JP2013127959A - Aqueous binder liquid for secondary battery negative electrode, aqueous paste for secondary battery negative electrode produced with aqueous binder liquid, secondary battery negative electrode, and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous binder liquid which allows the manufacturing of a negative electrode having excellent adhesiveness between an active material and a current collector and suffering a small change of thickness even after the repetition of charge and discharge, in application to a secondary battery negative electrode active material containing silicon, tin or germanium atoms.SOLUTION: The aqueous binder liquid for formation of a secondary battery negative electrode including an active material containing silicon, tin, or germanium atoms comprises: an acid-modified polyolefin resin (A) containing 0.1-10 mass% of an unsaturated carboxylic acid component; a crosslinking agent (B); and an aqueous medium. The content of the crosslinking agent (B) is 10-100 pts.mass to 100 pts.mass of the resin (A).

Description

  The present invention relates to an aqueous binder liquid for a secondary battery negative electrode, and further to a paste, a negative electrode and a secondary battery using the binder liquid.

  In recent years, with the demand for smaller and lighter portable electronic devices such as mobile phones and digital cameras, high-performance batteries have been actively developed, and the demand for secondary batteries with high energy density has increased. It is growing. In particular, lithium-ion batteries are being developed for use in electric vehicles in addition to applications such as mobile phones and notebook computers, and the range of their use is expanding greatly.

  In a lithium ion battery, an electrode having a configuration in which a separator is disposed between a positive electrode and a negative electrode is placed in a container together with an electrolytic solution (in the case of a lithium ion polymer battery, a gel or all solid electrolyte instead of a liquid electrolytic solution). It has a structure housed in.

  An electrode of a lithium ion battery is formed by layering an active material and, if necessary, a conductive material mainly made of a carbon material on a metal current collector such as an aluminum foil or a copper foil using a binder. . As the positive electrode active material, a lithium composite oxide containing a transition metal such as lithium cobaltate is used, and as the negative electrode active material, a carbon material or the like is mainly used. Such an electrode of a lithium ion battery is usually kneaded and prepared in the presence of a solvent such as N-methyl-2-pyrrolidone (NMP) by adding a binder or, if necessary, a conductive material to the active material. The obtained electrode paste is applied on a metal current collector by a doctor blade or the like and dried. Here, the binder is used for bonding the active material and the conductive material, and further to the metal current collector.

Conventionally, as a binder for a secondary battery electrode, a fluororesin such as polyvinylidene fluoride (PVDF) resin is mainly used, and a solution obtained by dissolving this in NMP is often used.
However, when PVDF is used as a binder, it is inferior in adhesiveness between active materials and between conductive materials, and also inferior in adhesiveness at the interface between the active material and the conductive material and the metal current collector. During the manufacturing process such as the process or the winding process, a part of the active material or the conductive material is peeled off from the metal current collector, which causes a micro short circuit and a variation in battery capacity.
Furthermore, since PVDF is inferior in swelling resistance to the electrolytic solution, the binder swells in the electrolytic solution by repeating charging and discharging, and between the active material and the conductive material, and between the active material and the conductive material and the metal current collector. The contact resistance between the active material and the conductive material may be partly peeled off from the metal current collector, resulting in inferior battery characteristics and further safety problems.
Moreover, since NMP used as a solvent for dissolving PVDF evaporates when the electrode paste is applied and dried on the metal current collector, it must be recovered safely. In addition, due to recent environmental laws and regulations, there are many places where it is not possible to use organic solvents that may affect the environment depending on the processing site.

  In recent years, a negative electrode active material having a charge / discharge capacity that greatly exceeds the theoretical capacity of a carbon material has been developed as a negative electrode active material of a lithium ion secondary battery. For example, a material containing a metal that can be alloyed with lithium such as silicon or tin is expected.

  However, when materials containing silicon atoms, tin atoms, or germanium atoms are used as the active material for secondary battery negative electrodes, the volume change associated with insertion and extraction of lithium during charging and discharging is large. It is difficult to maintain good adhesion with the body. These active materials repeatedly expand and contract during the charge / discharge cycle as lithium is inserted and extracted. Due to such expansion and contraction, the active material particles are pulverized or detached from the current collector. Due to the pulverization and desorption of the active material, the cycle characteristics of the lithium ion secondary battery are greatly degraded.

In order to solve these problems, the following techniques have been disclosed for secondary battery electrode binders.
That is, Patent Document 1 proposes a negative electrode for a secondary battery that uses an alkoxysilyl group-containing resin as a binder resin. As described in Patent Document 1, various studies have been made on a combination of an active material and a binder resin for binding the active material, but there is still room for improvement in cycle performance. Therefore, there is still a need for a negative electrode for a lithium ion secondary battery with better cycle performance.

  In patent document 2, the negative electrode for secondary batteries which uses a polyimide resin as a binder resin is proposed. However, the polyimide resin is used by dissolving it in NMP, and it was still necessary to recover the organic solvent that evaporates when drying.

JP 2009-43678 A JP 2007-149604 A

  The present invention solves the above-described problems, and when applied to an active material for a secondary battery negative electrode containing a silicon atom, a tin atom, or a germanium atom, it has excellent adhesiveness between the active material and the current collector. An object of the present invention is to provide an aqueous binder liquid that can produce a negative electrode with little change in thickness even after repeated discharges. Furthermore, it aims at providing the paste, negative electrode, and secondary battery using this binder liquid.

As a result of examining the above problems, the present inventors have reached the present invention. That is, the gist of the present invention is as follows.
(1) An acid-modified polyolefin resin which is a binder liquid for forming a secondary battery negative electrode having an active material containing a silicon atom, a tin atom or a germanium atom, and contains 0.1 to 10% by mass of an unsaturated carboxylic acid component It contains (A), a crosslinking agent (B), and an aqueous medium, and the content of (B) is 10 to 100 parts by mass with respect to 100 parts by mass of (A). Aqueous binder solution for secondary battery negative electrode.
(2) An acid-modified polyolefin resin which is a binder liquid for forming a secondary battery negative electrode having an active material containing a silicon atom, a tin atom or a germanium atom, and contains 0.1 to 10% by mass of an unsaturated carboxylic acid component An aqueous binder solution for a negative electrode of a secondary battery, comprising (A) and an aqueous medium, wherein the acid-modified polyolefin resin (A) is crosslinked by irradiation with radiation.
(3) The acid-modified polyolefin resin (A) contains 50 to 98% by mass of the acid-modified polyolefin resin (a) containing 50 to 98% by mass of the ethylene component and / or at least one of the propylene component and 1-butene component. An aqueous binder liquid for secondary battery negative electrode as described in (1) or (2), which is an acid-modified polyolefin resin (b).
(4) The unsaturated carboxylic acid component of the acid-modified polyolefin resin (A) is at least one selected from the group consisting of maleic anhydride, maleic acid, acrylic acid and methacrylic acid (1) to ( The aqueous binder solution for secondary battery negative electrode according to any one of 3). (5) The aqueous binder liquid for secondary battery negative electrode according to (1), (3) or (4), wherein the crosslinking agent (B) is an oxazoline compound, a carbodiimide compound or an isocyanate compound.
(6) The aqueous binder solution for secondary battery negative electrode according to any one of (2) to (4), wherein the radiation source of irradiation is γ rays and the irradiation amount is 1 to 100 kGy.
(7) A secondary battery negative electrode aqueous paste containing the secondary battery negative electrode aqueous binder liquid according to any one of (1) to (6) above and an active material containing a silicon atom, a tin atom or a germanium atom. .
(8) A secondary battery negative electrode formed using the aqueous paste for secondary battery negative electrode described in (7) above.
(9) A secondary battery formed using the secondary battery negative electrode described in (8) above.

  The aqueous binder liquid for secondary battery negative electrode of the present invention is excellent in adhesiveness between an active material containing a silicon atom, a tin atom or a germanium atom and a current collector. The secondary battery negative electrode formed using this binder liquid and an active material containing silicon atom, tin atom or germanium atom has little change in the thickness of the electrode even after repeated charge and discharge. Therefore, a secondary battery having excellent cycle characteristics can be obtained. Moreover, since the aqueous binder liquid for secondary battery negative electrodes of this invention uses an aqueous medium as a medium, the problem of organic solvents, such as an organic solvent evaporating at the time of electrode manufacture, can be eliminated.

Hereinafter, the present invention will be described in detail.
The aqueous binder liquid for secondary battery negative electrode of the present invention contains an acid-modified polyolefin resin (A), a cross-linking agent (B), and an aqueous medium. The content of the cross-linking agent (B) is an acid-modified polyolefin resin. (A) It is 10-100 mass parts with respect to 100 mass parts.

In the present invention, the acid-modified polyolefin resin (A) needs to have an unsaturated carboxylic acid component content of 0.1 to 10% by mass from the viewpoint of satisfying dispersion of the resin and resistance to the electrolytic solution. Yes, it is preferably 0.3 to 8% by mass, more preferably 0.5 to 6% by mass, and even more preferably 1 to 5% by mass.
If the content of the unsaturated carboxylic acid component is less than 0.1% by mass, the adhesion between the active material and the conductive material and the metal current collector may be lowered, and the resin is dispersed in the aqueous medium as described later. In such a case, the dispersion tends to be difficult. When the content of the unsaturated carboxylic acid component exceeds 10% by mass, the resistance to the electrolytic solution may decrease.
Examples of the unsaturated carboxylic acid component include unsaturated carboxylic acids and anhydrides thereof. Specifically, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid, croton In addition to acids, examples include half esters and half amides of unsaturated dicarboxylic acids. Of these, acrylic acid, methacrylic acid, maleic acid, and maleic anhydride are preferable, and acrylic acid and maleic anhydride are particularly preferable.
The form of the unsaturated carboxylic acid component is not particularly limited as long as it is copolymerized in the acid-modified polyolefin resin (A) by, for example, random copolymerization, block copolymerization, graft copolymerization, thermal degradation method or the like.
Incidentally, the acid anhydride introduced into the resin forms an acid anhydride structure in which the adjacent carboxyl group is dehydrated and cyclized in the dry state of the resin. May open to take the structure of a carboxylic acid or salt thereof.

Moreover, it is preferable that acid-modified polyolefin resin (A) contains 50-98 mass% of C2-C6 unsaturated hydrocarbon components from a viewpoint of dispersion | distribution of resin and the tolerance with respect to electrolyte solution, The content is more preferably 98% by mass, still more preferably 70 to 98% by mass, and most preferably 75 to 95% by mass.
When the content of the unsaturated hydrocarbon component having 2 to 6 carbon atoms is less than 50% by mass, the resistance to the electrolytic solution may be reduced. When the content exceeds 98% by mass, the content of the unsaturated carboxylic acid component is relatively high. Since it will fall, it may become difficult to make the resin water-based.

  Examples of unsaturated hydrocarbons having 2 to 6 carbon atoms include alkenes such as ethylene, propylene, 1-butene, isobutene, 1-pentene, 4-methyl-1-pentene, 3-methyl-1-pentene and 1-hexene. And dienes such as butadiene and isoprene. From the viewpoint of ease of production of the resin, ease of aqueous formation, and resistance to the electrolyte, ethylene, propylene or butene components (1-butene, isobutene Etc.) and these may be used in combination.

  The acid-modified polyolefin resin (A) is an acid-modified polyolefin resin (a) containing 50 to 98% by mass of an ethylene component, or an acid modification containing 50 to 98% by mass of at least one of a propylene component and a 1-butene component. The polyolefin resin (b) is preferable, and the acid-modified polyolefin resins (a) and (b) can be used in combination.

  In addition to the propylene component and the 1-butene component, the acid-modified polyolefin resin (b) preferably further contains an ethylene component in an amount of 1.5 to 45% by mass, and more preferably 2 to 30% by mass. More preferred. By containing an ethylene component, the flexibility of the resin increases and it becomes easy to be aqueous.

As a copolymerization component contained in acid-modified polyolefin resin (A), the following components may be contained within the range which does not impair the effect of this invention. That is, examples of such components include acrylic acid esters such as methyl acrylate, methyl methacrylate, and ethyl acrylate, and methacrylic acid esters, 1-pentene, 4-methyl-1-pentene, 3-methyl- Alkenes and dienes such as 1-pentene, 1-hexene and 1-octene, maleates such as dimethyl maleate, diethyl maleate and dibutyl maleate, (meth) acrylic acid amides, methyl vinyl ether, ethyl vinyl ether Alkyl vinyl ethers such as vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, vinyl versatate, vinyl esters, vinyl alcohol, 2-hydroxyethyl acrylate, glycidyl (meth) acrylate, (meth) acrylo Tolyl, styrene, substituted styrene, vinyl halides, vinylidene halides such, carbon monoxide, sulfur dioxide, and mixtures thereof.
Such a component is preferably 20% by mass or less of the acid-modified polyolefin resin (A). When it exceeds 20 mass%, when it is used as a binder, it tends to be difficult to achieve the effects of the present invention as described above.

  Specific examples of the acid-modified polyolefin resin (a) include ethylene- (meth) acrylic acid copolymer, ethylene-acrylic acid ester-maleic anhydride terpolymer, or ethylene-methacrylic acid ester-maleic anhydride terpolymer. An original copolymer is most preferred. Such resins include Lexpearl EAA series (Nippon Polyethylene), Primacol (Dow Chemical Japan), Nuclel series (Mitsui / DuPont Polychemical), Bondine series (Arkema), Lexpearl ET series. (Nippon Polyethylene Co., Ltd.).

  Specific examples of the acid-modified polyolefin resin (b) include, for example, REXTAC (Rexene, USA), Bestplast 408, Bestplast 708 (Huls, Germany), Ubetak APAO ( Ube Lexen) and the like, and polyolefin resins in which an unsaturated carboxylic acid component is introduced into these commercially available resins by the above-mentioned method, Yumex series (Sanyo Kasei Co., Ltd.), and the like. Of the above-mentioned commercially available resins, it is preferable to use Bestplast 408, Bestplast 708, and Umex series.

  The acid-modified polyolefin resin (A) is prepared by mixing two or more arbitrary polyolefin resins so that the unsaturated carboxylic acid component and the unsaturated hydrocarbon component having 2 to 6 carbon atoms have the constituent component ratio of the present invention. It is good.

  The molecular weight of the acid-modified polyolefin resin (A) is not particularly limited, but the mass average molecular weight is preferably 10,000 or more, more preferably 10,000 to 150,000, and 12,000 to 120,000. Is more preferable, 15,000 to 100,000 is particularly preferable, and 20,000 to 90,000 is most preferable. When the mass average molecular weight is less than 10,000, the electrodes are fragile, and the adhesiveness between the active materials and the adhesiveness between the active material and the current collector may be reduced. When the mass average molecular weight exceeds 150,000, it tends to be difficult to make the resin water-based. In addition, the weight average molecular weight of resin can be calculated | required on the basis of polystyrene resin using a gel permeation chromatography (GPC).

  The binder liquid of the present invention needs to contain a crosslinking agent (B) or the acid-modified polyolefin resin (A) is crosslinked by irradiation with radiation. By using such a binder liquid, the expansion and contraction of the active material accompanying the charge / discharge cycle can be suppressed.

  The content of the crosslinking agent (B) in the binder liquid needs to be 10 to 100 parts by mass, and preferably 15 to 80 parts by mass with respect to 100 parts by mass of the acid-modified polyolefin resin (A). More preferably, it is 20-80 mass parts, and it is especially preferable that it is 30-50 mass parts. When the content of the crosslinking agent (B) is less than 10 parts by mass, the suppression of expansion and contraction of the active material associated with the charge / discharge cycle tends not to be expressed. When the content exceeds 100 parts by mass, the binder liquid The resulting coating film tends to swell easily with the electrolytic solution, and the obtained electrode tends to have poor adhesiveness and flexibility, or deteriorate the stability of the binder solution.

  In the present invention, examples of the crosslinking agent (B) include a crosslinking agent having self-crosslinking property and a crosslinking agent having a plurality of functional groups that react with carboxyl groups in the molecule. Specific examples include isocyanate compounds, melanin compounds, urea compounds, epoxy compounds, carbodiimide compounds, oxazoline group-containing compounds, adipic acid dihydrazide compounds, among which oxazoline group-containing compounds, carbodiimide compounds, and isocyanate compounds are used. It is preferable.

  As an oxazoline group containing compound, the oxazoline compound containing 2-isopropenyl-2-oxazoline is mentioned as a preferable compound.

  Examples of the carbodiimide compound include water-soluble and / or water-dispersible polyfunctional carbodiimide resins having two or more carbodiimide groups in one molecule.

  As an isocyanate compound, the isocyanate compound which hexamethylene diisocyanate contains is mentioned as a preferable compound. Among these, non-blocking polyfunctional isocyanate compounds, that is, compounds containing two or more non-blocking isocyanate groups in one molecule are preferable. Here, “non-block type” means that the isocyanate group is not blocked (sometimes referred to as “protection” or “mask”) by a lactam-based or oxime-based compound (so-called blocking agent).

Among the cross-linking agents (B) that can be used in the present invention, commercially available oxazoline group-containing compounds include Nippon Shokubai Epochros series. Specifically, water-soluble type WS-500, WS-700, emulsion type K-1010E, K-1020E, K-1030E, K-2010E, K-2020E, K-2030E, etc. are mentioned.
Examples of commercially available carbodiimide compounds include carbodilite series manufactured by Nisshinbo Chemical Co., Ltd. as water-based compounds suitable for the present invention. Specifically, water-soluble type V-02, SV-02, emulsion type E-01, E-03A and the like can be mentioned.
Examples of commercially available isocyanate compounds include BASONAT PLR 8878 and BASONAT HW-100 manufactured by BASF, Bayhydur 3100, Bayhydur VPLS2150 / 1, SBU Isocyanate L801, and Desmodur N3400 manufactured by Sumitomo Bayer Urethane. , Death Module VPLS2102, Death Module VPLS2025 / 1, SBU Isocyanate 0772, Death Module DN, Takenate WD720, Takenate WD725, Takenate WD730, Asahi Kasei Kogyo Duranate WB40-100, Duranate WB40-80D , Duranate WX-1741, Coronate series made by Japan Polyurethanes, etc. And the like.

  The binder liquid of the present invention may use a cross-linked acid-modified polyolefin resin (A) obtained by irradiating radiation instead of adding the cross-linking agent (B) to the acid-modified polyolefin resin (A). .

  In this case, α rays, β (electron) rays, γ rays, X rays, ultraviolet rays, and the like can be used as radiation sources to be used. Of these, β (electron) rays, γ rays, and X rays from cobalt 60 are preferable, and γ ray irradiation treatment is most preferable. One of these radiations may be irradiated alone, or two may be irradiated at the same time, and further, one or more types of radiation may be irradiated after a certain period of time.

  Examples of the method of irradiating the acid-modified polyolefin resin (A) with radiation to crosslink include a method of irradiating the aqueous dispersion of the acid-modified polyolefin resin (A) described later with radiation. When irradiating the aqueous dispersion of the acid-modified polyolefin resin (A) with radiation, the aqueous dispersion placed in a container is placed near the radiation source. At this time, it is preferable to irradiate substantially uniformly during irradiation by either changing the position of the radiation source or the container or stirring the aqueous dispersion.

  The dose of radiation is not particularly limited, but is preferably 1 to 100 kGy, more preferably 10 to 75 kGy, and further preferably 25 to 50 kGy. When the amount of radiation is less than 1 kGy or exceeds 100 kGy, the suppression of expansion and contraction of the active material associated with the charge / discharge cycle tends not to appear or decreases. On the other hand, when the radiation amount exceeds 100 kGy, the flexibility of the obtained electrode tends to be lowered, the electrode adhesiveness is lowered, and the adhesive strength as a binder becomes insufficient.

  The binder liquid of the present invention needs to contain an aqueous medium. The medium of the binder liquid preferably contains water as a main component from the viewpoint of safety to workers and work environments. For the purpose of making the acid-modified polyolefin resin (A) and the crosslinking agent (B) aqueous, dissolving, and reducing the drying load, the medium may contain an organic solvent in addition to water. The amount of the organic solvent in the total amount of the medium is preferably 5% by mass or less, more preferably 3% by mass or less, and further preferably 1% by mass or less. The medium may contain a water-soluble basic compound that is added when the acid-modified polyolefin resin (A) is made aqueous.

  In the binder liquid of the present invention, the solid content concentration of the acid-modified polyolefin resin (A) and the crosslinking agent (B) is preferably 1 to 50% by mass, more preferably 3 to 40% by mass. Preferably, it is 5-30 mass%, and it is especially preferable. When the solid content concentration of (A) and (B) is more than 50% by mass, the handleability tends to decrease due to a significant increase in viscosity or solidification of the binder liquid. On the other hand, when the solid content concentration is less than 1% by mass, the handleability tends to be reduced due to a significant decrease in the viscosity of the binder liquid.

  As described above, the binder liquid of the present invention preferably uses water as an aqueous medium, and the binder liquid is preferably an aqueous dispersion. In the aqueous dispersion, it is preferable that the acid-modified polyolefin resin (A) and the crosslinking agent (B) are uniformly mixed and dispersed. In order to obtain such an aqueous dispersion, for example, a method of mixing a liquid material of an acid-modified polyolefin resin (A) prepared in advance and a liquid material of a crosslinking agent (B), or an acid-modified polyolefin resin (A And a raw material resin of a crosslinking agent (B) are mixed and heated and stirred together with water and a solvent to obtain an aqueous dispersion. Among these, the former is more preferable.

  The method for dispersing the acid-modified polyolefin resin (A) in the aqueous medium is not particularly limited. For example, the acid-modified polyolefin resin (A), the basic compound and the aqueous medium are heated and stirred in a sealed container under pressure. Can be used. The aqueous medium of the acid-modified polyolefin resin (A) is a medium mainly composed of water, and may contain a water-soluble organic solvent or a basic compound.

By adding a basic compound during dispersion of the acid-modified polyolefin resin (A) in the aqueous medium, the acid-modified polyolefin resin (A) can be uniformly dispersed in the aqueous medium, thereby improving the dispersion stability. An excellent binder liquid can be obtained.
Examples of basic compounds include ammonia and amines such as organic amine compounds. Specific examples of the organic amine compound include triethylamine, N, N-dimethylethanolamine, isopropylamine, iminobispropylamine, ethylamine, diethylamine, 3-ethoxypropylamine, 3-diethylaminopropylamine, sec-butylamine, propylamine, Examples thereof include methylaminopropylamine, methyliminobispropylamine, 3-methoxypropylamine, monoethanolamine, morpholine, N-methylmorpholine, N-ethylmorpholine and the like. Of these, triethylamine, N, N-dimethylethanolamine is preferably used.

  Moreover, it is preferable that content of the basic compound in the aqueous dispersion of acid-modified polyolefin resin (A) is 0.01-100 mass% with respect to resin solid content, and 0.05-40 mass% especially among them. It is preferable that it is 0.1-15 mass%. When the content of the basic compound is less than 0.01% by mass, the effect of adding the basic compound is poor, and it is difficult to obtain an aqueous dispersion excellent in dispersion stability. On the other hand, when the content of the basic compound exceeds 100% by mass, the binder is likely to be colored or gelled.

  By adding an organic solvent when the acid-modified polyolefin resin (A) is dispersed in an aqueous medium, the dispersion can be promoted and the dispersed particle size can be reduced. The amount of the organic solvent to be used is preferably 50% by mass or less in the aqueous medium, more preferably 1 to 45% by mass, further preferably 2 to 40% by mass, and 3 to 35% by mass. It is particularly preferred that When the amount of the organic solvent exceeds 50% by mass, the stability of the aqueous dispersion may be lowered depending on the organic solvent used.

  As the organic solvent, those having a solubility in water at 20 ° C. of 10 g / L or more are preferably used from the viewpoint of obtaining a good aqueous dispersion. More preferably, it is 20 g / L or more, Most preferably, it is 50 g / L or more.

  As the organic solvent, those having a boiling point of less than 250 ° C. at normal pressure are preferred from the viewpoint of easy removal, and those having a temperature of 50 ° C. or more and less than 185 ° C. are particularly preferred. An organic solvent having a boiling point of 250 ° C. or higher is difficult to be scattered from the resin coating film by drying, and may deteriorate the adhesion between the materials. Specific examples of the organic solvent used include, for example, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-amyl alcohol, isoamyl alcohol, sec-amyl alcohol. , Tert-amyl alcohol, 1-ethyl-1-propanol, 2-methyl-1-butanol, n-hexanol, cyclohexanol and other alcohols, methyl ethyl ketone, methyl isobutyl ketone, ethyl butyl ketone, cyclohexanone and other ketones, tetrahydrofuran , Ethers such as dioxane, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, 3-methoxybutyl acetate, Esters such as methyl lopionate, ethyl propionate, diethyl carbonate, dimethyl carbonate, glycol derivatives such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol ethyl ether acetate, Furthermore, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 3-methoxy-3-methyl-1-butanol, methoxybutanol, acetonitrile, dimethylformamide, dimethylacetamide, diacetone alcohol, ethyl acetoacetate, 1,2-dimethylglycerol, 1,3-dimethylglycerol, trimethylglycerol, etc. are mentioned. These organic solvents may be used in combination of two or more.

  Among the above organic solvents, ethanol, n-propanol, isopropanol, n-butanol, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, dioxane, ethylene glycol monoethyl ether, ethylene glycol monopropyl are effective because they are highly effective in promoting aqueous formation of resins. Ether, ethylene glycol monobutyl ether, and diethylene glycol monomethyl ether are preferable. Among these, an organic solvent having one hydroxyl group in the molecule is more preferable, and n-propanol, isopropanol, tetrahydrofuran, ethylene is preferable because the resin can be made aqueous with a small amount of addition. More preferred are glycol alkyl ethers.

  When the above-mentioned organic solvent is used for dispersing the acid-modified polyolefin resin (A), a part of the organic solvent is distilled out of the system by a solvent removal process generally called “stripping” after the dispersion. The amount of organic solvent can be reduced. By stripping, the content of the organic solvent in the aqueous dispersion can be 10% by mass or less, and if it is 5% by mass or less, it is environmentally preferable.

The acid-modified polyolefin resin (A) can be used after being hydrophilized. Examples of the hydrophilic treatment include sulfonation treatment, fluorine gas treatment, graft polymerization treatment, or discharge treatment, and one or more of these hydrophilic treatments can be performed. The sulfonation treatment is not particularly limited, but for example, a treatment immersed in a solution such as fuming sulfuric acid, sulfuric acid, chlorosulfuric acid, or sulfuryl chloride, a treatment in contact with SO ₃ gas, or SO gas and / or or SO ₂ discharge in the presence of gas can be cited a process to act. Among these, sulfonation treatment with fuming sulfuric acid is preferable because it has high reactivity and can be sulfonated relatively easily. In this case, sulfonic acid groups are mainly introduced.

  The aqueous dispersion of the acid-modified polyolefin resin (A) prepared as described above contains the acid-modified polyolefin resin (A), a basic compound, and an aqueous medium, and contains a non-volatile aqueous dispersion aid. It is preferable not to contain.

  Moreover, you may add the aqueous dispersion of another polymer to the aqueous dispersion of acid-modified polyolefin resin (A) as needed within the range which does not impair the effect of this invention. For example, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride resin, styrene-maleic acid resin, styrene-butadiene resin, butadiene resin, acrylonitrile-butadiene resin, poly (meth) Examples include aqueous dispersions such as acrylonitrile resin, (meth) acrylamide resin, chlorinated polyethylene resin, chlorinated polypropylene resin, polyester resin, modified nylon resin, phenol resin, silicone resin, epoxy resin, urethane resin, and mixtures thereof. .

  The aqueous paste for secondary battery negative electrode of the present invention contains the binder liquid of the present invention, a lithium ion battery negative electrode active material containing a silicon atom, a tin atom or a germanium atom, and a conductive material as required. Such a negative electrode active material has a large charge / discharge capacity per unit volume, and is useful for increasing the capacity of a battery. On the other hand, when these active materials are used, the volume change of the electrode active material layer due to charging / discharging is about five times that when a conventional graphite-based active material is used. Therefore, higher adhesiveness is required for the binder. Yes. Each of these negative electrode active materials and conductive materials may be contained in two or more.

Examples of the negative electrode active material containing a silicon atom include (1) silicon fine particles, (2) tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony or chromium, Examples include alloys with silicon, (3) compounds of boron, nitrogen, oxygen or carbon and silicon, and those having the metal exemplified in (2). Examples of silicon alloys or compounds include SiB ₄ , SiB ₆ , Mg ₂ Si, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi ₂ , Cu ₅ Si, FeSi ₂ , MnSi ₂ , NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ , ZnSi ₂ , SiC, Si ₃ N ₄ , Si ₂ N ₂ O, SiO _v (0 <v ≦ 2) or LiSiO.

Examples of the negative electrode active material containing a tin atom include (1) an alloy of silicon, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony or chromium and tin, ( 2) Oxygen or a compound of carbon and tin, and those having the metal exemplified in (1). Examples of tin alloys or compounds include SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSnO, Mg ₂ Sn, and the like.

  Examples of the negative electrode active material containing germanium atoms include silicon, an alloy of tin and germanium.

  The average particle size of the negative electrode active material is preferably 0.1 to 10 μm. The surface of the negative electrode active material may be subjected to a surface treatment with a silane coupling agent or the like.

  As the conductive material, a carbon material, a metal, or a compound thereof can be used. Examples of the carbon material include ketjen black, acetylene black, furnace black, graphite, and carbon fiber. Examples of the metal or compound thereof include nickel, cobalt, titanium, cobalt oxide, and titanium oxide. However, it is not limited to these.

  The content of the acid-modified polyolefin resin (A) and the crosslinking agent (B) in the aqueous paste for secondary battery negative electrode (the total content of (A) and (B)) is 0.01 to 8% by mass. Is preferred. When it exceeds 8 mass%, the electrical resistance value in the obtained electrode tends to increase. Moreover, when it is less than 0.01% by mass, it tends to be difficult to obtain sufficient adhesion between the active material, the conductive material, and the metal current collector.

In addition to the acid-modified polyolefin resin (A) and the cross-linking agent (B), a water-soluble polymer may be added to the aqueous paste for secondary battery negative electrode as necessary within a range not impairing the effects of the present invention. . Specific examples of the water-soluble polymer include cellulosic polymers such as carboxymethylcellulose, methylcellulose, and hydroxypropylcellulose, polyacrylates such as sodium polyacrylate, polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, acrylic acid, and acrylate. Examples include vinyl alcohol copolymers, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol, modified polyvinyl alcohol, and modified polyacrylic acid.
Of these, cellulose derivatives such as methylcellulose, carboxymethylcellulose, and hydroxymethylcellulose are effective. These celluloses improve the wettability between the metal current collector, the active material, and the conductive material.
As a compounding quantity of a water-soluble polymer, 0.01-5 mass parts is preferable with respect to a total of 100 mass parts of acid-modified polyolefin resin (A), a crosslinking agent (B), an active material, and an electrically conductive material, 0.01 -3 mass parts is more preferable, and 0.01-1.5 mass parts is still more preferable.

  The conditions and method for producing the secondary battery negative electrode aqueous paste in the present invention are not particularly limited, and the secondary battery negative electrode aqueous binder liquid, an active material containing a silicon atom, a tin atom or a germanium atom, and as necessary. After mixing the conductive material at normal temperature or at a suitably controlled temperature, mechanical dispersion treatment, ultrasonic dispersion treatment, or the like can be used. The mixing order is not particularly limited. Moreover, the other component mentioned above, a solvent, etc. can also be added as needed.

The secondary battery negative electrode of the present invention can be formed by using the secondary battery negative electrode aqueous binder liquid of the present invention. For example, the secondary battery negative electrode aqueous paste produced as described above is applied on the current collector. By applying and drying, a secondary battery negative electrode can be formed.
The current collector may be any material having conductivity, and examples thereof include aluminum, nickel, and copper. Although there is no restriction | limiting in particular in the thickness of an electrical power collector, Usually, a 5-50 micrometers thin film is used.
Examples of the method for applying the paste on the current collector include a method using a doctor blade, and the method for removing the aqueous medium is, for example, 60 to 150 ° C., preferably 70 to 130 ° C. and dried for 5 to 120 minutes. Furthermore, for example, a method of drying under reduced pressure at 120 ° C. for 12 hours can be mentioned. The thickness of the electrode after coating and drying is preferably 30 to 150 μm. In order to control the thickness and density of the electrode, it is preferable to press, for example, with a roll press.

  The secondary battery of the present invention is formed using the secondary battery negative electrode of the present invention. For example, the secondary battery negative electrode manufactured as described above is combined with the secondary battery positive electrode, the separator, and the electrolyte. A secondary battery can be formed by enclosing in a container according to a conventional method.

  Examples of the active material of the positive electrode constituting the secondary battery include lithium cobaltate, lithium nickelate, lithium manganate, lithium iron phosphate, and the separator includes polyethylene microporous membrane, polypropylene microporous membrane, polyethylene nonwoven fabric. , Polypropylene non-woven fabric, polyamide non-woven fabric, glass fiber, etc. The electrolyte is lithium hexafluorophosphate in a mixed solvent in which one or more non-aqueous solvents such as ethylene carbonate, diethyl carbonate, and propylene carbonate are mixed. And those to which a supporting electrolytic salt such as lithium perchlorate is added. Further, a solid electrolyte or a gel electrolyte may be used instead of the separator. Examples of the electrolyte include tetraethylammonium tetrafluoroborate, triethylmonomethylammonium tetrafluoroborate, tetraethylammonium hexafluorophosphate, ionic liquid, aqueous sulfuric acid solution, and aqueous potassium hydroxide solution. The solvent for dissolving the electrolyte (electrolytic solution solvent) is not particularly limited as long as it is generally used as an electrolytic solution solvent. Specific examples include carbonates such as propylene carbonate, ethylene carbonate, and butylene carbonate; lactones such as γ-butyrolactone; sulfolanes; nitriles such as acetonitrile; ionic liquids and the like. It can be used as a mixed solvent.

Hereinafter, the present invention will be described in detail with reference to examples.
Various properties described below were measured or evaluated by the following methods.

(1) Unsaturated carboxylic acid content of acid-modified polyolefin resin (A) The acid value of acid-modified polyolefin resin (A) was measured according to the method described in JIS K5407, and from that value, the unsaturated carboxylic acid content of (A) The carboxylic acid content was determined.

(2) Structure of Resin of Acid-Modified Polyolefin Resin (A) ¹ H-NMR analysis (manufactured by Varian, 300 MHz) was performed at 120 ° C. in orthodichlorobenzene (d ₄ ).

(3) Molecular weight of acid-modified polyolefin resin (A) Using GPC analysis (HLC-8020 manufactured by Tosoh Corporation, column is TSK-GEL), the sample was dissolved in tetrahydrofuran and measured at 40 ° C. At this time, the mass average molecular weight was determined from a calibration curve prepared with a polystyrene standard sample. When the sample was difficult to dissolve in tetrahydrofuran, orthodichlorobenzene was used.

(4) Coating Film Hardness Evaluation A secondary binder negative electrode aqueous binder solution was coated on a copper foil with a Mayer bar so that the coating thickness after drying was 3 μm, and dried at 150 ° C. for 90 seconds. The coating film hardness was evaluated by conducting a pencil scratch test on the binder liquid coated surface. As for the hardness of the pencil, the density symbol 9H is the hardest and 6B is the softest, and for two pencils whose density symbols are adjacent to each other, a pair of scratches on the coating film is 2 times or more and less than 2 times. The density symbol of the pencil that was determined and was less than twice was taken as the coating film hardness value.

(5) Evaluation of electrolyte swellability After the aqueous binder liquid for secondary battery negative electrode is dropped on the PTFE film, it is dried in hot air at 90 ° C. for 3 hours, and further dried in vacuum at 120 ° C. for 2 hours to form a binder liquid coating film. Obtained. After the obtained coating film is cut into a plurality of coating film pieces (5 mm × 5 mm), a coating film piece in an amount of 1 g in total weight is converted into diethyl carbonate / ethylene carbonate / ethyl methyl carbonate = 1/1 / It was immersed in 10 g of a mixed solvent of 1 (volume ratio) and incubated at 50 ° C. for 2 weeks in a sealed container. The electrolytic solution swelling ratio of the coating film was calculated as follows, and the electrolytic solution swelling property of the coating film was evaluated.
Electrolyte swelling rate [%] of coating film = ((total weight of coating film pieces after immersion in electrolytic solution [g] −total weight of coating film pieces before immersion in electrolytic solution [g]) / coating before immersion in electrolytic solution Total weight of membrane pieces [g]) × 100

(6) Electrode bonding strength A test sample having a width of 2.5 cm and a length of 10 cm was cut out from a secondary battery negative electrode formed by applying an aqueous paste for a secondary battery negative electrode on a copper foil, and the copper foil side had a sufficient thickness. The steel plate having the above was bonded with a double-sided tape. Cellophane tape (Nichiban Co., Ltd., CT-18, 18 mm width) was affixed to the active material layer of the test sample, and the stress was measured when it was peeled off at a rate of 50 mm / min from one side in the direction of 180 °. The measurement was carried out three times for each sample, and the average value was taken as the adhesive strength.

(7) Electrode flexibility After the electrode obtained in (6) is cut into a strip shape having a width of 1 cm and a length of 5 cm, the active material layer side is bent so that the outer side (copper foil side is the inner side) ( The state of the active material layer in the bent portion was evaluated as follows.
◎: No crack ○: Slightly fallen from surface layer △: Cracked ×: Active material layer peeled

(8) Cycle characteristics The charge / discharge test was done using the coin-type battery produced combining the secondary battery negative electrode and the lithium cobalt oxide electrode. The cycle characteristics were evaluated by repeatedly performing 1C-2.5V constant current discharge after 1C-4.1V constant current constant voltage charging in a 50 ° C environment. The discharge capacity at the first cycle was taken as 100%, the discharge capacity after 100 cycles was determined, and the discharge capacity retention rate was calculated as cycle characteristics.

(9) Change in thickness of active material layer Two coin-type batteries were evaluated in the same manner as in (8) above. However, one coin-type battery was disassembled after charging at the 100th cycle and the negative electrode was taken out. The electrolyte solution adhering to the electrode surface was wiped off with Kimwipe, and the thickness of the active material layer was measured. Another coin-type battery was disassembled after discharging the 100th cycle, and the negative electrode was taken out. The electrolyte solution adhering to the electrode surface was wiped off with Kimwipe, and the thickness of the active material layer was measured. By comparing with the thickness of the active material layer before charging, the change in thickness of the negative electrode active material accompanying charge / discharge was evaluated.

Reference example 1
<Production of aqueous dispersion “E-1” of acid-modified polyolefin resin>
Using a stirrer equipped with a 1 L glass container that can be sealed with a heater, acid-modified polyolefin resin (a) 60.0 g Bondine TX-8030 (manufactured by Arkema), 48.0 g isopropanol, basic compound 3.9 g of N, N-dimethylethanolamine and 188.1 g of distilled water were charged into a glass container and stirred at a rotation speed of a stirring blade of 300 rpm. No resin precipitation was observed at the bottom of the container, It was confirmed that it was floating. Therefore, while maintaining this state, the heater was turned on and heated after 10 minutes. Then, the system temperature was kept at 140 ° C. and further stirred for 60 minutes. Then, it cooled to room temperature (about 25 degreeC), stirring with air-cooling with the rotational speed of 300 rpm, and obtained the milky white uniform dispersion (solid content concentration 20 mass%).
290 g of the dispersion and 80 g of distilled water were placed in a 1 L eggplant flask, placed in an evaporator, and the aqueous medium was distilled off by reducing the pressure at 60 ° C. When about 87 g of the aqueous medium was distilled off, the heating was terminated, and the pressure was returned to normal pressure and cooled to room temperature. After cooling, the liquid component in the flask was pressure filtered (air pressure 0.2 MPa) with a 300 mesh stainless steel filter (wire diameter 0.035 mm, plain weave) to obtain a milky white uniform aqueous dispersion “E-1” (solid A partial concentration of 20% by weight).

Reference example 2
<Production of aqueous dispersion “E-2” of acid-modified polyolefin resin>
In a sealable pressure-resistant 1 liter glass container equipped with a stirrer and a heater, 90 g of Umex 1001 (manufactured by Sanyo Chemical Co., Ltd.) as acid-modified polyolefin resin (b), and 8 g of N, N-dimethylethanolamine as a basic compound Then, 240 g of organic solvent tetrahydrofuran and 260 g of distilled water were charged, sealed, and then heated to 130 ° C. (internal temperature) with stirring at 300 rpm. After being kept at 130 ° C. for 1 hour under stirring, the heater was turned off and naturally cooled to 60 ° C. to obtain a milky white uniform dispersion (solid content concentration 15% by mass).
290 g of the dispersion and 40 g of distilled water were placed in a 1 L eggplant flask, placed in an evaporator, and the aqueous medium was distilled off by reducing the pressure at 60 ° C. When about 160 g of the aqueous medium was distilled off, the heating was terminated, and the pressure was returned to normal pressure and cooled to room temperature. After cooling, the liquid component in the flask was subjected to pressure filtration (air pressure 0.2 MPa) with a 300 mesh stainless steel filter (wire diameter 0.035 mm, plain weave) to obtain a milky white uniform aqueous dispersion “E-2” (solid A partial concentration of 25% by weight).

Reference example 3
<Production of aqueous dispersion “E-3” of acid-modified polyolefin resin>
280 g of propylene-butene-ethylene terpolymer (manufactured by Huls Japan, Bestplast 708, propylene / butene / ethylene = 64.8 / 23.9 / 11.3 mass%) in a four-necked flask And heated and melted in a nitrogen atmosphere. Thereafter, while maintaining the system temperature at 170 ° C., 32.0 g of maleic anhydride as an unsaturated carboxylic acid and 6.0 g of dicumyl peroxide as a radical generator were added over 1 hour with stirring. The reaction was carried out for 1 hour. After completion of the reaction, the obtained reaction product was put into a large amount of acetone to precipitate a resin. This resin was further washed several times with acetone to remove unreacted maleic anhydride, and then dried under reduced pressure in a vacuum dryer to obtain an acid-modified polyolefin resin (b) “P-1”.
As the acid-modified polyolefin resin (b), a milky white uniform aqueous dispersion “E-3” (solid content concentration: 25 mass%) was prepared in the same manner as in Reference Example 2 except that “P-1” was used. Obtained.

  Table 1 shows the composition and molecular weight of the acid-modified polyolefin resin (A) used for the production of the aqueous dispersions “E-1” to “E-3”.

The following were used as a crosslinking agent.
K-1: Nippon Shokubai Epocross WS-700 (2-isopropenyl-2-oxazoline-containing oxazoline compound aqueous solution, solid content concentration 40% by mass)
K-2: Carbodilite E-01 manufactured by Nisshinbo Chemical Co., Ltd. (water-dispersible polyfunctional carbodiimide resin, solid concentration 40% by mass)
K-3: Basonto HW-100 (non-blocking polyfunctional isocyanate compound, isocyanate content: about 17%) manufactured by BASF was diluted with water, and a solution having a solid content concentration of 10% by mass was used.

Example 1
Using the acid-modified polyolefin resin aqueous dispersion “E-1” and the crosslinking agent “K-1”, the acid-modified polyolefin resin (solid content) is 100 parts by mass, and the crosslinking agent (solid content) is 10 parts by mass. The mixture was mixed and stirred at room temperature for 5 minutes to obtain a secondary battery negative electrode aqueous binder liquid “T-1”. Table 2 shows the evaluation results of the coating film hardness and electrolyte swellability of the obtained aqueous binder liquid for secondary battery negative electrode.
Also, metal silicon fine powder (manufactured by Mobara Rare Metals) as the negative electrode active material, acetylene black (manufactured by Denki Kagaku Co., Ltd., Denka Black) as the conductive material, and carboxymethyl cellulose (CMC) (Daiichi Kogyo Seiyaku) as the thickener Serogen BSH-6) aqueous solution and “T-1” as a secondary battery negative electrode aqueous binder solution, each having a solid content concentration of 91 mass%, 4 mass%, 1 mass%, 4 mass% Further, the paste was diluted with distilled water so that the solid content concentration of the paste was 45% by mass, and then sufficiently kneaded to prepare an aqueous paste for secondary battery negative electrode.
Using a 18 μm thick copper foil as a current collector, the obtained paste was applied to one side of the copper foil using a film applicator so that the thickness after drying was about 100 μm, and dried with hot air at 80 ° C. for 30 minutes. Then, in order to further remove moisture, it was vacuum-dried at 120 ° C. for 15 hours to form an active material layer on the copper foil to prepare a secondary battery negative electrode.
Using the secondary battery negative electrode obtained by the above preparation method, the active material layer formed on the copper foil was cut into a circular shape with an area of 2 cm ^{2 and} the electrode thickness was 60 μm and the electrode density was 1 A coin-type battery was fabricated by molding the composite electrode so as to be 4 g / cm ³ and combining it with a lithium cobalt oxide electrode, and sandwiching a polypropylene membrane separator (Cell Guard # 2400, manufactured by Cellguard) between both electrodes. Table 2 shows the characteristic values and evaluation results of the obtained negative electrode and battery.

Examples 2-28, Comparative Examples 1-9
The same method as in Example 1 except that the type of the aqueous dispersion of the acid-modified polyolefin resin, the type of the crosslinking agent, the solid content, the radiation source, and the irradiation amount were changed as shown in Table 2. Thus, in Examples 2 to 28 and Comparative Examples 4 to 9, secondary battery negative electrode aqueous binder liquids “T-2” to “T-34” were obtained. In Comparative Examples 1 to 3, aqueous dispersions “E-1” to “E-3” of acid-modified polyolefin resins were used as the aqueous binder liquid for secondary battery negative electrodes. Table 2 shows the evaluation results of the coating film hardness and electrolyte swellability of the obtained aqueous binder liquid for secondary battery negative electrode.
In addition, a secondary battery negative electrode aqueous paste, a secondary battery negative electrode, and a coin-type battery were prepared in the same manner as in Example 1 except that the obtained secondary battery negative electrode aqueous binder liquid was used. Table 2 shows the characteristic values and evaluation results of the obtained negative electrode and battery.

Comparative Example 10
As a binder for a secondary battery negative electrode, an NMP solution of PVDF resin (manufactured by Kureha, KF-L # 9210) “T-35” was used. Table 2 shows the evaluation results of coating film hardness and electrolyte swellability.
Further, a secondary battery negative electrode paste, a secondary battery negative electrode, and a coin-type battery were produced in the same manner as in Example 1 except that this binder solution was used. Table 2 shows the characteristic values and evaluation results of the obtained negative electrode and battery.

As is clear from Table 2, the aqueous binder liquid for secondary battery negative electrodes obtained in Examples 1 to 28 contains a specific amount of the crosslinking agent (B) or is acid-modified polyolefin crosslinked by radiation irradiation. Since the resin (A) is included, the coating film formed by applying the binder liquid has high coating film hardness, and the secondary battery negative electrode formed from the paste containing the binder liquid includes an active material layer and a copper foil. The adhesive strength was high. Moreover, the obtained secondary battery had a small negative electrode expansion / contraction associated with the charge / discharge cycle, and as a result, showed good cycle characteristics.
On the other hand, the secondary battery negative electrodes obtained in Comparative Examples 1 to 6 had high adhesive strength between the active material layer and the copper foil, but the binder liquid used had a content of the crosslinking agent (B). The resulting secondary battery has a large expansion / contraction of the negative electrode accompanying the charge / discharge cycle, as a result, because it does not contain the acid-modified polyolefin resin (A) that is less or cross-linked by radiation irradiation. Was inferior.
Moreover, in Comparative Examples 7-9, since the used binder liquid was a thing with much content of a crosslinking agent (B), the coating film obtained from this binder liquid is a thing which is easy to swell with electrolyte solution, Moreover, the obtained secondary battery negative electrode had a low adhesive strength between the active material layer and the copper foil and a low flexibility. The obtained secondary battery had large expansion / contraction of the negative electrode accompanying the charge / discharge cycle, and the cycle characteristics were inferior.
In Comparative Example 10, since a PVDF resin was used as the resin constituting the binder liquid, the coating film obtained from the binder liquid was easily swelled by the electrolytic solution. Moreover, the obtained secondary battery negative electrode had a low adhesive strength between the active material layer and the copper foil. The obtained secondary battery had large expansion / contraction of the negative electrode accompanying the charge / discharge cycle, and the cycle characteristics were inferior.

Claims (9)

  Acid-modified polyolefin resin (A), which is a binder liquid for forming a secondary battery negative electrode having an active material containing silicon atom, tin atom or germanium atom, and containing 0.1 to 10% by mass of unsaturated carboxylic acid component And a cross-linking agent (B) and an aqueous medium, wherein the content of (B) is 10 to 100 parts by mass with respect to 100 parts by mass of (A). Water-based binder liquid.   Acid-modified polyolefin resin (A), which is a binder liquid for forming a secondary battery negative electrode having an active material containing silicon atom, tin atom or germanium atom, and containing 0.1 to 10% by mass of unsaturated carboxylic acid component And an aqueous medium, and the acid-modified polyolefin resin (A) is crosslinked by irradiation with radiation.   Acid-modified polyolefin resin (A) contains 50 to 98% by mass of an acid-modified polyolefin resin (a) containing 50 to 98% by mass of an ethylene component and / or 50 to 98% by mass of at least one of a propylene component and a 1-butene component. The aqueous binder solution for a secondary battery negative electrode according to claim 1 or 2, wherein the aqueous binder solution is a polyolefin resin (b).   The unsaturated carboxylic acid component of the acid-modified polyolefin resin (A) is at least one selected from the group consisting of maleic anhydride, maleic acid, acrylic acid and methacrylic acid. The aqueous binder liquid for secondary battery negative electrodes as described in 2.   The aqueous binder solution for secondary battery negative electrode according to claim 1, wherein the crosslinking agent (B) is an oxazoline compound, a carbodiimide compound or an isocyanate compound.   The secondary binder negative electrode aqueous binder solution according to any one of claims 2 to 4, wherein the radiation source is γ-ray and the irradiation amount is 1 to 100 kGy.   An aqueous paste for a secondary battery negative electrode comprising the aqueous binder liquid for a secondary battery negative electrode according to any one of claims 1 to 6 and an active material containing a silicon atom, a tin atom or a germanium atom.   A secondary battery negative electrode formed using the aqueous paste for secondary battery negative electrode according to claim 7.   A secondary battery formed using the secondary battery negative electrode according to claim 8.