Electrolyte and secondary battery using the same

Abstract

To provide: an electrolyte solution which enables a secondary battery comprising a silicon negative electrode to have a longer service life and to inhibit the resistance from increasing; and a secondary battery which uses the same.SOLUTION: The present invention provides an electrolyte solution used in a battery that is provided with an electrode comprising a negative electrode material that contains elemental silicon and elemental carbon. The electrolyte solution contains less than 10 mass% of a fluorinated ether represented by general formula (1): HCF2CF2-O-R (1), where R is a fluorinated alkyl group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to an electrolyte and a secondary battery using the same. [Background technology]

[0002] It has been reported that using fluorine ethers, including 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, as a solvent in the electrolyte for lithium-ion batteries improves the battery life in the high-voltage range (Non-patent prior art 1). Specifically, lithium metal is used for the negative electrode and LiNi for the positive electrode. 0.5 Mn 1.5 The report discloses that high-voltage operating characteristics are improved by using O4 and mixing various fluorine ethers, such as 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, with propylene carbonate as a solvent.

[0003] Furthermore, it has been reported that the lifespan of silicon anodes can be improved by using fluoroethylene carbonate as an additive (Non-patent prior art 2). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Journal of the Electrochemical Society, 164 (1) A6412-A6416 (2017) [Non-Patent Document 2] Journal of the Electrochemical Society, 163 (8) A1705-A1716 (2016) [Overview of the project] [Problems that the invention aims to solve]

[0005] This disclosure aims to provide an electrolyte that enables improved lifespan and suppression of resistance increase in secondary batteries equipped with a silicon anode, and a secondary battery using the same. [Means for solving the problem]

[0006] This disclosure relates to a negative electrode material comprising silicon and carbon elements. Negative Equipped with the ultimate Lithium ion secondary An electrolyte used in batteries, The above negative electrode material contains Si and / or SiOa (0<a<2) and a carbon compound, The fluorinated ether represented by the following general formula (1) 0.5 to 3 mass% This electrolyte is characterized by containing [specific components]. HCF2CF2-OR (1) (In the formula, R is a fluorinated alkyl group.)

[0007] The fluorinated ether represented by the above general formula (1) is the fluorinated ether represented by the following general formulas (2) to (4). Conversion It is preferable that the fluorinated ether is at least one selected from the group consisting of ethers. HCF2CF2-O-CH2CF2CF2H (2) HCF2CF2-O-CH2CF2CF3(3) HCF2CF2-O-CH2CF3(4 )

[0008] This disclosure comprises an electrolyte as described above. Lithium ion It is also a rechargeable battery. In the above secondary battery, The lower limit of LiF formed on the negative electrode is 3.0 μg / cm 2 , and the upper limit is 4.1 μg / cm 2 It is preferable that this be the case. [Effects of the Invention]

[0009] This disclosure provides an electrolyte that enables improved battery life and suppression of resistance increase in secondary batteries equipped with a silicon anode. Furthermore, secondary batteries using the electrolyte of this disclosure exhibit improved battery life and suppressed resistance increase. [Modes for carrying out the invention]

[0010] Hereinafter, the present disclosure will be described in detail. The electrolytic solution of the present disclosure is an electrolytic solution suitably used for a battery including an electrode containing a negative electrode material having a silicon element and a carbon element, and is characterized by containing less than 10% by mass of a fluorinated ether represented by the following general formula (1). HCF2CF2-O-R (1) (In the formula, R is a fluorinated alkyl group.)

[0011] The present disclosure relates to an electrolytic solution for use in a secondary battery including the silicon negative electrode as described above. In the present disclosure, by using the specific fluorinated ether in a specific amount as an additive in the electrolytic solution for a lithium ion secondary battery, lithium fluoride (LiF) is formed as a reduction coating on the silicon negative electrode, and the formation thereof achieves a significant improvement in service life and suppression of resistance increase.

[0012] The lower limit of the LiF formed as described above is 3.0 μg / cm 2 is preferably, more preferably 3.1 μg / cm 2 is still more preferably, particularly preferably 3.2 μg / cm 2 . The upper limit is preferably 4.1 μg / cm 2 , more preferably 3.9 μg / cm 2 . If the amount of LiF formed on the negative electrode is too small, sufficient improvement in life characteristics may not be obtained, and if it is too large, the resistance tends to increase.

[0013] (Fluorinated Ether) The electrolytic solution of the present disclosure contains less than 10% by mass of the fluorinated ether represented by the following general formula (1). HCF2CF2-O-R (1) (In the formula, R is a fluorinated alkyl group.)

[0014] The fluorinated alkyl group is preferably a fluorinated alkyl group having 1 to 10 carbon atoms. Above all, a fluorinated alkyl group having 2 to 6 carbon atoms is more preferable.

[0015] If the number of carbon atoms in the alkyl fluoride is too small, the boiling point tends to be lower, and if the number of carbon atoms is too large, the viscosity tends to increase.

[0016] The above-mentioned fluorinated ether preferably has a fluorine content of 40 to 75% by mass. Having a fluorine content within this range results in a particularly excellent balance between non-flammability and compatibility. It is also preferable in terms of good oxidation resistance and safety. The lower limit of the fluorine content is more preferably 45% by mass, even more preferably 50% by mass, and particularly preferably 55% by mass. The upper limit is more preferably 70% by mass, and even more preferably 69% by mass. The fluorine content of fluorinated ether(I) is calculated based on the structural formula of fluorinated ether(I) using the formula {(number of fluorine atoms × 19) / molecular weight of fluorinated ether(I)} × 100 (%).

[0017] Examples of R include -CH2CF2CF3, -CF2CFHCF3, -CF2CF2CF2H, -CH2CF2CF2H, -CH2CH2CF2CF3, -CH2CF2CFHCF3, -CF2CF2CF2CF2H, -CH2CF2CF2CF2H, -CH2CH2CF2CF2H, -CH2CF(CF3)CF2H, -CF2CF2H, -CH2CF2H, -CH2CF3, -CF2CH3, etc.

[0018] Specific examples of the above fluorinated ether(I) include, for example, HCF2CF2-O-CH2CF2CF2H, HCF2CF2-O-CH2CF2CF3, HCF2CF2-O-CH2CF3, HCF2CF2-O-CF2CFHCF3, HCF2CF2-O-CF2CF2CF2H, HCF2CF2-O-CH2CH2CF2CF3, HCF2CF2-O-CH2CF2CF2CFHCF3, HCF2CF2-O-CF2CF2CF2CF2H, HCF2CF2-O-CH2CH2CF2CF2H, HCF2CF2-O-CH2CF(CF3)CF2H, HCF2CF2-O-CF2CF2H, and HCF2CF2-O-CH2CF2Hwall.

[0019] The fluorinated ether represented by the above general formula (1) is preferably at least one fluorinated ether selected from the group consisting of fluorinated ethers represented by the following general formulas (2) to (4).

[0020] HCF2CF2-O-CH2CF2CF2H (2) HCF2CF2-O-CH2CF2CF3(3) HCF2CF2-O-CH2CF3(4)

[0021] In particular, by including the fluorinated ether represented by the above general formulas (2) to (4) as an additive in the electrolyte, lithium fluoride (LiF) is formed as a reducing film on the silicon anode, which is advantageous in terms of significantly improving lifespan and suppressing resistance increase.

[0022] The content of the fluorinated ether mentioned above must be less than 10% by mass in the electrolyte. Keeping it within this range ensures that the electrolyte can be used effectively. In other words, if the content is too high, the viscosity of the electrolyte increases, and the ionic conductivity decreases, thus reducing the battery life. The upper limit of the fluorinated ether content is preferably 9.0% by mass, and more preferably 5.0% by mass. The lower limit of the fluorinated ether content is preferably 0.001% by mass, and more preferably 0.01% by mass.

[0023] The electrolyte of this disclosure preferably contains a solvent.

[0024] The above solvent preferably contains at least one selected from the group consisting of carbonates and carboxylic acid esters.

[0025] The above-mentioned carbonate may be a cyclic carbonate or a chain carbonate.

[0026] The above-mentioned cyclic carbonate may be a non-fluorinated cyclic carbonate or a fluorinated cyclic carbonate.

[0027] Examples of the above-mentioned non-fluorinated cyclic carbonates include non-fluorinated saturated cyclic carbonates, with non-fluorinated saturated alkylene carbonates having alkylene groups with 2 to 6 carbon atoms being preferred, and non-fluorinated saturated alkylene carbonates having alkylene groups with 2 to 4 carbon atoms being more preferred.

[0028] In particular, as the non-fluorinated saturated cyclic carbonate, at least one selected from the group consisting of ethylene carbonate, propylene carbonate, cis-2,3-pentylene carbonate, cis-2,3-butylene carbonate, 2,3-pentylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 1,2-butylene carbonate, and butylene carbonate is preferred because it has a high dielectric constant and suitable viscosity.

[0029] The above-mentioned non-fluorinated saturated cyclic carbonates may be used individually or in combination of two or more in any combination and ratio.

[0030] If the above-mentioned non-fluorinated saturated cyclic carbonate is included, the content of the above-mentioned non-fluorinated saturated cyclic carbonate is preferably 5 to 90% by volume, more preferably 10 to 60% by volume, and even more preferably 15 to 50% by volume relative to the above-mentioned solvent.

[0031] The above-mentioned fluorinated cyclic carbonate is a cyclic carbonate having a fluorine atom. Solvents containing fluorinated cyclic carbonates can be suitably used even under high voltage. In this specification, "high voltage" refers to a voltage of 4.2V or higher. Furthermore, the upper limit of "high voltage" is preferably 4.9V.

[0032] The above-mentioned fluorinated cyclic carbonate may be a fluorinated saturated cyclic carbonate or a fluorinated unsaturated cyclic carbonate.

[0033] The above-mentioned fluorinated saturated cyclic carbonate is a saturated cyclic carbonate having a fluorine atom, and specifically, the following general formula (A):

[0034] [ka] (In the formula, X 1 ~X 4 The same or different, each representing -H, -CH3, -C2H5, -F, a fluorinated alkyl group which may have an ether linkage, or a fluorinated alkoxy group which may have an ether linkage. However, X 1 ~X 4 At least one of the members is -F, a fluorinated alkyl group which may have an ether bond, or a fluorinated alkoxy group which may have an ether bond. Examples of compounds represented by ) are the above fluorinated alkyl groups such as -CF3, -CF2H, and -CH2F.

[0035] When the electrolyte of this disclosure is applied to a high-voltage lithium-ion secondary battery or the like, the oxidation resistance of the electrolyte is improved, and stable and excellent charge-discharge characteristics are obtained. In this specification, "ether bond" refers to a bond represented by -O-.

[0036] Due to its good dielectric constant and oxidation resistance, X 1 ~X 4 Preferably, one or two of these are -F, a fluorinated alkyl group which may have an ether linkage, or a fluorinated alkoxy group which may have an ether linkage.

[0037] Because it is expected to reduce viscosity at low temperatures, increase the flash point, and further improve the solubility of the electrolyte salt, X 1 ~X 4 Preferably, the element is -H, -F, a fluorinated alkyl group (a), a fluorinated alkyl group having an ether linkage (b), or a fluorinated alkoxy group (c).

[0038] The above-mentioned fluorinated alkyl group (a) is obtained by substituting at least one hydrogen atom of the alkyl group with a fluorine atom. The number of carbon atoms in the fluorinated alkyl group (a) is preferably 1 to 20, more preferably 1 to 17, even more preferably 1 to 7, and particularly preferably 1 to 5. If the number of carbon atoms becomes too large, the low-temperature properties may deteriorate and the solubility of the electrolyte salt may decrease. Conversely, if the number of carbon atoms is too small, a decrease in the solubility of the electrolyte salt, a decrease in discharge efficiency, and an increase in viscosity may occur.

[0039] Among the above-mentioned fluorinated alkyl groups (a), those having one carbon atom include CFH2-, CF2H-, and CF3-. In particular, CF2H- or CF3- are preferred in terms of high-temperature storage characteristics, and CF3- is the most preferred.

[0040] Of the above fluorinated alkyl groups (a), those with 2 or more carbon atoms are defined by the following general formula (a-1): R 1 -R 2 - (a-1) (In the formula, R 1 R is an alkyl group having 1 or more carbon atoms, which may contain a fluorine atom; 2 R is an alkylene group having 1 to 3 carbon atoms, which may contain a fluorine atom; however, R 1 and R 2 A fluorinated alkyl group represented by (at least one of which has a fluorine atom) can be preferably exemplified from the viewpoint of good solubility of the electrolyte salt. Note, R 1 and R 2 It may further contain atoms other than carbon atoms, hydrogen atoms, and fluorine atoms.

[0041] R 1 R is an alkyl group having 1 or more carbon atoms, which may contain a fluorine atom. 1 As such, linear or branched alkyl groups having 1 to 16 carbon atoms are preferred. 1 The number of carbon atoms is more preferably 1 to 6, and even more preferably 1 to 3.

[0042] R1 Specifically, as linear or branched alkyl groups, CH3-, CH3CH2-, CH3CH2CH2-, CH3CH2CH2CH2-,

[0043] [ka]

[0044] These are some examples.

[0045] Also, R 1If the alkyl group is a linear alkyl group with a fluorine atom, then the names are CF3-, CF3CH2-, CF3CF2-, CF3CH2CH2-, CF3CF2CH2-, CF3CF2CF2-, CF3CH2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CF2-, CF3CF2CH2CF2-, CF3CF2CH2CH2CH2-, CF3CF2CH2CH 2CH2-, CF3CH2CF2CH2CH2-, CF3CF2CF2CH2CH2-, CF3CF2CF2CF2CH2-, CF3CF2CH2CF2CH2-, CF3CF2CH2CH2CH2CH2-, CF3CF2C F2CF2CH2CH2-, CF3CF2CH2CF2CH2CH2-, HCF2-, HCF2CH2-, HCF2CF2-, HCF2CH2CH2-, HCF2CF2CH2-, HCF2CH2CF2-, HCF2CF2C H2CH2-, HCF2CH2CF2CH2-, HCF2CF2CF2CF2-, HCF2CF2CH2CH2CH2-, HCF2CH2CF2CH2CH2-, HCF2CF2CF2CF2CH2-, HCF2CF2CF2 CF2CH2CH2-, FCH2-, FCH2CH2-, FCH2CF2-, FCH2CF2CH2-, FCH2CF2CF2-, CH3CF2CH2-, CH3CF2CF2-, CH3CF2CH2CF2-, CH3CF2 Examples include CF2CF2-, CH3CH2CF2CF2-, CH3CF2CH2CF2CH2-, CH3CF2CF2CF2CH2-, CH3CF2CF2CH2CH2-, CH3CH2CF2CF2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, HCFClCF2CH2-, HCF2CFClCH2-, HCF2CFClCF2CFClCH2-, HCFClCF2CFClCF2CH2-, etc.

[0046] Also, R 1 If it is a branched alkyl group having a fluorine atom,

[0047] [ka]

[0048] [ka]

[0049] These are some examples of preferred structures. However, since the presence of CH3- or CF3- branches tends to increase viscosity, it is more preferable that the number of such branches be small (1) or zero.

[0050] R 2 R is an alkylene group having 1 to 3 carbon atoms, which may contain a fluorine atom. 2 The alkylene group may be linear or branched. An example of the smallest structural unit constituting such a linear or branched alkylene group is shown below. 2 These are composed of one or a combination of these.

[0051] (i) Linear minimal structural unit: -CH2-, -CHF-, -CF2-, -CHCl-, -CFCl-, -CCl2-

[0052] (ii) The smallest structural unit of a branched chain:

[0053] [ka]

[0054] Furthermore, among the examples above, it is preferable that the constituent units do not contain Cl, as this prevents the deHCl reaction by a base and is therefore more stable.

[0055] R 2 When the structure is linear, it consists only of the minimum linear structural units described above, with -CH2-, -CH2CH2-, or -CF2- being preferred. -CH2- or -CH2CH2- is more preferred because it can further improve the solubility of the electrolyte salt.

[0056] R 2If it is branched, it consists of at least one of the branched minimum structural units described above, and the general formula is:-(CX a X b )-(X a is H, F, CH3 or CF3;X b is CH3 or CF3. However, X b If it is CF3, X a Examples of materials that can be represented as (where is H or CH3) are preferred. These can particularly further improve the solubility of the electrolyte salt.

[0057] Preferred fluorinated alkyl(a) include, for example, CF3CF2-, HCF2CF2-, H2CFCF2-, CH3CF2-, CF3CHF-, CH3CF2-, CF3CF2CF2-, HCF2CF2CF2-, H2CFCF2CF2-, CH3CF2CF2-,

[0058] [ka]

[0059] [ka]

[0060] These are some examples.

[0061] The above-mentioned fluorinated alkyl group (b) having an ether linkage is obtained by substituting at least one hydrogen atom of the alkyl group having an ether linkage with a fluorine atom. The above-mentioned fluorinated alkyl group (b) having an ether linkage preferably has 2 to 17 carbon atoms. If the number of carbon atoms is too high, the viscosity of the above-mentioned fluorinated saturated cyclic carbonate will increase, and the number of fluorine-containing groups will increase, which may lead to a decrease in the solubility of the electrolyte salt due to a decrease in dielectric constant and a decrease in compatibility with other solvents. From this viewpoint, the number of carbon atoms of the above-mentioned fluorinated alkyl group (b) having an ether linkage is more preferably 2 to 10, and even more preferably 2 to 7.

[0062] The alkylene group constituting the ether portion of the fluorinated alkyl group (b) having the above ether linkage may be a linear or branched alkylene group. An example of the smallest structural unit constituting such a linear or branched alkylene group is shown below.

[0063] (i) Linear minimal structural unit: -CH2-, -CHF-, -CF2-, -CHCl-, -CFCl-, -CCl2-

[0064] (ii) The smallest structural unit of a branched chain:

[0065] [ka]

[0066] Alkylene groups may consist of these minimum structural units alone, or they may be composed of linear (i) units together, branched (ii) units together, or combinations of linear (i) and branched (ii) units. Preferred specific examples will be described later.

[0067] Furthermore, among the examples above, it is preferable that the constituent units do not contain Cl, as this prevents the deHCl reaction by a base and is therefore more stable.

[0068] A more preferred fluorinated alkyl group having an ether bond is the general formula (b-1): R 3 -(OR 4 ) n1 - (b-1) (In the formula, R 3 R may have a fluorine atom, preferably an alkyl group having 1 to 6 carbon atoms; 4 n1 is an integer from 1 to 3, where R is an alkylene group having 1 to 4 carbon atoms, which may have a fluorine atom; n1 is an integer from 1 to 3; however, 3 and R 4 Examples include those represented by (at least one of which has a fluorine atom).

[0069] R 3 and R4 Examples include the following, and these can be combined as appropriate to form a fluorinated alkyl group (b) having an ether bond represented by the above general formula (b-1), but are not limited to these.

[0070] (1)R 3 For example, the general formula is: X c 3C-(R 5 ) n2 -(3 X c The same or different, both are H or F;R 5 (1) is an alkylene group which may have 1 to 5 carbon atoms and a fluorine atom; n2 is preferably an alkyl group represented by 0 or 1.

[0071] If n2 is 0, R 3 Examples include CH3-, CF3-, HCF2-, and H2CF-.

[0072] A concrete example of the case where n2 is 1 is R 3The linearly chained elements are CF3CH2-, CF3CF2-, CF3CH2CH2-, CF3CF2CH2-, CF3CF2CF2-, CF3CH2CF2-, CF3CH2CH2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CF2-, CF3CF2CH2CH2CH2-, CF3CF2CH2CH2CH2-, C F3CH2CF2CH2CH2-, CF3CF2CF2CH2CH2-, CF3CF2CF2CF2CH2-, CF3CF2CH2CF2CH2-, CF3CF2CH2CH2CH2CH2-, CF3CF2CF 2CF2CH2CH2-, CF3CF2CH2CF2CH2CH2-, HCF2CH2-, HCF2CF2-, HCF2CH2CH2-, HCF2CF2CH2-, HCF2CH2CF2-, HCF2CF2CH 2CH2-, HCF2CH2CF2CH2-, HCF2CF2CF2CF2-, HCF2CF2CH2CH2CH2-, HCF2CH2CF2CH2CH2-, HCF2CF2CF2CF2CH2-, HCF2C F2CF2CF2CH2CH2-, FCH2CH2-, FCH2CF2-, FCH2CF2CH2-, CH3CF2-, CH3CH2-, CH3CF2CH2-, CH3CF2CF2-, CH3CH2CH2-, Examples include CH3CF2CH2CF2-, CH3CF2CF2CF2-, CH3CH2CF2CF2-, CH3CH2CH2CH2-, CH3CF2CH2CF2CH2-, CH3CF2CF2CF2CH2-, CH3CF2CF2CH2CH2-, CH3CH2CF2CF2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CH2CF2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, etc.

[0073] n2 is 1 and R 3 However, as for branched chains,

[0074] [ka]

[0075] These are some examples.

[0076] However, having branches such as CH3- and CF3- tends to increase viscosity, so R 3 is more preferably a linear one.

[0077] (2) In the -(OR 4 ) n1 - in the above general formula (b-1), n1 is an integer of 1 to 3, preferably 1 or 2. When n1=2 or 3, R 4 may be the same or different.

[0078] R 4 Preferable specific examples of the above include the following linear or branched ones.

[0079] Examples of linear groups include -CH2-, -CHF-, -CF2-, -CH2CH2-, -CF2CH2-, -CF2CF2-, -CH2CF2-, -CH2CH2CH2-, -CH2CH2CF2-, -CH2CF2CH2-, -CH2CF2CF2-, -CF2CH2CH2-, -CF2CF2CH2-, -CF2CH2CF2-, -CF2CF2CF2-, and the like.

[0080] Examples of branched groups include

[0081] [Chemical Formula]

[0082] and the like.

[0083] The aforementioned fluorinated alkoxy group (c) is a group in which at least one hydrogen atom of an alkoxy group is substituted with a fluorine atom. The fluorinated alkoxy group (c) preferably has 1 to 17 carbon atoms. More preferably, it has 1 to 6 carbon atoms.

[0084] As the aforementioned fluorinated alkoxy group (c), the general formula: X d 3C-(R 6 ) n3-O-(three X d are the same or different and each is H or F; R 6 is preferably an alkylene group having 1 to 5 carbon atoms which may have a fluorine atom; n3 is 0 or 1; provided that any one of the three X d contains a fluorine atom) is particularly preferred as the fluorinated alkoxy group represented by the formula.

[0085] Specific examples of the fluorinated alkoxy group (c) include a fluorinated alkoxy group in which an oxygen atom is bonded to the terminal of the alkyl group exemplified as R in the general formula (a-1). 1 .

[0086] The fluorine content of the fluorinated alkyl group (a), the fluorinated alkyl group (b) having an ether bond, and the fluorinated alkoxy group (c) in the fluorinated saturated cyclic carbonate is preferably 10% by mass or more. If the fluorine content is too low, the effect of reducing viscosity at low temperatures and the effect of increasing the flash point may not be sufficiently obtained. From this viewpoint, the fluorine content is more preferably 12% by mass or more, and further preferably 15% by mass or more. The upper limit is usually 76% by mass. The fluorine content of the fluorinated alkyl group (a), the fluorinated alkyl group (b) having an ether bond, and the fluorinated alkoxy group (c) is a value calculated by {(number of fluorine atoms × 19) / formula weight of each group} × 100 (%) based on the structural formula of each group.

[0087] In addition, from the viewpoint of good dielectric constant and oxidation resistance, the fluorine content of the entire fluorinated saturated cyclic carbonate is preferably 10% by mass or more, more preferably 15% by mass or more. The upper limit is usually 76% by mass. The fluorine content of the fluorinated saturated cyclic carbonate is a value calculated by {(number of fluorine atoms × 19) / molecular weight of the fluorinated saturated cyclic carbonate} × 100 (%) based on the structural formula of the fluorinated saturated cyclic carbonate.

[0088] Specific examples of the aforementioned fluorinated saturated cyclic carbonate include, for example, the following compounds.

[0089] X 1 to X 4 Specific examples of the fluorinated saturated cyclic carbonate in which at least one of them is -F include,

[0090]

Chemical Formula

[0091] In addition,

[0092]

Chemical Formula

[0093] and the like can also be used.

[0094] X 1 to X 4 Specific examples of the fluorinated saturated cyclic carbonate in which at least one of them is a fluorinated alkyl group (a) and all the rest are -H include,

[0095]

Chemical Formula

[0096]

Chemical Formula

[0097]

Chemical Formula

[0098] and the like.

[0099] X 1 to X 4A specific example of a fluorinated saturated cyclic carbonate in which at least one of the members is a fluorinated alkyl group (b) or a fluorinated alkoxy group (c) having an ether linkage, and the rest are all -H, is:

[0100] [ka]

[0101] [ka]

[0102] [ka]

[0103] [ka]

[0104] [ka]

[0105] [ka]

[0106] These are some examples.

[0107] In particular, the above-mentioned fluorinated saturated cyclic carbonate is preferably one of the following compounds.

[0108] [ka]

[0109] [ka]

[0110] Other examples of the above-mentioned fluorinated saturated cyclic carbonates include trans-4,5-difluoro-1,3-dioxolan-2-one, 5-(1,1-difluoroethyl)-4,4-difluoro-1,3-dioxolan-2-one, 4-methylene-1,3-dioxolan-2-one, 4-methyl-5-trifluoromethyl-1,3-dioxolan-2-one, 4-ethyl-5-fluoro-1,3-dioxolan-2-one, and 4-ethyl-5,5-difluoro-1,3- Examples include dioxolan-2-one, 4-ethyl-4,5-difluoro-1,3-dioxolan-2-one, 4-ethyl-4,5,5-trifluoro-1,3-dioxolan-2-one, 4,4-difluoro-5-methyl-1,3-dioxolan-2-one, 4-fluoro-5-methyl-1,3-dioxolan-2-one, 4-fluoro-5-trifluoromethyl-1,3-dioxolan-2-one, and 4,4-difluoro-1,3-dioxolan-2-one.

[0111] Among the above-mentioned fluorinated saturated cyclic carbonates, fluoroethylene carbonate, difluoroethylene carbonate, trifluoromethylethylene carbonate (3,3,3-trifluoropropylene carbonate), and 2,2,3,3,3-pentafluoropropylethylene carbonate are more preferred.

[0112] The above-mentioned fluorinated unsaturated cyclic carbonate is a cyclic carbonate having an unsaturated bond and a fluorine atom, and fluorinated ethylene carbonate derivatives substituted with substituents having an aromatic ring or a carbon-carbon double bond are preferred. Specifically, examples include 4,4-difluoro-5-phenylethylene carbonate, 4,5-difluoro-4-phenylethylene carbonate, 4-fluoro-5-phenylethylene carbonate, 4-fluoro-5-vinylethylene carbonate, 4-fluoro-4-phenylethylene carbonate, 4,4-difluoro-4-vinylethylene carbonate, 4,4-difluoro-4-allylethylene carbonate, 4-fluoro-4-vinylethylene carbonate, 4-fluoro-4,5-diallylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate, and 4,5-difluoro-4,5-diallylethylene carbonate.

[0113] The above-mentioned fluorinated cyclic carbonates may be used individually or in combination of two or more types in any combination and ratio.

[0114] If the above-mentioned fluorinated cyclic carbonate is included, the content of the above-mentioned fluorinated cyclic carbonate is preferably 5 to 90% by volume, more preferably 10 to 60% by volume, and even more preferably 15 to 45% by volume relative to the above-mentioned solvent.

[0115] The above-mentioned chain-like carbonate may be a non-fluorinated chain-like carbonate or a fluorinated chain-like carbonate.

[0116] Examples of the above-mentioned non-fluorinated linear carbonates include hydrocarbon-based linear carbonates such as CH3OCOOCH3 (dimethyl carbonate: DMC), CH3CH2OCOOCH2CH3 (diethyl carbonate: DEC), CH3CH2OCOOCH3 (ethyl methyl carbonate: EMC), CH3OCOOCH2CH2CH3 (methyl propyl carbonate), methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, dibutyl carbonate, methyl isopropyl carbonate, methyl-2-phenylphenyl carbonate, phenyl-2-phenylphenyl carbonate, trans-2,3-pentylene carbonate, trans-2,3-butylene carbonate, and ethylphenyl carbonate. Among these, it is preferable that it be at least one selected from the group consisting of ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate.

[0117] The above-mentioned non-fluorinated linear carbonates may be used individually or in combination of two or more types in any combination and ratio.

[0118] When the above-mentioned non-fluorinated linear carbonate is included, the content of the above-mentioned non-fluorinated linear carbonate is preferably 10 to 90% by volume, more preferably 20 to 85% by volume, and even more preferably 30 to 80% by volume relative to the above-mentioned solvent.

[0119] The above-mentioned fluorinated chain carbonate is a chain carbonate having fluorine atoms. Solvents containing fluorinated chain carbonates can be suitably used even under high voltage.

[0120] The above fluorinated chain carbonate is a general formula (B): Rf 2 OCOOR 7 (B) (In the formula, Rf 2 R is a fluorinated alkyl group having 1 to 7 carbon atoms. 7is an alkyl group having 1 to 7 carbon atoms which may contain a fluorine atom.) can be exemplified as the compound represented thereby.

[0121] Rf 2 is a fluorinated alkyl group having 1 to 7 carbon atoms, and R 7 is an alkyl group having 1 to 7 carbon atoms which may contain a fluorine atom. The fluorinated alkyl group is a group obtained by substituting at least one hydrogen atom of an alkyl group with a fluorine atom. When R 7 is an alkyl group containing a fluorine atom, it becomes a fluorinated alkyl group. Rf 2 and R 7 preferably have 1 to 7 carbon atoms, and more preferably 1 to 2 carbon atoms, from the viewpoint of low viscosity. If the number of carbon atoms is excessively large, the low-temperature characteristics may be deteriorated or the solubility of the electrolyte salt may be lowered. If the number of carbon atoms is excessively small, a decrease in the solubility of the electrolyte salt, a decrease in discharge efficiency, and further an increase in viscosity and the like may be observed.

[0122] Examples of the fluorinated alkyl group having 1 carbon atom include CFH₂-, CF₂H-, CF₃- and the like. In particular, CFH₂- or CF₃- is preferred in terms of high-temperature storage characteristics.

[0123] Examples of the fluorinated alkyl group having 2 or more carbon atoms include the following general formula (d-1): R 1 -R 2 - (d-1) (wherein R 1 is an alkyl group having 1 or more carbon atoms which may have a fluorine atom; R 2 is an alkylene group having 1 to 3 carbon atoms which may have a fluorine atom; provided that at least one of R 1 and R 2 has a fluorine atom) can be preferably exemplified as the fluorinated alkyl group represented by the formula from the viewpoint of good solubility of the electrolyte salt. Note that R 1 and R 2 may further have other atoms besides carbon atoms, hydrogen atoms and fluorine atoms.

[0124] R 1 is an alkyl group having 1 or more carbon atoms which may have a fluorine atom. R 1 is preferably a linear or branched alkyl group having 1 to 6 carbon atoms. R 1 more preferably has 1 to 3 carbon atoms.

[0125] R 1 specifically, examples of the linear or branched alkyl group include CH3-, CF3-, CH3CH2-, CH3CH2CH2-, CH3CH2CH2CH2-,

[0126] [Chemical Formula]

[0127] and the like.

[0128] Further, R 1If the alkyl group is a linear alkyl group with a fluorine atom, then the names are CF3-, CF3CH2-, CF3CF2-, CF3CH2CH2-, CF3CF2CH2-, CF3CF2CF2-, CF3CH2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CF2-, CF3CF2CH2CF2-, CF3CF2CH2CH2CH2-, CF3CF2CH2CH 2CH2-, CF3CH2CF2CH2CH2-, CF3CF2CF2CH2CH2-, CF3CF2CF2CF2CH2-, CF3CF2CH2CF2CH2-, CF3CF2CH2CH2CH2CH2-, CF3CF2C F2CF2CH2CH2-, CF3CF2CH2CF2CH2CH2-, HCF2-, HCF2CH2-, HCF2CF2-, HCF2CH2CH2-, HCF2CF2CH2-, HCF2CH2CF2-, HCF2CF2C H2CH2-, HCF2CH2CF2CH2-, HCF2CF2CF2CF2-, HCF2CF2CH2CH2CH2-, HCF2CH2CF2CH2CH2-, HCF2CF2CF2CF2CH2-, HCF2CF2CF2 CF2CH2CH2-, FCH2-, FCH2CH2-, FCH2CF2-, FCH2CF2CH2-, FCH2CF2CF2-, CH3CF2CH2-, CH3CF2CF2-, CH3CF2CH2CF2-, CH3CF2 Examples include CF2CF2-, CH3CH2CF2CF2-, CH3CF2CH2CF2CH2-, CH3CF2CF2CF2CH2-, CH3CF2CF2CH2CH2-, CH3CH2CF2CF2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, HCFClCF2CH2-, HCF2CFClCH2-, HCF2CFClCF2CFClCH2-, HCFClCF2CFClCF2CH2-, etc.

[0129] Also, R 1 If it is a branched alkyl group having a fluorine atom,

[0130] [ka]

[0131] [ka]

[0132] These are some examples of preferred structures. However, since the presence of CH3- or CF3- branches tends to increase viscosity, it is more preferable that the number of such branches be small (1) or zero.

[0133] R 2 R is an alkylene group having 1 to 3 carbon atoms, which may contain a fluorine atom. 2 The alkylene group may be linear or branched. An example of the smallest structural unit constituting such a linear or branched alkylene group is shown below. 2 These are composed of one or a combination of these.

[0134] (i) Linear minimal structural unit: -CH2-, -CHF-, -CF2-, -CHCl-, -CFCl-, -CCl2-

[0135] (ii) The smallest structural unit of a branched chain:

[0136] [ka]

[0137] Furthermore, among the examples above, it is preferable that the constituent units do not contain Cl, as this prevents the deHCl reaction by a base and is therefore more stable.

[0138] R 2 When the structure is linear, it consists only of the minimum linear structural units described above, with -CH2-, -CH2CH2-, or -CF2- being preferred. -CH2- or -CH2CH2- is more preferred because it can further improve the solubility of the electrolyte salt.

[0139] R 2If it is branched, it comprises at least one of the branched minimum structural units described above, and the general formula is -(CX a X b )-(X a is H, F, CH3 or CF3;X b is CH3 or CF3. However, X b If it is CF3, X a Examples of materials that can be represented as (where is H or CH3) are preferred. These can particularly further improve the solubility of the electrolyte salt.

[0140] Preferred fluorinated alkyl groups include, specifically, CF3CF2-, HCF2CF2-, H2CFCF2-, CH3CF2-, CF3CH2-, CF3CF2CF2-, HCF2CF2CF2-, H2CFCF2CF2-, CH3CF2CF2-,

[0141] [ka]

[0142] [ka]

[0143] These are some examples.

[0144] Among them, Rf 2 and R 7 The preferred fluorinated alkyl groups are CF3-, CF3CF2-, (CF3)2CH-, CF3CH2-, C2F5CH2-, CF3CF2CH2-, HCF2CF2CH2-, CF3CFHCF2CH2-, CFH2-, and CF2H-. CF3CH2-, CF3CF2CH2-, HCF2CF2CH2-, CFH2-, and CF2H- are more preferred due to their high flame retardancy, good rate characteristics, and excellent oxidation resistance.

[0145] R 7 If it is an alkyl group that does not contain a fluorine atom, it is an alkyl group with 1 to 7 carbon atoms. 7In terms of low viscosity, the carbon number is preferably 1 to 4, and more preferably 1 to 3.

[0146] Examples of alkyl groups that do not contain fluorine atoms include CH3-, CH3CH2-, (CH3)2CH-, and C3H7-. Among these, CH3- and CH3CH2- are preferred due to their low viscosity and good rate characteristics.

[0147] The above-mentioned fluorinated chain carbonate preferably has a fluorine content of 15 to 70% by mass. When the fluorine content is within the above range, compatibility with solvents and solubility of salts can be maintained. The above-mentioned fluorine content is more preferably 20% by mass or more, even more preferably 30% by mass or more, particularly preferably 35% by mass or more, more preferably 60% by mass or less, and even more preferably 50% by mass or less. In this disclosure, the fluorine content is determined based on the structural formula of the above-mentioned fluorinated chain carbonate. {(Number of fluorine atoms × 19) / Molecular weight of fluorinated chain carbonate} × 100 (%) This value was calculated using the method described above.

[0148] The above-mentioned fluorinated chain carbonate is preferably one of the following compounds in terms of its low viscosity.

[0149] [ka]

[0150] As the fluorinated chain carbonate mentioned above, methyl 2,2,2-trifluoroethyl carbonate (F3CH2COC(=O)OCH3) is particularly preferred.

[0151] The above-mentioned fluorinated chain carbonates may be used individually, or two or more may be used in any combination and ratio.

[0152] When the above-mentioned fluorinated chain carbonate is included, the content of the above-mentioned fluorinated chain carbonate is preferably 10 to 90% by volume, more preferably 20 to 85% by volume, and even more preferably 30 to 80% by volume relative to the above-mentioned solvent.

[0153] The above-mentioned carboxylic acid ester may be a cyclic carboxylic acid ester or a linear carboxylic acid ester.

[0154] The above-mentioned cyclic carboxylic acid ester may be a non-fluorinated cyclic carboxylic acid ester or a fluorinated cyclic carboxylic acid ester.

[0155] Examples of the above-mentioned non-fluorinated cyclic carboxylic acid esters include non-fluorinated saturated cyclic carboxylic acid esters, and non-fluorinated saturated cyclic carboxylic acid esters having an alkylene group with 2 to 4 carbon atoms are preferred.

[0156] Specific examples of non-fluorinated saturated cyclic carboxylic acid esters having an alkylene group with 2 to 4 carbon atoms include β-propiolactone, γ-butyrolactone, ε-caprolactone, δ-valerolactone, and α-methyl-γ-butyrolactone. Among these, γ-butyrolactone and δ-valerolactone are particularly preferred in terms of improving the degree of lithium ion dissociation and load characteristics.

[0157] The above-mentioned non-fluorinated saturated cyclic carboxylic acid esters may be used individually or in combination of two or more in any combination and ratio.

[0158] If the above-mentioned non-fluorinated saturated cyclic carboxylic acid ester is included, the content of the above-mentioned non-fluorinated saturated cyclic carboxylic acid ester is preferably 0 to 90% by volume relative to the above-mentioned solvent, more preferably 0.001 to 90% by volume, even more preferably 1 to 60% by volume, and particularly preferably 5 to 40% by volume.

[0159] The above-mentioned linear carboxylic acid ester may be a non-fluorinated linear carboxylic acid ester or a fluorinated linear carboxylic acid ester. When the above-mentioned solvent contains the above-mentioned linear carboxylic acid ester, the increase in resistance after high-temperature storage of the electrolyte can be further suppressed.

[0160] Examples of the above non-fluorinated linear carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, tert-butyl propionate, tert-butyl butyrate, sec-butyl propionate, sec-butyl butyrate, n-butyl butyrate, methyl pyrophosphate, ethyl pyrophosphate, tert-butyl formate, tert-butyl acetate, sec-butyl formate, sec-butyl acetate, n-hexyl pivalate, n-propyl formate, n-propyl Examples include propyl acetate, n-butyl formate, n-butyl pivalate, n-octyl pivalate, ethyl 2-(dimethoxyphosphoryl) acetate, ethyl 2-(dimethylphosphoryl) acetate, ethyl 2-(diethoxyphosphoryl) acetate, ethyl 2-(diethylphosphoryl) acetate, isopropyl propionate, isopropyl acetate, ethyl formate, ethyl 2-propynyl oxalate, isopropyl formate, isopropyl butyrate, isobutyl formate, isobutyl propionate, isobutyl butyrate, and isobutyl acetate.

[0161] Among these, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate are preferred, and ethyl propionate and propyl propionate are particularly preferred.

[0162] The above-mentioned non-fluorinated linear carboxylic acid esters may be used individually or in combination of two or more in any combination and ratio.

[0163] If the above-mentioned non-fluorinated linear carboxylic acid ester is included, the content of the above-mentioned non-fluorinated linear carboxylic acid ester is preferably 0 to 90% by volume relative to the above-mentioned solvent, more preferably 0.001 to 90% by volume, even more preferably 1 to 60% by volume, and particularly preferably 5 to 50% by volume.

[0164] The above-mentioned fluorinated linear carboxylic acid ester is a linear carboxylic acid ester having a fluorine atom. Solvents containing the fluorinated linear carboxylic acid ester can be suitably used even under high voltage.

[0165] The above fluorinated chain carboxylic acid esters are based on the following general formula: R 31 COOR 32 (In the formula, R 31 and R 32 These are alkyl groups that may contain fluorine atoms having 1 to 4 carbon atoms, and R 31 and R 32 At least one of them contains a fluorine atom. Fluorinated chain carboxylic acid esters represented by () are preferred because they have good compatibility with other solvents and oxidation resistance.

[0166] R 31 and R 32Examples include non-fluorinated alkyl groups such as methyl group (-CH3), ethyl group (-CH2CH3), propyl group (-CH2CH2CH3), isopropyl group (-CH(CH3)2), n-butyl group (-CH2CH2CH2CH3), and tert-butyl group (-C(CH3)3); -CF3, -CF2H, -CFH2, -CF2CF3, -CF2CF2H, -CF2CFH2, -CH2CF3, -CH2CF2H, -CH2CFH2, -CF2CF2CF3, -CF2CF2CF2H, -CF2CF2CFH2, -CH2CF2CF3, -CH2CF 2CF2H, -CH2CF2CFH2, -CH2CH2CF3, -CH2CH2CF2H, -CH2CH2CFH2, -CF(CF3)2, -CF(CF2H)2, -CF(CFH2)2, -CH(CF3)2, -CH(CF2H)2, -CH(CFH2)2, -CF(OCH) 3)CF3, -CF2CF2CF2CF3, -CF2CF2CF2CF2H, -CF2CF2CF2CFH2, -CH2CF2CF2CF3, -CH2CF2CF2CF2H, -CH2CF2CF2CFH2, -CH2CH2CF2CF3, -CH2CH2CF2CF2H, -C H2CH2CF2CFH2, -CH2CH2CH2CF3, -CH2CH2CH2CF2H, -CH2CH2CH2CFH2, -CF(CF3)CF2CF3, -CF(CF2H)CF2CF3, -CF(CFH2)CF2CF3, -CF(CF3)CF2CF2H, -CF( CF3)CF2CFH2, -CF(CF3)CH2CF3, -CF(CF3)CH2CF2H, -CF(CF3)CH2CFH2, -CH(CF3)CF2CF3, -CH(CF2H)CF2CF3, -CH(CFH2)CF2CF3, -CH(CF3)CF2CF2H, -CH (CF3)CF2CFH2, -CH(CF3)CH2CF3, -CH(CF3)CH2CF2H, -CH(CF3)CH2CFH2, -CF2CF(CF3)CF3, -CF2CF(CF2H)CF3, -CF2CF(CFH2)CF3, -CF2CF(CF3)CF2H, - CF2CF(CF3)CFH2, -CH2CF(CF3)CF3, -CH2CF(CF2H)CF3, -CH2CF(CFH2)CF3, -CH2CF(CF3)CF2H, -CH2CF(CF3)CFH2, -CH2CH(CF3)CF3, -CH2CH(CF2H)CF3,Examples include fluorinated alkyl groups such as -CH2CH(CFH2)CF3, -CH2CH(CF3)CF2H, -CH2CH(CF3)CFH2, -CF2CH(CF3)CF3, -CF2CH(CF2H)CF3, -CF2CH(CFH2)CF3, -CF2CH(CF3)CF2H, -CF2CH(CF3)CFH2, -C(CF3)3, -C(CF2H)3, and -C(CFH2)3. Among these, methyl groups, ethyl groups, -CF3, -CF2H, -CF2CF3, -CH2CF3, -CH2CF2H, -CH2CFH2, -CH2CH2CF3, -CH2CF2CF3, -CH2CF2CF3, -CH2CF2CF2H, and -CH2CF2CFH2 are particularly preferred due to their good compatibility with other solvents, viscosity, and oxidation resistance.

[0167] Specific examples of the above-mentioned fluorinated chain carboxylic acid esters include, for example, CF3CH2C(=O)OCH3 (methyl 3,3,3-trifluoropropionate), HCF2C(=O)OCH3 (methyl difluoroacetate), HCF2C(=O)OC2H5 (ethyl difluoroacetate), CF3C(=O)OCH2CH2CF3, CF3C(=O)OCH2C2F5, CF3C(=O)OCH2CF2CF2H (2,2,3,3-tetrafluoropropyl trifluoroacetate), CF3C(=O)OCH2CF3, CF3C(=O)OCH(CF3)2, ethyl pentafluorobutyrate, methyl pentafluoropropionate, ethyl pentafluoropropionate, methyl heptafluoroisobutyrate, isopropyl trifluorobutyrate, ethyl trifluoroacetate, tert-butyl trifluoroacetate, and n-butyl trifluoroacetate. Examples include one or more of the following: methyl tetrafluoro-2-(methoxy)propionate, 2,2-difluoroethyl acetate, 2,2,3,3-tetrafluoropropyl acetate, CH3C(=O)OCH2CF3 (2,2,2-trifluoroethyl acetate), 1H,1H-heptafluorobutyl acetate, methyl 4,4,4-trifluorobutyrate, 4,4,4-trifluorobutyrate, ethyl 3,3,3-trifluoropropionate, 3,3,3-trifluoropropionate 3,3,3-trifluoropropyl, ethyl 3-(trifluoromethyl)butyrate, methyl 2,3,3,3-tetrafluoropropionate, 2,2-difluorobutyl acetate, methyl 2,2,3,3-tetrafluoropropionate, methyl 2-(trifluoromethyl)-3,3,3-trifluoropropionate, and methyl heptafluorobutyrate. Among them, CF3CH2C(=O)OCH3, HCF2C(=O)OCH3, HCF2C(=O)OC2H5, CF3C(=O)OCH2C2F5, CF3C(=O)OCH2CF2CF2H, CF3C(=O)OCH2CF3, CF3C(=O)OCH(CF3)2, ethyl pentafluorobutyrate, methyl pentafluoropropionate, ethyl pentafluoropropionate, methyl heptafluoroisobutyrate, isopropyl trifluorobutyrate, ethyl trifluoroacetate, tert-butyl trifluoroacetate, n-butyl trifluoroacetate, methyl tetrafluoro-2-(methoxy)propionate, 2,2-difluoroethyl acetate, 2,2,3,3-tetrafluoropropyl acetate, CH3C(=O)OCH2CF3, 1H,1H-heptafluorobutyl acetate, 4,4,4-methyl trifluorobutyrate, Ethyl 4,4,4-trifluorobutyrate, ethyl 3,3,3-trifluoropropionate, 3,3,3-trifluoropropyl 3,3,3-trifluoropropionate, ethyl 3-(trifluoromethyl)butyrate, methyl 2,3,3,3-tetrafluoropropionate, butyl 2,2-difluoroacetate, methyl 2,2,3,3-tetrafluoropropionate, methyl 2-(trifluoromethyl)-3,3,3-trifluoropropionate, and methyl heptafluorobutyrate are preferred due to their good compatibility with other solvents and rate characteristics, CF3CH2C(=O)OCH3, HCF2C(=O)OCH3, HCF2C(=O)OC2H5, and CH3C(=O)OCH2CF3 are more preferred, and HCF2C(=O)OCH3, HCF2C(=O)OC2H5, and CH3C(=O)OCH2CF3 are particularly preferred.

[0168] The above-mentioned fluorinated chain carboxylic acid esters may be used individually, or two or more may be used in any combination and ratio.

[0169] If the above-mentioned fluorinated linear carboxylic acid ester is included, the content of the above-mentioned fluorinated linear carboxylic acid ester is preferably 10 to 90% by volume, more preferably 20 to 85% by volume, and even more preferably 30 to 80% by volume relative to the above-mentioned solvent.

[0170] The solvent preferably contains at least one selected from the group consisting of the cyclic carbonate, the linear carbonate, and the linear carboxylic acid ester, and more preferably contains the cyclic carbonate and at least one selected from the group consisting of the linear carbonate and the linear carboxylic acid ester. The cyclic carbonate is preferably a saturated cyclic carbonate. An electrolyte containing a solvent with the above composition can further improve the high-temperature storage characteristics and cycling characteristics of electrochemical devices.

[0171] When the solvent contains the cyclic carbonate and at least one selected from the group consisting of the linear carbonate and the linear carboxylic acid ester, it is preferable that the total amount of the cyclic carbonate and at least one selected from the group consisting of the linear carbonate and the linear carboxylic acid ester be 10 to 100% by volume, more preferably 30 to 100% by volume, and even more preferably 50 to 100% by volume.

[0172] When the solvent contains the cyclic carbonate and at least one selected from the group consisting of the linear carbonate and the linear carboxylic acid ester, the volume ratio of the cyclic carbonate to at least one selected from the group consisting of the linear carbonate and the linear carboxylic acid ester is preferably 5 / 95 to 95 / 5, more preferably 10 / 90 or more, even more preferably 15 / 85 or more, particularly preferably 20 / 80 or more, more preferably 90 / 10 or less, even more preferably 60 / 40 or less, and particularly preferably 50 / 50 or less.

[0173] The solvent may also preferably contain at least one selected from the group consisting of the non-fluorinated saturated cyclic carbonate, the non-fluorinated linear carbonate, and the non-fluorinated linear carboxylic acid ester, and more preferably contain the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated linear carbonate and the non-fluorinated linear carboxylic acid ester. An electrolyte containing a solvent of the above composition can be suitably used in electrochemical devices that operate at relatively low voltages.

[0174] When the above solvent contains the above non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the above non-fluorinated linear carbonate and the above non-fluorinated linear carboxylic acid ester, it is preferable that the total amount of the above non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the above non-fluorinated linear carbonate and the above non-fluorinated linear carboxylic acid ester be 5 to 100% by volume, more preferably 20 to 100% by volume, and even more preferably 30 to 100% by volume.

[0175] When the electrolyte contains the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated linear carbonate and the non-fluorinated linear carboxylic acid ester, the volume ratio of the non-fluorinated saturated cyclic carbonate to at least one selected from the group consisting of the non-fluorinated linear carbonate and the non-fluorinated linear carboxylic acid ester is preferably 5 / 95 to 95 / 5, more preferably 10 / 90 or more, even more preferably 15 / 85 or more, particularly preferably 20 / 80 or more, more preferably 90 / 10 or less, even more preferably 60 / 40 or less, and particularly preferably 50 / 50 or less.

[0176] The solvent may also preferably contain at least one selected from the group consisting of the fluorinated saturated cyclic carbonate, the fluorinated linear carbonate, and the fluorinated linear carboxylic acid ester, and more preferably contain the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated linear carbonate and the fluorinated linear carboxylic acid ester. An electrolyte containing a solvent of the above composition can be suitably used not only in electrochemical devices used at relatively low voltages, but also in electrochemical devices used at relatively high voltages.

[0177] When the solvent contains the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated linear carbonate and the fluorinated linear carboxylic acid ester, it is preferable that the total amount of the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated linear carbonate and the fluorinated linear carboxylic acid ester be 5 to 100% by volume, more preferably 10 to 100% by volume, and even more preferably 30 to 100% by volume.

[0178] When the solvent contains the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated linear carbonate and the fluorinated linear carboxylic acid ester, the volume ratio of the fluorinated saturated cyclic carbonate to at least one selected from the group consisting of the fluorinated linear carbonate and the fluorinated linear carboxylic acid ester is preferably 5 / 95 to 95 / 5, more preferably 10 / 90 or more, even more preferably 15 / 85 or more, particularly preferably 20 / 80 or more, more preferably 90 / 10 or less, even more preferably 60 / 40 or less, and particularly preferably 50 / 50 or less.

[0179] Furthermore, ionic liquids can also be used as the solvent. An "ionic liquid" is a liquid composed of ions, which are a combination of organic cations and anions.

[0180] The organic cation is not particularly limited, but examples include imidazolium ions such as dialkylimidazolium cations and trialkylimidazolium cations; tetraalkylammonium ions; alkylpyridinium ions; dialkylpyrrolidinium ions; and dialkylpiperidinium ions.

[0181] The anions that act as counters to these organic cations are not particularly limited, but examples include PF6 anion, PF3(C2F5)3 anion, PF3(CF3)3 anion, BF4 anion, BF2(CF3)2 anion, BF3(CF3) anion, bisoxalatoborate anion, P(C2O4)F2 anion, Tf(trifluoromethanesulfonyl) anion, Nf(nonafluorobutanesulfonyl) anion, bis(fluorosulfonyl)imide anion, bis(trifluoromethanesulfonyl)imide anion, bis(pentafluoroethanesulfonyl)imide anion, dicyanoamine anion, and halide anions.

[0182] The solvent is preferably a non-aqueous solvent, and the electrolyte of this disclosure is preferably a non-aqueous electrolyte. The solvent content is preferably 70 to 99.999% by mass in the electrolyte, more preferably 80% by mass or more, and even more preferably 92% by mass or less.

[0183] The electrolyte of this disclosure may further contain compound (5) represented by general formula (5).

[0184] General formula (5): [ka] (In the formula, A a+ is a metal ion, hydrogen ion, or onium ion. a is an integer from 1 to 3, b is an integer from 1 to 3, p is b / a, n203 is an integer from 1 to 4, n201 is an integer from 0 to 8, n202 is 0 or 1, Z 201 These are transition metals, elements of group III, IV, or V of the periodic table. X 201This includes O, S, an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms (alkylene groups, halogenated alkylene groups, arylene groups, and halogenated arylene groups may have substituents and heteroatoms in their structure, and when n202 is 1 and n203 is 2 to 4, there are X atoms in n203). 201 (These may be combined.) L 201 This includes halogen atoms, cyano groups, C1-C10 alkyl groups, C1-C10 halogenated alkyl groups, C6-C20 aryl groups, C6-C20 halogenated aryl groups (alkylene groups, halogenated alkylene groups, arylene groups, and halogenated arylene groups may have substituents and heteroatoms in their structure, and when n201 is 2-8, there are n201 L 201 (These may each join to form a ring) or -Z 203 Y 203 . Y 201 , Y 202 and Z 203 These are O, S, and NY, respectively, and are independent of each other. 204 , hydrocarbon group or fluorinated hydrocarbon group. Y 203 and Y 204 Each of these is independently H, F, a C1-C10 alkyl group, a C1-C10 halogenated alkyl group, a C6-C20 aryl group, or a C6-C20 halogenated aryl group (alkyl groups, halogenated alkyl groups, aryl groups, and halogenated aryl groups may have substituents or heteroatoms in their structure, Y 203 or Y 204 If multiple such elements exist, they may combine to form a ring.

[0185] A a+Examples include lithium ions, sodium ions, potassium ions, magnesium ions, calcium ions, barium ions, cesium ions, silver ions, zinc ions, copper ions, cobalt ions, iron ions, nickel ions, manganese ions, titanium ions, lead ions, chromium ions, vanadium ions, ruthenium ions, yttrium ions, lanthanide ions, actinide ions, tetrabutylammonium ions, tetraethylammonium ions, tetramethylammonium ions, triethylmethylammonium ions, triethylammonium ions, pyridinium ions, imidazolium ions, hydrogen ions, tetraethylphosphonium ions, tetramethylphosphonium ions, tetraphenylphosphonium ions, triphenylsulfonium ions, and triethylsulfonium ions.

[0186] When used in applications such as electrochemical devices, A a+ Lithium ions, sodium ions, magnesium ions, tetraalkylammonium ions, and hydrogen ions are preferred, with lithium ions being particularly preferred. a+ The valence a of the cation is an integer between 1 and 3. If it is greater than 3, the crystal lattice energy increases, which makes it difficult to dissolve in the solvent. Therefore, if solubility is required, 1 is more preferable. Similarly, the valence b of the anion is an integer between 1 and 3, with 1 being particularly preferable. The constant p, which represents the ratio of the cation to the anion, is necessarily determined by the ratio of their valencies b / a.

[0187] Next, we will explain the ligand portion of general formula (5). In this specification, Z in general formula (5) 201 The organic or inorganic part that is bonded to the molecule is called a ligand.

[0188] Z 201 The element is preferably Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf, or Sb, and more preferably Al, B, or P.

[0189] X 201 represents O, S, an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms. These alkylene and arylene groups may have substituents and heteroatoms in their structure. Specifically, instead of hydrogen atoms on the alkylene and arylene groups, halogen atoms, linear or cyclic alkyl groups, aryl groups, alkenyl groups, alkoxy groups, aryloxy groups, sulfonyl groups, amino groups, cyano groups, carbonyl groups, acyl groups, amide groups, and hydroxyl groups may be present as substituents, or nitrogen, sulfur, and oxygen may be introduced instead of carbon atoms on the alkylene and arylene. Also, when n202 is 1 and n203 is 2 to 4, the X atoms in n203 201 These components may be bonded together. An example of such a ligand is ethylenediaminetetraacetic acid.

[0190] L 201 This includes halogen atoms, cyano groups, C1-C10 alkyl groups, C1-C10 halogenated alkyl groups, C6-C20 aryl groups, C6-C20 halogenated aryl groups, or -Z 203 Y 203 (Z 203 , Y 203 (This will be explained later.) Here, alkyl and aryl groups also represent X 201 Similarly, the structure may have substituents and heteroatoms, and when n201 is 2 to 8, there are n201 L 201 Each of them may be joined together to form a ring. 201 Preferably, the element is a fluorine atom or a cyano group. In the case of a fluorine atom, the solubility and dissociation of the salt of the anionic compound are improved, and consequently, the ionic conductivity is improved. Furthermore, oxidation resistance is improved, which can suppress the occurrence of side reactions.

[0191] Y 201 , Y 202 and Z 203 These are O, S, and NY, respectively, and are independent of each other. 204, represents a hydrocarbon group or a fluorinated hydrocarbon group. 201 and Y 202 is O, S or NY 204 It is preferable that it is O, and more preferably that it is O. A characteristic of compound (5) is that it contains Y in the same ligand. 201 and Y 202 Z by 201 Because of the bond with Z 201 It forms a chelate structure. This chelate effect improves the heat resistance, chemical stability, and hydrolysis resistance of this compound. The constant n202 in this ligand is 0 or 1, but in particular, when it is 0, the chelate ring becomes a five-membered ring, so the chelate effect is most strongly exhibited and stability is increased, which is preferable. In this specification, a fluorinated hydrocarbon group is defined as a hydrocarbon group in which at least one hydrogen atom is replaced by a fluorine atom.

[0192] Y 203 and Y 204 Each of these is independently H, F, a C1-C10 alkyl group, a C1-C10 halogenated alkyl group, a C6-C20 aryl group, or a C6-C20 halogenated aryl group, and these alkyl and aryl groups may have substituents or heteroatoms in their structure, and Y 203 or Y 204 If multiple such elements exist, they may combine to form a ring.

[0193] Furthermore, the constant n203 related to the number of ligands described above is an integer between 1 and 4, preferably 1 or 2, and more preferably 2. Also, the constant n201 related to the number of ligands described above is an integer between 0 and 8, preferably 0 to 4, and more preferably 0, 2, or 4. Moreover, it is preferable that when n203 is 1, n201 is 2, and when n203 is 2, n201 is 0.

[0194] In general formula (5), alkyl groups, alkyl halides, aryl groups, and aryl halides also include those having other functional groups such as branching, hydroxyl groups, and ether bonds.

[0195] Compound (5) has the general formula: [ka] (In the formula, A a+ a, b, p, n201, Z 201 and L 201 The compound shown above is, or the general formula: [ka] (In the formula, A a+ a, b, p, n201, Z 201 and L 201 It is preferable that the compound is as shown above.

[0196] Compound (5) includes lithium oxalatoborate salts, which are given by the following formula: [ka] Lithium bis(oxalato)borate (LIBOB), represented by the following formula: [ka] Lithium difluorooxalatoborate (LIDFOB), indicated by

[0197] Compound (5) is also given by the following formula: [ka] Lithium difluorooxalatophosphanite (LIDFOP), represented by the following formula: [ka] Lithium tetrafluorooxalatophosphanite (LITFOP), represented by the following formula: [ka] Examples include lithium bis(oxalato)difluorophosphanite, as shown in the diagram.

[0198] Other specific examples of dicarboxylic acid complex salts in which the central element of the complex is boron include lithium bis(malonato)borate, lithium difluoro(malonato)borate, lithium bis(methylmalonato)borate, lithium difluoro(methylmalonato)borate, lithium bis(dimethylmalonato)borate, and lithium difluoro(dimethylmalonato)borate.

[0199] Specific examples of dicarboxylic acid complex salts in which phosphorus is the central element of the complex include lithium tris(oxalato)phosphate, lithium tris(malonato)phosphate, lithium difluorobis(malonato)phosphate, lithium tetrafluoro(malonato)phosphate, lithium tris(methylmalonato)phosphate, lithium difluorobis(methylmalonato)phosphate, lithium tetrafluoro(methylmalonato)phosphate, lithium tris(dimethylmalonato)phosphate, lithium difluorobis(dimethylmalonato)phosphate, and lithium tetrafluoro(dimethylmalonato)phosphate.

[0200] Specific examples of dicarboxylic acid complex salts in which the central element of the complex is aluminum include LiAl(C2O4)2 and LiAlF2(C2O4).

[0201] Among these, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tris(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate are more preferably used due to their availability and their ability to contribute to the formation of stable film-like structures. Lithium bis(oxalato)borate is particularly preferred as compound (5).

[0202] The content of compound (5) is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, more preferably 10% by mass or less, and more preferably 3% by mass or less, relative to the solvent, in order to obtain even better cycling characteristics.

[0203] The electrolyte of this disclosure preferably further comprises an electrolyte salt (excluding compound (5)). As the electrolyte salt, any salt that can be used in an electrolyte can be used, such as alkali metal salts, ammonium salts, other metal salts other than alkali metal salts (for example, light metal salts other than alkali metal salts), liquid salts (ionic liquids), inorganic polymer type salts, organic polymer type salts, etc.

[0204] Examples of electrolyte salts for secondary batteries include the following compounds: MPF6, MBF4, MClO4, MAsF6, MB(C6H5)4, MCH3SO3, MCF3SO3, MACl4, M2SiF6, MCl, MBr. (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K, preferably one metal selected from the group consisting of Li, Na, and K, more preferably Li or Na, and even more preferably Li.) By using these alkali metal salts, excellent battery capacity, cycle characteristics, and storage characteristics can be obtained. Among these, at least one selected from MPF6, MBF4, MClO4, and MAsF6 is preferred, with MPF6 being more preferred. By using these alkali metal salts, the internal resistance is further reduced, and a higher effect can be obtained.

[0205] Lithium salts are preferred as the electrolyte salts for the electrolyte solution of secondary batteries. Any lithium salt can be used as described above, specifically including the following: For example, LiPF6, LiBF4, LiClO4, LiAlF4, LiSbF6, LiTaF6, LiWF7, LiAsF6, LiAlCl4, LiI, LiBr, LiCl, LiB 10 Cl 10 Inorganic lithium salts such as Li2SiF6, Li2PFO3, and LiPO2F2; Lithium tungstate compounds such as LiWOF5; Lithium carboxylate salts such as HCO2Li, CH3CO2Li, CH2FCO2Li, CHF2CO2Li, CF3CO2Li, CF3CH2CO2Li, CF3CF2CO2Li, CF3CF2CF2CO2Li, CF3CF2CF2CF2CO2Li, and CF3CF2CF2CF2CO2Li; Lithium salts containing an S=O group, such as FSO3Li, CH3SO3Li, CH2FSO3Li, CHF2SO3Li, CF3SO3Li, CF3CF2SO3Li, CF3CF2CF2SO3Li, CF3CF2CF2CF2SO3Li, lithium methyl sulfate, lithium ethyl sulfate (C2H5OSO3Li), and lithium 2,2,2-trifluoroethyl sulfate; Lithium imide salts such as LiN(FCO)2, LiN(FCO)(FSO2), LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium bisperfluoroethanesulfonylimide, lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropanedisulfonylimide, lithium cyclic 1,2-ethanedisulfonylimide, lithium cyclic 1,3-propanedisulfonylimide, lithium cyclic 1,4-perfluorobutanedisulfonylimide, LiN(CF3SO2)(FSO2), LiN(CF3SO2)(C3F7SO2), LiN(CF3SO2)(C4F9SO2), LiN(POF2)2, etc. Lithium sulfamate compounds such as (CF3CH2)2NSO3Li, (CF3CH2)(CH3)NSO3Li, and (CNCH2)2NSO3Li; Lithium methide salts such as LiC(FSO2)3, LiC(CF3SO2)3, and LiC(C2F5SO2)3; Other formulas: LiPF a (C n F 2n+1 ) 6-aSalts represented by (wherein the formula a is an integer from 0 to 5 and n is an integer from 1 to 6) (e.g., LiPF3(C2F5)3, LiPF3(CF3)3, LiPF3(iso-C3F7)3, LiPF5(iso-C3F7), LiPF4(CF3)2, LiPF4(C2F5)2), LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF3CF3, LiBF3C2F5, LiBF3C3F7, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2, etc., fluorine-containing organolithium salts, LiSCN, LiB(CN)4, LiB(C6H5)4, Li2(C2O4), LiP(C2O4)3, Li2B 12 F b H 12-b Examples include (where b is an integer between 0 and 3).

[0206] Among these, LiPF6, LiBF4, LiSbF6, LiTaF6, LiPO2F2, FSO3Li, CF3SO3Li, LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropanedisulfonylimide, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, LiPF3(C2F5)3, etc. are particularly preferred because they have the effect of improving output characteristics, high-rate charge / discharge characteristics, high-temperature storage characteristics, and cycle characteristics, and at least one lithium salt selected from the group consisting of LiPF6, LiN(FSO2)2, and LiBF4 is most preferred.

[0207] These electrolyte salts may be used individually or in combination of two or more. Preferred examples of combinations of two or more include the use of LiPF6 and LiBF4, or LiPF6 and LiPO2F2, C2H5OSO3Li, or FSO3Li, which have the effect of improving high-temperature storage characteristics, load characteristics, and cycle characteristics.

[0208] In this case, there are no restrictions on the amount of LiBF4, LiPO2F2, C2H5OSO3Li, or FSO3Li blended relative to 100% by mass of the total electrolyte. It is arbitrary as long as it does not significantly impair the effects of the present disclosure. However, relative to the electrolyte of the present disclosure, it is usually 0.01% by mass or more, preferably 0.1% by mass or more, and usually 30% by mass or less, preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0209] Another example is the combined use of inorganic lithium salts and organic lithium salts, which have the effect of suppressing deterioration due to high-temperature storage. Preferred organic lithium salts include CF3SO3Li, LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropanedisulfonylimide, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, LiPF3(C2F5)3, etc. In this case, the ratio of organic lithium salt to 100% by mass of the total electrolyte is preferably 0.1% by mass or more, particularly preferably 0.5% by mass or more, and also preferably 30% by mass or less, particularly preferably 20% by mass or less.

[0210] The concentrations of these electrolyte salts in the electrolyte are not particularly limited as long as they do not impair the effects of the present disclosure. In order to maintain a good electrical conductivity of the electrolyte and ensure good battery performance, the total molar concentration of lithium in the electrolyte is preferably 0.3 mol / L or more, more preferably 0.4 mol / L or more, even more preferably 0.5 mol / L or more, and also preferably 3 mol / L or less, more preferably 2.5 mol / L or less, and even more preferably 2.0 mol / L or less.

[0211] If the total molar concentration of lithium is too low, the electrical conductivity of the electrolyte may be insufficient. On the other hand, if the concentration is too high, the electrical conductivity may decrease due to increased viscosity, which may reduce battery performance.

[0212] The electrolyte of this disclosure is general formula (6): [ka] (In the formula, X 21 is a base containing at least H or C, n21 is an integer from 1 to 3, Y 21 and Z 21 The group is the same or different and contains at least H, C, O or F, n22 is 0 or 1, Y 21 and Z 21 These may bond with each other to form a ring. The electrolyte may further contain compound (6) represented by ). When the electrolyte contains compound (6), the volume retention rate is less likely to decrease and the amount of gas generated is less likely to increase, even when stored at high temperatures.

[0213] If n21 is 2 or 3, then 2 or 3 X 21 They may be the same or different. Y 21 and Z 21 If there are multiple instances of Y, then there are multiple instances of Y. 21 and Z 21 They may be the same or different.

[0214] X 21 For example, -CY 21 Z 21 -(In the formula, Y 21 and Z 21 (As stated above) or -CY 21 =CZ 21 -(In the formula, Y 21 and Z 21 The group shown above is preferred.

[0215] Y 21 Preferably, at least one selected from the group consisting of H-, F-, CH3-, CH3CH2-, CH3CH2CH2-, CF3-, CF3CF2-, CH2FCH2-, and CF3CF2CF2- is used. Z 21Preferably, at least one selected from the group consisting of H-, F-, CH3-, CH3CH2-, CH3CH2CH2-, CF3-, CF3CF2-, CH2FCH2-, and CF3CF2CF2- is used.

[0216] Or, Y 21 and Z 21 These atoms can bond with each other to form a carbocyclic or heterocyclic ring, which may contain unsaturated bonds and may be aromatic. The number of carbon atoms in the ring is preferably 3 to 20.

[0217] Next, specific examples of compound (6) will be described. In the following examples, "analog" refers to an acid anhydride obtained by replacing a part of the structure of the exemplified acid anhydride with another structure, to the extent that it does not contradict the spirit of this disclosure. Examples include dimers, trimers, and tetramers consisting of multiple acid anhydrides, or isostructural isomers having branched chains but the same number of carbon atoms in the substituent, or those in which the substituents are attached to the acid anhydride at different sites.

[0218] Specific examples of acid anhydrides that form a five-membered ring structure include succinic anhydride, methylsuccinate anhydride (4-methylsuccinate anhydride), dimethylsuccinate anhydride (4,4-dimethylsuccinate anhydride, 4,5-dimethylsuccinate anhydride, etc.), 4,4,5-trimethylsuccinate anhydride, 4,4,5,5-tetramethylsuccinate anhydride, 4-vinylsuccinate anhydride, 4,5-divinylsuccinate anhydride, phenylsuccinate anhydride (4-phenylsuccinate anhydride), and 4,5-diphenylsuccinate anhydride. Examples include aqueous solutions, 4,4-diphenylsuccinic anhydride, citraconic anhydride, maleic anhydride, methylmaleic anhydride (4-methylmaleic anhydride), 4,5-dimethylmaleic anhydride, phenylmaleic anhydride (4-phenylmaleic anhydride), 4,5-diphenylmaleic anhydride, itaconic anhydride, 5-methylitaconic anhydride, 5,5-dimethylitaconic anhydride, phthalic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, and their analogues.

[0219] Specific examples of acid anhydrides forming a six-membered ring structure include cyclohexanedicarboxylic acid anhydride (such as cyclohexane-1,2-dicarboxylic acid anhydride), 4-cyclohexene-1,2-dicarboxylic acid anhydride, glutaric acid anhydride, glutaconic acid anhydride, 2-phenylglutaric acid anhydride, and their analogues.

[0220] Other specific examples of acid anhydrides that form a cyclic structure include 5-norbornene-2,3-dicarboxylic acid anhydride, cyclopentanetetracarboxylic acid dianhydride, pyromellitic anhydride, diglycolic acid anhydride, and their analogues.

[0221] Specific examples of acid anhydrides that form a cyclic structure and are substituted with halogen atoms include monofluorosuccinic anhydride (such as 4-fluorosuccinic anhydride), 4,4-difluorosuccinic anhydride, 4,5-difluorosuccinic anhydride, 4,4,5-trifluorosuccinic anhydride, trifluoromethylsuccinic anhydride, tetrafluorosuccinic anhydride (4,4,5,5-tetrafluorosuccinic anhydride), 4-fluoromaleic anhydride, 4,5-difluoromaleic anhydride, trifluoromethylmaleic anhydride, 5-fluoroitaconic anhydride, 5,5-difluoroitaconic anhydride, and their analogues.

[0222] Among the compounds (6), glutaric anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic acid anhydride, cyclopentanetetracarboxylic acid dianhydride, 4-cyclohexene-1,2-dicarboxylic acid anhydride, 3,4,5,6-tetrahydrophthalic anhydride, 5-norbornene-2,3-dicarboxylic acid anhydride, phenylsuccinic acid anhydride, 2-phenylglutaric acid anhydride, maleic anhydride, methylmaleic acid anhydride, trifluoromethyl Maleic anhydride, phenylmaleic anhydride, succinic anhydride, methylsuccinic anhydride, dimethylsuccinic anhydride, trifluoromethylsuccinic anhydride, monofluorosuccinic anhydride, tetrafluorosuccinic anhydride, etc. are preferred, maleic anhydride, methylmaleic anhydride, trifluoromethylmaleic anhydride, succinic anhydride, methylsuccinic anhydride, trifluoromethylsuccinic anhydride, tetrafluorosuccinic anhydride are more preferred, and maleic anhydride and succinic anhydride are even more preferred.

[0223] Compound (6) has the general formula (7):

[0224] [ka] (In the formula, X 31 ~X 34 (7) is a compound represented by the same or different group (containing at least H, C, O, or F), and the general formula (8):

[0225] [ka] (In the formula, X 41 and X 42 Preferably, is at least one selected from the group consisting of compounds (8) that are the same or different and represent a group containing at least H, C, O, or F.

[0226] X 31 ~X 34Preferably, it is the same or different, and selected from the group consisting of alkyl groups, fluorinated alkyl groups, alkenyl groups, and fluorinated alkenyl groups. 31 ~X 34 The number of carbon atoms is preferably 1 to 10, and more preferably 1 to 3.

[0227] X 31 ~X 34 More preferably, at least one selected from the group consisting of H-, F-, CH3-, CH3CH2-, CH3CH2CH2-, CF3-, CF3CF2-, CH2FCH2-, and CF3CF2CF2- is the same or different.

[0228] X 41 and X 42 Preferably, it is the same or different, and selected from the group consisting of alkyl groups, fluorinated alkyl groups, alkenyl groups, and fluorinated alkenyl groups. 41 and X 42 The number of carbon atoms is preferably 1 to 10, and more preferably 1 to 3.

[0229] X 41 and X 42 More preferably, at least one selected from the group consisting of H-, F-, CH3-, CH3CH2-, CH3CH2CH2-, CF3-, CF3CF2-, CH2FCH2-, and CF3CF2CF2- is the same or different.

[0230] Compound (7) is preferably one of the following compounds.

[0231] [ka]

[0232] Compound (8) is preferably one of the following compounds.

[0233] [ka]

[0234] The above electrolyte is less likely to experience a decrease in volume retention and less likely to experience a further increase in gas generation even when stored at high temperatures. Therefore, it is preferable that the electrolyte contains 0.0001 to 15% by mass of compound (6). The compound (6) content is more preferably 0.01 to 10% by mass, even more preferably 0.1 to 5% by mass, and particularly preferably 0.1 to 3.0% by mass.

[0235] When the electrolyte contains both compounds (7) and (8), the volume retention rate is less likely to decrease and the amount of gas generated is less likely to increase even when stored at high temperatures. Therefore, the electrolyte preferably contains 0.08 to 2.50% by mass of compound (7) and 0.02 to 1.50% by mass of compound (8) relative to the electrolyte, and more preferably contains 0.80 to 2.50% by mass of compound (7) and 0.08 to 1.50% by mass of compound (8).

[0236] The electrolyte of this disclosure may contain at least one selected from the group consisting of nitrile compounds represented by the following general formulas (9a), (9b), and (9c). [ka] (In the formula, R a and R b Each of these independently represents a hydrogen atom, a cyano group (CN), a halogen atom, an alkyl group, or an alkyl group in which at least some of the hydrogen atoms are replaced with halogen atoms. n represents an integer from 1 to 10. [ka] (In the formula, R c This includes hydrogen atoms, halogen atoms, alkyl groups, groups in which at least some of the hydrogen atoms of an alkyl group are substituted with halogen atoms, or NC-R c1 -X c1 -(R c1 X is an alkylene group. c1 represents an oxygen atom or a sulfur atom. ) represents a group represented by ). d and R eEach of these independently represents a hydrogen atom, a halogen atom, an alkyl group, or a group in which at least some of the hydrogen atoms of an alkyl group are substituted with halogen atoms. (m represents an integer from 1 to 10.) [ka] (In the formula, R f , R g , R h and R i Each of these independently represents a group containing a cyano group (CN), a hydrogen atom (H), a halogen atom, an alkyl group, or an alkyl group in which at least some of the hydrogen atoms are replaced with halogen atoms. However, R f , R g , R h and R i At least one of these groups contains a cyano group. (l represents an integer from 1 to 3.) This improves the high-temperature storage characteristics of electrochemical devices. The above nitrile compounds may be used alone, or two or more may be used in any combination and ratio.

[0237] In the above general formula (9a), R a and R b Each of these is independently a hydrogen atom, a cyano group (CN), a halogen atom, an alkyl group, or a group in which at least some of the hydrogen atoms of an alkyl group are substituted with halogen atoms. Examples of halogen atoms include fluorine, chlorine, bromine, and iodine. Among these, fluorine is preferred. Alkyl groups with 1 to 5 carbon atoms are preferred. Specific examples of alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, and tert-butyl groups. Examples of groups in which at least some of the hydrogen atoms of an alkyl group are substituted with halogen atoms include the aforementioned groups in which at least some of the hydrogen atoms of an alkyl group are substituted with halogen atoms. R a and R bIf is an alkyl group, or a group in which at least some of the hydrogen atoms of an alkyl group are substituted with halogen atoms, then R a and R b These elements may be bonded to each other to form a ring structure (for example, a cyclohexane ring). R a and R b It is preferable that this is a hydrogen atom or an alkyl group.

[0238] In the general formula (9a) above, n is an integer from 1 to 10. If n is 2 or greater, there are n R a They may all be the same, or at least some may be different. b The same applies to n. n is preferably an integer between 1 and 7, and more preferably an integer between 2 and 5.

[0239] Dinitrile and tricarbonitrile are preferred as nitrile compounds represented by the above general formula (9a). Specific examples of dinitriles include malononitrile, succinonitrile, glutalonitrile, adiponitrile, pimelonitrile, suberonitrile, azeranitrile, sebaconitrile, undecanedinitrile, dodecanedinitrile, methylmalononitrile, ethylmalononitrile, isopropylmalononitrile, tert-butylmalononitrile, methylsuccinonitrile, 2,2-dimethylsuccinonitrile, 2,3-dimethylsuccinonitrile, 2 ,3,3-trimethylsuccinonitrile, 2,2,3,3-tetramethylsuccinonitrile, 2,3-diethyl-2,3-dimethylsuccinonitrile, 2,2-diethyl-3,3-dimethylsuccinonitrile, bicyclohexyl-1,1-dicarbonitrile, bicyclohexyl-2,2-dicarbonitrile, bicyclohexyl-3,3-dicarbonitrile, 2,5-dimethyl-2,5-hexanedicarbonitrile, 2,3-diisobutyl-2,3- Dimethyl succinonitrile, 2,2-diisobutyl-3,3-dimethyl succinonitrile, 2-methyl glutaronitrile, 2,3-dimethyl glutaronitrile, 2,4-dimethyl glutaronitrile, 2,2,3,3-tetramethyl glutaronitrile, 2,2,4,4-tetramethyl glutaronitrile, 2,2,3,4-tetramethyl glutaronitrile, 2,3,3,4-tetramethyl glutaronitrile, 1,4-dicyanopentane, 2,6-disy Examples include anoheptane, 2,7-dicyanooctane, 2,8-dicyanononane, 1,6-dicyanodecane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, 3,3'-(ethylenedioxy)dipropionitrile, 3,3'-(ethylenedithio)dipropionitrile, 3,9-bis(2-cyanoethyl)-2,4,8,10-tetraoxaspiro[5,5]undecane, butanenitrile, phthalonitrile, etc. Of these, succinonitrile, glutalonitrile, and adiponitrile are particularly preferred. Furthermore, specific examples of tricarbonitrine include pentanetricarbonitrine, propanetricarbonitrine, 1,3,5-hexanetricarbonitrine, 1,3,6-hexanetricarbonitrine, heptanetricarbonitrine, 1,2,3-propanetricarbonitrine, 1,3,5-pentanetricarbonitrine, cyclohexanetricarbonitrine, triscyanoethylamine, triscyanoethoxypropane, tricyanoethylene, tris(2-cyanoethyl)amine, etc., with 1,3,6-hexanetricarbonitrine and cyclohexanetricarbonitrine being particularly preferred, and cyclohexanetricarbonitrine being the most preferred.

[0240] In the above general formula (9b), R c This includes hydrogen atoms, halogen atoms, alkyl groups, groups in which at least some of the hydrogen atoms of an alkyl group are substituted with halogen atoms, or NC-R c1 -X c1 -(R c1 X is an alkylene group. c1 represents an oxygen atom or a sulfur atom. ) is a group represented by R d and R e Each of these is independently a hydrogen atom, a halogen atom, an alkyl group, or a group in which at least some of the hydrogen atoms of an alkyl group are substituted with halogen atoms. Examples of halogen atoms, alkyl groups, and groups in which at least some of the hydrogen atoms of an alkyl group are substituted with halogen atoms are given for the general formula (9a) above. The above NC-R c1 -X c1 -R in c1 This is an alkylene group. A preferred alkylene group has 1 to 3 carbon atoms. R c , R d and R e Each of these is preferably independently a hydrogen atom, a halogen atom, an alkyl group, or a group in which at least some of the hydrogen atoms of an alkyl group are substituted with halogen atoms. R c , R d and R ePreferably, at least one of the groups is a halogen atom or a group in which at least some of the hydrogen atoms of an alkyl group are substituted with a halogen atom, and more preferably, a fluorine atom or a group in which at least some of the hydrogen atoms of an alkyl group are substituted with a fluorine atom. R d and R e If is an alkyl group, or a group in which at least some of the hydrogen atoms of an alkyl group are substituted with halogen atoms, then R d and R e These elements may be bonded to each other to form a ring structure (for example, a cyclohexane ring).

[0241] In the general formula (9b) above, m is an integer from 1 to 10. If m is 2 or greater, there are m R d They may all be the same, or at least some may be different. e The same applies to m. m is preferably an integer between 2 and 7, and more preferably an integer between 2 and 5.

[0242] Examples of nitrile compounds represented by the above general formula (9b) include acetonitrile, propionitrile, butyronitrile, isobutyronitrile, valeronitrile, isovaleronitrile, lauronitrile, 3-methoxypropionitrile, 2-methylbutyronitrile, trimethylacetonitrile, hexanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, fluoroacetonitrile, difluoroacetonitrile, trifluoroacetonitrile, 2-fluoropropionitrile, 3-fluoropropionitrile, 2,2-difluoropropionitrile, 2,3-difluoropropionitrile, 3,3-difluoropropionitrile, 2,2,3-trifluoropropionitrile, 3,3,3-trifluoropropionitrile, 3,3'-oxydipropionitrile, 3,3'-thiodipropionitrile, pentafluoropropionitrile, methoxyacetonitrile, benzonitrile, and the like. Of these, 3,3,3-trifluoropropionitrile is particularly preferred.

[0243] In the above general formula (9c), Rf , R g , R h and R i Each of these is independently a group containing a cyano group (CN), a hydrogen atom, a halogen atom, an alkyl group, or a group in which at least some of the hydrogen atoms of an alkyl group are substituted with halogen atoms. Examples of halogen atoms, alkyl groups, and groups in which at least some of the hydrogen atoms of an alkyl group are substituted with halogen atoms are given for the general formula (9a) above. Groups containing a cyano group include not only cyano groups but also groups in which at least some of the hydrogen atoms of an alkyl group are replaced with cyano groups. Examples of alkyl groups in this case include those shown for general formula (9a) above. R f , R g , R h and R i At least one of these groups is a cyano group. Preferably, R f , R g , R h and R i At least two of these groups contain a cyano group, and more preferably, R h and R i The group must contain a cyano group. h and R i If R is a group containing a cyano group, f and R g It is preferable that it be a hydrogen atom.

[0244] In the general formula (9c) above, l is an integer from 1 to 3. If l is 2 or greater, there are l R f They may all be the same, or at least some may be different. g The same applies to . l is preferably an integer between 1 and 2.

[0245] Examples of nitrile compounds represented by the above general formula (9c) include 3-hexendinitrile, mucononitrile, maleonitrile, fumaronitrile, acrylonitrile, methacrylonitrile, crotononitrile, 3-methylcrotononitrile, 2-methyl-2-butenenitrile, 2-pentennitrile, 2-methyl-2-pentennitrile, 3-methyl-2-pentennitrile, and 2-hexennitrile, with 3-hexendinitrile and mucononitrile being preferred, and 3-hexendinitrile being particularly preferred.

[0246] The content of the above nitrile compound is preferably 0.2 to 7% by mass relative to the electrolyte. This further improves the high-temperature storage characteristics and safety of the electrochemical device at high voltage. The lower limit of the total content of the above nitrile compound is more preferably 0.3% by mass, and even more preferably 0.5% by mass. The upper limit is more preferably 5% by mass, even more preferably 2% by mass, and particularly preferably 1.0% by mass.

[0247] The electrolyte of this disclosure may contain a compound having an isocyanate group (hereinafter sometimes abbreviated as "isocyanate"). The above isocyanate is not particularly limited, and any isocyanate can be used. Examples of isocyanates include monoisocyanates, diisocyanates, triisocyanates, and the like.

[0248] Specific examples of monoisocyanates include isocyanatomethane, isocyanatoethane, 1-isocyanatopropane, 1-isocyanatobutane, 1-isocyanatopentane, 1-isocyanatohexane, 1-isocyanathoheptane, 1-isocyanatooctane, 1-isocyanatononane, 1-isocyanatodecane, isocyanatocyclohexane, methoxycarbonyl isocyanate, ethoxycarbonyl isocyanate, propoxycarbonyl isocyanate, butoxycarbonyl isocyanate, methoxysulfonyl isocyanate, ethoxysulfonyl isocyanate, propoxysulfonyl isocyanate, butoxysulfonyl isocyanate, fluorosulfonyl isocyanate, methyl isocyanate, butyl isocyanate, phenyl isocyanate, 2-isocyanatoethyl acrylate, 2-isocyanatoethyl methacrylate, and ethyl isocyanate.

[0249] Specific examples of diisocyanates include 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, 1,6-diisocyanatohexane, 1,7-diisocyanathoheptane, 1,8-diisocyanatooctane, 1,9-diisocyanatononane, 1,10-diisocyanatodecane, 1,3-diisocyanatopropene, 1,4-diisocyanato-2-butene, 1,4-diisocyanato-2-fluorobutane, and 1,4-diisocyanato-2,3-difluorobutane. 1,5-Diisocyanato-2-pentene, 1,5-Diisocyanato-2-methylpentane, 1,6-Diisocyanato-2-hexene, 1,6-Diisocyanato-3-hexene, 1,6-Diisocyanato-3-fluorohexane, 1,6-Diisocyanato-3,4-Difluorohexane, Toluene diisocyanate, Xylene diisocyanate, Tolylene diisocyanate, 1,2-Bis(isocyanatomethyl)cyclohexane, 1,3-Bis(isocyanatomethyl) (Cyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, 1,2-diisocyanatocyclohexane, 1,3-diisocyanatocyclohexane, 1,4-diisocyanatocyclohexane, dicyclohexylmethane-1,1'-diisocyanate, dicyclohexylmethane-2,2'-diisocyanate, dicyclohexylmethane-3,3'-diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, isophorone diisocyanate Examples include bicyclo[2.2.1]heptane-2,5-diirbis(methyl isocyanate), bicyclo[2.2.1]heptane-2,6-diirbis(methyl isocyanate), 2,4,4-trimethylhexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, hexamethylene diisocyanate, 1,4-phenylenediisocyanate, octamethylene diisocyanate, tetramethylene diisocyanate, etc.

[0250] Specific examples of triisocyanates include 1,6,11-triisocyanatoundecane, 4-isocyanatomethyl-1,8-octamethylenediisocyanate, 1,3,5-triisocyanatemethylbenzene, 1,3,5-tris(6-isocyanatohexa-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and 4-(isocyanatomethyl)octamethylene=diisocyanate.

[0251] Among these, 1,6-diisocyanatohexane, 1,3-bis(isocyanatomethyl)cyclohexane, 1,3,5-tris(6-isocyanatohexa-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 2,4,4-trimethylhexamethylene diisocyanate, and 2,2,4-trimethylhexamethylene diisocyanate are preferred because they are readily available industrially, keep the manufacturing cost of the electrolyte low, and contribute to the formation of a stable film-like structure from a technical standpoint, making them more preferable to use.

[0252] The isocyanate content is not particularly limited and is arbitrary as long as it does not significantly impair the effects of this disclosure, but is preferably 0.001% by mass or more and 1.0% by mass or less relative to the electrolyte. If the isocyanate content is above this lower limit, a sufficient improvement in cycle characteristics can be brought about in non-aqueous electrolyte secondary batteries. If it is below this upper limit, an initial increase in resistance of non-aqueous electrolyte secondary batteries can be avoided. The isocyanate content is more preferably 0.01% by mass or more, even more preferably 0.1% by mass or more, particularly preferably 0.2% by mass or more, and more preferably 0.8% by mass or less, even more preferably 0.7% by mass or less, and particularly preferably 0.6% by mass or less.

[0253] The electrolyte of this disclosure may contain a cyclic sulfonic acid ester. The cyclic sulfonic acid ester is not particularly limited, and any cyclic sulfonic acid ester can be used. Examples of cyclic sulfonic acid esters include saturated cyclic sulfonic acid esters, unsaturated cyclic sulfonic acid esters, saturated cyclic disulfonic acid esters, and unsaturated cyclic disulfonic acid esters.

[0254] Specific examples of saturated cyclic sulfonic acid esters include 1,3-propanesultone, 1-fluoro-1,3-propanesultone, 2-fluoro-1,3-propanesultone, 3-fluoro-1,3-propanesultone, 1-methyl-1,3-propanesultone, 2-methyl-1,3-propanesultone, 3-methyl-1,3-propanesultone, 1,3-butanesultone, 1,4-butanesultone, 1-fluoro-1,4-butanesultone, 2-fluoro-1,4-butanesultone, 3-fluoro-1,4-butanesultone, 4-fluoro-1,4-butanesultone, 1-methyl-1,4-butanesultone, 2-methyl-1,4-butanesultone, 3-methyl-1,4-butanesultone, 4-methyl-1,4-butanesultone, and 2,4-butanesultone.

[0255] Specific examples of unsaturated cyclic sulfonic acid esters include 1-propene-1,3-sultone, 2-propene-1,3-sultone, 1-fluoro-1-propene-1,3-sultone, 2-fluoro-1-propene-1,3-sultone, 3-fluoro-1-propene-1,3-sultone, 1-fluoro-2-propene-1,3-sultone, 2-fluoro-2-propene-1,3-sultone, 3-fluoro-2-propene-1,3-sultone, 1-methyl-1-propene-1,3-sultone, and 2-methyl-1-propene n-1,3-sultone, 3-methyl-1-propene-1,3-sultone, 1-methyl-2-propene-1,3-sultone, 2-methyl-2-propene-1,3-sultone, 3-methyl-2-propene-1,3-sultone, 1-butene-1,4-sultone, 2-butene-1,4-sultone, 3-butene-1,4-sultone, 1-fluoro-1-butene-1,4-sultone, 2-fluoro-1-butene-1,4-sultone, 3-fluoro-1-butene-1,4-sultone, 4-fluoro-1-butene-1,4 -Sultone, 1-fluoro-2-butene-1,4-sultone, 2-fluoro-2-butene-1,4-sultone, 3-fluoro-2-butene-1,4-sultone, 4-fluoro-2-butene-1,4-sultone, 1,3-propensultone, 1-fluoro-3-butene-1,4-sultone, 2-fluoro-3-butene-1,4-sultone, 3-fluoro-3-butene-1,4-sultone, 4-fluoro-3-butene-1,4-sultone, 1-methyl-1-butene-1,4-sultone, 2-methyl-1-butene Examples include n-1,4-sultone, 3-methyl-1-butene-1,4-sultone, 4-methyl-1-butene-1,4-sultone, 1-methyl-2-butene-1,4-sultone, 2-methyl-2-butene-1,4-sultone, 3-methyl-2-butene-1,4-sultone, 4-methyl-2-butene-1,4-sultone, 1-methyl-3-butene-1,4-sultone, 2-methyl-3-butene-1,4-sultone, 3-methyl-3-butene-1,4-sultone, and 4-methyl-3-butene-14-sultone.

[0256] Among these, 1,3-propanesultone, 1-fluoro-1,3-propanesultone, 2-fluoro-1,3-propanesultone, 3-fluoro-1,3-propanesultone, and 1-propene-1,3-sultone are more preferably used due to their availability and their ability to contribute to the formation of stable film-like structures. The content of the cyclic sulfonic acid ester is not particularly limited and is arbitrary as long as it does not significantly impair the effects of this disclosure, but is preferably 0.001% by mass or more and 3.0% by mass or less relative to the electrolyte.

[0257] If the cyclic sulfonic acid ester content is above this lower limit, a sufficient improvement in cycle characteristics can be achieved in non-aqueous electrolyte secondary batteries. If it is below this upper limit, an increase in the manufacturing cost of non-aqueous electrolyte secondary batteries can be avoided. The cyclic sulfonic acid ester content is more preferably 0.01% by mass or more, even more preferably 0.1% by mass or more, particularly preferably 0.2% by mass or more, more preferably 2.5% by mass or less, even more preferably 2.0% by mass or less, and particularly preferably 1.8% by mass or less.

[0258] The electrolyte of this disclosure may further contain polyethylene oxide having a weight-average molecular weight of 2000 to 4000 and having -OH, -OCOOH, or -COOH at its terminus. By including such compounds, the stability of the electrode interface can be improved, thereby enhancing the properties of the electrochemical device. Examples of the polyethylene oxides mentioned above include polyethylene oxide monool, polyethylene oxide carboxylic acid, polyethylene oxide diol, polyethylene oxide dicarboxylic acid, polyethylene oxide triol, polyethylene oxide tricarboxylic acid, and the like. These may be used individually or in combination of two or more. In particular, a mixture of polyethylene oxide monool and polyethylene oxide diol, and a mixture of polyethylene carboxylic acid and polyethylene dicarboxylic acid are preferred, as they result in better characteristics of the electrochemical device.

[0259] If the weight-average molecular weight of the polyethylene oxide is too low, it may be more susceptible to oxidative decomposition. A weight-average molecular weight of 3000 to 4000 is more preferable. The above weight-average molecular weight can be measured by converting it to polystyrene equivalent using gel permeation chromatography (GPC).

[0260] The polyethylene oxide content mentioned above is 1 × 10⁻⁶ in the electrolyte. -6 ~1 × 10 -2 A concentration of mol / kg is preferred. Excessive polyethylene oxide content may impair the properties of the electrochemical device. The polyethylene oxide content mentioned above is 5 × 10 -6 A concentration of mol / kg or higher is more preferable.

[0261] The electrolyte of this disclosure may further contain, as additives, fluorinated saturated cyclic carbonates, unsaturated cyclic carbonates, overcharge inhibitors, and other known auxiliary agents. This makes it possible to suppress the deterioration of the characteristics of the electrochemical device.

[0262] Examples of fluorinated saturated cyclic carbonates include compounds represented by the general formula (A) described above. Among these, fluoroethylene carbonate, difluoroethylene carbonate, monofluoromethylethylene carbonate, trifluoromethylethylene carbonate, and 2,2,3,3,3-pentafluoropropylethylene carbonate (4-(2,2,3,3,3-pentafluoropropyl)-[1,3]dioxolan-2-one) are preferred. Fluorinated saturated cyclic carbonates may be used individually or in combination of two or more in any combination and ratio.

[0263] The content of the above-mentioned fluorinated saturated cyclic carbonate is preferably 0.001 to 10% by mass, more preferably 0.01 to 5% by mass, and even more preferably 0.1 to 3% by mass, relative to the above-mentioned electrolyte.

[0264] Examples of unsaturated cyclic carbonates include vinylene carbonates, ethylene carbonates substituted with substituents having aromatic rings or carbon-carbon double or carbon-carbon triple bonds, phenyl carbonates, vinyl carbonates, allyl carbonates, and catechol carbonates.

[0265] Examples of vinylene carbonates include vinylene carbonate, methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, phenyl vinylene carbonate, 4,5-diphenyl vinylene carbonate, vinyl vinylene carbonate, 4,5-divinyl vinylene carbonate, allyl vinylene carbonate, 4,5-diallyl vinylene carbonate, 4-fluoro vinylene carbonate, 4-fluoro-5-methyl vinylene carbonate, 4-fluoro-5-phenyl vinylene carbonate, 4-fluoro-5-vinyl vinylene carbonate, 4-allyl-5-fluoro vinylene carbonate, ethynylethylene carbonate, propargylethylene carbonate, methyl vinylene carbonate, and dimethyl vinylene carbonate.

[0266] Specific examples of ethylene carbonates substituted with substituents having aromatic rings or carbon-carbon double or carbon-carbon triple bonds include vinylethylene carbonate, 4,5-divinylethylene carbonate, 4-methyl-5-vinylethylene carbonate, 4-allyl-5-vinylethylene carbonate, ethynylethylene carbonate, 4,5-diethynylethylene carbonate, 4-methyl-5-ethynylethylene carbonate, 4-vinyl-5-ethynylethylene carbonate, and 4-allyl-5-ethynylethylene. Examples include nylethylene carbonate, phenylethylene carbonate, 4,5-diphenylethylene carbonate, 4-phenyl-5-vinylethylene carbonate, 4-allyl-5-phenylethylene carbonate, allylethylene carbonate, 4,5-diallylethylene carbonate, 4-methyl-5-allylethylene carbonate, 4-methylene-1,3-dioxolan-2-one, 4,5-dimethylene-1,3-dioxolan-2-one, and 4-methyl-5-allylethylene carbonate.

[0267] Among these, vinylene carbonate, methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, vinyl vinylene carbonate, 4,5-vinyl vinylene carbonate, allyl vinylene carbonate, 4,5-diallyl vinylene carbonate, vinyl ethylene carbonate, 4,5-divinylethylene carbonate, 4-methyl-5-vinylethylene carbonate, allyl ethylene carbonate, 4,5-diallyl ethylene carbonate, 4-methyl-5-allyl ethylene carbonate, 4-allyl-5-vinylethylene carbonate, ethynyl ethylene carbonate, 4,5-diethynylethylene carbonate, 4-methyl-5-ethynylethylene carbonate, and 4-vinyl-5-ethynylethylene carbonate are preferred as unsaturated cyclic carbonates. Furthermore, vinylene carbonate, vinylethylene carbonate, and ethynylethylene carbonate are particularly preferred because they form an even more stable interfacial protective film, with vinylene carbonate being the most preferred.

[0268] The molecular weight of the unsaturated cyclic carbonate is not particularly limited and can be any as long as it does not significantly impair the effects of this disclosure. Preferably, the molecular weight is 50 or more and 250 or less. Within this range, it is easy to ensure the solubility of the unsaturated cyclic carbonate in the electrolyte, and the effects of this disclosure are easily realized. More preferably, the molecular weight of the unsaturated cyclic carbonate is 80 or more, and more preferably 150 or less.

[0269] The method for producing unsaturated cyclic carbonates is not particularly limited, and they can be produced by any known method.

[0270] Unsaturated cyclic carbonates may be used individually or in combination of two or more types in any combination and ratio.

[0271] The content of the unsaturated cyclic carbonate is not particularly limited and is arbitrary as long as it does not significantly impair the effects of this disclosure. The content of the unsaturated cyclic carbonate is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more, per 100% by mass of the electrolyte. Furthermore, the content is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. Within the above range, electrochemical devices using the electrolyte are more likely to exhibit a sufficient improvement in cycle characteristics, and it is easier to avoid situations such as a decrease in high-temperature storage characteristics, an increase in gas generation, and a decrease in discharge capacity maintenance rate.

[0272] As unsaturated cyclic carbonates, in addition to the non-fluorinated unsaturated cyclic carbonates mentioned above, fluorinated unsaturated cyclic carbonates can also be suitably used. Fluorinated unsaturated cyclic carbonates are cyclic carbonates having unsaturated bonds and fluorine atoms. The number of fluorine atoms in a fluorinated unsaturated cyclic carbonate is not particularly limited, as long as it is one or more. In particular, the number of fluorine atoms is usually six or less, preferably four or less, and one or two atoms is most preferred.

[0273] Examples of fluorinated unsaturated cyclic carbonates include fluorinated vinylene carbonate derivatives and fluorinated ethylene carbonate derivatives substituted with substituents having aromatic rings or carbon-carbon double bonds.

[0274] Examples of fluorinated vinylene carbonate derivatives include 4-fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate, 4-fluoro-5-phenylvinylene carbonate, 4-allyl-5-fluorovinylene carbonate, and 4-fluoro-5-vinylvinylene carbonate.

[0275] Examples of fluorinated ethylene carbonate derivatives substituted with substituents having an aromatic ring or a carbon-carbon double bond include 4-fluoro-4-vinylethylene carbonate, 4-fluoro-4-allylethylene carbonate, 4-fluoro-5-vinylethylene carbonate, 4-fluoro-5-allylethylene carbonate, 4,4-difluoro-4-vinylethylene carbonate, 4,4-difluoro-4-allylethylene carbonate, 4,5-difluoro-4-vinylethylene carbonate, and 4,5-difluoro-4- Examples include lylethylene carbonate, 4-fluoro-4,5-divinylethylene carbonate, 4-fluoro-4,5-diallylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate, 4,5-difluoro-4,5-diallylethylene carbonate, 4-fluoro-4-phenylethylene carbonate, 4-fluoro-5-phenylethylene carbonate, 4,4-difluoro-5-phenylethylene carbonate, and 4,5-difluoro-4-phenylethylene carbonate.

[0276] Among them, fluorinated unsaturated cyclic carbonates include 4-fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate, 4-fluoro-5-vinylvinylene carbonate, 4-allyl-5-fluorovinylene carbonate, 4-fluoro-4-vinylethylene carbonate, 4-fluoro-4-allylethylene carbonate, 4-fluoro-5-vinylethylene carbonate, 4-fluoro-5-allylethylene carbonate, and 4,4-difluoro-4-vinylethylene carbonate. Carbonate, 4,4-difluoro-4-allylethylene carbonate, 4,5-difluoro-4-vinylethylene carbonate, 4,5-difluoro-4-allylethylene carbonate, 4-fluoro-4,5-divinylethylene carbonate, 4-fluoro-4,5-diallylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate, and 4,5-difluoro-4,5-diallylethylene carbonate are more preferably used because they form a stable interfacial protective film.

[0277] The molecular weight of the fluorinated unsaturated cyclic carbonate is not particularly limited and can be any as long as it does not significantly impair the effects of this disclosure. Preferably, the molecular weight is 50 or more and 500 or less. Within this range, it is easy to ensure the solubility of the fluorinated unsaturated cyclic carbonate in the electrolyte.

[0278] The method for producing the fluorinated unsaturated cyclic carbonate is not particularly limited, and it can be produced by arbitrarily selecting any known method. The molecular weight is more preferably 100 or more, and more preferably 200 or less.

[0279] Fluorinated unsaturated cyclic carbonates may be used individually or in any combination and ratio of two or more types. Furthermore, the content of fluorinated unsaturated cyclic carbonates is not particularly limited and is arbitrary as long as it does not significantly impair the effects of this disclosure. Typically, the content of fluorinated unsaturated cyclic carbonates is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, even more preferably 0.1% by mass or more, and also preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less, in 100% by mass of the electrolyte. Within this range, electrochemical devices using the electrolyte are more likely to exhibit a sufficient improvement in cycle characteristics, and it is easier to avoid situations such as a decrease in high-temperature storage characteristics, an increase in gas generation, and a decrease in discharge capacity maintenance rate.

[0280] The electrolyte of this disclosure may contain compounds having triple bonds. The type of compound is not particularly limited as long as it has one or more triple bonds in its molecule. Specific examples of compounds having a triple bond include the following compounds: Hydrocarbon compounds such as 1-pentine, 2-pentine, 1-hexine, 2-hexine, 3-hexine, 1-heptine, 2-heptine, 3-heptine, 1-octin, 2-octin, 3-octin, 4-octin, 1-nonine, 2-nonine, 3-nonine, 4-nonine, 1-dodecine, 2-dodecine, 3-dodecine, 4-dodecine, 5-dodecine, phenylacetylene, 1-phenyl-1-propyne, 1-phenyl-2-propyne, 1-phenyl-1-butine, 4-phenyl-1-butine, 4-phenyl-1-butine, 1-phenyl-1-pentine, 5-phenyl-1-pentine, 1-phenyl-1-hexine, 6-phenyl-1-hexine, diphenylacetylene, 4-ethynyltoluene, and dicyclohexylacetylene;

[0281] 2-Propynylmethyl carbonate, 2-Propynylethyl carbonate, 2-Propynylpropyl carbonate, 2-Propynylbutyl carbonate, 2-Propynylphenyl carbonate, 2-Propynylcyclohexyl carbonate, Di-2-Propynyl carbonate, 1-Methyl-2-Propynylmethyl carbonate, 1,1-Dimethyl-2-Propynylmethyl carbonate, 2-Butynylmethyl carbonate, 3-Butynylmethyl carbonate, 2-Pentynylmethyl carbonate Monocarbonates such as nates, 3-pentinylmethyl carbonate, and 4-pentinylmethyl carbonate; dicarbonates such as 2-butyn-1,4-diol dimethyl dicarbonate, 2-butyn-1,4-diol diethyl dicarbonate, 2-butyn-1,4-diol dipropyl dicarbonate, 2-butyn-1,4-diol dibutyl dicarbonate, 2-butyn-1,4-diol diphenyl dicarbonate, and 2-butyn-1,4-diol dicyclohexyl dicarbonate;

[0282] 2-propynyl acetate, 2-propynyl propionate, 2-propynyl butyrate, 2-propynyl benzoate, 2-propynyl cyclohexylcarboxylic acid, 1,1-dimethyl-2-propynyl acetate, 1,1-dimethyl-2-propynyl propionate, 1,1-dimethyl-2-propynyl butyrate, 1,1-dimethyl-2-propynyl benzoate, 1,1-dimethyl-2-propynyl cyclohexylcarboxylic acid, 2-butynyl acetate, 3-butynyl acetate, 2-pentynyl acetate, 3-pentynyl acetate, 4-pentynyl acetate, methyl acrylate, Ethyl acrylate, propyl acrylate, vinyl acrylate, 2-propenyl acrylate, 2-butenyl acrylate, 3-butenyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, vinyl methacrylate, 2-propenyl methacrylate, 2-butenyl methacrylate, 3-butenyl methacrylate, methyl 2-propate, ethyl 2-propate, propyl 2-propate, vinyl 2-propate, 2-propenyl 2-propate, 2-butenyl 2-propate, 3-butenyl 2-propate, 2 - Methyl butate, ethyl butate, propyl butate, vinyl butate, 2-propenyl butate, 2-butenyl butate, 3-butenyl butate, methyl butate, ethyl butate, propyl butate, vinyl butate, 2-propenyl butate, 2-butenyl butate, 3-butenyl butate, methyl pentinate, ethyl pentinate, propyl pentinate, vinyl pentinate, 2-propenyl pentinate, 2-butenyl pentinate Monocarboxylic acid esters such as 3-butenyl pentinate, methyl pentinate, ethyl pentinate, propyl pentinate, vinyl pentinate, 2-propenyl pentinate, 2-butenyl pentinate, 3-butenyl pentinate, methyl pentinate, ethyl pentinate, propyl pentinate, vinyl pentinate, 2-propenyl pentinate, 2-butenyl pentinate, 3-butenyl pentinate, fumarate esters, methyl trimethylacetate, ethyl trimethylacetate;

[0283] Dicarboxylic acid esters such as 2-butyne-1,4-diol diacetate, 2-butyne-1,4-diol dipropionate, 2-butyne-1,4-diol dibutyrate, 2-butyne-1,4-diol dibenzoate, 2-butyne-1,4-diol dicyclohexanecarboxylate, hexahydrobenzo[1,3,2]dioxathiolan-2-oxide (1,2-cyclohexanediol, 2,2-dioxide-1,2-oxathiolan-4-yl acetate, 2,2-dioxide-1,2-oxathiolan-4-yl acetate, etc.);

[0284] Oxalate diesters such as methyl 2-propynyl oxalate, ethyl 2-propynyl oxalate, propyl 2-propynyl oxalate, 2-propynyl vinyl oxalate, allyl 2-propynyl oxalate, di-2-propynyl oxalate, 2-butynylmethyl oxalate, 2-butynylethyl oxalate, 2-butynylpropyl oxalate, 2-butynyl vinyl oxalate, allyl 2-butynyl oxalate, di-2-butynyl oxalate, 3-butynylmethyl oxalate, 3-butynylethyl oxalate, 3-butynylpropyl oxalate, 3-butynyl vinyl oxalate, allyl 3-butynyl oxalate, and di-3-butynyl oxalate;

[0285] Phosphine oxides such as methyl(2-propynyl)(vinyl)phosphine oxide, divinyl(2-propynyl)phosphine oxide, di(2-propynyl)(vinyl)phosphine oxide, di(2-propenyl)2(-propynyl)phosphine oxide, di(2-propynyl)(2-propenyl)phosphine oxide, di(3-butenyl)(2-propynyl)phosphine oxide, and di(2-propynyl)(3-butenyl)phosphine oxide;

[0286] 2-propynyl methyl(2-propenyl)phosphinate, 2-propynyl 2-butenyl(methyl)phosphinate, 2-propynyl di(2-propenyl)phosphinate, 2-propynyl di(3-butenyl)phosphinate, 1,1-dimethyl-2-propynyl methyl(2-propenyl)phosphinate, 1,1-dimethyl-2-propynyl 2-butenyl(methyl)phosphinate, 1,1-dimethyl-2-propynyl di(2-propenyl)phosphinate, and Phosphinic acid esters such as 1,1-dimethyl-2-propynyl di(3-butenyl)phosphinate, 2-propenyl methyl(2-propynyl)phosphinate, 3-butenyl methyl(2-propynyl)phosphinate, 2-propenyl di(2-propynyl)phosphinate, 3-butenyl di(2-propynyl)phosphinate, 2-propynyl(2-propenyl)phosphinate, and 3-butenyl 2-propynyl(2-propenyl)phosphinate;

[0287] Methyl 2-propenyl phosphonate, methyl 2-butenyl phosphonate (2-propynyl), 2-propenylphosphonic acid (2-propynyl) (2-propenyl), 3-butenylphosphonic acid (3-butenyl) (2-propynyl), 2-propenylphosphonic acid (1,1-dimethyl-2-propynyl) (methyl), 2-butenylphosphonic acid (1,1-dimethyl-2-propynyl) (methyl), 2-propenylphosphonic acid (1,1-dimethyl-2-propynyl) (2-propenyl), and 3-butenylphosphonic acid (3-butenyl) (1,1-dimethyl-2-propynyl), Phosphonic acid esters such as tylphosphonic acid (2-propynyl)(2-propenyl), methylphosphonic acid (3-butenyl)(2-propynyl), methylphosphonic acid (1,1-dimethyl-2-propynyl)(2-propenyl), methylphosphonic acid (3-butenyl)(1,1-dimethyl-2-propynyl), ethylphosphonic acid (2-propynyl)(2-propenyl), ethylphosphonic acid (3-butenyl)(2-propynyl), ethylphosphonic acid (1,1-dimethyl-2-propynyl)(2-propenyl), and ethylphosphonic acid (3-butenyl)(1,1-dimethyl-2-propynyl);

[0288] Phosphate esters such as (methyl)(2-propenyl)(2-propynyl) phosphate, (ethyl)(2-propenyl)(2-propynyl) phosphate, (2-butenyl)(methyl)(2-propynyl) phosphate, (1,1-dimethyl-2-propynyl)(methyl)(2-propenyl) phosphate, (1,1-dimethyl-2-propynyl)(ethyl)(2-propenyl) phosphate, (2-butenyl)(1,1-dimethyl-2-propynyl)(methyl) phosphate, and (2-butenyl)(ethyl)(1,1-dimethyl-2-propynyl) phosphate;

[0289] Of these, compounds having an alkynyloxy group are preferred because they form a negative electrode film more stably in the electrolyte.

[0290] Furthermore, compounds such as 2-propynylmethyl carbonate, di-2-propynyl carbonate, 2-butyne-1,4-diol dimethyl dicarbonate, 2-propynyl acetate, 2-butyne-1,4-diol diacetate, methyl 2-propynyl oxalate, and di-2-propynyl oxalate are particularly preferred from the viewpoint of improving storage properties.

[0291] The compounds having the triple bond described above may be used individually or in any combination and ratio of two or more. There are no restrictions on the amount of the compound having the triple bond to be incorporated into the total electrolyte of this disclosure, and it is arbitrary as long as it does not significantly impair the effects of this disclosure. However, it is usually included in the electrolyte of this disclosure at a concentration of 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less, more preferably 1% by mass or less. When the above range is met, the effects such as output characteristics, load characteristics, cycle characteristics, and high-temperature storage characteristics are further improved.

[0292] In the electrolyte of this disclosure, an overcharge inhibitor can be used to effectively suppress battery rupture and ignition when an electrochemical device using the electrolyte enters an overcharged state or the like.

[0293] Overcharge prevention agents include unsubstituted or alkyl-substituted terphenyl derivatives such as biphenyl, o-terphenyl, m-terphenyl, and p-terphenyl; partially hydrogenated unsubstituted or alkyl-substituted terphenyl derivatives; cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran, diphenylcyclohexane, 1,1,3-trimethyl-3-phenylindan, cyclopentylbenzene, cyclohexylbenzene, cumene, 1,3-diisopropylbenzene, 1,4-diisopropylbenzene, t-butylbenzene, t-amylbenzene, t-hexylbenzene, anisole, and other aromatic compounds; 2-fluorobiphenyl, 4-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, o-cyclohexylfluorobenzene, p-cyclohexyl Examples include partially fluorinated compounds of the above aromatic compounds such as xylfluorobenzene, fluorotoluene, and benzotrifluoride; fluorinated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 1,6-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; aromatic acetates such as 3-propylphenyl acetate, 2-ethylphenyl acetate, benzylphenyl acetate, methylphenyl acetate, benzyl acetate, and phenethylphenyl acetate; aromatic carbonates such as diphenyl carbonate and methylphenyl carbonate; toluene derivatives such as toluene and xylene; and unsubstituted or alkyl-substituted biphenyl derivatives such as 2-methylbiphenyl, 3-methylbiphenyl, 4-methylbiphenyl, and o-cyclohexylbiphenyl. Among these, aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran are preferred. Diphenylcyclohexane, 1,1,3-trimethyl-3-phenylindan, 3-propylphenyl acetate, 2-ethylphenyl acetate, benzylphenyl acetate, methylphenyl acetate, benzyl acetate, diphenyl carbonate, and methylphenyl carbonate are also preferred.These may be used individually or in combination of two or more. When using two or more in combination, it is particularly preferable, from the viewpoint of balancing overcharge prevention characteristics and high-temperature storage characteristics, to use a combination of cyclohexylbenzene and t-butylbenzene or t-amylbenzene, or at least one selected from oxygen-free aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, and t-amylbenzene, and at least one selected from oxygen-containing aromatic compounds such as diphenyl ether and dibenzofuran.

[0294] The electrolyte used in this disclosure may be a carboxylic acid anhydride (except for compound (6)). Compounds represented by the following general formula (10) are preferred. The method for producing the carboxylic acid anhydride is not particularly limited, and it is possible to produce it by arbitrarily selecting a known method.

[0295] General formula (10): [ka] (In general formula (10), R 61 , R 62 Each of these independently represents a hydrocarbon group having 1 to 15 carbon atoms, which may have substituents.

[0296] R 61 , R 62 The type of monovalent hydrocarbon group is not particularly limited. For example, it may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group, or a combination of an aliphatic hydrocarbon group and an aromatic hydrocarbon group. The aliphatic hydrocarbon group may be a saturated hydrocarbon group or may contain an unsaturated bond (carbon-carbon double bond or carbon-carbon triple bond). Furthermore, the aliphatic hydrocarbon group may be linear or cyclic, and if linear, it may be straight or branched. Moreover, it may be a combination of a linear and a cyclic structure. Note that R 61 and R 62 These may be identical or different from one another.

[0297] Also, R 61 , R 62 When the hydrocarbon group has substituents, the type of substituent is not particularly limited as long as it does not contradict the spirit of this disclosure, but examples include halogen atoms such as fluorine, chlorine, bromine, and iodine atoms, and preferably fluorine atoms. Alternatively, substituents other than halogen atoms include substituents having functional groups such as ester groups, cyano groups, carbonyl groups, and ether groups, and preferably cyano groups and carbonyl groups. 61 , R 62 The hydrocarbon group may have only one of these substituents or may have two or more. If it has two or more substituents, the substituents may be the same or different from one another.

[0298] R 61 , R 62 The number of carbon atoms in each hydrocarbon group is usually 1 or more, and usually 15 or less, preferably 12 or less, more preferably 10 or less, and even more preferably 9 or less. 1 and R 2 When R is bonded to each other to form a divalent hydrocarbon group, the number of carbon atoms in that divalent hydrocarbon group is usually 1 or more, and usually 15 or less, preferably 13 or less, more preferably 10 or less, and even more preferably 8 or less. 61 , R 62 If the hydrocarbon group has a substituent containing a carbon atom, then the R includes that substituent. 61 , R 62 It is preferable that the total number of carbon atoms satisfies the above range.

[0299] Next, specific examples of acid anhydrides represented by the general formula (10) above will be described. In the following examples, "analogs" refer to acid anhydrides obtained by replacing a part of the structure of the exemplified acid anhydride with another structure, to the extent that it does not contradict the spirit of this disclosure. Examples include dimers, trimers, and tetramers consisting of multiple acid anhydrides, or isostructural isomers having branched chains but the same number of carbon atoms in the substituents, or those in which the substituents are attached to the acid anhydride at different sites.

[0300] First, R 61 , R 62 The following are specific examples of acid anhydrides that are identical.

[0301] R 61 , R 62 Specific examples of acid anhydrides in which the chain alkyl group is included are acetic anhydride, propionic anhydride, butanoic anhydride, 2-methylpropionic anhydride, 2,2-dimethylpropionic anhydride, 2-methylbutanoic anhydride, 3-methylbutanoic anhydride, 2,2-dimethylbutanoic anhydride, 2,3-dimethylbutanoic anhydride, 3,3-dimethylbutanoic anhydride, 2,2,3-trimethylbutanoic anhydride, 2,3,3-trimethylbutanoic anhydride, 2,2,3,3-tetramethylbutanoic anhydride, 2-ethylbutanoic anhydride, and their analogues.

[0302] R 61 , R 62 Specific examples of acid anhydrides in which the parent molecule is a cyclic alkyl group include cyclopropanecarboxylic acid anhydride, cyclopentanecarboxylic acid anhydride, cyclohexanecarboxylic acid anhydride, and their analogues.

[0303] R 61 , R 62 Specific examples of acid anhydrides in which the parent group is an alkenyl group include acrylic anhydride, 2-methylacrylic anhydride, 3-methylacrylic anhydride, 2,3-dimethylacrylic anhydride, 3,3-dimethylacrylic anhydride, 2,3,3-trimethylacrylic anhydride, 2-phenylacrylic anhydride, 3-phenylacrylic anhydride, 2,3-diphenylacrylic anhydride, 3,3-diphenylacrylic anhydride, 3-butenoic acid anhydride, 2-methyl-3-butenoic acid anhydride, 2,2-dimethyl-3-butenoic acid anhydride, 3-methyl-3-thenic acid anhydride, 2-methyl-3-methyl-3-butenoic acid anhydride, 2,2-dimethyl-3-methyl-3-butenoic acid anhydride, 3-pentenoic acid anhydride, 4-pentenoic acid anhydride, 2-cyclopentenecarboxylic acid anhydride, 3-cyclopentenecarboxylic acid anhydride, 4-cyclopentenecarboxylic acid anhydride, etc., and their analogues.

[0304] R 61 , R 62 Specific examples of acid anhydrides in which the parent group is an alkynyl group include propic anhydride, 3-phenylpropic anhydride, 2-butic anhydride, 2-pentic anhydride, 3-butic anhydride, 3-pentic anhydride, 4-pentic anhydride, and their analogues.

[0305] R 61 , R 62 Specific examples of acid anhydrides in which the group is an aryl group include benzoic acid anhydride, 4-methylbenzoic acid anhydride, 4-ethylbenzoic acid anhydride, 4-tert-butylbenzoic acid anhydride, 2-methylbenzoic acid anhydride, 2,4,6-trimethylbenzoic acid anhydride, 1-naphthalenecarboxylic acid anhydride, 2-naphthalenecarboxylic acid anhydride, and their analogues.

[0306] Also, R 61 , R 62 Examples of acid anhydrides substituted with halogen atoms are listed below, primarily examples of acid anhydrides substituted with fluorine atoms. However, acid anhydrides obtained by substituting some or all of these fluorine atoms with chlorine atoms, bromine atoms, or iodine atoms are also included in the list of exemplary compounds.

[0307] R 61 , R 62 Examples of acid anhydrides in which the linear alkyl group is substituted with a halogen atom include fluoroacetic anhydride, difluoroacetic anhydride, trifluoroacetic anhydride, 2-fluoropropionic anhydride, 2,2-difluoropropionic anhydride, 2,3-difluoropropionic anhydride, 2,2,3-trifluoropropionic anhydride, 2,3,3-trifluoropropionic anhydride, 2,2,3,3-tetrapropionic anhydride, 2,3,3,3-tetrapropionic anhydride, 3-fluoropropionic anhydride, 3,3-difluoropropionic anhydride, 3,3,3-trifluoropropionic anhydride, perfluoropropionic anhydride, and their analogues.

[0308] R61 , R 62 Examples of acid anhydrides in which the alkyl group is a cyclic alkyl group substituted with a halogen atom include 2-fluorocyclopentanecarboxylic acid anhydride, 3-fluorocyclopentanecarboxylic acid anhydride, 4-fluorocyclopentanecarboxylic acid anhydride, and their analogues.

[0309] R 61 , R 62 Examples of acid anhydrides in which the nucleotide is an alkenyl group substituted with a halogen atom include 2-fluoroacrylic anhydride, 3-fluoroacrylic anhydride, 2,3-difluoroacrylic anhydride, 3,3-difluoroacrylic anhydride, 2,3,3-trifluoroacrylic anhydride, 2-(trifluoromethyl)acrylic anhydride, 3-(trifluoromethyl)acrylic anhydride, 2,3-bis(trifluoromethyl)acrylic anhydride, 2,3,3-tris(trifluoromethyl)acrylic anhydride, and 2-(4-fluoro Examples include 2,3-(4-fluorophenyl)acrylic anhydride, 3-(4-fluorophenyl)acrylic anhydride, 2,3-bis(4-fluorophenyl)acrylic anhydride, 3,3-bis(4-fluorophenyl)acrylic anhydride, 2-fluoro-3-butenoic acid anhydride, 2,2-difluoro-3-butenoic acid anhydride, 3-fluoro-2-butenoic acid anhydride, 4-fluoro-3-butenoic acid anhydride, 3,4-difluoro-3-butenoic acid anhydride, 3,3,4-trifluoro-3-butenoic acid anhydride, and their analogues.

[0310] R 61 , R 62 Examples of acid anhydrides in which the alkynyl group is substituted with a halogen atom include 3-fluoro-2-propynic anhydride, 3-(4-fluorophenyl)-2-propynic anhydride, 3-(2,3,4,5,6-pentafluorophenyl)-2-propynic anhydride, 4-fluoro-2-butynic anhydride, 4,4-difluoro-2-butynic anhydride, 4,4,4-trifluoro-2-butynic anhydride, and their analogues.

[0311] R 61 , R 62Examples of acid anhydrides in which the aryl group is substituted with a halogen atom include 4-fluorobenzoic anhydride, 2,3,4,5,6-pentafluorobenzoic anhydride, 4-trifluoromethylbenzoic anhydride, and their analogues.

[0312] R 61 , R 62 Examples of acid anhydrides having substituents with functional groups such as esters, nitriles, ketones, and ethers include methoxyformic anhydride, ethoxyformic anhydride, methyl oxalic anhydride, ethyl oxalic anhydride, 2-cyanoacetic anhydride, 2-oxopropionic anhydride, 3-oxobutanoic anhydride, 4-acetylbenzoic anhydride, methoxyacetic anhydride, 4-methoxybenzoic anhydride, and their analogues.

[0313] Next, R 61 , R 62 The following are specific examples of acid anhydrides that are different from each other.

[0314] R 61 , R 62 The examples listed above, as well as all combinations of their related forms, are possible, but some representative examples are given below.

[0315] Examples of combinations of linear alkyl groups include propionic anhydride acetate, butanoic anhydride acetate, propionic butanoic anhydride, and 2-methylpropionic anhydride acetate.

[0316] Examples of combinations of linear alkyl groups and cyclic alkyl groups include cyclopentanoic anhydride acetate, cyclohexanoic anhydride acetate, and cyclopentanoic propionic anhydride acetate.

[0317] Examples of combinations of linear alkyl groups and alkenyl groups include acrylic anhydride acetate, 3-methylacrylic anhydride acetate, 3-butenic acid anhydride acetate, and propionic acid anhydride acetate.

[0318] Examples of combinations of linear alkyl groups and alkynyl groups include acetic acid propynic anhydride, acetic acid 2-butic anhydride, acetic acid 3-butic anhydride, acetic acid 3-phenylpropynic anhydride, propionic acid propynic anhydride, and the like.

[0319] Examples of combinations of linear alkyl groups and aryl groups include benzoic acid anhydride acetate, methylbenzoic acid anhydride acetate, 1-naphthalenecarboxylic acid anhydride acetate, and propionic acid benzoate anhydride.

[0320] Examples of combinations of linear alkyl groups and hydrocarbon groups having functional groups include fluoroacetic anhydride, trifluoroacetic anhydride, 4-fluorobenzoic anhydride, fluoroacetic acid propionic anhydride, alkyl oxalic acid anhydride, 2-cyanoacetic acid anhydride, 2-oxopropionic acid anhydride, methoxyacetic acid anhydride, methoxyacetic acid propionic anhydride, and the like.

[0321] Examples of combinations of cyclic alkyl groups include cyclopentanoic acid and cyclohexanoic anhydride, among others.

[0322] Examples of combinations of cyclic alkyl groups and alkenyl groups include cyclopentanoic anhydride acrylate, cyclopentanoic anhydride 3-methylacrylate, cyclopentanoic anhydride 3-butenoic anhydride, and cyclohexanoic anhydride acrylate.

[0323] Examples of combinations of cyclic alkyl groups and alkynyl groups include cyclopentanoic anhydride propynate, cyclopentanoic anhydride 2-butyrate, and cyclohexanoic anhydride propynate.

[0324] Examples of combinations of cyclic alkyl groups and aryl groups include cyclopentanoic anhydride benzoate, cyclopentanoic anhydride 4-methylbenzoic acid, and cyclohexanoic anhydride benzoate.

[0325] Examples of combinations of cyclic alkyl groups and hydrocarbon groups having functional groups include cyclopentanoic anhydride fluoroacetate, trifluoroacetic anhydride cyclopentanoic acid, 2-cyanoacetic anhydride cyclopentanoic acid, methoxyacetic anhydride cyclopentanoic acid, and fluoroacetic anhydride cyclohexanoic acid.

[0326] Examples of combinations of alkenyl groups include 2-methylacrylic anhydride acrylate, 3-methylacrylic anhydride acrylate, 3-butenic acid anhydride acrylate, and 3-methylacrylic anhydride 2-methylacrylic acid.

[0327] Examples of combinations of alkenyl and alkynyl groups include acrylic acid propynic anhydride, acrylic acid 2-butynic anhydride, and 2-methylacrylic acid propynic anhydride.

[0328] Examples of combinations of alkenyl and aryl groups include acrylate benzoic anhydride, 4-methylbenzoic anhydride, and 2-methylacrylate benzoic anhydride.

[0329] Examples of combinations of alkenyl groups and hydrocarbon groups having functional groups include fluoroacetic anhydride of acrylate, trifluoroacetic anhydride of acrylate, 2-cyanoacetic anhydride of acrylate, methoxyacetic anhydride of acrylate, fluoroacetic anhydride of 2-methylacrylate, and the like.

[0330] Examples of combinations of alkynyl groups include 2-butyric anhydride of propyic acid, 3-butyric anhydride of propyic acid, and 3-butyric anhydride of 2-butyric acid.

[0331] Examples of combinations of alkynyl and aryl groups include benzoic acid propynic anhydride, 4-methylbenzoic acid propynic anhydride, and benzoic acid 2-butynic anhydride.

[0332] Examples of combinations of an alkynyl group and a hydrocarbon group having a functional group include fluoroacetic anhydride of propynate, trifluoroacetic anhydride of propynate, 2-cyanoacetic anhydride of propynate, methoxyacetic anhydride of propynate, fluoroacetic anhydride of 2-butyrate, and the like.

[0333] Examples of combinations of aryl groups include 4-methylbenzoic anhydride, 1-naphthalenecarboxylic anhydride, and 1-naphthalenecarboxylic anhydride of 4-methylbenzoic acid.

[0334] Examples of combinations of aryl groups and hydrocarbon groups having functional groups include benzoic acid fluoroacetic anhydride, benzoic acid trifluoroacetic anhydride, benzoic acid 2-cyanoacetic anhydride, benzoic acid methoxyacetic anhydride, 4-methylbenzoic acid fluoroacetic anhydride, and the like.

[0335] Examples of combinations of hydrocarbon groups having functional groups include fluoroacetic acid trifluoroacetic anhydride, fluoroacetic acid 2-cyanoacetic anhydride, fluoroacetic acid methoxyacetic anhydride, trifluoroacetic acid 2-cyanoacetic anhydride, and the like.

[0336] Among the acid anhydrides forming the above chain structure, preferred are acetic anhydride, propionic anhydride, 2-methylpropionic anhydride, cyclopentanecarboxylic acid anhydride, cyclohexanecarboxylic acid anhydride, etc., acrylic acid anhydride, 2-methylacrylic acid anhydride, 3-methylacrylic acid anhydride, 2,3-dimethylacrylic acid anhydride, 3,3-dimethylacrylic acid anhydride, 3-butenoic acid anhydride, 2-methyl-3-butenoic acid anhydride, propynic acid anhydride, 2-butic acid anhydride, benzoic acid anhydride, 2-methylbenzoic acid anhydride, 4-methylbenzoic acid anhydride, 4-tert-butylbenzoic acid anhydride, trifluoroacetic acid anhydride, 3,3,3-trif The anhydride is oolopropionic anhydride, 2-(trifluoromethyl)acrylic anhydride, 2-(4-fluorophenyl)acrylic anhydride, 4-fluorobenzoic anhydride, 2,3,4,5,6-pentafluorobenzoic anhydride, methoxyformic anhydride, and ethoxyformic anhydride; more preferably, the anhydride is acrylic anhydride, 2-methylacrylic anhydride, 3-methylacrylic anhydride, benzoic anhydride, 2-methylbenzoic anhydride, 4-methylbenzoic anhydride, 4-tert-butylbenzoic anhydride, 4-fluorobenzoic anhydride, 2,3,4,5,6-pentafluorobenzoic anhydride, methoxyformic anhydride, and ethoxyformic anhydride.

[0337] These compounds are preferable in that they can form a durable film by appropriately bonding with lithium oxalate salts, thereby improving charge-discharge rate characteristics, input / output characteristics, and impedance characteristics, especially after durability testing.

[0338] There are no restrictions on the molecular weight of the carboxylic acid anhydride mentioned above; it can be any molecular weight as long as it does not significantly impair the effects of this disclosure. However, it is usually 90 or more, preferably 95 or more, while it is usually 300 or less, preferably 200 or less. When the molecular weight of the carboxylic acid anhydride is within the above range, the increase in viscosity of the electrolyte can be suppressed, and the film density can be optimized, thereby appropriately improving durability.

[0339] Furthermore, there are no particular restrictions on the method of producing the above-mentioned carboxylic acid anhydrides, and they can be produced by any known method. Any one of the carboxylic acid anhydrides described above may be included alone in the non-aqueous electrolyte of this disclosure, or two or more may be included in any combination and ratio.

[0340] Furthermore, there are no particular restrictions on the content of the above-mentioned carboxylic acid anhydride in the electrolyte of this disclosure, and it is optional as long as it does not significantly impair the effects of this disclosure. However, it is desirable to include it in the electrolyte of this disclosure at a concentration of usually 0.01% by mass or more, preferably 0.1% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less. When the content of the carboxylic acid anhydride is within the above range, the effect of improving cycle characteristics is more likely to occur, and the reactivity is suitable, so the battery characteristics are more likely to improve.

[0341] Other known additives may be used in the electrolyte of this disclosure. Other additives include hydrocarbon compounds such as pentane, heptane, octane, nonane, decane, cycloheptane, benzene, furan, naphthalene, 2-phenylbicyclohexyl, cyclohexane, 2,4,8,10-tetraoxaspiro[5.5]undecane, and 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]undecane; Fluorine-containing aromatic compounds such as fluorobenzene, difluorobenzene, hexafluorobenzene, benzotrifluoride, monofluorobenzene, 1-fluoro-2-cyclohexylbenzene, 1-fluoro-4-tert-butylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-2-cyclohexylbenzene, and fluorinated biphenyls; Carbonate compounds such as erythritol carbonate, spirobis-dimethylene carbonate, and methoxyethyl-methyl carbonate; Ether compounds such as dioxolane, dioxane, 2,5,8,11-tetraoxadodecane, 2,5,8,11,14-pentaoxapentadecane, ethoxymethoxyethane, trimethoxymethane, glyme, and ethyl monoglyme; Ketone compounds such as dimethyl ketone, diethyl ketone, and 3-pentanone; Acid anhydrides such as 2-allyl succinic anhydride; Ester compounds such as dimethyl oxalate, diethyl oxalate, ethylmethyl oxalate, di(2-propynyl) oxalate, methyl 2-propynyl oxalate, dimethyl succinate, di(2-propynyl) glutarate, methyl formate, ethyl formate, 2-propynyl formate, 2-butyne-1,4-diyldiformate, 2-propynyl methacrylate, and dimethyl malonate; Amide compounds such as acetamide, N-methylformamide, N,N-dimethylformamide, and N,N-dimethylacetamide; Ethylene sulfate, vinylene sulfate, ethylene sulfite, methyl fluorosulfonate, ethyl fluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate, busulfan, sulfone, diphenylsulfone, N,N-dimethylmethanesulfonamide, N,N-diethylmethanesulfonamide, methyl vinylsulfonate, ethyl vinylsulfonate, allyl vinylsulfonate, propargyl vinylsulfonate, methyl allylsulfonate, ethyl allylsulfonate, allyl allylsulfonate, propargyl allylsulfonate, 1,2-bis(vinylsulfonyloxy)ethane, propanedisulfonic anhydride, sulfobutyric anhydride, sulfobenzoic anhydride, sulfopropionic anhydride, ethanedisulfonic anhydride, methylenemethanedisulfonate, 2-propynyl methanesulfonate, pentenesulfite, pentafluorophenylmethanesulfonate, propylene sulfate, propylene sulfite, propane Insalton, butylene sulfite, butane-2,3-diyldimethanesulfonate, 2-butyne-1,4-diyldimethanesulfonate, 2-propynyl vinylsulfonic acid, bis(2-vinylsulfonylethyl) ether, 5-vinyl-hexahydro-1,3,2-benzodioxathiol-2-oxide, 2-(methanesulfonyloxy)propionic acid 2-propynyl, 5,5-dimethyl-1,2-oxathiolan-4-one 2,2-dioxy Sulfur-containing compounds such as 3-sulfo-propionic anhydride, trimethylene methane disulfonate, 2-methyltetrahydrofuran, trimethylene methane disulfonate, tetramethylene sulfoxide, dimethyl methane disulfonate, difluoroethyl methyl sulfone, divinyl sulfone, 1,2-bis(vinylsulfonyl)ethane, methyl ethylenebissulfonate, ethyl ethylenebissulfonate, ethylene sulfate, thiophene 1-oxide, etc. Nitrogen-containing compounds such as 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide, nitromethane, nitroethane, and ethylenediamine; Trimethyl phosphate, triethyl phosphate, triphenyl phosphate, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, dimethyl methylphosphonate, diethyl ethylphosphonate, dimethyl vinylphosphonate, diethyl vinylphosphonate, diethyl phosphonoethyl acetate, methyl dimethylphosphinate, ethyl diethylphosphinate, trimethylphosphin oxide, triethylphosphin oxide, bis(2,2-difluoroethyl) phosphate 2,2,2-trifluoroethyl, bis(2,2,3,3-tetrafluoropropyl) phosphate 2,2 2-Trifluoroethyl, bis(2,2,2-trifluoroethyl)methyl phosphate, bis(2,2,2-trifluoroethyl)ethyl phosphate, bis(2,2,2-trifluoroethyl)2,2-difluoroethyl phosphate, bis(2,2,2-trifluoroethyl)2,2,3,3-tetrafluoropropyl phosphate, tributyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, tris(1,1,1,3,3,3-hexafluoropropan-2-yl) phosphate, trioctyl phosphate, 2-phenylphenyldimethyl phosphate, 2-phenylphenyl phosphate Nyldiethyl, (2,2,2-trifluoroethyl)(2,2,3,3-tetrafluoropropyl)methyl phosphate, methyl 2-(dimethoxyphosphoryl)acetate, methyl 2-(dimethylphosphoryl)acetate, methyl 2-(diethoxyphosphoryl)acetate, methyl 2-(diethylphosphoryl)acetate, methyl methylenebisphosphonate, ethyl methylenebisphosphonate, methyl ethylenebisphosphonate, methyl butylenebisphosphonate, ethyl butylenebisphosphonate, 2-propynyl 2-(dimethoxy) acetate Phosphorus-containing compounds such as tris(phosphoryl), 2-propynyl 2-(dimethylphosphoryl) acetate, 2-propynyl 2-(diethoxyphosphoryl) acetate, 2-propynyl 2-(diethylphosphoryl) acetate, tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, tris(t-butyldimethylsilyl) phosphate, tris(trimethoxysilyl) phosphate, tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, tris(t-butyldimethylsilyl) phosphate, tris(trimethoxysilyl) phosphate, and trimethylsilyl polyphosphate; Boron-containing compounds such as tris(trimethylsilyl) borate and tris(trimethoxysilyl) borate; Silane compounds such as dimethoxyaluminoxytrimethoxysilane, diethoxyaluminoxytriethoxysilane, dipropoxyaluminoxytriethoxysilane, dibutoxyaluminoxytrimethoxysilane, dibutoxyaluminoxytriethoxysilane, titaniumtetrakis(trimethylsiloxide), titaniumtetrakis(triethylsiloxide), and tetramethylsilane; These are some examples. These can be used individually or in combination of two or more. By adding these additives, the volume retention characteristics and cycle characteristics after high-temperature storage can be improved. Among the other additives mentioned above, phosphorus-containing compounds are particularly preferred, with tris(trimethylsilyl) phosphate and tristrimethylsilyl phosphorous acid being preferred.

[0342] The amount of other additives is not particularly limited and is arbitrary as long as it does not significantly impair the effects of this disclosure. The amount of other additives is preferably 0.01% by mass or more, and also 5% by mass or less, in 100% by mass of the electrolyte. Within this range, the effects of the other additives can be sufficiently expressed, and situations such as a decrease in battery characteristics, such as high-load discharge characteristics, can be easily avoided. The amount of other additives is more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, even more preferably 3% by mass or less, and even more preferably 1% by mass or less.

[0343] The electrolyte of this disclosure may further contain, to the extent that it does not impair the effects of this disclosure, ether compounds that do not fall under the fluorinated ether represented by the above general formula (1), cyclic and chain-like carboxylic acid esters, nitrogen-containing compounds, boron-containing compounds, organosilicon-containing compounds, flame retardants, surfactants, high dielectric additives, cycle and rate characteristic improvers, sulfone compounds, etc., as additives.

[0344] The above ether compounds are preferably linear ethers having 2 to 10 carbon atoms and cyclic ethers having 3 to 6 carbon atoms. Examples of chain-like ethers having 2 to 10 carbon atoms include dimethyl ether, diethyl ether, di-n-butyl ether, dimethoxymethane, methoxyethoxymethane, diethoxymethane, dimethoxyethane, methoxyethoxyethane, diethoxyethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol, diethylene glycol dimethyl ether, pentaethylene glycol, triethylene glycol dimethyl ether, triethylene glycol, tetraethylene glycol, tetraethylene glycol dimethyl ether, and diisopropyl ether.

[0345] Furthermore, the ether compound may contain other fluorinated ethers other than the fluorinated ether represented by formula (1) above. Examples of such fluorinated ethers include those with the following general formula (I): Rf 4 -O-Rf 5 (I) (In the formula, Rf 4 and Rf 5 They are the same or different, and are alkyl groups having 1 to 10 carbon atoms or fluorinated alkyl groups having 1 to 10 carbon atoms. However, Rf 3 and Rf 4 At least one of them is a fluorinated alkyl group, excluding the fluorinated ether represented by formula (1) above. Examples include fluorinated ethers (I) represented by [formula]. By incorporating fluorinated ether(I), the flame retardancy of the electrolyte is improved, as well as its stability and safety at high temperatures and voltages.

[0346] In the above general formula (I), Rf 4 and Rf 5 At least one of them should be a fluorinated alkyl group having 1 to 10 carbon atoms, but from the viewpoint of further improving the flame retardancy of the electrolyte and its stability and safety at high temperature and high voltage, Rf 3 and Rf 4 However, it is preferable that both are fluorinated alkyl groups having 1 to 10 carbon atoms. In this case, Rf 3and Rf 4 They may be the same, or they may be different from one another. Among them, Rf 4 and Rf 5 However, they are the same or different, Rf 4 is a fluorinated alkyl group having 3 to 6 carbon atoms, and Rf 5 It is more preferable that the element is a fluorinated alkyl group having 2 to 6 carbon atoms.

[0347] Rf 4 and Rf 5 If the total number of carbon atoms is too low, the boiling point of the fluorinated ether will be too low, and Rf 4 or Rf 5 If the number of carbon atoms is too high, the solubility of the electrolyte salt decreases, negatively affecting its compatibility with other solvents, and the viscosity increases, thus reducing its rate characteristics. 4 The number of carbon atoms is 3 or 4, Rf 5 When the number of carbon atoms is 2 or 3, it is advantageous in that it has excellent boiling point and rate characteristics.

[0348] The above-mentioned fluorinated ether (I) preferably has a fluorine content of 40 to 75% by mass. When the fluorine content is within this range, it exhibits a particularly excellent balance between non-flammability and compatibility. It is also preferable in terms of good oxidation resistance and safety. The lower limit of the fluorine content is more preferably 45% by mass, even more preferably 50% by mass, and particularly preferably 55% by mass. The upper limit is more preferably 70% by mass, and even more preferably 66% by mass. The fluorine content of fluorinated ether(I) is calculated based on the structural formula of fluorinated ether(I) using the formula {(number of fluorine atoms × 19) / molecular weight of fluorinated ether(I)} × 100 (%).

[0349] Rf 4Examples include CF3CF2CH2-, CF3CFHCF2-, HCF2CF2CF2-, HCF2CF2CH2-, CF3CF2CH2CH2-, CF3CFHCF2CH2-, HCF2CF2CF2CF2-, HCF2CF2CF2CH2-, HCF2CF2CH2CH2-, HCF2CF(CF3)CH2-, etc. Also, Rf 5 Examples include -CH2CF2CF3, -CF2CFHCF3, -CF2CF2CF2H, -CH2CF2CF2H, -CH2CH2CF2CF3, -CH2CF2CFHCF3, -CF2CF2CF2CF2H, -CH2CF2CF2CF2H, -CH2CH2CF2CF2H, -CH2CF(CF3)CF2H, -CF2CF2H, -CH2CF2H, -CF2CH3, etc.

[0350] Specific examples of the above fluorinated ether(I) include, for example, HCF2CF2CH2OCF2CFHCF3, CF3CF2CH2OCF2CFHCF3, and C6F 13 OCH3, C6F 13 OC2H5, C8F 17 O CH3, C8F 17 Examples include OC2H5, CF3CFHCF2CH(CH3)OCF2CFHCF3, HCF2CF2OCH(C2H5)2, HCF2CF2OC4H9, HCF2CF2OCH2CH(C2H5)2, and HCF2CF2OCH2CH(CH3)2.

[0351] In particular, those containing HCF2- or CF3CFH- at one or both ends exhibit excellent polarizability and can yield fluorinated ether(I) with a high boiling point. The boiling point of the fluorinated ether(I) is preferably 67 to 120°C, more preferably 80°C or higher, and even more preferably 90°C or higher.

[0352] Examples of such fluorinated ethers (I) include one or more types such as CF3CH2OCF2CFHCF3, CF3CF2CH2OCF2CFHCF3, HCF2CF2CH2OCF2CFHCF3, HCF2CF2CH2OCH2CF2CF2H, and CF3CFHCF2CH2OCF2CFHCF3. In particular, it is preferable to select at least one from the group consisting of HCF2CF2CH2OCF2CFHCF3 (boiling point 106°C) and CF3CF2CH2OCF2CFHCF3 (boiling point 82°C), and more preferably HCF2CF2CH2OCF2CFHCF3 (boiling point 106°C), due to its advantages in terms of high boiling point, good compatibility with other solvents, and good solubility of electrolyte salts.

[0353] Examples of cyclic ethers having 3 to 6 carbon atoms include 1,2-dioxane, 1,3-dioxane, 2-methyl-1,3-dioxane, 4-methyl-1,3-dioxane, 1,4-dioxane, metaformaldehyde, 2-methyl-1,3-dioxolane, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 2-(trifluoroethyl)dioxolane, 2,2-bis(trifluoromethyl)-1,3-dioxolane, and their fluorinated compounds.

[0354] Among the ether compounds mentioned above, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether, and crown ether are preferred because they have high solvation ability to lithium ions and improve the degree of ion dissociation. Particularly preferred are dimethoxymethane, diethoxymethane, and ethoxymethoxymethane because they have low viscosity and provide high ionic conductivity.

[0355] Examples of the above-mentioned cyclic carboxylic acid esters include those with a total of 3 to 12 carbon atoms in their structural formula. Specifically, examples include gamma-butyrolactone, gamma-valerolactone, gamma-macoractone, epsilon-caprolactone, and 3-methyl-γ-butyrolactone. Among these, gamma-butyrolactone is particularly preferred from the viewpoint of improving the properties of electrochemical devices due to an improved degree of lithium ion dissociation.

[0356] The amount of cyclic carboxylic acid ester used as an additive is usually preferably 0.1% by mass or more, more preferably 1% by mass or more, per 100% by mass of the solvent. Within this range, the electrical conductivity of the electrolyte is improved, making it easier to improve the high-current discharge characteristics of the electrochemical device. Alternatively, the amount of cyclic carboxylic acid ester used is preferably 10% by mass or less, more preferably 5% by mass or less. By setting such an upper limit, the viscosity of the electrolyte is kept within an appropriate range, a decrease in electrical conductivity is avoided, an increase in negative electrode resistance is suppressed, and the high-current discharge characteristics of the electrochemical device are made easier to achieve within a good range.

[0357] Furthermore, fluorinated cyclic carboxylic acid esters (fluorinated lactones) can also be suitably used as the above-mentioned cyclic carboxylic acid esters. Examples of fluorinated lactones include the following formula (C):

[0358] [ka]

[0359] (In the formula, X 15 ~X 20 The elements are the same or different, and all are -H, -F, -Cl, -CH3, or fluorinated alkyl groups; however, X 15 ~X 20 (At least one of them is a fluorinated alkyl group.) Examples include fluorine-containing lactones shown as follows.

[0360] X 15 ~X 20Examples of fluorinated alkyl groups include -CFH2, -CF2H, -CF3, -CH2CF3, -CF2CF3, -CH2CF2CF3, and -CF(CF3)2. -CH2CF3 and -CH2CF2CF3 are preferred due to their high oxidation resistance and safety-enhancing effects.

[0361] X 15 ~X 20 If at least one of them is a fluorinated alkyl group, then -H, -F, -Cl, -CH3 or a fluorinated alkyl group is X 15 ~X 20 The substitution may occur at only one location or at multiple locations. Preferably, there are 1 to 3 locations, and more preferably 1 to 2 locations, from the viewpoint of good solubility of the electrolyte salt.

[0362] The substitution position of the fluorinated alkyl group is not particularly limited, but X is chosen because it yields a good synthesis yield. 17 and / or X 18 However, especially X 17 or X 18 It is preferable that X is a fluorinated alkyl group, particularly -CH2CF3 or -CH2CF2CF3. 15 ~X 20 The element is -H, -F, -Cl, or CH3, and -H is particularly preferred due to its good solubility as an electrolyte salt.

[0363] In addition to those shown in the above formula, other examples of fluorinated lactones include, for example, the following formula (D):

[0364] [ka]

[0365] (In the formula, A and B are either CX) 226 X 227 (X 226 and X 227(These are the same or different alkylene groups, which may have -H, -F, -Cl, -CF3, -CH3, or a hydrogen atom substituted with a halogen atom, or contain a heteroatom in the chain), and the other is an oxygen atom; Rf 12 X is a fluorinated alkyl group or fluorinated alkoxy group which may have an ether linkage; 221 and X 222 They are the same or different, and all are -H, -F, -Cl, -CF3, or CH3;X 223 ~X 225 (n=0 or 1) These alkyl groups may be the same or different, and may have -H, -F, -Cl, or hydrogen atoms substituted with halogen atoms, or may contain heteroatoms in the chain. Examples include fluorine-containing lactones, as shown in [reference].

[0366] The fluorine-containing lactone represented by formula (D) is shown in formula (E):

[0367] [ka]

[0368] (In the formula, A, B, Rf 12 , X 221 , X 222 and X 223 (This is the same as equation (D)) The five-membered ring structure shown is preferred because it is easy to synthesize and has good chemical stability. Furthermore, the combination of A and B yields the following formula (F):

[0369] [ka]

[0370] (In the formula, Rf 12 , X 221 , X 222 , X 223 , X 226 and X 227 (This is the same as equation (D)) Fluorine-containing lactones represented by the following formula (G):

[0371] [ka]

[0372] (In the formula, Rf 12 , X 221 , X 222 , X 223 , X 226 and X 227 (This is the same as equation (D)) There are fluorine-containing lactones, as shown by [this symbol].

[0373] Among these, the characteristics of the electrolyte in this disclosure are particularly improved by its ability to exhibit excellent properties such as high dielectric constant and high dielectric strength, as well as by its good solubility of the electrolyte salt and reduction of internal resistance.

[0374] [ka] These are some examples. By incorporating fluorinated cyclic carboxylic acid esters, effects such as improved ionic conductivity, enhanced safety, and improved stability at high temperatures can be obtained.

[0375] Examples of the above-mentioned chain-like carboxylic acid esters include those with a total of 3 to 7 carbon atoms in their structural formula. Specifically, examples include methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isobutyl propionate, n-butyl propionate, methyl butyrate, isobutyl propionate, t-butyl propionate, methyl butyrate, ethyl butyrate, n-propyl butyrate, isopropyl butyrate, methyl isobutyrate, ethyl isobutyrate, n-propyl isobutyrate, and isopropyl isobutyrate.

[0376] Among these, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, methyl butyrate, and ethyl butyrate are preferred from the viewpoint of improving ionic conductivity by reducing viscosity.

[0377] Examples of nitrogen-containing compounds include nitriles, fluorinated nitriles, carboxylic acid amides, fluorinated carboxylic acid amides, sulfonic acid amides and fluorinated sulfonic acid amides, acetamides, and formamides. Additionally, 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxaziridinone, 1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide can also be used. However, nitrile compounds represented by the above general formulas (1a), (1b), and (1c) are not included in the list of nitrogen-containing compounds.

[0378] Examples of the boron-containing compounds mentioned above include borate esters such as trimethylborate and triethylborate, borate ethers, and alkyl borates.

[0379] Examples of the organosilicon-containing compounds mentioned above include (CH3)4-Si, (CH3)3-Si-Si(CH3)3, and silicone oil.

[0380] Examples of the above-mentioned flame retardants include phosphate esters and phosphazene compounds. Examples of the above-mentioned phosphate esters include fluorine-containing alkyl phosphate esters, non-fluorine alkyl phosphate esters, and aryl phosphate esters. Among these, fluorine-containing alkyl phosphate esters are preferred because they can exhibit flame retardant effects even in small amounts.

[0381] Examples of the phosphazene compounds mentioned above include methoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, dimethylaminopentafluorocyclotriphosphazene, diethylaminopentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, and ethoxyheptafluorocyclotetraphosphazene.

[0382] Examples of the above-mentioned fluorine-containing alkyl phosphate esters include, specifically, the fluorine-containing dialkyl phosphate ester described in Japanese Patent Publication No. 11-233141, the cyclic alkyl phosphate ester described in Japanese Patent Publication No. 11-283669, or the fluorine-containing trialkyl phosphate ester.

[0383] Preferred non-combustible (flame retardant) agents include (CH3O)3P=O, (CF3CH2O)3P=O, (HCF2CH2O)3P=O, (CF3CF2CH2)3P=O, and (HCF2CF2CH2)3P=O.

[0384] The above-mentioned surfactant may be a cationic surfactant, anionic surfactant, nonionic surfactant, or amphoteric surfactant, but it is preferable that it contains a fluorine atom in order to obtain good cycle characteristics and rate characteristics.

[0385] Examples of surfactants containing such fluorine atoms include the following formula (30): Rf 6 COO - M + (30) (In the formula, Rf 6 M is a fluorine-containing alkyl group that may contain ether bonds with 3 to 10 carbon atoms; + is Li + na + , K + Or NHR'3 + (R' may be the same or different, and both are either hydrogen or an alkyl group with 1 to 3 carbon atoms.) Fluorine-containing carboxylates represented by the following formula (40): Rf 7SO3 - M + (40) (In the formula, Rf 7 M is a fluorine-containing alkyl group that may contain ether bonds with 3 to 10 carbon atoms; + is Li + na + , K + Or NHR'3 + (R' may be the same or different, and both are either hydrogen or an alkyl group with 1 to 3 carbon atoms.) A fluorine-containing sulfonate represented by [formula] is preferred.

[0386] The amount of the surfactant described above is preferably 0.01 to 2% by mass in the electrolyte, since this can reduce the surface tension of the electrolyte without degrading the charge-discharge cycle characteristics.

[0387] Examples of the above-mentioned high dielectric additives include sulfolane, methylsulfolane, γ-butyrolactone, and γ-valerolactone.

[0388] Examples of the cycle characteristic and rate characteristic improving agents mentioned above include methyl acetate, ethyl acetate, tetrahydrofuran, and 1,4-dioxane.

[0389] Furthermore, the electrolyte of this disclosure may be further combined with a polymer material to form a gel-like (plasticized) gel electrolyte.

[0390] Examples of such polymer materials include conventionally known polyethylene oxide and polypropylene oxide, and modified versions thereof (Japanese Patent Publication No. 8-222270, Japanese Patent Publication No. 2002-100405); polyacrylate polymers, polyacrylonitrile, and fluororesins such as polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymer (Japanese Patent Publication No. 4-506726, Japanese Patent Publication No. 8-507407, Japanese Patent Publication No. 10-294131); and composites of these fluororesins and hydrocarbon resins (Japanese Patent Publication No. 11-35765, Japanese Patent Publication No. 11-86630). In particular, it is desirable to use polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymer as polymer materials for gel electrolytes.

[0391] In addition, the electrolyte of this disclosure may also include ion-conducting compounds as described in Japanese Patent Application No. 2004-301934.

[0392] This ionic conductive compound is given by formula (101): A-(D)-B (101) [In the formula, D is from formula (201): -(D1) n -(FAE) m -(AE) p -(Y) q - (201) (In the formula, D1 is given by formula (10a):

[0393] [ka]

[0394] (wherein Rf is a fluorine-containing ether group which may have a crosslinkable functional group; R 10 (This refers to a group or bond that connects Rf to the main chain.) An ether unit having a fluorine-containing ether group in its side chain; FAE is given by equation (10b):

[0395] [ka]

[0396] (wherein Rfa is a hydrogen atom, and R is a fluorinated alkyl group which may have a crosslinkable functional group; R 11 (This refers to the group or bond that connects Rfa to the main chain.) An ether unit having a fluorinated alkyl group in its side chain; AE is given by equation (10c):

[0397] [ka]

[0398] (In the formula, R 13 R is a hydrogen atom, an alkyl group which may have a crosslinkable functional group, an aliphatic cyclic hydrocarbon group which may have a crosslinkable functional group, or an aromatic hydrocarbon group which may have a crosslinkable functional group; 12 is R 13 (A group or bond that connects to the main chain) The ether unit shown by; Y is given by equations (10d-1) to (10d-3):

[0399] [ka]

[0400] A unit containing at least one of the following; n is an integer from 0 to 200; m is an integer from 0 to 200; p is an integer from 0 to 10000; q is an integer from 1 to 100; however, n+m is not 0, and the order of combination of D1, FAE, AE, and Y is not specified. A and B are the same or different, and may contain a hydrogen atom, a fluorine atom and / or a crosslinkable functional group, an alkyl group, a phenyl group, a -COOH group, -OR (where R is a hydrogen atom or a fluorine atom and / or a crosslinkable functional group), an ester group, or a carbonate group (however, if the terminal of D is an oxygen atom, it is not a -COOH group, -OR, an ester group, or a carbonate group). This is an amorphous fluorine-containing polyether compound having a fluorine-containing group in its side chain, represented by [the formula shown].

[0401] The electrolyte of this disclosure may contain a sulfone compound. Preferred sulfone compounds are cyclic sulfones having 3 to 6 carbon atoms and chain sulfones having 2 to 6 carbon atoms. The number of sulfonyl groups in one molecule is preferably 1 or 2.

[0402] 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, tetramethylene sulfones, tetramethylene disulfones, hexamethylene sulfones, and hexamethylene disulfones are more preferred from the viewpoint of dielectric constant and viscosity, and tetramethylene sulfones (sulfolanes) are particularly preferred.

[0403] As sulfolanes, sulfolanes and / or sulfolane derivatives (hereinafter, sulfolanes may also be abbreviated as "sulfolanes") are preferred. As sulfolane derivatives, those in which one or more hydrogen atoms bonded to the carbon atoms constituting the sulfolane ring are substituted with fluorine atoms or alkyl groups are preferred.

[0404] Among them, 2-methylsulfolane, 3-methylsulfolane, 2-fluorosulfolane, 3-fluorosulfolane, 2,2-difluorosulfolane, 2,3-difluorosulfolane, 2,4-difluorosulfolane, 2,5-difluorosulfolane, 3,4-difluorosulfolane, 2-fluoro-3-methylsulfolane, 2-fluoro-2-methylsulfolane, 3-fluoro-3-methylsulfolane, 3-fluoro-2-methylsulfolane, 4-fluoro-3-methylsulfolane, 4-fluoro-2-methylsulfolane, 5-fluoro-3-methylsulfolane 5-fluoro-2-methylsulfolane, 2-fluoromethylsulfolane, 3-fluoromethylsulfolane, 2-difluoromethylsulfolane, 3-difluoromethylsulfolane, 2-trifluoromethylsulfolane, 3-trifluoromethylsulfolane, 2-fluoro-3-(trifluoromethyl)sulfolane, 3-fluoro-3-(trifluoromethyl)sulfolane, 4-fluoro-3-(trifluoromethyl)sulfolane, 3-sulfolene, 5-fluoro-3-(trifluoromethyl)sulfolane, etc. are preferred because they have high ionic conductivity and high input / output.

[0405] In addition, chain-like sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, n-propyl methyl sulfone, n-propyl ethyl sulfone, di-n-propyl sulfone, isopropyl methyl sulfone, isopropyl ethyl sulfone, diisopropyl sulfone, n-butyl methyl sulfone, n-butyl ethyl sulfone, t-butyl methyl sulfone, t-butyl ethyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, monofluoroethyl methyl sulfone, difluoroethyl methyl sulfone, trifluoroethyl methyl sulfone, pentafluoroethyl methyl sulfone, ethyl monofluoromethyl sulfone, ethyl difluoromethyl sulfone, ethyl trifluoromethyl sulfone, and perfluoroethyl methyl sulfone. Examples include ethyltrifluoroethyl sulfone, ethylpentafluoroethyl sulfone, di(trifluoroethyl) sulfone, perfluorodiethyl sulfone, fluoromethyl-n-propyl sulfone, difluoromethyl-n-propyl sulfone, trifluoromethyl-n-propyl sulfone, fluoromethylisopropyl sulfone, difluoromethylisopropyl sulfone, trifluoromethylisopropyl sulfone, trifluoroethyl-n-propyl sulfone, trifluoroethylisopropyl sulfone, pentafluoroethyl-n-propyl sulfone, pentafluoroethylisopropyl sulfone, trifluoroethyl-n-butyl sulfone, trifluoroethyl-t-butyl sulfone, pentafluoroethyl-n-butyl sulfone, and pentafluoroethyl-t-butyl sulfone.

[0406] Among these, dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, n-propyl methyl sulfone, isopropyl methyl sulfone, n-butyl methyl sulfone, t-butyl methyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, monofluoroethyl methyl sulfone, difluoroethyl methyl sulfone, trifluoroethyl methyl sulfone, pentafluoroethyl methyl sulfone, ethyl monofluoromethyl sulfone, ethyl difluoromethyl sulfone, ethyl trifluoromethyl sulfone, ethyl trifluoroethyl sulfone, ethyl pentafluoroethyl sulfone, trifluoromethyl-n-propyl sulfone, trifluoromethylisopropyl sulfone, trifluoroethyl-n-butyl sulfone, trifluoroethyl-t-butyl sulfone, trifluoromethyl-n-butyl sulfone, and trifluoromethyl-t-butyl sulfone are preferred because they have high ionic conductivity and high input / output capabilities.

[0407] The content of the sulfone compound is not particularly limited and is arbitrary as long as it does not significantly impair the effects of this disclosure, but is usually 0.3% by volume or more, preferably 0.5% by volume or more, more preferably 1% by volume or more, and usually 40% by volume or less, preferably 35% by volume or less, and more preferably 30% by volume or less, in 100% by volume of the solvent. If the content of the sulfone compound is within the above range, it is easy to obtain effects that improve durability such as cycle characteristics and storage characteristics, and the viscosity of the non-aqueous electrolyte can be set to an appropriate range, a decrease in electrical conductivity can be avoided, and the input / output characteristics and charge / discharge rate characteristics of the non-aqueous electrolyte secondary battery can be set to an appropriate range.

[0408] From the viewpoint of improving output characteristics, the electrolyte of this disclosure may also preferably contain, as an additive, at least one compound (11) selected from the group consisting of lithium fluorophosphate salts (excluding LiPF6) and lithium salts having an S=O group. Furthermore, when compound (11) is used as an additive, it is preferable to use a compound other than compound (11) as the electrolyte salt mentioned above.

[0409] Examples of lithium fluorophosphate salts include lithium monofluorophosphate (LiPO3F) and lithium difluorophosphate (LiPO2F2). Examples of lithium salts having the above-mentioned S=O group include lithium monofluorosulfonate (FSO3Li), lithium methyl sulfate (CH3OSO3Li), lithium ethyl sulfate (C2H5OSO3Li), and lithium 2,2,2-trifluoroethyl sulfate. Among the compounds (11), LiPO2F2, FSO3Li, and C2H5OSO3Li are preferred.

[0410] The content of compound (11) is preferably 0.001 to 20% by mass, more preferably 0.01 to 15% by mass, even more preferably 0.1 to 10% by mass, and particularly preferably 0.1 to 7% by mass, relative to the electrolyte.

[0411] The electrolyte of this disclosure may contain other additives as needed. Examples of other additives include metal oxides and glass.

[0412] The electrolyte of this disclosure preferably contains 5 to 200 ppm of hydrogen fluoride (HF). The inclusion of HF promotes the film formation of the additives mentioned above. If the HF content is too low, the film formation ability on the negative electrode decreases, and the characteristics of the electrochemical device tend to deteriorate. Conversely, if the HF content is too high, the oxidation resistance of the electrolyte tends to decrease due to the influence of HF. The electrolyte of this disclosure does not reduce the high-temperature storage recovery capacity rate of the electrochemical device even when containing HF within the above range. The HF content is more preferably 10 ppm or more, and even more preferably 20 ppm or more. The HF content is also more preferably 100 ppm or less, even more preferably 80 ppm or less, and particularly preferably 50 ppm or less. The HF content can be measured by neutralization titration.

[0413] The electrolytic solution of the present disclosure may be prepared by any method using the components described above.

[0414] The electrolytic solution of the present disclosure has a feature of suppressing alkali metal electrodeposition, and can be suitably applied to a secondary battery provided with an electrode having a negative electrode material containing a silicon element and a carbon element. A secondary battery including such a negative electrode, a positive electrode, and the electrolytic solution of the present disclosure is also one aspect of the present disclosure.

[0415] <Negative Electrode> In the present disclosure, the negative electrode preferably includes a negative electrode material layer and a current collector. In the present disclosure, the above negative electrode material contains a silicon element and a carbon element. In particular, it preferably contains Si and / or SiOa (0<a<2) and a carbon compound. In the present disclosure, the "negative electrode material" means a material contributing to conductivity, and refers to the negative electrode active material and / or conductive auxiliary agent described in detail below.

[0416] (Negative Electrode Active Material) The negative electrode active material used in the present disclosure preferably contains silicon as a constituent element. By including silicon as a constituent element, a high-capacity battery can be produced.

[0417] As the silicon-containing particles, silicon particles (Si), silicon oxide particles represented by the general formula SiOa (0<a<2), particles having a structure in which fine silicon particles are dispersed in a silicon-based compound, or a mixture thereof (hereinafter, these may be collectively referred to as "silicon-containing particles") are preferred. By using these, a negative electrode mixture for lithium ion secondary batteries with higher initial charge-discharge efficiency, high capacity and excellent cycle characteristics can be obtained. Among them, at least one selected from the group consisting of Si and SiOa (0<a<2) is preferred.

[0418] The silicon oxide in the present disclosure is a general term for amorphous silicon oxides, and the silicon oxide before disproportionation is represented by the general formula SiOa (0<a<2). a is preferably 0.5≦a≦1.6, more preferably 0.8≦a<1.6, and even more preferably 0.8≦a<1.3. This silicon oxide can be obtained, for example, by cooling and precipitating silicon monoxide gas generated by heating a mixture of silicon dioxide and metal silicon.

[0419] Particles having a structure in which fine silicon particles are dispersed in a silicon-based compound can be obtained by, for example, a method of firing a mixture of fine silicon particles and a silicon-based compound, or by subjecting silicon oxide particles before disproportionation represented by the general formula SiOa to a heat treatment at a temperature of 400°C or higher, preferably 800 to 1100°C in an inert non-oxidizing atmosphere such as argon to cause a disproportionation reaction. In particular, the material obtained by the latter method is preferable because fine silicon crystals are uniformly dispersed. Through the disproportionation reaction as described above, the size of the silicon nanoparticles can be set to 1 to 100 nm. Note that the silicon oxide in the particles having a structure in which silicon nanoparticles are dispersed in silicon oxide is desirably silicon dioxide. Note that it is possible to confirm that silicon nanoparticles (crystals) are dispersed in amorphous silicon oxide using a transmission electron microscope.

[0420] The physical properties of the silicon-containing particles can be appropriately selected depending on the target composite particles. For example, the average particle size is preferably 0.1 to 50 μm, the lower limit is more preferably 0.2 μm or more, and even more preferably 0.5 μm or more. The upper limit is more preferably 30 μm or less, and even more preferably 20 μm or less. The average particle size in the present invention refers to the weight average particle size in particle size distribution measurement by a laser diffraction method.

[0421] The BET specific surface area of the silicon-containing particles is 0.5 to 100 m 2 / g is preferable, and 1 to 20 m 2 / g is more preferable. When the BET specific surface area is 0.5 m 2 / g or more, there is no risk that the adhesiveness when applied to an electrode will decrease and the battery characteristics will deteriorate. In addition, 100 m 2If the content is / g or less, the proportion of silicon dioxide on the particle surface increases, and there is no risk of a decrease in battery capacity when used as a negative electrode material for lithium ion secondary batteries.

[0422] In addition, conductivity may be imparted by subjecting the silicon-containing particles to carbon coating or the like, so as to improve battery characteristics. Examples of methods for imparting conductivity include a method of mixing with conductive particles such as graphite, a method of coating the surface of the silicon-containing particles with a carbon film, and a method of combining both. The method of coating with a carbon film is preferred, and the method of chemical vapor deposition (CVD) is more preferred as the coating method.

[0423] In addition, as the negative electrode active material, a carbon compound such as graphite powder may be used together with Si and / or SiOa (0<a<2). Carbon compounds include natural graphite, artificial carbonaceous materials, artificial graphitized materials, carbonaceous materials {for example, natural graphite, coal coke, petroleum coke, coal pitch, petroleum pitch, or these pitches that have been oxidized, needle coke, pitch coke and carbon materials that have been partially graphitized, furnace black, acetylene black, Ketjen black, pitch-based carbon fibers and other pyrolysis products of organic materials, carbonizable organic materials (for example, coal tar pitch from soft pitch to hard pitch, or coal-based heavy oils such as carbonized liquefied oil, straight-run heavy oils such as atmospheric residue and vacuum residue, crude oil, ethylene tar and other cracked petroleum heavy oils produced as by-products during the pyrolysis of naphtha, etc., as well as aromatic hydrocarbons such as acenaphthylene, decacyclene, anthracene, and phenanthrene, N-ring compounds such as phenazine and acridine, S-ring compounds such as thiophene and bithiophene, biphene Examples include polyphenylenes such as nyl and terphenyl, polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, immobilized products thereof, nitrogen-containing organic polymers such as polyacrylonitrile and polypyrrole, sulfur-containing organic polymers such as polythiophene and polystyrene, natural polymers such as polysaccharides represented by cellulose, lignin, mannan, polygalacturonic acid, chitosan, and saccharose, thermoplastic resins such as polyphenylene sulfide and polyphenylene oxide, thermosetting resins such as furfuryl alcohol resin, phenol-formaldehyde resin, and imide resin, as well as carbonized products thereof, or solutions obtained by dissolving carbonizable organic materials in low molecular weight organic solvents such as benzene, toluene, xylene, quinoline, and n-hexane, and carbonaceous materials obtained by heat-treating these carbonized products once or more times in the range of 400 to 3200°C.

[0424] For carbon compounds, for example, the average particle size is preferably 1 to 100 μm, more preferably 3 μm or more, and even more preferably 5 μm or more. The upper limit is more preferably 80 μm or less, and even more preferably 20 μm or less. In this disclosure, the average particle size refers to the weight-average particle size measured by the particle size distribution method using laser diffraction.

[0425] The BET specific surface area of ​​carbon compounds ranges from 0.1 to 50 m². 2 / g is preferred, and 1 to 20 m 2 / g is more preferred. If the BET specific surface area is 0.1 m 2 / g or more, there is no risk that the adhesiveness when applied to an electrode will decrease and the battery characteristics will deteriorate. Further, if it is 50 m 2 / g or less, there is no risk that the battery capacity will decrease when used as a negative electrode material for lithium ion secondary batteries.

[0426] The mass ratio of the silicon-containing particles to the carbon compound is preferably 1 / 99 to 99 / 1, more preferably 5 / 95 to 95 / 5, and even more preferably 10 / 90 to 90 / 10.

[0427] The mass ratio of the Si and / or SiOa (0<a<2) to the carbon compound is preferably 1 / 99 to 99 / 1, more preferably 5 / 95 to 95 / 5, and even more preferably 10 / 90 to 90 / 10.

[0428] The content of the negative electrode active material in the negative electrode material layer is preferably 80.0 to 99.9 mass%, more preferably 90.0 to 99.0 mass%, relative to the mass of the solid content in the negative electrode mixture.

[0429] The content of the silicon-containing particles in the negative electrode material layer is preferably 20 to 40 mass%, more preferably 25 to 35 mass%, relative to the mass of the solid content in the negative electrode mixture. The content of the carbon compound in the negative electrode material layer is preferably 40 to 60 mass%, more preferably 65 to 75 mass%, relative to the mass of the solid content in the negative electrode mixture.

[0430] (Conductive Aid) The negative electrode material layer may further contain a conductive aid. In particular, when the negative electrode active material does not contain a carbon compound, it is preferable to include a conductive aid. Any known conductive material can be used as the conductive additive mentioned above. Specific examples include metallic materials such as copper and nickel, graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, and carbon compounds such as needle coke, carbon nanotubes, fullerenes, and amorphous carbon such as VGCF. These may be used individually or in any combination and ratio of two or more materials.

[0431] For the conductive additive, for example, the average particle size is preferably 0.05 to 100 μm, more preferably 0.1 μm or more, and even more preferably 0.15 μm or more. The upper limit is more preferably 10 μm or less, and even more preferably 5 μm or less. In this invention, the average particle size is expressed as the weight-average particle size measured by the particle size distribution method using laser diffraction.

[0432] The BET specific surface area of ​​the conductive additive is 0.1 to 1000 m². 2 / g is preferred, and 0.5 to 500m 2 / g is preferable.

[0433] As described above, carbon compounds can be used both as active materials and as conductive additives.

[0434] The conductive additive is typically contained in the negative electrode material layer in an amount of 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more, and typically 50% by mass or less, preferably 30% by mass or less, more preferably 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. Conversely, if the content is higher than this range, the battery capacity may decrease.

[0435] (Binding agent) The negative electrode material layer preferably contains a binder. The binder preferably contains a fluorine-containing copolymer that includes vinylidene fluoride (VdF) units and other monomer units other than VdF. The other monomers may be fluorinated monomers or non-fluorinated monomers.

[0436] Examples of fluorinated monomers (excluding VdF) include tetrafluoroethylene (TFE), vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene (CTFE), fluoroalkyl vinyl ether, hexafluoropropylene (HFP), (perfluoroalkyl)ethylene, 2,3,3,3-tetrafluoropropene, and trans-1,3,3,3-tetrafluoropropene.

[0437] As the fluoroalkyl vinyl ether, a fluoroalkyl vinyl ether having a fluoroalkyl group with 1 to 5 carbon atoms is preferred, and at least one selected from the group consisting of perfluoro(methyl vinyl ether) (PMVE), perfluoro(ethyl vinyl ether), and perfluoro(propyl vinyl ether) is more preferred.

[0438] As the fluorinated monomer, at least one selected from the group consisting of TFE, CTFE, 2,3,3,3-tetrafluoropropene, HFP, and fluoroalkyl vinyl ether is preferred, at least one selected from the group consisting of TFE and HFP is more preferred, and TFE is particularly preferred.

[0439] Fluorinated monomers (except VdF) may or may not have polar groups.

[0440] Examples of non-fluorinated monomers include non-fluorinated monomers that do not have polar groups, such as ethylene and propylene, and non-fluorinated monomers that have polar groups (hereinafter sometimes referred to as polar group-containing monomers).

[0441] When a non-fluorinated monomer having a polar group is used, the polar group is introduced into the fluorine-containing copolymer, thereby providing even better adhesion between the coated layer and the metal foil. The polar group is preferably at least one selected from the group consisting of carbonyl group-containing groups, epoxy groups, hydroxyl groups, sulfonic acid groups, sulfate groups, phosphoric acid groups, amino groups, amide groups, and alkoxy groups, more preferably at least one selected from the group consisting of carbonyl group-containing groups, epoxy groups, and hydroxyl groups, and even more preferably a carbonyl group-containing group. The hydroxyl groups mentioned above do not include hydroxyl groups that constitute part of the carbonyl group-containing group. Furthermore, the amino group mentioned above is a monovalent functional group obtained by removing hydrogen from ammonia, a primary or secondary amine.

[0442] The carbonyl group-containing group mentioned above is a functional group having a carbonyl group (-C(=O)-). The carbonyl group-containing group is preferably a group represented by the general formula: -COOR (where R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group) or a carboxylic acid anhydride group, and more preferably a group represented by the general formula: -COOR. The number of carbon atoms in the alkyl and hydroxyalkyl groups is preferably 1 to 16, more preferably 1 to 6, and even more preferably 1 to 3. Specific examples of groups represented by the general formula: -COOR include -COOCH2CH2OH, -COOCH2CH(CH3)OH, -COOCH(CH3)CH2OH, -COOH, -COOCH3, and -COOC2H5. If the group represented by the general formula -COOR is -COOH or contains -COOH, then -COOH may be a carboxylate salt such as a metal carboxylate salt or an ammonium carboxylate salt.

[0443] Furthermore, the above carbonyl group-containing groups include: General formula:-X-COOR The group may be represented as (where X is an atomic group whose main chain consists of 1 to 20 atoms and has a molecular weight of 500 or less, and R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group). The number of carbon atoms in the alkyl group and hydroxyalkyl group is preferably 1 to 16, more preferably 1 to 6, and even more preferably 1 to 3.

[0444] The amide group described above is preferably a group represented by the general formula: -CO-NRR' (where R and R' independently represent a hydrogen atom or a substituted or unsubstituted alkyl group), or a bond represented by the general formula: -CO-NR”- (where R represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted phenyl group).

[0445] The above polar group-containing monomers include hydroxyalkyl (meth)acrylates such as hydroxyethyl acrylate and 2-hydroxypropyl acrylate; alkylidenemalonate esters such as dimethyl methylidenemalonate; vinyl carboxyalkyl ethers such as vinyl carboxymethyl ether and vinyl carboxyethyl ether; carboxyalkyl (meth)acrylates such as 2-carboxyethyl acrylate and 2-carboxyethyl methacrylate; (meth)acryloyloxyalkyl dicarboxylic acid esters such as acryloyloxyethyl succinic acid, acryloyloxypropyl succinic acid, methacryloyloxyethyl succinic acid, acryloyloxyethyl phthalic acid, and methacryloyloxyethyl phthalic acid; monoesters of unsaturated dibasic acids such as monomethyl maleate, monoethyl maleate, monomethyl citraconic acid, and monoethyl citraconic acid; general formula (50): [ka] (In the formula, R 11 ~R 13 R independently represents a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms. 14 This represents a single bond or a hydrocarbon group with 1 to 8 carbon atoms. 1 (This represents inorganic cations and / or organic cations.) A monomer represented by (50); Examples include unsaturated dibasic acids such as maleic acid, maleic anhydride, citraconic acid, and citraconic anhydride; and so on.

[0446] As the polar group-containing monomer units that the fluorine-containing copolymer may contain, units based on monomer (50) represented by general formula (50) are preferred.

[0447] In general formula (50), Y1 represents an inorganic cation and / or an organic cation. Examples of inorganic cations include H, Li, Na, K, Mg, Ca, Al, and Fe. Examples of organic cations include NH4 and NH3R. 15 NH2R 15 2. NHR 15 3. NR 15 4(R 15 Each of these independently represents an alkyl group having 1 to 4 carbon atoms. Examples of cations include ( ). For Y1, H, Li, Na, K, Mg, Ca, Al, and NH4 are preferred, H, Li, Na, K, Mg, Al, and NH4 are more preferred, H, Li, Al, and NH4 are even more preferred, and H is particularly preferred. For convenience, specific examples of inorganic and organic cations are listed without symbols and valencies.

[0448] In general formula (50), R 11 ~R 13 R independently represents a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms. The hydrocarbon group is a monovalent hydrocarbon group. The number of carbon atoms in the hydrocarbon group is preferably 4 or less. Examples of the hydrocarbon group include alkyl groups, alkenyl groups, alkynyl groups, etc., with methyl or ethyl groups being preferred. 11 and R 12 R is preferably independently a hydrogen atom, a methyl group, or an ethyl group. 13 It is preferable that this is a hydrogen atom or a methyl group.

[0449] In general formula (50), R 14The symbol represents a single bond or a hydrocarbon group having 1 to 8 carbon atoms. The hydrocarbon group is a divalent hydrocarbon group. The number of carbon atoms in the hydrocarbon group is preferably 4 or less. Examples of the hydrocarbon group include alkylene groups and alkenylene groups with the above number of carbon atoms, and among these, at least one selected from the group consisting of methylene, ethylene, ethylidene, propyridene, and isopropylidene groups is preferred, with methylene being more preferred.

[0450] The monomer (50) is preferably at least one selected from the group consisting of (meth)acrylic acid and its salts, vinylacetic acid (3-butenic acid) and its salts, 3-pentenoic acid and its salts, 4-pentenoic acid and its salts, 3-hexenoic acid and its salts, 4-heptenoic acid and its salts, and 5-hexenoic acid and its salts.

[0451] Other monomers that are preferred include at least one selected from the group consisting of TFE, CTFE, (meth)acrylic acid, 2,3,3,3-tetrafluoropropene, HFP, and fluoroalkyl vinyl ethers. (Meth)acrylic acid includes acrylic acid and methacrylic acid.

[0452] The content of other monomer units in the fluorine-containing copolymer is preferably 0.0001 to 50.0 mol%, more preferably 0.01 mol% or more, even more preferably 0.10 mol% or more, more preferably 45.0 mol% or less, even more preferably 40.0 mol% or less, and particularly preferably 35.0 mol% or less, relative to the total monomer units.

[0453] The VdF unit content of the fluorine-containing copolymer is 50.0 to 99.9999 mol%, more preferably 55.0 mol% or more, even more preferably 60.0 mol% or more, particularly preferably 65.0 mol% or more, more preferably 99.99 mol% or less, and even more preferably 99.90 mol% or less, relative to the total monomer units.

[0454] When a fluorine-containing copolymer contains fluorinated monomer units as other monomer units, the content of fluorinated monomer units is preferably 0.0001 to 50.0 mol%, more preferably 2.0 mol% or more, even more preferably 3.0 mol% or more, particularly preferably 4.0 mol% or more, more preferably 45.0 mol% or less, even more preferably 40.0 mol% or less, and particularly preferably 35.0 mol% or less, relative to the total monomer units.

[0455] When a fluorinated copolymer contains fluorinated monomer units as other monomer units, the VdF unit content of the fluorinated copolymer is 50.0 to 99.999 mol%, more preferably 55.0 mol% or more, even more preferably 60.0 mol% or more, particularly preferably 65.0 mol% or more, more preferably 98.0 mol% or less, even more preferably 97.0 mol% or less, and particularly preferably 96.0 mol% or less, based on the total monomer units.

[0456] When a fluorine-containing copolymer contains non-fluorinated monomer units such as polar group-containing monomers as other monomer units, the content of non-fluorinated monomer units is preferably 0.0001 to 50.0 mol%, more preferably 0.01 mol% or more, even more preferably 0.10 mol% or more, more preferably 5.0 mol% or less, even more preferably 3.0 mol% or less, and particularly preferably 1.5 mol% or less, relative to the total monomer units.

[0457] When a fluorine-containing copolymer contains non-fluorinated monomer units as other monomer units, the VdF unit content of the fluorine-containing copolymer is preferably 50.0 to 99.999 mol%, more preferably 95.0 mol% or more, even more preferably 97.0 mol% or more, particularly preferably 98.5 mol% or more, more preferably 99.99 mol% or less, and even more preferably 99.90 mol% or less, relative to the total monomer units.

[0458] In this disclosure, the composition of the fluorine-containing copolymer can be measured, for example, by 19F-NMR spectroscopy. Furthermore, if the fluorine-containing copolymer contains polar group-containing monomer units as other monomer units, the content of the polar group-containing monomer units can be measured, for example, by acid-base titration of the acid group if the polar group is an acid group such as a carboxylic acid.

[0459] The weight-average molecular weight (in polystyrene equivalent) of the fluorine-containing copolymer is preferably 10,000 to 3,000,000, more preferably 30,000 or more, even more preferably 50,000 or more, particularly preferably 200,000 or more, more preferably 2,400,000 or less, even more preferably 2,200,000 or less, and particularly preferably 2,000,000 or less. The weight-average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as the solvent.

[0460] The number-average molecular weight (in polystyrene equivalent) of the fluorine-containing copolymer is preferably 7,000 to 1,500,000, more preferably 21,000 or more, even more preferably 35,000 or more, more preferably 1,400,000 or less, even more preferably 1,200,000 or less, and particularly preferably 1,100,000 or less. The number-average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as the solvent.

[0461] Examples of fluorine-containing copolymers include VdF / (meth)acrylic acid copolymer, VdF / TFE copolymer, VdF / HFP copolymer, VdF / fluoroalkyl vinyl ether copolymer, VdF / TFE / HFP copolymer, and VdF / 2,3,3,3-tetrafluoro Examples include propene copolymer, VdF / TFE / 2,3,3,3-tetrafluoropropene copolymer, VdF / TFE / (meth)acrylic acid copolymer, VdF / HFP / (meth)acrylic acid copolymer, VdF / CTFE copolymer, VdF / TFE / 4-pentenoic acid copolymer, VdF / TFE / 3-butenoic acid copolymer, VdF / TFE / HFP / (meth)acrylic acid copolymer, VdF / TFE / HFP / 4-pentenoic acid copolymer, VdF / TFE / HFP / 3-butenoic acid copolymer, VdF / TFE / 2-carboxyethyl acrylate copolymer, VdF / TFE / HFP / 2-carboxyethyl acrylate copolymer, VdF / TFE / acryloyloxyethyl succinic acid copolymer, and VdF / TFE / HFP / acryloyloxyethyl succinic acid copolymer.

[0462] As the fluorine-containing copolymer, at least one selected from the group consisting of VdF / TFE copolymer, VdF / CTFE copolymer, VdF / (meth)acrylic acid copolymer, VdF / 2,3,3,3-tetrafluoropropene copolymer, VdF / HFP copolymer, and VdF / fluoroalkyl vinyl ether copolymer is preferred.

[0463] The VdF / TFE copolymer contains VdF units and TFE units. By using the VdF / TFE copolymer as the copolymer, a negative electrode mixture can be formed very easily, and a negative electrode mixture with excellent slurry stability can be obtained, and a coating layer with excellent flexibility can be formed. The VdF unit content is preferably 50.0 to 95.0 mol%, more preferably 55.0 mol% or more, even more preferably 60.0 mol% or more, more preferably 92.0 mol% or less, and even more preferably 89.0 mol% or less, relative to the total monomer units of the VdF / TFE copolymer. The TFE unit content is preferably 50.0 to 5.0 mol%, more preferably 45.0 mol% or less, even more preferably 40.0 mol% or less, more preferably 8.0 mol% or more, and even more preferably 11.0 mol% or more, relative to the total monomer units of the VdF / TFE copolymer.

[0464] The VdF / TFE copolymer may contain units based on monomers copolymerizable with VdF and TFE (excluding VdF and TFE) in addition to VdF and TFE units. From the viewpoint of resistance to electrolyte swelling, the content of units based on monomers copolymerizable with VdF and TFE is preferably 3.0 mol% or less relative to the total monomer units of the VdF / TFE copolymer.

[0465] Examples of monomers copolymerizable with VdF and TFE include the fluorinated monomers and the non-fluorinated monomers mentioned above. Among the monomers copolymerizable with VdF and TFE, at least one selected from the group consisting of fluorinated monomers and polar group-containing monomers is preferred, and at least one selected from the group consisting of HFP, 2,3,3,3-tetrafluoropropene and monomer (4) is more preferred.

[0466] The weight-average molecular weight (polystyrene equivalent) of the VdF / TFE copolymer is preferably 50,000 to 2,000,000, more preferably 80,000 to 1,700,000, and even more preferably 100,000 to 1,500,000.

[0467] The number-average molecular weight (polystyrene equivalent) of the VdF / TFE copolymer is 35,000 to 1,400,000, more preferably 40,000 to 1,300,000, and even more preferably 50,000 to 1,200,000.

[0468] The VdF / CTFE copolymer contains VdF units and CTFE units. By using the VdF / CTFE copolymer as the copolymer, a negative electrode mixture can be formed very easily, and a coating layer that adheres extremely firmly to the metal foil can be formed. The VdF unit content is preferably 80.0 to 98.0 mol%, more preferably 85.0 mol% or more, even more preferably 90.0 mol% or more, more preferably 97.5 mol% or less, and even more preferably 97.0 mol% or less, relative to the total monomer units of the VdF / CTFE copolymer. The CTFE unit content is preferably 20.0 to 2.0 mol%, more preferably 15.0 mol% or less, even more preferably 10.0 mol% or less, more preferably 2.5 mol% or more, and even more preferably 3.0 mol% or more, relative to the total monomer units of the VdF / CTFE copolymer.

[0469] The VdF / CTFE copolymer may contain units based on monomers copolymerizable with VdF and CTFE (excluding VdF and CTFE) in addition to VdF and CTFE units. From the viewpoint of resistance to electrolyte swelling, the content of units based on monomers copolymerizable with VdF and CTFE is preferably 3.0 mol% or less relative to the total monomer units of the VdF / CTFE copolymer.

[0470] Monomers copolymerizable with VdF and CTFE include the fluorinated monomers and non-fluorinated monomers mentioned above. Among the monomers copolymerizable with VdF and CTFE, at least one selected from the group consisting of fluorinated monomers and polar group-containing monomers is preferred, at least one selected from the group consisting of TFE, HFP, 2,3,3,3-tetrafluoropropene and monomer (4) is more preferred, and TFE is even more preferred.

[0471] The weight-average molecular weight (polystyrene equivalent) of the VdF / CTFE copolymer is preferably 50,000 to 2,000,000, more preferably 80,000 to 1,700,000, and even more preferably 100,000 to 1,500,000.

[0472] The number-average molecular weight (polystyrene equivalent) of the VdF / CTFE copolymer is preferably 35,000 to 1,400,000, more preferably 40,000 to 1,300,000, and even more preferably 50,000 to 1,200,000.

[0473] The VdF / (meth)acrylic acid copolymer contains VdF units and (meth)acrylic acid units. By using the VdF / (meth)acrylic acid copolymer as the copolymer, a negative electrode mixture can be formed very easily, and a coating layer that adheres very firmly to the metal foil can be formed. The content of (meth)acrylic acid units is preferably 0.0001 to 5.0 mol%, more preferably 0.01 to 3.0 mol%, and even more preferably 0.10 to 1.5 mol%, relative to the total monomer units.

[0474] The VdF unit content of the VdF / (meth)acrylic acid copolymer is preferably 95.0 to 99.9999 mol%, more preferably 97.0 to 99.99 mol%, and even more preferably 98.5 to 99.90 mol%, relative to the total monomer units.

[0475] The weight-average molecular weight (in polystyrene equivalent) of the VdF / (meth)acrylic acid copolymer is preferably 50,000 to 3,000,000, more preferably 80,000 or more, even more preferably 100,000 or more, particularly preferably 200,000 or more, more preferably 2,400,000 or less, even more preferably 2,200,000 or less, and particularly preferably 2,000,000 or less.

[0476] The number-average molecular weight (polystyrene equivalent) of the VdF / (meth)acrylic acid copolymer is preferably 20,000 to 1,500,000, more preferably 40,000 or more, even more preferably 70,000 or more, particularly preferably 140,000 or more, more preferably 1,400,000 or less, even more preferably 1,200,000 or less, and particularly preferably 1,100,000 or less.

[0477] The VdF / 2,3,3,3-tetrafluoropropene copolymer contains VdF units and 2,3,3,3-tetrafluoropropene units. By using the VdF / 2,3,3,3-tetrafluoropropene copolymer as the copolymer, a negative electrode mixture can be formed very easily, and a coating layer with excellent flexibility and conductivity can be formed. The VdF unit content is preferably 50.0 to 98.0 mol%, more preferably 55.0 mol% or more, even more preferably 60.0 mol% or more, particularly preferably 65.0 mol% or more, more preferably 97.0 mol% or less, and even more preferably 96.0 mol% or less, relative to the total monomer units of the VdF / 2,3,3,3-tetrafluoropropene copolymer. The content of 2,3,3,3-tetrafluoropropene units is preferably 2.0 to 50.0 mol%, more preferably 3.0 mol% or more, even more preferably 4.0 mol% or more, more preferably 45.0 mol% or less, even more preferably 40.0 mol% or less, and particularly preferably 35.0 mol% or less, relative to the total monomer units of the VdF / TFE copolymer.

[0478] The VdF / 2,3,3,3-tetrafluoropropene copolymer may contain units based on monomers copolymerizable with VdF and 2,3,3,3-tetrafluoropropene (excluding VdF and 2,3,3,3-tetrafluoropropene), in addition to VdF units and 2,3,3,3-tetrafluoropropene units. From the viewpoint of resistance to electrolyte swelling, the content of units based on monomers copolymerizable with VdF and 2,3,3,3-tetrafluoropropene is preferably 3.0 mol% or less relative to the total monomer units of the VdF / 2,3,3,3-tetrafluoropropene copolymer.

[0479] Monomers that can copolymerize with VdF and 2,3,3,3-tetrafluoropropene include the fluorinated monomers and non-fluorinated monomers mentioned above. Among the monomers copolymerizable with VdF and 2,3,3,3-tetrafluoropropene, at least one selected from the group consisting of fluorinated monomers and polar group-containing monomers is preferred, and at least one selected from the group consisting of TFE, HFP and monomer (50) is more preferred.

[0480] The weight-average molecular weight (on a polystyrene basis) of the VdF / 2,3,3,3-tetrafluoropropene copolymer is preferably 10,000 to 2,000,000, more preferably 30,000 to 1,700,000, and even more preferably 5,000 to 1,500,000.

[0481] The number-average molecular weight (polystyrene equivalent) of the VdF / 2,3,3,3-tetrafluoropropene copolymer is preferably 7,000 to 1,400,000, more preferably 21,000 to 1,300,000, and even more preferably 35,000 to 1,200,000.

[0482] The VdF / HFP copolymer contains VdF units and HFP units. By using the VdF / HFP copolymer as the copolymer, a negative electrode mixture can be formed very easily, and a coating layer that adheres extremely firmly to the metal foil can be formed. The VdF unit content is preferably 80.0 to 98.0 mol%, more preferably 83.0 mol% or more, even more preferably 85.0 mol% or more, more preferably 97.0 mol% or less, and even more preferably 96.0 mol% or less, relative to the total monomer units of the VdF / HFP copolymer. The HFP unit content is preferably 20.0 to 2.0 mol%, more preferably 17.0 mol% or less, even more preferably 15.0 mol% or less, more preferably 3.0 mol% or more, and even more preferably 4.0 mol% or more, relative to the total monomer units of the VdF / HFP copolymer.

[0483] The VdF / HFP copolymer may contain units based on monomers copolymerizable with VdF and HFP (excluding VdF and HFP) in addition to VdF and HFP units. From the viewpoint of resistance to electrolyte swelling, the content of units based on monomers copolymerizable with VdF and HFP is preferably 3.0 mol% or less relative to the total monomer units of the VdF / HFP copolymer.

[0484] Examples of monomers copolymerizable with VdF and HFP include the fluorinated monomers and the non-fluorinated monomers mentioned above. Among the monomers copolymerizable with VdF and HFP, at least one selected from the group consisting of fluorinated monomers and polar group-containing monomers is preferred, at least one selected from the group consisting of TFE, 2,3,3,3-tetrafluoropropene and monomer (50) is more preferred, and monomer (50) is even more preferred.

[0485] The weight-average molecular weight (polystyrene equivalent) of the VdF / HFP copolymer is preferably 50,000 to 2,000,000, more preferably 80,000 to 1,700,000, and even more preferably 100,000 to 1,500,000.

[0486] The number-average molecular weight (polystyrene equivalent) of the VdF / HFP copolymer is preferably 35,000 to 1,400,000, more preferably 40,000 to 1,300,000, and even more preferably 50,000 to 1,200,000.

[0487] The VdF / fluoroalkyl vinyl ether copolymer contains VdF units and fluoroalkyl vinyl ether units. The VdF unit content is preferably 80.0 to 98.0 mol%, more preferably 83.0 mol% or more, even more preferably 85.0 mol% or more, more preferably 97.0 mol% or less, and even more preferably 96.0 mol% or less, relative to the total monomer units of the VdF / fluoroalkyl vinyl ether copolymer. The fluoroalkyl vinyl ether unit content is preferably 20.0 to 2.0 mol%, more preferably 17.0 mol% or less, even more preferably 15.0 mol% or less, more preferably 3.0 mol% or more, and even more preferably 4.0 mol% or more, relative to the total monomer units of the VdF / fluoroalkyl vinyl ether copolymer.

[0488] The VdF / fluoroalkyl vinyl ether copolymer may contain units based on monomers copolymerizable with VdF and fluoroalkyl vinyl ether (excluding VdF and fluoroalkyl vinyl ether), in addition to VdF units and fluoroalkyl vinyl ether units. From the viewpoint of resistance to electrolyte swelling, the content of units based on monomers copolymerizable with VdF and fluoroalkyl vinyl ether is preferably 3.0 mol% or less relative to the total monomer units of the VdF / fluoroalkyl vinyl ether copolymer.

[0489] Monomers copolymerizable with VdF and fluoroalkyl vinyl ethers include the fluorinated monomers and non-fluorinated monomers mentioned above. Among the monomers copolymerizable with VdF and fluoroalkyl vinyl ethers, at least one selected from the group consisting of fluorinated monomers and polar group-containing monomers is preferred, at least one selected from the group consisting of TFE, 2,3,3,3-tetrafluoropropene and monomer (4) is more preferred, and monomer (50) is even more preferred.

[0490] The weight-average molecular weight (in polystyrene substitution) of the VdF / fluoroalkyl vinyl ether copolymer is preferably 50,000 to 2,000,000, more preferably 8,000 to 1,700,000, and even more preferably 1,000,000 to 1,500,000.

[0491] The number-average molecular weight (on a polystyrene basis) of the VdF / fluoroalkyl vinyl ether copolymer is preferably 35,000 to 1,400,000, more preferably 40,000 to 1,300,000, and even more preferably 50,000 to 1,200,000.

[0492] The binder may also preferably further contain polyvinylidene fluoride (PVdF). PVdF is a polymer containing VdF units and is a polymer different from the fluorine-containing copolymer described above. PVdF may be a VdF homopolymer consisting only of VdF units, or it may be a polymer containing VdF units and units based on monomers copolymerizable with VdF.

[0493] In the above-mentioned PVdF, the monomer copolymerizable with VdF is preferably a monomer different from tetrafluoroethylene (TFE). That is, it is preferable that PVdF does not contain TFE units.

[0494] In the above PVdF, monomers copolymerizable with VdF include fluorinated monomers and non-fluorinated monomers, with fluorinated monomers being preferred. Examples of fluorinated monomers include vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene (CTFE), fluoroalkyl vinyl ether, hexafluoropropylene (HFP), (perfluoroalkyl)ethylene, 2,3,3,3-tetrafluoropropene, and trans-1,3,3,3-tetrafluoropropene. Examples of non-fluorinated monomers include ethylene and propylene.

[0495] In the above PVdF, the monomer copolymerizable with VdF is preferably at least one fluorinated monomer selected from the group consisting of CTFE, fluoroalkyl vinyl ether, HFP, and 2,3,3,3-tetrafluoropropene, and more preferably at least one fluorinated monomer selected from the group consisting of CTFE, HFP, and fluoroalkyl vinyl ether.

[0496] In the above PVdF, the content of monomer units copolymerizable with VdF is preferably 0 to 5.0 mol%, more preferably 0 to 3.0 mol%, relative to the total monomer units. In the above PVdF, the content of fluorinated monomer units copolymerizable with VdF is preferably less than 5.0 mol%, more preferably less than 3.0 mol%, and even more preferably less than 1.0 mol%, relative to the total monomer units.

[0497] In this disclosure, the composition of PVdF is, for example, 19 It can be measured by F-NMR.

[0498] The above PVdF may have a polar group. The above polar group is not particularly limited as long as it is a polar functional group, but at least one selected from the group consisting of carbonyl group-containing groups, epoxy groups, hydroxyl groups, sulfonic acid groups, sulfate groups, phosphoric acid groups, amino groups, amide groups, and alkoxy groups is preferred, at least one selected from the group consisting of carbonyl group-containing groups, epoxy groups, and hydroxyl groups is more preferred, and a carbonyl group-containing group is even more preferred. The above hydroxyl group does not include hydroxyl groups that constitute part of the above carbonyl group-containing group. Furthermore, the above amino group is a monovalent functional group obtained by removing hydrogen from ammonia, a primary or secondary amine.

[0499] The carbonyl group-containing group mentioned above is a functional group having a carbonyl group (-C(=O)-). The carbonyl group-containing group is preferably a group represented by the general formula: -COOR (where R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group) or a carboxylic acid anhydride group, and more preferably a group represented by the general formula: -COOR. The number of carbon atoms in the alkyl group and hydroxyalkyl group is preferably 1 to 16, more preferably 1 to 6, and even more preferably 1 to 3. Specific examples of groups represented by the general formula: -COOR include -COOCH2CH2OH, -COOCH2CH(CH3)OH, -COOCH(CH3)CH2OH, -COOH, -COOCH3, -COOC2H5, etc. If the group represented by the general formula: -COOR is -COOH or contains -COOH, then -COOH may be a carboxylate salt such as a metal carboxylate salt or an ammonium carboxylate salt.

[0500] Furthermore, the carbonyl group-containing group may also be a group represented by the general formula: -X-COOR (where X is composed of 2 to 15 main atoms, and the molecular weight of the atomic group represented by X is preferably 350 or less. R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group). The number of carbon atoms in the alkyl group and hydroxyalkyl group is preferably 1 to 16, more preferably 1 to 6, and even more preferably 1 to 3.

[0501] The amide group described above is preferably a group represented by the general formula: -CO-NRR' (where R and R' independently represent a hydrogen atom or a substituted or unsubstituted alkyl group), or a bond represented by the general formula: -CO-NR”- (where R represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted phenyl group).

[0502] The above polar group can be introduced into PVdF by polymerizing VdF with a monomer having the above polar group (hereinafter referred to as a polar group-containing monomer), or by reacting PVdF with a compound having the above polar group. However, from the viewpoint of productivity, polymerizing VdF with the above polar group-containing monomer is preferable.

[0503] Polymerizing VdF with the polar group-containing monomer yields PVdF containing VdF units and polar group-containing monomer units. In other words, PVdF preferably contains the polar group-containing monomer units. The content of the polar group-containing monomer units is preferably 0.001 to 5.0 mol%, more preferably 0.01 to 3.0 mol%, and even more preferably 0.10 to 1.5 mol%, relative to the total monomer units.

[0504] In this disclosure, the content of polar group-containing monomer units in PVdF can be measured, for example, by acid-base titration of the acid group when the polar group is an acid group such as a carboxylic acid.

[0505] The above polar group-containing monomers include hydroxyalkyl (meth)acrylates such as hydroxyethyl acrylate and 2-hydroxypropyl acrylate; unsaturated monobasic acids such as (meth)acrylic acid, crotonic acid, vinyl acetic acid (3-butenoic acid), 3-pentenoic acid, 4-pentenoic acid, 3-hexenoic acid, and 4-heptenoic acid; unsaturated dibasic acids such as maleic acid, maleic anhydride, citraconic acid, and citraconic anhydride; alkylidenemalonic acid esters such as dimethyl methylidenemalonate; vinyl carboxyalkyl ethers such as vinyl carboxymethyl ether and vinyl carboxyethyl ether; carboxyalkyl (meth)acrylates such as 2-carboxyethyl acrylate and 2-carboxyethyl methacrylate; acrylo Examples include (meth)acryloyloxyalkyl dicarboxylic acid esters such as yloxyethyl succinic acid, methacryloyloxyethyl succinic acid, acryloyloxyethyl phthalic acid, acryloyloxypropyl succinic acid, and methacryloyloxyethyl phthalic acid; monoesters of unsaturated dibasic acids such as monomethyl maleate, monoethyl maleate, monomethyl citraconate, and monoethyl citraconate; and the like.

[0506] When introducing the polar group into PVdF by reacting PVdF with the compound having the polar group, the compound having the polar group can be a monomer containing the polar group, or a silane-based coupling agent or titanate-based coupling agent having a group reactive with PVdF and a hydrolyzable group. The hydrolyzable group is preferably an alkoxy group. When using a coupling agent, it can be added to PVdF by reacting it with PVdF that has been dissolved or swollen in a solvent.

[0507] Alternatively, PVdF can be obtained by partially defluorinating PVdF with a base, and then further reacting the partially defluorinated PVdF with an oxidizing agent. Examples of the oxidizing agents include hydrogen peroxide, hypochlorite, palladium halide, chromium halide, alkali metal permanganate, peracid compounds, alkyl peroxide, and alkyl persulfate.

[0508] The VdF unit content of PVdF is preferably more than 95.0 mol%, more preferably more than 97.0 mol%, and even more preferably more than 99.0 mol%, relative to the total monomer units. Furthermore, the VdF unit content of PVdF is preferably 95.0 to 99.999 mol%, more preferably 97.0 mol% or more, even more preferably 98.5 mol% or more, more preferably 99.99 mol% or less, and even more preferably 99.90 mol% or less, relative to the total monomer units.

[0509] The weight-average molecular weight (polystyrene equivalent) of PVdF is preferably 50,000 to 3,000,000, more preferably 80,000 or more, even more preferably 100,000 or more, particularly preferably 200,000 or more, more preferably 2,400,000 or less, even more preferably 2,200,000 or less, and particularly preferably 2,000,000 or less. The weight-average molecular weight can be measured by gel permeation chromatography (GPC) using N,N-dimethylformamide as the solvent. The weight-average molecular weight of PVdF may also be 1,000,000 or more, or 1,500,000 or more.

[0510] The number-average molecular weight (polystyrene equivalent) of PVdF is preferably 20,000 to 1,500,000, more preferably 40,000 or more, even more preferably 70,000 or more, particularly preferably 140,000 or more, more preferably 1,400,000 or less, even more preferably 1,200,000 or less, and particularly preferably 1,100,000 or less. The number-average molecular weight can be measured using gel permeation chromatography (GPC) with dimethylformamide as the solvent.

[0511] The melting point of PVdF is preferably 100 to 240°C. This melting point can be determined using a differential scanning calorimetry (DSC) device as the temperature corresponding to the maximum value in the heat of fusion curve when the temperature is increased at a rate of 10°C / min.

[0512] When the binder contains PVdF and a fluorine-containing copolymer, the mass ratio of PVdF to the fluorine-containing copolymer in the binder (PVdF / fluorine-containing copolymer) is preferably 99 / 1 to 1 / 99, more preferably 97 / 3 to 3 / 97, even more preferably 95 / 5 to 5 / 95, especially preferably 90 / 10 to 10 / 90, particularly preferably 85 / 15 to 15 / 85, and most preferably 80 / 20 to 40 / 60.

[0513] The binder may contain other polymers in addition to PVdF and fluorine-containing copolymers. Examples of other polymers include polymethacrylate, polymethyl methacrylate, polyacrylonitrile, polyimide, polyamide, polyamide-imide, polycarbonate, styrene rubber, and butadiene rubber.

[0514] The fluorine-containing copolymer content in the binder is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, particularly preferably 10% by mass or more, most preferably 15% by mass or more, and may be 100% by mass or less, relative to the mass of the binder.

[0515] The binder content in the negative electrode mixture prepared for forming the negative electrode material layer is preferably 0.1 to 20% by mass, more preferably 0.2 to 10% by mass, and even more preferably 0.5 to 7% by mass, relative to the mass of solid content in the negative electrode mixture.

[0516] (solvent) The above-mentioned negative electrode mixture preferably contains a solvent. Examples of solvents include water or an organic solvent. An organic solvent is preferred because it significantly reduces the possibility of moisture remaining in the negative electrode material layer when the negative electrode mixture is used to form the negative electrode material layer.

[0517] Examples of organic solvents include nitrogen-containing organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and dimethylformamide; ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone; ester solvents such as ethyl acetate and butyl acetate; ether solvents such as tetrahydrofuran and dioxane; β-alkoxypropionamides such as β-methyl-N,N-dimethylpropionamide, β-n-butoxy-N,N-dimethylpropionamide, and β-n-hexyloxy-N,N-dimethylpropionamide; and general-purpose low-boiling point organic solvents such as mixed solvents thereof.

[0518] As an organic solvent, a solvent represented by general formula (60) can also be used.

[0519] General formula (60): [ka] (In the formula, R 1 , R 2 and R 3 R is independently an H or monovalent substituent, however R 1 , R 2 and R 3 The total number of carbon atoms is 6 or more, R 1 , R 2 and R 3 At least one of them is an organic group having a carbonyl group. 1 , R 2 and R 3 (Two of these may be joined together to form a ring.)

[0520] The solvent represented by general formula (60) is preferably at least one selected from the group consisting of 3-methoxy-N,N-dimethylpropanamide, N-ethyl-2-pyrrolidone (NEP), N-butyl-2-pyrrolidone (NBP), acryloylmorpholine, N-cyclohexyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, 3-butoxy-N,N-dimethylpropanamide, N,N,N',N'-tetraethylurea, N,N-dimethylacetoacetamide, N-octyl-2-pyrrolidone, and N,N-diethylacetamide.

[0521] As a solvent, water is preferred, or at least one selected from the group consisting of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and a solvent represented by general formula (1), due to its excellent coating properties. N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, 3-methoxy-N,N-dimethylpropanamide, N-ethyl-2-pyrrolidone (NEP), N-butyl-2-pyrrolidone (NBP), acryloylmorpholine, N-cyclohexyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, 3-butoxy- At least one selected from the group consisting of N,N-dimethylpropanamide, N,N,N',N'-tetraethylurea, N,N-dimethylacetacetamide, N-octyl-2-pyrrolidone, and N,N-diethylacetamide is more preferred, at least one selected from the group consisting of N-methyl-2-pyrrolidone, N,N-dimethylacetamide, 3-methoxy-N,N-dimethylpropanamide, N-ethyl-2-pyrrolidone, and N-butyl-2-pyrrolidone is even more preferred, and at least one selected from the group consisting of N-methyl-2-pyrrolidone and N,N-dimethylacetamide is particularly preferred.

[0522] The amount of solvent in the negative electrode mixture is determined considering factors such as its applicability to the current collector and its ability to form a thin film after drying. Typically, the ratio of binder to solvent is 0.5:99.5 to 20:80 by mass.

[0523] (Other ingredients) The negative electrode mixture of this disclosure may further contain other components such as leveling agents and reinforcing agents.

[0524] The above-mentioned negative electrode mixture can be prepared, for example, by mixing a binder and a solvent, and then adding a negative electrode active material to the resulting mixture and mixing further. The obtained negative electrode mixture is then uniformly applied to a current collector such as a metal foil or metal mesh, dried, and pressed as necessary to form a thin negative electrode material layer on the current collector, thus creating a thin-film electrode. Alternatively, the negative electrode active material and binder may be mixed first, and then the solvent may be added to prepare the negative electrode mixture.

[0525] The negative electrode of this disclosure comprises a negative electrode material layer and a current collector. The negative electrode material layer is formed using the negative electrode mixture described above and may be provided on one side of the current collector or on both sides.

[0526] Examples of current collectors for the negative electrode of this disclosure include metal foils or metal meshes such as iron, stainless steel, copper, aluminum, nickel, and titanium, as well as carbon materials such as carbon cloth and carbon paper, with copper foil being preferred.

[0527] The negative electrode of this disclosure can be suitably manufactured by a manufacturing method in which the negative electrode mixture of this disclosure is applied to a current collector. After applying the negative electrode mixture, the coating film may be dried, optionally heat-treated, and the resulting dried coating film may be pressed.

[0528] Examples of current collector shapes include metal foil, metal cylinders, metal coils, metal plates, expanded metal, punched metal, and foamed metal in the case of metal materials, and carbon plates, carbon thin films, and carbon cylinders in the case of carbon materials. Of these, metal foil is preferred. The thin film may be formed in a mesh shape as appropriate. The thickness of the thin film is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the thin film is thinner than this range, it may lack the necessary strength as a current collector. Conversely, if the thin film is thicker than this range, its handling may be impaired.

[0529] The thickness of the negative electrode plate is designed to match the positive electrode plate used and is not particularly limited, however, the thickness of the composite layer after subtracting the thickness of the core metal foil is usually 15 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and usually 300 μm or less, preferably 280 μm or less, more preferably 250 μm or less.

[0530] <Positive electrode> The positive electrode preferably consists of a positive electrode active material layer containing positive electrode active material and a current collector.

[0531] The positive electrode active material is not particularly limited as long as it is electrochemically capable of intercalating and releasing alkali metal ions, but for example, a material containing an alkali metal and at least one transition metal is preferred. Specific examples include alkali metal-containing transition metal composite oxides and alkali metal-containing transition metal phosphate compounds. Among these, alkali metal-containing transition metal composite oxides that produce high voltage are particularly preferred as the positive electrode active material. Examples of alkali metal ions include lithium ions, sodium ions, potassium ions, etc. In a preferred embodiment, the alkali metal ion may be a lithium ion. That is, in this embodiment, the alkali metal ion secondary battery is a lithium ion secondary battery.

[0532] Examples of the alkali metal-containing transition metal composite oxides mentioned above include: Formula (3-1): MaMn 2-b M 1 b O4 (wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0.9 ≤ a; 0 ≤ b ≤ 1.5; M) 1 Lithium manganese spinel composite oxide represented by at least one metal selected from the group consisting of Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge. Formula (3-2): MNi 1-c M 2 c O2 (wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0 ≤ c ≤ 0.5; M 2 (This refers to a lithium-nickel composite oxide represented by at least one metal selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge), or Formula (3-3):MCo 1-d M 3 d O2 (wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0 ≤ d ≤ 0.5; M 3 (This refers to at least one metal selected from the group consisting of Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge.) Examples include lithium-cobalt composite oxides represented by . In the above, M is preferably one metal selected from the group consisting of Li, Na, and K, more preferably Li or Na, and even more preferably Li.

[0533] In particular, MCoO2, MMnO2, MNiO2, MMn2O4, and MNi are used because they offer high energy density and can provide high-output secondary batteries. 0.8 Co 0.15 Al 0.05 O2, or MNi 1 / 3 Co 1 / 3 Mn1 / 3 O2 is preferred, and it is preferable that the compound is represented by the following formula (3-4). MNi h Co i Mn j M 5 k O2(3-4) (In the formula, M is M 5 (where represents at least one element selected from the group consisting of Fe, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge, and (h+i+j+k)=1.0, 0≦h≦1.0, 0≦i≦1.0, 0≦j≦1.5, and 0≦k≦0.2.)

[0534] Examples of the alkali metal-containing transition metal phosphate compounds mentioned above include the following formula (70): M e M 4 f (PO4) g (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K, M 4 Herein, M represents at least one selected from the group consisting of V, Ti, Cr, Mn, Fe, Co, Ni, and Cu, and is a compound represented by (0.5 ≤ e ≤ 3, 1 ≤ f ≤ 2, 1 ≤ g ≤ 3). In the above, M is preferably one metal selected from the group consisting of Li, Na, and K, more preferably Li or Na, and even more preferably Li.

[0535] Preferred transition metals for lithium-containing transition metal phosphate compounds include V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. Specific examples include iron phosphates such as LiFePO4, Li3Fe2(PO4)3, and LiFeP2O7, cobalt phosphates such as LiCoPO4, and those in which some of the transition metal atoms that make up the main component of these lithium transition metal phosphate compounds are substituted with other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, and Si. The lithium-containing transition metal phosphate compound described above is preferably one having an olivine-type structure.

[0536] Examples of other positive electrode active materials include MFePO4, MNi 0.8 Co 0.2 O2, M 1.2 Fe 0.4 Mn 0.4 O2, MNi 0.5 Mn 1.5 O4, MV3O6, M2MnO3 and the like. In particular, positive electrode active materials such as MNi 0.5 Mn 1.5 O4 are preferable in that their crystal structures do not collapse even when a secondary battery is operated at a voltage exceeding 4.4V or a voltage of 4.6V or higher. Therefore, an electrochemical device such as a secondary battery using the positive electrode material containing the positive electrode active materials exemplified above is less likely to suffer from a decrease in residual capacity and a less likely to change in resistance increase rate even when stored at high temperature, and is also preferable because the battery performance does not deteriorate even when operated at a high voltage.

[0537] Examples of other positive electrode active materials also include solid solution materials of M2MnO3 and MM 6 O2 (wherein M is at least one metal selected from the group consisting of Li, Na and K, and M 6 is a transition metal such as Co, Ni, Mn, or Fe), and the like.

[0538] Examples of the solid solution material include alkali metal manganese oxides represented by the general formula Mx[Mn(1-y)M 7 y]Oz. Here, M in the formula is at least one metal selected from the group consisting of Li, Na and K, and M 7 consists of at least one metal element other than M and Mn, and contains, for example, one or two or more elements selected from the group consisting of Co, Ni, Fe, Ti, Mo, W, Cr, Zr and Sn. In addition, the values of x, y, and z in the formula are in the ranges of 1<x<2, 0≦y<1, and 1.5<z<3. Among them, Li 1.2 Mn 0.5 Co 0.14 Ni 0.14Manganese-containing solid solution materials, such as Li2MnO3 (like O2) with LiNiO2 or LiCoO2 solid solution in a solid solution, are preferred because they can provide alkali metal ion secondary batteries with high energy density.

[0539] Furthermore, including lithium phosphate in the positive electrode active material is preferable because it improves continuous charging characteristics. There are no restrictions on the use of lithium phosphate, but it is preferable to use a mixture of the positive electrode active material and lithium phosphate. The amount of lithium phosphate used is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, relative to the total amount of the positive electrode active material and lithium phosphate, with an upper limit of preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less.

[0540] Furthermore, a positive electrode active material may be used in which a substance of a different composition is attached to its surface. Examples of surface-attached substances include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0541] 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 and impregnating them into the positive electrode active material, followed by drying; dissolving or suspending a surface-adhering substance precursor in a solvent and impregnating it into the positive electrode active material, then reacting it by heating, etc.; or adding it to the positive electrode active material precursor and simultaneously firing it. In addition, when attaching carbon, a method of mechanically attaching carbonaceous material afterwards, for example in the form of activated carbon, can also be used.

[0542] The amount of surface-adhered material is preferably 0.1 ppm or more, more preferably 1 ppm or more, and even more preferably 10 ppm or more, relative to the positive electrode active material by mass, with an upper limit of preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less. The surface-adhered material can suppress the oxidation reaction of the electrolyte on the surface of the positive electrode active material, thereby improving battery life. However, if the amount of adhesion is too small, the effect will not be fully realized, and if it is too large, it may hinder the movement of lithium ions in and out, potentially increasing resistance.

[0543] The particle shapes of the positive electrode active material can include conventionally used shapes such as lumpy, polyhedral, spherical, ellipsoidal, plate-like, needle-like, and columnar. Furthermore, primary particles may aggregate to form secondary particles.

[0544] The tap density of the positive electrode active material is preferably 0.5 g / cm³. 3 More preferably 0.8 g / cm³ 3 More preferably 1.0 g / cm³ 3 The above is the case. If the tap density of the positive electrode active material falls below the above lower limit, the amount of dispersion medium required during the formation of the positive electrode active material layer increases, as does the amount of conductive material and binder required, which may restrict the filling rate of the positive electrode active material into the positive electrode active material layer and thus limit the battery capacity. By using a composite oxide powder with a high tap density, a high-density positive electrode active material layer can be formed. Generally, a higher tap density is preferable, and there is no particular upper limit, but if it is too high, the diffusion of lithium ions using the electrolyte as a medium within the positive electrode active material layer becomes the rate-limiting step, which may lead to a decrease in load characteristics. Therefore, the upper limit is preferably 4.0 g / cm³. 3 More preferably, 3.7 g / cm³ 3 More preferably, 3.5 g / cm³ 3 The following applies: In this disclosure, the tap density is defined as the powder packing density (tap density) g / cm³ obtained when 5-10 g of positive electrode active material powder is placed in a 10 ml glass graduated cylinder and tapped 200 times with a stroke of approximately 20 mm. 3 We will seek it as follows.

[0545] The median diameter d50 of the positive electrode active material particles (or secondary particle diameter if primary particles aggregate to form secondary particles) is preferably 0.3 μm or more, more preferably 0.5 μm or more, even more preferably 0.8 μm or more, and most preferably 1.0 μm or more. It is also preferably 30 μm or less, more preferably 27 μm or less, even more preferably 25 μm or less, and most preferably 22 μm or less. If it falls below the lower limit, it may not be possible to obtain a high tap density product, and if it exceeds the upper limit, the diffusion of lithium within the particles will take longer, which may lead to a decrease in battery performance or cause problems such as streaking when creating the positive electrode of the battery, i.e., when the active material and conductive material or binder are slurryed with a solvent and applied as a thin film. Here, by mixing two or more of the above positive electrode active materials having different median diameters d50, the packing performance during positive electrode creation can be further improved.

[0546] In this disclosure, the median diameter d50 is measured using a known laser diffraction / scattering particle size distribution analyzer. When using the HORIBA LA-920 as the particle size distribution analyzer, a 0.1% by mass aqueous solution of sodium hexametaphosphate is used as the dispersion medium during measurement, and the measurement is performed after ultrasonic dispersion for 5 minutes with the measurement refractive index set to 1.24.

[0547] When primary particles aggregate to form secondary particles, the average primary particle diameter of the positive electrode active material is preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. The upper limit is preferably 5 μm or less, more preferably 4 μm or less, even more preferably 3 μm or less, and most preferably 2 μm or less. Exceeding the upper limit makes it difficult to form spherical secondary particles, which can adversely affect powder packing properties and may lead to a significant decrease in specific surface area, potentially degrading battery performance such as output characteristics. Conversely, below the lower limit usually results in underdeveloped crystals, which can cause problems such as poor reversibility of charge and discharge.

[0548] In this disclosure, the primary particle diameter is measured by observation using a scanning electron microscope (SEM). Specifically, it is determined by taking a photograph at 10,000x magnification, finding the longest value of the intercept between the left and right boundaries of the primary particle relative to a horizontal line for any 50 primary particles, and taking the average value.

[0549] The BET specific surface area of ​​the positive electrode active material is preferably 0.1 m². 2 / g or more, more preferably 0.2m 2 / g or more, more preferably 0.3m 2 The value is 1 / g or more, and the upper limit is preferably 50m 2 / g or less, more preferably 40m 2 / g or less, more preferably 30m 2 It is less than / g. If the BET specific surface area is smaller than this range, battery performance tends to decrease, and if it is larger, it becomes difficult to increase the tap density, which can cause problems with coating when forming the positive electrode active material layer.

[0550] In this disclosure, the BET specific surface area is defined as the value measured by a nitrogen adsorption BET single-point method using a gas flow method, after pre-drying the sample at 150°C for 30 minutes under nitrogen flow using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.), and then using a nitrogen-helium mixed gas that has been precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3.

[0551] When the secondary battery of this disclosure is used as a large lithium-ion secondary battery for hybrid vehicles or distributed power sources, high output is required, so it is preferable that the particles of the positive electrode active material consist mainly of secondary particles. The positive electrode active material particles preferably contain 0.5 to 7.0 volume percent of fine particles with an average secondary particle diameter of 40 μm or less and an average primary particle diameter of 1 μm or less. By including fine particles with an average primary particle diameter of 1 μm or less, the contact area with the electrolyte is increased, which allows for faster diffusion of lithium ions between the electrode and the electrolyte, and as a result, the output performance of the battery can be improved.

[0552] For the production of positive electrode active materials, general methods for producing inorganic compounds are used. In particular, various methods can be considered for producing spherical or ellipsoidal active materials. For example, a method can be used in which transition metal raw materials are dissolved or pulverized and dispersed in a solvent such as water, the pH is adjusted while stirring to create and recover spherical precursors, these are dried as needed, and then a Li source such as LiOH, Li2CO3, or LiNO3 is added and calcined at a high temperature to obtain the active material.

[0553] For the manufacture of the positive electrode, the positive electrode active material may be used alone, or two or more materials with different compositions may be used in any combination or ratio. In this case, a preferred combination is LiCoO2 and LiNi 0.33 Co 0.33 Mn 0.33 Examples include combinations with LiMn2O4 such as O2, or in which part of the Mn is substituted with other transition metals, or combinations with LiCoO2, or in which part of the Co is substituted with other transition metals.

[0554] The content of the above-mentioned positive electrode active material is preferably 50 to 99.5% by mass of the positive electrode mixture, and more preferably 80 to 99% by mass, in terms of high battery capacity. Furthermore, the content of the positive electrode active material in the positive electrode active material layer is preferably 80% by mass or more, more preferably 82% by mass or more, and particularly preferably 84% by mass or more. The upper limit is preferably 99% by mass or less, and more preferably 98% by mass or less. If the content of the positive electrode active material in the positive electrode active material layer is too low, the electrical capacitance may be insufficient. Conversely, if the content is too high, the strength of the positive electrode may be insufficient.

[0555] The above positive electrode mixture preferably further contains a binder, a thickener, a conductive material, and a solvent. As the binder mentioned above, any material can be used as long as it is safe for the solvent and electrolyte used during electrode manufacturing. Examples include: resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, chitosan, alginic acid, polyacrylic acid, polyimide, cellulose, and nitrocellulose; rubbery polymers such as SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluororubber, NBR (acrylonitrile-butadiene rubber), and ethylene-propylene rubber; styrene-butadiene-styrene block copolymer or its hydrogenated additives; and EPDM (ethylene methyl phosphate). Examples include thermoplastic elastomer polymers such as ethylene-propylene-diene terpolymer, styrene-ethylene-butadiene-styrene copolymer, styrene-isoprene-styrene block copolymer, or hydrogenated versions thereof; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, and propylene-α-olefin copolymer; fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride copolymer, and tetrafluoroethylene-ethylene copolymer; and polymer compositions having ionic conductivity for alkali metal ions (especially lithium ions). These may be used individually or in any combination and ratio of two or more types.

[0556] The binder content, as a percentage of the positive electrode active material layer, is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 1.5% by mass or more, and usually 80% by mass or less, preferably 60% by mass or less, more preferably 40% by mass or less, and most preferably 10% by mass or less. If the binder content is too low, the positive electrode active material cannot be sufficiently held, resulting in insufficient mechanical strength of the positive electrode and potentially degrading battery performance such as cycle characteristics. On the other hand, if it is too high, it may lead to a decrease in battery capacity and conductivity.

[0557] Examples of the thickening agents mentioned above include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, starch oxide, phosphated starch, casein, polyvinylpyrrolidone, and salts thereof. One of these may be used alone, or two or more may be used in any combination and ratio.

[0558] The ratio of the thickener to the active material is usually 0.1% by mass or more, preferably 0.2% by mass or more, more preferably 0.3% by mass or more, and usually within the range of 5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or less. If it is below this range, the coating properties may be significantly reduced. If it is above this range, the proportion of active material in the positive electrode active material layer will decrease, which may lead to problems such as a decrease in battery capacity or an increase in resistance between positive electrode active materials.

[0559] Any known conductive material can be used as the conductive material mentioned above. Specific examples include metallic materials such as copper and nickel, graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, and carbon materials such as needle coke, carbon nanotubes, fullerenes, and amorphous carbon such as VGCF. These materials may be used individually or in any combination and ratio of two or more materials. The conductive material is typically contained in the positive electrode active material layer in an amount of 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more, and typically 50% by mass or less, preferably 30% by mass or less, more preferably 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. Conversely, if the content is higher than this range, the battery capacity may decrease.

[0560] The solvent used to form the slurry is not particularly limited in type, as long as it is capable of dissolving or dispersing the positive electrode active material, conductive material, binder, and thickener used as needed. Either an aqueous solvent or an organic solvent may be used. Examples of aqueous solvents include water and mixtures of alcohol and water. Examples of organic solvents include aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide.

[0561] Suitable materials for the positive electrode current collector include metals such as aluminum, titanium, tantalum, stainless steel, and nickel, or their alloys; and carbon materials such as carbon cloth and carbon paper. Among these, metal materials, particularly aluminum or its alloys, are preferred.

[0562] Examples of current collector shapes include metal foil, metal cylinders, metal coils, metal plates, expanded metal, punched metal, and foamed metal in the case of metal materials, and carbon plates, carbon thin films, and carbon cylinders in the case of carbon materials. Of these, metal foil is preferred. The thin film may be formed in a mesh shape as appropriate. The thickness of the thin film is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the thin film is thinner than this range, it may lack the necessary strength as a current collector. Conversely, if the thin film is thicker than this range, its handling may be impaired.

[0563] Furthermore, it is preferable that a conductive additive is applied to the surface of the current collector, from the viewpoint of reducing the electrical contact resistance between the current collector and the positive electrode active material layer. Examples of conductive additives include carbon and precious metals such as gold, platinum, and silver.

[0564] The ratio of the thickness of the current collector to the thickness of the positive electrode active material layer is not particularly limited, but the value of (thickness of the positive electrode active material layer on one side immediately before electrolyte injection) / (thickness of the current collector) is preferably 20 or less, more preferably 15 or less, most preferably 10 or less, and also preferably 0.5 or more, more preferably 0.8 or more, most preferably 1 or more. If it exceeds this range, the current collector may generate heat due to Joule heating during high current density charging and discharging. If it falls below this range, the volume ratio of the current collector to the positive electrode active material increases, which may reduce the battery capacity.

[0565] The positive electrode can be manufactured by conventional methods. For example, the positive electrode active material can be mixed with the aforementioned binder, thickener, conductive material, solvent, etc., to form a slurry-like positive electrode mixture, which can then be applied to a current collector, dried, and pressed to increase its density.

[0566] The above-mentioned densification can be achieved by hand pressing, roller pressing, etc. The density of the positive electrode active material layer is preferably 1.5 g / cm³. 3 More preferably 2 g / cm³ 3 More preferably 2.2 g / cm³ 3 The above is true, and preferably 5 g / cm³ 3 More preferably, 4.5 g / cm³ 3 More preferably, 4 g / cm³ 3 The range is as follows. If the range is exceeded, the penetration of the electrolyte near the current collector / active material interface decreases, which can reduce charge / discharge characteristics, especially at high current densities, and may prevent high output from being obtained. Conversely, if the range is below this, the conductivity between the active materials decreases, increasing battery resistance and potentially preventing high output from being obtained.

[0567] When using the electrolyte of this disclosure, from the viewpoint of increasing high power output and stability at high temperatures, it is preferable that the area of ​​the positive electrode active material layer be large relative to the outer surface area of ​​the battery casing. Specifically, it is preferable that the sum of the electrode areas of the positive electrode be 15 times or more in area ratio to the surface area of ​​the secondary battery casing, and more preferably 40 times or more. The outer surface area of ​​the battery casing refers to the total area calculated from the length, width, and thickness of the case portion filled with the power generation elements, excluding the terminal protrusions, in the case of a bottomed rectangular shape. In the case of a bottomed cylindrical shape, it is the geometric surface area approximating the case portion filled with the power generation elements, excluding the terminal protrusions, as a cylinder. The sum of the electrode areas of the positive electrode refers to the geometric surface area of ​​the positive electrode mixture layer facing the mixture layer containing the negative electrode active material, and in a structure in which positive electrode mixture layers are formed on both sides via a current collector foil, it refers to the sum of the areas calculated separately for each surface.

[0568] The thickness of the positive electrode plate is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the composite layer, after subtracting the thickness of the metal foil of the core material, is preferably 10 μm or more, more preferably 20 μm or more, and preferably 500 μm or less, and more preferably 450 μm or less, as a lower limit for one side of the current collector.

[0569] Furthermore, a positive electrode plate with a substance of a different composition attached to its surface may also be used. Examples of surface-attached substances include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0570] <Separator> The secondary battery of this disclosure preferably further comprises a separator. The material and shape of the separator described above are not particularly limited as long as they are stable in the electrolyte and have excellent liquid retention properties, and known materials can be used. In particular, it is preferable to use a porous sheet or nonwoven fabric in the form of a material that is stable in the electrolyte of this disclosure, such as a resin, glass fiber, or inorganic material, and has excellent liquid retention properties.

[0571] As materials for the resin and glass fiber separator, for example, polyolefins such as polyethylene and polypropylene, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, and glass filters can be used. These materials, such as polypropylene / polyethylene two-layer films and polypropylene / polyethylene / polypropylene three-layer films, may be used individually or in any combination and ratio of two or more. In particular, the separator is preferably a porous sheet or nonwoven fabric made from polyolefins such as polyethylene and polypropylene, as it has good electrolyte permeability and shut-off effect.

[0572] The thickness of the separator is arbitrary, but is usually 1 μm or more, preferably 5 μm or more, more preferably 8 μm or more, and usually 50 μm or less, preferably 40 μm or less, and more preferably 30 μm or less. If the separator is too thin compared to the above range, the insulating properties and mechanical strength may decrease. If it is too thick compared to the above range, not only may the battery performance such as rate characteristics decrease, but the energy density of the electrolyte battery as a whole may decrease.

[0573] Furthermore, when using porous materials such as porous sheets or nonwoven fabrics as separators, the porosity of the separator is arbitrary, but is usually 20% or more, preferably 35% or more, more preferably 45% or more, and usually 90% or less, preferably 85% or less, and more preferably 75% or less. If the porosity is too small compared to the above range, the film resistance tends to increase and the rate characteristics tend to deteriorate. Also, if it is too large compared to the above range, the mechanical strength of the separator tends to decrease and the insulating properties tend to deteriorate.

[0574] Furthermore, while the average pore size of the separator is arbitrary, it is usually 0.5 μm or less, preferably 0.2 μm or less, and usually 0.05 μm or more. If the average pore size exceeds the above range, short circuits are more likely to occur. Conversely, if it falls below the above range, the film resistance increases and the rate characteristics may deteriorate.

[0575] On the other hand, inorganic materials such as oxides of alumina and silicon dioxide, nitrides of aluminum nitride and silicon nitride, and sulfates of barium sulfate and calcium sulfate are used, and these are available in particulate or fibrous form.

[0576] In terms of form, thin films such as nonwoven fabrics, woven fabrics, and microporous films are used. In the thin film form, those with a pore size of 0.01 to 1 μm and a thickness of 5 to 50 μm are preferably used. In addition to the above independent thin film forms, a separator can be used in which a composite porous layer containing the above inorganic particles is formed on the surface of the positive electrode and / or negative electrode using a resin binder. For example, a porous layer can be formed on both sides of the positive electrode using alumina particles with a 90% particle size of less than 1 μm and a fluororesin as a binder.

[0577] <Battery design> The electrode group may be either a laminated structure in which the positive electrode plate and the negative electrode plate are separated by the separator, or a structure in which the positive electrode plate and the negative electrode plate are spirally wound around the separator. 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, preferably 50% or more, and usually 90% or less, preferably 80% or less.

[0578] If the electrode group occupancy rate falls below the above range, the battery capacity will decrease. Conversely, if it exceeds the above range, the void space is small, and the internal pressure increases due to the expansion of materials and the vapor pressure of the electrolyte liquid component as the battery heats up. This reduces various characteristics of the battery, such as its charge / discharge cycle performance and high-temperature storage capabilities, and may even cause the gas release valve that releases the internal pressure to activate.

[0579] The current collection structure is not particularly limited, but in order to more effectively achieve improved high-current-density charge-discharge characteristics with the electrolyte of this disclosure, it is preferable to have a structure that reduces the resistance of the wiring and junction parts. When the internal resistance is reduced in this way, the effects of using the electrolyte of this disclosure are particularly well exhibited.

[0580] In electrode groups with the above-described laminated structure, a structure formed by bundling the metal core portions of each electrode layer and welding them to a terminal is preferably used. When the area of ​​a single electrode is large, the internal resistance increases, so it is also preferable to provide multiple terminals within the electrode to reduce the resistance. In electrode groups with the above-described wound structure, the internal resistance can be lowered by providing multiple lead structures for both the positive and negative electrodes and bundling them to a terminal.

[0581] The material of the outer casing is not particularly limited as long as it is a stable material for the electrolyte used. Specifically, metals such as nickel-plated steel, stainless steel, aluminum or aluminum alloy, magnesium alloy, or laminated films of resin and aluminum foil can be used. From the viewpoint of weight reduction, aluminum or aluminum alloy metals or laminated films are preferably used.

[0582] Outer cases using metals may be sealed by welding the metals together using laser welding, resistance welding, or ultrasonic welding, or by using a crimped structure with the metals connected via a resin gasket. Outer cases using laminate film may be sealed by heat-fusing the resin layers together. To improve sealing performance, a resin different from the resin used in the laminate film may be interposed between the resin layers. In particular, when a sealed structure is formed by heat-fusing the resin layers via a current collector terminal, since it is a joint between metal and resin, a resin having polar groups or a modified resin with introduced polar groups is preferably used as the interposing resin.

[0583] The shape of the secondary battery disclosed herein is arbitrary and can include cylindrical, prismatic, laminated, coin-type, and large shapes. The shape and configuration of the positive electrode, negative electrode, and separator can be changed and used according to the shape of each battery. [Examples]

[0584] Next, the present disclosure will be explained with reference to examples, but the present disclosure is not limited to such examples. In the following examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass," respectively.

[0585] The fluorinated ethers (A-1) to (A-3) used are shown below. (A-1) HCF2CF2OCH2CF2CF2H (A-2) HCF2CF2OCH2CF2CF3 (A-3) HCF2CF2OCH2CF3

[0586] The additives used are listed below. VC: Vinylen carbonate succinic anhydride maleic anhydride Adiponitrile FEC: Fluoroethylene carbonate VEC: Vinyl ethylene carbonate DFEC: Difluoroethylene carbonate CH3CH2OSO3Li FSO3Li Et2NSO3Li (CF3CH2)2NSO3L (CF3CH2)(CH3)NSO3Li (CNCH2)2NSO3Li Tritrimethylsilyl phosphate Tristriethylsilyl phosphate Tris-t-butyldimethylsilyl phosphate Tritrimethylsilyl phosphite Tristriethylsilyl phosphate Tris-t-butyldimethylsilyl phosphite

[0587] ( Reference Example 1) [Preparation of electrolyte solution] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 30 / 40 / 30, and LiPF6 was added to this mixture to a concentration of 1.0 mol / liter to prepare the basic electrolyte. A non-aqueous electrolyte was prepared by adding 0.001% by mass of fluoride ether (A-1) to the aforementioned basic electrolyte and mixing it.

[0588] [Fabrication of the negative electrode] Silicon oxide powder (SiO) as the negative electrode active material (average particle size 20 μm, BET specific surface area 2.7 m²) 2 ( / g) and graphite powder (average particle size 5μm, BET specific surface area 20m²) 2 A slurry was prepared by mixing 94% by mass of (30 / 70) (mass ratio) with 6% by mass of polyvinylidene fluoride (PVdF) as a binder, and then adding N-methyl-2-pyrrolidone (NMP) and mixing. The resulting slurry was applied to a negative electrode current collector made of 15 μm thick copper foil and dried. This was cut to a predetermined electrode size and rolled using a roll press to produce a negative electrode in which a negative electrode material layer was formed on the negative electrode current collector.

[0589] [Fabrication of the positive electrode] LiNi 0.8 Mn 0.1 Co 0.1 97 parts by mass of O2 (NMC811), 1.5 parts by mass of acetylene black as a conductive additive, and 1.5 parts by mass of polyvinylidene fluoride (8% by mass NMP solution) as a binder were added and mixed in a disperser to form a slurry. The resulting slurry was coated onto 20 μm thick aluminum foil, dried, and rolled in a press. The resulting material was then cut into a shape having a coated portion (positive electrode material layer) with a width of 50 mm and a length of 30 mm, and an uncoated portion with a width of 5 mm and a length of 9 mm, to form the positive electrode.

[0590] [Battery construction] The fabricated negative electrode, which had a negative electrode material layer on one side, was cut into a shape having a coated portion (negative electrode material layer) with a width of 52 mm and a length of 32 mm, and an uncoated portion with a width of 5 mm and a length of 9 mm, to form the negative electrode.

[0591] The positive and negative electrodes described above were placed facing each other via a 20 μm thick microporous polyethylene film (separator), the non-aqueous electrolyte obtained above was injected, and after the non-aqueous electrolyte had sufficiently permeated the separator, etc., it was sealed, pre-charged and aged to fabricate an aluminum laminate cell (lithium-ion secondary battery).

[0592] (Measurement of battery characteristics) [Cycle Characteristics] The obtained aluminum laminate cells were charged at 25°C using a constant current-constant voltage (CC / CV) charge (hereinafter referred to as CC / CV charge) to 4.2V with a current equivalent to 0.2C (0.1C cut-off), then discharged to 3V with a constant current of 0.2C. This was considered one cycle, and three cycles were performed. Subsequently, at 45°C, the cells were CC / CV charged to 4.2V with a current equivalent to 1.0C (0.1C cut-off), then discharged to 3V with a constant current of 1.0C. This was considered one cycle, and the initial discharge capacity was determined from the discharge capacity. The cycles were repeated, and the discharge capacity after 300 cycles was measured. The ratio of the discharge capacity after 300 cycles to the initial discharge capacity was calculated and defined as the capacity retention rate (%). Capacity retention rate (%) = (Discharge capacity after 300 cycles) ÷ (Initial discharge capacity at 1.0C) × 100 The results are shown as relative values, with the result of Comparative Example 1 set to 1.

[0593] [IV resistance] The above battery was charged to 50% of its state of charge (SOC), discharged at 1, 3, and 5C rates, and the voltage drop (V) was measured. From the obtained voltage and current values, the resistance value was calculated from the slope using the formula V=IR. The relative values ​​are listed in the table for Examples, with the value for Comparative Example 1 set to 1. The above SOC refers to the charge state, where SOC 100% represents the capacity when charged to 4.2V. For example, SOC 50% represents half the capacity of SOC 100%.

[0594] [LiF amount] After the test, the battery was disassembled, the negative electrode was removed, and a predetermined amount of water was added. After stirring, the solution was filtered, and the amount of F in the filtered solution was calculated using ion chromatography. The obtained value was then converted to LiF.

[0595] ( Reference Examples 2 to 4, Examples 5 to 7, Reference Examples 8 and 9, Examples 10 ~37) Except for the changes made to the type and amount of additives in the electrolyte solution as shown in Table 1. Reference A non-aqueous electrolyte was prepared in the same manner as in Example 1, and then a battery was fabricated and evaluated. The results are shown in Table 1.

[0596] (Comparative Example 1) A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that no additives were used. A battery was then constructed, and each evaluation was performed. The results are shown in Table 1.

[0597] (Comparative Example 2) Non-aqueous electrolytes were prepared in the same manner as in Example 1, except that the additives were changed as shown in Table 1. Batteries were then fabricated and each evaluation was performed. The results are shown in Table 1.

[0598] [Table 1]

[0599] Table 1 shows that using the electrolyte obtained in the examples improved the cycle characteristics of the secondary battery and suppressed the increase in IV resistance. [Industrial applicability]

[0600] A secondary battery using the electrolyte of this disclosure can be used as a power source for various purposes, such as a portable power source or an automobile power source.

Claims

1. A lithium-ion secondary battery comprising a negative electrode having a negative electrode material containing silicon and carbon elements, The above negative electrode material contains Si and / or SiOa (0 < a < 2) and a carbon compound. The lower limit of LiF formed on the negative electrode is 3.0 μg / cm³. ２ The upper limit is 4.1 μg / cm³. ２ And, A lithium-ion secondary battery comprising an electrolyte containing 0.5 to 3% by mass of a fluorinated ether represented by the following general formula (1). HCF 2 CF 2 -O-R (1) (In the formula, R is a fluorinated alkyl group.)

2. The lithium-ion secondary battery according to claim 1, wherein the fluorinated ether represented by the general formula (1) is at least one fluorinated ether selected from the group consisting of fluorinated ethers represented by the following general formulas (2) to (4). HCF 2 CF 2 -O-CH 2 CF 2 CF 2 H (2) HCF 2 CF 2 -O-CH 2 CF 2 CF 3 (3) HCF 2 CF 2 -O-CH 2 CF 3 (4)

Images