Lithium secondary battery electrode binder, electrode binder composition, negative electrode, and lithium secondary battery

Abstract

Provided is lithium secondary battery electrode binder capable of suppressing an increase in internal resistance due to charging and discharging. A lithium secondary battery electrode binder according to an embodiment of the present invention includes: (A) a polyisocyanate component including at least one selected from the group consisting of diphenylmethane diisocyanate and modified bodies thereof; (B) a polyol component including a hydrogenated polybutadiene polyol; (C) an active hydrogen group-containing carboxylic acid; and (D) an aqueous dispersion of a salt of a polyurethane obtained by reacting water as a chain extender. The salt of the polyurethane does not substantially contain a structure derived from an amine-based chain extender.

Description

Electrode binder for lithium secondary battery, electrode binder composition, negative electrode, and lithium secondary battery

[0001] An embodiment of the present invention relates to an electrode binder for a lithium secondary battery, an electrode binder composition, a negative electrode, and a lithium secondary battery.

[0002] Lithium secondary batteries, also known as lithium ion secondary batteries, are used as high-voltage, high-energy density power storage devices, for example, as power sources for driving electronic devices. Electrodes for lithium secondary batteries are typically produced by applying a mixture of an electrode active material, a conductive agent, and a binder to the surface of a current collector and drying the mixture. The binder is used to impart adhesive strength between the electrode active material and the current collector. Therefore, the binder has a significant effect on the characteristics of lithium secondary batteries.

[0003] Patent Document 1 discloses an electrode binder for lithium secondary batteries that contains an aqueous dispersion of a sodium salt of polyurethane obtained by reacting at least one of an aliphatic polyisocyanate and an alicyclic polyisocyanate, a hydrogenated polybutadiene polyol, a carboxylic acid having one or more active hydrogen groups, and a chain extender. According to Patent Document 1, this reduces electrode expansion due to charge and discharge, thereby improving charge and discharge cycle characteristics.

[0004] Patent No. 7161078

[0005] For example, when a silicon-based active material such as SiO is used as a negative electrode active material, the internal resistance increases during charge and discharge, leading to a deterioration in charge and discharge cycle characteristics. Therefore, there is a demand for an electrode binder that can suppress the increase in internal resistance during charge and discharge.

[0006] Although Patent Document 1 discloses the use of hydrogenated polybutadiene polyol and active hydrogen group-containing carboxylic acid as components constituting the aqueous dispersion of the polyurethane, an aliphatic or alicyclic polyisocyanate is used as the polyisocyanate, and chain extension is performed with an amine-based chain extender. Therefore, Patent Document 1 does not describe an aqueous dispersion of polyurethane obtained by using diphenylmethane diisocyanate and / or a modified product thereof together with a hydrogenated polybutadiene polyol and then chain extension with water.

[0007] An object of an embodiment of the present invention is to provide a binder for electrodes of a lithium secondary battery that can suppress an increase in internal resistance due to charge and discharge.

[0008] The present invention includes the following embodiments. [1] A binder for electrodes of lithium secondary batteries, comprising: (A) a polyisocyanate component containing at least one selected from the group consisting of diphenylmethane diisocyanate and modified products thereof; (B) a polyol component containing hydrogenated polybutadiene polyol; (C) an active hydrogen group-containing carboxylic acid; and (D) an aqueous dispersion of a polyurethane salt obtained by reacting water as a chain extender, wherein the polyurethane salt does not contain a structure derived from an amine-based chain extender, or if it does contain one, the content is less than 0.01 mol / kg. [2] The binder for electrodes of lithium secondary batteries according to [1], wherein the active hydrogen group-containing carboxylic acid contains an aliphatic carboxylic acid having two hydroxy groups. [3] The binder for electrodes of lithium secondary batteries according to [1] or [2], wherein the polyol component further contains a tri- or higher functional polyol having a molecular weight of 500 or less. [4] The binder for electrodes of lithium secondary batteries according to any one of [1] to [3], wherein the polyurethane has an acid value of 8 to 35 mgKOH / g. [5] The binder for an electrode of a lithium secondary battery according to any one of [1] to [4], wherein the salt of the polyurethane is an alkali metal salt. [6] The binder for an electrode of a lithium secondary battery according to any one of [1] to [5], wherein the binder is for a negative electrode of a lithium secondary battery containing, as a negative electrode active material, at least one selected from the group consisting of SiO, SiC, Si, and those obtained by pre-doping these with lithium ions.

[0009] [7] A binder composition for an electrode of a lithium secondary battery, comprising: (A) a polyisocyanate component containing at least one selected from the group consisting of diphenylmethane diisocyanate and modified products thereof; (B) a polyol component containing a hydrogenated polybutadiene polyol; (C) an active hydrogen group-containing carboxylic acid; and (D) a polyurethane salt obtained by reacting water as a chain extender, the polyurethane salt not containing a structure derived from an amine-based chain extender, or containing less than 0.01 mol / kg of the amine-based chain extender-derived structure, if any; a conductive agent; and water. [8] A negative electrode of a lithium secondary battery, comprising the electrode binder according to any one of [1] to [6] or the solid content of the electrode binder composition according to [7], and a negative electrode active material containing at least one selected from the group consisting of SiO, SiC, Si, and those pre-doped with lithium ions. [9] A lithium secondary battery comprising the negative electrode according to [8].

[0010] According to the embodiment of the present invention, it is possible to suppress an increase in internal resistance due to charging and discharging of a lithium secondary battery.

[0011] The electrode binder for a lithium secondary battery according to this embodiment includes an aqueous dispersion of a polyurethane salt (hereinafter, sometimes simply referred to as "polyurethane") obtained by reacting (A) a polyisocyanate component containing at least one selected from the group consisting of diphenylmethane diisocyanate and modified products thereof, (B) a polyol component containing a hydrogenated polybutadiene polyol, (C) an active hydrogen group-containing carboxylic acid, and (D) water as a chain extender. By using diphenylmethane diisocyanate and / or a modified product thereof as the polyisocyanate to be reacted with the hydrogenated polybutadiene polyol and by extending the chain with water, it is possible to suppress an increase in internal resistance due to charge and discharge of the lithium secondary battery and improve the charge and discharge cycle characteristics, as shown in the examples described below.

[0012] [(A) Polyisocyanate Component] In this embodiment, as the (A) polyisocyanate component, among aromatic polyisocyanates, at least one selected from the group consisting of (A1) diphenylmethane diisocyanate and modified products thereof (hereinafter, sometimes referred to as an “MDI-based isocyanate”) is used.

[0013] Examples of diphenylmethane diisocyanate (MDI) include 2,2'-diphenylmethane diisocyanate (2,2'-MDI), 2,4'-diphenylmethane diisocyanate (2,4'-MDI), 4,4'-diphenylmethane diisocyanate (4,4'-MDI, monomeric MDI), and polymeric MDI (polymethylene polyphenyl polyisocyanate). Any one of these may be used, or two or more may be used in combination. As is well known, polymeric MDI is a mixture of monomeric MDI and its polynuclear form, and is included in diphenylmethane diisocyanate (MDI).

[0014] Modified diphenylmethane diisocyanate includes diphenylmethane skeleton (Ph-CH ２ -Ph), and examples thereof include a dimer of MDI, carbodiimide-modified MDI, uretonimine-modified MDI, (trimer) isocyanurate-modified MDI, etc. Any one of these may be used alone, or two or more may be used in combination.

[0015] The polyisocyanate component (A) is basically composed of the MDI-based isocyanate (A1), but may contain other polyisocyanates as long as the effects of the other polyisocyanates are not impaired. More specifically, the amount of the MDI-based isocyanate (A1) in 100% by mass of the polyisocyanate component (A) is not particularly limited, but is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 100% by mass.

[0016] Examples of the other polyisocyanates include aromatic polyisocyanates other than MDI-based isocyanates (for example, tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), and modified products thereof), aliphatic polyisocyanates (for example, hexamethylene diisocyanate (HDI), tetramethylene diisocyanate, lysine diisocyanate, and modified products thereof), and alicyclic polyisocyanates (for example, isophorone diisocyanate (IPDI), dicyclohexylmethane 4,4′-diisocyanate (hydrogenated MDI), and modified products thereof).

[0017] The amount of the MDI isocyanate (A1) in the polyurethane is not particularly limited, and may be, for example, 10 to 45% by mass, 15 to 40% by mass, or 20 to 35% by mass, in terms of the content of the structure derived from the MDI isocyanate relative to 100% by mass of the polyurethane salt.

[0018] [(B) Polyol Component] In this embodiment, (B1) hydrogenated polybutadiene polyol is used as the (B) polyol component. Here, the (B) polyol component does not include the (C) active hydrogen group-containing carboxylic acid, even if the active hydrogen group-containing carboxylic acid has multiple hydroxy groups in one molecule.

[0019] The (B1) hydrogenated polybutadiene polyol preferably has an average of 1.3 or more hydroxy groups per molecule, more preferably an average of 1.5 to 2.5 hydroxy groups, and even more preferably an average of 1.7 to 2.2 hydroxy groups. In this specification, the number of hydroxy groups per molecule (number of functional groups) is a value calculated by the following formula: Number of functional groups = {(hydroxyl value) × (Mn)} / (56.1 × 1000).

[0020] The hydrogenated polybutadiene polyol (B1) is preferably a polybutadiene polyol having a 1,4-bonded, 1,2-bonded, or mixed polybutadiene structure in the molecule and having a hydroxyl group at its terminal, which has been hydrogenated (hydrogenated).More preferably, the hydrogenated polybutadiene polyol (B1) is a polybutadiene polyol having a hydroxyl group at each terminal of the polybutadiene structure, which has been hydrogenated.

[0021] The (B1) hydrogenated polybutadiene polyol is a polybutadiene polyol in which some or all of the unsaturated double bonds contained therein have been hydrogenated. The degree of hydrogenation of the (B1) hydrogenated polybutadiene polyol is not particularly limited, and for example, the iodine value may be 40 g / 100 g or less, 30 g / 100 g or less, 25 g / 100 g or less, or 15 g / 100 g or less. In this specification, the iodine value is measured in accordance with JIS K0070:1992.

[0022] The molecular weight of the (B1) hydrogenated polybutadiene polyol is not particularly limited, and for example, the number average molecular weight (Mn) may be 600 to 10,000, 800 to 6,000, 1,000 to 5,000, 1,200 to 4,000, or 1,500 to 3,500.

[0023] In this specification, the number average molecular weight (Mn) is a value measured by GPC (gel permeation chromatography) and calculated using a calibration curve of standard polystyrene. Specifically, the GPC conditions are as follows: column: "TSKgel G4000HXL + TSKgel G3000HXL + TSKgel G2000HXL + TSKgel G1000HXL + TSKgel G1000HXL" manufactured by Tosoh Corporation, mobile phase: THF (tetrahydrofuran), mobile phase flow rate: 1.0 mL / min, column temperature: 40°C, sample injection amount: 50 μL, sample concentration: 0.2 mass%.

[0024] The hydroxyl value of the (B1) hydrogenated polybutadiene polyol is not particularly limited and may be, for example, 10 to 200 mgKOH / g, 15 to 120 mgKOH / g, 20 to 100 mgKOH / g, 30 to 90 mgKOH / g, or 40 to 80 mgKOH / g. In this specification, the hydroxyl value is measured in accordance with Method A of JIS K1557-1:2007.

[0025] The (B) polyol component may be composed solely of (B1) hydrogenated polybutadiene polyol, or may contain (B2) non-hydrogenated polybutadiene polyol together with (B1) hydrogenated polybutadiene polyol.

[0026] The number of functional groups, number average molecular weight, and hydroxyl value of the polybutadiene polyol (B2) are not particularly limited, and those having numerical ranges similar to those of the hydrogenated polybutadiene polyol (B1) may be used.

[0027] The (B) polyol component may be composed solely of (B1) hydrogenated polybutadiene polyol, or solely of (B1) hydrogenated polybutadiene polyol and (B2) polybutadiene polyol. Preferably, the (B) polyol component contains (B3) a tri- or higher functional polyol having a molecular weight of 500 or less (hereinafter sometimes referred to as a "multifunctional polyol") in addition to (B1) hydrogenated polybutadiene polyol and (B2) polybutadiene polyol as an optional component. The inclusion of (B3) multifunctional polyol facilitates the expansion and contraction of the electrode during charge and discharge, and reduces electrode deformation after charge and discharge. This further improves charge and discharge cycle characteristics.

[0028] Examples of the polyfunctional polyol (B3) include trihydric alcohols such as trimethylolpropane, glycerin, trimethylolethane, butanetriol, pentanetriol, and hexanetriol, tetrahydric alcohols such as pentaerythritol, and those obtained by ring-opening addition of lactones and / or epoxides to these polyhydric alcohols as initiators. Any one of these may be used alone, or two or more may be used in combination. Trihydric alcohols and / or their ethylene oxide adducts are preferred.

[0029] The molecular weight of the polyfunctional polyol (B3) is preferably 92 to 350, more preferably 100 to 200. In the case of an adduct in which a plurality of moles of the above-mentioned lactone and / or epoxide are added, the molecular weight of the polyfunctional polyol (B3) is the number average molecular weight (Mn).

[0030] The amount of (B1) hydrogenated polybutadiene polyol in 100% by mass of the (B) polyol component is not particularly limited, but is preferably 40 to 100% by mass, more preferably 70 to 100% by mass, even more preferably 80 to 99.5% by mass, even more preferably 90 to 99% by mass, and even more preferably 95 to 98% by mass. The total amount of (B1) hydrogenated polybutadiene polyol and (B2) polybutadiene polyol is also not particularly limited, but is preferably 80 to 100% by mass, more preferably 85 to 99.5% by mass, even more preferably 90 to 99% by mass, and even more preferably 95 to 98% by mass, of 100% by mass of the (B) polyol component.

[0031] The amount of the polyfunctional polyol (B3) in 100% by mass of the polyol component (B) is not particularly limited, but is preferably 0 to 15% by mass, more preferably 0.5 to 10% by mass, even more preferably 1 to 7% by mass, and still more preferably 2 to 5% by mass.

[0032] The amount of (B1) hydrogenated polybutadiene polyol in the polyurethane is not particularly limited, and the content of the hydrogenated polybutadiene polyol-derived structure relative to 100% by mass of the polyurethane salt may be, for example, 30 to 85% by mass, 40 to 80% by mass, 50 to 78% by mass, or 55 to 75% by mass. The total amount of (B1) hydrogenated polybutadiene polyol and (B2) polybutadiene polyol in the polyurethane is also not particularly limited, and the total amount of the hydrogenated polybutadiene polyol-derived structure and the polybutadiene polyol-derived structure relative to 100% by mass of the polyurethane salt may be 40 to 85% by mass, 50 to 80% by mass, or 55 to 75% by mass.

[0033] The amount of the polyfunctional polyol (B3) in the polyurethane is not particularly limited, and may be, for example, 0 to 7 mass %, 0.5 to 5 mass %, or 1 to 3 mass % in terms of the content of the structure derived from the polyfunctional polyol relative to 100 mass % of the polyurethane salt.

[0034] [(C) Active Hydrogen Group-Containing Carboxylic Acid] In this embodiment, (C) active hydrogen group-containing carboxylic acid is used together with component (B) as a compound having an active hydrogen group that reacts with component (A). (C) active hydrogen group-containing carboxylic acid is a compound having one or more active hydrogen groups and a carboxy group. The number of active hydrogen groups in the carboxylic acid may be 1 to 3, and more preferably 1 or 2. The active hydrogen group is a group containing active hydrogen that reacts with an isocyanate group, and examples thereof include a hydroxy group, a primary amino group (—NH ２ ), and secondary amino group (—NHR).

[0035] Here, the concept of a carboxy group includes not only the acid type (—COOH) but also the salt type, i.e., a carboxylate group (—COOX, where X is a cation that forms a salt with a carboxylic acid), and the acid type and the salt type may be mixed. However, in the polyurethane contained in the electrode binder or electrode binder composition, the carboxy group derived from the carboxylic acid exists as a salt type. This makes it possible to make the polyurethane water-dispersible.

[0036] Examples of the (C) active hydrogen group-containing carboxylic acid include hydroxy acids such as dimethylolpropionic acid, dimethylolbutanoic acid, dimethylolvaleric acid, dihydroxymaleic acid, and dihydroxybenzoic acid, as well as derivatives thereof and salts thereof. Examples of the active hydrogen group-containing carboxylic acid also include amino acids such as alanine, aminobutyric acid, aminocaproic acid, glycine, glutamic acid, aspartic acid, histidine, and diaminobenzoic acid. Any one of these may be used alone, or two or more may be used in combination.

[0037] The active hydrogen group-containing carboxylic acid (C) is preferably an aliphatic carboxylic acid (C1) having two hydroxy groups. Examples of aliphatic carboxylic acids having two hydroxy groups include dimethylolpropionic acid, dimethylolbutanoic acid, and dimethylolvaleric acid, and those having 5 to 10 carbon atoms are preferably used. Any of these may be used alone or in combination of two or more.

[0038] The active hydrogen group-containing carboxylic acid (C) is preferably composed only of the above-mentioned component (C1), but may also contain an active hydrogen group-containing carboxylic acid other than component (C1). The amount of component (C1) in 100% by mass of the active hydrogen group-containing carboxylic acid (C) is not particularly limited, but is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0039] The amount of (C) active hydrogen group-containing carboxylic acid in the polyurethane is not particularly limited, and may be, for example, 1 to 15 mass %, 2 to 10 mass %, or 3 to 8 mass % as the content of the structure derived from the active hydrogen group-containing carboxylic acid relative to 100 mass % of the polyurethane salt.

[0040] [(D) Chain extender] In this embodiment, water is used as the chain extender of component (D). Generally, an amine-based chain extender such as diethylenetriamine is used as the chain extender. However, if an amine-based chain extender is used together with the above-mentioned (A1) MDI-based isocyanate and (B1) hydrogenated polybutadiene polyol, the internal resistance of the lithium secondary battery increases during charging and discharging, impairing the charge-discharge cycle characteristics. Therefore, in this embodiment, it is preferable that an amine-based chain extender is not substantially used, that is, the polyurethane salt is preferably substantially free of a structure derived from an amine-based chain extender.

[0041] Here, the amine chain extender refers to a compound having multiple primary and / or secondary amino groups that is generally used as a chain extender for polyurethane, and examples thereof include diamines such as ethylenediamine, trimethylenediamine, piperazine, and isophoronediamine, and polyamines such as diethylenetriamine, dipropylenetriamine, and triethylenetetramine.

[0042] "Substantially free of structures derived from amine chain extenders" means that the polyurethane salt does not contain structures derived from amine chain extenders, or if it does contain such structures, the content of the structures derived from amine chain extenders per 1 kg of polyurethane salt is less than 0.01 mol, i.e., less than 0.01 mol / kg. Therefore, the amount of amine chain extender used in preparing the polyurethane salt is less than 0.01 mol per kg of the polyurethane salt produced. The content of the structures derived from the amine chain extender is more preferably less than 0.005 mol / kg, and even more preferably 0 mol / kg (i.e., no amine chain extender is used).

[0043] [Electrode Binder] The electrode binder according to this embodiment contains an aqueous dispersion of a polyurethane salt obtained by reacting the above components (A) to (D). That is, in the polyurethane obtained by reacting the components (A) to (D), the carboxyl group derived from the component (C) is converted into a salt and dispersed in water. Therefore, the electrode binder contains water and the polyurethane salt dispersed in water.

[0044] More specifically, the polyurethane water dispersion contains a polyurethane salt obtained by chain-extending with water an isocyanate group-containing urethane prepolymer obtained by reacting components (A) to (C).

[0045] Examples of the polyurethane salt include alkali metal salts such as lithium salts, sodium salts, and potassium salts, and ammonium salts, and amine salts such as primary amines, secondary amines, and tertiary amines. Among these, from the viewpoints of adhesion of the electrode to the current collector and suppression of deformation of the electrode after charge and discharge, alkali metal salts are preferred as the polyurethane salt, and sodium salts are more preferred.

[0046] The carboxyl groups of polyurethane can be converted into salts by neutralization. Neutralization can be carried out before, during, or after the urethane-forming reaction. Examples of neutralizing agents include alkali metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide; tertiary amines such as trimethylamine, triethylamine, dimethylethanolamine, methyldiethanolamine, and triethanolamine; and ammonia.

[0047] The acid value, which is an index of the carboxyl group content in the polyurethane, is preferably 8 to 35 mgKOH / g. When the polyurethane has an acid value of 8 mgKOH / g or more, dispersibility in water can be improved, and when the acid value is 35 mgKOH / g or less, electrolyte resistance can be improved. The acid value of the polyurethane is more preferably 10 to 30 mgKOH / g or less, and even more preferably 15 to 25 mgKOH / g or less.

[0048] In this specification, the acid value can be determined in accordance with JIS K0070-1992 (neutralization titration method) from the amount (mg) of KOH required to neutralize the free carboxyl groups contained in 1 g of the solid content of the polyurethane water dispersion.

[0049] In this embodiment, the average particle size of the polyurethane water dispersion is not particularly limited and may be, for example, in the range of 0.005 to 0.5 μm, or 0.1 to 0.3 μm. The number average molecular weight (Mn) of the polyurethane is also not particularly limited and may be, for example, 10,000 or more, or 50,000 or more.

[0050] The method for producing the polyurethane aqueous dispersion is not particularly limited, but may include, for example, the following method. Component (A) is reacted with components (B) and (C) without a solvent or in an organic solvent containing no active hydrogen groups to synthesize an isocyanate group-containing urethane prepolymer. In this process, component (A) is used so that the isocyanate groups are in stoichiometric excess over the total amount of active hydrogen groups contained in components (B) and (C), e.g., the equivalent ratio NCO / OH of the isocyanate groups to the active hydrogen groups is 1.05 to 1.80 (more preferably 1.10 to 1.60). After synthesis of the urethane prepolymer, the carboxy groups of component (C) are neutralized with a neutralizing agent, and water, which serves as both a dispersion medium and a chain extender, is added to emulsify and disperse the urethane prepolymer in water. The emulsified dispersion is then stirred to complete the chain extension reaction with water, and the organic solvent used is then removed as necessary to obtain an aqueous dispersion of a polyurethane salt.

[0051] In synthesizing the urethane prepolymer, an organic solvent that is inert to isocyanate groups and capable of dissolving the resulting urethane prepolymer may be used. Examples of such organic solvents include dioxane, methyl ethyl ketone, acetone, dimethylformamide, tetrahydrofuran, N-methyl-2-pyrrolidone, toluene, and propylene glycol monomethyl ether acetate. In the electrode binder according to this embodiment, the dispersion medium in which the polyurethane salt is dispersed may or may not contain these organic solvents together with water. These organic solvents are preferably ultimately removed. When an organic solvent is contained, the amount of water is preferably 70% by mass or more, more preferably 90% by mass or more, relative to 100% by mass of the dispersion medium.

[0052] In the electrode binder according to this embodiment, the concentration of the polyurethane salt is not particularly limited, and may be, for example, 5 to 50% by mass, or 10 to 40% by mass.

[0053] [Electrode Binder Composition] The electrode binder composition for the lithium secondary battery according to this embodiment contains a polyurethane salt obtained by reacting the above components (A) to (D), a conductive agent, and water. In particular, the electrode binder composition contains the above polyurethane salt and the conductive agent dispersed in water. The electrode binder composition may be prepared, for example, by mixing the above aqueous dispersion of polyurethane with an aqueous dispersion of the conductive agent.

[0054] The conductive agent may be an electron-conductive material that does not adversely affect battery performance. Specific examples of the conductive agent include fibrous nanocarbon, carbon black such as acetylene black or ketjen black, natural graphite (e.g., scaly graphite, flake graphite, and earthy graphite), artificial graphite, carbon whiskers, carbon fibers, metal (e.g., copper, nickel, aluminum, silver, and gold) powder, metal fibers, and conductive ceramic materials. These may be used alone or in combination of two or more.

[0055] The conductive agent is preferably used in a state of being dispersed in a dispersion medium. Water is usually used as the dispersion medium, but polar organic solvents such as alcohols and ketone-based solvents, or mixtures of these polar organic solvents with water, may also be used. Examples of dispersion devices for dispersing the conductive agent in the dispersion medium include jet mills, high-pressure dispersion devices, and ultrasonic homogenizers.

[0056] When preparing an aqueous dispersion in which a conductive agent is dispersed in water, a dispersant may be added. Examples of dispersants include celluloses such as hydroxymethyl cellulose, carboxymethyl cellulose and alkali metal salts thereof, methyl cellulose, ethyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl methyl cellulose, cellulose nanofibers, polyacrylic acid, polyacrylic acid sodium salts, and other polycarboxylic acid compounds, compounds having a vinylpyrrolidone structure such as polyvinylpyrrolidone, polyvinyl alcohol, alginate sodium, xanthan gum, carrageenan, guar gum, agar, and starch. Among these, carboxymethyl cellulose salts are preferably used.

[0057] In the electrode binder composition, the concentration of the polyurethane salt is not particularly limited and may be, for example, 5 to 50% by mass or 10 to 40% by mass. The concentration of the conductive agent is also not particularly limited and may be, for example, 5 to 35% by mass or 15 to 30% by mass. When the electrode binder composition contains an organic solvent as a dispersion medium, the amount of water is preferably 70% by mass or more, and more preferably 90% by mass or more, relative to 100% by mass of the dispersion medium.

[0058] [Electrode Coating Liquid Composition] The electrode binder and electrode binder composition according to this embodiment are used to prepare an electrode coating liquid composition for producing an electrode for a lithium secondary battery. When an electrode binder is used, the electrode coating liquid composition (1) contains an electrode binder, an electrode active material, and a conductive agent. When an electrode binder composition is used, the electrode coating liquid composition (2) contains an electrode binder composition and an electrode active material.

[0059] These electrode coating liquid compositions are preferably used for producing negative electrodes of lithium secondary batteries. Therefore, the electrode active material is preferably a negative electrode active material. As the negative electrode active material, a material capable of inserting / extracting metallic lithium or lithium ions can be used.

[0060] Specific examples of the negative electrode active material include carbon materials such as natural graphite, artificial graphite, non-graphitizable carbon, and easily graphitizable carbon, metal materials such as metallic lithium, alloys, and tin compounds, lithium transition metal nitrides, crystalline metal oxides, amorphous metal oxides, silicon compounds, and conductive polymers. Any of these may be used alone or in combination of two or more.

[0061] Among these, the negative electrode active material preferably contains at least one silicon-based active material selected from the group consisting of SiO (silicon monoxide), SiC (silicon carbide), Si, and any of these pre-doped with lithium ions (e.g., Li—SiO). The negative electrode active material may be a mixture of a silicon-based active material and graphite, or only a silicon-based active material may be used as the negative electrode active material.

[0062] In the electrode coating liquid composition, the content of the polyurethane salt is not particularly limited, but is preferably 1 to 20 mass % relative to the content of the electrode active material (negative electrode active material), and more preferably 2 to 13 mass %.

[0063] In the above-mentioned electrode coating liquid composition (1), specific examples of the conductive agent are as described above in the electrode binder composition, and therefore further explanation will be omitted.

[0064] In the electrode coating liquid composition, the content of the conductive agent is not particularly limited, but is preferably 0.1 to 20 mass % relative to the content of the electrode active material (negative electrode active material), and more preferably 0.2 to 10 mass %.

[0065] The electrode coating liquid composition may contain a thickener such as a water-soluble polymer as a viscosity adjuster for forming a slurry of the composition. Examples of thickeners include celluloses such as carboxymethylcellulose salts, methylcellulose, ethylcellulose, hydroxymethylcellulose, hydroxypropylmethylcellulose, and hydroxyethylmethylcellulose; polycarboxylic acid compounds such as polyacrylic acid and sodium polyacrylate; compounds having a vinylpyrrolidone structure such as polyvinylpyrrolidone; polyacrylamide, polyethylene oxide, polyvinyl alcohol, sodium alginate, xanthan gum, carrageenan, guar gum, agar, and starch. These may be used alone or in combination. Among these, carboxymethylcellulose salts are preferred.

[0066] The content of the electrode active material (negative electrode active material) in the solid content of the electrode coating liquid composition is not particularly limited and may be, for example, 65 to 99 mass % or 75 to 97 mass %. The content of the dispersion medium such as water in the electrode coating liquid composition is not particularly limited and may be, for example, 20 to 80 mass % or 40 to 70 mass %.

[0067] The method for preparing the electrode coating liquid composition is not particularly limited. When mixing the above components, for example, a mortar, a mill mixer, a ball mill such as a planetary ball mill or a shaker ball mill, mechanofusion, etc. can be used.

[0068] [Negative electrode of lithium secondary battery] The negative electrode of the lithium secondary battery according to the embodiment can be produced by applying the above-mentioned electrode coating liquid composition to a current collector and evaporating the dispersion medium. That is, the negative electrode comprises a current collector and a negative electrode mixture layer (also referred to as an active material layer) formed on the current collector, the negative electrode mixture layer being made of a solid of the above-mentioned electrode coating liquid composition.

[0069] In one embodiment, the electrode coating liquid composition contains, as a negative electrode active material, at least one silicon-based active material selected from the group consisting of SiO, SiC, Si, and any of these pre-doped with lithium ions, together with the electrode binder or electrode binder composition. Therefore, the negative electrode of the lithium secondary battery according to one embodiment contains the solid content of the electrode binder or electrode binder composition, and a negative electrode active material containing the silicon-based active material.

[0070] The current collector can be an electronic conductor that does not adversely affect the constructed battery. Examples of current collectors for the negative electrode include copper, stainless steel, nickel, aluminum, titanium, calcined carbon, conductive polymers, conductive glass, and Al—Cd alloys, as well as copper or other materials whose surfaces have been treated with carbon, nickel, titanium, silver, or the like for the purpose of improving adhesion, conductivity, and oxidation resistance. The surfaces of these current collector materials may be subjected to an oxidation treatment. Examples of the shape of the current collector include foils, films, sheets, nets, punched or expanded materials, laths, porous materials, foams, and other molded products. The thickness of the current collector is not particularly limited, but a thickness of 1 to 100 μm is typically used.

[0071] The thickness of the negative electrode mixture layer is not particularly limited, and may be, for example, 15 to 150 μm.

[0072] [Lithium Secondary Battery] The lithium secondary battery according to the embodiment includes the negative electrode. Specifically, the lithium secondary battery includes a negative electrode, a positive electrode, a separator disposed between the negative electrode and the positive electrode, and an electrolyte, and the negative electrode is an electrode prepared using the electrode coating liquid composition. The positive electrode, separator, and electrolyte are not particularly limited, and known configurations can be used.

[0073] The lithium secondary battery according to the embodiment can be formed into any shape, such as a cylindrical shape, a coin shape, a rectangular shape, or any other shape. The basic configuration of the battery is the same regardless of the shape, and the design can be modified depending on the purpose. For example, in the case of a cylindrical shape, a negative electrode formed by applying a negative electrode active material to a negative electrode current collector and a positive electrode formed by applying a positive electrode active material to a positive electrode current collector are wound with a separator interposed between them, and the wound body is housed in a battery can, and a nonaqueous electrolyte is poured into the battery can, and insulating plates are placed on the top and bottom and sealed. In addition, when applied to a coin-type lithium secondary battery, a disc-shaped negative electrode, a separator, a disc-shaped positive electrode, and a stainless steel plate are stacked and housed in a coin-type battery can, and a nonaqueous electrolyte is poured into the battery can, and sealed.

[0074] The present invention will be explained in more detail below based on examples and comparative examples, but the present invention is not limited thereto.

[0075] Details of the polyisocyanate component and hydrogenated polybutadiene polyol used in the examples are as follows.

[0076] [Polyisocyanate component] Monomeric MDI: "Millionate MT-F" manufactured by Tosoh Corporation Modified MDI: Carbodiimide-modified MDI, "Millionate MTL" manufactured by Tosoh Corporation Polymeric MDI: "Millionate MR-200" manufactured by Tosoh Corporation TDI: "Takenate 500" manufactured by Mitsui Chemicals, Inc. HDI: "Duranate 50M-HDI" manufactured by Asahi Kasei Corporation

[0077] [Hydrogenated Polybutadiene Polyols] Hydrogenated polybutadiene polyol 1: Krasol HLBH-P2000 manufactured by CRAY VALLEY (Mn: 2100, hydroxyl value: 50.8 mg KOH / g, number of functional groups: 1.9) Hydrogenated polybutadiene polyol 2: Krasol HLBH-P3000 manufactured by CRAY VALLEY (Mn: 3100, hydroxyl value: 34.4 mg KOH / g, number of functional groups: 1.9)

[0078] [Polybutadiene polyol] Polybutadiene polyol: Krasol LBH-P2000 manufactured by CRAY VALLEY (Mn: 2000, hydroxyl value: 53.3 mg KOH / g, number of functional groups: 1.9)

[0079] [Synthesis of Polyurethane Water Dispersion] (Example 1: Binder 1) In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube, 65.66 parts by weight of hydrogenated polybutadiene polyol 1, 4.2 parts by weight of dimethylolpropionic acid, 1.8 parts by weight of trimethylolpropane, 28.34 parts by weight of monomeric MDI, and 150 parts by weight of methyl ethyl ketone were added and reacted at 75 ° C. for 4 hours to obtain a methyl ethyl ketone solution of urethane prepolymer with a free isocyanate group content of 2.53% by weight based on the solid content (NCO / OH = 1.36). This solution was cooled to 45 ° C., and an aqueous sodium hydroxide solution consisting of 1.25 parts by weight of sodium hydroxide and 270 parts by weight of water was gradually added as a neutralizing agent, and the mixture was emulsified and dispersed using a homogenizer. Subsequently, the emulsified dispersion was stirred at 40 ° C. for 1 hour to complete the chain extension reaction with water. The mixture was heated under reduced pressure to distill off the methyl ethyl ketone, thereby obtaining an aqueous dispersion of sodium salt of polyurethane (binder 1) with a solid content of 32% by mass.

[0080] (Examples 2 to 4, 6 to 9: Binders 2 to 4, 6 to 9) Aqueous dispersions of sodium salt of polyurethane (Binders 2 to 4, 6 to 9) were obtained in the same manner as in Example 1, except that the types and amounts of (A) polyisocyanate component, (B) polyol component, and (C) active hydrogen group-containing carboxylic acid, as well as the amount of sodium hydroxide, were changed as shown in Table 1 below. However, the amount of free isocyanate groups at the end of the urethane reaction to obtain the isocyanate group-containing urethane prepolymer was 2.27% by mass in Example 2, 2.48% by mass in Example 3, 1.99% by mass in Example 4, 2.53% by mass in Example 6, 2.03% by mass in Example 7, 2.31% by mass in Example 8, and 3.04% by mass in Example 9. The amount of water added as a dispersion medium was adjusted so that the solids concentration of the aqueous dispersion was 32% by mass.

[0081] (Example 5: Binder 5) In the synthesis method of Example 1, a methyl ethyl ketone solution of urethane prepolymer was obtained and cooled to 45°C, and then 3.17 parts by mass of triethylamine as a neutralizing agent was added to neutralize the solution, and then 270 parts by mass of water as a dispersion medium was added while stirring with a homogenizer to emulsify and disperse the solution. Otherwise, in the same manner as in Example 1, an aqueous dispersion of triethylamine salt of polyurethane with a solids content of 32% by mass (binder 5) was obtained.

[0082] (Example 10: Binder 10) A four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube was charged with 32.83 parts by weight of hydrogenated polybutadiene polyol 1, 32.83 parts by weight of polybutadiene polyol, 4.2 parts by weight of dimethylolpropionic acid, 1.8 parts by weight of trimethylolpropane, 28.34 parts by weight of monomeric MDI, and 150 parts by weight of methyl ethyl ketone. The mixture was reacted at 75 ° C. for 4 hours to obtain a methyl ethyl ketone solution of a urethane prepolymer having a free isocyanate group content of 2.53% by weight based on the solid content (NCO / OH = 1.35). This solution was cooled to 45 ° C., and an aqueous sodium hydroxide solution consisting of 1.25 parts by weight of sodium hydroxide and 270 parts by weight of water was gradually added as a neutralizing agent, followed by emulsification and dispersion using a homogenizer. Subsequently, the emulsified dispersion was stirred at 40 ° C. for 1 hour, completing the chain extension reaction with water. The mixture was heated under reduced pressure to remove the methyl ethyl ketone by distillation, thereby obtaining an aqueous dispersion of sodium salt of polyurethane (binder 10) having a solid content of 32% by mass.

[0083] (Comparative Example 1) In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube, 78.47 parts by weight of hydrogenated polybutadiene polyol 1, 1.8 parts by weight of trimethylolpropane, 19.73 parts by weight of monomeric MDI, and 150 parts by weight of methyl ethyl ketone were added, and the mixture was allowed to react at 75 ° C. for 4 hours to obtain a methyl ethyl ketone solution of urethane prepolymer with a free isocyanate group content of 1.76% by weight based on the solid content (NCO / OH = 1.37). After cooling this prepolymer solution to 45 ° C., 270 parts by weight of water was added as a dispersion medium while stirring with a homogenizer in an attempt to emulsify and disperse, but emulsification was not possible. Therefore, for Comparative Example 1, the following evaluation of the polyurethane aqueous dispersion and the preparation and evaluation of the battery were not performed.

[0084] (Comparative Examples 2 to 3: Binders C2 to C3) The types and amounts of the (A) polyisocyanate component, (B) polyol component, and (C) active hydrogen group-containing carboxylic acid were changed as shown in Table 1 below, and the rest of the procedure was the same as in Example 1 to obtain aqueous dispersions of sodium salt of polyurethane (binders C2 to C3) in Comparative Examples 2 to 3. However, the amount of free isocyanate groups at the end of the urethane reaction to obtain the isocyanate group-containing urethane prepolymer was set to 2.64 mass% in Comparative Example 2 and 2.66 mass% in Comparative Example 3. The amount of water added as a dispersion medium was adjusted so that the solids concentration of the aqueous dispersion would be 32 mass%.

[0085] (Comparative Example 4: Binder C4) Using the synthesis method of Example 1, a methyl ethyl ketone solution of urethane prepolymer was obtained and cooled to 45°C. An aqueous solution of sodium hydroxide consisting of 1.25 parts by mass of sodium hydroxide and 270 parts by mass of water as a neutralizing agent was then gradually added, and the mixture was emulsified and dispersed using a homogenizer. Subsequently, an aqueous solution of 0.41 parts by mass of diethylenetriamine diluted with 5 parts by mass of water was added, and a chain extension reaction was carried out for 1 hour. Otherwise, the same procedure as in Example 1 was repeated to obtain an aqueous dispersion of sodium salt of polyurethane (binder C4) with a solids content of 32% by mass. In the sodium salt of polyurethane, the content of the structure derived from the amine-based chain extender was 0.04 mol / kg.

[0086] Comparative Example 5: Binder C5 An aqueous dispersion of sodium salt of polyurethane (binder C5) having a solids content of 32 mass% was obtained in the same manner as in Comparative Example 4, except that 0.44 parts by mass of triethylenetetramine was used as the chain extender instead of 0.41 parts by mass of diethylenetriamine in the synthesis method of Comparative Example 4. In the sodium salt of polyurethane, the content of the structure derived from the amine-based chain extender was 0.03 mol / kg.

[0087] [Evaluation of Polyurethane Water Dispersions] For the obtained Binders 1 to 10 and Binders C2 to C5, the acid value of the polyurethane and the average particle size of the polyurethane water dispersion were measured. The results are shown in Table 1 below. The measurement method is as follows. In Table 1, the "amount of polyurethane salt" is the part by mass of the polyurethane salt produced via the chain extension reaction when the total amount of components (A) to (C), "(A) + (B) + (C)," is taken as 100 parts by mass. Furthermore, "Prepolymer: NCO / OH" is the equivalent ratio of hydroxy groups to isocyanate groups in the urethane prepolymer.

[0088] Acid value of polyurethane: Measured in accordance with JIS K0070-1992 (neutralization titration method).

[0089] Average particle size of polyurethane water dispersion: Measured using "Microtrac UPA-UZ152" manufactured by Nikkiso Co., Ltd., and calculated as the 50% cumulative particle size, i.e., d50 (median size).

[0090] [Fabrication of Lithium Secondary Battery] (Fabrication of Negative Electrode) SiO (average particle size 4.5 μm, specific surface area 5.5 m) was used as the negative electrode active material. ２A negative electrode slurry was prepared using 88.5 parts by mass of a cellulose acetate copolymer (cellulose acetate / g), 40 parts by mass of a fibrous nanocarbon aqueous dispersion (solid content concentration: 0.4% by mass) and 4.0 parts by mass of an acetylene black aqueous dispersion (solid content concentration: 25% by mass) as conductive agents, 50.0 parts by mass of a 2.0% by mass aqueous solution of carboxymethylcellulose sodium salt as a thickener, 28 parts by mass of an aqueous dispersion of polyurethane sodium salt as binder 1, and 6 parts by mass of ion-exchanged water. These were mixed in a planetary mixer to prepare a negative electrode slurry having a solid content of 46% by mass. A 10 μm-thick electrolytic copper foil was used as a current collector, and a negative electrode mixture layer composed of the negative electrode slurry was formed on the electrolytic copper foil. Specifically, the negative electrode slurry was coated on the electrolytic copper foil using a coating machine, roll-pressed, and then dried under reduced pressure at 130°C, yielding a negative electrode active material of 2.7 mg / cm. ２ As the binder, the above-mentioned binders 1 to 10 and binders C2 to C6 were used.

[0091] (Fabrication of Positive Electrode) LiNiCoAlO as a positive electrode active material ２ 92 parts by mass of (NCA), 4 parts by mass of acetylene black (Li-400 manufactured by Denka Co., Ltd.) as a conductive agent, 4 parts by mass of polyvinylidene fluoride as a binder, and 49.2 parts by mass of N-methyl-2-pyrrolidone as a dispersion medium were mixed in a planetary mixer to prepare a positive electrode slurry having a solid content of 67% by mass. This positive electrode slurry was coated onto aluminum foil having a thickness of 15 μm using a coating machine, dried at 130° C., and then subjected to a roll press treatment to obtain a positive electrode active material concentration of 16.6 mg / cm. ２ A positive electrode of 1000 .mu.m was obtained.

[0092] (Fabrication of Battery) The positive and negative electrodes obtained above were combined and laminated with a polyolefin (PE / PP / PE) separator sandwiched between the electrodes as a separator. The positive and negative electrodes were then ultrasonically welded to the positive and negative terminals. This laminate was placed in an aluminum laminate packaging material and heat-sealed, leaving an opening for injection. The positive electrode area was 18 cm. ２ , negative electrode area 19.8cm ２ Next, LiPF was dissolved in a solvent made of a mixture of ethylene carbonate and diethyl carbonate (30 / 70 vol ratio). ６An electrolyte solution in which 1.0 mol / L of hydroxybenzoates (HCO3) was dissolved was poured into the battery, and the opening was heat-sealed to obtain a battery for evaluation.

[0093] [Evaluation of negative electrode and battery performance] The adhesive strength (peel strength) of the prepared negative electrode was evaluated. In addition, the charge / discharge cycle characteristics, internal resistance after charge / discharge, and electrode expansion rate of the evaluation battery were evaluated. The evaluation test methods are as follows.

[0094] (Adhesion) A negative electrode was cut into a piece of 3 x 6 cm, folded 180° so that the coated surface was inward to a size of 3 x 3 cm, and then returned to its original position. The extent of loss of the active material on the coated surface (the length of the fallen portion relative to the folded portion) was visually determined. The evaluation criteria were as follows: A: 0% loss (no loss); B: 5% or less loss (very little electrolytic copper foil visible); C: More than 5% but less than 30% loss; D: 30% or more loss.

[0095] (Charge-Discharge Cycle Characteristics) The test battery was subjected to a charge-discharge cycle test using a charge-discharge device under the following conditions: CC (constant current) charging was performed to 4.2 V at a current density equivalent to 1 C, followed by switching to CV (constant voltage) charging at 4.2 V. Charging was performed for 1.5 hours or until the current density reached 0.1 C, and then CC discharging was performed to 2.7 V at a current density equivalent to 1 C. This cycle was repeated 200 times at 20°C, and the ratio of the 1 C discharge capacity after 200 cycles to the initial 1 C discharge capacity was calculated as the charge-discharge cycle retention (%). The rest between charge and discharge was 10 minutes. The evaluation criteria were as follows: A: Charge-discharge cycle retention of 95% or more B: Charge-discharge cycle retention of 90% or more but less than 95% C: Charge-discharge cycle retention of 80% or more but less than 90% D: Charge-discharge cycle retention of less than 80%

[0096] (Internal Resistance After Charge / Discharge) After the evaluation of the charge / discharge cycle characteristics, the cell impedance (mΩ) at a frequency of 1 kHz was measured using an AC milliohm high tester ("3560" manufactured by Hioki E.E. Corporation). The evaluation criteria were as follows: A: Cell impedance less than 110 mΩ B: Cell impedance 110 mΩ or more and less than 115 mΩ C: Cell impedance 115 mΩ or more and less than 120 mΩ D: Cell impedance 120 mΩ or more

[0097] (Electrode expansion rate after charge / discharge) The thickness of the negative electrode when the evaluation battery was assembled, the thickness of the battery before the evaluation of the charge / discharge cycle characteristics (cell thickness before evaluation), and the thickness of the battery after the evaluation of the charge / discharge cycle characteristics (cell thickness after evaluation) were measured with a micrometer and calculated using the following formulas: Electrode expansion rate = (cell thickness after evaluation - cell thickness before evaluation) / negative electrode composite layer thickness x 100% Negative electrode composite layer thickness = negative electrode thickness - copper foil thickness The evaluation criteria are as follows: A: Electrode expansion rate is less than 30% B: Electrode expansion rate is 30% or more and less than 35% C: Electrode expansion rate is 35% or more and less than 45% D: Electrode expansion rate is 45% or more

[0098]

[0099] The results are shown in Table 1. In Examples 1 to 10, when an MDI-based isocyanate was used as the polyisocyanate component combined with a polyol containing hydrogenated polybutadiene polyol and the chain was extended with water, the increase in internal resistance after charge and discharge was suppressed and good charge and discharge cycle characteristics were obtained. In addition, the adhesive strength between the current collector and the electrode active material was good and deformation of the electrode after charge and discharge was also suppressed.

[0100] In contrast, in Comparative Examples 2 and 3, which used aromatic polyisocyanates and aliphatic polyisocyanates other than MDI-based isocyanates as the polyisocyanate component, the increase in internal resistance after charge and discharge was large, resulting in poor charge and discharge cycle characteristics. Furthermore, the adhesive strength between the current collector and the electrode active material was poor, and the electrode deformation after charge and discharge was also significant.

[0101] In Comparative Examples 4 and 5, in which hydrogenated polybutadiene polyol and MDI-based isocyanate were combined but the chain was extended with an amine-based chain extender, the increase in internal characteristics after charge and discharge could not be suppressed, possibly because the expansion of the electrode due to the use of a silicon-based active material could not be accommodated, and the charge and discharge cycle characteristics were inferior.

[0102] The various numerical ranges described in this specification can be arbitrarily combined with their respective upper and lower limit values, and all such combinations are considered to be preferred numerical ranges described in this specification. Furthermore, a numerical range described as "X to Y" means from X to Y.

[0103] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their omissions, substitutions, modifications, etc. are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents.

Claims

1. An electrode binder for a lithium secondary battery, comprising: (A) a polyisocyanate component containing at least one selected from the group consisting of diphenylmethane diisocyanate and modified products thereof; (B) a polyol component containing hydrogenated polybutadiene polyol; (C) an active hydrogen group-containing carboxylic acid; and (D) an aqueous dispersion of a polyurethane salt obtained by reacting water as a chain extender, wherein the polyurethane salt does not contain a structure derived from an amine-based chain extender, or if it does contain one, the content is less than 0.01 mol / kg.

2. The electrode binder for a lithium secondary battery according to claim 1, wherein the active hydrogen group-containing carboxylic acid includes an aliphatic carboxylic acid having two hydroxy groups.

3. The electrode binder for a lithium secondary battery according to claim 1, wherein the polyol component further contains a polyol having three or more functional groups and a molecular weight of 500 or less.

4. The electrode binder for a lithium secondary battery according to claim 1, wherein the acid value of the polyurethane is 8 to 35 mgKOH / g.

5. The electrode binder for a lithium secondary battery according to claim 1, wherein the polyurethane salt is an alkali metal salt.

6. The electrode binder for a lithium secondary battery according to claim 1, which is for use in the negative electrode of a lithium secondary battery containing at least one material selected from the group consisting of SiO, SiC, Si and those pre-doped with lithium ions as a negative electrode active material.

7. A binder composition for electrodes of a lithium secondary battery, comprising: (A) a polyisocyanate component containing at least one selected from the group consisting of diphenylmethane diisocyanate and modified products thereof; (B) a polyol component containing hydrogenated polybutadiene polyol; (C) an active hydrogen group-containing carboxylic acid; and (D) a polyurethane salt obtained by reacting water as a chain extender, the polyurethane salt not containing a structure derived from an amine-based chain extender or, if it does contain a structure, the content of the structure derived from the amine-based chain extender is less than 0.01 mol / kg; a conductive agent; and water.

8. A negative electrode for a lithium secondary battery, comprising: a solid content of the electrode binder according to claim 1 or the electrode binder composition according to claim 7; and a negative electrode active material containing at least one selected from the group consisting of SiO, SiC, Si and any of these pre-doped with lithium ions.

9. A lithium secondary battery comprising the negative electrode according to claim 8.

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