JP2019197632A - Nonaqueous electrolyte and nonaqueous secondary battery - Google Patents

Abstract

To provide nonaqueous electrolyte and a nonaqueous secondary battery with excellent load characteristics and capable of restraining gas generation during high temperature storage, by restraining generation of complex cation composed of a transition metal and acetonitrile, in nonaqueous electrolyte containing acetonitrile excellent in balance of viscosity and relative dielectric constant, and fluorine-containing inorganic lithium salt.SOLUTION: Nonaqueous electrolyte contains a nonaqueous solvent containing acetonitrile, fluorine-containing inorganic lithium salt, and a compound represented by following general formula (1). (In the general formula (1), A is CRor nitrogen atom independently, R-Rare hydrogen atoms, alkyl group of 1C-4C, fluorine substitution alkyl group of 1C-4C, alkoxy group of 1C-4C, or fluorine substitution alkoxy group of 1C-4C).SELECTED DRAWING: None

Description

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

  Non-aqueous secondary batteries such as lithium ion secondary batteries are characterized by light weight, high energy, and long life, and are widely used as power sources for various portable electronic devices. In recent years, it is also spreading for industrial use represented by power tools such as electric tools; in-vehicle use for electric vehicles, electric bicycles and the like. Further, it has been attracting attention in the field of power storage such as a residential power storage system.

  It is desirable from a practical point of view to use a non-aqueous electrolyte as an electrolyte for a room temperature operation type lithium ion secondary battery. For example, a combination of a high dielectric constant solvent such as a cyclic carbonate and a low viscosity solvent such as a lower chain carbonate is exemplified as a general solvent. However, a normal high dielectric constant solvent has a high melting point, and depending on the type of electrolyte salt used in the non-aqueous electrolyte, it may cause deterioration in load characteristics (output characteristics) and low-temperature characteristics of the non-aqueous electrolyte. Can be.

  As one of the solvents for overcoming such problems, a nitrile solvent excellent in the balance between viscosity and relative dielectric constant has been proposed. Among them, acetonitrile has a high potential as a solvent used for an electrolyte solution of a lithium ion secondary battery. However, since acetonitrile has a fatal defect of electrochemically reducing and decomposing at the negative electrode, it has not been able to demonstrate practical performance. Several improvements have been proposed for this problem. The main improvement measures proposed so far are classified into the following three.

(1) Method for protecting negative electrode by combination with specific electrolyte salt, additive, etc., and suppressing reductive decomposition of acetonitrile For example, Patent Documents 1 and 2 include acetonitrile as a solvent, addition of specific electrolyte salt and There has been reported an electrolytic solution in which the effect of reductive decomposition of acetonitrile is reduced by combining with an agent. In the early days of lithium ion secondary batteries, as disclosed in Patent Document 3, an electrolytic solution containing a solvent obtained by simply diluting acetonitrile with propylene carbonate and ethylene carbonate has been reported. However, in Patent Document 3, the high-temperature durability performance is determined by evaluating only the internal resistance and battery thickness after high-temperature storage, so whether or not the battery actually operates when placed in a high-temperature environment. This information is not disclosed. Suppressing the reductive decomposition of an electrolytic solution containing a solvent based on acetonitrile by simply diluting with ethylene carbonate and propylene carbonate is actually a difficult task. As a method for suppressing reductive decomposition of a solvent, a method of combining a plurality of electrolyte salts and additives as in Patent Documents 1 and 2 is realistic.

(2) A method of suppressing reductive decomposition of acetonitrile by using a negative electrode active material that occludes lithium ions at a potential nobler than the reduction potential of acetonitrile. For example, Patent Document 4 uses a specific metal compound for the negative electrode. Thus, it is reported that a battery avoiding reductive decomposition of acetonitrile can be obtained. However, in applications where the energy density of lithium ion secondary batteries is important, it is overwhelmingly advantageous to use a negative electrode active material that occludes lithium ions at a base potential lower than the reduction potential of acetonitrile from the viewpoint of potential difference. . Therefore, in such a use, if the improvement measure of patent document 4 is applied, since the range of the voltage which can be used becomes narrow, it is disadvantageous.

(3) Method of maintaining a stable liquid state by dissolving a high concentration electrolyte salt in acetonitrile For example, Patent Document 5 discloses that lithium bis (trifluoromethanesulfonyl) imide has a concentration of 4.2 mol / L. It is described that reversible lithium insertion / extraction from / to a graphite electrode is possible when an electrolytic solution in which (LiN (SO ₂ CF ₃ ) ₂ ) is dissolved in acetonitrile is used. Patent Document 6 discloses a cell using an electrolytic solution in which lithium bis (fluorosulfonyl) imide (LiN (SO ₂ F) ₂ ) is dissolved in acetonitrile so that the concentration is 4.5 mol / L. As a result of charge / discharge measurement, Li ⁺ insertion / extraction reaction to graphite was observed, and it was reported that discharge was possible at a high rate.

International Publication No. 2012/057311 International Publication No. 2013/062056 JP-A-4-351860 JP 2009-21134 A International Publication No. 2013/146714 JP 2014-241198 A

  However, lithium ion secondary batteries using an electrolytic solution containing acetonitrile are inferior in high-temperature durability performance compared to existing lithium ion secondary batteries using an electrolytic solution containing a carbonate solvent. Has not yet reached full-scale practical use.

  From the results of various verification experiments, the reason why the acetonitrile-based lithium ion secondary battery is inferior in high-temperature durability is considered as follows.

  In a high temperature environment, the fluorine-containing inorganic lithium salt decomposes while extracting hydrogen from the methyl group of acetonitrile, and the decomposition product promotes elution of the positive electrode transition metal. A complex cation coordinated with acetonitrile on this eluting metal undergoes a reduction reaction on the negative electrode surface, adversely affecting the SEI (Solid Electrolyte Interface) formed as an electrolyte decomposition inhibitor, and generating gas. It is thought to induce.

  The present invention has been made in view of the above circumstances. Therefore, the present invention suppresses the formation of a complex cation composed of a transition metal and acetonitrile in a non-aqueous electrolyte containing acetonitrile and a fluorine-containing inorganic lithium salt, which has an excellent balance between viscosity and relative dielectric constant, An object of the present invention is to provide a non-aqueous electrolyte and a non-aqueous secondary battery that exhibit excellent load characteristics and can suppress gas generation during high-temperature storage when used in a battery.

The inventors of the present invention have made extensive studies to solve the above-described problems. As a result, even if it is a non-aqueous electrolyte containing acetonitrile as a non-aqueous solvent, when it contains a compound with a specific azole skeleton as an additive, the formation of complex cations consisting of transition metals and acetonitrile is suppressed. And while exhibiting the outstanding load characteristic, when it used for a battery, it discovered that the gas generation at the time of high temperature storage could be suppressed, and came to complete this invention.
That is, the present invention is as follows.

The non-aqueous electrolyte of the present invention is characterized by containing a non-aqueous solvent containing acetonitrile, a fluorine-containing inorganic lithium salt, and a compound represented by the following general formula (1).

  In the present invention, the compound represented by the general formula (1) is preferably 1-methylpyrazole.

  In this invention, it is preferable that content of the compound represented by the said General formula (1) is 0.01-10 mass% with respect to the whole nonaqueous electrolyte solution.

  In this invention, it is preferable that content of the said acetonitrile is 30-100 volume% with respect to the whole nonaqueous electrolyte solution.

In the present invention, the fluorine-containing inorganic lithium salt, preferably contains LiPF _6.

  The non-aqueous secondary battery of the present invention includes a positive electrode having a positive electrode active material layer containing at least one transition metal element selected from Ni, Mn, and Co on one side or both sides of a current collector. It comprises a negative electrode having a negative electrode active material layer on one side or both sides, and the non-aqueous electrolyte described above.

  In the present invention, the capacity retention rate in the output test after storage at 85 ° C. for 4 hours is preferably 75% or more.

  In this invention, it is preferable that the gas generation amount in a 60 degreeC storage test is 0.0025 ml or less as a conversion value per battery capacity 1mAh.

  According to the present invention, in a nonaqueous electrolytic solution containing acetonitrile having a good balance between viscosity and relative dielectric constant and a fluorine-containing inorganic lithium salt, the formation of a complex cation composed of a transition metal and acetonitrile is suppressed. It is possible to provide a non-aqueous electrolyte and a non-aqueous secondary battery that exhibit excellent load characteristics and can suppress gas generation during high-temperature storage when used in a battery.

It is a top view which shows roughly an example of the non-aqueous secondary battery of this embodiment. It is sectional drawing which cut | disconnected the non-aqueous secondary battery of FIG. 1 along the AA line, and looked at the arrow direction. 3A is a plan view for explaining the “width of the non-opposing portion of the negative electrode active material layer” in the laminated electrode body, and FIG. 3B is “the width of the non-opposing portion of the negative electrode active material layer” in the laminated electrode body. It is a top view for demonstrating. It is a top view for demonstrating "the width | variety of the non-opposing part of a negative electrode active material layer" in a wound electrode body. It is a typical top view for demonstrating the positive electrode for batteries. It is a typical top view for demonstrating the negative electrode for batteries.

  Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail. In the present specification, numerical ranges described using “to” include numerical values described before and after.

The non-aqueous electrolyte solution of the present embodiment (hereinafter also simply referred to as “electrolyte solution”) includes a non-aqueous solvent containing acetonitrile, a fluorine-containing inorganic lithium salt, a compound represented by the following general formula (1), It is characterized by containing.

  As a result, in a non-aqueous electrolyte solution containing acetonitrile and a fluorine-containing inorganic lithium salt having a good balance between viscosity and relative dielectric constant, generation of a complex cation composed of a transition metal and acetonitrile is suppressed, and excellent While exhibiting load characteristics, it can suppress gas generation during high-temperature storage when used as a battery.

<Details of non-aqueous electrolyte and non-aqueous secondary battery>
Hereinafter, each configuration of the non-aqueous electrolyte and the non-aqueous secondary battery according to the present embodiment will be specifically described. However, each configuration is not limited to the specific examples given below.

<1. Overall configuration of non-aqueous secondary battery>
The electrolyte solution of this embodiment can be used for a non-aqueous secondary battery, for example. As the non-aqueous secondary battery of this embodiment, for example, a positive electrode containing a positive electrode material capable of occluding and releasing lithium ions as a positive electrode active material, and a lithium ion occluding and releasing as a negative electrode active material. And a negative electrode containing one or more negative electrode materials selected from the group consisting of metallic lithium and a lithium ion secondary battery.

  Specifically, the non-aqueous secondary battery of the present embodiment may be the non-aqueous secondary battery illustrated in FIGS. 1 and 2. Here, FIG. 1 is a plan view schematically showing a non-aqueous secondary battery, and FIG. 2 is a cross-sectional view taken along the line AA in FIG.

  The non-aqueous secondary battery 1 includes a laminated electrode body formed by laminating a positive electrode 5 and a negative electrode 6 with a separator 7 in a battery exterior 2 constituted by two aluminum laminate films, and a non-aqueous electrolyte solution ( (Not shown). The battery exterior 2 is sealed by heat-sealing the upper and lower aluminum laminate films at the outer periphery thereof. The laminate in which the positive electrode 5, the separator 7, and the negative electrode 6 are sequentially laminated is impregnated with a nonaqueous electrolytic solution. However, in FIG. 2, each layer constituting the battery outer casing 2 and each layer of the positive electrode 5 and the negative electrode 6 are not shown separately in order to avoid the drawing from becoming complicated.

  For example, the aluminum laminate film constituting the battery casing 2 is preferably one in which both surfaces of an aluminum foil are coated with a polyolefin-based resin.

  The positive electrode 5 is connected to the positive electrode terminal 3 a through the lead piece 9 in the battery 1. Although not shown, the negative electrode 6 is also connected to the negative electrode terminal 4a in the battery 1 via a lead piece. The positive electrode terminal 3a and the negative electrode terminal 4a are each drawn out to the outside of the battery exterior 2 so that they can be connected to an external device or the like, and their ionomer portions together with one side of the battery exterior 2 It is heat-sealed.

  In the non-aqueous secondary battery 1 shown in FIGS. 1 and 2, each of the positive electrode 5 and the negative electrode 6 has a single laminated electrode body. It can be increased as appropriate. In the case of a laminated electrode body having a plurality of each of the positive electrode 5 and the negative electrode 6, the tabs of the same electrode are joined by welding or the like, and then joined to the positive electrode lead body 3 and the negative electrode lead body 4 by welding or the like. You may take out out of a battery. As the tab of the same polarity, an aspect constituted by an exposed portion of the current collector, an aspect constituted by welding a metal piece to the exposed portion of the current collector, and the like are possible.

  The positive electrode 5 includes a positive electrode active material layer made from a positive electrode mixture and a positive electrode current collector. The negative electrode 6 includes a negative electrode active material layer made from a negative electrode mixture and a negative electrode current collector. The positive electrode 5 and the negative electrode 6 are disposed so that the positive electrode active material layer and the negative electrode active material layer face each other with the separator 7 interposed therebetween.

  Hereinafter, the term “electrode” is also abbreviated as a general term for the positive electrode and the negative electrode.

  As each of these members, a material provided in a conventional lithium ion secondary battery can be used as long as each requirement in the present embodiment is satisfied. For example, the following materials may be used. Hereinafter, each member of the non-aqueous secondary battery will be described in detail.

<2. Electrolyte>
The electrolytic solution in the present embodiment comprises a non-aqueous solvent (hereinafter also simply referred to as “solvent”), a fluorine-containing inorganic lithium salt, and a compound represented by the above general formula (1) (a compound having an azole skeleton). Including at least. Although the fluorine-containing inorganic lithium salt is excellent in ionic conductivity, it has insufficient thermal stability and has the property of being easily hydrolyzed by a trace amount of water in the solvent to generate lithium fluoride and hydrogen fluoride. When the fluorine-containing inorganic lithium salt is decomposed, the ionic conductivity of the electrolytic solution containing the fluorine-containing inorganic lithium salt is reduced, and the generated lithium fluoride and hydrogen fluoride corrode materials such as electrodes and current collectors. In some cases, the battery may have a fatal adverse effect such as decomposition of the solvent.

  The electrolytic solution in the present embodiment preferably does not contain moisture, but may contain a very small amount of moisture as long as the solution of the problem of the present invention is not hindered. The water content is preferably 0 to 100 ppm with respect to the total amount of the electrolytic solution.

<2-1. Non-aqueous solvent>
Acetonitrile has high ion conductivity and can increase the diffusibility of lithium ions in the battery. Therefore, when the electrolytic solution contains acetonitrile, a collector in which lithium ions are difficult to reach at the time of discharge under a high load, particularly in a positive electrode in which the positive electrode active material layer is thickened to increase the filling amount of the positive electrode active material. Lithium ions can be diffused well to nearby regions. Therefore, a sufficient capacity can be extracted even during high-load discharge, and a non-aqueous secondary battery having excellent load characteristics can be obtained.

  By using acetonitrile as the non-aqueous solvent of the non-aqueous electrolyte solution, as described above, the ionic conductivity of the non-aqueous electrolyte solution is improved, so that the quick charge characteristics of the non-aqueous secondary battery can be enhanced. In constant current (CC) -constant voltage (CV) charging of a non-aqueous secondary battery, the capacity per unit time in the CC charging period is larger than the charging capacity per unit time in the CV charging period. When acetonitrile is used as the non-aqueous solvent of the non-aqueous electrolyte, the CC chargeable area can be increased (the CC charge time can be increased), and the charge current can be increased, so the non-aqueous secondary battery can be charged. The time from the start to the fully charged state can be greatly shortened.

  The non-aqueous solvent is not particularly limited as long as it contains 30 to 100% by volume of acetonitrile with respect to the total amount of the non-aqueous solvent, and may or may not contain other non-aqueous solvents.

  The term “non-aqueous solvent” as used in this embodiment refers to a component obtained by removing a lithium salt and a compound having an azole skeleton from an electrolyte solution. That is, when the electrolytic solution contains a solvent, a lithium salt, and a compound having an azole skeleton together with a liquid electrode protecting additive described later, the solvent and the liquid electrode protecting additive are combined. It is called “non-aqueous solvent”. The compounds having a lithium salt and an azole skeleton described later are not included in the non-aqueous solvent.

  Examples of the other non-aqueous solvents include alcohols such as methanol and ethanol; aprotic solvents and the like. Among these, an aprotic polar solvent is preferable.

Among the other non-aqueous solvents, specific examples of the aprotic solvent include, for example, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene. Cyclic carbonate represented by carbonate, 1,2-pentylene carbonate, trans-2,3-pentylene carbonate, cis-2,3-pentylene carbonate, and vinylene carbonate; fluoroethylene carbonate, 1,2-difluoroethylene Cyclic fluorinated carbonates typified by carbonate and trifluoromethylethylene carbonate; typified by γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone Lactones; sulfur compounds typified by sulfolane, dimethyl sulfoxide, and ethylene glycol sulfite; cyclic ethers typified by tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane; ethyl methyl carbonate, Chain carbonates represented by dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, ethyl propyl carbonate, and methyl trifluoroethyl carbonate; trifluorodimethyl carbonate, trifluoro Chain fluorinated carbonates typified by diethyl carbonate and trifluoroethyl methyl carbonate Mononitriles typified by propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile; alkoxy group-substituted nitriles typified by methoxyacetonitrile and 3-methoxypropionitrile; malononitrile, succinonitrile, glutaronitrile, Adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanooctane, 2,7-dicyanooctane 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, and dinitriles represented by 2,4-dimethylglutaronitrile; cyclic nitriles represented by benzonitrile Propionic acid Chain esters typified by methyl; chain ethers typified by dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; Rf ⁴ -OR ³ (Rf ⁴ is an alkyl containing fluorine) Group, R ³ is a fluorinated ether represented by an organic group which may contain fluorine; ketones represented by acetone, methyl ethyl ketone, and methyl isobutyl ketone, and halogens represented by these fluorinated products. A compound. These are used singly or in combination of two or more.

  Among these other non-aqueous solvents, it is more preferable to use one or more of cyclic carbonate and chain carbonate together with acetonitrile. Here, only one of those exemplified above as the cyclic carbonate and the chain carbonate may be selected and used, or two or more (for example, two or more of the cyclic carbonates exemplified above, Two or more of the exemplified chain carbonates or one or more of the exemplified cyclic carbonates and two or more of the exemplified chain carbonates may be used. Among these, as the cyclic carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate, or fluoroethylene carbonate is more preferable, and as the chain carbonate, ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate is more preferable. It is more preferable to use a cyclic carbonate.

  Acetonitrile is easily electrochemically reduced and decomposed. Therefore, it is preferable to perform at least one of mixing this with another solvent and adding an electrode protective additive for forming a protective film on the electrode.

  In order to increase the ionization degree of the lithium salt that contributes to charge / discharge of the non-aqueous secondary battery, the non-aqueous solvent preferably contains one or more cyclic aprotic polar solvents, and contains one or more cyclic carbonates. Is more preferable.

  The content of acetonitrile is 30 to 100% by volume, more preferably 35% by volume or more, and still more preferably 40% by volume or more with respect to the total amount of the non-aqueous solvent. The content of acetonitrile is more preferably 85% by volume or less, and still more preferably 66% by volume or less. When the content of acetonitrile is 30% by volume or more, ionic conductivity tends to increase and high output characteristics tend to be exhibited, and further, dissolution of the lithium salt can be promoted. When the content of acetonitrile in the non-aqueous solvent is within the above-mentioned range, the storage characteristics and other battery characteristics tend to be further improved while maintaining the excellent performance of acetonitrile. .

<2-2. Lithium salt>
The lithium salt in this embodiment is characterized by containing a fluorine-containing inorganic lithium salt. The “fluorine-containing inorganic lithium salt” refers to a lithium salt that does not contain a carbon atom in an anion but contains a fluorine atom in an anion and is soluble in acetonitrile. The “inorganic lithium salt” refers to a lithium salt that does not contain a carbon atom in an anion and is soluble in acetonitrile. “Organic lithium salt” refers to a lithium salt that contains a carbon atom in its anion and is soluble in acetonitrile.

The fluorine-containing inorganic lithium salt in the present embodiment forms a passive film on the surface of the metal foil that is the positive electrode current collector, and suppresses corrosion of the positive electrode current collector. This fluorine-containing inorganic lithium salt is also excellent from the viewpoints of solubility, conductivity, and ionization degree. For this reason, the fluorine-containing inorganic lithium salt must be added as a lithium salt. Specific examples of the fluorine-containing inorganic lithium salt include, for example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiSbF ₆ , Li ₂ B ₁₂ F _b H _12-b [b is an integer of 0 to 3, preferably Is an integer of 1 to 3, and LiN (SO ₂ F) ₂ .

These fluorine-containing inorganic lithium salts are used singly or in combination of two or more. As the fluorine-containing inorganic lithium salt, a compound that is a double salt of LiF and a Lewis acid is desirable. Among them, the use of a fluorine-containing inorganic lithium salt having a phosphorus atom is more preferable because it easily releases a free fluorine atom, LiPF ₆ is particularly preferred. When a fluorine-containing inorganic lithium salt having a boron atom is used as the fluorine-containing inorganic lithium salt, it is preferable because an excessive free acid component that may cause battery deterioration is easily captured. From such a viewpoint, LiBF ₄ is preferable. Particularly preferred. LiPF ₆ and LiBF ₄ may be contained simultaneously.

  There is no restriction | limiting in particular about content of the fluorine-containing inorganic lithium salt in the electrolyte solution of this embodiment. However, the content of the fluorine-containing inorganic lithium salt is preferably 0.2 mol or more, more preferably 0.5 mol or more, and further preferably 0.8 mol or more with respect to 1 L of the non-aqueous solvent. . Further, the content of the fluorine-containing inorganic lithium salt is preferably 15 mol or less, more preferably 4 mol or less, and still more preferably 2.8 mol or less with respect to 1 L of the non-aqueous solvent. When the content of fluorine-containing inorganic lithium salt is within the above range, the ionic conductivity tends to increase and high output characteristics tend to be exhibited, while maintaining the excellent performance of acetonitrile, storage characteristics and other battery characteristics Tends to be even better.

In addition to the fluorine-containing inorganic lithium salt, a lithium salt generally used for a non-aqueous secondary battery may be supplementarily added as the lithium salt in the present embodiment. Specific examples of other lithium salts include inorganic lithium salts that do not contain fluorine atoms such as LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiB ₁₀ Cl ₁₀ , and chloroborane Li in the anion; LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), lower aliphatic carboxylic acid Li, tetraphenylborate Li, etc. An organic lithium salt represented by LiN (SO ₂ C _m F _{2m + 1} ) ₂ [m is an integer of 1 to 8] such as LiN (SO ₂ CF ₃ ) ₂ or LiN (SO ₂ C ₂ F ₅ ) ₂ ; ₅ (CF ₃ ) and the like LiPF _n (C _p F _{2p + 1} ) _6-n [n is an integer of 1 to 5, p is an integer of 1 to 8] Salt; LiBF _q (C _s F _{2s + 1} ) _4-q such as LiBF ₃ (CF ₃ ) _4-q [q is an integer of 1 to 3, s is an integer of 1 to 8]; LiB (C ₂ Lithium bis (oxalato) borate (LiBOB) represented by O ₄ ) ₂ ; Halogenated LiBOB; Lithium oxalate difluoroborate (LiODFB) represented by LiBF ₂ (C ₂ O ₄ ); LiB (C ₃ O ₄ H ₂₎ lithium bis represented by ₂ (malonate) borate _{(LiBMB); LiPF 4 (C} 2 O 4) with lithium tetrafluoro-oxa Lato phosphate _represented, represented by LiPF _{2 (C 2} O _{4) 2} An organic lithium salt such as lithium difluorobis (oxalato) phosphate, a lithium salt bonded to a polyvalent anion; the following general formula (2a); (2b) and (2c):
^{_{LiC (SO 2 R 4) (}} SO 2 R 5) (SO 2 R 6) (2a)
LiN (SO ₂ OR ⁷ ) (SO ₂ OR ⁸ ) (2b)
LiN (SO ₂ R ⁹ ) (SO ₂ OR ¹⁰ ) (2c)
{In the formula, R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ , R ⁹ , and R ¹⁰ may be the same or different from each other, and represent a perfluoroalkyl group having 1 to 8 carbon atoms. Show. } May be used, and one or more of these may be used together with the fluorine-containing inorganic lithium salt.

In order to improve load characteristics and charge / discharge cycle characteristics of the non-aqueous secondary battery, it is preferable to supplementarily add an organic lithium salt having an oxalic acid group, and LiB (C ₂ O ₄ ) ₂ , LiBF ₂ ( It is particularly preferable to add one or more selected from the group consisting of C ₂ O ₄ ), LiPF ₄ (C ₂ O ₄ ), and LiPF ₂ (C ₂ O ₄ ) ₂ . The organic lithium salt having an oxalic acid group may be contained in the negative electrode (negative electrode active material layer) in addition to being added to the nonaqueous electrolytic solution.

  The addition amount of the organolithium salt having an oxalic acid group to the non-aqueous electrolyte is, as the amount per 1 L of the non-aqueous solvent, of the non-aqueous electrolyte is 0. The amount is preferably 005 mol or more, more preferably 0.02 mol or more, and further preferably 0.05 mol or more. However, if the amount of the organic lithium salt having an oxalic acid group in the non-aqueous electrolyte is too large, it may be precipitated. Therefore, the addition amount of the organic lithium salt having an oxalic acid group to the non-aqueous electrolyte is preferably less than 1.0 mol per liter of the non-aqueous solvent of the non-aqueous electrolyte. More preferably, it is less than 5 mol, and still more preferably less than 0.2 mol.

<2-3. Compound having azole skeleton>
The electrolytic solution in the present embodiment includes the above-described non-aqueous solvent containing acetonitrile, a fluorine-containing inorganic lithium salt, and a compound represented by the following general formula (1) as an additive.

  Specific examples of the compound having an azole skeleton include 1-methylpyrazole and 1-1H-tetrazole. These are used singly or in combination of two or more. By using a nitrogen-containing cyclic compound having no N—H group, it is possible to prevent dehydrogenation deterioration during a high-temperature cycle. Moreover, it is more preferable to use 1-methylpyrazole having a large polarity distribution because the electronic function of the N atom is improved.

When a compound that is a double salt of LiF and Lewis acid is used as the fluorine-containing inorganic lithium salt, it is desirable that there is no steric hindrance around the nitrogen atom in the compound having an azole skeleton. Therefore, R ¹ in the general formula (1) is preferably a hydrogen atom. By containing the compound having the azole skeleton represented by the general formula (1) as an additive in the electrolytic solution of the present embodiment, acetonitrile and a fluorine-containing inorganic lithium salt excellent in the balance between viscosity and relative dielectric constant In a non-aqueous electrolyte solution containing, the formation of a complex cation composed of transition metal and acetonitrile is suppressed, and excellent load characteristics are exhibited, and when used as a battery, gas generation during high-temperature storage is prevented. Can be suppressed. Although there is no restriction | limiting in particular about content of the compound which has azole skeleton in the electrolyte solution in this embodiment, It is preferable that it is 0.01-10 mass% on the basis of the whole quantity of electrolyte solution, and 0.02- It is more preferable that it is 5 mass%, and it is still more preferable that it is 0.1-1 mass%. Thereby, the production | generation of the complex cation which consists of a transition metal and acetonitrile can be suppressed, and high temperature durability can be improved.

  In the present embodiment, by adjusting the content of the compound having an azole skeleton within the above range, the reaction on the electrode surface can be suppressed without impairing the basic function as a non-aqueous secondary battery, The increase in internal resistance accompanying charging / discharging can be reduced.

  By preparing the electrolytic solution with the above-described composition, all of the cycle performance of the non-aqueous secondary battery, the high output performance in a low temperature environment, and other battery characteristics tend to be further improved. .

<2-4. Electrode protective additive>
The electrolyte solution in this embodiment may contain an additive for protecting the electrode in addition to the compound having an azole skeleton. As described above, when the electrolytic solution contains the additive for protecting the liquid electrode, the additive for protecting the liquid electrode is contained in the non-aqueous solvent. 30-100 volume% acetonitrile should just be contained with respect to the non-aqueous solvent containing an additive (total amount of the above-mentioned non-aqueous solvent and the additive for liquid system electrodes).

  The electrode protecting additive is not particularly limited as long as it does not hinder the problem solving according to the present embodiment. You may substantially overlap with the substance which plays the role as a solvent which melt | dissolves lithium salt (namely, the above-mentioned non-aqueous solvent). The electrode protecting additive is preferably a substance that contributes to improving the performance of the electrolytic solution and the non-aqueous secondary battery in this embodiment, but also includes substances that are not directly involved in the electrochemical reaction.

  Specific examples of the electrode protecting additive include, for example, 4-fluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, cis-4,5-difluoro. -1,3-dioxolan-2-one, trans-4,5-difluoro-1,3-dioxolan-2-one, 4,4,5-trifluoro-1,3-dioxolan-2-one, 4, Fluoroethylene carbonate represented by 4,5,5-tetrafluoro-1,3-dioxolan-2-one and 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one; Unsaturated bond-containing cyclic carbonates typified by vinylene carbonate, 4,5-dimethylvinylene carbonate, and vinylethylene carbonate; γ-butyrolactone, γ-valerolactone Lactones represented by γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone; cyclic ethers represented by 1,4-dioxane; ethylene sulfite, propylene sulfite, butylene sulfite, pentensal Examples thereof include cyclic sulfur compounds represented by phyto, sulfolane, 3-methylsulfolane, 1,3-propane sultone, 1,4-butane sultone, and tetramethylene sulfoxide. These are used singly or in combination of two or more.

  Acetonitrile, which is a component of a non-aqueous solvent, is easily electrochemically reduced and decomposed. Therefore, the non-aqueous solvent containing acetonitrile is a cyclic aprotic polar solvent as an additive for forming a protective film on the negative electrode. It is preferable to include one or more types, and it is more preferable to include one or more types of unsaturated bond-containing cyclic carbonates.

  There is no restriction | limiting in particular about content of the electrode protection additive in the electrolyte solution in this embodiment. However, the content of the electrode protecting additive with respect to the total amount of the non-aqueous solvent is preferably 0.1 to 30% by volume, more preferably 0.5 to 20% by volume, and 1 to 10% by volume. More preferably.

  In this embodiment, deterioration of electrolyte solution is suppressed, so that there is much content of the additive for electrode protection. However, the lower the content of the electrode protecting additive, the higher the high output characteristics of the non-aqueous secondary battery in a low temperature environment. Therefore, by adjusting the content of the electrode protecting additive within the above-mentioned range, excellent performance based on the high ionic conductivity of the electrolytic solution can be obtained without impairing the basic function as a non-aqueous secondary battery. There is a tendency to make the most of it. By preparing the electrolytic solution with such a composition, all of the cycle performance of the non-aqueous secondary battery, the high output performance in a low temperature environment, and other battery characteristics tend to be further improved.

<2-5. Other optional additives>
In this embodiment, for the purpose of improving the charge / discharge cycle characteristics of a non-aqueous secondary battery, high-temperature storage property, and safety (for example, prevention of overcharge, etc.), the non-aqueous electrolyte solution is used, for example, anhydrous Acid, maleic anhydride, cyclic acid anhydrides typified by phthalic anhydride, acid anhydride, sulfonic acid ester, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, phosphate ester [ethyl diethylphosphonoacetate _{(EDPA) :( C 2 H 5} O) 2 (P = O) -CH 2 (C = O) OC 2 H 5, trisphosphate _{(trifluoroethyl) (TFEP) :( CF 3 CH} 2 O) 3 P = O, triphenyl phosphate _{(TPP) :( C 6 H 5} O) 3 P = O , etc.] and the like, and Ren selected from derivatives of each of these compounds Additives, and it may be contained as appropriate. In particular, the phosphoric acid ester has an effect of suppressing side reactions during storage and is effective.

<3. Positive electrode>
The positive electrode 5 includes a positive electrode active material layer made from a positive electrode mixture and a positive electrode current collector. The positive electrode 5 is not particularly limited as long as it functions as a positive electrode of a non-aqueous secondary battery, and may be a known one. Note that the positive electrode active material layer is directed to the side facing the negative electrode 6 (the side in contact with the electrolytic solution).

  The positive electrode active material layer contains a positive electrode active material and optionally further contains a conductive additive and a binder.

  The positive electrode active material layer preferably contains a material capable of inserting and extracting lithium ions as the positive electrode active material. It is preferable that a positive electrode active material layer contains a conductive support agent and a binder as needed with a positive electrode active material. The use of such a material is preferable because a high voltage and a high energy density tend to be obtained.

Examples of the positive electrode active material include the following general formulas (3a) and (3b):
Li _x MO ₂ (3a)
Li _y M ₂ O ₄ (3b)
{In the formula, M represents one or more metal elements including at least one transition metal element, x represents a number of 0 to 1.1, and y represents a number of 0 to 2. }, A lithium-containing compound represented by each of the above and other lithium-containing compounds.
Examples of the lithium-containing compound represented by each of the general formulas (3a) and (3b) include lithium cobalt oxides typified by LiCoO ₂ ; LiMnO ₂ , LiMn ₂ O ₄ , and Li ₂ Mn ₂ O ₄ . Lithium manganese oxide typified; Lithium nickel oxide typified by LiNiO ₂ ; Li _z MO ₂ (M contains at least one transition metal element selected from Ni, Mn, and Co, and Ni, 2 or more metal elements selected from the group consisting of Mn, Co, Al, and Mg, and z represents a number of more than 0.9 and less than 1.2. Is mentioned.

The lithium-containing compound other than the lithium-containing compound represented by each of the general formulas (3a) and (3b) is not particularly limited as long as it contains lithium. Examples of such a lithium-containing compound include a composite oxide containing lithium and a transition metal element, a metal chalcogenide containing lithium, a metal phosphate compound containing lithium and a transition metal element, and lithium and a transition metal element. (For example, Li _t M _u SiO ₄ , M is as defined in the general formula (3a), t is a number from 0 to 1, and u is a number from 0 to 2). Can be mentioned. From the viewpoint of obtaining a higher voltage, lithium-containing compounds include lithium, cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), chromium, among others. A composite oxide containing at least one transition metal element selected from the group consisting of (Cr), vanadium (V), and titanium (Ti), and a metal phosphate compound are preferable.

More specifically, the lithium-containing compound is more preferably a composite oxide containing lithium and a transition metal element or a metal chalcogenide having lithium and a transition metal element, and a metal phosphate compound having lithium. General formulas (4a) and (4b):
^{_{Li v M I D 2 (4a}} )
Li _w M ^II PO ₄ (4b)
{In the formula, D represents oxygen or a chalcogen element, M ^I and M ^II each represent one or more transition metal elements, the values of v and w depend on the charge / discharge state of the battery, and v is 0.05 to 1.10, w represents a number from 0.05 to 1.10. }, Compounds represented by each of the above.

  The lithium-containing compound represented by the above general formula (4a) has a layered structure, and the compound represented by the above general formula (4b) has an olivine structure. These lithium-containing compounds are obtained by substituting a part of the transition metal element with Al, Mg, or other transition metal elements for the purpose of stabilizing the structure, and include these metal elements in the grain boundaries. It is also possible that the oxygen atom is partially substituted with a fluorine atom or the like, or at least a part of the surface of the positive electrode active material is coated with another positive electrode active material.

  As the positive electrode active material in the present embodiment, only the lithium-containing compound as described above may be used, or other positive electrode active material may be used in combination with the lithium-containing compound.

Examples of such other positive electrode active materials include metal oxides or metal chalcogenides having a tunnel structure and a layered structure; sulfur; a conductive polymer. Examples of the metal oxide or metal chalcogenide having a tunnel structure and a layered structure include MnO ₂ , FeO ₂ , FeS ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , TiS ₂ , MoS ₂ , and NbSe _2. And oxides, sulfides, selenides, and the like of metals other than lithium. Examples of the conductive polymer include conductive polymers represented by polyaniline, polythiophene, polyacetylene, and polypyrrole.

  The other positive electrode active materials described above are used alone or in combination of two or more, and are not particularly limited. However, since lithium ions can be stored and released reversibly and stably, and a high energy density can be achieved, the positive electrode active material layer has at least one transition selected from Ni, Mn, and Co. It is preferable to contain a metal element.

  When a lithium-containing compound and another positive electrode active material are used in combination as the positive electrode active material, the use ratio of both is preferably 80% by mass or more, and 85% by mass as the use ratio of the lithium-containing compound to the entire positive electrode active material. % Or more is more preferable.

  Examples of the conductive aid include carbon black typified by graphite, acetylene black, and ketjen black, and carbon fiber. The content ratio of the conductive assistant is preferably 10 parts by mass or less, more preferably 1 to 5 parts by mass with respect to 100 parts by mass of the positive electrode active material.

  Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, styrene butadiene rubber, and fluorine rubber. The content ratio of the binder is preferably 6 parts by mass or less, more preferably 0.5 to 4 parts by mass with respect to 100 parts by mass of the positive electrode active material.

  The positive electrode active material layer is formed by applying a positive electrode mixture-containing slurry, in which a positive electrode mixture obtained by mixing a positive electrode active material and, if necessary, a conductive additive and a binder in a solvent, is applied to a positive electrode current collector and dried (solvent removal) And is formed by pressing as necessary. There is no restriction | limiting in particular as such a solvent, A conventionally well-known thing can be used. For example, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, water and the like can be mentioned.

  The positive electrode current collector is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode current collector may have a surface coated with a carbon coat or may be processed into a mesh shape. The thickness of the positive electrode current collector is preferably 5 to 40 μm, more preferably 7 to 35 μm, and still more preferably 9 to 30 μm.

<4. Negative electrode>
The negative electrode 6 includes a negative electrode active material layer made from a negative electrode mixture and a negative electrode current collector. The negative electrode 6 is not particularly limited as long as it functions as a negative electrode of a non-aqueous secondary battery, and may be a known one. Note that the negative electrode active material layer is directed to the side facing the positive electrode 5 (the side in contact with the electrolytic solution).

From the viewpoint that the negative electrode active material layer can increase the battery voltage, lithium ion as a negative electrode active material is 0.4 V vs. It is preferable to contain a material that can be occluded at a lower potential than Li / Li ⁺ . It is preferable that a negative electrode active material layer contains a conductive support agent and a binder as needed with a negative electrode active material.

  Examples of the negative electrode active material include amorphous carbon (hard carbon), artificial graphite, natural graphite, graphite, pyrolytic carbon, coke, glassy carbon, organic polymer compound fired body, mesocarbon microbeads, carbon fiber, activated carbon In addition to carbon materials such as graphite, carbon colloid, and carbon black, metal lithium, metal oxide, metal nitride, lithium alloy, tin alloy, silicon alloy, intermetallic compound, organic compound, inorganic compound, metal complex And organic polymer compounds. A negative electrode active material is used individually by 1 type or in combination of 2 or more types.

  Examples of the conductive aid include carbon black typified by graphite, acetylene black, and ketjen black, and carbon fiber. The content ratio of the conductive assistant is preferably 20 parts by mass or less, more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material.

  Examples of the binder include PVDF, PTFE, polyacrylic acid, styrene butadiene rubber, and fluorine rubber. The content ratio of the binder is preferably 10 parts by mass or less, more preferably 0.5 to 6 parts by mass with respect to 100 parts by mass of the negative electrode active material.

  The negative electrode active material layer is coated with a negative electrode mixture-containing slurry in which a negative electrode mixture obtained by mixing a negative electrode active material and, if necessary, a conductive additive and a binder is dispersed in a solvent, and dried (solvent removal). And it forms by pressing as needed. There is no restriction | limiting in particular as such a solvent, A conventionally well-known thing can be used. For example, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, water and the like can be mentioned. The negative electrode current collector is made of a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. The negative electrode current collector may have a carbon coating on the surface or may be processed into a mesh shape. The thickness of the negative electrode current collector is preferably 5 to 40 μm, more preferably 6 to 35 μm, and still more preferably 7 to 30 μm.

<5. Separator>
The nonaqueous secondary battery 1 in the present embodiment preferably includes a separator 7 between the positive electrode 5 and the negative electrode 6 from the viewpoint of providing safety such as prevention of short circuit between the positive electrode 5 and the negative electrode 6 and shutdown. The separator 7 may be the same as that provided in a known non-aqueous secondary battery, and is preferably an insulating thin film having high ion permeability and excellent mechanical strength. Examples of the separator 7 include a woven fabric, a nonwoven fabric, and a synthetic resin microporous membrane. Among these, a synthetic resin microporous membrane is preferable.

  As the synthetic resin microporous membrane, for example, a microporous membrane containing polyethylene or polypropylene as a main component or a polyolefin microporous membrane such as a microporous membrane containing both of these polyolefins is suitably used. Examples of the nonwoven fabric include a porous film made of a heat resistant resin such as glass, ceramic, polyolefin, polyester, polyamide, liquid crystal polyester, and aramid.

  The separator 7 may have a configuration in which one type of microporous membrane is laminated or a plurality of microporous membranes may be laminated, or two or more types of microporous membranes may be laminated. The separator 7 may be configured to be laminated in a single layer or a plurality of layers using a mixed resin material obtained by melting and kneading two or more kinds of resin materials.

<6. Battery exterior>
Although the structure of the battery exterior 2 of the non-aqueous secondary battery 1 in this embodiment is not specifically limited, For example, the battery exterior of either a battery can or a laminate film exterior body can be used. As the battery can, for example, a metal can made of steel or aluminum can be used. As the laminate film outer package, for example, a laminate film having a three-layer structure of hot melt resin / metal film / resin can be used.

  Laminate film exterior is in a state where two sheets are stacked with the hot-melt resin side facing inward, or folded so that the hot-melt resin side faces inward, and the end is sealed by heat sealing It can be used as an exterior body. In the case of using a laminate film exterior body, the positive electrode lead body 3 (the positive electrode terminal 3a constituting the positive electrode lead body 3 and the lead tab 3b connected to the positive electrode terminal 3a) is connected to the positive electrode current collector, and the negative electrode lead body is connected to the negative electrode current collector. 4 (the negative electrode terminal 4a constituting the negative electrode lead body 4 and the lead tab 4b connected to the negative electrode terminal 4a) may be connected. In this case, lamination is performed in a state in which the end portions of the positive electrode terminal 3a and the negative electrode terminal 4a or the end portions of the lead tabs 3b and 4b connected to the positive electrode terminal 3a and the negative electrode terminal 4a are drawn out of the exterior body. The film exterior body may be sealed.

<7. Manufacturing method of battery>
The non-aqueous secondary battery 1 in the present embodiment has the above-described non-aqueous electrolyte, the positive electrode 5 having a positive electrode active material layer on one or both sides of the current collector, and the negative electrode active material layer on one or both sides of the current collector. It is produced by a known method using the negative electrode 6, the battery outer casing 2, and the separator 7 as necessary.

  First, the laminated body which consists of the positive electrode 5 and the negative electrode 6, and the separator 7 as needed is formed.

  For example, a mode in which a long positive electrode 5 and a negative electrode 6 are wound in a stacked state in which the long separator is interposed between the positive electrode 5 and the negative electrode 6 to form a laminate having a wound structure; A mode of forming a laminate having a laminated structure in which a positive electrode sheet and a negative electrode sheet obtained by cutting the negative electrode 5 and the negative electrode 6 into a plurality of sheets having a certain area and shape are alternately laminated via a separator sheet; It is possible to form a laminated body having a laminated structure in which long separators are folded in a zigzag manner, and positive electrode sheets and negative electrode sheets are alternately inserted between the zippered separators.

  Next, the above-described laminated body is accommodated in the battery exterior 2 (battery case), the electrolytic solution according to this embodiment is injected into the battery case, and the laminated body is immersed in the electrolytic solution and sealed. The nonaqueous secondary battery in this embodiment can be produced.

  Alternatively, an electrolyte solution in a gel state is prepared in advance by impregnating a base material made of a polymer material with an electrolytic solution, and a sheet-like positive electrode 5, negative electrode 6, electrolyte membrane, and separator 7 as necessary. After forming the laminated body of a laminated structure using, the nonaqueous secondary battery 1 can be produced by being accommodated in the battery exterior 2.

  The shape of the non-aqueous secondary battery 1 in the present embodiment is not particularly limited, and for example, a cylindrical shape, an elliptical shape, a rectangular tube shape, a button shape, a coin shape, a flat shape, a laminate shape, and the like are suitably employed.

  Here, when a non-aqueous electrolyte using acetonitrile is used, due to its high ion conductivity, lithium ions released from the positive electrode during the initial charge of the non-aqueous secondary battery are diffused throughout the negative electrode. There is a possibility. In a non-aqueous secondary battery, the area of the negative electrode active material layer is generally larger than that of the positive electrode active material layer. However, if lithium ions are diffused and occluded to a portion of the negative electrode active material layer that does not face the positive electrode active material layer, the lithium ion at a portion that does not face the positive electrode active material layer is discharged for the first time. Sometimes it is not released and stays in the negative electrode. Therefore, the contribution of the lithium ions that are not released becomes an irreversible capacity. For these reasons, in the non-aqueous secondary battery using the non-aqueous electrolyte containing acetonitrile, the initial charge / discharge efficiency may be lowered.

  On the other hand, when the area of the positive electrode active material layer is larger than or the same as that of the negative electrode active material layer, current concentration is likely to occur at the edge portion of the negative electrode active material layer during charging, and lithium dendrite is likely to be generated. .

  Ratio of the total area of the negative electrode active material layer to the area of the part where the positive electrode active material layer and the negative electrode active material layer face each other (the area of the whole negative electrode active material layer / the part where the positive electrode active material layer and the negative electrode active material layer face each other) The area ratio is preferably greater than 1.0 and less than 1.1, more preferably greater than 1.002 and less than 1.09, for the above reasons. More preferably, it is greater than 1.005 and less than 1.08, particularly preferably greater than 1.01 and less than 1.08. In a non-aqueous secondary battery using a non-aqueous electrolyte containing acetonitrile, by reducing the ratio of the total area of the negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other, The initial charge / discharge efficiency can be improved.

  Reducing the ratio of the total area of the negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other means that the negative electrode active material layer does not face the positive electrode active material layer. This means that the proportion of the area of the part is limited. As a result, among the lithium ions released from the positive electrode during the first charge, the amount of lithium ions occluded in the portion of the negative electrode active material layer that is not opposed to the positive electrode active material layer (that is, released from the negative electrode during the first discharge). Therefore, it is possible to reduce as much as possible the amount of lithium ion that becomes an irreversible capacity. Therefore, by designing the ratio of the total area of the negative electrode active material layer to the area of the portion where the positive electrode active material layer and the negative electrode active material layer face each other, the load characteristics of the battery can be improved by using acetonitrile. Thus, it is possible to increase the initial charge / discharge efficiency of the battery and further suppress the generation of lithium dendrite.

  3A, FIG. 3B, and FIG. 4 are drawings for explaining the “width of the non-opposing portion of the negative electrode active material layer” in the configuration of this embodiment in which the entire surface of the positive electrode active material layer faces the negative electrode active material layer ( Plan view). FIG. 3A and FIG. 3B are explanatory diagrams in the case where the electrode body composed of the positive electrode, the negative electrode, and the separator is a laminated electrode body (an electrode body that is simply formed by stacking them). FIG. 3A shows a case where a positive electrode having a circular positive electrode active material layer 50 in plan view and a negative electrode having a circular negative electrode active material layer 60 in plan view face each other. FIG. 3B shows a case where a positive electrode having a square positive electrode active material layer 50 in plan view is opposed to a negative electrode having a square negative electrode active material layer 60 in plan view. FIG. 4 is an explanatory diagram in the case where the electrode body composed of the positive electrode, the negative electrode, and the separator is a wound electrode body formed by winding these laminated bodies in a spiral shape. In these drawings, in order to facilitate understanding of the positional relationship between the positive electrode active material layer 50 and the negative electrode active material layer 60, current collectors and separators of the positive electrode and the negative electrode are not shown. In FIG. 4, a part of a portion where the positive electrode active material layer 50 and the negative electrode active material layer 60 are opposed to each other in the wound electrode body is illustrated in a plan view.

  3A and 3B, the front side (upper side in the direction perpendicular to the paper surface) in the drawing is the negative electrode active material layer 60, and the one indicated by the dotted line on the depth side is the positive electrode active material layer 50. The “width of the non-opposing portion of the negative electrode active material layer” in the laminated electrode body is the distance between the outer peripheral end of the negative electrode active material layer 60 and the outer peripheral end of the positive electrode active material layer 50 (in FIG. Length).

  Also in FIG. 4, as in FIGS. 3A and 3B, the front side in the drawing is the negative electrode active material layer 60, and the depth side dotted line is the positive electrode active material layer 50. A strip-shaped positive electrode and a strip-shaped negative electrode are used for forming the wound electrode body. The “width of the non-opposing portion of the negative electrode active material layer” refers to the outer end of the negative electrode active material layer 60 and the outer end of the positive electrode active material layer 50 in the direction orthogonal to the longitudinal direction of the belt-like positive electrode and the belt-like negative electrode. (The length of b in the figure).

  The length a shown in FIGS. 3A and 3B and the length b shown in FIG. 4 are defined so as to be in the range of the area ratio described above.

  As for the arrangement of the electrodes, there is a portion where the outer peripheral end of the negative electrode active material layer and the outer peripheral end of the positive electrode active material layer overlap, or a portion where the width is too small in the non-opposing portion of the negative electrode active material layer When designed, for example, when the length dimensions in one direction of the negative electrode active material layer and the positive electrode active material layer are combined, the outer peripheral ends overlap each other. At this time, when the electrode is displaced during battery assembly, the charge / discharge cycle characteristics of the non-aqueous secondary battery may be deteriorated. Therefore, in the electrode body used for the non-aqueous secondary battery, it is preferable to fix the position of the electrode in advance with tapes such as polyimide tape, polyphenylene sulfide tape, PP tape, or an adhesive.

  5 and 6 show an example of a battery positive electrode and a battery negative electrode. FIG. 5 is a schematic plan view for explaining the positive electrode for a battery. FIG. 6 is a schematic plan view for explaining a negative electrode for a battery.

  As shown in FIG. 5, the positive electrode active material layer 11 constituting the positive electrode 10 is formed with a width dimension c and a length dimension d perpendicular to the width dimension c. A positive electrode current collector 12 that overlaps with the positive electrode active material layer 11 is provided. The positive electrode current collector 12 has a protrusion part, and the periphery of the protrusion part is a tab part 13. The width dimension of the tab part 13 is formed by e.

  As shown in FIG. 6, the negative electrode active material layer 21 constituting the negative electrode 20 has a width dimension of f and a length dimension orthogonal to the width dimension f of g. A negative electrode current collector 22 is provided so as to overlap the negative electrode active material layer 21, and the negative electrode current collector 22 is partially provided with a protruding portion, and the periphery of the protruding portion is a tab portion 23. The width dimension of the tab part 23 is formed by h.

  In the embodiment shown in FIGS. 5 and 6, the width dimension f of the negative electrode active material layer 21 is slightly larger than the width dimension c of the positive electrode active material layer 11, and the length dimension g of the negative electrode active material layer 21. However, it is formed to be slightly larger than the length dimension d of the positive electrode active material layer 11. . The width dimensions c and f and the lengths are set so that the ratio of the area (f × g) of the negative electrode active material layer 21 to the area of the positive electrode active material layer (c × d) is in the area ratio range described above. Dimensions d and g are regulated.

  The width dimensions e and h of the tab portions 13 and 23 are formed to have substantially the same size. As shown in FIGS. 5 and 6, the tab portion 13 is formed on the left side of the positive electrode active material layer 11 and the tab portion 23 is formed on the right side of the negative electrode active material layer 21. Therefore, even if the positive electrode active material layer 11 and the negative electrode active material layer 21 are stacked, the tab portions 13 and 23 do not overlap.

  The non-aqueous secondary battery 1 in the present embodiment can function as a battery by initial charging. There are no particular restrictions on the method of initial charging. However, considering that the non-aqueous secondary battery 1 is stabilized by decomposition of a part of the electrolytic solution at the time of the initial charge, the initial charge is 0. 0 in order to effectively express this stabilization effect. It is preferable to be performed at 001 to 0.3C, more preferably at 0.002 to 0.25C, and still more preferably at 0.003 to 0.2C. It is also preferable that the initial charging is performed via a constant voltage charging in the middle. The constant current for discharging the rated capacity in 1 hour is 1C. By setting the voltage range in which the lithium salt is involved in the electrochemical reaction to be long, SEI (Solid Electrolyte Interface) is formed on the electrode surface, and the effect of suppressing the increase in internal resistance including the positive electrode 5 is suppressed. There is. In addition, the reaction product is not firmly fixed only on the negative electrode 6, and in some way, a good effect is given to members other than the negative electrode 6 (for example, the positive electrode 5, the separator 7, etc.). For this reason, it is very effective to perform the initial charge in consideration of the electrochemical reaction of the lithium salt dissolved in the non-aqueous electrolyte.

  The non-aqueous secondary battery 1 in this embodiment can also be used as a battery pack in which a plurality of non-aqueous secondary batteries 1 are connected in series or in parallel. From the viewpoint of managing the charge / discharge state of the battery pack, the operating voltage range per unit is preferably 2 to 5 V, more preferably 2.5 to 5 V, and 2.75 V to 5 V. Is particularly preferred.

  As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to the above-mentioned embodiment. The present invention can be variously modified without departing from the gist thereof.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples. Various evaluations were performed as follows.

(1) Production of Positive Electrode (P1) A composite oxide of lithium, nickel, manganese and cobalt having a number average particle diameter of 11 μm (LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , density 4.70 g as a positive electrode active material. / cm ³⁾ and, as a conductive additive and graphite carbon powder having an average particle diameter of 6.5 [mu] m (density 2.26 g / cm ³⁾ and the number of acetylene black powder having an average particle diameter of 48 nm (density 1.95 g / cm ³⁾ Polyvinylidene fluoride (PVdF; density 1.75 g / cm ³ ) as a binder was mixed at a mass ratio of 100: 4.2: 1.8: 4.6 to obtain a positive electrode mixture. N-methyl-2-pyrrolidone as a solvent was added to the obtained positive electrode mixture so as to have a solid content of 68% by mass and further mixed to prepare a positive electrode mixture-containing slurry. The positive electrode mixture-containing slurry was applied to one side of an aluminum foil having a thickness of 20 μm and a width of 200 mm to be a positive electrode current collector by a doctor blade method while adjusting the basis weight to be 24.0 mg / cm ² . The solvent was removed by drying. Then, the positive electrode (P1) which consists of a positive electrode active material layer and a positive electrode electrical power collector was obtained by rolling so that the density of a positive electrode active material layer might be 2.90 g / cm < ³ > with a roll press.

(2) Positive electrode immersion test An aluminum laminated bag was processed to 2.7 cm x 6 cm, sealed with the positive electrode (P1) punched out to 23 mm x 17 mm, and then prepared in each example or comparative example in an inert atmosphere. 0.5 mL of the non-aqueous electrolyte solution was injected. At this time, it was confirmed that the electrode surface was immersed in the electrolytic solution. After injecting the solution, it was sealed and kept at 60 ° C. for 24 hours with the aluminum laminated bag leaning vertically. After storage, the internal electrolyte and the positive electrode surface were observed. “○” (good) when the formation of a gel-like substance composed mainly of a complex cation salt composed of a transition metal and acetonitrile is not recognized, and “×” when the formation of the gel-like substance is recognized (Defect) was determined.

(3) Production of Negative Electrode (N1) Graphite carbon powder having a number average particle diameter of 12.7 μm (density 2.23 g / cm ³ ) and graphite carbon powder having a number average particle diameter of 6.5 μm (density 2.27 g) as a negative electrode active material. / Cm ³ ), carboxymethyl cellulose (density 1.60 g / cm ³ ) solution (solid concentration 1.83 mass%) and styrene butadiene latex (glass transition temperature: −5 ° C., number average particle size upon drying) : 120 nm, density 1.00 g / cm ³ , dispersion medium: water, solid content concentration 40% by mass) in a solid content mass ratio of 87.2: 9.7: 1.4: 1.7, A negative electrode mixture was obtained. Water was added to the obtained negative electrode mixture as a solvent so as to have a solid content of 45% by mass, and further mixed to prepare a negative electrode mixture-containing slurry. The negative electrode mixture-containing slurry was applied to one side of a copper foil having a thickness of 10 μm and a width of 200 mm to be a negative electrode current collector by a doctor blade method while adjusting the basis weight to be 10.6 mg / cm ^2. Was removed by drying. Then, it rolled so that the density of a negative electrode active material layer might be 1.50 g / cm < ³ > with a roll press, and the negative electrode (N1) which consists of a negative electrode active material layer and a negative electrode collector was obtained.

(4) Production of coin-type non-aqueous secondary battery A polypropylene gasket was set in a CR2032-type battery case (SUS304 / Al clad), and the positive electrode (P1) obtained in the above-described manner at the center thereof with a diameter of 15. What was punched into a 958 mm disk was set with the positive electrode active material layer facing upward. In this positive electrode, the area of the positive electrode active material layer was 2.00 cm ² . A glass fiber filter paper (GA-100 manufactured by ADVANTEC) punched into a disk shape having a diameter of 16.156 mm was set from above, and 100 μL of an electrolyte solution was injected. Then, the negative electrode (N1) obtained as described above ) Was punched into a disk shape having a diameter of 16.156 mm and set with the negative electrode active material layer facing downward. In this negative electrode, the area of the negative electrode active material layer was 2.05 cm ² . Furthermore, after setting the spacer and spring, the battery cap was fitted and crimped with a caulking machine. The overflowing electrolyte was wiped clean with a waste cloth. It was kept at 25 ° C. for 24 hours, and the laminate was sufficiently adjusted with the electrolyte solution to obtain a coin-type non-aqueous secondary battery (hereinafter also simply referred to as “coin battery”).

(5) Evaluation of coin-type non-aqueous secondary battery For the evaluation battery obtained as described above, first, the initial charge process and the initial charge / discharge capacity measurement were performed according to the following procedure (5-1). . Next, each battery was evaluated according to the procedures of (5-2) and (5-3). Charging / discharging was performed using charging / discharging apparatus ACD-01 (trade name) manufactured by Asuka Electronics Co., Ltd. and thermostatic bath PLM-63S (trade name) manufactured by Futaba Kagaku.

  Here, 1C means a current value at which a fully charged battery is discharged at a constant current and is expected to be discharged in 1 hour. It means a current value expected to be discharged from a fully charged state of 4.2 V to 3.0 V at a constant current and finished in 1 hour.

(5-1) Initial charging / discharging process of coin battery Until the ambient temperature of the coin battery is set to 25 ° C. and charging is performed with a constant current of 0.6 mA corresponding to 0.1 C, the battery voltage reaches 4.2V. After charging, the battery was charged at a constant voltage of 4.2 V for a total of 15 hours. Thereafter, the battery was discharged to 3.0 V with a constant current of 1.8 mA corresponding to 0.3 C. The discharge capacity at this time was defined as the initial capacity.

(5-2) 85 ° C. full charge storage test of coin-type non-aqueous secondary battery For the battery subjected to the first charge / discharge treatment by the method described in (5-1) above, the ambient temperature of the battery is set to 25 ° C. The battery was charged with a constant current of 6 mA corresponding to 1 C and reached 4.2 V, and then charged with a constant voltage of 4.2 V for 3 hours. Next, this non-aqueous secondary battery was stored in a constant temperature bath at 85 ° C. for 4 hours. Thereafter, the ambient temperature of the battery was returned to 25 ° C.

(5-3) Output test of coin-type non-aqueous secondary battery For the battery that was subjected to the 85 ° C. full charge storage test by the method described in (5-2) above, the ambient temperature of the battery was set to 25 ° C. and 1C The battery was charged with a constant current of 6 mA corresponding to 4 and reached 4.2 V, and then charged with a constant voltage of 4.2 V for a total of 3 hours. Thereafter, the battery was discharged to 3.0 V at a current value of 9 mA corresponding to 1.5 C, and the following capacity maintenance ratio was calculated as an output test measurement value.
Capacity retention rate = (capacity at 1.5 C discharge after 85 ° C. full charge storage test / initial capacity before 85 ° C. full charge storage test) × 100 [%]

(6) Production of Single Layer Laminated Battery The positive electrode (P1) obtained as described above was cut so that the area of the positive electrode active material layer was 30 mm × 50 mm and the exposed portion of the aluminum foil was included. And the aluminum lead piece for taking out an electric current was welded to the exposed part of aluminum foil, and the positive electrode with a lead was obtained by performing vacuum drying at 120 degreeC for 12 hours. The negative electrode (N1) obtained as described above was cut so that the area of the negative electrode active material layer was 32 mm × 52 mm and the exposed portion of the copper foil was included. And the lead piece made from nickel for taking out an electric current was welded to the exposed part of copper foil, and the negative electrode with a lead was obtained by performing vacuum drying at 80 degreeC for 12 hours. Next, the lead-attached positive electrode and the lead-attached negative electrode were superposed via a polyethylene microporous membrane separator (thickness: 21 μm) so that the mixture application surface of each electrode was opposed to form a laminated electrode body. This laminated electrode body was accommodated in a 90 mm × 80 mm aluminum laminate sheet outer package, and vacuum dried at 80 ° C. for 5 hours in order to remove moisture. Subsequently, after injecting each of the above-described electrolytes into the exterior body, the exterior body is sealed, so that a single-layer laminate type (pouch-type) non-aqueous secondary battery (hereinafter also simply referred to as “single-layer laminate battery”). .) Was produced. This single-layer laminated battery has a design capacity value of 23 mAh and a rated voltage value of 4.2V.

(7) Evaluation of single-layer laminated battery About the single-layer laminated battery obtained as mentioned above, the first charging / discharging process was performed according to the following procedures. Subsequently, the 4.2 V storage characteristics at 60 ° C. were evaluated. Charging / discharging was performed using charging / discharging apparatus ACD-01 (trade name) manufactured by Asuka Electronics Co., Ltd. and a thermostat PLM-73S (trade name) manufactured by Futaba Kagaku Co., Ltd.

  Here, 1C means a current value at which a fully charged battery is discharged at a constant current and is expected to be discharged in 1 hour. In the following, it means a current value that is expected to discharge from a fully charged state of 4.2 V to 3.0 V at a constant current and finish discharging in 1 hour.

(7-1) Initial charge / discharge treatment of single-layer laminated battery The ambient temperature of the single-layer laminated battery is set to 25 ° C., and the battery voltage is 4.2 V by charging with a constant current of 1.15 mA corresponding to 0.05C. Then, the battery was charged until it reached, and then charged at a constant voltage of 4.2 V, and charged for 3 hours. Thereafter, the battery was discharged to 3.0 V at a constant current of 6.9 mA corresponding to 0.3C.

(7-2) Single-layer laminated battery 60 ° C. storage test The single-layer laminated battery after the initial charge / discharge treatment was subjected to constant current charging at 25 ° C. until a current value of 0.3 C was 4.2 V. Thereafter, constant voltage charging was performed at 4.2 V for 1 hour. And the single layer laminated battery after this charge was stored in a 60 degreeC thermostat. After elapse of 720 hours, the single-layer laminated battery was taken out from the thermostat and returned to room temperature, and then the gas generation amount of the single-layer laminated battery was measured by a method of measuring the gas generation amount of each laminate cell.

(7-3) Gas generation amount measurement method The gas generation amount is Archimedes in which a single-layer laminated battery is placed in a container containing ultrapure water and the volume of the single-layer laminated battery is measured from the weight change before and after that. The method was used. As a device for measuring the volume from the change in weight, a hydrometer MDS-300 manufactured by Alpha Mirage was used.

[Example 1]
Under an inert atmosphere, 1.0 mol of LiPF ₆ was dissolved in acetonitrile (AcN). Next, an electrolytic solution was obtained by adding and mixing 0.1 part by mass of 1-methylpyrazole, which is an azole compound, as an additive to 100 parts by mass of the mixed solvent. This electrolyte solution was subjected to a positive electrode immersion test by the method described in (2) above.

[Examples 2 to 5, Comparative Example 1]
In Examples 2 to 5 and Comparative Example 1, electrolytic solutions were obtained in the same manner as in Example 1 except that the types and amounts of additives were as shown in Table 1, respectively. A positive electrode immersion test was conducted on these electrolytic solutions by the method described in (2) above.

  The electrolytic solution compositions and evaluation results in Examples 1 to 5 and Comparative Example 1 are shown in Table 1 below.

Abbreviations in the non-aqueous solvent column of Tables 1 to 3 have the following meanings, respectively.
AcN: Acetonitrile DEC: Diethyl carbonate EMC: Ethyl methyl carbonate EC: Ethylene carbonate VC: Vinylene carbonate LiPF _6: Lithium hexafluorophosphate LiFSI: Lithium bis (fluorosulfonyl) imide (LiN (SO ₂ F) ₂ )

  In an electrolytic solution containing a fluorine-containing inorganic lithium salt and a significant amount of acetonitrile, in Comparative Example 1 containing no azole compound, the formation of a gel was observed. This gel was found to contain a complex cation composed of a transition metal and acetonitrile from the analysis results. On the other hand, in Examples 1 to 5 containing an azole compound in an electrolytic solution containing a fluorine-containing inorganic lithium salt and a significant amount of acetonitrile, no gel-like product was observed.

  From these results, it became clear that the addition of the azole compound greatly contributed to the high temperature durability in the electrolytic solution containing a fluorine-containing inorganic lithium salt and a significant amount of acetonitrile.

  In Examples 1 to 5, the amount of the azole compound added is in the range of 0.01 to 10% by mass, preferably 0.02 to 5% by mass with respect to the total amount of the non-aqueous electrolyte. %, More preferably 0.05 to 3% by mass. More preferably, the addition amount is 0.10 to 1.0% by mass.

[Example 6]
The positive electrode (P1) and negative electrode (N1) produced as described above and an electrolyte prepared according to the composition described in Table 2 were combined to produce a coin battery according to the method described in (4) above. This coin battery is first charged / discharged by the method described in (5-1) above, and stored at 85 ° C. and charged by the method described in (5-2) and (5-3) above. Went.

[Example 7, Example 8, and Comparative Example 2]
In Example 7, Example 8, and Comparative Example 2, a coin battery was prepared in the same manner as in Example 6 except that the composition of the non-aqueous solvent, the type of additive, and the amount added were as shown in Table 2, respectively. Was made. The coin battery was first charged / discharged by the method described in (5-1) above, and the discharge capacity measurement and storage test were performed by the methods described in (5-2) and (5-3) above. .

  The electrolytic solution compositions and evaluation results in Examples 6 to 8 and Comparative Example 2 are shown in Table 2 below.

  From the comparison between Example 6 to Example 8 and Comparative Example 2, when the electrolytic solution containing acetonitrile was used, the capacity was maintained in the output test as compared to the case where the electrolytic solution containing no acetonitrile or azole compound was used. It was confirmed that the rate was significantly improved.

  As shown in Table 2, in Examples 6 to 8, the capacity retention rate in the output test after storage at 85 ° C. for 4 hours was 75% or more. Moreover, in Examples 6-8, it turned out that this capacity | capacitance maintenance factor can be 80% or more, Preferably it is 85% or more, More preferably, it can be 90% or more.

[Example 9]
The positive electrode (P1) and negative electrode (N1) produced as described above and the electrolyte prepared with the composition shown in Table 3 were combined to produce a single-layer laminated battery according to the method described in (6) above. This single-layer laminated battery is subjected to a first charge / discharge treatment by the method described in (7-1) above, and a 60 ° C. storage test and gas generation by the method described in (7-2) and (7-3) above. The quantity was measured.

[Comparative Example 3]
A single-layer laminated battery was produced in the same manner as in Example 9 except that 1-methylpyrazole was not added. This single-layer laminated battery is subjected to a first charge / discharge treatment by the method described in (7-1) above, and a 60 ° C. storage test and gas generation by the method described in (7-2) and (7-3) above. The quantity was measured. The electrolyte solution composition and evaluation results in Example 9 and Comparative Example 3 are shown in Table 3 below.

  From the comparison between Example 9 and Comparative Example 3, when an electrolyte containing 1-methylpyrazole, which is an azole compound, was used, gas was generated compared to when using an electrolyte containing no 1-methylpyrazole. It was confirmed that the amount was remarkably suppressed.

  Specifically, in the Example, it turned out that the gas generation amount in a 60 degreeC storage test is 0.06 ml or less. In the present embodiment, the gas generation amount can be preferably 0.05 ml or less, and more preferably 0.04 ml or less.

  Moreover, in the present Example, when the gas generation amount in a 60 degreeC storage test was converted per battery capacity 1mAh, it turned out that it is 0.0025 ml or less. Further, in this example, the gas generation amount (converted value per 1 mAh of battery capacity) in the 60 ° C. storage test can be preferably 0.002 ml or less.

DESCRIPTION OF SYMBOLS 1 Nonaqueous secondary battery 2 Battery exterior 3 Positive electrode lead body 3a Positive electrode terminal 3b Lead tab 4 Negative electrode lead body 4a Negative electrode terminal 4b Lead tab 5 Positive electrode 6 Negative electrode 7 Separator 9 Lead piece 10 Positive electrode 11 Positive electrode active material layer 12 Positive electrode collector 13 Tab Part 20 Negative electrode 21 Negative electrode active material layer 22 Negative electrode current collector 23 Tab part 50 Positive electrode active material layer 60 Negative electrode active material layer

Claims (8)

A non-aqueous electrolyte solution comprising a non-aqueous solvent containing acetonitrile, a fluorine-containing inorganic lithium salt, and a compound represented by the following general formula (1).

  The non-aqueous electrolyte solution according to claim 1, wherein the compound represented by the general formula (1) is 1-methylpyrazole.   3. The non-aqueous electrolyte according to claim 1, wherein the content of the compound represented by the general formula (1) is 0.01 to 10% by mass with respect to the entire non-aqueous electrolyte. .   4. The non-aqueous electrolyte solution according to claim 1, wherein a content of the acetonitrile is 30 to 100% by volume with respect to the whole non-aqueous electrolyte solution. The non-aqueous electrolyte solution according to claim 1, wherein the fluorine-containing inorganic lithium salt contains LiPF ₆ . A positive electrode having a positive electrode active material layer containing at least one transition metal element selected from Ni, Mn, and Co on one or both surfaces of a current collector;
A negative electrode having a negative electrode active material layer on one or both sides of the current collector, and
A non-aqueous secondary battery comprising the non-aqueous electrolyte solution according to claim 1.   The non-aqueous secondary battery according to claim 6, wherein a capacity maintenance rate in an output test after storage at 85 ° C. for 4 hours is 75% or more. The nonaqueous secondary battery according to claim 6 or 7, wherein a gas generation amount in a 60 ° C storage test is 0.0025 ml or less as a converted value per 1 mAh of battery capacity.

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