JP2016149313A - Binder composition for lithium ion secondary battery electrode, slurry composition for lithium ion secondary battery electrode, electrode for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binder composition for a lithium ion secondary battery electrode that can reduce the internal resistance of a lithium ion secondary battery and has excellent lifetime characteristic.SOLUTION: A binder composition for a lithium ion secondary battery electrode contains a compound (A) as an ethylenic unsaturated carboxylic acid compound in the range from not less than 20.0 wt% to not more than 75.0 wt%, and a copolymerizable compound (B) having ethylenic unsaturated bond having a solubility of 7 g or more with respect to water of 100 g at 20°C in the range from not less than 20.0 wt% to not more than 75.0 wt%, and also contains a water-soluble polymer X having an electrolyte swell rate of less than 120 wt%, and amphoteric dispersant Y having an acid value ranging from not less than 1 mgKOH/g to less than 30 mgKOH/g and an amine value ranging from 1 mgKOH/g to less than 30 mgKOH/g. The blend amount of the amphoteric dispersant ranges from 0.001 weight parts to not more than 10 weight parts with respect to the 100 weight parts of the water-soluble polymer X.SELECTED DRAWING: None

Description

  The present invention relates to a binder composition for a lithium ion secondary battery electrode, a slurry composition for a lithium ion secondary battery electrode, an electrode for a lithium ion secondary battery, and a lithium ion secondary battery.

  Lithium ion secondary batteries are small and lightweight, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Therefore, in recent years, improvement of battery members such as electrodes has been studied for the purpose of further improving the performance of lithium ion secondary batteries.

  Here, the electrode for lithium ion secondary batteries is normally provided with the electrical power collector and the electrode compound-material layer formed on the electrical power collector. For example, the electrode mixture layer is formed by applying a slurry composition obtained by dispersing and / or dissolving an electrode active material and a binder composition containing a binder in a solvent onto a current collector and drying the electrode. Is formed.

  Thus, in recent years, attempts have been made to improve the binder composition and the slurry composition used for forming the electrode mixture layer in order to achieve further improvement in the performance of secondary batteries such as lithium ion secondary batteries ( For example, see Patent Documents 1 and 2).

In Patent Literature 1, a slurry composition comprising an electrode active material, a binder composition containing crosslinked resin fine particles, an amphoteric resin type dispersant having a specific composition, and an aqueous liquid medium is used as an electrode mixture layer. A technique for exhibiting excellent cycle characteristics in a secondary battery has been proposed.
In Patent Document 2, a slurry composition containing an electrode active material, a conductive material, and a dispersant composed of an ionic surfactant such as an amphoteric surfactant is used for forming the electrode mixture layer. There has been proposed a technique for suppressing the aggregation of conductive materials to sufficiently form a conductive network and exhibiting excellent output characteristics for a secondary battery.

JP2013-93123A JP 2006-302617 A

However, it has been difficult for the slurry composition described in the above-mentioned patent document to impart sufficiently excellent life characteristics (cycle characteristics and storage stability) to the lithium ion secondary battery.
Furthermore, in the slurry composition described in the above-mentioned patent document, the resistance of the electrode mixture layer may not be sufficiently reduced, and the lithium ion secondary battery can exhibit sufficiently excellent rate characteristics. There wasn't.
Therefore, the conventional binder composition has room for further improvement in that the lithium ion secondary battery exhibits excellent life characteristics while reducing the internal resistance of the lithium ion secondary battery.

Then, an object of this invention is to provide the binder composition for lithium ion secondary battery electrodes which reduces the internal resistance of a lithium ion secondary battery, and is excellent in a lifetime characteristic collectively.
Another object of the present invention is to provide a slurry composition for a lithium ion secondary battery electrode that reduces the internal resistance of the lithium ion secondary battery and has excellent life characteristics.
The present invention also provides an electrode that reduces the internal resistance of the lithium ion secondary battery and also has excellent life characteristics, and a lithium ion secondary battery that has reduced internal resistance and excellent life characteristics. The purpose is to do.

  The present inventor has intensively studied for the purpose of solving the above problems. And this inventor is an ethylenically unsaturated carboxylic acid and / or its salt, and the copolymerizable compound which has the ethylenically unsaturated bond whose solubility with respect to 100 g of water in 20 degreeC is 7 g or more in predetermined ratio. Lithium provided with the electrode by using a binder composition containing a water-soluble polymer having a degree of electrolyte swell within a specific range obtained by copolymerizing the monomer composition The idea was to reduce the internal resistance of the ion secondary battery and improve the life characteristics.

  In addition, the present inventor further studied, and the binder composition containing the water-soluble polymer further includes an amphoteric dispersant exhibiting a predetermined acid value and an amine value in a predetermined quantitative ratio, whereby electrode physical properties are obtained. It has been found that the battery performance can be further improved by dramatically increasing the adhesion between the electrode mixture layer and the current collector, and the present invention has been completed.

  That is, the present invention aims to advantageously solve the above problems, and the binder composition for lithium ion secondary battery electrodes of the present invention comprises a water-soluble polymer X, an amphoteric dispersant Y and a solvent. A lithium ion secondary battery electrode binder composition, wherein the water-soluble polymer X is obtained by polymerizing a monomer composition containing the compound (A) and the compound (B). A) is an ethylenically unsaturated carboxylic acid compound comprising at least one of an ethylenically unsaturated carboxylic acid and a salt thereof, and the compound (B) has a solubility in 100 g of water at 20 ° C. of 7 g or more, A compound copolymerizable with the compound (A) having a polymerizable unsaturated bond, and the ratio of the compound (A) in all monomers of the monomer composition is 20.0% by mass or more and 75.0%. mass The ratio of the compound (B) in all the monomers is 20.0% by mass or more and 75.0% by mass or less, and the degree of swelling of the electrolytic solution of the water-soluble polymer X is less than 120% by mass. And the amphoteric dispersant Y has an acid value of 1 mgKOH / g or more and less than 30 mgKOH / g, an amine value of 1 mgKOH / g or more and less than 30 mgKOH / g, and the compounding amount of the amphoteric dispersant Y is The amount is 0.001 part by mass or more and 10 parts by mass or less per 100 parts by mass of the water-soluble polymer X. A water-soluble polymer obtained by polymerizing such a monomer composition containing the compound (A) and the compound (B) in a predetermined ratio and having an electrolyte swelling degree of less than 120% by mass; If a binder composition using an amphoteric dispersant exhibiting an acid value and an amine value in combination at a predetermined quantitative ratio is used for forming an electrode, the internal resistance of the lithium ion secondary battery equipped with the electrode is reduced and the lifetime is also reduced. The characteristics can be made excellent.

  Here, in the binder composition for a lithium ion secondary battery electrode of the present invention, the monomer composition further comprises a polyfunctional compound (C) having a polyoxyalkylene structure and two or more ethylenically unsaturated bonds. It is preferable that the ratio of the said polyfunctional compound (C) in all the monomers is 0.01 mass% or more and 20.0 mass% or less. If a water-soluble polymer is formed using the monomer composition containing the polyfunctional compound (C) in the above-mentioned proportion, the internal resistance of the lithium ion secondary battery can be further reduced, and the life characteristics are further improved. This is because it can be improved. In addition, by including the polyfunctional compound (C) in the monomer composition, it is possible to increase the solid content concentration of the slurry composition prepared using the binder composition of the present invention, thereby improving the productivity of the electrode. It is because it can be made.

  And in the binder composition for a lithium ion secondary battery electrode of the present invention, the monomer composition has the ratio of the compound (A) in all monomers to the compound (B) in all monomers. The value divided by the ratio is preferably less than 1.5. When the ratio of the compound (A) in all monomers and the ratio of the compound (B) in all monomers satisfy the above relationship, the water-soluble polymer X does not swell excessively in the electrolyte. This is because the interparticle distance between the electrode active materials is maintained and the lithium ion conductivity is ensured, so that the internal resistance of the lithium ion secondary battery can be further reduced. Furthermore, it is possible to achieve a reduction in internal resistance of the lithium ion secondary battery and an improvement in cycle characteristics in a balanced manner.

  In addition, in the binder composition for a lithium ion secondary battery electrode of the present invention, the electrolyte solution solubility of the amphoteric dispersant Y is preferably 5% or less. If the solubility of the electrolyte solution of the amphoteric dispersant Y is 5% or less, the elution of the amphoteric dispersant Y into the electrolyte solution can be sufficiently suppressed, and the life characteristics of the lithium ion secondary battery can be further improved. is there.

  Moreover, this invention aims at solving the said subject advantageously, The slurry composition for lithium ion secondary battery electrodes of this invention is the binder for lithium ion secondary battery electrodes in any one of the above-mentioned. A composition and an electrode active material are included. Thus, if any one of the above-mentioned binder compositions is used for the preparation of the slurry composition, the internal resistance of the lithium ion secondary battery including the electrode prepared using the slurry composition is reduced, and the lifetime is also reduced. The characteristics can be made excellent.

  Moreover, this invention aims at solving the said subject advantageously, The electrode for lithium ion secondary batteries of this invention is prepared using the above-mentioned slurry composition for lithium ion secondary battery electrodes. The electrode mixture layer is provided on a current collector. Thus, if an electrode mixture layer is formed using the slurry composition described above, a lithium ion secondary battery capable of having excellent life characteristics while reducing the internal resistance of the lithium ion secondary battery. A working electrode is obtained.

  Moreover, this invention aims at solving the said subject advantageously, The lithium ion secondary battery of this invention is equipped with a positive electrode, a negative electrode, electrolyte solution, and a separator, At least one of the said positive electrode and negative electrode Is an electrode for a lithium ion secondary battery as described above. Thus, if the electrode for lithium ion secondary batteries described above is used, a lithium ion secondary battery having reduced internal resistance and excellent life characteristics can be provided.

ADVANTAGE OF THE INVENTION According to this invention, the internal resistance of a lithium ion secondary battery can be reduced, and the lithium ion secondary battery electrode binder composition which is excellent in lifetime characteristics can be provided.
ADVANTAGE OF THE INVENTION According to this invention, the internal resistance of a lithium ion secondary battery can be reduced, and the slurry composition for lithium ion secondary battery electrodes which makes the lifetime characteristic excellent also can be provided.
According to the present invention, there are provided an electrode that reduces the internal resistance of a lithium ion secondary battery and also has excellent life characteristics, and a lithium ion secondary battery that has reduced internal resistance and excellent life characteristics. can do.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the binder composition for a lithium ion secondary battery electrode of the present invention is used for forming an electrode of a lithium ion secondary battery. And the slurry composition for lithium ion secondary battery electrodes of this invention is comprised including the binder composition for lithium ion secondary battery electrodes of this invention, and is used for formation of the electrode of a lithium ion secondary battery. Moreover, the electrode for lithium ion secondary batteries of this invention can be manufactured using the slurry composition for lithium ion secondary battery electrodes of this invention. Furthermore, the lithium ion secondary battery of the present invention is characterized by using the electrode for a lithium ion secondary battery of the present invention.

(Binder composition for lithium ion secondary battery electrode)
The binder composition for a lithium ion secondary battery electrode of the present invention includes a water-soluble polymer X as a binder, an amphoteric dispersant Y, and a solvent. The water-soluble polymer X has a compound (A) which is an ethylenically unsaturated carboxylic acid composed of at least one of an ethylenically unsaturated carboxylic acid and a salt thereof, and a solubility in 100 g of water at 20 ° C. is 7 g or more. In addition, it is obtained by polymerizing a monomer composition containing an ethylenically unsaturated bond and a compound (B) copolymerizable with the compound (A) at a predetermined ratio, and the electrolyte swelling degree is 120% by mass. The acid value of the amphoteric dispersant Y is 1 mgKOH / g or more and less than 30 mgKOH / g, the amine value is 1 mgKOH / g or more and less than 30 mgKOH / g, and the compounding amount of the amphoteric dispersant Y is water-soluble. It is characterized by being 0.001 part by mass or more and 10 parts by mass or less per 100 parts by mass of the conductive polymer X.

  Here, the binder composition for a lithium ion secondary battery electrode of the present invention is obtained by polymerizing a monomer composition containing the compound (A) and the compound (B) at a predetermined ratio, and the electrolyte swells. The binder contains a water-soluble polymer having a degree of less than 120% by mass and an amphoteric dispersant Y exhibiting a predetermined acid value and an amine value in a predetermined amount ratio with respect to the water-soluble polymer X. By using the composition for the production of an electrode, it is possible to exhibit excellent life characteristics in the lithium ion secondary battery while reducing the internal resistance of the lithium ion secondary battery.

In addition, by using the water-soluble polymer X and the amphoteric dispersant Y in a predetermined ratio with respect to the water-soluble polymer X, the internal resistance of the lithium ion secondary battery is reduced and the life characteristics are improved. The reason for this is not clear, but is presumed to be due to the following reason.
First, the compound (B) used for the preparation of the water-soluble polymer X is a highly polar monomer having high solubility in water. Therefore, the obtained water-soluble polymer X has a low affinity for the electrolyte solution usually used in lithium ion secondary batteries, and the resulting water-soluble polymer X is moderately swollen in the electrolyte solution (120 mass). Less than%). Therefore, it is presumed that the life characteristics such as the cycle characteristics are improved by maintaining the structure of the electrode plate and suppressing the swelling of the electrodes. On the other hand, the lithium ion conductivity is improved by the carboxyl group of the compound (A), the internal resistance of the lithium ion secondary battery is reduced, and the cycle characteristics are improved. In addition, the water-soluble polymer X suitably covers the electrode active material due to the contribution of the carboxyl group of the compound (A), the decomposition of the electrolyte solution on the surface of the electrode active material is suppressed, and the generation of gas is suppressed, which is preserved. It is presumed that stability can be improved.
Furthermore, by using a predetermined amount of the amphoteric dispersant Y in addition to the water-soluble polymer X described above, the electrode active material can be favorably dispersed in the slurry composition. In addition, since the amphoteric dispersant Y exhibits a predetermined acid value and amine value, the amphoteric dispersant Y is preferably used with both the water-soluble polymer X and the electrode active material via an acidic functional group or a basic functional group. By interacting, the physical properties of the electrode can be improved by increasing the binding force between the electrode active materials, and the elution of the amphoteric dispersant Y into the electrolytic solution can be suppressed. As a result, it is assumed that the battery performance such as the cycle characteristics of the lithium ion secondary battery is improved.

<Binder>
The binder is an electrode mixture layer formed on the current collector using the slurry composition for lithium ion secondary battery electrodes prepared using the binder composition for lithium ion secondary battery electrodes of the present invention. In the electrode manufactured by the above, the component contained in the electrode mixture layer can be held so as not to be detached from the electrode mixture layer.

  And the binder used for the binder composition for lithium ion secondary battery electrodes of the present invention polymerizes the monomer composition containing the compound (A) and the compound (B) at a predetermined ratio as described above. It is necessary to contain the water-soluble polymer X obtained in this way. In addition, the binder composition for lithium ion secondary battery electrodes of the present invention may optionally further contain a polymer other than the water-soluble polymer X as a binder.

[Water-soluble polymer X]
The water-soluble polymer X used as the binder of the binder composition for lithium ion secondary battery electrodes of the present invention is a water-soluble copolymer.
Here, in the present invention, the polymer is “water soluble” means that a mixture obtained by adding 1 part by weight of polymer (corresponding to a solid content) and stirring with respect to 100 parts by weight of ion-exchanged water has a temperature of 20 ° C. or higher. Adjust to at least one of the conditions within the range of 70 ° C. or less and within the range of pH 3 to 12 (using NaOH aqueous solution and / or HCl aqueous solution for pH adjustment), and pass through a 250 mesh screen. This means that the solid content of the residue remaining on the screen without passing through the screen does not exceed 50 mass% with respect to the solid content of the added polymer.

  And the water-soluble polymer X is obtained by superposing | polymerizing the monomer composition demonstrated in detail below. And usually this water-soluble polymer X has the same structural unit derived from the monomer contained in the monomer composition as the abundance ratio of each monomer in the monomer composition. Contains in proportions.

[[Monomer composition]]
The monomer composition used for the preparation of the water-soluble polymer X contains, for example, a monomer, an additive such as a polymerization initiator, and a polymerization solvent. And a monomer composition contains a compound (A) and a compound (B) in a predetermined ratio as a monomer. Specifically, the monomer composition has a compound (A) of 20.0% by mass or more and 75.0% by mass or less when the amount of all monomers in the monomer composition is 100% by mass. ) And 20.0 mass% or more and 75.0 mass% or less of the compound (B). The monomer composition optionally contains as a monomer a compound (A) and a polyfunctional compound (C) copolymerizable with the compound (B), and other compounds other than these. May be.

-Compound (A)-
As the compound (A), at least one of an ethylenically unsaturated carboxylic acid and a salt thereof can be used. Examples of the ethylenically unsaturated carboxylic acid include ethylenically unsaturated monocarboxylic acid and derivatives thereof, ethylenically unsaturated dicarboxylic acid and acid anhydrides thereof, and derivatives thereof. Examples of the ethylenically unsaturated carboxylate include sodium salts, potassium salts and lithium salts of ethylenically unsaturated carboxylic acids.
In addition, ethylenically unsaturated carboxylic acid and its salt may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Here, examples of the ethylenically unsaturated monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid. Examples of the ethylenically unsaturated monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic. Examples include acid and β-diaminoacrylic acid.
Examples of the ethylenically unsaturated dicarboxylic acid include maleic acid, fumaric acid, itaconic acid and the like. Examples of acid anhydrides of ethylenically unsaturated dicarboxylic acids include maleic anhydride, diacrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, and the like. Furthermore, examples of the ethylenically unsaturated dicarboxylic acid derivative include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, and fluoromaleic acid.

In the binder composition for a lithium ion secondary battery electrode of the present invention, as the compound (A), an ethylenically unsaturated carboxylate, preferably a lithium salt of an ethylenically unsaturated carboxylic acid can be used. If an ethylenically unsaturated carboxylate is used, the water solubility of the resulting water-soluble polymer X can be increased. Therefore, when preparing the water-soluble polymer X using water as a polymerization solvent, Even when the monomer concentration in the body composition is set to a high concentration, the heterogeneous progress of the polymerization due to the precipitation of the water-soluble polymer X can be prevented. Accordingly, the polymerization can be progressed uniformly while increasing the productivity by using the monomer composition having a high monomer concentration. Further, if a lithium salt of an ethylenically unsaturated carboxylic acid is used, lithium carboxylate base (—COOLi) is introduced into the resulting water-soluble polymer X, the stability of the slurry composition is improved, and lithium ions The cycle characteristics and storage characteristics of the secondary battery can be further improved and the internal resistance can be further reduced.
In addition, from the viewpoint of further improving the cycle characteristics of a lithium ion secondary battery including an electrode prepared using the binder composition of the present invention and further reducing internal resistance, the ethylenically unsaturated carboxylic acid compound may be acrylic. It is preferable to use acid, methacrylic acid or a salt thereof, and it is more preferable to use acrylic acid or acrylate.

  And the monomer which the monomer composition used for preparation of the water-soluble polymer X needs to be 20.0 mass% or more and 75.0 mass% or less for the ratio which the compound (A) mentioned above occupies. The proportion of the compound (A) in the monomer is preferably 21.0% by mass or more, more preferably 22.0% by mass or more, and 72.0% by mass or less. Preferably, it is 40.0 mass% or less. When the proportion of the compound (A) in the monomer is less than 20.0% by mass, the rigidity of the water-soluble polymer X is lowered, and the swelling of the electrode cannot be sufficiently suppressed. The adhesion between the layer and the current collector is lowered, and the cycle characteristics of the lithium ion secondary battery are lowered. On the other hand, when the proportion of the compound (A) in the monomer exceeds 75.0% by mass, the rigidity of the water-soluble polymer X becomes excessively high and becomes brittle, and the electrode is composed of the water-soluble polymer X. Cracks occur in the active material coating. As a result, the storage stability of the lithium ion secondary battery decreases due to the generation of gas due to the formation of a new interface of the electrode active material. In addition, internal resistance increases and cycle characteristics deteriorate.

-Compound (B)-
As the compound (B), a compound having an ethylenically unsaturated bond and having a solubility in 100 g of water at 20 ° C. of 7 g or more can be used. This is because the structural unit derived from the compound (B) having such solubility has low swellability with respect to the electrolytic solution and high polymerizability when water is used as a polymerization solvent. In the present invention, the ethylenically unsaturated carboxylic acid and the salt thereof are not included in the compound (B) but are included in the compound (A) even when the above-described solubility is satisfied.
Examples of the compound (B) include 2-hydroxypropyl methacrylate (100 or more), 2-hydroxypropyl acrylate (100 or more), 2-hydroxyethyl methacrylate (100 or more), 2-hydroxyethyl acrylate (100 or more), 2- (methacryloyloxy) ethyl phosphate (100 or more), acrylamide (100 or more), methacrylamide (100 or more), N-methylolacrylamide (100 or more), acrylonitrile (7), sodium styrenesulfonate (22), etc. And compounds having an ethylenically unsaturated bond and a highly polar functional group (hydroxyl group, amide group, nitrile group, phosphoric acid group, amino group, etc.) and ethylene glycol dimethacrylate (100 or more). it can. One of these may be used alone, or two or more of these may be used in combination at any ratio. Here, the numerical value in the parenthesis indicates water solubility (unit: g / 100 g) at a temperature of 20 ° C. The water solubility at 20 ° C. can be measured by the EPA method (EPA Chemical Fate testing Guideline CG-1500 Water Solubility).
In place of the compound (B), a water-soluble polymer X is prepared using a compound having a water solubility of less than 7 g at 20 ° C. such as methyl acrylate (6), ethyl acrylate (2), or butyl acrylate (2). As a result, the water-soluble polymer X swells excessively in the electrolytic solution, the structure of the electrode plate cannot be maintained, and the swelling of the electrode cannot be suppressed. As a result, the life characteristics such as cycle characteristics of the lithium ion secondary battery cannot be secured.
In addition, the compound (B) is used from the viewpoint of reducing moisture brought into the lithium ion secondary battery and suppressing gas generation, and other polymers that can be used in combination with the water-soluble polymer X (for example, styrene-butadiene described later) From the viewpoint of ensuring the stability of the particulate polymer (eg, a polymer based polymer), it is preferably not an organic salt such as an ammonium salt, a salt such as a sodium salt, or a potassium salt (particularly a metal salt), and can easily be converted into a salt. It is preferable not to have an acidic group (such as a phenolic hydroxyl group) to be converted.

  From the viewpoint of suppressing the swelling of the electrode in the electrolyte, further reducing the internal resistance, and further improving the cycle characteristics of the lithium ion secondary battery, the compound (B) is 2-hydroxyethyl acrylate. , Acrylamide, N-methylolacrylamide, and acrylonitrile are preferable, and 2-hydroxyethyl acrylate and acrylamide are more preferable.

  And the monomer which the monomer composition used for preparation of the water-soluble polymer X needs to be 20.0 mass% or more and 75.0 mass% or less in the ratio which the compound (B) mentioned above occupies. The proportion of the compound (B) in the monomer is preferably 30.0% by mass or more, and more preferably 60.0% by mass or more. When the proportion of the compound (B) in the monomer is less than 20.0% by mass, the electrode plate becomes excessively brittle, the structure cannot be maintained, cracks and the like occur, and the cycle characteristics deteriorate. Further, the storage stability is lowered, and the internal resistance of the lithium ion secondary battery cannot be sufficiently reduced. On the other hand, when the proportion of the compound (B) in the monomer exceeds 75.0% by mass, the swelling of the electrode cannot be sufficiently suppressed, and the adhesion between the electrode mixture layer and the current collector is low. The cycle characteristics of the lithium ion secondary battery deteriorate.

Moreover, it is preferable that the value (A / B) which remove | divided the ratio of the compound (A) in all the monomers by the ratio of the said compound (B) in all the monomers is less than 1.5. 0.0 or less is more preferable, 0.8 or less is further preferable, 0.2 or more is preferable, and 0.3 or more is more preferable.
When A / B is less than 1.5, the water-soluble polymer X does not swell excessively in the electrolyte, the interparticle distance between the electrode active materials is maintained, and lithium ion conductivity is also ensured. This is because the internal resistance of the lithium ion secondary battery can be further reduced.
In addition, when A / B is within the above range, it is possible to achieve a reduction in internal resistance of the lithium ion secondary battery and an improvement in cycle characteristics in a balanced manner.

-Polyfunctional compound (C)-
The monomer composition preferably includes a polyfunctional compound (C) having a polyoxyalkylene structure and two or more ethylenically unsaturated bonds as a monomer. By using such a polyfunctional compound (C) for the polymerization of the water-soluble polymer X, the water-soluble polymer X can be given moderately high rigidity and flexibility. Therefore, it is possible to suppress the deterioration of the cycle characteristics by suppressing the swelling of the electrode due to charge / discharge. In addition, the water-soluble polymer X can be easily polymerized due to the contribution of the ethylene oxide chain having a high affinity with water. In addition, lithium ion conductivity is ensured, and the internal resistance of the lithium ion secondary battery can be reduced. In addition, by including the polyfunctional compound (C) in the monomer composition, it is possible to increase the solid content concentration of the slurry composition prepared using the binder composition of the present invention, thereby improving the productivity of the electrode. Can be made.
Here, the polyfunctional compound (C) is represented by the general formula: — (C _m H _2m O) _n — [wherein, m is an integer of 1 or more, and n is an integer of 2 or more]. A compound having a polyoxyalkylene structure and two or more ethylenically unsaturated bonds can be used.
As the compound having a polyoxyalkylene structure and two or more ethylenically unsaturated bonds, one type may be used alone, or two or more types may be used in combination at any ratio.
In the present invention, a compound corresponding to the polyfunctional compound (C) is not included in the compound (B).

［式中、ｎは２以上の整数である］で表されるポリエチレングリコールジアクリレート。
（ＩＩ）下記一般式：

［式中、ｎは２以上の整数である］で表されるポリテトラメチレングリコールジアクリレート。
（ＩＩＩ）下記一般式：

［式中、ｎ１およびｎ２は、２以上の整数であり、互いに同一でも、異なっていても良い］で表されるエトキシ化ビスフェノールＡジアクリレート。
（ＩＶ）下記一般式：

［式中、ｎ１、ｎ２およびｎ３は、２以上の整数であり、互いに同一でも、異なっていても良い］で表されるエトキシ化グリセリントリアクリレート。
（Ｖ）下記一般式：

［式中、ｎ１、ｎ２、ｎ３およびｎ４は、２以上の整数であり、互いに同一でも、異なっていても良い］で表されるエトキシ化ペンタエリスリトールテトラアクリレート。 Here, as a polyfunctional compound (C), the poly (meth) acrylate of the polyol which has a polyoxyalkylene structure etc. are mentioned, for example. Specifically, the polyfunctional compound (C) is not particularly limited and includes the following compounds (I) to (V). In the present invention, “(meth) acrylate” means acrylate And / or methacrylate.
(I) The following general formula:

[Wherein n is an integer of 2 or more] polyethylene glycol diacrylate represented by
(II) The following general formula:

[Wherein n is an integer of 2 or more] polytetramethylene glycol diacrylate.
(III) The following general formula:

[Wherein, n1 and n2 are integers of 2 or more, and may be the same or different from each other].
(IV) The following general formula:

[Wherein n1, n2 and n3 are integers of 2 or more, and may be the same or different from each other].
(V) The following general formula:

[Wherein n1, n2, n3 and n4 are integers of 2 or more and may be the same or different from each other], and ethoxylated pentaerythritol tetraacrylate.

From the viewpoint of facilitating the polymerization of the water-soluble polymer X and improving the productivity of the electrode by making it possible to increase the solid content concentration of the slurry composition prepared using the binder composition of the present invention. The number (functional number) of ethylenically unsaturated bonds of the polyfunctional compound (C) is preferably 2 or more and 6 or less, and more preferably 2 or more and 4 or less.
Moreover, from the viewpoint of further increasing the productivity of the electrode, the polyfunctional compound (C) is preferably a bifunctional to hexafunctional polyacrylate, and more preferably a bifunctional to tetrafunctional polyacrylate. Among the 2- to 4-functional polyacrylates, bifunctional polyacrylates are particularly preferable from the viewpoint of improving the cycle characteristics and storage stability while reducing the internal resistance of the lithium ion secondary battery.

Furthermore, from the viewpoint of improving the stability of the slurry composition prepared using the binder composition of the present invention and the storage stability of the lithium ion secondary battery, the polyoxyalkylene structure (- _{(C m H 2m O) n} - an integer m of) is preferably 20 or less, more preferably 15 or less, particularly preferably 10 or less, or 2 or more. This is because if the integer m is too large, the stability of the slurry composition may decrease. Moreover, when the integer m is too small, the rigidity of the water-soluble polymer X becomes high, and the storage stability of the lithium ion secondary battery may be lowered.
For the same reason, the integer n of the polyoxyalkylene structure (— (C _m H _2m O) _n —) of the polyfunctional compound (C) is preferably 20 or less, and preferably 15 or less. More preferably, it is particularly preferably 10 or less, more preferably 2 or more, further preferably 3 or more, and particularly preferably 4 or more. This is because if the integer n is too large, the stability of the slurry composition may decrease. In addition, when the integer n is too small, the rigidity of the water-soluble polymer X becomes high, and the storage stability of the lithium ion secondary battery may be lowered. In addition, when the polyfunctional compound (C) has a plurality of polyoxyalkylene structures (— (C _m H _2m O) _n —) in the molecule, the average value of the integers n of the plurality of polyoxyalkylene structures is It is preferable to be included in the range, and it is more preferable that the integer n of all the polyoxyalkylene structures is included in the above range.

  And it is preferable that the monomer which the monomer composition used for preparation of water-soluble polymer X contains is 0.01 mass% or more in the ratio which the polyfunctional compound (C) mentioned above occupies. More preferably, it is more preferably 0.1% by mass or more, still more preferably 20.0% by mass or less, and even more preferably 10.0% by mass or less. The content is more preferably 0% by mass or less, and particularly preferably 2.0% by mass or less. When the proportion of the polyfunctional compound (C) in the monomer is 0.01% by mass or more, the swelling of the electrode can be sufficiently suppressed, and the cycle characteristics of the lithium ion secondary battery are further improved. be able to. On the other hand, the proportion of the polyfunctional compound (C) in the monomer is 20.0% by mass or less, so that the rigidity of the water-soluble polymer X is prevented from becoming excessively high and brittle. Further, it is possible to suppress a decrease in storage stability of the lithium ion secondary battery due to gas generation. In addition, an increase in internal resistance due to gelation of the water-soluble polymer X can be suppressed.

-Other compounds-
The monomer composition used for the preparation of the water-soluble polymer X may contain a known compound copolymerizable with the above-described compound (A), compound (B), and polyfunctional compound (C). . And the monomer which the monomer composition used for preparation of the water-soluble polymer X contains 20.0 mass% or less for the ratio which the other compounds except these (A)-(C) occupy. Preferably, it is 10.0 mass% or less.
More specifically, as other compounds, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, nonyl acrylate , Decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, perfluoroalkyl ethyl acrylate, phenyl acrylate, and the like; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate Methacrylic acid esters such as vinyl acetate, glycidyl methacrylate, 2; -Vinyl pyridine, etc. are mentioned.

  In particular, when the water-soluble polymer X prepared using a monomer composition containing the above-mentioned acrylic acid ester and methacrylic acid ester (collectively referred to as “(meth) acrylic acid ester”) is included in the slurry composition The slurry composition tends to foam. Therefore, by suppressing foaming of the slurry composition during electrode production, an electrode mixture layer having a uniform thickness without pinholes is formed, the internal resistance of the lithium ion secondary battery is reduced, and the cycle characteristics and storage stability are also improved. From the viewpoint of improving the property, the monomer composition preferably has a (meth) acrylic acid ester ratio in all monomers of 10.0% by mass or less, and 5.0% by mass or less. More preferably, it is more preferably 1.0% by mass or less, even more preferably 0.1% by mass or less, and even more preferably 0% by mass (that is, the monomer composition is a (meth) acrylic acid ester). It is particularly preferable that

-Additives-
As additives to be added to the monomer composition used for the preparation of the water-soluble polymer X, known additives that can be used for polymerization reactions such as polymerization initiators such as potassium persulfate and polymerization accelerators such as tetramethylethylenediamine An additive is mentioned. In addition, the kind and compounding quantity of an additive can be arbitrarily selected according to a polymerization method etc.

-Polymerization solvent-
As a polymerization solvent blended in the monomer composition used for the preparation of the water-soluble polymer X, a known solvent capable of dissolving or dispersing the above-described monomer can be used depending on the polymerization method and the like. Among these, water is preferably used as the polymerization solvent. As the polymerization solvent, an aqueous solution of an arbitrary compound or a mixed solution of a small amount of an organic medium and water may be used.

[[Preparation of water-soluble polymer X]]
The water-soluble polymer X used as the binder of the binder composition of the present invention is obtained by mixing a monomer composition obtained by mixing the above-described monomers, additives and polymerization solvent by a known method, for example, radicals. It is obtained by polymerizing. In addition, the solution containing the water-soluble polymer X and the polymerization solvent obtained by polymerizing the monomer composition may be used for preparing the binder composition as it is, or may be used for solvent substitution or optional components. You may use for preparation of a binder composition, after adding etc.

  Here, examples of the polymerization method include known polymerization methods such as aqueous solution polymerization, slurry polymerization, suspension polymerization, and emulsion polymerization. However, the operation for removing the solvent is unnecessary, the safety of the solvent is high, and the interface Since there is no problem of mixing of the activator, aqueous solution polymerization using water as a polymerization solvent is preferable. In aqueous solution polymerization, the monomer composition is adjusted to a predetermined concentration, and the dissolved oxygen in the reaction system is sufficiently replaced with an inert gas. Then, a radical polymerization initiator is added, and if necessary, heating or ultraviolet rays are added. It is a method of performing a polymerization reaction by irradiating light.

In addition, when using water as a polymerization solvent and polymerizing the monomer composition described above in water to prepare an aqueous solution containing the water-soluble polymer X, the pH of the aqueous solution is adjusted to 8 or more and 9 or less after polymerization. It is preferable to do. If the aqueous solution obtained is neutralized and the pH is adjusted to 8-9, thixotropy is imparted to the slurry composition, the stability of the slurry composition is increased, and the storage stability of the lithium ion secondary battery is increased. This is because it can be further increased.
Here, when a monomer composition containing an ethylenically unsaturated carboxylic acid is used as the compound (A), it is preferable to use a basic lithium compound when neutralizing the aqueous solution. If a basic lithium compound is used, the carboxylic acid group in the water-soluble polymer X becomes a carboxylic acid lithium base (—COOLi), and the thixotropy and stability of the slurry composition are further improved, and the lithium ion secondary This is because the internal resistance of the battery is reduced, and in addition, cycle characteristics and storage stability are improved. As the basic lithium compound, lithium carbonate (Li ₂ CO ₃ ) or lithium hydroxide (LiOH) can be used, and lithium hydroxide is preferably used.

[[Properties of water-soluble polymer X]]
The water-soluble polymer X prepared as described above needs to have an electrolyte swelling degree of less than 120% by mass, preferably 118% by mass or less, and 115% by mass or less. Is more preferably 100% by mass or more, more preferably 103% by mass or more, and still more preferably 105% by mass or more. If the degree of swelling of the electrolytic solution of the water-soluble polymer X is 120% by mass or more, the water-soluble polymer X will swell excessively in the electrolytic solution and the electrode plate structure cannot be maintained, and the life characteristics such as cycle characteristics will be reduced. To do. On the other hand, if the degree of swelling of the electrolyte solution of the water-soluble polymer X is 100% by mass or more, lithium ion conductivity is ensured and the internal resistance of the lithium ion secondary battery can be further reduced. In addition, it is possible to secure the flexibility of the water-soluble polymer X, suppress cracking and peeling of the water-soluble polymer X, and further improve the storage stability of the lithium ion secondary battery. Furthermore, it becomes possible to improve the adhesiveness of an electrode compound-material layer and a collector by making electrolyte solution swelling degree of the water-soluble polymer X into the above-mentioned range.
In addition, the electrolyte solution swelling degree of water-soluble polymer X can be measured by the method as described in the Example of this specification. Moreover, the electrolyte solution swelling degree of the water-soluble polymer X can be adjusted, for example, by changing the type and amount of the compound (A) or the compound (B) in the monomer composition.

[Other polymers]
The binder composition of the present invention containing the above-described water-soluble polymer X as a binder may further contain a polymer other than the above-described water-soluble polymer X as a binder.

Examples of the polymer other than the above-described water-soluble polymer X include known polymers such as a water-insoluble particulate polymer that can be dispersed in the solvent of the binder composition. Specifically, examples of the particulate polymer include a conjugated diene polymer, an acrylic polymer, a fluorine polymer, and a silicon polymer. These polymers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Among these, from the viewpoint of improving the adhesion between the electrode mixture layer and the current collector and improving the cycle characteristics of the lithium ion secondary battery, a conjugated diene polymer and an acrylic polymer are preferable, and a conjugated diene type is preferable. A polymer is more preferred.
The particulate polymer is obtained, for example, by polymerizing a monomer composition for particulate polymer containing a monomer, an additive such as a polymerization initiator, and a polymerization solvent. And usually, the particulate polymer is a structural unit derived from the monomer contained in the monomer composition for particulate polymer, and the abundance ratio of each monomer in the monomer composition. In the same proportion. Hereinafter, a conjugated diene polymer preferable as a particulate polymer will be described in detail as an example.

[[Conjugated Diene Polymer]]
The conjugated diene polymer is a polymer containing a structural unit derived from a conjugated diene monomer, and includes hydrogenated products thereof.
Specific examples of conjugated diene polymers include aliphatic conjugated diene polymers such as polybutadiene and polyisoprene; aromatic vinyl / aliphatic conjugated diene copolymers such as styrene-butadiene polymers (SBR); acrylonitrile-butadiene. Examples thereof include vinyl cyanide-conjugated diene copolymers such as a base polymer (NBR); hydrogenated SBR, hydrogenated NBR, and the like. Among these, aromatic vinyl / aliphatic conjugated diene copolymers such as styrene-butadiene-based polymers (SBR) are preferable. And for example, an aromatic vinyl / aliphatic conjugated diene copolymer includes an aromatic vinyl monomer, an aliphatic conjugated diene monomer, and optionally a carboxyl group-containing monomer, a hydroxyl group-containing monomer, and a fluorine-containing monomer. It is obtained by polymerizing a monomer composition containing a monomer and other monomers.
Hereinafter, an aromatic vinyl monomer, an aliphatic conjugated diene monomer, a carboxyl group-containing monomer, a hydroxyl group-containing monomer, a fluorine-containing monomer used for the preparation of an aromatic vinyl / aliphatic conjugated diene copolymer. The monomer and other monomers will be described in detail.

-Aromatic vinyl monomer-
Examples of the aromatic vinyl monomer used for the preparation of the aromatic vinyl / aliphatic conjugated diene copolymer include styrene, α-methylstyrene, vinyltoluene, and divinylbenzene. These may be used alone or in combination of two or more. Among these, styrene is preferable.
The monomer contained in the particulate polymer monomer composition used for the preparation of the aromatic vinyl / aliphatic conjugated diene copolymer has a proportion of 35% by mass of the above-mentioned aromatic vinyl monomer. Preferably, it is 45% by mass or more, more preferably 55% by mass or more, preferably 80% by mass or less, more preferably 70% by mass or less, More preferably, it is 65 mass% or less.

-Aliphatic conjugated diene monomer-
Examples of the aliphatic conjugated diene monomer used for the preparation of the aromatic vinyl / aliphatic conjugated diene copolymer include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1, Examples include 3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like. These may be used alone or in combination of two or more. Among these, 1,3-butadiene is preferable.
The monomer contained in the particulate polymer monomer composition used for the preparation of the aromatic vinyl / aliphatic conjugated diene copolymer has a proportion of 20 mass by the aliphatic conjugated diene monomer described above. % Or more, more preferably 30% by mass or more, preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less. 35% by mass or less is particularly preferable.

-Carboxyl group-containing monomer-
The carboxyl group-containing monomer used for the preparation of the aromatic vinyl / aliphatic conjugated diene copolymer should be the same as the “compound (A)” described above in the section “Water-soluble polymer X”. Can do. These may be used alone or in combination of two or more. Of these, itaconic acid is preferred.
And the monomer which the monomer composition for particulate polymers used for preparation of an aromatic vinyl / aliphatic conjugated diene copolymer has a ratio of the above-mentioned carboxyl group-containing monomer is 0.5. It is preferably at least mass%, more preferably at least 1 mass%, preferably at most 6 mass%, more preferably at most 3 mass%.

-Hydroxyl group-containing monomer-
The hydroxyl group-containing monomers used for the preparation of the aromatic vinyl / aliphatic conjugated diene copolymer include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxy Butyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, 2-hydroxyethyl methyl For example, fumarate. These may be used alone or in combination of two or more. Among these, 2-hydroxyethyl acrylate is preferable.
The monomer contained in the particulate polymer monomer composition used for the preparation of the aromatic vinyl / aliphatic conjugated diene copolymer has a ratio of the above-mentioned hydroxyl group-containing monomer of 0.5%. It is preferably at least mass%, more preferably at least 0.8 mass%, preferably at most 5 mass%, more preferably at most 2 mass%.

-Other monomers-
The particulate polymer monomer composition used for the preparation of the aromatic vinyl / aliphatic conjugated diene copolymer includes the above-mentioned aromatic vinyl monomer, aliphatic conjugated diene monomer, and carboxyl group-containing monomer. Any monomer that can be copolymerized with the monomer and the hydroxyl group-containing monomer may be contained.
Specifically, as an arbitrary monomer, a fluorine-containing monomer such as 2,2,2-trifluoroethyl methacrylate, a sulfate group-containing monomer such as acrylamide-2-methylpropanesulfonic acid; Amide group-containing monomers such as acrylamide and methacrylamide; crosslinkable monomers (crosslinkable monomers) such as allyl glycidyl ether, allyl (meth) acrylate and N-methylol acrylamide; olefins such as ethylene and propylene Halogen-containing monomers such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and butyl vinyl ether; methyl vinyl Ketone, ethyl vinyl ketone, butyl vinyl ketone Vinyl ketones such as hexyl vinyl ketone and isopropenyl vinyl ketone; heterocycle-containing vinyl compounds such as N-vinyl pyrrolidone, vinyl pyridine and vinyl imidazole; amino group-containing monomers such as aminoethyl vinyl ether and dimethylaminoethyl vinyl ether; acrylonitrile; Examples include α, β-unsaturated nitrile monomers such as methacrylonitrile. These may be used alone or in combination of two or more.
And the monomer contained in the monomer composition for particulate polymer used for the preparation of the conjugated diene polymer is an aromatic vinyl monomer, an aliphatic conjugated diene monomer, a carboxyl group-containing monomer and The proportion of monomers other than the hydroxyl group-containing monomer is preferably 6% by mass or less, more preferably 3% by mass or less, and still more preferably 1% by mass or less.

  A method for producing a conjugated diene polymer such as an aromatic vinyl / aliphatic conjugated diene copolymer is not particularly limited, and a particulate polymer monomer composition containing the above-described monomer is, for example, a solution. It can be obtained by polymerization by a polymerization method, suspension polymerization method, bulk polymerization method, emulsion polymerization method or the like. As the polymerization reaction, addition polymerization such as ionic polymerization, radical polymerization, and living radical polymerization can be used. In addition, the additive and polymerization solvent contained in the monomer composition for particulate polymer used for the preparation of the conjugated diene polymer are not particularly limited, and known ones can be used.

[[Properties of particulate polymer]]
Here, the particulate polymer as the binder preferably has an electrolyte swelling degree of 140% by mass or more, preferably less than 800% by mass, and more preferably less than 500% by mass. When the degree of swelling of the electrolytic solution of the particulate polymer is 140% by mass or more, lithium ion conductivity is ensured, and the internal resistance of the lithium ion secondary battery can be further reduced. In addition, it is surmised that the SEI film generated during initial aging due to good lithium ion conductivity is the cause, but the storage stability of the lithium ion secondary battery can be improved. On the other hand, if the degree of swelling of the electrolyte solution of the particulate polymer is less than 800% by mass, the rigidity of the particulate polymer can be ensured particularly during a high-temperature cycle, and the swelling of the electrode can be sufficiently suppressed. The cycle characteristics of the battery can be improved.
In addition, the electrolyte solution swelling degree of the particulate polymer can be measured in the same manner as the method for measuring the electrolyte solution swelling degree of the “water-soluble polymer X” described in the examples of the present specification.
Further, for example, the degree of electrolyte solution swelling of the aromatic vinyl / aliphatic conjugated diene copolymer is determined depending on the kind and amount of the aromatic vinyl monomer in the particulate polymer monomer composition, It can adjust by changing the gel amount controlled by superposition | polymerization temperature.

The particulate polymer preferably has a gel content of 85% by mass or more, more preferably 88% by mass or more, further preferably 90% by mass or more, and 98% by mass or less. Preferably, it is 95 mass% or less, and it is still more preferable that it is 93 mass% or less. When the gel content of the particulate polymer Z is within the above-described range, the adhesion between the electrode mixture layer formed using the binder composition of the present invention and the current collector can be improved. In addition, the internal resistance of the lithium ion secondary battery can be further reduced, and the cycle characteristics and storage stability can be further improved.
The gel content of the particulate polymer can be measured by the method described in the examples of this specification. In addition, the gel content can be adjusted by changing the polymerization temperature, the type and amount of additives such as a molecular weight modifier, the conversion rate (monomer consumption) at the time of reaction termination, etc. If the amount of the molecular weight modifier to be reduced is reduced, the gel content can be increased, and if the amount of the molecular weight modifier used during polymerization is increased, the gel content can be reduced.

[[Blend polymer content]]
The blending amount of the particulate polymer is preferably 5 parts by mass or more, more preferably 20 parts by mass or more, still more preferably 50 parts by mass or more, per 100 parts by mass of the water-soluble polymer. It is particularly preferably at least part by mass, preferably at most 300 parts by mass, more preferably at most 200 parts by mass, and even more preferably at most 160 parts by mass. If the blending amount of the particulate polymer is 5 parts by mass or more per 100 parts by mass of the water-soluble polymer, the adhesion between the electrode mixture layer formed using the binder composition and the current collector is secured, and lithium ions The life characteristics of the secondary battery can be further improved. Moreover, if the blending amount of the particulate polymer is 300 parts by mass or less per 100 parts by mass of the water-soluble polymer, it is not difficult to prepare a slurry composition due to excessive thickening, and in addition, an electrode active material Without excessively reducing the liquid retention space, the particulate polymer is present in the vicinity of the water-soluble polymer X and the electrode active material, and the cycle characteristics and storage stability of the lithium ion secondary battery can be further improved. .

<Amotropic dispersant Y>
The amphoteric dispersant Y is a dispersant composed of a compound having both an acidic functional group and a basic functional group in its molecular structure, and can contribute to an improvement in dispersibility of the electrode active material in the slurry composition. It is. And as mentioned above, the amphoteric dispersant Y requires that the acid value and the amine value are within a specific range. In the present invention, the polymer corresponding to the water-soluble polymer X is not included in the amphoteric dispersant Y even if both of its acid value and amine value satisfy the above specific range, Included in coalescence X.
Here, the acid value of the amphoteric dispersant Y can be measured according to JIS K 0070: 1992. The amine value of the amphoteric dispersant Y represents the total amine value and can be measured according to ASTM D2074.

[Acid value]
The acid value of the amphoteric dispersant Y needs to be 1 mgKOH / g or more and less than 30 mgKOH / g, preferably 2 mgKOH / g or more, more preferably 3 mgKOH / g or more, and 20 mgKOH / g. Is preferably less than 10 mgKOH / g. When the acid value is less than 1 mgKOH / g, the binding ability of the amphoteric dispersant Y decreases, and the adhesion and cycle characteristics of the electrode mixture layer and the current collector decrease. On the other hand, when the acid value exceeds 30 mgKOH / g, the internal resistance increases, and the cycle characteristics and the storage stability decrease. Furthermore, when the acid value is more than 30 mg KOH / g, when a particulate polymer, particularly a conjugated diene polymer such as a styrene-butadiene polymer, is used, the slurry is excessively thickened and the productivity of the electrode is reduced. May decrease.

[Amine number]
The amine value of the amphoteric dispersant Y needs to be 1 mgKOH / g or more and less than 30 mgKOH / g, preferably 2 mgKOH / g or more, more preferably 3 mgKOH / g or more, and 20 mgKOH / g. Is preferably less than 10 mgKOH / g. When the amine value is less than 1 mgKOH / g, the binding ability of the amphoteric dispersant Y is lowered, and the adhesion and cycle characteristics of the electrode mixture layer and the current collector are lowered. On the other hand, when the amine value is more than 30 mgKOH / g, the internal resistance increases, and the cycle characteristics and storage stability decrease.

[Electrolytic solution solubility]
The amphoteric dispersant Y preferably has an electrolyte solubility of 5% or less, more preferably 1% or less. When the solubility of the electrolyte solution of the amphoteric dispersant Y is 5% or less, elution of the amphoteric dispersant Y into the electrolyte solution in the lithium ion secondary battery is suppressed, and cycle characteristics and life characteristics can be improved.
Here, the electrolyte solubility of the amphoteric dispersant Y can be measured by the method described in the examples of the present specification. Moreover, the electrolyte solution solubility of the amphoteric dispersant Y can be adjusted, for example, by adjusting the number of acidic functional groups and the number of basic functional groups per molecule constituting the amphoteric dispersant Y and the molecular weight. It can be adjusted by controlling the affinity.

[Weight average molecular weight]
The compound constituting the amphoteric dispersant Y is preferably a polymer. The weight average molecular weight of the polymer constituting the amphoteric dispersant Y is preferably 500 or more, more preferably 2,000 or more, still more preferably 3,000 or more, preferably 150,000 or less, more preferably 50. 1,000 or less. If the weight average molecular weight is within the above range, elution into the electrolyte is suppressed while ensuring the dispersibility of the amphoteric dispersant Y in the electrode active material, etc., and the cycle characteristics and storage stability of the lithium ion secondary battery Can be improved. The weight average molecular weight of the polymer constituting the amphoteric dispersant Y refers to a polystyrene-converted weight average molecular weight measured by gel permeation chromatography (developing solvent: tetrahydrofuran).

[Structure of amphoteric dispersant Y]
Examples of the acidic functional group possessed by the compound constituting the amphoteric dispersant Y include a carboxyl group, an acid anhydride group, a sulfonic acid group, a thiol group, a phosphoric acid group, an acidic phosphoric acid ester group, and a phosphonic acid group. Groups are preferred. The acidic phosphate group is a group in which a part of the hydroxyl group bonded to the phosphorus atom of the phosphate group is substituted with an alkoxy group. The alkoxy group is a lower alkoxy group having 1 to 8 carbon atoms. Preferably mentioned. These acidic functional groups may be neutralized with known basic compounds and may be salified. Moreover, the compound which comprises the amphoteric dispersant Y may have one acidic functional group in one molecule, and may have two or more acidic functional groups. Further, when the compound constituting the amphoteric dispersant Y has two or more acidic functional groups, the two or more acidic functional groups may be composed of only one kind, or may be composed of a plurality of kinds. Good.

The basic functional group possessed by the compound constituting the amphoteric dispersant Y includes amino groups (primary amino groups, secondary amino groups, tertiary amino groups), imino groups, ammonium bases (tertiary ammonium bases). , A quaternary ammonium base), a heterocyclic group having a basic nitrogen atom such as an imidazole group, and the like, and an amino group is preferable. These basic functional groups may be neutralized by known acidic compounds and may be salified. Further, the compound constituting the amphoteric dispersant Y may have one basic functional group in one molecule, or may have two or more basic functional groups. Furthermore, when the compound constituting the amphoteric dispersant Y has two or more basic functional groups, the two or more basic functional groups may be composed of only one kind or composed of a plurality of kinds. May be.
In the compound constituting the amphoteric dispersant Y, the position where the acidic functional group and the basic functional group are located is not particularly limited. For example, when the compound is a polymer, the acidic functional group and the basic functional group are , Each may be located on the main chain of the polymer, or may be located on the side chain.

[Production method and specific examples of amphoteric dispersant Y]
The production method of the amphoteric dispersant Y is not particularly limited. For example, a polymer as a compound constituting the amphoteric dispersant Y is a known method using a monomer containing an acidic functional group or a monomer containing a basic functional group. It can be produced by copolymerization or by introducing the acidic functional group or basic functional group into the polymer after polymerization by a modification reaction or the like.

As the amphoteric dispersant Y, a commercially available product can also be used. Examples of commercially available products that can be used include DISPERBYK (registered trademark) -191 (acid value: 30 mgKOH / g, amine value: 20 mgKOH / g), DISPERBYK-2001 (acid value: 19 mgKOH / g, amine value: 29 mgKOH / g), DISPERBYK-2010 (acid value: 20 mgKOH / g, amine value: 20 mgKOH / g), DISPERBYK-2012 (acid value 7 mgKOH / g, amine value 7 mgKOH / g), etc. (Registered Trademark) -U (acid value: 24 mgKOH / g, amine value: 19 mgKOH / g) and other ANTI-TERRA series products (manufactured by Big Chemie), Disparon (registered trademark) DA-234 (acid value: 16 mgKOH / g) , Amine value: 20 mgKOH / g), disparon DA-325 (acid value: 14 mgKOH / g, amine value: 20 mgKOH / g), etc. (Manufactured by Enomoto Kasei Co., Ltd.), Azisper (registered trademark) PB-821 (acid value: 17 mg KOH / g, amine value: 10 mg KOH / g), Azisper PB-822 (acid value: 14 mg KOH / g, amine value: 17 mg KOH / g) ), Azisper PB-881 (acid value: 17 mgKOH / g, amine value: 17 mgKOH / g) and the like Azisper series products (manufactured by Ajinomoto Fine Techno Co., Ltd.).
In addition, as an amphoteric dispersing agent Y, what mixed 2 or more types of dispersing agents can also be used. For such mixing, it is possible to use a commercially available dispersant exhibiting a predetermined acid value and amine value alone as exemplified above, and does not exhibit a predetermined acid value and / or a predetermined amine value. Commercially available dispersants can also be used. Here, as a commercially available dispersant that does not exhibit a predetermined acid value and / or a predetermined amine value, DISPERBYK-187 (acid value: 35 mgKOH / g, amine value: 35 mgKOH / g), DISPERBYK-2020 (acid value: 37 mgg KOH / g, amine value: 36 mg KOH / g), DISPERBYK-2025 (acid value: 38 mg KOH / g, amine value: 37 mg KOH / g), DISPERBYK-198 (acid value 0 mg KOH / g, amine value: 4 mg KOH / g), and DISPERBYK-199 (acid value: 1.5 mgKOH / g, amine value: 0 mgKOH / g) and the like (all are manufactured by BYK Chemie). Examples of the amphoteric dispersant Y obtained by mixing two or more dispersants include DISPERBYK-198 (acid value 0 mgKOH / g, amine value: 4 mgKOH / g) and DISPERBYK-199 (acid value: 1.5 mgKOH). / G, amine value: 0 mg KOH / g).

[Amount of amphoteric dispersant Y]
The compounding amount of the amphoteric dispersant Y needs to be 0.001 part by mass or more and 10 parts by mass or less per 100 parts by mass of the water-soluble polymer X, preferably 0.01 parts by mass or more, It is more preferably at least part by mass, more preferably at most 5 parts by mass, and even more preferably at most 3 parts by mass. When the blending amount of the amphoteric dispersant Y is less than 0.001 part by mass per 100 parts by mass of the water-soluble polymer X, the dispersibility of the electrode active material in the slurry composition is lowered, and the binding force between the active materials is ensured. The electrode physical properties such as adhesion between the electrode mixture layer and the current collector are deteriorated. As a result, the swelling of the electrode cannot be suppressed, the cycle characteristics are lowered, and the internal resistance is increased and the storage stability is decreased. In addition, it becomes difficult to ensure the productivity of the electrodes. On the other hand, when the compounding amount of the amphoteric dispersant Y exceeds 10 parts by mass per 100 parts by mass of the water-soluble polymer X, the internal resistance increases. In addition, the swelling of the electrode cannot be sufficiently suppressed, and the adhesion between the electrode mixture layer and the current collector cannot be ensured, resulting in a decrease in cycle characteristics and storage stability.

<Solvent>
As the solvent of the binder composition of the present invention, a known solvent that can dissolve or disperse the binder described above can be used. Among these, water is preferably used as the solvent. In addition, at least part of the solvent of the binder composition is not particularly limited, and a binder other than the water-soluble polymer X, the amphoteric dispersant Y, and the water-soluble polymer X added as necessary is prepared. The polymerization solvent contained in the monomer composition used in the process can be used.

<Other ingredients>
In addition to the components described above, the binder composition of the present invention may contain known components that can be optionally blended. Such known ingredients include thickeners, such as carboxymethylcellulose, thickening polysaccharides, alginic acid, starch and other natural thickeners, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid. Or a synthetic thickener (excluding those corresponding to the water-soluble polymer X). Among these, carboxymethyl cellulose and polyacrylic acid are preferable from the viewpoint of imparting thixotropy to the slurry composition and enhancing the stability of the slurry composition.

  In addition, when manufacturing a slurry composition, an electrode, and a lithium ion secondary battery using the other components described above, the other components are previously mixed with the water-soluble polymer X and the amphoteric dispersant Y to form a binder composition. May be used for the preparation of the slurry composition, or without being mixed in advance with the binder composition containing the water-soluble polymer X and the amphoteric dispersant Y, and at the time of preparation of the slurry composition, You may mix with the binder composition containing the conductive polymer X and the amphoteric dispersant Y.

<Preparation of binder composition>
The binder composition of this invention can be prepared by mixing said each component. Specifically, the binder composition is obtained by mixing the above components using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a grinder, an ultrasonic disperser, a homogenizer, a planetary mixer, a fill mix, etc. Product can be prepared.
In addition, when the water-soluble polymer X is prepared by polymerizing a monomer composition in an aqueous solvent, it can be mixed as it is in an aqueous solution to prepare a binder composition containing water as a solvent. .
Further, for example, after mixing the water-soluble polymer X and the electrode active material, the preparation of the binder composition and the preparation of the slurry composition described later may be performed simultaneously, such as adding the amphoteric dispersant Y.

(Slurry composition for lithium ion secondary battery electrode)
The slurry composition for a lithium ion secondary battery electrode of the present invention includes the above-described binder composition for a lithium ion secondary battery electrode of the present invention and an electrode active material. And if an electrode is produced using the slurry composition of this invention, the internal resistance of a lithium ion secondary battery provided with the said electrode will be reduced, and the lifetime characteristic (cycle characteristic and storage stability) shall be excellent. can do.
And especially the slurry composition for lithium ion secondary battery electrodes of this invention can be used conveniently as a slurry composition for lithium ion secondary battery negative electrodes.

(Slurry composition for negative electrode of lithium ion secondary battery)
Therefore, in the following, first, the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention that can be prepared using the binder composition of the present invention will be described.

  Here, the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention contains the binder composition described above, a negative electrode active material, and a dispersion medium such as water and other components added as necessary. . That is, the slurry composition for a lithium ion secondary battery negative electrode includes the above-described water-soluble polymer X, 0.001 part by mass or more and 10 parts by mass or less amphoteric dispersant Y per 100 parts by mass of water-soluble polymer X, and the negative electrode active material. It contains at least a substance and a dispersion medium such as water, and optionally further contains other components such as a particulate polymer and a thickener.

<Negative electrode active material>
Here, as the negative electrode active material of the lithium ion secondary battery, a material that can occlude and release lithium is usually used. Examples of the material that can occlude and release lithium include a carbon-based negative electrode active material, a non-carbon-based negative electrode active material, and an active material that combines these materials.

[Carbon-based negative electrode active material]
Here, the carbon-based negative electrode active material refers to an active material having carbon as a main skeleton capable of inserting lithium (also referred to as “dope”). Examples of the carbon-based negative electrode active material include carbonaceous materials and graphite. Quality materials.

The carbonaceous material is a material having a low graphitization degree (ie, low crystallinity) obtained by carbonizing a carbon precursor by heat treatment at 2000 ° C. or lower. In addition, although the minimum of the heat processing temperature at the time of carbonizing is not specifically limited, For example, it can be 500 degreeC or more.
Examples of the carbonaceous material include graphitizable carbon that easily changes the carbon structure depending on the heat treatment temperature, and non-graphitic carbon having a structure close to an amorphous structure typified by glassy carbon. .
Here, as the graphitizable carbon, for example, a carbon material using tar pitch obtained from petroleum or coal as a raw material can be mentioned. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch carbon fibers, pyrolytic vapor grown carbon fibers, and the like.
In addition, examples of the non-graphitizable carbon include a phenol resin fired body, polyacrylonitrile-based carbon fiber, pseudo-isotropic carbon, furfuryl alcohol resin fired body (PFA), and hard carbon.

The graphite material is a material having high crystallinity close to that of graphite obtained by heat-treating graphitizable carbon at 2000 ° C. or higher. In addition, although the upper limit of heat processing temperature is not specifically limited, For example, it can be 5000 degrees C or less.
Examples of the graphite material include natural graphite and artificial graphite.
Here, as the artificial graphite, for example, artificial graphite obtained by heat-treating carbon containing graphitizable carbon mainly at 2800 ° C. or higher, graphitized MCMB heat-treated at 2000 ° C. or higher, and mesophase pitch-based carbon fiber at 2000 ° C. Examples thereof include graphitized mesophase pitch-based carbon fibers that have been heat-treated.
In the present invention, as the carbon-based negative electrode active material, natural graphite (amorphous coated natural graphite) whose surface is at least partially coated with amorphous carbon may be used.

[Non-carbon negative electrode active material]
The non-carbon-based negative electrode active material is an active material excluding a carbon-based negative electrode active material made of only a carbonaceous material or a graphite material, and examples of the non-carbon-based negative electrode active material include a metal-based negative electrode active material. .

  The metal-based negative electrode active material is an active material containing a metal, and usually contains an element capable of inserting lithium in the structure, and the theoretical electric capacity per unit mass when lithium is inserted is 500 mAh / g or more. Is an active material. As the metal-based negative electrode active material, for example, lithium metal, a single metal capable of forming a lithium alloy (for example, Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.) and alloys thereof, and oxides, sulfides, nitrides, silicides, carbides, phosphides, and the like thereof are used.

  Among metal-based negative electrode active materials, an active material containing silicon (silicon-based negative electrode active material) is preferable. This is because the capacity of the lithium ion secondary battery can be increased by using the silicon-based negative electrode active material.

Examples of silicon-based negative electrode active materials include silicon (Si), alloys containing silicon, SiO, SiO _x , and a composite of a Si-containing material obtained by coating or combining a Si-containing material with conductive carbon and conductive carbon. Etc. In addition, these silicon type negative electrode active materials may be used individually by 1 type, and may be used in combination of 2 types.

Examples of the alloy containing silicon include an alloy composition containing silicon and at least one element selected from the group consisting of titanium, iron, cobalt, nickel, and copper.
Examples of the alloy containing silicon include an alloy composition containing silicon, aluminum, and a transition metal such as iron, and further containing a rare earth element such as tin and yttrium.

SiO _x is a compound containing at least one of SiO and SiO ₂ and Si, and x is usually 0.01 or more and less than 2. Then, SiO _x, for example, can be formed by using a disproportionation reaction of silicon monoxide (SiO). Specifically, SiO _x can be prepared by heat-treating SiO, optionally in the presence of a polymer such as polyvinyl alcohol, to produce silicon and silicon dioxide. The heat treatment can be performed at a temperature of 900 ° C. or higher, preferably 1000 ° C. or higher, in an atmosphere containing an organic gas and / or vapor after grinding and mixing SiO and optionally a polymer.

  As a composite of Si-containing material and conductive carbon, for example, a pulverized mixture of SiO, a polymer such as polyvinyl alcohol, and optionally a carbon material is heat-treated in an atmosphere containing, for example, an organic gas and / or steam. Can be mentioned. In addition, the composite material is a method in which the surface of SiO particles is coated by a chemical vapor deposition method using an organic gas, etc., and SiO particles and graphite or artificial graphite are formed into composite particles (granulated by a mechanochemical method). ) Can also be obtained by a known method such as a method.

From the viewpoint of increasing the capacity of the lithium ion secondary battery, the silicon-based negative electrode active material is preferably an alloy containing silicon and SiO _x .

<Dispersion medium>
The dispersion medium for the slurry composition for a lithium ion secondary battery negative electrode is not particularly limited, and a known dispersion medium can be used. Among these, water is preferably used as the dispersion medium. In addition, at least one part of the dispersion medium of a slurry composition can be made into the solvent which the binder composition used for preparation of a slurry composition contained, without being specifically limited.

<Other ingredients>
In addition to the above components and the components described above in the section of “Binder composition for lithium ion secondary battery electrodes”, the slurry composition for a lithium ion secondary battery negative electrode includes a conductive material, a reinforcing material, a leveling agent, and an electrolytic solution added. You may contain components, such as an agent. These are not particularly limited as long as they do not affect the battery reaction, and known ones such as those described in International Publication No. 2012/115096 can be used. These components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

(Method for preparing slurry composition for negative electrode of lithium ion secondary battery)
The said slurry composition for lithium ion secondary battery negative electrodes can be prepared by disperse | distributing said each component to a dispersion medium. Specifically, the above components and the dispersion medium are mixed using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crushed crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, a fill mix, etc. Thus, a slurry composition can be prepared.
Here, water is usually used as the dispersion medium, but an aqueous solution of an arbitrary compound or a mixed solution of a small amount of an organic medium and water may be used.

Here, from the viewpoint of securing the performance of the lithium ion secondary battery while enhancing the stability of the slurry composition and the productivity of the negative electrode, the content of the water-soluble polymer X in the slurry composition is determined by the negative electrode active material 100. It is preferably 0.5 parts by mass or more per part by mass, more preferably 0.7 parts by mass or more, preferably 10 parts by mass or less, and more preferably 1.8 parts by mass or less. preferable.
Further, in the slurry composition, the range of the essential amount and the preferable amount of the amphoteric dispersant Y relative to the blending amount of the water-soluble polymer X, and the suitable amount of the particulate polymer relative to the blending amount of the water-soluble polymer X. The range is the same as the range in the binder composition of the present invention.
Furthermore, when a slurry composition contains a thickener, it is preferable that content of the thickener in a slurry composition is 0.1 to 5 mass parts with respect to 100 mass parts of negative electrode active materials. By making the compounding quantity of a thickener into the above-mentioned range, the thixotropy and stability of a slurry composition are securable.

(Slurry composition for positive electrode of lithium ion secondary battery)
Next, the slurry composition for lithium ion secondary battery positive electrodes which can be prepared using the binder composition of this invention is demonstrated.

The slurry composition for a lithium ion secondary battery positive electrode of the present invention includes the binder composition described above, a positive electrode active material, a dispersion medium such as water added as necessary, a conductive material, and other agents such as a thickener. Containing ingredients. That is, the slurry composition for a lithium ion secondary battery positive electrode includes the above-described water-soluble polymer X, 0.001 part by mass or more and 10 parts by mass or less of amphoteric dispersant Y per 100 parts by mass of water-soluble polymer X, and positive electrode active material. It contains at least a substance and a dispersion medium such as water, and optionally further contains other components such as a particulate polymer, a conductive material and a thickener. Here, the slurry composition for a lithium ion secondary battery positive electrode of the present invention preferably contains carboxymethyl cellulose as a thickener.
In addition, since the same thing as the slurry composition for lithium ion secondary battery negative electrodes mentioned above can be used as a dispersion medium and other components of the slurry composition for lithium ion secondary battery positive electrodes, it demonstrates below. Omitted.

<Positive electrode active material>
As the positive electrode active material, a compound containing a transition metal, for example, a transition metal oxide, a transition metal sulfide, a composite metal oxide of lithium and a transition metal, or the like can be used. In addition, as a transition metal, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo etc. are mentioned, for example.

Here, as the transition metal oxide, for example, MnO, MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , Cu ₂ V ₂ O ₃ , amorphous V ₂ O—P ₂ O ₅ , amorphous Examples include MoO ₃ , amorphous V ₂ O ₅ , and amorphous V ₆ O ₁₃ .
Examples of the transition metal sulfide include TiS ₂ , TiS ₃ , amorphous MoS ₂ , and FeS.
Examples of the composite metal oxide of lithium and transition metal include a lithium-containing composite metal oxide having a layered structure, a lithium-containing composite metal oxide having a spinel structure, and a lithium-containing composite metal oxide having an olivine structure. It is done.

Examples of the lithium-containing composite metal oxide having a layered structure include lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing nickel oxide (LiNiO ₂ ), and Co—Ni—Mn lithium-containing composite oxide (Li (Co Mn Ni) O ₂ ), Ni—Mn—Al lithium-containing composite oxide, Ni—Co—Al lithium-containing composite oxide, solid solution of LiMaO ₂ and Li ₂ MbO _3, and the like. Note that examples of the lithium-containing composite oxide of Co—Ni—Mn include Li [Ni _0.5 Co _0.2 Mn _0.3 ] O ₂ and Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ . Examples of the solid solution of LiMaO ₂ and Li ₂ MbO ₃ include xLiMaO _2. (1-x) Li ₂ MbO ₃ . Here, x represents a number satisfying 0 <x <1, Ma represents one or more transition metals having an average oxidation state of 3+, and Mb represents one or more transition metals having an average oxidation state of 4+. Represent. Examples of such a solid solution include Li [Ni _0.17 Li _0.2 Co _0.07 Mn _0.56 ] O ₂ .
In this specification, the “average oxidation state” indicates an average oxidation state of the “one or more transition metals”, and is calculated from the molar amount and valence of the transition metal. For example, when “one or more transition metals” is composed of 50 mol% Ni ²⁺ and 50 mol% Mn ⁴⁺ , the average oxidation state of “one or more transition metals” is (0. 5) × (2 +) + (0.5) × (4 +) = 3+

Examples of lithium-containing composite metal oxides having a spinel structure include lithium manganate (LiMn ₂ O ₄ ) and compounds in which part of Mn of lithium manganate (LiMn ₂ O ₄ ) is substituted with another transition metal Is mentioned. Specific examples include _{Li s [Mn 2-t Mc} t] O 4 , such as LiNi _0.5 Mn _1.5 O _4. Here, Mc represents one or more transition metals having an average oxidation state of 4+. Specific examples of Mc include Ni, Co, Fe, Cu, and Cr. T represents a number satisfying 0 <t <1, and s represents a number satisfying 0 ≦ s ≦ 1. As the positive electrode active material, a lithium-excess spinel compound represented by Li _{1 + x} Mn _2−x O ₄ (0 <X <2) can also be used.

Examples of the lithium-containing composite metal oxide having an olivine type structure include olivine type phosphorus represented by Li _y MdPO ₄ such as olivine type lithium iron phosphate (LiFePO ₄ ) and olivine type lithium manganese phosphate (LiMnPO ₄ ). An acid lithium compound is mentioned. Here, Md represents one or more transition metals having an average oxidation state of 3+, and examples thereof include Mn, Fe, and Co. Y represents a number satisfying 0 ≦ y ≦ 2. Furthermore, in the olivine-type lithium phosphate compound represented by Li _y MdPO ₄ , Md may be partially substituted with another metal. Examples of the metal that can be substituted include Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, and Mo.

<Method for preparing slurry composition for positive electrode of lithium ion secondary battery>
The said slurry composition for lithium ion secondary battery positive electrodes can be prepared by disperse | distributing said each component to a dispersion medium similarly to the slurry composition for lithium ion secondary battery negative electrodes. In addition, the ratio of each said component in the slurry composition for positive electrodes can be adjusted suitably.

(Electrode for lithium ion secondary battery)
The electrode for lithium ion secondary batteries of this invention has the electrode compound-material layer obtained using the slurry composition of this invention. More specifically, the electrode for a lithium ion secondary battery of the present invention includes a current collector and an electrode mixture layer formed on the current collector, and the electrode mixture layer includes at least an electrode active layer. A water-soluble polymer X as a substance and a binder, and 0.001 part by mass or more and 10 parts by mass or less of an amphoteric dispersant Y per 100 parts by mass of the water-soluble polymer X are contained. In addition, each component contained in the electrode mixture layer was contained in the above-mentioned slurry composition for lithium ion secondary battery electrodes, and a suitable abundance ratio of each of these components is the electrode slurry. It is the same as the preferred abundance ratio of each component in the composition.
And since the said electrode for lithium ion secondary batteries is prepared using the binder composition for lithium ion secondary battery electrodes of this invention, while reducing the internal resistance of a lithium ion secondary battery, lifetime characteristic (Cycle characteristics and storage stability) can be improved.

<Manufacture of electrodes for lithium ion secondary batteries>
The lithium ion secondary battery electrode includes, for example, a step of applying the above-described slurry composition for a lithium ion secondary battery electrode on a current collector (application step), and a lithium applied on the current collector. The slurry composition for an ion secondary battery electrode is dried to produce an electrode mixture layer on the current collector (drying step).

[Coating process]
The method for coating the lithium ion secondary battery electrode slurry composition on the current collector is not particularly limited, and a known method can be used. Specifically, as a coating method, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, or the like can be used. At this time, the slurry composition may be applied to only one side of the current collector or may be applied to both sides. The thickness of the slurry film on the current collector after application and before drying can be appropriately set according to the thickness of the electrode mixture layer obtained by drying.

  Here, as the current collector to which the slurry composition is applied, an electrically conductive and electrochemically durable material 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 these, a copper foil is particularly preferable as the current collector used for the negative electrode. The current collector used for the positive electrode is particularly preferably an aluminum foil. In addition, the said material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

[Drying process]
A method for drying the slurry composition on the current collector is not particularly limited, and a known method can be used. For example, drying with warm air, hot air, low-humidity air, vacuum drying, irradiation with infrared rays, electron beams, or the like. A drying method is mentioned. Thus, by drying the slurry composition on the current collector, an electrode mixture layer is formed on the current collector, and a lithium ion secondary battery electrode including the current collector and the electrode mixture layer is obtained. be able to.

Note that after the drying step, the electrode mixture layer may be subjected to pressure treatment using a die press or a roll press. By the pressure treatment, the adhesion between the electrode mixture layer and the current collector can be improved.
Furthermore, when the electrode mixture layer includes a curable polymer, it is preferable to cure the polymer after the electrode mixture layer is formed.

(Lithium ion secondary battery)
The lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolytic solution, and a separator. For example, the lithium ion secondary battery electrode (negative electrode) of the present invention is used as the negative electrode. And since the said lithium ion secondary battery uses the negative electrode for lithium ion secondary batteries of this invention, internal resistance is reduced and it is excellent in a lifetime characteristic (cycle characteristic and storage stability).
In the following, a lithium ion secondary battery using the above negative electrode for a lithium ion secondary battery will be described. However, as a lithium ion secondary battery that can be produced using the binder composition of the present invention, only the positive electrode of the present invention is used. Examples include a lithium ion secondary battery that is a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery in which both the positive electrode and the negative electrode are electrodes for the lithium ion secondary battery of the present invention.

<Positive electrode>
As the positive electrode of the lithium ion secondary battery, a known positive electrode used as a positive electrode for a lithium ion secondary battery can be used. Specifically, as the positive electrode, for example, a positive electrode formed by forming a positive electrode mixture layer on a current collector can be used.
As the current collector, one made of a metal material such as aluminum can be used. As the positive electrode mixture layer, a layer containing a known positive electrode active material, a conductive material, and a binder can be used.

<Electrolyte>
As the electrolytic solution, an electrolytic solution in which an electrolyte is dissolved in a solvent can be used.
Here, as the solvent, an organic solvent capable of dissolving the electrolyte can be used. Specifically, examples of the solvent include alkyl carbonate solvents such as ethylene carbonate, propylene carbonate, and γ-butyrolactone, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, methyl acetate, and dimethoxyethane. , Dioxolane, methyl propionate, methyl formate and the like can be used.
A lithium salt can be used as the electrolyte. As lithium salt, the thing as described in Unexamined-Japanese-Patent No. 2012-204303 can be used, for example. Among these lithium salts, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li are preferable as the electrolyte because they are easily dissolved in an organic solvent and exhibit a high degree of dissociation.

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

<Method for producing lithium ion secondary battery>
In the lithium ion secondary battery, for example, a positive electrode and a negative electrode are overlapped via a separator, and this is wound into a battery container according to the shape of the battery as necessary. It can be manufactured by injecting and sealing the liquid. In order to prevent an increase in pressure inside the lithium ion secondary battery, overcharge / discharge, etc., an overcurrent prevention element such as a fuse or a PTC element, an expanded metal, a lead plate, etc. may be provided as necessary. . The shape of the lithium ion secondary battery may be any of, for example, a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples. In the following description, “%” and “part” representing amounts are based on mass unless otherwise specified.
In Examples and Comparative Examples, electrolyte swelling degree of water-soluble polymer X, glass transition temperature and gel content of particulate polymer, electrolyte solubility of dispersant (including amphoteric dispersant Y), electrode productivity The adhesion between the negative electrode composite material layer and the current collector, the rate characteristics of the lithium ion secondary battery, the cycle characteristics, the swelling of the negative electrode after the cycle, and the storage stability were evaluated using the following methods, respectively.

<Electrolytic solution swelling>
An aqueous solution containing the water-soluble polymer X was dried in an environment of 50% humidity and a temperature of 23 to 25 ° C. to form a film having a thickness of 1 ± 0.3 mm. The film formed was dried with a vacuum dryer at a temperature of 60 ° C. for 10 hours, then cut and weighed approximately 1 g. The mass of the obtained film piece is defined as W0. The film piece was subjected to an electrolyte solution (composition: LiPF ₆ solution having a concentration of 1.0 M (solvent: ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3/7 (volume ratio)) in an environment at a temperature of 60 ° C. The mixture was immersed for 3 days in a mixed solvent and 2% by volume of vinylene carbonate (solvent ratio) as an additive)) and swollen. Thereafter, the film piece was pulled up and the surface electrolyte was wiped with Kimwipe, and then the mass was measured. Let the mass of the film piece after swelling be W1.
And electrolyte solution swelling degree was computed using the following formulas.
Electrolyte swelling degree (mass%) = W1 / W0 × 100
<Glass transition temperature>
The aqueous dispersion containing the particulate polymer was dried for 3 days in an environment of 50% humidity and a temperature of 23 to 26 ° C. to form a film having a thickness of 1 ± 0.3 mm. The formed film was dried with a vacuum dryer at a temperature of 60 ° C. for 10 hours. Then, using the dried film as a sample, in accordance with JIS K7121, a differential scanning calorimeter (DSC6220SII, manufactured by Nanotechnology Co., Ltd.) under a measurement temperature of −100 ° C. to 180 ° C. and a heating rate of 5 ° C./min. Was used to measure the glass transition temperature Tg (° C.).
<Gel content>
The aqueous dispersion containing the particulate polymer was dried in an environment of 50% humidity and a temperature of 23 to 25 ° C. to form a film having a thickness of 1 ± 0.3 mm. The formed film was dried with a vacuum dryer at a temperature of 60 ° C. for 10 hours. Thereafter, the dried film was cut into 3 to 5 mm square, and about 1 g was precisely weighed. The mass of the film piece obtained by cutting is defined as w0. This film piece was immersed in 50 g of tetrahydrofuran (THF) for 24 hours. Then, the film piece pulled up from THF was vacuum-dried at 105 degreeC for 3 hours, and the mass w1 of insoluble matter was measured.
And gel content was computed using the following formulas.
Gel content (mass%) = (w1 / w0) × 100
<Solubility of electrolyte>
About 1 g of the dispersant was placed on a 100 mesh SUS wire mesh (measured in advance) (applied to the wire mesh if the dispersant is in the form of a viscous liquid) and vacuum dried at 105 ° C. for 3 hours, The total mass of the dispersant and the wire mesh was measured, and the mass Y0 of the dispersant before immersion in the electrolyte was calculated.
Thereafter, the above-described wire net with the dispersant attached thereto was mixed with 50 g of an electrolytic solution (composition: LiPF ₆ solution having a concentration of 1.0 M (solvent is EC / EMC) = 3/7 (volume ratio)), and vinylene carbonate as an additive. 2 vol% (solvent ratio) was added))) and immersed in an environment at a temperature of 57 to 63 ° C. for 72 hours. Thereafter, the wire mesh was pulled up, the total mass of the dispersant and the wire mesh was measured, and the mass Y1 after immersion of the dispersant in the electrolyte was calculated.
And electrolyte solution solubility was computed using the following formulas.
Electrolytic solution solubility (% by mass) = {(Y0−Y1) / Y0} × 100
The larger the value of the obtained electrolyte solution solubility, the easier the dispersant is dissolved in the electrolyte solution. For example, when the dispersant is completely dissolved in the electrolyte solution, the electrolyte solution solubility is 100% by mass, which is completely dissolved. If not, it is 0% by mass.
<Electrode productivity>
The solid content concentration of the slurry composition prepared so that the viscosity was 3000 ± 300 mPa · s (B-type viscometer, measured at 60 rpm) was evaluated according to the following criteria. The higher the solid content concentration of the slurry composition, the easier the drying of the slurry composition and the higher the productivity.
A: Solid content concentration of 48% by mass or more B: Solid content concentration of 45% by mass or more and less than 48% by mass C: Solid content concentration of less than 45% by mass <Adhesiveness between negative electrode composite material layer and current collector>
The produced negative electrode for a lithium ion secondary battery was cut into a rectangle having a length of 100 mm and a width of 10 mm to obtain a test piece, and a cellophane tape (specified in JIS Z1522) was formed on the surface of the negative electrode mixture layer with the surface having the negative electrode mixture layer facing down. The stress was measured when one end of the current collector was pulled in the vertical direction at a pulling speed of 50 mm / min and peeled off (the cellophane tape was fixed to the test stand). The measurement was performed 3 times, the average value was calculated | required, this was made into peeling peel strength, and the following references | standards evaluated. It shows that it is excellent in the adhesiveness of a negative mix layer and a collector, so that the value of peeling peel strength is large.
A: Peeling peel strength is 3.0 N / m or more B: Peeling peel strength is 2.5 N / m or more and less than 3.0 N / m C: Peeling peel strength is 1.5 N / m or more and less than 2.5 N / m D: Peeling peel strength less than 1.5 N / m <Rate characteristics of lithium ion secondary battery>
The prepared lithium ion secondary battery was allowed to stand at 25 ° C. for 5 hours after electrolyte injection. Next, the cell voltage was charged to 3.65 V by a constant current method at a temperature of 25 ° C. and 0.2 C, and then an aging treatment was performed at a temperature of 60 ° C. for 12 hours. And it discharged to cell voltage 3.00V by the constant current method of temperature 25 degreeC and 0.2C. Then, CC-CV charge (upper limit cell voltage 4.40V) was performed at a constant current of 0.2C, and CC discharge was performed to 3.00V at a constant current of 0.2C.
Next, a constant current charge / discharge of 0.5 C was performed between 4.40 and 3.00 V in an environment at a temperature of 25 ° C., and the discharge capacity at this time was defined as C0. Then, CC-CV charge was similarly performed at a constant current of 0.5 C and discharge was performed at a constant current of 0.5 C under an environment of a temperature of −20 ° C., and the discharge capacity at this time was defined as C1. Then, as a rate characteristic, a capacity change rate represented by ΔC = (C1 / C0) × 100 (%) was obtained and evaluated according to the following criteria. The larger the value of the capacity change rate ΔC, the higher the discharge capacity at a high current and the lower the internal resistance.
A: ΔC is 40% or more B: ΔC is 38% or more and less than 40% C: ΔC is 35% or more and less than 38% D: ΔC is less than 35% <Cycle characteristics of lithium ion secondary battery>
The prepared lithium ion secondary battery was allowed to stand at a temperature of 25 ° C. for 5 hours after electrolyte injection. Next, the cell voltage was charged to 3.65 V by a constant current method at a temperature of 25 ° C. and 0.2 C, and then an aging treatment was performed at a temperature of 60 ° C. for 12 hours. And it discharged to cell voltage 3.00V by the constant current method of temperature 25 degreeC and 0.2C. Then, CC-CV charge (upper limit cell voltage 4.40V) was performed by the constant current method of 0.2C, and CC discharge was performed to 3.00V by the constant current method of 0.2C.
Then, 100 cycles of charge / discharge operations were performed at a cell voltage of 4.40 to 3.00 V and a charge / discharge rate of 1.0 C in an environment at a temperature of 25 ° C. And the capacity | capacitance of the 1st cycle, ie, the initial stage discharge capacity X1, and the discharge capacity X2 of the 100th cycle are measured, and the capacity | capacitance change rate shown by (DELTA) C '= (X2 / X1) x100 (%) is calculated | required, It was evaluated according to the criteria. The larger the value of the capacity change rate ΔC ′, the better the cycle characteristics.
A: ΔC ′ is 88% or more B: ΔC ′ is 85% or more and less than 88% C: ΔC ′ is 83% or more and less than 85% D: ΔC ′ is less than 83% <bulge of negative electrode after cycle>
The lithium ion secondary battery after the cycle test described above was discharged to a cell voltage of 3.00 V at a constant current of 25 ° C. and 0.2 C, and then charged to CC-CV at a constant current of 1.0 C (upper limit) A cell voltage of 4.30 V) was carried out. The lithium ion secondary battery was disassembled, the negative electrode was taken out, and the thickness T1 of the negative electrode mixture layer was measured with a thickness gauge. The thickness of the negative electrode mixture layer before production of the lithium ion secondary battery was T0, and the thickness change rate represented by ΔT = {(T1−T0) / T0)} × 100 (%) was determined and evaluated according to the following criteria. . The rate of change of the thickness of the negative electrode represented by ΔT is due to the contribution of the increase in thickness due to the collapse of the electrode plate structure during the cycle, the increase in thickness due to precipitation of Li, etc. on the negative electrode surface, and the smaller the negative electrode after the cycle Indicates that is not inflated.
A: ΔT is less than 20% B: ΔT is not less than 20% and less than 25% C: ΔT is not less than 25% and less than 30% D: ΔT is not less than 30% <Storage stability of lithium ion secondary battery>
The prepared lithium ion secondary battery was allowed to stand at a temperature of 25 ° C. for 5 hours after electrolyte injection. Next, the cell voltage was charged to 3.65 V by a constant current method at a temperature of 25 ° C. and 0.2 C, and then an aging treatment was performed at a temperature of 60 ° C. for 12 hours. And it discharged to cell voltage 3.00V by the constant current method of temperature 25 degreeC and 0.2C. Then, CC-CV charge (upper limit cell voltage 4.30V) was performed by the constant current method of 0.2C, and CC discharge was performed to cell voltage 3.00V by the constant current method of 0.2C.
Next, the cell volume (V0) of the lithium ion secondary battery was calculated by the Archimedes method. Thereafter, the cell voltage was charged to 4.40 V by a constant current method at a temperature of 25 ° C. and 0.2 C, and left for 3 days under the condition of a temperature of 80 ± 2 ° C. Then, a constant current method at a temperature of 25 ° C. and 0.2 C The cell voltage was discharged to 3.00V. Then, the volume (V1) of the cell was measured, the amount of gas generation was calculated by the following calculation formula, and evaluated according to the following criteria. The smaller the amount of gas generated, the better the storage stability (high temperature storage characteristics).
Gas generation amount (mL) = V1 (mL) −V0 (mL)
A: Gas generation amount is less than 2 mL B: Gas generation amount is 2 mL or more and less than 3 mL C: Gas generation amount is 3 mL or more and less than 4 mL D: Gas generation amount is 4 mL or more

Example 1
<Preparation of aqueous solution containing water-soluble polymer X1>
720 g of ion-exchanged water was charged into a 1 L flask with a septum, heated to a temperature of 40 ° C., and the inside of the flask was replaced with nitrogen gas at a flow rate of 100 mL / min. Next, 10 g of ion-exchanged water, 9.5 g (25.0%) of acrylic acid as the compound (A), 28.5 g (75.0%) of acrylamide as the compound (B), and ion-exchanged water ( 10 g) was mixed and injected into the flask with a syringe. Thereafter, 8.0 g of a 2.5% aqueous solution of potassium persulfate as a polymerization initiator was added to the flask with a syringe. Further, 15 minutes later, 40 g of a 2.0% aqueous solution of tetramethylethylenediamine as a polymerization accelerator was added by a syringe. After 4 hours, 4.0 g of a 2.5% aqueous solution of potassium persulfate as a polymerization initiator was added to the flask, and 20 g of a 2.0% aqueous solution of tetramethylethylenediamine as a polymerization accelerator was further added. The temperature was raised to 40 ° C. to proceed the polymerization reaction. After 3 hours, 0.8 g of a 2.5% aqueous solution of sodium hydrogen sulfite and 0.8 g of a 2.5% aqueous solution of potassium persulfate were added, the temperature was raised to 80 ° C., and the reaction was continued for 1 hour, so that no reaction occurred. Polymerization of the product proceeded. Thereafter, the flask was opened in the air to stop the polymerization reaction.
Thereafter, the pH of the product was adjusted to 8 using a 10% aqueous solution of lithium hydroxide to obtain an aqueous solution containing the water-soluble polymer X1. And the electrolyte solution swelling degree of water-soluble polymer X1 was measured. The results are shown in Table 1.
<Preparation of aqueous dispersion containing particulate polymer (styrene-butadiene polymer)>
In a 5 MPa pressure vessel with a stirrer, 65 parts (63.1%) of styrene as an aromatic vinyl monomer, 35 parts (34.0%) of 1,3-butadiene as an aliphatic conjugated diene monomer, carboxyl group 2 parts (1.9%) itaconic acid as a monomer containing, 1 part (1.0%) 2-hydroxyethyl acrylate as a hydroxyl group-containing monomer, and t-dodecyl mercaptan as a molecular weight regulator. 3 parts, 5 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water as a solvent, and 1 part of potassium persulfate as a polymerization initiator were added and stirred sufficiently. The polymerization was started by warming.
When the monomer consumption reached 95.0%, the reaction was stopped by cooling. A 5% aqueous sodium hydroxide solution was added to the aqueous dispersion containing the polymer thus obtained to adjust the pH to 8. Then, the unreacted monomer was removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion of a particulate polymer made of a styrene-butadiene polymer. The obtained particulate polymer had a gel content of 92% and a glass transition temperature of 10 ° C.
<Preparation of slurry composition for negative electrode of lithium ion secondary battery>
In a planetary mixer, 100 parts of a mixture of artificial graphite and natural graphite (theoretical capacity: 360 mAh / g) as a negative electrode active material and an aqueous solution (solid content concentration: 6.5%) containing a water-soluble polymer X1 are solid content. 1.0 part by weight, and amphoteric dispersant Y1 (“DISPERBYK-2012” manufactured by BYK-Chemie Co., Ltd., acid value 7 mgKOH / g, amine value 7 mgKOH / g, electrolyte solution solubility of less than 0.5%) is 0. 01 parts (1 part per 100 parts of water-soluble polymer X) was added, further diluted with ion-exchanged water to a solid content concentration of 60%, and then kneaded at a rotational speed of 45 rpm for 60 minutes. Further thereafter, 1.5 parts (150 parts per 100 parts of water-soluble polymer) of the aqueous dispersion containing the particulate polymer composed of the above-mentioned styrene-butadiene polymer (solid content concentration: 40%) corresponding to the solid content. The mixture was added and kneaded for 40 minutes at a rotational speed of 40 rpm. Then, ion-exchanged water was added so that the viscosity was 3000 ± 300 mPa · s (B-type viscometer, measured at 60 rpm) (the amount of ion-exchanged water was 80 parts), and a slurry for a lithium ion secondary battery negative electrode A composition was prepared. In addition, the solid content concentration of the slurry composition at this time was 47 mass%. The productivity of the electrode was evaluated based on this solid content concentration. The results are shown in Table 1.
<Manufacture of negative electrode for lithium ion secondary battery>
The slurry composition for a negative electrode of a lithium ion secondary battery is applied to a surface of a copper foil having a thickness of 15 μm, which is a current collector, with a comma coater so that a coating amount is 12.8 to 13.2 mg / cm ^2. Applied. The copper foil coated with the slurry composition for a lithium ion secondary battery negative electrode is conveyed at a rate of 300 mm / min for 2 minutes in an oven at a temperature of 80 ° C. and further for 2 minutes in an oven at a temperature of 110 ° C. By this, the slurry composition on copper foil was dried and the negative electrode original fabric was obtained.
Then, the obtained negative electrode fabric is pressed by a roll press machine so that the density becomes 1.68 to 1.72 g / cm ^3, and further, in order to remove moisture, the environment is set to 105 ° C. under vacuum conditions. After 4 hours, a negative electrode was obtained. Using this negative electrode, the adhesion between the negative electrode mixture layer and the current collector was evaluated. The results are shown in the table below.
<Manufacture of positive electrode for lithium ion secondary battery>
In a planetary mixer, 100 parts of LiCoO ₂ as a positive electrode active material, 2 parts of acetylene black as a conductive material (HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd.), PVDF (polyvinylidene fluoride as a binder) 2) 2 parts of Kureha Chemical Co., Ltd., KF-1100) is added, and further, 2-methylpyrrhodone as a dispersion medium is added and mixed so that the total solid content is 67%, and used for a lithium ion secondary battery positive electrode A slurry composition was prepared.
The obtained slurry composition for a lithium ion secondary battery positive electrode is applied to a current collector of 20 μm thick aluminum foil with a comma coater so that the coating amount becomes 25.5 to 26.5 mg / cm ^2. It was applied to. Thereafter, the aluminum foil coated with the slurry composition for a positive electrode of a lithium ion secondary battery was dried by conveying it in an oven at a temperature of 60 ° C. at a rate of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a positive electrode raw material.
And the obtained positive electrode raw material was pressed with a roll press machine so that the density was 3.40 to 3.50 g / cm ^3, and further, the temperature was 120 ° C. under vacuum conditions for the purpose of removing the dispersion medium. For 3 hours to obtain a positive electrode.
<Manufacture of lithium ion secondary batteries>
A wound cell (equivalent to a discharge capacity of 800 mAh) was prepared using a single-layer polypropylene separator, the negative electrode and the positive electrode, and placed in an aluminum wrapping material. Thereafter, a LiPF ₆ solution having a concentration of 1.0 M as an electrolytic solution (a solvent is a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3/7 (volume ratio)), and vinylene carbonate as an additive is 2% by volume (solvent. Ratio) containing). Further, in order to seal the opening of the aluminum packaging material, heat sealing at a temperature of 150 ° C. was performed to close the aluminum packaging material, and a lithium ion secondary battery was manufactured. Using this lithium ion secondary battery, rate characteristics, cycle characteristics, swelling of the negative electrode after cycling, and storage stability were evaluated. The results are shown in Table 1.

(Examples 2 to 6)
Except that the amount of the amphoteric dispersant Y1 was changed as shown in Table 1, a slurry composition for a lithium ion secondary battery negative electrode, a slurry composition for a lithium ion secondary battery positive electrode, and a lithium ion secondary were prepared in the same manner as in Example 1. A negative electrode for a secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery were produced. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

(Examples 7 to 9)
Instead of the amphoteric dispersant Y1, the amphoteric dispersant Y2 ("DISPERBYK-2001" manufactured by Big Chemie, acid value 19 mgKOH / g, amine value 29 mgKOH / g, electrolyte solubility less than 0.5%), amphoteric dispersant Y3 ( "DISPERBYK-2010" manufactured by Big Chemie, acid value 20 mgKOH / g, amine value 20 mgKOH / g, electrolyte solubility of less than 0.5%, amphoteric dispersant Y4 (DISPERBYK-198 (acid value 0 mgKOH / g, amine manufactured by Big Chemie) 1: 2 (mass ratio) mixture of DISPERBYK-199 (acid value 1.5 mgKOH / g, amine value 0 mgKOH / g), mixed acid value 1 mgKOH / g, amine value 1.3 mg / KOH The slurry composition for a lithium ion secondary battery negative electrode and the lithium ion secondary battery positive electrode slurry were the same as in Example 1, except that the electrolyte solubility after mixing was 2.5%. A Li composition, a negative electrode for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery were manufactured, and various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1. .

(Examples 10 to 21)
Except for using the water-soluble polymer X prepared in the same manner as the water-soluble polymer X1, except that the monomers shown in Table 2 were used in the proportions shown in the table, In the same manner as in Example 1, a slurry composition for a lithium ion secondary battery negative electrode, a slurry composition for a lithium ion secondary battery positive electrode, a negative electrode for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary A battery was manufactured. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

In addition to the one used in Example 1 for the preparation of the water-soluble polymer X, in Examples 12 to 14 and 16 to 19, polyethylene glycol diacrylate (manufactured by Kyoeisha Chemical Co., Ltd.) was used as the polyfunctional compound (C). , Light acrylate 9EG-A, corresponding to compound (I) with n = 9, functional number = 2), and in Example 15, ethoxylated pentaerythritol tetraacrylate (Shin Nakamura Chemical Co., Ltd.) was used as polyfunctional compound (C). ), ATM-35E, n1 + n2 + n3 + n4 = 35 compound (V), functional number = 4) was used.
In addition, in Example 20, methacrylamide was used as the compound (B) in addition to acrylamide in the preparation of the water-soluble polymer X, and in Example 21, 2-hydroxyethyl acrylate was used as the compound (B). .

(Comparative Example 1)
Except not using the amphoteric dispersant Y1, a slurry composition for a lithium ion secondary battery negative electrode, a slurry composition for a lithium ion secondary battery positive electrode, a negative electrode for a lithium ion secondary battery, lithium ion is the same as in Example 1. A positive electrode for a secondary battery and a lithium ion secondary battery were produced. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 3.

(Comparative Example 2)
Except that the amount of the amphoteric dispersant Y1 was changed as shown in Table 3, a slurry composition for a negative electrode of a lithium ion secondary battery, a slurry composition for a positive electrode of a lithium ion secondary battery, and a lithium ion secondary were prepared in the same manner as in Example 1. A negative electrode for a secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery were produced. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 3.

(Comparative Examples 3 and 4)
A water-soluble polymer prepared in the same manner as the water-soluble polymer X1 except that the monomers shown in Table 3 were used in the proportions shown in the table, were used instead of the water-soluble polymer X1, and the amphoteric dispersion was used. Instead of the agent Y1, the dispersant Y5 ("DISPERBYK-2015" manufactured by BYK-Chemie Corporation, acid value 10 mgKOH / g, amine value 0 mgKOH / g, electrolyte solubility 85%), dispersant Y6 ("DISPERBYK-198 manufactured by BYK-Chemie Corporation") ”, An acid value of 0 mg KOH / g, an amine value of 4 mg KOH / g, and an electrolytic solution solubility of 90%) in the same manner as in Example 1, except that the slurry composition for a negative electrode of a lithium ion secondary battery was used. A slurry composition for a positive electrode of a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery were produced. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 3.

(Comparative Examples 5-7)
Except that the water-soluble polymer prepared in the same manner as the water-soluble polymer X1 was used except that the monomers shown in Table 3 were used in the proportions shown in the table, the water-soluble polymer X1 was used. As in Example 1, slurry composition for lithium ion secondary battery negative electrode, slurry composition for lithium ion secondary battery positive electrode, negative electrode for lithium ion secondary battery, positive electrode for lithium ion secondary battery, and lithium ion secondary battery Manufactured. Various evaluations were performed in the same manner as in Example 1. The results are shown in Table 3.
In Comparative Example 5, methyl methacrylate was used for preparing the water-soluble polymer X as a compound other than the compound (A), the compound (B) and the polyfunctional compound (C).

In the table below,
“AA” indicates acrylic acid;
“AAm” indicates acrylamide,
“MAAm” indicates methacrylamide;
“HEA” refers to 2-hydroxyethyl acrylate,
“MMA” indicates methyl methacrylate;
“PEGDA” indicates polyethylene glycol diacrylate,
“EPETA” refers to ethoxylated pentaerythritol tetraacrylate.

From Examples 1 to 21 and Comparative Examples 1 to 7 in the above table, in Examples 1 to 21, the internal resistance of the lithium ion secondary battery is sufficiently reduced, and the life characteristics (cycle characteristics and storage stability) are improved. You can see that it is excellent. In addition, in Examples 1-21, it turns out that the swelling of an electrode is fully suppressed and the productivity of an electrode and the adhesiveness of a negative mix layer and a collector are ensured.
Further, from Examples 1 to 6 in the above table, by changing the amount of the amphoteric dispersant Y, the internal resistance of the lithium ion secondary battery is further reduced, and the productivity of the electrode, the negative electrode mixture layer and the collector layer are collected. It can be seen that the adhesion, cycle characteristics, and storage stability of the electrical conductor can be further improved.
Then, from Examples 1 and 7 to 9 in the above table, by changing the acid value and amine value of the amphoteric dispersant Y, the lithium ion secondary battery is further suppressed from swelling while the lithium ion secondary battery is further swollen. It can be seen that the storage stability of the battery and the productivity of the electrode can be further improved.
Furthermore, from Examples 1 and 10 to 21 in the above table, the swelling of the electrode of the lithium ion secondary battery is further increased by changing the type and blending ratio of the monomer when preparing the water-soluble polymer X. It can be seen that the internal resistance can be further reduced while suppressing, and the productivity, cycle characteristics and storage stability of the electrode can be further improved.

ADVANTAGE OF THE INVENTION According to this invention, the internal resistance of a lithium ion secondary battery can be reduced, and the lithium ion secondary battery electrode binder composition which is excellent in lifetime characteristics can be provided.
ADVANTAGE OF THE INVENTION According to this invention, the internal resistance of a lithium ion secondary battery can be reduced, and the slurry composition for lithium ion secondary battery electrodes which makes the lifetime characteristic excellent also can be provided.
According to the present invention, there are provided an electrode that reduces the internal resistance of a lithium ion secondary battery and also has excellent life characteristics, and a lithium ion secondary battery that has reduced internal resistance and excellent life characteristics. can do.

Claims (7)

A binder composition for a lithium ion secondary battery electrode comprising a water-soluble polymer X, an amphoteric dispersant Y and a solvent,
The water-soluble polymer X is obtained by polymerizing a monomer composition containing the compound (A) and the compound (B),
The compound (A) is an ethylenically unsaturated carboxylic acid compound composed of at least one of an ethylenically unsaturated carboxylic acid and a salt thereof,
The compound (B) has a solubility in 100 g of water at 20 ° C. of 7 g or more and is a compound copolymerizable with the compound (A) having an ethylenically unsaturated bond,
The ratio of the compound (A) in all monomers of the monomer composition is 20.0 mass% or more and 75.0 mass% or less, and the ratio of the compound (B) in all monomers is 20.0 mass% or more and 75.0 mass% or less,
The degree of swelling of the electrolyte solution of the water-soluble polymer X is less than 120% by mass,
The amphoteric dispersant Y has an acid value of 1 mgKOH / g or more and less than 30 mgKOH / g, and an amine value of 1 mgKOH / g or more and less than 30 mgKOH / g,
And the compounding quantity of the amphoteric dispersant Y is 0.001 part by mass or more and 10 parts by mass or less per 100 parts by mass of the water-soluble polymer X.
A binder composition for a lithium ion secondary battery electrode.   The monomer composition further includes a polyfunctional compound (C) having a polyoxyalkylene structure and two or more ethylenically unsaturated bonds, and the ratio of the polyfunctional compound (C) in all monomers is The binder composition for a lithium ion secondary battery electrode according to claim 1, wherein the binder composition is 0.01% by mass or more and 20.0% by mass or less.   The said monomer composition has the value which remove | divided the ratio of the said compound (A) in all the monomers by the ratio of the said compound (B) in all the monomers, and is less than 1.5. Or the binder composition for lithium ion secondary battery electrodes of 2.   The binder composition for a lithium ion secondary battery electrode according to any one of claims 1 to 3, wherein the solubility of the electrolyte solution of the amphoteric dispersant Y is 5% or less.   The slurry composition for lithium ion secondary battery electrodes containing the binder composition for lithium ion secondary battery electrodes in any one of Claims 1-4, and an electrode active material.   The electrode for lithium ion secondary batteries provided with the electrode compound-material layer prepared using the slurry composition for lithium ion secondary battery electrodes of Claim 5 on a collector.   A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolytic solution, and a separator, wherein at least one of the positive electrode and the negative electrode is the electrode for a lithium ion secondary battery according to claim 6.