WO2019132036A1 - Positive electrode mixture paste for lithium ion battery - Google Patents

Abstract

This positive electrode mixture paste for a lithium ion battery contains a positive electrode active substance, a conductive material, a binder, an organic polymer, and a solvent. The organic polymer, when the concentration thereof in a solvent is 0.001-3 mass%, exhibits stringiness in the solvent. The content of the organic polymer with respect to the total solid amount of the positive electrode mixture paste is preferably 0.001-0.1 mass%. The weight average molecular weight of the organic polymer is preferably 2.2- 30 million.

Description

Positive mix paste for lithium ion battery

The present invention relates to a positive electrode mixture paste for lithium ion battery and a method for producing the same, a lithium ion battery electrode and a lithium ion battery including a positive electrode mixture layer manufactured using the positive electrode mixture paste for lithium ion battery, and The present invention relates to a method for improving the storage stability of a positive electrode material mixture paste for lithium ion batteries.

Lithium ion batteries have higher energy density per unit weight and volume than lead storage batteries and nickel hydrogen batteries, and so contribute to the downsizing and weight reduction of mounted electronic devices. In recent years, hybrid cars and electric cars have been widely used as an approach for zero emission of cars, and the performance improvement of lithium ion batteries is important for improving the fuel efficiency and extending the driving distance.

A lithium ion battery generally has a structure in which a non-aqueous electrolytic solution is filled in a three-layer structure of a positive electrode, a separator, and a negative electrode. The positive electrode and the negative electrode are manufactured, for example, by coating a current collector with a mixture paste in which an active material, a conductive material, and a binder are mixed. At present, an aqueous process in which an aqueous slurry (mixture paste) is coated and dried on a copper foil serving as a current collector is mainly used as a method of manufacturing a negative electrode, and an organic method such as N-methylpyrrolidone is used as a method of manufacturing a positive electrode. A non-aqueous process in which a positive electrode mixture paste is produced using a solvent and applied to an aluminum foil serving as a current collector is the mainstream.

However, the positive electrode mixture paste may gradually lose its fluidity, and may have problems such as thickening and gelation. When the positive electrode mixture paste loses its fluidity, it not only becomes difficult to obtain a uniform coating thickness, but in some cases, it can not be applied and leads to waste of material. In particular, lithium-nickel transition metal complex oxides show this problem remarkably.

In order to solve this problem, for example, Patent Document 1 discloses a technology for suppressing the gelation of the positive electrode mixture paste by preparing the positive electrode mixture paste so as not to show strong alkalinity even when dispersed in water. Etc. are disclosed.

Japanese Patent Laid-Open No. 2000-90917

However, preparing the positive electrode material mixture paste so as not to show strong alkalinity by the method described in Patent Document 1 requires not only strict pH control but also dispersing the positive electrode active material in water once, A process of filtering out the dispersion liquid and taking out the positive electrode active material and drying it is necessary, which causes the complexity of the operation and the reduction of the yield. Moreover, there is also a possibility that performance degradation of the positive electrode active material itself may be caused by performing the above-mentioned treatment.

The present invention provides a positive electrode material mixture positive electrode material mixture paste for lithium ion batteries in which storage stability is improved by suppressing thickening and gelation by a simple method.

The present invention includes, in one aspect, a positive electrode active material, a conductive material, a binder, an organic polymer, and a solvent, wherein the organic polymer has a concentration of 0.001% by mass to 3% by mass. The present invention relates to a positive electrode mixture paste for a lithium ion battery, which is an organic polymer exhibiting spinnability.

The present invention, in another aspect, is a method for producing a positive electrode mixture paste for lithium ion batteries, comprising the steps of mixing a positive electrode active material, a conductive material, a binder, an organic polymer, and a solvent, The polymer relates to a method for producing a positive electrode mixture paste for lithium ion batteries, which is an organic polymer exhibiting spinnability in the solvent having a concentration of 0.001% by mass to 3% by mass.

The present invention, in still another aspect, is a method for improving the storage stability of a positive electrode material mixture paste for lithium ion batteries containing a positive electrode active material, a conductive material, a binder, and a solvent, wherein the positive electrode mixture paste for lithium ion batteries And a step of mixing the positive electrode active material, the conductive material, the binder, the organic polymer, and the solvent in the production process, wherein the concentration of the organic polymer is 0.001% by mass or more and 3% by mass or less The present invention relates to a method for improving the storage stability of a positive electrode material mixture paste for a lithium ion battery, which is an organic polymer exhibiting spinnability in the solvent.

The present invention relates, in yet another aspect, to a lithium ion battery electrode including a positive electrode mixture layer formed using the positive electrode mixture paste for a lithium ion battery of the present invention.

In still another aspect, the present invention relates to a lithium ion battery including a positive electrode mixture layer formed using the positive electrode mixture paste for a lithium ion battery of the present invention.

According to the present invention, using the positive electrode mixture paste for lithium ion batteries and the positive electrode mixture paste for lithium ion batteries in which storage stability is improved by suppressing thickening and gelation by a simple method The electrode for lithium ion batteries and lithium ion batteries which were produced can be provided. Moreover, the storage stability improvement method of the positive electrode mixture paste for lithium ion batteries can be provided.

The present invention is based on the finding that when the positive electrode mixture paste for lithium ion batteries contains an organic polymer exhibiting spinnability under predetermined conditions, thickening and gelation are suppressed.

That is, in one embodiment, the present invention is a positive electrode mixture paste for a lithium ion battery, comprising a positive electrode active material, a conductive material, a binder, an organic polymer, and a solvent, wherein the organic polymer has a concentration of A positive electrode for a lithium ion battery, which is an organic polymer exhibiting spinnability in the above-mentioned solvent having a content of 0.001% by mass or more and 3% by mass or less (hereinafter sometimes abbreviated as “spinky organic polymer”) The present invention relates to a mixture paste (hereinafter may be abbreviated as “positive electrode mixture paste”). The phrase "the organic polymer is spiny in a solvent having a concentration of 0.001% by mass to 3% by mass" means that the concentration of the organic polymer in the solvent is 0.001 It means that the solution which is concentration of mass% or more and 3 mass% or less exhibits spinnability.
More specifically, when the solvent is water, the organic polymer exhibits spinnability in an aqueous solution having a concentration of 0.001% by mass to 3% by mass and a liquid temperature of 25 ° C. “The organic polymer is an organic polymer exhibiting spinnability in an aqueous solution having a concentration of 0.001% by mass to 3% by mass and a liquid temperature of 25 ° C.” It means that an aqueous solution having a concentration of 0.001% by mass or more and 3% by mass or less and a liquid temperature of 25 ° C. exhibits spinnability.
In addition, when the solvent is N methyl pyrrolidone, the organic polymer is an organic polymer exhibiting spinnability in an N methyl pyrrolidone solution having a concentration of 0.001% by mass to 3% by mass and a liquid temperature of 25 ° C. It is a polymer, and “the organic polymer is an organic polymer exhibiting spinnability in an N-methylpyrrolidone solution having a concentration of 0.001% to 3% by mass and a liquid temperature of 25 ° C.”, This means that the N-methylpyrrolidone solution having a concentration of 0.001% by mass to 3% by mass and a liquid temperature of 25 ° C. exhibits spinnability.

Although the details of the mechanism of the effect expression of the present invention are not clear, the following can be presumed. In the present invention, by containing the spinnable organic polymer in the positive electrode mixture paste, the spinnable organic polymer forms a polymer network, for example, by interaction with water as a solvent (for example, hydrogen bond). By confining water and suppressing the reaction between water and an alkaline component such as LiO ₂ contained in the positive electrode active material lithium metal composite oxide, it becomes possible to suppress thickening and gelation, It is considered that the stability is improved. Even when the solvent is N methyl pyrrolidone, the interaction between a trace amount of water contained in N methyl pyrrolidone and the spinnable organic polymer enables suppression of thickening and gelation, and storage stability Is considered to be an improvement. As described above, since thickening and gelation of the positive electrode mixture paste are suppressed, the dispersibility of solid components such as the positive electrode active material and the conductive material in the positive electrode mixture paste is improved, so that uniform positive electrode synthesis is achieved. It becomes possible to form an agent layer. Therefore, in one embodiment, reduction in the initial capacity of the battery can also be suppressed. In one embodiment, it is also possible to improve the concentration of solid content in the positive electrode mixture paste. According to the present invention, the storage stability of the positive electrode mixture paste can be improved by a simple method of adding and mixing a spinnable organic polymer in the production process of the positive electrode mixture paste. Therefore, when the positive electrode material mixture paste of the present invention is used for producing a lithium ion battery electrode (positive electrode), it is considered that cost reduction can be achieved in the production of a lithium ion battery. In one embodiment, the solid content of the positive electrode mixture paste can be increased, so the amount of solvent such as N-methylpyrrolidone can be reduced, and the energy required for drying to remove it can be reduced. Cost reduction can be achieved. However, these are only estimates, and the present invention is not interpreted as being limited to these mechanisms.

The positive electrode material mixture paste of the present invention contains a positive electrode active material, a conductive material, a binder, a spinnable organic polymer, a solvent, and other components added as necessary. The mass ratio of the positive electrode active material, the conductive material, and the binder (binder) contained in the positive electrode mixture paste of the present invention may be the same as that of a conventionally known battery, and can be arbitrarily adjusted according to the use suitability of the battery. Examples of the other components include thickeners, reinforcing materials, antioxidants, additives having a function of suppressing the decomposition of the electrolyte, and the like, and these other components may be known ones. Can. Examples of the thickener include polysaccharide thickeners, alginic acid, carboxymethylcellulose, starch, polyacrylic acid, polyvinyl alcohol, polyvinyl pyrrolidone and the like.

[Positive electrode active material]
In recent years, a highly alkaline positive electrode active material containing a large amount of nickel and manganese has come to be used for the purpose of obtaining a high capacity lithium ion secondary battery. When such a positive electrode active material is used, there is a problem that the positive electrode mixture paste gradually loses fluidity, thickens, and gels. When such a positive electrode active material is used, the present invention can be effectively utilized.
The positive electrode active material may be any active material capable of inserting and extracting lithium and capable of charge and discharge reaction, for example, LiCoO ₂ , LiNiO ₂ , Li ₂ MnO ₄ , Li rich type (Li (Li (Li (Li (Li Examples thereof include lithium metal complex oxides such as _x Me _1-x ) O ₂ (Me = Co, Ni, Mn), etc. These compounds may be partially element-substituted, in particular, LiO ₂ etc. When using a lithium metal complex oxide (LiNiO ₂ system) mainly containing LiNiO ₂ containing a large amount of alkali component or a lithium metal complex oxide mainly containing Li-rich type as a positive electrode active material, particularly lithium nickel containing in the case of using a composite oxide as a positive electrode active material, the present invention can be effectively utilized. for example, lithium metal complex mainly composed of LiNiO ₂ type or Li-rich type as a positive electrode active material When a positive electrode mixture paste is prepared using an oxide and water as the solvent, the elution of LiOH is strong, and the positive electrode mixture paste exhibits strong alkalinity of about pH 12, so that the present invention can be effectively utilized. The positive electrode active material is used as particulate matter, and the average particle diameter thereof can be, for example, 2 μm or more and 40 μm or less.

The content of the positive electrode active material in the positive electrode mixture paste of the present invention is preferably 80% by mass or more, more preferably 90% by mass or more, from the viewpoint of increasing the capacity with respect to the total solid content of the positive electrode mixture paste. And, from the viewpoint of improving the binding strength of the positive electrode mixture layer to the current collector, it is preferably 99% by mass or less, more preferably 98% by mass or less.

[Conductive material]
The conductive material is for efficiently performing charge / discharge reaction and enhancing the electrical conductivity, and examples thereof include carbon materials such as acetylene black, ketjen black, graphite, CNT (carbon nanotube), etc. It can be used alone or in combination of two or more.

The content of the conductive material in the positive electrode mixture paste of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, from the viewpoint of improving the conductivity relative to the total solid content of the positive electrode mixture paste. And from the viewpoint of improving the battery capacity, it is preferably 10% by mass or less, more preferably 5% by mass or less.

[binder]
The binder has an adhesive function between the positive electrode mixture layer and the current collector, and when the solvent is water, for example, sodium polyacrylate, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and styrene butadiene rubber (SBR), carboxyl cellulose etc. are mentioned, These can be used individually or in mixture of 2 or more types. Among them, sodium polyacrylate is preferable from the viewpoint of the improvement of the electrochemical stability and the improvement of the binding strength between the positive electrode mixture layer and the current collector. When the solvent is N methyl pyrrolidone, for example, polyvinylidene fluoride (PVDF) is generally used as a binder. PVDF is prone to gelation due to the alkali component. In addition, since N-methylpyrrolidone contains a trace amount of water, the binder and the alkali component derived from the water and the positive electrode active material easily cause gelation of the binder. Therefore, the present invention is remarkably effective in a system using PVDF as a binder.

The content of the binder in the positive electrode mixture paste of the present invention is preferably 0.5% by mass or more from the viewpoint of improving the binding strength between the positive electrode mixture layer and the current collector with respect to the total solid content of the positive electrode mixture paste. More preferably, it is 1% by mass or more, and from the viewpoint of improving the battery capacity, it is preferably 10% by mass or less, more preferably 5% by mass or less.

[solvent]
[water]
In recent years, from the viewpoint of reducing the cost of raw materials and reducing the environmental load, it has been desired to adopt an aqueous process also for the preparation of a positive electrode. In one embodiment, the positive electrode mixture paste of the present invention contains water as a dispersion medium capable of dispersing the positive electrode active material and the conductive material, and as a solvent capable of dissolving the binder and the spinnable organic polymer. When water is used as a solvent, a part of lithium (Li) ions contained in the positive electrode active material is eluted and the positive electrode mixture paste becomes alkaline, gradually losing its fluidity, thickening, and causing gelation. It occurs. However, as described above, since the positive electrode mixture paste of the present invention contains a specific organic polymer, thickening and gelation are suppressed. The water contained in the positive electrode mixture paste of the present invention is preferably pure water or purified water. The content of water in the positive electrode mixture paste of the present invention is preferably 30 parts by mass or more, relative to 100 parts by mass of the total solid content of the positive electrode mixture paste, from the viewpoint of improving the coating properties of the positive electrode mixture paste. More preferably, it is 40 parts by mass or more, and from the same viewpoint, it is preferably 80 parts by mass or less, more preferably 70 parts by mass or less.

[N methyl pyrrolidone]
In another embodiment, the positive electrode material mixture paste of the present invention is N methyl as a dispersion medium capable of dispersing the positive electrode active material and the conductive material, and as a solvent capable of dissolving the binder and the spinnable organic polymer. Contains pyrrolidone. The content of N methyl pyrrolidone in the positive electrode mixture paste of the present invention is preferably 10% by weight or more, more preferably 20% by weight or more, from the viewpoint of improving the coatability of the positive electrode mixture paste. Preferably, it is 50% by weight or less, more preferably 40% by weight or less.

[Spring thread organic polymer]
The positive electrode mixture paste of the present invention contains a spinnable organic polymer from the viewpoint of improving storage stability or from the viewpoint of improving storage stability and increasing the solid content of the positive electrode mixture paste.

[Definition of spinnability]
Here, the spinnability is a so-called "threading" property in which the stretching property of the object appears, and for example, "natto threading" etc. can be mentioned as a prominent example. The spinnability is the property of exhibiting a continuous thread-like structure without breaking up and forming droplets when the liquid composition is dropped at a low speed or stretched while holding one end thereof, for example, “mucus of animals and plants "Yarning" etc. are mentioned as an example. Incidentally, spinnability is one of the elastic relaxation phenomena of liquid compositions, and it is known that surface tension and viscosity are physical properties completely independent of each other. Here, even if it is a normal polymer solution, for example, if the concentration is a high concentration of 100 g / L or more, the above-mentioned spinnable behavior is often exhibited, but the system in question is extremely high in viscosity and the polymer solution Are significantly less fluid. The spinnability referred to in the present invention refers to spinnability in which aqueous liquid compositions of special organic polymers can be developed while maintaining high fluidity under extremely dilute concentrations.

[Definition of a spinnable organic polymer]
The spinnable organic polymer referred to in the present invention is an organic polymer in which a solution obtained by dissolving a spinnable organic polymer in a solvent exhibits the above spinnability. The spinnable organic polymer is generally different from a so-called "thickening organic polymer" in which a high molecular weight organic polymer is expressed. When the solvent is water, the solution is an aqueous solution, and when the solvent is N methyl pyrrolidone, the solution is an N methyl pyrrolidone solution.
In the present invention, a spinnable organic polymer is, for example, an organic polymer exhibiting spinnability in an aqueous solution or N methyl pyrrolidone solution having a concentration of 3% by mass or less, preferably an aqueous solution or its concentration at a concentration of 1% by mass or less. It is an organic polymer exhibiting spinnability in an N-methylpyrrolidone solution, more preferably an organic polymer exhibiting spinnability in an aqueous solution or N-methylpyrrolidone solution having a concentration of 0.5% by mass or less. And it is an organic polymer which exhibits spinnability in an aqueous solution or N methyl pyrrolidone solution whose concentration is 0.001 mass% or more, preferably in an aqueous solution or N methyl pyrrolidone solution whose concentration is 0.01 mass% or more. It is an organic polymer exhibiting spinnability.

In one embodiment of the present invention containing water as the solvent, the spinnability of the organic polymer is determined by the following method. Using an organic polymer aqueous solution obtained by dissolving 0.5 parts by weight of an organic polymer in 99.5 parts by weight of purified water, it is judged by a method according to the following [Spinability evaluation method], and has spinnability And spinnable organic polymer.
In another embodiment of the present invention containing N-methyl pyrrolidone as the solvent, the presence or absence of spinnability of the organic polymer is determined by the following method. Using an N-methylpyrrolidone solution of an organic polymer obtained by dissolving 1 part by weight of an organic polymer in 99 parts by weight of N-methylpyrrolidone, it is determined by a method according to the following [Spinability evaluation method] and has spinnability In the case, a spinnable organic polymer is used.

[Method for determining spinnability]
When the dropping operation is gently performed from a Pasteur pipette (glass such as ASAHITECHNO GLASS, IK-PAS-5P) with an inner diameter of 1 mm of tip, the aqueous solution or N-methylpyrrolidone solution in which a thread is twisted exhibits spinnability in the present invention Make an aqueous solution or N methyl pyrrolidone solution. The long threading solution is made into an aqueous solution having strong (or high) spinnability or N-methylpyrrolidone solution. The aqueous solution or N methyl pyrrolidone solution is well stirred at 25 ° C. and used for determination, and at least the tip of the Pasteur pipette is separated by 5 mm from the dropping point to perform the dropping operation. With regard to the aqueous solution having a strong spinnability or the N-methylpyrrolidone solution, it is easier to confirm if the dropping operation is performed from a higher position. The dropping operation may be performed a plurality of times to confirm. Usually, the "yarn" confirmed during the dropping operation is thinner than 1 mm.

The higher the spinnability imparting effect, that is, the higher the spinnability of the organic polymer, the lower the concentration, and the intended storage stability is improved, or the storage stability is improved, and the solid content in the positive electrode material mixture paste High concentration of

The spinnable organic polymer includes cross-linked polymers and non-cross-linked polymers. Among them, non-cross-linked polymers have higher spinnability and are preferred in the present invention.

In one embodiment of the present invention comprising water as a solvent, the spinnable organic polymer is, for example, sulfonic acid group (—SO ₂ —OH), sulfuric acid group (—O—SO ₂ —OH) and salts thereof The polymer A containing the structural unit derived from the ethylenically unsaturated monomer a1 which has at least 1 sort (s) of groups chosen from group, or a polyethylene oxide (PEO) is mentioned. These can be used 1 type or in combination of 2 or more types.

As the monomer a1, for example, 2- (meth) acryloyloxyethane sulfonic acid, 2- (meth) acryloyloxypropane sulfonic acid, 2- (meth) acrylamido-2-alkyl (1 to 4 carbon atoms) propane sulfone Monomers such as acid, vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, vinyl sulfuric acid and the like can be mentioned. Among them, 2- (meth) acryloyloxyethanesulfonic acid, 2- (meth) acryloyloxypropanesulfonic acid, 2- (meth) acrylamido-2-alkyl (carbon) because of high polymerizability and easy to obtain high molecular weight. The number 1 to 4) propane sulfonic acid and styrene sulfonic acid are preferable, 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and styrene sulfonic acid are more preferable, and from the viewpoint of improving the storage stability of the positive electrode mixture paste And AMPS are more preferred. These constituent monomers may be used in the acid form, or some or all of the sulfonic acid group and / or the sulfuric acid group may be neutralized with a base to be used as a salt group.

As a counter ion which forms a salt type group of a sulfonic acid group or a sulfuric acid group, for example, metal ion, ammonium ion, alkyl or alkenyl ammonium ion having 1 to 22 carbon atoms in total, alkyl or alkenyl substitution having 1 to 22 carbon atoms There may be mentioned pyridinium ion, alkanol ammonium ion having 1 to 22 carbon atoms in total, alkali ion such as sodium ion, potassium ion or ammonium ion is preferable, and sodium ion and potassium ion are more preferable.

In the polymer A, the monomer a1 may be used alone or in combination of two or more types, and when the monomer a1 is two or more types, as the arrangement of the structural units derived from these constituent monomers, in particular, There is no limitation, and random arrangement, alternating arrangement, or block arrangement may be used.

The polymer A is preferably a copolymer of the monomer a1 and another polymerizable monomer from the viewpoint of improving the storage stability of the positive electrode mixture paste, and as the polymerizable monomer, it is preferably It is at least one monomer a2 selected from unsaturated carboxylic acids and salts thereof, more preferably at least one monomer a2 selected from ethylenically unsaturated carboxylic acids and salts thereof.

As the monomer a2, from the viewpoint of improving the storage stability of the positive electrode mixture paste, preferably (meth) acrylic acid [(meth) acrylic acid is acrylic acid (AA), methacrylic acid or a mixture thereof. ] And salts thereof, styrene carboxylic acid and salts thereof, maleic acid monomers [maleic anhydride, maleic acid, maleic acid monoester, and maleic acid monoamide or a mixture of two or more thereof] and salts thereof, and itacon It is an acid and its salt etc., and 1 or more types chosen from these can be used. Among these, (meth) acrylic acid and a salt thereof, styrenecarboxylic acid and a salt thereof are preferable, (meth) acrylic acid and a salt thereof are more preferable, and acrylic acid and a salt thereof are further preferable because copolymerization is easy. preferable. As a counter ion which forms a salt here, it is sufficient if it is the said counter ion.

When the polymer A is a copolymer containing a structural unit derived from the monomer a1 and a structural unit derived from the monomer a2, the structural unit derived from the monomer a1 in all the structural units in the polymer A The ratio of is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, from the viewpoint of improving the storage stability of the positive electrode mixture aqueous paste, and the spinnability is enhanced. From the viewpoint, it is preferably 99 mol% or less, more preferably 98 mol% or less, and still more preferably 96 mol% or less.

When the polymer A is a copolymer containing a structural unit derived from the monomer a1 and a structural unit derived from the monomer a2, the structural unit derived from the monomer a1 in all the structural units in the polymer A And the molar ratio of the structural unit derived from the monomer a2 (the structural unit derived from the monomer a1 / the structural unit derived from the monomer a2) is preferably from the viewpoint of improving the storage stability of the positive electrode mixture paste Is 3 or more, more preferably 4 or more, further preferably 9 or more, and preferably 99 or less, more preferably 50 or less, and still more preferably 24 or less from the viewpoint of enhancing spinnability.

In the polymer A, the arrangement of the structural unit derived from the monomer a1 and the structural unit derived from the monomer a2 is not particularly limited, and may be random arrangement, alternating arrangement, or block arrangement.

When the polymer A is a copolymer containing a structural unit derived from the monomer a1 and a structural unit derived from the monomer a2, it further includes a structural unit derived from another polymerizable monomer a3 Although the ratio of the structural unit derived from the monomer a3 in all the structural units in the polymer A is preferably 2 mol% or less, more preferably 1 mol% or less, still more preferably 0.5 mol% or less Still more preferably, it is 0 mol%.

Specifically, the spinnable organic polymer is preferably a homopolymer of PEO, a monomer a1, a salt thereof, a monomer a1 and a monomer, from the viewpoint of improving the storage stability of the positive electrode mixture paste. a copolymer selected from a2 and salts thereof, more preferably PEO, homopolymers of AMPS, salts thereof, copolymers of AMPS and AA, and salts thereof selected from salts thereof, More preferably, it is one or more selected from PEO, a copolymer of AMPS and AA, and a salt thereof, and improves the storage stability of the positive electrode mixture paste, suppresses the decrease in the initial capacity of the battery, and improves the maintainability of the discharge capacity. From the viewpoint, more preferably, it is PEO exhibiting high spinnability. When the spinnable organic polymer is a copolymer of AMPS and AA or a salt thereof, the ratio of the structural unit derived from AMPS to the total structural units constituting the spinnable organic polymer is the same as that of the positive electrode mixture paste. From the viewpoint of improving storage stability, it is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, and from the viewpoint of improving spinnability, preferably 99 mol% or less More preferably, it is 98 mol% or less, still more preferably 96 mol% or less.

The synthesis method of the polymer A is not particularly limited, and a known method can be selected. In the polymerization, hydrophilic polymers such as starch / cellulose, derivatives of starch / cellulose, polyvinyl alcohol, polyacrylic acid (salt), cross-linked polyacrylic acid (salt), hypophosphorous acid (salt), etc. Chain transfer agents may be added. When polymer A polymerizes a monomer unit mainly composed of at least one selected from AMPS and a salt thereof, bulk polymerization and precipitation polymerization can be performed, but it is possible to control performance and polymerization. From the viewpoint of easiness, it is preferable to carry out aqueous solution polymerization and reverse phase suspension polymerization by making the monomer unit water-soluble.

In synthesizing Polymer A, peroxide initiators such as potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide and the like may be used as a polymerization initiator, or 2, 2 Azo initiators such as' -azobis (2-amidinopropane) dihydrochloride may be used, or these may be used in combination with reducing agents such as sodium sulfite, sodium bisulfite, ferrous sulfate, L-ascorbic acid, etc. It may be used as a redox type initiator system. The polymerization may be initiated by irradiation with ultraviolet light, electron beam, γ-ray or the like. Activation energy etc. can be used. In addition, redox polymerization may be performed using a reducing agent such as sodium sulfite, sodium bisulfite, ferrous sulfate, L-ascorbic acid and the like in combination.

In another embodiment of the present invention including N methyl pyrrolidone as a solvent, the spinnable organic polymer is obtained from the viewpoint of improving the storage stability of the positive electrode mixture paste and increasing the solid content of the positive electrode mixture paste, The polymer is preferably a polymer containing a structural unit derived from ethylene oxide (EO), more preferably polyethylene oxide (PEO) exhibiting high spinnability.

The weight average molecular weight of the spinnable organic polymer is preferably 2.2 million or more, more preferably 2.5 million or more, still more preferably 3 million from the viewpoint of improving the storage stability of the positive electrode mixture paste and suppressing the decrease in initial capacity of the battery. From the above and from the same viewpoint, it is preferably 30 million or less, more preferably 20 million or less, and still more preferably 10 million or less. In addition, the weight average molecular weight of a spinnable organic polymer can be measured by the method as described in the below-mentioned Example.

In one embodiment of the present invention containing water as a solvent, the content of the spinnable organic polymer in the positive electrode mixture paste of the present invention is the storage stability of the positive electrode mixture paste with respect to the total solid content of the positive electrode mixture paste. From the viewpoint of improving the properties, it is preferably 0.001% by mass or more, more preferably 0.002% by mass or more, and from the viewpoint of suppressing the initial capacity reduction of the battery, preferably 0.1% by mass or less, more preferably It is 0.03 mass% or less.
In another embodiment of the present invention containing water as a solvent, the content of the spinnable organic polymer in the positive electrode mixture paste of the present invention is the content of the positive electrode mixture paste relative to the total solid content of the positive electrode mixture paste. From the viewpoint of improving storage stability, it is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, and from the viewpoint of suppressing the initial capacity decrease of the battery, preferably 0.1% by mass or less, more Preferably it is 0.03 mass% or less.

In one embodiment of the present invention containing water as a solvent, the pH at 25 ° C. of the positive electrode mixture paste of the present invention is preferably 7 or more, more preferably 10 or more, and further preferably from the viewpoint of suppressing the initial capacity decrease It is preferably 11 or more, and preferably 14 or less from the viewpoint of improving the storage stability of the positive electrode mixture paste. The pH of the positive electrode mixture paste can be measured by the method described in the examples.

The concentration of total solids in the positive electrode material mixture paste of the present invention is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 65% by mass or more, from the viewpoint of cost reduction in manufacturing lithium ion batteries. The content is more preferably 70% by mass or more, and preferably 90% by mass or less, and more preferably 80% by mass or less from the viewpoint of securing a good coating property of the paste.

[Method of producing positive electrode mixture paste]
The present invention relates, in one embodiment, to a method for producing a positive electrode mixture paste of the present invention (hereinafter sometimes referred to as “the method for producing the present invention”).

The manufacturing method of the present invention includes, in one embodiment, a step of mixing a positive electrode active material, a conductive material, a binder, an organic polymer, and a solvent,
The present invention relates to a method for producing a positive electrode material mixture paste for lithium ion battery, which is an organic polymer exhibiting spinnability in a solvent having a concentration of 0.001% by mass to 3% by mass.
In the production method of the present invention, the solvent is, for example, water, and the organic polymer has spinelability in an aqueous solution having a concentration of 0.001% by mass to 3% by mass and a liquid temperature of 25 ° C. It is an organic polymer that exhibits
In the production method of the present invention, the solvent is, for example, N methyl pyrrolidone, and the organic polymer has a concentration of 0.001 mass% or more and 3 mass% or less in an aqueous solution having a liquid temperature of 25 ° C. It is an organic polymer that exhibits threadability.

More specifically, the production method of the present invention includes the step of mixing the positive electrode active material, the conductive material, the binder, the spinnable organic polymer, and the solvent, and preferably, a solid content other than the spinnable organic polymer A step of adding a solution obtained by dissolving a spinnable organic polymer in a solvent is added to a mixture containing a solvent, for example, a mixture containing a positive electrode active material, a conductive material, a binder and a solvent. In the positive electrode material mixture paste of the present invention, for example, a conductive material and a solution obtained by dissolving a binder in a solvent are mixed and stirred until they become homogeneous to prepare a slurry [1] to prepare the slurry [1]. A positive electrode active material and a solvent are added, and the mixture is stirred until it becomes homogeneous to obtain a slurry [2]. A solution obtained by dissolving a spinnable organic polymer in a solvent is added to the slurry [2] and stirred until homogeneous. It can be obtained by It is not limited to the mixing of the respective components, the means of stirring the slurry [1] and the slurry [2]. For example, a self-revolving stirrer can be used.

The production method of the present invention includes, for example, a step of mixing a positive electrode active material, a conductive material, a binder, a spinnable organic polymer, and water, and from the viewpoint of increasing capacity, preferably other than spinnable organic polymer The method includes the step of adding an aqueous solution of a spinnable organic polymer to a mixture containing solid content and water, for example, a mixture containing a positive electrode active material, a conductive material, a binder and water. In the positive electrode material mixture paste of the present invention, for example, a conductive material and an aqueous solution of a binder are mixed and stirred until they become homogeneous to prepare a slurry [1], and a positive electrode active material and water are added to the slurry [1]. The mixture is stirred until it becomes homogeneous to obtain a slurry [2], and an aqueous solution of a spinnable organic polymer is added to the slurry [2], and the mixture can be obtained by stirring until it becomes homogeneous. It is not limited to the mixing of the respective components, the means of stirring the slurry [1] and the slurry [2]. For example, a self-revolving stirrer can be used.

The production method of the present invention includes, for example, a step of mixing a positive electrode active material, a conductive material, a binder, a spinnable organic polymer and N-methylpyrrolidone, and from the viewpoint of increasing the concentration, preferably a spinnable organic polymer A mixture containing solid content other than N methyl pyrrolidone, for example, a mixture containing a positive electrode active material, a conductive material, a binder, and N methyl pyrrolidone, an N methyl pyrrolidone solution (additive composition) of a spinnable organic polymer Including the step of adding. In the positive electrode material mixture paste of the present invention, for example, a conductive material and an N-methylpyrrolidone solution of a binder are mixed, and the mixture is stirred until it becomes homogeneous to prepare a slurry [1]. Add N-Methylpyrrolidone as necessary to the substance and stir until it becomes homogeneous to make a slurry [2], add N-methylpyrrolidone solution of spinnable organic polymer to the slurry [2] and stir until homogeneous It can be obtained by It is not limited to the mixing of the respective components, the means of stirring the slurry [1] and the slurry [2]. For example, a self-revolving stirrer can be used.

[Additive composition]
The present invention, in one embodiment, is an additive composition used for preparation of a positive electrode mixture paste. The additive composition comprises an organic polymer and N methyl pyrrolidone, wherein the organic polymer is dissolved in N methyl pyrrolidone. The content of the spinnable organic polymer in the additive composition is set so that, for example, the positive electrode material mixture paste of the present invention can be prepared by mixing with the above-mentioned slurry [2]. From the viewpoint of exhibiting high spinnability, the content is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and from the viewpoint of securing the solubility of the organic polymer, preferably 5% by mass or less More preferably, it is 3% by mass or less. The additive composition of the present invention may contain, as optional components, for example, a thickener, a reinforcing material, an antioxidant, an additive having a function of suppressing the decomposition of the electrolytic solution, etc., and these components. Any known one can be used. The amount of optional components in the additive composition is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 2% by mass or less, from the viewpoint of storage stability of the positive electrode mixture paste .
In addition, the present invention relates, in one embodiment, to the use of the additive composition of the present invention for the preparation of a positive electrode mixture paste for lithium ion batteries.

[How to improve storage stability]
The present invention relates, in one embodiment, to a method for improving the storage stability of the positive electrode material mixture paste of the present invention (hereinafter sometimes referred to as “the method for improving the storage stability of the present invention”).

The storage stability improvement method of the present invention is, in one embodiment, a method for improving the storage stability of a positive electrode material mixture paste for lithium ion batteries, which contains a positive electrode active material, a conductive material, a binder and a solvent.
Including a step of mixing a positive electrode active material, a conductive material, a binder, an organic polymer, and a solvent in the process of producing the positive electrode mixture paste,
The organic polymer is
The present invention relates to a method of improving the storage stability of a positive electrode material mixture paste for a lithium ion battery, which is an organic polymer exhibiting spinnability in a solvent having a concentration of 0.001% by mass to 3% by mass.
In the storage stability improving method of the present invention, the solvent is, for example, water, and the organic polymer is in an aqueous solution having a concentration of 0.001% by mass to 3% by mass and a liquid temperature of 25 ° C. It is an organic polymer exhibiting spinnability.
In the storage stability improving method of the present invention, the solvent is, for example, N methyl pyrrolidone, and the organic polymer is N having a concentration of 0.001% by mass to 3% by mass and a liquid temperature of 25 ° C. It is an organic polymer that exhibits spinnability in methyl pyrrolidone solution.

[Electrode for lithium ion battery]
The present invention relates, in one embodiment, to a lithium ion battery electrode (hereinafter also referred to as “the electrode of the present invention”) including a positive electrode mixture layer formed using the positive electrode mixture paste of the present invention. The electrode of the present invention can be produced by a known method for producing an electrode except that the positive electrode mixture paste of the present invention is used. For example, after the positive electrode mixture paste of the present invention is applied to a current collector and dried, It is obtained by processing according to a predetermined size by pressing accordingly. For the current collector, a conventionally known current collector can be used.

[Lithium ion battery]
The present invention relates, in one embodiment, to a lithium ion battery (hereinafter also referred to as "the battery of the present invention") including the electrode of the present invention.

The shape of the battery of the present invention may be any shape such as coin shape, cylindrical shape, square shape, and laminated shape.

The battery of the present invention can be manufactured by a known method for manufacturing a lithium ion battery except that the electrode of the present invention is used. As one embodiment of a method of manufacturing a lithium ion battery, for example, the electrode (positive electrode) of the present invention and a negative electrode are stacked via a separator, wound or stacked in a battery shape, and inserted into a battery container or a laminate container. And a method in which the container is filled with an electrolytic solution and sealed.

In one embodiment, the separator is a member having a function such as insulation between the positive electrode and the negative electrode, and further holding an electrolytic solution. As a separator, thin microporous membranes, such as polyethylene, a polypropylene, or those laminated products, can be used, for example.

As the electrolytic solution, usually, a solution in which an electrolyte is dissolved in an organic solvent can be used. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate and propylene carbonate; linear carbonates such as diethyl carbonate, dimethyl carbonate and methyl ethyl carbonate; and the like, and these may be used alone or in combination of two or more . The electrolyte refers to an ionic compound having a function of dissolving in an organic solvent to conduct electricity. As the electrolyte, for example, lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ CO ₂ , LiCl, LiBr, LiSCN, etc. alone or in combination of two or more You may use together.

The present application further discloses the following invention.
[1] containing a positive electrode active material, a conductive material, a binder, an organic polymer, and a solvent,
The positive electrode material mixture paste for lithium ion batteries, wherein the organic polymer is an organic polymer exhibiting spinnability in a solvent having a concentration of 0.001% by mass to 3% by mass.
[2] The content of the organic polymer relative to the total solid content of the positive electrode mixture paste is preferably 0.001% by mass or more, more preferably 0.002% by mass or more, and preferably 0.1 The positive electrode mixture paste according to the above [1], which is not more than mass%, more preferably not more than 0.03 mass%.
[3] The weight average molecular weight of the organic polymer is preferably 2.2 million or more, more preferably 2.5 million or more, still more preferably 3 million or more, and preferably 30 million or less, more preferably 20 million or less, furthermore The positive electrode mixture paste according to the above [1] or [2], which is preferably 10,000,000 or less.
[4] The positive electrode mixture paste according to any one of [1] to [3], wherein the solvent is preferably water.
[5] The pH of the positive electrode mixture paste at 25 ° C. is preferably 7 or more, more preferably 10 or more, still more preferably 11 or more, and preferably 14 or less. Positive electrode mixture paste.
[6] The organic polymer preferably has at least one group selected from the group consisting of sulfonic acid group (-SO ₂ -OH), sulfuric acid group (-O-SO ₂ -OH) and salts thereof. The positive electrode mixture paste according to any one of the above [1] to [5], which is one or more selected from polymer A containing a structural unit derived from the ethylenically unsaturated monomer a1 and polyethylene oxide.
[7] Preferably, the monomer a1 is 2- (meth) acryloyloxyethanesulfonic acid, 2- (meth) acryloyloxypropanesulfonic acid, 2- (meth) acrylamido-2-alkyl (having 1 to 6 carbon atoms) 4) At least one selected from propanesulfonic acid, vinylsulfonic acid, allylsulfonic acid, styrenesulfonic acid, vinylsulfuric acid and salts thereof, more preferably 2- (meth) acryloyloxyethanesulfonic acid, 2- (Meth) acryloyloxypropane sulfonic acid, 2- (meth) acrylamido-2-alkyl (1 to 4 carbon atoms) propane sulfonic acid, styrene sulfonic acid, and one or more selected from salts thereof, more preferably 2-acrylamido-2-methylpropane sulfonic acid, styrene sulfonic acid, and the like The positive electrode material mixture paste according to the above [6], which is one or more selected from the salts of the following, more preferably one or more selected from AMPS and salts thereof.
[8] A copolymer, wherein the polymer A contains a structural unit derived from at least one monomer a2 selected from unsaturated carboxylic acids and salts thereof, and a structural unit derived from the monomer a1 The positive electrode mixture paste according to the above [6] or [7].
[9] Monomer a2 is preferably one or more selected from (meth) acrylic acid, styrene carboxylic acid, maleic acid monomers, itaconic acid, and salts thereof, and more preferably (meth) acrylic acid. It is one or more selected from acid, styrene carboxylic acid, and these salts, more preferably, one or more selected from (meth) acrylic acid and its salt, still more preferably, selected from acrylic acid and its salt The positive electrode material mixture paste according to the above [8], which is one or more kinds.
[10] The molar ratio of the structural unit derived from the monomer a1 in the polymer A is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, and preferably The positive electrode material mixture paste according to the above [8] or [9], which is 99 mol% or less, more preferably 98 mol% or less, still more preferably 96 mol% or less.
[11] The molar ratio of the structural unit derived from the monomer a1 to the structural unit derived from the monomer a2 in all the structural units in the polymer A (structural unit derived from the monomer a1 / monomer a2 The constituent unit derived from “(3)” is preferably 3 or more, more preferably 4 or more, further preferably 9 or more, and preferably 99 or less, more preferably 50 or less, still more preferably 24 or less. The positive electrode mixture paste according to any one of [10] to [10].
[12] The organic polymer is preferably one or more selected from PEO, a homopolymer of monomer a1, a salt thereof, a copolymer of monomer a1 and monomer a2, and a salt thereof, Preferably, it is one or more selected from PEO, homopolymers of AMPS, salts thereof, copolymers of AMPS and AA, and salts thereof, more preferably PEO, copolymers of AMPS and AA, and salts thereof More preferably PEO, and more preferably
The monomer a1 is ethylenically unsaturated having at least one group selected from a sulfonic acid group (—SO ₂ —OH), a sulfuric acid group (—O—SO ₂ —OH) and a group in the salt form thereof. It is a monomer,
The positive electrode mixture paste according to any one of the above [1] to [5], wherein the monomer a2 is at least one monomer selected from unsaturated carboxylic acids and salts thereof.
[13] The positive electrode mixture paste according to any one of the above [1] to [3], wherein the solvent is preferably N methyl pyrrolidone.
[14] The positive electrode mixture paste according to the above [13], wherein the organic polymer is preferably a polymer containing a structural unit derived from ethylene oxide, more preferably polyethylene oxide.
[15] The positive electrode mixture paste according to any one of the above [1] to [14], wherein the positive electrode active material is preferably a lithium metal composite oxide, more preferably a lithium nickel-containing composite oxide .
[16] The concentration of total solids in the positive electrode mixture paste is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 65% by mass or more, and still more preferably 70% by mass or more. And the positive electrode material mixture paste in any one of said [1] to [15] which is preferably 90 mass% or less, more preferably 80 mass% or less.
[17] An electrode for a lithium ion battery, including a positive electrode mixture layer formed using the positive electrode mixture paste according to any one of the above [1] to [16].
[18] A lithium ion battery including a positive electrode mixture layer formed using the positive electrode mixture paste according to any one of the above [1] to [16].
[19] An organic polymer and N methyl pyrrolidone, wherein the organic polymer is dissolved in N methyl pyrrolidone,
The additive composition, wherein the organic polymer exhibits spinnability in an N-methylpyrrolidone solution having a concentration of 0.001% by mass to 3% by mass and a liquid temperature of 25 ° C.
[20] Use of the additive composition according to the above [19] for the preparation of a positive electrode material mixture paste for lithium ion batteries.
[21] including the step of mixing the positive electrode active material, the conductive material, the binder, the organic polymer, and water,
The method for producing a positive electrode mixture paste for lithium ion battery, wherein the organic polymer is an organic polymer that exhibits spinnability in an aqueous solution having a concentration of 0.001% to 3% by mass and a liquid temperature of 25 ° C. .
[22] The method for producing a positive electrode material mixture paste for a lithium ion battery according to [21], wherein an aqueous solution of an organic polymer is added to a mixture containing a positive electrode active material, a conductive material, a binder and water in the step.
[23] A method for improving the storage stability of a positive electrode material mixture paste for a lithium ion battery, comprising a positive electrode active material, a conductive material, a binder, and water,
Including a step of mixing a positive electrode active material, a conductive material, a binder, an organic polymer, and water in the process of producing the positive electrode mixture paste,
The storage stability of a positive electrode material mixture paste for lithium ion battery, wherein the organic polymer is an organic polymer exhibiting spinnability in an aqueous solution having a concentration of 0.001% to 3% by mass and a liquid temperature of 25 ° C. How to improve.
[24] The storage stability of the positive electrode material mixture paste for a lithium ion battery according to the above [23], wherein an aqueous solution of an organic polymer is added to a mixture containing a positive electrode active material, a conductive material, a binder and water in the step How to improve.
[25] including the step of mixing the positive electrode active material, the conductive material, the binder, the organic polymer, and N-methylpyrrolidone,
The organic polymer is
A method for producing a positive electrode mixture paste for lithium ion battery, which is an organic polymer exhibiting spinnability in an N-methylpyrrolidone solution having a concentration of 0.001% by mass to 3% by mass and a solution temperature of 25 ° C. .
[26] A method for improving the storage stability of a positive electrode material mixture paste for a lithium ion battery, comprising a positive electrode active material, a conductive material, a binder, and water,
Including the step of mixing the positive electrode active material, the conductive material, the binder, the organic polymer, and N-methylpyrrolidone in the production process of the positive electrode mixture paste,
The organic polymer is
Storage stability of positive electrode material mixture paste for lithium ion battery, which is an organic polymer exhibiting spinnability in N methyl pyrrolidone solution having a concentration of 0.001% by mass to 3% by mass and a solution temperature of 25 ° C. How to improve.

Hereinafter, the present disclosure will be described by way of examples, but the present disclosure is not limited thereto.

[Definition of weight average molecular weight]
The weight average molecular weight of the organic polymer can be determined by gel permeation chromatography (GPC) measurement under the following measurement conditions. Polyethylene oxide (PEO) is used as a standard sample, and the weight average molecular weight in terms of PEO is used.

[GPC method measurement conditions]
As a column, PW / GMPWXL / GMPWXL (manufactured by Tosoh Corp.), as an eluent, 0.2 M phosphate buffer (KH ₂ PO ₄ , Na ₂ HPO ₄ , pH = 7) / CH ₃ CN = 9/1 (weight ratio) The column temperature was 40.degree. C., the flow rate was 1.0 mL / min, and the sample concentration was 1 to 100 .mu.g / mL. A RALLS (90 ° light scattering analyzer) was used as a detector. The approximate value of the weight average molecular weight can also be estimated using RID (differential refractometer). GPC analysis using RID is, for example, column: GMPWXL + GMPWXL, eluent: 0.2 M phosphate buffer / CH ₃ CN = 9/1 (weight ratio), column temperature: 40 ° C., flow rate: 0.5 mL / min, Concentration: Measure as 0.05 mg / mL.

[PH measurement of positive electrode mixture paste]
The pH value of the positive electrode mixture paste at 25 ° C. is a value measured using a pH meter (D-54 manufactured by Horiba, Ltd.), and the value after 1 minute of immersing the electrode of the pH meter in the positive electrode mixture paste is there.

[Solid content concentration of positive electrode mixture paste and each component]
The total solid content concentration of the positive electrode mixture paste and the solid content concentration of each component were calculated by drying at 150 ° C. for 24 hours and measuring the weight loss.

[Synthesis of spiny organic polymer]
Synthesis example of [copolymer of sodium 2-acrylamido-2-methylpropane sulfonate / sodium acrylate = 95: 5 (molar ratio)] 6.00 g of sugar ester (S-770, Mitsubishi Chemical Foods Co., Ltd.) A solution A is prepared by dissolving it in 800 g of n-hexane and refluxing it under a nitrogen atmosphere. Next, 600 g of 2-acrylamido-2-methylpropane sulfonic acid, 160 g of sodium hydroxide, 10 g of acrylic acid, 2,2'-azobis (2-methylpropionamidine) dihydrochloride (V-50, Wako Pure Chemical Industries, Ltd. A solution B is prepared by dissolving 0.80 g of the stock (manufactured by K.K.) in 510 g of ion exchange water. With respect to the solution A, the solution B was dropped and dispersed over 1 hour while maintaining the reaction temperature at 10 ° C. or less, and the solution was further stirred for 30 minutes. After azeotropic dehydration and drying, 674 g of a colorless granular polymer (Na salt of AMPS-AA) was obtained. As a result of GPC measurement of the obtained polymer, the weight average molecular weight was 7,800,000. The average particle size of the polymer was 220 μm.

[Preparation of positive electrode mixture paste]
(1) Positive electrode mixture paste of Example 1 A binder (sodium polyacrylate, manufactured by Wako Pure Chemical Industries, Ltd., "high viscosity") was dissolved in water to obtain an 8% by mass aqueous binder solution. Next, 0.65 g of a conductive material (acetylene black, manufactured by Denka, "HS-100") and 8.13 g of a binder aqueous solution are mixed to prepare a slurry [1], and then, the slurry [1] is prepared. A slurry [2] was prepared by adding 15 g of a positive electrode active material (NCA, “NC-02” manufactured by Nippon Chemical Industrial Co., Ltd.) and 1.6 g of water and mixing them. The solid content concentration in the slurry [2] is 64.2% by mass, and the mass ratio of the positive electrode active material, the conductive material, and the binder is 92: 4: 4 (in terms of solid content).
Next, 0.26 g of a 0.2 mass% aqueous solution of an organic polymer (polyethylene oxide, weight average molecular weight: 4,000,000, manufactured by Wako Pure Chemical Industries, Ltd.) is added to slurry [2] and mixed. A positive electrode mixture paste was prepared. The solid content in the positive electrode mixture paste is a positive electrode active material, a conductive material, a binder, and an organic polymer, and the total solid concentration in the positive electrode mixture paste is 63.6% by mass, and the positive electrode active material, conductive material The mass ratio of the binder to the organic polymer is 92: 4: 4: 0.003 (in terms of solid content). The contents of the organic polymers described in Tables 3 and 4 are values relative to the total solid content in the positive electrode mixture paste (the same applies to Examples 2 to 5 and Comparative Examples 1 to 5 below). The content of water is 57 parts by mass with respect to 100 parts by mass of the total solid content in the positive electrode mixture paste. Awatori Neritaro (ARV-310) was used to mix each component. The pH (25 ° C.) immediately after preparation of the positive electrode material mixture paste of Example 1 is 13.2, and the pH (25 ° C.) after storage for 1 week in a polyethylene container under an atmosphere of 25 ° C. is also 13.2 there were.

(2) Cathode mix paste of Example 2 A slurry [2] is prepared by the same method as in Example 1, and then, to a slurry [2], an organic polymer aqueous solution (polyethylene oxide, weight average molecular weight: 4,000,000, A positive electrode mixture paste of Example 2 was prepared by adding and mixing 0.26 g of a 0.5% aqueous solution manufactured by Wako Pure Chemical Industries, Ltd.). The solid content in the positive electrode mixture paste is a positive electrode active material, a conductive material, a binder, and an organic polymer, and the total solid concentration in the positive electrode mixture paste is 63.6% by mass, and the positive electrode active material, conductive material The mass ratio of the binder to the organic polymer is 92: 4: 4: 0.008 (in terms of solid content). The pH (25 ° C.) immediately after preparation of the positive electrode mixture paste of Example 2 is 13.2, and the pH (25 ° C.) after storage for 1 week in a polyethylene container under an atmosphere of 25 ° C. is also 13.2 there were.

(3) Cathode mix paste of Example 3 A slurry [2] is prepared by the same method as in Example 1, and then, the organic compound synthesized in the above-mentioned [Synthesis of spiny organic polymer] into a slurry [2] A positive electrode material mixture paste of Example 3 was prepared by adding and mixing 0.26 g of a 1% by mass aqueous solution of a polymer (Na salt of AMPS-AA). The solid content in the positive electrode mixture paste is a positive electrode active material, a conductive material, a binder, and an organic polymer, and the total solid concentration in the positive electrode mixture paste is 63.6% by mass, and the positive electrode active material, conductive material The mass ratio of the binder to the organic polymer is 92: 4: 4: 0.016 (in terms of solid content). The pH (25 ° C.) immediately after preparation of the positive electrode mixture paste of Example 3 is 13.2, and the pH (25 ° C.) after storage for 1 week in a polyethylene container under an atmosphere of 25 ° C. is also 13.2 there were.

(4) Positive Electrode Mixture Paste of Comparative Example 1 The slurry [2] prepared in Example 1 was used as the positive electrode mixture paste of Comparative Example 1.

(5) Cathode mix paste of Comparative Example 2 A slurry [2] is prepared by the same method as in Example 1, and then, to a slurry [2], a 0.2 mass% sodium polyacrylate aqueous solution (manufactured by Aldrich Co.) The positive electrode mixture paste of Comparative Example 2 was prepared by adding and mixing 0.26 g of polyacrylic acid (weight-average molecular weight: 4,000,000) neutralized and dissolved with an aqueous solution of sodium hydroxide). The solid content in the positive electrode mixture paste is a positive electrode active material, a conductive material, a binder, and an organic polymer, and the total solid concentration in the positive electrode mixture paste is 63.6% by mass, and the positive electrode active material, conductive material The mass ratio of the binder to the organic polymer is 92: 4: 4: 0.003 (in terms of solid content).

(6) Cathode mix paste of Comparative Example 3 0.65 g of conductive material (acetylene black, manufactured by Denka, "HS-100"), binder (N-methylpyrrolidone solution of polyvinylidene fluoride (solid content: 12 mass%), A slurry [1] is prepared by mixing 5.42 g of “KF polymer L # 1120”, manufactured by Kureha Co., Ltd., and then the positive electrode active material (NCA, manufactured by Nippon Chemical Industrial Co., Ltd.) “NC 15 g of “-02”) and 4.31 g of a solvent (N methyl pyrrolidone, manufactured by Wako Pure Chemical Industries, Ltd.) were added and mixed to prepare a non-aqueous positive electrode mixture paste. The solid content in the non-aqueous positive electrode mixture paste is a positive electrode active material, a conductive material, and a binder, and the total solid concentration in the non-aqueous positive electrode mixture paste is 64.2 mass%. The mass ratio of the material to the binder is 92: 4: 4 (in terms of solid content).

(7) Cathode mix paste of Example 4 Conductive material (acetylene black, manufactured by Denka, "HS-100") 0.65 g, binder (N methyl pyrrolidone solution of polyvinylidene fluoride (solid content 12 mass%), Kureha Co., Ltd., “KF polymer L # 1120” 5.42 g is mixed to prepare a slurry [1], and then, the slurry [1] is prepared by mixing positive electrode active material (NCA, manufactured by Nippon Chemical Industrial Co., Ltd. “NC-02 15 g) and 4.31 g of a solvent (N methyl pyrrolidone, manufactured by Wako Pure Chemical Industries, Ltd.) were added and mixed to prepare a slurry [2]. The solid content in the slurry [2] is a positive electrode active material, a conductive material, and a binder, and the total solid concentration in the non-aqueous positive electrode mixture paste is 64.2% by mass, and the positive electrode active material, the conductive material, and the binder The mass ratio of (F) is 92: 4: 4 (solid content conversion).
Next, 0.26 g of a 1 wt% N methyl pyrrolidone solution of polyethylene oxide (weight average molecular weight: 4,000,000, manufactured by Wako Pure Chemical Industries, Ltd.) was added to slurry [2] and mixed, thereby the positive electrode of Example 4 A mixture paste was prepared. The total solid concentration of the positive electrode mixture paste is 63.6% by mass, and the mass ratio of the positive electrode active material, the conductive material, the binder, and the polyethylene oxide is 92: 4: 4: 0.016 (in terms of solid content). is there.

(2) The positive electrode mixture paste of Example 5 (high concentration product of Example 4)
A slurry [1] is prepared in the same manner as in Example 4, and then 15 g of a positive electrode active material (NCA, “NC-02” manufactured by Nippon Chemical Industrial Co., Ltd.) is added to the slurry [1], and polyethylene oxide (weight average) A positive electrode material mixture paste of Example 5 was prepared by adding and mixing 0.21 g of a 1% by weight N methyl pyrrolidone solution of molecular weight: 4,000,000, manufactured by Wako Pure Chemical Industries, Ltd.). The total solid concentration of the positive electrode mixture paste is 76.6% by mass, and the mass ratio of the positive electrode active material, the conductive material, the binder, and the polyethylene oxide is 92: 4: 4: 0.013 (in terms of solid content). is there.

(4) Cathode mix paste of Comparative Example 4 A slurry [2] is prepared by the same method as in Example 4, and then a slurry [2] is polyacrylic acid (weight average molecular weight: 4,000,000, manufactured by Aldrich) The positive electrode material mixture paste of Comparative Example 4 was prepared by adding and mixing 0.26 g of 1 wt% N methyl pyrrolidone solution. The total solid concentration of the positive electrode mixture paste is 63.6% by mass, and the mass ratio of the positive electrode active material, the conductive material, the binder, and the polyacrylic acid is 92: 4: 4: 0.016 (in terms of solid content) It is.

(5) Cathode mix paste of Comparative Example 5 A slurry [1] was prepared by the same method as in Example 4, and then, the slurry [1] was coated with a cathode active material (NCA, manufactured by Nippon Chemical Industrial Co., Ltd. "NC-02 And 0.21 g of 1% by weight N methyl pyrrolidone solution of polyacrylic acid (weight average molecular weight: 4,000,000, manufactured by Aldrich) were added and mixed, but the paste was still wet powdery. It did not become.

[Tip thread determination]
The organic polymers used to prepare the positive electrode material mixture pastes of Examples 1 to 3 and Comparative Example 2 were respectively dissolved in purified water to prepare an aqueous solution of an organic polymer of 0.5% by mass. Table 1 shows the results of determining the presence or absence of spinnability based on the spinnability test described in the text for these aqueous solutions of organic polymers.
The organic polymers used to prepare the positive electrode mixture pastes of Examples 4 to 5 and Comparative Examples 4 to 5 were dissolved in N methyl pyrrolidone, respectively, to prepare solutions of 1 mass% organic polymer in N methyl pyrrolidone. Table 2 shows the results of determination of the presence or absence of spinnability based on the spinnability determination method described in the text for N methyl pyrrolidone solutions of these organic polymers.

2. Storage stability test of positive electrode mixture paste The positive electrode mixture pastes of Examples 1 to 5 and Comparative Examples 1 to 4 were each put in a sample bottle, sealed, and allowed to stand at room temperature for 3 days. The condition after 3 days was observed, the results were evaluated according to the following criteria, and the results are shown in Table 2.
A: A good paste state is maintained without gelation.
B: It is gelled and coating is difficult.
C: It is gelled or solidified and coating is very difficult.

3. Preparation of electrode (positive electrode) and battery [Use of positive electrode mixture paste of Examples 1 to 3 and Comparative Examples 1 to 3]
The positive electrode material mixture paste is coated on a 10 μm thick stainless steel foil so that the positive electrode capacity density is 1.0 to 1.2 mAh / cm ^2, and dried at 100 ° C. for 12 hours using a vacuum dryer. The electrode material in which the positive electrode mixture layer was formed on the current collector was produced. The positive electrode material was punched and pressed to a diameter of 13 mm to obtain an electrode (positive electrode). On the positive electrode, a separator of 19 mm in diameter and coin-like metal lithium of 15 mm in diameter and 0.5 in thickness were disposed to prepare a 2032 type coin cell. As an electrolytic solution, 1 M LiPF ₆ EC / DEC (volume ratio) = 3/7 was used. For formation of the positive electrode mixture layer, as the positive electrode mixture paste of Examples 1 to 3 and Comparative Examples 1 to 3, the positive electrode mixture paste immediately after preparation and one week in a polyethylene container under an atmosphere of 25 ° C. The positive electrode mixture paste after storage was used.
[Use of positive electrode mixture paste of Examples 4 to 5 and Comparative Examples 3 to 5]
The positive electrode material mixture paste is coated on a 20 μm thick aluminum foil so that the positive electrode capacity density is 1.0 to 1.2 mAh / cm ^2, and dried at 100 ° C. for 12 hours using a vacuum dryer. The electrode material in which the positive electrode mixture layer was formed on the current collector was produced. The positive electrode material was punched and pressed to a diameter of 13 mm to obtain an electrode (positive electrode). On the positive electrode, a separator of 19 mm in diameter and coin-like metal lithium of 15 mm in diameter and 0.5 in thickness were disposed to prepare a 2032 type coin cell. As an electrolytic solution, 1 M LiPF ₆ EC / DEC (volume ratio) = 3/7 was used. For formation of the positive electrode mixture layer, the positive electrode mixture paste immediately after preparation was used as each of the positive electrode mixture pastes of Examples 4 to 5 and Comparative Examples 3 to 5.

4. Charge / Discharge Test A 3-cycle charge / discharge test was conducted under the conditions described below using a coin cell, and the discharge capacity in the third cycle is shown in Table 3 and Table 4. The discharge capacity of the coin cell using the positive electrode mixture paste immediately after preparation for forming the positive electrode mixture layer is shown in the column of “initial discharge capacity” in Tables 3 and 4. Further, the discharge capacity of the coin cell using the positive electrode mixture paste after storage for one week is shown in the column of “Discharge capacity after storage” in Table 3.
[Charge and discharge conditions]
30 ° C, 0.1 CA, charging 4.3 V CC / CV 1/10 C cutoff discharge CC 2.0 V cutoff

As shown in Table 3, the storage stability of the positive electrode material mixture pastes of Examples 1 to 3 containing spinnable organic polymers was the same as the positive electrode material mixture pastes of Comparative Examples 1 to 2 which did not contain spinnable organic polymers. In comparison, it was good. On the other hand, the positive electrode mixture pastes of Comparative Examples 1 and 2 which do not contain a spinnable organic polymer and the non-aqueous positive electrode mixture paste of Comparative Example 3 are gelled after storage for one week, and coating on the current collector itself Was difficult.

In addition, as shown in Table 3, when the water-based positive electrode material mixture pastes of Examples 1 to 3 containing a spinnable organic polymer are used for forming a positive electrode material mixture layer, the non-water-based positive electrode material mixture paste of Comparative Example 3 As can be seen from the comparison with the case where the above was used to form the positive electrode mixture layer, it was confirmed that the initial discharge had an original capacity comparable to that of the non-aqueous system. When the positive electrode mixture paste of Example 1 is used to form a positive electrode mixture layer, even when the positive electrode mixture paste is stored for one week, the positive electrode mixture paste immediately after preparation is used. A discharge capacity equal to the initial discharge capacity was obtained, in other words, the maintainability of the discharge capacity was good.

As shown in Table 4, the storage stability of the positive electrode mixture pastes of Examples 4 to 5 containing spiny organic polymers was higher than that of Comparative Examples 4 to 5 containing an organic polymer having no spinnability. It was good compared with. On the other hand, the positive electrode mixture of Comparative Example 5 containing an organic polymer without spinnability has a high solid content concentration of 76.6% and does not become paste-like, and coating on the current collector itself is difficult. there were. However, the positive electrode mixture containing the spinnable organic polymer of Example 5 was in the form of a paste and could be applied to the current collector. From this, it is understood that when using a spinnable organic polymer, it is possible to prepare a positive electrode mixture paste having a high concentration of solid content.

According to the present invention, it is possible to provide a water-based positive electrode mixture paste in which thickening and gelation are suppressed and storage stability is improved by a simple method. Therefore, the present invention can contribute to the reduction of the initial capacity of the battery and the cost reduction in the manufacture of the battery.
In addition, the present invention can increase the solid concentration in the non-aqueous positive electrode mixture paste by a simple method, and because the storage stability is good, it can contribute to cost reduction in the manufacture of lithium ion batteries. .
According to the present invention, since thickening and gelation of the positive electrode mixture paste are suppressed, the dispersibility of solid components such as the positive electrode active material and the conductive material in the positive electrode mixture paste becomes good, and homogeneous positive electrode combination is achieved. Since the agent layer can be formed, quality improvement of the lithium ion battery electrode and the lithium ion battery can be expected.

Claims (12)

1. A positive electrode material mixture paste for a lithium ion battery comprising a positive electrode active material, a conductive material, a binder, an organic polymer, and a solvent,
   The organic polymer is
   A positive electrode material mixture paste for lithium ion battery, which is an organic polymer exhibiting spinnability in the solvent having a concentration of 0.001% by mass or more and 3% by mass or less.
2. The positive electrode mixture paste according to claim 1, wherein the content of the organic polymer is 0.001% by mass or more and 0.1% by mass or less based on the total solid content of the positive electrode mixture paste.
3. The positive electrode mixture paste according to claim 1, wherein a weight average molecular weight of the organic polymer is 2.2 million or more and 30 million or less.
4. The positive electrode mixture paste according to any one of claims 1 to 3, wherein the solvent is water.
5. Ethylenically unsaturated unit amount having at least one group selected from the group consisting of a sulfonic acid group (-SO ₂ -OH), a sulfuric acid group (-O-SO ₂ -OH) and a group of their salt type 5. The positive electrode mixture paste according to any one of claims 1 to 4, which is at least one selected from polymer A containing a constituent unit derived from the body a1 and polyethylene oxide.
6. The polymer A is a copolymer comprising a constituent unit derived from at least one monomer a2 selected from unsaturated carboxylic acids and salts thereof, and a constituent unit derived from the monomer a1. The positive electrode mixture paste according to Item 5.
7. The positive electrode material mixture paste according to claim 5 or 6, wherein a molar ratio of constituent units derived from the monomer a1 in the polymer A is 70 mol% or more.
8. The positive electrode mixture paste according to any one of claims 1 to 3, wherein the solvent is N methyl pyrrolidone.
9. The positive electrode mixture paste according to claim 8, wherein the organic polymer contains a structural unit derived from ethylene oxide.
10. The positive electrode mixture paste according to any one of claims 1 to 9, wherein the positive electrode active material is a lithium nickel-containing composite oxide.
11. An electrode for a lithium ion battery, comprising a positive electrode mixture layer formed using the positive electrode mixture paste according to any one of claims 1 to 10.
12. A lithium ion battery comprising a positive electrode mixture layer formed using the positive electrode mixture paste according to any one of claims 1 to 10.