Method for producing sulfur-based active material

Abstract

To maintain a capacity maintenance rate of an active material constituting an electrode of a lithium ion secondary battery, and improve volume energy density.SOLUTION: A method for producing a sulfur-based active material includes (1) a step of mixing an acrylic resin, a sulfur, and an iron compound containing divalent or trivalent iron ions, to obtain a raw material for firing, and (2) a step of firing the raw material for firing, wherein the raw material for firing is subjected to heating history once.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a sulfur-based active material. [Background technology]

[0002] Lithium-ion secondary batteries are primarily used in portable electronic devices due to their large charge / discharge capacity. Their use in electric vehicles is also increasing, and improvements in their performance are expected.

[0003] Patent Document 1 describes a positive electrode active material for lithium ion secondary batteries obtained by heating raw material powders containing sulfur powder and polyacrylonitrile powder in a non-oxidizing atmosphere. Patent Document 2 aims to provide a low-cost positive electrode active material by using industrial rubber.

[0004] On the other hand, it has been proposed to increase the battery capacity of lithium-ion secondary batteries by using materials that can absorb and release more lithium ions, such as silicon (Si) and tin (Sn), as the negative electrode active material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2010 / 044437 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-92449 Summary of the Invention [Problem to be solved by the invention]

[0006] However, polyacrylonitrile is inherently expensive, and its quality (particularly particle size) affects battery performance, such as charge / discharge capacity and cycle characteristics. Therefore, obtaining polyacrylonitrile of consistent quality increases costs. While industrial rubber is inexpensive, improving cycle characteristics presents challenges. The materials proposed as negative electrode active materials suffer from poor cycle characteristics after repeated charge / discharge due to large volume changes associated with the absorption and release of lithium ions. Carbon materials such as graphite and hard carbon are also used, but these materials have already reached their theoretical capacity, making significant capacity improvements unlikely.

[0007] Furthermore, typical sulfur-based active materials often use excess sulfur as a raw material, resulting in the problem of unreacted sulfur or low-molecular-weight sulfur compounds remaining in the material after heat treatment. This unreacted sulfur acts as an insulating material and becomes an impurity in batteries, and low-molecular-weight sulfur compounds significantly deteriorate with cycling. Therefore, to produce sulfur-based active materials with good cycle characteristics, a process to remove unreacted sulfur and low-molecular-weight sulfur compounds, known as a desulfurization process, is required. However, this desulfurization process requires high temperatures, which are disadvantageous in terms of energy and cost. [Means for solving the problem]

[0008] The present disclosure provides: (1) a step of mixing an acrylic resin, sulfur, and an iron compound containing divalent or trivalent iron ions to obtain a firing raw material; and (2) A step of firing the firing raw material A method for producing a sulfur-based active material comprising: A method for producing a sulfur-based active material, in which the firing raw material is subjected to a single heating history; Regarding. [Effects of the Invention]

[0009] According to the present disclosure, a method for producing a sulfur-based active material can be provided that allows for the production of a sulfur-based active material with improved cycle characteristics despite requiring only one heating history. Specifically, the present disclosure provides a sulfur-based active material produced by adding an iron complex to an acrylic polymer and sulfur and then subjecting the material to a heat treatment, resulting in a material with excellent cycle characteristics without the need for a process for removing unreacted sulfur or low-molecular-weight sulfur compounds. Therefore, the method requires only one heating history, which is advantageous in terms of cost and energy.

[0010] In this specification, the term "cycle characteristics" refers to the ability of a secondary battery to maintain its charge / discharge capacity despite repeated charge / discharge. Therefore, a secondary battery that experiences a large decrease in charge / discharge capacity and a low capacity retention rate with repeated charge / discharge has poor cycle characteristics, whereas a secondary battery that experiences a small decrease in charge / discharge capacity and a high capacity retention rate has excellent cycle characteristics. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a reaction apparatus used in the production of a sulfur-based active material in an example of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012] The configuration of the present disclosure will be described in detail below. The upper and lower limit values ​​associated with terms such as "greater than or equal to," "less than or equal to," "greater than," and "less than" used to describe a numerical range can be arbitrarily combined, and the numerical values ​​in the examples can also be used as the upper and / or lower limits. Furthermore, a numerical range that includes a lower or upper limit is understood to also disclose a numerical range that does not include that lower or upper limit, unless it is contrary to the spirit of the present disclosure. Conversely, a numerical range that does not include a lower or upper limit is understood to also disclose a numerical range that includes that lower or upper limit, unless it is contrary to the spirit of the present disclosure.

[0013] One embodiment of the present disclosure is a method for producing a sulfur-based active material, including: (1) a step of mixing an acrylic resin, sulfur, and an iron compound containing divalent or trivalent iron ions to obtain a firing raw material; and (2) a step of firing the firing raw material, wherein the firing raw material is subjected to a single heating history.

[0014] The content of the iron compound containing divalent or trivalent iron ions in the firing raw material is preferably 10 parts by mass or more and 300 parts by mass or less with respect to 100 parts by mass of the acrylic resin.

[0015] The step (1) preferably includes a step of mixing the acrylic resin, the sulfur, and the iron compound containing divalent or trivalent iron ions, all in a powder state.

[0016] The firing temperature in step (2) is preferably higher than 250°C and lower than 500°C.

[0017] The firing temperature in the step (2) is preferably higher than the temperature at which the iron compound containing divalent or trivalent iron ions thermally decomposes.

[0018] The ratio of the amount of sulfur to the total amount of the acrylic resin and the iron compound in the firing raw material is preferably 1.5 to 5.0 in terms of parts by mass.

[0019] The acrylic resin is preferably a polymer obtained by polymerizing at least one compound selected from the group consisting of acrylate compounds represented by the following formula (1), or at least one polymer selected from the group consisting of polymers obtained by polymerizing at least one compound selected from the group consisting of acrylate compounds represented by the following formula (1) and at least one compound selected from the group consisting of diacrylate compounds represented by the following formula (2):

[0020] R 12is an alkyl group having from 1 to 6 carbon atoms, and Y is a linear hydrocarbylene group having from 2 to 6 carbon atoms, and in the hydrocarbylene group, it is preferred that the number of substituents is from 1 to 4, the number of carbon atoms in the alkyl substituent is from 1 to 4, and the number of ether bonds in the carbon skeleton constituting the hydrocarbylene group is from 1 to 2.

[0021] The iron compound is preferably one or more compounds selected from the group consisting of iron salts and iron complexes.

[0022] The iron compound is preferably one or more compounds selected from the group consisting of organic acid salts of iron, inorganic acid salts of iron, neutral iron complexes, and iron complex salts.

[0023] The iron compound is preferably one or more compounds selected from the group consisting of iron (II) oxalate, iron (II) acetate, iron (III) nitrate, and ferrocene.

[0024] The temperature of the heating history is preferably a temperature above 100°C.

[0025] Another embodiment of the present disclosure is a method for producing a sulfur-based active material by the method for producing a sulfur-based active material, and then (3) producing an electrode using the sulfur-based active material by a conventional method. The method for producing an electrode comprises:

[0026] Another embodiment of the present disclosure is a method for producing a lithium ion secondary battery, comprising the steps of: producing an electrode by the above-described electrode production method; and (4) using the electrode to produce a lithium ion secondary battery by a conventional method.

[0027] <Firing ingredients> (acrylic resin) In the present disclosure, the acrylic resin is a polymer obtained by polymerizing at least one compound selected from the group consisting of acrylate compounds represented by the following formula (1), or at least one polymer selected from the group consisting of polymers obtained by polymerizing at least one compound selected from the group consisting of acrylate compounds represented by the following formula (1) and at least one compound selected from the group consisting of diacrylate compounds represented by the following formula (2). CH2=C(R 11 )COOR 12 (1) (where R 11 is a hydrogen atom or a methyl group, and R 12 is an alkyl group. CH2=C(R 21 )COO-Y-OCO(R 22 )C=CH2(2) (where R 21 and R 22 are the same or different and are a hydrogen atom or a methyl group, and Y is a linear hydrocarbylene group, which may have at least one substituent selected from the group consisting of a hydroxyl group and an alkyl group, and the carbon skeleton constituting the hydrocarbylene group may have an ether bond via an oxygen atom. However, when there are two or more ether bonds, there are always two or more carbon atoms between adjacent oxygen atoms.

[0028] In formula (1), R 11 is preferably a methyl group, and R 12is preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, and among these, a methyl group, an n-butyl group, an i-butyl group, or a t-butyl group is preferred. Examples of compounds represented by formula (1) include methyl (meth)acrylate, butyl (meth)acrylate, etc., and more preferably methyl methacrylate and butyl methacrylate. Here, the "(meth)acrylate" in methyl (meth)acrylate and butyl (meth)acrylate refers to either "acrylate" or "methacrylate" (the same applies hereinafter). An even more preferred example of a compound represented by formula (1) is butyl methacrylate.

[0029] In equation (2), R 21 and R 22 are preferably a methyl group. The number of carbon atoms in the hydrocarbylene group (straight chain) of Y is preferably 2 to 6, more preferably 2 or 3. The number of substituents in Y is preferably 1 to 4, more preferably 1 or 2. The substituents in Y are preferably one or more substituents selected from the group consisting of hydroxyl groups and alkyl groups having 1 to 4 carbon atoms, and the alkyl groups having 1 to 4 carbon atoms are preferably methyl groups. When the carbon skeleton of Y has an ether bond via an oxygen atom, for example, the portion corresponding to -YO- is preferably represented by the following formula (3) (however, in formula (3), the substituents in Y are not taken into consideration). -(CH2) l -(CH2CH2O) m -(CH2CH2CH2O) n - (3) (Here, l is between 0 and 6, m is between 0 and 3, and n is between 0 and 2. However, l, m, and n cannot all be 0 at the same time.)

[0030] In formula (3), it is preferred that l is 1, 2, 3, 4, 5 or 6, and m and n are 0; alternatively, m is 1, 2 or 3, and l and n are 0; or alternatively, n is 1 or 2, and l and m are 0.

[0031] Examples of the compound represented by formula (2) include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyne glycol di(meth)acrylate, glycerin di(meth)acrylate, etc. Among these, ethylene glycol dimethacrylate is preferred.

[0032] Preferred examples of acrylic resins include homopolymers of methyl (meth)acrylate, homopolymers of butyl (meth)acrylate, copolymers of methyl (meth)acrylate and ethylene glycol di(meth)acrylate, and copolymers of butyl (meth)acrylate and ethylene glycol di(meth)acrylate. Of these, methacrylate-type acrylic resins are preferred. More preferred examples of acrylic resins include copolymers of butyl methacrylate and ethylene glycol dimethacrylate.

[0033] One or more types of acrylic resins can be used.

[0034] [Form of acrylic resin] In the present disclosure, the acrylic resin is preferably in the form of fine particles. Here, "fine particles" refers to particles with a particle diameter of less than 300.0 μm. The particle diameter is preferably less than 270.0 μm, more preferably less than 200.0 μm, even more preferably less than 100.0 μm, even more preferably less than 50.0 μm, even more preferably less than 20.0 μm, even more preferably less than 15.0 μm, even more preferably less than 13.0 μm, even more preferably less than 10.0 μm, and even more preferably less than 6.0 μm. While the lower limit of the particle diameter is not particularly limited, it is typically greater than 0.1 μm, preferably greater than 1.0 μm. The particle diameter is measured using a precision particle size distribution analyzer, Multisizer 3, manufactured by Beckman Coulter, Inc.

[0035] The acrylic resin may be in the form of spherical particles or porous particles. When the acrylic resin is porous, its oil absorption is preferably greater than 100 mL / 100 g, more preferably greater than 110 mL / 100 g, even more preferably greater than 120 mL / 100 g, even more preferably greater than 130 mL / 100 g, and even more preferably greater than 140 mL / 100 g. The oil absorption is a value measured in accordance with JIS K 5101-13-2:2004. More specifically, it can be measured by the method described in paragraph 0069 of JP 2017-88501 A.

[0036] [Weight average molecular weight (Mw) of acrylic resin] The Mw of the acrylic resin is not particularly limited as long as it has the above structure. However, the Mw of the acrylic resin is usually in the range of more than 2,000 and less than 1,500,000. The Mw is a value measured by gel permeation chromatography (GPC) (calibrated with polystyrene).

[0037] [Acquisition or production of acrylic resin] The acrylic resins are commercially available or can be prepared by conventional methods within the knowledge of one skilled in the art, such as those manufactured by Sekisui Plastics Co., Ltd.

[0038] (sulfur) Sulfur can be used in various forms such as powdered sulfur, insoluble sulfur, precipitated sulfur, and colloidal sulfur, with precipitated sulfur and colloidal sulfur being preferred.

[0039] Regarding sulfur, from the viewpoint of the effects of the present disclosure, the ratio of the amount of sulfur to the total amount of acrylic resin and iron compound in the firing raw material (sulfur ratio) is preferably 1.5 or more and 5.0 or less in parts by mass. The ratio is more preferably 2.0 or more, even more preferably 2.5 or more, even more preferably greater than 2.5, even more preferably greater than 2.6, even more preferably greater than 2.7, even more preferably greater than 2.8, and even more preferably greater than 2.9. On the other hand, the ratio is more preferably less than 4.0, even more preferably 3.5 or less, even more preferably less than 3.4, even more preferably less than 3.3, even more preferably less than 3.2, and even more preferably less than 3.1.

[0040] The sulfur content is preferably 50 parts by mass or more, more preferably 100 parts by mass or more, even more preferably 300 parts by mass or more, even more preferably more than 400 parts by mass, even more preferably 500 parts by mass or more, and even more preferably more than 500 parts by mass, relative to 100 parts by mass of the acrylic resin. When the sulfur content is 50 parts by mass or more, charge / discharge capacity and cycle characteristics tend to be improved. On the other hand, there is no particular upper limit for the sulfur content, but it is usually less than 1000 parts by mass, preferably less than 900 parts by mass, even more preferably less than 800 parts by mass, and even more preferably less than 700 parts by mass. When the sulfur content is less than 1000 parts by mass, it tends to be advantageous in terms of cost.

[0041] Although any of various allotropes of sulfur can be used, sulfur containing S8 sulfur, which is solid at room temperature and pressure, is preferred, and simple S8 sulfur is more preferred.

[0042] (iron compounds containing divalent or trivalent iron ions) The iron compound containing divalent or trivalent iron ions is not particularly limited as long as it decomposes during firing and reacts with sulfur to produce iron disulfide, and various compounds can be used. Examples of such iron compounds include iron acid salts and iron complexes. Examples of iron acid salts include both organic and inorganic iron acid salts. On the other hand, examples of iron complexes include neutral iron complexes and salts of iron complex ions (iron complex salts).

[0043] Examples of organic acid salts of iron include divalent iron (Fe 2+ ) and organic acid salts, and trivalent iron (Fe 3+ ) and an organic acid salt. Of these, a salt of divalent iron and an organic acid is preferred. The organic acid is not particularly limited, and may be one having a carboxyl group (-COOH) or one having a sulfo group (-SO3H), but one having a carboxyl group is preferred. Specific examples of organic acids include fatty acids, oxalic acid, tartaric acid, citric acid, malic acid, and succinic acid. Specific examples of fatty acids include those having 1 to 6 carbon atoms, such as acetic acid, propionic acid, and butyric acid. Of these, acetic acid and oxalic acid are preferred. Preferred examples of iron organic acid salts include iron(II) acetate and iron(II) oxalate. These may be hydrates. One or more types of iron organic acid salts can be used.

[0044] Examples of inorganic salts of iron include divalent iron (Fe 2+ ) and inorganic acid salts, and trivalent iron (Fe 3+ ) and an inorganic acid. Of these, a salt of trivalent iron and an inorganic acid is preferred. Specific examples of inorganic acids include hydrochloric acid, sulfuric acid, and nitric acid. Of these, nitric acid is preferred. Preferred examples of inorganic acid salts of iron include iron(II) chloride, iron(III) chloride, iron(II) sulfate, iron(III) sulfate, iron(II) nitrate, and iron(III) nitrate. These may also be hydrates. One or more inorganic acid salts of iron can be used.

[0045] As an iron complex, for example, divalent iron (Fe 2+) complexes and trivalent iron (Fe 3+ ) complexes. The iron complex may be in the form of a neutral complex or a complex salt. The ligand coordinated to the iron ion is not particularly limited, and examples thereof include halogen atoms such as chlorine and bromine atoms, cyano groups, dicyclopentadienyl groups, and N,N'-bis(salicylidene)ethylenediamine. Examples of iron complexes include potassium hexacyanidoferrate(II) ([Fe(CN)6]K4), potassium hexacyanidoferrate(III) ([Fe(CN)6]K3), sodium tetrachloroferrate(III) ([FeCl4]Na), dicyclopentadienyl iron(II) (ferrocene), and N,N'-bis(salicylidene)ethylenediaminatoiron(III) chloride. One or more iron complexes can be used.

[0046] The iron compound containing divalent or trivalent iron ions can be at least one selected from the group consisting of the above-mentioned organic acid salts of iron, inorganic acid salts of iron, neutral iron complexes, and iron complex salts. Of these, organic acid salts of iron, inorganic acid salts of iron, and neutral iron complexes are preferred.

[0047] From the viewpoint of the effects of the present disclosure, the content of the iron compound containing divalent or trivalent iron ions is preferably 10 parts by mass or more and 300 parts by mass or less per 100 parts by mass of the acrylic resin. The content is more preferably 20 parts by mass or more, even more preferably more than 20 parts by mass, even more preferably more than 30 parts by mass, even more preferably more than 40 parts by mass, even more preferably 50 parts by mass or more, even more preferably more than 60 parts by mass, even more preferably more than 70 parts by mass, and even more preferably more than 75 parts by mass. On the other hand, the content is preferably less than 300 parts by mass, even more preferably less than 250 parts by mass, even more preferably less than 200 parts by mass, even more preferably less than 150 parts by mass, and even more preferably 100 parts by mass or less.

[0048] (Conductive carbon materials) The firing raw material may contain a carbon material having electrical conductivity. This is because the conductivity of the sulfur-based active material can be improved. As such a conductive carbon material, a carbon material having a graphite structure is preferable. As the carbon material, for example, those having a condensed aromatic ring structure such as carbon black, acetylene black, ketjen black, graphite, carbon nanotube (CNT), carbon fiber (CF), graphene, and fullerene can be used. As the conductive carbon material, one or more types can be used.

[0049] Among these, acetylene black, carbon black, and ketjen black are preferred because they are inexpensive and have excellent dispersibility. Furthermore, small amounts of CNTs or graphene may be used in combination with acetylene black, carbon black, or ketjen black. Such a combination system can further improve the cycle characteristics of lithium-ion secondary batteries without significantly increasing costs. The amount of CNTs or graphene used in combination is preferably 8% by mass or more, more preferably more than 8% by mass, of the total amount of conductive carbon material, and is preferably 12% by mass or less, more preferably less than 12% by mass.

[0050] The content of the conductive carbon material is preferably 5 parts by mass or more, more preferably more than 5 parts by mass, and even more preferably more than 10 parts by mass, relative to 100 parts by mass of the acrylic resin. A content of 5 parts by mass or more tends to facilitate the achievement of the objective of further improving the charge / discharge capacity and cycle characteristics. On the other hand, the content is preferably 50 parts by mass or less, more preferably less than 50 parts by mass, and even more preferably less than 40 parts by mass. A content of 50 parts by mass or less keeps the proportion of sulfur-containing structures in the sulfur-based active material from decreasing relatively, and tends to facilitate the achievement of the objective of further improving the charge / discharge capacity and cycle characteristics.

[0051] (Other ingredients) The firing raw materials may contain other materials commonly used in this field, as desired.

[0052] <Production of sulfur-based active materials> In the present disclosure, the sulfur-based active material can be produced by firing a firing raw material obtained by mixing an acrylic resin, sulfur, and an iron compound containing divalent or trivalent iron ions.

[0053] (Process (1)) Step (1) is a step of mixing an acrylic resin, sulfur, and an iron compound containing divalent or trivalent iron ions to obtain a calcination raw material for calcination. The method of mixing is not particularly limited as long as it is a method that thoroughly mixes these components, but in the present disclosure, at least the following wet method, in which mixing is performed using a solvent, or the dry method, in which mixing is performed without using a solvent, can be cited as preferred mixing methods.

[0054] [WET method] In the present disclosure, the WET method refers to a method for preparing a firing raw material, (1-a-1) a step of adding the acrylic resin and the iron compound containing divalent or trivalent iron ions to an organic solvent and mixing them to obtain a liquid mixture; (1-a-2) removing the organic solvent from the liquid mixture to obtain a dry mixture; and (1-a-3) Mixing the dry mixture with sulfur It includes:

[0055] In step (1-a-1), the method for adding the acrylic resin and the iron compound containing divalent or trivalent iron ions to the organic solvent is not particularly limited, as long as they can be mixed to obtain a liquid mixture. For example, (1) the acrylic resin and the iron compound containing divalent or trivalent iron ions may be simultaneously added to the organic solvent and mixed, (2) the acrylic resin may be added to the organic solvent and mixed, and then the iron compound containing divalent or trivalent iron ions may be added and mixed, or (3) the iron compound containing divalent or trivalent iron ions may be added to the organic solvent and mixed, and then the acrylic resin may be added and mixed.

[0056] In step (1-a-1), the organic solvent may be any organic solvent commonly used in this field, and examples of such solvents include N-methyl-2-pyrrolidone, N,N-dimethylformaldehyde, alcohol, hexane, water, acetone, ethers such as tetrahydrofuran, etc. Furthermore, the organic solvent is preferably one that dissolves the acrylic resin, as this contributes to good mixing. One or more of these solvents may be used.

[0057] The organic solvent and the acrylic resin and / or the iron compound containing divalent or trivalent iron ions can be mixed, for example, by stirring in a container such as a beaker.

[0058] In step (1-a-2), the organic solvent can be removed by a conventional method, such as by a method involving heating, or by a drying method not involving heating. For example, the removal can be carried out by subjecting the liquid mixture to a drying method such as drying under reduced pressure.

[0059] The dry mixture thus obtained is preferably pulverized before being subjected to the next step. This is because it is expected that the mixing in step (1-a-3) can be carried out more efficiently. The pulverization can be carried out by a conventional method, for example, using a cutter mill or a freezing pulverizer. In particular, it is preferable to perform coarse pulverization using a cutter mill and then fine pulverization using a freezing pulverizer.

[0060] For the pulverized product, the preferred particle size is 1 μm or more in median diameter, more preferably greater than 1 μm, even more preferably greater than 2 μm, even more preferably greater than 3 μm, and even more preferably greater than 4 μm. The median diameter is preferably 40 μm or less, more preferably less than 40 μm, even more preferably less than 30 μm, even more preferably less than 20 μm, even more preferably less than 15 μm, and even more preferably less than 10 μm. From the perspective of the effects of the present disclosure, the median diameter is preferably within the above range. The median diameter can be measured by the method described below.

[0061] In the step (1-a-3), the dry mixture and sulfur can be mixed by a conventional method, for example, by using a blender.

[0062] [DRY method] In the present disclosure, the DRY method refers to a method for preparing a firing raw material, (1-b) The method includes a step of mixing the acrylic resin, the sulfur, and the iron compound containing divalent or trivalent iron ions, all in a powder state.

[0063] Here, powder refers to a state in which the solid raw materials are sufficiently finely divided to be suitable for mixing for the purposes of this disclosure. The particle size of the particles constituting the powder is not particularly limited as long as mixing is carried out satisfactorily, but the median diameter is typically, for example, in the range of 1 μm to 40 μm. From the perspective of the effects of this disclosure, the particle size is preferably greater than 1 μm, more preferably greater than 2 μm, even more preferably greater than 3 μm, and even more preferably greater than 4 μm, while preferably less than 40 μm, more preferably less than 40 μm, more preferably less than 30 μm, even more preferably less than 20 μm, even more preferably less than 15 μm, and even more preferably less than 10 μm. The median diameter can be measured by the method described below.

[0064] The mixing can be carried out by a conventional method, for example, in the same manner as in the mixing in the above step (1-a-3).

[0065] In both the wet and dry methods, it is desirable to thoroughly mix the firing raw materials in advance. Furthermore, when a conductive carbon material or the like is added to the firing raw materials, these additives may be mixed in advance so that they are contained in the firing raw materials before firing.

[0066] The calcined raw material thus obtained may be used as it is in the next step (2), or may be formed into pellets, if desired, before being used in step (2).

[0067] (Process (2)) Step (2) is a step of calcining the calcination raw material obtained above. Calcination of the calcination raw material can be carried out by a conventional method, for example, by heating the calcination raw material at a predetermined temperature increase rate until it reaches a predetermined temperature, maintaining the predetermined temperature for a predetermined time, and then allowing it to cool naturally.

[0068] [Non-oxidizing atmosphere] The firing is preferably carried out in a non-oxidizing atmosphere. A non-oxidizing atmosphere is an atmosphere substantially free of oxygen, and is employed to suppress oxidative degradation and excessive thermal decomposition of the constituent components. Specifically, this refers to an inert gas atmosphere such as nitrogen or argon, or a sulfur gas atmosphere. Therefore, the modification is carried out, for example, in a quartz tube under an inert gas atmosphere.

[0069] [Temperature increase rate] The temperature rise rate is preferably, for example, in the range of 50°C / h to 500°C / h. The temperature rise rate is preferably greater than 100°C / h, more preferably greater than 150°C / h. On the other hand, the temperature rise rate is more preferably less than 400°C / h, and even more preferably less than 350°C / h. When the temperature rise rate is within such a range, it tends to be easier to achieve the objective of improving charge / discharge capacity and cycle characteristics.

[0070] [Baking temperature and time] The calcination temperature refers to the temperature after the temperature rise of the calcination raw material is completed and is maintained for a certain period of time to calcinate the calcination raw material. The temperature is preferably in the range of more than 250°C and less than 500°C. A temperature above 250°C tends to avoid insufficient sulfurization reaction and prevent a decrease in the charge / discharge capacity of the target product. On the other hand, a temperature below 500°C tends to prevent decomposition of the calcination raw material and prevent a decrease in yield and a decrease in charge / discharge capacity. The temperature is more preferably above 300°C, even more preferably above 350°C, and even more preferably above 380°C. On the other hand, less than 480°C is more preferable, and less than 450°C is even more preferable.

[0071] From the viewpoint of the effects of the present disclosure, the firing temperature in the step (2) is preferably higher than the temperature at which the iron compound containing divalent or trivalent iron ions thermally decomposes.

[0072] The time for maintaining the calcination temperature may be appropriately set depending on the type of calcination raw material, the calcination temperature, etc. For example, in the case of the treatment method exemplified in the Examples section, the time is preferably 1 hour or more and 6 hours or less. A time of 1 hour or more tends to allow the calcination to proceed sufficiently, while a time of 6 hours or less tends to prevent excessive thermal decomposition of the constituent components. The time is preferably more than 1 hour, more preferably more than 1.5 hours. On the other hand, the time is preferably less than 6 hours, more preferably less than 4 hours.

[0073] [Device] The calcination can be carried out, for example, in a muffle furnace (FIG. 1), or can be carried out using a continuous apparatus such as a twin-screw extruder. The use of a continuous apparatus has the advantage that the sulfur-based active material can be produced continuously through a series of operations, such as kneading, pulverizing, and mixing the raw materials while calcining them in the apparatus.

[0074] A muffle furnace (Figure 1) is a furnace partitioned by a hot plate or the like to prevent the heat source (heater) from being exposed inside the furnace in order to prevent sample contamination. In Figure 1, muffle furnace 1 has heater 2 at the bottom of the furnace, which is partitioned by a hot plate. A lid 3 is installed on the front of the furnace (on the left end in the figure), and the furnace is designed to maintain an atmosphere of inert gas 4 inside. A thermocouple (not shown) is attached to the lid, allowing the temperature inside the furnace to be measured during firing. Inside the furnace, two tiers of stainless steel rectangular trays 5 and 6 are installed, one on the upper tier and one on the lower tier, for firing the raw materials.

[0075] Gas (e.g., an inert gas such as argon (Ar) gas) can be continuously supplied to and discharged from the inside of the furnace through a gas inlet pipe 7 and a gas outlet pipe 8. The gas outlet pipe 8 is connected to a trap tank 10 containing an aqueous sodium hydroxide solution 9, and exhaust gas from the muffle furnace 1 attempting to exit through the gas outlet pipe 8 to the outside first passes through the aqueous sodium hydroxide solution 9 in the trap tank 10 before being released to the outside. Therefore, even if the exhaust gas contains hydrogen sulfide gas generated by the reaction, it is neutralized by the aqueous sodium hydroxide solution and removed from the exhaust gas.

[0076] (Unreacted sulfur removal process) The treated product obtained after calcination contains unreacted sulfur, which is the sulfur that sublimed during calcination and then cooled and precipitated, but in the method of the present disclosure, it is not necessary to remove these residues. However, the residues may be removed by a method that does not involve heating, such as drying under reduced pressure or washing with a solvent.

[0077] (Crushing, classification) The obtained sulfur-based active material can be pulverized to a predetermined particle size and classified to obtain particles of a size suitable for electrode production. From the viewpoint of the effects of the present disclosure, the particle size distribution preferably has a median diameter of approximately 1 μm or more and 40 μm or less. The median diameter is preferably greater than 1 μm, more preferably greater than 2 μm, even more preferably greater than 3 μm, even more preferably greater than 4 μm, and even more preferably greater than 5 μm. The median diameter is preferably less than 40 μm, more preferably less than 30 μm, even more preferably less than 20 μm, even more preferably less than 15 μm, and even more preferably less than 10 μm. The median diameter can be determined by measuring the volume-based cumulative 50% diameter (median diameter D50) using a laser diffraction / scattering particle size distribution analyzer (LA-960 manufactured by Horiba, Ltd.) with water as the dispersion medium.

[0078] In the firing method using the twin-screw extruder described above, the shearing during kneading can produce the sulfur-based active material and simultaneously pulverize the produced sulfur-based active material.

[0079] (heating history) In the present disclosure, the heating history refers to the history of heat treatment that the calcined raw material undergoes. The heating history typically refers to a temperature reached by the calcined raw material exceeding 50°C, more typically exceeding 60°C, even more typically exceeding 70°C, even more typically exceeding 80°C, even more typically exceeding 90°C, even more typically exceeding 100°C, even more typically exceeding 110°C, even more typically exceeding 120°C, even more typically exceeding 130°C, even more typically exceeding 140°C, and even more typically exceeding 150°C. In the production method of the present disclosure, the calcined raw material does not undergo any heating history other than the calcination in step (2) above.

[0080] <Sulfur-based active material> The sulfur-based active material obtained above will be described below. The sulfur-based active material obtained above contains a sulfur-modified acrylic resin (acrylic resin sulfide) and iron disulfide, and the composite active material contains unreacted sulfur, and contains at least carbon, sulfur, and iron as constituent elements. The sulfur content shown below is the amount contained in the sulfur-based active material. Furthermore, the fact that the sulfur-based active material obtained above contains iron disulfide is based on a comparison with the diffraction intensity peak profile of iron disulfide (pyrite) obtained by X-ray diffraction measurement.

[0081] (Sulfur content) The range of sulfur content in the sulfur-based active material thus obtained will be described. When unreacted sulfur is not removed after firing, the sulfur content in the sulfur-based active material is typically greater than 55.0 mass%, more typically greater than 60.0 mass%, even more typically greater than 61.0 mass%, even more preferably greater than 62.0 mass%, and even more typically greater than 63.0 mass%. Meanwhile, the sulfur content is usually less than 70.0 mass% or less than 65.0 mass%. However, when a conductive carbon material is added, the sulfur content may be slightly lower due to the influence of the carbon constituting the conductive carbon material. In such cases, the sulfur content is considered to be approximately 5.0 mass% lower than the above-mentioned sulfur content. Furthermore, when unreacted sulfur is removed after firing without a heating history, the sulfur content decreases by the amount removed.

[0082] <Lithium-ion secondary battery> The sulfur-based active material of the present disclosure can be used as an electrode active material for a lithium-ion secondary battery, i.e., as a positive electrode active material or a negative electrode active material. That is, a lithium-ion secondary battery electrode can be fabricated in the same manner as a general lithium-ion secondary battery electrode, except that the sulfur-based active material is used. Furthermore, a lithium-ion secondary battery can be fabricated in the same manner as a general lithium-ion secondary battery, except that the lithium-ion secondary battery electrode is used. The lithium-ion secondary battery fabricated in this manner has a large charge / discharge capacity and excellent cycle characteristics.

[0083] 1. When sulfur-based active materials are used as positive electrode active materials The lithium ion secondary battery of the present disclosure can be produced in accordance with a conventional method by using a positive electrode containing the above-described sulfur-based active material (positive electrode active material), a negative electrode, an electrolyte, and, if desired, components such as a separator.

[0084] (positive electrode) The positive electrode for a lithium-ion secondary battery can be fabricated in the same manner as a general positive electrode for a lithium-ion secondary battery, except that the sulfur-based active material is used as the positive electrode active material. For example, the positive electrode can be fabricated by mixing particulate sulfur-based active material with a conductive additive, a binder, and a solvent to prepare a paste-like positive electrode material, applying the positive electrode material to a current collector, and then drying the paste. Alternatively, the positive electrode can be fabricated by kneading the sulfur-based active material with the conductive additive, the binder, and a small amount of solvent in a mortar or the like, forming a film, and then pressing the film onto a current collector using a press or the like.

[0085] [Conductive additive] Examples of the conductive additive include vapor grown carbon fiber (VGCF), carbon powder, carbon black (CB), acetylene black (AB), ketjen black (KB), graphite, or fine powder of a metal that is stable at a positive electrode potential, such as aluminum or titanium. These conductive additives can be used alone or in combination.

[0086] [Binder] Examples of binders include polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyimide (PI), polyamide-imide (PAI), carboxymethyl cellulose (CMC), polyvinyl chloride (PVC), acrylic resin, methacrylic resin (PMA), polyacrylonitrile (PAN), modified polyphenylene oxide (PPO), polyethylene oxide (PEO), polyethylene (PE), polypropylene (PP), etc. These binders can be used alone or in combination of two or more.

[0087] [solvent] Examples of the solvent include N-methyl-2-pyrrolidone, N,N-dimethylformaldehyde, alcohol, hexane, water, etc. These solvents can be used alone or in combination of two or more.

[0088] [Amount] The amounts of the materials constituting the positive electrode are not particularly limited, but for example, it is preferable to mix 2 parts by mass or more and 100 parts by mass or less of a conductive additive, 2 parts by mass or more and 50 parts by mass or less of a binder, and an appropriate amount of a solvent with respect to 100 parts by mass of a sulfur-based active material.

[0089] [Current collector] The current collector may be one generally used for the positive electrode of a lithium-ion secondary battery. Examples of current collectors include aluminum foil, aluminum mesh, punched aluminum sheet, expanded aluminum sheet, stainless steel foil, stainless steel mesh, punched stainless steel sheet, expanded stainless steel sheet, foamed nickel, nonwoven nickel fabric, copper foil, copper mesh, punched copper sheet, expanded copper sheet, titanium foil, titanium mesh, nonwoven carbon fabric, and woven carbon fabric. Among these, current collectors made of highly graphitized carbon nonwoven fabric and woven carbon fabric are suitable as current collectors when the sulfur-based active material of the present disclosure is used as the positive electrode active material because they do not contain hydrogen and have low reactivity with sulfur. Raw materials for highly graphitized carbon fibers include various pitches (i.e., by-products of petroleum, coal, coal tar, etc.) and polyacrylonitrile fiber (PAN), which are commonly used as carbon fiber materials. One type of current collector may be used, or two or more types may be used in combination.

[0090] (Negative electrode) Examples of anode materials that can be used include known metallic lithium, carbon-based materials such as graphite, silicon-based materials such as silicon thin films, and alloy-based materials such as copper-tin and cobalt-tin. Lithium-free materials, such as carbon-based, silicon-based, and alloy-based materials among the above-mentioned anode materials, are advantageous in that they are less likely to cause short circuits between the positive and negative electrodes due to dendrite formation. However, when these lithium-free anode materials are used in combination with the positive electrode of the present disclosure, neither the positive nor negative electrodes contain lithium. Therefore, a lithium pre-doping process is required to pre-insert lithium into either or both of the negative and positive electrodes. Known methods for pre-doping lithium can be used. For example, when doping lithium into the anode, lithium can be inserted into a half-cell using metallic lithium as the counter electrode by electrochemical doping, or by pre-doping, in which metallic lithium foil is attached to the electrode and then left in an electrolyte solution to allow lithium to diffuse into the electrode. The above-mentioned electrolytic doping method can also be used when pre-doping the positive electrode with lithium. As a lithium-free negative electrode material, a silicon-based material, which is a high-capacity negative electrode material, is particularly preferred, and among them, thin-film silicon, which has a thin electrode thickness and is advantageous in terms of capacity per volume, is more preferred.

[0091] (electrolyte) The electrolyte used in a lithium ion secondary battery can be an organic solvent in which an electrolyte alkali metal salt is dissolved. The organic solvent is preferably at least one selected from non-aqueous solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl ether, γ-butyrolactone, and acetonitrile. The electrolyte can be LiPF6, LiBF4, LiAsF6, LiCF3SO3, LiI, or LiClO4. The electrolyte concentration may be approximately 0.5 mol / L or more and 1.7 mol / L or less. The electrolyte is not limited to a liquid. For example, when the lithium ion secondary battery is a lithium polymer secondary battery, the electrolyte is solid (e.g., polymer gel).

[0092] (separator) In addition to the negative electrode, positive electrode, and electrolyte described above, a lithium-ion secondary battery may also include components such as a separator. The separator is interposed between the positive electrode and negative electrode, allowing ions to move between the positive electrode and negative electrode and preventing internal short-circuiting between the positive electrode and negative electrode. If the lithium-ion secondary battery is a sealed type, the separator is also required to have the function of retaining the electrolyte. As the separator, a thin, microporous or nonwoven membrane made of a material such as polyethylene, polypropylene, polyacrylonitrile, aramid, polyimide, cellulose, or glass is preferably used.

[0093] (shape) The shape of the lithium ion secondary battery is not particularly limited, and it can be in various shapes such as a cylindrical type, a laminated type, a coin type, a button type, and the like.

[0094] 2. When sulfur-based active materials are used as negative electrode active materials The lithium ion secondary battery of the present disclosure can be produced in accordance with a conventional method by using a negative electrode containing the above-described sulfur-based active material (negative electrode active material), a positive electrode, an electrolyte, and, if desired, components such as a separator.

[0095] (Negative electrode) The negative electrode for a lithium-ion secondary battery can be fabricated in the same manner as a general negative electrode for a lithium-ion secondary battery, except that the sulfur-based active material is used as the negative electrode active material. For example, the negative electrode can be fabricated by mixing particulate sulfur-based active material with a conductive additive, a binder, and a solvent to prepare a paste-like negative electrode material, applying the paste to a current collector, and then drying the paste. Alternatively, the negative electrode can be fabricated by kneading the sulfur-based active material with the conductive additive, the binder, and a small amount of solvent in a mortar or the like, forming a film, and then pressing the film onto a current collector using a press or the like.

[0096] The conductive additive, binder, and solvent can be the same as those used in the above case where a sulfur-based active material is used as the positive electrode active material, and the same current collector can also be used.

[0097] (positive electrode) The positive electrode material is not particularly limited as long as it is, for example, a lithium-containing transition metal oxide or solid solution oxide, or a substance that can electrochemically absorb and release lithium ions. Examples of lithium-containing transition metal oxides include Li-Co composite oxides such as LiCoO2, LiNi x Co y Mn z Examples of the solid solution oxide include Li·Ni·Co·Mn-based composite oxides such as LiO2, Li·Ni-based composite oxides such as LiNiO2, and Li·Mn-based composite oxides such as LiMn2O4. a Mn x Co y Ni z O2 (1.150≦a≦1.430, 0.450≦x≦0.600, 0.100≦y≦0.150, 0.200≦z≦0.280), LiMn x Co y Ni z O2 (0.300≦x≦0.850, 0.100≦y≦0.300, 0.100≦z≦0.300), LiMn 1.5 Ni 0.5O4, etc. These compounds may be used alone or in combination.

[0098] The electrolyte, separator, and shape of the lithium ion secondary battery can also be the same as those used in the above case where a sulfur-based active material is used as the positive electrode active material. [Example]

[0099] The present disclosure will be described based on examples, but the present disclosure is not limited to only the examples.

[0100] The various chemicals used in the examples and comparative examples are listed below. The various chemicals were purified according to conventional methods as necessary.

[0101] <Materials used in the test> Acrylic resin 1: Spherical acrylic resin consisting of a homopolymer of methyl methacrylate (Techpolymer MB-4 manufactured by Sekisui Plastics Co., Ltd., particle size: 4 μm) Acrylic resin 2: spherical acrylic resin consisting of a homopolymer of methyl methacrylate (Parapet GF-P manufactured by Kuraray Co., Ltd., particle size: 270 μm) Iron compound 1 (organic acid salt): Iron(II) oxalate dihydrate (Iron(II) oxalate dihydrate, Grade 1, manufactured by Kanto Chemical Co., Ltd.) Iron compound 2 (organic acid salt): Iron(II) acetate (Iron(II) acetate manufactured by Kanto Chemical Co., Ltd.) Sulfur: Precipitated sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.

[0102] Production Example 1 (Preparation of firing raw materials by the dry method) According to the formulation in Table 1, acrylic resin, sulfur, and an iron compound were mixed in a blender in powder form to obtain a firing raw material for firing.

[0103] Example 1 <Production of sulfur-based active materials> (Reaction Apparatus) The raw materials were fired in a muffle furnace (Fig. 1). The muffle furnace in Fig. 1 was as described above.

[0104] (Firing process) First, the firing raw material was placed in a SUS container, and the atmosphere in the muffle furnace was replaced with Ar gas three times using a vacuum pump. Then, Ar gas was continuously supplied from the gas inlet tube at a flow rate of 100 mL / min, and 30 minutes after the start of supply, heating of the muffle furnace began. The temperature was increased at a rate of 5 ° C. / min, and when the temperature of the firing raw material reached 400 ° C., heat treatment was performed for 2 hours while maintaining the temperature at 400 ° C. Next, while adjusting the flow rate of Ar gas, the temperature of the fired product was naturally cooled to 25 ° C. under an Ar gas atmosphere, and then the fired product was removed from the muffle furnace.

[0105] (Crushing process) The fired product was pulverized using a cutter mill (free speed mill, FS-20, manufactured by LabNect Co., Ltd.).

[0106] (Classification process) In order to remove coarse particles from the pulverized fired product, the product was classified using a stainless steel sieve with a mesh of 32 μm to obtain a sulfur-based active material.

[0107] <Fabrication of lithium-ion secondary batteries> A lithium ion secondary battery was fabricated as follows.

[0108] (positive electrode) The sulfur-based active material obtained above was used as the active material, acetylene black as the conductive additive, and acrylic resin as the binder. These were weighed in a ratio of 85:10:5 (mass%) of active material, conductive additive, and binder, and placed in a container. MilliQ water was used as a dispersant and the mixture was stirred and mixed using a centrifugal mixer (ARE-250, manufactured by Thinky Corporation) to produce a uniform slurry. The resulting slurry was applied to a 20 μm aluminum foil using an applicator with a 60 μm slit width. The compressed electrode was heated in a dryer at 120 °C for 3 hours, dried, and punched out to a diameter of 11 mm to obtain an electrode (positive electrode). The mass of the electrode was then measured, and the amount of active material in the electrode was calculated from the above ratio.

[0109] (Negative electrode) As the negative electrode, a metallic lithium foil (disk-shaped, 14 mm in diameter and 500 μm in thickness, manufactured by Honjo Metals Co., Ltd.) was used.

[0110] (electrolyte) The electrolyte used was a non-aqueous electrolyte prepared by dissolving LiPF6 in a mixed solvent of ethylene carbonate and diethyl carbonate. The ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1:1. The concentration of LiPF6 in the electrolyte was 1.0 mol / L.

[0111] (lithium-ion secondary battery) A coin battery was fabricated using the above positive electrode, negative electrode, and electrolyte. Specifically, in a dry room, a separator (Celgard 2400, a 25 μm thick polypropylene microporous membrane manufactured by Celgard Corporation), a glass nonwoven fabric filter (440 μm thick, GA100 manufactured by Advantec Corporation), and an electrolyte were filled between the positive electrode and negative electrode to form an electrode assembly battery. This electrode assembly battery was housed in a battery case (CR2032 type coin battery material, manufactured by Hosen Co., Ltd.) made of a stainless steel container. The above electrolyte was poured into the battery case. The battery case was sealed using a crimping machine to obtain the lithium ion secondary battery of Example 1.

[0112] Examples 2 to 6 and Comparative Examples 1 to 3 A sulfur-based active material and a lithium-ion secondary battery were produced in the same manner as in Example 1, except for making appropriate changes according to Table 1. However, when a desulfurization step was performed (for example, in the cases of Comparative Examples 1 and 3), the desulfurization step described below was performed after the pulverization step.

[0113] (Desulfurization process) To remove unreacted sulfur (free elemental sulfur) and low-molecular-weight sulfur compounds remaining in the fired product, the following process was carried out. The fired product was crushed in a mortar, placed in a glass tube oven, and heated at 250°C for 3 hours while evacuating to obtain a fired product from which unreacted sulfur had been removed (or which contained only trace amounts of unreacted sulfur). The heating rate was 10°C / min.

[0114] <Measurement of discharge capacity and capacity retention rate> The coin-shaped lithium-ion secondary batteries prepared in each Example and Comparative Example were charged and discharged at a current value equivalent to 50 mA (0.1 C) per 1 g of positive electrode active material at a test temperature of 30° C. The discharge end voltage was 1.0 V, and the charge end voltage was 3.0 V. Charging and discharging were repeated, and the battery discharge capacity (mAh) was observed after 1, 2, 3, and 10 cycles.

[0115] The second discharge capacity (mAh / g) was taken as the initial capacity. The larger the initial capacity, the greater the charge / discharge capacity of the lithium-ion secondary battery, and the more preferable it can be evaluated. In addition, the third discharge capacity DC3 (mAh / g) and the tenth discharge capacity DC 10 (mAh / g) according to the following formula (a): Capacity retention rate (%)=(DC 10 / DC3)×100 (a) As explained above, the higher the capacity retention rate, the better the cycle characteristics of the lithium ion secondary battery.

[0116] <Sulfur mass ratio (%)> The mass ratio (%) of sulfur in the sulfur-based active material was determined by calculating the proportion of sulfur in the total mass of the sulfur-based active material from the mass of sulfur measured using a Dionex ion chromatograph DX-320 and a Dionex column (IonPac AS12A).

[0117] [Table 1]

[0118] <Embodiment> The following describes a preferred embodiment.

[0119] [1] (1) A step of mixing an acrylic resin, sulfur, and an iron compound containing divalent or trivalent iron ions to obtain a firing raw material; and (2) A step of firing the firing raw material A method for producing a sulfur-based active material comprising: A method for producing a sulfur-based active material, wherein the firing raw material is subjected to a single heating history. [2] The method for producing a sulfur-based active material according to [1] above, wherein the content of the iron compound containing the divalent or trivalent iron ion in the firing raw material is 10 parts by mass or more and 300 parts by mass or less, preferably 20 parts by mass or more and less than 250 parts by mass, more preferably more than 20 parts by mass and less than 250 parts by mass, even more preferably more than 30 parts by mass and less than 200 parts by mass, even more preferably more than 40 parts by mass and less than 150 parts by mass, and even more preferably 50 parts by mass or more and 100 parts by mass or less, relative to 100 parts by mass of the acrylic resin. [3] The method for producing a sulfur-based active material according to [1] or [2], wherein the step (1) comprises mixing the acrylic resin, the sulfur, and the iron compound containing divalent or trivalent iron ions, all in a powder state. [4] The method for producing a sulfur-based active material according to any one of [1] to [3], wherein the temperature of the firing in the step (2) is higher than 250°C and lower than 500°C, preferably higher than 300°C and lower than 480°C, more preferably higher than 350°C and lower than 450°C, and even more preferably higher than 380°C and lower than 450°C. [5] The method for producing a sulfur-based active material according to any one of [1] to [4], wherein the firing temperature in the step (2) is higher than the temperature at which the iron compound containing the divalent or trivalent iron ion thermally decomposes. [6] The method for producing a sulfur-based active material according to any one of [1] to [5], wherein the ratio of the amount of sulfur to the total amount of the acrylic resin and the iron compound in the firing raw material is 1.5 or more and 5.0 or less, preferably 2.0 or more and less than 4.0, more preferably 2.5 or more and less than 3.5, even more preferably more than 2.5 and less than 3.5, even more preferably more than 2.6 and less than 3.4, even more preferably more than 2.7 and less than 3.3, even more preferably more than 2.8 and less than 3.2, and even more preferably more than 2.9 and less than 3.1. [7] The method for producing a sulfur-based active material according to any one of [1] to [6], wherein the acrylic resin is a polymer obtained by polymerizing at least one selected from the group consisting of acrylate compounds represented by the following formula (1), or at least one polymer selected from the group consisting of polymers obtained by polymerizing at least one selected from the group consisting of acrylate compounds represented by the following formula (1) and at least one selected from the group consisting of diacrylate compounds represented by the following formula (2): CH2=C(R 11 )COOR 12 (1) (where R 11 is a hydrogen atom or a methyl group, and R 12 is an alkyl group. CH2=C(R 21 )COO-Y-OCO(R 22 )C=CH2(2) (where R 21 and R 22are the same or different and are a hydrogen atom or a methyl group, and Y is a linear hydrocarbylene group, which may have at least one substituent selected from the group consisting of a hydroxyl group and an alkyl group, and the carbon skeleton constituting the hydrocarbylene group may have an ether bond via an oxygen atom. However, when there are two or more ether bonds, there are always two or more carbon atoms between adjacent oxygen atoms. [8]R 12 is an alkyl group having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms; Y is a linear hydrocarbylene group having 2 to 6 carbon atoms, preferably 2 or 3 carbon atoms; the hydrocarbylene group has 1 to 4 substituents, preferably 1 or 2; the alkyl group as the substituent has 1 to 4 carbon atoms, preferably 1; and the carbon skeleton constituting the hydrocarbylene group has 1 to 2 ether bonds. [9] The method for producing a sulfur-based active material according to any one of [1] to [8], wherein the iron compound is one or more compounds selected from the group consisting of iron salts and iron complexes.

[10] The method for producing a sulfur-based active material according to any one of [1] to [8], wherein the iron compound is one or more compounds selected from the group consisting of organic acid salts of iron, inorganic acid salts of iron, neutral iron complexes, and iron complex salts.

[11] The method for producing a sulfur-based active material according to any one of [1] to [8], wherein the iron compound is one or more compounds selected from the group consisting of iron (II) oxalate, iron (II) acetate, iron (III) nitrate, and ferrocene.

[12] The method for producing a sulfur-based active material according to any one of [1] to

[11] , wherein the temperature of the heating history is higher than 50°C, more preferably higher than 60°C, even more preferably higher than 70°C, even more preferably higher than 80°C, even more preferably higher than 90°C, higher than 100°C, preferably higher than 110°C, more preferably higher than 120°C, even more preferably higher than 130°C, even more preferably higher than 140°C, even more preferably higher than 150°C.

[13] After producing a sulfur-based active material by the method for producing a sulfur-based active material according to any one of [1] to

[12] , (3) A step of preparing an electrode using the sulfur-based active material by a conventional method. A method for manufacturing an electrode, comprising:

[14] After producing an electrode by the method for producing an electrode according to

[13] above, (4) A step of producing a lithium ion secondary battery using the electrode by a conventional method. A method for producing a lithium ion secondary battery comprising the steps of: [Explanation of symbols]

[0120] 1 muffle furnace 2 heaters 3 Lid 4. Inert gas 5 Tray (upper) 6 Tray (lower) 7 Gas inlet pipe 8 Gas exhaust pipe 9. Sodium hydroxide solution 10 Trap tank

Claims

1. (1) a step of mixing an acrylic resin, sulfur, and an iron compound containing divalent or trivalent iron ions to obtain a firing raw material; and (2) A step of firing the firing raw material A method for producing a sulfur-based active material comprising: the content of the iron compound containing the divalent or trivalent iron ion in the firing raw material is 10 parts by mass or more and 300 parts by mass or less relative to 100 parts by mass of the acrylic resin, the content of the sulfur in the firing raw material is 50 parts by mass or more and less than 1000 parts by mass with respect to 100 parts by mass of the acrylic resin, The method for producing a sulfur-based active material, wherein the firing raw material is subjected to a single heating history.

2. the content of the iron compound containing the divalent or trivalent iron ion in the firing raw material is 10 parts by mass or more and less than 150 parts by mass relative to 100 parts by mass of the acrylic resin, The method for producing a sulfur-based active material according to claim 1, wherein the content of the sulfur in the firing raw material is 300 parts by mass or more and less than 700 parts by mass with respect to 100 parts by mass of the acrylic resin.

3. 3. The method for producing a sulfur-based active material according to claim 1 or 2, wherein the step (1) includes a step of mixing the acrylic resin, the sulfur, and the iron compound containing divalent or trivalent iron ions, all in a powder state.

4. The method for producing a sulfur-based active material according to any one of claims 1 to 3, wherein the firing temperature in the step (2) is higher than 250 ° C. and lower than 500 ° C.

5. The baking temperature in the step (2) is a temperature higher than the temperature at which the iron compound containing the divalent or trivalent iron ion thermally decomposes. The method for producing a sulfur-based active material according to any one of claims 1 to 4.

6. The ratio of the amount of sulfur to the total amount of the acrylic resin and the iron compound in the firing raw material is 1.5 to 5.0 in terms of parts by mass. The method for producing a sulfur-based active material according to any one of claims 1 to 5.

7. The acrylic resin is a polymer obtained by polymerizing at least one selected from the group consisting of acrylate compounds represented by the following formula (1), or the group consisting of at least one selected from the group consisting of acrylate compounds represented by the following formula (1) and at least one selected from the group consisting of diacrylate compounds represented by the following formula (2): The method for producing a sulfur-based active material according to any one of claims 1 to 6, wherein the polymer is at least one selected from the group consisting of polymers obtained by polymerizing at least one selected from the group consisting of diacrylate compounds represented by the following formula (2): CH 2 =C(R 11 )COOR 12 (1) (where R 11 is a hydrogen atom or a methyl group, and R 12 is an alkyl group.) CH 2 =C(R 21 )COO-Y-OCO(R 22 )C=CH 2 (2) (where R 21 and R 22 are the same or different and are a hydrogen atom or a methyl group, and Y is a linear hydrocarbylene group, which may have at least one substituent selected from the group consisting of a hydroxyl group and an alkyl group, and the carbon skeleton constituting the hydrocarbylene group may have an ether bond via an oxygen atom, provided that when there are two or more ether bonds, there are always two or more carbon atoms between adjacent oxygen atoms.

8. R 12 is an alkyl group having 1 to 6 carbon atoms, Y is a linear hydrocarbylene group having 2 to 6 carbon atoms, the hydrocarbylene group has 1 to 4 substituents, the alkyl group as the substituent has 1 to 4 carbon atoms, and the carbon skeleton constituting the hydrocarbylene group has 1 to 2 ether bonds.

9. The method for producing a sulfur-based active material according to any one of claims 1 to 8, wherein the iron compound is one or more compounds selected from the group consisting of iron acid salts and iron complexes.

10. The iron compound is one or more compounds selected from the group consisting of an organic acid salt of iron, an inorganic acid salt of iron, a neutral iron complex, and an iron complex salt. The method for producing a sulfur-based active material according to any one of claims 1 to 8.

11. The iron compound is one or more compounds selected from the group consisting of iron oxalate (II), iron acetate (II), iron nitrate (III), and ferrocene. The method for producing a sulfur-based active material according to any one of claims 1 to 8.

12. The method for producing a sulfur-based active material according to any one of claims 1 to 11, wherein the temperature of the heating history is a temperature higher than 50 ° C.

13. After producing a sulfur-based active material by the method for producing a sulfur-based active material according to any one of claims 1 to 12, (3) A step of producing an electrode using the sulfur-based active material A method for manufacturing an electrode, comprising:

14. After the electrode is produced by the method for producing an electrode according to claim 13, (4) A step of producing a lithium ion secondary battery using the electrode. A method for producing a lithium ion secondary battery, comprising:

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