Positive electrode material for lithium sulfur battery and method for manufacturing same

Abstract

The present invention provides a positive electrode material for a lithium sulfur battery, which achieves both good cycle characteristics and good rate characteristics. The present invention relates to a positive electrode material for a lithium sulfur battery, the positive electrode material containing a porous carbon material that has a pore diameter of 1.0 nm to 5.0 nm inclusive at the cumulative volume of 70% and a sulfur compound that is supported by the porous carbon material, wherein the ratio of the mass loss amount in the temperature range of 500°C to 1000°C to the mass loss amount in the temperature range of 30°C to 1000°C is 3% or more at a heating rate of 10°C / minute in a nitrogen atmosphere.

Description

Cathode material for lithium-sulfur batteries and method for manufacturing the same

[0001] This disclosure relates to a cathode material for lithium-sulfur batteries and a method for manufacturing the same.

[0002] Lithium-sulfur batteries are secondary batteries with a high energy density per unit mass, and for example, mesoporous sulfur-carbon composites in which sulfur is arranged in mesopores are used. As lighter batteries than conventional lithium-ion batteries, lithium-sulfur batteries are expected to be used in applications such as large power equipment like electric vehicles and aerospace applications like drones. However, lithium-sulfur batteries have a problem in that the LiS intermediate dissolves into the organic electrolyte, reducing the cycle capacity retention rate.

[0003] Patent Document 1 discloses a sulfur-carbon composite cathode comprising a positive electrode current collector and a positive electrode composite material layer formed on one or both surfaces of the positive electrode current collector, wherein the average pore size of the carbon particles is 0.1 nm to 20 nm. However, the improvement in cycle characteristics is not sufficient, and improvement in rate characteristics is also desired.

[0004] Japanese Patent Publication No. 2023-49469

[0005] This disclosure aims to provide a cathode material for lithium-sulfur batteries that achieves both cycle characteristics and rate characteristics.

[0006] A positive electrode material for a lithium-sulfur battery according to one embodiment of the present disclosure comprises a porous carbon material having a pore diameter of 1 nm or more and 5 nm or less at a volume cumulative rate of 70%, and a sulfur compound supported on the porous carbon material, wherein, under conditions of a nitrogen atmosphere and a heating rate of 10°C / min, the ratio of the mass loss in the temperature range of 500°C to 1000°C to the mass loss in the temperature range of 30°C to 1000°C is 3% or more.

[0007] A positive electrode material for a lithium-sulfur battery according to one embodiment of the present disclosure comprises a porous carbon material having a pore diameter of 1 nm or more and 5 nm or less at a volume cumulative rate of 70%, and a sulfur compound supported on the porous carbon material, wherein the sulfur compound is a compound containing sulfur and carbon.

[0008] A method for producing a positive electrode material for a lithium-sulfur battery according to one embodiment of the present disclosure includes the steps of mixing a porous carbon material having a pore diameter of 1 nm or more and 5 nm or less at a volume cumulative rate of 70%, with a sulfur compound containing sulfur and carbon, and heating the resulting mixture.

[0009] A method for manufacturing a positive electrode material for a lithium-sulfur battery according to one embodiment of the present disclosure includes the steps of: preparing a support in which a sulfur source is supported on a porous carbon material having a pore diameter of 1 nm or more and 5 nm or less over a cumulative volume of 70%; contacting the support with an organic compound; and heat-treating the resulting contact.

[0010] According to the positive electrode material for lithium-sulfur batteries disclosed herein, a lithium-sulfur battery that achieves both excellent cycle characteristics and rate characteristics can be obtained.

[0011] The figure shows the amount of mass loss of the positive electrode materials for lithium-sulfur batteries prepared in Examples 1 to 9 and Comparative Examples 1 to 2 measured within the temperature range from room temperature to 1000 °C, and the amount of mass loss plotted against temperature. The figure shows the amount of mass loss of the positive electrode materials for lithium-sulfur batteries prepared in Example 1 and Example 7, the sulfur compound prepared in Production Example 4, and elemental sulfur measured within the temperature range from room temperature to 800 °C, and the amount of mass loss plotted against temperature. The figure shows the pore size distribution and cumulative distribution of the porous carbon material used in the examples. The figure shows the pore size distribution and cumulative distribution of the surface-modified porous carbon material manufactured in Production Example 3. The figure shows the pore size distribution and cumulative distribution of the porous carbon material (ECP600JD) used in Comparative Example 2. The figure shows the discharge capacity of the lithium-sulfur secondary batteries prepared using the positive electrode materials for lithium-sulfur batteries prepared in Examples 1 to 9 and Comparative Example 1, and the discharge capacity plotted against the number of cycles. The figure shows the discharge capacity of the lithium-sulfur secondary batteries prepared using the positive electrode materials for lithium-sulfur batteries prepared in Examples 1 to 9 and Comparative Example 1, and the discharge capacity (near 200 to 1200 mAh / S-g) plotted against the number of cycles. The figure shows the amount of mass loss of the components extracted from the positive electrode materials for lithium-sulfur batteries prepared in Example 1, Example 7, and Example 8, the sulfur compound prepared in Production Example 4, and elemental sulfur measured within the temperature range from room temperature to 800 °C, and the amount of mass loss plotted against temperature. The figure shows the measurement results by 1H NMR of the components extracted from the positive electrode material for lithium-sulfur batteries prepared in Example 7.

[0012] Hereinafter, embodiments of the present disclosure will be described in detail. However, the embodiments shown below are merely examples for embodying the technical idea of the present disclosure, and the present disclosure is not limited to the following. In this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.

[0013] <<Positive electrode material for lithium-sulfur batteries (1)>> The positive electrode material for lithium-sulfur batteries of the present disclosure comprises a porous carbon material having a pore diameter of 1 nm or more and 5 nm or less at a volume cumulative of 70%, and a sulfur compound supported on the porous carbon material, and is characterized in that, under conditions of a nitrogen atmosphere and a heating rate of 10°C / min, the ratio of the mass loss in the temperature range of 500°C to 1000°C to the mass loss in the temperature range of 30°C to 1000°C is 3% or more.

[0014] Since a sulfur compound containing sulfur and carbon is supported on a porous carbon material, when the sulfur compound becomes a Li intermediate during charging and discharging, its reactivity with the electrolyte decreases, improving cycle characteristics. At the same time, the wettability of the porous carbon material increases, increasing the proportion of sulfur compounds adhering to the carbon particle surface, which changes the reactivity with Li ions and improves rate characteristics. Furthermore, if the pore size of the porous carbon material is large, the proportion of sulfur compounds present on the surface is small, and the impact on rate characteristics is small. However, in porous carbon materials where the pore size at 70% volume cumulative is between 1 nm and 5 nm, the pore size is small, so compared to carbon materials with larger pore sizes, a larger proportion of sulfur compounds are present on the carbon surface, which is thought to improve rate characteristics. In the lithium-sulfur battery cathode material of this disclosure, since the sulfur compound is supported on a porous carbon material, it is thought that the sulfur source penetrates sufficiently into the pores, and a sufficient amount of sulfur compounds are also present on the surface of the porous carbon material, thus improving rate characteristics.

[0015] In the lithium-sulfur battery cathode material of this disclosure, under conditions of a nitrogen atmosphere and a heating rate of 10°C / min, the ratio of the mass loss in the temperature range of 500°C to 1000°C to the mass loss in the temperature range of 30°C to 1000°C is 3% or more, preferably 5% or more, more preferably 7% or more, and even more preferably 8% or more. Within this range, the proportion of sulfur compounds containing sulfur and carbon is high, which is desirable. Below 3%, the proportion of sulfur compounds that dissipate below 500°C is high, resulting in a large amount of sulfur compounds consisting solely of sulfur, and thus the effects of this disclosure cannot be obtained. The upper limit is not particularly limited, but for example, it may be 20% or less, or even 10% or less.

[0016] <Porous Carbon Material> The porous carbon material used in the positive electrode material for the lithium-sulfur battery of the present disclosure is not particularly limited, and examples thereof include mesoporous carbon, Ketjen black, acetylene black, activated carbon, carbon nanotubes, multi-layer graphene, graphite, and the like. Among these carbon materials, a carbon material having voids inside secondary particles is preferable, and examples thereof include mesoporous carbon, Ketjen black, acetylene black, etc., and it may contain at least one selected from the group consisting of these. The carbon material may be used alone or in combination of two or more.

[0017] The pore diameter at a volume accumulation of 70% obtained by the QSDFT method of the porous carbon material is 1 nm or more and 5 nm or less, preferably 2 nm or more and 4 nm or less. Also, the pore diameter at a volume accumulation of 80% may be 1 nm or more and 5 nm or less, preferably 2 nm or more and 4 nm or less. Further, it is preferable that the volume ratio of pores having a pore diameter of 1.5 nm or more and 4 nm or less is 50% or more, more preferably 60% or more, and still more preferably 70% or more. Also, it is preferable that the ratio of pores having a pore diameter of 1.5 nm or more and 5 nm or less is 70% or more on a volume basis, and it is also preferable that the ratio of pores having a pore diameter of 2 nm or more and 4 nm or less is 60% or more on a volume basis. When it is within the above-described range, elution of the intermediate from the pores is reduced and the cycle characteristics tend to improve, and in addition, the effects of the present disclosure can be easily obtained. Here, the QSDFT method is the quenched solid density functional method, and the pore distribution is calculated by applying the QSDFT method to the measured adsorption isotherm, and the pore diameter at a predetermined volume accumulation is calculated.

[0018] The specific surface area of the porous carbon material is preferably 500 m ２ / g or more, more preferably 1000 m ２ / g or more, and still more preferably 1500 m ２ / g or more. The upper limit is not particularly limited, but 3000 m ２It may be less than or equal to / g. The specific surface area may be calculated, for example, from the gas adsorption method. Based on the BET (Brunauer, Emmett, Teller) theory, the value measured by the single-point or multi-point method using nitrogen gas from the nitrogen adsorption / desorption curve obtained by the nitrogen adsorption / desorption measurement method may be used. In general, porous carbon materials with a large specific surface area tend to have a high charge / discharge capacity of sulfur-carbon composites.

[0019] The porous carbon material may consist of secondary particles formed by the aggregation of primary particles, and may also consist of secondary particles having interconnected pores where voids are linked internally. The 50% particle size D50 in the volume-based cumulative particle size distribution of the secondary particles of the porous carbon material may be between 0.1 μm and 30 μm, and preferably 1 μm or larger. The upper limit of the 50% particle size D50 is preferably 10 μm or less. D50 is measured, for example, using a laser diffraction particle size distribution analyzer. When D50 is within the above range, the reaction between lithium and sulfur compounds proceeds easily because the pore depth does not become too deep, and the charge-discharge capacity of the sulfur-carbon composite tends to be high.

[0020] The particle size of the primary particles constituting the secondary particles of the porous carbon material may be, for example, 1 nm to 20 μm. The lower limit of the primary particle particle size is preferably 2 nm, more preferably 5 nm, even more preferably 100 nm, and particularly preferably 1 μm. The upper limit of the primary particle particle size is preferably 10 μm. The particle size of the primary particles is calculated, for example, by calculating the equivalent spherical diameter from the contour lengths of 20 primary particles for each of the 10 selected secondary particles in an image observed using a scanning electron microscope (SEM), transmission electron microscope (TEM), or scanning transmission electron microscope (STEM), and taking the arithmetic mean of these values. The aforementioned numbers are examples and not limited thereto, but in order to reduce measurement errors between samples, it is preferable to measure at least the aforementioned number of particles as the lower limit of the number of particles to be selected.

[0021] The aspect ratio of the porous carbon material is preferably 1 or more and 5 or less, more preferably 1 or more and 3 or less. The closer the aspect ratio is to 1, the higher the sphericity and the more uniform the reaction between lithium and sulfur in the particles, making it suitable for the porous carbon material for lithium-sulfur batteries.

[0022] By subjecting the porous carbon material to surface treatment, functional groups are formed on the surface of the carbon material. When the carbon material with functional groups formed is heated in an inert gas atmosphere, the functional groups present on the surface decompose according to the heating temperature, generating decomposition gases such as CO, CO ２ and the like. Examples of such functional groups that generate decomposition gases include carboxyl groups, functional groups having a lactone ring, acid anhydride groups, phenolic hydroxyl groups, carbonyl groups, ether groups, and groups having a quinone structure. In the case of carboxyl groups, CO is generated at 100°C to 400°C, and in the case of functional groups having a lactone ring, CO is generated at 190°C to 650°C. ２ The acid anhydride group decomposes at 350°C to 620°C, generating CO ２ and CO together. On the other hand, the phenolic hydroxyl group decomposes at 600°C to 700°C, generating CO and water. The carbonyl group decomposes at 700°C to 980°C, the ether group decomposes at 700°C, and the group having a quinone structure decomposes at 700°C to 980°C, generating CO. The desorption amount of CO ２ desorbed in the temperature range of 30°C to 1000°C is a physical property related to the abundance of carboxyl groups, functional groups having a lactone ring, and acid anhydride groups, and the desorption amount of CO ２ desorbed in the temperature range of 400°C to 1000°C is a physical property related to the abundance of functional groups having a lactone ring and acid anhydride groups. And the ratio of the desorption amount of CO ２ represents the abundance ratio of functional groups having a lactone ring and acid anhydride groups.

[0023] The desorption amount of CO ２ desorbed in the temperature range of 30°C to 1000°C with respect to the desorption amount of CO ２The ratio of the amount of CO to be eliminated is preferably 75% or more, more preferably 85% or more, even more preferably 90% or more, and particularly preferably 95% or more. Below 75%, the proportion of weakly acidic functional groups such as lactone rings in the functional groups present on the surface of the carbon material decreases, and there is a tendency for the reverse Coulomb efficiency to decrease. When this ratio is high, CO to be eliminated at low temperatures. ２ CO has a low concentration and desorbs at high temperatures. ２ This means that there is a high proportion of weakly acidic functional groups, with a low amount of strongly acidic carboxyl groups and a high amount of weakly acidic groups such as lactone rings. Acidic functional groups are thought to capture Li ions in the electrolyte, and then conduct Li ions into the sulfur. When the functional group is weakly acidic, the conduction of Li ions from the functional group to the sulfur proceeds smoothly, whereas when the functional group is strongly acidic, the adsorption of Li ions by the functional group is strong, and the conduction of Li ions is weak. Therefore, a higher proportion of weakly acidic functional groups is preferable because it increases the reverse Coulomb efficiency and the discharge capacity.

[0024] The total amount of acidic functional groups can be measured by the Boehm method. The Boehm method is a method for quantifying the amount of acidic functional groups present on the surface of a sample by adding an alkali to the sample, reacting it, and then back-titrating the alkali concentration with an acid. The total amount of acidic functional groups is determined by the aforementioned CO, CO ２ These are physical properties related to the abundance of carboxyl groups, phenolic hydroxyl groups, lactone groups, and acid anhydride groups, which are among the functional groups that generate decomposition gases.

[0025] The total amount of acidic functional groups is 0.3 mmol / g or more, preferably 0.5 mmol / g or more, and more preferably 1.0 mmol / g or more. There is no particular upper limit, but 4 mmol / g or less is preferred. Below 0.3 mmol / g, the initial discharge capacity tends to be lower. This is thought to be because a larger total amount of acidic functional groups results in a smaller amount of Li irreversibly adsorbed.

[0026] Porous carbon materials can be produced by oxidation treatment as needed. Examples of oxidation treatment methods include heating in air and treatment with nitric acid. In the heating method in air, the heating temperature is not particularly limited, but is preferably between 100°C and 400°C, and more preferably between 200°C and 400°C. Below 100°C, the amount of target acidic functional groups does not increase, and above 400°C, carbon is burned by oxygen, and the mass tends to decrease significantly. The heating time is also not particularly limited, but is preferably between 1 hour and 24 hours, and more preferably between 3 hours and 12 hours. Below 1 hour, the amount of modified acidic functional groups is small, so the effect on battery characteristics is small. On the other hand, even if heat treatment is performed in air for a long period of time exceeding 24 hours, the increase in the amount of acidic functional groups is small, which is undesirable from the viewpoint of low yield.

[0027] <Sulfur compounds supported on porous carbon materials> Sulfur compounds are supported (immobilized) on porous carbon materials, and examples of such sulfur compounds include not only elemental sulfur, but also sulfur polymers S8, chain-like sulfur polymers, polysulfides produced during the charging and discharging process of lithium-sulfur batteries, and reaction products of these with hydrocarbons, etc. Examples of polysulfides include Li ２ S ８ Li ２ S ６ Li ２ S ４ Li ２ S ２ These include, and it is thought that reaction products of chain-like sulfur polymers, hydrocarbon crosslinks, and Li also exist. Among these, compounds containing sulfur and carbon are preferred, and crosslinks of sulfur polymers and hydrocarbons are more preferred.

[0028] In crosslinked products of sulfur polymers and hydrocarbons, the hydrocarbon may contain heteroatoms such as oxygen and nitrogen atoms in addition to carbon and hydrogen atoms, but it is preferable that it consists only of carbon and hydrogen atoms in order to have high reactivity with sulfur. Preferred hydrocarbons are compounds having an aromatic ring or alicyclic structure, and it is also preferable that they have two or more unsaturated bonds. Specific hydrocarbons include, for example, 1,3-diisopropenylbenzene, norbornadiene, limonene, ethylene glycol dimethacrylate, and dicyclopentadiene.

[0029] The aforementioned crosslinked material can be produced by heating sulfur, such as a sulfur polymer, and hydrocarbons at 150°C or higher, preferably 180°C or higher.

[0030] The reactant is preferably amorphous with low crystallinity, as it offers less resistance to the insertion and removal of Li ions.

[0031] The content of porous carbon material in the positive electrode material for lithium-sulfur batteries may be, for example, 25% by mass or more and 95% by mass or less, preferably 50% by mass or more and 90% by mass or less, and more preferably 67% by mass or more and 80% by mass or less. "67% by mass" refers to the content when the mixing ratio of the sulfur-containing material to the carbon material is 2:1. When the content of the sulfur-containing material is within these ranges, the capacity reduction of the sulfur-carbon composite is reduced.

[0032] <<Positive electrode material for lithium-sulfur batteries (2)>> Another embodiment of the positive electrode material for lithium-sulfur batteries of the present disclosure comprises a porous carbon material having a pore diameter of 1 nm or more and 5 nm or less at a volume cumulative of 70%, and a sulfur compound supported on the porous carbon material, wherein the sulfur compound is a compound containing sulfur and carbon.

[0033] In the positive electrode material for lithium-sulfur batteries according to this embodiment, the porous carbon material having a pore diameter of 1 nm or more and 5 nm or less at a volume cumulative of 70% is as described above.

[0034] As described above, the sulfur compound supported on the porous carbon material is as described above. Furthermore, in the positive electrode material for lithium sulfur batteries according to this embodiment, the sulfur compound supported on the porous carbon material is a compound containing sulfur and carbon.

[0035] Since a sulfur compound containing sulfur and carbon is supported on a porous carbon material, when the sulfur compound becomes a Li intermediate during charging and discharging, its reactivity with the electrolyte decreases, improving the cycle characteristics. At the same time, the wettability of the porous carbon material increases, increasing the proportion of sulfur compounds adhering to the carbon particle surface, which changes the reactivity with Li ions and improves the rate characteristics. Furthermore, if the pore size of the porous carbon material is large, the proportion of sulfur compounds present on the surface is small, and the impact on the rate characteristics is small. However, in porous carbon materials where the pore size at 70% volume cumulative is between 1 nm and 5 nm, the pore size is small, so compared to carbon materials with larger pore sizes, the proportion of sulfur compounds present on the carbon surface is larger, which is thought to improve the rate characteristics. In the positive electrode material for lithium sulfur batteries according to this embodiment, since the sulfur compound is supported on a porous carbon material, it is thought that the sulfur source penetrates sufficiently into the pores, and a sufficient amount of sulfur compounds are also present on the surface of the porous carbon material, thus improving the rate characteristics.

[0036] The sulfur compounds supported (immobilized) on porous carbon materials are compounds containing sulfur and carbon, and specifically include reaction products of hydrocarbons with elemental sulfur, sulfur polymer S8, chain-like sulfur polymers, and polysulfides produced during the charging and discharging process of lithium-sulfur batteries. Examples of polysulfides include Li ２ S ８ Li ２ S ６ Li ２ S ４ Li ２ S ２ Examples include the reaction products of a chain-like sulfur polymer, a crosslinked hydrocarbon, and Li, with the crosslinked sulfur polymer and hydrocarbon being preferred.

[0037] In crosslinked products of sulfur polymers and hydrocarbons, the hydrocarbon may contain heteroatoms such as oxygen and nitrogen atoms in addition to carbon and hydrogen atoms, but it is preferable that it consists only of carbon and hydrogen atoms in order to have high reactivity with sulfur. Preferred hydrocarbons are compounds having an aromatic ring or alicyclic structure, and it is also preferable that they have two or more unsaturated bonds. Specific hydrocarbons include, for example, 1,3-diisopropenylbenzene, norbornadiene, limonene, ethylene glycol dimethacrylate, and dicyclopentadiene.

[0038] The aforementioned crosslinked material can be produced by heating sulfur, such as a sulfur polymer, and hydrocarbons at 150°C or higher, preferably 180°C or higher.

[0039] The reactant is preferably amorphous with low crystallinity, as it offers less resistance to the insertion and removal of Li ions.

[0040] The fact that a sulfur compound supported on a porous carbon material is a compound containing sulfur and carbon can be confirmed, for example, by extracting the sulfur compound from the porous carbon material supported with a solvent and analyzing the extracted sulfur compound. Solvents used for extracting sulfur compounds include polar solvents such as chloroform, dichloromethane, tetrahydrofuran (THF), dioxane, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), and acetonitrile; non-polar organic solvents such as toluene, xylene, hexane, cyclohexane, and benzene; and mixtures of the aforementioned polar and non-polar solvents.

[0041] Sulfur compounds can be analyzed by differential thermal-thermal-mass analysis (TG-DTA) and nuclear magnetic resonance spectroscopy (NMR). When using differential thermal-thermal-mass analysis, under conditions of a nitrogen atmosphere and a heating rate of 10°C / min, if the ratio of the mass loss in the temperature range of 500°C to 1000°C to the mass loss in the temperature range of 30°C to 1000°C is 3% or more, then it can be determined that the sulfur compound is a compound containing sulfur and carbon. The ratio of the mass loss is preferably 5% or more, more preferably 7% or more, and even more preferably 8% or more. Within this range, the proportion of sulfur compounds containing sulfur and carbon is high, which is desirable. If it is less than 3%, the proportion of sulfur compounds that scatter below 500°C is high, and the amount of sulfur compounds consisting only of sulfur is high, so the effects of this disclosure cannot be obtained. The upper limit is not particularly limited, but for example it may be 20% or less, or 10% or less.

[0042] <Positive Electrode of Lithium-Sulfur Battery> The positive electrode material for lithium-sulfur batteries of this disclosure is placed on a current collector and serves as the positive electrode of a lithium-sulfur battery. The positive electrode can be manufactured by compounding the positive electrode material for lithium-sulfur batteries of this disclosure with a liquid medium, binder, conductive additive, etc., as needed, coating it onto a current collector, and then drying and pressure molding to form a positive electrode active material layer on the current collector.

[0043] The liquid medium may be an organic solvent, water, or the like, depending on the application. Examples of organic solvents include amide solvents such as N-methyl-2-pyrrolidone (NMP), ketone solvents such as diisopropyl ketone, diisobutyl ketone, and methyl ethyl ketone, hydrocarbon solvents such as heptane, ether solvents such as tetrahydrofuran, dimethoxyethane, and dioxolane, amine solvents such as diethylenetriamine, and ester solvents. The organic solvent may be used alone or in combination of two or more. The content of the liquid medium may be, for example, 10% to 90% by mass relative to the total mass of the electrode composition.

[0044] A binder is a material that helps, for example, the adhesion of the positive electrode active material to a conductive additive, and the adhesion of the electrode composition to the current collector. Examples of binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butylene rubber, fluororubber, and various copolymers. The binder content may be, for example, 0.05% to 50% by mass relative to the total mass of the electrode composition.

[0045] Conductive additives are, for example, materials that improve the electrical conductivity of the positive electrode composition layer. Examples of conductive additives include graphite such as modified graphene, natural graphite, and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; and carbon materials such as graphene and carbon nanotubes. The content of the conductive additive may be, for example, 0.5% by mass or more and 30% by mass or less based on the total mass of the electrode composition.

[0046] Examples of current collectors include metals such as copper, stainless steel, aluminum, nickel, and titanium; composite materials with surfaces treated with carbon, nickel, titanium, silver, etc., such as copper and stainless steel; and carbon foil. When manufacturing lightweight lithium-sulfur batteries, for example, aluminum and carbon foil are preferred as lightweight current collectors. The adhesion strength of the positive electrode composition layer and other components can also be enhanced by forming fine irregularities on the surface of the current collector. Furthermore, various forms are possible, such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics. The thickness of the current collector may be, for example, 3 μm to 500 μm.

[0047] <<Lithium-Sulfur Secondary Battery>> A lithium-sulfur battery is equipped with the above-mentioned positive electrode for lithium-sulfur batteries. A lithium-sulfur battery is composed of a positive electrode for lithium-sulfur batteries, a negative electrode, and an electrolyte, etc., placed between the positive and negative electrodes. A lithium-sulfur battery may also be equipped with a separator as needed. The electrolyte may be contained in the positive electrode, negative electrode, and separator for lithium-sulfur batteries.

[0048] <Negative Electrode> Any known negative electrode can be used as the negative electrode constituting the lithium-sulfur battery. Examples of negative electrode materials include Li metal, Li-Si alloy, Li-Al alloy, Li-In alloy, and lithium titanate (for example, Li ４ Ti ５ O １２ and Li ２ TiO ３ ), lithium titanium composite oxide (for example, Li ４ Ti ５ -xMn ｘ O １２ ;0<x≦0.3), LiC ｘ (x ≤ 6), etc. These negative electrode materials may have some lithium replaced by other alkali metals. Examples of negative electrode materials include Li metal, Li-Si alloy, Li-Al alloy, Li-In alloy, Li ｘ C (x ≤ 6) is preferred. With these materials, a high voltage can be extracted from the lithium-sulfur battery.

[0049] <Separator> The separator can be made of any known material, such as porous polyethylene or polypropylene. Alternatively, a known separator may be used after being coated.

[0050] <Electrolyte> The electrolyte only needs to contain a lithium salt, and can be appropriately selected from lithium salts used in conventional lithium-ion batteries. The lithium salt may contain, for example, an anion containing the element fluorine. Specifically, an example of a lithium salt containing an anion containing the element fluorine is LiPF ６ LiBF ４ LiSbF ６ LiAsF ６ LiSO ３ CF ３, LiN (SO ２ CF ３ ) ２ Examples include (LiTFSI). Also, electrolytes include lithium nitrate and LiClO2. ４ The electrolyte may also contain lithium salts that do not contain fluorine elements. One of these can be used alone, or two or more can be used in combination.

[0051] The electrolyte may contain an organic solvent. As the organic solvent, carbonate solvents, ether solvents, ester solvents, amide solvents, nitrile solvents, and sulfur-containing solvents may be used, or an organic solvent in which some elements of the above organic solvents are substituted with fluorine may be used. Examples of organic solvents include carbonate solvents such as propionate carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, and vinylene carbonate; ether solvents such as 1,3-dioxolane, 1,2-dimethoxyethane, 1,3-dimethoxypropane, 2,2,3,3-tetrafluoropropyldifluoromethyl ether, and tetrahydrofuran; ester solvents such as methyl formate, methyl acetate, and γ-butyllactone; amide solvents such as N,N-dimethylacetamide and N,N-dimethylformamide; and sulfur-containing solvents such as sulfolane, dimethyl sulfoxide, and 1,3-propanesalton.

[0052] <<Method for manufacturing a positive electrode material for lithium-sulfur batteries (1)>> The method for manufacturing a positive electrode material for lithium-sulfur batteries according to the present disclosure is characterized by comprising the steps of mixing a porous carbon material having a pore diameter of 1 nm or more and 5 nm or less at a volume cumulative of 70%, with a sulfur compound containing sulfur and carbon, and heating the obtained mixture.

[0053] As previously mentioned, porous carbon materials with a pore diameter of 1 nm to 5 nm at a cumulative volume of 70%, and sulfur compounds containing sulfur and carbon, are as described above. The method for mixing these materials is not particularly limited, and known methods can be used.

[0054] When mixing a porous carbon material with a sulfur compound containing sulfur and carbon, the amount of sulfur compound used relative to the porous carbon material is preferably 50:50 or more, more preferably 40:60 or more, in terms of mass ratio of porous carbon material to sulfur compound. Furthermore, it is preferable that the ratio be 20:80 or less, and more preferably 30:70 or less. To uniformly mix the porous carbon material and the sulfur compound, a ball mill, jet mill, high-speed shear mixer, etc., may be used.

[0055] The heating temperature of the resulting mixture is not particularly limited, but is preferably between 100°C and 350°C, and more preferably between 150°C and 300°C. Below 100°C, the temperature is below the melting point of the sulfur compound, so the sulfur compound may not be impregnated into the pores of the porous carbon material. Above 350°C, the temperature is above the decomposition temperature of the sulfur compound, so the sulfur compound becomes less likely to be impregnated into the pores of the porous carbon material. The heating time is also not particularly limited, but is preferably between 1 hour and 24 hours, and more preferably between 2 hours and 20 hours.

[0056] The heating of the mixture of porous carbon material and sulfur source is preferably carried out in a closed system using a pressure vessel or the like to prevent the sulfur source and its reactants from evaporating from the reaction system. The heating time is preferably 1 hour or more, more preferably 2 hours or more. The heating time is preferably 7 hours or less, more preferably 6 hours or less.

[0057] <<Method for manufacturing a positive electrode material for lithium sulfur batteries (2)>> Another embodiment of the present disclosure provides a method for manufacturing a positive electrode material for lithium sulfur batteries, comprising the steps of: preparing a support in which a sulfur source is supported on a porous carbon material having a pore diameter of 1 nm or more and 5 nm or less with a cumulative volume of 70%; contacting the support with an organic compound; and heat-treating the resulting contact.

[0058] In the process of preparing the support, there are no particular limitations on the method for obtaining a support in which a sulfur source is supported on a porous carbon material. For example, one method involves mixing a porous carbon material with a pore diameter of 1 nm to 5 nm at a volume cumulative rate of 70% with a sulfur source, and then heating the resulting mixture. The porous carbon material with a pore diameter of 1 nm to 5 nm at a volume cumulative rate of 70% is as described above.

[0059] The sulfur source used in the process of preparing the support material is a substance containing the element sulfur, for example, elemental sulfur (S ８ ), lithium sulfide (Li ２ S), polysulfide compounds (Li ２ S ｘ (x = 2 to 8), sodium sulfide (Na ２ Examples include metal sulfides such as S), thiols, thioethers, disulfides, and polysulfides. These sulfur sources may be used individually or in combination of two or more.

[0060] When mixing porous carbon material with a sulfur source, the amount of sulfur source used relative to the porous carbon material is preferably 50:50 or more, more preferably 40:60 or more, in terms of mass ratio of porous carbon material to sulfur source. Furthermore, a ratio of 20:80 or less, and more preferably 30:70 or less, is preferred. To uniformly mix the porous carbon material and sulfur source, a ball mill, jet mill, high-speed shear mixer, etc., may be used.

[0061] The heating temperature of the mixture of porous carbon material and sulfur source is not particularly limited, but is preferably 100°C to 350°C, more preferably 130°C to 320°C, and even more preferably 150°C to 300°C. Below 100°C, the temperature will be below the melting point of the sulfur source, and the sulfur source may not be impregnated into the pores of the porous carbon material. Above 350°C, the temperature will be above the decomposition temperature of the sulfur source, and the sulfur source may not be impregnated into the pores of the porous carbon material. The heating time is also not particularly limited, but is preferably 1 hour to 24 hours, and more preferably 2 hours to 20 hours.

[0062] The heating of the mixture of porous carbon material and sulfur source may be carried out in a closed system using a pressure vessel or the like to prevent the sulfur source and its reactants from evaporating from the reaction system. The product obtained by heating the mixture of porous carbon material and sulfur source can be a supported material in which the sulfur source is supported on the porous carbon material.

[0063] Hydrocarbons are preferred as the organic compounds used in the process of contacting the support material with the organic compound. Hydrocarbons may contain heteroatoms such as oxygen atoms and nitrogen atoms in addition to carbon atoms and hydrogen atoms. Hydrocarbons are preferably compounds having an aromatic ring or alicyclic structure, or compounds that form a cyclic structure upon heating, and may also have two or more unsaturated bonds. Specific examples of hydrocarbons include polyacrylonitrile, polyethylene oxide, polyvinyl alcohol, 1,3-diisopropenylbenzene, norbornadiene, limonene, ethylene glycol dimethacrylate, and dicyclopentadiene. The organic compounds may be dissolved in solvents such as dimethylformamide, chloroform, and water.

[0064] When bringing a support material into contact with an organic compound, the amount of organic compound used relative to the support material is preferably 97:3 or higher in mass ratio of support material to organic compound, and more preferably 95:5 or higher. Furthermore, it is preferable that the ratio be 80:20 or lower, and more preferably 90:10 or lower.

[0065] The organic compound may be dissolved in a solvent such as dimethylformamide, chloroform, or water. If the organic compound is dissolved in a solvent, the solvent containing the organic compound should be brought into contact with the support. After contact, it is preferable to remove the solvent by heating at a temperature of 50°C to 100°C, for example.

[0066] The heating temperature in the heat treatment step of the obtained contact is not particularly limited, but is preferably 100°C to 350°C, and more preferably 150°C to 300°C. Within this range, the reaction between the organic compound and the organic compound contained in the support material easily forms compounds containing sulfur and carbon, particularly crosslinked products of sulfur polymers and hydrocarbons. The crosslinked products of sulfur polymers and hydrocarbons are as described above. The heating time is not particularly limited, but is preferably 1 hour to 24 hours, and more preferably 2 hours to 20 hours.

[0067] Examples are described below. Unless otherwise specified, "%" refers to mass.

[0068] Manufacturing Example 1: 100 g of nitric acid adjusted to 6 N and 10 g of porous carbon material (AT Electrode Co., Ltd., AP20-0001HC) were transferred to a glass beaker and stirred at room temperature for 2 hours. After stirring, the mixture was filtered, washed with pure water, dried at 150°C for 15 hours, and then heat-treated at 350°C for 5 hours in an air atmosphere to produce a surface-modified porous carbon material.

[0069] Manufacturing Example 2: A surface-modified porous carbon material was prepared in the same manner as in Manufacturing Example 1, except that the heat treatment time in an atmospheric environment was changed to 10 hours.

[0070] Manufacturing Example 3: A surface-modified porous carbon material was prepared by heat-treating 10 g of porous carbon material (AP20-0001HC, manufactured by AT Electrode Co., Ltd.) at 350°C for 10 hours in an air atmosphere.

[0071] Preparation Example 4: 2.7 g of sulfur was dissolved in a glass vial at 185°C, and 0.3 g of 1,3-diisopropenylbenzene (DIB) was added and the mixture was stirred at 185°C for 30 minutes. After cooling to room temperature, a solid sulfur compound (prepolymer) containing sulfur and carbon, which is presumed to have the structure shown below, was prepared.

[0072] In the same manner as in the previous example, except that 1,3-diisopropenylbenzene was replaced with 5-ethylidene-2-norbornene (ENB), a solid sulfur compound (prepolymer) containing sulfur and carbon, which is presumed to have the structure shown below, was prepared.

[0073] In the same manner as in the previous example, except that 1,3-diisopropenylbenzene was replaced with limonene (d-Limonene), a solid sulfur compound (prepolymer) containing sulfur and carbon, which is presumed to have the structure shown below, was prepared.

[0074] In the same manner as in the previous example, except that 1,3-diisopropenylbenzene was replaced with ethylene glycol dimethacrylate (EDGMA), a solid sulfur compound (prepolymer) containing sulfur and carbon, which is presumed to have the structure shown below, was prepared.

[0075] The following evaluations were performed using untreated porous carbon material (AP20-0001HC, manufactured by AT Electrode Co., Ltd.), untreated porous carbon material (ECP600JD, manufactured by Lion Specialty Chemicals Co., Ltd., used in Comparative Example 2), and porous carbon materials prepared in Manufacturing Examples 1, 2, and 3. The evaluation results are shown in Table 1.

[0076] <Total Acidic Functional Groups> The total amount of acidic functional groups was measured using the Boehm method (H.P. Boehm, Adzan. Catal, 16, 179 (1966)) as a reference. Specifically, 50 mL of sodium hydroxide aqueous solution (0.05 mol / L) was added to 1 g of porous carbon material and stirred with rollers for 4 hours. After stirring, 10 mL of the filtrate obtained by filtration separation was taken, and sulfuric acid aqueous solution (0.025 mol / L) was added dropwise, and the titration volume when the pH reached approximately 8.4 was measured. As a blank test, 10 mL of sodium hydroxide aqueous solution (0.05 mol / L) was taken, and sulfuric acid aqueous solution (0.025 mol / L) was added dropwise, and the titration volume when the pH reached approximately 8.4 was measured. The total amount of acidic functional groups was calculated using the following formula. Total acidic functional group amount (mol / g) = {(a - b) × 0.025 × 2 × 50 / 10} / S a: Sulfuric acid titration volume in the blank test (mL) b: Sulfuric acid titration volume when the sample is reacted (mL) S: Sample mass (g)

[0077] <CO ２ Desorption Ratio > The amount of carbon dioxide gas generated from a porous carbon material was measured in a temperature range from room temperature to 1000°C using a temperature-controlled desorption gas photoionization mass spectrometer (TPD type R, manufactured by Rigaku Corporation). Specifically, 4 mg to 15 mg of the sample was taken and introduced into the glass tube of the temperature-controlled desorption gas photoionization mass spectrometer. He gas was flowed through at a rate of 300 mL / min, and the temperature was raised to 1000°C at a rate of 10°C / min. The generated gas profile corresponding to m / z = 44 obtained by a quadrupole mass spectrometer was used as the generated carbon dioxide gas profile. From the obtained profile, the ratio of the total amount of carbon dioxide gas generated to the amount of carbon dioxide gas generated from 400°C to 1000°C was calculated.

[0078] <Peak pore diameter of carbon, pore diameter at 70% volume accumulation, and specific surface area> For the obtained carbon material, the volume of open pores (pore diameter 0.4 nm to 100 nm) into which gas can enter was measured using a surface area / pore analyzer (product name: Nova Touch, manufactured by Anton Paar). Specifically, after dehydration treatment at 150°C for 1 hour while evacuating, the amount of nitrogen adsorbed was measured at 77 K and a pressure range of 0.0001 Torr to 760 Torr using nitrogen as the adsorbent, and the amount of nitrogen adsorbed was taken as the volume of the open pores. Furthermore, the pore distribution was calculated by applying the rapid solid density functional theory (QSDFT method) to the obtained adsorption isotherms. In the QSDFT method, a cylindrical pore model was used for fitting, and the pore diameter at 70% volume accumulation, the peak pore diameter, and the specific surface area were calculated. Figure 3 shows the pore distribution of the surface-modified porous carbon material produced in Production Example 2. Figure 4 shows the pore distribution of the surface-modified porous carbon material produced in Manufacturing Example 3. Figure 5 shows the pore distribution of the porous carbon material (ECP600JD) used in Comparative Example 2.

[0079] <D50> The volume-based particle size distribution was measured using a laser diffraction particle size distribution analyzer (MASTERSIZER 3000, Malvern). The measurement samples were prepared as follows: A diluted dispersant was obtained by diluting 2 mL of dispersant (ADEKA® L-44) with 170 mL of aqueous solvent and dispersing it with a touch mixer. An appropriate amount of porous carbon material, 2.5 mL of water, and 2.5 mL of the diluted dispersant were placed in a test tube so that the laser intensity of the measuring device was within the appropriate range, and after dispersing with a touch mixer for several seconds, the measurement sample was obtained by dispersing with ultrasound for 120 seconds. The volume-average particle size was calculated as the 50% particle size D50, where the volume integrated value from the small particle size side in the volume-based particle size distribution is 50%.

[0080] <Aspect Ratio> A porous carbon material (AP20-0001HC, manufactured by AT Electrode Co., Ltd.) before impregnation with sulfur compounds was mounted on a carbon tape, and the shape of the porous carbon material was observed using an electron microscope (FLEX SEM1000II, manufactured by Hitachi High-Technologies Corporation). The observation conditions were an acceleration voltage of 5 kV and a magnification of 10,000x. Any particle whose particle shape could be confirmed (visually observed from the SEM image, where the arithmetic mean of the major and minor axes is D) was used. ５０ For 47 particles ranging from 0.1 to 1.5 times the original size, the aspect ratio was calculated using Image J, and the resulting aspect ratio was 1.15.

[0081]

[0082] Comparative Example 1: 2 g of porous carbon material (AP20-0001HC, manufactured by AT Electrode Co., Ltd.) and 3 g of sulfur powder were mixed. The resulting mixture was placed in a pressure-resistant container and heat-treated at 150°C for 3 hours. After heat treatment, 5 g was placed in a stainless steel container and heat-treated at 300°C for 3 hours to produce the lithium-sulfur battery cathode material of Comparative Example 1.

[0083] Comparative Example 2: 0.5 g of carbon material (ECP600JD, manufactured by Lion Specialty Chemicals Co., Ltd.) and 2.5 g of sulfur powder were mixed. The resulting mixture was placed in a heat-resistant container and heat-treated at 150°C for 3 hours to obtain a sulfur-carbon composite. 0.3 g of polyacrylonitrile and 12 mL of dimethylformamide were dissolved in a beaker, and 3 g of the sulfur-carbon composite was added and dispersed. Pure water was then added dropwise while stirring. After adding 30 mL, stirring was stopped, the mixture was filtered, and the dimethylformamide was washed off with pure water. The resulting mixture was dried at 50°C for 1 hour, and the resulting powder was heat-treated at 300°C for 3 hours to produce the lithium-sulfur cathode material of Comparative Example 2.

[0084] Example 1 Two g of porous carbon material (AP20-0001HC, manufactured by AT Electrode Co., Ltd.) and three g of the prepolymer prepared in Manufacturing Example 4 were mixed in a mortar. The resulting mixture was placed in a pressure-resistant container and heat-treated at 200°C for three hours to produce the lithium sulfur battery cathode material of Example 1.

[0085] Example 2 A cathode material for a lithium-sulfur battery of Example 2 was prepared in the same manner as in Example 1, except that the prepolymer was changed to the prepolymer prepared in Manufacturing Example 5.

[0086] Example 3 A cathode material for a lithium sulfur battery of Example 3 was obtained in the same manner as in Example 1, except that the prepolymer was changed to the prepolymer prepared in Manufacturing Example 6.

[0087] Example 4 A cathode material for a lithium sulfur battery of Example 4 was prepared in the same manner as in Example 1, except that the prepolymer was changed to the prepolymer prepared in Manufacturing Example 7.

[0088] Example 5 A cathode material for a lithium-sulfur battery was prepared in the same manner as in Example 1, except that the porous carbon material prepared in Manufacturing Example 1 was used.

[0089] Example 6 A positive electrode material for a lithium sulfur battery was prepared in the same manner as in Example 1, except that the porous carbon material prepared in Manufacturing Example 2 was used.

[0090] Example 7 Two g of porous carbon material (AP20-0001HC, manufactured by AT Electrode Co., Ltd.) and two g of sulfur powder were mixed. The resulting mixture was placed in a pressure vessel and heat-treated at 150°C for three hours. Subsequently, the lithium sulfur battery cathode material of Example 7 was prepared in the same manner as in Example 6, except that the weight of the sulfur-carbon composite was changed to 4.7 g and the weight of 1,3-diisopropenylbenzene was changed to 0.3 g.

[0091] Example 8 A lithium sulfur battery cathode material for Example 8 was prepared in the same manner as in Example 7, except that the carbon material prepared in Manufacturing Example 3 was used as the porous carbon material.

[0092] Example 9 1.2 g of the porous carbon material prepared in Production Example 3 and 1.8 g of sulfur powder were mixed. The resulting mixture was placed in a pressure vessel and heat-treated at 150°C for 3 hours to obtain a sulfur-carbon composite. 0.3 g of polyacrylonitrile and 12 mL of dimethylformamide were placed in a beaker and stirred to dissolve. 3 g of the sulfur / carbon composite was added to the solution and stirred to disperse it, then pure water was added dropwise while stirring. After adding 30 mL dropwise, stirring was stopped, the mixture was filtered, and the dimethylformamide was washed off with pure water. The resulting mixture was dried at 50°C for 1 hour, and the resulting powder was heat-treated at 300°C for 3 hours to produce the lithium-sulfur battery cathode material of Example 9.

[0093] The lithium-sulfur battery cathode materials prepared in Comparative Examples 1 and 2 and Examples 1 to 9 were evaluated as follows. The evaluation results are shown in Table 2.

[0094] <Ratio of Mass Loss> The mass loss of the lithium-sulfur battery cathode materials prepared in each example and comparative example was measured in the temperature range from room temperature to 1000°C using a differential thermal-thermal-mass simultaneous measurement device (Rigaku Corporation, Thermo plus EVO2 TG-DTA8122). Specifically, 5 mg to 15 mg of the sample was taken into an alumina cell, introduced into the balance of the differential thermal-thermal-mass simultaneous measurement device, nitrogen gas was flowed through at 100 mL / min, and the temperature was raised to 1000°C at a heating rate of 10°C / min. Using alumina as a standard substance, the mass loss was profiled, and the mass loss in the temperature range from 30°C to 1000°C and the mass loss in the temperature range from 500°C to 1000°C were calculated. Using these calculated values, the ratio of the mass loss in the temperature range from 500°C to 1000°C to the mass loss in the temperature range from 30°C to 1000°C was determined. Figures 1 and 2 show the mass loss plotted against temperature.

[0095] <Battery Characteristics> A slurry composition for a lithium-sulfur secondary battery cathode was prepared by mixing 85% by mass of the lithium-sulfur battery cathode material prepared in Comparative Example 1 and Examples 1 to 6, 10% by mass of carbon black, and 5% by mass of styrene-butadiene rubber (SBR) / carboxymethylcellulose (CMC) / polyvinylpyrrolidone (PVP) (=2.0 / 2.5 / 0.5).

[0096] The obtained positive electrode slurry composition was applied to a current collector and dried at 50°C for 30 minutes. Carbon-coated aluminum foil was used as the current collector. The dried product was pressed using a roll press to obtain an active material layer density of 1.0 g / cm³. ３ After pressing to achieve the desired shape, the material was cut to the specified size to produce a positive electrode for a lithium-sulfur secondary battery.

[0097] Preparation of non-aqueous electrolyte: Fluoroethylene carbonate (FEC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 71:100 to obtain a mixture. Lithium hexafluorophosphate (LiPF) was added to the obtained mixture. ６ A non-aqueous electrolyte was prepared by dissolving the substance in a solution to a concentration of 1.0 mol / L.

[0098] For the assembly of the lithium-sulfur secondary battery, lead electrodes were attached to the obtained positive electrode, a separator made of porous polypropylene (Cellguard 2400) was placed, and these were housed in a bag-shaped laminate pack. After housing, the components were vacuum-dried at 50°C to remove moisture adsorbed on each part. After vacuum drying, metallic lithium for the negative electrode, which was placed on a SUS foil, was placed in the laminate pack facing the positive electrode via the porous polypropylene, the non-aqueous electrolyte prepared above was injected, and the pack was sealed to obtain a laminate-type lithium-sulfur secondary battery for evaluation.

[0099] The obtained evaluation batteries were placed in a constant temperature bath at 25°C, and rate capacity retention rate evaluation tests were conducted with charge and discharge voltages ranging from 1.0V to 3.0V. The discharge currents used were those that would be drawn at capacities of 0.1C, 0.2C, 0.5C, 1C, and 2C. The rate characteristics were evaluated by dividing the obtained discharge capacity at the 2C rate by the discharge capacity at the 0.1C rate and the second cycle. The evaluation results are shown in Table 2. Figure 6 shows the discharge capacity plotted against the number of cycles. Figure 7 shows the same results as in Figure 6, but with a different display range for charge and discharge capacities.

[0100]

[0101] In Examples 1 to 9, the lithium-sulfur battery cathode materials, fabricated under a nitrogen atmosphere and a heating rate of 10°C / min, showed improved cycle characteristics and rate characteristics in a ratio of 3% or more between the mass loss in the 500°C to 1000°C temperature range and the mass loss in the 30°C to 1000°C temperature range. On the other hand, the lithium-sulfur battery cathode material fabricated in Comparative Example 1, where this ratio was less than 3%, showed inferior cycle characteristics and rate characteristics. The lithium-sulfur battery cathode material fabricated in Comparative Example 2, consisting of a porous carbon material with a pore diameter exceeding 5 nm at a volume cumulative of 70%, showed inferior rate characteristics.

[0102] <Extraction of Sulfur Compounds> 1 g of the cathode material from Example 1, Example 7, Example 8, and Production Example 4 was placed in 10 mL of chloroform, stirred for 10 minutes, filtered, and the filtrate was collected. By evaporating the chloroform, only the sulfur compounds supported on the porous carbon material were extracted.

[0103] <Ratio Analysis of Mass Loss of Sulfur Compounds> The mass loss of sulfur compounds extracted from the cathode materials of Examples 1, 7, 8, and Production Example 4, as well as elemental sulfur (sulfur powder, 195-04625, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), was measured in the temperature range from room temperature to 1000°C using a differential thermal-thermal mass analyzer (Thermo plus EVO2 TG-DTA8122, manufactured by Rigaku Corporation). Specifically, 5 mg to 15 mg of the sample was taken into an alumina cell, introduced into the balance of the differential thermal-thermal mass analyzer, and nitrogen gas was flowed through at 100 mL / min, raising the temperature to 1000°C at a heating rate of 10°C / min. The mass loss was profiled using alumina as a standard substance. The results are shown in Figure 8. While the sulfur carrier (Comparative Example 1) did not lose weight at temperatures above 350°C, the sulfur compounds extracted from Examples 1, 7, 8, and Production Example 4 underwent weight loss at temperatures above 350°C. From these results, it can be inferred that in the cathode materials of Examples 1, 7, 8, and Production Example 4, sulfur and organic compounds are supported on porous carbon in the form of composite compounds.

[0104] <NMR Measurement> ¹H NMR measurements were performed on the sulfur compound extracted above for Example 7. The results are shown in Figure 9. The peaks around 0.5 to 2.0 ppm are thought to represent protons originating from the methyl group, and the peaks around 2.0 to 3.5 ppm are thought to represent protons from the methylene group. The peaks around 0.5 ppm to 3.5 ppm suggest polymerization of diisopropenylbenzene.

[0105] The lithium-sulfur battery cathode material disclosed herein exhibits excellent cycle characteristics and rate characteristics, making it suitable for use in large power equipment applications such as electric vehicles and aerospace applications such as drones.

[0106] This disclosure includes the following embodiments: (1) A positive electrode material for a lithium sulfur battery comprising a porous carbon material having a pore diameter of 1 nm or more and 5 nm or less in a volume cumulative 70% and a sulfur compound supported on the porous carbon material, wherein, under conditions of a nitrogen atmosphere and a heating rate of 10°C / min, the ratio of the mass loss in the temperature range of 500°C to 1000°C to the mass loss in the temperature range of 30°C to 1000°C is 3% or more. (2) A positive electrode material for a lithium sulfur battery comprising a porous carbon material having a pore diameter of 1 nm or more and 5 nm or less in a volume cumulative 70% and a sulfur compound supported on the porous carbon material, wherein the sulfur compound is a compound containing sulfur and carbon. (3) The specific surface area of ​​the porous carbon material is 500 m². ２ (Item 4) A positive electrode material for a lithium sulfur battery according to item 1 or 2, wherein the amount is 1 / g or more. (Item 4) A positive electrode material for a lithium sulfur battery according to any one of items 1 to 3, wherein the 50% particle size D50 in the cumulative particle size distribution of the porous carbon material is 0.1 μm or more and 30 μm or less. (Item 5) A positive electrode material for a lithium sulfur battery according to any one of items 1 to 4, wherein the aspect ratio of the porous carbon material is 1 or more and 5 or less. (Item 6) The porous carbon material is such that, in heating-generated gas mass spectrometry, CO is desorbed in a temperature range of 30°C to 1000°C under a heating rate of 10°C / min. ２ CO2 desorbed in the temperature range of 400°C to 1000°C relative to the amount of CO2 desorbed. ２(Item 7) A positive electrode material for a lithium sulfur battery according to any one of items 1 to 5, wherein the ratio of the amount of desorption is 75% or more. (Item 7) A method for producing a positive electrode material for a lithium sulfur battery, comprising the steps of: mixing a porous carbon material having a pore diameter of 1 nm or more and 5 nm or less at a volume cumulative of 70%, with a sulfur compound containing sulfur and carbon; and heating the obtained mixture. (Item 8) A method for producing a positive electrode material for a lithium sulfur battery according to item 7, wherein the sulfur compound is amorphous. (Item 9) A method for producing a positive electrode material for a lithium sulfur battery according to item 7 or 8, wherein the sulfur compound is a crosslinked product of a chain-like sulfur polymer and a hydrocarbon. (Item 10) A method for producing a positive electrode material for a lithium sulfur battery according to item 9, wherein the hydrocarbon is a cyclic hydrocarbon or an aromatic hydrocarbon. (Item 11) A method for producing a positive electrode material for a lithium sulfur battery, comprising the steps of: preparing a support on which a sulfur source is supported on a porous carbon material having a pore diameter of 1 nm or more and 5 nm or less at a volume cumulative of 70%, contacting the support with an organic compound; and heat-treating the obtained contact.

Claims

1. A positive electrode material for a lithium-sulfur battery comprising a porous carbon material having a pore diameter of 1 nm to 5 nm in a cumulative volume of 70%, and a sulfur compound supported on the porous carbon material, wherein, under conditions of a nitrogen atmosphere and a heating rate of 10°C / min, the ratio of the mass loss in the temperature range of 500°C to 1000°C to the mass loss in the temperature range of 30°C to 1000°C is 3% or more.

2. A positive electrode material for a lithium-sulfur battery comprising a porous carbon material having a pore diameter of 1 nm or more and 5 nm or less in a cumulative volume of 70%, and a sulfur compound supported on the porous carbon material, wherein the sulfur compound is a compound containing sulfur and carbon.

3. The specific surface area of ​​the porous carbon material is 500 m². ２ A positive electrode material for a lithium-sulfur battery according to claim 1 or 2, wherein the amount is 1 / g or more.

4. The positive electrode material for a lithium sulfur battery according to any one of claims 1 to 3, wherein the 50% particle size D50 in the cumulative particle size distribution of the porous carbon material is 0.1 μm or more and 30 μm or less.

5. The positive electrode material for a lithium sulfur battery according to any one of claims 1 to 4, wherein the aspect ratio of the porous carbon material is 1 or more and 5 or less.

6. The porous carbon material, when subjected to heating-generated gas mass spectrometry, desorbs CO in a temperature range of 30°C to 1000°C under a heating rate of 10°C / min. ２ CO2 desorbed in the temperature range of 400°C to 1000°C relative to the amount of CO2 desorbed. ２ A positive electrode material for a lithium sulfur battery according to any one of claims 1 to 5, wherein the ratio of the amount of desorption is 75% or more.

7. A method for producing a positive electrode material for a lithium sulfur battery, comprising the steps of: mixing a porous carbon material having a pore diameter of 1 nm or more and 5 nm or less at a cumulative volume of 70% with a sulfur compound containing sulfur and carbon; and heating the resulting mixture.

8. The method for producing a positive electrode material for a lithium sulfur battery according to claim 7, wherein the sulfur compound is amorphous.

9. The method for producing a positive electrode material for a lithium sulfur battery according to claim 7 or 8, wherein the sulfur compound is a crosslinked product of a chain-like sulfur polymer and a hydrocarbon.

10. The method for producing a positive electrode material for a lithium sulfur battery according to claim 9, wherein the hydrocarbon is a cyclic hydrocarbon or an aromatic hydrocarbon.

11. A method for producing a positive electrode material for a lithium sulfur battery, comprising the steps of: preparing a support in which a sulfur source is supported on a porous carbon material having a pore diameter of 1 nm or more and 5 nm or less over a cumulative 70% of its volume; contacting the support with an organic compound; and heat-treating the resulting contact.

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