time (for example, 10 hours) at an arbitrary voltage in a voltage range (typically a voltage range of 4.2 V or more) that is predicted to include the oxidation potential of the electrolyte to be measured. The current value at that time is measured. More specifically, the voltage is increased stepwise (for example, in steps of 0.2 V) within the above voltage range, and constant voltage charging is performed for a predetermined time (for example, about 10 hours) at each step. Measure the current value. The potential when the current value during constant voltage charging is greater than 0.1 mA is defined as the oxidation potential (oxidation decomposition potential) of the electrolytic solution.

The reduction potential (vs. Li ^/ Li ⁺ ) of the battery electrolyte is desirably equal to or lower than the lower limit operating potential (vs. Li ^/ Li ⁺ ) of the negative electrode active material. For example, the difference from the operating potential (vs. Li ^/ Li ⁺ ) of the negative electrode active material is greater than 0 V (typically about 0.1 V to 2.0 V, preferably about 0.2 V to 1.0 V). An electrolytic solution can be preferably employed.

<Fluorinated carbonate>
In the battery electrolyte according to a preferred embodiment, one or more fluorinated carbonates (both fluorinated cyclic carbonates and fluorinated chain carbonates can be preferably used) as the fluorine-containing non-aqueous solvent. Containing. Usually, it is preferable to use a fluorinated carbonate having one carbonate structure in one molecule. The fluorine substitution rate of such a fluorinated carbonate is usually suitably 10% or more, for example, 20% or more (typically 20% or more and 100% or less, eg 20% or more and 80% or less). According to the battery electrolyte containing a fluorinated carbonate having a fluorine substitution rate of 30% or more (typically 30% or more and 100% or less, for example, 30% or more and 70% or less), a higher oxidation potential (high oxidation resistance) is obtained. It can be realized.

<Fluorinated cyclic carbonate>
Preferable examples of the battery electrolyte in the technology disclosed herein include a battery electrolyte having a composition containing at least one fluorinated cyclic carbonate as the fluorine-containing non-aqueous solvent. Of all the components excluding the supporting salt from the battery electrolyte (hereinafter also referred to as “component other than the supporting salt”), the amount of the fluorinated cyclic carbonate can be, for example, 5% by mass or more. 10 mass% or more is suitable and 20 mass% or more (for example, 30 mass% or more) is preferable. Substantially 100% by mass (typically 99% by mass or more) of the components other than the supporting salt may be a fluorinated cyclic carbonate. Usually, from the viewpoints of lowering the viscosity of the battery electrolyte, improving ion conductivity, etc., it is appropriate that the amount of the fluorinated cyclic carbonate in the components other than the supporting salt is 90% by mass or less, and 80% by mass % Or less (for example, 70% by mass or less). In addition, the quantity of the said fluorinated cyclic carbonate points out the total amount, when the said electrolyte solution for batteries contains 2 or more types of fluorinated cyclic carbonates.

  The fluorinated cyclic carbonate is preferably one having 2 to 8 carbon atoms (more preferably 2 to 6, for example 2 to 4, typically 2 or 3). When there are too many carbon atoms, the viscosity of the battery electrolyte solution may increase or the ionic conductivity may decrease. For example, a fluorine-containing carbonate represented by the following formula (C1) can be preferably used.

R ¹¹ , R ¹² and R ¹³ in the above formula (C1) are each independently a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 4 (more preferably 1 or 2, typically 1) carbon atoms. And haloalkyl groups, and halogen atoms other than fluorine (preferably chlorine atoms). The haloalkyl group may be a group having a structure in which one or more hydrogen atoms of the alkyl group are substituted with a halogen atom (for example, a fluorine atom or a chlorine atom, preferably a fluorine atom). A compound in which one or two of R ¹¹ , R ¹² and R ¹³ are fluorine atoms is preferred. For example, a compound in which at least one of R ¹² and R ¹³ is a fluorine atom is preferable. From the viewpoint of reducing the viscosity of the battery electrolyte, a compound in which R ¹¹ , R ¹² and R ¹³ are all fluorine atoms or hydrogen atoms can be preferably employed.

  Specific examples of the fluorinated cyclic carbonate represented by the above formula (C1) include monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), 4,4-difluoroethylene carbonate, trifluoroethylene carbonate, perfluoroethylene. Carbonate, 4-fluoro-4-methylethylene carbonate, 4,5-difluoro-4-methylethylene carbonate, 4-fluoro-5-methylethylene carbonate, 4,4-difluoro-5-methylethylene carbonate, 4- (fluoro Methyl) -ethylene carbonate, 4- (difluoromethyl) -ethylene carbonate, 4- (trifluoromethyl) -ethylene carbonate, 4- (fluoromethyl) -4-fluoroethylene carbonate, -(Fluoromethyl) -5-fluoroethylene carbonate, 4-fluoro-4,5-dimethylethylene carbonate, 4,5-difluoro-4,5-dimethylethylene carbonate, 4,4-difluoro-5,5-dimethylethylene carbonate, etc. Is mentioned. As difluoroethylene carbonate, any of trans-difluoroethylene carbonate (trans-DFEC) and cis-difluoroethylene carbonate (cis-DFEC) can be used. Usually, the use of trans-DFEC is more preferable. Since trans-DFEC exhibits a liquid state at normal temperature (for example, 25 ° C.), there is an advantage that it is superior in handling property compared to solid cis-DFEC at normal temperature.

<Fluorinated chain carbonate>
In the technique disclosed herein, the battery electrolyte includes, for example, the following formula (C2), instead of or in addition to the fluorinated cyclic carbonate as described above, as the fluorine-containing nonaqueous solvent. ) Can be used.

At least one (preferably both) of R ²¹ and R ²² in the formula (C2) is an organic group containing fluorine, and may be, for example, a fluorinated alkyl group or a fluorinated alkyl ether group. It may be a fluorinated alkyl group or a fluorinated alkyl ether group further substituted with a halogen atom other than fluorine. One of R ²¹ and R ²² may be an organic group that does not contain fluorine (for example, an alkyl group or an alkyl ether group). Each of R ²¹ and R ²² is preferably an organic group having 1 to 6 carbon atoms (more preferably 1 to 4, for example 1 to 3, typically 1 or 2). When there are too many carbon atoms, the viscosity of the battery electrolyte solution may increase or the ionic conductivity may decrease. For the same reason, usually, it is preferable that at least one of R ²¹ and R ²² is linear, more preferably R ²¹ and R ²² are both linear. For example, a fluorine chain carbonate in which R ²¹ and R ²² are both fluorinated alkyl groups and the total number of carbon atoms thereof is 1 or 2 can be preferably used.

  Specific examples of the fluorinated chain carbonate represented by the above formula (C2) include fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, trifluoromethyl methyl carbonate, fluoromethyl difluoromethyl carbonate, bis (fluoromethyl) carbonate, bis ( Difluoromethyl) carbonate, bis (trifluoromethyl) carbonate, (2-fluoroethyl) methyl carbonate, ethylfluoromethyl carbonate, (2,2-difluoroethyl) methyl carbonate, (2-fluoroethyl) fluoromethyl carbonate, ethyldifluoro Methyl carbonate, (2,2,2-trifluoroethyl) methyl carbonate, (2,2-difluoroethyl) fluoromethyl carbonate, (2-fluoro Ethyl) difluoromethyl carbonate, ethyl trifluoromethyl carbonate, ethyl- (2-fluoroethyl) carbonate, ethyl- (2,2-difluoroethyl) carbonate, bis (2-fluoroethyl) carbonate, ethyl- (2,2, 2-trifluoroethyl) carbonate, 2,2-difluoroethyl-2′-fluoroethyl carbonate, bis (2,2-difluoroethyl) carbonate, 2,2,2-trifluoroethyl-2′-fluoroethyl carbonate, 2,2,2-trifluoroethyl-2 ′, 2′-difluoroethyl carbonate, bis (2,2,2-trifluoroethyl) carbonate, pentafluoroethyl methyl carbonate, pentafluoroethyl fluoromethyl carbonate, pentafluor Ethyl ethyl carbonate, bis (pentafluoroethyl) carbonate.

  The battery electrolyte according to a preferred embodiment includes at least one fluorinated cyclic carbonate and at least one fluorinated chain carbonate as the fluorine-containing nonaqueous solvent. In the battery electrolyte having such a composition, the fluorinated chain carbonate (preferably, fluorinated linear carbonate) makes the electrolyte liquid at room temperature (for example, 25 ° C.) or reduces the viscosity of the electrolyte. Can help to make.

  Such a fluorine-containing non-aqueous solvent is 1% by mass or more (typically 5% by mass to 100% by mass, for example, 30% by mass to 100% by mass) of all components excluding the supporting salt from the battery electrolyte. And preferably 50 to 100% by mass) in the battery electrolyte. That is, in addition to the supporting salt and the fluorine-containing nonaqueous solvent, the battery electrolyte solution can contain other components as necessary. As a typical example, in order to reduce the viscosity of the battery electrolyte, a non-aqueous solvent containing no fluorine as a constituent element can be preferably used. The proportion of the non-aqueous solvent that does not contain a fluorine atom is usually preferably 70% by mass or less, more preferably 60% by mass (for example, 50% by mass) of components other than the supporting salt contained in the battery electrolyte. %) Or less. Alternatively, various additives (for example, film forming agents such as vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, etc .; compounds capable of generating gas during overcharge, such as biphenyl, cyclohexylbenzene, etc., to the extent that the effects of the present invention are not significantly impaired; A dispersant such as methyl cellulose (CMC); a thickener;

  In the above description, a method for exchanging only the electrolyte using the pretreatment cell (more specifically, the electrode body and the battery case included in the battery) is described. Then, a pretreated negative electrode (negative electrode having a coated negative electrode active material) is taken out of the battery, and a new lithium ion secondary battery can be constructed using the pretreated negative electrode, the positive electrode, and the battery electrolyte. Alternatively, an electrode body in which a pretreated negative electrode and a positive electrode are opposed to each other (typically via a separator) can be taken out as one body and used for the construction of a new battery as described above. When a new battery is constructed using a pretreated negative electrode or an electrode body including the negative electrode, other battery components (for example, a positive electrode, a separator, and a battery case) are those described above as components of a pretreatment cell, for example. It can be appropriately selected from among them.

  Although not intended to be particularly limited, as a nonaqueous electrolyte secondary battery according to an embodiment of the present invention, a flatly wound electrode body (wound electrode body), a nonaqueous electrolyte solution, Is taken as an example of a non-aqueous electrolyte secondary battery (unit cell) in a form of being accommodated in a flat rectangular parallelepiped (rectangular) container, and FIGS. In the following drawings, members / parts having the same action are denoted by the same reference numerals, and redundant description may be omitted or simplified. The dimensional relationship (length, width, thickness, etc.) in each figure does not reflect the actual dimensional relationship.

As shown in FIGS. 2 and 3, for example, the non-aqueous electrolyte secondary battery according to an embodiment of the technology disclosed herein includes a wound electrode body 80 together with a non-aqueous electrolyte (not shown). The battery case 50 is accommodated in a flat rectangular parallelepiped (square) battery case 50 corresponding to the shape of 80. The battery case 50 includes a flat rectangular parallelepiped (square) battery case main body 52 having an open upper end, and a lid 54 that closes the opening. A positive electrode terminal 70 and a negative electrode terminal 72 for external connection are provided on the upper surface (that is, the lid body 54) of the battery case 50 so that some of the terminals protrude from the lid body 54 to the outside of the battery. . The lid 54 is provided with a safety valve 55 for discharging gas generated inside the battery case to the outside of the case.
For example, the non-aqueous electrolyte secondary battery 100 having such a configuration is provided in the lid 54 after the electrode body 80 is accommodated in the opening of the case 50 and the lid 54 is attached to the opening of the case 50. It can be constructed by injecting a non-aqueous electrolyte from the electrolyte injection hole (not shown) and then closing the injection hole.

As shown in FIGS. 3 and 4, the electrode body 80 includes a positive electrode sheet 10 in which a positive electrode active material layer 14 containing a positive electrode active material is held by a long sheet-like positive electrode current collector 12, and a negative electrode active material. The negative electrode active material layer 24 is rolled up with the negative electrode sheet 20 held on the long sheet-like negative electrode current collector 22, and the obtained wound body is pressed and ablated from the side surface to be flattened. It is molded into a shape. Typically, an insulating layer that prevents direct contact between the positive electrode active material layer 14 and the negative electrode active material layer 24 is disposed between the positive electrode active material layer 14 and the negative electrode active material layer 24. In a preferred embodiment, two long sheet-like separators 40 are used as the insulating layer. For example, the electrode body 80 is configured by winding these separators 40 together with the positive electrode sheet 10 and the negative electrode sheet 20. The insulating layer may be directly coated on the surface of the positive electrode active material layer 14 and / or the negative electrode active material layer 24.
The positive electrode sheet 10 is formed such that the positive electrode active material layer 14 is not provided (or removed) at one end portion along the longitudinal direction, and the positive electrode current collector 12 is exposed. Similarly, the negative electrode sheet 20 is formed such that the negative electrode active material layer 24 is not provided (or removed) at one end portion along the longitudinal direction, and the negative electrode current collector 22 is exposed. Yes. A positive electrode terminal 70 is joined to the exposed end portion of the positive electrode current collector 12, and a negative electrode terminal 72 is joined to the exposed end portion of the negative electrode current collector 22.

  The non-aqueous electrolyte secondary battery disclosed here (typically a lithium ion secondary battery) can be used for various applications, but is pretreated (more specifically, the surface of the negative electrode active material by pretreatment). The effect of the film applied to the film is suitably exhibited, and the battery performance (for example, energy density and durability) is superior to the conventional one. Therefore, using such a property, for example, as shown in FIG. 6, it can be suitably used as a driving power source mounted on the vehicle 1. The vehicle 1 is typically an automobile, and may be, for example, a hybrid automobile (HV), a plug-in hybrid automobile (PHV), an electric automobile (EV), a fuel cell automobile, an electric wheelchair, or an electric assist bicycle. Therefore, as another aspect of the present invention, there is provided a vehicle 1 provided with any of the nonaqueous electrolyte secondary batteries 100 disclosed herein, preferably as a power source. The vehicle 1 may include a plurality of nonaqueous electrolyte secondary batteries 100, typically in the form of an assembled battery to which they are connected.

  Hereinafter, some examples relating to the present invention will be described, but the present invention is not intended to be limited to such examples. In the following description, “parts” and “%” are based on mass unless otherwise specified.

First, each electrolytic solution used in the following experiment will be described.
<Non-aqueous electrolyte>
(Electrolytic solution A)
LiPF ₆ was dissolved to a concentration of 1 mol / L in a mixed solvent containing EC and DMC at a volume ratio of 30:70 to prepare a non-aqueous electrolyte A.
When the oxidation potential and the reduction potential of the electrolytic solution A were measured according to the method described above, the oxidation potential was 4.6 V to 4.8 V (vs. Li ^/ Li ⁺ ), and the reduction potential was 1.5 V (vs. Li). / Li ⁺ ).
(Electrolytic solution B)
LiPF ₆ was dissolved to a concentration of 1 mol / L in a mixed solvent containing MFEC and EMC at a volume ratio of 1: 1 to prepare a non-aqueous electrolyte B.
When the oxidation potential and the reduction potential of this electrolytic solution B were measured according to the above-described method, the oxidation potential was 4.9 V to 5.1 V, and the reduction potential was 1.98 V (vs. Li / Li ⁺ ).

<Example 1>
(Preparation of positive electrode sheet)
As the positive electrode active material, LiNi _0.5 Mn _1.5 O ₄ having an average particle diameter of 6 μm and a BET specific surface area of 0.7 m ² / g was prepared. This positive electrode active material, acetylene black (conductive material), and PVdF (binder) were dispersed in NMP so that the mass ratio thereof was 89: 8: 3 to prepare a slurry composition. This composition was applied to one side of a 15 μm thick long aluminum foil (positive electrode current collector) and dried to form a positive electrode active material layer. The positive electrode active material layer with current collector by a roll press, the density of the positive electrode active material layer was adjusted to 2.3 g / cm ^3, the theoretical capacity (design capacity) C _c to obtain a positive electrode sheet of 60mAh .

(Preparation of negative electrode sheet)
A natural graphite material having an average particle diameter of 20 μm and a BET specific surface area of 2.5 m ² / g was prepared as a negative electrode active material. This negative electrode active material, CMC (thickening agent), and SBR (binder) are mixed with ion-exchanged water so that the mass ratio thereof becomes 98.6: 0.7: 0.7. A composition was prepared. This composition was applied to one side of a 10 μm thick copper foil (negative electrode current collector) and dried to form a negative electrode active material layer. The current collector with the negative electrode active material layer was roll-pressed to adjust the density of the negative electrode active material layer to 1.4 g / cm ³ and cut into a rectangular shape having the same size as the positive electrode sheet to obtain a negative electrode sheet. The coating amount of the composition was adjusted so that the theoretical capacity ratio (C _c / C _a ) between the positive electrode and the negative electrode was 1.5.

(Construction of pretreatment cell)
The prepared positive electrode sheet and negative electrode sheet were opposed to each other through a separator sheet (a porous sheet having a PP / PE / PP three-layer structure), and wound to prepare a wound electrode body. In addition, 0.05 mol / L of electrolyte A (nonaqueous electrolyte containing LiPF ₆ at a concentration of 1 mol / L in a mixed solvent of EC: DMC volume ratio 30:70) as a pretreatment electrolyte LiBOB (oxalato complex compound) was dissolved at a concentration of. The electrode body and the electrolytic solution A containing LiBOB were accommodated in a battery case made of an appropriate size laminate, and sealed with a part (opening) remaining. The pretreatment cell is provided with a positive electrode terminal and a negative electrode terminal connected to the positive electrode sheet and the pretreatment negative electrode, respectively, and drawn to the outside of the laminate film.

(Preprocessing)
The pretreatment cell constructed as described above was pretreated according to the following procedure.
(1) CC charge to 4.9V at a rate of 1 / 3C.
(2) Pause (hold) for 10 minutes.
(3) CC discharge to 3.5V at a rate of 1 / 3C.
(4) Pause for 10 minutes.
After repeating the above operations (1) to (4) for 3 cycles, the pretreatment cell was disassembled, and all the electrolyte solution in the cell was discharged using a centrifugation method. It was confirmed that the discharge capacity in the third cycle CCCV discharge was not significantly different from the theoretical capacity.

(Construction of non-aqueous electrolyte secondary battery)
After pouring electrolyte B into a cell (battery case) containing an electrode body with a pretreated negative electrode sheet, the non-sealed portion is sealed, and the non-aqueous electrolyte secondary battery according to this example ( Lithium ion secondary battery) was constructed.

<Example 2>
A lithium ion secondary battery according to this example was constructed in the same manner as in Example 1 except that the electrolytic solution (battery electrolytic solution) for constructing the battery was changed from the electrolytic solution B to the electrolytic solution A.

<Example 3>
A lithium ion secondary battery according to this example was constructed in the same manner as in Example 2 except that LiBOB was not used when constructing the pretreatment cell.

<Example 4>
A lithium ion secondary battery according to this example was constructed in the same manner as Example 3 except that the electrolyte B was used as the pretreatment electrolyte and the battery electrolyte.

<Example 5>
A lithium ion secondary battery according to this example was constructed in the same manner as in Example 1 except that the pretreatment electrolyte was changed from the electrolyte A to the electrolyte B.

<Measurement of reduction potential (vs. Li ^/ Li ⁺ )>
The reduction potential (vs. Li ^/ Li ⁺ ) of the pretreatment electrolyte solution and LiBOB (oxalato complex compound) used in each example was measured by the method described above. As a result, the reduction potential of LiBOB was 1.73 V (vs. Li / Li ⁺ ). The configuration of the battery according to each example and the reduction potential (vs. Li ^/ Li ⁺ ) of the pretreatment electrolyte are shown in the corresponding columns of Table 2.

<Performance evaluation>
(Initial capacity)
At a temperature of 25 ° C., the battery according to each example was subjected to a conditioning process with the same charge / discharge pattern as the pretreatment. That is, (1) a constant current (CC) charge at a rate of 1/3 C until the positive electrode potential becomes 4.9 V, and then rest for 10 minutes. (2) 1/3 C until the positive electrode potential becomes 3.5 V. The operation of resting for 10 minutes after CC discharge at a rate was repeated 3 cycles. The discharge capacity at the third cycle was defined as the initial capacity (initial discharge capacity).

(Initial resistance)
Next, each battery after the initial capacity measurement was subjected to CC charging at a temperature of 25 ° C. until the SOC reached 60% at a rate of 1 / 3C. CC discharge was performed at a discharge rate of 1C, 3C, 5C, and 10C for each battery cell prepared to have an SOC of 60%, and a voltage drop for 10 seconds after the discharge was measured. The measured voltage drop value (V) was divided by the corresponding current value (for example, 20 mA for 1 / 3C) to calculate the IV resistance (Ω), and the average value was taken as the initial resistance. The results are shown in the column of “initial resistance” in Table 2 and FIG.

  As is apparent from Table 2 and FIG. 5, the batteries of Examples 4 and 5 using “electrolyte B” as the pretreatment electrolyte had an initial resistance of about 6Ω, whereas “electrolyte A”. In the batteries of Examples 1 to 3 using the initial resistance, the initial resistance was suppressed to about half (about 3Ω). From this result, it was shown that the initial resistance of the battery can be lowered by performing the pretreatment without using a fluorine-containing nonaqueous solvent. This result is considered to be because a low-resistance film derived from an oxalato complex compound could be formed on the surface of the negative electrode active material by performing the above pretreatment without using a fluorine-containing nonaqueous solvent. In other words, it is considered that a low-resistance film could be suitably formed on the surface of the negative electrode active material by using an electrolyte for pretreatment having a reduction potential lower than that of the oxalato complex compound (LiBOB).

(Cycle characteristic test)
Next, for each battery after the initial resistance measurement, the following charge / discharge operations (1) to (4) were repeated 100 cycles in a thermostat at a temperature of 60 ° C.
(1) CC charge to 4.9V at 2C rate.
(2) Pause for 10 minutes.
(3) CC discharge to 3.5V at a rate of 2C.
(4) Pause for 10 minutes.
Thereafter, the discharge capacity was measured in the same manner as the initial capacity. The capacity retention rate (%) of the cycle characteristics was calculated as the ratio of the discharge capacity at the 100th cycle to the initial capacity ((capacity after 100 cycles / initial capacity) × 100 (%)). The results are shown in the column of “capacity maintenance ratio” in Table 2 and FIG.

As apparent from Table 2 and FIG. 5, in the batteries of Example 2 and Example 3 using “electrolyte A” as the battery electrolyte, the capacity retention rate after 100 cycles was about 20%, In the batteries of Examples 1, 4 and 5 using the “electrolytic solution B”, the capacity retention ratio was improved by about twice or more to about 50%. Such an increase in the capacity retention rate is considered to be due to the fact that in Examples 1, 4 and 5, the oxidative decomposition of the electrolyte was significantly suppressed. From this result, it was shown that the capacity retention rate can be increased by using a fluorine-containing non-aqueous solvent as the battery electrolyte.
Thus, according to the said manufacturing method, the nonaqueous electrolyte secondary battery by which the oxidative decomposition and reductive decomposition of electrolyte solution were suppressed can be implement | achieved. In non-aqueous electrolyte secondary batteries in which the decomposition of the electrolyte is highly suppressed, the internal resistance (typically the resistance of the negative electrode) is reduced, and higher battery performance (for example, higher battery capacity and durability) is exhibited. It was shown to get.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here.

1 Automobile (vehicle)
10 Positive electrode sheet (positive electrode)
12 Positive electrode current collector 14 Positive electrode active material layer 20 Negative electrode sheet (negative electrode)
22 Negative electrode current collector 24 Negative electrode active material layer 40 Separator sheet (separator)
DESCRIPTION OF SYMBOLS 50 Battery case 52 Battery case main body 54 Cover body 55 Safety valve 70 Positive electrode terminal 72 Negative electrode terminal 80 Winding electrode body 100 Nonaqueous electrolyte secondary battery

Claims (11)

A method of manufacturing a non-aqueous electrolyte secondary battery comprising:
Containing a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, a pretreatment electrolyte substantially free of a fluorine-containing nonaqueous solvent, and an oxalato complex compound in a pretreatment cell;
Performing a pretreatment for applying a current between the positive electrode and the negative electrode to form a film derived from the oxalato complex compound on the surface of the negative electrode active material; and a negative electrode having a negative electrode active material on which the film is formed; Constructing a non-aqueous electrolyte secondary battery using the positive electrode and the battery electrolyte;
Including
Here, the said battery electrolyte solution used in order to construct | assemble this nonaqueous electrolyte secondary battery is a manufacturing method of the nonaqueous electrolyte secondary battery containing a fluorine-containing nonaqueous solvent.   The manufacturing method according to claim 1, wherein a lithium transition metal composite oxide having a layered structure or a spinel structure containing a lithium element and at least one transition metal element as constituent metal elements is used as the positive electrode active material.   The manufacturing method according to claim 1, wherein a lithium nickel manganese composite oxide having a spinel structure is used as the positive electrode active material.   The manufacturing method according to any one of claims 1 to 3, wherein the pretreatment electrolytic solution is one having a reduction potential based on metallic lithium that is lower than that of the oxalato complex compound.   The production method according to any one of claims 1 to 4, wherein at least lithium bis (oxalato) borate is used as the oxalato complex compound.   The said pre-processing is a manufacturing method as described in any one of Claim 1 to 5 performed so that the electric potential on the basis of metallic lithium of the said negative electrode may become lower than the reduction potential on the basis of metallic lithium of the said oxalato complex compound at least.   The said battery electrolyte solution is a manufacturing method as described in any one of Claim 1 to 6 containing a fluorinated carbonate as said fluorine-containing non-aqueous solvent.   The manufacturing method according to claim 1, wherein the battery electrolyte includes a fluorinated cyclic carbonate as the fluorine-containing nonaqueous solvent.   The manufacturing method according to claim 1, wherein the battery electrolyte contains monofluoroethylene carbonate and / or difluoroethylene carbonate as the fluorine-containing nonaqueous solvent.   The manufacturing method as described in any one of Claim 1 to 9 with which the operating upper limit electric potential of the said positive electrode is set to 4.5 V or more on the basis of metallic lithium.   A non-aqueous electrolyte secondary battery obtained by the production method according to claim 1.

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