Electrode active material, electrode, and lithium ion secondary battery

Abstract

To provide an electrode active material made of a predetermined organic sulfur material, and a lithium ion secondary battery formed by containing an electrode formed by containing an electrode component layer in which a volume energy density is improved by performing a press processing of the electrode component formed by containing the electrode active material, that is, formed by containing a positive electrode or a negative electrode, and the electrode.SOLUTION: An electrode active material is an electrode active material formed by an organic sulfur material obtained by deforming particles of an acryl resin with sulfur. In each of optimal five particles of the organic sulfur material, when a particle diameter is d(μm), and a test force at a moment when a breaking of each particle in a fine compression test is P(mN), a mean value of a breaking strength Cs(MPa) calculated a following formula is less than 47.4: Cs=2.48×P / πd2 (however, d is a mean value of a diameter calculated in a binary direction orthogonal to each particle of the organic sulfur material, and π is a circular constant (3.14)).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a novel electrode active material, an electrode comprising the electrode active material, and a lithium ion secondary battery comprising the electrode. [Background technology]

[0002] Lithium-ion secondary batteries have a large charge / discharge capacity and are primarily used as batteries for portable electronic devices. 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, which is obtained by heating raw material powder containing sulfur powder and polyacrylonitrile powder in a non-oxidizing atmosphere.

[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 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the cathode active material of Patent Document 1 has the problem that the raw material, polyacrylonitrile, is expensive, and polyacrylonitrile with stable quality is particularly expensive, making it difficult to provide lithium-ion secondary batteries at low cost. The above-mentioned materials proposed as anode active materials have the problem that they exhibit poor cycle characteristics when repeatedly charged and discharged due to large volume changes associated with the absorption and release of lithium ions. In addition, carbon materials such as graphite and hard carbon are also used, but they have already reached their theoretical capacity, and significant capacity improvements are not expected.

[0007] In addition, even if the capacity of the electrode active material is improved, the capacity per unit volume when used as an electrode, that is, the volumetric energy density (mAh / cm 3 ) is not improved, it will hinder efforts to miniaturize batteries.

[0008] The present disclosure provides an electrode active material made of a predetermined organic sulfur material, an electrode comprising an electrode composition layer having an improved volumetric energy density obtained by pressing an electrode composition comprising the electrode active material, i.e., a positive electrode or a negative electrode, and a lithium ion secondary battery comprising the electrode. [Means for solving the problem]

[0009] As a result of intensive research to solve the above problems, the present inventors have found that an electrode with improved volumetric energy density can be obtained by using an organosulfur material that is an acrylic resin particle modified with sulfur and has a breaking strength of less than a predetermined value. After further research, the present inventors have completed the present disclosure.

[0010] That is, the present disclosure relates to an electrode active material comprising an organic sulfur material in which acrylic resin particles are modified with sulfur, wherein the average value of the breaking strength Cs (MPa) calculated by the following formula for each of any five particles of the organic sulfur material is less than 47.4, where d (μm) is the particle diameter and P (mN) is the test force at the moment when the particles break in a microcompression test. Cs=2.48×P / πd2 (where d is the average diameter of the particles of the organosulfur material measured in two perpendicular directions, and π is the constant of the circumference of a circle (3.14).) [Effects of the Invention]

[0011] According to the present disclosure, it is possible to provide an electrode active material made of a predetermined organic sulfur material, an electrode comprising an electrode composition layer having an improved volumetric energy density by pressing an electrode composition comprising the electrode active material, i.e., a positive electrode or a negative electrode, and a lithium ion secondary battery comprising the electrode.

[0012] In this specification, the term "volumetric energy density" refers to the discharge capacity (mAh / cm) of an electrode (electrode composition layer) per unit volume. 3 ) Furthermore, "cycle characteristics" refers to the characteristic of a secondary battery that maintains 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]

[0013] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating a reaction apparatus used in the production of an organosulfur material in an embodiment of the present disclosure. [Figure 2] 1 shows SEM (Scanning Electron Microscope) images of the surfaces of electrodes (positive electrodes) of Example 1 and Comparative Example 1 of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0014] In the present disclosure, the upper and lower limit values ​​of "greater than or equal to," "less than or equal to," and "to" used to describe a numerical range can be arbitrarily combined, and in addition, the numerical values ​​in the examples can be combined with the upper and lower limit values. Furthermore, when a numerical range is specified by "to," it means that both end values ​​are included unless otherwise specified. Furthermore, in the present disclosure, a numerical range indicated as including both end values ​​is understood to simultaneously indicate a numerical range that does not include either end value, or even a numerical range that does not include both end values, unless it is contrary to the spirit of the present disclosure.

[0015] One embodiment of the present disclosure is an electrode active material made of an organic sulfur material in which acrylic resin particles are modified with sulfur, and the electrode active material has an average breaking strength Cs (MPa) of less than 47.4, calculated by the following formula for each of any five particles of the organic sulfur material, where d (μm) is the particle diameter and P (mN) is the test force at the moment when the particles break in a microcompression test. Cs=2.48×P / πd 2 (where d is the average diameter of the particles of the organosulfur material measured in two perpendicular directions, and π is the constant of the circumference of a circle (3.14).)

[0016] While not intending to be bound by theory, the mechanism by which an electrode (electrode composition layer) with improved volumetric energy density is obtained in the present disclosure is believed to be as follows. That is, an organosulfur material having a breaking strength below a predetermined value, as defined in the present disclosure, is more likely to be crushed and deformed by the pressing process used to manufacture the electrode than one having a breaking strength equal to or greater than the predetermined value. This makes it easier for the gaps between particles of the organosulfur material to be filled, forming a denser electrode composition layer (electrode composition layer), which is believed to improve the volumetric energy density.

[0017] The median diameter of the organic sulfur material is preferably less than 12.0 μm.

[0018] This is because it is thought that the gaps between particles of the organic sulfur material are easily filled.

[0019] The acrylic resin preferably contains at least one polymer selected from the group consisting of a polymer obtained by polymerizing at least one compound selected from the group consisting of acrylate compounds represented by the following formula (1), a polymer 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), and a polymer obtained by polymerizing a monomer containing methacrylonitrile. 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 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.

[0020] This is because it is easy to obtain and is believed to be able to easily exert the effects of the present disclosure.

[0021] R 12 is an alkyl group having 1 to 6 carbon atoms, and Y is a hydrocarbylene group having 2 to 6 carbon atoms, and in the hydrocarbylene group, it is preferred that the number of substituents is 1 to 4, the alkyl group as the substituent has 1 to 4 carbon atoms, and the carbon skeleton constituting the hydrocarbylene group has 1 or 2 ether bonds.

[0022] This is because it is easy to obtain and is believed to be able to easily exert the effects of the present disclosure.

[0023] The particle diameter of the acrylic resin particles is preferably 0.1 to 300.0 μm.

[0024] This is because it is thought that the gaps between particles of the organic sulfur material are easily filled.

[0025] The acrylic resin particles preferably have a porous structure.

[0026] This is because it is thought that the gaps between particles of the organic sulfur material are easily filled.

[0027] The amount of sulfur in the organic sulfur material is preferably 50.00% by mass or more.

[0028] This is because it is believed that the charge / discharge capacity can be more easily improved with a larger sulfur content.

[0029] Another embodiment of the present disclosure is an electrode composition layer obtained by pressing an electrode composition comprising the electrode active material, the electrode composition layer having a density of 1.50 g / cm 3 The above is the electrode composition layer.

[0030] This is because the volume energy density can be improved.

[0031] Another embodiment of the present disclosure is an electrode comprising the electrode composition layer.

[0032] Another embodiment of the present disclosure is a lithium ion secondary battery comprising the electrode.

[0033] <Organic sulfur materials> The organic sulfur material of the present disclosure is obtained by modifying acrylic resin particles with sulfur, and for each of any five particles, when the particle diameter is d (μm) and the test force at the moment when the particles break in a microcompression test is P (mN), the average value of the breaking strength Cs (MPa) calculated by the following formula is less than 47.4. Cs=2.48×P / πd 2 (where d is the average diameter of the particles of the organosulfur material measured in two perpendicular directions, and π is the constant of the circumference of a circle (3.14).)

[0034] (Breaking strength Cs) The breaking strength Cs (MPa) of the organic sulfur material is a value that can be determined by the microcompression test described in the Examples section below.

[0035] From the viewpoint of the effects of the present disclosure, the breaking strength Cs (MPa) is preferably 40.0 MPa or less, more preferably 30.0 MPa or less, even more preferably 25.0 MPa or less, even more preferably less than 23.2 MPa, even more preferably 20.0 MPa or less, even more preferably 15.0 MPa or less, even more preferably 10.0 MPa or less, and even more preferably 5.0 MPa or less.

[0036] The breaking strength Cs (MPa) can be adjusted by, for example, using acrylic resin particles with a lower degree of cross-linking to obtain an organosulfur material with a lower breaking strength. This is because organosulfur materials modified with acrylic resin particles are more easily crushed and deformed than those with a higher degree of cross-linking. Alternatively, the breaking strength can be reduced by using porous acrylic resin particles compared to non-porous acrylic resin particles.

[0037] (constituent elements) The mass ratio (%) of the constituent elements of the organic sulfur material was determined by elemental analysis as described in the Examples section below.

[0038] Organic sulfur materials are primarily composed of carbon and sulfur, and a higher sulfur content tends to improve charge / discharge capacity. Therefore, a higher sulfur content is preferable. Generally, the sulfur content is preferably 50.00% by mass or more, more preferably 53.00% by mass or more, even more preferably 55.00% by mass or more, even more preferably 56.00% by mass or more, and even more preferably 60.00% by mass or more in the organic sulfur material. However, when a conductive carbon material is added, even if the sulfur content is slightly lower due to the influence of the carbon constituting the conductive carbon material, improvements in charge / discharge capacity and cycle characteristics may be expected. In such cases, the sulfur content may be approximately 5.00% by mass lower than the above-mentioned sulfur content. The total amount of carbon and sulfur in the organic sulfur material is preferably 90.00% by mass or more, more preferably 95.00% by mass or more, and even more preferably 96.00% by mass or more.

[0039] Furthermore, by calcination (modification), hydrogen (H) in the acrylic resin reacts with sulfur to form hydrogen sulfide, which is then reduced from the sulfide. Therefore, the hydrogen content of the organic sulfur material is preferably 1.80% by mass or less, more preferably 1.40% by mass or less, even more preferably 1.00% by mass or less, even more preferably 0.90% by mass or less, even more preferably 0.80% by mass or less, even more preferably 0.70% by mass or less, even more preferably 0.60% by mass or less, and even more preferably 0.52% by mass or less. When the hydrogen content is 1.80% by mass or less, calcination tends to be sufficient. Therefore, in this case, charge / discharge capacity tends to be improved.

[0040] (true density) True density of organic sulfur materials (g / cm 3 ) is a value calculated from the weight and volume obtained by the method described in the Examples section below.

[0041] True density (g / cm 3 ) may vary depending on the type of acrylic resin particles used. However, when the acrylic resin particles used in the examples of the present disclosure are used, if the baking (modification) has progressed sufficiently, the3 It falls within the range of.

[0042] (median diameter) The median diameter (μm) of the organic sulfur material is a value measured by the method described in the Examples section below.

[0043] The median diameter (μm) is preferably less than 12.0 μm, more preferably 11.0 μm or less, even more preferably 10.0 μm or less, even more preferably 9.0 μm or less, even more preferably 8.5 μm or less, even more preferably 8.3 μm or less, and even more preferably 6.0 μm or less. The lower limit of the median diameter (μm) is not particularly limited in terms of the effects of the present disclosure, but is typically about 0.1 μm or more, or 1.0 μm or more. To adjust the median diameter, for example, a smaller median diameter can be obtained by using acrylic resin particles with a smaller particle diameter, or by thoroughly pulverizing the resulting organosulfur material.

[0044] (electrode active material) The organosulfur material of the present disclosure can be used as an electrode active material, i.e., a positive electrode active material or a negative electrode active material, particularly as an electrode active material for a lithium ion secondary battery.

[0045] <Production of organic sulfur materials> In the present disclosure, the organosulfur material can be produced by modifying particles of a specific acrylic resin with sulfur so that the breaking strength is less than a predetermined value. An organosulfur material with a lower breaking strength can be produced, for example, by using acrylic resin particles with a lower degree of crosslinking.

[0046] (acrylic resin) The acrylic resin contains at least one polymer selected from the group consisting of a polymer obtained by polymerizing at least one selected from the group consisting of acrylate compounds (acrylate monomers) represented by the following formula (1), a polymer 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 (crosslinking component monomers) represented by the following formula (2), and a polymer obtained by polymerizing a monomer containing methacrylonitrile. 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 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.

[0047] 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 the compound 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 the compound represented by formula (1) is butyl methacrylate.

[0048] In equation (2), R 21 and R 22 are preferably a methyl group. The hydrocarbylene group of Y preferably has 2 to 6 carbon atoms, more preferably 2 or 3. The number of substituents on Y is preferably 1 to 4, more preferably 1 or 2. The substituents on 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 one represented by the following formula (3) (however, in formula (3), the substituents on Y are not taken into consideration). -(CH2) l -(CH2CH2O) m -(CH2CH2CH2O) n - (3) (Here, l is a number between 0 and 6, m is a number between 0 and 3, and n is a number between 0 and 2. However, l, m, and n cannot all be 0 at the same time.)

[0049] 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.

[0050] 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.

[0051] 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 homopolymers of methyl (meth)acrylate and copolymers of methyl methacrylate and ethylene glycol dimethacrylate.

[0052] One or more types of acrylic resins can be used.

[0053] <Form of acrylic resin> In the present disclosure, the acrylic resin is in the form of particles. Here, the particles preferably have 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, even more preferably 100.0 μm or less, even more preferably 50.0 μm or less, even more preferably 20.0 μm or less, even more preferably 15.0 μm or less, even more preferably 13.0 μm or less, even more preferably 10.0 μm or less, and even more preferably 6.0 μm or less. While the lower limit of the particle diameter is not particularly limited, it is typically, for example, 0.1 μm or more, preferably 1.0 μm or more. The particle diameter is measured using a precision particle size distribution analyzer, Multisizer 3, manufactured by Beckman Coulter, Inc.

[0054] The acrylic resin may be spherical particles or porous particles. When the acrylic resin is porous, its oil absorption is preferably 100 ml / 100 g or more, more preferably 110 ml / 100 g or more, even more preferably 120 ml / 100 g or more, even more preferably 130 ml / 100 g or more, and even more preferably 140 ml / 100 g or more. 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.

[0055] <Degree of cross-linking of acrylic resin> In the present disclosure, the degree of crosslinking of the acrylic resin can be adjusted by the proportion (mass%) of the crosslinking component monomer contained in the acrylic resin. For example, in the case of a copolymer of methyl (meth)acrylate and ethylene glycol di(meth)acrylate, the degree of crosslinking of the acrylic resin can be increased by increasing the proportion (mass%) of the crosslinking component monomer ethylene glycol di(meth)acrylate, and conversely, the degree of crosslinking of the acrylic resin can be decreased by decreasing the proportion (mass%) of the crosslinking component monomer.

[0056] <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 within the range of 2,000 to 1,500,000. The Mw is a value measured by gel permeation chromatography (GPC) (calibrated with polystyrene).

[0057] <<Acquisition or production of acrylic resin>> The acrylic resins are commercially available or can be prepared by conventional methods within the knowledge of those skilled in the art, such as those manufactured by Sekisui Plastics Co., Ltd. and Kuraray Co., Ltd.

[0058] (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. Elemental sulfur can be used. The amount of sulfur is preferably 50 parts by mass or more, more preferably 100 parts by mass or more, even more preferably 150 parts by mass or more, even more preferably 200 parts by mass or more, and even more preferably 250 parts by mass or more, per 100 parts by mass of acrylic resin particles. An amount of sulfur of 100 parts by mass or more tends to improve charge / discharge capacity and cycle characteristics. On the other hand, there is no particular upper limit to the amount of sulfur, but it is usually 1000 parts by mass or less, preferably 750 parts by mass or less, more preferably 500 parts by mass or less, even more preferably 400 parts by mass or less, and even more preferably 350 parts by mass or less. An amount of sulfur of 1000 parts by mass or less tends to be cost-effective. One or more types of sulfur can be used.

[0059] (Other additives) When modifying an acrylic resin with sulfur, other additives commonly used in this field may be added to the acrylic resin in advance, if desired. Examples of such additives include conductive carbon materials. The conductive carbon materials can improve the conductivity of the organic sulfur material.

[0060] <Conductive carbon materials> The conductive carbon material is preferably a carbon material having a graphite structure. Examples of the carbon material that can be used include carbon black, acetylene black, ketjen black, graphite, carbon nanotubes (CNT), carbon fibers (CF), graphene, and fullerenes, which have a condensed aromatic ring structure. One or more conductive carbon materials can be used.

[0061] 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 and 12% by mass or less of the total amount of conductive carbon material.

[0062] The amount of the conductive carbon material is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, relative to 100 parts by mass of the acrylic resin. A blending amount 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 blending amount is preferably 50 parts by mass or less, more preferably 40 parts by mass or less. A blending amount of 50 parts by mass or less tends to prevent a relative decrease in the proportion of sulfur-containing structures in the organic sulfur material, and tends to facilitate the achievement of the objective of further improving the charge / discharge capacity and cycle characteristics.

[0063] (Denaturation process) The modification of the acrylic resin particles with sulfur can be carried out by a conventional method, for example, by baking a baking raw material containing the acrylic resin particles and sulfur. The baking can be carried out by a conventional method, for example, by heating the baking raw material (containing the acrylic resin, sulfur, and optionally other additives) at a predetermined temperature increase rate until it reaches a predetermined temperature, maintaining the predetermined temperature for a predetermined time, and then naturally cooling.

[0064] <Preparation of firing ingredients> For the modification, it is desirable to thoroughly mix the acrylic resin particles and sulfur in advance. If a conductive carbon material or the like is added to the acrylic resin in advance, these additives are also mixed together. The mixing can be carried out by a conventional method, for example, using a high-speed blender. On the other hand, the acrylic resin, sulfur, and, if desired, additives can be molded into pellets.

[0065] <Non-oxidizing atmosphere> The modification 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.

[0066] <Heating rate> The temperature rise rate is preferably, for example, within a range of 50 to 500°C / h. The temperature rise rate is more preferably 100°C / h or higher. On the other hand, the temperature rise rate is more preferably 400°C / h or lower, even more preferably 300°C / h or lower, and even more preferably 200°C / h or lower. 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.

[0067] <Baking temperature and time> The calcination temperature refers to the temperature after the temperature rise of the calcination raw materials is completed, and is maintained for a certain period of time to calcinate the calcination raw materials. The temperature is preferably in the range of 250 to 550°C. A temperature of 250°C or higher 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 of 550°C or lower tends to prevent decomposition of the calcination raw materials, and to prevent a decrease in yield and a decrease in charge / discharge capacity. The temperature is more preferably 300°C or higher, and even more preferably 350°C or higher, while more preferably 500°C or lower, and even more preferably 450°C or lower. The time maintained at the calcination temperature can be appropriately set depending on the type of calcination raw materials, the calcination temperature, etc., but is preferably, for example, 1 to 6 hours. A temperature of 1 hour or more tends to allow the calcination to proceed sufficiently, and a temperature of 6 hours or less tends to prevent excessive thermal decomposition of the constituent components.

[0068] ≪Device≫ The calcination can be carried out using the apparatus shown in Fig. 1, or alternatively, it can be carried out using a continuous apparatus such as a twin-screw extruder. When a continuous apparatus is used, there is an advantage that the organic sulfur material can be produced continuously through a series of operations, such as kneading, pulverizing, and mixing the calcination raw materials while calcining them in the apparatus.

[0069] (Residue removal process) The treated product obtained after calcination contains unreacted sulfur, which is the sulfur that sublimed during calcination and then cooled and precipitated. These residues can cause deterioration in cycle characteristics, so it is desirable to remove them as much as possible. The removal of residues can be carried out by conventional methods, such as reduced-pressure heating drying, hot air drying, and solvent washing.

[0070] (Crushing, classification) The obtained organic sulfur material can be pulverized to a predetermined particle size and classified to obtain particles of a size suitable for electrode production. The particle size distribution of the particles is preferably less than 12.0 μm in median diameter, more preferably 11.0 μm or less, even more preferably 10.0 μm or less, even more preferably 9.0 μm or less, even more preferably 8.5 μm or less, even more preferably 8.3 μm or less, and even more preferably 6.0 μm or less. The lower limit of the median diameter (μm) is not particularly limited from the viewpoint of the effects of the present disclosure, but is typically 0.1 μm or more or 1.0 μm or more. The median diameter can be reduced by using acrylic resin particles with small particle diameters or by thoroughly performing the above-mentioned pulverization. In the firing method using a twin-screw extruder described above, the organic sulfur material produced can be pulverized simultaneously with the production of the organic sulfur material due to shear during kneading.

[0071] <Lithium-ion secondary battery> The organosulfur material of the present disclosure can be used as an electrode active material, i.e., as a positive electrode active material or a negative electrode active material, in electrodes, particularly in electrodes of lithium ion secondary batteries. That is, a lithium secondary battery electrode can be fabricated in the same manner as in fabricating a general lithium ion secondary battery electrode, except for using the organosulfur material. Furthermore, a lithium ion secondary battery can be fabricated in the same manner as in fabricating a general lithium ion secondary battery, except for using the lithium ion secondary battery electrode. The same applies to electrodes for batteries other than lithium ion secondary batteries and batteries other than lithium ion secondary batteries. The electrode fabricated in this manner is characterized by its electrode composition having excellent volumetric energy density.

[0072] 1. When using organic sulfur materials 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 organic sulfur material (positive electrode active material), a negative electrode, an electrolyte, and, if desired, components such as a separator.

[0073] (positive electrode) A positive electrode for a lithium-ion secondary battery can be fabricated in the same manner as a typical positive electrode for a lithium-ion secondary battery, except that the above-mentioned organic sulfur material is used as the positive electrode active material. For example, the positive electrode can be fabricated by mixing a particulate organic sulfur material with a conductive additive, a binder, and a solvent to prepare a paste-like electrode composition, applying the electrode composition to a current collector, pressing the electrode composition using a press or the like to bond the electrode composition to the current collector, drying, and forming an electrode composition layer (positive electrode composition layer) on the current collector. Alternatively, the positive electrode can be fabricated by kneading the organic sulfur material with a conductive additive, a binder, and a small amount of solvent using a mortar or the like to form an electrode composition, forming the electrode composition into a film, and pressing the film using a press or the like to bond the electrode composition to the current collector to form an electrode composition layer (positive electrode composition layer) on the current collector.

[0074] The pressure bonding using the press or the like can usually be carried out at a linear pressure of 280 kg / cm or less. The electrode active material of the present disclosure is easily crushed and deformed by such a load.

[0075] [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.

[0076] [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.

[0077] [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.

[0078] [Amount] The amounts of these materials constituting the positive electrode are not particularly limited, but it is preferable to mix, for example, 2 to 100 parts by mass of a conductive additive, 2 to 50 parts by mass of a binder, and an appropriate amount of a solvent with 100 parts by mass of an organic sulfur material.

[0079] [Current collector] The current collector may be any material commonly used in lithium-ion secondary battery positive electrodes. 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, nickel foam, nickel nonwoven fabric, copper foil, copper mesh, punched copper sheet, expanded copper sheet, titanium foil, titanium mesh, carbon nonwoven 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 organic sulfur material of the present disclosure is used as a positive electrode active material because they do not contain hydrogen and have low reactivity with sulfur. As raw materials for highly graphitized carbon fibers, various pitches (i.e., by-products of petroleum, coal, coal tar, etc.) and polyacrylonitrile fiber (PAN), which are commonly used as carbon fiber materials, can be used.

[0080] (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 a pre-doping method 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.

[0081] (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 concentration of the electrolyte may be approximately 0.5 mol / L to 1.7 mol / L. 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).

[0082] (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.

[0083] (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.

[0084] (Density of Positive Electrode Composition Layer) Density of the positive electrode composition layer (g / cm 3 ) is a value measured by the method described in the Examples section below.

[0085] Density of the positive electrode composition layer (g / cm 3) is preferably 1.50 or more, more preferably 1.53 or more, even more preferably 1.56 or more, and even more preferably 1.59 or more; More preferably, the density (g / cm 3 ) is preferably as large as possible, and there is no particular upper limit, but it is usually considered to be, for example, about 2.00 or less.

[0086] 2. When using organic sulfur materials 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 organic sulfur material (negative electrode active material), a positive electrode, an electrolyte, and, if desired, components such as a separator.

[0087] (Negative electrode) A lithium-ion secondary battery negative electrode can be fabricated in the same manner as a typical lithium-ion secondary battery negative electrode, except that the above-mentioned organic sulfur material is used as the negative electrode active material. For example, the negative electrode can be fabricated by mixing a particulate organic sulfur material with a conductive additive, a binder, and a solvent to prepare a paste-like electrode composition, applying the electrode composition to a current collector, pressing the electrode composition using a press or the like to bond the electrode composition to the current collector, drying, and forming an electrode composition layer (negative electrode composition layer) on the current collector. Alternatively, the negative electrode can be fabricated by kneading the organic sulfur material with a conductive additive, a binder, and a small amount of solvent using a mortar or the like to form an electrode composition, forming the electrode composition into a film, and pressing the film using a press or the like to bond the electrode composition to the current collector to form an electrode composition layer (negative electrode composition layer) on the current collector.

[0088] The pressure bonding using the press or the like can usually be carried out at a linear pressure of 280 kg / cm or less. The electrode active material of the present disclosure is easily crushed and deformed by such a load.

[0089] The conductive additive, binder, and solvent can be the same as those used in the above case where an organic sulfur material is used as the positive electrode active material, and the same current collector can also be used.

[0090] (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 0.5 O4, etc. These compounds may be used alone or in combination.

[0091] The electrolyte, separator, and shape of the lithium ion secondary battery can also be the same as those used in the above case where an organic sulfur material is used as the positive electrode active material.

[0092] (Density of negative electrode composition layer) Density of the negative electrode composition layer (g / cm 3 ) is the density (g / cm 3), it is preferably 1.50 or more, more preferably 1.53 or more, even more preferably 1.56 or more, even more preferably 1.59 or more, and even more preferably 1.60 or more. On the other hand, the density (g / cm 3 ) is preferably as large as possible, and there is no particular upper limit, but it is usually considered to be, for example, about 2.00 or less. [Example]

[0093] The present disclosure will be described based on examples, but the present disclosure is not limited to only the examples.

[0094] The various chemicals used in the examples and comparative examples are listed below. The various chemicals were purified according to conventional methods as necessary.

[0095] <Materials used in the test> Acrylic resin particles 1: Spherical acrylic resin consisting of methyl methacrylate and ethylene glycol dimethacrylate copolymer (Techpolymer MBX-20 manufactured by Sekisui Plastics Co., Ltd., particle size: 20 μm, degree of cross-linking: standard) Acrylic resin particles 2: Spherical acrylic resin consisting of methyl methacrylate and ethylene glycol dimethacrylate copolymer (Techpolymer MBX-5 manufactured by Sekisui Plastics Co., Ltd., particle size: 5 μm, degree of cross-linking: standard) Acrylic resin particles 3: Spherical acrylic resin consisting of methyl methacrylate and ethylene glycol dimethacrylate copolymer (Techpolymer MB30X-20 manufactured by Sekisui Plastics Co., Ltd., particle size: 20 μm, degree of cross-linking: high) Sulfur: Precipitated sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.

[0096] Example 1 <Production of organic sulfur materials> (Preparation of raw materials) According to the formulation in Table 1, the materials were mixed in a blender to obtain a raw material for firing (a raw material for firing).

[0097] (Reaction Apparatus) The raw materials were fired using a reactor 1 shown in Figure 1. The reactor 1 includes a cylindrical, bottomed quartz glass reactor 3 for containing and firing raw materials 2, the reactor 3 having an outer diameter of 60 mm, an inner diameter of 50 mm, and a height of 300 mm, a silicone lid 4 for closing the top opening of the reactor 3, an alumina protective tube 5 (Nikkato Corporation's "Alumina SSA-S"; outer diameter 4 mm, inner diameter 2 mm, length 250 mm) that passes through the lid 4, two gas inlet pipes 6 and a gas outlet pipe 7 (Nikkato Corporation's "Alumina SSA-S"; outer diameter 6 mm, inner diameter 4 mm, length 150 mm), and an electric furnace 8 (crucible furnace; opening width φ80 mm, heating height 100 mm) that heats the reactor 3 from the bottom side.

[0098] The alumina protective tube 5 is formed to a length that extends downward from the lid 4 to the raw material 2 contained at the bottom of the reaction vessel 3, and a thermocouple 9 is inserted inside. The alumina protective tube 5 is used as a protective tube for the thermocouple 9. The tip of the thermocouple 9, protected by the closed tip of the alumina protective tube 5, is inserted into the raw material 2 and functions to measure the temperature of the raw material 2. The output of the thermocouple 9 is input to a temperature controller 10 of the electric furnace 8, as shown by the solid arrow in the figure, and the temperature controller 10 functions to control the heating temperature of the electric furnace 8 based on the input from this thermocouple 9.

[0099] The gas inlet pipe 6 and the gas outlet pipe 7 are formed so that their lower ends protrude 3 mm downward from the lid 4. Ar (argon) gas is continuously supplied to the gas inlet pipe 6 from a gas supply system (not shown). The gas outlet pipe 7 is connected to a trap tank 12 containing an aqueous sodium hydroxide solution 11. The exhaust gas attempting to escape from the reaction vessel 3 through the gas outlet pipe 7 to the outside first passes through the aqueous sodium hydroxide solution 11 in the trap tank 12 before being released to the outside. Therefore, even if the exhaust gas contains hydrogen sulfide gas generated by the vulcanization reaction, it is neutralized by the aqueous sodium hydroxide solution and removed from the exhaust gas.

[0100] (Firing process) First, with raw material 2 placed at the bottom of reaction vessel 3, Ar gas was continuously supplied from the gas supply system at a flow rate of 80 ml / min. 30 minutes after the start of supply, heating in electric furnace 8 was initiated. The temperature was increased at a rate of 150°C / h. When the temperature of the raw material reached the firing temperature (400°C) in Table 1, firing was continued for 2 hours while maintaining this firing temperature. Next, the reaction product was allowed to cool naturally to 25°C in an Ar gas atmosphere while adjusting the flow rate of Ar gas, and then the product was removed from reaction vessel 3.

[0101] (Removal of unreacted sulfur) To remove unreacted sulfur (free elemental sulfur) remaining in the product after the calcination step, the following steps were performed: The product was pulverized in a mortar, and 2 g of the pulverized material was placed in a glass tube oven and heated at 250 °C for 3 hours while evacuating to obtain an organic sulfur material from which unreacted sulfur had been removed (or which contained only trace amounts of unreacted sulfur). The heating rate was 10 °C / min.

[0102] (Classification work) In order to remove coarse particles from the fired product, the fired product was classified using a stainless steel sieve with a mesh of 32 μm to obtain an organic sulfur material 1.

[0103] <Fabrication of lithium-ion secondary batteries> A lithium ion secondary battery was fabricated as follows.

[0104] (positive electrode) Organic sulfur material 1 was used as the active material, acetylene black as the conductive additive, and acrylic resin as the binder. These were weighed to a ratio of active material:conductive additive:binder = 90:5:5 (mass%), placed in a container, and stirred and mixed using milliQ water as a dispersant using a planetary centrifugal mixer (ARE-250, manufactured by Thinky Corporation) to produce a uniform electrode composition slurry. The electrode composition slurry was applied to a 20 μm-thick aluminum foil current collector using an applicator with a 400 μm slit width to form an electrode composition layer. This was then pressed using a roll press (a small roll press manufactured by Hosen Co., Ltd.) at a linear pressure of 280 kg / cm, and then heated and dried in a dryer at 120 °C for 3 hours. An electrode composition layer (positive electrode composition layer) was then formed on the current collector, and the electrode (positive electrode) was obtained by punching out to a diameter of 11 mm. The electrode was then weighed, and the amount of active material in the electrode was calculated from the above ratio.

[0105] (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.

[0106] (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.

[0107] (lithium-ion secondary battery) A coin battery was fabricated using the above positive and negative electrodes. Specifically, in a dry room, a separator (Celgard 2400 manufactured by Celgard, a 25 μm thick polypropylene microporous membrane) and a glass nonwoven fabric filter (440 μm thick, GA100 manufactured by Advantec) were sandwiched between the positive and negative electrodes 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 solution 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.

[0108] Examples 2 to 7 and Comparative Example 1 The firing raw materials, organic sulfur materials, positive electrodes, and lithium ion secondary batteries were prepared in the same manner as in Example 1, except that appropriate changes were made according to the formulations and conditions in Table 1.

[0109] <Evaluation> (Elemental analysis of organic sulfur materials) The organosulfur materials produced in the examples and comparative examples were subjected to elemental analysis.

[0110] The mass ratio (%) of carbon, hydrogen, sulfur, and nitrogen to the total amount of organic sulfur materials was calculated from the masses measured using a fully automated elemental analyzer, vario MICRO cube, manufactured by Elementar. The results are shown in Table 1.

[0111] (True density of organic sulfur materials) The true density of the organic sulfur material was measured by a pycnometer (M-Ultrapyc 1200e, manufactured by Anton Paar) using helium as the measurement gas, as a volume (cm 3 ) and the separately measured weight (g).

[0112] (Median diameter of organic sulfur materials) The median diameter (D50: particle size at which the cumulative frequency reaches 50%) of each organic sulfur material obtained above was determined. Specifically, the organic sulfur material was thoroughly dispersed in water by ultrasonic treatment, and the frequency distribution and cumulative volume distribution curve were determined using a laser diffraction / scattering particle size distribution analyzer (HORIBA Particle Size Distribution Analyzer LA-960). The particle size at the 50% point on the cumulative volume distribution curve was taken as the median diameter.

[0113] (Fracture strength of organic sulfur materials Cs (MPa)) For each of the organic sulfur materials obtained above, a microcompression tester (MCT-510, manufactured by Shimadzu Corporation) was used to measure the test force P (mN) at which the particles of the organic sulfur material broke using an indenter. That is, after a trace amount of the organic sulfur material was scattered on a sample stage, five random particles were compressed one by one using an indenter, and the test force P (mN) at which the particles of the organic sulfur material broke was determined. In addition, the particle diameter d (μm) of each particle was measured in two perpendicular directions and the average value was calculated.

[0114] The breaking strength Cs (MPa) was calculated from the test force P (mN) and particle diameter d (μm) using the following formula (where π is the constant of the circumference of a circle (3.14)). Cs=2.48×P / πd 2

[0115] The average value of the fracture strength Cs (MPa) for the five particles was calculated and used as the fracture strength Cs (MPa) of the organosulfur material.

[0116] (Measurement of discharge capacity and capacity retention rate) The coin-type lithium-ion secondary batteries fabricated in each Example and Comparative Example were charged and discharged at a current value equivalent to 50 mA per 1 g of positive electrode active material from the first to ninth charge / discharge cycles at a test temperature of 30°C, and at a current value equivalent to 250 mA per 1 g of positive electrode active material from the tenth to thirtieth charge / discharge cycles. The discharge end voltage was 1.0 V, and the charge end voltage was 3.0 V. The battery discharge capacities (mAh) at the first and second charge / discharge cycles, as well as the battery discharge capacities (mAh) at the tenth and thirtieth charge / discharge cycles, were observed.

[0117] 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 capacity retention rate (%) was calculated using the following formula from the 10th discharge capacity DC10 (mAh / g) and the 30th discharge capacity DC30 (mAh / g). Capacity maintenance rate (%)=(DC30 / DC10)×100

[0118] (Density of electrode composition layer) For the electrode obtained above, the density of the electrode composition layer (positive electrode) was calculated by multiplying the weight (g) of the electrode composition layer by the volume (cm 3 ) was calculated from the weight (g) of the electrode composition layer and the volume (cm 3 ) was calculated as follows: Weight of electrode composition layer: Actual measured weight of electrode - Actual measured weight of current collector Volume of electrode composition layer: measured area of ​​electrode composition layer × (measured thickness of electrode − measured thickness of current collector)

[0119] (DC30 per unit volume of electrode composition layer) The DC30 per unit volume of the electrode composition layer (positive electrode) is calculated by multiplying the 30th discharge capacity DC30 (mAh / g) calculated above by the density (g / cm) of the electrode composition layer calculated above. 3 ) and the active material ratio 0.9 (mass ratio of the active material in the electrode composition).

[0120] (Images of the electrode surface before and after pressing) In the above-mentioned positive electrode production process, the part of the positive electrode that was cut off before pressing with the roll press machine was used as the electrode before pressing, and the part of the positive electrode other than the part punched out with a diameter of φ11 after pressing was used as the electrode after pressing, and their surfaces were observed with a scanning electron microscope (SEM).

[0121] 2, it can be seen that the electrode surface after pressing in Example 1 is flattened with no particle irregularities, and almost all particles are crushed. On the other hand, in Comparative Example 1, particle irregularities can be seen even after pressing, and much of the positive electrode active material remains uncrushed.

[0122] [Table 1]

[0123] From the table, the lithium ion secondary battery of the example of the present disclosure has a discharge capacity per unit volume (mAh / cm 3 ), that is, the energy density per unit volume is superior to that of the comparative example. The capacity retention rate (%) also shows an excellent value.

[0124] <Embodiment> Examples of embodiments of the present disclosure are provided below.

[0125] [1] An electrode active material made of an organic sulfur material in which acrylic resin particles are modified with sulfur, an electrode active material in which, for each of any five particles of the organic sulfur material, the average value of the breaking strength Cs (MPa) calculated by the following formula, where d (μm) is the particle diameter and P (mN) is the test force at the moment when the particles break in a microcompression test, is less than 47.4, preferably 40.0 or less, more preferably 30.0 or less, even more preferably 25.0 or less, still more preferably 23.2 or less, even more preferably 20.0 or less, still more preferably 15.0 or less, still more preferably 10.0 or less, and still more preferably 5.0 or less; Cs=2.48×P / πd 2 (where d is the average diameter of the particles of the organosulfur material measured in two perpendicular directions, and π is the constant of the circumference of a circle (3.14).) [2] The electrode active material according to the above [1], wherein the median diameter of the organic sulfur material is less than 12.0 μm, preferably 0.1 μm to 11.0 μm, more preferably 0.1 μm to 11.0 μm, even more preferably 0.1 μm to 10.0 μm, even more preferably 0.1 μm to 9.0 μm, even more preferably 0.1 μm to 8.5 μm, even more preferably 0.1 μm to 8.3 μm, even more preferably 0.1 μm to 6.0 μm, and even more preferably 1.0 μm to 6.0 μm. [3] 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): A polymer 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), and Polymers obtained by polymerizing monomers containing methacrylonitrile The electrode active material according to [1] or [2] above, which contains at least one polymer selected from the group consisting of: 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 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. [4]R12 is an alkyl group having 1 to 6 carbon atoms, preferably 1 to 4, and Y is a hydrocarbylene group having 2 to 6 carbon atoms, preferably 2 or 3, in which the hydrocarbylene group has 1 to 4, preferably 1 or 2, substituents in the alkyl group as the substituent have 1 to 4, preferably 1, carbon atom, and the carbon skeleton constituting the hydrocarbylene group has 1 to 2 ether bonds; [5] The electrode active material according to any one of the above [1] to [4], wherein the particle size of the acrylic resin particles is 0.1 to 300.0 μm, preferably 0.1 to 270.0 μm, more preferably 0.1 to 200.0 μm, even more preferably 0.1 to 100.0 μm, even more preferably 0.1 to 50.0 μm, even more preferably 0.1 to 20.0 μm, even more preferably 0.1 to 15.0 μm, even more preferably 0.1 to 10.0 μm, even more preferably 0.1 to 6.0 μm, and even more preferably 1.0 to 6.0 μm. [6] The electrode active material according to any one of the above [1] to [5], wherein the acrylic resin particles have a porous structure. [7] The electrode active material according to any one of the above [1] to [6], wherein the amount of sulfur in the organic sulfur material is 50.00% by mass or more, preferably 53.00% by mass or more, more preferably 55.00% by mass or more, even more preferably 56.00% by mass or more, and still more preferably 60.00% by mass or more. [8] An electrode composition layer obtained by pressing an electrode composition containing the electrode active material according to any one of [1] to [7] above, wherein the density is 1.50 g / cm 3 or more, preferably 1.53 g / cm 3 More preferably, 1.56 g / cm 3 More preferably, 1.59 g / cm 3 More preferably, 1.60 g / cm 3 The electrode composition layer, [9] An electrode comprising the electrode composition layer according to [8] above.

[10] A lithium ion secondary battery comprising the electrode according to [9] above. [Explanation of symbols]

[0126] 1. Reactor 2 Raw materials 3 Reaction vessel 4 Silicone lids 5 Alumina protection tube 6 Gas inlet pipe 7 Gas exhaust pipe 8 Electric Furnace 9 Thermocouples 10 Temperature Controller 11 Sodium hydroxide solution 12 Trap tank

Claims

1. The electrode active material is an organic sulfur material obtained by modifying acrylic resin particles with sulfur, The median diameter of the organic sulfur material is less than 12.0 μm, An electrode active material in which an average value of breaking strength Cs (MPa) calculated by the following formula for each of any five particles of the organic sulfur material is less than 47.4, where d (μm) is the particle diameter and P (mN) is the test force at the moment when particle breakage occurs in a microcompression test. Cs=2.48×P / πd 2 (where d is the average value of diameters measured in two perpendicular directions for particles of the organosulfur material, and π is the constant of the circumference of a circle (3.14).)

2. 2. The electrode active material according to claim 1, wherein the median diameter of the organic sulfur material is less than 9.0 μm.

3. 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): A polymer 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), and Polymers obtained by polymerizing monomers containing methacrylonitrile 3. The electrode active material according to claim 1, which comprises at least one polymer selected from the group consisting of: 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, Y is a 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.

4. R 12 is an alkyl group having 1 to 6 carbon atoms; Y is a 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 or 2 ether bonds.

5. The electrode active material according to any one of claims 1 to 4, wherein the particle diameter of the acrylic resin particles is 0.1 to 300.0 µm.

6. The electrode active material according to any one of claims 1 to 5, wherein the acrylic resin particles have a porous structure.

7. The electrode active material according to any one of claims 1 to 6, wherein the amount of sulfur in the organic sulfur material is 50.00% by mass or more.

8. An electrode composition layer obtained by pressing an electrode composition comprising the electrode active material according to any one of claims 1 to 7, and having a density of 1.50 g / cm 3 This is the electrode composition layer.

9. An electrode comprising a layer of the electrode composition of claim 8.

10. A lithium ion secondary battery comprising the electrode according to claim 9.

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