Electrolyte for secondary battery and secondary battery

Abstract

This secondary battery comprises: a positive electrode; a negative electrode; and an electrolyte including an electrolytic salt and a solvent. The electrolytic salt includes an imide anion, and the imide anion includes at least one of the anions represented by formulas (1), (2), (3), and (4), respectively. The solvent includes at least one of a carboxylic ester compound and a diether compound, wherein the carboxylic ester compound includes a compound represented by formula (5), and the diether compound includes a compound represented by formula (6).

Description

[Technical Field]

[0001] The present technology relates to an electrolyte for a secondary battery and a secondary battery. [Background technology]

[0002] Due to the widespread use of various electronic devices such as mobile phones, secondary batteries have been developed as a power source that is small, lightweight, and has high energy density. These secondary batteries contain a positive electrode, a negative electrode, and an electrolyte (secondary battery electrolyte), and various studies have been conducted on the configuration of these secondary batteries.

[0003] Specifically, the electrolyte is R F 1 -S(=O)2-NH-S(=O)2-NH-S(=O)2-R F 2 (For example, see Patent Document 1.) The electrolyte salt of the electrolyte solution contains an imide compound represented by FS(=O)2-N - -C(=O)-N - -S(=O)2-F or FS(=O)2-N - -S(=O)2-C6H4-S(=O)2-N - It contains an imide anion represented by -S(=O)2-F (see, for example, Non-Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Chinese Patent No. 102786443 [Non-patent literature]

[0005] [Non-Patent Document 1] Faiz Ahmed et al., “Novel divalent organo-lithium salts with high electrochemical and thermal stability for aqueous rechargeable Li-Ion batteries”, Electrochimica Acta, 298, 2019, 709-716 [Non-patent document 2] Faiz Ahmed et al., “Highly conductive divalent fluorosulfonyl imide based electrolytes improving Li-ion battery performance :Additive potentiating”, Journal of Power Sources, 455, 2020, 227980 Summary of the Invention

[0006] Although various studies have been conducted on the configuration of secondary batteries, the battery characteristics of the secondary batteries are still insufficient and there is room for improvement.

[0007] There is a demand for an electrolyte solution for a secondary battery and a secondary battery that can provide excellent battery characteristics.

[0008] According to one embodiment of the present technology, an electrolyte solution for a secondary battery includes an electrolyte salt and a solvent. The electrolyte salt includes an imide anion, and the imide anion includes at least one of anions represented by formulas (1), (2), (3), and (4). The solvent includes at least one of a carboxylic acid ester compound and a diether compound, and the carboxylic acid ester includes a compound represented by formula (5), and the diether compound includes a compound represented by formula (6).

[0009] [ka] (R1 and R2 are each either a fluorine group or a fluorinated alkyl group. W1, W2, and W3 are each either a carbonyl group (>C=O), a sulfinyl group (>S=O), or a sulfonyl group (>S(=O)2).)

[0010] [ka] (Each of R3 and R4 is either a fluorine group or a fluorinated alkyl group. Each of X1, X2, X3 and X4 is either a carbonyl group, a sulfinyl group or a sulfonyl group.)

[0011] [ka] (R5 is a fluorinated alkylene group. Y1, Y2, and Y3 each are any one of a carbonyl group, a sulfinyl group, and a sulfonyl group.)

[0012] [ka] (R6 and R7 each represent a fluorine group or a fluorinated alkyl group. R8 represents an alkylene group, a phenylene group, a fluorinated alkylene group, or a fluorinated phenylene group. Z1, Z2, Z3, and Z4 each represent a carbonyl group, a sulfinyl group, or a sulfonyl group.)

[0013] R9-C(=O)-O-R10 (5) (R9 and R10 are each either an alkyl group or a fluorinated alkyl group, provided that R9 has 1 or more and 10 or less carbon atoms, and R10 has 2 or more and 10 or less carbon atoms.)

[0014] R11-O-R12-O-R13-O-R14 (6) (Each of R11 and R14 is either an alkyl group or a fluorinated alkyl group. Each of R12 and R13 is either an alkylene group or a fluorinated alkylene group.)

[0015] A secondary battery according to an embodiment of the present technology includes a positive electrode, a negative electrode, and an electrolyte solution, and the electrolyte solution has a configuration similar to that of the electrolyte solution for a secondary battery according to the embodiment of the present technology described above.

[0016] According to the electrolyte solution for a secondary battery or the secondary battery of one embodiment of the present technology, the electrolyte solution for a secondary battery contains an electrolyte salt and a solvent, the solvent contains at least one of a carboxylic acid ester compound and a diether compound, the electrolyte salt contains at least one of the anions shown in formula (1), formula (2), formula (3), and formula (4) as an imide anion, the carboxylic acid ester compound contains the compound shown in formula (5), and the diether compound contains the compound shown in formula (6), so that excellent battery characteristics can be obtained.

[0017] Note that the effects of the present technology are not necessarily limited to the effects described here, but may be any of a series of effects related to the present technology described below. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a perspective view illustrating a configuration of a secondary battery according to an embodiment of the present technology. [Figure 2] FIG. 2 is a cross-sectional view illustrating the configuration of the battery element shown in FIG. [Figure 3] FIG. 1 is a block diagram illustrating a configuration of an application example of a secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. The description will be made in the following order. 1. Electrolyte for secondary batteries 1-1.Configuration 1-2. Manufacturing method 1-3. Action and effects 2. Secondary battery 2-1.Configuration 2-2.Operation 2-3. Manufacturing method 2-4. Action and effects 3. Variations 4. Uses of secondary batteries

[0020] <1. Electrolyte for secondary batteries> First, an electrolyte solution for a secondary battery (hereinafter simply referred to as "electrolyte solution") according to one embodiment of the present technology will be described.

[0021] <1-1.Configuration> The electrolyte solution described here is used in a secondary battery, which is an electrochemical device. However, the electrolyte solution may also be used in other electrochemical devices. The type of other electrochemical device is not particularly limited, but specifically includes a capacitor.

[0022] The electrolytic solution is a liquid electrolyte and contains an electrolyte salt and a solvent, and the solvent contains one or both of a carboxylic acid ester compound and a diether compound.

[0023] [Electrolyte salt] The electrolyte salt is a compound that ionizes in a solvent and contains an anion and a cation, but the type of electrolyte salt may be one type or two or more types.

[0024] (anion) The anion contains an imide anion, and the imide anion contains one or more of the anions represented by formula (1), formula (2), formula (3), and formula (4). That is, the electrolyte salt contains an imide anion as the anion.

[0025] Hereinafter, the anion represented by formula (1) will be referred to as the "first imide anion," the anion represented by formula (2) as the "second imide anion," the anion represented by formula (3) as the "third imide anion," and the anion represented by formula (4) as the "fourth imide anion."

[0026] However, the first imide anion may be of one type or two or more types, and the same applies to the second imide anion, the third imide anion, and the fourth imide anion.

[0027] [ka] (R1 and R2 are each either a fluorine group or a fluorinated alkyl group. W1, W2, and W3 are each either a carbonyl group, a sulfinyl group, or a sulfonyl group.)

[0028] [ka] (Each of R3 and R4 is either a fluorine group or a fluorinated alkyl group. Each of X1, X2, X3 and X4 is either a carbonyl group, a sulfinyl group or a sulfonyl group.)

[0029] [ka] (R5 is a fluorinated alkylene group. Y1, Y2, and Y3 each are any one of a carbonyl group, a sulfinyl group, and a sulfonyl group.)

[0030] [ka] (R6 and R7 each represent a fluorine group or a fluorinated alkyl group. R8 represents an alkylene group, a phenylene group, a fluorinated alkylene group, or a fluorinated phenylene group. Z1, Z2, Z3, and Z4 each represent a carbonyl group, a sulfinyl group, or a sulfonyl group.)

[0031] The reasons why the anion contains an imide anion are as follows. First, during charging and discharging of a secondary battery using an electrolyte solution, a high-quality coating derived from the electrolyte salt is formed on the surface of each of the positive and negative electrodes. This suppresses reactions between the electrolyte solution (especially the solvent) and the positive and negative electrodes, respectively, thereby suppressing decomposition of the electrolyte solution. Second, the above-mentioned coating is utilized to improve the migration rate of cations near the surfaces of the positive and negative electrodes. Third, the migration rate of cations is also improved in the electrolyte solution.

[0032] As shown in formula (1), the first imide anion is a chain anion (divalent negative ion) containing two nitrogen atoms (N) and three functional groups (W1 to W3).

[0033] Each of R1 and R2 is not particularly limited as long as it is either a fluorine group (-F) or a fluorinated alkyl group. That is, each of R1 and R2 may be the same group or different groups. Therefore, each of R1 and R2 is not a hydrogen group (-H) or an alkyl group, etc.

[0034] A fluorinated alkyl group is an alkyl group in which one or more hydrogen groups (-H) have been replaced with a fluorine group, and the fluorinated alkyl group may be linear or branched with one or more side chains.

[0035] The number of carbon atoms in the fluorinated alkyl group is not particularly limited, but specifically, is 1 to 10. This is because the solubility and ionization property of the electrolyte salt containing the first imide anion are improved.

[0036] Specific examples of fluorinated alkyl groups include a perfluoromethyl group (-CF3) and a perfluoroethyl group (-C2F5).

[0037] Each of W1 to W3 is not particularly limited as long as it is any one of a carbonyl group, a sulfinyl group, and a sulfonyl group. That is, each of W1 to W3 may be the same group as each other, or may be different groups as each other. Of course, any two of W1 to W3 may be the same group as each other.

[0038] As shown in formula (2), the second imide anion is a chain anion (trivalent negative ion) containing three nitrogen atoms and four functional groups (X1 to X4).

[0039] The details for each of R3 and R4 are similar to the details for each of R1 and R2.

[0040] Each of X1 to X4 is not particularly limited as long as it is any one of a carbonyl group, a sulfinyl group, and a sulfonyl group. That is, each of X1 to X4 may be the same group as each other, or may be different groups as each other. Of course, any two of X1 to X4 may be the same group as each other, or any three of X1 to X4 may be the same group as each other.

[0041] As shown in formula (3), the third imide anion is a cyclic anion (divalent negative ion) containing two nitrogen atoms, three functional groups (Y1 to Y3), and one connecting group (R5).

[0042] The fluorinated alkylene group represented by R5 is an alkylene group in which one or more hydrogen groups have been substituted with fluorine groups, provided that the fluorinated alkylene group may be linear or branched having one or more side chains.

[0043] The number of carbon atoms in the fluorinated alkylene group is not particularly limited, but specifically, is 1 to 10. This is because the solubility and ionization property of the electrolyte salt containing the tertiary imide anion are improved.

[0044] Specific examples of fluorinated alkylene groups include a perfluoromethylene group (-CF2-) and a perfluoroethylene group (-C2F4-).

[0045] Each of Y1 to Y3 is not particularly limited as long as it is any one of a carbonyl group, a sulfinyl group, and a sulfonyl group. That is, each of Y1 to Y3 may be the same group as each other, or may be different groups as each other. Of course, any two of Y1 to Y3 may be the same group as each other.

[0046] As shown in formula (4), the quaternary imide anion is a chain anion (divalent negative ion) containing two nitrogen atoms (N), four functional groups (Z1 to Z4), and one connecting group (R8).

[0047] The details for each of R6 and R7 are similar to the details for each of R1 and R2.

[0048] R8 is not particularly limited as long as it is any one of an alkylene group, a phenylene group, a fluorinated alkylene group and a fluorinated phenylene group.

[0049] The alkylene group may be linear or branched with one or more side chains. The number of carbon atoms in the alkylene group is not particularly limited, but is typically 1 to 10. This is because the solubility and ionization properties of the electrolyte salt containing the quaternary imide anion are improved. Specific examples of the alkylene group include a methylene group (-CH-), an ethylene group (-CH-), and a propylene group (-CH-).

[0050] Details regarding the fluorinated alkylene group of R8 are the same as those regarding the fluorinated alkylene group of R5.

[0051] A fluorinated phenylene group is a phenylene group in which one or more hydrogen groups have been substituted with fluorine groups. A specific example of a fluorinated phenylene group is a monofluorophenylene group (—C6H3F—).

[0052] Each of Z1 to Z4 is not particularly limited as long as it is any one of a carbonyl group, a sulfinyl group, and a sulfonyl group. That is, each of Z1 to Z4 may be the same group as each other, or may be different groups as each other. Of course, any two of Z1 to Z4 may be the same group as each other, or any three of Z1 to Z4 may be the same group as each other.

[0053] Specific examples of the first imide anion include anions represented by the formulas (1-1) to (1-30).

[0054] [ka]

[0055] [ka]

[0056] [ka]

[0057] Specific examples of the second imide anion include anions represented by the formulas (2-1) to (2-22).

[0058] [ka]

[0059] [ka]

[0060] Specific examples of the third imide anion include anions represented by the formulas (3-1) to (3-15).

[0061] [ka]

[0062] Specific examples of the quaternary imide anion include anions represented by the formulas (4-1) to (4-65).

[0063] [ka]

[0064] [ka]

[0065] [ka]

[0066] [ka]

[0067] [ka]

[0068] [ka]

[0069] [ka]

[0070] (cation) The type of cation is not particularly limited. Specifically, the cation contains one or more types of light metal ions. That is, the electrolyte salt contains light metal ions as cations. This is because a high voltage can be obtained.

[0071] The type of light metal ion is not particularly limited, but specific examples include alkali metal ions and alkaline earth metal ions. Specific examples of alkali metal ions include sodium ions and potassium ions. Specific examples of alkaline earth metal ions include beryllium ions, magnesium ions, and calcium ions. Additionally, the light metal ions may be aluminum ions.

[0072] Among these, it is preferable that the light metal ions contain lithium ions, since this allows a sufficiently high voltage to be obtained.

[0073] (Content) The content of the electrolyte salt in the electrolytic solution is not particularly limited and can be set arbitrarily. In particular, the content of the electrolyte salt is preferably 0.2 mol / kg to 2 mol / kg, because this allows high ionic conductivity to be obtained. The "content of the electrolyte salt" described here refers to the content of the electrolyte salt relative to the solvent.

[0074] To determine the content of electrolyte salt, the secondary battery is disassembled to recover the electrolyte solution, and the electrolyte solution is then analyzed using inductively coupled plasma (ICP) emission spectroscopy, which determines the weight of the solvent and the weight of the electrolyte salt, allowing the content of the electrolyte salt to be calculated.

[0075] The procedure for determining the content described here is similar to the procedure for determining the content of components of the electrolyte solution other than the electrolyte salt, which will be described later. "Components of the electrolyte solution other than the electrolyte salt" refers to other solvents, other electrolyte salts, additives, etc.

[0076] [solvent] The solvent may contain only the carboxylic acid ester compound, may contain only the diether compound, or may contain both the carboxylic acid ester compound and the diether compound.

[0077] (carboxylic acid ester compounds) The carboxylic acid ester compound is a chain-like ester compound containing a carboxyl group (—C(═O)—O—), and more specifically, includes a compound represented by formula (5). However, the type of carboxylic acid ester compound may be one type or two or more types.

[0078] R9-C(=O)-O-R10 (5) (R9 and R10 are each either an alkyl group or a fluorinated alkyl group, provided that R9 has 1 or more and 10 or less carbon atoms, and R10 has 2 or more and 10 or less carbon atoms.)

[0079] The reason why the solvent contains a carboxylic acid ester compound is that the carboxylic acid ester compound has a lower viscosity than the carbonate ester compound described below, and therefore the conductivity of the electrolyte is improved.

[0080] The alkyl group may be linear or branched having one or more side chains. Specific examples of alkyl groups having 1 to 10 carbon atoms include methyl, ethyl, propyl, and butyl groups. Specific examples of alkyl groups having 2 to 10 carbon atoms include ethyl, propyl, and butyl groups. Details regarding fluorinated alkyl groups are as described above.

[0081] Since the carbon number of R9 is 1 or more, the carboxylic acid ester compound may be an acetate ester, a propionate ester, a butyrate ester, or any other ester. Also, since the carbon number of R10 is 2 or more, the carboxylic acid ester compound is not methyl carboxylate, but ethyl carboxylate, propyl carboxylate, or the like.

[0082] The upper limit of the number of carbon atoms in R9 is 10 or less because this ensures the solubility and compatibility of the carboxylic acid ester compound. The reason why the upper limit of the number of carbon atoms in R10 is 10 or less is the same as the reason why the upper limit of the number of carbon atoms in R9 is 10 or less. It is more preferable that the number of carbon atoms in each of R9 and R10 is 4 or less, as this further improves the solubility and compatibility of the carboxylic acid ester compound.

[0083] Specific examples of the carboxylic acid ester compound include ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, propyl butyrate, and ethyl pivalate.

[0084] Among these, it is preferable that the carboxylic acid ester compound contains one or more of propyl acetate, ethyl propionate, and propyl propionate, because the conductivity of the electrolyte solution is sufficiently improved.

[0085] The content of the carboxylic acid ester compound in the solvent is not particularly limited and can be set as desired. In particular, the content of the carboxylic acid ester compound is preferably 5% by weight to 80% by weight, because this allows the conductivity of the electrolyte to be sufficiently and stably improved.

[0086] (diether compounds) The diether compound is a chain compound containing two ether bonds (—O—), and more specifically, includes a compound represented by formula (6). However, the type of diether compound may be one type or two or more types.

[0087] R11-O-R12-O-R13-O-R14 (6) (Each of R11 and R14 is either an alkyl group or a fluorinated alkyl group. Each of R12 and R13 is either an alkylene group or a fluorinated alkylene group.)

[0088] The reason why the solvent contains a diether compound is the same as the reason why the solvent contains a carboxylic acid ester compound: the diether compound has a lower viscosity than the carbonate ester compound described below, which improves the conductivity of the electrolyte solution.

[0089] The details of the alkyl group, fluorinated alkyl group, alkylene group, and fluorinated alkylene group are as described above. The number of carbon atoms in each of the alkyl group, fluorinated alkyl group, alkylene group, and fluorinated alkylene group is not particularly limited, but is preferably 1 to 10. This is because the solubility and compatibility of the diether compound are improved.

[0090] Specific examples of diether compounds include glycol ethers (so-called glymes), more specifically diethylene glycol dimethyl ether.

[0091] The content of the diether compound in the solvent is not particularly limited and can be set as desired. In particular, the content of the diether compound is preferably 5% by weight to 80% by weight, because this allows the conductivity of the electrolyte to be sufficiently and stably improved.

[0092] When the solvent contains both a carboxylic acid ester compound and a diether compound, the contents of the carboxylic acid ester compound and the diether compound in the solvent are preferably 5% by weight to 80% by weight for the same reason. The contents described here are the sum of the contents of the carboxylic acid ester compound and the diether compound.

[0093] [Other solvents] The solvent may further contain other solvents, as this improves the ionic conductivity of the electrolyte. The other solvents contain one or more non-aqueous solvents (organic solvents), and the electrolyte containing the non-aqueous solvent is a so-called non-aqueous electrolyte. The non-aqueous solvents include esters and ethers, and more specifically, carbonate ester compounds, carboxylic acid ester compounds, lactone compounds, and the like.

[0094] Carbonate compounds include cyclic carbonates and chain carbonates. Specific examples of cyclic carbonates include ethylene carbonate and propylene carbonate. Specific examples of chain carbonates include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0095] The carboxylic acid ester compound is a chain carboxylic acid ester, etc. However, the above-mentioned carboxylic acid ester compounds are excluded from the chain carboxylic acid esters described here. Specific examples of the chain carboxylic acid ester include methyl acetate, methyl propionate, and methyl butyrate.

[0096] The lactone compound is a lactone, etc. Specific examples of lactones include γ-butyrolactone and γ-valerolactone.

[0097] The ethers may be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, or the like.

[0098] [Other electrolyte salts] The electrolyte solution may further contain one or more of the other electrolyte salts. This is because the cation migration rate is further increased near the surfaces of the positive electrode and the negative electrode, and also in the electrolyte solution. The content of the other electrolyte salts in the electrolyte solution is not particularly limited and can be set as desired.

[0099] The type of other electrolyte salt is not particularly limited, but specifically includes light metal salts such as lithium salts, although the above-mentioned electrolyte salts are excluded from the lithium salts described here.

[0100] Specific examples of lithium salts include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium trifluoromethanesulfonate (LiCFSO), lithium bis(fluorosulfonyl)imide (LiN(FSO)), lithium bis(trifluoromethanesulfonyl)imide (LiN(CFSO)), lithium tris(trifluoromethanesulfonyl)methide (LiC(CFSO)), lithium bis(oxalato)borate (LiB(CO)), lithium difluorooxalatoborate (LiBF(CO)), lithium difluorodi(oxalato)borate (LiPF(CO)), and lithium tetrafluorooxalatophosphate (LiPF(CO)), lithium monofluorophosphate (LiPFO), and lithium difluorophosphate (LiPFO).

[0101] Among these, the other electrolyte salt preferably contains one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, and lithium difluorophosphate, because this sufficiently improves the cation migration rate near the surfaces of the positive electrode and negative electrode, and also in the electrolyte solution.

[0102] [Additives] The electrolyte may further contain one or more additives. This is because, during charging and discharging of a secondary battery using the electrolyte, a coating derived from the additive is formed on the surface of each of the positive electrode and the negative electrode, thereby suppressing the decomposition reaction of the electrolyte. The content of the additive in the electrolyte is not particularly limited and can be set as desired.

[0103] The type of additive is not particularly limited, but specific examples include unsaturated cyclic carbonates, fluorinated cyclic carbonates, sulfonates, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfates, nitrile compounds, and isocyanate compounds.

[0104] The unsaturated cyclic carbonate is a cyclic carbonate containing an unsaturated carbon bond (carbon-carbon double bond). The number of unsaturated carbon bonds is not particularly limited, and may be one or two or more. Specific examples of the unsaturated cyclic carbonate include vinylene carbonate, vinylethylene carbonate, and methyleneethylene carbonate.

[0105] A fluorinated cyclic carbonate is a cyclic carbonate containing fluorine as a constituent element. That is, a fluorinated cyclic carbonate is a compound in which one or more hydrogen groups of a cyclic carbonate are substituted with fluorine groups. Specific examples of fluorinated cyclic carbonates include monofluoroethylene carbonate and difluoroethylene carbonate.

[0106] The sulfonate esters include cyclic monosulfonates, cyclic disulfonates, chain monosulfonates, and chain disulfonates. Specific examples of cyclic monosulfonates include 1,3-propane sultone, 1-propene-1,3-sultone, 1,4-butane sultone, 2,4-butane sultone, and methanesulfonic acid propargyl ester. Specific examples of cyclic disulfonates include cyclodisone.

[0107] Specific examples of dicarboxylic acid anhydrides include succinic anhydride, glutaric anhydride, and maleic anhydride. Specific examples of disulfonic acid anhydrides include ethanedisulfonic anhydride and propanedisulfonic anhydride. Specific examples of sulfate esters include ethylene sulfate (1,3,2-dioxathiolane 2,2-dioxide).

[0108] Nitrile compounds are compounds containing one or more cyano groups (-CN). Specific examples of nitrile compounds include octanenitrile, benzonitrile, phthalonitrile, succinonitrile, glutaronitrile, adiponitrile, sebaconitrile, 1,3,6-hexanetricarbonitrile, 3,3'-oxydipropionitrile, 3-butoxypropionitrile, ethylene glycol bispropionitrile ether, 1,2,2,3-tetracyanopropane, tetracyanopropane, fumaronitrile, 7,7,8,8-tetracyanoquinodimethane, cyclopentanecarbonitrile, 1,3,5-cyclohexanetricarbonitrile, and 1,3-bis(dicyanomethylidene)indane.

[0109] The isocyanate compound is a compound containing one or more isocyanate groups (-NCO). A specific example of the isocyanate compound is hexamethylene diisocyanate.

[0110] <1-2. Manufacturing method> When producing an electrolytic solution, an electrolyte salt is added to a solvent containing one or both of a carboxylic acid ester compound and a diether compound, and the solvent is then stirred. In this case, the solvent may further contain another solvent, or another electrolyte salt may be added to the solvent, or an additive may be added to the solvent. As a result, the electrolyte salt is dispersed or dissolved in the solvent, and the electrolytic solution is prepared.

[0111] <1-3. Actions and Effects> According to this electrolytic solution, the electrolytic solution contains an electrolyte salt and a solvent, the solvent contains one or both of a carboxylic acid ester compound and a diether compound, the electrolyte salt contains one or more of the anions shown in each of formulas (1) to (4) as an imide anion, the carboxylic acid ester compound contains the compound shown in formula (5), and the diether compound contains the compound shown in formula (6).

[0112] In this case, as described above, when a secondary battery using an electrolyte solution is charged and discharged, a high-quality coating derived from the electrolyte salt is formed on the surfaces of the positive and negative electrodes, suppressing decomposition of the electrolyte solution. In addition, the migration rate of cations near the surfaces of the positive and negative electrodes is improved, and the migration rate of cations is also improved in the electrolyte solution.

[0113] Moreover, as described above, the viscosity of the electrolyte is reduced, and therefore the conductivity of the electrolyte is improved.

[0114] Therefore, excellent battery characteristics can be obtained in a secondary battery using an electrolytic solution.

[0115] In particular, if the electrolyte salt contains light metal ions as cations, a higher voltage can be obtained, resulting in a greater effect. In this case, if the light metal ions contain lithium ions, a higher voltage can be obtained, resulting in an even greater effect.

[0116] Furthermore, if the content of the electrolyte salt in the electrolytic solution is 0.2 mol / kg to 2 mol / kg, high ionic conductivity can be obtained, and therefore a greater effect can be obtained.

[0117] Furthermore, if the carboxylic acid ester compound contains one or more of propyl acetate, ethyl propionate, and propyl propionate, the conductivity of the electrolyte solution is sufficiently improved, thereby achieving a greater effect.

[0118] Furthermore, if the content of one or both of the carboxylic acid ester compound and the diether compound in the solvent is 10% by weight to 80% by weight, the conductivity of the electrolyte solution is sufficiently and stably improved, thereby achieving a greater effect.

[0119] Furthermore, if the electrolyte solution further contains one or more additives selected from the group consisting of unsaturated cyclic carbonates, fluorinated cyclic carbonates, sulfonates, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfates, nitrile compounds, and isocyanate compounds, the decomposition reaction of the electrolyte solution is suppressed, thereby achieving even greater effects.

[0120] Furthermore, if the electrolyte solution further contains one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, and lithium difluorophosphate as other electrolyte salts, the cation migration rate is further improved, thereby achieving even greater effects.

[0121] <2. Secondary battery> Next, a secondary battery using the above-mentioned electrolyte will be described.

[0122] The secondary battery described here is a secondary battery that obtains battery capacity by utilizing the absorption and desorption of electrode reactants, and is equipped with a positive electrode, a negative electrode, and an electrolyte.

[0123] In this secondary battery, the charge capacity of the negative electrode is larger than the discharge capacity of the positive electrode. That is, the electrochemical capacity per unit area of ​​the negative electrode is set to be larger than the electrochemical capacity per unit area of ​​the positive electrode. This is to prevent deposition of electrode reactants on the surface of the negative electrode during charging.

[0124] The type of electrode reactant is not particularly limited, but specifically, the electrode reactant is a light metal such as an alkali metal or alkaline earth metal. Specific examples of alkali metals include lithium, sodium, and potassium, and specific examples of alkaline earth metals include beryllium, magnesium, and calcium. However, the electrode reactant may be another light metal such as aluminum.

[0125] In the following, we will take the case where the electrode reactant is lithium as an example. A secondary battery that obtains battery capacity by utilizing the absorption and desorption of lithium is called a lithium ion secondary battery. In this lithium ion secondary battery, lithium is absorbed and desorbed in the ionic state.

[0126] <2-1.Configuration> Fig. 1 shows a perspective view of a secondary battery, and Fig. 2 shows a cross-sectional view of the battery element 20 shown in Fig. 1. However, Fig. 1 shows a state in which the exterior film 10 and the battery element 20 are separated from each other, and the cross section of the battery element 20 taken along the XZ plane is shown by a broken line. Fig. 2 shows only a portion of the battery element 20.

[0127] 1 and 2, this secondary battery includes an exterior film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 41 and 42. The secondary battery described here is a laminate film type secondary battery that uses a flexible or pliable exterior film 10.

[0128] [Exterior film and sealing film] 1, the exterior film 10 is an exterior member that houses the battery element 20, and has a bag-like structure that is sealed when the battery element 20 is housed inside. As a result, the exterior film 10 houses an electrolyte solution together with a positive electrode 21 and a negative electrode 22, which will be described later.

[0129] Here, the exterior film 10 is a single film-like member that is folded in a folding direction F. The exterior film 10 is provided with a recessed portion 10U (so-called deep drawn portion) for accommodating the battery element 20.

[0130] Specifically, the exterior film 10 is a three-layer laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order from the inside out, and when the exterior film 10 is folded, the outer peripheral edges of the opposing fusion layers are fused to each other. The fusion layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protection layer contains a polymer compound such as nylon.

[0131] However, the configuration (number of layers) of the exterior film 10 is not particularly limited, and may be one layer, two layers, or four or more layers.

[0132] The sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32. However, one or both of the sealing films 41 and 42 may be omitted.

[0133] The sealing film 41 is a sealing member that prevents outside air and the like from entering the inside of the exterior film 10. The sealing film 41 also contains a polymer compound such as polyolefin that has adhesiveness to the positive electrode lead 31, and a specific example of the polyolefin is polypropylene.

[0134] The configuration of the sealing film 42 is the same as the configuration of the sealing film 41, except that the sealing film 42 is a sealing member that has adhesiveness to the negative electrode lead 32. That is, the sealing film 42 contains a polymer compound such as polyolefin that has adhesiveness to the negative electrode lead 32.

[0135] [Battery element] As shown in FIGS. 1 and 2, the battery element 20 is a power generating element including a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown), and is housed inside the exterior film 10.

[0136] This battery element 20 is a so-called wound electrode body. That is, in the battery element 20, the positive electrode 21 and the negative electrode 22 are stacked on top of each other with a separator 23 interposed therebetween, and the positive electrode 21, the negative electrode 22, and the separator 23 are wound around a winding axis P, which is an imaginary axis extending in the Y-axis direction. As a result, the positive electrode 21 and the negative electrode 22 are wound while facing each other with the separator 23 interposed therebetween.

[0137] The three-dimensional shape of battery element 20 is not particularly limited. Here, the three-dimensional shape of battery element 20 is flat, and therefore the cross section of battery element 20 intersecting with winding axis P (cross section along the XZ plane) has a flat shape defined by a major axis J1 and a minor axis J2. This major axis J1 is an imaginary axis that extends in the X-axis direction and has a length greater than that of minor axis J2, and minor axis J2 is an imaginary axis that extends in the Z-axis direction intersecting with the X-axis direction and has a length smaller than that of major axis J1. Here, the three-dimensional shape of battery element 20 is a flat cylindrical shape, and therefore the cross section of battery element 20 has a flat, approximately elliptical shape.

[0138] (positive electrode) As shown in FIG. 2, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B.

[0139] The positive electrode current collector 21A has a pair of surfaces on which the positive electrode active material layer 21B is provided. The positive electrode current collector 21A contains a conductive material such as a metal material, and a specific example of the metal material is aluminum.

[0140] The positive electrode active material layer 21B contains one or more types of positive electrode active materials capable of absorbing and releasing lithium, but may also contain one or more types of other materials such as a positive electrode binder and a positive electrode conductive agent.

[0141] Here, the positive electrode active material layer 21B is provided on both sides of the positive electrode current collector 21A. However, the positive electrode active material layer 21B may be provided on only one side of the positive electrode current collector 21A, on the side where the positive electrode 21 faces the negative electrode 22. The method for forming the positive electrode active material layer 21B is not particularly limited, and specifically, it may be one or more of coating methods or the like.

[0142] The type of positive electrode active material is not particularly limited, but specifically includes a lithium-containing compound. This lithium-containing compound is a compound containing lithium and one or more transition metal elements as constituent elements, and may further contain one or more other elements as constituent elements. The type of other element is not particularly limited as long as it is an element other than lithium and transition metal elements, but specifically, the other element is an element belonging to Groups 2 to 15 of the long period periodic table. The type of lithium-containing compound is not particularly limited, but specifically, the lithium-containing compound is an oxide, a phosphate compound, a silicate compound, a borate compound, etc.

[0143] Specific examples of oxides are LiNiO2, LiCoO2, LiCo 0.98 Al 0.01 Mg 0.01 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2, Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 )O2 and LiMn2O4. Specific examples of phosphate compounds include LiFePO4, LiMnPO4, LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4, etc.

[0144] The positive electrode binder contains one or more of synthetic rubbers and polymeric compounds. Specific examples of synthetic rubbers include styrene-butadiene rubber, fluorine-containing rubber, and ethylene-propylene-diene. Specific examples of polymeric compounds include polyvinylidene fluoride, polyimide, and carboxymethyl cellulose.

[0145] The positive electrode conductive agent contains one or more conductive materials such as carbon materials, and specific examples of the carbon materials include graphite, carbon black, acetylene black, and ketjen black. However, the conductive material may also be a metal material or a polymer compound.

[0146] (Negative electrode) As shown in FIG. 2, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B.

[0147] The negative electrode current collector 22A has a pair of surfaces on which the negative electrode active material layer 22B is provided. The negative electrode current collector 22A contains a conductive material such as a metal material, and a specific example of the metal material is copper.

[0148] The negative electrode active material layer 22B contains one or more types of negative electrode active materials capable of absorbing and releasing lithium, but may also contain one or more types of other materials such as a negative electrode binder and a negative electrode conductive agent.

[0149] Here, the anode active material layer 22B is provided on both sides of the anode current collector 22A. However, the anode active material layer 22B may be provided on only one side of the anode current collector 22A on the side where the anode 22 faces the positive electrode 21. The method for forming the anode active material layer 22B is not particularly limited, and specifically includes one or more of a coating method, a vapor phase method, a liquid phase method, a thermal spraying method, and a firing method (sintering method).

[0150] The type of negative electrode active material is not particularly limited, but specifically includes one or both of a carbon material and a metal-based material. This is because a high energy density can be obtained. Specific examples of carbon materials include graphitizable carbon, non-graphitizable carbon, and graphite (natural graphite and artificial graphite). A metal-based material is a material containing, as a constituent element, one or more of a metal element and a metalloid element that can form an alloy with lithium. Specific examples of the metal element and the metalloid element include one or both of silicon and tin. This metal-based material may be a simple substance, an alloy, a compound, a mixture of two or more of these, or a material containing two or more of these phases. Specific examples of metal-based materials are TiSi2 and SiO x (0 <x≦2、または0.2<x<1.4)などである。

[0151] The details regarding the negative electrode binder and the negative electrode conductive agent are the same as the details regarding the positive electrode binder and the positive electrode conductive agent, respectively.

[0152] (separator) 2, the separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22, and allows lithium ions to pass through while preventing contact (short circuit) between the positive electrode 21 and the negative electrode 22. The separator 23 contains a polymer compound such as polyethylene.

[0153] (electrolyte) The electrolyte solution is impregnated into each of the positive electrode 21, the negative electrode 22, and the separator 23, and has the above-described configuration. That is, the electrolyte solution contains an electrolyte salt and a solvent, the electrolyte salt contains an imide anion, and the solvent contains one or both of a carboxylic acid ester compound and a diether compound.

[0154] [Positive and negative leads] 1, the positive electrode lead 31 is a positive electrode terminal connected to the positive electrode current collector 21A of the positive electrode 21, and is led from the inside to the outside of the exterior film 10. The positive electrode lead 31 contains a conductive material such as a metal material, and a specific example of the metal material is aluminum. The shape of the positive electrode lead 31 is not particularly limited, but specifically, the positive electrode lead 31 is either a thin plate shape or a mesh shape.

[0155] As shown in FIG. 1 , the negative electrode lead 32 is a negative electrode terminal connected to the negative electrode current collector 22A of the negative electrode 22, and is led from the inside to the outside of the exterior film 10. This negative electrode lead 32 contains a conductive material such as a metal material, and a specific example of the metal material is copper. Here, the lead-out direction of the negative electrode lead 32 is the same as the lead-out direction of the positive electrode lead 31. Note that the details regarding the shape of the negative electrode lead 32 are the same as the details regarding the shape of the positive electrode lead 31.

[0156] <2-2. Operation> When the secondary battery is charged, lithium is released from the positive electrode 21 in the battery element 20 and is absorbed into the negative electrode 22 via the electrolyte. On the other hand, when the secondary battery is discharged, lithium is released from the negative electrode 22 in the battery element 20 and is absorbed into the positive electrode 21 via the electrolyte. During these charging and discharging times, lithium is absorbed and released in an ionic state.

[0157] <2-3. Manufacturing method> When manufacturing a secondary battery, the positive electrode 21 and the negative electrode 22 are each produced according to the procedure described below as an example, and the secondary battery is assembled using the positive electrode 21, the negative electrode 22, and an electrolyte solution, and then the secondary battery is subjected to a stabilization treatment. The procedure for preparing the electrolyte solution is as described above.

[0158] [Preparation of positive electrode] First, a paste-like cathode mixture slurry is prepared by adding a mixture (cathode mixture) of a cathode active material, a cathode binder, and a cathode conductive agent to a solvent. This solvent may be an aqueous solvent or an organic solvent. Next, the cathode mixture slurry is applied to both sides of the cathode current collector 21A to form the cathode active material layer 21B. Finally, the cathode active material layer 21B is compression-molded using a roll press or the like. In this case, the cathode active material layer 21B may be heated, or the compression molding may be repeated multiple times. As a result, the cathode active material layer 21B is formed on both sides of the cathode current collector 21A, thereby producing the cathode 21.

[0159] [Preparation of negative electrode] The negative electrode 22 is formed by a procedure similar to that for producing the positive electrode 21 described above. Specifically, first, a mixture (negative electrode mixture) of a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent is poured into a solvent to prepare a paste-like negative electrode mixture slurry. Details regarding the solvent are as described above. Next, the negative electrode mixture slurry is applied to both surfaces of the negative electrode current collector 22A to form the negative electrode active material layer 22B. Finally, the negative electrode active material layer 22B is compression-molded. As a result, the negative electrode active material layer 22B is formed on both surfaces of the negative electrode current collector 22A, and the negative electrode 22 is produced.

[0160] [Secondary battery assembly] First, a positive electrode lead 31 is connected to the positive electrode current collector 21A of the positive electrode 21 using a joining method such as welding, and a negative electrode lead 32 is connected to the negative electrode current collector 22A of the negative electrode 22 using a joining method such as welding.

[0161] Next, the positive electrode 21 and the negative electrode 22 are stacked together with the separator 23 interposed therebetween, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound together to produce a wound body (not shown). This wound body has the same configuration as the battery element 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with an electrolyte solution. Next, the wound body is pressed using a press or the like to form the wound body into a flat shape.

[0162] Next, after the roll is housed inside the recess 10U, the exterior film 10 (fusion layer / metal layer / surface protection layer) is folded so that the exterior films 10 face each other. Next, the outer peripheral edges of two sides of the facing fusion layers are bonded to each other using an adhesive method such as heat fusion, thereby housing the roll inside the bag-shaped exterior film 10.

[0163] Finally, an electrolyte solution is poured into the bag-shaped exterior film 10, and then the outer peripheral edges of the remaining sides of the opposing fusion layers are bonded to each other using an adhesive method such as heat fusion. In this case, a sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and a sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32.

[0164] This allows the wound body to be impregnated with the electrolyte, producing a wound electrode body, the battery element 20. The battery element 20 is then sealed inside the bag-shaped exterior film 10, and a secondary battery is assembled.

[0165] [Secondary battery stabilization] The assembled secondary battery is charged and discharged. Various conditions, such as the ambient temperature, the number of charge / discharge cycles (number of cycles), and the charge / discharge conditions, can be set as desired. This forms a coating on the surface of each of the positive electrode 21 and the negative electrode 22, electrochemically stabilizing the state of the secondary battery. This completes the secondary battery.

[0166] <2-4. Actions and Effects> This secondary battery includes an electrolyte solution having the above-described structure, and therefore, for the reasons described above, can provide excellent battery characteristics.

[0167] In particular, if the secondary battery is a lithium ion secondary battery, a sufficient battery capacity can be stably obtained by utilizing the absorption and release of lithium, and therefore a greater effect can be obtained.

[0168] Other functions and effects of this secondary battery are similar to those of the above-mentioned electrolyte solution.

[0169] <3. Modifications> The configuration of the secondary battery described above can be modified as appropriate as described below, although the series of modifications described below may be combined with each other.

[0170] [Variation 1] As described above, the electrolytic solution may contain other electrolyte salts in addition to the electrolyte salt containing the imide anion.

[0171] In particular, it is preferable that the electrolyte solution contains lithium hexafluorophosphate as another electrolyte salt, and that the content of the electrolyte salt in the electrolyte solution is optimized in relation to the content of lithium hexafluorophosphate in the electrolyte solution.

[0172] Specifically, the electrolyte salt contains a cation and an imide anion, and the hexafluorophosphate ion contains a lithium ion and a hexafluorophosphate ion.

[0173] In this case, the sum T (mol / kg) of the cation content C1 in the electrolyte solution and the lithium ion content C2 in the electrolyte solution is preferably 0.7 mol / kg to 2.2 mol / kg. Furthermore, the ratio R (mol%) of the number of moles M2 of hexafluorophosphate ions in the electrolyte solution to the number of moles M1 of imide anions in the electrolyte solution is preferably 13 mol% to 6000 mol%. This is because the migration rates of cations and lithium ions near the surfaces of the positive electrode 21 and the negative electrode 22 are sufficiently increased, and the migration rates of cations and lithium ions are also sufficiently increased in the electrolyte solution.

[0174] The "cation content in the electrolyte" described here refers to the content of cations relative to the solvent, and the "lithium ion content in the electrolyte" refers to the content of lithium ions relative to the solvent. The sum T is calculated based on the formula T = C1 + C2, and the ratio R is calculated based on the formula R = (M2 / M1) × 100.

[0175] When calculating the sum T and the ratio R, the secondary battery is disassembled to recover the electrolyte, and the electrolyte is then analyzed using ICP atomic emission spectrometry. This identifies the contents C1 and C2 and the numbers of moles M1 and M2, and allows the sum T and the ratio R to be calculated.

[0176] In this case, the same effect can be obtained because the electrolyte solution contains an electrolyte salt. In this case, particularly when the electrolyte salt is used in combination with another electrolyte salt (lithium hexafluorophosphate), the total amount (sum T) of the two is optimized, and the mixing ratio (ratio R) of the two is also optimized. This further improves the migration speeds of cations and lithium ions near the surfaces of the positive electrode 21 and the negative electrode 22, and also further improves the migration speeds of cations and lithium ions in the electrolyte solution. Therefore, even greater effects can be obtained.

[0177] [Variation 2] A porous film separator 23 was used. However, although not specifically shown here, a laminated separator including a polymer compound layer may also be used.

[0178] Specifically, the laminated separator includes a porous membrane having a pair of surfaces and a polymer compound layer provided on one or both surfaces of the porous membrane. This is because the separator improves adhesion to each of the positive electrode 21 and the negative electrode 22, thereby suppressing misalignment (winding misalignment) of the battery element 20. This prevents swelling of the secondary battery even if a side reaction such as a decomposition reaction of the electrolyte solution occurs. The polymer compound layer includes a polymer compound such as polyvinylidene fluoride. This is because excellent physical strength and excellent electrochemical stability can be obtained.

[0179] One or both of the porous film and the polymer compound layer may contain one or more types of insulating particles. This is because the insulating particles promote heat dissipation when the secondary battery generates heat, thereby improving the safety (heat resistance) of the secondary battery. The insulating particles contain one or both of an inorganic material and a resin material. Specific examples of inorganic materials include aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. Specific examples of resin materials include acrylic resin and styrene resin.

[0180] When a laminated separator is produced, a precursor solution containing a polymer compound and a solvent is prepared, and then the precursor solution is applied to one or both sides of a porous film. In this case, multiple insulating particles may be added to the precursor solution as needed.

[0181] Even when this laminated separator is used, the same effect can be obtained because lithium ions are able to move between the positive electrode 21 and the negative electrode 22. In this case, as described above, the safety of the secondary battery is particularly improved, and therefore, a greater effect can be obtained.

[0182] [Variation 3] An electrolyte solution, which is a liquid electrolyte, was used, but although not specifically shown here, an electrolyte layer, which is a gel electrolyte, may also be used.

[0183] In the battery element 20 using the electrolyte layer, the positive electrode 21 and the negative electrode 22 are stacked with the separator 23 and the electrolyte layer interposed therebetween, and the positive electrode 21, the negative electrode 22, the separator 23, and the electrolyte layer are wound together. The electrolyte layer is interposed between the positive electrode 21 and the separator 23, and also between the negative electrode 22 and the separator 23.

[0184] Specifically, the electrolyte layer contains a polymer compound together with an electrolytic solution, and the electrolytic solution is held by the polymer compound. This is because leakage of the electrolytic solution is prevented. The composition of the electrolytic solution is as described above. The polymer compound contains polyvinylidene fluoride, etc. When forming the electrolyte layer, a precursor solution containing the electrolytic solution, the polymer compound, a solvent, etc. is prepared, and then the precursor solution is applied to one or both surfaces of each of the positive electrode 21 and the negative electrode 22.

[0185] Even when this electrolyte layer is used, the same effect can be obtained because lithium ions can move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer. In this case, leakage of the electrolyte solution is prevented as described above, and therefore a greater effect can be obtained.

[0186] <4. Uses of secondary batteries> The uses (application examples) of secondary batteries are not particularly limited. Secondary batteries used as power sources may be the main power source for electronic devices, electric vehicles, etc., or may be auxiliary power sources. A main power source is a power source that is used preferentially regardless of the presence or absence of other power sources. An auxiliary power source is a power source that is used in place of the main power source, or a power source that can be switched from the main power source.

[0187] Specific examples of uses for secondary batteries are as follows: Electronic devices such as video cameras, digital still cameras, mobile phones, laptop computers, headphone stereos, portable radios, and portable information terminals. Storage devices such as backup power supplies and memory cards. Power tools such as power drills and power saws. Battery packs installed in electronic devices. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric cars (including hybrid cars). Power storage systems such as home or industrial battery systems that store power in preparation for emergencies. In these uses, one secondary battery may be used, or multiple secondary batteries may be used.

[0188] The battery pack may use a single cell or a battery pack. An electric vehicle is a vehicle that operates (runs) using a secondary battery as a driving power source, and may be a hybrid vehicle that also has a driving source other than the secondary battery. A home power storage system can use the power stored in a secondary battery, which is a power storage source, to power home electrical appliances, etc.

[0189] Here, an example of an application of the secondary battery will be specifically described. The configuration of the application described below is merely an example and can be modified as appropriate.

[0190] The block diagram of a battery pack is shown in Figure 3. The battery pack described here is a battery pack (a so-called soft pack) that uses one secondary battery, and is installed in electronic devices such as smartphones.

[0191] 3, the battery pack includes a power supply 51 and a circuit board 52. The circuit board 52 is connected to the power supply 51 and includes a positive terminal 53, a negative terminal 54, and a temperature detection terminal 55.

[0192] The power source 51 includes one secondary battery. In this secondary battery, the positive electrode lead is connected to the positive electrode terminal 53, and the negative electrode lead is connected to the negative electrode terminal 54. The power source 51 can be connected to the outside via the positive electrode terminal 53 and the negative electrode terminal 54, and is therefore capable of charging and discharging. The circuit board 52 includes a control unit 56, a switch 57, a PTC element 58, and a temperature detection unit 59. However, the PTC element 58 may be omitted.

[0193] The control unit 56 includes a central processing unit (CPU) and memory, and controls the operation of the entire battery pack. The control unit 56 detects and controls the usage state of the power source 51 as necessary.

[0194] When the voltage of power supply 51 (secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, control unit 56 turns off switch 57 to prevent charging current from flowing through the current path of power supply 51. The overcharge detection voltage is not particularly limited, but specifically, it is 4.20V±0.05V, and the overdischarge detection voltage is not particularly limited, but specifically, it is 2.40V±0.1V.

[0195] Switch 57 includes a charge control switch, a discharge control switch, a charge diode, a discharge diode, etc., and switches between the presence and absence of a connection between power supply 51 and an external device in response to an instruction from control unit 56. Switch 57 includes a field effect transistor (MOSFET) using a metal oxide semiconductor, etc., and the charge / discharge current is detected based on the ON resistance of switch 57.

[0196] Temperature detection unit 59 includes a temperature detection element such as a thermistor, measures the temperature of power supply 51 using temperature detection terminal 55, and outputs the temperature measurement result to control unit 56. The temperature measurement result measured by temperature detection unit 59 is used when control unit 56 controls charging and discharging in the event of abnormal heat generation, and when control unit 56 performs correction processing when calculating the remaining capacity. [Example]

[0197] An embodiment of the present technology will be described.

[0198] <Examples 1 to 30 and Comparative Examples 1 to 4> As will be described below, after the secondary battery was fabricated, the battery characteristics of the secondary battery were evaluated.

[0199] [Secondary battery production] The laminate film type secondary battery (lithium ion secondary battery) shown in FIGS. 1 and 2 was fabricated by the following procedure.

[0200] (Preparation of positive electrode) First, the positive electrode active material (lithium-containing compound (oxide) LiNi 0.82 Co 0.14 Al 0.04 A positive electrode mixture was prepared by mixing 91 parts by mass of ethylenediamine fluoride (O2), 3 parts by mass of a positive electrode binder (polyvinylidene fluoride), and 6 parts by mass of a positive electrode conductive agent (carbon black). The positive electrode mixture was then added to a solvent (organic solvent N-methyl-2-pyrrolidone), and the organic solvent was stirred to prepare a paste-like positive electrode mixture slurry. The positive electrode mixture slurry was then applied to both sides of a positive electrode current collector 21A (a strip-shaped aluminum foil with a thickness of 12 μm) using a coating device, and the positive electrode mixture slurry was then dried to form a positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B was compression-molded using a roll press. The positive electrode 21 was thus fabricated.

[0201] (Preparation of negative electrode) First, 93 parts by mass of a negative electrode active material (artificial graphite, a carbon material; the interplanar spacing of the (002) plane measured using X-ray diffraction method = 0.3358 nm) and 7 parts by mass of a negative electrode binder (styrene butadiene rubber) were mixed together to prepare a negative electrode mixture. Next, the negative electrode mixture was added to a solvent (water, an aqueous solvent), and the organic solvent was stirred to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of a negative electrode current collector 22A (a strip-shaped copper foil with a thickness of 15 μm) using a coating device, and the negative electrode mixture slurry was dried to form a negative electrode active material layer 22B. Finally, the negative electrode active material layer 22B was compression-molded using a roll press. This produced the negative electrode 22.

[0202] (Preparation of Electrolyte) First, a solvent was prepared.

[0203] The solvents used were carboxylic acid ester compounds propyl acetate (AcPr), ethyl propionate (PrEt), and propyl propionate (PrPr), and a diether compound diethylene glycol dimethyl ether (DG). Other solvents used included ethylene carbonate (EC), a cyclic carbonate, and gamma-butyrolactone (GBL), a lactone. The composition of the mixed solvent (content (wt%)) is shown in Tables 1 and 2.

[0204] The electrolyte salt was added to this mixed solvent, and the solvent was then stirred.

[0205] The cation of the electrolyte salt is lithium ion (Li + ) was used. The anions of the electrolyte salts used were the first imide anions shown in formulas (1-5), (1-6), (1-21), and (1-22), the second imide anion shown in formula (2-5), the third imide anion shown in formula (3-5), and the fourth imide anion shown in formula (4-37). The contents (mol / kg) of the electrolyte salts were as shown in Tables 1 and 2.

[0206] This resulted in the preparation of an electrolytic solution containing an electrolyte salt, which was a lithium salt containing an imide anion as an anion, and a solvent containing either a carboxylic acid ester compound or a diether compound.

[0207] As shown in Table 3, for comparison, hexafluorophosphate ion (PF6 - An electrolyte solution was prepared in the same manner as above, except that carboxylic acid ester compound and diether compound were not used.

[0208] For comparison, hexafluorophosphate ion (PF6 - ) was used, and an electrolyte solution was prepared in the same manner as above, except that a carboxylic acid ester compound or a diether compound was used.

[0209] Furthermore, for comparison, an electrolyte solution was prepared in the same manner except that an imide anion was used as the anion and neither a carboxylic acid ester compound nor a diether compound was used.

[0210] (Secondary battery assembly) First, a positive electrode lead 31 (aluminum foil) was welded to the positive electrode current collector 21A of the positive electrode 21, and a negative electrode lead 32 (copper foil) was welded to the negative electrode current collector 22A of the negative electrode 22.

[0211] Next, the positive electrode 21 and the negative electrode 22 were stacked together with a separator 23 (a microporous polyethylene film having a thickness of 15 μm) interposed therebetween, and then the positive electrode 21, the negative electrode 22, and the separator 23 were wound to prepare a wound body. Next, the wound body was pressed using a press machine to form the wound body into a flat shape.

[0212] Next, the exterior film 10 (fusion layer / metal layer / surface protection layer) was folded so as to sandwich the wound body accommodated in the recess 10U, and then the outer peripheral edges of two sides of the fusion layer were heat-sealed to each other, thereby accommodating the wound body inside the bag-shaped exterior film 10. The exterior film 10 used was an aluminum laminate film in which a fusion layer (a polypropylene film with a thickness of 30 μm), a metal layer (aluminum foil with a thickness of 40 μm), and a surface protection layer (a nylon film with a thickness of 25 μm) were laminated in this order from the inside.

[0213] Finally, after pouring the electrolyte solution into the bag-shaped exterior film 10, the outer peripheral edges of the remaining side of the adhesive layer were heat-sealed together in a reduced pressure environment. In this case, a sealing film 41 (a polypropylene film having a thickness of 5 μm) was inserted between the exterior film 10 and the positive electrode lead 31, and a sealing film 42 (a polypropylene film having a thickness of 5 μm) was inserted between the exterior film 10 and the negative electrode lead 32. As a result, the wound body was impregnated with the electrolyte solution, and the battery element 20 was produced.

[0214] Thus, the battery element was sealed inside the exterior film 10, and a secondary battery was assembled.

[0215] (Stabilization of secondary batteries) The secondary battery was charged and discharged for one cycle in a room temperature environment (temperature = 23°C). During charging, it was charged at a constant current of 0.1 C until the voltage reached 4.1 V, and then at that voltage of 4.1 V, it was charged at a constant voltage of 0.05 C. During discharging, it was discharged at a constant current of 0.1 C until the voltage reached 2.5 V. 0.1 C is the current value that fully discharges the battery capacity (theoretical capacity) in 10 hours, and 0.05 C is the current value that fully discharges the battery capacity in 20 hours.

[0216] As a result, a coating was formed on the surface of each of the positive electrode 21 and the negative electrode 22, which electrochemically stabilized the state of the secondary battery, thereby completing a laminate film type secondary battery.

[0217] After the secondary battery was completed, the electrolyte solution was analyzed using inductively coupled plasma (ICP) emission spectroscopy. As a result, it was confirmed that the type and content (mol / kg) of electrolyte salts (cations and anions), the type and content (wt%) of solvents (carboxylic acid ester compounds and diether compounds), and the type and content (wt%) of other solvents were as shown in Tables 1 to 3.

[0218] [Evaluation of battery characteristics] The battery characteristics were evaluated, and the results shown in Tables 1 to 3 were obtained. Here, the high-temperature cycle characteristics, high-temperature storage characteristics, and low-temperature load characteristics were evaluated.

[0219] (High temperature cycle characteristics) First, the discharge capacity (discharge capacity at the first cycle) was measured by charging and discharging the secondary battery in a high-temperature environment (temperature = 60 °C). The charge and discharge conditions were the same as those for stabilizing the secondary battery described above.

[0220] Subsequently, the secondary battery was repeatedly charged and discharged in the same environment until the total number of cycles reached 100, and the discharge capacity (discharge capacity at the 100th cycle) was measured under the same charge and discharge conditions as those used for stabilizing the secondary battery described above.

[0221] Finally, the cycle retention rate, which is an index for evaluating high-temperature cycle characteristics, was calculated based on the formula: cycle retention rate (%)=(discharge capacity at 100th cycle / discharge capacity at 1st cycle)×100.

[0222] (High temperature storage characteristics) First, the discharge capacity (discharge capacity before storage) was measured by charging and discharging the secondary battery for one cycle in a room temperature environment (temperature = 23 ° C.) The charge and discharge conditions were the same as those for stabilizing the secondary battery described above.

[0223] Subsequently, the secondary battery was charged in the same environment, and the charged secondary battery was stored in a high-temperature environment (temperature = 80 °C) (storage time = 10 days), and then discharged in a room-temperature environment to measure the discharge capacity (discharge capacity after storage). The charge / discharge conditions were the same as those for stabilizing the secondary battery described above.

[0224] Finally, the storage retention rate, which is an index for evaluating high-temperature storage characteristics, was calculated based on the formula: storage retention rate (%)=(discharge capacity after storage / discharge capacity before storage)×100.

[0225] (Low temperature load characteristics) First, the discharge capacity (discharge capacity at the first cycle) was measured by charging and discharging the secondary battery one cycle at room temperature (temperature = 23 ° C.) under the same charge and discharge conditions as those used for stabilizing the secondary battery described above.

[0226] Next, the secondary battery was repeatedly charged and discharged in a low-temperature environment (temperature = -10°C) until the total number of cycles reached 100, and the discharge capacity (discharge capacity at the 100th cycle) was measured. The charge and discharge conditions were the same as those used for stabilizing the secondary battery described above, except that the discharge current was changed to 1C. 1C is the current value at which the battery capacity is fully discharged in 1 hour.

[0227] Finally, the load retention rate, which is an index for evaluating low-temperature load characteristics, was calculated based on the formula: load retention rate (%)=(discharge capacity at 100th cycle / discharge capacity at 1st cycle)×100.

[0228] [Table 1]

[0229] [Table 2]

[0230] [Table 3]

[0231] [Consideration] As shown in Tables 1 to 3, the cycle retention rate, storage retention rate, and load retention rate each varied greatly depending on the composition of the electrolyte solution.

[0232] Specifically, when the electrolyte salt did not contain an imide anion and the solvent did not contain a carboxylic acid ester compound or a diether compound (Comparative Example 1), the cycle retention rate, storage retention rate, and load retention rate all decreased.

[0233] Furthermore, when the electrolyte salt did not contain an imide anion but the solvent contained either a carboxylic acid ester compound or a diether compound (Comparative Examples 2 and 3), the load retention rate increased in some cases, but the cycle retention rate and storage retention rate each decreased, compared to when the electrolyte salt did not contain an imide anion and the solvent did not contain either a carboxylic acid ester compound or a diether compound (Comparative Example 1).

[0234] Furthermore, when the electrolyte salt contained an imide anion but the solvent contained neither a carboxylic acid ester compound nor a diether compound (Comparative Example 4), the cycle retention rate, storage retention rate, and load retention rate all increased compared to when the electrolyte salt did not contain an imide anion and the solvent did not contain either a carboxylic acid ester compound or a diether compound (Comparative Example 1), but the cycle retention rate, storage retention rate, and load retention rate all did not increase sufficiently.

[0235] In contrast, when the electrolyte salt contained an imide anion and the solvent contained either a carboxylic acid ester compound or a diether compound (Examples 1 to 30), high cycle retention, high storage retention, and high load retention were obtained.

[0236] That is, when the electrolyte solution contained an imide anion and the solvent contained a carboxylic acid ester compound (Example 3), the cycle retention rate, storage retention rate, and load retention rate all increased significantly compared to when the electrolyte salt did not contain an imide anion and the solvent did not contain a carboxylic acid ester compound (Comparative Example 1).

[0237] Furthermore, when the electrolyte solution contained an imide anion and the solvent contained a diether compound (Example 19), the cycle retention rate, storage retention rate, and load retention rate all significantly increased compared to when the electrolyte salt did not contain an imide anion and the solvent did not contain a diether compound (Comparative Example 1).

[0238] In this case (Examples 1 to 30), the following trends were particularly observed. First, when the electrolyte salt contained a light metal ion (lithium ion) as a cation, the cycle retention rate, storage retention rate, and load retention rate were all sufficiently high. Second, when the content of the electrolyte salt was 0.2 mol / kg to 2 mol / kg relative to the solvent, the cycle retention rate, storage retention rate, and load retention rate were all sufficiently high. Third, when the content of the carboxylic acid ester compound was 5 wt % to 80 wt %, the cycle retention rate, storage retention rate, and load retention rate were all sufficiently high. Fourth, when the content of the diether compound was 5 wt % to 80 wt %, the cycle retention rate, storage retention rate, and load retention rate were all sufficiently high.

[0239] <Examples 31 to 66> As shown in Tables 4 to 7, secondary batteries were produced in the same manner as in Examples 3 and 19, except that either an additive or another electrolyte salt was added to the electrolytic solution, and then the battery characteristics were evaluated.

[0240] Details of the additives are as follows. The unsaturated cyclic carbonates used were vinylene carbonate (VC), vinylethylene carbonate (VEC), and methyleneethylene carbonate (MEC). The fluorinated cyclic carbonates used were monofluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC). The sulfonates used were the cyclic monosulfonates propane sultone (PS) and propene sultone (PRS), and the cyclic disulfonate cyclodisone (CD). The dicarboxylic anhydride used was succinic anhydride (SA). The disulfonic anhydride used was propanedisulfonic anhydride (PSAH). The sulfate used was ethylene sulfate (DTD). The nitrile compound used was succinonitrile (SN). The isocyanate compound used was hexamethylene diisocyanate (HMI).

[0241] Other electrolyte salts used were lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB), and lithium difluorophosphate (LiPF2O2).

[0242] The contents (wt %) of the additives and other electrolyte salts in the electrolyte solution were as shown in Tables 4 to 7. In this case, after the secondary battery was completed, the electrolyte solution was analyzed using ICP atomic emission spectroscopy, and it was confirmed that the contents of the additives and other electrolyte salts were as shown in Tables 4 to 7.

[0243] [Table 4]

[0244] [Table 5]

[0245] [Table 6]

[0246] [Table 7]

[0247] As shown in Tables 1, 4, and 6, when the electrolyte solution contained an additive (Examples 31 to 43, 49 to 61), one or more of the cycle retention rate, storage retention rate, and load retention rate were increased more than when the electrolyte solution did not contain an additive (Examples 3 and 19).

[0248] Furthermore, as shown in Tables 2, 5, and 7, when the electrolyte solution contained other electrolyte salts (Examples 44 to 48, 62 to 66), high cycle retention rates, high storage retention rates, and high load retention rates were obtained, similar to when the electrolyte solution did not contain other electrolyte salts (Examples 3 and 19). In this case, depending on the type of other electrolyte salt, one or more of the cycle retention rate, storage retention rate, and load retention rate increased.

[0249] <Examples 67 to 130> As shown in Tables 8 to 11, secondary batteries were produced in the same manner as in Examples 3 and 19, except that another electrolyte salt (lithium hexafluorophosphate (LiPF6)) was added to the electrolytic solution, and then the battery characteristics were evaluated.

[0250] In this case, the electrolyte salt and other electrolyte salts were added to the solvent, and the solvent was then stirred. The contents (mol / kg) of the electrolyte salt, the contents (mol / kg) of the other electrolyte salts, the sum T (mol / kg), and the ratio R (mol%) were as shown in Tables 8 to 11.

[0251] [Table 8]

[0252] [Table 9]

[0253] [Table 10]

[0254] [Table 11]

[0255] As shown in Tables 8 to 11, when the two conditions that the sum T was 0.7 mol / kg to 2.2 mol / kg and the ratio R was 13 mol% to 6000 mol% were met (Examples 71, 103, etc.), the cycle retention rate, storage retention rate, and load retention rate each increased more than when these two conditions were not met (Examples 67, 99, etc.).

[0256] [summary] The results shown in Tables 1 to 11 indicate that when the electrolyte solution contains an electrolyte salt and a solvent, the solvent contains one or both of a carboxylic acid ester compound and a diether compound, the electrolyte salt contains one or more of the anions shown in formulas (1) to (4) as imide anions, the carboxylic acid ester compound contains the compound shown in formula (5), and the diether compound contains the compound shown in formula (6), the cycle retention rate, storage retention rate, and load retention rate are all improved. Therefore, the secondary battery achieved excellent high-temperature cycle characteristics, excellent high-temperature storage characteristics, and excellent low-temperature load characteristics, resulting in excellent battery characteristics.

[0257] The present technology has been described above with reference to an embodiment and examples. However, the configuration of the present technology is not limited to the configuration described in the embodiment and examples, and can be modified in various ways.

[0258] Specifically, the battery element has been described as having a wound structure. However, the structure of the battery element is not particularly limited, and may be a stacked structure or a zigzag structure. In the stacked structure, the positive and negative electrodes are alternately stacked with a separator interposed therebetween, while in the zigzag structure, the positive and negative electrodes are folded in a zigzag pattern while facing each other with the separator interposed therebetween.

[0259] Although the electrode reactant is lithium in the above description, the electrode reactant is not particularly limited. Specifically, as described above, the electrode reactant may be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium, and calcium. Alternatively, the electrode reactant may be other light metals such as aluminum.

[0260] The effects described in this specification are merely examples, and the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present technology.

Claims

1. A positive electrode and a negative electrode; an electrolyte solution containing an electrolyte salt and a solvent; Equipped with The electrolyte salt contains an imide anion, and the imide anion contains at least one of anions represented by formula (1), formula (2), formula (3), and formula (4), the solvent contains at least one of a carboxylic acid ester compound and a diether compound, The carboxylic acid ester compound includes a compound represented by formula (5), The diether compound includes a compound represented by formula (6), the content of the electrolyte salt in the electrolytic solution is 0.2 mol / kg or more and 2 mol / kg or less; the electrolyte solution further contains lithium hexafluorophosphate, the electrolytic solution further contains at least one of vinylethylene carbonate, methyleneethylene carbonate, a fluorinated cyclic carbonate, a sulfate ester, and an isocyanate compound; the electrolyte salt comprises a cation and the imide anion; The lithium hexafluorophosphate contains lithium ions and hexafluorophosphate ions, the sum of the content of the cations in the electrolytic solution and the content of the lithium ions in the electrolytic solution is 0.7 mol / kg or more and 2.2 mol / kg or less; a ratio of the number of moles of the hexafluorophosphate ions in the electrolyte solution to the number of moles of the imide anions in the electrolyte solution is 13 mol% or more and 6000 mol% or less; Secondary battery. 【Chemistry 1】 (R1 and R2 are each a fluorine group or a fluorinated alkyl group. W1, W2, and W3 are each a carbonyl group (>C=O), a sulfinyl group (>S=O), and a sulfonyl group (>S(=O) 2 ) is one of the following. 【Chemistry 2】 (Each of R3 and R4 is either a fluorine group or a fluorinated alkyl group. Each of X1, X2, X3 and X4 is either a carbonyl group, a sulfinyl group or a sulfonyl group.) 【Transformation 3】 (R5 is a fluorinated alkylene group. Y1, Y2, and Y3 each are any one of a carbonyl group, a sulfinyl group, and a sulfonyl group.) 【Chemistry 4】 (R6 and R7 each represent a fluorine group or a fluorinated alkyl group. R8 represents an alkylene group, a phenylene group, a fluorinated alkylene group, or a fluorinated phenylene group. Z1, Z2, Z3, and Z4 each represent a carbonyl group, a sulfinyl group, or a sulfonyl group.) R9-C(=O)-O-R10...(5) (R9 and R10 are each either an alkyl group or a fluorinated alkyl group, provided that R9 has 1 or more and 10 or less carbon atoms, and R10 has 2 or more and 10 or less carbon atoms.) R11-O-R12-O-R13-O-R14...(6) (Each of R11 and R14 is either an alkyl group or a fluorinated alkyl group. Each of R12 and R13 is either an alkylene group or a fluorinated alkylene group.)

2. The carboxylic acid ester compound includes at least one of propyl acetate, ethyl propionate, and propyl propionate. The secondary battery according to claim 1 .

3. the content of at least one of the carboxylic acid ester compound and the diether compound in the solvent is 5% by weight or more and 80% by weight or less; The secondary battery according to claim 1 .

4. The electrolyte solution further contains at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, and lithium difluorophosphate. The secondary battery according to claim 1 .

5. It is a lithium-ion secondary battery. The secondary battery according to any one of claims 1 to 4.

6. an electrolyte solution containing an electrolyte salt and a solvent, The electrolyte salt contains an imide anion, and the imide anion contains at least one of anions represented by formula (1), formula (2), formula (3), and formula (4), the solvent contains at least one of a carboxylic acid ester compound and a diether compound, The carboxylic acid ester compound includes a compound represented by formula (5), The diether compound includes a compound represented by formula (6), the content of the electrolyte salt in the electrolytic solution is 0.2 mol / kg or more and 2 mol / kg or less; the electrolyte solution further contains lithium hexafluorophosphate, the electrolytic solution further contains at least one of vinylethylene carbonate, methyleneethylene carbonate, a fluorinated cyclic carbonate, a sulfate ester, and an isocyanate compound; the electrolyte salt comprises a cation and the imide anion; The lithium hexafluorophosphate contains lithium ions and hexafluorophosphate ions, the sum of the content of the cations in the electrolytic solution and the content of the lithium ions in the electrolytic solution is 0.7 mol / kg or more and 2.2 mol / kg or less; a ratio of the number of moles of the hexafluorophosphate ions in the electrolyte solution to the number of moles of the imide anions in the electrolyte solution is 13 mol% or more and 6000 mol% or less; Electrolyte for secondary batteries. 【Transformation 5】 (R1 and R2 are each either a fluorine group or a fluorinated alkyl group. W1, W2, and W3 are each either a carbonyl group, a sulfinyl group, or a sulfonyl group.) 【Transformation 6】 (Each of R3 and R4 is either a fluorine group or a fluorinated alkyl group. Each of X1, X2, X3 and X4 is either a carbonyl group, a sulfinyl group or a sulfonyl group.) 【Transformation 7】 (R5 is a fluorinated alkylene group. Y1, Y2, and Y3 each are any one of a carbonyl group, a sulfinyl group, and a sulfonyl group.) 【Transformation 8】 (R6 and R7 each represent a fluorine group or a fluorinated alkyl group. R8 represents an alkylene group, a phenylene group, a fluorinated alkylene group, or a fluorinated phenylene group. Z1, Z2, Z3, and Z4 each represent a carbonyl group, a sulfinyl group, or a sulfonyl group.) R9-C(=O)-O-R10...(5) (R9 and R10 are each either an alkyl group or a fluorinated alkyl group, provided that R9 has 1 or more and 10 or less carbon atoms, and R10 has 2 or more and 10 or less carbon atoms.) R11-O-R12-O-R13-O-R14...(6) (Each of R11 and R14 is either an alkyl group or a fluorinated alkyl group. Each of R12 and R13 is either an alkylene group or a fluorinated alkylene group.)

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