WO2012023626A1

WO2012023626A1 - Binder composition for use in electrodes

Info

Publication number: WO2012023626A1
Application number: PCT/JP2011/068818
Authority: WO
Inventors: 武志茂木; 博紀北口; 幸志樫下
Original assignee: Jsr株式会社
Priority date: 2010-08-20
Filing date: 2011-08-16
Publication date: 2012-02-23
Also published as: TW201209116A; JPWO2012023626A1

Abstract

A binder composition for use in electrodes, which contains a polymer that comprises structural units (A) derived from a monomer represented by general formula (1) and structural units (B) derived from an α,β-unsaturated nitrile monomer, and which is characterized in that: the content of the structural units (A) is 5 to 60% by mass; the content of the structural units (B) is 5 to 40% by mass; and the total content of the structural units (A) and (B) is 10 to 70% by mass. In general formula (1), R¹ is a hydrogen atom or a methyl group, and R² is a C_1-18 fluorinated hydrocarbon group.

Description

Electrode binder composition

The present invention relates to an electrode binder composition.

In electrochemical devices such as secondary batteries such as lithium ion secondary batteries and nickel metal hydride secondary batteries; capacitors such as lithium ion capacitors and electric double layer capacitors, a laminate in which an electrode active material layer is formed on a current collector The electrode which consists of consists of. The electrode active material layer in this electrode is formed by applying an electrode slurry onto a current collector to form a coating film, then drying the coating film, and preferably further pressing the dried coating film. . The electrode slurry is prepared by mixing an electrode binder composition and an electrode active material. The binder composition for electrodes is a dispersion in which a binder component such as polyvinylidene fluoride is dispersed in a solution or dispersion medium dissolved in a solvent.
In an electrochemical device having such an electrode, characteristics such as capacity, cycle characteristics, and discharge rate characteristics are problematic. These characteristics are greatly influenced by the characteristics of the binder as well as the type and amount of the electrode active material and the electrolyte contained in the electrode. For example, if the binding property of the binder is insufficient, a sufficient amount of electrode active material is not bound on the current collector, or the binding force between the electrode active materials is insufficient. The capacity becomes insufficient. In addition, the binding force of the binder may decrease due to repeated charging and discharging. In this case, when charging and discharging are repeated, the electrode active material gradually falls off from the current collector, and as a result, the capacity of the electrochemical device decreases with time (the cycle characteristics are poor). .
As described above, the binder used in the electrochemical device collects the electrode active material due to high adhesion between the electrode active material and the current collector, high binding property between the electrode active materials, and repeated charge and discharge. High binding durability that does not fall off the electric body is required.
In view of the above circumstances, several binder compositions have been proposed that have a high binding property and a high binding durability.
For example, JP 2002-42819 A discloses a binder composition containing a polymer having a structural unit derived from a fluorine-containing (meth) acrylate.
Japanese Patent No. 3539448 (JP-A-8-287915) has a structural unit derived from (meth) acrylate, a structural unit derived from acrylonitrile, and a structural unit derived from an unsaturated carboxylic acid at the same time. Binder compositions containing polymers have been proposed and have achieved some success.
In recent years, electrochemical devices have begun to be installed in automobiles. For example, secondary batteries such as lithium ion secondary batteries are used as main power sources for electric vehicles and hybrid cars, and capacitors such as electric double layer capacitors are used as auxiliary power sources for large vehicles such as trucks.
Since automobiles have significantly different usage environments (especially usage temperatures) depending on the area of use and seasonal factors, electrochemical devices mounted on automobiles are required to exhibit stable performance over a wide temperature range. However, it has been pointed out that when a conventionally known binder composition is applied to a vehicle-mounted application, various problems resulting from the use temperature occur. For example, it has been pointed out that an electrochemical device manufactured using the binder composition described in JP-A-2002-42819 has deteriorated discharge rate characteristics when subjected to high-speed discharge in a low temperature environment. The electrochemical device manufactured using the binder composition of the above-mentioned Japanese Patent No. 3539448 has a problem that the electrochemical stability in a high temperature environment is low, and self-discharge occurs when left in a high temperature environment.

The present invention has been made based on the above situation.
An object of the present invention is to provide a binder composition for an electrode that provides an electrochemical device that has high binding properties and is excellent in both discharge rate characteristics in a low temperature environment and electrochemical stability in a high temperature environment. Is to provide.
According to the present invention, the above objects and advantages of the present invention are:
Structural unit (A) derived from a monomer represented by the following general formula (1) and
Structural unit derived from α, β-unsaturated nitrile monomer (B)
Containing a polymer having
The content ratio of the structural unit (A) is 5 to 60% by mass,
The content of the structural unit (B) is 5 to 40% by mass, and
This is achieved by a binder composition for electrodes in which the total content of the structural unit (A) and the structural unit (B) is 10 to 70% by mass.

(However, R ¹ Represents a hydrogen atom or a methyl group, R ² Represents a fluorinated hydrocarbon group having 1 to 18 carbon atoms. )
Hereinafter, the binder composition for electrodes of the present invention will be described in detail.
<Binder composition for electrode>
The binder composition for electrodes of the present invention is a polymer having a structural unit (A) derived from the monomer represented by the general formula (1) and a structural unit (B) derived from an α, β-unsaturated nitrile monomer. (Hereinafter referred to as “specific polymer”). This binder composition for electrodes further contains a liquid medium and can optionally contain a thickener. The binder composition for electrodes of the present invention may further contain other components such as an emulsifier, a polymerization initiator or a residue thereof, a surfactant, and a neutralizing agent.
[Specific polymer]
The specific polymer contained in the binder composition for an electrode of the present invention has a structural unit (A) and a derived structural unit (B). This specific polymer may have another structural unit in addition to the structural unit (A) and the structural unit (B).
(Structural unit (A))
The specific polymer in this invention has the structural unit (A) derived from the monomer represented by the said General formula (1).
R in the general formula (1) ² Examples thereof include a fluorinated alkyl group having 1 to 18 carbon atoms, a fluorinated aryl group having 6 to 18 carbon atoms, and a fluorinated aralkyl group having 7 to 18 carbon atoms. R ² Is preferably a fluorinated alkyl group having 1 to 11 carbon atoms, and particularly preferably a group represented by the following general formula (2).

(However, R ³ Represents a hydrogen atom or a fluorinated hydrocarbon group having 1 to 10 carbon atoms, R ⁴ Represents a fluorinated hydrocarbon group having 1 to 10 carbon atoms. )
R in the general formula (2) ³ And R ⁴ The fluorinated hydrocarbon group having 1 to 10 carbon atoms is preferably a fluorinated alkyl group having 1 to 10 carbon atoms.
Preferable specific examples of the group represented by the general formula (2) include, for example, 2,2,2-trifluoroethyl group, 1,1,1-trifluoropropan-2-yl group, 2- (perfluoro Octyl) ethyl group, 2,2,3,3-tetrafluoropropyl group, 2,2,3,4,4,4-hexafluorobutyl group, 1H, 1H, 9H-perfluoro-1-nonyl group, 1H , 1H, 11H-perfluoroundecyl group, perfluorooctyl group, etc., among which 2,2,2-trifluoroethyl group and 2,2,2-trifluoroisopropyl group are more preferable, In particular, 2,2,2-trifluoroethyl group is preferable.
In the general formula (2), R ³ Is a hydrogen atom and R ⁴ Is preferably a fluorinated alkyl group having 1 to 3 carbon atoms.
As the monomer represented by the general formula (1) for deriving the structural unit (A), only one of the above may be used alone, or two or more selected from the above may be used in combination. May be.
(Structural unit (B))
The specific polymer in the present invention has a structural unit (B) derived from an α, β-unsaturated nitrile monomer together with the structural unit (A).
Specific examples of the α, β-unsaturated nitrile monomer leading to the structural unit (B) include (meth) acrylonitrile, α-chloroacrylonitrile, vinylidene cyanide and the like. In these, (meth) acrylonitrile is preferable and acrylonitrile is especially preferable. These α, β-unsaturated nitrile monomers can be used singly or in combination of two or more.
(Other structural unit types)
As described above, the specific polymer in the present invention may have another structural unit in addition to the structural unit (A) and the structural unit (B). As such another structural unit, a structural unit (C) derived from an unsaturated carboxylic acid monomer,
Structural unit (D) derived from a monomer represented by the following general formula (3),
Structural units (E) derived from at least one monomer selected from the group consisting of conjugated dienes and aromatic vinyl monomers and
Structural units derived from other monomers (F)
Can be mentioned.

(However, R ⁵ Represents a hydrogen atom or a methyl group, R ⁶ Represents a hydrocarbon group having 1 to 18 carbon atoms. )
Examples of the unsaturated carboxylic acid monomer that leads to the structural unit (C) include unsaturated monocarboxylic acid, unsaturated dicarboxylic acid, monoalkyl ester of unsaturated dicarboxylic acid, monoamide of unsaturated dicarboxylic acid, and the like.
Examples of the monocarboxylic acid include (meth) acrylic acid and crotonic acid;
Examples of the unsaturated dicarboxylic acid include maleic acid, fumaric acid, itaconic acid, and the like. Among the above, (meth) acrylic acid and itaconic acid are preferable as the unsaturated carboxylic acid monomer for leading the structural unit (C), and methacrylic acid is particularly preferable.
These unsaturated carboxylic acid monomers can be used singly or in combination of two or more.
R in the general formula (3) ⁶ Is preferably an alkyl group having 1 to 12 carbon atoms, for example, methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, n-amyl group, i- An amyl group, n-hexyl group, 2-ethylhexyl group, n-octyl group, i-nonyl group, n-decyl group, etc. can be mentioned.
The monomer represented by the general formula (3) for deriving the structural unit (D) can be used alone or in combination of two or more.
Among the monomers leading to the structural unit (E), examples of conjugated dienes include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 2- Such as chloro-1,3-butadiene (chloroprene);
Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, and divinylbenzene.
Monomers that lead to the structural unit (E) can be used singly or in combination of two or more.
Examples of other monomers that lead to the structural unit (F) include hydroxyalkyl (meth) acrylates such as hydroxymethyl (meth) acrylate and hydroxyethyl (meth) acrylate;
Polyfunctional (meth) acrylate monomers such as ethylene glycol di (meth) acrylate;
Carboxylic acid vinyl esters such as vinyl acetate and vinyl propionate;
Unsaturated dicarboxylic acid anhydrides;
Monoamides of unsaturated dicarboxylic acids;
Examples thereof include aminoalkylamides of ethylenically unsaturated carboxylic acids such as aminoethylacrylamide, dimethylaminomethylmethacrylamide, and methylaminopropylmethacrylamide, and one or more selected from these are used. be able to.
(Content ratio of each structural unit in the specific polymer)
The content ratio of the structural unit (A) in the specific polymer is 5 to 60% by mass, preferably 7 to 55% by mass in all the structural units. When the content rate of a structural unit (A) is too small, there exists a possibility that the cycling characteristics of the electrochemical device obtained may fall. On the other hand, when the content ratio of the structural unit (A) is excessive, it may be difficult to form an electrode active material layer having high adhesion to the current collector.
The content ratio of the structural unit (B) in the specific polymer is 5 to 40% by mass, preferably 5 to 35% by mass, based on all the structural units. When the content ratio of the structural unit (B) is too small, self-discharge may be large when the resulting electrochemical device is stored in a high temperature environment, and the durability may be low. On the other hand, when the content ratio of the structural unit (B) is excessive, the obtained electrode active material layer tends to be hard and brittle, and the adhesion and flexibility to the current collector may be low. There is.
In the specific polymer of the present invention, the total content of the structural unit (A) and the structural unit (B) is 10 to 70% by mass, preferably 15 to 65% by mass, based on all the structural units. . When this ratio is within the above range, the discharge rate characteristics under a low temperature environment and the electrochemical stability under a high temperature environment are further improved, which is preferable.
When the specific polymer in the present invention has the structural unit (C) together with the structural unit (A) and the structural unit (B), the electrode active material is aggregated when the binder composition of the present invention is mixed with the electrode active material. Therefore, it is possible to produce a slurry for an electrode having good dispersibility of the electrode active material. On the other hand, the specific polymer having too much content of the structural unit (C) is inferior in oxidation resistance, so that the polymer is oxidatively deteriorated by repeated charge and discharge, and the electrode active material layer cannot be retained. As a result, there may be a disadvantage that the charge / discharge characteristics deteriorate with time. Considering these, the content ratio of the structural unit (C) in the specific polymer is preferably 10% by mass or less, more preferably 1 to 5% by mass in all the structural units.
When the binder composition for an electrode containing the specific polymer having the structural unit (D) together with the structural unit (A) and the structural unit (B) is applied to the positive electrode or the electrode of the capacitor, the current collector and the electrode active material layer There is an advantage that the adhesion between them is improved. On the other hand, a specific polymer having too much content of the structural unit (D) is inferior in ionic conductivity and oxidation resistance, resulting in disadvantages such as an increase in electrode resistance and deterioration of charge / discharge characteristics over time. There is a case. Considering these, the content ratio of the structural unit (D) in the specific polymer is preferably 90% by mass or less, and more preferably 25 to 80% by mass in all the structural units.
When a binder composition for an electrode containing a specific polymer having the structural unit (E) together with the structural unit (A) and the structural unit (B) is applied to the negative electrode, a carbon material generally used as a negative electrode active material ( For example, there is an advantage of having an appropriate binding property to graphite. Furthermore, the obtained electrode layer has good flexibility and adhesion to the current collector. On the other hand, the specific polymer having too much content of the structural unit (E) is inferior in its ionic conductivity and oxidation resistance, and therefore has the disadvantages of increased electrode resistance and deterioration over time in charge / discharge characteristics. Considering these facts, the content ratio of the structural unit (E) in the specific polymer is preferably 75% by mass or less, more preferably 40 to 60% by mass in all the structural units.
It is preferable that the content rate of the structural unit (F) in a specific polymer shall be 10 mass% or less in all the structural units. By setting the ratio in this range, it is possible to suppress deterioration of ion conductivity and adhesion due to the introduction of the structural units (C), (D), and (E).
When the binder composition for an electrode of the present invention is applied to a positive electrode or a capacitor electrode, the specific polymer contained in the composition includes the structural unit (C) and the structural unit together with the structural unit (A) and the structural unit (B). It has a unit (D) and it is preferable that these content rates are as follows in all the structural units.
Structural unit (A): 10 to 50% by mass, especially 15 to 40% by mass
Structural unit (B): 5 to 30% by mass, especially 10 to 30% by mass
Total of structural unit (A) and structural unit (B): 20 to 60% by mass, especially 25 to 50% by mass
Structural unit (C): 2 to 5% by mass
Structural unit (D): 30 to 75% by mass, especially 35 to 60% by mass
The specific polymer contained in the electrode binder composition applied to the positive electrode or the capacitor electrode has a content ratio of the structural unit (E) and the structural unit (F) of 5% by mass or less in each of the structural units. It is preferable to contain neither the structural unit (E) nor the structural unit (F).
When the binder composition for an electrode of the present invention is applied to a negative electrode, the specific polymer contained in the composition includes the structural unit (C) and the structural unit (E) together with the structural unit (A) and the structural unit (B). It is preferable that these content ratios are as follows in all structural units.
Structural unit (A): 10 to 50% by mass, especially 15 to 40% by mass
Structural unit (B): 5 to 30% by mass, especially 10 to 30% by mass
Total of structural unit (A) and structural unit (B): 20 to 60% by mass, especially 25 to 50% by mass
Structural unit (C): 2 to 5% by mass
Structural unit (E): 45-55 mass%
The specific polymer contained in the binder composition for an electrode applied to the negative electrode is preferably such that the content ratio of the structural unit (D) and the structural unit (F) is 5% by mass or less in all the structural units. It is preferable that neither the structural unit (D) nor the structural unit (F) is contained.
[Method for producing specific polymer]
The specific polymer can be produced by polymerizing a mixture of the monomers described above. The polymerization method of the monomer mixture is not particularly limited, but it is preferable to use an emulsion polymerization method. When obtaining a specific polymer by the emulsion polymerization method, an emulsifier, a polymerization initiator, a molecular weight regulator and the like can be appropriately used.
As said emulsifier, anionic surfactant, nonionic surfactant, amphoteric surfactant etc. can be used individually by 1 type or in combination of 2 or more types. Specific examples of the anionic surfactant include, for example, higher alcohol sulfates, alkylbenzene sulfonates, aliphatic sulfonates, and polyethylene glycol alkyl ether sulfates;
Specific examples of the nonionic surfactant may include, for example, polyethylene glycol alkyl ester, polyethylene glycol alkyl ether, polyethylene glycol alkylphenyl ether, and the like. As the amphoteric surfactant, a salt in which the anion portion is a carboxylate salt, a sulfate ester salt, a sulfonate salt or a phosphate ester salt and the cation portion is an amine salt or a quaternary ammonium salt can be used. Specific examples of such amphoteric surfactants include betaines such as lauryl betaine and stearyl betaine;
Examples thereof include surfactants of amino acid type such as lauryl-β-alanine, lauryl di (aminoethyl) glycine, octyldi (aminoethyl) glycine.
The use ratio of such an emulsifier is preferably 0.5 to 5 parts by mass with respect to a total of 100 parts by mass of the monomers used.
Specific examples of the polymerization initiator include water-soluble polymerization initiators such as sodium persulfate, potassium persulfate, and ammonium persulfate;
Oil-soluble polymerization initiators such as benzoyl peroxide, lauryl peroxide, 2,2′-azobisisobutyronitrile;
Examples thereof include a redox polymerization initiator in combination with a reducing agent such as sodium bisulfite. These polymerization initiators can be used alone or in combination of two or more.
The use ratio of the polymerization initiator is preferably 0.3 to 3 parts by mass with respect to 100 parts by mass in total of the monomers used.
Specific examples of the molecular weight regulator include halogenated hydrocarbons such as chloroform and carbon tetrachloride;
mercaptan derivatives such as n-hexyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, thioglycolic acid;
Xanthogen derivatives such as dimethylxanthogen disulfide and diisopropylxanthogen disulfide;
Other molecular weight regulators such as terpinolene and α-methylstyrene dimer can be mentioned.
It is preferable that the usage-amount of a molecular weight modifier shall be 5 mass parts or less with respect to 100 mass parts of total of the monomer used.
Emulsion polymerization is preferably carried out in a suitable aqueous medium, particularly preferably in water. The total content of the monomers in the aqueous medium can be 10 to 50% by weight, and preferably 20 to 40% by weight.
The conditions for emulsion polymerization are not particularly limited. For example, the polymerization temperature can be 40 to 85 ° C. and the polymerization time can be 2 to 16 hours.
Particularly preferred emulsion polymerization methods are as follows. That is,
In an aqueous medium containing at least a polymerization initiator,
In this method, emulsion polymerization is started by adding an emulsion of a monomer mixture (hereinafter referred to as “monomer emulsion”), and, if necessary, polymerization is continued after the addition of the monomer emulsion is completed.
The temperature of the aqueous medium containing the polymerization initiator is preferably 40 to 85 ° C, and more preferably 60 to 80 ° C. At this time, in order to avoid decomposition of the polymerization initiator in the temperature raising process, after raising the temperature of the aqueous medium to some extent (for example, after reaching 40 to 70 ° C.), a polymerization initiator is added thereto, and after the polymerization initiator is added. It is preferable to start adding the monomer emulsion before the excessive time has elapsed.
The aqueous medium containing a polymerization initiator may further contain optional components such as the molecular weight regulator described above. The monomer emulsified liquid can be prepared by adding a monomer and an emulsifier and other optional components as required to an aqueous medium, and sufficiently stirring them. The monomer content in the emulsion is preferably 40 to 80% by weight, more preferably 50 to 70% by weight.
The addition of the monomer emulsion into the aqueous medium containing the polymerization initiator is preferably performed slowly so that the polymerization initiator is not unevenly distributed in the reaction solution and a non-uniform polymerization reaction does not occur. The addition time is preferably 0.5 to 6 hours, and more preferably 1 to 4 hours.
It is preferable to continue the polymerization after completing the addition of the monomer emulsion. In this case, the temperature of the continuous polymerization is preferably 40 to 85 ° C, more preferably 60 to 80 ° C. The continuous polymerization time is preferably 0.5 to 6 hours, more preferably 1 to 4 hours. The total polymerization time from the start of addition of the monomer emulsion is preferably 1 to 12 hours, and more preferably 3 to 8 hours.
[Characteristics of specific polymer]
The specific polymer contained in the electrode binder composition of the present invention preferably has a glass transition temperature (Tg) of −45 to 25 ° C.
The glass transition temperature (Tg) of the specific polymer can be measured as follows. About 4 g of the latex in which the specific polymer is dispersed is poured into a 5 cm × 4 cm Teflon (registered trademark) petri dish and dried in a thermostat at 70 ° C. for 24 hours to obtain a film having a thickness of about 100 μm. About 10 mg of sample is cut out from the obtained film, and this is collected in an aluminum container and sealed. Then, using a differential scanning calorimeter (NETZSCH-Ger atebau GmbH, model “DSC204F1”), the temperature range of −80 ° C. to 100 ° C. at a temperature rising rate of 20 ° C./min in an air atmosphere is shown. Scanning calorimetry is performed, and the glass transition temperature Tg is obtained based on the obtained DSC chart. When obtaining the glass transition temperature (Tg) from the DSC chart, it is performed in accordance with the method for obtaining the midpoint glass transition temperature described in JIS K7121.
(Liquid medium)
The binder composition for electrodes of the present invention contains a liquid medium together with the above specific polymer. The liquid state body can be an aqueous medium or a non-aqueous medium.
The electrode binder composition of the present invention is in the form of a slurry or latex in which the specific polymer as described above is dispersed in an aqueous medium, or in the form of a solution in which the specific polymer is dissolved in a non-aqueous medium. Is preferred.
The aqueous medium contains water. The aqueous medium can contain a small amount of a non-aqueous medium in addition to water. Examples of such a non-aqueous medium include amide compounds, hydrocarbons, alcohols, ketones, esters, amine compounds, lactones, sulfoxides, sulfone compounds, and the like, and one or more selected from these are used. can do. The content ratio of such a non-aqueous medium is preferably 10% by mass or less, and more preferably 5% by mass or less, based on the whole of the aqueous medium. It is most preferable that it consists only of.
The specific polymer is preferably particulate in an aqueous medium. The number average particle diameter of the specific polymer in the aqueous medium is preferably 50 to 190 nm, and more preferably 70 to 185 nm. When the number average particle diameter of the specific polymer is within the above range, migration of the polymer particles does not occur in the drying step when forming the electrode active material layer, and therefore the composition of the obtained electrode active material layer is uniform. As a result, a sufficient number of effective adhesion points are obtained among the electrode active material, the polymer particles, and the current collector, so that high binding properties can be obtained, which is preferable.
The number average particle diameter of the specific polymer is a number from the hydrodynamic diameter measured by a dynamic light scattering method using water as a dispersion medium using a laser particle size analysis system “LPA-3000s / 3100” manufactured by Otsuka Electronics Co., Ltd. It can be calculated as an average value.
On the other hand, the non-aqueous medium can be suitably used as long as it can dissolve the specific polymer. Specific examples of the non-aqueous medium include aliphatic hydrocarbons such as n-octane, isooctane, nonane, decane, decalin, pinene, and chlorododecane;
Cycloaliphatic hydrocarbons such as cyclopentane, cyclohexane, cycloheptane, methylcyclopentane;
Aromatic hydrocarbons such as chlorobenzene, chlorotoluene, ethylbenzene, diisopropylbenzene, cumene;
Alcohols such as methanol, ethanol, propanol, isopropanol, butanol, benzyl alcohol, glycerin;
Ketones such as acetone, methyl ethyl ketone, cyclopentanone, isophorone;
Ethers such as methyl ethyl ether, diethyl ether, tetrahydrofuran, dioxane;
lactones such as γ-butyrolactone and δ-butyrolactone;
lactams such as β-lactams;
Linear or cyclic amide compounds such as dimethylformamide, N-methylpyrrolidone, dimethylacetamide;
Compounds having a nitrile group, such as methylene cyanohydrin, ethylene cyanohydrin, 3,3′-thiodipropionitrile, acetonitrile;
Nitrogen-containing heterocyclic compounds such as pyridine and pyrrole;
Glycol compounds such as ethylene glycol and propylene glycol;
Diethylene glycol or derivatives such as diethylene glycol, diethylene glycol monoethyl ether, diethylene glycol ethyl butyl ether;
Examples thereof include esters such as ethyl formate, ethyl lactate, propyl lactate, methyl benzoate, methyl acetate, and methyl acrylate.
The content ratio of the specific polymer in the electrode binder composition of the present invention is preferably 20 to 60% by mass, and more preferably 25 to 50% by mass.
(Thickener)
The above thickener can be contained in the electrode binder composition of the present invention in order to further improve the applicability, charge / discharge characteristics and the like of the electrode binder composition.
Examples of such thickeners include cellulose derivatives such as carboxymethylcellulose, methylcellulose, and hydroxypropylcellulose;
In addition to polyacrylates such as sodium polyacrylate,
Polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, (meth) acrylic acid-vinyl alcohol copolymer, maleic acid-vinyl alcohol copolymer, modified polyvinyl alcohol, polyethylene glycol, ethylene-vinyl alcohol copolymer, polyvinyl acetate partial ken And the like.
The content of the thickener in the electrode binder composition of the present invention is 20% by weight or less based on the total solid content of the electrode binder composition (total mass of components other than the liquid medium in the composition). It is preferably 0.1 to 10% by weight.
(Preferred embodiment of electrode binder composition)
The binder composition for electrodes of the present invention is preferably in the form of a latex in which the specific polymer is in the form of particles and dispersed in an aqueous medium. As the electrode binder composition of the present invention, the polymerization reaction mixture after synthesizing (polymerizing) the specific polymer as described above in an aqueous medium is used as it is after adjusting the liquidity as necessary. It is particularly preferred. Therefore, the electrode binder composition of the present invention can contain other components such as an emulsifier, a polymerization initiator or a residue thereof, a surfactant, and a neutralizer in addition to the polymer particles and the aqueous medium. The content ratio of these other components is preferably 3% by weight or less, more preferably 2% by weight or less as a ratio of the total weight of the other components to the solid content of the composition.
The solid content concentration of the electrode binder composition (the ratio of the total mass of components other than the liquid medium in the composition to the total mass of the composition) is preferably 20 to 60% by weight, 25 More preferably, it is ~ 50% by weight.
The liquid property of the binder composition for electrodes is preferably near neutral, more preferably pH 6.0 to 8.5, and particularly preferably pH 7.0 to 8.0. For adjusting the liquidity of the composition, a known water-soluble acid or base can be used. Examples of the acid include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid and the like;
Examples of the base include sodium hydroxide, potassium hydroxide, lithium hydroxide, and aqueous ammonia.
The binder composition for electrodes of the present invention contains a polymer having a structural unit (A) and a structural unit (B). Therefore, as will be apparent from the examples described later, high binding properties are obtained, and the electrochemical device is excellent in both discharge rate characteristics in a low temperature environment and electrochemical stability in a high temperature environment. Can be given.
<Slurry for electrodes>
The slurry for an electrode of the present invention is
Electrode active material and
The electrode binder composition of the present invention as described above
Containing. The electrode slurry of the present invention may contain other components as required in addition to the electrode active material and the electrode binder composition of the present invention.
(Electrode active material)
The electrode active material is appropriately selected according to the type of the target electrochemical device.
When the electrode binder composition of the present invention is applied to an electrode slurry (positive electrode slurry) for forming a positive electrode of a lithium ion secondary battery, examples of the electrode active material (positive electrode active material) include lithium cobalt oxide. Lithium nickelate, lithium manganate, lithium iron phosphate, ternary nickel cobalt lithium manganate and the like can be suitably used.
When the electrode binder composition of the present invention is applied to an electrode slurry (negative electrode slurry) for forming a negative electrode of a lithium ion secondary battery, examples of the electrode active material (negative electrode active material) include carbon materials, Carbon or the like can be suitably used. Examples of the carbon material include carbon materials obtained by firing organic polymer compounds, coke, pitch, and the like. Examples of the organic polymer compounds that are precursors of the carbon materials include phenol resins and polyacrylonitrile. And cellulose. Examples of the carbon include artificial graphite and natural graphite.
When the electrode binder composition of the present invention is applied to an electrode slurry for forming an electrode for an electric double layer capacitor, examples of the electrode active material include graphite, non-graphitizable carbon, and hard carbon;
Carbon material obtained by firing coke, pitch, etc .;
A polyacene organic semiconductor (PAS) or the like can be used.
(Other ingredients)
The electrode slurry of the present invention may further contain a thickener, a dispersant, a surfactant, an antifoaming agent, and the like as necessary.
As said thickener, the same thing as what was illustrated above as a thickener which the binder composition for electrodes of this invention can contain arbitrarily;
Examples of the dispersant include sodium hexametaphosphate, sodium tripolyphosphate, and sodium polyacrylate;
Examples of the surfactant include a nonionic surfactant or an anionic surfactant as a latex stabilizer.
The content ratio of these other components is preferably 10% by weight or less based on the total solid content of the slurry for electrodes of the present invention (total mass of components other than the liquid medium in the composition). It is more preferable that it is ~ 5% by weight.
(Preferred embodiment of slurry for electrode)
The electrode slurry preferably contains 0.1 to 10 parts by mass, and 0.3 to 4 parts by mass of the electrode binder composition in terms of solid content with respect to 100 parts by mass of the electrode active material. More preferably. When the content ratio of the electrode binder composition is 0.1 to 10 parts by mass in terms of solid content, the specific polymer becomes difficult to dissolve in the electrolyte solution used in the electrochemical device. An adverse effect on device characteristics due to the rise can be suppressed.
The electrode slurry is prepared by mixing the electrode binder composition of the present invention, the electrode active material as described above, and other components used as necessary. As a means for mixing them, for example, a known mixing device such as a stirrer, a defoamer, a bead mill, a high-pressure homogenizer, or the like can be used.
The preparation of the electrode slurry is preferably performed under reduced pressure, thereby preventing bubbles from being generated in the obtained electrode active material layer.
The electrode slurry as described above contains the electrode binder composition of the present invention to form an electrode active material layer having high adhesion between the electrode active materials and between the electrode active material and the current collector. In addition, it is possible to provide an electrochemical device excellent in both discharge rate characteristics in a low temperature environment and electrochemical stability in a high temperature environment.
<Electrode>
The electrode in the present invention is
A current collector,
An electrode active material layer formed through a process of applying and drying the electrode slurry described above on the surface of the current collector;
Is provided. After the coating film is dried, press working is preferably performed.
(Current collector)
As the current collector, for example, a metal foil, an etching metal foil, an expanded metal, or the like can be used. Specific examples of these materials include metals such as aluminum, copper, nickel, tantalum, stainless steel, titanium, and the like, which can be appropriately selected and used according to the type of the target electrochemical device.
For example, when forming the positive electrode of a lithium ion secondary battery, it is preferable to use aluminum among the above as a collector. In this case, the thickness of the current collector is preferably 5 to 30 μm, and more preferably 8 to 25 μm.
On the other hand, when forming the negative electrode of a lithium ion secondary battery, it is preferable to use copper among the above as the current collector. In this case, the thickness of the current collector is preferably 5 to 30 μm, and more preferably 8 to 25 μm.
Furthermore, when forming an electrode for an electric double layer capacitor, it is preferable to use aluminum or copper among the above as the current collector. In this case, 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.
(Formation of electrode active material layer)
The electrode active material layer in the electrode is formed by applying and drying the electrode slurry on the surface of the current collector as described above.
As a method for applying the electrode slurry onto the current collector, for example, an appropriate method such as a doctor blade method, a reverse roll method, a comma bar method, a gravure method, or an air knife method can be applied.
The coating film is preferably dried in a temperature range of 20 to 250 ° C., more preferably 50 to 150 ° C., preferably for 1 to 120 minutes, more preferably 5 to 60 minutes.
The dried coating film is preferably subjected to press working. Examples of means for performing the pressing include a roll press machine, a high-pressure super press machine, a soft calendar, and a 1-ton press machine. The press working conditions are appropriately set according to the type of processing machine used and the desired thickness and density of the electrode active material layer.
The electrode active material layer has a thickness of 40 to 100 μm and a density of 1.3 to 2.0 g / cm. ³ It is preferable that
(Characteristics of electrode)
The electrode formed as described above is
Since the electrode active material layer is formed using the electrode slurry containing the binder composition of the present invention, the electrode active material layer has high adhesion between the electrode active materials and between the electrode active material and the current collector. Is. Further, when this electrode is used, an electrochemical device excellent in both discharge rate characteristics in a low temperature environment and electrochemical stability in a high temperature environment can be obtained.
The electrode of the present invention can be suitably used as an electrode of an electrochemical device such as a lithium ion secondary battery, an electric double layer capacitor, or a lithium ion capacitor.
In the case of constituting a secondary battery such as a lithium ion secondary battery, the electrode formed using the binder composition of the present invention exhibits a performance superior to that of the prior art, both as a positive electrode and a negative electrode. As is clear from the examples, it is preferable in that a higher effect can be obtained when used as a positive electrode.
<Electrochemical device>
The electrochemical device in the present invention includes the electrode as described above.
The electrochemical device according to the present invention has a structure in which the electrode as described above is opposed to the counter electrode via the electrolytic solution, and is preferably isolated by the presence of the separator.
As a manufacturing method thereof, for example, two electrodes (two of a positive electrode and a negative electrode or two of a capacitor electrode) are overlapped via a separator, and this is wound or folded in accordance with the battery shape. And injecting the electrolyte into the battery container and sealing it. The shape of the battery can be an appropriate shape such as a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, or a flat shape.
The electrolytic solution is appropriately selected and used according to the type of target electrochemical device. As the electrolytic solution, a solution in which an appropriate electrolyte is dissolved in a solvent is used.
When manufacturing a lithium ion secondary battery, a lithium compound is used as an electrolyte. Specifically, for example, 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 , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N etc. can be mentioned. The electrolyte concentration in this case is preferably 0.5 to 3.0 mol / L, more preferably 0.7 to 2.0 mol / L.
When manufacturing an electric double layer capacitor, for example, tetraethylammonium tetrafluoroborate, triethylmethylammonium tetrafluoroborate, tetraethylammonium hexafluorophosphate or the like is used as an electrolyte. The electrolyte concentration in this case is preferably 0.5 to 3.0 mol / L, more preferably 0.7 to 2.0 mol / L.
The type and concentration of the electrolyte in manufacturing the lithium ion capacitor are the same as in the case of the lithium ion secondary battery.
In any case, examples of the solvent used in the electrolyte include carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate;
lactones such as γ-butyrolactone;
Ethers such as trimethoxysilane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran;
Sulfoxides such as dimethyl sulfoxide;
Oxolane derivatives such as 1,3-dioxolane, 4-methyl-1,3-dioxolane;
Nitrogen-containing compounds such as acetonitrile and nitromethane;
Esters such as methyl formate, methyl acetate, butyl acetate, methyl propionate, ethyl propionate, phosphate triester;
Glyme compounds such as diglyme, triglyme and tetraglyme;
Ketones such as acetone, diethyl ketone, methyl ethyl ketone, methyl isobutyl ketone;
Sulfone compounds such as sulfolane;
Oxazolidinone derivatives such as 2-methyl-2-oxazolidinone;
Examples include sultone compounds such as 1,3-propane sultone, 1,4-butane sultone, 2,4-butane sultone, and 1,8-naphtha sultone.
Such an electrochemical device has high adhesion between the electrode active materials and between the electrode active material and the current collector in the electrode active material layer, and also has a discharge rate characteristic in a low temperature environment and electrochemical in a high temperature environment. Excellent in both stability and stability. Therefore, this electrochemical device is suitable as a secondary battery or a capacitor mounted on an automobile such as an electric vehicle, a hybrid car, and a truck, as well as a secondary battery used for AV equipment, OA equipment, communication equipment, It is also suitable as a capacitor.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. However, the present invention is not limited to these examples.
“Parts” in the following examples and comparative examples are based on mass unless otherwise specified.
The evaluation methods of electrodes and electrochemical devices in the following examples and comparative examples are as follows.
<Evaluation of electrode>
(1) Peel strength of electrode active material layer A test piece having a width of 2 cm and a length of 12 cm was cut out from the electrode (laminate). The surface of the test piece on the electrode active material layer side was attached to an aluminum plate with a double-sided tape. A tape having a width of 18 mm (JIS Z1522-compliant product, trade name “Cerotape (registered trademark)”, manufactured by Nichiban Co., Ltd.) was attached to the current collector side surface of the test piece on the aluminum plate.
While maintaining the angle with the aluminum plate at 90 °, the peel strength (mN / 2 cm) when this tape was pulled upward at a speed of 50 mm / min and peeled at a peel angle of 90 ° was measured 6 times. The average value was calculated as the peel strength (mN / 2 cm) of the electrode active material layer. “MN / 2 cm” is a unit indicating the peel strength per 2 cm width.
It can be determined that the greater the peel strength value, the higher the adhesion strength between the current collector and the electrode active material layer, and the more difficult the electrode active material layer peels from the current collector. In particular, this value is good when it is 90 mN / 2 cm or more.
<Evaluation of lithium ion secondary battery>
(1) Low temperature rate characteristics (3.0C / 0.2C)
First, after repeating a cycle of charging a lithium ion secondary battery at −20 ° C. by a constant current (0.2 C) / constant voltage (3.8 V) method and discharging by a constant current (0.2 C) method three times. The discharge capacity (C _0.2 ) of was measured. Next, this battery was charged at −20 ° C. by a constant current (0.2 C) / constant voltage (3.8 V) method and discharged by a constant current ( _3.0 C) method (C _3.0 ). Was measured.
Using these measured values, the low temperature rate characteristic (3.0 C / 0.2 C) (%) of the lithium ion secondary battery was calculated by the following formula.
Low-temperature rate characteristic (%) = {(C _3.0 ) ÷ (C _0.2 )} × 100
It can be determined that the larger the value of the low temperature rate characteristic is, the smaller the change in the characteristic of the electrode is in the low temperature environment. In particular, this value is good when it is 80% or more.
In the measurement conditions, “1C” indicates a current value at which discharge is completed in one hour after constant current discharge of a cell having a certain electric capacity. For example, “0.1 C” is a current value at which discharge is completed over 10 hours, and 10 C is a current value at which discharge is completed over 0.1 hours.
(2) Self-discharge rate in a high temperature environment First, a lithium ion secondary battery is charged at a normal temperature (25 ° C.) by a constant current (0.2 C) / constant voltage (3.8 V) method, and a constant current (0.2 C) is obtained. ) The discharge capacity (C _before ) when discharged by the method was measured. Next, the battery was charged at a normal temperature (25 ° C.) by a constant current (0.2 C) / constant voltage (3.8 V) method, left at 85 ° C. for 3 days, and then allowed to cool to normal temperature (25 ° C.). In addition, the discharge capacity (C _after ) when discharged by the constant current (0.2 C) method was measured.
Using these measured values, the self-discharge rate (%) was calculated by the following formula.
Self-discharge rate (%) = [{(C _before ) − (C _after )} ÷ (C _before )] × 100
It can be determined that the smaller the value of the self-discharge rate, the more self-discharge is suppressed in a high temperature environment. In particular, this value is good when it is less than 30%.
(3) Cycle characteristics A cycle in which a lithium ion secondary battery was charged by a constant current (0.2 C) / constant voltage (3.8 V) system and discharged by a constant current (0.2 C) system was repeated 50 times. In this case, the third cycle discharge capacity _{(C 3Cycles)} and 50th cycle discharge capacity _{(C 50Cycles)} was measured to calculate the cycle characteristics (%) by the following equation.
Cycle characteristics (%) = {(C _{50 Cycles} ) / (C 3 _Cycles )} × 100
It can be determined that the deterioration of the battery characteristics due to the oxidative decomposition of the binder due to charging and discharging is suppressed as the value of the cycle characteristics is closer to 100%. In particular, this value is good when it is 80% or more.
<Evaluation of electric double layer capacitor>
(1) Self-discharge rate in high temperature environment (%)
The voltage (V _before ) after charging the electric double layer capacitor at room temperature (25 ° C.) for 1 hour by a constant current (10 mA / F) / constant voltage (2.5 V) method was measured. Next, the voltage (V _after ) _after this electric double layer capacitor was left at 85 ° C. for 3 days was measured.
Using these measured values, the self-discharge rate (%) was calculated by the following formula.
Self-discharge rate (%) = [{(V _before ) − (V _after )} ÷ (V _before )] × 100
It can be determined that the smaller the value of the self-discharge rate, the more the self-discharge is suppressed in a high temperature environment. In particular, this value is good when it is less than 30%.
(2) Cycle characteristics The cycle in which the electric double layer capacitor was charged by the constant current (1C) / constant voltage (3.5 V) method and discharged by the constant current (1C) method was repeated 100 times. In this case, the third cycle discharge capacity _{(C 3Cycles)} and 100 th cycle discharge capacity _{(C 100Cycles)} was measured to calculate the cycle characteristics (%) by the following equation.
Cycle characteristics (%) = {(C 100 _Cycles ) / (C 3 _Cycles )} × 100
It can be determined that the deterioration of the battery characteristics due to the oxidative decomposition of the binder due to charging and discharging is suppressed as the value of the cycle characteristics is closer to 100%. In particular, this value is good when it is 80% or more.
<Preparation Example of Electrode Binder Composition>
Example 1
In a 7-liter separable flask, 150 parts of water and 0.2 part of sodium dodecylbenzenesulfonate were charged, and the inside of the separable flask was sufficiently purged with nitrogen.
On the other hand, in another container, 60 parts of water, ether sulfate type emulsifier (trade name “ADEKA rear soap SR1025”, manufactured by ADEKA Co., Ltd.) as an emulsifier, 0.8 parts in terms of solid content, and 2,2,2 as monomers -A monomer emulsion containing 25 parts of trifluoroethyl methacrylate, 25 parts of acrylonitrile, 10 parts of methyl methacrylate, 40 parts of 2-ethylhexyl acrylate and 5 parts of methacrylic acid and containing a mixture of the above monomers was stirred well.
Thereafter, the temperature inside the separable flask was started, and when the temperature inside the separable flask reached 60 ° C., 0.5 part of ammonium persulfate was added as a polymerization initiator. Then, when the temperature inside the separable flask reaches 70 ° C., the addition of the monomer emulsion prepared above is started, and the monomer emulsion is added while maintaining the temperature inside the separable flask at 70 ° C. Slowly added over time. Thereafter, the temperature inside the separable flask was raised to 85 ° C., and this temperature was maintained for 3 hours to carry out the polymerization reaction. After 3 hours, the separable flask was cooled to stop the reaction, and ammonium water was added to adjust the pH to 7.6, thereby preparing an electrode binder composition (s1).
The solid content concentration of the obtained binder composition for electrodes (s1) was 30% by mass. The polymer in the electrode binder composition (s1) was in the form of particles having a glass transition temperature of −10 ° C. and a number average particle diameter of 100 nm.
Examples 2 to 6 and Comparative Examples 1 to 5 and 7
The electrode binder compositions (s2) to (s6) and (r1) to (r5) and (r7) were carried out in the same manner as in Example 1 except that the monomers were used in accordance with the formulation shown in Table 1 below. ) Were prepared respectively.
The glass transition temperature of the polymer in each obtained binder composition for electrodes and the number average particle diameter of the polymer particles are shown in Table 1 below.
Example 7
In a 7-liter separable flask, 150 parts of water and 0.2 part of sodium dodecylbenzenesulfonate were charged, and the inside of the separable flask was sufficiently purged with nitrogen.
On the other hand, in another container, 60 parts of water, ether sulfate type emulsifier (trade name “ADEKA rear soap SR1025”, manufactured by ADEKA Co., Ltd.) as an emulsifier, 0.8 parts in terms of solid content, and 2,2,2 as monomers -A monomer emulsion containing 25 parts of trifluoroethyl methacrylate, 25 parts of acrylonitrile, 10 parts of methyl methacrylate, 40 parts of 2-ethylhexyl acrylate and 5 parts of methacrylic acid and containing a mixture of the above monomers was stirred well.
After adding the total amount of the monomer emulsion to the separable flask, the temperature increase was started, and when the temperature inside the separable flask reached 60 ° C., 0.5 parts of ammonium persulfate as a polymerization initiator was used. Was added. Next, the temperature inside the separable flask was raised to 70 ° C., and this temperature was maintained for 3 hours, and then the temperature was raised to 85 ° C. to conduct a polymerization reaction for another 3 hours. Thereafter, the separable flask was cooled to stop the reaction, and then ammonium water was added to adjust the pH to 7.6 to prepare an electrode binder composition (s7). The solid content concentration of the obtained binder composition for electrodes (s7) was 30% by mass. The polymer in the electrode binder composition (s7) was in the form of particles having a glass transition temperature of −10 ° C. and a number average particle diameter of 100 nm.
Comparative Example 6
An electrode binder composition (r6) was prepared in the same manner as in Example 7 except that the monomer was used in accordance with the formulation shown in Table 1 below.
The glass transition temperature of the polymer and the number average particle diameter of the polymer particles in the obtained binder composition for electrodes (r6) are shown in Table 1 below.
Example 8
In a temperature-controllable autoclave equipped with a stirrer, 200 parts of water, 0.6 part of sodium dodecylbenzenesulfonate, 1.0 part of potassium persulfate and 0.5 part of sodium bisulfite and 2,2,2 as monomers -25 parts of trifluoroethyl methacrylate, 25 parts of acrylonitrile, 16 parts of styrene, 35 parts of butadiene and 4 parts of methacrylic acid were charged all at once and a polymerization reaction was carried out at 80 ° C for 6 hours to obtain a polymer dispersion. Thereafter, an aqueous ammonium solution was added to the obtained polymer dispersion to adjust the pH to 7.4, 1 part of sodium polyacrylate was added as a thickener, and the remaining monomer was removed by steam distillation. Then, the binder composition for electrodes (s8) was prepared by concentrating under reduced pressure until the solid content concentration was 48% by mass.
The glass transition temperature of the polymer and the number average particle diameter of the polymer particles in the obtained electrode binder composition (s8) are shown in Table 1 below.
Comparative Example 8
An electrode binder composition (r8) was prepared in the same manner as in Example 8 except that the monomer was used in accordance with the formulation shown in Table 1 below.
The glass transition temperature of the polymer and the number average particle diameter of the polymer particles in the obtained binder composition for electrodes (r8) are shown in Table 1 below.

<Production and Evaluation of Lithium Ion Secondary Battery (1), Example of Applying Binder Composition for Electrode of the Present Invention to Positive Electrode>
Examples 9 to 15 and Comparative Examples 9 to 15
Using the electrode binder compositions (s1) to (s7) and (r1) to (r7) prepared in Examples 1 to 7 and Comparative Examples 1 to 7, lithium ion secondary batteries were prepared as follows. Manufactured and evaluated.
(1) Manufacture of positive electrode for lithium ion secondary battery Biaxial planetary mixer (trade name “TK Hibismix 2P-03”, manufactured by Primics Co., Ltd.), thickener (trade name “CMC800H”, Daicel Chemical) Industrial Co., Ltd.) 1 part (in terms of solid content), 100 parts of lithium iron phosphate (in terms of solid content) as the positive electrode active material, 5 parts of acetylene black (in terms of solid content) and 70 parts of water as the conductive agent, Stirring was performed at 60 rpm for 1 hour. Thereafter, 2 parts of each electrode binder composition prepared in the above Examples and Comparative Examples (in terms of solid content) was added, and the mixture was further stirred for 1 hour to obtain a paste. After 90 parts of water was added to the obtained paste to adjust the solid content concentration to 40% by mass, it was stirred at 200 rpm using a stirring defoamer (trade name “Awatori Nertaro”, manufactured by Shinkey Co., Ltd.). The mixture was stirred and mixed for 2 minutes at 1,800 rpm for 5 minutes, and further under reduced pressure at 1,800 rpm for 1.5 minutes to prepare a positive electrode slurry.
Next, the positive electrode slurry prepared above was uniformly applied to the surface of a current collector made of an aluminum foil having a thickness of 30 μm by a doctor blade method so that the film thickness of the coated film after drying was 90 μm. The coating film was obtained by drying for 20 minutes. Then, an electrode active material layer was formed by pressing using a roll press so that the density of the film was 1.7 g / cm ³ to form a laminate. By punching the laminate, a disc-shaped positive electrode for a lithium ion secondary battery having a diameter of 15.95 mm was manufactured.
The peel strength of the electrode active material layer in each of the obtained positive electrodes for lithium ion secondary batteries is shown in Table 2 below.
(2) Manufacture of negative electrode for lithium ion secondary battery A biaxial planetary mixer (product name “TK Hibismix 2P-03” manufactured by PRIMIX Corporation) and 4 parts of polyvinylidene fluoride (PVDF) (in terms of solid content) ), 100 parts of graphite (in terms of solid content) and 80 parts of N-methylpyrrolidone (NMP) were added as the negative electrode active material, and the mixture was stirred at 60 rpm for 1 hour. Then, after adding 20 parts of NMP further, using a stirring defoamer (product name “Awatori Neraro” manufactured by Shinky Co., Ltd.), the pressure was further reduced at 200 rpm for 2 minutes and then at 1,800 rpm for 5 minutes. Below, the slurry for negative electrodes was prepared by stirring and mixing for 1.5 minutes at 1,800 rpm.
The negative electrode slurry prepared above is uniformly applied to the surface of a current collector made of copper foil having a thickness of 20 μm by a doctor blade method so that the film thickness after drying is 150 μm, and dried at 120 ° C. for 20 minutes. A coating film was obtained. Then, it pressed using the roll press machine so that the density of a film | membrane might be 1.8 g / cm < ³ >, and the laminated body was formed. By punching the laminate, a disc-shaped negative electrode for a lithium ion secondary battery having a diameter of 16.16 mm was produced.
(3) Manufacture of Lithium Ion Secondary Battery A negative electrode for a lithium ion secondary battery was placed on a bipolar coin cell (trade name “HS Flat Cell”, manufactured by Hosen Co., Ltd.) in a glove box. Next, a separator (trade name “Celguard # 2400”, manufactured by Celgard Co., Ltd.) made of a disk-shaped polypropylene porous film having a diameter of 18 mm is placed on the negative electrode, and an electrolyte solution is added so that air does not enter. Injected. Next, after placing a positive electrode for a lithium ion secondary battery on this separator, a lithium ion secondary battery was manufactured by tightening and sealing the outer body of the bipolar coin cell with a screw.
The electrolytic solution used here is a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethyl methyl carbonate = 1/1 (mass ratio).
Table 2 below shows the low-temperature rate characteristics, the self-discharge rate under a high-temperature environment, and the cycle characteristics of each obtained lithium ion secondary battery.

As understood from the results in Table 2, when the electrode binder compositions (s1) to (s7) of the present invention are used, a positive electrode for a lithium ion secondary battery having a high peel strength of the electrode active material layer can be obtained. . And it was confirmed that the lithium ion secondary battery provided with such a positive electrode is excellent in both discharge rate characteristics in a low temperature environment and electrochemical stability in a high temperature environment.
In particular, binder compositions for electrodes (s1) to (s3) using 2,2,2-trifluoroethyl methacrylate as the specific fluorine-containing (meth) acrylate and acrylonitrile as the α, β-unsaturated nitrile compound are as follows: In addition, a lithium ion secondary battery positive electrode for a lithium ion secondary battery having a higher peel strength of the electrode active material layer can be obtained, and further excellent in discharge rate characteristics in a low temperature environment and electrochemical stability in a high temperature environment. It was confirmed that
<Production and Evaluation of Lithium Ion Secondary Battery (2), Example of Applying Electrode Binder Composition of the Present Invention to Negative Electrode>
Examples 16 to 18 and Comparative Examples 16 to 18
The electrode binder compositions (s1), (s7) and (s8) and (r5) to (r6) and (r8) prepared in Examples 1, 7 and 8 and Comparative Examples 5, 6 and 8 were used, respectively. Thus, lithium ion secondary batteries were manufactured and evaluated as follows.
(1) Manufacture of negative electrode for lithium ion secondary battery Biaxial planetary mixer (trade name “TK Hibismix 2P-03”, manufactured by Primix Co., Ltd.), thickener (trade name “CMC2200”, Daicel Chemical) 1 part (in terms of solid content) manufactured by Kogyo Co., Ltd., 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, 1 part (in terms of solid content) of each electrode binder composition prepared in the above Examples and Comparative Examples was added and further stirred for 1 hour to obtain a paste. After adding 34 parts of water to the obtained paste and adjusting the solid content concentration to 50% by mass, using a stirring defoamer (trade name “Awatori Neritaro”, manufactured by Shinky Co., Ltd.), 200 rpm The mixture was stirred and mixed for 2 minutes at 1,800 rpm for 5 minutes and further under reduced pressure at 1,800 rpm for 1.5 minutes to prepare a negative electrode slurry.
Next, the negative electrode slurry prepared above was uniformly applied to the surface of a current collector made of copper foil having a thickness of 20 μm by a doctor blade method so that the thickness of the coating film after drying was 80 μm. The coating film was obtained by drying for 20 minutes. Then, the electrode active material layer was formed by pressing using a roll press so that the density of the film was 1.8 g / cm ³ to form a laminate. By punching the laminate, a disc-shaped negative electrode for a lithium ion secondary battery having a diameter of 16.16 mm was produced.
The peel strength of the electrode active material layer in each of the obtained negative electrodes for lithium ion secondary batteries is shown in Table 3 below.
(2) Manufacture of a positive electrode for a lithium ion secondary battery A biaxial planetary mixer (trade name “TK Hibismix 2P-03”, manufactured by Primics Co., Ltd.), 5 parts of polyvinylidene fluoride (in terms of solid content), positive electrode As active materials, 100 parts of lithium iron phosphate (in terms of solid content), 5 parts of acetylene black (in terms of solid content) and 25 parts of N-methylpyrrolidone (NMP) as the conductive agent were added and stirred at 60 rpm for 1 hour. Then, after further adding 10 parts of NMP, the mixture was further depressurized at 200 rpm for 2 minutes, then at 1,800 rpm for 5 minutes using a stirring defoamer (trade name “Awatori Nertaro”, manufactured by Shinky Co., Ltd.). A slurry for positive electrode was prepared by stirring and mixing at 1,800 rpm for 1.5 minutes below.
Next, the positive electrode slurry prepared above was uniformly applied to the surface of a current collector made of an aluminum foil having a thickness of 30 μm by a doctor blade method so that the film thickness of the coated film after drying was 90 μm. The coating film was obtained by drying for 20 minutes. Then, an electrode active material layer was formed by pressing using a roll press so that the density of the film was 1.7 g / cm ³ to form a laminate. By punching the laminate, a disc-shaped positive electrode for a lithium ion secondary battery having a diameter of 15.95 mm was manufactured.
(3) Production of lithium ion secondary battery Lithium ion secondary batteries were produced and evaluated in the same manner as in Examples 9 to 15 and Comparative Examples 9 to 15 except that the negative electrode and positive electrode produced above were used. .
The evaluation results are shown in Table 3.

As understood from the results in Table 3, when the electrode binder compositions (s1), (s7) and (s8) of the present invention are used, the electrode active material layer has a high peel strength for a lithium ion secondary battery. A negative electrode is obtained. And it was confirmed that the lithium ion secondary battery provided with such a negative electrode is excellent in both discharge rate characteristics in a low temperature environment and electrochemical stability in a high temperature environment.
However, when compared with the case where the binder composition for an electrode of the present invention is applied to a positive electrode for a lithium ion secondary battery, the difference between the example and the comparative example is about the low temperature rate characteristics and the self-discharge rate under a high temperature environment. Small (see Table 2 above). From this, it was found that the electrode binder composition of the present invention has a greater effect when applied to the positive electrode.
<Production and Evaluation of Electric Double Layer Capacitor, Example of Applying Electrode Binder Composition of the Present Invention to Capacitor Electrode>
Examples 19 and 20 and Comparative Examples 19-21
(1) Manufacture of electrodes for electric double-layer capacitors Activated carbon (trade name “Kuraray Coal YP”) as an electrode active material in a biaxial planetary mixer (trade name “TK Hibismix 2P-03”, manufactured by Primix Co., Ltd.) , Kuraray Chemical Co., Ltd. 100 parts, conductive carbon (trade name “Denka Black”, manufactured by Denki Kagaku Kogyo Co., Ltd.), thickener (trade name “CMC2200”, manufactured by Daicel Chemical Industries, Ltd.) ) 2 parts and 278 parts of water were added and stirred at 60 rpm for 1 hour. Thereafter, 4 parts (in terms of solid content) of each electrode binder composition produced in the above Examples and Comparative Examples were added, and the mixture was further stirred for 1 hour to obtain a paste. After adding 58 parts of water to the obtained paste to adjust the solid content concentration to 25% by mass, using a stirring defoamer (trade name “Awatori Neritaro”, manufactured by Shinky Co., Ltd.), 200 rpm For 2 minutes, then at 1,800 rpm for 5 minutes, and further under reduced pressure at 1,800 rpm for 1.5 minutes to prepare an electrode slurry.
Next, the positive electrode slurry prepared above is uniformly applied to the surface of a current collector made of an aluminum foil having a thickness of 20 μm by a doctor blade method so that the thickness of the coating film after drying becomes 150 μm. The coating film was obtained by drying for 20 minutes. Then, an electrode active material layer was formed by pressing using a roll press so that the density of the film was 1.5 g / cm ³ to form a laminate. By punching the laminate, two types of disc-shaped electrodes for electric double layer capacitors having a diameter of 15.95 mm and 16.16 mm were manufactured.
The peel strength of the electrode active material layer in the obtained electric double layer capacitor electrode is shown in Table 4 below.
(2) Manufacture and Evaluation of Electric Double Layer Capacitor An electrode for an electric double layer capacitor having a diameter of 16.16 mm is placed on a bipolar coin cell (trade name “HS Flat Cell”, manufactured by Hosen Co., Ltd.) in a glove box. Placed. Next, a disk-shaped cellulose separator having a diameter of 18 mm (trade name “TF4535”, manufactured by Nippon Kogyo Paper Industries Co., Ltd.) was placed on the electrode, and an electrolyte was injected so that air did not enter. Next, an electrode for an electric double layer capacitor having a diameter of 15.95 mm was placed on the separator, and then the outer body of the bipolar coin cell was tightened and sealed to manufacture an electric double layer capacitor.
The electrolytic solution used here is a propylene carbonate solution containing 1 mol / L triethylmethylammonium tetrafluoroborate.
Table 4 below shows the self-discharge rate and cycle characteristics of each electric double layer capacitor obtained under a high temperature environment.

From the results of Table 4, when the electrode binder compositions (s1) and (s7) of the present invention are used, both the discharge rate characteristics under a low temperature environment and the electrochemical stability under a high temperature environment are excellent. It has been found that an electric double layer capacitor can be obtained.

Claims

Structural unit (A) derived from a monomer represented by the following general formula (1) and structural unit (B) derived from an α, β-unsaturated nitrile monomer
Containing a polymer having
The content ratio of the structural unit (A) is 5 to 60% by mass,
The content ratio of the structural unit (B) is 5 to 40 mass%, and the total content ratio of the structural unit (A) and the structural unit (B) is 10 to 70 mass%. The binder composition for electrodes.

(However, R 1 represents a hydrogen atom or a methyl group, and R 2 represents a fluorinated hydrocarbon group having 1 to 18 carbon atoms.)
The polymer is a structural unit derived from an unsaturated acid monomer (C) and a structural unit derived from a monomer represented by the following general formula (3) (D)
The electrode binder composition according to claim 1, wherein the composition is for a positive electrode.

(However, R 5 represents a hydrogen atom or a methyl group, and R 6 represents a hydrocarbon group having 1 to 18 carbon atoms.)
The polymer further comprises a structural unit (C) derived from an unsaturated carboxylic acid monomer and a structural unit (E) derived from at least one monomer selected from the group consisting of conjugated dienes and aromatic vinyl monomers.
The electrode binder composition according to claim 1, wherein the composition is for a negative electrode.
The polymer is
In an aqueous medium having a temperature of 40 to 85 ° C. containing at least a polymerization initiator,
The binder composition for an electrode according to any one of claims 1 to 3, which is produced through a step of starting polymerization by adding an emulsion of a monomer mixture.
An electrode slurry comprising the electrode active material and the electrode binder composition according to any one of claims 1 to 3.
A current collector,
An electrode active material layer formed through a step of applying and drying the electrode slurry according to claim 5 on the surface of the current collector.
An electrochemical device comprising the electrode according to claim 6.