JP5854867B2 - Method for producing electrode composition - Google Patents

Description

The present invention relates to a method for producing an electrode composition. More specifically, the present invention relates to a method for producing an electrode composition that can be suitably used as a composition for forming an electrode used in a secondary battery or the like.

Secondary batteries are rechargeable batteries that can be repeatedly charged and discharged. In recent years, due to the growing interest in environmental problems, not only electronic devices such as mobile phones and laptop computers, but also automobiles and airplanes. Is also being used. In response to the growing demand for secondary batteries, research is actively conducted. In particular, lithium-ion batteries that are light, small, and high in energy density are attracting attention from various industries. Development is actively underway.

A lithium ion battery is mainly composed of a positive electrode, an electrolyte, a negative electrode, and a separator, and an electrode in which an electrode composition is applied on a current collector is used. Among the electrode compositions, the positive electrode composition used for forming the positive electrode mainly consists of a positive electrode active material, a conductive additive, a binder and a solvent, and the negative electrode composition used for forming the negative electrode is mainly composed of It consists of a negative electrode active material, a binder, and a solvent. In these electrode compositions, polyvinylidene fluoride (PVDF) is generally used as a binder and N-methyl-2-pyrrolidone (NMP) is generally used as a solvent.
This is because PVDF is chemically and electrically stable and NMP is a time-stable solvent that dissolves PVDF.

However, PVDF does not have a high dissolution concentration, and is generally used at a concentration of 10% or less. When PVDF is used, it is difficult to increase the solid content concentration. In addition, since NMP has a high boiling point, when NMP is used as a solvent, there is a problem that much energy is required for volatilization of the solvent when forming an electrode. In addition, in recent years, an aqueous electrode composition that does not use an organic solvent for the electrode composition has been demanded against the background of increasing interest in environmental problems.
In particular, as seen in the negative electrode composition, the water-based composition has an advantage that the amount of the binder used can be suppressed as compared with the solvent-based composition.

As a binder used in an aqueous electrode composition, a form in which two components of a water-soluble polymer and an emulsion (an aqueous dispersion of polymer particles) are used in combination has been studied. The water-soluble polymer has a dispersion performance and a viscosity adjusting function (thickening function). In addition, the emulsion has a property of binding electrode active materials to each other (binding property, a material having binding property is also referred to as a “binding agent” because of its performance). It plays the role of giving flexibility and flexibility. Thus, the water-soluble polymer and the emulsion share the functions required for the binder. A typical example of the water-soluble polymer is carboxymethylcellulose (CMC). CMC is generally used as a water-soluble polymer of the negative electrode composition, and CMC is the center of investigation as a candidate for the water-soluble polymer in the positive electrode composition. Further, styrene butadiene rubber (SBR) is generally used as an emulsion, particularly an emulsion of a negative electrode composition.

A water-based electrode composition using a water-soluble polymer alone or an electrode formed therefrom includes a current collector, a binder that is a polyacrylate, and a negative electrode active material, and is formed on the surface of the current collector. A negative electrode for a battery having a negative electrode active material layer is disclosed (for example, see Patent Document 1). Moreover, the binder composition for batteries containing (1) the polymer polymerized using the acidic monomer and (2) the latex whose pH is 4-10 is disclosed (for example, refer patent document 2). .

JP 2009-80971 A (page 1-2) JP-A-11-149929 (page 1-2)

Various studies have been made on aqueous electrode compositions, taking the above as an example, but among them, a binder having sufficient performance as an aqueous electrode composition has not yet been developed. There has been a demand for a binder that can be suitably used for an electrode composition.
In Patent Document 1, polyacrylate, which is a water-soluble polymer, is used as a binder, but the binder is composed of polyacrylate alone without being used together with an emulsion. However, since it is not used in combination with an emulsion, it cannot be said that the binder is sufficient in terms of binding properties, electrode flexibility and flexibility.
On the other hand, in patent document 2, the form using the binder which used together the CMC which is a water-soluble polymer, and the latex which is an emulsion is disclosed. Emulsions are generally used in combination with CMC because they are generally not sufficiently dispersible and have a low viscosity, making them difficult to use alone as binders.
In general, when a water-based electrode composition is formed, a method is generally used in which a water-soluble polymer is used to disperse an electrode active material and, if necessary, a conductive additive, and an emulsion is added thereto. Here, as a water-soluble polymer, a solid polymer that is water-solubilized with water or alkaline water is generally used, but the solid polymer dissolves in a lump when it is made into an aqueous solution. However, it takes time to prepare the aqueous polymer solution, and as a result, it takes time to prepare the electrode composition.
Thus, the development of binders used in water-based electrode compositions is underway. From the viewpoint of industrial production, it is important not only to provide binders but also to simplify the production of electrode compositions. Therefore, a method for producing an electrode composition that satisfies both of these requirements has been demanded.

This invention is made | formed in view of the said present condition, and provides the manufacturing method of the electrode composition which can produce simply the electrode composition from which the obtained electrode exhibits the outstanding battery performance. With the goal.

The present inventor has made various studies on a method for producing a water-based electrode composition, and a water-soluble polymer containing 10 to 60% by mass of a structural unit derived from a metal salt monomer of an ethylenically unsaturated carboxylic acid as a binder (bonded). To use it as an agent. Since such a water-soluble polymer can be easily produced by adding an alkaline aqueous solution to an alkali-soluble resin, an aqueous electrode composition can be obtained by using such a water-soluble polymer as a binder. It has been found that it can be easily produced. The water-soluble polymer thus obtained exhibits excellent performance as a binder because of its excellent dispersibility and thickening properties. By using this water-soluble polymer as a binder, it is suitable as an electrode material with excellent battery performance. It has also been found that a water-based electrode composition can be obtained, and has arrived at the present invention by conceiving that the above problems can be solved brilliantly.

That is, the present invention is a method for producing an electrode composition comprising an electrode active material, a binder, and water, wherein the production method includes a step of kneading the electrode active material, the binder, and water, The binder includes a water-soluble polymer containing 10 to 60% by mass of a structural unit derived from a metal salt monomer of an ethylenically unsaturated carboxylic acid, and the water-soluble polymer is a total light transmittance of a 2% by mass aqueous solution. Is 90 to 100%, a method for producing an electrode composition.
The present invention is described in detail below.

The method for producing an electrode composition of the present invention is to produce an electrode composition containing an electrode active material, a binder, and water. The electrode composition includes an electrode active material, a binder, and water. As long as it contains, other components, such as the water-dispersed resin (emulsion) mentioned later, a dispersing agent, and a conductive support agent, may be included. Moreover, each of these components may contain 1 type, or may contain 2 or more types.
The method for producing the electrode composition of the present invention includes a step of kneading the electrode active material, the binder, and water, but may include other steps as long as this step is included.

The kneading step in the present invention is a step of kneading the electrode active material, the binder, and water. By kneading in this way, the binder and the electrode active material are uniformly dispersed in water. As the kneading step, a step of adding water and an electrode active material to the binder and kneading is preferable.
In the kneading step, kneading is performed using beads, a ball mill, a stirring mixer, a biaxial planetary mixing and kneading apparatus (for example, TK Hibismix (registered trademark) (manufactured by Primix)), and the like. be able to.
As the kneading step, other components may be added as long as the binder, water and the electrode active material are added. As the kneading step, a binder containing a water-soluble polymer dissolved in water as a solvent, The step of adding a dispersing agent in some cases, further dispersing by mixing and kneading the conductive assistant as necessary, adding the electrode active material to the solution and dispersing by further kneading is also a process of the present invention. This is one of the preferred embodiments.

The method for producing an electrode composition of the present invention preferably further includes a step of adding a water-dispersed resin after the kneading step. When the electrode composition is prepared by such a procedure, the electrode active material can be easily and sufficiently uniformly dispersed. Suitable water-dispersed resins and blending ratios will be described later.

Although the said electrode composition contains an electrode active material, a binder, and water, as content of the electrode active material in an electrode composition, it is 85-99 mass with respect to 100 mass% of whole quantity of an electrode composition. % Is preferred. More preferably, it is 90-98 mass%.
Moreover, as content of the said binder, it is preferable that it is 0.1-6 mass% with respect to 100 mass% of electrode active materials. When the content of the binder is within this range, the dispersibility and the viscosity adjusting function are sufficiently exhibited, the electrode active material and a filler such as a conductive auxiliary agent described later are bonded, and the amount of binder used in the electrode is suppressed. be able to. More preferably, it is 0.2-3 mass%.
As content of the said water, it is preferable that it is 50-300 mass% with respect to 100 mass% of electrode active materials. When the water content is within this range, a slurry having an appropriate viscosity can be produced. More preferably, it is 70-200 mass%.

The water-soluble polymer is preferably obtained by neutralizing an alkali-soluble resin containing a structural unit derived from an ethylenically unsaturated carboxylic acid monomer with a metal salt. Here, “obtained by neutralization” does not mean that the acid groups contained in the alkali-soluble resin are all neutralized with metal salts, but at least a part of the acid groups contained in the alkali-soluble resin. If it is neutralized, what remains the acid group which is not neutralized is also included in what is obtained by neutralization. In addition, the metal salt is excessively added to the acid group contained in the alkali-soluble resin for neutralization, and all the acid groups contained in the alkali-soluble resin are neutralized with the metal salt, and the excess metal salt remains. Is also included in the form obtained by neutralization. A preferred form of neutralization will be described later.
The metal salt is preferably an alkali metal salt such as lithium, sodium, or potassium. More preferably, it is a lithium salt. As these metal salts, 1 type may be used and 2 or more types may be used.

Examples of the method for neutralizing the alkali-soluble resin with the above metal salt include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide; alkali metals such as lithium hydrogen carbonate, sodium hydrogen carbonate and potassium hydrogen carbonate. And a method of neutralizing the alkali-soluble resin with an aqueous solution such as hydrogen carbonate. By neutralizing the alkali-soluble resin with these metal salts, a uniform aqueous solution is obtained and a transparent solution is obtained as an appearance.
Here, the transparent solution means that the total light transmittance of the 2% by mass aqueous solution is 90 to 100%. That is, the water-soluble polymer has a total light transmittance of 90 to 100% in a 2% by mass aqueous solution. The total light transmittance is preferably 95% or more, and more preferably 97% or more.
The water-soluble polymer preferably has a 2% by weight aqueous solution having a haze of 10 or less, more preferably 3 or less.
The total light transmittance and haze can be measured using a haze meter (product name “NDH5000”, manufactured by Nippon Denshoku Industries Co., Ltd.).

As said neutralization reaction, it is preferable to neutralize 60-150% of carboxylic acid which the structural unit derived from the ethylenically unsaturated carboxylic acid monomer in the said alkali-soluble resin has with a metal salt. The neutralization rate is more preferably 70 to 110%, and still more preferably 80 to 100%.
Thus, the water-soluble polymer in the present invention is obtained by neutralizing 60 to 150% of a carboxylic acid having a structural unit derived from an ethylenically unsaturated carboxylic acid monomer in an alkali-soluble resin with a metal salt. It is also one of the preferred embodiments of the present invention.
The neutralization rate is the amount of metal salt charged for neutralization reaction relative to the amount of carboxylic acid in the structural unit derived from the ethylenically unsaturated carboxylic acid monomer in the alkali-soluble resin subjected to neutralization reaction. It is defined by the ratio of Therefore, when the amount of carboxylic acid is more than the amount of carboxylic acid and the metal salt is charged excessively, the neutralization rate exceeds 100%.

In the neutralization reaction, the pH of the aqueous solution containing the water-soluble polymer after neutralization is preferably 6 or more. More preferably, it is 7 or more. Moreover, as an upper limit of pH, it is preferable not to exceed 9.
The pH can be measured by measuring a value at 25 ° C. using a glass electrode type hydrogen ion meter F-21 (product name, manufactured by HORIBA, Ltd.).

The water-soluble polymer preferably has a weight average molecular weight of 500,000 to 3,000,000. When the weight average molecular weight is less than 500,000, the dispersibility required for the water-soluble polymer can be expressed, but the viscosity adjustment function may not be sufficient, and may not be sufficient for improving the binding property between particles. is there. The weight average molecular weight is more preferably 700,000 to 2,000,000.
The weight average molecular weight can be measured by gel permeation chromatography (GPC apparatus, developing solvent; tetrahydrofuran) in terms of polystyrene under the following apparatus and measurement conditions.
GPC device: HLC-8120 (product name, manufactured by Tosoh Corporation)
Column: TSK-gel GMHXL (product name, manufactured by Tosoh Corporation)
Eluent: Tetrahydrofuran (THF)
Standard material for calibration curve: Polystyrene eluent flow rate: 1 ml / min
Column temperature: 40 ° C
Measuring method: The alkali-soluble resin before neutralization is dissolved in the eluent so that the solid content of the measurement target is 0.1% by mass, and filtered using a filter to obtain a measurement sample.

The water-soluble polymer preferably has a 2% by weight aqueous solution having a viscosity of 50 to 20,000 mPa · s. By using the alkali-soluble resin that becomes a water-soluble polymer having such a viscosity range after neutralization, the function of adjusting the viscosity of the electrode composition can be sufficiently exerted. Among them, the viscosity of a 2% by weight aqueous solution of a water-soluble polymer obtained by neutralizing a carboxylic acid having a structural unit derived from an ethylenically unsaturated carboxylic acid monomer in an alkali-soluble resin with a 100% metal salt is 50 to 20 More preferably, it is 1,000 mPa · s. More preferably, it is 100-10,000 mPa * s, Most preferably, it is 120-3,000 mPa * s.
The viscosity can be measured using a B-type viscometer (manufactured by Tokyo Keiki Co., Ltd.) at 25 ± 1 ° C. and 30 rpm.

The alkali-soluble resin contains a structural unit derived from an ethylenically unsaturated carboxylic acid monomer, but is derived from an ethylenically unsaturated carboxylic acid monomer with respect to 100% by mass of the total amount of structural units of the alkali-soluble resin. It is preferable that 10 to 60% by mass of the structural unit and 10 to 90% by mass of the structural unit derived from the ethylenically unsaturated carboxylic acid ester monomer are essential. By using such a material as an alkali-soluble resin, a binder containing a water-soluble polymer obtained by neutralization can be adhered, flexible, and electrode-forming without impairing the dispersibility and viscosity adjusting function. Even better.

The structural unit derived from the ethylenically unsaturated carboxylic acid monomer represents a structure in which the carbon-carbon double bond of the ethylenically unsaturated carboxylic acid monomer is a single bond.
Examples of the ethylenically unsaturated carboxylic acid monomer include ethylenically unsaturated monocarboxylic acid monomers such as (meth) acrylic acid, crotonic acid, and isocrotonic acid; itaconic acid, maleic acid, fumaric acid, citraconic acid, Examples thereof include ethylenically unsaturated dicarboxylic acid monomers such as mesaconic acid and glutaconic acid, and acid anhydrides thereof. Among these, ethylenically unsaturated monocarboxylic acid monomers such as acrylic acid and methacrylic acid are preferable, and acrylic acid and methacrylic acid are more preferable. As these ethylenically unsaturated carboxylic acid monomers, 1 type may be used and 2 or more types may be used.

A part of the carboxylic acid contained in the ethylenically unsaturated carboxylic acid monomer may be in the form of a metal salt as long as an alkali-soluble resin can be synthesized by a polymerization method described later. In the case where a part of the carboxylic acid possessed by the ethylenically unsaturated carboxylic acid monomer is a metal salt, among the carboxylic acids possessed by the ethylenically unsaturated carboxylic acid monomer, the form of the metal salt It is preferable that it is 50 mol% or less. More preferably, it is 30 mol% or less, More preferably, it is 10 mol% or less.
Examples of the metal salt of the carboxylic acid include alkali metal salts of carboxylic acid such as lithium, sodium, and potassium.

The structural unit derived from the ethylenically unsaturated carboxylic acid ester monomer represents a structure in which the carbon-carbon double bond of the ethylenically unsaturated carboxylic acid ester monomer is a single bond.
Examples of the ethylenically unsaturated carboxylic acid ester monomer include esters such as acrylic acid, methacrylic acid, and crotonic acid. Preferably, for example, the general formula (1);
_{CH 2 = CR-C (=} O) -OR '(1)
(In the formula, R represents a hydrogen atom or a methyl group. R ′ represents an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a hydroxyalkyl group having 1 to 10 carbon atoms, or Represents a group containing a polyalkylene glycol group.).

Examples of R ′ in the general formula (1) include alkyl groups having 1 to 10 carbon atoms such as a methyl group, an ethyl group, a propyl group, a butyl group, an octyl group, and a 2-ethylhexyl group; a cyclopentyl group, a cyclohexyl group, and the like. A cycloalkyl group having 3 to 10 carbon atoms; a hydroxyalkyl group having 1 to 10 carbon atoms such as hydroxyethyl group, hydroxypropyl group and hydroxybutyl group; a structure in which a polyethylene glycol group or the like is added to (meth) acrylic acid or the like. And a group containing a polyalkylene glycol group.
Among these, from the viewpoint of stability at the time of emulsion polymerization described later, those having high hydrophobicity are preferable, that is, alkyl groups having 1 to 10 carbon atoms and cycloalkyl groups having 3 to 10 carbon atoms are preferable. More preferably, they are a C1-C8 alkyl group and a C3-C8 cycloalkyl group, More preferably, they are a C1-C6 alkyl group. When R ′ in the general formula (1) is an alkyl group, the glass transition temperature (Tg) of the resulting water-soluble polymer is preferably reduced. R ′ is particularly preferably an alkyl group having 1 to 4 carbon atoms, and most preferably an alkyl group having 1 to 3 carbon atoms. As these ethylenically unsaturated carboxylic acid ester monomers, one type may be used, or two or more types may be used.

The content ratio of the structural unit derived from the ethylenically unsaturated carboxylic acid monomer in the alkali-soluble resin is preferably 10 to 60% by mass with respect to 100% by mass of the total amount of structural units of the alkali-soluble resin. It is. By setting the content of the structural unit derived from the ethylenically unsaturated carboxylic acid monomer in such a range, the obtained alkali-soluble resin has sufficient solubility in water, and a uniform aqueous solution can be obtained. Further, when the polymerization reaction is carried out by an emulsion polymerization method described later, it can be easily produced. More preferably, it is 15-50 mass% as a content of the structural unit derived from the ethylenically unsaturated carboxylic acid monomer in alkali-soluble resin, More preferably, it is 20-45 mass%.

The content ratio of the structural unit derived from the ethylenically unsaturated carboxylic acid ester monomer in the alkali-soluble resin is preferably 10 to 90% by mass with respect to 100% by mass of the total amount of the structural units of the alkali-soluble resin. Is. An ethylenically unsaturated carboxylic acid ester monomer is a monomer having a carboxyl group and is a hydrophobic monomer but contains a polar group. By setting the content of the structural unit derived from the monomer in such a range, the obtained alkali-soluble resin has sufficient solubility in water and can obtain a uniform aqueous solution, and the polymerization reaction will be described later. When it is carried out by the emulsion polymerization method, it becomes easy to become the core of the emulsion droplets, so that it can be easily produced by emulsion polymerization. The content of the structural unit derived from the ethylenically unsaturated carboxylic acid ester monomer in the alkali-soluble resin is more preferably 30 to 80% by mass, and still more preferably 40 to 75% by mass.

As the alkali-soluble resin, as long as it contains a structural unit derived from an ethylenically unsaturated carboxylic acid monomer and a structural unit derived from an ethylenically unsaturated carboxylic acid ester monomer, it is derived from other polymerizable monomers. The structural unit may be included.

Examples of the other polymerizable monomers include styrene monomers such as styrene, α-methylstyrene, and ethyl vinylbenzene; (meth) acrylic acid amide, N, N-dimethyl (meth) acrylamide, and the like. (Meth) acrylamide monomers; polyfunctional allyl monomers such as vinyl acetate and diallyl phthalate; conjugated diene monomers such as butadiene and isobrene; acrylonitrile and methacrylonitrile.
Moreover, the (meth) acrylic ester and vinyl compound which have polyalkylene oxide group which has hydrophobic groups, such as a C5-C30 alkyl group which may be halogenated at the terminal, can also be used. In that case, by having a hydrophobic group at the end of the alkylene oxide, the viscosity of the electrode composition can be changed by the association of the hydrophobic group.
The alkylene oxide terminal hydrophobic group is preferably an alkyl group having 5 to 30 carbon atoms, and more preferably an alkyl group having 10 to 20 carbon atoms. As these other polymerizable monomers, one type may be used, or two or more types may be used.

When the alkali-soluble resin contains structural units derived from other polymerizable monomers, the content is 30% by mass or less with respect to 100% by mass of the total amount of structural units of the alkali-soluble resin. Is preferred. More preferably, it is 10 mass% or less, More preferably, it is 5 mass% or less.

That is, as the ratio of the structural units in the alkali-soluble resin, when the total amount of the structural units of the alkali-soluble resin is 100% by mass, (the structural unit derived from the ethylenically unsaturated carboxylic acid monomer) / (ethylenic) Structural unit derived from unsaturated carboxylic acid ester monomer) / (Structural unit derived from other polymerizable monomer) = 10-60 mass% / 10-90 mass% / 0-30 mass% is there.

The said alkali-soluble resin can be manufactured by superposing | polymerizing so that each monomer component used as the origin of the structural unit which the alkali-soluble resin mentioned above contains may be contained in the content rate mentioned above. The method for polymerizing the monomer component is not particularly limited, and examples thereof include emulsion polymerization, reverse phase suspension polymerization, suspension polymerization, solution polymerization, aqueous solution polymerization, and bulk polymerization. Among these polymerization methods, the emulsion polymerization method is preferable.
The emulsion polymerization method is a method in which a high molecular weight copolymer can be easily polymerized at a high concentration, and the viscosity of the polymerization solution is low. A water-soluble polymer having a weight average molecular weight of 500,000 or more can be easily produced by preparing an alkali-soluble resin as an aqueous dispersion by an emulsion polymerization method and neutralizing and solubilizing (homogenizing) with a metal salt. Therefore, selecting an emulsion polymerization method as a method for producing an alkali-soluble resin is advantageous in terms of production cost.

The emulsion polymerization can be performed using an emulsifier. The emulsifier is not particularly limited. For example, anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, polymer surfactants, and radically polymerizable in the structure of these surfactants. And reactive surfactants having an unsaturated group. These emulsifiers may be used alone or in combination of two or more.

Examples of the reactive surfactant include Latemul PD (manufactured by Kao Corporation), Adekaria Soap SR (manufactured by Adeka Company), Aqualon HS (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Aqualon KH (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) Elminol RS (manufactured by Sanyo Chemical Co., Ltd.) and the like.

The polymerization reaction can be performed using a polymerization initiator. As the polymerization initiator, those usually used as a polymerization initiator can be used, and are not particularly limited as long as they can generate radical molecules by heat. Examples of the polymerization initiator include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; 2,2′-azobis (2-amidinopropane) dihydrochloride, 4,4′-azobis (4-cyano). Water-soluble azo compounds such as pentanoic acid; thermal decomposition initiators such as hydrogen peroxide; hydrogen peroxide and ascorbic acid, t-butyl hydroperoxide and rongalite, potassium persulfate and metal salts, ammonium persulfate and sodium bisulfite And redox initiators. These polymerization initiators may be used alone or in combination of two or more.
In addition, when performing emulsion polymerization especially as a polymerization method, a water-soluble initiator is preferably used among these polymerization initiators.

The polymerization reaction may be performed using a chain transfer agent for the purpose of adjusting the molecular weight. The chain transfer agent is not particularly limited, and examples thereof include halogenated substituted alkanes, alkyl mercaptans, thioesters, and alcohols. These chain transfer agents may be used alone or in combination of two or more.
The amount of the chain transfer agent used is preferably 0.1 to 1 part by weight with respect to 100 parts by weight of the total amount of monomer components used for the polymerization reaction. More preferably, it is 0.1-0.5 weight part.

Although it does not specifically limit as polymerization temperature in the case of performing the said polymerization reaction by emulsion polymerization, For example, 20-100 degreeC is preferable, More preferably, it is 50-90 degreeC. The polymerization time is not particularly limited, but 1 to 10 hours is preferable in consideration of productivity.
Moreover, when performing emulsion polymerization, a hydrophilic solvent, an additive, etc. can be added in the range which does not have a bad influence on the copolymer (alkali-soluble resin) obtained.

When the polymerization reaction is carried out by emulsion polymerization, the method for adding each monomer component to the reaction system is not particularly limited, and the reaction mode is a batch polymerization method, a monomer component dropping method, a pre-emulsion method. A power feed method, a seed method, a multistage addition method, or the like can be used. Among these, the pre-emulsion method is preferable.

The nonvolatile content of the emulsion (alkali-soluble resin) obtained after the emulsion polymerization reaction is preferably 20 to 60%. When the nonvolatile content is in the range of 20 to 60%, it becomes easy to maintain the fluidity and dispersion stability of the obtained emulsion. Moreover, it is preferable also from the point of the production efficiency of the target polymer.
Although it does not specifically limit as an average particle diameter of the said emulsion, Preferably it is 10 nm-1 micrometer, More preferably, it is 30-500 nm. When the particle diameter of the emulsion is within this range, it is possible to reduce the possibility that the viscosity becomes too high, or the dispersion stability cannot be maintained and aggregation occurs.

As an electrode active material in this invention, both a positive electrode active material and a negative electrode active material are mentioned. That is, the electrode composition in the present invention may be a positive electrode composition containing a positive electrode active material or a negative electrode composition containing a negative electrode active material, and the method for producing the electrode composition of the present invention Is preferable both as a method for producing a positive electrode composition and a method for producing a negative electrode composition.

The positive electrode active material is preferably a compound that can occlude and release lithium ions. By using such a positive electrode active material, it can be suitably used as a positive electrode of a lithium ion battery. Examples of the compound that can occlude and release lithium ions include lithium-containing metal oxides. Examples of such metal oxides include lithium cobaltate, lithium iron phosphate, a compound having an olivine structure, lithium manganese phosphate, Lithium manganate, lithium nickelate, LiNi _1-xy Co _x Mn _y O ₂ and LiNi _1-xy Co _x Al _y O ₂ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) Transition metal oxides such as ternary oxides, solid solution materials incorporating a plurality of transition metals (electrochemically inactive layered Li ₂ MnO ₃ and electrochemically active layered LiMO (M = Co , Solid solutions) with transition metals such as Ni) and the like.
As these positive electrode active materials, 1 type may be used and 2 or more types may be used.

The positive electrode active material preferably contains a compound having an olivine structure. That is, it is one of the preferred embodiments of the present invention that the positive electrode active material is a positive electrode active material containing a compound having an olivine structure.

As the compound having the olivine structure, the following general formula (2);
LixAyDzPO ₄ (2)
(In the formula, A represents at least one selected from the group consisting of Cr, Mn, Fe, Co, Ni and Cu. D represents Mg, Ca, Sr, Ba, Ti, Zn, B, Al, It represents at least one selected from the group consisting of Ga, In, Si, Ge, Sc, Y and rare earth elements, where x, y and z are 0 <x <2, 0 <y <1.5, 0 ≦ z <. It is preferably a compound having a structure represented by 1.5). In such a compound, an oxygen atom in the structure is bonded to phosphorus to form a (PO ₄ ) ^3- polyanion, and since oxygen is immobilized in the crystal structure, a combustion reaction occurs in principle. Absent. Therefore, since the electrode active material containing the compound having the structure represented by the general formula (2) is excellent in safety, it can be suitably used particularly for applications to medium and large power supplies.

As A in the said General formula (2), Fe, Mn, and Ni are preferable, More preferably, it is Fe.
Moreover, as D in the said General formula (2), Mg, Ca, Ti, and Al are preferable.

As the compound having the olivine structure, lithium iron phosphate and lithium manganese phosphate are preferable. More preferably, it is lithium iron phosphate. Further, as the positive electrode active material, it is preferable to use a material whose surface is partially or entirely coated with carbon in order to supplement conductivity. As content of carbon which coat | covers a positive electrode active material, 0.5-20 weight part is preferable with respect to 100 weight part of positive electrode active materials, and 0.8-5 weight part is more preferable.

The positive electrode active material is preferably a positive electrode active material containing lithium iron phosphate as a main component. Among the compounds having the olivine structure, lithium iron phosphate is more preferable, and the main component of the positive electrode active material is preferable. Lithium iron phosphate has high stability against overcharge and uses abundant resources such as iron and phosphoric acid, so that it is inexpensive and preferable in terms of manufacturing cost.
The above-mentioned “containing lithium iron phosphate as a main component” means that the content of lithium iron phosphate is 50% by mass or more with respect to 100% by mass of the whole positive electrode active material, but 80% by mass or more. It is preferable that it is 90% by mass or more. Most preferably, it consists only of lithium iron phosphate.

Examples of the negative electrode active material include carbon materials such as graphite, natural graphite, and artificial graphite, polyacene conductive polymers, composite metal oxides such as lithium titanate, and lithium alloys. Among these, a carbon material is preferable.
As these negative electrode active materials, 1 type may be used and 2 or more types may be used.

As described above, the electrode composition in the present invention preferably contains a water-dispersed resin (emulsion). Although it does not restrict | limit especially as water dispersion resin, For example, non-fluorine-type polymers, such as an acrylic polymer, a nitrile polymer, a diene polymer; PVDF, polytetrafluoroethylene (PTFE), (meth) acryl modified fluorine-type polymer, etc. And the like. Among these, as the water-dispersed resin, those having excellent binding property between particles and flexibility (film flexibility) are preferable. Therefore, acrylic polymers, nitrile polymers, and (meth) acryl-modified fluoropolymers are used. preferable.

In particular, when a positive electrode active material is used as the electrode active material and the electrode composition in the present invention is a positive electrode composition, an emulsion of a polymer having a structure in which a fluorine-containing polymer is (meth) acryl-modified is used. While having the chemically and electrically stable properties of the coalesced polymer, the low binding properties, low adhesion of the resulting coating film, and the brittleness of the coating film, which are the disadvantages of fluorine-containing polymers, are made of acrylic. This is preferable because it is improved by modification.
In addition, an emulsion having a structure in which PVDF or PTFE is (meth) acryl-modified is also a particle having an “IPN structure” in which PVDF or PTFE itself is a polymer having crystallinity, but acrylic is included in the fluoropolymer. Is preferable because the crystallinity is lowered and the film forming temperature of the emulsion is also lowered. Such an emulsion of a (meth) acryl-modified fluorine-containing polymer is, for example, in the presence of water-dispersed particles of PVDF or PTFE, an emulsion having a functional group such as (meth) acrylic acid ester or carboxylic acid or sulfonic acid. It can be obtained by emulsion polymerization of a saturated monomer or the like.

When the water-dispersed resin is used, the content of the water-dispersed resin in the electrode composition is preferably 0.5 to 7% by mass with respect to 100% by mass of the electrode active material. When the content of the water-dispersed resin is within this range, the binding property, the flexibility of the film and the flexibility can be further improved. More preferably, it is 1-5 mass%.

The electrode composition in the present invention preferably further contains a conductive additive, particularly when the electrode composition is a positive electrode composition. The conductive assistant is used to increase the output of the lithium ion battery, and conductive carbon is mainly used. Examples of the conductive carbon include carbon black, fiber-like carbon, and graphite. Among these, ketjen black and acetylene black are preferable.
Ketjen Black has a hollow shell structure and is easy to form a conductive network. For this reason, it is preferable because equivalent performance can be achieved with an addition amount of about half that of conventional carbon black. Acetylene black is preferable because it is produced by using a high-purity acetylene gas, and the carbon black has very few impurities and the surface crystallites are developed.

When using the said conductive support agent, it is preferable that it is 0.5-10 mass% with respect to 100 mass% of electrode active materials as content of the conductive support agent in an electrode composition. When the content of the conductive auxiliary is within this range, the electrode resistance can be sufficiently reduced and the effect as the conductive auxiliary can be exhibited. More preferably, it is 1-6 mass%.

The electrode composition in the present invention can further contain a dispersant as required, particularly when it contains a conductive additive. By using the dispersant, it is possible to further increase the dispersibility of the electrode active material and the conductive auxiliary agent and reduce the viscosity of the electrode composition, and to set the concentration of the solid content of the electrode composition high.
The dispersant is not particularly limited, and various dispersants such as anionic, nonionic or cationic surfactants or polymer dispersants such as a copolymer of styrene and maleic acid are used. Can do. When the dispersant is used, the dispersant is preferably used in an amount of 1 to 20% by mass with respect to 100% by mass of the conductive additive. When the content of the dispersing agent is within such a range, it is possible to sufficiently secure dispersibility when the electrode active material and the conductive auxiliary agent are mixed. The amount of the dispersant used is more preferably 3 to 15% by mass.
Thus, by using a dispersing agent together and improving the uniform dispersion stability of the electrode active material and the conductive additive in the electrode composition, the contact resistance between the electrode active material particles can be reduced, and a good electrode It becomes possible to achieve the conductivity of the membrane.

Examples of the content ratio of the components contained in the composition when the electrode composition is a positive electrode composition include a water-soluble polymer, a positive electrode active material, a conductive additive, an emulsion, and these in a solid content The ratio of other components other than the above components is water-soluble polymer / positive electrode active material / conductive aid / emulsion / other components = 0.2 to 3.0 / 70 to 95/2 to 20/1 to 10 / It is preferable that it is 0-5. When the positive electrode composition contains a constituent component in such a content ratio, it is possible to improve output characteristics and electrical characteristics when an electrode formed from the positive electrode composition is used as a positive electrode of a battery. . More preferably, it is 0.3-2.0 / 80-93 / 3-10 / 2-5 / 5-0.
In addition, other components here refer to components other than the above-mentioned water-soluble polymer, positive electrode active material, conductive additive, and emulsion, and include dispersants and other thickeners.

Moreover, as an example of the content rate of the structural component contained in the composition in the case where the electrode composition is a negative electrode composition, a water-soluble polymer in a solid content, a negative electrode active material, a conductive auxiliary agent, an emulsion, and The ratio of other components other than these components is water-soluble polymer / negative electrode active material / conductive aid / emulsion / other components = 0.2-2 / 85-99 / 0-10 / 0.5- It is preferably 9/0 to 5. When the negative electrode composition contains a constituent component in such a content ratio, it is possible to improve output characteristics and electrical characteristics when an electrode formed from the negative electrode composition is used as a negative electrode of a battery. . More preferably, it is 0.5-1.5 / 90-99 / 0-5 / 0.8-2 / 0-3.
In addition, the other component here represents components other than the above-mentioned water-soluble polymer, negative electrode active material, conductive additive, and emulsion, and includes a dispersant and other thickeners.

The electrode composition in the present invention preferably has a viscosity of 1 to 20 Pa · s. When the viscosity of the electrode composition is in such a range, it is possible to ensure appropriate fluidity during coating, which is preferable in terms of workability. More preferably, it is 2-12 Pa.s, More preferably, it is 2-10 Pa.s.

The electrode composition preferably has a thixo value of 2.5-8. When it is 2.5 or less, the coating liquid flows and becomes easy to repel, and when it is 8 or more, the coating liquid does not have fluidity and is difficult to apply. More preferably, it is 3-6.
The viscosity of the electrode composition can be measured using a B-type viscometer (manufactured by Tokyo Keiki Co., Ltd.) at 25 ± 1 ° C. and 30 rpm. The thixo value of the electrode composition is a value obtained by measuring the viscosity at 25 ± 1 ° C., 6 rpm and 60 rpm using a B-type viscometer (manufactured by Tokyo Keiki Co., Ltd.) and dividing the viscosity at 6 rpm by the viscosity at 60 rpm. Can be sought.

The electrode composition preferably has a pH of 6 to 10 at 25 ° C. When the pH is in such a range, the current collector is hardly corroded, and the battery performance of the material can be fully exhibited.
The pH can be measured by measuring a value at 25 ° C. using a glass electrode type hydrogen ion meter F-21 (product name, manufactured by HORIBA, Ltd.).

The electrode composition is obtained by the method for producing an electrode composition of the present invention, and contains the above-described binder containing a water-soluble polymer, an electrode active material, and water. The dispersion stability and viscosity adjusting function of the electrode active material are ensured, and the coating film forming ability, adhesion to the substrate and flexibility are excellent. An electrode obtained by coating such an electrode composition on a current collector can exhibit sufficient performance as an electrode for a secondary battery.

An electrode obtained by coating an electrode composition obtained by the method for producing an electrode composition of the present invention on a current collector is also one aspect of the present invention. Further, a secondary battery manufactured using such an electrode is also one aspect of the present invention.
The current collector is not particularly limited, and examples thereof include an aluminum current collector and a copper foil.

In addition, the secondary battery of the present invention preferably has an electric capacity maintenance rate (simply referred to as “100 cycle maintenance rate”) after 100 cycles of charging / discharging 100 times of 85% or more. More preferably, it is 90% or more, More preferably, it is 95% or more.
The electric capacity of the secondary battery can be measured by evaluation using a charge / discharge measuring apparatus as performed in Examples described later.

The method for producing an electrode composition of the present invention has the above-described configuration, and an electrode composition in which the obtained electrode is excellent in battery performance can be easily produced. Therefore, the electrode composition is preferably used as a method for producing an electrode composition. It is something that can be done.

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples. Unless otherwise specified, “part” means “part by weight” and “%” means “mass%”.

(Synthesis Example 1; synthesis of alkali-soluble resin (1))
In a four-necked separable flask equipped with a stirrer, thermometer, cooler, nitrogen inlet tube, and dropping funnel, ion-exchanged water (115 parts), polyoxyethylene dodecyl ether sulfonate ammonium salt (1.5 parts) I put it in. While stirring at an internal temperature of 68 ° C., nitrogen was gently flowed to completely replace the inside of the reaction vessel with nitrogen.
Next, polyoxyethylene dodecyl ether sulfonate (1.5 parts) was dissolved in ion-exchanged water (92 parts). As a polymer monomer, a mixture of ethyl acrylate (65 parts) and methacrylic acid (35 parts) was added to prepare a pre-emulsion. 5% of the pre-emulsion containing the monomer was put into a reaction vessel and stirred, and then sodium bisulfite (0.017 part) was added. Separately, ammonium persulfate (0.23 parts) was dissolved in ion-exchanged water (23 parts) to prepare a polymerization initiator aqueous solution. 5% of this polymerization initiator aqueous solution was put into the reaction vessel, and initial polymerization was performed for 20 minutes. The temperature in the reaction vessel was kept at 72 ° C., and the remaining pre-emulsion and initiator aqueous solution were uniformly added dropwise over 2 hours. After completion of dropping, the dropping tank was washed with ion-exchanged water (8 parts) and then charged into the reaction vessel. The internal temperature was kept at 72 ° C. and stirring was further continued for 1 hour, followed by cooling to complete the reaction to obtain an emulsion (alkali-soluble resin (1)) having a solid content of 30%.

(Synthesis Example 2: Synthesis of alkali-soluble resin (2))
As in Synthesis Example 1, except that ethyl acrylate (59.8 parts), methacrylic acid (40 parts), and 1,6-hexanediol diacrylate (0.2 parts) were used as the monomers for the polymer. Thus, an emulsion (alkali-soluble resin (2)) having a solid content of 30% was obtained.

(Synthesis Example 3; synthesis of alkali-soluble resin (3))
30% solid content in the same manner as in Synthesis Example 1 except that ethyl acrylate (59.9 parts), methacrylic acid (40 parts), and diallyl phthalate (0.1 parts) were used as the monomer of the polymer. Emulsion (alkali-soluble resin (3)) was obtained.

(Comparative Synthesis Example 1; Synthesis of acrylic emulsion)
An emulsion having a solid content of 30% was obtained in the same manner as in Synthesis Example 1 except that ethyl acrylate (95 parts) and methacrylic acid (5 parts) were used as the polymer monomers.

(Preparation Example 1; Preparation of aqueous polymer solution (1))
To the alkali-soluble resin (1) obtained in Synthesis Example 1 (4.00 parts / solid content 1.2 parts), 5% lithium hydroxide / monohydrate aqueous solution (4.01 parts) and ion-exchanged water (53 .42 parts) was added and stirred for 5 minutes using a self-revolving stirrer (ARE-310 manufactured by Sinky Corporation) to obtain an aqueous polymer solution (1).
The solid content, total light transmittance, viscosity, and pH of the obtained polymer aqueous solution (1) were measured and evaluated as follows. The measurement and evaluation results are shown in Table 1.

<Solid content of aqueous polymer solution>
The aqueous polymer solution was dried at 110 ° C. for 1 hour, and the solid content was calculated from the weight before drying and the weight after drying.
<Total light transmittance of aqueous polymer solution>
Using a haze meter (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.), the solution was put into the cell and the total light transmittance was determined. The total light transmittance of water was 100%.
<Viscosity of aqueous polymer solution>
Using a B-type viscometer (manufactured by Tokyo Keiki Co., Ltd.), the viscosity at 25 ± 1 ° C. and 30 rpm was measured.
<PH of aqueous polymer solution>
The value at 25 ° C. was measured using a glass electrode type hydrogen ion meter F-21 (product name, manufactured by HORIBA, Ltd.).

(Preparation Example 2; Preparation of aqueous polymer solution (2))
To the alkali-soluble resin (1) obtained in Synthesis Example 1 (3.00 parts / solid content 0.9 parts), 5% lithium hydroxide / monohydrate aqueous solution (3.01 parts) and ion-exchanged water (50 .73 parts) was added, and the mixture was stirred for 5 minutes using a self-revolving stirrer (ARE-310, manufactured by Sinky Corporation). Further, a styrene-maleic acid copolymer (active ingredient 27%) (0.85 parts) was added and stirred for 3 minutes with a self-revolving stirrer to obtain an aqueous polymer solution (2).
The solid content, total light transmittance, viscosity, and pH of the obtained aqueous polymer solution (2) were measured and evaluated in the same manner as in Preparation Example 1. The measurement and evaluation results are shown in Table 1.

(Preparation Example 3; Preparation of aqueous polymer solution (3))
To the alkali-soluble resin (2) obtained in Synthesis Example 2 (3.00 parts / solid content 0.9 parts), a 5% lithium hydroxide monohydrate aqueous solution (3.44 parts) and ion-exchanged water (50 .49 parts) was added, and the mixture was stirred for 5 minutes using a self-revolving stirrer (ARE-310, manufactured by Sinky Corporation). Further, a styrene-maleic acid copolymer (active ingredient 27%) (0.85 parts) was added, and the mixture was stirred with a self-revolving stirrer for 3 minutes to obtain an aqueous polymer solution (3).
The solid content, total light transmittance, viscosity and pH of the obtained aqueous polymer solution (3) were measured and evaluated in the same manner as in Preparation Example 1. The measurement and evaluation results are shown in Table 1.

(Preparation Example 4; Preparation of aqueous polymer solution (4))
To the alkali-soluble resin (1) obtained in Synthesis Example 1 (4.00 parts / solid content 1.2 parts), 5% lithium hydroxide / monohydrate aqueous solution (2.81 parts) and ion-exchanged water (54 .19 parts) was added and stirred for 5 minutes using a self-revolving stirrer (ARE-310 manufactured by Sinky Corporation) to obtain an aqueous polymer solution (4).
The solid content, total light transmittance, viscosity, and pH of the obtained aqueous polymer solution (4) were measured and evaluated in the same manner as in Preparation Example 1. The measurement and evaluation results are shown in Table 1.

(Preparation Example 5; Preparation of aqueous polymer solution (5))
To the alkali-soluble resin (3) obtained in Synthesis Example 3 (3.00 parts / solid content 0.9 parts), 5% lithium hydroxide / monohydrate aqueous solution (2.73 parts) and ion-exchanged water (50 .87 parts) was added and stirred for 5 minutes using a self-revolving stirrer (ARE-310, manufactured by Sinky Corporation). Further, a styrene-maleic acid copolymer (active ingredient 27%) (0.85 parts) was added, and the mixture was stirred for 3 minutes with a self-revolving stirrer to obtain an aqueous polymer solution (5).
The solid content, total light transmittance, viscosity, and pH of the obtained aqueous polymer solution (5) were measured and evaluated in the same manner as in Preparation Example 1. The measurement and evaluation results are shown in Table 1.

(Comparative Preparation Example 1; Preparation of aqueous lithium polyacrylate)
5% lithium hydroxide monohydrate aqueous solution (11.66 parts) and ion-exchanged water (41.51 parts) were added to polyacrylic acid (trade name “AS58”, manufactured by Nippon Shokubai Co., Ltd.) (1.00 part). The mixture was stirred for 5 minutes using a self-revolving stirrer (ARE-310, manufactured by Sinky Corporation). Furthermore, stirring for 5 minutes was performed twice to obtain a lithium polyacrylate aqueous solution.
The solid content, total light transmittance, viscosity, and pH of the obtained lithium polyacrylate aqueous solution were measured and evaluated in the same manner as in Preparation Example 1. The measurement and evaluation results are shown in Table 1.

(Comparative Preparation Example 2; Preparation of CMC aqueous solution)
Ion-exchanged water (99.00 parts) was added to carboxymethylcellulose (CMC1380, manufactured by Daicel Chemical Industries, Ltd.) (1.00 part), and the mixture was stirred for 10 minutes using a self-revolving stirrer (ARE-310 manufactured by Sinky Corporation). . A lump was left, and stirring was further performed twice for 10 minutes to obtain a 1% carboxymethylcellulose aqueous solution (CMC aqueous solution). In general, carboxymethyl cellulose tends to be agglomerated when dissolved (the outside is semi-dissolved), and it takes time to completely dissolve in this state.
The solid content, total light transmittance, viscosity, and pH of the obtained CMC aqueous solution were measured and evaluated in the same manner as in Preparation Example 1. The measurement and evaluation results are shown in Table 1.

(Comparative Preparation Example 3; Preparation of VDF-Acrylic Modified Emulsion Aqueous Solution)
Ion exchange water (49.00 parts) was added to VDF-acrylic modified emulsion (manufactured by Arkema; VDF: acrylic = 70: 30) (1.00 part) and stirred to obtain a VDF-acrylic modified emulsion aqueous solution. It was.
The solid content, total light transmittance, and viscosity of the obtained VDF-acrylic modified emulsion aqueous solution were measured and evaluated in the same manner as in Preparation Example 1. The measurement and evaluation results are shown in Table 1.

(Comparative Preparation Example 4; Preparation of SBR emulsion aqueous solution)
Ion-exchanged water (49.00 parts) was added to SBR emulsion (manufactured by JSR) (1.00 part) and stirred to obtain an aqueous SBR emulsion solution.
The solid content, total light transmittance, and viscosity of the obtained aqueous SBR emulsion solution were measured and evaluated in the same manner as in Preparation Example 1. The measurement and evaluation results are shown in Table 1.
In Table 1, the unit of the amount of each component is “parts”.

(Comparative Preparation Example 5; Preparation of acrylic emulsion aqueous solution)
A 5% lithium hydroxide / monohydrate aqueous solution (0.57 parts) and ion-exchanged water (55.63 parts) were added to the acrylic emulsion (4.00 parts) synthesized in Comparative Synthesis Example 1, and the revolution type The mixture was stirred for 5 minutes using a stirrer (ARE-310, manufactured by Sinky Corporation). Furthermore, stirring for 5 minutes was performed twice to obtain an acrylic emulsion aqueous solution.
The solid content, total light transmittance, viscosity, and pH of the obtained acrylic emulsion aqueous solution were measured and evaluated in the same manner as in Preparation Example 1. The measurement and evaluation results are shown in Table 1.
In Table 1, the unit of the amount of each component is “parts”.

Example 1
5% lithium hydroxide / monohydrate aqueous solution (0.979 parts) was added to water (1) (13.045 parts) and alkali-soluble resin (1) (0.976 parts) and stirred to obtain an aqueous polymer solution. Produced. Water (2) (18.9 parts), acetylene black HS-100 (manufactured by Denka) (1.80 parts), lithium iron phosphate (Chinese product) (27.0 parts) were added to the prepared polymer aqueous solution. Kneaded. After kneading, an acrylic modified vinylidene fluoride emulsion (VDF-acryl modified emulsion) (1.87 parts) was further added and mixed to obtain a positive electrode composition (1).
The viscosity, thixo value, pH, electrode formability, and electrical characteristics of the obtained positive electrode composition (1) were measured and evaluated as follows. The measurement and evaluation results are shown in Table 2.

<Viscosity of positive electrode composition>
Using a B-type viscometer (manufactured by Tokyo Keiki Co., Ltd.), the viscosity at 25 ± 1 ° C. and 30 rpm was measured.
<Thixotropic value of positive electrode composition>
Using a B-type viscometer (manufactured by Tokyo Keiki Co., Ltd.), the viscosity at 25 ± 1 ° C., 6 rpm and 60 rpm was measured, and the value obtained by dividing the viscosity at 6 rpm by the viscosity at 60 rpm was determined.
<PH of positive electrode composition>
The value at 25 ° C. was measured using a glass electrode type hydrogen ion meter F-21 (product name, manufactured by HORIBA, Ltd.).

<Electrode formability>
Using a variable applicator, the positive electrode composition was applied so as to have a predetermined film thickness, and dried at 100 ° C. for 10 minutes to produce a positive electrode.
The produced positive electrode was subjected to a bending test at φ10 mm and evaluated according to the following evaluation criteria.
Evaluation criteria:
○ ・ ・ ・ No problem.
Δ: There was no volume shrinkage crack during film formation, but cracking occurred when the electrode was bent.
X: Volume shrinkage cracks occurred during film formation.

<Electrical characteristics (charge / discharge evaluation)>
Using an applicator, the positive electrode composition was applied, dried at 100 ° C. for 10 minutes, pressed at room temperature for 5 minutes, and dried under reduced pressure at 80 ° C. to prepare an electrode sheet. Using the produced electrode sheet, a coin cell (CR2032) was produced as described below, and battery evaluation was performed under the following conditions using a charge / discharge measuring apparatus ACD-001 (product name, manufactured by Asuka Electronics Co., Ltd.).
Coin cell positive electrode: positive electrode composition negative electrode of Table 2: Li foil electrolyte solution: 1 mol% / L LiPF ₆ EC / EMC = 1/1 (manufactured by Kishida Chemical Co., Ltd.)
Battery evaluation conditions (for lithium iron phosphate)
Charging condition: 0.5C CC-CV Cut-off 4.0V
Discharge condition: 0.5C CC Cut-off 2.5V
Battery evaluation conditions (for lithium cobaltate and nickel manganese lithium cobaltate)
Charging condition: 0.2C CC Cut-off 4.3V
Discharge condition: 0.5C CC Cut-off 2.8V

(Example 2)
5% lithium hydroxide / monohydrate aqueous solution (0.784 parts) was added to water (1) (13.212 parts) and alkali-soluble resin (1) (0.782 parts), and the mixture was further stirred. A maleic acid copolymer (0.222 parts) was added and stirred to prepare an aqueous polymer solution. Water (2) (18.8 parts), acetylene black HS-100 (1.80 parts) and lithium iron phosphate (Chinese product) (27.0 parts) were added to the prepared polymer aqueous solution and kneaded. After kneading, an acrylic-modified vinylidene fluoride emulsion (1.87 parts) was further added and mixed and dispersed to obtain a positive electrode composition (2).
The viscosity, thixo value, pH, electrode formability, and electrical characteristics of the obtained positive electrode composition (2) were measured and evaluated in the same manner as in Example 1. The measurement and evaluation results are shown in Table 2.

(Example 3)
5% lithium hydroxide monohydrate aqueous solution (0.447 parts) was added to water (1) (6.552 parts) and alkali-soluble resin (2) (0.390 parts), and the mixture was further stirred. A maleic acid copolymer (0.111 parts) was added and stirred to prepare an aqueous polymer solution. Water (2) (26.2 parts), acetylene black HS-100 (1.95 parts) and lithium iron phosphate (Chinese product) (27.0 parts) were added to the prepared polymer aqueous solution and kneaded. After kneading, an acrylic-modified vinylidene fluoride emulsion (1.87 parts) was further added and mixed and dispersed to obtain a positive electrode composition (3).
The viscosity, thixo value, pH, electrode formability, and electrical characteristics of the obtained positive electrode composition (3) were measured and evaluated in the same manner as in Example 1. The measurement and evaluation results are shown in Table 2.

Example 4
5% lithium hydroxide monohydrate aqueous solution (1.567 parts) was added to water (1) (26.427 parts) and alkali-soluble resin (1) (1.562 parts), and the mixture was further stirred. A maleic acid copolymer (0.444 parts) was added and stirred to prepare an aqueous polymer solution. Water (2) (7.3 parts), acetylene black HS-100 (1.80 parts), lithium iron phosphate (Chinese product) (27.6 parts) are added to the prepared polymer aqueous solution and kneaded to form a positive electrode composition. A product (4) was obtained.
The viscosity, thixo value, pH, electrode formability, and electrical characteristics of the obtained positive electrode composition (4) were measured and evaluated in the same manner as in Example 1. The measurement and evaluation results are shown in Table 2.

(Example 5)
5% lithium hydroxide monohydrate aqueous solution (0.596 parts) was added to water (1) (8.736 parts) and alkali-soluble resin (2) (0.520 parts), and the mixture was further stirred. A maleic acid copolymer (0.148 parts) was added and stirred to prepare an aqueous polymer solution. Water (2) (11.8 parts), acetylene black HS-100 (2.60 parts), Cellseed C-10N (trade name, manufactured by Nippon Chemical Industry Co., Ltd .; lithium cobaltate) (36.4) Part) was added and kneaded. After kneading, an acrylic-modified vinylidene fluoride emulsion (1.67 parts) was further added and mixed and dispersed to obtain a positive electrode composition (5).
The viscosity, thixo value, pH, electrode formability, and electrical characteristics of the obtained positive electrode composition (5) were measured and evaluated in the same manner as in Example 1. The measurement and evaluation results are shown in Table 2.

(Example 6)
5% lithium hydroxide / monohydrate aqueous solution (0.552 parts) was added to water (1) (13.44 parts) and alkali-soluble resin (1) (0.786 parts), and the mixture was further stirred. A maleic acid copolymer (0.222 parts) was added and stirred to prepare an aqueous polymer solution. Water (2) (18.8 parts), acetylene black HS-100 (1.80 parts) and lithium iron phosphate (Chinese product) (27.0 parts) were added to the prepared polymer aqueous solution and kneaded. After kneading, an acrylic-modified vinylidene fluoride emulsion (1.87 parts) was further added and mixed and dispersed to obtain a positive electrode composition (6).
The viscosity, thixo value, pH, electrode formability, and electrical characteristics of the positive electrode composition (6) obtained were measured and evaluated in the same manner as in Example 1. The measurement and evaluation results are shown in Table 2.

(Example 7)
5% LiOH / H ₂ O aqueous solution (0.472 parts) is added to water (1) (9.83 parts) and the resin of Synthesis Example 3 (0.520 parts), and the mixture is stirred, and further a styrene-maleic acid copolymer. (0.148 parts) was added and stirred to prepare an aqueous polymer solution. Water (2) (11.02 parts), acetylene black HS-100 (2.40 parts), cell seed NMC111 (trade name, manufactured by Nippon Chemical Industry Co., Ltd .; lithium nickel manganese cobaltate Ni: Co: Mn = 1: 1: 1) (36.8 parts) was added and kneaded. After kneading, an acrylic modified vinylidene fluoride emulsion (1.25 parts) was further added and mixed and dispersed to obtain a positive electrode composition (7).
The viscosity, thixo value, pH, electrode formability, and electrical characteristics of the obtained positive electrode composition (7) were measured and evaluated in the same manner as in Example 1. The measurement and evaluation results are shown in Table 2.

(Comparative Example 1)
Add water (12.9 parts), 2% lithium polyacrylate aqueous solution (24.0 parts) and stir, and then add styrene-maleic acid copolymer (0.44 parts) and stir to prepare an aqueous polymer solution. did. Acetylene black HS-100 (1.80 parts) and lithium iron phosphate (Chinese product) (27.6 parts) were added to the prepared polymer aqueous solution and kneaded to obtain a comparative positive electrode composition (1).
The viscosity, thixo value, pH, electrode formability, and electrical characteristics of the obtained comparative positive electrode composition (1) were measured and evaluated in the same manner as in Example 1. The measurement and evaluation results are shown in Table 2.
In Table 2, the column of the composition of each component is represented as “number of parts added / solid content (parts)”. For the solid content of 5% LiOH.H ₂ O (5% lithium hydroxide monohydrate aqueous solution), a value obtained by converting only lithium is described.

(Reference Example 1)
NMP (57.4 parts) was dissolved by adding Kyner HSV900 (trade name, manufactured by Arkema; vinylidene fluoride polymer) (1.20 parts), acetylene black HS-100 (2.40 parts), iron phosphate Lithium (Chinese product) (36.4 parts) was added and kneaded to obtain a reference positive electrode composition (1).
The viscosity, thixo value, pH, electrode formability, and electrical characteristics of the obtained reference positive electrode composition (1) were measured and evaluated in the same manner as in Example 1. The measurement and evaluation results are shown in Table 2.

(Reference Example 2)
NMP (27.8 parts) was dissolved by adding Kyner HSV900 (trade name, manufactured by Arkema; vinylidene fluoride polymer) (1.20 parts), acetylene black HS-100 (2.00 parts), cell seed NMC111 ( Product name, manufactured by Nippon Chemical Industry Co., Ltd .; lithium nickel manganese cobaltate Ni: Co: Mn = 1: 1: 1) (36.8 parts) was added and kneaded to obtain a reference positive electrode composition (2).
The viscosity, thixo value, pH, electrode formability, and electrical characteristics of the obtained reference positive electrode composition (2) were measured and evaluated in the same manner as in Example 1. The measurement and evaluation results are shown in Table 2.

From the results of Examples and Comparative Examples, the following was found.
From the results of Preparation Examples 1 to 5, it was found that the alkali-soluble resin in the present invention becomes an aqueous solution that is easily viscous but fluid and easy to handle by mixing with an aqueous alkali solution. This means that, when the alkali-soluble resin in the present invention is used, an aqueous polymer solution can be easily prepared, so that an electrode composition can be easily produced. On the other hand, from the results of Comparative Preparation Examples 1 and 2, when polyacrylic acid or CMC was used instead of the alkali-soluble resin in the present invention to prepare a polymer aqueous solution, it took time to stir and easily It can be seen that an aqueous polymer solution cannot be prepared. Furthermore, when the amount used is large, the lump becomes large, so that a significant difference occurs in the dissolution time. Moreover, when the content of the structural unit derived from the metal salt monomer of unsaturated carboxylic acid is low from the comparative preparation examples 3 and 4, when using the VDF-based acrylic modified emulsion or SBR emulsion, and the comparative preparation example 5, It was found that the total light transmittance was low and it was in the state of an aqueous dispersion.
From the results of Example 4 and Comparative Example 1, when a binder containing a water-soluble polymer prepared from an alkali-soluble resin in the present invention was used, when lithium polyacrylate was used as the binder, In comparison, it was proved that solid brittleness was particularly eliminated and electrode formation was improved. And even the water-soluble polymer alone prepared from the alkali-soluble resin in the present invention has electrode forming properties without impairing the viscosity adjusting function and the dispersing function, and can function as a binder in the electrode composition. Proved to be.
Furthermore, in the battery using the electrode prepared using the positive electrode composition obtained in Examples 1 to 7, the initial discharge was compared with the battery (Reference Examples 1 and 2) prepared using the solvent (NMP). The results are inferior in terms of capacity and cycle retention rate, and it has been found that sufficient performance is exhibited from the viewpoint of battery characteristics.
In the above examples, specific materials are used as electrode active materials, alkali-soluble resins, metal salts used as neutralizing agents, and specific materials are used as conductive aids, emulsions, and additives. However, by using a binder containing the water-soluble polymer in the present invention as a binder, an electrode composition in which the obtained electrode is excellent in battery performance can be easily produced. The same applies to the case of using the water-soluble polymer in the present invention.
Therefore, it can be said from the results of the above-described embodiments that the present invention can be applied in the entire technical scope of the present invention and in various forms disclosed in this specification, and can exhibit advantageous effects.

Claims (5)

A method for producing an electrode composition comprising an electrode active material, a binder, and water,
The production method includes a step of kneading an electrode active material, a binder, and water ;
A step of adding an aqueous dispersion resin of any one of an acrylic polymer, a nitrile polymer, and a (meth) acryl-modified fluoropolymer after the kneading step,
The binder is derived from 10 to 60% by mass of a structural unit derived from an ethylenically unsaturated carboxylic acid monomer and 100% by mass of the total amount of structural units, and derived from an ethylenically unsaturated carboxylic acid ester monomer. Including a water-soluble polymer obtained by neutralizing an alkali-soluble resin containing 10 to 90% by mass of a structural unit with a metal salt,
The method for producing an electrode composition, wherein the water-soluble polymer has a total light transmittance of 90 to 100% in a 2% by mass aqueous solution. The water-soluble polymer is obtained by neutralizing 60 to 150% of a carboxylic acid having a structural unit derived from an ethylenically unsaturated carboxylic acid monomer in an alkali-soluble resin with a metal salt. The manufacturing method of the electrode composition as described in any one of. 3. The method for producing an electrode composition according to claim 1, wherein the water-soluble polymer has a 2 mass% aqueous solution having a viscosity of 50 to 20,000 mPa · s. The process of manufacturing an electrode composition by the manufacturing method of the electrode composition in any one of Claims 1-3 , and the process of coating the electrode composition manufactured by the process on a collector is included. An electrode manufacturing method characterized by the above. A method for producing a secondary battery, comprising a step of producing a secondary battery using the electrode produced by the method for producing an electrode according to claim 4 .