Electrodes and secondary batteries

Abstract

To provide a secondary battery with a large charge / discharge capacity and excellent cycle characteristics. [Solution] An electrode having a porous metal current collector and an electrode layer, wherein the electrode layer comprises an active material and an electrolyte, the active material is made of a sulfur-containing material, and the sulfur-containing material comprises a sulfur-modified compound.

Description

[Technical Field]

[0001] This invention relates to electrodes that can be used in secondary batteries. [Background technology]

[0002] The characteristics of secondary batteries depend on their constituent components, such as electrodes, separators, and electrolytes, and research and development of each component is actively underway. In electrodes, the active material is important along with the binder and current collector, and research and development of active materials is also actively being conducted.

[0003] Sulfur-modified polyacrylonitrile compounds are known as electrode materials that can provide electrodes with large charge and discharge capacities. For example, Patent Documents 1 to 5 propose electrodes and secondary batteries using sulfur-modified polyacrylonitrile compounds. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2020 / 090986 [Patent Document 2] Japanese Patent Publication No. 2014-96327 [Patent Document 3] Japanese Patent Publication No. 2020-21677 [Patent Document 4] International Publication No. 2022 / 004696 [Patent Document 5] International Publication No. 2022 / 004697 [Overview of the project] [Problems that the invention aims to solve]

[0005] When batteries were manufactured using sulfur-containing materials as described in Patent Document 1, etc., there were problems with low discharge capacity and poor cycle characteristics. [Means for solving the problem]

[0006] As a result of diligent research, the inventors of this invention have concluded that An electrode having a porous metal current collector and an electrode layer, The electrode layer comprises an active material and an electrolyte, The active material consists of a sulfur-containing material, We have found that an electrode characterized in that the sulfur-containing material includes a sulfur-modified compound can solve the above problem. [Effects of the Invention]

[0007] The present invention provides a secondary battery with a large charge / discharge capacity and excellent cycle characteristics. [Modes for carrying out the invention]

[0008] A. Electrode The electrode of this disclosure is an electrode having a porous metal current collector and an electrode layer, The electrode layer contains an active material and an electrolyte. The above active material consists of a sulfur-containing material. The above sulfur-containing material is characterized by containing a sulfur-modified compound. The following describes in detail each component used in the electrode of the present invention.

[0009] <Electrode layer> The electrode layer in this disclosure comprises an active material and an electrolyte, wherein the active material is made of a sulfur-containing material. The electrode layer in this disclosure may not contain a binder or a conductive additive. In this specification, the electrode layer when the electrode is a positive electrode may be referred to as the "positive electrode active material layer," and the electrode layer when the electrode is a negative electrode may be referred to as the "negative electrode active material layer." The thickness of the electrode layer can typically be 1 μm to 3000 μm.

[0010] <Sulfur-containing materials> The sulfur-containing material of this disclosure includes a sulfur-modified compound. The sulfur-containing material of this disclosure may contain at least a sulfur-modified compound, and may further contain elemental sulfur and impurities. In this disclosure, elemental sulfur can refer to sulfur that does not form a stable interaction with a sulfur-modified compound. Specifically, elemental sulfur is not particularly limited, but examples include α-sulfur, β-sulfur, and γ-sulfur having an S8 structure.

[0011] <Total sulfur content> In this disclosure, total sulfur content refers to the total content of sulfur atoms. The total sulfur content in a sulfur-containing material can be calculated from the results of analysis using a CHNS analyzer capable of analyzing sulfur and oxygen.

[0012] The total sulfur content in the sulfur-containing material of this disclosure is preferably 30% to 90% by mass, more preferably 31% to 85% by mass, even more preferably 32% to 80% by mass, even more preferably 33% to 75% by mass, even more preferably 33% to 70% by mass, even more preferably 35% to 70% by mass, even more preferably 43% to 65% by mass, and most preferably 43% to 60% by mass.

[0013] <Sulfur-modified compounds> As the sulfur-modified compound contained in the sulfur-containing material of this disclosure, for example, a compound in which sulfur and an atom in an organic compound are covalently bonded can be used. A method for producing such a sulfur-modified compound is to heat elemental sulfur and an organic compound.

[0014] Examples of the above-mentioned organic compounds include acrylic compounds, polyether compounds, pitch compounds, polynuclear aromatic ring compounds, aliphatic hydrocarbon compounds, and thienoacene compounds. In other words, examples of the above-mentioned sulfur-modified compounds include sulfur-modified acrylic compounds, sulfur-modified polyether compounds, sulfur-modified pitch compounds, sulfur-modified polynuclear aromatic ring compounds, sulfur-modified aliphatic hydrocarbon compounds, polythienoacene compounds, and polysulfurized carbons.

[0015] In this disclosure, from the viewpoint of increasing the discharge capacity of the secondary battery and improving its cycle characteristics, the sulfur-modified compound is preferably selected from the group consisting of sulfur-modified acrylic compounds, sulfur-modified polyether compounds, and sulfur-modified polynuclear aromatic ring compounds, and is more preferably a sulfur-modified acrylic compound.

[0016] The total sulfur content in the sulfur-modified compound is not particularly limited, but from the viewpoint of further increasing the discharge capacity, it is preferably 20% to 80% by mass, more preferably 25% to 75% by mass, more preferably 25% to 70% by mass, more preferably 30% to 70% by mass, even more preferably 33% to 70% by mass, even more preferably 35% to 70% by mass, even more preferably 43% to 65% by mass, and most preferably 43% to 60% by mass. Here, the total sulfur content in the sulfur-modified compound can be calculated from the analysis results using a CHNS analyzer capable of analyzing sulfur and oxygen.

[0017] In this disclosure, from the viewpoint of increasing discharge capacity, the sulfur-modified compound is preferably present in 70 parts by mass or more, more preferably in 75 parts by mass or more, even more preferably in 80 parts by mass or more, even more preferably in 90 parts by mass or more, even more preferably in 95 parts by mass or more, and most preferably in 98 parts by mass or more per 100 parts by mass of the sulfur-containing material.

[0018] In this disclosure, the content of sulfur-modified compounds in sulfur-containing materials can be measured by known methods. For example, the content of sulfur-modified compounds can be measured by thermogravimetric analysis of sulfur-containing materials. In thermogravimetric analysis, the weight change is measured until 350°C is reached, under conditions where the heating start temperature is 100°C or lower and the heating rate is a constant rate of 10°C / min. The content (mass%) of sulfur-modified compounds in the sulfur-containing material can be calculated from the remaining amount at the end of the measurement according to the following formula. Sulfur-modified compound content (mass%) = 100 - {(weight of sulfur-containing material before heating - amount remaining at the end of measurement) / weight of sulfur-containing material before heating} × 100

[0019] <Sulfur-modified acrylic compounds> As the sulfur-modified acrylic compound used in the sulfur-containing material of this disclosure, for example, a compound in which sulfur and an atom in the acrylic compound are covalently bonded can be used. A method for producing such a sulfur-modified acrylic compound is to heat elemental sulfur and the acrylic compound.

[0020] Examples of acrylic compounds in this disclosure include polyacrylonitrile compounds and other acrylic compounds.

[0021] In this disclosure, examples of sulfur-modified acrylic compounds include sulfur-modified polyacrylonitrile compounds and other sulfur-modified acrylic compounds. From the viewpoint of increasing discharge capacity, the sulfur-modified acrylic compound is preferably a sulfur-modified polyacrylonitrile compound.

[0022] The total sulfur content in the sulfur-modified acrylic compound is not particularly limited, but from the viewpoint of further increasing the discharge capacity, it is preferably 20% to 80% by mass, more preferably 25% to 75% by mass, even more preferably 25% to 70% by mass, and most preferably 30% to 70% by mass. Here, the total sulfur content in the sulfur-modified acrylic compound can be calculated from the results of analysis using a CHNS analyzer capable of analyzing sulfur and oxygen.

[0023] <Sulfur-modified polyacrylonitrile compounds> The sulfur-modified polyacrylonitrile compounds in this disclosure can be, for example, compounds in which sulfur and atoms in the polyacrylonitrile compound are covalently bonded. A method for producing such sulfur-modified polyacrylonitrile compounds includes heating elemental sulfur with a polyacrylonitrile compound. Furthermore, the sulfur-modified polyacrylonitrile compounds in this disclosure may include those obtained by heating elemental sulfur with particles in which hydrocarbons are surrounded by an outer shell made of a polyacrylonitrile compound. The contained hydrocarbons can be saturated or unsaturated aliphatic hydrocarbons having 3 to 8 carbon atoms.

[0024] In this disclosure, the polyacrylonitrile compound may contain any constituent units derived from at least one of acrylonitrile and methacrylonitrile. From the viewpoint of increasing discharge capacity, it is preferable that the polyacrylonitrile compound contains at least constituent units derived from acrylonitrile.

[0025] From the viewpoint of increasing discharge capacity, the content of constituent units derived from acrylonitrile and methacrylonitrile is preferably 10 parts by mass or more, and more preferably 30 parts by mass or more, per 100 parts by mass of the polyacrylonitrile compound.

[0026] When a polyacrylonitrile compound contains structural units derived from acrylonitrile, from the viewpoint of increasing discharge capacity, the content of structural units derived from acrylonitrile is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 50 parts by mass or more, even more preferably 80 parts by mass or more, even more preferably 85 parts by mass or more, even more preferably 90 parts by mass or more, even more preferably 95 parts by mass or more, and most preferably 100 parts by mass, i.e., the polyacrylonitrile compound consists only of structural units derived from acrylonitrile.

[0027] When a polyacrylonitrile compound contains constituent units derived from methacrylonitrile, from the viewpoint of increasing discharge capacity, the content of constituent units derived from methacrylonitrile is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 30 parts by mass or more and 95 parts by mass or less, even more preferably 30 parts by mass or more and 90 parts by mass or less, even more preferably 30 parts by mass or more and 85 parts by mass or less, and most preferably 30 parts by mass or more and 80 parts by mass or less.

[0028] Polyacrylonitrile compounds may contain constituent units derived from monomers other than acrylonitrile and methacrylonitrile. Examples of other monomers include acrylic monomers such as (meth)acrylic acid esters, (meth)acrylamide, ethylene glycol (meth)acrylate, 1,6-hexanediol (meth)acrylate, neopentyl glycol di(meth)acrylate, and glycerin di(meth)acrylate; and conjugated dienes such as butadiene and isoprene. Two or more of these other monomers can be used in combination. Here, “(meth)acrylate” represents either “acrylate” or “methacrylate”. “(meth)acrylic” represents either “acrylic” or “methacrylic”.

[0029] When the sulfur-containing material of the present disclosure contains a sulfur-modified polyacrylonitrile-based compound which is preferable as a sulfur-modified compound, the Raman spectrum of the sulfur-containing material of the present disclosure may be any one as long as the sulfur-containing material of the present disclosure can exhibit a desired effect. However, from the viewpoint of increasing the discharge capacity and excellent cycle characteristics, the Raman shift is 1327 cm -1 ±10 cm -1 It is preferable that a peak exists within the range. From the viewpoint of increasing the discharge capacity, as the Raman spectrum of the sulfur-containing material, in addition to the above range of 1327 cm -1 ±10 cm -1 within the range of 1531 cm -1 ±10 cm -1 within the range, 939 cm -1 ±10 cm -1 within the range, 479 cm -1 ±10 cm -1 within the range, 377 cm -1 ±10 cm -1 [[ID=2८]]within the range and 318 cm -1 ±10 cm -1 it is preferable that it has a peak within at least one of the ranges within the range of, and 1531 cm -1 ±10 cm -1 within the range, 939 cm -1 ±10 cm -1 within the range, 479 cm -1 ±10 cm -1 within the range, 377 cm -1 ±10 cm -1 within the range and 318 cm -1 ±10 cm -1 it is more preferable that it has a peak within at least two of the ranges within the range of, and 1531 cm -1 ±10 cm -1 within the range, 939 cm -1 ±10 cm -1 within the range, 479 cm -1 ±10 cm-1 Within the range of 377cm -1 ±10cm -1 Within the range of 318cm -1 ±10cm -1 It is even more preferable that the peaks are located within the entire range.

[0030] From the perspective of increasing discharge capacity, the Raman spectrum of the sulfur-containing material of this disclosure is 1327 cm⁻¹. -1 ±10cm -1 Peak intensity A1 (1327cm) within the range -1 ±10cm -1 The maximum peak within the range, and 300cm -1 From 1800cm -1 (The difference from the smallest peak within the range) and 1531cm -1 ±10cm -1 Peak intensity B1 (1531cm) within the range -1 ±10cm -1 The maximum peak within the range, and 300cm -1 From 1800cm -1 The ratio (A1 / B1) of the difference from the minimum peak within the range is preferably 0.30 to 5.0, more preferably 0.50 to 4.5, even more preferably 0.70 to 4.0, and most preferably 0.80 to 3.5.

[0031] The above Raman spectrum was obtained using a JASCO NRS-3100 (excitation wavelength λ=532nm, grating: 600 l / mm, resolution: 1cm). -1 Measurement can be performed with an exposure time of 30 seconds and a slit width of φ50 μm.

[0032] <Other sulfur-modified acrylic compounds> Other sulfur-modified acrylic compounds in this disclosure include methods of heating elemental sulfur and homopolymers or copolymers of other acrylic monomers that do not contain structural units derived from acrylonitrile or methacrylonitrile. The other acrylic monomers can be the same as those described above as other acrylic monomers in the "sulfur-modified polyacrylonitrile compounds."

[0033] <Sulfur-modified polynuclear aromatic ring compounds> The above-mentioned sulfur-modified polynuclear aromatic ring compound can be, for example, a compound in which sulfur is covalently bonded to an atom in the polynuclear aromatic ring compound. The sulfur-modified polynuclear aromatic ring compound can be produced, for example, by heating a mixture of elemental sulfur and a polynuclear aromatic ring compound as an organic compound. Examples of polynuclear aromatic ring compounds include benzene-based aromatic ring compounds such as naphthalene, anthracene, tetracene, pentacene, phenanthrene, chrysene, picene, pyrene, benzopyrene, perylene, and coronene; aromatic ring compounds in which a portion of the benzene-based aromatic ring compound is a five-membered ring; or heteroatom-containing heteroaromatic ring compounds in which some of the carbon atoms are replaced by sulfur, oxygen, nitrogen, etc. Furthermore, these polynuclear aromatic ring compounds may have substituents such as chain-like or branched alkyl groups, alkoxyl groups, hydroxyl groups, carboxyl groups, amino groups, aminocarbonyl groups, aminothio groups, mercaptothiocarbonylamino groups, and carboxyalkylcarbonyl groups, which have 1 to 12 carbon atoms.

[0034] <Sulfur-modified polyether compounds> As the sulfur-modified polyether compound mentioned above, the same one described in Japanese Patent Publication No. 2022-65974 can be used.

[0035] <Method for manufacturing sulfur-containing materials> In this disclosure, a method for producing a sulfur-containing material can be described as a method having a heating step of heating a mixture of elemental sulfur and an organic compound. The above manufacturing method may also include a mechanochemical treatment step in which a mechanochemical treatment is performed on the heat-treated product after the heating step.

[0036] In the above-mentioned mechanochemical treatment process, mechanochemical treatment refers to a process that generates a chemical reaction by utilizing the high energy locally produced by mechanical energy such as friction and compression during the crushing process of a solid material.

[0037] The above-described mechanochemical treatment can involve applying mechanical energy such as impact, friction, compression, or shear to the heat-treated material, or applying a combination of these. Known equipment can be used for the mechanochemical treatment, including mixing devices such as ball mills, vibratory mills, planetary ball mills, cyclone mills, and media-stirring mills; pulverizers such as ball media mills, roller mills, and mortars; and jet pulverizers that can primarily apply forces such as impact and abrasion to the heat-treated material.

[0038] In this disclosure, from the viewpoint of increasing the discharge capacity, the above device is preferably a mixing device such as a ball mill, vibratory mill, planetary ball mill, cyclone mill, or media-stirring mill, or a grinder such as a ball media mill, roller mill, or mortar and pestle, more preferably a mixing device such as a ball mill, vibratory mill, planetary ball mill, or media-stirring mill, and even more preferably a ball mill, vibratory mill, planetary ball mill, or cyclone mill.

[0039] The environment for mechanochemical treatment may be an oxidizing atmosphere or a non-oxidizing atmosphere, but a non-oxidizing atmosphere is preferred. An oxidizing atmosphere refers to an atmosphere containing oxidizing gases, such as an atmosphere containing oxygen, ozone, or nitrogen dioxide. A non-oxidizing atmosphere refers to an atmosphere that does not contain oxidizing gases, such as an atmosphere consisting of nitrogen or argon.

[0040] In this disclosure, from the viewpoint of increasing discharge capacity, the environment in which the mechanochemical treatment is performed is preferably a non-oxidizing atmosphere consisting of nitrogen or argon, and more preferably a non-oxidizing atmosphere consisting of nitrogen.

[0041] <Electrolytes> The electrode layer of this disclosure contains an electrolyte. The electrolyte is not particularly limited, but known electrolytes can be used. Examples of electrolytes include liquid electrolytes obtained by dissolving a support electrolyte in an organic solvent, polymer gel electrolytes obtained by dissolving a support electrolyte in an organic solvent and gelling it with a polymer, polymer electrolytes obtained by dispersing a support electrolyte in a polymer without containing an organic solvent, and inorganic solid electrolytes. Furthermore, two or more of the above electrolytes may be used in combination. In this disclosure, the electrolyte is preferably a liquid electrolyte or a polymer gel electrolyte, and more preferably a liquid electrolyte, from the viewpoint of increasing the discharge capacity and being easy to manufacture.

[0042] From the viewpoint of further increasing the discharge capacity, the electrolyte content is preferably 1 to 300 parts by mass, more preferably 10 to 200 parts by mass, and most preferably 15 to 150 parts by mass, per 100 parts by mass of the total of the active material and conductive additive.

[0043] In the present disclosure, as the supporting electrolyte used in the liquid electrolyte and the polymer gel electrolyte, in the case of a lithium-ion secondary battery, conventionally known lithium salts are used. Examples of the supporting electrolyte include 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 derivatives thereof. Among these, from the viewpoint of further increasing the discharge capacity, 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.

[0044] From the viewpoint of further increasing the discharge capacity, the content of the supporting electrolyte in the liquid electrolyte or the polymer gel electrolyte is preferably 0.5 mol / L to 7 mol / L, and more preferably 0.8 mol / L to 1.8 mol / L.

[0045] As the supporting electrolyte used in the polymer electrolyte, in the case of a lithium-ion secondary battery, for example, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(SO2F)2, LiC(CF3SO2)3, LiB(CF3SO)4, LiB(C2O4)2 can be mentioned.

[0046] In the present disclosure, as the solid electrolyte, in the case of a lithium-ion secondary battery, for example, Li 1+x A x B 2-x (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+xA 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 (when A = B, Al, Ga, Cr, Fe, 0 < x < 0.4; when 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 halogen 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 Crystals having a perovskite structure with lithium ion conductivity such as LiTiO3; Li7 - La3Zr2O 13 and other crystals having a garnet structure; glasses such as 50Li4SiO4·50Li3BO 33 , 90Li3BO3·10Li2SO4; sulfides such as 70Li2S·30P2S5, 75Li2S·25P2S5, Li6PS5Cl, Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , Li6PS5P 1.44 C l3 、Li 10 GeP2S 12 、Li 3.25 Ge 0.25 P 0.75Lithium phosphorus sulfide crystals such as S4; 30Li2S·26B2S3·44LiI, 50Li2S·17P2S5·33LiBH, 50Li2S·50GeS2, 63Li2S·36SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 70Li2S·50GeS2, and other lithium phosphorus sulfide glasses; Li7P3S 11 Li 3.25 P 0.95 S4, Li 10 GeP2S 12 Li 9.6 P3S 12 Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 Examples include glass ceramics and the like.

[0047] In the case of sodium-ion secondary batteries, a support electrolyte in which lithium atoms are replaced with sodium atoms, as used in lithium-ion secondary batteries as described above, can be used. In the case of potassium-ion secondary batteries, magnesium-ion secondary batteries, calcium-ion secondary batteries, and aluminum-ion secondary batteries, known electrolytes can be used.

[0048] In this disclosure, organic solvents commonly used for liquid electrolytes can be used for liquid electrolytes and polymer gel electrolytes. Specific examples of organic solvents include saturated cyclic carbonate compounds, saturated cyclic ester compounds, sulfoxide compounds, sulfone compounds, amide compounds, saturated linear carbonate compounds, linear ether compounds, cyclic ether compounds, and saturated linear ester compounds. Among these, saturated cyclic carbonate compounds, saturated cyclic ester compounds, sulfoxide compounds, sulfone compounds, and amide compounds are preferred, with saturated cyclic carbonate compounds being more preferred, from the viewpoint of having a high dielectric constant that increases the dielectric constant of the electrolyte and further increases the discharge capacity. Furthermore, saturated linear carbonate compounds, linear ether compounds, cyclic ether compounds, and saturated linear ester compounds are preferred, with saturated linear carbonate compounds being more preferred, from the viewpoint of being able to lower the viscosity of the electrolyte and improve the mobility of electrolyte ions, thereby improving battery characteristics such as power density.

[0049] Examples of the saturated cyclic carbonate compounds mentioned above include ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, 1,2-propylene carbonate, 1,3-propylene carbonate, 1,2-butylene carbonate, 1,3-butylene carbonate, and 1,1-dimethylethylene carbonate.

[0050] Examples of the saturated cyclic ester compounds mentioned above include γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-hexanolactone, and δ-octanolactone.

[0051] Examples of the above sulfoxide compounds include dimethyl sulfoxide, diethyl sulfoxide, dipropyl sulfoxide, diphenyl sulfoxide, and thiophene.

[0052] Examples of the above sulfone compounds include dimethyl sulfone, diethyl sulfone, dipropyl sulfone, diphenyl sulfone, sulfolane (also called tetramethylene sulfone), 3-methylsulfolane, 3,4-dimethylsulfolane, 3,4-diphenylmethylsulfolane, sulfolene, 3-methylsulfolene, 3-ethylsulfolene, and 3-bromomethylsulfolene. Among these, sulfolane and tetramethylsulfolane are preferred from the viewpoint of increasing discharge capacity.

[0053] Examples of the above-mentioned amide compounds include N-methylpyrrolidone, dimethylformamide, and dimethylacetamide.

[0054] Examples of the saturated chain carbonate compounds mentioned above include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl butyl carbonate, methyl-t-butyl carbonate, diisopropyl carbonate, and t-butylpropyl carbonate.

[0055] Examples of the above-mentioned linear ether compounds and cyclic ether compounds include dimethoxyethane, ethoxymethoxyethane, diethoxyethane, tetrahydrofuran, 2-methylfuran, 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, and glymes. Among these, dioxolane and glymes are preferred from the viewpoint of further increasing discharge capacity.

[0056] Examples of the saturated chain ester compounds mentioned above include monoester compounds and diester compounds having a total of 2 to 8 carbon atoms in the molecule. Specific examples of saturated chain ester compounds include methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isobutyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, ethyl trimethylacetate, methyl malonate, ethyl malonate, methyl succinate, ethyl succinate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, ethylene glycol diacetyl, propylene glycol diacetyl, and the like. Among these, methyl formate, ethyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isobutyl acetate, butyl acetate, methyl propionate, and ethyl propionate are preferred from the viewpoint of increasing discharge capacity.

[0057] Other organic solvents that can be used in the preparation of electrolytes include, for example, acetonitrile, propionitrile, nitromethane and their derivatives, and various ionic liquids.

[0058] Examples of polymers used in polymer gel electrolytes include polyethylene oxide, polypropylene oxide, polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate, polyethylene, polyvinylidene fluoride, and polyhexafluoropropylene. There are no particular restrictions on the blending ratio of polymers in the polymer gel electrolyte or the gelation method; known blending ratios and known gelation methods in this art can be adopted.

[0059] Examples of polymers used in polymer electrolytes include polyethylene oxide, polypropylene oxide, polystyrene sulfonic acid, and polyvinylidene fluoride. There are no particular restrictions on the blending ratio of polymers in the polymer electrolyte or the method of compounding; known blending ratios and known compounding methods in this art can be adopted.

[0060] The electrolyte may contain other known additives, such as electrode film-forming agents, antioxidants, flame retardants, and overcharge prevention agents, to improve battery life and safety. From the viewpoint of further increasing discharge capacity, the content of other additives is usually 0.01 to 10 parts by mass, and preferably 0.1 to 5 parts by mass, per 100 parts by mass of electrolyte.

[0061] <Other ingredients> The electrode layer of this disclosure contains a sulfur-containing material and an electrolyte, but may contain other components as needed. When the above electrode layer is used as a positive electrode active material layer or a negative electrode active material layer, other components include binders and conductive additives, and may also contain active materials other than sulfur-containing materials, viscosity modifiers, reinforcing materials, antioxidants, etc., as needed.

[0062] <Binding agent> The electrode layer of this disclosure contains 0 to 30 parts by mass of a binder per 100 parts by mass of sulfur-containing material in the electrode layer.

[0063] The binders used in this disclosure may be those known as binders for electrode layers. Examples of binders include styrene-butadiene rubber, butadiene rubber, polyethylene, polypropylene, polyamide, polyamide-imide, polyimide, polyacrylonitrile, polyurethane, polyvinylidene fluoride, polytetrafluoroethylene, ethylene-propylene-diene rubber, fluororubber, styrene-acrylic acid copolymer, ethylene-vinyl alcohol copolymer, acrylonitrile butadiene rubber, styrene-isoprene rubber, polymethyl methacrylate, polyacrylate, polyvinyl alcohol, polyvinyl ether, carboxymethylcellulose, sodium carboxymethylcellulose, methylcellulose, cellulose nanofiber, polyethylene oxide, starch, polyvinylpyrrolidone, polyvinyl chloride, and polyacrylic acid. Only one binder may be used, or two or more may be used in combination. Among these, styrene-butadiene rubber, sodium carboxymethylcellulose, and polyacrylic acid are more preferred from the viewpoint of excellent binding properties.

[0064] <Conductive additive> As the conductive additive mentioned above, those known as conductive additives for electrode layers can be used. Examples of conductive additives include carbon materials such as natural graphite, artificial graphite, carbon black, Ketjenblack, acetylene black, channel black, furnace black, lamp black, thermal black, carbon nanotubes, vapor-grown carbon fiber (VGCF), single-wall carbon nanotubes, multi-wall carbon nanotubes, graphene, flake graphite, fullerene, and needle coke; metal powders such as aluminum powder, nickel powder, and titanium powder; conductive metal oxides such as zinc oxide and titanium oxide; and sulfides such as La2S3, Sm2S3, Ce2S3, and TiS2. From the viewpoint of increasing discharge capacity, preferred conductive additives include single-wall carbon nanotubes, multi-wall carbon nanotubes, carbon black, Ketjenblack, acetylene black, furnace black, graphene, and flaked graphite, with graphene and flaked graphite being more preferred. Only one conductive additive may be used, or two or more may be used in combination.

[0065] The average particle diameter of the conductive additive is preferably 0.01 μm to 100 μm, and more preferably 0.01 μm to 50 μm, from the viewpoint of increasing the discharge capacity. In this disclosure, "average particle diameter" refers to the 50% particle diameter measured by laser diffraction scattering. In laser diffraction scattering, the particle diameter is the volume-based diameter, and the secondary particle diameter of the object being measured is measured. When measuring the average particle diameter by laser diffraction scattering, the object being measured is dispersed in a dispersion medium such as water before measurement.

[0066] From the viewpoint of increasing discharge capacity, the content of the conductive additive in the electrode layer is preferably 0.01 to 50 parts by mass, more preferably 0.05 to 20 parts by mass, even more preferably 0.1 to 10 parts by mass, and most preferably 0.15 to 8.0 parts by mass, per 100 parts by mass of the sulfur-containing material in the electrode layer.

[0067] In the present disclosure, exfoliated graphite refers to a substance in which graphitic materials are exfoliated, and means a substance having a layered structure in which 1 to several thousand layers of unit layers of graphite are stacked. Graphitic materials are layered compounds having unit layers composed of carbon. Graphitic materials include, in addition to graphite, expanded graphite in which the interlayer of graphite is expanded, and oxidized graphite obtained by oxidizing graphite with an oxidizing agent.

[0068] In the present disclosure, the average thickness of exfoliated graphite is 10 nm to 200 nm. When the average thickness is less than 10 nm or greater than 200 nm, the dispersibility in the electrode may decrease. The average thickness of exfoliated graphite is preferably 20 nm to 100 nm, more preferably 25 nm to 50 nm, and most preferably 30 nm to 40 nm.

[0069] In the present disclosure, the thickness of exfoliated graphite is the thickness in the direction perpendicular to the laminated surface of exfoliated graphite, and the average thickness of exfoliated graphite is the average value of the thicknesses of any 30 or more exfoliated graphite. The thickness of exfoliated graphite can be measured, for example, using a SEM image obtained by photographing exfoliated graphite with a scanning electron microscope (SEM). Note that exfoliated graphite composed of a single unit layer is called graphene, and the thickness is theoretically about 0.335 nm.

[0070] In the present disclosure, the specific surface area of exfoliated graphite is 10 m 2 / g to 40 m 2 / g. In the present invention, the specific surface area of exfoliated graphite is a measured value by the BET method and is measured in accordance with JIS Z8830 (Method for measuring specific surface area of powder (solid) by gas adsorption). When the specific surface area of exfoliated graphite is less than 10 m 2 / g or greater than 40 m 2 / g, the dispersibility in the electrode may decrease. The specific surface area of exfoliated graphite is preferably 12 m 2 / g to 30 m 2 / g, and more preferably 15 m 2 / g to 20 m 2 / g.

[0071] In this disclosure, the bulk density of the flake graphite is 0.05 g / cm³. 3 ~0.3g / cm 3 In this invention, the bulk density of the flake graphite is measured in accordance with JIS K1469 (Acetylene Black for Batteries). The bulk density of the flake graphite is 0.05 g / cm³. 3 If it is smaller than or equal to 0.3 g / cm³ 3 If the value is greater than this, the dispersibility in the electrode may decrease. The bulk density of the flake graphite is 0.055 g / cm³. 3 ~0.2g / cm 3 Preferably, it is 0.06 g / cm³. 3 ~0.1g / cm 3 It is even more preferable that this be the case.

[0072] <Other> In this disclosure, as an active material other than sulfur-containing material (hereinafter sometimes referred to as "other active material"), known active materials can be used, for example, the positive electrode active material and negative electrode active material described in "B. Battery" below can be used.

[0073] In this disclosure, viscosity modifiers known as viscosity modifiers for electrode layers can be used. Examples of viscosity modifiers include cellulosic polymers such as carboxymethylcellulose, methylcellulose, and hydroxypropylcellulose, and their ammonium salts and alkali metal salts; (modified) poly(meth)acrylic acid and its ammonium salts and alkali metal salts; (modified) polyvinyl alcohols such as acrylic acid or copolymers of acrylic acid and vinyl alcohol, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, modified polyacrylic acid, starch oxide, starch phosphate, casein, various modified starches, cellulose nanofibers, acrylonitrile-butadiene copolymer hydrogenates, etc. These may also be used as dispersants.

[0074] In this disclosure, known reinforcing materials for electrode layers can be used as the reinforcing material. Examples of reinforcing materials include various inorganic and organic spherical, plate-shaped, rod-shaped, or fibrous fillers.

[0075] In this disclosure, known antioxidants for electrode layers can be used as antioxidants. Examples of antioxidants include phenol compounds, hydroquinone compounds, organophosphorus compounds, sulfur compounds, phenylenediamine compounds, polymer-type phenol compounds, and the like.

[0076] The method for forming the electrode layer according to this disclosure can be any method capable of forming the electrode layer, for example, by applying an electrode layer forming composition containing the sulfur-containing material, electrolyte, and other components as needed to a current collector and drying it as appropriate. The electrode layer forming composition may also contain a solvent as needed.

[0077] Examples of solvents used in electrode layer forming compositions include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl 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, diethyltriamine, N,N-dimethylaminopropylamine, polyethylene oxide, tetrahydrofuran, dimethyl sulfoxide, sulfolane, γ-butyrolactone, water, and alcohol. The amount of solvent used can be adjusted according to the coating method.

[0078] There are no particular limitations on the method for preparing the electrode layer forming composition, but examples include mixing the above-mentioned sulfur-containing material or sulfur-containing battery material, other components as needed, and a solvent using a conventional ball mill, sand mill, bead mill, pigment disperser, lye crusher, ultrasonic disperser, homogenizer, rotation / revolution mixer, planetary mixer, film mixer, disper, jet paster, etc. In the preparation, it is preferable to prepare the composition in a low dew point environment or an inert atmosphere that can keep the electrolyte stable.

[0079] The coating method is not particularly limited, and can be applied to, for example, a current collector using various methods such as die coating, comma coating, curtain coating, spray coating, gravure coating, flexo coating, knife coating, doctor blade coating, reverse roll coating, brush coating, and dipping. From the viewpoint of obtaining a good surface condition of the coating film in accordance with the physical properties such as viscosity of the electrode layer forming composition, die coating, doctor blade coating, knife coating, comma coating, or dipping is preferred. For coating, it is preferable to coat in a low dew point environment or an inert atmosphere in which the electrolyte can be kept stable.

[0080] Drying to remove some of the solvent from the electrolyte contained in the electrode layer may or may not be performed after coating. If drying is performed, the drying method is not particularly limited and can be natural drying, heating, reduced pressure, or a combination of these methods. The heating temperature can be 30°C to 100°C. As for the heating and reduced pressure equipment, heating furnaces, infrared heating furnaces, vacuum ovens, etc. can be used.

[0081] The electrode layer may be press-treated as needed. Examples of pressing methods include die pressing and roll pressing.

[0082] <Current collector> The electrode of this disclosure has a porous metal current collector. In this disclosure, a porous metal current collector is any current collector having voids, such as conductive materials with voids, including titanium, titanium alloys, aluminum, aluminum alloys, copper, nickel, stainless steel, nickel-plated steel, and conductive resins. These conductive materials may have their surfaces coated with carbon or metal. This also includes insulating resins with metal coatings on their surfaces that have voids.

[0083] Examples of current collector shapes include foil, plate, and mesh. Among these, aluminum with voids is preferred from the viewpoint of conductivity and cost, and more preferably aluminum with voids in the form of foil, plate, or mesh. When the current collector is made of aluminum, its thickness is preferably 1 μm to 3000 μm from the viewpoint of increasing the discharge capacity and being easy to manufacture.

[0084] In secondary battery electrodes, the surface of the current collector may be surface-treated or coated with carbon or the like to improve adhesion and electrical characteristics. However, in the current collector of the present invention, the current collector includes the surface treatment layer and coating layer.

[0085] <Application> The applications of the electrodes of this disclosure are not particularly limited, but batteries are one example. Examples of batteries include primary batteries and secondary batteries. Examples of secondary batteries include lithium-ion secondary batteries, sodium-ion secondary batteries, potassium-ion secondary batteries, magnesium-ion secondary batteries, calcium-ion secondary batteries, and aluminum-ion secondary batteries. That is, lithium-sulfur secondary batteries, sodium-sulfur secondary batteries, potassium-sulfur secondary batteries, magnesium-sulfur secondary batteries, calcium-sulfur secondary batteries, and aluminum-sulfur secondary batteries are also possible.

[0086] From a practical standpoint, the electrodes of this disclosure are preferably used as electrodes for lithium-ion primary batteries, lithium-sulfur primary batteries, lithium-ion secondary batteries, and lithium-sulfur secondary batteries, and more preferably as electrodes for lithium-ion secondary batteries and lithium-sulfur secondary batteries. The electrodes of this disclosure can be used as either positive or negative electrodes, but are preferably used as positive electrodes from the viewpoint of increasing discharge capacity and being easier to manufacture.

[0087] Furthermore, when the above electrodes are used as electrodes for a lithium-ion secondary battery, a pre-doping process involving the insertion of lithium may be performed beforehand. The lithium pre-doping method can follow any known method, such as the electrolytic doping method, which involves assembling a half-cell using metallic lithium as the counter electrode and electrochemically doping it with lithium, or the diffusion doping method, which involves attaching metallic lithium foil to the electrode and leaving it in a liquid electrolyte, utilizing the diffusion of lithium into the electrode.

[0088] Furthermore, when the above electrodes are used as electrodes for a sodium-ion secondary battery, a pre-doping process involving the insertion of sodium may be performed beforehand. Any known method can be used for sodium pre-doping; for example, the doping method described above can be used.

[0089] In this disclosure, the electrodes may be pressed as necessary. Examples of pressing methods include die pressing and roll pressing.

[0090] <Other> The basis weight of the electrode layer in this disclosure is 3 mg / cm², which allows the battery characteristics to be fully realized. 2 ~200 mg / cm³ 2 Preferably, it is 5 mg / cm³ 2 ~100mg / cm 2 It is even more preferable that this be the case.

[0091] In this disclosure, the basis weight of the electrode layer refers to the mass per unit area, and assuming the porosity is the same, a larger basis weight indicates a thicker electrode layer.

[0092] In this disclosure, the electrode layer may be present on one side of the current collector or on both sides.

[0093] B.Battery 1. Electrode The battery of this disclosure has the electrodes described in section "A. Electrodes" above, but may have other configurations as needed.

[0094] The battery described herein has a large discharge capacity and excellent cycle characteristics.

[0095] 2. Other components Other components include a counter electrode used in conjunction with the above-mentioned electrode, an electrolyte, a separator, etc.

[0096] <Counter electrode> The counter electrode is an electrode used in conjunction with the electrode mentioned above. If the electrode is the positive electrode, the counter electrode is the negative electrode. If the electrode is the negative electrode, the counter electrode is the positive electrode. The positive and negative electrodes used as counter electrodes for the above electrodes will be described below.

[0097] <Negative electrode> As the counter electrode used above, a negative electrode having a negative electrode active material layer can be used. As the above-mentioned negative electrode active material layer, one containing at least a known active material (hereinafter sometimes referred to as "negative electrode active material") can be used.

[0098] In the case of lithium-ion secondary batteries, examples of negative electrode active materials include natural graphite, artificial graphite, non-graphitizable carbon, easily graphitizable carbon, lithium, lithium alloys, silicon, silicon alloys, silicon oxide, silicon carbide, tin, tin alloys, 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, as well as LiVO2, Li2VO4, Li4Ti5O 12Examples of composite oxides include the following. The negative electrode active material may be a single type or a combination of two or more types.

[0099] In the case of sodium-ion secondary batteries, among the negative electrode active materials used in lithium-ion secondary batteries as described above, negative electrode active materials that do not contain lithium atoms, and negative electrode active materials in which lithium atoms are replaced with sodium atoms can be used. Furthermore, if the negative electrode active material is lithium or a lithium alloy, or sodium or a sodium alloy, the electrode itself may be used without using a current collector. In addition, potassium, magnesium, calcium, aluminum, zinc, etc. can be used as other negative electrode active materials.

[0100] The above-mentioned negative electrode active material layer contains the above-mentioned negative electrode active material, but may also contain, if necessary, a binder, a conductive additive, etc. The binder and conductive additive used in the negative electrode active material layer described above can be the same as those described in section "A. Electrode" above, so a detailed explanation is omitted here. The surface of the negative electrode active material layer may be coated with ceramic material, resin, solid electrolyte, conductive additive, etc.

[0101] <Positive electrode> As the positive electrode used as the counter electrode mentioned above, one having a positive electrode active material layer can be used. As the positive electrode active material layer mentioned above, one containing at least a known active material (hereinafter sometimes referred to as "positive electrode active material") can be used. Examples of the above-mentioned positive electrode active materials include lithium transition metal composite oxides, lithium-containing transition metal phosphate compounds, and lithium-containing silicate compounds. The positive electrode active material may be used alone or in combination of two or more types.

[0102] Examples of transition metals in the above-mentioned lithium transition metal composite oxides include vanadium, titanium, chromium, manganese, iron, cobalt, nickel, and copper. Specific examples of lithium transition metal composite oxides include lithium cobalt composite oxides such as LiCoO2, lithium nickel composite oxides such as LiNiO2, lithium manganese composite oxides such as LiMnO2, LiMn2O4, and Li2MnO3, and those in which some of the main transition metal atoms are replaced with other metals such as aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, lithium, nickel, copper, zinc, magnesium, gallium, and zirconium. Specific examples of lithium transition metal composite oxides in which some of the main transition metal atoms are replaced with other metals include, for example, Li 1.1 Mn 1.8 Mg 0.1 O4, Li 1.1 Mn 1.85 Al 0.05 O4, LiSa 0.5 Co 0.2 Mn 0.3 O2, LiLiLi 0.8 Co 0.1 Mn 0.1 O2, LiLiLi 0.5 Mn 0.5 O2, LiLiLi 0.80 Co 0.17 Al 0.03 O2, LiLiLi 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, LiSa 0.5 Mn 1.5 Examples include O4, Li2MnO3-LiMO2 (M=Co,Ni,Mn), etc.

[0103] Examples of the transition metal in the lithium-containing transition metal phosphate compound include vanadium, titanium, manganese, iron, cobalt, nickel, etc. Specific examples of the lithium-containing transition metal phosphate compound include, for example, iron phosphate compounds such as LiFePO4, LiMn x Fe 1-x PO4 (0 < x < 1), iron sulfate compounds such as LiFeSO4F, cobalt phosphate compounds such as LiCoPO4, and those obtained by substituting part of the transition metal atoms that are the main components of these lithium transition metal phosphate compounds with other metals such as aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, lithium, nickel, copper, zinc, magnesium, gallium, zirconium, niobium, etc., and vanadium phosphate compounds such as Li3V2(PO4)3.

[0104] Examples of the lithium-containing silicate compound include Li2FeSiO4.

[0105] The above positive electrode active material layer contains the above-known active materials, but may contain, for example, a binder, a conductive aid, etc. as required. Regarding the binder and the conductive aid used in the above positive electrode active material layer, the same ones as those described in the section of "A. Electrode" above can be used, so the description here will be omitted.

[0106] <Electrolyte> As the above electrolyte, the same ones as those described in the section of "A. Electrode" above can be used.

[0107] (1 - 3) Separator The above-mentioned separator can be any material that allows lithium ions to pass through and prevents contact between the positive and negative electrodes, and is not particularly limited. For example, a microporous polymer film, nonwoven fabric, or ion-conducting film can be used. Examples of films include polymer compounds and their derivatives mainly composed of 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 carboxymethylcellulose and hydroxypropylcellulose, poly(meth)acrylic acid and its various esters, copolymers and mixtures thereof, etc. These films may be coated with ceramic materials such as alumina and silica, or with magnesium oxide, aramid resin, or polyvinylidene fluoride.

[0108] These films may be used individually or layered to form a multilayer film. Furthermore, various additives may be used in these films, and their type and content are not particularly limited. Among these films, films made of polyethylene, polypropylene, polyvinylidene fluoride, or polysulfone are preferred from the viewpoint of further increasing the discharge capacity of the secondary battery.

[0109] <Other> In this disclosure, the shape of the battery is not particularly limited and can be various shapes such as coin-type, cylindrical, prismatic, laminated, etc.

[0110] As the outer casing material for the battery, laminate film or a metal container can be used. The thickness of the outer casing material is usually 0.5 mm or less, preferably 0.3 mm or less. Examples of outer casing material shapes include flat (thin), rectangular, cylindrical, coin-shaped, and button-shaped.

[0111] As the laminate film, a multilayer film having a metal layer between resin films can also be used. For weight reduction, aluminum foil or aluminum alloy foil is preferred for the metal layer. The resin film can be a polymer material such as polypropylene, polyethylene, nylon, or polyethylene terephthalate. The laminate film can be sealed by heat fusion to form the shape of the exterior component. Metal containers can be formed from, for example, stainless steel, aluminum, or aluminum alloys. As aluminum alloys, alloys containing elements such as magnesium, zinc, and silicon are preferred. By reducing the content of transition metals such as iron, copper, nickel, and chromium in aluminum or aluminum alloys to 1% by mass or less, long-term reliability and heat dissipation in high-temperature environments can be dramatically improved.

[0112] <About Batteries> The battery described herein may be either a primary battery or a secondary battery, but it is preferably a secondary battery because it is useful as an in-vehicle battery. [Examples]

[0113] The present invention will be described in further detail below with reference to examples and comparative examples. However, the present invention is not limited in any way by the following examples. In the examples, "parts" and "%" refer to mass unless otherwise specified. The sulfur content was calculated from the results of analysis using a CHNS analyzer capable of analyzing sulfur and oxygen.

[0114] [Manufacturing of sulfur-containing material A] A heat-resistant glass tube with an outer diameter of 10 mm and an inner diameter of 6 mm was heated and expanded in the center to create a volumetric pipette-type glass furnace tube with an expanded section in the center with an outer diameter of 30 mm and a length of 50 mm, and thin tubes with an outer diameter of 10 mm and a length of 150 mm at both ends. Five g of a raw material PAN mixture, prepared by mixing polyacrylonitrile powder (Sigma-Aldrich, average particle size 200 μm, weight-average molecular weight: approximately 150,000) and sulfur powder (Sigma-Aldrich, average particle size 200 μm) in a weight ratio of 1:3, was placed in the expansion section of the reactor tube. The reactor tube was then positioned at a 15° incline, and after purging the inside of the reactor tube with nitrogen gas, it was heated at 300°C for 15 minutes while rotating at 3 rotations per minute to obtain the intermediate product. During heating, nitrogen gas was supplied from the lower end of the reactor tube at a flow rate of 100 ml / min so that the generated hydrogen sulfide gas could be discharged from the upper end of the reactor tube. In addition, although the entire expansion section of the reactor tube was heated, sulfur that sublimated and adhered to the narrow tube section was heated as needed to dissolve it and refluxed back into the expansion section. The obtained intermediate product was placed in a glass tube oven and heated at 260°C for 1 hour under vacuum suction to remove elemental sulfur. The obtained sulfur-modified compound was pulverized using a ball mill, and then coarse particles were removed using a sieve with a mesh size of 40 μm to obtain sulfur-containing material A with an average particle size of 10 μm. The total sulfur content of sulfur-containing material A was 49% by mass, and the elemental sulfur content in sulfur-containing material A was 0% by mass.

[0115] [Total sulfur content] The total sulfur content (mass%) in the sulfur-containing materials obtained in the examples and comparative examples was calculated from the results of analysis using a CHNS analyzer (Elementar Analysensysteme GmbH, model: varioMICROcube) capable of analyzing sulfur and oxygen. The combustion tube temperature was 1150°C, the reduction tube temperature was 850°C, and a tin boat was used as the sample container. The elemental sulfur content was measured using thermogravimetric analysis. Specifically, using a thermal analyzer (Hitachi High-Tech Science Corporation, model: STA7300), the weight change was measured until the temperature reached 350°C, with the heating start temperature set to 100°C or lower and the heating rate set to a constant rate of 10°C / min. The elemental sulfur content (mass%) in the sulfur-containing material was calculated from the remaining amount at the end of the measurement according to the following formula. The amount of elemental sulfur (mass %) = 100 - {(weight of sulfur-containing material before heating - change in weight at the end of measurement) / weight of sulfur-containing material before heating} × 100

[0116] Secondary batteries were fabricated using the sulfur-containing materials obtained in the examples and comparative examples. (Preparation of liquid electrolytes) Liquid electrolyte A was prepared by dissolving LiPF6 at a concentration of 1.5 mol / L in a mixed solvent consisting of 50% by volume of ethylene carbonate and 50% by volume of diethyl carbonate.

[0117] (Manufacturing Example 1) In accordance with Experimental Example 1 of International Publication No. 2016 / 148252, flaked graphite A was prepared from natural graphite. Specifically, 74 parts of 1-butyl-3-methylimidazolium hexafluorophosphate and 26 parts of polyethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, product name: polyethylene glycol 20000) were mixed, heated and dissolved, and 10 parts of natural graphite (manufactured by Fujifilm Wako Pure Chemical Industries) were dispersed. 0.6 g of this dispersion was then divided into 0.5 cm 3 The dispersion was collected in vials, capped, and then irradiated with 2450 MHz microwaves at 165°C for 30 minutes using a microwave synthesis device (Initiator+, manufactured by Biotage Japan). After this, the dispersion was washed with acetone, filtered, and then heated and dried in an oven to obtain flaked graphite A. The average thickness of flaked graphite A was 63 nm, and the specific surface area was 17 m². 2 It was / g.

[0118] (Manufacturing example 2) In Manufacturing Example 1, the procedure was the same as in Manufacturing Example 2, except that the microwave irradiation was changed from 165°C for 30 minutes to 200°C for 30 minutes, to obtain flaked graphite B. The average thickness of flaked graphite B was 25 nm, and the specific surface area was 26 m². 2 It was / g.

[0119] (1) Preparation of the positive electrode In the mass portion described in the electrode layer preparation process in Table 1, the components were mixed using a rotation / revolution mixer to prepare the respective electrode layer forming compositions. Under the conditions shown in the electrode fabrication process in Table 2, each electrode molding composition in Table 1 was applied to the current collector using the doctor blade method. At this time, the basis weight of the electrode layer was 25 mg / cm². 2 (If both sides are coated, 50 mg / cm²) 2 The electrode was coated to achieve the following result. Subsequently, this electrode was cut to a predetermined size, and a disc-shaped positive electrode was prepared. In the positive electrode prepared in this study, the binder content in the electrode layer was 0 parts by mass per 100 parts by mass of sulfur-containing material in the electrode layer.

[0120] (2) Preparation of the negative electrode A 500 μm thick lithium metal sheet was cut to a predetermined size to prepare a disc-shaped negative electrode.

[0121] (3) Manufacturing of secondary batteries The previously prepared positive and negative electrodes were placed in a coin-type rechargeable battery (φ20mm, thickness 3.2mm) with a glass filter acting as a separator in between. Then, the previously prepared electrolyte solution A was injected into the coin-type rechargeable battery, the case was sealed, and each coin-type rechargeable battery was fabricated. The fabrication procedures (1) to (3) were carried out in an atmosphere with a dew point of -70°C.

[0122] (4) Evaluation method The secondary battery prepared as described above was placed in a constant temperature bath at 25°C, with a charge termination voltage of 3.0V and a discharge termination voltage of 1.0V. A charge-discharge cycle of 30 cycles was performed at a charge rate of 0.1C and a discharge rate of 0.1C. The discharge capacity (mAh / g) was measured at the 5th and 30th cycles. The ratio of the discharge capacity at the 30th cycle to the discharge capacity at the 5th cycle was defined as the capacity retention rate (%), and the cycle characteristics were evaluated. The results are shown in Table 2. In this disclosure, "g" in discharge capacity (mAh / g) represents the mass of the active material in the positive electrode active material layer.

[0123] [Table 1]

[0124] [Table 2]

Claims

1. An electrode having a porous metal current collector and an electrode layer, The electrode layer comprises an active material and an electrolyte, The active material consists of a sulfur-containing material, An electrode characterized in that the sulfur-containing material contains a sulfur-modified compound.

2. The electrode according to claim 1, wherein the material of the porous metal current collector is aluminum.

3. The electrode according to claim 1 or 2, wherein the sulfur-modified compound is a sulfur-modified acrylic compound.

4. The electrode according to claim 3, wherein the sulfur-modified acrylic compound is a sulfur-modified polyacrylonitrile compound.

5. The electrode according to claim 3, characterized in that the amount of binder in the electrode layer is 0 parts by mass per 100 parts by mass of sulfur-containing material.

6. A secondary battery having the electrode described in any one of claims 1 to 5 as the positive electrode.

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