Chalcogen-based active material, electrode, lithium-ion secondary battery, and method for manufacturing the same

Abstract

The present application aims to improve the volumetric energy density of an active material constituting an electrode of a lithium ion secondary battery while maintaining the capacity retention rate thereof. The present application provides a method for preparing a sulfur-based active material, comprising the following steps: (1) mixing an acrylic resin, sulfur, and an iron compound containing divalent or trivalent iron ions to obtain a raw material; and (2) calcining the raw material; wherein the median particle size of the iron compound is 12.00 pm or less.

Description

TECHNICAL FIELD

[0001] The present application relates to a novel chalcogen-based active material, an electrode comprising the chalcogen-based active material, a lithium-ion secondary battery comprising the electrode, and a method for producing the same. BACKGROUND

[0002] Lithium-ion secondary batteries are mainly used as batteries for portable electronic devices because of their large charge and discharge capacity. In addition, lithium-ion secondary batteries are increasingly used as batteries for electric vehicles, and their performance is expected to be improved.

[0003] Patent Document 1 describes a chalcogen-based active material obtained by calcining a raw material comprising a polymer and sulfur, the polymer comprising methacrylonitrile as a monomer component.

[0004] On the other hand, as a negative electrode active material, it has been proposed to use a material capable of absorbing and releasing more lithium ions, such as silicon (Si), tin (Sn), and the like, in order to improve the battery capacity of lithium-ion secondary batteries.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT DOCUMENTS

[0007] Patent Document 1: JP 2020-167144 A SUMMARY

[0008] PROBLEMS ADDRESSED BY THE INVENTION

[0009] However, active materials using polymers as in Patent Document 1 tend to reduce the true density, and thus even if the charge and discharge capacity per unit mass is large, the charge and discharge capacity per unit volume (volume energy density) tends to be poor in comparison.

[0010] In addition, the above-mentioned materials proposed as negative electrode active materials undergo a large change in volume when absorbing and releasing lithium ions, and thus have a problem of poor cycle characteristics when repeating charging and discharging. Although carbon materials such as graphite and hard carbon are also used, their capacity has almost reached the theoretical limit, and a large improvement in capacity cannot be expected.

[0011] An object of the present application is to provide a novel chalcogen-based active material having a good volume energy density while maintaining the capacity retention rate, an electrode (i.e., a positive electrode or a negative electrode) comprising the chalcogen-based active material, a lithium-ion secondary battery comprising the electrode, and a method for producing the same.

[0012] METHOD FOR SOLVING THE PROBLEM

[0013] The present application relates to a method for producing a chalcogen-based active material, the method comprising the steps of:

[0014] (1) mixing an acrylic resin, sulfur, and an iron compound containing divalent or trivalent iron ions to obtain a raw material; and

[0015] (2) firing the raw material,

[0016] wherein the median particle diameter of the iron compound is 12.00 μm or less.

[0017] Effects of the Invention

[0018] According to the present application, it is possible to provide a novel sulfur-based active material having a good volumetric energy density while maintaining a capacity retention rate, an electrode (i.e., a positive electrode or a negative electrode) containing the sulfur-based active material, a lithium ion secondary battery containing the electrode, and a method for producing the same.

[0019] Herein, the "cycle characteristics" refer to the characteristics of a secondary battery that can maintain the charge / discharge capacity even when the charge / discharge is repeated. Therefore, when the charge / discharge is repeated, the cycle characteristics of a secondary battery in which the charge / discharge capacity decreases to a high degree and the capacity retention rate is low are poor, and, on the contrary, the cycle characteristics of a secondary battery in which the charge / discharge capacity decreases to a low degree and the capacity retention rate is high are excellent. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a cross-sectional view of a reaction apparatus used for producing a sulfur-based active material in an embodiment of the present application. DETAILED DESCRIPTION

[0021] The present application will be described in detail below. In addition, the numerical values of the upper limit and the lower limit related to "or more", "or less", "higher than", "lower than", and the like used to describe a numerical range can be arbitrarily combined, and the numerical values in the embodiments can be these upper limit and / or lower limit. In addition, unless it is contrary to the purpose of the present application, the numerical range indicated to include the lower limit or the upper limit is understood to disclose the numerical range not including the lower limit or the upper limit; on the contrary, unless it is contrary to the purpose of the present application, the numerical range indicated not to include the lower limit or the upper limit is understood to disclose the numerical range including the lower limit or the upper limit.

[0022] One embodiment of the present application is a method for producing a sulfur-based active material, the method including the steps of: (1) mixing an acrylic resin, sulfur, and an iron compound containing divalent or trivalent iron ions to obtain a raw material; and (2) firing the raw material; wherein the median particle diameter of the iron compound is 12.00 μm or less.

[0023] In the production method of the present application, by reducing the median particle diameter of the iron compound, it is possible to obtain a sulfur-based active material having a good volumetric energy density while maintaining a capacity retention rate.

[0024] The content of the iron compound containing divalent or trivalent iron ions in the raw materials is preferably 50 parts by mass or more and 300 parts by mass or less relative to 100 parts by mass of the acrylic resin.

[0025] Step (1) preferably includes the following sub-steps: (1-a-1) adding the acrylic resin and the iron compound containing divalent or trivalent iron ions to an organic solvent and mixing 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.

[0026] Step (1) preferably includes the following sub-steps: (1-b) mixing the acrylic resin, sulfur, and the iron compound containing divalent or trivalent iron ions in a powder state.

[0027] The baking temperature in step (2) is preferably higher than 250°C and lower than 500°C.

[0028] The baking temperature in step (2) is preferably higher than the temperature at which the iron compound containing divalent or trivalent iron ions thermally decomposes.

[0029] The content of sulfur in the raw materials is preferably greater than 50 parts by mass and less than 1000 parts by mass relative to 100 parts by mass of the acrylic resin.

[0030] The acrylic resin is preferably at least one selected from the group consisting of a polymer obtained by polymerizing at least one monomer selected from the group consisting of the acrylate compounds represented by the following formula (1); or a polymer obtained by polymerizing at least one monomer selected from the group consisting of the acrylate compounds represented by the above formula (1) and at least one monomer selected from the group consisting of the diacrylate compounds represented by the above formula (2).

[0031] CH2=C(R 11 )COOR 12 (1)

[0032] In the formula, R 11 is a hydrogen atom or a methyl group, and R 12 is an alkyl group,

[0033] CH2=C(R 21 )COO-Y-OCO(R 22 )C=CH2(2)

[0034] In the formula, R 21 and R 22the same or different, each is a hydrogen atom or a methyl group; Y is a straight-chain hydrocarbylene group which can have at least one substituent selected from a hydroxyl group and an alkyl group, and the carbon skeleton constituting the hydrocarbylene group can have an ether bond having an oxygen atom, provided that when there are two or more ether bonds, there are always two or more carbon atoms interposed between adjacent oxygen atoms.

[0035] R is an alkyl group having 1 or more and 6 or less carbon atoms, Y is a straight-chain hydrocarbylene group having 2 or more and 6 or less carbon atoms, the number of substituents in the hydrocarbylene group is 1 or more and 4 or less, the number of carbon atoms of the alkyl group as the substituent is 1 or more and 4 or less, and the number of ether bonds possessed by the carbon skeleton constituting the hydrocarbylene group is 1 or more and 2 or less. 12 R is an alkyl group having 1 or more and 6 or less carbon atoms, Y is a straight-chain hydrocarbylene group having 2 or more and 6 or less carbon atoms, the number of substituents in the hydrocarbylene group is 1 or more and 4 or less, the number of carbon atoms of the alkyl group as the substituent is 1 or more and 4 or less, and the number of ether bonds possessed by the carbon skeleton constituting the hydrocarbylene group is 1 or more and 2 or less.

[0036] Another embodiment of the present application is a method of producing a lithium-ion secondary battery, the method further comprising, after producing the electrode by the method of producing an electrode, (4) producing a lithium-ion secondary battery by a conventional method using the electrode.

[0037] Another embodiment of the present application is a method of producing a lithium-ion secondary battery, the method further comprising, after producing the electrode by the method of producing an electrode, (4) producing a lithium-ion secondary battery by a conventional method using the electrode.

[0038] Another embodiment of the present application is a chalcogen-based active material obtained by calcining a raw material containing an acrylic resin, sulfur, and an iron compound containing divalent or trivalent iron ions, the composition elements including at least carbon, sulfur, and iron, wherein the median particle diameter of the iron compound is 12.00 μm or less, the chalcogen-based active material contains iron disulfide, and the content of sulfur as a composition element is 40.0 mass% or more.

[0039] When X-ray diffraction measurement is performed using CuKα rays, the chalcogen-based active material preferably has a half-value width of 0.20° or more for a peak showing the maximum diffraction intensity in the range of 2θ = 33.04° (±1.0°).

[0040] The true density of the chalcogen-based active material is preferably greater than 2.4 g / cm 3 and less than 3.6 g / cm 3 .

[0041] In the chalcogen-based active material, the carbon content is preferably greater than 5.0 mass% and less than 30.0 mass%.

[0042] When performing X-ray diffraction measurements using CuKα rays, the preferred θ values ​​for chalcogenide active materials are 2θ = 25.5° (±1.0°), 28.51° (±1.0°), 33.04° (±1.0°), 37.07° (±1.0°), and 40.76° (±1.0°).

[0043] Each of the ranges at 47.42° (±1.0°) and 56.27° (±1.0°) has its own peak.

[0044] The acrylic resin is preferably selected from at least one of the following polymers: a polymer obtained by polymerizing at least one monomer selected from the acrylate compounds represented by formula (1) above; or a polymer obtained by polymerizing at least one monomer selected from the acrylate compounds represented by formula (1) above and at least one monomer selected from the diacrylate compounds represented by formula (2) above.

[0045] Preferred R 12 Y is an alkyl group having one or more but no more than six carbon atoms, and Y is a straight-chain alkylene group having two or more but no more than six carbon atoms. In the alkylene group, the number of substituents is one or more but no more than four, the number of carbon atoms of the alkyl group that is a substituent is one or more but no more than four, and the number of ether bonds in the carbon skeleton constituting the alkylene group is one or more but no more than two.

[0046] The median particle size of the sulfur-based active material is preferably above 1 μm and below 40 μm.

[0047] Relative to 100 parts by weight of acrylic resin, the content of iron compounds containing divalent or trivalent iron ions in the raw materials is more than 50 parts by weight and less than 300 parts by weight, and the sulfur content is more than 50 parts by weight and less than 1000 parts by weight.

[0048] <Raw materials>

[0049] (Acrylic resin)

[0050] In this invention, the acrylic resin is at least one of the following polymers: a polymer obtained by polymerizing at least one monomer selected from acrylate compounds represented by formula (1); or a polymer obtained by polymerizing at least one monomer selected from acrylate compounds represented by formula (1) and at least one monomer selected from diacrylate compounds represented by formula (2).

[0051] CH2=C(R 11 COOR 12 (1)

[0052] In the formula, R 11 It is a hydrogen atom or a methyl group, R 12 It is an alkyl group.

[0053] CH2=C(R 21 )COO-Y-OCO(R 22 )C=CH2 (2)

[0054] wherein R 21 and R 22 are the same or different, each being a hydrogen atom or a methyl group; and Y is a straight-chain hydrocarbylene group which can have at least one substituent selected from the group consisting of a hydroxyl group and an alkyl group having 1 or more and 4 or less carbon atoms, and the carbon skeleton constituting the straight-chain hydrocarbylene group can have an ether bond containing an oxygen atom, provided that when there are two or more ether bonds, there are always two or more carbon atoms interposed between adjacent oxygen atoms.

[0055] In formula (1), R 11 is preferably a methyl group, and R 12 is preferably an alkyl group having 1 or more and 6 or less carbon atoms, more preferably an alkyl group having 1 or more and 4 or less carbon atoms, among which a methyl group, a n-butyl group, an iso-butyl group or a t-butyl group is more preferable. Examples of the compound represented by formula (1) include methyl (meth)acrylate, butyl (meth)acrylate and the like, more preferably methyl methacrylate and butyl methacrylate. Here, "(meth)acrylate" of methyl (meth)acrylate and butyl (meth)acrylate represents "acrylate" or "methacrylate" (the same applies hereinafter). Another preferable example of the compound represented by formula (1) is butyl methacrylate.

[0056] In formula (2), R 21 and R 22 are each preferably a methyl group. The number of carbon atoms in the hydrocarbylene (straight-chain) group of Y is preferably 2 or more and 6 or less, more preferably 2 or 3. The number of substituents in Y is preferably 1 or more and 4 or less, more preferably 1 or 2. As the substituents in Y, one or more substituents selected from the group consisting of a hydroxyl group and an alkyl group having 1 or more and 4 or less carbon atoms are preferable; as the alkyl group having 1 or more and 4 or less carbon atoms, a methyl group is preferable. When the carbon skeleton of Y has an ether bond containing an oxygen atom, for example, the portion corresponding to -Y-O- is preferably represented by the following formula (3) (provided that the substituents in Y are not considered in formula (3)):

[0057] -(CH2) l -(CH2CH2O) m -(CH2CH2CH2O) n -(3)

[0058] wherein 1 is 0 or more and 6 or less, m is 0 or more and 3 or less, and n is 0 or more and 2 or less. However, 1, m and n are not simultaneously 0.

[0059] In formula (3), preferably, 1 is 1, 2, 3, 4, 5, or 6, m and n are 0; m is 1, 2, or 3, 1 and n are 0; or n is 1 or 2, 1 and m are 0.

[0060] 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, neopentyl glycol di(meth)acrylate, glycerol di(meth)acrylate, and the like. Of these, ethylene glycol dimethacrylate is preferred.

[0061] Preferred examples of the acrylic resin include a homopolymer of methyl (meth)acrylate, a homopolymer of butyl (meth)acrylate, a copolymer of methyl (meth)acrylate and ethylene glycol di(meth)acrylate, a copolymer of butyl (meth)acrylate and ethylene glycol di(meth)acrylate, and the like. Of these, as the acrylic resin, a methacrylate-based acrylic resin is preferred. More preferred examples of the acrylic resin include a copolymer of butyl methacrylate and ethylene glycol dimethacrylate.

[0062] One or more kinds of acrylic resins can be used.

[0063] [Form of the acrylic resin]

[0064] In the present application, the acrylic resin is preferably in the form of fine particles. Here, fine particles refer to particles having a particle diameter of 300.0 μm or less. The particle diameter is preferably 270.0 μm or less, more preferably 200.0 μm or less, further preferably 100.0 μm or less, further preferably 50.0 μm or less, further preferably 20.0 μm or less, further preferably 15.0 μm or less, further preferably 13.0 μm or less, further preferably 10.0 μm or less, further preferably 6.0 μm or less. On the other hand, the lower limit of the particle diameter is usually, for example, 0.1 μm or more, preferably 1.0 μm or more, but is not particularly limited thereto. The particle diameter is a value (median particle diameter) measured by a precision particle size distribution measuring apparatus Multisizer 3 manufactured by Beckman Coulter, Inc.

[0065] The acrylic resin can be a spherical fine particle or a porous fine particle. When the acrylic resin is porous, the oil absorption amount thereof is preferably 100 mL / 100 g or more, more preferably 110 mL / 100 g or more, further preferably 120 mL / 100 g or more, further preferably 130 mL / 100 g or more, further preferably 140 mL / 100 g or more. The oil absorption amount is a value measured according to JIS K 5101-13-2:2004. More specifically, it can be measured by the method described in paragraph 0069 of JP 2017-88501 A.

[0066] [Weight average molecular weight (Mw) of the acrylic resin]

[0067] 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 greater than 2000 and less than 1500000. The Mw is a value measured by gel permeation chromatography (GPC) (calibrated with polystyrene).

[0068] [Acquisition or preparation of the acrylic resin]

[0069] The acrylic resin can be commercially available or can be prepared by a conventional method known to those skilled in the art. Examples of commercially available acrylic resins include acrylic resins produced by Sekisui Kasei Co., Ltd.

[0070] (Sulfur)

[0071] As the sulfur, various forms of sulfur such as powdered sulfur, insoluble sulfur, precipitated sulfur, colloidal sulfur, and the like can be used. Of these, precipitated sulfur and colloidal sulfur are preferred.

[0072] The content of the sulfur is preferably greater than 50 parts by mass, more preferably greater than 100 parts by mass, further preferably greater than 300 parts by mass, further preferably greater than 400 parts by mass, further preferably greater than 500 parts by mass, relative to 100 parts by mass of the acrylic resin. When the content is greater than 50 parts by mass, there is a tendency for the charge and discharge capacity and the cycle characteristics to improve. On the other hand, the content of the sulfur has no upper limit, but is usually preferably less than 1000 parts by mass, more preferably less than 900 parts by mass, further preferably less than 800 parts by mass, further preferably less than 700 parts by mass. When the content is 1000 parts by mass or less, there is an advantage in terms of cost.

[0073] As the sulfur, various allotropes can be used, but an allotrope containing S8 sulfur which is solid at normal temperature and pressure is preferred, and S8 sulfur alone is more preferred.

[0074] (Iron compound containing divalent or trivalent iron ion)

[0075] The iron compound containing divalent or trivalent iron ion is not particularly limited as long as it decomposes during the calcination process and reacts with the sulfur to produce iron disulfide, and various such iron compounds can be used. Examples of such iron compounds include ferrite salts, iron complexes, and the like. Examples of the ferrite salts include organic acid salts of iron and inorganic acid salts of iron. On the other hand, examples of the iron complexes include neutral iron complexes and iron complex ion salts (iron complex salts).

[0076] Examples of the organic acid salts of iron include divalent iron (Fe 2+) and salts of organic acids, ferric iron (Fe3+) 3+ Salts of ferrous iron and organic acids, etc. Salts of ferrous iron and organic acids are preferred. Organic acids can be, but are not particularly limited to, organic acids having a carboxyl group (-COOH), organic acids having a sulfonyl group (-SO3H), etc. Organic acids having a carboxyl group are preferred. Specific examples of organic acids include fatty acids, oxalic acid, tartaric acid, citric acid, malic acid, succinic acid, etc. Specific examples of fatty acids include, for example, fatty acids having one or more but less than six carbon atoms, such as acetic acid, propionic acid, butyric acid, etc. Acetic acid and oxalic acid are preferred. Preferred examples of organic acid salts of iron include ferric acetate(II), ferric oxalate(II), etc. They can be hydrates. One or more organic acid salts of iron can be used.

[0077] Examples of inorganic salts of iron include ferrous iron (Fe2+). 2+ ) and salts of inorganic acids, ferric iron (Fe3+) 3+ And salts of inorganic acids, etc. Specific examples of inorganic acids include hydrochloric acid, sulfuric acid, nitric acid, etc. Among them, nitric acid is preferred. Preferred examples of inorganic acid salts of iron include ferric chloride (II), ferric chloride (III), ferric sulfate (II), ferric sulfate (III), ferric nitrate (II), ferric nitrate (III), etc. They can be hydrates. One or more inorganic acid salts of iron can be used.

[0078] Examples of iron complexes include, for example, divalent iron (Fe²⁺). 2+ Complexes, trivalent iron (Fe) 3+ Iron complexes can be neutral complexes or complex salts. There are no particular limitations on the ligands coordinating with the iron ion; examples include halogen atoms such as chlorine and bromine atoms, cyano groups, dicyclopentadienyl groups, and N,N'-bis(salicylene)ethylenediamine. Examples of iron complexes include: potassium hexacyanoferrate(II) ([Fe(CN)6]K4), potassium hexacyanoferrate(III) ([Fe(CN)6]K3), sodium ferric chloride(III) ([FeCl4]Na), dicyclopentadienylferric(II) (ferrocene), and N,N'-bis(salicylene)ethylenediamine ferric chloride(III). One or more iron complexes may be used.

[0079] For iron compounds containing divalent or trivalent iron ions, at least one selected from the above-mentioned organic acid salts of iron, inorganic acid salts of iron, neutral iron complexes, and iron complex salts can be used. Among these, organic acid salts of iron, inorganic acid salts of iron, or neutral iron complexes are preferred.

[0080] The median particle diameter (D50) of the iron compound containing divalent or trivalent iron ions is 12.00 μm or less. The median diameter is preferably 10.00 μm or less, more preferably 8.00 μm or less, further preferably 6.00 μm or less, further preferably 5.00 μm or less, further preferably 4.50 μm or less, further preferably 4.30 μm or less, further preferably 4.29 μm or less, further preferably 4.00 μm or less, further preferably 3.00 μm or less. On the other hand, the lower limit of the median particle diameter is not particularly limited, but is usually about 0.10 μm or more, and can be about 1.00 μm or about 2.00 μm. The median particle diameter can be measured by the method described in the "Examples" section below.

[0081] The specific surface area of the iron compound containing divalent or trivalent iron ions is preferably 1.0 m 2 / g or more, more preferably 2.0 m 2 / g or more, further preferably 2.5 m 2 / g or more, further preferably 2.8 m 2 / g or more, further preferably 3.0 m 2 / g or more, further preferably 4.0 m 2 / g or more, further preferably 4.2 m 2 / g or more, further preferably 4.5 m 2 / g or more. On the other hand, the upper limit of the specific surface area is not particularly limited, but is usually about 40.0 m 2 / g or less, and can be about 20.0 m 2 / g or less, or about 10.0 m 2 / g or less. The specific surface area can be measured with a full-automatic surface area analyzer Macsorb (HM-model 1201, manufactured by MOUNTECH Corporation).

[0082] The iron compound having a median particle diameter of 12.00 μm or less can be produced by a conventional method, for example, by pulverizing the iron compound with a pulverizer. As such a pulverizer, a pulverizer manufactured by Japan Analytical Industry Co., Ltd. (for example, JFC-2000 or the like), a pulverizer manufactured by Labonect Co. (for example, Free Speed Mill FS-20 or the like), or a pulverizer manufactured by Aishin Nano Technologies CO., LTD (for example, Nano Jetmizer NJ-30 or the like) can be used.

[0083] From the effect of the present application, the content of the iron compound containing divalent or trivalent iron ions is preferably 50 parts by mass or more and 300 parts by mass or less with respect to 100 parts by mass of the acrylic resin. The content is more preferably greater than 50 parts by mass, further preferably greater than 60 parts by mass, further preferably greater than 70 parts by mass, further preferably greater than 75 parts by mass. On the other hand, the content is more preferably less than 250 parts by mass, further preferably less than 200 parts by mass, further preferably less than 150 parts by mass, further preferably less than 100 parts by mass.

[0084] (electrically conductive carbon material)

[0085] The raw material can contain an electrically conductive carbon material. This is because it can improve the electrical conductivity of the sulfur-based active material. As such an electrically conductive carbon material, a carbon material having a graphite structure is preferable. As the carbon material, a carbon material having a condensed aromatic ring structure, such as carbon black, acetylene black, ketjen black, graphite, carbon nanotube (CNT), carbon fiber (CF), graphene, fullerene, or the like, can be used. One or more electrically conductive carbon materials can be used.

[0086] Among them, acetylene black, carbon black, and ketjen black are preferable because they are inexpensive and have good dispersibility. In addition, a small amount of CNT, graphene, or the like can also be used in combination with acetylene black, carbon black, or ketjen black. Such a combined system can further improve the cycle characteristics of the lithium ion secondary battery without significantly increasing the cost. In addition, the total amount of CNT or graphene is preferably 8% by mass or more and 12% by mass or less of the total amount of the electrically conductive carbon material.

[0087] The content of the electrically conductive carbon material is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, with respect to 100 parts by mass of the acrylic resin. When the content is 5 parts by mass or more, it is often easy to achieve the purpose of further improving the charge and discharge capacity and the cycle characteristics. On the other hand, the content is preferably 50 parts by mass or less, more preferably 40 parts by mass or less. When the content is 50 parts by mass or less, the proportion of the sulfur-containing structure in the sulfur-based active material does not decrease relatively, and it is easy to achieve the purpose of further improving the charge and discharge capacity and the cycle characteristics.

[0088] <other materials>

[0089] The raw material can also appropriately contain other materials commonly used in the field as needed.

[0090] <manufacture of sulfur-based active material>

[0091] In the present application, the sulfur-based active material can be produced by calcining a raw material in which an acrylic resin, sulfur, and an iron compound containing divalent or trivalent iron ions are mixed.

[0092] (step (1))

[0093] Step (1) is a step of mixing an acrylic resin, sulfur, and an iron compound containing a divalent or trivalent iron ion to obtain a raw material for calcination. The mixing is only required to be sufficient mixing of these components, and is not particularly limited. In the present application, as a preferred mixing method, examples include at least wet (WET) method mixing with a solvent or dry (DRY) method mixing without using a solvent, which will be mentioned later.

[0094] [WET method]

[0095] In the present application, the wet method includes the following steps for preparing a raw material,

[0096] (1-a-1) adding an acrylic resin and an iron compound containing a divalent or trivalent iron ion to an organic solvent and mixing to obtain a liquid mixture;

[0097] (1-a-2) removing the organic solvent from the liquid mixture to obtain a dry mixture; and

[0098] (1-a-3) mixing the dry mixture with sulfur.

[0099] In sub-step (1-a-1), the method of adding an acrylic resin and an iron compound containing a divalent or trivalent iron ion to an organic solvent is not particularly limited, as long as a liquid mixture can be obtained by mixing. For example, (1) an acrylic resin and an iron compound containing a divalent or trivalent iron ion can be simultaneously added to an organic solvent and mixed, (2) an acrylic resin can be added to an organic solvent and mixed, and then an iron compound containing a divalent or trivalent iron ion can be further added and mixed, or (3) an iron compound containing a divalent or trivalent iron ion can be added to an organic solvent and mixed, and then an acrylic resin can be further added and mixed.

[0100] In sub-step (1-a-1), as the organic solvent, a commonly used organic solvent in the art can be used, for example, N-methyl-2-pyrrolidone, N,N-dimethylformamide, an alcohol, hexane, water, acetone, an ether (such as tetrahydrofuran, etc.), and the like. In addition, an organic solvent that dissolves the acrylic resin is preferred. This is because it contributes to good mixing. These solvents can be used in one or more.

[0101] The mixing of the acrylic resin and / or the iron compound containing a divalent or trivalent iron ion with the organic solvent can be performed by stirring in a container such as a beaker, etc.

[0102] In step (1-a-2), the removal of the organic solvent can be performed by a conventional method. For example, it can be performed by a drying method such as heat drying, reduced pressure drying, reduced pressure heat drying, etc. on the liquid mixture.

[0103] The dry mixture thus obtained is preferably pulverized before the next step. This is because, in this case, the mixing in sub-step (1-a-3) can be more appropriately performed. The pulverization can be performed by a conventional method, for example, using a chopper, etc. In particular, after performing coarse pulverization using a chopper, fine pulverization is preferably performed using a freezer mill.

[0104] For the pulverized product, the preferred particle size (in terms of median particle size) is 1 μm or more, more preferably greater than 1 μm, further preferably greater than 2 μm, further preferably greater than 3 μm, further preferably greater than 4 μm. In addition, the median particle size is preferably 40 μm or less, more preferably less than 40 μm, further preferably less than 30 μm, further preferably less than 20 μm, further preferably less than 15 μm, further preferably less than 10 μm. From the effect of the present application, the median particle size is preferably within the above range. The median particle size can be measured by the method described in the Example section below.

[0105] In sub-step (1-a-3), the mixing of the dry mixture and sulfur can be performed by a conventional method, for example, a method in which a mixer, etc. can be used for the mixing.

[0106] [Dry method]

[0107] In the present application, the dry method includes the following steps for preparing the raw material,

[0108] (1-b) mixing the acrylic resin, sulfur, and the iron compound containing divalent or trivalent iron ions in a powder state.

[0109] Here, the powder refers to a state in which each of the solid materials is made fine enough to be mixed appropriately for the purpose of the present application. As for the size of the particles constituting the powder, there is no particular limitation as long as the mixing can be appropriately performed, but the median particle size is generally, for example, in the range of 1 μm or more and 40 μm or less. From the effect of the present application, the particle size of the particles is preferably greater than 1 μm, more preferably greater than 2 μm, further preferably greater than 3 μm, further preferably greater than 4 μm, and at the same time, is preferably 40 μm or less, more preferably less than 40 μm, more preferably less than 30 μm, further preferably less than 20 μm, further preferably less than 15 μm, further preferably less than 10 μm. The median particle size can be measured by the method described in the Example section below.

[0110] The mixing can be performed by a conventional method, for example, in the same manner as the mixing in sub-step (1-a-3) described above.

[0111] In the wet method and the dry method, the raw material is preferably mixed sufficiently in advance. In addition, when the electrically conductive carbon material, etc. is added to the raw material, these additives can also be mixed in advance before the calcination so as to be included in the raw material in advance.

[0112] The thus obtained raw material can be used as it is in the next step (2), or it can be granulated if necessary, and then used in step (2).

[0113] (Step (2))

[0114] Step (2) is a step of calcining the raw material obtained above. The calcination of the raw material can be performed by a conventional method, for example, by heating the raw material at a predetermined temperature- increasing rate until a predetermined temperature is reached, maintaining the predetermined temperature for a predetermined time, and then naturally cooling.

[0115] [Non-oxidizing atmosphere]

[0116] The calcination is preferably performed in a non-oxidizing atmosphere. The non-oxidizing atmosphere refers to an atmosphere substantially free of oxygen, which is used to suppress oxidative deterioration and excessive pyrolysis of the constituent components. Specifically, the non-oxidizing atmosphere refers to an inert gas environment (such as nitrogen, argon, etc.), a sulfur gas environment, and the like. Thus, the calcination can be performed in, for example, a quartz tube under an inert gas environment.

[0117] [Rate of temperature increase]

[0118] The rate of temperature increase is preferably in the range of, for example, 50°C / h or more and 500°C / h or less. The rate of temperature increase is preferably greater than 50°C / h, more preferably greater than 100°C / h. On the other hand, the rate of temperature increase is preferably less than 500°C / h, more preferably less than 400°C / h, further preferably less than 300°C / h, and further preferably less than 200°C / h. When the rate of temperature increase is in this range, it tends to be easy to achieve the object of improving the charge-discharge capacity and the cycle characteristics.

[0119] [Calcination temperature / time]

[0120] The calcination temperature refers to the temperature after the temperature increase of the raw material is completed, which is maintained for a certain period of time to calcine the raw material. The temperature is preferably in the range of higher than 250°C and lower than 550°C. When the temperature is higher than 250°C, it is possible to avoid insufficient vulcanization reaction and prevent the charge-discharge capacity of the target from decreasing. On the other hand, when the temperature is lower than 550°C, it is possible to avoid decomposition of the raw material and prevent the yield and the charge-discharge capacity from decreasing. The temperature is more preferably higher than 300°C, further preferably higher than 350°C, and further preferably higher than 380°C. On the other hand, the temperature is more preferably lower than 500°C, more preferably lower than 480°C, and more preferably lower than 450°C.

[0121] From the viewpoint of the effects of the present application, the calcination temperature in step (2) is preferably higher than the temperature at which the iron compound containing divalent or trivalent iron ions thermally decomposes.

[0122] The time for which the calcination temperature is maintained can be appropriately set depending on the kind of the raw material, the calcination temperature, etc., but is preferably 1 hour or more and 6 hours or less. When the time is 1 hour or more, there is a tendency that calcination can be sufficiently performed, and when the time is 6 hours or less, there is a tendency that excessive pyrolysis of the constituent components can be prevented. The time is preferably more than 1 hour, and more preferably more than 1.5 hours. On the other hand, the time is preferably less than 6 hours, and more preferably less than 4 hours.

[0123] [Apparatus]

[0124] The calcination can be performed using the apparatus shown in Fig. 1, or can be performed using a continuous apparatus such as a double screw extruder, etc. When a continuous apparatus is used, there are advantages that the sulfur-based active material can be continuously produced through a series of operations, for example, kneading, pulverization, mixing of the raw material, calcination, etc. in the apparatus. Figure 1

[0125] (Step of removing residues)

[0126] In the processed product obtained after the calcination, some unreacted sulfur, etc. which is precipitated upon cooling of the sulfur sublimated during the calcination can remain. Since these residues can cause deterioration of the cycle characteristics, it is preferable to remove these residues as much as possible. The removal of the residues can be performed according to a conventional method, for example, reduced pressure heat drying, hot air drying, solvent washing, etc.

[0127] (Pulverization / classification)

[0128] The obtained sulfur-based active material can be pulverized into particles having a predetermined particle diameter and classified to obtain particles having a particle diameter suitable for production of an electrode. From the effect of the present application, the preferred particle size distribution of the particles is that the median particle diameter is about 1 μm or more and 40 μm or less. The median particle diameter is preferably more than 1 μm, more preferably more than 2 μm, further preferably more than 3 μm, further preferably more than 4 μm. In addition, the median particle diameter is preferably less than 40 μm, more preferably less than 30 μm, further preferably less than 20 μm, further preferably less than 15 μm, further preferably less than 10 μm. The median particle diameter can be measured by the method described in the Example section below.

[0129] In addition, in the calcination method using a double screw extruder as described above, the sulfur-based active material produced can be pulverized by shearing during the kneading while the sulfur-based active material is being produced.

[0130] [Sulfur-based active material]

[0131] ​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 is an active material in which they are compounded, and contains at least carbon, sulfur, and iron as constituent elements. The sulfur content, carbon content, and hydrogen content shown below refer to the amounts of the respective elements contained in the sulfur-based active material. In addition, the obtained sulfur-based active material contains iron disulfide based on a comparison of the peak shape of the diffraction intensity of iron disulfide (pyrite) obtained by X-ray diffraction measurement.

[0132] (Sulfur content)

[0133] In the sulfur-based active material thus obtained, the sulfur content in the sulfur-based active material is preferably greater than 40.0 mass%, more preferably greater than 45.0 mass%, further preferably greater than 50.0 mass%, and further preferably greater than 55.0 mass%. However, when a conductive carbon material is mixed, even if the sulfur content is slightly low, it is expected to achieve the effect of improving the charge and discharge capacity and cycle characteristics due to the influence of carbon constituting the conductive carbon material. In this case, the sulfur content can be about 5.0 mass% less than the above-mentioned sulfur content.

[0134] (Carbon content)

[0135] From the effects of the present application, the carbon content is preferably greater than 5.0 mass% and less than 30.0 mass%. The carbon content is more preferably greater than 6.0 mass%, further preferably greater than 7.0 mass%, further preferably greater than 8.0 mass%, and further preferably greater than 8.5 mass%. On the other hand, the content is more preferably less than 29.0 mass%, further preferably less than 25.0 mass%.

[0136] (Total content of sulfur and carbon)

[0137] In addition, the total content of carbon and sulfur in the sulfur-based active material is preferably greater than 60 mass%, more preferably greater than 65 mass%. On the other hand, the total content is preferably less than 95 mass%, more preferably less than 90 mass%, and further preferably less than 85 mass%.

[0138] (Hydrogen content)

[0139] The hydrogen (H) in the acrylic resin is reduced from hydrogen sulfide generated by reacting with sulfur by calcination. Therefore, the hydrogen content of the sulfur-based active material is preferably less than 1.00 mass%, more preferably less than 0.70 mass%, and further preferably less than 0.50 mass%. When the content is less than 1.00 mass%, there is a tendency for calcination (sulfuration reaction) to be sufficient. Therefore, in this case, the charge and discharge capacity tends to be improved.

[0140] (True density)

[0141] From the viewpoint of the effects of the present application, the true density of the chalcogen-based active material is preferably greater than 2.4 g / cm 3 and less than 3.6 g / cm 3 . The true density is more preferably greater than 2.5 g / cm 3 , further preferably 2.6 g / cm 3 . The above, further preferably greater than 2.6 g / cm 3 . On the other hand, the true density is more preferably less than 3.5 g / cm 3 , further preferably less than 3.2 g / cm 3 , further preferably less than 3.1 g / cm 3 . In the present application, the true density is the density when the volume occupied by the chalcogen-based active material alone is taken as the volume for calculating the density, and specifically, it is calculated by the method described in the Examples section.

[0142] < Lithium-ion secondary battery >

[0143] The chalcogen-based active material of the present application 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, the method for producing a lithium-ion secondary battery electrode is the same as that for producing a conventional lithium-ion secondary battery electrode, except that the chalcogen-based active material is used; and the method for producing a lithium-ion secondary battery is the same as that for producing a conventional lithium-ion secondary battery, except that the lithium-ion secondary battery electrode is used. The lithium-ion secondary battery thus produced has a large charge-discharge capacity and excellent cycle characteristics.

[0144] 1. Use of the chalcogen-based active material as a positive electrode active material

[0145] The lithium-ion secondary battery of the present application can be produced according to a conventional method, using a negative electrode and an electrolyte, as well as components such as a separator, if necessary, in addition to a positive electrode containing the above-described chalcogen-based active material (positive electrode active material).

[0146] (Positive electrode)

[0147] The method for producing a lithium-ion secondary battery positive electrode is the same as that for producing a conventional lithium-ion secondary battery positive electrode, except that the above-described chalcogen-based active material is used as a positive electrode active material. For example, a paste-like positive electrode material is prepared by mixing the chalcogen-based active material in a particulate state with a conductive aid, a binder, and a solvent, the positive electrode material is coated on a current collector, and then it is dried to produce a positive electrode. As another method, a positive electrode can also be produced by, for example, kneading the chalcogen-based active material together with a conductive aid, a binder, and a small amount of a solvent using a mortar or the like and forming a film, and then pressing it on a current collector using a press or the like.

[0148] [Conductive aid]

[0149] Examples of the conductive aid include, for example, vapor grown carbon fiber (VGCF), carbon powder, carbon black (CB), acetylene black (AB), ketjen black (KB), graphite, or a fine powder of a metal stable at the potential of the positive electrode, such as aluminum, titanium, and the like. One or two or more of these conductive aids can be used.

[0150] [Binder]

[0151] Examples of the binder 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 ether (PPO), polyethylene oxide (PEO), polyethylene (PE), polypropylene (PP), and the like. One or more of these binders can be used.

[0152] [Solvent]

[0153] Examples of the solvent include N-methyl-2-pyrrolidone, N,N-dimethylformamide, alcohol, hexane, water, and the like. One or more of these solvents can be used.

[0154] [Blending amount]

[0155] The blending amount of these materials constituting the positive electrode is not particularly limited, but, for example, with respect to 100 parts by mass of the sulfur-based active material, it is preferable to blend 2 parts by mass or more and 100 parts by mass or less of the conductive aid, 2 parts by mass or more and 50 parts by mass or less of the binder, and an appropriate amount of the solvent.

[0156] [Current collector]

[0157] As the current collector, a current collector conventionally used for the positive electrode of a lithium ion secondary battery can be used. Examples of the current collector include, for example, a current collector composed of an aluminum foil, an aluminum mesh, a punched aluminum sheet, an expanded aluminum sheet, a stainless steel foil, a stainless steel mesh, a punched stainless steel sheet, an expanded stainless steel sheet, a nickel foam, a nickel nonwoven fabric, a copper foil, a copper mesh, a punched copper sheet, an expanded copper sheet, a titanium foil, a titanium mesh, a carbon nonwoven fabric, a carbon woven fabric, and the like. Among these, when the sulfur-based active material of the present application is used as the positive electrode active material, a current collector composed of a carbon nonwoven fabric or a carbon woven fabric made of carbon having a high degree of graphitization is suitable as the current collector because the current collector does not contain hydrogen and has low reactivity with sulfur. As a raw material of the carbon fiber having a high degree of graphitization, various pitches (i.e., by-products of petroleum, coal, and coal tar) used as carbon fiber materials, polyacrylonitrile fibers (PAN), and the like can be used. The current collector can be used alone or in combination of two or more.

[0158] (Negative electrode)

[0159] As the negative electrode material, known metal 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 can be used. When a lithium-free material (for example, a carbon-based material, a silicon-based material, an alloy-based material, or the like) among the above negative electrode materials is used as the negative electrode material, there is an advantage that short circuit between the positive electrode and the negative electrode due to generation of dendrites is less likely to occur. However, when these lithium-free negative electrode materials are used in combination with the positive electrode of the present application, neither the positive electrode nor the negative electrode contains lithium. Therefore, a lithium pre-doping treatment in which lithium is inserted in advance into either one of the negative electrode and the positive electrode or both of them is required. As a method of pre-doping lithium, a known method can be employed. For example, when lithium is doped in the negative electrode, there is a method of doping lithium by an electrolytic doping method in which a half cell is assembled using metal lithium as a counter electrode and lithium is doped by an electrochemical method, and there is a method of doping lithium by a pasting pre-doping method in which a metal lithium foil is pasted on an electrode and then left in an electrolyte, and doping is performed using diffusion of lithium to the electrode. Furthermore, when lithium is pre-doped in the positive electrode, the above electrolytic doping method can also be used. As the lithium-free negative electrode material, a silicon-based negative electrode material having a high capacity is particularly preferable, and among them, a thin film silicon in which the electrode thickness is thin and thus has an advantage in terms of capacity per unit volume is more preferable.

[0160] (Electrolyte)

[0161] As the electrolyte for the lithium ion secondary battery, an electrolyte obtained by dissolving an alkali metal salt as an electrolyte in an organic solvent can be used. As the organic solvent, at least one of non-aqueous solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl ether, γ-butyrolactone, and acetonitrile is preferably used. As the electrolyte, LiPF6, LiBF4, LiAsF6, LiCF3SO3, LiI, LiClO4, or the like can be used. The concentration of the electrolyte can be about 0.5 mol / L or more and 1.7 mol / L or less. Furthermore, the electrolyte is not limited to a liquid state. For example, when the lithium ion secondary battery is a lithium polymer secondary battery, the electrolyte is in a solid state (for example, a polymer gel state).

[0162] (Separator)

[0163] In addition to the above negative electrode, positive electrode, and electrolyte, the lithium ion secondary battery can include a member such as a separator. The separator is located between the positive electrode and the negative electrode, allows ions to migrate between the positive electrode and the negative electrode, and prevents internal short circuit between the positive electrode and the negative electrode. If the lithium ion secondary battery is of a sealed type, the separator is required to have a function of retaining the electrolyte. As the separator, a thin and microporous or non-woven fabric film made of polyethylene, polypropylene, polyacrylonitrile, aramid, polyimide, cellulose, glass, or the like is preferably used.

[0164] (Shape)

[0165] The shape of the lithium ion secondary battery is not particularly limited, and various shapes such as a cylindrical shape, a stacked shape, a coin shape, a button shape, and the like can be used.

[0166] 2. Use of a sulfur-based active material as a negative electrode active material

[0167] The lithium ion secondary battery of the present application can be produced according to a conventional method using, in addition to the negative electrode containing the above-described sulfur-based active material (negative electrode active material), a positive electrode and an electrolyte, and members such as a separator (if necessary).

[0168] (Negative electrode)

[0169] The production method of the lithium ion secondary battery negative electrode is the same as that of a conventional lithium ion secondary battery negative electrode except that the above-described sulfur-based active material is used as the negative electrode active material. For example, a paste-like negative electrode material is prepared by mixing the sulfur-based active material in a particulate state with a conductive aid, a binder, and a solvent, the negative electrode material is coated on a current collector, and then dried to produce a negative electrode. As another method, a positive electrode can also be produced by, for example, kneading the sulfur-based active material together with a conductive aid, a binder, and a small amount of a solvent using a mortar or the like and forming a film, and then pressing the film on a current collector using a press or the like.

[0170] As the conductive aid, the binder, and the solvent, the same materials as in the case where a sulfur-based active material is used as a positive electrode active material can be used, and the same applies to the current collector.

[0171] (Positive electrode)

[0172] The positive electrode material is not particularly limited, and is, for example, a lithium-containing transition metal oxide or a solid solution oxide, or a substance capable of electrochemically absorbing and releasing lithium. Examples of the lithium-containing transition metal oxide include, for example, Li-Co-based composite oxides such as LiCoO2and the like; Li-Ni-Co-Mn-based composite oxides such as LiNi x Co y Mn z O2and the like; Li-Ni-based composite oxides such as LiNiO2and the like; and Li-Mn-based composite oxides such as LiMn2O4and the like. Examples of the solid solution oxide include, for example, Li 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 zO2 (0.300≤x≤0.850, 0.100≤y≤0.300, 0.100≤z≤0.300), LiMn 1.5 Ni 0.5 O4, etc. These compounds can be used alone or in combination.

[0173] For the electrolyte, separator, and shape of the lithium-ion secondary battery, the same materials can be used as in the case where sulfide active materials are used as positive electrode active materials.

[0174] Example

[0175] Although the present invention will be described with reference to embodiments, it is not limited to the embodiments.

[0176] The various chemicals used in the examples and comparative examples are listed below. Each chemical was purified as needed using conventional methods.

[0177] <Materials used in the experiment>

[0178] Acrylic Resin 1: Spherical acrylic resin made from methyl methacrylate homopolymer (TECHPOLYMER MB-4 manufactured by Sekisui Kasei Corporation, particle size: 4μm)

[0179] Iron compound 1 (organic acid salt): Ferric oxalate(II) dihydrate (ferric oxalate(II) dihydrate produced by Kanto Chemical Co., Inc., analytical grade reagent)

[0180] Iron compound 2 (organic acid salt): Ferric acetate (II) (Ferric acetate (II) manufactured by Kanto Chemical Co., Ltd.)

[0181] Sulfur: Precipitated sulfur produced by Tsurumi Chemical Industry Co., Ltd.

[0182] Organic solvent (wet process): Acetone (premium grade acetone produced by YONEYAMA YAKUHIN KOGYO CO.,LTD.)

[0183] Production Example 1 (Fine Grinding of Iron Compounds)

[0184] Before the kneading step, the iron compound is pre-crushed as needed using a cryogenic grinder (JFC-2000 manufactured by Japan Analysis Industries Co., Ltd.), a shredder (Free Speed ​​Mill FS-20 manufactured by Labonect), or a dry jet mill (Nano Jetmizer NJ-30 manufactured by Aishin Nano Technologies Co., Ltd.), as shown in Table 1 below.

[0185]

[0186] Production of Example 2 (raw material prepared by wet method)

[0187] According to the proportions in Table 3, the acrylic resin was added to an organic solvent and mixed well, and then an iron compound was further added to the mixture to obtain a liquid mixture. Then, the organic solvent was removed from the liquid mixture, and the mixture was pulverized with a cutter mill (LAB MILL manufactured by OSAKA CHEMICAL Co., Ltd.) to obtain a dry mixture.

[0188] The dry mixture thus obtained was mixed with sulfur using a blender to obtain a raw material for calcination.

[0189] Further, in Comparative Example 2, acrylic resin 1 and sulfur were mixed using a blender to obtain a raw material for calcination; and in Comparative Example 3, iron compound 1 and sulfur were mixed using a blender to obtain a raw material for calcination.

[0190] Example 1

[0191] <Production of sulfur-based active material>

[0192] (Raw material for calcination)

[0193] As described in Table 3, the raw material prepared by the wet method was used as a raw material for calcination.

[0194] (Reaction apparatus)

[0195] Figure 1 The reaction apparatus 1 shown was used for calcination of the raw material. The reaction apparatus 1 included a reaction vessel 3, 60 mm in outer diameter, 50 mm in inner diameter, and 300 mm in height, made of a bottom cylindrical quartz glass, for containing and calcining the raw material 2; a silica cap 4 for closing the upper opening of the reaction vessel 3; an alumina guard tube 5 ( "Alumina SSA-S" manufactured by NIKKATO CORPORATION, 4 mm in outer diameter, 2 mm in inner diameter, and 250 mm in length) that penetrated the silica cap 4; a pair of gas introduction tube 6 and gas exhaust tube 7 (both were "Alumina SSA-S" manufactured by NIKKATO CORPORATION, 6 mm in outer diameter, 4 mm in inner diameter, and 150 mm in length); and an electric furnace 8 (crucible furnace, opening width: 60 mm, heating height: 100 mm) for heating the reaction vessel 3 from the bottom.

[0196] ​The alumina protection tube 5 has a length from the lower portion of the lid 4 to the raw material 2 contained in the bottom of the reaction vessel 3, and the thermocouple 9 is inserted into the alumina protection tube 5. The alumina protection tube 5 serves as a protection tube for the thermocouple 9. The tip of the thermocouple 9 is inserted into the raw material 2 to measure the temperature of the raw material 2, while being protected by the alumina protection tube 5 that encloses the tip. As shown by the solid arrow in the figure, the output of the thermocouple 9 is input to the temperature controller 10 of the electric furnace 8, and the temperature controller 10 controls the heating temperature of the electric furnace 8 in accordance with the input of the thermocouple 9.

[0197] The lower ends of the gas introduction pipe 6 and the gas discharge pipe 7 protrude 3 mm downward from the lid 4. Argon (Ar) is continuously supplied from a gas supply system (not shown) to the gas introduction pipe 6. In addition, the gas discharge pipe 7 is connected to a collection tank 12 that contains an aqueous sodium hydroxide solution 11. When the exhaust gas discharged from the reaction vessel 3 is discharged to the outside through the gas discharge pipe 7, it first passes through the aqueous sodium hydroxide solution 11 in the collection tank 12 and then is discharged to the outside. Therefore, even if the exhaust gas contains hydrogen sulfide gas generated by the vulcanization reaction, the hydrogen sulfide gas is neutralized by the aqueous sodium hydroxide solution and is removed from the exhaust gas.

[0198] (Baking Step)

[0199] First, the raw material 2 is placed in the bottom of the reaction vessel 3, and argon is continuously supplied from the gas supply system at a flow rate of 80 mL / min, and after 30 minutes from the start of the supply, the electric furnace 8 starts heating. This step is performed at a temperature increase rate of 150°C / h. Then, when the temperature of the raw material reaches the baking temperature (400°C) in Table 3, the baking is performed for 2 hours while maintaining this baking temperature. Next, while adjusting the argon flow rate, the temperature of the reaction product is naturally cooled to 25°C in an argon atmosphere, and then the product is taken out of the reaction vessel 3.

[0200] (Removal of Unreacted Sulfur)

[0201] In order to remove unreacted sulfur (sulfur in a free state) remaining in the product after the baking step, the following step is performed. That is, the product is pulverized in a mortar, and then 2 g of the pulverized product is placed in a glass tube furnace and heated at a temperature of 250°C for 3 hours while being vacuumed, to obtain a sulfur-based active material in which unreacted sulfur has been removed (or contains only a trace amount of unreacted sulfur). The temperature increase rate is set to 10°C / min.

[0202] (Classification Step)

[0203] In order to remove coarse particles in the baked material, the baked material is classified using a 32-μm stainless steel screen to obtain a sulfur-based active material.

[0204] <Manufacture of Lithium Ion Secondary Battery>

[0205] The lithium ion secondary battery was produced as follows.

[0206] (Positive electrode)

[0207] The sulfur-based active material obtained above was used as an active material, acetylene black was used as a conductive aid, and an acrylic resin was used as a binder. The active material: conductive aid: binder was weighed at a ratio of 90:5:5 (wt%) and put into a container and mixed by stirring with a planetary centrifugal mixer (ARE-250 manufactured by THINKY CORPORATION) using milliQ water as a dispersant to make a uniform slurry. The slurry obtained was coated onto a 20-μm aluminum foil using an applicator with a slit width of 60 μm, and then pressed using a roll press to obtain an electrode, which was then dried by heating at 120°C for 3 hours and then punched into a 14-mm-diameter disk. The mass of the electrode was measured, and the content of the active material in the electrode was calculated according to the above ratio.

[0208] (Negative electrode)

[0209] For the negative electrode, a metal lithium foil (disk-shaped, 14 mm in diameter, 500 μm in thickness, manufactured by Honjo Metal Co., Ltd.) was used.

[0210] (Electrolyte)

[0211] The electrolyte was a nonaqueous electrolyte in which LiPF6 was dissolved 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.

[0212] (Lithium ion secondary battery)

[0213] A coin battery was produced using the above positive electrode and negative electrode. Specifically, in a dry room, a separator (Celgard 2400 manufactured by Celgard LLC, a 25-μm-thick polypropylene microporous film) and a glass nonwoven fabric filter (GA100 manufactured by ADVANTEC, 440 μm in thickness) were sandwiched between the positive electrode and the negative electrode to form an electrode body battery. This electrode body battery was housed in a battery case (a member for a CR2032-type coin battery manufactured by Hohsen Corporation) made of stainless steel. The above electrolyte was injected into the battery case. The battery case was sealed with a caulking machine to obtain the lithium ion secondary battery of Example 1.

[0214] Examples 2 to 5 and Comparative Examples 1 to 4

[0215] Each of the raw materials, the sulfur-based active material, and the lithium-ion secondary battery was produced in the same manner as in Example 1, except that appropriate changes were made in accordance with Table 3.

[0216] <Measurement of discharge capacity and capacity retention>

[0217] Each of the button lithium-ion secondary batteries produced in the examples and comparative examples was subjected to charge and discharge at a current value of 50 mA per 1 g of positive electrode active material from the first to the ninth times and at a current value of 100 mA per 1 g of positive electrode active material from the tenth to the thirtieth times at a test temperature of 30°C. The discharge termination voltage was set to 1.0 V, and the charge termination voltage was set to 3.0 V. While repeating the charge and discharge, the capacity (mAh) of the battery at the tenth and thirtieth times of discharge was observed.

[0218] The second time of discharge capacity (mAh / g) was defined as the initial capacity. The greater the initial capacity, the greater the charge and discharge capacity of the lithium-ion secondary battery, which can be evaluated as more excellent. Furthermore, the capacity retention (%) can be calculated from the tenth time of discharge capacity DC 10 (mAh / g) and the thirtieth time of discharge capacity DC 30 (mAh / g) according to the following formula (a):

[0219] Capacity retention (%) = (DC 30 / DC 10 ) x 100 (a)

[0220] As described above, it can be said that the higher the capacity retention, the better the cycle characteristics of the lithium-ion secondary battery.

[0221] <Elemental analysis>

[0222] Elemental analysis was performed on the sulfur-based active materials produced in the examples and comparative examples.

[0223] For carbon, hydrogen, sulfur, and nitrogen, the mass ratio (%) to the total amount of the sulfur-based active material was calculated using the mass measured by a fully automated elemental analyzer varioMICRO cube produced by Elementar. The results are shown in Table 3.

[0224] <True density>

[0225] Thermogravimetric analysis was performed on the sulfur-based active materials prepared in the examples and comparative examples, and the true density (g / cm 3 ) of each material was calculated from the measurement results.

[0226] The equipment used for thermal gravimetric analysis was TGA Q500 manufactured by TA Instruments. The measurement conditions were that after heating to 750°C under an argon atmosphere, air was introduced to completely decompose the measurement sample. Then, the ash content ratio (wt%) was calculated from the measured weight reduction ratio (wt%). From the weight reduction ratio of Comparative Example 2, it was seen that the acrylic resin sulfide had been completely decomposed, and from the weight reduction ratio of Comparative Example 3, it was seen that the amount of iron disulfide (FeS2) had been reduced by 36 mass%. The true density of the acrylic resin sulfide in Comparative Example 2 was 1.8 g / cm 3 (Experimental value). On the other hand, the true density of iron disulfide in Comparative Example 3 was 5.0 g / cm 3 (Literature value). From the obtained values, the true density of the sulfur-based active material was calculated by the following formula.

[0227] True density of sulfur-based active material (g / cm 3 ) = (A + B) / (A / 1.8 + B / 5.0)

[0228] A: weight ratio of acrylic resin sulfide (wt%)

[0229] B: weight ratio of iron disulfide (wt%)

[0230] The results are shown in Table 2 below.

[0231] Table 2

[0232]

[0233] Median particle diameter

[0234] The median particle diameter was calculated by measuring the cumulative 50% particle diameter (median particle diameter D50) on a volume basis using a laser diffraction / scattering type particle size distribution analyzer (particle size distribution analyzer PSA1090L manufactured by Anton Paar GmbH) with water as the dispersion medium.

[0235]

[0236]

[0237]

[0238] <Embodiment>

[0239] The preferred embodiment is shown below.

[0240] [1] A method of producing a sulfur-based active material, the method comprising the steps of:

[0241] (1) mixing an acrylic resin, sulfur, and an iron compound containing divalent or trivalent iron ions to obtain a raw material; and

[0242] (2) calcining the raw material,

[0243] wherein the median particle diameter of the iron compound is 12.00 pm or less, preferably 10.00 pm or less, more preferably 8.00 pm or less, further preferably 6.00 pm or less, further preferably 5.00 pm or less, further preferably 4.50 pm or less, further preferably 4.30 pm or less, further preferably 4.29 pm or less, further preferably 4.00 pm or less, further preferably 3.00 pm or less.

[0244] [2] The method according to the above [1], wherein the content of the iron compound containing divalent or trivalent iron ions in the raw material is 50 parts by mass or more and 300 parts by mass or less, preferably more than 60 parts by mass and less than 250 parts by mass, more preferably more than 70 parts by mass and less than 200 parts by mass, further preferably more than 75 parts by mass and less than 150 parts by mass, further preferably more than 75 parts by mass and 100 parts by mass or less, with respect to 100 parts by mass of the acrylic resin.

[0245] [3] The method according to the above [1] or [2], wherein the step (1) comprises the following sub-steps:

[0246] (1-a-1) adding an acrylic resin and an iron compound containing divalent or trivalent iron ions to an organic solvent and mixing to obtain a liquid mixture;

[0247] (1-a-2) removing the organic solvent from the liquid mixture to obtain a dry mixture; and

[0248] (1-a-3) mixing the dry mixture with sulfur.

[0249] [4] The method according to the above [1] or [2], wherein the step (1) comprises the following sub-steps:

[0250] (1-b) mixing an acrylic resin, sulfur, and an iron compound containing divalent or trivalent iron ions in a powder state.

[0251] [5] The method according to any one of the above [1] to [4], wherein the calcination temperature in the step (2) is higher than 250°C and lower than 550°C, preferably higher than 300°C and lower than 500°C, more preferably higher than 350°C and lower than 450°C, further preferably higher than 380°C and lower than 450°C.

[0252] [6] The method according to any one of the above [1] to [5], wherein the baking temperature in step (2) is higher than a temperature at which the iron compound containing divalent or trivalent iron ions is thermally decomposed.

[0253] [7] The method according to any one of the above [1] to [6], wherein the sulfur content in the raw material is greater than 50 parts by mass and less than 1000 parts by mass, preferably greater than 100 parts by mass and less than 900 parts by mass, more preferably greater than 300 parts by mass and less than 800 parts by mass, further preferably greater than 400 parts by mass and less than 700 parts by mass, further preferably greater than 500 parts by mass and less than 700 parts by mass, with respect to 100 parts by mass of the acrylic resin.

[0254] [8] The method according to any one of the above [1] to [7], wherein the acrylic resin is at least one selected from the group consisting of a polymer obtained by polymerizing at least one monomer selected from the group consisting of acrylate compounds represented by the following formula (1); or a polymer obtained by polymerizing at least one monomer selected from the group consisting of acrylate compounds represented by the following formula (1) and at least one monomer selected from the group consisting of diacrylate compounds represented by the following formula (2),

[0255] CH2=C(R 11 )COOR 12 (1)

[0256] wherein R 11 is a hydrogen atom or a methyl group, and R 12 is an alkyl group,

[0257] CH2=C(R 21 )COO-Y-OCO(R 22 )C=CH2 (2)

[0258] wherein R 21 and R 22 are the same or different, each being a hydrogen atom or a methyl group; and Y is a straight-chain hydrocarbylene group which can have at least one substituent selected from the group consisting of a hydroxyl group and an alkyl group, and the carbon skeleton constituting the straight-chain hydrocarbylene group can have an ether bond containing an oxygen atom, provided that, when there are two or more ether bonds, there are always two or more carbon atoms interposed between adjacent oxygen atoms.

[0259] [9] The method according to the above [8], wherein R 12is an alkyl group having 1 or more and 6 or less carbon atoms, preferably 1 or more and 4 or less carbon atoms, Y is a straight-chain hydrocarbylene group having 2 or more and 6 or less carbon atoms, preferably 2 or 3 carbon atoms, in the hydrocarbylene group, the number of substituents is 1 or more and 4 or less, preferably 1 or 2, the number of carbon atoms of the alkyl group as the substituent is 1 or more and 4 or less, preferably 1, and the number of ether bonds possessed by the carbon skeleton constituting the hydrocarbylene group is 1 or more and 2 or less.

[0260]

[10] A method for producing an electrode, the method further comprising the following step after the production of the chalcogen-based active material by the method for producing a chalcogen-based active material according to any one of the above-mentioned [1] to [9]:

[0261] (3) producing an electrode by a conventional method using the chalcogen-based active material.

[0262]

[11] A method for producing a lithium-ion secondary battery, the method further comprising the following step after the production of the electrode by the method for producing an electrode according to

[10] :

[0263] (4) producing a lithium-ion secondary battery by a conventional method using the electrode.

[0264]

[12] A chalcogen-based active material obtained by calcining a raw material containing an acrylic resin, sulfur, and an iron compound containing divalent or trivalent iron ions,

[0265] comprising at least carbon, sulfur, and iron,

[0266] wherein the median particle diameter of the iron compound is 12.00 μm or less, preferably 10.00 μm or less, more preferably 8.00 μm or less, further preferably 6.00 μm or less, further preferably 5.00 μm or less, further preferably 4.50 μm or less, further preferably 4.30 μm or less, further preferably 4.29 μm or less, further preferably 4.00 μm or less, further preferably 3.00 μm or less,

[0267] the chalcogen-based active material contains iron disulfide,

[0268] the content of sulfur as a constituent element is 40.0 mass% or more, preferably 45.0 mass% or more, more preferably 50.0 mass% or more, further preferably 55.0 mass% or more.

[0269]

[13] The chalcogen-based active material according to the above-mentioned

[12] , wherein when X-ray diffraction measurement is performed using CuKα rays, the half-value width of the peak showing the maximum diffraction intensity in the range of 2θ = 33.04° (±1.0°) is 0.20 or more.

[0270]

[14] The chalcogen active material according to any one of the above

[12] or

[13] , wherein the true density is greater than 2.4 g / cm 3 and less than 3.6 g / cm 3 , preferably greater than 2.5 g / cm 3 and less than 3.5 g / cm 3 , more preferably 2.6 g / cm 3 or more and less than 3.2 g / cm 3 , further preferably greater than 2.6 g / cm 3 and less than 3.2 g / cm 3 , further preferably greater than 2.6 g / cm 3 and less than 3.1 g / cm 3 .

[0271]

[15] The chalcogen active material according to any one of the above

[12] to

[14] , wherein the carbon content is greater than 5.0 mass% and less than 30.0 mass%, preferably greater than 6.0 mass% and less than 29.0 mass%, more preferably greater than 7.0 mass% and less than 25.0 mass%, further preferably greater than 8.0 mass% and less than 25.0 mass%, further preferably greater than 8.5 mass% and less than 25.0 mass%.

[0272]

[16] The chalcogen active material according to any one of the above

[12] to

[15] , wherein when X-ray diffraction measurement is performed using CuKa rays, peaks are present in each of the ranges of 2Θ = 25.5° (±1.0°), 28.51° (±1.0°), 33.04° (±1.0°), 37.07° (±1.0°), 40.76° (±1.0°), 47.42° (±1.0°), and 56.27° (±1.0°).

[0273]

[17] The chalcogen active material according to any one of the above

[12] to

[16] , wherein the acrylic resin is at least one selected from the group consisting of a polymer obtained by polymerizing at least one monomer selected from the group consisting of acrylate compounds represented by the following formula (1); or a polymer obtained by polymerizing at least one monomer selected from the group consisting of acrylate compounds represented by the following formula (1) and at least one monomer selected from the group consisting of diacrylate compounds represented by the following formula (2),

[0274] CH2=C (R 11 ) COOR 12 (1)

[0275] in the formula, R 11 is a hydrogen atom or a methyl group, and R 12 is an alkyl group,

[0276] CH2=C (R21 ) COO-Y-OCO (R 22 ) C=CH2 (2)

[0277] wherein R 21 and R 22 are the same or different, each being a hydrogen atom or a methyl group; and Y is a straight-chain alkylene group which can have at least one substituent selected from a hydroxyl group and an alkyl group, and the carbon skeleton constituting the straight-chain alkylene group can have an ether linkage containing an oxygen atom, provided that when there are two or more ether linkages, there are always two or more carbon atoms interposed between adjacent oxygen atoms.

[0278]

[18] The chalcogen-based active material according to the above

[17] , wherein R 12 is an alkyl group having 1 or more and 6 or less carbon atoms, preferably 1 or more and 4 or less carbon atoms, Y is a straight-chain alkylene group having 2 or more and 6 or less carbon atoms, preferably 2 or 3 carbon atoms, the number of substituents in the alkylene group is 1 or more and 4 or less, preferably 1 or 2, the number of carbon atoms of the alkyl group as the substituent is 1 or more and 4 or less, preferably 1, and the number of ether linkages possessed by the carbon skeleton constituting the alkylene group is 1 or more and 2 or less.

[0279]

[19] The chalcogen-based active material according to any one of the above

[12] to

[18] , wherein the median particle diameter is 1 μm or more and 40 μm or less, preferably more than 2 μm and less than 30 μm, more preferably more than 3 μm and less than 20 μm, further preferably more than 4 μm and less than 15 μm, further preferably more than 4 μm and less than 10 μm.

[0280]

[20] The chalcogen-based active material according to any one of the above

[12] to

[19] , wherein, with respect to 100 parts by mass of the acrylic resin, the content of the iron compound containing divalent or trivalent iron ions in the raw material is 50 parts by mass or more and 300 parts by mass or less, preferably more than 60 parts by mass and less than 250 parts by mass, more preferably more than 70 parts by mass and less than 200 parts by mass, further preferably more than 75 parts by mass and less than 150 parts by mass, further preferably more than 75 parts by mass and 100 parts by mass or less, the sulfur content is more than 50 parts by mass and less than 1000 parts by mass, preferably more than 100 parts by mass and less than 900 parts by mass, more preferably more than 300 parts by mass and less than 800 parts by mass, further preferably more than 400 parts by mass and less than 700 parts by mass, further preferably more than 500 parts by mass and 700 parts by mass or less.

[0281] List of Reference Signs

[0282] 1. Reaction apparatus

[0283] 2. Raw material

[0284] 3. Reaction vessel

[0285] 4. Silica gel cap

[0286] 5. Alumina protection tube

[0287] 6. Gas inlet tube

[0288] 7. Gas outlet tube

[0289] 8. Electric furnace

[0290] 9. Thermocouple

[0291] 10. Temperature controller

[0292] 11. Sodium hydroxide aqueous solution

[0293] 12. Trapping tank

Claims

1. A method for preparing sulfide-based active materials, the method comprising the following steps: (1) Mix acrylic resin, sulfur and iron compounds containing divalent or trivalent iron ions to obtain raw materials; (2) Roasting the raw materials. The median particle size of the sulfur-based active material is 4.6 μm to 7.4 μm. The roasting temperature in step (2) is higher than 250℃ and lower than 550℃. The heating rate in step (2) is above 50℃ / h and below 500℃ / h. The sulfur content in the raw materials is greater than 100 parts by weight and less than 1000 parts by weight relative to 100 parts by weight of acrylic resin. Relative to 100 parts by weight of acrylic resin, the content of iron compounds containing divalent or trivalent ferric ions in the raw materials is greater than 70 parts by weight and less than 200 parts by weight. The acrylic resin is a polymer obtained by polymerizing at least one monomer selected from acrylate compounds represented by formula (1) below. CH2=C (R 11 ) COOR 12 (1) In the formula, R 11 It is a hydrogen atom or a methyl group, R 12 It is an alkyl group having one or more but no more than six carbon atoms. The iron compound containing divalent or trivalent iron ions is an organic acid salt of iron. The median particle size of the iron compound is below 12.00 μm.

2. The method according to claim 1, wherein, Step (1) includes the following sub-steps: (1-a-1) Acrylic resin and an iron compound containing divalent or trivalent ferric ions are added to an organic solvent and mixed to obtain a liquid mixture; (1-a-2) Remove the organic solvent from the liquid mixture to obtain a dry mixture; (1-a-3) The dry mixture is mixed with sulfur.

3. The method according to claim 1 or 2, wherein, Step (1) includes the following sub-steps: (1-b) The acrylic resin, sulfur, and iron compound containing divalent or trivalent iron ions are mixed in powder form.

4. The method according to claim 1 or 2, wherein, The roasting temperature in step (2) is higher than the thermal decomposition temperature of iron compounds containing divalent or trivalent iron ions.

5. The method according to claim 1, wherein, The iron compound is at least one selected from the group consisting of iron fatty acids, oxalic acid, tartaric acid, citric acid, malic acid, succinate, or hydrates thereof.

6. A method for preparing an electrode, wherein after preparing a sulfide-based active material by any one of the methods for preparing sulfide-based active materials according to claims 1-5, the method further includes the following step: (3) The electrode is prepared using the sulfide active material by conventional methods.

7. A method for preparing a lithium-ion secondary battery, wherein after preparing the electrode by the method for preparing the electrode according to claim 6, the method further includes the following steps: (4) Using the electrode, prepare a lithium-ion secondary battery by conventional methods.

8. A sulfur-based active material, obtained by calcining a raw material comprising acrylic resin, sulfur, and an iron compound containing divalent or trivalent ferric ions. The constituent elements include at least carbon, sulfur, and iron. The median particle size of the sulfur-based active material is 4.6 μm to 7.4 μm. The roasting temperature is above 250°C and below 550°C. The heating rate of the roasting is above 50℃ / h and below 500℃ / h. The acrylic resin is a polymer obtained by polymerizing at least one monomer selected from acrylate compounds represented by formula (1) below. CH2=C (R 11 ) COOR 12 (1) In the formula, R 11 It is a hydrogen atom or a methyl group, R 12 It is an alkyl group having one or more but no more than six carbon atoms. The iron compounds containing divalent or trivalent iron ions are organic acid salts of iron. Relative to 100 parts by weight of the acrylic resin, the content of the iron compound containing divalent or trivalent ferric ions is greater than 70 parts by weight and less than 200 parts by weight. in, The median particle size of iron compounds is below 12.00 μm. Sulfur-based active materials include iron disulfide. The content of sulfur as a constituent element is 40.0% by mass or more.

9. The sulfur-based active material according to claim 8, wherein, When X-ray diffraction measurements were performed using CuKα rays, the half-width of the peak showing the maximum diffraction intensity in the range of 2θ = 33.04° (±1.0°) was greater than 0.

20.

10. The sulfide-based active material according to claim 8 or 9, wherein, True density greater than 2.4 g / cm³ 3 And less than 3.6 g / cm 3 .

11. The sulfide-based active material according to claim 8 or 9, wherein, The carbon content is greater than 5.0% by mass and less than 30.0% by mass.

12. The sulfide-based active material according to claim 8 or 9, wherein, When X-ray diffraction measurements were performed using CuKα rays, each peak was observed in the ranges of 2θ = 25.5° (±1.0°), 28.51° (±1.0°), 33.04° (±1.0°), 37.07° (±1.0°), 40.76° (±1.0°), 47.42° (±1.0°), and 56.27° (±1.0°).

13. The sulfide-based active material according to claim 8 or 9, wherein, Relative to 100 parts by weight of acrylic resin, the content of iron compounds containing divalent or trivalent iron ions in the raw materials is greater than 75 parts by weight and less than 150 parts by weight, and the sulfur content is greater than 100 parts by weight and less than 1000 parts by weight.

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