阅读说明：本技术 锂离子电极用粘合剂、锂离子电池用电极和锂离子电池用电极的制造方法 (Binder for lithium ion electrode, electrode for lithium ion battery, and method for producing electrode for lithium ion battery ) 是由 太田智也 那须浩太郎 川北健一 末永卓也 森悠辅 大泽康彦 草地雄树 佐藤一 赤间弘 于 2018-04-20 设计创作，主要内容包括：本发明提供一种粘合剂,该粘合剂能够制作锂离子电池用电极,该锂离子电池用电极具有能够保持电极的形状、并且电极的能量密度不会降低的构成。一种锂离子电极用粘合剂,其为在锂离子电极中使活性物质彼此粘接的粘合剂,其特征在于,上述粘合剂的玻璃化转变温度为60℃以下,溶解度参数为8～13(cal/cm<Sup>3</Sup>)<Sup>1/2</Sup>,在频率10<Sup>-1</Sup>～10<Sup>1</Sup>Hz的范围内在20℃测定的储能剪切模量和损耗剪切模量为2.0×10<Sup>3</Sup>～5.0×10<Sup>7</Sup>Pa,上述粘合剂是以来自(甲基)丙烯酸烷基酯单体的结构单元作为必要部分的丙烯酸系聚合物,构成上述粘合剂的单体中的上述(甲基)丙烯酸烷基酯单体的比例以单体的总重量为基准计为50重量％以上,含氟单体的比例以单体的总重量为基准计小于3重量％。(The invention provides a binder which can be used for manufacturing an electrode for a lithium ion battery, wherein the electrode for the lithium ion battery has a structure which can keep the shape of the electrode and can not reduce the energy density of the electrode. A binder for a lithium ion electrode, which is a binder for binding active materials to each other in a lithium ion electrode, characterized in that the glass transition temperature of the binder is 60 ℃ or lower,A solubility parameter of 8 to 13 (cal/cm) 3 ) 1/2 At a frequency of 10 ‑1 ～10 1 The storage shear modulus and the loss shear modulus measured at 20 ℃ in the range of Hz were 2.0X 10 3 ～5.0×10 7 Pa, the binder is an acrylic polymer having a structural unit derived from an alkyl (meth) acrylate monomer as an essential part, the proportion of the alkyl (meth) acrylate monomer in the monomers constituting the binder is 50% by weight or more based on the total weight of the monomers, and the proportion of the fluorine-containing monomer is less than 3% by weight based on the total weight of the monomers.)

1. A binder for a lithium ion electrode, which is a binder for binding active materials to each other in a lithium ion electrode,

The glass transition temperature of the adhesive is below 60 ℃, and the solubility parameter is 8-13 (cal/cm)³)^1/2At a frequency of 10^-1～10¹The storage shear modulus and the loss shear modulus measured at 20 ℃ in the range of Hz were 2.0X 10³～5.0×10⁷Pa，

The adhesive is an acrylic polymer comprising structural units derived from an alkyl (meth) acrylate monomer as an essential part, wherein the alkyl (meth) acrylate monomer is contained in the adhesive in a proportion of 50 wt% or more based on the total weight of the monomers, and the fluorine-containing monomer is contained in a proportion of less than 3 wt% based on the total weight of the monomers.

2. The binder for a lithium ion electrode according to claim 1, wherein the binder comprises two or more alkyl (meth) acrylate monomers as constituent monomers, and the total content thereof is 50% by weight or more based on the total weight of the constituent monomers.

3. The binder for a lithium ion electrode according to claim 1 or 2, wherein the binder comprises a monovinyl monomer copolymerizable with the alkyl (meth) acrylate monomer as a constituent monomer.

4. The binder for a lithium ion electrode according to any one of claims 1 to 3, wherein the binder contains a (meth) acrylic acid monomer as a constituent monomer.

5. An electrode for a lithium ion battery, comprising a non-bonded body of the binder according to any one of claims 1 to 4 and a coated electrode active material, wherein the coated electrode active material has a coating layer comprising a coating resin on at least a part of a surface of the electrode active material that stores and releases lithium ions.

6. The electrode for a lithium ion battery according to claim 5, wherein a weight ratio of the coated electrode active material to the binder is 90/10 to 99.99/0.01.

7. The electrode for a lithium ion battery according to claim 5 or 6, wherein a thickness of an electrode active material layer constituting the electrode is 150 μm or more.

8. A method for manufacturing an electrode for a lithium ion battery, characterized in that a mixture of a coated electrode active material and a binder for a lithium ion electrode is pressurized to form an electrode active material layer composed of a non-bonded body including the mixture of the coated electrode active material and the binder,

The coated electrode active material has a coating layer containing a coating resin on at least a part of the surface of an electrode active material that stores and releases lithium ions,

The binder for a lithium ion electrode is a binder for binding active materials in a lithium ion electrode, and has a glass transition temperature of 60 ℃ or less and a solubility parameter of 8 to 13 (cal/cm)³)^1/2At a frequency of 10^-1～10¹The storage shear modulus and the loss shear modulus measured at 20 ℃ in the range of Hz were 2.0X 10³～5.0×10⁷Pa, an acrylic polymer having a structural unit derived from an alkyl (meth) acrylate monomer as an essential part, wherein the alkyl (meth) acrylate monomer is contained in the monomers constituting the adhesive in a proportion of 50 wt% or more based on the total weight of the monomers, and the fluorine-containing monomer is contained in a proportion of less than 3 wt% based on the total weight of the monomers.

9. The method for manufacturing an electrode for a lithium ion battery according to claim 8, wherein the binder contains two or more alkyl (meth) acrylate monomers as constituent monomers, and the total content thereof is 50% by weight or more based on the total weight of the constituent monomers.

10. The method for manufacturing an electrode for a lithium ion battery according to claim 8 or 9, wherein the binder contains a monovinyl monomer copolymerizable with the alkyl (meth) acrylate monomer as a constituent monomer.

11. The method for manufacturing an electrode for a lithium ion battery according to any one of claims 8 to 10, wherein the binder contains a (meth) acrylic acid monomer as a constituent monomer.

12. The method for producing an electrode for a lithium ion battery according to any one of claims 8 to 11, wherein a weight ratio of the coated electrode active material to the binder in the mixture is 90/10 to 99.99/0.01.

13. The method for producing an electrode for a lithium ion battery according to any one of claims 8 to 12, wherein,

The mixture is an electrolyte-containing mixture further containing an electrolyte,

An electrode active material layer is formed by pressurizing the mixture containing the electrolyte solution.

14. The method for manufacturing an electrode for a lithium ion battery according to any one of claims 8 to 13, wherein the thickness of the electrode active material layer is 150 μm or more.

Technical Field

The present invention relates to a binder for a lithium ion electrode, an electrode for a lithium ion battery, and a method for producing an electrode for a lithium ion battery.

Background

In recent years, reduction of carbon dioxide emissions is strongly desired for environmental protection. In the automobile industry, introduction of Electric Vehicles (EV) and Hybrid Electric Vehicles (HEV) has been expected to reduce carbon dioxide emissions, and secondary batteries for driving motors, which are key to practical use of these vehicles, have been extensively developed. As a secondary battery, a lithium ion battery capable of achieving high energy density and high output density has attracted attention.

patent document 1 describes a battery electrode in which an active material layer containing a binder is used as an electrode capable of holding an active material having a small particle diameter on a surface layer of the active material layer of the electrode and reinforcing the electrode structure.

Disclosure of Invention

Problems to be solved by the invention

In the battery electrode described in patent document 1, in order to maintain the shape of the electrode, it is necessary to add a binder separately from the active material. However, the electrode shape retention property by the binder material is not sufficient. Further, if a binder such as polyvinylidene fluoride, which is a type that retains its shape by forming a cured product, is not used in combination, it is difficult to form an active material layer and retain the shape of an electrode.

Further, if the binder and the adhesive are used together, there is a problem that the energy density of the electrode is reduced according to the volume of the binder and the adhesive.

The present invention has been made in view of the above problems, and an object thereof is to provide a binder that can produce an electrode for a lithium ion battery having a structure that can hold the shape of the electrode and that does not decrease the energy density of the electrode, an electrode including the binder, and a method for producing the electrode for a lithium ion battery.

Means for solving the problems

The present inventors have conducted intensive studies to solve the above problems, and as a result, have completed the present invention.

That is, the present invention relates to a binder for a lithium ion electrode, which is a binder for binding active materials to each other in a lithium ion electrode, wherein the binder has a glass transition temperature of 60 ℃ or less and a solubility parameter of 8 to 13 (cal/cm)³)^1/2At a frequency of 10^-1～10¹The storage shear modulus and the loss shear modulus measured at 20 ℃ in the range of Hz were 2.0X 10³～5.0×10⁷Pa, the binder being an acrylic polymer comprising structural units derived from an alkyl (meth) acrylate monomer as an essential part, the proportion of the alkyl (meth) acrylate monomer in the monomers constituting the binder being 50% by weight or more based on the total weight of the monomers, and the proportion of the fluorine-containing monomer being less than 3% by weight based on the total weight of the monomers; an electrode for a lithium ion battery, comprising a non-bonded body of the binder and a coated electrode active material, wherein the coated electrode active material has a coating layer comprising a coating resin on at least a part of a surface of the electrode active material that stores and releases lithium ions; and a method for producing an electrode for a lithium ion battery, characterized in that a mixture of a coated electrode active material and a binder for a lithium ion electrode is pressurized to form an electrode active material layer comprising a non-bonded body comprising the mixture of the coated electrode active material and the binder, the coated electrode active material has a coating layer comprising a coating resin on at least a part of the surface of an electrode active material that stores and releases lithium ions, the binder for a lithium ion electrode is a binder that bonds active materials to each other in a lithium ion electrode, the binder has a glass transition temperature of 60 ℃ or less, and has a solubility parameter of 8 to 13 (cal/cm)³)^1/2At a frequency of 10^-1～10¹The storage shear modulus and the loss shear modulus measured at 20 ℃ in the range of Hz were 2.0X 10³～5.0×10⁷Pa, the adhesive is an acrylic polymer having a structural unit derived from an alkyl (meth) acrylate monomer as an essential part, and the alkyl (meth) acrylate in the monomers constituting the adhesive isThe proportion of the polyester monomer is 50 wt% or more based on the total weight of the monomers, and the proportion of the fluorine-containing monomer is less than 3 wt% based on the total weight of the monomers.

ADVANTAGEOUS EFFECTS OF INVENTION

The electrode for a lithium ion battery using the binder for a lithium ion electrode of the present invention can maintain the shape of the electrode without containing a binder for bonding electrode active materials to each other by curing to maintain the shape of the electrode. Further, the energy density of the electrode is not reduced by not containing the binder.

Further, since the shape of the electrode is stable, the shape of the electrode can be prevented from collapsing during charging and discharging, and the electrode having excellent cycle characteristics can be obtained.

Detailed Description

The present invention will be described in detail below.

The binder for a lithium ion electrode of the present invention is a binder for binding active materials in a lithium ion electrode, wherein the binder has a glass transition temperature of 60 ℃ or less and a solubility parameter of 8 to 13 (cal/cm)³)^1/2At a frequency of 10^-1～10¹The storage shear modulus and the loss shear modulus measured at 20 ℃ in the range of Hz were 2.0X 10³～5.0×10⁷Pa, the binder is an acrylic polymer having a structural unit derived from an alkyl (meth) acrylate monomer as an essential part, the proportion of the alkyl (meth) acrylate monomer in the monomers constituting the binder is 50% by weight or more based on the total weight of the monomers, and the proportion of the fluorine-containing monomer is less than 3% by weight based on the total weight of the monomers.

The binder of the present invention is a binder for a lithium ion electrode. The lithium ion electrode is an electrode used in a lithium ion battery, and is the same as the "electrode for a lithium ion battery" in the present specification.

The glass transition temperature (hereinafter sometimes referred to as Tg) of the adhesive of the present invention is 60 ℃ or lower. If Tg exceeds 60 ℃, the binder does not have appropriate flexibility, and thus shape retention of the electrode becomes difficult. The Tg of the binder is preferably 40 ℃ or less, more preferably 20 ℃ or less, from the viewpoint of stability of the electrode shape.

In the present specification, Tg is measured by a method (DSC method) defined in ASTM D3418-82 using DSC20 and SSC/580 manufactured by Seiko electronics Co.

In addition, the solubility parameter (hereinafter sometimes also referred to as SP value, in units of (cal/cm) of the adhesive of the present invention³)^1/2]Is 8 to 13. If the SP value is less than 8, the binder does not absorb the electrolyte solution, and it becomes difficult to pass lithium ions, so that the ionic resistance in the electrode active material layer increases. When the SP value exceeds 13, the binder dissolves in the electrolyte, and thus the electrode shape is difficult to be maintained.

The SP value of the binder is preferably 8.5 to 12.5, more preferably 9 to 12, from the viewpoints of the lithium ion conductivity by the absorption of the electrolyte and the stability of the electrode shape in the electrolyte.

The SP value in the present invention is calculated by a method described in the following documents proposed by Fedors et al.

"POLYMER ENGINEERING AND SCIENCE, February,1974, Vol.14, No.2, Robert F.Fedors (pp. 147-154)"

In addition, the adhesives of the present invention are at frequency 10^-1～10¹The storage shear modulus and the loss shear modulus measured at 20 ℃ in the range of Hz were 2.0X 10³～5.0×10⁷Pa。

If the storage shear modulus exceeds 5.0X 10⁷Pa, or loss shear modulus exceeding 2.0X 10⁷Pa, the binder does not have appropriate flexibility, and thus shape retention of the electrode becomes difficult. In addition, the shear modulus at storage is less than 2.0X 10³Pa, or loss shear modulus less than 5.0X 10³The same applies to Pa.

From the aspect of stability of electrode shape, the binder of the present invention is used at frequency 10^-1～10¹The storage shear modulus and the loss shear modulus measured at 20 ℃ in the range of Hz are preferably 5.0X 10³～2.0×10⁷Pa、More preferably 1.0X 10⁴～1.0×10⁷Pa。

It should be noted that the storage shear modulus and the loss shear modulus in the present invention can be measured as follows: 0.8g of a binder was used,The die (2) was molded at a pressure of 30MPa by using an ADVANCED RHEOMETRIC EXPANSION SYSTEM manufactured by TA LtdAt a frequency of 0.1 to 10Hz (10)^-1～10¹Hz), temperature 20 ℃, strain 0.1% (auto strain control: the minimum stress allowed to be 1.0g/cm, the maximum stress allowed to be 500g/cm, the maximum additional strain 200%, and the strain adjustment 200%).

The storage shear modulus and loss shear modulus of the adhesives of the invention are at frequency 10^-1～10¹In the range of Hz, 2.0X 10³～5.0×10⁷Pa means at a frequency of 10^-1～10¹The storage shear modulus and the loss shear modulus are included in the above range in all regions of the range of Hz.

The Tg of the adhesive of the present invention can be lowered by lengthening (extending) the alkyl chain of the alkyl (meth) acrylate monomer, and can be increased by shortening the alkyl chain of the alkyl (meth) acrylate monomer.

The SP value of the adhesive of the present invention can be increased by copolymerizing an alkyl (meth) acrylate monomer with a monovinyl monomer containing a nitrile group, a hydroxyl group, or the like, and can be decreased by copolymerizing with a monovinyl monomer containing a fluorine group, a siloxane, or the like.

The storage shear modulus and the loss shear modulus of the adhesive of the present invention can be adjusted by adjusting the Tg value, adjusting the molecular weight of the acrylic polymer, or adjusting the amount of the crosslinking agent to be added.

The adhesive of the present invention is an acrylic polymer containing a structural unit derived from an alkyl (meth) acrylate monomer as an essential part, and the weight ratio of the alkyl (meth) acrylate monomer in the monomers constituting the adhesive is 50% by weight or more based on the total weight of the monomers.

The weight ratio (% by weight) of the alkyl (meth) acrylate monomer can be measured by the following method: the polymer was dissolved in a supercritical fluid, and the obtained oligomer components were analyzed by gas chromatography-mass spectrometry (GC-MS).

If the weight ratio of the alkyl (meth) acrylate monomer in the monomers constituting the binder is less than 50% by weight based on the total weight of the monomers, the binder does not have an appropriate binding force and the stability of the electrode shape is lowered.

Examples of the alkyl (meth) acrylate monomer include 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl methacrylate, methyl acrylate, and 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate having a hydroxyl group at the end of the alkyl chain.

In addition, a multifunctional acrylate is also included in the above-mentioned alkyl (meth) acrylate monomer. Examples of the multifunctional acrylate include 1, 6-hexanediol methacrylate and ethylene glycol dimethacrylate. The weight ratio of the multifunctional acrylate is preferably 0.1 to 3% by weight based on the total weight of the monomers, from the viewpoint of stability of the electrode shape.

The adhesive of the present invention preferably contains two or more alkyl (meth) acrylate monomers as constituent monomers, the total content of which is 50% by weight or more based on the total weight of the constituent monomers. As described above, preferable combinations of the alkyl (meth) acrylate monomers include a combination of n-butyl acrylate and 2-ethylhexyl acrylate, a combination of methyl acrylate and n-butyl acrylate, or a combination of methyl methacrylate and isobutyl methacrylate.

From the aspect of shape retention, the weight ratio of the alkyl (meth) acrylate monomer in the monomers constituting the binder is preferably 65% by weight or more based on the total weight of the monomers.

In the adhesive of the present invention, as a monomer other than the alkyl (meth) acrylate monomer, a (meth) acrylic acid monomer is preferably contained as a constituent monomer. When the (meth) acrylic acid monomer is contained as a constituent monomer, by-products such as lithium hydroxide generated in the battery can be neutralized, and corrosion of the electrode can be prevented.

The weight proportion of the (meth) acrylic monomer is preferably 0.1 to 15% by weight based on the total weight of the constituent monomers.

The adhesive of the present invention may also contain a monovinyl monomer copolymerizable with the alkyl (meth) acrylate monomer as a constituent monomer.

As the monovinyl monomer, a monovinyl monomer (e.g., dimethylsiloxane) containing a fluoro group, siloxane, or the like can be used.

The weight proportion of fluoromonomer of the adhesive of the invention is less than 3% by weight, based on the total weight of the monomers. When the binder contains 3 wt% or more of the fluorine-containing monomer, the concealing property with respect to the electrode active material is reduced, and the adhesive force and flexibility are insufficient, so that it is difficult to maintain the electrode shape.

From the viewpoint of stability of the electrode shape, the weight ratio of the fluorine-containing monomer is preferably less than 2% by weight, more preferably 0% by weight (in an exclusive state), based on the total weight of the monomers.

The weight ratio of the fluorine-containing monomer in the adhesive of the present invention can be measured by the following method: the polymer was dissolved in a supercritical fluid, and the obtained oligomer components were analyzed by gas chromatography-mass spectrometry (GC-MS).

The lower limit of the weight average molecular weight of the adhesive of the present invention is preferably 10,000, more preferably 50,000, and still more preferably 100,000, and the upper limit thereof is preferably 1,000,000, more preferably 800,000, still more preferably 500,000, and particularly preferably 400,000.

The weight average molecular weight of the binder of the present invention can be determined by gel permeation chromatography (hereinafter abbreviated as GPC) measurement under the following conditions.

The device comprises the following steps: "HLC-8120 GPC" [ manufactured by Tosoh corporation ]

Column: "TSKgel GMHXL" (2 columns), "a column comprising 1 each TSKgel Multipore HXL-M linked" [ all manufactured by Tosoh Corp. ]

Sample solution: 0.25% by weight tetrahydrofuran solution

Solution injection amount: 10 μ L

Flow rate: 0.6 mL/min

Measuring temperature: 40 deg.C

The detection device comprises: refractive index detector

Reference substance: standard polystyrene (manufactured by Tosoh corporation)

The adhesive of the present invention can be produced by a known polymerization method (solution polymerization) using a known polymerization initiator { an azo initiator [2,2 ' -azobis (2-methylpropionitrile), 2 ' -azobis (2-methylbutyronitrile, 2 ' -azobis (2, 4-dimethylvaleronitrile, etc.) ], a peroxide initiator (benzoyl peroxide, di-t-butyl peroxide, lauryl peroxide, etc.) }.

The amount of the polymerization initiator to be used is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight, and still more preferably 0.1 to 1.5% by weight based on the total weight of the monomers, from the viewpoint of adjusting the molecular weight to a preferable range.

The polymerization temperature and the polymerization time are adjusted depending on the kind of the polymerization initiator, and the polymerization is carried out at a polymerization temperature of preferably-5 to 150 ℃ (more preferably 30 to 120 ℃) and a reaction time of preferably 0.1 to 50 hours (more preferably 2 to 24 hours).

Examples of the solvent used for the polymerization include esters (having 2 to 8 carbon atoms, such as ethyl acetate and butyl acetate), alcohols (having 1 to 8 carbon atoms, such as methanol, ethanol and octanol), hydrocarbons (having 4 to 8 carbon atoms, such as n-butane, cyclohexane and toluene), and ketones (having 3 to 9 carbon atoms, such as methyl ethyl ketone), and the amount thereof is preferably 5 to 900% by weight, more preferably 10 to 400% by weight, particularly preferably 30 to 300% by weight, based on the total weight of the monomers, and the monomer concentration is preferably 10 to 95% by weight, more preferably 20 to 90% by weight, particularly preferably 30 to 80% by weight, from the viewpoint of adjusting the molecular weight to a preferable range.

In the polymerization, a known chain transfer agent, for example, a mercapto compound (e.g., dodecyl mercaptan, n-butyl mercaptan, etc.) and/or a halogenated hydrocarbon (e.g., carbon tetrachloride, carbon tetrabromide, benzyl chloride, etc.) can be used.

The electrode for a lithium ion battery of the present invention is characterized by comprising a non-bonded body of the binder of the present invention and a coated electrode active material, wherein the coated electrode active material has a coating layer comprising a coating resin on at least a part of the surface of the electrode active material that stores and releases lithium ions.

Hereinafter, the constituent elements of the lithium ion battery electrode of the present invention will be described.

The coated electrode active material is an electrode active material having a coating layer on a part of the surface of the electrode active material. The coating layer contains a coating resin.

When the surface of the electrode active material is coated with the coating layer, it is easy to keep the distance between the electrode active materials constant, and it is preferable to easily maintain the conductive path.

The electrode active material may be a positive electrode active material or a negative electrode active material. If the electrode active material is a positive electrode active material, the lithium ion battery electrode becomes a positive electrode, and if the electrode active material is a negative electrode active material, the lithium ion battery electrode becomes a negative electrode.

Examples of the positive electrode active material as the electrode active material include a composite oxide of lithium and a transition metal { a composite oxide of 1 type of transition metal (LiCoO)₂、LiNiO₂、LiAlMnO₄、LiMnO₂And LiMn₂O₄Etc.), a composite oxide (e.g., LiFeMnO) in which the transition metal element is 2 kinds₄、LiNi_1-xCo_xO₂、LiMn_1-yCo_yO₂、LiNi_1/3Co_1/3Al_1/3O₂And LiNi_0.8Co_0.15Al_0.05O₂) And a composite oxide of 3 or more transition metal elements [ e.g.LiM_aM’_bM”_cO₂(M, M 'and M' are each a different transition metal element, satisfying a + b + c of 1. for example, LiNi_1/3Mn_1/3Co_1/3O₂) Etc. of]Etc.), lithium-containing transition metal phosphates (e.g., LiFePO₄、LiCoPO₄、LiMnPO₄And LiNiPO₄) Transition metal oxide (e.g., MnO)₂And V₂O₅) Transition metal sulfides (e.g., MoS)₂And TiS₂) And conductive polymers (e.g., polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, and polyvinylcarbazole), and two or more of them may be used in combination.

The lithium-containing transition metal phosphate may be obtained by replacing a part of the transition metal sites with another transition metal.

Examples of the negative electrode active material as the electrode active material include carbon-based materials [ e.g., graphite, non-graphitizable carbon, amorphous carbon, resin-fired products (e.g., products obtained by firing and carbonizing a phenol resin, a furan resin, or the like), cokes (e.g., pitch coke, needle coke, petroleum coke, or the like), silicon carbide, carbon fibers, or the like ], conductive polymers (e.g., polyacetylene, polypyrrole, or the like), silicon-based compounds (silicon, silicon oxide (SiOx), Si-C composites, Si-Al alloys, Si-Li alloys, Si-Ni alloys, Si-Fe alloys, Si-Ti alloys, Si-Mn alloys, Si-Cu alloys, and Si-Sn alloys), metals (tin, aluminum, zirconium, titanium, or the like), metal oxides (titanium oxides, lithium-titanium oxides, silicon oxides, and the like), and metal alloys (e.g., Li-Sn alloys), Li-Al alloy, Li-Al-Mn alloy, etc.), and mixtures thereof with carbon-based materials.

The Si — C composite includes a silicon particle or a silicon oxide particle whose surface is coated with carbon and/or silicon carbide.

Among the negative electrode active materials, those that do not contain lithium or lithium ions inside may be subjected to a preliminary doping treatment in which a part or all of the active material contains lithium or lithium ions.

The coating layer contains a coating resin and may further contain a conductive aid described later as necessary.

The coated electrode active material is a material in which a part or all of the surface of the electrode active material is coated with a coating layer, but even when the coated electrode active materials are in contact with each other and the coating layers are in contact with each other in the electrode active material layer, the coating layers are not integrated with each other and the interface thereof is not lost. That is, the coated electrode active materials are not irreversibly bonded to each other by the coating resin at the contact surface, and can be separated without breaking the coating layer that coats the active materials.

Examples of the coating resin included in the coating layer include thermoplastic resins, thermosetting resins, and the like, and examples of preferable coating resins include acrylic resins, urethane resins, silicone resins, and butadiene resins [ styrene-butadiene copolymer resins, butadiene polymers { butadiene rubber, liquid polybutadiene, and the like } ]. These resins are preferable because they can follow the volume change of the active material by forming an elastomer.

As the coating resin, an acrylic resin is particularly preferable.

Among these, the coating resin having a liquid absorption rate of 10% or more when immersed in the electrolyte solution and a tensile elongation at break of 10% or more in a saturated liquid-absorbed state is more preferable.

The liquid absorption rate when the coating resin was immersed in the electrolyte was determined as follows: the weight of the coating resin before and after immersion in the electrolyte solution was measured, and the liquid absorption rate was determined by the following equation.

Liquid absorption rate (%) [ (weight of coating resin after electrolytic solution impregnation-weight of coating resin before electrolytic solution impregnation)/weight of coating resin before electrolytic solution impregnation ] × 100

As the electrolyte solution for determining the liquid absorption rate, it is preferable to use a solution prepared by mixing Ethylene Carbonate (EC), diethyl carbonate (DEC) in the following formula EC: DEC ═ 3: 7 in a volume ratio of 1mol/L in a mixed solvent₆An electrolyte solution as an electrolyte.

The immersion in the electrolyte was performed at 50 ℃ for 3 days when the liquid absorption rate was calculated. The resin for coating was saturated and absorbed by dipping at 50 ℃ for 3 days. The saturated liquid-absorbed state is a state in which the weight of the coating resin does not increase even if the coating resin is further immersed in the electrolytic solution.

The electrolyte used in the production of a lithium ion battery using the electrode for a lithium ion battery of the present invention is not limited to the above electrolyte, and other electrolytes may be used.

When the liquid absorption rate is 10% or more, lithium ions can easily permeate through the coating resin, and therefore the ionic resistance in the electrode active material layer can be kept low. If the liquid absorption rate is less than 10%, the conductivity of lithium ions is lowered, and the performance as a lithium ion battery may not be sufficiently exhibited.

The liquid absorption rate is preferably 20% or more, more preferably 30% or more.

The upper limit of the liquid absorption rate is preferably 400%, and more preferably 300%.

The tensile elongation at break in the saturated liquid absorption state can be determined as follows: the coating resin was punched into a dumbbell shape, and the obtained sample was immersed in an electrolyte solution at 50 ℃ for 3 days in the same manner as the measurement of the liquid absorption rate to bring the coating resin into a saturated liquid absorption state, and the measurement was carried out in accordance with ASTM D683 (test piece shape type II). The tensile elongation at break is a value obtained by calculating the elongation until the test piece is broken in the tensile test using the following formula.

Tensile elongation at break (%) [ (length of test piece at break-length of test piece before test)/length of test piece before test ] × 100

When the tensile elongation at break of the coating resin in a saturated liquid-absorbed state is 10% or more, the coating resin has appropriate flexibility, and therefore peeling of the coating layer due to a volume change of the electrode active material during charge and discharge is easily suppressed.

The tensile elongation at break is preferably 20% or more, more preferably 30% or more.

The upper limit of the tensile elongation at break is preferably 400%, and more preferably 300%.

The acrylic resin used for the coating resin is preferably a resin containing a polymer (a1) containing an acrylic monomer (a) as an essential constituent monomer.

The polymer (a1) is particularly preferably a polymer of a monomer composition containing, as the acrylic monomer (a), a monomer (a1) having a carboxyl group or an acid anhydride group and a monomer (a2) represented by the following general formula (1).

CH₂＝C(R¹)COOR² (1)

[ in the formula (1), R¹Is a hydrogen atom or a methyl group, R²Is a C4-12 straight chain or C3-36 branched chain alkyl.]

Examples of the monomer (a1) having a carboxyl group or an acid anhydride group include monocarboxylic acids having 3 to 15 carbon atoms such as (meth) acrylic acid (a11), crotonic acid, and cinnamic acid; dicarboxylic acids having 4 to 24 carbon atoms such as maleic acid (anhydride), fumaric acid, itaconic acid (anhydride), citraconic acid, and mesaconic acid; and a tri-to tetra-or higher polycarboxylic acid having 6 to 24 carbon atoms such as aconitic acid. Among these, (meth) acrylic acid (a11) is preferable, and methacrylic acid is more preferable.

In the monomer (a2) represented by the above general formula (1), R¹Represents a hydrogen atom or a methyl group. R¹Preferably methyl.

R²Preferably, the alkyl group is a linear or branched alkyl group having 4 to 12 carbon atoms or a branched alkyl group having 13 to 36 carbon atoms.

(a21)R²Is an ester compound of a C4-12 straight chain or branched alkyl group

Examples of the linear alkyl group having 4 to 12 carbon atoms include butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, and dodecyl.

Examples of the branched alkyl group having 4 to 12 carbon atoms include 1-methylpropyl (sec-butyl), 2-methylpropyl, 1-dimethylethyl (tert-butyl), 1-methylbutyl, 1-dimethylpropyl, 1, 2-dimethylpropyl, 2-dimethylpropyl (neopentyl), 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1-dimethylbutyl, 1, 2-dimethylbutyl, 1, 3-dimethylbutyl, 2-dimethylbutyl, 2, 3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1-methylhexyl, 2-methylhexyl, 4-methylhexyl, and, 5-methylhexyl, 1-ethylpentyl, 2-ethylpentyl, 3-ethylpentyl, 1-dimethylpentyl, 1, 2-dimethylpentyl, 1, 3-dimethylpentyl, 2-dimethylpentyl, 2, 3-dimethylpentyl, 2-ethylpentyl, 1-methylheptyl, 2-methylheptyl, 3-methylheptyl, 4-methylheptyl, 5-methylheptyl, 6-methylheptyl, 1-dimethylhexyl, 1, 2-dimethylhexyl, 1, 3-dimethylhexyl, 1, 4-dimethylhexyl, 1, 5-dimethylhexyl, 1-ethylhexyl, 2-ethylhexyl, 1-methyloctyl, 2-methyloctyl, 3-methylpentyl, 2-methylpentyl, 1-dimethylpentyl, 1, 2-dimethylpenty, 4-methyloctyl, 5-methyloctyl, 6-methyloctyl, 7-methyloctyl, 1-dimethylheptyl, 1, 2-dimethylheptyl, 1, 3-dimethylheptyl, 1, 4-dimethylheptyl, 1, 5-dimethylheptyl, 1, 6-dimethylheptyl, 1-ethylheptyl, 2-ethylheptyl, 1-methylnonyl, 2-methylnonyl, 3-methylnonyl, 4-methylnonyl, 5-methylnonyl, 6-methylnonyl, 7-methylnonyl, 8-methylnonyl, 1-dimethyloctyl, 1, 2-dimethyloctyl, 1, 3-dimethyloctyl, 1, 4-dimethyloctyl, 1, 5-dimethyloctyl, 1, 6-dimethyloctyl group, 1, 7-dimethyloctyl group, 1-ethyloctyl group, 2-ethyloctyl group, 1-methyldecyl group, 2-methyldecyl group, 3-methyldecyl group, 4-methyldecyl group, 5-methyldecyl group, 6-methyldecyl group, 7-methyldecyl group, 8-methyldecyl group, 9-methyldecyl group, 1-dimethylnonyl group, 1, 2-dimethylnonyl group, 1, 3-dimethylnonyl group, 1, 4-dimethylnonyl group, 1, 5-dimethylnonyl group, 1, 6-dimethylnonyl group, 1, 7-dimethylnonyl group, 1, 8-dimethylnonyl group, 1-ethylnonyl group, 2-ethylnonyl group, 1-methylundecyl group, 2-ethyloctyl group, 1-ethyloctyl group, 2-ethyloctyl group, 3-methylundecyl, 4-methylundecyl, 5-methylundecyl, 6-methylundecyl, 7-methylundecyl, 8-methylundecyl, 9-methylundecyl, 10-methylundecyl, 1-dimethyldecyl, 1, 2-dimethyldecyl, 1, 3-dimethyldecyl, 1, 4-dimethyldecyl, 1, 5-dimethyldecyl, 1, 6-dimethyldecyl, 1, 7-dimethyldecyl, 1, 8-dimethyldecyl, 1, 9-dimethyldecyl, 1-ethyldecyl, 2-ethyldecyl and the like. Among these, butyl and 2-ethylhexyl are particularly preferable.

(a22)R²an ester compound which is a branched alkyl group having 13 to 36 carbon atoms

Examples of the branched alkyl group having 13 to 36 carbon atoms include 1-alkylalkyl [ 1-methyldodecyl, 1-butyleicosyl, 1-hexyloctadecyl, 1-octylhexadecyl, 1-decyltetradecyl, 1-undecyltridecyl, etc. ], 2-alkylalkyl [ 2-methyldodecyl, 2-hexyloctadecyl, 2-octylhexadecyl, 2-decyltetradecyl, 2-undecyltridecyl, 2-dodecylhexadecyl, 2-tridecylpentadecyl, 2-decyltecyloctadecyl, 2-tetradecyloctadecyl, 2-hexadecyloctadecyl, 2-tetradecyleicosyl, 2-hexadecyleicosyl, etc. ], 3 to 34-alkylalkyl (3-alkylalkyl, 3-hexadecyl, C, 4-alkyl group, 5-alkyl group, 32-alkyl group, 33-alkyl group, 34-alkyl group, etc.), and mixed alkyl groups containing 1 or more branched alkyl groups such as residues obtained by removing hydroxyl groups from oxo alcohols obtained from propylene oligomers (heptamer to undecene), ethylene/propylene (molar ratio 16/1 to 1/11) oligomers, isobutylene oligomers (heptamer to octamer), α -olefin (carbon number 5 to 20) oligomers (tetramer to octamer), etc. Among these, 2-decyltetradecyl group is particularly preferable.

The polymer (A1) preferably further contains an ester compound (a3) of a monohydric aliphatic alcohol having 1 to 3 carbon atoms and (meth) acrylic acid.

Examples of the monohydric aliphatic alcohol having 1 to 3 carbon atoms constituting the ester compound (a3) include methanol, ethanol, 1-propanol, and 2-propanol.

The content of the ester compound (A3) is preferably 10 to 60 wt%, more preferably 15 to 55 wt%, and further preferably 20 to 50 wt% based on the total weight of the polymer (a1) from the viewpoint of suppressing a volume change of the electrode active material.

The polymer (a1) may further contain a salt of an anionic monomer (a4) having a polymerizable unsaturated double bond and an anionic group.

Examples of the structure having a polymerizable unsaturated double bond include a vinyl group, an allyl group, a styryl group, and a (meth) acryloyl group.

Examples of the anionic group include a sulfonic acid group and a carboxyl group.

The anionic monomer having a polymerizable unsaturated double bond and an anionic group is a compound obtained by combining these, and examples thereof include vinylsulfonic acid, allylsulfonic acid, styrenesulfonic acid, and (meth) acrylic acid.

The term (meth) acryloyl means acryloyl and/or methacryloyl.

Examples of the cation constituting the salt (a4) of an anionic monomer include lithium ion, sodium ion, potassium ion, and ammonium ion.

In the case of the salt (a4) containing an anionic monomer, the content thereof is preferably 0.1 to 15% by weight, more preferably 1 to 15% by weight, and further preferably 2 to 10% by weight based on the total weight of the coating resin, from the viewpoint of internal resistance and the like.

The polymer (a1) preferably contains (meth) acrylic acid (a11) and an ester compound (a21), and more preferably further contains an ester compound (a 3).

Particularly preferred are copolymers of methacrylic acid as the (meth) acrylic acid (a11), 2-ethylhexyl methacrylate as the ester compound (a21), methacrylic acid as the ester compound (a3), 2-ethylhexyl methacrylate, and methyl methacrylate.

The coating resin is preferably obtained by polymerizing a monomer composition comprising (meth) acrylic acid (a11), the monomer (a2), an ester compound (a3) of a monohydric aliphatic alcohol having 1 to 3 carbon atoms and (meth) acrylic acid, and, if necessary, a salt (a4) of an anionic monomer having a polymerizable unsaturated double bond and an anionic group, wherein the weight ratio of the monomer (a2) to the (meth) acrylic acid (a11) [ the ester compound (a 21)/the (meth) acrylic acid (a11) ] is 10/90 to 90/10.

When the weight ratio of the monomer (a2) to the (meth) acrylic acid (a11) is 10/90 to 90/10, the adhesion between the polymer obtained by polymerizing the monomer and the electrode active material is good, and peeling is difficult.

The weight ratio is preferably 30/70 to 85/15, more preferably 40/60 to 70/30.

In addition, the monomers constituting the polymer (a1) may include, in addition to the monomer (a1) having a carboxyl group or an acid anhydride group, the monomer (a2) represented by the above general formula (1), the ester compound (A3) of a monohydric aliphatic alcohol having 1 to 3 carbon atoms and (meth) acrylic acid, and the salt (a4) of an anionic monomer having a polymerizable unsaturated double bond and an anionic group, a radically polymerizable monomer (a5) copolymerizable with the monomer (a1), the monomer (a2) represented by the above general formula (1), and the ester compound (A3) of a monohydric aliphatic alcohol having 1 to 3 carbon atoms and (meth) acrylic acid, within a range that does not impair the physical properties of the polymer (a 1).

As the radical polymerizable monomer (a5), a monomer containing no active hydrogen is preferable, and the following monomers (a51) to (a58) can be used.

The monomer (a51) is a (meth) acrylic acid alkyl ester formed from a (meth) acrylic acid and a straight-chain aliphatic monohydric alcohol having 13 to 20 carbon atoms, an alicyclic monohydric alcohol having 5 to 20 carbon atoms, or an aromatic aliphatic monohydric alcohol having 7 to 20 carbon atoms, and includes (i) straight-chain aliphatic monohydric alcohol (tridecanol, myristyl alcohol, pentadecyl alcohol, hexadecanol, heptadecyl alcohol, stearyl alcohol, nonadecyl alcohol, eicosyl alcohol, etc.); (ii) alicyclic monohydric alcohols (cyclopentanol, cyclohexanol, cycloheptanol, cyclooctanol, etc.); (iii) aromatic aliphatic monohydric alcohols (benzyl alcohol, etc.); and a mixture of 2 or more of these (i) to (iii), and a hydrocarbyl (meth) acrylate formed with (meth) acrylic acid.

The monomer (a52) is a poly (n-2 to 30) oxyalkylene (c 2 to c 4) alkyl (c 1 to c 18) ether (meth) acrylate, and examples thereof include a (meth) acrylate which is a 10-mol adduct of ethylene oxide (hereinafter abbreviated as EO) of methanol, and a (meth) acrylate which is a 10-mol adduct of propylene oxide (hereinafter abbreviated as PO) of methanol.

The monomer (a53) is a nitrogen-containing vinyl compound, and examples thereof include the compounds described in the following (a53-1) to (a 53-5).

(a53-1) amide group-containing vinyl Compound

(i) (meth) acrylamide compounds having 3 to 30 carbon atoms, such as N, N-dialkyl (1 to 6 carbon atoms) or diaralkyl (7 to 15 carbon atoms) (meth) acrylamide (N, N-dimethylacrylamide, N-dibenzylacrylamide, etc.), diacetone acrylamide.

(ii) An amide group-containing vinyl compound having 4 to 20 carbon atoms other than the (meth) acrylamide compound, for example, N-methyl-N-vinylacetamide, cyclic amide [ pyrrolidone compound (having 6 to 13 carbon atoms, for example, N-vinylpyrrolidone, etc.) ].

(a53-2) Nitrogen-containing (meth) acrylate Compound

(i) Dialkyl (C1-4) aminoalkyl (C1-4) (meth) acrylates, such as N, N-dimethylaminoethyl (meth) acrylate, N-diethylaminoethyl (meth) acrylate, t-butylaminoethyl (meth) acrylate, morpholinoethyl (meth) acrylate.

(ii) Quaternary ammonium compounds (quaternized with a quaternizing agent such as methyl chloride, dimethyl sulfate, benzyl chloride, or dimethyl carbonate) of quaternary ammonium group-containing (meth) acrylates, for example, tertiary amino group-containing (meth) acrylates [ (N, N-dimethylaminoethyl (meth) acrylate, N-diethylaminoethyl (meth) acrylate, etc. ].

(a53-3) heterocycle-containing vinyl Compound

Pyridine compounds (having 7 to 14 carbon atoms, such as 2-vinylpyridine or 4-vinylpyridine), imidazole compounds (having 5 to 12 carbon atoms, such as N-vinylimidazole), pyrrole compounds (having 6 to 13 carbon atoms, such as N-vinylpyrrole), pyrrolidone compounds (having 6 to 13 carbon atoms, such as N-vinyl-2-pyrrolidone).

(a53-4) nitrile group-containing vinyl Compound

A nitrile group-containing vinyl compound having 3 to 15 carbon atoms, such as (meth) acrylonitrile, cyanostyrene, cyanoalkyl (having 1 to 4 carbon atoms) acrylate.

(a53-5) other nitrogen-containing vinyl Compound

Nitro group-containing vinyl compounds (having 8 to 16 carbon atoms, e.g., nitrostyrene), and the like

The monomer (a54) is a vinyl group-containing hydrocarbon, and examples thereof include the compounds described in the following (a54-1) to (a 54-3).

(a54-1) vinyl group-containing aliphatic hydrocarbon

Olefins having 2 to 18 or more carbon atoms (e.g., ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.), dienes having 4 to 10 or more carbon atoms (e.g., butadiene, isoprene, 1, 4-pentadiene, 1, 5-hexadiene, 1, 7-octadiene, etc.), etc

(a54-2) alicyclic unsaturated hydrocarbon

Cyclic unsaturated compounds having 4 to 18 or more carbon atoms, for example, cyclic olefins (e.g., cyclohexene), (di) cyclodiolefins (e.g., (di) cyclopentadiene), terpenes (e.g., pinene and limonene), indenes

(a54-3) vinyl-containing aromatic hydrocarbons

Aromatic unsaturated compounds having 8 to 20 or more carbon atoms, such as styrene, alpha-methylstyrene, vinyltoluene, 2, 4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene

The monomer (a55) is a vinyl ester, and examples thereof include aliphatic vinyl esters [ e.g., alkenyl esters of aliphatic carboxylic acids (monocarboxylic acids or dicarboxylic acids) having 4 to 15 carbon atoms (e.g., vinyl acetate, vinyl propionate, vinyl butyrate, diallyl adipate, isopropenyl acetate, and methoxy vinyl acetate) ], aromatic vinyl esters [ e.g., alkenyl esters of aromatic carboxylic acids (monocarboxylic acids or dicarboxylic acids) (e.g., vinyl benzoate, diallyl phthalate, and methyl 4-vinylbenzoate), and aromatic ring-containing esters of aliphatic carboxylic acids (e.g., acetoxystyrene) ].

The monomer (a56) is a vinyl ether, and examples thereof include aliphatic vinyl ethers [ e.g., a vinyl alkyl (C1-10) ether (e.g., vinyl methyl ether, vinyl butyl ether, vinyl-2-ethylhexyl ether, etc.), a vinyl alkoxy (C1-6) alkyl (C1-4) ether (e.g., vinyl-2-methoxyethyl ether, methoxybutadiene, 3, 4-dihydro-1, 2-pyran, 2-butoxy-2' -vinyloxyethyl ether, vinyl-2-ethylmercaptoethyl ether, etc.), a poly (2-4) (methyl) allyloxyalkane (C2-6) (e.g., diallyloxyethane, triallyloxyethane, tetraallyloxybutane, tetramethylallyloxyethane, etc.) ], an aliphatic vinyl ether [ e.g., a vinyl alkyl (C1-15) ether having an alkyl group (C1-10), a vinyl (e.g., aromatic vinyl ether (C8-20, such as vinyl phenyl ether, phenoxy styrene).

The monomer (a57) is a vinyl ketone, and examples thereof include aliphatic vinyl ketones (having 4 to 25 carbon atoms, for example, vinyl methyl ketone and vinyl ethyl ketone) and aromatic vinyl ketones (having 9 to 21 carbon atoms, for example, vinyl phenyl ketone).

The monomer (a58) is an unsaturated dicarboxylic acid diester, and examples thereof include an unsaturated dicarboxylic acid diester having 4 to 34 carbon atoms, such as a dialkyl fumarate (2 alkyl groups each being a linear, branched or alicyclic group having 1 to 22 carbon atoms), and a dialkyl maleate (2 alkyl groups each being a linear, branched or alicyclic group having 1 to 22 carbon atoms).

Among the radical polymerizable monomers exemplified as (a5), the monomer (a51), the monomer (a52) and the monomer (a53) are preferable in view of voltage resistance.

In the polymer (a1), the content of the monomer (a1) having a carboxyl group or an acid anhydride group, the monomer (a2) represented by the general formula (1), the ester compound (A3) of a monohydric aliphatic alcohol having 1 to 3 carbon atoms and (meth) acrylic acid, the salt (a4) of an anionic monomer having a polymerizable unsaturated double bond and an anionic group, and the radical polymerizable monomer (a5) is preferably 0.1 to 80% by weight of (a1), 0.1 to 99.9% by weight of (a2), (0 to 60% by weight of (A3), (0 to 15% by weight of (a4), and 0 to 99.8% by weight of (a5), based on the weight of the polymer (a 1).

When the content of the monomer is within the above range, the liquid absorption property in the nonaqueous electrolytic solution is good.

The lower limit of the weight average molecular weight of the polymer (a1) is preferably 3,000, more preferably 50,000, and still more preferably 60,000, and the upper limit thereof is preferably 2,000,000, more preferably 1,500,000, still more preferably 1,000,000, and particularly preferably 120,000.

The weight average molecular weight of the polymer (a1) can be determined by gel permeation chromatography (hereinafter abbreviated as GPC) measurement under the following conditions.

The device comprises the following steps: "HLC-8120 GPC" [ manufactured by Tosoh corporation ]

Column: "TSKgel GMHXL" (2 columns), "a column comprising 1 each TSKgel Multipore HXL-M linked" [ all manufactured by Tosoh Corp. ]

Sample solution: 0.25% by weight tetrahydrofuran solution

Solution injection amount: 10 μ L

Flow rate: 0.6 mL/min

measuring temperature: 40 deg.C

The detection device comprises: refractive index detector

Reference substance: standard polystyrene (manufactured by Tosoh corporation)

The polymer (a1) can be produced by a known polymerization method (bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc.) using a known polymerization initiator { azo initiator [2,2 '-azobis (2-methylpropanenitrile), 2' -azobis (2, 4-dimethylvaleronitrile, etc.) ], a peroxide initiator (benzoyl peroxide, di-t-butyl peroxide, lauryl peroxide, etc.) }.

The amount of the polymerization initiator to be used is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight, and still more preferably 0.1 to 1.5% by weight based on the total weight of the monomers, and the polymerization temperature and the polymerization time are adjusted according to the kind of the polymerization initiator, and the polymerization is carried out at a polymerization temperature of preferably-5 to 150 ℃ (more preferably 30 to 120 ℃) and a reaction time of preferably 0.1 to 50 hours (more preferably 2 to 24 hours).

Examples of the solvent used in the solution polymerization include esters (having 2 to 8 carbon atoms, such as ethyl acetate and butyl acetate), alcohols (having 1 to 8 carbon atoms, such as methanol, ethanol and octanol), hydrocarbons (having 4 to 8 carbon atoms, such as n-butane, cyclohexane and toluene), and ketones (having 3 to 9 carbon atoms, such as methyl ethyl ketone), and the amount thereof is preferably 5 to 900% by weight, more preferably 10 to 400% by weight, particularly preferably 30 to 300% by weight, based on the total weight of the monomers, and the monomer concentration is preferably 10 to 95% by weight, more preferably 20 to 90% by weight, particularly preferably 30 to 80% by weight, from the viewpoint of adjusting the molecular weight to a preferred range.

Examples of the dispersion medium in the emulsion polymerization and suspension polymerization include water, alcohols (e.g., ethanol), esters (e.g., ethyl propionate), and light naphtha, and examples of the emulsifier include metal salts of higher fatty acids (having 10 to 24 carbon atoms) (e.g., sodium oleate and sodium stearate), metal salts of sulfuric esters of higher alcohols (having 10 to 24 carbon atoms) (e.g., sodium lauryl sulfate), ethoxylated tetramethyldecynediol, sodium sulfoethyl methacrylate, and dimethyl aminomethyl methacrylate. Polyvinyl alcohol, polyvinyl pyrrolidone, etc. may be further added as a stabilizer.

The monomer concentration of the solution or dispersion is preferably 5 to 95% by weight, more preferably 10 to 90% by weight, more preferably 15 to 85% by weight, and the amount of the polymerization initiator is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight, based on the total weight of the monomers.

In the polymerization, a known chain transfer agent, for example, a mercapto compound (e.g., dodecyl mercaptan, n-butyl mercaptan, etc.) and/or a halogenated hydrocarbon (e.g., carbon tetrachloride, carbon tetrabromide, benzyl chloride, etc.) can be used.

The acrylic resin as the coating resin may be a crosslinked polymer obtained by crosslinking the polymer (a1) with a crosslinking agent (a ') having a reactive functional group that reacts with a carboxyl group, preferably with a polyepoxide compound (a ' 1) [ polyglycidyl ether (bisphenol a diglycidyl ether, propylene glycol diglycidyl ether, glycerol triglycidyl ether, and the like) and polyglycidyl amine (N, N-diglycidylaniline, 1, 3-bis (N, N-diglycidylaminomethyl)) and/or a polyol compound (a ' 2) (ethylene glycol, and the like) ].

As a method for crosslinking the polymer (a1) with the crosslinking agent (a'), there is a method in which the electrode active material is coated with the polymer (a1) and then crosslinked. Specifically, the following methods can be mentioned: the electrode active material is mixed with a resin solution containing a polymer (a1) and desolvated to produce a coated electrode active material in which the electrode active material is coated with the polymer (a1), and then a solution containing a crosslinking agent (a ') is mixed with the coated electrode active material and heated to cause a crosslinking reaction with the desolvation, thereby causing a reaction in which the polymer (a1) is crosslinked by the crosslinking agent (a') on the surface of the electrode active material.

The heating temperature is adjusted depending on the kind of the crosslinking agent, and is preferably 70 ℃ or higher in the case of using the polyepoxy compound (a '1) as the crosslinking agent, and is preferably 120 ℃ or higher in the case of using the polyol compound (a' 2) as the crosslinking agent.

The coating layer may further include a conductive aid, wherein the coating layer including the positive electrode active material preferably includes a conductive aid.

The conductive assistant is selected from materials having conductivity, and specifically, carbon [ graphite, carbon black (acetylene black, ketjen black, furnace black, channel black, thermal black, etc.) ], carbon fibers such as PAN-based carbon fiber and pitch-based carbon fiber, carbon nanofibers, carbon nanotubes, and metals [ nickel, aluminum, stainless steel (SUS), silver, copper, titanium, etc. ], can be used.

These conductive aids may be used singly or in combination of two or more. In addition, alloys or metal oxides thereof may also be used. From the viewpoint of electrical stability, aluminum, stainless steel, carbon, silver, copper, titanium and a mixture thereof are preferable, silver, aluminum, stainless steel and carbon are more preferable, and carbon is further preferable. The conductive aid may be a material in which a conductive material (a metal material in the above conductive material) is coated around a particulate ceramic material or a resin material by plating or the like. A polypropylene resin kneaded with graphene is also preferable as the conductive assistant.

The average particle size of the conductive aid is not particularly limited, but is preferably 0.01 to 10 μm, more preferably 0.02 to 5 μm, and still more preferably 0.03 to 1 μm, from the viewpoint of electrical characteristics of the electrode for a lithium ion battery. In the present specification, the particle diameter of the conductive auxiliary agent refers to the maximum distance L among the distances between any two points on the contour line of the particles formed of the conductive auxiliary agent. As the value of "average particle diameter of conductive assistant", the following values were used: a value calculated as an average value of particle diameters of particles observed in several to several tens of fields of view by using an observation means such as a Scanning Electron Microscope (SEM) or a Transmission Electron Microscope (TEM).

The shape (form) of the conductive auxiliary is not limited to the particle form, and may be a form other than the particle form, for example, a fibrous conductive auxiliary.

Examples of the fibrous conductive aid include: conductive fibers in which metal or graphite having good conductivity is uniformly dispersed in synthetic fibers; a metal fiber obtained by fiberizing a metal such as stainless steel; conductive fibers in which the surfaces of organic fibers are coated with metal; a conductive fiber in which the surface of an organic material is coated with a resin containing a conductive substance; and so on.

The average fiber diameter of the fibrous conductive auxiliary agent is preferably 0.1 to 20 μm.

When the coating layer contains a conductive auxiliary, the weight of the conductive auxiliary contained in the coating layer is preferably 15 to 75 wt% with respect to the total weight of the coating resin and the conductive auxiliary.

When the coating layer of the positive electrode-coated electrode active material contains a conductive auxiliary agent, even when an SEI film is formed on the surface of the electrode active material after the precharge, the conductive path between the active materials is maintained by the effect of the conductive auxiliary agent contained in the coating layer, and the increase in resistance due to the formation of the SEI film can be suppressed.

The non-bonded body means that the positions of the coated electrode active materials are not irreversibly fixed by a binder (also referred to as binder).

In other words, the electrode active material layer does not contain a binder.

Examples of the binder include known binders for lithium ion batteries such as starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, and styrene-butadiene copolymer.

In the electrode active material layer in the electrode for a lithium ion battery according to the present invention, the positions of the coated electrode active materials are fixed by the binder, but the electrode active materials are reversibly fixed without containing the binder, and the electrode active materials can be separated without breaking the coated electrode active materials, and the separated coated electrode active materials can be formed into an electrode active material molded body by applying pressure again.

In a conventional lithium ion battery, an electrode active material layer is produced by dispersing electrode active material particles and a binder in a solvent, applying the obtained slurry to the surface of a current collector or the like, and heating and drying the applied slurry, and therefore the electrode active material layer is fixed to the binder. At this time, the electrode active materials are fixed to each other by the binder, and the positions of the electrode active material particles are fixed. When the electrode active material layer is fixed by the binder, excessive stress is applied to the electrode active material particles due to expansion and contraction during charge and discharge, and the electrode active material particles are easily self-disintegrated.

Further, since the electrode active material layer is fixed to the surface of the electrode collector by the binder, cracks may be generated in the electrode active material layer fixed by the binder or the electrode active material layer may be peeled or detached from the surface of the collector due to expansion or contraction during charge and discharge of the electrode active material particles.

In the case of a non-bonded body including a mixture of a coated electrode active material and a binder, even if the coated electrode active materials are in contact with each other in the electrode active material layer, the coating resins are not irreversibly bonded to each other at the contact surface, and the bonding is temporary and can be detached without breaking the coating of the electrode active material, so that the coated electrode active materials are not irreversibly fixed to each other by the coating resin. Therefore, in the electrode active material layer including a non-bonded body including a mixture of the coated electrode active material and the binder, the coated electrode active materials are not bonded to each other.

The weight ratio of the coated electrode active material to the binder in the electrode for a lithium ion battery is preferably 90/10 to 99.99/0.01, more preferably 95/5 to 99.9/0.1.

In the above ratio, the amount of the binder is not excessive, so that the energy density of the electrode is not lowered, and the shape retaining function of the electrode by the binder can be suitably exhibited.

The thickness of the electrode active material layer constituting the electrode for a lithium ion battery is preferably 150 μm or more, more preferably 200 μm or more, and further preferably 400 μm or more. Further, it is preferably 2000 μm or less.

When the thickness of the electrode active material layer is large, the ratio of the electrode active material layer in the battery increases when the battery is a laminate battery, and a battery with high energy density can be obtained.

Next, a method for manufacturing an electrode for a lithium ion battery according to the present invention will be described.

The method for manufacturing an electrode for a lithium ion battery according to the present invention is characterized in that an electrode active material layer composed of a non-bonded body including a mixture of a coated electrode active material and a binder for a lithium ion electrode is formed by pressurizing the mixture of the coated electrode active material and the binder, the coated electrode active material has a coating layer including a coating resin on at least a part of a surface of an electrode active material that stores and releases lithium ions, the binder for a lithium ion electrode is a binder that bonds active materials to each other in a lithium ion electrode, the binder has a glass transition temperature of 60 ℃ or less, and has a solubility parameter of 8 to 13 (cal/cm)³)^1/2At a frequency of 10^-1～10¹The storage shear modulus and the loss shear modulus measured at 20 ℃ in the range of Hz were 2.0X 10³～5.0×10⁷Pa，The adhesive is an acrylic polymer containing structural units derived from an alkyl (meth) acrylate monomer as an essential part, the proportion of the alkyl (meth) acrylate monomer in the monomers constituting the adhesive is 50 wt% or more based on the total weight of the monomers, and the proportion of the fluorine-containing monomer is less than 3 wt% based on the total weight of the monomers.

The coated electrode active material can be obtained, for example, by: and (2) putting the electrode active substance into a universal mixer, stirring at 30-50 rpm, dropwise adding a resin solution containing the coating resin for 1-90 minutes in the state, mixing, further mixing with a conductive additive according to needs, heating to 50-200 ℃ in the stirring state, reducing the pressure to 0.007-0.04 MPa, and keeping for 10-150 minutes, thereby obtaining the electrode active substance.

The adhesive may be produced and prepared by the above-described production method and the like.

The mixture of the coated electrode active material and the binder may be prepared by mixing the coated electrode active material and the binder using a known method.

The mixture does not contain the above-mentioned binder.

In addition, the mixture may further contain a conductive material in addition to the above-described conductive aid contained in the coating layer. When the conductive material is contained, a conductive path between the active materials is easily maintained, which is preferable.

As the conductive material, the same conductive aid as that contained in the coating layer can be used, and the same is preferable.

The mixture is preferably prepared such that the weight ratio of the coated electrode active material to the binder in the mixture is 90/10 to 99.99/0.01.

The binder used in the method for producing an electrode for a lithium ion battery of the present invention preferably contains two or more alkyl (meth) acrylate monomers as constituent monomers, and the total content thereof is 50% by weight or more based on the total weight of the constituent monomers.

The adhesive may contain a monovinyl monomer copolymerizable with the alkyl (meth) acrylate monomer as a constituent monomer.

In addition, the adhesive preferably contains a (meth) acrylic monomer as a constituent monomer.

In the method for manufacturing an electrode for a lithium ion battery according to the present invention, the mixture is pressurized to form an electrode active material layer.

Examples of the method of forming the electrode active material layer by applying pressure include: a method of filling the mixture into a mold and performing extrusion molding; a method of molding by extrusion molding; a method of forming by calender forming (calender processing).

The thickness of the electrode active material layer to be formed is preferably 150 μm or more, more preferably 200 μm or more, and further preferably 400 μm or more. Further, it is preferably 2000 μm or less.

The extrusion molding can be performed using any of a press device and a press tool such as a hydraulic press device. For example, the mixture is charged into a cylindrical bottomed container, a round bar-shaped pressing tool having a diameter slightly smaller than the inner diameter of the cylinder is inserted from above, and the mixture is compressed by a pressing device, thereby obtaining a cylindrical molded body.

The shape of the molded article to be produced is preferably 150 μm or more in thickness.

In the case of a cylindrical shaped article, the diameter is preferably 10 to 70 mm.

Further, by changing the shape of the pressing tool, a molded body having an arbitrary shape can be obtained.

The compression condition in the extrusion molding is preferably 40 to 3000 MPa. The pressing time is preferably 1 to 300 seconds.

Extrusion molding may be performed on the current collector. The mixture is disposed on a current collector and extruded to obtain an electrode active material layer on the current collector.

The electrode active material layer obtained on the current collector can be used together with the current collector as an electrode for a lithium ion battery.

Examples of the material constituting the positive electrode collector as the collector include copper, aluminum, titanium, stainless steel, nickel, calcined carbon, conductive polymers, and conductive glass. In addition, as the positive electrode current collector, a resin current collector composed of a conductive agent and a resin may be used.

Examples of the material constituting the negative electrode current collector as the current collector include metal materials such as copper, aluminum, titanium, stainless steel, nickel, and alloys thereof. Among them, copper is preferable in terms of weight reduction, corrosion resistance, and high conductivity. The negative electrode current collector may be a current collector made of calcined carbon, a conductive polymer, a conductive glass, or the like, or may be a resin current collector made of a conductive agent and a resin.

As the conductive agent constituting the resin current collector together with the positive electrode current collector and the negative electrode current collector, the same conductive material as an arbitrary component of the mixture can be suitably used.

Examples of the resin constituting the resin collector include Polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), Polycycloolefin (PCO), polyethylene terephthalate (PET), polyether nitrile (PEN), Polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), Polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVdF), an epoxy resin, a silicone resin, and a mixture thereof.

From the viewpoint of electrical stability, Polyethylene (PE), polypropylene (PP), polymethylpentene (PMP) and Polycycloolefin (PCO) are preferable, and Polyethylene (PE), polypropylene (PP) and polymethylpentene (PMP) are more preferable.

Examples of the method for obtaining the molded article of the electrode composition by extrusion molding include a method using a known extrusion molding machine.

Examples of the extrusion molding machine include an extrusion molding machine having: a raw material cylinder for supplying raw material; a die head (also referred to as a mold) mounted on the raw material discharge side of the raw material barrel; and a rotary shaft-shaped screw for extruding the raw material disposed in the raw material cylinder toward the die.

The mixture is charged into the raw material barrel, and the mixture moved in the raw material barrel by the rotation of the screw is extruded from the die, whereby a cylindrical molded article can be obtained. The shape of the molded article can be appropriately adjusted by adjusting the shape of the die and the rotation speed of the screw.

The shape of the cylindrical molded article discharged from the die is not particularly limited, and is preferably a cylindrical shape or a quadrangular prism shape. The cylindrical molded body discharged from the die was cut into a predetermined length, thereby obtaining an electrode having an electrode active material layer.

As a method for obtaining an electrode composition molded body by calendar molding, a method using a known roll press apparatus can be mentioned.

The mixture is fed from a continuous mixer such as a kneader, and the mixture of the active material and the electrolyte spread to a constant thickness on a smooth surface such as a film by a doctor blade or the like is subjected to a roll-pressing treatment, whereby a sheet-like molded body can be obtained. The sheet-like molded body is cut into pieces having a predetermined length, thereby obtaining an electrode having an electrode active material layer.

Through the above steps, an electrode for a lithium ion battery having an electrode active material layer can be manufactured.

The electrode active material layer obtained by the above-described steps does not use a binder and does not undergo a step of curing the mixture by heating or the like, but the shape of the electrode can be maintained by the appropriate shape-retaining property of the binder with respect to the coating resin contained in the coating layer that coats the electrode active material.

In the production of a lithium ion battery, it is preferable that the electrode for a lithium ion battery produced by the method for producing an electrode for a lithium ion battery of the present invention is housed in a battery container together with a separator, and an electrolyte solution is injected so as to permeate the electrode active material layer.

As the electrode active material layer to be contained in the battery container, both of the positive electrode for a lithium ion battery and the negative electrode for a lithium ion battery manufactured by the method for manufacturing an electrode for a lithium ion battery of the present invention may be used, or only one of them may be used.

When only one of them is used, a known counter electrode can be used as the electrode on the opposite side.

The electrode for a lithium ion battery obtained in the present invention maintains a certain shape, and therefore, handling is easy, and the electrode for a lithium ion battery is easily accommodated in a battery container.

In addition, when the electrode active material layer is formed on the current collector as described above, a lithium ion battery may be manufactured using the electrode active material layer as an electrode together with the current collector.

Examples of the separator include known separators for lithium ion batteries, such as a porous film made of polyethylene or polypropylene, a laminated film of a porous polyethylene film and a porous polypropylene film, a nonwoven fabric made of synthetic fibers (polyester fibers, aramid fibers, and the like), glass fibers, and the like, and a separator having ceramic fine particles such as silica, alumina, titania, and the like adhered to the surfaces thereof.

As the electrolytic solution, an electrolytic solution containing an electrolyte and a nonaqueous solvent, which is used in the production of a lithium ion battery, can be used.

As the electrolyte, an electrolyte used in a known electrolytic solution can be used, and preferable electrolytes include, for example: LiPF₆、LiBF₄、LiSbF₆、LiAsF₆And LiClO₄Lithium salt electrolyte of inorganic acid, LiN (FSO)₂)₂、LiN(CF₃SO₂)₂And LiN (C)₂F₅SO₂)₂And LiC (CF) or a sulfonyl imide electrolyte having a fluorine atom₃SO₂)₃And a sulfonyl methide electrolyte having a fluorine atom.

As the nonaqueous solvent used in the injected electrolytic solution, an aprotic solvent can be preferably used.

The aprotic solvent is a solvent having no hydrogen-donating ionic group (a group having a dissociative hydrogen atom, such as an amino group, a hydroxyl group, and a thio group), and as a solvent which can be preferably used, a lactone compound, a cyclic or chain carbonate, a chain carboxylate, a cyclic or chain ether, a phosphate ester, a nitrile compound, an amide compound, a sulfone, and the like, and a mixture thereof are used, and a cyclic carbonate, a chain carbonate, and a mixed solvent of a cyclic carbonate and a chain carbonate are more preferable.

Examples of the lactone compound include a 5-membered ring lactone compound (e.g., γ -butyrolactone and γ -valerolactone) and a 6-membered ring lactone compound (e.g., δ -valerolactone).

Examples of the cyclic carbonate include propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, and the like.

Examples of the chain carbonate include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate, di-n-propyl carbonate, and the like.

Examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, propyl acetate, and methyl propionate.

Examples of the cyclic ether include tetrahydrofuran, tetrahydropyran, 1, 3-dioxolane, 1, 4-dioxane, and the like.

Examples of the chain ether include dimethoxymethane and 1, 2-dimethoxyethane.

Examples of the phosphate ester include trimethyl phosphate, triethyl phosphate, ethyldimethyl phosphate, diethylmethyl phosphate, tripropyl phosphate, tributyl phosphate, tris (trifluoromethyl) phosphate, tris (trichloromethyl) phosphate, tris (trifluoroethyl) phosphate, tris (trifluoroperfluoroethyl) phosphate, 2-ethoxy-1, 3, 2-dioxaphospholan-2-one, 2-trifluoroethoxy-1, 3, 2-dioxaphospholan-2-one, and 2-methoxyethoxy-1, 3, 2-dioxaphospholan-2-one.

The nitrile compound may include acetonitrile and the like. Examples of the amide compound include N, N-dimethylformamide (hereinafter also referred to as DMF) and the like. Examples of the sulfone include chain sulfones such as dimethyl sulfone and diethyl sulfone, and cyclic sulfones such as sulfolane.

The aprotic solvent may be used alone or in combination of two or more.

The concentration of the electrolyte contained in the electrolyte solution is preferably 0.3 to 3M in terms of battery characteristics at low temperatures.

In the method for producing an electrode for a lithium ion battery according to the present invention, it is also preferable that the mixture is an electrolyte-containing mixture further containing an electrolyte, and the electrode active material layer is formed by pressurizing the electrolyte-containing mixture.

As the electrolytic solution contained in the mixture containing the electrolytic solution, the above-described electrolytic solution can be used.

As the electrolytic solution contained in the electrolyte-containing mixture, an electrolytic solution in which the solvent contains ethylene carbonate is particularly preferable, and an electrolytic solution in which a mixed solvent of ethylene carbonate and diethyl carbonate is more preferable.

With this method, an electrode containing an electrolyte can be produced in a simple process.