Carbon-composited sulfur polymer for positive electrode of lithium-sulfur secondary battery

Abstract

To provide a carbon-composited sulfur material for a positive electrode of a lithium-sulfur secondary battery, the carbon-composited sulfur material giving a lithium-sulfur secondary battery having high battery capacity after repeated charge and discharge cycles, and having high flexibility.SOLUTION: The carbon-composited sulfur polymer for a positive electrode of a lithium-sulfur secondary battery includes at least: a sulfur polymer matrix formed of sulfur chains and crosslinking reaction residues crosslinking between the sulfur chains; and a carbon material dispersed in the sulfur polymer matrix, the crosslinking reaction residue being a crosslinking reaction residue of a glycoluril derivative represented by the following general formula (1): [formula].SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery, which is obtained by reacting sulfur with a crosslinking agent to form a composite with a carbon material. [Background technology]

[0002] Currently, the majority of batteries used in electric vehicles and the like are lithium ion secondary batteries that use a transition metal composite oxide as the active material of the positive electrode.

[0003] In contrast, lithium-sulfur secondary batteries, which use sulfur as the positive electrode active material, have the potential to increase battery capacity due to the high theoretical specific capacity of sulfur. Furthermore, because sulfur is abundant in nature, raw material costs may be lower than those for positive electrode active materials that use transition metals. Therefore, lithium-sulfur secondary batteries are expected to be an alternative to lithium-ion secondary batteries, which use transition metal composite oxides as the positive electrode active material.

[0004] However, since sulfur itself has low electrical conductivity, the use of sulfur as a positive electrode active material does not actually increase battery capacity. Therefore, attempts have been made to improve the electrical conductivity of the positive electrode material and increase battery capacity by dispersing a conductive carbon material in sulfur to form a carbon-sulfur composite material.

[0005] For example, Patent Document 1 discloses a method for producing a sulfur / carbon composite conductive material obtained only from initial sulfur and initial carbon, the method comprising the following successive steps: placing 50% to 90% by weight of initial sulfur and 50% to 10% by weight of initial carbon having a specific surface area of 200 m / g or less into a reactor under atmospheric pressure so that the sum of the respective proportions of the initial sulfur and the initial carbon reaches 100%; hermetically sealing the reactor under atmospheric pressure; and heating the reactor to a heating temperature (Tc) ranging from 115°C to 400°C without externally adjusting the pressure inside the reactor, and maintaining the reactor at the heating temperature (Tc) for a predetermined time to form the sulfur / carbon composite conductive material in powder form by heat treatment.

[0006] Additionally, Non-Patent Documents 1 and 2 disclose carbon / sulfur composite cathode materials for lithium-sulfur batteries. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2012-533862 [Non-patent literature]

[0008] [Non-Patent Document 1] “A high ordered nanostructured carbon-sulfur cathode for lithium-sulfur batteries”, NATURE MATERIALS, VOL 8, 2009, 500-506 [Non-patent document 2] “Carbon onion / sulfur hybrid cathodes via inverse vulcanization for lithium-sulfur batteries”, Sustainable Energy Fuels, 2018, 2, 133-146 Summary of the Invention [Problem to be solved by the invention]

[0009] Carbon-sulfur composite materials in which carbon is composited with sulfur, such as those described in Patent Document 1 and Non-Patent Documents 1 and 2, contribute to improving the battery capacity to some extent when used in lithium-sulfur secondary batteries, but further improvement in battery capacity is required.

[0010] Furthermore, because lithium-sulfur secondary batteries are used for long periods of time through repeated charge and discharge cycles, they are required to have not only high battery capacity but also long life. Therefore, lithium-sulfur secondary batteries must have excellent cycle life characteristics as electrochemical performance, and therefore are required to have high battery capacity after repeated discharge and charge.

[0011] Furthermore, because lithium-sulfur secondary batteries are used for long periods of time, the battery materials must be highly flexible, as this can absorb shocks caused by volumetric expansion and contraction of the battery, improving the cycle characteristics of the lithium-sulfur battery.

[0012] Therefore, an object of the present invention is to provide a carbon-sulfur composite material for a positive electrode of a lithium-sulfur secondary battery that provides a lithium-sulfur secondary battery with a high battery capacity after repeated charge and discharge, and that is highly flexible. [Means for solving the problem]

[0013] As a result of extensive research, the present inventors have found that a carbon-composite sulfur polymer obtained by dispersing a carbon material in a sulfur polymer, which is a crosslinked reaction product of sulfur and a glycoluril derivative having a predetermined structure, can be used as a carbon-composite sulfur polymer for the positive electrode of a lithium-sulfur secondary battery, which provides a lithium-sulfur secondary battery with a high battery capacity after repeated charge and discharge and excellent physical durability due to its high flexibility, and have thereby completed the present invention.

[0014] That is, the present invention (1) is a carbon-composite sulfur polymer including at least a sulfur polymer matrix composed of sulfur chains and crosslinking reaction residues that crosslink the sulfur chains, and a carbon material dispersed in the sulfur polymer matrix, The crosslinking reaction residue is represented by the following general formula (1):

[0015] [ka]

[0016] (In the formula, R 1 , R 2 , R 3 and R 4 one, two, three or all of the groups are substituents capable of reacting with sulfur, and the substituents capable of reacting with sulfur are selected from the group consisting of linear or branched alkenyl groups having 2 to 15 carbon atoms (which may contain a halogen element), linear or branched alkynyl groups having 2 to 15 carbon atoms (which may contain a halogen element), sulfide groups, mercapto groups, glycidyl groups, cyano groups, carbonyl groups, and linear or branched hydrocarbon groups having 1 to 15 carbon atoms and having a halogen, and R 1 , R 2 , R 3 and R 4 When one, two or three of the above are substituents capable of reacting with sulfur, the remaining are groups selected from the group consisting of a linear or branched alkyl group having 1 to 15 carbon atoms (which may contain a halogen element), a linear or branched alkoxy group having 2 to 15 carbon atoms (which may contain a halogen element), an aryl group having 6 to 20 carbon atoms, an amino group, an amido group, an imino group, a carboxyl group, a hydroxyl group, an ester group, a nitro group, a nitrile group, a sulfonyl group, a silyl group and a hydrogen atom. 1 , R 2 , R 3 and R 4 may be the same or different.) a crosslinking reaction residue of a glycoluril derivative represented by the formula: The present invention provides a carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery, characterized by the above.

[0017] The present invention (2) is a carbon-composite sulfur polymer comprising at least a sulfur polymer matrix which is a crosslinked reaction product of sulfur and a crosslinking agent, and a carbon material dispersed in the sulfur polymer matrix, The crosslinking agent is represented by the following general formula (1):

[0018] [ka]

[0019] (In the formula, R 1 , R 2 , R 3 and R 4 one, two, three or all of the groups are substituents capable of reacting with sulfur, and the substituents capable of reacting with sulfur are selected from the group consisting of linear or branched alkenyl groups having 2 to 15 carbon atoms (which may contain a halogen element), linear or branched alkynyl groups having 2 to 15 carbon atoms (which may contain a halogen element), sulfide groups, mercapto groups, glycidyl groups, cyano groups, carbonyl groups, and linear or branched hydrocarbon groups having 1 to 15 carbon atoms and having a halogen, and R 1 , R 2 , R 3 and R 4 When one, two or three of the above are substituents capable of reacting with sulfur, the remaining are groups selected from the group consisting of a linear or branched alkyl group having 1 to 15 carbon atoms (which may contain a halogen element), a linear or branched alkoxy group having 2 to 15 carbon atoms (which may contain a halogen element), an aryl group having 6 to 20 carbon atoms, an amino group, an amido group, an imino group, a carboxyl group, a hydroxyl group, an ester group, a nitro group, a nitrile group, a sulfonyl group, a silyl group and a hydrogen atom. 1 , R 2 , R 3 and R 4 may be the same or different.) The glycoluril derivative is represented by the formula: The present invention provides a carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery, characterized by the above.

[0020] The present invention (3) also provides a carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery according to (2), characterized in that the sulfur polymer is a crosslinked reaction product of the sulfur and 5.0 to 100.0 parts by mass of the crosslinking agent per 100.0 parts by mass of the sulfur.

[0021] The present invention (4) also provides a carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery according to any one of (1) to (3), characterized in that the content of the carbon material is 1.0 to 30.0 mass %.

[0022] The present invention (5) also provides a carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery according to any one of (1) to (4), characterized in that the carbon material is a conductive carbon powder. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a highly flexible carbon-sulfur composite material for a positive electrode of a lithium-sulfur secondary battery, which provides a lithium-sulfur secondary battery with a high battery capacity after repeated charge and discharge. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a diagram showing charge-discharge curves of the carbon-composite sulfur polymer of Example 1. [Figure 2] FIG. 1 is a graph showing the charge / discharge curve (30 cycles) of an electrode prepared using the carbon-composite sulfur polymer of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0025] A carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery according to a first embodiment of the present invention is a carbon-composite sulfur polymer including at least a sulfur polymer matrix composed of sulfur chains and crosslinking reaction residues that crosslink the sulfur chains, and a carbon material dispersed in the sulfur polymer matrix, The crosslinking reaction residue is represented by the following general formula (1):

[0026] [ka]

[0027] (In the formula, R 1 , R 2 , R 3 and R 4 one, two, three or all of the groups are substituents capable of reacting with sulfur, and the substituents capable of reacting with sulfur are selected from the group consisting of linear or branched alkenyl groups having 2 to 15 carbon atoms (which may contain a halogen element), linear or branched alkynyl groups having 2 to 15 carbon atoms (which may contain a halogen element), sulfide groups, mercapto groups, glycidyl groups, cyano groups, carbonyl groups, and linear or branched hydrocarbon groups having 1 to 15 carbon atoms and having a halogen, and R 1 , R 2 , R 3 and R 4 When one, two or three of the above are substituents capable of reacting with sulfur, the remaining are groups selected from the group consisting of a linear or branched alkyl group having 1 to 15 carbon atoms (which may contain a halogen element), a linear or branched alkoxy group having 2 to 15 carbon atoms (which may contain a halogen element), an aryl group having 6 to 20 carbon atoms, an amino group, an amido group, an imino group, a carboxyl group, a hydroxyl group, an ester group, a nitro group, a nitrile group, a sulfonyl group, a silyl group and a hydrogen atom. 1 , R 2 , R 3 and R 4 may be the same or different.) a crosslinking reaction residue of a glycoluril derivative represented by the formula: The carbon-composite sulfur polymer for the positive electrode of a lithium-sulfur secondary battery is characterized by the following.

[0028] The carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery according to the first embodiment of the present invention comprises a carbon-composite sulfur polymer containing at least a sulfur polymer matrix and a carbon material dispersed in the sulfur polymer matrix. That is, the carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery according to the first embodiment of the present invention is a sulfur polymer containing a carbon material, and the carbon material is dispersed in the sulfur polymer.

[0029] The sulfur polymer according to the first embodiment of the present invention for use in a carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery is composed of a large number of sulfur chains and crosslinking reaction residues of a crosslinking agent that are bonded to the sulfur chains and crosslink the sulfur chains. In other words, the sulfur polymer is obtained by crosslinking sulfur (sulfur molecules) with a crosslinking agent, and therefore has a molecular structure in which a large number of sulfur chains, each of which is a chain of sulfur atoms, are connected by reaction residues of the crosslinking agent. The length of the sulfur chains in the sulfur polymer is not particularly limited, but is preferably S1 to S2. 32 More preferably, S4 to S8.

[0030] Examples of the carbon material for the carbon-composite sulfur polymer for use in the positive electrode of a lithium-sulfur secondary battery according to the first embodiment of the present invention include conductive carbon powders such as ketjen black and acetylene black, carbon nanofibers, graphene, etc. Among these, ketjen black, acetylene black, carbon nanofibers, etc. are preferred as the carbon material.

[0031] When the carbon material is a conductive carbon powder, the primary particle size of the conductive carbon powder is preferably 0.01 to 100 μm, more preferably 0.01 to 10 μm.

[0032] The crosslinking reaction residue in the carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the first embodiment of the present invention is a crosslinking reaction residue of a glycoluril derivative represented by general formula (1).

[0033] The carbonaceous material content in the carbon-sulfur polymer composite for a lithium-sulfur secondary battery positive electrode according to the first embodiment of the present invention is preferably 1.0 to 30.0 mass %, more preferably 3.0 to 15.0 mass %. When the carbonaceous material content in the carbon-sulfur polymer composite for a lithium-sulfur secondary battery positive electrode is within the above range, a uniform composite having a high sulfur content is likely to be obtained.

[0034] A carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery according to a second embodiment of the present invention is a carbon-composite sulfur polymer including at least a sulfur polymer matrix which is a crosslinked reaction product of sulfur and a crosslinking agent, and a carbon material dispersed in the sulfur polymer matrix, The crosslinking agent is represented by the following general formula (1):

[0035] [ka]

[0036] (In the formula, R 1 , R 2 , R 3 and R 4 one, two, three or all of the groups are substituents capable of reacting with sulfur, and the substituents capable of reacting with sulfur are selected from the group consisting of linear or branched alkenyl groups having 2 to 15 carbon atoms (which may contain a halogen element), linear or branched alkynyl groups having 2 to 15 carbon atoms (which may contain a halogen element), sulfide groups, mercapto groups, glycidyl groups, cyano groups, carbonyl groups, and linear or branched hydrocarbon groups having 1 to 15 carbon atoms and having a halogen, and R 1 , R 2 , R 3 and R 4When one, two or three of the above are substituents capable of reacting with sulfur, the remaining are groups selected from the group consisting of a linear or branched alkyl group having 1 to 15 carbon atoms (which may contain a halogen element), a linear or branched alkoxy group having 2 to 15 carbon atoms (which may contain a halogen element), an aryl group having 6 to 20 carbon atoms, an amino group, an amido group, an imino group, a carboxyl group, a hydroxyl group, an ester group, a nitro group, a nitrile group, a sulfonyl group, a silyl group and a hydrogen atom. 1 , R 2 , R 3 and R 4 may be the same or different.) The glycoluril derivative is represented by the formula: The carbon-composite sulfur polymer for the positive electrode of a lithium-sulfur secondary battery is characterized by the following.

[0037] The carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery according to the second embodiment of the present invention comprises a carbon-composite sulfur polymer containing at least a sulfur polymer matrix and a carbon material dispersed in the sulfur polymer matrix. That is, the carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery according to the second embodiment of the present invention is a sulfur polymer containing a carbon material, and the carbon material is dispersed in the sulfur polymer.

[0038] The sulfur polymer in the carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery according to the second embodiment of the present invention is a crosslinked reaction product of sulfur and a crosslinking agent. That is, the sulfur polymer is obtained by crosslinking sulfur (sulfur molecules) with a crosslinking agent, and has a molecular structure in which many sulfur chains, each of which is a chain of sulfur atoms, are connected by reactive residues of the crosslinking agent.

[0039] The sulfur (molecular sulfur) in the carbon-composite sulfur polymer for use in the positive electrode of a lithium-sulfur secondary battery according to the second embodiment of the present invention is a raw material for the sulfur polymer and typically exists as a cyclic molecule of S8. When the raw material sulfur (sulfur molecule) is heated or heated in the presence of a catalyst, a portion of the molecular chain is cleaved, resulting in ring-opening, or further cleavage of the molecular chain after ring-opening generates a linear sulfur chain of eight or fewer atoms. The raw material sulfur (sulfur molecule) is not particularly limited and may be produced from any raw material or by any production method. The crystal form of sulfur is not particularly limited and may be any of α-sulfur (orthorhombic sulfur), β-sulfur (monoclinic sulfur), γ-sulfur (monoclinic sulfur), or a mixture thereof.

[0040] The crosslinking agent for the carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery according to the second embodiment of the present invention is a glycoluril derivative represented by the general formula (1).

[0041] The sulfur polymer is preferably a crosslinked reaction product of sulfur and 5.0 to 100.0 parts by mass of a crosslinking agent per 100.0 parts by mass of sulfur, and more preferably a crosslinked reaction product of sulfur and 10.0 to 80.0 parts by mass of a crosslinking agent per 100.0 parts by mass of sulfur.

[0042] Examples of the carbon material for the carbon-sulfur polymer composite for use in the positive electrode of a lithium-sulfur secondary battery according to the second embodiment of the present invention include conductive carbon powders such as ketjen black and acetylene black, carbon nanofibers, graphene, etc. Among these, ketjen black, acetylene black, carbon nanofibers, etc. are preferred as the carbon material.

[0043] When the carbon material is a conductive carbon powder, the primary particle size of the conductive carbon powder is preferably 0.01 to 100 μm, more preferably 0.01 to 10 μm.

[0044] In the carbon-sulfur polymer composite for a lithium-sulfur secondary battery positive electrode according to the second embodiment of the present invention, the carbon material content is preferably 1.0 to 30.0 mass %, more preferably 3.0 to 15.0 mass %. When the carbon material content in the carbon-sulfur polymer composite for a lithium-sulfur secondary battery positive electrode is within the above range, a uniform composite having a high sulfur content is likely to be obtained.

[0045] The glycoluril derivative according to the carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery of the first embodiment of the present invention and the carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery of the second embodiment of the present invention is represented by the general formula (1):

[0046] [ka]

[0047] (In the formula, R 1 , R 2 , R 3 and R 4 one, two, three or all of the groups are substituents capable of reacting with sulfur, and the substituents capable of reacting with sulfur are selected from the group consisting of linear or branched alkenyl groups having 2 to 15 carbon atoms (which may contain a halogen element), linear or branched alkynyl groups having 2 to 15 carbon atoms (which may contain a halogen element), sulfide groups, mercapto groups, glycidyl groups, cyano groups, carbonyl groups, and linear or branched hydrocarbon groups having 1 to 15 carbon atoms and having a halogen, and R 1 , R 2 , R 3 and R 4 When one, two or three of the above are substituents capable of reacting with sulfur, the remaining are groups selected from the group consisting of a linear or branched alkyl group having 1 to 15 carbon atoms (which may contain a halogen element), a linear or branched alkoxy group having 2 to 15 carbon atoms (which may contain a halogen element), an aryl group having 6 to 20 carbon atoms, an amino group, an amido group, an imino group, a carboxyl group, a hydroxyl group, an ester group, a nitro group, a nitrile group, a sulfonyl group, a silyl group and a hydrogen atom. 1 , R 2 , R3 and R 4 may be the same or different.) It is a glycoluril derivative represented by the formula:

[0048] In general formula (1), R 1 , R 2 , R 3 and R 4 is any one of the following (i) to (iii), and among these, (i) is preferred. (i)R 1 , R 2 , R 3 and R 4 are all substituents capable of reacting with sulfur, that is, groups selected from the group consisting of straight-chain or branched alkenyl groups (which may contain a halogen element) having 2 to 15, preferably 2 to 10, and particularly preferably 3, carbon atoms, straight-chain or branched alkynyl groups (which may contain a halogen element) having 2 to 15 carbon atoms, sulfide groups, mercapto groups, glycidyl groups, cyano groups, carbonyl groups, and straight-chain or branched hydrocarbon groups having 1 to 15 carbon atoms and containing a halogen. (ii)R 1 , R 2 , R 3 and R 4 Among these, two are substituents capable of reacting with sulfur, that is, groups selected from the group consisting of straight-chain or branched alkenyl groups (which may contain a halogen element) having 2 to 15 carbon atoms, preferably 2 to 10, and particularly preferably 3 carbon atoms, straight-chain or branched alkynyl groups (which may contain a halogen element) having 2 to 15 carbon atoms, sulfide groups, mercapto groups, glycidyl groups, cyano groups, carbonyl groups, and straight-chain or branched hydrocarbon groups having 1 to 15 carbon atoms and having a halogen, and one is a group selected from the group consisting of straight-chain or branched alkyl groups (which may contain a halogen element) having 1 to 15 carbon atoms, preferably 1 to 10 carbon atoms, straight-chain or branched alkoxy groups (which may contain a halogen element) having 2 to 15 carbon atoms, preferably 2 to 10 carbon atoms, aryl groups having 6 to 20 carbon atoms, preferably 6 to 10 carbon atoms, amino groups, amido groups, imino groups, carboxyl groups, hydroxyl groups, ester groups, nitro groups, nitrile groups, sulfonyl groups, silyl groups, and hydrogen atoms. (iii)R 1 , R 2 , R 3 and R 4 one of them is a substituent capable of reacting with sulfur, that is, a group selected from the group consisting of a linear or branched alkenyl group having 2 to 15 carbon atoms, preferably 2 to 10 carbon atoms, and particularly preferably 3 carbon atoms (which may contain a halogen element), a linear or branched alkynyl group having 2 to 15 carbon atoms (which may contain a halogen element), a sulfide group, a mercapto group, a glycidyl group, a cyano group, a carbonyl group, and a linear or branched hydrocarbon group having 1 to 15 carbon atoms and which has a halogen; and two of them are groups selected from the group consisting of a linear or branched alkyl group having 1 to 15 carbon atoms, preferably 1 to 10 carbon atoms (which may contain a halogen element), a linear or branched alkoxy group having 2 to 15 carbon atoms, preferably 2 to 10 carbon atoms (which may contain a halogen element), an aryl group having 6 to 20 carbon atoms, preferably 6 to 10 carbon atoms, an amino group, an amido group, an imino group, a carboxyl group, a hydroxyl group, an ester group, a nitro group, a nitrile group, a sulfonyl group, a silyl group, and a hydrogen atom. In addition, R 1 , R 2 , R 3 and R 4 may be the same or different. Furthermore, the term "sulfur-reactive substituent" refers to a group that can react with sulfur in a crosslinking reaction with sulfur by heating in the presence of a catalyst such as a dithiocarbamate catalyst, and examples thereof include a linear or branched alkenyl group having 2 to 15 carbon atoms, preferably 2 to 10 carbon atoms (which may contain a halogen element), a linear or branched alkynyl group having 2 to 15 carbon atoms, preferably 2 to 10 carbon atoms (which may contain a halogen element), a sulfide group, a mercapto group, a glycidyl group, a cyano group, a carbonyl group, and a linear or branched hydrocarbon group having 1 to 15 carbon atoms, preferably 1 to 10 carbon atoms, which has a halogen. Furthermore, "which may contain a halogen element" refers to both groups in which no hydrogen atoms are substituted with halogen atoms and groups in which some of the hydrogen atoms are substituted with halogen atoms. For example, examples of the alkyl group include a methyl group or a chloromethyl group, examples of the alkenyl group include a 2-propen-1-yl group (allyl group), a 2-methyl-2-propen-1-yl group, or a 2-buten-1-yl group, examples of the alkynyl group include an ethynyl group, examples of the alkoxy group include a 2-hydroxyethyl group, and examples of the mercapto group include a 2-mercaptoethyl group.

[0049] The glycoluril derivative represented by the general formula (1) includes the glycoluril derivative represented by the following formula (1A):

[0050] [ka]

[0051] Examples of the tetraallyl glycoluril include 1,3,4,6-tetraallyl glycoluril represented by the following formula:

[0052] The carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the first embodiment of the present invention and the carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the second embodiment of the present invention have a composite modulus of elasticity measured by a nanoindentation test of preferably 0.10 to 12.0 GPa, more preferably 0.10 to 11.0 GPa, and particularly preferably 1.0 to 11.0 GPa. A lower composite modulus measured by the nanoindentation test indicates higher flexibility. The procedure and conditions for the nanoindentation test in the present invention are as follows. The carbon composite sulfur polymer was crushed into fine powder, embedded in epoxy resin, and cross-sectioned using an ultramicrotome. Measurement conditions were as follows: Berkovich indenter (made of diamond), maximum load: 250 μN, loading / unloading time: 5 seconds, maximum load holding time: 2 seconds.

[0053] The carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the first embodiment of the present invention and the carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the second embodiment of the present invention have a composite modulus measured by a powder compression test of preferably 0.10 to 40.0 GPa, more preferably 0.10 to 35.0 GPa, and particularly preferably 1.0 to 35.0 GPa. A lower composite modulus measured by the powder compression test indicates higher flexibility. The procedure and conditions for the powder compression test in the present invention are as follows. The fine powder obtained by pulverizing the carbon composite sulfur polymer is compressed at a test speed of 10 mm / min and a pressure of 250 MPa to obtain a stress-strain curve. Pre-compression is carried out 10 times under the same conditions, and the composite elastic modulus is obtained from the slope of the stress-strain curve in the strain range of 0.15 to 0.4% after the 11th compression.

[0054] The average particle size of the carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the first embodiment of the present invention and the carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the second embodiment of the present invention is preferably 1 to 40 μm, more preferably 3 to 30 μm.

[0055] In the present invention, the average particle size is a median size measured by a laser diffraction / scattering method.

[0056] The carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the first embodiment of the present invention and the carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the second embodiment of the present invention are sulfur polymers obtained by a crosslinking reaction between sulfur and a glycoluril derivative represented by general formula (1), and a carbon material is dispersed in the sulfur polymer. Therefore, a lithium-sulfur secondary battery using the carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the first embodiment of the present invention and the carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the second embodiment of the present invention as a positive electrode material has a high battery capacity after repeated charge and discharge.

[0057] Furthermore, the carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the first embodiment of the present invention and the carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the second embodiment of the present invention are sulfur polymers obtained by a crosslinking reaction between sulfur and a glycoluril derivative represented by general formula (1), in which a carbon material is dispersed and blended. Therefore, they are highly flexible, and a lithium-sulfur secondary battery using the carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the first embodiment of the present invention and the carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the second embodiment of the present invention as a positive electrode material has high durability against physical fluctuations.

[0058] The carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the first embodiment of the present invention and the carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the second embodiment of the present invention may be obtained by any production method. As a method for producing the carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the first embodiment of the present invention and the carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the second embodiment of the present invention, the following method for producing a carbon-composite sulfur polymer for use in a positive electrode of a lithium-sulfur secondary battery according to the present invention is preferably used.

[0059] The method for producing a carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery of the present invention includes a first step of adding sulfur, a crosslinking agent, and a catalyst as reaction raw materials to a reaction vessel; a second step of heating and melting sulfur while stirring the reaction raw material, and then adding a carbonaceous material to the reaction raw material in a fluidized state while stirring the reaction raw material to obtain a carbonaceous material mixed reaction raw material; a third step of reacting the carbonaceous material mixed reaction raw material at 120 to 220°C to obtain a carbon-composite sulfur polymer; and the crosslinking agent is a glycoluril derivative represented by general formula (1); The present invention relates to a method for producing a carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery, the method comprising the steps of:

[0060] The first step in the method for producing a carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery of the present invention is a step of adding sulfur as reaction raw materials, a glycoluril derivative represented by general formula (1) as a crosslinking agent, and a catalyst to a reaction vessel.

[0061] The sulfur (sulfur molecules) used in the first step are a raw material for sulfur polymers and typically exist as cyclic molecules of S8. When the raw material sulfur (sulfur molecules) is heated or heated in the presence of a catalyst, a portion of the molecular chain is cleaved, resulting in ring-opening, or further cleavage of the molecular chain after ring-opening produces a linear sulfur chain of 8 atoms or less. The raw material sulfur (sulfur molecules) is not particularly limited and may be produced from any raw material or by any production method. The crystalline form of sulfur is not particularly limited and may be any of α-sulfur (orthorhombic sulfur), β-sulfur (monoclinic sulfur), γ-sulfur (monoclinic sulfur), or a mixture thereof.

[0062] The crosslinking agent in the first step is a raw material for a sulfur polymer, and is a crosslinking agent for crosslinking the raw material sulfur (sulfur molecules) to form a sulfur polymer.

[0063] The crosslinking agent in the first step is a glycoluril derivative represented by general formula (1). The glycoluril derivative represented by general formula (1) in the method for producing a carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery of the present invention is the same as the glycoluril derivative represented by general formula (1) in the carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery of the first embodiment of the present invention and the carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery of the second embodiment of the present invention.

[0064] The catalyst for the first step is a catalyst for promoting the reaction between sulfur and a crosslinking agent. Examples of the catalyst for the first step include dithiocarbamate catalysts. Dithiocarbamate catalysts are represented by the general formula (3): R 7 R 8 NCS2 - (3) In general formula (3), R is a salt of an anion represented by the formula (3) and a metal cation.7 and R 8 R is a straight or branched alkyl group having 1 to 6 carbon atoms, preferably a straight alkyl group having 1 to 3 carbon atoms, and specific examples thereof include methyl, ethyl, and propyl. 7 and R 8 may have the same structure or different structures. Examples of metal cations that serve as counter cations to the anions represented by general formula (3) include zinc ions, sodium ions, silver ions, iron ions, ammonium ions, cobalt ions, nickel ions, copper ions, lithium ions, and manganese ions. Examples of dithiocarbamate catalysts include zinc diethyldithiocarbamate, zinc dimethyldithiocarbamate, copper diethyldithiocarbamate, silver diethyldithiocarbamate, and disodium dimethyldithiocarbamate. Of these, zinc diethyldithiocarbamate and copper diethyldithiocarbamate are preferred.

[0065] Examples of the catalyst used in the first step include zinc diethyldithiocarbamate, zinc dimethyldithiocarbamate, copper diethyldithiocarbamate, silver diethyldithiocarbamate, and disodium dimethyldithiocarbamate.

[0066] In the first step, the amount of the crosslinking agent added is not particularly limited, but is preferably 5.0 to 100.0 parts by mass, more preferably 10.0 to 80.0 parts by mass, relative to 100.0 parts by mass of sulfur. When the amount of the crosslinking agent added is within the above range, a flexible carbon-composite sulfur polymer with a high sulfur content can be obtained.

[0067] In the first step, the amount of catalyst added is not particularly limited, but is preferably 0.10 to 5.0 parts by mass, more preferably 0.50 to 3.0 parts by mass, relative to 100.0 parts by mass of the total of sulfur and crosslinking agent. When the amount of catalyst added is within the above range, the carbon-composite sulfur polymer can be obtained in good yield.

[0068] In the first step, the method for adding sulfur, a crosslinking agent, and a catalyst to a reaction vessel is not particularly limited, and for example, sulfur, a crosslinking agent, and a catalyst may be added separately to the reaction vessel, or sulfur, a crosslinking agent, and a catalyst may be mixed in advance in different vessels and then added to the reaction vessel. In addition, in the first step, after adding sulfur, a crosslinking agent, and a catalyst to the reaction vessel, these reaction raw materials may be stirred and mixed before starting heating of the reaction raw materials in the second step, or heating of the reaction raw materials may be started in the second step without stirring and mixing of the reaction raw materials.

[0069] The second step in the method for producing a carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery of the present invention is a step of heating the reaction raw materials in a reaction vessel while stirring them, and then adding a carbon material to the reaction raw materials in a fluidized state to obtain a carbon material-mixed reaction raw material.

[0070] In the second step, the reaction raw materials in the reaction vessel are first heated while stirring to melt the sulfur, and then the sulfur, crosslinking agent, and catalyst are stirred and mixed in the molten sulfur state. In the second step, the temperature of the reaction raw materials when the carbonaceous material is added to the reaction raw materials is a temperature equal to or higher than the temperature at which the reaction raw materials become fluidized due to the melting of sulfur, preferably 120 to 220°C, more preferably 140 to 180°C, and particularly preferably 140 to 160°C. In the second step, before mixing the carbonaceous material with the reaction raw materials (sulfur, crosslinking agent, and catalyst), the sulfur, crosslinking agent, and catalyst are stirred and mixed in the molten sulfur state, thereby obtaining a reaction raw material with a high degree of dispersion of the crosslinking agent and catalyst in the sulfur. Therefore, in the third step, the reaction efficiency between the sulfur and the crosslinking agent in the reaction raw materials mixed with the carbonaceous material is increased, resulting in a composite material that achieves both a high conversion rate to a sulfur polymer and high dispersibility in the carbonaceous material. In the second step, a small amount of reaction between sulfur and the crosslinking agent may occur due to heating of the reaction raw materials before adding the carbon material to the reaction raw materials, but as long as the reaction does not hinder dispersion of the carbon material in the reaction raw materials, a small amount of reaction between sulfur and the crosslinking agent may occur due to heating of the reaction raw materials before adding the carbon material to the reaction raw materials.

[0071] In the second step, next, in a state in which the sulfur is molten, a carbonaceous material is added to the reaction raw material in a fluidized state while stirring the reaction raw material, thereby obtaining a carbonaceous material mixed reaction raw material.

[0072] Examples of the carbon material used in the second step include conductive carbon powder such as ketjen black and acetylene black, carbon nanofiber, graphene, etc. Among these, ketjen black, acetylene black, carbon nanofiber, etc. are preferred as the carbon material.

[0073] When the carbon material is a conductive carbon powder, the primary particle size of the conductive carbon powder is preferably 0.01 to 100 μm, more preferably 0.01 to 10 μm.

[0074] In the second step, while the sulfur in the reactant is in a molten state, a predetermined amount of carbonaceous material is added to the fluidized reactant in one or multiple batches while stirring the reactant. To achieve a good dispersion, it is preferable to continue stirring after adding the predetermined amount of carbonaceous material. In the second step, the reactant is in a fluidized state when the carbonaceous material is added. Adding the carbonaceous material to the reactant while stirring the fluidized reactant results in a good dispersion of the carbonaceous material in the reactant. The reactant enters the pores of the carbonaceous material while maintaining uniformity and polymerizes, achieving both a high conversion rate and good dispersibility in the carbonaceous material. The fluidized state of the reactant refers to a state in which the viscosity of the dissolved reactant is low and can be easily stirred with a stirrer, such as a magnetic stirrer. In the second step, the viscosity of the reactant when the carbonaceous material is added can be, for example, 10,000 mPa·s or less.

[0075] In the second step, the amount of the carbonaceous material added is not particularly limited, but is preferably 1.0 to 30.0 parts by mass, more preferably 3.0 to 15.0 parts by mass, relative to 100.0 parts by mass of the reaction raw materials. When the amount of the carbonaceous material added is within the above range, a uniform composite material having a high sulfur content can be obtained.

[0076] In the second step, the temperature of the reaction raw materials when the addition of the carbonaceous material to the reaction raw materials is started varies depending on the amount of sulfur used, the crystalline state of the sulfur used as the raw material, and, if a mixture of sulfur with different crystalline states is used as the raw material, the mixing ratio thereof. Therefore, the temperature of the reaction raw materials when the addition of the carbonaceous material to the reaction raw materials is started is appropriately selected depending on the amount of sulfur used, the crystalline state of the sulfur used as the raw material, and, if a mixture of sulfur with different crystalline states is used as the raw material, the mixing ratio thereof. In the second step, the temperature of the reaction raw materials when the addition of the carbonaceous material to the reaction raw materials is started is preferably 120 to 220°C, more preferably 140 to 180°C, and particularly preferably 140 to 160°C.

[0077] In the second step, the carbonaceous material is added to the reaction raw materials while the reaction raw materials are in a fluidized state. The timing for ending the addition of the carbonaceous material to the reaction raw materials varies depending on the reaction scale, and is appropriately selected within a range in which the effects of the present invention are achieved while the reaction raw materials are in a fluidized state. In the second step, the temperature of the reaction raw materials when the addition of the carbonaceous material to the reaction raw materials is ended is preferably 120 to 220°C, more preferably 140 to 180°C, and particularly preferably 140 to 160°C. If the temperature of the reaction raw materials becomes too high in the second step, sulfur polymerization will proceed excessively, reducing the fluidity of the reaction raw materials and reducing the dispersibility of the carbonaceous material in the reaction raw materials. Therefore, in the second step, it is preferable to end the addition of the carbonaceous material to the reaction raw materials within the above temperature range.

[0078] In the second step, the time from the start of adding the carbonaceous material to the reaction raw materials to the end of adding the carbonaceous material to the reaction raw materials is preferably 0 to 15 minutes, more preferably 1 to 10 minutes, thereby obtaining a carbon-composite sulfur polymer in which the carbonaceous material is highly dispersed.

[0079] In the second step, it is preferable to add at least 50 mass % of the carbonaceous material to the reaction raw material, more preferably at least 80 mass %, and particularly preferably the entire amount, within 10 minutes from the start of adding the carbonaceous material to the reaction raw material, thereby obtaining a carbon-composite sulfur polymer in which the carbonaceous material is highly dispersible.

[0080] In the second step, it is preferable to add at least 50 mass % of the carbonaceous material to the reaction raw materials while the temperature of the reaction raw materials is 220° C. or less, more preferably at least 80 mass % of the carbonaceous material is added, and particularly preferably the entire amount is added, thereby obtaining a carbon-composite sulfur polymer in which the carbonaceous material is highly dispersible.

[0081] In the second step, it is preferable to add the entire amount of the carbonaceous material to the reaction raw materials when the viscosity of the reaction raw materials is 10,000 mPa·s or less, thereby obtaining a carbon-composite sulfur polymer in which the carbonaceous material is highly dispersible.

[0082] In the second step, the carbonaceous material is added to the fluidized reactant while stirring the reactant, thereby obtaining a carbonaceous material mixed reactant.

[0083] In the second step, the third step may be carried out immediately after the addition of the carbonaceous material to the reaction raw material is completed, or the third step may be carried out after continuing to heat the carbonaceous material mixed reaction raw material for a predetermined time.

[0084] The third step in the method for producing a carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery of the present invention is a step in which the mixed reaction raw carbon material obtained by carrying out the second step is reacted at 120 to 220°C to obtain a carbon-composite sulfur polymer.

[0085] In the third step, the carbonaceous material mixed reaction raw material is reacted at 120 to 220°C, and in a state where the carbonaceous material is dispersed in a mixture of sulfur and a crosslinking agent in the carbonaceous material mixed reaction raw material, the sulfur and the crosslinking agent are reacted to produce a sulfur polymer, thereby obtaining a carbon-composite sulfur polymer in which the carbonaceous material is dispersed in the sulfur polymer.

[0086] In the third step, the reaction temperature is 120 to 220°C, more preferably 130 to 200°C. In the third step, the reaction time is not particularly limited and may be appropriately selected as long as it is within a range in which the reaction between sulfur and the crosslinking agent occurs. In the third step, the carbonaceous material mixed reaction raw material may be reacted while being stirred, or may be reacted while being left to stand.

[0087] The second and third steps may be carried out in an open air atmosphere, or may be carried out in an inert gas atmosphere such as nitrogen gas.

[0088] In this manner, the third step is carried out to obtain a carbon-composite sulfur polymer, that is, a carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery in which a carbon material is dispersed in the sulfur polymer. [Example]

[0089] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples shown below.

[0090] Example 1 12.6 g of sulfur (Kanto Chemical Co., Ltd.), 1.4 g of TA-G (1,3,4,6-tetraallylglycoluril, Shikoku Chemical Industry Co., Ltd.), and 0.14 g of zinc diethyldithiocarbamate (Tokyo Chemical Industry Co., Ltd.) were weighed and added to a polyfluoroalkoxy resin (PFA) container. Next, the reaction raw materials were lightly mixed with a spatula, a stirrer was placed in the container, and the mixture was heated in an oil bath at 170°C while stirring with a magnetic stirrer. The time was measured starting from the point where the thermocouple in the reaction raw materials indicated 140°C. After heating for 3 minutes, the stirrer was removed. Next, 0.74 g of Ketjenblack (porous hollow carbon black, Lion Specialty Chemicals, primary particle size 34 nm) was added and quickly mixed with a spatula. Next, the mixture was preheated at 170°C for 10 to 15 minutes while being kneaded by hand with the flat part of the spatula to mix evenly. The container was then removed from the oil bath and heated in a constant temperature oven at 140°C for 6 hours under a nitrogen stream. After heating, the container was allowed to cool naturally to room temperature under a nitrogen atmosphere to obtain a carbon-composite sulfur polymer. The obtained carbon-composite sulfur polymer was placed in an agate mortar and pestle, and then pre-pulverized using a freeze-pulverizer (ASTONE Corporation, HTPT-01) under liquid nitrogen freezing conditions. The pulverized product was then sieved through a 100 μm sieve, and particles that did not pass through the sieve were removed to obtain a pulverized carbon-composite sulfur polymer. The particle size distribution of the pulverized carbon-composite sulfur polymer was measured by laser diffraction and scattering using a particle size distribution analyzer (SHIMADZU Corporation, SALD-7500), and the median diameter was found to be 17.3 μm. The resulting pulverized carbon-composite sulfur polymer was then subjected to the following charge-discharge test and nanoindentation test, the results of which are shown in Table 1 and FIG.

[0091] <Fabrication of electrodes using carbon-composite sulfur polymers, fabrication of coin cells, and charge / discharge tests> The pulverized carbon composite sulfur polymer obtained above, acetylene black (Denka Black HS-100, manufactured by Denka Corporation), and binder (sodium carboxymethyl cellulose (CMC) (Daicel Corporation, product number 2200)) were weighed out so that the mass ratio of the sulfur polymer in the carbon composite sulfur polymer was 63%, the total of the carbon material and acetylene black in the carbon composite sulfur polymer was 32%, and the binder was 5%. Next, the carbon composite sulfur polymer pulverized product and acetylene black were placed in an agate mortar and mixed, and then a binder was added and further mixed. Next, pure water was added in several batches and mixed in the mortar. The prepared sample was mixed in a planetary centrifugal mixer (2000 rpm, 3 min) to obtain a slurry. An electrode was applied to aluminum foil with a film thickness of 200 μm and dried at 40°C for 12 hours. The obtained electrode was punched out with a φ16 hole. The punched electrode was pressed in a uniaxial press to achieve a porosity of approximately 30-40%. The prepared electrode was placed in a glass tube oven and vacuum dried at 50°C for 14 hours. Coin cells (CR2032) were fabricated by assembling electrodes made of lithium foil, a separator, and sulfur polymer in a glove box filled with high-purity argon. The electrolyte was 1M LiTFSI (Sigma-Aldrich) / 0.2M LiNO3 (Ström Chemicals) dissolved in 1,3-dioxolane (Sigma-Aldrich) / 1,2-dimethoxyethane (Kishida Chemical). Electrochemical measurements were performed using a Meiden Hokuto HJ1001SD8. Constant-current discharge / charge voltages were measured at 0.05 C (1 C - 1675 mAh / g) between 1.0 and 3.0 V at 25 °C. All discharge / charge capacities were calculated based on the weight of sulfur.

[0092] (Measurement of composite elastic modulus) <Nanoindentation test procedure and conditions> The carbon composite sulfur polymer pulverized material obtained above was embedded in epoxy resin and cross-sectioned using an ultramicrotome. Measurements were performed using a HYSITRON TI Premier Multi Scale with a Berkovich indenter (diamond), a maximum load of 250 μN, a loading / unloading time of 5 seconds, and a maximum load holding time of 2 seconds.

[0093] <Powder compression test procedures and conditions> The carbon composite sulfur polymer pulverized material obtained above was packed into a cylindrical jig with an inner diameter of 6 mm, and a stress-strain curve was obtained during compression using an Instron Universal Testing Machine 5969 at a test speed of 10 mm / min and a pressure of 250 MPa. Pre-compression was performed 10 times under the same conditions, and the elastic modulus was obtained from the slope of the stress-strain curve in the strain range of 0.15 to 0.4% after the 11th compression.

[0094] (Comparative Example 1) 14.0 g of sulfur (manufactured by Kanto Chemical Co., Ltd.) was weighed and added to a polyfluoroalkoxy resin (PFA) container. Next, a stirrer was placed in the container, and the mixture was heated in an oil bath at 170°C while stirring with a magnetic stirrer. The time was measured starting from the point where the thermocouple in the reaction raw material indicated 140°C. After heating for 3 minutes, the stirrer was removed. Next, 0.74 g of Ketjenblack (porous hollow carbon black, Lion Specialty Chemicals, primary particle size 34 nm) was added and quickly mixed with a spatula. Next, the mixture was preheated at 170°C for 10 to 15 minutes while being kneaded by hand with the flat part of the spatula to mix evenly. The container was then removed from the oil bath and heated in a constant temperature oven under a nitrogen stream for 6 hours. After heating, the container was allowed to cool naturally to room temperature under a nitrogen atmosphere to obtain a carbon-carbon composite sulfur. The obtained carbon composite sulfur was pulverized and classified in the same manner as in Example 1, and the particle size distribution was measured. As a result, a pulverized carbon composite sulfur product with a median particle size of 12.6 μm was obtained. The resulting carbon composite sulfur pulverized product was then subjected to the above-mentioned charge / discharge test, nanoindentation test, and powder compression test. The results are shown in Table 1.

[0095] [Table 1]

Claims

1. A carbon-composite sulfur polymer including at least a sulfur polymer matrix composed of sulfur chains and crosslinking reaction residues that crosslink the sulfur chains, and a carbon material dispersed in the sulfur polymer matrix, The crosslinking reaction residue is represented by the following general formula (1): 【Chemical 1】 (In the formula, R １ , R ２ , R ３ and R ４ one, two, three or all of the groups are substituents capable of reacting with sulfur, and the substituents capable of reacting with sulfur are selected from the group consisting of linear or branched alkenyl groups having 2 to 15 carbon atoms (which may contain a halogen element), linear or branched alkynyl groups having 2 to 15 carbon atoms (which may contain a halogen element), sulfide groups, mercapto groups, glycidyl groups, cyano groups, carbonyl groups, and linear or branched hydrocarbon groups having 1 to 15 carbon atoms and containing a halogen, and R １ , R ２ , R ３ and R ４ When one, two or three of the above are substituents capable of reacting with sulfur, the remaining are groups selected from the group consisting of a linear or branched alkyl group having 1 to 15 carbon atoms (which may contain a halogen element), a linear or branched alkoxy group having 2 to 15 carbon atoms (which may contain a halogen element), an aryl group having 6 to 20 carbon atoms, an amino group, an amido group, an imino group, a carboxyl group, a hydroxyl group, an ester group, a nitro group, a nitrile group, a sulfonyl group, a silyl group and a hydrogen atom. １ , R ２ , R ３ and R ４ may be the same or different.) a crosslinking reaction residue of a glycoluril derivative represented by the formula: A carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery, characterized by:

2. A carbon-composite sulfur polymer including at least a sulfur polymer matrix which is a crosslinked reaction product of sulfur and a crosslinking agent, and a carbon material dispersed in the sulfur polymer matrix, The crosslinking agent is represented by the following general formula (1): 【Chemical 1】 (In the formula, R １ , R ２ , R ３ and R ４ one, two, three or all of the groups are substituents capable of reacting with sulfur, and the substituents capable of reacting with sulfur are selected from the group consisting of linear or branched alkenyl groups having 2 to 15 carbon atoms (which may contain a halogen element), linear or branched alkynyl groups having 2 to 15 carbon atoms (which may contain a halogen element), sulfide groups, mercapto groups, glycidyl groups, cyano groups, carbonyl groups, and linear or branched hydrocarbon groups having 1 to 15 carbon atoms and containing a halogen, and R １ , R ２ , R ３ and R ４ When one, two or three of the above are substituents capable of reacting with sulfur, the remaining are groups selected from the group consisting of a linear or branched alkyl group having 1 to 15 carbon atoms (which may contain a halogen element), a linear or branched alkoxy group having 2 to 15 carbon atoms (which may contain a halogen element), an aryl group having 6 to 20 carbon atoms, an amino group, an amido group, an imino group, a carboxyl group, a hydroxyl group, an ester group, a nitro group, a nitrile group, a sulfonyl group, a silyl group and a hydrogen atom. １ , R ２ , R ３ and R ４ may be the same or different.) The glycoluril derivative is represented by the formula: A carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery, characterized by:

3. The carbon-composite sulfur polymer for a positive electrode of a lithium-sulfur secondary battery according to claim 2, characterized in that the sulfur polymer is a crosslinked reaction product of the sulfur and 5.0 to 100.0 parts by mass of the crosslinking agent per 100.0 parts by mass of the sulfur.

4. The carbon-sulfur polymer composite for a positive electrode of a lithium-sulfur secondary battery according to claim 1 or 2, characterized in that the content of the carbon material is 1.0 to 30.0 mass %.

5. 3. The carbon-sulfur polymer composite for a positive electrode of a lithium-sulfur secondary battery according to claim 1, wherein the carbon material is a conductive carbon powder.

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