JP6052290B2 - Slurry composition for lithium ion secondary battery electrode, electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a slurry composition for a lithium ion secondary battery electrode, an electrode for a lithium ion secondary battery, and a lithium ion secondary battery.

  In recent years, portable terminals such as notebook computers, mobile phones, and PDAs (Personal Digital Assistants) have been widely used. Lithium ion secondary batteries are frequently used as secondary batteries used as power sources for these portable terminals. Mobile terminals are required to have more comfortable portability, and are rapidly becoming smaller, thinner, lighter, and higher performance. As a result, mobile terminals are used in various places. In addition, secondary batteries are also required to be smaller, thinner, lighter, and have higher performance as with mobile terminals.

  In order to improve the performance of secondary batteries, improvements to electrodes, electrolytes, and other battery members have been studied. Of these, the electrode is usually obtained by mixing an electrode active material and, if necessary, a conductive material such as conductive carbon in a solvent to obtain a slurry composition, applying the slurry composition to a current collector, and drying. Manufactured.

  Conventionally, an organic solvent has often been used as the solvent. However, the use of an organic solvent has a problem that it requires a cost for recycling the organic solvent or requires safety by using the organic solvent. Therefore, in recent years, it has been studied to produce an electrode using water as a solvent (see Patent Documents 1 and 2).

JP 2003-308441 A JP 2003-217573 A

  In a lithium ion secondary battery, battery characteristics such as high temperature cycle characteristics (hereinafter sometimes referred to as “high temperature cycle characteristics”) and low temperature output characteristics (hereinafter also referred to as “low temperature characteristics” as appropriate). Improvement is required. Here, since the electrode is manufactured using the slurry composition as described above, it is considered that the properties of the slurry composition affect the performance of the lithium ion secondary battery. Therefore, development of a technology capable of improving the performance of the lithium ion secondary battery by controlling the properties of the slurry composition is required.

  The present invention was devised in view of the above problems, and a slurry composition for a lithium ion secondary battery capable of realizing a lithium ion secondary battery excellent in high temperature cycle characteristics and low temperature characteristics, and lithium ion using the same It aims at providing the electrode for secondary batteries, and a lithium ion secondary battery.

The inventor has intensively studied to solve the above problems. As a result, the present inventors have found that a slurry composition for a lithium ion secondary battery containing water has a predetermined amount of a hydroxyl group-containing monomer unit, a fluorine-containing (meth) acrylate ester monomer unit, and an acid. It has been found that by including a water-soluble polymer containing a group-containing monomer unit, the high-temperature cycle characteristics and low-temperature characteristics of a lithium ion secondary battery can be improved, and the present invention has been completed.
That is, the present invention is as follows.

[1] including an electrode active material, a water-soluble polymer and water,
Lithium ion secondary, wherein the water-soluble polymer includes a hydroxyl group-containing monomer unit of 0.5 wt% to 10 wt%, a fluorine-containing (meth) acrylic acid ester monomer unit, and an acid group-containing monomer unit. A slurry composition for battery electrodes.
[2] The slurry composition according to [1], wherein the water-soluble polymer has a 1% by weight aqueous solution viscosity of 10 mPa · s to 1000 mPa · s.
[3] The slurry composition according to [1] or [2], wherein the water-soluble polymer further contains 0.05% by weight to 2% by weight of a crosslinkable monomer unit.
[4] The slurry according to any one of [1] to [3], wherein the amount of the water-soluble polymer is 0.1 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. Composition.
[5] Any one of [1] to [4], wherein a ratio of the fluorine-containing (meth) acrylic acid ester monomer unit in the water-soluble polymer is from 0.1% by weight to 50% by weight. The slurry composition according to item.
[6] The slurry composition according to any one of [1] to [5], wherein a ratio of the acid group-containing monomer unit in the water-soluble polymer is 20% by weight or more and 50% by weight or less. .
[7] The slurry composition according to any one of [1] to [6], wherein the water-soluble polymer contains 25% by weight or more and 75% by weight or less of a (meth) acrylic acid ester monomer unit.
[8] The slurry composition according to any one of [1] to [7], further including a particulate binder.
[9] The slurry composition according to [8], wherein the particulate binder is an acrylic soft polymer or a diene soft polymer.
[10] The slurry according to any one of [1] to [9], wherein the acid group-containing monomer is an ethylenically unsaturated carboxylic acid monomer or an ethylenically unsaturated sulfonic acid monomer. Composition.
[11] An electrode for a lithium ion secondary battery obtained by forming a film of the slurry composition according to any one of [1] to [10] on a current collector and drying the film.
[12] A lithium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte solution,
The lithium ion secondary battery whose one or both of the said positive electrode and a negative electrode are the electrodes for lithium ion secondary batteries as described in [11].

  ADVANTAGE OF THE INVENTION According to this invention, the slurry composition for lithium ion secondary batteries which can implement | achieve the lithium ion secondary battery which is excellent in a high temperature cycling characteristic and a low temperature characteristic, and the electrode for lithium ion secondary batteries using the same, and lithium ion secondary A secondary battery can be provided.

  Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and may be arbitrarily modified and implemented without departing from the scope of the claims of the present invention and the equivalents thereof.

  In the following description, (meth) acrylic acid means acrylic acid and methacrylic acid. Moreover, (meth) acrylate means an acrylate and a methacrylate. Furthermore, (meth) acrylonitrile means acrylonitrile and methacrylonitrile.

  Furthermore, that a substance is water-soluble means that an insoluble content is less than 0.5% by weight when 0.5 g of the substance is dissolved in 100 g of water at 25 ° C. Further, that a certain substance is water-insoluble means that an insoluble content is 90% by weight or more when 0.5 g of the substance is dissolved in 100 g of water at 25 ° C.

[1. Slurry composition for lithium ion secondary battery electrode]
The slurry composition of this invention is a slurry composition for lithium ion secondary battery electrodes, Comprising: An electrode active material, a water-soluble polymer, and water are included. Moreover, it is preferable that the slurry composition of this invention contains a particulate-form binder.

[1.1. Electrode active material)
Among the electrode active materials, as the electrode active material for the positive electrode (hereinafter sometimes referred to as “positive electrode active material” as appropriate), a material capable of inserting and desorbing lithium ions is usually used. Such positive electrode active materials are roughly classified into those made of inorganic compounds and those made of organic compounds.

  Examples of the positive electrode active material made of an inorganic compound include transition metal oxides, transition metal sulfides, lithium-containing composite metal oxides of lithium and transition metals, and the like. Examples of the transition metal include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo.

Examples of the transition metal oxide include MnO, MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , Cu ₂ V ₂ O ₃ , amorphous V ₂ O—P ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O _{13 and the} like can be mentioned. Among them, MnO, V ₂ O ₅ , V ₆ O ₁₃ and TiO ₂ are preferable from the viewpoint of cycle stability and capacity.

Examples of the transition metal sulfide include TiS ₂ , TiS ₃ , amorphous MoS ₂ , FeS, and the like.

  Examples of the lithium-containing composite metal oxide include a lithium-containing composite metal oxide having a layered structure, a lithium-containing composite metal oxide having a spinel structure, and a lithium-containing composite metal oxide having an olivine structure.

Examples of the lithium-containing composite metal oxide having a layered structure include lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing nickel oxide (LiNiO ₂ ), lithium composite oxide of Co—Ni—Mn, Ni—Mn— Examples thereof include a lithium composite oxide of Al and a lithium composite oxide of Ni—Co—Al.

Examples of the lithium-containing composite metal oxide having a spinel structure include lithium manganate (LiMn ₂ O ₄ ) or Li [Mn _3/2 M] in which a part of Mn of lithium manganate is substituted with another transition metal. _1/2 ] O ₄ (where M is Cr, Fe, Co, Ni, Cu, etc.).

Examples of the lithium-containing composite metal oxide having an olivine type structure include Li _X MPO ₄ (wherein M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti). Olivine type lithium phosphate compound represented by the formula: at least one selected from the group consisting of Al, Si, B and Mo, wherein X represents a number satisfying 0 ≦ X ≦ 2.

  Examples of the positive electrode active material made of an organic compound include conductive polymer compounds such as polyacetylene and poly-p-phenylene.

Moreover, you may use the positive electrode active material which consists of a composite material which combined the inorganic compound and the organic compound.
Alternatively, for example, a composite material covered with a carbon material may be produced by reducing and firing an iron-based oxide in the presence of a carbon source material, and the composite material may be used as a positive electrode active material. Iron-based oxides tend to have poor electrical conductivity, but can be used as a high-performance positive electrode active material by using a composite material as described above.

Furthermore, you may use as a positive electrode active material what carried out the element substitution of the said compound partially.
Moreover, you may use the mixture of said inorganic compound and organic compound as a positive electrode active material.
As the positive electrode active material, one type may be used alone, or two or more types may be used in combination at any ratio.

  The volume average particle diameter of the positive electrode active material particles is preferably 1 μm or more, more preferably 2 μm or more, preferably 50 μm or less, more preferably 30 μm or less. By setting the average particle diameter of the positive electrode active material particles in the above range, the amount of the binder in preparing the positive electrode active material layer can be reduced, and the decrease in the capacity of the lithium ion secondary battery can be suppressed. Moreover, it becomes easy to adjust the viscosity of the slurry composition of the present invention to an appropriate viscosity that is easy to apply, and a uniform positive electrode can be obtained. Here, the volume average particle diameter employs a particle diameter at which the cumulative volume calculated from the small diameter side is 50% in the particle size distribution measured by the laser diffraction method.

  The amount of the positive electrode active material is a ratio of the positive electrode active material in the electrode active material layer, and is preferably 90% by weight or more, more preferably 95% by weight or more, preferably 99.9% by weight or less, more preferably 99% by weight. % Or less. By setting the amount of the positive electrode active material in the above range, the capacity of the lithium ion secondary battery can be increased, and the flexibility of the positive electrode and the adhesion between the current collector and the positive electrode active material layer can be improved.

Among the electrode active materials, an electrode active material for a negative electrode (hereinafter also referred to as “negative electrode active material” as appropriate) is a substance that transfers electrons in the negative electrode. As the negative electrode active material, a material that can occlude and release lithium ions is usually used.
An example of a suitable negative electrode active material is carbon. Examples of carbon include natural graphite, artificial graphite, and carbon black. Among these, natural graphite is preferably used.

  Further, as the negative electrode active material, it is preferable to use a negative electrode active material containing at least one selected from the group consisting of tin, silicon, germanium, and lead. This is because a negative electrode active material containing these elements has a small irreversible capacity. Among these, a negative electrode active material containing silicon is preferable. By using a negative electrode active material containing silicon, the electric capacity of the lithium ion secondary battery can be increased.

  A negative electrode active material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Therefore, two or more kinds of the negative electrode active materials may be used in combination. Among these, it is preferable to use a negative electrode active material containing a combination of carbon and one or both of metallic silicon and a silicon-based active material. In a negative electrode active material containing a combination of carbon and one or both of metallic silicon and a silicon-based active material, Li insertion and desorption from one or both of metallic silicon and a silicon-based active material occurs at a high potential, It is presumed that Li insertion and desorption from carbon occur at low potential. For this reason, since expansion and contraction are suppressed, the cycle characteristics of the lithium ion secondary battery can be improved.

Examples of the silicon-based active material include SiO, SiO ₂ , SiO _x (0.01 ≦ x <2), SiC, SiOC, and the like, and SiO _x , SiC, and SiOC are preferable. Among these, it is particularly preferable to use SiO _x as the silicon-based active material from the viewpoint of suppressing the swelling of the negative electrode active material itself. SiO _x is a compound formed from one or both of SiO and SiO ₂ and metallic silicon. This SiO _x can be produced, for example, by cooling and precipitating silicon monoxide gas generated by heating a mixture of SiO ₂ and metal silicon.

When carbon is used in combination with one or both of metallic silicon and a silicon-based active material, it is preferable that one or both of metallic silicon and the silicon-based active material is combined with conductive carbon. By combining with conductive carbon, swelling of the negative electrode active material itself can be suppressed.
Examples of the compounding method include a method of compounding one or both of metallic silicon and silicon-based active material with carbon; conductive carbon and one or both of metallic silicon and silicon-based active material The method of compounding by granulating a mixture; etc. are mentioned.

  Examples of the method for coating one or both of metallic silicon and silicon-based active material with carbon include, for example, a method in which one or both of metallic silicon and silicon-based active material are subjected to heat treatment, and disproportionation; A method of performing chemical vapor deposition by subjecting one or both of the materials to a heat treatment; and the like.

Specific examples of these methods include a method of subjecting SiO _x to heat treatment in an atmosphere containing at least one or both of an organic gas and an organic vapor. This heat treatment is preferably 900 ° C. or more, more preferably 1000 ° C. or more, further preferably 1050 ° C. or more, particularly preferably 1100 ° C. or more, preferably 1400 ° C. or less, more preferably 1300 ° C. or less, particularly preferably 1200. Perform in the temperature range below ℃. According to this method, SiO _x can be disproportionated into a composite of silicon and silicon dioxide, and carbon can be chemically deposited on the surface.

  Another specific example is the following method. That is, one or both of metallic silicon and silicon-based active material is heat-treated in an inert gas atmosphere to disproportionate to obtain a silicon composite. This heat treatment is preferably performed at 900 ° C. or higher, more preferably 1000 ° C. or higher, particularly preferably 1100 ° C. or higher, and preferably 1400 ° C. or lower, more preferably 1300 ° C. or lower. The silicon composite thus obtained is preferably pulverized to a particle size of 0.1 μm to 50 μm. The pulverized silicon composite is heated at 800 ° C. to 1400 ° C. under an inert gas stream. The heated silicon composite is subjected to a heat treatment in an atmosphere containing at least one or both of an organic gas and an organic vapor to chemically vapor-deposit carbon on the surface. This heat treatment is preferably performed at 800 ° C. or higher, more preferably 900 ° C. or higher, particularly preferably 1000 ° C. or higher, preferably 1400 ° C. or lower, more preferably 1300 ° C. or lower, particularly preferably 1200 ° C. or lower.

  Moreover, the following method is also mentioned as another specific example. That is, one or both of metal silicon and silicon-based active material is subjected to chemical vapor deposition with one or both of organic gas and organic vapor. This chemical vapor deposition treatment is preferably performed in a temperature range of 500 ° C to 1200 ° C, more preferably 500 ° C to 1000 ° C, and particularly preferably 500 ° C to 900 ° C. This is heat-treated in an inert gas atmosphere to disproportionate. This heat treatment is preferably performed at 900 ° C. or higher, more preferably 1000 ° C. or higher, particularly preferably 1100 ° C. or higher, and preferably 1400 ° C. or lower, more preferably 1300 ° C. or lower.

  In the case of using a negative electrode active material containing a combination of carbon and one or both of metallic silicon and a silicon-based active material, the amount of silicon atoms in the negative electrode active material is 0.1 parts by weight with respect to 100 parts by weight of the total carbon atoms. It is preferable that it is -50 weight part. Thereby, a conductive path is formed satisfactorily and the conductivity of the negative electrode can be improved.

  When a negative electrode active material including a combination of carbon and one or both of metallic silicon and a silicon-based active material is used, a weight ratio of carbon to one or both of metallic silicon and a silicon-based active material (“carbon weight” / It is preferable that “weight of metal silicon and silicon-based active material”) be within a predetermined range. Specifically, the weight ratio is preferably 50/50 or more, more preferably 70/30 or more, preferably 97/3 or less, more preferably 90/10 or less. Thereby, the cycling characteristics of a lithium ion secondary battery can be improved.

The negative electrode active material is preferably sized in the form of particles. When the shape of the particles is spherical, a higher-density electrode can be formed when forming an electrode for a lithium ion secondary battery (hereinafter, also referred to as “electrode” as appropriate).
The volume average particle diameter of the particles of the negative electrode active material is appropriately selected in consideration of other constituent requirements of the lithium ion secondary battery, and is preferably 0.1 μm or more, more preferably 1 μm or more, and particularly preferably 5 μm or more. The thickness is preferably 100 μm or less, more preferably 50 μm or less, and particularly preferably 20 μm or less.

The specific surface area of the negative electrode active material is preferably 2 m ² / g or more, more preferably 3 m ² / g or more, particularly preferably 5 m ² / g or more, preferably 20 m ² / g or less, from the viewpoint of improving the output density. More preferably, it is 15 m ² / g or less, particularly preferably 10 m ² / g or less. The specific surface area of the negative electrode active material can be measured by, for example, the BET method.

  The amount of the negative electrode active material is a ratio of the negative electrode active material in the electrode active material layer, preferably 85% by weight or more, more preferably 88% by weight or more, preferably 99% by weight or less, more preferably 97% by weight or less. It is. By setting the amount of the negative electrode active material in the above range, it is possible to realize a negative electrode that exhibits flexibility and adhesion while exhibiting a high capacity.

[1.2. Water-soluble polymer)
The water-soluble polymer usually has an action of uniformly dispersing the electrode active material in the slurry composition of the present invention. Further, the water-soluble polymer has an action of adjusting the viscosity of the slurry composition and can function as a thickener. Furthermore, the water-soluble polymer acts to bind the electrode active material and the current collector by interposing between the electrode active materials and between the electrode active material and the current collector in the electrode active material layer. Can play. In addition, the water-soluble polymer can form a stable layer that covers the electrode active material in the electrode active material layer, and can exert an action of suppressing decomposition of the electrolytic solution.

[1.2.1. Hydroxyl-containing monomer unit]
The water-soluble polymer includes a hydroxyl group-containing monomer unit. A hydroxyl group-containing monomer unit is a structural unit having a structure formed by polymerizing a hydroxyl group-containing monomer.

  Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl acrylate, 2-hydroxy methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, and 3-chloro-2-hydroxypropyl methacrylate. Hydroxyalkyl (meth) such as di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, and 2-hydroxyethyl methyl fumarate Acrylates; allyl alcohol, monoallyl ethers of polyhydric alcohols; vinyl alcohol, and the like. Among these, hydroxyalkyl (meth) acrylate is preferable, hydroxyalkyl acrylate is more preferable, and 2-hydroxyethyl acrylate is particularly preferable. Moreover, a hydroxyl-containing monomer and a hydroxyl-containing monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. The hydroxyl group-containing monomer does not include a monomer containing a carboxyl group.

  The proportion of the hydroxyl group-containing monomer unit in the water-soluble polymer is usually 0.5% by weight or more, preferably 1% by weight or more, more preferably 1.5% by weight or more, and usually 10% by weight or less, preferably It is 8% by weight or less, more preferably 5% by weight or less. When the ratio of the hydroxyl group-containing monomer unit is at least the lower limit of the above range, the dispersibility of the particles such as the electrode active material and the particulate binder can be increased in the slurry composition of the present invention. Moreover, by being below an upper limit, the cycle characteristic of a lithium ion secondary battery can be improved and battery life can be lengthened. Here, the ratio of the hydroxyl group-containing monomer unit in the water-soluble polymer usually corresponds to the ratio (preparation ratio) of the hydroxyl group-containing monomer in all monomers of the water-soluble polymer.

[1.2.2. Fluorine-containing (meth) acrylic acid ester monomer unit]
The water-soluble polymer contains a fluorine-containing (meth) acrylic acid ester monomer unit. The fluorine-containing (meth) acrylic acid ester monomer unit is a structural unit having a structure formed by polymerizing a fluorine-containing (meth) acrylic acid monomer.

  Examples of the fluorine-containing (meth) acrylic acid ester monomer include monomers represented by the following formula (I).

In the above formula (I), R ¹ represents a hydrogen atom or a methyl group.
In the above formula (I), R ² represents a hydrocarbon group containing a fluorine atom. The carbon number of the hydrocarbon group is preferably 1 or more, and preferably 18 or less. Moreover, the number of fluorine atoms contained in R ² may be one or two or more.

  Examples of fluorine-containing (meth) acrylic acid ester monomers represented by formula (I) include (meth) acrylic acid alkyl fluoride, (meth) acrylic acid fluoride aryl, and (meth) acrylic acid fluoride. Aralkyl is mentioned. Of these, alkyl fluoride (meth) acrylate is preferable. Specific examples of such monomers include 2,2,2-trifluoroethyl (meth) acrylate, β- (perfluorooctyl) ethyl (meth) acrylate, 2,2, (meth) acrylic acid. 3,3-tetrafluoropropyl, (meth) acrylic acid 2,2,3,4,4,4-hexafluorobutyl, (meth) acrylic acid 1H, 1H, 9H-perfluoro-1-nonyl, (meth) 1H, 1H, 11H-perfluoroundecyl acrylate, perfluorooctyl (meth) acrylate, trifluoromethyl (meth) acrylate, 3 [4] (1-trifluoromethyl-2, 2- (Meth) acrylic acid perfluoroalkyl esters such as bis [bis (trifluoromethyl) fluoromethyl] ethynyloxy] benzooxy] 2-hydroxypropyl Le, and the like. Moreover, a fluorine-containing (meth) acrylic acid ester monomer and a fluorine-containing (meth) acrylic acid ester monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Also good.

  The proportion of the fluorine-containing (meth) acrylic acid ester monomer unit in the water-soluble polymer is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, and particularly preferably 0.5% by weight or more. Yes, preferably 50% by weight or less, more preferably 45% by weight or less, and particularly preferably 40% by weight or less. When the ratio of the fluorine-containing (meth) acrylic acid ester monomer unit is not less than the lower limit of the above range, the output characteristics such as the low-temperature characteristics of the lithium ion secondary battery can be improved. Moreover, by being below the upper limit of the said range, the cycle characteristic of a lithium ion secondary battery can be improved and battery life can be lengthened. Here, the ratio of the fluorine-containing (meth) acrylate monomer units in the water-soluble polymer is usually the ratio of the fluorine-containing (meth) acrylate monomer units in all monomers of the water-soluble polymer ( It matches the charging ratio).

[1.2.3. (Acid group-containing monomer unit)
The water-soluble polymer includes an acid group-containing monomer unit. The acid group-containing monomer unit is a structural unit having a structure formed by polymerizing an acid group-containing monomer.

  An acid group refers to a group that exhibits acidity. Examples of acid groups include carboxylic acid groups such as carboxyl groups and carboxylic anhydride groups, sulfonic acid groups, and phosphoric acid groups. Of these, carboxylic acid groups and sulfonic acid groups are preferred.

  Examples of the acid group-containing monomer include an ethylenically unsaturated carboxylic acid monomer, an ethylenically unsaturated sulfonic acid monomer, and an ethylenically unsaturated phosphoric acid monomer.

  Examples of the ethylenically unsaturated carboxylic acid monomer include an ethylenically unsaturated monocarboxylic acid monomer and derivatives thereof, an ethylenically unsaturated dicarboxylic acid monomer and acid anhydrides thereof, and derivatives thereof. Examples of ethylenically unsaturated monocarboxylic acid monomers include acrylic acid, methacrylic acid, and crotonic acid. Examples of derivatives of ethylenically unsaturated monocarboxylic acid monomers include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxy. Acrylic acid and (beta) -diaminoacrylic acid are mentioned. Examples of ethylenically unsaturated dicarboxylic acid monomers include maleic acid, fumaric acid, and itaconic acid. Examples of acid anhydrides of ethylenically unsaturated dicarboxylic acid monomers include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Examples of derivatives of ethylenically unsaturated dicarboxylic acid monomers include maleic acid substituted with hydrocarbon groups such as methylmaleic acid, dimethylmaleic acid, phenylmaleic acid; chloromaleic acid, dichloromaleic acid, fluoromaleic acid And maleic esters such as methylallyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, fluoroalkyl maleate, and the like. Among these, ethylenically unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid are preferable. This is because the solubility of the obtained water-soluble polymer in water can be further increased.

  Examples of ethylenically unsaturated sulfonic acid monomers include monomers sulfonated one of conjugated double bonds of diene compounds such as isoprene and butadiene, vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, sulfone. Examples include ethyl methacrylate, sulfopropyl methacrylate, sulfobutyl methacrylate, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 3-allyloxy-2-hydroxypropanesulfonic acid (HAPS), and salts thereof. Examples of the salt include lithium salt, sodium salt, potassium salt and the like.

Examples of the ethylenically unsaturated phosphoric acid monomer include monomers having an ethylenically unsaturated group and a -OP (= O) (-OR ^a ) -OR ^b group (R ^a and R ^b is independently a hydrogen atom or any organic group.) or a salt thereof. Specific examples of the organic group as R ^a and R ^b include an aliphatic group such as an octyl group and an aromatic group such as a phenyl group. Specific examples of the ethylenically unsaturated phosphoric acid monomer include a compound containing a phosphoric acid group and an allyloxy group, and a phosphoric acid group-containing (meth) acrylic acid ester. Examples of the compound containing a phosphoric acid group and an allyloxy group include 3-allyloxy-2-hydroxypropane phosphoric acid. Examples of phosphoric acid group-containing (meth) acrylic acid esters include dioctyl-2-methacryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, monomethyl-2-methacryloyloxyethyl phosphate, dimethyl-2-methacrylate. Leuoxyethyl phosphate, monoethyl-2-methacryloyloxyethyl phosphate, diethyl-2-methacryloyloxyethyl phosphate, monoisopropyl-2-methacryloyloxyethyl phosphate, diisopropyl-2-methacryloyloxyethyl phosphate, mono n-butyl -2-methacryloyloxyethyl phosphate, di-n-butyl-2-methacryloyloxyethyl phosphate, monobutoxyethyl-2-methacryloyloxyethyl phosphate , Dibutoxyethyl-2-methacryloyloxyethyl phosphate, mono (2-ethylhexyl) -2-methacryloyloxyethyl phosphate, and di (2-ethylhexyl) -2-methacryloyloxyethyl phosphate.

Among the above-described examples, preferred are ethylenically unsaturated carboxylic acid monomers and ethylenically unsaturated sulfonic acid monomers, and more preferred are acrylic acid, methacrylic acid, itaconic acid and 2- Acrylamide-2-methylpropanesulfonic acid is mentioned, acrylic acid and methacrylic acid are more preferable, and methacrylic acid is particularly preferable.
As the acid group-containing monomer and the acid group-containing monomer unit, one type may be used alone, or two or more types may be used in combination at any ratio.

  In the water-soluble polymer, the ratio of the acid group-containing monomer unit is preferably 20% by weight or more, more preferably 25% by weight or more, particularly preferably 30% by weight or more, and preferably 50% by weight or less. The amount is preferably 45% by weight or less, particularly preferably 40% by weight or less. When the ratio of the acid group-containing monomer unit is at least the lower limit of the above range, the adhesion between the electrode active material layer and the current collector can be enhanced. Moreover, by being below the upper limit of the said range, the cycle characteristic of a lithium ion secondary battery can be improved and battery life can be lengthened. Here, the ratio of the acid group-containing monomer unit in the water-soluble polymer usually corresponds to the ratio (preparation ratio) of the acid group-containing monomer in all the monomers of the water-soluble polymer.

[1.2.4. Crosslinkable monomer unit)
The water-soluble polymer preferably further contains a crosslinkable monomer unit. The crosslinkable monomer unit is a structural unit having a structure formed by polymerizing a crosslinkable monomer. By including a crosslinkable monomer unit, the water-soluble polymer can be crosslinked, so that the strength and stability of the electrode active material layer can be increased. In addition, swelling of the electrode active material layer with respect to the electrolytic solution can be suppressed, and the low temperature characteristics of the lithium ion secondary battery can be improved.

  As the crosslinkable monomer, a monomer capable of forming a crosslinked structure upon polymerization can be used. Examples of the crosslinkable monomer include monomers having two or more reactive groups per molecule. More specifically, a monofunctional monomer having a heat-crosslinkable crosslinkable group and one olefinic double bond per molecule, and a polyfunctional having two or more olefinic double bonds per molecule. Ionic monomers.

  Examples of thermally crosslinkable groups contained in the monofunctional monomer include epoxy groups, N-methylolamide groups, oxetanyl groups, oxazoline groups, and combinations thereof. Among these, an epoxy group is more preferable in terms of easy adjustment of crosslinking and crosslinking density.

  Examples of the crosslinkable monomer having an epoxy group as a thermally crosslinkable group and having an olefinic double bond include vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, o-allylphenyl glycidyl. Unsaturated glycidyl ethers such as ether; butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododecadiene Monoepoxides of dienes or polyenes such as; alkenyl epoxides such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene; and glycidyl acrylate, glycidyl methacrylate, Glycidyl crotonate, glycidyl Unsaturated carboxylic acids such as -4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl-4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexene carboxylic acid, glycidyl ester of 4-methyl-3-cyclohexene carboxylic acid Glycidyl esters; and the like.

  Examples of the crosslinkable monomer having an N-methylolamide group as a thermally crosslinkable group and having an olefinic double bond have a methylol group such as N-methylol (meth) acrylamide (meta ) Acrylamides.

  Examples of the crosslinkable monomer having an oxetanyl group as a heat crosslinkable group and having an olefinic double bond include 3-((meth) acryloyloxymethyl) oxetane, 3-((meth) Acryloyloxymethyl) -2-trifluoromethyloxetane, 3-((meth) acryloyloxymethyl) -2-phenyloxetane, 2-((meth) acryloyloxymethyl) oxetane, and 2-((meth) acryloyloxymethyl ) -4-trifluoromethyloxetane.

  Examples of the crosslinkable monomer having an oxazoline group as a thermally crosslinkable group and having an olefinic double bond include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2- Oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and And 2-isopropenyl-5-ethyl-2-oxazoline.

  Examples of multifunctional monomers having two or more olefinic double bonds include allyl (meth) acrylate, ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, Tetraethylene glycol di (meth) acrylate, trimethylolpropane-tri (meth) acrylate, dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, trimethylolpropane-diallyl Examples include ethers, allyl or vinyl ethers of polyfunctional alcohols other than those described above, triallylamine, methylenebisacrylamide, and divinylbenzene.

Among these, as the crosslinkable monomer, ethylene dimethacrylate, allyl glycidyl ether, glycidyl methacrylate and divinylbenzene are preferable, and ethylene dimethacrylate and glycidyl methacrylate are more preferable.
Moreover, a crosslinking | crosslinked monomer and a crosslinking | crosslinked monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  In the water-soluble polymer, the proportion of the crosslinkable monomer unit is preferably 0.05% by weight or more, more preferably 0.1% by weight or more, particularly preferably 0.2% by weight or more, preferably 2%. % By weight or less, more preferably 1.5% by weight or less, particularly preferably 1% by weight or less. When the ratio of the crosslinkable monomer unit is not less than the lower limit of the above range, the cycle characteristics of the lithium ion secondary battery can be improved and the battery life can be extended. Moreover, the adhesiveness of an electrode active material layer and a collector can be improved because it is below the upper limit of the said range. Usually, the ratio of the crosslinkable monomer unit in the water-soluble polymer coincides with the ratio (charge ratio) of the crosslinkable monomer in all the monomers of the water-soluble polymer.

[1.2.5. Arbitrary structural unit)
The water-soluble polymer has any structural unit other than the above-mentioned hydroxyl group-containing monomer unit, fluorine-containing (meth) acrylate monomer unit, acid group-containing monomer unit and crosslinkable monomer unit. May be included.
For example, the water-soluble polymer may contain (meth) acrylic acid ester monomer units other than the fluorine-containing (meth) acrylic acid ester monomer units. The (meth) acrylic acid ester monomer unit is a structural unit having a structure formed by polymerizing a (meth) acrylic acid ester monomer. However, among the (meth) acrylate monomers, those containing fluorine are distinguished from (meth) acrylate monomers as fluorine-containing (meth) acrylate monomers.

  Examples of (meth) acrylic acid ester monomers include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, Acrylic acid alkyl esters such as 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; and methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t -Butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl Methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n- tetradecyl methacrylate, methacrylic acid alkyl esters such as stearyl methacrylate. Among these, acrylic acid alkyl ester is preferable. Moreover, a (meth) acrylic acid ester monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  In the water-soluble polymer, the proportion of the (meth) acrylic acid ester monomer unit is preferably 25% by weight or more, more preferably 30% by weight or more, particularly preferably 35% by weight or more, and preferably 75%. % By weight or less, more preferably 70% by weight or less, particularly preferably 65% by weight or less. When the amount of the (meth) acrylic acid ester monomer unit is not less than the lower limit of the above range, the adhesion of the electrode active material layer to the current collector can be increased. Moreover, the softness | flexibility of an electrode can be improved because it is below the upper limit of the said range. Here, the ratio of the (meth) acrylic acid ester monomer unit in the water-soluble polymer is usually the ratio of the (meth) acrylic acid ester monomer in all the monomers of the water-soluble polymer (preparation ratio). Match.

  For example, the water-soluble polymer may contain a reactive surfactant unit. The reactive surfactant unit is a structural unit obtained by polymerizing a reactive surfactant monomer. The reactive surfactant unit forms part of the water-soluble polymer and can function as a surfactant.

  The reactive surfactant monomer is a monomer having a polymerizable group that can be copolymerized with another monomer and having a surface active group (hydrophilic group and hydrophobic group). Usually, the reactive surfactant monomer has a polymerizable unsaturated group, and this group also acts as a hydrophobic group after polymerization. Examples of the polymerizable unsaturated group that the reactive surfactant monomer has include a vinyl group, an allyl group, a vinylidene group, a propenyl group, an isopropenyl group, and an isobutylidene group. One kind of the polymerizable unsaturated group may be used alone, or two or more kinds may be used in combination at any ratio.

  The reactive surfactant monomer usually has a hydrophilic group as a portion that exhibits hydrophilicity. Reactive surfactant monomers are classified into anionic, cationic and nonionic surfactants depending on the type of hydrophilic group.

Examples of the anionic hydrophilic group include —SO ₃ M, —COOM, and —PO (OM) ₂ . Here, M represents a hydrogen atom or a cation. Examples of cations include alkali metal ions such as lithium, sodium and potassium; alkaline earth metal ions such as calcium and magnesium; ammonium ions; ammonium ions of alkylamines such as monomethylamine, dimethylamine, monoethylamine and triethylamine; and And ammonium ions of alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine.
Examples of the cationic hydrophilic group include —Cl, —Br, —I, and —SO ₃ OR ^X. Here, R ^X represents an alkyl group. Examples of R ^X is methyl group, an ethyl group, a propyl group, and isopropyl group.
-OH is mentioned as an example of a nonionic hydrophilic group.

  Examples of suitable reactive surfactant monomers include compounds represented by the following formula (II).

In the formula (II), R represents a divalent linking group. Examples of R include -Si-O- group, methylene group and phenylene group.
In the formula (II), R ³ represents a hydrophilic group. An example of R ³ includes —SO ₃ NH ₄ .
In the formula (II), n represents an integer of 1 to 100.

Another example of a suitable reactive surfactant monomer has a structural unit having a structure formed by polymerizing ethylene oxide and a structural unit having a structure formed by polymerizing butylene oxide, and Examples include compounds having an alkenyl group having a terminal double bond and —SO ₃ NH ₄ at the terminal (for example, trade names “Latemul PD-104” and “Latemul PD-105”, manufactured by Kao Corporation).
A reactive surfactant monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  In the water-soluble polymer, the ratio of the reactive surfactant unit is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, particularly preferably 0.5% by weight or more, preferably 5%. % By weight or less, more preferably 4% by weight or less, particularly preferably 2% by weight or less. The dispersibility of the slurry composition can be improved by setting the ratio of the reactive surfactant unit to the lower limit value or more of the above range. Moreover, durability of an electrode can be improved by setting it as below an upper limit. Here, the ratio of the reactive surfactant unit in the water-soluble polymer usually coincides with the ratio (charge ratio) of the reactive surfactant monomer in all monomers of the water-soluble polymer.

  A further example of an arbitrary structural unit that the water-soluble polymer may have includes a structural unit having a structure formed by polymerizing the following monomers. That is, aromatic vinyl monomers such as styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene, divinyl benzene, etc. Unsaturated carboxylic acid amide monomers such as acrylamide; α, β-unsaturated nitrile compound monomers such as acrylonitrile and methacrylonitrile; olefin monomers such as ethylene and propylene; vinyl chloride, vinylidene chloride, etc. Halogen atom-containing monomers; vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate; vinyl ether monomers such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether; methyl vinyl ketone, ethyl Vinyl keto , Vinyl ketone monomers such as butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; and heterocyclic-containing vinyl compound monomers such as N-vinyl pyrrolidone, vinyl pyridine, and vinyl imidazole; Examples include a structural unit having a structure to be formed.

[1.2.6. Properties of water-soluble polymer)
The viscosity of a 1% by weight aqueous solution of the water-soluble polymer is preferably 10 mPa · s or more, more preferably 20 mPa · s or more, particularly preferably 50 mPa · s or more, preferably 1000 mPa · s or less, more preferably 800 mPa · s. s or less, particularly preferably 500 mPa · s or less. By setting the viscosity to be equal to or higher than the lower limit of the above range, the strength of the water-soluble polymer can be increased and the durability of the electrode can be improved. Moreover, the coating strength of the slurry composition of this invention can be made favorable by setting it as an upper limit or less, and the adhesive strength of a collector and an electrode active material layer can be improved. The viscosity can be adjusted by, for example, the molecular weight of the water-soluble polymer. Here, the viscosity is a value when measured at 25 ° C. and a rotation speed of 60 rpm using a B-type viscometer under the condition of pH = 8.

The weight average molecular weight of the water-soluble polymer is preferably 500 or more, more preferably 700 or more, particularly preferably 1000 or more, preferably 500,000 or less, more preferably 450,000 or less, and particularly preferably 400,000 or less. By setting the weight average molecular weight of the water-soluble polymer to be equal to or higher than the lower limit of the above range, the strength of the water-soluble polymer can be increased and the durability of the electrode can be improved. Moreover, the adhesive strength of a collector and an electrode active material layer can be improved by setting it as an upper limit or less.
Here, the weight average molecular weight of the water-soluble polymer is polystyrene using gel permeation chromatography (GPC) as a developing solvent, a solution obtained by dissolving 0.85 g / ml sodium nitrate in a 10% by volume aqueous solution of dimethylformamide. It can be obtained as a conversion value.

[1.2.7. Method for producing water-soluble polymer]
The water-soluble polymer can be produced, for example, by polymerizing a monomer composition containing the above-described monomer in an aqueous solvent. At this time, the ratio of each monomer in the monomer composition is usually a structural unit in the water-soluble polymer (for example, an acidic group-containing monomer unit, a fluorine-containing (meth) acrylic acid monomer unit, The ratio of the acid group-containing monomer unit and the crosslinkable monomer unit).

The aqueous solvent is not particularly limited as long as the water-soluble polymer can be dispersed. Usually, the boiling point at normal pressure is preferably 80 ° C. or higher, more preferably 100 ° C. or higher, preferably 350 ° C. or lower, more preferably 300 ° C. or lower. Examples of the aqueous solvent will be given below. In the following examples, the number in parentheses after the solvent name is the boiling point (unit: ° C) at normal pressure, and the value after the decimal point is a value rounded off or rounded down.
Examples of aqueous solvents include water (100); ketones such as diacetone alcohol (169) and γ-butyrolactone (204); ethyl alcohol (78), isopropyl alcohol (82), normal propyl alcohol (97) and the like. Alcohols: propylene glycol monomethyl ether (120), methyl cellosolve (124), ethyl cellosolve (136), ethylene glycol tertiary butyl ether (152), butyl cellosolve (171), 3-methoxy-3-methyl-1-butanol (174), Ethylene glycol monopropyl ether (150), diethylene glycol monobutyl ether (230), triethylene glycol monobutyl ether (271), dipropylene glycol monomethyl ether (188), etc. Glycol ethers; and 1,3-dioxolane (75), 1,4-dioxolane (101), ethers such as tetrahydrofuran (66) and the like. Among these, water is particularly preferable from the viewpoint that it is not flammable and a polymer dispersion can be easily obtained. Further, water may be used as the main solvent, and an aqueous solvent other than the above-described water may be mixed and used within a range in which the dispersion state of the polymer can be ensured.

  The polymerization method is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used. As the polymerization method, any method such as ion polymerization, radical polymerization, and living radical polymerization can be used. It is easy to obtain a high molecular weight body, and since the polymer is obtained in a state of being dispersed in water as it is, no redispersion treatment is necessary, and it can be used for the production of the slurry composition of the present invention. From the viewpoint of efficiency, the emulsion polymerization method is particularly preferable.

  The emulsion polymerization method is usually performed by a conventional method. For example, the method is described in “Experimental Chemistry Course” Vol. 28, (Publisher: Maruzen Co., Ltd., edited by The Chemical Society of Japan). That is, water, an additive such as a dispersant, an emulsifier, a crosslinking agent, a polymerization initiator, and a monomer are added to a sealed container equipped with a stirrer and a heating device so as to have a predetermined composition, and the composition in the container This is a method in which a product is stirred to emulsify monomers and the like in water, and the temperature is increased while stirring to initiate polymerization. Or after emulsifying the said composition, it is the method of putting into a sealed container and starting reaction similarly.

  Examples of polymerization initiators include organic compounds such as lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 3,3,5-trimethylhexanoyl peroxide, and the like. Peroxides; azo compounds such as α, α′-azobisisobutyronitrile; ammonium persulfate; and potassium persulfate. A polymerization initiator may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  For example, an emulsifier, a dispersant, a polymerization initiator, and the like are generally used in these polymerization methods, and the amount used is usually an amount generally used.

The polymerization temperature and polymerization time can be arbitrarily selected depending on the polymerization method and the type of polymerization initiator. Usually, the polymerization temperature is about 30 ° C. or more, and the polymerization time is about 0.5 to 30 hours.
Further, additives such as amines may be used as a polymerization aid.

  Usually, a reaction solution containing a water-soluble polymer is obtained by polymerization. The obtained reaction solution is usually acidic, and the water-soluble polymer is often dispersed in an aqueous solvent. Thus, the water-soluble polymer dispersed in the aqueous solvent can usually be made soluble in the aqueous solvent by adjusting the pH of the reaction solution to 7 to 13, for example. You may take out a polymer from the reaction liquid obtained in this way. However, usually, water is used as an aqueous solvent, and the slurry composition of the present invention is produced using a water-soluble polymer dissolved in water.

  Examples of the method for alkalinizing the pH to 7 to 13 include alkaline metal aqueous solutions such as lithium hydroxide aqueous solution, sodium hydroxide aqueous solution and potassium hydroxide aqueous solution; alkaline earth such as calcium hydroxide aqueous solution and magnesium hydroxide aqueous solution. Metal aqueous solution: A method of mixing an alkaline aqueous solution such as an aqueous ammonia solution with the reaction solution. One kind of the alkaline aqueous solution may be used alone, or two or more kinds may be used in combination at any ratio.

[1.2.8. Amount of water-soluble polymer]
The amount of the water-soluble polymer is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, particularly preferably 0.5 parts by weight or more, preferably 100 parts by weight of the electrode active material. Is 10 parts by weight or less, more preferably 8 parts by weight or less, and particularly preferably 5 parts by weight or less. Adhesive strength can be ensured when the amount of the water-soluble polymer is not less than the lower limit of the above range. Moreover, a low temperature characteristic can be improved by being below an upper limit.

[1.3. water〕
The slurry composition of the present invention contains water. Water functions as a solvent or a dispersion medium, and can disperse the electrode active material or dissolve the water-soluble polymer.

  As the solvent, a solvent other than water may be used in combination with water. For example, when a liquid that can dissolve the particulate binder and the water-soluble polymer is combined with water, the dispersion of the electrode active material is stabilized by adsorbing the particulate binder and the water-soluble polymer on the surface of the electrode active material. Therefore, it is preferable.

  The type of liquid to be combined with water is preferably selected from the viewpoint of drying speed and environment. Preferred examples include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ketones such as ethyl methyl ketone and cyclohexanone; ethyl acetate, butyl acetate, γ-butyrolactone, Esters such as ε-caprolactone; Nitriles such as acetonitrile and propionitrile; Ethers such as tetrahydrofuran and ethylene glycol diethyl ether: Alcohols such as methanol, ethanol, isopropanol, ethylene glycol, and ethylene glycol monomethyl ether; N-methyl Examples include amides such as pyrrolidone and N, N-dimethylformamide; among them, N-methylpyrrolidone (NMP) is preferable. One of these may be used alone, or two or more of these may be used in combination at any ratio.

  The amount of the solvent is preferably adjusted so that the viscosity of the slurry composition of the present invention becomes a viscosity suitable for coating. Specifically, the solid content concentration of the slurry composition of the present invention is preferably 30% by weight or more, more preferably 35% by weight or more, preferably 70% by weight or less, more preferably 65% by weight or less. The amount is adjusted to be used. Here, the solid content of the slurry composition indicates a substance that remains as a constituent component of the electrode active material layer after the slurry composition is dried.

[1.4. (Particulate binder)
The slurry composition of the present invention preferably contains a particulate binder. By including the particulate binder, the binding property of the electrode active material layer can be improved, and the strength against mechanical force applied to the electrode during handling such as winding and transportation can be improved. In addition, since it becomes difficult for the electrode active material to fall off the electrode active material layer, the risk of a short circuit or the like due to foreign matter is reduced. Furthermore, since the electrode active material can be stably held in the electrode active material layer, durability such as cycle characteristics and high-temperature storage characteristics can be improved. Moreover, the particulate binder can be bound to the electrode active material not by a surface but by a point by being particulate. For this reason, most of the surface of the electrode active material is not covered with the binder, so that the field of exchange of ions between the electrolytic solution and the electrode active material can be widened. Therefore, the output resistance of the lithium ion secondary battery can be improved by reducing the internal resistance.

  Various polymers can be used as the particulate binder, but a water-insoluble polymer is usually used. Examples of the polymer that forms the particulate binder include polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, poly An acrylonitrile derivative or the like may be used.

Furthermore, you may use the particle | grains of the soft polymer illustrated below as a particulate-form binder. That is, as a soft polymer, for example,
(I) Polybutyl acrylate, polybutyl methacrylate, polyhydroxyethyl methacrylate, polyacrylamide, polyacrylonitrile, butyl acrylate / styrene copolymer, butyl acrylate / acrylonitrile copolymer, butyl acrylate / acrylonitrile / glycidyl methacrylate copolymer, etc. An acrylic soft polymer which is a homopolymer of acrylic acid or a methacrylic acid derivative or a copolymer thereof with a monomer copolymerizable therewith;
(Ii) isobutylene-based soft polymers such as polyisobutylene, isobutylene-isoprene rubber, isobutylene-styrene copolymer;
(Iii) Polybutadiene, polyisoprene, butadiene / styrene random copolymer, isoprene / styrene random copolymer, acrylonitrile / butadiene copolymer, acrylonitrile / butadiene / styrene copolymer, butadiene / styrene / block copolymer, styrene -Diene soft polymers such as butadiene, styrene, block copolymers, isoprene, styrene, block copolymers, styrene, isoprene, styrene, block copolymers;
(Iv) silicon-containing soft polymers such as dimethylpolysiloxane, diphenylpolysiloxane, dihydroxypolysiloxane;
(V) Liquid polyethylene, polypropylene, poly-1-butene, ethylene / α-olefin copolymer, propylene / α-olefin copolymer, ethylene / propylene / diene copolymer (EPDM), ethylene / propylene / styrene copolymer Olefinic soft polymers such as polymers;
(Vi) Vinyl-based soft polymers such as polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, vinyl acetate / styrene copolymer;
(Vii) epoxy-based soft polymers such as polyethylene oxide, polypropylene oxide, epichlorohydrin rubber;
(Viii) Fluorine-containing soft polymers such as vinylidene fluoride rubber and tetrafluoroethylene-propylene rubber;
(Ix) Other soft polymers such as natural rubber, polypeptide, protein, polyester thermoplastic elastomer, vinyl chloride thermoplastic elastomer, polyamide thermoplastic elastomer, and the like. Among these, a diene soft polymer and an acrylic soft polymer are preferable. In addition, these soft polymers may have a cross-linked structure or may have a functional group introduced by modification.

  The diene soft polymer is a polymer containing an aliphatic conjugated diene monomer unit. The aliphatic conjugated diene monomer unit is a structural unit having a structure formed by polymerizing an aliphatic conjugated diene monomer.

  Examples of the aliphatic conjugated diene monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene; And pentadiene having a conjugated double bond in a chain and a substituted product thereof; and hexadiene having a conjugated double bond in a side chain and a substituted product thereof. Of these, 1,3-butadiene is preferred. Moreover, an aliphatic conjugated diene monomer and an aliphatic conjugated diene monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  In the diene soft polymer, the proportion of the aliphatic conjugated diene monomer unit is preferably 20% by weight or more, more preferably 30% by weight or more, preferably 70% by weight or less, more preferably 60% by weight or less, Particularly preferred is 55% by weight or less. Here, the ratio of the aliphatic conjugated diene monomer unit in the diene soft polymer is usually equal to the ratio (preparation ratio) of the aliphatic conjugated diene monomer in all the monomers of the diene soft polymer.

  Moreover, it is preferable that a diene soft polymer contains an aromatic vinyl monomer unit. The aromatic vinyl monomer unit is a structural unit having a structure formed by polymerizing an aromatic vinyl monomer.

  Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, vinyltoluene, and divinylbenzene. Of these, styrene is preferred. The diene soft polymer is preferably a polymer containing both an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit. For example, a styrene-butadiene copolymer is preferable. Moreover, an aromatic vinyl monomer and an aromatic vinyl monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The proportion of the aromatic vinyl monomer unit in the diene soft polymer is preferably 30% by weight or more, more preferably 35% by weight or more, preferably 79.5% by weight or less, more preferably 69% by weight or less. is there. Here, the ratio of the aromatic vinyl monomer unit in the diene soft polymer usually matches the ratio (charge ratio) of the aromatic vinyl monomer in all the monomers of the diene soft polymer.

  The diene soft polymer preferably contains an ethylenically unsaturated carboxylic acid monomer unit. The ethylenically unsaturated carboxylic acid monomer unit means a structural unit having a structure formed by polymerizing an ethylenically unsaturated carboxylic acid monomer. Since the ethylenically unsaturated carboxylic acid monomer unit is a structural unit containing a carboxyl group (—COOH group) and having a high strength, the binding property of the electrode active material layer to the current collector can be improved, or the electrode active material The strength of the layer can be improved. Therefore, when the diene soft polymer contains an ethylenically unsaturated carboxylic acid monomer unit, peeling of the electrode active material layer from the current collector can be stably prevented, and the mechanical strength of the electrode active material layer can be prevented. Can be improved.

  Examples of the ethylenically unsaturated carboxylic acid monomer include the same examples as those exemplified in the section of the water-soluble polymer. Moreover, an ethylenically unsaturated carboxylic acid monomer and an ethylenically unsaturated carboxylic acid monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The proportion of the ethylenically unsaturated carboxylic acid monomer unit in the diene soft polymer is preferably 0.5% by weight or more, more preferably 1% by weight or more, particularly preferably 2% by weight or more, preferably 10% by weight. % Or less, more preferably 8% by weight or less, and particularly preferably 7% by weight or less. Here, the ratio of the ethylenically unsaturated carboxylic acid monomer unit in the diene soft polymer is usually the ratio of the ethylenically unsaturated carboxylic acid monomer in all the monomers of the diene soft polymer (preparation ratio). Match.

  The diene soft polymer may contain any structural unit other than those described above as long as the effects of the present invention are not significantly impaired. Examples of monomers corresponding to the above arbitrary structural units include vinyl cyanide monomers, unsaturated carboxylic acid alkyl ester monomers, unsaturated monomers containing hydroxyalkyl groups, and unsaturated carboxylic acids. Examples include acid amide monomers. One of these may be used alone, or two or more of these may be used in combination at any ratio.

  Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and α-ethylacrylonitrile. Of these, acrylonitrile and methacrylonitrile are preferable.

  Examples of unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, and dimethyl itaco. Nates, monomethyl fumarate, monoethyl fumarate, and 2-ethylhexyl acrylate. Of these, methyl methacrylate is preferable.

  Examples of the unsaturated monomer containing a hydroxyalkyl group include β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, 3-chloro-2- Examples include hydroxypropyl methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, and 2-hydroxyethyl methyl fumarate. Among these, β-hydroxyethyl acrylate is preferable.

  Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, and N, N-dimethylacrylamide. Of these, acrylamide and methacrylamide are preferable.

  Further, the diene soft polymer has a structure formed by polymerizing monomers used in usual emulsion polymerization such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, etc. Units may be included.

  The acrylic soft polymer is a polymer containing a (meth) acrylic acid ester monomer unit. However, as mentioned above, among the (meth) acrylate monomers, those containing fluorine are distinguished from (meth) acrylate monomers as fluorine-containing (meth) acrylate monomers. .

  Examples of the (meth) acrylic acid ester monomer include the same examples as those exemplified in the section of the water-soluble polymer. Moreover, a (meth) acrylic acid ester monomer and a (meth) acrylic acid ester monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The proportion of the (meth) acrylic acid ester monomer unit in the acrylic soft polymer is preferably 50% by weight or more, more preferably 70% by weight or more, particularly preferably 90% by weight or more, and preferably 99% by weight or less. More preferably, it is 98 weight% or less, Most preferably, it is 97 weight% or less. Here, the ratio of the (meth) acrylic acid ester monomer unit in the acrylic soft polymer is usually the ratio (preparation ratio) of the (meth) acrylic acid ester monomer in all monomers of the acrylic soft polymer. Match.

  The acrylic soft polymer is preferably a copolymer containing a combination of a (meth) acrylonitrile monomer unit and a (meth) acrylic acid ester monomer unit. The (meth) acrylonitrile monomer unit means a structural unit having a structure formed by polymerizing (meth) acrylonitrile. Since an acrylic soft polymer containing a combination of a (meth) acrylonitrile monomer unit and a (meth) acrylic acid ester monomer unit is stable to oxidation and reduction, it is easy to obtain a battery having a long life.

  The acrylic soft polymer may contain only a structural unit having a structure formed by polymerizing acrylonitrile as a (meth) acrylonitrile monomer unit, and has a structure formed by polymerizing methacrylonitrile. It may contain only structural units, and includes both a structural unit having a structure formed by polymerizing acrylonitrile and a structural unit having a structure formed by polymerizing methacrylonitrile in an arbitrary ratio. May be.

  When the acrylic soft polymer contains a combination of a (meth) acrylonitrile monomer unit and a (meth) acrylate monomer unit, a (meth) acrylonitrile monomer unit relative to the (meth) acrylate monomer unit The weight ratio (weight ratio represented by “(meth) acrylonitrile monomer unit / (meth) acrylate monomer unit”) is preferably within a predetermined range. Specifically, the weight ratio is preferably 1/99 or more, more preferably 2/98 or more, 30/70 or less, and more preferably 25/75 or less. By setting the weight ratio to be equal to or higher than the lower limit of the range, it is possible to prevent the electrode binder from increasing due to swelling of the particulate binder in the electrolytic solution, and it is possible to suppress a decrease in rate characteristics of the secondary battery. Here, the weight ratio of (meth) acrylonitrile monomer unit to (meth) acrylic acid ester monomer unit in acrylic soft polymer is usually (meth) acrylic acid ester in all monomers of acrylic soft polymer. This corresponds to the ratio of (meth) acrylonitrile monomer to monomer.

  The acrylic soft polymer preferably contains an ethylenically unsaturated carboxylic acid monomer unit. Since the ethylenically unsaturated carboxylic acid monomer unit is a structural unit containing a carboxyl group (—COOH group) and having a high strength, the binding property of the electrode active material layer to the current collector can be improved, or the electrode active material The strength of the layer can be improved. Therefore, when the acrylic soft polymer contains an ethylenically unsaturated carboxylic acid monomer unit, peeling of the electrode active material layer from the current collector can be stably prevented, and the mechanical strength of the electrode active material layer can be prevented. Can be improved.

  Examples of the ethylenically unsaturated carboxylic acid monomer include the same examples as those exemplified in the section of the water-soluble polymer. Moreover, an ethylenically unsaturated carboxylic acid monomer and an ethylenically unsaturated carboxylic acid monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The proportion of the ethylenically unsaturated carboxylic acid monomer unit in the acrylic soft polymer is preferably 0.5% by weight or more, more preferably 1% by weight or more, particularly preferably 2% by weight or more, preferably 10% by weight. % Or less, more preferably 8% by weight or less, and particularly preferably 7% by weight or less. Here, the ratio of the ethylenically unsaturated carboxylic acid monomer unit in the acrylic soft polymer is usually the ratio (preparation ratio) of the ethylenically unsaturated carboxylic acid monomer in all the monomers of the acrylic soft polymer. Match.

  The acrylic soft polymer may contain a crosslinkable monomer unit. A crosslinkable monomer is a monomer that can form a crosslinked structure during or after polymerization by heating or irradiation with energy rays. When the acrylic soft polymer contains a crosslinkable monomer unit, the particulate binders can be crosslinked, or the water-soluble polymer and the particulate binder can be crosslinked.

  Examples of the crosslinkable monomer include those similar to the examples given in the section of the water-soluble polymer. Moreover, a crosslinking | crosslinked monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  Furthermore, the crosslinkable monomer unit may be introduced into the acrylic soft polymer by copolymerizing the crosslinkable monomer with the (meth) acrylic acid ester monomer unit. The crosslinkable monomer unit is introduced into the acrylic soft polymer by introducing a crosslinkable group into the acrylic soft polymer by a conventional modification means using a compound having a crosslinkable group (crosslinking agent). Also good.

As the crosslinking agent, for example, an organic peroxide, a crosslinking agent that exhibits an effect by heat or light, and the like are used. Moreover, a crosslinking agent may be used individually by 1 type, and may be used combining 2 or more types by arbitrary ratios.
Among the cross-linking agents, an organic peroxide and a cross-linking agent capable of causing a cross-linking reaction by heat are preferable because they contain a heat cross-linkable cross-linking group.

  The ratio of the crosslinkable monomer unit in the acrylic soft polymer is preferably 0.01 with respect to 100 parts by weight of the total amount of the (meth) acrylonitrile monomer unit and the (meth) acrylic acid ester monomer unit. Part by weight or more, more preferably 0.05 part by weight or more, preferably 5 parts by weight or less, more preferably 4 parts by weight or less, and particularly preferably 3 parts by weight or less.

  In addition to the above-mentioned (meth) acrylonitrile monomer unit, (meth) acrylic acid ester monomer unit, ethylenically unsaturated carboxylic acid monomer unit and crosslinkable group monomer unit, the acrylic soft polymer Can also include any structural unit. Examples of monomers corresponding to these arbitrary structural units include styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, α-methyl. Aromatic vinyl monomers such as styrene and divinylbenzene; Olefin monomers such as ethylene and propylene; Diene monomers such as butadiene and isoprene; Monomers containing halogen atoms such as vinyl chloride and vinylidene chloride; Vinyl acetate Vinyl ester monomers such as vinyl propionate and vinyl butyrate; vinyl ether monomers such as methyl vinyl ether, ethyl vinyl ether and butyl vinyl ether; methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone and isopropenyl Such as vinyl ketone Nyl ketone monomers; N-vinyl pyrrolidone, vinyl pyridine, vinyl ring-containing vinyl compound monomers such as vinyl imidazole; Unsaturated carboxylic acid amide monomers such as acrylamide and acrylamide-2-methylpropane sulfonic acid; Can be mentioned. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios. However, the amount of any structural unit is small from the viewpoint of remarkably exhibiting the advantages of including the (meth) acrylonitrile monomer unit and the (meth) acrylic acid ester monomer unit in combination as described above. It is particularly preferable that it does not contain any structural unit.

  Furthermore, one kind of particulate binder may be used alone, or two or more kinds may be used in combination at any ratio.

  The weight average molecular weight of the polymer forming the particulate binder is preferably 10,000 or more, more preferably 20,000 or more, preferably 1,000,000 or less, more preferably 500,000 or less. When the weight average molecular weight of the polymer forming the particulate binder is in the above range, the strength of the electrode and the dispersibility of the electrode active material are easily improved.

  The glass transition temperature of the particulate binder is preferably −75 ° C. or higher, more preferably −55 ° C. or higher, particularly preferably −35 ° C. or higher, preferably 40 ° C. or lower, more preferably 30 ° C. or lower, still more preferably. 20 ° C. or lower, particularly preferably 15 ° C. or lower. When the glass transition temperature of the particulate binder is in the above range, characteristics such as flexibility and winding property of the electrode and binding property between the electrode active material layer and the current collector are highly balanced, which is preferable. The glass transition temperature of the particulate binder can be adjusted by combining various monomers.

  The volume average particle diameter D50 of the particulate binder is preferably 50 nm or more, more preferably 70 nm or more, preferably 500 nm or less, more preferably 400 nm or less. When the volume average particle diameter D50 of the particulate binder is in the above range, the strength and flexibility of the obtained electrode can be improved.

  The amount of the particulate binder is preferably 0.5 parts by weight or more, more preferably 0.7 parts by weight or more, particularly preferably 1 part by weight or more, preferably 10 parts by weight with respect to 100 parts by weight of the electrode active material. Parts or less, more preferably 7 parts by weight or less, and particularly preferably 5 parts by weight or less. By setting the amount of the binder to be equal to or higher than the lower limit of the above range, durability such as cycle characteristics and high-temperature storage characteristics of the lithium ion secondary battery can be improved. Moreover, the low temperature characteristic of a lithium ion secondary battery can be made favorable by setting it as below an upper limit.

  The method for producing the particulate binder is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method may be used. Among these, the emulsion polymerization method and the suspension polymerization method are preferable because they can be polymerized in water and used as they are as the material of the slurry composition of the present invention. Moreover, when manufacturing a particulate binder, it is preferable to contain a dispersing agent in the reaction system.

[1.5. (Optional ingredients)
The slurry composition of this invention can contain arbitrary components other than the electrode active material mentioned above, a water-soluble polymer, water, and a particulate binder. Examples thereof include conductive materials, reinforcing materials, leveling agents, thickeners, nanoparticles, electrolyte additives, and the like. Moreover, these components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The conductive material is a component that can improve electrical contact between the electrode active materials. By including a conductive material, the discharge rate characteristics of the lithium ion secondary battery can be improved.
Examples of the conductive material include furnace black, acetylene black, ketjen black, carbon black, graphite, vapor grown carbon fiber, and conductive carbon such as carbon nanotube. A conductive material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
The amount of the conductive material is preferably 1 to 20 parts by weight, more preferably 1 to 10 parts by weight, with respect to 100 parts by weight of the electrode active material.

As the reinforcing material, for example, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used. A reinforcing material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. By using the reinforcing material, a tough and flexible electrode can be obtained, and a lithium ion secondary battery exhibiting excellent long-term cycle characteristics can be realized.
The amount of the reinforcing material is preferably 0.01 parts by weight or more, more preferably 1 part by weight or more, preferably 20 parts by weight or less, more preferably 10 parts by weight with respect to 100 parts by weight of the electrode active material. It is as follows. By setting the amount of the reinforcing material in the above range, the lithium ion secondary battery can exhibit high capacity and high load characteristics.

Examples of the leveling agent include surfactants such as alkyl surfactants, silicone surfactants, fluorine surfactants, and metal surfactants. A leveling agent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. By using a leveling agent, it is possible to prevent the repelling that occurs during the application of the slurry composition of the present invention, and to improve the smoothness of the electrode.
The amount of the leveling agent is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. When the leveling agent is within the above range, the productivity, smoothness, and battery characteristics during electrode production are excellent. Moreover, the dispersibility of an electrode active material can be improved in the slurry composition of this invention by containing surfactant, Furthermore, the smoothness of the electrode obtained by it can be improved.

  Examples of the thickener include cellulose polymers such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose and salts thereof; (modified) poly (meth) acrylic acid and salts thereof; (modified) polyvinyl alcohol, acrylic acid or acrylic Polyvinyl alcohols such as copolymers of acid salts and vinyl alcohol, maleic anhydride or maleic acid or copolymers of fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified polyacrylic acid, oxidized starch, phosphorus Acid starch, casein, various modified starches, acrylonitrile-butadiene copolymer hydride; and the like. Among these, cellulose polymers and salts thereof, (modified) poly (meth) acrylic acid and salts thereof are preferable, and cellulose polymers and salts thereof are more preferable. Examples of the salt include ammonium salt and alkali metal salt. One of these may be used alone, or two or more of these may be used in combination at any ratio. Here, “(modified) poly” means “unmodified poly” or “modified poly”. The amount of the thickener is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. When the thickener is in the above range, the dispersibility of the electrode active material in the slurry composition of the present invention can be further enhanced, so that a smooth electrode can be obtained. For this reason, it is possible to realize further excellent load characteristics and cycle characteristics.

Examples of the nanoparticles include particles such as fumed silica and fumed alumina. One kind of nanoparticles may be used alone, or two or more kinds of nanoparticles may be used in combination at any ratio. Since the thixotropy of the slurry composition of this invention can be adjusted when it contains a nanoparticle, the leveling property of the electrode obtained by it can be improved.
The amount of the nanoparticles is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. When the nanoparticles are in the above range, the stability and productivity of the slurry composition of the present invention can be improved, and high battery characteristics can be realized.

Examples of the electrolytic solution additive include vinylene carbonate. One electrolyte solution additive may be used alone, or two or more electrolyte solution additives may be used in combination at any ratio. By using the electrolytic solution additive, for example, decomposition of the electrolytic solution can be suppressed.
The amount of the electrolytic solution additive is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. By setting the amount of the electrolytic solution additive in the above range, a lithium ion secondary battery excellent in cycle characteristics and high temperature characteristics can be realized.

[1.6. Properties of slurry composition]
Since it has the above-described configuration, the slurry composition of the present invention usually has the following advantages.
The slurry composition of the present invention is excellent in dispersibility. That is, in the slurry composition of the present invention, components such as an electrode active material, a particulate binder, and a conductive material are uniformly dispersed. Therefore, also in the electrode active material layer manufactured using the slurry composition of this invention, since the said component can be disperse | distributed uniformly, the characteristic of a lithium ion secondary battery can be improved.

  Moreover, the slurry composition of this invention is excellent in dispersion stability. That is, the slurry composition of the present invention can maintain high dispersibility over a long period of time. Moreover, the slurry composition of the present invention is less likely to cause a change in viscosity over time. Therefore, since the slurry composition of the present invention hardly changes its properties due to storage, it can be stored for a long period of time.

  The reason why such excellent dispersibility and dispersion stability are obtained is not necessarily clear, but according to the study of the present inventor, it is presumed as follows. That is, due to the action of the hydroxyl group and acid group of the water-soluble polymer, the water-soluble polymer has a high affinity for water and also has a high affinity for the electrode active material. Therefore, in the slurry composition, a part of the water-soluble polymer is liberated in water, but another part of the water-soluble polymer is adsorbed on the surface of the electrode active material. Since the water-soluble polymer adsorbed on the electrode active material covers the surface of the electrode active material with a stable layer, the dispersibility of the electrode active material in water is improved. Also, the layer is stable and is not easily destroyed by the passage of time and temperature. Furthermore, since the water-soluble polymer has a high affinity for water, it is highly water-soluble and hardly causes precipitation. Therefore, it is considered that the slurry composition of the present invention is excellent in dispersibility and dispersion stability.

  Moreover, the slurry composition of this invention can improve a viscosity and thixotropy. The reason why the viscosity and thixotropy can be improved in this way is not necessarily clear, but according to the study of the present inventor, it is presumed as follows. That is, the water-soluble polymer of the present invention acts as a thickener in the slurry composition. In particular, the thixotropy of the slurry composition containing the water-soluble polymer can be improved by the action of the hydroxyl group-containing monomer unit. Therefore, it is considered that the viscosity and thixotropy of the slurry composition can be improved to an extent suitable for application.

[1.7. Method for producing slurry composition]
The slurry composition of the present invention can be produced, for example, by mixing an electrode active material, a water-soluble polymer and water, and if necessary, a particulate binder and optional components. The specific procedure at this time is arbitrary. For example, when producing a slurry composition containing an electrode active material, a water-soluble polymer, water, a particulate binder and a conductive material, the electrode active material, the water-soluble polymer, the particulate binder and the conductive material are simultaneously added to water. Method of mixing; after dissolving water-soluble polymer in water, mixing particulate binder dispersed in water, and then mixing electrode active material and conductive material; electrode in particulate binder dispersed in water And a method of mixing an active material and a conductive material, and mixing a water-soluble polymer dissolved in water into the mixture.

  Examples of the mixing means include mixing equipment such as a ball mill, a sand mill, a bead mill, a roll mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a homomixer, and a planetary mixer.

[2. Electrode for lithium ion secondary battery]
The electrode of the present invention (electrode for a lithium ion secondary battery) can be obtained by a production method including forming a film of the slurry composition of the present invention on a current collector and drying the film.

[2.1. Current collector]
The current collector is not particularly limited as long as it has electrical conductivity and is electrochemically durable, but a metal material is preferable because it has heat resistance. Examples of the material for the current collector include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum. Among them, the current collector used for the positive electrode is preferably aluminum, and the current collector used for the negative electrode is preferably copper. One kind of the above materials may be used alone, or two or more kinds thereof may be used in combination at any ratio.

The shape of the current collector is not particularly limited, but a sheet shape having a thickness of about 0.001 mm to 0.5 mm is preferable.
In order to increase the adhesion strength with the electrode active material layer, the current collector is preferably used after roughening the surface in advance. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. In the mechanical polishing method, for example, an abrasive cloth paper to which abrasive particles are fixed, a grindstone, an emery buff, a wire brush provided with a steel wire, or the like is used. In order to increase the adhesion strength and conductivity of the electrode active material layer, an intermediate layer may be formed on the surface of the current collector.

[2.2. Application of slurry composition)
After preparing the current collector, a film of the slurry composition of the present invention is formed on the current collector. Under the present circumstances, the film | membrane of a slurry composition is normally formed by apply | coating the slurry composition of this invention. Moreover, a slurry composition may be apply | coated to the single side | surface of a collector, and may be apply | coated to both surfaces.

There is no restriction | limiting in the coating method, For example, methods, such as a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, are mentioned.
Further, the thickness of the slurry composition film can be appropriately set according to the thickness of the target electrode active material layer.

  Since the slurry composition of the present invention has excellent coating properties, it is possible to easily form a uniform film by the above coating. Moreover, since the slurry composition of this invention is excellent in a dispersibility and dispersion stability, the obtained film | membrane is excellent in the uniformity of a composition normally. Furthermore, the slurry composition of this invention has high viscosity by including a water-soluble polymer. Therefore, in the film | membrane of the slurry composition of this invention, since a convection does not arise easily, a migration is suppressed.

[2.3. (Drying the membrane)
After forming the slurry composition film, the liquid such as water is removed from the film by drying. Thereby, the electrode active material layer containing an electrode active material and a water-soluble polymer is formed in the surface of an electrical power collector, and an electrode is obtained.

Examples of the drying method include drying with warm air, hot air, low-humidity air, or the like; vacuum drying; drying with irradiation of energy rays such as infrared rays, far infrared rays, or electron beams. Among these, a drying method by irradiation with far infrared rays is preferable.
The drying temperature and drying time are preferably a temperature and a time at which water can be removed from the slurry composition film. Specifically, the drying time is preferably 1 minute to 30 minutes, and the drying temperature is preferably 40 ° C to 180 ° C.

[2.4. Arbitrary process]
After drying the slurry composition film, it is preferable to apply pressure treatment to the electrode active material layer, for example, using a die press or a roll press, if necessary. By the pressure treatment, the porosity of the electrode active material layer can be lowered. The porosity is preferably 5% or more, more preferably 7% or more, preferably 30% or less, more preferably 20% or less. By setting the porosity to be equal to or higher than the lower limit of the above range, a high volume capacity can be easily obtained, and the electrode active material layer can be made difficult to peel from the current collector. Moreover, high charging efficiency and discharge efficiency are acquired by setting it as an upper limit or less.

  Furthermore, when the electrode active material layer includes a polymer that can be cured by a curing reaction such as a crosslinking reaction, the polymer may be cured after the electrode active material layer is formed.

[2.5. Other matters related to electrodes]
The thickness of the electrode active material layer formed as described above can be arbitrarily set according to the required battery performance.
For example, the thickness of the positive electrode active material layer is preferably 5 μm or more, more preferably 10 μm or more, preferably 300 μm or less, more preferably 250 μm or less. When the thickness of the positive electrode active material layer is in the above range, high characteristics can be realized in both load characteristics and energy density.
Further, for example, the thickness of the negative electrode active material layer is preferably 5 μm or more, more preferably 20 μm or more, particularly preferably 30 μm or more, preferably 1000 μm or less, more preferably 500 μm or less, still more preferably 300 μm or less, particularly preferably. Is 250 μm or less. When the thickness of the negative electrode active material layer is in the above range, load characteristics and cycle characteristics can be improved.

  The amount of water in the electrode active material layer is preferably 1000 ppm or less, and more preferably 500 ppm or less. By setting the moisture content of the electrode active material layer within the above range, an electrode having excellent durability can be realized. The amount of water can be measured by a known method such as the Karl Fischer method. Such a low water content can be achieved by appropriately adjusting the composition of the structural unit in the water-soluble polymer. In particular, the fluorine-containing (meth) acrylic acid ester monomer unit is preferably in the range of 0.5% by weight or more, more preferably 1% by weight or more, and preferably 20% by weight or less, more preferably 10% by weight or less. By doing so, the amount of water can be reduced.

  In the electrode of the present invention, the adhesion strength between the current collector and the electrode active material layer is strong. The reason why such a strong adhesion strength is obtained is not necessarily clear, but according to the study of the present inventor, it is presumed as follows. That is, the hydroxyl group (—OH group) and acid group of the hydroxyl group-containing monomer unit have high polarity. Therefore, the water-soluble polymer can cause a strong interaction with the polar groups present on the surfaces of the electrode active material and the current collector, and thus can be firmly bound to the electrode active material and the current collector. In particular, it is considered that high binding properties can be expressed by the action of acid groups. Therefore, the water-soluble polymer can act as a binder, and the water-soluble polymer increases the strength of the binding between the electrode active materials and the binding between the electrode active material and the current collector. It is presumed that the adhesion with the active material layer is improved. Moreover, since the slurry composition of this invention has high dispersibility, it is thought that the composition of a structural component is uniform also in the electrode active material layer regardless of the position. Therefore, in the electrode active material layer, a portion where the adhesion strength with the current collector is locally weak is unlikely to occur. Therefore, since the current collector and the electrode active material layer do not peel off starting from the portion, it is possible to improve the adhesion between the current collector and the electrode active material layer. Inferred.

  Furthermore, the electrode of the present invention has high flexibility and is not easily damaged even when bent. The reason for such a high flexibility is not necessarily clear, but according to the study of the present inventor, it is presumed as follows. That is, as described above, the electrode active material layer formed using the slurry composition of the present invention can improve the uniformity of the composition, so that a locally weak portion is generated in the electrode active material layer. Can be suppressed. For this reason, since the generation | occurrence | production of the breakage which started from the said part can be prevented, it is guessed that it is hard to break even if an electrode is bent.

[3. Lithium ion secondary battery]
The lithium ion secondary battery of this invention is equipped with a positive electrode, a negative electrode, and electrolyte solution. The lithium ion secondary battery of the present invention may include a separator. However, one or both of the negative electrode and the positive electrode is an electrode of the present invention. By providing the electrode of the present invention, the lithium ion secondary battery of the present invention is excellent in cycle characteristics and output characteristics, and in particular, the high temperature cycle characteristics and the low temperature characteristics can be remarkably improved. The reason why the lithium ion secondary battery of the present invention is excellent in cycle characteristics and output characteristics is not clear, but according to the study of the present inventors, it is presumed that the reason is as follows.

In the electrode of the present invention, the adhesion strength between the electrode active material layer and the current collector is high. Therefore, even if the electrode active material repeatedly expands and contracts due to charge and discharge, the electrode active material layer and the current collector are unlikely to peel off. Further, since the water-soluble polymer has high binding properties, the contact between the electrode active material layers and the contact between the electrode active material and the conductive material are hardly impaired. For this reason, since the electric conduction path is not easily cut by charging / discharging, the degree of increase in resistance accompanying charging / discharging is low.
Moreover, in the electrode of this invention, a part of water-soluble polymer has adhered to the surface of the electrode active material. That is, it is considered that at least a part of the surface of the electrode active material is covered with a water-soluble polymer film. Since the coating can suppress decomposition of the electrolytic solution, it is possible to suppress an increase in resistance caused by a gas generated by the decomposition of the electrolytic solution.
For these reasons, it is assumed that the lithium ion secondary battery of the present invention can exhibit excellent cycle characteristics.

Furthermore, since the fluorine-containing (meth) acrylic acid ester monomer unit has high ionic conductivity, the water-soluble polymer also has high ionic conductivity. Therefore, even if the water-soluble polymer film covers the surface of the electrode active material, the degree of resistance increase due to the film can be reduced. Therefore, the resistance of the electrode can be suppressed.
Moreover, the swelling property of the water-soluble polymer with respect to electrolyte solution can be made small by including a fluorine-containing (meth) acrylic acid ester monomer unit. Therefore, swelling of the electrode can be suppressed in the lithium ion secondary battery. Therefore, swelling of the electrode active material layer can be suppressed, and the distance between the electrode active materials can be reduced. Therefore, the internal resistance of the electrode can be suppressed.
Furthermore, in general, polymers containing fluorine-containing (meth) acrylic acid ester monomer units tend to become less compatible with the electrolyte solution, but in the water-soluble polymer according to the present invention, hydroxyl group-containing monomer units. In addition, it is considered that the compatibility with the electrolytic solution is not deteriorated by the action of the acid group-containing monomer unit. Rather, since the water-soluble polymer has a hydroxyl group and an acid group, the affinity of the water-soluble polymer with respect to the polar solvent is increased, and the electrode active material layer has excellent wettability with respect to the electrolytic solution. Accordingly, since the electrolytic solution can easily enter the electrode active material layer, the electric reaction field between the electrolytic solution and the electrode active material can be easily widened, and the internal resistance of the battery can be suppressed. .
For these reasons, it is assumed that the lithium ion secondary battery of the present invention can exhibit excellent output characteristics.

[3.1. Electrolyte)
As the electrolytic solution, for example, a solution obtained by dissolving a lithium salt as a supporting electrolyte in a non-aqueous solvent may be used. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and other lithium salts. In particular, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li that are easily soluble in a solvent and exhibit a high degree of dissociation are preferably used. One of these may be used alone, or two or more of these may be used in combination at any ratio.

  The amount of the supporting electrolyte is preferably 1% by weight or more, more preferably 5% by weight or more, and preferably 30% by weight or less, more preferably 20% by weight or less with respect to the electrolytic solution. If the amount of the supporting electrolyte is too small or too large, the ionic conductivity is lowered, and the charging characteristics and discharging characteristics of the secondary battery may be lowered.

  The solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. Examples of the solvent include alkyl carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and methyl ethyl carbonate (MEC); Examples include esters such as butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; and the like. In particular, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferred because high ion conductivity is easily obtained and the use temperature range is wide. A solvent may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Moreover, you may make an electrolyte solution contain an additive as needed. As the additive, for example, carbonate compounds such as vinylene carbonate (VC) are preferable. An additive may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

Examples of the electrolytic solution other than the above include a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide and polyacrylonitrile with an electrolytic solution; an inorganic solid electrolyte such as lithium sulfide, LiI, and Li ₃ N; Can do.

[3.2. separator〕
As the separator, a porous substrate having a pore portion is usually used. Examples of separators include (a) a porous separator having pores, (b) a porous separator having a polymer coating layer formed on one or both sides, and (c) a porous resin coat containing inorganic ceramic powder. And a porous separator having a layer formed thereon. Examples of these include polypropylene, polyethylene, polyolefin or aramid porous separators; for solid polymer electrolytes such as polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile or polyvinylidene fluoride hexafluoropropylene copolymers Or a polymer film for a gel polymer electrolyte; a separator coated with a gelled polymer coat layer; a separator coated with a porous film layer composed of an inorganic filler and an inorganic filler dispersant; and the like.

[3.3. Method for producing lithium ion secondary battery]
The manufacturing method of the lithium ion secondary battery of the present invention is not particularly limited. For example, the above-described negative electrode and positive electrode may be overlapped via a separator, and this may be wound or folded in accordance with the shape of the battery and placed in the battery container, and the electrolyte may be injected into the battery container and sealed. Furthermore, if necessary, an expanded metal; an overcurrent prevention element such as a fuse or a PTC element; a lead plate or the like may be inserted to prevent an increase in pressure inside the battery or overcharge / discharge. The shape of the battery may be any of, for example, a laminate cell type, a coin type, a button type, a sheet type, a cylindrical type, a square type, and a flat type.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the embodiments shown below, and may be arbitrarily modified and implemented without departing from the scope of the claims of the present invention and its equivalent scope.
In the following description, “%” and “part” representing amounts are based on weight unless otherwise specified. In addition, the operations described below were performed under normal temperature and normal pressure conditions unless otherwise specified.

[Evaluation item]
(1) Adhesion strength The electrodes produced in the examples and comparative examples were cut into rectangles having a length of 100 mm and a width of 10 mm to obtain test pieces. Cellophane tape was affixed on the surface of the electrode active material layer of the test piece with the surface of the electrode active material layer facing down. At this time, a cellophane tape defined in JIS Z1522 was used. The cellophane tape was fixed on a horizontal test bench. Then, the stress when one end of the current collector was pulled vertically upward at a pulling speed of 50 mm / min and peeled was measured. This measurement was performed three times, the average value of the measured values was obtained, and the average value was taken as the peel strength. The higher the peel strength, the higher the binding force of the electrode active material layer to the current collector, that is, the higher the adhesion strength.

(2) Flexibility The electrodes manufactured in Examples and Comparative Examples were cut into rectangles having a length of 100 mm and a width of 10 mm to obtain test pieces. With the electrode active material layer of this test piece on the outside and the current collector side on the inside, the test piece is wrapped around a SUS rod having various bending diameters, and the minimum bending diameter that does not crack the electrode active material layer is visually observed. Observed. It shows that it is excellent in the softness, so that this bending diameter is small.

(3) Dispersion stability About the slurry composition for lithium ion secondary battery electrodes manufactured by the Example and the comparative example, the viscosity (eta) 0 in 60 rpm was measured with the B-type viscosity meter. The slurry composition was stored at room temperature for 7 days, and after storage, the viscosity η1 at 60 rpm was measured. Δη (%) = η1 / η0 × 100 was calculated. The smaller the value of Δη, the better the dispersion stability.

(4) Cycle characteristics In the examples and comparative examples, a lithium ion secondary battery of a laminate type cell was produced and allowed to stand for 24 hours in an environment of 25 ° C. Thereafter, this secondary battery was charged and discharged to 4.2 V and discharged to 3.0 V by a 1 C constant current method in an environment of 25 ° C., and the initial capacity C0 was measured. Furthermore, this secondary battery was repeatedly charged and discharged in the same manner as the above-described charging and discharging in a 60 ° C. environment, and the capacity C2 after 1000 cycles was measured. The high-temperature cycle characteristics were evaluated by a capacity retention rate represented by ΔC = C2 / C0 × 100 (%). It shows that it is excellent in high temperature cycling characteristics, so that this capacity | capacitance maintenance factor is high.

(5) Low temperature characteristics In the examples and comparative examples, lithium ion secondary batteries of laminate type cells were produced and allowed to stand for 24 hours in an environment of 25 ° C. Thereafter, in a 25 ° C. environment, an operation of charging with a constant current method of 0.1 C over 5 hours was performed, and the voltage V0 at that time was measured. Thereafter, a discharge operation was performed at a discharge rate of 1 C in a -10 ° C environment, and the voltage V1 15 seconds after the start of discharge was measured. The low temperature characteristics were evaluated by a voltage change represented by ΔV = V0−V1. It shows that it is excellent in a low-temperature characteristic, so that this voltage change is small.

[Example 1]
(1-1. Production of water-soluble polymer)
In a 5 MPa pressure vessel with a stirrer, 4 parts 2-hydroxyethyl acrylate (hydroxyl group-containing monomer), 32.5 parts methacrylic acid (acid group-containing monomer), 0.8 ethylene dimethacrylate (crosslinkable monomer) Parts, 2,2,2-trifluoroethyl methacrylate (fluorine-containing (meth) acrylic acid ester monomer) 7.5 parts, ethyl acrylate (optional monomer) 55.2 parts, sodium dodecylbenzenesulfonate ( Surfactant) 0.1 part, t-dodecyl mercaptan (molecular weight regulator) 0.1 part, ion-exchanged water 150 part, and potassium persulfate (polymerization initiator) 0.5 part were added and sufficiently stirred. Then, it heated to 60 degreeC and superposition | polymerization was started. When the polymerization conversion reached 96%, the reaction was stopped by cooling to obtain a mixture containing a water-soluble polymer. 10% aqueous ammonia was added to the mixture containing the water-soluble polymer to adjust the pH to 8 to obtain an aqueous solution containing the desired water-soluble polymer. A part of this aqueous solution was taken out, the concentration was adjusted to 1%, and the viscosity of the adjusted aqueous solution was measured.

(1-2. Production of particulate binder)
In a 5 MPa pressure vessel equipped with a stirrer, 76 parts of 2-ethylhexyl acrylate, 20 parts of acrylonitrile, 4 parts of itaconic acid, 1 part of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and potassium persulfate as a polymerization initiator 8 parts was added and stirred thoroughly. Then, it heated to 50 degreeC and superposition | polymerization was started. When the polymerization conversion reached 96%, the reaction was stopped by cooling to obtain a mixture containing a particulate binder. The mixture containing the particulate binder was adjusted to pH 8 by adding a 5% aqueous sodium hydroxide solution. Then, after removing the unreacted monomer from the mixture containing the particulate binder by heating under reduced pressure, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired particulate binder.

(1-3. Production of positive electrode)
100 parts of LiCoO ₂ having a volume average particle diameter of 12 μm as the positive electrode active material, ₂ parts of acetylene black (“HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd.) as the conductive material, and the aqueous solution of the above step (1-1) as the thickener 2 parts of an aqueous solution containing a conductive polymer corresponding to the solid content, 2 parts of the aqueous dispersion containing the particulate binder in the above step (1-2) as a binder prepared to a concentration of 40%, and Ion exchange water was mixed. The amount of ion-exchanged water was such that the total solid concentration was 40%. These were mixed by a planetary mixer to prepare a positive electrode slurry composition. This positive electrode slurry composition was evaluated for dispersion stability in the manner described above.

  The slurry composition for positive electrode was applied on a 20 μm-thick aluminum foil as a current collector with a comma coater so that the film thickness after drying was about 130 μm and dried. This drying was performed by conveying the aluminum foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a positive electrode raw material. This positive electrode original fabric was rolled with a roll press to obtain a positive electrode having a positive electrode active material layer thickness of 80 μm. About this positive electrode, the adhesive strength and the softness | flexibility were evaluated in the way mentioned above.

(1-4. Production of binder composition for negative electrode)
In a 5 MPa pressure vessel with a stirrer, 33.5 parts of 1,3-butadiene, 3.5 parts of itaconic acid, 62 parts of styrene, 1 part of 2-hydroxyethyl acrylate, 0.4 part of sodium dodecylbenzenesulfonate as an emulsifier, ion exchange 150 parts of water and 0.5 part of potassium persulfate as a polymerization initiator were added and sufficiently stirred. Then, it heated to 50 degreeC and superposition | polymerization was started. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a particulate binder (SBR). The mixture containing the particulate binder was adjusted to pH 8 by adding a 5% aqueous sodium hydroxide solution. Then, after removing the unreacted monomer from the mixture containing the particulate binder by heating under reduced pressure, the mixture is cooled to 30 ° C. or lower, and an aqueous dispersion containing the desired particulate binder (a binder composition for negative electrode) Product).

(1-5. Production of slurry composition for negative electrode)
In a planetary mixer with a disper, 100 parts of artificial graphite (volume average particle diameter: 24.5 μm) having a specific surface area of 5.5 m ² / g as a negative electrode active material, and carboxymethyl cellulose (manufactured by Nippon Paper Chemical Co., Ltd. “ 1 part of a 2% aqueous solution of “MAC-350HC”) corresponding to the solid content was added, and the solid content concentration was adjusted to 65% with ion-exchanged water, and then mixed at 25 ° C. for 60 minutes. Next, after adjusting to 60% of solid content concentration with ion-exchange water, it mixed for 15 minutes at 25 degreeC, and the liquid mixture was obtained. 1.0 part of the aqueous dispersion containing the particulate binder in the above step (1-4) and ion-exchanged water are added to the mixed liquid, and the final solid content concentration is adjusted to 52%. And mixed for another 10 minutes. This was defoamed under reduced pressure to obtain a negative electrode slurry composition having good fluidity.

(1-6. Production of negative electrode)
Apply the slurry composition for negative electrode obtained in the above step (1-5) on a copper foil having a thickness of 20 μm, which is a current collector, with a comma coater so that the film thickness after drying becomes about 150 μm. And dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Then, the negative electrode original fabric was obtained by heat-processing at 120 degreeC for 2 minute (s). This negative electrode original fabric was rolled with a roll press to obtain a negative electrode having a negative electrode active material layer thickness of 80 μm.

(1-7. Preparation of separator)
A single-layer polypropylene separator (“Celguard 2500” manufactured by Celgard) was cut into a 5 × 5 cm ² square.

(1-8. Lithium ion secondary battery)
An aluminum packaging exterior was prepared as the battery exterior. The positive electrode obtained in the above step (1-3) was cut into a 4 × 4 cm ² square and placed so that the surface on the current collector side was in contact with the aluminum packaging exterior. On the surface of the positive electrode active material layer of the positive electrode, the square separator obtained in the above step (1-7) was disposed. Furthermore, the negative electrode obtained in the above step (1-6) was cut into a 4.2 × 4.2 cm ² square, and this was placed on the separator so that the surface on the negative electrode active material layer side faces the separator. An electrolyte solution (solvent: ethylene carbonate / diethyl carbonate / vinylene carbonate = 68.5 / 30 / 1.5 volume ratio, electrolyte: LiPF ₆ having a concentration of 1 M) was injected so that no air remained. Furthermore, in order to seal the opening of the aluminum packaging material, heat sealing at 150 ° C. was performed to close the aluminum exterior, and a lithium ion secondary battery was manufactured. About this lithium ion secondary battery, the high temperature cycling characteristic and the low temperature characteristic were evaluated in the way mentioned above.

[Example 2]
In the above step (1-1), lithium ion was changed in the same manner as in Example 1 except that the amount of 2-hydroxyethyl acrylate was changed to 0.8 parts and the amount of ethyl acrylate was changed to 58.4 parts. Secondary batteries were manufactured and evaluated.

[Example 3]
In the above step (1-1), lithium ion was changed in the same manner as in Example 1 except that the amount of 2-hydroxyethyl acrylate was changed to 9.5 parts and the amount of ethyl acrylate was changed to 49.7 parts. Secondary batteries were manufactured and evaluated.

[Example 4]
In the step (1-1), a lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that 4 parts of 2-hydroxyethyl methacrylate was used instead of 2-hydroxyethyl acrylate.

[Example 5]
Copolymerization was carried out in the same manner as in the above step (1-1) except that vinyl acetate was used instead of 2-hydroxyethyl acrylate, and the resulting polymer was hydrolyzed with sodium hydroxide to produce acetic acid. The vinyl unit was converted to a vinyl alcohol unit to obtain an aqueous solution containing a water-soluble polymer. Here, the vinyl acetate unit refers to a structural unit having a structure formed by polymerizing vinyl acetate. Moreover, a vinyl alcohol unit shows the structural unit which has a structure formed by superposing | polymerizing vinyl alcohol. A lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that the aqueous solution containing the water-soluble polymer thus obtained was used as a thickener in the above step (1-3).

[Example 6]
A lithium ion secondary battery was manufactured in the same manner as in Example 1 except that 7.5 parts of perfluorooctyl acrylate was used instead of 2,2,2-trifluoroethyl methacrylate in the above step (1-1). Manufactured and evaluated.

[Example 7]
A lithium ion secondary battery was prepared in the same manner as in Example 1 except that 7.5 parts of perfluorobutyl acrylate was used instead of 2,2,2-trifluoroethyl methacrylate in the above step (1-1). Manufactured and evaluated.

[Example 8]
Same as Example 1 except that the amount of 2,2,2-trifluoroethyl methacrylate was changed to 0.2 parts and the amount of ethyl acrylate was changed to 62.5 parts in the above step (1-1). Thus, a lithium ion secondary battery was manufactured and evaluated.

[Example 9]
In the above step (1-1), the procedure was the same as in Example 1 except that the amount of 2,2,2-trifluoroethyl methacrylate was changed to 48 parts and the amount of ethyl acrylate was changed to 14.7 parts. A lithium ion secondary battery was manufactured and evaluated.

[Example 10]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the amount of methacrylic acid was changed to 22 parts and the amount of ethyl acrylate was changed to 65.7 parts in the above step (1-1). And evaluated.

[Example 11]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the amount of methacrylic acid was changed to 48 parts and the amount of ethyl acrylate was changed to 39.7 parts in the above step (1-1). And evaluated.

[Example 12]
In the above step (1-1), the same procedure as in Example 1 was performed except that 25 parts of 2-acrylamido-2-methylpropanesulfonic acid was used instead of methacrylic acid and the amount of ethyl acrylate was changed to 62.7 parts. A lithium ion secondary battery was manufactured and evaluated.

[Example 13]
In the above step (1-1), 30.0 parts of methacrylic acid and 5.0 parts of 2-acrylamido-2-methylpropanesulfonic acid are used in combination as the acid group-containing monomer, and the amount of ethyl acrylate is 52.7. A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except that the part was changed to a part.

[Example 14]
In the step (1-1), the lithium ion secondary was changed in the same manner as in Example 1 except that the amount of ethylene dimethacrylate was changed to 0.1 part and the amount of ethyl acrylate was changed to 55.9 parts. A battery was manufactured and evaluated.

[Example 15]
In the step (1-1), the lithium ion secondary was changed in the same manner as in Example 1 except that the amount of ethylene dimethacrylate was changed to 1.8 parts and the amount of ethyl acrylate was changed to 54.2 parts. A battery was manufactured and evaluated.

[Example 16]
In the above step (1-1), a lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that 0.8 part of glycidyl methacrylate was used instead of ethylene dimethacrylate.

[Example 17]
In the above step (1-1), a lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that 0.8 part of allyl glycidyl ether was used instead of ethylene dimethacrylate.

[Example 18]
In the above step (1-3), a lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that no binder was used.

[Example 19]
(19-1. Production of slurry composition for negative electrode)
In a planetary mixer with a disper, 100 parts of artificial graphite (average particle size: 24.5 μm) having a specific surface area of 5.5 m ² / g as a negative electrode active material, and the water-soluble heavy of the above step (1-1) as a thickener 2 parts of the aqueous solution containing the coalesced was added in an amount corresponding to the solid content, and ion-exchanged water was further added to adjust the solid content concentration to 65%, followed by mixing at 25 ° C. for 60 minutes. Next, ion-exchanged water was added to adjust the solid content concentration to 60%, and the mixture was further mixed at 25 ° C. for 15 minutes to obtain a mixed solution. 1.0 part of the aqueous dispersion containing the particulate binder in the above step (1-4) and ion-exchanged water are added to the mixed liquid, and the final solid content concentration is adjusted to 52%. And mixed for another 10 minutes. This was defoamed under reduced pressure to obtain a slurry composition for negative electrode having good fluidity. With respect to this negative electrode slurry composition, the dispersion stability was evaluated in the manner described above.

(19-2. Production of negative electrode)
Apply the slurry composition for negative electrode obtained in the above step (19-1) on a copper foil having a thickness of 20 μm, which is a current collector, with a comma coater so that the film thickness after drying is about 150 μm. And dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Then, the negative electrode original fabric was obtained by heat-processing at 120 degreeC for 2 minute (s). This negative electrode original fabric was rolled with a roll press to obtain a negative electrode having a negative electrode active material layer thickness of 80 μm. About this negative electrode, the adhesive strength and the softness | flexibility were evaluated in the way mentioned above.

(19-3. Production of positive electrode)
A positive electrode was produced in the same manner as in Step (1-3) of Example 1 except that 1 part of a 2% aqueous solution of carboxymethyl cellulose (“MAC350HC” manufactured by Nippon Paper Chemical Co., Ltd.) was used as a thickener. .

(19-4. Lithium ion secondary battery)
In the same manner as in the step (1-8) of Example 1, except that the negative electrode was obtained in the step (19-2) and the positive electrode was obtained in the step (19-3), A lithium ion secondary battery was manufactured. About this lithium ion secondary battery, the high temperature cycling characteristic and the low temperature characteristic were evaluated in the way mentioned above.

[Example 20]
Implemented except that 90 parts of artificial graphite (volume average particle diameter: 24.5 μm) and 10 parts of SiO _x (volume average particle diameter: 5 μm) were used as the negative electrode active material in combination with a specific surface area of 5.5 m ² / g. In the same manner as in Example 19, a lithium ion secondary battery was produced and evaluated.

[Example 21]
Implemented except that 70 parts of artificial graphite (volume average particle diameter: 24.5 μm) and 30 parts of SiO _x (volume average particle diameter: 8 μm) were used in combination as the negative electrode active material with a specific surface area of 5.5 m ² / g. In the same manner as in Example 19, a lithium ion secondary battery was produced and evaluated.

[Example 22]
²⁰⁰ g of silicon oxide powder (SiO _x : x = 1.02) having a volume average particle diameter of 3 μm and a BET specific surface area of 12 m ² / g was placed in a silicon nitride tray. Then, it left still in the processing furnace which can hold | maintain an atmosphere. Next, argon gas was introduced into the processing furnace to replace the inside of the processing furnace with argon. While flowing argon gas at a flow rate of 2 NL / min, the temperature was raised to 1200 ° C. at a heating rate of 300 ° C./hour, and held for 3 hours. After holding, the temperature began to drop and cooled to room temperature. After reaching room temperature, the powder was collected. The obtained powder was a powder having a volume average particle size of 3.5 μm and a BET specific surface area of 11 m ² / g. When an X-ray diffraction pattern by Cu—Kα ray was measured for this powder, a diffraction line attributed to Si (111) near 2θ = 28.4 ° was present in the measured X-ray diffraction pattern. Analysis by the Scherrer method from the half-value width of this diffraction line revealed that the obtained powder was a silicon composite powder having a crystallite size of 40 nm of silicon dispersed in silicon dioxide. confirmed.

  A lithium ion secondary battery was produced and evaluated in the same manner as in Example 19 except that the silicon composite powder thus obtained was used as the negative electrode active material.

[Example 23]
The granular polycrystalline silicon produced by introducing polycrystalline silicon fine particles into a fluidized bed with an internal temperature of 800 ° C. and feeding monosilane was pulverized using a jet mill. Thereafter, the powder obtained by pulverization was classified with a classifier to obtain a polycrystalline silicon powder having a volume average particle diameter D50 = 10.2 μm. Analysis by the Scherrer method from the full width at half maximum of the X-ray diffraction line confirmed that the crystallite size was 44 nm.

  A lithium ion secondary battery was produced and evaluated in the same manner as in Example 19 except that the polycrystalline silicon powder thus obtained was used as the negative electrode active material.

[Comparative Example 1]
In the above step (1-3), a lithium ion secondary battery was obtained in the same manner as in Example 1, except that 1 part of carboxymethyl cellulose (“MAC350HC” manufactured by Nippon Paper Chemical Co., Ltd.) was used as a thickener. Were manufactured and evaluated.

[Comparative Example 2]
In the above step (1-3), a lithium ion secondary battery was prepared in the same manner as in Example 1 except that 1 part of polyvinyl alcohol (“Poval 117” manufactured by Kuraray Co., Ltd.) was used as a thickener. Manufactured and evaluated.

[Comparative Example 3]
In the above step (1-3), a lithium ion secondary was prepared in the same manner as in Example 1, except that 1 part of polyacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd., molecular weight 1000000) was used as the thickener. A battery was manufactured and evaluated.

[Comparative Example 4]
In the above step (1-1), the same procedure as in Example 1 was carried out except that the amount of ethyl acrylate was changed to 53.5 parts without using 2,2,2-trifluoroethyl methacrylate and ethylene dimethacrylate. A lithium ion secondary battery was manufactured and evaluated.

[Comparative Example 5]
In the above step (19-1), lithium was used in the same manner as in Example 19 except that 1 part of a 2% aqueous solution of carboxymethylcellulose (“MAC350HC” manufactured by Nippon Paper Chemical Co., Ltd.) was used as the thickener. An ion secondary battery was manufactured and evaluated.

[result]
The results of each Example and Comparative Example are shown in Tables 1-6. Here, the meanings of the abbreviations in the following table are as follows.
LCO: LiCoO ₂
Si-based active material A: silicon composite powder Si-based active material B: polycrystalline silicon powder OH monomer: hydroxyl group-containing monomer β-HEA: 2-hydroxyethyl acrylate HEMA: 2-hydroxyethyl methacrylate F monomer : Fluorine-containing (meth) acrylic acid ester monomer 3FM: 2,2,2-trifluoroethyl methacrylate PFOA: Perfluorooctyl acrylate PFBA: Perfluorobutyl acrylate Acid monomer: Acid group-containing monomer MAA: Methacryl Acid AMPS: 2-acrylamido-2-methylpropanesulfonic acid EDMA: Ethylene dimethacrylate GMA: Glycidyl methacrylate AGE: Allyl glycidyl ether EA: Ethyl acrylate ACL: Acrylic rubber SBR: Styrene butadiene rubber CMC: Carboxy Chill cellulose PVOH: polyvinyl alcohol PAA: Polyacrylic acid

[Consideration]
Among the examples and comparative examples described above, Examples 1 to 18 and Comparative Examples 1 to 4 were obtained by applying the slurry composition to the positive electrode, and Examples 19 to 23 and Comparative Example 5 were prepared using the slurry composition as the negative electrode. It is applied. From the above table, it can be seen that the present invention can realize a lithium ion secondary battery having excellent high-temperature cycle characteristics and low-temperature characteristics. Moreover, by comparing an Example and a comparative example, it turns out that the slurry composition of this invention is excellent in dispersion stability. Furthermore, it turns out that the electrode manufactured using the slurry composition of this invention is excellent in adhesive strength and a softness | flexibility.

Claims (12)

Including an electrode active material, a water-soluble polymer and water,
Lithium ion secondary, wherein the water-soluble polymer includes a hydroxyl group-containing monomer unit of 0.5 wt% to 10 wt%, a fluorine-containing (meth) acrylic acid ester monomer unit, and an acid group-containing monomer unit. A slurry composition for battery electrodes.   The slurry composition of Claim 1 whose 1 weight% aqueous solution viscosity of the said water-soluble polymer is 10 mPa * s-1000 mPa * s.   The slurry composition according to claim 1 or 2, wherein the water-soluble polymer further contains 0.05 wt% to 2 wt% of a crosslinkable monomer unit.   The slurry composition as described in any one of Claims 1-3 whose quantity of the said water-soluble polymer is 0.1 weight part-10 weight part with respect to 100 weight part of electrode active materials.   The slurry as described in any one of Claims 1-4 whose ratio of the said fluorine-containing (meth) acrylic acid ester monomer unit in the said water-soluble polymer is 0.1 to 50 weight%. Composition.   The slurry composition as described in any one of Claims 1-5 whose ratio of the said acid group containing monomer unit in the said water-soluble polymer is 20 to 50 weight%.   The slurry composition as described in any one of Claims 1-6 in which the said water-soluble polymer contains 25 to 75 weight% of (meth) acrylic acid ester monomer units.   The slurry composition according to any one of claims 1 to 7, further comprising a particulate binder.   The slurry composition according to claim 8, wherein the particulate binder is an acrylic soft polymer or a diene soft polymer.   The slurry composition according to any one of claims 1 to 9, wherein the acid group-containing monomer is an ethylenically unsaturated carboxylic acid monomer or an ethylenically unsaturated sulfonic acid monomer.   The electrode for lithium ion secondary batteries obtained by forming the film | membrane of the slurry composition as described in any one of Claims 1-10 on a collector, and drying the said film | membrane. A lithium ion secondary battery comprising a positive electrode, a negative electrode and an electrolyte solution,
The lithium ion secondary battery whose one or both of the said positive electrode and a negative electrode are the electrodes for lithium ion secondary batteries of Claim 11.