Electrolyte, lithium-sulfur secondary battery, and module

Abstract

Provided is an electrolyte solution with which it is possible to obtain a lithium-sulfur secondary battery that has excellent cycle characteristics and is not susceptible to gas generation. An electrolyte solution for a lithium-sulfur secondary battery having a positive electrode and a negative electrode, the positive electrode containing a sulfur-based electrode active material containing at least one substance selected from elemental sulfur, lithium polysulfide (Li2Sn: 1 < n < 8), an organic sulfur compound, and an inorganic sulfur compound, and the negative electrode containing a sulfur-based electrode active material containing at least one substance selected from elemental sulfur, lithium polysulfide (Li2Sn: 1 < n < 8), an organic sulfur compound, and an inorganic sulfur compound. The negative electrode contains a material that absorbs and releases lithium ions, the electrolyte solution contains a non-aqueous electrolyte and a solvent, the solvent contains a chain diether, and the value [sigma] {[sigma] * P ([sigma])} of the chain diether in the range of # imgabs0 # is within the range represented by general formula (1). The general formula (1): 0lt; sigma {sigma * P (sigma)} lt; 0.24 (In the formula, sigma represents shielding charge density, and P (sigma) represents sigma-distribution).

Description

Technical Field

[0001] The present invention relates to an electrolyte, a lithium-sulfur secondary battery, and components. Background Art

[0002] As a high-capacity secondary battery, the lithium-ion secondary battery has been widely popularized, and further, as a high-capacity secondary battery, the lithium-sulfur secondary battery has been studied. Among these various batteries, the performance of the electrolyte has a great influence on the performance of the battery.

[0003] Patent Document 1 describes a lithium-sulfur secondary battery using a solvent containing vinylene carbonate.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: WO 2021 / 090666 Summary of the Invention

[0007] Technical Problem to be Solved by the Invention

[0008] An object of the present invention is to provide an electrolyte for a lithium-sulfur secondary battery that can achieve excellent cycle characteristics and is less likely to generate gas.

[0009] Technical Solution for Solving the Technical Problem

[0010] The present invention (1) relates to an electrolyte for a lithium-sulfur secondary battery having a positive electrode and a negative electrode, the positive electrode containing a sulfur-based electrode active material, the sulfur-based electrode active material including at least one selected from elemental sulfur, polysulfide lithium (Li2S n : 1 < n < 8), organic sulfur compounds, and inorganic sulfur compounds, and the negative electrode containing a material that absorbs and releases lithium ions.

[0011] The electrolyte contains a non-aqueous electrolyte and a solvent.

[0012] The solvent contains a chain-like diether, and the Σ{σ×P(σ)} value in the range of is in the range shown by the following general formula (1).

[0013] General formula (1): 0 < Σ{σ×P(σ)} < 0.24

[0014] (In the formula, σ represents the shielding charge density, and P(σ) represents the σ-profile.)

[0015] The present invention (2) is the electrolyte according to the present invention (1), wherein the chain-like diether is a fluorinated chain-like diether.

[0016] The electrolyte of the present invention (3) is the electrolyte described in the present invention (1) or (2), wherein the chain-like diether is at least one selected from the compounds represented by the following general formula (A) and the compounds represented by the following general formula (B).

[0017] General formula (A):

[0018] [Chemical formula 1]

[0019]

[0020] (In the formula, R 1a ~R 10a are independently a halogen atom, a hydrogen atom, an alkyl group having 2 or less carbon atoms, or a fluoroalkyl group having 2 or less carbon atoms. Among them, at least one of R 1a ~R 10a is a halogen atom or a fluoroalkyl group having 2 or less carbon atoms.)

[0021] General formula (B):

[0022] [Chemical formula 2]

[0023]

[0024] (In the formula, R 1b ~R 8b are independently a halogen atom, a hydrogen atom, an alkyl group having 2 or less carbon atoms, or a fluoroalkyl group having 2 or less carbon atoms.)

[0025] The electrolyte of the present invention (4) is an electrolyte which is any combination of any one of the present inventions (1) to (3), wherein the chain-like diether is at least one selected from the compounds represented by the following formulae.

[0026] [Chemical formula 3]

[0027]

[0028] The electrolyte of the present invention (5) is an electrolyte which is any combination of any one of the present inventions (1) to (4), wherein the content of the chain-like diether is 3 to 90% by mass based on the total amount of the electrolyte.

[0029] The present invention (6) is a lithium-sulfur secondary battery which has a positive electrode and a negative electrode, the positive electrode contains a sulfur-based electrode active material, the sulfur-based electrode active material contains at least one selected from elemental sulfur, polysulfide lithium (Li2S n : 1 < n < 8), organic sulfur compounds, and inorganic sulfur compounds, the negative electrode contains a material that absorbs and releases lithium ions, and the lithium-sulfur secondary battery uses an electrolyte which is any combination of any one of the present inventions (1) to (5).

[0030] The present invention (7) is a component that includes the lithium-sulfur secondary battery described in the present invention (6).

[0031] Advantages of the Invention

[0032] According to the present invention, it is possible to provide an electrolyte for a lithium-sulfur secondary battery that can achieve excellent cycle characteristics and is not prone to gas generation. Detailed Description of the Invention

[0033] Hereinafter, the present invention will be specifically described.

[0034] The present invention provides an electrolyte for a lithium-sulfur secondary battery, which has a positive electrode and a negative electrode. The positive electrode contains a sulfur-based electrode active material, and the sulfur-based electrode active material includes at least one selected from elemental sulfur, polysulfide lithium (Li2S n : 1 < n < 8), organic sulfur compounds, and inorganic sulfur compounds. The negative electrode contains a material that absorbs and releases lithium ions. The electrolyte contains a non-aqueous electrolyte and a solvent, and the solvent contains a chain-like diether. The Σ{σ×P(σ)} value of the chain-like diether within the range is within the range shown by the following general formula (1).

[0035] General formula (1): 0 < Σ{σ×P(σ)} < 0.24

[0036] (In the formula, σ represents the shielding charge density, and P(σ) represents the σ-distribution.)

[0037] The electrolyte of the present invention uses a solvent containing a chain-like diether (hereinafter, also referred to as chain-like diether (1)). The Σ{σ×P(σ)} value of the chain-like diether within the range is within the above range. Therefore, a lithium-sulfur secondary battery with excellent cycle characteristics and not prone to gas generation can be obtained.

[0038] The present inventors have found that the above chain-like diether (1) does not coordinate with sulfur but can coordinate with lithium. By using a chain-like diether with such specific properties, compared with the case of using conventional solvents such as fluorinated monoethers and vinylene carbonate, the dissolution and diffusion of polysulfide lithium (Li2S n ) generated during the charge and discharge of the lithium-sulfur secondary battery due to electrode reactions can be effectively suppressed. As a result, the cycle characteristics (discharge capacity after charge and discharge cycles) can be improved, and the generation of gas can also be suppressed. In contrast, fluorinated monoethers neither coordinate with lithium nor with sulfur, so they cannot suppress the diffusion of polysulfide lithium. It is considered that vinylene carbonate can suppress the dissolution of polysulfide lithium to some extent by forming a film derived from vinylene carbonate on the sulfur positive electrode, but the suppression effect is insufficient.

[0039] The Σ{σ×P(σ)} value of the chain-like diether (1) is greater than 0, and can be 0.00001 or more. From the viewpoint of further improving the cycle characteristics, it is preferably 0.01 or more, more preferably 0.10 or more, further preferably 0.12 or more, still further preferably 0.14 or more, particularly preferably 0.16 or more, and most preferably 0.17 or more.

[0040] In addition, the Σ{σ×P(σ)} value of the chain-like diether (1) is less than 0.24. From the viewpoint of further suppressing gas generation, it is preferably 0.23 or less, more preferably 0.22 or less, further preferably 0.21 or less, and still further preferably 0.20 or less.

[0041] In the above general formula (1), σ represents the shielding charge density, and P(σ) represents the σ-distribution.

[0042] The shielding charge density σ is the charge density on the molecular surface calculated by the COSMO-RS (Conductor like Screening Model for Real Solvents) method.

[0043] The σ-distribution P(σ) is calculated by dividing the molecular surface into segments of a certain area, and represents the degree of segments of the shielding charge density.

[0044] σ×P(σ) is the product of the charge density and the number of the above segments, and represents the charge density distribution on the molecular surface.

[0045] Σ{σ×P(σ)} represents the sum of σ×P(σ) within the range of the range of.

[0046] It is considered that the range has a high Lewis basicity on the molecular surface, which is favorable for the formation of intermolecular interactions such as coordination bonds and hydrogen bonds. Therefore, the chain-like diether with a low Σ{σ×P(σ)} value (within the above range) has a low coordination force with lithium polysulfide, and can suppress the dissolution of lithium polysulfide into the electrolyte.

[0047] The shielding charge density σ and the σ-distribution P(σ) can be calculated using the software "COSMOtherm" (manufactured by MOLSIS).

[0048] As the chain-like diether (1), at least one selected from the compounds represented by the following general formula (A) (hereinafter, also referred to as compound (A).) and the compounds represented by the following general formula (B) (hereinafter, also referred to as compound (B).) can be mentioned.

[0049] General formula (A):

[0050] [Chemical formula 4]

[0051]

[0052] (In the formula, R 1a ~R 10a are independently a halogen atom, a hydrogen atom, an alkyl group having 2 or less carbon atoms, or a fluoroalkyl group having 2 or less carbon atoms. Among them, at least one of R 1a ~R 10a is a halogen atom or a fluoroalkyl group having 2 or less carbon atoms.)

[0053] General formula (B):

[0054] [Chemical formula 5]

[0055]

[0056] (In the formula, R 1b ~R 8b are independently a halogen atom, a hydrogen atom, an alkyl group having 2 or less carbon atoms, or a fluoroalkyl group having 2 or less carbon atoms.)

[0057] As the halogen atom of R 1a ~R 10a in general formula (A), fluorine atom, chlorine atom, bromine atom, iodine atom, etc. can be mentioned, preferably fluorine atom, chlorine atom, more preferably fluorine atom.

[0058] As the above alkyl group of R 1a ~R 10a in general formula (A), it may be an alkyl group having no fluorine atom or an alkyl group having no halogen atom. As the above alkyl group, -CH3, -CH2CH3 can be mentioned, preferably -CH3.

[0059] As the above fluoroalkyl group of R 1a ~R 10a in general formula (A), -CF3, -CHF2, -CH2F, -CH2CF3, -CF2CF3, -CH2CHF2, -CH2CH2F, etc. can be mentioned.

[0060] As the above fluoroalkyl group, a fluoroalkyl group having 1 carbon atom, that is, -CF3, -CHF2, -CH2F, is preferred, and -CF3 is more preferred.

[0061] In general formula (A), at least one of R 1a ~R 10a is a halogen atom or a fluoroalkyl group having 2 or less carbon atoms, preferably a fluorine atom or a fluoroalkyl group having 2 or less carbon atoms.

[0062] In general formula (A), R 1a ~R 3a and R8a ~R 10a Independently is a halogen atom, a hydrogen atom or a fluoroalkyl group having 2 or less carbon atoms, R 4a ~R 7a Independently is preferably a halogen atom or a hydrogen atom, R 1a ~R 3a and R 8a ~R 10a Independently is a fluorine atom, a hydrogen atom or a fluoroalkyl group having 2 or less carbon atoms, R 4a ~R 7a Independently is preferably a fluorine atom or a hydrogen atom.

[0063] As the compound (A), for example, the compounds represented by the following formula can be cited.

[0064] [Chemical formula 6]

[0065]

[0066] As R in the general formula (B) 1b ~R 8b The halogen atoms include fluorine atom, chlorine atom, bromine atom, iodine atom, etc., preferably fluorine atom and chlorine atom, and more preferably fluorine atom.

[0067] As R in the general formula (B) 1b ~R 8b The above alkyl group may be an alkyl group having no fluorine atom or an alkyl group having no halogen atom. As the above alkyl group, -CH3, -CH2CH3 can be cited, and preferably -CH3.

[0068] As R in the general formula (B) 1b ~R 8b The fluoroalkyl groups include -CF3, -CHF2, -CH2F, -CH2CF3, -CF2CF3, -CH2CHF2, -CH2CH2F, etc.

[0069] As the above fluoroalkyl group, preferably a fluoroalkyl group having 1 carbon atom, that is, -CF3, -CHF2, -CH2F, and more preferably -CF3.

[0070] As the compound (B), for example, the compounds represented by the following formula can be cited.

[0071] [Chemical formula 7]

[0072]

[0073] The chain-like diether (1) is preferably a fluoro chain-like diether.

[0074] As the chain-like diether (1), the compound (A) is preferred, and at least one selected from the compounds represented by the following formulas is more preferred.

[0075] [Chemical formula 8]

[0076]

[0077] As the chain-like diether (1), at least one selected from the compounds represented by the following formulas is further preferred.

[0078] [Chemical formula 9]

[0079]

[0080] As the chain-like diether (1), at least one selected from the compounds represented by the following formulas is particularly preferred.

[0081] [Chemical formula 10]

[0082]

[0083] From the viewpoint of further improving the cycle characteristics and further suppressing the generation of gas, the content of the chain-like diether (1) is preferably 3 to 90% by mass relative to the total amount of the above electrolyte. The above content is more preferably 5% by mass or more, further preferably 10% by mass or more, further more preferably 25% by mass or more, further more preferably 30% by mass or more, further more preferably 35% by mass or more, particularly preferably 40% by mass or more. In addition, it is more preferably 80% by mass or less, further preferably 70% by mass or less, further more preferably 65% by mass or less, and particularly preferably 60% by mass or less.

[0084] The electrolyte of the present invention contains a solvent containing the above chain-like diether (1). Here, the "solvent" refers to a compound having volatility among the liquid components contained in the electrolyte. In the electrolyte of a lithium-sulfur battery, a non-aqueous electrolyte is contained. Such a non-aqueous electrolyte is a component that does not have volatility. The "solvent" in the present invention refers to a substance used in combination with these non-aqueous electrolytes in the electrolyte, and means various volatile liquid compounds such as carbonate compounds, ether compounds, and ester compounds. In addition, two or more of them can be used in combination.

[0085] The above solvent is preferably a non-aqueous solvent, and the electrolyte of the present invention is preferably a non-aqueous electrolyte.

[0086] The electrolyte of the present invention may contain a solvent other than the chain-like diether (1) (hereinafter, referred to as "other solvent").

[0087] As the above-mentioned other solvents, there is no particular limitation, and various solvents that can be used as solvents in electrolytes in the battery field can be used. Specifically, vinylene carbonate, fluorinated saturated cyclic carbonates, fluorinated chain carbonates, ether compounds (excluding chain diethers (1)), fluorinated ethers (excluding chain diethers (1)), fluorinated esters, etc. can be cited.

[0088] Hereinafter, these other solvents will be described in detail.

[0089] (Vinylene carbonate)

[0090] Vinylene carbonate is a compound represented by the following formula (3).

[0091] [Chemical formula 11]

[0092]

[0093] If the above-mentioned solvent contains chain diethers (1) and vinylene carbonate, a lithium-sulfur secondary battery with more excellent cycle characteristics can be obtained.

[0094] It should be noted that the improvement in cycle characteristics caused by vinylene carbonate is considered to be due to the formation of a film derived from vinylene carbonate on the sulfur positive electrode.

[0095] (Fluorinated saturated cyclic carbonates)

[0096] As the above-mentioned fluorinated saturated cyclic carbonates, the compound represented by the formula (4) is preferred.

[0097] [Chemical formula 12]

[0098]

[0099] (In the formula, R 21 ~R 24 are the same or different and each represents -H, -CH3, -F, a fluorinated alkyl group that may have an ether bond, or a fluorinated alkoxy group that may have an ether bond. Among them, at least one of R 21 ~R 24 is -F, a fluorinated alkyl group that may have an ether bond, or a fluorinated alkoxy group that may have an ether bond.)

[0100] As the above-mentioned fluorinated alkyl group, a fluorinated alkyl group having 1 to 10 carbon atoms is preferred, a fluorinated alkyl group having 1 to 6 carbon atoms is more preferred, and a fluorinated alkyl group having 1 to 4 carbon atoms is further preferred.

[0101] The above-mentioned fluorinated alkyl group can be linear or branched.

[0102] As the above-mentioned fluoroalkoxy group, a fluoroalkoxy group having 1 to 10 carbon atoms is preferred, a fluoroalkoxy group having 1 to 6 carbon atoms is more preferred, and a fluoroalkoxy group having 1 to 4 carbon atoms is further preferred.

[0103] The above-mentioned fluoroalkoxy group may be linear or branched.

[0104] As R 21 ~R 24 , they may be the same or different, and are preferably at least one selected from -H, -CH3, -F, -CF3, -C4F9, -CHF2, -CH2F, -CH2CF2CF3, -CH2-CF(CF3)2, -CH2-O-CH2CHF2CF2H, -CH2CF3 and -CF2CF3.

[0105] At this time, at least one of R 21 ~R 24 is at least one selected from -F, -CF3, -C4F9, -CHF2, -CH2F, -CH2CF2CF3, -CH2-CF(CF3)2, -CH2-O-CH2CHF2F2H, -CH2CF3 and -CF2CF3.

[0106] As the above-mentioned fluorinated saturated cyclic carbonate, at least one selected from the following compounds is preferred.

[0107] [Chemical formula 13]

[0108]

[0109] In the present invention, other solvents are more preferably compounds represented by the following general formula among cyclic saturated carbonates.

[0110] [Chemical formula 14]

[0111]

[0112] (In the formula, R 1 is a fluoro group or an alkyl group having 1 to 4 carbon atoms containing a fluoro group and may have an ether bond and / or an unsaturated bond.)

[0113] The above compounds are particularly preferred for improving the battery output. Further, it is most preferred to use fluoroethylene carbonate represented by the following general formula.

[0114] [Chemical formula 15]

[0115]

[0116] (Fluorinated chain carbonate)

[0117] As the above-mentioned fluorinated chain carbonate, a compound represented by the following general formula is preferred.

[0118] [Chemical Formula 16]

[0119]

[0120] (In the formula, R 31 and R 32 are the same or different and represent an alkyl group that may have an ether bond and may also have a fluorine atom. Among them, R 31 and R 32 any one of them has a fluorine atom.)

[0121] As the above-mentioned alkyl group, an alkyl group having 1 to 10 carbon atoms is preferred, an alkyl group having 1 to 6 carbon atoms is more preferred, and an alkyl group having 1 to 4 carbon atoms is further preferred.

[0122] The above-mentioned alkyl group can be linear or branched.

[0123] As R 31 and R 32 , which are the same or different, are preferably at least one selected from -CH3, -CF3, -CHF2, -CH2F, -C2H5, -CH2CF3, -CH2CHF2, and -CH2CF2CF2H.

[0124] At this time, at least one of R 31 and R 32 is at least one selected from -CF3, -CHF2, -CH2F, -CH2CHF2, -CH2CF3, and -CH2CF2CF2H.

[0125] As the above-mentioned fluorinated chain carbonate, at least one selected from the following compounds is preferred.

[0126] [Chemical Formula 17]

[0127]

[0128] (Fluorinated ester)

[0129] As the above-mentioned fluorinated ester, a compound represented by the following general formula is preferred.

[0130] [Chemical Formula 18]

[0131]

[0132] (In the formula, R 41 and R 42 are the same or different and represent an alkyl group that may have an ether bond and may also have a fluorine atom, and may be bonded to each other to form a ring. Among them, R 41 and R 42Any of them has a fluorine atom. )

[0133] The alkyl group is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 6 carbon atoms, and still more preferably an alkyl group having 1 to 4 carbon atoms.

[0134] The above-mentioned alkyl group may be linear or branched.

[0135] As R 41 and R 42 , the same or different, preferably at least one selected from -CH3, -C2H5, -CHF2, -CH2F, -CH(CF3)2, -CHFCF3, -CF3 and -CH2CF3.

[0136] At this time, R 41 and R 42 At least one of them is at least one selected from -CHF2, -CH(CF3)2, -CHFCF3, -CF3 and -CH2CF3.

[0137] R 41 and R 42 Bonding to each other to form a ring means that R 41 and R 42 With R 41 and R 42 The carbon atoms and oxygen atoms that are bonded to each other together form a ring, R 41 and R 42 As a fluoroalkylene group, it constitutes a part of the ring. 41 and R 42 When they are bonded to each other to form a ring, R 41 and R 42 , preferably at least one selected from -CH2CH2CH(CH2CF3)-, -CH(CF3)CH2CH2-, -CHFCH2CH2-, -CH2CH2CHF- and -CH2CH2CH(CF3)-.

[0138] The fluorinated ester is preferably at least one selected from the following compounds.

[0139] [Chemistry 19]

[0140]

[0141] (Ether compound)

[0142] As the ether compound, a compound represented by the following general formula (2) (excluding the chain diether (1)) can be preferably used.

[0143] R 2 -(OCHR 3(CH2) x -OR 3 (2)

[0144] (In the formula, R 2 and R 3 are each independently selected from an alkyl group having 1 to 9 carbon atoms which may be substituted with fluorine, a phenyl group which may be substituted with a halogen atom, and a cyclohexyl group which may be substituted with a halogen atom, and among them, they may also form a ring together. R 3 each independently represents H or CH3, and x represents 0 to 10.)

[0145] The compound represented by the above general formula (2) can be classified into a non-fluorinated ether compound and a fluorinated ether compound. Hereinafter, the above ether compounds will be classified into non-fluorinated ether compounds and fluorinated ether compounds and described in detail separately.

[0146] (Non-fluorinated ether compound)

[0147] As the non-fluorinated ether compound, a compound represented by the following general formula (excluding the chain-like diether (1)) can be preferably used.

[0148] R 54 -(OCHR 53 CH2) x -OR 55

[0149] (In the formula, R 54 and R 55 are each independently selected from an alkyl group having 1 to 9 carbon atoms without fluorine, a phenyl group which may be substituted with a halogen atom, and a cyclohexyl group which may be substituted with a halogen atom, and among them, they may also form a ring together. R 53 each independently represents H or CH3, and x represents 0 to 10.)

[0150] Examples of the alkyl group in the above formula include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, isopentyl, hexyl, heptyl, octyl, nonyl, etc. If the number of carbon atoms of the alkyl group is greater than 9, the polarity of the ether compound becomes weak, and thus there is a tendency for the solubility of the alkali metal salt to decrease. Therefore, the number of carbon atoms of the alkyl group is preferably small, preferably methyl and ethyl, and most preferably methyl.

[0151] Examples of the phenyl group which may be substituted with a halogen atom are not particularly limited, and include 2-chlorophenyl, 3-chlorophenyl, 4-chlorophenyl, 2,4-dichlorophenyl, 2-bromophenyl, 3-bromophenyl, 4-bromophenyl, 2,4-dibromophenyl, 2-iodophenyl, 3-iodophenyl, 4-iodophenyl, 2,4-iodophenyl, etc.

[0152] The cyclohexyl group that can be substituted by a halogen atom is not particularly limited, and examples thereof include 2-chlorocyclohexyl, 3-chlorocyclohexyl, 4-chlorocyclohexyl, 2,4-dichlorocyclohexyl, 2-bromocyclohexyl, 3-bromocyclohexyl, 4-bromocyclohexyl, 2,4-dibromocyclohexyl, 2-iodocyclohexyl, 3-iodocyclohexyl, 4-iodocyclohexyl, 2,4-diiodocyclohexyl, and the like.

[0153] R 53 represents H or CH3, and when x is 2 or more, they are each independent of one another. x represents 0 to 10, which is the number of repetitions of the ethylene oxide unit. x is preferably 1 to 6, more preferably 2 to 5, and most preferably 3 or 4.

[0154] Examples of the above ether compound include tetrahydrofuran (THF), 1,3-dioxolane, 1,4-dioxane, or ethylene glycol dimethyl ether (glyme), or derivatives thereof.

[0155] The ether compounds represented by the above general formula may together form a ring. As such a cyclic compound, when x is 0, examples include tetrahydrofuran (THF) and 2-methyltetrahydrofuran as its derivative, and when x is 1, examples include 1,3-dioxolane and 1,4-dioxane.

[0156] Ethylene glycol dimethyl ether is represented by the above general formula (2) (wherein R 3 represents H, x represents 1 or more, and it is a straight-chain compound.), and examples include monoethylene glycol dimethyl ether (G1, x = 1), diethylene glycol dimethyl ether (G2, x = 2), triethylene glycol dimethyl ether (G3, x = 3), and tetraethylene glycol dimethyl ether (G4, x = 4). As monoethylene glycol dimethyl ether (G1), examples include methyl monoethylene glycol dimethyl ether, ethyl monoethylene glycol dimethyl ether, etc., and as diethylene glycol dimethyl ether (G2), examples include ethyl diethylene glycol dimethyl ether, butyl diethylene glycol dimethyl ether, etc.

[0157] As the above ether compound, if ethylene glycol dimethyl ether with x being 1 to 10 is used, the thermal stability, ionic conductivity, and electrochemical stability of the electrolyte can be further improved, and an electrolyte capable of withstanding high voltage can be formed. The ether compound that can be used in the electrolyte can be used alone or in the form of a mixture of two or more.

[0158] (Fluoroether compound)

[0159] The above other solvent may be a fluoroether compound represented by the following general formula (5).

[0160] Rf-(OR 51 ) n1 -O-R 52 (5)

[0161] (In the formula, Rf is an alkyl group having a fluorine atom, and can form a branched chain or a ring having 1 to 5 carbon atoms. R 51 is an alkyl group which may have a fluorine atom, and R 52 is an alkyl group having no fluorine, having 1 to 9 carbon atoms, and can form a branched chain or a ring. n1 is 0 or 2.)

[0162] The compound represented by the above formula (5) is not particularly limited. For example, HC F2CF2OCH2CH2CH3, HCF2CF2OCH2CH2CH2CH3, HCF2CF2CH2OCH2CH3, HCF2CF2CH2OCH2CH2CH3, HCF2CF2CH2OCH2CH2CH2CH3, CF3CHFCF2OCH2CH3, CF3CHFCF2OCH2CH2CH3, HCF2CF2OCH2CH3 can be cited. Two or more of these compounds can also be used in combination.)

[0163] The above fluorinated ether compound may contain a fluorinated ether represented by the following general formula (5-1).

[0164] Rf1-(OR 51 ) n1 -O-Rf2 (5-1)

[0165] (In the formula, Rf1 and Rf2 are the same or different and are alkyl groups having a fluorine atom. R 51 is an alkyl group which may have a fluorine atom, and n1 is 0 or 2. The number of carbon atoms in one molecule is 5 or more)

[0166] Examples of the fluorinated ether represented by the above formula (5-1) include HCF2CF2CH2OCF2CH FCF3, HCF2CF2CH2OCF2CF2H, CF3CF2CH2OCF2CHFCF3, and CF3CF2CH2OCF2CF2H.)

[0167] As the above fluorinated ether compound, a fluorinated monoether is preferred. If the above solvent contains a chain-like diether (1) and a fluorinated monoether, a lithium-sulfur secondary battery having more excellent cycle characteristics and less likely to generate gas can be obtained.)

[0168] Examples of the above fluorinated monoether include compounds in which n1 = 0 in the above general formulas (5) and (5-1).

[0169] Two or more of the above "other solvents" can be used in combination. When the electrolyte of the present invention contains the above "other solvents", the content is preferably 20 to 90% by mass based on the total amount of the electrolyte. By setting it within the above range, it is preferable for improving the battery output.)

[0170] As the above-mentioned "other solvent", at least one selected from vinylene carbonate and fluorinated monoethers is particularly preferably used. At this time, the content of the above-mentioned "other solvent" is preferably 5 to 80% by mass, more preferably 10% by mass or more, further preferably 20% by mass or more, and further preferably 70% by mass or less, and further preferably 60% by mass or less, based on the total amount of the electrolyte.

[0171] The electrolyte of the present invention may contain non-fluorinated ether compounds such as dimethoxyethane and 1,3-dioxolane as the above-mentioned "other solvent", and preferably has a small content. The content of the non-fluorinated ether compound is preferably 70% by mass or less, more preferably 65% by mass or less, and further preferably 60% by mass or less, based on the total amount of the electrolyte.

[0172] The electrolyte of the present invention also preferably does not contain non-fluorinated ether compounds.

[0173] (Non-aqueous electrolyte containing lithium ions)

[0174] The electrolyte of the present invention contains a non-aqueous electrolyte containing lithium ions.

[0175] The non-aqueous electrolyte containing lithium ions is preferably a lithium salt. The lithium salt can be represented by LiX, where X is a substance that becomes a counter anion. The above lithium salt can be used alone or in a mixture of two or more.

[0176] As X, there is no particular limitation, and it is preferably selected from Cl, Br, I, BF4, PF6, CF3SO3, ClO4, CF3CO2, AsF6, SbF6, AlCl4, bis(trifluoromethanesulfonyl)amide (TFSA), N(CF3SO2)2, N(CF3CF2SO2)2, PF3(C2F5)3, N(FSO2)2, N(FSO2)(CF3SO2), N(CF3CF2SO2)2, N(C2F4S2O4), N(C3F6S2O4), N(CN)2, N(CF3SO2)(CF3CO), R4FBF3 (where R4F = n-C m F 2m+1 、m is a natural number from 1 to 4, and n is normal), and R5BF3 (where R5 = n-C P H 2p+1 , p is a natural number from 1 to 5, and n is normal), and at least one of them. From the viewpoints of solubility in ether compounds and ease of formation of coordination structures, N(FSO2)2, N(CF3SO2)2, N(CF3CF2SO2)2, PF6, and ClO4 are more preferred. PF6 and N(CF3SO2)2 are most preferred.

[0177] The above non-aqueous electrolyte is preferably contained in the electrolyte solution in a proportion of 3.0 to 30% by mass. By setting it within this range, it can be used as a good electrolyte solution. The above lower limit is more preferably 5.0% by mass, and further preferably 8.0% by mass. The above upper limit is more preferably 20% by mass, and further preferably 15% by mass.

[0178] In the electrolyte solution of the present invention, the mixing ratio (solvent) / (non-aqueous electrolyte) of the above solvent and non-aqueous electrolyte is preferably 0.1 at the lower limit and 5.0 (in terms of molar conversion) at the upper limit. If it is within the above range, the coordination of the fluoroether with alkali metal ions is good, so it is preferred. The above mixing ratio is more preferably 0.5 at the lower limit and 4.0 at the upper limit.

[0179] Furthermore, in addition to the above lithium salt compound, a lithium salt compound represented by the following general formula (hereinafter, referred to as "second lithium salt compound") can be used in combination. There is no problem even if two or more kinds are used in combination of the above second lithium salt compounds.

[0180] [Chemical formula 20]

[0181]

[0182] By using these compounds in combination, it is preferred in terms of achieving high battery life and improving battery output.

[0183] The above second lithium salt compound is preferably contained in the electrolyte solution in a proportion of 0.001 to 10% by mass.

[0184] The lower limit of the content of the above second lithium salt is more preferably 0.01% by mass, and further preferably 0.1% by mass. The upper limit of the content of the above second lithium salt is more preferably 5% by mass, and further preferably 3% by mass.

[0185] The electrolyte solution of the present invention may further contain a cyclic borate ester. By containing the above cyclic borate ester, a further good capacity retention rate can be achieved.

[0186] The above cyclic borate ester is not particularly limited. For example, it is preferably at least one selected from the following compounds.

[0187] [Chemical formula 21]

[0188]

[0189] The above electrolyte solution preferably contains 0.01% by mass or more of the above cyclic borate ester, and more preferably 0.5% by mass or more. The upper limit is not particularly limited, and is preferably 1.0% by mass.

[0190] The electrolyte solution of the present invention may contain a phosphate ester. By containing the phosphate ester, it is preferred in terms of achieving high battery life and improving battery output.

[0191] The content of the phosphate ester is preferably 0.001 to 10% by mass relative to the total amount of the electrolyte solution.

[0192] The lower limit of the above phosphate ester content is more preferably 0.01% by mass, and further preferably 0.1% by mass. The upper limit of the above phosphate ester content is more preferably 5% by mass, and further preferably 3% by mass.

[0193] Specific examples of the above phosphate esters include the following compounds.

[0194] Phosphate (methyl)(2-propenyl)(2-propynyl) ester, phosphate (ethyl)(2-propenyl)(2-propynyl) ester, phosphate (2-butenyl)(methyl)(2-propynyl) ester, phosphate (2-butenyl)(ethyl)(2-propynyl) ester, phosphate (1,1-dimethyl-2-propynyl)(methyl)(2-propenyl) ester, phosphate (1,1-dimethyl-2-propynyl)(ethyl)(2-propenyl) ester, phosphate (2-butenyl)(1,1-dimethyl-2-propynyl)(methyl) ester, and phosphate (2-butenyl)(ethyl)(1,1-dimethyl-2-propynyl) ester, etc.

[0195] Trimethyl phosphite, triethyl phosphite, triphenyl phosphite, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, dimethyl methylphosphonate, diethyl ethylphosphonate, dimethyl vinylphosphonate, diethyl vinylphosphonate, ethyl diethylphosphonoacetate, methyl dimethylphosphinate, ethyl diethylphosphinate, trimethylphosphine oxide, triethylphosphine oxide, bis(2,2-difluoroethyl) 2,2,2-trifluoroethyl phosphate, bis(2,2,3,3-tetrafluoropropyl) 2,2,2-trifluoroethyl phosphate, 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-phenylphenyl dimethyl phosphate, 2-phenylphenyl diethyl phosphate, (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, methylene bisphosphonic acid dimethyl ester, methylene bisphosphonic acid diethyl ester, ethylene bisphosphonic acid dimethyl ester, ethylene bisphosphonic acid diethyl ester, butylene bisphosphonic acid dimethyl ester, butylene bisphosphonic acid diethyl ester, 2-propynyl 2-(dimethoxyphosphoryl) acetate, 2-propynyl 2-(dimethylphosphoryl) acetate, 2-propynyl 2-(diethoxyphosphoryl) acetate, 2-propynyl 2-(diethylphosphoryl) acetate, tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, tris(trimethoxysilyl) phosphate, tris(trimethylsilyl) phosphite, tris(triethylsilyl) phosphite, tris(trimethoxysilyl) phosphite, trimethylsilyl polyphosphate and other phosphorus-containing compounds.

[0196] The electrolyte of the present invention can be a gel-like gel electrolyte. The gel electrolyte has a composition obtained by injecting an electrolyte into a matrix polymer containing an ion-conductive polymer. As the electrolyte, the above-mentioned electrolyte of the present invention is used. Examples of the ion-conductive polymer used as the matrix polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), a copolymer of vinylidene fluoride - hexafluoropropylene (VDF-HEP), poly(methyl methacrylate) (PMMA) and their copolymers. In the polyalkylene oxide-based polymer, electrolyte salts such as lithium salts can be sufficiently dissolved.

[0197] The electrolyte of the present invention is used in a lithium-sulfur secondary battery, the lithium-sulfur secondary battery having a positive electrode and a negative electrode, the positive electrode containing a sulfur-based electrode active material, the sulfur-based electrode active material comprising elemental sulfur, polysulfide lithium (Li2Sn : (where 1 < n < 8), at least one of an organic sulfur compound and an inorganic sulfur compound, and the negative electrode contains a material that absorbs and releases lithium ions. That is, if this electrolyte is used in such a lithium-sulfur secondary battery, the above various effects can be particularly appropriately obtained. The positive electrode and the negative electrode are described in detail below.

[0198] In addition, the present invention also provides a lithium-sulfur secondary battery having the above electrolyte as an essential component. Hereinafter, the lithium-sulfur secondary battery of the present invention will also be described in detail.

[0199] (Battery)

[0200] The lithium-sulfur secondary battery according to the present invention can be made into, for example, the following structure: The above positive electrode or negative electrode and the counter electrode are arranged at intervals with a separator therebetween, and an electrolyte is contained in the separator to form a battery cell. A plurality of such battery cells are stacked or wound and housed in a case. The current collectors of the positive electrode or negative electrode and the counter electrode are respectively led out to the outside of the case and electrically connected to the electrode tabs (terminals). It should be noted that the electrolyte can also be made into a gel electrolyte.

[0201] (Positive electrode containing sulfur)

[0202] The above positive electrode contains a sulfur-based electrode active material selected from at least one of elemental sulfur, polysulfide lithium (Li2S n : where 1 < n < 8), an organic sulfur compound and an inorganic sulfur compound. As the organic sulfur compound, organic disulfide compounds and carbon sulfide compounds can be cited. As the inorganic sulfur compound, metal polysulfides represented by MS x (M = Ni, Cu, Fe, 0 < x ≤ 2), etc. In addition, a composite material of these sulfur-based electrode active materials and a carbon material is preferably used.

[0203] By using the above composite material, the above sulfur-based electrode active material can be present in the pores, thereby reducing the resistance, so it is preferred.

[0204] Regarding the content of the sulfur-based electrode active material contained in the above positive electrode active material in the above composite material, from the viewpoint of more excellent cycle performance and further reduction of overvoltage, it is preferably 40 to 99% by mass, more preferably 50% by mass or more, further preferably 60% by mass or more, more preferably 90% by mass or less, and further preferably 85% by mass or less, relative to the above composite material. When the above positive electrode active material is the above elemental sulfur, the content of sulfur contained in the above positive electrode active material is equal to the content of the above elemental sulfur.

[0205] The content of sulfur is obtained by measuring the weight change when heated from room temperature to 600 °C at a heating rate of 10 °C / min in a helium atmosphere.

[0206] As the content of the carbon material in the above composite material, from the viewpoint of more excellent cycle performance and further reduction of overvoltage, it is preferably 1 to 60% by mass, more preferably 10% by mass or more, further preferably 15% by mass or more, more preferably 45% by mass or less, and further preferably 40% by mass or less, relative to the above positive electrode active material.

[0207] The carbon material used in the composite material of sulfur and carbon material preferably has pores. The above "pores" include micropores, mesopores and macropores. The above micropores refer to pores having a diameter of 0.1 nm or more and 2 nm or less. The above mesopores refer to pores having a diameter greater than 2 nm and 50 nm or less. The above macropores refer to pores having a diameter greater than 50 nm.

[0208] In the present invention, as the above carbon material, a carbon material having a pore volume ratio (micropore / mesopore) of the micropore pore volume to the mesopore pore volume of 1.5 or more is particularly preferably used. As the above pore volume ratio, it is more preferably 2.0 or more. The upper limit of the above pore volume ratio is not particularly limited and may be 3.0 or less. It is speculated that if the above carbon material has pores, the dissolution of the above positive electrode active material can be suppressed to a considerable extent. It should be noted that the above pore volume does not take into account the macropore volume.

[0209] In the present invention, the BET specific surface area, the average pore diameter and the pore volume of the pores can be obtained by placing a sample (carbon material, composite material) at liquid nitrogen temperature and using a nitrogen adsorption isotherm obtained by adsorbing nitrogen on the sample. Specifically, using the nitrogen adsorption isotherm, the BET specific surface area of the sample can be obtained by the Brenauer-Emmet-Telle (BET) method. In addition, using the nitrogen adsorption isotherm, the average pore diameter and the pore volume of the pores of the sample can be obtained by the QSDFT method (quenched solid density functional theory). In order to obtain these parameters, as a measuring device, it is only necessary to perform the measurement using, for example, a specific surface area / pore size distribution measuring device (Autosorb) manufactured by Quantachrome Instruments.

[0210] In the above composite material, from the viewpoint of more excellent cycle performance and further reduction of overvoltage, it is preferable that the above positive electrode active material is contained in the above pores of the above carbon material. It is speculated that if the above positive electrode active material is contained in the above pores, the dissolution of the above positive electrode active material can be suppressed to a considerable extent.

[0211] The case where the above positive electrode active material is contained in the above pores can be confirmed by measuring the BET specific surface area of the above composite material. When the above positive electrode active material is contained in the above pores, the BET specific surface area of the above composite material is smaller than the BET specific surface area of only the above carbon material.

[0212] As the above carbon material, porous carbon having macropores and mesopores is preferred.

[0213] From the viewpoint of more excellent cycle performance and further reduction of overvoltage, it is preferred that the above carbon material has a BET specific surface area of 500 to 2500 m 2 / g. The above BET specific surface area is more preferably 700 m 2 / g or more, and more preferably 2000 m 2 / g or less.

[0214] From the viewpoint of more excellent cycle performance and further reduction of overvoltage, it is preferred that the above carbon material has an average particle size of 1 to 50 nm. The above average particle size is more preferably 2 nm or more, and more preferably 30 nm or less.

[0215] As a method for manufacturing the above carbon material, there is no particular limitation, and for example, a method of forming a composite of a decomposable polymer and a non-decomposable (thermosetting) organic component and removing the decomposable polymer from the composite can be cited. For example, it can be manufactured by using the organic-organic interaction between phenolic resin and a thermally decomposable polymer to prepare a regular nanostructured polymer and carbonizing it.

[0216] As a method for manufacturing the above composite material, there is no particular limitation, and a method of vaporizing the above positive electrode active material and depositing it on the above carbon material can be cited. After deposition, the excess above positive electrode active material can be removed by heating at about 150 °C.

[0217] In the above positive electrode, a thickener, a binder, and a conductive agent may be further included on the basis of the above chalcogen-based electrode active material. And, the positive electrode can be manufactured by coating a slurry (paste) of these electrode materials on a conductive carrier (current collector) and drying to support the electrode materials on the carrier.

[0218] As the current collector, current collectors such as foils, meshes, expanded metal plates (porous metals), and perforated metals formed of conductive metals such as aluminum, nickel, copper, and stainless steel can be cited. In addition, a resin having conductivity or a resin containing a conductive filler can also be used as the current collector. The thickness of the current collector is, for example, 5 to 30 μm, but is not limited to this range.

[0219] In the above electrode material (the total amount of the chalcogen-based electrode active material and other components, not including the current collector), the content of the chalcogen-based electrode active material is preferably 50 to 98% by mass, and more preferably 65 to 75% by mass. If the content of the active material is within the above range, the energy density can be improved, and thus it is preferred.

[0220] The thickness of the electrode material (the thickness of one side of the coating layer) is preferably 10 to 500 μm, more preferably 20 to 300 μm, and further preferably 20 to 150 μm.

[0221] The above-mentioned binder can be polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylic acid (PAA), lithium polyacrylate (PAALi), polyalkylene oxides such as the ring-opening polymer of ethylene oxide or a monosubstituted epoxide, or a mixture thereof, etc.

[0222] Examples of the above-mentioned thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts, etc. One kind can be used alone, or two or more kinds can be used in any combination and ratio.

[0223] The above-mentioned conductive agent is an additive added to improve conductivity, and can be carbon powders such as graphite, Ketjen black, inverse opal carbon, acetylene black, various carbon fibers such as vapor-grown carbon fiber (VGCF), carbon nanotube (CNT), etc. In addition, the electrode material can contain a supporting salt (the components contained in the following electrolyte).

[0224] <Negative electrode>

[0225] The negative electrode in the lithium-sulfur secondary battery of the present invention contains a material that absorbs and releases lithium ions. The negative electrode active material contained in the negative electrode functions in a manner of absorbing and dissociating alkali metal ions. As the negative electrode active material, at least one selected from lithium, sodium, carbon, silicon, aluminum, tin, antimony, and magnesium is preferred. More specifically, metal materials such as lithium titanate, lithium metal, sodium metal, lithium-aluminum alloy, sodium-aluminum alloy, lithium-tin alloy, sodium-tin alloy, lithium-silicon alloy, sodium-silicon alloy, lithium-antimony alloy, sodium-antimony alloy, etc. can be used; carbon materials such as natural graphite, artificial graphite, carbon black, acetylene black, graphite, activated carbon, carbon fiber, coke, soft carbon, hard carbon, etc., which are crystalline carbon materials or non-crystalline carbon materials, etc., can be used, which are the conventionally known negative electrode materials. Among them, from the viewpoint of being able to form a battery with excellent capacity and input-output characteristics, it is preferred to use carbon materials or lithium, lithium-transition metal composite oxides. Depending on the situation, two or more negative electrode active materials can also be used in combination.

[0226] The negative electrode may also contain the above active material, binder, and conductive agent. In addition, these electrode materials can also be supported on a conductive carrier (current collector) to fabricate the negative electrode. As the current collector, the same current collector as described above can be used.

[0227] A separator is usually disposed between the positive electrode and the negative electrode. As the separator, for example, a glass fiber separator that absorbs and retains the electrolyte described later, a porous sheet containing a polymer, and a non-woven fabric can be cited. The porous sheet is composed of, for example, a microporous polymer. As such a polymer constituting the porous sheet, for example, polyolefins such as polyethylene (PE) and polypropylene (PP); a laminate having a three-layer structure of PP / PE / PP, polyimide, and aromatic polyamide can be cited. In particular, polyolefin-based microporous separators and glass fiber separators have the property of being chemically stable to organic solvents and can suppress the reactivity with the electrolyte to a low level, so they are preferred. The thickness of the separator containing the porous sheet is not limited. In the application of a secondary battery for driving a vehicle motor, the overall thickness of a single layer or multiple layers is preferably 4 to 60 μm. In addition, the maximum fine pore diameter of the separator containing the porous sheet is preferably 10 μm or less (usually about 10 to 100 nm), and the porosity is preferably 20 to 80%.

[0228] As the non-woven fabric, cotton, rayon, acetate, nylon (registered trademark), polyester; polyolefins such as PP and PE; and non-woven fabrics such as polyimide and aromatic polyamide that are conventionally known can be used alone or in combination. The porosity of the non-woven fabric separator is preferably 50 to 90%. In addition, the thickness of the non-woven fabric separator is preferably 5 to 200 μm, and particularly preferably 10 to 100 μm. If the thickness is less than 5 μm, the retention of the electrolyte becomes poor, and if it is greater than 200 μm, the resistance sometimes increases.

[0229] The assembly having the above lithium-sulfur secondary battery is also one of the present inventions.

[0230] Above, the embodiments have been described, but it can be understood that various changes can be made to the embodiments and details without departing from the gist and scope of the claims.

[0231] Examples

[0232] Next, examples are given to explain the present invention in more detail, but the present invention is not limited to these examples.

[0233] Examples and Comparative Examples

[0234] (Preparation of Electrolyte)

[0235] Each component was mixed so as to have the composition described in Table 4 to obtain a non-aqueous electrolyte.

[0236] (Manufacture of Button-Type Lithium-Sulfur Secondary Battery)

[0237] A composite material containing a carbon material and a specified sulfur as a positive electrode active material (sulfur content: 70% by mass), carbon black as a conductive material, carboxymethyl cellulose (CMC) dispersed in pure water, and styrene-butadiene rubber are mixed in such a way that the solid component ratio reaches 92 / 3 / 2.5 / 2.5 (mass% ratio) to prepare a positive electrode mixture slurry. The obtained positive electrode mixture slurry is uniformly coated on an aluminum foil current collector with a thickness of 25 μm, and after drying, it is compression-molded by a press to form a positive electrode. The positive electrode laminate is punched into a size with a diameter of 1.6 cm by a punching machine to produce a circular positive electrode.

[0238] In addition, a lithium foil punched into a circular shape with a diameter of 1.6 cm is used as the negative electrode.

[0239] (Manufacture of Battery Cell before Test)

[0240] The positive electrode and the negative electrode are opposed to each other with a microporous polypropylene film (separator) with a thickness of 25 μm in between, and the obtained non-aqueous electrolyte is injected. After the electrolyte fully penetrates into the separator and the like, it is sealed and pre-discharged, pre-charged, and aged to manufacture a button-type lithium-sulfur secondary battery.

[0241] The obtained button-type lithium-sulfur secondary battery is evaluated based on the following criteria.

[0242] (Cycling Test)

[0243] The secondary battery manufactured above is subjected to a cycling test at 45°C. In the cycling test, it is charged at a constant current equivalent to 0.2C until 2.9V, and then discharged at a constant current of 0.1C until 1.0V, and this is repeated 100 times. Here, 1C represents the current value when discharging the reference capacity of the battery in 1 hour. For example, 0.2C represents 1 / 5 of this current value. The discharge capacity value after 100 cycles is shown in Table 4.

[0244] (Gas Generation Amount)

[0245] The volume of the secondary battery manufactured above and the volume of the secondary battery after the above 100 cycles are measured by the Archimedes method, and the gas generation amount (ml) is obtained from the volume change.

[0246] The results calculated by setting the value of Comparative Example 1 to 100 are shown in Table 4.

[0247] It should be noted that the symbols of the components recorded in Table 4 represent the compounds shown in Tables 1 to 3 respectively.

[0248] [Table 1]

[0249]

[0250] Table 2

[0251]

[0252] Table 3

[0253]

[0254] Table 4

[0255]

[0256] Industrial applicability

[0257] The lithium-sulfur secondary battery using the electrolyte of the present invention can be used as various power sources such as a mobile power source and a power source for an automobile.

Claims

1. An electrolyte, characterized in that, For a lithium-sulfur secondary battery, the lithium-sulfur secondary battery having a positive electrode and a negative electrode, The positive electrode contains a chalcogen-based electrode active material, and the chalcogen-based electrode active material includes at least one selected from elemental sulfur, polysulfide lithium (Li2S n : 1 < n < 8), organic sulfur compounds, and inorganic sulfur compounds, the negative electrode contains a material for absorbing and releasing lithium ions, the electrolyte contains a non-aqueous electrolyte and a solvent, The solvent contains a chain diether, and the value of Σ{σ×P(σ)} of the chain diether within the range of σ≥0.01 is within the range shown in the following general formula (1). General formula (1): 0 < Σ{σ×P(σ)} < 0.24 In general formula (1), σ represents the shielding charge density, and P(σ) represents the σ-distribution.

2. The electrolyte according to claim 1, wherein, The chain-like diether is a fluorinated chain-like diether.

3. The electrolyte according to claim 1 or 2, wherein, The chain-like diether is at least one selected from the compounds represented by the following general formula (A) and the compounds represented by the following general formula (B), General formula (A): In general formula (A), R 1a ~R 10a are each independently a halogen atom, a hydrogen atom, an alkyl group having 2 or fewer carbon atoms, or a fluoroalkyl group having 2 or fewer carbon atoms, provided that at least one of R 1a ~R 10a is a halogen atom or a fluoroalkyl group having 2 or fewer carbon atoms; General formula (B): In general formula (B), R 1b ~R 8b are each independently a halogen atom, a hydrogen atom, an alkyl group having 2 or fewer carbon atoms, or a fluoroalkyl group having 2 or fewer carbon atoms.

4. The electrolyte according to any one of claims 1 to 3, wherein, The chain-like diether is at least one selected from the compounds represented by the following formula, 5. The electrolyte according to any one of claims 1 to 4, wherein, The content of the chain-like diether is 3 to 90% by mass based on the total amount of the electrolyte.

6. A lithium-sulfur secondary battery, characterized in that, Having a positive electrode and a negative electrode, The positive electrode contains a chalcogen-based electrode active material, and the chalcogen-based electrode active material includes at least one selected from elemental sulfur, polysulfide lithium (Li2S n : 1 < n < 8), organic sulfur compounds, and inorganic sulfur compounds, the negative electrode contains a material for absorbing and releasing lithium ions, The lithium-sulfur secondary battery uses the electrolyte according to any one of claims 1 to 5.

7. A component, characterized in that, Equipped with the lithium-sulfur secondary battery according to claim 6.

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