JP7793938B2 - Electrode active material, electrode, and lithium ion secondary battery - Google Patents

Description

This disclosure relates to a novel electrode active material, an electrode comprising the electrode active material, and a lithium-ion secondary battery comprising the electrode.

Lithium-ion secondary batteries have a large charge/discharge capacity and are therefore primarily used as batteries for portable electronic devices. Their use as batteries for electric vehicles is also increasing, and improvements in their performance are expected.

Patent Document 1 describes a positive electrode active material for lithium-ion secondary batteries obtained by heating raw material powders containing sulfur powder and polyacrylonitrile powder in a non-oxidizing atmosphere.

On the other hand, it has been proposed to increase the battery capacity of lithium-ion secondary batteries by using materials capable of absorbing and releasing more lithium ions, such as silicon (Si) and tin (Sn), as the negative electrode active material.

International Publication No. 2010/044437

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

Furthermore, even if the capacity of an electrode active material is improved, unless the capacity per unit volume when used as an electrode, i.e., the volumetric energy density (mAh/cm ³ ), is improved, it will hinder the miniaturization of batteries.

The present disclosure provides an electrode (i.e., a positive electrode or negative electrode) comprising an electrode active material made of a specified organic sulfur material, an electrode composition layer having an improved volumetric energy density obtained by pressing an electrode composition containing the electrode active material, and a lithium-ion secondary battery comprising the electrode.

As a result of extensive research into solving the above-mentioned problems, the inventors discovered that electrodes with improved volumetric energy density can be obtained by using an organic sulfur material, which is an acrylic resin particle modified with sulfur and has a breaking strength below a predetermined value. Further research led to the completion of the present disclosure.

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/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).)

The present disclosure makes it possible to provide an electrode active material made of a specified 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 negative electrode, and a lithium-ion secondary battery comprising the electrode.

In this specification, "volumetric energy density" refers to the discharge capacity (mAh/ ^cm3 ) of an electrode (electrode composition layer) per unit volume. Furthermore, "cycle characteristics" refers to the ability of a secondary battery to maintain its charge/discharge capacity despite repeated charge/discharge. Therefore, a secondary battery that experiences a large decrease in charge/discharge capacity and a low capacity retention rate with repeated charge/discharge has poor cycle characteristics, whereas a secondary battery that experiences a small decrease in charge/discharge capacity and a high capacity retention rate has excellent cycle characteristics.

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. 1 shows scanning electron microscope (SEM) images of the surfaces of electrodes (positive electrodes) of Example 1 and Comparative Example 1 of the present disclosure.

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

One embodiment of the present disclosure is an electrode active material made of an organic sulfur material obtained by modifying acrylic resin particles with sulfur, wherein 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 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).)

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 this disclosure is believed to be as follows. That is, organosulfur materials having a breaking strength below a predetermined value, as defined in this disclosure, are more likely to be crushed and deformed by the pressing process used to manufacture the electrode than those 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 result in improved volumetric energy density.

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

This is because it is thought to easily fill the gaps between particles of organic sulfur materials.

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( ^R11 ) ^COOR12 (1)

(wherein 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)

(wherein R ²¹ and R ²² are the same or different and each represent a hydrogen atom or a methyl group; Y is a hydrocarbylene group; the hydrocarbylene group 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.)

This is because it is easy to obtain and is believed to be able to easily achieve the effects of this disclosure.

It is preferred that 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 having 1 to 4 substituents, the alkyl group as the substituent having 1 to 4 carbon atoms, and the carbon skeleton constituting the hydrocarbylene group having 1 or 2 ether bonds.

This is because it is easy to obtain and is believed to be able to easily achieve the effects of this disclosure.

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

This is because it is thought to easily fill the gaps between particles of organic sulfur materials.

It is preferable that the acrylic resin particles have a porous structure.

This is because it is thought to easily fill the gaps between particles of organic sulfur materials.

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

This is because it is believed that a higher sulfur content makes it easier to improve charge/discharge capacity.

Another embodiment of the present disclosure is an electrode composition layer obtained by pressing an electrode composition containing the electrode active material, the electrode composition layer having a density of 1.50 g/cm ³ or more.

This is because it can improve the volumetric energy density.

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

Another embodiment of the present disclosure is a lithium-ion secondary battery comprising the electrode.

<Organic sulfur material>
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 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).)

(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.

From the perspective 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.

To adjust the breaking strength Cs (MPa), for example, if you want to obtain an organosulfur material with a lower breaking strength, you can use acrylic resin particles with a lower degree of cross-linking. This is because organosulfur materials made from modified acrylic resin particles are more easily crushed and deformed than those made with particles with a higher degree of cross-linking. Alternatively, using porous acrylic resin particles can also reduce the breaking strength compared to non-porous acrylic resin particles.

(constituent elements)
The mass ratios (%) of the constituent elements of the organic sulfur material were determined by elemental analysis as described in the Examples section below.

Organosulfur 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 preferred range of sulfur content in the organic sulfur material is 50.00 mass% or more, more preferably 53.00 mass% or more, even more preferably 55.00 mass% or more, even more preferably 56.00 mass% or more, and even more preferably 60.00 mass% or more. However, when a conductive carbon material is added, due to the influence of the carbon that makes up the conductive carbon material, improved charge/discharge capacity and cycle characteristics may be expected even if the sulfur content is slightly lower. In such cases, the sulfur content may be approximately 5.00 mass% lower than the above-mentioned sulfur content. The total amount of carbon and sulfur in the organic sulfur material is preferably 90.00 mass% or more, more preferably 95.00 mass% or more, and even more preferably 96.00 mass% or more.

Furthermore, during baking (modification), hydrogen (H) in the acrylic resin reacts with sulfur to form hydrogen sulfide, which is then removed 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, baking tends to be sufficient. Therefore, in this case, charge/discharge capacity tends to improve.

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

The true density (g/cm ³ ) may vary depending on the type of acrylic resin particles used, but when the acrylic resin particles used in the examples of the present disclosure are used, if the baking (modification) has progressed sufficiently, the true density will fall within the range of 1.6 to 2.0 g/cm ³ .

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

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. While there is no particular lower limit for the median diameter (μm) from the perspective of the effects of the present disclosure, it is typically 0.1 μm or more, or approximately 1.0 μm or more. To adjust the median diameter to a smaller size, for example, acrylic resin particles with a smaller particle size may be used, or the resulting organic sulfur material may be thoroughly pulverized.

(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.

<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.

(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( ^R11 ) ^COOR12 (1)

(wherein 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)

(wherein R ²¹ and R ²² are the same or different and each represent a hydrogen atom or a methyl group; Y is a hydrocarbylene group; the hydrocarbylene group 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.)

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

In formula (2), both R ²¹ and R ²² are preferably methyl groups. The number of carbon atoms in the hydrocarbylene group of Y is preferably 2 to 6, and more preferably 2 or 3. The number of substituents in Y is preferably 1 to 4, and more preferably 1 or 2. The substituents in Y are preferably one or more substituents selected from the group consisting of hydroxyl groups and alkyl groups having 1 to 4 carbon atoms, and the alkyl groups having 1 to 4 carbon atoms are preferably methyl groups. When the carbon skeleton of Y has an ether bond via an oxygen atom, for example, the portion corresponding to -Y-O- is preferably represented by formula (3) below (however, in formula (3), the substituents in Y are not taken into consideration).

-(CH ₂ ) _l -(CH ₂ CH ₂ O) _m -(CH ₂ CH ₂ CH ₂ O) _n - (3)

(Here, l is a number from 0 to 6, m is a number from 0 to 3, and n is a number from 0 to 2. However, l, m, and n cannot all be 0 at the same time.)

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.

Examples of compounds 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, and glycerin di(meth)acrylate. Of these, ethylene glycol dimethacrylate is preferred.

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.

One or more types of acrylic resin can be used.

<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 more preferably 270.0 μm or less, even 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, even more preferably 6.0 μm or less. On the other hand, the lower limit of the particle diameter is not particularly limited, but is usually, for example, 0.1 μm or more, preferably 1.0 μm or more. The particle diameter is a value measured using a precision particle size distribution analyzer, Multisizer 3, manufactured by Beckman Coulter, Inc.

The acrylic resin may be in the form of spherical particles or porous particles. When the acrylic resin is porous, its oil absorption is preferably 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 using the method described in paragraph 0069 of JP 2017-88501 A.

<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.

<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).

<<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.

(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. Amounts of sulfur of 100 parts by mass or more tend 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. Amounts of sulfur of 1000 parts by mass or less tend to be cost-effective. One or more types of sulfur can be used.

(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.

<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 those having a condensed aromatic ring structure, such as carbon black, acetylene black, ketjen black, graphite, carbon nanotubes (CNT), carbon fibers (CF), graphene, and fullerene. One or more conductive carbon materials can be used.

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 combinations 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.

The amount of the conductive carbon material is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more, per 100 parts by mass of the acrylic resin. A blending amount of 5 parts by mass or more tends to make it easier to achieve the objective of further improving charge/discharge capacity and cycle characteristics. On the other hand, the blending amount is preferably 50 parts by mass or less, and 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 make it easier to achieve the objective of further improving charge/discharge capacity and cycle characteristics.

(Modification step)
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.

<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.

<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.

<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.

<Baking temperature and time>
The calcination temperature refers to the temperature after the temperature of the calcination raw materials has been raised, 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 may 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.

≪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.

(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.

(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 the production of electrodes. 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 usually about 0.1 μm or more, or 1.0 μm or more. The median diameter can be reduced by using acrylic resin particles with a small particle diameter or by sufficiently performing the above-mentioned pulverization. In the firing method using the twin-screw extruder described above, the organic sulfur material produced can also be pulverized simultaneously with the production of the organic sulfur material due to shear during kneading.

<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.

1. When an organic sulfur material is used as a positive electrode active material 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.

(positive electrode)
The 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 then 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.

The above-mentioned pressing using a 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 under this level of load.

[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. One or more of these conductive additives can be used.

[Binder]
Examples of binders include polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyimide (PI), polyamideimide (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.

[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.

[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.

[Current collector]
The current collector may be one generally used for 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, foamed nickel, 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 used as carbon fiber materials, can be used.

(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 the negative electrode or the positive electrode, or both. 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 assembled 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.

(electrolyte)
The electrolyte used in lithium ion secondary batteries can be an organic solvent containing an electrolyte alkali metal salt dissolved therein. 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. Examples of the electrolyte that can be used include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiI, and LiClO ₄ . The electrolyte concentration may be approximately 0.5 mol/L to 1.7 mol/L. The electrolyte is not limited to a liquid form. For example, when the lithium ion secondary battery is a lithium polymer secondary battery, the electrolyte is solid (e.g., polymer gel).

(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.

(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.

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

The density (g/cm ³ ) of the positive electrode composition layer is preferably 1.50 or more, more preferably 1.53 or more, even more preferably 1.56 or more, and still more preferably 1.59 or more.
It is more preferably 1.60 or more. On the other hand, the higher the density (g/cm ³ ), the better, and although there is no particular upper limit, it is usually considered to be, for example, about 2.00 or less.

2. When an organic sulfur material is used as a negative electrode active material 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.

(Negative electrode)
The negative electrode for a lithium ion secondary battery can be fabricated in the same manner as a general negative electrode for a lithium ion secondary battery, except that the 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 then 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.

The above-mentioned pressing using a 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 under this level of load.

The conductive additive, binder, and solvent can be the same as those used above when an organic sulfur material is used as the positive electrode active material, and the current collector can also be the same as those used above.

(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 capable of electrochemically absorbing and releasing lithium ions. Examples of lithium-containing transition metal oxides include Li-Co-based composite oxides _such as _LiCoO2 , Li _- Ni-Co _{- Mn} -based composite oxides such as _LiNiO2 , Li-Ni-based composite oxides such as LiNiO2, and Li-Mn- _based composite oxides such as _LiMn2O4 . Examples of solid solution _oxides include _{LiaMnxCoyNizO2 ( 1.150} ≦a≦1.430 _{, 0.450} ≦x≦0.600, _0.100 ≦y≦0.150, 0.200≦z≦0.280) _{, LiMnxCoyNizO2} (0.300≦x≦0.850, 0.100≦y≦0.300, 0.100≦z≦ _0.300 ), and _{LiMn1.5Ni0.5O4 .} These compounds may be used alone or in combination.

The electrolyte, separator, and shape of the lithium-ion secondary battery can be the same as those described above when an organic sulfur material is used as the positive electrode active material.

(Density of Negative Electrode Composition Layer)
The density (g/cm ³ ) of the negative electrode composition layer 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, similar to the density (g/cm ³ ) of the positive electrode composition layer. On the other hand, the higher the density (g/cm ³ ), the better, and although there is no particular upper limit, it is usually considered to be, for example, about 2.00 or less.

This disclosure will be described based on examples, but is not limited to these examples.

The various chemicals used in the examples and comparative examples are listed below. Where necessary, the various chemicals were purified according to standard methods.

<Materials used in the test>
Acrylic resin particles 1: spherical acrylic resin composed of methyl methacrylate and ethylene glycol dimethacrylate copolymer (Techpolymer MBX-20 manufactured by Sekisui Plastics Co., Ltd., particle size: 20 μm, degree of crosslinking: standard)
Acrylic resin particles 2: spherical acrylic resin composed of methyl methacrylate and ethylene glycol dimethacrylate copolymer (Techpolymer MBX-5 manufactured by Sekisui Plastics Co., Ltd., particle size: 5 μm, degree of crosslinking: standard)
Acrylic resin particles 3: spherical acrylic resin composed 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.

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).

(Reaction Apparatus)
The raw materials to be fired were fired using a reactor 1 shown in Figure 1. The reactor 1 includes a cylindrical, bottomed quartz glass reactor 3 for accommodating and firing the 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 ("Alumina SSA-S" manufactured by Nikkato Corporation, outer diameter 4 mm, inner diameter 2 mm, length 250 mm) that penetrates the lid 4, two gas inlet pipes 6 and a gas outlet pipe 7 (both manufactured by Nikkato Corporation, "Alumina SSA-S" manufactured by Nikkato Corporation, 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.

The alumina protective tube 5 is formed long enough to extend from the lid 4 downward 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 the 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.

The gas inlet pipe 6 and 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. Exhaust gas attempting to escape from the reaction vessel 3 through the gas outlet pipe 7 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.

(Firing process)
First, with raw material 2 contained 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 carried out 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.

(Removal of unreacted sulfur)
To remove unreacted sulfur (free elemental sulfur) remaining in the product after the calcination step, the following process was carried out. 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 under vacuum to obtain an organic sulfur material from which unreacted sulfur had been removed (or which contained only a trace amount of unreacted sulfur). The heating rate was 10°C/min.

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

<Fabrication of Lithium-ion Secondary Battery>
A lithium ion secondary battery was fabricated as follows.

(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 so that the 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 prepare a uniform electrode composition slurry. The prepared electrode composition slurry was applied to a 20 μm thick aluminum foil current collector using an applicator with a slit width of 400 μm to form an electrode composition layer, which 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 to form an electrode composition layer (positive electrode composition layer) on the current collector, and then punched out to φ11 to obtain an electrode (positive electrode). Thereafter, the weight of the electrode was measured, and the amount of active material in the electrode was calculated from the above ratio.

(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.

(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.

(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, a 25 μm thick polypropylene microporous membrane manufactured by Celgard) 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 battery. This electrode 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.

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.

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

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.

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

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

(Breaking strength Cs (MPa) of organic sulfur material)
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 particles of the organic sulfur material broke using an indenter. That is, after a trace amount of the organic sulfur material was sprayed onto a sample stage, five random particles were compressed one by one using an indenter, and the test force P (mN) at which 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.

The breaking strength Cs (MPa) was calculated from the test force P (mN) and the 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

The average breaking strength Cs (MPa) of the five particles was calculated and used as the breaking strength Cs (MPa) of that organic sulfur material.

(Measurement of discharge capacity and capacity retention rate)
The coin-type lithium-ion secondary batteries prepared in each Example and Comparative Example were charged and discharged at a current value corresponding 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 corresponding 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 charge/discharge cycles were repeated, and 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.

The second discharge capacity (mAh/g) was defined 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 is. The capacity retention rate (%) was calculated from the 10th discharge capacity DC10 (mAh/g) and the 30th discharge capacity DC30 (mAh/g) using the following formula:
Capacity maintenance rate (%) = (DC30/DC10) x 100

(Density of electrode composition layer)
For the electrode obtained above, the density of the electrode composition layer (positive electrode) was calculated from the weight (g) and volume (cm ³ ) of the electrode composition layer. The weight (g) and volume (cm ³ ) of the electrode composition layer were determined as follows.
Weight of electrode composition layer: actual measured value of electrode weight−actual measured value of current collector Volume of electrode composition layer: actual measured value of area of electrode composition layer×(actual measured value of electrode thickness−actual measured value of current collector thickness)

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

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

In Figure 2, in the case of Example 1, it can be seen that the electrode surface after pressing was flattened, with no particle irregularities, and almost all particles were crushed. On the other hand, in the case of Comparative Example 1, particle irregularities could be seen even after pressing, and much of the positive electrode active material was observed to remain uncrushed.

As can be seen from the table, the lithium ion secondary batteries of the examples of the present disclosure are superior to the comparative examples in terms of the 30th discharge capacity per unit volume (mAh/ ^cm3 ), i.e., the energy density per unit volume. They also show excellent capacity retention rates (%).

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

[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 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, preferably 40.0 or less, more preferably 30.0 or less, even more preferably 25.0 or less, even more preferably 23.2 or less, even more preferably 20.0 or less, even more preferably 15.0 or less, even more preferably 10.0 or less, and even more preferably 5.0 or less, 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] The electrode active material according to [1] above, 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
The electrode active material according to the above [1] or [2], which contains at least one polymer selected from the group consisting of polymers obtained by polymerizing a monomer containing methacrylonitrile;

_CH2 =C( ^R11 ) ^COOR12 (1)

(wherein 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)

(wherein R ²¹ and R ²² are the same or different and each represent a hydrogen atom or a methyl group; Y is a hydrocarbylene group; the hydrocarbylene group 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] The electrode active material according to any one of the above [1] to [3], wherein R ¹² 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, and the hydrocarbylene group has 1 to 4, preferably 1 or 2, substituents, the alkyl group as the substituent has 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 diameter 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, even more preferably 1.0 to 6.0 μm;
[6] The electrode active material according to any one of [1] to [5] above, wherein the acrylic resin particles have a porous structure.
[7] The electrode active material according to any one of [1] to [6] above, 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 electrode composition layer has a density of 1.50 g/cm ³ or more, preferably 1.53 g/cm ³ or more, more preferably 1.56 g/cm ³ or more, even more preferably 1.59 g/cm ³ or more, and still more preferably 1.60 g/cm ³ or more.
[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.

1 Reaction apparatus 2 Raw material 3 Reaction vessel 4 Silicone lid 5 Alumina protective tube 6 Gas inlet tube 7 Gas outlet tube 8 Electric furnace 9 Thermocouple 10 Temperature controller 11 Sodium hydroxide aqueous solution 12 Trap tank

Claims (10)

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).) The electrode active material according to claim 1 , wherein the organosulfur material has a median diameter of less than 9.0 μm. 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
3. The electrode active material according to claim 1, which comprises at least one polymer selected from the group consisting of polymers obtained by polymerizing a monomer containing methacrylonitrile.

_CH2 =C( ^R11 ) ^COOR12 (1)

(wherein 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)

(wherein R ²¹ and R ²² are the same or different and each represent a hydrogen atom or a methyl group; Y is a hydrocarbylene group; the hydrocarbylene group 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. The electrode active material according to claim 1, wherein 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 substituents have 1 to 4 carbon atoms, and the carbon skeleton constituting the hydrocarbylene group has 1 or 2 ether bonds. 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. The electrode active material according to any one of claims 1 to 5, wherein the acrylic resin particles have a porous structure. 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 claim 1, wherein the electrode composition layer has a density of 1.50 g/cm ³ or more. An electrode comprising the electrode composition layer of claim 8. A lithium ion secondary battery comprising the electrode according to claim 9.