JP7544641B2 - Nonaqueous electrolyte and power storage device using same - Google Patents

Description

The present invention relates to a non-aqueous electrolyte that can improve the capacity retention rate after cycle testing and an electricity storage device using the same.

In recent years, power storage devices, particularly lithium batteries, have been widely used in small electronic devices such as mobile phones and laptop computers, electric vehicles, and for power storage. The batteries in these electronic devices and vehicles deteriorate over long periods of use, making it necessary to replace them. For this reason, there is a demand for lithium batteries that can suppress deterioration due to repeated charging and discharging, in other words, have good cycle characteristics. In this specification, the term lithium battery is used as a concept that also includes so-called lithium ion secondary batteries.

A lithium battery is mainly composed of a positive electrode and a negative electrode containing a material capable of absorbing and releasing lithium, and a non-aqueous electrolyte solution made of a lithium salt and a non-aqueous solvent, and carbonates such as ethylene carbonate (EC) and propylene carbonate (PC) are used as the non-aqueous solvent.
In addition, as the negative electrode, metallic lithium, metal compounds (such as simple metals, oxides, and alloys with lithium) capable of absorbing and releasing lithium, and carbon materials are known. In particular, lithium batteries using carbon materials such as coke, artificial graphite, and natural graphite, and silicon materials capable of absorbing and releasing lithium, have been widely put to practical use.

For example, in lithium batteries that use highly crystallized carbon materials such as natural graphite or artificial graphite as the negative electrode material, the solvent in the nonaqueous electrolyte is reduced and decomposed on the surface of the negative electrode during charging, generating decomposition products and gases that inhibit the desired electrochemical reactions of the battery, resulting in a decrease in cycle characteristics. In addition, lithium batteries that use lithium metal or its alloys, or metal elements or oxides such as tin or silicon as the negative electrode material have a high initial capacity, but become pulverized during cycling, which accelerates the reduction and decomposition of the nonaqueous solvent compared to negative electrodes made of carbon materials, resulting in a significant decrease in battery performance such as battery capacity and cycle characteristics. If these decomposition products of the nonaqueous solvent further accumulate, lithium cannot be smoothly absorbed and released into the negative electrode, and cycle characteristics are likely to decrease.

Attempts have been made to improve cycle characteristics by surface treating the negative electrode. For example, methods of coating the negative electrode surface with a carbon precursor compound using chemical vapor deposition or the sol-gel method have problems such as low uniformity of coating on the negative electrode surface or high environmental impact of waste liquid used for coating. Patent Document 1 describes a method that improves the uniformity of the negative electrode surface coating with a relatively low environmental impact, in which a carbon precursor compound is dissolved in liquid carbon dioxide and the negative electrode material is sintered at a high temperature of several hundred degrees.

U.S. Patent Publication: US2017/0149061 A1

The present invention aims to provide a non-aqueous electrolyte that can improve the capacity retention rate after cycle testing in an electricity storage device, and an electricity storage device using the same.

The inventors of the present invention have conducted extensive research into a method for coating the surface of a negative electrode that does not require the high-temperature sintering process described in Patent Document 1, and have discovered that coating the surface of the negative electrode with a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent can improve the capacity retention rate of an electricity storage device after cycle testing, thus completing the present invention.

That is, the present invention provides the following (1) or (2).

(1) A nonaqueous electrolyte for an electricity storage device, in which an electrolyte salt is dissolved in a nonaqueous solvent, the nonaqueous electrolyte containing a compound represented by the following general formula (I):

（式中、Ｇは単糖残基または２～１０個の単糖単位を含む多糖類残基を表すが、Ｇは糖由来の水酸基は含有しない。Ｒ^１は炭素数１～８のアルキル基を表し、Ｒ^２は少なくとも１つの水素原子がフッ素原子で置換されていても良い炭素数１～８のアルキル基を表し、ｍは０または１を表し、ｎは１以上の整数を表し、ｍ＋ｎ≧２である。）

(In the formula, G represents a monosaccharide residue or a polysaccharide residue containing 2 to 10 monosaccharide units, but G does not contain a hydroxyl group derived from a sugar. ^R1 represents an alkyl group having 1 to 8 carbon atoms, ^R2 represents an alkyl group having 1 to 8 carbon atoms in which at least one hydrogen atom may be substituted with a fluorine atom, m represents 0 or 1, n represents an integer of 1 or more, and m+n≧2.)

(2) An electricity storage device comprising a nonaqueous electrolyte solution in which an electrolyte salt is dissolved in a nonaqueous solvent, the nonaqueous electrolyte solution being the nonaqueous electrolyte solution described in (1) above.

The present invention provides a nonaqueous electrolyte that can improve the capacity retention rate after cycle testing in an electricity storage device, and an electricity storage device using the same.

The present invention relates to a non-aqueous electrolyte and an electricity storage device using the same.

[Non-aqueous electrolyte]
The nonaqueous electrolyte of the present invention is a nonaqueous electrolyte for an electricity storage device, which is characterized in that the nonaqueous electrolyte contains an electrolyte salt dissolved in a nonaqueous solvent and contains a compound represented by general formula (I) above.

The reason why the nonaqueous electrolyte of the present invention improves the cycle characteristics of an electricity storage device is not necessarily clear, but is thought to be as follows.
One of the factors that cause the cycle characteristics of the power storage device to decrease is that the decomposition products of the non-aqueous solvent accumulate on the negative electrode, making it difficult to smoothly absorb and release lithium into and from the negative electrode. It is believed that the formation of a coating derived from the compound represented by the general formula (I) of the present invention on the negative electrode suppresses the reaction with the non-aqueous solvent on the negative electrode, thereby improving the cycle characteristics. In addition, in a system using a negative electrode (Si negative electrode) containing silicon as a negative electrode active material, since Si and oxygen atoms have a strong interaction, the compound represented by the general formula (I) has multiple oxygen atoms in the molecule, and the oxygen atoms derived from sugar strongly interact with Si on the surface of the negative electrode to form a coating, which is believed to improve the cycle characteristics.

The compound contained in the nonaqueous electrolyte of the present invention is represented by the following general formula (I).

（式中、Ｇは単糖残基または２～１０個の単糖単位を含む多糖類残基を表すが、Ｇは糖由来の水酸基は含有しない。Ｒ^１は炭素数１～８のアルキル基を表し、Ｒ^２は少なくとも１つの水素原子がフッ素原子で置換されていても良い炭素数１～８のアルキル基を表し、ｍは０または１を表し、ｎは１以上の整数を表し、ｍ＋ｎ≧２である。）

(In the formula, G represents a monosaccharide residue or a polysaccharide residue containing 2 to 10 monosaccharide units, but G does not contain a hydroxyl group derived from a sugar. ^R1 represents an alkyl group having 1 to 8 carbon atoms, ^R2 represents an alkyl group having 1 to 8 carbon atoms in which at least one hydrogen atom may be substituted with a fluorine atom, m represents 0 or 1, n represents an integer of 1 or more, and m+n≧2.)

In the general formula (I), G represents a monosaccharide residue or a polysaccharide residue containing 2 to 10 monosaccharide units, but does not contain a hydroxyl group derived from a sugar. Specific examples of G include the following monosaccharide residues or polysaccharide residues.
In the following specific examples, the numbers in parentheses represent the sum of m and n in the above general formula (I).

[Monosaccharide residue]
Specific examples of monosaccharide residues include aldotriose (2), ketotriose (2), isosorbide (2), isomannide (2), erythrulose (3), erythrose (3), deoxyribose (3), ribose (4), arabinose (4), apiose (4), xylose (4), lyxose (4), ribulose (4), xylulose (4), fucose (4), rhamnose (4), allose (5), altrose (5), glucose (5), mannose (5), gulose (5), idose (5), galactose (5), talose (5), psicose (5), fructose (5), sorbose (5), tagatose (5), and sedoheptulose (6) residues.

[Polysaccharide residue]
Specific examples of polysaccharide residues include sucralose (5), lactosediamine (6), hyalobiuronic acid (6), trehalosamine (7), lactosamine (7), primeverose (7), rutinose (7), scillabiose (7), vicianose (7), trehalose (8), isotrehalose (8), neotrehalose (8), kojibiose (8), nigerose (8), maltose (8), maltulose (8), and isomaltose. Residues of disaccharides such as sucrose (8), isomaltulose (8), sophorose (8), laminarabiose (8), cellobiose (8), cellobionic acid (8), gentiobiose (8), lactose (8), lactobionic acid (8), lactulose (8), melibiose (8), neolactose (8), sucrose (saccharose) (8), turanose (8), galactosucrose (8), maltitol (9), and lactitol (9); trisaccharide residues such as maltotriose (9), solatriose (10), cellotriose (11), gentianose (11), isomaltotriose (11), isopanose (11), maltotriose (11), manninotriose (11), melezitose (11), panose (11), planteose (11), raffinose (11), and umbelliferose (11); lycotetraose (13), maltotetraose (14), Examples of such saccharides include tetrasaccharide residues such as stachyose (14), pentasaccharide residues such as maltopentaose (17) and verbascose (17), hexasaccharide residues such as maltohexaose (20), and cyclic oligosaccharide residues such as α-cycloadenosine (12), β-cycloadenosine (14), α-cyclodextrin (18), β-cyclodextrin (21), γ-cyclodextrin (24), and δ-cyclodextrin (27).

Among these, G is preferably a monosaccharide residue or a polysaccharide residue containing 2 to 4 monosaccharide units, more preferably a monosaccharide residue or a disaccharide residue, even more preferably a monosaccharide residue or a disaccharide residue having 4 to 12 carbon atoms, and most preferably a glucose residue, a ribose residue, a sucrose residue, or an isomannide residue.

In the formula, R ¹ represents an alkyl group having 1 to 8 carbon atoms. Specific examples of the alkyl group having 1 to 8 carbon atoms include linear alkyl groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, and n-octyl groups, branched alkyl groups such as isopropyl, isobutyl, sec-butyl, tert-butyl, tert-amyl, and 2-ethylhexyl groups, and cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl groups. Among these, methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, and isopropyl groups are preferred, and methyl, ethyl, n-propyl, and isopropyl groups are most preferred.

R ² represents an alkyl group having 1 to 8 carbon atoms in which at least one hydrogen atom may be substituted with a fluorine atom. Specific examples of the alkyl group having 1 to 8 carbon atoms in which at least one hydrogen atom may be substituted with a fluorine atom include linear alkyl groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, and n-octyl groups, branched alkyl groups such as isopropyl, isobutyl, sec-butyl, tert-butyl, tert-amyl, and 2-ethylhexyl groups, cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl groups, and fluoromethyl, difluoromethyl, trifluoromethyl, 2-fluoroethyl, 2,2-difluoroethyl, 2,2,2-trifluoroethyl, 3-fluoropropyl, 3,3-difluoropropyl, 3,3,3-trifluoropropyl, 2,2,3,3-tetrafluoropropyl, and tetrafluoropropyl groups. Preferred examples of the alkyl group include those in which a portion of the hydrogen atoms has been substituted with a fluorine atom, such as a trifluoropropyl group or a 2,2,3,3,3-pentafluoropropyl group. Among these, an alkyl group having 1 to 4 carbon atoms in which at least one hydrogen atom may be substituted with a fluorine atom and selected from a methyl group, an ethyl group, an n-propyl group, an n-butyl group, a trifluoromethyl group, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethyl group, an isopropyl group, an isobutyl group, a sec-butyl group and a tert-butyl group is preferred, an alkyl group having 1 to 4 carbon atoms selected from a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an isopropyl group, an isobutyl group, a sec-butyl group and a tert-butyl group or a trifluoromethyl group is more preferred, and a methyl group, an ethyl group or a trifluoromethyl group is most preferred.

m represents 0 or 1, n represents an integer of 1 or more, m+n≧2, and it is preferable that m is 0 and n is 2 to 10, or m is 1 and n is 2 to 9. When m is an integer of 2 or more, two or more R ² may be the same or different, but it is preferable that all of the two or more R ² are the same.

Specific examples of the general formula (I) are described above, but the present invention is not limited to these. The anomeric carbon may have a mixture of α and β configurations.

Among the above compounds, A1 to A72 are preferable, A1 to A60 are more preferable, and A1 to A12 and A37 to A60 are particularly preferable. In the above, for example, compound A1 is a compound in which G is an α-D-glucose residue, R ² = CH ₃ , m = 0, and n = 5 in general formula (I), and compound A2 is a compound in which G is an α-D-glucose residue, R ² = CH ₂ CH ₃ , m = 0, and n = 5 in general formula (I).

The compound represented by general formula (I) can be synthesized, for example, by a method in which a compound represented by R ¹ OH is reacted with a corresponding monosaccharide or polysaccharide in an acidic environment to introduce a group represented by R ¹ -O-; a method in which a compound represented by R ² COOH or (R ² CO) ₂ O is reacted with a corresponding monosaccharide or polysaccharide to esterify the monosaccharide or polysaccharide and introduce a group represented by R ² -C(═O)O-; or a method in which these methods are appropriately combined.

The term "residue" refers to a partial structure of a compound, and a sugar residue refers to a partial structure obtained by removing a hydroxyl group from the chemical structure of a sugar. For example, the monosaccharide residue of β-D-glucose is represented by the structure excluding the hydroxyl group (-OH) in the following formula (II). In this case, the oxygen atom in the hydroxyl group (-OH) in the following formula (II) is usually an oxygen atom derived from a monosaccharide or polysaccharide, but even in such cases, the structure excluding the hydroxyl group (-OH) is considered to be the sugar residue in this specification.

In the non-aqueous electrolyte of the present invention, the content of the compound represented by the general formula (I) contained in the non-aqueous electrolyte is preferably 0.01 to 10% by mass relative to the total amount of the non-aqueous electrolyte, since this improves the capacity retention rate after cycle testing. Also, 0.05% by mass or more is more preferable, 0.1% by mass or more is even more preferable, and 0.5% by mass or more is particularly preferable. Also, 3% by mass or less is more preferable, 2% by mass or less is even more preferable, and 1.5% by mass or less is particularly preferable.

In the non-aqueous electrolyte of the present invention, the capacity retention rate after cycle testing is further improved by combining the compound represented by the general formula (I) with the non-aqueous solvent, electrolyte salt, and other additives described below.

[Non-aqueous solvent]
As used herein, the term "solvent" refers to a substance for dissolving a solute.
The non-aqueous solvent used in the non-aqueous electrolyte of the present invention is preferably one or more selected from cyclic carbonates, chain esters, lactones, ethers and amides. In order to synergistically improve cycle characteristics, it is preferable to include a chain ester, more preferably to include a chain carbonate, and most preferably to include both a cyclic carbonate and a chain carbonate.

The term "chain ester" is used as a concept that includes chain carbonates and chain carboxylic acid esters.

The cyclic carbonate may be one or more selected from ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 4-fluoro-1,3-dioxolan-2-one (FEC), trans- or cis-4,5-difluoro-1,3-dioxolan-2-one (hereinafter collectively referred to as "DFEC"), vinylene carbonate (VC), vinylethylene carbonate (VEC) and 4-ethynyl-1,3-dioxolan-2-one (EEC), and more preferably one or more selected from EC, PC, FEC, VC and EEC.

The content of the cyclic carbonate is not particularly limited, but is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, based on the total amount of the nonaqueous electrolyte, and is preferably 90% by mass or less, more preferably 70% by mass or less, even more preferably 50% by mass or less, and most preferably 40% by mass or less, since this further improves the capacity retention rate after cycle testing without impairing Li-ion permeability.

In addition, among the cyclic carbonates, it is preferable to use at least one of cyclic carbonates having an unsaturated bond such as a carbon-carbon double bond or a carbon-carbon triple bond, or a fluorine atom, since this improves cycle characteristics, and it is more preferable to use both a cyclic carbonate having an unsaturated bond such as a carbon-carbon double bond or a carbon-carbon triple bond, and a cyclic carbonate having a fluorine atom. As the cyclic carbonate having an unsaturated bond such as a carbon-carbon double bond or a carbon-carbon triple bond, VC, VEC, or EEC is more preferable, and as the cyclic carbonate having a fluorine atom, FEC or DFEC is more preferable.

The content of the cyclic carbonate having an unsaturated bond of a carbon-carbon double bond or a carbon-carbon triple bond is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more, based on the total amount of the nonaqueous electrolyte, and is preferably 8% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, since this further improves the capacity retention rate after cycle testing without impairing Li ion permeability.

The content of the cyclic carbonate having fluorine atoms is preferably 0.05% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more, based on the total amount of the nonaqueous electrolyte, and is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, and most preferably 15% by mass or less, which is preferable because it further improves the capacity retention rate after cycle testing without impairing Li-ion permeability.

These solvents may be used alone, or in combination of two or more, the capacity retention rate after cycle testing is further improved, and it is particularly preferable to use three or more in combination. Suitable combinations of these cyclic carbonates include EC and PC, EC and VC, PC and VC, VC and FEC, EC and FEC, PC and FEC, FEC and DFEC, EC and DFEC, PC and DFEC, VC and DFEC, VEC and DFEC, VC and EEC, EC and EEC, EC and PC and VC, EC and PC and FEC, EC and VC and FEC, EC and VC and VEC, EC and EEC and FEC, PC and VC and FEC, EC and VC and DFEC, PC and VC and DFEC, EC and PC and VC and FEC, or EC and PC and VC and DFEC. Of the above combinations, the combinations of EC and VC, EC and FEC, PC and FEC, EC and PC and VC, EC and PC and FEC, EC and VC and FEC, EC and VC and EEC, EC and EEC and FEC, PC and VC and FEC, or EC and PC and VC and FEC are more preferred.

Suitable examples of the chain ester include one or more asymmetric chain carbonates selected from methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, and ethyl propyl carbonate; one or more symmetric chain carbonates selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, and dibutyl carbonate; pivalic acid esters such as methyl pivalate, ethyl pivalate, and propyl pivalate; and one or more chain carboxylic acid esters selected from methyl propionate, ethyl propionate, propyl propionate, methyl acetate, and ethyl acetate (EA).

Among the chain esters, chain esters having a methyl group selected from dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, methyl propionate, methyl acetate, and ethyl acetate are preferred, and chain carbonates having a methyl group are particularly preferred.

The content of the chain ester in the nonaqueous solvent used in the nonaqueous electrolyte of the present invention is not particularly limited, but is preferably in the range of 5 to 90 mass% based on the total amount of the nonaqueous electrolyte. If the content is 5 mass% or more, the viscosity of the nonaqueous electrolyte does not become too high, and it is more preferably 10 mass% or more, even more preferably 30 mass% or more, and particularly preferably 50 mass% or more. In addition, if the content is preferably 90 mass% or less, more preferably 85 mass% or less, the electrical conductivity of the nonaqueous electrolyte is reduced, and there is little risk of a decrease in the capacity retention rate after cycle testing, so the above range is preferable.

From the viewpoint of improving the capacity retention rate after cycle testing, the ratio of cyclic carbonate to chain ester is preferably 10:90 to 50:50 (mass ratio), and particularly preferably 30:70 to 40:60.

Other non-aqueous solvents include one or more selected from cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, and 1,4-dioxane; chain ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane; amides such as dimethylformamide; sulfones such as sulfolane; and lactones such as γ-butyrolactone (GBL), γ-valerolactone, and α-angelicalactone.

The above-mentioned other non-aqueous solvents are usually used in combination to achieve appropriate physical properties. Suitable combinations include, for example, a combination of a cyclic carbonate, a chain ester, and a lactone, or a combination of a cyclic carbonate, a chain ester, and an ether, and the combination of a cyclic carbonate, a chain ester, and a lactone is more preferred, and among lactones, it is even more preferred to use GBL.

The content of other non-aqueous solvents is preferably 1% by mass or more, more preferably 2% by mass or more, and is preferably 40% by mass or less, more preferably 30% by mass or less, and particularly preferably 20% by mass or less, based on the total amount of the non-aqueous electrolyte. Within this concentration range, there is little risk of a decrease in electrical conductivity or a decrease in the capacity retention rate after cycle testing due to decomposition of the solvent.

For the purpose of further improving the capacity retention rate after cycle testing, it is preferable to further add other additives to the non-aqueous electrolyte.
Specific examples of the other additives include the following compounds (A) to (J).

(A) One or more nitriles selected from acetonitrile, propionitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile and sebaconitrile.

(B) Aromatic compounds having a branched alkyl group, such as tert-butylbenzene, tert-amylbenzene, or 1-fluoro-4-tert-butylbenzene, or aromatic compounds such as cyclohexylbenzene, biphenyl, terphenyl (o-, m-, or p-isomer), fluorobenzene, methyl phenyl carbonate, ethyl phenyl carbonate, or diphenyl carbonate.

(C) One or more isocyanate compounds selected from methyl isocyanate, ethyl isocyanate, butyl isocyanate, phenyl isocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, 1,4-phenylene diisocyanate, 2-isocyanatoethyl acrylate, and 2-isocyanatoethyl methacrylate.

(D) One or more triple bond-containing compounds selected from 2-propynyl methyl carbonate, 2-propynyl acetate, 2-propynyl formate, 2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, 2-propynyl 2-(methanesulfonyloxy)propionate, di(2-propynyl)oxalate, 2-butyne-1,4-diyl dimethanesulfonate, and 2-butyne-1,4-diyl diformate.

(E) One or more S=O group-containing compounds selected from sultones such as 1,3-propane sultone (PS), 1,3-butane sultone, 2,4-butane sultone, 1,4-butane sultone, 1,3-propene sultone, or 2,2-dioxide-1,2-oxathiolane-4-yl acetate, cyclic sulfites such as ethylene sulfite, sulfonic acid esters such as butane-2,3-diyl dimethanesulfonate, butane-1,4-diyl dimethanesulfonate, or methylenemethane disulfonate, and vinyl sulfone compounds such as divinyl sulfone and 1,2-bis(vinylsulfonyl)ethane or bis(2-vinylsulfonylethyl)ether.

(F) The cyclic acetal compound is not particularly limited as long as it has an "acetal group" in the molecule. Specific examples include cyclic acetal compounds such as 1,3-dioxolane, 1,3-dioxane, and 1,3,5-trioxane.

(G) One or more phosphorus-containing compounds selected from trimethyl phosphate, tributyl phosphate, trioctyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, ethyl 2-(diethoxyphosphoryl)acetate, and 2-propynyl 2-(diethoxyphosphoryl)acetate.

The type of (H) carboxylic acid anhydride is not particularly limited as long as it is a compound having a "C(=O)-O-C(=O) group" in the molecule. Specific examples include chain carboxylic acid anhydrides such as acetic anhydride or propionic anhydride, or cyclic acid anhydrides such as succinic anhydride, maleic anhydride, 3-allyl succinic anhydride, glutaric anhydride, itaconic anhydride, or 3-sulfo-propionic anhydride.

(J) The phosphazene compound is not particularly limited as long as it is a compound having an "N=P-N group" in the molecule. Specific examples include cyclic phosphazene compounds such as methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, and ethoxyheptafluorocyclotetraphosphazene.

Among the above, it is preferable to include at least one selected from (A) nitrile, (B) aromatic compound, and (C) isocyanate compound, since this further improves the capacity retention rate after cycle testing.

Of the (A) nitriles, one or more selected from succinonitrile, glutaronitrile, adiponitrile, and pimelonitrile are more preferred.

(B) Among the aromatic compounds, one or more selected from biphenyl, terphenyl (o-, m-, p-isomer), fluorobenzene, cyclohexylbenzene, tert-butylbenzene, and tert-amylbenzene are more preferred, and one or more selected from biphenyl, o-terphenyl, fluorobenzene, cyclohexylbenzene, and tert-amylbenzene are particularly preferred.

(C) Of the isocyanate compounds, one or more selected from hexamethylene diisocyanate, octamethylene diisocyanate, 2-isocyanatoethyl acrylate, and 2-isocyanatoethyl methacrylate are more preferred.

The content of the compounds (A) to (C) is preferably 0.01 to 7 mass% based on the total amount of the non-aqueous electrolyte. In this range, the coating is formed sufficiently without becoming too thick, and the capacity retention rate after cycle testing can be improved. The content is more preferably 0.05 mass% or more based on the total amount of the non-aqueous electrolyte, particularly preferably 0.1 mass% or more, and more preferably 5 mass% or less, particularly preferably 3 mass% or less.

In addition, it is preferable to include at least one selected from (D) a triple bond-containing compound, (E) a cyclic or chain-like S=O group-containing compound selected from sultones, cyclic sulfites, sulfonic acid esters, and vinyl sulfones, (F) a cyclic acetal compound, (G) a phosphorus-containing compound, (H) a cyclic acid anhydride, and (J) a cyclic phosphazene compound, since this can improve the capacity retention rate after cycle testing.

(D) As the triple bond-containing compound, one or more selected from 2-propynyl methyl carbonate, 2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, di(2-propynyl)oxalate, and 2-butyne-1,4-diyl dimethanesulfonate are preferred, and one or more selected from 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, di(2-propynyl)oxalate, and 2-butyne-1,4-diyl dimethanesulfonate are more preferred.

(E) Suitable examples of cyclic S=O group-containing compounds include one or more selected from 1,3-propane sultone (PS), 1,3-butane sultone, 1,4-butane sultone, 2,4-butane sultone, 1,3-propene sultone, 2,2-dioxido-1,2-oxathiolan-4-yl acetate, methylene methane disulfonate, and ethylene sulfite.

As the (E) chain-like S=O group-containing compound, one or more selected from butane-2,3-diyl dimethanesulfonate, butane-1,4-diyl dimethanesulfonate, dimethyl methanedisulfonate, pentafluorophenyl methanesulfonate, divinyl sulfone, and bis(2-vinylsulfonylethyl)ether are preferred.

Among the cyclic or chain-like S=O group-containing compounds, one or more selected from 1,3-propane sultone, 1,4-butane sultone, 2,4-butane sultone, 2,2-dioxido-1,2-oxathiolan-4-yl acetate, pentafluorophenyl methanesulfonate, and divinyl sulfone are more preferred.

(F) As the cyclic acetal compound, 1,3-dioxolane or 1,3-dioxane is preferred, and 1,3-dioxane is more preferred.

(G) As the phosphorus-containing compound, ethyl 2-(diethoxyphosphoryl)acetate or 2-propynyl 2-(diethoxyphosphoryl)acetate is preferred, with 2-propynyl 2-(diethoxyphosphoryl)acetate being more preferred.

(H) As the cyclic acid anhydride, succinic anhydride, maleic anhydride, or 3-allyl succinic anhydride is preferred, and succinic anhydride or 3-allyl succinic anhydride is more preferred.

(J) As the cyclic phosphazene compound, a cyclic phosphazene compound such as methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, or phenoxypentafluorocyclotriphosphazene is preferred, and methoxypentafluorocyclotriphosphazene or ethoxypentafluorocyclotriphosphazene is more preferred.

The content of each of the compounds (D) to (J) is preferably 0.001 to 5 mass% based on the total amount of the non-aqueous electrolyte. Within this range, the coating is formed sufficiently without becoming too thick, and the capacity retention rate after cycle testing can be further improved. The content is more preferably 0.01 mass% or more based on the total amount of the non-aqueous electrolyte, particularly preferably 0.1 mass% or more, and more preferably 3 mass% or less, particularly preferably 2 mass% or less.

In addition, for the purpose of further improving the capacity retention rate after the cycle test, it is preferable that the nonaqueous electrolyte solution further contains one or more lithium salts selected from the group consisting of lithium salts having an oxalic acid skeleton, lithium salts having a phosphate skeleton, and lithium salts having an S═O group.
Specific examples of the lithium salt include at least one lithium salt having an oxalic acid skeleton selected from lithium bis(oxalato)borate [LiBOB], lithium difluoro(oxalato)borate [LiDFOB], lithium tetrafluoro(oxalato)phosphate [LiTFOP], and lithium difluorobis(oxalato)phosphate [LiDFOP], lithium salts having a phosphoric acid skeleton such as LiPO ₂ F ₂ and Li ₂ PO ₃ F, and lithium trifluoro((methanesulfonyl)oxy)borate [LiTFMSB], lithium pentafluoro((methanesulfonyl)oxy)phosphate [LiPFMSP], lithium methylsulfate [LMS], lithium ethylsulfate [LES], lithium 2,2,2-trifluoroethylsulfate [LFES], and FSO ₃ Li having one or more S=O groups, and more preferably one or more lithium salts selected from LiBOB, LiDFOB, LiTFOP, _LiDFOP , _LiPO2F2 , LiTFMSB, LMS, LES, LFES, and _FSO3Li .

The proportion of each of the lithium salts in the non-aqueous electrolyte is preferably 0.01% by mass or more and 8% by mass or less with respect to the total amount of the non-aqueous electrolyte. If it is in this range, the capacity retention rate after cycle testing can be further improved. It is more preferably 0.1% by mass or more, even more preferably 0.3% by mass or more, particularly preferably 0.4% by mass or more, and more preferably 6% by mass or less, even more preferably 3% by mass or less.

(Electrolyte Salt)
As the electrolyte salt used in the present invention, the following lithium salts are preferably mentioned.
Specific examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiBF ₄ , and LiClO ₄ , lithium salts containing a chain-like fluorinated alkyl group such as LiN(SO ₂ F) ₂ [LiFSI], LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiC(SO ₂ CF ₃ ) ₃ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₃ (C ₂ F ₅ ) ₃ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (iso-C ₃ F ₇ ) ₃ , and LiPF ₅ (iso-C ₃ F ₇ ), and (CF ₂ ) _{2 .} Preferred examples of the lithium salt include lithium salts having a cyclic fluorinated alkylene chain, such as (SO ₂ ) ₂ NLi or (CF ₂ ) ₃ (SO ₂ ) ₂ NLi. Preferred examples of the lithium salt include at least one type of lithium salt selected from these. These may be used alone or in combination of two or more types.
Among these, one or more selected from LiPF ₆ , LiBF ₄ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ and LiN(SO ₂ F) ₂ [LiFSI] are preferred, and LiPF ₆ is most preferred. The concentration of each electrolyte salt is usually preferably 4 mass% or more, more preferably 8 mass% or more, and even more preferably 11 mass% or more, based on the total amount of the nonaqueous electrolyte. Also, it is preferably 28 mass% or less, more preferably 23 mass% or less, and even more preferably 20 mass% or less.
In addition, as a suitable combination of these electrolyte salts, it is preferable that the non-aqueous electrolyte contains LiPF ₆ and further contains at least one lithium salt selected from LiBF ₄ , LiN(SO ₂ CF ₃ ) ₂ and LiN(SO ₂ F) ₂ [LiFSI], and a combination containing LiPF ₆ and further containing LiFSI is more preferable, and the ratio of each lithium salt other than LiPF ₆ to the total amount of the non-aqueous electrolyte is preferably 0.01% by mass or more, since the capacity retention rate after the cycle test is improved. In addition, it is preferable that the ratio is 15% by mass or less with respect to the total amount of the non-aqueous electrolyte, since there is little concern that the capacity retention rate after the cycle test will decrease. More preferably, it is 0.1% by mass or more, particularly preferably 0.3% by mass or more with respect to the total amount of the non-aqueous electrolyte, most preferably 0.6% by mass or more, more preferably 13% by mass or less, particularly preferably 11% by mass or less, and most preferably 9% by mass or less.

[Production of non-aqueous electrolyte]
The non-aqueous electrolyte of the present invention can be obtained, for example, by mixing the non-aqueous solvent and adding thereto the electrolyte salt and the compound represented by the general formula (I) to the non-aqueous electrolyte.
In this case, it is preferable that the compounds to be added to the non-aqueous solvent and non-aqueous electrolyte used are previously purified to have as few impurities as possible, within the range that does not significantly reduce productivity.

The nonaqueous electrolyte of the present invention can be used in the first to third electricity storage devices described below, and not only liquid but also gelled nonaqueous electrolytes can be used. Furthermore, the nonaqueous electrolyte of the present invention can also be used for solid polymer electrolytes. In particular, it is preferable to use it for the first electricity storage device (i.e., for lithium batteries) or the third electricity storage device (i.e., for lithium ion capacitors) that use lithium salt as the electrolyte salt, more preferably for lithium batteries, and most preferably for lithium secondary batteries.

[First power storage device (lithium battery)]
In this specification, the term "lithium battery" is a general term for lithium primary batteries and lithium secondary batteries. In addition, in this specification, the term "lithium secondary battery" is used as a concept including so-called lithium ion secondary batteries. The lithium battery, which is the first power storage device of the present invention, is composed of a positive electrode, a negative electrode, and the non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent. The components such as the positive electrode and the negative electrode other than the non-aqueous electrolyte can be used without any particular limitation.
For example, a composite metal oxide containing one or more elements selected from the group consisting of cobalt, manganese, and nickel and lithium is used as a positive electrode active material for a lithium secondary battery. These positive electrode active materials can be used alone or in combination of two or more.
Examples of such lithium composite metal _oxides include _LiCoO2 , LiCo1 _{- xMxO2} (wherein M is one or more elements selected from Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, and Cu, 0.001≦x≦ _0.05 ), LiMn2O4 _{, LiNiO2 , LiCo1} -xNixO2 (0.01< _x < _{1 ) , LiCo1} / _{3Ni1 / 3Mn1 /3O2 , LiNi0.5Mn0.3Co0.2O2 , LiNi0.6Mn0.2Co0.2O2 , LiNi0.8Mn0.1 Preferred} examples _of the _oxide include _{one or} more selected from _Co0.1O2 , _{LiNi0.8Co0.15Al0.05O2} , a solid solution of _Li2MnO3 and _LiMO2 (M is a transition metal such as Co, Ni, Mn, Fe, etc.), and LiNi1 _/ 2Mn3 _{/ 2O4} , and more preferred are two or more selected from _these . Also, _LiCoO2 and _LiMn2O4 , _{LiCoO2 and LiNiO2} , and _LiMn2O4 and _LiNiO2 may be used in combination.

Furthermore, a lithium-containing olivine-type phosphate can also be used as the positive electrode active material. In particular, a lithium-containing olivine-type phosphate containing at least one selected from iron, cobalt, nickel, and manganese is preferable. Specific examples thereof include _LiFePO4 , _LiCoPO4 , _LiNiPO4 , and _LiMnPO4 .
These lithium-containing olivine-type phosphates may be partially substituted with other elements, and part of the iron, cobalt, nickel, and manganese may be substituted with one or more elements selected from Co, Mn, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W, and Zr, or may be coated with a compound or carbon material containing these other elements. Among these, _LiFePO4 or _LiMnPO4 is preferred.
The lithium-containing olivine-type phosphate can also be used by mixing with, for example, the above-mentioned positive electrode active material.

There are no particular limitations on the conductive agent for the positive electrode, so long as it is an electron-conductive material that does not undergo chemical changes. Examples include graphite such as natural graphite (e.g., flake graphite) and artificial graphite, and carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. Graphite and carbon black may also be mixed appropriately. The amount of conductive agent added to the positive electrode mixture is preferably 1 to 10% by mass, and more preferably 2 to 5% by mass.

The positive electrode is prepared by mixing the positive electrode active material with a conductive agent such as acetylene black or carbon black, and a binder such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a copolymer of styrene and butadiene (SBR), a copolymer of acrylonitrile and butadiene (NBR), carboxymethyl cellulose (CMC), or an ethylene propylene diene terpolymer, adding a high boiling point solvent such as 1-methyl-2-pyrrolidone to the mixture and kneading it to form a positive electrode mixture, applying the positive electrode mixture to a collector such as aluminum foil or a stainless steel lath plate, drying, pressurizing, and then heat-treating the mixture at a temperature of about 50° C. to 250° C. for about 2 hours under vacuum.
The density of the positive electrode excluding the current collector is usually 1.5 g/ ^cm3 or more, and in order to further increase the battery capacity, it is preferably 2 g/ ^cm3 or more, more preferably 3 g/ ^cm3 or more, and even more preferably 3.6 g/ ^cm3 or more, and is preferably 4 g/ ^cm3 or less.

Examples of the negative electrode active material for lithium secondary batteries include lithium metal, lithium alloys, and carbon materials capable of absorbing and releasing lithium (e.g., graphitizable carbon, non-graphitizable carbon with a (002) plane spacing of 0.37 nm (nanometers) or more, and graphite with a (002) plane spacing of 0.34 nm or less), tin (simple substance), tin compounds, silicon (simple substance), silicon compounds, and _{lithium titanate compounds such as Li4Ti5O12 ,} which may be used alone or in combination of two or more.
Among these, in terms of the ability to absorb and release lithium ions, it is more preferable to use highly crystalline carbon materials such as artificial graphite and natural graphite, and it is particularly preferable to use carbon materials having a graphite-type crystal structure in which the lattice spacing (d 002 ) of the ( ₀₀₂ ) lattice plane is 0.340 nm or less, particularly 0.335 to 0.337 nm.
By using artificial graphite particles having a block structure in which a plurality of flat graphitic fine particles are aggregated or bonded to each other non-parallel, or graphite particles obtained by repeatedly applying mechanical actions such as compression force, friction force, shear force, etc. to spheroidized flake-like natural graphite particles, the density of the portion excluding the negative electrode current collector is press-molded to a density of 1.5 g/ ^cm3 or more, and the ratio I(110)/I(004) of the peak intensity I(110) of the (110) plane of the graphite crystal to the peak intensity I(004) of the (004) plane obtained by X-ray diffraction measurement of the negative electrode sheet is preferably 0.01 or more, since this further improves the amount of metal eluted from the positive electrode active material and improves the charged storage characteristics, and is more preferably 0.05 or more, and even more preferably 0.1 or more. Moreover, since excessive treatment may result in a decrease in crystallinity and a decrease in the discharge capacity of the battery, the upper limit of I(110)/I(004) is preferably 0.5 or less, and more preferably 0.3 or less.
In addition, it is preferable that the highly crystalline carbon material (core material) is coated with a carbon material having a lower crystallinity than the core material, since this leads to a further improved capacity retention rate after cycle testing. The crystallinity of the coating carbon material can be confirmed by TEM.
When a highly crystalline carbon material is used, it tends to react with the non-aqueous electrolyte during charging, increasing the interface resistance and decreasing the capacity retention rate after a cycle test. However, the lithium secondary battery according to the present invention has a good capacity retention rate after a cycle test.

Metal compounds capable of absorbing and releasing lithium as the negative electrode active material include compounds containing at least one metal element such as Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Mg, Sr, and Ba. These metal compounds may be used in any form, such as a simple substance, an alloy, an oxide, a nitride, a sulfide, a boride, or an alloy with lithium, but a simple substance, an alloy, an oxide, or an alloy with lithium is preferred because it can increase the capacity. Among these, compounds containing at least one element selected from Si, Ge, and Sn are preferred, and compounds containing at least one element selected from Si and Sn are particularly preferred because they can increase the capacity of the battery.

In addition, metal oxides containing titanium atoms capable of absorbing and releasing lithium as negative electrode active materials can be mentioned. These metal oxides containing titanium have small expansion and contraction during charging and discharging, and are flame retardant, so they are preferable in terms of improving the safety of the battery. Among them, those containing Li ₄ Ti ₅ O ₁₂ are preferable because they improve the battery characteristics.

The negative electrode can be produced by kneading a conductive agent, a binder, and a high boiling point solvent in the same manner as in the production of the positive electrode described above to form a negative electrode mixture, applying this negative electrode mixture to a copper foil or the like current collector, drying, pressurizing and molding, and then heat treating the mixture in a vacuum at a temperature of about 50° C. to 250° C. for about 2 hours.
The density of the negative electrode excluding the current collector is usually 1.1 g/ ^cm3 or more, and in order to further increase the battery capacity, it is preferably 1.3 g/ ^cm3 or more, particularly preferably 1.5 g/ ^cm3 or more, and is preferably 2 g/ ^cm3 or less.

There is no particular limitation on the structure of the lithium battery, and a coin-type battery having a single-layer or multi-layer separator, a cylindrical battery, a square battery, a laminate battery, etc. can be used.
The battery separator is not particularly limited, but may be a single-layer or multi-layer microporous film, woven fabric, nonwoven fabric, or the like, made of polyolefin such as polypropylene or polyethylene.

[Second Electricity Storage Device (Electric Double Layer Capacitor)]
The second electricity storage device is an electricity storage device that stores energy by utilizing the electric double layer capacitance of the electrolyte and the electrode interface. An example of the present invention is an electric double layer capacitor. Preferred electrode materials used in this electricity storage device are materials containing C atoms or materials containing Si atoms, and specific examples thereof include activated carbon and silicon. The double layer capacitance increases roughly in proportion to the surface area.

[Third Power Storage Device (Lithium Ion Capacitor)]
The third type of power storage device is a power storage device that stores energy by utilizing the intercalation of lithium ions into a negative electrode, which is a carbon material such as graphite or a material containing Si atoms. It is called a lithium ion capacitor (LIC). The positive electrode may be, for example, one that utilizes an electric double layer between an activated carbon electrode and an electrolyte, or one that utilizes a doping/dedoping reaction of a π-conjugated polymer electrode. The electrolyte contains at least a lithium salt such as _LiPF6 .
The lithium secondary battery of the present invention has excellent cycle characteristics even when the end-of-charge voltage is 4.2 V or more, particularly 4.3 V or more, and further has good characteristics even when the end-of-charge voltage is 4.4 V or more. The end-of-discharge voltage can be usually 2.8 V or more, further 2.5 V or more, but the lithium secondary battery of the present invention can be 2.0 V or more. There is no particular limitation on the current value, but it is usually used in the range of 0.1 to 30 C. Furthermore, the lithium battery of the present invention can be charged and discharged at -40 to 100°C, preferably -10 to 80°C.

In the present invention, measures to prevent an increase in the internal pressure of a lithium battery can be taken by providing a safety valve to the battery lid or by making cuts in components such as the battery can or gasket. In addition, as a safety measure to prevent overcharging, a current cut-off mechanism that detects the internal pressure of the battery and cuts off the current can be provided on the battery lid.

Each solvent and electrolyte salt were mixed in a fixed amount to prepare a reference electrolyte solution as shown in Table 1. The unit M of the concentration of the electrolyte salt in Table 1 indicates mol/L. The composition of the reference electrolyte solution as shown in mass ratio is 31.4 mass% EC, 56.1 mass% MEC, and 12.5 mass% _LiPF6 .
A non-aqueous electrolyte solution was prepared by adding 1.0% by mass of the compound represented by the general formula (I) shown in Table 1 to the reference electrolyte solution. For example, in Example 1, the non-aqueous electrolyte solution was prepared by adding 1.0% by mass of the above-mentioned compound A1 (i.e., a compound in which G is an α-D-glucose residue, R ² = CH ₃ , m = 0, and n = 5 in the general formula (I)) to the reference electrolyte solution.

Examples 1 to 5, Comparative Example 1
[Preparation of lithium ion secondary battery 1]
LiCoO ₂ (LCO); 94 mass% and acetylene black (conductive agent); 3 mass% were mixed, and added to a solution in which polyvinylidene fluoride (binder); 3 mass% had been dissolved in 1-methyl-2-pyrrolidone in advance, and mixed to prepare a positive electrode mixture paste. This positive electrode mixture paste was applied to one side of an aluminum foil (current collector), dried, pressurized, and cut out to a predetermined size to prepare a positive electrode sheet. The density of the part excluding the current collector of the positive electrode was 3.6 g / cm ^3. In addition, 85 mass% of artificial graphite (negative electrode active material) and 10 mass% of silicon monoxide (negative electrode active material) were mixed, and 1.7 mass% of carboxymethylcellulose (thickener) and 3.3 mass% of butadiene copolymer (binder) were added to water and mixed to prepare a negative electrode mixture paste.
This negative electrode mixture paste was applied to both sides of a copper foil (current collector), dried, pressed, and cut into a predetermined size to prepare a negative electrode sheet.
The density of the negative electrode excluding the current collector was 1.5 g/cm ^3. The positive electrode sheet, the microporous polyethylene film separator, and the negative electrode sheet were laminated in this order, and a nonaqueous electrolyte solution having the composition shown in Table 1, which was prepared by mixing the respective components at room temperature, was added to prepare a laminated battery.

[Evaluation of cycle characteristics]
The battery prepared by the above method was charged in a thermostatic chamber at 45° C. at a constant current of 1 C to a final voltage of 4.2 V, and then discharged at a constant current of 1 C to a discharge voltage of 2.7 V, forming one cycle, and this cycle was repeated until 200 cycles were reached. The capacity retention rate after 200 cycles was calculated using the following formula.
Capacity retention rate (%)=(discharge capacity at 200th cycle/discharge capacity at 1st cycle)×100
The battery characteristics are shown in Table 1.

In Table 1 above, the capacity retention rate after 200 cycles was improved in Examples 1 to 5 compared to Comparative Example 1. From this result, it can be said that the nonaqueous electrolyte of the present invention can improve the capacity retention rate after cycle testing without discharging waste liquid or high-temperature sintering, which are environmentally burdensome, as a negative electrode surface treatment.

By using the nonaqueous electrolyte of the present invention, it is possible to obtain an electricity storage device with excellent capacity retention after cycle testing while reducing the environmental impact.

Claims (7)

The nonaqueous electrolyte for an electricity storage device contains a compound represented by the following general formula (I), the nonaqueous electrolyte comprising an electrolyte salt dissolved in a nonaqueous solvent:

(In the formula, G represents a monosaccharide residue or a polysaccharide residue containing 2 to 10 monosaccharide units, but G does not contain a hydroxyl group derived from a sugar. ^R1 represents an alkyl group having 1 to 8 carbon atoms, ^R2 represents an alkyl group having 1 to 8 carbon atoms in which at least one hydrogen atom may be substituted with a fluorine atom, m represents 0 or 1, n represents an integer of 1 or more, and m+n≧2.) The nonaqueous electrolyte for an electricity storage device according to claim 1, wherein G in the general formula (I) is a monosaccharide residue or a disaccharide residue having 4 to 12 carbon atoms. 3. The nonaqueous electrolyte for an electricity storage device according to claim 1, wherein R ² in the general formula (I) is an alkyl group having 1 to 4 carbon atoms or a trifluoromethyl group, m is 0, and n is 2 to 10. The nonaqueous electrolyte for an electricity storage device according to claim 1 or 2, wherein in the general formula (I), R ¹ is a methyl group, R ² is an alkyl group having 1 to 4 carbon atoms or a trifluoromethyl group, m is 1, and n is 2 to 9. The nonaqueous electrolyte for an electricity storage device according to any one of claims 1 to 4, containing 0.01 to 10 mass % of the compound represented by the general formula (I). The nonaqueous electrolyte for an electricity storage device according to claim 1 , wherein the nonaqueous electrolyte contains LiPF ₆ . An electricity storage device comprising a negative electrode containing Si atoms, a nonaqueous electrolyte in which an electrolyte salt is dissolved in a nonaqueous solvent, and a positive electrode, the nonaqueous electrolyte being the nonaqueous electrolyte according to any one of claims 1 to 6.