Non-aqueous electrolyte solution and non-aqueous electrolyte secondary battery containing the non-aqueous electrolyte solution

Abstract

The present invention provides a non-aqueous liquid electrolyte that can undergo capacity loss during continuous charging of a cell. A non-aqueous liquid electrolyte containing oxalato-complex anions (A), LiPF6, a symmetrical chain-form carbonate, and a chain-form carboxylic acid ester (C) in which the viscosity at 25°C is 0.01-0.47 cP, wherein the non-aqueous liquid electrolyte is characterized in that: the ratio (A / B) of the amount (mass) of oxalato-complex anions (A) to the amount (mass) of PF6 - anions (B) is 0.0001-0.30; and the total amount of the symmetrical chain-form carbonate and the chain-form carboxylic acid ester (C) in which the viscosity at 25°C is 0.01-0.47 cP, relative to the total amount of the non-aqueous liquid electrolyte, is 1-45 mass%.

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous electrolyte solution and a non-aqueous electrolyte secondary battery using the non-aqueous electrolyte solution. [Background technology]

[0002] Lithium nonaqueous electrolyte secondary batteries, which use a lithium-containing transition metal oxide as a positive electrode and a nonaqueous solvent as an electrolyte, can achieve high energy density and are therefore used in a wide range of applications, from small power sources for mobile phones, laptop computers, etc. to large power sources for automobiles, railways, and load leveling. However, in recent years, there has been an increasing demand for higher performance in nonaqueous electrolyte secondary batteries, and there is a strong demand for improvements in various characteristics.

[0003] For example, Patent Document 1 discloses a nonaqueous electrolyte solution containing fluoroethylene carbonate, a chain carbonate, and a chain carboxylic acid ester, and discloses that a nonaqueous electrolyte secondary battery including this electrolyte solution can suppress deterioration associated with charge-discharge cycles at high temperatures and can improve discharge capacity at low temperatures.

[0004] Patent Document 2 discloses a non-aqueous electrolyte solution containing a mixture of ethylene carbonate, methyl acetate and / or ethyl acetate, and ethyl methyl carbonate at a specific concentration, and containing lithium bis(oxalato)borate as a main electrolyte, and discloses that a non-aqueous electrolyte secondary battery including this electrolyte solution can improve the discharge capacity at low temperatures.

[0005] Patent Document 3 discloses a non-aqueous electrolyte solution containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate as solvents, and a chain carboxylic acid ester such as ethyl propionate, and containing a specific oxalatolithium salt and lithium fluorophosphate, as well as vinylene carbonate and / or fluoroethylene carbonate as additives, and discloses that a non-aqueous electrolyte secondary battery containing this electrolyte solution has reduced internal resistance (DC resistance) and can suppress deterioration associated with rapid charge-discharge cycles at room temperature and high temperatures.

[0006] Patent Document 4 discloses a nonaqueous electrolyte solution containing a specific lithium salt electrolyte and several types of lithium salt additives, and discloses that a nonaqueous electrolyte secondary battery including this electrolyte solution exhibits good low-temperature input / output characteristics after high-temperature storage and can suppress deterioration due to high-temperature storage. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] US Patent Application Publication No. 2012 / 0007560 [Patent Document 2] US Patent Application Publication No. 2006 / 0172202 [Patent Document 3] European Patent Application Publication No. 3422458 [Patent Document 4] International Publication No. 2016 / 009994 Summary of the Invention [Problem to be solved by the invention]

[0008] In recent years, non-aqueous electrolyte secondary batteries have been required to meet increasingly higher performance requirements, particularly for battery-equipped automobiles, and there has been a strong demand for improved battery durability. However, the non-aqueous electrolyte secondary batteries described in Patent Documents 1 to 4 have a problem of large capacity loss during continuous charging.

[0009] An object of the present invention is to solve the above problems in non-aqueous electrolyte secondary batteries and to provide a non-aqueous electrolyte that can suppress capacity loss during continuous charging. [Means for solving the problem]

[0010] As a result of extensive research to solve the above problems, the present inventors have found that oxalato complex anions and PF6 - The present inventors have found that the above-mentioned problems can be solved by incorporating specific amounts of a symmetric chain carbonate and a chain carboxylic acid ester having a viscosity of 0.01 to 0.47 cP at 25° C., which contain anions in a specific ratio, and have arrived at the present invention. The present invention provides the following specific embodiments, etc.

[0011] [1] A non-aqueous electrolyte solution containing an oxalato complex anion (A), LiPF6, a symmetric chain carbonate, and a chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C, wherein the PF6 - A non-aqueous electrolyte solution characterized in that the ratio (A / B) of the content (mass) of the oxalato complex anion (A) to the content (mass) of the anion (B) is 0.0001 to 0.30, and the total content of the symmetric chain carbonate and the chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C is 1 to 45 mass% with respect to the total amount of the non-aqueous electrolyte solution. [2] The nonaqueous electrolyte solution according to [1], wherein the content of the chain carboxylic acid ester having a viscosity of 0.01 to 0.47 cP at 25°C relative to the total amount of the nonaqueous electrolyte solution is 0.1 to 44 mass% (preferably 0.1 to 10 mass%, more preferably 0.1 to 5 mass%). [3] The nonaqueous electrolyte solution according to [1] or [2], wherein the chain ester compound having a viscosity of 0.01 to 0.47 cP at 25° C. is a compound represented by the following formula (I): R 1 COOCH3···(I) (In formula (I), R 1is a hydrogen atom or an alkyl group having 1 or 2 carbon atoms, and the hydrogen atom bonded to the carbon atom of the alkyl group may be substituted with a halogen atom. 1 is a methyl group. [5] The nonaqueous electrolyte solution according to any one of [1] to [3], wherein the chain ester compound having a viscosity of 0.01 to 0.47 cP at 25° C. is methyl acetate or methyl propionate. [6] The nonaqueous electrolyte solution according to any one of [1] to [3], wherein the chain ester compound having a viscosity of 0.01 to 0.47 cP at 25° C. is methyl acetate. [7] The nonaqueous electrolyte solution according to any one of [1] to [6], further containing an anion (D) having an FSO2 skeleton as an auxiliary agent. [8] The nonaqueous electrolyte solution according to [7], wherein the anion (D) having an FSO2 skeleton is a fluorosulfonate anion. [9] The nonaqueous electrolyte solution according to [7] or [8], wherein the ratio (A / D) of the content of the oxalato complex anion (A) to the content of the anion (D) having an FSO2 skeleton is 0.01 to 10 (preferably 0.01 to 1.5).

[10] The nonaqueous electrolyte solution according to any one of [7] to [9], wherein the ratio (A / D) of the content of the oxalato complex anion (A) to the content of the anion (D) having an FSO2 skeleton is 0.01 to 0.7.

[11] The nonaqueous electrolyte solution according to any one of [1] to

[10] , wherein the ratio of the total content (mass) of the symmetric chain carbonate and the chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C to the content (mass) of the LiPF6 is 0.01 to 3.5.

[12] The nonaqueous electrolyte solution according to any one of [1] to

[11] , wherein the oxalato complex anion (A) is a non-fluorinated bis(oxalato)borate anion and / or a difluorobis(oxalato)phosphate anion.

[13] The nonaqueous electrolyte solution according to any one of [1] to

[12] , wherein the oxalato complex anion (A) is a non-fluorinated bis(oxalato)borate anion.

[14] A nonaqueous electrolyte battery comprising: a positive electrode having a positive electrode active material capable of absorbing and desorbing metal anions; a negative electrode having a negative electrode active material capable of absorbing and desorbing metal anions; and the nonaqueous electrolyte solution according to any one of [1] to

[13] .

[15] The nonaqueous electrolyte battery according to

[14] , wherein the positive electrode active material contains a lithium transition metal compound represented by the following composition formula (3): Li a1 Ni b1 M c1 O2···(3) (In the composition formula (3), the numerical values ​​are 0.90≦a1≦1.10, 0.20≦b1≦0.98, and 0.01≦c1≦0.50, and b1+c1=1 is satisfied. M represents at least one element selected from the group consisting of Co, Mn, Al, Mg, Zr, Fe, Ti, and Er.)

[16] The nonaqueous electrolyte battery according to

[15] , wherein in the formula (3), M contains Mn.

[17] The nonaqueous electrolyte battery according to any one of

[14] to

[16] , wherein the negative electrode active material contains a carbon-based material.

[18] The density of the negative electrode active material layer in the negative electrode is 0.8 to 1.7 g / cm 3 The nonaqueous electrolyte battery according to any one of

[14] to

[17] , wherein

[19] The density of the negative electrode active material layer in the negative electrode is 0.8 to 1.4 g / cm 3 The nonaqueous electrolyte battery according to any one of

[14] to

[18] , wherein

[20] The nonaqueous electrolyte battery according to any one of

[14] to

[19] , wherein the porosity of the negative electrode active material layer in the negative electrode is 10 to 80%.

[21] The nonaqueous electrolyte battery according to any one of

[14] to

[20] , wherein the porosity of the negative electrode active material layer in the negative electrode is 10 to 50%. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a nonaqueous electrolyte solution that can suppress capacity loss during continuous charging, and also to provide a nonaqueous electrolyte secondary battery that includes the nonaqueous electrolyte solution. The present inventors speculate as follows as to why the non-aqueous electrolyte solution having the configuration of the present invention exhibits such excellent effects. In the prior art described in Patent Documents 1 to 3, a specific lithium salt additive and a specific solvent are combined to obtain battery characteristics that both protect the negative electrode surface and improve the conductivity of the electrolyte, but the specific solvent increases side reactions on the positive electrode surface, resulting in capacity degradation during continuous charging. Furthermore, in the prior art described in Patent Document 4, the use of multiple lithium salt additives suppresses decomposition of the lithium electrolyte on the negative electrode surface, improving the battery's high-temperature battery characteristics. However, because the lithium salt additives have a low degree of dissociation and low lithium ion conductivity, excess lithium salt additive increases the overvoltage during battery charging, resulting in increased resistance and capacity degradation during continuous charging.

[0013] Meanwhile, the present invention is characterized by including a specific anion-containing lithium salt with a relatively high degree of dissociation among lithium salt additives in the electrolyte solution, and further including a specific low-molecular-weight carboxylic acid ester and a symmetrical chain carbonate at specific concentrations. The symmetrical chain carbonate and the specific low-molecular-weight carboxylic acid ester have low viscosity and high lithium conductivity, and by using them within a specific concentration range, side reactions on the positive electrode surface can be suppressed. In addition, the electrolyte-derived PF6 - When the ratio of the anions derived from the lithium salt additive to the anions is within a specific range, no excess Li salt additive remains, and the effect of achieving both the conduction of lithium ions in the electrolyte and the protection of the electrode surface is significant, thereby making it possible to suppress capacity loss during continuous charging of the nonaqueous electrolyte secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0014] The following describes in detail the embodiments of the present invention. However, the following description is merely an example (typical example) of the present invention, and the present invention is not limited to the contents thereof as long as it does not depart from the gist of the claims.

[0015] A non-aqueous electrolyte according to one embodiment of the present invention is a non-aqueous electrolyte containing an oxalate complex anion (A), LiPF6, a symmetric chain carbonate, and a chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C, and the PF6 - The ratio (A / B) of the content (mass) of the oxalato complex anion (A) to the content (mass) of the anion (B) is 0.0001 to 0.30, and the total content of the symmetric chain carbonate and the chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C is 1 to 45 mass% relative to the total amount of the nonaqueous electrolyte. Each component will be described below.

[0016] [1. Non-aqueous electrolyte] A non-aqueous electrolyte according to one embodiment of the present invention contains an electrolyte, a non-aqueous solvent for dissolving the electrolyte, and an oxalate complex anion (A), similar to a typical non-aqueous electrolyte. The electrolyte contains LiPF6, and the non-aqueous solvent contains specific amounts of a symmetric chain carbonate and a specific ester compound (C). Each component is described below.

[0017] [1-1. Oxalato complex anion (A)] The non-aqueous electrolyte solution according to this embodiment contains an oxalate complex anion (A).

[0018] (counter cation) As the counter cation of the oxalato complex anion, monovalent cations and divalent cations can be used. As the monovalent cation, lithium ion, sodium ion, and potassium ion are preferred, with lithium ion being particularly preferred. As the divalent cation, magnesium ion and calcium ion are preferred, with magnesium ion being particularly preferred. These can be used alone or in combination of two or more. The oxalato complex anion (A) in the nonaqueous electrolyte is preferably contained as an oxalato complex salt, more preferably as an oxalato complex lithium salt.

[0019] (anion) Examples of oxalato complex anions include: oxalato complex oxalatoborate anions such as difluorooxalatoborate anion and bis(oxalato)borate anion; oxalatophosphate anions such as tetrafluorooxalatophosphate anion, difluorobis(oxalato)phosphate, and tris(oxalato)phosphate; are preferred. Among these, from the viewpoint of suppressing an increase in resistance during continuous charging, bis(oxalato)borate anion or bis(oxalato)phosphate anion is more preferred, non-fluorinated bis(oxalato)borate anion or difluorobis(oxalato)phosphate anion is even more preferred, and non-fluorinated bis(oxalato)borate anion is particularly preferred. From the viewpoint of protecting the electrode surface, oxalatophosphate anion is more preferred, and difluorobis(oxalato)phosphate anion is even more preferred.

[0020] The content of the oxalate complex anion (A) (total content when two or more types are used) is usually 0.001 mass% or more, preferably 0.01 mass% or more, and usually 5 mass% or less, preferably 3 mass% or less, more preferably 2 mass% or less, and particularly preferably 1 mass% or less, based on the total amount of the nonaqueous electrolyte solution. The identification and content measurement of the oxalato complex anion (A) are carried out by nuclear magnetic resonance (NMR) spectroscopy.

[0021] [1-2. Electrolytes] [1-2-1.LiPF6] The non-aqueous electrolyte according to this embodiment contains LiPF6. The concentration of LiPF6 in the non-aqueous electrolyte is not particularly limited, but is usually 8% by mass or more, preferably 8.5% by mass or more, more preferably 9% by mass or more, and usually 18% by mass or less, preferably 17% by mass or less, more preferably 16% by mass or less, based on the total amount of the non-aqueous electrolyte. When the LiPF6 concentration is within the above range, the electrical conductivity is appropriate for battery operation, and sufficient output characteristics tend to be obtained.

[0022] (Oxalato complex anion (A) / PF6 - Anion (B) In this embodiment, PF6 contained in the non-aqueous electrolyte - The ratio (A / B) of the content (mass) of the oxalato complex anion (A) to the content (mass) of the anion (B) is 0.0001 to 0.30. The lower limit of the ratio (A / B) is preferably 0.001 or more, more preferably 0.01 or more, and particularly preferably 0.03 or more. The upper limit of the ratio (A / B) is preferably 0.25 or less, more preferably 0.20 or less, and particularly preferably 0.15 or less. When the ratio (A / B) is within a specific range, the effects obtained by the configuration of this embodiment become more pronounced.

[0023] [1-2-3. Other electrolytes] The nonaqueous electrolyte according to one embodiment of the present invention may contain an electrolyte other than the oxalate complex salt corresponding to the above "1-1. Oxalate Complex Anion (A)" and LiPF. The electrolyte is not particularly limited as long as it is known to be used for this application, but a lithium salt is usually used.

[0024] Examples thereof include lithium tungstate salts, lithium carboxylate salts, lithium sulfonate salts, lithium imide salts, lithium methide salts, and fluorine-containing organic lithium salts, in addition to the oxalate complex salts and LiPF6 corresponding to the above "1-1. Oxalate Complex Anion (A)".

[0025] Among them, lithium sulfonate salts include CH3SO3Li; Lithium imide salts include LiN(FSO2)2, LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium cyclic 1,2-perfluoroethanedisulfonylimide, and lithium cyclic 1,3-perfluoropropanedisulfonylimide; Lithium methide salts include LiC(CF3SO2)3 and LiC(C2F5SO2)3 are more preferable in terms of improving low-temperature output characteristics, high-rate charge / discharge characteristics, impedance characteristics, high-temperature storage characteristics, cycle characteristics, and the like. The combination of LiPF6 and the electrolyte salt is not particularly limited, but LiPF6 and LiN(CF3SO2)2 are preferred.

[0026] When the non-aqueous electrolyte solution contains other electrolytes, their total concentration is not particularly limited, but is usually 8% by mass or more, preferably 8.5% by mass or more, more preferably 9% by mass or more, and usually 18% by mass or less, preferably 17% by mass or less, more preferably 16% by mass or less, and even more preferably 15% by mass or less, relative to the total amount of the non-aqueous electrolyte solution. When the total concentration of other electrolytes is within the above range, the electrical conductivity becomes appropriate for battery operation, and sufficient output characteristics tend to be obtained.

[0027] [1-3. Non-aqueous solvents] [1-3-1. Specific non-aqueous solvents (C)] The nonaqueous electrolyte solution according to this embodiment contains a symmetric chain carbonate and a chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C (hereinafter also referred to as "specific nonaqueous solvent (C)"), and the total content of the specific nonaqueous solvent (C) contained in the nonaqueous electrolyte solution is 1 to 45 mass%.

[0028] The total content of the specific nonaqueous solvent (C) contained in the nonaqueous electrolyte solution is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more. The total content of the specific nonaqueous solvent (C) contained in the nonaqueous electrolyte solution is preferably 43% by mass or less, more preferably 40% by mass or less, even more preferably 38% by mass or less, and particularly preferably 35% by mass or less. When the total content of the specific nonaqueous solvent (C) is within the above range, a good balance is achieved between electrode surface protection by the auxiliary and lithium ion conduction, and the charging characteristics of the nonaqueous electrolyte secondary battery can be efficiently improved.

[0029] [1-3-1 - Chain carboxylic acid esters with a viscosity of 0.01 to 0.47 cP at 1.25°C] In this specification, "a chain carboxylic acid ester having a viscosity of 0.01 to 0.47 cP at 25°C" means a chain carboxylic acid ester compound having a viscosity of 0.01 to 0.47 cP at 25°C as determined by an Ubbelohde viscometer and an oscillating densitometer. Specific examples of the chain carboxylic acid ester having a viscosity of 0.01 to 0.47 cP at 25° C. preferably include compounds represented by the following formula (I). R 1 COOCH3···(I)

[0030] In the above formula (I), R 1 is a hydrogen atom or an alkyl group having 1 or 2 carbon atoms, and the hydrogen atom bonded to the carbon atom of the alkyl group may be substituted with a halogen atom. R 1 is, for example, a methyl group, an ethyl group, a difluoromethyl group, a trifluoromethyl group, a 2,2,2-trifluoroethyl group, etc., and is preferably a methyl group or an ethyl group, more preferably a methyl group. Specific preferred examples of the compound represented by formula (I) include methyl acetate and methyl propionate.

[0031] The content of the chain carboxylic acid ester contained in the nonaqueous electrolyte solution is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, relative to the total amount of the nonaqueous electrolyte solution, and is preferably 44% by mass or less, more preferably 30% by mass or less, even more preferably 15% by mass or less, particularly preferably 10% by mass or less, and even more preferably 5% by mass or less. When the content of the chain carboxylic acid ester is within the above range, the viscosity of the nonaqueous electrolyte solution falls within an appropriate range, a decrease in electrical conductivity is avoided, and the charge / discharge characteristics of the nonaqueous electrolyte secondary battery can be improved. The chain carboxylic acid esters may be used alone or in any combination and ratio of two or more thereof. When two or more chain carboxylic acid esters are used in combination, the total content of the chain carboxylic acid esters should be within the above range. The chain carboxylic acid ester having a viscosity of 0.01 to 0.47 cP at 25° C. is identified and its content is measured by gas chromatography.

[0032] (Viscosity measurement method at 25°C) The viscosity measurement at 25°C is carried out using an Ubbelohde viscometer and an oscillating densitometer.

[0033] [1-3-1-2. Symmetrical chain carbonate] In this specification, the term "symmetric chain carbonate" refers to a compound having a chemical structure that is symmetrical with respect to the carbonate group. Specifically, the symmetric chain carbonate is a carbonate compound represented by the following formula (II). R 2 O-(C=O)-OR 2 (II)

[0034] In the above formula (II), R 2 represents an alkyl group, and a hydrogen atom bonded to a carbon atom of the alkyl group may be substituted with a halogen atom. R 2is, for example, a methyl group, an ethyl group, a difluoromethyl group, a trifluoromethyl group, a 2,2,2-trifluoroethyl group, etc., and from the viewpoint of low viscosity, a methyl group or an ethyl group is preferable, and a methyl group is more preferable. Specific preferred examples of the compound represented by formula (II) include dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, and diisopropyl carbonate, and dimethyl carbonate or diethyl carbonate is preferable, and dimethyl carbonate is more preferable.

[0035] (Content) The content of the symmetric chain carbonate contained in the nonaqueous electrolyte solution is preferably 1% by mass or more, more preferably 10% by mass or more, and particularly preferably 20% by mass or more, relative to the total amount of the nonaqueous electrolyte solution, and is preferably less than 45% by mass, more preferably 40% by mass or less, and even more preferably 35% by mass or less. When the content of the symmetric chain carbonate is within the above range, the nonaqueous electrolyte solution exhibits an appropriate viscosity over a wide temperature range, a decrease in electrical conductivity is avoided, and the charge / discharge characteristics of the nonaqueous electrolyte secondary battery can be improved. The identification and content of symmetric chain carbonate is determined by gas chromatography.

[0036] (Specific non-aqueous solvent (C) / LiPF6) In this embodiment, the ratio (by mass) of the specific nonaqueous solvent (C) to the LiPF6 content (by mass) in the nonaqueous electrolyte solution is 0.01 to 3.5. The lower limit of this ratio is preferably 0.01 or more, more preferably 0.05 or more, and particularly preferably 0.1 or more. The upper limit of this ratio is preferably 0.25 or less, more preferably 3.0 or less, and particularly preferably 2.8. When the ratio of the content of the specific non-aqueous solvent (C) to the content of LiPF6 contained in the non-aqueous electrolyte solution is within a specific range, the effects obtained by the configuration of this embodiment become more pronounced.

[0037] [1-3-2. Other non-aqueous solvents] Furthermore, as with general nonaqueous electrolyte solutions, the electrolyte solution may contain a nonaqueous solvent other than the symmetric chain carbonate and the chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C, as long as the effect of the invention according to this embodiment is not impaired. The nonaqueous solvent to be used is not particularly limited as long as it dissolves the above-mentioned electrolyte, and known organic solvents can be used. Examples of organic solvents include, but are not limited to, saturated cyclic carbonates, asymmetric chain carbonates, chain carboxylic acid esters having a viscosity at 25°C of not 0.01 to 0.47 cP (hereinafter also referred to as "other chain carboxylic acid esters"), cyclic carboxylic acid esters, ether compounds, and sulfone compounds. These may be used alone or in combination of two or more. The combination of two or more organic solvents is not particularly limited, and examples thereof include saturated cyclic carbonates and asymmetric chain carbonates, cyclic carboxylic acid esters and asymmetric chain carbonates, and saturated cyclic carbonates, asymmetric chain carbonates and other chain carboxylic acid esters. Among these, saturated cyclic carbonates and asymmetric chain carbonates, and saturated cyclic carbonates, asymmetric chain carbonates and other chain carboxylic acid esters are preferred.

[0038] [1-3-2-1. Saturated cyclic carbonates] Examples of saturated cyclic carbonates include those having an alkylene group having 2 to 4 carbon atoms, and saturated cyclic carbonates having 2 or 3 carbon atoms are preferably used from the viewpoint of improving battery characteristics resulting from an improved degree of lithium ion dissociation.

[0039] Specific examples of saturated cyclic carbonates include ethylene carbonate, propylene carbonate, and butylene carbonate. Among these, ethylene carbonate or propylene carbonate is preferred, and ethylene carbonate, which is less susceptible to oxidation and reduction, is more preferred. The saturated cyclic carbonates may be used alone or in any combination and ratio of two or more.

[0040] The content of the saturated cyclic carbonate is not particularly limited and may be any as long as it does not significantly impair the effects of the present invention, but is usually 3% by volume or more, preferably 5% by volume or more, and is usually 90% by volume or less, preferably 85% by volume or less, more preferably 80% by volume or less, relative to the total amount of the nonaqueous solvent in the nonaqueous electrolyte solution. By setting it in this range, a decrease in electrical conductivity due to a decrease in the dielectric constant of the nonaqueous electrolyte solution can be avoided, and the large current discharge characteristics, stability with respect to the negative electrode, and cycle characteristics of the nonaqueous electrolyte secondary battery tend to be in good ranges, and the oxidation and reduction resistance of the nonaqueous electrolyte solution tend to be improved, and stability during high-temperature storage tend to be improved. In this embodiment, the volume % refers to the volume at 25° C. and 1 atmosphere.

[0041] [1-3-2-2. Asymmetric chain carbonate] As the asymmetric chain carbonate, one having 4 to 7 carbon atoms is usually used, and in order to adjust the viscosity of the electrolyte solution within an appropriate range, a chain carbonate having 4 or 5 carbon atoms is preferably used.

[0042] Specifically, examples of the asymmetric chain carbonate include n-propyl isopropyl carbonate, ethyl methyl carbonate, and methyl-n-propyl carbonate, with ethyl methyl carbonate being particularly preferred.

[0043] In addition, asymmetric chain carbonates having fluorine atoms (hereinafter sometimes abbreviated as "fluorinated asymmetric chain carbonates") can also be suitably used. The number of fluorine atoms in the fluorinated asymmetric chain carbonate is not particularly limited as long as it is 1 or more, but is usually 6 or less, and preferably 4 or less. When the fluorinated asymmetric chain carbonate has multiple fluorine atoms, the multiple fluorine atoms may be bonded to the same carbon or different carbons. Examples of the fluorinated asymmetric chain carbonate include fluorinated dimethyl carbonate derivatives such as fluoromethyl methyl carbonate; fluorinated ethyl methyl carbonate derivatives such as 2-fluoroethyl methyl carbonate; and fluorinated diethyl carbonate derivatives such as ethyl-(2-fluoroethyl) carbonate.

[0044] The asymmetric chain carbonates may be used alone or in any combination of two or more in any ratio.

[0045] The content of the asymmetric chain carbonate is not particularly limited, but is usually 15% by volume or more, preferably 20% by volume or more, more preferably 25% by volume or more, and usually 90% by volume or less, preferably 85% by volume or less, more preferably 80% by volume or less, relative to the total amount of nonaqueous solvent in the nonaqueous electrolyte. By setting the content of the asymmetric chain carbonate within the above range, the viscosity of the nonaqueous electrolyte can be set within an appropriate range, a decrease in ionic conductivity can be suppressed, and the output characteristics of the nonaqueous electrolyte secondary battery can be easily set within a good range.

[0046] (Combination with non-fluorinated carbonate) Furthermore, the non-aqueous electrolyte solution according to one embodiment of the present invention preferably contains a non-fluorinated cyclic carbonate and / or a non-fluorinated asymmetric chain carbonate. Among these, from the viewpoint of significantly improving battery performance, a combination of ethylene carbonate or propylene carbonate and ethyl methyl carbonate is more preferable, and a combination of ethylene carbonate and ethyl methyl carbonate is even more preferable.

[0047] The contents of the non-fluorinated cyclic carbonate and the non-fluorinated asymmetric chain carbonate are not particularly limited and may be any as long as they do not significantly impair the effects of the present invention. The content of ethylene carbonate is usually 15% by volume or more, preferably 20% by volume or more, and usually 45% by volume or less, preferably 40% by volume or less, based on the total amount of non-aqueous solvent in the non-aqueous electrolyte solution. The content of ethyl methyl carbonate is usually 20% by volume or more, preferably 30% by volume or more, and usually 50% by volume or less, preferably 45% by volume or less, based on the total amount of non-aqueous solvent in the non-aqueous electrolyte solution. By setting the contents of ethylene carbonate and ethyl methyl carbonate within the above ranges, excellent high-temperature stability and suppression of gas generation tend to be achieved.

[0048] [1-3-2-3. Other chain carboxylic acid esters] Other examples of chain carboxylic acid esters include propyl acetate, butyl acetate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, methyl valerate, methyl isobutyrate, ethyl isobutyrate, and methyl pivalate. Among these, propyl acetate and butyl acetate are preferred in terms of improving battery characteristics. Chain carboxylic acid esters in which some of the hydrogen atoms of the above-mentioned compounds are substituted with fluorine atoms (e.g., ethyl trifluoroacetate, etc.) can also be used suitably. The content of the other chain carboxylic acid ester is usually 1% by volume or more, preferably 5% by volume or more, and more preferably 15% by volume or more, based on the total amount of the nonaqueous solvent. This range improves the electrical conductivity of the nonaqueous electrolyte and facilitates the enhancement of the large-current discharge characteristics of the nonaqueous electrolyte battery. Furthermore, the content of the chain carboxylic acid ester is usually 70% by volume or less, preferably 50% by volume or less, and more preferably 40% by volume or less. By setting the upper limit in this way, the viscosity of the nonaqueous electrolyte can be kept within an appropriate range, a decrease in electrical conductivity can be avoided, an increase in negative electrode resistance can be suppressed, and the large-current discharge characteristics of the nonaqueous electrolyte secondary battery can be easily maintained within a favorable range.

[0049] [1-3-2-4. Cyclic carboxylic acid esters] Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone. Among these, γ-butyrolactone is more preferred. Cyclic carboxylic acid esters in which some of the hydrogen atoms in the above-mentioned compounds are substituted with fluorine can also be used. The content of the cyclic carboxylic acid ester is typically 1% by volume or more, preferably 5% by volume or more, and more preferably 15% by volume or more, based on the total amount of the nonaqueous solvent. This range improves the electrical conductivity of the nonaqueous electrolyte and facilitates the enhancement of the large-current discharge characteristics of the nonaqueous electrolyte battery. The content of the cyclic carboxylic acid ester is typically 70% by volume or less, preferably 50% by volume or less, and more preferably 40% by volume or less. Setting the upper limit in this manner makes it possible to maintain the viscosity of the nonaqueous electrolyte within an appropriate range, avoid a decrease in electrical conductivity, suppress an increase in negative electrode resistance, and facilitate the enhancement of the large-current discharge characteristics of the nonaqueous electrolyte secondary battery within a favorable range.

[0050] [1-3-2-5. Ether compounds] Preferred ether compounds include chain ethers having 3 to 10 carbon atoms, such as dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether, and cyclic ethers having 3 to 6 carbon atoms, such as tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 1,3-dioxane, 2-methyl-1,3-dioxane, 4-methyl-1,3-dioxane, and 1,4-dioxane. Note that some of the hydrogen atoms in the above-mentioned ether compounds may be substituted with fluorine atoms. Among these, as the chain ether having 3 to 10 carbon atoms, dimethoxymethane, diethoxymethane, or ethoxymethoxymethane is preferred because it has a high solvation ability for lithium ions, improves ionic dissociation, has low viscosity, and provides high ionic conductivity, and as the cyclic ether having 3 to 6 carbon atoms, tetrahydrofuran, 1,3-dioxane, 1,4-dioxane, or the like is preferred because it provides high ionic conductivity.

[0051] The content of the ether-based compound is not particularly limited and may be any amount as long as it does not significantly impair the effects of the present invention. However, it is usually 1% by volume or more, preferably 2% by volume or more, more preferably 3% by volume or more, and usually 30% by volume or less, preferably 25% by volume or less, more preferably 20% by volume or less, based on the total amount of the non-aqueous solvent. When the content of the ether-based compound is within the above-mentioned preferred range, it is easy to ensure the effects of improving the degree of lithium ion dissociation of the ether and improving ionic conductivity due to reduced viscosity. Furthermore, when the negative electrode active material is a carbonaceous material, the phenomenon of co-insertion of the chain ether with the lithium ion can be suppressed, thereby allowing the input / output characteristics and charge / discharge rate characteristics to be within appropriate ranges.

[0052] [1-3-2-6. Sulfone compounds] The sulfone compound is not particularly limited and may be a cyclic sulfone or a chain sulfone. In the case of a cyclic sulfone, the carbon number is usually 3 to 6, preferably 3 to 5, and in the case of a chain sulfone, the carbon number is usually 2 to 6, preferably 2 to 5. In addition, the number of sulfonyl groups in one molecule of the sulfone compound is not particularly limited, but is usually 1 or 2.

[0053] Examples of cyclic sulfones include monosulfone compounds such as trimethylene sulfones, tetramethylene sulfones, and hexamethylene sulfones; and disulfone compounds such as trimethylene disulfones, tetramethylene disulfones, and hexamethylene disulfones. Among these, from the viewpoints of dielectric constant and viscosity, tetramethylene sulfones, tetramethylene disulfones, hexamethylene sulfones, and hexamethylene disulfones are more preferred, and tetramethylene sulfones (sulfolanes) are particularly preferred.

[0054] Examples of sulfolanes include sulfolane and sulfolane derivatives. Preferred sulfolane derivatives are those in which one or more hydrogen atoms bonded to carbon atoms constituting the sulfolane ring are substituted with a fluorine atom, an alkyl group, or a fluorine-substituted alkyl group.

[0055] Among these, 2-methylsulfolane, 3-methylsulfolane, 2-fluorosulfolane, 3-fluorosulfolane, 2,3-difluorosulfolane, 2-trifluoromethylsulfolane, 3-trifluoromethylsulfolane, etc. are preferred because they provide high ionic conductivity in the electrolyte and high input / output of the battery.

[0056] Examples of the chain sulfone include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, pentafluoroethyl methyl sulfone, etc. Among these, dimethyl sulfone, ethyl methyl sulfone, and monofluoromethyl methyl sulfone are preferred in terms of improving the high-temperature storage stability of the electrolyte solution.

[0057] The content of the sulfone compound is not particularly limited and may be any content as long as it does not significantly impair the effects of the present invention, but is usually 0.3% by volume or more, preferably 0.5% by volume or more, more preferably 1% by volume or more, and is usually 40% by volume or less, preferably 35% by volume or less, more preferably 30% by volume or less, based on the total amount of the nonaqueous solvent in the nonaqueous electrolyte solution. If the content of the sulfone compound is within the above range, an electrolyte solution with excellent high-temperature storage stability tends to be obtained.

[0058] [1-4. Auxiliaries] The non-aqueous electrolyte solution according to this embodiment may contain various auxiliary agents within a range that does not significantly impair the effects of the present invention. As the auxiliary agent, any conventionally known agent may be used. Note that, one auxiliary agent may be used alone, or two or more auxiliary agents may be used in any combination and ratio.

[0059] Examples of auxiliary agents that may be contained in the non-aqueous electrolyte solution include cyclic carbonates having a carbon-carbon unsaturated bond, fluorine-containing cyclic carbonates, compounds having an isocyanato group, compounds having an isocyanuric acid skeleton, sulfur-containing organic compounds, phosphorus-containing organic compounds, organic compounds having a cyano group, silicon-containing compounds, aromatic compounds, cyclic compounds having an ether bond, carboxylic acid anhydrides, borate anions without an oxalic acid skeleton, anions having an FSO skeleton, monofluorophosphate anions, difluorophosphate anions, etc. Examples include compounds described in WO 2015 / 111676. The cyclic compound having an ether bond can be used as an auxiliary agent in a non-aqueous electrolyte solution, and some can also be used as a non-aqueous solvent as described in "1-3. Non-aqueous solvent." When the cyclic compound having an ether bond is used as an auxiliary agent, it is used in an amount of less than 1% by volume.

[0060] The content of the auxiliary agent is not particularly limited and may be any amount as long as it does not significantly impair the effects of the present invention, but is usually 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and is usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, and particularly preferably less than 1% by mass, relative to the total amount of the nonaqueous electrolyte solution.

[0061] [1-4-1. Anion with FSO2 skeleton (D)] The nonaqueous electrolyte solution according to this embodiment preferably contains an anion (D) having an FSO2 skeleton as an auxiliary agent.

[0062] (counter cation) As the counter cation of the anion (D) having an FSO2 skeleton, monovalent cations and divalent cations can be used. As the monovalent cation, lithium ion, sodium ion, and potassium ion are preferred, with lithium ion being particularly preferred. As the divalent cation, magnesium ion and calcium ion are preferred, with magnesium ion being particularly preferred. These can be used alone or in combination of two or more. The anion (D) having an FSO2 skeleton in the nonaqueous electrolyte solution is preferably contained as a salt having an FSO2 skeleton, more preferably as a lithium salt of an anion having an FSO2 skeleton.

[0063] (anion) Examples of anions (D) having an FSO2 skeleton include: FSO3 - Fluorosulfonate anions such as; (FSO2)2N - , (FSO2)(CF3SO2)N - , (FSO2)(F2PO)N - , (FSO2)(FPO2)N 2- Fluorosulfonylimide anions such as; (FSO2)3C - (FSO2)3C - Fluorosulfonylmethide anions such as; From the viewpoint of suppressing an increase in resistance during continuous charging, a fluorosulfonate anion is preferred.

[0064] The content of the anion (D) having an FSO skeleton (the total content when there are two or more types) is 0.001 mass% or more, preferably 0.01 mass% or more and 5 mass% or less, preferably 3 mass% or less, more preferably 2 mass% or less, and particularly preferably 1 mass% or less, based on the total amount of the nonaqueous electrolyte solution. The identification and content measurement of the anion (D) having the FSO2 skeleton are carried out by nuclear magnetic resonance (NMR) spectroscopy.

[0065] (Oxalato complex anion (A) / FSO2 skeleton anion (D)) In this embodiment, the ratio (A / D) of the content of the oxalato complex anion (A) to the content of the anion (D) having an FSO2 skeleton contained in the nonaqueous electrolyte solution is typically 0.01 to 10. The lower limit of the ratio (A / D) is preferably 0.03 or more, more preferably 0.05 or more, even more preferably 0.1 or more, and particularly preferably 0.5 or more. The upper limit of the ratio (A / D) is preferably 5 or less, more preferably 1.5 or less, even more preferably 1.1 or less, and particularly preferably 0.7. When the ratio of the content of the oxalato complex anion (A) to the content of the anion (D) having the FSO2 skeleton contained in the nonaqueous electrolyte solution is within a specific range, the effects obtained by the configuration of this embodiment become more pronounced.

[0066] [2. Non-aqueous electrolyte secondary battery] A nonaqueous electrolyte secondary battery according to one embodiment of the present invention is a nonaqueous electrolyte secondary battery including a positive electrode having a positive electrode active material capable of absorbing and releasing metal ions, and a negative electrode having a negative electrode active material capable of absorbing and releasing metal ions, and containing a nonaqueous electrolyte.

[0067] [2-1. Non-aqueous electrolyte] The nonaqueous electrolyte solution used is the nonaqueous electrolyte solution described above. Note that, other nonaqueous electrolyte solutions may be mixed with the nonaqueous electrolyte solution described above within the scope of the present invention.

[0068] [2-2. Negative electrode] The negative electrode is composed of a negative electrode active material layer containing a negative electrode active material and a binder, and a current collector.

[0069] [2-2-1. Negative electrode active material] The negative electrode active material used in the negative electrode is not particularly limited as long as it can electrochemically absorb and release metal ions. Specific examples include carbon-based materials, materials containing metal elements and / or metalloid elements that can be alloyed with Li, lithium-containing metal composite oxide materials, and mixtures thereof. Among these, carbon-based materials are preferred because they have good cycle characteristics and safety, as well as excellent continuous charge characteristics. These materials may be used alone or in any combination of two or more.

[0070] [2-2-1-1. Carbon-based materials] Examples of carbonaceous materials include natural graphite, artificial graphite, amorphous carbon, carbon-coated graphite, graphite-coated graphite, and resin-coated graphite. Of these, natural graphite is preferred. One type of carbonaceous material may be used alone, or two or more types may be used in any combination and ratio. Examples of natural graphite include scaly graphite, flake graphite, and / or graphite particles obtained by subjecting such graphite to treatment such as spheroidization or densification. Among these, spherical or ellipsoidal graphite particles that have been subjected to spheroidization treatment are particularly preferred from the viewpoint of particle packing properties or charge / discharge rate characteristics. The average particle size (d50) of the graphite particles is usually 1 μm or more and 100 μm or less.

[0071] [2-2-1-2. Physical properties of carbon-based materials] The carbonaceous material as the negative electrode active material preferably satisfies at least one of the characteristics such as physical properties and shape shown in the following items (1) to (4), and it is particularly preferable that it simultaneously satisfies several of them. (1) X-ray diffraction parameters The d value (interlayer distance) of the lattice plane (002 plane) of carbon-based materials determined by X-ray diffraction using the Gakushin method is usually 0.335 nm or more and 0.360 nm or less. Also, the crystallite size (Lc) of carbon-based materials determined by X-ray diffraction using the Gakushin method is usually 1.0 nm or more. (2) Volume-based average particle size The volume-based average particle size of the carbon-based material is the volume-based average particle size (median diameter) determined by a laser diffraction / scattering method, and is usually 1 μm or more and 100 μm or less. (3) Raman R value, Raman half-width The Raman R value of a carbon-based material is a value measured using argon ion laser Raman spectroscopy, and is usually 0.01 or more and 1.5 or less. In addition, the 1580 cm -1 The Raman half-width in the vicinity is not particularly limited, but is usually 10 cm -1 More than 100cm -1 The following is the result. (4) BET specific surface area The BET specific surface area of ​​a carbon-based material is the value of the specific surface area measured using the BET method, and is usually 0.1 m 2 ·g -1 More than 100m 2 ·g -1 The following is the result.

[0072] The negative electrode active material may contain two or more carbonaceous materials with different properties, where the properties refer to X-ray diffraction parameters, volume-based average particle size, Raman R value, Raman half-width, and BET specific surface area. Preferred examples include a case where the volume-based particle size distribution is not symmetrical about the median diameter, a case where two or more carbon-based materials having different Raman R values ​​are contained, and a case where two or more carbon-based materials having different X-ray parameters are contained.

[0073] [2-2-1-3. Materials containing metallic and / or semi-metallic elements that can be alloyed with Li] Any conventionally known particles containing a metal element and / or a metalloid element that can be alloyed with Li can be used, but from the viewpoint of capacity and cycle life, it is preferable that the particles are, for example, a simple substance of a metal and / or a metalloid element selected from the group consisting of Sb, Si, Sn, Al, As, and Zn, or a compound thereof. Furthermore, when the material containing a metal element and / or a metalloid element that can be alloyed with Li contains two or more elements, the material may be an alloy material made of an alloy of these metals. In addition, examples of the material of the metal element and / or metalloid element that can be alloyed with Li include oxides, nitrides, carbides, etc. These may contain two or more kinds of metal elements and / or metalloid elements that can be alloyed with Li. Among them, metallic Si (hereinafter sometimes referred to as Si) or a Si-containing inorganic compound is preferable in terms of achieving a high capacity. In addition, the material of the metal element and / or metalloid element that can be alloyed with Li may already be alloyed with Li at the time of manufacturing the negative electrode described later.

[0074] In this specification, Si or a Si-containing inorganic compound is collectively referred to as a Si compound. Specific examples of the Si compound include SiO x (0 ≦ x ≦ 2), etc. Specific examples of the metal compound alloyed with Li include Li y Si(0 < y ≦ 4.4), Li2SiO 2+z (0 < z ≦ 2), etc. As the Si compound, a Si oxide (SiO x1 , 0 < x1 ≦ 2) is preferable in terms of having a larger theoretical capacity compared to graphite, or amorphous Si or nano-sized Si crystals are preferable in terms of allowing easy entry and exit of alkali ions such as lithium ions and being able to obtain a high capacity. When the material containing the metal element and / or metalloid element that can be alloyed with Li is in the form of particles, its average particle diameter (d50) is usually 0.01 μm or more and 10 μm or less from the viewpoint of cycle life.

[0075] [2-2-1-4. Mixture of the material containing the metal element and / or metalloid element that can be alloyed with Li and the carbon-based material] The mixture of the material containing the metal element and / or metalloid element that can be alloyed with Li and the carbon-based material used as the negative electrode active material may be a mixture in which the material containing the metal element and / or metalloid element that can be alloyed with Li and the carbon-based material described above are mixed in the state of independent particles, or may be a composite in which the material containing the metal element and / or metalloid element that can be alloyed with Li exists on the surface or inside of the carbon-based material. The content of the material containing a metal element and / or a metalloid element that can be alloyed with Li relative to the total of the material containing a metal element and / or a metalloid element that can be alloyed with Li and the carbon-based material is usually 1 mass% or more and 99 mass% or less.

[0076] [2-2-1-5. Lithium-containing metal composite oxide materials] The lithium-containing metal composite oxide material used as the negative electrode active material is not particularly limited as long as it is capable of absorbing and releasing lithium ions. However, from the viewpoint of high current density charge / discharge characteristics, a lithium-containing metal composite oxide material containing titanium is preferred, a composite oxide of lithium and titanium (hereinafter sometimes abbreviated as "lithium titanium composite oxide") is more preferred, and a lithium titanium composite oxide having a spinel structure is particularly preferred because it significantly reduces output resistance. Furthermore, the lithium and / or titanium of the lithium titanium composite oxide may be substituted with another metal element, for example, at least one element selected from the group consisting of Al, Ga, Cu, and Zn. As a lithium titanium composite oxide, Li 4 / 3 Ti 5 / 3 O4, Li1Ti2O4 and Li 4 / 5 Ti 11 / 5 O4 is preferred. In addition, examples of lithium titanium composite oxides in which part of lithium and / or titanium is substituted with other elements include Li 4 / 3 Ti 4 / 3 Al 1 / 3 O4 is preferred.

[0077] [2-2-1-6. Surface coating of negative electrode active material] The negative electrode active material may have a substance (surface-attached substance) attached to its surface, the substance having a different composition from the negative electrode active material. Examples of the surface-attached substance include oxides such as aluminum oxide, sulfates such as lithium sulfate, and carbonates such as lithium carbonate. These surface-adhering substances can be attached to the surface of the negative electrode active material, for example, by dissolving or suspending them in a solvent, adding them to the negative electrode active material by impregnation, and then drying. The amount of the surface-adhering substance is preferably 1 μmol / g or more, more preferably 10 μmol / g or more, and is usually 1 mmol / g or less, relative to the positive electrode active material. In this specification, the term "negative electrode active material" also refers to a negative electrode active material having the surface-adhering substance attached to its surface.

[0078] [2-2-2. Negative electrode structure and manufacturing method] The negative electrode can be produced by any known method as long as it does not significantly impair the effects of the present invention. For example, the negative electrode can be produced by adding a binder, a solvent such as an aqueous solvent or an organic solvent, and optionally a thickener, a conductive material, a filler, etc. to the negative electrode active material to form a slurry, which is then applied to a current collector, dried, and pressed to form a negative electrode active material layer. In this case, in order to increase the packing density of the negative electrode active material, it is preferable to compact it using a hand press, a roller press, etc.

[0079] [2-2-2-1. Active material content] The content of the negative electrode active material in the negative electrode active material layer is usually 80% by mass or more and 99.5% by mass or less.

[0080] [2-2-2-2. Thickener] Thickeners are usually used to adjust the viscosity of the slurry. Examples of thickeners include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, etc. These may be used alone or in any combination and ratio of two or more. When a thickener is used, the ratio of the thickener to the negative electrode active material is usually 0.1 mass % or more and 5 mass % or less.

[0081] [2-2-2-3. Binder] The binder for binding the negative electrode active material is not particularly limited as long as it is a material that is stable to the non-aqueous electrolyte solution and the solvent used in producing the electrode. Specific examples include rubbery polymers such as SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluororubber, NBR (acrylonitrile-butadiene rubber), and ethylene-propylene rubber; and fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, and tetrafluoroethylene-ethylene copolymer. These may be used alone or in any combination and ratio of two or more. The ratio of the binder to the negative electrode active material is usually 0.1 mass % or more and 20 mass % or less.

[0082] In particular, when the binder contains a rubber-like polymer such as SBR as a main component, the ratio of the binder to the negative electrode active material is preferably 0.1% by mass to 5% by mass, and when the binder contains a fluorine-based polymer such as polyvinylidene fluoride as a main component, the ratio of the binder to the negative electrode active material is preferably 1% by mass to 15% by mass.

[0083] [2-2-2-4. Current collector] Any known current collector can be used to support the negative electrode active material. Examples of the negative electrode current collector include metal materials such as aluminum, copper, nickel, stainless steel, and nickel-plated steel, but copper is particularly preferred from the standpoints of ease of processing and cost. The current collector may be in the form of a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punched metal, a foamed metal, or the like. Of these, a metal foil or a metal thin film is preferred. The metal foil or the metal thin film may be formed into a mesh as appropriate. When the negative electrode current collector is in the form of a plate or film, the thickness of the current collector is not limited, but is usually 1 μm or more and 1 mm or less.

[0084] [2-2-2-5. Thickness and density of negative electrode active material layer] The thickness of the negative electrode active material layer is the thickness of the entire negative electrode minus the thickness of the current collector. Although there are no particular limitations, from the viewpoint of high capacity and high output, it is usually 15 μm or more and 300 μm or less. The density of the negative electrode active material layer is usually 0.8 g cm -3 More than 2.2g cm -3 The density of the negative electrode active material layer is 0.9 g cm -3 More than 1.0 g cm is preferable. -3 More than 1.1 g cm is preferable. -3 Above 1.2 g cm is particularly preferable. -3 Above 1.7 g cm is most preferable. -3 Preferably less than 1.6 g cm -3 The following is particularly preferred: 1.5 g cm -3 The following is particularly preferred: 1.4 g cm -3 The following is most preferable: If the density of the negative electrode active material layer is within this range, electrolyte diffusion within the negative electrode active material layer and conductivity between the active materials will be good, thereby reducing side reactions such as Li metal deposition on the negative electrode during continuous charging. The density of the negative electrode active material layer is measured by measuring the thickness and weight of the negative electrode active material layer.

[0085] [2-2-2-6. Porosity of negative electrode active material layer] The porosity of the negative electrode active material layer refers to the proportion of pore volume in the volume of the negative electrode active material layer, and is typically 10% or more and 80% or less. The porosity of the negative electrode active material layer is preferably 20% or more, more preferably 28% or more, particularly preferably 32% or more, and most preferably 35% or more. The porosity of the negative electrode active material layer is preferably 70% or less, more preferably 60% or less, particularly preferably 55% or less, and most preferably 50% or less. If the porosity of the negative electrode active material layer is within this range, electrolyte diffusion within the negative electrode active material layer and conductivity between the active materials are improved, thereby reducing side reactions such as Li metal deposition on the negative electrode during continuous charging. The porosity of the negative electrode active material layer is measured by measuring the volume of pores of 5.4 nm or more using mercury intrusion porosimetry.

[0086] [2-3. Positive electrode] The positive electrode is composed of a positive electrode active material layer containing a positive electrode active material and a binder, and a current collector.

[0087] [2-3-1. Positive electrode active material] The positive electrode active material used in the positive electrode is not particularly limited as long as it can electrochemically absorb and release metal ions. Specific examples include lithium transition metal compounds. These may be used alone or in any combination of two or more.

[0088] [2-3-1-1. Lithium transition metal compounds] Examples of lithium transition metal compounds include sulfides, phosphate compounds, silicate compounds, borate compounds, lithium transition metal composite oxides, etc. Among these, phosphate compounds and lithium transition metal composite oxides are preferred, and lithium transition metal composite oxides are more preferred. Examples of lithium transition metal composite oxides include those having a spinel structure that allows three-dimensional diffusion, and those having a layered structure that allows two-dimensional diffusion of lithium ions.

[0089] Those having a spinel structure are generally represented by the following composition formula (1). Li x’ M'2O4···(1) (In formula (1), x' is 1≦x'≦1.5, and M' represents at least one transition metal element.) Specifically, LiMn2O4, LiCoMnO4, LiNi 0.5 Mn 1.5 Examples include O4 and LiCoVO4.

[0090] Those having a layered structure are generally represented by the following composition formula (2). Li 1+x MO2···(2) (In formula (2), x is −0.1≦x≦0.5, and M represents at least one transition metal element.) Specifically, LiCoO2, LiNiO2, LiNi 0.85 Co 0.10 Al 0.05 O2, LiNi0.80 Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.05 Ni 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, Li 1.05 Ni 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 Examples include O2.

[0091] Among these, from the viewpoint of improving the battery capacity, a lithium transition metal composite oxide having a layered structure is preferred, and a transition metal composite oxide represented by the following composition formula (3) is more preferred. Li a1 Ni b1 M c1 O2···(3) (In formula (3), a1, b1, and c1 are numerical values ​​that satisfy 0.90≦a1≦1.10, 0.30≦b1≦0.98, and 0.01≦c1≦0.5, respectively, and satisfy 0.50≦b1+c1 and b1+c1=1. M represents at least one element selected from the group consisting of Mn, Al, Mg, Zr, Fe, Ti, and Er.) In the composition formula (3), it is preferable that the value d1 satisfies 0.01≦d1≦0.50.

[0092] In particular, from the viewpoint of the structural stability of the lithium transition metal composite oxide, it is more preferable that the lithium transition metal composite oxide be a transition metal oxide represented by the following composition formula (4). Li a2 Ni b2 Co c2 M d2 O2···(4) (In formula (4), a2, b2, and c2 are numerical values ​​that satisfy 0.90≦a2≦1.10, 0.50≦b2≦0.98, and 0.01≦c2<0.50, respectively, and b2+c2=1 is satisfied. M represents at least one element selected from the group consisting of Mn, Al, Mg, Zr, Fe, Ti, and Er.) A preferred example of the lithium transition metal oxide represented by the composition formula (4) is LiNi 0.85 Co 0.10 Al 0.05 O2, LiNi 0.80 Co 0.15 Al 0.05 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, Li 1.05 Ni 0.50 Co 0.20 Mn 0.30 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 Examples include O2. In each composition formula, M preferably contains Mn or Al, more preferably contains Mn, and further preferably is Mn or Al, because this increases the structural stability of the lithium transition metal oxide and suppresses structural deterioration during repeated charge and discharge.

[0093] [2-3-1-2. Introduction of different elements] Furthermore, elements (foreign elements) other than the elements contained in the above composition formula may be incorporated into the lithium transition metal composite oxide.

[0094] [2-3-1-3. Surface coating of positive electrode active material] The positive electrode active material may have a substance (surface-attached substance) attached to its surface, the substance having a different composition from the positive electrode active material. Examples of the surface-attached substance include oxides such as aluminum oxide, sulfates such as lithium sulfate, and carbonates such as lithium carbonate. These surface-adhering substances can be attached to the surface of the positive electrode active material by, for example, dissolving or suspending them in a solvent, adding them to the positive electrode active material by impregnation, and drying them. The amount of the surface-adhering substance is preferably 1 μmol / g or more, more preferably 10 μmol / g or more, and is usually 1 mmol / g or less, relative to the positive electrode active material. In this specification, a positive electrode active material having the surface-adhering substance attached to its surface is also referred to as a "positive electrode active material."

[0095] [2-3-2. Positive electrode structure and manufacturing method] The configuration and manufacturing method of the positive electrode are described below. In this embodiment, a positive electrode using a positive electrode active material can be manufactured by a conventional method. That is, a positive electrode can be obtained by a coating method in which a positive electrode active material, a binder, and, if necessary, a conductive material and a thickener are mixed in a dry state to form a sheet and then pressed onto a positive electrode current collector, or by dissolving or dispersing these materials in a solvent such as an aqueous solvent or an organic solvent to form a slurry, which is then applied to a positive electrode current collector and dried to form a positive electrode active material layer on the current collector. Furthermore, for example, the above-mentioned positive electrode active material may be roll-formed into a sheet electrode, or may be compression-molded into a pellet electrode. In this case, in order to increase the packing density of the positive electrode active material, it is preferable to compact it using a hand press, roller press, or the like. Hereinafter, the case where the slurry is sequentially applied to the positive electrode current collector and then dried will be described.

[0096] [2-3-2-1. Active material content] The content of the positive electrode active material in the positive electrode active material layer is usually 80% by mass or more and 99.5% by mass or less.

[0097] [2-3-2-2.Conductive materials] Any known conductive material can be used as the conductive material. Specific examples include metal materials such as copper and nickel; graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; and carbon-based materials such as amorphous carbon such as needle coke. One conductive material may be used alone, or two or more conductive materials may be used in any combination and ratio. The conductive material is typically used so that it is contained in the positive electrode active material layer in an amount of 0.01% by mass to 50% by mass.

[0098] [2-3-2-3. Binder] When the positive electrode active material layer is formed by, for example, a coating method, the binder used in producing the positive electrode active material layer is not particularly limited as long as it is a material that can be dissolved or dispersed in a liquid medium for the slurry. However, in view of weather resistance, chemical resistance, heat resistance, flame retardancy, and the like, fluorine-based resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene; and CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide are preferred. Also usable are mixtures, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, etc. The binder may be used alone or in any combination and ratio of two or more types. Furthermore, when a resin is used as a binder, the weight-average molecular weight of the resin is optional as long as it does not significantly impair the effects of the present invention, but is usually from 10,000 to 3,000,000. When the molecular weight is in this range, the strength of the electrode is improved, and the electrode can be suitably formed. The proportion of the binder in the positive electrode active material layer is usually 0.1 mass % or more and 80 mass % or less.

[0099] [2-3-2-4. Current collector] The material of the positive electrode current collector is not particularly limited, and any known material can be used. Specific examples include metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum. Among these, aluminum is preferred. The current collector may be in the form of a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punched metal, a foamed metal, or the like. Of these, a metal foil or a metal thin film is preferred. The metal foil or the metal thin film may be formed into a mesh as appropriate. When the current collector of the positive electrode is in the form of a plate or film, the thickness of the current collector is optional, but is usually 1 μm or more and 1 mm or less.

[0100] [2-3-2-5. Thickness and density of the positive electrode active material layer] The thickness of the positive electrode active material layer is the thickness obtained by subtracting the thickness of the current collector from the thickness of the entire positive electrode. Although there are no particular limitations, from the viewpoint of high capacity and high output, it is usually 10 μm or more and 500 μm or less on one side of the current collector. In addition, the density of the positive electrode active material layer is usually 1.5 g cm -3 More than 4.5g cm -3 The following is the result. The density of the positive electrode active material layer is measured by measuring the thickness and weight of the positive electrode active material layer.

[0101] [2-3-2-6. Surface coating of positive electrode active material layer] In addition, the positive electrode plate may have a substance of a different composition attached to its surface, and the substance may be the same as the surface-attached substance that may be attached to the surface of the positive electrode active material.

[0102] [2-4. Separator] A separator is usually interposed between the positive electrode and the negative electrode to prevent short circuits, and in this case, the non-aqueous electrolyte is usually impregnated into the separator before use. There are no particular limitations on the material or shape of the separator, and any known material can be used as long as it does not significantly impair the effects of the invention according to this embodiment.

[0103] [2-4-1. Materials] The separator material is not particularly limited as long as it is stable against the non-aqueous electrolyte solution, but preferred examples include oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, sulfates such as barium sulfate and calcium sulfate, inorganic materials such as glass filters made of glass fiber, and resins such as polyolefins, more preferably polyolefins, and particularly preferably polyethylene or polypropylene. These materials may be used alone or in any combination and ratio of two or more. The above materials may also be used in a laminated state.

[0104] [2-4-2.Form] The form is not particularly limited, but preferably, a thin film such as a nonwoven fabric, a woven fabric, or a microporous film is used. A thin film with a pore size of 0.01 to 1 μm and a thickness of 1 to 50 μm is preferably used. In addition to an independent thin film, a separator may be used in which a composite porous layer containing inorganic particles is formed on the surface of the positive electrode and / or negative electrode using a resin binder. The separator is preferably a microporous film or a nonwoven fabric because of its excellent liquid retention.

[0105] [2-4-3. Porosity] When a porous material such as a porous sheet or nonwoven fabric is used as the separator, the porosity of the separator is not limited, but is usually 20% or more and 90% or less. [2-4-4. Air permeability] The air permeability of a separator in a nonaqueous electrolyte secondary battery can be determined by its Gurley value. The Gurley value indicates the difficulty of air passing through the film in the thickness direction, and is expressed as the number of seconds required for 100 mL of air to pass through the film. The Gurley value of a separator can be any value, but is usually 10 to 1000 seconds / 100 mL.

[0106] [2-5.Battery design] [2-5-1. Electrode group] The electrode group may have either a laminated structure of the positive electrode plate and the negative electrode plate sandwiched between the separator, or a structure of the positive electrode plate and the negative electrode plate spirally wound with the separator sandwiched between them. The ratio of the volume of the electrode group to the internal volume of the battery (hereinafter referred to as the electrode group occupancy rate) is usually 40% or more and 90% or less.

[0107] [2-5-2. Current collection structure] When the electrode group has the aforementioned laminated structure, a structure in which the metal core portions of each electrode layer are bundled and welded to a terminal is preferably used. A structure in which multiple terminals are provided within the electrode to reduce resistance is also preferably used. When the electrode group has the aforementioned wound structure, the internal resistance can be reduced by providing multiple lead structures on each of the positive electrode and negative electrode and bundling them to a terminal.

[0108] [2-5-3.Protection elements] The protective element may be a PTC (Positive Temperature Coefficient) element whose resistance increases with heat generation due to excessive current, a thermal fuse, a thermistor, or a valve (current cutoff valve) that cuts off the current flowing in the circuit due to a sudden rise in the internal pressure or temperature of the battery when abnormal heat is generated. It is preferable to select the above protective element so that it will not operate under normal use at high current, and it is even more preferable to design it so that abnormal heat generation or thermal runaway does not occur even without the protective element.

[0109] [2-5-4. Exterior body] A non-aqueous electrolyte secondary battery is usually constructed by housing the above-mentioned non-aqueous electrolyte, negative electrode, positive electrode, separator, etc. in an exterior body (exterior case). There are no limitations on this exterior body, and any known exterior body can be used as long as it does not significantly impair the effects of the present invention. The material of the exterior case is not particularly limited as long as it is stable against the non-aqueous electrolyte solution used, but from the viewpoint of weight reduction, metals such as aluminum or aluminum alloys, and laminate films are preferably used. Examples of exterior cases using the above metals include those in which metals are welded together by laser welding, resistance welding, or ultrasonic welding to form a sealed, airtight structure, and those in which the above metals are used via a resin gasket to form a crimped structure.

[0110] [2-5-5. Shape] The shape of the exterior case is also arbitrary, and may be, for example, cylindrical, rectangular, laminated, coin-shaped, large, or the like. [Example]

[0111] Next, specific embodiments of the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. The abbreviations of the compounds used in the examples and comparative examples are shown below: The viscosity of the chain carboxylic acid ester was measured at 25°C using an Ubbelohde viscometer and an oscillating densitometer. DMC: Dimethyl carbonate MA: Methyl acetate (viscosity at 25°C 0.36 cP) MP: Methyl propionate (viscosity at 25°C 0.44 cP) EP: Ethyl propionate (viscosity at 25°C 0.49 cP) LiBOB: Lithium bis(oxalato)borate LiFSO3: Lithium fluorosulfonate Li[PF2(C2O4)2]: Lithium difluorobis(oxalato)phosphate LiPO2F2: Lithium difluorophosphate

[0112] Example A [Fabrication of non-aqueous electrolyte secondary battery] <Preparation of positive electrode> Li as the positive electrode active material 1.00 Ni 0.33 Mn 0.33 Co 0.33 85 mass of O2 The active material layer of the positive electrode was prepared by mixing 10 parts by mass of acetylene black as a conductive material and 5 parts by mass of polyvinylidene fluoride (PVdF) as a binder in N-methyl-2-pyrrolidone to form a slurry. The slurry was uniformly applied to a 15 μm thick aluminum foil, dried, and then roll-pressed to form a positive electrode. The density of the active material layer of the positive electrode was 2.6 g / cm. 3 It was.

[0113] <Preparation of negative electrode> 49 parts by weight of graphite powder was mixed with 50 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose: 1% by weight) as a thickener and 1 part by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber: 50% by weight) as a binder, and the mixture was mixed in a disperser to form a slurry. The resulting slurry was uniformly applied to a 10 μm-thick copper foil, dried, and roll-pressed to form a negative electrode. The density of the negative electrode active material layer in the negative electrode used in the examples was 1.35 g / cm 3 The porosity of the negative electrode active material layer, determined by measuring the volume of pores of 5.4 nm or more using mercury intrusion porosimetry, was 40.8%.

[0114] <Preparation of non-aqueous electrolyte> [Examples A-1 to A-3, Reference Examples A-4 to A-6, Comparative Examples A-1 to A-5] In a dry argon atmosphere, a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 3:3:4) was mixed with 1.15 mol / L (13.9 mass%, estimated density 1.26 g / cm) of thoroughly dried LiPF. 3Using the non-aqueous electrolyte solution in which symmetric chain carbonate and chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C, oxalate complex anion (A)-containing salt, an anion (D) having an FSO2 skeleton, and other compounds were further added in the combinations shown in Table 1. Comparative Example A-1 does not contain the symmetric chain carbonate and chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C, nor the oxalate complex anion (A)-containing salt. The "content (mass%)" in the table indicates the content of each compound when the total non-aqueous electrolyte solution is taken as 100 mass%. [Comparative example A-6] In a dry argon atmosphere, a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 3:1:6) was added with 1.15 mol / L (13.7 mass%, estimated density 1.27 g / cm) of thoroughly dried LiPF. 3 ) was dissolved in the non-aqueous electrolyte solution as a reference, and non-aqueous electrolyte solutions were prepared that further contained a symmetric chain carbonate and a chain carboxylic acid ester (C) having a viscosity at 25°C of 0.01 to 0.47 cP in the combinations shown in Table 1. [Comparative example A-7] In a dry argon atmosphere, a mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3:7) was added with 1.15 mol / L (14.1 mass%, estimated density 1.24 g / cm) of thoroughly dried LiPF. 3 Using the non-aqueous electrolyte solution in which symmetric chain carbonate and chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C, salt containing an anion (D) having an FSO2 skeleton, and other compounds were further added in the combinations shown in Table 1, to prepare non-aqueous electrolyte solutions.

[0115] <Production of non-aqueous electrolyte secondary battery> The positive electrode, negative electrode, and polyolefin separator were stacked in this order, and the resulting battery element was wrapped in an aluminum laminate film, and the nonaqueous electrolyte solution of each of the above-mentioned Examples or Comparative Examples was poured into the battery element, followed by vacuum sealing to prepare a sheet-like nonaqueous electrolyte secondary battery.

[0116] [Evaluation of non-aqueous electrolyte secondary batteries] The non-aqueous electrolyte secondary battery prepared by the above procedure was evaluated as follows. ·Initial charge / discharge In a thermostatic bath at 25°C, a sheet-shaped nonaqueous electrolyte secondary battery was charged at a constant current of 0.05C (the current value required to discharge the rated capacity in 1 hour based on the hourly discharge capacity is defined as 1C; the same applies below) to 3.7V, then charged at a constant current and constant voltage of 0.2C to a voltage of 4.3V, and then discharged at a constant current of 0.2C to 2.5V. The nonaqueous electrolyte secondary battery was further charged at a constant current and constant voltage of 0.2C to 4.1V, and then stored at 60°C for 24 hours to stabilize it. Thereafter, a constant current discharge was performed at 25°C to 2.5V.

[0117] Capacity retention rate after continuous charging The above initially charged and discharged non-aqueous electrolyte secondary battery was subjected to constant current-constant voltage charging at 0.2 C up to a voltage of 4.3 V, and then subjected to constant current discharging at 0.2 C down to 2.5 V, and the discharge capacity at this time was taken as the initial capacity (C1). Next, constant voltage charging of 4.3 V was carried out at 60° C. for 7 days. This nonaqueous electrolyte secondary battery was subjected to constant current discharge at 0.2 C to 2.5 V in a thermostatic chamber at 25° C., and then constant current-constant voltage charging at 0.2 C to a voltage of 4.3 V. Thereafter, a constant current discharge was performed at 0.2 C to 2.5 V, and the discharge capacity at this time was defined as the capacity after continuous charge (C2), and the ratio (C2 / C1) of the initial capacity (C1) to the capacity after continuous charge (C2) was defined as the "capacity retention rate after continuous charge" (shown in Table 1 as a relative value with Comparative Example A-1 set to 100). It can be said that the larger the capacity retention rate after continuous charging, the more preferable it is.

[0118] Table 1 shows the capacity retention rate after continuous charging. As is clear from Table 1, the content of the symmetric chain carbonate according to the present invention and the chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C is within a specific concentration range, and the PF6 of the oxalato complex anion (A) is - When a nonaqueous electrolyte solution having a content ratio (A / B) of symmetric chain carbonate to anion (B) within a specific range is used, the capacity retention rate after continuous charge of the nonaqueous electrolyte secondary battery can be increased, and the performance of the nonaqueous electrolyte secondary battery can be improved. On the other hand, when a nonaqueous electrolyte solution having a content of the symmetric chain carbonate and the chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C outside a specific concentration range is used, or when a nonaqueous electrolyte solution not containing a symmetric chain carbonate is used, no improvement in the capacity retention rate after continuous charge is observed. Furthermore, even when a non-aqueous electrolyte solution containing a difluorophosphate anion-containing salt used in the prior art (Patent Document 4) was used without adding an oxalate complex anion (A)-containing salt, no improvement in the capacity retention rate after continuous charging was observed.

[0119] [Table 1]

[0120] Example B [Fabrication of non-aqueous electrolyte secondary battery] <Preparation of non-aqueous electrolyte> [Examples B-1 to B-5, Comparative Examples B-1 to B-3, B-5 ​​to B-6, B-9 to B-11] In a dry argon atmosphere, a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 3:3:4) was mixed with 1.15 mol / L (13.9 mass%, estimated density 1.26 g / cm) of thoroughly dried LiPF. 3Based on the non-aqueous electrolyte solution in which the symmetric chain carbonate and the chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C, other esters, salts containing oxalate complex anions (A), salts containing anions (D) having an FSO2 skeleton, and other compounds were further added in the combinations shown in Tables 2 and 3. Comparative Example B-1 does not contain the symmetric chain carbonate and the chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C, nor the salts containing oxalate complex anions (A). The "content (mass%)" in the tables indicates the content of each compound when the total non-aqueous electrolyte solution is taken as 100 mass%. [Comparative examples B-4, B-7~B-8] In a dry argon atmosphere, a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 3:1:6) was added with 1.15 mol / L (13.7 mass%, estimated density 1.27 g / cm) of thoroughly dried LiPF. 3 ) was dissolved in the non-aqueous electrolyte solution as a reference, and non-aqueous electrolyte solutions containing a symmetric chain carbonate, a chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C, an oxalate complex anion (A)-containing salt, and an anion (D) having an FSO2 skeleton were further prepared in the combinations shown in Table 2 or Table 3.

[0121] <Production of non-aqueous electrolyte secondary battery> A positive electrode and a negative electrode were prepared in the same manner as in Example A, and the positive electrode, negative electrode, and polyolefin separator were laminated in this order: negative electrode, separator, positive electrode. The battery element thus obtained was wrapped in an aluminum laminate film, and the nonaqueous electrolyte solution of each of the above-mentioned Examples or Comparative Examples was poured into it, followed by vacuum sealing to prepare a sheet-shaped nonaqueous electrolyte secondary battery.

[0122] [Evaluation of non-aqueous electrolyte secondary batteries] Continuous charge capacity loss The non-aqueous electrolyte secondary battery prepared by the above procedure was evaluated as follows. The nonaqueous electrolyte secondary battery, which had been initially charged and discharged in the same manner as in Example A above, was subjected to constant current / constant voltage charging at 0.2 C up to a voltage of 4.3 V. Subsequently, constant voltage charging at 4.3 V was carried out for 7 days at 60° C., and the amount of electricity that flowed during this constant voltage charging was defined as the “continuous charge capacity loss” (shown in Table 2 as a relative value with Comparative Example B-1 set to 100). It can be said that the smaller the continuous charge capacity loss, the more preferable it is.

[0123] Tables 2 and 3 show the continuous charge capacity loss. As is clear from Tables 2 and 3, the content of the symmetric chain carbonate according to the present invention and the chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C are within a specific concentration range, and the PF6 of the oxalato complex anion (A) is - When a non-aqueous electrolyte solution having a content ratio (A / B) of 0.01 to 0.47 cP at 25°C is used, the continuous charge capacity loss of the non-aqueous electrolyte secondary battery can be reduced and the performance of the non-aqueous electrolyte secondary battery can be improved. On the other hand, when the non-aqueous electrolyte solution does not contain a chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C or an oxalato complex anion (A), when the content of the symmetric chain carbonate and the chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C exceeds a specific concentration range, or when the oxalato complex anion (A) is PF6 - When a non-aqueous electrolyte with a ratio (A / B) of anion (B) exceeding a certain level was used, no improvement in continuous charge capacity loss was observed. Furthermore, no improvement in continuous charge capacity loss was observed when a non-aqueous electrolyte solution was used in which ethyl propionate (Patent Document 3), which is used in conventional technology, was added without adding a chain carboxylic acid ester having a viscosity of 0.01 to 0.47 cP at 25°C, or a non-aqueous electrolyte solution in which difluorophosphate anion (Patent Document 4) was added without adding the compound represented by formula (A).

[0124] [Table 2]

[0125] [Table 3]

[0126] Example C [Fabrication of non-aqueous electrolyte secondary battery] [Example C-1, Comparative Examples C-3 to C-4] In a dry argon atmosphere, a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 3:3:4) was mixed with 1.15 mol / L (13.9 mass%, estimated density 1.26 g / cm) of thoroughly dried LiPF. 3 Using the non-aqueous electrolyte solution in which symmetric chain carbonate and chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C, other esters, salts containing oxalate complex anions (A), and salts containing anions (D) having an FSO2 skeleton as the base, non-aqueous electrolyte solutions were prepared in the combinations shown in Table 4. The "content (mass%)" in the table indicates the content of each compound when the entire non-aqueous electrolyte solution is taken as 100 mass%. [Comparative examples C-1 to C-2] In a dry argon atmosphere, a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 3:1:6) was added with 1.15 mol / L (13.7 mass%, estimated density 1.27 g / cm) of thoroughly dried LiPF. 3 Using the non-aqueous electrolyte solution in which symmetric chain carbonate and chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C, a salt containing an oxalate complex anion (A), and a salt containing an anion (D) having an FSO2 skeleton were further prepared in the combinations shown in Table 3, based on the non-aqueous electrolyte solution in which symmetric chain carbonate and chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C were further added.

[0127] <Production of non-aqueous electrolyte secondary battery> A positive electrode and a negative electrode were prepared in the same manner as in Example A, and the positive electrode, negative electrode, and polyolefin separator were laminated in this order: negative electrode, separator, positive electrode. The battery element thus obtained was wrapped in an aluminum laminate film, and the nonaqueous electrolyte solution of each of the above-mentioned Examples or Comparative Examples was poured into it, followed by vacuum sealing to prepare a sheet-shaped nonaqueous electrolyte secondary battery.

[0128] [Evaluation of non-aqueous electrolyte secondary batteries] Charging resistance increase rate The non-aqueous electrolyte secondary battery prepared by the above procedure was evaluated as follows. A nonaqueous electrolyte secondary battery initially charged and discharged in the same manner as in Example A above was charged at a constant current and constant voltage of 0.2 C to a voltage of 3.7 V at 25°C. The battery was then charged at 0.05 C, 0.1 C, 0.25 C, 0.5 C, 0.75 C, and 1 C at 25°C, and the voltage was measured 10 seconds after the start of the charging process. The internal resistance (R1) was calculated from this current-voltage line. Next, constant-current / constant-voltage charging was performed at 0.2 C to a voltage of 4.3 V. Subsequently, constant-voltage charging at 4.3 V was performed for 7 days at 60 °C. This nonaqueous electrolyte secondary battery was placed in a thermostatic chamber at 25 °C, discharged at 0.2 C to 2.5 V, and then charged at 0.2 C to a voltage of 3.7 V. This battery was charged at 0.05 C, 0.1 C, 0.25 C, 0.5 C, 0.75 C, and 1 C at 25 °C, and the voltage was measured 10 seconds after the start of each charge. The internal resistance was calculated from this current-voltage line and defined as the resistance after continuous charge (R2). The rate of change between R1 and R2 [(R2 - R1) / R1] was defined as the "charge resistance increase rate" (Table 3 shows the relative values, with Comparative Example C-1 set to 100).

[0129] Table 4 shows the rate of increase in charging resistance. As is clear from Table 4, the content of the symmetric chain carbonate according to the present invention and the chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C is within a specific concentration range, and the PF6 of the oxalato complex anion (A) is -When a non-aqueous electrolyte containing an anion (D) having an FSO2 skeleton and having a content ratio (A / B) of the anion to the anion (B) within a specific range is used, the rate of increase in charge resistance of the non-aqueous electrolyte secondary battery can be reduced, and the performance of the non-aqueous electrolyte secondary battery can be improved. On the other hand, when the anion (D) having an FSO2 skeleton is not contained, or when the content of the symmetric chain carbonate and the chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C exceeds a specific concentration range, no improvement in the rate of increase in charge resistance was observed. Furthermore, even when a non-aqueous electrolyte solution containing lithium difluorophosphate, which is used in the prior art (Patent Document 4), was used without adding a salt containing an oxalate complex anion (A), no improvement in the rate of increase in charging resistance of the non-aqueous electrolyte secondary battery was observed.

[0130] [Table 4]

Claims

1. an oxalato complex anion (A); LiPF ６ and, A non-aqueous electrolyte solution containing a symmetric chain carbonate and a chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C, PF ６ － a ratio (A / B) of the content (mass) of the oxalato complex anion (A) to the content (mass) of the anion (B) of 0.0001 to 0.30; The nonaqueous electrolyte solution is characterized in that the total content of the symmetric chain carbonate and the chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C is 1 to 45 mass% relative to the total amount of the nonaqueous electrolyte solution.

2. 2. The nonaqueous electrolyte solution according to claim 1, wherein the content of the chain carboxylic acid ester having a viscosity of 0.01 to 0.47 cP at 25° C. is 0.1 to 44 mass% relative to the total amount of the nonaqueous electrolyte solution.

3. 3. The nonaqueous electrolyte solution according to claim 1, wherein the chain ester compound having a viscosity of 0.01 to 0.47 cP at 25° C. is a compound represented by the following formula (I): R １ COOCH ３ ・・・(I) (In formula (I), R １ is a hydrogen atom or an alkyl group having 1 or 2 carbon atoms, and the hydrogen atom bonded to the carbon atom of the alkyl group may be substituted with a halogen atom.

4. R in the formula (I) １ The nonaqueous electrolyte solution according to claim 3 , wherein is a methyl group.

5. As an auxiliary agent, FSO ２ The anion (D) having a skeleton according to any one of claims 1 to 4. The non-aqueous electrolyte solution according to any one of claims 1 to 14.

6. The FSO ２ 6. The nonaqueous electrolyte solution according to claim 5, wherein the ratio (A / D) of the content of the oxalato complex anion (A) to the content of the skeleton-containing anion (D) is 0.01 to 10.

7. The FSO ２ 7. The nonaqueous electrolyte solution according to claim 5, wherein the ratio (A / D) of the content of the oxalato complex anion (A) to the content of the skeleton-containing anion (D) is 0.01 to 0.

7.

8. The LiPF ６ 8. The nonaqueous electrolyte solution according to claim 1, wherein a ratio of a total content (mass) of the symmetric chain carbonate and the chain carboxylic acid ester (C) having a viscosity of 0.01 to 0.47 cP at 25°C to ... is 0.01 to 3.

5.

9. The non-aqueous electrolyte solution according to any one of claims 1 to 8, wherein the oxalato complex anion (A) is a non-fluorinated bis(oxalato)borate anion and / or a difluorobis(oxalato)phosphate anion.

10. A non-aqueous electrolyte battery comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and the non-aqueous electrolyte solution according to any one of claims 1 to 9.

11. A non-aqueous electrolyte battery as described in claim 10, wherein the positive electrode active material is capable of absorbing and releasing lithium ions, and the negative electrode active material is capable of absorbing and releasing lithium ions.

12. 12. The nonaqueous electrolyte battery according to claim 10, wherein the positive electrode active material comprises a lithium transition metal compound represented by the following composition formula (3): Li ａ１ Ni ｂ１ M ｃ１ O ２ ・・・(3) (In the composition formula (3), the numerical values ​​are 0.90≦a1≦1.10, 0.20≦b1≦0.98, and 0.01≦c1≦0.50, and b1+c1=1 is satisfied. M represents at least one element selected from the group consisting of Co, Mn, Al, Mg, Zr, Fe, Ti, and Er.)

13. The nonaqueous electrolyte battery according to claim 12 , wherein M in the formula (3) includes Mn.

14. The nonaqueous electrolyte battery according to any one of claims 10 to 13, wherein the negative electrode active material comprises a carbon-based material.

15. The density of the negative electrode active material layer in the negative electrode is 0.8 to 1.7 g / cm ３ The nonaqueous electrolyte battery according to any one of claims 10 to 14,

16. 16. The nonaqueous electrolyte battery according to claim 10, wherein the porosity of the negative electrode active material layer in the negative electrode is 10 to 80%.

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