JP7704031B2 - Binder composition for secondary battery, slurry composition for secondary battery functional layer, functional layer for secondary battery, and secondary battery - Google Patents

Description

The present invention relates to a binder composition for secondary batteries, a slurry composition for functional layers of secondary batteries, functional layers for secondary batteries, and secondary batteries.

Secondary batteries such as lithium-ion secondary batteries are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Secondary batteries generally include battery components such as electrodes (positive and negative electrodes) and a separator that isolates the positive and negative electrodes to prevent short circuits between the positive and negative electrodes.

Here, as the battery component of the secondary battery, a component having a functional layer containing a binder and, optionally, particles (hereinafter referred to as "functional particles") that are blended in order to cause the battery component to exhibit a desired function is used.
Specifically, the separator for the secondary battery is provided with an adhesive layer containing a binder on a separator substrate, or a porous membrane layer containing a binder and non-conductive particles as functional particles. The electrode for the secondary battery is provided with an electrode mixture layer containing a binder and electrode active material particles as functional particles on a current collector, or an electrode substrate provided with an electrode mixture layer on a current collector, and further provided with the above-mentioned adhesive layer or porous membrane layer.

In order to achieve further performance improvement of secondary batteries, attempts have been made to improve binder compositions containing binding materials. For example, Patent Document 1 discloses an acrylic aqueous dispersion for electrochemical cells, which is characterized by containing at least a water-soluble resin (a) obtained by polymerizing a monomer group containing a polymerizable monomer of an unsaturated carboxylic acid and (meth)acrylamide, and organic particles (b) (excluding the water-soluble resin (a)). According to Patent Document 1, the above-mentioned acrylic aqueous dispersion has sufficient adhesion to a current collector, etc., and by using this acrylic aqueous dispersion as a binder composition to prepare a secondary battery, the cycle characteristics of the secondary battery can be improved.

JP 2012-151108 A

However, the conventional binder compositions described above require further improvement in the adhesion of the functional layer obtained using the binder composition and in the cycle characteristics of the secondary battery.

Therefore, an object of the present invention is to provide a binder composition for secondary batteries that can form a functional layer having excellent adhesiveness and can enable the secondary battery to exhibit excellent cycle characteristics.
Another object of the present invention is to provide a slurry composition for a secondary battery functional layer, which is capable of forming a functional layer having excellent adhesiveness and enabling the secondary battery to exhibit excellent cycle characteristics.
An object of the present invention is to provide a functional layer for a secondary battery that has excellent adhesiveness and allows the secondary battery to exhibit excellent cycle characteristics.
Another object of the present invention is to provide a secondary battery having excellent cycle characteristics.

The present inventors have conducted extensive research with the aim of solving the above problems. The inventors have newly discovered that by using a binder composition containing two specific types of polymers in a solvent, it is possible to increase the adhesion of the functional layer and improve the cycle characteristics of the secondary battery, and have thus completed the present invention.

That is, the present invention aims to advantageously solve the above problems, and the binder composition for secondary batteries of the present invention includes a polymer A, a polymer B, and a solvent, and the polymer A has a total content of a monomer unit having a hydroxyl group and a monomer unit having an amide group of 50% by mass or more and 90% by mass or less, a content of a monomer unit having a carboxylic acid group of 10% by mass or more and 50% by mass or less, and the polymer B has a content of a monomer unit having two carboxylic acid groups of 2% by mass or more and 5% by mass or less, a content of an aromatic vinyl monomer unit of 15% by mass or more and 88% by mass or less, and a content of an aliphatic conjugated diene monomer unit of 10% by mass or more and 80% by mass or less. By using a binder composition containing the above-mentioned polymer A and polymer B in a solvent, a functional layer having excellent adhesiveness can be formed. And, a battery member having the functional layer can exhibit excellent cycle characteristics in a secondary battery.
In the present invention, "containing a monomer unit" means that "a polymer obtained using that monomer contains a repeating unit derived from the monomer." In addition, in the present invention, the "content (mass %)" of each monomer unit (each repeating unit) contained in the polymer can be measured by a nuclear magnetic resonance (NMR) method such as ^1H -NMR or ^13C -NMR.

In the binder composition for a secondary battery of the present invention, the weight average molecular weight of the polymer A is preferably 1,000,000 or more and 15,000,000 or less. When the weight average molecular weight of the polymer A is within the above-mentioned range, the adhesiveness of the functional layer and the cycle characteristics of the secondary battery can be further improved.
In the present invention, the "weight average molecular weight" is a value measured by gel permeation chromatography, and specifically, it can be measured by the method described in the examples of this specification.

In the binder composition for a secondary battery of the present invention, the polymer A preferably has a swelling degree in an electrolyte of 150 mass % or less. When the swelling degree in an electrolyte of the polymer A is equal to or less than the above-mentioned value, the cycle characteristics of the secondary battery can be further improved.
In the present invention, the "degree of swelling in an electrolyte solution" can be measured by the method described in the Examples of this specification.

In the binder composition for secondary batteries of the present invention, the proportion of the polymer B in the total of the polymer A and the polymer B is preferably 5% by mass or more and 45% by mass or less. If the proportion of the amount of the polymer B in the total amount of the polymer A and the polymer B is within the above-mentioned range, it is possible to further improve the cycle characteristics of the secondary battery while suppressing excessive thickening of the slurry composition prepared using the binder composition.

The present invention also aims to advantageously solve the above problems, and the slurry composition for a secondary battery functional layer of the present invention is characterized by containing functional particles and any of the binder compositions described above. By using a slurry composition containing functional particles and any of the binder compositions described above, a functional layer with excellent adhesion can be formed. And, a battery member including the functional layer can provide a secondary battery with excellent cycle characteristics.

The present invention also aims to advantageously solve the above problems, and the functional layer for a secondary battery of the present invention is characterized in that it is formed using the above-mentioned slurry composition for a secondary battery functional layer. The functional layer formed from the above-mentioned slurry composition has excellent adhesiveness. Furthermore, by using a battery component including the functional layer, it is possible to cause the secondary battery to exhibit excellent cycle characteristics.

The present invention also aims to advantageously solve the above problems, and the secondary battery of the present invention is characterized by having the above-mentioned functional layer for a secondary battery. A secondary battery including a battery member having the above-mentioned functional layer has excellent cycle characteristics.

In this specification, a functional layer containing a binder and electrode active material particles is referred to as an "electrode mixture layer," a functional layer containing a binder and non-conductive particles is referred to as a "porous membrane layer," and a functional layer containing a binder but neither electrode active material particles nor non-conductive particles is referred to as an "adhesive layer."

According to the present invention, it is possible to provide a binder composition for secondary batteries that can form a functional layer having excellent adhesiveness and can cause the secondary battery to exhibit excellent cycle characteristics.
Furthermore, according to the present invention, it is possible to provide a slurry composition for a secondary battery functional layer, which is capable of forming a functional layer having excellent adhesiveness and enabling the secondary battery to exhibit excellent cycle characteristics.
According to the present invention, it is possible to provide a functional layer for a secondary battery that has excellent adhesiveness and allows the secondary battery to exhibit excellent cycle characteristics.
Furthermore, according to the present invention, a secondary battery having excellent cycle characteristics can be provided.

Hereinafter, an embodiment of the present invention will be described in detail.
Here, the binder composition for secondary batteries of the present invention is used for the manufacture of secondary batteries, and can be used, for example, for the preparation of the slurry composition for secondary battery functional layers of the present invention. The slurry composition for secondary battery functional layers of the present invention can be used to form any functional layer (e.g., electrode mixture layer, porous membrane layer, adhesive layer) that performs functions such as electron transfer, reinforcement, or adhesion in a secondary battery. Furthermore, the functional layer for secondary batteries of the present invention is formed from the slurry composition for secondary battery functional layers of the present invention. The secondary battery of the present invention includes a battery member having the functional layer for secondary batteries of the present invention.

(Binder composition for secondary batteries)
The binder composition of the present invention is a composition in which the polymer A and the polymer B are dissolved and/or dispersed in a solvent. The binder composition of the present invention may contain components other than the polymer A, the polymer B, and the solvent (hereinafter, referred to as "other components").

Here, the polymer A has a total content of monomer units having a hydroxyl group and monomer units having an amide group of 50% by mass or more and 90% by mass or less, and a content of monomer units having a carboxylic acid group of 10% by mass or more and 50% by mass or less. The polymer B has a content of monomer units having two carboxylic acid groups of 2% by mass or more and 5% by mass or less, a content of aromatic vinyl monomer units of 15% by mass or more and 88% by mass or less, and a content of aliphatic conjugated diene monomer units of 10% by mass or more and 80% by mass or less.

Furthermore, since the binder composition of the present invention contains polymer A and polymer B, each having the composition described above, in a solvent, the use of the binder composition of the present invention can enhance the adhesion of the functional layer and improve the cycle characteristics of the secondary battery.
The reason why the binder composition of the present invention can thus improve both the adhesion of the functional layer and the cycle characteristics of the secondary battery is not clear, but is presumed to be as follows.
First, the polymer B contains an aromatic vinyl monomer unit and an aliphatic conjugated diene monomer unit, and can function as a binder having both flexibility and strength. On the other hand, according to the study by the present inventor, when a binder composition and a slurry composition (hereinafter, these may be collectively abbreviated as "slurry composition, etc.") containing a binder consisting of a polymer containing an aromatic vinyl monomer unit and an aliphatic conjugated diene monomer unit are stored in a tank, there is a problem that the binder floats in the slurry composition, etc. and gathers near the liquid surface. And, even if a slurry composition, etc. in which the uniformity is impaired due to the floating of the binder is used, it is not possible to achieve both the adhesiveness of the functional layer and the cycle characteristics of the secondary battery. Specifically, when a slurry composition, etc. near the tank liquid surface where the binder gathers is used, the resistance increases and the cycle characteristics decrease, while when a slurry composition, etc. near the bottom of the tank where the binder is thin is used, the adhesiveness of the functional layer cannot be ensured.
In contrast, the polymer B contained in the binder composition of the present invention not only contains aromatic vinyl monomer units and aliphatic conjugated diene monomer units in a predetermined range, but also contains monomer units having two carboxylic acid groups in a predetermined range. Therefore, the polymer B can interact well with the polymer A (particularly, at least one of the hydroxyl group and the amide group of the polymer A) also contained in the binder composition through the carboxylic acid group by hydrogen bonding or the like. This interaction with the polymer A can suppress the non-uniformity of the slurry composition caused by the floating of the polymer B.
Therefore, by using the binder composition of the present invention, a slurry composition can be obtained in which polymer A and polymer B are well distributed throughout. It is therefore believed that by using this slurry composition, a functional layer with excellent adhesiveness can be formed, and the battery component including this functional layer can enable the secondary battery to exhibit excellent cycle characteristics.

<Polymer A>
Polymer A is a component that can suppress floating of polymer B in a slurry composition or the like, can function as a binder together with polymer B, and can also function as a viscosity adjuster for a slurry composition prepared using the binder composition.

<<Composition>>
Polymer A contains at least one of a monomer unit having a hydroxyl group and a monomer unit having an amide group, and also contains a monomer unit having a carboxylic acid group. Polymer A may contain repeating units other than the monomer unit having a hydroxyl group, the monomer unit having an amide group, and the monomer unit having a carboxylic acid group (hereinafter referred to as "other repeating units").

[Hydroxyl Group-Containing Monomer Unit]
Examples of monomers having a hydroxyl group capable of forming a monomer unit having a hydroxyl group include hydroxymethylacrylamide, hydroxyethylacrylamide, hydroxypropylacrylamide, hydroxymethylmethacrylamide, hydroxyethylmethacrylamide, hydroxypropylmethacrylamide, hydroxymethylacrylate, hydroxyethylacrylate, hydroxypropylacrylate, hydroxybutylacrylate, hydroxymethylmethacrylate, hydroxyethylmethacrylate, hydroxypropylmethacrylate, and hydroxybutylmethacrylate. These may be used alone or in combination of two or more. Among these, from the viewpoint of further improving the cycle characteristics of the secondary battery while sufficiently suppressing the floating of the polymer B in the slurry composition, etc., hydroxyethylacrylamide and hydroxyethylacrylate are preferred, and hydroxyethylacrylamide is more preferred.
In the present invention, a monomer having both a hydroxyl group and an amide group is included in the monomer having a hydroxyl group, but is not included in the monomer having an amide group.

And, when the total repeating units (total monomer units) contained in polymer A are 100% by mass, the content ratio of monomer units having a hydroxyl group is in the range of 0% by mass or more and 90% by mass or less. Here, the content ratio of monomer units having a hydroxyl group in polymer A is preferably 10% by mass or more, preferably 75% by mass or less, and more preferably 55% by mass or less. If the ratio of monomer units having a hydroxyl group in polymer A is 10% by mass or more, the floating of polymer B in a slurry composition or the like can be sufficiently suppressed and the adhesion of the functional layer can be further improved. On the other hand, if the ratio of monomer units having a hydroxyl group in polymer A is 75% by mass or less, the cycle characteristics of the secondary battery can be further improved.

[Monomer unit having an amide group]
Examples of monomers having an amide group capable of forming a monomer unit having an amide group include acrylamide, methacrylamide, dimethylacrylamide, diethylacrylamide, and diacetoneacrylamide. These may be used alone or in combination of two or more. Among these, acrylamide and methacrylamide are preferred from the viewpoint of sufficiently suppressing floating of the polymer B in the slurry composition or the like.

And, when the total repeating units (total monomer units) contained in the polymer A are 100% by mass, the content ratio of the monomer units having an amide group is in the range of 0% by mass or more and 90% by mass or less. Here, the content ratio of the monomer units having an amide group in the polymer A is preferably 10% by mass or more, preferably 75% by mass or less, and more preferably 55% by mass or less. If the ratio of the monomer units having an amide group in the polymer A is 10% by mass or more, the floating of the polymer B in the slurry composition or the like can be sufficiently suppressed and the adhesiveness of the functional layer can be further improved. In addition, the coating defects when forming the functional layer by applying the slurry composition can be suppressed, and the cycle characteristics of the secondary battery can be further improved. On the other hand, if the ratio of the monomer units having an amide group in the polymer A is 75% by mass or less, the adhesiveness of the functional layer can be further improved.

[Total of monomer units having a hydroxyl group and monomer units having an amide group]
Here, when the total repeating units (total monomer units) contained in the polymer A is 100% by mass, the total content of the monomer units having a hydroxyl group and the monomer units having an amide group must be 50% by mass or more and 90% by mass or less, preferably 53% by mass or more, more preferably 55% by mass or more, even more preferably 70% by mass or more, preferably 88% by mass or less, and more preferably 85% by mass or less. If the total of the proportion of the monomer units having a hydroxyl group and the proportion of the monomer units having an amide group in the polymer A is less than 50% by mass, the floating of the polymer B in the slurry composition or the like cannot be suppressed, and both the adhesiveness of the functional layer and the cycle characteristics of the secondary battery cannot be improved in a well-balanced manner. On the other hand, if the total of the proportion of the monomer units having a hydroxyl group and the proportion of the monomer units having an amide group in the polymer A exceeds 90% by mass, the slurry composition becomes excessively viscous, and both the adhesiveness of the functional layer and the cycle characteristics of the secondary battery cannot be improved in a well-balanced manner.
As described above, it is sufficient that polymer A contains at least one of a monomer unit having a hydroxyl group and a monomer unit having an amide group. However, from the viewpoint of improving the adhesion of the functional layer and the cycle characteristics of the secondary battery in a well-balanced manner while sufficiently suppressing floating of polymer B in a slurry composition or the like, it is preferable that polymer A contains both a monomer unit having a hydroxyl group and a monomer unit having an amide group.

[Monomer unit having a carboxylic acid group]
Examples of monomers having a carboxylic acid group capable of forming a monomer unit having a carboxylic acid group include monocarboxylic acids and derivatives thereof, dicarboxylic acids and acid anhydrides thereof, and derivatives thereof.
Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid.
Examples of the monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, and α-chloro-β-E-methoxyacrylic acid.
The dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid.
Examples of dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, and maleic acid monoesters such as nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate.
Examples of the acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleic anhydride.
Furthermore, as the monomer having a carboxylic acid group, an acid anhydride which generates a carboxylic acid group upon hydrolysis can also be used.
These may be used alone or in combination of two or more. Among these, acrylic acid and methacrylic acid are preferred from the viewpoint of improving both the adhesion of the functional layer and the cycle characteristics of the secondary battery in a well-balanced manner while suppressing excessive thickening of the slurry composition.

And, when the total repeating units (total monomer units) contained in polymer A is 100% by mass, the content ratio of the monomer units having a carboxylic acid group must be 10% by mass or more and 50% by mass or less, preferably 15% by mass or more, more preferably 18% by mass or more, preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 25% by mass or less. If the proportion of the monomer units having a carboxylic acid group in polymer A is less than 10% by mass, the slurry composition will be excessively thickened, and it will not be possible to improve both the adhesion of the functional layer and the cycle characteristics of the secondary battery in a well-balanced manner. On the other hand, if the proportion of the monomer units having a carboxylic acid group in polymer A is more than 50% by mass, the adhesion of the functional layer will decrease.

[Other repeating units]
The other repeating units contained in the polymer A are not particularly limited. For example, the other repeating units include monomer units derived from known monomers, such as aliphatic conjugated diene monomer units and aromatic vinyl monomer units described later in the section on "polymer B", and (meth)acrylic acid ester monomer units. The polymer A may contain one type of other repeating unit, or two or more types.
Here, when all repeating units (all monomer units) contained in polymer A are taken as 100 mass%, the content of other repeating units is preferably 10 mass% or less, more preferably 5 mass% or less, even more preferably 1 mass% or less, and particularly preferably 0 mass%.
In the present invention, "(meth)acrylic" means acrylic and/or methacrylic.

<<Properties>>
[Water solubility]
The polymer A is preferably water-soluble. That is, the polymer A is preferably a water-soluble polymer. If the polymer A is a water-soluble polymer, the polymer A and the polymer B can interact more favorably, particularly in a slurry composition containing water as a solvent. Therefore, the adhesion of the functional layer and the cycle characteristics of the secondary battery can be improved in a well-balanced manner while sufficiently suppressing the floating of the polymer B in the slurry composition.
In the present invention, a polymer being "water-soluble" means that when 0.5 g of the polymer is dissolved in 100 g of water at a temperature of 25°C, the insoluble matter is less than 1.0 mass%.

[Electrolyte swelling degree]
The degree of swelling in electrolyte of the polymer A is preferably 150% by mass or less, more preferably 145% by mass or less, and even more preferably 140% by mass or less. If the degree of swelling in electrolyte of the polymer A is 150% by mass or less, the cycle characteristics of the secondary battery can be further improved. Here, the lower limit of the degree of swelling in electrolyte of the polymer A is not particularly limited, but is usually 100% by mass or more.
The degree of swelling of the polymer A in an electrolyte solution can be adjusted, for example, by changing the type and amount of the monomer used in preparing the polymer A.

[Weight average molecular weight]
The weight average molecular weight of the polymer A is preferably 1,000,000 or more, more preferably 2,000,000 or more, even more preferably 5,000,000 or more, particularly preferably 6,000,000 or more, and is preferably 15,000,000 or less, more preferably 12,000,000 or less, and even more preferably 9,000,000 or less. If the weight average molecular weight of the polymer A is 1,000,000 or more, the adhesiveness of the functional layer can be further improved. On the other hand, if the weight average molecular weight of the polymer A is 15,000,000 or less, the cycle characteristics of the secondary battery can be further improved.
The weight average molecular weight of polymer A can be adjusted, for example, by changing the type and amount of a polymerization initiator and/or a polymerization accelerator used in the preparation of polymer A.

<<Preparation method>>
The above-mentioned polymer A is not particularly limited, and can be prepared by any method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. In addition, as the polymerization method, addition polymerization such as ionic polymerization, radical polymerization, living radical polymerization, etc. can be used. In addition, as the polymerization initiator, a known polymerization initiator can be used. In addition, other additives that can be used during polymerization (e.g., emulsifier, dispersant, polymerization aid, chain transfer agent, molecular weight regulator, polymerization accelerator) can be generally used, and the amount of use thereof is also generally used.

<Polymer B>
Polymer B is a component that functions as a binder, imparting adhesiveness to the functional layer formed using a slurry composition containing the binder composition, and also retaining components contained in the functional layer (e.g., functional particles such as electrode active material particles and non-conductive particles) from detaching from the functional layer.

<<Composition>>
Polymer B includes a monomer unit having two carboxylic acid groups, an aromatic vinyl monomer unit, and an aliphatic conjugated diene monomer unit. Polymer B may include a repeating unit other than the monomer unit having two carboxylic acid groups, the aromatic vinyl monomer unit, and the aliphatic conjugated diene monomer unit (hereinafter, referred to as an "arbitrary repeating unit").

[Monomer unit having two carboxylic acid groups]
Examples of monomers having two carboxylic acid groups that can form a monomer unit having two carboxylic acid groups include dicarboxylic acids and their acid anhydrides, as well as derivatives thereof. Specific examples of these include those described above in the section on "polymer A". The monomers having two carboxylic acid groups may be used alone or in combination of two or more. Here, itaconic acid is preferred as the monomer having two carboxylic acid groups from the viewpoint of improving both the adhesion of the functional layer and the cycle characteristics of the secondary battery in a well-balanced manner while sufficiently suppressing the floating of polymer B in a slurry composition or the like, and further from the viewpoint of enhancing the manufacturing stability of polymer B.

And, when the total repeating units (total monomer units) contained in polymer B is 100% by mass, the content ratio of the monomer units having two carboxylic acid groups must be 2% by mass or more and 5% by mass or less, preferably 2.5% by mass or more, more preferably 2.7% by mass or more, more preferably 3% by mass or more, preferably 4.5% by mass or less, more preferably 4% by mass or less, and even more preferably 3.5% by mass or less. If the ratio of the monomer units having two carboxylic acid groups in polymer B is less than 2% by mass, the floating of polymer B in the slurry composition or the like cannot be suppressed, and both the adhesion of the functional layer and the cycle characteristics of the secondary battery cannot be improved in a well-balanced manner. On the other hand, if the ratio of the monomer units having two carboxylic acid groups in polymer B is more than 5% by mass, it is presumed that this is due to an increase in the amount of water carried into the secondary battery and the generation of coarse particles made of polymer B, but the cycle characteristics of the secondary battery are reduced.

[Aromatic vinyl monomer unit]
Examples of aromatic vinyl monomers capable of forming aromatic vinyl monomer units include styrene, α-methylstyrene, butoxystyrene, and vinylnaphthalene. These may be used alone or in combination of two or more. Among these, styrene is preferred.

And, when the total repeating units (total monomer units) contained in polymer B is 100% by mass, the content ratio of aromatic vinyl monomer units must be 15% by mass or more and 88% by mass or less, preferably 35% by mass or more, more preferably 45% by mass or more, even more preferably 50% by mass or more, preferably 85% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. If the ratio of aromatic vinyl monomer units in polymer B is less than 15% by mass, the strength of polymer B cannot be sufficiently ensured, the cycle characteristics of the secondary battery are reduced, and the adhesiveness of the functional layer is reduced. On the other hand, if the ratio of aromatic vinyl monomer units in polymer B is more than 88% by mass, polymer B becomes excessively rigid and the adhesiveness of the functional layer is reduced.

[Aliphatic conjugated diene monomer unit]
Examples of the aliphatic conjugated diene monomer capable of forming the aliphatic conjugated diene monomer unit include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), and 2,3-dimethyl-1,3-butadiene. These may be used alone or in combination of two or more. Among these, 1,3-butadiene is preferred.

And, when the total repeating units (total monomer units) contained in polymer B is 100% by mass, the content ratio of the aliphatic conjugated diene monomer unit must be 10% by mass or more and 80% by mass or less, preferably 10.5% by mass or more, more preferably 15% by mass or more, even more preferably 25% by mass or more, preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less. If the ratio of the aliphatic conjugated diene monomer unit in polymer B is less than 10% by mass, the flexibility of polymer B cannot be sufficiently ensured, and the adhesiveness of the functional layer is reduced. On the other hand, if the ratio of the aliphatic conjugated diene monomer unit in polymer B is more than 80% by mass, polymer B becomes excessively flexible, the cycle characteristics of the secondary battery are reduced, and the adhesiveness of the functional layer is reduced.

[Optional repeating unit]
The optional repeating unit contained in the polymer B is not particularly limited. For example, the optional repeating unit may be a monomer unit derived from a known monomer, such as a monomer unit having a hydroxyl group and a monomer unit having an amide group described in the section "Polymer A" or a (meth)acrylic acid ester monomer unit. The polymer B may contain one type of the optional repeating unit, or may contain two or more types.
From the viewpoint of sufficiently suppressing the floating of the polymer B in the slurry composition, etc., the polymer B preferably contains a monomer unit having a hydroxyl group as an arbitrary repeating unit. Here, when the total repeating units (total monomer units) contained in the polymer B are 100 mass%, the content ratio of the monomer unit having a hydroxyl group is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, preferably 3 mass% or less, more preferably 2 mass% or less, and even more preferably 1 mass% or less. If the ratio of the monomer unit having a hydroxyl group in the polymer B is within the above-mentioned range, it is possible to improve both the adhesion of the functional layer and the cycle characteristics of the secondary battery in a well-balanced manner while sufficiently suppressing the floating of the polymer B in the slurry composition, etc.

<<Properties>>
[Water dispersibility]
The polymer B is preferably water-dispersible (insoluble in water). That is, the polymer B is preferably a water-dispersible polymer. If the polymer B is a water-dispersible polymer, the adhesiveness of the functional layer and the cycle characteristics of the secondary battery can be improved in a well-balanced manner, particularly when a slurry composition containing water as a solvent is used.
In the present invention, the term "water-dispersible" means that when 0.5 g of the polymer is dissolved in 100 g of water at 25°C, the insoluble portion is 90 mass % or more.

[Glass transition temperature]
The glass transition temperature of the polymer B is preferably −20° C. or higher, more preferably −10° C. or higher, and is preferably 50° C. or lower, and more preferably 40° C. or lower. When the glass transition temperature of the polymer B is −20° C. or higher, thickening of the slurry composition can be sufficiently suppressed. On the other hand, when the glass transition temperature of the polymer B is 50° C. or lower, the adhesiveness of the functional layer can be improved.
The glass transition temperature of the polymer B can be adjusted, for example, by changing the type and amount of the monomer, polymerization initiator and/or polymerization accelerator used in the preparation of the polymer B.
In the present invention, the "glass transition temperature" can be measured by the method described in the Examples of this specification.

<<Preparation method>>
The above-mentioned polymer B is not particularly limited, and can be prepared by any method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. In addition, as the polymerization method, addition polymerization such as ionic polymerization, radical polymerization, living radical polymerization, etc. can be used. In addition, seed polymerization, block polymerization, graft polymerization, etc. can also be used for preparing the polymer B. In addition, as the polymerization initiator, a known polymerization initiator can be used. In addition, other additives (e.g., emulsifier, dispersant, polymerization aid, chain transfer agent, molecular weight regulator, polymerization accelerator) that can be used during polymerization can be generally used, and the amount used is also generally used.

<<Proportion of Polymer B in the Total of Polymer A and Polymer B>>
Here, when the total amount of the polymer A and the polymer B contained in the binder composition is 100% by mass, the amount of the polymer B is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, particularly preferably 30% by mass or more, preferably 45% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less. If the ratio of the polymer B in the total of the polymer A and the polymer B is 5% by mass or more, the thickening of the slurry composition can be sufficiently suppressed. On the other hand, if the ratio of the polymer B in the total of the polymer A and the polymer B is 45% by mass or less, the cycle characteristics of the secondary battery can be further improved.

<Solvent>
As the solvent contained in the binder composition of the present invention, a known solvent capable of dissolving or dispersing the above-mentioned polymer A and polymer B can be used. Among them, it is preferable to use water as the solvent. At least a part of the solvent in the binder composition is not particularly limited and can be the polymerization solvent used in the preparation of polymer A and/or polymer B.

<Other ingredients>
In addition to the above-mentioned components, the binder composition of the present invention may contain a conductive assistant, a reinforcing material, a leveling agent, a viscosity modifier, an electrolyte additive, a preservative, a mildewproofing agent, an antifoaming agent, a polymerization inhibitor, and a binder other than polymer A and polymer B. These are not particularly limited as long as they do not affect the battery reaction, and known ones, for example, those described in International Publication No. 2012/115096, can be used. In addition, the other components may be used alone or in combination of two or more kinds in any ratio.

<Method of preparing binder composition>
The binder composition of the present invention can be prepared by mixing the above-mentioned polymer A, polymer B, and solvent, as well as other components that are optionally used, by a known method. Specifically, the binder composition can be prepared by mixing the above-mentioned components using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, or a Filmix.
When polymer A and polymer B are prepared by polymerization in an aqueous solvent, they can be mixed as they are in the form of an aqueous solution or aqueous dispersion to prepare a binder composition containing water as a solvent.

(Slurry composition for secondary battery functional layer)
The slurry composition of the present invention is a composition used for forming a functional layer, and contains the above-mentioned binder composition, and optionally contains functional particles and other components. That is, the slurry composition of the present invention usually contains polymer A, polymer B, and a solvent, and optionally contains functional particles and other components. And since the slurry composition of the present invention contains the above-mentioned binder composition, a functional layer having excellent adhesiveness can be obtained by drying the slurry composition of the present invention, for example, on a substrate. And, by using a battery component having the functional layer, it is possible to exhibit excellent cycle characteristics in a secondary battery.

<Binder Composition>
As the binder composition, the above-mentioned binder composition of the present invention containing at least the polymer A, the polymer B, and a solvent is used.
In addition, the blending amount of the binder composition in the slurry composition is not particularly limited. When the slurry composition is an electrode slurry composition, from the viewpoint of sufficiently increasing the adhesion of the electrode mixture layer, which is the functional layer, and the cycle characteristics of the secondary battery, the total amount of the polymer A and the polymer B in the total amount of the electrode active material particles, the polymer A, and the polymer B is preferably 0.5 mass% or more, more preferably 1.0 mass% or more, more preferably 7.0 mass% or less, and more preferably 4.0 mass% or less.
In addition, when the slurry composition is a slurry composition for a porous membrane layer, from the viewpoint of sufficiently increasing the adhesion of the porous membrane layer, which is a functional layer, and the cycle characteristics of a secondary battery, the total amount of polymer A and polymer B in the total amount of non-conductive particles, polymer A, and polymer B, which is 100 mass%, is preferably 0.5 mass% or more, more preferably 1.0 mass% or more, and more preferably 9.0 mass% or less, and more preferably 6.0 mass% or less.

<Functional particles>
Here, examples of functional particles for enabling the functional layer to exhibit the intended function include electrode active material particles when the functional layer is an electrode mixture layer, and non-conductive particles when the functional layer is a porous membrane layer.

<<Electrode active material particles>>
The electrode active material particles are not particularly limited, and may be particles made of known electrode active materials used in secondary batteries. Specifically, for example, the negative electrode active material particles that can be used in the negative electrode mixture layer of a lithium ion secondary battery, which is an example of a secondary battery, are not particularly limited, and may be particles made of the following negative electrode active materials.

[Negative electrode active material]
Examples of negative electrode active materials for lithium ion secondary batteries include carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials that are combinations of these.
Here, the carbon-based negative electrode active material refers to an active material having carbon as the main skeleton into which lithium can be inserted (also referred to as "doped"). Examples of the carbon-based negative electrode active material include carbonaceous materials and graphite materials.

Examples of the carbonaceous material include graphitic carbon and non-graphitic carbon having a structure close to an amorphous structure, such as glassy carbon.
Here, examples of graphitizable carbon include carbon materials made from tar pitch obtained from petroleum or coal. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fiber, and pyrolytic vapor-grown carbon fiber.
Examples of non-graphitizable carbon include phenol resin baked body, polyacrylonitrile carbon fiber, pseudo-isotropic carbon, furfuryl alcohol resin baked body (PFA), and hard carbon.

Furthermore, examples of the graphite material include natural graphite and artificial graphite.
Examples of the artificial graphite include artificial graphite obtained by heat-treating carbon containing graphitizable carbon mainly at 2800°C or higher, graphitized MCMB obtained by heat-treating MCMB at 2000°C or higher, and graphitized mesophase pitch-based carbon fiber obtained by heat-treating mesophase pitch-based carbon fiber at 2000°C or higher.

The metal-based negative electrode active material is an active material containing a metal, and usually refers to an active material that contains an element capable of inserting lithium in its structure and has a theoretical electric capacity per unit mass of 500 mAh/g or more when lithium is inserted. Examples of the metal-based active material include lithium metal, elemental metals capable of forming lithium alloys (e.g., Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.), and alloys thereof, as well as oxides, sulfides, nitrides, silicides, carbides, and phosphides thereof. Among these, the metal-based negative electrode active material is preferably an active material containing silicon (silicon-based negative electrode active material). This is because the use of a silicon-based negative electrode active material can increase the capacity of a lithium-ion secondary battery.

Examples of silicon-based negative electrode active materials include silicon (Si), alloys containing silicon, SiO, SiO _x , composites of Si-containing materials and conductive carbon obtained by coating or compounding Si-containing materials with conductive carbon, etc. Note that these silicon-based negative electrode active materials may be used alone or in combination of two or more.

In addition, from the viewpoint of further improving the cycle characteristics of the secondary battery while sufficiently ensuring the cell capacity of the secondary battery, it is preferable to use both particles made of a carbon-based negative electrode active material (carbon-based negative electrode active material particles) and silicon-based negative electrode active material particles (silicon-based negative electrode active material particles) as the negative electrode active material particles.
The amounts of the carbon-based negative electrode active material particles and the silicon-based negative electrode active material particles in the slurry composition are not particularly limited.
The amount of the carbon-based negative electrode active material particles in the total amount of the negative electrode active material particles, the polymer A, and the polymer B, which is 100% by mass, is preferably 50% by mass or more, more preferably 60% by mass or more, preferably 90% by mass or less, and more preferably 85% by mass or less. If the ratio of the carbon-based negative electrode active material particles to the total amount of the negative electrode active material particles, the polymer A, and the polymer B is 50% by mass or more, the buffering action of the carbon-based negative electrode active material particles (particularly, particles made of a graphite material) and the silicon-based negative electrode active material can be ensured, and the cell capacity can be improved, and if it is 90% by mass or less, the cycle characteristics of the secondary battery can be sufficiently improved.
The amount of silicon-based negative electrode active material particles in the total amount of the negative electrode active material particles, polymer A, and polymer B (100% by mass) is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 40% by mass or less, and more preferably 30% by mass or less. If the proportion of silicon-based negative electrode active material particles in the total amount of the negative electrode active material particles, polymer A, and polymer B is 5% by mass or more, the amount of active material per unit area of the negative electrode can be sufficiently secured to improve the cell capacity, and if it is 40% by mass or less, the cycle characteristics of the secondary battery can be sufficiently improved.

[Non-conductive particles]
The non-conductive particles to be blended in the porous membrane layer are not particularly limited, and may be any known non-conductive particles used in secondary batteries.
Specifically, both inorganic and organic fine particles can be used as the non-conductive particles, but inorganic fine particles are usually used. Among them, materials that are stable in the use environment of the secondary battery and are electrochemically stable are preferred as the material of the non-conductive particles. From this viewpoint, preferred examples of materials of the non-conductive particles include oxide particles such as aluminum oxide (alumina), hydrated aluminum oxide (boehmite), silicon oxide, magnesium oxide (magnesia), calcium oxide, titanium oxide (titania), BaTiO ₃ , ZrO, and alumina-silica composite oxide; nitride particles such as aluminum nitride and boron nitride; covalently bonded crystal particles such as silicon and diamond; sparingly soluble ion crystal particles such as barium sulfate, calcium fluoride, and barium fluoride; clay fine particles such as talc and montmorillonite; and the like. In addition, these particles may be subjected to element substitution, surface treatment, solid solution formation, and the like as necessary.
The non-conductive particles may be used alone or in combination of two or more kinds.

<Other ingredients>
Other components that can be blended in the slurry composition are not particularly limited, and include the same components as those that can be blended in the binder composition of the present invention. The other components may be used alone or in combination of two or more in any ratio.

<Preparation of Slurry Composition>
The method for preparing the slurry composition is not particularly limited.
For example, when the slurry composition is a slurry composition for an electrode, the binder composition, electrode active material particles, and other components used as necessary can be mixed in the presence of a solvent to prepare the slurry composition.
In addition, when the slurry composition is a slurry composition for a porous membrane layer, the binder composition, the non-conductive particles, and other components used as necessary can be mixed in the presence of a solvent to prepare the slurry composition.
When the slurry composition is a slurry composition for an adhesive layer, the binder composition can be used as is or after diluting with a solvent as a slurry composition, or the binder composition and other components used as necessary can be mixed in the presence of a solvent to prepare a slurry composition.
The solvent used in preparing the slurry composition includes the solvent contained in the binder composition. The mixing method is not particularly limited, but mixing is performed using a stirrer or disperser that can be commonly used.

(Functional layer for secondary batteries)
The functional layer of the present invention is a layer that performs functions such as electron transfer, reinforcement, or adhesion in a secondary battery. Examples of the functional layer include an electrode mixture layer that transfers electrons via an electrochemical reaction, a porous membrane layer that improves heat resistance and strength, and an adhesive layer that improves adhesion. The functional layer of the present invention is formed from the above-mentioned slurry composition of the present invention, and can be formed, for example, by applying the above-mentioned slurry composition to the surface of a suitable substrate to form a coating film, and then drying the formed coating film. That is, the functional layer of the present invention is made of a dried product of the above-mentioned slurry composition, and usually contains at least polymer A and polymer B. Note that each component contained in the functional layer is contained in the above-mentioned slurry composition, so the preferred ratio of each component is the same as the preferred ratio of each component in the slurry composition.

Since the functional layer of the present invention is formed from the slurry composition of the present invention containing the binder composition of the present invention, it has excellent adhesion and can enable a secondary battery having a battery component equipped with the functional layer of the present invention to exhibit excellent cycle characteristics.

<Base material>
Here, there is no limitation on the substrate to which the slurry composition is applied, and for example, a coating film of the slurry composition may be formed on the surface of a release substrate, the coating film may be dried to form a functional layer, and the release substrate may be peeled off from the functional layer. In this way, the functional layer peeled off from the release substrate may be used as a free-standing film to form a battery component of a secondary battery.
However, from the viewpoint of omitting the step of peeling off the functional layer and increasing the manufacturing efficiency of the battery component, it is preferable to use a current collector, a separator substrate, or an electrode substrate as the substrate. Specifically, when preparing the electrode mixture layer, it is preferable to apply the slurry composition onto the current collector as the substrate. Also, when preparing the porous membrane layer or the adhesive layer, it is preferable to apply the slurry composition onto the separator substrate or the electrode substrate.

<<Current collector>>
As the current collector, a material having electrical conductivity and electrochemical durability is used. Specifically, as the current collector, for example, a current collector made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. can be used. Among them, copper foil is particularly preferable as the current collector used for the negative electrode. Also, aluminum foil is particularly preferable as the current collector used for the positive electrode. Note that the above-mentioned materials may be used alone or in combination of two or more kinds in any ratio.

<<Separator substrate>>
The separator substrate is not particularly limited, but may be any of known separator substrates such as an organic separator substrate. The organic separator substrate is a porous member made of an organic material, and examples of the organic separator substrate include microporous membranes or nonwoven fabrics containing polyolefin resins such as polyethylene and polypropylene, aromatic polyamide resins, etc., and polyethylene microporous membranes and nonwoven fabrics are preferred because of their excellent strength.

<<Electrode base material>>
The electrode substrate (positive electrode substrate and negative electrode substrate) is not particularly limited, but examples thereof include an electrode substrate in which an electrode mixture layer containing electrode active material particles and a binder is formed on the above-mentioned current collector.
The electrode active material particles contained in the electrode mixture layer in the electrode substrate are not particularly limited, and for example, the electrode active material particles described above in the section "Slurry composition for secondary battery functional layer" can be used. In addition, any binder used for electrode mixture layers can be used as the binder contained in the electrode mixture layer of the electrode substrate. In addition, at least one of the polymer A and the polymer B described above in the section "Binder composition for secondary battery" may be used as the binder. That is, the functional layer of the present invention may be used as the electrode mixture layer in the electrode substrate.

<Method of forming functional layer>
Examples of methods for forming a functional layer on a substrate such as the current collector, separator substrate, or electrode substrate include the following methods.
1) A method in which the slurry composition of the present invention is applied to the surface of a substrate (in the case of an electrode substrate, the surface on the electrode mixture layer side; the same applies hereinafter) and then dried;
2) a method of immersing a substrate in the slurry composition of the present invention and then drying it; and 3) a method of applying the slurry composition of the present invention onto a release substrate, drying it to produce a functional layer, and transferring the obtained functional layer to the surface of the substrate.
Among these, the method 1) is particularly preferred because it is easy to control the thickness of the functional layer. Specifically, the method 1) includes a step of applying the slurry composition onto a substrate (application step) and a step of drying the slurry composition applied onto the substrate to form a functional layer (drying step).

<<Coating process>>
In the coating step, the method for coating the slurry composition on the substrate is not particularly limited, and examples thereof include a doctor blade method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.

<<Drying process>>
In the drying step, the method for drying the slurry composition on the substrate is not particularly limited and may be any known method. Examples of the drying method include drying with warm air, hot air, or low-humidity air, vacuum drying, and drying by irradiation with infrared rays or electron beams.

(Battery component having functional layer)
The battery member (separator and electrode) having the functional layer of the present invention may have components other than the functional layer of the present invention and the substrate as described above, as long as the effects of the present invention are not significantly impaired. Such components are not particularly limited, and include an electrode mixture layer, a porous membrane layer, and an adhesive layer that do not correspond to the functional layer of the present invention.
In addition, the battery member may have a plurality of types of functional layers of the present invention. For example, the electrode may have an electrode mixture layer formed from the electrode slurry composition of the present invention on the current collector, and a porous membrane layer and/or an adhesive layer formed from the porous membrane layer and/or adhesive layer slurry composition of the present invention on the electrode mixture layer. For example, the separator may have a porous membrane layer formed from the porous membrane layer slurry composition of the present invention on the separator substrate, and an adhesive layer formed from the adhesive layer slurry composition of the present invention on the porous membrane layer.
A battery member having the functional layer of the present invention can be well bonded to adjacent battery members, and can also cause the secondary battery to exhibit excellent cycle characteristics.

(Secondary battery)
The secondary battery of the present invention includes the functional layer of the present invention. More specifically, the secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte, and the functional layer for the secondary battery is included in at least one of the positive electrode, the negative electrode, and the separator, which are battery components. The secondary battery of the present invention can exhibit excellent cycle characteristics.

<Positive electrode, negative electrode and separator>
At least one of the positive electrode, negative electrode, and separator used in the secondary battery of the present invention is a battery member having the functional layer of the present invention described above. Note that the positive electrode, negative electrode, and separator not having the functional layer of the present invention are not particularly limited, and known positive electrodes, negative electrodes, and separators can be used.

<Electrolyte>
As the electrolyte, an organic electrolyte in which a supporting electrolyte is dissolved in an organic solvent is usually used. As the supporting electrolyte, for example, in a lithium ion secondary battery, a lithium _salt is used. As the lithium salt, for example, _LiPF6 , _LiAsF6 , _LiBF4 , _LiSbF6 , _{LiAlCl4 , LiClO4} , _CF3SO3Li , _C4F9SO3Li , _CF3COOLi , ( _CF3CO ) _2NLi , ( _CF3SO2 ) _2NLi , ( _C2F5SO2 )NLi, etc. _are listed. Among them, _LiPF6 , _LiClO4 , and _CF3SO3Li are preferred because _they are easily dissolved in a solvent _and show a _high degree _of dissociation. The electrolyte may be used alone or in combination of two or more. In general, the lithium ion conductivity tends to increase as the supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. For example, in a lithium ion secondary battery, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), etc.; esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; and the like are preferably used. A mixture of these solvents may also be used. Among them, carbonates are preferred because they have a high dielectric constant and a wide stable potential region. Usually, the lower the viscosity of the solvent used, the higher the lithium ion conductivity tends to be, so the lithium ion conductivity can be adjusted by the type of solvent.
The concentration of the electrolyte in the electrolytic solution can be appropriately adjusted. Known additives may also be added to the electrolytic solution.

<Secondary Battery Manufacturing Method>
The secondary battery of the present invention described above can be manufactured, for example, by stacking a positive electrode and a negative electrode with a separator therebetween, wrapping or folding the stack as necessary, and placing the stack in a battery container, and then injecting an electrolyte into the battery container and sealing it. At least one of the positive electrode, negative electrode, and separator is a battery member having the functional layer of the present invention. In addition, the battery container may be filled with an expand metal, an overcurrent prevention element such as a fuse or a PTC element, a lead plate, or the like as necessary to prevent pressure rise inside the battery and overcharging and discharging. The shape of the battery may be any of, for example, a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type, and the like.

The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" expressing amounts are based on mass unless otherwise specified.
In addition, in a polymer produced by copolymerizing multiple types of monomers, the ratio of a repeating unit (monomer unit) formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (feed ratio) of the certain monomer to all monomers used in the polymerization of the polymer, unless otherwise specified.
In the examples and comparative examples, the weight average molecular weight and swelling degree of the electrolyte of the polymer A, the glass transition temperature of the polymer B, the suppression of thickening of the slurry composition (slurry composition for negative electrode and slurry composition for porous membrane layer), the adhesion of the functional layer (negative electrode mixture layer and porous membrane layer), the suppression of floating of the polymer B in the slurry composition, and the cycle characteristics of the secondary battery were measured and evaluated by the following methods.

<Weight average molecular weight of polymer A>
The weight average molecular weight of polymer A was measured by gel permeation chromatography (GPC). First, polymer A was added to about 5 mL of eluent so that the solid concentration was about 0.5 g/L, and slowly dissolved at room temperature. After visually confirming the dissolution of polymer A, the solution was gently filtered through a 0.45 μm filter to prepare a measurement sample. Then, a calibration curve was created using a standard substance, and the weight average molecular weight was calculated as a standard substance equivalent value.
The measurement conditions are as follows.
<<Measurement conditions>>
Column: Showa Denko Co., Ltd., product name: Shodex OHpak (SB-G, SB-807HQ, SB-806MHQ)
Eluent: 0.1M Tris buffer (with 0.1M potassium chloride)
Flow rate: 0.5 mL/min Sample concentration: 0.05 g/L (solid concentration)
Injection volume: 200μL
Column temperature: 40°C
Detector: Differential refractive index detector RI (manufactured by Tosoh Corporation, product name "RI-8020")
Standard material: Monodisperse pullulan (Showa Denko)
<Electrolyte Swelling Degree of Polymer A>
A composition containing polymer A and water (aqueous solution of polymer A) was dried under an environment of relative humidity 50% and temperature 23 ° C to 25 ° C to form a film with a thickness of 1 ± 0.3 mm. The formed film was dried for 10 hours in a vacuum dryer at a temperature of 60 ° C, then cut into film pieces, and the mass W0 of the obtained film pieces was precisely weighed. Next, the obtained film pieces were immersed in a 1.0 M LiPF ₆ solution (solvent: mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (volume ratio), additive: vinylene carbonate 2 volume % (solvent ratio)) as an electrolyte in an environment of a temperature of 60 ° C for 72 hours. After immersion for 72 hours, the film pieces were pulled out, the electrolyte on the surface was wiped with a Kimwipe, and the mass W1 of the swollen film pieces was precisely weighed, and the electrolyte swelling degree was calculated from the following formula.
Electrolyte swelling degree (mass%) = W1/W0×100
<Glass Transition Temperature of Polymer B>
A composition containing polymer B and water (aqueous dispersion of polymer B) was dried for 3 days in an environment with a humidity of 50% and a temperature of 23 to 26° C. to obtain a film having a thickness of 1±0.3 mm. This film was dried for 10 hours in a vacuum dryer at a temperature of 60° C. Thereafter, the glass transition temperature of the dried film was measured using a differential scanning calorimeter (DSC6220SII, manufactured by Nano Technology Corporation) in accordance with JIS K7121 under the conditions of a measurement temperature of −100° C. to 180° C. and a heating rate of 5° C./min.
<Suppression of thickening of slurry composition>
<<Slurry Composition for Negative Electrode (Examples 1 to 20, Comparative Examples 1 to 6)>>
In a planetary mixer with a disperser, 68.6 parts of artificial graphite (volume average particle diameter: 24.5 μm, specific surface area: 4 m ² /g) as negative electrode active material particles and 29.4 parts of silicon-based negative electrode active material particles (SiO _x ), as well as the same amount (solid content equivalent amount) of an aqueous solution of polymer A as used in the preparation of the negative electrode slurry composition in each Example and Comparative Example were added, and the solid content concentration was adjusted to 58% with ion-exchanged water, and mixed for 60 minutes at room temperature. Next, the solid content concentration was adjusted to 50% with ion-exchanged water, and after further mixing for 15 minutes, a defoaming treatment was performed under reduced pressure to obtain a mixture for viscosity measurement. The viscosity of this mixture for viscosity measurement was η1. The viscosity was measured using a B-type viscometer at a temperature of 25° C., a spindle rotation speed of 60 rpm, and a spindle rotation time of 60 seconds (hereinafter, the same applies to the measurement conditions for viscosities η2, η3, and η4).
Next, a mixture for viscosity measurement was obtained in the same manner as above, except that a mixture of polymer A and polymer B (binder composition) in the same amount (solid content equivalent) as that used in the preparation of the negative electrode slurry composition in each Example and Comparative Example was used instead of the aqueous solution of polymer A. The viscosity of this mixture for viscosity measurement was defined as η2.
The viscosity ratio of the above η1 to η2 (= η2/η1) was calculated, and the inhibition of thickening of the slurry composition was evaluated according to the following criteria. The smaller the viscosity ratio value, the more the thickening of the slurry composition is inhibited, and the easier the preparation and handling of the slurry composition.
A: Viscosity ratio is less than 1.1 B: Viscosity ratio is 1.1 or more and less than 1.2 C: Viscosity ratio is 1.2 or more and less than 1.3 D: Viscosity ratio is 1.3 or more <<Slurry composition for porous membrane layer (Example 21, Comparative Examples 7 to 9)>>
A mixture was obtained by mixing 100 parts of alumina (volume average particle size: 0.5 μm) as non-conductive particles, 1.0 part of ammonium polycarboxylate (manufactured by Toa Gosei, product name "Aron A-6114") as a dispersant, and water. The amount of water was adjusted so that the solid content concentration was 50%. The mixture was treated using a media-less dispersing device to disperse alumina and obtain a dispersion. 2.0 parts of sodium salt of carboxymethylcellulose (etherification degree: 1.0, aqueous solution viscosity at solid content concentration of 1.0 mass%: 500 mPa·s) were added to the obtained dispersion and mixed. The sodium salt of carboxymethylcellulose added was dissolved in the mixed liquid. Next, an aqueous solution of polymer A in the same amount (solid content equivalent amount) as that used in the preparation of the slurry composition for the porous membrane layer in each Example and Comparative Example, and 0.2 parts of an aliphatic polyether type nonionic surfactant as a wetting agent were added to this mixed liquid, and water was further added so that the solid content concentration was 40%, to obtain a mixed liquid for viscosity measurement. This mixed solution was designated as η3.
Next, in place of the aqueous solution of polymer A, use the same amount (solid content equivalent amount) of the mixture of polymer A and polymer B (binder composition) as that used in the preparation of the slurry composition for porous membrane layer in each embodiment and comparative example, obtain the mixture for viscosity measurement in the same manner as above.The viscosity of the mixture for viscosity measurement is η4.
The viscosity ratio of the above-mentioned η3 to η4 (=η4/η3) was calculated, and the inhibition of thickening of the slurry composition was evaluated according to the same criteria as those for the above-mentioned negative electrode slurry composition.
<Adhesion of Functional Layer>
<<Negative Electrode Mixture Layer (Examples 1 to 20, Comparative Examples 1 to 6)>>
A rectangular test piece having a width of 1 cm and a length of 10 cm was cut out from the negative electrode. The obtained test piece was fixed with the current collector side facing up. Cellophane tape was attached to the surface of the current collector of the fixed test piece, and the stress was measured when the cellophane tape was peeled off from one end of the test piece in the 180° direction at a speed of 50 mm/min. The cellophane tape used was specified in JIS Z1522. This measurement was performed five times in total, and the average value was taken as the peel strength and evaluated according to the following criteria. The higher the peel strength, the better the adhesion of the negative electrode composite layer and the better the adhesion to the current collector.
A: Peel strength is 10 N/m or more B: Peel strength is 8 N/m or more and less than 10 N/m C: Peel strength is 4 N/m or more and less than 8 N/m D: Peel strength is less than 4 N/m <<Porous membrane layer (Example 21, Comparative Examples 7 to 9)>>
A rectangular test piece having a length of 100 mm and a width of 10 mm was cut out from a separator having a porous membrane layer on one side. Cellophane tape was fixed to the test table in advance. The cellophane tape used was specified in JIS Z1522.
Then, the test piece cut out from the separator was attached to cellophane tape with the porous membrane layer facing down. Then, one end of the separator substrate was pulled in the vertical direction at a pulling speed of 100 mm/min to measure the stress when peeled off. This measurement was performed three times in total, and the average value was taken as the peel strength and evaluated according to the following criteria. The higher the peel strength, the better the adhesion of the porous membrane layer and the better the adhesion to the separator substrate.
A: Peel strength is 100 N/m or more B: Peel strength is 80 N/m or more and less than 100 N/m C: Peel strength is 50 N/m or more and less than 80 N/m D: Peel strength is less than 50 N/m <Suppression of floating of polymer B in slurry composition>
The slurry composition was poured into a 100 mL graduated cylinder up to the 100 mL line and left to stand at room temperature for 48 hours. After standing, the slurry composition (slurry near the liquid surface) present on the graduated cylinder from the 100 mL to 90 mL lines and the slurry composition (slurry near the bottom) present on the graduated cylinder from the 0 mL to 10 mL lines were extracted, diluted with ion-exchanged water to a concentration of 3%, centrifuged, and the supernatant was separated as a measurement sample. The measurement sample derived from the slurry near the liquid surface was called the "measurement sample (liquid surface side)" and the measurement sample derived from the slurry near the bottom was called the "measurement sample (bottom side)".
The volume average particle diameter (dv) of the two measurement samples obtained was measured using a capillary particle size distribution analyzer (manufactured by MATEC, product name "CHDF2000 type") under conditions of flow rate: 1.4 mL/min, pressure: about 2.76 MPa (about 4,000 psi), and temperature: 35° C., and the masses of polymer B contained in the measurement sample (liquid surface side) and the measurement sample (bottom side) were calculated. From these values, the float inhibition degree was calculated using the following formula.
Floating inhibition degree = "Mass of polymer B in measurement sample (bottom side)" / "Mass of polymer B in measurement sample (liquid surface side)"
The degree of inhibition of floating of the polymer B in the slurry composition was evaluated based on the degree of inhibition of floating, according to the following criteria. A higher value of the degree of inhibition of floating indicates that the floating of the polymer B in the slurry composition is more suppressed.
A: Floating suppression degree is 0.9 or more and less than 1.1 B: Floating suppression degree is 0.7 or more and less than 0.9 C: Floating suppression degree is 0.5 or more and less than 0.7 D: Floating suppression degree is less than 0.5 <Cycle characteristics of secondary battery>
After injecting the electrolyte, the lithium ion secondary battery was left to stand for 24 hours in an environment of 25° C., and then charged to a cell voltage of 4.35 V by a constant current method of 0.1 C and discharged to a cell voltage of 3.0 V, and the initial capacity C0 was measured. Furthermore, in an environment of 45° C., the battery was charged to a cell voltage of 4.35 V by a constant current method of 1.0 C, and discharged to a cell voltage of 3.0 V by a charging mode and a fixed current method, and the capacity C1 after 100 cycles was measured. Then, the capacity retention rate (%)=(C1/C0)×100 was calculated and evaluated according to the following criteria. The larger the capacity retention rate, the better the cycle characteristics of the lithium ion secondary battery.
A: Capacity retention rate is 95% or more. B: Capacity retention rate is 90% or more and less than 95%. C: Capacity retention rate is 80% or more and less than 90%. D: Capacity retention rate is less than 80%.

Example 1
<Preparation of Polymer A>
789 parts of ion-exchanged water was put into a 1L glass flask, heated to a temperature of 40° C., and the flask was replaced with nitrogen gas at a flow rate of 100 mL/min. Next, 45 parts of acrylamide as a monomer having an amide group, 25 parts of acrylic acid as a monomer having a carboxylic acid group, and 30 parts of hydroxyethylacrylamide as a monomer having a hydroxyl group were mixed and poured into the flask. Then, 8.9 parts of a 2.5% aqueous solution of potassium persulfate as a polymerization initiator was added into the flask with a syringe. 15 minutes after the addition of potassium persulfate, 22.2 parts of a 2.0% aqueous solution of tetramethylethylenediamine as a polymerization promoter was added with a syringe to start the polymerization reaction.
Four hours after the addition of the polymerization initiator, 4.4 parts of a 2.5% aqueous solution of potassium persulfate as a polymerization initiator was added to the flask, and 11.1 parts of a 2.0% aqueous solution of tetramethylethylenediamine as a polymerization promoter was added, and the temperature was raised to 60°C and maintained, and the polymerization reaction was allowed to proceed. Three hours after the addition of the polymerization initiator, the flask was opened to the air to stop the polymerization reaction, and an 8% aqueous solution of lithium hydroxide was added, and the polymerization product was adjusted to pH 8.0 while stirring at a temperature of 80°C for 6 hours, to obtain a composition containing polymer A, which is a water-soluble polymer, and water (aqueous solution of polymer A). The weight average molecular weight and electrolyte swelling degree of the obtained polymer A were measured. The results are shown in Table 1.
<Preparation of Polymer B>
Into a 5 MPa pressure vessel A equipped with a stirrer, 3.15 parts of styrene (first addition) as an aromatic vinyl monomer, 1.66 parts of 1,3-butadiene (first addition) as an aliphatic conjugated diene monomer, 0.2 parts of sodium lauryl sulfate as an emulsifier, 20 parts of ion-exchanged water, and 0.03 parts of potassium persulfate as a polymerization initiator were placed, thoroughly stirred, and then heated to 60° C. to initiate polymerization. The mixture was allowed to react for 6 hours to obtain seed particles.
After the above reaction, the mixture was heated to 75° C., and addition of a mixture of 56.85 parts of styrene (second addition) as an aromatic vinyl monomer, 33.84 parts of 1,3-butadiene (second addition) as an aliphatic conjugated diene monomer, 3.5 parts of itaconic acid as a monomer having two carboxylic acid groups, 0.25 parts of tert-dodecyl mercaptan as a chain transfer agent, and 0.35 parts of sodium lauryl sulfate as an emulsifier was started from another vessel B to pressure vessel A, and at the same time, addition of 1 part of potassium persulfate as a polymerization initiator was started to pressure vessel A to start a second-stage polymerization.
Four hours after the start of the second-stage polymerization (after 70% of the entire monomer composition had been added), 1 part of hydroxyethyl acrylate as a monomer having a hydroxyl group was added to the pressure vessel A over 1.5 hours.
That is, the overall monomer composition used was 60 parts of styrene as an aromatic vinyl monomer, 35.5 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 3.5 parts of itaconic acid as a monomer having two carboxylic acid groups, and 1 part of hydroxyethyl acrylate as a monomer having a hydroxyl group.
After 5.5 hours from the start of the second-stage polymerization, the addition of the mixture containing these monomer compositions was completed, and the mixture was then heated to 85° C. and reacted for 6 hours.
When the polymerization conversion rate reached 97%, the reaction was stopped by cooling. A 5% aqueous solution of sodium hydroxide was added to the mixture containing the polymer to adjust the pH to 8. Then, unreacted monomers were removed by heating and vacuum distillation. The mixture was further cooled to obtain a composition containing water-dispersed polymer B and water (aqueous dispersion of polymer B). The glass transition temperature of the obtained polymer B was measured. The results are shown in Table 1.
<Preparation of Binder Composition>
The aqueous solution of polymer A obtained as described above and the aqueous dispersion of polymer B were mixed so that the mass ratio of the solid content of polymer A to that of polymer B was 70:30 (polymer A:polymer B), to obtain a binder composition. Using this binder composition and the aqueous solution of polymer A described above, the suppression of thickening of the slurry composition was evaluated. The results are shown in Table 1.
<Preparation of negative electrode slurry composition>
In a planetary mixer with a disperser, 68.6 parts of artificial graphite (volume average particle diameter: 24.5 μm, specific surface area: 4 m ² /g) as negative electrode active material particles and 29.4 parts of silicon-based negative electrode active material particles (SiO _x ), as well as 2 parts of the binder composition obtained as described above (solid content equivalent amount) were added, and the solid content concentration was adjusted to 58% with ion-exchanged water, and mixed for 60 minutes at room temperature. Next, the solid content concentration was adjusted to 50% with ion-exchanged water, and further mixed for 15 minutes to obtain a mixed liquid. Then, the obtained mixed liquid was defoamed under reduced pressure to obtain a negative electrode slurry composition with good fluidity. Using this negative electrode slurry composition, the floating suppression of polymer B in the slurry composition was evaluated. The results are shown in Table 1.
<Production of negative electrode>
The above-mentioned negative electrode slurry composition was applied to a copper foil (current collector) having a thickness of 18 μm with a comma coater so that the film thickness after drying was 105 μm and the coating amount was 10 mg / cm ^2. The copper foil coated with the negative electrode slurry composition was conveyed at a speed of 0.5 m / min in an oven at a temperature of 75 ° C. for 2 minutes and then in an oven at a temperature of 120 ° C. for 2 minutes to dry the slurry composition on the copper foil and obtain a negative electrode raw material. The negative electrode raw material was rolled with a roll press to obtain a negative electrode with a negative electrode composite layer thickness of 80 μm. The adhesiveness of the functional layer (negative electrode composite layer) was evaluated using this negative electrode. The results are shown in Table 1.
<Production of Positive Electrode>
A planetary mixer was charged with ₉₅ parts of LiCoO2 having a spinel structure as a positive electrode active material, 3 parts of PVDF (polyvinylidene fluoride) as a positive electrode binder in terms of solid content, 2 parts of acetylene black as a conductive material, and 20 parts of N-methylpyrrolidone as a solvent, and mixed to obtain a positive electrode slurry composition.
The obtained positive electrode slurry composition was applied to an aluminum foil (current collector) having a thickness of 20 μm by a comma coater so that the film thickness after drying was about 100 μm. The aluminum foil coated with the positive electrode slurry composition was conveyed at a speed of 0.5 m/min in an oven at a temperature of 60° C. for 2 minutes, and then in an oven at a temperature of 120° C. for 2 minutes, thereby drying the positive electrode slurry composition on the aluminum foil and obtaining a positive electrode raw material. The positive electrode raw material was rolled by a roll press to obtain a positive electrode having a positive electrode composite layer thickness of 70 μm.
<Preparing the separator>
A single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm; produced by a dry method; porosity 55%) was prepared. This separator was cut into a 5 cm×5 cm square and used for producing a secondary battery.
<Preparation of secondary battery>
An aluminum packaging exterior was prepared as the exterior of the battery. The positive electrode was cut into a square of 4 cm x 4 cm, and the surface on the collector side was placed in contact with the aluminum packaging exterior. Next, the square separator was placed on the surface of the positive electrode composite layer of the positive electrode. Furthermore, the negative electrode was cut into a square of 4.2 cm x 4.2 cm, and placed on the separator so that the surface on the negative electrode composite layer side faces the separator. Then, a LiPF ₆ solution with a concentration of 1.0 M was filled as the electrolyte (solvent is a mixed solvent of ethylene carbonate (EC) / diethyl carbonate (DEC) = 1 / 2 (volume ratio), containing 2 volume % vinylene carbonate (solvent ratio) as an additive). Furthermore, in order to seal the opening of the aluminum packaging, the aluminum packaging exterior was closed by heat sealing at 150 ° C., and a laminate cell type lithium ion secondary battery was produced. The cycle characteristics of the obtained lithium ion secondary battery were evaluated. The results are shown in Table 1.

(Examples 2 to 7)
In preparing Polymer A, the amounts of acrylamide, acrylic acid, and/or hydroxyethylacrylamide used were changed to change the composition of Polymer A as shown in Table 1. In the same manner as in Example 1, except that, a binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a secondary battery were prepared and various evaluations were performed. The results are shown in Table 1.

(Example 8)
In preparing Polymer A, hydroxyethyl acrylate was used instead of hydroxyethyl acrylamide, and the composition of Polymer A was changed as shown in Table 1. In the same manner as in Example 1, except for this, a binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a secondary battery were prepared and various evaluations were performed. The results are shown in Table 1.

(Examples 9 to 12)
In preparing Polymer B, the amounts of 1,3-butadiene, styrene, and/or itaconic acid used were changed to change the composition of Polymer B as shown in Tables 1 and 2. In the same manner as in Example 1, except that, a binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a secondary battery were prepared and various evaluations were performed. The results are shown in Tables 1 and 2.
The amounts of 1,3-butadiene (BD) and styrene (ST) added in the first and second increments in each example are shown below immediately after the abbreviations of the respective monomers as (amount added in the first increment, amount added in the second increment).
Example 9: BD (1.66 parts, 33.84 parts), ST (3.15 parts, 57.85 parts)
Example 10: BD (1.66 parts, 33.84 parts), ST (3.15 parts, 55.35 parts)
Example 11: BD (1.66 parts, 58 parts), ST (3.15 parts, 32.69 parts)
Example 12: BD (1.66 parts, 8.84 parts), ST (3.15 parts, 81.85 parts)

Example 13
In preparing Polymer A, the amount of the 2.5% aqueous solution of potassium persulfate used as the polymerization initiator was changed from 8.9 parts to 13.4 parts, and the amount of the 2.0% aqueous solution of tetramethylethylenediamine used as the polymerization accelerator was changed from 22.2 parts to 33.3 parts, but the binder composition, the negative electrode slurry composition, the negative electrode, the positive electrode, the separator, and the secondary battery were prepared in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 2.

(Example 14)
In preparing Polymer A, the amount of the 2.5% aqueous solution of potassium persulfate used as the polymerization initiator was changed from 8.9 parts to 6.7 parts, and the amount of the 2.0% aqueous solution of tetramethylethylenediamine used as the polymerization accelerator was changed from 22.2 parts to 16.7 parts, but the binder composition, the negative electrode slurry composition, the negative electrode, the positive electrode, the separator, and the secondary battery were prepared and various evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

(Examples 15 and 16)
In preparing Polymer A, acrylamide, acrylic acid, hydroxyethylacrylamide, and n-butyl acrylate were used as monomers, and the composition of Polymer A was changed as shown in Table 2. In the same manner as in Example 1, except for this, a binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a secondary battery were prepared and various evaluations were performed. The results are shown in Table 2.

(Examples 17 and 18)
In preparing the binder composition, except that the mass ratio of polymer A and polymer B was changed as shown in Table 2, the binder composition, the negative electrode slurry composition, the negative electrode, the positive electrode, the separator, and the secondary battery were prepared and various evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

(Example 19)
In preparing Polymer B, hydroxyethyl acrylate was not used, and the amount of 1,3-butadiene used was changed (amount added in the first step: 1.66 parts, amount added in the second step: 34.84 parts) to change the composition of Polymer B as shown in Table 2. Except for this, a binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a secondary battery were prepared in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 2.

(Example 20)
In preparing the binder composition, except that the polymer B prepared as follows was used, the binder composition, the negative electrode slurry composition, the negative electrode, the positive electrode, the separator, and the secondary battery were prepared and various evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.
<Preparation of Polymer B>
233.3 parts of cyclohexane, 0.006972 parts of N,N,N',N'-tetramethylethylenediamine, and 20.5 parts of styrene as an aromatic vinyl monomer were added to a 5 MPa pressure-resistant reactor A equipped with a stirrer, and while stirring at 40°C, 0.12812 parts of n-butyllithium was added and polymerization was carried out for 1 hour while raising the temperature to 50°C. Subsequently, 76.0 parts of isoprene as an aliphatic conjugated diene monomer was continuously added to the reactor over 1 hour while controlling the temperature to maintain 55°C. After the addition of isoprene was completed, polymerization was carried out for another 1 hour.
Next, the inside of the pressure vessel A was heated to 85°C, and the reaction was continued for another 2 hours. When the polymerization conversion rate reached 98%, 105.8 parts of dichlorodimethylsilane was added as a coupling agent and a coupling reaction was carried out for 2 hours to form a styrene-isoprene coupling block copolymer. Then, 0.12816 parts of methanol was added and mixed well to deactivate the active terminal. Ion-exchanged water and potassium lauryl sulfate were added to carry out emulsification. Furthermore, 3.5 parts of itaconic acid as a monomer having two carboxylic acid groups and 0.1 parts of potassium persulfate were added to obtain a composition containing polymer B, which is a water-dispersible polymer, and water (aqueous dispersion of polymer B).

(Example 21)
The negative electrode slurry composition and the negative electrode were prepared as follows, and the porous membrane layer slurry composition and the separator with the porous membrane layer were prepared as follows. Then, in the production of the secondary battery, the positive electrode and the secondary battery were prepared in the same manner as in Example 1, except that the following negative electrode and the separator with the porous membrane were used, and various evaluations were performed. The results are shown in Table 2.
<Preparation of negative electrode slurry composition and negative electrode>
A negative electrode slurry composition was prepared in the same manner as in Example 1, except that a binder composition obtained by using a sodium salt of carboxymethyl cellulose (degree of etherification: 1.0, aqueous solution viscosity at a solid content concentration of 1.0 mass%: 3,500 mPa s) was used instead of polymer A.
A negative electrode was produced in the same manner as in Example 1, except that the negative electrode slurry composition obtained as described above was used.
<Preparation of slurry composition for porous membrane layer>
100 parts of alumina (volume average particle size: 0.5 μm) as non-conductive particles, 1.0 part of ammonium polycarboxylate (manufactured by Toa Gosei, product name "Aron A-6114") as a dispersant, and water were mixed to obtain a mixture. The amount of water was adjusted so that the solid content concentration was 50%. The mixture was treated using a media-less dispersing device to disperse alumina and obtain a dispersion. 2.0 parts of sodium salt of carboxymethylcellulose (etherification degree: 1.0, aqueous solution viscosity at solid content concentration of 1.0 mass%: 500 mPa·s) were added to the obtained dispersion and mixed. The sodium salt of carboxymethylcellulose added was dissolved in the mixed liquid. Next, 5.0 parts (solid content equivalent amount) of the binder composition prepared in the same manner as in Example 1 and 0.2 parts of an aliphatic polyether type nonionic surfactant as a wetting agent were added to this mixed liquid, and water was further added so that the solid content concentration was 40%, to obtain a slurry composition for a porous membrane layer. This slurry composition for a porous membrane layer was used to evaluate the ability of the polymer B to inhibit floating in the slurry composition. The results are shown in Table 2.
<Preparation of separator with porous membrane layer>
A single-layer polypropylene separator substrate (width 250 mm, length 1000 m, thickness 12 μm) manufactured by a wet method was prepared. The redispersed slurry composition for the porous membrane layer was applied to both surfaces of the separator substrate with a gravure coater (coating speed: 20 m/min) so that the thickness after drying was 2.5 μm. Next, the separator substrate coated with the slurry composition for the porous membrane layer was dried in a drying oven at 50 ° C. and wound up to produce a separator having a porous membrane layer on both sides of the separator substrate. This separator was cut into a square of 5 cm x 5 cm and used for the production of a secondary battery.
In addition, the separator having a porous membrane layer on one side was prepared in the same manner as above, except that the slurry composition for porous membrane layer was applied on one surface of the separator substrate.Then, the separator having a porous membrane layer on one side was used to evaluate the adhesion of the functional layer (porous membrane layer).The results are shown in Table 2.

(Comparative Examples 1 to 2)
Except for changing the amounts of acrylamide, acrylic acid, and hydroxyethylacrylamide used during the preparation of polymer A to change the composition of polymer A as shown in Table 1, a binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a secondary battery were prepared and various evaluations were performed in the same manner as in Example 1. The results are shown in Table 3.

(Comparative Examples 3 to 6)
In preparing Polymer B, the amounts of 1,3-butadiene, styrene, and/or itaconic acid used were changed to change the composition of Polymer B as shown in Table 3. In the same manner as in Example 1, except for this, a binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, a separator, and a secondary battery were prepared and various evaluations were performed. The results are shown in Table 3.
The amounts of 1,3-butadiene (BD) and styrene (ST) added for the first and second times in each comparative example are shown below immediately after the abbreviations of the respective monomers as (amount added for the first time, amount added for the second time).
Comparative example 3: BD (1.66 parts, 34.34 parts), ST (3.15 parts, 58.35 parts)
Comparative Example 4: BD (1.66 parts, 31.34 parts), ST (3.15 parts, 55.85 parts)
Comparative Example 5: BD (1.66 parts, 80.34 parts), ST (3.15 parts, 10.35 parts)
Comparative Example 6: BD (1.66 parts, 0.84 parts), ST (3.15 parts, 89.85 parts)

(Comparative Example 7)
Except for using the polymers A and B prepared in the same manner as in Comparative Example 3, a binder composition, a slurry composition for negative electrodes, a negative electrode, a positive electrode, a separator having a porous membrane, and a secondary battery were prepared in the same manner as in Example 21, and various evaluations were performed. The results are shown in Table 3.

(Comparative Example 8)
Except for using the polymer A prepared in the same manner as in Comparative Example 1, a binder composition, a slurry composition for negative electrode, a negative electrode, a positive electrode, a separator having a porous membrane, and a secondary battery were prepared in the same manner as in Example 21, and various evaluations were performed. The results are shown in Table 3.

(Comparative Example 9)
Except for using acrylic acid instead of itaconic acid in the preparation of polymer B, the binder composition, the negative electrode slurry composition, the negative electrode, the positive electrode, the separator having a porous membrane, and the secondary battery were prepared in the same manner as in Comparative Example 8, and various evaluations were performed. The results are shown in Table 3.

In addition, in Tables 1 to 3 shown below,
"AAm" indicates an acrylamide unit;
"AA" represents an acrylic acid unit;
"HEAm" indicates a hydroxyethylacrylamide unit;
"HEA" indicates hydroxyethyl acrylate units;
"BA" indicates n-butyl acrylate units;
"IP" indicates an isoprene unit;
"BD" indicates a 1,3-butadiene unit;
"ST" indicates a styrene unit;
"IA" represents an itaconic acid unit;
The "ratio of hydroxyl group+amide group" refers to the total content of monomer units having a hydroxyl group and monomer units having an amide group.

From Tables 1 and 2, it can be seen that in Examples 1 to 21 using binder compositions containing polymer A and polymer B each having a predetermined composition, it is possible to form a functional layer (negative electrode mixture layer, porous membrane layer) having excellent adhesiveness, and to cause the secondary battery to exhibit excellent cycle characteristics. In addition, it can be seen that in Examples 1 to 21, thickening of the slurry composition and floating of polymer B in the slurry composition can be suppressed.
On the other hand, from Table 3, in Comparative Examples 1 to 9 using binder compositions in which the composition of polymer A or polymer B is outside the specified range, it is found that a functional layer (negative electrode mixture layer, porous membrane layer) having excellent adhesiveness cannot be formed, and the cycle characteristics of the secondary battery are deteriorated. Furthermore, it is found that in Comparative Examples 1 and 8, the thickening of the slurry composition and the floating of polymer B in the slurry composition cannot be suppressed. In addition, it is found that in Comparative Examples 2 to 7 and 9, the floating of polymer B in the slurry composition cannot be suppressed.

According to the present invention, it is possible to provide a binder composition for secondary batteries that can form a functional layer having excellent adhesiveness and can cause the secondary battery to exhibit excellent cycle characteristics.
Furthermore, according to the present invention, it is possible to provide a slurry composition for a secondary battery functional layer, which is capable of forming a functional layer having excellent adhesiveness and enabling the secondary battery to exhibit excellent cycle characteristics.
According to the present invention, it is possible to provide a functional layer for a secondary battery that has excellent adhesiveness and allows the secondary battery to exhibit excellent cycle characteristics.
Furthermore, according to the present invention, a secondary battery having excellent cycle characteristics can be provided.

Claims (7)

comprising a polymer A, a polymer B, and a solvent;
The polymer A has a total content of monomer units having a hydroxyl group and monomer units having an amide group of 50% by mass or more and 90% by mass or less, a content of monomer units having a carboxylic acid group of 10% by mass or more and 25% by mass or less, and a content of monomer units having a hydroxyl group of 10% by mass or more,
the monomer unit having a hydroxyl group is selected from a hydroxyethylacrylamide unit and a hydroxyethylacrylate unit, the monomer unit having an amide group is selected from an acrylamide unit and a methacrylamide unit, and the monomer unit having a carboxylic acid group is selected from an acrylic acid unit and a methacrylic acid unit;
The polymer B has a content of monomer units having two carboxylic acid groups of 2% by mass or more and 5% by mass or less, a content of aromatic vinyl monomer units of 15% by mass or more and 88% by mass or less, and a content of aliphatic conjugated diene monomer units of 10% by mass or more and 80% by mass or less,
a ratio of the polymer B to a total of the polymer A and the polymer B is 5% by mass or more and 45% by mass or less. The binder composition for secondary batteries according to claim 1, wherein the weight average molecular weight of the polymer A is 1,000,000 or more and 15,000,000 or less. The binder composition for secondary batteries according to claim 1 or 2, wherein the electrolyte swelling degree of the polymer A is 150 mass% or less. The binder composition for secondary batteries according to any one of claims 1 to 3, wherein the polymer A is an addition polymer. A slurry composition for a secondary battery functional layer, comprising functional particles selected from electrode active material particles and non-conductive particles, and the binder composition for a secondary battery according to any one of claims 1 to 4. A functional layer for a secondary battery formed using the slurry composition for a secondary battery functional layer according to claim 5. A secondary battery comprising the functional layer for a secondary battery according to claim 6.