Manufacturing method of lithium ion secondary battery

Abstract

To provide a manufacturing method of a lithium ion secondary battery having an increased discharge capacity, excellent cycle characteristics, and light weight.SOLUTION: The present disclosure is a manufacturing method of a lithium ion secondary battery, including: a charge / discharge treatment step of performing a charge / discharge treatment on a first lithium ion secondary battery including a positive electrode having a positive electrode active material layer including a sulfur-modified compound, a first liquid electrolyte, and a negative electrode; and a replacement step of replacing the first liquid electrolyte with a second liquid electrolyte to obtain a second lithium ion secondary battery after the charge / discharge treatment step. In the manufacturing method of the lithium ion secondary battery, the first liquid electrolyte comprises a solvent selected from a group consisting of a saturated cyclic carbonate compound and a saturated chain carbonate compound, the second liquid electrolyte comprises a solvent selected from the group consisting of saturated cyclic ether compounds and saturated chain ether compounds.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a lithium-ion secondary battery. [Background technology]

[0002] Lithium ion secondary batteries are used for a variety of purposes. The characteristics of lithium ion secondary batteries depend on their constituent materials, such as electrodes, separators, and electrolytes, and research and development of each of these components is being actively conducted. In the positive electrode, the active material in the positive electrode active material layer is important, along with binders, conductive additives, current collectors, and the like, and research and development is being actively conducted. For example, sulfur-modified polyacrylonitrile compounds are known as active materials (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-153296 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-099342 [Non-patent literature]

[0004] [Non-Patent Document 1] Energies 2014,7,4588-4600 Summary of the Invention [Problem to be solved by the invention]

[0005] There is a demand for active materials capable of forming lithium ion secondary batteries with increased discharge capacity and excellent cycle characteristics. Furthermore, lithium ion secondary batteries for general use, such as electronic devices and transportation equipment, are required to be lightweight. However, the lithium ion secondary batteries of Patent Documents 1 and 2 use a mixed solvent of ethylene carbonate and diethyl carbonate in the liquid electrolyte, which is likely to result in a problem of a large battery mass due to the high density of the liquid electrolyte.

[0006] The present disclosure has been made in consideration of the above problems, and has as its main object to provide a method for manufacturing a lithium ion secondary battery that has increased discharge capacity, excellent cycle characteristics, and is lightweight. In the present disclosure, the term "cycle characteristics" refers to the ability of a lithium-ion secondary battery to maintain its charge / discharge capacity even after repeated charge / discharge. Therefore, a lithium-ion secondary battery that experiences a large decrease in charge / discharge capacity and a low capacity retention rate with repeated charge / discharge cycles has poor cycle characteristics, whereas a lithium-ion secondary battery that experiences a small decrease in charge / discharge capacity and a high capacity retention rate has excellent cycle characteristics. [Means for solving the problem]

[0007] As a result of extensive research, the present inventors have found that a method for manufacturing a lithium ion secondary battery that satisfies certain conditions can solve the above-mentioned problems.

[0008] That is, the present disclosure provides a method for manufacturing a lithium ion secondary battery, a charge-discharge treatment step of charging and discharging a first lithium ion secondary battery including a positive electrode having a positive electrode active material layer containing a sulfur-modified compound, a first liquid electrolyte, and a negative electrode; and an exchange step of exchanging the first liquid electrolyte with a second liquid electrolyte to obtain a second lithium ion secondary battery after the charge / discharge treatment step, the first liquid electrolyte contains a solvent selected from the group consisting of saturated cyclic carbonate compounds and saturated chain carbonate compounds; The method for producing a lithium ion secondary battery is characterized in that the second liquid electrolyte contains a solvent selected from the group consisting of saturated cyclic ether compounds and saturated chain ether compounds.

[0009] In the present disclosure, the sulfur-modified compound is preferably a sulfur-modified acrylic compound.

[0010] In the present disclosure, the sulfur-modified acrylic compound is preferably a sulfur-modified polyacrylonitrile compound.

[0011] In the present disclosure, the sulfur content of the sulfur-modified compound is preferably within the range of 10% by mass to 80% by mass.

[0012] In the present disclosure, the density of the first liquid electrolyte at 25°C is 1.21 g / cm 3 ~1.60g / cm 3 and the density of the second liquid electrolyte at 25°C is within the range of 0.80 g / cm 3 ~1.20g / cm 3 It is preferable that the range is within the range of

[0013] In the present disclosure, the charge / discharge treatment step is carried out at a discharge end potential of the positive electrode of 0.3 V (Li + / Li)~1.8V(Li + Discharge was performed under the condition that the end-of-charge potential of the positive electrode was 2.0 V (Li + / Li)~4.3V(Li + It is preferable to charge under the condition that the charge is 0.1 W / Li. [Effects of the Invention]

[0014] According to the present disclosure, it is possible to provide a method for producing a lithium ion secondary battery that has increased discharge capacity, excellent cycle characteristics, and is lightweight. DETAILED DESCRIPTION OF THE INVENTION

[0015] The method for manufacturing a lithium ion secondary battery according to the present disclosure will now be described in detail.

[0016] A. Manufacturing method of lithium-ion secondary battery The method for producing a lithium ion secondary battery of the present disclosure includes a charge / discharge treatment step of charging / discharging a first lithium ion secondary battery including a positive electrode having a positive electrode active material layer containing a sulfur-modified compound, a first liquid electrolyte, and a negative electrode, and an exchange step of exchanging the first liquid electrolyte with a second liquid electrolyte to obtain a second lithium ion secondary battery after the charge / discharge treatment step, wherein the first liquid electrolyte contains a solvent selected from the group consisting of saturated cyclic carbonate compounds and saturated chain carbonate compounds, and the second liquid electrolyte contains a solvent selected from the group consisting of saturated cyclic ether compounds and saturated chain ether compounds.

[0017] Generally, in lithium-ion secondary batteries that use a liquid electrolyte, the mass of the liquid electrolyte accounts for 20% or more of the mass of the lithium-ion secondary battery. One method for reducing the weight of a lithium-ion secondary battery is to use a liquid electrolyte with a low density. An example of a liquid electrolyte with a low density is a liquid electrolyte containing a solvent selected from the group consisting of saturated cyclic ether compounds and saturated chain ether compounds. However, as shown in Non-Patent Document 1, it has been found that lithium-ion secondary batteries that contain a sulfur-modified compound as a positive electrode active material and use a liquid electrolyte containing a solvent selected from the group consisting of saturated cyclic ether compounds and saturated chain ether compounds have reduced cycle characteristics.

[0018] The method for manufacturing a lithium ion secondary battery according to the present disclosure can solve these problems and provide a lithium ion secondary battery that has increased discharge capacity, excellent cycle characteristics, and is lightweight.

[0019] The reason for this effect is presumed to be as follows. First, by charging and discharging a lithium ion secondary battery that includes a sulfur-modified compound as a positive electrode active material and that uses a liquid electrolyte containing a solvent selected from the group consisting of saturated cyclic carbonate compounds and saturated chain carbonate compounds, a coating suitable for the liquid electrolyte containing a solvent selected from the group consisting of saturated cyclic ether compounds and saturated chain ether compounds is presumed to be formed on the surface of the sulfur-modified compound. Then, by using a positive electrode that includes the sulfur-modified compound with the coating formed on its surface as a positive electrode active material, even if a lithium ion secondary battery is fabricated and charged and discharged using a liquid electrolyte containing a solvent selected from the group consisting of saturated cyclic ether compounds and saturated chain ether compounds, the cycle characteristics are presumed to be not degraded as in the prior art.

[0020] The method for manufacturing a lithium ion secondary battery according to the present disclosure can also be used as a method for recycling lithium ion secondary batteries.

[0021] 1. Charging and discharging process The charge / discharge treatment step in the present disclosure is a step of charging / discharging the first lithium ion secondary battery.

[0022] (1) First lithium-ion secondary battery The first lithium ion secondary battery used in the above steps may include a positive electrode having a positive electrode active material layer containing a sulfur-modified compound, a first liquid electrolyte, and a negative electrode. The first lithium ion secondary battery is different from the second lithium ion secondary battery obtained by the manufacturing method of the present disclosure.

[0023] (1-1) Positive electrode The positive electrode in the present disclosure has a positive electrode active material layer containing a sulfur-modified compound. In the present disclosure, the positive electrode active material layer is an electrode layer of the positive electrode. In the present disclosure, the sulfur-modified compound effectively functions as a positive electrode active material.

[0024] (1-1-1) Sulfur-modified compounds In the present disclosure, the sulfur-modified compound contained in the positive electrode active material layer may be the same as that described in the section "(2) Sulfur-modified compound" in "A. Method for manufacturing lithium-ion secondary battery" below, and therefore, a description thereof will be omitted here.

[0025] From the viewpoint of increasing the discharge capacity, the content of the sulfur-modified compound is preferably 75 parts by mass to 99.5 parts by mass, more preferably 80 parts by mass to 99 parts by mass, and even more preferably 85 parts by mass to 98 parts by mass, relative to 100 parts by mass of the positive electrode active material layer.

[0026] (1-1-2) Other ingredients In the present disclosure, the positive electrode active material layer contains a sulfur-modified compound, but may contain other components as necessary.

[0027] In the present disclosure, other components contained in the positive electrode active material layer include a binder, a conductive additive, an active material other than the sulfur-modified compound, a viscosity adjuster, a reinforcing material, an antioxidant, and the like.

[0028] As the binder, a binder known in the art for use in a positive electrode active material layer can be used. Examples of binders include styrene-butadiene rubber, butadiene rubber, polyethylene, polypropylene, polyamide, polyamideimide, polyimide, polyacrylonitrile, polyurethane, polyvinylidene fluoride, polytetrafluoroethylene, ethylene-propylene-diene rubber, fluororubber, styrene-acrylic acid ester 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 nanofiber, polyethylene oxide, starch, polyvinylpyrrolidone, polyvinyl chloride, and polyacrylic acid. Only one binder may be used, or two or more binders may be used in combination. Among these, aqueous binders are preferred from the viewpoint of low environmental impact and excellent binding properties, and styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid are more preferred.

[0029] From the viewpoint of further increasing the discharge capacity, the content of the binder in the positive electrode active material layer is preferably 1 part by mass to 30 parts by mass, and more preferably 1 part by mass to 20 parts by mass, relative to 100 parts by mass of the sulfur-modified compound in the positive electrode active material layer.

[0030] The conductive additive may be any known conductive additive for the positive electrode active material layer. Examples of the conductive additive include carbon materials such as natural graphite, artificial graphite, carbon black, ketjen black, acetylene black, channel black, furnace black, lamp black, thermal black, carbon nanotubes, vapor-grown carbon fiber (VGCF), graphene, 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. The conductive additive may be used alone or in combination of two or more.

[0031] From the viewpoint of increasing the discharge capacity, the average particle diameter of the conductive additive used in the positive electrode active material layer is preferably 0.0001 μm to 100 μm, and more preferably 0.01 μm to 50 μm. In the present disclosure, the "average particle diameter" refers to the 50% particle diameter measured by a laser diffraction light scattering method. In the laser diffraction light scattering method, the particle diameter is a volume-based diameter, and the secondary particle diameter of the object to be measured is measured. When measuring the average particle diameter by the laser diffraction light scattering method, the object to be measured is dispersed in a dispersion medium such as water and then measured.

[0032] From the viewpoint of further increasing the discharge capacity, the content of the conductive additive in the positive electrode active material layer is preferably 0.05 parts by mass to 20 parts by mass, more preferably 0.1 parts by mass to 10 parts by mass, and even more preferably 0.5 parts by mass to 8.0 parts by mass, relative to 100 parts by mass of the sulfur-modified compound in the positive electrode active material layer.

[0033] Active materials other than the sulfur-modified compounds (hereinafter, sometimes referred to as "other active materials") include materials known as active materials, such as lithium transition metal composite oxides, lithium-containing transition metal phosphate compounds, and lithium-containing silicate compounds.

[0034] As the viscosity modifier, a known viscosity modifier for the positive electrode active material layer can be used. Examples of the viscosity modifier include cellulose polymers such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose, and their ammonium salts and alkali metal salts; (modified) poly(meth)acrylic acid and their ammonium salts and alkali metal salts; (modified) polyvinyl alcohols such as copolymers of acrylic acid or acrylic acid salts with vinyl alcohol, and copolymers of maleic anhydride or maleic acid or fumaric acid with vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, modified polyacrylic acid, oxidized starch, starch phosphate, casein, various modified starches, and hydrogenated acrylonitrile-butadiene copolymers.

[0035] The reinforcing material may be any known material for reinforcing positive electrode active material layers, including various inorganic and organic spherical, plate-like, rod-like, or fibrous fillers.

[0036] The antioxidant may be any known antioxidant for the positive electrode active material layer, such as a phenol compound, a hydroquinone compound, an organic phosphorus compound, a sulfur compound, a phenylenediamine compound, or a polymeric phenol compound.

[0037] (1-1-3) Thickness and Formation Method of Positive Electrode Active Material Layer The thickness of the positive electrode active material layer can usually be set to 1 μm to 1000 μm.

[0038] The method for forming the positive electrode active material layer may be any known method capable of forming a positive electrode active material layer, and examples thereof include a method in which a composition for forming a positive electrode active material layer containing the sulfur-modified compound, other components that are included as necessary, and a solvent is applied to a current collector described below to form a coating film, and then the solvent is dried and removed from the coating film.

[0039] Examples of the solvent 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, alcohol, etc. The amount of the solvent used can be adjusted depending on the coating method. For example, in the case of the doctor blade method, the amount of solvent used is preferably 20 to 300 parts by mass, and more preferably 30 to 200 parts by mass, per 100 parts by mass of the total amount of the sulfur-modified compound, binder, and conductive aid, from the viewpoint of ease of production.

[0040] The method for preparing the composition for forming a positive electrode active material layer is not particularly limited, and examples thereof include methods using a conventional ball mill, sand mill, bead mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, rotation-revolution mixer, planetary mixer, Filmix, Disper, jet paster, etc.

[0041] The application method is not particularly limited, and various methods can be used, such as a die coater method, a comma coater method, a curtain coater method, a spray coater method, a gravure coater method, a flexo coater method, a knife coater method, a doctor blade method, a reverse roll method, a brush coating method, a dipping method, etc. The die coater method, the doctor blade method, the knife coater method, and the comma coater method are preferred from the viewpoint of being able to obtain a good surface state of the coating film in accordance with the physical properties such as viscosity and drying properties of the positive electrode active material layer-forming composition.

[0042] The drying and removal method is not particularly limited, and may be heating, decompression, or a combination thereof. The heating temperature may be 40°C to 200°C. Heating and decompression devices may include a heating furnace, an infrared heating furnace, a vacuum oven, etc. This drying volatilizes volatile components such as the solvent, forming a positive electrode active material layer. Thereafter, the positive electrode active material layer may be pressed, if necessary. Examples of pressing methods include a mold pressing method and a roll pressing method.

[0043] (1-1-4) Other configurations In the present disclosure, the positive electrode has a positive electrode active material layer, but may have other components as necessary, such as a current collector.

[0044] The current collector may be made of a conductive material such as titanium, titanium alloy, aluminum, aluminum alloy, copper, nickel, stainless steel, nickel-plated steel, or conductive resin. The surface of these conductive materials may be coated with carbon. The current collector may be in the form of a foil, plate, mesh, or porous. Among these, aluminum is preferred, and aluminum foil is more preferred, from the viewpoints of conductivity and cost. When the current collector is in the form of a foil, its thickness is preferably 1 μm to 1000 μm, from the viewpoints of increasing discharge capacity and ease of manufacture.

[0045] The positive electrode may be subjected to a pressing process, if necessary. Examples of the pressing process include a mold pressing method and a roll pressing method.

[0046] The positive electrode may be subjected to a pre-doping treatment for inserting lithium in advance. The pre-doping method of lithium may be performed according to a known method, for example, an electrolytic doping method in which a half cell is assembled using metallic lithium as a counter electrode and lithium is electrochemically doped, or a diffusion doping method in which metallic lithium foil is attached to the electrode and left in a liquid electrolyte to dope the electrode by utilizing the diffusion of lithium into the electrode.

[0047] In the present disclosure, the surface of the positive electrode may be coated with a coating material, such as a polymer coating material such as polyvinylidene fluoride, or an inorganic coating material such as alumina or silica.

[0048] (1-2) Negative electrode The negative electrode in the present disclosure has a negative electrode active material layer.

[0049] (1-2-1) Negative electrode active material layer In the present disclosure, the negative electrode active material layer refers to an electrode layer of a negative electrode. The negative electrode active material layer may contain a known negative electrode active material.

[0050] Negative electrode active materials include natural graphite, artificial graphite, non-graphitizable carbon, easily graphitizable carbon, lithium, lithium alloys, silicon, silicon alloys, silicon oxide, 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, and Li4Ti5O. 12 Examples of the negative electrode active material include composite oxides such as those mentioned above. Only one type of negative electrode active material may be used, or two or more types may be used in combination. In the present disclosure, the negative electrode active material is preferably silicon, a silicon alloy, silicon oxide, lithium, or a lithium alloy, and more preferably lithium, from the viewpoint of further increasing the discharge capacity.

[0051] The negative electrode active material layer contains a negative electrode active material, and may contain, for example, a binder, a conductive additive, and the like, as necessary. The binder and conductive additive used in the negative electrode active material layer may be the same as those described in the section "(1-1-2) Other components" of "(1) First lithium ion secondary battery" in "1. Charge / discharge treatment step" in "A. Manufacturing method for lithium ion secondary battery" above, and therefore further description thereof will be omitted here.

[0052] (1-2-2) Other configurations The negative electrode in the present disclosure has the above-described negative electrode active material layer, but may also contain other components as necessary. Examples of other components include a current collector. The current collector described in the section "(1-1-4) Other components" of "(1) First lithium ion secondary battery" under "1. Charge / discharge treatment process" in "A. Manufacturing method of lithium ion secondary battery" can be used, and therefore a description thereof will be omitted here.

[0053] In the present disclosure, the surface of the negative electrode may be coated with a coating material, such as a polymer coating material such as polyvinylidene fluoride, or an inorganic coating material such as alumina or silica.

[0054] (1-3) First liquid electrolyte The first liquid electrolyte can be obtained by dissolving a supporting electrolyte in a solvent selected from the group consisting of saturated cyclic carbonate compounds and saturated chain carbonate compounds. In the present disclosure, from the viewpoint of increasing discharge capacity and excellent cycle characteristics, the density of the first liquid electrolyte at 25°C is 1.21 g / cm 3 ~1.60g / cm 3 It is preferable that the range is 1.21 g / cm 3 ~1.40g / cm 3 More preferably, it is in the range of 1.22 g / cm 3 ~1.38g / cm 3 Even more preferably, it is in the range of 1.25 g / cm 3 ~1.35g / cm 3 It is most preferable that the range is: The density at 25°C was measured in accordance with JIS Z8804:2012 "6. Method for measuring density and specific gravity using a pycnometer" using a 5 ml Gay-Lussac pycnometer at 25°C.

[0055] Examples of supporting electrolytes used in the first liquid 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), LiNO3, LiSbF6, LiSiF5, LiSCN, LiClO4, LiCl, LiF, LiBr, LiI, LiAlF4, LiAlCl4, LiPO2F2, 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide lithium, 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, LiNO3, 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide lithium, and LiC(CF3SO2)3, derivatives of LiCF3SO3, and derivatives of LiC(CF3SO2)3.

[0056] The content of the supporting electrolyte in the first liquid electrolyte is preferably 0.5 mol / L to 7 mol / L, and more preferably 0.8 mol / L to 1.8 mol / L, from the viewpoint of further increasing the discharge capacity.

[0057] The solvent used in the first liquid electrolyte may contain at least one selected from the group consisting of saturated cyclic carbonate compounds and saturated chain carbonate compounds. Other solvents, such as acetonitrile, propionitrile, nitromethane, derivatives thereof, and various ionic liquids, may also be used in combination, provided they do not adversely affect the lithium-ion secondary battery of the present disclosure. The content of the compound selected from the group consisting of saturated cyclic carbonate compounds and saturated chain carbonate compounds in the solvent of the first liquid electrolyte is preferably 60% by volume or more, more preferably 80% by volume or more, more preferably 85% by volume or more, even more preferably 90% by volume or more, even more preferably 95% by volume or more, and most preferably 98% by volume or more, from the viewpoints of increasing discharge capacity and achieving excellent cycle characteristics. In the present disclosure, "volume %" represents the volume percentage measured in an environment of 25°C.

[0058] Examples of the saturated cyclic carbonate compound include ethylene carbonate, vinylene carbonate, fluoroethylene carbonate, 1,2-propylene carbonate, 1,3-propylene carbonate, 1,2-butylene carbonate, 1,3-butylene carbonate, 1,1-dimethylethylene carbonate, etc. These solvents may be used alone or in combination of two or more. Examples of the saturated chain carbonate compound include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl butyl carbonate, methyl-t-butyl carbonate, diisopropyl carbonate, t-butyl propyl carbonate, etc. These solvents may be used alone or in combination of two or more.

[0059] In the present disclosure, from the viewpoint of being able to form a lithium ion secondary battery that has increased discharge capacity, excellent cycle characteristics, and is lightweight, among the saturated cyclic carbonate compounds and saturated chain carbonate compounds described above, it is preferable to use one or more compounds selected from the group consisting of ethylene carbonate, vinylene carbonate, fluoroethylene carbonate, 1,2-propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, and it is more preferable to use one or more compounds selected from the group consisting of ethylene carbonate, fluoroethylene carbonate, and diethyl carbonate.

[0060] The first liquid electrolyte may contain other known additives, such as an electrode film-forming agent, an antioxidant, a flame retardant, an overcharge inhibitor, etc., in order to improve the life and safety of the lithium-ion secondary battery. From the viewpoint of further increasing the discharge capacity, the content of the 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 the first liquid electrolyte.

[0061] (1-4) Other configurations Another component of the first lithium-ion secondary battery is a separator. The separator may be any material that allows lithium ions to pass through and prevents contact between the positive electrode and the negative electrode. Examples of such separators include, but are not limited to, polymeric microporous films and nonwoven fabrics. Examples of such films include 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, polymers based on poly(meth)acrylic acid and its various esters, derivatives thereof, copolymers, and mixtures thereof. These films may be coated with ceramic materials such as alumina and silica, magnesium oxide, aramid resin, or polyvinylidene fluoride.

[0062] These films may be used alone or may be laminated to form a multilayer film. Furthermore, these films may contain various additives, the type and content of which 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 lithium ion secondary battery.

[0063] (2) Sulfur-modified compounds (2-1) Material The sulfur-modified compound contained in the positive electrode active material layer may be, for example, a compound in which sulfur and an atom in an organic compound form a covalent bond, etc. Examples of a method for producing such a sulfur-modified compound include a method of heating elemental sulfur and an organic compound.

[0064] In the sulfur-modified compound, the sulfur that forms a covalent bond or the like with an atom derived from an organic compound may consist of one sulfur atom, or may consist of multiple sulfur atoms such as a disulfide or trisulfide. In the case of multiple sulfur atoms, it is sufficient that some of the sulfur atoms interact with each other. For example, when the multiple sulfur atoms are linear sulfur, the sulfur at at least one end may form a stable interaction. Examples of stable interactions include a covalent bond or an ionic bond.

[0065] Examples of the organic compound include acrylic compounds, polyether compounds, pitch compounds, polynuclear aromatic ring compounds, aliphatic hydrocarbon compounds, and thienoacene compounds. That is, examples of the sulfur-modified compound 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 polycarbon sulfides.

[0066] In the present disclosure, from the viewpoint of further increasing the discharge capacity, the sulfur-modified compound is preferably selected from the group consisting of a sulfur-modified acrylic compound, a sulfur-modified polynuclear aromatic ring compound, and a sulfur-modified polyether compound, and is more preferably a sulfur-modified acrylic compound.

[0067] The sulfur content of the sulfur-modified compound is not particularly limited, but from the viewpoint of further increasing the discharge capacity, it is preferably in the range of 10% by mass to 80% by mass, more preferably in the range of 20% by mass to 80% by mass, even more preferably in the range of 30% by mass to 80% by mass, even more preferably in the range of 35% by mass to 75% by mass, even more preferably in the range of 40% by mass to 75% by mass, even more preferably in the range of 45% by mass to 70% by mass, even more preferably in the range of 45% by mass to 65% by mass, and most preferably in the range of 45% by mass to 60% by mass. Here, the "sulfur content" can refer to the total content of sulfur atoms per total mass of the sulfur-modified compound. The sulfur content of the sulfur-modified compound can be calculated from the analysis results using a CHNS analyzer capable of analyzing sulfur and oxygen.

[0068] (2-1-1) Sulfur-modified acrylic compounds The sulfur-modified acrylic compound may be, for example, a compound in which sulfur and an atom in the acrylic compound form a covalent bond, etc. Examples of a method for producing such a sulfur-modified acrylic compound include a method of heating elemental sulfur and an acrylic compound.

[0069] In the present disclosure, examples of the sulfur-modified acrylic compound include a sulfur-modified polyacrylonitrile compound 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.

[0070] When the sulfur-modified compound is a sulfur-modified acrylic compound, the sulfur content is not particularly limited, but from the viewpoint of further increasing the discharge capacity, it is preferably in the range of 10% by mass to 80% by mass, more preferably in the range of 20% by mass to 80% by mass, even more preferably in the range of 30% by mass to 80% by mass, even more preferably in the range of 35% by mass to 75% by mass, even more preferably in the range of 40% by mass to 75% by mass, even more preferably in the range of 45% by mass to 70% by mass, even more preferably in the range of 45% by mass to 65% by mass, and most preferably in the range of 45% by mass to 60% by mass.

[0071] (2-1-1-1) Sulfur-modified polyacrylonitrile compounds The sulfur-modified polyacrylonitrile-based compound in the present disclosure may be, for example, a compound in which sulfur and an atom in a polyacrylonitrile-based compound are covalently bonded. Examples of methods for producing such sulfur-modified polyacrylonitrile-based compounds include a method of heating elemental sulfur and a polyacrylonitrile-based compound. Furthermore, the sulfur-modified polyacrylonitrile-based compound in the present disclosure may include a compound obtained by heating elemental sulfur and particles in which a hydrocarbon is encapsulated in an outer shell made of a polyacrylonitrile-based compound. The encapsulated hydrocarbon may be a saturated or unsaturated aliphatic hydrocarbon having 3 to 8 carbon atoms.

[0072] In the present disclosure, the polyacrylonitrile-based compound may be any compound containing a structural unit derived from at least one of acrylonitrile and methacrylonitrile. From the viewpoint of increasing discharge capacity, the polyacrylonitrile-based compound preferably contains at least a structural unit derived from acrylonitrile.

[0073] From the viewpoint of increasing the discharge capacity, the content of the structural units derived from acrylonitrile and methacrylonitrile is preferably 10 parts by mass or more, and more preferably 30 parts by mass or more, in 100 parts by mass of the polyacrylonitrile compound.

[0074] When the polyacrylonitrile-based compound contains a structural unit derived from acrylonitrile, from the viewpoint of increasing the discharge capacity, the content of the structural unit 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-based compound is composed only of structural units derived from acrylonitrile.

[0075] When the polyacrylonitrile-based compound contains a structural unit derived from methacrylonitrile, from the viewpoint of increasing the discharge capacity, the content of the structural unit derived from methacrylonitrile is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 30 to 95 parts by mass, even more preferably 30 to 90 parts by mass, even more preferably 30 to 85 parts by mass, and most preferably 30 to 80 parts by mass, in 100 parts by mass of the polyacrylonitrile-based compound.

[0076] The polyacrylonitrile compound may contain a constituent unit derived from a monomer other than acrylonitrile and methacrylonitrile. Examples of the other monomer include acrylic monomers such as (meth)acrylate, (meth)acrylic acid ester, (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" refers to either "acrylate" or "methacrylate", and "(meth)acrylic" refers to either "acrylic" or "methacrylic".

[0077] The Raman spectrum of the sulfur-modified polyacrylonitrile-based compound of the present disclosure may be any spectrum that allows the lithium ion secondary battery of the present disclosure to exhibit the desired effects. From the viewpoint of increasing the discharge capacity, the Raman spectrum of the sulfur-modified polyacrylonitrile-based compound of the present disclosure may be any spectrum that allows the lithium ion secondary battery of the present disclosure to exhibit the desired effects. -1 ±10cm -1 From the viewpoint of increasing the discharge capacity, it is preferable that the Raman spectrum of the sulfur-modified polyacrylonitrile compound has a peak in the range of 1327 cm as described above. -1 ±10cm -1 Outside the range of 1531cm -1 ±10cm -1 Within the range of 939cm -1 ±10cm -1 Within the range of 479cm -1 ±10cm -1 Within the range of 377cm -1 ±10cm -1 Within the range of 318cm -1 ±10cm -1 and preferably has at least one peak in the range of 1531 cm -1 ±10cm -1 Within the range of 939cm -1 ±10cm -1 Within the range of 479cm -1 ±10cm -1 Within the range of 377cm -1 ±10cm -1 Within the range of 318cm -1 ±10cm -1 More preferably, the peaks are in at least two ranges within the range of 1531 cm -1 ±10cm -1 Within the range of 939cm -1 ±10cm -1 Within the range of 479cm -1 ±10cm -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 within the entire range of the above range.

[0078] From the viewpoint of increasing the discharge capacity, the Raman spectrum of the sulfur-modified polyacrylonitrile compound is -1 ±10cm -1 Peak intensity A1 (1327 cm -1 ±10cm -1 and the maximum peak in the range of 300 cm -1 From 1800cm -1 (difference between the smallest peak in the range of 1531 cm -1 ±10cm -1 Peak intensity B1 (1531 cm -1 ±10cm -1 and the maximum peak in the range of 300 cm -1 From 1800cm -1 The ratio (A1 / B1) of the peak A1 to the peak B1 (difference from the smallest 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.

[0079] The above Raman spectra were obtained using a JASCO NRS-3100 (excitation wavelength λ = 532 nm, grating: 600 l / mm, resolution: 1 cm -1 Measurement can be performed under the following conditions: exposure time: 30 seconds, slit width: φ50 μm.

[0080] (2-1-1-2) Other sulfur-modified acrylic compounds In the present disclosure, other sulfur-modified acrylic compounds can be prepared by heating a homopolymer or copolymer of elemental sulfur and 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 in the above section "(2-1-1-1) Sulfur-modified polyacrylonitrile compounds."

[0081] (2-1-2) Sulfur-modified polynuclear aromatic ring compounds The sulfur-modified polynuclear aromatic ring compound in the present disclosure may be, for example, a compound in which sulfur and an atom in the polynuclear aromatic ring compound are covalently bonded. The sulfur-modified polynuclear aromatic ring compound can be produced, for example, by heating a mixture of elemental sulfur and the polynuclear aromatic ring compound as an organic compound.

[0082] 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 compounds is a five-membered ring, and heteroatom-containing heteroaromatic ring compounds in which a portion of the carbon atoms of these compounds are substituted with sulfur, oxygen, nitrogen, etc. Furthermore, these polynuclear aromatic ring compounds may have a substituent such as a linear or branched alkyl group having 1 to 12 carbon atoms, an alkoxyl group, a hydroxyl group, a carboxyl group, an amino group, an aminocarbonyl group, an aminothio group, a mercaptothiocarbonylamino group, or a carboxyalkylcarbonyl group.

[0083] When the sulfur-modified compound is a sulfur-modified polynuclear aromatic ring compound, the sulfur content is not particularly limited, but from the viewpoint of further increasing the discharge capacity, it is preferably in the range of 10% by mass to 80% by mass, more preferably in the range of 20% by mass to 80% by mass, even more preferably in the range of 30% by mass to 80% by mass, even more preferably in the range of 35% by mass to 75% by mass, even more preferably in the range of 40% by mass to 75% by mass, even more preferably in the range of 45% by mass to 70% by mass, even more preferably in the range of 45% by mass to 65% by mass, and most preferably in the range of 45% by mass to 60% by mass.

[0084] (2-1-3) Sulfur-modified polyether compounds As the sulfur-modified polyether compound, the same compounds as those described in JP-A-2022-65974 can be used.

[0085] (2-2) Manufacturing method The method for producing the sulfur-modified compound may be any method capable of producing a compound having a desired sulfur content, and may include a method having a heating step of heating a mixture of elemental sulfur and an organic compound. The production method may also include a mechanochemical treatment step of mechanochemically treating the heat-treated product after the heating step.

[0086] The heating step in the above-mentioned production method is a step of heating a mixture of elemental sulfur and an organic compound. From the viewpoints of increasing the discharge capacity and improving the safety of the lithium-ion secondary battery, the heating step is preferably performed in a non-oxidizing atmosphere at 200°C to 600°C, more preferably at 250°C to 500°C.

[0087] The mechanochemical treatment in the mechanochemical treatment step refers to a process that induces a chemical reaction by utilizing high energy generated locally due to mechanical energy such as friction and compression during the pulverization process of a solid substance. From the viewpoint of easily adjusting the sulfur content, it is preferable that the production method includes a mechanochemical treatment step. It is presumed that the mechanochemical treatment easily increases the proportion of sulfur that forms covalent bonds with atoms derived from organic compounds contained in the sulfur-modified compound. More specifically, it is presumed that the mechanochemical treatment allows elemental sulfur (such as elemental sulfur that did not react in the heating step) contained in the heat-treated product to react with the sulfur-modified compound.

[0088] The mechanochemical treatment can apply mechanical energy such as impact, friction, compression, shear, etc., or a combination of these to the heat-treated material. Known devices can be used as the device for carrying out the mechanochemical treatment, including mixing devices such as a ball mill, vibration mill, planetary ball mill, cyclone mill, and media-agitated mill, crushers such as a ball media mill, roller mill, and mortar, and jet crushers that can apply forces such as impact and grinding to the heat-treated material.

[0089] In the present disclosure, from the viewpoint of further increasing the discharge capacity, the above-mentioned device is preferably a mixing device such as a ball mill, a vibration mill, a planetary ball mill, a cyclone mill, or a media-agitated mill, or a grinder such as a ball media mill, a roller mill, or a mortar, more preferably a mixing device such as a ball mill, a vibration mill, a planetary ball mill, or a media-agitated mill, and even more preferably a ball mill, a vibration mill, a planetary ball mill, or a cyclone mill.

[0090] The environment in which the mechanochemical treatment is performed 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 an oxidizing gas, such as an atmosphere containing oxygen, ozone, or nitrogen dioxide. A non-oxidizing atmosphere refers to an atmosphere not containing an oxidizing gas, such as an atmosphere consisting of nitrogen or argon.

[0091] In the present disclosure, from the viewpoint of increasing the discharge capacity and improving the safety of the lithium ion secondary battery, 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.

[0092] The production method may include a step other than the heating step and the mechanochemical treatment step, such as a sulfur content adjusting step that is carried out between the heating step and the mechanochemical treatment step and adjusts the elemental sulfur content of the heat-treated product obtained in the heating step.

[0093] The sulfur content adjustment step may involve adding elemental sulfur to the heat-treated product to increase the sulfur content in the heat-treated product used in the mechanochemical treatment step, or removing elemental sulfur from the heat-treated product to reduce the elemental sulfur content in the heat-treated product used in the mechanochemical treatment step.

[0094] (3) Charging and discharging process The charge / discharge treatment in the charge / discharge treatment step may be any method that can charge and discharge the first lithium ion secondary battery, such as absorbing and releasing chemical species that serve as charge carriers (e.g., ions such as lithium ions).

[0095] From the viewpoint of increasing the discharge capacity and achieving excellent cycle characteristics, the charge-discharge treatment is performed so that the discharge end potential of the positive electrode is 0.3 V (hereinafter referred to as "V(Li + / Li)~1.8V(Li + It is preferable to discharge under the condition that the voltage is 0.5V (Li + / Li)~1.3V(Li + It is more preferable to discharge under conditions where the V is 0.8V (Li + / Li)~1.2V(Li + It is even more preferable to discharge under conditions where the voltage is 0.9V(Li + / Li)~1.1V(Li + It is most preferable to discharge under the condition that the current is 0.1 W / Li.

[0096] From the viewpoint of increasing the discharge capacity and achieving excellent cycle characteristics, the charge-discharge treatment is performed so that the end-of-charge potential of the positive electrode is 2.0 V (Li + / Li)~4.3V(Li + It is preferable to charge under conditions where the voltage is 2.7V (Li + / Li)~4.0V(Li + It is more preferable to charge under conditions where the voltage is 2.8V (Li + / Li)~3.5V(Li + It is even more preferable to charge under conditions where the voltage is 2.9V (Li + / Li)~3.3V(Li + It is even more preferable to charge under conditions where the voltage is 2.9V (Li + / Li)~3.1V(Li + It is most preferable to charge under the condition that the charge is 0.1% / Li.

[0097] From the viewpoint of increasing discharge capacity and achieving excellent cycle characteristics, the number of charge / discharge cycles in the charge / discharge treatment is preferably within the range of 1 to 20 cycles, more preferably within the range of 1 to 15 cycles, even more preferably within the range of 1 to 13 cycles, even more preferably within the range of 1 to 10 cycles, even more preferably within the range of 1 to 8 cycles, and most preferably within the range of 3 to 8 cycles. In the present disclosure, charge and discharge are considered to be one cycle, but only the first cycle can be considered to be one cycle consisting of discharge alone.

[0098] From the viewpoint of increasing the discharge capacity and achieving excellent cycle characteristics, the charge / discharge rate in the charge / discharge treatment is preferably within the range of 0.01C rate (i.e., 100 hours charge, 100 hours discharge) to 5C rate (i.e., 0.2 hour charge, 0.2 hour discharge), more preferably within the range of 0.05C rate (i.e., 20 hours charge, 20 hours discharge) to 2C rate (i.e., 0.5 hour charge, 0.5 hour discharge), and most preferably within the range of 0.1C rate (i.e., 10 hours charge, 10 hours discharge) to 1C rate (i.e., 1 hour charge, 1 hour discharge).

[0099] From the viewpoint of increasing the discharge capacity and achieving excellent cycle characteristics, the temperature during charge and discharge in the charge and discharge treatment is preferably within the range of 10°C to 60°C, more preferably within the range of 10°C to 50°C, even more preferably within the range of 15°C to 50°C, and most preferably within the range of 20°C to 45°C.

[0100] 2.Replacement process The exchanging step in the present disclosure is a step of exchanging the first liquid electrolyte contained in the first lithium-ion secondary battery with a second liquid electrolyte after the charge / discharge treatment step described above to obtain a second lithium-ion secondary battery. That is, the first lithium-ion secondary battery is disassembled, and the first liquid electrolyte is removed from the components of the first lithium-ion secondary battery and replaced with the second liquid electrolyte, thereby producing a second lithium-ion secondary battery, which is the lithium-ion secondary battery of the present disclosure. The exchanging step may also include a step of washing the positive electrode, negative electrode, etc. of the first lithium-ion secondary battery using dimethyl carbonate (DMC) or the like after removing the first liquid electrolyte. From the viewpoints of increasing discharge capacity and achieving excellent cycle characteristics, the exchanging step is preferably performed in an atmosphere with a dew point temperature of −100°C to −30°C.

[0101] The negative electrode may be the same as that of the first lithium-ion secondary battery, or a new negative electrode may be used.The separator may be the same as that of the first lithium-ion secondary battery, or a new separator may be used.

[0102] (1) Second liquid electrolyte The second liquid electrolyte can be obtained by dissolving a supporting electrolyte in a solvent selected from the group consisting of saturated cyclic ether compounds and saturated chain ether compounds. In the present disclosure, from the viewpoint of obtaining a lithium ion secondary battery that has increased discharge capacity, excellent cycle characteristics, and is lightweight, the second liquid electrolyte has a density of 0.80 g / cm at 25°C. 3 ~1.20g / cm 3 It is preferable that the range is 0.80 g / cm 3 ~1.19g / cm 3 More preferably, it is in the range of 0.81 g / cm 3 ~1.18g / cm 3 Even more preferably, it is in the range of 0.82 g / cm 3 ~1.18g / cm 3 It is most preferable that the range is: The density at 25°C was measured in accordance with JIS Z8804:2012 "6. Method for measuring density and specific gravity using a pycnometer" using a 5 ml Gay-Lussac pycnometer at 25°C.

[0103] The supporting electrolyte used in the second liquid electrolyte can be the same as the supporting electrolyte described in the section "(1-3) First liquid electrolyte" in "1. Charge / discharge treatment step" of "A. Manufacturing method for lithium ion secondary battery."

[0104] The content of the supporting electrolyte in the second liquid electrolyte is preferably 0.3 mol / L to 7 mol / L, and more preferably 0.5 mol / L to 1.8 mol / L, from the viewpoint of further increasing the discharge capacity.

[0105] The solvent used in the second liquid electrolyte may contain at least one selected from the group consisting of saturated cyclic ether compounds and saturated chain ether compounds. Other solvents, such as silane, acetonitrile, propionitrile, nitromethane, or derivatives thereof, or various ionic liquids, may also be used in combination, provided they do not adversely affect the lithium-ion secondary battery of the present disclosure. The content of the compound selected from the group consisting of saturated cyclic ether compounds and saturated chain ether compounds in the solvent of the second liquid electrolyte is preferably 60% by volume or more, more preferably 80% by volume or more, more preferably 85% by volume or more, even more preferably 90% by volume or more, still more preferably 95% by volume or more, and most preferably 98% by volume or more, from the viewpoints of increasing discharge capacity and achieving excellent cycle characteristics. In the present disclosure, "volume %" represents the volume percentage measured in an environment of 25°C.

[0106] Examples of the saturated cyclic ether compound and saturated chain ether compound include 1,2-dimethoxyethane, ethoxymethoxyethane, diethoxyethane, tetrahydrofuran, 1,3-dioxolane, 2-methyl-1,3-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, and diethyl ether. ether, dipropyl ether, methyl propyl ether, methyl butyl ether, propyl butyl ether, ethylene glycol bis(trifluoromethyl)ether, diethylene glycol bis(trifluoroethyl)ether, 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl)ether, tris(2,2,2-trifluoroethyl)orthoformate, glymes, etc. These solvents may be used alone or in combination of two or more. In the present disclosure, among the saturated cyclic ether compounds and saturated chain ether compounds described above, it is preferable to use one or more compounds selected from the group consisting of 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, dipropyl ether, methyl propyl ether, and glymes, from the viewpoint of being able to form a lithium ion secondary battery that has increased discharge capacity, excellent cycle characteristics, and is lightweight.

[0107] The second liquid electrolyte may contain other known additives such as an electrode film-forming agent, an antioxidant, a flame retardant, an overcharge inhibitor, etc., in order to improve the life and safety of the lithium ion secondary battery. From the viewpoint of further increasing the discharge capacity, the content of the 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 the second liquid electrolyte.

[0108] (2) Anode of the second lithium-ion secondary battery In the present disclosure, the negative electrode of the first lithium-ion secondary battery may be used as it is as the negative electrode of the second lithium-ion secondary battery, or a new negative electrode may be used. As the new negative electrode, one similar to that described in the section "(1-2) Negative Electrode" of "1. Charging and Discharging Treatment Step" in "A. Manufacturing Method of Lithium-ion Secondary Battery" can be used, and therefore a description thereof will be omitted here.

[0109] B. Other The present disclosure includes the following aspects. [1] A method for manufacturing a lithium ion secondary battery, a charge-discharge treatment step of charging and discharging a first lithium ion secondary battery including a positive electrode having a positive electrode active material layer containing a sulfur-modified compound, a first liquid electrolyte, and a negative electrode; and an exchange step of exchanging the first liquid electrolyte with a second liquid electrolyte to obtain a second lithium ion secondary battery after the charge / discharge treatment step, the first liquid electrolyte contains a solvent selected from the group consisting of saturated cyclic carbonate compounds and saturated chain carbonate compounds; A method for producing a lithium ion secondary battery, wherein the second liquid electrolyte contains a solvent selected from the group consisting of saturated cyclic ether compounds and saturated chain ether compounds.

[0110] [2] The method for producing a lithium ion secondary battery according to [1], wherein the sulfur-modified compound is a sulfur-modified acrylic compound.

[0111] [3] The method for producing a lithium ion secondary battery according to [2], wherein the sulfur-modified acrylic compound is a sulfur-modified polyacrylonitrile compound.

[0112] [4] The method for producing a lithium ion secondary battery according to any one of [1] to [3], wherein the sulfur content of the sulfur-modified compound is within a range of 10% by mass to 80% by mass.

[0113] [5] The density of the first liquid electrolyte at 25°C is 1.21 g / cm 3 ~1.60g / cm 3 is within the range of The density of the second liquid electrolyte at 25°C is 0.80 g / cm 3 ~1.20g / cm 3 The method for producing a lithium ion secondary battery according to any one of [1] to [4], wherein the range is:

[0114] [6] In the charge-discharge treatment step, the discharge end potential of the positive electrode is 0.3 V (Li + / Li)~1.8V(Li + Discharge was performed under the condition that the end-of-charge potential of the positive electrode was 2.0 V (Li + / Li)~4.3V(Li + The method for producing a lithium ion secondary battery according to any one of [1] to [5], characterized in that charging is carried out under conditions such that:

[0115] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiment that has substantially the same configuration as the technical idea described in the claims and exhibits similar effects is included within the technical scope of the present disclosure. [Example]

[0116] The present disclosure will be described in more detail below with reference to examples and comparative examples. However, the present disclosure is not limited to the following examples. In the examples, "parts" and "%" are by mass unless otherwise specified.

[0117] [Production Example 1: Production of sulfur-modified compound] Only the heating step was performed according to the manufacturing example of JP 2013-054957 A. Specifically, 20 g of a raw polyacrylonitrile mixture (hereinafter sometimes referred to as the "raw PAN mixture"), consisting of 10 parts by mass of polyacrylonitrile powder (Sigma-Aldrich, average particle size 200 μm) and 30 parts by mass of elemental sulfur (Sigma-Aldrich, average particle size 200 μm), was placed in a bottomed cylindrical glass tube with an outer diameter of 45 mm and a length of 120 mm. A silicone stopper equipped with a gas inlet tube and a gas outlet tube was attached to the opening of the glass tube. After the air inside the glass tube was replaced with nitrogen, the lower part of the glass tube was inserted into a crucible-type electric furnace. While introducing nitrogen through the gas inlet tube to remove the generated hydrogen sulfide, the tube was heated at 400°C for 1 hour, yielding Heat-Treated Product 1. The sulfur vapor condensed at the top or lid of the glass tube and refluxed. The obtained heat-treated product 1 was placed in a glass tube oven at 260° C., and heated at a reduced pressure of 20 hPa for 3 hours to remove elemental sulfur, thereby obtaining a sulfur-containing material A, which is a sulfur-modified polyacrylonitrile-based compound.

[0118] [Production Example 2: Production of sulfur-carbon composite compound] 20 g of a mixture containing 75 parts by weight of elemental sulfur (Sigma-Aldrich, average particle size 200 μm) and 25 parts by weight of Ketjen Black (Lion Corporation, EC600JD) was placed in a cylindrical glass tube with a bottom, outer diameter 45 mm, and length 120 mm. A silicone stopper equipped with a gas inlet and outlet was attached to the end of the glass tube. After the air inside the glass tube was replaced with nitrogen, the bottom of the glass tube was inserted into a crucible-type electric furnace. The gas tube was sealed and heated at 155 °C for 12 hours to obtain a sulfur-carbon composite compound, sulfur-containing material a. Note that sulfur-containing material a does not constitute a compound in which sulfur forms a covalent bond with an atom in an organic compound, and therefore does not qualify as a sulfur-modified compound.

[0119] [Sulfur content] The sulfur contents of the sulfur-containing material A and the sulfur-containing material a were calculated from the analysis results using a CHNS analyzer (model: varioMICROcube, manufactured by Elementar Analysensysteme GmbH) 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 analysis results showed that the sulfur content of the sulfur-containing material A was 48.0 mass %, and the sulfur content of the sulfur-containing material a was 75.0 mass %.

[0120] [Fabrication of Lithium-ion Secondary Battery] A lithium ion secondary battery was fabricated using the sulfur-containing material A or the sulfur-containing material a. (1) Preparation of the positive electrode A composition for forming a positive electrode active material layer was prepared by mixing 94.0 parts by mass of sulfur-containing material A or sulfur-containing material a as a positive electrode active material, 2.5 parts by mass of acetylene black (manufactured by Denka) and 0.5 parts by mass of single-walled carbon nanotubes (manufactured by OCSiAl) as conductive additives, 1.5 parts by mass of styrene-butadiene rubber (aqueous dispersion, manufactured by Zeon Corporation) and 1.5 parts by mass of sodium carboxymethyl cellulose (manufactured by Daicel FineChem) as binders, using a rotation-revolution mixer. In the case of sulfur-containing material A, the composition for forming a positive electrode active material layer was applied onto a carbon-coated aluminum foil (thickness: 20 μm) by a doctor blade method and dried for 1 hour at 90° C. Thereafter, this electrode was cut to a predetermined size and vacuum-dried for 2 hours at 130° C. to prepare a disk-shaped positive electrode. In the case of the sulfur-containing material a, the composition for forming a positive electrode active material layer was applied onto a carbon-coated aluminum foil (thickness: 20 μm) by a doctor blade method and dried for 1 hour at 80° C. Thereafter, this electrode was cut to a predetermined size and dried for 1 hour at 80° C. in a nitrogen atmosphere to prepare a disk-shaped positive electrode.

[0121] (2) Preparation of the negative electrode A 500 μm thick piece of lithium metal was cut to a predetermined size to prepare a disk-shaped negative electrode.

[0122] (3) Preparation of liquid electrolyte (3-1)Liquid electrolyte A Liquid electrolyte A was prepared by dissolving LiPF6 at a concentration of 1.0 mol / L in a mixed solvent consisting of 50% by volume of fluoroethylene carbonate and 50% by volume of diethyl carbonate. The density of liquid electrolyte A at 25°C, determined using a 5 ml Gay-Lussac type pycnometer at 25°C in accordance with JIS Z8804:2012 "6. Methods for measuring density and specific gravity using a pycnometer", is 1.32 g / cm 3 It was.

[0123] (3-2) Liquid electrolyte B Liquid electrolyte B was prepared by dissolving LiPF6 at a concentration of 1.0 mol / L in a mixed solvent consisting of 50% by volume of ethylene carbonate and 50% by volume of diethyl carbonate. The density of liquid electrolyte B at 25°C, determined using a 5 ml Gay-Lussac type pycnometer at 25°C in accordance with JIS Z8804:2012 "6. Methods for measuring density and specific gravity using a pycnometer", is 1.25 g / cm 3 It was.

[0124] (3-3)Liquid electrolyte C Liquid electrolyte C was prepared by dissolving LiPF6 at a concentration of 1.0 mol / L in a mixed solvent consisting of 30% by volume of ethylene carbonate and 70% by volume of ethyl methyl carbonate. The density of liquid electrolyte C at 25°C, determined using a 5 ml Gay-Lussac type pycnometer at 25°C in accordance with JIS Z8804:2012 "6. Methods for measuring density and specific gravity using a pycnometer", is 1.22 g / cm 3 It was.

[0125] (3-4)Liquid electrolyte D Liquid electrolyte D was prepared by dissolving LiN(CF3SO2)2 at a concentration of 1.0 mol / L in a mixed solvent consisting of 50% by volume of 1,2-dimethoxyethane and 50% by volume of 1,3-dioxolane, and then adding LiNO3 so that the amount was 2 parts by mass per 100 parts by mass of the total liquid electrolyte. The density of liquid electrolyte D at 25°C, determined using a 5 ml Gay-Lussac type pycnometer at 25°C in accordance with JIS Z8804:2012 "6. Methods for measuring density and specific gravity using a pycnometer", is 1.17 g / cm 3 It was.

[0126] (3-5)Liquid electrolyte E Liquid electrolyte E was prepared by dissolving 0.4 mol / L of LiN(CF3SO2)2, 0.1 mol / L of lithium 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide, and 0.4 mol / L of LiNO3 in a mixed solvent consisting of 48 vol% of 1,2-dimethoxyethane, 17 vol% of 1,3-dioxolane, and 35 vol% of (trifluoromethyl)trimethylsilane. The density of liquid electrolyte E at 25°C, determined using a 5 ml Gay-Lussac type pycnometer at 25°C in accordance with JIS Z8804:2012 "6. Methods for measuring density and specific gravity using a pycnometer", is 1.02 g / cm 3 It was.

[0127] (3-6)Liquid electrolyte F Liquid electrolyte F was prepared by dissolving LiN(CF3SO2)2 at a concentration of 0.2 mol / L and LiNO3 at a concentration of 0.4 mol / L in a mixed solvent consisting of 48 vol% of 1,2-dimethoxyethane and 52 vol% of methyl propyl ether. The density of liquid electrolyte F at 25°C, determined using a 5 ml Gay-Lussac type pycnometer at 25°C in accordance with JIS Z8804:2012 "6. Methods for measuring density and specific gravity using a pycnometer", is 0.83 g / cm 3 It was.

[0128] (3-7)Liquid electrolyte G Liquid electrolyte G was prepared by dissolving 0.2 mol / L LiN(CF3SO2)2, 0.2 mol / L LiN(SO2F)2, 0.1 mol / L lithium 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide, and 0.1 mol / L LiNO3 in a mixed solvent consisting of 75 vol% 1,2-dimethoxyethane, 5 vol% 1,3-dioxolane, and 20 vol% (trifluoromethyl)trimethylsilane. The density of liquid electrolyte G at 25°C, determined using a 5 ml Gay-Lussac type pycnometer at 25°C in accordance with JIS Z8804:2012 "6. Methods for measuring density and specific gravity using a pycnometer", is 0.98 g / cm 3 It was.

[0129] (4) Fabrication of lithium-ion secondary batteries The previously prepared positive and negative electrodes were placed in a case with a glass filter as a separator between them. The first liquid electrolyte shown in Table 1 was then poured into each case, and the case was sealed to prepare a lithium-ion secondary battery (coin type, 20 mm in diameter and 3.2 mm thick). This preparation was carried out in an atmosphere with a dew point of -70°C.

[0130] [Charge / discharge treatment process] The lithium ion secondary battery prepared above was placed in a thermostatic chamber at 30°C, and the end-of-charge potential of the positive electrode was set to 3.0 V (Li + / Li), and the discharge end potential of the positive electrode was 1.0 V (Li + / Li), that is, the charge cut-off voltage was 3.0 V, the discharge cut-off voltage was 1.0 V, and charge and discharge were performed for 10 cycles at a charge rate of 0.1 C and a discharge rate of 0.1 C.

[0131] [Replacement process] The lithium ion secondary battery that had undergone the charge / discharge treatment process was disassembled, the positive electrode, negative electrode, and glass filter were removed from the case, and the positive electrode was washed with dimethyl carbonate (DMC). The cleaned positive electrode, a newly prepared negative electrode, and a newly prepared glass filter as a separator were placed in a new case, and then the specified second liquid electrolyte shown in Table 1 was poured into each case, and the case was sealed to prepare a lithium ion secondary battery (coin type with a diameter of 20 mm and a thickness of 3.2 mm). This process was carried out in an atmosphere with a dew point temperature of -70°C.

[0132] [Battery evaluation] The lithium ion secondary battery produced through the above exchange process was placed in a thermostatic chamber at 30°C, and the end-of-charge potential of the positive electrode was set to 3.0 V (Li + / Li), and the discharge end potential of the positive electrode was 1.0 V (Li + / Li), i.e., the end-of-charge voltage was 3.0 V, the end-of-discharge voltage was 1.0 V, and the charge / discharge cycle was performed at a charge rate of 0.5 C and a discharge rate of 0.5 C for 200 cycles, and the discharge capacities (mAh / g) at the 5th and 200th cycles were measured. The results of the discharge capacity (mAh / g) at the 5th cycle are shown in Table 1. In the present disclosure, "g" in the discharge capacity (mAh / g) represents the mass of the active material in the positive electrode active material layer. The ratio of the discharge capacity at the 200th 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 1. The comparative example in which the first liquid electrolyte and the second liquid electrolyte are the same is equivalent to a general battery evaluation that does not undergo a charge-discharge treatment process.

[0133] [Table 1]

[0134] The above results show that the lithium ion secondary battery that underwent the charge / discharge treatment process and replacement process of the examples had an increased discharge capacity, excellent cycle characteristics (capacity retention rate), and was lightweight due to the use of a second liquid electrolyte with low density. Therefore, the manufacturing method for a lithium ion secondary battery of the present disclosure can provide a lithium ion secondary battery that has a large discharge capacity, excellent cycle characteristics, and is lightweight.

Claims

1. A method for manufacturing a lithium ion secondary battery, comprising: a charge-discharge treatment step of charging and discharging a first lithium ion secondary battery including a positive electrode having a positive electrode active material layer containing the sulfur-modified compound, a first liquid electrolyte, and a negative electrode; and an exchange step of exchanging the first liquid electrolyte with a second liquid electrolyte to obtain a second lithium ion secondary battery after the charge / discharge treatment step, the first liquid electrolyte contains a solvent selected from the group consisting of saturated cyclic carbonate compounds and saturated chain carbonate compounds; a second liquid electrolyte containing a solvent selected from the group consisting of saturated cyclic ether compounds and saturated chain ether compounds;

2. 2. The method for producing a lithium ion secondary battery according to claim 1, wherein the sulfur-modified compound is a sulfur-modified acrylic compound.

3. 3. The method for producing a lithium ion secondary battery according to claim 2, wherein the sulfur-modified acrylic compound is a sulfur-modified polyacrylonitrile compound.

4. 2. The method for producing a lithium ion secondary battery according to claim 1, wherein the sulfur content of the sulfur-modified compound is within a range of 10% by mass to 80% by mass.

5. The density of the first liquid electrolyte at 25°C is 1.21 g / cm ３ ~1.60 g / cm ３ is within the range of The density of the second liquid electrolyte at 25°C is 0.80 g / cm ３ ~1.20 g / cm ３ The method for producing a lithium ion secondary battery according to claim 1, wherein the temperature is within the range of

6. The charge-discharge treatment step is carried out so that the discharge end potential of the positive electrode is 0.3 V (Li ＋ / Li) to 1.8V (Li ＋ Discharge was performed under the condition that the end-of-charge potential of the positive electrode was 2.0 V (Li ＋ / Li) to 4.3V (Li ＋ 2. The method for producing a lithium ion secondary battery according to claim 1, wherein charging is performed under the condition that:

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