Nonaqueous electrolyte and power storage device using the same

Abstract

This non-aqueous electrolyte solution for a power storage device comprises: a non-aqueous solvent with an electrolyte salt dissolved therein; and a phosphonate ester represented by general formula (I). Also provided is a power storage device using this non-aqueous electrolyte solution. (In the formula, R1 is a C2-6 alkenyl group or a C3-6 alkynyl group; R2 and R3 are each independently a C3-6 alkynyl group.)

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous electrolyte and an electricity storage device using the same. [Background technology]

[0002] In recent years, electricity storage devices, especially lithium secondary batteries, have been widely used as power sources for small electronic devices such as mobile phones and laptop computers, as well as for electric vehicles and power storage. Because these electronic devices and vehicles may be used in a wide range of temperatures, such as the high temperatures of midsummer and the low temperatures of extreme cold, electricity storage devices are required to have well-balanced improved electrochemical properties over a wide temperature range. Reducing CO2 emissions is an urgent priority, particularly in order to prevent global warming. Among environmentally friendly vehicles equipped with energy storage devices such as lithium secondary batteries and capacitors, hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs) are expected to become more widespread as soon as possible. Because automobiles travel long distances, they may be used in a wide range of temperatures, from extremely hot tropical regions to extremely cold regions. Therefore, these on-board energy storage devices, in particular, are required to maintain their electrochemical properties even when used in a wide temperature range, from high to low temperatures. In this specification, the term lithium secondary battery is used as a concept that also includes so-called lithium ion secondary batteries.

[0003] A lithium secondary battery is mainly composed of a positive electrode and a negative electrode containing a material capable of absorbing and releasing lithium ions, and a non-aqueous electrolyte solution consisting 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. Known negative electrodes include metallic lithium, metal compounds (simple metals, metal oxides, alloys with lithium, etc.) that can occlude and release lithium ions, and carbon materials. In particular, lithium secondary batteries that use carbon materials that can occlude and release lithium ions, such as coke, artificial graphite, and natural graphite, have been widely put to practical use.

[0004] For example, in lithium secondary batteries that use highly crystalline carbon materials such as natural graphite or artificial graphite as the negative electrode material, the solvent in the nonaqueous electrolyte undergoes reductive decomposition on the negative electrode surface during charging. The decomposition products and gases generated by this reductive decomposition inhibit the desired electrochemical reactions of the battery, resulting in a deterioration in the cycle performance of the lithium secondary battery. Furthermore, accumulation of decomposition products of the nonaqueous solvent hinders smooth absorption and desorption of lithium ions into and from the negative electrode, which can lead to a deterioration in the electrochemical performance when the battery is used over a wide temperature range. Furthermore, it is known that lithium secondary batteries using lithium metal, its alloys, or metals such as tin or silicon, or metal oxides as negative electrode materials have high initial capacity but undergo pulverization during cycle use, which accelerates the reductive decomposition of the non-aqueous solvent compared to negative electrodes made of carbon materials, resulting in a significant decrease in battery performance such as battery capacity and cycle characteristics. Furthermore, the pulverization of these negative electrode materials and the accumulation of decomposition products of the non-aqueous solvent make it difficult for lithium ions to be absorbed and released into the negative electrode, which leads to a decrease in electrochemical characteristics when used over a wide temperature range.

[0005] On the other hand, in lithium secondary batteries using, for example, LiCoO2, LiMn2O4, LiNiO2, LiFePO4, etc. as the positive electrode, the nonaqueous solvent in the nonaqueous electrolyte undergoes partial oxidative decomposition locally at the interface between the positive electrode material and the nonaqueous electrolyte in a charged state. The decomposition products and gases generated by this oxidative decomposition inhibit the desired electrochemical reactions of the battery, and it has been found that the electrochemical characteristics of the lithium secondary battery also deteriorate when used over a wide temperature range.

[0006] As described above, the decomposition products and gases generated when the non-aqueous electrolyte decomposes on the positive and negative electrodes impede the smooth movement of lithium ions and cause battery swelling, resulting in reduced battery performance. Despite this, electronic devices incorporating lithium secondary batteries are becoming increasingly multifunctional, leading to increased power consumption. Therefore, the capacity of lithium secondary batteries is being increasingly increased, and the volume occupied by the non-aqueous electrolyte within the battery is being reduced in order to increase the density of the electrodes and reduce the amount of wasted space within the battery. Therefore, even a small amount of decomposition of the non-aqueous electrolyte can easily degrade the electrochemical characteristics when used over a wide temperature range.

[0007] Patent Document 1 describes that by adding at least one phosphorus compound selected from the group consisting of specific phosphine oxides, phosphonate esters, and phosphinate esters to a non-aqueous electrolyte solution, it is possible to suppress the deterioration of battery characteristics in a high-temperature environment. Patent Document 2 describes that the discharge capacity retention rate and resistance value retention rate at 25° C. are improved by adding a specific phosphate ester or phosphonate ester to a non-aqueous electrolyte solution. Patent Document 3 describes that the energy efficiency of a lithium-air battery is significantly improved by combining an organic solvent that is a specific phosphate ester and / or phosphonate ester with lithium nitrate having a concentration within a specific range. Patent Document 4 describes that adding an alkynyl compound having a specific structure in which alkynyl groups are bonded via specific groups to a non-aqueous electrolyte solution improves the cycle characteristics at low and high temperatures and the load characteristics after high-temperature charged storage. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-55031 [Patent Document 2] Japanese Patent Publication No. 2020-72023 [Patent Document 3] International Publication No. 2020 / 141578 [Patent Document 4] International Publication No. 2011 / 096450 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a nonaqueous electrolyte solution that can improve the discharge capacity retention rate and gas generation suppression effect of an electricity storage device after high-temperature storage, and an electricity storage device using the same. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above problems and have found that adding a compound in which a specific alkynyl group is introduced into a phosphonate ester having a specific alkenyl group or alkynyl group to a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent specifically improves the discharge capacity retention rate and gas generation suppression effect of an electricity storage device after high-temperature storage, and have completed the present invention. Such effects are not at all suggested in Patent Documents 1 to 4.

[0011] That is, the present invention provides the following (1) to (17).

[0012] (1) A non-aqueous electrolyte solution for an electricity storage device, which is a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent, characterized by containing a phosphonate ester represented by the following general formula (I): [ka] (In the formula, R 1 represents an alkenyl group having 2 to 6 carbon atoms or an alkynyl group having 3 to 6 carbon atoms, and R 2 and R 3 each independently represents an alkynyl group having 3 to 6 carbon atoms. (2) The nonaqueous electrolyte solution for an electricity storage device according to (1) above, wherein the content of the phosphonate ester represented by general formula (I) is 0.001% by mass or more and 5% by mass or less. (3) R in the general formula (I) 1 The nonaqueous electrolyte solution for an electricity storage device according to (1) or (2) above, wherein is a vinyl group, an allyl group, a 1-methylallyl group, a 2-methylallyl group, a crotyl group, a butenyl group, or a propynyl group. (4) R in the general formula (I) 1 is a vinyl group or an allyl group. (5) R in the general formula (I) 2 and R 3 are each independently a 2-propynyl group, a 2-butynyl group, a 3-butynyl group, a 1-methyl-2-propynyl group, a 1,1-dimethyl-2-propynyl group, a 1-ethyl-1-methyl-2-propynyl group, or a 4-pentynyl group. (6) The non-aqueous electrolyte solution for an electricity storage device according to any one of (1) to (5), further comprising one or more lithium salts (a) selected from the group consisting of lithium salts having a phosphate skeleton and lithium salts having an S(=O) group. (7) The nonaqueous electrolyte solution for an electricity storage device according to (6) above, wherein the content of the lithium salt (a) is 0.01% by mass or more and 8% by mass or less. (8) The non-aqueous electrolyte solution for an electricity storage device according to any one of (1) to (7), wherein the electrolyte salt comprises one or more lithium salts (b) selected from the group consisting of LiPF6, LiBF4, LiN(SO2CF3)2, LiN(SO2C2F5)2 and LiN(SO2F)2 [LiFSI]. (9) The nonaqueous electrolyte solution for an electricity storage device according to (8) above, wherein the content of the lithium salt (b) is 4% by mass or more and 28% by mass or less. (10) The non-aqueous electrolyte solution for an electricity storage device according to any one of (1) to (9), wherein the phosphonate ester comprises one or more selected from the group consisting of di-2-propynyl vinylphosphonate, di-2-propynyl allylphosphonate, di-2-propynyl 1-methylallylphosphonate, di-2-propynyl 2-methylallylphosphonate, di-2-propynyl crotylphosphonate, di-2-propynyl butenylphosphonate, and di-2-propynyl propynylphosphonate. (11) The non-aqueous electrolyte solution for an electricity storage device according to any one of (1) to (10) above, wherein the non-aqueous solvent contains at least one selected from the group consisting of saturated cyclic carbonates, chain esters, lactones, ethers, and amides. (12) The non-aqueous electrolyte solution for an electricity storage device according to any one of (1) to (11), wherein the non-aqueous solvent contains a saturated cyclic carbonate and a chain ester, and the mass ratio of the cyclic carbonate to the chain ester is 10:90 to 50:50. (13) The nonaqueous electrolyte solution for an electricity storage device according to any one of (1) to (12) above, further comprising at least one of a cyclic carbonate having an unsaturated bond and a cyclic carbonate having a fluorine atom. (14) The nonaqueous electrolyte solution for an electricity storage device according to (13) above, wherein the content of the cyclic carbonate having an unsaturated bond is 0.05% by mass or more and 8% by mass or less. (15) An electricity storage device comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte solution in which an electrolyte salt is dissolved in a nonaqueous solvent, wherein the nonaqueous electrolyte solution is the nonaqueous electrolyte solution according to any one of (1) to (14). (16) The electricity storage device according to (15) above, wherein the electricity storage device is a lithium battery. (17) The electricity storage device according to (15) or (16) above, wherein the ratio of the atomic concentration of Ni to the atomic concentration of all transition metal elements in the positive electrode active material in the positive electrode is 50 atomic % or more. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a nonaqueous electrolyte solution and an electricity storage device using the same that can improve the discharge capacity retention rate and gas generation suppression effect of an electricity storage device after high-temperature storage. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention relates to a non-aqueous electrolyte and an electricity storage device using the same.

[0015] [Non-aqueous electrolyte] The nonaqueous electrolyte of the present invention is a nonaqueous electrolyte for an electricity storage device, which comprises an electrolyte salt dissolved in a nonaqueous solvent, and is characterized by containing a phosphonic acid ester represented by the general formula (I) above.

[0016] The reason why the nonaqueous electrolyte solution of the present invention can improve the discharge capacity retention rate and gas generation suppression effect of an electricity storage device after high-temperature storage is not entirely clear, but is thought to be as follows. The compound represented by general formula (I) used in the present invention is a phosphonate ester having a specific alkenyl group or alkynyl group, and therefore, reductive decomposition is promoted. Furthermore, the compound represented by general formula (I) has R 1 Alkenyl or alkynyl groups specific to R 2 and R 3 The polymerizable compound has specific alkynyl groups, which accelerates the polymerization reaction and forms a strong, heat-resistant coating. This prevents the coating from becoming brittle even in high-temperature environments and suppresses decomposition of the solvent, potentially improving both the discharge capacity retention rate and gas generation suppression effect of the energy storage device after high-temperature storage.

[0017] (phosphonate esters) The phosphonate ester contained in the non-aqueous electrolyte solution of the present invention is represented by the following general formula (I).

[0018] [ka] (In the formula, R1 represents an alkenyl group having 2 to 6 carbon atoms or an alkynyl group having 3 to 6 carbon atoms, and R 2 and R 3 each independently represents an alkynyl group having 3 to 6 carbon atoms.

[0019] In the general formula (I), R 1 is preferably a vinyl group, an allyl group, a 1-methylallyl group, a 2-methylallyl group, a crotyl group, a butenyl group, or a propynyl group, more preferably a vinyl group, an allyl group, a 1-methylallyl group, a 2-methylallyl group, or a crotyl group, even more preferably a vinyl group, an allyl group, or a crotyl group, still more preferably a vinyl group or an allyl group, and particularly preferably an allyl group.

[0020] In the general formula (I), R 2 and R 3 each independently represents an alkynyl group having 3 to 6 carbon atoms. Specific examples thereof include linear alkynyl groups such as a 2-propynyl group, a 2-butynyl group, a 3-butynyl group, a 4-pentynyl group, and a 4-heptynyl group; and branched alkynyl groups such as a 1-methyl-2-propynyl group, a 1,1-dimethyl-2-propynyl group, a 1-methyl-3-butynyl group, and a 1-methyl-4-pentynyl group. Among these, a 2-propynyl group, a 2-butynyl group, a 3-butynyl group, a 1-methyl-2-propynyl group, a 1,1-dimethyl-2-propynyl group, a 1-ethyl-1-methyl-2-propynyl group, and a 4-pentynyl group are more preferred, and a 2-propynyl group is even more preferred.

[0021] Specific examples of the compound represented by the general formula (I) include the following compounds.

[0022] [ka]

[0023] [ka]

[0024]

change

[0025]

change

[0026] Among the above preferred examples, di-2-propynyl vinylphosphonate (compound 1-1), di-3-butynyl vinylphosphonate (compound 1-4), di-1-methyl-2-propynyl vinylphosphonate (compound 1-6), di-1,1-dimethyl-2-propynyl vinylphosphonate (compound 1-8), di-1-ethyl-1-methyl-2-propynyl vinylphosphonate (compound 1-10), di-2-butynyl vinylphosphonate (compound 1-12), di-2-propynyl allylphosphonate (compound 2-1), di-3-butynyl allylphosphonate (compound 2-4), di-1-methyl-2-propynyl allylphosphonate (compound 2-6), di-1,1-dimethyl-2-propynyl allylphosphonate (compound 2-8), di-1-ethyl-1-methyl-2-propynyl allylphosphonate (compound 2-10), di-2-butynyl allylphosphonate (compound 2-12), di-2-propynyl 1-methylallylphosphonate (compound 3-1), di-2-propynyl 2-methylallylphosphonate (compound 4-1), di-2-propynyl crotylphosphonate (compound 5-1), di-2-propynyl 3-butenylphosphonate (compound 6-1), and di-2-propynyl propynylphosphonate (compound 7-1) are preferred.Among these, di-2-propynyl vinylphosphonate (compound 1-1), di-1-methyl-2-propynyl vinylphosphonate (compound 1-6), di-1,1-dimethyl-2-propynyl vinylphosphonate (compound 1-8), di-1-ethyl-1-methyl-2-propynyl vinylphosphonate (compound 1-10), di-2-butynyl vinylphosphonate (compound 1-12), di-2-propynyl allylphosphonate (compound 2-1), and di-1-methyl-2-propynyl allylphosphonate (compound 2-2) are particularly preferred. 2-6), di-1,1-dimethyl-2-propynyl allylphosphonate (compound 2-8), di-1-ethyl-1-methyl-2-propynyl allylphosphonate (compound 2-10), di-2-propynyl 1-methylallylphosphonate (compound 3-1), di-2-propynyl 2-methylallylphosphonate (compound 4-1), di-2-propynyl crotylphosphonate (compound 5-1), di-2-propynyl butenylphosphonate (compound 6-1), and di-2-propynyl propynylphosphonate (compound 7-2). More preferred are at least one selected from the group consisting of di-2-propynyl vinylphosphonate (compound 1-1), di-2-propynyl allylphosphonate (compound 2-1), di-2-propynyl 1-methylallylphosphonate (compound 3-1), di-2-propynyl 2-methylallylphosphonate (compound 4-1), di-2-propynyl crotylphosphonate (compound 5-1), di-2-propynyl butenylphosphonate (compound 6-1), and di-2-propynyl propynylphosphonate (compound 7-

[0044] More preferred are one or more selected from the group consisting of di-2-propynyl vinylphosphonate (compound 1-1), di-2-propynyl allylphosphonate (compound 2-1), and di-2-propynyl crotylphosphonate (compound 5-1), more preferred are di-2-propynyl vinylphosphonate (compound 1-1) or di-2-propynyl allylphosphonate (compound 2-1), and particularly preferred is di-2-propynyl allylphosphonate (compound 2-1). The non-aqueous electrolyte according to the present invention may contain one or more phosphonate esters represented by the general formula (I).

[0027] The content of the phosphonate ester represented by the general formula (I) in the nonaqueous electrolyte of the present invention is preferably 0.001% by mass or more, and preferably 5% by mass or less, more preferably 2% by mass or less, based on the total amount of the nonaqueous electrolyte (assuming the total amount of the nonaqueous electrolyte is 100% by mass). If the content is 5% by mass or less or 2% by mass or less, there is little risk of excessive film formation on the electrode, resulting in deterioration of high-temperature characteristics. If the content is 0.001% by mass or more, sufficient film formation can be achieved, further improving the discharge capacity retention rate after high-temperature storage. The content is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.15% by mass or more, even more preferably 0.25% by mass or more, even more preferably 0.35% by mass or more, even more preferably 0.55% by mass or more, particularly preferably 0.80% by mass or more, even more preferably 1.5% by mass or less, and even more preferably 1.2% by mass or less.

[0028] (Lithium salt (a)) The nonaqueous electrolyte solution according to the present invention preferably further contains one or more lithium salts (a) selected from the group consisting of lithium salts having a phosphate skeleton and lithium salts having an S(=O group). By further containing the lithium salt (a), the discharge capacity retention rate after high-temperature storage and the gas generation suppression effect can be further improved. Specific examples of the lithium salt (a) include lithium salts having a phosphate skeleton, such as LiPOF and LiPOF; and lithium salts having one or more S(=O) groups selected from the group consisting of 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 FSOLi. It is more preferable that the lithium salt (a) contains one or more lithium salts selected from the group consisting of LiPOF, LiTFMSB, LMS, LES, LFES, and FSOLi, and even more preferable that it contains LiPOF.

[0029] The content of the lithium salt (a) in the non-aqueous electrolyte solution according to the present invention is preferably 0.01% by mass or more and 8% by mass or less, based on the total amount of the non-aqueous electrolyte solution. This range further improves the discharge capacity retention rate after high-temperature storage and the gas generation suppression effect. The content is more preferably 0.1% by mass or more, even more preferably 0.3% by mass or more, and particularly preferably 0.4% by mass or more, based on the total amount of the non-aqueous electrolyte solution, and more preferably 6% by mass or less, even more preferably 3% by mass or less, and particularly preferably 2% by mass or less.

[0030] (electrolyte salt) The electrolyte salt used in the present invention preferably includes the following lithium salt (b). Specific examples of the lithium salt (b) include inorganic lithium salts such as LiPF, LiBF, or LiClO; lithium salts containing a chain-like fluorinated alkyl group such as LiN(SOF)[LiFSI], LiN(SOCF), LiN(SOCF) , LiCFSO, LiC(SOCF), LiPF(CF), LiPF(CF), LiPF(CF), LiPF(iso-CF) and LiPF(iso-CF); and lithium salts having a cyclic fluorinated alkylene chain such as (CF)(SO)NLi and (CF)(SO)NLi, and these may be used in combination. Among these, one or more selected from the group consisting of LiPF6, LiBF4, LiN(SO2CF3)2, LiN(SO2C2F5)2 and LiN(SO2F)2 [LiFSI] are more preferred, and LiPF6 is even more preferred. The content of the lithium salt (b) in the non-aqueous electrolyte according to the present invention is preferably 4% by mass or more, more preferably 9% by mass or more, and even more preferably 13% by mass or more, based on the total amount of the non-aqueous electrolyte, and the upper limit thereof is preferably 28% by mass or less, more preferably 23% by mass or less, and even more preferably 20% by mass or less, based on the total amount of the non-aqueous electrolyte. A preferred combination of these electrolyte salts is one in which the non-aqueous electrolyte contains LiPF6 and at least one lithium salt selected from the group consisting of LiBF4, LiN(SO2CF3)2, and LiN(SO2F)2 [LiFSI]. A combination containing LiPF6 and LiFSI is even more preferred. A content of lithium salts other than LiPF6 in the non-aqueous electrolyte of the present invention is preferably 0.01% by mass or more relative to the total amount of the non-aqueous electrolyte, as this improves the characteristics after high-temperature charged storage (hereinafter also referred to as "high-temperature charged storage characteristics") and also enhances the effect of suppressing gas generation. A content of 11% by mass or less relative to the total amount of the non-aqueous electrolyte is preferred, as this reduces the risk of deterioration of high-temperature charged storage characteristics. The content is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.6% by mass or more, and preferably 10% by mass or less, more preferably 9% by mass or less, even more preferably 6% by mass or less relative to the total amount of the non-aqueous electrolyte.

[0031] (non-aqueous solvent) The nonaqueous solvent used in the nonaqueous electrolyte solution according to the present invention is preferably one or more selected from the group consisting of cyclic carbonates, chain esters, lactones, ethers, and amides. Since the electrochemical properties are synergistically improved over a wide temperature range, it is preferable to contain a chain ester, more preferable to contain a chain carbonate, even more preferable to contain both a cyclic carbonate and a chain ester, and particularly preferable to contain both a cyclic carbonate and a chain carbonate. The term "chain ester" is used as a concept including chain carbonates and chain carboxylic acid esters.

[0032] The cyclic carbonate preferably further contains at least one saturated cyclic carbonate. Examples of the saturated cyclic carbonate include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, and 2,3-butylene carbonate, preferably at least one selected from the group consisting of ethylene carbonate and propylene carbonate, and more preferably ethylene carbonate.

[0033] The content of the cyclic carbonate in the non-aqueous electrolyte according to the present invention is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and is preferably 90% by mass or less, more preferably 70% by mass or less, even more preferably 50% by mass or less, and particularly preferably 40% by mass or less, based on the total amount of the non-aqueous electrolyte. When the content of the cyclic carbonate is equal to or less than the upper limit, the discharge capacity retention rate after high-temperature storage and the gas generation suppression effect are further improved without impairing the Li-ion permeability, which is preferable.

[0034] Furthermore, the nonaqueous electrolyte solution according to the present invention preferably further contains at least one of 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, and more preferably further contains a cyclic carbonate having an unsaturated bond. The nonaqueous electrolyte solution according to the present invention preferably contains such a cyclic carbonate, since this improves the discharge capacity retention rate after high-temperature storage and the gas generation suppression effect. Preferred cyclic carbonates having an unsaturated bond include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), or 4-ethynyl-1,3-dioxolan-2-one (EEC), with vinylene carbonate being more preferred. Preferred cyclic carbonates having a fluorine atom include 4-fluoro-1,3-dioxolan-2-one (FEC) or trans- or cis-4,5-difluoro-1,3-dioxolan-2-one (hereinafter, both are collectively referred to as "DFEC").

[0035] The content of the cyclic carbonate having an unsaturated bond in the nonaqueous electrolyte according to the present invention 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. A content within the above range is preferred because it further improves the discharge capacity retention rate after high-temperature storage and the gas generation suppression effect without impairing Li-ion permeability.

[0036] The content of the fluorine atom-containing cyclic carbonate in the nonaqueous electrolyte according to the present invention is preferably 0.05% by mass or more, more preferably 1% by mass or more, even more preferably 3% by mass or more, and is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, and particularly preferably 15% by mass or less, based on the total amount of the nonaqueous electrolyte. A content within the above range is preferable because it further improves the discharge capacity retention rate after high-temperature storage and the gas generation suppression effect without impairing Li-ion permeability.

[0037] These solvents may be used alone, or in combination of two or more, since the effect of improving electrochemical properties over a wide temperature range is further enhanced, and it is particularly preferred to use a combination of three or more. Preferred 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 VC and EEC, 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, combinations such as 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, with the combination of EC and VC being even more preferred.

[0038] Suitable examples of the chain ester include one or more asymmetric chain carbonates selected from the group consisting of 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 the group consisting of 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 the group consisting of methyl propionate, ethyl propionate, propyl propionate, methyl acetate, and ethyl acetate.

[0039] Among the chain esters, a chain ester having a methyl group selected from the group consisting of dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, methyl propionate, methyl acetate, and ethyl acetate is preferred, a chain carbonate having a methyl group is more preferred, and at least one selected from methyl ethyl carbonate and dimethyl carbonate is even more preferred.

[0040] When chain carbonates are used, it is preferable to use two or more types. It is more preferable to contain both symmetric chain carbonates and asymmetric chain carbonates, and it is even more preferable that the content of the symmetric chain carbonate is greater than that of the asymmetric chain carbonate.

[0041] The content of the chain ester in the non-aqueous electrolyte according to the present invention is not particularly limited, but is preferably 5% by mass or more and 90% by mass or less, based on the total amount of the non-aqueous electrolyte. A content of 5% by mass or more prevents the viscosity of the non-aqueous electrolyte from becoming too high, while a content of 90% by mass or less reduces the risk of the electrical conductivity of the non-aqueous electrolyte decreasing and the cycle characteristics deteriorating. The content is more preferably 10% by mass or more, even more preferably 30% by mass or more, particularly preferably 50% by mass or more, and more preferably 85% by mass or less.

[0042] When the non-aqueous electrolyte solution according to the present invention contains both a cyclic carbonate and a chain ester, the ratio of the cyclic carbonate to the chain ester contained in the non-aqueous electrolyte solution is preferably 10:90 to 50:50 (mass ratio) of cyclic carbonate:chain ester, and more preferably 30:70 to 40:60, from the viewpoint of improving electrochemical properties at high temperatures.

[0043] Suitable examples of other non-aqueous solvents include one or more selected from the group consisting of 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.

[0044] 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, GBL is even more preferred.

[0045] The content of the other non-aqueous solvent 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 even more 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 high-temperature charged storage characteristics due to decomposition of the solvent.

[0046] For the purposes of further improving the high-temperature charged storage characteristics and suppressing gas generation, it is preferable to further add other additives to the non-aqueous electrolyte solution. Specific examples of other additives include the following compounds (A) to (J).

[0047] (A) One or more nitriles selected from the group consisting of nitriles having one cyano group in the molecule, such as acetonitrile, propionitrile, butyronitrile, pentanenitrile, hexanenitrile, decanenitrile, undecanenitrile, dodecanenitrile, cyclohexanecarbonitrile, acrylonitrile, methacrylonitrile, and crotononitrile; nitriles having two cyano groups in the molecule, such as malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, sebaconitrile, methylmalononitrile, ethylmalononitrile, bicyclohexyl-1,1-dicarbonitrile, and 1,2-dicyanobenzene; and nitriles having three cyano groups in the molecule, such as 1,2,3-propanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,3,5-cyclohexanetricarbonitrile, and 1,3,5-benzenetricarbonitrile.

[0048] (B) Aromatic compounds having a branched alkyl group, such as cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, or 1-fluoro-4-tert-butylbenzene; aromatic compounds such as biphenyl, terphenyl (o-, m-, or p-isomer), fluorobenzene, methyl phenyl carbonate, ethyl phenyl carbonate, or diphenyl carbonate. Among the aromatic compounds, one or more selected from the group consisting of biphenyl, terphenyl (o-, m-, p-isomer), fluorobenzene, cyclohexylbenzene, tert-butylbenzene, and tert-amylbenzene are more preferred, and one or more selected from the group consisting of biphenyl, o-terphenyl, fluorobenzene, cyclohexylbenzene, and tert-amylbenzene are even more preferred.

[0049] (C) One or more isocyanate compounds selected from the group consisting of methyl isocyanate, ethyl isocyanate, butyl isocyanate, phenyl isocyanate, vinyl isocyanate, propargyl isocyanate, cyclohexyl isocyanate, phenyl isocyanate, monomethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, 1,4-phenylene diisocyanate, 2-isocyanatoethyl acrylate, 2-isocyanatoethyl methacrylate, 1,3-diisocyanatopropane, carbonyl diisocyanate, 1,4-diisocyanato-2-fluorobutane, and 1,3-bis(isocyanatomethyl)cyclohexane. Among the isocyanate compounds, one or more selected from the group consisting of hexamethylene diisocyanate, octamethylene diisocyanate, 2-isocyanatoethyl acrylate, 2-isocyanatoethyl methacrylate, and 1,3-bis(isocyanatomethyl)cyclohexane are more preferred.

[0050] (D) One or more triple bond-containing compounds selected from the group consisting of 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. The triple bond-containing compound is preferably at least one selected from the group consisting of 2-propynyl methyl carbonate, 2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, di(2-propynyl)oxalate, and 2-butyne-1,4-diyl dimethanesulfonate, and more preferably at least one selected from the group consisting of 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, di(2-propynyl)oxalate, and 2-butyne-1,4-diyl dimethanesulfonate.

[0051] (E) Cyclic sulfonic acid esters such as 1,3-propane sultone, 1,3-butane sultone, 2,4-butane sultone, 1,4-butane sultone, 1,5-pentane sultone, 1-fluoro-1,3-propane sultone, 1-methyl-1,3-propane sultone, 1-propene-1,3-sultone, 2-propene-1,3-sultone, 1-fluoro-1-propene-1,3-sultone, 1-methyl-1-propene-1,3-sultone, methylenemethane disulfonate, ethylene methane disulfonate, 2,2-dioxide-1,2-oxathiolan-4-yl acetate; methyl fluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate, busulfan, methyl methanesulfonyloxyacetate, pentafluorophenyl methanesulfonate, methyl vinylsulfonate, allyl vinylsulfonate, and vinyl sulfonic acid 2-Propynyl, propargyl allylsulfonate, methoxycarbonylmethyl methanedisulfonate, ethoxycarbonylmethyl methanedisulfonate, methoxycarbonylmethyl 1,3-butanedisulfonate, ethoxycarbonylmethyl 1,3-butanedisulfonate, 1-methoxycarbonylethyl 1,3-butanedisulfonate, 1-ethoxycarbonylethyl 1,3-butanedisulfonate, butane-2,3-diyl dimethanesulfonate, butane-1,4-diyl one or more S═O group-containing compounds selected from the group consisting of chain sulfonic acid esters, such as alkyl disulfonic acid esters, e.g., dimethanesulfonate; vinyl sulfone compounds, such as divinyl sulfone, 1,2-bis(vinylsulfonyl)ethane, and bis(2-vinylsulfonylethyl)ether; chain sulfate esters, such as dimethyl sulfate, ethyl methyl sulfate, and diethyl sulfate; cyclic sulfate esters, such as 1,2-ethylene sulfate, 1,2-propylene sulfate, 1,3-propylene sulfate, and 1,2-butylene sulfate; chain sulfite esters, such as dimethyl sulfite, ethyl methyl sulfite, and diethyl sulfite; and cyclic sulfite esters, such as 1,2-ethylene sulfite, 1,2-propylene sulfite, 1,3-propylene sulfite, 1,2-butylene sulfite, and 1-vinyl-1,2-ethylene sulfite.

[0052] The S═O group-containing compound can be classified into cyclic S═O group-containing compounds and chain S═O group-containing compounds, and preferred examples of the cyclic S═O group-containing compounds include one or more compounds selected from the group consisting of 1,3-propane sultone, 1,3-butane sultone, 1,4-butane sultone, 2,4-butane sultone, 1-propene-1,3-sultone, 2,2-dioxide-1,2-oxathiolan-4-yl acetate, methylenemethane disulfonate, 1,2-ethylene sulfate, 1,2-ethylene sulfite, and 1-vinyl-1,2-ethylene sulfite. Among the chain S=O group-containing compounds, preferred are one or more selected from the group consisting of butane-2,3-diyl dimethanesulfonate, butane-1,4-diyl dimethanesulfonate, dimethylmethanedisulfonate, pentafluorophenylmethanesulfonate, divinyl sulfone, and bis(2-vinylsulfonylethyl)ether. Among the cyclic or chain S=O group-containing compounds, more preferred are one or more selected from the group consisting of 1,3-propanesultone, 1,4-butanesultone, 2,4-butanesultone, 1,2-ethylene sulfate, 1,2-ethylene sulfite, 1-vinyl-1,2-ethylene sulfite, 2,2-dioxide-1,2-oxathiolan-4-yl acetate, pentafluorophenylmethanesulfonate, and divinyl sulfone.

[0053] (F) Cyclic acetal compounds having an "acetal group" in the molecule. The type of cyclic acetal compound is not particularly limited as long as it contains 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. The cyclic acetal compound is preferably 1,3-dioxolane or 1,3-dioxane, and more preferably 1,3-dioxane.

[0054] (G) One or more phosphorus-containing compounds selected from the group consisting of trimethyl phosphate, tributyl phosphate, trioctyl phosphate, tris(2,2,2-trifluoroethyl)phosphate, ethyl 2-(diethoxyphosphoryl)acetate, and 2-propynyl 2-(diethoxyphosphoryl)acetate. As the phosphorus-containing compound, ethyl 2-(diethoxyphosphoryl)acetate or 2-propynyl 2-(diethoxyphosphoryl)acetate is preferred, and 2-propynyl 2-(diethoxyphosphoryl)acetate is more preferred.

[0055] (H) Acid anhydrides having a "C(=O)-OC(=O) group," "C(=O)-OS(=O) group," or "S(=O)-OS(=O) group" in the molecule. Specific examples thereof include one or more acid anhydrides selected from the group consisting of acetic anhydride, acrylic anhydride, methacrylic anhydride, cyclohexanecarboxylic anhydride, propynoic anhydride, benzoic anhydride, fluoroacetic anhydride, 4-fluorobenzoic anhydride, acetic propionic anhydride, succinic anhydride, maleic anhydride, citraconic anhydride, 4-fluorosuccinic anhydride, allylsuccinic anhydride, glutaric anhydride, itaconic anhydride, 1,2-oxathiolan-5-one 2,2-dioxide, and 1,2,6-oxadithiane 2,2,6,6-tetraoxide. As the acid anhydride, methacrylic anhydride, succinic anhydride, maleic anhydride, allyl succinic anhydride, and 1,2,6-oxadithiane 2,2,6,6-tetraoxide are preferred, and succinic anhydride, allyl succinic anhydride, and 1,2,6-oxadithiane 2,2,6,6-tetraoxide are more preferred.

[0056] (J) Phosphazene compounds having an "N=PN group" in the molecule. The type of phosphazene compound is not particularly limited as long as it contains an "N=PN group" in the molecule. Specific examples include cyclic phosphazene compounds such as methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, and ethoxyheptafluorocyclotetraphosphazene.

[0057] The cyclic phosphazene compound is preferably a cyclic phosphazene compound such as methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene or phenoxypentafluorocyclotriphosphazene, and more preferably methoxypentafluorocyclotriphosphazene or ethoxypentafluorocyclotriphosphazene.

[0058] (K) The organic compound having an isocyanuric acid skeleton (hereinafter also referred to as "isocyanurate compound") is not particularly limited as long as it is an organic compound having at least one isocyanuric acid skeleton in the molecule. Examples of the organic compound having an isocyanuric acid skeleton include the following compounds.

[0059] [ka]

[0060] In particular, from the viewpoint of forming a stable interface protective coating, an isocyanurate compound having a saturated or unsaturated aliphatic hydrocarbon group which may have a halogen atom is preferred, an isocyanurate compound having an unsaturated aliphatic hydrocarbon group containing a terminal carbon-carbon unsaturated bond is more preferred, and triallyl isocyanurate is even more preferred.

[0061] The silicon-containing compound (L) is not particularly limited as long as it is a compound having at least one silicon atom in the molecule. Examples of silicon-containing compounds include boric acid compounds such as tris(trimethylsilyl) borate, tris(trimethoxysilyl) borate, tris(triethylsilyl) borate, and tris(dimethylvinylsilyl) borate; phosphate compounds such as tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, tris(triphenylsilyl) phosphate, tris(trimethoxysilyl) phosphate, and tris(dimethylvinylsilyl) phosphate; tris(trimethylsilyl) phosphite, tris(triethylsilyl) phosphite, tris(triphenylsilyl) phosphite, tris(trimethoxysilyl) phosphite, and tris(dimethylvinylsilyl) phosphite. phosphorous compounds such as trimethylsilyl methanesulfonate and trimethylsilyl tetrafluoromethanesulfonate; sulfonic acid compounds such as trimethylsilyl methanesulfonate and trimethylsilyl tetrafluoromethanesulfonate; silane compounds such as tetramethylsilane, trimethylvinylsilane, dimethyldivinylsilane, methyltrivinylsilane, and tetravinylsilane; disilane compounds such as hexamethyldisilane, hexaethyldisilane, 1,1,2,2-tetramethyldisilane, and 1,2-diphenyltetramethyldisilane; disiloxane compounds such as hexamethyldisiloxane, 1,3-divinyltetramethyldisiloxane, and 1,1,3,3-tetramethyl-1,3-diphenyldisiloxane; etc. In particular, from the viewpoint of forming a stable interface protective coating, disilane compounds and disiloxane compounds are preferred, disiloxane compounds are more preferred, hexamethyldisiloxane and 1,3-divinyltetramethyldisiloxane are even more preferred, and 1,3-divinyltetramethyldisiloxane is particularly preferred.

[0062] Among the above, it is preferable to contain at least one selected from the group consisting of (A) nitriles, (B) aromatic compounds, and (C) isocyanate compounds, since this further improves the electrochemical properties at high temperatures.

[0063] The content of the compounds (A) to (C) is preferably 0.01% by mass or more and 7% by mass or less, based on the total amount of the non-aqueous electrolyte. Within this range, the coating is formed sufficiently without being too thick, improving high-temperature charged storage characteristics and suppressing gas generation. The content is more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, based on the total amount of the non-aqueous electrolyte, and more preferably 5% by mass or less, even more preferably 3% by mass or less.

[0064] Furthermore, it is preferable to include at least one selected from the group consisting of (D) a triple bond-containing compound, (E) an S=O group-containing compound, (F) a cyclic acetal compound, (G) a phosphorus-containing compound, (H) an acid anhydride, (J) a cyclic phosphazene compound, (K) an organic compound having an isocyanuric acid skeleton, and (L) a silicon-containing compound, since this can improve high-temperature charged storage characteristics and suppress gas generation.

[0065] The content of each of the compounds (D) to (L) is preferably 0.001% by mass or more and 5% by mass or less, based on the total amount of the non-aqueous electrolyte. Within this range, the coating is formed sufficiently without being too thick, further improving high-temperature charged storage characteristics and suppressing gas generation. The content is more preferably 0.01% by mass or more, even more preferably 0.1% by mass or more, based on the total amount of the non-aqueous electrolyte, and more preferably 3% by mass or less, even more preferably 2% by mass or less.

[0066] In order to further improve the electrochemical properties at high temperatures, it is preferable that the non-aqueous electrolyte solution further contains a lithium salt (c) having an oxalic acid skeleton. Specific examples of the lithium salt (c) include lithium bis(oxalato)borate [LiBOB], lithium difluoro(oxalato)borate [LiDFOB], lithium tetrafluoro(oxalato)phosphate [LiTFOP], and lithium difluorobis(oxalato)phosphate [LiDFOP].

[0067] The content of the lithium salt (c) in the non-aqueous electrolyte according to the present invention is preferably 0.01% by mass or more and 8% by mass or less, based on the total amount of the non-aqueous electrolyte. This range further improves the high-temperature charged storage characteristics and further suppresses gas generation. The content is more preferably 0.1% by mass or more, even more preferably 0.3% by mass or more, and particularly preferably 0.4% by mass or more, based on the total amount of the non-aqueous electrolyte. It is more preferably 6% by mass or less, even more preferably 3% by mass or less.

[0068] In this specification, the composition of the nonaqueous electrolyte solution refers to the composition at the time of shipping of an electricity storage device into which the nonaqueous electrolyte solution has been injected. However, it is not necessarily necessary to analyze the composition of the nonaqueous electrolyte solution at the time of shipping, and the electricity storage device may be manufactured so that the composition at the time of shipping falls within a desired range by, for example, measuring the contents of the constituent components during production of the nonaqueous electrolyte solution or during injection of the nonaqueous electrolyte solution into the electricity storage device. That is, when preparing the nonaqueous electrolyte solution, the components may be mixed so that the ratio of each component is a predetermined composition. After preparing the nonaqueous electrolyte solution, the nonaqueous electrolyte solution itself can be analyzed to confirm its composition. Alternatively, the nonaqueous electrolyte solution may be recovered from a completed electricity storage device and subjected to analysis. Examples of a method for recovering the nonaqueous electrolyte solution include a method in which the electrolyte solution is collected by partially or completely opening the electricity storage device container or by providing a hole in the electricity storage device container. The opened electricity storage device container may be centrifuged to recover the electrolyte solution, or an extraction solvent (e.g., acetonitrile dehydrated to a water content of 10 ppm or less) may be placed in the opened electricity storage device container or the extraction solvent may be brought into contact with the electricity storage device element to extract the electrolyte. The nonaqueous electrolyte solution recovered by such a method can be subjected to analysis. Alternatively, the recovered nonaqueous electrolyte solution may be diluted to achieve conditions suitable for analysis before use.

[0069] The optimal analytical method for nonaqueous electrolytes varies depending on the type of nonaqueous electrolyte's composition, but specific examples include inductively coupled plasma (ICP) atomic emission spectroscopy, nuclear magnetic resonance (hereinafter sometimes abbreviated as NMR), and liquid chromatography such as gas chromatography and ion chromatography. The NMR analysis method is described below. In an inert atmosphere, the nonaqueous electrolyte is dissolved in a dehydrated solvent dehydrated to 10 ppm or less, and the solution is placed in an NMR tube for NMR measurement. Alternatively, a double-walled NMR tube may be used, with the nonaqueous electrolyte placed in one tube and the deuterated solvent in the other. Examples of deuterated solvents include deuterated acetonitrile and deuterated dimethyl sulfoxide. The concentrations of the components of a nonaqueous electrolyte can be determined by dissolving a specified amount of a standard substance in a deuterated solvent and calculating the concentration of each component from the spectral ratio. Alternatively, the concentrations of one or more components of the nonaqueous electrolyte can be determined in advance using another analytical method, such as gas chromatography, and the concentration can be calculated from the spectral ratio of the known component to the other component. The nuclear magnetic resonance analyzer used is preferably one with a proton resonance frequency of 400 MHz or higher. 1 H, 31 P, 19 F, 11 Examples include B. These analytical techniques may be used alone or in combination of two or more.

[0070] [Method for producing non-aqueous electrolyte] The non-aqueous electrolyte of the present invention can be obtained, for example, by mixing the non-aqueous solvents described above, and then adding the electrolyte salt and the compound represented by 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 solution be purified in advance to minimize the amount of impurities, within the range that does not significantly reduce productivity.

[0071] [Electricity storage device] The nonaqueous electrolyte solution of the present invention can be used in an electricity storage device, and not only a liquid but also a gelled nonaqueous electrolyte can be used as the nonaqueous electrolyte. Furthermore, the nonaqueous electrolyte solution of the present invention can also be used for a solid polymer electrolyte. In particular, it is preferably used for an electricity storage device that uses a lithium salt as the electrolyte salt. The electric storage device according to the present invention is an electric storage device including a positive electrode, a negative electrode, and a nonaqueous electrolyte solution in which an electrolyte salt is dissolved in a nonaqueous solvent, and is characterized in that the nonaqueous electrolyte solution is the nonaqueous electrolyte solution according to the present invention. The electric storage device according to the present invention is preferably a lithium battery or capacitor that uses a lithium salt as the electrolyte salt, and more preferably a lithium battery.

[0072] [Lithium battery] In this specification, the term "lithium battery" is a general term for lithium primary batteries and lithium secondary batteries. Furthermore, in this specification, the term "lithium secondary battery" is used to conceptually include so-called lithium ion secondary batteries. The lithium battery, which is an electricity storage device according to the present invention, comprises a positive electrode, a negative electrode, and the non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent. The components of the positive electrode, negative electrode, etc. other than the non-aqueous electrolyte solution can be used without any particular limitation.

[0073] (Cathode active material) As a positive electrode active material for a lithium secondary battery, 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. 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, LiCo 1-x M x O2 (wherein M is one or more elements selected from the group consisting of Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn and Cu, 0.001≦x≦0.05), LiMn2O4, LiNiO2, LiCo 1-x Ni x O2(0.01 <x<1)、LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3O2, LiNi 0.5 Mn 0.3 Co 0.2 O2, LiNi 7.0 Mn 1.5 Co 1.5 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, solid solutions of Li2MnO3 and LiMO2 (M is a transition metal such as Co, Ni, Mn, or Fe), and LiNi 1 / 2 Mn 3 / 2 Suitable examples include one or more selected from the group consisting of LiCoO2 and LiMn2O4, and two or more can be used in combination. LiCoO2 and LiMn2O4, LiCoO2 and LiNiO2, or LiMn2O4 and LiNiO2 can also be used in combination.

[0074] In particular, positive electrode active materials containing Ni are preferred for use as positive electrode active materials in electricity storage devices because they have a large theoretical Li absorption capacity. However, positive electrode active materials containing Ni tend to cause decomposition of the nonaqueous solvent on the positive electrode surface due to the catalytic action of Ni, which increases the battery resistance. While battery characteristics tend to deteriorate particularly in high-temperature environments, the lithium secondary battery according to the present invention can suppress this deterioration in battery characteristics. From the perspective of improving the capacity of an electricity storage device, the above-mentioned effect is more pronounced when a positive electrode active material is used in which the ratio of the atomic concentration of Ni to the atomic concentration of all transition metal elements in the positive electrode active material is preferably greater than 30 atomic%, more preferably 50 atomic% or more, and particularly preferably 75 atomic% or more. Specific examples of these include LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2, LiNi 7.0 Mn 1.5 Co 1.5 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2, LiNi 0.8 Co 0.15Al 0.05 Among these, nickel, cobalt, and manganese-based ternary positive electrode active materials (NCM) are preferred, and LiNi 0.8 Mn 0.1 Co 0.1 O2, LiNi 7.0 Mn 1.5 Co 1.5 O2 and LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 More preferably, one or more selected from O2.

[0075] Lithium-containing olivine-type phosphates can also be used as the positive electrode active material. In particular, lithium-containing olivine-type phosphates containing at least one element selected from the group consisting of iron, cobalt, nickel, and manganese are preferred. Specific examples include LiFePO4, LiCoPO4, LiNiPO4, and LiMnPO4. These lithium-containing olivine-type phosphates may be partially substituted with other elements, such as by substituting a portion of the iron, cobalt, nickel, and manganese with one or more elements selected from the group consisting of Co, Mn, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W, and Zr, or by coating with a compound or carbon material containing these other elements. Of these, LiFePO4 or LiMnPO4 is preferred. The lithium-containing olivine-type phosphate can also be used by mixing it with the above-mentioned positive electrode active material, for example.

[0076] The positive electrode active material is not particularly limited, but when a positive electrode active material containing Co or Ni is used, the battery characteristics can be particularly improved. 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2 and LiNi 0.8 Co 0.15 Al0.05 A preferred example is O2.

[0077] The conductive agent for the positive electrode is not particularly limited as 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% by mass or more and 10% by mass or less, more preferably 2% by mass or more and 5% by mass or less.

[0078] The positive electrode can be produced 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), styrene-butadiene copolymer (SBR), acrylonitrile-butadiene copolymer (NBR), carboxymethyl cellulose (CMC), or ethylene propylene diene terpolymer, adding a high-boiling point solvent such as 1-methyl-2-pyrrolidone and kneading the mixture to form a positive electrode mixture, applying the positive electrode mixture to a current collector such as aluminum foil or a stainless steel lath plate, drying, pressurizing, and then heat-treating the mixture in a vacuum at a temperature of about 50°C to 250°C for about 2 hours.

[0079] (Negative electrode active material) Examples of negative electrode active materials for lithium secondary batteries include lithium metal, lithium alloys, and carbon materials capable of absorbing and releasing lithium ions (e.g., easily graphitizable carbon, non-graphitizable carbon with a (002) plane spacing of 0.37 nm or more, and graphite with a (002) plane spacing of 0.34 nm or less), tin (element), tin compounds, silicon (element), silicon compounds, and Li4Ti5O 12 These lithium titanate compounds can be used singly or in combination of two or more. Among these, it is preferable to use highly crystalline carbon materials such as artificial graphite and natural graphite in terms of the ability to absorb and release lithium ions, and the lattice spacing (d002 It is more preferable to use a carbon material having a graphite crystal structure in which the average particle diameter is 0.340 nm or less (preferably 0.335 to 0.337 nm). By using artificial graphite particles with a block structure in which a plurality of flat graphite particles are aggregated or bonded in a non-parallel manner, or graphite particles that have been subjected to a spheroidizing treatment by repeatedly applying mechanical forces such as compression, friction, and shear forces to flake-like natural graphite particles, the density of the negative electrode excluding the current collector can be reduced to 1.5 g / cm. 3 When the negative electrode sheet is pressed to a density of 100 or more, the ratio I(110) / I(004) of the peak intensity I(110) of the (110) plane of the graphite crystals obtained by X-ray diffraction measurement to the peak intensity I(004) of the (004) plane 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 can reduce the crystallinity and decrease the discharge capacity of the battery, the upper limit is preferably 0.5 or less, and more preferably 0.3 or less. Furthermore, it is preferable that a highly crystalline carbon material (core material) is coated with a carbon material with lower crystallinity than the core material, since this further improves the high-temperature charged storage characteristics. The crystallinity of the coating carbon material can be confirmed using a transmission electron microscope (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 deteriorating the high-temperature charged storage characteristics. However, the lithium secondary battery according to the present invention has good high-temperature charged storage characteristics.

[0080] In addition, examples of the metal compound capable of occluding and releasing lithium ions 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, Ba, etc. These metal compounds may be used in any form such as a single substance, alloy, oxide, nitride, sulfide, boride, alloy with lithium, etc., but a single substance, alloy, oxide, or alloy with lithium is preferable because the capacity can be increased. Among them, those containing at least one element selected from Si, Ge, and Sn are preferable, and those containing at least one element selected from Si and Sn are particularly preferable because the battery capacity can be increased.

[0081] Furthermore, as the metal compound capable of occluding and releasing lithium ions as the negative electrode active material, a metal compound containing Si element and Ti element is preferable for improving battery characteristics. Among the metal compounds containing Si element, SiO which is a composite material of Si and SiO2 x is preferable because it can further improve battery characteristics including cycle retention rate. The range of x is 0 < x < 2. Among the metal compounds containing Ti element, Li4Ti5O 12 and titanium-containing metal oxides mainly composed of TiNb2O7 have small expansion and contraction during charge and discharge and are flame-retardant, so they are preferable in terms of enhancing battery safety.

[0082] From the above, the negative electrode active material for the lithium secondary battery is not particularly limited as long as it can occlude and release lithium ions, but lithium metal, carbon material, silicon metal, metal oxide containing Si element (SiO x ) and metal oxide containing Ti element (Li4Ti5O 12 , TiNb2O7, etc.) are preferably used alone or in combination of two or more selected from the group consisting of, and it is more preferable to use alone or in combination of two or more selected from carbon material, silicon metal, and SiO x . As the negative electrode active material, a carbon material and silicon metal or SiO xWhen used in combination with silicon metal or SiO x The weight ratio is not particularly limited, but is preferably 30 mass % or less, more preferably 10 mass % or less, based on the mass of the entire negative electrode mixture including the negative electrode active material, conductive agent, binder, and high-boiling point solvent.

[0083] The negative electrode can be produced by kneading a conductive agent, a binder, and a high-boiling point solvent similar to those used in producing the positive electrode to form a negative electrode mixture, then applying this negative electrode mixture to a copper foil or other current collector, drying, pressurizing and molding, and then heat-treating it 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 / cm 3 or more, and in order to further increase the capacity of the battery, it is preferably 1.4 g / cm 3 More preferably, it is 1.7 g / cm or more. 3 and preferably 2 g / cm 3 The following is the result.

[0084] Furthermore, examples of the negative electrode active material for a lithium primary battery include lithium metal and lithium alloys.

[0085] There are no particular limitations on the structure of the lithium battery, and coin-type batteries, cylindrical batteries, prismatic batteries, laminated batteries, etc. having single-layer or multi-layer separators 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.

[0086] The lithium secondary battery of the present invention has excellent cycle characteristics even when the end-of-charge voltage is 4.2 V or higher, particularly 4.3 V or higher, and also has good characteristics at 4.4 V or higher. The end-of-discharge voltage can usually be 2.8 V or higher, and even 2.5 V or higher, but the lithium secondary battery of the present invention can be 2.0 V or higher. There are no particular limitations 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.

[0087] In the present invention, measures to prevent an increase in the internal pressure of a lithium battery can be adopted, such as providing a safety valve in the battery lid or making cuts in components such as the battery can or gasket. Also, as a safety measure to prevent overcharging, a current interruption mechanism that detects the internal pressure of the battery and interrupts the current can be provided in the battery lid.

[0088] [Capacitor] Examples of capacitors containing the nonaqueous electrolyte of the present invention include electric double layer capacitors and lithium ion capacitors. An electric double layer capacitor is an energy storage device that stores energy by utilizing the electric double layer capacitance at the interface between an electrolyte and an electrode. The most typical electrode active material used in this energy storage device is activated carbon. The electric double layer capacitance increases roughly in proportion to the surface area. A lithium-ion capacitor (LIC) is an energy storage device that stores energy by intercalating lithium ions into a carbon material such as graphite as the negative electrode. The positive electrode can be, for example, one that uses an electric double layer between an activated carbon electrode and an electrolyte, or one that uses the doping / dedoping reaction of a π-conjugated polymer electrode. The electrolyte contains a lithium salt such as LiPF6. [Example]

[0089] Examples of synthesis of the compounds of the present invention and examples of lithium ion secondary batteries using the nonaqueous electrolytes of the present invention are shown below, but the present invention is not limited to these synthesis examples and examples.

[0090] Synthesis Example 1 [Di-2-propynyl vinylphosphonate (Compound 1-1)] 10 g (92.6 mmol) of vinylphosphonic acid, 44 g (370 mmol) of thionyl chloride, and 0.1 g (1.4 mmol) of N,N-dimethylformamide were stirred in 100 mL of 1,2-dichloroethane at 60° C. for 4 hours. After the reaction was completed, the mixture was allowed to cool to room temperature and then concentrated under reduced pressure to obtain 12.5 g of vinylphosphonic acid dichloride. 6.7 g (46.3 mmol) of vinylphosphonic acid dichloride, 5.2 g (92.6 mmol) of propargyl alcohol, and 0.1 g (0.8 mmol) of N,N-dimethylaminopyridine were dissolved in 60 mL of 1,2-dichloroethane and cooled to 0°C. 9.4 g (92.6 mmol) of triethylamine was added dropwise to this solution over 30 minutes at 0-10°C, and the mixture was stirred at room temperature for 1 hour and 30 minutes. After the reaction was completed, 20 mL of water was added and the mixture was separated. The organic layer was washed with 20 mL of water, and the solvent was evaporated under reduced pressure. The residue was purified by silica gel column chromatography to obtain 6.0 g of di-2-propynyl vinylphosphonate (yield: 70%). Regarding the obtained di-2-propynyl vinylphosphonate (compound 1), 1 The results of H-NMR measurement are shown below. 1 H-NMR (400MHz, CDCl3): δ=6.44-6.04(m,3H), 4.70(d,4H,J=10.5Hz), 2.56(s,2H).

[0091] Synthesis Example 2 [Di-2-propynyl allylphosphonate (Compound 2-1)] Synthesis was carried out in the same manner as in Synthesis Example 1, except that the vinylphosphonic acid in Synthesis Example 1 was changed to allylphosphonic acid. Regarding the obtained di-2-propynyl allylphosphonate (compound 2-1), 1 The results of H-NMR measurement are shown below. 1H-NMR (400MHz, CDCl3): δ=5.87-5.73(m,1H), 5.33-5.23(m,2H), 4.73-4.67(m,4H), 2.76(ddt,2H,J=22.4Hz,7.4Hz,1.2Hz), 2.58(t,2H,J=2.5Hz).

[0092] Synthesis Example 3 [Di-2-propynyl crotylphosphonate (Compound 5-1)] Synthesis was carried out in the same manner as in Synthesis Example 1, except that the vinylphosphonic acid in Synthesis Example 1 was changed to crotylphosphonic acid. Regarding the obtained di-2-propynyl crotylphosphonate (compound 5-1), 1 The results of H-NMR measurement are shown below. 1 H-NMR (400MHz, CDCl3): δ=5.82-5.64(m,1H), 5.52-5.38(m,1H), 4.75-4.68(m,4H), 2.81-2.62(m,2H), 2.58(t,2H,J=2.5Hz), 1.80-1.67(m,3H).

[0093] Examples 1-1 to 2-3, Comparative Examples 1-1, 2-1 to 2-6 [Fabrication of Lithium-ion Secondary Battery] Cathode active material (LiNi 0.8 Mn 0.1 Co 0.1 A mixture of 90% by mass of O2 [NCM (8 / 1 / 1)], 3% by mass of acetylene black (conductive agent), and 3% by mass of KS-4 (registered trademark) (conductive agent) was added to a solution in which 4% by mass of polyvinylidene fluoride (binder) had been dissolved in 1-methyl-2-pyrrolidone, and mixed to prepare a positive electrode mixture paste. This positive electrode mixture paste was applied to both sides of an aluminum foil (current collector), dried, pressed, and cut to a specified size to prepare a rectangular positive electrode sheet. The density of the positive electrode, excluding the current collector, was 2.5 g / cm. 3 It was. In addition, 98% by mass of artificial graphite (negative electrode active material), 1% by mass of carboxymethyl cellulose (thickener), and 1% by 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 copper foil (current collector), dried, pressed, and cut to a specified size to prepare a negative electrode sheet. The density of the negative electrode excluding the current collector was 1.4 g / cm. 3 Then, the positive electrode sheet, a separator made of a polyolefin laminated microporous film, and a negative electrode sheet were laminated in this order, and nonaqueous electrolyte solutions having the compositions shown in Tables 1 and 2 were added to each of them to prepare laminate batteries. In Tables 1 to 3, EC stands for ethylene carbonate, MEC stands for methyl ethyl carbonate, and VC stands for vinylene carbonate.

[0094] [Evaluation of characteristics after high-temperature charging storage] <Initial discharge capacity> The laminated battery prepared by the above method was subjected to the following pretreatment, and then charged in a thermostatic chamber at 25°C at a constant current and voltage of 0.2 C for 7 hours up to a cut-off voltage of 4.2 V, and then discharged at a constant current of 0.2 C down to a cut-off voltage of 2.7 V to determine the initial discharge capacity at 25°C. (Pretreatment) The battery was charged at a constant current of 0.05C for 1 hour at a constant temperature of 25°C and then left to stand for 6 hours. It was then charged at 0.2C to 4.2V and left to stand in a 60°C thermostatic chamber for 48 hours. It was placed in a thermostatic chamber at 25°C and discharged to a cut-off voltage of 2.75V at a constant current of 0.2C. It was then charged again at 0.2C to 4.2V, and then discharged to a cut-off voltage of 2.75V at a constant current of 0.2C.

[0095] <High-temperature charging storage test> Next, this laminated battery was charged for 7 hours in a thermostatic bath at 60°C at a constant current and voltage of 1C to an end voltage of 4.2V, and the temperature of the thermostatic bath was raised to 60°C. The battery was then stored in this state at 4.2V for 20 days for the tests described in Table 1 and for 10 days for the tests described in Table 2. After that, the battery was placed in a thermostatic bath at 25°C and discharged at a constant current of 0.2C to an end voltage of 2.75V.

[0096] <Discharge capacity after high-temperature charging storage> Thereafter, the discharge capacity at 25° C. after high-temperature charged storage was determined in the same manner as in the measurement of the initial discharge capacity.

[0097] <Discharge capacity retention rate after high-temperature charging storage> The discharge capacity retention rate after high-temperature charging storage was calculated from the following formula using the initial 25°C discharge capacity and the 25°C discharge capacity after high-temperature charging storage. Discharge capacity retention rate at 25°C after high-temperature charging storage (%) = (discharge capacity at 25°C after high-temperature charging storage / initial discharge capacity at 25°C) x 100

[0098] <Evaluation of gas generation amount after high-temperature charging storage> The amount of gas generated after high-temperature storage under charge was measured by Archimedes' method. The amount of gas generated is a relative value when the amount of gas generated measured in a laminated battery equipped with a non-aqueous electrolyte containing no compound of general formula (I) is taken as 100%.

[0099] The results of the battery characteristics are shown in Tables 1 and 2.

[0100] [Table 1]

[0101] [Table 2]

[0102] Examples 3-1 to 3-2, Comparative Example 3-1 [Fabrication of Lithium-ion Secondary Battery] The positive electrode mixture is mixed with the positive electrode active material (LiNi 0.70 Mn 0.15 Co 0.15 A laminate-type battery was fabricated in the same manner as in Example 1-1, except that the positive electrode mixture paste was prepared by mixing 90 mass% of O2 [NCM (7 / 1.5 / 1.5)] and 7 mass% of acetylene black (conductive agent), and adding and mixing the mixture to a solution in which 3 mass% of polyvinylidene fluoride (binder) had been dissolved in 1-methyl-2-pyrrolidone.

[0103] [Evaluation of characteristics after high-temperature charging storage] <Initial discharge capacity> The laminated battery prepared by the above method was subjected to pretreatment, and then charged in a thermostatic chamber at 25°C at a constant current and voltage of 0.2 C up to a cut-off voltage of 4.4 V, and discharged at a constant current of 0.2 C down to a cut-off voltage of 2.8 V to determine the initial discharge capacity at 25°C.

[0104] <High-temperature charging storage test> Next, this laminated battery was charged in a thermostatic bath at 60°C at a constant current and voltage of 1 C to an end voltage of 4.4 V, the temperature of the thermostatic bath was raised to 60°C, and the battery was stored for 14 days while being maintained at 4.2 V. Thereafter, the battery was placed in a thermostatic bath at 25°C and discharged at a constant current of 0.2 C to an end voltage of 2.8 V.

[0105] <Discharge capacity after high-temperature charging storage> Thereafter, the discharge capacity at 25° C. after high-temperature charged storage was determined in the same manner as in the measurement of the initial discharge capacity.

[0106] <Evaluation of discharge capacity retention rate after high-temperature charging storage and amount of gas generation after high-temperature charging storage> The discharge capacity retention rate after high-temperature storage under charge and the amount of gas generated after high-temperature storage under charge were measured in the same manner as in Example 1-1. The results of the battery characteristics are shown in Table 3.

[0107] [Table 3]

[0108] In each of the Examples and Comparative Examples shown in Tables 1 to 3, the compound represented by the general formula (I) was mixed with an electrolyte solution having the formulation shown in the column "Composition of electrolyte salt Composition of non-aqueous solvent (volume ratio of solvent)" in Tables 1 to 3 so that the content of the compound represented by the general formula (I) relative to the total amount of the non-aqueous electrolyte solution was the amount shown in Tables 1 to 3, thereby preparing the non-aqueous electrolyte solution according to each of the Examples and Comparative Examples.

[0109] In Tables 1 to 3, the examples using the nonaqueous electrolyte solution of the present invention were able to significantly reduce the amount of gas generated while maintaining a high capacity after high-temperature storage compared to the comparative examples not containing the compound of general formula (I). From these results, it can be said that the nonaqueous electrolyte solution of the present invention achieves a good balance between improving the discharge capacity retention rate during high-temperature storage and reducing gas generation. [Industrial Applicability]

[0110] The nonaqueous electrolyte solution of the present invention can be used to obtain an electricity storage device with excellent electrochemical properties over a wide temperature range. In particular, when used as a nonaqueous electrolyte solution for electricity storage devices such as lithium secondary batteries installed in hybrid electric vehicles, plug-in hybrid electric vehicles, battery electric vehicles, etc., it can provide an electricity storage device whose electrochemical properties are resistant to deterioration over a wide temperature range.

Claims

1. A non-aqueous electrolyte solution for an electricity storage device, which comprises an electrolyte salt dissolved in a non-aqueous solvent, and which contains a phosphonate ester represented by the following general formula (I) in an amount of 0.001 mass % or more and 5 mass % or less: 【Chemical 1】 (In the formula, R １ represents an alkenyl group having 2 to 6 carbon atoms or an alkynyl group having 3 to 6 carbon atoms, and R ２ and R ３ each independently represents an alkynyl group having 3 to 6 carbon atoms.

2. A non-aqueous electrolyte solution for an electricity storage device, comprising an electrolyte salt dissolved in a non-aqueous solvent, wherein the non-aqueous solvent contains one or more selected from the group consisting of saturated cyclic carbonates, chain esters, lactones, ethers and amides, and contains a phosphonic acid ester represented by the following general formula (I): 【Chemistry 2】 (In the formula, R 1 represents an alkenyl group having 2 to 6 carbon atoms or an alkynyl group having 3 to 6 carbon atoms, and R 2 and R 3 each independently represent an alkynyl group having 3 to 6 carbon atoms.)

3. R in the general formula (I) １ The nonaqueous electrolyte solution for an electricity storage device according to claim 1 or 2, wherein is a vinyl group, an allyl group, a 1-methylallyl group, a 2-methylallyl group, a crotyl group, a butenyl group, or a propynyl group.

4. R in the general formula (I) １ The nonaqueous electrolyte solution for an electricity storage device according to claim 1 or 2, wherein is a vinyl group or an allyl group.

5. R in the general formula (I) ２ and R ３ are each independently a 2-propynyl group, a 2-butynyl group, a 3-butynyl group, a 1-methyl-2-propynyl group, a 1,1-dimethyl-2-propynyl group, a 1-ethyl-1-methyl-2-propynyl group, or a 4-pentynyl group.

6. The nonaqueous electrolyte solution for an electricity storage device according to any one of claims 1 to 5, further comprising one or more lithium salts (a) selected from the group consisting of lithium salts having a phosphate skeleton and lithium salts having an S(=O) group.

7. The nonaqueous electrolyte solution for an electricity storage device according to claim 6 , wherein the content of the lithium salt (a) is 0.01% by mass or more and 8% by mass or less.

8. The electrolyte salt is LiPF ６ , LiBF ４ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ and LiN(SO ２ F) ２ The nonaqueous electrolyte solution for an electricity storage device according to any one of claims 1 to 7, comprising one or more lithium salts (b) selected from the group consisting of [LiFSI].

9. 9. The nonaqueous electrolyte solution for an electricity storage device according to claim 8, wherein the content of the lithium salt (b) is 4% by mass or more and 28% by mass or less.

10. 10. The nonaqueous electrolyte solution for an electricity storage device according to any one of claims 1 to 9, wherein the phosphonate ester comprises at least one selected from the group consisting of di-2-propynyl vinylphosphonate, di-2-propynyl allylphosphonate, di-2-propynyl 1-methylallylphosphonate, di-2-propynyl 2-methylallylphosphonate, di-2-propynyl crotylphosphonate, di-2-propynyl butenylphosphonate, and di-2-propynyl propynylphosphonate.

11. 11. The nonaqueous electrolyte solution for an electricity storage device according to claim 1, wherein the nonaqueous solvent contains a saturated cyclic carbonate and a chain ester, and the mass ratio of the cyclic carbonate to the chain ester is 10:90 to 50:

50.

12. The nonaqueous electrolyte solution for an electricity storage device according to any one of claims 1 to 11, further comprising at least one of a cyclic carbonate having an unsaturated bond and a cyclic carbonate having a fluorine atom.

13. The nonaqueous electrolyte solution for an electricity storage device according to claim 12 , wherein the content of the cyclic carbonate having an unsaturated bond is 0.05% by mass or more and 8% by mass or less.

14. An electricity storage device comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte solution in which an electrolyte salt is dissolved in a nonaqueous solvent, wherein the nonaqueous electrolyte solution is the nonaqueous electrolyte solution according to any one of claims 1 to 13.

15. The power storage device according to claim 14, wherein the power storage device is a lithium battery.

16. The electricity storage device according to claim 14 or 15, wherein a ratio of an atomic concentration of Ni to an atomic concentration of all transition metal elements in a positive electrode active material in the positive electrode is 50 atomic % or more.

17. An electricity storage device comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte solution in which an electrolyte salt is dissolved in a nonaqueous solvent, The non-aqueous electrolyte solution is a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent, and contains a phosphonate ester represented by the following general formula (I): a ratio of the atomic concentration of Ni to the atomic concentration of all transition metal elements in the positive electrode active material in the positive electrode is 50 atomic % or more; 【Chemistry 3】 (In the formula, R 1 represents an alkenyl group having 2 to 6 carbon atoms or an alkynyl group having 3 to 6 carbon atoms, and R 2 and R 3 each independently represent an alkynyl group having 3 to 6 carbon atoms.)

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