JP2016103482A - Electrode slurry, electrode and electrochemical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode slurry having a high binding property, by which an electrode having a small internal resistance and superior charge and discharge characteristics and arranged to be able to keep them over a long period of time can be manufactured.SOLUTION: An electrode slurry according to the present invention comprises: polymer particles including (A) 5-40 pts.mass of constitutional units originating from α,β-unsaturated nitrile compounds, (B) 1-10 pts.mass of constitutional units originating from a compound represented by the general formula (1), and (E) 40 pts.mass of constitutional units originating from (meth)acrylate compounds other than (B) the constitutional units (except hydroxyethyl acrylate), and having a number average particle diameter of 50-350 nm; a binder composition for an electrode; and graphite as an active material. (In the general formula (1), Ris a univalent hydrocarbon group, and Ris a bivalent hydrocarbon group.)SELECTED DRAWING: None

Description

  The present invention relates to an electrode binder composition, an electrode slurry containing the binder composition and an active material, an electrode obtained by applying the slurry to a current collector, and an electrochemical device including the electrode.

  In recent years, a power storage device having a high voltage and a high energy density has been required as a power source for driving electronic equipment. In particular, lithium ion secondary batteries and lithium ion capacitors are expected as power storage devices having high voltage and high energy density.

  The electrode used for such an electricity storage device is produced by applying and drying a mixture of an active material and an electrode binder onto a current collector. The properties required for such an electrode binder include increasing the bonding ability between the active materials and the adhesive force between the active material and the current collector (hereinafter also simply referred to as “binding properties”), It is possible to reduce the internal resistance of the battery due to the electrode binder. For example, since the electrode binder has high binding properties, the electrode folding method, the winding radius, and the like can be easily designed, and the storage device can be miniaturized. Moreover, favorable charge / discharge characteristics can be realized by reducing the internal resistance of the battery resulting from the electrode binder.

  Until now, several techniques for improving the above-mentioned characteristics by controlling the binder composition have been proposed (see, for example, Patent Documents 1 to 3).

JP 2000-299109 A JP 2010-205722 A JP 2010-245035 A

  However, the conventional binder composition may have insufficient binding properties, and it has been difficult to maintain the binding properties and good charge / discharge characteristics over a long period of time.

  Accordingly, some aspects of the present invention provide an electrode that has high binding properties, low internal resistance, excellent charge / discharge characteristics, and can maintain them for a long period of time by solving the above problems. The present invention provides a possible electrode binder composition.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following aspects or application examples.

（式中、Ｒ¹は一価の炭化水素基、Ｒ²は二価の炭化水素基である。） [Application Example 1]
One aspect of the binder composition for electrodes according to the present invention is:
(A) 5 to 40 parts by mass of a structural unit derived from an α, β-unsaturated nitrile compound;
(B) 1 to 10 parts by mass of a structural unit derived from a compound represented by the following general formula (1),
Including polymer particles containing
The number average particle diameter of the polymer particles is 50 to 350 nm.

(In the formula, R ¹ is a monovalent hydrocarbon group, and R ² is a divalent hydrocarbon group.)

[Application Example 2]
In the electrode binder composition of Application Example 1, the compound represented by the general formula (1) may be hydroxyethyl methacrylate.

[Application Example 3]
In the electrode binder composition of Application Example 1 or Application Example 2, the pH may be 6 or more and 8 or less.

[Application Example 4]
One aspect of the electrode slurry according to the present invention is characterized by containing an active material and the electrode binder composition of any one of Application Examples 1 to 3.

[Application Example 5]
One aspect of the electrode according to the present invention comprises a current collector, and an active material layer formed by applying and drying the electrode slurry of Application Example 4 on the surface of the current collector, To do.

[Application Example 6]
One aspect of the electrochemical device according to the present invention includes the electrode of Application Example 5.

  According to the binder composition for an electrode according to the present invention, it is possible to increase the bonding ability between the active materials and the adhesive force between the active material and the current collector, and the internal resistance can be reduced. It is possible to produce an electrode excellent in the above. Moreover, according to the binder composition for electrodes which concerns on this invention, it becomes possible to produce an electrode with favorable binding property and charging / discharging characteristic over a long period of time.

  Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments, and based on ordinary knowledge of those skilled in the art without departing from the spirit of the present invention. It should be understood that modifications, improvements, and the like appropriately added to the embodiments described above fall within the scope of the present invention.

（式中、Ｒ¹は一価の炭化水素基、Ｒ²は二価の炭化水素基である。） 1. Electrode binder composition The electrode binder composition according to the present embodiment comprises (A) 5 to 40 parts by mass of a structural unit derived from an α, β-unsaturated nitrile compound, and (B) the following general formula (1). The polymer particle containing 1-10 mass parts of structural units derived from the compound shown by these, The number average particle diameter of the said polymer particle is 50-350 nm, It is characterized by the above-mentioned.

(In the formula, R ¹ is a monovalent hydrocarbon group, and R ² is a divalent hydrocarbon group.)

  The binder composition for an electrode according to the present embodiment is used as a binder of an active material, and specifically, a binder between positive electrode active material particles and a positive electrode active material and a collector metal foil, or It acts as a binder between the negative electrode active material particles and between the negative electrode active material and the current collector metal foil. In that case, the polymer particles are contained in an amount of 0.1 to 10 parts by mass, preferably 0.5 to 5 parts by mass in solid content with respect to 100 parts by mass of the positive electrode active material or the negative electrode active material. Can be prepared as a slurry. When the content of the polymer particles is less than 0.1 parts by mass, the binding property may be deteriorated. When the content is more than 10 parts by mass, battery characteristics when assembled as a battery tend to be adversely affected. Hereinafter, each component contained in the binder composition for electrodes which concerns on this Embodiment is demonstrated in detail.

1.1. Polymer Particles The polymer particles contained in the electrode binder according to the present embodiment include (A) a structural unit derived from an α, β-unsaturated nitrile compound (hereinafter also referred to as “(A) structural unit”). And (B) a structural unit derived from the compound represented by the general formula (1) (hereinafter also referred to as “(B) structural unit”). In the present invention, the “structural unit” means a polymer obtained by polymerizing a monomer to form a repeating unit, and the monomer constitutes a repeating unit.

1.1.1. (A) Structural Unit By containing the (A) structural unit, the polymer particles can be appropriately swollen by the electrolytic solution. That is, since the solvent enters the network structure composed of polymer chains and the network interval is widened, the solvated lithium ions can easily move through the network structure. As a result, it is considered that the diffusibility of lithium ions is improved. Thereby, since electrode resistance can be reduced, the favorable charging / discharging characteristic of an electrode is implement | achieved.

  (A) Specific examples of the α, β-unsaturated nitrile compound used for constituting the structural unit include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, vinylidene cyanide and the like. Among these, acrylonitrile and methacrylonitrile are preferable, and acrylonitrile is more preferable. In addition, these (A) structural units can be used individually by 1 type or in combination of 2 or more types.

  (A) The content rate of a structural unit is 5-40 mass parts when all the structural units are 100 mass parts, It is preferable that it is 7-35 mass parts, and it is more preferable that it is 10-30 mass parts. preferable. (A) When the content rate of a structural unit exists in the said range, it is excellent in affinity with the electrolyte solution to be used, and a swelling rate does not become large too much, and it can contribute to the improvement of a battery characteristic.

1.1.2. (B) Constituent unit When the polymer particles contain the (B) constituent unit, the active material is good without aggregating the active material when the electrode binder composition of the present invention and the active material are mixed. A mixture (slurry) dispersed in can be prepared. Thereby, the electrode produced by applying the mixture has a nearly uniform distribution. As a result, an electrode with few binding defects can be manufactured. That is, it is considered that the binding property of the polymer particles is improved.

  Moreover, when the binder for electrodes containing the polymer particle which contains (A) a structural unit and (B) does not contain a structural unit is used, the swelling degree with respect to the electrolyte solution of this polymer particle becomes large, and electrode resistance falls. On the other hand, the adhesion between the active materials and the interface between the active material layer and the current collector is lowered, and the electrode structure cannot be sufficiently maintained, and the charge / discharge characteristics may be deteriorated. However, by using a binder for electrodes including polymer particles containing (A) structural unit and (B) structural unit as in the present invention, the degree of swelling of the polymer particles with respect to the electrolyte solution due to their synergistic effect Becomes larger, the electrode resistance is lowered, and the active material can be sufficiently retained.

上記一般式（１）中、Ｒ¹は一価の炭化水素基であるが、炭素数が１〜６の置換もしくは非置換のアルキル基であることが好ましく、メチル基であることがさらに好ましい。また、Ｒ²は二価の炭化水素基であるが、炭素数が１〜６の置換もしくは非置換のアルキレン基であることが好ましい。（Ｂ）構成単位を構成するために用いられる上記一般式（１）で示される化合物の具体例としては、２−ヒドロキシエチルメタクリレート、２−ヒドロキシプロピルメタクリレート、３−ヒドロキシプロピルメタクリレート、４−ヒドロキシブチルメタクリレート、５−ヒドロキシペンチルメタクリレート、６−ヒドロキシヘキシルメタクリレート等が挙げられる。これらの中でも、２−ヒドロキシエチルメタクリレートが好ましい。なお、これら（Ｂ）構成単位は、一種単独でまたは二種以上を組み合わせて用いることができる。 (B) The structural unit is derived from a compound represented by the following general formula (1).

In the general formula (1), R ¹ is a monovalent hydrocarbon group, preferably a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, and more preferably a methyl group. R ² is a divalent hydrocarbon group, preferably a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms. (B) Specific examples of the compound represented by the general formula (1) used for constituting the structural unit include 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl. Examples include methacrylate, 5-hydroxypentyl methacrylate, and 6-hydroxyhexyl methacrylate. Among these, 2-hydroxyethyl methacrylate is preferable. In addition, these (B) structural units can be used individually by 1 type or in combination of 2 or more types.

  Moreover, there is a hydroxyalkyl acrylate as a compound having a similar structure to the compound represented by the general formula (1). However, as shown in the examples described later, the binder composition for an electrode including a structural unit derived from hydroxyalkyl acrylate cannot exhibit the high binding property as obtained in the present invention.

  (B) The content rate of a structural unit is 1-10 mass parts when all the structural units are 100 mass parts, and it is preferable that it is 2-5 mass parts. (B) When the content rate of a structural unit exists in the said range, the binding property of the polymer particle obtained can be improved. (B) When the content rate of a structural unit is less than the said range, the binding property of the polymer particle obtained may become inadequate. On the other hand, even if the content ratio of the structural unit (B) exceeds the above range, the binding property of the resulting polymer particles may be insufficient.

1.1.3. (C) Constituent Unit Derived from Conjugated Diene Compound The polymer particles contained in the electrode binder composition according to the present embodiment are composed of (C) a constituent unit derived from a conjugated diene compound (hereinafter referred to as “(C) constituent unit”. It is preferable that it also contains "."

  (C) By containing a structural unit, a polymer particle can have strong binding property. That is, since rubber elasticity derived from the conjugated diene compound is imparted to the polymer particles, it becomes possible to follow changes such as volume shrinkage and expansion of the electrode. Thereby, it is thought that it has the durability which improves a binding property and maintains a charging / discharging characteristic for a long term.

(C) Specific examples of the conjugated diene compound used for constituting the structural unit include 1,
3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes Etc. Of these, 1,3-butadiene is preferred. In addition, these (C) structural units can be used individually by 1 type or in combination of 2 or more types.

  (C) The content ratio of the structural unit is preferably 60 parts by mass or less, more preferably 25 to 55 parts by mass, and preferably 35 to 50 parts by mass when the total structural unit is 100 parts by mass. It is particularly preferred. (C) When the content rate of a structural unit exists in the said range, the further improvement of binding property will be attained.

1.1.4. (D) Constituent Unit Derived from Aromatic Vinyl Compound Polymer particles contained in the electrode binder composition according to the present embodiment are composed of (D) a constituent unit derived from an aromatic vinyl compound (hereinafter referred to as “(D)”. It is preferable that the component further includes a “structural unit”.

  (D) Specific examples of the aromatic vinyl compound used for constituting the structural unit include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene and the like. Of these, styrene is preferred. In addition, these (D) structural units can be used individually by 1 type or in combination of 2 or more types.

  (D) The content ratio of the structural unit is preferably 60 parts by mass or less, more preferably 10 to 55 parts by mass, and more preferably 20 to 50 parts by mass when all the structural units are 100 parts by mass. It is particularly preferred. (D) When the content rate of a structural unit exists in the said range, a polymer particle has moderate binding property with respect to the graphite used as an active material. Moreover, the obtained active material layer has good flexibility and binding property to the current collector.

1.1.5. (E) Constituent Unit Derived from (Meth) acrylate Compound The polymer particles contained in the electrode binder composition according to the present embodiment are derived from (E) (meth) acrylate compound other than (B) constituent unit. It is preferable to further contain a structural unit (hereinafter also referred to as “(E) structural unit”). In this specification, “(meth) acrylic acid” means both “acrylic acid” and “methacrylic acid”. In addition, the term “˜ (meth) acrylate” means both “˜acrylate” and “˜methacrylate”.

  (E) Specific examples of the (meth) acrylate compound used for constituting the structural unit include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n -Butyl (meth) acrylate, isobutyl (meth) acrylate, n-amyl (meth) acrylate, isoamyl (meth) acrylate, hexyl (meth) acrylate, 2-hexyl (meth) acrylate, octyl (meth) acrylate, isononyl (meth) ) Acrylate, decyl (meth) acrylate, hydroxymethyl acrylate, hydroxyethyl acrylate, ethylene glycol (meth) acrylate, and the like. Among these, methyl (meth) acrylate, n-butyl (meth) acrylate, and isobutyl (meth) acrylate are preferable, and methyl (meth) acrylate is more preferable. In addition, these (E) structural units can be used individually by 1 type or in combination of 2 or more types.

(E) The content ratio of the structural unit is preferably 40 parts by mass or less, more preferably 5 to 35 parts by mass, and 10 to 30 parts by mass when all the structural units are 100 parts by mass. It is particularly preferred. (E) When the content ratio of the structural unit is within the above range, the resulting polymer particles have an appropriate affinity with the electrolytic solution, and the electrode binder serves as an electrical resistance component in the electrochemical device. While suppressing an increase in resistance, it is possible to prevent a decrease in binding property due to excessive absorption of the electrolytic solution.

1.1.6. (F) Constituent Unit Derived from Unsaturated Carboxylic Acid The polymer particles contained in the electrode binder composition according to the present embodiment are composed of (F) a constituent unit derived from an unsaturated carboxylic acid (hereinafter referred to as “(F) It is preferable that the component further includes a “structural unit”.

  When the polymer particles contain the structural unit (F), when the binder composition of the present invention and the active material are mixed, the active material is well dispersed without causing the active material to aggregate (slurry). Can be produced. Thereby, the electrode produced by applying the mixture has a nearly uniform distribution. As a result, an electrode with few binding defects can be manufactured. That is, it is considered that the binding property is improved and the anti-dusting property is improved.

  (F) Specific examples of the unsaturated carboxylic acid used for constituting the structural unit include mono- or dicarboxylic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. Can be mentioned. Among these, acrylic acid, methacrylic acid, and itaconic acid are particularly preferable. These (F) structural units can be used individually by 1 type or in combination of 2 or more types.

  (F) The content ratio of the structural unit is preferably 10 parts by mass or less, more preferably 0.3 to 8% by mass, and more preferably 0.5 to 6 when the total structural unit is 100 parts by mass. It is particularly preferable that the content is% by mass. (F) When the content rate of a structural unit is the said range, it is excellent in the dispersion stability of a polymer particle at the time of slurry preparation for electrodes, and does not produce an aggregate easily. Further, an increase in slurry viscosity over time can be suppressed.

1.1.7. Constituent Units Derived from Other Comonomers The polymer particles contained in the binder composition for an electrode according to the present embodiment include, in addition to the above constituent units, monomer compounds copolymerizable with these (hereinafter, It may contain structural units derived simply from “other comonomer”.

  Specific examples of other comonomer include alkyl amides of ethylenically unsaturated carboxylic acids such as (meth) acrylamide and N-methylol acrylamide; vinyl carboxylic acid esters such as vinyl acetate and vinyl propionate; Examples thereof include acid anhydrides of saturated dicarboxylic acids; monoalkyl esters; monoamides; aminoalkylamides of ethylenically unsaturated carboxylic acids such as aminoethylacrylamide, dimethylaminomethylmethacrylamide, and methylaminopropylmethacrylamide. In addition, these copolymerization monomers can be used individually by 1 type or in combination of 2 or more types, and a crosslinkable copolymerization monomer can also be used together.

1.1.8. Number average particle diameter of polymer particles The number average particle diameter of the polymer particles is 50 to 350 nm, and preferably 70 to 300 nm. When the number average particle diameter of the polymer particles is in the above range, the binding property tends to be improved in the drying step when forming the electrode. The obtained electrode is preferable because a sufficient number of effective adhesion points tend to be formed between the active material, the polymer particles, and the current collector.

The number average particle diameter of the polymer particles can be determined by using a particle size distribution measuring apparatus based on a dynamic light scattering method. As such a particle size distribution measuring apparatus, for example, Coulter LS230, LS100, LS13320 (above, manufactured by Beckman Coulter. Inc), FPAR-1000 (manufactured by Otsuka Electronics Co., Ltd.), ALV5000 (
ALV). These particle size distribution measuring devices are not intended to evaluate only the primary particles of the polymer particles, but can also evaluate the secondary particles formed by aggregation of the primary particles. Therefore, the particle size distribution measured by these particle size distribution measuring devices can be used as an indicator of the dispersion state of the polymer particles contained in the electrode slurry. The number average particle diameter of the polymer particles can also be measured by a method of centrifuging the electrode slurry and precipitating the active material particles, and then measuring the supernatant with the above particle size distribution measuring apparatus. .

1.2. Method for Producing Polymer Particles The method for synthesizing the polymer particles contained in the electrode binder composition according to the present embodiment is not particularly limited, but can be easily produced by a two-stage emulsion polymerization process.

1.2.1.1 Stage Polymerization Step (I) The monomer component used in the first stage emulsion polymerization step includes, for example, an α, β-unsaturated nitrile compound, a conjugated diene compound, and an aromatic vinyl. Non-carboxylic acid monomers such as compounds, (meth) acrylate compounds, and other copolymerization monomers, and carboxylic acid monomers such as unsaturated carboxylic acids are contained. (I) The content ratio of the non-carboxylic acid monomer contained in the monomer component is 80 to 92% by mass in a total of 100% by mass of the non-carboxylic acid monomer and the carboxylic acid monomer. It is preferable that it is 82-92 mass%. When the content ratio of the non-carboxylic acid monomer is 80 to 92% by mass, the dispersion stability of the polymer particles is excellent at the time of preparing the slurry for the electrode, and aggregates hardly occur. Further, an increase in slurry viscosity over time can be suppressed.

  (I) In the monomer component, the content ratio of the (meth) acrylate compound in the non-carboxylic acid monomer is preferably 14 to 30% by mass. When the content ratio of the (meth) acrylate compound is in the above range, the dispersion stability of the polymer particles is excellent during the preparation of the electrode slurry, and aggregates are hardly generated. In addition, the obtained polymer particles have moderate affinity with the electrolytic solution, and can prevent a decrease in binding property due to excessive absorption of the electrolytic solution.

  (I) In the monomer component, the content of the conjugated diene compound in the non-carboxylic acid monomer is preferably 10 to 60% by mass, and the ratio of the aromatic vinyl compound is 20 to 50% by mass. It is preferable. Moreover, it is preferable that the ratio of itaconic acid in a carboxylic acid-type monomer is 50-85 mass%.

1.2.2.2 Second-stage polymerization step (II) The monomer component used in the second-stage emulsion polymerization step includes, for example, an α, β-unsaturated nitrile compound, a conjugated diene compound, and an aromatic vinyl. Non-carboxylic acid monomers such as compounds, (meth) acrylate compounds, and other copolymerization monomers, and carboxylic acid monomers such as unsaturated carboxylic acids are contained. (II) The content ratio of the non-carboxylic acid monomer contained in the monomer component is 94 to 99% by mass in a total of 100% by mass of the non-carboxylic acid monomer and the carboxylic acid monomer. It is preferable that it is 96-98 mass%. When the content ratio of the non-carboxylic acid monomer is within the above range, the dispersion stability of the polymer particles is excellent during the preparation of the electrode slurry, and aggregates are hardly generated. Further, an increase in slurry viscosity over time can be suppressed.

  (II) In the monomer, the content ratio of the (meth) acrylate compound in the non-carboxylic acid monomer is preferably 11.5% by mass or less. When the content ratio of the (meth) acrylate compound is 11.5% by mass or less, the obtained polymer particles have an appropriate affinity with the electrolytic solution, and have binding properties due to excessive absorption of the electrolytic solution. Decline can be prevented.

  Further, in the polymer particle constituent monomer, the mass ratio ((I) / (II) ratio) of (I) monomer component to (II) monomer component is 0.05 to 0.5. It is preferable that it is 0.1 to 0.4. When the ratio (I) / (II) is in the above range, the dispersion stability of the polymer particles is excellent during the preparation of the electrode slurry, and aggregates are hardly generated. Further, an increase in slurry viscosity over time can be suppressed.

1.2.3. Emulsion polymerization The emulsion polymerization step is carried out in an aqueous medium in the presence of an emulsifier, a polymerization initiator, and a molecular weight regulator. Hereinafter, each material used in the emulsion polymerization step will be described.

1.2.3.1. Emulsifiers Specific examples of emulsifiers include sulfate esters of higher alcohols, alkylbenzene sulfonates, alkyl diphenyl ether disulfonates, aliphatic sulfonates, aliphatic carboxylates, dehydroabietic acid salts, and formalin condensates of naphthalene sulfonic acid. Nonionic surfactants such as sulfate salts of nonionic surfactants; Nonionic surfactants such as alkyl ester type, alkylphenyl ether type, and alkyl ether type of polyethylene glycol; perfluorobutyl sulfonate, Fluorosurfactants such as fluoroalkyl group-containing phosphates, perfluoroalkyl group-containing carboxylates, and perfluoroalkylethylene oxide adducts can be mentioned. In the emulsion polymerization step, these emulsifiers can be used alone or in combination of two or more.

1.2.3.2. Polymerization initiator Specific examples of the polymerization initiator include water-soluble polymerization initiators such as lithium persulfate, potassium persulfate, sodium persulfate, and ammonium persulfate; cumene hydroperoxide, benzoyl peroxide, t-butyl hydroperoxide, Examples thereof include oil-soluble polymerization initiators such as acetyl peroxide, diisopropylbenzene hydroperoxide, and 1,1,3,3-tetramethylbutyl hydroperoxide. Of these, potassium persulfate, sodium persulfate, cumene hydroperoxide, and t-butyl hydroperoxide are preferable. In the emulsion polymerization step, these polymerization initiators can be used singly or in combination of two or more. The amount of the polymerization initiator used is not particularly limited, and is appropriately adjusted in consideration of the combination of the monomer composition, the pH of the polymerization reaction system, other additives, and the like.

1.2.3.3. Molecular weight regulators Specific examples of molecular weight regulators include n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan, and the like; dimethylxanthogen disulfide Xanthogen compounds such as diisopropylxanthogen disulfide; thiuram compounds such as terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram monosulfide; 2,6-di-t-butyl-4-methylphenol, styrenated phenol Phenol compounds such as allyl alcohol; halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, carbon tetrabromide; α-ben Vinyl ethers such as ruoxystyrene, α-benzyloxyacrylonitrile, α-benzyloxyacrylamide; triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexylthioglycolate, α-methylstyrene Dimer etc. are mentioned. In the emulsion polymerization step, these molecular weight regulators can be used singly or in combination of two or more.

1.2.4. Conditions for Emulsion Polymerization The first stage emulsion polymerization step is preferably performed under conditions where the polymerization temperature is 40 to 80 ° C. and the polymerization time is 2 to 4 hours. In the first stage emulsion polymerization step, the polymerization conversion rate is preferably 50% or more, and more preferably 60% or more. The second emulsion polymerization step is preferably performed under conditions where the polymerization temperature is 40 to 80 ° C. and the polymerization time is 2 to 6 hours.

  After completion of the emulsion polymerization, it is preferable to neutralize the dispersion so that the pH of the dispersion is 6 or more and 8 or less by adding a neutralizing agent. Although it does not specifically limit as a neutralizing agent to be used, Usually, metal hydroxides, such as sodium hydroxide and potassium hydroxide, and ammonia are mentioned. By setting the pH of the dispersion in the range of 6 or more and 8 or less, the stability of the dispersion is further improved. When the total solid content concentration in the emulsion polymerization step is 50% by mass or less, the reaction can proceed with good dispersion stability, but it is preferably 45% by mass or less, more preferably 40% by mass or less. Further, by performing concentration after the neutralization treatment, highly solid differentiation can be achieved while further improving the stability of the particles.

1.3. Other additives You may add various additives, such as a water-soluble thickener, to the binder composition for electrodes which concerns on this Embodiment as needed. Specific examples of additives include water-soluble thickeners such as carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch, casein; hexametaphosphate soda, tripolyphosphate Examples thereof include dispersants such as soda, sodium pyrophosphate, and sodium polyacrylate; and latex stabilizers such as nonionic and anionic surfactants.

2. Electrode Slurry The electrode slurry according to the present embodiment contains an active material and the electrode binder composition.

2.1. Active material The active material is not particularly limited. When used for a lithium ion secondary battery electrode, carbon can be used as the negative electrode active material. Specific examples of carbon include carbon materials obtained by firing organic polymer compounds such as phenol resin, polyacrylonitrile, and cellulose; carbon materials obtained by firing coke and pitch; artificial graphite; natural graphite and the like Can be mentioned. Moreover, when using for an electric double layer capacitor electrode, activated carbon, activated carbon fiber, silica, alumina, etc. can be used. When used for a lithium ion capacitor electrode, carbon materials such as graphite, non-graphitizable carbon, hard carbon, coke, polyacene organic semiconductor (PAS), and the like can be used.

2.2. Additives The slurry for electrodes according to the present embodiment includes a thickener, a dispersant such as sodium hexametaphosphate, sodium tripolyphosphate, and sodium polyacrylate, and a nonionic or anionic surfactant as a latex stabilizer. Additives such as antifoaming agents can be added.

2.3. Preparation of electrode slurry The electrode slurry according to the present embodiment contains 0.1 to 10 parts by mass of the electrode binder composition described above in terms of solid content with respect to 100 parts by mass of the active material. It is preferable that 0.3 to 4 parts by mass is contained. When the content of the electrode binder composition is in the above range, the electrode binder composition is difficult to dissolve in the electrolytic solution, and adverse effects on battery characteristics due to an increase in overvoltage can be suppressed.

  In the preparation of the electrode slurry according to the present embodiment, in order to mix the electrode binder composition, the active material, and the additive used as necessary, a stirrer, a defoamer, a bead mill, a high-pressure homogenizer, etc. Can be used. The preparation of the electrode slurry is preferably performed under reduced pressure. Thereby, it can prevent that a bubble arises in the active material layer obtained.

3. Electrode The electrode according to the present embodiment includes a current collector and an active material layer formed by applying and drying the above-described electrode slurry on the surface of the current collector.

3.1. Current collector Specific examples of the current collector include metal foil, etching metal foil, and expanded metal. Specific examples of the material constituting the current collector include metal materials such as aluminum, copper, nickel, tantalum, stainless steel, and titanium, and can be appropriately selected and used according to the type of the target power storage device. . The thickness of the current collector is preferably 5 to 30 μm and more preferably 8 to 25 μm when constituting an electrode for a lithium ion secondary battery. In the case of constituting an electrode for an electric double layer capacitor, the thickness of the current collector is preferably 5 to 100 μm, more preferably 10 to 70 μm, and particularly preferably 15 to 30 μm. .

3.2. Formation of Active Material Layer Specific examples of means for applying the electrode slurry include a doctor blade method, a reverse roll method, a comma bar method, a gravure method, and an air knife method. Moreover, as conditions for the drying process of the coating film of the slurry for electrodes, it is preferable that processing temperature is 20-250 degreeC, and it is more preferable that it is 50-150 degreeC. Moreover, it is preferable that processing time is 1-120 minutes, and it is more preferable that it is 5-60 minutes.

Specific examples of the pressing means include a high pressure super press, a soft calender, a 1-ton press machine, and the like. The conditions for press working are appropriately set according to the processing machine to be used. The active material layer thus formed has a thickness of 40 to 100 μm and a density of 1.3 to 2.0 g / cm ³ . The electrode thus obtained can be suitably used as an electrode for electrochemical devices such as lithium ion secondary batteries, electric double layer capacitors, and lithium ion capacitors.

4). Electrochemical Device An electrochemical device such as a lithium ion secondary battery or a lithium ion capacitor can be manufactured using the electrode according to this embodiment. For example, when a lithium ion secondary battery is configured, an electrolytic solution in which an electrolyte made of a lithium compound is dissolved in a solvent is used.

Specific examples of the _{electrolyte, LiClO 4, LiBF 4, LiI} , LiPF 6, LiCF 3 SO 3, LiAsF 6, LiSbF 6, LiAlCl 4, LiCl, LiBr, LiB (C 2 H 5) 4, LiCH 3 SO 3, Examples include LiC ₄ F ₉ SO ₃ and Li (CF ₃ SO ₂ ) ₂ N.

Specific examples of the solvent include carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; lactones such as γ-butyrolactone; trimethoxysilane, 1,2-dimethoxyethane, diethyl Ethers such as ether, 2-ethoxyethane, tetrahydrofuran and 2-methyltetrahydrofuran; sulfoxides such as dimethyl sulfoxide; oxolanes such as 1,3-dioxolane and 4-methyl-1,3-dioxolane; acetonitrile, nitromethane and the like Nitrogen-containing compounds; esters such as methyl formate, methyl acetate, butyl acetate, methyl propionate, ethyl propionate, phosphoric acid triester; diglyme, triglyme, tetragrass Glymes such as acetone; ketones such as acetone, diethyl ketone, methyl ethyl ketone and methyl isobutyl ketone; sulfones such as sulfolane; oxazolidinones such as 2-methyl-2-oxazolidinone; 1,3-propane sultone, 1,4- Examples include sultone such as butane sultone, 2,4-butane sultone, and 1,8-naphtha sultone.

  When an electric double layer capacitor is configured using the electrode according to the present embodiment, an electrolyte such as tetraethylammonium tetrafluoroborate, triethylmethylammonium tetrafluoroborate, tetraethylammonium hexafluorophosphate is dissolved in the above solvent. The electrolyte solution used is used. In the case where a lithium ion capacitor is configured using the electrode according to the present embodiment, the same electrolytic solution as in the case of configuring the above lithium ion secondary battery can be used.

5. EXAMPLES Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, “parts” and “%” are based on mass unless otherwise specified.

5.1. Production of lithium ion secondary battery 5.1.1. Production of Negative Electrode (1) Production Method Thickener (trade name “CMC2200”, manufactured by Daicel Chemical Industries, Ltd.) 1 to a biaxial planetary mixer (product name “TK Hibismix 2P-03” manufactured by PRIMIX Corporation) Parts (in terms of solid content), 100 parts of graphite (in terms of solid content) and 68 parts of water were added as the negative electrode active material, and the mixture was stirred at 60 rpm for 1 hour. Thereafter, 2 parts (in terms of solid content) of the electrode binder composition prepared in the following section “5.5. Preparation of Electrode Binder Composition” was added, and the mixture was further stirred for 1 hour to obtain a paste. Water was added to the obtained paste to adjust the solid content to 50%, and then the mixture was stirred at 200 rpm for 2 minutes at 1800 rpm at 200 rpm using a stirring defoamer (trade name “Netaro Awatori” manufactured by Shinky Co., Ltd.). The mixture was stirred and mixed for 5 minutes at 1,800 rpm for 1.5 minutes under vacuum to prepare a slurry for electrodes. The prepared electrode slurry was uniformly applied to the surface of a current collector made of copper foil by a doctor blade method so that the film thickness after drying was 80 μm, and was dried at 120 ° C. for 20 minutes. Then, the negative electrode was obtained by pressing with a roll press machine so that the density of an active material layer might be 1.8 g / cm < ³ >.

(2) Binding evaluation (peel strength measurement)
A test piece having a width of 2 cm and a length of 12 cm was cut out from the prepared negative electrode, and the surface of the test piece on the active material layer side was attached to an aluminum plate using a double-sided tape. On the other hand, a 18 mm wide tape (manufactured by Nichiban Co., Ltd., trade name “Cello Tape (registered trademark)”, prescribed in JIS Z1522) was attached to the surface of the current collector of the test piece. The strength (mN / 2 cm) when this 18 mm wide tape was peeled in the 90 ° direction at a speed of 50 mm / min was measured 6 times, and the average value was calculated as the peel strength (mN / 2 cm). Note that the greater the peel strength value, the higher the adhesion strength between the current collector and the active material layer, and it can be evaluated that the active material layer is less likely to peel from the current collector, but the peel strength value is 20 mN / 2 cm. If it is above, it can be determined to be good.

5.1.2. Production of positive electrode Biaxial planetary mixer (product name "TK Hibismix 2P-03" manufactured by PRIMIX Corporation) and electrode binder (product name "KF polymer # 1 manufactured by Kureha Corporation")
120 ”) 4.0 parts (in terms of solid content), 3.0 parts of conductive assistant (trade name“ Denka Black 50% press product ”manufactured by Denki Kagaku Kogyo Co., Ltd.), LiCoO _{2 having a} particle size of 5 μm as a positive electrode active material. 100 parts (in terms of solid content) and 36 parts of N-methylpyrrolidone (NMP) were added, and the mixture was stirred at 60 rpm for 2 hours. After adding NMP to the obtained paste to adjust the solid content to 65%, using a stirring defoaming machine (trade name “Awatori Netaro”, manufactured by Shinky Co., Ltd.), 2 minutes at 200 rpm, 1800 rpm The mixture was stirred and mixed for 5 minutes at 1,800 rpm for 1.5 minutes under vacuum to prepare a slurry for electrodes. The prepared electrode slurry was uniformly applied to the surface of the current collector made of aluminum foil by a doctor blade method so that the film thickness after drying was 80 μm, and was dried at 120 ° C. for 20 minutes. Then, the secondary battery positive electrode was obtained by pressing with a roll-press machine so that the density of an active material layer may be 3.0 g / cm < ³ >.

5.1.3. Assembly of Lithium Ion Secondary Battery The negative electrode cut out to 50 mm × 25 mm was placed on a film-like exterior aluminum seal made of aluminum inside a bipolar single-layer laminate cell in a glove box. Next, on the negative electrode, a separator (made by Celgard, trade name “Celguard # 2400”, thickness 25 μm) made of a polypropylene porous film cut out to 54 mm × 27 mm is placed, and air is prevented from entering. An electrolyte was injected into the cell. Thereafter, the positive electrode cut out to 48 mm × 23 mm was placed on the separator. And the exterior aluminum seal similar to the said exterior aluminum seal was mounted on this positive electrode. Thus, the laminated body which consists of an exterior aluminum seal, a negative electrode, a separator, a positive electrode, and an exterior aluminum seal was obtained. Then, the outer peripheral edge part of the two exterior aluminum seals was joined together and sealed with the heating sealing device. And the secondary battery (electrochemical device) which consists of a bipolar | monopolar single layer laminated cell was produced by inject | pouring electrolyte solution so that air might not enter between each layer. The electrolytic solution used was a solution in which LiPF ₆ was dissolved at a concentration of 1 mol / liter in a solvent of ethylene carbonate / ethyl methyl carbonate = 1/1. These operations were performed in a glove box.

5.2. Evaluation of internal direct current resistance value (DC-IR) before cycle characteristic evaluation The cell produced in the above-mentioned section "5.1.3. Assembly of lithium ion secondary battery" is placed in a thermostat set to 25 ° C. The battery was charged to 50% DOD (3.8 V) at a constant current (0.2 C). After that, the voltage change when charging at a constant current (0.5C) for 10 seconds is read, and after a pause for 1 minute, the voltage change when discharging at a constant current (0.5C) for 10 seconds is further performed. I read. The voltage at the time of charging / discharging was read by the same method except having changed the electric current value from 0.5C to 1.0C, 2.0C, 3.0C, 5.0C. A graph was created with the applied current value (A) as the horizontal axis and the voltage value (V) as the vertical axis, and the slope value of the straight line connecting the plot points was calculated at each charge / discharge time. The gradient values were taken as internal DC resistance values (DC-IR) during charging and discharging, respectively.

  In the measurement conditions, “DOD” indicates the ratio of the discharge capacity to the charge capacity. For example, “charge to 50% DOD” indicates that only 50% of the capacity is charged when the total capacity is 100%.

5.3. Evaluation of 60 ° C. Cycle Characteristics After the evaluation of “5.2. Evaluation of Internal DC Resistance Value (DC-IR)”, the same cell is placed in a thermostat set at 60 ° C., and constant current (2 .0C), charging starts at a constant voltage (4.2V) when the voltage reaches 4.2V, and charging is completed when the current value reaches 0.01C (cut) Off). Thereafter, discharging was started at a constant current (2.0 C), and the time when the voltage reached 3.0 V was regarded as the completion of discharging (cutoff), and the discharge capacity at the first cycle was calculated. Thus, charging / discharging was repeated 100 times, and the discharge capacity at the 100th cycle was calculated. A value obtained by dividing the discharge capacity at the 100th cycle thus measured by the discharge capacity at the first cycle was defined as a 100 cycle discharge maintenance ratio (%). It can be determined that the discharge capacity maintenance rate at the 100th cycle is 40% or more.

5.4. Evaluation of resistance change rate After the evaluation of “5.3.60 ° C. cycle characteristics”, the same as the method described in “5.2. Evaluation of internal direct current resistance (DC-IR) before cycle characteristics evaluation” The internal direct current resistance value (DC-IR) at the time of discharge after cycle characteristic evaluation was measured by various methods.
The ratio of the internal DC resistance value after the cycle characteristic evaluation measured in this section to the internal DC resistance value (DC-IR) before the cycle characteristic evaluation is defined as the resistance change rate. It can be judged that it is small. In addition, when the resistance change rate is 10 or less, it can be determined to be good.

5.5. Preparation of electrode binder composition 5.5.1. Example 1
In a temperature-controllable autoclave equipped with a stirrer, water 200 parts, sodium dodecylbenzenesulfonate 0.6 part, potassium persulfate 1.0 part, sodium bisulfite 0.5 part, α-methylstyrene dimer 0.2 Part, 0.2 part of dodecyl mercaptan and the first-stage polymerization component shown in Table 1 were charged all at once, and the temperature was raised to 70 ° C. to carry out the polymerization reaction for 2 hours. After confirming that the polymerization addition rate was 80% or more, the second-stage polymerization component shown in Table 1 was added over 6 hours while maintaining the reaction temperature at 70 ° C. When 3 hours passed from the start of addition of the second stage polymerization component, 1.0 part of α-methylstyrene dimer and 0.3 part of dodecyl mercaptan were added. After the addition of the second stage polymerization component, the temperature was raised to 80 ° C., and further reacted for 2 hours. After completion of the polymerization reaction, the pH of the latex was adjusted to 7.5, and 5 parts of sodium tripolyphosphate (in terms of solid content) was added. Then, the residual monomer was processed by steam distillation, and the binder composition for electrodes was obtained by concentrating to 50% of solid content under reduced pressure.

  It was 90 nm when the number average particle diameter of the polymer particle contained in the obtained binder composition for electrodes was measured with the measuring apparatus which uses a dynamic light scattering method as a measurement principle. A light scattering measurement device (manufactured by ALV, trade name “ALV5000”) using a 22 mW He—Ne laser (λ = 632.8 nm) as a light source was used for this measurement device.

  It was 7.2 when pH of the obtained binder composition for electrodes was measured using the pH meter (the product made by Toa TD Corporation, "HM-7J").

  Using the obtained binder composition for electrodes, each electrode was prepared by the above-described method for preparing a lithium ion secondary battery negative electrode, and various physical properties were measured. The peel strength of the lithium ion secondary battery negative electrode was 32 mN / 2 cm, the cycle characteristics were 52%, and the resistance change rate was 8.

5.5.2. Examples 2-16, Comparative Examples 1-8
Except having set it as the composition shown in Table 1-Table 3, it carried out similarly to Example 1, and obtained the binder composition for electrodes. Using the obtained electrode binder composition, the number average particle size and pH were measured, and the above-described lithium ion secondary battery negative electrode was prepared to measure various physical properties. Further, a lithium ion secondary battery was assembled in the same manner as in Example 1, and the cycle characteristics and the resistance change rate were measured. The measurement results are also shown in Tables 1 to 3.

  As shown in Tables 1 to 3, the electrode binder compositions of Examples 1 to 16 were compared with the electrode compositions of Comparative Examples 1 to 8, and current collectors and electrodes in lithium ion secondary batteries The results were excellent in various properties such as binding properties to the layer, cycle characteristics, and resistance change rate.

The present invention is not limited to the above-described embodiments, and various modifications can be made. For example, the present invention includes substantially the same configuration (for example, a configuration having the same function, method, and result, or a configuration having the same purpose and effect) as the configuration described in the embodiment. In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that achieves the same effect as the configuration described in the embodiment or a configuration that can achieve the same object. In addition, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

Claims (5)

(A) 5 to 40 parts by mass of a structural unit derived from an α, β-unsaturated nitrile compound;
(B) 1 to 10 parts by mass of a structural unit derived from a compound represented by the following general formula (1),
(E) polymer particles containing 40 parts by mass or less of a structural unit derived from a (meth) acrylate compound other than the structural unit (B) (excluding hydroxyethyl acrylate), and the number of the polymer particles An electrode binder composition having an average particle size of 50 to 350 nm;
With graphite as the active material,
An electrode slurry containing

(In the formula, R ¹ is a monovalent hydrocarbon group, and R ² is a divalent hydrocarbon group.)   The slurry for electrodes according to claim 1, wherein the compound represented by the general formula (1) is hydroxyethyl methacrylate.   The electrode slurry according to claim 1 or 2, wherein the pH of the electrode binder composition is 6 or more and 8 or less.   An electrode comprising: a current collector; and an active material layer produced using the electrode slurry according to any one of claims 1 to 3 on a surface of the current collector.   An electrochemical device comprising the electrode according to claim 4.