JP5794942B2 - A binder for an electrode of a lithium secondary battery, and a lithium secondary battery using an electrode manufactured using the binder. - Google Patents

Description

  The present invention relates to a binder for an electrode of a lithium secondary battery, and a lithium secondary battery using an electrode manufactured using the binder.

  Recently, portable electronic devices such as mobile phones, notebook computers, personal digital assistants (PDAs), video cameras, and digital cameras have become widely used, and as these electronic devices are increasingly required to be smaller and lighter, drive power supplies There is an increasing demand for a battery that is smaller, lighter, thinner, and has a higher capacity, and research on this issue is actively underway. Lithium secondary batteries have high voltage and good energy density, and have been widely used as power sources for portable electronic devices. However, as the display industry has been reduced in size and weight, there is a need for a battery that is further reduced in size and weight, resulting in higher driving voltage, longer life, and longer life than conventional lithium secondary batteries. Improved battery characteristics such as high energy density are required. Recently, development of medium- or large-sized lithium secondary batteries for in-vehicle use, industrial use, etc. has been promoted, and there is an expectation for the development of high capacity and high output. Therefore, efforts to improve the performance of various components of the lithium battery are continued in order to satisfy such requirements. The characteristics of the battery are greatly influenced by the electrode, electrolyte and other battery materials used. In particular, in the case of electrodes, the characteristics are determined by the electrode active material, the current collector, and the binder that provides an adhesive force between them. Is determined. For example, the amount and type of active material used can determine the amount of lithium ions that can bind to the active material, the higher the amount of active material and the higher the specific capacity active material, the higher the capacity. A battery can be obtained. In addition, when the binder has an excellent adhesive force between the active materials and between the active material and the current collector, electrons and lithium ions move smoothly in the electrode, and the internal resistance of the electrode is reduced. Therefore, highly efficient charging / discharging becomes possible. In the case of a high-capacity battery, a composite electrode such as carbon and graphite, carbon and silicon is required as an anode active material, so that the volume expansion and contraction of the active material greatly occurs during charging and discharging. The binder must have excellent elasticity in addition to excellent adhesive force, and must maintain its original adhesive force and restoring force despite repeated considerable expansion and contraction of the electrode volume. As a binder for obtaining such an electrode, one obtained by dissolving a fluororesin such as polytetrafluoroethylene or polyvinylidene fluoride in an organic solvent is known. However, since the fluororesin is not sufficiently high in adhesion to the metal constituting the current collector and is not sufficiently high in flexibility, it can be obtained particularly when a wound battery is manufactured. There is a problem that a crack occurs in the obtained electrode layer, or peeling between the obtained electrode layer and the current collector occurs. In order to maintain sufficient adhesive strength, the amount of input must be large, so there is a limit to downsizing, and there is a disadvantage that manufacturing is complicated because it is used in combination with an organic solvent. . On the other hand, a binder made of styrene-butadiene latex (SBR) is known as a binder capable of forming a highly flexible electrode layer with high adhesion to the metal constituting the current collector. (Patent Documents 1, 2, and 3). Although it has excellent elastic characteristics, the adhesive strength is weak, and the structure of the electrode cannot be maintained as charging and discharging are repeated, and the battery life cannot be said to be sufficient. In recent years, due to the demand for higher battery capacity, there is a tendency to reduce the content of the binder component as a material constituting the electrode layer, and the electrode layer is subjected to press working in the electrode manufacturing process. Yes. However, in an electrode layer having a low binder component content, the electrode layer is easily peeled off from the current collector during pressing. Therefore, not only does the electrode material contaminate the press machine, but it has been pointed out that the electrode is incorporated in the battery in a state where a part of the electrode layer is peeled off, and the reliability of the battery performance is lowered. Such a problem becomes prominent when a polymer having a low glass transition temperature and a high tackiness is used as a binder component. Therefore, it is suppressed by using a latex having a high glass transition temperature, for example, room temperature or higher. can do. However, when a binder having a high glass transition temperature of the polymer is used, the obtained electrode layer has a problem that it is low in flexibility and easily cracks. The charge / discharge cycle characteristics cannot be obtained.

Japanese Patent Laid-Open No. 5-21068 Japanese Patent Laid-Open No. 11-7948 Japanese Patent Laid-Open No. 2001-210318

  The present invention has been made on the basis of the circumstances as described above, and its purpose is to have high adhesion to the current collector, no peeling during press working, high flexibility, An object of the present invention is to provide a lithium secondary battery excellent in charge and discharge characteristics using a binder excellent in adhesion and electrolyte resistance and an electrode manufactured using the binder.

(Component A) polyisocyanate, (Component B) a compound having two or more active hydrogen groups, (Component C) a compound having one or more active hydrogen groups and a hydrophilic group, and (Component D) a chain extender, A binder for an electrode of a lithium secondary battery comprising a polyurethane water dispersion comprising : a polyisocyanate having three or more isocyanate groups as the component (A) with respect to the polyurethane in the polyurethane water dispersion. A binder for an electrode of a lithium secondary battery, which is contained in an amount of 2% by weight to 30% by weight and the component (B) contains a polycarbonate polyol, a polyester polyol having an aromatic ring, and / or a polyether polyol having an aromatic ring. Is the first gist. The (Component A) preferably contains an alicyclic and / or aromatic isocyanate. The second gist of the present invention is a lithium secondary battery using an electrode using the binder for an electrode of the lithium secondary battery. That is, the present inventors obtain a binder that has high adhesion to the current collector, does not cause peeling during press processing, has high flexibility, and has excellent binding properties and electrolyte resistance. In order to achieve this, we have conducted extensive research. In the course of the study, (A component) polyisocyanate, (B component) a compound having two or more active hydrogen groups, (C component) a compound having one or more active hydrogen groups and a hydrophilic group, and (D Component: A binder for an electrode of a lithium secondary battery comprising a polyurethane water dispersion comprising a chain extender, wherein the (component A) is a polyurethane water dispersion of a polyisocyanate having three or more isocyanate groups. A polyurethane water dispersion containing 2% by weight or more and 30% by weight or less with respect to the polyurethane in the body , wherein the component (B) contains a polycarbonate polyol, a polyester polyol having an aromatic ring, and / or a polyether polyol having an aromatic ring. The present inventors have found that the intended purpose can be achieved by using the binder for electrodes using the present invention.

  The binder for the electrode of the lithium secondary battery of the present invention has high adhesion to the current collector, does not cause peeling at the time of pressing, has high flexibility, and has binding properties and electrolyte resistance. It is excellent and a lithium secondary battery excellent in charge / discharge characteristics can be obtained by using an electrode using the binder.

  Next, embodiments of the present invention will be described in detail.

  The binder for an electrode of the lithium secondary battery of the present invention includes (A component) polyisocyanate, (B component) a compound having two or more active hydrogen groups, (C component) one or more active hydrogen groups and hydrophilicity. A binder for an electrode of a lithium secondary battery comprising a polyurethane water dispersion comprising a compound having a group and (D component) chain extender, wherein the (A component) has three or more isocyanate groups. It is a polyurethane water dispersion which contains the polyisocyanate which has and the said (B component) contains a polycarbonate polyol, the polyester polyol which has an aromatic ring, and / or the polyether polyol which has an aromatic ring.

  The bifunctional diisocyanate of the (component A) is not particularly limited, and diisocyanates generally used in the art can be used. Specific examples include aliphatic diisocyanates, alicyclic diisocyanates, aromatic diisocyanates, and araliphatic diisocyanates. Aliphatic diisocyanates include tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1, Examples include 5-diisocyanate and 3-methylpentane-1,5-diisocyanate. Examples of the alicyclic diisocyanate include isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane, and the like. be able to. Aromatic diisocyanates include tolylene diisocyanate, 2,2′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 4,4′-diphenylmethane diisocyanate (MDI), 4,4′-dibenzyl diisocyanate, 1,5- Examples thereof include naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, and 1,4-phenylene diisocyanate. Examples of the araliphatic diisocyanate include dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, α, α, α, α-tetramethylxylylene diisocyanate. It can also be used individually or in combination of 2 or more types.

As the trifunctional or higher polyisocyanate of (Component A), for example, the aforementioned bifunctional isocyanate is used as a main raw material, and these trimers (biuret or isocyanurate), adducts with trifunctional alcohols such as trimethylolpropane, Examples thereof include adducts with trifunctional phenols such as phloroglysin, formalin condensates of benzene isocyanate (polymethylene polyphenylene polyisocyanate), lysine triisocyanate, etc., and allophanate and / or isocyanurate bond-containing modified isocyanate mixtures. It can also be used individually or in combination of 2 or more types. Of the polyisocyanates, alicyclic and / or aromatic isocyanates are preferable from the viewpoint of binding properties and resistance to electrolytic solution. Specifically, the diisocyanate is 4,4′-dicyclohexylmethane diisocyanate, isophorone. As the diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane, and polyfunctional polyisocyanate, the isocyanurate type is preferable.
The content of the polyisocyanate having 3 or more isocyanate groups of the (Component A) is preferably 2% by weight or more and 30% by weight or less with respect to the polyurethane in the polyurethane water dispersion.

  The component (B) contains a polycarbonate polyol, a polyester polyol having an aromatic ring, and / or a polyether polyol having an aromatic ring.

  The polycarbonate polyol is not particularly limited, and a polycarbonate polyol generally used in the technical field can be used. Specifically, carbonate polyol of 1,6-hexanediol, carbonate polyol of 1,4-butanediol and 1,6-hexanediol, carbonate of 1,5-pentanediol and 1,6-hexanediol, 3- Carbonate polyols of methyl-1,5-pentanediol and 1,6-hexanediol, carbonates of 1,9-nonanediol and 2-methyl-1,8-octanediol, 1,4-cyclohexanedimethanol and 1,6 -Hexanediol carbonate, 1,4-cyclohexanedimethanol carbonate, and these are PCDL T-6001, T-6002, T-5651, T-5651, T-5650J, T manufactured by Asahi Kasei Chemicals Corporation. -4671, T-4672, Kuraray ( ) Kuraray polyol C-590, C-1050, C-1050R, C-1090, C-2050, C-2050R, C-2070, C-2070R, C-2090, C-2090R, C-3090, C -3090R, C-4090, C-4090R, C-5090, C-5090R, C-1065N, C-2065N, C-1015N, C-2015N and Ube Industries ETERNACOLL UH-50, UH-100 , UH-200, UH-300, UM-90 (3/1), UM-90 (1/1), UM-90 (1/3), UC-100, and the like.

  The polyester polyol having an aromatic ring can be generally obtained by condensation reaction of a dibasic acid and a dihydric alcohol. Specific examples of the dibasic acid include, but are not limited to, aromatic dibasic acids such as phthalic acid, isophthalic acid, terephthalic acid, 1,4-naphthalenedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid. . Specific examples of the dihydric alcohol include, but are not limited to, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3 -Aliphatic glycols such as methyl-1,5-pentanediol, alicyclic glycols such as cyclohexanediol, and aromatic glycols such as alkylene oxide adducts of bisphenol A.

  Specific examples of the polyether polyol having an aromatic ring include an alkylene oxide adduct of bisphenol A (ethylene oxide adduct, propylene oxide adduct of bisphenol A) and the like.

  In addition, as the component (B), polyester polyol and polyether polyol can be used in combination as long as the effects obtained in the present invention are not impaired. Specific examples of the polyether polyol include triols such as glycerin, hexanetriol, trimethylolethane, and trimethylolpropane, and alkanolamines such as triethanolamine, triisopropanolamine, and tributanolamine. To do. Moreover, what uses pentaerythritol as a starting material is mentioned as a tetrafunctional alcohol component. Using these polyhydric alcohols as starting materials, polyether polyols are synthesized by polyaddition of alkylene oxide in the presence of a basic catalyst. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, and tetrahydrofuran.

  The polycarbonate polyol, aromatic polyester polyol and / or polyether polyol having an aromatic ring preferably has a number average molecular weight of 300 or more and 3,000 or less. When the number average molecular weight is less than 300, the binding property is inferior, and when the number average molecular weight exceeds 3000, the electrolyte solution resistance is inferior.

  As said (B component), in order to localize a urethane bond in a molecule | numerator, you may add single-chain low molecular weight diols, such as ethylene glycol and 1, 4- butanediol. Moreover, in order to introduce | transduce a branched structure into a molecule | numerator as said (B component), the oxyalkylene derivative of a polyhydric alcohol and / or a polyhydric alcohol can be used. Specific examples of the compound include polyhydric alcohols such as trimethylolpropane, glycerin, and pentaerythritol, oxyalkylene derivatives thereof, polyhydric alcohols and oxyalkylene derivatives and polycarboxylic acids, polyhydric carboxylic acid anhydrides, or Mention may be made of ester compounds from polyvalent carboxylic acid esters. The component (B) may be added with a single-chain low molecular weight diol such as ethylene glycol or 1,4-butanediol in order to localize the urethane bond in the polyurethane. As described above, a branched structure is introduced into the polyurethane, and localization of the urethane bond is preferable because an effect of improving the electrolytic solution resistance of the electrode using the binder containing the urethane water dispersion can be obtained.

  Moreover, it is preferable that content of the said (B component) is 30 to 75 weight% with respect to the polyurethane in the said polyurethane water dispersion. When the content is less than 30% by weight, the binding property is inferior, and when it exceeds 75% by weight, the electrolytic solution resistance is inferior.

  (C component) of the present invention is a compound having one or more active hydrogen groups and a hydrophilic group.

  Examples of the hydrophilic group include an anionic hydrophilic group, a cationic hydrophilic group, and a nonionic hydrophilic group. Specifically, as the anionic hydrophilic group, a carboxyl group and a salt thereof, a sulfonic acid group and a salt thereof are cationic. Examples of the hydrophilic hydrophilic group include tertiary ammonium salts and quaternary ammonium salts, and the nonionic hydrophilic group includes a group consisting of ethylene oxide repeating units, a group consisting of ethylene oxide repeating units and other alkylene oxide repeating units, etc. Is mentioned.

  Examples of the compound containing one or more active hydrogen groups and a carboxyl group include 2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolvaleric acid, dioxymaleic acid, 2, In addition to carboxylic acid-containing compounds such as 6-dioxybenzoic acid and 3,4-diaminobenzoic acid, derivatives thereof, and salts thereof, polyester polyols obtained using these are included. Further examples include amino acids such as alanine, aminobutyric acid, aminocaproic acid, glycine, glutamic acid, aspartic acid, and histidine, and carboxylic acids such as succinic acid, adipic acid, maleic anhydride, phthalic acid, and trimellitic anhydride.

  Examples of the compound having one or more active hydrogen groups and sulfonic acid groups and salts thereof include, for example, 2-oxyethanesulfonic acid, phenolsulfonic acid, sulfobenzoic acid, sulfosuccinic acid, 5-sulfoisophthalic acid, sulfanilic acid, 1 , 3-phenylenediamine-4,6-disulfonic acid, sulfonic acid-containing compounds such as 2,4-diaminotoluene-5-sulfonic acid and their derivatives, and polyester polyols, polyamide polyols obtained by copolymerizing these, Examples thereof include polyamide polyester polyol. By neutralizing these carboxyl groups or sulfonic acid groups into salts, the finally obtained polyurethane can be made water-dispersible. Examples of the neutralizing agent in this case include non-volatile bases such as sodium hydroxide and potassium hydroxide, tertiary amines such as trimethylamine, triethylamine, dimethylethanolamine, methyldiethanolamine and triethanolamine, and volatile properties such as ammonia. Examples include bases. Neutralization can be performed before, during or after the urethanization reaction.

Examples of the compound containing one or more active hydrogen groups and a tertiary ammonium salt include alkanolamines such as methylaminoethanol and methyldiethanolamine. By neutralizing these with organic carboxylic acids such as formic acid and acetic acid and inorganic acids such as hydrochloric acid and sulfuric acid to form salts, the polyurethane can be made water-dispersible. Neutralization can be performed before, during or after the urethanization reaction. Of these, those obtained by neutralizing methyldiethanolamine with an organic carboxylic acid are preferred from the viewpoint of ease of emulsification.
A compound having one or more active hydrogen groups and a quaternary ammonium salt is obtained by converting the alkanolamine such as methylaminoethanol and methyldiethanolamine to a dialkyl sulfate such as methyl chloride and alkyl bromide such as methyl bromide and dimethyl sulfate. A quaternized compound. Among these compounds, methyldiethanolamine is quaternized with dimethylsulfate from the viewpoint of ease of emulsification.

  The compound having one or more active hydrogen groups and a nonionic hydrophilic group is not particularly limited, but is preferably a compound containing at least 30% by weight or more of ethylene oxide repeating units and having a number average molecular weight of 300 to 20,000. Nonionic groups such as polyoxyethylene glycol or polyoxyethylene-polyoxypropylene copolymer glycol, polyoxyethylene-polyoxybutylene copolymer glycol, polyoxyethylene-polyoxyalkylene copolymer glycol or monoalkyl ethers thereof Examples thereof include polyester compounds and polyester polyether polyols obtained by copolymerizing these compounds.

  As the (C component), the above compounds may be used alone or in combination.

In the case of an anionic hydrophilic group-containing compound, the content of (C component) is preferably 5 to 50 mgKOH / g, and more preferably 5 to 45 mgKOH / g, indicating the anionic hydrophilic group content. Is more preferable. When the acid value is less than 5 mgKOH / g, there is a problem that dispersibility in water becomes difficult. Moreover, when an acid value exceeds 50 mgKOH / g, there exists a problem that electrolyte solution resistance falls. When using a nonionic group containing compound, it is 1-30 weight part, It is preferable to use especially 5-20 weight part.

  Among these, (C component) is preferably a compound containing one or more active hydrogen groups and a carboxyl group in the molecule from the viewpoint of adhesion to the current collector.

  (D component) can use the chain extender generally used in the said technical field. Although not particularly limited, specifically, diamine or polyamine can be used. Examples of diamines include ethylene diamine, trimethylene diamine, piperazine, isophorone diamine, and amino group-containing silane coupling agents. Examples of polyamines include diethylene triamine, dipropylene triamine, and triethylene tetramine. . As the component (D), in order to introduce an internal cross-linked structure of polyurethane and improve the electrolytic solution resistance, it is preferable to contain a triamine or higher polyamine. Specific examples of the polyamine include the polyamines described above.

  The number average molecular weight of the polyurethane in the polyurethane water dispersion of the present invention is preferably as large as possible by introducing a branched structure or an internal cross-linked structure, and is preferably 50,000 or more. This is because when the molecular weight is increased to make it insoluble in a solvent, a coating film excellent in electrolytic solution resistance can be obtained.

  The method for producing the polyurethane water dispersion of the present invention is not particularly limited, but in general, (Component B) a compound having two or more active hydrogen groups, (Component C) one or more activities A stoichiometric excess of the (A component) polyisocyanate from the sum of the hydrogen groups, the compound having a hydrophilic group, and the active hydrogen group having reactivity with the isocyanate group contained in the (D component) chain extender. (Equivalent ratio of isocyanate group and reactive functional group: 1: 0.85 to 1.1) was reacted in the absence of a solvent or in an organic solvent having no active hydrogen group to synthesize an isocyanate-terminated urethane prepolymer. Thereafter, the anionic hydrophilic group or the cationic hydrophilic group (component C) is neutralized or quaternized as necessary, and then dispersed and emulsified in water. Then, an isocyanate group in the emulsion micelle is added by adding an equivalent (D component) chain extender (equivalent ratio of isocyanate group to chain extender 1: 0.5 to 0.9) less than the remaining isocyanate group. (Component D) A chain extender is subjected to an interfacial polymerization reaction to form a urea bond. Thereby, the crosslinking density in the emulsified micelle is improved, and a three-dimensional crosslinked structure is formed. Thus, by forming the three-dimensional crosslinked structure, a coating film having excellent electrolytic solution resistance can be obtained. Then, the polyurethane water dispersion can be obtained by removing the solvent used as needed. In addition, chain extension can also be performed by water molecules present in the system during dispersion emulsification in water without using polyamine or the like as the (D component). In addition, in the synthesis | combination of a urethane prepolymer, you may use the solvent which is inactive with an isocyanate group and can melt | dissolve the urethane prepolymer to produce | generate. Examples of these solvents include dioxane, methyl ethyl ketone, dimethylformamide, tetrahydrofuran, N-methyl-2-pyrrolidone, toluene, and propylene glycol monomethyl ether acetate. These hydrophilic organic solvents used in the reaction are preferably finally removed.

  The average particle size of the polyurethane water dispersion of the present invention is preferably in the range of 0.005 to 0.5 μm from the viewpoint of the amount added, coating properties, and binding properties.

The crosslink density of the polyurethane resin of the polyurethane water dispersion of the present invention is preferably 0.01 to 0.50 per 1000 molecular weight of the polyurethane resin. Here, the crosslinking density can be determined by calculating according to the following equation (1). That is, the polyisocyanate (A) having a molecular weight MW _A1 and the functional group number F _A1 is WA ₁ g, the polyisocyanate (A) having a molecular weight MW _A2 and the functional group number F _A2 is WA ₂ g, the molecular weight MW _AJ and the functional group number F _AJ the polyisocyanate (a) and W _{Aj g} and (j is an integer of 1 or more), the molecular weight MW _B1, the active hydrogen group-containing compound functional groups F _B1 and (B) and W _B1 g, molecular weight MW _B2 and functionality The active hydrogen group-containing compound (B) of F _B2 is W _B2 g, the molecular weight MW _Bk and the active hydrogen group-containing compound (B) having the functional group number F _Bk is _WBkg (k is an integer of 1 or more), and the molecular weight MW _The compound (C) having one or more active hydrogen groups having a functional group number F _C1 and a hydrophilic group (C) having W _C1 g, a molecular weight MW _Cm and one or more active hydrogen groups having a functional group number F _Cm and a hydrophilic group Compound (C) is W _Cmg (m is an integer of 1 or more), molecular weight MW ₁ , and chain extender (D) having a functional group number F ₁ is WD ₁ g and molecular weight MW _Dn, crosslink density per 1000 molecular weight chain length agent functionality F _dn the (D) W _Dn g (n is an integer of 1 or more) resin solid content contained in the aqueous polyurethane dispersion obtained by reacting the Can be calculated by the following formula.

When the crosslink density is 0.01 or less, the crosslink density is low, so that the electrolytic solution resistance and heat resistance are poor. When it exceeds 0.50, the flexibility of the polyurethane resin is lowered and the binding property is poor.

  In the polyurethane water dispersion of the present invention, the urethane bond amount in the urethane resin is preferably 150 to 2000 g / eq, and more preferably 200 to 1000 g / eq. When the urethane bond amount is 150 g / eq or less, the urethane bond amount is too large, so that the flexibility of the polyurethane resin is lowered and the binding property is poor, and when it exceeds 2000 g / eq, the electrolytic solution resistance and the heat resistance are poor. In the polyurethane water dispersion of the present invention, the urea bond amount in the urethane resin is preferably 300 to 20000 g / eq, and more preferably 400 to 10000 g / eq. When the urea bond amount is 300 g / eq or less, the urea bond amount is too large, so the flexibility of the polyurethane resin is lowered and the binding property is inferior. When it exceeds 20000 g / eq, workability during synthesis may be deteriorated. , And the electrolyte solution resistance and heat resistance are inferior.

  In the present invention, a crosslinking agent may be used in combination with the polyurethane resin aqueous dispersion. Specific examples of the cross-linking agent include aziridines, oxazolines, modified polyisocyanates, polyepoxide compounds, and the like. The cross-linking agents may be used alone or in combination.

  The positive electrode and the negative electrode used in the lithium secondary battery of the present invention include an electrode active material, a conductive agent, a current collector of the electrode active material, and a binder that binds the electrode active material and the conductive agent to the current collector. Composed.

  The lithium secondary battery of this invention is comprised from the electrode manufactured using the binder containing the said polyurethane water dispersion. The binder can be used for either the positive electrode or the negative electrode.

  In the lithium secondary battery of the present invention, as the binder for the electrode that does not use the polyurethane resin aqueous dispersion, polyvinylidene fluoride, polyvinylidene fluoride, hexafluoropropylene, perfluoromethyl vinyl ether, and tetrafluoroethylene are used. Polymers such as polyvinylidene fluoride copolymer resins such as copolymers, fluororesins such as polytetrafluoroethylene and fluororubber, styrene-butadiene rubber, ethylene-propylene rubber, styrene-acrylonitrile copolymer can be used. Although there is, it is not limited to this.

The positive electrode active material used for the positive electrode of the lithium secondary battery of the present invention is not particularly limited as long as it can insert and desorb lithium ions. Examples include metal oxides such as CuO, Cu ₂ O, MnO ₂ , MoO ₃ , V ₂ O ₅ , CrO ₃ , MoO ₃ , Fe ₂ O ₃ , Ni ₂ O ₃ , CoO ₃ , LixCoO ₂ , LixNiO _2. , LixMn ₂ O ₄ , LiFePO ₄ and other complex oxides of lithium and transition metals, TiS ₂ , MoS ₂ , NbSe _{3 and} other metal chalcogenides, polyacene, polyparaphenylene, polypyrrole, polyaniline and other conductive polymers Compounds and the like. Among these, a composite oxide of lithium and one or more selected from transition metals such as cobalt, nickel, and manganese, which is generally called a high voltage system, is preferable in terms of lithium ion release properties and high voltage. . Specific examples of the composite oxide of cobalt, nickel, manganese and lithium include LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNixCo (1-x) O ₂ , LiMnaNibCoc (a + b + c = 1) and the like. It is done. In addition, these lithium composite oxides doped with a small amount of elements such as fluorine, boron, aluminum, chromium, zirconium, molybdenum, iron, etc., or the surface of lithium composite oxide particles are made of carbon, MgO, Al ₂ O ₃ , those treated with SiO ₂ or the like can also be used. Two or more kinds of the positive electrode active materials can be used in combination.

As the negative electrode active material used for the negative electrode of the present invention, any known active material can be used without particular limitation as long as it can insert / extract metallic lithium or lithium ions. For example, carbon materials such as natural graphite, artificial graphite, non-graphitizable carbon, and graphitizable carbon can be used. In addition, metallic materials such as metallic lithium, alloys, tin compounds, lithium transition metal nitrides, crystalline metal oxides, amorphous metal oxides, silicon compounds, conductive polymers, etc. can be used. , Li ₄ Ti ₅ O ₁₂ , NiSi ₅ C _{6 and the} like.

  A conductive agent is used for the positive electrode and the negative electrode of the lithium secondary battery of the present invention. Any electrically conductive material that does not adversely affect battery performance can be used as the conductive agent. Usually, carbon black such as acetylene black and ketchin black is used, but natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), artificial graphite, carbon whisker, carbon fiber and metal (copper, nickel, aluminum, A conductive material such as silver, gold, etc.) powder, metal fiber, or conductive ceramic material may be used. These can be included as a mixture of two or more. The addition amount is preferably 0.1 to 30% by weight, particularly preferably 0.2 to 20% by weight, based on the amount of the active material.

  As the current collector for the electrode active material of the lithium secondary battery of the present invention, any electronic conductor can be used as long as it does not adversely affect the constructed battery. For example, as a positive electrode current collector, aluminum, titanium, stainless steel, nickel, calcined carbon, conductive polymer, conductive glass, etc., in addition to aluminum for the purpose of improving adhesiveness, conductivity, and oxidation resistance. A material obtained by treating the surface of copper or copper with carbon, nickel, titanium, silver or the like can be used. In addition to the current collector for negative electrode, copper, stainless steel, nickel, aluminum, titanium, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., adhesion, conductivity, oxidation resistance For the purpose of improving the properties, it is possible to use a surface of copper or the like treated with carbon, nickel, titanium, silver or the like. The surface of these current collector materials can be oxidized. Moreover, about the shape, molded bodies, such as a film form, a sheet form, a net form, the punched or expanded thing, a lath body, a porous body, and a foam other than foil shape, are also used. The thickness is not particularly limited, but a thickness of 1 to 100 μm is usually used.

  The electrode of the lithium secondary battery of the present invention is a paste prepared by mixing an electrode active material, a conductive agent, a current collector of the electrode active material, and a binder that binds the electrode active material and the conductive agent to the current collector. Can be manufactured by preparing a solid electrode material and applying it to an aluminum foil or copper foil to be a current collector and volatilizing the dispersion medium.

  In the electrode material of the present invention, a thickener such as a water-soluble polymer can be used as a viscosity modifier for pasting. Specifically, celluloses such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxymethylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose; polycarboxylic acid-based compounds such as polyacrylic acid and sodium polyacrylate; polyvinylpyrrolidone and the like A compound having a vinylpyrrolidone structure; one or more selected from polyacrylamide, polyethylene oxide, polyvinyl alcohol, sodium alginate, xanthan gum, carrageenan, guar gum, agar, starch and the like can be used, among which carboxymethylcellulose salt Is preferred.

  The method and order of mixing the electrode materials are not particularly limited. For example, the active material and the conductive agent can be mixed and used in advance. For mixing in this case, a mortar, a mill mixer, a planetary ball mill is used. Alternatively, a ball mill such as a shaker type ball mill, a mechano-fusion, or the like can be used.

  As the separator used in the lithium secondary battery of the present invention, a separator used in a normal lithium secondary battery can be used without particular limitation, and examples thereof include porous materials made of polyethylene, polypropylene, polyolefin, polytetrafluoroethylene, and the like. Resin, ceramic, non-woven fabric and the like.

  The electrolytic solution used in the lithium secondary battery of the present invention may be an electrolytic solution used in a normal lithium secondary battery, and common ones such as an organic electrolytic solution and an ionic liquid can be used.

Examples of the electrolyte salt used in the lithium secondary battery of the present invention include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCl, LiBr, LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiI, LiAlCl ₄ , NaClO ₄ , NaBF ₄ , NaI, and the like. In particular, inorganic lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (SO ₂ CxF2x + 1) An organic lithium salt represented by (SO ₂ CyF2y + 1) can be given. Here, x and y represent 0 or an integer of 1 to 4, and x + y is 2 to 8. Specifically, as the organic lithium salt, LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₂ F ₅ ), LiN (SO ₂ CF ₃ ) (SO ₂ C ₃ F ₇ ) LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) (SO ₂ C ₃ F ₇ ), LiN (SO ₂ C ₂ F ₅ ) (SO ₂ C ₄ F ₉ ) and the like. Among them, it is preferable to use LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiN (SO ₂ F) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ or the like as the electrolyte because it has excellent electrical characteristics. The above electrolyte salt may be used alone or in combination of two or more. Such a lithium salt is usually contained in the electrolytic solution at a concentration of 0.1 to 2.0 mol / liter, preferably 0.3 to 1.5 mol / liter.

  The organic solvent for dissolving the electrolyte salt of the lithium secondary battery of the present invention is not particularly limited as long as it is an organic solvent used for a non-aqueous electrolyte solution of a normal lithium secondary battery. For example, a carbonate compound, a lactone compound, Examples include ether compounds, sulfolane compounds, dioxolane compounds, ketone compounds, nitrile compounds, and halogenated hydrocarbon compounds. Specifically, carbonates such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, ethylene glycol dimethyl carbonate, propylene glycol dimethyl carbonate, ethylene glycol diethyl carbonate, vinylene carbonate, lactones such as γ-butyl lactone, Ethers such as dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,4-dioxane, sulfolanes such as sulfolane and 3-methylsulfolane, dioxolanes such as 1,3-dioxolane, 4-methyl-2- Ketones such as pentanone, nitriles such as acetonitrile, pyropionitrile, valeronitrile, benzonitrile, 1,2-di Halogenated hydrocarbons such as Roroetan, other methyl formate, dimethyl formamide, diethyl formamide, dimethyl sulfoxide, imidazolium salts, and ionic liquids such as such as quaternary ammonium salts. Furthermore, a mixture thereof may be used. Among these organic solvents, it is particularly preferable to contain one or more types of non-aqueous solvents selected from the group consisting of carbonates because they are excellent in electrolyte solubility, dielectric constant and viscosity.

  In the lithium secondary battery of the present invention, when used as a polymer electrolyte or a polymer gel electrolyte, the polymer compounds such as ether, ester, siloxane, acrylonitrile, vinylidene fluoride, hexafluoropropylene, acrylate, methacrylate, styrene, vinyl acetate , Polymers such as vinyl chloride and oxetane, polymers having a copolymer structure thereof, or cross-linked products thereof, and the like may be one kind or two or more kinds. The polymer structure is not particularly limited, but a polymer having an ether structure such as polyethylene oxide is particularly preferable.

  In the lithium secondary battery of the present invention, a liquid battery is an electrolyte solution, a gel battery is a precursor solution in which a polymer is dissolved in an electrolyte solution, and a solid electrolyte battery is a polymer before crosslinking in which an electrolyte salt is dissolved in a battery container. Accommodate.

  The lithium secondary battery according to the present invention can be formed into a cylindrical shape, a coin shape, a square shape, or any other shape, and the basic configuration of the battery is the same regardless of the shape, and the design is changed according to the purpose. Can be implemented. For example, in a cylindrical type, a wound body in which 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 through a separator. It is housed in a battery can, sealed with a non-aqueous electrolyte injected, and insulating plates placed on top and bottom. 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 stored in a coin-type battery can, and a non-aqueous electrolyte is injected. Sealed.

Next, examples will be described together with comparative examples. However, the present invention is not limited to these examples.
[Synthesis of polyurethane water dispersion]
(Synthesis Example 1)
A four-necked flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen blowing tube was charged with Newpol BPE-20NK (trade name, manufactured by Sanyo Chemical Industries, Ltd., ethylene oxide adduct of bisphenol A, average hydroxyl value of 360 mgKOH / g). , Active hydrogen groups 2) 121.4 parts by weight, dimethylolpropionic acid (active hydrogen groups 2) 16.3 parts by weight, dicyclohexylmethane diisocyanate 138.2 parts by weight, duranate 24A-100 (trade name, manufactured by Asahi Kasei Chemicals, 24.0 parts by weight of biuret type isocyanate) and 200 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 a urethane prepolymer having a free isocyanate group content of 3.5% based on the nonvolatile content. The solution was cooled to 45 ° C., neutralized by adding 12.3 parts by weight of triethylamine, and then 900 parts by weight of water was gradually added and emulsified and dispersed using a homogenizer. Subsequently, an amine aqueous solution in which 6.6 parts by weight of ethylenediamine (2 active hydrogen groups) was diluted with 100 parts by weight of water was added, and a chain extension reaction was performed for 1 hour. The solvent was removed under reduced pressure at 50 ° C. to obtain a polyurethane water dispersion A having a nonvolatile content of about 30%.
(Synthesis Example 2)
Newpol BPE-20NK 121.4 parts by weight Kuraray polyol P-1020 (trade name, manufactured by Kuraray Co., Ltd., polyester polyol comprising 3-methyl-1,5-pentanediol and terephthalic acid, average hydroxyl value 110 mgKOH / g, activity 2) Same as Synthesis Example 1 except that 177.2 parts by weight, dicyclohexylmethane diisocyanate was changed to 87.0 parts by weight, duranate 24A-100 was changed to 19.5 parts by weight, and ethylenediamine was changed to 4.5 parts by weight. The polyurethane water dispersion B was obtained.
(Synthesis Example 3)
New Paul BPE-20NK 121.4 parts by weight Duranol T-4671 (trade name, manufactured by Asahi Kasei Chemicals, polycarbonate polyol, average hydroxyl value 112 mgKOH / g, number of active hydrogen groups 2) 190.7 parts by weight dicyclohexylmethane diisocyanate 138 2 parts by weight of isophorone diisocyanate 78.0 parts by weight and Duranate 24A-100 24.0 parts by weight of Duranate TPA-100 (trade name, manufactured by Asahi Kasei Chemicals Corporation, isocyanurate type isocyanate) 15.0 parts by weight of ethylenediamine A polyurethane water dispersion C was obtained in the same manner as in Synthesis Example 1 except that 6.6 parts by weight was changed to 9.2 parts by weight of metaxylenediamine (number of active hydrogen groups 2).
(Synthesis Example 4)
A polyurethane water dispersion D was obtained in the same manner as in Synthesis Example 3 except that 9.2 parts by weight of metaxylenediamine was changed to 4.6 parts by weight of diethylenetriamine (number of active hydrogen groups 3).
(Synthesis Example 5)
New Paul BPE-20NK 121.4 parts by weight Duranol T-4671 202.7 parts by weight, dicyclohexylmethane diisocyanate 138.2 parts by weight tolylene diisocyanate 63.0 parts by weight, Duranate 24A-100 24.0 parts by weight Except that the chain extension reaction with ethylenediamine was changed to the chain extension reaction with water to 24 parts by weight (18 parts by weight solids) of Coronate L (trade name, manufactured by Nippon Polyurethane Industry, TDI-TMP adduct, solid content 75%) Manufacture was carried out in the same manner as in Synthesis Example 1 to obtain polyurethane water dispersion E.
(Synthesis Example 6)
New Pole BPE-20NK 121.4 parts by weight ETERNACOLL UM-90 (1/3) (product name, Ube Industries, polycarbonate polyol, average hydroxyl value 125 mgKOH / g, number of active hydrogen groups 2) 160.4 parts by weight Trimethylolpropane (number of active hydrogen groups 3) was changed to 3.0 parts by weight, dicyclohexylmethane diisocyanate was changed to 96.3 parts by weight, and ethylenediamine 6.6 parts by weight was changed to 14.8 parts by weight of isophoronediamine (number of active hydrogen groups 2). Except for the above, production was carried out in the same manner as in Synthesis Example 1 to obtain a polyurethane water dispersion F.
(Synthesis Example 7)
121.4 parts by weight of New Pole BPE-20NK is polyTHF 1000 (trade name, manufactured by BASF, polytetramethylene ether glycol, average hydroxyl value 110 mg KOH / g, number of active hydrogen groups 2) 177.2 parts by weight of dicyclohexylmethane diisocyanate A polyurethane water dispersion G was obtained in the same manner as in Synthesis Example 1 except that 106.5 parts by weight of ethylenediamine was changed to 5.5 parts by weight.
(Synthesis Example 8)
Newpol BPE-20NK 121.4 parts by weight Kuraray polyol P-1010 (trade name, manufactured by Kuraray Co., Ltd., polyester polyol comprising 3-methyl-1,5-pentanediol and adipic acid, average hydroxyl value 110 mgKOH / g, activity Production was carried out in the same manner as in Synthesis Example 1 except that 190.7 parts by weight of hydrogen groups, 138.2 parts by weight of dicyclohexylmethane diisocyanate were changed to 93.0 parts by weight of isophorone diisocyanate, and 5.4 parts by weight of ethylenediamine were changed. A polyurethane water dispersion H was obtained.
[Evaluation of polyurethane water dispersion]
The following methods were used for each measurement regarding the obtained polyurethane water dispersion. The results are shown in Table 1 below.
(Nonvolatile content of polyurethane water dispersion)
It measured according to JIS K 6828.
(Crosslinking density in resin solids of polyurethane water dispersion)
It was calculated from the formula (1).
(Measurement of average particle size of polyurethane water dispersion)
The average particle size was measured with Microtrac UPA-UZ152 (manufactured by Nikkiso Co., Ltd.), and the 50% average value was calculated as the particle size.
(Acid value of polyurethane resin, urethane bond amount, urea bond amount)
It calculated from the charged amount at the time of the synthesis | combination of a urethane resin, and the free isocyanate group content with respect to the non volatile matter after reaction.

[Production of electrodes]
Table 2 below shows the binder used in the production of the electrodes.

[Preparation of negative electrode]
(Negative electrode 1)
100 g of natural graphite as a negative electrode active material, 0.5 g of carbon black as a conductive agent (Supercal-P, manufactured by Timcal) and carboxymethyl cellulose (CMC) as a thickener (Daiichi Kogyo Seiyaku, product name: Cellogen WS-C) 100 g of a 2 wt% aqueous solution and 6.7 g of a 30 wt% solution of the polyurethane water dispersion A as a binder were mixed with a planetary mixer to prepare a negative electrode slurry so as to have a solid content of 50%. This negative electrode slurry was coated on an electrolytic copper foil having a thickness of 10 μm with a coating machine, dried at 120 ° C., and then subjected to a roll press treatment, to obtain a negative electrode 1 having a negative electrode active material of 7 mg / cm ² .
(Negative electrode 2-9)
The polyurethane water dispersion A was prepared in the same manner as the negative electrode 1 except that the polyurethane water dispersion A in Table 2 was changed to SBR.
(Negative electrode 10)
As a negative electrode active material, SiO (average particle size 4.5 μm, specific surface area 5.5 m ² / g) 100 g, as a conductive agent 5 g of carbon black (manufactured by Timcal, Super-P) and as a thickener carboxymethyl cellulose (CMC) (Daiichi Kogyo Seiyaku Co., Ltd., product name: Serogen WS-C) 2% by weight aqueous solution 100g, and 30% by weight polyurethane water dispersion D 6.7g as a binder were mixed with a planetary mixer, solid content 50% A negative electrode slurry was prepared so that This negative electrode slurry was coated on an electrolytic copper foil having a thickness of 10 μm with a coating machine, dried at 120 ° C., and then subjected to a roll press treatment to obtain a negative electrode having a negative electrode active material of 2.5 mg / cm ² .
(Negative electrode 11)
It was prepared in the same manner as the negative electrode 10 except that the polyurethane water dispersion was changed to SBR.
(Negative electrode 12)
As a negative electrode active material, Li ₄ Ti ₅ O ₁₂ 100 g, as a conductive agent 5 g of carbon black (manufactured by Timcal, Super-P) and as a thickener carboxymethylcellulose (CMC) (Daiichi Kogyo Seiyaku, product name: Serogen WS— C) 100 g of a 2 wt% aqueous solution and 6.7 g of a 30 wt% solution of the polyurethane water dispersion F as a binder were mixed with a planetary mixer to prepare a negative electrode slurry so as to have a solid content of 50%. This negative electrode slurry was coated on an electrolytic copper foil having a thickness of 10 μm with a coating machine, dried at 120 ° C., and then subjected to a roll press treatment to obtain a negative electrode having a negative electrode active material of 9.7 mg / cm ² .
(Negative electrode 13)
It was prepared in the same manner as the negative electrode 12 except that the polyurethane water dispersion was changed to SBR.
[Preparation of positive electrode]
(Positive electrode 1)
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ 100 g as a positive electrode active material, 7.8 g of carbon black (Super-P, manufactured by Timcal) as a conductive agent, 6 g of polyvinylidene fluoride as a binder, dispersion As a medium, 61.3 g of N-methyl-2-pyrrolidone (NMP) was mixed with a planetary mixer to prepare a positive electrode slurry so as to have a solid content of 65%. This positive electrode slurry was coated on an aluminum foil having a thickness of 20 μm with a coating machine, dried at 130 ° C., and then subjected to a roll press treatment to obtain a positive electrode having a positive electrode active material of 13.8 mg / cm ² .
(Positive electrode 2-3)
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ 100 g as the positive electrode active material, 7.8 g of carbon black (manufactured by Timcal, Super-P) as the conductive agent, and carboxymethyl cellulose (CMC) as the thickener ( Daiichi Kogyo Seiyaku Co., Ltd., Product Name: Serogen WS-C) 100 g of 2 wt% aqueous solution and 6.7 g of the 30 wt% solution of polyurethane water dispersion shown in Table 2 as a binder were mixed with a planetary mixer, and the solid content was 50%. A positive electrode slurry was prepared so that This positive electrode slurry was coated on an aluminum foil having a thickness of 20 μm with a coating machine, dried at 130 ° C., and then subjected to a roll press treatment to obtain a positive electrode having a positive electrode active material of 13.8 mg / cm ² .
(Positive electrode 4)
100 g of LiMn ₂ O _{4 as} a positive electrode active material, ₅ g of carbon black (manufactured by Timcal, Super-P) as a conductive agent, 6 g of polyvinylidene fluoride as a binder, and N-methyl-2-pyrrolidone (NMP) as a dispersion medium 59.8 g was mixed with a planetary mixer to prepare a positive electrode slurry so as to have a solid content of 65%. This positive electrode slurry was coated on an aluminum foil having a thickness of 20 μm with a coating machine, dried at 130 ° C., and then subjected to a roll press treatment to obtain a positive electrode having a positive electrode active material of 22 mg / cm ² .
(Positive electrode 5)
LiMn ₂ O ₄ 100 g as a positive electrode active material, carbon black (manufactured by Timcal, Super-P) as a conductive agent, 5 g, carboxymethyl cellulose (CMC) as a thickener (product name: Cellogen WS-C ) 100 g of a 2 wt% aqueous solution and 6.7 g of the 30 wt% solution of the polyurethane water dispersion shown in Table 2 as a binder were mixed with a planetary mixer to prepare a positive electrode slurry so as to have a solid content of 50%. This positive electrode slurry was coated on an aluminum foil having a thickness of 20 μm with a coating machine, dried at 130 ° C., and then subjected to a roll press treatment to obtain a positive electrode having a positive electrode active material of 22 mg / cm ² .
(Positive electrode 6)
100 g of LiFePO _{4 as a} positive electrode active material, ₅ g of carbon black (Super-P, manufactured by Timcal) as a conductive agent, 6 g of polyvinylidene fluoride as a binder, and N-methyl-2-pyrrolidone (NMP) as a dispersion medium. 7g was mixed with the planetary mixer, and the positive electrode slurry was prepared so that it might become 45% of solid content. This positive electrode slurry was coated on an aluminum foil having a thickness of 20 μm with a coating machine, dried at 130 ° C., and then subjected to a roll press treatment to obtain a positive electrode having a positive electrode active material of 14.5 mg / cm ² .
(Positive electrode 7)
LiFePO ₄ 100 g as a positive electrode active material, carbon black (manufactured by Timcal, Super-P) as a conductive agent, 5 g, carboxymethyl cellulose (CMC) as a thickener (Daiichi Kogyo Seiyaku, product name: Serogen WS-C) 2 A positive electrode slurry was prepared so as to have a solid content of 50% by mixing 100 g of a weight% aqueous solution and 6.7 g of the 30% by weight polyurethane water dispersion shown in Table 2 as a binder with a planetary mixer. This positive electrode slurry was coated on an aluminum foil having a thickness of 20 μm with a coating machine, dried at 130 ° C., and then subjected to a roll press treatment to obtain a positive electrode having a positive electrode active material of 14.5 mg / cm ² .
[Electrode evaluation]
Evaluation was performed based on the following evaluation items and evaluation criteria.
(Evaluation of binding properties)
After the coated surface of the electrode obtained above was bent 180 ° outward and returned, the degree of falling off of the active material on the coated surface was visually determined. The results are shown in Table 2.
Evaluation criteria:
5 points: 0% dropout 4 points: 25% dropout 3 points: 50% dropout 2 points: 75% dropout 1 point: 100% dropout (electrolytic solution resistance evaluation)
The electrode obtained above was EC (ethylene carbonate) / PC (propylene carbonate) / DMC (dimethyl carbonate) / EMC (ethyl methyl carbonate) / DEC (diethyl carbonate) = 1/1/1/1/1 (vol). The appearance of the coating film after being immersed in the mixed solvent at 60 ° C. for 7 days was visually judged. The results are shown in Table 3 below.
Evaluation criteria ○: No change in the coating film △: Several points of swelling occur in the coating film ×: The coating film peels off.

[Create lithium secondary battery]
The positive electrode and negative electrode obtained above are combined as shown in Table 4 below, and a polyolefin (PE / PP) separator is sandwiched between the electrodes as a separator, and a positive electrode terminal and a negative electrode terminal are ultrasonically welded to each positive and negative electrode. did. This laminate was put in an aluminum laminate packaging material, and heat sealed, leaving an opening for injection. The positive electrode area of 18cm ^2, to prepare a liquid injection before batteries with anode area 19.8cm ^2. Next, an electrolytic solution in which LiPF ₆ (1.0 mol / L) was dissolved in a solvent in which ethylene carbonate and diethyl carbonate (30/70 vol ratio) were mixed was poured, the opening was heat sealed, and an evaluation battery was prepared. Obtained.

[Battery performance evaluation]
About the produced lithium secondary battery, the battery performance was evaluated according to the following evaluation items and evaluation criteria at 20 ° C. The results are shown in Table 5.
(Cell impedance)
For the cell impedance, an impedance analyzer (manufactured by ZAHNER) was used to measure the resistance value at a frequency of 1 kHz.
(Charge / discharge cycle characteristics)
The charge / discharge cycle characteristics were measured under the following conditions.
When LiNi _1/3 Co _1/3 Mn _1/3 O ₂ or LiMn ₂ O ₄ is used as the positive electrode active material and natural graphite is used as the negative electrode active material, CC (constant current) up to 4.2 V at a current density equivalent to 1C. ) Charging, followed by switching to CV (constant voltage) charging at 4.2V, charging for 1.5 hours, and then performing a CC discharge to 2.7V at a current density equivalent to 1C for 300 cycles at 20 ° C. The 1C discharge capacity ratio after 300 cycles to the initial 1C discharge capacity at this time was defined as the 1C charge / discharge cycle retention rate.
When LiFePO ₄ is used as the positive electrode active material and natural graphite is used as the negative electrode active material, CC (constant current) charging is performed up to 4.0 V at a current density equivalent to 1 C, followed by CV (constant voltage) charging at 4.0 V. After charging for 1.5 hours, a cycle of CC discharge to 2.0 V at a current density equivalent to 1 C is performed 300 cycles at 20 ° C., and the 1 C discharge capacity ratio after 300 cycles to the initial 1 C discharge capacity at this time is 1 C The charge / discharge cycle retention rate was used.
When LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is used as the positive electrode active material and Li ₄ Ti ₅ O ₁₂ is used as the negative electrode active material, CC (constant current) up to 2.9 V at a current density equivalent to 1C. Charge, then switch to CV (constant voltage) charge at 2.9V, charge for 1.5 hours, and then perform a cycle of CC discharge to 1.0V at a current density equivalent to 1C, 300 cycles at 20 ° C. The 1C discharge capacity ratio after 300 cycles with respect to the initial 1C discharge capacity was defined as the 1C charge / discharge cycle retention rate.
When LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is used as the positive electrode active material and SiO is used as the negative electrode active material, CC (constant current) charging is performed up to 4.2 V at a current density equivalent to 1 C, and then After switching to CV (constant voltage) charging at 4.2V and charging for 1.5 hours, 50 cycles of CC discharge to 2.7V at a current density equivalent to 1C were performed at 20 ° C, and the initial 1C discharge at this time The 1C discharge capacity ratio after 50 cycles with respect to the capacity was defined as the 1C charge / discharge cycle retention rate.

From Table 5, the case where the aqueous resin composition of the present invention is used is superior to the case where the conventionally used SBR or polyvinylidene fluoride is used, and the cell impedance is low, after the cycle characteristics. It can be seen that the capacity retention rate of is kept high.

The binder of this invention can be utilized as a binder of the electrode for lithium secondary batteries, and the electrode manufactured from it is used for manufacture of various lithium secondary batteries. The obtained lithium secondary battery is a medium- or large-sized lithium battery mounted on various portable devices such as mobile phones, notebook computers, personal digital assistants (PDAs), video cameras, and digital cameras, as well as electric bicycles and electric vehicles. Can be used for secondary batteries.

Claims (3)

(Component A) polyisocyanate, (Component B) a compound having two or more active hydrogen groups, (Component C) a compound having one or more active hydrogen groups and a hydrophilic group, and (Component D) a chain extender, A binder for an electrode of a lithium secondary battery comprising a polyurethane water dispersion comprising : a polyisocyanate having three or more isocyanate groups as the component (A) with respect to the polyurethane in the polyurethane water dispersion. A lithium secondary battery comprising 2% by weight or more and 30% by weight or less , wherein the component (B) contains a polycarbonate polyol, a polyester polyol having an aromatic ring, and / or a polyether polyol having an aromatic ring. Binder for electrodes. The binder for an electrode of a lithium secondary battery according to claim 1, wherein the (component A) contains an alicyclic and / or aromatic isocyanate. Lithium secondary battery, characterized by using an electrode with claim 1 or by an electrode binder for a lithium secondary battery according to any one of 2.