Positive electrode active material for lithium sulfur batteries, positive electrode material, positive electrode, and lithium sulfur battery

Abstract

The present invention provides: a positive electrode active material for lithium sulfur batteries, which contains a sulfur polymer that can be synthesized at a lower temperature than ever before; a positive electrode material; a positive electrode; and a lithium sulfur battery.　The present invention provides a positive electrode active material for lithium sulfur batteries, which contains a sulfur-containing polymer compound, the sulfur-containing polymer compound having a structural unit that is represented by general formula (1) -R1-R-R1-(S)n- or the like. (In formula (1), n represents a number of 1 or more, R represents an organic group, and R 1 represents a divalent organic group that is derived from a polycondensable functional group.)

Description

Positive electrode active material for lithium-sulfur batteries, positive electrode material, positive electrode, and lithium-sulfur battery

[0001] The present invention relates to a positive electrode active material for a lithium-sulfur battery, a positive electrode material, a positive electrode, and a lithium-sulfur battery.

[0002] Lithium-sulfur batteries have been attracting attention as the next generation of lithium-ion batteries. Lithium-sulfur batteries have a theoretical energy density exceeding that of consumer lithium-ion batteries, and are attracting attention as a post-lithium-ion battery. For example, Non-Patent Document 1 reports technology related to lithium-sulfur batteries and proposes a lithium-sulfur battery with an excellent capacitance (800 mAh / g).

[0003] Sulfur polymers are also attracting attention as an electrode material for lithium-sulfur batteries. Sulfur polymers can be synthesized from sulfur waste, which is estimated to amount to 7 million tons per year. Therefore, if we can construct lithium-sulfur batteries using sulfur polymers, we can achieve a shift away from fossil fuels, which is promising from the perspective of achieving the SDGs.

[0004] Chun. W. et. al. Nat. Chem. 2013, 5, 518

[0005] However, one of the challenges of using sulfur polymers as electrode materials in lithium-sulfur batteries is the complexity of their synthesis. For example, synthesizing sulfur polymers represented by -(S)n- generally requires high-temperature conditions of 180°C or higher. Therefore, to obtain the energy needed to synthesize the sulfur polymer, fossil fuels must be burned, generating carbon dioxide. In other words, the process of fabricating lithium-sulfur batteries, which are considered promising from the perspective of the SDGs, is faced with the dilemma of consuming fossil fuels while generating carbon dioxide. From this perspective, there is a strong demand for the development of positive electrode materials for lithium-sulfur batteries containing sulfur polymers that can be synthesized under milder conditions.

[0006] The present invention has been made in view of the above, and aims to provide a positive electrode active material for a lithium-sulfur battery, a positive electrode material, a positive electrode, and a lithium-sulfur battery, which contain a sulfur polymer that can be synthesized at a lower temperature than conventional ones.

[0007] As a result of extensive research into achieving the above object, the present inventors have discovered that the above object can be achieved by a sulfur-containing polymer compound having a specific structure, and have thus completed the present invention.

[0008] That is, the present invention includes, for example, the subject matter described in the following items. Item 1: A positive electrode active material for a lithium-sulfur battery containing a sulfur-containing polymer compound, wherein the sulfur-containing polymer compound is represented by the following general formula (1): １ -R-R １ - (S) ｎ - (1) (In formula (1), n ​​represents a number of 1 or more, R represents an organic group, and two R １ are the same or different and represent a divalent organic group derived from a polycondensable functional group), １ -R-(S) ｎ - (1') (wherein n, R and R １ respectively represent n, R and R in the formula (1). １ (which has the same meaning as the following formula (1a): -R-(S) ｎ - (1a) (in formula (1a), n and R have the same meanings as n and R in formula (1), respectively), or the following general formula (1") -CO-(S) ｎ Item 2: A positive electrode active material for a lithium-sulfur battery, having a structural unit represented by the formula (1") (wherein n has the same meaning as n in the formula (1)). １ is -CH ２ -CH(OH)-, -CH ２ -CH ２Item 1. The positive electrode active material for a lithium-sulfur battery according to Item 1, wherein the sulfur-containing polymer compound is —CH(OH)—, —CO—, —COO—, or —NHCO—. Item 3. The positive electrode active material for a lithium-sulfur battery according to Item 1 or 2, wherein the sulfur-containing polymer compound has a crosslinked structure. Item 4. A positive electrode material for a lithium-sulfur battery, comprising the positive electrode active material for a lithium-sulfur battery according to any one of Items 1 to 3. Item 5. A positive electrode for a lithium-sulfur battery, comprising the positive electrode material for a lithium-sulfur battery according to Item 4. Item 6. A lithium-sulfur battery comprising the positive electrode for a lithium-sulfur battery according to Item 5. Item 7. The lithium-sulfur battery according to Item 6, comprising a liquid electrolyte or a solid electrolyte.

[0009] The positive electrode active material for lithium-sulfur batteries of the present invention can be synthesized at a lower temperature than conventional materials and is suitable as a positive electrode active material for lithium-sulfur batteries.

[0010] 1 is a scheme showing an outline of the synthesis reaction of a sulfur-containing polymer compound carried out in Example 1. FIG. 2 is a scheme showing an outline of the synthesis reaction of a sulfur-containing polymer compound carried out in Example 2. FIG. 3(a) is a scheme showing an outline of the synthesis reaction of a sulfur-containing polymer compound carried out in Example 3, FIG. 3(b) is a table summarizing the results of elemental analysis of the obtained sulfur-containing polymer compound, and FIG. 3(c) is the result of Raman measurement of the obtained sulfur-containing polymer compound. FIG. 3(a) is a scheme showing an outline of the synthesis reaction of a sulfur-containing polymer compound carried out in Example 4, and FIG. 3(b) is the result of Raman measurement of the obtained sulfur-containing polymer compound.

[0011]

[0023] In the present specification, the terms "contain" and "comprise" include the concepts of "contain," "comprise," "consist essentially of," and "consist only of."

[0012] 1. Positive electrode active material for lithium-sulfur battery The positive electrode active material for lithium-sulfur battery of the present invention contains a sulfur-containing polymer compound. The sulfur-containing polymer compound is represented by the following general formula (1) -R １ -R-R １ - (S) ｎ - (1) (In formula (1), n ​​represents a number of 1 or more, R represents an organic group, and two R １are the same or different and represent a divalent organic group derived from a polycondensable functional group), １ -R-(S) ｎ - (1') (wherein n, R and R １ respectively represent n, R and R in the formula (1). １ (which has the same meaning as the following formula (1a): -R-(S) ｎ - (1a) (in formula (1a), n and R have the same meanings as n and R in formula (1), respectively), or the following general formula (1") -CO-(S) ｎ - (1") (wherein n has the same meaning as n in formula (1)).

[0013] The cathode active material for lithium-sulfur batteries of the present invention (hereinafter sometimes simply referred to as the "cathode active material of the present invention") contains the sulfur-containing polymer compound as an essential component, as described above. Compared to conventional sulfur polymers, such sulfur-containing polymer compounds can be produced at lower temperatures, and in particular, can be easily synthesized even at room temperature. Therefore, the cathode active material of the present invention can further reduce the environmental impact during its production process and reduce production costs, making it a promising raw material for cathode materials from the perspective of achieving the SDGs.

[0014] (Sulfur-Containing Polymer Compound) The sulfur-containing polymer compound, which is an essential component of the positive electrode active material of the present invention, has, in its structural units, a structural unit represented by the formula (1), a structural unit represented by the formula (1′), a structural unit represented by the formula (1a), or a structural unit represented by the formula (1″).

[0015] In the formula (1), n ​​represents the number of sulfur repeats. In the formula (1), n ​​is not particularly limited as long as it is a number of 1 or more. In terms of the positive electrode active material of the present invention easily improving battery characteristics, particularly easily increasing the capacitance of an all-solid-state battery, n is preferably 2 or more, more preferably 3 or more, even more preferably 4 or more, and particularly preferably 5 or more. The upper limit of n is not particularly limited, and can be, for example, 10,000 or less, preferably 5,000 or less, more preferably 3,000 or less, even more preferably 1,000 or less, and particularly preferably 500 or less. n can also be 10 or less. The value of n is determined by the ratio of the sulfur-containing polymer compound １ It can be calculated based on the results of H-NMR spectrum and elemental analysis.

[0016] In the formula (1), R can be, for example, a divalent or higher organic group, preferably a divalent organic group, a trivalent organic group, or a tetravalent organic group. A divalent organic group is a group containing one or more carbon atoms, for example, a group formed by removing two hydrogen atoms from an organic compound. A trivalent organic group is a group containing one or more carbon atoms, for example, a group formed by removing three hydrogen atoms from an organic compound. A tetravalent organic group is a group containing one or more carbon atoms, for example, a group formed by removing four hydrogen atoms from an organic compound.

[0017] Examples of R in the formula (1) include an alkylene group (-C ｍ H ２ｍ-, m is an integer), an alkylene group which may have one or more substituents X, an alkylene group which may have one or more ether bonds (-O-) inserted therein, an alkenylene group which may have one or more substituents X, an alkynylene group which may have one or more substituents X, a cycloalkylene group which may have one or more substituents X, a cycloalkenylene group which may have one or more substituents X, a cycloalkadienylene group which may have one or more substituents X, an arylene group which may have one or more substituents X, an aralkylene group which may have one or more substituents X, a non-aromatic heterocyclic group which may have one or more substituents X, and a heteroarylene group which may have one or more substituents X.

[0018] In the alkylene group optionally having one or more substituents X and the alkylene group optionally having one or more ether bonds (—O—) inserted therein, the number of carbon atoms in the alkylene group is not particularly limited and can be, for example, 1 or more and 20 or less, preferably 2 or more, and preferably 15 or less, more preferably 10 or less, and even more preferably 8 or less.

[0019] Specific examples of the "alkylene group which may have one or more substituents X and which may have one or more ether bonds (-O-) inserted therein" include "-(CH ２ ) ｉ -O-(CH ２ ) ｊ -O-(CH ２ ) ｋ In this case, i, j, and k may be the same or different and may be 1 or greater and 20 or less. i and k may be the same or different and are preferably 10 or less, more preferably 5 or less, even more preferably 3 or less, and particularly preferably 2 or less. j is preferably 15 or less, more preferably 10 or less, even more preferably 5 or less, and particularly preferably 4 or less.

[0020] In the alkenylene group which may have one or more substituents X, the number of carbon atoms of the alkenylene group is not particularly limited and can be, for example, 2 or more and 20 or less, preferably 3 or more, and preferably 15 or less, more preferably 10 or less, and even more preferably 8 or less.

[0021] In the alkynylene group which may have one or more substituents X, the number of carbon atoms of the alkynylene group is not particularly limited and can be, for example, 2 or more and 20 or less, preferably 3 or more, and preferably 15 or less, more preferably 10 or less, and even more preferably 8 or less.

[0022] The number of carbon atoms in the cycloalkylene group, cycloalkenylene group, and cycloalkadienylene group is not particularly limited, and can be, for example, 3 or more and 20 or less, preferably 4 or more, and more preferably 15 or less, more preferably 10 or less, and even more preferably 8 or less.

[0023] The number of carbon atoms in the arylene group is not particularly limited and may be, for example, 6 to 18. The number of carbon atoms in the aralkylene group is not particularly limited and may be, for example, 6 to 18.

[0024] The non-aromatic heterocyclic group may be monocyclic, bicyclic, tricyclic, or tetracyclic, and may contain, for example, carbon atoms and 1 to 4 heteroatoms selected from oxygen, sulfur, and nitrogen atoms as ring-constituting atoms. The non-aromatic heterocyclic group may be saturated or unsaturated.

[0025] Examples of the heteroarylene group include monocyclic aromatic heterocyclic groups (for example, 5- or 6-membered monocyclic aromatic heterocyclic groups) and aromatic fused heterocyclic groups (for example, 5- to 18-membered aromatic fused heterocyclic groups).

[0026] The type of the substituent X is not particularly limited, and examples thereof include a hydrocarbon group, a halo group, a nitro group, a cyano group, an oxo group, a thioxo group, a sulfo group, a sulfamoyl group, a sulfinamoyl group, and a sulfenamoyl group. The hydrocarbon group is an alkyl group, an alkenyl group, an alkylene group, an alkynyl group, a cycloalkyl group, a cycloalkenyl group, a cycloalkadienyl group, an aryl group, an aralkyl group, or the like, and has, for example, 1 to 10 carbon atoms.

[0027] The substituent X may be a polymer chain, specifically, -R １ - (S) ｎ That is, R in the formula (1) may have two -R １ - (S) ｎ - and then -R １ - (S) ｎ In this case, the sulfur-containing polymer compound can form a three-dimensional network structure. １ - (S) ｎ -, then R １ is bonded to R, and -(S) ｎ The terminal of the - moiety is hydrogen or an alkali metal as described below.

[0028] In formula (1), R is preferably divalent. Specifically, R in formula (1) is preferably an "alkylene group which may have one or more substituents X," an "alkylene group which may have one or more substituents X and into which one or more ether bonds (—O—) are inserted," or an "arylene group which may have one or more substituents X." In this case, the sulfur-containing polymer compound can be easily produced, and the capacitance of the lithium ion battery can be further increased.

[0029] Among these, R is more preferably "an alkylene group which may have one or more substituents X" or "an alkylene group which may have one or more substituents X and into which one or more ether bonds (-O-) may be inserted", still more preferably "an alkylene group which has no substituent X" or "an alkylene group which has no substituent X and into which one or more ether bonds (-O-) may be inserted", and particularly preferably "an alkylene group which has no substituent X" or "an alkylene group which has no substituent X and into which one or more ether bonds (-O-) are inserted". In either case, the alkylene group may be straight-chain or branched.

[0030] In the formula (1), two R １ R are the same or different and are divalent organic groups derived from polycondensable functional groups. １ is not particularly limited as long as it is a divalent organic group derived from a polycondensable functional group. The divalent organic group is a group containing one or more carbon atoms, and means, for example, a group formed by removing two hydrogen atoms from an organic compound. In formula (1), two R １ are preferably the same as each other, and -R １ -R-R １ It is more preferable that the - site is symmetrical with R as the center.

[0031] The type of the polycondensable functional group is not particularly limited, and among them, the polycondensable functional group is a group represented by the following formula (4): Y-(S) ｎ -Y (4) (in formula (4), n represents a number of 1 or more, and two Ys may be the same or different and represent a hydrogen atom or an alkali metal), which is a functional group capable of polycondensation with a sulfur polymer. In formula (4), it is preferred that the two Ys are the same.

[0032] Examples of the polycondensable functional group include monovalent groups such as an epoxy group (a group obtained by removing one hydrogen atom from ethylene oxide), a glycidyl group, -C(=O)X (X is a halogen atom such as chlorine or fluorine), -COOH, and -NCO. The polycondensable functional group is preferably a group other than a halo group (such as a fluoro group or a chloro group).

[0033] When the polycondensable functional group is an epoxy group, R １ is -CH ２ -CH(OH)-. R in formula (1) １ Ga-CH ２ In the case of -CH(OH)-, the carbon atom not having a hydroxyl group can be bonded to R, and the carbon atom having a hydroxyl group can be bonded to S, or vice versa. ２ In —CH(OH)—, one carbon atom having a hydroxyl group bonded thereto can be bonded to S, and the other carbon atom having a hydroxyl group bonded thereto can be bonded to R.

[0034] When the polycondensable functional group is a glycidyl group, R １ is -CH ２ -CH ２ -CH(OH)-. R in formula (1) １ Ga-CH ２ -CH ２ In the case of -CH(OH)-, the terminal carbon not having a hydroxyl group can be bonded to R, and the carbon having a hydroxyl group can be bonded to S, or vice versa. ２ -CH ２ In —CH(OH)—, one carbon atom having a hydroxyl group bonded thereto can be bonded to S, and the other carbon atom having a hydroxyl group bonded thereto can be bonded to R.

[0035] When the polycondensable functional group is —C(═O)X, R in formula (1) １ is —CO—.

[0036] When the polycondensable functional group is —COOH, R １ is —COO—. １ is —COO—, the ester carbon of each of the two —COO—s is bonded to R, and the ester oxygen is bonded to S.

[0037] When the polycondensable functional group is —NCO, R １ is —NHCO—. １is —NHCO—, the nitrogen of each of the two —NHCO—'s is bonded to R, and the oxygen is bonded to S.

[0038] In the formula (1), R １ is the aforementioned -CH ２ -CH(OH)-, -CH ２ -CH ２ Preferably, it is —CH(OH)—, —CO—, —COO—, or —NHCO—. In this case, the sulfur-containing polymer compound is easy to produce and is less susceptible to decomposition, making the structure more stable. １ is -CH ２ It is more preferably —CH(OH)—.

[0039] In the formula (1), R and R １ In one embodiment, R is an alkylene group which may have one or more substituents X, and two R １ Ga-CH ２ -CH(OH)-, -CH ２ -CH ２ In another embodiment, R is an alkylene group which may have one or more substituents X and into which one or more ether bonds (—O—) are inserted, and two R １ Ga-CH ２ -CH(OH)-, -CH ２ -CH ２ Examples of the combination include —CH(OH)—, —CO—, —COO—, and —NHCO—.

[0040] In formula (1), -(S) ｎ The terminal of the - moiety is hydrogen or an alkali metal as described below.

[0041] On the other hand, in formula (1′), n, R and R １ are, as described above, n, R and R in the formula (1), respectively. １ and preferred embodiments thereof are also the same as n, R and R in the formula (1). １ is the same as

[0042] In formula (1'), R is preferably divalent. Specifically, R in formula (1) is preferably "an alkylene group which may have one or more substituents X", "an alkylene group which may have one or more substituents X and into which one or more ether bonds (-O-) are inserted", or "an arylene group which may have one or more substituents X". In this case, the production of the sulfur-containing polymer compound becomes easier, and the electrostatic capacity of the lithium ion battery can be further increased. In either case, the alkylene group may be either linear or branched.

[0043] The sulfur-containing polymer compound has the following formula (1a) -R-(S): ｎ -(1a) (wherein n and R have the same meanings as n and R in the formula (1), respectively).

[0044] In formula (1a), R is preferably divalent, trivalent, or tetravalent. When R is divalent, the sulfur-containing polymer compound is linear, and when R is trivalent or tetravalent, the sulfur-containing polymer compound can have a branched, i.e., crosslinked, structure. For convenience, R is expressed as divalent in formula (1a) and formula (1), but as described above, R also includes groups with a valence of two or more.

[0045] R in formula (1a) is preferably a "linear or branched alkylene group which may have one or more substituents X," a "linear or branched alkylene group which may have one or more substituents X and into which one or more ether bonds (—O—) are inserted," or an "arylene group which may have one or more substituents X," and is particularly preferably a "linear or branched alkylene group which does not have a substituent X." In this case, production of the sulfur-containing polymer compound is facilitated, and the electrostatic capacity of the lithium ion battery can be further increased.

[0046] In formula (1a), R may have 1 to 20 carbon atoms, preferably 1 or more, and preferably 15 or less, more preferably 10 or less, and even more preferably 8 or less.

[0047] In formula (1a), the divalent R is (CH ２ ) ｍ (m is 1 to 20, preferably 1 to 8, more preferably 1 to 6), and trivalent R is CH(CH ２ ) ｍ (CH ２ ) ｋ (m and k may be the same or different and are 1 to 20, preferably 1 to 8, more preferably 2 to 6, and particularly preferably 1), and tetravalent R is C(CH ２ ) ｍ (CH ２ ) ｋ (CH ２ ) ｌ (CH ２ ) ｐ (m, k, l and p may be the same or different and each represent 1 to 20, preferably 1 to 8, more preferably 2 to 6, and particularly preferably 1).

[0048] The sulfur-containing polymer compound is represented by the formula (1"), which is -C(=O)-(S) ｎ -

[0049] The sulfur-containing polymer compound may have other structural units as long as it has the structural unit represented by the formula (1), the structural unit represented by the formula (1'), the structural unit represented by the formula (1a), or the structural unit represented by the formula (1"), or the structural unit represented by the formula (1"); alternatively, the sulfur-containing polymer compound of the present invention may be formed solely of the structural unit represented by the formula (1'), the structural unit represented by the formula (1a), or the structural unit represented by the formula (1"). The sulfur-containing polymer compound of the present invention preferably contains 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more of the structural unit represented by the formula (1'), the structural unit represented by the formula (1a), or the structural unit represented by the formula (1")

[0050] The sulfur-containing polymer compound preferably has a structural unit represented by the formula (1) or preferably has a structural unit represented by the formula (1a). In the latter case, excellent battery capacity (electrostatic capacitance) can be achieved for the all-solid-state battery.

[0051] The sulfur-containing polymer compound may have a crosslinked structure. An example of a sulfur-containing polymer compound having a crosslinked structure is a sulfur-containing polymer compound having a structural unit represented by the formula (1) and R is a substituent X in a polymer chain (specifically, -R １ - (S) ｎ Examples of the polymer include a polymer having a substituent (-).

[0052] Another example of a sulfur-containing polymer compound having a crosslinked structure is a sulfur-containing polymer compound having a structural unit represented by the formula (1a) and wherein R is a trivalent or higher (e.g., trivalent or tetravalent) organic group (e.g., R is CH(CH ２ ) (CH ２ Specific examples of such polymers include polymers having a structure represented by the following formula (a):

[0053]

[0054] The weight-average molecular weight of the sulfur-containing polymer compound is not particularly limited. For example, the weight-average molecular weight of the sulfur-containing polymer compound is 1,000 or more and 100,000 or less. The weight-average molecular weight of the sulfur-containing polymer compound is preferably 4,000 or more and 20,000 or less. The weight-average molecular weight (Mw) referred to in this specification is a value measured by gel permeation chromatography (GPC).

[0055] In the sulfur-containing polymer compound, the content of S (elemental sulfur) is not particularly limited. For example, in terms of easily imparting excellent characteristics to a lithium-sulfur battery, the content is preferably 30% by mass or more and 99% by mass. The lower limit is more preferably 35% by mass, even more preferably 40% by mass, particularly preferably 45% by mass, and more preferably 99% by mass.

[0056] (Method for Producing Sulfur-Containing Polymer Compound) The method for producing a sulfur-containing polymer compound is not particularly limited. For example, a sulfur-containing polymer compound can be obtained by reacting a linear sulfur polymer with a compound having at least two polycondensable functional groups (hereinafter referred to as compound C). More specifically, a sulfur-containing polymer compound can be obtained by polycondensation of a linear sulfur polymer with compound C having two polycondensable functional groups. Such a method for producing a sulfur-containing polymer compound by polycondensation using compound C is suitable as a method for obtaining a sulfur-containing polymer compound having a structural unit represented by formula (1), a sulfur-containing polymer compound having a structural unit represented by formula (1'), and a sulfur-containing polymer compound having a structural unit represented by formula (1').

[0057] The linear sulfur polymer may be, for example, a polymer represented by the following formula (4): Y-(S) ｎ -Y (4) (in formula (4), n represents a number of 1 or more, and two Ys may be the same or different and represent a hydrogen atom or an alkali metal), can be used. In particular, from the viewpoint of excellent reactivity, it is preferable that both of the two Ys represent an alkali metal, and more preferably sodium.

[0058] In the formula (4), n is not particularly limited as long as it is a number of 1 or more. In terms of the positive electrode active material of the present invention easily improving battery characteristics, particularly easily increasing the capacitance of an all-solid-state battery, n is preferably 2 or more, more preferably 3 or more, even more preferably 4 or more, and particularly preferably 5 or more. The upper limit of n is not particularly limited, and can be, for example, 10,000 or less, preferably 5,000 or less, more preferably 3,000 or less, even more preferably 1,000 or less, and particularly preferably 500 or less. n can also be 10 or less. The value of n can be calculated using a MALDI-TOF MS spectrum.

[0059] The linear sulfur polymer can be obtained, for example, by reacting a sulfur source with a metal source. The sulfur source may be, for example, elemental sulfur or a compound containing a sulfur atom. However, elemental sulfur is preferred because it is easy to obtain a linear sulfur polymer. Examples of elemental sulfur include cyclic sulfur composed of sulfur atoms, and typically, an eight-membered sulfur ring can be used as the sulfur source. Such a sulfur source can be produced by a known method or can be obtained from a commercially available product.

[0060] Examples of the metal source include alkali metals and alkali metal compounds. The alkali metal is not particularly limited, and examples include sodium, potassium, and lithium, with sodium being preferred. Examples of alkali metal compounds include alkali metal sulfides, with sodium sulfide being preferred. The alkali metal compound may be a hydrate. In terms of the ease of reaction and the possibility of mass synthesis, the metal source is preferably an alkali metal compound, more preferably an alkali metal sulfide, and particularly preferably sodium sulfide, from the viewpoint of the ease of reaction and the possibility of mass synthesis.

[0061] The method for reacting the sulfur source and the metal source is not particularly limited, and examples thereof include a method in which the sulfur source and the metal source are mixed in a solvent. When a solvent is used in the reaction, the type is not particularly limited, and various organic solvents, including water, can be used. When the metal source is an alkali metal compound, particularly an alkali metal sulfide, it is preferable to use an aqueous solvent, and water is particularly preferred. When the metal source is an alkali metal, it is preferable to use an organic solvent, and it is particularly preferred to use a polar solvent such as dimethylacetamide.

[0062] In the reaction of the sulfur source and the metal source, the ratio of the two to be used is not particularly limited. ｎIn order to facilitate control of the chain length of the - moiety, i.e., the value of n, the amount of the metal source used per mole of the sulfur source is preferably 0.1 to 20 moles, more preferably 0.5 to 10 moles, even more preferably 0.8 to 8 moles, and particularly preferably 1 to 3 moles. The reaction temperature when reacting the sulfur source with the metal source is not particularly limited and can be, for example, 0 to 200°C, preferably 15 to 80°C. The reaction time of the sulfur source with the metal source is also not particularly limited and can be, for example, 10 minutes to 48 hours, preferably 30 minutes to 24 hours. The reaction can be carried out, for example, under an inert gas atmosphere such as nitrogen.

[0063] The reaction of the sulfur source with the metal source provides the linear sulfur polymer used to prepare the sulfur-containing polymeric compound.

[0064] The polycondensable functional group in the compound C is the same as described above. Therefore, the polycondensable functional group in the compound C is preferably a functional group capable of polycondensing with the sulfur polymer represented by the formula (4).

[0065] That is, examples of polycondensable functional groups include monovalent groups such as an epoxy group (a group obtained by removing one hydrogen atom from ethylene oxide), a glycidyl group, -C(=O)X (X is a halogen atom such as chlorine or fluorine), -COOH, and -NCO. In the production of a sulfur-containing polymer compound having a structural unit represented by formula (1), the polycondensable functional group is preferably other than a halo group (a fluoro group, a chloro group, etc.). In the production of a sulfur-containing polymer compound having a structural unit represented by formula (1'), examples of polycondensable functional groups include, in addition to the monovalent groups described above, halogen atoms. In the production of a sulfur-containing polymer compound having a structural unit represented by formula (1"), examples of the two polycondensable functional groups include halogen atoms.

[0066] The number of polycondensable functional groups possessed by compound C is preferably 6 or less, more preferably 5 or less. The number of polycondensable functional groups possessed by compound C may be 2 or 3, and it is particularly preferred that the number is 2.

[0067] The compound C is represented by the following general formula (2): ２ -R-R ２ (2) (In formula (2), R is an organic group, two R ２ and are the same or different functional groups capable of polycondensation. Such compounds are so-called bifunctional compounds.

[0068] In formula (2), R has the same meaning as R in formula (1). Therefore, examples of R in formula (2) include an alkylene group (-C ｍ H ２ｍ -, m is an integer), an alkylene group which may have one or more substituents X and into which one or more ether bonds (-O-) may be inserted, an alkenylene group which may have one or more substituents X, an alkynylene group which may have one or more substituents X, a cycloalkylene group which may have one or more substituents X, a cycloalkenylene group which may have one or more substituents X, a cycloalkadienylene group which may have one or more substituents X, an arylene group which may have one or more substituents X, an aralkylene group which may have one or more substituents X, a non-aromatic heterocyclic group which may have one or more substituents X, and a heteroarylene group which may have one or more substituents X. The substituent X has the same meaning as the substituent X which may be contained in the above-mentioned formula (1) (however, when R in formula (2) has a substituent X, it is preferable that the substituent X is other than the above-mentioned polymer chain).

[0069] In formula (2), R is preferably an alkylene group optionally having one or more substituents X, an alkylene group optionally having one or more substituents X and optionally having one or more ether bonds (—O—) inserted therein, or an arylene group optionally having one or more substituents X. In this case, polycondensation with the linear sulfur polymer is likely to occur, facilitating the production of the sulfur-containing polymer compound and enabling the capacity of the lithium ion battery to be further increased.

[0070] Among these, R is more preferably an alkylene group which may have one or more substituents X, or an alkylene group which may have one or more substituents X and into which one or more ether bonds (—O—) are inserted; still more preferably an alkylene group which has no substituent X, or an alkylene group which has no substituent X and into which one or more ether bonds (—O—) are inserted; and particularly preferably an alkylene group which has no substituent X, or an alkylene group which has no substituent X and into which one or more ether bonds (—O—) are inserted.

[0071] In formula (2), R ２ is a functional group capable of polycondensation. ２ Examples of compound C include monovalent groups such as an epoxy group (a group obtained by removing one hydrogen atom from ethylene oxide), a halogen atom, a glycidyl group, -C(=O)X (X is a halogen atom such as chlorine or fluorine), -COOH, and -NCO. Examples of compound C include 1,2,7,8-diepoxyoctane and adipoyl chloride.

[0072] However, when producing a sulfur-containing polymer compound having a structural unit represented by the formula (1), two R ２ are the same or different and include monovalent groups such as an epoxy group (a group obtained by removing one hydrogen atom from ethylene oxide), a glycidyl group, -C(=O)X (X is a halogen atom such as chlorine or fluorine), -COOH, and -NCO; ２ Preferably, neither of the two R ２ On the other hand, when a sulfur-containing polymer compound having a structural unit represented by the formula (1') is produced, it is preferable that two R ２ One of the R groups can be exemplified by a monovalent group such as an epoxy group (a group obtained by removing one hydrogen atom from ethylene oxide), a glycidyl group, -C(=O)X (X is a halogen atom such as chlorine or fluorine), -COOH, and -NCO, and is not a halo group, and the other R ２is a halo group. In this case, the halo group is, for example, a chlorine atom, a fluorine atom, or a bromine atom.

[0073] In the formula (2), R and R ２ In the case of producing a sulfur-containing polymer compound having a structural unit represented by the formula (1), one embodiment of the compound represented by the formula (2) is a compound in which R (a divalent organic group) is an alkylene group which may have one or more substituents X, and two R ２ is an epoxy group (a group obtained by removing one hydrogen atom from ethylene oxide), -C(=O)X (X is a halogen atom such as chlorine or fluorine), -COOH, or -NCO. In addition, when producing a sulfur-containing polymer compound having a structural unit represented by formula (1'), one embodiment of the compound represented by formula (2) is a compound in which R (divalent organic group) is an alkylene group which may have one or more substituents X, two R ２ and the other is a chlorine atom.

[0074] In the case of producing a sulfur-containing polymer compound having a structural unit represented by formula (1), specific examples of the compound represented by formula (2) include compounds represented by the following formulas (2-1) to (2-7) and (2-7a).

[0075]

[0076] When a sulfur-containing polymer compound having a structural unit represented by the formula (1') is produced, a specific example of the compound represented by the formula (2) is epichlorohydrin.

[0077] When producing a sulfur-containing polymer compound having a structural unit represented by the formula (1"), specific examples of the compound C include COCl ２ Examples include:

[0078] The compound C may be a bifunctional compound represented by the formula (2) or a trifunctional or higher functional compound. For example, when the compound C is a trifunctional compound, for example, the compound represented by the formula (2) may further include another R ２ Specifically, the hydrogen atom of R in the compound represented by formula (2) can be further bonded to R ２ In this case, R ２ is R in the formula (2) ２ and three R ２ are preferably all the same. Specific examples of bifunctional or higher functional compounds include compounds represented by the following formulae (2-8) to (2-11).

[0079]

[0080] In the method for producing a sulfur-containing polymer compound, the method for reacting a linear sulfur polymer with the compound C is not particularly limited. For example, a method of reacting the linear sulfur polymer with the compound C in a solvent can be employed. From the viewpoint of easily increasing the reactivity of the two, the reaction between the linear sulfur polymer and the compound C is preferably carried out at an interface. Specifically, a solution 1 in which the linear sulfur polymer is dissolved and a solution 2 in which the compound C is dissolved are prepared, and the interfacial reaction can be carried out using these solutions. Therefore, the solvents used to prepare the solution 1 and the solution 2 are phase-separable (i.e., insoluble) solvents.

[0081] Another example of the method for reacting a linear sulfur polymer with the compound C is a method in which the reaction between the linear sulfur polymer and the compound C is carried out in a solvent A. In this case, for example, the solvent used in the reaction to obtain the linear sulfur polymer and the solvent A used in the reaction between the linear sulfur polymer and the compound C may be the same or different, and from the viewpoint of simplicity, they are preferably the same. The reaction to obtain the linear sulfur polymer is the reaction between the sulfur source and the metal source described above.

[0082] Examples of the solvent for preparing the solution 1 include water and aqueous solvents such as alcohol compounds, as well as polar solvents such as dimethylacetamide and acetonitrile. Of these, the solvent for preparing the solution 1 is preferably water.

[0083] On the other hand, the solvent for preparing Solution 2 is preferably an organic solvent that undergoes phase separation from the aqueous solvent. Examples of such organic solvents include hydrocarbon solvents such as benzene, toluene, xylene, and hexane; ketone solvents such as acetone, methyl ethyl ketone, and isophorone; alcohol solvents such as tert-butyl alcohol, benzyl alcohol, phenoxyethanol, and phenylpropylene glycol; halogenated hydrocarbon solvents such as methylene chloride and chloroform; ether solvents such as 1,2-dimethoxyethane, tetrahydrofuran, 1,4-dioxane, and anisole; ester solvents such as ethyl acetate, propyl acetate, ethyl carbitol acetate, and butyl carbitol acetate; amide solvents such as N,N-dimethylformamide and N,N-dimethylacetamide; and carbonate solvents such as dimethyl carbonate, diethyl carbonate, and propylene carbonate. The solvent for preparing Solution 2 is preferably a halogenated hydrocarbon solvent, and more preferably chloroform.

[0084] The concentration of Solution 1 is not particularly limited and can be, for example, 0.1 to 500 g / L, preferably 0.5 to 300 g / L, more preferably 1 to 200 g / L, and even more preferably 2 to 100 g / L. The concentration of Solution 2 is not particularly limited and can be, for example, 0.1 to 500 g / L, more preferably 0.2 to 300 g / L, and even more preferably 0.5 to 200 g / L.

[0085] Examples of the solvent A include the same solvents as those used to prepare the solution 1 or the solution 2, and among these, tetrahydrofuran, acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, and the like can be preferably used.

[0086] In the reaction between the linear sulfur polymer and the compound C, the ratio of the two is not particularly limited. For example, 0.05 to 10 moles of the compound C can be used per mole of the linear sulfur polymer. In the production method of the present invention, the compound C is preferably used in an amount of 0.1 to 8 moles, more preferably 0.2 to 5 moles, even more preferably 0.25 to 3 moles, and particularly preferably 0.3 to 2.5 moles, per mole of the linear sulfur polymer. Therefore, even when the interfacial reaction is performed using the solution 1 and the solution 2, the amount of the compound C used per mole of the linear sulfur polymer can be within the above-mentioned range.

[0087] The interfacial reaction using Solution 1 and Solution 2 can be carried out, for example, by a method similar to that of known interfacial reactions. In this interfacial reaction, a catalyst can also be used, if necessary. Examples of the catalyst include phase transfer catalysts conventionally used in interfacial reactions, such as ammonium salts having a long-chain alkyl group, such as hexadecyltrimethylammonium bromide. The amount of catalyst used is not particularly limited, and can be the same amount as in conventional interfacial reactions. Usually, a phase transfer catalyst can be used in a so-called catalytic amount.

[0088] In the method for producing a sulfur-containing polymer compound, the reaction temperature for reacting a linear sulfur polymer with the compound C is not particularly limited. In particular, the reaction between the linear sulfur polymer and the compound C is carried out by a polycondensation reaction, which allows the reaction temperature to be lower than that of conventional sulfur-containing polymer compounds, and can be, for example, 0 to 100°C, preferably 10 to 80°C, more preferably 15 to 40°C, and particularly preferably 15 to 30°C. In other words, the sulfur-containing polymer compound can be produced at around room temperature. The same temperature can also be used when the above-mentioned interfacial reaction is employed. The reaction time can be appropriately set depending on conditions such as concentration and temperature.

[0089] After the reaction between the linear sulfur polymer and the compound C is completed, the reaction product can be separated and obtained by an appropriate method. For example, after the reaction is completed, the reaction product can be separated and obtained by combining one or more appropriate means such as filtration, centrifugation, distillation, drying, etc. In the interfacial reaction as described above, insoluble matter is generated at the interface, and the reaction product can be obtained by treating this with the appropriate means.

[0090] The resulting reaction product is the target sulfur-containing polymer compound. The resulting sulfur-containing polymer compound can be purified by an appropriate method.

[0091] When producing a sulfur-containing polymer compound having a structural unit represented by formula (1a), it is preferable to use a halogenated organic compound having two or more halo groups, preferably a halogenated organic compound having two, three, or four halo groups bonded thereto, instead of compound C. Examples of the halo group in such a halogenated organic compound include F, Cl, Br, and I, preferably Cl or Br, and more preferably Br.

[0092] The halogenated organic compound is Br-R ２ In this case, R ２ As for (CH ２ ) ｍ (m is 1 to 20, preferably 1 to 8, more preferably 2 to 6), CX(CH ２ ) ｍ (CH ２ ) ｋ (m and k may be the same or different and are 1 to 20, preferably 1 to 8, more preferably 1 to 6, and particularly preferably 1; X is a halo group, preferably Br), C(CH ２ ) ｍ (CH ２ ) ｋ (CH ２ X) ｌ (CH ２ X) ｐ (m, k, l and p are the same or different and are 1 to 20, preferably 1 to 8, more preferably 2 to 6, and particularly preferably one or two Xs are the same or different and are a halo group, preferably Br).

[0093] Examples of halogenated organic compounds include dibromomethane, dichloromethane, 1,2-dibromoethane, 1,2-dichloroethane, 1,2,3-tribromopropane, 1,2,3-trichloropropane, pentaerythrityl tetrabromide, pentaerythrityl tetrachloride, 1,4-dibromobutane, 1,4-chlorobutane, 1,6-dibromohexane, 1,6-dichlorohexane, 1,8-dibromooctane, 1,8-dichlorooctane, 1,10-dibromodecane, and 1,10-chlorodecane. hexane, 1,12-dibromododecane, 1,12-dichlorododecane, 1,1,2-tribromoethane, 1,1,2-trichloroethane, 1,1,2,2-tetrabromoethane, 1,1,2,2-tetrachloroethane, 1,2,3,4-tetrabromobutane, 1,2,3,4-tetrachlorobutane, 1,2,5,6-tetrabromohexane, 1,2,5,6-tetrachlorohexane, 1,2,5,6-tetrabromocyclooctane, 1,2,5,6-tetrachlorocyclooctane, and the like.

[0094] When a sulfur-containing polymer compound having a structural unit represented by the formula (1a) is produced using 1,2-dibromoethane, R in the formula (1a) is divalent and is (CH ２ ) ２ When a sulfur-containing polymer compound having a structural unit represented by the formula (1a) is produced using 1,2,3-tribromopropane, R in the formula (1a) is trivalent and is CH(CH ２ ) (CH ２ ) (i.e., an isopropyl group). When a sulfur-containing polymer compound having a structural unit represented by formula (1a) is produced using pentaerythrityl tetrabromide, R in formula (1a) is tetravalent and is C(CH ２ ) (CH ２ ) (CH ２ ) (CH ２ ) are listed.

[0095] When a sulfur-containing polymer compound is produced using the halogenated organic compound, the production conditions can be the same as those in the above-described method for producing a sulfur-containing polymer compound by polycondensation using compound C, except that a halogenated organic compound is used instead of compound C. That is, a sulfur-containing polymer compound having a structural unit represented by formula (1a) can be produced by interfacially reacting a linear sulfur polymer obtained from formula (4) with the halogenated organic compound.

[0096] (Positive Electrode Active Material) The positive electrode active material of the present invention may contain other components, other compounds, etc., as long as it contains the sulfur-containing polymer compound described above. For example, the positive electrode active material of the present invention may contain a known positive electrode active material in addition to the sulfur-containing polymer compound described above. The positive electrode active material of the present invention preferably contains 80% by mass or more of the sulfur-containing polymer compound described above, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more. The positive electrode active material of the present invention may consist essentially of the sulfur-containing polymer compound, or may consist solely of the sulfur-containing polymer compound.

[0097] The sulfur-containing polymer compound, which is an essential component of the cathode active material of the present invention, can be produced at a lower temperature than conventional sulfur polymers, and in particular, can be easily synthesized even at room temperature as described above. Therefore, the cathode active material of the present invention can further reduce the environmental load during its production process and reduce production costs, making it a promising raw material for cathode materials from the perspective of achieving the SDGs.

[0098] Furthermore, since the positive electrode active material of the present invention contains a sulfur-containing polymer compound, when applied as a positive electrode material for a lithium-sulfur battery, it can provide the lithium-sulfur battery with excellent capacity, and can impart to the lithium-sulfur battery, for example, battery characteristics comparable to those of known sulfur polymers.

[0099] Therefore, the positive electrode active material of the present invention can be suitably used as a positive electrode material for lithium-sulfur batteries.

[0100] 2. Lithium-sulfur battery The positive electrode active material of the present invention can be suitably used as a positive electrode material for a lithium-sulfur battery. The type of lithium-sulfur battery is not particularly limited as long as it contains the positive electrode active material of the present invention. For example, the battery may be a battery using a liquid electrolyte (liquid battery) or a solid battery using a solid electrolyte.

[0101] (Liquid Battery) The positive electrode material for a lithium-sulfur battery containing the positive electrode active material for a lithium-sulfur battery of the present invention can form the positive electrode of a battery using a liquid electrolyte (liquid battery). Hereinafter, a positive electrode used in a battery using a liquid electrolyte will be referred to as a liquid battery positive electrode, and a positive electrode material for a lithium-sulfur battery used in a battery using a liquid electrolyte will be referred to as a liquid battery positive electrode material.

[0102] The positive electrode material for a liquid battery may contain, in addition to the positive electrode active material of the present invention, components used in the positive electrode materials of known lithium-sulfur batteries (particularly lithium-sulfur secondary batteries). Examples of such components include a conductive material and a binder. However, as described above, the positive electrode material does not necessarily need to contain a conductive material or a binder.

[0103] In the positive electrode material for a liquid battery, examples of the conductive material include various known conductive additives. Examples of the conductive additive include various carbon materials, specifically natural graphite, artificial graphite, conductive carbon black, graphene, and carbon fiber. Examples of carbon fiber include carbon nanofibers and carbon nanotubes. Other conductive additives that can be used include metal powders such as copper and nickel, metal fibers, and conductive ceramic materials.

[0104] In the positive electrode material for liquid batteries, examples of the binder include various resin materials, specifically polyethylene, polypropylene, etc., as well as polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyethylene terephthalate, polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polyethylene oxide (PEO), etc.

[0105] In the positive electrode material for a liquid battery, the content ratio of the positive electrode active material of the present invention is not particularly limited. For example, the positive electrode active material is preferably contained in an amount of 20 to 95 mass %, more preferably 30 to 90 mass %, based on the total mass of the positive electrode active material, conductive material, and binder contained in the positive electrode material for a liquid battery. Note that the positive electrode material may consist solely of the positive electrode active material.

[0106] When the positive electrode material for a liquid battery contains a conductive material, the content ratio thereof is not particularly limited. For example, the conductive material is preferably contained in an amount of 5 to 70 mass %, more preferably 10 to 50 mass %, based on the total mass of the positive electrode active material, conductive material, and binder contained in the positive electrode material. When the positive electrode material for a liquid battery contains a binder, the content ratio thereof is not particularly limited. For example, the binder is preferably contained in an amount of 1 to 20 mass %, more preferably 3 to 10 mass %, based on the total mass of the positive electrode active material, conductive material, and binder contained in the positive electrode material.

[0107] The method for preparing the positive electrode material for a liquid battery is not particularly limited, and for example, a wide variety of known methods for preparing positive electrode materials can be employed. For example, the positive electrode material for a liquid battery can be prepared by mixing a positive electrode active material, a conductive material, and a binder in a predetermined ratio using an appropriate method. When preparing the positive electrode material for a liquid battery, a solvent can be used to disperse the positive electrode active material, the conductive material, and the binder. Examples of the solvent include water and various organic solvents, such as lower alcohol compounds having 1 to 3 carbon atoms and NMP (N-methyl-2-pyrrolidone). When the positive electrode material for a liquid battery contains a solvent, it is in the form of, for example, a slurry or a paste.

[0108] A positive electrode for a liquid battery can be produced using the above-described positive electrode material for a liquid battery. The method for producing such a positive electrode is not particularly limited, and a wide variety of known methods can be employed. For example, a positive electrode can be produced by applying a positive electrode material containing the above-described positive electrode active material to a metal foil (current collector). This allows for the production of a positive electrode (positive electrode for a liquid battery) in which the positive electrode active material of the present invention is supported on the metal foil. Metal foils for producing a positive electrode for a liquid battery include, for example, aluminum, titanium, platinum, molybdenum, stainless steel, and copper foils.

[0109] The positive electrode for the liquid battery is formed from the positive electrode material for a lithium-sulfur battery containing the positive electrode active material of the present invention, and can be produced by a simple method. Furthermore, the resulting lithium-sulfur battery (liquid battery) has a high capacity and excellent charge / discharge characteristics due to the presence of the positive electrode.

[0110] In addition to the positive electrode, the liquid battery may also include a negative electrode, an electrolyte, and a separator.

[0111] The type of anode used in the liquid battery is not particularly limited, and examples thereof include a wide range of anodes used in known lithium-sulfur batteries (particularly lithium-sulfur secondary batteries). For example, commercially available metallic lithium can be used as the anode. Alternatively, an anode can be fabricated by coating a metal foil (current collector) with a negative electrode material containing a negative electrode active material. Examples of metal foils in this case include aluminum, titanium, platinum, molybdenum, stainless steel, and copper. The type of anode active material is also not particularly limited, and examples thereof include a wide range of anode active materials used in known lithium-sulfur batteries. Specific examples include metallic materials such as lithium metal, lithium-aluminum alloys, lithium-tin alloys, lithium-lead alloys, and lithium-silicon alloys, as well as carbon materials such as natural graphite, artificial graphite, carbon black, acetylene black, graphite, and activated carbon. Similar to the positive electrode, the anode material can also include a conductive material, a solvent, and the like.

[0112] In the liquid battery, the type of electrolyte is not particularly limited, and for example, a known liquid electrolyte used in a lithium-sulfur battery can be used.

[0113] The liquid electrolyte may be a solution in which an electrolyte is dissolved in a solvent. The electrolyte contained in the liquid electrolyte may be a known lithium salt, such as LiNO ３ , LiPF ６ , LiClO ４ , LiBF ４ , LiBOB, LiAsF ６ , LiCF ３ SO ３ , LiTFSI, LiFSI, etc.

[0114] Examples of the solvent contained in the liquid electrolyte include water, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, propyl acetate, fluoroethylene carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, 1,3-dioxane, 1,2-dimethoxyethane, sulfolane, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether.

[0115] The concentration of the liquid electrolyte is not particularly limited, and can be in the same range as the electrolyte concentration of known liquid electrolytes.

[0116] The separator used in the liquid battery may be a known separator, for example, a separator formed of a polyolefin resin such as polyethylene or polypropylene, polyimide, polyvinyl alcohol, a fluororesin such as aminated polyethylene oxide polytetrafluoroethylene, an acrylic resin, nylon, aromatic aramid, inorganic glass, ceramics, etc. The separator may be in the form of a porous membrane, a nonwoven fabric, a woven fabric, etc.

[0117] (Solid-state battery) A lithium-sulfur battery cathode material containing the lithium-sulfur battery cathode active material of the present invention can form a cathode of a solid-state battery. When the lithium-sulfur battery is a solid-state battery, the lithium-sulfur battery may be either a semi-solid-state battery or an all-solid-state battery. Hereinafter, a cathode used in a solid-state battery will be referred to as a solid-state battery cathode, and a lithium-sulfur battery cathode material used in a solid-state battery will be referred to as a solid-state battery cathode material.

[0118] The positive electrode material for a solid battery can include, in addition to the positive electrode active material of the present invention, for example, a known solid electrolyte, a conductive material, etc. The type of solid electrolyte is not particularly limited, and for example, a wide range of known solid electrolytes can be used. Known sulfide-based solid electrolytes, for example, include Li ２ S (lithium sulfide)-P ２ S ５ Examples of the conductive material include sulfides such as diphosphorus pentasulfide, and various oxide-based inorganic materials. Examples of the conductive material include known conductive additives, and specific examples include carbon materials such as carbon black, ketjen black, acetylene black, particulate graphite, and fibrous carbon.

[0119] In the positive electrode material for a solid battery, the content ratio of the positive electrode active material of the present invention is not particularly limited. For example, the content ratio of the positive electrode active material of the present invention relative to the total amount of the positive electrode material for a solid battery can be 50 mass% or more, preferably 60 mass% or more, and more preferably 70 mass% or more. Furthermore, the positive electrode material for a solid battery may consist solely of the positive electrode active material of the present invention. Preferably, the content ratio of the positive electrode active material of the present invention relative to the total amount of the positive electrode material for a solid battery is 95 mass% or less.

[0120] The method for producing a positive electrode for a solid battery using the positive electrode material for a solid battery is not particularly limited, and the same method as that for producing a positive electrode applied to a known solid battery can be adopted. In addition to the above-mentioned positive electrode for a solid battery, the solid battery can also include a solid electrolyte layer and a negative electrode, which can have the same configuration as that of a known solid battery.

[0121] In specifying the inventions included in the present disclosure, the components (properties, structures, functions, etc.) described in each embodiment of the present disclosure may be combined in any manner. In other words, the present disclosure includes all subject matter consisting of all combinations of the components that can be combined as described in this specification.

[0122] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0123] (Example 1) A sulfur-containing polymer compound was synthesized according to the reaction scheme shown in Figure 1. First, sulfur (523 mg, 2.04 mmol) and Na ２ S (684 mg, 4.08 mmol, pentahydrate) was dissolved in 10 mL of water and then filtered to obtain Solution 1 of a linear sulfur polymer (abbreviated as LS). Next, 1,2,7,8-diepoxyoctane (abbreviated as OctdiEpo, 239 μL, 2.04 mmol) represented by the formula (2-2) was dissolved in 10 mL of chloroform to prepare Solution 2, and 0.005 mmol of hexadecyltrimethylammonium bromide was further added to Solution 2 as an interphase transfer catalyst. Solution 2 was added to Solution 1, and the mixture was stirred at room temperature (25°C) for one day to carry out an interfacial reaction (polycondensation reaction). Solutions 1 and 2 were prepared so that the molar ratio of LS to OctdiEpo (LS:OctdiEpo) was 2:1. During the interfacial reaction, insoluble matter was generated between the water layer and the chloroform layer, and was filtered off. The resulting solid matter was washed with water and then chloroform, and then dried under reduced pressure to obtain the target sulfur-containing polymer compound 1. This sulfur-containing polymer compound 1 was used as a positive electrode active material 1.

[0124] (Example 2) A sulfur-containing polymer compound was synthesized according to the reaction scheme shown in Figure 2. First, sulfur (523 mg, 2.04 mmol) and Na ２S (684 mg, 4.08 mmol, pentahydrate) was dissolved in 10 mL of water and then filtered to obtain Solution 1 of a linear sulfur polymer (abbreviated as LS). Next, ethylene glycol diglycidyl ether (abbreviated as EGdiEpo, 355 μL, 2.04 mmol) represented by the formula (2-4) was dissolved in 10 mL of chloroform to prepare Solution 2, and 0.005 mmol of hexadecyltrimethylammonium bromide was further added to Solution 2 as an interphase transfer catalyst. This Solution 2 was added to Solution 1, and the mixture was stirred at room temperature (25°C) for 1 day to carry out an interfacial reaction (polycondensation reaction). Solutions 1 and 2 were prepared so that the molar ratio of LS to EGdiEpo (LS:EGdiEpo) was 2:1. During the interfacial reaction, insoluble matter was generated between the water layer and the chloroform layer, and was filtered off. The resulting solid matter was washed with water and then chloroform, and then dried under reduced pressure to obtain the target sulfur-containing polymer compound 2. The sulfur-containing polymer compound 2 was used as the positive electrode active material 2.

[0125] Example 3 A sulfur-containing polymer compound was synthesized according to the reaction scheme shown in Figure 3(a). First, sulfur (5.74 g, 0.0224 mol) and Na ２ S・5H ２ O (29.9 g, 0.178 mol) was dissolved in 300 mL of water and then filtered to obtain a solution of linear sulfur polymer (abbreviated as LS). ２ S・5H ２ O is the molar ratio (sulfur:Na ２ S・5H ２The sulfur-containing polymer compound 3 was prepared in a ratio of 1:8 with 1,2-dibromoethane (50.1 g, 0.267 mol). The resulting solution was stirred at room temperature (25°C) for one day to allow for an interfacial reaction (polycondensation reaction). Insoluble matter formed during the reaction, which was filtered off. The resulting solid was washed with water and chloroform, followed by drying under reduced pressure, yielding the target sulfur-containing polymer compound 3 (yield: 14.1 g). From the results of elemental analysis (Figure 3(b)), the sulfur number n was estimated to be 1.8. Raman spectroscopy (Figure 3(c)) of the resulting sulfur-containing polymer compound 3 revealed C-S bonds and S-S bonds, confirming the synthesis of a sulfur-containing polymer having the structure represented by the scheme in Figure 3(a). This sulfur-containing polymer compound 3 was used as the positive electrode active material 3.

[0126] Example 4 A sulfur-containing polymer compound was synthesized according to the reaction scheme shown in Figure 4(a). First, sulfur (22.7 g, 0.0885 mol) and Na ２ S・5H ２ O (29.8 g, 0.177 mol) was dissolved in 300 mL of water and then filtered to obtain an LS aqueous solution. ２ S・5H ２ O is the molar ratio (sulfur:Na ２ S・5H ２ The sulfur-containing polymer compound 4 was prepared in a ratio of 1:2 with 1,2-dibromoethane (50.0 g, 0.266 mol). The resulting solution was stirred at room temperature (25°C) for one day to carry out an interfacial reaction (polycondensation reaction). Insoluble matter formed during the reaction, which was filtered off. The resulting solid was washed with water and chloroform, followed by drying under reduced pressure, yielding the target sulfur-containing polymer compound 4 (yield: 26.4 g). From the results of elemental analysis (Figure 4(b)), the sulfur number n was estimated to be 4.4. Raman spectroscopy of the resulting sulfur-containing polymer compound 4 revealed C-S bonds and S-S bonds, confirming the synthesis of a sulfur-containing polymer having the structure represented by the scheme in Figure 4(a). This sulfur-containing polymer compound 4 was used as the positive electrode active material 4.

[0127] Example 5 Sulfur-containing polymer compound 5 was obtained in the same manner as in Example 4, except that 1,2,3-tribromopropane was used instead of 1,2-dibromoethane and a catalytic amount of hexadecyltrimethylammonium bromide was used as the phase transfer catalyst. From the results of elemental analysis, the sulfur number n of the obtained sulfur-containing polymer compound 5 was estimated to be 4.4. This sulfur-containing polymer compound 5 was used as positive electrode active material 5.

[0128] (Test Example) Lithium-sulfur batteries were fabricated using the positive electrode active materials obtained in the Examples and Comparative Examples, and their performance was confirmed. Two types of lithium-sulfur batteries were fabricated: a liquid battery and an all-solid-state battery, and tests were conducted on each. Two types of electrolytes for the liquid batteries, electrolytic solution A and electrolytic solution B, were prepared as follows.

[0129] <Electrolyte A> Electrolyte A was prepared by mixing LiTFSI (lithium bis(trifluoromethane)sulfonimide) and LiNO ３ was dissolved in a 1:1 (volume ratio) mixed solvent of 1,3-dioxane and 1,2-dimethoxyethane to give a LiTFSI concentration of 0.38M and LiNO ３ An electrolyte solution with a concentration of 0.31M was prepared.

[0130] <Electrolyte Solution B> As electrolyte solution B, LiTFSI was dissolved in a 1:1 (volume ratio) mixed solvent of sulfolane and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether to prepare an electrolyte solution with a LiTFSI concentration of 0.38 M.

[0131] Test Example 1-1: A solution was prepared by dissolving the positive electrode active material 1 obtained in Example 1 in N-methylpyrrolidone. Highly conductive carbon black (KS6L, graphite) was added as a conductive material, and polyethylene (Solef5130) was added as a binder to prepare a positive electrode material. In this positive electrode material, the mass ratio of the positive electrode active material, conductive material, and binder (positive electrode active material:conductive material:binder) was 75:20:5. A positive electrode (Φ14 mm) was obtained by applying this positive electrode material to a carbon-coated aluminum foil. A CR2032 cell was fabricated using this positive electrode, metallic lithium (Φ16 mm) as a negative electrode, polypropylene as a separator, and the above-mentioned electrolyte solution A as the electrolyte.

[0132] Test Example 1-2 A CR2032 cell was fabricated in the same manner as in Test Example 1-1, except that the mass ratio of the positive electrode active material, conductive material, and binder (positive electrode active material:conductive material:binder) was 50:45:5.

[0133] Test Example 1-3 A CR2032 cell was fabricated in the same manner as in Test Example 1-2, except that electrolyte solution B was used instead of electrolyte solution A.

[0134] Test Example 1-4 A CR2032 cell was fabricated in the same manner as in Test Example 1-1, except that the mass ratio of the positive electrode active material, conductive material, and binder (positive electrode active material:conductive material:binder) was 50:50:0.

[0135] Test Example 1-5 A CR2032 cell was fabricated in the same manner as in Test Example 1-3, except that the mass ratio of the positive electrode active material, conductive material, and binder (positive electrode active material:conductive material:binder) was 50:50:0.

[0136] Test Example 2-1 A CR2032 cell was fabricated in the same manner as in Test Example 1-1, except that the positive electrode active material 2 obtained in Example 2 was used instead of the positive electrode active material 1.

[0137] Test Example 2-2 A CR2032 cell was fabricated in the same manner as in Test Example 2-1, except that the mass ratio of the positive electrode active material, conductive material, and binder (positive electrode active material:conductive material:binder) was 50:45:5.

[0138] Test Example 2-3 A CR2032 cell was fabricated in the same manner as in Test Example 2-2, except that electrolyte solution B was used instead of electrolyte solution A.

[0139] Test Example 2-4 A CR2032 cell was fabricated in the same manner as in Test Example 2-1, except that the mass ratio of the positive electrode active material, conductive material, and binder (positive electrode active material:conductive material:binder) was 50:50:0.

[0140] Test Example 2-5 A CR2032 cell was fabricated in the same manner as in Test Example 2-3, except that the mass ratio of the positive electrode active material, conductive material, and binder (positive electrode active material:conductive material:binder) was 50:50:0.

[0141] Test Example 3 140 mg of the positive electrode active material 1 obtained in Example 1 and Li as a solid electrolyte were mixed. ２ S-P ２ S ５ A positive electrode composite was prepared using 60 mg of lithium sulfide (75% by mass, 25% by mass of phosphorus pentasulfide) and 10 mg of acetylene black as a conductive material. ２ S-P ２ S ５ A layer of lithium sulfide (75% by mass, phosphorus pentasulfide 25% by mass) was prepared. An InLi foil (In foil 100 μm, Φ8 mm, Li foil 200 μm, Φ4 mm) was prepared as a counter electrode layer. A pressed powder half cell (Φ10 mm) was fabricated using 10 mg of the above positive electrode composite, 80 mg of the SE layer, and the InLi foil. This fabrication was entirely carried out in a glove box.

[0142] (Evaluation Method 1: CR2032 Cell) The battery performance (charge capacity, discharge capacity, and efficiency) was evaluated using the CR2032 cells obtained in each test example. Charge and discharge evaluation was performed at 1 to 3 V and a rate of 0.01 C.

[0143] (Results of Evaluation Method 1) Table 1 shows the results of the charge / discharge test by Evaluation Method 1. The results demonstrate that the positive electrode active materials obtained in the examples function as battery materials.

[0144]

[0145] (Evaluation Method 2: Half Cell) Battery performance (charge capacity, discharge capacity, and efficiency) was evaluated using the half cell obtained in Test Example 3. Charge and discharge evaluation was performed at 0.4 to 2.4 V and a rate of 0.01 C.

[0146] (Results of Evaluation Method 2) Table 2 shows the results of the charge-discharge test by Evaluation Method 2. These results demonstrate that the positive electrode active material obtained in the example functions as a battery material even when applied to an all-solid-state battery. In addition, although not shown in Table 2, the first cycle capacitance was 41 mAh / g. －１ It was.

[0147]

[0148] Furthermore, in Test Example 3, half cells were similarly prepared using the cathode active material obtained in Example 3, 4, or 5 instead of the cathode active material 1 obtained in Example 1, and evaluations were carried out using these half cells in the same manner as in Evaluation Method 2. It was confirmed that efficiencies equivalent to those shown in Table 2 could be achieved. These results demonstrate that the cathode active materials of Examples 3 to 5 also function as battery materials when applied to all-solid-state batteries.

Claims

1. A positive electrode active material for a lithium-sulfur battery containing a sulfur-containing polymer compound, the sulfur-containing polymer compound being represented by the following general formula (1) -R １ -R-R １ - (S) ｎ (In formula (1), n ​​represents a number of 1 or more, R represents an organic group, and two R １ are the same or different and each represents a divalent organic group derived from a functional group capable of polycondensation), １ -R-(S) ｎ (1') (wherein n, R and R １ respectively represent n, R and R in the formula (1). １ (which has the same meaning as above), represented by the following general formula (1a): -R-(S) ｎ - (1a) (wherein n and R are the same as n and R in the formula (1), respectively), or the following general formula (1") -CO-(S): ｎ A positive electrode active material for a lithium-sulfur battery, comprising a structural unit represented by the following formula:

2. The above R １ is -CH ２ -CH(OH)-, -CH ２ -CH ２ The positive electrode active material for a lithium-sulfur battery according to claim 1, which is -CH(OH)-, -CO-, -COO-, or -NHCO-.

3. The positive electrode active material for a lithium-sulfur battery according to claim 1, wherein the sulfur-containing polymer compound has a crosslinked structure.

4. A positive electrode material for a lithium-sulfur battery, comprising the positive electrode active material for a lithium-sulfur battery according to any one of claims 1 to 3.

5. A positive electrode for a lithium-sulfur battery, comprising the positive electrode material for a lithium-sulfur battery according to claim 4.

6. A lithium-sulfur battery comprising the positive electrode for a lithium-sulfur battery according to claim 5.

7. The lithium-sulfur battery of claim 6, comprising a liquid electrolyte or a solid electrolyte.

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