JP2015125964A - Composition for forming secondary battery electrode, secondary battery electrode and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition for forming a secondary battery electrode containing a conductive assistant, which is excellent in dispersion stability of the conductive assistant and dispersion stability of a mixture slurry, and also to provide an electrode and a secondary battery having excellent discharge capacity, by using the composition for forming a secondary battery electrode.SOLUTION: A composition for forming a secondary battery electrode contains a polyvinyl alcohol-polyvinylpyrrolidone graft copolymer and a carbon material (C) serving as a conductive assistant.

Description

  The present invention relates to a composition for forming a secondary battery electrode for producing an electrode constituting a secondary battery, a secondary battery electrode and a secondary battery obtained using the same. It is related with the composition for secondary battery electrode formation for manufacturing a lithium secondary battery, the electrode for secondary batteries, and a secondary battery especially.

  In recent years, small portable electronic devices such as digital cameras and mobile phones have always been required to reduce weight and minimize volume, and the batteries to be mounted are light and small. A battery having a large discharge capacity is required. In addition, large non-aqueous electrolyte secondary batteries are demanded in place of conventional lead-acid batteries in large-sized secondary batteries for automobiles and the like.

  In order to meet these demands, lithium secondary batteries are being actively developed. A positive electrode and a negative electrode are used as electrodes of the lithium secondary battery. The positive electrode is obtained by fixing an electrode mixture composed of a positive electrode active material containing lithium ions, a conductive additive, an organic binder, and the like to the surface of a current collector of metal foil. On the other hand, the negative electrode is obtained by fixing an electrode mixture composed of a negative electrode active material from which lithium ions can be inserted and removed, a conductive additive, an organic binder, and the like to the surface of a current collector of metal foil.

  In general, lithium transition metal composite oxides such as lithium cobaltate and lithium manganate are used as the positive electrode active material, but these have low electronic conductivity and have sufficient battery performance when used alone. I can't get it. Therefore, an attempt has been made to improve the conductivity by adding a material having excellent conductivity as a conductive additive and reduce the internal resistance of the electrode. In general, carbon materials such as carbon black (for example, acetylene black) and graphite (graphite) have been studied.

  On the other hand, graphite is usually used as the negative electrode active material. Although graphite itself has conductivity, it is known that charge and discharge characteristics are improved by adding carbon black such as acetylene black as a conductive aid together with graphite. This is because the graphite particles generally used are large, so if graphite alone is used, the gap when filled in the electrode layer will increase. However, when carbon black is used as a conductive additive, fine carbon black is used. This is probably because the contact area is increased by filling the gaps between the graphite particles and the electrical conductivity is increased. However, in this case as well, the conductive effect is reduced if the dispersion of the conductive aid is insufficient.

As described above, reducing the internal resistance of the electrode is one of the very important elemental technologies for improving the efficiency of discharging with a large current and charging / discharging.
However, a carbon material (conducting aid) having excellent conductivity has a strong cohesive force, and it is difficult to uniformly mix and disperse in a slurry for forming an electrode mixture of a lithium secondary battery, and is a conducting aid. When the dispersibility and particle size of the carbon material are insufficiently controlled, the internal resistance of the electrode cannot be reduced because a uniform conductive network is not formed, and as a result, the lithium transition metal composite oxide or graphite that is the active material Thus, there arises a problem that the battery performance is deteriorated due to insufficient performance. In addition, if the dispersion of the conductive additive in the electrode mixture is insufficient, a resistance distribution occurs on the electrode plate due to partial aggregation, and current is concentrated when used as a battery. Problems such as heat generation and accelerated deterioration may occur.

  Moreover, the slurry for forming an electrode mixture tends to increase in particle size over time, resulting in a decrease in coatability and a decrease in battery productivity. Therefore, it is necessary to maintain the dispersibility and particle size of the carbon material. It is necessary to maintain the dispersibility and particle size of the carbon material.

  In the lithium secondary battery, the dispersion of the carbon material, which is a conductive auxiliary agent, is considered as one of the important technologies in the lithium secondary battery, and several proposals have been made. For example, Patent Document 1 describes an example in which an organic dye derivative having an acidic functional group or a triazine derivative having an acidic functional group is used as a dispersing agent when dispersing a carbon material that is a conductive additive. Patent Document 2 describes an example in which a polyvinyl acetal resin is used as a dispersant. According to these methods, it is possible to prepare a dispersion and mixture slurry of a carbon material excellent in dispersion stability, and the improvement in battery performance which is considered to be caused by the dispersion effect of the carbon material is achieved. In order to stably produce batteries, further aging stability of the dispersion is required.

International Publication No. 2008/108360 JP 2011-184664 A

  The problem to be solved by the present invention is to form a secondary battery electrode that is excellent in the dispersion stability of the conductive assistant and the dispersion stability of the composite slurry in the composition for forming a secondary battery electrode containing the conductive assistant. It is to provide a composition. Moreover, it is providing the electrode and secondary battery which were excellent in discharge capacity by using this.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that when dispersing a carbon material as a conductive additive, at least one of a resin, that is, a polyvinyl alcohol-polyvinylpyrrolidone graft copolymer. Is used as a dispersant to obtain a composition for forming a secondary battery electrode (dispersion and mixture slurry) that is excellent in dispersion stability, excellent in electrode adhesion, and effective in improving the performance of a secondary battery. The present invention has been found and achieved.

  That is, the embodiment of the present invention relates to a composition for forming a secondary battery electrode comprising a polyvinyl alcohol-polyvinylpyrrolidone graft copolymer and a carbon material (C) as a conductive auxiliary agent.

In addition, the embodiment of the present invention further relates to the above-mentioned composition for forming a secondary battery electrode comprising an organic dye derivative having an acidic functional group and / or a derivative (D) which is a triazine derivative having an acidic functional group.
Moreover, the embodiment of this invention is related with the said composition for secondary battery electrode formation which contains a solvent (E) further.

Moreover, the embodiment of this invention is related with the said composition for secondary battery electrode formation which further contains a binder (F).
Moreover, the embodiment of this invention is related with the said composition for secondary battery electrode formation which further contains an active material (G).
Moreover, the embodiment of the present invention is the above composition for forming a secondary battery electrode, wherein the ratio of the average particle size of the active material (G) / the dispersed particle size (D50) of the carbon material (C) is 2 or more and 100 or less. Related to things.

  In addition, an embodiment of the present invention relates to an electrode for a secondary battery, which is an electrode having a composite material layer on a current collector, wherein the composite material layer is formed of the composition for forming a secondary battery electrode.

  An embodiment of the present invention is a secondary battery comprising a positive electrode having a positive electrode mixture layer on a current collector, a negative electrode having a negative electrode mixture layer on the current collector, and an electrolyte. The present invention relates to a secondary battery in which at least one of a positive electrode and a negative electrode is the secondary battery electrode.

  According to a preferred embodiment of the present invention, it is possible to provide an electrode-forming composition that is excellent in dispersibility of an active material and a conductive additive. Moreover, the electrode and the secondary battery using the electrode forming composition of the present invention can improve charge / discharge cycle characteristics. This is not only because the dispersion of carbon material particles and the mixture slurry, which are excellent in dispersion stability, can be prepared by using a dispersant, but also by using a resin, that is, a polyvinyl alcohol / polyvinylpyrrolidone graft copolymer. This is considered to cause a uniform and strong interaction between the active material (E) and the carbon material (C) during electrode production. Therefore, the composition for forming a secondary battery electrode of the present invention can be used for a lithium secondary battery, a nickel hydride secondary battery, a nickel cadmium secondary battery, an alkaline manganese battery, a lead battery, a fuel cell, a capacitor, and the like. In particular, it is suitable for use in a lithium secondary battery.

<Polyvinyl alcohol-polyvinylpyrrolidone graft copolymer>
Hereinafter, the present invention will be described in detail.
The polyvinyl alcohol-polyvinylpyrrolidone graft copolymer of the present invention (hereinafter sometimes simply referred to as “graft copolymer”) has a proportion of vinylpyrrolidone units in the graft copolymer of 2 to 90 mol%. Is preferred. When the ratio of the vinylpyrrolidone unit is out of this range, performance deterioration such as dispersibility is observed.

  The degree of polymerization of the polyvinyl alcohol segment in the graft copolymer of the present invention is preferably 100 to 3500. When the degree of polymerization of the polyvinyl alcohol segment is less than 100, performance deterioration such as a decrease in dispersibility is observed, and when the degree of polymerization exceeds 3500, the viscosity of the polymer solution increases and becomes difficult to handle.

  Furthermore, it is preferable that the weight average molecular weights of a polyvinylpyrrolidone segment are 1000-1 million. When the weight average molecular weight of the polyvinyl pyrrolidone segment is less than 1000, performance degradation such as dispersibility is observed. On the other hand, if it exceeds 1,000,000, the viscosity of the polymer solution becomes high and becomes difficult to handle.

Although the manufacturing method of the graft copolymer of this invention is not specifically limited, The method of grafting polyvinylpyrrolidone to polyvinyl alcohol is used. Alternatively, a method of grafting polyvinyl alcohol to polyvinyl pyrrolidone and then acetalizing so that the trunk and the branch are reversed can be used. Grafting can be performed by a known method.

  In order to use the graft copolymer of the present invention as a dispersant, the graft copolymer may be mixed with a dispersion target such as a carbon material or an active material and a solvent.

  In the present invention, the polyvinyl alcohol-polyvinylpyrrolidone graft copolymer mainly functions as a dispersant for the carbon material (C) and the active material (G), and for creating an electrode film state suitable for improving battery performance. It is thought that he also plays a role.

Moreover, in this invention, polyvinyl alcohol resin (a) can be used together as a dispersing agent further to polyvinyl alcohol-polyvinylpyrrolidone graft copolymer.

<Polyvinyl alcohol resin (a)>
There is no restriction | limiting in particular about the manufacturing method of polyvinyl alcohol resin (a), The various polyvinyl alcohol resin synthesize | combined by the well-known method and commercially available polyvinyl alcohol resin can be used. A typical synthesis method includes a method of producing polyvinyl alcohol by saponifying a polymer obtained by polymerizing a vinyl alcohol precursor such as vinyl acetate with an alkali.

  The polyvinyl alcohol resin (a) is represented by the following general formula (1).

General formula (1)

一般式（１）におけるpは、６９．５〜９９．９ｍｏｌ％であり、ｑは０．１〜３０．５ｍｏｌ％であり、ｐ＋ｑ＝１００．０ｍｏｌ％である。
また、ポリビニルアルコール樹脂（ａ）の平均分子量は１，０００〜８００，０００が好ましく、８，０００〜１１０，０００がより好ましい。

P in General formula (1) is 69.5-99.9 mol%, q is 0.1-30.5 mol%, and p + q = 100.0 mol%.
The average molecular weight of the polyvinyl alcohol resin (a) is preferably 1,000 to 800,000, and more preferably 8,000 to 110,000.

There is no restriction on the arrangement of the two structural units represented by the general formula (1), and the arrangement of the structural units may be random.

  Examples of commercially available polyvinyl alcohol resins include Kuraray Poval PVA-102, Kuraray Poval PVA-103, Kuraray Poval PVA-110, Kuraray Poval PVA-205, Kura Lepoval PVA-405, Kuraray Poval PVA-HC, Kuraray Poval PVA- L8 (Kuraray Polyvinyl Alcohol Resin), Denkapoval K-17C, Denkapoval B-05, Denkapoval B-24 (Electrochemical Industry Polyvinyl Alcohol Resin), etc. Absent.

In the present invention, the polyvinyl alcohol resin (a) that can be added to the polyvinyl alcohol-polyvinylpyrrolidone graft copolymer mainly functions as a dispersant and has an electrode film state suitable for improving battery performance. It is thought that it also has a role to create.

<Carbon material (C)>
The carbon material (C) is not particularly limited as long as it is a conductive carbon material, but graphite, carbon black, conductive carbon fibers (carbon nanotubes, carbon nanofibers, carbon fibers), fullerene, etc. It can be used alone or in combination of two or more. From the viewpoint of conductivity, availability, and cost, it is preferable to use carbon black.

  Carbon black is a furnace black produced by continuously pyrolyzing a gas or liquid raw material in a reactor, especially ketjen black using ethylene heavy oil as a raw material. Channel black that has been rapidly cooled and precipitated, thermal black obtained by periodically repeating combustion and thermal decomposition using gas as a raw material, and particularly various types such as acetylene black using acetylene gas as a raw material, or 2 More than one type can be used in combination. Ordinarily oxidized carbon black, hollow carbon and the like can also be used.

  The oxidation treatment of carbon is performed by treating carbon at a high temperature in the air or by secondary treatment with nitric acid, nitrogen dioxide, ozone, etc., for example, such as phenol group, quinone group, carboxyl group, carbonyl group. This is a treatment for directly introducing (covalently bonding) an oxygen-containing polar functional group to the carbon surface, and is generally performed to improve the dispersibility of carbon. However, since it is common for the conductivity of carbon to fall, so that the introduction amount of a functional group increases, it is preferable to use the carbon which has not been oxidized.

As the specific surface area of the carbon black used increases, the number of contact points between the carbon black particles increases, which is advantageous in reducing the internal resistance of the electrode. Specifically, the specific surface area (BET) determined from the adsorption amount of nitrogen is 20 m ² / g or more and 1500 m ² / g or less, preferably 50 m ² / g or more and 1500 m ² / g or less, more preferably 100 m ^2. / G or more and 1500 m ² / g or less are desirable. When carbon black having a specific surface area of less than 20 m ² / g is used, it may be difficult to obtain sufficient conductivity, and carbon black of more than 1500 m ² / g may be difficult to obtain from commercially available materials. is there.

  Further, the particle size of the carbon black to be used is preferably 0.005 to 1 μm, particularly preferably 0.01 to 0.2 μm in terms of primary particle size. However, the primary particle diameter here is a value obtained by averaging the particle diameters measured with an electron microscope.

  Examples of commercially available carbon black include Toka Black # 4300, # 4400, # 4500, # 5500 (Tokai Carbon Co., Furnace Black), Printex L and the like (Degussa Co., Furnace Black), Raven 7000, 5750, 5250, 5000 ULTRA III, 5000 ULTRA, etc., Conductex SC ULTRA, Conductex 975 ULTRA, etc. (Columbian manufactured by Furnace Black), # 2350, # 2400B, # 30050B, # 3030B, # 3230B, # 3350B, # 3400B, # 5400B, etc. (Manufactured by Chemical Co., Furnace Black), MONARCH1400, 1300, 900, VulcanXC-72R, BlackPearls2000, etc. Furnace Black), Ensaco 250G, Ensaco 260G, Ensaco 350G, SuperP-Li, (manufactured by TIMCAL), Ketjen Black EC-300J, EC-600JD (manufactured by Akzo), Denka Black, Denka Black HS-100, FX-35 (Electrochemistry) (Industry company make, acetylene black) etc. are mentioned, However, It is not limited to these. Examples of graphite include, but are not limited to, natural graphite such as artificial graphite, flake graphite, massive graphite, and earthy graphite, and two or more kinds may be used in combination.

  As the conductive carbon fibers, those obtained by firing from petroleum-derived raw materials are preferable, but those obtained by firing from plant-derived raw materials can also be used. For example, VGCF manufactured by Showa Denko KK manufactured with petroleum-derived raw materials can be used.

<Derivative (D)>
The derivative (D) used in the present invention will be described. The derivative (D) used in the present invention is an organic dye derivative having an acidic functional group or a triazine derivative having an acidic functional group. In particular, a triazine derivative having an acidic functional group represented by the following general formula (2) or an organic dye derivative having an acidic functional group represented by the general formula (6) is preferable. First, the triazine derivative having an acidic functional group represented by the general formula (2) will be described.

General formula (2)

^[X 1 _{is, -NH -, - O -,} - CONH -, - SO 2 NH -, - CH 2 NH -, - CH 2 NHCOCH 2 NH- or ^-X 3 ^{-Y-X 4} - represents, X ² and ^{X 4,} each independently, represent -NH- or ^-O-, X 3 _{is, -CONH -, - SO 2 NH} -, - CH 2 NH -, - NHCO- or -NHSO ₂ - and represent , Y represents an alkylene group which may have a substituent, an alkenylene group which may have a substituent or an arylene group which may have a substituent, Z represents —SO ₃ M, —COOM, -P (O) (-OM) ₂ or -O-P (O) (-OM) ₂ , M represents one equivalent of a 1 to 3 valent cation, and Q represents -O-R ⁶ , ^{-NH-R 6,} a halogen group, ^-X 1 -R ⁵ or ^-X 2 -Y-Z, ^{R 6} is a hydrogen atom, Have an alkyl group or a substituted group may have a substituent represents an alkenyl group. u represents an integer of 1 to 4. R ⁵ represents an organic dye residue, a heterocyclic residue which may have a substituent, an aromatic ring residue which may have a substituent, or a group represented by the following general formula (3) Represents. ]

General formula (3)

^{[X 5} represents -NH- or -O-, ^{X 6} and ^{X 7} are each independently, -NH -, - O -, - CONH -, - SO 2 NH -, - CH 2 NH- or —CH ₂ NHCOCH ₂ NH—, R ⁷ and R ⁸ are each independently an organic dye residue, a heterocyclic residue which may have a substituent, or an aromatic which may have a substituent. Represents a group ring residue or —Y—Z, and Y and Z have the same meanings as Y and Z in formula (3). ]

In the above, examples of the organic dye residue in R ⁵ , R ⁷ , and R ⁸ include diketopyrrolopyrrole dyes, azo dyes such as azo, disazo, polyazo, phthalocyanine dyes, anthraquinones, diaminodianthraquinones, anthra Anthraquinone dyes such as pyrimidine, flavantron, anthanthrone, indanthrone, pyranthrone, violanthrone, quinacridone dye, dioxazine dye, perinone dye, perylene dye, thioindigo dye, isoindoline dye, isoindolinone Residues such as dyes based on dyes, quinophthalone dyes, selenium dyes, metal complex dyes, and the like. In particular, in order to increase the effect of suppressing the short circuit of the battery due to metal, it is preferable to use an organic dye residue that is not a metal complex dye, among which an azo dye, a diketopyrrolopyrrole dye, a metal-free phthalocyanine dye, Quinacridone dyes and dioxazine dye residues are preferred because they exhibit excellent dispersibility.

In the above, examples of the heterocyclic residue and aromatic ring residue in R ⁵ , R ⁷ , or R ⁸ include thiophene, furan, pyridine, pyrazole, pyrrole, imidazole, isoindoline, isoindolinone, and benzine. Examples include heterocyclic residues such as imidazolone, benzthiazole, benztriazole, indole, quinoline, carbazole and acridine, and aromatic ring residues such as benzene, naphthalene, anthracene, fluorene, phenanthrene and anthraquinone. In particular, a heterocyclic residue containing any one of S, N, and O heteroatoms is preferable because it exhibits an effect of excellent dispersibility.

  Y in general formula (3) and general formula (4) represents an alkylene group, alkenylene group or arylene group which may have a substituent, but preferably has 20 or less carbon atoms, more preferably 10 or less carbon atoms. . Particularly preferred embodiments include an optionally substituted phenylene group, biphenylene group, naphthylene group or an alkylene group which may have a side chain having 10 or less carbon atoms.

A preferred embodiment of the alkenyl group which may have also alkyl groups and substituents have a substituent in R ⁶ are those having 20 or less carbon atoms. More preferably, an alkyl group which may have a side chain having 10 or less carbon atoms is exemplified. Here, the alkyl group having a substituent and the alkenyl group having a substituent are a group in which a hydrogen atom of an alkyl group or an alkenyl group is substituted with a halogen group such as a fluorine atom, a chlorine atom or a bromine atom, a hydroxyl group or a mercapto group. Can be mentioned.

M represents one equivalent of 1 to 3 valent cations, for example, a hydrogen ion (proton), a metal cation, or a quaternary ammonium cation. Moreover, when it has two or more M in the structure (one molecule) of a dispersing agent, M may be only one kind of a proton, a metal cation, and a quaternary ammonium cation, and may be a combination of two or more kinds.
Examples of the metal cation include metal cations such as lithium, sodium, potassium, calcium, barium, magnesium, aluminum, nickel, and cobalt.
The quaternary ammonium cation is a single compound having a structure represented by the general formula (4) or a mixture.

General formula (4)

[R ⁹ , R ¹⁰ , R ¹¹ , or R ¹² each independently has a hydrogen atom, an alkyl group that may have a substituent, an alkenyl group that may have a substituent, or a substituent. Represents an aryl group which may be substituted. ]

R ⁹ , R ¹⁰ , R ¹¹ , or R ¹² may be the same or different. Moreover, when R < ⁹ >, R < ¹⁰ >, R < ¹¹ > or R < ¹² > has a carbon atom, carbon number is 1-40, Preferably it is 1-30, More preferably, it is 1-20.

  Specific examples of the quaternary ammonium cation include dimethylammonium, trimethylammonium, diethylammonium, triethylammonium, hydroxyethylammonium, dihydroxyethylammonium, 2-ethylhexylammonium, dimethylaminopropylammonium, laurylammonium, stearylammonium and the like. However, it is not limited to these.

Next, the organic dye derivative having an acidic functional group represented by the general formula (5) will be described.
General formula (5)

^{[X 8} is a direct _{bond, -NH -, - O -,} - CONH -, - SO 2 NH -, - CH 2 NH -, - CH 2 NHCOCH 2 NH -, - X 9 -Y- or -X ⁹ -Y-X ¹⁰ - ^represents, X 9 _{is, -CONH -, - SO 2 NH} -, - CH 2 NH -, - NHCO- or -NHSO ₂ - represents, X ¹⁰ is, -NH- or -O Y represents an alkylene group that may have a substituent, an alkenylene group that may have a substituent, or an arylene group that may have a substituent, Z represents —SO ₃ M, -COOM, -P (O) (- OM) 2 or -O-P (O) (- OM) represents a _2, M represents one equivalent of a monovalent to trivalent ^{cation, R 13} is an organic dye residue Represents a group, and v represents an integer of 1 to 4. ]

The organic dye residue for R ^{13 has} the same meaning as the organic dye residue for R ⁵ , R ⁷ , or R ⁸ described above. In particular, in order to increase the effect of suppressing the short circuit of the battery due to metal, it is preferable to use an organic dye residue that is not a metal complex dye, among which an azo dye, a diketopyrrolopyrrole dye, a metal-free phthalocyanine dye, Quinacridone dyes and dioxazine dye residues are preferred because they exhibit excellent dispersibility.

  M in the general formula (6) has the same meaning as M in the general formula (3).

  A method for synthesizing the derivative (D) used in the present invention is not particularly limited, and examples thereof include Japanese Patent Publication No. 39-28884, Japanese Patent Publication No. 45-11026, Japanese Patent Publication No. 45-29755, It can be synthesized by the methods described in JP-B-64-5070, JP-A-2004-217842, and the like.

  In the present invention, it is considered that the derivative (D) mainly functions as a dispersant and also plays a role for creating an electrode film state suitable for improving battery performance.

<Solvent (E)>
Examples of the solvent (E) that may be used in the battery composition of the present invention (sometimes referred to as a solvent or a liquid medium in the present specification) include alcohols, glycols, cellosolves, and amino alcohols. Amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, phosphoric acid esters, ethers, and nitriles.

Among these, it is preferable to use a polar solvent having a relative dielectric constant of 15 or more. The relative dielectric constant is one of the indices indicating the strength of the polarity of the solvent, and is described in Asahara et al., “Solvent Handbook” (Kodansha Scientific Co., Ltd., 1990).
For example, methyl alcohol (dielectric constant: 33.1), ethyl alcohol (23.8), 2-propanol (18.3), 1-butanol (17.1), 1,2-ethanediol (38.66) ), 1,2-propanediol (32.0), 1,3-propanediol (35.0), 1,4-butanediol (31.1), diethylene glycol (31.69), 2-methoxyethanol ( 16.93), 2-ethoxyethanol (29.6), 2-aminoethanol (37.7), acetone (20.7), methyl ethyl ketone (18.51), formamide (111.0), N-methylformamide (182.4), N, N-dimethylformamide (36.71), N-methylacetamide (191.3), N, N-dimethylacetamide (3 .78), N-methylpropionamide (172.2), N-methyl-2-pyrrolidone (32.0), hexamethylphosphoric triamide (29.6), dimethyl sulfoxide (48.9), sulfolane (43.3) ), Acetonitrile (37.5), propionitrile (29.7) and the like, but are not limited thereto.

  In particular, the use of a polar solvent having a relative dielectric constant of 15 or more and 200 or less, preferably 15 or more and 100 or less, more preferably 20 or more and 100 or less is excellent in dispersibility of the active material and the conductive assistant. It is preferable. The solvent is selected in view of reactivity with the active material, solubility in the binder resin, and the like. It is preferable to select a solvent having high dispersibility, low reactivity with the active material, and high solubility of the binder resin. Furthermore, from the viewpoint of reducing environmental burdens and economic advantages, when recovering and reusing the solvent discharged in the electrode manufacturing process, it is preferable to use a single solvent instead of a mixed solvent.

  As the solvent satisfying the relative permittivity, the reactivity with the active material, and the solubility of the binder resin and having versatility in a single use, an amide solvent is preferable, and in particular, N, N-dimethylformamide, It is preferable to use an amide aprotic non-aqueous solvent such as N, N-diethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, N-methyl-2-pyrrolidone, hexamethylphosphoric triamide. In particular, in the use mode of the present invention, N-methyl-2-pyrrolidone is preferable.

<Active material (G)>
When the composition of the present invention is used for a positive electrode mixture or a negative electrode mixture, in addition to the polyvinyl alcohol-polyvinylpyrrolidone graft copolymer, carbon material (C), derivative (D), and solvent (E), an active material is used. (G) may contain at least a positive electrode active material or a negative electrode active material.

The positive electrode active material for the lithium ion secondary battery is not particularly limited, but metal oxides capable of doping or intercalating lithium ions, metal compounds such as metal sulfides, and conductive polymers are used. be able to.
Examples thereof include transition metal oxides such as Fe, Co, Ni, and Mn, composite oxides with lithium, and inorganic compounds such as transition metal sulfides. Specifically, transition metal oxide powders such as MnO, V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , layered structure lithium nickelate, lithium cobaltate, lithium manganate, spinel structure lithium manganate, etc. Examples thereof include composite oxide powders of lithium and transition metals, lithium iron phosphate materials that are phosphate compounds having an olivine structure, transition metal sulfide powders such as TiS ₂ and FeS, and the like. In addition, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Moreover, you may mix and use said inorganic compound and organic compound.

The negative electrode active material for the lithium ion secondary battery is not particularly limited as long as it can be doped or intercalated with lithium ions. For example, metal Li, alloys thereof such as tin alloys, silicon alloys, lead alloys, etc., Li _X Fe ₂ O ₃ , Li _X Fe ₃ O ₄ , Li _X WO ₂ , lithium titanate, lithium vanadate, silicon Metal oxides such as lithium oxide, conductive polymers such as polyacetylene and poly-p-phenylene, amorphous carbonaceous materials such as soft carbon and hard carbon, artificial graphite such as highly graphitized carbon materials, or natural Examples thereof include carbonaceous powders such as graphite, carbon black, mesophase carbon black, resin-fired carbon materials, air-growth carbon fibers, and carbon fibers. These negative electrode active materials can be used alone or in combination.

  These active materials (G) preferably have an average particle size in the range of 0.05 to 100 μm, and more preferably in the range of 0.1 to 50 μm. The average particle diameter of the active material (G) in the present specification is an average value of particle diameters of the active material (G) measured with an electron microscope.

<Binder (F)>
The composition of the present invention preferably further contains a binder. As binders to be used, ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol (other than (a) polyvinyl alcohol resin, polyvinyl alcohol-polyvinylpyrrolidone graft copolymer), maleic acid, acrylic acid, acrylic acid ester, methacrylic acid Polymers or copolymers containing acid, methacrylic acid ester, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc. as structural units; polyurethane resin, polyester resin, phenol resin, epoxy resin, phenoxy resin, urea resin, melamine Resin, alkyd resin, acrylic resin, formaldehyde resin, silicone resin, fluororesin; cellulose resin such as carboxymethylcellulose; styrene-butadiene rubber, fluororubber Examples thereof include conductive resins such as polyaniline and polyacetylene. Moreover, the modified body and mixture of these resin, and a copolymer may be sufficient. In particular, it is preferable to use a polymer compound containing a fluorine atom in the molecule, for example, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene, etc. from the viewpoint of resistance. In particular, in the use mode of the present invention, polyvinylidene fluoride is preferred.

  Moreover, as for the weight average molecular weight of these resin as a binder, 10,000-1,000,000 are preferable. When the molecular weight is small, the resistance of the binder may decrease. When the molecular weight is increased, the resistance of the binder is improved, but the viscosity of the binder itself is increased and the workability is lowered.

  The composition of the present invention can be used for a positive electrode mixture or a negative electrode mixture. When used for a positive electrode composite or a negative electrode composite, an active material (G) (positive electrode) is added to the composition containing the polyvinyl alcohol / polyvinylpyrrolidone graft copolymer, a carbon material (C), and a solvent (E). Active material or negative electrode active material), more preferably, it is preferably used as a positive / negative electrode mixture slurry containing a binder (F). In addition, the composition can contain a polyvinyl alcohol resin (a) and a derivative (D).

The proportion of the active material in the total solid content in the electrode mixture slurry is preferably 80% by weight or more and 99% by weight or less. Further, the proportion of the carbon material (C) as a conductive additive in the total solid content in the electrode mixture slurry is preferably 0.1% by weight or more and 15% by weight or less.
In the present invention, the proportion of the polyvinyl alcohol / polyvinylpyrrolidone graft copolymer, the polyvinyl alcohol resin (a) and the derivative (D) in the mixture slurry is the carbon material as the conductive material and the active material (G). It is preferable that it is 0.01 to 7.5 weight% with respect to the sum total of the weight of (C). More preferably, it is 0.01 to 5 weight%, More preferably, it is 0.01 to 2.5 weight%. When the derivative (D) is added, the proportion is preferably 1% by weight or more and 80% by weight or less, preferably 10% by weight or more and 60% by weight or less, based on the total weight of the polyvinyl alcohol / polyvinylpyrrolidone graft copolymer. More preferred. And the ratio of the binder component in the total solid content in the electrode mixture slurry is preferably 1% by weight or more and 10% by weight or less. In addition, the appropriate viscosity of the electrode mixture slurry depends on the method of applying the electrode mixture slurry, but generally it is preferably 100 mPa · s or more and 30,000 mPa · s or less.

<Composition for forming secondary battery electrode>
Next, the manufacturing method of the composition for secondary battery electrode formation (it may only be called a "composition") is demonstrated. In the composition of the present invention, for example, in the presence of a polyvinyl alcohol / polyvinylpyrrolidone graft copolymer, a carbon material (C) as a conductive auxiliary agent is dispersed in a solvent (E), and the dispersion is optionally mixed. , Polyvinyl alcohol resin (a), derivative (D), active material (G) (positive electrode active material or negative electrode active material), and / or binder (F). The order of addition of each component is not limited to this. Moreover, you may add a solvent further as needed. In the present specification, unless otherwise specified, the “dispersion” is composed of a polyvinyl alcohol / polyvinylpyrrolidone graft copolymer, a carbon material (C) as a conductive auxiliary agent, and a solvent (E). The composition for secondary battery electrode formation which can contain D) shall be pointed out. The “mixed material slurry” refers to a composition for forming a secondary battery electrode, wherein the “dispersion” further contains an active material (G) (positive electrode active material or negative electrode active material) and a binder (F). Shall point to.

  In the production method described above, the polyvinyl alcohol / polyvinylpyrrolidone graft copolymer, and if the derivative (D) is contained, the derivative (D) is completely or partially dissolved in the solvent (E), and the conductive auxiliary agent is added to the solution. When the carbon material (C) is added and mixed, the polyvinyl alcohol / polyvinylpyrrolidone graft copolymer, and if the derivative (D) is further included, the derivative (D) acts on the carbon material (C) (for example, adsorption) ) And dispersed in the solvent. The concentration of the carbon material (C) in the dispersion at this time is 1% by weight or more, although depending on the characteristic value of the carbon material such as the specific surface area and surface functional group amount of the carbon material (C) to be used. 50 weight% or less is preferable, More preferably, it is 5 weight% or more and 35 weight% or less. When the concentration of the carbon material (C) is too low, the production efficiency is deteriorated, and when the concentration of the carbon material (C) is too high, the viscosity of the dispersion is remarkably increased, and the dispersion efficiency and the efficiency of the contamination removing process described later The workability of the dispersion may be reduced. In particular, when a step for removing contamination is added, the viscosity of the dispersion is preferably 5 mPa · s or more and 10,000 mPa · s or less, more preferably 5,000 mPa · s or less, and still more preferably 3,000 mPa · s or less. And

The dispersed particle size of the carbon material (C) as a conductive additive in the composition for forming a secondary battery electrode is 0.03 μm or more and 2 μm or less, preferably 0.05 μm or more and 1 μm or less, more preferably 0. Desirably, the thickness is from 0.05 μm to 0.5 μm.
The dispersed particle diameter of the carbon material (C) in the present specification is the particle diameter (D50) at 50% when the volume ratio of the particles is integrated from the small particle diameter in the volume particle size distribution. It is a value measured by a particle size distribution meter of a dynamic light scattering method (in the examples of this specification, “Microtrack UPA” manufactured by Nikkiso Co., Ltd.).

  In addition, as a device for dispersing the polyvinyl alcohol / polyvinylpyrrolidone graft copolymer and the derivative (D) in the solvent while acting (for example, adsorbing) the derivative (D) on the carbon material (C), A disperser used for pigment dispersion or the like can be used. For example, mixers such as dispersers, homomixers, planetary mixers, homogenizers ("Clearmix" manufactured by M Technique, PRIMIX "Fillmix", etc.), paint conditioners (manufactured by Red Devil), ball mills, sand mills ( Media type dispersers such as “Dynomill” manufactured by Shinmaru Enterprises, Inc.), Attritor, Pearl Mill (“DCP Mill” manufactured by Eirich), Coball Mill, etc., Wet Jet Mill (“Genus PY” manufactured by Genus, Sugino Machine Co., Ltd.) Media-less dispersers such as “Starburst” manufactured by Nanomizer, “Nanomizer” manufactured by Nanomizer, etc., “Claire SS-5” manufactured by M Technique, and “MICROS” manufactured by Nara Machinery Co., other roll mills, etc. It is not limited to. Moreover, as the disperser, it is preferable to use a disperser that has been subjected to a metal contamination prevention treatment from the disperser.

  For example, when using a media-type disperser, the agitator and vessel are dispersed using a ceramic or resin disperser, or the surface of the metal agitator and vessel is treated with tungsten carbide spraying or resin coating. It is preferable to use a machine. And as a media, it is preferable to use ceramic beads, such as glass beads, zirconia beads, and alumina beads, and among them, the use of zirconia beads is preferable. Moreover, also when using a roll mill, it is preferable to use a ceramic roll. Only one type of dispersion device may be used, or a plurality of types of devices may be used in combination. Further, in the case of a positive or negative electrode active material in which particles are easily broken or crushed by a strong impact, a medialess disperser such as a roll mill or a homogenizer is preferable to a media type disperser.

  In addition, it is preferable to include a step of removing contaminants such as metal foreign matters during dispersion. Carbon black, graphite, and carbon materials such as carbon fiber often contain metallic foreign matters derived from their manufacturing processes (as line contamination and catalysts). It is very important to prevent short circuit. In the present invention, due to the effect of the polyvinyl alcohol / polyvinylpyrrolidone graft copolymer, the agglomeration of the carbon materials (C) is well loosened, and the viscosity of the dispersion is low, so the carbon material concentration in the dispersion is high. However, it is possible to remove metallic foreign matters efficiently. Examples of methods for removing metallic foreign substances include iron removal with a magnet, filtration, and centrifugation.

  As a method for adding the binder (F), the above-mentioned polyvinyl alcohol / polyvinylpyrrolidone graft copolymer is used, and when the derivative (D) is contained, the carbon material (C) as a conductive auxiliary agent is used as a solvent in the presence of the derivative (D). There is a method in which a solid binder component is added and dissolved while stirring the dispersion obtained by dispersing the dispersion. Moreover, what melt | dissolved the binder in the solvent is produced beforehand and the method of mixing with the said dispersion is mentioned. Further, after the binder (F) is added to the dispersion, the dispersion treatment may be performed again by the dispersion apparatus. Further, when the polyvinyl alcohol-polyvinylpyrrolidone graft copolymer, and further containing the derivative (D), in the presence of the derivative (D), when the carbon material (C) as a conductive additive is dispersed in the solvent (E), A part or all of the binder (F) may be added at the same time to carry out the dispersion treatment.

  As a method for adding the active material (G) (positive electrode active material or negative electrode active material), in the presence of the derivative (D) in the presence of the polyvinyl alcohol / polyvinylpyrrolidone graft copolymer and the derivative (D), the conductive additive And a method of adding and dispersing the positive electrode active material or the negative electrode active material while stirring the dispersion obtained by dispersing the carbon material (C) as a solvent in the solvent (E). Further, when the polyvinyl alcohol / polyvinylpyrrolidone graft copolymer and the derivative (D) are contained, when the carbon material as the conductive auxiliary agent is dispersed in the solvent in the presence of the derivative (D), the positive electrode active material or the negative electrode A part or all of the active material may be added at the same time for dispersion treatment. When the polyvinyl alcohol / polyvinylpyrrolidone graft copolymer and the derivative (D) are contained, the carbon material (C) as a conductive additive is dispersed in the solvent (E) in the presence of the derivative (D). A method of adding and dispersing the positive electrode active material or the negative electrode active material after adding the binder component in a solid or solution while stirring the dispersion can be mentioned. Furthermore, when the polyvinyl alcohol / polyvinylpyrrolidone graft copolymer, carbon material (C), solvent (E), active material (G), binder (F) and derivative (D) are included, the derivative (D) is mixed. Also, distributed processing can be performed at the same time. As an apparatus for mixing and dispersing, the above-described dispersers used for ordinary pigment dispersion and the like can be used.

The size of the active material (G) to be used is preferably in the range of 0.05 to 100 μm, and more preferably in the range of 0.1 to 50 μm, in terms of average particle size. The average particle diameter of an active material here is an average value of the major axis of each primary particle in an image observed with a scanning electron microscope (SEM). However, in order to increase the reaction area of the active material, an active material may be an aggregate (secondary particle) that is obtained by granulating fine primary particles after the synthesis process or after synthesis. Measures the major axis of the secondary particles and sets the average particle size of the active material.
The ratio of the average particle diameter of the active material (G) to the dispersed particle diameter (D50) of the carbon material (C) described above (average particle diameter of the active material (G) / dispersed particle diameter of the carbon material (C) (D50 )), It is preferably 2 or more and 100 or less. More preferably, it is 9 or more and 70 or less.

As described above, the composition of the present invention can be usually produced, distributed and used as a dispersion (liquid) containing a solvent, a paste or the like. This is because even if the conductive auxiliary agent or active material and the dispersing agent are mixed in a dry powder state, the dispersing agent cannot be uniformly applied to the conductive auxiliary agent or the active material. This is because, by dispersing the conductive additive and the active material in the solvent in the presence of, the dispersant can be made to act uniformly on the conductive additive and the active material. Further, as described below, when the electrode mixture layer is formed on the current collector, it is preferable to apply the liquid dispersion as uniformly as possible and dry it.
However, for example, a dispersion produced by a liquid phase method is used to remove the solvent once to make a dry powder for reasons of transportation cost, etc., and then re-disperse the dry powder with an appropriate solvent. You may use for formation of. Therefore, the composition of the present invention is not limited to a liquid dispersion, and may be a composition in a dry powder state.

  Of the composition for forming a secondary battery electrode of the present invention, the mixture slurry is coated on a current collector and dried to form a mixture layer, whereby a secondary battery electrode can be obtained.

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

  There is no restriction | limiting in particular as a method of apply | coating a mixture slurry and the composition for base layer formation on a collector, A well-known method can be used. Specific examples include die coating method, dip coating method, roll coating method, doctor coating method, knife coating method, spray coating method, gravure coating method, screen printing method or electrostatic coating method, and the like. Examples of methods that can be used include standing drying, blower dryers, hot air dryers, infrared heaters, and far-infrared heaters, but are not particularly limited thereto.

  Moreover, you may perform the rolling process by a lithographic press, a calender roll, etc. after application | coating. The thickness of the electrode mixture layer is generally 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

  A secondary battery can be obtained by using the above electrode for at least one of a positive electrode and a negative electrode. Secondary batteries include lithium ion secondary batteries, sodium ion secondary batteries, magnesium secondary batteries, alkaline secondary batteries, lead storage batteries, nickel metal hydride batteries, nickel cadmium batteries, sodium sulfur secondary batteries, lithium air batteries. Secondary batteries, fuel cells, and the like, preferably lithium ion secondary batteries, nickel metal hydride batteries, and fuel cells, more preferably lithium ion secondary batteries, nickel metal hydride batteries, and particularly preferably lithium ion secondary batteries. Next battery. In each secondary battery, conventionally known electrolytes, separators, and the like can be appropriately used.

(Electrolyte)
A case of a lithium ion secondary battery will be described as an example. As the electrolytic solution, an electrolyte containing lithium dissolved in a non-aqueous solvent is used. As the electrolyte, LiBF ₄ , LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₃ C , LiI, LiBr, LiCl, LiAlCl, LiHF ₂ , LiSCN, or LiBPh _4, but are not limited thereto.

  The non-aqueous solvent is not particularly limited. For example, carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; γ-butyrolactone, γ-valerolactone, and γ Lactones such as octanoic lactone; tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1, Glymes such as 2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. And the like. These solvents may be used alone or in combination of two or more.

  Furthermore, the electrolytic solution can be used in the form of a polymer electrolyte that is held in a polymer matrix and is in the form of a gel. Examples of the polymer matrix include, but are not limited to, an acrylate resin having a polyalkylene oxide segment, a polyphosphazene resin having a polyalkylene oxide segment, and a polysiloxane having a polyalkylene oxide segment.

(separator)
Examples of the separator include, but are not limited to, a polyethylene nonwoven fabric, a polypropylene nonwoven fabric, a polyamide nonwoven fabric and those obtained by subjecting them to a hydrophilic treatment.

(Battery structure / configuration)
The structure of the lithium ion secondary battery using the composition of the present invention is not particularly limited, but is usually composed of a positive electrode and a negative electrode, and a separator provided as necessary, a paper type, a cylindrical type, a button type, It can be made into various shapes according to the purpose of use, such as a laminated type.

  EXAMPLES Hereinafter, although this invention is demonstrated in more detail based on an Example, this invention is not limited to these. In the examples, “part” represents “part by weight” and “%” represents “% by weight”. The polyvinyl alcohol / polyvinylpyrrolidone graft copolymer, polyvinyl alcohol resin (a) carbon material (C), and binder (F) used in Synthesis Examples, Examples and Comparative Examples are shown below. Further, N-methyl-2-pyrrolidone used as the solvent (E) may be abbreviated as “NMP”.

<Polyvinyl alcohol / polyvinylpyrrolidone graft copolymer>
(Synthesis Example 1)
(Synthesis of a copolymer obtained by grafting polyvinylpyrrolidone to polyvinyl alcohol)
80 g of polyvinyl alcohol (polymerization degree 1700, saponification degree 98 to 99 mol%) was dissolved in 400 g of pure water, then 20 g of vinyl pyrrolidone was added and mixed, and deoxygenated by nitrogen purge. Subsequently, the temperature of the reaction system was adjusted to 70 ° C. A solution prepared by dissolving 1 g of 2,2′-azobis (2-methylbutyronitrile) in isopropyl alcohol was added thereto to initiate polymerization. During the polymerization, the temperature was maintained at 70 to 90 ° C. and reacted for 3 hours to obtain a 20% aqueous solution of polyvinyl alcohol / polyvinylpyrrolidone graft copolymer. Then, after washing with excess water and drying, a white powdery polyvinyl alcohol / polyvinylpyrrolidone graft copolymer (A-1) was obtained. The weight average molecular weight of the polyvinylpyrrolidone segment of this polymer was 50,000, and the proportion of vinylpyrrolidone units was 6 mol%. Thereafter, N-methyl-2-pyrrolidone was added for dilution. V. = 20%. Thereafter, the mixture was cooled to obtain a resin solution (A′-1) containing a polyvinyl alcohol / polyvinylpyrrolidone graft copolymer (A-1).
(Synthesis Example 2)
Polyvinyl alcohol / polyvinylpyrrolidone graft copolymer (A-2) and polyvinyl alcohol were treated in the same manner as in Example 1 except that the amount of 2,2′-azobis (2-methylbutyronitrile) added in the grafting was 5 g. A resin solution (A′-2) containing an alcohol / polyvinylpyrrolidone graft copolymer (A-2) was obtained. The weight average molecular weight of the polyvinylpyrrolidone segment of this polymer was 5000, and the proportion of vinylpyrrolidone units was 6 mol%.
(Synthesis Example 3)
In the grafting, 40 mg of 1 wt% copper sulfate, 4 g of 28 wt% aqueous ammonia and 36 g of 30 wt% aqueous hydrogen peroxide were added instead of 2,2'-azobis (2-methylbutyronitrile) to initiate polymerization. The resin solution (A′-3) containing the polyvinyl alcohol / polyvinylpyrrolidone graft copolymer (A-3) and the polyvinyl alcohol / polyvinylpyrrolidone graft copolymer (A-3) Got. The weight average molecular weight of the polyvinylpyrrolidone segment of this polymer was 3000, and the proportion of vinylpyrrolidone units was 7 mol%.
(Synthesis Example 4)
Polyvinyl alcohol / polyvinylpyrrolidone graft copolymer (A-4) and polyvinyl alcohol / polyvinyl pyrrolidone graft copolymer were used in the same manner as in Example 1 except that the amount of 2,2′-azobis (2-methylbutyronitrile) added in the grafting was 10 g. A resin solution (A′-4) containing an alcohol / polyvinylpyrrolidone graft copolymer (A-4) was obtained. The weight average molecular weight of the polyvinylpyrrolidone segment of this polymer was 2500, and the proportion of vinylpyrrolidone units was 3 mol%.

(Comparative Synthesis Example 1)
600 g of pure water was added to polyvinyl alcohol (polymerization degree 1700, saponification degree 98 to 99 mol%) and stirred uniformly. The temperature of this solution was adjusted to 15 ° C., 140 g of 35% by weight hydrochloric acid and 110 g of n-butyraldehyde were added, and the reaction was carried out while maintaining this temperature. Thereafter, the reaction system was held at 60 ° C. for 3 hours to complete the reaction, washed with excess water, and dried to obtain a white powdery polyvinyl acetal (B-1). Thereafter, N-methyl-2-pyrrolidone was added for dilution. V. = 20%. Then, it cooled and obtained the resin solution (B'-1) containing polyvinyl acetal (B-1).

The identification of the polymer of the said Example and comparative example, and the molecular weight of the polyvinylpyrrolidone segment were performed with the following method. Moreover, the pigment dispersibility of the obtained polymer was evaluated by the following method.

<Polymer identification>
The polymer obtained was subjected to 13C-NMR measurement using deuterated dimethyl sulfoxide as a measurement solvent, and it was confirmed that a peak derived from polyvinylpyrrolidone was observed.

<Molecular weight of polyvinylpyrrolidone segment>

Since it is difficult to directly measure the molecular weight of grafted polyvinylpyrrolidone, the molecular weight of the polyvinylpyrrolidone homopolymer formed simultaneously with grafting was measured. That is, when the target polyvinyl alcohol / polyvinylpyrrolidone graft copolymer aqueous solution is added to t-butyl alcohol, the polyvinyl alcohol / polyvinylpyrrolidone graft copolymer is insolubilized. However, since the polyvinylpyrrolidone homopolymer is dissolved, t-butyl alcohol was distilled off under reduced pressure to obtain a polyvinylpyrrolidone homopolymer, and then the weight average molecular weight was measured by gel permeation chromatography (GPC). The molecular weight measurement conditions by GPC are as follows.

GPC device: HLC-8020RI detection (manufactured by TOSOH)
Column: TSK guard column PWXL, TSKgel G2500 PWXL, TSKgel G3000 PWXL, TSKgel G4000 PWXL, TSKgel G6000 PWXL (manufactured by TOSOH)
Eluent: 0.08M aqueous sodium acetate solution / acetonitrile = 50/50% by weight
Flow rate: 0.7 mL / min
Temperature: 40 ° C

<Manufacture of secondary battery electrode forming composition (dispersion)>
[Example 1]
A carbon material dispersion was prepared according to the composition shown in Table 1. First, 80.0 parts of N-methyl-2-pyrrolidone as a solvent was stirred with a mixer, and the resin solution (A′-1) containing the resin (A-1) prepared in Synthesis Example 1 (solid content 20%) ) Was added and dissolved by stirring. Next, after adding 16 parts of Denka Black HS-100 (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive auxiliary agent and mixing with a mixer, the mixture is further dispersed with a sand mill, in one aspect of the composition for forming a secondary battery electrode. A dispersion 1 was obtained.

[Example 2]
According to the composition shown in Table 1, a dispersion 2 was obtained in the same manner as in Example 1 except that the carbon material was changed to Super-PLi (manufactured by TIMCAL).
[Examples 3 to 12]
In accordance with the composition shown in Table 1, Denka Black HS-100 (manufactured by Denki Kagaku Kogyo Co., Ltd.) or Super-PLi (manufactured by TIMCAL) is used as the carbon material, and the resin solution (A′-1) is used as the dispersant. Dispersions 3 to 12 were obtained in the same manner as in Example 1 except that the solutions (A′-2) to (A′-4) were changed.

[Examples 13 and 14]
According to the composition shown in Table 1, 16 parts of Denka Black HS-100 (manufactured by Denki Kagaku Kogyo Co., Ltd.) as the carbon material and various resin solutions 3 comprising (A′-1) to (A′-4) as the dispersant Parts and the derivative (D-1) or (D-2) shown in Table 5 were added to 0.2 parts and 80.8 parts of N-methyl-2-pyrrolidone in the same manner as in Example 1. Dispersions 13 and 14 were obtained.

[Example 15]
According to the composition shown in Table 1, while stirring 82.0 parts of N-methyl-2-pyrrolidone as a solvent with a mixer, 2.0 parts of the resin solution (A′-1) as a dispersant was added and dissolved by stirring. A dispersion 15 was obtained in the same manner as Example 1 except for the above.

[Comparative Examples 1 and 2]
According to the composition shown in Table 1, Denka Black HS-100 (manufactured by Denki Kagaku Kogyo Co., Ltd.) or Super-PLi (manufactured by TIMCAL) as a carbon material, and a resin solution (B ′ Dispersions 16 and 17 were obtained in the same manner as in Example 1 except for changing to -1).

<Evaluation of dispersion>
(Evaluation of dispersion stability)
The dispersion particle size was used as an index for evaluating the dispersibility of the dispersion. The results are shown in Table 1. Dispersion particle size is measured by using a dynamic light scattering particle size distribution meter ("MICROTRACK UPA" manufactured by Nikkiso Co., Ltd.). The particle diameter (D50) at 50% was determined. This particle size (D50) corresponds to the dispersed particle size of the carbon material (C).
A sample solution for measurement was prepared as follows. While stirring 100 g of N-methyl-2-pyrrolidone, 1 to 4 drops of the various dispersions obtained above were added to the liquid and stirred at 1,000 rpm for 5 minutes. The sample liquid for measurement was set in the above particle size distribution meter, and after confirming that the loading index (laser scattering intensity) was in the range of 0.8 to 1.2, the dispersed particle size was measured. When the loading index exceeded 1.2 in the above preparation method, the sample solution was appropriately diluted with N-methyl-2-pyrrolidone so as to be in the range of 0.8 to 1.2. The measurement time was 60 seconds / once, and the average value of the values obtained by three consecutive measurements was used.
Table 1 shows the results of evaluating the dispersibility of the dispersion. The smaller the value, the better the dispersibility and the more uniform and good dispersion. The dispersion particle size of the dispersion was measured twice immediately after production of various dispersions and after the dispersion was stored at 50 ° C. for 10 days.
In Table 1, “storage stability 2/1” means the ratio of “dispersion particle diameter of dispersion stored at 50 ° C. for 10 days / dispersion particle diameter of dispersion immediately after production”, from 1.00 The smaller the discrepancy, the better the storage stability.

<Carbon material (C)>
A: Denka Black HS-100 (manufactured by Denki Kagaku Kogyo Co., Ltd.): Acetylene black, primary particle diameter 48 nm, specific surface area 48 m ² / g, hereinafter abbreviated as “HS-100”.
F: Super-P Li (manufactured by TIMCAL): furnace black. Primary particle size 40 nm, specific surface area 62 m ² / g.

Table 2 shows the derivatives used in Examples 13-14.

Regarding the dispersibility of the carbon material dispersion of the present invention, as shown in Table 1, all of the dispersions have good dispersibility of the carbon material, and are a dispersion in which the carbon material is uniformly dispersed. confirmed. In addition, it was confirmed that the carbon material dispersions in the examples were excellent in storage stability as compared with the comparative examples in that the dispersion particle size immediately after production and the dispersion particle size after storage at 50 ° C. for 10 days were small. It was.

<Manufacture of secondary battery electrode forming composition (positive electrode mixture slurry)>
[Example 16]
13.8 parts of Dispersion 1 produced in Example 1 and 17.5 parts of an N-methyl-2-pyrrolidone solution of W # 1100 (solid content 12%) as a binder are sampled and mixed with a disper to homogenize. . While this mixture was stirred with a disper, 68.6 parts of LiCoO ₂ (hereinafter abbreviated as LCO) having an average particle diameter of 6.7 μm was gradually added as a positive electrode active material, and the solid content of the mixture slurry was 73%. Then, N-methyl-2-pyrrolidone was further added as a solvent and mixed with a disper for 30 minutes to produce a positive electrode mixture slurry.

[Examples 17-24, 28-30, 34, 35, Comparative Examples 3-7]
A positive electrode mixture slurry was produced in the same manner as in Example 16 except that the materials shown in Table 3 were changed. As active materials, LCO, LiMn ₂ O ₄ (hereinafter abbreviated as LMO) having an average particle diameter of 12 μm, LiNi _(1/3) Mn _(1/3) Co _{(1/3) having} an average particle diameter of 15 μm Any of O ₂ (hereinafter abbreviated as NMC) was used.

[Example 25]
15.6 parts of the dispersion 10 produced in Example 10 and 31.3 parts of an N-methyl-2-pyrrolidone solution (solid content 8%) of W # 7200 as a binder (F) were collected and mixed uniformly with a disper. Turn into. While stirring this mixed liquid with a disper, 45 parts of LiFePO ₄ (hereinafter abbreviated as LFP-01) having an average particle diameter of 1 μm having a carbon coat layer on the surface was gradually added as a positive electrode active material, and then a mixture slurry N-methyl-2-pyrrolidone was further added as a solvent so that the solid content of the mixture became 50%, and the mixture was mixed with a disper for 30 minutes to produce a positive electrode mixture slurry.

[Examples 26, 31, 32, and 36]
A positive electrode mixture slurry was produced in the same manner as in Example 25 except that the materials shown in Table 3 were changed.

[Example 27]
15.6 parts of the dispersion 23 produced in Example 23 and 28.8 parts of an N-methyl-2-pyrrolidone solution of W # 7200 (8% solid content) as a binder (F) were collected and mixed with a disper and homogeneous. Turn into. While stirring this mixed liquid with a disper, 45 parts of LiFePO ₄ (hereinafter abbreviated as LFP-02) having an average particle diameter of 3 μm having a carbon coat layer on the surface was gradually added as a positive electrode active material, and then a mixture slurry N-methyl-2-pyrrolidone was further added as a solvent so that the solid content of the mixture became 50%, and the mixture was mixed with a disper for 30 minutes to produce a positive electrode mixture slurry.

[Example 33]
A positive electrode mixture slurry was produced in the same manner as in Example 27 except that the materials shown in Table 3 were changed.

<Binder (F)>
KF polymer W # 1100 (manufactured by Kureha): polyvinylidene fluoride (PVDF), molecular weight: 280,000. Hereinafter, it may be abbreviated as “W # 1100”.
KF polymer W # 7200 (manufactured by Kureha): polyvinylidene fluoride (PVDF), molecular weight: 630,000. Hereinafter, it may be abbreviated as “W # 7200”.

<Manufacture of secondary battery electrode forming composition (negative electrode mixture slurry)>
[Example 37]
11.3 parts of the dispersion 3 produced in Example 4 and 28.8 parts of an N-methyl-2-pyrrolidone solution of W # 7200 (solid content 8%) as a binder (F) were mixed with a disper to homogenize. Thereafter, 55.8 parts of artificial graphite having an average particle diameter of 15 μm was gradually added as a negative electrode active material while stirring the liquid. Next, N-methyl-2-pyrrolidone as a solvent (D) is added and further mixed so that the solid content of the mixture slurry is 60%, and the negative electrode composite which is one embodiment of the composition for forming a secondary battery electrode is formed. A material slurry was produced.

[Comparative Example 8]
Except having changed into the material shown in Table 4, it carried out similarly to Example 37, and adjusted the negative mix slurry.

[Example 38]
17.8 parts of the dispersion 16 produced in Example 16 and 33.8 parts of an N-methyl-2-pyrrolidone solution of W # 7200 (solid content 8%) as a binder (F) were mixed with a disper and homogenized. Thereafter, 51.3 parts of Li ₄ Ti ₅ O ₁₂ (hereinafter sometimes abbreviated as LTO) having an average particle diameter of 5 μm was gradually added as the negative electrode active material while stirring the liquid. Next, N-methyl-2-pyrrolidone was added and mixed as a solvent (D) so that the solid content of the mixture slurry was 57%, thereby producing a negative electrode mixture slurry.

[Comparative Example 9]
Except having changed into the material shown in Table 4, it carried out similarly to Example 38, and adjusted the negative mix slurry.

The average particle diameter of the active material was calculated from an observation image obtained from a scanning electron microscope (SEM). Here, for LCO, LMO, LFP, artificial graphite, and LTO, the major axis of 100 primary particles was measured and calculated from the average value. For NMC, the major axis of 100 secondary particles was measured and calculated from the average value.

<Evaluation of composite slurry>
(Dispersibility evaluation)
The dispersibility of the positive electrode mixture slurry and the negative electrode mixture slurry was evaluated by evaluating the particle size using a grind gauge (according to JIS K5600-2-5). The smaller the numerical value, the better the dispersibility and the more uniform and good dispersion. The particle size of the mixed slurry was measured immediately after the production of various slurries and after the slurry was stored at 50 ° C. for 3 days. In the measurement, the particle size was measured immediately after slurry production and after defoaming with a planetary defoaming device. Moreover, about the mixed material slurry preserve | saved for 3 days at 50 degreeC, after re-stirring with a disper, after carrying out defoaming with a planetary rotation type defoaming apparatus, the particle size was measured.

<Manufacture of secondary battery electrodes (positive electrode, negative electrode)>
The prepared positive electrode mixture slurry is applied onto a 20 μm thick aluminum foil serving as a current collector using a doctor blade so that the thickness of the electrode after drying the coating film is 100 μm. Preparation and this were dried with a 120 degreeC drying furnace, and the coating material was obtained. This was further subjected to a rolling process by a roll press to produce a positive electrode having a thickness of 85 μm.

The prepared positive electrode mixture slurry is applied onto a 20 μm thick aluminum foil serving as a current collector using a doctor blade so that the thickness of the electrode after drying the coated film is 80 μm. Preparation and this were dried with a 120 degreeC drying furnace, and the coating material was obtained. This was further subjected to a rolling process by a roll press to produce a negative electrode having a thickness of 70 μm.

<Manufacture of secondary batteries (coin-type batteries)>
The positive electrode or negative electrode obtained by the above method was punched into a diameter of 16 mm as a working electrode, and a metal lithium foil was used as a counter electrode. A porous separator made of polypropylene is laminated between the working electrode and the counter electrode, and LiPF ₆ is mixed at a concentration of 1M in an electrolyte solution (a mixed solvent in which ethylene carbonate and diethyl carbonate are mixed at a ratio of 1: 1 (volume ratio)). A coin-type battery was manufactured in such a way that the gap was filled with the dissolved non-aqueous electrolyte solution). The coin-type battery was manufactured in a glove box substituted with argon gas, and then the battery characteristics were evaluated as follows.

<Evaluation of secondary battery (coin-type battery)>
(Cycle characteristics)
About the obtained coin-type battery, charging / discharging measurement was performed using the charging / discharging apparatus (SM-8 by Hokuto Denko). When the active material used was LiCoO ₂ , constant current charging was continued at a charging current of 1.7 mA up to a charging end voltage of 4.3 V. After the battery voltage reached 4.3 V, constant current discharge was performed at a discharge current of 1.7 mA until the discharge end voltage of 2.8 V was reached. These charge / discharge cycles are defined as one cycle, and 50 cycles of charge / discharge are repeated to obtain “discharge capacity maintenance rate = discharge capacity at the 50th cycle / discharge capacity at the first cycle”, and according to the following criteria depending on the discharge capacity maintenance rate. Judged.
A: “Discharge capacity maintenance rate is 95% or more”
○: “Discharge capacity maintenance rate is 90% or more and less than 95%”
Δ: “Discharge capacity maintenance ratio is 85% or more and less than 90%”
×: “Discharge capacity maintenance rate is less than 85%”

Moreover, when the active material to be used is LiMn ₂ O ₄ , the case of LiCoO ₂ except that the charge current is 1.0 mA, the charge end voltage is 4.3 V, the discharge current is 1.0 mA, and the discharge end voltage is 3.0 V. Similarly, the cycle characteristics were measured.

When the active material used is LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , the charging current is 2.0 mA, the charging end voltage is 4.3 V, the discharging current is 2.0 mA, and the discharging end voltage is 3. The cycle characteristics were measured in the same manner as LiCoO ₂ except that the voltage was 0V.

Further, the active material to be used, in the case of LiFePO _4, the charging current 1.0 mA, charge end voltage 4.2 V, the discharge current 1.0 mA, except for using discharge end voltage 2.0 V, in the case of LiCoO ₂ Similarly, the cycle characteristics were measured.

  In Tables 5 and 6, “storage stability 2/1” means the ratio of “particle size of composite slurry stored at 50 ° C. for 3 days / particle size of composite slurry immediately after production”. The smaller the deviation, the better the storage stability.

  As shown in Tables 5 and 6, it was confirmed that the composite slurry according to the present invention in Examples 16 to 36 was a composition excellent in dispersibility of the conductive additive and the active material. In particular, it was confirmed that the dispersion of the present invention had a small change in particle size when stored at 50 ° C. for 3 days compared with the comparative example, and was excellent in storage stability.

Moreover, in the battery using the electrode for secondary batteries formed from the composition for secondary battery electrode formation of this invention, it became clear that it is excellent in cycling characteristics (discharge capacity maintenance factor) with respect to the comparative example. In addition, in the composition for forming a secondary battery electrode (Examples 34 and 35) in which a resin and a pigment derivative are used in combination with the CB dispersion, this effect is remarkable and it is confirmed that the cycle characteristics are good. It was done. Furthermore, the ratio of the average particle size of the active material (E) used to the dispersed particle size (D50) of the carbon material (C) in the CB dispersion (active material average particle size / carbon material dispersed particle size (D50)) The battery cycle characteristics (discharge capacity retention rate) tended to be improved for those having 2 or more, more preferably 9 or more, and why the cycle characteristics were improved in the examples. Although it is not clear, the use of the resin of the present invention has the effect of improving the dispersion stability of the carbon material dispersion and the composite slurry, so that the resin exists in the vicinity of the surface of the carbon material and the active material. Therefore, when manufacturing a coated product using a mixture slurry, it has a good influence on the material distribution after drying, such as the formation of a conductive path, or the cycle characteristics are improved by increasing the film strength. I guess it might be.

Further, when the difference between the average particle diameter of the active material (E) and the dispersed particle diameter (D50) of the carbon material (C) is large, the battery performance was improved. Considering this, it can be inferred that this is due to a change in the state of the coating film when the mixture slurry dries. During drying, the distance between particles in the slurry (between the active material and the carbon material) gradually decreases and eventually aggregates, but this aggregation proceeds in a manner that minimizes the interfacial energy of the aggregates. I think that the. At this time, if the particle sizes of the active material and the carbon material are within a certain range, it is considered that the carbon material is disposed so as to cover the surface of the active material, and the interfacial energy is reduced at that time. As a result, when the dispersed particle size of the active material / carbon material is 2 to 100, the carbon material is disposed so as to cover the surface of the active material, and a uniform and strong conductive path is formed in the electrode film. It seems that battery performance will improve.

Claims (8)

  A composition for forming a secondary battery electrode, comprising a polyvinyl alcohol-polyvinylpyrrolidone graft copolymer and a carbon material (C) as a conductive auxiliary agent.   The composition for forming a secondary battery electrode according to claim 1, further comprising an organic dye derivative having an acidic functional group and / or a derivative (D) which is a triazine derivative having an acidic functional group. Furthermore, the composition for secondary battery electrode formation of Claim 1 or 2 containing a solvent (E). Furthermore, the composition for secondary battery electrode formation in any one of Claims 1-3 which comprises a binder (F). Furthermore, the composition for secondary battery electrode formation in any one of Claims 1-4 which comprises an active material (G). The composition for secondary battery electrode formation of Claim 5 whose ratio of the average particle diameter of an active material (G) / the dispersion particle diameter (D50) of a carbon material (C) is 2-100. The electrode for secondary batteries which is an electrode which has a composite material layer on an electrical power collector, Comprising: A composite material layer is formed with the composition for secondary battery electrode formation in any one of Claims 1-6. A secondary battery comprising a positive electrode having a positive electrode mixture layer on a current collector, a negative electrode having a negative electrode mixture layer on a current collector, and an electrolyte, wherein at least one of the positive electrode or the negative electrode is claimed. Item 8. A secondary battery, which is an electrode for a secondary battery according to Item 7.