JP2016051600A - Nonaqueous electrolytic solution for power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a nonaqueous electrolytic solution for a power storage device which enables the reduction in the electrical resistance of a nonaqueous electrolytic solution, and which enables the enhancement in characteristic enough to maintain a high capacity even after the repetition of charge and discharge; and a power storage device.SOLUTION: A nonaqueous electrolytic solution for a power storage device comprises: a nonaqueous solvent; and an electrolyte dissolved in the solvent. The electrolyte is a lithium salt which can dissolve in the nonaqueous solvent, and it includes a boric acid compound consisting of tetraboric acid or its salt, or metaboric acid or its salt.SELECTED DRAWING: None

Description

  The present invention relates to a nonaqueous electrolytic solution for an electricity storage device such as a lithium 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. These secondary batteries include aqueous batteries such as lead-acid batteries and nickel / cadmium batteries, and non-aqueous electrolyte batteries. Among these, positive and negative electrodes that can occlude and release lithium, non-aqueous electrolytes, and the like. Non-aqueous electrolyte secondary battery consisting of has various advantages compared to other secondary batteries in terms of high voltage, high energy density, excellent safety, environmental issues, etc. .

  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 secondary battery is mentioned. In the negative electrode active material of a lithium secondary battery, a carbon material is an example of a material having excellent cycle characteristics. Among carbon materials, graphite material 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 mixed 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, as the electrolyte of the non-aqueous electrolyte, the non-aqueous electrolyte in which LiBF ₄ and LiPF ₆ are dissolved has high conductivity indicating the transfer of lithium ions, and the oxidative decomposition voltage of LiBF ₄ and LiPF ₆ is high. Therefore, it is known to be stable at a high voltage, and contributes to drawing out the characteristics of the high voltage and high energy density of the lithium secondary battery.

  On the other hand, when using a non-aqueous electrolyte secondary battery such as a lithium secondary battery as each power source, for non-aqueous electrolyte, the electrical resistance is lowered to increase the conductivity of lithium ions, Even after repeated charging and discharging, there is a demand for a long life span 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 includes the addition of a vinylsulfone derivative having a specific structure in a non-aqueous electrolyte, and Patent Document 4 includes lithium salts other than a bifunctional lithium salt having a specific structure. It is known to add a lithium salt 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 studies, the present inventors have unexpectedly found that tetraboric acid or a salt thereof, or metaboric acid or a salt that has not been conventionally known for the purpose and has a simple structure. It has been found that a specific boric acid compound consisting of the salt is effective for achieving the above object. That is, the specific boric acid compound not only increases the solubility of the lithium electrolyte in the non-aqueous electrolyte and decreases the electric resistance of the non-aqueous electrolyte, but also has a high capacity even after repeated charging and discharging. And so-called cycle characteristics were improved.
On the other hand, such an effect is a peculiar thing seen also about a specific boric acid compound also with a boric acid compound, for example, it is hardly seen with typical boric acid compounds, such as orthoboric acid and its salt.

The present invention is based on the above new findings and 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 tetraboric acid or a salt thereof, or metaboro Alternatively, a nonaqueous electrolytic solution for an electricity storage device, comprising a boric acid compound composed of a salt thereof.
(2) The tetraboric acid salt or metaboric acid salt is an alkali metal salt, polyvalent metal salt, ammonium salt, quaternary ammonium salt, imidazolium salt, or pyridinium salt that is soluble in a non-aqueous solvent. The non-aqueous electrolyte for electrical storage devices as described in said (1).
(3) The nonaqueous electrolytic solution for an electricity storage device according to (1), wherein the tetraboric acid salt or metaboric acid salt is an alkali metal salt.
(4) The nonaqueous electrolytic solution for an electricity storage device according to any one of (1) to (3), wherein the tetraboric acid compound is contained in an amount of 0.0001 to 10% by weight.

(5) The nonaqueous electrolysis for an electricity storage device according to any one of (1) to (4), wherein the nonaqueous solvent contains a chain carbonate ester, a saturated cyclic carbonate ester, and an unsaturated cyclic carbonate ester. liquid.
(6) The non-aqueous solvent contains 30 to 80% by weight, 10 to 50% by weight, and 0.01 to 5% by weight of the chain carbonate, saturated cyclic carbonate, and unsaturated cyclic carbonate, respectively. The non-aqueous electrolyte for electrical storage devices as described in said (5) containing.

(7) The electricity storage according to any one of (1) to (6), further including a second additive composed of a carboxylic acid anhydride, a carboxylate salt, a sulfonate salt, a sulfur-containing compound, and boron. Non-aqueous electrolyte for devices.
(8) The lithium salt is LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , 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 LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), which is at least one lithium salt selected from the group described in any one of (1) to (7) above Nonaqueous electrolyte for electricity storage devices.
(9) An electricity storage device using the nonaqueous electrolytic solution according to any one of (1) to (8) above.
(10) The livestock device according to (9), 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, the non-aqueous electrolyte for electrical storage devices, such as a lithium secondary battery excellent in the favorable initial characteristic and cycling characteristics, is provided.

Hereinafter, the nonaqueous electrolytic solution of the present invention and the electricity storage device using the same will be described in detail.
<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 (CF ₂ HCF ₂ CH ₂ OCF ₂ CF ₂ H), 1,1,2,2-tetrafluoroethyl-2,2 , 3,3,3-pentafluoro-propyl ether _{(CF 3 CF 2 CH 2 OCF} 2 CF 2 H), ethoxy-2,2,2-trifluoro-ethoxy - ethane _{(CF 3 CH 2 OCH 2 CH} 2 OCH 2 CH _And fluorine-substituted ethers such as ₃ ). These can be used individually by 1 type or in combination of 2 or more types.

  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 a chain carbonate having 3 to 9 carbon atoms in total. 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. Of these, R ₁ and R ₂ are preferably hydrogen (the compound of (I) is 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 other various 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 total carbon atoms) include γ-butyrolactone, γ-valerolactone, γ-caprolactone, ε-caprolactone, and the like. 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, propionic acid. Mention may be made of methyl, ethyl propionate, propionate-n-propyl, propionate-isopropyl, propionate-n-butyl, propionate isobutyl, propionate-t-butyl. 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 preferable.

  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 ) Alkylsulfonic acid imide salts, perfluoroalkylsulfonic acid methide salts 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.

<Boric acid compound>
The nonaqueous electrolytic solution of the present invention contains a boric acid compound composed of tetraboric acid or a salt thereof, or metaboric acid or a salt thereof.
As the salt of tetraboric acid and the salt of metaboric acid, a compound soluble in a non-aqueous solvent is preferable. As long as it dissolves, the type of the salt is not limited. For example, alkali metal salts such as lithium, sodium and potassium; polyvalent metal salts such as calcium, magnesium, manganese and iron; tetramethylammonium, tetraethylammonium, tetrapropylammonium, Ammonium salts such as tetrabutylammonium; imidazolium salts such as dimethylimidazolium, dimethylimidazolium, and ethylmethylimidazolium; pyrididium salts such as methylpyridium and ethylpyridium can be used. Among the above, alkali metal salts such as lithium, sodium and potassium are preferable.

  The content of the boric acid compound in the nonaqueous electrolytic solution of the present invention is preferably 0.0001 to 10% by weight, more preferably 0.001 to 2% by weight, particularly preferably 0.01 to 1% by weight. is there. If the concentration is less than 0.0001% by weight, 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, which is not preferable.

<Second additive substance>
In the nonaqueous electrolytic solution of the present invention, for the purpose of improving the life performance and resistance performance of the electricity storage device, it can be used in combination with a second additive substance in addition to the boric acid compound. The second additive substance is not particularly limited as long as the purpose can be exhibited. For example, the following are mentioned.
Succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride or rhohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, phenylsuccinic anhydride Carboxylic acid anhydrides such as
Ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, propene sultone, methyl methanesulfonate, methylene methane disulfonic acid, ethylene methane disulfonic acid, busulfan, sulfolane, sulfolene, dimethyl sulfone, diphenyl sulfone, methyl phenyl sulfone , Sulfur-containing compounds such as dibutyl disulfide, dicyclohexyl disulfide, tetramethylthiuram monosulfide, N, N-dimethylmethanesulfonamide, N, N-diethylmethanesulfonamide; lithium acetate, lithium propinate lithium oxalate, lithium malonate, Carboxylates such as lithium difluoromalonate, lithium succinate, lithium tetrafluorosuccinate, lithium adipate, lithium glutarate; methanesulfo Lithium, sulfonic acid salts of lithium trifluoromethane menthane sulfonic _{acid; 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 , 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 , boron salts such as LiBF (CO ₂ CF ₃ ) ₃ , LiB (CO ₂ CH ₃ ) ₄ , LiB (CO ₂ CF ₃ ) ₄ ; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3 -Nitrogen-containing compounds such as methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, N-methylsuccinimide; hydrocarbon compounds such as heptane, octane, cycloheptane; fluorobenzene, di Fluorine-containing aromatic compounds such as fluorobenzene, hexafluorobenzene and benzotrifluoride can be used. Of these, carboxylic acid anhydrides, sulfur-containing compounds, carboxylates, sulfonates, or boron salts are preferred.

  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%.

  The nonaqueous electrolytic solution for an electricity storage device of the present invention essentially comprises a nonaqueous solvent, a lithium salt dissolved in the nonaqueous solvent, tetraboric acid or a salt thereof, or a boric acid compound composed of metaboric acid or a salt thereof. When producing such a nonaqueous electrolytic solution of the present invention, (1) a method of first dissolving a lithium salt as an electrolyte in a nonaqueous solvent and adding the boric acid compound later, (2) the above method in a nonaqueous solvent There are a method in which a boric acid compound is first dissolved and a lithium salt that becomes an electrolyte later is added, and (3) a method in which a lithium salt that becomes an electrolyte and the boric acid compound are simultaneously added to a non-aqueous solvent. Any of the above (1) to (3) may be used, and among these, (1) is preferable from the viewpoint of the solubility of the boric acid compound in the nonaqueous solvent and the stability of the nonaqueous electrolytic solution.

  A second additive substance may be further added to the nonaqueous electrolytic solution for an electricity storage device of the present invention. A second additive material can be added. The order of addition is not particularly limited, but when adding carboxylates, sulfonates, boron salts and the like, it is preferable to add them after the boric acid compound.

<Power storage device>
The non-aqueous electrolyte of the present invention can be 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 is a double layer. Will describe a typical lithium ion secondary battery.

  As the negative electrode active material constituting the negative electrode, carbon materials capable of doping / de-doping lithium ions, metallic lithium, lithium-containing alloys, silicon capable of being alloyed with lithium, silicon alloys, tin, Tin alloy, tin oxide capable of doping / de-doping lithium ions, silicon oxide, transition metal oxide capable of doping / de-doping lithium ions, doping / desorption of lithium ions Any of the transition metal nitrogen compounds which can be doped, 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), a composite oxide of lithium and one or more transition metals (lithium transition metal composite oxide), or a transition metal atom that is a main component of these lithium transition metal composite oxides. Composite oxides partially substituted with other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, Yb, FeS ₂ , TiS ₂ , chalcogenide of transition elements such as V ₂ 0 ₅ , MoO ₃ , MoS ₂ or polymers such as polyacetylene and polypyrrole can be used. Possible lithium transition metal composite oxides and metal composite oxide materials in which transition metal atoms are partially substituted are preferred.

  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 liquid.
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. it can.

  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.

<Preparation of electrolytes 1-1 to 1-8>
As a reference electrolyte 1-1, a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and fluoroethylene carbonate (FEC) (volume mixing ratio is 30: 65: 5), LiPF6 as a lithium salt is 1 mol / liter. It was prepared by containing and dissolving at a concentration of 1 liter.
Next, a predetermined amount of the compound shown in Table 1 was added to the reference electrolyte solution 1-1 to prepare electrolyte solutions 1-2 to 1-8.

<Preparation of electrolytic solutions 2-1 to 2-10>
As a reference electrolyte solution 2-1, a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and fluoroethylene carbonate (FEC) (volume mixing ratio is 30: 65: 5), and 1 mol of LiPF ₆ as a lithium salt After adding to a concentration of 1 / liter, 0.5% vinylene carbonate (VC) was added and dissolved.
Next, a predetermined amount of the compounds shown in Table 2 was added to this reference electrolyte solution 2-1, to prepare electrolyte solutions 2-2 to 2-10.

<Production of battery>
A flat wound electrode group in which 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 through a separator, and non-aqueous electrolysis A battery cell having a shape of width 30 mm × height 30 mm × thickness 2.0 mm in which the liquid was housed in a case was produced.
The positive electrode is composed of 5% by weight of polyvinylidene fluoride as a binder, 4% by weight of acetylene black as a conductive agent, and positive electrode active material LiNi _0.5 Mn _{0. 0 as} a lithium-nickel-manganese-cobalt composite oxide powder _. N-methylpyrrolidone was added to a positive electrode mixture obtained by mixing ₃ Co _0.2 O ₂ 91% by weight with N-methylpyrrolidone, and this was applied to both sides of an aluminum foil current collector having a thickness of 18 μm. 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 weight of artificial graphitizable carbon powder, 2.0% by weight of styrene butadiene rubber (SBR) as a binder and 2.2% by weight 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 a liquid cell inlet, and after reducing the pressure, the inlet was sealed.
b. In the state which kept the sealed battery cell in 45 degreeC atmosphere, after charging at 4.4 mA to 4.4V, it discharged at 8 mA to 3.0V.
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 evaluation At 25 ° C., the battery was charged to 50% SOC, and discharged in each environment at 0.2 C, 0.5 C, 1.0 C, and 2.0 C for 10 seconds to obtain a DC resistance value. .
b. Resistance increase rate (%)
From the initial DC resistance value obtained by the above resistance evaluation method and the DC resistance value after performing cycle evaluation under a predetermined condition, the rate of increase in resistance was determined by the following formula (1).
Resistance increase rate (%) = ((DC resistance value after cycle test-initial DC resistance value)
/ Initial DC resistance value) x 100 (1)
c. Capacity retention rate After charging at a 1C rate in a 45 ° C atmosphere, discharging was performed at a 1C rate in the same atmosphere, and the discharge capacity value was taken as the initial capacity value. Next, 300 times were repeated under the same conditions, and the discharge capacity value at the 300th time was taken as the post-cycle capacity value. The capacity retention rate was determined from the initial capacity value and the post-cycle capacity value using the following formula.
Capacity retention rate (%) = (Capacity value after cycle / Initial capacity value) × 100 (2)

<Examples 1-5>
Using the non-aqueous electrolytes 1-1 to 1-8 shown in Table 1 above, using the above battery production procedure, the laminated batteries of Examples 1 to 6 and Comparative Examples 1 and 2 were produced. Table 3 shows the results obtained for the respective DC resistance values in an atmosphere of 25 ° C. and −20 ° C.

  As shown in Table 3, the addition of lithium tetraborate and lithium metaborate is effective in reducing DC resistance. Particularly, the resistance reduction effect is remarkable in a low temperature environment.

<Examples 7 to 14>
Using the non-aqueous electrolytes of 2-1 to 10 shown in Table 2, the laminated batteries of Examples 7 to 14 and Comparative Example 3 were produced by using the above battery production procedure, and at 25 ° C. in an atmosphere. The initial resistance value was determined.
Next, charging and discharging were repeated 300 times at a 1C rate in an atmosphere of 45 ° C., and after obtaining an initial capacity value and a post-cycle discharge capacity value after 300 times, a DC resistance value after a cycle test was obtained in the same manner. The resistance increase rate and the capacity maintenance rate were obtained, respectively, and the results are shown in Table 4.

  As shown in Table 4, compared with Comparative Example 3, Examples 7 to 15 have a resistance reduction effect and a resistance increase suppression effect. In addition, the addition of lithium tetraborate is effective in improving the cycle retention rate. Furthermore, there is a further improvement in capacity retention when combined with other additives.

  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 (10)

  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 tetraboric acid or a salt thereof, or metaboric acid or a salt thereof A nonaqueous electrolytic solution for an electricity storage device, comprising a boric acid compound comprising a salt.   2. The tetraboric acid salt or metaboric acid salt is an alkali metal salt, polyvalent metal salt, ammonium salt, quaternary ammonium salt, imidazolium salt, or pyridinium salt that is soluble in a non-aqueous solvent. A nonaqueous electrolytic solution for an electricity storage device according to 1.   The nonaqueous electrolytic solution for an electricity storage device according to claim 1, wherein the salt of tetraboric acid or the salt of metaboric acid is an alkali metal salt.   The nonaqueous electrolytic solution for an electricity storage device according to any one of claims 1 to 3, wherein the tetraboric acid compound is contained in an amount of 0.0001 to 10% by weight.   The nonaqueous electrolytic solution for an electricity storage device according to any one of claims 1 to 4, wherein the nonaqueous solvent contains a chain carbonate ester, a saturated cyclic carbonate ester, and an unsaturated cyclic carbonate ester.   The non-aqueous solvent contains 30 to 80% by weight, 10 to 50% by weight, and 0.01 to 5% by weight of chain carbonate, saturated cyclic carbonate, and unsaturated cyclic carbonate, respectively. Item 6. A nonaqueous electrolytic solution for an electricity storage device according to Item 5.   Furthermore, the nonaqueous water for electrical storage devices of any one of Claims 1-6 containing the 2nd additive consisting of a carboxylic anhydride, carboxylate, a sulfonate, a sulfur-containing compound, or a boron salt. Electrolytic solution. The lithium salt is LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , 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 at least one lithium salt selected from the group of LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) 8. Nonaqueous electrolysis for an electricity storage device according to claim 1. liquid.   The electrical storage device which uses the nonaqueous electrolyte solution in any one of Claims 1-8.   The livestock device according to claim 9, wherein the electricity storage device is a lithium secondary battery.