JP2019169304A - Nonaqueous electrolyte solution for power storage device - Google Patents

Abstract

To provide: a nonaqueous electrolyte solution for a power storage device, which is improved and which enables the decrease in the electric resistance of a nonaqueous electrolyte solution and allows a high capacity to be retained even after the iteration of charge and discharge; and a power storage device.SOLUTION: A nonaqueous electrolyte solution for a power storage device is arranged by dissolving an electrolyte in a nonaqueous solvent. In the nonaqueous electrolyte solution, the electrolyte is a lithium salt which dissolves in the nonaqueous solvent, and contains a lithium boron compound represented by the following formula (1): (Li)[(-O-)B(OOC-(A)-COO)][B(-O-)](1) (where "A" is an alkylene group with 1-6 carbon atoms, an alkenylene group with 2-6 carbon atoms, an alkynylene group with 2-6 carbon atoms, or a phenylene group, the alkylene group may have an oxygen or sulfur atom in a main chain, "n" and "p" are 1 or 2, which are independent of each other; "q" is 0-3, and "m", "x", "y" and "z" are 0-10, which are independent of one another.)SELECTED DRAWING: None

Description

  The present invention relates to a nonaqueous electrolytic solution for an electricity storage device such as a lithium ion secondary battery.

  In recent years, with the widespread use of various portable electronic devices such as portable electronic terminals typified by mobile phones and notebook computers, secondary batteries play an important role as their power source. Examples of these secondary batteries include an aqueous battery and a non-aqueous electrolyte battery. Among them, the non-aqueous electrolyte secondary battery including a positive electrode and a negative electrode that can occlude and release lithium ions and the like and a non-aqueous electrolyte has a high voltage and high energy density, excellent safety, environmental problems, etc. In this respect, it has various advantages compared with other secondary batteries.

  As non-aqueous electrolyte secondary batteries currently in practical use, for example, a composite oxide of lithium and a transition metal is used as a positive electrode active material, and a material capable of doping and dedoping lithium is used as a negative electrode active material. A lithium ion secondary battery is mentioned. In the negative electrode active material of a lithium ion secondary battery, a carbon material is mentioned as a material which has the outstanding cycling characteristics. Among carbon materials, graphite is expected as a material that can improve the energy density per unit volume.

Further, in order to improve the characteristics of the lithium secondary battery, not only the characteristics of the negative electrode / positive electrode but also the characteristics of the non-aqueous electrolyte responsible for transferring lithium ions are required. As such a non-aqueous electrolyte, a lithium salt such as LiBF ₄ , LiPF ₆ , LiClO ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ was dissolved in an aprotic organic solvent. A non-aqueous solution is used (Non-Patent Document 1). Carbonates are known as typical examples of aprotic organic solvents, and the use of various carbonate compounds such as ethylene carbonate, propylene carbonate, and dimethyl carbonate has been proposed (Patent Documents 1 and 2).

On the other hand, a non-aqueous electrolyte in which LiBF ₄ , LiPF _{6 and the} like are dissolved as an electrolyte of the non-aqueous electrolyte has high conductivity indicating the transfer of lithium ions, and the oxidative decomposition voltage of LiBF ₄ and LiPF ₆ is high. It is known to be stable at high voltage, and contributes to drawing out the characteristics of the lithium secondary battery such as high voltage and high energy density.

  On the other hand, when using a non-aqueous electrolyte secondary battery such as a lithium secondary battery as each power source, the electrical resistance of the non-aqueous electrolyte is lowered to increase the conductivity of lithium ions, and charging, Even after repeated discharges, there is a demand for a long life that suppresses a decrease in battery capacity and maintains a high capacity, so-called cycle characteristics.

In order to achieve such an object, various proposals have conventionally been made for non-aqueous electrolytes to specify the structure of a lithium salt that is an electrolyte or to add a specific compound. For example, Patent Document 3 proposes adding a vinyl sulfone derivative having a specific structure to a nonaqueous electrolytic solution. Patent Document 4 proposes to add a lithium salt other than a bifunctional lithium salt having a specific structure and having no boron atom.
However, conventional non-aqueous electrolytes are not always satisfactory, including the cost, and further techniques are required for non-aqueous electrolytes for power storage devices.

JP-A-4-184872 Japanese Patent Laid-Open No. 10-27625 JP 11-329494 A Japanese Patent Laid-Open No. 2014-22334

  The present invention improves the solubility of the electrolyte in the non-aqueous electrolyte, lowers the electrical resistance of the non-aqueous electrolyte, and maintains a high capacity even after repeated many times of charging and discharging, so-called cycle It aims at providing the nonaqueous electrolyte for electrical storage devices, such as a lithium secondary battery which improved the characteristic, and the electrical storage device using this nonaqueous electrolytic solution.

  As a result of various researches, the present inventors have found a non-aqueous electrolyte solution for an electricity storage device that can achieve the above-described object, and an electricity storage device that uses the non-aqueous electrolyte solution, and have reached the present invention. is there.

The present invention has the following gist.
(1) A nonaqueous electrolytic solution for an electricity storage device obtained by dissolving an electrolyte in a nonaqueous solvent, wherein the electrolyte is a lithium salt dissolved in the nonaqueous solvent and represented by the following formula (1) A nonaqueous electrolytic solution for an electricity storage device, comprising a boron compound.
_{(Li) m [(-O-)} n B (OOC- (A) z -COO) p] x [B (-O-) q] y (1)
(In the formula, A is an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, an alkynylene group having 2 to 6 carbon atoms, or a phenylene group, and the alkylene group is oxygen in the main chain. May have an atom or a sulfur atom, n and p are each independently 1 or 2, q is 0 to 4, and m, x, y and z are each independently 0-10)

(2) In the lithium boron compound, in formula (1), A is an alkylene group having 1 to 6 carbons or an alkenylene group having 2 to 6 carbons, and n and p are integers of 1 or 2. , M, x, y, z are non-aqueous electrolytes as described in said (1) which are compounds which are 0-4.
(3) In the formula (1), A is an alkylene group having carbon 2 or 4, and the alkylene group has an oxygen atom or a sulfur atom in the main chain as described in (1) or (2) above. Non-aqueous electrolyte.
(4) The lithium boron compound is LiBO (OOC-COO), LiBO (OOCCH ₂ COO), LiBO (OOC (CH ₂ ) ₂ COO), LiBO (OOC (CF ₂ ) ₂ COO), LiBO (OOC (CH _{2) 3 COO), LiBO (} OOC (CH 2 C (= CH 2)) COO), LiBO (OOCCH 2 SCH 2 COO), LiBO (OOCC 2 H 4 SC 2 H 4 COO), Li 2 B 4 O 5 (OOC-COO) ₂ , Li ₂ B ₄ O ₅ (OOCCH ₂ COO) ₂ , Li ₂ B ₄ O ₅ (OOCCH ₂ SCH ₂ COO) ₂ , Li ₂ B ₄ O ₅ (OOC (CH ₂ C (= CH _{2)) COO) 2, Li} 4 B 2 O 3 (OOC-COO) 2, Li 4 B 2 O 3 (OOCCH 2 COO) 2, Li 4 B 2 O 3 (OOCCH 2 SCH 2 COO) 2, or Li ₄ B ₂ O ₃ ( _{OC (CH 2 C (= CH} 2)) COO) 2 in the above (1) to a non-aqueous electrolyte solution according to any one of (3).
(5) The nonaqueous electrolytic solution according to any one of (1) to (4), wherein the lithium boron compound is contained in an amount of 0.01 to 10% by mass in the nonaqueous electrolytic solution.
(6) The nonaqueous electrolytic solution according to any one of (1) to (5), wherein the nonaqueous solvent contains a chain carbonate ester, a saturated cyclic carbonate ester, and an unsaturated cyclic carbonate ester.
(7) The above, wherein the content of the chain carbonate ester, saturated cyclic carbonate ester, and unsaturated cyclic carbonate ester is 30 to 80% by mass, 10 to 50% by mass, and 0.01 to 5% by mass, respectively. The nonaqueous electrolytic solution according to (6).

(8) The lithium salt is LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF _{3 SO 2) (C 2 F 5} SO 2), and a _{LiN (CF 3 SO 2) (} C 4 F 9 at least one lithium salt selected from the group consisting of SO _2), (1) to (7 The nonaqueous electrolytic solution according to any one of the above.
(9) Further, it contains at least one additive selected from the group consisting of sulfur-containing compounds, cyclic acid anhydrides, carboxylic acid compounds, boron fluoride compounds, phosphorus fluoride compounds, silicon-containing compounds, and boron-containing compounds. The nonaqueous electrolytic solution according to any one of (1) to (8) above.
(10) An electricity storage device using the nonaqueous electrolytic solution according to any one of (1) to (9) above.
(11) The livestock device according to (10), wherein the electricity storage device is a lithium secondary battery.

The non-aqueous electrolyte according to the present invention not only lowers the electric resistance of the non-aqueous electrolyte by increasing the solubility of the lithium electrolyte in the non-aqueous electrolyte, but also maintains a high capacity even after repeated charging and discharging. However, so-called cycle characteristics are improved. For this reason, electrical storage devices, such as a lithium secondary battery excellent in the favorable initial characteristic and cycling characteristics, are provided.
Although it is not always clear whether the non-aqueous electrolyte of the present invention has the above-mentioned effects, the lithium boron compound used in the present invention is composed of lithium ions that become cations, boron, oxygen, and dicarboxylic acid. Since it is composed of anions, it is likely to dissociate in the electrolytic solution, and it is considered that a film that facilitates the passage of lithium ions on the electrode surface is formed by decomposition of the dissociated anions. Further, it is considered that the anion composed of boron, oxygen, and dicarboxylic acid easily reacts with moisture in the electrolyte solution or on the electrode surface, and moisture that easily affects battery performance is effectively removed.

Hereinafter, the nonaqueous electrolytic solution of the present invention and the electricity storage device using the same will be described.
<Nonaqueous solvent>
As the nonaqueous solvent used in the nonaqueous electrolytic solution of the present invention, various solvents can be used. For example, an aprotic polar solvent is preferable. Specific examples thereof are ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, trifluoromethylethylene carbonate, fluoroethylene carbonate. And cyclic carbonates such as 4,5-difluoroethylene carbonate; lactones such as γ-ptilolactone and γ-valerolactone; cyclic sulfones such as sulfolane; cyclic ethers such as tetrahydrofuran and dioxane; ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate , Methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, ethyl Chain carbonates such as propyl carbonate and methyl trifluoroethyl carbonate; nitriles such as acetonitrile; chain ethers such as dimethyl ether; chain carboxylic acid esters such as methyl propionate; chain glycol ethers such as dimethoxyethane; , 2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3,3-pentafluoropropyl ether, ethoxy And fluorine-containing ethers such as -2,2,2-trifluoroethoxy-ethane. These can be used alone or in combination of two or more.

  As the non-aqueous solvent, it is more preferable to use a carbonate-based solvent such as cyclic carbonate and chain carbonate from the viewpoint of ion conductivity. It is more preferable to use a combination of a cyclic carbonate and a chain carbonate as the carbonate solvent. Among the above, as the cyclic carbonate, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate are preferable. Among the above-mentioned chain carbonates, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate are preferable. In the case of using a carbonate-based solvent, another non-aqueous solvent such as a nitrile compound or a sulfone-based solvent can be further added as necessary from the viewpoint of improving battery physical properties.

  As the nonaqueous solvent, in the present invention, it is particularly preferable to contain a chain carbonate ester, a saturated cyclic carbonate ester, and an unsaturated cyclic carbonate ester. In the case of containing these three kinds of carbonates, it is particularly preferable since the effects of the present invention are exhibited. In the nonaqueous solvent used in the present invention, the chain carbonate ester, the saturated cyclic carbonate ester, and the unsaturated cyclic carbonate ester are 30 to 80% by weight, 10 to 50% by weight, respectively, in the nonaqueous electrolytic solution. And 0.01 to 5% by weight, and more preferably 50 to 70% by weight, 20 to 30% by weight, and 0.1 to 2% by weight, respectively.

  When the chain carbonate ester is smaller than 30% by weight, the viscosity of the electrolytic solution is increased, and in addition, it solidifies at a low temperature, so that sufficient characteristics cannot be obtained. If it is large, the dissociation / solubility of the lithium salt will decrease, and the ionic conductivity of the electrolyte will decrease. When the saturated cyclic carbonate is less than 10% by weight, the dissociation / solubility of the lithium salt is lowered, and the ionic conductivity of the electrolyte is lowered. Conversely, when the saturated cyclic carbonate is more than 50% by weight, the electrolyte In addition, the viscosity of the resin increases and, at the same time, solidifies at a low temperature, so that sufficient characteristics cannot be obtained.

  In addition, when the unsaturated cyclic carbonate is smaller than 0.01% by weight, a good film is not formed on the negative electrode surface, so that the cycle characteristics are deteriorated. Conversely, when the unsaturated cyclic carbonate is larger than 5% by weight, for example, When stored at a high temperature, the electrolyte solution is likely to generate gas, and the pressure in the battery is increased, which is undesirable in practice.

  Examples of the chain carbonate used in the present invention include chain carbonates having 3 to 9 carbon atoms. Specifically, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, n-propyl isopropyl carbonate, di-n-butyl carbonate, di-t-butyl carbonate, n-butyl isobutyl carbonate, n-butyl-t-butyl carbonate, isobutyl-t-butyl carbonate, ethyl methyl carbonate, methyl-n-propyl carbonate, n-butyl methyl carbonate, isobutyl methyl carbonate, t-butyl methyl carbonate, ethyl-n-propyl carbonate, n-butyl ethyl carbonate, isobutyl ethyl carbonate, t-butyl ethyl carbonate, n-butyl-n-propyl carbonate, isobutyl-n- B pills carbonate, t- butyl -n- propyl carbonate, n- butyl isopropyl carbonate, isobutyl isopropyl carbonate, and t-butyl isopropyl carbonate. Among these, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate are preferable, but are not particularly limited. Two or more of these chain carbonates may be mixed.

  Examples of the saturated cyclic carbonate used in the present invention include ethylene carbonate, propylene carbonate, butylene carbonate, and fluoroethylene carbonate. Among these, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate are more preferable. By using propylene carbonate, a stable nonaqueous electrolytic solution can be provided in a wide temperature range. Two or more of these saturated cyclic carbonates may be mixed.

Examples of the unsaturated cyclic carbonate used in the present invention include vinylene carbonate derivatives represented by the following general formula (I).

In the above general formula (I), R ₁ and R ₂ are each independently a hydrogen atom, a halogen atom, or an alkyl group that may contain a halogen atom having 1 to 12 carbon atoms. Among them, preferably R ₁ and R ₂ are hydrogen (a vinylene carbonate).

  Specific examples of the vinylene carbonate derivative include the following compounds. Vinylene carbonate, fluorovinylene carbonate, methyl vinylene carbonate, fluoromethyl vinylene carbonate, ethyl vinylene carbonate, propyl vinylene carbonate, butyl vinylene carbonate, dimethyl vinylene carbonate, diethyl vinylene carbonate, dipropyl vinylene carbonate, etc. are limited thereto. It is not a thing.

Among these compounds, vinylene carbonate is effective and advantageous in terms of cost. In addition, regarding the said vinylene carbonate derivative, it is at least 1 type, and it is also possible to be independent or to mix.
Moreover, as another unsaturated cyclic carbonate used by this invention, the alkenyl ethylene carbonate represented by the following general formula (II) is mentioned.

In the above formula (II), R _{3 to} R ₆ each independently represent a hydrogen atom, a halogen atom, a hydrocarbon group that may contain a halogen atom having 1 to 12 carbon atoms, or a carbon number of 2 to 2. 12 alkenyl groups, at least one of which is an alkenyl group having 2 to 12 carbon atoms. Especially, when one of R < ₃ > -R < ₆ > is a vinyl group and the remainder is hydrogen (the compound of (II) is 4-vinyl ethylene carbonate), it is preferable.

  Specific examples of the alkenylethylene carbonate include compounds such as 4-vinylethylene carbonate, 4-vinyl-4-methylethylene carbonate, 4-vinyl-4-ethylethylene carbonate, 4-vinyl-4-n-propylethylene carbonate, and the like. Can be mentioned.

  The nonaqueous solvent used in the present invention may contain other various solvents in addition to the above components. Examples of these various other solvents include cyclic carboxylic acid esters, chain esters having 3 to 9 carbon atoms, and chain ethers having 3 to 6 carbon atoms. These various other solvents are preferably contained in the nonaqueous electrolytic solution in an amount of 0.2 to 10% by weight, particularly preferably 0.5 to 5% by weight.

  Examples of the cyclic carboxylic acid ester (lactone compound having 3 to 9 carbon atoms) include γ-butyrolactone, γ-valerolactone, γ-caprolactone, and ε-caprolactone. Among these, γ-butyrolactone and γ-valerolactone are more preferable, but not particularly limited. Two or more of these cyclic carboxylic acid esters may be mixed.

  Examples of the chain ester having 3 to 9 carbon atoms include methyl acetate, ethyl acetate, acetic acid-n-propyl, acetic acid-isopropyl, acetic acid-n-butyl, acetic acid isobutyl, acetic acid-t-butyl, and methyl propionate. And ethyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate and t-butyl propionate. Of these, ethyl acetate, methyl propionate, and ethyl propionate are preferred.

  Examples of the chain ether having 3 to 6 carbon atoms include dimethoxymethane, dimethoxyethane, diethoxymethane, diethoxyethane, ethoxymethoxymethane, and ethoxymethoxyethane. Of these, dimethoxyethane and diethoxyethane are more preferred.

  Further, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene and the like can be used. .

<Lithium salt>
A lithium salt is used as the solute of the nonaqueous electrolytic solution of the present invention. The lithium salt is not particularly limited as long as it can be dissolved in the non-aqueous solvent. Specific examples thereof are as follows.
(A) Inorganic lithium salt:
LiPF _6, LiAsF _6, inorganic fluoride salts LiBF ₄ or the _{like, LiClO 4, LiBrO 4, LiIO} 4, perhalogenate etc. like.

(B) Organic lithium salt:
Organic sulfonates such as LiCF ₃ SO ₃ ; perfluoro such as LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) Alkyl sulfonic acid imide salt; Perfluoroalkyl sulfonic acid methide salt such as LiC (CF ₃ SO ₂ ) ₃ ; LiPF (CF ₃ ) ₅ , LiPF ₂ (CF ₃ ) ₄ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₂ ( _{C 2 F 5) 4, LiPF} 3 (C 2 F 5) 3, LiPF (n-C 3 F 7) 5, LiPF 2 (n-C 3 F 7) 4, LiPF 3 (n-C 3 F 7) _{3, LiPF (iso-C 3} F 7) 5, LiPF 2 (iso-C 3 F 7) 4, LiPF 3 (iso-C 3 F 7) 3, LiB (CF 3) 4, LiBF (CF 3 _{3, LiBF 2 (CF 3)} 2, LiBF 3 (CF 3), LiB (C 2 F 5) 4, LiBF (C 2 F 5) 3, LiBF 2 (C 2 F 5) 2, LiBF 3 (C 2 _{F 5), LiB (n-} C 3 F 7) 4, LiBF (n-C 3 F 7) 3, LiBF 2 (n-C 3 F 7) 2, LiBF 3 (n-C 3 F 7), LiB Some fluorine such as (iso-C ₃ F ₇ ) ₄ , LiBF (iso-C ₃ F ₇ ) ₃ , LiBF ₂ (iso-C ₃ F ₇ ) ₂ , LiBF ₃ (iso-C ₃ F ₇ ) Examples thereof include inorganic fluoride salt fluorophosphate substituted with a perfluoroalkyl group, and fluorine-containing organic lithium salt of perfluoroalkyl.

In the present invention, among the above, LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₂ F ₅ SO ₂ ) LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) is more preferable. Two or more of these lithium salts may be mixed.

  The concentration of the lithium salt, which is the solute of the nonaqueous electrolytic solution of the present invention, is preferably 0.5 to 3 mol / liter, particularly 0.7 to 2 mol / liter. If this concentration is too low, the ionic conductivity of the non-aqueous electrolyte is insufficient due to an absolute concentration shortage. If the concentration is too high, the ionic conductivity decreases due to an increase in viscosity, and precipitation at a low temperature occurs. Since it is likely to occur and causes problems, the performance of the nonaqueous electrolyte battery is undesirably lowered.

<Lithium boron compound>
The nonaqueous electrolytic solution of the present invention contains a lithium boron compound represented by the following formula (1).
_{(Li) m [(-O-)} n B (OOC- (A) z -COO) p] x [B (-O-) q] y (1)
In the formula (1), A, m, n, p, x, and y are as defined above.

Among these, in formula (1), A is preferably an alkylene group having 1 to 6 carbon atoms, and an alkenylene group having 2 to 6 carbon atoms or an alkynylene group having 2 to 6 carbon atoms is preferable.
Preferable examples of the alkylene group include methylene, ethylene, difluoromethylene, tetrafluoroethylene, hydroxyethylene, propylene, butylene, cyclopropylene, cyclobutylene, cyclohexylene and the like. As a preferable example of the alkylene group having an oxygen atom or a sulfur atom in the main chain, an alkylene group having 1 to 4 carbon atoms is preferably bonded to the oxygen atom or the sulfur atom.
Preferable examples of the alkenylene group include vinylene, propenylene, butenylene, propenyl and the like. In particular, an alkenylene group having 2 to 6 carbon atoms having a double bond is preferable.

Preferable examples of the alkynylene group include ethynylene, propynylene, butynylene, pentynylene and the like. An alkynylene group having 3 to 6 carbon atoms is particularly preferable.
Preferable examples of the phenylene group include phenylene and difluorophenylene.

In the formula (1), when A is an alkylene group, an alkenylene group, an alkynylene group, a phenylene group, or an alkylene group having an oxygen atom or a sulfur atom in the main chain, the hydrogen atom of these groups is halogen, It may be optionally substituted with a hydroxyl group, a cyano group or a nitro group.
In the formula (1), n and p are each independently preferably an integer of 1 or 2, and m, x, y and z are each independently preferably 0 or 1 to 10. It is an integer.

Preferable specific examples of the lithium boron compound include LiBO (OOC-COO), LiBO (OOCCH ₂ COO), LiBO (OOC (CH ₂ ) ₂ COO), LiBO (OOC (CF ₂ ) ₂ COO), LiBO (OOC). (CH ₂ ) ₃ COO), LiBO (OOC (CH ₂ C (═CH ₂ )) COO), LiBO (OOC (C (CH ₂ ) ₃ ) COO), LiBO (OOCCH ₂ OCH ₂ COO), LiBO (OOCCH _{2 SCH 2 COO), LiBO (} OOCC 2 H 4 SC 2 H 4 COO), Li 2 B 4 O 5 (OOC-COO) 2, Li 2 B 4 O 5 (OOCCH 2 COO) 2, Li 2 B 4 O _{5 (OOCCH 2 SCH 2 COO)} 2, Li 2 B 4 O 5 (OOC (CH 2 C (= CH 2)) C _{O) 2, Li 4 B 2} O 3 (OOC-COO) 2, Li 4 B 2 O 3 (OOCCH 2 COO) 2, Li 4 B 2 O 3 (OOCCH 2 SCH 2 COO) 2, Li 4 B 2 O ₃ (OOC (CH ₂ C (═CH ₂ )) COO) ₂ .

Among them, LiBO (OOC-COO), LiBO (OOCCH ₂ COO), LiBO (OOC (CH ₂ ) ₂ COO), LiBO (OOC (CF ₂ ) ₂ COO), LiBO (OOC (CH ₂ ) ₃ COO), LiBO (OOC (CH ₂ C (═CH ₂ )) COO),
_{LiBO (OOCCH 2 SCH 2 COO)} , LiBO (OOCC 2 H 4 SC 2 H 4 COO), Li 2 B 4 O 5 (OOC-COO) 2, Li 2 B 4 O 5 (OOCCH 2 COO) 2, Li 2 _{B 4 O 5 (OOCCH 2 SCH} 2 COO) 2, Li 2 B 4 O 5 (OOC (CH 2 C (= CH 2)) COO) 2, Li 4 B 2 O 3 (OOC-COO) 2, Li 4 _{B 2 O 3 (OOCCH 2 COO} ) 2, Li 4 B 2 O 3 (OOCCH 2 SCH 2 COO) 2, Li 4 B 2 O 3 (OOC (CH 2 C (= CH 2)) COO) like ₂ is preferably .

  These lithium boron compounds can be obtained by known production methods in the same manner as lithium salts such as lithium tetraborate. For example, by reacting boric acid, a lithium compound such as lithium hydroxide or lithium carbonate, and an aqueous solution of a corresponding carboxylic acid compound at 20 to 80 ° C., the precursor crystal is obtained. Can be dehydrated at 200 to 400 ° C. to obtain the lithium boron compound.

  The content of the lithium boron compound in the nonaqueous electrolytic solution of the present invention is preferably 0.01 to 10% by mass, more preferably 0.1 to 5% by mass, and particularly preferably 0.1% in the nonaqueous electrolytic solution. ~ 2% by volume is preferred. When the concentration is less than 0.01% by mass, the resistance reduction effect is reduced. On the other hand, if it exceeds 10% by weight, the film resistance becomes high and the life performance deteriorates.

<Other additive substances>
In the non-aqueous electrolyte of the present invention, other additive substances may be contained in addition to the lithium salt and the lithium boron compound in order to improve the life performance and resistance performance of the electricity storage device. Examples of such other additive substances are selected from the group consisting of sulfur-containing compounds (excluding the organic carboxylates represented by the above formula (1)), cyclic acid anhydrides, carboxylic acid compounds, and boron-containing compounds. One or more compounds can be used.

  Examples of the sulfur-containing compound include 1,3-propane sultone (PS), propene sultone, ethylene sulfite, hexahydrobenzo [1,3,2] dioxathiolane-2-oxide (1,2-cyclohexanediol cyclic sulfite Also), 5-vinyl-hexahydro 1,3,2-benzodioxathiol-2-oxide, 1,4-butanediol dimethanesulfonate, 1,3-butanediol dimethanesulfonate, methylenemethane disulfonic acid, ethylene Examples include methanedisulfonic acid, N, N-dimethylmethanesulfonamide, N, N-diethylmethanesulfonamide, divinylsulfone, 1,2-bis (vinylsulfonyl) methane, and the like.

  Examples of the cyclic acid anhydride include glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, succinic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride 4-cyclohexene-1,2-dicarboxylic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, phenylsuccinic anhydride, 2- Carboxylic anhydride such as phenylglutaric anhydride, phthalic anhydride, pyromellitic anhydride, fluorosuccinic anhydride, tetrafluorosuccinic anhydride, 1,2-ethanedisulfonic anhydride, 1,3-propanedisulfone Acid anhydride, 1,4-butanedisulfonic anhydride, 1,2-benzenedisulfonic anhydride, tetraf Oro-1,2-ethanedisulfonic anhydride, hexafluoro-1,3-propanedisulfonic anhydride, octafluoro-1,4-butanedisulfonic anhydride, 3-fluoro-1,2-benzenedisulfonic anhydride Products, 4-fluoro-1,2-benzenedisulfonic anhydride, 3,4,5,6-tetrafluoro-1,2-benzenedisulfonic anhydride, and the like.

  Examples of the carboxylic acid compound include lithium oxalate, lithium malonate, lithium difluoromalonate, lithium succinate, lithium tetrafluorosuccinate, lithium adipate, lithium glutarate, lithium acetonedicarboxylate, lithium 2-oxobutyrate, and oxal. Lithium acetate, lithium 2-oxoglutarate, lithium acetoacetate, lithium 3-oxocyclobutanecarboxylate, lithium 3-oxocyclopentanecarboxylate, lithium 2-oxovalerate, lithium pyruvate, lithium glyoxylate, 3,3-dimethyl Lithium 2-oxobutyrate, lithium 2-hydroxypropionate, lithium 2-methyl lactate, lithium tartrate, lithium cyanoacetate, lithium 2-mercaptopropionate, lithium methylenebis (thioglycolate) thio 3-succinate (Tilthio) lithium propionate, lithium 3,3′-thiodipropionate, lithium dithiodiglycolate, lithium 2,2′-thiodiglycolate, lithium thiazolidine-2,4-dicarboxylate, lithium acetylthioacetate, etc. It is done.

Examples of the boron-containing compound include LiBF ₂ (C ₂ O ₄ ), LiB (C ₂ O ₄ ) ₂ , LiBF ₂ (CO ₂ CH ₂ CO ₂ ), LiB (CO ₂ CH ₂ CO ₂ ) ₂ , LiB (CO ₂ CF ₂ CO ₂ ) ₂ , LiBF ₂ (CO ₂ CF ₂ CO ₂ ), LiBF ₃ (CO ₂ CH ₃ ), LiBF ₃ (CO ₂ CF ₃ ), LiBF ₂ (CO ₂ CH ₃ ) ₂ , LiBF ₂ ( _{CO 2 CF 3) 2, LiBF} (CO 2 CH 3) 3, LiBF (CO 2 CF 3) 3, LiB (CO 2 CH 3) 4, LiB (CO 2 CF 3) 4, Li 2 B 2 O 7, li ₂ B ₂ O ₄ and the like.

  As said 2nd additive substance, each 1 type may be used independently and 2 or more types may be used together. In addition, when the water electrolyte adds the second additive substance, the content of the second additive substance in the non-aqueous electrolyte is 0.01 to 5% by mass, although it varies depending on the second additive substance. Preferably, it is 0.1-2 mass%.

<Power storage device>
The non-aqueous electrolyte of the present invention is used in various power storage devices such as a lithium ion secondary battery, an electric double layer capacitor, a hybrid battery in which one of a positive electrode and a negative electrode is a battery and the other electrode is a double layer. it can. Hereinafter, a lithium ion secondary battery as a representative example will be described.

  As a negative electrode active material constituting a negative electrode in a lithium ion secondary battery, a carbon material capable of doping / dedoping lithium ions, metallic lithium, a lithium-containing alloy, or silicon capable of being alloyed with lithium , Silicon alloy, tin, tin alloy, tin oxide capable of doping / de-doping lithium ion, silicon oxide, transition metal oxide capable of doping / de-doping lithium ion, lithium ion Any of the transition metal nitrogen compounds that can be doped / dedoped, or a mixture thereof can be used.

  The negative electrode generally has a configuration in which a negative electrode active material is formed on a current collector such as a copper foil or expanded metal. In order to improve the adhesion of the negative electrode active material to the current collector, for example, it may contain a polyvinylidene fluoride binder, a latex binder, etc., and carbon black, amorphous whisker carbon, etc. are added as a conductive aid. May be used.

As the carbon material constituting the negative electrode active material, for example, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), graphites, organic polymer compound fired bodies (phenol resin, furan resin, etc.) are suitable. And carbonized by firing at a suitable temperature), carbon fiber, activated carbon and the like. The carbon material may be graphitized. As the carbon material, a carbon material having a (002) plane spacing (d002) of 0.340 nm or less, particularly measured by X-ray diffraction, is preferable, or a graphite having a true density of 1.70 g / cm ³ or more or close thereto. A highly crystalline carbon material having properties is desirable. When such a carbon material is used, the energy density of the nonaqueous electrolyte battery can be increased.

  Further, those containing boron in the carbon material, those coated with a metal such as gold, platinum, silver, copper, Sn, Si, or those coated with amorphous carbon can be used. One type of these carbon materials may be used, or two or more types may be used in combination as appropriate.

  Silicon, silicon alloy, tin, tin alloy that can be alloyed with lithium, tin oxide that can be doped / undoped with lithium ions, silicon oxide, transition metals that can be doped / undoped with lithium ions In the case of using an oxide, any of the above-described carbonaceous materials has a higher theoretical capacity per weight and is a suitable material.

On the other hand, the positive electrode active material constituting the positive electrode can be formed from various materials that can be charged and discharged. Examples thereof include lithium-containing transition metal oxides, lithium-containing transition metal composite oxides using one or more transition metals, transition metal oxides, transition metal sulfides, metal oxides, and olivine-type metal lithium salts. For _example, in _{LiCoO 2, LiNiO 2, LiMn 2} O 4, LixMO 2 such as LiMnO ₂ (where, M is one or more transition metals, x is different according to the charge and discharge state of the battery, usually 0.05 ≦ x ≦ 1.20), and a composite oxide of lithium and one or more transition metals (lithium transition metal composite oxide).

Furthermore, some of the transition metal atoms that are the main component of the lithium transition metal composite oxide are Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, It is possible to use complex oxides substituted with other metals such as Si and Yb, chalcogenides of transition elements such as FeS ₂ , TiS ₂ , V ₂ 0 ₅ , MoO ₃ and MoS _2, or polymers such as polyacetylene and polypyrrole. it can. Of these, lithium transition metal composite oxides capable of doping and dedoping Li and metal composite oxide materials in which transition metal atoms are partially substituted are preferable.

  In addition, a material in which a substance having a composition different from that of the substance constituting the main cathode active material is attached to the surface of the cathode active material can be used. Surface adhering substances include aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, etc .; lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate And sulfates such as aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate.

  The positive electrode generally has a configuration in which a positive electrode active material is formed on a current collector such as an aluminum, titanium, or stainless steel foil, or an expanded metal. In order to improve the adhesion of the positive electrode active material to the current collector, for example, polyvinylidene fluoride binder and latex binder, carbon black, amorphous whisker, graphite etc. to improve the electron conductivity in the positive electrode It may contain.

  The separator is preferably a membrane that electrically insulates the positive electrode from the negative electrode and is permeable to lithium ions. For example, a porous membrane such as a microporous polymer film is used. As the microporous polymer film, a porous polyolefin film is particularly preferable, and more specifically, a porous polyethylene film, a porous polypropylene film, or a multilayer film of a porous polyethylene film and a polypropylene film is preferable. Furthermore, a polymer electrolyte can also be used as a separator. As the polymer electrolyte, for example, a polymer material in which a lithium salt is dissolved, a polymer material swollen with an electrolytic solution, and the like can be used, but the polymer electrolyte is not limited thereto.

The non-aqueous electrolyte of the present invention may be used for the purpose of obtaining a polymer electrolyte by swelling a polymer substance with the non-aqueous electrolyte, or a separator having a combination of a porous polyolefin film and a polymer electrolyte. A non-aqueous electrolyte may be soaked in.
The shape of the lithium ion secondary battery using the non-aqueous electrolyte of the present invention is not particularly limited, and may be various shapes such as a cylindrical shape, a square shape, an aluminum laminate type, a coin shape, and a button shape. Can do.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples, and can be modified within the scope of the present invention.

<Production of battery>
Separator with a thickness of 23 μm (F23DHA, manufactured by Toray Battery Separator Film Fuel Chemical Co., Ltd.), a positive electrode formed by applying a positive electrode mixture to an aluminum current collector and a negative electrode formed by applying a negative electrode mixture to a copper current collector The flat wound electrode group wound through the case was housed in a case to produce a battery cell having a rectangular parallelepiped shape of 30 mm long × 30 mm wide × 2.0 mm thick. Using this battery cell, a battery was prepared according to the following procedure.

The positive electrode is made of 5% by mass of polyvinylidene fluoride as a binder, 4% by mass of acetylene black as a conductive agent, and a positive electrode active material LiNi _0.5 Mn ₀ that is a composite oxide powder of lithium-nickel-manganese-cobalt. _.3 Co _0.2 O ₂ 91% by mass of N-methylpyrrolidone was added to a positive electrode mixture prepared to prepare a paste, which was applied to both sides of an aluminum foil current collector having a thickness of 18 μm. Then, after removing the solvent by drying, it was produced by rolling with a roll press.

  The negative electrode is a slurry prepared by mixing 95.8% by mass of artificial graphitizable carbon powder, 2.0% by mass of styrene butadiene rubber (SBR) as a binder and 2.2% by mass of carboxymethyl cellulose and using water as a dispersion medium. The slurry was applied to both sides of a copper foil having a thickness of 12 μm, and the solvent was dried and removed, followed by rolling with a roll press. A polyethylene microporous membrane was used for the separator.

Using the battery cell produced above, a battery was produced in the following procedure.
a. 0.55 g of various electrolytes were weighed, poured into the injection port of the battery cell, and after reducing the pressure, the injection port was sealed.
b. In a state where the sealed battery cell was kept in an atmosphere of 25 ° C., the battery cell was charged at 8 mA to 4.2 V, and then discharged at 8 mA to 3.0 V.
c. The internal gas of the battery cell discharged to 3.0 V was removed under reduced pressure to produce a battery.

<Battery evaluation>
About the battery produced above, the charge / discharge characteristic was measured as follows.
a. Resistance change rate Before high temperature cycle test, charge to SOC (State of Charge) 50% at 25 ° C, and under each environment at 0.2C, 0.5C, 1.0C, 2.0C respectively After discharging for 10 seconds, the initial DC resistance value was determined.
Then, after charging to 4.2 V at 1 C rate in a 45 ° C. atmosphere, discharging to 3.0 V at 1 C rate in the same atmosphere and repeating until reaching 200 cycles, the same as before the high temperature cycle test The DC resistance value after cycling was determined under the conditions.

From the initial DC resistance value and the DC resistance value after the cycle, the resistance change rate (%) was obtained using the following formula (2).
Resistance change rate (%) = (resistance value after cycle / initial resistance value) × 100 (2)

b. Capacity maintenance rate After charging to 4.2 V at a 1C rate in a 45 ° C. atmosphere, discharging was performed to 3.0 V at a 1C rate in the same atmosphere, and the discharge capacity value was taken as the initial capacity value. Then, the same conditions were repeated until 200 cycles were reached. From the initial capacity value and the capacity value after the cycle, the capacity retention rate (%) was obtained using the following formula (3).
Capacity retention rate (%) = (capacity value after cycle / initial capacity value) × 100 (3)

<Examples 1 to 10>
LiPF ₆ is dissolved as a lithium salt in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio is 30:70) to a concentration of 1 mol / liter, and the total mass is 1g of vinylene carbonate was added so that it might become 100g, and the reference | standard electrolyte solution 1 was prepared.
Next, the lithium boron compound shown in Table 1 was added to the reference electrolyte solution 1 so as to have the addition amount shown in Table 1, and the electrolyte solutions of Examples 1 to 10 were prepared. In addition, the addition amount (%) in Table 1 is mass% with respect to the total mass (100 mass%) of the reference electrolyte solution 1 and the added lithium boron compound.

  The laminated batteries of Examples 1 to 10 and Comparative Example 1 were produced using the above-described battery production procedures using the electrolytic solutions prepared above and the reference electrolytic solution 1 respectively. For each of the batteries of Examples 1 to 10 and Comparative Example 1, the resistance change rate and the capacity maintenance rate were determined in accordance with the procedure of the resistance change rate and the capacity maintenance rate described above. The results are shown in Table 1.

  As shown in Table 1, the batteries of Examples 1 to 10 using an electrolytic solution containing a lithium boron compound in the electrolytic solution are compared to the battery of Comparative Example 1 using the reference electrolytic solution 1 not containing these, While the high temperature capacity retention rate was significantly improved, Examples 1, 5, 9, and 10 also greatly improved the resistance change rate of the high temperature cycle.

<Examples 11 to 15>
LiPF ₆ concentration of 1 mol / liter as a lithium salt with respect to a mixed solvent (volume ratio 25: 70: 5) of ethylene carbonate (EC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) In this manner, a reference electrolyte solution 2 was prepared.
Next, a lithium boron compound LiBO (OOCCH ₂ SCH ₂ COO) was added to the reference electrolyte solution 2 so that the addition amount was 0.5% by mass to prepare an electrolyte solution of Example 11. Furthermore, the electrolyte solution of Examples 12-15 was prepared by adding the 2nd additive shown in Table 2 to the electrolyte solution of this Example 11 so that it might become the addition amount shown in Table 2. FIG. The addition amount (%) is mass% relative to the total mass (100 mass%) of the reference electrolyte solution 2 and the added compound.

Using each of the electrolytic solutions prepared above, the laminated batteries of Examples 11 to 15 were produced using the battery production procedure described above.
For each of the batteries of Examples 11 to 15, the resistance change rate and the capacity maintenance rate were obtained according to the procedure of the resistance change rate and the capacity maintenance rate described above. The results are shown in Table 2.

  As shown in Table 2, the batteries of Examples 12 to 15 using the electrolytic solution containing the lithium boron compound and the second additive are the batteries of Example 11 using the electrolytic solution not containing the second additive. Compared to the above, the improvement of the high temperature capacity maintenance rate and the resistance change rate of the high temperature cycle could be improved, and the resistance change rate improvement of Examples 13 and 15 was particularly large.

The non-aqueous electrolyte for power storage devices of the present invention is widely used for power storage devices such as power supplies for various consumer devices such as mobile phones and laptop computers, power supplies for industrial equipment, storage batteries, and power supplies for automobiles.

Claims (11)

A nonaqueous electrolytic solution for an electricity storage device obtained by dissolving an electrolyte in a nonaqueous solvent, wherein the electrolyte is a lithium salt dissolved in the nonaqueous solvent, and a lithium boron compound represented by the following formula (1): A nonaqueous electrolytic solution for an electricity storage device, comprising:
_{(Li) m [(-O-)} n B (OOC- (A) z -COO) p] x [B (-O-) q] y (1)
(In the formula, A is an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, an alkynylene group having 2 to 6 carbon atoms, or a phenylene group, and the alkylene group is oxygen in the main chain. May have an atom or a sulfur atom, n and p are each independently 1 or 2, q is 0 to 4, and m, x, y and z are each independently 0-10)   In the formula (1), the lithium boron compound is an alkylene group having 1 to 6 carbons or an alkenylene group having 2 to 6 carbons, n and p are integers of 1 or 2, m, The nonaqueous electrolytic solution according to claim 1, wherein x, y, and z are compounds having 0 to 4.   The lithium boron compound is a compound in which A is an alkylene group having 2 or 4 carbons in the formula (1), and the alkylene group is a compound having an oxygen atom or a sulfur atom in the main chain. The non-aqueous electrolyte described in 1. The lithium boron compound is LiBO (OOC-COO), LiBO (OOCCH ₂ COO), LiBO (OOC (CH ₂ ) ₂ COO), LiBO (OOC (CF ₂ ) ₂ COO), LiBO (OOC (CH ₂ ) ₃ COO), LiBO (OOC (CH 2 C (= CH 2)) COO), LiBO (OOCCH 2 SCH 2 COO), LiBO (OOCC 2 H 4 SC 2 H 4 COO), Li 2 B 4 O 5 (OOC- COO) ₂ , Li ₂ B ₄ O ₅ (OOCCH ₂ COO) ₂ , Li ₂ B ₄ O ₅ (OOCCH ₂ SCH ₂ COO) ₂ , Li ₂ B ₄ O ₅ (OOC (CH ₂ C (= CH ₂ )) _{COO) 2, Li 4 B 2} O 3 (OOC-COO) 2, Li 4 B 2 O 3 (OOCCH 2 COO) 2, Li 4 B 2 O 3 (OOCCH 2 SCH 2 COO) 2, or Li ₄ B ₂ O ₃ (OOC _{CH 2 C (= CH 2)} ) COO) is _2, the non-aqueous electrolyte according to any one of claims 1-3.   The nonaqueous electrolytic solution according to any one of claims 1 to 4, wherein the lithium boron compound is contained in an amount of 0.01 to 10% by mass in the nonaqueous electrolytic solution.   The nonaqueous electrolytic solution according to any one of claims 1 to 5, wherein the nonaqueous solvent contains a chain carbonate ester, a saturated cyclic carbonate ester, and an unsaturated cyclic carbonate ester.   The content of the chain carbonate ester, the saturated cyclic carbonate ester, and the unsaturated cyclic carbonate ester is 30 to 80% by mass, 10 to 50% by mass, and 0.01 to 5% by mass, respectively. The non-aqueous electrolyte described. The lithium salt is LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ). 8. The method according to claim 1, wherein the lithium salt is at least one lithium salt selected from the group consisting of (C ₂ F ₅ SO ₂ ) and LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ). The non-aqueous electrolyte described in 1.   Furthermore, it contains at least one additive selected from the group consisting of sulfur-containing compounds, cyclic acid anhydrides, carboxylic acid compounds, boron fluoride compounds, phosphorus fluoride compounds, silicon-containing compounds, and boron-containing compounds. Item 9. The nonaqueous electrolytic solution according to any one of Items 1 to 8.   The electrical storage device which uses the nonaqueous electrolyte solution in any one of Claims 1-9.   The livestock device according to claim 10, wherein the electricity storage device is a lithium secondary battery.