WO2019146720A1 - Lithium ion secondary battery positive electrode - Google Patents

Abstract

One embodiment provides a lithium ion secondary battery positive electrode that has the same charge/discharge characteristics as lithium ion secondary battery positive electrodes produced by means of conventional non-aqueous processes but is obtained by means of an aqueous process that uses an aqueous binder. One embodiment of the present disclosure relates to a lithium ion secondary battery positive electrode that includes a collector and a mixture layer that is formed on the collector. The mixture layer includes, as a binder, polymer particles that contain: a structural unit (A) that is derived from a compound that is represented by formula (I); and a structural unit (B) that is derived from at least one type of compound selected from compounds represented by formula (II), compounds represented by formula (III), and unsaturated dibasic acids. Structural unit (A) is 50–99.9 mass% of the total structural units of the polymer particles, and structural unit (B) is 0.1–20 mass% of the total structural units of the polymer particles.

Description

Positive electrode for lithium ion secondary battery

The present disclosure relates to a positive electrode for a lithium ion secondary battery.

Lithium ion batteries have higher energy density per unit weight and volume than lead storage batteries and nickel hydrogen batteries, and so contribute to the downsizing and weight reduction of mounted electronic devices. In recent years, hybrid cars and electric cars have been widely used as an approach for zero emission of cars, and the performance improvement of lithium ion batteries is important for improving the fuel efficiency and extending the driving distance.

The lithium ion secondary battery is generally composed of members such as a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator. Among them, the positive electrode is prepared by dispersing a positive electrode active material and a conductive material in an organic solvent such as N methyl pyrrolidone etc. together with a binder to prepare a positive electrode mixture, applying it on the current collector surface, and evaporating the solvent. It is done. On the other hand, the negative electrode is manufactured by an aqueous process in which an aqueous emulsion of a styrene-butadiene copolymer rubber manufactured by an emulsion polymerization method is used as a binder and a carboxymethylcellulose aqueous solution having a thickening action is mixed with a negative electrode active material together with a thickener. (E.g., Patent Document 1).

Patent No. 3101775

In recent years, the adoption of a water-based process such as a negative electrode has been desired for the positive electrode, because the electrode manufacturing cost can be reduced by reducing the use of organic solvents, and the environmental load and working environment can be improved.
However, when styrene-butadiene copolymer rubber (SBR), which is a water-based binder mainly used for the negative electrode, is applied as it is to the positive electrode, the electrochemical resistance of the polymer is poor, and the charge / discharge characteristics tend to be deteriorated.

The present disclosure provides, in one or more embodiments, lithium obtained by an aqueous process using an aqueous binder, having charge and discharge characteristics equivalent to those of a positive electrode for a lithium ion secondary battery produced by a conventional non-aqueous process. Provided are a positive electrode for an ion secondary battery and a lithium ion secondary battery.

［式（Ｉ）中、Ｒ¹は、水素原子又はメチル基を示す。Ｒ²は、炭素数１以上６以下の直鎖又は分岐鎖のアルキル基、及び、－ＣＨ₂ＯＲ³から選ばれる少なくとも１種を示す。Ｒ³は、炭素数４以上６以下の直鎖又は分岐鎖のアルキル基を示す。Ｘは、－Ｏ－又は－ＮＨ－を示す。］

［式（ＩＩ）中、Ｒ¹は、水素原子又はメチル基を示し、Ｍは、水素原子又はカチオンを示す。］

［式（ＩＩＩ）中、Ｒ¹は、水素原子又はメチル基を示し、Ｘは、－Ｏ－又は－ＮＨ－を示す。Ｒ⁴は、－(ＣＨ₂)_nＯＨ、－Ｒ⁵ＳＯ₃Ｍ、－Ｒ⁶Ｎ（Ｒ⁷)（Ｒ⁸）及び－Ｒ⁶Ｎ⁺（Ｒ⁷）（Ｒ⁸）（Ｒ⁹）・Ｙ^-から選ばれる少なくとも１種を示す。ｎは、１以上４以下である。Ｒ⁵は、炭素数１以上５以下の直鎖又は分岐鎖のアルキレン基を示す。Ｍは、水素原子又はカチオンを示す。Ｒ⁶は、炭素数１以上４以下の直鎖又は分岐鎖のアルキレン基を示す。Ｒ⁷及びＲ⁸は同一又は異なり、炭素数１以上３以下の直鎖又は分岐鎖のアルキル基を示す。Ｒ⁹は、炭素数１以上３以下の直鎖又は分岐鎖のアルキル基を示す。Ｙ^-は、アニオンを示す。］ The present disclosure relates, in one aspect, to a positive electrode for a lithium ion secondary battery including a current collector and a mixture layer formed on the current collector, and the mixture layer has the following formula (I And at least one selected from a compound represented by the following formula (II), a compound represented by the following formula (III), and an unsaturated dibasic acid: A polymer particle containing a constituent unit (B) derived from the compound of (1) as a binder, and the content of the constituent unit (A) in all constituent units of the polymer particle is 50% by mass or more and 99.9% by mass or less A positive electrode for a lithium ion secondary battery (hereinafter referred to as "the positive electrode of the present disclosure"), wherein the content of the structural unit (B) in all the structural units of the polymer particle is 0.1% by mass or more and 20% by mass or less Say).

[In Formula (I), R ¹ represents a hydrogen atom or a methyl group. R ² represents at least one selected from a linear or branched alkyl group having 1 or more and 6 or less carbon atoms, and —CH ₂ OR ³ . R ³ represents a linear or branched alkyl group having 4 to 6 carbon atoms. X represents -O- or -NH-. ]

[In Formula (II), R ¹ represents a hydrogen atom or a methyl group, and M represents a hydrogen atom or a cation. ]

[In Formula (III), R ¹ represents a hydrogen atom or a methyl group, and X represents -O- or -NH-. R ⁴ is-(CH ₂ ) _n OH, -R ⁵ SO ₃ M, -R ⁶ N (R ⁷ ) (R ⁸ ) and -R ⁶ N ⁺ (R ⁷ ) (R ⁸ ) (R ⁹ ). Y ^- represents at least one member selected from. n is 1 or more and 4 or less. R ⁵ represents a linear or branched alkylene group having 1 to 5 carbon atoms. M represents a hydrogen atom or a cation. R ⁶ represents a linear or branched alkylene group having 1 to 4 carbon atoms. R ⁷ and R ⁸ are the same or different and each represents a linear or branched alkyl group having 1 to 3 carbon atoms. R ⁹ represents a linear or branched alkyl group having 1 to 3 carbon atoms. Y ^- represents an anion. ]

The present disclosure relates, in one aspect, to a method for producing the positive electrode of the present disclosure, which comprises applying a positive electrode active material and an aqueous slurry containing polymer particles used for the positive electrode of the present disclosure on a current collector and drying. The present invention relates to a method for producing a positive electrode for a lithium ion secondary battery, including the method.

The present disclosure relates, in one aspect, to a lithium ion secondary battery including the positive electrode of the present disclosure.

According to the present disclosure, in one aspect, a lithium ion di obtained by an aqueous process using an aqueous binder, having charge and discharge characteristics equivalent to those of a positive electrode for lithium ion secondary battery produced by a conventional non-aqueous process The effect that the positive electrode for the next battery can be provided can be exhibited.

FIG. 1 is a graph showing the results of charge and discharge tests of Example 1, Comparative Example 1 and Reference Example 1. FIG. 2 is a graph showing the results of the cyclic voltammetry test of Example 1. FIG. 3 is a graph showing the results of the cyclic voltammetry test of Comparative Example 1. FIG. 4 is a graph showing the results of the cyclic voltammetry test of Reference Example 1.

In the present disclosure, a positive electrode having a charge / discharge characteristic equivalent to that of a positive electrode for a lithium ion secondary battery produced by a conventional non-aqueous process can be obtained by an aqueous process by containing predetermined polymer particles in the positive electrode mixture layer. Based on the knowledge that

That is, the present disclosure relates, in one aspect, to a positive electrode for a lithium ion secondary battery including a current collector and a mixture layer formed on the current collector, wherein the mixture layer has the above formula The structural unit (A) derived from the compound represented by (I), and the compound represented by the above formula (II), the compound represented by the above formula (III), and at least an unsaturated dibasic acid A polymer particle containing a structural unit (B) derived from one type of compound is contained as a binder, and the content of the structural unit (A) in all the structural units of the polymer particle is 50% by mass or more and 99.9% by mass or less The positive electrode for a lithium ion secondary battery, wherein the content of the structural unit (B) in all the structural units of the polymer particle is 0.1% by mass or more and 20% by mass or less.

Although the details of the mechanism of the onset of effects of the present disclosure are not clear, the following can be presumed.
In the present disclosure, by containing predetermined polymer particles in the positive electrode mixture layer, it is possible to withstand a high voltage atmosphere in a charge and discharge field when the electrode of the present disclosure is used in a lithium ion secondary battery. This is considered to enable charging and discharging while suppressing the deterioration of the battery characteristics.
However, these are only estimates, and the present disclosure may not be interpreted as being limited to these mechanisms.

Hereinafter, the positive electrode for a lithium ion secondary battery of the present disclosure will be specifically described.

[Mixture layer]
The mixture layer used for the positive electrode of the present disclosure contains a binder. The binder plays a role in fixing the active material to the surface of the current collector. The binder may be a water based binder in one or more embodiments. An aqueous binder means the binder disperse | distributed to an aqueous medium. Examples of the aqueous medium include water such as distilled water, ion exchanged water, and ultrapure water.

(Polymer particles)
In the present disclosure, the polymer particles contained in the mixture layer as a binder include the structural unit (A) and the structural unit (B). The structural units (A) and (B) are each a structural unit derived from a monofunctional monomer of a compound described later. A monofunctional monomer refers to a monomer having one unsaturated bond.

<Constituent unit (A)>
The structural unit (A) is a structural unit derived from a compound represented by the following formula (I) (hereinafter, also referred to as “monomer (A)”). A monomer (A) may be used individually by 1 type, and may be used together 2 or more types.

In formula (I), R ¹ represents a hydrogen atom or a methyl group from the viewpoint of easiness of synthesis. R ² is at least one selected from a linear or branched alkyl group having 1 to 6 carbon atoms, and —CH ₂ OR ³ from the viewpoints of charge and discharge characteristics, affinity to an electrolyte, and binder physical properties Is more preferably a linear or branched alkyl group having 1 to 6 carbon atoms, and still more preferably a linear or branched alkyl group having 1 to 4 carbon atoms. R ³ represents a linear or branched alkyl group having 4 to 6 carbon atoms. X represents -O- or -NH-. In the present disclosure, R ¹ in the above formula (I), formula (II) described later, and formula (III) are each independently.

As a monomer (A), for example, methyl (meth) acrylate, ethyl acrylate, normal propyl (meth) acrylate, isopropyl (meth) acrylate, normal butyl (meth) acrylate, isobutyl (meth) acrylate, secondary butyl (meth) acrylate Alkyl esters (meth) acrylates such as tertiary butyl (meth) acrylate, normal pentyl (meth) acrylate, normal hexyl (meth) acrylate; cycloalkyl group-containing esters (meth) acrylates such as cyclohexyl (meth) acrylate; methyl ( Meta) acrylamide, ethyl (meth) acrylamide, normal propyl (meth) acrylamide, isopropyl (meth) acrylamide, normal butyl (meth) a Monofunctional (meth), such as lylamide, isobutyl (meth) acrylamide, secondary butyl (meth) acrylamide, tertiary butyl (meth) acrylamide, normal pentyl (meth) acrylamide, normal hexyl (meth) acrylamide, and cyclohexyl (meth) acrylamide Acrylamide; One or a combination of two or more selected from acrylamide; Among these, from the viewpoints of charge and discharge characteristics, affinity to electrolyte solution and binder physical properties, methyl methacrylate (MMA), ethyl methacrylate (EMA), normal butyl methacrylate (BMA), ethyl acrylate (EA) and normal butyl acrylate ( One or a combination of two or more selected from BA) is preferable. In the present disclosure, (meth) acrylate means methacrylate or acrylate, and (meth) acrylamide means methacrylamide or acrylamide.

The content of the structural unit (A) in all the structural units of the polymer particle in the present disclosure is 50% by mass or more, preferably 60% by mass or more, and 70% by mass or more from the viewpoint of easiness of synthesis. Preferably, 80% by mass or more is more preferable, 90% by mass or more is still more preferable, and from the same viewpoint, it is 99.9% by mass or less, preferably 99.5% by mass or less, and 99% by mass or less 98 mass% or less is more preferable, 97 mass% or less is still more preferable. More specifically, the content of the structural unit (A) is 50% by mass or more and 99.9% by mass or less, preferably 60% by mass or more and 99.5% by mass or less, and 70% by mass or more and 99% by mass The following is more preferable, 80 to 98 mass% is more preferable, and 90 to 97 mass% is still more preferable. The content of the structural unit (A) can be determined by a known analysis method or analyzer. When a structural unit (A) consists of a structural unit derived from two or more types of monomers (A), content of a structural unit (A) says those total content.

<Constituent unit (B)>
The structural unit (B) is a compound represented by the following formula (II) (hereinafter, also referred to as “monomer (B1)”), a compound represented by the following (III) (hereinafter, also referred to as “monomer (B2)” And a component unit derived from at least one compound (hereinafter also referred to as monomer (B)) selected from unsaturated dibasic acids (hereinafter also referred to as “monomer (B3)”), charge / discharge characteristics, electrolytic solution The structural unit (B) is preferably a structural unit derived from the monomer (B1) from the viewpoint of affinity to the binder and physical properties of the binder. A monomer (B) may be used individually by 1 type, and may be used together 2 or more types.

In the above formula (II), R ¹ is a hydrogen atom or a methyl group from the viewpoint of easiness of synthesis. M is a hydrogen atom or a cation from the viewpoint of charge / discharge characteristics, dispersion stability and binder physical properties. The cation is preferably at least one of an alkali metal ion and an ammonium ion from the viewpoint of charge and discharge characteristics, dispersion stability and binder physical properties, and more preferably at least one selected from ammonium ion, lithium ion, sodium ion and potassium ion Further, at least one of lithium ion and sodium ion is more preferable.

When M in the formula (II) is a cation, the monomer (B1) is, for example, an alkali (ammonia, sodium hydroxide, lithium hydroxide, potassium hydroxide, etc.) and a monomer in which M is a hydrogen atom; It may be a sum, or it may be one which is neutralized after becoming a constituent unit of a polymer obtained by polymerizing a monomer in which M is a hydrogen atom. From the viewpoint of controlling the polymerization reaction, it is preferable to be one which is neutralized after becoming a constituent unit of the polymer after polymerization.

Examples of the monomer (B1) include one or a combination of two or more selected from acrylic acid, methacrylic acid, and salts thereof. Examples of the salt include at least one selected from ammonium salt, sodium salt, lithium salt and potassium salt.

In Formula (III), R ¹ represents a hydrogen atom or a methyl group, and X represents -O- or -NH-. R ⁴ is-(CH ₂ ) _n OH, -R ⁵ SO ₃ M, -R ⁶ N (R ⁷ ) (R ⁸ ) and -R ⁶ N ⁺ (R ⁷ ) (R ⁸ ) (R ⁹ ). Y ^- represents at least one member selected from. n represents an average added mole number and is 1 or more and 4 or less. R ⁵ represents a linear or branched alkylene group having 1 to 5 carbon atoms. M represents a hydrogen atom or a cation. As a cation, the same thing as the cation of M in Formula (II) mentioned above is mentioned. In the present disclosure, M in Formula (II) and Formula (III) is each independent. R ⁶ represents a linear or branched alkylene group having 1 to 4 carbon atoms. R ⁷ and R ⁸ are the same or different and each represents a linear or branched alkyl group having 1 to 3 carbon atoms. R ⁹ represents a linear or branched alkyl group having 1 to 3 carbon atoms. Y ^- represents an anion. Examples of the anion include halide ions such as chloride ion, bromide ion and fluoride ion; sulfate ion; phosphate ion; and the like.

When M in the formula (III) is a cation, the monomer (B2) may be, for example, one obtained by neutralizing a monomer in which M is a hydrogen atom with an alkali, or M is a hydrogen atom. It may be a component unit of a polymer obtained by polymerizing a certain monomer and then neutralized. From the viewpoint of controlling the polymerization reaction, it is preferable to be one which is neutralized after becoming a constituent unit of the polymer after polymerization.

When X in the formula (III) is —O—, as the monomer (B2), a hydroxyl group-containing ester (eg, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate or the like) from the viewpoint of easiness of synthesis And at least one selected from nitrogen-containing esters (meth) acrylates such as meta) acrylates; and dimethylaminoethyl (meth) acrylates, dimethylaminopropyl (meth) acrylates, trimethylammonioethyl (meth) acrylates, etc .; At least one selected from hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate is preferred, and at least one of hydroxyethyl methacrylate and hydroxyethyl acrylate is more preferred.
When X in the formula (III) is —NH—, examples of the monomer (B2) include 2-acrylamido-2-methylpropanesulfonic acid (AMPS).

The monomer (B3) is an unsaturated dibasic acid, and includes at least one selected from unsaturated dibasic acids having 4 to 12 carbon atoms and salts thereof, from the viewpoint of easiness of synthesis. The carbon number is preferably 4 or more and 8 or less, and more preferably 4 or more and 6 or less.

As the monomer (B3), maleic acid, fumaric acid, citraconic acid, mesaconic acid, itaconic acid, 2-pentenedioic acid, 3-hexenedioic acid and salts thereof can be mentioned from the viewpoint of easiness of synthesis, At least one selected from maleic acid, fumaric acid, itaconic acid and salts thereof is preferable, and at least one of maleic acid and its salts is more preferable.

When the monomer (B3) is a salt of unsaturated dibasic acid, the salt is preferably at least one selected from ammonium salt, lithium salt, sodium salt and potassium salt, from the viewpoint of dispersion stability and binder physical properties, At least one of lithium salt and sodium salt is more preferred.

As the salt of the unsaturated dibasic acid of the monomer (B3), the unsaturated dibasic acid may be neutralized with an alkali, or may be neutralized after polymerization using the unsaturated dibasic acid. You may use what. From the viewpoint of controlling the polymerization reaction, it is preferable to be one which is neutralized after becoming a constituent unit of the polymer after polymerization.

The content of the structural unit (B) in all the structural units of the polymer particle in the present disclosure is 0.1% by mass or more, and 0.5% by mass or more, from the viewpoint of charge / discharge characteristics, dispersion stability and binder physical properties. The above is preferable, 1% by mass or more is more preferable, 2% by mass or more is further preferable, 3% by mass or more is more preferable, and from the same viewpoint, it is 20% by mass or less and preferably 15% by mass or less 10 mass% or less is more preferable, 8 mass% or less is more preferable, and 6 mass% or less is still more preferable. More specifically, the content of the structural unit (B) is 0.1% by mass to 20% by mass, preferably 0.5% by mass to 15% by mass, and 1% by mass to 10% by mass. The following is more preferable, 2 to 8 mass% is further preferable, and 3 to 6 mass% is further more preferable. The content of the structural unit (B) can be determined by a known analysis method or analyzer. When a structural unit (B) consists of a structural unit derived from two or more types of monomers (B), content of a structural unit (B) says those total content.

The ratio (A / B) of the content of the structural unit (A) to the content of the structural unit (B) in the polymer particle in the present disclosure is 500 or less from the viewpoint of charge / discharge characteristics, dispersion stability and binder physical properties Preferably, 100 or less is more preferable, 50 or less is further preferable, and 5 or more is preferable, 10 or more is more preferable, and 20 or more is more preferable from the viewpoint of dispersion stability and binder physical properties. More specifically, the content ratio (A / B) is preferably 5 or more and 500 or less, more preferably 10 or more and 100 or less, and still more preferably 20 or more and 50 or less.

The polymer particle in the present disclosure may contain other constituent units other than the constituent unit (A) and the constituent unit (B) as long as the effects of the present disclosure are not impaired. The other structural unit is a structural unit (hereinafter also referred to as “structural unit (C)”) of a monomer copolymerizable with the monomers (A) and (B) (hereinafter also referred to as “monomer (C)”) I hope there is. The monomers (C) may be used alone or in combination of two or more. As a monomer (C), a crosslinking | crosslinked monomer is mentioned, for example.

The total content of the structural units (A) and (B) in all the structural units of the polymer particle in the present disclosure is preferably 80% by mass or more from the viewpoint of charge / discharge characteristics, affinity to the electrolyte and binder physical properties, 90 mass% or more is more preferable, and 100 mass% is further more preferable.

The polymer particle in the present disclosure does not include a structural unit derived from a crosslinkable monomer in one or more embodiments.
The polymer particle in the present disclosure, in one or more other embodiments, includes a structural unit derived from a crosslinkable monomer. Examples of the crosslinkable monomer include crosslinkable monomers having two or more vinyl groups, and specific examples include polyfunctional (meth) acrylates. When the polymer particle in the present disclosure includes a structural unit derived from a polyfunctional (meth) acrylate, the content of the structural unit derived from the polyfunctional (meth) acrylate in all the structural units of the polymer particle in the present disclosure is one or more In the embodiment, from the viewpoint of battery characteristics, 2% by mass or less is preferable, 1% by mass or less is more preferable, and less than 0.5% by mass is more preferable. In addition, the content of the structural unit derived from the polyfunctional (meth) acrylate in all the structural units of the polymer particle in the present disclosure is, in one or more other embodiments, the structural unit (A) and the structural unit (A) 2 mol% or less is preferable with respect to the sum total mole number of a structural unit (B), 1 mol% or less is more preferable, and 0.5 mol% or less is still more preferable.

[Method of producing polymer particles]
The polymer particles in the present disclosure can be produced, for example, by copolymerizing the monomer (A) and the monomer (B), and optionally, the other monomer (C). That is, the present disclosure relates, in one aspect, to a method for producing a polymer particle, which comprises a polymerization step of polymerizing a monomer mixture comprising the monomer (A) and the monomer (B), and optionally the monomer (C). Examples of the polymerization method include known polymerization methods such as an emulsion polymerization method, a solution polymerization method, a suspension polymerization method, and a bulk polymerization method, and the emulsion polymerization method is preferable from the viewpoint of easiness of production of the polymer.

In the present disclosure, the content of the structural unit (A) in all the structural units of the polymer particles can be regarded as the ratio of the amount of the monomer (A) used to the total amount of monomers used for polymerization. The content of the structural unit (B) in all the structural units of the polymer particles can be regarded as the ratio of the amount of the monomer (B) used to the total amount of monomers used for the polymerization. The ratio (A / B) of the content of the structural unit (A) to the structural unit (B) should be regarded as the ratio of the amount of monomer (A) used to the amount of monomer (B) in the total amount of monomers used for polymerization. Can. The total content of the structural unit (A) and the structural unit (B) in all the structural units of the polymer particle should be regarded as the ratio of the total amount of monomer (A) and monomer (B) to the total amount of monomers used for polymerization. Can. The content of the structural unit (C) in the polymer particles can be regarded as the ratio of the amount of the monomer (C) used to the total number of moles of the monomers (A) and (B) used for the polymerization.

Examples of the emulsion polymerization method include known methods using an emulsifier and methods using substantially no emulsifier, so-called soap-free emulsion polymerization method, and from the viewpoint of charge / discharge characteristics and reduction of ion resistance of positive electrode, soap-free Emulsion polymerization is preferred. As the polymer particle in the present disclosure, for example, a polymer obtained by emulsion polymerization, preferably soap-free emulsion polymerization, of a monomer mixture containing the monomer (A), the monomer (B) and, if necessary, the other monomer (C) Particles are included.

When an emulsifying agent is used in the polymerization step, a water-soluble emulsifying agent is preferable as the emulsifying agent from the viewpoint of polymerization stability. Examples of the water-soluble emulsifier include at least one surfactant selected from an anionic surfactant, a nonionic surfactant and a reactive surfactant from the viewpoint of polymerization stability, and the binding property is lowered. From the viewpoint of suppression, reactive surfactants are preferred. A reactive surfactant refers to a surfactant that is incorporated into the polymer during polymerization.

Examples of anionic surfactants include alkyl aryl sulfonates such as sodium dodecyl benzene sulfonate; alkyl sulfonates such as sodium lauryl sulfonate; alkyl sulfates such as sodium lauryl sulfate; polyoxyethylene lauryl ether Anionic surfactants having a polyoxyethylene group such as sodium sulfate and sodium polyoxyethylene nonylphenyl ether sulfate; and the like.

Examples of nonionic surfactants include polyoxyethylene alkylphenyl ethers such as polyoxyethylene nonylphenyl ether; and polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether; and the like.

Examples of the reactive surfactant include reactive emulsifiers having a vinyl polymerizable double bond in the molecule, and specific examples include polyoxyalkylene alkenyl ether and the like.

The amount of the emulsifier used for the emulsion polymerization is preferably 0.05% by mass or less, more preferably 0.02% by mass or less, and more preferably 0.01% by mass or less based on the total amount of monomers from the viewpoint of suppressing the decrease in binding property. Is more preferred, and substantially 0% by weight is even more preferred. In the present disclosure, the amount of emulsifier used for emulsion polymerization can be the amount of surfactant used in the polymerization step.

A polymerization initiator can be used in the polymerization step. From the viewpoint of polymerization stability, a water-soluble polymerization initiator is preferable as the polymerization initiator. Examples of the water-soluble polymerization initiator include, from the viewpoint of polymerization stability, persulfates such as potassium persulfate and ammonium persulfate; peroxides such as hydrogen peroxide and t-butyl hydroperoxide; Persulfates are preferred, and ammonium persulfate is more preferred.

The amount of the polymerization initiator used in the polymerization step is preferably 0.01 mol% or more, more preferably 0.05 mol% or more, still more preferably 0.1 mol% or more, and 5 mol, with respect to the total amount of monomers. % Or less is preferable, 3 mol% or less is more preferable, and 1 mol% or less is more preferable.

In the polymerization step, water such as ion exchanged water can be used as a solvent. The amount of water used in the polymerization step can be, for example, 40 parts by mass or more and 1500 parts by mass or less (6.25 to 71.4% by mass in terms of polymerization solid content) with respect to 100 parts by mass of the total amount of monomers.

In the polymerization step, a reducing agent that can be used in combination with the polymerization initiator can be used. Examples of the reducing agent include sulfite, pyrosulfite and the like.

A chain transfer agent can be used in the polymerization step. As a chain transfer agent, a known chain transfer agent can be used, and examples thereof include isopropyl alcohol, n-dodecyl mercaptan, octyl mercaptan, tert-butyl mercaptan, thioglycolic acid, thiomalic acid, thiosalicylic acid, mercaptoethanol and the like. Mercapto compounds are mentioned.

The polymerization conditions may be appropriately set according to the type of polymerization initiator, monomer, and solvent to be used. For example, the polymerization reaction can be carried out in a nitrogen atmosphere at a temperature range of 60 to 100 ° C., and the polymerization time can be set to, for example, 0.5 to 20 hours.

The arrangement of each constituent unit constituting the polymer particle in the present disclosure may be random, block or graft. Compositional analysis of the polymer can be performed by, for example, NMR spectrum, UV-vis spectrum, IR spectrum, affinity chromatography and the like.

The average particle diameter of the polymer particles in the present disclosure is preferably 0.2 μm or more, more preferably 0.3 μm or more, and preferably 1 μm or less from the viewpoints of charge / discharge characteristics, affinity to the electrolyte, and binder physical properties. 0.9 micrometer or less is more preferable, 0.8 micrometer or less is further more preferable, and less than 0.7 micrometer is still more preferable. More specifically, the average particle diameter of the polymer particles is preferably 0.2 μm or more and 1 μm or less, more preferably 0.2 μm or more and 0.9 μm or less, still more preferably 0.2 μm or more and 0.8 μm or less, and 0.2 μm or more More preferably, it is less than 0.7 μm, and more preferably, more than 0.3 μm and less than 0.7 μm.

The content of the polymer particles in the mixture layer in the present disclosure is preferably 0.5% by mass or more, more preferably 1% by mass or more, and further preferably 1.5% by mass or more from the viewpoint of binding property and battery capacity. From the same viewpoint, 15% by mass or less is preferable, 10% by mass or less is more preferable, and 5% by mass or less is more preferable. More specifically, 0.5 mass% or more and 15 mass% or less are preferable, as for content of the polymer particle in a mixture layer, 1 mass% or more and 10 mass% or less are more preferable, and 1.5 mass% or more 5 % Or less is more preferable.

The surface tension of the polymer particle dispersion in which the polymer particles in the present disclosure are dispersed in an aqueous medium is preferably 55 mN / m or more, more preferably 60 mN / m or more, and 72 mN / m from the viewpoint of improving binder physical properties and battery characteristics. The following are preferred. The surface tension can be measured by the method described in the examples. More specifically, the surface tension of the polymer particle dispersion is preferably 55 mN / m or more and 72 mN / m or less, and more preferably 60 mN / m or more and 72 mN / m or less.

The glass transition point (Tg) of the polymer particles in the present disclosure is preferably −30 ° C. or higher, more preferably −20 ° C. or higher, from the viewpoint of binding property and battery characteristics, and the same viewpoint Therefore, 30 ° C. or less is preferable, 25 ° C. or less is more preferable, and 20 ° C. or less is more preferable. More specifically, the Tg of the polymer particles is preferably −30 ° C. or more and 30 ° C. or less, more preferably −20 ° C. or more and 25 ° C. or less, and still more preferably −20 ° C. or more and 20 ° C. or less.

As one embodiment of the mixture layer in the present disclosure, for example, one containing the above-described polymer particle, positive electrode active material, and optional components (for example, conductive material, thickener) optionally added It can be mentioned. The mass ratio of each component contained in the mixture layer can be arbitrarily adjusted according to the use suitability of the battery.

(Positive electrode active material)
The positive electrode active material may be any active material capable of storing and releasing lithium and capable of charge and discharge reaction, for example, lithium iron phosphate, lithium such as LiCoO ₂ , LiNiO ₂ , Li ₂ MnO _{4 and the} like Metal complex oxides can be mentioned. These compounds may be partially element-substituted. The average particle diameter of the positive electrode active material can be, for example, 2 μm or more and 40 μm or less.

The content of the positive electrode active material in the mixture layer in the present disclosure is preferably 80% by mass or more, more preferably 90% by mass or more, from the viewpoint of increasing battery capacity, and to the current collector of the mixture layer. From the viewpoint of improving the binding property, 99% by mass or less is preferable, and 98% by mass or less is more preferable. More specifically, 80 mass% or more and 99 mass% or less are preferable, and, as for content of a positive electrode active material, 90 mass% or more and 98 mass% or less are more preferable.

(Conductive material)
The conductive material is for performing charge / discharge reaction efficiently to enhance conductivity. Examples of the conductive material include carbon materials such as acetylene black, ketjen black, and graphite, and these can be used singly or in combination of two or more.

The content of the conductive material in the mixture layer in the present disclosure is preferably 0.5% by mass or more, more preferably 1% by mass or more, from the viewpoint of conductivity improvement, and 10% from the viewpoint of battery capacity improvement. % Or less is preferable and 5 mass% or less is more preferable. More specifically, 0.5 mass% or more and 10 mass% or less are preferable, and, as for content of a electrically conductive material, 1 mass% or more and 5 mass% or less are more preferable.

(Thickener)
As the thickener, for example, polysaccharide thickeners, alginic acid, carboxymethylcellulose, starch, polyacrylic acid, polyvinyl alcohol, polyvinyl pyrrolidone and the like can be mentioned. Among them, carboxymethyl cellulose is preferable from the viewpoint of assisting the binder action of the polymer particles.

The content of the thickener in the mixture layer in the present disclosure is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and 0.8% by mass from the viewpoint of binding property and battery characteristics. The above is more preferable, 10% by mass or less is preferable, 8% by mass or less is more preferable, and 5% by mass or less is still more preferable. More specifically, the content of the thickener is preferably 0.1 mass% to 10 mass%, more preferably 0.5 mass% to 8 mass%, and 0.8 mass% to 5 mass%. The following is more preferable.

(binder)
The mixture layer in the present disclosure can further include conventionally known binders as the binder component in addition to the above-described polymer particles.

[Current collector]
As a collector used for the positive electrode of this indication, it can select from the material which has electroconductivity, for example, metal foils, such as copper foil, aluminum foil, stainless steel foil, etc. are mentioned.

[Method of manufacturing positive electrode for lithium ion secondary battery]
The positive electrode of the present disclosure is prepared, for example, by preparing an aqueous slurry (positive electrode mixture paste) containing the above-described positive electrode active material, the above-described polymer particles, and an aqueous medium described later, and applying this aqueous slurry to a current collector. It is obtained by drying out the aqueous medium in the slurry. That is, the present disclosure provides, in one aspect, a method for producing a positive electrode for a lithium ion secondary battery, including the steps of applying an aqueous slurry containing the above-described positive electrode active material and the above-described polymer particles onto a current collector and drying. Hereinafter, the present invention relates to “the manufacturing method of the present disclosure”.

The production method of the present disclosure can further include the step of blending the polymer particles, the positive electrode active material, and an aqueous medium to prepare the aqueous slurry (blending step). The mixing can be performed using, for example, a known mixing device such as a stirrer, a disper, or a homomixer. The compounding quantity of each component in the said compounding process can be made to be the same as that of content of each component of the above-mentioned compound material layer.

The production method of the present disclosure can include a polymerization step of polymerizing a monomer mixture containing the monomer (A) and the monomer (B), and optionally the monomer (C) to obtain polymer particles. The polymerization method in the polymerization step of the production method of the present disclosure, the types of each component that can be used for polymerization, and the amount thereof to be used can be the same as the polymerization step of the above-described polymer particle production method.

(Aqueous medium)
Examples of the aqueous medium include water such as ion exchange water, distilled water, and ultrapure water. Examples of the form of the polymer particles present in the aqueous slurry include a polymer particle dispersion in which the polymer particles are dispersed in an aqueous medium, or a polymer particle emulsion in which the polymer particles are emulsified and dispersed in water. . As the polymer particle dispersion, for example, a mixed solution containing polymer particles obtained by the above-mentioned emulsion polymerization method can be used as it is.

(Optional ingredient)
The aqueous slurry may contain optional components other than the polymer particles and the aqueous medium as long as the effects of the present disclosure are not impaired. Examples of optional components include surfactants, the above-mentioned thickeners, antifoaming agents, neutralizing agents and the like.

As surfactant, well-known surfactant is mentioned, For example, surfactant which may be used as an emulsifier mentioned above may be sufficient. The content of the surfactant in the aqueous slurry is preferably 0.05% by mass or less, and more preferably 0.02% by mass or less, based on the total solid content of the aqueous slurry, from the viewpoint of improving binder physical properties and battery characteristics. Preferably, 0.01% by weight or less is more preferable, and substantially 0% by weight is even more preferable. In the present disclosure, the content of surfactant in the aqueous slurry also includes a surfactant derived from an emulsifier used in emulsion polymerization.

Lithium-ion rechargeable battery
The present disclosure relates, in one aspect, to a lithium ion secondary battery (hereinafter, also referred to as “the lithium ion secondary battery of the present disclosure”) including the positive electrode of the present disclosure. As an embodiment of the lithium ion secondary battery of the present disclosure, one having the positive electrode, the negative electrode, the electrolytic solution and the separator of the present disclosure can be mentioned. The negative electrode, the electrolytic solution and the separator may not be particularly limited, and known ones can be used.

In the lithium ion secondary battery of the present disclosure, an operation of charging to a voltage of 3.0 V to 4.2 V at a current of 0.5 C and discharging to a voltage of 4.2 V to 3 V at a current of 0.5 C under an environment of 30 ° C. The capacity retention ratio after 50 cycles is preferably 60% or more, more preferably 80% or more, with respect to the capacity (100%) of the first cycle, from the viewpoint of prolonging the life of the battery. % Or more is more preferable.

［式（Ｉ）中、Ｒ¹は、水素原子又はメチル基を示す。Ｒ²は、炭素数１以上６以下の直鎖又は分岐鎖のアルキル基、及び、－ＣＨ₂ＯＲ³から選ばれる少なくとも１種を示す。Ｒ³は、炭素数４以上６以下の直鎖又は分岐鎖のアルキル基を示す。Ｘは、－Ｏ－又は－ＮＨ－を示す。］

［式（ＩＩ）中、Ｒ¹は、水素原子又はメチル基を示し、Ｍは、水素原子又はカチオンを示す。］

［式（ＩＩＩ）中、Ｒ¹は、水素原子又はメチル基を示し、Ｘは、－Ｏ－又は－ＮＨ－を示す。Ｒ⁴は、－(ＣＨ₂)_nＯＨ、－Ｒ⁵ＳＯ₃Ｍ、－Ｒ⁶Ｎ（Ｒ⁷)（Ｒ⁸）及び－Ｒ⁶Ｎ⁺（Ｒ⁷）（Ｒ⁸）（Ｒ⁹）・Ｙ^-から選ばれる少なくとも１種を示す。ｎは、１以上４以下である。Ｒ⁵は、炭素数１以上５以下の直鎖又は分岐鎖のアルキレン基を示す。Ｍは、水素原子又はカチオンを示す。Ｒ⁶は、炭素数１以上４以下の直鎖又は分岐鎖のアルキレン基を示す。Ｒ⁷及びＲ⁸は同一又は異なり、炭素数１以上３以下の直鎖又は分岐鎖のアルキル基を示す。Ｒ⁹は、炭素数１以上３以下の直鎖又は分岐鎖のアルキル基を示す。Ｙ^-は、アニオンを示す。］ The present disclosure further relates to one or more embodiments described below.
<1> A positive electrode for a lithium ion secondary battery, comprising: a current collector; and a mixture layer formed on the current collector,
The mixture layer includes a constituent unit (A) derived from a compound represented by the following formula (I), a compound represented by the following formula (II), a compound represented by the following formula (III), and A polymer particle containing a structural unit (B) derived from at least one compound selected from saturated dibasic acids as a binder,
The content of the structural unit (A) in all the structural units of the polymer particle is 50% by mass or more and 99.9% by mass or less,
The positive electrode for lithium ion secondary batteries in which content of the structural unit (B) in all the structural units of the said polymer particle is 0.1 mass% or more and 20 mass% or less.

[In Formula (I), R ¹ represents a hydrogen atom or a methyl group. R ² represents at least one selected from a linear or branched alkyl group having 1 or more and 6 or less carbon atoms, and —CH ₂ OR ³ . R ³ represents a linear or branched alkyl group having 4 to 6 carbon atoms. X represents -O- or -NH-. ]

[In Formula (II), R ¹ represents a hydrogen atom or a methyl group, and M represents a hydrogen atom or a cation. ]

[In Formula (III), R ¹ represents a hydrogen atom or a methyl group, and X represents -O- or -NH-. R ⁴ is-(CH ₂ ) _n OH, -R ⁵ SO ₃ M, -R ⁶ N (R ⁷ ) (R ⁸ ) and -R ⁶ N ⁺ (R ⁷ ) (R ⁸ ) (R ⁹ ). Y ^- represents at least one member selected from. n is 1 or more and 4 or less. R ⁵ represents a linear or branched alkylene group having 1 to 5 carbon atoms. M represents a hydrogen atom or a cation. R ⁶ represents a linear or branched alkylene group having 1 to 4 carbon atoms. R ⁷ and R ⁸ are the same or different and each represents a linear or branched alkyl group having 1 to 3 carbon atoms. R ⁹ represents a linear or branched alkyl group having 1 to 3 carbon atoms. Y ^- represents an anion. ]

The content of the structural unit (A) in all the structural units of the <2> polymer particles is 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, and further 80% by mass or more Preferably, 90 mass% or more is still more preferable, The positive electrode for lithium ion secondary batteries as described in <1>.
The content of the structural unit (A) in all the structural units of the <3> polymer particles is 99.9% by mass or less, preferably 99.5% by mass or less, and more preferably 99% by mass or less, 98% by mass The positive electrode for a lithium ion secondary battery according to <1> or <2>, wherein% or less is more preferable, and 97% by mass or less is still more preferable.
The content of the structural unit (A) in all the structural units of the <4> polymer particles is 50% by mass or more and 99.9% by mass or less, preferably 60% by mass or more and 99.5% by mass or less, and 70% by mass % Or more and 99% by mass or less is more preferable, 80% by mass or more and 98% by mass or less is further preferable, and 90% by mass or more and 97% by mass or less is still more preferable. Lithium ion according to any of <1> to <3> Positive electrode for secondary battery.
The content of the structural unit (B) in all the structural units of the <5> polymer particles is 0.1% by mass or more, preferably 0.5% by mass or more, and more preferably 1% by mass or more, 2% by mass % Or more is more preferable, and 3 mass% or more is further preferable, The positive electrode for lithium ion secondary batteries in any one of <1> to <4>.
The content of the structural unit (B) in all the structural units of the <6> polymer particles is 20% by mass or less, preferably 15% by mass or less, more preferably 10% by mass or less, and further 8% by mass or less The positive electrode for a lithium ion secondary battery according to any one of <1> to <5>, preferably 6% by mass or less.
The content of the structural unit (B) in all the structural units of the <7> polymer particles is 0.1% by mass or more and 20% by mass or less, preferably 0.5% by mass or more and 15% by mass or less, and 1% by mass % Or more and 10% by mass or less is more preferable, 2% by mass or more and 8% by mass or less is further preferable, and 3% by mass or more and 6% by mass or less is still more preferable. Lithium ion according to any of <1> to <6> Positive electrode for secondary battery.
The ratio (A / B) of the content of the structural unit (A) to the content of the structural unit (B) in the polymer particles is preferably 500 or less, more preferably 100 or less, and still more preferably 50 or less, The positive electrode for lithium ion secondary batteries in any one of <1> to <7>.
The ratio (A / B) of the content of the structural unit (A) to the content of the structural unit (B) in the polymer particles is preferably 5 or more, more preferably 10 or more, and still more preferably 20 or more. The positive electrode for lithium ion secondary batteries in any one of <1> to <8>.
The ratio (A / B) of the content of the structural unit (A) to the content of the structural unit (B) in the polymer particles is preferably 5 or more and 500 or less, more preferably 10 or more and 100 or less, and 20 or more 50 or less is still more preferable, The positive electrode for lithium ion secondary batteries in any one of <1> to <9>.
<11> The lithium according to any one of <1> to <10>, wherein a surface tension of the polymer particle dispersion in which the polymer particles are dispersed in an aqueous medium is preferably 55 mN / m or more, more preferably 60 mN / m or more. Positive electrode for ion secondary battery.
<12> The positive electrode for a lithium ion secondary battery according to any one of <1> to <11>, wherein the surface tension of the polymer particle dispersion is preferably 72 mN / m or less.
The surface tension of the <13> polymer particle dispersion is preferably 55 mN / m or more and 72 mN / m or less, and more preferably 60 mN / m or more and 72 mN / m or less, The lithium ion according to any one of <1> to <12> Positive electrode for secondary battery.
<14> The lithium according to any one of <1> to <13>, wherein the total content of the structural unit (A) and the structural unit (B) in all the structural units of the polymer particle is 80% by mass or more. Positive electrode for ion secondary battery.
<15> In the above formula (I), R ¹ is a hydrogen atom or a methyl group, R ² is a linear or branched alkyl group having 1 to 6 carbon atoms, and X is —O—
The constituent unit B is a constituent unit derived from the compound represented by the formula (II), and in the formula (II), R ¹ is a hydrogen atom or a methyl group, and M is a hydrogen atom or a cation. The positive electrode for lithium ion secondary batteries in any one of <1> to <14>.
<16> The polymer particle is selected from a compound represented by the formula (I), a compound represented by the formula (II), a compound represented by the formula (III), and an unsaturated dibasic acid <14> for a lithium ion secondary battery according to any one of <1> to <15>, which is a polymer particle obtained by emulsion polymerization of a monomer mixture containing at least one compound of the present invention and a polyfunctional monomer selectively. Positive electrode.
<17> The amount of emulsifier used for the above-mentioned emulsion polymerization is preferably 0.05% by mass or less, more preferably 0.02% by mass or less, still more preferably 0.01% by mass or less, based on the total amount of monomers. The positive electrode for a lithium ion secondary battery according to <16>, wherein 0% by mass is further more preferable.
<18> The positive electrode for a lithium ion secondary battery according to <16> or <17>, wherein the emulsion polymerization is soap-free emulsion polymerization.
The <19> polymer particle is a positive electrode for lithium ion secondary batteries in any one of <1> to <18> which does not contain the structural | constituent unit derived from a crosslinkable monomer.
0.2 micrometer or more is preferable and, as for the average particle diameter of a <20> polymer particle, the positive electrode for lithium ion secondary batteries in any one of <1> to <19> more preferable than 0.3 micrometer.
The average particle diameter of the <21> polymer particles is preferably 1 μm or less, more preferably 0.9 μm or less, still more preferably 0.8 μm or less, still more preferably less than 0.7 μm, any of <1> to <20> A positive electrode for a lithium ion secondary battery according to any one of the above.
The average particle diameter of the <22> polymer particles is preferably 0.2 μm or more and 1 μm or less, more preferably 0.2 μm or more and 0.9 μm or less, still more preferably 0.2 μm or more and 0.8 μm or less, and more than 0.2 μm or more. The positive electrode for a lithium ion secondary battery according to any one of <1> to <21>, more preferably less than 7 μm, and still more preferably more than 0.3 μm and less than 0.7 μm.
0.5 mass% or more is preferable, as for content of the polymer particle in a <23> compound material layer, 1 mass% or more is more preferable, 1.5 mass% or more is still more preferable, <1> to <22> The positive electrode for lithium ion secondary batteries as described in any one.
15 mass% or less is preferable, as for content of the polymer particle in a <24> compound material layer, 10 mass% or less is more preferable, 5 mass% or less is still more preferable, It is described in either of <1> to <23> Positive electrode for lithium ion secondary batteries.
The content of the polymer particles in the <25> composite material layer is preferably 0.5 mass% to 15 mass%, more preferably 1 mass% to 10 mass%, and 1.5 mass% to 5 mass%. The positive electrode for a lithium ion secondary battery according to any one of <1> to <24>, further preferably.
It is a manufacturing method of the positive electrode for lithium ion secondary batteries in any one of <26><1> to <25>, Comprising:
Applying a positive electrode active material, and an aqueous slurry containing polymer particles used for a positive electrode for a lithium ion secondary battery according to any one of <1> to <25> onto a current collector and drying the lithium The manufacturing method of the positive electrode for ion secondary batteries.
<27> A lithium ion secondary battery including the positive electrode for a lithium ion secondary battery according to any one of <1> to <25>.

Hereinafter, the present disclosure will be described by way of examples, but the present disclosure is not limited thereto.

1. Measurement of each parameter [Measurement of average particle size of polymer particles]
The average particle diameter of the polymer particles is measured with a dispersion medium (water) at room temperature and until the predetermined light amount range of the device is reached using a particle size measurement device of laser diffraction method (LA-920 manufactured by Horiba, Ltd.) did. The results are shown in Table 1.

[Measurement of surface tension]
A polymer particle dispersion adjusted to 20 ° C. (a solution diluted with pure water so as to be 0.03% by mass as solid content) is placed in a petri dish, and is subjected to the Wilhelmy method (a method of immersing a platinum plate and pulling it up at a constant speed) The surface tension was measured using a surface tension meter ("CBVP-Z" manufactured by Kyowa Interface Chemicals Co., Ltd.). The results are shown in Table 1.

[Measurement of glass transition point (Tg)]
The polymer particle dispersion was dried at 40 ° C. for 3 days to obtain a 1 mm thick film. The film was vacuum dried in a vacuum dryer at 80 ° C. for 12 hours. The obtained film-like resin was measured using a differential scanning calorimeter ("DSC7000X" manufactured by Hitachi High-Tech Science Co., Ltd.) at a measurement temperature of -80 ° C to 180 ° C and a temperature rising rate of 5 ° C / minute according to JIS K7121. The Tg was measured and the results are shown in Table 1.

2. Preparation of polymer particle dispersions a, b, d to h and non-aqueous binder c For preparation of polymer particle dispersions a to d shown in Table 1, the following raw materials were used.
<Monomer (A)> [The following R ¹ , R ² and X mean the symbols in the formula (I)]
MMA: methyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.) (R ¹ : CH ₃ , R ² : CH ₃ , X: O)
EA: Ethyl acrylate (manufactured by Wako Pure Chemical Industries, Ltd.) (R ¹ : H, R ² : C ₂ H ₅ , X: O)
BA: (manufactured by Wako Pure Chemical Industries, Ltd.) Butyl acrylate ^{(R 1: H, R 2} : C 4 H 9, X: O)
<Monomer (B)>
AA: acrylic acid (manufactured by Wako Pure Chemical Industries, Ltd.) (R ¹ : H, M: H) [R ¹ , M means a symbol in the formula (II)]
AMPS: 2-acrylamido-2-methylpropane sulfonic acid (manufactured by Tokyo Kasei Kogyo Co., ^{Ltd.) (R 1: H, X} : -NH-, R 4: -C (CH 3) 2 CH 2 -SO 3 H) [R ¹ , X and R ⁴ mean the symbols in formula (III)]
<Monomer (C)>
EGDMA: ethylene glycol dimethacrylate (manufactured by Wako Pure Chemical Industries)
<Polymerization initiator>
APS: ammonium persulfate <neutralizing salt>
Na: Sodium <Emulsifier>
Sodium dodecyl benzene sulfonate

(Polymer particle dispersion a)
First, 74 g of MMA as monomer (A) and 120 g of EA, 6 g of AA as monomer (B), and 340 g of ion-exchanged water are placed in a four-neck separable flask made of 1 L glass and under nitrogen atmosphere for a fixed time Stir for 0.5 h). Then, after raising the temperature of the reaction solution in the flask to about 70 ° C., a polymerization initiator solution in which 1 g of APS is dissolved in 10 g of ion exchanged water is added to the flask, and the reaction solution in the flask is at about 70-75 ° C. Polymerization and aging were carried out by holding for 6 hours to obtain a polymer particle dispersion. Thereafter, the polymer particle dispersion in the flask is cooled to room temperature, neutralized by adding 29.14 g of 1N aqueous NaOH solution, and then aggregates are removed using a 200 mesh filter cloth to a concentration of about 40 mass%. The mixture was concentrated to obtain polymer particle dispersion a. The amounts and types of the respective components used for the preparation of polymer particle dispersion a are shown in Table 1.

(Polymer particle dispersion d, f, g, h)
The same as polymer particle dispersion a except that the monomers (A) and (B) to be the constitutional units shown in Table 1 were changed, and the kind of the neutralization salt was changed as shown in Table 1 Polymer particle dispersions d, f, g and h were obtained by the method. The amounts and types of the respective components used for the preparation of the respective polymer particle dispersions obtained are shown in Table 1.

(Polymer particle dispersion e)
194 g of EA as the monomer (A), 6 g of AA as the monomer (B), 1.0 g of EGDMA as the monomer (C) (0.5 mol% with respect to the total number of moles of the monomers (A) and (B)) 340 g of exchange water was placed in a 1 L glass four-neck separable flask with an inner volume of 1. The mixture was stirred under a nitrogen atmosphere for a fixed time (0.5 hours). Then, after raising the temperature of the reaction solution in the flask to about 70 ° C., a polymerization initiator solution in which 1 g of APS is dissolved in 10 g of ion exchanged water is added to the flask, and the reaction solution in the flask is at about 70-75 ° C. Polymerization and aging were carried out by holding for 6 hours to obtain a polymer particle dispersion. Thereafter, the polymer particle dispersion in the flask is cooled to room temperature, neutralized by adding 29.14 g of 1 N aqueous LiOH solution, and then the aggregate is removed using a 200 mesh filter cloth to a concentration of 30 to 35% by mass The solution was concentrated to a degree to obtain a polymer particle dispersion e. The amounts and types of the respective components used for the preparation of polymer particle dispersion e are shown in Table 1.

(Polymer particle dispersion b)
The following SBR was used for the polymer particle dispersion b.
SBR: Styrene butadiene rubber (manufactured by Nippon Zeon, "BM-400B", solid content 40% by mass)

(Non-aqueous binder c)
The following PVDF was used for the non-aqueous binder c.
PVDF: polyvinylidene fluoride solution in N-methylpyrrolidone (Kureha company, “KF polymer L # 1120”, solid content 12% by mass)

3. Preparation of Positive Electrode for Lithium Ion Secondary Battery (Examples 1 to 6, Comparative Example 1 and Reference Example 1)
(Positive electrode of Example 1)
A conductive material (acetylene black, manufactured by Denka, “Li-100”) 0.33 g and 1.5% of a thickener (carboxymethylcellulose sodium, manufactured by Wako Pure Chemical Industries, Ltd.) aqueous solution 4.4 g and a positive electrode active material (“NCM523” Made by Nippon Chemical Industrial Co., Ltd., composition: LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ) 10.23 g is mixed to prepare a slurry [1], and then 1.5% carboxymethylcellulose sodium (CMC) is added to the slurry [1]. A slurry [2] was prepared by mixing 2.93 g of water and 1.52 g of water. Next, 0.83 g of the prepared polymer particle dispersion a was mixed to prepare a positive electrode mixture paste. The contents (in terms of solid content) of the respective components in the positive electrode mixture paste are shown in Table 2. "Awatori Neritaro (ARV-310)" was used for mixing of each component.
Next, the positive electrode material mixture paste is coated on a 10 μm thick stainless steel foil (made by As One) so that the positive electrode capacity density is 1.0 mAh / cm ^2, and a vacuum dryer is used for 12 hours at 100 ° C. It dried and the positive electrode of Example 1 by which the compound material layer was formed on the collector was produced.

(Positive electrode of Examples 2 to 6)
The positive electrodes of Examples 2 to 6 were produced in the same manner as in Example 1 except that the polymer particle dispersion shown in Table 2 was used as a binder.

(Positive electrode of Comparative Example 1)
A positive electrode of Comparative Example 1 was produced in the same manner as Example 1, except that polymer particle dispersion b was used instead of polymer particle dispersion a. The content (in terms of solid content) of each component in the positive electrode mixture paste of Comparative Example 1 is shown in Table 2.

(Positive electrode of Reference Example 1)
0.33 g of a conductive material (acetylene black, manufactured by Denka, “HS-100”), 3.5 g of a non-aqueous binder c, and a positive electrode active material (“NCM523”, manufactured by Nippon Chemical Industrial Co., Ltd., composition: LiNi _0.5 Co _0.2 Mn _0.3 10.2 g of O ₂ ) and ₂ g of a solvent (N methyl pyrrolidone, manufactured by Wako Pure Chemical Industries, Ltd.) were mixed to prepare a slurry [1]. Next, 2 g of non-aqueous binder c was mixed to prepare a non-aqueous positive electrode mixture paste. The content (in terms of solid content) of each component in the non-aqueous positive electrode mixture paste is shown in Table 2.
Next, a non-aqueous positive electrode material mixture paste is coated on a 10 μm thick stainless steel foil (made by As One) so that the positive electrode capacity density is 1.0 mAh / cm ^2, and a vacuum dryer is used at 100 ° C. After drying for 12 hours, the positive electrode of Reference Example 1 in which the positive electrode mixture layer was formed on the current collector was produced.

4. Preparation of Coin Cell The positive electrodes of Examples 1 to 6, Comparative Example 1 and Reference Example 1 were punched and pressed to a diameter of 13 mm. Then, on each of the pressed positive electrodes, a separator of 19 mm in diameter [manufactured by Hohsen] and a coin-like metal lithium foil of 15 mm in diameter and 0.5 in thickness were disposed as a negative electrode to produce a 2032 type coin cell. As an electrolytic solution, 1 M LiPF 6 EC / DEC (volume ratio) = 3/7 was used.

5. Evaluation The charge / discharge characteristics of Example 1, Comparative Example 1 and Reference Example 1 were evaluated by the following charge / discharge test and electrochemical resistance test by cyclic voltammetry.

[Charge and discharge test]
The charge / discharge test was performed under the environment of 30 ° C. using the produced coin cell. For charging, constant-current charging was performed at 0.1 C (0.5 C after the fourth cycle) to 4.2 V, and constant-voltage charging was performed for 10 minutes. The discharge was constant current discharge at 0.1 C (0.5 C from the fourth cycle) up to 3.0 V. This charge and discharge was repeated 50 cycles. The results are shown in FIG. As shown in FIG. 1, in Example 1 in which predetermined polymer particles were used as a water-based binder, it was found that the charge-discharge cycle characteristics similar to those of Reference Example 1 in which a non-water-based binder was used.

[Electrochemical resistance test by cyclic voltammetry]
A coin cell using the positive electrode of Example 1, Comparative Example 1 and Reference Example 1 was produced by the same production method as the coin cell used in the charge and discharge test, and cyclic voltammetry was measured under the following measurement conditions using a potentiogalvanostat. did. The respective cyclic voltammograms are shown in FIGS.

<Measurement conditions>
Sweep voltage 2.5V to 4.5V
Sweep speed 0.1mV / s
4 sweep cycles

As shown in FIGS. 2 to 4, the cyclic voltammograms of Example 1 and Reference Example 1 had substantially the same profile. On the other hand, in the cyclic voltammogram of Comparative Example 1, a reduction peak is observed around 3.5 V, and the peak intensity of the oxidation peak observed around 3.8 V decreases with each cycle, etc. The electrochemical durability was not sufficient compared to Example 1.

[Capacity retention rate]
When the discharge capacity at the fourth cycle is S mAh / g and the discharge capacity at the 50th cycle is F mAh / g in the above charge and discharge test, the capacity retention rate was calculated by the following equation.
Capacity retention rate (%) = F ÷ S × 100

From the above, the positive electrode of the present disclosure can obtain charge / discharge characteristics equivalent to those of a positive electrode for a lithium ion secondary battery produced by a conventional non-aqueous process by using predetermined polymer particles as an aqueous binder. all right.

The positive electrode of the present disclosure is useful as a positive electrode of a lithium ion secondary battery.

Claims (10)

What is claimed is: 1. A positive electrode for a lithium ion secondary battery comprising: a current collector; and a mixture layer formed on the current collector,
The mixture layer includes a constituent unit (A) derived from a compound represented by the following formula (I), a compound represented by the following formula (II), a compound represented by the following formula (III), and A polymer particle containing a structural unit (B) derived from at least one compound selected from saturated dibasic acids as a binder,
The content of the structural unit (A) in all the structural units of the polymer particle is 50% by mass or more and 99.9% by mass or less,
The positive electrode for lithium ion secondary batteries in which content of the structural unit (B) in all the structural units of the said polymer particle is 0.1 mass% or more and 20 mass% or less.

[In Formula (I), R ¹ represents a hydrogen atom or a methyl group. R ² represents at least one selected from a linear or branched alkyl group having 1 or more and 6 or less carbon atoms, and —CH ₂ OR ³ . R ³ represents a linear or branched alkyl group having 4 to 6 carbon atoms. X represents -O- or -NH-. ]

[In Formula (II), R ¹ represents a hydrogen atom or a methyl group, and M represents a hydrogen atom or a cation. ]

[In Formula (III), R ¹ represents a hydrogen atom or a methyl group, and X represents -O- or -NH-. R ⁴ is-(CH ₂ ) _n OH, -R ⁵ SO ₃ M, -R ⁶ N (R ⁷ ) (R ⁸ ) and -R ⁶ N ⁺ (R ⁷ ) (R ⁸ ) (R ⁹ ). Y ^- represents at least one member selected from. n is 1 or more and 4 or less. R ⁵ represents a linear or branched alkylene group having 1 to 5 carbon atoms. M represents a hydrogen atom or a cation. R ⁶ represents a linear or branched alkylene group having 1 to 4 carbon atoms. R ⁷ and R ⁸ are the same or different and each represents a linear or branched alkyl group having 1 to 3 carbon atoms. R ⁹ represents a linear or branched alkyl group having 1 to 3 carbon atoms. Y ^- represents an anion. ] The positive electrode for a lithium ion secondary battery according to claim 1, wherein the surface tension of the polymer particle dispersion in which the polymer particles are dispersed in an aqueous medium is 55 mN / m or more. The positive electrode for a lithium ion secondary battery according to claim 1 or 2, wherein the total content of the structural unit (A) and the structural unit (B) in all the structural units of the polymer particle is 80% by mass or more. In the above formula (I), R ¹ is a hydrogen atom or a methyl group, R ² is a linear or branched alkyl group having 1 to 6 carbon atoms, and X is —O—
The constituent unit B is a constituent unit derived from the compound represented by the formula (II), and in the formula (II), R ¹ is a hydrogen atom or a methyl group, and M is a hydrogen atom or a cation. The positive electrode for lithium ion secondary batteries in any one of Claim 1 to 3. The polymer particle is at least one selected from a compound represented by the formula (I), a compound represented by the formula (II), a compound represented by the formula (III), and an unsaturated dibasic acid. The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 4, which is a polymer particle obtained by emulsion polymerization of a monomer mixture containing a compound of a species and a polyfunctional monomer selectively. The positive electrode for a lithium ion secondary battery according to claim 5, wherein an amount of an emulsifier used for the emulsion polymerization is 0.05% by mass or less with respect to a total amount of monomers. The positive electrode for a lithium ion secondary battery according to any one of claims 5 or 6, wherein the emulsion polymerization is soap-free emulsion polymerization. The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 7, wherein an average particle size of the polymer particles is 0.2 μm or more and less than 0.7 μm. It is a manufacturing method of the positive electrode for lithium ion secondary batteries in any one of Claims 1-8, Comprising:
A lithium ion secondary comprising a step of applying and drying an aqueous slurry containing a positive electrode active material and the polymer particles used for the positive electrode for a lithium ion secondary battery according to any one of claims 1 to 8 on a current collector. The manufacturing method of the positive electrode for secondary batteries. A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to any one of claims 1 to 8.

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