JP6992490B2 - Conductive aid dispersion, its use and its manufacturing method - Google Patents

Description

The present invention relates to a carbon black dispersion liquid having excellent dispersibility, storage stability, and conductivity. Further, the present invention relates to an electrode coating liquid having excellent coatability and film forming property using the dispersion liquid. Further, the present invention relates to a battery electrode mixture layer and a lithium ion secondary battery having excellent battery characteristics using the electrode coating liquid.

In recent years, non-aqueous electrolyte secondary batteries have come to be widely used in small portable electronic devices such as digital cameras and mobile phones, and automobiles and the like. These electronic devices are always required to minimize the volume of the device and reduce the weight, and it is possible to realize a compact, lightweight, large capacity, safe and long-life battery for the mounted battery. It has been demanded.

In order to meet such demands, secondary batteries such as lithium ion secondary batteries are being actively developed. For example, from the viewpoint of the electrode active material, a metal oxide material composed of Li, Ni, and one or more metal elements selected mainly from the group consisting of Al, Ti, Mn, Fe, and Co is used as the positive electrode active material. By using it, it is possible to realize a small and large capacity battery, and by using lithium iron phosphate, lithium manganate, lithium titanate, etc. as the electrode active material, it is possible to realize a safe and long-life battery. Each is known.

As a means for increasing the capacity of the battery other than improving the electrode active material, it has been studied to improve the composition ratio of the electrode active material in the battery electrode mixture layer. By using a highly conductive material that exhibits good conductivity even in a small amount, the ratio of the conductive auxiliary agent can be reduced, and as a result, the ratio of the electrode active material can be improved.

Such materials include, for example, fibrous materials such as carbon nanotubes and carbon nanofibers, carbon black with a highly developed structure, hollow carbon black having a large number of particles per unit weight due to having pores, and the like. Is expected.

In general, it is particularly important to uniformly disperse the conductive additive particles in order to effectively develop conductivity. By uniformly controlling and dispersing the particles, it becomes possible to more effectively form a conductive path in the coating film.

However, it is difficult to control and uniformly disperse the above-mentioned highly conductive material because its shape and the properties of the particle surface are significantly different from those of carbon black which has been conventionally used. Therefore, although the conductive path formed by the conductive auxiliary agent is important, the influence of the type of the conductive auxiliary agent particle and its processing state on the conductivity, conductivity, peel strength, etc. of the secondary battery is detailed. Was not known, and the design of the optimum processing state was required.

Further, as in the case of using conventional carbon black, it is particularly important that the coating liquid for electrodes using these highly conductive materials is in a state where it can be easily applied in large quantities industrially. In particular, in consideration of the environment and production costs, the amount of solvent used and the energy used during drying can be reduced by using a conductive auxiliary agent dispersion liquid or electrode coating liquid that is uniformly dispersed at a higher concentration. Is required to do.

As a means for uniformly dispersing the above-mentioned carbon black in a solvent at a high concentration, for example, in Patent Documents 1 and 2, for example, carbon black having a high specific surface area is treated by a dispersant after allowing a dispersant to act on it. Dispersion liquid of a conductive auxiliary agent in which hollow carbon black having pores and pores is uniformly dispersed in a solvent, and a coating liquid for an electrode using the dispersion liquid are disclosed. Further, Patent Document 1 discloses that when the amount of the dispersant used becomes too large, the film-forming property and the battery characteristics deteriorate.
However, the influence of these carbon black dispersion treatment states on the conductivity and conductivity of the battery electrode mixture layer has not been sufficiently investigated.

On the other hand, it has been proposed to improve the battery characteristics of the battery electrode mixture layer by designing the particle size distribution of the conductive auxiliary agent. For example, in Patent Documents 3 and 4, acetylene black is mainly used as a conductive auxiliary agent, and the size and ratio of the cumulative 10% particle diameter and the cumulative 90% particle diameter are designed so as to exhibit good conductivity. It is disclosed that conductive auxiliaries particles can be placed.
However, when two types of conductive auxiliary agents having significantly different particle diameters and specific surface areas are used, the optimum average dispersed particle size and composition ratio for each conductive auxiliary agent have not been investigated.

Further, for example, Patent Document 5 discloses a suitable particle size distribution when carbon black and particles on the order of micrometer such as graphite are used in combination. It is described that by using a small particle size conductive auxiliary agent and a large particle size conductive auxiliary agent in combination, packing in the battery electrode mixture layer can be improved and high conductivity can be exhibited. ing.

However, regarding a suitable dispersion treatment state when a conductive auxiliary agent having an average primary particle diameter of 20 to 50 nm and a BET specific surface area of 300 to 1400 m ² / g, particularly hollow carbon black having pores, is selected as the highly conductive material. The reality was that sufficient consideration had not been made.
If this material is used alone after having a particle size distribution set in the same way as conventional carbon black, it may not be possible to obtain good battery characteristics and it may deteriorate, and further, this is changed from conventional carbon black. Good conductivity, conductivity, and peel strength even when designed by changing from the assumed optimum particle size distribution to a large particle size or small particle size, or when used in combination with micrometer-order particles such as graphite. Etc. have been found by the inventor in some cases.

When a conductive auxiliary agent having an average primary particle diameter of 20 to 50 nm and a BET specific surface area of 300 to 1400 m ² / g, particularly hollow carbon black having pores, is selected as the highly conductive material, it should be handled in the same manner as conventional carbon black. Even so, it is difficult to obtain good battery characteristics, and it is difficult to design as a high-capacity electrode mixture layer.

Japanese Unexamined Patent Publication No. 2014-194001 Japanese Unexamined Patent Publication No. 2000-348537 Japanese Unexamined Patent Publication No. 2013-045761 Japanese Unexamined Patent Publication No. 2013-08437 Japanese Unexamined Patent Publication No. 2013-145766

In view of the above situation, in the present invention, it is possible to obtain an electrode mixture coating film having excellent conductivity as compared with a conventionally known carbon black dispersion liquid and an electrode coating liquid obtained by using the carbon black dispersion liquid. It is an object to provide a conductive auxiliary agent dispersion liquid and an electrode coating liquid that can be produced. Another object of the present invention is to provide a stable conductive auxiliary agent dispersion liquid having excellent storage stability and a coating liquid for electrodes. Another problem is to provide a stable battery electrode mixture layer having good battery characteristics and excellent adhesion.

The present inventors have focused on the physical and chemical properties of the electrode active material, the conductive auxiliary agent, and the binder component, and as a result of examining in detail the quantitative relationship between them and the treatment state of the conductive auxiliary agent, the conductive auxiliary material has been investigated. It has been found that when at least two kinds of carbon materials having different specific surface areas are used as the agent and used within a specific ratio range, a conductive auxiliary agent dispersion liquid capable of obtaining particularly excellent conductivity can be obtained. Furthermore, they have found that it is possible to obtain a battery electrode mixture layer having excellent strength and conductivity of a coating film and stability in a long-term use environment, and have completed the present invention.

That is, an embodiment of the present invention is a conductive auxiliary agent dispersion liquid containing at least two or more different carbon materials as a conductive auxiliary agent and N-methyl-2-pyrrolidone as a solvent, and is the first type of conductive auxiliary agent. However, the average primary particle diameter is 20 to 50 nm, the BET specific surface area is 300 to 1400 m ² / g, the average dispersed particle diameter (cumulative 50% particle diameter) is 200 to 2500 nm, and the second type of conductive auxiliary agent has an average primary particle diameter of 20 to 70 nm. , BET specific surface area 10 to 200 m ² / g, average dispersed particle diameter (cumulative 50% particle diameter) 200 to 2400 nm, and the mass ratio of the first type of conductive auxiliary agent to the second type of conductive auxiliary agent is 20 to 80. : The present invention relates to a conductive auxiliary agent dispersion liquid having a value of 80 to 20.

Further, in the embodiment of the present invention, the first kind of conductive auxiliary agent and the second kind of conductive auxiliary agent are carbon black, and the mass ratio of the first kind of conductive auxiliary agent and the second kind of conductive auxiliary agent is 35 to 65: The present invention relates to the above-mentioned conductive auxiliary agent dispersion liquid, which is 65 to 35.

Further, an embodiment of the present invention is characterized in that the first kind of conductive auxiliary agent is hollow carbon black, and the average dispersed particle size (cumulative 50% particle size) of the first kind of conductive auxiliary agent is 200 to 1500 nm. The present invention relates to the above-mentioned conductive auxiliary agent dispersion liquid.

Further, in the embodiment of the present invention, the average dispersed particle size (cumulative 50% particle size) of the first kind of conductive auxiliary agent is 200 to 1500 nm, and the average dispersed particle size (cumulative 50% particle size) of the second kind of conductive auxiliary agent. The present invention relates to the above-mentioned conductive auxiliary agent dispersion liquid, which is characterized by having a diameter) of 800 to 2400 nm.

Further, an embodiment of the present invention relates to the above-mentioned conductive auxiliary agent dispersion liquid further containing a dispersant.

Further, the embodiment of the present invention further relates to the above-mentioned conductive auxiliary agent dispersion liquid containing at least one of a water-soluble polymer (A) or a resin fine particle (B) as a component as a binder.

Further, in an embodiment of the present invention, an electrode comprising the above-mentioned conductive auxiliary agent dispersion further containing one or more electrode active materials selected from the group consisting of lithium iron phosphate and lithium titanate as electrode active materials. The coating liquid for electrodes may further contain an additive, and when the amount of all solid components contained in the coating liquid for electrodes is 100 parts by mass, the electrodes The amount of active material is 90 parts by mass or more and 94 parts by mass or less, the amount of conductive aid is 3 parts by mass or more and 7 parts by mass or less, the amount of binder is 2.5 parts by mass or more and 5 parts by mass or less, and the amount of additive is 0 parts by mass or more and 0. The present invention relates to a coating liquid for an electrode, which is characterized in that it is 5 parts by mass or less (however, the total amount of the binder and the additive is 5 parts by mass or less).

Further, an embodiment of the present invention relates to the above-mentioned coating liquid for electrodes, which is characterized in that the average particle size of the electrode active material is 0.2 to 6 μm.

Further, in the embodiment of the present invention, Li (Ni _x M1 _y M2 _z ) O ₂ (x = 0.3 to 0.9, y = 0.01 to) is further added to the above-mentioned conductive auxiliary agent dispersion liquid as an electrode active material. 0.69, z = 0.01 to 0.69, x + y + z = 1. M1 and M2 are elements selected from the group consisting of Al, Ti, Mn, Fe and Co, respectively, and M1 and M2 are different elements. ), And an electrode coating solution containing one or more electrode active substances selected from the group consisting of lithium manganate, wherein the electrode coating solution may further contain an additive. Further, when the amount of all solid components contained in the coating liquid for electrodes is 100 parts by mass, the electrode active material is 94 parts by mass or more and 98 parts by mass or less, and the conductive auxiliary agent is 1 part by mass or more and 4 parts by mass or less. The feature is that the amount of the binder is 1 part by mass or more and 4 parts by mass or less, and the amount of the additive is 0 parts by mass or more and 0.5 parts by mass or less (however, the total amount of the binder and the additive is 4 parts by mass or less). Regarding the coating liquid for electrodes.

Further, an embodiment of the present invention relates to the above-mentioned coating liquid for electrodes, which is characterized in that the average particle size of the electrode active material is 1 to 15 μm.

Further, an embodiment of the present invention is characterized in that the amount of the first type of conductive auxiliary agent is 25 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the total amount of the binder and the additive. Regarding the work liquid.

Further, in the embodiment of the present invention, when the additive is a dispersant and the amount of all solid components contained in the coating liquid for electrodes is 100 parts by mass, the dispersant is 0.02 parts by mass or more. The present invention relates to the above-mentioned coating liquid for electrodes, which is characterized by having 5 parts by mass.

Further, in the embodiment of the present invention, the first kind of conductive auxiliary agent and the second kind of conductive auxiliary agent are carbon black, respectively, and the amount of all solid components contained in the coating liquid for electrodes is 100 g, and the first kind of conductive is conductive. When the sum of the products of the amounts of the auxiliary agent, the second kind of conductive auxiliary agent and the electrode active material and the specific surface area of each is the total surface area bm ² , the value of (amount of additive / total surface area b) is 0.00005. The present invention relates to the above-mentioned coating liquid for electrodes, which satisfies ≦ (amount of additive / total surface area b) ≦ 0.00045. (The total surface area b is (the amount of the first type of conductive auxiliary agent x the specific surface area of the first type of conductive auxiliary agent + the amount of the second type of conductive auxiliary agent x the specific surface area of the second type of conductive auxiliary agent + the electrode active material. Calculated as amount x specific surface area of electrode active material x 0.2))

Further, an embodiment of the present invention relates to a battery electrode mixture layer formed by applying the above-mentioned electrode coating liquid.

Further, an embodiment of the present invention is a lithium ion secondary battery including a positive electrode having a positive electrode mixture layer on a current collector, a negative electrode having a negative electrode mixture layer on the current collector, and an electrolyte containing lithium. The present invention relates to a lithium ion secondary battery in which at least one of a positive electrode and a negative electrode is provided with the battery electrode mixture layer.

Further, an embodiment of the present invention is a method for producing a dispersion liquid of the first kind of conductive auxiliary agent used for manufacturing the above-mentioned conductive auxiliary agent dispersion liquid, and the mixers operated under the condition of a shear rate of 15,000 s ^-1 or more. The present invention relates to a method for producing a first type of conductive auxiliary agent dispersion liquid, which comprises performing a dispersion treatment using a media mill or a dispersion treatment using a media mill.

Further, in the embodiment of the present invention, (I) the first kind of conductive auxiliary agent is dispersed and treated with a media mill, and then (II) the second kind of conductive auxiliary agent is added, and the shear rate is 15000 s ^-1 or more. The present invention relates to a method for producing the above-mentioned conductive auxiliary agent dispersion liquid, which is characterized in that it is produced by dispersion treatment with the mixers operated in the above.

Further, in the embodiment of the present invention, (i) the dispersion liquid of the first kind of conductive auxiliary agent and the dispersion liquid of the second kind of conductive auxiliary agent are dispersed and treated with mixers operated under the condition of shearing speed of 15000s ^-1 or more. Alternatively, the above-mentioned conductive auxiliary agent dispersion is characterized by being manufactured through a step of producing each by dispersion treatment using a media mill and (ii) a step of mixing the above-mentioned two kinds of conductive auxiliary agent dispersion liquids. Regarding the method of producing a liquid.

Further, in the embodiment of the present invention, the first type using a mixer or a media mill in which the first type of conductive auxiliary agent and the second type of conductive auxiliary agent are operated at the same time under the condition of a shear rate of 15000s ^-1 or more is used. The average dispersed particle size (cumulative 50% particle size) of the conductive auxiliary agent is 200 to 2500 nm, and the average dispersed particle size (cumulative 50% particle size) of the second type of conductive auxiliary agent is 200 to 2400 nm. The present invention relates to a method for producing the above-mentioned conductive auxiliary agent dispersion liquid, which is characterized by being produced through the dispersion treatment step of the above.

Further, an embodiment of the present invention is a method for producing a coating liquid for an electrode through a step of simultaneously dispersing a conductive auxiliary agent and an electrode active material in a solvent, in which the conductive auxiliary agent is dispersed alone in the solvent. The average dispersed particle size (cumulative 50% particle size) of the first type of conductive auxiliary agent after treatment is 200 to 2500 nm, and the average dispersed particle size (cumulative 50% particle size) of the second type of conductive auxiliary agent is 200 to 2400 nm. The present invention relates to a method for producing a coating liquid for an electrode, which is characterized in that it is produced through a dispersion treatment step equivalent to that in the case of.

According to the present invention, it is possible to obtain a conductive auxiliary agent dispersion having good storage stability, which contains the first type of conductive auxiliary agent and the second type of conductive auxiliary agent, and as a result, it is coated with good rheology and storage stability. It is possible to obtain a high-concentration coating liquid for electrodes with excellent workability.

Further, when the electrode mixture layer for a secondary battery is prepared using the electrode coating liquid, it is possible to obtain a homogeneous and good coating film having excellent adhesion to the substrate.

Further, when the electrode mixture layer for a secondary battery prepared by using the electrode coating liquid is used as an electrode, it has excellent conductivity and is used for a long period of time while maintaining the high capacity property of the electrode active material. A good electrode with excellent stability in the environment can be obtained, and as a result, it can be used well even under stricter charge / discharge conditions than before.

Hereinafter, the details of the present invention will be described. In this specification, "positive electrode active material or negative electrode active material" may be abbreviated as "electrode active material", and "metal current collector" may be abbreviated as "current collector".

<Conductive aid>
In the present invention, the first kind of conductive auxiliary agent and the second kind of conductive auxiliary agent are used. Hollow carbon black having holes is used exclusively as the first type of conductive auxiliary agent, and carbon black is used exclusively as the second type of conductive auxiliary agent, but the present invention is not limited thereto. As the conductive auxiliary agent used in the present invention, various carbon blacks such as commercially available hollow carbon black, furnace black, channel black, thermal black, and acetylene black can be used. Further, the usual oxidation-treated carbon black, graphitized carbon black, and the like can also be used.

The average primary particle size of the first-class conductive auxiliary agent used in the production of the coating liquid for electrodes is 20 to 50 nm, more preferably 25 to 45 nm. The average primary particle size of the second type conductive auxiliary agent is 20 to 70 nm, more preferably 20 to 50 nm. Further, it is particularly preferable that the shape of the primary particles is spherical. The average primary particle size referred to here indicates an arithmetic average particle size measured by an electron microscope, and this physical property value is generally used to represent the physical properties of a conductive auxiliary agent.

BET specific surface area and pH are known as other physical property values representing the physical properties of the conductive auxiliary agent. The BET specific surface area refers to the specific surface area measured by the BET method by nitrogen adsorption (hereinafter, simply referred to as the specific surface area), and this specific surface area corresponds to the surface area of carbon black. Generally, the larger the specific surface area, the more homogeneous. Moreover, it becomes difficult to obtain a stable coating liquid. The pH changes under the influence of functional groups and impurities on the surface of carbon black.

The first type of conductive auxiliary agent used in the present invention has a BET specific surface area of 300 to 1400 m ² / g, preferably 350 to 1300 m ² / g, more preferably 350 to 900 m ² / g, and 500 to 500 to 900 m 2 / g. 800 m ² / g is particularly preferable. The second type of conductive auxiliary agent has a BET specific surface area of 10 to 200 m ² / g, preferably 30 to 140 m ² / g, and particularly preferably 30 to 70 m ² / g. As long as it is the above-mentioned conductive auxiliary agent having a specific surface area of BET, various commercially available products and synthetic products can be used alone, or two or more kinds of conductive auxiliary agents can be used in combination.

Further, when a conductive auxiliary agent prepared by mixing two or more types of conductive auxiliary agents is used as the first type of conductive auxiliary agent or the second type of conductive auxiliary agent, the BET specific surface area thereof is a certain conductive auxiliary agent i. BET specific surface area is Sim ² / g, and the ratio of a certain conductive auxiliary agent _i to the first or second type of conductive auxiliary agent when the amount of the first or second type of conductive auxiliary agent is 1. Can be calculated based on the following formula (A) as the sum of the products of the BET specific surface area and the ratio of each conductive auxiliary agent type when G _i .
Formula (A) (BET specific surface area of mixed conductive auxiliary agent) = Σ (S _i · G _i )
For example, the specific surface area of carbon black prepared by mixing carbon black having a BET specific surface area of 800 m ² / g and carbon black having a mass ratio of 1200 m ² / g at a mass ratio of 1: 1 is 1000 m ² / g.

The ratio of the first type of conductive auxiliary agent to the second type of conductive auxiliary agent in the total amount of the conductive auxiliary agent is 20:80 to 80:20, preferably 25:75 to 75:25, and is preferably 35:65. It is more preferably to 65:35, and particularly preferably 40:60 to 60:40.

The average dispersed particle diameter (cumulative 50% particle diameter) of the first type of conductive auxiliary agent in the conductive auxiliary agent dispersion liquid is 200 to 2500 nm, more preferably 200 to 1500 nm, and more preferably 250 to 1200 nm. It is more preferably 300 to 900 nm, and particularly preferably 300 to 900 nm. The average dispersed particle size (cumulative 50% particle size) of the second type of conductive auxiliary agent is 200 to 2400 nm, more preferably 800 to 2400 nm, and particularly preferably 1200 to 2300 nm. When the average dispersed particle size is within this range, not only the dispersion stability of the particles and the homogeneity in the coating film are good, but also the good conductivity and conductivity when the battery electrode mixture layer is used. Can be obtained. The average dispersed particle size (cumulative 50% particle size) of the conductive auxiliary agent in the present invention is a D50 value measured by a laser light diffraction / scattering type particle size distribution meter.

The conductive auxiliary agent used in the present invention is not particularly limited as long as it has the primary particle size and specific surface area, but is acetylene black, furnace black, hollow carbon black, graphitized carbon black, and the like. Carbon black, which has high conductivity and is industrially produced, is particularly preferably used. Among these carbon blacks, hollow carbon black having excellent conductivity per mass and having a large BET specific surface area is particularly preferably used as the first type of conductive auxiliary agent. As the second type of conductive auxiliary agent, carbon black having a developed structure is preferable, and acetylene black having excellent purity is particularly preferably used. Examples of hollow carbon black include Ketjen Black (manufactured by Lion Specialty Chemicals), and examples of acetylene black include Denka Black (manufactured by Denka). Various grades are available from the market. Can be done.

In the present invention, the amount of the conductive auxiliary agent contained in the coating liquid for electrodes varies depending on the type of the electrode active material. Li (Ni _x M1 _y M2 _z ) O ₂ (x = 0.3 to 0.9, y = 0.01 to 0.69, z = 0.01 to 0.69, x + y + z = 1 as the electrode active material. M1 and M2 are elements selected from the group consisting of Al, Ti, Mn, Fe and Co, respectively, and M1 and M2 are different elements), and one or more electrodes selected from the group consisting of lithium manganate. When an active material is used, it is preferably 1 part by mass or more and 4 parts by mass or less, preferably 1 part by mass or more and 3 parts by mass or less, with respect to 100 parts by mass of all solid components contained in the coating liquid for electrodes. It is more preferably 5.5 parts by mass or more and 3 parts by mass or less, and particularly preferably 1.5 parts by mass or more and 2.5 parts by mass or less.
When one or more electrode active materials selected from the group consisting of lithium iron phosphate and lithium titanate are used as the electrode active material, the amount of all solid components contained in the coating liquid for the electrode is 100 parts by mass. On the other hand, it is preferably 3 parts by mass or more and 7 parts by mass or less, preferably 3 parts by mass or more and 6 parts by mass or less, more preferably 3.5 parts by mass or more and 6 parts by mass or less, and 4 parts by mass or more and 5.5 parts by mass or less. Is more preferable, and 4 parts by mass or more and 5 parts by mass or less are particularly preferable.
By blending the conductive auxiliary agent in this amount ratio, the primary particle size or the BET specific surface area can be increased when the first or second type of conductive auxiliary agent is used alone, or with the first or second type of conductive auxiliary agent. It is possible to obtain remarkably excellent conductivity and conductivity as compared with the case where they are used in combination with significantly different materials.

Further, in the present invention, when the total amount of the binder and the additive contained in the coating liquid for electrodes is 100 parts by mass, the first type of conductive auxiliary agent is preferably 25 parts by mass or more and 100 parts by mass or less. , 25 parts by mass or more and 75 parts by mass or less, and particularly preferably 30 parts by mass or more and 60 parts by mass or less.
Although the mechanism of action is not clear, the binder layer coated with the electrode active material is filled with the first type of conductive auxiliary agent having an excellent number of particles per mass in a uniformly dispersed state, resulting in good conductivity and good conductivity. It is speculated that conductivity has come to be developed. In particular, when the composition ratio of the conductive auxiliary agent is low, if the amount of the conductive auxiliary agent of the first type is less than 25 parts by mass, the conductive path of the conductive auxiliary agent may be divided by the binder to obtain high resistance, and 100 mass by mass. If the portion is exceeded, the coating film may peel off due to insufficient binding force between the conductive auxiliary agent particles.

<Binder>
The binder used in the present invention contains at least one of the water-soluble polymer (A) and the resin fine particles (B) as a component. Hereinafter, each binder component will be described.

<Water-soluble polymer (A)>
In the present invention, a water-soluble polymer can be used as the binder.

The water-soluble polymer (A) used in the present invention is obtained by mixing 1 g of the water-soluble polymer (A) in 99 g of a medium of purified water at 25 ° C, stirring the mixture, and allowing the mixture to stand at 25 ° C for 24 hours. It can be completely dissolved in an aqueous medium without separation and precipitation.

The water-soluble polymer (A) is not particularly limited as long as it is a resin other than the emulsion state, but for example, an acrylic resin, a polyurethane resin, a polyester resin, a polyamide resin, a polyimide resin, a polyallylamine resin, and a phenol resin. Examples thereof include polymer compounds containing polysaccharide resins such as epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, formaldehyde resin, silicon resin, fluororesin and carboxymethyl cellulose. Further, a modified product, a mixture or a copolymer of these resins may be used. These binders may be used alone or in combination of two or more.

As the water-soluble polymer (A), a resin of a polysaccharide such as carboxymethyl cellulose or methyl cellulose, and a metal salt or an ammonium salt thereof are preferably used. Among these polymers, methyl cellulose or carboxymethyl cellulose, which functions well as a dispersant or thickener in water and has excellent adhesion and adhesion of a coating film, and a metal salt or ammonium salt thereof are particularly preferable. Used.

The water-soluble polymer (A) has a viscosity of 1% aqueous solution of 5 mPa · s or more and 100,000 mPa · s or less and a viscosity of 1% aqueous solution of 10 mPa · s or more and 10,000 mPa · s or less at a liquid temperature of 25 ° C. It is more preferably 20 mPa · s or more and 5000 mPa · s or less, further preferably 30 mPa · s or more and 2000 mPa · s or less, and particularly preferably 30 mPa · s or more and 1000 mPa · s or less.

If the viscosity of the 1% aqueous solution is small, the resistance and adhesion of the water-soluble polymer (A) may decrease. When the viscosity of the 1% aqueous solution increases, the resistance and adhesion of the water-soluble polymer (A) improve, but the viscosity of the water-soluble polymer (A) itself increases, the workability decreases, and it acts as a flocculant. The dispersed particles may be significantly aggregated. From the industrial applicability assumed by the present invention, in order to design a battery with a higher capacity, the storage stability of the conductive auxiliary agent dispersion and the coating liquid for electrodes and the film forming property can be ensured. It is desirable to reduce the ratio of the binder in the electrode mixture layer by using a polymer having a large molecular weight.

<Resin fine particles (B)>
In the present invention, resin fine particles can be used as one of the binder components.

The resin fine particles (B) used in the present invention can be added to an electrode coating liquid in the form of an aqueous emulsion in which the binder resin is not dissolved in water and is dispersed in the state of fine particles. ..

The aqueous emulsion of the resin fine particles (B) to be used is not particularly limited, but (meth) acrylic emulsion, nitrile emulsion, urethane emulsion, diene emulsion (styrene butadiene rubber), etc.), fluorine emulsion (polyfluorinated vinylendene, etc.) Polytetrafluoroethylene, etc.) and the like. Unlike the water-soluble polymer, the emulsion preferably has excellent bondability and flexibility (flexibility of the film) between particles.

The resin fine particles (B) are preferably functional group-containing crosslinked resin fine particles. Further, non-fluorine-based resin fine particles are more preferable, and (meth) acrylic resin fine particles are particularly preferable. By using the non-fluorine-based resin fine particles, the particle volume and the number of particles per mass can be increased, and better binding property, adhesion and flexibility can be obtained.

(Particle diameter of resin fine particles (B))
The average particle size of the aqueous emulsion of the resin fine particles (B) used is preferably 0.05 to 5 μm from the viewpoint of the bondability of the coating film and the stability of the particles in the coating liquid for electrodes. , 0.1 to 1 μm, more preferably 50 to 500 nm, further preferably 50 to 350 nm, and particularly preferably 50 to 300 nm.
The average particle size of the resin fine particles (B) in the present invention represents the volume average particle size, and is a value measured by a dynamic light scattering method.

When a (meth) acrylic emulsion is used, it is preferable to contain crosslinked resin fine particles described below. The crosslinked resin fine particles indicate resin fine particles having an internal crosslinked structure (three-dimensional crosslinked structure). The cross-linked resin fine particles have a cross-linked structure, so that the electrolytic solution elution resistance can be ensured, and the effect can be enhanced by adjusting the cross-linking inside the particles. Further, since the crosslinked resin fine particles contain a specific functional group, it is possible to contribute to the adhesion to the current collector. Furthermore, by adjusting the crosslinked structure and the amount of functional groups, it is possible to obtain a coating liquid for electrodes having excellent durability of the power storage device.

The (meth) acrylic functional group-containing crosslinked resin fine particles preferably used in the present invention are obtained by emulsion-polymerizing an ethylenically unsaturated monomer in water with a radical polymerization initiator in the presence of a surfactant. The obtained resin fine particles. Then, it is preferable to obtain the ethylenically unsaturated monomers (C1) and (C2) by emulsion polymerization at the following ratios.
(C1) From the group consisting of an ethylenically unsaturated monomer (c1) having a monofunctional or polyfunctional alkoxysilyl group and a monomer (c2) having two or more ethylenically unsaturated groups in one molecule. At least one monomer selected, 0.1 to 20 parts by mass (C2) other than the monomers (c1) to (c2) with respect to 100 parts by mass of the total ethylenically unsaturated monomer. It is an ethylenically unsaturated monomer (c3) of the above, and 80 to 99.9 parts by mass with respect to 100 parts by mass of the total ethylenically unsaturated monomer.

Of the ethylenically unsaturated monomers constituting the crosslinked resin fine particles in the (meth) acrylic emulsion preferably used in the present invention, (c1) and (c3) are contained in one molecule unless otherwise specified. It indicates a monomer having one ethylenically unsaturated group.

(About the monomer group (C1))
The functional groups (alkoxysilyl group, ethylenically unsaturated group) of the monomer contained in the monomer group (C1) are self-crosslinking reactive functional groups, which mainly cause internal cross-linking during particle synthesis. Has the effect of forming. Sufficient internal cross-linking of particles can improve the electrolytic solution resistance. Therefore, the crosslinked resin fine particles can be obtained by using the monomer contained in the monomer group (C1). Further, by sufficiently performing particle cross-linking, the electrolytic solution resistance can be improved. In addition, the alkoxysilyl group or ethylenically unsaturated group remaining inside or on the surface of the particles contributes to the interparticle crosslinking of the binder composition. In particular, the alkoxysilyl group is preferable because it has an effect of contributing to the improvement of the adhesion to the current collector.

In the present invention, the monomer contained in the monomer group (C1) is used in an amount of 0.1 to 20% by mass in the entire ethylenically unsaturated monomer (total 100% by mass) used for emulsion polymerization. It is characterized by that. It is preferably 0.2 to 10% by mass.

(About the monomer group (C2))
The crosslinked resin fine particles in the (meth) acrylic emulsion preferably used in the present invention are the above-mentioned monomer (c1) having an ethylenically unsaturated group and an alkoxysilyl group in one molecule. And / or, in addition to the monomer (c2) having two or more ethylenically unsaturated groups in one molecule, as the monomer group (C2), other than the monomers (c1) and (c2). , Can be obtained by simultaneously emulsifying and polymerizing a monomer (c3) having an ethylenically unsaturated group.

The monomer (c3) is not particularly limited as long as it is a monomer other than the monomers (c1) and (c2) and has an ethylenically unsaturated group, but for example, 1 in one molecule. Monomer (c4) having two ethylenically unsaturated groups and a monofunctional or polyfunctional epoxy group, and a single amount having one ethylenically unsaturated group and a monofunctional or polyfunctional amide group in one molecule. At least one monomer selected from the group consisting of the body (c5) and a monomer (c6) having one ethylenically unsaturated group in one molecule and a monofunctional or polyfunctional hydroxyl group, and a single molecule. A monomer (c7) having an ethylenically unsaturated group other than the molecules (c1), (c2), (c4) to (c6) can be used. By using the monomers (c4) to (c6), an epoxy group, an amide group, or a hydroxyl group can be left in or on the surface of the crosslinked resin fine particles, whereby the adhesion of the current collector and the like can be maintained. It is possible to improve the physical properties of. The functional groups of the monomers (c4) to (c6) are likely to remain inside or on the surface of the particles even after particle synthesis, and even a small amount has a large adhesive effect to the current collector. Further, a part thereof may be used for a crosslinking reaction, and by adjusting the degree of crosslinking of these functional groups, it is possible to balance the electrolytic solution resistance and the adhesion.

A part of the functional group of the monomer contained in the monomers (c4) to (c6) may react during particle polymerization and be used for in-particle crosslinking. In the present invention, the monomer contained in the monomers (c4) to (c6) is 0.1 to 20% by mass in the entire ethylenically unsaturated monomer (100% by mass in total) used for emulsion polymerization. It is preferably used, more preferably 1 to 15% by mass, and particularly preferably 1 to 10% by mass.

The monomer (c7) is not particularly limited as long as it is a monomer other than the monomers (c1), (c2), (c4) to (c6) and has an ethylenically unsaturated group. For example, a monomer (c8) having one ethylenically unsaturated group in one molecule and an alkyl group having 8 to 18 carbon atoms, one ethylenically unsaturated group in one molecule, and a cyclic structure. Examples thereof include the monomer (c9) having. When the monomer (c8) and / or the monomer (c9) is used for emulsion polymerization as the monomer (c7), the monomer (c7) contains other monomers. (May be said), the entire monomer (c1), (c2), (c4) to (c6) and (c7) in which the monomers (c8) and (c9) have an ethylenically unsaturated group). It is preferable that the total content is 30 to 95% by mass. It is preferable to use the monomer (c8) or the monomer (c9) because it is excellent in particle stability and electrolytic solution resistance during particle synthesis.

Examples of the monomer (c7) other than the monomer (c8) and the monomer (c9) include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and n-butyl (meth). ) Alkyl group-containing ethylenically unsaturated monomers such as acrylates, pentyl (meth) acrylates and heptyl (meth) acrylates; nitrile group-containing ethylenically unsaturated monomers such as (meth) acrylonitrile; perfluoromethylmethyl (meth). ) Acrylate, perfluoroethylmethyl (meth) acrylate, 2-perfluorobutylethyl (meth) acrylate, 2-perfluorohexylethyl (meth) acrylate, 2-perfluorooctylethyl (meth) acrylate, 2-perfluoroiso Nonylethyl (meth) acrylate, 2-perfluorononylethyl (meth) acrylate, 2-perfluorodecylethyl (meth) acrylate, perfluoropropylpropyl (meth) acrylate, perfluorooctylpropyl (meth) acrylate, perfluorooctyl Perfluoroalkyl group-containing ethylenically unsaturated monomer having a perfluoroalkyl group having 1 to 20 carbon atoms such as amyl (meth) acrylate and perfluorooctylundecyl (meth) acrylate; perfluorobutylethylene and perfluorohexyl. Perfluoroalkyl such as ethylene, perfluorooctylethylene, perfluorodecylethylene, perfluoroalkyl group-containing ethylenically unsaturated monomer such as alkylenes; polyethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, ethoxy Polyethylene glycol (meth) acrylate, propoxypolyethylene glycol (meth) acrylate, n-butoxypolyethylene glycol (meth) acrylate, n-pentoxypolyethylene glycol (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate , Monomer Polypropylene Glycol (Meta) Acrylate, ethoxyPolymer Glycol (Meta) Acrylate, Propoxy Polypropylene Glycol (Meta) Acrylate, n-Butoxy Polypropylene Glycol (Meta) Acrylate, n-Pentoxy Polypropylene Glycol (Meta) Acrylate, Phenoxy Polypropylene Glycoly Le (meth) acrylate, polytetramethylene glycol (meth) acrylate, methoxypolytetramethylene glycol (meth) acrylate, phenoxytetraethylene glycol (meth) acrylate, hexaethylene glycol (meth) acrylate, methoxyhexaethylene glycol (meth) acrylate Ethylene unsaturated monomer having a polyether chain such as; Ethylene unsaturated monomer having a polyester chain such as lactone-modified (meth) acrylate; (meth) dimethylaminoethylmethyl chloride salt, trimethyl-3. -(1- (Meta) acrylamide-1,1-dimethylpropyl) ammonium chloride, trimethyl-3- (1- (meth) acrylamide propyl) ammonium chloride, and trimethyl-3- (1- (meth) acrylamide-1, 4-Diammonium base-containing ethylenically unsaturated monomers such as 1-dimethylethyl) ammonium chloride; vinyl acetate, vinyl butyrate, vinyl propionate, vinyl hexanoate, vinyl caprylate, vinyl laurate, vinyl palmitate, stearic acid Fatty acid vinyl-based monomers such as vinyl; Vinyl ether-based ethylenically unsaturated monomers such as butyl vinyl ether and ethyl vinyl ether; 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene Α-olefin-based ethylenically unsaturated monomers such as; allyl monomers such as allyl acetate and allyl cyanide; vinyl monomers such as vinyl cyanide, vinylcyclohexane and vinylmethylketone; acetylene, ethynyltoluene and the like Examples include ethynyl monomers.

Examples of the monomer (c7) other than the monomer (c8) and the monomer (c9) include maleic acid, fumaric acid, itaconic acid, citraconic acid, and alkyl or alkenyl monoesters thereof. , Phthalate β- (meth) acryloxyethyl monoester, isophthalic acid β- (meth) acryloxyethyl monoester, terephthalic acid β- (meth) acryloxie ethyl monoester, succinic acid β- (meth) acryloxyethyl Carboxyl group-containing ethylenically unsaturated monomers such as monoesters, acrylic acids, methacrylic acid, crotonic acids and carcinic acids; tertiary butyl group-containing ethylenically unsaturated monomers such as tertiary butyl (meth) acrylates; Sulf group-containing ethylenically unsaturated monomers such as vinyl sulfonic acid and styrene sulfonic acid; phosphate group-containing ethylenically unsaturated monomers such as (2-hydroxyethyl) methacrylate acid phosphate; diacetone (meth) acrylamide. , Acrolein, N-vinylformamide, vinylmethylketone, vinylethylketone, acetoacetoxyethyl (meth) acrylate, acetoacetoxypropyl (meth) acrylate, acetoacetoxybutyl (meth) acrylate, etc. Examples thereof include a body (a monomer having one ethylenically unsaturated group and a keto group in one molecule).

Further, among the monomers (c7), ethylenically unsaturated monomers having a carboxyl group, a tertiary butyl group (terchery butanol is desorbed to become a carboxyl group by heat), a sulfo group, and a phosphate group are used. The resin fine particles obtained by the copolymerization have the functional groups remaining in the particles and on the surface even after the polymerization, have the effect of improving physical properties such as the adhesion of the current collector, and at the same time prevent aggregation during synthesis. However, it can be preferably used because it may maintain the particle stability after synthesis.

Some of the carboxyl group, tert-butyl group, sulfo group, and phosphoric acid group may react during polymerization and be used for in-particle cross-linking. When a monomer containing a carboxyl group, a tertiary butyl group, a sulfo group, and a phosphate group is used, 0.1 in the total ethylenically unsaturated monomer used for emulsion polymerization (100% by mass in total). It is preferably contained in an amount of about 10% by mass, more preferably 1 to 5% by mass. Further, these functional groups may be used for cross-linking within or between particles by reacting during drying.

For these monomers (c7), in order to adjust the polymerization stability of the particles, the glass transition temperature, the film forming property and the physical characteristics of the coating film, two or more kinds of the monomers as mentioned above are used in combination. Can be used. Further, for example, the combined use of (meth) acrylonitrile has the effect of developing rubber elasticity.

(Method for producing crosslinked resin fine particles in a (meth) acrylic emulsion preferably used in the present invention)
The crosslinked resin fine particles in the (meth) acrylic emulsion preferably used in the present invention are synthesized by a conventionally known emulsion polymerization method.

As the emulsifier used in the emulsion polymerization in the present invention, conventionally known emulsifiers such as a reactive emulsifier having an ethylenically unsaturated group and a non-reactive emulsifier having no ethylenically unsaturated group can be arbitrarily used. can.

Reactive emulsifiers having an ethylenically unsaturated group can be further broadly classified into anionic and nonionic nonionic emulsifiers. In particular, when an anionic reactive emulsifier or a nonionic reactive emulsifier having an ethylenically unsaturated group is used, the dispersed particle size of the copolymer becomes fine and the particle size distribution becomes narrow, so that it is used as a binder for a secondary battery electrode. This is preferable because it can improve the electrolyte resistance. As the anionic reactive emulsifier or nonionic reactive emulsifier having an ethylenically unsaturated group, one type may be used alone or a plurality of types may be used in combination.
Further, the particle size of the resin fine particles (B) can be adjusted by changing the amount of the emulsifier used in the emulsion polymerization reaction. For example, in general, the particle size can be reduced by increasing the amount of emulsifier.

The amount of the emulsifier used in the present invention is not necessarily limited, and can be appropriately selected according to the physical characteristics required when the crosslinked resin fine particles are used as the final binder. For example, the emulsifier is usually preferably 0.1 to 30 parts by mass, more preferably 0.3 to 20 parts by mass, and 0. It is more preferably in the range of 5 to 10 parts by mass.

A water-soluble protective colloid can also be used in combination with the emulsion polymerization of the crosslinked resin fine particles in the (meth) acrylic emulsion preferably used in the present invention. Examples of the water-soluble protective colloid include polyvinyl alcohols such as partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol, and modified polyvinyl alcohol; cellulose derivatives such as hydroxyethyl cellulose, hydroxypropyl cellulose, and carboxymethyl cellulose salt; and natural polysaccharides such as guagam. Examples include saccharides, which can be used alone or in combination of multiple species. The amount of the water-soluble protective colloid used is 0.1 to 5 parts by mass, more preferably 0.5 to 2 parts by mass, per 100 parts by mass of the total ethylenically unsaturated monomer.

(Aqueous medium used in emulsion polymerization)
Examples of the aqueous medium used for emulsion polymerization of the crosslinked resin fine particles in the (meth) acrylic emulsion preferably used in the present invention include water, and a hydrophilic organic solvent does not impair the object of the present invention. Can be used in.

(Polymerization initiator used in emulsion polymerization)
The polymerization initiator used for obtaining the crosslinked resin fine particles in the (meth) acrylic emulsion preferably used in the present invention is not particularly limited as long as it has the ability to initiate radical polymerization, and is known. An oil-soluble polymerization initiator or a water-soluble polymerization initiator can be used. It is preferable to use 0.1 to 10.0 parts by mass of these polymerization initiators with respect to 100 parts by mass of the ethylenically unsaturated monomer.

(Conditions for emulsion polymerization)
It should be noted that the polymerization can be carried out not only by the above-mentioned polymerization initiator but also by a photochemical reaction, irradiation or the like. The polymerization temperature is equal to or higher than the polymerization start temperature of each polymerization initiator. For example, in the case of a peroxide-based polymerization initiator, the temperature may be usually about 70 ° C. The polymerization time is not particularly limited, but is usually 2 to 24 hours.

(Other materials used in the reaction)
Further, if necessary, as a buffer, sodium acetate, sodium citrate, sodium bicarbonate, etc., and as a chain transfer agent, octyl mercaptan, 2-ethylhexyl thioglycolate, octyl thioglycolate, stearyl mercaptan, lauryl mercaptan, etc. , T-dodecyl mercaptans and other mercaptans can be used in appropriate amounts.

When a monomer having an acidic functional group such as a carboxyl group-containing ethylenically unsaturated monomer is used for the polymerization of the crosslinked resin fine particles in the (meth) acrylic emulsion preferably used in the present invention, before the polymerization. It can be neutralized with a basic compound after polymerization. Upon neutralization, it can be neutralized with ammonia or alkylamines such as trimethylamine, triethylamine, butylamine; alcoholamines such as 2-dimethylaminoethanol, diethanolamine, triethanolamine, aminomethylpropanol; bases such as morpholine. .. However, it is a highly volatile base that is highly effective in drying properties, and preferred bases are aminomethylpropanol and ammonia. Neutralization is particularly preferable from the viewpoint of dispersion stability of the emulsion.

In the present invention, the amount of the binder contained in the coating liquid for electrodes varies depending on the type of the electrode active material. Li (Ni _x M1 _y M2 _z ) O ₂ (x = 0.3 to 0.9, y = 0.01 to 0.69, z = 0.01 to 0.69, x + y + z = 1 as the electrode active material. M1 and M2 are elements selected from the group consisting of Al, Ti, Mn, Fe and Co, respectively, and M1 and M2 are different elements), and one or more electrodes selected from the group consisting of lithium manganate. When an active material is used, it is preferably 1 part by mass or more and 4 parts by mass or less, preferably 1 part by mass or more and 3.5 parts by mass or less, with respect to 100 parts by mass of all solid components contained in the coating liquid for electrodes. 1, 1 part by mass or more and 3 parts by mass or less is more preferable, 1.5 parts by mass or more and 3 parts by mass or less is further preferable, 1.5 parts by mass or more and 2.5 parts by mass or less is further preferable, and 1.5 parts by mass or more and 2 by mass. More than parts by mass is particularly preferable.
When one or more electrode active materials selected from the group consisting of lithium iron phosphate and lithium titanate are used as the electrode active material, the amount of all solid components contained in the electrode coating liquid is 100 parts by mass. On the other hand, it is 2.5 parts by mass or more and 5 parts by mass or less, more preferably 3 parts by mass or more and 4.5 parts by mass or less, and particularly preferably 3 parts by mass or more and 4 parts by mass or less.

These binders are mainly used industrially to obtain excellent resistance, but when an electrode active material or a conductive auxiliary agent having a high specific surface area is used, the adhesion to the substrate when formed into a coating film is achieved. Is weak and often difficult to paint and process. Therefore, when a material having a high specific surface area is used, there is a demand for a material design that can obtain sufficient adhesion even with a small amount of binder.

<Electrode active material>
In the present invention, lithium iron phosphate is exclusively used as the electrode active material, but the present invention is not limited thereto. As long as the electrode active material is within the above range, various commercially available products and synthetic products can be used alone or in combination of two or more.

The method for synthesizing the electrode active material used in the present invention is not particularly limited, and is described in, for example, JP-A-2011-192644, JP-A-2012-1466639, JP-A-2016-143527, and the like. It can be synthesized by the method used.

The electrode active material in the present invention is Li (Ni _x M1 _y M2 _z ) O ₂ (x = 0.3 to 0.9, y = 0.01 to 0.69, z = 0.01 to 0.69, x + y + z = 1. M1 and M2 are elements selected from the group consisting of Al, Ti, Mn, Fe and Co, respectively, and M1 and M2 are different elements), lithium iron phosphate, lithium titanate, and manganic acid. It is preferably at least one selected from the group consisting of lithium.
Li (Ni _x Mn _y Co _z ) O ₂ (x = 0.2 to 0.6, y = 0.01 to 0.39, z = 0.01 to 0.39, x + y + z = 1), Li (Ni) _x Co _y Al _z ) O ₂ (x = 0.6 to 0.9, y = 0.09 to 0.3, z = 0.01 to 0.1, x + y + z = 1), lithium iron phosphate and titanium It is more preferably one or more selected from the group consisting of lithium acid acid, further preferably lithium iron phosphate or lithium titanate, and particularly preferably lithium iron phosphate.

Li (Ni _x M1 _y M2 _z ) O ₂ (x = 0.3 to 0.9, y = 0.01 to 0.69, z = 0.01 to 0.69, x + y + z = 1 as the electrode active material. M1 and M2 are elements selected from the group consisting of Al, Ti, Mn, Fe and Co, respectively, and M1 and M2 are different elements), and one or more electrodes selected from the group consisting of lithium manganate. When an active material is used and when one or more electrode active materials selected from the group consisting of lithium iron phosphate and lithium titanate are used, the density, particle size, and specific surface area of the electrode active material particles are used. The compounding ratio of the electrode active material, which can be designed into a high-capacity battery while maintaining the conductivity and the conductivity in a suitable state, is greatly different.

Li (Ni _x M1 _y M2 _z ) O ₂ (x = 0.3 to 0.9, y = 0.01 to 0.69, z = 0.01 to 0.69, x + y + z = 1. M1 and M2 are Elements selected from the group consisting of Al, Ti, Mn, Fe and Co, respectively, M1 and M2 are different elements), and one or more electrode active materials selected from the group consisting of lithium manganate. The average primary particle size is preferably in the range of 0.05 to 20 μm, more preferably in the range of 0.1 to 12 μm, still more preferably in the range of 0.2 to 10 μm, and 0. It is particularly preferable that it is in the range of 2 to 5 μm. The average primary particle size of the electrode active material as used herein is an average value of the primary particle size of the electrode active material measured with an electron microscope.

Further, the granules or aggregates of these electrode active materials preferably have an average particle diameter in the range of 0.05 to 50 μm, more preferably in the range of 0.1 to 20 μm. It is more preferably in the range of about 15 μm, and particularly preferably in the range of 2 to 15 μm. The average particle size of the electrode active material referred to in the present specification is a D50 value measured by a laser light diffraction / scattering type particle size distribution meter.

Further, these electrode active materials preferably have a BET specific surface area of 0.1 to 10 m ² / g, more preferably 0.1 to 5 m ² / g, and more preferably 0.1 to 3 m ² / g. Is more preferable, and 0.1 to 1 m ² / g is particularly preferable. As long as it is an electrode active material having a BET specific surface area, various commercially available products and synthetic products can be used alone, or two or more kinds of electrode active materials can be used in combination.

In the present invention, the amount of these electrode active materials added is 94 parts by mass or more and 98 parts by mass or less, and 94 parts by mass or more, with respect to 100 parts by mass of all solid components contained in the coating liquid for electrodes. 97 parts by mass or less is more preferable, and 95 parts by mass or more and 97 parts by mass or less is particularly preferable. From the assumed industrial usage, it is desirable to fill a large amount of electrode active material in order to improve the battery capacity, and the effect of the present invention is when the ratio of the conductive additive to the total solid content is small. It is desirable that the amount of the electrode active material is large as long as the conductivity and the strength of the coating film are not impaired.

On the other hand, one or more electrode active materials selected from the group consisting of lithium iron phosphate and lithium titanate preferably have an average primary particle size in the range of 0.05 to 20 μm, preferably 0.05 to 20 μm. It is more preferably in the range of 10 μm, further preferably in the range of 0.05 to 3 μm, and particularly preferably in the range of 0.1 to 1 μm. The average primary particle size of the electrode active material as used herein is an average value of the primary particle size of the electrode active material measured with an electron microscope.

Further, the granules or aggregates of these electrode active materials preferably have an average particle diameter in the range of 0.05 to 20 μm, more preferably in the range of 0.1 to 10 μm, and 0. It is more preferably in the range of 2 to 10 μm, and particularly preferably in the range of 0.2 to 6 μm. The average particle size of the electrode active material referred to in the present specification is a D50 value measured by a laser light diffraction / scattering type particle size distribution meter.

Further, these electrode active materials preferably have a BET specific surface area of 1 to 20 m ² / g, more preferably 3 to 20 m ² / g, and even more preferably 5 to 20 m ² / g. The one of 15 m ² / g is particularly preferable. As long as it is an electrode active material having a BET specific surface area, various commercially available products and synthetic products can be used alone, or two or more kinds of electrode active materials can be used in combination.

In the present invention, the amount of these electrode active materials added is 90 parts by mass or more and 94 parts by mass or less, and 90 parts by mass or more, with respect to 100 parts by mass of all solid components contained in the coating liquid for electrodes. It is preferably 93 parts by mass or less, and particularly preferably 91 parts by mass or more and 93 parts by mass or less. Since it is desirable to fill a large amount of the electrode active material in order to improve the battery capacity from the assumed industrial usage method, it is desirable that the amount of the electrode active material is large within a range that does not impair the conductivity and the strength of the coating film.

<Additives>
In the present invention, a dispersant can be particularly used as the additive. By dispersing the conductive auxiliary agent using the dispersant, it is possible to obtain a conductive auxiliary agent dispersion liquid having a higher concentration and better storage stability. The additive in the present application is a component other than the electrode active material, the conductive auxiliary agent, and the binder, most of which remains as a non-volatile component in the electrode mixture layer when the electrode coating liquid is dried. .. Further, as an additive, an antiseptic, an antifungal agent, an antifoaming agent and the like can be used.

There are no particular restrictions on the additives used in the present invention, and they can be used alone or in combination of two or more, regardless of whether they are commercially available products or synthetic products.

Dispersants that function suitably in an aqueous solvent include, for example, water-soluble polymers such as polyvinylpyrrolidone, polyvinylacetal, polyvinyl alcohol, and polyacrylic acid, acrylic polymers and copolymers, surfactants, and water-soluble ones. Polymers, various commercially available dispersants, and the like can be used. Since it needs to be adsorbed to the conductive auxiliary agent in order to function as a dispersant, it is particularly preferable to completely dissolve it in a solvent.

The dispersant has a viscosity of 1% aqueous solution of 0.5 mPa · s or more and less than 5 mPa · s at a liquid temperature of 25 ° C. and a viscosity of 1% aqueous solution of 0.5 mPa · s or more and 4 mPa · s or less. It is preferably 0.5 mPa · s or more and 3.5 mPa · s or less.
When the dispersion treatment is performed using a media mill, the lower the viscosity of the liquid, the higher the liquid feeding efficiency, and the uniform and good dispersion can be obtained by the treatment in a short time. Therefore, from the viewpoint of production efficiency, the dispersant aqueous solution can be obtained. The lower the viscosity, the more desirable.

When a dispersant is used as an additive in the present invention, the conductive auxiliary agent and the electrode active material can be uniformly dispersed in the solvent by adding a sufficient amount of the dispersant. When the amount of all solid components contained in the coating liquid for electrodes is 100 parts by mass, the total amount of the conductive auxiliary agent and the dispersant used for the dispersion treatment of the electrode active material is 0.02 parts by mass or more and 0.5 parts by mass. It is preferably 0.02 parts by mass or less, more preferably 0.02 parts by mass or more and 0.3 parts by mass or less, further preferably 0.02 parts by mass or more and 0.2 parts by mass or less, and 0.02. It is particularly preferable that the amount is 0 parts by mass or more and 0.15 parts by mass or less. By blending the dispersant in this amount ratio, it is possible to obtain good processability while exhibiting the good conductivity and conductivity of the present invention. The dispersant is a non-conductive component, and generally has lower electrochemical stability and resistance to a non-aqueous electrolyte solution as compared with the material used for the binder. Therefore, when the compounding ratio of the dispersant exceeds 0.5 parts by mass, the characteristics may deteriorate over time even if the initial characteristics are good. The compounding ratio of the dispersant is preferably as small as possible within the range in which the conductive auxiliary agent can be suitably dispersed.

Further, the amount of all solid components contained in the coating liquid for electrodes is 100 g, and the product of the electrode active material, the first type of conductive auxiliary agent and the second type of conductive auxiliary agent, the respective amounts and the respective specific surface areas. When the total surface area is bm ² , the value of (amount of additive / total surface area b) is preferably 0.00005 or more and 0.00045 or less, and 0.00005 or more and 0.00040 or less. More preferably, it is more preferably 0.00005 or more and 0.00035 or less, further preferably 0.00005 or more and 0.00030 or less, further preferably 0.00005 or more and 0.00025 or less, and 0. It is more preferably 0.0005 or more and 0.00020 or less, and particularly preferably 0.00010 or more and 0.00020 or less.
The total surface area b is (amount of the first type of conductive auxiliary agent x specific surface area of the first type of conductive auxiliary agent + amount of the second type of conductive auxiliary agent x specific surface area of the second type of conductive auxiliary agent + amount of the electrode active material. It can be calculated as × specific surface area of the electrode active material × 0.2) (note that 0.2 multiplied by the specific surface area of the electrode active material is a correction coefficient).
The larger the amount of the additive used, the larger the resistance value estimated from the rate characteristic evaluation (discharge capacity characteristic evaluation) of the battery, but the larger the total surface area with respect to the amount of the additive, the larger the resistance value increases. The inventor has found that it is no longer observed and it is possible to obtain good rate characteristics. Although the mechanism of action is not clear, the dissolved structure and energetic state are different between the additive in the state of being adsorbed on the particles and the additive in the state of being dissolved or dispersed in the electrolytic solution without being adsorbed. Therefore, it is presumed that there are large differences in the behavior as a resistance component and the electrochemical stability.

In the present invention, the dispersion treatment state of the electrode active material fine particles and the conductive auxiliary agent fine particles, particularly the conductive auxiliary agent fine particles, is important. The value of the specific surface area used in the present application is the specific surface area measured by the BET method by nitrogen adsorption, but when these fine particles are not uniformly disintegrated and a large amount of agglomerated particles on the order of several hundred μm remain, the above specific surface area is determined. It may differ from the specific surface area that contributes to adsorption and interaction with the dispersant, and the good effects of the present application may not be obtained.

Further, the weighting of the BET specific surface area of the electrode active material and the conductive auxiliary agent in the total surface area bm ² is different. The reason for this is that the primary particle diameters of the electrode active material fine particles and the conductive auxiliary agent fine particles are generally significantly different, or the surface states of the fine particles are significantly different, resulting in a large difference in the strength of interaction with the dispersant. Is possible.

The compounding ratio of the additive when the amount of all solid components contained in the coating liquid for electrodes is 100 parts by mass is treated as a non-conductive component that is not an electrode active material and is included in the compounding ratio of the binder. ..

<Water>
Water is used in the manufacture of electrodes for secondary batteries such as lithium ion secondary batteries. In the present invention, one or more other solvents are used as long as the solubility of the water-soluble polymer (A), the dispersion stability of the resin fine particles (B), the chemical stability of these binders and the battery performance are not impaired. It may be used together. When another solvent is used in combination, it is preferably a water-soluble organic solvent, and particularly preferably a water-soluble organic solvent having a hydroxyl group. From the industrial applicability assumed by the present invention, the ratio of water in the solvent is preferably 70% or more, more preferably 85% or more, still more preferably 95% or more. It is particularly preferred to use water alone.

<Manufacturing method of conductive auxiliary agent dispersion liquid and electrode coating liquid>
In the present invention, the conductive auxiliary agent dispersion liquid contains at least the first kind of conductive auxiliary agent, the second kind of conductive auxiliary agent, and water. The electrode coating liquid contains at least the first kind of conductive auxiliary agent, the second kind of conductive auxiliary agent, a binder, an electrode active material, and water.
The conductive auxiliary agent dispersion liquid and the electrode coating liquid of the present invention are produced by a method of collectively kneading the materials, a method of applying a shearing force with a mixer or the like, a method of treating with a media mill, or the like. be able to.

It is particularly preferable that the coating liquid for electrodes of the present invention is produced by dispersing and dispersing a conductive auxiliary agent and then sequentially adding a binder material and an electrode active material.
By first dispersing the conductive auxiliary agent, which is difficult to disperse, the conductive auxiliary agent can be uniformly controlled and dispersed. In addition, the subsequent dissolution / dispersion treatment process of the binder material and the electrode active material can be controlled more precisely, and a good coating liquid for an electrode can be produced in a short time. It is desirable not to provide a treatment step for forming the conductive auxiliary agent and the electrode active material into composite particles. This not only increases the time required to prepare the battery electrode mixture layer, but also significantly changes the preferable compounding ratio of the materials and the average dispersed particle size of the conductive auxiliary agent when intentionally compounded. Is presumed.

When the conductive auxiliary agent is dispersed in a solvent to obtain a conductive auxiliary agent dispersion liquid and then the electrode active material is added to perform the dispersion treatment, the coarse particles contained in the conductive auxiliary agent dispersion liquid must be 100 μm or less. Is more preferable, 80 μm or less is more preferable, 50 μm or less is further preferable, and 20 μm or less is particularly preferable. When the remaining coarse particles are large or remain in a large amount, the surface of the coating film becomes rough due to the coarse particles, and a good coating film may not be obtained. The coarse particles contained in the conductive auxiliary agent dispersion liquid in the present invention are the particle diameters at which the particles begin to condense, as measured by a grind gauge.

In the present invention, the first type of conductive auxiliary agent is preferably mixed with a mixer operated under the condition of a shear rate of 15000 s ^-1 or more, or dispersed with a media mill to obtain a conductive auxiliary agent dispersion liquid, and is dispersed with a media mill. It is more preferable to process. When the dispersion treatment is carried out using a media mill, it is particularly preferable to use a dispersant. In particular, when the first type of conductive auxiliary agent granulated in an aqueous solvent is dispersed, it may be difficult for the granulated particles to get wet, but the dispersion treatment using a media mill should improve the production efficiency. Can be done. The concentration of the first type of conductive auxiliary agent is preferably 2% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 18% by mass or less, and 5% by mass or more and 15% by mass or less. Is particularly preferred.

Further, in the present invention, the conductive auxiliary agent dispersion liquid has a shear rate of 15,000 s by adding (I) the first step of dispersing the first type of conductive auxiliary agent with a media mill and (II) the second type of conductive auxiliary agent. -It is particularly preferable that the product is manufactured through a second step of dispersion treatment with mixers operated under the conditions of ^-1 or more. By going through the above steps, it is possible to obtain a conductive auxiliary agent dispersion having a higher concentration than when the first and second types of conductive auxiliary agent dispersions are prepared and mixed. Further, when the dispersion treatment is performed using a dispersant, the first type of conductive auxiliary agent having a large specific surface area requires a larger amount of the dispersant than the second type of conductive auxiliary agent, but the first type of conductive auxiliary agent is required. Since the second type of conductive auxiliary agent can be dispersed by using the dispersant that is not adsorbed by the agent, it is possible to design a small amount of the dispersant contained in the electrode mixture layer.
In general, the first type of conductive auxiliary agent requires more strength and energy for the dispersion treatment than the second type of conductive auxiliary agent, and it is difficult to treat them uniformly. By going through the above process, it is possible to efficiently obtain the conductive auxiliary agent dispersion liquid while applying the optimum processing force to each conductive auxiliary agent to make the particle dispersion treatment state suitable. The dispersed particle size of the first type of conductive auxiliary agent in the conductive auxiliary agent dispersion liquid produced through the above process is the dispersed particle size in the state immediately after being produced through the step (I). The dispersed particle size of the second kind of conductive auxiliary agent is a value when the same treatment step (dispersor shape, rotation speed, treatment time) is applied in a state where the first kind of conductive auxiliary agent is not contained.

Further, in general, the processing power of the media mill is very large as compared with mixers having a mechanism of dispersing by shearing force in the presence of a sufficient solvent. Therefore, even after the step (II), the particle size distribution of the first type of conductive auxiliary agent has almost the same shape as that immediately after the step (I).
It is extremely difficult to properly analyze dissimilar fine particles having similar refractive index, primary particle diameter and secondary particle diameter by optical particle size distribution measurement. Therefore, it is difficult to separately measure and manage the particle size distribution of each of the first and second types of conductive auxiliaries in a state where both the first and second types of conductive auxiliaries are contained. It is possible to control the dispersion treatment state of the conductive auxiliary agent.

The concentration of the first type conductive auxiliary agent in the step (I) is preferably 2% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 18% by mass or less, and 5% by mass or more and 15% by mass or less. The following is particularly preferable. Further, the total concentration of the first type of conductive auxiliary agent and the second type of conductive auxiliary agent in the step (II) is preferably 5% by mass or more and 20% by mass or less, and 7% by mass or more and 18% by mass or less. Is particularly preferred.

Further, in the present invention, the conductive auxiliary agent dispersion liquid is (i) dispersed by using a mixer or a media mill in which the first kind of conductive auxiliary agent is operated under the condition of a shear rate of 15000 s ^-1 or more. Step of preparing the conductive auxiliary agent of the type, (ii) Mixers operating the conductive auxiliary agent of the second type under the condition of shear rate of 15000s ^-1 or more, or dispersion treatment using a media mill for the second type It can be produced through a step of preparing a conductive auxiliary agent dispersion liquid and (iii) a step of mixing the respective conductive auxiliary agent dispersion liquids produced through the above steps to obtain a conductive auxiliary agent dispersion liquid. By going through the above process, it is possible to precisely control the dispersion treatment state of each conductive auxiliary agent, but on the other hand, it can be achieved when an electrode active material that can be easily dispersed treatment is used. The solid content concentration of the coating liquid for electrodes may be low.

Further, in the present invention, the conductive auxiliary agent dispersion liquid uses a mixer or a media mill that operates the first type of conductive auxiliary agent and the second type of conductive auxiliary agent at the same time under the condition of a shear rate of 15000s ^-1 or more. hand,
When the average dispersed particle size (cumulative 50% particle size) of the first type conductive auxiliary agent is 200 to 2500 nm and the average dispersed particle size (cumulative 50% particle size) of the second type conductive auxiliary agent is 200 to 2400 nm. It is preferable to carry out the production through the same dispersion treatment step as above. (However, in the same dispersion treatment step, the shape and operating speed of the dispersion processing machine that disperses the conductive auxiliary agent dispersion liquid are the average dispersed particle diameter of the conductive auxiliary agent by dispersing the first type of conductive auxiliary agent alone. To produce a conductive auxiliary agent dispersion having an average dispersed particle size of 200 to 2400 nm by separately dispersing the second type of conductive auxiliary agent under the condition that a conductive auxiliary agent dispersion having a size of 200 to 2500 nm can be produced. The value obtained by dividing the concentration of the conductive auxiliary agent in the dispersion treatment liquid of the conductive auxiliary agent by the dispersion treatment time is the value obtained by dividing the concentration of the conductive auxiliary agent in the dispersion liquid of the conductive auxiliary agent by the dispersion treatment time. It is the same as the value divided by.) In addition, the production conditions of the coating liquid for electrodes to be set are that the average dispersed particle size when the first type of conductive auxiliary agent is dispersed alone in the solvent is 200 nm. It is more preferably the same as the condition of 1500 nm or less, further preferably the same as the condition of 250 nm or more and 1200 nm or less, and particularly preferably the same as the condition of 300 nm or more and 900 nm or less.

Further, in the present invention, as the electrode coating liquid, there is also a method of producing the electrode coating liquid through a step of simultaneously dispersing the conductive auxiliary agent and the electrode active material in a solvent, and the conductive auxiliary agent is used alone. The same dispersion treatment step as when the average dispersed particle size of the first type of conductive auxiliary agent is 200 to 2500 nm and the average dispersed particle size of the second type of conductive auxiliary agent is 200 to 2400 nm after being dispersed in a solvent is performed. Can be manufactured after. (However, in the same dispersion treatment step, the shape and operating speed of the dispersion treatment machine that disperses the coating liquid for electrodes are determined by dispersing the conductive auxiliary agent alone and the average dispersed particle diameter of the first type of conductive auxiliary agent. Is set to be the same as the conditions under which a conductive auxiliary agent dispersion having a diameter of 200 to 2500 nm can be produced, and the value obtained by dividing the concentration of the conductive auxiliary agent in the coating solution for electrodes by the dispersion treatment time is the above-mentioned conductive auxiliary. It is the same as the value obtained by dividing the concentration of the conductive auxiliary agent in the agent dispersion by the dispersion treatment time.) Further, the manufacturing conditions of the electrode coating liquid to be set are that the first type of conductive auxiliary is used alone. It is more preferable that the average dispersed particle size when dispersed in a solvent is 200 nm or more and 1500 nm or less, more preferably 250 nm or more and 1200 nm or less, and 300 nm or more and 900 nm or less. It is particularly preferable that the conditions are the same.

In general, it is difficult to appropriately analyze dissimilar fine particles having a large difference in refractive index, primary particle diameter, and secondary particle diameter, such as an electrode active material and a conductive auxiliary agent, by optical particle size distribution measurement. Therefore, it is difficult to obtain the particle size distribution of the conductive auxiliary agent fine particles contained in the electrode coating liquid of the present application as an appropriate analytical value, but by adopting the above manufacturing method, the conductive auxiliary agent and the electrode active material are dispersed at the same time. Even in the case of treatment, the dispersed state of the conductive auxiliary agent can be controlled in a preferable state.

As the disperser, a disperser usually used for pigment dispersion or the like can be used. For example, mixers such as dispersers, homomixers, and planetary mixers, homogenizers ("Clearmix" manufactured by M-Technique, "Fillmix" manufactured by PRIMIX, "Abramix" manufactured by Silverson, etc.), paint conditioners (, etc.) Red Devil), colloid mills (PUC "PUC colloid mill", IKA "colloid mill MK"), cone mills (IKA "corn mill MKO", etc.), ball mills, sand mills (Symmal Enterprises) Media type disperser such as "Dyno Mill" manufactured by Dyno Mill, Attritor, Pearl Mill ("DCP Mill" manufactured by Eirich, etc.), Wet Jet Mill ("Genus PY" manufactured by Genus, "Star Burst" manufactured by Sugino Machine Limited" , Nanomizer, etc.), M-Technique's "Claire SS-5", Nara Machinery's "MICROS", and other medialess dispersers, and other roll mills, etc., but are limited to these. is not it.

<Electrode>
A battery electrode mixture layer can be formed and an electrode can be obtained by applying and drying an electrode coating solution prepared by using the conductive auxiliary agent dispersion of the present invention on a metal current collector.

(Metal current collector)
The material and shape of the metal current collector used for the electrode are not particularly limited, and those suitable for various secondary batteries can be appropriately selected. For example, examples of the material of the current collector include metals and alloys such as aluminum, copper, nickel, titanium, and stainless steel. As the shape, a foil on a flat plate is generally used, but a roughened surface, a perforated foil, or a mesh-shaped current collector can also be used.

The method of applying the electrode coating liquid on the current collector is not particularly limited, and a known method can be used. Specific examples thereof include a die coating method, a dip coating method, a roll coating method, a doctor coating method, a knife coating method, a spray coating method, a gravure coating method, a screen printing method, an electrostatic coating method, and the like, and drying. As the method, a stand-alone dryer, a blower dryer, a warm air dryer, an infrared heater, a far-infrared heater, and the like can be used, but the method is not particularly limited thereto.

In the present invention, the mass of the battery electrode mixture layer obtained by completely drying the solvent after coating on the metal collector is preferably 5 to 40 mg per 1 cm ² of the metal collector. It is more preferably to 30 mg, and particularly preferably 5 to 25 mg.

In the present invention, the post-drying thickness of the battery electrode mixture layer obtained by completely drying the solvent after coating on the metal collector is preferably 30 to 500 μm, preferably 40 to 300 μm. Is more preferable, 40 to 200 μm is further preferable, and 40 to 120 μm is particularly preferable. The film thickness after drying is a film thickness in a state where the rolling process is not performed, and is a value obtained by measuring with a contact type film thickness type such as Digimicro (manufactured by Nikon Corporation). Generally, as the film thickness increases, cracks and peeling of the coating film are more likely to occur, so that stronger adhesion is required. In the present invention, even if a conductive auxiliary agent that lowers the adhesion at a high specific surface area is used, the adhesion can be maintained sufficiently strong, so that a battery electrode mixture layer having a high film thickness and a high capacity can be provided. Can be designed.

Further, after coating, rolling processing may be performed by a lithographic press, a calendar roll, or the like. The thickness of the electrode mixture layer after the rolling treatment is generally 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

<Secondary battery>
The battery electrode mixture layer prepared from the electrode coating liquid of the present invention can be particularly preferably used in a lithium ion secondary battery, and can be particularly preferably used as a positive electrode mixture layer.

(Electrolytic solution)
The case of a lithium ion secondary battery will be described as an example. As the electrolytic solution, an electrolyte containing lithium is dissolved in a non-aqueous solvent. Electrolytes include LiBF ₄ , LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₃ C. , LiI, LiBr, LiCl, LiAlCl, LiHF ₂ , LiSCN, LiBPh ₄ (where Ph is a phenyl group) and the like, but are not limited thereto.

The non-aqueous solvent is not particularly limited, and is, for example, carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethylmethyl carbonate, and diethyl carbonate; γ-butyrolactone, γ-valerolactone, and γ. -Lactones such as octanoic lactones; tetrahydrofuran, 2-methyltetrachloride, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1, Glymes such as 2-dibutoxyetane; esters such as methylformate, methylacetate, and methylpropionate; sulfoxides such as dimethylsulfoxide and sulfolane; and nitriles such as acetonitrile. Each of these solvents may be used alone, or two or more kinds may be mixed and used.

(separator)
Examples of the separator include polyethylene non-woven fabric, polypropylene non-woven fabric, polyamide non-woven fabric, and those obtained by subjecting them to a hydrophilic treatment, but the separator is not particularly limited thereto.

(Battery structure / configuration)
The lithium ion secondary battery using the electrode coating liquid of the present invention contains at least a positive electrode having a positive electrode mixture layer on the current collector, a negative electrode having a negative electrode mixture layer on the current collector, and lithium. Equipped with an electrolyte containing.
Further, the structure of the lithium ion secondary battery using the coating liquid for electrodes prepared by using the conductive auxiliary agent dispersion liquid of the present invention is not particularly limited, but is usually provided with a positive electrode and a negative electrode as needed. It is composed of a separator and can have various shapes such as a paper type, a cylindrical type, a button type, a laminated type, etc. according to the purpose of use.

In the present invention, conventionally known dispersants, resins, additives and the like may be used in combination for the purpose of adjusting the physical characteristics of the coating film and the like as long as the above problems are not hindered.

Hereinafter, the present invention will be described in detail based on Examples, but the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded. In this example, parts represent parts by mass,% represents mass%, and D50 represents an average dispersed particle diameter (cumulative 50% particle diameter).
The conductive auxiliary agent (carbon black may be abbreviated as "CB"), the binder, the electrode active material, etc. used in Examples and Comparative Examples are shown below. In addition, although only the composition of each raw material is described in each table, the remaining component not particularly described is water.

<Synthesis of resin fine particles (B)>
[Synthesis Example 1-1]
In a reaction vessel equipped with a stirrer, a thermometer, a dropping funnel, and a recirculator, 40 parts of ion-exchanged water and 0.2 part of ADEKA REASORP SR-10 (manufactured by ADEKA Corporation) as an emulsifier are charged, and methyl methacrylate is separately prepared. 48.5 parts, butyl acrylate 50 parts, acrylic acid 1 part, 3-methacryloxypropyltrimethoxysilane 0.5 parts, ion-exchanged water 53 parts and ADEKA CORPORATION SR-10 as a surfactant (manufactured by ADEKA Corporation) Further, 1% by mass of the pre-emulsion in which the two parts were mixed in advance was added. After raising the internal temperature to 70 ° C. and sufficiently substituting with nitrogen, 10% by mass of 10 parts of a 5% by mass aqueous solution of potassium persulfate was added to initiate polymerization. After keeping the inside of the reaction system at 70 ° C. for 5 minutes, the rest of the preemulsion and the rest of the 5% by mass aqueous solution of potassium persulfate were added dropwise over 3 hours while keeping the temperature at 70 ° C., and stirring was continued for another 2 hours. After confirming that the conversion rate exceeded 98% by solid content measurement, the temperature was cooled to 30 ° C. 25% by mass of ammonia water was added to adjust the pH to 8.5, and the solid content was further adjusted to 40% by mass with ion-exchanged water to obtain an aqueous emulsion containing 40% by mass of the resin fine particles (B) (hereinafter). , B-1). The solid content was determined by the residual amount baked at 150 ° C. for 20 minutes. The dispersed particle size of the resin fine particles (B) was 0.155 μm.

[Synthesis Example 1-2]
In a reaction vessel equipped with a stirrer, a thermometer, a dropping funnel, and a recirculator, 40 parts of ion-exchanged water and 0.2 part of ADEKA REASORP SR-10 (manufactured by ADEKA Corporation) as a surfactant are charged separately. 50 parts of styrene, 45 parts of 2-ethylhexyl acrylate, 1.5 parts of methyl methacrylate, 1 part of acrylic acid, 2 parts of diacetone acrylamide, 0.5 part of 3-methacryloxypropyltrimethoxysilane, 53 parts of ion-exchanged water and surface activity. As an agent, 1.8 parts of Adecaria Soap SR-10 (manufactured by ADEKA Corporation) was further added in an amount of 1% of the pre-emulsion mixed in advance. After raising the internal temperature to 70 ° C. and sufficiently substituting with nitrogen, 10% of 10 parts of a 5% aqueous solution of potassium persulfate was added to initiate polymerization. After keeping the inside of the reaction system at 70 ° C. for 5 minutes, the rest of the preemulsion and the rest of the 5% aqueous solution of potassium persulfate were added dropwise over 3 hours while keeping the internal temperature at 70 ° C., and stirring was continued for another 2 hours. .. After confirming that the conversion rate exceeded 98% by solid content measurement, the temperature was cooled to 30 ° C. 25% aqueous ammonia was added to adjust the pH to 8.5, and the solid content was adjusted to 48% with ion-exchanged water to obtain an aqueous emulsion containing 48% by mass of the resin fine particles (B) (hereinafter, B). Abbreviated as -2). The solid content was determined by the residual amount baked at 150 ° C. for 20 minutes. The dispersed particle size of the resin fine particles (B) was 0.211 μm.

[Synthesis Example 1-3]
Synthesis was carried out in the same manner as in Synthesis Example 1-1 except that the amount of the surfactant was changed to obtain aqueous emulsions B-3, B-4 and B-5 containing 40% by mass of the resin fine particles (B). .. The dispersed particle size of the resin fine particles (B) was 0.102 μm for B-3, 0.297 μm for B-4, and 0.488 μm for B-5.

<Synthesis of dispersant>
[Synthesis Example 2-1]
200.0 parts of n-butanol was charged in a reaction vessel equipped with a gas introduction tube, a thermometer, a condenser and a stirrer, and replaced with nitrogen gas. The inside of the reaction vessel was heated to 110 ° C., and 100.0 parts of styrene, 60.0 parts of acrylic acid, 40.0 parts of dimethylaminoethyl methacrylate, and V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) 12 as a polymerization initiator. A mixture of 0.0 parts was added dropwise over 2 hours to carry out a polymerization reaction. After completion of the dropping, the reaction was further carried out at 110 ° C. for 3 hours, then 0.6 part of V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the reaction was further continued at 110 ° C. for 1 hour to obtain a copolymer (1). ) A solution was obtained. The acid value of the copolymer (1) was 219.1 (mgKOH / g). Further, after cooling to room temperature, 74.2 parts of dimethylaminoethanol was added for neutralization. This is an amount that neutralizes acrylic acid 100%. Further, 400 parts of water was added to make it aqueous, and then the mixture was heated to 100 ° C., and butanol was azeotropically boiled with water to distill off butanol. Diluted with water to obtain an aqueous solution of the amphoteric resin type dispersant (1) having a non-volatile content of 20% (hereinafter abbreviated as D-1). The viscosity of the aqueous solution of the amphoteric resin type dispersant (1) having a non-volatile content of 20% was 40 mPa · s.

<Conductive aid>
-Denka Black HS-100 (manufactured by Denka Co., Ltd.): Acetylene black, average primary particle diameter 48 nm, specific surface area 39 m ² / g, hereinafter abbreviated as HS-100.
-Denka Black Granular Product (manufactured by Denka Co., Ltd.): Acetylene black, average primary particle diameter 35 nm, specific surface area 69 m ² / g, hereinafter abbreviated as granular product.
-Denka Black FX-35 (manufactured by Denka Co., Ltd.): Acetylene black, average primary particle diameter 26 nm, specific surface area 133 m ² / g, hereinafter abbreviated as FX-35.
-SuperP Li (manufactured by Timcal): furnace black, average primary particle diameter 40 nm, specific surface area 62 m ² / g, hereinafter abbreviated as SuperP.
-Ketchen Black EC-300J (manufactured by Lion Specialty Chemicals Co., Ltd.): Hollow carbon black, average primary particle diameter 40 nm, specific surface area 800 m ² / g, hereinafter abbreviated as EC-300J.
-Ketchen Black EC-600JD (manufactured by Lion Specialty Chemicals): Hollow carbon black, average primary particle diameter 34 nm, specific surface area 1270 m ² / g, hereinafter abbreviated as EC-600JD.
-Ketchen Black EC-200L (manufactured by Lion Specialty Chemicals Co., Ltd.): Hollow carbon black, average primary particle diameter 40 nm, specific surface area 377 m ² / g, hereinafter abbreviated as EC-200L.
-TIMREX KS6 (manufactured by Timcal): Artificial graphite, average particle diameter 3.4 μm, specific surface area 20 m ² / g, hereinafter abbreviated as KS-6.

<Binder>
(Water-soluble polymer (A))
CMC Daicel # 1120, 1% aqueous solution viscosity 20 to 50 mPa · s (25 ° C, 60 rpm), etherification degree 0.6 to 0.8 (manufactured by Daicel FineChem): Sodium carboxymethyl cellulose, hereinafter abbreviated as # 1120. ..
CMC Daicel # 1140, 1% aqueous solution viscosity 100-200 mPa · s (25 ° C, 60 rpm), etherification degree 0.6-0.8 (manufactured by Daicel FineChem): Sodium carboxymethyl cellulose, hereinafter abbreviated as # 1140. ..
CMC Daicel # 1240, 1% aqueous solution viscosity 30-40 mPa · s (25 ° C, 60 rpm), etherification degree 0.8-1.0 (manufactured by Daicel FineChem): Sodium carboxymethyl cellulose, hereinafter abbreviated as # 1240. ..
CMC Daicel # 1260, 1% aqueous solution viscosity 80-150 mPa · s (25 ° C, 60 rpm), etherification degree 0.8-1.0 (manufactured by Daicel FineChem): Sodium carboxymethyl cellulose, hereinafter abbreviated as # 1260. ..
CMC Daicel # 1350, 1% aqueous solution viscosity 200 to 300 mPa · s (25 ° C, 60 rpm), etherification degree 1.0 to 1.5 (manufactured by Daicel FineChem): Sodium carboxymethyl cellulose, hereinafter abbreviated as # 1350. ..
-Polyvinylpyrrolidone K-90 (manufactured by Nippon Shokubai Co., Ltd.), 1% aqueous solution viscosity 8 mPa · s (25 ° C, 60 rpm)

(Resin fine particles (B))
-Polytetrafluoroethylene 30-J (solid content 60% aqueous dispersion, average particle size 0.2 μm) (manufactured by Mitsui DuPont Fluorochemical Co., Ltd.), hereinafter abbreviated as PTFE.
-LA-132, average particle diameter 5.8 μm (manufactured by Chengdu Index Power Sources)
B-1, average particle diameter 0.155 μm
B-2, average particle diameter 0.211 μm
B-3, average particle diameter 0.102 μm
・ B-4, average particle diameter 0.297 μm
B-5, average particle diameter 0.488 μm

<Dispersant>
D-1, 1% aqueous solution viscosity 3.1 mPa · s (25 ° C, 60 rpm).
Demor N (manufactured by Kao): β-naphthalene sulfonic acid formalin condensate sodium salt, 1% aqueous solution viscosity 3.2 mPa · s (25 ° C, 60 rpm).
Demol EP (25% solid content aqueous solution) (manufactured by Kao Corporation): Special polycarboxylic acid type polymer surfactant, 1% aqueous solution viscosity 3.5 mPa · s (25 ° C, 60 rpm). ..
-Polyacrylic acid 25000 (manufactured by Wako Pure Chemical Industries, Ltd., weight average molecular weight 25000), 1% aqueous solution viscosity 3.4 mPa · s (25 ° C, 60 rpm). Hereinafter, it is abbreviated as PAA.

<Electrode active material>
-HED ^TM NCM-111 1040 (manufactured by BASF Toda Battery Materials Co., Ltd.): Three-way active material for positive electrode (LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ), average particle diameter 5.3 μm, specific surface area 0.5 m ² / g, hereinafter abbreviated as NCM111.
-M12 (manufactured by Alleees): Lithium iron phosphate for positive electrode, average particle diameter 4.0 μm, specific surface area 12 m ² / g.
-Life power P2 (manufactured by Johnson Matthey): Carbon-coated lithium iron phosphate for positive electrode, average particle diameter 0.45 μm, specific surface area 15.4 m ² / g.
-Lithium titanate (Li ₄ Ti ₅ O ₁₂ ), primary particle diameter 700 nm, specific surface area 7 m ² / g. Hereinafter, it is abbreviated as LTO.

<Evaluation of conductive auxiliary agent dispersion>
The evaluation of the conductive auxiliary agent dispersion used in Examples and Comparative Examples was performed by measuring the viscosity and the average particle size.

To measure the average dispersed particle size of the conductive auxiliary agent, the conductive auxiliary agent dispersion is diluted to an appropriate concentration by NMP, and then ultrasonically treated, and the particle size is measured by the laser light diffraction / scattering method. This was performed by measuring the average particle size using a distribution meter (“Microtrack MT3000” manufactured by Microtrac Bell, Inc., light source wavelength 780 nm).
As for various measurement conditions, the transmittance of the dispersion diluted with purified water by the above method at the time of loading was 0.88 or more and 0.92 or less, the particle condition was set as an absorbent particle, the solvent condition was set, and the solvent refractive index was 1.333. , The obtained cumulative 50% diameter is expressed as the D50 value. The measurement result is obtained by measuring the background value of the purified water solvent having a liquid temperature of 25 ° C., then filling the measuring container with the sample having a liquid temperature of 25 ° C. prepared by the above method, and performing the measurement under the above measurement conditions. Obtained.

<Evaluation of aqueous emulsion of resin fine particles (B)>
The evaluation of the aqueous emulsion of the resin fine particles (B) was performed by measuring the average particle size (volume average particle size Mv).
To measure the average particle size of the resin fine particles (B), the aqueous emulsion of the resin fine particles (B) was diluted with purified water to an appropriate concentration, and then ultrasonically treated using a solution as a measurement sample for dynamic light scattering. This was performed by measuring the average particle size (volume average particle size Mv) using a particle size distribution meter (“Nanotrack UPA-EX” manufactured by Nikkiso Co., Ltd., light source wavelength 780 nm). As for various measurement conditions, the loading index value of the dispersion liquid diluted with purified water by the above method is 0.7 or more and 1.3 or less, and the particle conditions are permeable particles, particle shape sphere, density 1.2, and refractive index 1. As 50 (however, in the case of fluorine-based resin fine particles, absorbent particles, particle shape sphere, density 2.2), the solvent conditions are as follows: solvent refractive index 1.33, solvent viscosity at liquid temperature 20 ° C. 1.00 mPa · s. , The solvent viscosity was set to 0.89 mPa · s at a liquid temperature of 25 ° C., and the obtained volume average particle diameter was expressed as an Mv value. The measurement result is obtained by measuring the background value of the purified water solvent having a liquid temperature of 25 ° C., then filling the measuring container with the sample having a liquid temperature of 25 ° C. prepared by the above method, and performing the measurement under the above measurement conditions. Obtained. Of the resin fine particles (B) used in the examples, only PTFE has the conditions set as the fluorine-based resin fine particles.

The viscosity value was measured using a B-type viscometer (“BL” manufactured by Toki Sangyo Co., Ltd.), and the dispersion was sufficiently stirred with a spatula at a dispersion temperature of 25 ° C. and a B-type viscometer rotor rotation speed of 60 rpm. Later, I went immediately. The rotor used for the measurement was No. 1 when the viscosity value was less than 100 mPa · s. If 1 is 100 or more and less than 500 mPa · s, No. If 2 is 500 or more and less than 2000 mPa · s, No. If 3 is 2000 or more and less than 10000 mPa · s, No. No. 4 was used, and evaluation was not possible when the viscosity value was 10,000 mPa · s or more. The storage stability was evaluated from the change in viscosity value after the carbon black dispersion was allowed to stand at 50 ° C. for 10 days and stored. The smaller the change, the better the stability. ◯: No problem (good), Δ: No problem (there is a change in viscosity but can be used), and ×: Extremely poor.

<Preparation of conductive auxiliary agent dispersion>
[Production Examples 1 to 8, Production Example 1-1 to Production Example 1-4, Production Example 2-1 to Production Example 2-2]
Purified water and the dispersant are charged in a stainless steel container so that the total amount of the 1st or 2nd type conductive auxiliary agent dispersion liquid is 5000 parts according to the composition shown in Table 1, and the mixture is sufficiently mixed and dissolved, and then the disperser is stirred. Below, various conductive aids were added. Then, using a bead mill (Dynomill MULTI LAB, capacity 300 mL, manufactured by Simmal Enterprises) filled with 1.25 mmφ zirconia beads as a medium, the mixture was dispersed for a predetermined time to prepare the first or second type of conductive auxiliary agent dispersion. did.

[Example 1-1 to Example 1-14, Comparative Example 1-1 to Comparative Example 1-6]
With the first type of conductive auxiliary agent dispersion prepared in Production Examples 1 to 8, Production Examples 1-1 to 1-4, and Production Examples 2-1 to 2-2 according to the composition shown in Table 2. The second kind of conductive auxiliary agent dispersion was sufficiently mixed to obtain each conductive auxiliary agent dispersion.

<Preparation of conductive auxiliary agent dispersion liquid containing binder>
[Examples 2-1 to 2-20, Comparative Examples 2-1 to 2-8]
According to the composition shown in Table 3, Examples 1-1 to 1 are placed in a glass bottle so that the total amount of the conductive auxiliary agent dispersion liquid containing the water-soluble polymer (A) and the resin fine particles (B) as the binder is 300 g. -14 and various conductive auxiliary agent dispersions, binders, dispersants, and purified water prepared in Comparative Examples 1-1 to 1-6 were charged, sufficiently mixed and dissolved, and each containing various binder components. A conductive auxiliary agent dispersion was obtained.

[Reference Example 3-1 to Reference Example 3-4]
Purified water and the water-soluble polymer (A) are charged according to the composition shown in Table 4, and after being sufficiently mixed and dissolved, a second type of conductive auxiliary agent is charged under stirring with a dispersion, and Magic Lab (manufactured by IKA) is used. Then, the dispersion treatment was carried out for 20 minutes according to the conditions shown in Table 4 to obtain each conductive auxiliary agent dispersion liquid containing the second kind of conductive auxiliary agent.
The conductive auxiliary agent dispersions prepared in Reference Example 3-1 to Reference Example 3-3 had no coarse particles, had a low viscosity, and had good storage stability. On the other hand, the conductive auxiliary agent dispersion prepared in Reference Example 3-4 was a dispersion in which a large number of large coarse particles remained and the viscosity value was not stable over time. By evaluating the average dispersed particle size of these conductive auxiliary agent dispersions, they are contained in the conductive auxiliary agent dispersions of Examples 3-1 to 3-10 and Comparative Examples 3-1 to 3-3. Data on the average dispersed particle size (D50) of the second type of conductive auxiliary agent were obtained. The average dispersed particle size (D50) of the conductive auxiliary agent added in each Example and Comparative Example is equivalent to the average dispersed particle size (D50) when treated at the same shear rate of each reference example. The various conductive auxiliary agent dispersions produced by the dispersion treatment with the bead mill in Table 1 have a much stronger dispersion treatment power than the mixers, so that the average dispersion before and after the dispersion treatment with the mixers is performed. The particle size is almost the same.

[Examples 3-1 to 3-10, Comparative Examples 3-1 to 3-3]
According to the composition shown in Table 4, various first type of conductive auxiliary agent dispersions prepared in Production Example 2 or Production Example 2-1 are charged in a glass bottle, and then the second type of conductive auxiliary agent and a binder (water-soluble polymer) are charged. (A) and resin fine particles (B)) and a dispersant are charged, and a dispersion treatment is performed for 20 minutes according to the conditions shown in Table 4 using a magic lab (MK module manufactured by IKA) to assist the first type of conductivity. Each conductive auxiliary agent dispersion containing the agent and the second kind of conductive auxiliary agent was obtained.
The conductive auxiliary agent dispersions produced in Examples 3-1 to 3-10 had no coarse particles, had a low viscosity, and had good storage stability. On the other hand, the conductive auxiliary agent dispersion prepared in Comparative Example 3-1 had an increase in viscosity with time, and the conductive auxiliary agent dispersion prepared in Comparative Example 3-2 had a large number of large coarse particles remaining. Moreover, it became a dispersion liquid whose viscosity value was not stable over time.

<Preparation of coating liquid for electrodes>
[Examples 4-1 to 4-26, Comparative Examples 4-1 to 4-8, Reference Examples 4-1 to 4-4]
According to the composition shown in Table 5, Examples 2-1 to 2-11 and Examples 2-13 to 2-17 are placed in a glass bottle so that the total amount of the coating liquid for electrodes is 200 parts by mass. Examples 2-20, Examples 3-2 to 3-3, Examples 3-5 to 3-10, and Comparative Examples 2-1 to 2-8, Comparative Example 3-1. Various conductive additive dispersions, electrode active materials, and purified water prepared in Comparative Example 3-3 were charged and sufficiently mixed with a disper to obtain a coating liquid for each electrode.
The coating liquids for electrodes obtained in Examples 4-1 to 4-26 have sufficiently small coarse particles, good viscosity and viscosity, and maintain a good state even after the storage stability test. rice field.
On the other hand, the coating liquids for electrodes obtained in Comparative Example 4-1 and Comparative Examples 4-4 to 4-7 were coating liquids having unstable viscosities. It can be inferred that the coating liquids for electrodes obtained in Comparative Examples 4-5 to 4-7 had unstable viscosities because the average dispersed particle size of the conductive auxiliary agent was too fine. Further, when the first type of conductive auxiliary agent is mainly used as the conductive auxiliary agent as in Comparative Example 4-1 and Comparative Example 4-4, the viscosity is not stable because the number of particles of the conductive auxiliary agent is remarkably large. It can be inferred that it became a coating liquid. On the other hand, in Comparative Example 4-2 and Comparative Example 4-3, since the second kind of conductive auxiliary agent which can easily stabilize the particles was mainly used, it is possible to obtain a coating liquid for an electrode having good storage stability. In the subsequent cell evaluation, the high resistance in the battery characteristics becomes an issue.

[Example 4-27]
According to the composition shown in Table 5, the conductive auxiliary agent dispersion prepared in Example 2-3 and the electrode active material were charged in an ointment container, and a rotation / revolution mixer (Awatori Rentaro ARE-310, manufactured by Shinky Co., Ltd.) was used. Then, the mixture was mixed at 2000 rpm for 5 minutes to obtain a coating liquid for electrodes.

[Example 4-28]
1164 parts of purified water and 45 parts of the dispersant (D-1) were charged in a glass bottle and sufficiently mixed and dissolved. Next, 45 parts of the first type of conductive auxiliary agent (EC-300J), 45 parts of the second kind of conductive auxiliary agent (HS-100), and 1656 parts of the positive electrode active material (M12) were mixed with the mixed powder under dispersion stirring. Only 1/3 of the total amount was charged and dispersed in a bead mill (Dynomill MULTI LAB, manufactured by Symmulenterprises) filled with 1.25 mmφ zirconia beads as a medium for 10 minutes.
After that, a mixed powder of various conductive auxiliaries and the positive electrode active material (M12) was charged in only 1/3 of the total amount and dispersed in a bead mill for 10 minutes, then the remaining mixed powder was charged and further dispersed in a bead mill for 1.5 hours. did. Finally, 45 parts of the binder (# 1350) was charged and sufficiently mixed and dissolved under stirring with the disper to obtain an electrode coating liquid.

[Comparative Example 4-9]
In a dispersion container of a planetary mixer (Hibismix 2P-03, manufactured by Primix Corporation), 120 parts of purified water, 5.6 parts of the first type of conductive auxiliary agent (EC-300J), and the second type of conductive auxiliary agent (HS-100). ) 5.6 parts and 11.2 parts of the binder (# 1350) were charged and treated at a rotation speed of 40 rpm for 90 minutes. Next, 1/4 of the total amount (257.6 parts) of the positive electrode active material (M12) was added and treated at a rotation speed of 40 rpm for 30 minutes, and this step was repeated 4 times to obtain the positive electrode active material (M12). I prepared all of them. Then, after further kneading at a rotation speed of 40 rpm for 4 hours, 67 parts of purified water was added and diluted to obtain an electrode coating liquid.
The obtained coating liquid for electrodes has not been uniformly dispersed, and a large number of large coarse particles exceeding 100 μm remain so that appropriate evaluation by a particle size distribution meter cannot be performed. It became a coating liquid for electrodes with poor properties.

<Preparation of battery electrode mixture layer>
[Examples 5-1 to 5-27, Comparative Examples 5-1 to 5-8, Reference Examples 5-1 to 5-4]
The coating liquid for each electrode obtained in each of the above Examples, Comparative Examples, and Reference Examples was applied onto an aluminum foil having a thickness of 20 μm as a current collector using a doctor blade, and then using a hot plate. The coating film was heated at 70 ° C. for 10 minutes and then heated and dried at 120 ° C. under reduced pressure for 30 minutes to prepare each coating film having a film thickness of 85 to 95 μm and a basis weight of 12 mg / cm ² after drying of the battery electrode mixture layer. The obtained battery electrode mixture layer was evaluated by adhesion (peeling strength test).

(Evaluation of coating film)
A desktop tensile tester (Strograph E3, manufactured by Toyo Seiki Seisakusho Co., Ltd.) was used to measure the peel strength, and the peel strength was evaluated by a 180-degree peel test method. Specifically, a 100 mm × 20 mm size double-sided tape (No. 5000NS, manufactured by Nitoms Co., Ltd.) was attached onto a metal plate, and the produced battery electrode mixture layer was brought into close contact with the other surface of the double-sided tape. A peeling test was performed by pulling upward at a constant speed (50 mm / min). The results of the peel strength test are: ◎: No problem (especially good, peel strength 150 mN / cm or more), ○: No problem (good, peel strength 100 mN / cm or more), Δ: The peel strength is lower than in the case of 〇. No problem (possible, peel strength 50 mN / cm or more), ×: weak strength and easy peeling (extremely poor, peel strength less than 50 mN / cm or cannot be evaluated). The evaluation results are shown in Table 6.

From Table 6, the battery electrode mixture layers of Examples 5-1 to 5-27 are Comparative Example 5-1 and Comparative Example 5-4 to Comparative Example 5-5 and Comparative Example 5-7 to Comparative Example 5. It was found that the adhesion (peeling strength test result) of the coating film was superior to that of the battery electrode mixture layer of -8. Further, Comparative Example 5-5, Comparative Example 5-7 and Comparative Example 5-8 were coating films that were peeled off during the 180-degree peeling test. The larger the ratio of the first type of conductive auxiliary agent in the coating film, the lower the adhesiveness. Further, when the first type of conductive auxiliary agent is finely dispersed, the adhesiveness is not only lowered but also curved. It was found that the coating film was easily peeled off when it was used. It is necessary to use a large amount of binder as in Reference Example 5-2 in order to secure the adhesiveness while improving the film forming property by using the first kind of conductive auxiliary agent. However, a part of the conductive auxiliary agent of the first kind is replaced with the conductive auxiliary agent of the second kind, or the coarse particles of the conductive auxiliary agent of the first kind are sufficiently treated, and the average dispersed particle diameter is not made fine and the large particles are used. It was found that by controlling the diameter side, a coating film having good adhesion can be obtained even when the amount of the binder used is suppressed. When the second kind of conductive auxiliary agent is mainly used as the conductive auxiliary agent as in Comparative Examples 5-2 and 5-3, the specific surface area of the particles is small and the number of particles is small, so that the adhesion is good. A coating film can be obtained, but the high resistance in battery characteristics in the subsequent cell evaluation becomes an issue.

<Assembly of cell for evaluation of positive electrode of lithium ion secondary battery>
[Examples 6-1 to 6-25, Comparative Examples 6-1 to 6-8, Reference Examples 6-1 to 6-4]
Battery electrode mixture layer prepared earlier (Examples 5-1 to 5-12, Examples 5-15 to 5-27, Comparative Examples 5-1 to 5-8, Reference Example 5- 1 to the battery electrode mixture layer of Reference Example 5-4) was rolled by a roller press machine to prepare a positive electrode mixture layer having a density of the mixture layer of 2.0 g / cm ³ . A separator (porous polyolefin film) made of a porous polypropylene film is inserted and laminated between the working electrode and the counter electrode with a metal lithium foil (thickness 0.15 mm) as the counter electrode. , A bipolar sealed metal cell (manufactured by Hosen Co., Ltd.) filled with an electrolytic solution (a non-aqueous electrolytic solution in which LiPF ₆ is dissolved at a concentration of 1 M in a mixed solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 1: 1). HS flat cell) was assembled. The cells were assembled in a glove box replaced with argon gas.

(Discharge capacity characteristics)
The above-mentioned cells were charged / discharged at 25 ° C. using a charging / discharging device (SM-8 manufactured by Hokuto Denko Co., Ltd.). The charge / discharge current value of each C rate is appropriately changed depending on the composition ratio of the electrode active material, the amount of the electrode mixture layer, and the open capacity of the electrode active material. For example, in Example 6-1 the charging current is 0. Constant current constant voltage charging at 77mA (0.2C) with a charge termination voltage of 4.3V (after performing a cutoff current of 0.12mA, discharge current 0.77mA (0.2C) and 7.66mA (2C) ) Or 11.48 mA (3C), constant current discharge was performed until the discharge end voltage reached 2.0 V, and the discharge capacity was determined for each.
The result of the discharge capacity characteristic is expressed by the following (formula) B based on the measurement result in the mixture layer having the same composition ratio using only acetylene black as the conductive auxiliary agent, and the better the discharge capacity characteristic, the better. It can be inferred that the conductivity of the battery electrode mixture layer in the positive electrode evaluation cell is good.
(Equation) B discharge capacity characteristic = (2C or 3C discharge capacity of each target example / 2C or 3C discharge capacity when only acetylene black is used as the conductive auxiliary agent) × 100 (%)
Table 7 shows the results of evaluation based on the following criteria. In addition, the comparison of the influence of the composition ratio of the conductive auxiliary agent, the binder, and the dispersant on the discharge capacity characteristics and the dispersion treatment state of the conductive auxiliary agent fine particles is the same conductive auxiliary agent compounding ratio (the first kind of conductive auxiliary agent). It is desirable to carry out between (composition ratio) in which the sum of the two types of conductive aids is the same. This is because, for example, when the ratio of the electrode active material is reduced and the ratio of the conductive auxiliary agent is increased, a coating film having better conductivity is naturally obtained, which is not a comparison of the conductive auxiliary agent itself.
-Discharge capacity characteristics ◎: "The ratio of discharge capacity characteristics is 120% or more. It is particularly excellent."
◯: “The ratio of discharge capacity characteristics is 105% or more and less than 120%. It is excellent.”
Δ: “The ratio of the discharge capacity characteristics is 80 or more and less than 105%. Possible. However, if the discharge capacity characteristics of 2C and 3C are both Δ, it is considered as defective because it is the same as the conventional technology.”
△△: "Ratio of discharge capacity characteristics is less than 80%. Inferior (defective)."
X: "The ratio of discharge capacity characteristics is less than 70% or cannot be measured. It is inferior."

(Cycle characteristics)
[Examples 7-1 to 7-9, Comparative Examples 7-1 to 7-2, Reference Example 7-1]
The positive cell for evaluation prepared earlier is fully charged at 25 ° C. using a charging / discharging device (SM-8 manufactured by Hokuto Denko Co., Ltd.) with a constant current constant voltage charging (upper limit voltage 4.3V) with a charging rate of 1.0C. Charging is performed, and charging / discharging is performed with a constant current at the same rate as during charging to a discharge lower limit voltage of 2.0 V as one cycle (charging / discharging interval pause time: 30 minutes). This cycle is performed for a total of 50 cycles for charging / discharging. went. The capacity retention rate is a percentage of the discharge capacity of the 50th cycle with respect to the discharge capacity of the first cycle. When the capacity retention rate is 95% or more, ◎ (extremely good), and when 90% or more and less than 95%, ○ ( Good), 80% or more and less than 90% was evaluated as Δ (possible), and less than 80% was evaluated as × (impossible). The evaluation results are shown in Table 8.

From Tables 7 and 8, Examples 6-1 to 6-25 (Examples 7-1 to 7-9) using the electrodes of the present invention are shown in Comparative Examples 6-1 to 6-. Compared with 8 (Comparative Example 7-1 to Comparative Example 7-2) and Reference Example 6-4 (Reference Example 7-1), the discharge voltage, discharge capacity characteristics, and capacity retention rate after 50 cycles are also better. It was a good result.
From Examples 6-1 to 6-4 and Comparative Examples 6-1 to 6-4, especially when the first kind of conductive auxiliary agent and the second kind of conductive auxiliary agent are used in a specific composition ratio. It turned out that good results can be obtained. Further, when the first kind of conductive auxiliary agent is used after performing dispersion treatment from Examples 6-5 to 6-7, Comparative Example 6-1 and Comparative Examples 6-5 to 6-7. The dispersion treatment state of the conductive auxiliary agent is particularly important, and good results cannot be obtained with the first type of conductive auxiliary agent alone, and good characteristics can be obtained by keeping the average dispersed particle size large. I found that I could do it.

On the other hand, from Reference Example 6-1 to Reference Example 6-3, when the ratio of the electrode active material is low and the conductive auxiliary agent is sufficient, the first type of conductive auxiliary agent and the second type of conductive auxiliary agent are used alone. The results are the same as when used. It can be inferred that the difference in conductivity did not appear in any of the examples because the amount of the conductive auxiliary agent required for conducting the conduction between the electrode active materials was sufficient. The effect of the present invention can be particularly remarkable in a design in which the ratio of the electrode active material is high and the ratio of the conductive auxiliary agent is limited.

Further, from Examples 6-17 to 6-24 and Reference Example 6-4, and from Examples 7-3 to 7-9 and Reference Example 7-1, electrodes prepared using a dispersant were used. It was found that the smaller the compounding ratio of the dispersant in the mixture layer, the better the result. It is desirable that the compounding ratio of the dispersant is as small as possible in the process of producing the conductive auxiliary agent dispersion liquid, the coatability of the coating liquid for electrodes, and the adhesion of the coating film, and when it exceeds 0.5%. It was found that the cycle characteristics were significantly deteriorated.

Further, in particular, in the electrode mixture layer prepared using a dispersant from Examples 6-17 to 6-21, 6-22 to 6-24, and Reference Example 6-4. Was found to be greatly affected by not only the compounding ratio of the dispersant in the mixture layer but also the total surface area b of the conductive auxiliary agent and the electrode active material. When comparing the discharge capacity characteristics of Examples 6-23 and 6-24 in 2C and 3C, the results of Example 6-23 were better in the entire measurement region, although there was a slight difference. .. Even when the dispersants are blended in the same ratio, the larger the total surface area b, the smaller the influence of the dispersants on the battery characteristics.
Using the first type of conductive auxiliary agent, which is difficult to disperse, it is necessary to use a dispersant in order to obtain a conductive auxiliary agent dispersion liquid with high concentration and excellent workability and a coating liquid for electrodes. It was found that the effect on the battery characteristics when the electrode mixture layer with a small compounding ratio was used differs greatly depending on the materials constituting the mixture layer and their ratios.

Claims (19)

A conductive auxiliary agent dispersion liquid containing at least two different carbon materials as a conductive auxiliary agent and water as a solvent. The first type of conductive auxiliary agent has an average primary particle diameter of 20 to 50 nm and a BET specific surface area of 300 to 300. 1400m ² / g, average dispersed particle diameter (cumulative 50% particle diameter) 200-2500nm, the second type of conductive auxiliary agent has an average primary particle diameter 20-70nm, BET specific surface area 10-200m ² / g, average dispersed particle diameter. (Cumulative 50% particle size) is 200 to 2400 nm, and the mass ratio of the first type of conductive auxiliary agent to the second type of conductive auxiliary agent is 20 to 80:80 to 20. Dispersion liquid. The first type of conductive auxiliary agent and the second type of conductive auxiliary agent are carbon black, and the mass ratio of the first type of conductive auxiliary agent to the second type of conductive auxiliary agent is 35 to 65:65 to 35. The conductive auxiliary agent dispersion liquid according to claim 1. The first kind of conductive auxiliary agent is hollow carbon black, and the average dispersed particle diameter (cumulative 50% particle diameter) of the first kind of conductive auxiliary agent is 200 to 1500 nm, according to claim 1 or 2. Conductive aid dispersion. The average dispersed particle size (cumulative 50% particle size) of the first type of conductive auxiliary agent is 200 to 1500 nm, and the average dispersed particle size (cumulative 50% particle size) of the second type conductive auxiliary agent is 800 to 2400 nm. The conductive auxiliary agent dispersion liquid according to any one of claims 1 to 3. The conductive auxiliary agent dispersion liquid according to any one of claims 1 to 4, further comprising a dispersant. The conductive auxiliary agent dispersion liquid according to any one of claims 1 to 5, further comprising at least one of a water-soluble polymer (A) or a resin fine particle (B) as a binder as a component. A coating liquid for an electrode, which comprises the conductive auxiliary agent dispersion liquid according to claim 6 and further contains one or more kinds of electrode active materials selected from the group consisting of lithium iron phosphate and lithium titanate as electrode active materials. And,
The coating liquid for electrodes may further contain an additive, and when the amount of all solid components contained in the coating liquid for electrodes is 100 parts by mass, the electrode active material is 90 parts by mass or more and 94 parts by mass. The amount of the conductive auxiliary agent is 3 parts by mass or more and 7 parts by mass or less, the amount of the binder is 2.5 parts by mass or more and 5 parts by mass or less, and the amount of the additive is 0 parts by mass or more and 0.5 parts by mass or less (however, the binder). And the total amount of additives is 5 parts by mass or less), which is a coating liquid for electrodes. The coating liquid for an electrode according to claim 7, wherein the average particle size of the electrode active material is 0.2 to 6 μm. In addition to the conductive additive dispersion liquid according to claim 6, Li (Ni _x M1 _y M2 _z ) O ₂ (x = 0.3 to 0.9, y = 0.01 to 0.69, y = 0.01 to 0.69, as an electrode active material, z = 0.01 to 0.69, x + y + z = 1. M1 and M2 are elements selected from the group consisting of Al, Ti, Mn, Fe and Co, respectively, and M1 and M2 are different elements), and manganese. An electrode coating liquid containing one or more electrode active materials selected from the group consisting of lithium acid acid.
The coating liquid for electrodes may further contain an additive, and when the amount of all solid components contained in the coating liquid for electrodes is 100 parts by mass, the electrode active material is 94 parts by mass or more and 98 parts by mass or more. By mass or less, conductive aid is 1 part by mass or more and 4 parts by mass or less, the amount of binder is 1 part by mass or more and 4 parts by mass or less, and the amount of additive is 0 parts by mass or more and 0.5 parts by mass or less (however, added with the binder). A coating liquid for electrodes, characterized in that the total amount of the agents is 4 parts by mass or less). The coating liquid for an electrode according to claim 9, wherein the electrode active material has an average particle size of 1 to 15 μm. The electrode coating according to any one of claims 7 to 10, wherein the first kind of conductive auxiliary agent is 25 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the total amount of the binder and the additive. liquid. The additive is a dispersant, and when the amount of all solid components contained in the coating liquid for electrodes is 100 parts by mass, the dispersant is 0.02 parts by mass or more and 0.5 parts by mass. The coating liquid for electrodes according to any one of claims 7 to 11. The first type of conductive auxiliary agent and the second type of conductive auxiliary agent are carbon black, respectively, and the amount of all solid components contained in the electrode coating liquid is 100 g, the first type of conductive auxiliary agent and the second type of conductive auxiliary agent. And when the sum of the products of the amount of the electrode active material and the specific surface area of each is the total surface area bm ² , the value of (amount of additive / total surface area b) is 0.00005 ≦ (amount of additive / total surface area). b) ≤ 0.00045
The coating liquid for an electrode according to any one of claims 7 to 12, which is characterized by satisfying the above conditions.
(The total surface area b is (the amount of the first type of conductive auxiliary agent x the specific surface area of the first type of conductive auxiliary agent + the amount of the second type of conductive auxiliary agent x the specific surface area of the second type of conductive auxiliary agent + the electrode active material. Calculated as amount x specific surface area of electrode active material x 0.2)) A battery electrode mixture layer formed by applying the electrode coating liquid according to any one of claims 7 to 13. A lithium ion secondary battery comprising a positive electrode having a positive electrode mixture layer on the current collector, a negative electrode having a negative electrode mixture layer on the current collector, and an electrolyte containing lithium, at least of the positive electrode and the negative electrode. One is a lithium ion secondary battery provided with the battery electrode mixture layer according to claim 14. (I) After the first kind of conductive auxiliary agent is dispersed and treated with a media mill, further
(II) The conductive auxiliary according to any one of claims 1 to 6, wherein the second kind of conductive auxiliary agent is added and dispersed treatment is performed with mixers operated under the condition of a shear rate of 15000 s ^-1 or more. Method for producing agent dispersion. (I) Disperse the dispersion liquid of the first kind of conductive auxiliary agent and the dispersion liquid of the second kind of conductive auxiliary agent by dispersion treatment with mixers operated under the condition of shear rate of 15000s ^-1 or more, or by using a media mill. The process of making each by processing,
(Ii) A step of mixing the above two types of conductive auxiliary agent dispersions,
The method for producing a conductive auxiliary agent dispersion liquid according to any one of claims 1 to 6, wherein the conductive auxiliary agent is produced. Using a mixer or media mill that operates the first type of conductive auxiliary agent and the second type of conductive auxiliary agent at the same time under the condition of shear rate of 15000s ^-1 or more, the average dispersed particle size of the first type of conductive auxiliary agent. Manufactured through the same dispersion treatment step as when the (cumulative 50% particle size) is 200 to 2500 nm and the average dispersed particle size (cumulative 50% particle size) of the second type of conductive auxiliary agent is 200 to 2400 nm. The method for producing a conductive auxiliary agent dispersion liquid according to any one of claims 1 to 6, wherein the method is characterized by the above-mentioned method. This is a method of producing a coating liquid for electrodes through a step of simultaneously dispersing a conductive auxiliary agent and an electrode active material in a solvent. The conductive auxiliary agent is dispersed alone in a solvent to treat the first type of conductive auxiliary agent. The same dispersion treatment step as when the average dispersed particle size (cumulative 50% particle size) is 200 to 2500 nm and the average dispersed particle size (cumulative 50% particle size) of the second type of conductive auxiliary agent is 200 to 2400 nm. The method for producing an electrode coating liquid according to any one of claims 7 to 13, wherein the coating liquid is produced.