JP6070266B2 - Slurry composition for positive electrode of lithium ion secondary battery, method for producing positive electrode for lithium ion secondary battery, positive electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a slurry composition for a lithium ion secondary battery positive electrode, a method for producing a positive electrode for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery.

  Lithium ion secondary batteries are small and lightweight, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Therefore, in recent years, various attempts such as the development of new electrode materials have been made with respect to lithium ion secondary batteries.

  A lithium ion secondary battery is mainly composed of electrodes (positive electrode and negative electrode), an electrolytic solution, and a separator. As an electrode for a lithium ion secondary battery, an electrode active material layer composed of an electrode active material, a conductive material, a binder and the like is formed on a current collector. In addition, an electrode active material layer can be formed by apply | coating the slurry composition formed by disperse | distributing an electrode active material, a electrically conductive material, a binder, etc. to a solvent on a collector, and drying it.

Here, with regard to the slurry composition used for forming the electrode, in recent years, interest in an aqueous slurry composition using an aqueous medium as a dispersion medium has been increased from the viewpoint of reducing environmental load.
As the aqueous slurry composition, for example, an aqueous slurry containing a water-soluble polymer having a weight average molecular weight of 500,000 or more for the purpose of improving the strength of the electrode to be formed and improving the binding properties of the electrode active material and the conductive material. Compositions have been proposed. Specifically, in Patent Document 1, for example, an electrode active material, a conductive material, and 5 to 50% by mass of an ethylenically unsaturated carboxylate monomer unit, and a water-soluble material having a weight average molecular weight of 500,000 or more An aqueous slurry composition containing a polymer and an aqueous dispersion of polymer particles has been proposed.

International Publication No. 2012/008539

However, in a secondary battery including an electrode obtained by using the aqueous slurry composition of Patent Document 1, a water-soluble polymer having a large weight average molecular weight is unlikely to swell with respect to an electrolytic solution and hinders movement of lithium ions. Therefore, there is a problem that the electrical characteristics such as output characteristics of the lithium ion secondary battery are impaired. In addition, since a water-soluble polymer having a large weight average molecular weight exhibits an aggregating action, the aqueous slurry composition of Patent Document 1 containing the water-soluble polymer has low stability, and as a result, the aqueous slurry composition is There has also been a problem that the electrical characteristics such as the output characteristics of the lithium ion secondary battery including the electrode formed by using it are impaired. That is, the conventional aqueous slurry composition has room for improvement in terms of improving the electrical characteristics of a lithium ion secondary battery formed using the aqueous slurry composition.
In addition, the electrical characteristics of the lithium ion secondary battery were particularly liable to be impaired in a low temperature environment in which the movement of lithium ions is likely to be hindered due to the solidification and viscosity increase of the solvent constituting the electrolytic solution.

Further, since further increase in capacity is required for lithium ion secondary batteries, in recent years, manganese (Mn) or nickel (Ni) as an electrode active material (positive electrode active material) in a positive electrode of a lithium ion secondary battery. There has been proposed a technique for increasing the capacity of a lithium ion secondary battery by using a compound containing.
However, alkali components such as lithium carbonate (Li ₂ CO ₃ ) and lithium hydroxide (LiOH) used during the production of the active material remain in the positive electrode active material containing Mn and Ni described above. Therefore, when a water-based slurry composition containing a positive electrode active material containing Mn or Ni is applied onto a current collector made of aluminum or the like to produce a positive electrode, alkali content is eluted from the positive electrode active material, and the current collector is The problem of corrosion occurs.
Therefore, the water-based slurry composition used for the formation of the positive electrode not only solves the above-mentioned problem that the electrical characteristics are impaired, but also corrodes the current collector while achieving high capacity of the lithium ion secondary battery. Is also required to be suppressed.

Therefore, the present invention is an aqueous slurry composition used for forming a positive electrode of a lithium ion battery, and sufficiently ensures the electrical characteristics of the lithium ion secondary battery formed using the aqueous slurry composition. An object of the present invention is to provide a positive electrode slurry composition that can sufficiently inhibit corrosion of a current collector even when a positive electrode active material containing Mn or Ni is used as a positive electrode active material. And
Moreover, an object of this invention is to provide the manufacturing method of the positive electrode for lithium ion secondary batteries using the slurry composition for positive electrodes.
Furthermore, the present invention provides a positive electrode for a lithium ion secondary battery that can sufficiently suppress corrosion of a current collector and can constitute a lithium ion secondary battery having excellent electrical characteristics. For the purpose.
Another object of the present invention is to provide a lithium ion secondary battery that can sufficiently inhibit corrosion of the current collector of the positive electrode and has excellent electrical characteristics.

The present inventors have intensively studied to achieve the above object. The inventors of the present invention have a polymer in which the content ratio and weight average molecular weight of the acidic functional group-containing monomer unit are within a specific range, and the content ratio of the acidic functional group-containing monomer unit is in a specific range. It is possible to sufficiently suppress corrosion of the current collector caused by the positive electrode active material containing at least one of Mn and Ni by using the slurry composition containing the particulate polymer in In addition, the present inventors have found that a lithium ion secondary battery having excellent electrical characteristics can be provided, and have completed the present invention.
In order to achieve the above object, the gist of the present invention is as follows.

[1] a positive electrode active material containing at least one of Mn and Ni;
A polymer A having a content ratio of acidic functional group-containing monomer units of 15 to 60% by mass and a weight average molecular weight of 10,000 to 200,000;
A particulate polymer B in which the content of the acidic functional group-containing monomer unit is 10% by mass or less;
Conductive material;
A slurry composition for a positive electrode of a lithium ion secondary battery comprising water.
As described above, when the aqueous slurry composition containing the specific polymer A is used, the current collector is sufficiently corroded even when the positive electrode active material containing at least one of Mn and Ni is used. Can be suppressed. Moreover, if a positive electrode is formed using a positive electrode active material containing at least one of Mn and Ni and a slurry composition containing the specific polymer A and the particulate polymer B, the battery capacity and A lithium ion secondary battery having excellent electrical characteristics such as low-temperature output characteristics can be obtained.

[2] The above [1], wherein the ratio (a / b) of the mass (a) of the polymer A to the mass (b) of the particulate polymer B is in the range of 0.01 to 0.3. The slurry composition for a lithium ion secondary battery positive electrode described in 1.
Thus, if the ratio (a / b) of the mass (a) of the polymer A to the mass (b) of the particulate polymer B in the slurry composition is within the above range, corrosion of the current collector is suitable. The dispersion of each component in the slurry composition of the present invention is made good while suppressing the adhesion between the positive electrode active material layer formed using the slurry composition and the current collector, the lithium ion secondary The electric characteristics of the battery can be further improved.

[3] The slurry composition for a lithium ion secondary battery positive electrode according to [1] or [2], wherein the polymer A includes a fluorine-containing (meth) acrylic acid ester monomer unit.
Thus, if the polymer A contains a fluorine-containing (meth) acrylic acid ester monomer unit, the low-temperature output characteristics of the lithium ion secondary battery obtained by using the slurry composition of the present invention are sufficiently secured. can do.

[4] The particulate polymer B described in any one of [1] to [3], including a (meth) acrylic acid ester monomer unit and a (meth) acrylonitrile monomer unit. Slurry composition for positive electrode of lithium ion secondary battery.
Thus, if the particulate polymer B contains a (meth) acrylic acid ester monomer unit and a (meth) acrylonitrile monomer unit, the flexibility of the positive electrode obtained by using the slurry composition of the present invention. And the binding force of the particulate polymer B is sufficient, and the strength of the positive electrode and the electrical characteristics of the lithium ion secondary battery can be sufficiently secured.

[5] A step of applying the slurry composition for a lithium ion secondary battery positive electrode according to any one of [1] to [4] on the current collector; A method for producing a positive electrode for a lithium ion secondary battery, comprising: drying the slurry composition for a lithium ion secondary battery positive electrode to form a positive electrode active material layer.
If the positive electrode manufactured by such a manufacturing method is used using the above-described slurry composition for a lithium ion secondary battery positive electrode, corrosion of the positive electrode current collector is sufficiently suppressed, and excellent electrical A lithium ion secondary battery having characteristics can be obtained.

[6] A positive electrode active material containing at least one of Mn and Ni;
A polymer A having a content ratio of acidic functional group-containing monomer units of 15 to 60% by mass and a weight average molecular weight of 10,000 to 200,000;
The positive electrode for lithium ion secondary batteries containing the particulate polymer B whose content rate of an acidic functional group containing monomer unit is 10 mass% or less, and a electrically conductive material.
Thus, if the specific polymer A is contained, corrosion of the current collector can be sufficiently suppressed even when a positive electrode active material containing at least one of Mn and Ni is used. In addition, if a positive electrode active material containing at least one of Mn and Ni is used and the positive electrode containing the specific polymer A and the particulate polymer B is used, the electric capacity such as battery capacity and low temperature output characteristics can be obtained. A lithium ion secondary battery having excellent characteristics can be formed.

[7] The above [6], wherein the ratio (a / b) of the mass (a) of the polymer A to the mass (b) of the particulate polymer B is in the range of 0.01 to 0.3. The positive electrode for lithium ion secondary batteries as described in 2.
Thus, if the ratio (a / b) of the mass (a) of the polymer A to the mass (b) of the particulate polymer B is within the above range, the corrosion of the current collector is suitably suppressed, The adhesion between the positive electrode active material layer and the current collector and the electrical characteristics of the lithium ion secondary battery can be further improved.

[8] The positive electrode for a lithium ion secondary battery according to [6] or [7], wherein the polymer A includes a fluorine-containing (meth) acrylic acid ester monomer unit.
Thus, if the polymer A contains a fluorine-containing (meth) acrylic acid ester monomer unit, the low-temperature output characteristics of a lithium ion secondary battery using the positive electrode can be sufficiently secured.

[9] The particulate polymer B according to any one of [6] to [8], wherein the particulate polymer B includes a (meth) acrylic acid ester monomer unit and a (meth) acrylonitrile monomer unit. Positive electrode for lithium ion secondary battery.
Thus, if the particulate polymer B contains the (meth) acrylic acid ester monomer unit and the (meth) acrylonitrile monomer unit, the flexibility of the positive electrode can be secured and the particulate polymer The binding force of the polymer B becomes sufficient, and the strength of the positive electrode and the electrical characteristics of the lithium ion secondary battery using the positive electrode can be sufficiently secured.

[10] A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to any one of [6] to [9], a negative electrode, an electrolytic solution, and a separator.
A lithium ion secondary battery including the above-described positive electrode for a lithium ion secondary battery can suppress corrosion of the current collector of the positive electrode and is excellent in electrical characteristics such as battery capacity and low temperature output characteristics.

[11] The lithium ion secondary battery according to [10], wherein the electrolytic solution includes an electrolyte and a solvent, and a content ratio of ethylene carbonate in the solvent is 30 to 60% by volume.
A lithium ion secondary battery using an electrolytic solution using a solvent having such a content ratio of ethylene carbonate can dissolve a large amount of lithium salt such as LiPF _{6 in the} electrolytic solution, and has a high lithium ion concentration. Excellent electrical characteristics because it can be maintained at a level. Moreover, low-temperature output characteristics can be ensured by setting the content ratio of ethylene carbonate having a high freezing point to an appropriate level.

ADVANTAGE OF THE INVENTION According to this invention, when it uses for a lithium ion secondary battery as a positive electrode, it is possible to fully ensure the electrical property of a lithium ion secondary battery, and fully suppresses corrosion of a collector. A slurry composition suitable as a positive electrode material for a lithium ion secondary battery, and a method for producing a positive electrode for a lithium ion secondary battery using the slurry composition can be provided.
In addition, according to the present invention, a positive electrode for a lithium ion secondary battery that can sufficiently suppress corrosion of a current collector and can constitute a lithium ion secondary battery having excellent electrical characteristics is provided. Can be provided.
Furthermore, according to the present invention, it is possible to provide a lithium ion secondary battery that can sufficiently suppress corrosion of the current collector of the positive electrode and has excellent electrical characteristics.

<Slurry composition for positive electrode of lithium ion secondary battery>
The slurry composition for a lithium ion secondary battery positive electrode of the present invention is a positive electrode active material containing at least one of Mn and Ni, and the content ratio of the acidic functional group-containing monomer unit is 15 to 60% by mass, and the weight An aqueous slurry composition comprising a polymer A having an average molecular weight of 10,000 to 200,000, a particulate polymer B having a content ratio of acidic functional group-containing monomer units of 10% by mass or less, a conductive material, and water. It is a thing.

In the present specification, “the positive electrode active material containing at least one of Mn and Ni” is appropriately referred to as “the Mn and / or Ni-containing positive electrode active material” and the “content ratio of the acidic functional group-containing monomer unit”. “Polymer A having a weight average molecular weight of 10,000 to 200,000” having a weight average molecular weight of 15 to 60% by mass is “acidic polymer A” and the content ratio of the acidic functional group-containing monomer unit is 10% by mass or less. The “particulate polymer B” is abbreviated as “particulate polymer B”.
Further, in the present specification, (meth) acrylic acid means acrylic acid and / or methacrylic acid, and (meth) acrylic acid ester means acrylic acid ester and / or methacrylic acid ester. “Including a body unit” means “a polymer obtained using the monomer contains a structural unit derived from the monomer”.

(Positive electrode active material containing at least one of Mn and Ni)
The slurry composition for a lithium ion secondary battery positive electrode of the present invention uses a positive electrode active material containing Mn and / or Ni as a positive electrode active material. The positive electrode active material is an electrode active material used in the positive electrode, and is a material that transfers electrons in the positive electrode of the lithium ion secondary battery. And if Mn and / or Ni containing positive electrode active material is used, the capacity | capacitance of a lithium ion secondary battery can be raised.
Here, the Mn and / or Ni-containing positive electrode active material is not particularly limited as long as it is an active material containing at least one of Mn and Ni as a transition metal, but a viewpoint of further increasing the capacity of the lithium ion secondary battery. Is preferably a positive electrode active material containing at least Ni, and more preferably a positive electrode active material containing Ni and Mn. From the viewpoint of ensuring sufficient battery safety in addition to increasing the capacity, a positive electrode active material composed of Li, O, Ni, Mn, Co, and Fe is more preferable. Even more preferable is a positive electrode active material composed of O, Ni, Mn, and Co.

  Specifically, examples of the Mn and / or Ni-containing positive electrode active material include lithium and a lithium-containing composite metal oxide containing at least one of Mn and Ni as a transition metal. The lithium-containing composite metal oxide may contain transition metals such as Ti, V, Cr, Fe, Co, Cu, and Mo in addition to Mn and Ni.

Here, as the Mn-containing positive electrode active material, for example, a lithium composite oxide of Co—Ni—Mn, and a compound in which lithium manganate (LiMn ₂ O ₄ ) and a part of Mn thereof are substituted with other transition metals Is mentioned.
Examples of the Ni-containing positive electrode active material include lithium-containing nickel oxide (LiNiO ₂ ) and Ni—Co—Al lithium composite oxide.
As the positive electrode active material containing Mn and Ni, a lithium composite oxide of Ni—Mn—Al can be given.
Then, as the Mn and / or Ni-containing cathode active material, in view of the high capacity of lithium ion secondary _{batteries, Li a Ni b Co c Mn} d O 2 (0 <a ≦ 2,0 <b <1, A positive electrode active material represented by a general formula of 0 ≦ c <1 0 <d <1) is preferable. Examples of such positive electrode active materials include Li _1.2 Ni _0.17 Co _0.07 Mn _0.56 O ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ . Among these, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is particularly preferable as the positive electrode active material from the viewpoint of increasing the capacity of the lithium ion secondary battery.

<Acid polymer A>
The acidic polymer A contained in the slurry composition for a positive electrode of a lithium ion secondary battery of the present invention is an acidic functional substance which is an alkaline functional substance such as lithium hydroxide (LiOH) eluted from a positive electrode active material containing Mn and / or Ni. It is a polymer that can be neutralized by a group.
In addition, the lithium salt of the acidic polymer A produced by the neutralization can release lithium ions in the electrolyte of a lithium ion secondary battery including an electrode obtained using the slurry composition of the present invention. it can. Therefore, in the lithium ion secondary battery including the positive electrode formed using the slurry composition containing the acidic polymer A, the lithium ion concentration in the electrolytic solution can be maintained at a high level. Further, in the lithium ion secondary battery, the freezing point of the electrolytic solution is lowered due to the increase of the lithium ion concentration in the electrolytic solution due to the presence of the lithium salt of the acidic polymer A. Therefore, the ease of movement of lithium ions in the electrolytic solution in the low temperature range is ensured, and the electrical characteristics (for example, low temperature output characteristics) of the lithium ion secondary battery can be improved.

  The acidic polymer A includes an acidic functional group-containing monomer unit. Here, the content ratio of the acidic functional group-containing monomer unit of the acidic polymer A needs to have a lower limit of 15% by mass or more, preferably 20% by mass or more, more preferably 30% by mass or more. It is necessary to make the upper limit 60 mass% or less, More preferably, it is 50 mass% or less, Most preferably, it is 40 mass% or less. When the content ratio of the acidic functional group-containing monomer unit in the acidic polymer A is 15% by mass or more, corrosion of the current collector can be suppressed. Moreover, when it is set as a lithium ion secondary battery, discharge | release of lithium ion in the above-mentioned electrolyte becomes enough, and low temperature output characteristics can be ensured. Further, when the content ratio of the acidic functional group-containing monomer unit of the acidic polymer A is 60% by mass or less, the aggregation of the acidic polymer A is suppressed and the release of lithium ions becomes sufficient, and the low temperature output characteristics are secured. can do. Moreover, the flexibility of the positive electrode can be secured, and accordingly, the cycle characteristics of the lithium ion secondary battery can be secured. Furthermore, by making the content ratio of the acidic functional group-containing monomer unit of the acidic polymer A within the above range, the adhesion between the positive electrode active material layer obtained by using the slurry composition of the present invention and the current collector Sex can be secured.

  The lower limit of the weight average molecular weight of the acidic polymer A needs to be 10,000 or more, preferably 15,000 or more, more preferably 20,000 or more, particularly preferably 50,000 or more, and the upper limit thereof needs to be 200,000 or less. , Preferably 150,000 or less, more preferably 100,000 or less, particularly preferably 80000 or less. When the weight average molecular weight of the acidic polymer A is 10,000 or more, when the lithium ion secondary battery is formed, the acidic polymer A can be prevented from being dissolved in the electrolytic solution of the lithium ion secondary battery. . Therefore, the problem of the increase in the viscosity of the electrolytic solution and the accompanying suppression of the movement of lithium ions is less likely to occur, and electrical characteristics such as low-temperature output characteristics and cycle characteristics of the lithium ion secondary battery can be ensured. Furthermore, when the weight average molecular weight of the acidic polymer A is 50000 or more, the adhesion between the positive electrode active material layer and the current collector in the positive electrode obtained using the slurry composition of the present invention is improved. be able to. Further, since the acidic polymer A has a weight average molecular weight of 200,000 or less, the swelling property of the acidic polymer A in the electrolytic solution is ensured, and electrical properties such as low-temperature output characteristics and cycle characteristics of the lithium ion secondary battery are secured. Good characteristics can be obtained. Further, the acidic polymer A does not exhibit a strong aggregating action, and the slurry composition has sufficient stability, and the electrical characteristics such as the output characteristics of the lithium ion secondary battery formed using the slurry composition. Good characteristics can be obtained. That is, when the weight average molecular weight of the acidic polymer A is more than 200,000, the acidic polymer A hardly swells when the lithium ion secondary battery is formed, and the lithium ion migration is inhibited by the acidic polymer A and the lithium ion is inhibited. The electrical characteristics of the secondary battery deteriorate. Further, the stability of the slurry composition is lowered, and the electrical characteristics of the lithium ion secondary battery are lowered. In addition, the weight average molecular weight of acidic polymer A can be adjusted by using a well-known molecular weight regulator at the time of preparation of acidic polymer A.

The acidic polymer A is water soluble. When the acidic polymer A is water-soluble, in the aqueous slurry composition, it can be favorably adsorbed on the positive electrode active material, and the dispersibility of the positive electrode active material can be improved. Thus, the capacity | capacitance of a lithium ion secondary battery can be made high because the positive electrode active material is disperse | distributing uniformly. Here, the acidic polymer A is water-soluble means that the acidic polymer A is dissolved at a concentration of 10% by mass or more in an aqueous medium having a pH of more than 7 and 9 or less at 25 ° C., preferably 25 ° C. And dissolved in an aqueous medium having a pH of more than 7 at a concentration of 10% by mass or more. In addition, the solubility to the aqueous medium of the acidic polymer A can be adjusted by changing the content rate of an acidic functional group containing monomer, for example.
The slurry composition for a lithium ion secondary battery positive electrode of the present invention usually has a pH of more than 7 at 25 ° C. due to the influence of an alkaline corrosive substance or the like of the Mn and / or Ni-containing positive electrode active material. Therefore, the acidic polymer A that is water-soluble can be sufficiently dissolved in the slurry composition. And in the electrolyte solution of the lithium ion secondary battery containing the positive electrode obtained using this slurry composition, unlike the particulate polymer B which maintains particulate shape, the positive electrode active material in an amorphous state, It exists around the conductive material and the particulate polymer B.

  Here, the acidic polymer A is prepared by addition polymerization of a monomer composition containing an acidic functional group-containing monomer and any other monomer. Accordingly, carboxymethylcellulose, which is a cellulose derivative formed by condensation polymerization of β-glucose, is not included in the acidic polymer A used in the present invention. Examples of acidic functional group-containing monomers that can be used in the production of acidic polymer A include phosphate group-containing monomers, sulfonic acid group-containing monomers, and carboxyl group-containing monomers. it can. The acidic polymer A is preferably prepared using at least a carboxyl group-containing monomer. This is because, when the carboxyl group becomes a lithium salt, lithium is easily ionized, so that the acidic polymer A having a carboxyl group can sufficiently lower the freezing point of the electrolytic solution.

The phosphate group-containing monomer that can be used in the production of the acidic polymer A is a monomer having a phosphate group and a polymerizable group that can be copolymerized with other monomers. As this phosphate group-containing monomer, a monomer having —O—P (═O) (— OR ¹ ) —OR ² group (R ¹ and R ² are independently a hydrogen atom, or any Or an organic salt thereof. Specific examples of the organic group as R ¹ and R ² include an aliphatic group such as an octyl group and an aromatic group such as a phenyl group.

  As a phosphate group containing monomer which can be used for manufacture of the said acidic polymer A, the compound containing a phosphate group and an allyloxy group, and a phosphate group containing (meth) acrylic acid ester can be mentioned, for example. Examples of the compound containing a phosphate group and an allyloxy group include 3-allyloxy-2-hydroxypropane phosphate. Examples of phosphoric acid group-containing (meth) acrylic acid esters include dioctyl-2-methacryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, monomethyl-2-methacryloyloxyethyl phosphate, dimethyl-2-methacryloyloxy Ethyl phosphate, monoethyl-2-methacryloyloxyethyl phosphate, diethyl-2-methacryloyloxyethyl phosphate, monoisopropyl-2-methacryloyloxyethyl phosphate, diisopropyl-2-methacryloyloxyethyl phosphate, mono n-butyl-2 -Methacryloyloxyethyl phosphate, di-n-butyl-2-methacryloyloxyethyl phosphate, monobutoxyethyl-2-methacryloyloxyethyl phosphate, dibu Xylethyl-2-methacryloyloxyethyl phosphate, mono (2-ethylhexyl) -2-methacryloyloxyethyl phosphate, di (2-ethylhexyl) -2-methacryloyloxyethyl phosphate, monoethyl-2-acryloyloxyethyl phosphate, etc. Is mentioned.

  The sulfonic acid group-containing monomer that can be used in the production of the acidic polymer A is a monomer having a sulfonic acid group and a polymerizable group that can be copolymerized with other monomers. Examples of sulfonic acid group-containing monomers include sulfonic acid group-containing monomers having no functional groups other than sulfonic acid groups and polymerizable groups, or salts thereof, sulfonic acid groups, and polymerizable groups. And a monomer or a salt thereof containing an amide group, and a monomer or a salt thereof containing a hydroxyl group in addition to a sulfonic acid group and a polymerizable group.

  Examples of the sulfonic acid group-containing monomer having no functional group other than the sulfonic acid group and the polymerizable group include a monomer obtained by sulfonating one of conjugated double bonds of a diene compound such as isoprene and butadiene. Vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, sulfoethyl methacrylate, sulfopropyl methacrylate, sulfobutyl methacrylate and the like. Moreover, as the salt, lithium salt, sodium salt, potassium salt etc. are mentioned, for example. Examples of the monomer containing an amide group in addition to the sulfonic acid group and the polymerizable group include 2-acrylamido-2-methylpropanesulfonic acid (AMPS). Moreover, as the salt, lithium salt, sodium salt, potassium salt etc. are mentioned, for example. Examples of the monomer containing a hydroxyl group in addition to the sulfonic acid group and the polymerizable group include 3-allyloxy-2-hydroxypropanesulfonic acid (HAPS). Moreover, as the salt, lithium salt, sodium salt, potassium salt etc. are mentioned, for example.

  The carboxyl group-containing monomer that can be used for the production of the acidic polymer A can be a monomer having a carboxyl group and a polymerizable group. Specific examples of the carboxyl group-containing monomer include an ethylenically unsaturated carboxylic acid monomer.

  Examples of the ethylenically unsaturated carboxylic acid monomer include ethylenically unsaturated monocarboxylic acid and derivatives thereof, ethylenically unsaturated dicarboxylic acid and acid anhydrides thereof, and derivatives thereof. Examples of ethylenically unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of ethylenically unsaturated monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, And β-diaminoacrylic acid. Examples of ethylenically unsaturated dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of acid anhydrides of ethylenically unsaturated dicarboxylic acids include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Examples of derivatives of ethylenically unsaturated dicarboxylic acids include methyl maleate such as methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid; and diphenyl maleate, nonyl maleate And maleate esters such as decyl maleate, dodecyl maleate, octadecyl maleate and fluoroalkyl maleate.

  These acidic functional group-containing monomers may be used alone or in combination of two or more. Therefore, the acidic polymer A used in the present invention may contain only one type of acidic functional group-containing monomer unit, or may contain two or more types in combination. Among these acidic functional group-containing monomers, acrylic acid, methacrylic acid, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), monoethyl are used from the viewpoint of storage stability of the resulting slurry composition. 2-Methacryloyloxyethyl phosphate and monoethyl-2-acryloyloxyethyl phosphate are more preferable, and methacrylic acid is particularly preferable.

  The acidic polymer A used in the present invention can contain other monomer units in addition to the acidic functional group-containing monomer units. Examples of such other monomer units include fluorine-containing (meth) acrylate monomer units, fluorine-free (meth) acrylate monomer units, crosslinkable monomer units, reactive interfaces Activator units are mentioned. Among these, from the viewpoint of the low-temperature output characteristics of the lithium ion secondary battery obtained using the slurry composition of the present invention, the acidic polymer A may contain a fluorine-containing (meth) acrylate monomer unit. preferable. In the present specification, “(meth) acrylic acid ester monomer unit” simply refers to “a (meth) acrylic acid monomer unit not containing fluorine”.

  Examples of the fluorine-containing (meth) acrylic acid ester monomer that can be used for the production of the acidic polymer A include monomers represented by the following formula (I).

In the above formula (I), R ³ represents a hydrogen atom or a methyl group.
In the above formula (I), R ⁴ represents a hydrocarbon group containing a fluorine atom. The carbon number of the hydrocarbon group is usually 1 or more and 18 or less. The number of fluorine atoms contained in R ⁴ may be 1 or 2 or more.

  Examples of fluorine-containing (meth) acrylic acid ester monomers represented by formula (I) include (meth) acrylic acid alkyl fluoride, (meth) acrylic acid fluoride aryl, and (meth) acrylic acid fluoride. Aralkyl is mentioned. Of these, alkyl fluoride (meth) acrylate is preferable. Specific examples of such a monomer include (meth) acrylic acid β- (perfluorooctyl) ethyl, (meth) acrylic acid 2,2,3,3-tetrafluoropropyl, (meth) acrylic acid 2, 2,3,4,4,4-hexafluorobutyl, (meth) acrylic acid 1H, 1H, 5H-octafluoropentyl, (meth) acrylic acid 1H, 1H, 2H, 2H-heptadecafluorodecyl, (meth) 1H, 1H, 9H-perfluoro-1-nonyl acrylate, 1H, 1H, 11H-perfluoroundecyl (meth) acrylate, perfluorooctyl (meth) acrylate, 2,2,2 (meth) acrylic acid -Trifluoromethyl, 2,2,2-trifluoroethyl (meth) acrylate, (meth) acrylic acid 3 [4 [1-trifluoromethyl-2,2-bis [bi (Meth) acrylic acid perfluoroalkyl esters such as (trifluoromethyl) fluoromethyl] ethynyloxy] benzooxy] 2-hydroxypropyl may be mentioned, and these may be used alone or in combination of two or more. May be used.

  Among these fluorine-containing (meth) acrylic acid ester monomers, from the viewpoint of further improving the low-temperature output characteristics of the lithium ion secondary battery, methacrylic acid 1H, 1H, 5H-octafluoropentyl, methacrylic acid 1H, 1H, 2H, 2H-heptadecafluorodecyl and 2,2,2-trifluoroethyl methacrylate are preferred, and 2,2,2-trifluoroethyl methacrylate is particularly preferred.

  The content ratio of the fluorine-containing (meth) acrylic acid ester monomer unit in the acidic polymer A used in the present invention is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0. 0.5% by mass or more, particularly preferably 6% by mass or more, preferably 50% by mass or less, more preferably 30% by mass or less, and particularly preferably 20% by mass or less. By setting the content ratio of the fluorine-containing (meth) acrylic acid ester monomer unit to 0.1% by mass or more, the low-temperature output characteristics of the lithium ion secondary battery can be improved. On the other hand, by making the content ratio of the fluorine-containing (meth) acrylic acid ester monomer unit 50% by mass or less, defluorination is made difficult to occur, and corrosion of electrodes and the like in lithium ion secondary batteries due to fluorine is suppressed. And good cycle characteristics can be ensured.

  Examples of fluorine-free (meth) acrylic acid ester monomers that can be used in the production of the acidic polymer A include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, Examples include (meth) acrylic acid alkyl esters such as (meth) acrylic acid hexyl and (meth) acrylic acid-2-ethylhexyl. These may be used alone or in combination of two or more.

  Among these (meth) acrylic acid ester monomers, 2-ethylhexyl acrylate is used to facilitate copolymerization and to improve the adhesion between the positive electrode active material layer and the current collector. Ethyl acrylate and butyl acrylate are preferable, and ethyl acrylate and butyl acrylate are particularly preferable.

  In the acidic polymer A used in the present invention, the content ratio of the (meth) acrylic acid ester monomer unit is preferably 50% by mass or more, more preferably 55% by mass or more, and particularly preferably 60% by mass or more. Preferably it is 90 mass% or less, More preferably, it is 65 mass% or less. By setting the content ratio of the (meth) acrylic acid ester monomer unit to 50% by mass or more, it is obtained using the flexibility of the positive electrode obtained using the slurry composition of the present invention and the slurry composition of the present invention. The low-temperature output characteristics of the secondary battery can be ensured, and the adhesion between the positive electrode active material layer obtained by using the slurry composition of the present invention and the current collector is excellent by setting it to 90% by mass or less. It can be.

  In addition, in the acidic polymer A, it is preferable that the content rate of an ethyl acrylate monomer unit is 0-60 mass% from a viewpoint of ensuring the softness | flexibility of the positive electrode obtained using the slurry composition of this invention. The content ratio of the butyl acrylate monomer unit is preferably 25 to 60% by mass.

As the crosslinkable monomer that can be used in the production of the acidic polymer A, a monomer that can form a crosslinked structure when polymerized can be used. Examples of the crosslinkable monomer include monomers having two or more reactive groups per molecule. More specifically, a monofunctional monomer having a heat-crosslinkable crosslinkable group and one olefinic double bond per molecule, and a polyfunctional having two or more olefinic double bonds per molecule. Ionic monomers.
Examples of thermally crosslinkable groups contained in the monofunctional monomer include epoxy groups, N-methylolamide groups, oxetanyl groups, oxazoline groups, and combinations thereof. Among these, an epoxy group is more preferable in terms of easy adjustment of crosslinking and crosslinking density.

  Examples of the crosslinkable monomer having an epoxy group as a thermally crosslinkable group and having an olefinic double bond include vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, o-allylphenyl glycidyl. Unsaturated glycidyl ethers such as ether; butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododecadiene Monoepoxides of dienes or polyenes such as; alkenyl epoxides such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene; and glycidyl acrylate, glycidyl methacrylate, Glycidyl crotonate Unsaturated carboxylic acids such as sidyl-4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl-4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexene carboxylic acid, glycidyl ester of 4-methyl-3-cyclohexene carboxylic acid Examples include glycidyl esters of acids.

  Examples of the crosslinkable monomer having an N-methylolamide group as a thermally crosslinkable group and having an olefinic double bond have a methylol group such as N-methylol (meth) acrylamide (meta ) Acrylamides.

  Examples of the crosslinkable monomer having an oxetanyl group as a heat crosslinkable group and having an olefinic double bond include 3-((meth) acryloyloxymethyl) oxetane, 3-((meth) Acryloyloxymethyl) -2-trifluoromethyloxetane, 3-((meth) acryloyloxymethyl) -2-phenyloxetane, 2-((meth) acryloyloxymethyl) oxetane, and 2-((meth) acryloyloxymethyl ) -4-trifluoromethyloxetane.

  Examples of the crosslinkable monomer having an oxazoline group as a thermally crosslinkable group and having an olefinic double bond include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2- Oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline is mentioned.

  Examples of multifunctional monomers having two or more olefinic double bonds include allyl (meth) acrylate, ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, Tetraethylene glycol di (meth) acrylate, trimethylolpropane-tri (meth) acrylate, dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, trimethylolpropane-diallyl Ethers, allyl or vinyl ethers of polyfunctional alcohols other than those mentioned above, triallylamine, methylene bisacrylamide, and divinylbenzene.

  Among these, as a crosslinkable monomer, ethylene dimethacrylate is particularly used from the viewpoint of suppressing the increase in viscosity of the slurry composition because it crosslinks during drying and improving the strength of the positive electrode produced using the slurry composition. Allyl glycidyl ether and glycidyl methacrylate can be preferably used.

  The content ratio of the crosslinkable monomer unit in the acidic polymer A used in the present invention is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and particularly preferably 0.5% by mass or more. The content is preferably 2% by mass or less, more preferably 1.5% by mass or less, and particularly preferably 1% by mass or less. By setting the content ratio of the crosslinkable monomer unit within the above range, the swelling degree of the acidic polymer A can be set to an appropriate range, and the durability of the positive electrode obtained using the slurry composition of the present invention can be improved. it can.

  The reactive surfactant that can be used for the production of the acidic polymer A has a polymerizable group that can be copolymerized with other monomers, and has a surfactant group (hydrophilic group and hydrophobic group). It is a monomer having The reactive surfactant unit obtained by the polymerization of the reactive surfactant constitutes a part of the molecule of the acidic polymer A and can exert a surfactant action. Therefore, the stability during the production of the acidic polymer A is stable. Becomes higher.

  Examples of suitable reactive surfactants include compounds represented by the following formula (II).

In the formula (II), R ⁵ represents a divalent linking group. Examples of R ⁵ include a —Si—O— group, a methylene group, and a phenylene group. In the formula (II), R ⁶ represents a hydrophilic group. An example of R ⁶ includes —SO ₃ NH ₄ . In the formula (II), n is an integer of 1 or more and 100 or less. A reactive surfactant may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Another example of a suitable reactive surfactant has a polymerized unit based on ethylene oxide and a polymerized unit based on butylene oxide, and further has an alkenyl group having a terminal double bond and —SO ₃ NH ₄ at the terminal. Examples thereof include compounds (for example, trade names “Latemul PD-104” and “Latemul PD-105” manufactured by Kao Corporation).

  The content ratio of the reactive surfactant unit in the acidic polymer A used in the present invention is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and particularly preferably 0.5% by mass or more. , Preferably 5% by mass or less, more preferably 4% by mass or less, and particularly preferably 2% by mass or less. When the ratio of the reactive surfactant unit is 0.1% by mass or more, the dispersibility of the acidic polymer A can be improved in the slurry composition during the production of the composite particles. On the other hand, the durability of the positive electrode can be improved by setting the ratio of the reactive surfactant unit to 5% by mass or less.

  Examples of monomer units other than those described above that may be contained in the acidic polymer A used in the present invention include monomer units derived from the following monomers. That is, styrene monomers such as styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene, and divinyl benzene; Amide monomers such as acrylamide; α, β-unsaturated nitrile compound monomers such as acrylonitrile and methacrylonitrile; Olefin monomers such as ethylene and propylene; Halogen atom-containing monomers such as vinyl chloride and vinylidene chloride Mer: vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate; vinyl ether monomers such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether; methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl Tone, hexyl vinyl ketone, vinyl ketone monomers such as isopropenyl vinyl ketone; and a single monomer obtained by polymerizing one or more of heterocyclic compound-containing vinyl compound monomers such as N-vinyl pyrrolidone, vinyl pyridine and vinyl imidazole. A monomer unit is mentioned. The content ratio of these units in the acidic polymer A is preferably 0 to 10% by mass, more preferably 0 to 5% by mass.

  The acidic polymer A used in the present invention can be produced by any production method. For example, a monomer composition containing a monomer containing an acidic functional group-containing monomer and providing another arbitrary unit as necessary can be produced by addition polymerization in an aqueous solvent. As the aqueous solvent used in the polymerization reaction, known aqueous solvents such as those described in JP 2011-204573 A can be used, and among these, water is preferable.

  By the addition polymerization reaction in the aqueous solvent as described above, an aqueous dispersion of the acidic polymer A in which the acidic polymer A is dispersed in the aqueous solvent is obtained. The acidic polymer A may be taken out from the aqueous dispersion thus obtained, and may be used as it is for the preparation of the slurry composition.

  When the aqueous dispersion of acidic polymer A is used as it is for the preparation of the slurry composition, the pH of the aqueous dispersion is preferably 3 or more, preferably 10 or less, more preferably 7 or less. When the pH of the aqueous dispersion of the acidic polymer A is 3 or more, the corrosion of the apparatus due to the acid and the mixing of metal impurities into the slurry composition accompanying the corrosion of the apparatus can be suppressed. Moreover, when the pH of the aqueous dispersion of the acidic polymer A is 10 or less, corrosion of the current collector can be suppressed, and handling becomes good because of low viscosity.

  In the slurry composition for a lithium ion secondary battery positive electrode of the present invention, the content of the acidic polymer A is not particularly limited, but is preferably 0.01 parts by mass or more, more preferably 0 per 100 parts by mass of the positive electrode active material. 0.05 parts by mass or more, preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 0.5 parts by mass or less, particularly preferably 0.2 parts by mass or less, particularly preferably 0.2 parts by mass. It is below mass parts. By setting the content of the acidic polymer A within such a range, the alkaline corrosive substance eluted from the Mn and / or Ni-containing positive electrode active material is neutralized, and corrosion of the current collector is sufficiently suppressed. Can do. Moreover, the electrical characteristics such as the low-temperature output characteristics of the lithium ion secondary battery using the positive electrode obtained by using the slurry composition of the present invention can be made sufficiently excellent.

<Particulate polymer B>
The slurry composition for a positive electrode of a lithium ion secondary battery of the present invention contains a particulate polymer B.
In the positive electrode active material layer formed on the current collector using the slurry composition of the present invention, the particulate polymer B is prepared so that components contained in the positive electrode active material layer do not desorb from the positive electrode active material layer. It is a component that can be retained, that is, a component that functions mainly as a binder (binder). In general, when the particulate polymer B in the positive electrode active material layer is immersed in the electrolytic solution, the particulate polymer B maintains a granular shape while absorbing and swelling the electrolytic solution, and binds the positive electrode active material and the conductive material. The positive electrode active material and the conductive material are prevented from falling off from the current collector. By including the particulate polymer B in the slurry composition for a lithium ion secondary battery positive electrode of the present invention, the positive electrode active material and the conductive material are not unevenly distributed in the positive electrode formed using the slurry composition. The lithium ion secondary battery using the positive electrode is excellent in output characteristics. Therefore, the lithium ion secondary battery using the positive electrode can keep various performances favorable.

  In the particulate polymer B used in the present invention, the content ratio of the acidic functional group-containing monomer unit is more than 0% by mass, preferably 0.5% by mass or more, more preferably 1% by mass or more, It is necessary to set it as 10 mass% or less, Preferably it is 7 mass% or less, More preferably, it is 5 mass% or less. The particulate polymer B contains an acidic functional group-containing monomer (that is, the content ratio of the acidic functional group-containing monomer unit of the particulate polymer B is more than 0% by mass). Adhesive force is ensured, and electrical characteristics such as cycle characteristics of the lithium ion secondary battery obtained using the slurry composition of the present invention can be secured. Further, when the content ratio of the acidic functional group-containing monomer unit of the particulate polymer B is 10% by mass or less, the production stability and storage stability of the particulate polymer B can be increased, and further, the acidic weight It can be satisfactorily bonded to the coalescence A, the positive electrode active material, the conductive material, and the like, and as a result, contributes to ensuring various performances including good electrical characteristics of the lithium ion secondary battery.

  Here, the particulate polymer B can be prepared by addition polymerization of a monomer composition containing an acidic functional group-containing monomer and any other monomer. Examples of the acidic functional group-containing monomer that can be used in the production of the particulate polymer B include, for example, the phosphoric acid group-containing monomer, the sulfonic acid group-containing monomer exemplified in the section of the acidic polymer A, And a carboxyl group containing monomer can be mentioned, and these may be used individually by 1 type and may be used in combination of 2 or more types. Among these, from the viewpoint of the storage stability of the particulate polymer B, acrylic acid, methacrylic acid, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), monoethyl-2-methacryloyloxyethyl phosphate, monoethyl 2-acryloyloxyethyl phosphate is preferred, acrylic acid, itaconic acid, and methacrylic acid are more preferred, and itaconic acid is particularly preferred.

  The particulate polymer B preferably contains at least one of a (meth) acrylate monomer unit and an α, β-unsaturated nitrile monomer unit in addition to the acidic functional group-containing monomer unit. It is more preferable that a (meth) acrylic acid ester monomer unit and an α, β-unsaturated nitrile monomer unit are included, and a (meth) acrylic acid ester monomer unit and a (meth) acrylonitrile monomer unit. It is particularly preferred that In the present specification, (meth) acrylonitrile means acrylonitrile and / or methacrylonitrile.

  Examples of the (meth) acrylic acid ester monomer that can be used for the production of the particulate polymer B include, for example, (meth) acrylic acid ester monomers not containing fluorine exemplified in the section of the acidic polymer A The same thing is mentioned. In addition, these may be used individually by 1 type and may be used in combination of 2 or more types. The (meth) acrylic acid ester monomer preferably has 4 or more carbon atoms, more preferably 6 or more carbon atoms, particularly preferably 8 or more carbon atoms, preferably 13 or less carbon atoms, more preferably Carbon number is 11 or less. By using the (meth) acrylic acid ester monomer having 4 or more carbon atoms, the swellability of the particulate polymer B in the electrolytic solution is lowered, and the life of the lithium ion secondary battery is improved. Moreover, by using a (meth) acrylic acid ester monomer having 13 or less carbon atoms, the hydrolysis resistance of the particulate polymer B can be improved, and the storage stability can be ensured. Of these, 2-ethylhexyl acrylate is particularly preferable.

  The content ratio of the (meth) acrylic acid ester monomer unit in the particulate polymer B is preferably 50% by mass or more, more preferably 60% by mass or more, preferably 95% by mass or less, more preferably 90%. It is below mass%. By making the content ratio of the monomer unit derived from the (meth) acrylic acid ester monomer 50% by mass or more, the flexibility of the positive electrode obtained using the slurry composition of the present invention is improved, and the positive electrode is cracked. It can be difficult. Moreover, by setting it as 95 mass% or less, the mechanical strength and binding force as a binder of the particulate polymer B can be improved.

  As the α, β-unsaturated nitrile monomer that can be used in the production of the particulate polymer B, acrylonitrile and methacrylonitrile are preferable, and acrylonitrile is particularly preferable in order to improve the mechanical strength and binding force as a binder. . In addition, these may be used individually by 1 type and may be used in combination of 2 or more types.

  The content ratio of the α, β-unsaturated nitrile monomer unit in the particulate polymer B is preferably 3% by mass or more, more preferably 5% by mass or more, preferably 40% by mass or less, more preferably. 30% by mass or less. By setting the content ratio of the α, β-unsaturated nitrile monomer unit to 3% by mass or more, the mechanical strength and binding force of the particulate polymer B as a binder can be increased. Moreover, by setting it as 40 mass% or less, the softness | flexibility of the positive electrode obtained using the slurry composition of this invention improves, and it can make a positive electrode hard to crack.

  Furthermore, the particulate polymer B may contain monomer units derived from monomers other than those described above. When the example of such a monomer is given, the thing similar to what was illustrated in the term of the acidic polymer A will be mentioned. In addition, these may be used individually by 1 type and may be used in combination of 2 or more types.

  The production method of the particulate polymer B is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method may be used. As the polymerization method, addition polymerization such as radical polymerization and living radical polymerization can be used. As the polymerization initiator, known polymerization initiators, for example, those described in JP 2012-184201 A can be used.

  The particulate polymer B is usually produced in the form of a dispersion dispersed in the form of particles in an aqueous medium. Similarly, in the slurry composition for a lithium battery positive electrode of the present invention, the particulate polymer B is also dispersed in an aqueous medium. Included. When dispersed in an aqueous medium in the form of particles, the 50% volume average particle size of the particles of the particulate polymer B is preferably 25 nm or more, preferably 200 nm or less, more preferably 185 nm or less, particularly preferably. It is 160 nm or less. By making the volume average particle size of the particles of the particulate polymer B 50 nm or more, the stability of the slurry composition of the present invention can be enhanced. Moreover, the binding force of the particulate polymer B can be raised by setting it as 200 nm or less.

  The particulate polymer B is usually stored and transported in the form of the dispersion. The solid content concentration of such a dispersion is usually 15% by mass or more, preferably 20% by mass or more, more preferably 30% by mass or more, and usually 70% by mass or less, preferably 65% by mass or less, more preferably. 60% by mass or less. When the solid content concentration of the dispersion is within this range, workability in producing the slurry composition is good.

  The pH of the dispersion containing the particulate polymer B is preferably 5 or more, more preferably 7 or more, preferably 13 or less, more preferably 11 or less. By keeping the pH of the dispersion in the above range, the stability of the particulate polymer B is improved.

  The glass transition temperature (Tg) of the particulate polymer B is preferably −50 ° C. or higher, more preferably −45 ° C. or higher, particularly preferably −40 ° C. or higher, preferably 25 ° C. or lower, more preferably 15 ° C. Hereinafter, it is particularly preferably 5 ° C. or lower. By keeping the glass transition temperature of the particulate polymer B in the above range, the strength and flexibility of the positive electrode produced using the slurry composition produced by the production method of the present invention is improved, and high low temperature output characteristics Can be realized.

  In the slurry composition for a lithium ion secondary battery positive electrode of the present invention, the content of the particulate polymer B is not particularly limited, but is preferably 0.1 parts by mass or more, more preferably per 100 parts by mass of the positive electrode active material. 0.5 parts by mass or more, particularly preferably 0.8 parts by mass or more, preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and particularly preferably 3 parts by mass or less. By setting the content of the particulate polymer B to 0.1 parts by mass or more per 100 parts by mass of the positive electrode active material, the binding property with the positive electrode active material, the conductive material, and the current collector can be improved. Moreover, when the positive electrode obtained by using the slurry composition of the present invention is applied to a lithium ion secondary battery, the inhibition of movement of lithium ions by the particulate polymer B is suppressed by setting it to 10 parts by mass or less. The internal resistance of the lithium ion secondary battery can be reduced.

  In the slurry composition for a lithium ion secondary battery positive electrode of the present invention, the ratio (a / b) of the mass (a) of the acidic polymer A to the mass (b) of the particulate polymer B is preferably 0.01. As mentioned above, More preferably, it is 0.03 or more, Preferably it is 0.3 or less, More preferably, it is 0.2 or less. When the ratio (a / b) of the mass (a) of the acidic polymer A to the mass (b) of the particulate polymer B is 0.01 or more, the amount of the acidic polymer A becomes sufficient, and the current collector Can be suitably suppressed. Moreover, the adhesiveness of the positive electrode active material layer manufactured using the slurry composition of this invention and a collector can be made favorable. And the ratio (a / b) of the mass (a) of the acidic polymer A to the mass (b) of the particulate polymer B is 0.3 or less, thereby suppressing aggregation of the particulate polymer B, Dispersibility can be improved. More specifically, the acidic polymer A has an effect of adhering the particulate polymers B by cross-linking by intermolecular interaction, and becomes a factor for forming a positive electrode active material layer having a suitable strength. When the mass of the coalescence A is excessive compared to the mass of the particulate polymer, the effect of adhering is too strong, causing aggregation of the particulate polymer B, and changing the viscosity of the resulting slurry composition, When the slurry composition is applied onto the current collector, there may be a problem such as application defects due to aggregates. When a / b is 0.3 or less, the mass (a) of the acidic polymer A with respect to the mass (b) of the particulate polymer B is not excessive, and the occurrence of the above problems is sufficiently suppressed. As a result, the adhesion between the positive electrode active material layer manufactured using the slurry composition of the present invention and the current collector and the electrical characteristics of the lithium ion secondary battery may be improved. it can.

<Conductive material>
The slurry composition for a lithium ion secondary battery positive electrode of the present invention contains a conductive material. The conductive material is not particularly limited, and examples thereof include conductive carbon materials such as acetylene black, ketjen black (registered trademark), carbon black, and graphite; fibers and foils of various metals, and acetylene black is particularly preferable. . By including a conductive material in the slurry composition, the electrical contact between the Mn and / or Ni-containing positive electrode active materials can be improved, thereby using the positive electrode obtained using the slurry composition of the present invention. The electrical characteristics (for example, low temperature output characteristics) and other characteristics of the lithium ion secondary battery can be improved.

  The conductive material preferably has a particulate shape, and the particle diameter is preferably 1 nm or more, more preferably 5 nm or more, preferably 500 nm or less, more preferably 100 nm or less. By setting the particle diameter of the conductive material to 1 nm or more, the dispersibility of the conductive material can be maintained in a good state. By setting the particle size of the conductive material to 500 nm or less, the specific surface area can be set to a desired large value, and thereby the effect of the conductive material (improvement of electrical contact between the positive electrode active materials) can be expressed well. As a result, the resistance can be made smaller than desired. In addition, 50% volume average particle diameter is used as the average particle diameter of the conductive material particles.

  The content of the conductive material in the slurry composition for a lithium ion secondary battery positive electrode of the present invention is not particularly limited, but is preferably 1 part by mass or more, more preferably 1.5 parts by mass per 100 parts by mass of the positive electrode active material. As described above, it is particularly preferably 2 parts by mass or more, preferably 10 parts by mass or less, more preferably 8 parts by mass or less. By making content of an electroconductive material into said range, the high capacity | capacitance and high load characteristic of a lithium ion secondary battery using the positive electrode obtained using the slurry composition of this invention can be made compatible.

<Other ingredients>
In addition to the above components, the slurry composition for a lithium ion secondary battery positive electrode of the present invention has, for example, a reinforcing material, a dispersant, an antioxidant, a thickener such as carboxymethylcellulose, and a function of suppressing the decomposition of the electrolytic solution. You may contain components, such as an electrolyte solution additive. As these other components, known components can be used, for example, those described in JP2012-204303A.

  The slurry composition for a lithium ion secondary battery positive electrode of the present invention can be obtained by mixing each of the above components and water. Examples of the mixing means include ball mills, sand mills, bead mills, pigment dispersers, crackers, ultrasonic dispersers, homogenizers, planetary mixers and the like. Moreover, mixing is normally performed in the range of room temperature to 80 degreeC for 10 minutes-several hours.

  Although the solid content concentration in the slurry composition for a lithium ion secondary battery positive electrode of the present invention is not particularly limited, it is preferably 50% by mass or more, more preferably 60% by mass, from the viewpoint of physical properties of the slurry composition and drying efficiency. % Or more, preferably 95% by mass or less, more preferably 90% by mass or less.

<Method for producing positive electrode for lithium ion secondary battery>
Next, the manufacturing method of the positive electrode for lithium ion secondary batteries of this invention is demonstrated. The manufacturing method of the positive electrode for lithium ion secondary batteries of this invention apply | coated the said slurry composition for lithium ion secondary battery positive electrodes on the electrical power collector (application process), and the electrical power collector. A step of drying the slurry composition to form a positive electrode active material layer (drying step).

(Coating process)
The method for applying the slurry composition for a positive electrode of the lithium ion secondary battery on the current collector is not particularly limited, and a known method can be used. For example, a doctor blade method, a zip method, a reverse roll method, Examples include a direct roll method, a gravure method, an extrusion method, and a brush coating method. At this time, the slurry composition may be applied to only one side of the current collector or may be applied to both sides. The thickness of the slurry film on the current collector after application and before drying can be appropriately set according to the thickness of the positive electrode active material layer obtained by drying.

  As the current collector, a current collector made of aluminum or an aluminum alloy can be used. At this time, aluminum and an aluminum alloy may be used in combination, or different types of aluminum alloys may be used in combination. The current collector is generally made of an electrically conductive and electrochemically durable material, and in particular, aluminum and aluminum alloys have excellent heat resistance and are electrochemically stable. It is a current collector material.

  Examples of the aluminum alloy include an alloy of aluminum and one or more elements selected from the group consisting of iron, magnesium, zinc, manganese, and silicon.

The shape of the current collector is not particularly limited, but a sheet shape having a thickness of 0.001 mm to 0.5 mm is preferable.
Further, the current collector may be subjected to a roughening treatment in advance in order to increase the adhesive strength of the positive electrode active material layer. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. In the mechanical polishing method, for example, an abrasive cloth paper to which abrasive particles are fixed, a grindstone, an emery buff, a wire brush provided with a steel wire, or the like is used.

(Drying process)
A method for drying the slurry composition on the current collector is not particularly limited, and a known method can be used. For example, drying with warm air, hot air, low-humidity air, vacuum drying, irradiation with infrared rays, electron beams, or the like. A drying method is mentioned. Although it does not specifically limit as drying conditions, For example, when using the drying method by infrared irradiation, it dries in 50-150 degreeC oven. Thus, the positive electrode for lithium ion secondary batteries provided with a positive electrode active material layer and a collector can be obtained by drying the slurry composition on a collector.

  In addition, you may provide the process of performing a pressurization process to a positive electrode active material layer using a die press or a roll press after a drying process. By the pressure treatment, the adhesion between the positive electrode active material layer and the current collector can be improved.

<Positive electrode for lithium ion secondary battery>
Next, the positive electrode for lithium ion secondary batteries of this invention is demonstrated. The positive electrode for a lithium ion secondary battery of the present invention has a positive electrode active material containing at least one of Mn and Ni (Mn and / or Ni-containing positive electrode active material) and a content ratio of acidic functional group-containing monomer units of 15. Particulate polymer B having a polymer A (acidic polymer A) having a weight average molecular weight of 10,000 to 200,000 and a content ratio of acidic functional group-containing monomer units of 10% by mass or less. (Particulate polymer B) and a conductive material.

  The positive electrode active material containing Mn and / or Ni, the acidic polymer A, the particulate polymer B, and the conductive material in the positive electrode for a lithium ion secondary battery of the present invention are a slurry composition for a positive electrode of a lithium ion secondary battery. The thing similar to what was mentioned in the item of the thing can be used.

  And the positive electrode for lithium ion secondary batteries of this invention can be manufactured with the manufacturing method of the positive electrode for lithium ion secondary batteries of the above-mentioned this invention, for example. Moreover, the positive electrode for a lithium ion secondary battery of the present invention provides a slurry composition containing a Mn and / or Ni-containing positive electrode active material, an acidic polymer A, a particulate polymer B, and a conductive material, It is also possible to produce composite particles by dry granulating the slurry composition, supplying the composite particles onto a current collector, and forming a positive electrode active material layer on the current collector by pressure molding or the like. it can. The positive electrode for a lithium ion secondary battery of the present invention obtained by these methods has sufficiently suppressed corrosion of the current collector and has excellent electrical characteristics when used in a lithium ion secondary battery. Demonstrate. Here, the thickness of the positive electrode active material layer is preferably in the range of 50 to 120 μm. By setting the thickness of the positive electrode active material layer within the above range, the positive electrode can be prevented from cracking and the capacity of the lithium ion secondary battery can be increased.

<Lithium ion secondary battery>
The lithium ion secondary battery of this invention is equipped with the positive electrode for lithium ion secondary batteries of the said invention, a negative electrode, electrolyte solution, and a separator.

(Negative electrode)
As the negative electrode of the lithium ion secondary battery of the present invention, various negative electrodes commonly used for negative electrodes for lithium ion secondary batteries can be used. For example, a thin plate of metallic lithium can be used. Alternatively, for example, a material including a current collector and a negative electrode active material layer formed on the surface of the current collector can be used.

  As the current collector for the negative electrode, for example, a material made of a metal material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, or platinum is used. Among these, copper is particularly preferable from the viewpoint of having high electrical conductivity and being electrochemically stable.

The negative electrode active material layer is a layer containing a negative electrode active material and a binder.
As the negative electrode active material and the binder, known materials can be used, for example, those described in JP 2012-204303 A. A binder similar to the particulate polymer B used in the positive electrode may be used. In addition, the negative electrode active material layer may contain components other than the negative electrode active material and the binder as necessary.

  The negative electrode is produced, for example, by preparing a negative electrode slurry composition containing a negative electrode active material, a binder, and water, forming a layer of the negative electrode slurry composition on a current collector, and drying the layer. Alternatively, the negative electrode slurry composition is dried and granulated to form composite particles, the composite particles are supplied onto the current collector, and the negative electrode active material layer is formed on the current collector by pressure molding or the like. May be manufactured.

(Electrolyte)
As the electrolytic solution of the lithium ion secondary battery of the present invention, an electrolytic solution in which an electrolyte is dissolved in a solvent is usually used. As the solvent, an organic solvent is preferably used.
A lithium salt is used as the electrolyte. As lithium salt, the thing as described in Unexamined-Japanese-Patent No. 2012-204303 can be used, for example. Among these lithium salts, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li are preferable, and LiPF ₆ is particularly preferable because it is easily dissolved in an organic solvent and exhibits a high degree of dissociation. The higher the dissociation electrolyte, the higher the lithium ion conductivity. In addition, an electrolyte may be used individually by 1 type and may be used in combination of 2 or more types.

  The solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the electrolyte. For example, a high dielectric constant solvent such as ethylene carbonate, propylene carbonate, γ-butyrolactone, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, diethyl Those to which a viscosity adjusting solvent such as carbonate, ethyl methyl carbonate, dimethyl carbonate, methyl acetate, dimethoxyethane, dioxolane, methyl propionate, methyl formate and the like are added are preferable. And it is especially preferable to contain ethylene carbonate as a solvent. This is because ethylene carbonate has a high relative dielectric constant and can dissolve a large amount of lithium salt, and since its molecular size is small, its viscosity is low and it does not significantly inhibit the movement of lithium ions at room temperature.

  And the content rate of the ethylene carbonate in the solvent of the lithium ion secondary battery of this invention at the temperature of 25 degreeC becomes like this. Preferably it is 30 volume% or more, More preferably, it is 35 volume% or more, Most preferably, it is 37 volume% or more. , Preferably it is 60 volume% or less, More preferably, it is 55 volume% or less, More preferably, it is 47 volume% or less. Although ethylene carbonate has the above-described excellent points, it has a high freezing point, so that it solidifies or greatly increases the viscosity in a low temperature range. Therefore, if the content ratio of ethylene carbonate is increased too much, the electrical characteristics, particularly the low-temperature output characteristics, of the lithium ion secondary battery at low temperatures are deteriorated. The positive electrode using the slurry composition of the present invention contains the above-mentioned acidic polymer A, and the acidic polymer A has the effect of lowering the freezing point of the electrolytic solution as described above. In the secondary battery, even when the content ratio of ethylene carbonate at 25 ° C. is 30% by volume or more, the low-temperature output characteristics can be improved. Moreover, when the content ratio of ethylene carbonate at 25 ° C. is 30% by volume or more, the lithium salt can be dissolved well and other electrical characteristics of the lithium ion secondary battery can be secured.

  Moreover, you may contain an additive in electrolyte solution. Examples of the additive include carbonate compounds such as vinylene carbonate (VC).

The relative dielectric constant of the electrolytic solution at a temperature of 25 ° C. is not particularly limited, but is preferably in the range of 20 to 100, more preferably 20 to 90, and particularly preferably 25 to 90. When the relative dielectric constant of the electrolytic solution is within the above range, an electrolyte such as LiPF ₆ can be sufficiently dissolved.

  The viscosity of the electrolytic solution is not particularly limited, but the viscosity at a temperature of 25 ° C. (according to a B-type viscometer) is used to suppress the change in the lithium ion concentration in the electrolytic solution and ensure the electrical characteristics of the lithium ion secondary battery. The measured value) is preferably 3 mPa · s or less.

(Separator)
As a separator, the thing of Unexamined-Japanese-Patent No. 2012-204303 can be used, for example. Among these, the thickness of the entire separator can be reduced, thereby increasing the ratio of the electrode active material in the secondary battery and increasing the capacity per volume. A microporous film made of a resin such as polyethylene, polypropylene, polybutene, or polyvinyl chloride is preferable.

(Method for producing lithium ion secondary battery)
The lithium ion secondary battery of the present invention includes, for example, a battery container in which the above-described positive electrode and negative electrode of the present invention are stacked via a separator, and this is wound or folded according to the battery shape as necessary. It can be manufactured by injecting the electrolyte solution into the battery container and sealing it. In order to prevent an increase in pressure inside the lithium ion secondary battery, overcharge / discharge, etc., an overcurrent prevention element such as a fuse or a PTC element, an expanded metal, a lead plate, etc. may be provided as necessary. . The shape of the lithium ion secondary battery may be any of, for example, a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like. The lithium ion secondary battery obtained in this manner has sufficiently suppressed corrosion of the current collector of the positive electrode and has excellent electrical characteristics.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples. In the following description, “%” and “part” representing amounts are based on mass unless otherwise specified.
In Examples and Comparative Examples, the corrosion inhibitory effect of the current collector, the adhesion strength between the positive electrode active material layer and the current collector, the cycle characteristics of the lithium ion secondary battery, and the low temperature output characteristics of the lithium ion secondary battery are evaluated. The following methods were used.

[Corrosion suppression effect of current collector]
The positive electrode slurry composition for lithium ion secondary batteries prepared in each Example and Comparative Example was applied on a 20 μm aluminum foil (current collector) so that the film thickness after drying was about 70 μm, and the temperature was adjusted to 50 ° C. And dried for 20 minutes to obtain a positive electrode sample. In the obtained positive electrode sample, a 10 cm × 10 cm range on the surface of the positive electrode active material layer side (that is, the side on which the slurry composition is applied) is visually observed, and a coating defect portion having a diameter of 0.5 mm or more is observed. By confirming the number of spots where the current occurred, the corrosion inhibitory effect of the current collector was evaluated. This means that the fewer occurrences of defective coating parts, the less hydrogen gas bubbles are generated due to alkali corrosion of the aluminum foil (current collector), and there are fewer irregularities on the surface of the positive electrode active material due to the bubbles. It shows that the corrosion of the electric body is suppressed.
A: The location where the coating failure occurs cannot be confirmed, and the whole is smooth. B: The location where the coating failure occurs is 1 or more and less than 5 locations C: The location where the coating failure occurs is 5 locations or more and less than 10 locations D: 10 or more occurrences of defective coating

[Adhesion strength between positive electrode active material layer and current collector]
The positive electrodes for lithium ion secondary batteries produced in Examples and Comparative Examples were cut into rectangles having a length of 100 mm and a width of 10 mm to obtain test pieces. Cellophane tape was affixed on the surface of the positive electrode active material layer of this test piece with the surface of the positive electrode active material layer facing down. At this time, a cellophane tape defined in JIS Z1522 was used. The cellophane tape was fixed on a horizontal test bench. Then, the stress when one end of the current collector was pulled vertically upward at a pulling speed of 50 mm / min and peeled was measured. This measurement was performed three times, the average value of the measured values was obtained, and the average value was taken as the peel strength. It shows that the adhesion strength between the positive electrode active material layer and the current collector is higher as the peel strength is higher.
A: Stress is 20 N / m or more B: Stress is 15 N / m or more and less than 20 N / m C: Stress is 10 N / m or more and less than 15 N / m D: Stress is less than 10 N / m

[Cycle characteristics]
The lithium ion secondary battery of the laminate type cell produced by the Example and the comparative example was left still for 24 hours in 25 degreeC environment. Thereafter, this lithium ion secondary battery was charged to 4.2 V by a low current method of 0.5 C in an environment of 25 ° C., and charged and discharged to 3.0 V, and the initial capacity C0 was measured. did. Furthermore, this lithium ion secondary battery was repeatedly charged and discharged in the same manner as the above charge and discharge in an environment of 60 ° C., and the capacity C2 after 200 cycles was measured. The cycle characteristics (high-temperature cycle characteristics) were evaluated based on the capacity retention rate represented by ΔC = C2 / C0 × 100 (%). It shows that it is excellent in cycling characteristics, so that this capacity | capacitance maintenance factor is high.
A: Capacity maintenance ratio ΔC is 85% or more B: Capacity maintenance ratio ΔC is 80% or more and less than 85% C: Capacity maintenance ratio ΔC is 70% or more and less than 80% D: Capacity maintenance ratio ΔC is less than 70%

[Low temperature output characteristics]
The laminate type cells prepared in Examples and Comparative Examples were allowed to stand for 24 hours in an environment at 25 ° C. Thereafter, an operation of charging with a low current method of 1 C over 5 hours was performed in an environment of 25 ° C., and the voltage V0 at that time was measured. Thereafter, a discharge operation was performed at a discharge rate of 1 C in a -10 ° C environment, and the voltage V1 15 seconds after the start of discharge was measured. The low temperature output characteristic was evaluated by a voltage drop represented by ΔV = V0−V1. It shows that it is excellent in low temperature output characteristics, so that this voltage drop is small.
A: Voltage drop ΔV is 120 mV or more and less than 140 mV B: Voltage drop ΔV is 140 mV or more and less than 160 mV C: Voltage drop ΔV is 160 mV or more and less than 180 mV D: Voltage drop ΔV is 180 mV or more and less than 200 mV E: Voltage drop ΔV is 200 mV or more

Acidic polymers 1 to 16 and particulate polymers 1 to 4 were produced as follows. In addition, the weight average molecular weight of the obtained acidic polymer was measured by GPC (gel permeation chromatography) under the following conditions.
Measuring device: GPC manufactured by Tosoh Corporation (model number: HLC-8220)
Molecular weight column: TSKgel SuperHZM-M (manufactured by Tosoh Corporation)
Mobile fluid: Tetrahydrofuran Flow rate: 0.6 ml / min
Standard material for calibration curve: polystyrene Measurement method: A solid polymer was dissolved in a mobile solution so that the solid content was 0.5% by mass and filtered through a 0.45 μm filter.

  Further, the glass transition temperature (Tg) of the obtained particulate polymer was measured using DSC6200R manufactured by Seiko Instruments Inc. based on JIS K7121. Specifically, the temperature is raised to 150 ° C. at 10 ° C./min for the first time and kept for 10 minutes, then cooled to −80 ° C. at 10 ° C./min and kept for 10 minutes, and then heated to 150 ° C. at every heating rate. The temperature was raised at a temperature of 10 ° C., and the extrapolated glass transition start temperature (° C.) was determined using the DSC curve measured at the time of the second temperature rise, and used as the glass transition temperature.

[Production of Acidic Polymer 1]
In a 5 MPa pressure vessel with a stirrer, 30 parts of methacrylic acid (acidic functional group-containing monomer), 10 parts of 2,2,2-trifluoroethyl methacrylate (fluorine-containing (meth) acrylic acid ester monomer), acrylic acid 28.8 parts of butyl ((meth) acrylate monomer), 29.2 parts of ethyl acrylate ((meth) acrylate monomer), 0.8 part of ethylene dimethacrylate (crosslinkable monomer) , Ammonium polyoxyalkylene alkenyl ether sulfate ("Latemul PD-104" manufactured by Kao Corporation, reactive surfactant) 1.2 parts, 0.1 part of t-dodecyl mercaptan (molecular weight modifier), 150 parts of ion-exchanged water, and 0.5 part of potassium persulfate (polymerization initiator) was added and stirred sufficiently. Then, it heated to 60 degreeC and superposition | polymerization was started. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain an aqueous dispersion of acidic polymer 1.
The weight average molecular weight of the acidic polymer 1 was 50,000, and the pH of the aqueous dispersion of the acidic polymer 1 was 5.

[Production of Acidic Polymer 2]
Acidic polymer 1 was used except that 20 parts of methacrylic acid (acidic functional group-containing monomer) and 39.2 parts of ethyl acrylate ((meth) acrylic acid ester monomer unit) were used. An aqueous dispersion of polymer 2 was obtained.
The weight average molecular weight of the acidic polymer 2 was 50000, and the pH of the aqueous dispersion of the acidic polymer 2 was 5.3.

[Production of acidic polymer 3]
60 parts of methacrylic acid (acidic functional group-containing monomer), 28 parts of ethyl acrylate ((meth) acrylic acid ester monomer unit), and butyl acrylate ((meth) acrylic acid ester monomer unit) ) Was used in the same manner as the acidic polymer 1 except that an aqueous dispersion of the acidic polymer 3 was obtained.
The weight average molecular weight of the acidic polymer 3 was 50000, and the pH of the aqueous dispersion of the acidic polymer 3 was 4.

[Production of Acidic Polymer 4]
Acidic polymer 1 was used except that 15 parts of methacrylic acid (acidic functional group-containing monomer) and 44.2 parts of ethyl acrylate ((meth) acrylic acid ester monomer unit) were used. An aqueous dispersion of polymer 4 was obtained.
The weight average molecular weight of the acidic polymer 4 was 50000, and the pH of the aqueous dispersion of the acidic polymer 4 was 5.5.

[Production of acidic polymer 5]
Instead of 30 parts of methacrylic acid (acidic functional group-containing monomer), 15 parts of 2-acrylamido-2-methylpropanesulfonic acid (acidic functional group-containing monomer) is used and ethyl acrylate ((meth) acrylic acid) An aqueous dispersion of acidic polymer 5 was obtained in the same manner as acidic polymer 1 except that the ester monomer unit) was changed to 44.2 parts.
The weight average molecular weight of the acidic polymer 5 was 50000, and the pH of the aqueous dispersion of the acidic polymer 5 was 3.

[Production of Acidic Polymer 6]
An aqueous dispersion of acidic polymer 6 was obtained in the same manner as acidic polymer 1 except that 0.05 part of t-dodecyl mercaptan (molecular weight modifier) was used.
The weight average molecular weight of the acidic polymer 6 was 100,000, and the pH of the aqueous dispersion of the acidic polymer 6 was 5.

[Production of acidic polymer 7]
An aqueous dispersion of acidic polymer 7 was obtained in the same manner as acidic polymer 1 except that 0.2 part of t-dodecyl mercaptan (molecular weight modifier) was used.
The weight average molecular weight of the acidic polymer 7 was 25000, and the pH of the aqueous dispersion of the acidic polymer 7 was 5.

[Production of Acidic Polymer 8]
Without using 2,2,2-trifluoroethyl methacrylate (fluorine-containing (meth) acrylic acid ester monomer), 39.2 parts of ethyl acrylate ((meth) acrylic acid ester monomer unit) Except that, an aqueous dispersion of the acidic polymer 8 was obtained in the same manner as in the acidic polymer 1.
The weight average molecular weight of the acidic polymer 8 was 50000, and the pH of the aqueous dispersion of the acidic polymer 8 was 5.

[Production of Acidic Polymer 9]
15 parts of 2,2,2-trifluoroethyl methacrylate (fluorine-containing (meth) acrylate monomer) and 23.8 parts of butyl acrylate ((meth) acrylate monomer unit) Except that, an aqueous dispersion of the acidic polymer 9 was obtained in the same manner as in the acidic polymer 1.
The weight average molecular weight of the acidic polymer 9 was 50000, and the pH of the aqueous dispersion of the acidic polymer 9 was 5.

[Production of Acidic Polymer 10]
5 parts of 2,2,2-trifluoroethyl methacrylate (fluorine-containing (meth) acrylate monomer) and 34.2 parts of ethyl acrylate ((meth) acrylate monomer unit) Except that, an aqueous dispersion of the acidic polymer 10 was obtained in the same manner as in the acidic polymer 1.
The weight average molecular weight of the acidic polymer 10 was 50000, and the pH of the aqueous dispersion of the acidic polymer 10 was 5.

[Production of Acidic Polymer 11]
An aqueous dispersion of acidic polymer 11 was obtained in the same manner as acidic polymer 1 except that 0.025 part of t-dodecyl mercaptan (molecular weight modifier) was used.
The weight average molecular weight of the acidic polymer 11 was 200,000, and the pH of the aqueous dispersion of the acidic polymer 11 was 5.

[Production of Acidic Polymer 12]
An aqueous dispersion of acidic polymer 12 was obtained in the same manner as acidic polymer 1 except that the amount of t-dodecyl mercaptan (molecular weight modifier) was 0.33 part.
The weight average molecular weight of the acidic polymer 12 was 15000, and the pH of the aqueous dispersion of the acidic polymer 12 was 5.

[Production of Acidic Polymer 13]
10 parts of methacrylic acid (acidic functional group-containing monomer), 39.2 parts of ethyl acrylate ((meth) acrylate monomer unit), butyl acrylate ((meth) acrylate monomer unit) ) Was changed to 38.8 parts, and an aqueous dispersion of acidic polymer 13 was obtained in the same manner as acidic polymer 1.
The weight average molecular weight of the acidic polymer 13 was 50000, and the pH of the aqueous dispersion of the acidic polymer 11 was 6.

[Acid polymer 14]
As the acidic polymer 14, polyacrylic acid (weight average molecular weight 150,000, manufactured by Wako Pure Chemical Industries) was used. Water was added to the acidic polymer 14 to obtain an aqueous dispersion of the acidic polymer 14. The pH of the aqueous dispersion of the acidic polymer 14 was 3.

[Production of Acidic Polymer 15]
An aqueous dispersion of acidic polymer 15 was obtained in the same manner as acidic polymer 1 except that 0.3 part of t-dodecyl mercaptan (molecular weight modifier) was used.
The weight average molecular weight of the acidic polymer 15 was 8000, and the pH of the aqueous dispersion of the acidic polymer 15 was 5.

[Production of Acidic Polymer 16]
An aqueous dispersion of acidic polymer 16 was obtained in the same manner as acidic polymer 1 except that 0.02 part of t-dodecyl mercaptan (molecular weight modifier) was used.
The weight average molecular weight of the acidic polymer 16 was 400,000, and the pH of the aqueous dispersion of the acidic polymer 16 was 5.

[Production of particulate polymer 1]
In a 5 MPa pressure vessel with a stirrer, 4 parts of itaconic acid (acidic functional group-containing monomer), 76 parts of 2-ethylhexyl acrylate ((meth) acrylic acid ester monomer), acrylonitrile ((meth) acrylonitrile monomer) 20 parts, 1 part of sodium dodecylbenzenesulfonate (surfactant), 150 parts of ion-exchanged water, and 0.8 part of potassium persulfate (polymerization initiator) were added and sufficiently stirred. Then, it heated to 50 degreeC and superposition | polymerization was started. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing the particulate polymer 1. A 5% aqueous sodium hydroxide solution was added to the mixture containing the particulate polymer 1 to adjust the pH to 8. Then, after removing the unreacted monomer from the mixture containing the particulate polymer 1 by heating and vacuum distillation, the mixture is cooled to 30 ° C. or lower, and an aqueous dispersion containing the desired particulate polymer 1 is obtained. Obtained. The glass transition temperature (Tg) of the particulate polymer 1 was −37 ° C.

[Production of particulate polymer 2]
Except that 2 parts of methacrylic acid (acidic functional group-containing monomer) is used in place of 4 parts of itaconic acid (acidic functional group-containing monomer) and 22 parts of acrylonitrile ((meth) acrylonitrile monomer) are used. In the same manner as in the particulate polymer 1, an aqueous dispersion of the particulate polymer 2 was obtained. The glass transition temperature (Tg) of the particulate polymer 2 was −39 ° C.

[Production of particulate polymer 3]
Instead of 4 parts of itaconic acid (acidic functional group-containing monomer), 10 parts of methacrylic acid (acidic functional group-containing monomer) are used, and 2-ethylhexyl acrylate ((meth) acrylic acid ester monomer) is used. An aqueous dispersion of the particulate polymer 3 was obtained in the same manner as the particulate polymer 1, except that the amount was 70 parts. The glass transition temperature (Tg) of the particulate polymer 3 was −6 ° C.

[Production of particulate polymer 4]
Except that itaconic acid (acidic functional group-containing monomer) is 20 parts and 2-ethylhexyl acrylate ((meth) acrylic acid ester monomer) is 60 parts, the same as the particulate polymer 1, An aqueous dispersion of the particulate polymer 4 was obtained. The glass transition temperature (Tg) of the particulate polymer 4 was 88 ° C.

—Example 1—
The slurry composition, positive electrode, and lithium ion secondary battery of Example 1 were manufactured by the following procedure.

[1-1. Production of slurry composition]
100 parts of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (“NMC111” manufactured by Nippon Kagaku Kogyo Co., Ltd.) with a volume average particle size of 15 μm as a positive electrode active material in a planetary mixer with a disper, and acetylene black as a conductive material 2 parts (“HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd.) and 1 part carboxymethylcellulose (“MAC-350HC” manufactured by Nippon Paper Chemical Co., Ltd.) as a thickener were added in an amount corresponding to the solid content and mixed with stirring for 10 minutes. Further, 0.1 part of the aqueous dispersion of acidic polymer 1 was added in an amount corresponding to the solid content, adjusted to a solid content concentration of 83% with ion-exchanged water, and then mixed at 25 ° C. for 60 minutes. Further, as a binder, 2 parts of the aqueous dispersion containing the particulate polymer 1 prepared to a concentration of 40% was added in an amount equivalent to the solid content, and after adjusting the solid content concentration to 65% with ion-exchanged water, the planetary The mixture was mixed with a mixer to prepare a slurry composition (pH 10.5) for a positive electrode of a lithium ion secondary battery. Using this slurry composition, the corrosion inhibitory effect of the current collector was evaluated in the manner described above.

[1-2. Production of positive electrode for lithium ion secondary battery]
Apply the above slurry composition for a lithium ion secondary battery positive electrode on a 20 μm-thick aluminum foil as a current collector with a comma coater so that the film thickness after drying is about 100 μm, and then dry. It was. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Then, it heat-processed for 2 minutes in 120 degreeC oven, and obtained the electrode raw material (positive electrode raw material). And the obtained positive electrode original fabric was rolled with the roll press, and the positive electrode for lithium ion secondary batteries whose thickness of a positive electrode active material layer is 100 micrometers was obtained. The adhesion strength of this positive electrode was evaluated in the manner described above.

[1-3. Production of negative electrode binder]
In a 5 MPa pressure vessel with a stirrer, 33.5 parts of 1,3-butadiene, 3.5 parts of itaconic acid, 62 parts of styrene, 1 part of 2-hydroxyethyl acrylate, 0.4 part of sodium dodecylbenzenesulfonate (surfactant) Then, 150 parts of ion-exchanged water and 0.5 part of potassium persulfate (polymerization initiator) were added and sufficiently stirred. Then, it heated to 50 degreeC and superposition | polymerization was started. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a particulate binder (SBR). The mixture containing the particulate binder was adjusted to pH 8 by adding a 5% aqueous sodium hydroxide solution. Then, after removing the unreacted monomer from the mixture containing the particulate binder by heating under reduced pressure, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired particulate binder.

[1-4. Production of slurry composition for negative electrode]
In a planetary mixer with a disper, 100 parts of artificial graphite (volume average particle diameter: 24.5 μm) having a specific surface area of 5.5 m ² / g as a negative electrode active material, and carboxymethyl cellulose (manufactured by Nippon Paper Chemical Co., Ltd. “ 1 part of a 2% aqueous solution of “MAC-350HC”) corresponding to the solid content was added, and the solid content concentration was adjusted to 65% with ion-exchanged water, and then mixed at 25 ° C. for 60 minutes. Next, after adjusting to 60% of solid content concentration with ion-exchange water, it mixed for 15 minutes at 25 degreeC, and the liquid mixture was obtained. In the above mixed liquid, 1.0 part of an aqueous dispersion containing the particulate binder in the above step 1-3 in a solid content equivalent amount and ion-exchanged water are added and adjusted so that the final solid content concentration is 52%, Mix for another 10 minutes. This was defoamed under reduced pressure to obtain a negative electrode slurry composition having good fluidity.

[1-5. Production of negative electrode]
The slurry composition for negative electrode obtained in the above step 1-4 was applied on a copper foil having a thickness of 20 μm, which is a current collector, with a comma coater so that the film thickness after drying was about 150 μm, Dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Then, the negative electrode original fabric was obtained by heat-processing at 120 degreeC for 2 minute (s). This negative electrode original fabric was rolled with a roll press to obtain a negative electrode having a negative electrode active material layer thickness of 80 μm.

[1-6. Preparation of separator]
A single-layer polypropylene separator (“CELGARD (registered trademark) 2500” manufactured by Celgard) was cut into a 5 × 5 cm ² square.

[1-7. Lithium ion secondary battery]
An aluminum packaging exterior was prepared as the battery exterior. The positive electrode obtained in the above step 1-2 was cut into a 4 × 4 cm ² square and arranged so that the current collector-side surface was in contact with the aluminum packaging exterior. On the surface of the positive electrode active material layer of the positive electrode, the square separator obtained in Step 1-6 was disposed. Furthermore, the negative electrode obtained in the above step 1-5 was cut into a square of 4.2 × 4.2 cm ² and arranged on the separator so that the surface on the negative electrode active material layer side faces the separator. Electrolytic solution 1 (solvent: EC / DEC / VC = 40.0 / 58.5 / 1.5 volume ratio (25 ° C.), electrolyte: LiPF _{6 at} a concentration of 1 M, relative permittivity (25 ° C.): 36.5, Viscosity (25 ° C.): 1.2 mPa · s)) was injected so that no air remained. Furthermore, in order to seal the opening of the aluminum packaging material, heat sealing at 150 ° C. was performed to close the aluminum exterior, and a lithium ion secondary battery was manufactured. With respect to this lithium ion secondary battery, the cycle characteristics and the low temperature output characteristics were evaluated in the manner described above.

—Example 2—
The same as Example 1 except that Li _1.2 Ni _0.17 Co _0.07 Mn _0.56 O ₂ was used instead of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as the positive electrode active material. In addition, a slurry composition for a positive electrode of a lithium ion secondary battery (pH 10), a positive electrode, and a lithium ion secondary battery were manufactured, and the above items were evaluated.

—Example 3—
A slurry composition for a positive electrode of a lithium ion secondary battery (pH 11) in the same manner as in Example 1 except that LiNiO ₂ was used instead of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as the positive electrode active material. A positive electrode and a lithium ion secondary battery were manufactured, and the above items were evaluated.

-Examples 4 to 9-
A slurry composition for a lithium ion secondary battery positive electrode (respectively pH 10) was used in the same manner as in Example 1 except that the aqueous dispersions of acidic polymers 2 to 7 were used instead of the aqueous dispersion of acidic polymer 1, respectively. .8 10.1 11.3 11.3 10.5 10.5), a positive electrode, and a lithium ion secondary battery were manufactured, and the above items were evaluated.

-Example 10-
A slurry composition for a positive electrode of a lithium ion secondary battery (pH 10.6) was used in the same manner as in Example 1 except that the aqueous dispersion of the particulate polymer 2 was used instead of the aqueous dispersion of the particulate polymer 1. ), A positive electrode, and a lithium ion secondary battery were manufactured, and the above items were evaluated.

-Examples 11-13-
A slurry composition for a lithium ion secondary battery positive electrode (respectively pH 10) was used in the same manner as in Example 1 except that the aqueous dispersion of acidic polymers 8 to 10 was used instead of the aqueous dispersion of acidic polymer 1, respectively. .5 10.6 10.5), a positive electrode and a lithium ion secondary battery were manufactured, and the above-mentioned items were evaluated.

-Examples 14 and 15-
A slurry composition for a positive electrode of a lithium ion secondary battery (respectively pH 10.2), except that the blending amount of the acidic polymer 1 was 0.5 parts and 0.02 parts respectively corresponding to the solid content. 11.3), a positive electrode, and a lithium ion secondary battery were manufactured, and the above items were evaluated.

-Example 16-
As in Example 1, a slurry composition for lithium ion secondary battery positive electrode (pH 10.5) and a positive electrode were produced, and instead of electrolytic solution 1, electrolytic solution 2 (solvent: EC / DEC / VC = 50.0 / 48.5 / 1.5 volume ratio (25 ° C.), electrolyte: LiPF _{6 at} a concentration of 1 M, relative dielectric constant (25 ° C.): 45.4, viscosity (25 ° C.): 1.3 mPa · s) A lithium ion secondary battery was manufactured in the same manner as in Example 1 except that was used, and the above items were evaluated.

-Example 17-
Similarly to Example 1, a slurry composition for lithium ion secondary battery positive electrode (pH 10.5) and a positive electrode were produced, and instead of electrolytic solution 1, electrolytic solution 3 (solvent: EC / DEC / VC = 33.0 / 65.5 / 1.5 volume ratio (25 ° C.), electrolyte: LiPF _{6 at} a concentration of 1 M, relative dielectric constant (25 ° C.): 30.2, viscosity (25 ° C.): 1.1 mPa · s) A lithium ion secondary battery was manufactured in the same manner as in Example 1 except that was used, and the above items were evaluated.

-Example 18-
The slurry composition for a lithium ion secondary battery positive electrode (pH 9.5), a positive electrode, and lithium, except that the blending amount of the acidic polymer 1 was 0.85 part corresponding to the solid content, as in Example 1. An ion secondary battery was manufactured and evaluated for the above items.

-Examples 19 and 20-
A slurry composition for a positive electrode of a lithium ion secondary battery (both pH values) was used in the same manner as in Example 1 except that the aqueous dispersions of acidic polymers 11 and 12 were used in place of the aqueous dispersion of acidic polymer 1, respectively. 10.5), a positive electrode and a lithium ion secondary battery were manufactured, and the above-mentioned items were evaluated.

-Example 21-
A slurry composition for a positive electrode of a lithium ion secondary battery (pH 10.3) was used in the same manner as in Example 1 except that an aqueous dispersion of particulate polymer 3 was used instead of the aqueous dispersion of particulate polymer 1. ), A positive electrode, and a lithium ion secondary battery were manufactured, and the above items were evaluated.

-Comparative Examples 1-4-
A slurry composition for a lithium ion secondary battery positive electrode (respectively pH 11) was used in the same manner as in Example 1 except that the aqueous dispersion of acidic polymers 13 to 16 was used instead of the aqueous dispersion of acidic polymer 1 respectively. .5 10.2 10.5 11), a positive electrode, and a lithium ion secondary battery were manufactured, and the above items were evaluated.

—Comparative Example 5—
A slurry composition for a positive electrode of a lithium ion secondary battery (pH 10.2) was used in the same manner as in Example 1 except that an aqueous dispersion of particulate polymer 4 was used instead of the aqueous dispersion of particulate polymer 1. ), A positive electrode, and a lithium ion secondary battery were manufactured, and the above items were evaluated.

—Comparative Example 6—
A lithium ion secondary battery positive electrode slurry composition (pH 12), a positive electrode, and a lithium ion secondary battery were produced in the same manner as in Example 1 except that the aqueous dispersion of acidic polymer 1 was not used. The items were evaluated.

  In the table, MA is methacrylic acid, AMPS is 2-acrylamido-2-methylpropanesulfonic acid, TFEM is 2,2,2-trifluoroethyl methacrylate, EA is ethyl acrylate, and BA is acrylic. Butyl acid, EDM represents ethylene dimethacrylate, IA represents itaconic acid, 2EHA represents 2-ethylhexyl acrylate, AN represents acrylonitrile, and AA represents acrylic acid.

  As is clear from the results of the table, the content of the acidic functional group-containing monomer unit is within a specific range and the weight average molecular weight is within a specific range, and the acidic functional group contains The lithium ion secondary batteries of Examples 1 to 21 obtained using a slurry composition containing the particulate polymer B having a monomer unit content of not more than a specific value include the acidic polymer A. The corrosion of the current collector was suppressed as compared with Comparative Example 7 that was not, and the low-temperature output characteristics, the cycle characteristics, and the adhesion strength between the positive electrode active material layer and the current collector were remarkably excellent.

In Comparative Example 1, the content ratio of the acidic functional group-containing monomer unit in the acidic polymer was low, the current collector corrosion-inhibiting effect was inferior to Examples 1-21, and the low-temperature output characteristics were also inferior.
Although the comparative example 2 has a high content ratio of the acidic functional group-containing monomer unit in the acidic polymer and the corrosion inhibitory effect of the current collector is sufficient, the acidic polymer A is a (meth) acrylic ester monomer unit. And since the fluorine-containing (meth) acrylic ester monomer unit was not included, the low-temperature output characteristics were inferior to those of Examples 1 to 21. Furthermore, since the content ratio of the acidic functional group-containing monomer unit in the acidic polymer is high, the flexibility of the electrode plate is low, and the adhesion strength is inferior to Examples 1-21.
In Comparative Example 3, since the weight average molecular weight of the acidic polymer is small, dissolution in the electrolytic solution proceeds, and the current collector corrosion inhibiting effect is good. On the other hand, the low temperature output characteristics as compared with Examples 1-21 And the cycle characteristics were inferior.
In Comparative Example 4, since the acidic polymer has a large weight average molecular weight, the acidic polymer A hardly swells in the electrolytic solution, and the current collector corrosion suppression effect is generally good, but compared with Examples 1-21. Thus, the low-temperature output characteristics were inferior.
In Comparative Example 5, since the content ratio of the acidic functional group-containing monomer unit in the particulate polymer B is high and cannot be bound well, the positive electrode active material and the acidic polymer A and a positive electrode active material layer having a preferable structure can be formed. It was inferior about the low-temperature output characteristic and cycling characteristics compared with Examples 1-21.

Claims (7)

A positive electrode active material containing at least one of Mn and Ni;
A polymer A having a content ratio of acidic functional group-containing monomer units of 15 to 60% by mass and a weight average molecular weight of 10,000 to 200,000;
The content of the acidic functional group-containing monomer unit is 2 to 10% by mass, the content of the (meth) acrylonitrile monomer unit is 5 to 30% by mass, and the content of the (meth) acrylic acid ester monomer unit. Particulate polymer B in which is 60 to 90% by mass ;
Conductive material;
water and,
Only including,
The polymer A is an addition polymer,
The ratio (a / b) of the mass (a) of the polymer A to the mass (b) of the particulate polymer B is in the range of 0.01 to 0.3.
A slurry composition for a positive electrode of a lithium ion secondary battery. The slurry composition for a lithium ion secondary battery positive electrode according to claim 1 , wherein the polymer A contains a fluorine-containing (meth) acrylic acid ester monomer unit. Applying a slurry composition for a lithium ion secondary battery positive electrode according to claim 1 or 2 on a current collector;
Drying the slurry composition for a lithium ion secondary battery positive electrode coated on the current collector to form a positive electrode active material layer;
The manufacturing method of the positive electrode for lithium ion secondary batteries containing. A positive electrode active material containing at least one of Mn and Ni;
A polymer A having a content ratio of acidic functional group-containing monomer units of 15 to 60% by mass and a weight average molecular weight of 10,000 to 200,000;
The content of the acidic functional group-containing monomer unit is 2 to 10% by mass, the content of the (meth) acrylonitrile monomer unit is 5 to 30% by mass, and the content of the (meth) acrylic acid ester monomer unit. Particulate polymer B in which is 60 to 90% by mass ;
Conductive material;
Only including,
The polymer A is an addition polymer,
The ratio (a / b) of the mass (a) of the polymer A to the mass (b) of the particulate polymer B is in the range of 0.01 to 0.3.
Positive electrode for lithium ion secondary battery. The positive electrode for a lithium ion secondary battery according to claim 4 , wherein the polymer A contains a fluorine-containing (meth) acrylic acid ester monomer unit. A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to claim 4 or 5 , a negative electrode, an electrolytic solution, and a separator. The electrolytic solution includes an electrolyte and a solvent,
The lithium ion secondary battery of Claim 6 whose content rate of ethylene carbonate in the said solvent is 30-60 volume%.