Sulfur-modified polyacrylonitrile, electrode active material containing the sulfur-modified polyacrylonitrile, secondary battery electrode containing the electrode active material, method for manufacturing the electrode, and non-aqueous electrolyte secondary battery using the electrode

Abstract

The present invention provides a sulfur-modified polyacrylonitrile, an electrode active material containing the sulfur-modified polyacrylonitrile, a secondary battery electrode containing the electrode active material, a method for manufacturing the electrode, and a non-aqueous electrolyte secondary battery using the electrode. The total sulfur content of the sulfur-modified polyacrylonitrile is 30% by mass to 55% by mass, and the content of free sulfur obtained by the solvent extraction method is 0.05 mass ppm to 4% by mass.

Description

Technical Field

[0001] The present invention relates to a sulfur-modified polyacrylonitrile, an electrode active material containing the sulfur-modified polyacrylonitrile, a secondary battery electrode containing the electrode active material, a method for manufacturing the electrode, and a non-aqueous electrolyte secondary battery using the electrode. Background Art

[0002] Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are small and lightweight, have a high energy density, and can be repeatedly charged and discharged, and are widely used as power sources for portable electronic devices such as portable personal computers, handy videocameras, and information terminals. In addition, from the viewpoint of environmental problems, the practical application of electric vehicles using non-aqueous electrolyte secondary batteries and hybrid vehicles that utilize electric power for part of their power is underway. Therefore, in recent years, further improvement in the performance of secondary batteries has been sought.

[0003] The characteristics of non-aqueous electrolyte secondary batteries depend on components such as electrodes, separators, and electrolytes that constitute them, and research and development of each component are being actively carried out. Among the electrodes, the electrode active material is important together with a binder, a current collector material, etc., and research and development of the electrode active material are being actively carried out.

[0004] A sulfur-modified polyacrylonitrile obtained by heat-treating a mixture of polyacrylonitrile and sulfur in a non-oxidizing atmosphere has a large charge-discharge capacity and is known as an electrode active material with little decrease in charge-discharge capacity (hereinafter, sometimes also referred to as cycle characteristics) accompanying repeated charge and discharge (for example, refer to Patent Documents 1 to 3). Research has been conducted on sulfur-modified polyacrylonitrile mainly as an electrode active material for the positive electrode, and research has also been conducted on the electrode active material for the negative electrode (for example, refer to Patent Document 3).

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: International Publication No. 2010 / 044437

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2014-022123

[0009] Patent Document 3: Japanese Patent Application Laid-Open No. 2014-096327 Summary of the Invention

[0010] Problems to be Solved by the Invention

[0011] Non-aqueous electrolyte secondary batteries seek to further improve battery characteristics, and electrode active materials also seek higher performance. If a secondary battery is stored for a long period in a charged state, the amount of stored electricity decreases due to self-discharge, and self-discharge is particularly likely to occur at high temperatures. Sulfur-modified polyacrylonitrile is known as an electrode active material for non-aqueous electrolyte secondary batteries that can achieve little self-discharge at room temperature and excellent power storage characteristics, but the power storage characteristics at high temperatures are insufficient.

[0012] Solution to the problem

[0013] The inventors conducted in-depth research and found that when the total amount of free sulfur in sulfur-modified polyacrylonitrile is within a specific range, an electrode with excellent power storage characteristics even at high temperatures can be obtained, thus completing the present invention. That is, the present invention is a sulfur-modified polyacrylonitrile, wherein the total sulfur content is 30% by mass to 55% by mass, and the content of free sulfur obtained by solvent extraction is 0.05 mass ppm to 4% by mass.

[0014] Advantages of the invention

[0015] According to the present invention, a non-aqueous electrolyte secondary battery can be provided, which has a large charge-discharge capacity and excellent power storage characteristics even at high temperatures. Detailed description of the invention

[0016] In the present invention, sulfur-modified polyacrylonitrile refers to a compound obtained by heat-treating polyacrylonitrile and elemental sulfur in a non-oxidizing atmosphere. The polyacrylonitrile may also be a homopolymer of acrylonitrile. In addition, it may also be a copolymer of acrylonitrile and other monomers. When the polyacrylonitrile is a copolymer, if the content of acrylonitrile becomes low, the battery performance becomes low. Therefore, the content of acrylonitrile in the copolymer is preferably at least 90% by mass or more. Examples of other monomers include acrylic acid, vinyl acetate, N-vinylformamide, and N,N'-methylenebis(acrylamide).

[0017] In the sulfur-modified polyacrylonitrile of the present invention, it is characterized in that the total sulfur content is 30% by mass to 55% by mass, and the content of free sulfur obtained by solvent extraction is 0.05 mass ppm to 4% by mass. When the total sulfur content is less than 30% by mass, it may be impossible to obtain a large charge-discharge capacity, and when it is more than 55% by mass, it may be impossible to obtain excellent cycle characteristics. The total sulfur content of the sulfur-modified polyacrylonitrile of the present invention is preferably 30% by mass to 45% by mass, and more preferably 35% by mass to 40% by mass. It should be noted that the sulfur content of sulfur-modified polyacrylonitrile can be calculated based on the analysis results of a CHN analyzer capable of analyzing sulfur and oxygen.

[0018] Free sulfur is elemental sulfur contained in sulfur-modified polyacrylonitrile. When the content of free sulfur obtained by the solvent extraction method in the sulfur-modified polyacrylonitrile of the present invention is less than 0.05 mass ppm and more than 4 mass%, excellent cycle characteristics at high temperatures may sometimes not be obtained. The content of free sulfur obtained by the solvent extraction method is preferably 0.05 mass ppm to 500 mass ppm, more preferably 0.07 mass ppm to 300 mass ppm, and most preferably 0.1 mass ppm to 200 mass ppm.

[0019] The solvent extraction method is a method for extracting and quantifying free sulfur in sulfur-modified polyacrylonitrile using a solvent. The extraction method can be an immersion extraction method in which the sulfur-modified polyacrylonitrile is repeatedly immersed in the solvent and separated from the extract by filtration or the like; it can also be a continuous extraction method using a Soxhlet extractor or the like (for example, refer to JIS K6234 (Rubber - Determination of free sulfur), ISO7269 (Rubber - Determination of free sulfur)). The solvent used for extraction is not particularly limited as long as it can extract free sulfur from sulfur-modified polyacrylonitrile, does not react with elemental sulfur, and does not dissolve impurities. Examples of extraction solvents include hexane, toluene, diethyl ether, tetrahydrofuran, methanol, ethanol, acetone, chloroform, carbon disulfide, etc. From the perspective of less elution of impurities, methanol and ethanol are preferred. The elemental sulfur after extraction can be quantified by spectrophotometry, and the measurement wavelength is set to 264 nm, which is the absorption maximum of sulfur. It should be noted that the extraction method and quantification method can also be other methods as long as they can ensure the same level of accuracy as the above methods.

[0020] The particle size of the sulfur-modified polyacrylonitrile of the present invention is preferably 0.1 μm to 50 μm in terms of average particle size. The particle size is the diameter based on volume, and in the laser diffraction light scattering method, the diameter of the secondary particles is measured. In the present invention, the average particle size refers to the 50% particle size (D50) measured by the laser diffraction light scattering method. To make the average particle size of sulfur-modified polyacrylonitrile less than 0.1 μm, a large amount of labor is required and further improvement in battery performance cannot be expected. When it is greater than 50 μm, peeling of the electrode binder layer or the like may sometimes easily occur. The average particle size of the sulfur-modified polyacrylonitrile of the present invention is more preferably 0.5 μm to 30 μm, and further preferably 1 μm to 20 μm.

[0021] The mass reduction rate of the sulfur-modified polyacrylonitrile of the present invention at 150°C to 350°C obtained by thermogravimetric analysis is preferably 0.2% by mass to 15% by mass. It should be noted that in thermogravimetric analysis, the starting temperature of heating is set to below 100°C, and the heating rate is set to a constant rate of 10°C / minute. The sulfur-modified polyacrylonitrile has partial structures shown in the following formulas (1) and (2). The polysulfide structure of formula (1) undergoes sulfur detachment upon heating to become the disulfide structure of formula (2). The mass reduction at 150°C to 350°C obtained by thermogravimetric analysis is considered to be due to the detached sulfur.

[0022]

[0023] (In the formula, n represents an integer of 1 or more.)

[0024] Regarding the sulfur-modified polyacrylonitrile, the one with more of the partial structure shown in formula (1) can obtain a large charge-discharge capacity. However, when the heating mass reduction rate at 150°C to 350°C obtained by thermogravimetric analysis exceeds 15% by mass, the power storage characteristics may sometimes deteriorate. In addition, when it is less than 0.2% by mass, the charge-discharge capacity may sometimes decrease. The mass reduction rate of the sulfur-modified polyacrylonitrile at 150°C to 350°C obtained by thermogravimetric analysis is more preferably 0.25% by mass to 2% by mass, further preferably 0.3% by mass to 1.7% by mass, and most preferably 0.5% by mass to 1.5% by mass.

[0025] The sulfur-modified polyacrylonitrile of the present invention is obtained by the following manufacturing method, which includes a heat treatment step of heat-treating polyacrylonitrile and elemental sulfur. The mixing ratio of polyacrylonitrile to elemental sulfur is preferably 100 parts by mass to 1500 parts by mass of elemental sulfur relative to 100 parts by mass of polyacrylonitrile, and further preferably 150 parts by mass to 1000 parts by mass. Considering the aspect of uniform sulfur modification, polyacrylonitrile and elemental sulfur are preferably powders. When the particle sizes of polyacrylonitrile and elemental sulfur are too small, micronization requires a large amount of labor, and when they are too large, sulfur modification is insufficient. Therefore, the average particle size of polyacrylonitrile and elemental sulfur is preferably 1 μm to 1000 μm.

[0026] Polyacrylonitrile and elemental sulfur can be directly heat-treated. Considering the aspect of uniform sulfur modification, they can also be pre-mixed before the heat treatment step and then heat-treated.

[0027] The heat treatment temperature of polyacrylonitrile and elemental sulfur is preferably 250°C to 550°C, and further preferably 350°C to 450°C. In addition, in order to make sulfur modification uniform, it is preferable to heat while mixing polyacrylonitrile and elemental sulfur, or while mixing an intermediate of sulfur-modified polyacrylonitrile and sulfur.

[0028] The heat treatment is carried out in a non-oxidizing atmosphere. The non-oxidizing atmosphere means that the oxygen concentration in the gas phase is 5 vol% or less, preferably 2 vol% or less, and more preferably an atmosphere substantially free of oxygen. For example, it can be an inert gas atmosphere such as nitrogen, helium, or argon, or a sulfur gas atmosphere.

[0029] The hydrogen sulfide generated by the heat treatment is preferably discharged outside the heating container. To discharge hydrogen sulfide, an inert gas can be introduced into the heating container, and hydrogen sulfide is discharged together with the inert gas. In the case where sulfur vapor flows out together with hydrogen sulfide, the reaction ratio between polyacrylonitrile and elemental sulfur will change. Therefore, as long as the flowing sulfur is refluxed into the heating container or sulfur in the amount of the flowing-out amount is added.

[0030] The sulfur-modified polyacrylonitrile obtained by the heat treatment contains free sulfur, and the free sulfur is removed by heating. When the heating temperature is low, it takes a long time to remove free sulfur, and when it is too high, it costs to remove. Therefore, it is preferably 260 to 600 °C, more preferably 300 to 550 °C, and further preferably 350 to 500 °C. The heating for removing free sulfur is preferably carried out under an inert gas stream or under reduced pressure conditions, and more preferably under reduced pressure conditions. The pressure in the case of reduced pressure is preferably 100 hPa or less, more preferably 50 hPa or less, and most preferably 25 hPa or less. In particular, in order to make the heating mass reduction rate at 150 °C to 350 °C obtained by thermogravimetric analysis be 0.2 mass% to 2 mass%, at 260 °C, reduced pressure is carried out at a pressure of 20 hPa for 10 hours or more; at 300 °C, reduced pressure is carried out at a pressure of 20 hPa for 1 hour or more; at 350 °C, reduced pressure is carried out at a pressure of 20 hPa for 0.5 hour to 15 hours.

[0031] The sulfur-modified polyacrylonitrile of the present invention has a large charge-discharge capacity as an electrode active material, has excellent cycle characteristics, and can preferably be used as an electrode active material for an electrode of a non-aqueous electrolyte secondary battery. Specifically, an electrode is manufactured by forming an electrode mixture layer in the following manner: adding the sulfur-modified polyacrylonitrile, a binder, and a conductive additive of the present invention to a solvent, coating the prepared slurry on a current collector, and drying.

[0032] It should be noted that the sulfur-modified polyacrylonitrile of the present invention can be used alone as an electrode active material or can be used in combination with other sulfur-based active materials. As other sulfur-based active materials, the following can be cited: organic polysulfide (R-S-Sm-R: R is a hydrocarbon group, m = 1 to 50), carbon-sulfur polymer ((C2S x ) y ∶x = 2.5 to 50, y ≥ 2), etc.

[0033] The binder can be a binder known for use as an electrode binder. For example, the following can be cited: styrene-butadiene rubber, butadiene rubber, polyethylene, polypropylene, polyamide, polyamideimide, polyimide, polyacrylonitrile, polyurethane, polyvinylidene fluoride, polytetrafluoroethylene, ethylene-propylene-diene rubber, fluororubber, styrene-acrylate copolymer, ethylene-vinyl alcohol copolymer, acrylonitrile-butadiene rubber, styrene-isoprene rubber, polymethyl methacrylate, polyacrylate, polyvinyl alcohol, polyvinyl ether, carboxymethyl cellulose, sodium carboxymethyl cellulose, methyl cellulose, cellulose nanofibers, polyethylene oxide, starch, polyvinylpyrrolidone, polyvinyl chloride, polyacrylic acid, etc.

[0034] As the binder, considering the aspects of low environmental load and excellent adhesiveness, an aqueous binder is preferred, and styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid are particularly preferred. The binder can be used alone or in combination of two or more.

[0035] The content of the binder in the slurry is preferably 1 to 30 parts by mass, more preferably 1 to 20 parts by mass, relative to 100 parts by mass of the sulfur-modified polyacrylonitrile of the present invention.

[0036] The conductive additive can be a conductive additive known for use as an electrode conductive additive. Specifically, the following can be cited: carbon materials such as natural graphite, artificial graphite, carbon black, Ketjen black, acetylene black, channel black, furnace black, lamp black, pyrolytic carbon black, carbon nanotubes, vapor grown carbon fiber (VGCF), graphene, fullerenes, needle cokes, etc.; metal powders such as aluminum powder, nickel powder, titanium powder, etc.; conductive metal oxides such as zinc oxide, titanium oxide, etc.; sulfides such as La2S3, Sm2S3, Ce2S3, TiS2, etc. The average particle size of the conductive additive is preferably 0.0001 μm to 100 μm, more preferably 0.01 μm to 50 μm.

[0037] The content of the conductive additive in the slurry is generally 0.1 to 50 parts by mass, preferably 1 to 30 parts by mass, more preferably 2 to 20 parts by mass, relative to 100 parts by mass of the sulfur-modified polyacrylonitrile of the present invention.

[0038] Examples of solvents for preparing the slurry include: propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, acetonitrile, propionitrile, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, nitromethane, N-methylpyrrolidone, N,N-dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, polyethylene oxide, dimethyl sulfoxide, sulfolane, γ-butyrolactone, water, alcohols, etc. The amount of the solvent used can be adjusted according to the coating method of the slurry. For example, in the case of the doctor blade method, relative to 100 parts by mass of the total amount of sulfur-modified polyacrylonitrile, binder, and conductive additive, the solvent is preferably 20 to 300 parts by mass, more preferably 30 to 200 parts by mass.

[0039] The slurry may sometimes contain other components. Examples of other components include viscosity modifiers, reinforcing materials, antioxidants, etc.

[0040] There is no particular limitation on the method for preparing the slurry. Examples include methods using ordinary ball mills, sand mills, bead mills, pigment dispersers, kneaders, ultrasonic dispersers, homogenizers, rotation / revolution stirrers, planetary stirrers, Filmix, JETPASTER, etc.

[0041] As the current collector, conductive materials such as titanium, titanium alloy, aluminum, aluminum alloy, copper, nickel, stainless steel, nickel-plated steel, etc. are used. These conductive materials sometimes have carbon coated on the surface. Examples of the shape of the current collector include foil shape, plate shape, mesh shape, etc. Among them, aluminum is preferred from the viewpoints of conductivity and price, and the foil shape is preferred. The thickness of the foil in the case of the foil shape is usually 1 to 100 μm.

[0042] The method for coating the slurry on the current collector is not particularly limited, and methods such as die coating method, comma coating method, curtain coater method, spray coating method, gravure coating method, flexographic coating method, doctor blade coater method, doctor blade method, reverse roll method, brush coating method, dipping method, etc. can be used. From the aspect of being able to obtain a good surface state of the coating layer according to the physical properties such as viscosity and drying property of the slurry, the die coating method, doctor blade method, and doctor blade coater method are preferred.

[0043] The coating of the slurry can be carried out on one side of the current collector or on both sides. In the case of coating on both sides of the current collector, each side can be coated sequentially or both sides can be coated simultaneously. In addition, it can be continuously coated on the surface of the current collector or intermittently coated on the surface of the current collector, and can be coated in a striped pattern. The thickness, length, and width of the coating layer can be appropriately determined according to the size of the battery.

[0044] As a method for drying the slurry coated on the current collector, there is no particular limitation, and various methods such as drying using warm air, hot air, low-humidity air, vacuum drying, and irradiation with far-infrared rays, infrared rays, electron beams, etc. by standing in a heating furnace or the like can be used. By this drying, volatile components such as solvents volatilize from the coating film of the slurry, and an electrode mixture layer is formed on the current collector. Then, the electrode can be subjected to a pressing treatment as needed. As a method for the pressing treatment, for example, a die pressing method and a roll pressing method can be cited.

[0045] The electrode of the present invention has the same configuration as a known electrode. Specifically, it includes a current collector and an electrode mixture layer formed on the current collector. Moreover, the electrode mixture layer contains the sulfur-modified polyacrylonitrile of the present invention.

[0046] The electrode of the present invention is not particularly limited and can be used in a non-aqueous secondary battery having a non-aqueous electrolyte. The non-aqueous electrolyte can also be any of a liquid electrolyte, a gel electrolyte, a solid electrolyte, etc. The electrode of the present invention can be more preferably used in a lithium-ion secondary battery. The electrode of the present invention can be used as a positive electrode or a negative electrode.

[0047] A non-aqueous electrolyte secondary battery generally consists of a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator. When the electrode of the present invention is used as the positive electrode, an electrode having a known negative electrode active material can be used as the negative electrode. When the electrode of the present invention is used as the negative electrode, an electrode having a known positive electrode active material can be used as the positive electrode. It should be noted that the negative electrode when the electrode of the present invention is used as the positive electrode and the positive electrode when the electrode of the present invention is used as the negative electrode are called counter electrodes.

[0048] As known negative electrode active materials, for example, natural graphite, artificial graphite, difficult-to-graphitize carbon, easy-to-graphitize carbon, lithium, lithium alloy, silicon, silicon alloy, silicon oxide, tin, tin alloy, tin oxide, phosphorus, germanium, indium, copper oxide, antimony sulfide, titanium oxide, iron oxide, manganese oxide, cobalt oxide, nickel oxide, lead oxide, ruthenium oxide, tungsten oxide, zinc oxide can be cited. In addition, composite oxides such as LiVO2, Li2VO4, Li4Ti5O 12 etc. can be cited. These negative electrode active materials can be used alone or in combination of two or more.

[0049] As known positive electrode active materials, for example, lithium transition metal composite oxides, lithium-containing transition metal phosphate compounds, lithium-containing silicate compounds, etc. can be cited.

[0050] As the transition metal of the lithium transition metal composite oxide, vanadium, titanium, chromium, manganese, iron, cobalt, nickel, copper, etc. are preferred. As specific examples of the lithium transition metal composite oxide, there can be cited: lithium cobalt composite oxides such as LiCoO2; lithium nickel composite oxides such as LiNiO2; lithium manganese composite oxides such as LiMnO2, LiMn2O4, Li2MnO3; lithium transition metal composite oxides in which part of the transition metal atoms that are the main body of these lithium transition metal composite oxides are replaced by other metals such as aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, lithium, nickel, copper, zinc, magnesium, gallium, zirconium, etc. As a specific example of the lithium transition metal composite oxide in which part of the transition metal atoms that are the main body are replaced by other metals, for example, there can be cited: Li 1.1 Mn 1.8 Mg 0.1 O4, Li 1.1 Mn 1.85 Al 0.05 O4, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.5 Mn 0.5 O2, LiNi 0.80 Co 0.17 Al 0.03 O2, LiNi 0.80 Co 0.15 Al 0.05 O2, Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiMn 1.8 Al 0.2 O4, LiNi 0.5 Mn 1.5 O4, Li2MnO3-LiMO2 (M = Co, Ni, Mn), etc.

[0051] As the transition metal of the lithium-containing transition metal phosphate compound, vanadium, titanium, manganese, iron, cobalt, nickel, etc. are preferred. As specific examples, for example, there can be cited: LiFePO4, LiMn x Fe 1-xIron phosphate compounds such as PO4 (0 < x < 1); iron sulfate compounds such as LiFeSO4F; cobalt phosphate compounds such as LiCoPO4; lithium-containing transition metal phosphate compounds in which part of the transition metal atoms that are the main body of these lithium-containing transition metal phosphate compounds are replaced by other metals such as aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, lithium, nickel, copper, zinc, magnesium, gallium, zirconium, niobium, etc.; vanadium phosphate compounds such as Li3V2(PO4)3, etc.

[0052] Examples of the lithium-containing silicate compound include Li2FeSiO4, etc. These positive electrode active materials can be used alone or in combination of two or more.

[0053] The counter electrode can be manufactured by replacing the sulfur-modified polyacrylonitrile of the present invention described above with the known negative electrode active material or the known positive electrode active material.

[0054] Examples of the non-aqueous electrolyte include: a liquid electrolyte obtained by dissolving a supporting electrolyte in an organic solvent; a polymer gel electrolyte obtained by dissolving a supporting electrolyte in an organic solvent and gelating with a polymer; a pure polymer electrolyte in which a supporting electrolyte is dispersed in a polymer without an organic solvent; an inorganic solid electrolyte, etc.

[0055] Examples of the supporting electrolyte used in the liquid electrolyte and the polymer gel electrolyte include, for example, lithium salts known in the past. For example, LiPF6, LiBF4, LiAsF6, LiCF3SO3, LiCF3CO2, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(SO2F)2, LiC(CF3SO2)3, LiB(CF3SO3)4, LiB(C2O4)2, LiBF2(C2O4), LiSbF6, LiSiF5, LiSCN, LiClO4, LiCl, LiF, LiBr, LiI, LiAlF4, LiAlCl4, LiPO2F2, and their derivatives, etc. Among them, it is preferable to use one or more selected from the group consisting of LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(SO2F)2, LiC(CF3SO2)3, derivatives of LiCF3SO3, and derivatives of LiC(CF3SO2)3.

[0056] The content of the supporting electrolyte in the liquid electrolyte and the polymer gel electrolyte is preferably 0.5 to 7 mol / L, more preferably 0.8 to 1.8 mol / L.

[0057] Examples of supporting electrolytes used in pure polymer electrolytes include, for example: LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(SO2F)2, LiC(CF3SO2)3, LiB(CF3SO3)4, LiB(C2O4)2.

[0058] Examples of inorganic solid electrolytes include: Li 1+x A x B 2-y (PO4)3 (A = Al, Ge, Sn, Hf, Zr, Sc, Y, B = Ti, Ge, Zn, 0 < x < 0.5), LiMPO4 (M = Mn, Fe, Co, Ni), phosphate-based materials such as Li3PO4, Li3XO4 (X = As, V), Li 3+x A x B 1-x O4 (A = Si, Ge, Ti, B = P, As, V, 0 < x < 0.6), Li 4+x A x Si 1-x O4 (A = B, Al, Ga, Cr, Fe, 0 < x < 0.4) (A = Ni, Co, 0 < x < 0.1), Li 4-3y Al y SiO4 (0 < y < 0.06), Li 4-2y Zn y GeO4 (0 < y < 0.25), LiAlO2, Li2BO4, Li4XO4 (X = Si, Ge, Ti), lithium titanates (LiTiO2, LiTi2O4, Li4TiO4, Li2TiO3, Li2Ti3O7, Li4Ti5O 12 ) and other lithium composite oxides, compounds containing lithium and halogens such as LiBr, LiF, LiCl, LiPF6, LiBF4, compounds containing lithium and nitrogen such as LiPON, LiN(SO2CF3)2, LiN(SO2C2F5)2, Li3N, LiN(SO2C3F7)2, La 0.55 Li 0.35 TiO3 and other crystals with a perovskite structure having lithium ion conductivity, Li7−La3Zr2O 13 and other crystals with a garnet-type structure, glasses such as 50Li4SiO4·50Li3BO3, Li 10 GeP2S 12 、Li 3.25 Ge 0.25 P 0.75Crystals of lithium / phosphorus sulfide systems such as S4, 30Li2S·26B2S3·44LiI, 63Li2S·36SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 70Li2S·50GeS2, 50Li2S·50GeS2, etc., glasses of lithium / phosphorus sulfide systems such as Li7P3S 11 、Li 3.25 P 0.95 、S4, etc., glass ceramics, etc.

[0059] As the organic solvents used for preparing the liquid non-aqueous electrolyte in the present invention, one or a combination of two or more organic solvents commonly used in liquid non-aqueous electrolytes can be used. Specifically, for example, saturated cyclic carbonate compounds, saturated cyclic ester compounds, sulfoxide compounds, sulfone compounds, amide compounds, saturated chain carbonate compounds, chain ether compounds, cyclic ether compounds, saturated chain ester compounds, etc. can be cited.

[0060] Among the organic solvents, saturated cyclic carbonate compounds, saturated cyclic ester compounds, sulfoxide compounds, sulfone compounds, and amide compounds have a high relative dielectric constant, so they play a role in increasing the dielectric constant of the non-aqueous electrolyte. Saturated cyclic carbonate compounds are particularly preferred.

[0061] As the saturated cyclic carbonate compounds, for example, ethylene carbonate, 1,2-propylene carbonate, 1,3-propylene carbonate, 1,2-butylene carbonate, 1,3-butylene carbonate, 1,1-dimethylethylene carbonate, etc. can be cited.

[0062] As the saturated cyclic ester compounds, for example, γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-caprolactone, δ-octalactone, etc. can be cited. As the sulfoxide compounds, for example, dimethyl sulfoxide, diethyl sulfoxide, dipropyl sulfoxide, diphenyl sulfoxide, thiophene, etc. can be cited.

[0063] As the sulfone compounds, for example, dimethyl sulfone, diethyl sulfone, dipropyl sulfone, diphenyl sulfone, sulfolane (also known as tetramethylene sulfone), 3-methyl sulfolane, 3,4-dimethyl sulfolane, 3,4-diphenyl sulfolane, cyclobutene sulfone, 3-methyl cyclobutene sulfone, 3-ethyl cyclobutene sulfone, 3-bromomethyl cyclobutene sulfone, etc. are cited, and sulfolane and tetramethyl sulfolane are preferred.

[0064] As the amide compounds, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, etc. can be cited.

[0065] Among the organic solvents, saturated chain carbonate compounds, chain ether compounds, cyclic ether compounds, and saturated chain ester compounds can reduce the viscosity of the liquid electrolyte, improve the mobility of electrolyte ions, etc., and enable excellent battery characteristics such as output density. In addition, since it has a low viscosity, it can improve the performance of the liquid electrolyte at low temperatures. Saturated chain carbonate compounds are particularly preferred.

[0066] Examples of the saturated chain carbonate compounds include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethyl butyl carbonate, methyl tert-butyl carbonate, diisopropyl carbonate, tert-butyl propyl carbonate, etc.

[0067] Examples of the chain ether compounds or cyclic ether compounds include dimethoxyethane, ethoxymethoxyethane, diethoxyethane, tetrahydrofuran, dioxolane, dioxane, 1,2-bis(methoxycarbonyloxy)ethane, 1,2-bis(ethoxycarbonyloxy)ethane, 1,2-bis(ethoxycarbonyloxy)propane, ethylene glycol bis(trifluoroethyl) ether, propylene glycol bis(trifluoroethyl) ether, ethylene glycol bis(trifluoromethyl) ether, diethylene glycol bis(trifluoroethyl) ether, etc. Among them, dioxolane is preferred.

[0068] As the saturated chain ester compounds, monoesters and diesters with a total of 2 to 8 carbon atoms in the molecule are preferred. As specific compounds, for example, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isobutyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl pivalate, ethyl pivalate, methyl malonate, ethyl malonate, methyl succinate, ethyl succinate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, diacetyl ethylene glycol, diacetyl propylene glycol, etc. are exemplified. Methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isobutyl acetate, butyl acetate, methyl propionate, and ethyl propionate are preferred.

[0069] In addition, as the organic solvents for preparing the liquid electrolyte, for example, acetonitrile, propionitrile, nitromethane, their derivatives, and various ionic liquids can also be used.

[0070] Examples of the polymers used in the polymer gel electrolyte include polyethylene oxide, polypropylene oxide, polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate, polyethylene, polyvinylidene fluoride, polyhexafluoropropylene, etc. Examples of the polymers used in the pure polymer electrolyte include polyethylene oxide, polypropylene oxide, and polystyrene sulfonic acid. There are no particular restrictions on the compounding ratio and the method of compounding in the gel electrolyte, as long as the compounding ratio and the compounding method known in the technical field are adopted.

[0071] For the non-aqueous electrolyte, in order to improve battery life, improve safety, etc., for example, it may also contain known other additives such as an electrode film-forming agent, an antioxidant, a flame retardant, an overcharge prevention agent, etc. When using other additives, it is usually 0.01 parts by mass to 10 parts by mass, preferably 0.1 parts by mass to 5 parts by mass, based on 100 parts by mass of the entire non-aqueous electrolyte.

[0072] As the separator, a microporous film of a polymer commonly used in non-aqueous electrolyte secondary batteries can be used, and there is no particular limitation. As the film, for example, films formed from a polymer compound, its derivatives, copolymers, mixtures, etc. mainly composed of the following substances can be cited: polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene chloride, polyacrylonitrile, polyacrylamide, polytetrafluoroethylene, polysulfone, polyethersulfone, polycarbonate, polyamide, polyimide, polyethers such as polyethylene oxide and polypropylene oxide, various celluloses such as carboxymethyl cellulose and hydroxypropyl cellulose, poly(meth)acrylic acid and its various esters, etc. These films can also be coated with ceramic materials such as alumina and silica, magnesium oxide, aramid resin, and polyvinylidene fluoride.

[0073] These films can be used alone or these films can be laminated and used as a multilayer film. Moreover, various additives can be used in these films, and their types and contents are not particularly limited. Among these films, in the secondary battery manufactured by the manufacturing method of the secondary battery, a film composed of polyethylene, polypropylene, polyvinylidene fluoride, and polysulfone is preferably used. It should be noted that in the case where the non-aqueous electrolyte is a pure polymer electrolyte or an inorganic solid electrolyte, the separator may not be included.

[0074] The shape of the secondary battery is not particularly limited, and various shapes such as coin type, cylindrical type, square type, and laminated type can be adopted.

[0075] As the outer package member of the secondary battery, a laminated film or a metal container can be used. The thickness of the outer package member is usually 0.5 mm or less, preferably 0.3 mm or less. As the shape of the outer package member, the following can be cited: flat type (thin type), square type, cylindrical type, coin type, button type, etc.

[0076] The laminated film can also be a multilayer film having a metal layer between resin films. The metal layer is preferably aluminum foil or aluminum alloy foil for weight reduction. The resin film can use, for example, polymer materials such as polypropylene, polyethylene, nylon, and polyethylene terephthalate. The laminated film can be sealed by heat welding to form the shape of the outer package member.

[0077] A metal container can be formed of, for example, stainless steel, aluminum, or an aluminum alloy. As the aluminum alloy, an alloy containing elements such as magnesium, zinc, and silicon is preferred. In aluminum or an aluminum alloy, by setting the content of transition metals such as iron, copper, nickel, and chromium to 1% or less, the long-term reliability and heat dissipation in a high-temperature environment can be dramatically improved.

[0078] Examples

[0079] Hereinafter, the present invention will be described in further detail by way of examples and comparative examples. However, the present invention is not limited by any of the following examples, etc. It should be noted that "parts" and "%" in the examples are by mass unless otherwise specified.

[0080] Raw material PAN mixture: 10 parts by mass of polyacrylonitrile powder (manufactured by Sigma-Aldrich, average particle size 200 μm) and 30 parts by mass of sulfur powder (manufactured by Sigma-Aldrich, average particle size 200 μm) were mixed using a mortar to prepare the raw materials for sulfur-modified polyacrylonitrile in Production Examples 1 to 4.

[0081] [Production Example 1]

[0082] Sulfur-modified polyacrylonitrile was produced by the method of the production example according to Japanese Patent Application Laid-Open No. 2013-054957. That is, after accommodating 20 g of the raw material PAN mixture in a bottomed cylindrical glass tube having an outer diameter of 45 mm and a length of 120 mm, a silicone plug having a gas inlet tube and a gas outlet tube was attached to the opening of the glass tube. After replacing the air inside the glass tube with nitrogen, the lower part of the glass tube was placed in a crucible-type electric furnace, and while introducing nitrogen from the gas inlet tube and removing the generated hydrogen sulfide, it was heated at 400°C for 1 hour. It should be noted that sulfur vapor condensed and refluxed in the upper part or the lid of the glass tube. The obtained intermediate product was placed in a glass tube oven at 260°C, depressurized, and heated at 20 hPa for 3 hours to remove sulfur. The obtained sulfur-modified product was pulverized using a ball mill and classified with a sieve to obtain sulfur-modified polyacrylonitrile SPAN1 having an average particle size of 10 μm.

[0083] [Production Example 2]

[0084] In Production Example 1, the time for removing sulfur from the intermediate product was changed from 3 hours to 24 hours, and otherwise, the same operations as in Production Example 1 were performed to obtain sulfur-modified polyacrylonitrile SPAN2.

[0085] [Production Example 3]

[0086] In Production Example 1, the temperature for removing sulfur from the intermediate product was changed from 260°C to 300°C, and otherwise, the same operations as in Production Example 1 were performed to obtain sulfur-modified polyacrylonitrile SPAN3.

[0087] [Production Example 4]

[0088] In Production Example 1, the conditions for removing sulfur from the intermediate product were changed from 3 hours at 260 °C and a reduced pressure of 20 hPa to 24 hours at 300 °C and normal pressure under a nitrogen stream. Otherwise, the same operations as in Production Example 1 were carried out, and sulfur-modified polyacrylonitrile SPAN4 was obtained.

[0089] [Production Example 5]

[0090] While heating the central part of a heat-resistant glass tube with an outer diameter of 10 mm and an inner diameter of 6 mm to expand it, a glass furnace core tube in the form of a whole pipette with an expanded part having an outer diameter of 30 mm and a length of 50 mm in the central part and thin tubes with an outer diameter of 10 mm and a length of 150 mm at both ends was produced.

[0091] 5 g of the raw material PAN mixture was placed in the expanded part of the furnace core tube, and the heating part was set in a 70 mm tubular electric furnace so that the furnace core tube was inclined at 5°. After replacing the inside of the furnace core tube with nitrogen, it was heated at 400 °C for 1 hour while rotating once per minute to obtain an intermediate product. It should be noted that the gaps at both ends of the tubular electric furnace were filled with glass wool for heat insulation. During heating, nitrogen could be supplied at a flow rate of 100 ml / min from the lower end of the furnace core tube, and the generated hydrogen sulfide gas was discharged from the upper end of the furnace core tube. In addition, the entire expanded part was set as the heating part of the furnace core tube, but the sulfur sublimated and adhered to the thin tube part could be appropriately heated to dissolve and reflux to the expanded part.

[0092] The obtained intermediate product was placed in a glass tube oven at 300 °C, and the pressure was reduced and heated at 20 hPa for 3 hours to remove sulfur. After crushing the obtained sulfur-modified product using a ball mill and classifying it with a sieve, sulfur-modified polyacrylonitrile SPAN5 with an average particle diameter of 10 μm was obtained.

[0093] [Production Example 6]

[0094] In Production Example 5, the temperature for removing sulfur from the intermediate product was changed from 300 °C to 350 °C, and the time was changed from 3 hours to 24 hours. Otherwise, the same operations as in Production Example 5 were carried out, and sulfur-modified polyacrylonitrile SPAN6 was obtained.

[0095] [Production Example 7]

[0096] In Production Example 1, the conditions for removing sulfur from the intermediate product were changed from 3 hours at 260 °C and a reduced pressure of 20 hPa to 24 hours at 260 °C and normal pressure under a nitrogen stream. Otherwise, the same operations as in Production Example 1 were carried out, and sulfur-modified polyacrylonitrile SPAN7 was obtained.

[0097] [Production Example 8]

[0098] In Production Example 1, the condition for removing sulfur from the intermediate product was changed from 260 °C to 180 °C, and other than that, the same operations as in Production Example 1 were carried out to obtain sulfur-modified polyacrylonitrile SPAN8.

[0099] [Production Example 9]

[0100] In Production Example 5, the condition for removing sulfur from the intermediate product was changed from 3 hours under reduced pressure of 20 hPa at 300 °C to 24 hours under normal pressure at 260 °C in a nitrogen stream, and other than that, the same operations as in Production Example 5 were carried out to obtain sulfur-modified polyacrylonitrile SPAN9.

[0101] [Production Example 10]

[0102] In Production Example 1, the condition for removing sulfur from the intermediate product was changed from 260 °C to 180 °C, and other than that, the same operations as in Production Example 1 were carried out to obtain sulfur-modified polyacrylonitrile SPAN10.

[0103] The total sulfur content, free sulfur content, and heating mass reduction rate of SPAN1 to 10 were calculated by the following methods. The results are shown in Table 1. It should be noted that SPAN1 to 5, 8, and 10 are the sulfur-modified polyacrylonitrile of the present invention, so as Examples 1 to 7, SPAN6, 7, and 9 are used as Comparative Examples 1 to 3.

[0104] [Total sulfur content]

[0105] Calculated based on the analysis results using a CHN analyzer (manufactured by Elementar Analysensysteme GmbH, model: varioMICROcube) capable of analyzing sulfur and oxygen. It should be noted that the combustion tube temperature was set to 1150 °C, the reduction tube temperature was set to 850 °C, and a tin boat was used as the sample container.

[0106] [Free sulfur content]

[0107] The free sulfur extracted in accordance with JIS K6234 was quantified by spectrophotometry using ethanol as a solvent. It should be noted that the measurement wavelength was set to 264 nm.

[0108] [Heating mass reduction rate]

[0109] Thermogravimetric analysis was carried out using a thermogravimetry / differential thermal simultaneous analysis device, and the mass reduction rate at 150 °C to 350 °C relative to the weight before heating was taken as the heating mass reduction rate. It should be noted that the heating rate was set to 10 °C / minute.

[0110] [Table 1]

[0111]

[0112] 〔Manufacture of electrodes〕

[0113] Using the sulfur-modified polyacrylonitrile of Examples 1 to 7 and Comparative Examples 1 to 3, the electrodes of Examples 1 to 7 and Comparative Examples 1 to 3 were fabricated by the following method.

[0114] 92.0 parts by mass of sulfur-modified polyacrylonitrile as an electrode active material, 3.5 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive additive, 1.5 parts by mass of carbon nanotubes (manufactured by Showa Denko K.K., trade name VGCF), 1.5 parts by mass of styrene-butadiene rubber (aqueous dispersion, manufactured by Zeon Corporation, Japan) and 1.5 parts by mass of carboxymethyl cellulose (manufactured by Daicel Finechem Co., Ltd.), and 120 parts by mass of water as a solvent were mixed using a rotation / revolution stirrer to prepare a slurry. The slurry composition was applied to a current collector of stainless steel foil (thickness 20 μm) by a doctor blade method and dried at 90°C for 3 hours. Then, the electrode was cut into a specified size and vacuum-dried at 120°C for 2 hours to fabricate a disk-shaped electrode.

[0115] 〔Manufacture of positive electrode 1〕

[0116] 90.0 parts by mass of Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2 (manufactured by Nippon Chemical Industry Co., Ltd., trade name: NCM111, hereinafter referred to as NCM), 5.0 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive additive, 5.0 parts by mass of polyvinylidene fluoride (manufactured by Kureha Corporation) as a binder were mixed with 100 parts by mass of N-methylpyrrolidone and dispersed using a rotation / revolution stirrer to prepare a slurry. The slurry composition was applied to a current collector of aluminum foil (thickness 20 μm) by a doctor blade method and dried at 90°C for 3 hours. Then, the electrode was cut into a specified size and vacuum-dried at 120°C for 2 hours to fabricate a disk-shaped positive electrode 1.

[0117] 〔Manufacture of negative electrode 1〕

[0118] Lithium metal with a thickness of 500 μm was cut into a specified size to fabricate a disk-shaped negative electrode 1.

[0119] 〔Preparation of non-aqueous electrolyte〕

[0120] LiPF6 was dissolved in a mixed solvent composed of 50% by volume of ethylene carbonate and 50% by volume of diethyl carbonate at a concentration of 1.0 mol / L to prepare an electrolyte solution.

[0121] 〔Battery Assembly〕

[0122] The electrodes of Examples 1 to 7 and Comparative Examples 1 to 3 were used as the positive electrodes, and the negative electrode 1 was used as the negative electrode. They were held in the case with a glass filter as the separator in between. Then, the previously prepared non-aqueous electrolyte was injected into the case, and the case was sealed and closed to fabricate non-aqueous electrolyte secondary batteries (coin type with φ20 mm and thickness of 3.2 mm) of Examples 8 to 14 and Comparative Examples 4 to 6.

[0123] In addition, the electrodes of Examples 1 to 7 and Comparative Examples 1 to 3 were used as the negative electrodes, and the positive electrode 1 was used as the positive electrode. They were held in the case with a polypropylene microporous membrane as the separator in between. Then, the previously prepared non-aqueous electrolyte was injected into the case, and the case was sealed and closed to fabricate non-aqueous electrolyte secondary batteries (coin type with φ20 mm and thickness of 3.2 mm) of Examples 15 to 21 and Comparative Examples 7 to 9.

[0124] 〔Evaluation 1: Evaluation as a Positive Electrode Active Material (Stored at 50 °C)〕

[0125] The non-aqueous electrolyte secondary batteries of Examples 8 to 14 and Comparative Examples 4 to 6 were placed in a thermostat at 25 °C. The charging cut-off voltage was set to 3.0 V, and the discharging cut-off voltage was set to 1.0 V. Charge and discharge were performed at a charging rate of 0.2C and a discharging rate of 0.2C for 12 cycles, and the charge and discharge capacities were measured. Among them, after the charging in the 11th cycle, it was stored at 50 °C for 2 weeks and then discharged. The pre-storage charging capacity (the charging capacity of the 11th cycle), the post-storage discharging capacity (the discharging capacity of the 11th cycle), the irreversible capacity (the difference between the charging capacity of the 11th cycle and the charging capacity of the 12th cycle), and the self-discharge capacity (the difference between the pre-storage charging capacity and the sum of the post-storage discharging capacity and the irreversible capacity) are shown in Table 2. It should be noted that each capacity was the capacity per unit mass of sulfur-modified polyacrylonitrile as the positive electrode active material.

[0126] [Table 2]

[0127]

[0128] 〔Evaluation 2: Evaluation as a Positive Electrode Active Material (Stored at 60 °C)〕

[0129] In Evaluation 1, the storage temperature for 2 weeks was changed from 50 °C to 60 °C, and other than that, the same operations as in Evaluation 1 were performed. The pre-storage charging capacity, the post-storage discharging capacity, and the irreversible capacity are shown in Table 3.

[0130] [Table 3]

[0131]

[0132] 〔Evaluation 3: Evaluation as a negative electrode active material (stored at 50°C)〕

[0133] Regarding the non-aqueous electrolyte secondary batteries of Examples 15 to 21 and Comparative Examples 7 to 9, the charge cut-off voltage was changed to 3.2 V and the discharge cut-off voltage was changed to 0.8 V. Otherwise, the same operations as in Evaluation 1 were performed. The charge capacity before storage, the discharge capacity after storage, and the irreversible capacity are shown in Table 4. It should be noted that each capacity was set as the capacity per unit mass of NCM as the positive electrode active material.

[0134] [Table 4]

[0135]

[0136] 〔Evaluation 4: Evaluation as a negative electrode active material (stored at 60°C)〕

[0137] In Evaluation 3, the storage temperature for 2 weeks was changed from 50°C to 60°C. Otherwise, the same operations as in Evaluation 1 were performed. The charge capacity before storage, the discharge capacity after storage, and the irreversible capacity are shown in Table 5.

[0138] [Table 5]

[0139]

[0140] The discharge capacity of the charged non-aqueous electrolyte secondary battery decreases due to self-discharge and an increase in irreversible capacity, especially more at high temperatures than at low temperatures. This is the reason why the discharge capacity after storage is smaller than the charge capacity before storage in Tables 2 to 5.

Claims

1. A sulfur-modified polyacrylonitrile, wherein, the total sulfur content is 30% by mass to 55% by mass, and the content of free sulfur obtained by the solvent extraction method is 0.05 mass ppm to 4% by mass. The total sulfur content is measured by a carbon, hydrogen, and nitrogen analyzer under the following conditions: the combustion tube temperature is set at 1150 °C, the reduction tube temperature is set at 850 °C, and a tin boat is used as the sample container.

2. The sulfur-modified polyacrylonitrile according to claim 1, wherein, the heating mass reduction rate at 150 °C to 350 °C obtained by thermogravimetric analysis is 0.2% by mass to 15% by mass.

3. An electrode active material containing the sulfur-modified polyacrylonitrile according to claim 1 or 2.

4. A secondary battery electrode comprising the electrode active material according to claim 3.

5. A non-aqueous electrolyte secondary battery using the secondary battery electrode according to claim 4 as a positive electrode.

6. A non-aqueous electrolyte secondary battery using the secondary battery electrode according to claim 4 as a negative electrode.

7. A method for manufacturing a non-aqueous electrolyte secondary battery electrode, the non-aqueous electrolyte secondary battery electrode comprising an electrode active material containing sulfur-modified polyacrylonitrile, the method for manufacturing the non-aqueous electrolyte secondary battery electrode comprising: Sorting step 1 of sorting sulfur-modified polyacrylonitrile with a total sulfur content of 30% by mass to 55% by mass and a free sulfur content of 0.05 mass ppm to 4% by mass obtained by the solvent extraction method as the electrode active material of the non-aqueous electrolyte secondary battery electrode, wherein the total sulfur content is measured by a carbon, hydrogen, and nitrogen analyzer under the following conditions: the combustion tube temperature is set at 1150 °C, the reduction tube temperature is set at 850 °C, and a tin boat is used as the sample container.

8. A method for manufacturing a non-aqueous electrolyte secondary battery electrode, the non-aqueous electrolyte secondary battery electrode comprising an electrode active material containing sulfur-modified polyacrylonitrile, the method for manufacturing the non-aqueous electrolyte secondary battery electrode comprising: Sorting step 1 of sorting sulfur-modified polyacrylonitrile with a total sulfur content of 30% by mass to 55% by mass and a free sulfur content of 0.05 mass ppm to 4% by mass obtained by the solvent extraction method; and Sorting step 2 of sorting, from the sulfur-modified polyacrylonitrile sorted in the sorting step 1, sulfur-modified polyacrylonitrile with a heating mass reduction rate at 150 °C to 350 °C obtained by thermogravimetric analysis of 0.2% by mass to 15% by mass as the electrode active material of the non-aqueous electrolyte secondary battery electrode, wherein the total sulfur content is measured by a carbon, hydrogen, and nitrogen analyzer under the following conditions: the combustion tube temperature is set at 1150 °C, the reduction tube temperature is set at 850 °C, and a tin boat is used as the sample container.

9. An application of the sulfur-modified polyacrylonitrile according to claim 1 or 2 as an electrode active material.

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