Electrolyte solution, its manufacturing method, and secondary battery

Abstract

The present invention provides an electrolyte solution that makes it possible to obtain a more substantial discharge capacity from initial discharge, even with less of the electrolyte solution, and that also has more substantially superior cycle characteristics. The present invention relates to an electrolyte solution for a secondary battery. The electrolyte solution includes an electrolyte and a solvent. The electrolyte includes a total of 0.8–2.0 mol / L of lithium nitrate and a sulfonyl group–containing lithium salt. The solvent includes a straight-chain ether and a fluorinated ether.

Description

[Technical field]

[0001] The present invention relates to an electrolyte solution, a method for producing the same, and a secondary battery. [Background technology]

[0002] Conventionally, secondary batteries have a structure in which a positive electrode, a negative electrode, a separator, and an electrolyte are enclosed in an exterior body. In such secondary batteries, it is important to reduce the amount of electrolyte from the viewpoint of energy density. In addition, cycle characteristics that suppress the decrease in discharge capacity even with repeated charging and discharging are also important.

[0003] However, there is a problem in that reducing the amount of electrolyte also reduces the discharge capacity.

[0004] Meanwhile, in Patent Document 1, an attempt is made to improve the charge / discharge characteristics by using an aqueous electrolyte solution containing a non-aqueous solvent selected from the group consisting of acyclic ethers, cyclic ethers, polyethers, and sulfones; a lithium salt; and a nitrile additive. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US 7,354,680 B2 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the inventors of the present invention have found that the conventional techniques give rise to the following new problems. (1) When the amount of electrolyte was reduced, a problem occurred in which the discharge capacity was not sufficient even from the first discharge. (2) The discharge capacity decreased with repeated charging and discharging, and sufficient cycle characteristics were not obtained.

[0007] An object of the present invention is to provide an electrolyte solution which has sufficiently excellent discharge characteristics and / or cycle characteristics even when the amount of the electrolyte solution is reduced. [Means for solving the problem]

[0008] The present invention relates to An electrolytic solution for a secondary battery, comprising an electrolyte and a solvent, the electrolyte comprises a sulfonyl group-containing lithium salt and lithium nitrate; the total content of the sulfonyl group-containing lithium salt and the lithium nitrate is 0.8 mol / L or more and 2.0 mol / L or less; For electrolytes, the solvent includes linear ethers and fluorinated ethers. Effect of the Invention

[0009] A secondary battery comprising the electrolyte of the present invention can obtain a sufficient discharge capacity even from the first discharge even if the amount of electrolyte is reduced. The secondary battery comprising the electrolyte of the present invention also has sufficiently excellent cycle characteristics. [Brief description of the drawings]

[0010] [Figure 1] 1 is a graph showing initial discharge curves of secondary batteries containing the electrolyte solutions prepared in Examples 1 and 2 and Comparative Example 1. [Diagram 2] 1 is a graph showing the relationship between the initial discharge capacity and the dilution ratio of secondary batteries containing the electrolyte solutions prepared in Examples 1 and 2 and Comparative Example 1. [Diagram 3] 1 is a graph showing the relationship between the discharge capacity and the number of cycles of secondary batteries prepared using the electrolyte solutions of Example 1 and Comparative Example 1. [Figure 4] FIG. 1 is a schematic cross-sectional view of a secondary battery (cylindrical secondary battery) provided as one embodiment of the present invention. [Diagram 5] FIG. 1 is a schematic perspective view of a secondary battery (flat laminate film type secondary battery) provided as one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [Secondary battery] The present invention provides a secondary battery. In this specification, the term "secondary battery" refers to a battery that can be repeatedly charged and discharged. The term "secondary battery" is not limited to the name, and may include electrochemical devices such as "electricity storage devices."

[0012] The secondary battery of the present invention includes a positive electrode, a negative electrode, and an electrolyte, and typically further includes a separator disposed between the positive electrode and the negative electrode. The secondary battery of the present invention is typically configured such that the positive electrode, the negative electrode, the electrolyte, the separator, and the like are enclosed in an exterior body.

[0013] (electrolyte) The electrolyte is a non-aqueous electrolyte, which means that the medium through which the electrolyte ions move does not contain water, that is, the electrolyte uses only an organic solvent as the medium.

[0014] In the present invention, the electrolytic solution includes an electrolyte and a solvent.

[0015] · electrolyte In the present invention, the electrolyte of the electrolytic solution includes a sulfonyl group-containing lithium salt and lithium nitrate. If the electrolyte does not include either or both of the sulfonyl group-containing lithium salt and lithium nitrate, sufficient discharge characteristics and / or sufficient cycle characteristics cannot be obtained. To dissolve in a linear ether, a sulfonyl group-containing lithium salt such as LiTFSI with a large degree of dissociation is required, and without lithium nitrate, a redox shuttle occurs. Since the electrolyte is dissolved in the solvent in the electrolytic solution, the electrolytic solution has the form of a solution. A solution refers to a state or form in which the electrolyte is uniformly dispersed at a molecular level in the solvent to such an extent that the electrolytic solution has visual transparency at room temperature (e.g., 25°C).

[0016] In this specification, the discharge characteristics refer to the characteristics that allow a sufficient discharge capacity to be obtained from the first discharge. The cycle characteristic refers to the characteristic that the discharge capacity is sufficiently maintained through repeated charging and discharging.

[0017] The sulfonyl group-containing lithium salt is an organic lithium salt containing a sulfonyl group (-SO2-) in its molecular structure. Specific examples of the sulfonyl group-containing lithium salt include one or more compounds selected from the group consisting of sulfonylimide-based lithium salts represented by the following general formula (S1) and sulfonic acid lithium salts represented by the following general formula (S2). From the viewpoint of further improving discharge characteristics and cycle characteristics, the sulfonyl group-containing lithium salt is preferably a sulfonylimide-based lithium salt represented by the following general formula (S1).

[0018] [ka]

[0019] In formula (S1), R 1 and R 2 are each independently a halogen atom or a halogen atom-containing hydrocarbon group having 1 to 10 carbon atoms, and from the viewpoint of further improving discharge characteristics and cycle characteristics, are preferably a halogen atom or a halogen atom-containing hydrocarbon group having 1 to 5 carbon atoms, and more preferably a halogen atom-containing hydrocarbon group having 1 to 3 carbon atoms. 1 and R 2Regarding the halogen atom-containing hydrocarbon group, the halogen atom-containing hydrocarbon group is a monovalent hydrocarbon group, and may be a saturated aliphatic hydrocarbon group, an unsaturated aliphatic hydrocarbon group, or an aromatic hydrocarbon group as long as it contains a halogen atom, and from the viewpoint of further improving discharge characteristics and cycle characteristics, a saturated aliphatic hydrocarbon group (alkyl group) is preferred. The number of halogen atoms contained in the halogen atom-containing hydrocarbon group is not particularly limited, and it is sufficient that at least a part of the hydrogen atoms of the hydrocarbon group are substituted with halogen atoms. From the viewpoint of further improving discharge characteristics and cycle characteristics, it is preferred that all hydrogen atoms of the halogen atom-containing hydrocarbon group are substituted with halogen atoms. The halogen atom may be a fluorine atom, a chlorine atom, or a bromine atom, and from the viewpoint of further improving discharge characteristics and cycle characteristics, a fluorine atom is preferred. When the halogen atom-containing hydrocarbon group is a saturated aliphatic hydrocarbon group and all hydrogen atoms are substituted with fluorine atoms, the halogen atom-containing hydrocarbon group may be referred to as a perfluoroalkyl group. R 1 and R 2 Preferred examples of the halogen atom-containing hydrocarbon group for R include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, and a perfluoropentyl group. 1 and R 2 From the viewpoint of further improving the discharge characteristics and cycle characteristics, it is preferable that each of them represents the same group.

[0020] Examples of such a compound represented by general formula (S1) (which may also be referred to as compound (S1) or sulfonylimide lithium salt (S1)) include the following compounds.

[0021] [Table 1]

[0022] [ka]

[0023] In formula (S2), R 3 R is a halogen atom or a halogen atom-containing hydrocarbon group having 1 to 10 carbon atoms, and from the viewpoint of further improving discharge characteristics and cycle characteristics, it is preferably a halogen atom or a halogen atom-containing hydrocarbon group having 1 to 5 carbon atoms, and more preferably a halogen atom-containing hydrocarbon group having 1 to 3 carbon atoms. 3 Regarding the halogen atom-containing hydrocarbon group, R 1 and R 2 As long as it is a monovalent hydrocarbon group and contains a halogen atom, it may be a saturated aliphatic hydrocarbon group, an unsaturated aliphatic hydrocarbon group, or an aromatic hydrocarbon group, and from the viewpoint of further improving discharge characteristics and cycle characteristics, a saturated aliphatic hydrocarbon group (alkyl group) is preferred. The number of halogen atoms contained in the halogen atom-containing hydrocarbon group is not particularly limited, and it is sufficient that at least a part of the hydrogen atoms of the hydrocarbon group are substituted with halogen atoms. From the viewpoint of further improving discharge characteristics and cycle characteristics, it is preferred that all hydrogen atoms of the halogen atom-containing hydrocarbon group are substituted with halogen atoms. The halogen atom may be a fluorine atom, a chlorine atom, or a bromine atom, and from the viewpoint of further improving discharge characteristics and cycle characteristics, a fluorine atom is preferred. When the halogen atom-containing hydrocarbon group is a saturated aliphatic hydrocarbon group and all hydrogen atoms are substituted with fluorine atoms, the halogen atom-containing hydrocarbon group may be referred to as a perfluoroalkyl group. R 3 Preferred halogen-containing hydrocarbon groups for R 1 and R 2 The same groups as the preferred halogen atom-containing hydrocarbon groups for are mentioned.

[0024] Examples of such a compound represented by general formula (S2) (which may also be referred to as compound (S2) or lithium sulfonate (S2)) include the following compounds.

[0025] [Table 2]

[0026] Sulfonyl group-containing lithium salts are commercially available. For example, compound (s1-1) is available as LiFSI (manufactured by Nippon Shokubai Co., Ltd.). Furthermore, for example, compound (s1-2) is available as LiTFSI (manufactured by Toyama Pharmaceutical Co., Ltd.). Furthermore, for example, compound (s1-3) is available as LiBETI (manufactured by Iolitec). Furthermore, for example, compound (s1-5) is available as LiN(C4F9SO2)2 (manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd.). Furthermore, for example, compound (s2-2) is available as LiCF3SO3 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). Furthermore, for example, compound (s2-5) is available as LiC4F9SO3 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.).

[0027] The content of the sulfonyl group-containing lithium salt is not particularly limited as long as the total content of the sulfonyl group-containing lithium salt and lithium nitrate is within the range described below. From the viewpoint of further improving discharge characteristics and cycle characteristics, it is preferably 0.1 mol / L or more and 1.0 mol / L or less, more preferably 0.2 mol / L or more and 0.9 mol / L or less, even more preferably 0.3 mol / L or more and 0.9 mol / L or less, particularly preferably 0.4 mol / L or more and 0.8 mol / L or less, and most preferably 0.4 mol / L or more and 0.6 mol / L or less. The sulfonyl group-containing lithium salt may contain two or more compounds with different structures, and in that case, the total content of them may be within the above range. The unit "mol / L" means the number of moles contained in 1 L of the total amount of the electrolyte.

[0028] The content of lithium nitrate is not particularly limited as long as the total content of the sulfonyl group-containing lithium salt and lithium nitrate is within the range described below, and from the viewpoint of further improving the discharge characteristics and cycle characteristics, the content is preferably 0.1 mol / L or more and 1.0 mol / L or less, more preferably 0.2 mol / L or more and 0.9 mol / L or less, even more preferably 0.3 mol / L or more and 0.9 mol / L or less, particularly preferably 0.4 mol / L or more and 0.8 mol / L or less, and most preferably 0.4 mol / L or more and 0.6 mol / L or less.

[0029] The total content of the sulfonyl group-containing lithium salt and lithium nitrate is 0.8 mol / L or more and 2.0 mol / L or less, and from the viewpoint of further improving the discharge characteristics and cycle characteristics, it is preferably 0.8 mol / L or more and 1.8 mol / L or less, more preferably 0.8 mol / L or more and 1.6 mol / L or less, and even more preferably 0.9 mol / L or more and 1.2 mol / L or less. If the total content is too high, the electrical conductivity decreases due to an increase in viscosity. If the total content is too low, the electrical conductivity decreases and the amount of polysulfide elution increases. As a result, sufficient discharge characteristics and / or sufficient cycle characteristics are not obtained. The sulfonyl group-containing lithium salt may contain two or more compounds having different structures, and in that case, the total amount of the contents of the compounds and the lithium nitrate content may be within the above range.

[0030] The present invention does not preclude the electrolyte from containing electrolytes other than the sulfonyl group-containing lithium salt and lithium nitrate (hereinafter, sometimes referred to as other electrolytes). The content of the other electrolyte is usually equal to or less than the smaller content of the sulfonyl group-containing lithium salt and lithium nitrate, and may be, for example, 1 mol / L or less, particularly 0.5 mol / L or less. From the viewpoint of further improving discharge characteristics and cycle characteristics, the content of the other electrolyte is preferably as small as possible, and more preferably 0 mol / L.

[0031] · solvent In the present invention, the solvent of the electrolyte solution includes a linear ether and a fluorinated ether. If the solvent does not include either or both of a linear ether and a fluorinated ether, sufficient discharge characteristics and / or sufficient cycle characteristics may not be obtained.

[0032] The linear ether may be any linear ether used as a glyme-based solvent in the field of secondary batteries. For example, the linear ether may be one or more compounds selected from the group consisting of linear ethers represented by the following general formula (G). Here, the term "linear ether" as used in the present invention means that at least the ethyleneoxy structural unit is not branched (i.e., does not have a branched structure). Therefore, R' and R'' in the following general formula (G) do not necessarily have to have a linear structure, and may have a branched structure. In one preferred embodiment, the linear ether used in the electrolyte solution in the present invention is a glycol ether in which not only the ethyleneoxy structural unit is not branched, but also R' and R'' are not branched.

[0033] [ka]

[0034] In formula (G), R' and R'' are each independently a hydrocarbon group having 1 to 10 carbon atoms, preferably a hydrocarbon group having 1 to 5 carbon atoms, more preferably a hydrocarbon group having 1 to 3 carbon atoms, from the viewpoint of further improving discharge characteristics and cycle characteristics. The hydrocarbon group for R' and R'' is a monovalent hydrocarbon group, and may be a saturated aliphatic hydrocarbon group, an unsaturated aliphatic hydrocarbon group, or an aromatic hydrocarbon group, and is preferably a saturated aliphatic hydrocarbon group (alkyl group) from the viewpoint of further improving discharge characteristics and cycle characteristics. Examples of preferred hydrocarbon groups for R' and R'' include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, and a decyl group. From the viewpoint of further improving discharge characteristics and cycle characteristics, it is preferred that R' and R'' represent the same group.

[0035] n is an integer of 1 or more and 10 or less, and from the viewpoint of further improving the discharge characteristics and cycle characteristics, n is preferably an integer of 1 or more and 5 or less, more preferably an integer of 1 or more and 3 or less, and even more preferably 1.

[0036] Specific preferred examples of such linear ethers include ethylene glycol ethers, diethylene glycol ethers, triethylene glycol ethers, and tetraethylene glycol ethers. From the viewpoint of further improving discharge characteristics and cycle characteristics, ethylene glycol ethers (particularly monoglyme), diethylene glycol ethers (particularly diglyme) or mixtures thereof are preferred, and ethylene glycol ethers (particularly monoglyme) are more preferred.

[0037] Examples of ethylene glycol ethers include the following compounds: Ethylene glycol dimethyl ether (dimethoxyethane; monoglyme), ethylene glycol ethyl methyl ether, ethylene glycol methyl propyl ether, ethylene glycol butyl methyl ether, ethylene glycol methyl pentyl ether, ethylene glycol methyl hexyl ether, ethylene glycol methyl heptyl ether, ethylene glycol methyl octyl ether; Ethylene glycol diethyl ether, ethylene glycol ethyl propyl ether, ethylene glycol butyl ethyl ether, ethylene glycol ethyl pentyl ether, ethylene glycol ethyl hexyl ether, ethylene glycol ethyl heptyl ether, ethylene glycol ethyl octyl ether; Ethylene glycol dipropyl ether, ethylene glycol butyl propyl ether, ethylene glycol propyl pentyl ether, ethylene glycol propyl hexyl ether, ethylene glycol propyl heptyl ether, ethylene glycol propyl octyl ether.

[0038] Diethylene glycol ethers include, for example, the following compounds: Diethylene glycol dimethyl ether (diglyme), diethylene glycol ethyl methyl ether, diethylene glycol methyl propyl ether, diethylene glycol butyl methyl ether, diethylene glycol methyl pentyl ether, diethylene glycol methyl hexyl ether, diethylene glycol methyl heptyl ether, diethylene glycol methyl octyl ether; Diethylene glycol diethyl ether, diethylene glycol ethyl propyl ether, diethylene glycol butyl ethyl ether, diethylene glycol ethyl pentyl ether, diethylene glycol ethyl hexyl ether, diethylene glycol ethyl heptyl ether, diethylene glycol ethyl octyl ether; Diethylene glycol dipropyl ether, diethylene glycol butyl propyl ether, diethylene glycol propyl pentyl ether, diethylene glycol propyl hexyl ether, diethylene glycol propyl heptyl ether, diethylene glycol propyl octyl ether.

[0039] Examples of triethylene glycol ethers include the following compounds: Triethylene glycol dimethyl ether (triglyme), triethylene glycol ethyl methyl ether, triethylene glycol methyl propyl ether, triethylene glycol butyl methyl ether, triethylene glycol methyl pentyl ether, triethylene glycol methyl hexyl ether, triethylene glycol methyl heptyl ether, triethylene glycol methyl octyl ether; triethylene glycol diethyl ether, triethylene glycol ethyl propyl ether, triethylene glycol butyl ethyl ether, triethylene glycol ethyl pentyl ether, triethylene glycol ethyl hexyl ether, triethylene glycol ethyl heptyl ether, triethylene glycol ethyl octyl ether; Triethylene glycol dipropyl ether, triethylene glycol butyl propyl ether, triethylene glycol propyl pentyl ether, triethylene glycol propyl hexyl ether, triethylene glycol propyl heptyl ether, triethylene glycol propyl octyl ether.

[0040] Examples of tetraethylene glycol ethers include the following compounds: Tetraethylene glycol dimethyl ether (tetraglyme), tetraethylene glycol ethyl methyl ether, tetraethylene glycol methyl propyl ether, tetraethylene glycol butyl methyl ether, tetraethylene glycol methyl pentyl ether, tetraethylene glycol methyl hexyl ether, tetraethylene glycol methyl heptyl ether, tetraethylene glycol methyl octyl ether; Tetraethylene glycol diethyl ether, tetraethylene glycol ethyl propyl ether, tetraethylene glycol butyl ethyl ether, tetraethylene glycol ethyl pentyl ether, tetraethylene glycol ethyl hexyl ether, tetraethylene glycol ethyl heptyl ether, tetraethylene glycol ethyl octyl ether; Tetraethylene glycol dipropyl ether, tetraethylene glycol butyl propyl ether, tetraethylene glycol propyl pentyl ether, tetraethylene glycol propyl hexyl ether, tetraethylene glycol propyl heptyl ether, tetraethylene glycol propyl octyl ether.

[0041] Linear ethers are commercially available. For example, dimethoxyethane (monoglyme) is available from Toyama Pharmaceutical Co., Ltd. For example, diglyme is available as (Toyama Pharmaceutical Co., Ltd.). For example, triglyme is available as (Toyama Pharmaceutical Co., Ltd.). For example, tetraglyme is available as (Toyama Pharmaceutical Co., Ltd.).

[0042] The content of the linear ether may be within the range described below, provided that the content of the fluorinated ether relative to the total amount of the linear ether and the fluorinated ether is within the range described below. The linear ether may contain two or more linear ethers having different structures, provided that the total content thereof is within the range described above.

[0043] The fluorinated ether is a linear or cyclic ether compound containing a fluorine atom and an ether bond. Specifically, the fluorinated ether is one or more compounds selected from the group consisting of linear ether compounds represented by the following general formula (E1) and cyclic ether compounds represented by the following general formula (E2). From the viewpoint of further improving discharge characteristics and cycle characteristics, the fluorinated ether is preferably a linear ether compound represented by the following general formula (E1). Here, the "linear ether compound" in the present invention means having a structure that can be generally represented by (E1). Specifically, R in the following general formula (E1) 11 、 R 12 and R 13 In one preferred embodiment, the fluorinated ether used in the electrolyte solution of the present invention not only has a structure that can be represented by the following general formula (E1), but also has a structure that can be represented by the following general formula (E2): 11 , R 12 and R 13 is a fluorinated ether that does not have a branched structure.

[0044] [ka]

[0045] In formula (E1), R 11 and R 12 At least one of R is a fluorine atom-containing monovalent hydrocarbon group having 1 to 10 carbon atoms, and from the viewpoint of further improving discharge characteristics and cycle characteristics, R is preferably a fluorine atom-containing monovalent hydrocarbon group having 1 to 5 carbon atoms, and more preferably a fluorine atom-containing monovalent hydrocarbon group having 1 to 3 carbon atoms. 11 and R 12Regarding the fluorine atom-containing monovalent hydrocarbon group, the fluorine atom-containing monovalent hydrocarbon group may be a saturated aliphatic monovalent hydrocarbon group, an unsaturated aliphatic monovalent hydrocarbon group, or an aromatic monovalent hydrocarbon group, and from the viewpoint of further improving the discharge characteristics and cycle characteristics, a saturated aliphatic monovalent hydrocarbon group (alkyl group) is preferred. The number of fluorine atoms contained in the fluorine atom-containing monovalent hydrocarbon group is not particularly limited, and it is sufficient that at least a part of the hydrogen atoms in the hydrocarbon group are substituted with halogen atoms. From the viewpoint of further improving the discharge characteristics and cycle characteristics, it is preferred that more than half of the total number of all hydrogen atoms and fluorine atoms in the fluorine atom-containing monovalent hydrocarbon group are fluorine atoms. R 11 and R 12 and R are the above-mentioned fluorine atom-containing monovalent hydrocarbon groups. 11 and R 12 may represent the same group or different groups.

[0046] Specifically, the fluorine atom-containing monovalent hydrocarbon group is a hydrocarbon group represented by the following general formula (F).

[0047] [ka]

[0048] In formula (F), A is a hydrogen atom or a fluorine atom, and from the viewpoint of further improving the discharge characteristics and cycle characteristics, A is a hydrogen atom. r1 is an integer of 0 or more and 10 or less, and from the viewpoint of further improving the discharge characteristics and cycle characteristics, is preferably an integer of 1 or more and 10 or less, more preferably an integer of 1 or more and 5 or less, even more preferably an integer of 1 or more and 3 or less, particularly preferably 1 or 2, and most preferably 2. r2 is an integer of 0 or more and 10 or less, and from the viewpoint of further improving the discharge characteristics and cycle characteristics, is preferably an integer of 0 or more and 5 or less, more preferably an integer of 0 or more and 3 or less, even more preferably an integer of 0 or more and 2 or less, particularly preferably 0 or 1, and most preferably 0. r3 is an integer of 0 or more and 9 or less, and from the viewpoint of further improving the discharge characteristics and cycle characteristics, is preferably an integer of 0 or more and 5 or less, more preferably an integer of 0 or more and 3 or less, even more preferably an integer of 0 or more and 2 or less, and particularly preferably 0 or 1. r1+r2 is an integer of 1 or more and 10 or less, and from the viewpoint of further improving the discharge characteristics and cycle characteristics, is preferably an integer of 1 or more and 5 or less, more preferably an integer of 1 or more and 3 or less, even more preferably 2 or 3, and particularly preferably 2. r1+r2+r3 is an integer of 1 or more and 10 or less, and from the viewpoint of further improving the discharge characteristics and cycle characteristics, is preferably an integer of 1 or more and 6 or less, more preferably an integer of 1 or more and 5 or less, even more preferably an integer of 1 or more and 3 or less, and particularly preferably 2 or 3. In formula (F), the difluoroethylene unit for r1, the monofluoroethylene unit for r2, and the ethylene unit for r3 are arranged successively for each unit to form a block, but are not limited thereto and may be arranged randomly.) From the viewpoint of further improving discharge characteristics and cycle characteristics, it is preferable that these units are arranged successively for each unit in the order described in formula (F) to form a block.

[0049] In formula (E1), R 11 and R 12 When only one of the groups is a fluorine atom-containing monovalent hydrocarbon group, the other is a monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably a monovalent hydrocarbon group having 1 to 5 carbon atoms, more preferably a monovalent hydrocarbon group having 1 to 3 carbon atoms, from the viewpoint of further improving discharge characteristics and cycle characteristics. The monovalent hydrocarbon group may be a saturated aliphatic hydrocarbon group, an unsaturated aliphatic hydrocarbon group, or an aromatic hydrocarbon group, and preferably a saturated aliphatic hydrocarbon group (alkyl group) from the viewpoint of further improving discharge characteristics and cycle characteristics. Examples of the monovalent hydrocarbon group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, and a decyl group.

[0050] In formula (E1), R 13 is a divalent hydrocarbon group having 2 to 4 carbon atoms, and from the viewpoint of further improving discharge characteristics and cycle characteristics, is preferably a divalent hydrocarbon group having 2 or 3 carbon atoms, and more preferably a divalent hydrocarbon group having 2 carbon atoms. The divalent hydrocarbon group is a saturated aliphatic divalent hydrocarbon group, and examples thereof include an ethylene group, a propylene group, and a butylene group.

[0051] In formula (E1), p is an integer of 0 or 1. From the viewpoint of further improving the discharge characteristics and cycle characteristics, p is preferably 0.

[0052] Examples of such a compound represented by general formula (E1) (which may also be referred to as compound (E1) or linear ether compound (E1)) include compounds represented by the following general formulae (e1-1) to (e1-2).

[0053] [ka]

[0054] In formula (e1-1), R 11 and R 12 are R in formula (E1), 11 and R 12 Therefore, R in formula (e1-1) 11 and R 12 The fluorine atom-containing monovalent hydrocarbon group in formula (E1) also corresponds to R 11 and R 12 The same applies to the fluorine atom-containing monovalent hydrocarbon group described above. Preferred R in formula (e1-1) 11 and R 12 are also preferred R 11 and R 12 The same applies to R in formula (e1-1). 11 and R 12 Preferred fluorine atom-containing monovalent hydrocarbon groups for 11 and R 12The preferred fluorine atom-containing monovalent hydrocarbon groups are the same as those in the above.

[0055] Specific examples of the compound represented by general formula (e1-1) (which may also be referred to as compound (e1-1) or ether compound (e1-1)) include the following compounds.

[0056] [Table 3]

[0057] Compound (e1-1) is commercially available or can be prepared by known methods. For example, compound (e1-1-1) is available from Manchester Organics. Furthermore, for example, compound (e1-1-2) is available from Manchester Organics. Furthermore, for example, compound (e1-1-3) is available from Manchester Organics. Furthermore, for example, compound (e1-1-4) is available from Angene.

[0058] [ka]

[0059] In formula (e1-2), R 11 、 R 12 and R 13 are R in formula (E1), 11 、 R 12 and R 13 Therefore, R in formula (e1-2) 11 and R 12 The fluorine atom-containing monovalent hydrocarbon group in formula (E1) also corresponds to R 11 and R 12 The same applies to the fluorine atom-containing monovalent hydrocarbon group in formula (e1-2). 13The divalent hydrocarbon group for 13 The same applies to the divalent hydrocarbon group. Preferred R in formula (e1-2) 11 、 R 12 and R 13 are also preferred R 11 、 R 12 and R 13 The same applies to R in formula (e1-2). 11 and R 12 Preferred fluorine atom-containing monovalent hydrocarbon groups for 11 and R 12 The preferred fluorine atom-containing monovalent hydrocarbon groups for R in formula (e1-2) are the same as those for 13 Preferred divalent hydrocarbon groups for are also R 13 The preferred divalent hydrocarbon groups are the same as those mentioned above.

[0060] Specific examples of the compound represented by general formula (e1-2) (which may also be referred to as compound (e1-2) or glycol ether compound (e1-2)) include the following compounds.

[0061] [Table 4]

[0062] Compound (e1-2) is commercially available or can be prepared by known methods.

[0063] [ka]

[0064] In formula (E2), R 14 is a fluorine atom-containing monovalent hydrocarbon group having 1 to 10 carbon atoms, and R in formula (E1) 11 and R 12 Therefore, R in formula (E2)14 The fluorine atom-containing monovalent hydrocarbon group in the formula (E1) is 11 and R 12 The same applies to the fluorine atom-containing monovalent hydrocarbon group described above. Preferred R in formula (E2) 14 is also a preferred R 11 and R 12 The same applies to R in formula (E2). 14 Preferred fluorine atom-containing monovalent hydrocarbon groups for 11 and R 12 The preferred fluorine atom-containing monovalent hydrocarbon groups are the same as those in the above.

[0065] Specific examples of the compound represented by general formula (E2) (which may also be referred to as compound (E2) or cyclic ether compound (E2)) include the following compounds.

[0066] [Table 5]

[0067] Compound (e2-1) is commercially available or can be prepared by known methods. For example, compound (e2-1) is available from Manchester Organics.

[0068] The viscosity of the fluorinated ether is not particularly limited and may be, for example, 0.1 mPa or more and 3.0 mPa or less, and from the viewpoint of further improving the discharge characteristics and cycle characteristics, it is preferably 0.5 mPa or more and 2.5 mPa or less, and more preferably 1.0 mPa or more and 2.5 mPa or less.

[0069] The dielectric constant of the fluorinated ether is not particularly limited and may be, for example, 3 or more and 20 or less, and from the viewpoint of further improving the discharge characteristics and cycle characteristics, it is preferably 4 or more and 18 or less, and more preferably 5 or more and 10 or less.

[0070] The boiling point of the fluorinated ether is not particularly limited and may be, for example, 50°C or higher and 150°C or lower. From the viewpoint of further improving the discharge characteristics and cycle characteristics, it is preferably 60°C or higher and 120°C or lower, and more preferably 80°C or higher and 110°C or lower.

[0071] The content of the fluorinated ether is not particularly limited, and from the viewpoint of further improving the discharge characteristics and cycle characteristics, it is preferably 20% by volume or more and 60% by volume or less, more preferably 20% by volume or more and 55% by volume or less, even more preferably 40% by volume or more and 55% by volume or less, and particularly preferably 45% by volume or more and 55% by volume or less, based on the total amount of the linear ether and the fluorinated ether. The fluorinated ether may contain two or more kinds of fluorinated ethers having different structures, and in that case, the total content thereof may be within the above range.

[0072] The linear ether and the fluorinated ether are contained in the electrolyte as the main solvent. The total content of the linear ether and the fluorinated ether is usually 80% by volume or more based on the total amount of the electrolyte, and from the viewpoint of further improving the discharge characteristics and cycle characteristics, it is preferably 90% by volume or more, more preferably 98% by volume or more, and even more preferably 100% by volume. The linear ether and the fluorinated ether may each contain two or more kinds of ethers having different structures, and in that case, the total content thereof may be within the above range.

[0073] The present invention does not preclude the electrolyte from containing a solvent other than the linear ether and the fluorinated ether (hereinafter, sometimes referred to as other solvent). The content of the other solvent is usually equal to or less than the smaller content of each linear ether, and from the viewpoint of further improving the discharge characteristics and cycle characteristics, it is preferably equal to or less than 20 volume %, more preferably equal to or less than 10 volume %, and even more preferably equal to or less than 2 volume % relative to the total amount of the electrolyte. From the viewpoint of further improving the discharge characteristics and cycle characteristics, the content of the other solvent is preferably as small as possible, and more preferably 0 volume %.

[0074] · Additives The electrolyte of the present invention may contain additives such as LiPF6, LiAsF6, LiBOB, LiDFOB, LiI, R-SH (thiol), P2S5, and Li2Sn (lithium polysulfide).

[0075] The content of the additive is not particularly limited, and may be, for example, 1 w / v% or less, particularly 0.5 w / v% or less. From the viewpoint of further improving discharge characteristics and cycle characteristics, the content of the additive is preferably as small as possible, and more preferably 0 w / v%. The additive may contain two or more kinds of additives, and in that case, the total content of the additives may be within the above range. The unit "w / v%" means the number of grams contained in 100 mL of the total amount of the electrolyte.

[0076] (Electrolyte Solution Manufacturing Method) The electrolyte solution can be produced by dissolving the sulfonyl group-containing lithium salt and lithium nitrate in a straight-chain ether, and then diluting the solution with a fluorinated ether to adjust the total content of the sulfonyl group-containing lithium salt and lithium nitrate to the above-mentioned range. Even if an electrolyte solution is prepared by adding and mixing a sulfonyl group-containing lithium salt and lithium nitrate with a fluorinated ether and then diluting with a straight-chain ether, the electrolyte solution of the present invention cannot be obtained because the sulfonyl group-containing lithium salt and lithium nitrate are not soluble. Even if an electrolyte solution is prepared by adding and mixing a sulfonyl group-containing lithium salt and lithium nitrate to a mixed solvent of a linear ether and a fluorinated ether, the electrolyte solution of the present invention cannot be obtained because the sulfonyl group-containing lithium salt and lithium nitrate are not soluble.

[0077] The dilution ratio of the fluorinated ether may be any ratio such that the content of the fluorinated ether relative to the total amount of the linear ether and the fluorinated ether in the electrolytic solution falls within the above range, and is preferably 20% to 60%, more preferably 20% to 55%, even more preferably 40% to 55%, and particularly preferably 45% to 55%. In this specification, the dilution ratio refers to the ratio (particularly volume ratio) of the amount of the solvent used for dilution to the total amount of the solvent after dilution.

[0078] The ambient temperature during the production of the electrolyte solution is usually room temperature, and may be, for example, 5°C or higher and 30°C or lower.

[0079] In the secondary battery, the ratio of the volume (μL) of the electrolyte to the weight (mg) of sulfur in the positive electrode (EL / S ratio) is preferably 1 or more and 15 or less, more preferably 1 or more and 12 or less, even more preferably 1 or more and 10 or less, and particularly preferably 2 or more and 10 or less, from the viewpoint of further improving the discharge characteristics and cycle characteristics. In the present invention, excellent discharge characteristics can be obtained even if the amount of electrolyte is reduced. From the viewpoint of further improving the discharge characteristics, the EL / S ratio is preferably 1 or more and 10 or less, more preferably 2 or more and 8 or less (particularly 2 or more and less than 8), more preferably 3 or more and 8 or less (particularly 3 or more and less than 8), and even more preferably 4 or more and 6 or less. From the viewpoint of further improving cycle characteristics, the EL / S ratio is preferably 5 or more and 15 or less, more preferably 8 or more and 12 or less, further preferably 8 or more and 11 or less, and particularly preferably 9 or more and 11 or less.

[0080] (Positive and negative electrodes) The positive electrode and the negative electrode are electrodes capable of absorbing and releasing lithium ions. Therefore, the secondary battery of the present invention is a secondary battery in which lithium ions move between the positive electrode and the negative electrode via the electrolyte to charge and discharge the battery. The secondary battery of the present invention corresponds to a so-called "lithium ion secondary battery" because lithium ions are involved in charging and discharging.

[0081] In the secondary battery of the present invention, the positive electrode is preferably a sulfur electrode containing at least sulfur from the viewpoint of further improving discharge characteristics and cycle characteristics. In a broad sense, the term "sulfur electrode" refers to an electrode having sulfur (S) as an active component (i.e., active material). In a narrow sense, the term "sulfur electrode" refers to an electrode containing at least sulfur, for example, an electrode containing sulfur (S) such as S8 and / or polymeric sulfur, particularly such a sulfur positive electrode.

[0082] The sulfur electrode is an electrode containing at least sulfur, and may further contain a conductive assistant and / or a binder, etc. In this case, the sulfur content in the sulfur electrode may be 5% by weight to 95% by weight, preferably 50% by weight to 90% by weight, more preferably 50% by weight to 80% by weight, based on the total weight of the electrode (particularly the positive electrode layer described below).

[0083] Examples of the conductive assistant contained in the sulfur electrode used as the positive electrode include carbon materials such as graphite, carbon fiber, carbon black, and carbon nanotubes, and one or more of these materials can be used in combination. Examples of the carbon fiber include vapor growth carbon fiber (VGCF (registered trademark)). Examples of the carbon black include acetylene black and / or Ketjen black. Examples of the carbon nanotubes include multi-wall carbon nanotubes (MWCNTs) such as single-wall carbon nanotubes (SWCNTs) and / or double-wall carbon nanotubes (DWCNTs). Materials other than carbon materials can be used as long as they have good electrical conductivity, and for example, metal materials such as Ni powder and / or conductive polymer materials can be used. From the viewpoint of further improving the discharge characteristics and cycle characteristics, the conductive assistant is preferably carbon black, and more preferably Ketjen black.

[0084] Examples of the binder contained in the sulfur electrode used as the positive electrode include fluorine-based resins such as polyvinylidene fluoride (PVdF) and / or polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA)-based resins, carboxymethyl cellulose (CMC), and / or styrene-butadiene copolymer rubber (SBR)-based resins. A conductive polymer may also be used as the binder. Examples of the conductive polymer that can be used include substituted or unsubstituted polyaniline, polypyrrole, polythiophene, and (co)polymers consisting of one or two selected from these. From the viewpoint of further improving the discharge characteristics and cycle characteristics, the binder is preferably SBR, CMC, or a mixture thereof, and more preferably a mixture of SBR and CMC.

[0085] The sulfur electrode usually includes a positive electrode layer (particularly, may be referred to as a sulfur-containing positive electrode layer or a sulfur positive electrode layer) and a positive electrode current collector (foil) on which the positive electrode layer is formed. In this case, the positive electrode layer is provided on at least one side of the positive electrode current collector. The positive electrode may be provided with a positive electrode layer on both sides of the positive electrode current collector, or may be provided with a positive electrode layer on one side of the positive electrode current collector. From the viewpoint of further increasing the capacity of the secondary battery, a preferred positive electrode is provided with a positive electrode layer on both sides of the positive electrode current collector.

[0086] The positive electrode layer of the sulfur electrode may contain other positive electrode active materials in addition to sulfur. The other positive electrode active materials are not particularly limited as long as they are materials that contribute to the absorption and release of lithium ions, and examples thereof include lithium transition metal composite oxides containing lithium and at least one transition metal selected from the group consisting of cobalt, nickel, manganese, and iron. For example, the other positive electrode active materials may be lithium cobalt oxide (LCO), lithium nickel oxide, lithium manganese oxide, lithium titanate, or materials in which a part of the transition metal is replaced with another metal. Such other positive electrode active materials may be contained as a single type, or may be contained in combination of two or more types.

[0087] The sulfur electrode can usually be obtained by mixing together sulfur and a binder (and, if necessary, a conductive assistant and / or other positive electrode active material), adding an organic solvent to prepare a slurry, applying the slurry onto a positive electrode current collector by any coating method, and drying the slurry.

[0088] The positive electrode current collector used in the positive electrode is a member that contributes to collecting and supplying electrons generated in the active material due to the battery reaction. Such a current collector may be a sheet-like metal member and may have a porous or perforated form. For example, the current collector may be a metal foil, a punched metal, a net, an expanded metal, or the like. The positive electrode current collector used in the positive electrode is preferably made of a metal foil containing at least one selected from the group consisting of aluminum, stainless steel, nickel, and the like, and may be, for example, an aluminum foil.

[0089] The negative electrode is not particularly limited, but is preferably a metallic lithium electrode from the viewpoint of further improving discharge characteristics and cycle characteristics. Metallic lithium is a substance that contributes to the absorption and release of lithium ions. In a broad sense, the term "metallic lithium electrode" refers to an electrode having metallic lithium (Li) as an active component (i.e., anode active material). In a narrow sense, the term "metallic lithium electrode" refers to an electrode comprising metallic lithium, for example, an electrode comprising lithium metal or a lithium alloy, and particularly a negative electrode of such metallic lithium (for example, metallic lithium alone). Although the metallic lithium electrode may contain components other than lithium metal or lithium alloy, in a preferred embodiment, it is an electrode made of a metallic lithium body (for example, an electrode made of a lithium metal alone having a purity of 90% or more, preferably a purity of 95% or more, and more preferably a purity of 98% or more).

[0090] The negative electrode can be made of, for example, a plate-like or foil-like material, but is not limited thereto, and can also be formed (shaped) using a powder.

[0091] The metallic lithium electrode (negative electrode) may be used supported by a negative electrode current collector. For example, the metallic lithium electrode may be formed on a negative electrode current collector. The negative electrode current collector may be a current collector (or metal foil) similar to the positive electrode current collector. From the viewpoint of further improving discharge characteristics and cycle characteristics, the negative electrode current collector is preferably a copper foil.

[0092] The positive and negative electrodes are alternately arranged with a separator to be described later. The positive and negative electrodes may have a planar laminated structure, a wound structure, or a stack-and-folded structure together with the separator to be described later. In detail, the secondary battery may have a planar laminated structure in which the positive electrode, the negative electrode, and the separator arranged between the positive electrode and the negative electrode are laminated in a planar shape, or may have a wound structure in which the positive electrode, the negative electrode, and the separator arranged between the positive electrode and the negative electrode are wound in a roll shape, or may have a so-called stack-and-folded structure in which the positive electrode, the negative electrode, and the separator arranged between the positive electrode and the negative electrode are laminated and then folded.

[0093] (Separator) The separator is a member provided from the viewpoint of preventing short circuits due to contact between the positive and negative electrodes and retaining the electrolyte. In other words, the separator is a member that allows ions to pass while preventing electronic contact between the positive and negative electrodes. Preferably, the separator is a porous or microporous insulating member, and may have a membrane form due to its small thickness.

[0094] The separator may be an inorganic separator or an organic separator. Examples of inorganic separators include glass filters and glass fibers. Examples of organic separators include porous membranes made of synthetic resins such as polytetrafluoroethylene, polypropylene, and / or polyethylene, and a structure in which two or more of these porous membranes are laminated can also be used. Among them, polyolefin porous membranes are preferable because they have excellent short-circuit prevention effects and can improve the safety of the battery due to their shutdown effect.

[0095] (Exterior body) The exterior body may be a flexible pouch (soft bag) or a hard case (hard housing). When the exterior body is a flexible pouch, the flexible pouch is usually formed from a laminate film, and the seal part is formed by heat-sealing the periphery. The laminate film is generally a film in which a metal foil and a polymer film are laminated, and specifically, a three-layer structure consisting of an outer layer polymer film / metal foil / inner layer polymer film is exemplified. The outer layer polymer film is for preventing damage to the metal foil due to permeation of moisture and the like and contact, and polymers such as polyamide and polyester can be suitably used. The metal foil is for preventing permeation of moisture and gas, and foils such as copper, aluminum, and stainless steel can be suitably used. The inner layer polymer film is for protecting the metal foil from the electrolyte stored inside and for melt sealing during heat sealing, and polyolefin or acid-modified polyolefin can be suitably used. The thickness of the laminate film is not particularly limited, and may be, for example, 1 μm or more and 1 mm or less. When the exterior body is a flexible pouch, it is heat-sealed at the periphery of the secondary battery in a plan view.

[0096] When the exterior body is a hard case, the hard case is usually formed from a metal plate, and the peripheral portion is irradiated with a laser to form a seal portion. The metal plate is generally made of a metal material such as aluminum, nickel, iron, copper, or stainless steel. The thickness of the metal plate is not particularly limited, and may be, for example, 1 μm or more and 1 mm or less.

[0097] [Examples of secondary batteries] Specific examples of a cylindrical secondary battery and a flat laminate film secondary battery will be described below.

[0098] FIG. 12 shows a schematic cross-sectional view of a cylindrical secondary battery 100. In the secondary battery 100, an electrode structure 121 and a pair of insulating plates 112, 113 are housed inside an electrode structure housing member 111 having a substantially hollow cylindrical shape. The electrode structure 121 can be produced, for example, by stacking a positive electrode 122 and a negative electrode 124 via a separator 126 to obtain an electrode structure, and then winding the electrode structure. The electrode structure housing member (for example, a battery can) 111 has a hollow structure with one end closed and the other end open, and is made of iron (Fe) and / or aluminum (Al) or the like. The pair of insulating plates 112, 113 are arranged to sandwich the electrode structure 121 and extend perpendicularly to the wound circumferential surface of the electrode structure 121. A battery cover 114, a safety valve mechanism 115, and a thermosensitive resistor element (e.g., a PTC element, a positive temperature coefficient element) 116 are crimped to the open end of the electrode structure housing member 111 via a gasket 117, thereby sealing the electrode structure housing member 111. The battery cover 114 is made of, for example, the same material as the electrode structure housing member 111. The safety valve mechanism 115 and the thermosensitive resistor element 116 are provided inside the battery cover 114, and the safety valve mechanism 115 is electrically connected to the battery cover 114 via the thermosensitive resistor element 116. In the safety valve mechanism 115, when the internal pressure exceeds a certain level due to an internal short circuit and / or external heating, the disk plate 115A is inverted. This cuts off the electrical connection between the battery cover 114 and the electrode structure 121. In order to prevent abnormal heat generation due to a large current, the resistance of the thermosensitive resistor element 116 increases with increasing temperature. The gasket 117 is made of, for example, an insulating material. The surface of the gasket 117 may be coated with asphalt or the like.

[0099] A center pin 118 is inserted into the winding center of the electrode structure 121. However, the center pin 118 does not have to be inserted into the winding center. A positive electrode lead portion 123 made of a conductive material such as aluminum is connected to the positive electrode 122. Specifically, the positive electrode lead portion 123 is attached to the positive electrode (e.g., a positive electrode current collector). A negative electrode lead portion 125 made of a conductive material such as copper is connected to the negative electrode 124. Specifically, the negative electrode lead portion 125 is attached to the negative electrode (e.g., a negative electrode current collector). The negative electrode lead portion 125 is welded to the electrode structure housing member 111 and is electrically connected to the electrode structure housing member 111. The positive electrode lead portion 123 is welded to the safety valve mechanism 115 and is electrically connected to the battery lid 114. In the example shown in FIG. 12, the negative electrode lead portion 125 is provided in one location (the outermost portion of the wound electrode structure), but it may be provided in two locations (the outermost and innermost portions of the wound electrode structure).

[0100] The electrode structure 121 is formed by laminating a positive electrode 122 and a negative electrode 124 with a separator 126 interposed therebetween. When the positive electrode is formed of a positive electrode layer and a positive electrode current collector (foil), the positive electrode layer is not formed in the region of the positive electrode (e.g., the positive electrode current collector) where the positive electrode lead portion 123 is attached.

[0101] The secondary battery 100 can be manufactured, for example, according to the following procedure.

[0102] First, a sulfur electrode (positive electrode) and a metallic lithium electrode (negative electrode) are prepared. For example, a sulfur-containing positive electrode layer is formed on both sides of a positive electrode current collector to obtain a positive electrode. A metallic lithium foil material is cut out to obtain a negative electrode.

[0103] Next, the positive electrode lead portion 123 is attached to the positive electrode current collector by welding or the like. Also, the negative electrode lead portion 125 is attached to the negative electrode by welding or the like. Next, the positive electrode 122 and the negative electrode 124 are laminated and wound via a separator 126 made of a microporous polyethylene film (more specifically, the electrode structure (i.e., the laminated structure) of the positive electrode 122 / separator 126 / negative electrode 124 / separator 126 is wound) to produce the electrode structure 121, and then a protective tape (not shown) is attached to the outermost periphery. Then, the center pin 118 is inserted into the center of the electrode structure 121. Next, the electrode structure 121 is sandwiched between a pair of insulating plates 112 and 113, and the electrode structure 121 is stored inside the electrode structure storage member 111. In this case, the tip of the positive electrode lead portion 123 is attached to the safety valve mechanism 115 and the tip of the negative electrode lead portion 125 is attached to the electrode structure housing member 111 by using a welding method or the like. Then, the electrolyte is injected based on a reduced pressure method to impregnate the separator 126 with the electrolyte. Next, the battery lid 114, the safety valve mechanism 115, and the thermal resistor element 116 are crimped to the open end of the electrode structure housing member 111 via the gasket 117.

[0104] Next, a flat laminate film type secondary battery will be described. A schematic exploded perspective view of such a secondary battery is shown in FIG. 13. In this secondary battery, an electrode structure 221 similar to that described above is basically housed inside an exterior member 200 made of a laminate film. The electrode structure 221 can be produced by laminating a positive electrode and a negative electrode with a separator interposed therebetween, and then winding the laminated structure. A positive electrode lead portion 223 is attached to the positive electrode, and a negative electrode lead portion 225 is attached to the negative electrode. The outermost periphery of the electrode structure 221 is protected by a protective tape. The positive electrode lead portion 223 and the negative electrode lead portion 225 protrude in the same direction from the inside to the outside of the exterior member 200. The positive electrode lead portion 223 is formed of a conductive material such as aluminum. The negative electrode lead portion 225 is formed of a conductive material such as copper, nickel, and / or stainless steel.

[0105] The exterior member 200 is a single film that can be folded in the direction of the arrow R shown in FIG. 13, and a recess (e.g., embossment) for accommodating the electrode structure 221 is provided in a part of the exterior member 200. The exterior member 200 is, for example, a laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order. In the manufacturing process of the secondary battery, the exterior member 200 is folded so that the fusion layers face each other via the electrode structure 221, and then the outer peripheral edges of the fusion layers are fused together. However, the exterior member 200 may be one in which two separate laminate films are bonded together via an adhesive or the like. The fusion layer is made of, for example, a film of polyethylene and / or polypropylene. The metal layer is made of, for example, an aluminum foil. The surface protection layer is made of, for example, nylon and / or polyethylene terephthalate. Among them, the exterior member 200 is preferably an aluminum laminate film in which a polyethylene film, an aluminum foil, and a nylon film are laminated in this order. However, the exterior member 200 may be a laminate film having another laminated structure, a polymer film such as polypropylene, or a metal film. Specifically, the exterior member 200 may be made of a moisture-resistant aluminum laminate film in which a nylon film, an aluminum foil, and a non-oriented polypropylene film are laminated in this order from the outside.

[0106] In order to prevent the intrusion of outside air, an adhesive film 201 is inserted between the exterior member 200 and the positive electrode lead portion 223, and between the exterior member 200 and the negative electrode lead portion 225. The adhesive film 201 may be made of a material having adhesion to the positive electrode lead portion 223 and the negative electrode lead portion 225, such as a polyolefin resin, and more specifically, may be made of a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene. EXAMPLES

[0107] [reagent] The following reagents were used: LiTFSI (lithium bistrifluoromethanesulfonylimide): manufactured by Toyama Pharmaceutical Co., Ltd. Lithium nitrate (LiNO3): Kanto Chemical Dimethoxyethane (DME): Toyama Pharmaceutical Co., Ltd. Hydrofluoroether (HFE): manufactured by Daikin Industries (corresponding to the above compound (e1-1-2)) (viscosity 1.6 mPa, dielectric constant 6.4, boiling point 92°)

[0108] Example 1 Preparation of electrolyte To 1 L of dimethoxyethane (DME), LiTFSI was added at 1 mol / L and LiNO3 was added at 1 mol / L and stirred to obtain solution A. Solution A was diluted with HFE so that the volume ratio of solution A:HFE was 3:1 to obtain an electrolyte solution (dilution rate 25%).

[0109] -Creating laminated cells A composite of sulfur, Ketjen black, and binder (SBR (styrene butadiene rubber) and CMC (carboxymethyl cellulose)) was dispersed in a solvent mainly composed of water to prepare a slurry, which was then applied to an Al foil and dried to obtain a positive electrode. The sulfur content in the positive electrode layer was 66% by weight. A lithium metal foil (copper current collector) was prepared as the negative electrode. The lithium purity in the lithium metal foil was 99.9%. A polyethylene separator was prepared as the separator. A separator was placed between the positive and negative electrodes to obtain a laminate. The laminate was housed in a laminated exterior body, and an electrolyte was injected into it. The inside of the exterior body was degassed, and the opening was heat-sealed. The electrolyte was sufficiently impregnated into the positive electrode and separator by hydrostatic pressure impregnation. The cell was clamped with a pressure tool to obtain a laminated cell. In the laminated cell, the ratio of the weight of the electrolyte to the weight of sulfur in the positive electrode (EL / S ratio) was 5.

[0110] Example 2 An electrolyte solution and a laminate type cell were obtained in the same manner as in Example 1, except that solution A was diluted with HFE (dilution rate 50%) so that the volume ratio of solution A:HFE was 1:1.

[0111] Comparative Example 1 A laminate type cell was obtained in the same manner as in Example 1, except that Solution A was used as the electrolyte without dilution.

[0112] [Discharge capacity measurement (discharge characteristics)] Charge and discharge were performed under the following conditions, and the initial charge and discharge curve was created and shown in Figure 1. The relationship between the initial discharge capacity and the dilution ratio is shown in Figure 2. Standby time: 2 hours Cut-off potential: 2.8 to 1.85 V (CC discharge / CC / CV charge) Rest time: 10 minutes (after each discharge / charge) Rate: 0.2C (calculated based on discharge capacity of 1000mAh / g) Amount of electrolyte: EL / S ratio = 5 (EL / S ratio is the ratio of electrolyte amount [μL] to sulfur weight [mg]) The cell was pressurized with a fixture at 5 cN·m.

[0113] It was found that the discharge capacity increased by dilution. It was found that by diluting the 2 mol / L electrolyte with a fluorinated ether, the discharge capacity can be maintained even with a low amount of electrolyte, and in fact the discharge capacity can be increased. This makes it possible to design batteries with low EL / S, and improve the energy density. The following factors (1) and / or (2) are thought to be the reasons why the discharge capacity increases with dilution: · Factor (1): The viscosity of the electrolyte decreases, improving the load characteristics, making it harder to reach the cutoff potential and resulting in an increase in discharge capacity; · Factor (2): The electrolyte reaches deeper into the pores, increasing the utilization rate of the active material.

[0114] [Evaluation of cycle characteristics] The cells using the electrolyte solution of Example 1 or Comparative Example 1 were charged and discharged 20 times, and the change in discharge capacity is shown in Fig. 3. The cells using the electrolyte solution of Example 1 or Comparative Example 1 were laminated type cells obtained by the same method as Example 1 or Comparative Example 1, except that the EL / S ratio was set to 10. It was found that the discharge capacity retention rate was improved by dilution. [Industrial Applicability]

[0115] The secondary battery according to the present invention can be used in various fields where battery use or power storage is expected. By way of example only, the secondary battery according to the present invention can be used in electronics packaging fields. The secondary battery according to an embodiment of the present invention can also be used in the electrical, information, and communication fields where mobile devices and the like are used (e.g., electrical and electronic devices fields including small electronic devices such as mobile phones, smartphones, notebook computers, digital cameras, activity meters, arm computers, electronic paper, wearable devices, RFID tags, card-type electronic money, and smart watches, or mobile device fields), household and small industrial applications (e.g., power tools, golf carts, household, nursing care, and industrial robots), large industrial applications (e.g., forklifts, elevators, and port cranes), transportation systems (e.g., hybrid cars, electric cars, buses, trains, electrically assisted bicycles, and electric motorcycles), power system applications (e.g., various power generation, road conditioners, smart grids, and general household storage systems), medical applications (medical devices such as earphones and hearing aids), pharmaceutical applications (medical management systems), as well as the IoT field and space and deep sea applications (e.g., space probes, submersible research vessels, and the like).

Claims

1. A battery comprising: a sulfur electrode containing sulfur as a positive electrode; a metallic lithium electrode as a negative electrode; and an electrolyte; The electrolytic solution includes an electrolyte and a solvent, the electrolyte contains a sulfonyl group-containing lithium salt and lithium nitrate, and may or may not contain any other electrolyte other than the sulfonyl group-containing lithium salt and the lithium nitrate; the total content of the sulfonyl group-containing lithium salt and the lithium nitrate is 0.8 mol / L or more and 2.0 mol / L or less; The content of the sulfonyl group-containing lithium salt is 0.1 mol / L or more, The lithium nitrate content is 0.1 mol / L or more, the content of the other electrolyte is equal to or less than the smaller of the contents of the sulfonyl group-containing lithium salt and the lithium nitrate, The solvents include linear ethers and fluorinated ethers; a total content of the linear ether and the fluorinated ether is 80% by volume or more based on a total amount of the electrolyte solution, A secondary battery, wherein the content of the fluorinated ether is 20% by volume or more and 60% by volume or less with respect to the total amount of the linear ether and the fluorinated ether.

2. The secondary battery according to claim 1 , wherein the fluorinated ether is a linear or cyclic ether compound containing a fluorine atom and an ether bond.

3. 3. The secondary battery according to claim 1, wherein the fluorinated ether is one or more compounds selected from the group consisting of linear ether compounds represented by the following general formula (E1) and cyclic ether compounds represented by the following general formula (E2): 【Chemistry 1】 (In formula (E1), R １１ and R １２ At least one of R is a fluorine atom-containing monovalent hydrocarbon group having 1 to 10 carbon atoms; １１ and R １２ when one of the groups is the fluorine atom-containing monovalent hydrocarbon group, the other group is a monovalent hydrocarbon group having 1 to 10 carbon atoms; R １３ is a divalent hydrocarbon group having 2 to 4 carbon atoms; p is an integer of 0 or 1. 【Chemistry 2】 (In formula (E2), R １４ is a fluorine atom-containing monovalent hydrocarbon group having 1 to 10 carbon atoms).

4. The secondary battery according to claim 3 , wherein the fluorine atom-containing monovalent hydrocarbon group is a hydrocarbon group represented by the following general formula (F): 【Chemistry 3】 (In formula (F), A is a hydrogen atom or a fluorine atom; r1 is an integer of 0 or more and 10 or less; r2 is an integer of 0 or more and 10 or less; r3 is an integer of 0 or more and 9 or less; r1+r2 is an integer of 1 or more and 10 or less; r1+r2+r3 is an integer of 1 or more and 10 or less; the difluoroethylene units for r1, the monofluoroethylene units for r2, and the ethylene units for r3 may be arranged randomly).

5. The secondary battery according to any one of claims 1 to 4, wherein the linear ether is a linear ether represented by the following general formula (G): 【Chemistry 4】 (In formula (G), R′ and R″ are each independently a hydrocarbon group having 1 to 10 carbon atoms; n is an integer of 1 to 10).

6. The secondary battery according to any one of claims 1 to 5, wherein the sulfonyl group-containing lithium salt is one or more compounds selected from the group consisting of sulfonylimide lithium salts represented by the following general formula (S1) and sulfonate lithium salts represented by the following general formula (S2): 【Chemistry 5】 (In formula (S1), R １ and R ２ are each independently a halogen atom or a halogen-containing hydrocarbon group having from 1 to 10 carbon atoms; and 【Chemistry 6】 (In formula (S2), R ３ is a halogen atom or a halogen atom-containing hydrocarbon group having from 1 to 10 carbon atoms).

7. 7. The secondary battery according to claim 1, wherein the content of the sulfonyl group-containing lithium salt is 1.0 mol / L or less.

8. 8. The secondary battery according to claim 1, wherein the lithium nitrate content is 1.0 mol / L or less.

9. The secondary battery according to any one of claims 1 to 8, wherein the ratio of the weight of the electrolyte to the weight of sulfur in the positive electrode (EL / S ratio) is 1 or more and 10 or less.

10. The secondary battery according to any one of claims 1 to 9, wherein the secondary battery is a lithium ion secondary battery.

11. The method for producing a secondary battery according to any one of claims 1 to 10, further comprising dissolving a sulfonyl group-containing lithium salt and lithium nitrate in a straight-chain ether, and then diluting the resulting solution with a fluorinated ether to adjust the total content of the sulfonyl group-containing lithium salt and the lithium nitrate to 0.8 mol / L or more and 2.0 mol / L or less, thereby producing an electrolyte solution.

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