Non-aqueous electrolyte and power storage device using the same

Abstract

The present application is a nonaqueous electrolyte solution for power storage devices and a power storage device using the same, the nonaqueous electrolyte solution for power storage devices being a nonaqueous electrolyte solution in which an electrolyte salt is dissolved in a nonaqueous solvent, containing a phosphonate represented by the following general formula (I). (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, R 2 and R 3 each independently represent an alkynyl group having 3 to 6 carbon atoms.)

Description

Technical Field

[0001] This invention relates to non-aqueous electrolytes and energy storage devices using them. Background Technology

[0002] In recent years, energy storage devices, especially lithium-ion batteries, have been widely used as power sources for small electronic devices such as mobile phones and laptops, as well as for electric vehicles and other energy storage applications. These electronic devices and vehicles may operate over a wide temperature range, from the high temperatures of summer to the extreme low temperatures. Therefore, energy storage devices are required to maintain a good balance in their electrochemical characteristics across this wide temperature range.

[0003] In particular, to prevent global warming, reducing CO2 emissions has become a top priority. Environmental protection vehicles equipped with energy storage devices including lithium-ion batteries and capacitors require rapid adoption of hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs). Because vehicles travel long distances, they can be used in a wide range of temperatures, from extremely hot tropical regions to extremely cold regions. Therefore, it is especially important that the electrochemical properties of these onboard energy storage devices remain unchanged even when used across a wide temperature range.

[0004] It should be noted that, in this specification, the term "lithium secondary battery" is used to refer to a concept that also includes so-called lithium-ion secondary batteries.

[0005] Lithium-ion batteries are mainly composed of positive and negative electrodes containing materials that can absorb and release lithium ions, and a non-aqueous electrolyte containing lithium salts and non-aqueous solvents. As a non-aqueous solvent, carbonates such as ethylene carbonate (EC) and propylene carbonate (PC) are used.

[0006] In addition, known negative electrodes include metallic lithium, metal compounds (metal elements, metal oxides, alloys formed with lithium, etc.) that can absorb and release lithium ions, and carbon materials. In particular, lithium secondary batteries made using carbon materials such as coke, artificial graphite, and natural graphite that can absorb and release lithium ions have been widely put into practical use.

[0007] For example, in lithium-ion batteries using highly crystallized carbon materials such as natural graphite and artificial graphite as the negative electrode material, the solvent in the non-aqueous electrolyte undergoes reductive decomposition on the negative electrode surface during charging. It is known that the decomposition products and gas generated by this reductive decomposition hinder the desired electrochemical reactions of the battery, thus reducing the cycle performance of the aforementioned lithium-ion batteries. Furthermore, if the decomposition products of the non-aqueous solvent accumulate, lithium ions cannot be readily absorbed and released to the negative electrode, easily leading to a decrease in electrochemical performance over a wide temperature range.

[0008] It is known that lithium-ion batteries using lithium metal, its alloys, elemental metals such as tin or silicon, or metal oxides as anode materials, while having high initial capacity, undergo micronization during cycling. Therefore, compared to carbon-based anode materials, this leads to accelerated reduction and decomposition of non-aqueous solvents, significantly reducing battery performance such as capacity and cycle characteristics. Furthermore, if micronization of these anode materials and the accumulation of non-aqueous solvent decomposition products occur, lithium ions cannot be readily absorbed and released to the anode, resulting in a decline in electrochemical characteristics over a wide temperature range.

[0009] On the other hand, it is known that in lithium-ion secondary batteries using materials such as LiCoO2, LiMn2O4, LiNiO2, and LiFePO4 as positive electrodes, the non-aqueous solvent in the non-aqueous electrolyte undergoes partial oxidative decomposition at the interface between the positive electrode material and the non-aqueous electrolyte during charging. The decomposition products and gas generated by this oxidative decomposition hinder the desired electrochemical reactions of the battery; therefore, the aforementioned lithium-ion secondary batteries still experience a decrease in electrochemical characteristics when used over a wide temperature range.

[0010] As mentioned above, the decomposition products and gas generation during the decomposition of non-aqueous electrolytes at the positive and negative electrodes hinder the smooth movement of lithium ions or cause battery expansion, thus reducing battery performance. Despite this, the multifunctionality of electronic devices equipped with lithium-ion batteries continues to advance, showing a trend of increasing power consumption. Therefore, the high capacity of lithium-ion batteries is gradually being achieved, and the volume occupied by non-aqueous electrolytes within the battery is decreasing in order to increase electrode density or reduce the volume of unused space within the battery. Consequently, the electrochemical characteristics are easily reduced over a wide temperature range due to the decomposition of even a small amount of non-aqueous electrolyte.

[0011] Patent document 1 describes how, by including at least one phosphorus compound selected from the group consisting of specific phosphine oxides, phosphonates, and hypophosphonates in a non-aqueous electrolyte, it is possible to suppress the degradation of battery characteristics under high-temperature conditions.

[0012] Patent document 2 describes how, by including specific phosphate esters and phosphonates in a non-aqueous electrolyte, the discharge capacity retention rate and resistance value retention rate at 25°C are improved.

[0013] Patent document 3 describes how the energy efficiency of lithium-air batteries can be significantly improved by combining an organic solvent that is a specific phosphate ester and / or phosphonate with lithium nitrate at a concentration within a specific range.

[0014] Patent document 4 describes how adding an alkyne compound with a specific structure in which an alkyne group is bonded by a specific group to a non-aqueous electrolyte can improve the cycling characteristics at low and high temperatures, as well as the load characteristics after high-temperature charging and storage.

[0015] Existing technical documents

[0016] Patent documents

[0017] Patent Document 1: Japanese Patent Application Publication No. 2013-55031

[0018] Patent Document 2: Japanese Patent Application Publication No. 2020-72023

[0019] Patent Document 3: International Publication No. 2020 / 141578

[0020] Patent Document 4: International Publication No. 2011 / 096450 Summary of the Invention

[0021] The problem the invention aims to solve

[0022] The purpose of this invention is to provide a non-aqueous electrolyte that can improve the discharge capacity retention rate and gas generation resistance of energy storage devices after high-temperature storage, and an energy storage device using the same.

[0023] Solution for solving the problem

[0024] In order to solve the above-mentioned problems, the inventors conducted repeated and in-depth research and discovered that, for non-aqueous electrolytes containing electrolyte salts dissolved in non-aqueous solvents, by containing compounds obtained by introducing specific alkyne groups into specific phosphonates having alkenyl or alkyne groups, the discharge capacity retention rate and anti-gas generation effect of the energy storage device after high-temperature storage are specifically improved, thus completing the present invention. This effect was not disclosed at all in the aforementioned patent documents 1 to 4.

[0025] That is, the present invention provides (1) to (17) as described below.

[0026] (1) A non-aqueous electrolyte for energy storage devices, characterized in that it is a non-aqueous electrolyte containing an electrolyte salt dissolved in a non-aqueous solvent, and contains a phosphonate ester as shown in the following general formula (I).

[0027]

[0028] (where R is in the formula) 1 R represents an alkenyl group with 2 to 6 carbon atoms or an alkynyl group with 3 to 6 carbon atoms. 2 and R 3 Each group independently represents an alkynyl group with 3 to 6 carbon atoms.

[0029] (2) The non-aqueous electrolyte for energy storage devices according to (1) above, wherein the content of the phosphonate ester represented by the above general formula (I) is more than 0.001% by mass and less than 5% by mass.

[0030] (3) The non-aqueous electrolyte for energy storage devices according to (1) or (2) above, wherein R in the aforementioned general formula (I) 1 It can be vinyl, allyl, 1-methylallyl, 2-methylallyl, crotonyl, butenyl, or propynyl.

[0031] (4) The non-aqueous electrolyte for energy storage devices according to (1) or (2) above, wherein R in the aforementioned general formula (I) 1 It is vinyl or allyl.

[0032] (5) The non-aqueous electrolyte for energy storage devices according to any one of (1) to (4) above, wherein R in the aforementioned general formula (I) 2 and R 3 Each of them independently is 2-propynyl, 2-butynyl, 3-butynyl, 1-methyl-2-propynyl, 1,1-dimethyl-2-propynyl, 1-ethyl-1-methyl-2-propynyl or 4-pentynyl.

[0033] (6) The non-aqueous electrolyte for storage devices according to any one of (1) to (5) above, wherein the non-aqueous electrolyte further contains one or more lithium salts (a) selected from the group consisting of lithium salts having a phosphate backbone and lithium salts having an S (=O) group.

[0034] (7) The non-aqueous electrolyte for energy storage devices according to (6) above, wherein the content of the aforementioned lithium salt (a) is 0.01% by mass or more and 8% by mass or less.

[0035] (8) The non-aqueous electrolyte for storage devices according to any one of (1) to (7) above, 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].

[0036] (9) The non-aqueous electrolyte for energy storage devices according to (8) above, wherein the content of the aforementioned lithium salt (b) is 4% by mass or more and 28% by mass or less.

[0037] (10) The non-aqueous electrolyte for storage devices according to any one of (1) to (9) above, wherein the aforementioned phosphonate comprises one or more selected from the group consisting of vinylphosphonate di-2-propynyl ester, allylphosphonate di-2-propynyl ester, 1-methylallylphosphonate di-2-propynyl ester, 2-methylallylphosphonate di-2-propynyl ester, crotonylphosphonate di-2-propynyl ester, butenylphosphonate di-2-propynyl ester and propynylphosphonate di-2-propynyl ester.

[0038] (11) The non-aqueous electrolyte for storage devices according to any one of (1) to (10) above, wherein the aforementioned non-aqueous solvent comprises one or more selected from the group consisting of saturated cyclic carbonates, chain esters, lactones, ethers and amides.

[0039] (12) The non-aqueous electrolyte for storage devices according to any one of (1) to (11) above, wherein the non-aqueous solvent comprises saturated cyclic carbonate and chain ester, and the mass ratio of the cyclic carbonate to the chain ester is 10:90 to 50:50.

[0040] (13) The non-aqueous electrolyte for storage devices according to any one of (1) to (12) above further comprises at least one of a cyclic carbonate having unsaturated bonds and a cyclic carbonate having fluorine atoms.

[0041] (14) The non-aqueous electrolyte for energy storage devices according to (13) above, wherein the content of the aforementioned cyclic carbonate with unsaturated bonds is 0.05% by mass or more and 8% by mass or less.

[0042] (15) An energy storage device, characterized in that it comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, wherein the non-aqueous electrolyte is any one of (1) to (14) above.

[0043] (16) The energy storage device according to (15) above, wherein the energy storage device is a lithium battery.

[0044] (17) The energy storage device according to (15) or (16) above, wherein the atomic concentration of Ni in the positive electrode active material of the aforementioned positive electrode is more than 50 atomic% relative to the atomic concentration of all transition metal elements.

[0045] The effects of the invention

[0046] According to the present invention, a non-aqueous electrolyte capable of improving the discharge capacity retention rate and anti-gas generation effect of energy storage devices after high-temperature storage, and an energy storage device using the same, are provided. Detailed Implementation

[0047] This invention relates to non-aqueous electrolytes and energy storage devices using them.

[0048] [Non-aqueous electrolyte]

[0049] The non-aqueous electrolyte of the present invention is a non-aqueous electrolyte for energy storage devices, characterized in that it is a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, and contains a phosphonate ester represented by the aforementioned general formula (I).

[0050] The reason why the non-aqueous electrolyte of the present invention can improve the discharge capacity retention rate and anti-gas generation effect of energy storage devices after high-temperature storage may not be clear, but it can be considered as follows.

[0051] The compounds represented by general formula (I) used in this invention are specific phosphonates having alkenyl or alkynyl groups, thus promoting reductive decomposition. Furthermore, it can be considered that the compounds represented by general formula (I) are due to R... 1 Having specific alkenyl or ynyl groups, R 2 and R 3 It possesses specific alkynyl groups, thus further promoting the polymerization reaction and forming a robust coating with high heat resistance. Therefore, the coating does not become brittle even at high temperatures, can inhibit solvent decomposition, and can simultaneously improve the discharge capacity retention rate and anti-gas generation effect of the energy storage device after high-temperature storage.

[0052] (phosphonates)

[0053] The phosphonates contained in the non-aqueous electrolyte of the present invention are represented by the following general formula (I).

[0054]

[0055] (where R is in the formula) 1 R represents an alkenyl group with 2 to 6 carbon atoms or an alkynyl group with 3 to 6 carbon atoms. 2 and R 3 Each group independently represents an alkynyl group with 3 to 6 carbon atoms.

[0056] In the aforementioned general formula (I), R 1 Preferably, it is vinyl, allyl, 1-methylallyl, 2-methylallyl, crotonyl, butenyl or propynyl, more preferably vinyl, allyl, 1-methylallyl, 2-methylallyl or crotonyl, further preferably vinyl, allyl or crotonyl, even more preferably vinyl or allyl, and particularly preferably allyl.

[0057] In the aforementioned general formula (I), R 2 and R 3 Each group independently represents an alkynyl group having 3 to 6 carbon atoms. Specifically, suitable examples include straight-chain alkynyl groups such as 2-propynyl, 2-butynyl, 3-butynyl, 4-pentynyl, or 4-heptyynyl; and branched-chain alkynyl groups such as 1-methyl-2-propynyl, 1,1-dimethyl-2-propynyl, 1-methyl-3-butynyl, or 1-methyl-4-pentynyl. More preferably, these are 2-propynyl, 2-butynyl, 3-butynyl, 1-methyl-2-propynyl, 1,1-dimethyl-2-propynyl, 1-ethyl-1-methyl-2-propynyl, or 4-pentynyl, and even more preferably, 2-propynyl.

[0058] Specifically, the following compounds may be suitably listed as compounds represented by the aforementioned general formula (I).

[0059]

[0060]

[0061]

[0062]

[0063] In the above-mentioned suitable examples, the preferred materials are selected from vinylphosphonate di-2-propynyl ester (compound 1-1), vinylphosphonate di-3-butynyl ester (compound 1-4), vinylphosphonate di-1-methyl-2-propynyl ester (compound 1-6), vinylphosphonate di-1,1-dimethyl-2-propynyl ester (compound 1-8), vinylphosphonate di-1-ethyl-1-methyl-2-propynyl ester (compound 1-10), vinylphosphonate di-2-butynyl ester (compound 1-12), allylphosphonate di-2-propynyl ester (compound 2-1), allylphosphonate di-3-butynyl ester (compound 2-4), and allylphosphonate di-1-methyl-2-propynyl ester. One or more of the following compounds are included in the group consisting of 1-propynyl ester (compounds 2-6), allylphosphonic acid di-1,1-dimethyl-2-propynyl ester (compounds 2-8), allylphosphonic acid di-1-ethyl-1-methyl-2-propynyl ester (compounds 2-10), allylphosphonic acid di-2-butynyl ester (compounds 2-12), 1-methylallylphosphonic acid di-2-propynyl ester (compounds 3-1), 2-methylallylphosphonic acid di-2-propynyl ester (compounds 4-1), crotonylphosphonic acid di-2-propynyl ester (compounds 5-1), 3-butenylphosphonic acid di-2-propynyl ester (compounds 6-1) and propynylphosphonic acid di-2-propynyl ester (compounds 7-1).Among these, more preferred are vinylphosphonate di-2-propynyl ester (compound 1-1), vinylphosphonate di-1-methyl-2-propynyl ester (compound 1-6), vinylphosphonate di-1,1-dimethyl-2-propynyl ester (compound 1-8), vinylphosphonate di-1-ethyl-1-methyl-2-propynyl ester (compound 1-10), vinylphosphonate di-2-butynyl ester (compound 1-12), allylphosphonate di-2-propynyl ester (compound 2-1), and allylphosphonate di-1-methyl- 2-Propylene ester (compounds 2-6), allylphosphonic acid di-1,1-dimethyl-2-propyne ester (compounds 2-8), allylphosphonic acid di-1-ethyl-1-methyl-2-propyne ester (compounds 2-10), 1-methylallylphosphonic acid di-2-propyne ester (compounds 3-1), 2-methylallylphosphonic acid di-2-propyne ester (compounds 4-1), crotonylphosphonic acid di-2-propyne ester (compounds 5-1), butenylphosphonic acid di-2-propyne ester (compounds 6-1), and propyne phosphonic acid di-2- One or more of the group consisting of propyne esters (compound 7-1), more preferably selected from vinylphosphonic acid di-2-propyne ester (compound 1-1), allylphosphonic acid di-2-propyne ester (compound 2-1), 1-methylallylphosphonic acid di-2-propyne ester (compound 3-1), 2-methylallylphosphonic acid di-2-propyne ester (compound 4-1), crotonylphosphonic acid di-2-propyne ester (compound 5-1), butenylphosphonic acid di-2-propyne ester (compound 6-1) and propynephosphonic acid di-2-propyne ester. It is selected from one or more of the group consisting of esters (compound 7-1), more preferably from one or more of the group consisting of vinylphosphonate di-2-propynyl ester (compound 1-1), allylphosphonate di-2-propynyl ester (compound 2-1) and crotonylphosphonate di-2-propynyl ester (compound 5-1), more preferably vinylphosphonate di-2-propynyl ester (compound 1-1) or allylphosphonate di-2-propynyl ester (compound 2-1), and particularly preferably allylphosphonate di-2-propynyl ester (compound 2-1).

[0064] The non-aqueous electrolyte of the present invention may contain one or more phosphonates represented by the aforementioned general formula (I).

[0065] The content of the phosphonate ester represented by the aforementioned general formula (I) in the non-aqueous electrolyte of the present invention is preferably 0.001% by mass or more relative to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is set to 100% by mass), and preferably 5% by mass or less, more preferably 2% by mass or less. If this content is 5% by mass or less or 2% by mass or less, there is less concern about excessive film formation on the electrode and a decrease in high-temperature characteristics, and if it is 0.001% by mass or more, sufficient film formation is achieved, which can further improve the discharge capacity retention rate after high-temperature storage. This content is more preferably 0.05% by mass or more, more preferably 0.1% by mass or more, more preferably 0.15% by mass or more, more preferably 0.25% by mass or more, more preferably 0.35% by mass or more, more preferably 0.55% by mass or more, particularly preferably 0.80% by mass or more, and more preferably 1.5% by mass or less, more preferably 1.2% by mass or less.

[0066] (Lithium salt(a))

[0067] The non-aqueous electrolyte of the present invention preferably further contains one or more lithium salts (a) selected from the group consisting of lithium salts having a phosphate backbone and lithium salts having an S (=O) group. By also containing lithium salt (a), the discharge capacity retention rate and anti-gas generation effect after high-temperature storage can be further improved.

[0068] As a specific example of the aforementioned lithium salt (a), lithium salts having a phosphate skeleton, such as LiPO2F2 and Li2PO3F, can be suitably listed; lithium salts having an S (=O) group selected from the group consisting of lithium trifluoro((methanesulfonyl)oxy)borate [LiTFMSB], lithium pentafluoro((methanesulfonyl)oxy)phosphate [LiPFMSP], lithium methyl sulfate [LMS], lithium ethyl sulfate [LES], 2,2,2-trifluoroethyl lithium sulfate [LFES], and FSO3Li. More preferably, the aforementioned lithium salt (a) includes one or more lithium salts selected from the group consisting of LiPO2F2, LiTFMSB, LMS, LES, LFES, and FSO3Li, and even more preferably includes LiPO2F2.

[0069] The content of the aforementioned lithium salt (a) in the non-aqueous electrolyte of the present invention is preferably 0.01% by mass or more and 8% by mass or less relative to the total amount of the non-aqueous electrolyte. If it is within this range, the discharge capacity retention rate and anti-gas generation effect after high-temperature storage can be further improved. More preferably, the aforementioned content is 0.1% by mass or more, further preferably 0.3% by mass or more, particularly preferably 0.4% by mass or more relative to the total amount of the non-aqueous electrolyte, and more preferably 6% by mass or less, further preferably 3% by mass or less, particularly preferably 2% by mass or less.

[0070] (electrolyte salts)

[0071] The following lithium salts (b) can be suitably listed as electrolyte salts used in this invention.

[0072] Specific examples of the aforementioned lithium salts (b) may include inorganic lithium salts such as LiPF6, LiBF4, or LiClO4; lithium salts containing chain-like fluoroalkyl groups such as LiN(SO2F)2[LiFSI], LiN(SO2CF3)2, LiN(SO2C2F5)2, LiCF3SO3, LiC(SO2CF3)3, LiPF4(CF3)2, LiPF3(C2F5)3, LiPF3(CF3)3, LiPF3(iso-C3F7)3, and LiPF5(iso-C3F7); and lithium salts having cyclic fluoroalkyl chains such as (CF2)2(SO2)2NLi and (CF2)3(SO2)2NLi. One or more of these may be used in combination.

[0073] Among these, one or more are selected from the group consisting of LiPF6, LiBF4, LiN(SO2CF3)2, LiN(SO2C2F5)2 and LiN(SO2F)2[LiFSI], and LiPF6 is even more preferred.

[0074] The content of the aforementioned lithium salt (b) in the non-aqueous electrolyte of 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 relative to the total amount of the non-aqueous electrolyte. Furthermore, its upper limit relative to the total amount of the non-aqueous electrolyte is preferably 28% by mass or less, more preferably 23% by mass or less, and even more preferably 20% by mass or less.

[0075] Furthermore, as a suitable combination of these electrolyte salts, it is preferable that the non-aqueous electrolyte contains LiPF6 and further contains at least one lithium salt selected from the group consisting of LiBF4, LiN(SO2CF3)2, and LiN(SO2F)2 [LiFSI], and more preferably a combination containing LiPF6 and further containing LiFSI. If the content of lithium salts other than LiPF6 in the non-aqueous electrolyte of the present invention is 0.01% by mass or more relative to the total amount of the non-aqueous electrolyte, the characteristics after high-temperature charging and storage (hereinafter also referred to as "high-temperature charging and storage characteristics") are improved, and the effect of suppressing gas generation is also improved. Therefore, it is preferable that if the content is 11% by mass or less relative to the total amount of the non-aqueous electrolyte, there is less concern about the reduction of high-temperature charging and storage characteristics. The aforementioned content is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, more preferably 0.6% by mass or more relative to the total amount of the non-aqueous electrolyte, and preferably 10% by mass or less, more preferably 9% by mass or less, and more preferably 6% by mass or less.

[0076] (Non-aqueous solvent)

[0077] As the non-aqueous solvent used in the non-aqueous electrolyte of the present invention, one or more may be suitably selected from the group consisting of cyclic carbonates, linear esters, lactones, ethers, and amides. From the viewpoint of synergistically improving electrochemical properties over a wide temperature range, it is preferable to include linear esters, more preferably linear carbonates, even more preferably both cyclic carbonates and linear esters, and particularly preferably both cyclic carbonates and linear carbonates.

[0078] It should be noted that the term "chain ester" is used to refer to both chain carbonates and chain carboxylic esters.

[0079] As a cyclic carbonate, it is preferable to further include at least one type of saturated cyclic carbonate. Saturated cyclic carbonates include one or more types selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, and 2,3-butylene carbonate, preferably one or more types selected from the group consisting of ethylene carbonate and propylene carbonate, and more preferably ethylene carbonate.

[0080] The content of the aforementioned cyclic carbonate in the non-aqueous electrolyte of the present invention is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more relative to the total amount of the non-aqueous electrolyte. Furthermore, it 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. If the content of the aforementioned cyclic carbonate is below the above-mentioned upper limit, the permeability of Li ions will not be impaired, and the discharge capacity retention rate and anti-gas generation effect after high-temperature storage are further improved, thus it is preferred.

[0081] Furthermore, the non-aqueous electrolyte of the present invention preferably includes at least one of cyclic carbonates having unsaturated bonds such as carbon-carbon double bonds or carbon-carbon triple bonds and cyclic carbonates having fluorine atoms, and more preferably includes cyclic carbonates having unsaturated bonds. If the non-aqueous electrolyte of the present invention includes such cyclic carbonates, the discharge capacity retention rate and anti-gas generation effect after high-temperature storage are improved, and therefore it is preferred. As a cyclic carbonate having unsaturated bonds, vinylene carbonate (VC), vinyl ethylene carbonate (VEC), or 4-ethynyl-1,3-dioxolane-2-one (EEC) is preferred, and vinylene carbonate is more preferred. As a cyclic carbonate having fluorine atoms, 4-fluoro-1,3-dioxolane-2-one (FEC) or trans- or cis-4,5-difluoro-1,3-dioxolane-2-one (hereinafter collectively referred to as "DFEC") is preferred.

[0082] The content of the aforementioned cyclic carbonates with unsaturated bonds in the non-aqueous electrolyte of 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 relative to the total amount of the non-aqueous electrolyte. Furthermore, it is preferably 8% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less. If this content is within the above range, the permeability of Li ions will not be impaired, and the discharge capacity retention rate and anti-gas generation effect after high-temperature storage are further improved, thus it is preferred.

[0083] The content of the aforementioned cyclic carbonates containing fluorine atoms in the non-aqueous electrolyte of the present invention is preferably 0.05% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more relative to the total amount of the non-aqueous electrolyte. Furthermore, it 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. If this content is within the above range, the permeability of Li ions will not be impaired, and the discharge capacity retention rate and anti-gas generation effect after high-temperature storage are further improved, therefore it is preferred.

[0084] These solvents can be used in combination, or, when two or more are used in combination, the improvement in electrochemical properties over a wide temperature range is further enhanced. Therefore, it is preferred, and particularly preferred, to use three or more in combination. Suitable combinations of these cyclic carbonates are 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 DFEC, PC and VC and DFEC, EC and PC and VC and FEC, or EC and PC and VC and DFEC, etc. Among the aforementioned 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, and combinations of EC and VC are even more preferred.

[0085] As chain esters, suitable examples 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; and one or more chain carboxylic acid esters selected from the group consisting of methyl pivalate, ethyl pivalate, propyl pivalate, methyl propionate, ethyl propionate, propyl propionate, methyl acetate, and ethyl acetate.

[0086] Among the aforementioned chain esters, preferably are chain esters containing methyl groups 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, more preferably are chain carbonates containing methyl groups, and even more preferably at least one selected from methyl ethyl carbonate and dimethyl carbonate.

[0087] Furthermore, when using chain carbonates, it is preferable to use two or more types. More preferably, it includes both symmetrical chain carbonates and asymmetrical chain carbonates, and even more preferably, the content of symmetrical chain carbonates is greater than that of asymmetrical chain carbonates.

[0088] The content of the chain ester in the non-aqueous electrolyte of the present invention is not particularly limited, but is preferably 5% by mass or more and 90% by mass or less relative to the total amount of the non-aqueous electrolyte. If the content is 5% by mass or more, the viscosity of the non-aqueous electrolyte will not become too high, and if it is 90% by mass or less, there is less concern about a decrease in the conductivity and cycle characteristics of the non-aqueous electrolyte, which is therefore preferred. More preferably, the content is 10% by mass or more, further preferably 30% by mass or more, particularly preferably 50% by mass or more, and even more preferably 85% by mass or less.

[0089] When the non-aqueous electrolyte of the present invention contains both cyclic carbonates and chain esters, from the viewpoint of improving the electrochemical properties at high temperatures, the ratio of cyclic carbonates to chain esters in the non-aqueous electrolyte is preferably 10:90 to 50:50 by mass, and more preferably 30:70 to 40:60.

[0090] Other non-aqueous solvents suitable examples include one or more cyclic ethers selected from the group consisting of tetrahydrofuran, 2-methyltetrahydrofuran or 1,4-dioxane; chain ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane or 1,2-dibutoxyethane; amides such as dimethylformamide; sulfones such as sulfolane; and lactones such as γ-butyrolactone [GBL], γ-valerolactone or α-angelicolactone.

[0091] To achieve suitable physical properties, the other non-aqueous solvents mentioned above are usually used in combination. Suitable combinations include, for example, combinations of cyclic carbonates with linear esters and lactones, or combinations of cyclic carbonates with linear esters and ethers, more preferably combinations of cyclic carbonates with linear esters and lactones, and among the lactones, GBL is even more preferred.

[0092] The content of other non-aqueous solvents relative to the total amount of non-aqueous electrolyte is preferably 1% by mass or more, more preferably 2% by mass or more, and preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less. Within this concentration range, there are fewer concerns about decreased conductivity and reduced high-temperature charging and storage characteristics due to solvent decomposition.

[0093] To further improve the high-temperature charging and preservation characteristics and suppress gas production, it is preferable to add other additives to the non-aqueous electrolyte.

[0094] Specific examples of other additives include the following compounds (A) to (J).

[0095] (A) One or more nitriles selected from the group consisting of acetonitrile, propionitrile, butyronitrile, pentonitrile, hexonitrile, decanonitrile, undecanenitrile, dodecanenitrile, cyclohexanecarboxylonitrile, acrylonitrile, methacrylonitrile, crotonitrile, etc., which have one cyano group in the molecule; malononitrile, butyronitrile, glutaronitrile, adiponitrile, heptacyanide, octanoic acid nitrile, sebacate, methylmalonitrile, ethylmalonitrile, dicyclohexyl-1,1-dicarboxylonitrile, 1,2-dicyanobenzene, etc., which have two cyano groups in the molecule; and 1,2,3-propanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,3,5-cyclohexanetricarbonitrile, 1,3,5-benzenetricarbonitrile, etc., which have three cyano groups in the molecule.

[0096] (B) Aromatic compounds with branched alkyl groups, such as cyclohexylbenzene, tert-butylbenzene, tert-pentylbenzene or 1-fluoro-4-tert-butylbenzene; aromatic compounds such as biphenyl, terphenyl (ortho, meta, para), fluorobenzene, methyl phenyl carbonate, ethyl phenyl carbonate or diphenyl carbonate.

[0097] Among aromatic compounds, more preferably one or more are selected from the group consisting of biphenyl, terphenyl (ortho, meta, para), fluorobenzene, cyclohexylbenzene, tert-butylbenzene, and tert-amylbenzene, and even more preferably one or more are selected from the group consisting of biphenyl, ortho-terphenyl, fluorobenzene, cyclohexylbenzene, and tert-amylbenzene.

[0098] (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, ethyl 2-isocyanate acrylate, ethyl 2-isocyanate methacrylate, 1,3-diisocyanopropane, carbonyl diisocyanate, 1,4-diisocyano-2-fluorobutane, and 1,3-bis(isocyanomethyl)cyclohexane.

[0099] More preferably, among the isocyanate compounds, one or more are selected from the group consisting of hexamethylene diisocyanate, octamethylene diisocyanate, ethyl 2-isocyanate acrylate, ethyl 2-isocyanate methacrylate, and 1,3-bis(isocyanomethyl)cyclohexane.

[0100] (D) One or more compounds containing a triple bond selected from the group consisting of 2-propynyl methylcarboxylic acid, 2-propynyl acetate, 2-propynyl formic acid, 2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynyl vinyl sulfonate, 2-propynyl 2-(methanesulfonyloxy)propionic acid, di(2-propynyl) oxalate, 2-butyn-1,4-dimethyl dimethanesulfonate, and 2-butyn-1,4-dimethyl diformate.

[0101] As a compound containing a triple bond, it is preferably selected from one or more of the group consisting of 2-propynyl methylcarboxylate, 2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, di(2-propynyl) oxalate and 2-butyn-1,4-dimethyl dimethanesulfonate, and more preferably from one or more of the group consisting of 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, di(2-propynyl) oxalate and 2-butyn-1,4-dimethyl dimethanesulfonate.

[0102] (E) Selected from 1,3-propanesulfonate lactone, 1,3-butanesulfonate lactone, 2,4-butanesulfonate lactone, 1,4-butanesulfonate lactone, 1,5-pentanesulfonate lactone, 1-fluoro-1,3-propanesulfonate lactone, 1-methyl-1,3-propanesulfonate lactone, 1-propene-1,3-sulfonate lactone, 2-propene-1,3-sulfonate lactone, 1-fluoro-1-propene-1,3-sulfonate lactone, 1-methyl-1-propene-1,3-sulfonate lactone, methylene disulfonate, ethylene disulfonate, 2,2-dioxo-1,2-oxathiolan-4-yl acetate (2,2-dioxido-1,2-oxathiolan-4-yl) Cyclic sulfonates such as acetate; methyl fluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate, butyl dimethanesulfonate, methyl methanesulfonyloxyacetate, pentafluorophenyl methanesulfonate, methyl vinyl sulfonate, allyl vinyl sulfonate, 2-propynyl vinyl sulfonate, allyl sulfonyl propargyl, methyl methanedisulfonate methoxycarbonyl methyl ester, methyl methanedisulfonate ethoxycarbonyl methyl ester, methyl 1,3-butanedisulfonate methoxycarbonyl methyl ester, methyl 1,3-butanedisulfonate ethoxycarbonyl methyl ester, 1,3-butanedisulfonate 1-methoxycarbonyl ethyl ester, 1,3-butanedisulfonate 1-ethoxycarbonyl ethyl ester, butane-2,3-dimethyl dimethanesulfonate, butane-1,4-dimethyl dimethanesulfonate, and other alkyl disulfonate esters and other chain sulfonates. Esters; vinyl sulfone compounds such as divinyl sulfone, 1,2-bis(vinylsulfonyl)ethane or bis(2-vinylsulfonylethyl) ether; chain sulfates such as dimethyl sulfate, methyl ethyl sulfate, and diethyl sulfate; cyclic sulfates such as 1,2-ethylene sulfate, 1,2-propylene sulfate, 1,3-propylene sulfate, and 1,2-butylene sulfate; chain sulfites such as dimethyl sulfite, methyl ethyl sulfite, and diethyl sulfite; and compounds containing one or more S=O groups in the group consisting of cyclic sulfites 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.

[0103] As for the aforementioned compounds containing the S=O group, they can be classified into cyclic compounds containing the S=O group and chain compounds containing the S=O group. Among the cyclic compounds containing the S=O group, one or more selected from the group consisting of 1,3-propanesulfonate lactone, 1,3-butanesulfonate lactone, 1,4-butanesulfonate lactone, 2,4-butanesulfonate lactone, 1-propene-1,3-sulfonate lactone, 2,2-dioxo-1,2-oxothiacyclopentan-4-yl acetate, methylene disulfonate, 1,2-ethylene sulfate, 1,2-ethylene sulfite, and 1-vinyl-1,2-ethylene sulfite can be appropriately listed. Furthermore, among the chain-like compounds containing an S=O group, one or more may be suitably selected from the group consisting of 2,3-dimethyl dimethanesulfonate, 1,4-dimethyl dimethanesulfonate, pentafluorophenyl methanesulfonate, divinyl sulfone, and bis(2-vinylsulfonylethyl) ether. Among the aforementioned cyclic or chain-like compounds containing an S=O group, one or more may be selected from the group consisting of 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, 2,4-butanesulfonate lactone, 1,2-ethylene sulfate, 1,2-ethylene sulfite, 1-vinyl-1,2-ethylene sulfite, 2,2-dioxo-1,2-oxothiacyclopentan-4-yl acetate, pentafluorophenyl methanesulfonate, and divinyl sulfone.

[0104] (F) Cyclic acetals containing an "acetal group" within the molecule. There is no particular limitation on the type of acetal as long as it contains an "acetal group" within the molecule. Specific examples include cyclic acetals such as 1,3-dioxolane, 1,3-dioxane, or 1,3,5-trioxane.

[0105] As a cyclic acetal compound, it is preferably 1,3-dioxolane or 1,3-dioxane, more preferably 1,3-dioxane.

[0106] (G) is selected from one or more phosphorus-containing compounds in the group consisting of trimethyl phosphate, tributyl phosphate, trioctyl phosphate, tri(2,2,2-trifluoroethyl) phosphate, ethyl 2-(diethoxyphosphoryl)acetate and 2-(diethoxyphosphoryl)acetic acid 2-propynyl ester.

[0107] As a phosphorus-containing compound, ethyl 2-(diethoxyphosphoryl)acetate or 2-(diethoxyphosphoryl)acetic acid 2-propynyl ester is preferred, and more preferably 2-(diethoxyphosphoryl)acetic acid 2-propynyl ester is preferred.

[0108] (H) Anhydrides that have an intramolecular "C(=O)-OC(=O) group", "C(=O)-OS(=O)2 group" or "S(=O)2-OS(=O)2 group". Specific examples include one or more anhydrides selected from the group consisting of acetic anhydride, acrylic anhydride, methacrylic anhydride, cyclohexanecarboxylic anhydride, propionic 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.

[0109] The preferred acid anhydrides are methacrylic anhydride, succinic anhydride, maleic anhydride, allyl succinic anhydride, and 1,2,6-oxadithiane-2,2,6,6-tetraoxide, and more preferably succinic anhydride, allyl succinic anhydride, and 1,2,6-oxadithiane-2,2,6,6-tetraoxide.

[0110] (J) Phosphazene compounds containing an "N=PN group" within the molecule. There is no particular limitation on the type of phosphazene compound as long as it contains an "N=PN group" within the molecule. Specific examples include cyclic phosphazene compounds such as methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, or ethoxyheptafluorocyclotetraphosphazene.

[0111] As a cyclic phosphazene compound, the preferred cyclic phosphazene compounds are methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, or phenoxypentafluorocyclotriphosphazene, and more preferably methoxypentafluorocyclotriphosphazene or ethoxypentafluorocyclotriphosphazene.

[0112] (K) As an organic compound having an isocyanuric acid skeleton (hereinafter also referred to as "isocyanurate compound"), there is no particular limitation as long as it is an organic compound having at least one isocyanuric acid skeleton in its molecule. Examples of organic compounds having an isocyanuric acid skeleton include the following compounds.

[0113]

[0114] In particular, from the viewpoint of forming a stable protective coating at the interface, isocyanurate compounds that optionally have halogen atoms and saturated or unsaturated aliphatic hydrocarbon groups are preferred, isocyanurate compounds that have unsaturated aliphatic hydrocarbon groups containing carbon-carbon unsaturated bonds at the ends are more preferred, and triallyl isocyanurate is even more preferred.

[0115] (L) As a silicon-containing compound, there are no special restrictions as long as it is a compound with at least one silicon atom in its molecule.

[0116] Examples of silicon-containing compounds include borate compounds such as tri(trimethylsilyl) borate, tri(trimethoxysilyl) borate, tri(triethylsilyl) borate, and tri(dimethylvinylsilyl) borate; phosphate compounds such as tri(trimethylsilyl) phosphate, tri(triethylsilyl) phosphate, tri(triphenylsilyl) phosphate, tri(trimethoxysilyl) phosphate, and tri(dimethylvinylsilyl) phosphate; and tri(trimethylsilyl) phosphite, tri(triethylsilyl) phosphite, tri(triphenylsilyl) phosphite, and tri(trimethoxysilyl) phosphite. Alkyl esters, tri(dimethylvinylsilyl) phosphite and other phosphorous compounds; trimethylsilyl methanesulfonate, trimethylsilyl tetrafluoromethanesulfonate and other sulfonic acid compounds; tetramethylsilane, trimethylvinylsilane, dimethyldivinylsilane, methyltrivinylsilane, tetravinylsilane and other silane compounds; hexamethyldisilane, hexaethyldisilane, 1,1,2,2-tetramethyldisilane, 1,2-diphenyltetramethyldisilane and other disilane compounds; hexamethyldisiloxane, 1,3-divinyltetramethyldisiloxane, 1,1,3,3-tetramethyl-1,3-diphenyldisiloxane and other disiloxane compounds, etc.

[0117] From the viewpoint of forming a stable interface protective coating, disilane compounds and disiloxane compounds are preferred, more preferably disiloxane compounds, even more preferably hexamethyldisiloxane and 1,3-divinyltetramethyldisiloxane, and particularly preferably 1,3-divinyltetramethyldisiloxane.

[0118] If the above-mentioned compounds include at least one of the following groups: (A) nitrile compounds, (B) aromatic compounds and (C) isocyanate compounds, the electrochemical properties at high temperatures are further improved, and therefore preferred.

[0119] The content of the compounds mentioned in (A) to (C) is preferably 0.01% by mass or more and 7% by mass or less relative to the total amount of the non-aqueous electrolyte. Within this range, the coating will not become too thick but can be sufficiently formed, which can improve the high-temperature charging preservation characteristics and suppress gas generation. This content is more preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 5% by mass or less, and more preferably 3% by mass or less relative to the total amount of the non-aqueous electrolyte.

[0120] Furthermore, if the compound contains at least one of the following: (D) compounds containing a triple bond, (E) compounds containing an S=O group, (F) cyclic acetal compounds, (G) phosphorus-containing compounds, (H) acid anhydrides, (J) cyclic phosphazene compounds, (K) organic compounds having an isocyanuric acid skeleton, and (L) silicon-containing compounds, the high-temperature charging and preservation characteristics can be improved and gas generation can be suppressed, and therefore it is preferred.

[0121] The content of each of the aforementioned compounds (D) to (L) relative to the total amount of the non-aqueous electrolyte is preferably 0.001% by mass or more and 5% by mass or less. Within this range, the coating will not become too thick but can be sufficiently formed, which can further improve the high-temperature charging preservation characteristics and suppress gas generation. This content is more preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 3% by mass or less, and more preferably 2% by mass or less, relative to the total amount of the non-aqueous electrolyte.

[0122] In addition, for the purpose of further improving the electrochemical properties at high temperatures, it is preferable to further include a lithium salt with an oxalic acid skeleton in the non-aqueous electrolyte (c).

[0123] Specific examples of the aforementioned lithium salts (c) may include lithium bis(oxalate)borate [LiBOB], lithium difluoro(oxalate)borate [LiDFOB], lithium tetrafluoro(oxalate)phosphate [LiTFOP], and lithium difluorobis(oxalate)phosphate [LiDFOP].

[0124] The content of the aforementioned lithium salt (c) in the non-aqueous electrolyte of the present invention is preferably 0.01% by mass or more and 8% by mass or less relative to the total amount of the non-aqueous electrolyte. If it is within this range, the high-temperature charging and storage characteristics can be further improved, and gas generation can be further suppressed. This content is more preferably 0.1% by mass or more, more preferably 0.3% by mass or more, particularly preferably 0.4% by mass or more, and even more preferably 6% by mass or less, and more preferably 3% by mass or less relative to the total amount of the non-aqueous electrolyte.

[0125] In this specification, the composition of the non-aqueous electrolyte refers to the composition of the energy storage device containing the non-aqueous electrolyte at the time of shipment. It is not necessarily required to analyze the composition of the non-aqueous electrolyte at the time of shipment. It is sufficient to determine the content of the constituent components during the manufacturing of the non-aqueous electrolyte or when injecting it into the energy storage device, and to manufacture the energy storage device in a manner that ensures the composition at the time of shipment falls within the desired range.

[0126] That is, non-aqueous electrolytes can be mixed in a predetermined manner, with each component in the ratio specified during preparation. Alternatively, the composition of the non-aqueous electrolyte can be confirmed by analysis after preparation. Furthermore, non-aqueous electrolytes can be recovered from completed storage devices and analyzed. Methods for recovering non-aqueous electrolytes include: opening part or all of the storage device container or creating a hole in the storage device container to extract the electrolyte. The electrolyte can be recovered by centrifuging the opened storage device container, or by injecting an extraction solvent (e.g., preferably acetonitrile dehydrated to a water content of 10 ppm or less) into the opened storage device container or by contacting the extraction solvent with the storage device elements. The non-aqueous electrolyte recovered using this method can be analyzed. Additionally, to prepare the recovered non-aqueous electrolyte under conditions suitable for analysis, it can be diluted and analyzed.

[0127] The optimal analytical method for non-aqueous electrolytes varies depending on the composition of the electrolyte. Specifically, methods include inductively coupled plasma (ICP) luminescence spectrophotometry, nuclear magnetic resonance (NMR), gas chromatography, ion chromatography, and liquid chromatography. The NMR-based analytical method is described below. Under an inactive atmosphere, the non-aqueous electrolyte is dissolved in a dehydrated solvent (dehydrated to below 10 ppm) and placed in an NMR tube for NMR measurement. Alternatively, a sleeve can be used as the NMR tube, with the non-aqueous electrolyte placed in one and the dehydrated solvent in the other, followed by NMR measurement. Examples of dehydrated solvents include deuterated acetonitrile and deuterated dimethyl sulfoxide. When the concentration of the components of the non-aqueous electrolyte is determined, a specified amount of a standard substance can be dissolved in the dehydrated solvent, and the concentration of each component can be calculated based on the ratio of the spectra. Alternatively, the concentrations of one or more components constituting the non-aqueous electrolyte can be pre-determined using other analytical methods such as gas chromatography, and the concentration can be calculated based on the spectral ratio of the known component to the other components. The nuclear magnetic resonance (NMR) analyzer used is preferably one with a proton resonance frequency of 400 MHz or higher. Examples of nuclei that can be determined include... 1 H, 31 P, 19 F, 11 B, etc.

[0128] These analytical methods can be used individually or in combination of two or more.

[0129] [Manufacturing method of non-aqueous electrolyte]

[0130] The non-aqueous electrolyte of the present invention can be obtained, for example, by mixing the aforementioned non-aqueous solvent, adding the aforementioned electrolyte salt thereto, and adding the aforementioned compound of general formula (I) to the non-aqueous electrolyte.

[0131] At this point, the non-aqueous solvent used and the compounds added to the non-aqueous electrolyte are preferably substances that have been pre-refined to minimize impurities without significantly reducing productivity.

[0132] [Electronic Storage Equipment]

[0133] The non-aqueous electrolyte of this invention can be used in energy storage devices. As a non-aqueous electrolyte, it can be either a liquid or a gelled substance. Furthermore, the non-aqueous electrolyte of this invention can also be used as a solid polymer electrolyte. Preferably, it is used in energy storage devices where lithium salts are used as the electrolyte salt.

[0134] The energy storage device of the present invention is characterized in that it comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, wherein the non-aqueous electrolyte is the non-aqueous electrolyte described in the present invention. The energy storage device of the present invention is preferably a lithium battery and capacitor using a lithium salt as the electrolyte salt, and more preferably a lithium battery.

[0135] [Lithium-ion batteries]

[0136] In this specification, lithium battery refers to both primary lithium batteries and secondary lithium batteries. Additionally, in this specification, the term secondary lithium battery is used to encompass the concept of lithium-ion secondary batteries.

[0137] The lithium battery used in the energy storage device described in this invention includes a positive electrode, a negative electrode, and the aforementioned non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent. Components such as the positive electrode and negative electrode, other than the non-aqueous electrolyte, may be used without particular limitation.

[0138] (Positive electrode active material)

[0139] As a positive electrode active material for lithium secondary batteries, a composite metal oxide containing one or more elements selected from the group consisting of cobalt, manganese, and nickel, and formed with lithium, can be used. These positive electrode active materials can be used alone or in combination of two or more.

[0140] Suitable examples of such lithium composite metal oxides include, for instance, LiCoO2 and LiCo. 1-x M x O2 (where 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, LiCo1-x Ni x O2(0.01 <x<1)、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 0.15 Al 0.05 Solid solutions of O2, Li2MnO3 and LiMO2 (where M is a transition metal such as Co, Ni, Mn, Fe, etc.), and LiNi 1 / 2 Mn 3 / 2 One or more of the following O4 groups can be used in combination: two or more O4 groups. Additionally, they can be used in combinations such as LiCoO2 with LiMn2O4, LiCoO2 with LiNiO2, and LiMn2O4 with LiNiO2.

[0141] In particular, Ni-containing positive electrode active materials are preferred for use as positive electrode active materials in energy storage devices due to their theoretically high Li uptake. However, Ni-containing positive electrode active materials tend to experience decomposition of non-aqueous solvents at the positive electrode surface due to the catalytic effect of Ni, which can easily increase the battery resistance. In particular, there is a tendency for battery characteristics to degrade at high temperatures, but the lithium secondary battery described in this invention can suppress these degradations. From the viewpoint of improving the capacity of energy storage devices, the above-mentioned effects become significant when using positive electrode active materials in which the atomic concentration of Ni relative to the atomic concentration of all transition metal elements exceeds 30 atomic%, and are therefore preferred, more preferably 50 atomic% or more, and particularly preferably 75 atomic% or more.

[0142] As specific examples, LiCo can be appropriately listed. 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 0.15 Al0.05 O2, etc. Among these, ternary cathode active materials (NCM) based on nickel, cobalt, and manganese are preferred, and those selected from LiNi are more preferred. 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 One or more of the following: O2.

[0143] Lithium-containing olivine-type phosphates can also be used as positive electrode active materials. Particularly preferred are lithium-containing olivine-type phosphates containing at least one type selected from the group consisting of iron, cobalt, nickel, and manganese. Specific examples include LiFePO4, LiCoPO4, LiNiPO4, and LiMnPO4.

[0144] These lithium-containing olivine-type phosphates may be optionally substituted with other elements, or a portion of iron, cobalt, nickel, and manganese may be substituted 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 they may be covered with compounds or carbon materials containing these other elements. Among these, LiFePO4 or LiMnPO4 are preferred.

[0145] In addition, lithium-containing olivine-type phosphates can also be used in combination with, for example, the aforementioned positive electrode active materials.

[0146] There are no particular limitations on the positive electrode active material; however, using positive electrode active materials containing Co or Ni can significantly improve battery characteristics. Suitable examples of positive electrode active materials include, for instance, LiCoO2 and LiCo. 1 / 3 Ni 1 / 3 Mn 1 / 3O2, 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 Al 0.05 O2.

[0147] The conductive agent for the positive electrode is not particularly limited as long as it is an electron-conducting material that does not undergo chemical change. Examples include natural graphite (flake graphite, etc.) and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black. Alternatively, graphite and carbon black can be appropriately mixed. 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.

[0148] The positive electrode can be manufactured as follows: The aforementioned positive electrode active material is mixed with conductive agents such as acetylene black and carbon black, as well as binders such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene copolymer (SBR), acrylonitrile-butadiene copolymer (NBR), carboxymethyl cellulose (CMC), and ethylene-propylene diene terpolymer. A high-boiling-point solvent such as 1-methyl-2-pyrrolidone is added and the mixture is kneaded to form a positive electrode mixture. This positive electrode mixture is then coated onto aluminum foil or stainless steel strips of the current collector, dried, and pressurized. Finally, it is heated under vacuum at a temperature of approximately 50°C to 250°C for about 2 hours to produce the electrode.

[0149] (Negative electrode active material)

[0150] As negative electrode active materials for lithium secondary batteries, materials such as lithium metal, lithium alloys, and carbon materials capable of absorbing and releasing lithium ions (easily graphitized carbon, difficult-to-graphitize carbon with an (002) plane spacing of 0.37 nm or more, graphite with an (002) plane spacing of 0.34 nm or less, etc.), tin (elemental), tin compounds, silicon (elemental), silicon compounds, and Li4Ti5O can be used. 12 One or more of lithium titanate compounds, etc.

[0151] Among these, in terms of lithium-ion adsorption and release capabilities, highly crystalline carbon materials such as artificial graphite and natural graphite are preferred, and even more preferred are interfacial spacers (d) with lattice planes (002). 002 It is a carbon material with a graphite-type crystal structure below 0.340 nm (preferably 0.335 to 0.337 nm).

[0152] Artificial graphite particles with a blocky structure, obtained by aggregating or combining multiple flat graphitic microparticles that are not parallel to each other, such as graphite particles obtained by repeatedly applying mechanical actions such as compression, friction, and shearing forces to flake-like natural graphite particles and performing spheroidization treatment, are used to compress and shape the density of the portion of the negative electrode, excluding the current collector, to 1.5 g / cm³. 3When the ratio I(110) / I(004) of the peak intensity I(110) of the (110) plane of the graphite crystal obtained by X-ray diffraction of the negative electrode sheet at a density above to the peak intensity I(004) of the (004) plane reaches 0.01 or more, the amount of metal dissolved from the positive electrode active material is further improved, and the charge storage characteristics are improved, so it is preferably, more preferably reaches 0.05 or more, and further preferably reaches 0.1 or more. In addition, sometimes due to excessive treatment, the crystallinity decreases and the discharge capacity of the battery decreases, so the upper limit is preferably 0.5 or less, more preferably 0.3 or less.

[0153] In addition, if a carbon material (core material) with high crystallinity is covered with a carbon material having lower crystallinity than the core material, the high-temperature charge storage characteristics become better, so it is preferably. The crystallinity of the covering carbon material can be confirmed by a transmission electron microscope (TEM).

[0154] If a carbon material with high crystallinity is used, there is a tendency that it reacts with the non-aqueous electrolyte during charging and the high-temperature charge storage characteristics deteriorate due to an increase in the interfacial resistance. However, in the lithium secondary battery of the present invention, the high-temperature charge storage characteristics become good.

[0155] In addition, regarding metal compounds capable of occluding and releasing lithium ions as the negative electrode active material, compounds containing at least one of metal elements such as Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Mg, Sr, Ba, etc. can be cited. These metal compounds can be used in any form such as a simple substance, an alloy, an oxide, a nitride, a sulfide, a boride, an alloy formed with lithium, etc. Any of a simple substance, an alloy, an oxide, and an alloy formed with lithium can achieve high capacity, so it is preferably. Among them, it is preferably contains at least one element selected from Si, Ge, and Sn, and a compound containing at least one element selected from Si and Sn can make the battery achieve high capacity, so it is particularly preferably.

[0156] Furthermore, regarding metal compounds capable of occluding and releasing lithium ions as the negative electrode active material, metal compounds containing Si element and Ti element can improve the battery characteristics, so it is preferably. Among the metal compounds containing Si element, the composite material of Si and SiO2, that is, SiO x can further improve the battery characteristics including the cycle retention rate, so it is preferably. It should be noted that the range of the aforementioned x is 0 < x < 2. Among the metal compounds containing Ti element, the titanium-containing metal oxides with Li4Ti5O 12 and / or TiNb2O7 as the main component have small expansion and contraction during charge and discharge and exhibit flame retardancy. Therefore, they are preferably in terms of improving the battery safety.

[0157] In summary, there are no particular limitations on the aforementioned negative electrode active materials for lithium secondary batteries, as long as they can absorb and release lithium ions. Preferably, materials selected from lithium metal, carbon materials, silicon metal, and metal oxides containing Si (SiO2) are used. x ) and metal oxides containing Ti (Li4Ti5O) 12 One or more of the following materials are selected from the group consisting of TiNb2O7, etc., and more preferably, materials selected from carbon materials, silicon metal and SiO2 are used. x One or more of the above.

[0158] As the aforementioned negative electrode active material, it is used in combination with carbon materials and silicon metal or SiO2. x In the case of silicon metal or SiO x The weight ratio is not particularly limited, but it is preferably 30% by mass or less, more preferably 10% by mass or less, relative to the total mass of the negative electrode mixture containing the negative electrode active material, conductive agent, binder, and high-boiling-point solvent.

[0159] The negative electrode can be made as follows: using the same conductive agent, binder, and high-boiling-point solvent as the positive electrode, the negative electrode mixture is mixed to form a negative electrode mixture. The negative electrode mixture is then coated onto the copper foil of the current collector, dried, and pressed into shape. Finally, it is heated under vacuum at a temperature of about 50°C to 250°C for about 2 hours to produce the negative electrode.

[0160] The density of the negative electrode, excluding the current collector, is typically 1.1 g / cm³. 3 In order to further improve the battery capacity, a value of 1.4 g / cm³ is preferred. 3 The above, and more preferably 1.7 g / cm 3 The above, and preferably 2g / cm 3 the following.

[0161] In addition, lithium metal or lithium alloys can be listed as negative electrode active materials used in primary lithium batteries.

[0162] There are no particular limitations on the structure of lithium batteries. They can be coin-shaped, cylindrical, prismatic, or laminated batteries with single or multiple separators.

[0163] As a separator for batteries, there are no particular limitations; single-layer or multi-layered microporous films, woven fabrics, non-woven fabrics, etc., made of polypropylene, polyethylene, or other polyolefins can be used.

[0164] The lithium secondary battery of this invention exhibits excellent cycle characteristics when the charging termination voltage is 4.2V or higher, especially 4.3V or higher, and furthermore, its characteristics are good when the charging termination voltage is 4.4V or higher. The discharging termination voltage can typically be set to 2.8V or higher, and further, to 2.5V or higher; in this invention, the lithium secondary battery can be set to 2.0V or higher. There are no particular limitations on the current value, and it is generally used in the range of 0.1 to 30C. Furthermore, the lithium battery of this invention can be charged and discharged at -40 to 100°C, preferably -10 to 80°C.

[0165] In this invention, as a countermeasure against the rise in internal pressure of the lithium battery, methods such as installing a safety valve on the battery cover or making cuts on components such as the battery canister and gaskets can be employed. Furthermore, as a safety measure to prevent overcharging, a current-blocking mechanism that senses the internal pressure of the battery and blocks the current can be installed on the battery cover.

[0166] [Capacitor]

[0167] Examples of capacitors that incorporate the non-aqueous electrolyte of the present invention include double-layer capacitors and lithium-ion capacitors.

[0168] A double-layer capacitor is an energy storage device that utilizes the capacity of the electric double layer at the interface between the electrolyte and the electrodes. Activated carbon is the most typical electrode active material used in this device. The double-layer capacity increases approximately proportionally to the surface area.

[0169] Lithium-ion capacitors (LICs) are energy storage devices that utilize the insertion of lithium ions into carbon materials such as graphite, which serve as the negative electrode. Positive electrodes can include, for example, those utilizing the electric double layer between an activated carbon electrode and the electrolyte, or those utilizing the doping / dedoping reaction of a π-conjugated polymer electrode. The electrolyte contains lithium salts such as LiPF6.

[0170] Example

[0171] The following examples illustrate the synthesis of compounds of the present invention and embodiments of lithium-ion secondary batteries obtained using the non-aqueous electrolyte of the present invention, but the present invention is not limited to these synthesis examples and embodiments.

[0172] Synthetic Example 1 [Di-2-propynyl vinylphosphonate (Compound 1-1)]

[0173] 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 at 60 °C for 4 hours in 100 mL of 1,2-dichloroethane. After the reaction was completed, the mixture was allowed to cool naturally to room temperature and then concentrated under reduced pressure to obtain 12.5 g of vinylphosphonic acid diacyl chloride.

[0174] 6.7 g (46.3 mmol) of vinylphosphonic dichloroisocyanurate, 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. Triethylamine (9.4 g, 92.6 mmol) was added dropwise to the 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 complete, 20 mL of water was added for separation. The organic layer was washed with 20 mL of water, and the solvent was removed by vacuum distillation. The residue was purified by silica gel column chromatography to obtain 6.0 g of vinylphosphonic di-2-propargyl ester (yield: 70%).

[0175] Regarding the obtained vinylphosphonate di-2-propynyl ester (compound 1), the following is shown. 1 ¹H-NMR measurement results.

[0176] 1 H-NMR (400MHz, CDCl3): δ=6.44-6.04(m,3H), 4.70(d,4H,J=10.5Hz), 2.56(s,2H).

[0177] Synthetic Example 2 [Allylphosphonic acid di-2-propynyl ester (compound 2-1)]

[0178] The vinylphosphonic acid in Synthesis Example 1 was replaced with allylphosphonic acid, but otherwise synthesized in the same manner as in Synthesis Example 1.

[0179] Regarding the obtained allylphosphonic acid di-2-propynyl ester (compound 2-1), the following is shown. 1 ¹H-NMR measurement results.

[0180] 1 H-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).

[0181] Synthetic Example 3 [Crotonylphosphonate di-2-propynyl ester (Compound 5-1)]

[0182] The vinylphosphonic acid in Synthesis Example 1 was replaced with crotonylphosphonic acid, but otherwise synthesized in the same manner as in Synthesis Example 1.

[0183] Regarding the obtained crotonylphosphonate di-2-propynyl ester (compound 5-1), the following is shown. 1 ¹H-NMR measurement results.

[0184] 1H-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).

[0185] Examples 1-1 to 2-3, Comparative Examples 1-1, 2-1 to 2-6

[0186] [The manufacture of lithium-ion secondary batteries]

[0187] The positive electrode active material (LiNi) 0.8 Mn 0.1 Co 0.1 O2 (NCM (8 / 1 / 1)) 90% by mass, acetylene black (conductive agent) 3% by mass, and KS-4 (registered trademark) (conductive agent) 3% by mass are mixed and added to a solution obtained by dissolving 4% by mass of polyvinylidene fluoride (binder) in 1-methyl-2-pyrrolidone, and then mixed to prepare a positive electrode paste. This positive electrode paste is coated onto both sides of an aluminum foil (current collector), dried, pressurized, and cut to the specified size to form rectangular positive electrode sheets. The density of the positive electrode portion excluding the current collector is 2.5 g / cm³. 3 .

[0188] In addition, a negative electrode paste was prepared by adding 98% by mass of artificial graphite (negative electrode active material), 1% by mass of carboxymethyl cellulose (thickener), and 1% by mass of a copolymer of butadiene (binder) to water and mixing them. This negative electrode paste was then coated onto both sides of a copper foil (current collector), dried, pressurized, and cut to the specified size to fabricate the negative electrode sheet. The density of the portion of the negative electrode excluding the current collector was 1.4 g / cm³. 3 Furthermore, a laminated battery was fabricated by stacking a positive electrode, a polyolefin microporous film separator, and a negative electrode in that order, and adding non-aqueous electrolytes with the compositions described in Tables 1 and 2 respectively.

[0189] It should be noted that in Tables 1-3, EC stands for ethylene carbonate, MEC stands for methyl ethyl carbonate, and VC stands for vinylene carbonate.

[0190] [Evaluation of characteristics after high-temperature charging and storage]

[0191] Initial discharge capacity

[0192] Using the laminated battery prepared by the above method, the following pretreatment was performed. Then, it was charged in a constant temperature bath at 25°C with a constant current of 0.2C and a constant voltage for 7 hours until the termination voltage was 4.2V. It was then discharged at a constant current of 0.2C until the termination voltage was 2.7V. The initial discharge capacity at 25°C was then calculated.

[0193] (Preprocessing)

[0194] Charge at a constant current of 0.05C for 1 hour in a 25°C constant temperature bath, then let stand for 6 hours. Afterward, charge at 0.2C to 4.2V and let stand in a 60°C constant temperature bath for 48 hours. Place in a 25°C constant temperature bath and temporarily discharge at a constant current of 0.2C until the termination voltage is 2.75V. Charge again at 0.2C to 4.2V, then discharge at a constant current of 0.2C until the termination voltage is 2.75V.

[0195] High-Temperature Charging and Storage Test

[0196] Next, the laminated battery was charged in a 60°C constant temperature bath at a constant current of 1C and a constant voltage for 7 hours until the termination voltage reached 4.2V. The temperature of the constant temperature bath was then raised to 60°C and maintained at 4.2V. The battery was stored for 20 days in the experiment recorded in Table 1 and for 10 days in the experiment recorded in Table 2. Afterward, it was placed in a 25°C constant temperature bath and temporarily discharged at a constant current of 0.2C until the termination voltage reached 2.75V.

[0197] <Discharge capacity after high-temperature charging and storage>

[0198] Then, following the same procedure as the initial discharge capacity determination, the discharge capacity at 25°C after high-temperature charging and storage was calculated.

[0199] <Discharge capacity retention rate after high-temperature charging and storage>

[0200] Using the initial 25°C discharge capacity and the 25°C discharge capacity after high-temperature charging and storage, the discharge capacity retention rate after high-temperature charging and storage is calculated by the following formula.

[0201] Discharge capacity retention rate at 25℃ after high-temperature charging and storage (%) = (Discharge capacity at 25℃ after high-temperature charging and storage / Initial discharge capacity at 25℃) × 100

[0202] <Evaluation of gas production after high-temperature charging and storage>

[0203] The gas production after high-temperature charging and storage was determined using the Archimedes method. The gas production is a relative value with the gas production measured using a laminated battery with a non-aqueous electrolyte that does not contain compounds of general formula (I) set at 100%.

[0204] The results of the battery characteristics are shown in Tables 1 and 2.

[0205] [Table 1]

[0206] Table 1

[0207]

[0208] [Table 2]

[0209] Table 2

[0210]

[0211] Examples 3-1 to 3-2, Comparative Example 3-1

[0212] [The manufacture of lithium-ion secondary batteries]

[0213] The positive electrode paste was changed to: the positive electrode active material (LiNi) 0.70 Mn 0.15 Co 0.15 O2 (NCM (7 / 1.5 / 1.5)) 90% by mass and acetylene black (conductive agent) 7% by mass are mixed and added to a solution obtained by dissolving polyvinylidene fluoride (binder) 3% by mass in 1-methyl-2-pyrrolidone. The positive electrode paste is obtained by mixing. Otherwise, the laminated battery is made in the same manner as in Examples 1-1.

[0214] [Evaluation of characteristics after high-temperature charging and storage]

[0215] Initial discharge capacity

[0216] Using the laminated battery prepared by the above method, pretreatment is performed. Then, it is charged in a constant temperature bath at 25°C with a constant current and constant voltage of 0.2C to a termination voltage of 4.4V, and discharged at a constant current of 0.2C to a termination voltage of 2.8V. The initial discharge capacity at 25°C is then calculated.

[0217] High-Temperature Charging and Storage Test

[0218] Next, the laminated battery was charged in a 60°C constant temperature bath at a constant current and constant voltage of 1C until the termination voltage reached 4.4V. The temperature of the constant temperature bath was then raised to 60°C, and the battery was stored at 4.2V for 14 days. Afterward, it was placed in a 25°C constant temperature bath and temporarily discharged at a constant current of 0.2C until the termination voltage reached 2.8V.

[0219] <Discharge capacity after high-temperature charging and storage>

[0220] Then, following the same procedure as the initial discharge capacity determination, the discharge capacity at 25°C after high-temperature charging and storage was calculated.

[0221] Evaluation of discharge capacity retention and gas production after high-temperature charging and storage.

[0222] The discharge capacity retention rate and gas production after high-temperature charging and storage were measured using the same procedure as in Example 1-1.

[0223] The results of the battery characteristics are shown in Table 3.

[0224] [Table 3]

[0225] Table 3

[0226]

[0227] It should be noted that in the various embodiments and comparative examples shown in Tables 1 to 3, the electrolytes formed by the formulations described in the column “Composition of electrolyte salts and composition of non-aqueous solvents (volume ratio of solvents)” in Tables 1 to 3 were mixed with the compounds shown in the general formula (I) above, in such a way that the content of the compound shown in the general formula (I) above relative to the total content of the non-aqueous electrolyte was as shown in Tables 1 to 3, thereby preparing the non-aqueous electrolytes described in the various embodiments and comparative examples.

[0228] In the examples using the non-aqueous electrolyte of the present invention shown in Tables 1 to 3 above, compared with the comparative examples that do not contain the compound of general formula (I), the high capacity maintained after high-temperature storage was achieved, and the amount of gas generated was significantly suppressed. Based on this result, it can be said that the non-aqueous electrolyte of the present invention can achieve a good balance between improving the discharge capacity retention rate and suppressing gas generation during high-temperature storage.

[0229] Industrial availability

[0230] When the non-aqueous electrolyte of the present invention is used, an energy storage device with excellent electrochemical characteristics over a wide temperature range can be obtained. In particular, when used as a non-aqueous electrolyte for energy storage devices such as lithium secondary batteries installed in hybrid electric vehicles, plug-in hybrid electric vehicles, and battery electric vehicles, an energy storage device whose electrochemical characteristics are not easily degraded over a wide temperature range can be obtained.

Claims

1. A non-aqueous electrolyte for energy storage devices, characterized in that, It is a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, wherein the non-aqueous solvent comprises one or more selected from the group consisting of saturated cyclic carbonates, chain esters, lactones, ethers, and amides, and the non-aqueous electrolyte for the storage device contains a phosphonate represented by the following general formula (I). In the formula, R 1 R represents an alkenyl group with 2 to 6 carbon atoms or an alkynyl group with 3 to 6 carbon atoms. 2 and R 3 Each group independently represents an alkynyl group with 3 to 6 carbon atoms. The content of the phosphonate ester represented by the general formula (I) is more than 0.001% by mass and less than 5% by mass.

2. A non-aqueous electrolyte for energy storage devices, characterized in that, It is a non-aqueous electrolyte containing an electrolyte salt dissolved in a non-aqueous solvent, and contains phosphonates represented by the following general formula (I). In the formula, R 1 R represents an alkenyl group with 2 to 6 carbon atoms or an alkynyl group with 3 to 6 carbon atoms. 2 and R 3 Each group independently represents an alkynyl group with 3 to 6 carbon atoms. The content of the phosphonate ester represented by the general formula (I) is more than 0.001% by mass and less than 5% by mass.

3. The non-aqueous electrolyte for energy storage devices according to claim 1 or 2, wherein, R in the general formula (I) 1 It can be vinyl, allyl, 1-methylallyl, 2-methylallyl, crotonyl, butenyl, or propynyl.

4. The non-aqueous electrolyte for energy storage devices according to claim 1 or 2, wherein, R in the general formula (I) 1 It is vinyl or allyl.

5. The non-aqueous electrolyte for energy storage devices according to claim 1 or 2, wherein, R in the general formula (I) 2 and R 3 Each of them independently is 2-propynyl, 2-butynyl, 3-butynyl, 1-methyl-2-propynyl, 1,1-dimethyl-2-propynyl, 1-ethyl-1-methyl-2-propynyl or 4-pentynyl.

6. The non-aqueous electrolyte for energy storage devices according to claim 1 or 2, wherein, The non-aqueous electrolyte also contains one or more lithium salts (a) selected from the group consisting of lithium salts having a phosphate backbone and lithium salts having an S (=O) group.

7. The non-aqueous electrolyte for energy storage devices 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 non-aqueous electrolyte for energy storage devices according to claim 1 or 2, 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.

9. The non-aqueous electrolyte for energy storage devices 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. The non-aqueous electrolyte for energy storage devices according to claim 1 or 2, wherein, The phosphonate comprises one or more selected from the group consisting of vinylphosphonate di-2-propynyl ester, allylphosphonate di-2-propynyl ester, 1-methylallylphosphonate di-2-propynyl ester, 2-methylallylphosphonate di-2-propynyl ester, crotonylphosphonate di-2-propynyl ester, butenylphosphonate di-2-propynyl ester, and propynylphosphonate di-2-propynyl ester.

11. The non-aqueous electrolyte for energy storage devices according to claim 1 or 2, wherein, The non-aqueous solvent comprises saturated cyclic carbonates and chain esters, wherein the mass ratio of the cyclic carbonates to the chain esters is 10:90 to 50:

50.

12. The non-aqueous electrolyte for energy storage devices according to claim 1 or 2, further comprising at least one of a cyclic carbonate having unsaturated bonds and a cyclic carbonate having fluorine atoms.

13. The non-aqueous electrolyte for energy storage devices according to claim 12, wherein, The content of the cyclic carbonate with unsaturated bonds is 0.05% by mass or more and 8% by mass or less.

14. An energy storage device, characterized in that, It comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, wherein the non-aqueous electrolyte is the non-aqueous electrolyte according to any one of claims 1 to 13.

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

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

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