JP2013030288A - Binder composition for electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binder material for an electrode which is excellent in all of ionic conductivity, oxidation resistance and adhesion.SOLUTION: The binder composition for an electrode of an electric power storage device includes polymer and a liquid medium. The polymer includes 5-50 pts.mass of a repeating unit originating from at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene, and 1-10 pts.mass of a repeating unit originating from an unsaturated carboxylic acid with respect to 100 pts.mass of the polymer. Measurement was made on a solid matter which was prepared by drying the binder composition for an electrode at 120°C for one hour, under the conditions of 70°C for 24 hours and using a mixture solvent (EC:DEC=1:2(volume ratio )) including ethylene carbonate (EC) and diethylcarbonate (DEC) as a solvent. The result of the measurement was that the proportional of the solvent insoluble was 25-70 mass%.

Description

The present invention relates to an electrode binder composition.
The binder composition contains a specific polymer, is excellent in ionic conductivity and adhesion, and is suitable as a binder material for an electrode of an electricity storage device. Since the binder composition is further excellent in oxidation resistance, it can be particularly suitably used for forming a positive electrode of an electricity storage device.

In recent years, a power storage device having a high voltage and a high energy density is required as a power source for driving electronic equipment. In particular, lithium ion batteries, lithium ion capacitors, and the like are expected as power storage devices with high voltage and high energy density.
The electrode used for such an electricity storage device is usually produced by applying and drying a mixture of active material particles and polymer particles functioning as an electrode binder onto the current collector surface. The properties required for the polymer particles used for the electrode include the binding ability between the active material particles and the binding ability between the active material particles and the current collector, the abrasion resistance in the step of winding the electrode, Examples thereof include resistance to falling off, in which fine powder of the active material is not generated from the electrode composition layer (hereinafter also simply referred to as “active material layer”) applied by cutting or the like. 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. In addition, it has been empirically clarified that the quality of the active material particles is substantially proportional to the ability to bind the active material particles, the binding ability between the active material particles and the current collector, and the powder-off resistance. . Therefore, in the present specification, hereinafter, the term “adhesiveness” may be used in a comprehensive manner.

As the electrode binder, it is advantageous to use a fluorine-containing organic polymer excellent in ionic conductivity and oxidation resistance, such as polyvinylidene fluoride (PVDF). However, organic polymers containing fluorine atoms generally have poor adhesion, and thus have a problem with the mechanical strength and durability of the resulting electrode. Therefore, various techniques for improving the adhesion while maintaining the ionic conductivity and oxidation resistance of the organic polymer have been studied and proposed.
For example, Patent Document 1 proposes a technique for achieving both the lithium ion conductivity and oxidation resistance of the negative electrode binder and adhesion by using PVDF and a rubber polymer in combination. Patent Document 2 proposes a technique for improving adhesion by dissolving PVDF in a specific organic solvent, applying it on the current collector surface, and then removing the solvent at a low temperature. ing. Further, Patent Document 3 proposes a technique for improving adhesion by applying an electrode binder having a structure having a side chain having a fluorine atom to a main chain made of a vinylidene fluoride copolymer.

JP 2011-3529 A JP 2010-55847 A JP 2002-42819 A

However, according to the technique of Patent Document 1 in which a fluorine-containing organic polymer and a rubber polymer are used in combination, the adhesion is improved, but the ionic conductivity of the organic polymer is reduced and the oxidation resistance is greatly impaired. Therefore, an electricity storage device manufactured using this has a problem that charge / discharge characteristics are irreversibly deteriorated by repeated charge / discharge or overcharge. On the other hand, according to the techniques of Patent Documents 2 and 3 using only a fluorine-containing organic polymer as an electrode binder, the level of adhesion is still insufficient.
Thus, in the prior art, an electrode binder material that is excellent in both ionic conductivity and oxidation resistance and adhesion is not known. In particular, when a binder made of an organic polymer is applied to the positive electrode, a high degree of oxidation resistance that can withstand the oxidization of the positive electrode reaction is required, so that ionic conductivity, oxidation resistance, and adhesiveness are required. No positive electrode binder material that has reached the practical level has been known yet.
This invention is made | formed in view of such a present condition, The objective is to provide the binder material for electrodes which is excellent in all of ionic conductivity, oxidation resistance, and adhesiveness.

The above objects and advantages of the present invention are as follows:
A binder composition for an electrode of an electricity storage device containing a polymer and a liquid medium,
The polymer is not more than 5 to 50 parts by mass of repeating units derived from at least one selected from the group consisting of vinylidene fluoride, ethylene tetrafluoride and propylene hexafluoride with respect to 100 parts by mass of the polymer. 1 to 10 parts by mass of a repeating unit derived from a saturated carboxylic acid, and a solid obtained by drying the electrode binder composition at 120 ° C. for 1 hour, ethylene carbonate (EC) and diethyl carbonate ( DEC) is a mixed solvent (EC: DEC = 1: 2 (volume ratio)) as a solvent, and the ratio of the solvent-insoluble content measured at 70 ° C. for 24 hours is 25 to 70% by mass. This is achieved by the electrode binder composition.

The binder composition for an electrode of the present invention is excellent in ionic conductivity and can produce an electrode having a high degree of adhesion. An electricity storage device including an electrode manufactured using the binder composition for an electrode of the present invention has extremely good charge / discharge characteristics, which is one of electrical characteristics.
Since the binder composition for an electrode of the present invention is further excellent in oxidation resistance, it can be particularly suitably used for forming a positive electrode of an electricity storage device.

2 is a DSC chart of polymer particles obtained in Example 3. 2 is a DSC chart of polymer particles obtained in Synthesis Example 1. 6 is a DSC chart of polymer particles obtained in Synthesis Example 2. 6 is a DSC chart of polymer particles obtained in Synthesis Example 3.

  Hereinafter, preferred embodiments of the present invention will be described. It should be understood that the present invention is not limited only to the embodiments described below, and includes various modified examples that are implemented without departing from the scope of the present invention.

1. Electrode binder composition The electrode binder composition of the present invention is as described above.
A binder composition for an electrode of an electricity storage device containing a polymer and a liquid medium,
The polymer is not more than 5 to 50 parts by mass of repeating units derived from at least one selected from the group consisting of vinylidene fluoride, ethylene tetrafluoride and propylene hexafluoride with respect to 100 parts by mass of the polymer. 1 to 10 parts by mass of a repeating unit derived from a saturated carboxylic acid, and a solid obtained by drying the electrode binder composition at 120 ° C. for 1 hour, ethylene carbonate (EC) and diethyl carbonate ( DEC) as a solvent (EC: DEC = 1: 2 (volume ratio)) as a solvent, the ratio of solvent-insoluble matter (hereinafter also referred to as “EC / DEC-insoluble matter”) measured at 70 ° C. for 24 hours. ) Is 25 to 70% by mass.

Along with the long life of electronic equipment in recent years, it has been demanded that the power storage device that is the power source for driving has a long life, and it is required to improve the charge / discharge characteristics more than before. Has been. Specifically, the following two characteristics are required. First, it is required that the capacity does not change even when charging and discharging are repeatedly performed on the power storage device. The second requirement is that the capacity does not change even when the power storage device is overcharged. One of the indexes representing such characteristics is “remaining capacity ratio”. It has been empirically confirmed that an electricity storage device having a high remaining capacity ratio is excellent in both repeated charge / discharge resistance and overcharge resistance. Hereinafter, repeated charge / discharge resistance and overcharge resistance may be collectively expressed by the term “charge / discharge characteristics”.
Conventional fluorine-containing organic polymers are excellent in ionic conductivity and oxidation resistance, and thus have been used extensively for electrodes. However, they have not satisfied the severe demands on the remaining capacity in recent years. Therefore, in the prior art, studies have been made to improve the remaining capacity ratio of the obtained electricity storage device by variously modifying the fluorine-containing organic polymer, but the purpose is still sufficient. Has not been achieved.
As a result of repeated investigations in view of the above circumstances, the inventors of the present invention provide an electrode binder composition containing the specific polymer as described above and having an EC / DEC insoluble content in a specific range. As a result, the present invention has been found.
The EC / DEC insoluble content measured for the solid obtained by drying the binder composition for an electrode of the present invention at 120 ° C. for 1 hour is 25 to 70% by mass. This EC / DEC insoluble matter is a requirement for ensuring that the binder component contained in the binder composition for an electrode of the present invention exhibits an appropriate affinity for the electrolytic solution. Even if the obtained electricity storage device repeats charging / discharging or overcharges, the electricity storage characteristics are not impaired. The reason why the charge / discharge characteristics of the electricity storage device are improved when the EC / DEC insoluble content of the electrode binder composition is in a specific range is not yet clear, but the present inventors presume as follows.

An EC / DEC mixed solvent of EC: DEC = 1: 2 (volume ratio) is generally used as a model of an electrolytic solution used in an electricity storage device. Therefore, the EC / DEC insoluble content is 25 to 70% by mass means that a part of the binder component in contact with the electrolytic solution in the obtained electricity storage device is dissolved and the remaining part remains without being dissolved. It means that. When a part (only) of the binder component is dissolved at a certain ratio, the binder becomes moderately porous, and as a result, the electrolyte solution can penetrate into every corner of the binder component. Since the binder component has a function of binding the electrode active materials to each other and the active material and the current collector, the electrolytic solution can penetrate into every corner of the binder component, so that the active material and the current collector are electrolyzed. The number of reaction points and reaction area that come into contact with the liquid will increase, and as a result, deterioration of the binder component due to local electrode reaction is suppressed, and it is assumed that the charge / discharge characteristics of the electricity storage device are improved. .
The present inventors have empirically found that the EC / DEC insoluble matter measured at 70 ° C. for 24 hours correlates with the charge / discharge characteristics of the electricity storage device.

The EC / DEC insoluble content is preferably 30 to 65% by mass, more preferably 35 to 60% by mass.
The EC / DEC insoluble matter in the present invention can be measured as follows.
First, about 10 g of the electrode binder composition is taken into a suitable container (for example, a petri dish) and dried at 120 ° C. for 1 hour to form a film. 1 g of the obtained membrane was accurately weighed, and this was measured in a closed container of a mixed solvent composed of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC: DEC = 1: 2 (volume ratio)). Soak in 100 mL. The whole is then shaken at 70 ° C. for 24 hours with an amplitude of 30 mm and an amplitude frequency of 30 times / minute. The liquid after shaking is filtered through a 300-mesh wire net to remove insolubles, and then the weight (Y (g)) of the residue (dissolved part) obtained by distilling off the mixed solvent is measured. Then, by substituting this value into the following formula (1), the EC / DEC insoluble matter can be obtained.
EC / DEC insoluble matter (%) = {(1-Y) / 1} × 100 (1)
The EC / DEC insoluble content in such a range can be controlled by the composition of the polymer contained in the electrode binder composition of the present invention. This will be described later.

Hereafter, each component which the binder composition for electrodes of this invention contains is demonstrated in detail.
1.1 Polymer The polymer contained in the binder composition for an electrode of the present invention is:
5 to 50 parts by mass of a repeating unit derived from at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene, and 1 to 10 parts by mass of a repeating unit derived from an unsaturated carboxylic acid, Containing.
Examples of the unsaturated carboxylic acid include mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, and one or more selected from these are used. be able to. As the unsaturated carboxylic acid, it is preferable to use one or more selected from acrylic acid and methacrylic acid, and methacrylic acid is particularly preferable.
The polymer contained in the binder composition for electrodes of the present invention,
In addition to the repeating unit derived from at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene, and the repeating unit derived from unsaturated carboxylic acid, other non-polymerizable copolymerizable with these. It may further have a repeating unit derived from a saturated monomer.
Examples of such other unsaturated monomers include unsaturated carboxylic acid esters, α, β-unsaturated nitrile compounds, and other monomers.

As the unsaturated carboxylic acid ester, a (meth) acrylic acid ester can be preferably used, and examples thereof include, for example, an alkyl ester of (meth) acrylic acid, a cycloalkyl ester of (meth) acrylic acid, ( Examples thereof include hydroxyalkyl esters of (meth) acrylic acid. Specific examples of the alkyl ester of (meth) acrylic acid include alkyl esters of (meth) acrylic acid having an alkyl group having 1 to 10 carbon atoms, such as (meth) acrylic. Methyl methacrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, (meth) acrylic N-amyl acid, i-amyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, nonyl (meth) acrylate, (meth) acrylic Such as decyl acid;
Examples of the cycloalkyl ester of (meth) acrylic acid include cyclohexyl (meth) acrylate and the like;
Examples of the hydroxyalkyl ester of (meth) acrylic acid include hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, and the like, and one or more selected from these are used. be able to. Among these, it is preferable that it is an alkyl ester of (meth) acrylic acid, and is selected from methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate and 2-ethylhexyl acrylate. It is more preferable to use one or more.
In the present specification, “(meth) acrylic acid” is a concept encompassing both “acrylic acid” and “methacrylic acid”.

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. be able to. Among these, at least one selected from acrylonitrile and methacrylonitrile is preferable, and acrylonitrile is particularly preferable.
Examples of the other monomers include aromatic vinyl compounds such as styrene, α-methylstyrene, p-methylstyrene, and chlorostyrene;
Alkyl amides of unsaturated carboxylic acids such as (meth) acrylamide, N-methylol acrylamide;
Unsaturated dicarboxylic acid anhydrides;
Examples thereof include aminoalkylamides of unsaturated carboxylic acids such as aminoethylacrylamide, dimethylaminomethylmethacrylamide, and methylaminopropylmethacrylamide, and one or more selected from these can be used.

The polymer contained in the binder composition for electrodes of the present invention,
The repeating unit derived from at least one selected from the group consisting of vinylidene fluoride, ethylene tetrafluoride and propylene hexafluoride has 5 to 50 parts by mass with respect to the total mass of the polymer, and this value is 15 It is preferable that it is -40 mass%, and it is more preferable that it is 20-30 mass%.
The polymer has 1 to 10 parts by mass of a repeating unit derived from an unsaturated carboxylic acid with respect to the total mass of the polymer, and this value is preferably 2.5 to 7.5% by mass. .
The content ratio of the repeating units derived from other unsaturated monomers in the polymer to the total mass of the polymer is preferably as follows.
α, β-unsaturated nitrile compound: preferably 25% by mass or less, more preferably 10% by mass or less, still more preferably 5% by mass or less, most preferably α, β-unsaturated nitrile compound.
Other monomer: Preferably it is 10 mass% or less, More preferably, it is 5 mass% or less, Most preferably, no other monomer is used.
By setting the content ratio of the repeating unit derived from each monomer as described above, the EC / DEC insoluble content can be set within the above-mentioned predetermined range. The discharge characteristics can be improved, which is preferable. More preferably, the polymer contained in the binder composition for electrodes of the present invention does not have a repeating unit derived from a monomer having two or more polymerizable double bonds. Here, the monomer having two or more polymerizable double bonds is, for example, an alkenyl ester of (meth) acrylic acid, divinylbenzene, a poly (meth) acrylic acid ester of a polyhydric alcohol, a conjugated diene compound, or the like. .

1.1.1 Polymer Alloy As a polymer contained in the binder composition for an electrode of the present invention,
It may be a copolymer obtained by polymerizing a mixture containing at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene and propylene hexafluoride, and an unsaturated carboxylic acid in one step. ,
A polymer A having a repeating unit derived from at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene and propylene hexafluoride;
A polymer B having a repeating unit derived from an unsaturated carboxylic acid;
It is preferable that the polymer composite contains a low resistance and oxidation resistance and adhesion of the obtained electrode at the same time.
The polymer complex is preferably a polymer alloy.
“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 as a polymer contained in the binder composition for an electrode of the present invention means “a polymer alloy in which different types of polymer components are not bonded by a covalent bond”. It is called a molecular complex or IPN (interpenetrating polymer network). The polymer alloy in the present invention is preferably a polymer composed of a polymer complex or a polymer composed of IPN, and more preferably a polymer composed of IPN.

The polymer A constituting the polymer alloy is excellent in ionic conductivity, and the hard segment of the crystalline resin is aggregated to give the main chain a pseudo-crosslinking point such as C—H—F—C. Conceivable. For this reason, when the polymer A is used alone as the binder resin, its ionic conductivity and oxidation resistance are good, but the adhesion and flexibility are insufficient, and therefore the adhesion is low. On the other hand, although the polymer B constituting the polymer alloy is excellent in adhesion and flexibility, it has low oxidation resistance. Therefore, when this is used alone as an electrode (particularly positive electrode) as a binder resin, charge / discharge is performed. Since it is oxidized and decomposed by repeated charging or overcharging, it is impossible to obtain an electricity storage device having excellent repeated charging and discharging resistance and overcharge resistance.
However, by using a polymer alloy containing polymer A and polymer B, ionic conductivity, oxidation resistance, and adhesion can be expressed simultaneously, and both repeated charge / discharge resistance and overcharge resistance can be achieved. It has become possible to produce an electrode that provides an electricity storage device that is superior to the above. When a polymer alloy consists only of the polymer A and the polymer B, oxidation resistance can be improved more and it is preferable.

Such a polymer alloy preferably has 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 A constituting the polymer alloy is present alone, it generally has an endothermic peak (melting temperature) at -50 to 250 ° C. The polymer B constituting the polymer alloy generally has an endothermic peak (glass transition temperature) different from that of the polymer A. For this reason, when the polymer A and the polymer B are present in phase separation in the polymer, for example, as in the core-shell structure, two endothermic peaks should be observed at -50 to 250 ° C. However, when there is only one endothermic peak at −50 to 250 ° C., it can be estimated that the polymer is a polymer alloy.
Furthermore, when the temperature of only one endothermic peak of the polymer which is a polymer alloy is in the range of −30 to + 30 ° C., the polymer has better flexibility and adhesion to the active material layer. Therefore, adhesion can be further improved, which is preferable.

1.1.2 Polymer A
The polymer, which is a polymer alloy that the electrode binder composition of the present invention preferably contains, is a polymer having a repeating unit derived from at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene. Contains coalescence A. In addition to the repeating unit derived from at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene, and propylene hexafluoride, the polymer A further includes repeating units derived from other unsaturated monomers. You may have. Here, as the other unsaturated monomer, the unsaturated carboxylic acid, unsaturated carboxylic acid ester, α, β-unsaturated nitrile compound and other monomers described above can be used.
The content ratio of the repeating unit derived from at least one selected from vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene in the polymer A is preferably 80% by mass with respect to the total mass of the polymer A. It is above, More preferably, it is 90 mass% or more.
The content ratio of the repeating unit derived from vinylidene fluoride in the polymer A is preferably 50 to 99% by mass and more preferably 80 to 98% by mass with respect to the total mass of the polymer A. The content ratio of the repeating unit derived from tetrafluoroethylene in the polymer A is preferably 50% by mass or less, more preferably 1 to 30% by mass, and further preferably 2 to 20% by mass. (A) The content ratio of the repeating unit derived from hexafluoropropylene in the polymer particles is preferably 50% by mass or less, more preferably 1 to 30% by mass, and further preferably 2 to 25% by mass. is there.
The polymer A is most preferably composed of only a repeating unit derived from at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene.

1.1.3 Polymer B
The polymer which is a polymer alloy that is preferably contained in the binder composition for an electrode of the present invention contains a polymer B having a repeating unit derived from an unsaturated carboxylic acid. The polymer B may further have a repeating unit derived from another unsaturated monomer in addition to the repeating unit derived from the unsaturated carboxylic acid. Here, as the other unsaturated monomer, the unsaturated carboxylic acid ester, α, β-unsaturated nitrile compound and other monomers described above can be used.
In general, a component such as polymer B has good adhesion, but is considered to have poor ionic conductivity and oxidation resistance, and has not been used for positive electrodes. However, in the present invention, by using such a polymer B as a polymer alloy particle together with the polymer A, it has succeeded in developing sufficient ionic conductivity and oxidation resistance while maintaining good adhesion. It is a thing.
The content ratio of the repeating unit derived from each monomer in the polymer B is preferably as follows with respect to the total mass of the polymer B.
Unsaturated carboxylic acid: preferably 1 to 15% by mass, more preferably 2 to 10% by mass, still more preferably 3 to 7.5% by mass
Unsaturated carboxylic acid ester: 70 to 99% by mass, more preferably 75 to 95% by mass, still more preferably 80 to 90% by mass
α, β-unsaturated nitrile compound: preferably 25% by mass or less, more preferably 10% by mass or less, more preferably 5% by mass or less, most preferably not using an α, β-unsaturated nitrile compound Monomer: preferably 10% by mass or less, more preferably 5% by mass or less, and most preferably no other monomer is used.

1.1.4 Polymer Alloy Synthesis The polymer alloy that is preferably contained in the electrode binder composition of the present invention has a particularly limited synthesis method as long as it has the above-described configuration. Although it is not a thing, it can synthesize | combine easily, for example by well-known emulsion polymerization process or combining this suitably.
For example, first, a polymer A having a repeating unit derived from at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene, and propylene hexafluoride is synthesized by a known method, and then the polymer A is synthesized. The monomer for constituting the polymer B is added, and the monomer is sufficiently absorbed into the stitch structure of the polymer particles made of the polymer A. The polymer alloy can be easily produced by a method of synthesizing the polymer B by polymerizing the absorbed monomer. When producing a polymer alloy by such a method, it is essential for the polymer A to sufficiently absorb the monomer of the polymer B. 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, and 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. The 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 B in the stitch structure of the polymer A is preferably performed in a known medium used for emulsion polymerization, for example, in water.
The content of the polymer A in the polymer alloy is preferably 3 to 60% by mass, more preferably 5 to 55% by mass, and 10 to 50% by mass in 100% by mass of the polymer alloy. Is more preferable, and 20 to 40% by mass is particularly preferable. When the polymer alloy contains the polymer A in the above range, the balance between the ionic conductivity and the oxidation resistance and the adhesion becomes better. Moreover, when the polymer B 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 A in the above range, so that the entire polymer alloy It is possible to set the content ratio of each repeating unit in the above-mentioned preferable range, and this makes the EC / DEC insoluble content an appropriate value. As a result, the charge / discharge characteristics of the obtained electricity storage device are good. It will be a thing.

1.1.5 Production method of polymer (emulsion polymerization conditions)
Production of the polymer in the present invention, that is,
One-stage polymerization of a polymer having a repeating unit derived from at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene and propylene hexafluoride and a repeating unit derived from a repeating unit derived from an unsaturated carboxylic acid The polymerization when synthesized with
The polymerization of the polymer A and the polymerization of the polymer B in the presence of the polymer A can be performed in the presence of a known polymerization initiator, molecular weight regulator, emulsifier (surfactant) and the like, respectively.
Examples of the polymerization initiator include water-soluble polymerization initiators such as sodium persulfate, potassium persulfate, and ammonium persulfate;
Oil-soluble polymerization initiators such as benzoyl peroxide, lauryl peroxide, 2,2′-azobisisobutyronitrile;
Examples thereof include a redox polymerization initiator composed of a combination of a reducing agent such as sodium bisulfite, iron (II) salt or tertiary amine and an oxidizing agent such as persulfate or organic peroxide. These polymerization initiators can be used singly or in combination of two or more.
The proportion of the polymerization initiator used is the sum of the monomers used (the total of the monomers used when the polymer particles are synthesized by one-step polymerization, and the single monomer that leads to the polymer A in the production of the polymer A). In the case of polymerizing polymer B in the presence of polymer A, the total of monomers leading to polymer B. The same shall apply hereinafter.) 0.3-3 parts by mass with respect to 100 parts by mass It is preferable that

Examples of the molecular weight regulator include halogenated hydrocarbons such as chloroform and carbon tetrachloride;
mercaptan compounds such as n-hexyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, t-dotezyl mercaptan, thioglycolic acid;
Xanthogen compounds such as dimethylxanthogen disulfide and diisopropylxanthogen disulfide;
Other molecular weight regulators such as terpinolene and α-methylstyrene dimer can be mentioned. These molecular weight regulators can be used singly or in combination of two or more.
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.
Examples of the emulsifier include an anionic surfactant, a nonionic surfactant, an amphoteric surfactant, and a fluorine-based surfactant.
Examples of the anionic surfactant include higher alcohol sulfates, alkylbenzene sulfonates, aliphatic sulfonates, polyethylene glycol alkyl ether sulfates;
Examples of the nonionic surfactant include polyethylene glycol alkyl esters, polyethylene glycol alkyl ethers, polyethylene glycol alkyl phenyl ethers, and the like.
Examples of amphoteric surfactants include those in which the anion moiety is composed of a carboxylate, sulfate ester, sulfonate or phosphate ester salt, and the cation moiety is composed of an amine salt, a quaternary ammonium salt, or the like. Can be mentioned. Specific examples of such amphoteric surfactants include betaine compounds such as lauryl betaine and stearyl betaine;
Examples thereof include surfactants of amino acid type such as lauryl-β-alanine, lauryl di (aminoethyl) glycine, octyldi (aminoethyl) glycine.

Examples of the fluorosurfactant include fluorobutyl sulfonate, phosphoric acid ester having a fluoroalkyl group, a salt of a carboxylic acid having a fluoroalkyl group, and a fluoroalkylethylene oxide adduct. Examples of such commercially available fluorosurfactants include F-top EF301, EF303, and EF352 (manufactured by Tochem Products);
Megafuck F171, F172, F173 (manufactured by DIC Corporation);
Fluorard FC430, FC431 (manufactured by Sumitomo 3M);
Asahi Guard AG710, Surflon S-381, S-382, SC101, SC102, SC103, SC104, SC105, SC106, Surfinol E1004, KH-10, KH-20, KH-30, KH-40 (Asahi Glass Co., Ltd.) ); Tergent 250, 251, 222F, FTX-218 (manufactured by Neos Co., Ltd.) and the like. As an emulsifier, the 1 type (s) or 2 or more types selected from the above can be used.
The use ratio of the emulsifier is preferably 0.01 to 10 parts by mass, and more preferably 0.02 to 5 parts by mass with respect to 100 parts by mass in total of the monomers used.
The emulsion polymerization is preferably carried out in a suitable aqueous medium, particularly preferably in water. The total content of the monomers in the aqueous medium can be 10 to 50% by 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.

1.2 Liquid medium The electrode binder composition of the present invention further contains a liquid medium.
The liquid medium is preferably an aqueous medium containing water. This aqueous medium can contain a small amount of non-aqueous medium in addition to water. Examples of such a non-aqueous medium include amide compounds, hydrocarbons, alcohols, ketones, esters, amine compounds, lactones, sulfoxides, sulfone compounds, and the like, and one or more selected from these are used. can do. The content ratio of such a non-aqueous medium is preferably 10% by mass or less, and more preferably 5% by mass or less, based on the entire aqueous medium. The aqueous medium does not contain a non-aqueous medium. Most preferably, it consists only of water.
The binder composition for electrodes of the present invention uses an aqueous medium as a medium, and preferably contains no non-aqueous medium other than water, so that it has a low adverse effect on the environment and is highly safe for handling workers. In this regard, a composition containing an organic solvent as a medium causes problems of disposal and cost, and requires fireproof storage equipment due to characteristics such as flammability, and has special skills and considerations in handling. There is a disadvantage that is necessary.

1.3 Electrode binder composition The electrode binder composition of the present invention is preferably in the form of a slurry or latex in which the polymer as described above is dispersed in the liquid medium as described above.
The polymer is preferably particulate in an aqueous medium. The average particle diameter (Da) of the polymer in the aqueous medium is preferably in the range of 50 to 400 nm, and more preferably in the range of 100 to 250 nm. When the average particle diameter of the polymer particles is in the above range, the stability of the composition itself is improved, and the binding property between the electrode active materials and the current collector and the electrode active material layer in the obtained electrode are improved. The adhesion between them becomes even better.
The average particle diameter of the polymer particles is determined using a particle size distribution measuring apparatus based on the light scattering method. Examples of such a particle size distribution measuring apparatus include Coulter LS230, LS100, LS13320 (above, manufactured by Beckman Coulter. Inc), 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 indicator of the dispersion state of the polymer particles contained in the electrode binder composition. The average particle size of the polymer particles is determined after the slurry for the electrode is centrifuged and the active material particles are precipitated by preparing the slurry for the electrode using the electrode binder composition. It can also be measured by a method of measuring with the above particle size distribution measuring apparatus.

The electrode binder composition of the present invention is preferably in the form of a latex in which the polymer is in the form of particles and dispersed in an aqueous medium. As the electrode binder composition of the present invention, a polymer is synthesized (polymerized), preferably after the reaction is stopped, the polymerization reaction mixture is adjusted if necessary, and then this is used as it is. It is particularly preferable to use it as a binder composition for an electrode of the invention. Therefore, the binder composition for an electrode of the present invention is usually used for emulsion polymerization of an emulsifier, a polymerization initiator or its residue, a surfactant, a neutralizing agent, in addition to a polymer and a liquid medium (preferably an aqueous medium). Other components such as the components used or their residues can be included. The content ratio of these other components is preferably 3% by mass or less, more preferably 2% by mass or less, as a ratio of the total mass of the other components to the solid content of the composition.
The solid content concentration of the electrode binder composition (the ratio of the total mass of components other than the liquid medium in the composition to the total mass of the composition) is preferably 20 to 60% by mass, 25 More preferably, it is -50 mass%.

The liquid property of the electrode binder composition is preferably near neutral, more preferably pH 6.0 to 8.5, and particularly preferably pH 7.0 to 8.0. For adjusting the liquidity of the composition, a known water-soluble acid or base can be used. Examples of the acid include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid and the like;
Examples of the base include sodium hydroxide, potassium hydroxide, lithium hydroxide, and aqueous ammonia.
The electrode binder composition of the present invention preferably does not contain the above-mentioned polymer, liquid medium, components usually used for emulsion polymerization and the residue thereof, and other components other than acid or base for adjusting liquidity. .
The binder composition for electrodes of the present invention as described above can be suitably used as an electrode material for electrochemical devices such as lithium ion secondary batteries, electric double layer capacitors, and lithium ion capacitors. This embodiment is particularly preferred because the electrode binder composition exhibits the advantageous effects of the present invention to the maximum when used as a positive electrode material of a lithium ion secondary battery.

2 Electrode slurry As described above, an electrode slurry can be produced using the electrode binder composition of the present invention.
The electrode slurry is a dispersion used to form an active material layer on the current collector after being applied to the surface of the current collector, and the electrode slurry as described above according to the present invention. The binder composition for use and the active material are contained at least, and other components other than these may be contained as necessary.

2.1 Active Material The active material is appropriately selected according to the type of the target power storage device.
For electrode slurry for forming a positive electrode of a lithium ion secondary battery (slurry for the positive electrode), as the active material (positive electrode active material), for example, _{Li 1 + x M y N z} O 2 ( however, M is Co, Ni And at least one selected from Mn, N is at least one selected from Al and Sn, O represents an oxygen atom, and x, y, and z are 0.10 ≧ x ≧ 0, 4.00 ≧, respectively. y ≧ 0.85, a number in the range of 2.00 ≧ z ≧ 0), for example, lithium cobaltate, lithium nickelate, lithium manganate, ternary nickel cobalt lithium manganate In addition,
A lithium atom-containing oxide having an olivine structure can be preferably used.
The lithium atom-containing oxide having the olivine structure has the following general formula (1):
Li _1-x M _x (XO ₄ ) (1)
(In the formula (1), M is a metal ion selected from the group consisting of Mg, Ti, V, Nb, Ta, Cr, Mn, Fe, Co, Ni, Cu, Zn, A1, Ga, Ge, and Sn. At least one of;
X is at least one selected from the group consisting of Si, S, P and V;
x is a number and satisfies the relationship 0 <x <1. )
And a compound having an olivine type crystal structure. X in the above formula (1) is selected according to the valences of M and X so that the valence of the entire formula (1) becomes zero.
The lithium atom-containing oxide having the olivine structure has different electrode potentials depending on the type of the metal element M. Therefore, the battery voltage can be arbitrarily set by selecting the type of the metal element M. As typical oxides containing lithium atoms having an olivine structure, 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 etc. can be mentioned. Among these, LiFePO ₄ is particularly preferable because it is easy to obtain an iron compound as a raw material and is inexpensive. In addition, a compound obtained by substituting Fe ions in the above compounds with Co ions, Ni ions, or Mn ions has the same crystal structure as each of the above compounds, and thus has the same effect as a positive electrode active material.

In the case of the slurry for electrodes (slurry for negative electrodes) for forming the negative electrode of a lithium ion secondary battery, as an active material (negative electrode active material), a carbon material, carbon, etc. can be used suitably, for example. Examples of the carbon material include carbon materials obtained by firing organic polymer compounds, coke, pitch, and the like. Examples of the organic polymer compounds that are precursors of the carbon materials include phenol resins and polyacrylonitrile. And cellulose. Examples of the carbon include artificial graphite and natural graphite.
In the case of an electrode slurry for forming an electrode for an electric double layer capacitor, examples of the active material include graphite, non-graphitizable carbon, and hard carbon;
Carbon material obtained by firing coke, pitch, etc .;
A polyacene organic semiconductor (PAS) or the like can be used.
The active material is preferably in the form of particles, and the average particle diameter (Db) is preferably in the range of 0.4 to 10 μm, and more preferably in the range of 0.5 to 7 μm.

2.2 Other Components The electrode slurry may contain other components as necessary in addition to the components described above. Examples of such other components include a conductivity-imparting agent, water, and a non-aqueous system. A medium, a thickener, etc. can be mentioned.

2.2.1 Conductivity-imparting agent Specific examples of the conductivity-imparting agent include carbon in a lithium ion secondary battery;
In nickel-metal hydride secondary batteries, cobalt oxide is the positive electrode:
For the negative electrode, nickel powder, cobalt oxide, titanium oxide, carbon and the like are used. In both the batteries, examples of carbon include graphite, activated carbon, acetylene black, furnace black, graphite, carbon fiber, and fullerene. Among these, acetylene black or furnace black can be preferably used. The use ratio of the conductivity-imparting agent is preferably 20 parts by mass or less, more preferably 1 to 15 parts by mass, and particularly preferably 2 to 10 parts by mass with respect to 100 parts by mass of the active material particles.
In the case of an electrode slurry for forming an electrode for an electric double layer capacitor, it is preferable not to contain a conductivity-imparting agent.

2.3.2 Water The electrode slurry may further contain water. By containing water, the stability of the electrode slurry is improved, and the electrode can be produced with good reproducibility. Water has a higher evaporation rate than a high boiling point solvent (for example, N-methylpyrrolidone, etc.) generally used in electrode slurries (especially positive electrode slurries), and productivity is reduced by shortening the solvent removal time. Improvement, suppression of particle migration, etc. can be expected.
When the electrode binder composition of the present invention contains water as a liquid medium, the water in the electrode slurry may consist only of water brought from the electrode binder composition, or the electrode binder composition. The total of the water brought in from the thing and the water added newly may be sufficient.

2.3.3 Non-aqueous medium The slurry for electrodes may contain a non-aqueous medium having a standard boiling point of 80 to 350 ° C. from the viewpoint of improving the applicability. Specific examples of such a non-aqueous medium include amide compounds such as N-methylpyrrolidone, dimethylformamide, N, N-dimethylacetamide;
Hydrocarbons such as toluene, xylene, n-dodecane, tetralin;
Alcohols such as 2-ethyl-1-hexanol, 1-nonanol, lauryl alcohol;
Ketones such as methyl ethyl ketone, cyclohexanone, phorone, acetophenone, isophorone;
Esters such as benzyl acetate, isopentyl butyrate, methyl lactate, ethyl lactate, butyl lactate;
amine compounds such as o-toluidine, m-toluidine, p-toluidine;
lactones such as γ-butyrolactone and δ-butyrolactone;
Examples thereof include sulfoxide and sulfone compounds such as dimethyl sulfoxide and sulfolane, and one or more selected from these compounds can be used. Among these, it is preferable to use N-methylpyrrolidone from the viewpoints of stability of polymer particles, workability when applying an electrode slurry, and the like.
However, it is preferable that the electrode slurry does not contain a non-aqueous medium from the viewpoints of reducing environmental load, ensuring worker safety, and reducing management costs.

2.2.4 Thickener The electrode slurry may contain a thickener from the viewpoint of improving the coating property. Examples of the thickener include cellulose compounds such as carboxymethylcellulose, methylcellulose, and hydroxypropylcellulose;
An ammonium salt or an alkali metal salt of the cellulose compound;
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. Among these, particularly preferred thickeners include alkali metal salts of carboxymethyl cellulose and alkali metal salts of poly (meth) acrylic acid.
Examples of commercially available products of these thickeners include CMC1120, CMC1150, CMC2200, CMC2280, and CMC2450 (above, manufactured by Daicel Chemical Industries, Ltd.) as alkali metal salts of carboxymethylcellulose.
The proportion of the thickener used in the electrode slurry is preferably 20% by mass or less, more preferably 0.1 to 15% by mass, and still more preferably 0, based on the total solid content of the electrode slurry. 5 to 10% by mass.

2.3 Method for producing electrode slurry The electrode binder composition of the present invention is contained in an amount of 0.1 to 10 parts by mass in terms of solid content with respect to 100 parts by mass of the active material. Preferably, 0.3 to 4 parts by mass is contained. When the content of the electrode binder composition is 0.1 to 10 parts by mass in terms of solid content, good adhesion is expressed, and as a result, the charge / discharge characteristics of the obtained electricity storage device are made better. Can do.
The electrode slurry is prepared by mixing the electrode binder composition of the present invention, the active material as described above, and other components used as necessary. As means for mixing them, known mixing devices such as a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, and a Hobart mixer can be used.
The electrode slurry is preferably prepared under reduced pressure, whereby bubbles can be prevented from being generated in the obtained active material layer. The degree of pressure reduction is preferably about 5.0 × 10 ^{4 to} 5.0 × 10 ⁵ Pa as an absolute pressure.
For the mixing and stirring for producing the positive electrode slurry, it is necessary to select a mixer capable of stirring to such an extent that no agglomerates of active material particles remain in the slurry and, if necessary, a sufficient dispersion condition. The degree of dispersion is preferably mixed and dispersed so that aggregates larger than at least 100 μm are eliminated. The degree of dispersion can be measured with a grain gauge.
By forming the electrode slurry as described above into the electrode binder composition of the present invention, an electrode having an active material layer having high adhesion between active materials and between an active material and a current collector is formed. In addition, an electricity storage device including such an electrode has excellent charge / discharge characteristics.

3 Electrode The electrode in this invention can be manufactured using the slurry for electrodes prepared from the binder composition for electrodes of this invention.
The electrode in the present invention is
A current collector,
The active material layer formed through the process of apply | coating the slurry for electrodes demonstrated above and drying on the surface of the said electrical power collector is provided. After the coating film is dried, press working is preferably performed.

3.1 Current collector As the current collector, for example, a metal foil, an etching metal foil, an expanded metal, or the like can be used. Specific examples of these materials include metals such as aluminum, copper, nickel, tantalum, stainless steel, and titanium, and can be appropriately selected and used depending on the type of the target power storage device.
For example, when forming the positive electrode of a lithium ion secondary battery, it is preferable to use aluminum among the above as a collector. In this case, the thickness of the current collector is preferably 5 to 30 μm, and more preferably 8 to 25 μm.
On the other hand, when forming the negative electrode of a lithium ion secondary battery, it is preferable to use copper among the above as the current collector. In this case, the thickness of the current collector is preferably 5 to 30 μm, and more preferably 8 to 25 μm.
Furthermore, when forming an electrode for an electric double layer capacitor, it is preferable to use aluminum or copper among the above as the current collector. In this case, the thickness of the current collector is preferably 5 to 100 μm, more preferably 10 to 70 μm, and particularly preferably 15 to 30 μm.

3.2 Formation of Active Material Layer The active material layer in the electrode is formed by applying an electrode slurry to the surface of the current collector as described above and drying it.
As a method for applying the electrode slurry onto the current collector, for example, an appropriate method such as a doctor blade method, a reverse roll method, a comma bar method, a gravure method, or an air knife method can be applied.
The drying treatment of the coating film is preferably performed in a temperature range of 20 to 250 ° C., more preferably 50 to 150 ° C., preferably for a processing time of 1 to 120 minutes, more preferably 5 to 60 minutes.
The dried coating film is preferably subjected to press working. Examples of means for performing the pressing include a roll press machine, a high-pressure super press machine, a soft calendar, and a 1-ton press machine. The conditions for the press working are appropriately set according to the type of processing machine used and the desired thickness and density of the active material layer.
The preferable thickness and density of the active material layer vary depending on the application.
In the case of a lithium ion secondary battery negative electrode, the thickness is preferably 40 to 100 μm and the density is preferably 1.3 to 1.9 g / cm ³ ;
In the case of a lithium ion secondary battery positive electrode, the thickness is preferably 40-100 μm and the density is preferably 2.0-5.0 g / cm ³ ; and in the case of an electric double layer capacitor electrode, the thickness is 50-200 μm. And the density is preferably 0.9 to 1.8 g / cm ³ .

4 Power Storage Device The power storage device in the present invention includes the electrode as described above.
The electricity storage device according to the present invention has a structure in which the electrode as described above is opposed to the counter electrode via the electrolytic solution, and is preferably isolated by the presence of the separator.
As the manufacturing method, for example, two electrodes (two of a positive electrode and a negative electrode, or two of a capacitor electrode) are overlapped via a separator, and this is wound or folded according to the battery shape to form a battery container. And injecting the electrolyte into the battery container and sealing it. The shape of the battery can be an appropriate shape such as a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, or a flat shape.
The electrolytic solution is appropriately selected and used depending on the type of the target electricity storage device. As the electrolytic solution, a solution in which an appropriate electrolyte is dissolved in a solvent is used.
When manufacturing a lithium ion secondary battery, a lithium compound is used as an electrolyte. Specifically, for example _{LiClO 4, LiBF 4, LiI,} LiPF 6, LiCF 3 SO 3, LiAsF 6, LiSbF 6, LiAlCl 4, LiCl, LiBr, LiB (C 2 H 5) 4, LiCH 3 SO 3, LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, and the like can be given. The electrolyte concentration in this case is preferably 0.5 to 3.0 mol / L, more preferably 0.7 to 2.0 mol / L.
When manufacturing an electric double layer capacitor, for example, tetraethylammonium tetrafluoroborate, triethylmethylammonium tetrafluoroborate, tetraethylammonium hexafluorophosphate or the like is used as an electrolyte. The electrolyte concentration in this case is preferably 0.5 to 3.0 mol / L, more preferably 0.7 to 2.0 mol / L.
The type and concentration of the electrolyte in manufacturing the lithium ion capacitor are the same as in the case of the lithium ion secondary battery.

In any case, examples of the solvent used in the electrolyte include carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate;
lactones such as γ-butyrolactone;
Ethers such as trimethoxysilane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran;
Sulfoxides such as dimethyl sulfoxide;
Oxolane derivatives such as 1,3-dioxolane, 4-methyl-1,3-dioxolane;
Nitrogen-containing compounds such as acetonitrile and nitromethane;
Esters such as methyl formate, methyl acetate, butyl acetate, methyl propionate, ethyl propionate, phosphate triester;
Glyme compounds such as diglyme, triglyme and tetraglyme;
Ketones such as acetone, diethyl ketone, methyl ethyl ketone, methyl isobutyl ketone;
Sulfone compounds such as sulfolane;
Oxazolidinone derivatives such as 2-methyl-2-oxazolidinone;
Examples include sultone compounds such as 1,3-propane sultone, 1,4-butane sultone, 2,4-butane sultone, and 1,8-naphtha sultone.

  Such an electricity storage device has high adhesiveness between the active materials and between the active material and the current collector in the active material layer, and is excellent in charge / discharge characteristics, and therefore can withstand repeated use. Therefore, this power storage device is suitable as a secondary battery or capacitor mounted on an automobile such as an electric vehicle, a hybrid car, or a truck, and also used as a secondary battery or a capacitor for AV equipment, OA equipment, communication equipment, etc. It is also suitable.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.
“Part” and “%” in Examples and Comparative Examples are based on mass unless otherwise specified.

Example 1
<Preparation and Evaluation of Binder Composition>
(1) Synthesis of Polymer A After the inside of an autoclave having an internal volume of about 6 L equipped with an electromagnetic stirrer was sufficiently substituted with nitrogen, 2.5 L of deoxygenated pure water and 25 g of ammonium perfluorodecanoate were charged as an emulsifier The mixture was heated to 350 ° C. while stirring at 350 rpm. Next, a mixed gas composed of 70% of vinylidene fluoride (VDF) as a monomer and 30% of propylene hexafluoride (HFP) was charged until the internal pressure reached 20 kg / cm ² . 25 g of Freon 113 solution containing 20% of diisopropyl peroxydicarbonate as a polymerization initiator was injected using nitrogen gas to initiate polymerization. During the polymerization, a mixed gas composed of 60.2% VDF and 39.8% HFP was sequentially injected so that the internal pressure was maintained at 20 kg / cm ² to maintain the pressure at 20 kg / cm ² . During the polymerization, stirring and heating were continued to maintain the reaction temperature at 60 ° C. Furthermore, since the polymerization rate decreased as the polymerization progressed, the same amount of the same polymerization initiator solution as that described above was injected using nitrogen gas after 3 hours, and the reaction was continued for another 3 hours. Thereafter, heating was stopped and cooling of the reaction solution was started, and at the same time stirring was stopped. Next, the reaction was stopped by releasing the pressure of the reaction system to release unreacted monomers, and an aqueous dispersion containing 40% of polymer A fine particles was obtained.
As a result of analyzing the obtained polymer A by ¹⁹ F-NMR, the mass composition ratio of each monomer was VDF / HFP = 21/4.
Further, the obtained polymer A was measured for particle size distribution 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 number average particle size determined from the distribution was 140 nm.

(2) Synthesis of polymer alloy particles (polymerization of polymer B)
After fully replacing the inside of the 7 L separable flask with nitrogen, 1,600 g of an aqueous dispersion containing the fine particles of the polymer A obtained in the above (1) (corresponding to 25 parts in terms of the polymer A), Emulsifier “ADEKA rear soap SR1025” (trade name, manufactured by ADEKA Corporation) 0.5 part, methyl methacrylate (MMA) 30 parts, 2-ethylhexyl acrylate (EHA) 40 parts and methacrylic acid (MAA) 5 parts; 130 parts of water was sequentially added and stirred at 70 ° C. for 3 hours to allow the polymer A to absorb the monomer. Next, 20 mL of a tetrahydrofuran solution containing 0.5 part of azobisisobutyronitrile as an oil-soluble polymerization initiator was added, the temperature was raised to 75 ° C., the reaction was performed for 3 hours, and the reaction was further performed at 85 ° C. for 2 hours. It was. Then, after cooling, the reaction was stopped, and the aqueous dispersion (binder composition) containing 40% polymer particles was obtained by adjusting the pH to 7 with a 2.5N aqueous sodium hydroxide solution.

(3) Evaluation of polymer alloy particle The number average particle diameter calculated | required from the particle size distribution measured using the particle size distribution measuring apparatus "FPAR-1000" about the aqueous dispersion obtained above was 330 nm.
Further, when the obtained polymer particles were measured by a differential scanning calorimeter (DSC), the melting temperature Tm was not observed, and the single glass transition temperature Tg was observed at -2 ° C. The polymer particles are considered to be polymer alloy particles.
Further, the EC / DEC insoluble content of the obtained aqueous dispersion was measured as follows.
About 10 g of the obtained aqueous dispersion was taken into a Teflon (registered trademark) petri dish having a diameter of 8 cm and dried at 120 ° C. for 1 hour to form a film. 1 g of the obtained film (polymer) was accurately weighed, and this was measured in a sealed container with a mixed solvent consisting of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC: DEC = 1: 2 (volume). And the mixture was shaken at 70 ° C. for 24 hours under the conditions of an amplitude of 30 mm and an amplitude frequency of 30 times / minute. The liquid after shaking was filtered through a 300-mesh wire mesh to remove insolubles, and then the weight (Y (g)) of the residue (dissolved part) obtained by distilling off the mixed solvent was measured. The insoluble content (EC / DEC insoluble content) of the polymer particles obtained by substituting this value into the following formula (1) was 58%.
EC / DEC insoluble matter (%) = {(1-Y) / 1} × 100 (1)

<Preparation of active material particles>
Commercially available lithium iron phosphate (LiFePO ₄ ) was pulverized in an agate mortar and classified using a sieve to prepare active material particles having a particle diameter (D50 value) of 0.5 μm.

<Preparation of slurry for positive electrode>
A biaxial planetary mixer (product name "TK Hibismix 2P-03" manufactured by PRIMIX Co., Ltd.) and a thickener (product name "CMC1120", manufactured by Daicel Chemical Industries, Ltd.) 1 part (solid content conversion) Then, 100 parts by mass of the active material particles prepared in <Preparation of active material particles>, 5 parts of acetylene black, and 68 parts of water were added and stirred at 60 rpm for 1 hour. Next, the binder composition prepared in <Preparation of Binder Composition> is added so that the polymer particles contained in the composition are in the amount (parts) described in Table 1, and further stirred for 1 hour. To obtain a paste. After adding water to the obtained paste to adjust the solid content concentration to 50%, using a stirring defoamer (manufactured by Shinkey Co., Ltd., trade name “Awatori Netaro”) at 200 rpm for 2 minutes, A positive electrode slurry was prepared by stirring and mixing at 1,800 rpm for 5 minutes and further under vacuum (about 5.0 × 10 ³ Pa) at 1,800 rpm for 1.5 minutes.

<Manufacture and evaluation of positive electrode and electricity storage device>
(1) Production of positive electrode The positive electrode slurry prepared above was uniformly applied to the surface of a current collector made of aluminum foil by a doctor blade method so that the film thickness after drying was 100 μm. Dried for minutes. Then, the positive electrode was obtained by pressing with a roll press so that the density of a film | membrane (active material layer) might be 1.9 g / cm < ³ >.

(3) Manufacture of negative electrode A biaxial planetary mixer (product name "TK Hibismix 2P-03" manufactured by PRIMIX Co., Ltd.), 4 parts of polyvinylidene fluoride (PVDF) (solid content conversion), as a negative electrode active material 100 parts of graphite (in terms of solid content) and 80 parts of N-methylpyrrolidone (NMP) were added and stirred at 60 rpm for 1 hour. Then, after further adding 20 parts of NMP, using a stirring defoaming machine (product name “Netaro Awatori” manufactured by Shinky Co., Ltd.) for 2 minutes at 200 rpm, then 5 minutes at 1,800 rpm and further vacuuming Below, the slurry for negative electrodes was prepared by stirring and mixing for 1.5 minutes at 1,800 rpm.
The negative electrode slurry prepared above was uniformly applied to the surface of the current collector made of copper foil by the doctor blade method so that the film thickness after drying was 150 μm, and dried at 120 ° C. for 20 minutes. Then, the negative electrode was obtained by pressing using a roll-press machine so that the density of a film | membrane may be 1.5 g / cm < ³ >.

(4) Assembly of lithium ion battery cell In a glove box substituted with Ar so that the dew point is −80 ° C. or lower, the negative electrode manufactured in “(2) Manufacturing of negative electrode” above is punched and molded to a diameter of 16.16 mm Was placed on a bipolar coin cell (trade name “HS Flat Cell” manufactured by Hosen Co., Ltd.). Next, a separator made of a polypropylene porous membrane punched to a diameter of 24 mm (product name “Celguard # 2400”, manufactured by Celgard Co., Ltd.) was placed, and after injecting 500 μL of electrolytic solution so that air did not enter, A lithium ion battery is manufactured by placing the positive electrode manufactured in the above-mentioned “(1) Manufacturing of positive electrode” by punching and molding the positive electrode to a diameter of 15.95 mm, and sealing the outer body of the two-pole coin cell with a screw. A cell (electric storage device) was assembled.
The electrolyte used here is LiPF ₆ dissolved in a mixed solvent (EC: EMC = 1: 1 (mass ratio)) composed of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a concentration of 1 mol / L. Solution.

(5) Evaluation of electricity storage device (durability evaluation)
The battery cell produced above is placed in a constant temperature bath at 25 ° C., charging is started at a constant current (0.2 C), and charging is continued at a constant voltage (4.1 V) when the voltage reaches 4.1 V. The charging was completed (cut off) when the current value reached 0.01C. Next, discharging was started at a constant current (0.2 C), and the time when the voltage reached 2.5 V was regarded as discharging completion (cut-off) (aging charge / discharge).
The cell after the aging charge / discharge is put in a thermostat at 25 ° C., and charging is started at a constant current (0.2 C). When the voltage reaches 4.1 V, the cell is continuously maintained at a constant voltage (4.1 V). Charging was continued, and charging was completed (cut off) when the current value reached 0.01C. Next, discharging was started at a constant current (0.2 C), and when the voltage reached 2.5 V, discharging was completed (cut-off), and C1 that was the initial value of the discharge capacity at 0.2 C was measured.
The cell after measuring the initial value of the discharge capacity is placed in a constant temperature bath at 60 ° C., and charging is started at a constant current (0.2 C). When the voltage reaches 4.4 V, the constant voltage (4. 4V), charging was continued for 72 hours (overcharge acceleration test). Next, the charged cell was placed in a constant temperature bath of 25 ° C., the cell temperature was lowered to 25 ° C., and then discharging was started at a constant current (0.2 C). As discharge completion (cut-off), C2 which is a value of discharge capacity after application of thermal stress and overcharge stress at 0.2 C was measured.
The residual capacity ratio obtained by substituting the above measured values into the following formula (2) was 99.7%.
Remaining capacity ratio (%) = (C2−C1) ÷ C1 × 100 (2)
When the remaining capacity ratio is 98% or more, it can be evaluated that the durability (charge / discharge resistance and overcharge resistance) is good.
In the above measurement conditions, “1C” indicates a current value at which discharge is completed in one hour after constant current discharge of a cell having a certain electric capacity. For example, “0.1 C” is a current value at which discharge is completed over 10 hours, and “10 C” is a current value at which discharge is completed over 0.1 hours.

Examples 2-11 and Comparative Examples 1-6
<Preparation of binder composition>
A polymer having the composition shown in Table 1 in the same manner as in Example 1 except that the composition of the monomer gas and the amount of the emulsifier were appropriately changed in “(1) Synthesis of Polymer A” in Example 1 above. An aqueous dispersion containing fine particles of A was prepared, and water was removed under reduced pressure or added according to the solid content concentration of the aqueous dispersion to obtain an aqueous dispersion having a solid content concentration of 40%.
Next, in “(2) Synthesis of polymer alloy particles” in Example 1, the above-mentioned aqueous dispersion was used in the amount shown in Table 1 in terms of solid content, and the type and amount (parts) of each monomer were determined. The aqueous dispersions (binder compositions) containing the polymer particles having the number average particle diameters described in Table 1 were obtained by changing the amounts of the emulsifiers appropriately as shown in Table 1, respectively. .
The results of DSC measurement (whether or not it is a polymer alloy) and EC / DEC insoluble matter measurement performed on the obtained fine particles are shown together in Table 1.
<Preparation of active material particles>
In “Preparation of active material particles” in Example 1 above, active material particles having particle diameters (D50 values) described in Table 1 were prepared by appropriately changing the openings of the sieves used.
<Preparation of slurry for positive electrode>
A positive electrode slurry was prepared in the same manner as in “Preparation of positive electrode slurry” in Example 1, except that the active material particles and the binder composition were each prepared in the above amounts and used in the amounts shown in Table 1. .
<Manufacture and evaluation of positive electrode and electricity storage device>
A positive electrode and an electricity storage device were produced and evaluated in the same manner as in Example 1 except that each material obtained above was used.
The evaluation results are shown in Table 1.

Abbreviations of each component in Table 1 have the following meanings.
[Monomer of Polymer A]
VDF: Vinylidene fluoride HFP: Propylene hexafluoride TFE: Tetrafluoroethylene [monomer of polymer B]
-Unsaturated carboxylic acid-
MAA: methacrylic acid AA: acrylic acid-unsaturated carboxylic acid ester-
MMA: Methyl methacrylate BMA: Butyl methacrylate EHA: 2-ethylhexyl acrylate BA: Butyl acrylate EA: Ethyl acrylate-unsaturated nitrile-
AN: Acrylonitrile-Other-
DVB: Divinylbenzene [whether it is a polymer alloy? ]
A: A polymer alloy.
X: Not a polymer alloy.
The notation “-” in Table 1 indicates that the monomer corresponding to the column was not used.

As described above, it was estimated from the DSC chart that the polymer particles were a polymer alloy.
A DSC chart of the polymer particles obtained in Example 3 is shown in FIG.
In addition, DSC charts of the polymer particles synthesized in the following Synthesis Examples 1 to 3 are shown in FIGS.

Synthesis example 1
80% of structural units derived from vinylidene fluoride (VDF) in the same manner as in Example 1 except that the composition of the monomer gas was changed in “(1) Synthesis of Polymer A” in Example 1 above. An aqueous dispersion containing fine particles of polymer A composed of 20% of a structural unit derived from hexafluoropropylene (HFP) was obtained (the subsequent “(2) synthesis of polymer alloy particles” was not performed. .)

Synthesis example 2
After the inside of the 7-liter separable flask was sufficiently purged with nitrogen, 1.0 part of emulsifier “ADEKA rear soap SR1025” (trade name, manufactured by ADEKA Corporation), 30 parts of methyl methacrylate (MMA), acrylic acid 2 -40 parts of ethylhexyl (EHA), 5 parts of methacrylic acid (MAA) and 145 parts of water and 130 parts of water were sequentially charged. Next, 20 mL of a tetrahydrofuran solution containing 0.5 part of azobisisobutyronitrile as an oil-soluble polymerization initiator was added, the temperature was raised to 75 ° C., the reaction was performed for 3 hours, and the reaction was further performed at 85 ° C. for 2 hours. It was. Thereafter, the reaction was stopped after cooling, and the aqueous dispersion containing 40% of polymer particles was obtained by adjusting the pH to 7 with a 2.5N aqueous sodium hydroxide solution.

Synthesis example 3
In “(2) Synthesis of polymer alloy particles” in Example 1 above, 1,600 g of an aqueous dispersion containing the fine particles of polymer A (corresponding to 25 parts in terms of polymer A) was added to the emulsifier “ADEKA rear soap SR1025”. (Product name, manufactured by ADEKA Co., Ltd.) After adding 0.5 parts, the temperature was raised to 75 ° C., 30 parts of methyl methacrylate (MMA), 40 parts of 2-ethylhexyl acrylate (EHA), methacrylic acid (MAA) 5 parts, 130 parts of water and 0.5 part of azobisisobutyronitrile were added almost simultaneously to initiate polymerization, and the reaction was carried out at 75 ° C. for 3 hours and then at 85 ° C. for 2 hours. In the same manner as in Example 1, an aqueous dispersion containing 40% polymer particles was obtained.

FIG. 2 shows the case of polymer A only,
FIG. 3 shows the case of polymer B only.
FIG. 4 corresponds to a mixture of polymer A and polymer B, respectively, and FIG. 1 corresponds to polymer alloy particles made of polymer A and polymer B.
The melting temperature Tm of the polymer A was observed in FIG. 2, and the glass transition temperature Tg of the polymer B was observed in FIG.
In FIG. 4, since the melting temperature Tm of the polymer A and the glass transition temperature Tg of the polymer B are both observed, it is considered that the present polymer particles are a mixture of the polymer A and the polymer B. for,
Referring to FIG. 1, neither the melting temperature Tm of polymer A nor the glass transition temperature Tg of polymer B is observed, and a single new glass transition at a temperature different from the Tm of polymer A and the Tg of polymer B. Since the temperature Tg is generated, this polymer particle is considered to be a polymer alloy.

Claims (9)

A binder composition for an electrode of an electricity storage device containing a polymer and a liquid medium,
The polymer is not more than 5 to 50 parts by mass of repeating units derived from at least one selected from the group consisting of vinylidene fluoride, ethylene tetrafluoride and propylene hexafluoride with respect to 100 parts by mass of the polymer. 1 to 10 parts by mass of a repeating unit derived from a saturated carboxylic acid, and a solid obtained by drying the electrode binder composition at 120 ° C. for 1 hour, ethylene carbonate (EC) and diethyl carbonate ( DEC) is a mixed solvent (EC; DEC = 1: 2 (volume ratio)) as a solvent, and the ratio of the solvent insoluble content measured at 70 ° C. for 24 hours is 25 to 70% by mass. The binder composition for electrodes. The polymer is dispersed as particles in the composition;
The binder composition for electrodes according to claim 1, wherein the polymer particles have an average particle diameter (Da) of 50 to 400 nm. The polymer is
A polymer A having a repeating unit derived from at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene and propylene hexafluoride, and a polymer B having a repeating unit derived from an unsaturated carboxylic acid The binder composition for electrodes according to claim 1 or 2.   The binder composition for electrodes according to claim 3, wherein the polymer B further has a repeating unit derived from an unsaturated carboxylic acid ester.   The electrode binder composition according to claim 3 or 4, wherein the polymer is a polymer alloy particle comprising the polymer A and the polymer B.   The binder composition for electrodes according to claim 3 or 4 whose content rate of polymer A in said polymer particles is 1-60 mass% to 100 mass parts of polymer particles.   The binder composition for electrodes according to any one of claims 1 to 6, which is used for forming a positive electrode of an electricity storage device.   The electrode of the electrical storage device manufactured using the binder composition for electrodes as described in any one of Claims 1-7.   An electricity storage device comprising the electrode according to claim 8.

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