Binder composition for secondary battery, slurry composition for secondary battery functional layer, functional layer for secondary battery, and secondary battery

Abstract

The purpose of the present invention is to provide a binder composition for secondary batteries, which is capable of forming a functional layer that exhibits excellent adhesion, and which enables a secondary battery to exhibit excellent cycle characteristics. A binder composition according to the present invention contains a polymer A, a polymer B and a solvent. With respect to the polymer A, the total of the content ratios of a monomer unit having a hydroxyl group and a monomer unit having an amide group is from 50% by mass to 90% by mass (inclusive), while the content ratio of a monomer unit having a carboxylic acid group is from 10% by mass to 50% by mass (inclusive). With respect to the polymer B, the content ratio of a monomer unit having two carboxylic acid groups is from 2% by mass to 5% by mass (inclusive), the content ratio of an aromatic vinyl monomer unit is from 15% by mass to 88% by mass (inclusive), and the content ratio of an aliphatic conjugated diene monomer unit is from 10% by mass to 80% by mass (inclusive).

Description

Technical Field

[0001] The present invention relates to a binder composition for a secondary battery, a slurry composition for a functional layer of a secondary battery, a functional layer for a secondary battery, and a secondary battery.

Background Art

[0002] Secondary batteries such as lithium-ion secondary batteries are small, lightweight, have a high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. A secondary battery generally includes battery members such as electrodes (a positive electrode and a negative electrode) and a separator that separates the positive electrode and the negative electrode to prevent a short circuit between the positive electrode and the negative electrode.

[0003] Here, as a battery member of a secondary battery, a member including a binder and optionally a functional layer including particles (hereinafter referred to as "functional particles") blended to exhibit a desired function for the battery member is used. Specifically, as a separator of a secondary battery, a separator having an adhesive layer containing a binder or a porous membrane layer containing a binder and non-conductive particles as functional particles on a separator substrate is used. As an electrode of a secondary battery, an electrode having an electrode mixture layer containing a binder and electrode active material particles as functional particles on a current collector, or an electrode having an electrode mixture layer on a current collector and further having the above-described adhesive layer or porous membrane layer on an electrode substrate having the electrode mixture layer is used.

[0004] To achieve further performance improvement of secondary batteries, improvements to binder compositions containing binders have conventionally been attempted. For example, in Patent Document 1, a water-soluble resin (a) obtained by polymerizing a monomer group containing at least a polymerizable monomer of unsaturated carboxylic acids and (meth)acrylamide, and an acrylic-based aqueous dispersion for an electrochemical cell characterized by containing organic particles (b) (excluding the water-soluble resin (a)) are disclosed. And according to Patent Document 1, the above-mentioned acrylic-based aqueous dispersion has sufficient adhesion to a current collector or the like, and by using this acrylic-based aqueous dispersion as a binder composition to fabricate a secondary battery, the cycle characteristics of the secondary battery can be improved.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, for the above-mentioned conventional binder composition, further improvement in the adhesiveness of the functional layer obtained using the binder composition and the cycle characteristics of the secondary battery has been demanded.

[0007] Therefore, an object of the present invention is to provide a binder composition for a secondary battery that can form a functional layer with excellent adhesiveness and can exhibit excellent cycle characteristics in the secondary battery. Another object of the present invention is to provide a slurry composition for a secondary battery functional layer that can form a functional layer with excellent adhesiveness and can exhibit excellent cycle characteristics in the secondary battery. And an object of the present invention is to provide a functional layer for a secondary battery that has excellent adhesiveness and can exhibit excellent cycle characteristics in the secondary battery. Furthermore, an object of the present invention is to provide a secondary battery having excellent cycle characteristics.

Means for Solving the Problems

[0008] The present inventors have conducted intensive studies for the purpose of solving the above problems. As a result, the present inventors have newly found that by using a binder composition containing two predetermined polymers in a solvent, the adhesiveness of the functional layer can be enhanced and the cycle characteristics of the secondary battery can be improved, and thus completed the present invention.

[0009] That is, the present invention aims to advantageously solve the above problems. The binder composition for a secondary battery of the present invention contains polymer A, polymer B, and a solvent. In polymer A, the total content ratio of monomer units having a hydroxyl group and monomer units having an amide group is 50% by mass or more and 90% by mass or less, and the content ratio of monomer units having a carboxylic acid group is 10% by mass or more and 50% by mass or less. In polymer B, the content ratio of monomer units having two carboxylic acid groups is 2% by mass or more and 5% by mass or less, the content ratio of aromatic vinyl monomer units is 15% by mass or more and 88% by mass or less, and the content ratio of aliphatic conjugated diene monomer units is 10% by mass or more and 80% by mass or less. By using the binder composition containing the above-described polymer A and polymer B in a solvent, a functional layer excellent in adhesiveness can be formed. And according to the battery member provided with the functional layer, excellent cycle characteristics of the secondary battery can be exhibited. In the present invention, "containing monomer units" means that "repeating units derived from the monomer are contained in the polymer obtained by using the monomer". Further, in the present invention, the "content ratio (mass%)" of each monomer unit (each repeating unit) contained in the polymer is 1 measurable by using nuclear magnetic resonance (NMR) methods such as H-NMR and 13 C-NMR.

[0010] Here, it is preferable that the weight average molecular weight of polymer A in the binder composition for a secondary battery of the present invention is 1,000,000 or more and 15,000,000 or less. If the weight average molecular weight of polymer A is within the above-described 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 using the method described in the examples of this specification.

[0011] Further, in the binder composition for secondary batteries of the present invention, it is preferable that the degree of swelling of the polymer A in the electrolyte is 150% by mass or less. If the degree of swelling of the polymer A in the electrolyte is below the above-described value, the cycle characteristics of the secondary battery can be further improved. In the present invention, the "degree of swelling in the electrolyte" can be measured using the method described in the examples of this specification.

[0012] And, in the binder composition for secondary batteries of the present invention, it is preferable that the ratio of the polymer B in the total of the polymer A and the polymer B is 5% by mass or more and 45% by mass or less. If the ratio of the amount of the polymer B in the total of the amount of the polymer A and the amount of the polymer B is within the above-described range, while suppressing excessive thickening of the slurry composition prepared using the binder composition, the cycle characteristics of the secondary battery can be further improved.

[0013] Moreover, this invention aims to advantageously solve the above problems, and the slurry composition for the functional layer of a secondary battery of the present invention is characterized by including functional particles and any of the above-described binder compositions. By using a slurry composition containing functional particles and any of the above-described binder compositions, a functional layer excellent in adhesiveness can be formed. And according to the battery member provided with the functional layer, excellent cycle characteristics can be exhibited in the secondary battery.

[0014] Moreover, this invention aims to advantageously solve the above problems, and the functional layer for a secondary battery of the present invention is characterized by being formed using the slurry composition for the functional layer of a secondary battery described above. The functional layer formed from the above-described slurry composition is excellent in adhesiveness. And by using the battery member provided with the functional layer, excellent cycle characteristics can be exhibited in the secondary battery.

[0015] Furthermore, the present invention aims to advantageously solve the above problems, and the secondary battery of the present invention is characterized by including the above-described functional layer for a secondary battery. A secondary battery including a battery member having the above-described functional layer has excellent cycle characteristics.

[0016] In the present 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 film layer", and a functional layer containing a binder and containing neither electrode active material particles nor non-conductive particles is referred to as an "adhesive layer".

Effects of the Invention

[0017] According to the present invention, it is possible to provide a binder composition for a secondary battery that can form a functional layer having excellent adhesiveness and can exhibit excellent cycle characteristics in a secondary battery. Further, according to the present invention, it is possible to provide a slurry composition for a secondary battery functional layer that can form a functional layer having excellent adhesiveness and can exhibit excellent cycle characteristics in a secondary battery. And, according to the present invention, it is possible to provide a functional layer for a secondary battery that has excellent adhesiveness and can exhibit excellent cycle characteristics in a secondary battery. Furthermore, according to the present invention, it is possible to provide a secondary battery having excellent cycle characteristics.

Modes for Carrying Out the Invention

[0018] Hereinafter, embodiments 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 for example, it can be used in the preparation of the slurry composition for the functional layer of the secondary batteries of the present invention. And the slurry composition for the functional layer of the secondary batteries of the present invention can be used in the formation of any functional layer (for example, electrode composite layer, porous membrane layer, adhesive layer) that undertakes functions such as electron transfer, reinforcement or adhesion in the secondary battery. Further, the functional layer for secondary batteries of the present invention is formed from the slurry composition for the functional layer of the secondary batteries of the present invention. And the secondary battery of the present invention includes a battery member having the functional layer for secondary batteries of the present invention.

[0019] (Binder composition for secondary batteries) The binder composition of the present invention is a composition in which polymer A and polymer B are dissolved and / or dispersed in a solvent. Note that the binder composition of the present invention may contain components other than polymer A, polymer B, and the solvent (hereinafter referred to as "other components").

[0020] Here, in the above polymer A, the total content ratio of the monomer unit having a hydroxyl group and the monomer unit having an amide group is 50% by mass or more and 90% by mass or less, and the content ratio of the monomer unit having a carboxylic acid group is 10% by mass or more and 50% by mass or less. Further, in the above polymer B, the ratio of the monomer unit having two carboxylic acid groups is 2% by mass or more and 5% by mass or less, the ratio of the aromatic vinyl monomer unit is 15% by mass or more and 88% by mass or less, and the ratio of the aliphatic conjugated diene monomer unit is 10% by mass or more and 80% by mass or less.

[0021] And since the binder composition of the present invention contains polymer A and polymer B having the above-described compositions respectively in a solvent, by using the binder composition of the present invention, the adhesiveness of the functional layer can be enhanced and the cycle characteristics of the secondary battery can be improved. Thus, the reason why both the adhesiveness of the functional layer and the cycle characteristics of the secondary battery can be improved by the binder composition of the present invention is not clear, but it is presumed as follows. First, Polymer B contains an aromatic vinyl monomer unit and an aliphatic conjugated diene monomer unit, and can function as a binder material having both flexibility and strength. On the other hand, according to the study by the present inventors, when a binder composition and a slurry composition (hereinafter, these may be collectively abbreviated as "slurry composition etc.") containing a binder material made 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 material floats in the slurry composition etc. and accumulates near the liquid surface. And, even when using a slurry composition etc. whose uniformity is impaired by the floating of the binder material, it was not possible to achieve both the adhesiveness of the functional layer and the cycle characteristics of the secondary battery. Specifically, when using the slurry composition etc. near the tank liquid surface where the binder material accumulates, the resistance increases and the cycle characteristics deteriorate. On the other hand, when using the slurry composition etc. near the tank bottom where the binder material is dilute, it was not possible to ensure the adhesiveness of the functional layer. In contrast, Polymer B contained in the binder composition of the present invention not only contains an aromatic vinyl monomer unit and an aliphatic conjugated diene monomer unit in a ratio within a predetermined range, but also contains a monomer unit having two carboxylic acid groups in a ratio within a predetermined range. Therefore, Polymer B can interact well with Polymer A (particularly, at least one of the hydroxyl group and the amide group of the Polymer A) contained in the binder composition through the carboxylic acid group by means of hydrogen bonding or the like. By this interaction with Polymer A, it is possible to suppress the non-uniformity of the slurry composition etc. due to the floating of Polymer B. Therefore, by using the binder composition of the present invention, it is possible to obtain a slurry composition in which Polymer A and Polymer B are evenly distributed. Therefore, by using this slurry composition, it is possible to form a functional layer having excellent adhesiveness, and it is considered that a battery member provided with the functional layer can exhibit excellent cycle characteristics in a secondary battery.

[0022] <Polymer A> Polymer A is a component that can suppress the floating of Polymer B in the slurry composition etc., can function as a binder material together with Polymer B, and can further function as a viscosity regulator for the slurry composition prepared using the binder composition.

[0023] [Composition] Polymer A contains at least one of a monomer unit having a hydroxyl group and a monomer unit having an amide group, and contains a monomer unit having a carboxylic acid group. Note that 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").

[0024] [Monomer unit having a hydroxyl group] Examples of the monomer having a hydroxyl group that can form 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 sufficiently suppressing the floating of Polymer B in a slurry composition or the like and further improving the cycle characteristics of the secondary battery, hydroxyethylacrylamide and hydroxyethylacrylate are preferable, and hydroxyethylacrylamide is more preferable. In the present invention, a monomer having both a hydroxyl group and an amide group is included in the monomer having a hydroxyl group and not included in the monomer having an amide group.

[0025] 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, floating of Polymer B in a slurry composition or the like can be sufficiently suppressed and the adhesiveness 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.

[0026] [Monomer unit having an amide group] Examples of the monomer 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 preferable from the viewpoint of sufficiently suppressing the floating of Polymer B in a slurry composition or the like.

[0027] When the total repeating units (total monomer units) contained in Polymer A is 100% by mass, the content ratio of 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 monomer units having an amide 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 an amide group in Polymer A is 10% by mass or more, floating of Polymer B in a slurry composition or the like can be sufficiently suppressed and the adhesiveness of the functional layer can be further improved. In addition, coating defects when forming the functional layer by coating 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 monomer units having an amide group in Polymer A is 75% by mass or less, the adhesiveness of the functional layer can be further improved.

[0028] [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 Polymer A is 100% by mass, the total of the content ratio of monomer units having a hydroxyl group and the content ratio of monomer units having an amide group needs to 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, still 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 ratio of monomer units having a hydroxyl group and the ratio of monomer units having an amide group in Polymer A is less than 50% by mass, floating of Polymer B in a 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 well in balance. On the other hand, if the total of the ratio of monomer units having a hydroxyl group and the ratio of monomer units having an amide group in Polymer A exceeds 90% by mass, the slurry composition becomes excessively thickened, and both the adhesiveness of the functional layer and the cycle characteristics of the secondary battery cannot be improved well in balance. As described above, the polymer A may contain at least one of a monomer unit having a hydroxyl group and a monomer unit having an amide group. However, from the viewpoint of sufficiently suppressing the floating of the polymer B in a slurry composition or the like and improving the adhesion of the functional layer and the cycle characteristics of the secondary battery in a well-balanced manner, the polymer A preferably contains both a monomer unit having a hydroxyl group and a monomer unit having an amide group.

[0029] [Monomer unit having a carboxylic acid group] Examples of the monomer having a carboxylic acid group that can form a monomer unit having a carboxylic acid group include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, and their derivatives. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, crotonic acid, and the like. Examples of the monocarboxylic acid derivative include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, and the like. Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid, and the like. Examples of the dicarboxylic acid derivative 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 anhydride of the dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, and the like. In addition, as the monomer having a carboxylic acid group, an acid anhydride that generates a carboxylic acid group by hydrolysis can also be used. These may be used alone or in combination of two or more. Among these, from the viewpoint of suppressing excessive thickening of the slurry composition and improving both the adhesion of the functional layer and the cycle characteristics of the secondary battery in a well-balanced manner, acrylic acid and methacrylic acid are preferable.

[0030] When the total repeating units (total monomer units) contained in Polymer A are taken as 100% by mass, the content ratio of the monomer unit having a carboxylic acid group needs to 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 still more preferably 25% by mass or less. When the ratio of the monomer unit having a carboxylic acid group in Polymer A is less than 10% by mass, the slurry composition will thicken excessively, and it is impossible to improve both the adhesiveness of the functional layer and the cycle characteristics of the secondary battery in a well-balanced manner. On the other hand, when the ratio of the monomer unit having a carboxylic acid group in Polymer A exceeds 50% by mass, the adhesiveness of the functional layer decreases.

[0031] [Other repeating units] The other repeating units contained in Polymer A are not particularly limited. For example, as the other repeating units, monomer units derived from known monomers such as the aliphatic conjugated diene monomer units and aromatic vinyl monomer units described later in the section of "Polymer B" and (meth)acrylate monomer units can be mentioned. Polymer A may contain one kind of other repeating units or two or more kinds of other repeating units. Here, when the total repeating units (total monomer units) contained in Polymer A are taken as 100% by mass, the content ratio of the other repeating units is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 1% by mass or less, and particularly preferably 0% by mass. In the present invention, "(meth)acryl" means acrylic and / or methacrylic.

[0032] [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, while sufficiently suppressing the floating of the polymer B in the slurry composition or the like, the adhesiveness of the functional layer and the cycle characteristics of the secondary battery can be improved in a well-balanced manner. In the present invention, the 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 content is less than 1.0 mass%.

[0033] [Degree of swelling in the electrolyte solution] The polymer A preferably has a degree of swelling in the electrolyte solution of 150 mass% or less, more preferably 145 mass% or less, and still more preferably 140 mass% or less. If the degree of swelling in the electrolyte solution of the polymer A is 150 mass% or less, the cycle characteristics of the secondary battery can be further improved. Here, the lower limit of the degree of swelling in the electrolyte solution of the polymer A is not particularly limited, but is usually 100 mass% or more. Note that the degree of swelling in the electrolyte solution of the polymer A can be adjusted, for example, by changing the type and amount of the monomer used in the preparation of the polymer A.

[0034] [Weight average molecular weight] The polymer A preferably has a weight average molecular weight of 1,000,000 or more, more preferably 2,000,000 or more, still more preferably 5,000,000 or more, particularly preferably 6,000,000 or more, preferably 15,000,000 or less, more preferably 12,000,000 or less, and still 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. Incidentally, the weight-average molecular weight of Polymer A can be adjusted, for example, by changing the type and / or amount of the polymerization initiator and / or polymerization accelerator used in the preparation of Polymer A.

[0035] [[Preparation Method]] The above-described Polymer A is not particularly limited and can be prepared by any method such as solution polymerization method, suspension polymerization method, bulk polymerization method, emulsion polymerization method, etc. Further, as the polymerization method, addition polymerization such as ionic polymerization, radical polymerization, living radical polymerization, etc. can be used. Further, as the polymerization initiator, known polymerization initiators can be used. Incidentally, other additives (for example, emulsifier, dispersant, polymerization aid, chain transfer agent, molecular weight regulator, polymerization accelerator) that can be used during polymerization can be those generally used, and the amount used is also the generally used amount.

[0036] [Polymer B] Polymer B is a component that functions as a binder, imparts adhesiveness to a functional layer formed using a slurry composition containing a binder composition, and holds components (for example, functional particles such as electrode active material particles and non-conductive particles) contained in the functional layer so as not to detach from the functional layer.

[0037] [[Composition]] Polymer B contains a monomer unit having two carboxylic acid groups, an aromatic vinyl monomer unit, and an aliphatic conjugated diene monomer unit. Incidentally, Polymer B may contain repeating units 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 "arbitrary repeating units").

[0038] [Monomer Unit Having Two Carboxylic Acid Groups] Examples of the monomer having two carboxylic acid groups that can form a monomer unit having two carboxylic acid groups include dicarboxylic acids, their acid anhydrides, and their derivatives. Specific examples thereof include the same ones as those described above in the section of "Polymer A". Note that the monomer having two carboxylic acid groups may be used alone or in combination of two or more. Here, as the monomer having two carboxylic acid groups, from the viewpoint of sufficiently suppressing the floating of Polymer B in a slurry composition or the like and improving both the adhesiveness of the functional layer and the cycle characteristics of the secondary battery in a well-balanced manner, and further from the viewpoint of enhancing the production stability of Polymer B, itaconic acid is preferable.

[0039] When the total repeating units (total monomer units) contained in Polymer B are 100% by mass, the content ratio of the monomer unit having two carboxylic acid groups needs to 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, still more preferably 3% by mass or more, preferably 4.5% by mass or less, more preferably 4% by mass or less, and still more preferably 3.5% by mass or less. When the ratio of the monomer unit having two carboxylic acid groups in Polymer B is less than 2% by mass, the floating of Polymer B in a 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, when the ratio of the monomer unit having two carboxylic acid groups in Polymer B exceeds 5% by mass, although it is presumed to be due to an increase in the amount of water brought into the secondary battery and the generation of coarse particles composed of Polymer B, the cycle characteristics of the secondary battery deteriorate.

[0040] [Aromatic vinyl monomer unit] Examples of the aromatic vinyl monomer that can form an aromatic vinyl monomer unit include styrene, α-methylstyrene, butoxystyrene, and vinylnaphthalene. These may be used alone or in combination of two or more. Among these, styrene is preferable.

[0041] When the total repeating units (total monomer units) contained in Polymer B are taken as 100% by mass, the content ratio of the aromatic vinyl monomer units needs to 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, still more preferably 50% by mass or more, preferably 85% by mass or less, more preferably 80% by mass or less, and still more preferably 70% by mass or less. When the ratio of the 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 deteriorate, and the adhesiveness of the functional layer decreases. On the other hand, when the ratio of the aromatic vinyl monomer units in Polymer B exceeds 88% by mass, Polymer B becomes excessively rigid and the adhesiveness of the functional layer decreases.

[0042] [Aliphatic conjugated diene monomer units] Examples of the aliphatic conjugated diene monomer that can form the aliphatic conjugated diene monomer units 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.

[0043] When the total repeating units (total monomer units) contained in Polymer B are taken as 100% by mass, the content ratio of the aliphatic conjugated diene monomer units needs to be 10% by mass or more and 80% by mass or less, preferably 10.5% by mass, more preferably 15% by mass or more, still more preferably 25% by mass or more, preferably 60% by mass or less, more preferably 50% by mass or less, and still more preferably 45% by mass or less. When the ratio of the aliphatic conjugated diene monomer units 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 decreases. On the other hand, when the ratio of the aliphatic conjugated diene monomer units in Polymer B exceeds 80% by mass, Polymer B becomes excessively flexible, the cycle characteristics of the secondary battery deteriorate, and the adhesiveness of the functional layer decreases.

[0044] [Any repeating unit] The arbitrary repeating unit contained in polymer B is not particularly limited. For example, as the arbitrary repeating unit, monomer units having a hydroxyl group and monomer units having an amide group described above in the section of "Polymer A", and monomer units derived from known monomers such as (meth)acrylate monomer units can be mentioned. Note that polymer B may contain one kind of arbitrary repeating unit or may contain two or more kinds. And from the viewpoint of sufficiently suppressing the floating of polymer B in a slurry composition or the like, 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 polymer B are 100% by mass, the content ratio of the monomer unit having a hydroxyl group is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, preferably 3% by mass or less, more preferably 2% by mass or less, and still more preferably 1% by mass or less. If the ratio of the monomer unit having a hydroxyl group in polymer B is within the above-mentioned range, it is possible to sufficiently suppress the floating of polymer B in a slurry composition or the like and to improve both the adhesiveness of the functional layer and the cycle characteristics of the secondary battery in a well-balanced manner.

[0045] [Properties] [Water dispersibility] Polymer B is preferably water-dispersible (insoluble in water). That is, polymer B is preferably a water-dispersible polymer. If polymer B is a water-dispersible polymer, it is possible to improve the adhesiveness of the functional layer and the cycle characteristics of the secondary battery in a well-balanced manner, particularly when used in a slurry composition or the like containing water as a solvent. In the present invention, the polymer being "water-dispersible" 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 90% by mass or more.

[0046] [Glass transition temperature] The polymer B preferably has a glass transition temperature of -20°C or higher, more preferably -10°C or higher, preferably 50°C or lower, and more preferably 40°C or lower. If the glass transition temperature of the polymer B is -20°C or higher, the thickening of the slurry composition can be sufficiently suppressed. On the other hand, if the glass transition temperature of the polymer B is 50°C or lower, the adhesiveness of the functional layer can be improved. Incidentally, the glass transition temperature of the polymer B can be adjusted, for example, by changing the types and amounts of the monomers, polymerization initiators, and / or polymerization accelerators used in the preparation of the polymer B. In the present invention, the "glass transition temperature" can be measured using the method described in the examples of this specification.

[0047] <<Preparation method>> The above-described polymer B is not particularly limited and can be prepared by any method such as solution polymerization method, suspension polymerization method, bulk polymerization method, emulsion polymerization method, etc. Also, as the polymerization method, addition polymerization such as ionic polymerization, radical polymerization, living radical polymerization, etc. can be used. And for the preparation of the polymer B, seed polymerization, block polymerization, graft polymerization, etc. can also be used. Also, as the polymerization initiator, known polymerization initiators can be used. Incidentally, other additives that can be used during polymerization (for example, emulsifiers, dispersants, polymerization aids, chain transfer agents, molecular weight regulators, polymerization accelerators) can be those generally used, and the amount used is also the generally used amount.

[0048] <<Ratio of polymer B in the total of polymer A and polymer B>> Here, when the total amount of Polymer A and Polymer B contained in the binder composition is 100% by mass, the amount of Polymer B is preferably 5% by mass or more, more preferably 10% by mass or more, still 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 still more preferably 35% by mass or less. If the proportion of Polymer B in the total of Polymer A and Polymer B is 5% by mass or more, thickening of the slurry composition can be sufficiently suppressed. On the other hand, if the proportion of Polymer B in the total of Polymer A and Polymer B is 45% by mass or less, the cycle characteristics of the secondary battery can be further improved.

[0049] <Solvent> As the solvent contained in the binder composition of the present invention, a known solvent capable of dissolving or dispersing the above-described Polymer A and Polymer B can be used. Among them, it is preferable to use water as the solvent. Note that at least a part of the solvent of the binder composition can be the polymerization solvent used for the preparation of Polymer A and / or Polymer B without particular limitation.

[0050] <Other Components> In addition to the above-described components, the binder composition of the present invention may contain a conductive auxiliary agent, a reinforcing material, a leveling agent, a viscosity modifier, an electrolyte additive, an antiseptic agent, an antifungal 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. Further, the other components may be used alone or in combination of two or more in any ratio.

[0051] <Method for Preparing Binder Composition> And the binder composition of the present invention can be prepared by mixing the above-described polymer A, polymer B, and solvent, and other components optionally used, by a known method. Specifically, the binder composition can be prepared by mixing the above components using a mixer such as a ball mill, sand mill, bead mill, pigment disperser, attritor, ultrasonic disperser, homogenizer, planetary mixer, or film mixer. When polymer A and polymer B are prepared by polymerization in an aqueous solvent, they can be directly mixed in the state of an aqueous solution or an aqueous dispersion to prepare a binder composition containing water as a solvent.

[0052] (Slurry Composition for Secondary Battery Functional Layer) The slurry composition of the present invention is a composition used for forming a functional layer, contains the above-described binder composition, and optionally further 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 further contains functional particles and other components. And since the slurry composition of the present invention contains the above-described binder composition, a functional layer excellent in adhesiveness can be obtained by drying the slurry composition of the present invention, for example, on a substrate. And by using a battery member provided with the functional layer, excellent cycle characteristics can be exhibited in a secondary battery.

[0053] <Binder Composition> As the binder composition, the above-described binder composition of the present invention containing at least polymer A, polymer B, and a solvent is used. Incidentally, the blending amount of the binder composition in the slurry composition is not particularly limited. When the slurry composition is a slurry composition for an electrode, from the viewpoint of sufficiently enhancing the adhesiveness of the electrode mixture layer as 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 100% by mass of the electrode active material particles, the polymer A, and the polymer B is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, preferably 7.0% by mass or less, and more preferably 4.0% by mass or less. Further, when the slurry composition is a slurry composition for a porous membrane layer, from the viewpoint of sufficiently enhancing the adhesiveness of the porous membrane layer as 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 100% by mass of the non-conductive particles, the polymer A, and the polymer B is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, preferably 9.0% by mass or less, and more preferably 6.0% by mass or less.

[0054] <Functional particles> Here, examples of the functional particles for causing 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.

[0055] <<Electrode active material particles>> And the electrode active material particles are not particularly limited, and particles composed of known electrode active materials used in secondary batteries can be mentioned. Specifically, for example, as the negative electrode active material particles that can be used in the negative electrode mixture layer of a lithium ion secondary battery as an example of a secondary battery, particles composed of the following negative electrode active materials can be used without particular limitation.

[0056] [Negative electrode active material] Examples of the negative electrode active material for a lithium ion secondary battery include carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials combining these. Here, the carbon-based negative electrode active material refers to an active material with a carbon 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.

[0057] Examples of the carbonaceous materials include graphitizable carbon having a structure close to an amorphous structure typified by graphitizable carbon and vitreous carbon. Here, examples of the graphitizable carbon include carbon materials obtained from tar pitch derived from petroleum or coal. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, and pyrolytic vapor-grown carbon fibers. Examples of the non-graphitizable carbon include fired phenol resin, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, fired furfuryl alcohol resin (PFA), and hard carbon.

[0058] Furthermore, examples of the graphite materials include natural graphite and artificial graphite. Here, examples of the artificial graphite include artificial graphite obtained by heat-treating carbon mainly containing graphitizable carbon at 2800°C or higher, graphitized MCMB obtained by heat-treating MCMB at 2000°C or higher, and graphitized mesophase pitch-based carbon fibers obtained by heat-treating mesophase pitch-based carbon fibers at 2000°C or higher.

[0059] In addition, a metal-based negative electrode active material is an active material containing a metal, usually including an element in its structure that allows the insertion of lithium, and refers to an active material with a theoretical capacitance per unit mass of 500 mAh / g or more when lithium is inserted. Examples of metal-based active materials include lithium metal, single metals that can form lithium alloys (such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.) and their alloys, as well as their oxides, sulfides, nitrides, silicides, carbides, phosphides, etc. Among these, as the metal-based negative electrode active material, an active material containing silicon (silicon-based negative electrode active material) is preferred. This is because by using a silicon-based negative electrode active material, the lithium-ion secondary battery can be made to have a higher capacity.

[0060] 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 compositing Si-containing materials with conductive carbon, and the like. These silicon-based negative electrode active materials may be used alone or in combination of two or more.

[0061] As for the negative electrode active material particles, from the perspective of sufficiently ensuring the cell capacity of the secondary battery and further improving the cycle characteristics 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). The amounts of carbon-based negative electrode active material particles and silicon-based negative electrode active material particles in the slurry composition are not particularly limited. The amount of carbon-based negative electrode active material particles in the total of 100% by mass of the negative electrode active material particles, Polymer A, and Polymer B 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 proportion of the carbon-based negative electrode active material particles in the total of the negative electrode active material particles, Polymer A, and Polymer B is 50% by mass or more, the buffering action between 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. If it is 90% by mass or less, the cycle characteristics of the secondary battery can be sufficiently improved. Also, the amount of silicon-based negative electrode active material particles in the total of 100% by mass of the negative electrode active material particles, Polymer A, and Polymer B is preferably 5% by mass or more, more preferably 10% by mass or more, preferably 40% by mass or less, and more preferably 30% by mass or less. If the proportion of the silicon-based negative electrode active material particles in the total 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 ensured, and the cell capacity can be improved. If it is 40% by mass or less, the cycle characteristics of the secondary battery can be sufficiently improved.

[0062] [Non-conductive particles] Also, the non-conductive particles incorporated in the porous film layer are not particularly limited, and known non-conductive particles used in secondary batteries can be mentioned. Specifically, as the non-conductive particles, both inorganic fine particles and organic fine particles can be used, but usually inorganic fine particles are used. Among them, as the material of the non-conductive particles, a material that stably exists in the usage environment of the secondary battery and is electrochemically stable is preferable. From this perspective, preferable examples of the material 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), BaTiO3, ZrO, and alumina-silica composite oxides; nitride particles such as aluminum nitride and boron nitride; covalent crystal particles such as silicon and diamond; sparingly soluble ionic crystal particles such as barium sulfate, calcium fluoride, and barium fluoride; clay fine particles such as talc and montmorillonite; and the like. Further, these particles may be subjected to element substitution, surface treatment, solid solution formation, etc. as necessary. In addition, the above-described non-conductive particles may be used alone or in combination of two or more kinds.

[0063] <Other Components> As other components that can be blended in the slurry composition, without particular limitation, the same components as those that can be blended in the binder composition of the present invention can be mentioned. In addition, the other components may be used alone or in combination of two or more kinds in any ratio.

[0064] <Preparation of Slurry Composition> The method for preparing the slurry composition is not particularly limited. For example, when the slurry composition is an electrode slurry composition, the binder composition, the 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 it is or diluted with a solvent to be used 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 the preparation of the slurry composition includes those contained in the binder composition. The mixing method is not particularly limited, but mixing is usually carried out using a commonly used stirrer or a disperser.

[0065] (Functional layer for secondary battery) The functional layer of the present invention is a layer that undertakes functions such as electron transfer, reinforcement, or adhesion in a secondary battery. Examples of the functional layer include an electrode composite layer that transfers electrons through an electrochemical reaction, a porous film layer that improves heat resistance and strength, and an adhesive layer that improves adhesiveness. The functional layer of the present invention is formed from the above-described slurry composition of the present invention. For example, after applying the above-described slurry composition to the surface of a suitable substrate to form a coating film, the formed coating film can be dried to form it. That is, the functional layer of the present invention consists of the dried product of the above-described slurry composition and usually contains at least polymer A and polymer B. Since each component contained in the functional layer was contained in the above-described slurry composition, the preferred abundance ratio of each of these components is the same as the preferred abundance ratio of each component in the slurry composition.

[0066] 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 adhesiveness and can exhibit excellent cycle characteristics in a secondary battery having a battery member provided with the functional layer of the present invention.

[0067] (Substrate) Here, there is no limitation on the substrate to which the slurry composition is applied. 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. Thus, the functional layer peeled off from the release substrate can also be used as a self-supporting film for forming battery members of a secondary battery. However, from the viewpoint of increasing the manufacturing efficiency of battery members by omitting the step of peeling the functional layer, 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 a current collector as the substrate. Further, when preparing the porous membrane layer or the adhesive layer, it is preferable to apply the slurry composition onto a separator substrate or an electrode substrate.

[0068] <<Current collector>> As the current collector, a material having electrical conductivity and being electrochemically durable is used. Specifically, as the current collector, for example, a current collector made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like can be used. Among them, a copper foil is particularly preferable as the current collector used for the negative electrode. Also, an aluminum foil is particularly preferable as the current collector used for the positive electrode. Note that the above materials may be used alone or in combination of two or more in any ratio.

[0069] <<Separator substrate>> The separator substrate is not particularly limited, and known separator substrates such as organic separator substrates can be mentioned. The organic separator substrate is a porous member made of an organic material. Examples of the organic separator substrate include microporous membranes or nonwoven fabrics containing polyolefin resins such as polyethylene and polypropylene, and aromatic polyamide resins. Microporous membranes or nonwoven fabrics made of polyethylene are preferable because of their excellent strength.

[0070] <<Electrode substrate>> As the electrode substrate (positive electrode substrate and negative electrode substrate), although not particularly limited, examples include an electrode substrate in which an electrode mixture layer containing electrode active material particles and a binder is formed on the current collector described above. 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. Further, as the binder contained in the electrode mixture layer of the electrode substrate, any binder used for the electrode mixture layer can be used. In addition, as the binder, at least one of the polymer A and the polymer B described above in the section "Binder Composition for Secondary Battery" may be used. That is, the functional layer of the present invention may be used as the electrode mixture layer in the electrode substrate.

[0071] <Method for Forming Functional Layer> Examples of the method for forming a functional layer on the above-described substrates such as a current collector, a separator substrate, and an electrode substrate include the following methods. 1) A method of applying the slurry composition of the present invention to the surface of the substrate (in the case of an electrode substrate, the surface on the side of the electrode mixture layer, the same applies hereinafter) and then drying it; 2) A method of immersing the 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 on 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 of 1) is particularly preferable because it is easy to control the layer thickness of the functional layer. The method of 1) specifically includes a step of applying the slurry composition on the substrate (coating step) and a step of drying the slurry composition applied on the substrate to form a functional layer (drying step).

[0072] <<Coating Step>> In the coating step, the method of applying the slurry composition on the substrate is not particularly limited, and examples include methods such as the doctor blade method, the reverse roll method, the direct roll method, the gravure method, the extrusion method, and the brush coating method.

[0073] <<Drying Step>> In addition, in the drying process, as the method for drying the slurry composition on the substrate, a known method can be used without particular limitation. Examples of the drying method include drying with warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with infrared rays, electron beams, etc.

[0074] (Battery member provided with a functional layer) The battery member (separator and electrode) provided with the functional layer of the present invention may include the above-described functional layer of the present invention and components other than the substrate, as long as the effects of the present invention are not significantly impaired. Such components include, without particular limitation, an electrode composite layer, a porous film layer, and an adhesive layer that do not correspond to the functional layer of the present invention. In addition, the battery member may include a plurality of types of the functional layers of the present invention. For example, the electrode may include an electrode composite layer formed from the slurry composition for electrodes of the present invention on a current collector, and a porous film layer and / or an adhesive layer formed from the slurry composition for the porous film layer and / or the adhesive layer of the present invention on the electrode composite layer. Also, for example, the separator may include a porous film layer formed from the slurry composition for the porous film layer of the present invention on a separator substrate, and an adhesive layer formed from the slurry composition for the adhesive layer of the present invention on the porous film layer. The battery member provided with the functional layer of the present invention can adhere well to an adjacent battery member and can exhibit excellent cycle characteristics in a secondary battery.

[0075] (Secondary battery) The secondary battery of the present invention includes the above-described 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 electrolytic solution, and the above-described functional layer for secondary batteries is included in at least one of the positive electrode, the negative electrode, and the separator, which are battery members. And the secondary battery of the present invention can exhibit excellent cycle characteristics.

[0076] (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 provided with the functional layer of the present invention described above. Note that as the positive electrode, negative electrode, and separator that do not have the functional layer of the present invention, known positive electrodes, negative electrodes, and separators can be used without particular limitation.

[0077] <Electrolyte> As the electrolyte, usually, an organic electrolyte in which a supporting electrolyte is dissolved in an organic solvent is used. As the supporting electrolyte, for example, a lithium salt is used in a lithium ion secondary battery. Examples of the lithium salt include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, (C2F5SO2)NLi, and the like. Among them, LiPF6, LiClO4, and CF3SO3Li are preferable because they are easily soluble in the solvent and exhibit a high degree of dissociation. Note that the electrolyte may be used alone or in combination of two or more kinds. Usually, the higher the degree of dissociation of the supporting electrolyte used, the higher the lithium ion conductivity tends to be, so the lithium ion conductivity can be adjusted according to the type of the supporting electrolyte.

[0078] 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); 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; etc. are preferably used. Also, a mixture of these solvents may 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 according to the type of solvent. Note that the concentration of the electrolyte in the electrolyte can be adjusted as appropriate. Also, known additives may be added to the electrolyte.

[0079] <Method for manufacturing a secondary battery> The above-described secondary battery of the present invention can be manufactured, for example, by overlapping a positive electrode and a negative electrode with a separator interposed therebetween, winding, folding, etc. this as necessary and putting it into a battery container, and injecting an electrolyte into the battery container and sealing it. Note that at least one of the positive electrode, negative electrode, and separator is a battery member provided with the functional layer of the present invention. Also, an expandable metal, an overcurrent prevention element such as a fuse and a PTC element, a lead plate, etc. may be put into the battery container as necessary to prevent an increase in pressure inside the battery and overcharge / discharge. The shape of the battery may be, for example, a coin type, button type, sheet type, cylindrical type, rectangular type, flat type, etc., any of which is acceptable.

Examples

[0080] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the following description, “%” and “parts” representing amounts are on a mass basis unless otherwise specified. In addition, in a polymer produced by copolymerizing a plurality of types of monomers, unless otherwise specified, the ratio of the repeating unit (monomer unit) formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (charge ratio) of the certain monomer in all the monomers used for polymerizing the polymer. In Examples and Comparative Examples, the weight-average molecular weight and electrolyte swelling degree of Polymer A, the glass transition temperature of Polymer B, the thickening suppression of the slurry compositions (the slurry composition for the negative electrode and the slurry composition for the porous film layer), the adhesiveness of the functional layers (the negative electrode composite layer and the porous film layer), the floating suppression of Polymer B in the slurry composition, and the cycle characteristics of the secondary battery were measured and evaluated by the following methods, respectively.

[0081] <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 the eluent so that the solid content concentration became about 0.5 g / L, and it was gently dissolved at room temperature. After visually confirming the dissolution of Polymer A, it was gently filtered through a 0.45-μm filter to prepare a measurement sample. Then, by creating a calibration curve with a standard substance, the weight-average molecular weight as a standard substance conversion value was calculated. The measurement conditions are as follows. <<Measurement conditions>> Column: Manufactured by Showa Denko K.K., product name Shodex OHpak (SB-G, SB-807HQ, SB-806MHQ) Eluent: 0.1 M Tris buffer (added with 0.1 M potassium chloride) Flow rate: 0.5 mL / min Sample concentration: 0.05 g / L (solid content concentration) Injection volume: 200 μL Column temperature: 40 °C Detector: Differential refractive index detector RI (manufactured by Tosoh Corporation, product name "RI-8020") Standard substance: Monodisperse pullulan (manufactured by Showa Denko K.K.) <Electrolyte swelling degree of Polymer A> A composition containing polymer A and water (aqueous solution of polymer A) was dried in an environment with a relative humidity of 50% and a temperature of 23°C to 25°C to form a film with a thickness of 1 ± 0.3 mm. After drying the formed film in a vacuum dryer at 60°C for 10 hours, it was 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 LiPF6 solution (solvent: ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (volume ratio) mixed solvent, additive: 2 volume% (solvent ratio) vinylene carbonate) as an electrolyte for 72 hours at a temperature of 60°C. After pulling up the film pieces after 72 hours of immersion and wiping the electrolyte on the surface with Kimwipe, 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 with a thickness of 1 ± 0.3 mm. This film was dried in a vacuum dryer at 60°C for 10 hours. Then, using the dried film as a sample, 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, a differential scanning calorimeter (manufactured by Nanotechnology Co., Ltd., DSC6220SII) was used to measure the glass transition temperature. <Thickening inhibition of slurry composition> <<Slurry composition for negative electrode (Examples 1 to 20, Comparative Examples 1 to 6)>> In a planetary mixer equipped 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 silicon-based negative electrode active material particles (SiO X)29.4 parts, and an aqueous solution of Polymer A in the same amount (equivalent amount of solid content) as that used for preparing the negative electrode slurry composition in each example and comparative example were added, adjusted to a solid content concentration of 58% with ion-exchanged water, and mixed at room temperature for 60 minutes. Next, it was adjusted to a solid content concentration of 50% with ion-exchanged water, further mixed for 15 minutes, and then defoamed under reduced pressure to obtain a mixed solution for viscosity measurement. The viscosity of this mixed solution for viscosity measurement was designated as η1. The viscosity was measured using a B-type viscometer under the conditions of a temperature of 25°C, a spindle rotation speed of 60 rpm, and a spindle rotation time of 60 seconds (hereinafter, the measurement conditions for viscosities η2, η3, and η4 are the same). Next, a mixed solution for viscosity measurement was obtained in the same manner as above, except that a mixture (binder composition) of Polymer A and Polymer B in the same amount (equivalent amount of solid content) as that used for preparing 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 mixed solution for viscosity measurement was designated as η2. The viscosity ratio (=η2 / η1) of η1 and η2 described above was calculated, and the thickening suppression of the slurry composition was evaluated according to the following criteria. The smaller the value of the viscosity ratio, the more the thickening of the slurry composition is suppressed, indicating that the preparation and handling of the slurry composition are easy. 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)>> 100 parts of alumina as non-conductive particles (volume average particle diameter: 0.5 μm), 1.0 part of ammonium polycarboxylate as a dispersant (manufactured by Toagosei Co., Ltd., product name "Aron A-6114"), 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 dispersion device to disperse the alumina and obtain a dispersion. 2.0 parts of sodium carboxymethyl cellulose (degree of etherification: 1.0, aqueous solution viscosity at a solid content concentration of 1.0 mass%: 500 mPa·s) was added to the obtained dispersion and mixed. The added sodium carboxymethyl cellulose dissolved in the mixture. Next, an aqueous solution of polymer A in the same amount (equivalent amount of solid content) as that used in the preparation of the slurry composition for the porous film layer in each example and comparative example, and 0.2 part of an aliphatic polyether type nonionic surfactant as a wetting agent were added to this mixture, and further water was added so that the solid content concentration became 40% to obtain a mixture for viscosity measurement. This was designated as η3 of this mixture. Next, a mixture (binder composition) of polymer A and polymer B in the same amount (equivalent amount of solid content) as that used in the preparation of the slurry composition for the porous film layer in each example and comparative example was used instead of the aqueous solution of polymer A, and a mixture for viscosity measurement was obtained in the same manner as above. The viscosity of this mixture for viscosity measurement was designated as η4. The viscosity ratio (=η4 / η3) of η3 and η4 described above was calculated, and the thickening suppression of the slurry composition was evaluated according to the same criteria as the slurry composition for the negative electrode described above. <Adhesion of the functional layer> <<Negative electrode composite layer (Examples 1 to 20, Comparative Examples 1 to 6)>> A rectangular test piece with 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. After sticking cellophane tape to the surface of the current collector of the fixed test piece, the stress 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 was measured. As the cellophane tape, the one specified in JIS Z1522 was used. This measurement was performed 5 times in total, and the average value was taken as the peel strength and evaluated according to the following criteria. The greater 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 with 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. Also, cellophane tape was fixed to the test bench in advance. As this cellophane tape, the one specified in JIS Z1522 was used. Then, the test piece cut out from the separator was attached to the cellophane tape with the porous membrane layer facing down. After that, the stress when one end of the separator substrate was pulled vertically at a pulling speed of 100 mm / min and peeled off was measured. This measurement was performed 3 times in total, and the average value was used as the peel strength and evaluated according to the following criteria. The greater the peel strength, the better the adhesiveness of the porous membrane layer and the better it adheres 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 Polymer B Floating in the Slurry Composition> The slurry composition was put into a 100 mL graduated cylinder up to the 100 mL mark and allowed to stand at room temperature for 48 hours. After standing, the slurry composition existing from the 100 mL mark to the 90 mL mark of the graduated cylinder (slurry near the liquid surface) and the slurry composition existing from the 0 mL mark to the 10 mL mark of the graduated cylinder (slurry near the bottom) 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 designated as "measurement sample (liquid surface side)", and the measurement sample derived from the slurry near the bottom was designated as "measurement sample (bottom side)". For the two obtained measurement samples, using a capillary type particle size distribution analyzer (manufactured by MATEC, product name "CHDF2000 type"), the volume average particle diameter (dv) was measured under the 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 floating suppression rate was calculated using the following formula. Floating suppression rate = "Mass of polymer B in the measurement sample (bottom side)" / "Mass of polymer B in the measurement sample (liquid surface side)" And the floating suppression of polymer B in the slurry composition was evaluated according to the following criteria based on the value of the floating suppression rate. The larger the value of the floating suppression rate, the more the floating of polymer B in the slurry composition is suppressed. A: The floating suppression rate is 0.9 or more and less than 1.1 B: The floating suppression rate is 0.7 or more and less than 0.9 C: The floating suppression rate is 0.5 or more and less than 0.7 D: The floating suppression rate is less than 0.5 <Cycle characteristics of secondary battery> After injecting the electrolyte into the lithium-ion secondary battery, it was left standing in an environment of 25 °C for 24 hours, and then charge and discharge operations were performed by the constant current method of 0.1C until the cell voltage reached 4.35V and discharged until the cell voltage reached 3.0V, and the initial capacity C0 was measured. Further, in an environment of 45 °C, charging was performed by the constant current method of 1.0C until the cell voltage reached 4.35V, and charging and discharging were repeated by discharging in the same constant current method as the charging mode until the cell voltage reached 3.0V, 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: The capacity retention rate is 95% or more B: The capacity retention rate is 90% or more and less than 95% C: The capacity retention rate is 80% or more and less than 90% D: The capacity retention rate is less than 80%

[0082] (Example 1) <Preparation of polymer A> 789 parts of ion-exchanged water were charged into a 1 L glass flask, heated to 40 °C, and the inside of the flask was purged 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 hydroxyethyl acrylamide as a monomer having a hydroxyl group were mixed and injected 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. Fifteen minutes after the addition of potassium persulfate, 22.2 parts of a 2.0% aqueous solution of tetramethylethylenediamine as a polymerization accelerator was added with a syringe to initiate the polymerization reaction. Four hours after adding the polymerization initiator, 4.4 parts of a 2.5% aqueous solution of potassium persulfate as a polymerization initiator was added into the flask, and further 11.1 parts of a 2.0% aqueous solution of tetramethylethylenediamine as a polymerization accelerator was added. The temperature was raised to 60 °C and maintained to proceed the polymerization reaction. Three hours after adding the polymerization initiator, the flask was opened to the air to stop the polymerization reaction, an 8% aqueous solution of lithium hydroxide was added, and the polymerization product was adjusted to pH 8.0 with stirring at 80 °C for 6 hours to obtain a composition (aqueous solution of polymer A) containing polymer A and water, which is a water-soluble polymer. 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> 3.15 parts of styrene as an aromatic vinyl monomer (first addition), 1.66 parts of 1,3-butadiene as an aliphatic conjugated diene monomer (first addition), 0.2 part of sodium lauryl sulfate as an emulsifier, 20 parts of ion-exchanged water, and 0.03 part of potassium persulfate as a polymerization initiator were put into a 5 MPa pressure-resistant vessel A equipped with a stirrer. After sufficiently stirring, it was heated to 60 °C to initiate polymerization and reacted for 6 hours to obtain seed particles. After the above reaction, the mixture was heated to 75°C, and addition to the pressure-resistant container A of the following components from another container B was started: 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 part of tert-dodecyl mercaptan as a chain transfer agent, and 0.35 part of sodium lauryl sulfate as an emulsifier. Simultaneously, addition to the pressure-resistant container A of 1 part of potassium persulfate as a polymerization initiator was started to initiate the second-stage polymerization. Also, 4 hours after the start of the second-stage polymerization (after 70% of the total monomer composition had been added), 1 part of hydroxyethyl acrylate as a monomer having a hydroxyl group was added to the pressure-resistant container A over 1.5 hours. That is, as the total monomer composition, 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 were used. 5.5 hours after the start of the second-stage polymerization, addition of the total amount of the mixture containing these monomer compositions was completed, and then the mixture was further heated to 85°C and reacted for 6 hours. When the polymerization conversion rate reached 97%, the reaction was stopped by cooling. To the mixture containing this polymer, an aqueous 5% sodium hydroxide solution was added to adjust the pH to 8. Then, unreacted monomers were removed by heating under reduced pressure distillation. After further cooling, a composition containing the polymer B, which is a water-dispersible polymer, and water (aqueous dispersion of polymer B) was obtained. 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 and the aqueous dispersion of polymer B obtained as described above were mixed so that the mass ratio of the solid content equivalent amounts of polymer A and polymer B was 70:30 (polymer A: polymer B) to obtain a binder composition. Using this binder composition and the above-described aqueous solution of polymer A, the thickening suppression of the slurry composition was evaluated. The results are shown in Table 1. <Preparation of Slurry Composition for Negative Electrode> To a planetary mixer equipped 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 ) were added, and 2 parts (equivalent amount of solid content) of the binder composition obtained as described above was added. It was adjusted to a solid content concentration of 58% with ion-exchanged water and mixed at room temperature for 60 minutes. Next, it was adjusted to a solid content concentration of 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 suppression of floating of polymer B in the slurry composition was evaluated. The results are shown in Table 1. <Manufacture of negative electrode> The above-mentioned negative electrode slurry composition was applied onto a copper foil (current collector) with a thickness of 18 μm by 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 this negative electrode slurry composition was conveyed at a speed of 0.5 m / min for 2 minutes in an oven at 75°C and further for 2 minutes in an oven at 120°C to dry the slurry composition on the copper foil and obtain a negative electrode precursor. This negative electrode precursor was rolled by a roll press to obtain a negative electrode with a thickness of 80 μm for the negative electrode composite layer. Using this negative electrode, the adhesiveness of the functional layer (negative electrode composite layer) was evaluated. The results are shown in Table 1. <Manufacture of positive electrode> To a planetary mixer, 95 parts of LiCoO2 having a spinel structure as a positive electrode active material, 3 parts of PVDF (polyvinylidene fluoride) as a binder for the positive electrode in terms of solid content equivalent, 2 parts of acetylene black as a conductive material, and 20 parts of N-methylpyrrolidone as a solvent were added and mixed to obtain a positive electrode slurry composition. The obtained slurry composition for the positive electrode was applied onto an aluminum foil (current collector) with a thickness of 20 μm using a comma coater so that the film thickness after drying would be about 100 μm. The aluminum foil coated with this slurry composition for the positive electrode was conveyed through an oven at a temperature of 60°C for 2 minutes at a speed of 0.5 m / min and then through an oven at a temperature of 120°C for 2 minutes, thereby drying the slurry composition for the positive electrode on the aluminum foil to obtain a positive electrode raw sheet. This positive electrode raw sheet was rolled using a roll press to obtain a positive electrode with a thickness of 70 μm for the positive electrode composite layer. <Preparation of Separator> A single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm; manufactured by the dry process; porosity 55%) was prepared. This separator was cut into a 5 cm × 5 cm square and used for the fabrication of the secondary battery. <Fabrication of Secondary Battery> As the battery exterior, an aluminum packaging exterior was prepared. The above positive electrode was cut out into a 4 cm × 4 cm square and arranged such that the surface on the current collector side was in contact with the aluminum packaging exterior. Next, the above square separator was placed on the surface of the positive electrode composite layer of the positive electrode. Further, the negative electrode was cut out into a 4.2 cm × 4.2 cm square and placed on the separator such that the surface on the negative electrode composite layer side faced the separator. Thereafter, a 1.0 M LiPF6 solution (the solvent was a mixed solvent of ethylene carbonate (EC) / diethyl carbonate (DEC) = 1 / 2 (volume ratio), and it contained 2 volume% (solvent ratio) of vinylene carbonate as an additive) was filled as the electrolyte. Further, in order to seal the opening of the aluminum packaging, heat sealing was performed at 150°C to close the aluminum packaging exterior, and a laminated cell type lithium ion secondary battery was manufactured. The cycle characteristics of the obtained lithium ion secondary battery were evaluated. The results are shown in Table 1.

[0083] (Examples 2 to 7) When preparing Polymer A, except for changing the usage amounts of acrylamide, acrylic acid, and / or hydroxyethyl acrylamide to change the composition of Polymer A as shown in Table 1, in the same manner as in Example 1, a binder composition, a slurry composition for a negative electrode, a negative electrode, a positive electrode, a separator, and a secondary battery were prepared, and various evaluations were conducted. The results are shown in Table 1.

[0084] (Example 8) When preparing Polymer A, except for using hydroxyethyl acrylate instead of hydroxyethyl acrylamide and changing the composition of Polymer A as shown in Table 1, in the same manner as in Example 1, a binder composition, a slurry composition for a negative electrode, a negative electrode, a positive electrode, a separator, and a secondary battery were prepared, and various evaluations were conducted. The results are shown in Table 1.

[0085] (Examples 9 to 12) When preparing Polymer B, except for changing the usage amounts of 1,3-butadiene, styrene, and / or itaconic acid to change the composition of Polymer B as shown in Table 1 and Table 2, in the same manner as in Example 1, a binder composition, a slurry composition for a negative electrode, a negative electrode, a positive electrode, a separator, and a secondary battery were prepared, and various evaluations were conducted. The results are shown in Table 1 and Table 2. Note that the amounts of the first addition and the second addition of 1,3-butadiene (BD) and styrene (ST) in each example are shown below as (amount of the first addition, amount of the second addition) immediately after the abbreviations of the respective monomers. 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)

[0086] (Example 13) When preparing the polymer A, except that the amount of the 2.5% aqueous solution of potassium persulfate as a polymerization initiator was changed from 8.9 parts to 13.4 parts and the amount of the 2.0% aqueous solution of tetramethylethylenediamine as a polymerization accelerator was changed from 22.2 parts to 33.3 parts, a binder composition, a slurry composition for a negative electrode, 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.

[0087] (Example 14) When preparing the polymer A, except that the amount of the 2.5% aqueous solution of potassium persulfate as a polymerization initiator was changed from 8.9 parts to 6.7 parts and the amount of the 2.0% aqueous solution of tetramethylethylenediamine as a polymerization accelerator was changed from 22.2 parts to 16.7 parts, a binder composition, a slurry composition for a negative electrode, 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.

[0088] (Examples 15 and 16) When preparing the polymer A, except that the composition of the polymer A was changed as shown in Table 2 using acrylamide, acrylic acid, hydroxyethylacrylamide, and n-butyl acrylate as monomers, a binder composition, a slurry composition for a negative electrode, 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.

[0089] (Examples 17 and 18) When preparing the binder composition, except that the mass ratio of the polymer A and the polymer B was changed as shown in Table 2, a binder composition, a slurry composition for a negative electrode, 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.

[0090] (Example 19) In the preparation of Polymer B, without using hydroxyethyl acrylate and by changing the amount of 1,3-butadiene used (the amount added in the first addition: 1.66 parts, the amount added in the second addition: 34.84 parts), except that the composition of Polymer B was changed as shown in Table 2, a binder composition, a slurry composition for a negative electrode, 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.

[0091] (Example 20) In the preparation of the binder composition, except that Polymer B prepared as follows was used, a binder composition, a slurry composition for a negative electrode, 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. (Preparation of Polymer B) To a 5 MPa pressure-resistant reactor A equipped with a stirrer, 233.3 parts of cyclohexane, 0.006972 part of N,N,N',N'-tetramethylethylenediamine, and 20.5 parts of styrene as an aromatic vinyl monomer were added, and while stirring at 40 °C, 0.12812 part of n-butyllithium was added, and polymerization was carried out for 1 hour while raising the temperature to 50 °C. Subsequently, while controlling the temperature to maintain 55 °C, 76.0 parts of isoprene as an aliphatic conjugated diene monomer were continuously added to the reactor over 1 hour. After the addition of isoprene was completed, polymerization was carried out for another 1 hour. Next, the inside of the pressure-resistant vessel A was set to 85 °C, and the reaction was further carried out for 2 hours. When the polymerization conversion rate reached 98%, 105.8 parts of dichlorodimethylsilane as a coupling agent were added, and a coupling reaction was carried out for 2 hours to form a styrene-isoprene coupling block copolymer. Then, 0.12816 part 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. Further, 3.5 parts of itaconic acid as a monomer having two carboxylic acid groups and 0.1 part of potassium persulfate were added to obtain a composition containing Polymer B, which is a water-dispersed polymer, and water (aqueous dispersion of Polymer B).

[0092] (Example 21) A negative electrode slurry composition and a negative electrode were prepared as follows, and a separator having a porous film layer slurry composition and a porous film layer was prepared as follows. When manufacturing the secondary battery, a positive electrode and a secondary battery were prepared and various evaluations were conducted in the same manner as in Example 1, except that a separator having the following negative electrode and porous film was used. The results are shown in Table 2. <Preparation of Negative Electrode Slurry Composition and Negative Electrode> A binder composition obtained by using the 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) instead of Polymer A was used, and a negative electrode slurry composition was prepared in the same manner as in Example 1. Then, 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 Porous Film Layer Slurry Composition> 100 parts of alumina as non-conductive particles (volume average particle diameter: 0.5 μm), 1.0 part of ammonium polycarboxylate as a dispersant (manufactured by Toagosei Co., Ltd., product name "Aron A-6114"), 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 dispersion device to disperse the alumina and obtain a dispersion. 2.0 parts of the sodium salt of carboxymethyl cellulose (degree of etherification: 1.0, aqueous solution viscosity at a solid content concentration of 1.0 mass%: 500 mPa·s) were added to the obtained dispersion and mixed. The added sodium salt of carboxymethyl cellulose dissolved in the mixed solution. Next, 5.0 parts (equivalent amount of solid content) of the binder composition prepared in the same manner as in Example 1 and 0.2 part of an aliphatic polyether type nonionic surfactant as a wetting agent were added to this mixed solution, and further water was added so that the solid content concentration became 40% to obtain a porous film layer slurry composition. Using this porous film layer slurry composition, the suppression of floating of Polymer B in the slurry composition was evaluated. The results are shown in Table 2. <Manufacture of Separator with Porous Film Layer> A single-layer separator substrate made of polypropylene (width 250 mm, length 1000 m, thickness 12 μm) produced by a wet method was prepared. Then, the re-dispersed slurry composition for the porous film layer was applied onto both surfaces of the separator substrate with a gravure coater (coating speed: 20 m / min) so that the thickness after drying would be 2.5 μm. Next, the separator substrate coated with the slurry composition for the porous film layer was dried in a drying oven at 50°C and wound up to produce a separator having porous film layers on both sides of the separator substrate. This separator was cut into a 5 cm × 5 cm square and used for the production of a secondary battery. Also, a separator having a porous film layer on one side was produced in the same manner as above except that the slurry composition for the porous film layer was applied onto one surface of the separator substrate. Then, the adhesiveness of the functional layer (porous film layer) was evaluated using this separator having a porous film layer on one side. The results are shown in Table 2.

[0093] (Comparative Examples 1 - 2) When preparing Polymer A, except that the usage amounts of acrylamide, acrylic acid, and hydroxyethyl acrylamide were changed and the composition of Polymer A was changed as shown in Table 1, a binder composition, a slurry composition for the negative electrode, 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 3.

[0094] (Comparative Examples 3 - 6) When preparing Polymer B, except that the usage amounts of 1,3 - butadiene, styrene, and / or itaconic acid were changed and the composition of Polymer B was changed as shown in Table 3, a binder composition, a slurry composition for the negative electrode, 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 3. In addition, the amounts of 1,3 - butadiene (BD) and styrene (ST) at the first addition and the second addition in each comparative example are shown below as (amount of the first addition, amount of the second addition) immediately after the abbreviations of the respective monomers. 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)

[0095] (Comparative Example 7) A binder composition, a slurry composition for a negative electrode, a negative electrode, a positive electrode, a separator provided with a porous membrane, and a secondary battery were prepared in the same manner as in Example 21, except that polymers A and B prepared in the same manner as in Comparative Example 3 were used, and various evaluations were performed. The results are shown in Table 3.

[0096] (Comparative Example 8) A binder composition, a slurry composition for a negative electrode, a negative electrode, a positive electrode, a separator provided with a porous membrane, and a secondary battery were prepared in the same manner as in Example 21, except that polymer A prepared in the same manner as in Comparative Example 1 was used, and various evaluations were performed. The results are shown in Table 3.

[0097] (Comparative Example 9) A binder composition, a slurry composition for a negative electrode, a negative electrode, a positive electrode, a separator provided with a porous membrane, and a secondary battery were prepared in the same manner as in Comparative Example 8, except that acrylic acid was used instead of itaconic acid in the preparation of polymer B, and various evaluations were performed. The results are shown in Table 3.

[0098] In Tables 1 to 3 shown below, "AAm" represents an acrylamide unit, "AA" represents an acrylic acid unit, "HEAm" represents a hydroxyethylacrylamide unit, "HEA" represents a hydroxyethyl acrylate unit, "BA" represents an n-butyl acrylate unit, "IP" represents an isoprene unit, "BD" represents a 1,3-butadiene unit, "ST" represents a styrene unit, "IA" represents itaconic acid units, The "ratio of hydroxyl group + amide group" indicates the total content ratio of monomer units having a hydroxyl group and monomer units having an amide group.

[0099] [Table 1]

[0100] [Table 2]

[0101] [Table 3]

[0102] From Tables 1 and 2, it can be seen that in Examples 1 to 21 using binder compositions containing Polymer A and Polymer B having respective predetermined compositions, it is possible to form functional layers (negative electrode composite material layer, porous film layer) with excellent adhesiveness and to exhibit excellent cycle characteristics in secondary batteries. 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, it can be seen that in Comparative Examples 1 to 9 using binder compositions in which the composition of Polymer A or Polymer B is outside the predetermined range, it is not possible to form functional layers (negative electrode composite material layer, porous film layer) with excellent adhesiveness, and the cycle characteristics of the secondary battery are degraded. Furthermore, it can be seen that in Comparative Examples 1 and 8, thickening of the slurry composition and floating of Polymer B in the slurry composition cannot be suppressed. In addition, it can be seen that in Comparative Examples 2 to 7 and 9, floating of Polymer B in the slurry composition cannot be suppressed.

Industrial Applicability

[0103] According to the present invention, it is possible to provide a binder composition for a secondary battery that can form a functional layer with excellent adhesiveness and can exhibit excellent cycle characteristics in a secondary battery. Further, according to the present invention, it is possible to provide a slurry composition for a secondary battery functional layer that can form a functional layer having excellent adhesiveness and can exhibit excellent cycle characteristics in a secondary battery. And, according to the present invention, it is possible to provide a functional layer for a secondary battery that has excellent adhesiveness and can exhibit excellent cycle characteristics in a secondary battery. Furthermore, according to the present invention, it is possible to provide a secondary battery having excellent cycle characteristics.

Claims

1. It contains polymer A, polymer B, and a solvent, In the polymer A, the total content ratio of monomer units having a hydroxyl group and monomer units having an amide group is 50% by mass or more and 90% by mass or less, the content ratio of monomer units having a carboxylic acid group is 10% by mass or more and 25% by mass or less, and the content ratio of monomer units having a hydroxyl group is 10% by mass or more. The monomer unit having a hydroxyl group is selected from a hydroxyethylacrylamide unit and a hydroxyethyl acrylate 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. In the polymer B, the content ratio of monomer units having two carboxylic acid groups is 2% by mass or more and 5% by mass or less, the content ratio of aromatic vinyl monomer units is 15% by mass or more and 88% by mass or less, and the content ratio of aliphatic conjugated diene monomer units is 10% by mass or more and 80% by mass or less. A binder composition for a secondary battery, wherein the ratio of the polymer B in the total of the polymer A and the polymer B is 5% by mass or more and 45% by mass or less.

2. The binder composition for a secondary battery 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.

3. The binder composition for a secondary battery according to Claim 1 or 2, wherein the electrolyte swelling degree of the polymer A is 150% by mass or less.

4. The binder composition for a secondary battery according to any one of Claims 1 to 3, wherein the polymer A is an addition polymer.

5. 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.

6. A functional layer for a secondary battery, formed using the slurry composition for a secondary battery functional layer according to Claim 5.

7. A secondary battery comprising the functional layer for a secondary battery according to Claim 6.

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