JP2014135198A - 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 an electrode, excellent in dispersibility of an active material and a conductive assistant, and further to provide a secondary battery excellent in long-term charge/discharge cycle characteristics.SOLUTION: There are provided: a composition for forming a secondary battery electrode, including a polyvinyl acetal resin, a derivative of an organic dye derivative having an acid functional group and/or a triazine derivative having an acid functional group, and a carbon material serving as a conductive assistant; the composition for forming a secondary battery electrode, further including a solvent, a binder and an active material; and a secondary battery including a secondary battery electrode formed by using the composition for forming a secondary battery electrode.

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, there has always been a demand for miniaturized portable electronic devices such as digital cameras and mobile phones to minimize the volume and reduce the weight. Batteries are needed. 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 industrial demands, lithium secondary batteries are being actively developed. As an electrode of a lithium secondary battery, a positive electrode in which an electrode mixture composed of a positive electrode active material containing lithium ions, a conductive additive, an organic binder, and the like is fixed to the surface of a current collector of a metal foil, and a lithium ion A negative electrode is used in which an electrode mixture made of a removable negative electrode active material, a conductive additive, an organic binder, and the like is fixed to the surface of a current collector of a 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, attempts have been made to improve the conductivity and reduce the internal resistance of the electrode by adding a carbon material such as carbon black (for example, acetylene black) or graphite (graphite) as a conductive aid.

  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 considered because the contact area increases and the resistance decreases by filling the gaps between the graphite particles. 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 enabling discharge with a large current and improving the charge / discharge efficiency.
However, a carbon material (conducting aid) excellent in conductivity has a strong cohesive force, and it is difficult to uniformly mix and disperse it in the slurry for forming an electrode mixture of a lithium secondary battery. And, when the dispersibility and particle size control of the carbon material that is the conductive auxiliary agent are insufficient, the internal resistance of the electrode cannot be reduced because the uniform conductive network is not formed, and as a result, the lithium that is the active material There arises a problem that the performance of the transition metal composite oxide or graphite cannot be sufficiently obtained. 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.

  In addition, when forming an electrode mixture layer on an electrode current collector such as a metal foil, repeated charging and discharging a large number of times, the interface between the current collector and the electrode mixture layer, and the active material inside the electrode mixture There is a problem that the adhesion at the interface of the conductive auxiliary agent is deteriorated and the battery performance is lowered. This is because the active material and the electrode mixture layer repeat expansion and contraction due to lithium ion doping and dedoping during charging and discharging, so that the electrode mixture layer and the current collector interface, and the active material and conductive auxiliary agent interface It is considered that local shear stress is generated and the adhesion at the interface is deteriorated. In this case as well, if the dispersion of the conductive additive is insufficient, the adhesion reduction becomes significant. This is presumably because the presence of coarse aggregated particles makes it difficult to relieve stress.

  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 produce a battery stably, further dispersion stability over time is required. Further, as battery performance, further improvement of charge / discharge cycle characteristics of the battery (suppression of capacity reduction when charge / discharge is repeated) 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 the charging / discharging cycling characteristics of a battery by using this.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors use the polyvinyl acetal resin (A) and the derivative (B) as a dispersant when dispersing the carbon material as the conductive auxiliary agent. As a result, it was found that a composition for forming a secondary battery electrode (dispersion and mixture slurry) excellent in dispersion stability and exhibiting the effect of improving the performance of the secondary battery can be obtained, and the present invention has been achieved. Is.

  That is, the embodiment of the present invention includes a polyvinyl acetal resin (A), an organic dye derivative having an acidic functional group and / or a derivative (B) that is a triazine derivative having an acidic functional group, and a carbon material that is a conductive auxiliary agent. The present invention relates to a composition for forming a secondary battery electrode comprising (C).

  Moreover, the embodiment of this invention is related with the said composition for battery electrode formation which contains a solvent (D) 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 (E).

  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 (E) / 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.

  Furthermore, 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 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 a dispersion of carbon material particles and a mixture slurry excellent in dispersion stability can be prepared by using a dispersant, but also by using a polyvinyl acetal resin (A) and a derivative (B) in combination. It seems that uniform and strong contact between the active material (E) and the carbon material (C) occurs during the 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.

Hereinafter, the present invention will be described in detail.
<Derivative (B)>
First, the derivative (B) used in the present invention will be described. The derivative (B) 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 (1) or an organic dye derivative having an acidic functional group represented by the general formula (4) is preferable. First, the triazine derivative having an acidic functional group represented by the general formula (1) will be described.

General formula (1)

[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 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) ₂ , M represents one equivalent of a 1 to 3 valent cation, and Q represents -O-R ² , —NH—R ² , a halogen group, —X ¹ —R ¹ or —X ² —Y—Z, wherein R ² represents a hydrogen atom or an alkyl group which may have a substituent. Or the alkenyl group which may have a substituent is represented. n represents an integer of 1 to 4. R ¹ 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 (2) Represents. ]

General formula (2)

[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—, wherein R ³ and R ⁴ 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 (1). ]

In the above, examples of the organic dye residue in R ¹ , R ³ and R ⁴ 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, quinophthalone dyes, selenium dyes, metal complex dyes, etc. 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 ¹ , R ³ , and R ⁴ include thiophene, furan, pyridine, pyrazole, pyrrole, imidazole, isoindoline, isoindolinone, and benzimidazole. Examples thereof include heterocyclic residues such as lone, 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 (1) and general formula (2) 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 an alkyl group and a substituted group which may have a substituent in R ² 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 (3) or a mixture.

General formula (3)

[R ⁵ , R ⁶ , R ⁷ and R ⁸ each independently have a hydrogen atom, an alkyl group which may have a substituent, an alkenyl group which may have a substituent, or a substituent. Represents a good aryl group. ]

R ⁵ , R ⁶ , R ⁷ and R ⁸ may be the same or different. Moreover, when R < ⁵ >, R < ⁶ >, R < ⁷ >, R < ⁸ > 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.

［Ｘ⁸は、直接結合、−ＮＨ−、−Ｏ−、−ＣＯＮＨ−、−ＳＯ₂ＮＨ−、−ＣＨ₂ＮＨ−、−ＣＨ₂ＮＨＣＯＣＨ₂ＮＨ−、−Ｘ⁹−Ｙ−または−Ｘ⁹−Ｙ−Ｘ¹⁰−を表し、Ｘ⁹は、−ＣＯＮＨ−、−ＳＯ₂ＮＨ−、−ＣＨ₂ＮＨ−、−ＮＨＣＯ−または−ＮＨＳＯ₂−を表し、Ｘ¹⁰は、−ＮＨ−または−Ｏ−を表し、Ｙは、置換基を有してもよいアルキレン基、置換基を有してもよいアルケニレン基または置換基を有してもよいアリーレン基を表し、Ｚは、−ＳＯ₃Ｍ、−ＣＯＯＭ、−Ｐ（Ｏ）（−ＯＭ）₂または−Ｏ−Ｐ（Ｏ）（−ＯＭ）₂を表し、Ｍは１〜３価のカチオンの一当量を表し、Ｒ⁹は、有機色素残基を表し、ｎは、１〜４の整数を表す。］ Next, the organic dye derivative having an acidic functional group represented by the general formula (4) will be described.
General formula (4)

[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, and 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 R ⁹ represents an organic dye residue. Represents a group, and n represents an integer of 1 to 4. ]

The organic dye residue of R ^{9 has} the same meaning as the organic dye residue in R ¹ , R ³ and R ⁴ 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 (4) has the same meaning as M in the general formula (1).

  The method for synthesizing the derivative (B) 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.

  The said derivative | guide_body (B) may mix and use 1 type (s) or 2 or more types in arbitrary ratios.

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

<Polyvinyl acetal resin (A)>
The polyvinyl acetal resin (A) used in the present invention repeats the vinyl alcohol structure represented by the following formula (5), the vinyl acetate structure represented by the formula (6), and the vinyl acetal structure represented by the general formula (7). It is a polymer containing as a unit.

Formula (5)

Formula (6)

［一般式（７）中、αは、０または１〜８、好ましくは１〜６、更に好ましくは１〜４の整数である。］
また、ポリビニルアセタール樹脂（Ａ）中の一般式（７）で示される構造は、単一構造のみならず、異なる複数の構造を含んでも良い。 General formula (7)

[In General formula (7), (alpha) is an integer of 0 or 1-8, Preferably 1-6, More preferably, 1-4. ]
Further, the structure represented by the general formula (7) in the polyvinyl acetal resin (A) may include not only a single structure but also a plurality of different structures.

There is no restriction | limiting in particular about the manufacturing method of the polyvinyl acetal resin (A) used for this invention, The various polyvinyl acetal resin synthesize | combined by the well-known method and a commercially available thing can also be used.
As a typical synthesis method, a polymer obtained by polymerizing a vinyl alcohol precursor such as vinyl acetate is saponified with an alkali, and a part thereof is changed to a vinyl alcohol structure represented by the formula (5). And acetalization by reacting the above compounds. The kind of aldehyde acted at this time can react individually or in multiple types.

  It was found that the dispersion stability of the carbon material (C) tends to be influenced by the content of the vinyl alcohol structural unit represented by the formula (5) in the polyvinyl acetal resin. The content of vinyl alcohol structural units in the entire polyvinyl acetal resin is preferably 12 to 30% by weight, and more preferably 14 to 25% by weight. Further, the content of the vinyl acetate structural unit represented by the formula (6) in the entire polyvinyl acetal resin is preferably 10% by weight or less, and more preferably 5% by weight or less.

  In the vinyl acetal structural unit represented by the general formula (7), the kind of the acetal group is not particularly limited, but the butyral group (α = 3) has relatively good battery performance and will be described later. This is preferable because the solubility in a solvent (particularly N-methyl-2-pyrrolidone) is also good.

  Further, it has been found that the solubility of the polyvinyl acetal resin in N-methyl-2-pyrrolidone has a correlation with the average molecular weight or the average degree of polymerization of the polyvinyl acetal resin. If the average molecular weight of the polyvinyl acetal resin is 100,000 or less, an amount sufficient as an addition amount in the present invention is preferably dissolved in N-methyl-2-pyrrolidone, and if it is 50,000 or less, the dissolution rate is high, and more preferable. . Further, if the average degree of polymerization is 2000 or less, an amount sufficient as an addition amount in the present invention is preferably dissolved in N-methyl-2-pyrrolidone, and if it is 800 or less, it is more preferable because the dissolution rate is large.

  Examples of commercially available polyvinyl acetal resins include, for example, ESREC BL-1, BL-10, BM-1, BH-3 (polyvinyl butyral resin manufactured by Sekisui Chemical Co., Ltd.), ESREC BX-1, BX-L, KS-10 ( Polyvinyl acetal resin), Denkabutyral # 3000-1, # 3000-K, # 4000-2 (polyvinyl butyral resin manufactured by Denki Kagaku Kogyo), Mobital LPB16H, B20H, B30T, B30H, B30HH, B45M (manufactured by Kuraray Co., Ltd.) Polyvinyl butyral resin) and the like, but is not limited thereto.

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

<Carbon material (C)>
As the conductive aid in the present invention, a carbon material is most preferable. 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 amount of nitrogen adsorbed 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. If 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.

<Solvent (D)>
Examples of the solvent (D) 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.

  Solvents may be used singly or as a mixture of two or more in any proportion, but when recovering and reusing the solvent discharged in the electrode manufacturing process from the viewpoint of reducing environmental impact and economic advantages Is preferably not a mixed solvent but a single 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 (E)>
When the composition of the present invention is used for a positive electrode mixture or a negative electrode mixture, in addition to the polyvinyl acetal resin (A), derivative (B), carbon material (C) as a conductive additive, and solvent (D), At least a positive electrode active material or a negative electrode active material is contained.

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, and transition metal sulfide powders such as TiS ₂ and FeS. 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, 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.

  The size of these active materials (E) is preferably such that the average particle diameter is in the range of 0.05 to 100 μm, more preferably in the range of 0.1 to 50 μm. The average particle diameter of the active material (E) as used herein is an average value of particle diameters of the active material (E) 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, maleic acid, acrylic acid, acrylic ester, methacrylic acid, methacrylic ester, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc. Polymer or copolymer containing as a structural unit: polyurethane resin, polyester resin, phenol resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, acrylic resin, formaldehyde resin, silicone resin, fluorine resin; carboxymethylcellulose Such cellulose resins; rubbers such as styrene-butadiene rubber and fluororubber; and 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.

<Use of composition of the present invention>
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, one or more derivatives (B) selected from the polyvinyl acetal resin (A) and an organic dye derivative having an acidic functional group or a triazine derivative having an acidic functional group; In addition, the composition containing the carbon material (C) as the conductive assistant and the solvent (D) contains an active material (E) (positive electrode active material or negative electrode active material), preferably further a binder (F). It is preferable to use it as a positive / negative electrode mixed slurry.

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 acetal resin (A) in the mixture slurry and one or more derivatives (B) selected from an organic dye derivative having an acidic functional group or a triazine derivative having an acidic functional group Is preferably 0.01 to 7.5% by weight based on the total weight of the active material (E) and the carbon material (C) as the conductive additive. More preferably, it is 0.01 to 5 weight%, More preferably, it is 0.01 to 2.5 weight%. 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.

<The manufacturing method of the composition of this invention>
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, a carbon material (C) as a conductive auxiliary agent is dispersed in a solvent (D) in the presence of a polyvinyl acetal resin (A) and a derivative (B), and the dispersion is necessary. Accordingly, the active material (E) (positive electrode active material or negative electrode active material) and / or the binder (F) can be mixed. 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 a two-piece consisting of a polyvinyl acetal resin (A), a derivative (B), a carbon material (C) as a conductive additive, and a solvent (D). It shall refer to the composition for secondary battery electrode formation. Further, the “composite slurry” is a secondary battery electrode forming composition that further includes an active material (E) (positive electrode active material or negative electrode active material) and a binder (F) in the “dispersion”. Shall point to.

  In the above production method, the polyvinyl acetal resin (A) and the derivative (B) are completely or partially dissolved in the solvent (D), and the carbon material (C) as a conductive additive is added and mixed in the solution. Thus, the resin (A) and the derivative (B) are dispersed in the solvent while acting (for example, adsorbing) on the carbon material (C). 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. It is desirable that the thickness is not less than 05 μm and not more than 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.).

  Further, as a device for dispersing the resin (A) and the derivative (B) in the solvent while acting (for example, adsorbing) 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 effects of the polyvinyl acetal resin (A) and the derivative (B), the aggregation of the carbon materials (C) is well loosened, and the viscosity of the dispersion is lowered. Even when it is high, the metallic foreign matter can be efficiently removed. 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), in the presence of the resin (A) and the derivative (B), while stirring the dispersion formed by dispersing the carbon material (C) as a conductive assistant in a solvent, The method of adding and dissolving a binder component is mentioned. 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 carbon material (C) as a conductive additive is dispersed in the solvent (D) in the presence of the resin (A) and the derivative (B), a part or all of the binder (F) is added simultaneously. To perform distributed processing.

  As a method for adding the active material (E) (positive electrode active material or negative electrode active material), in the presence of the resin (A) and the derivative (B), the carbon material (C) as a conductive auxiliary agent is used as the solvent (D). A method of adding and dispersing the positive electrode active material or the negative electrode active material while stirring the dispersed dispersion can be mentioned. In addition, when the carbon material as a conductive additive is dispersed in a solvent in the presence of the resin (A) and the derivative (B), a part or all of the positive electrode active material or the negative electrode active material is simultaneously added and dispersed. Processing can also be performed. Further, in the presence of the resin (A) and the derivative (B), the binder component is solid or in solution while stirring the dispersion formed by dispersing the carbon material (C) as the conductive additive in the solvent (D). Examples of the method include adding and dispersing a positive electrode active material or a negative electrode active material after the addition. Furthermore, the resin (A), the derivative (B), the carbon material (C), the solvent (D), the active material (E), and the binder (F) can be mixed and simultaneously dispersed. 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 (E) 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 (E) to the dispersed particle diameter (D50) of the carbon material (C) described above (average particle diameter of the active material (E) / 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.

<Electrode>
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.

<Secondary battery>
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, sodium sulfur secondary batteries, lithium air secondary batteries, etc. In the secondary battery, conventionally known electrolytes, separators, and the like can be used as appropriate.

(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 electrolytes, 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”. Moreover, the polyvinyl acetal resin (A), the derivative (B), the carbon material (C), and the binder (F) used in Examples and Comparative Examples are shown below. Further, N-methyl-2-pyrrolidone used as the solvent (D) may be abbreviated as “NMP”.

<Polyvinyl acetal resin (A)>
-ESREC BL-1 (manufactured by Sekisui Chemical Co., Ltd.): polyvinyl butyral resin, repeating unit containing a hydroxyl group: 25%, calculated molecular weight: 19,000, hereinafter sometimes abbreviated as “BL-1”.
-ESREC BL-S (manufactured by Sekisui Chemical Co., Ltd.): polyvinyl butyral resin, repeating unit containing a hydroxyl group: 15%, calculated molecular weight: 23,000, hereinafter abbreviated as “BL-S”.
-ESREC BM-1 (manufactured by Sekisui Chemical Co., Ltd.): polyvinyl butyral resin, repeating unit containing a hydroxyl group: 24%, calculated molecular weight: 40,000, hereinafter abbreviated as "BM-1".
-SREC BH-3 (manufactured by Sekisui Chemical Co., Ltd.): polyvinyl butyral resin, repeating unit containing a hydroxyl group: 24%, calculated molecular weight: 110,000, hereinafter abbreviated as “BH-3”.
-SREC BH-S (manufactured by Sekisui Chemical Co., Ltd.): polyvinyl butyral resin, repeating unit containing a hydroxyl group: 14%, calculated molecular weight: 66,000, hereinafter abbreviated as “BH-S”.
-ESREC BX-1 (manufactured by Sekisui Chemical Co., Ltd.): polyvinyl acetal resin, repeating unit containing a hydroxyl group: 27%, calculated molecular weight: 100,000, hereinafter may be abbreviated as "BX-1".
Denkabutyral # 3000-1 (manufactured by Denki Kagaku Kogyo Co., Ltd.): polyvinyl butyral resin, repeating unit containing a hydroxyl group: 19%, average degree of polymerization: 600, hereinafter sometimes abbreviated as “# 3000-1”.
Denkabutyral # 3000-K (manufactured by Denki Kagaku Kogyo Co., Ltd.): polyvinyl butyral resin, repeating unit containing a hydroxyl group: 12%, average degree of polymerization: 800, hereinafter sometimes abbreviated as “# 3000-K”.
Denkabutyral # 5000-A (manufactured by Denki Kagaku Kogyo Co., Ltd.): polyvinyl butyral resin, repeating unit containing a hydroxyl group: 16%, average degree of polymerization: 2000, hereinafter sometimes abbreviated as “# 5000-A”.
Mobital LPB16H (manufactured by Kuraray Co., Ltd.): polyvinyl butyral resin, repeating unit containing a hydroxyl group: 18%, average molecular weight 15000, hereinafter sometimes abbreviated as “B16H”.

<Derivative (B)>
Table 1 shows the structure of an organic dye derivative having an acidic functional group.

The structure of the triazine derivative having an acidic functional group is shown in Table 2.

<Carbon material (C)>
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 sometimes abbreviated as “HS-100”.
Denka black granular product (manufactured by Denki Kagaku Kogyo Co., Ltd.): acetylene black, primary particle diameter 35 nm, specific surface area 68 m ² / g, hereinafter sometimes abbreviated as “granular product”.
# 3400B (manufactured by Mitsubishi Chemical Corporation): furnace black, primary particle diameter 21 nm, specific surface area 165 m ² / g.
Super-P Li (manufactured by TIMCAL): furnace black. Primary particle diameter 40 nm, specific surface area 62 m ² / g.

<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 (dispersion)>
[Examples 1 to 6]
According to the composition shown in Table 3, a carbon material dispersion was prepared. First, 79 parts of N-methyl-2-pyrrolidone as a solvent (D) was stirred with a mixer, 0.8 parts of various polyvinyl acetal resins (A), and various derivatives (B) 0. Two parts were added to completely or partially dissolve the resin (A) and the derivative (B). Next, after adding 20 parts of various carbon materials (C) as a conductive additive and mixing with a mixer, dispersion is further performed with a sand mill, and dispersions 1 to 6 which are one embodiment of a composition for forming a secondary battery electrode Got.

[Examples 7 and 8]
According to the composition shown in Table 3, 20 parts of # 3400B as carbon material (C), 0.2 part of various derivatives (B) shown in Table 2, 1 part of various polyvinyl acetal resins (A), and solvent (D) As in Examples 1 to 6 except that the content was changed to 78.8 parts of N-methyl-2-pyrrolidone, Dispersion 7 and Dispersion 8 were obtained.

[Examples 9 and 10]
According to the composition shown in Table 3, 20 parts of Super-PLi as carbon material (C), 0.4 parts of various derivatives (B) shown in Table 2, 1 part of various polyvinyl acetal resins (A), and a solvent ( Dispersion 9 and Dispersion 10 were obtained in the same manner as in Examples 1 to 6, except that 7) part of N-methyl-2-pyrrolidone was changed as D).

[Comparative Example 1]
According to the composition shown in Table 3, a carbon material dispersion was prepared. First, 79 parts of N-methyl-2-pyrrolidone as a solvent (D) was stirred with a mixer, and 1 part of B-01 shown in Table 1 was added as a derivative (B) to partially dissolve the derivative (B). I let you. Next, 20 parts of HS-100 was added as a carbon material (C) serving as a conductive additive and mixed with a mixer, and then dispersed with a sand mill to obtain dispersion 11.

[Comparative Example 2]
According to the composition shown in Table 3, a dispersion 12 was obtained in the same manner as in Comparative Example 1 except that 1 part of BL-1 was used as the polyvinyl acetal resin (A) instead of the derivative (B).

[Comparative Example 3]
According to the composition shown in Table 3, a dispersion 13 was obtained in the same manner as in Comparative Example 1 except that the carbon material (C) was changed to a granular product and the derivative (B) was changed to B-04 shown in Table 2. It was.

[Comparative Example 4]
According to the composition shown in Table 3, a dispersion 14 was obtained in the same manner as in Comparative Example 3 except that BH-3 was used as the polyvinyl acetal resin (A) instead of the derivative (B).

[Comparative Example 5]
According to the composition shown in Table 3, 20 parts of # 3400B as carbon material (C), 1.2 parts of B-07 shown in Table 2 as derivative (B), and N-methyl-2 as solvent (D) Dispersion 15 was obtained in the same manner as Comparative Example 1 except that the amount was changed to 78.8 parts of pyrrolidone.

[Comparative Example 6]
According to the composition shown in Table 3, Dispersion 16 was obtained in the same manner as Comparative Example 5 except that # 3000-1 was used as the polyvinyl acetal resin (A) instead of the derivative (B).

[Comparative Example 7]
According to the composition shown in Table 3, 20 parts of Super-PLi as carbon material (C), 1.4 parts of B-10 shown in Table 2 as derivative (B), and N-methyl as solvent (D) Dispersion 17 was obtained in the same manner as Comparative Example 1 except that the amount was changed to 78.6 parts of -2-pyrrolidone.

[Comparative Example 8]
According to the composition shown in Table 3, a dispersion 18 was obtained in the same manner as in Comparative Example 7 except that B16H was used as the polyvinyl acetal resin (A) instead of the derivative (B).

(Dispersibility evaluation of dispersion (measurement of dispersed particle size))
The dispersion particle size was used as an index for evaluating the dispersibility of the dispersion. 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 dispersing 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 measurement sample liquid was set in the above particle size distribution meter, and measurement was performed after confirming that the loading index (laser scattering intensity) was in the range of 0.8 to 1.2. 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 3 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 the production of various dispersions and after the dispersion was stored at 50 ° C. for 10 days.

  In Table 3, “storage stability (2) / (1)” means the ratio of “dispersion particle size of dispersion stored at 50 ° C. for 10 days / dispersion particle size of dispersion immediately after production”, The smaller the deviation from 1.00, the better the storage stability.

  As shown in Table 3, it was confirmed that all of the dispersions were excellent in dispersibility of the conductive assistant and were uniformly dispersed in the conductive assistant. In particular, it was confirmed that the dispersion of the present invention had a small change in dispersed particle size when stored at 50 ° C. for 10 days as compared with the comparative example, and was excellent in storage stability.

<Manufacture of secondary battery electrode forming composition (positive electrode mixture slurry)>
[Example 11]
11 parts of the dispersion 1 produced in Example 1 and 17.3 parts of an NMP solution of W # 1100 (solid content 12%) as a binder (F) were mixed and homogenized with a disper, and then the liquid was stirred. As the positive electrode active material, 68.6 parts of LiCoO ₂ having an average particle diameter of 6.7 μm (hereinafter sometimes abbreviated as LCO-01) was gradually added. Next, N-methyl-2-pyrrolidone as a solvent (D) is added and further mixed so that the solid content of the mixture slurry is 73%, and the positive electrode composite which is one embodiment of the composition for forming a secondary battery electrode is formed. A material slurry was produced.

[Examples 13 to 17, Comparative Examples 9 to 12]
A positive electrode mixture slurry was produced in the same manner as in Example 11 except that the materials shown in Table 4 were changed. As active materials, LCO-01, LiCoO _{2 having} an average particle diameter of 20 μm (hereinafter sometimes abbreviated as LCO-02), LiMn ₂ O _{4 having} an average particle diameter of 12 μm (hereinafter abbreviated as LMO). Or LiNi _(1/3) Mn _(1/3) Co _(1/3) O ₂ (hereinafter sometimes abbreviated as NMC-01) having an average particle size of 15 μm was used.

[Example 18]
11 parts of the dispersion 7 produced in Example 7 and 17.2 parts of an NMP solution of W # 1100 (solid content 12%) as a binder (F) were mixed and homogenized with a disper, and the liquid was stirred. As the positive electrode active material, 68.6 parts of NMC-01 was gradually added. Next, N-methyl-2-pyrrolidone was added and mixed as a solvent (D) so that the solid content of the mixture slurry would be 73% to produce a positive electrode mixture slurry.

[Example 20, Comparative Examples 13 and 14]
A positive electrode mixture slurry was produced in the same manner as in Example 18 except that the materials shown in Table 4 were changed. As the active material, NMC-01, LiNi _(1/3) Mn _(1/3) Co _(1/3) O ₂ (hereinafter, abbreviated as NMC-02 _{) having} an average particle diameter of 11.5 μm may be used. ) Was used.

[Example 21]
11 parts of the dispersion 9 produced in Example 9 and 17.0 parts of an NMP solution of W # 1100 (solid content 12%) as a binder (F) were mixed and homogenized with a disper, and then the liquid was stirred. As the positive electrode active material, 68.6 parts of NMC-02 was gradually added. Next, N-methyl-2-pyrrolidone was added and mixed as a solvent (D) so that the solid content of the mixture slurry would be 73% to produce a positive electrode mixture slurry.

[Example 22]
After 12.5 parts of the dispersion 10 produced in Example 10 and 29.1 parts of an NMP solution of W # 7200 (8% solids) as a binder (F) were mixed and homogenized with a disper, the liquid was stirred. However, 45 parts of LiFePO ₄ (hereinafter sometimes 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. Next, N-methyl-2-pyrrolidone was added and mixed as a solvent (D) so that the solid content of the mixture slurry would be 50% to produce a positive electrode mixture slurry.

[Comparative Examples 15 and 16]
A positive electrode mixture slurry was produced in the same manner as in Example 22 except that the materials shown in Table 4 were changed.

[Example 23]
After 12.5 parts of the dispersion 1 produced in Example 1 and 29.7 parts of NMP solution of W # 7200 (solid content 8%) as a binder (F) were mixed and homogenized with a disper, the liquid was stirred. However, 45 parts of LiFePO ₄ (hereinafter sometimes 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. Next, N-methyl-2-pyrrolidone was added and mixed as a solvent (D) so that the solid content of the mixture slurry would be 50% to produce a positive electrode mixture slurry.

[Example 12]
68.6 parts of LCO-01 as a positive electrode active material, 2.2 parts of HS-100 as a carbon material as a conductive additive, 0.02 part of derivative B-01 described in Table 1, and BL-1 as a polyvinyl acetal resin. 09 copies,
After mixing 17.3 parts of W # 1100 NMP solution (solid content 12%) as a binder with a planetary mixer, N-methyl-2-pyrrolidone was added so that the solid content of the mixture slurry would be 80%. Kneaded. Furthermore, N-methyl-2-pyrrolidone was added and mixed so that the solid content of the mixture slurry would be 73% to produce a positive electrode mixture slurry.

[Example 19]
68.6 parts of NMC-01 as a positive electrode active material, 2.2 parts of # 3400B as a carbon material as a conductive additive, 0.02 part of derivative B-07 described in Table 2, and # 3000-1 as a polyvinyl acetal resin. After 11 parts and 17.2 parts of N # solution of W # 1100 (solid content 12%) as a binder were mixed with a planetary mixer, N-methyl-2-pyrrolidone was mixed so that the solid content of the mixture slurry was 80%. And kneaded. Furthermore, N-methyl-2-pyrrolidone was added and mixed so that the solid content of the mixture slurry would be 73% to produce a positive electrode mixture slurry.

<Manufacture of secondary battery electrode forming composition (negative electrode mixture slurry)>
[Example 24]
9 parts of the dispersion 1 produced in Example 1 and 28.9 parts of W # 7200 NMP solution (solid content 8%) as a binder (F) were mixed and homogenized with a disper, and the liquid was stirred. As a negative electrode active material, 55.8 parts of artificial graphite having an average particle diameter of 15 μm was gradually added. 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 Examples 17 and 18]
Except having changed into the material shown in Table 5, it carried out similarly to Example 24, and adjusted the negative mix slurry.

[Example 25]
After 14.3 parts of the dispersion 7 produced in Example 7 and 33.5 parts of an NMP solution of W # 7200 (solid content 8%) as a binder (F) were mixed by a disper and homogenized, the liquid was stirred. However, 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 a negative electrode active material. 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 Examples 19 and 20]
A negative electrode mixture slurry was prepared in the same manner as in Example 25 except that the materials shown in Table 5 were changed.

  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 dispersibility of composite slurry)
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 positive electrode mixture slurry was applied onto a 20 μm-thick aluminum foil serving as a current collector using a doctor blade, and then dried under reduced pressure to adjust the electrode thickness to 100 μm. Furthermore, the rolling process by a roll press was performed and the positive electrode from which thickness becomes 85 micrometers was manufactured.

  The negative electrode mixture slurry was applied onto a copper foil having a thickness of 20 μm serving as a current collector using a doctor blade, and then dried under reduced pressure to adjust the thickness of the electrode to 80 μm. Furthermore, the rolling process by a roll press was performed and the negative electrode from which thickness becomes 70 micrometers was manufactured.

<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. LiPF ₆ in a working electrode, a counter electrode, a separator inserted between the working electrode and the counter electrode (porous polypropylene film), and an electrolytic solution (ethylene carbonate and diethyl carbonate mixed at a ratio of 1: 1 (volume ratio)) A non-aqueous electrolyte solution having a concentration of 1M dissolved therein. The coin-type battery was manufactured in a glove box substituted with argon gas, and then the battery characteristics were evaluated as follows.

(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 to be used was LiCoO ₂ , constant current charging was continued to a charge end voltage of 4.3 V at a charging current of 1.7 mA. 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%”

When LiMn ₂ O ₄ is used as the active material, LiCoO ₂ is used except that the charging current is 1.0 mA, the charging end voltage is 4.3 V, the discharging current is 1.0 mA, and the discharging end voltage is 3.0 V. The cycle characteristics were measured in the same manner as described above.

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 set to 0.0 V.

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.

Further, when the active material used is artificial graphite, the same as in the case of LiCoO ₂ except that the charging current is 1.8 mA, the charging end voltage is 0.1 V, the discharging current is 1.8 mA, and the discharging end voltage is 2.0 V. Cycle characteristics were measured.

Further, when the active material used is Li ₄ Ti ₅ O ₁₂ , LiCoO except that the charging current is 1.0 mA, the charging end voltage is 1.0 V, the discharging current is 1.0 mA, and the discharging end voltage is 2.0 V. _The cycle characteristics were measured in the same manner as in ₂ .

  In Tables 4 and 5, “active material / carbon material dispersion particle size ratio” means the ratio of average particle size of active material (E) / dispersed particle size (D50) of carbon material (C).

  In Tables 6 and 7, “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 from 1, the better the storage stability.

  As shown in Tables 6 and 7, it was confirmed that the composite slurry according to the present invention in Examples 11 to 25 was a composition excellent in dispersibility of the conductive assistant 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. Further, a dispersion (G) composed of N-methyl-2-pyrrolidone as a polyvinyl acetal resin (A), a derivative (B), a carbon material (C) as a conductive auxiliary agent and a solvent (D), and a binder (F) And a battery using a mixture slurry prepared by mixing the active material (E), cycle characteristics more than a battery using a mixture slurry prepared by mixing the above (A) to (E) together There was a tendency that the (discharge capacity retention ratio) was more excellent. Furthermore, the ratio of the average particle diameter of the active material (E) to be used and the dispersed particle diameter (D50) of the carbon material (C) in the dispersion (G) (active material average particle diameter / carbon material dispersed particle diameter ( When D50)) was 2 or more, more preferably 9 or more, the battery cycle characteristics (discharge capacity retention rate) tended to improve.

In the battery using the composition for forming a secondary battery electrode of the present invention and the electrode for a secondary battery formed from the composition, the reason why it is excellent in dispersion stability and cycle characteristics is not clear, but is presumed as follows. doing.
In the dispersion (G) in which the polyvinyl acetal resin (A) and one or more derivatives (B) selected from an organic dye derivative having an acidic functional group and / or a triazine derivative having an acidic functional group are used as a dispersant. The derivative (B) strongly acts (for example, adsorbs) on the surface of the carbon material (for example, carbon black), while the acidic functional group possessed by the derivative (B) and the polar functional group possessed by the polyvinyl acetal resin (A) act (for example, It is considered that the interaction (for example, adsorption) between the resin (A) and the carbon material (C) is strengthened by hydrogen bonding. Therefore, it is considered that the dispersion stability (storage stability) of the carbon material is improved.

  Further, when the active material (E) enters here, the action (for example, adsorption) of the resin (A) occurs also with the active material (E). Since the resin adsorbs to the active material (E) surface without the resin (A) being detached from the carbon material surface due to the effect, the dispersion of the carbon material (C) is maintained while the coating material is being dried. It seems that uniform and strong contact between the substance (E) and the carbon material (C) occurs, which contributes to improvement of battery performance.

  Further, it is considered that the battery performance is improved when the difference between the average particle size of the active material (E) and the dispersed particle size (D50) of the carbon material (C) is large. When the mixture slurry dries, the distance between particles in the slurry (between active material and active material, between carbon material and carbon material, between active material and carbon material) gradually becomes shorter as the solvent evaporates. Although it aggregates, it is thought that this aggregation progresses in the form of making the interfacial energy of the aggregate as small as possible. At this time, in order to reduce the interfacial energy of the aggregate, (1) the particles having similar surface energies are aggregated and / or (2) the aggregate is aggregated so that the surface area (interface) of the aggregate is smaller. It is possible. In particular, when it seems that uniform and strong contact between the active material (E) and the carbon material (C) described above occurs, the active material and the carbon material (C) are aggregated with each other (those having close surface energies). Rather than do it, if the fine carbon material (C) agglomerates around a larger active material, the contribution of the effect of reducing the surface area of the agglomerate becomes larger, and it seems that the energy is more stable. It is. As a result, it seems that the battery performance is improved by forming a more uniform and strong conductive path in the electrode film.

  On the other hand, when the polyvinyl acetal resin (A) is used alone as a dispersant, competitive adsorption of the resin (A) occurs between the carbon material (C) and the active material (E) when the active material (E) is mixed, The dispersion of the carbon material (C) is not sufficiently maintained during the drying of the coating film, and the active material (E) and the carbon material (C) are aggregated in the active material (E) and the carbon material (C). It seems that the contact is uneven and weak. In addition, when the derivative (B) is used alone as a dispersant, the dispersion stability of the carbon material (C) is also due to an electrical interaction (repulsive action) caused by polarization or dissociation of the acidic functional group of the derivative (B). It seems to have been defeated. When the active material (E) is mixed here, an increase in the ionic strength of the dispersion system (due to dissociation of unreacted raw materials (metal salts) and by-products, etc.) derived from the active material occurs, and the electrical properties of the derivative (B) It is considered that the repulsive action is weakened. This effect becomes more prominent in the process in which the mixture slurry is concentrated when the coating film is dried. As a result, the dispersion of the carbon material (C) is not sufficiently maintained, and the contact between the active material (E) and the carbon black is uneven. It seems that it is weak.

Claims (7)

  2 comprising a polyvinyl acetal resin (A), an organic dye derivative having an acidic functional group and / or a derivative (B) which is a triazine derivative having an acidic functional group, and a carbon material (C) which is a conductive aid. A composition for forming a secondary battery electrode.   The composition for forming a secondary battery electrode according to claim 1, further comprising a solvent (D).   The composition for forming a secondary battery electrode according to claim 1 or 2, further comprising a binder (F).   The composition for forming a secondary battery electrode according to any one of claims 1 to 3, further comprising an active material (E).   The composition for forming a secondary battery electrode according to claim 4, wherein the ratio of the average particle diameter of the active material (E) / the dispersed particle diameter (D50) of the carbon material (C) is 2 or more and 100 or less.   An electrode for a secondary battery, which is an electrode having a composite layer on a current collector, wherein the composite layer is formed by the composition for forming a secondary battery electrode according to claim 4 or 5.   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 7. A secondary battery which is an electrode for a secondary battery according to Item 6.