Binder for electrode of lithium secondary battery, binder composition for electrode, negative electrode, and lithium secondary battery

Abstract

Provided is a binder for an electrode of a lithium secondary battery, said binder being capable of suppressing an increase in internal resistance due to charge and discharge. A binder for an electrode of a lithium secondary battery according to an embodiment contains an aqueous dispersion of a polyurethane salt obtained by reacting components (A), (B), (C), and (D), the polyurethane salt substantially not containing a structure derived from an amine-based chain extender: (A) a polyisocyanate component; the polyurethane resin contains at least one selected from the group consisting of diphenylmethane diisocyanate and a modified body thereof; (B) a polyol component comprising a hydrogenated polybutadiene polyol; (C) carboxylic acid containing an active hydrogen group; and (D) water as a chain extender.

Description

Technical Field

[0001] Embodiments of the present invention relate to an electrode binder for a lithium secondary battery, an electrode binder composition, a negative electrode, and a lithium secondary battery. Background Technology

[0002] Lithium-ion batteries, also known as lithium-ion secondary batteries, are high-voltage, high-energy-density energy storage devices, used in applications such as power supplies for electronic devices. The electrodes of lithium-ion batteries are typically manufactured by coating a mixture of electrode active materials, conductive agents, and binders onto the surface of the current collector and then drying it. The binder is used to provide adhesion between the electrode active materials and the current collector. Therefore, the binder has a significant impact on the characteristics of lithium-ion batteries.

[0003] As an electrode binder for lithium secondary batteries, Patent Document 1 discloses an electrode binder comprising an aqueous dispersion of a sodium salt of polyurethane, which is 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 caused by charge and discharge, thereby improving charge-discharge cycle characteristics.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Patent No. 7161078 Summary of the Invention

[0007] The technical problem that the invention aims to solve

[0008] For example, when using silicon-based active materials such as SiO as the negative electrode active material, charging and discharging cause an increase in internal resistance, which in turn leads to a decrease in charge-discharge cycle characteristics. Therefore, there is a need for electrode binders that can suppress the increase in internal resistance caused by charging and discharging.

[0009] Patent Document 1 discloses the use of hydrogenated polybutadiene polyol and carboxylic acid containing active hydrogen groups as components of the aforementioned polyurethane aqueous dispersion, but uses aliphatic or alicyclic polyisocyanate as the polyisocyanate, and further uses an amine chain extender for chain extension. Therefore, Patent Document 1 does not describe an aqueous dispersion of polyurethane obtained by using diphenylmethane diisocyanate and / or its modified form together with hydrogenated polybutadiene polyol and performing chain extension with water.

[0010] The purpose of this invention is to provide an electrode binder for lithium secondary batteries that can suppress the increase in internal resistance caused by charging and discharging.

[0011] Technical means for solving problems

[0012] The present invention includes the embodiments shown below.

[0013] [1] An electrode binder for a lithium secondary battery, comprising an aqueous dispersion of a polyurethane salt obtained by reacting the following components (A), (B), (C) and (D), wherein the polyurethane salt does not contain a structure derived from an amine chain extender, or even if it does contain a structure derived from an amine chain extender, the content of the structure derived from the amine chain extender is less than 0.01 mol / kg, (A) a polyisocyanate component comprising at least one selected from the group consisting of diphenylmethane diisocyanate and its modifiers; (B) a polyol component comprising hydrogenated polybutadiene polyol; (C) a carboxylic acid containing an active hydrogen group; and (D) water as a chain extender.

[0014] [2] The electrode binder of the lithium secondary battery according to [1], wherein the carboxylic acid containing an active hydrogen group comprises an aliphatic carboxylic acid having two hydroxyl groups.

[0015] [3] The electrode binder for the lithium secondary battery according to [1] or [2], wherein the polyol component further comprises a polyol with a molecular weight of less than 500 and having a higher or more trifunctionality.

[0016] [4] An electrode binder for a lithium secondary battery according to any one of [1] to [3], wherein the acid value of the polyurethane is 8 mg KOH / g to 35 mg KOH / g.

[0017] [5] An electrode binder for a lithium secondary battery according to any one of [1] to [4], wherein the salt of the polyurethane is an alkali metal salt.

[0018] [6] An electrode binder for a lithium secondary battery according to any one of [1] to [5], wherein the electrode binder for the lithium secondary battery is used for the negative electrode of the lithium secondary battery, the negative electrode of the lithium secondary battery comprising at least one selected from the group consisting of SiO, SiC, Si and substances pre-doped with lithium ions therein as a negative electrode active material.

[0019] [7] An electrode binder composition for a lithium secondary battery comprises: a polyurethane salt obtained by reacting the following components (A), (B), (C) and (D), wherein the polyurethane salt does not contain a structure derived from an amine chain extender, or even if it does contain a structure derived from an amine chain extender, its content is less than 0.01 mol / kg; a conductive agent; and water, (A) a polyisocyanate component comprising at least one selected from the group consisting of diphenylmethane diisocyanate and its modifiers; (B) a polyol component comprising hydrogenated polybutadiene polyol; (C) a carboxylic acid containing an active hydrogen group; and (D) water as a chain extender.

[0020] [8] A negative electrode of a lithium secondary battery comprising: a solid component of an electrode binder as described in any one of [1] to [6] above or an electrode binder composition as described in [7] above; and a negative electrode active material comprising at least one selected from the group consisting of SiO, SiC, Si and substances pre-doped with lithium ions therein.

[0021] [9] A lithium secondary battery having the negative electrode described above [8].

[0022] Invention Effects

[0023] According to an embodiment of the present invention, the increase in internal resistance caused by the charging and discharging of a lithium secondary battery can be suppressed. Detailed Implementation

[0024] The electrode binder of the lithium secondary battery of this embodiment comprises an aqueous dispersion of a polyurethane salt (hereinafter sometimes simply referred to as "polyurethane") obtained by reacting the following components (A), (B), (C), and (D): (A) a polyisocyanate component comprising at least one selected from the group consisting of diphenylmethane diisocyanate and its modified forms; (B) a polyol component comprising hydrogenated polybutadiene polyol; (C) a carboxylic acid containing an active hydrogen group; and (D) water as a chain extender. By using diphenylmethane diisocyanate and / or its modified forms as the polyisocyanate that reacts with the hydrogenated polybutadiene polyol, and by using water for chain extension, as shown in the examples described later, the increase in internal resistance caused by the charging and discharging of the lithium secondary battery can be suppressed, and the charge-discharge cycle characteristics can be improved.

[0025] [(A) Polyisocyanate component]

[0026] In this embodiment, as the (A) polyisocyanate component, in the aromatic polyisocyanate, at least one selected from the group consisting of (A1) diphenylmethane diisocyanate and its modifiers (hereinafter, sometimes referred to as "MDI-based isocyanate") is used.

[0027] Examples of diphenylmethane diisocyanates (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 them may be used, or two or more may be used in combination. Furthermore, it is well known that polymeric MDI is a mixture of monomeric MDI and its polynuclear forms contained within diphenylmethane diisocyanate (MDI).

[0028] As a modifier of diphenylmethane diisocyanate, there are no particular limitations as long as it has a diphenylmethane skeleton (Ph-CH2-Ph). Examples include: MDI dimer, carbodiimide-modified MDI, urea-ketone-imide-modified MDI, (trimeric) isocyanurate-modified MDI, etc. Any one of them can be used, or two or more can be used in combination.

[0029] The (A) polyisocyanate component is essentially composed of (A1)MDI-based isocyanates, but may also contain other polyisocyanates as long as their effectiveness is not impaired. More specifically, the amount of (A1)MDI-based isocyanate in 100% by mass of the (A) polyisocyanate component is not particularly limited, but is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and particularly preferably 100% by mass.

[0030] Other polyisocyanates mentioned above include: aromatic polyisocyanates other than MDI-based isocyanates (e.g., toluene diisocyanate (TDI), phenyl diisocyanate (XDI) and their modified forms), aliphatic polyisocyanates (e.g., hexamethylene diisocyanate (HDI), tetramethylene diisocyanate, lysine diisocyanate and their modified forms), and alicyclic polyisocyanates (e.g., isophorone diisocyanate (IPDI), dicyclohexylmethane 4,4'-diisocyanate (hydrogenated MDI) and their modified forms).

[0031] The amount of (A1)MDI isocyanate in polyurethane is not particularly limited. The content of the structure derived from MDI isocyanate relative to 100% by mass of the polyurethane salt can be, for example, 10% to 45% by mass, 15% to 40% by mass, or 20% to 35% by mass.

[0032] [(B) Polyol components]

[0033] In this embodiment, hydrogenated polybutadiene polyol (B1) can be used as the (B) polyol component. Here, even if the carboxylic acid containing an active hydrogen group, which is the (C) component, has multiple hydroxyl groups in one molecule, the (B) polyol component does not contain the carboxylic acid containing the active hydrogen group.

[0034] As for (B1) hydrogenated polybutadiene polyol, it is preferable to use a hydrogenated polybutadiene polyol having an average of 1.3 or more hydroxyl groups per molecule, more preferably a hydrogenated polybutadiene polyol having an average of 1.5 to 2.5 hydroxyl groups, and even more preferably a hydrogenated polybutadiene polyol having an average of 1.7 to 2.2 hydroxyl groups. In this specification, the number of hydroxyl groups (number of functional groups) in each molecule is a value calculated using the following formula.

[0035] Number of functional groups = {(hydroxyl value) × (Mn)} / (56.1 × 1000)

[0036] As the (B1) hydrogenated polybutadiene polyol, it is preferable to use a substance with a structure obtained by hydrogenation (hydrogenation) of a polybutadiene polyol having a 1,4-bonded, 1,2-bonded, or mixed polybutadiene structure and terminal hydroxyl groups. More preferably, the (B1) hydrogenated polybutadiene polyol has a structure obtained by hydrogenating a polybutadiene polyol having hydroxyl groups at both ends of a polybutadiene structure.

[0037] (B1) Hydrogenated polybutadiene polyols are formed by hydrogenating some or all of the unsaturated double bonds contained in polybutadiene polyols. The degree of hydrogenation of (B1) hydrogenated polybutadiene polyols is not particularly limited; for example, the iodine value can be below 40g / 100g, below 30g / 100g, below 25g / 100g, or below 15g / 100g. In this specification, the iodine value is determined according to JIS K0070:1992.

[0038] (B1) There is no particular limitation on the molecular weight of hydrogenated polybutadiene polyols. For example, the number average molecular weight (Mn) can be 600~10000, 800~6000, 1000~5000, 1200~4000, or 1500~3500.

[0039] In this specification, the number-average molecular weight (Mn) is determined by GPC (gel permeation chromatography) and calculated using a standard curve based on standard polystyrene. Specifically, the GPC conditions are as follows: column: TSKgel G4000 HXL + TSKgel G3000 HXL + TSKgel G2000 HXL + TSKgel G1000 HXL + TSKgel G1000 HXL (manufactured by Higashi Soy Co., Ltd.); mobile phase: THF (tetrahydrofuran); mobile phase flow rate: 1.0 mL / min; column temperature: 40 °C; injection volume: 50 μL; sample concentration: 0.2% by mass.

[0040] (B1) The hydroxyl value of hydrogenated polybutadiene polyol is not particularly limited; for example, it can be 10~200 mgKOH / g, 15~120 mgKOH / g, 20~100 mgKOH / g, 30~90 mgKOH / g, or 40~80 mgKOH / g. In this specification, the hydroxyl value is determined according to Method A of JIS K1557-1:2007.

[0041] (B) The polyol component may consist of only (B1) hydrogenated polybutadiene polyol, or it may contain both (B1) hydrogenated polybutadiene polyol and (B2) non-hydrogenated polybutadiene polyol.

[0042] (B2) There are no particular limitations on the number of functional groups, number-average molecular weight, and hydroxyl value of polybutadiene polyols, and the same numerical range as that of (B1) hydrogenated polybutadiene polyols can be used.

[0043] (B) The polyol component may consist solely of (B1) hydrogenated polybutadiene polyol or solely of (B1) hydrogenated polybutadiene polyol and (B2) polybutadiene polyol. Preferably, the (B) polyol component comprises (B1) hydrogenated polybutadiene polyol and (B2) polybutadiene polyol as an optional component, and also comprises (B3) a polyol with a molecular weight of 500 or less that is trifunctional or more (hereinafter, sometimes referred to as "multifunctional polyol"). By including (B3) multifunctional polyol, it is easier to follow the expansion and contraction of the electrode during charging and discharging, and easier to reduce electrode deformation after charging and discharging. Therefore, charge-discharge cycle characteristics can be further improved.

[0044] Examples of (B3) multifunctional polyols include triols such as trimethylolpropane, glycerol, trimethylolethane, glycerol, glycerol, and pentaerythritol, tetraols such as pentaerythritol, or substances obtained by ring-opening addition of lactones and / or epoxides using these polyols as initiators. Any one of these polyols may be used, or two or more may be used in combination. Triols and / or their ethylene oxide adducts are preferred.

[0045] (B3) The molecular weight of the polyfunctional polyol is preferably 92 to 350, more preferably 100 to 200. It should be noted that, in the case of an adduct formed by adding multiple moles of the above-mentioned lactone and / or epoxide, the molecular weight of (B3) polyfunctional polyol is the number average molecular weight (Mn).

[0046] The amount of (B1) hydrogenated polybutadiene polyol in 100% by mass of the polyol component (B) 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 in 100% by mass of the (B) polyol component, it 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.

[0047] (B) The amount of (B3) polyfunctional polyol in 100% by mass of polyol component 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 even more preferably 2% to 5% by mass.

[0048] The amount of (B1) hydrogenated polybutadiene polyol in the polyurethane is not particularly limited. Relative to 100% by mass of the polyurethane salt, the content of the structure derived from the hydrogenated polybutadiene polyol can 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. Relative to 100% by mass of the polyurethane salt, the total amount of the structure derived from the hydrogenated polybutadiene polyol and the structure derived from the polybutadiene polyol can be 40% to 85% by mass, 50% to 80% by mass, or 55% to 75% by mass.

[0049] The amount of (B3) polyol in polyurethane is not particularly limited, but can be 0 to 7% by mass relative to 100% by mass of the polyurethane salt, as the content of the structure derived from the polyol, for example, 0.5% to 5% by mass, or 1% to 3% by mass.

[0050] [(C) Carboxylic acids containing active hydrogen groups]

[0051] In this embodiment, as a compound having an active hydrogen group that reacts with component (A), component (B) and carboxylic acid containing an active hydrogen group (C) can be used simultaneously. The carboxylic acid containing an active hydrogen group (C) is a compound having a carboxyl group and one or more active hydrogen groups. The number of active hydrogen groups in this carboxylic acid can be 1 to 3, more preferably 1 or 2. An active hydrogen group refers to a group containing active hydrogen that reacts with an isocyanate group; examples include hydroxyl, primary amino (-NH2), and secondary amino (-NHR).

[0052] Here, the carboxyl group is a concept that includes not only the acidic form (-COOH) but also the salt form, namely the carboxylate (-COOX, a cation that forms a salt with a carboxylic acid). The acidic and salt forms can also coexist. However, in the polyurethane contained in the electrode binder or electrode binder composition, the carboxyl group derived from this carboxylic acid exists in the salt form. As a result, the polyurethane can be made water-dispersible.

[0053] Examples of carboxylic acids containing an active hydrogen group (C) include, for example, dimethylolpropionic acid, dimethylolbutyric acid, dimethylolvalerate, dihydroxymaleic acid, dihydroxybenzoic acid, and other hydroxy acids and their derivatives, as well as their salts. Examples of amino acids containing an active hydrogen group also include, for example, alanine, aminobutyric acid, aminocaproic acid, glycine, glutamic acid, aspartic acid, histidine, diaminobenzoic acid, and other amino acids. Any one of these can be used, or two or more can be used in combination.

[0054] As the carboxylic acid containing an active hydrogen group (C), an aliphatic carboxylic acid having two hydroxyl groups (C1) is preferred. Examples of aliphatic carboxylic acids having two hydroxyl groups include dimethylolpropionic acid, dimethylolbutyric acid, and dimethylolvalerate, with aliphatic carboxylic acids having 5 to 10 carbon atoms being preferred. Any one of them may be used, or two or more may be used in combination.

[0055] (C) The carboxylic acid containing an active hydrogen group is preferably composed only of the above-mentioned component (C1), but may also contain carboxylic acids containing active hydrogen groups other than component (C1). The amount of component (C1) in 100% by mass of the carboxylic acid containing an active hydrogen group 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.

[0056] The amount of (C) carboxylic acid containing active hydrogen groups in polyurethane is not particularly limited. Relative to 100% by mass of the polyurethane salt, the content of the structure derived from the carboxylic acid containing active hydrogen groups can be, for example, 1% to 15% by mass, 2% to 10% by mass, or 3% to 8% by mass.

[0057] [(D) Chain extender]

[0058] In this embodiment, water can be used as component (D), i.e., the chain extender. Typically, amine-based chain extenders such as diethylenetriamine can be used, but if an amine-based chain extender is used in conjunction with the aforementioned (A1) MDI-based isocyanate and (B1) hydrogenated polybutadiene polyol, the internal resistance will increase due to the charging and discharging of the lithium secondary battery, and the charge-discharge cycle characteristics will be impaired. Therefore, in this embodiment, it is preferable not to use amine-based chain extenders substantially, i.e., the polyurethane salt does not substantially contain a structure derived from an amine-based chain extender.

[0059] Here, amine chain extenders refer to compounds with multiple primary and / or secondary amino groups that are commonly used as chain extenders for polyurethanes. Examples include: ethylenediamine, trimethylenediamine, piperazine, isophorone diamine, and other diamines; diethylenetriamine, dipropylenetriamine, and trimethylenetetramine, and other polyamines.

[0060] The phrase "substantially does not contain structures derived from amine chain extenders" means that the polyurethane salt does not contain any structures derived from amine chain extenders, or even if it does, the content of structures derived from amine chain extenders is less than 0.01 mol / kg relative to 1 kg of polyurethane salt. Therefore, the amount of amine chain extender used in preparing the polyurethane salt is less than 0.01 mol relative to 1 kg of polyurethane salt produced. More preferably, the content of structures derived from this amine chain extender is less than 0.005 mol / kg, and even more preferably 0 mol / kg (i.e., no amine chain extender is used).

[0061] [Electrode binder]

[0062] The electrode binder of this embodiment comprises an aqueous dispersion of a polyurethane salt obtained by reacting components (A) to (D) above. That is, the polyurethane obtained by reacting components (A) to (D) is dispersed in water by salting the carboxyl groups derived from component (C). Therefore, the electrode binder comprises water and a polyurethane salt dispersed in the water.

[0063] More specifically, the above-mentioned polyurethane aqueous dispersion includes a salt of polyurethane obtained by chain extension of an isocyanate-containing urethane prepolymer obtained by reacting components (A) to (C) with water.

[0064] Examples of salts for the aforementioned polyurethane include alkali metal salts such as lithium salts, sodium salts, and potassium salts; and amine salts such as ammonium salts, primary amines, secondary amines, and tertiary amines. From the viewpoint of ensuring the adhesion of the electrode to the current collector and suppressing electrode deformation after charging and discharging, alkali metal salts are preferred, and sodium salts are more preferred as salts for the polyurethane.

[0065] The carboxyl groups of polyurethane can be neutralized to form salts. This neutralization can occur before, during, or after the urethane esterification 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.

[0066] The acid value, which serves as an indicator of the carboxyl content in the aforementioned polyurethane, is preferably 8 to 35 mgKOH / g. By setting the acid value of the polyurethane to 8 mgKOH / g or higher, its dispersibility in water can be improved; by setting the acid value to 35 mgKOH / g or lower, its resistance to electrolytes can be improved. More preferably, the acid value of the polyurethane is 10 to 30 mgKOH / g or lower; even more preferably, it is 15 to 25 mgKOH / g or lower.

[0067] In this specification, the acid value can be determined according to JIS K0070-1992 (neutralization titration method) by the amount of KOH (mg) required to neutralize the free carboxyl groups contained in 1g of solid components of the polyurethane aqueous dispersion.

[0068] In this embodiment, the average particle size of the polyurethane aqueous dispersion is not particularly limited, and can be, for example, in the range of 0.005 to 0.5 μm, or 0.1 to 0.3 μm. Furthermore, the number-average molecular weight (Mn) of the polyurethane is not particularly limited, and can be, for example, 10,000 or more, or 50,000 or more.

[0069] The method for manufacturing the above-mentioned polyurethane aqueous dispersion is not particularly limited, and for example, the following method can be used. Component (A) is reacted with components (B) and (C) in a solvent-free or organic solvent without active hydrogen groups to synthesize a urethane prepolymer containing isocyanate groups. In this case, component (A) is used in a stoichiometric excess of isocyanate groups relative to the total amount of active hydrogen groups contained in components (B) and (C), for example, in an isocyanate group to active hydrogen group equivalence ratio (NCO / OH) of 1.05 to 1.80 (more preferably 1.10 to 1.60). After synthesizing the above-mentioned urethane prepolymer, the carboxyl groups of component (C) are neutralized using a neutralizing agent, and water, which also serves as a dispersion medium and chain extender, is added to emulsify and disperse the urethane prepolymer in water. Then, the chain extension reaction of water is completed by stirring the emulsion dispersion, and the organic solvent used is removed as needed, thereby obtaining an aqueous dispersion of a polyurethane salt.

[0070] In the synthesis of the above-mentioned urethane prepolymer, an organic solvent that is inactive to the isocyanate groups and can dissolve the generated urethane prepolymer can 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 of this embodiment, the dispersion medium in which the polyurethane salt is dispersed may or may not contain these organic solvents along with water. These organic solvents are preferably eventually removed. When organic solvents are present, the amount of water relative to 100% by mass of the dispersion medium is preferably 70% by mass or more, more preferably 90% by mass or more.

[0071] In the electrode binder of this embodiment, the concentration of the polyurethane salt is not particularly limited, and can be, for example, 5% to 50% by mass or 10% to 40% by mass.

[0072] [Electrode binder composition]

[0073] The electrode binder composition for the lithium secondary battery of this embodiment comprises a salt of polyurethane obtained by reacting the components (A) to (D) described above, a conductive agent, and water. Specifically, the electrode binder composition comprises the polyurethane salt and the conductive agent in a state where the polyurethane salt and the conductive agent are dispersed in water. The electrode binder composition can be prepared, for example, by mixing an aqueous dispersion of the polyurethane with an aqueous dispersion of the conductive agent.

[0074] As a conductive agent, electronically conductive materials that do not adversely affect battery performance can be used. Specific examples of conductive agents include: fibrous carbon nanofibers, carbon blacks such as acetylene black / Ketjen black, natural graphite (flake graphite, flaky graphite, amorphous graphite, etc.), artificial graphite, carbon whiskers, carbon fibers, metal powders (copper, nickel, aluminum, silver, gold, etc.), metal fibers, conductive ceramic materials, and other conductive materials. Any one of these materials or a combination of two or more can be used.

[0075] The conductive agent is preferably used in a dispersion medium. Water is typically used as the dispersion medium, but polar organic solvents such as alcohols and ketones, or mixtures of these polar organic solvents and water, can also be used. Examples of dispersion devices for dispersing the conductive agent in the dispersion medium include jet mills, high-pressure dispersers, and ultrasonic homogenizers.

[0076] When preparing an aqueous dispersion of a conductive agent in water, a dispersant can be added. Examples of dispersants include: hydroxymethyl cellulose, carboxymethyl cellulose and its alkali metal salts, methyl cellulose, ethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose and other cellulose compounds, cellulose nanofibers, polyacrylic acid, sodium polyacrylate and other polycarboxylic acid compounds, compounds with a vinylpyrrolidone structure such as polyvinylpyrrolidone, polyvinyl alcohol, sodium alginate, xanthan gum, carrageenan, guar gum, agar, starch, etc. Among these, carboxymethyl cellulose salts are preferred.

[0077] In the electrode binder composition, the concentration of the polyurethane salt is not particularly limited, and can 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 can be, for example, 5% to 35% by mass, or 15% to 30% by mass. When the electrode binder composition contains an organic solvent in the dispersion medium, the amount of water relative to 100% by mass of the dispersion medium is preferably 70% by mass or more, more preferably 90% by mass or more.

[0078] [Electrode Coating Solution Composition]

[0079] The electrode binder and electrode binder composition of this embodiment are used to prepare an electrode coating liquid composition for manufacturing electrodes for lithium secondary batteries. When using an electrode binder, the electrode coating liquid composition (1) comprises an electrode binder, an electrode active material, and a conductive agent. When using an electrode binder composition, the electrode coating liquid composition (2) comprises an electrode binder composition and an electrode active material.

[0080] These electrode coating compositions are preferably used to manufacture the negative electrode of a lithium secondary battery. Therefore, the electrode active material is preferably a negative electrode active material. As the negative electrode active material, a material capable of inserting / deintercalating metallic lithium or lithium ions can be used.

[0081] Specific examples of negative electrode active materials include: natural graphite, artificial graphite, carbon materials such as difficult-to-graphitize carbon and easy-to-graphitize carbon, metallic materials such as lithium metal or alloys and tin compounds, lithium transition metal nitrides, crystalline metal oxides, amorphous metal oxides, silicon compounds, and conductive polymers. Any one of these materials can be used, or a combination of two or more can be used.

[0082] From the perspective of achieving high capacity, the negative electrode active material preferably includes at least one silicon-based active material selected from the group consisting of SiO (silicon monoxide), SiC (silicon carbide), Si, and materials pre-doped with lithium ions (e.g., Li-SiO). The negative electrode active material can be a mixture of silicon-based active material and graphite, or it can be a silicon-based active material used alone.

[0083] In the electrode coating liquid composition, the content of the polyurethane salt is not particularly limited, but is preferably 1% to 20% by mass, more preferably 2% to 13% by mass, relative to the content of the electrode active material (negative electrode active material).

[0084] In the above-described electrode coating liquid composition (1), the specific conductive agent is as described in the electrode adhesive composition, and the description is omitted.

[0085] In the electrode coating liquid composition, the content of the conductive agent is not particularly limited, but it is preferably 0.1% to 20% by mass, more preferably 0.2% to 10% by mass, relative to the content of the electrode active material (negative electrode active material).

[0086] The electrode coating composition may contain a water-soluble polymer or other thickener as a viscosity modifier to slurry the composition. Examples of thickeners include: cellulose compounds such as carboxymethyl cellulose salts, methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl methyl cellulose; polycarboxylic acid compounds such as polyacrylic acid and sodium polyacrylate; compounds with a vinylpyrrolidone structure such as polyvinylpyrrolidone; polyacrylamide; polyethylene oxide; polyvinyl alcohol; sodium alginate; xanthan gum; carrageenan; guar gum; agar; and starch. Any one of these or a combination of two or more can be used. Carboxymethyl cellulose salts are preferred.

[0087] The content of electrode active material (negative electrode active material) in the solid component of the electrode coating liquid composition is not particularly limited, and can be, for example, 65% to 99% by mass or 75% to 97% by mass. The content of dispersion medium such as water in the electrode coating liquid composition is not particularly limited, and can be, for example, 20% to 80% by mass or 40% to 70% by mass.

[0088] There are no particular limitations on the preparation method of the electrode coating liquid composition. When mixing the above components, a ball mill such as a mortar and pestle, a stirring mixer, a planetary ball mill or a vibratory ball mill, or a mechanical fusion machine can be used.

[0089] [Negative electrode of a lithium secondary battery]

[0090] The negative electrode of the lithium secondary battery according to the embodiment can be manufactured by coating the above-described electrode coating liquid composition onto a current collector and evaporating the dispersion medium. That is, the negative electrode includes a current collector and a negative electrode mixture layer (also called an active material layer) formed on the current collector, the negative electrode mixture layer containing the solid of the above-described electrode coating liquid composition.

[0091] In one embodiment, the electrode coating liquid composition, while containing the aforementioned electrode binder or electrode binder composition, also includes at least one silicon-based active material selected from SiO, SiC, Si, and substances pre-doped with lithium ions therein as the negative electrode active material. Therefore, the negative electrode of a lithium secondary battery according to one embodiment comprises: the solid component of the electrode binder or electrode binder composition, and the negative electrode active material containing the aforementioned silicon-based active material.

[0092] As a current collector, an electron conductor that does not adversely affect the battery structure can be used. For the negative electrode, current collectors can be made of materials such as copper, stainless steel, nickel, aluminum, titanium, sintered carbon, conductive polymers, conductive glass, and Al-Cd alloys. To improve adhesion, conductivity, and oxidation resistance, current collectors made by treating the surface of copper with carbon, nickel, titanium, or silver can also be used. The surfaces of these current collector materials can be oxidized. Examples of current collector shapes include: foil, film, sheet, mesh, perforated or stretched materials, grid-like structures, porous structures, and foamed structures. The thickness of the current collector is not particularly limited, but typically ranges from 1 to 100 μm.

[0093] The thickness of the negative electrode mixture layer is not particularly limited; for example, it can be 15~150μm.

[0094] [Lithium-ion rechargeable battery]

[0095] The lithium secondary battery of the embodiment includes the aforementioned negative electrode. Specifically, the lithium-ion secondary battery includes a negative electrode, a positive electrode, a separator disposed between the negative and positive electrodes, and an electrolyte. The negative electrode is an electrode made using the aforementioned electrode coating solution composition. There are no particular limitations on the positive electrode, separator, and electrolyte; known structures can be used.

[0096] The lithium secondary battery of the embodiment can be formed into cylindrical, coin-shaped, square, or other arbitrary shapes. The basic structure of the battery is the same regardless of the shape, and it can be implemented by design changes according to the purpose. For example, in the cylindrical type, a negative electrode formed by coating a negative electrode active material on a negative electrode current collector and a positive electrode formed by coating a positive electrode active material on a positive electrode current collector are wound together by a separator and placed in a battery can. A non-aqueous electrolyte is injected, and the can is sealed with insulating plates placed on top and bottom. In addition, in the case of coin-shaped lithium secondary batteries, a disc-shaped negative electrode, a separator, a disc-shaped positive electrode, and a stainless steel plate are stacked in a coin-shaped battery can, a non-aqueous electrolyte is injected, and the can is sealed.

[0097] Example

[0098] The present invention will now be described in more detail based on embodiments and comparative examples, but is not limited thereto.

[0099] The details of the polyisocyanate components and hydrogenated polybutadiene polyols used in the examples are as follows.

[0100] [Polyisocyanate ingredient]

[0101] ·Single MDI: "Militor MT-F" manufactured by Tosato Co., Ltd.

[0102] • Modified MDI: Carbodiimide modified MDI, manufactured by Toso Corporation, "Milionite MTL"

[0103] ·Polymerized MDI: "Militor MR-200" manufactured by Tosato Co., Ltd.

[0104] ·TDI: Mitsui Chemicals Co., Ltd.'s "TDI 500"

[0105] ·HDI: "Dynamic 50M-HDI" manufactured by Asahi Kasei Co., Ltd.

[0106] [Hydrogenated polybutadiene polyol]

[0107] • Hydrogenated polybutadiene polyol 1: Krasol HLBH-P2000 manufactured by CRAY VALLEY (Mn: 2100, hydroxyl value: 50.8 mg KOH / g, functional group number: 1.9)

[0108] • Hydrogenated polybutadiene polyol 2: Krasol HLBH-P3000 manufactured by CRAY VALLEY (Mn: 3100, hydroxyl value: 34.4 mg KOH / g, functional group number: 1.9)

[0109] [Polybutadiene polyol]

[0110] • Polybutadiene polyol: Krasol LBH-P2000 manufactured by CRAY VALLEY (Mn: 2000, hydroxyl value: 53.3 mg KOH / g, functional group number: 1.9)

[0111] Synthesis of polyurethane aqueous dispersions

[0112] (Example 1: Adhesive 1)

[0113] In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube, 65.66 parts by mass of hydrogenated polybutadiene polyol 1, 4.2 parts by mass of dimethylolpropionic acid, 1.8 parts by mass of trimethylolpropane, 28.34 parts by mass of monomer MDI, and 150 parts by mass of methyl ethyl ketone were added. The mixture was 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 mass relative to the solids (NCO / OH = 1.36). The solution was cooled to 45°C, and an aqueous sodium hydroxide solution containing 1.25 parts by mass of sodium hydroxide as a neutralizing agent and 270 parts by mass of water was slowly added. The mixture was then emulsified and dispersed using a homogenizer. The emulsion dispersion was then stirred at 40°C for 1 hour to complete the water-based chain extension reaction. The methyl ethyl ketone was removed by distillation under reduced pressure to obtain an aqueous dispersion (binder 1) of a sodium salt of polyurethane with a solids content of 32% by mass.

[0114] (Examples 2-4, 6-9: Adhesives 2-4, 6-9)

[0115] The types and amounts of (A) polyisocyanate components, (B) polyol components, and (C) carboxylic acids containing active hydrogen groups, as well as the amount of sodium hydroxide, were changed as shown in Table 1 below. Otherwise, the procedure was the same as in Example 1 to obtain aqueous dispersions of sodium salts of polyurethanes (binders 2-4, 6-9) for Examples 2-4 and 6-9. Specifically, the amount of free isocyanate groups at the end of the urethane reaction when obtaining the isocyanate-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. Furthermore, the amount of water added as the dispersion medium was adjusted so that the solid content concentration of the aqueous dispersion reached 32% by mass.

[0116] (Example 5: Adhesive 5)

[0117] In the synthesis method of Example 1, a methyl ethyl ketone solution of the urethane prepolymer was obtained and cooled to 45°C. Then, 3.17 parts by mass of triethylamine as a neutralizing agent were added for neutralization. Then, while stirring using a homogenizer, 270 parts by mass of water as a dispersion medium were added to emulsify and disperse the prepolymer. Otherwise, the process was the same as in Example 1 to obtain an aqueous dispersion (binder 5) of a triethylamine salt of polyurethane with a solid content of 32% by mass.

[0118] (Example 10: Adhesive 10)

[0119] In a four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet tube, 32.83 parts by mass of hydrogenated polybutadiene polyol 1, 32.83 parts by mass of polybutadiene polyol, 4.2 parts by mass of dimethylolpropionic acid, 1.8 parts by mass of trimethylolpropane, 28.34 parts by mass of monomer MDI, and 150 parts by mass of methyl ethyl ketone were added. The mixture was 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 mass relative to the solid content (NCO / OH = 1.35). The solution was cooled to 45°C, and an aqueous sodium hydroxide solution containing 1.25 parts by mass of sodium hydroxide as a neutralizing agent and 270 parts by mass of water was slowly added. The mixture was then emulsified and dispersed using a homogenizer. The emulsion dispersion was then stirred at 40°C for 1 hour to complete the water-based chain extension reaction. The methyl ethyl ketone was removed by distillation under heating and reduced pressure to obtain an aqueous dispersion of sodium salt of polyurethane with a solid content of 32% by mass (binder 10).

[0120] (Comparative Example 1)

[0121] In a four-necked flask equipped with a stirrer, reflux cooling tube, thermometer, and nitrogen purge tube, 78.47 parts by mass of hydrogenated polybutadiene polyol 1, 1.8 parts by mass of trimethylolpropane, 19.73 parts by mass of monomer MDI, and 150 parts by mass of methyl ethyl ketone were added. The mixture was reacted 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 mass relative to the solid content (NCO / OH = 1.37). The prepolymer solution was cooled to 45°C, and then 270 parts by mass of water as a dispersion medium were added while stirring with a homogenizer to emulsify and disperse it, but emulsification was not achieved. Therefore, for Comparative Example 1, the evaluation of the polyurethane aqueous dispersion and the fabrication and evaluation of the battery were not performed.

[0122] (Comparative Examples 2-3: Adhesives C2-C3)

[0123] The types and amounts of (A) polyisocyanate, (B) polyol, and (C) carboxylic acid containing active hydrogen groups were changed as shown in Table 1 below. Otherwise, the procedure was the same as in Example 1 to obtain aqueous dispersions of sodium polyurethane salts (binders C2-C3) for Comparative Examples 2-3. Specifically, the amount of free isocyanate groups at the end of the urethane reaction when obtaining the isocyanate-containing urethane prepolymer was 2.64% by mass in Comparative Example 2 and 2.66% by mass in Comparative Example 3. Furthermore, the amount of water added as the dispersion medium was adjusted so that the solids concentration of the aqueous dispersion reached 32% by mass.

[0124] (Comparative Example 4: Adhesive C4)

[0125] In the synthesis method of Example 1, a methyl ethyl ketone solution of the urethane prepolymer was obtained and cooled to 45°C. Then, an aqueous solution of sodium hydroxide containing 1.25 parts by mass of sodium hydroxide as a neutralizing agent and 270 parts by mass of water was slowly added, and the mixture was emulsified and dispersed using a homogenizer. Next, an aqueous solution prepared by diluting 0.41 parts by mass of diethylenetriamine with 5 parts by mass of water was added, and a chain extension reaction was carried out for 1 hour. Otherwise, the procedure was the same as in Example 1 to obtain an aqueous dispersion of the sodium salt of polyurethane (binder C4) with a solid content of 32% by mass. The sodium salt of this polyurethane contained 0.04 mol / kg of structure derived from the amine chain extender.

[0126] (Comparative Example 5: Adhesive C5)

[0127] In the synthesis method of Comparative Example 4, 0.44 parts by mass of triethylenetetramine was used instead of 0.41 parts by mass of diethylenetriamine as a chain extender, and everything else was the same as in Comparative Example 4, resulting in an aqueous dispersion of the sodium salt of polyurethane (binder C5) with a solid content of 32% by mass. The content of the structure derived from the amine chain extender in the sodium salt of this polyurethane was 0.03 mol / kg.

[0128] Evaluation of polyurethane aqueous dispersions

[0129] For the obtained binders 1-10 and binders C2-C5, the acid value of the polyurethane and the average particle size of the polyurethane aqueous dispersion were determined. The results are shown in Table 1 below. The determination method is as follows. It should be noted that in Table 1, "amount of polyurethane salt" refers to the mass fraction of polyurethane salt generated after the chain extension reaction when the total mass fraction of components (A)-(C) "(A)+(B)+(C)" is set to 100 parts by mass. In addition, "prepolymer:NCO / OH" is the equivalent ratio of hydroxyl groups to isocyanate groups in the urethane prepolymer.

[0130] • Acid value of polyurethane: determined according to JIS K0070-1992 (neutralization titration method).

[0131] • Average particle size of polyurethane aqueous dispersion: Measured using Nikkiso Co., Ltd.'s "Microtrac UPA-UZ152", and calculated as the 50% cumulative particle size, i.e., d50 (median particle size).

[0132] [Making of Lithium-ion Secondary Batteries]

[0133] (Making the negative electrode)

[0134] SiO₂ (average particle size 4.5 μm, specific surface area 5.5 m²) was used as the negative electrode active material. 2 A negative electrode slurry was prepared by mixing 88.5 parts by weight of a fibrous nano-carbon aqueous dispersion (solid content concentration: 0.4 wt%) as a conductive agent, 4.0 parts by weight of an acetylene black aqueous dispersion (solid content concentration: 25 wt%), 50.0 parts by weight of a 2.0 wt% aqueous solution of sodium carboxymethyl cellulose as a thickener, 28 parts by weight of an aqueous dispersion of sodium polyurethane as binder 1, and 6 parts by weight of deionized water using a planetary mixer to achieve a solid content of 46 wt%. A negative electrode mixture layer containing the above negative electrode slurry was formed on a 10 μm thick electrolytic copper foil as a current collector. Specifically, the negative electrode slurry was coated onto the electrolytic copper foil using a coating machine, rolled, and then dried under reduced pressure at 130°C to obtain a negative electrode active material concentration of 2.7 mg / cm³. 2 The negative electrode. As binders, binders 1 to 10 and binders C2 to C6 as described above are used.

[0135] (The production of the positive electrode)

[0136] A positive electrode slurry was prepared by mixing 92 parts by mass of LiNiCoAlO2 (NCA) as the positive electrode active material, 4 parts by mass of acetylene black (Denka Co., Ltd. "Li-400") as the conductive agent, 4 parts by mass of polyvinylidene fluoride as the binder, and 49.2 parts by mass of N-methyl-2-pyrrolidone as the dispersion medium using a planetary mixer to achieve a solid content of 67% by mass. The positive electrode slurry was then coated onto a 15 μm thick aluminum foil using a coating machine, dried at 130°C, and rolled to obtain a positive electrode active material concentration of 16.6 mg / cm³. 2 The positive pole.

[0137] (Battery manufacturing)

[0138] The obtained positive and negative electrodes were combined and laminated with a polyolefin (PE / PP / PE) separator between them. Positive and negative terminals were ultrasonically welded onto each electrode. The laminate was then placed in aluminum laminate packaging material, leaving an opening for liquid injection, and heat-sealed. A positive electrode with an area of ​​18 cm² was fabricated. 2 The negative electrode area is 19.8 cm². 2 The battery before electrolyte injection was then prepared. Next, an electrolyte solution containing LiPF6 (1.0 mol / L) was injected into a solvent containing a mixture of ethylene carbonate and diethyl carbonate (30 / 70 vol ratio), and the opening was heat-sealed to obtain an evaluation battery.

[0139] [Evaluation of negative electrode and battery performance]

[0140] The adhesion (peel strength) of the fabricated negative electrode was evaluated. Additionally, for the evaluation battery, the charge-discharge cycle characteristics, internal resistance after charge-discharge, and electrode expansion rate were evaluated. The evaluation test methods are described below.

[0141] (Adhesive strength)

[0142] Cut the negative electrode into 3cm × 6cm pieces. Bend the coated surface 180° inwards to form a 3×3cm section, then fold it back. Visually assess the degree of active material detachment from the coated surface (the length of the detached portion relative to the bent portion). The evaluation criteria are as follows.

[0143] A: 0% shedding (no shedding)

[0144] B: Less than 5% shedding (electrolytic copper foil is rarely seen)

[0145] C: Shedding rate exceeding 5% but less than 30%

[0146] D: More than 30% shedding

[0147] (charge-discharge cycle characteristics)

[0148] For the evaluation battery, charge-discharge cycle tests were conducted using a charge-discharge device under the following conditions: The battery was charged to 4.2V at a current density CC (constant current) equivalent to 1C, then switched to CV (constant voltage) charging at 4.2V for 1.5 hours or until the current density reached 0.1C. It was then discharged to 2.7V at a current density CC equivalent to 1C. This cycle was performed 200 times at 20°C. The ratio of the 1C discharge capacity after 200 cycles to the initial 1C discharge capacity was calculated as the charge-discharge cycle retention rate (%). The rest time between charging and discharging was set to 10 minutes. The evaluation criteria are as follows.

[0149] A: Charge-discharge cycle retention rate of over 95%.

[0150] B: Charge-discharge cycle retention rate is above 90% and below 95%.

[0151] C: Charge-discharge cycle retention rate is above 80% and less than 90%.

[0152] D: Charge-discharge cycle retention rate is less than 80%.

[0153] (Internal resistance after charging and discharging)

[0154] For the batteries evaluated for the above charge-discharge cycle characteristics, the battery impedance (mΩ) at a frequency of 1 kHz was measured using an AC milliohm meter (Hioki Electric Co., Ltd. "3560"). The evaluation criteria are as follows.

[0155] A: Battery impedance is less than 110mΩ

[0156] B: Battery impedance is above 110mΩ and below 115mΩ

[0157] C: Battery impedance is above 115mΩ and below 120mΩ

[0158] D: Battery impedance is above 120mΩ

[0159] (Electrode expansion rate after charge and discharge)

[0160] The thickness of the negative electrode during battery assembly for evaluation, the thickness of the battery before the evaluation of the above-mentioned charge-discharge cycle characteristics (battery thickness before evaluation), and the thickness of the battery after the evaluation of the above-mentioned charge-discharge cycle characteristics (battery thickness after evaluation) were measured using a micrometer and calculated using the following formula.

[0161] Electrode expansion rate = (Battery thickness after evaluation - Battery thickness before evaluation) / Negative electrode flux layer thickness × 100%

[0162] Negative electrode coating thickness = Negative electrode thickness - Copper foil thickness

[0163] The evaluation criteria are as follows.

[0164] A: Electrode expansion rate is less than 30%.

[0165] B: Electrode expansion rate is 30% or more but less than 35%.

[0166] C: Electrode expansion rate is 35% or higher and less than 45%.

[0167] D: Electrode expansion rate is above 45%.

[0168] [Table 1]

[0169]

[0170] The results are shown in Table 1. For Examples 1-10, if MDI-based isocyanate is used as the polyisocyanate component in combination with a polyol containing hydrogenated polybutadiene polyol and chain extension is performed with water, the increase in internal resistance after charge and discharge can be suppressed, and good charge-discharge cycle characteristics can be obtained. In addition, the adhesion between the current collector and the electrode active material is good, and the deformation of the electrode after charge and discharge is also suppressed.

[0171] In contrast, in Comparative Examples 2-3, which used aromatic polyisocyanates and aliphatic polyisocyanates other than MDI-based isocyanates as polyisocyanate components, the internal resistance increased significantly after charge and discharge, and the charge-discharge cycle characteristics were poor. Furthermore, the adhesion between the current collector and the electrode active material was poor, and the electrode deformation after charge and discharge was also significant.

[0172] In Comparative Examples 4 and 5, where hydrogenated polybutadiene polyol was combined with MDI-based isocyanate but chain extension was performed using an amine-based chain extender, the increase in internal characteristics after charge and discharge could not be suppressed, perhaps because the electrode expansion caused by the use of silicon-based active materials could not be followed, resulting in poor charge and discharge cycle characteristics.

[0173] It should be noted that the various numerical ranges described in this specification can be arbitrarily combined with their upper and lower limits, and all combinations thereof are described in this specification as preferred numerical ranges. Furthermore, the description of the numerical range "X~Y" refers to X and below Y.

[0174] The foregoing has described several embodiments of the present invention, but these embodiments are given by way of example only and are not intended to limit the scope of the invention. These embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments, as well as their omissions, substitutions, and modifications, are included in the scope and spirit of the invention, and are also included in the scope of the invention as described in the claims and its equivalents.

Claims

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

2. The binder for electrodes of lithium secondary batteries according to claim 1, wherein, the carboxylic acid containing an active hydrogen group contains an aliphatic carboxylic acid having 2 hydroxyl groups.

3. The binder for electrodes of lithium secondary batteries according to claim 1, wherein, the polyol component further contains a polyol of three or more functionalities having a molecular weight of 500 or less.

4. The binder for electrodes of lithium secondary batteries according to claim 1, wherein, the polyurethane has an acid value of 8 mgKOH / g to 35 mgKOH / g.

5. The binder for electrodes of lithium secondary batteries according to claim 1, wherein, the salt of polyurethane is an alkali metal salt.

6. The binder for electrodes of lithium secondary batteries according to claim 1, wherein, the binder for electrodes of lithium secondary batteries is used for a negative electrode of a lithium secondary battery, the negative electrode of a lithium secondary battery containing at least one selected from the group consisting of SiO, SiC, Si, and a substance in which lithium ions are pre-doped among them as a negative electrode active material.

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

8. A negative electrode of a lithium secondary battery, characterized by comprising a negative electrode active material according to any one of claims 1 to 7. comprising: the binder for electrodes of claim 1 or the solid content of the binder composition for electrodes of claim 7; and a negative electrode active material containing at least one selected from the group consisting of SiO, SiC, Si, and a substance in which lithium ions are pre-doped among them.

9. A lithium secondary battery provided with the negative electrode of claim 8.

Images