WO2014057749A1

WO2014057749A1 - Electrode binder composite

Info

Publication number: WO2014057749A1
Application number: PCT/JP2013/073858
Authority: WO
Inventors: 修小瀬; 博紀北口; 智隆篠田; 一郎梶原
Original assignee: Jsr株式会社
Priority date: 2012-10-12
Filing date: 2013-08-29
Publication date: 2014-04-17
Also published as: JP6269966B2; JPWO2014057749A1

Abstract

An objective of the present invention is to provide an electrode binder composite whereby an accumulator device is given wherein charge-discharge capacitance is large, and deterioration in capacitance owing to repeated charge-discharge cycles is small. The present invention is an accumulator device electrode binder composite, including at least (A) polymer particles, (B) at least one type of polymer selected from a group comprising polyamic acid and a partially imidized polymer thereof, and (C) a liquid medium.

Description

Electrode binder composition

The present invention relates to an electrode binder composition.

In recent years, an electric storage device having a high voltage and a high energy density has been demanded as a driving power source for electric vehicles, electronic devices, and the like. As power storage devices for this application, lithium ion secondary batteries, lithium ion capacitors, and the like are expected.
The electrode used for such an electricity storage device is usually produced by applying and drying a mixture of an electrode active material and polymer particles functioning as a binder onto the surface of the current collector. Examples of the properties required for the polymer particles include the following properties.
・ Binding ability between electrode active materials and binding ability between electrode active material and current collector,
・ Abrasion resistance in the process of winding the electrode,
-Powder fall resistance, etc. in which fine powder or the like of the composition layer is not generated even by cutting after forming the electrode composition layer.
When the polymer particles satisfy these various required characteristics, the degree of freedom in designing the structure of the electricity storage device, such as the method of folding the obtained electrode and setting the winding radius, is increased, and the miniaturization of the device is achieved. Can do. Hereinafter, the electrode active material layer is also referred to as “electrode active material layer” or simply “active material layer” in the present specification.
It has been empirically found that the quality of the electrode active materials is substantially proportional to the ability to bond the electrode active materials to each other, the ability to bond the electrode active material layer to the current collector, and the powder-off resistance. Therefore, in the present specification, hereinafter, the term “adhesiveness” may be used in a comprehensive manner.
In recent years, in order to achieve the demand for higher output and higher energy density of such an electricity storage device, studies are being made to apply a material having a large lithium storage capacity. For example, silicon can reversibly occlude and release lithium by forming an intermetallic compound with lithium. The theoretical capacity of silicon is about 4,200 mAh / g at the maximum, which is extremely large compared with the theoretical capacity of about 370 mAh / g of a carbon material that has been conventionally used. Therefore, the capacity of the electricity storage device should be greatly improved by using the silicon material as the negative electrode active material. However, since the volume change due to charging / discharging is large in silicon materials, when the conventionally used electrode binder material is applied to silicon materials, the initial adhesion cannot be maintained, and a remarkable capacity is associated with charging / discharging. A decrease occurs.
As an electrode binder material for holding such a silicon material in the active material layer, a method of applying polyimide has been proposed (Japanese Patent Application Laid-Open Nos. 2007-95670, 2011-192563, and 2011-204592). ). These techniques are based on the technical idea of restraining the volume change of the silicon material by constraining the silicon material with the rigid molecular structure of polyimide. In these documents, after applying a slurry for an electrode containing polyamic acid to the current collector surface to form a coating film, the polyimide is heated by heating the coating film at a high temperature to thermally imidize the polyamic acid. It is described as generating. However, binder materials using these polyimides have insufficient adhesion, and the electrodes deteriorate due to repeated charge and discharge, so that there is a problem that sufficient durability cannot be exhibited.

The present invention has been made to overcome the above-described current situation. The objective of this invention is providing the binder composition for electrodes which provides the electrical storage device with a large charge / discharge capacity | capacitance and few extents of capacity | capacitance deterioration by repetition of a charging / discharging cycle.
According to the present invention, the above objects and advantages of the present invention are:
At least (A) polymer particles,
(B) at least one polymer selected from the group consisting of a polyamic acid and a partially imidized polymer thereof, and (C) a liquid medium, and a binder composition for an electrode of an electricity storage device, Achieved.

FIG. 1 is a DSC chart of the polymer particles synthesized in Synthesis Example A2-1.

Hereinafter, preferred embodiments of the present invention will be described in detail. It should be understood that the present invention is not limited to only the embodiments described below, and includes various modified examples that are implemented without departing from the scope of the present invention.
In this specification, “(meth) acrylic acid” is a concept encompassing both “acrylic acid” and “methacrylic acid”. Further, “˜ (meth) acrylate” is a concept encompassing both “˜acrylate” and “˜methacrylate”.
1. Electrode binder composition
The binder composition for an electrode of the present embodiment is a binder composition used for producing an electrode used for an electricity storage device, and includes at least (A) polymer particles, (B) polyamic acid and a partial imide thereof. It contains at least one polymer selected from the group consisting of polymerized polymers, and (C) a liquid medium.
The content ratio of the polymer (B) in the binder composition for an electrode of the present invention is as follows: (A) the content of the polymer particles is Ma (parts by mass), In this case, the ratio of Ma / Mb is preferably 1 to 50, and preferably 5 to 30. Further, the content ratio of the polymer (B) with respect to the total amount of the binder composition for an electrode of the present invention is preferably 5,000 to 100,000 ppmw, more preferably 10,000 to 50,000 ppmw, In particular, it is preferably 15,000 to 30,000 ppmw. Said "ppmw" is a unit showing 1 / 1,000,000 of mass standards.
By making the content rate of (B) polymer in the binder composition for electrodes into the said range, while the electrical storage capacity of the electrical storage device obtained increases, charging / discharging characteristics also improve.
That is, in an electric storage device, generally, a binder (polymer) attached to the surface of an active material prevents movement of a charge transfer material (for example, solvated lithium ions) between the electrolytic solution and the active material. The storage capacity is reduced by the amount attached. However, by setting the content ratio of the polymer (B) within the above range, the swelling property of the binder with respect to the electrolytic solution can be improved without impairing the binder action. Since the binder swollen with the electrolytic solution does not hinder the movement of the charge transfer material, the electricity storage device using the binder has a large electricity storage capacity.
Furthermore, by setting the content ratio of (B) polymer within the above range, in the electrode of the electricity storage device, (A) flexibility due to the contribution of polymer particles and (B) mechanical strength due to the contribution of polymer Will be expressed in a well-balanced manner. Therefore, since such an electrode can follow the volume change of the active material accompanying charging / discharging while maintaining the adhesiveness as a binder, it exhibits excellent charging / discharging characteristics.
(C) The ratio of the liquid medium used is the solid content concentration of the electrode binder composition (the ratio of the total mass of components other than the liquid medium (C) in the electrode binder composition to the total mass of the electrode binder composition). The same shall apply hereinafter) is preferably in a proportion of 5 to 80% by mass, more preferably in a proportion of 20 to 70% by mass.
Hereinafter, each component contained in the binder composition for electrodes of the present embodiment will be described in detail.
1.1 (A) Polymer particles
The (A) polymer particle in the binder composition for electrodes of the present invention is a component that becomes a binder in the active material layer.
(A) The average particle diameter of the polymer particles is preferably in the range of 50 to 400 nm, more preferably in the range of 100 to 250 nm. (A) Adsorption of (A) polymer particles to the surface of the electrode active material in an electrode produced using the binder composition for an electrode of the present invention by having the average particle diameter of the polymer particles in the above range. Thus, (A) the polymer particles can follow and move with the movement of the electrode active material. As a result, since any one of the electrode active material particles and the polymer particles can be prevented from being migrated alone, deterioration of electrical characteristics associated with charge / discharge can be suppressed.
This average particle size is determined by measuring the particle size distribution using a particle size distribution measuring apparatus based on the dynamic light scattering method, and the cumulative frequency of the number of particles when the particles are accumulated in ascending order of particle size is 50%. It is a value of a particle diameter (D50). Examples of such a particle size distribution measuring apparatus include HORIBA LB-550, SZ-100 series (manufactured by Horiba, Ltd.), FPAR-1000 (manufactured by Otsuka Electronics Co., Ltd.), and the like. 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 index of the dispersion state of the (A) polymer particles contained in the electrode binder composition. (A) The average particle diameter of the polymer particles is determined by centrifuging the electrode slurry prepared by using the electrode binder composition of the present invention to precipitate the electrode active material, and then using the supernatant liquid for the above particle size. It can also be measured by a method of measuring with a distribution measuring device.
As this (A) polymer particle, for example,
A repeating unit derived from a conjugated diene compound;
Repeating units derived from aromatic vinyl compounds and
Particles containing a polymer having the following (hereinafter referred to as “polymer particles A1”),
Examples thereof include particles containing a polymer having a repeating unit derived from a monomer having a fluorine atom (hereinafter referred to as “polymer particle A2”), and any of these may be used. preferable.
1.1.1 Polymer particles A1
The polymer particle A1 is a particle containing a polymer having a repeating unit derived from a conjugated diene compound and a repeating unit derived from an aromatic vinyl compound.
When this polymer particle A1 is measured by a differential scanning calorimeter (DSC), it preferably has only one endothermic peak in the temperature range of −40 to + 25 ° C. The temperature of this endothermic peak is more preferably in the range of −30 to + 20 ° C., and further preferably in the range of −25 to + 10 ° C. When the polymer particle A1 in DSC analysis has only one endothermic peak and the peak temperature is in the above range, the polymer exhibits good adhesion and has a moderate flexibility in the thick material layer. This is preferable because it can be given. The above endothermic peak is considered to be the glass transition temperature Tg of the polymer particle A1.
The polymer particle A1 is a repeating unit derived from an unsaturated carboxylic acid ester, a repeating unit derived from an α, β-unsaturated nitrile compound, a repeating unit derived from an unsaturated carboxylic acid, and a repeat derived from another monomer. You may further have 1 or more types of repeating units selected from the group which consists of a unit.
Since the polymer particle A1 in the present invention is a component that becomes a binder in the active material layer, in addition to the binding property and the affinity for the conductivity-imparting agent, the swelling property to the electrolytic solution is important. Moreover, it is preferable that the electrode slurry prepared by using the electrode binder composition of the present invention is stable over time. From such a viewpoint, the polymer particle A1 contains, in addition to the repeating unit derived from the conjugated diene compound and the repeating unit derived from the aromatic vinyl compound, the repeating unit derived from the α, β-unsaturated nitrile compound and the unsaturated unit. It is preferable to further have at least one repeating unit selected from the group consisting of repeating units derived from carboxylic acid, and more preferable to have both of these.
The conjugated diene compound is a monomer having a function of improving the binding property of the binder component. The content ratio of the repeating unit derived from the conjugated diene compound in the polymer particle A1 is preferably 30 to 60 parts by mass, and preferably 35 to 55 parts by mass when all the repeating units are 100 parts by mass. More preferred. When the content ratio of the repeating unit derived from the conjugated diene compound is in the above range, the binding property of the polymer particle A1 can be further increased. Examples of the conjugated diene compound include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene and the like. , One or more selected from these can be used. As the conjugated diene compound, 1,3-butadiene is particularly preferable.
The aromatic vinyl compound has a function of improving the affinity of the binder component for the conductivity-imparting agent when the electrode slurry prepared using the electrode binder composition of the present invention contains a conductivity-imparting agent. It is a monomer. The content ratio of the repeating unit derived from the aromatic vinyl compound in the polymer particle A1 is preferably 10 to 40 parts by mass, and 15 to 35 parts by mass when the total repeating units are 100 parts by mass. Is more preferable. When the content ratio of the repeating unit derived from the aromatic vinyl compound is in the above range, the polymer particle A1 has an appropriate binding property to the current collector and the electrode active material (particularly graphite). In addition, it is preferable in that the flexibility of the active material layer is not impaired. Examples of the aromatic vinyl compound include styrene, α-methylstyrene, p-methylstyrene, chlorostyrene, and the like, and one or more selected from these can be used. Styrene is preferably used as the aromatic vinyl compound.
The unsaturated carboxylic acid ester is a monomer having a function of adjusting the affinity of the binder component for the electrolytic solution. The content ratio of the repeating unit derived from the unsaturated carboxylic acid ester in the polymer particle A1 is preferably 5 to 30 parts by mass, and preferably 6 to 20 parts by mass when all the repeating units are 100 parts by mass. It is more preferable. When the content ratio of the repeating unit derived from the unsaturated carboxylic acid ester is in the above range, the affinity of the binder component to the electrolyte solution becomes appropriate, and as a result, the binder component becomes an electrical resistance component in the electrode. It is possible to prevent an increase in the internal resistance of the electrode and to prevent a decrease in binding property due to excessive absorption of the electrolytic solution. Examples of unsaturated carboxylic acid esters that can be used include alkyl esters of unsaturated carboxylic acids, hydroxyalkyl esters of unsaturated carboxylic acids, and the like. Specific examples thereof include alkyl esters of unsaturated carboxylic acids such as methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, ( N-butyl (meth) acrylate, i-butyl (meth) acrylate, n-amyl (meth) acrylate, i-amyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, ( 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, etc .;
Examples of the hydroxyalkyl ester of the unsaturated carboxylic acid may include, for example, hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, ethylene glycol (meth) acrylate, and the like. One or more can be used. Among these, 1 selected from the group consisting of methyl (meth) acrylate, ethyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, hydroxymethyl (meth) acrylate and hydroxyethyl (meth) acrylate It is preferable to use at least one species, and it is particularly preferable to use at least one selected from the group consisting of methyl (meth) acrylate, hydroxymethyl (meth) acrylate, and hydroxyethyl (meth) acrylate.
The α, β-unsaturated nitrile compound is a monomer having a function of improving the swellability of the binder component to the electrolytic solution. As a result, the diffusibility of ions into the binder is improved. As a result, it is considered that the electrode resistance is lowered and an electrode capable of realizing better charge / discharge characteristics is provided. The content ratio of the repeating unit derived from the α, β-unsaturated nitrile compound in the polymer particle A1 is preferably 35 parts by mass or less when the total repeating unit is 100 parts by mass, and 5 to 25 parts by mass. It is more preferable that When the content ratio of the repeating unit derived from the α, β-unsaturated nitrile compound is in the above range, it has excellent affinity with the electrolyte used, and the swelling rate does not become too large, contributing to the improvement of battery characteristics. Will be. Examples of the α, β-unsaturated nitrile compound include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, vinylidene cyanide, and one or more selected from these are used. can do. As the α, β-unsaturated nitrile compound, it is preferable to use one or more selected from the group consisting of acrylonitrile and methacrylonitrile, and it is more preferable to use acrylonitrile.
The unsaturated carboxylic acid is a monomer having a function of improving the stability of the electrode slurry prepared by using the electrode binder composition of the present invention. The content ratio of the repeating unit derived from the unsaturated carboxylic acid in the polymer particle A1 is preferably 15 parts by mass or less, and 0.3 to 10 parts by mass when the total repeating unit is 100 parts by mass. It is more preferable. When the content ratio of the repeating unit derived from the unsaturated carboxylic acid is in the above range, the dispersion stability of the polymer particles A1 at the time of preparing the slurry for the electrode is excellent, and it is difficult for the aggregate to be generated. The increase in viscosity of the slurry over time can be suppressed. Examples of the unsaturated carboxylic acid include (meth) acrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, and the like, and one or more selected from these can be used. As the unsaturated carboxylic acid, it is particularly preferable to use one or more selected from the group consisting of acrylic acid, methacrylic acid and itaconic acid.
The other monomers are monomers that do not belong to the above categories. The content ratio of the repeating units derived from the other monomers in the polymer particle A1 is preferably 1 part by mass or less and 0.1 parts by mass or less when the total repeating unit is 100 parts by mass. It is more preferable. Specific examples of other monomers include ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, hexa Crosslinkable monomers such as (meth) acrylic acid dipentaerythritol, divinylbenzene;
A fluorine-containing monomer having an ethylenically unsaturated bond, such as vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene;
(Meth) acrylamide;
N-methylol acrylamide;
Carboxylic acid vinyl esters such as vinyl acetate and vinyl propionate;
An acid anhydride of an ethylenically unsaturated dicarboxylic acid;
Examples thereof include aminoalkylamides of ethylenically unsaturated carboxylic acids such as aminoethylacrylamide, dimethylaminomethylmethacrylamide, and methylaminopropylmethacrylamide, and one or more selected from these can be used. . In the polymer particle A1, it is particularly preferable not to use other monomers.
The polymer particle A1 is preferably a particle composed only of a polymer having a repeating unit as described above.
1.1.2 Synthesis of polymer particle A1
The method for synthesizing the polymer particles A1 in the present invention is not particularly limited, but can be synthesized by, for example, a known emulsion polymerization method. Emulsion polymerization is preferably carried out in a suitable aqueous medium, particularly preferably in water.
In the emulsion polymerization for the synthesis of the polymer particles A1, a predetermined monomer mixture is preferably present at 40 to 80 ° C., preferably 4 to 12 in the presence of an emulsifier, a polymerization initiator, a molecular weight regulator, and the like. This can be done by emulsion polymerization over time. You may change reaction temperature in the middle of superposition | polymerization. Here, the total solid content concentration in the emulsion polymerization (the ratio of the total mass of components other than the aqueous medium in the polymerization system to the total mass of the polymerization system) is 50% by mass or less, whereby the dispersion stability of the polymer particles obtained is reduced. Can advance the polymerization reaction in a good state. The total solid content concentration is more preferably 45% by mass or less, and still more preferably 40% by mass or less.
The use ratio of the emulsifier in the emulsion polymerization for the synthesis of the polymer particles A1 is preferably 0.1 to 2.0 parts by mass with respect to 100 parts by mass in total of the monomers used. More preferably, it is set to ~ 1.0 part by mass. Examples of the emulsifier include sulfate esters of higher alcohols, alkylbenzene sulfonates, alkyl diphenyl ether disulfonates, aliphatic sulfonates, aliphatic carboxylates, dehydroabietic acid salts, naphthalene sulfonic acid / formalin condensates, Anionic surfactants such as sulfate salts of ionic surfactants;
Nonionic surfactants such as alkyl esters of polyethylene glycol, alkyl phenyl ethers of polyethylene glycol, alkyl ethers of polyethylene glycol;
Fluorosurfactants such as perfluorobutyl sulfonate, perfluoroalkyl group-containing phosphate ester, perfluoroalkyl group-containing carboxylate, and perfluoroalkylethylene oxide adducts can be mentioned, and selected from these More than one kind can be used.
The use ratio of the polymerization initiator is preferably 0.5 to 2 parts by mass with respect to 100 parts by mass in total of the monomers used. 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, acetyl peroxide, diisopropylbenzene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, azobisisobutyronitrile, 1, Oil-soluble polymerization initiators such as 1′-azobis (cyclohexanecarbonitrile) can be appropriately selected and used. Of these, potassium persulfate, sodium persulfate, cumene hydroperoxide or t-butyl hydroperoxide is particularly preferably used.
The proportion of the molecular weight regulator used is preferably 0.1 to 2.0 parts by mass with respect to 100 parts by mass in total of the monomers used. Examples of the molecular weight modifier include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-stearyl mercaptan;
Xanthogen compounds such as dimethylxanthogen disulfide and diisopropylxanthogen disulfide;
Thiuram compounds such as terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram monosulfide;
Phenolic compounds such as 2,6-di-tert-butyl-4-methylphenol and styrenated phenol;
Allyl compounds such as allyl alcohol;
Halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, carbon tetrabromide;
In addition to vinyl ether compounds such as α-benzyloxystyrene, α-benzyloxyacrylonitrile, α-benzyloxyacrylamide,
And triphenylethane, pentaphenylethane, acrolein, metaacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate, α-methylstyrene dimer, and the like. Can be used.
After completion of the emulsion polymerization of the polymer particles A1, it is preferable to adjust the pH to about 5 to 10 by adding a neutralizing agent to the polymerization mixture. The pH is more preferably 6 to 9, and further preferably 7 to 8.5. Although it does not specifically limit as a neutralizing agent used here, For example, metal hydroxides, such as sodium hydroxide and potassium hydroxide; Ammonia etc. can be mentioned. By setting to the above pH range, the blending stability of the polymer particles is improved.
By concentrating the polymerization mixture after the neutralization treatment, the solid content concentration can be increased while maintaining good stability of the polymer particles.
1.1.2 Polymer particle A2
The polymer particle A2 in the binder composition for electrodes of the present invention is a particle containing a polymer having a repeating unit derived from a monomer having a fluorine atom.
The polymer particle A2 in the present invention may have only a repeating unit derived from a monomer having a fluorine atom, and other monomers in addition to the repeating unit derived from a monomer having a fluorine atom. It may have a repeating unit derived from.
The preferable content ratio of the repeating unit derived from the monomer having a fluorine atom in the polymer particle A2 in the present invention is preferably 3% by mass or more, more preferably 5%, based on the total mass of the polymer particle A2. It is ˜50 mass%, more preferably 15 to 40 mass%, and particularly preferably 20 to 30 mass%.
Examples of the monomer having a fluorine atom include an olefin compound having a fluorine atom and a (meth) acrylic acid ester having a fluorine atom. Examples of the olefin compound having a fluorine atom include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, trifluorochloroethylene, and perfluoroalkyl vinyl ether. Examples of the (meth) acrylic acid ester having a fluorine atom include a compound represented by the following general formula (1), (meth) acrylic acid 3 [4 [1-trifluoromethyl-2,2-bis [bis (tri Fluoromethyl) fluoromethyl] ethynyloxy] benzooxy] 2-hydroxypropyl and the like.

(In the general formula (1), R ¹ Is a hydrogen atom or a methyl group, R ² Is a C1-C18 hydrocarbon group containing a fluorine atom. )
R in the general formula (1) ² Examples thereof include a fluorinated alkyl group having 1 to 12 carbon atoms, a fluorinated aryl group having 6 to 16 carbon atoms, and a fluorinated aralkyl group having 7 to 18 carbon atoms. An alkyl group is preferable. R in the general formula (1) ² Preferable specific examples of are, for example, 2,2,2-trifluoroethyl group, 2,2,3,3,3-pentafluoropropyl group, 1,1,1,3,3,3-hexafluoropropane- 2-yl group, β- (perfluorooctyl) ethyl group, 2,2,3,3-tetrafluoropropyl group, 2,2,3,4,4,4-hexafluorobutyl group, 1H, 1H, 5H -Octafluoropentyl group, 1H, 1H, 9H-perfluoro-1-nonyl group, 1H, 1H, 11H-perfluoroundecyl group, perfluorooctyl group and the like can be mentioned. Among these, the monomer having a fluorine atom is preferably an olefin compound having a fluorine atom, particularly preferably at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene. .
The monomer having a fluorine atom may be used alone or in combination of two or more.
Examples of the other monomers include unsaturated carboxylic acid esters, hydrophilic monomers (excluding those corresponding to unsaturated carboxylic acid esters; the same applies hereinafter), crosslinkable monomers, α-olefins, Aromatic vinyl compounds (excluding those corresponding to the above-mentioned hydrophilic monomers and crosslinkable monomers; the same shall apply hereinafter) and the like, and one or more selected from these may be used. can do.
It is preferable that the polymer particle A2 has a structural unit derived from the unsaturated carboxylic acid ester among the above, because adhesion can be further improved. The point that the stability of the slurry for an electrode using the binder composition for an electrode of the present invention is improved when the polymer particle A2 has a structural unit derived from an unsaturated carboxylic acid among the hydrophilic monomers. Is preferable. Moreover, when the polymer particle A2 has a repeating unit derived from the α, β-unsaturated nitrile compound among the hydrophilic monomers, the swelling property of the polymer particle with respect to the electrolytic solution can be further improved. . That is, the presence of a nitrile group facilitates the penetration of the solvent (medium) into the network structure composed of polymer chains and the network spacing is widened, so that the charge transfer material (solvated ions) can easily move through this network structure. Become. Thereby, it is thought that the diffusibility of ion improves, As a result, electrode resistance falls and it is preferable at the point which can implement | achieve more favorable charge / discharge characteristics.
The preferred content ratios of the repeating units derived from other monomers in the polymer particle A2 in the present invention are as follows based on the total mass of the polymer particle A2.
Repeating unit derived from unsaturated carboxylic acid ester: preferably 95% by mass or less, more preferably 50 to 90% by mass, still more preferably 60 to 80% by mass;
Repeating units derived from hydrophilic monomers: preferably 35% by mass or less, more preferably 2-30% by mass, still more preferably 4-20% by mass; and
Repeating unit derived from a crosslinkable monomer: preferably 2% by mass or less, more preferably 1% by mass or less.
Examples of the unsaturated carboxylic acid ester include an unsaturated carboxylic acid alkyl ester, an unsaturated carboxylic acid cycloalkyl ester, an unsaturated carboxylic acid hydroxyalkyl ester, and an unsaturated carboxylic acid polyhydric alcohol ester. it can.
Examples of the alkyl ester of the unsaturated carboxylic acid include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, and (meth) acrylic acid n. -Butyl, i-butyl (meth) acrylate, n-amyl (meth) acrylate, i-amyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (meth) acryl N-octyl acid, nonyl (meth) acrylate, decyl (meth) acrylate, etc .;
Examples of the cycloalkyl ester of the unsaturated carboxylic acid include cyclohexyl (meth) acrylate and the like;
Examples of the hydroxyalkyl ester of the unsaturated carboxylic acid include hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, and the like, and one or more selected from these can be used. Can do.
Examples of the hydrophilic monomer include unsaturated carboxylic acids, α, β-unsaturated nitrile compounds, and compounds having a hydroxyl group. Examples of the unsaturated carboxylic acid include (meth) acrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid and the like;
Examples of the α, β-unsaturated nitrile compound include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, vinylidene cyanide and the like;
Examples of the compound having a hydroxyl group include p-hydroxystyrene, and one or more selected from these compounds can be used.
Examples of the crosslinkable monomer include ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, hexa (meth) ) Dipentaerythritol acrylate, etc .;
Examples of the α-olefin include ethylene and propylene;
Examples of the aromatic vinyl compound include styrene, α-methylstyrene, p-methylstyrene, chlorostyrene, and the like, and any one or more selected from these can be used. .
The polymer particle A2 in the present invention is a monomer other than the above-described monomer having a fluorine atom, unsaturated carboxylic acid ester, hydrophilic monomer, crosslinkable monomer, α-olefin and aromatic vinyl compound. It is preferable not to contain a repeating unit derived from a monomer.
1.1.2.1 Polymer alloy particles
As the polymer particle A2 in the present invention, polymer particles having a repeating unit derived from a monomer having a fluorine atom as described above may be used as they are, or
It may be a polymer alloy particle containing a polymer (A2a) having a repeating unit derived from a monomer having a fluorine atom and a polymer (a2b) having a repeating unit derived from an unsaturated carboxylic acid ester. . When the polymer particle A2 is a polymer alloy particle, it is preferable in that ionic conductivity, oxidation resistance, and adhesion can be expressed simultaneously.
“Polymer alloy” is a “generic name for multi-component polymers obtained by mixing or chemical bonding of two or more components” according to the definition in “Iwanami Physical and Chemical Dictionary 5th edition. Iwanami Shoten”. “Polymer blends physically mixed with different polymers, block and graft copolymers in which different polymer components are covalently bonded, polymer complexes in which different polymers are associated by intermolecular forces, and different polymers entangled with each other IPN (Interpenetrating Polymer Network, etc.). However, the polymer alloy particles contained in the binder composition of the present invention are preferably particles made of IPN among “polymer alloys in which different types of polymer components are not bonded by covalent bonds”.
The polymer (A2a) constituting the polymer alloy particles is excellent in ionic conductivity, and the hard segment of the crystalline resin is aggregated to give a pseudo-crosslinking point such as C—H—F—C to the main chain. It is thought that there is. For this reason, when the polymer (A2a) is used alone as a binder material, its ionic conductivity and oxidation resistance are good, but its adhesion and flexibility are insufficient, so that the adhesion is low. On the other hand, although the polymer (A2b) constituting the polymer alloy particles is excellent in adhesion and flexibility, it has low oxidation resistance. Therefore, when this is used alone as a binder material for an electrode (particularly a positive electrode), Since charging and discharging are repeated to cause oxidative decomposition and alteration, good charge / discharge characteristics cannot be obtained.
However, by using the polymer alloy particles containing the polymer (A2a) and the polymer (A2b), ionic conductivity and oxidation resistance, and adhesion can be expressed simultaneously, and good charge / discharge characteristics It has become possible to produce an electrode having When the polymer alloy particles are composed of the polymer (A2a) and the polymer (A2b) only, the oxidation resistance can be further improved, which is preferable.
The polymer alloy particles preferably have only one endothermic peak in the temperature range of −50 to 250 ° C. when measured by differential scanning calorimetry (DSC) according to JIS K7121. The temperature of this endothermic peak is more preferably in the range of −30 to + 30 ° C.
When the polymer (A2a) constituting the polymer alloy particles is present alone, it generally has an endothermic peak (melting temperature) at -50 to 250 ° C. The polymer (A2b) constituting the polymer alloy particles generally has an endothermic peak (glass transition temperature) different from that of the polymer (A2a). For this reason, when the polymer (A2a) and the polymer (A2b) in the particles are present in phase separation as in, for example, a core-shell structure, two endothermic peaks should be observed at −50 to 250 ° C. It is. However, when there is only one endothermic peak at −50 to 250 ° C., it can be estimated that the particles are polymer alloy particles.
Furthermore, when the temperature of only one endothermic peak of the polymer alloy particles is in the range of −30 to + 30 ° C., the particles can impart better flexibility and tackiness to the active material layer. Therefore, the adhesiveness can be further improved, which is preferable.
1.1.2.2 Polymer (A2a)
The polymer alloy particle as the polymer particle A2 in the present invention contains a polymer (A2a) having a repeating unit derived from a monomer having a fluorine atom. In this polymer (A2a), the content ratio of the repeating unit derived from the monomer having a fluorine atom is preferably 80% by mass or more, more preferably 90% by mass with respect to the total mass of the polymer A. That's it.
As described above, the monomer having a fluorine atom preferably contains at least one selected from the group consisting of vinylidene fluoride, ethylene tetrafluoride and propylene hexafluoride. It is preferable that all are at least one selected from vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene.
The polymer (A2a) may further have a repeating unit derived from another unsaturated monomer in addition to the repeating unit derived from the monomer having a fluorine atom. Examples of the other unsaturated monomers include unsaturated carboxylic acid alkyl esters, unsaturated carboxylic acid cycloalkyl esters, hydrophilic monomers, crosslinkable monomers, α-olefins and aromatics described above. Vinyl compounds can be used.
The preferable content ratio of the repeating unit derived from each monomer in the polymer (A2a) is as follows based on the total mass of the polymer (A2a).
Repeating units derived from vinylidene fluoride: preferably 50 to 99% by mass, more preferably 80 to 98% by mass;
Repeating units derived from tetrafluoroethylene: preferably 50% by mass or less, more preferably 1-30% by mass, still more preferably 2-20% by mass; and
Repeating units derived from hexafluoropropylene: preferably 50% by mass or less, more preferably 1 to 30% by mass, still more preferably 2 to 25% by mass.
Most preferably, the polymer (A2a) is composed of only a repeating unit derived from at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene.
1.1.2.3 Polymer (A2b)
The polymer alloy particle as the polymer particle A2 in the present invention has a repeating unit derived from another copolymerizable unsaturated monomer other than the monomer having a fluorine atom. The other unsaturated compound is preferably the unsaturated carboxylic acid ester described above, and in addition, a hydrophilic monomer, a crosslinkable monomer, an α-olefin, an aromatic vinyl compound, etc. are used in combination. can do.
In general, components such as the polymer (A2b) have good adhesion, but are considered to have poor ionic conductivity and oxidation resistance and have not been used for positive electrodes. However, in the present invention, by using such a polymer (A2b) as a polymer alloy particle together with the polymer (A2a), sufficient ionic conductivity and oxidation resistance are expressed while maintaining good adhesion. Has been successful.
The content ratio of the repeating unit derived from each monomer in the polymer (A2b) is as follows. The following are values when the mass of the polymer (A2b) is 100% by mass.
Repeating unit derived from unsaturated carboxylic acid ester: preferably 50% by mass or more, more preferably 60 to 95% by mass;
Repeating unit derived from a hydrophilic monomer: preferably 50% by mass or less, more preferably 5 to 40% by mass;
Repeating unit derived from a crosslinkable monomer: preferably 10% by mass or less, more preferably 5% by mass or less, further preferably 3% by mass or less, particularly preferably not containing this;
Repeating units derived from α-olefins: preferably 10% by weight or less, more preferably 5% by weight or less, further preferably 3% by weight or less, particularly preferably not containing this; and
A repeating unit derived from an aromatic vinyl compound: preferably 10% by mass or less, more preferably 5% by mass or less, further preferably 3% by mass or less, and particularly preferably not contain it.
The polymer (A2b) does not contain a repeating unit derived from a monomer other than the unsaturated carboxylic acid ester, hydrophilic monomer, crosslinkable monomer, α-olefin and aromatic vinyl compound exemplified above. It is preferable.
1.1.2.4 Synthesis of polymer alloy particles
The polymer alloy particle as the polymer particle A2 in the present invention is not particularly limited as long as it has the above-described configuration. For example, a known emulsion polymerization step or a combination thereof is appropriately combined. It can be easily synthesized.
For example, first, a polymer (A2a) having a repeating unit derived from a monomer having a fluorine atom is synthesized by a known method, and then
A monomer for constituting the polymer (A2b) was added to the polymer (A2a), and the monomer was sufficiently absorbed in the stitch structure of the polymer particles made of the polymer (A2a). Thereafter, a polymer alloy can be easily synthesized by a method of synthesizing the polymer (A2b) by polymerizing the absorbed monomer in the stitch structure of the polymer (A2a). When producing a polymer alloy by such a method, it is essential for the polymer (A2a) to sufficiently absorb the monomer of the polymer (A2b). When the absorption temperature is too low or the absorption time is too short, only a core-shell type polymer or a part of the surface layer becomes a polymer having an IPN type structure, and the polymer alloy in the present invention may not be obtained. Many. However, if the absorption temperature is too high, the pressure of the polymerization system becomes too high, which is disadvantageous in terms of reaction system handling and reaction control, and even if the absorption time is excessively long, further advantageous results are not obtained. .
From the above viewpoint, the absorption temperature is preferably 30 to 100 ° C., more preferably 40 to 80 ° C .;
The absorption time is preferably 1 to 12 hours, more preferably 2 to 8 hours. At this time, it is preferable to lengthen the absorption time when the absorption temperature is low, and a short absorption time is sufficient when the absorption temperature is high. Appropriate conditions are such that the value obtained by multiplying the absorption temperature (° C.) and the absorption time (h) is generally in the range of 120 to 300 (° C. · h), preferably 150 to 250 (° C. · h).
The operation of absorbing the monomer of the polymer (A2b) in the network structure of the polymer (A2a) is preferably performed in a known medium used for emulsion polymerization, for example, in water.
The content of the polymer (A2a) in the polymer alloy particles is preferably 3 to 60% by mass, more preferably 5 to 55% by mass, and more preferably 10 to 50% by mass in 100% by mass of the polymer alloy particles. %, More preferably 20 to 40% by mass. When the polymer alloy contains the polymer (A2a) in the above range, the balance between the ionic conductivity and the oxidation resistance and the adhesion becomes better. Moreover, when the polymer (A2b) in which the content ratio of the repeating unit derived from each monomer is in the above preferred range is used, the polymer alloy contains the polymer (A2a) in the above range, It becomes possible to set the content ratio of each repeating unit in the entire polymer alloy within the above-mentioned preferable range, and this ensures that the charge / discharge characteristics of the electricity storage device are good.
1.1.2.5 Synthesis of polymer particle A2
Synthesis of polymer particles A2 in the present invention, that is,
The polymerization when a polymer having a repeating unit derived from a monomer having a fluorine atom is synthesized by one-step polymerization;
Polymerization of polymer (A2a), and
Polymerization of polymer (A2b) in the presence of polymer (A2a)
Can be carried out in the presence of a known emulsifier (surfactant), a polymerization initiator, a molecular weight modifier, and the like.
This emulsion polymerization is preferably carried out in a suitable aqueous medium, particularly preferably in water. The total content of the monomers in the emulsion polymerization system can be 10 to 50% by mass, and preferably 20 to 40% by mass. The conditions for emulsion polymerization are preferably a polymerization time of 2 to 24 hours at a polymerization temperature of 40 to 85 ° C, and more preferably a polymerization time of 3 to 20 hours at a polymerization temperature of 50 to 80 ° C.
The proportion of the emulsifier used is the total of the monomers used (the total of the monomers used when the polymer particles A2 are synthesized by one-step polymerization, and the polymer (A2a) in the synthesis of the polymer (A2a)). The total of monomers leading to polymer (A2b) in the presence of polymer (A2a), the sum of monomers leading to polymer (A2b). The amount is preferably 0.01 to 10 parts by mass, more preferably 0.02 to 5 parts by mass with respect to parts.
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.
The use ratio of the molecular weight regulator is preferably 5 parts by mass or less with respect to 100 parts by mass in total of the monomers used.
As said emulsifier, a polymerization initiator, and a molecular weight modifier, the thing same as what was illustrated above as what can be used for the synthesis | combination of polymer particle A1, respectively can be used.
1.2 (B) Polymer
The polymer (B) in the electrode binder composition of the present invention is at least one polymer selected from the group consisting of polyamic acid and partially imidized polymers thereof. When the binder composition for electrodes contains the polymer (B), the binding property between the active material layer produced using the binder composition for electrodes of the present invention and the current collector is (A). This is better than when only polymer particles are used. Therefore, even if the volume change of the active material due to charging / discharging occurs, the active material layer is held on the electrode without peeling from the current collector, and the capacity reduction due to repeated charging / discharging is effectively suppressed. be able to.
(B) When the polymer is a partially imidized polymer of polyamic acid, the imidation ratio is preferably 75% or less, more preferably 50% or less, and particularly preferably 30% or less. Is preferred. Since the partially imidized polymer having an imidization ratio in the above range has high solubility in water and an organic solvent, it is easy to synthesize the imidized polymer and prepare a binder composition for an electrode, and the binder composition. It is possible to improve the stability of the slurry for the electrode adjusted by using this, which is preferable.
Said imidation rate represents the ratio which the number of the imide ring structure occupies with respect to the sum total of the number of amic acid structures and the number of imide ring structures in an imidation polymer in percentage. The imidization rate of polyamic acid is ¹ It can be determined using 1 H-NMR.
1.2.1 (B) Synthesis of polymer
A polyamic acid can be obtained by reacting a tetracarboxylic dianhydride and a diamine. The partial imide polymer of polyamic acid can be obtained by dehydrating and ring-closing a part of the amic acid structure of the polyamic acid to imidize it.
Examples of the tetracarboxylic dianhydride used to synthesize the polymer (B) in the present invention include an aliphatic tetracarboxylic dianhydride, an alicyclic tetracarboxylic dianhydride, and an aromatic tetracarboxylic dianhydride. An anhydride etc. can be mentioned.
Among the above, the tetracarboxylic dianhydride preferably includes an aromatic tetracarboxylic dianhydride. The tetracarboxylic dianhydride in the present invention consists only of an aromatic tetracarboxylic dianhydride, or
From the viewpoint of stability of the binder composition for an electrode of the present invention, it is preferably composed of only a mixture of an aromatic tetracarboxylic dianhydride and an alicyclic tetracarboxylic dianhydride. In the latter case, the use ratio of the alicyclic tetracarboxylic dianhydride is preferably 30 mol% or less, more preferably 20 mol% or less, based on the total tetracarboxylic dianhydride.
Specific examples of the tetracarboxylic dianhydride used for synthesizing the polymer (B) in the present invention include aliphatic tetracarboxylic dianhydrides such as butanetetracarboxylic dianhydride;
Examples of the alicyclic tetracarboxylic dianhydride include 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 2,3,5-tricarboxycyclopentylacetic acid dianhydride, 1,3,3a, 4, 5,9b-Hexahydro-5- (tetrahydro-2,5-dioxo-3-furanyl) -naphtho [1,2-c] furan-1,3-dione, 1,3,3a, 4,5,9b- Hexahydro-8-methyl-5- (tetrahydro-2,5-dioxo-3-furanyl) -naphtho [1,2-c] furan-1,3-dione, 3-oxabicyclo [3.2.1] octane -2,4-dione-6-spiro-3 '-(tetrahydrofuran-2', 5'-dione), 5- (2,5-dioxotetrahydro-3-furanyl) -3-methyl-3-cyclohexene- No 1,2-dicarboxylic acid 3,5,6-tricarboxy-2-carboxymethylnorbornane-2: 3,5: 6-dianhydride, 2,4,6,8-tetracarboxybicyclo [3.3.0] octane-2 : 4,6: 8-dianhydride, 4,9-dioxatricyclo [5.3.1.02,6] undecane-3,5,8,10-tetraone and the like;
Examples of the aromatic tetracarboxylic dianhydride include pyromellitic dianhydride and the like, and also tetracarboxylic dianhydrides described in JP 2010-97188 A.
Examples of the diamine used for synthesizing the polymer (B) in the present invention include aliphatic diamines, alicyclic diamines, aromatic diamines, diaminoorganosiloxanes, and the like.
The diamine used when synthesizing the polymer (B) in the present invention preferably contains 30% by mole or more, more preferably 50% by mole or more of the aromatic diamine, based on the total diamine. In particular, it is preferable to contain 80 mol% or more.
Specific examples of the diamine used for synthesizing the polymer (B) in the present invention include aliphatic diamines such as 1,1-metaxylylenediamine, 1,3-propanediamine, tetramethylenediamine, and pentamethylene. Diamine, hexamethylenediamine, etc .;
Examples of alicyclic diamines include 1,4-diaminocyclohexane, 4,4′-methylenebis (cyclohexylamine), 1,3-bis (aminomethyl) cyclohexane and the like;
Examples of aromatic diamines include p-phenylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl sulfide, 1,5-diaminonaphthalene, 2,2′-dimethyl-4,4′-diaminobiphenyl, 4,4′-diamino-2,2′-bis (trifluoromethyl) biphenyl, 2,7-diaminofluorene, 4,4′-diaminodiphenyl ether, 2,2-bis [4- (4-aminophenoxy) phenyl ] Propane, 9,9-bis (4-aminophenyl) fluorene, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, 2,2-bis (4-aminophenyl) hexafluoropropane 4,4 ′-(p-phenylenediisopropylidene) bisaniline, 4,4 ′-(m-phenylenediisopropylene Riden) bisaniline, 1,4-bis (4-aminophenoxy) benzene, 4,4′-bis (4-aminophenoxy) biphenyl, 2,6-diaminopyridine, 3,4-diaminopyridine, 2,4-diamino Pyrimidine, 3,6-diaminoacridine, 3,6-diaminocarbazole, N-methyl-3,6-diaminocarbazole, N-ethyl-3,6-diaminocarbazole, N-phenyl-3,6-diaminocarbazole, N , N′-bis (4-aminophenyl) -benzidine, N, N′-bis (4-aminophenyl) -N, N′-dimethylbenzidine, 1,4-bis- (4-aminophenyl) -piperazine, 3,5-diaminobenzoic acid and the like;
Examples of the diaminoorganosiloxane include 1,3-bis (3-aminopropyl) -tetramethyldisiloxane, and the like, and diamines described in JP 2010-97188 A can be used.
(B) The ratio of the tetracarboxylic dianhydride and the diamine used in the polymer synthesis reaction is such that the acid anhydride group of the tetracarboxylic dianhydride is 0. A ratio of 9 to 1.2 equivalents is preferable, and a ratio of 1.0 to 1.1 equivalents is more preferable.
The reaction of tetracarboxylic dianhydride and diamine for synthesizing polyamic acid is preferably in an organic solvent, preferably at −20 to 150 ° C., more preferably at 0 to 100 ° C., preferably 0.1 to 24 hours, more preferably 0.5 to 12 hours. Here, as the organic solvent, for example, an aprotic polar solvent, a phenol and a derivative thereof, an alcohol, a ketone, an ester, an ether, a hydrocarbon, or the like, which can be generally used for a polyamic acid synthesis reaction, can be used. . The organic solvent is particularly preferably selected from the group consisting of N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, tetramethylurea and hexamethylphosphortriamide. Is to use one or more.
The dehydration ring closure reaction of polyamic acid for synthesizing a partially imidized polymer is preferably performed by adding a dehydrating agent and a dehydration ring closure catalyst in a method of heating polyamic acid or in a solution in which polyamic acid is dissolved in an organic solvent. It is performed by the method of heating.
The reaction temperature in the method of heating the polyamic acid is preferably 180 to 250 ° C, more preferably 180 to 220 ° C. When the reaction temperature is less than 180 ° C., the dehydration ring-closing reaction does not proceed sufficiently, and when the reaction temperature exceeds 250 ° C., the molecular weight of the imidized polymer obtained may decrease. The reaction time in the method of heating the polyamic acid is preferably 0.5 to 20 hours, more preferably 2 to 10 hours.
In the method of adding a dehydrating agent and a dehydrating ring-closing catalyst to the polyamic acid solution, the dehydrating agent may be used in an amount of 0.01 to 1.0 mol per mol of the polyamic acid amic acid structure. Preferably;
The use ratio of the dehydration ring-closing catalyst is preferably 0.01 to 10 mol with respect to 1 mol of the dehydrating agent used. The reaction temperature of the dehydration ring closure reaction is preferably 0 to 180 ° C, more preferably 10 to 150 ° C. The reaction time is preferably 1 to 10 hours, more preferably 2 to 5 hours.
Examples of the dehydration ring closure catalyst include tertiary amines such as pyridine, collidine, lutidine, and triethylamine;
Examples of the dehydrating agent include acid anhydrides such as acetic anhydride, propionic anhydride, and trifluoroacetic anhydride.
Examples of the organic solvent used in the dehydration ring-closing reaction include the organic solvents exemplified as those used for the synthesis of polyamic acid.
As described above, a solution containing the polymer (B) is obtained.
1.3 Liquid medium
The binder composition for electrodes of the present invention contains (C) a liquid medium.
The (C) liquid medium in the electrode binder composition of the present invention can be an aqueous medium or a non-aqueous medium.
The aqueous medium contains water. The aqueous medium can contain a small amount of a water-soluble non-aqueous medium in addition to water. The content ratio of the water-soluble non-aqueous medium in the aqueous medium is preferably 10% by mass or less, more preferably 5% by mass or less, based on the entire aqueous medium.
On the other hand, the non-aqueous medium contains only a non-aqueous medium without containing water.
Examples of the 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 can be used. Can do. 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-methyl-2-pyrrolidone, 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.
As the liquid medium (C) in the electrode binder composition of the present invention, it is preferable to use an aqueous medium, and it is most preferable to use only water without containing a non-aqueous medium.
1.4 Electrode binder composition and method for preparing the same
The electrode binder composition of the present invention is a solution in which at least (A) polymer particles and (B) polymer as described above are dissolved in (C) liquid medium, or these are (C) liquid medium It is preferably a slurry or latex dispersed in, and particularly preferably a latex. Since the electrode binder composition is in a latex form, the stability of the electrode slurry prepared by mixing it with an electrode active material and the like is improved, and the application property of the electrode slurry to the current collector is also good. This is preferable.
(A) The polymer particles can be obtained as a latex dispersed in water according to the above preferred synthesis method.
(C) When an aqueous medium is used as the liquid medium, (A) the latex of the polymer particles can be directly used for the preparation of the binder composition for electrodes. Therefore, the binder composition for an electrode of the present invention comprises (A) the polymer particles, (B) the polymer, and (C) the liquid catalyst, and (A) the polymerization catalyst used for the synthesis of the polymer particles or the residue thereof. Even if it contains residual monomers, emulsifiers, surfactants, pH adjusters, etc., the effects of the present invention are not diminished. However, from the viewpoint of maintaining the battery characteristics of the obtained electricity storage device at a sufficiently high level, it is preferable that the content ratio of the components derived from the production of the polymer particles (A) is as small as possible. It is preferably 5% by mass or less, more preferably 1% by mass or less, still more preferably 0.5% by mass or less, particularly preferably at all, based on the solid content of the composition. Is not to.
On the other hand, when (C) a non-aqueous medium is used as the liquid medium, (A) the polymer particles are in a solid state isolated from latex, a solution state in which the polymer particles are dissolved in the non-aqueous medium, or dispersed in the non-aqueous medium. It can use for preparation of the binder composition for electrodes in the state of the prepared dispersion liquid. Isolation of the (A) polymer particles from the latex can be performed by a known method.
(B) According to the above preferred synthesis method, the polymer (B) is obtained as a solution dissolved in an organic solvent.
(C) When an aqueous medium is used as the liquid medium, (B) the polymer is isolated from the solution, and preferably dissolved or dispersed in an aqueous medium, preferably water, to prepare a binder composition for an electrode. It is preferable to provide. Isolation of the polymer (B) from the solution can be performed by a known method. When the isolated (B) polymer is dissolved in the aqueous medium, the liquidity of the aqueous medium to be used is preferably adjusted to the alkaline side. The pH of the aqueous medium used here is preferably 7.0 to 9.5, and more preferably 7.5 to 9.0. For adjusting the liquidity of the aqueous medium, for example, ammonia water is preferably used. In order to disperse the isolated (B) polymer in an aqueous medium, a known method such as the method described in JP2011-144374A can be used.
On the other hand, when a non-aqueous medium is used as the liquid medium (C), the polymer solution (B) obtained by the above preferred synthesis method can be directly used for the preparation of the electrode binder composition.
The most preferred method for preparing the binder composition for an electrode of the present invention is by mixing (A) a latex of polymer particles and (B) an aqueous solution of the polymer. In this case, the concentration of the polymer particles (A) in the latex is preferably 15 to 70% by mass, more preferably 20 to 60% by mass;
The concentration of the polymer (B) in the aqueous solution is preferably 1 to 20% by mass, and more preferably 1 to 10% by mass.
The electrode binder composition of the present invention preferably has a neutral or slightly basic liquidity, more preferably has a pH of 7.0 to 9.5, and particularly preferably has a pH of 7.5 to 9.0. It is preferable. A known acid or base can be used to adjust the liquidity of the composition. 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.
Therefore, the binder composition for electrodes of the present invention may contain the above acid or base within a range necessary for adjusting the liquidity.
2. Slurry for electrode
The electrode slurry of the present invention as described above can be used to produce an electrode slurry. The electrode slurry refers to a dispersion used for forming an electrode active material layer on the surface of a current collector. The electrode slurry in the present invention contains at least the electrode binder composition of the present invention and an electrode active material (hereinafter also simply referred to as “active material”).
2.1 Electrode active material
The shape of the active material in the electrode slurry produced using the electrode binder composition of the present invention is preferably granular. The average particle diameter (average median particle diameter, D50 value) of the particles is preferably 0.1 to 100 μm, and more preferably 1 to 20 μm.
The proportion of the active material used is preferably such that the amount of the (A) polymer particles in the binder composition for an electrode is 0.1 to 25 parts by mass with respect to 100 parts by mass of the active material. It is more preferable that the ratio be ~ 15 parts by mass. By setting it as such a usage rate, it is possible to produce an electrode that is excellent in adhesion, and has low electrode resistance and excellent charge / discharge characteristics.
Examples of the active material in the electrode slurry produced using the electrode binder composition of the present invention include carbon materials, oxides containing lithium atoms, compounds containing silicon atoms, lead compounds, tin compounds, arsenic compounds, and antimony. A compound, an aluminum compound, a polyacene organic semiconductor (PAS), etc. can be mentioned.
Examples of the carbon material include amorphous carbon, graphite, natural graphite, mesocarbon microbeads (MCMB), pitch-based carbon fibers, and the like.
Examples of the oxide containing lithium atoms include lithium cobaltate, lithium nickelate, lithium manganate, ternary nickel cobalt lithium manganate, LiFePO ₄ , LiCoPO ₄ , LiMnPO ₄ , Li _0.90 Ti _0.05 Nb _0.05 Fe _0.30 Co _0.30 Mn _0.30 PO ₄ And so on.
Examples of the compound containing a silicon atom include a silicon simple substance, a silicon oxide, a silicon alloy, and the like, and a silicon material described in JP-A No. 2004-185810 can be used. As the silicon oxide, the composition formula SiO _x A silicon oxide represented by (0 <x <2, preferably 0.1 ≦ x ≦ 1) is preferable. The silicon alloy is preferably an alloy of silicon and at least one transition metal selected from the group consisting of titanium, zirconium, nickel, copper, iron and molybdenum. These transition metal silicides are preferably used because they have high electronic conductivity and high strength. In addition, since the active material contains these transition metals, the transition metal present on the surface of the active material is oxidized to an oxide having a hydroxyl group on the surface, so that the binding force with the binder component becomes better. However, it is preferable. The silicon content in the silicon alloy is preferably 10 mol% or more, more preferably 20 to 70 mol%, based on all the metal elements in the alloy. As the silicon alloy, it is more preferable to use a silicon-nickel alloy or a silicon-titanium alloy, and it is particularly preferable to use a silicon-titanium alloy. The compound containing a silicon atom may be single crystal, polycrystalline, or amorphous.
“Oxide” in the above is a concept that means a compound or salt composed of oxygen and an element having an electronegativity smaller than that of oxygen. In addition to metal oxide, metal phosphate, nitrate, halogen It is a concept including oxo acid salts, sulfonic acid salts and the like.
When the electrode binder composition of the present invention is used to produce an electricity storage device, particularly a positive electrode of a lithium ion secondary battery, the active material contained in the electrode slurry may be an oxide containing lithium atoms. preferable.
When the binder composition for an electrode of the present invention is used to produce an electricity storage device, particularly a negative electrode of a lithium ion secondary battery, the active material contained in the electrode slurry contains a compound containing a silicon atom. Preferably there is. Since silicon atoms have a large occlusion capacity for lithium, the active material containing a compound containing silicon atoms can increase the storage capacity of the resulting storage device, and as a result, increase the output and energy density of the storage device. can do. The proportion of the compound containing silicon atoms in the active material is preferably 1% by mass or more, more preferably 1 to 50% by mass, still more preferably 5 to 45% by mass, particularly 10%. It is preferable to be ~ 40% by mass. The active material for the negative electrode is preferably composed of a mixture of a compound containing a silicon atom and a carbon material. Since the carbon material has a small volume change due to charge / discharge, the influence of the volume change of the compound containing silicon atoms can be mitigated by using a mixture of the compound containing silicon atoms and the carbon material as the negative electrode active material. And the adhesion between the active material layer and the current collector can be further improved. The negative electrode active material is particularly preferably composed of a mixture of a compound containing a silicon atom and graphite.
When the electrode binder composition of the present invention is used to produce an electrode for an electric double layer capacitor, the active material contained in the electrode slurry is, for example, a carbon material, an aluminum compound, a silicon oxide, or the like. Is preferred.
Furthermore, when the electrode binder composition of the present invention is used to produce an electrode for a lithium ion capacitor, examples of the active material contained in the electrode slurry include carbon materials and polyacene organic semiconductors (PAS). It is preferable to use it.
2.2 Optional additives
The slurry for electrodes in the present invention may contain other components as necessary in addition to the components described above. Examples of such other components include a conductivity-imparting agent, a thickener, and a liquid medium (however, excluding a part brought in from the electrode binder composition).
2.2.1 Conductivity imparting agent
The ratio of the conductivity-imparting agent in the electrode slurry is preferably 20 parts by mass or less, more preferably 1 to 15 parts by mass, and particularly 2 to 10 parts by mass with respect to 100 parts by mass of the active material. preferable.
Specific examples of the conductivity-imparting agent include carbon in a lithium ion secondary battery. Examples of carbon include activated carbon, acetylene black, ketjen black, furnace black, graphite, carbon fiber, and fullerene. Among these, acetylene black or furnace black can be preferably used.
2.2.2 Thickener
The electrode slurry can contain a thickener from the viewpoint of improving the coatability. The use ratio of the thickener is such that the ratio (Wv / Wa) of the weight (Wv) of the thickener to the weight (Wa) of the active material in the electrode slurry is 0.001 to 0.1. is there. This ratio (Wv / Wa) is preferably 0.005 to 0.05.
Specific examples of the thickener include, for example, cellulose derivatives such as carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxymethylcellulose, hydroxypropylmethylcellulose, and hydroxyethylmethylcellulose;
An ammonium salt or an alkali metal salt of the cellulose derivative;
Polycarboxylic acids such as poly (meth) acrylic acid, modified poly (meth) acrylic acid;
An alkali metal salt of the polycarboxylic acid;
Polyvinyl alcohol (co) polymers such as polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymer;
Examples thereof include water-soluble polymers such as saponified products of copolymers of unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid and fumaric acid and vinyl esters.
2.3 Liquid medium
Since the slurry for electrodes contains the binder composition for electrodes, it will contain the (C) liquid medium which the binder composition for electrodes contained. However, the electrode slurry may additionally contain a further liquid medium in addition to the liquid medium brought in from the electrode binder composition.
The use ratio of the liquid medium (including the amount brought in from the electrode binder composition) in the electrode slurry is the solid content concentration of the electrode slurry (the total mass of components other than the liquid medium in the electrode slurry is the electrode slurry). Is the ratio of 30 to 70% by mass, and more preferably 40 to 60% by mass.
The liquid medium additionally contained in the electrode slurry may be the same as or different from the liquid medium (C) contained in the electrode binder composition. ) The liquid medium is preferably selected from the liquid media described above.
2.4 Method for preparing electrode slurry
The electrode slurry may be prepared by any method as long as it contains the above-described components.
However, from the viewpoint of preparing an electrode slurry having better dispersibility and stability more efficiently and inexpensively, an active material and optional additional components used as necessary are added to the electrode binder composition. In addition, it can be prepared by mixing them.
In order to mix the binder composition for electrodes and other components, it can carry out by stirring by a well-known method.
The preparation of the electrode slurry (mixing operation of each component) is preferably performed at least part of the process under reduced pressure. Thereby, it can prevent that a bubble arises in the active material layer obtained. As the degree of decompression, the absolute pressure is 5.0 × 10 ⁴ ~ 5.0 × 10 ⁵ It is preferable to be about Pa.
As mixing and stirring for preparing the electrode slurry, it is necessary to select a mixer that can stir to such an extent that no agglomerates of active material particles remain in the slurry and sufficient dispersion conditions as necessary. The degree of dispersion can be measured by a particle gauge, but it is preferable to mix and disperse so that aggregates larger than at least 100 μm are eliminated. Examples of the mixer that meets such conditions include a ball mill, a bead mill, a sand mill, a defoamer, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, and a Hobart mixer. it can.
3. Method for manufacturing electrode for power storage device
The electrode for an electricity storage device is formed by coating the slurry for an electrode produced using the binder composition for an electrode of the present invention on the surface of an appropriate current collector such as a metal foil, and then forming the coating film It can manufacture by removing a liquid medium from. The electrode produced in this manner is formed by binding an active material layer containing the above-described polymer and active material, and optional additional components used as necessary, on a current collector. . The electrode having the layer formed from the above-described electrode slurry on the surface of the current collector has excellent binding properties between the current collector and the active material layer, and is one of the electrical characteristics of charge / discharge rate characteristics Is good.
The current collector is not particularly limited as long as it is made of a conductive material. In a lithium ion secondary battery, a current collector made of metal such as iron, copper, aluminum, nickel, and stainless steel is used. In particular, when aluminum is used for the positive electrode and copper is used for the negative electrode, it is used for the positive electrode of the present invention. The effect of the slurry is most apparent. As the current collector in the nickel metal hydride secondary battery, a punching metal, an expanded metal, a wire mesh, a foam metal, a mesh metal fiber sintered body, a metal plated resin plate, or the like is used.
The shape and thickness of the current collector are not particularly limited, but are preferably in the form of a sheet having a thickness of about 0.001 to 0.5 mm.
There is no restriction | limiting in particular about the coating method to the electrical power collector of the slurry for electrodes. The coating can be performed by an appropriate method such as a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a dipping method, or a brush coating method. The coating amount of the electrode slurry is not particularly limited, but the thickness of the active material layer formed after removing the liquid medium is preferably 0.005 to 5 mm, and preferably 0.01 to 2 mm. It is more preferable to use the amount.
The method for removing the liquid medium from the coated film after coating is not particularly limited, and may be, for example, drying with hot air, hot air, low-humidity air; vacuum drying; (far) drying by irradiation with infrared rays, electron beams, or the like. . The drying speed is appropriately set so that the liquid medium can be removed as quickly as possible within a speed range in which the active material layer does not crack due to stress concentration or the active material layer does not peel from the current collector. be able to.
Furthermore, it is preferable to increase the density of the active material layer by pressing the current collector after removal of the liquid medium. The density of the active material layer after pressing is 1.5 to 3.8 g / cm when the electrode is used as a positive electrode. ³ Preferably, 1.7 to 3.6 g / cm ³ And more preferably;
When the electrode is used as the negative electrode, 1.2 to 1.9 g / cm ³ Preferably, 1.3 to 1.8 g / cm ³ More preferably.
Examples of the pressing method include a mold press and a roll press. The press conditions should be set appropriately depending on the type of press equipment used and the desired density of the active material layer. This condition can be easily set by a few preliminary experiments by those skilled in the art. For example, in the case of a roll press, the linear pressure of the roll press machine is 0.1 to 10 t / cm, preferably 0.5 to 5 t. For example, at a roll temperature of 20 to 100 ° C. at a pressure of 50 cm / cm, the coating film feed speed (roll rotation speed) after removal of the dispersion medium is 1 to 80 m / min, preferably 5 to 50 m / min. it can.
It is preferable that the pressed coating film is further heated under reduced pressure to completely remove the liquid medium. The degree of pressure reduction in this case is preferably 50 to 200 Pa as an absolute pressure, and more preferably 75 to 150 Pa. The heating temperature is preferably 100 to 200 ° C, more preferably 120 to 180 ° C. The heating time is preferably 2 to 12 hours, and more preferably 4 to 8 hours.
The electrode for an electricity storage device manufactured in this way is excellent in adhesion between the current collector and the active material layer, and has good cycle characteristics, which is one of electrical characteristics.
4). Power storage device
An electricity storage device can be manufactured using the electrode for an electricity storage device of the present invention as described above.
The electricity storage device includes the above-described electrode, further contains an electrolytic solution, and can be manufactured according to a conventional method using components such as a separator. As a specific manufacturing method, for example, a negative electrode and an electrode are overlapped via a separator, and this is wound or folded according to the shape of the battery, and stored in a battery container, and an electrolytic solution is injected into the battery container. Can be mentioned. The shape of the battery can be an appropriate shape such as a coin shape, a cylindrical shape, a square shape, or a laminate shape.
The electrolyte solution may be liquid or gel, and the one that effectively expresses the function as a battery is selected from the known electrolyte solutions used for the electricity storage device depending on the type of the negative electrode active material and the electrode active material. That's fine.
The electrolytic solution can be a solution in which an electrolyte is dissolved in a suitable solvent.
As the electrolyte, for example, in the lithium ion secondary battery, any conventionally known lithium salt can be used, and specific examples thereof include, for example, LiClO. ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiB ₁₀ Cl ₁₀ LiAlCl ₄ , LiCl, LiBr, LiB (C ₂ H ₅ ) ₄ , LiCF ₃ SO ₃ , LiCH ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, lower fatty acid lithium carboxylate and the like can be exemplified.
The solvent for dissolving the electrolyte is not particularly limited, and specific examples thereof include carbonate compounds such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate;
Lactone compounds such as γ-butyl lactone;
Ether compounds such as trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran;
Examples thereof include sulfoxide compounds such as dimethyl sulfoxide, and one or more selected from these can be used.
The concentration of the electrolyte in the electrolytic solution is preferably 0.5 to 3.0 mol / L, more preferably 0.7 to 2.0 mol / L.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.
<(A) Synthesis of polymer particles>
Synthesis Example A1-1
(1) Synthesis In a temperature-controllable autoclave equipped with a stirrer, 200 parts by mass of water, 0.6 part by mass of sodium dodecylbenzenesulfonate, 1.0 part by mass of potassium persulfate, 0.5 part by mass of sodium bisulfite, α-Methylstyrene dimer 0.5 part by mass, dodecyl mercaptan 0.3 part by mass and the monomers shown in Table 1 were charged all at once, then the temperature was raised to 70 ° C., and this temperature was maintained for 8 hours. A polymerization reaction was performed. Thereafter, the temperature was further raised to 80 ° C., and this temperature was maintained for 3 hours to continue the polymerization reaction, thereby obtaining a latex. After adding ammonium water with a concentration of 15% by mass to this latex and adjusting the pH to 7.5, 50 parts by mass of a sodium tripolyphosphate aqueous solution with a concentration of 10% by mass (corresponding to 5 parts by mass in terms of sodium tripolyphosphate) added. Subsequently, the residual monomer was removed by steam distillation and concentrated under reduced pressure to obtain an aqueous dispersion containing 50% by mass of polymer particles P1-1.
(2) Measurement of average particle size Particle size distribution of polymer particles P1 obtained using a particle size distribution measuring apparatus (model “FPAR-1000” manufactured by Otsuka Electronics Co., Ltd.) having a dynamic light scattering method as a measurement principle. The average particle size (D50) determined from the particle size distribution was 170 nm.
(3) DSC measurement When the polymer particle P1-1 contained in the obtained water dispersion was measured with the differential scanning calorimeter (DSC), only one glass transition temperature Tg was observed at -31 degreeC. No melting temperature was observed.
Synthesis Examples A1-2 and A1-3
In Synthesis Example A1-1, polymer particles P1-2 and P1 were synthesized in the same manner as in Synthesis Example A1-1 except that the types and amounts of the charged monomers were as described in Table 1. -3 was obtained, respectively, to obtain an aqueous dispersion containing 50% by mass.
The average particle diameter and Tg of the polymer particles P1-2 and P1-3 measured in the same manner as in Synthesis Example A1-1 are shown in Table 1, respectively.

Abbreviations in the monomer column in Table 1 have the following meanings, respectively.
BD: 1,3-butadiene ST: Styrene AN: Acrylonitrile AA: Acrylic acid TA: Itaconic acid MMA: Methyl methacrylate HEMA: 2-hydroxyethyl methacrylate synthesis Example A2-1
(1) Synthesis of polymer (A2a) After the inside of an autoclave having an internal volume of about 6 L equipped with an electromagnetic stirrer was sufficiently purged with nitrogen, 2.5 L of deoxygenated water and 25 g of ammonium perfluorodecanoate as an emulsifier Was heated to 60 ° C. while stirring at 350 rpm. Next, a mixed gas composed of 70% by mass of vinylidene fluoride (VF) and 30% by mass of propylene hexafluoride (HFP) as monomers was charged until the internal pressure reached 20 kg / cm ² . Furthermore, 25 g of Freon 113 (CClF ₂ -CCl ₂ F) solution containing 20% by mass of diisopropyl peroxydicarbonate as a polymerization initiator was injected using nitrogen gas to initiate polymerization. During the polymerization, a mixed gas composed of 65% by mass of VF and 35% by mass of HFP was sequentially injected so that the internal pressure was maintained at 20 kg / cm ² . Since the polymerization rate decreased as the polymerization progressed, the same amount of the same polymerization initiator solution as above was injected with nitrogen gas after 3 hours from the start of polymerization, and the reaction was continued for another 3 hours. Then, simultaneously with cooling the reaction liquid, stirring was stopped, and the reaction was stopped by releasing unreacted monomers, whereby an aqueous dispersion containing 40% by mass of polymer (A2a1) fine particles was obtained. As a result of analyzing the obtained polymer by ¹⁹ F-NMR, the mass composition ratio of the monomer was VF: HFP = 24: 1.
(2) Synthesis of polymer alloy particles 62.5 parts by mass of an aqueous dispersion containing fine particles of the polymer (A2a1) obtained in the above step after sufficiently replacing the inside of a 7 L separable flask with nitrogen Polymer (corresponding to 25 parts by mass in terms of A2a1)), emulsifier “ADEKA rear soap SR1025” (trade name, manufactured by ADEKA Corporation) 0.5 part by mass, methyl methacrylate (MMA) 30 parts by mass, acrylic acid 2- 40 parts by mass of ethylhexyl (EHA), 5 parts by mass of methacrylic acid (MAA) and 130 parts by mass of water were charged in this order, and stirred at 70 ° C. for 3 hours to allow the polymer (A2a1) to absorb the monomer. Next, 20 mL of a tetrahydrofuran solution containing 0.5 part by mass of azobisisobutyronitrile, which is an oil-soluble polymerization initiator, is added, heated to 75 ° C. and reacted for 3 hours, and further reacted at 85 ° C. for 2 hours. went. Then, after cooling, the reaction was stopped, and the aqueous dispersion containing 40% by mass of polymer particles P2-1 was obtained by adjusting the pH to 7.0 with a 2.5N aqueous sodium hydroxide solution.
(3) Measurement of average particle diameter Polymer particle P2-1 obtained by using a particle size distribution measuring apparatus (model “FPAR-1000” manufactured by Otsuka Electronics Co., Ltd.) having a dynamic light scattering method as a measurement principle. The particle size distribution was measured, and the average particle size determined from the particle size distribution was 330 nm.
(4) DSC analysis When the polymer particle P2-1 contained in the obtained aqueous dispersion was measured by a differential scanning calorimeter (DSC), only one glass transition temperature Tg was observed at -5 ° C. Since this polymer particle P2-1 shows only one Tg despite being composed of two types of polymers, it can be presumed to be a polymer alloy particle.
During the DSC measurement, the melting temperature of the polymer particles P2-1 was not observed.
The DSC chart measured here is shown in FIG.
Synthesis Example A2-2
In the synthesis of the polymer (A2a) in the synthesis example A2-1 (1),
(1) of Synthesis Example A2-1 except that the composition of the VF / HFP mixed gas charged before the start of the reaction and the composition of the VF / HFP mixed gas (VF / HFP) sequentially injected to maintain the internal pressure during the polymerization were changed. In the same manner as in the synthesis of the polymer (A2a), an aqueous dispersion containing 40% by mass of the fine particles of the polymer (A2a2) was obtained. The mass composition ratio of the monomer analyzed by ¹⁹ F-NMR for the obtained polymer was VF: HFP = 20: 5.
An aqueous dispersion containing fine particles of the polymer (A2a2) obtained above in place of the aqueous dispersion containing fine particles of the polymer (A2a1) in the synthesis of (2) polymer alloy particles of the synthesis example A2-1 62.5 parts by mass (corresponding to 25 parts by mass in terms of polymer (A2a2)), and 5 parts by mass of acrylic acid (MA) instead of methacrylic acid (MAA) were used. 2) In the same manner as the synthesis of the polymer alloy particles, an aqueous dispersion containing 40% by mass of the polymer particles P5 was obtained.
The average particle diameter and Tg of polymer particles P2-2 measured in the same manner as in Synthesis Example A2-1 are shown in Table 2.
Synthesis Example A2-3
A separable flask having a volume of 7 liters was charged with 150 parts by mass of water and 0.2 parts by mass of sodium dodecylbenzenesulfonate, and the inside of the separable flask was sufficiently purged with nitrogen.
On the other hand, in another container, 60 parts by mass of water, ether sulfate type emulsifier (trade name “Adekaria soap SR1025”, manufactured by ADEKA Co., Ltd.) as an emulsifier, 0.8 parts by mass in terms of solid content and 2 as a monomer , 2,2-trifluoroethyl methacrylate (TFEMA) 20 parts by mass, acrylonitrile (AN) 10 parts by mass, methyl methacrylate (MMA) 25 parts by mass, 2-ethylhexyl acrylate (EHA) 40 parts by mass and acrylic acid (AA) 5 A monomer emulsion containing a mixture of the above monomers was prepared by adding parts by mass and stirring sufficiently.
Thereafter, the temperature inside the separable flask was started, and when the internal temperature reached 60 ° C., 0.5 parts by mass 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 temperature inside the separable flask is maintained at 70 ° C. The emulsion was added slowly over 3 hours. 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 then the pH was adjusted to 7.6 by adding ammonium water having a concentration of 15% by mass, thereby containing 30% by mass of the polymer (P2-3). An aqueous dispersion was obtained.
The average particle diameter and Tg of polymer particles P2-2 measured in the same manner as in Synthesis Example A2-1 are shown in Table 2. In the DSC measurement, the melting temperature of the polymer particles P2-2 was not observed.

Abbreviations in the monomer column in Table 2 have the following meanings, respectively.
VF: Vinylidene fluoride HFP: Propylene hexafluoride TFEMA: 2,2,2-trifluoroethyl methacrylate MMA: Methyl methacrylate EHA: 2-ethylhexyl acrylate MAA: Methacrylic acid AA: Acrylic acid AN: Acrylonitrile Table 2 The amount of the monomer having a fluorine atom is an analytical value for Synthesis Examples A2-1 and A2-2, and a charged amount for A2-3.
<(B) Synthesis of polymer>
Synthesis Example B-1
A 3 L flask equipped with a stirrer, a thermometer and a condenser was heated with a heat gun in a reduced pressure state to remove residual moisture inside the container, and then filled with dry nitrogen gas. In this flask, 1,170 g of N-methyl-2-pyrrolidone (NMP) that had been subjected to dehydration by a dehydration distillation method using calcium hydride as a solvent in advance, and 3,3 ′, 4, as tetracarboxylic dianhydride. 80.56 g (0.250 mol) of 4′-benzophenonetetracarboxylic dianhydride and 50.06 g (0.250 mol) of 4,4′-diaminodiphenyl ether as diamine were charged and reacted at 25 ° C. with stirring for 3 hours. Was performed to obtain a polymer solution containing 10% by mass of the polyamic acid B1.
The solution viscosity of this polymer solution was 16,200 mPa · s.
Synthesis examples B-2 to B-4
In the above Synthesis Example B-1, the polyamic acid B2 was prepared in the same manner as in Synthesis Example B-1, except that the types and amounts of the tetracarboxylic dianhydride and diamine used were as shown in Table 3. A solution containing 10% by mass of ~ B4 was obtained.
The solution viscosities of these polyamic acid solutions are shown in Table 3.

Abbreviations in the tetracarboxylic dianhydride column and the diamine column in Table 3 have the following meanings, respectively.
BTDA: 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride PMDA: pyromellitic dianhydride TDA: 4- (2,5-dioxotetrahydrofuran-3-yl) -1,2,3 , 4-Tetrahydronaphthalene-1,2-carboxylic anhydride DDE: 4,4′-diaminodiphenyl ether DDP: 4,4′-diaminobiphenyl <Synthesis of active material containing silicon>
Synthesis Example A-1
A mixture of pulverized silicon dioxide powder (average particle size 10 μm) and carbon powder (average particle size 35 μm) was placed in an electric furnace adjusted to a temperature in the range of 1,100 to 1,600 ° C. under a nitrogen stream (0 0.5 NL / min), heat treatment was performed for 10 hours to obtain a silicon oxide powder (average particle size 8 μm) represented by the composition formula SiOx (x = 0.5 to 1.1).
300 g of this silicon oxide powder was placed in a batch-type heating furnace, and the temperature was increased from room temperature (25 ° C.) to 1,100 ° C. at a temperature increase rate of 300 ° C./h while maintaining a reduced pressure of 100 Pa absolute by a vacuum pump. Warm up. Next, while maintaining the pressure in the heating furnace at 2,000 Pa, heat treatment (graphite coating treatment) was performed at 1,100 ° C. for 5 hours while introducing methane gas at a flow rate of 0.5 NL / min. After the completion of the graphite coating treatment, the powder was cooled to room temperature at a temperature decrease rate of 50 ° C./h to obtain about 330 g of graphite-coated silicon oxide powder.
This graphite-coated silicon oxide is a conductive powder (active material) in which the surface of silicon oxide is coated with graphite, and the average particle diameter thereof is 10.5 μm. The ratio of the graphite coating in the case of mass% was 2 mass%.
Example 1
(1) Preparation of aqueous solution of (B) polymer (polyamic acid) 100 g of the solution containing polyamic acid B1 obtained in Synthesis Example B-1 was dropped into about 1 L of water to be solidified. The coagulated product was thoroughly washed in running water to sufficiently remove NMP, and then dried under reduced pressure overnight at room temperature to obtain a solid polyamic acid. Next, 10 g of the above solid polyamic acid was put into 90 g of a 2% by mass ammonia aqueous solution (pH 11) and stirred at room temperature for 3 hours to obtain an aqueous solution containing 10% by mass of polyamic acid.
(2) Preparation of binder composition 190 g (95 g in terms of polymer particles) of the aqueous dispersion containing the polymer particles P1-1 obtained in Synthesis Example A1-1 and 50 g of the polyamic acid aqueous solution obtained above ( A binder composition was obtained by mixing 5 g) in terms of polyamic acid. The solid content concentration of this binder composition was 41.7% by mass, and the pH measured using a pH meter (product name “D-51S” manufactured by Horiba, Ltd.) was 7.6.
(3) Adhesion test of binder composition The binder composition prepared above was applied on a 10 cm square copper plate and a glass plate, respectively, so that the film thickness after solvent removal was about 90 μm, and at 60 ° C. By heating for 30 minutes, thin films of the binder composition were formed on the copper plate and the glass plate, respectively.
For the thin film of the binder composition formed above, a cross-cut peel test in accordance with JIS K5400 was performed.
Specifically, using a cutter, 11 cuts were made from the surface of the thin film to the depth reaching the copper plate or the glass plate at 1 mm intervals, both vertically and horizontally, and the thin film was divided into a grid-like area of 100 squares. An adhesive tape (manufactured by Terraoka Co., Ltd., product number “650S”) was applied to the entire surface of these 100 square areas and immediately peeled off, and the number of remaining squares was counted.
The evaluation results are shown in Table 4 as the number of remaining cells in 100 cells.
From the examination by the present inventors, it has been empirically clarified that the adhesion between the active material layer and the current collector is proportional to the adhesion between the copper plate and the polymer film in this test. Yes. Further, it has been empirically revealed that the binding property as a binder for binding active materials is proportional to the adhesion between the glass plate and the polymer film in this test. For this reason, when the adhesion between the glass plate and the polymer film is good, it can be estimated that the adhesion as a binder of the polymer binding the active materials is good,
When the adhesion between the Cu plate and the polymer film is good, it can be estimated that the adhesion between the current collector and the active material layer is good.
In this case, if the number of remaining squares is 80 or more, it can be determined that the adhesion is good,
If this number is 90 or more, it can be determined that the adhesion is excellent (very good). The number of remaining cells is most preferably 100 out of 100 grids.
(4) Preparation of electrode slurry Graphite with an average particle size (D50 value) of 22 μm as a negative electrode active material in a biaxial planetary mixer (product name “TK Hibismix 2P-03” manufactured by PRIMIX Corporation) 80 parts by mass (product name “SMG-HE1” manufactured by Hitachi Chemical Co., Ltd.) and 20 parts by mass of graphite-coated silicon oxide (C / SiO) prepared in Synthesis Example A-1 and acetylene black (electrochemical) 1 part by mass of Kogyo Co., Ltd. (trade name “Denka Black 50% press product”) was added and mixed at 20 rpm for 3 minutes. Next, 50 g of carboxymethyl cellulose (CMC: Nippon Paper Industries Co., Ltd. (Chemical Business Division), trade name “MAC-500LC”), which was previously adjusted to a solid content concentration of 2 mass%, and 15.5 g of ion-exchanged water were added, Mixed at 60 rpm for 30 minutes. Thereafter, 2.4 g of the binder composition and 27 g of ion-exchanged water were added thereto, and the mixture was further mixed at 30 rpm for 15 minutes. Next, in order to remove bubbles in the slurry, by using a stirring defoaming machine (trade name “ARV930-TWIN” manufactured by Shinkey Co., Ltd.), stirring and mixing at 600 rpm for 5 minutes under a reduced pressure of 25 kPa absolute pressure, A slurry for an electrode having a solid content concentration of 1% by mass and a total solid content concentration of 52% by mass of the binder resin ((A) polymer particles) was prepared.
(5) Manufacture of electrode for electricity storage device On the surface of a current collector made of copper foil having a thickness of 10 μm, the electrode slurry prepared in “(4) Preparation of slurry for electrode” was applied to the active material layer after removing the solvent. The film thickness was adjusted to 15 mg / cm ² and applied uniformly by the doctor blade method, followed by drying at 120 ° C. for 5 minutes to form a coating film. Subsequently, the above-mentioned coating film was subjected to a roll temperature adjustment at a roll temperature of 30 ° C., a linear pressure of 1 t / cm, and a feed rate of 0.5 m / min. And the density of the electrode layer was adjusted to 1.60 g / cm ³ . Furthermore, the electrode for electrical storage devices was obtained by heating for 6 hours at 160 ° C. under reduced pressure of 100 Pa absolute pressure to remove a trace amount of water in the active material layer.
The density of the active material layer in this electrode for an electricity storage device was 1.62 g / cm ³ .
(6) Manufacture of electricity storage device In the glove box purged with argon so that the dew point is −80 ° C. or less, the electrode manufactured in “(5) Production of electrode for electricity storage device” was punched and molded to a diameter of 15.5 mm. The product was placed on a bipolar coin cell (trade name “HS Flat Cell” manufactured by Hosen Co., Ltd.) with the active material layer facing upward. Next, a separator (made by Celgard, trade name “Celgard # 2400”) made of a polypropylene porous film punched to a diameter of 24 mm was placed on the above electrode, and 500 μL of electrolyte was injected so that air did not enter. Thereafter, a 200 μm-thick lithium foil having a diameter of 16.6 mm was placed as a counter electrode, and the outer body of the two-pole coin cell was closed with a screw to be sealed. A power storage device was assembled.
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).
This operation was repeated to produce a total of two electricity storage devices. One of them was subjected to “(7) Evaluation of electricity storage device (evaluation of charge / discharge cycle characteristics)”, and the other was subjected to “(8) Evaluation of film thickness change rate of active material layer”.
(7) Evaluation of electricity storage device (Evaluation of charge / discharge cycle characteristics)
About the electricity storage device manufactured in the above “(6) Production of electricity storage device”, charging is started at a constant current (0.2 C), and when the voltage becomes 0.01 V, the charge continues to the constant voltage (0.01 V). Then, the charging was continued and the time when the current value reached 0.05 C was regarded as the completion of charging (cut-off). Next, discharging was started at a constant current (0.2 C), and when the voltage reached 2.0 V, the discharge was completed (cutoff), and the initial charge / discharge was completed.
Next, 0.5 C charge / discharge was performed as follows for the above-described electricity storage device that was charged and discharged for the first time.
First, charging starts at a constant current (0.5C), and when the voltage reaches 0.01V, charging continues at a constant voltage (0.01V), and when the current value reaches 0.05C. Was charged (cut off). Next, discharge was started at a constant current (0.2 C), and when the voltage reached 2.0 V, the discharge was completed (cutoff), and the discharge capacity at 0.5 C (0.5 C discharge capacity in the first cycle) = A) was measured.
This charge / discharge of 0.5C was repeated, and when the 0.5C discharge capacity at the 100th cycle was B, the capacity retention rate after 100 cycles was calculated by the following mathematical formula (1).
Capacity maintenance rate (%) = B / A × 100 (1)
The evaluation results are shown in Table 4.
If the capacity retention rate after 100 cycles is 90% or more and less than 95%, it can be determined that the charge / discharge cycle characteristics are excellent, and if it is 95% or more, the charge / discharge cycle characteristics are extremely excellent. Can be determined.
(8) Evaluation of rate of change of film thickness of active material layer For the electricity storage device obtained in “(6) Production of electricity storage device”, charging was started at a constant current (0.2 C), and the voltage was reduced to 0.01V At that time, charging was continued at a constant voltage (0.01 V), and charging was completed (cut off) when the current value reached 0.05C. Next, discharging was started at a constant current (0.2 C), and when the voltage reached 2.0 V, the discharge was completed (cutoff), and the initial charge / discharge was completed.
Next, about the said electrical storage device which performed initial charge / discharge, charge starts with a constant current (0.2C), and when a voltage becomes 0.01V, it charges with a constant voltage (0.01V) continuously. Continuing, the time when the current value reached 0.05 C was defined as the completion of charging (cut-off).
This electricity storage device was disassembled in a dry room (room temperature 25 ° C.) having a dew point of −60 ° C. or less, and an electrode for electricity storage device (negative electrode) was taken out. Subsequently, this electrode was immersed in dimethyl carbonate for 1 minute and washed in a dry room. After taking out the electrode from dimethyl carbonate, the dimethyl carbonate was vaporized and removed by standing in a dry room for 30 minutes.
The ratio of the active material layer thickness of the electrode after charging to the active material layer thickness of the electrode immediately after production (uncharged state) measured in advance was measured. (Film thickness ratio after charging) was calculated by the following mathematical formula (2).
Film thickness ratio after charge (%) = (film thickness after charge) / (film thickness immediately after manufacture) × 100 (2)
The evaluation results are shown in Table 4.
When this value exceeds 130%, the active material layer indicates that the volume expansion of the active material accompanying charging is not relaxed, and there is a concern that the active material may peel off when mechanical stress is applied to the active material. is there. On the other hand, if this value is 130% or less, it indicates that the active material is firmly held in the active material layer despite the volume expansion of the active material with charging, and the active material is peeled off. It can be evaluated that the electrode is a good electrode with suppressed.
(9) Evaluation of Storage Stability of Binder Composition 50 g of the binder composition prepared in “(2) Preparation of binder composition” above is placed in a 100 mL vial and sealed, and left at 5 ° C. for 3 months. And stored. Using the binder composition after storage, an electricity storage device was produced and evaluated in the same manner as in the above (4) to (8). The evaluation results are shown in Table 4.
Examples 2 to 11 and Comparative Examples 1 and 2
In Example 1 above, the aqueous dispersion containing (A) polymer particles of the type and amount described in Table 4 and the (B) polymer (polyamic acid) of the type and amount described in Table 4 are contained. A binder composition was prepared in the same manner as in Example 1 except that the NMP solution was used. Using this binder composition, an electrode slurry was prepared in the same manner as in Example 1 except that the amounts of graphite and graphite-coated silicon oxide (C / SiO) were changed as shown in Table 4, respectively. Manufactured and evaluated.
The evaluation results are shown in Table 4.
Example 12
(1) (A) Preparation of NMP dispersion of polymer particles To 200 g of an aqueous dispersion containing polymer particles P1-3 obtained in Synthesis Example A1-3 (100 g in terms of polymer particles), 210 g of NMP was added. After the addition, an NMP dispersion containing 50% by mass of polymer particles P1-3 was obtained by concentrating using an evaporator until the total mass became 200 g.
(2) Preparation of binder composition 200 g of NMP dispersion (100 g in terms of polymer particles) containing the polymer particles P1-3 obtained above and the polyamic acid B3 obtained in Synthesis Example B-3 are contained. A binder composition was obtained by mixing 100 g of NMP solution (10 g in terms of polyamic acid). The solid content concentration of the binder composition was 37.7% by mass, and the pH measured using a pH meter was 8.1.
(3) Evaluation A binder composition was prepared in the same manner as in Example 1 except that the binder composition prepared above was used. An electrode slurry was prepared in the same manner as in Example 1 except that this binder composition was used, and an electricity storage device was produced and evaluated.
The evaluation results are shown in Table 4.

The invention's effect

The electrode binder composition of the present invention can produce an electrode having excellent adhesion and charge / discharge characteristics. Since the electrode manufactured using the binder composition for an electrode of the present invention is excellent in mechanical strength, it is excellent in electrode characteristics even when an electrode active material exhibiting a significant volume change during charge / discharge is used. Is.

Claims

At least (A) polymer particles,
A binder composition for an electrode of an electricity storage device, comprising (B) at least one polymer selected from the group consisting of a polyamic acid and a partially imidized polymer thereof, and (C) a liquid medium.
The (A) polymer particles are
The binder composition for electrodes according to claim 1, which is a particle containing a polymer having a repeating unit derived from a conjugated diene compound and a repeating unit derived from an aromatic vinyl compound.
The polymer particle (A) further has a repeating unit having at least one repeating unit selected from the group consisting of a repeating unit derived from an α, β-unsaturated nitrile compound and a repeating unit derived from an unsaturated carboxylic acid. The binder composition for electrodes according to claim 2, which is a particle containing coalesced particles.
The binder composition for an electrode according to claim 1, wherein the (A) polymer particle is a particle containing a polymer having a repeating unit derived from a monomer having a fluorine atom.
The (A) polymer particles are
The binder for electrodes according to claim 4, which is a polymer alloy particle comprising a polymer having a repeating unit derived from a monomer having a fluorine atom and a polymer having a repeating unit derived from an unsaturated carboxylic acid ester. Composition.
The electrode binder composition according to any one of claims 1 to 5, wherein the liquid medium (C) is water.
The method for producing a binder composition for an electrode according to claim 6, wherein the method comprises a step of mixing (A) a latex of polymer particles and (B) an aqueous solution of the polymer.
An electrode slurry for an electricity storage device, comprising the electrode binder composition according to any one of claims 1 to 5 and an electrode active material.