Binder for non-aqueous electrolyte secondary battery electrode, electrode composition for non-aqueous electrolyte secondary battery, and electrode for non-aqueous electrolyte secondary battery

Abstract

To provide a binder for non-aqueous electrolyte secondary battery electrode having excellent battery capacity retention, an electrode composition for non-aqueous electrolyte secondary battery and an electrode for non-aqueous electrolyte secondary battery electrode.SOLUTION: A binder for non-aqueous electrolyte secondary battery electrode contains at least carboxymethylcellulose with a carboxymethyl substitution degree per anhydrous glucose unit of cellulose of 0.5 to 1.2 and / or its salt, and molybdate. Preferably, the molybdate is contained in 30 to 200 wt.% to 100 wt.% as solid content of the carboxymethyl cellulose or its salt.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a binder for non-aqueous electrolyte secondary battery electrodes, an electrode composition for non-aqueous electrolyte secondary batteries, and an electrode for non-aqueous electrolyte secondary batteries.

Background Art

[0002] In recent years, electronic devices, particularly portable devices such as mobile phones, PDAs (personal digital assistants), and notebook computers, have become smaller, lighter, thinner, and more highly functional, and the spread of portable devices has advanced. Along with the diversification of the usage range of such portable devices, the batteries that drive them have become extremely important components. Among batteries, non-aqueous electrolyte secondary batteries typified by lithium-ion secondary batteries, which have a high energy density and a high capacity, are widely used.

[0003] Generally, a non-aqueous electrolyte secondary battery is manufactured as follows. That is, a negative electrode containing a negative electrode active material made of a carbon material capable of occluding and releasing lithium ions and the like, and a positive electrode containing a positive electrode active material made of a lithium-containing transition metal composite oxide (for example, LiCoO2, LiNiO2, LiMn2O4, etc.) are each formed in a sheet shape on the surface of a metal foil as a current collector substrate (current collector), and a sheet-shaped positive electrode and a sheet-shaped negative electrode are obtained. Then, the sheet-shaped positive electrode and the sheet-shaped negative electrode are wound or laminated via a separator also formed in a sheet shape and housed in a case. The sheet-shaped positive electrode and the sheet-shaped negative electrode have a structure including a metal foil serving as a current collector substrate (current collector) and a binder layer containing an active material formed on the surface thereof, and a negative electrode active material slurry (or paste) or a positive electrode active material slurry (or paste) can be applied and dried on the current collector material to form them.

[0004] The negative electrode active material slurry (paste) contains a binder in addition to a negative electrode active material made of a carbon material capable of occluding and releasing lithium ions and the like. As a binder, a binder for a negative electrode mainly composed of styrene / butadiene latex (SBR) is disclosed in Patent Document 1.

[0005] According to Patent Document 1, carboxymethyl cellulose as a water-soluble thickener is dissolved in water to prepare an aqueous solution, and SBR and a negative electrode active material are mixed therein to produce a slurry. The slurry is applied onto a substrate as a coating solution and dried to form a sheet-shaped negative electrode.

[0006] On the other hand, in the production of the positive electrode of a non-aqueous electrolyte secondary battery, organic solvents such as N-methyl-2-pyrrolidone (NMP) have conventionally been used as the solvent. However, in recent years, water has been used as the solvent in view of reducing the cost required for handling and the environmental impact during discharge.

[0007] The positive electrode active material slurry (paste) contains a binder in addition to a lithium-containing transition metal composite oxide (for example, LiCoO2, LiNiO2, LiMn2O4, etc.) as the positive electrode active material and carbon as the conductive material. As the binder, cellulose having a viscosity of 4000 mPa·s or more in a 1% aqueous solution, such as carboxymethyl cellulose, is described in Patent Document 2. Patent Document 2 describes that carboxymethyl cellulose is put into pure water together with a conductive material, polytetrafluoroethylene (PTFE), etc. to prepare an active material paste.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

[0009] However, both Patent Document 1 and Patent Document 2 had problems with the battery capacity retention rate after the cycle test.

[0010] Therefore, an object of the present invention is to obtain a binder for a non-aqueous electrolyte secondary battery electrode having an excellent battery capacity retention rate.

Summary of the Invention

Means for Solving the Problem

[0011] As a result of intensive efforts, the present inventors have found that the problems can be solved by the following [1] to [7]. That is, according to the present invention, 〔1〕 A binder for a non-aqueous electrolyte secondary battery electrode, comprising at least carboxymethyl cellulose having a carboxymethyl substitution degree of 0.5 to 1.2 per anhydrous glucose unit and / or a salt thereof and a molybdate. 〔2〕 The binder for a non-aqueous electrolyte secondary battery electrode according to [1], wherein the molybdate is contained in a range of 30 to 200% by weight based on 100% by weight of the solid content of the carboxymethyl cellulose or a salt thereof. 〔3〕 The carboxymethylated cellulose or a salt thereof is prepared by preparing 2 liters of a 0.3% by mass aqueous solution of the carboxymethyl cellulose or a salt thereof having a dry mass B, filtering all of it through a 250-mesh filter under reduced pressure conditions of -200 mmHg, and measuring the dry mass A of the residue on the filter after filtration. The binder for a non-aqueous electrolyte secondary battery electrode according to [1] or [2], wherein the ratio of the dry mass A to the dry mass B is less than 50 ppm. 〔4〕 The binder for a non-aqueous electrolyte secondary battery electrode according to any one of [1] to [3], wherein the molybdate contains at least one selected from ammonium molybdate and lithium molybdate. 〔5〕 An electrode composition for a non-aqueous electrolyte secondary battery, comprising the binder for a non-aqueous electrolyte secondary battery electrode according to any one of [1] to [4] and a silicon-based compound. 〔6〕 An electrode for a non-aqueous electrolyte secondary battery, using the electrode composition for a non-aqueous electrolyte secondary battery according to [5]. 〔7〕 A non-aqueous electrolyte secondary battery, using the electrode composition for a non-aqueous electrolyte secondary battery according to [5].

Advantages of the Invention

[0012] According to the present invention, a binder for a non-aqueous electrolyte secondary battery electrode having an excellent battery capacity retention rate can be obtained.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, a binder for a non-aqueous electrolyte secondary battery electrode of the present invention (hereinafter sometimes referred to as "binder for electrode") will be described. The binder for electrode of the present invention contains at least carboxymethyl cellulose having a degree of carboxymethyl substitution per anhydrous glucose unit of 0.5 to 1.2 and / or a salt thereof, and a molybdate.

[0014] <Component A: Carboxymethyl cellulose or a salt thereof> In the present invention, carboxymethyl cellulose or a salt thereof has a structure in which a hydroxyl group in a glucose residue constituting cellulose is substituted with a carboxymethyl ether group. Carboxymethyl cellulose may be in the form of a salt. Examples of the salt of carboxymethyl cellulose may include metal salts such as sodium carboxymethyl cellulose salt.

[0015] In the present invention, cellulose means a polysaccharide having a structure in which D-glucopyranose (simply referred to as "glucose residue", "anhydrous glucose" as well) is linked by β,1-4 bonds. Cellulose is generally classified into natural cellulose, regenerated cellulose, microcrystalline cellulose, microcrystalline cellulose excluding amorphous regions, etc. from the origin, production method, etc.

[0016] Examples of natural cellulose include bleached pulp or unbleached pulp (bleached wood pulp or unbleached wood pulp); linter, purified linter; cellulose produced by microorganisms such as acetic acid bacteria, etc. The raw materials for bleached pulp or unbleached pulp are not particularly limited, and examples include wood, cotton, straw, bamboo, etc. Also, the manufacturing method of bleached pulp or unbleached pulp is not particularly limited, and it may be a mechanical method, a chemical method, or a method combining the two in the middle. Examples of bleached pulp or unbleached pulp classified by the manufacturing method include mechanical pulp, chemical pulp, groundwood pulp, sulfite pulp, kraft pulp, etc. Furthermore, in addition to pulp for papermaking, dissolving pulp may be used. Dissolving pulp is chemically purified pulp, which is mainly dissolved in chemicals and used as the main raw material for artificial fibers, cellophane, etc.

[0017] Examples of regenerated cellulose include those obtained by dissolving cellulose in a solvent such as a copper-ammonia solution, a cellulose xanthate solution, a morpholine derivative, etc. and then spinning it again.

[0018] Examples of microcrystalline cellulose include those obtained by depolymerizing cellulose-based materials such as the above natural cellulose and regenerated cellulose (e.g., acid hydrolysis, alkaline hydrolysis, enzymatic hydrolysis, blasting treatment, vibration ball mill treatment, etc.), and those obtained by mechanically treating the cellulose-based materials.

[0019] It is important that the degree of carboxymethyl substitution per anhydroglucose unit of the carboxymethyl cellulose or its salt of the present invention is 0.5 or more, and more preferably 0.6 or more. If the degree of carboxymethyl substitution is less than 0.5, there is a risk that the dissolution in water will not be sufficient.

[0020] In the present invention, the anhydroglucose unit means each anhydroglucose (glucose residue) constituting cellulose. The degree of carboxymethyl substitution (also referred to as the degree of etherification) indicates the ratio of the hydroxyl groups (-OH) in the glucose residues constituting cellulose that are substituted with carboxymethyl ether groups (-OCH2COOH). The degree of carboxymethyl substitution may be abbreviated as DS or CM-DS.

[0021] The upper limit of the degree of carboxymethyl substitution per anhydroglucose unit of carboxymethyl cellulose or its salt is preferably 1.2 or less, more preferably 1.0 or less.

[0022] The degree of carboxymethyl substitution can be confirmed by measuring the amount of a base such as sodium hydroxide required to neutralize the carboxymethyl cellulose in the sample. In this case, when the carboxymethyl ether group of carboxymethyl cellulose or its salt is in the form of a salt, it should be converted to carboxymethyl cellulose in advance before measurement. During the measurement, back titration using a base and an acid, and appropriate combination of indicators such as phenolphthalein can be used.

[0023] In the present invention, carboxymethyl cellulose or its salt preferably has a viscosity of 1,000 to 20,000 mPa·s, more preferably 1,500 to 15,000 mPa·s, and even more preferably 2,000 to 10,000 mPa·s for a 1% by mass aqueous solution measured with a B-type viscometer (30 rpm) at 25°C. Since the viscosity within the above range makes it difficult to sediment and a good coating property electrode slurry can be prepared, it is suitable for non-aqueous electrolyte secondary batteries.

[0024] Also, for carboxymethyl cellulose or a salt thereof, when the dry mass of the residue on the filter when filtering all 2 liters of an aqueous solution containing 0.3% by mass of the carboxymethyl cellulose or its salt through a 250-mesh filter under a reduced pressure condition of -200 mmHg is defined as mass M, and the mass of the carboxymethyl cellulose or its salt dissolved in the aqueous solution is defined as mass m, the ratio of mass M to mass m is preferably less than 50 ppm. If it is 50 ppm or more, when an electrode is formed using carboxymethyl cellulose or its salt, appearance defects such as streaks and pinholes may occur in the electrode, and the quality of the battery may deteriorate. The lower limit of the ratio of mass M to mass m is not particularly limited, and the smaller the better.

[0025] In the present invention, the production method of carboxymethyl cellulose or its salt is not limited, and a known production method of carboxymethyl cellulose or its salt can be applied. That is, the carboxymethyl cellulose or its salt in the present invention can be produced by treating cellulose as a raw material with a mercerizing agent (alkali) to prepare mercerized cellulose (alkali cellulose), and then adding an etherifying agent to cause an etherification reaction.

[0026] As the raw material cellulose, any of the above-mentioned celluloses can be used without particular limitation, but those with high cellulose purity are preferred, and in particular, it is preferable to use dissolving pulp and linters. By using these, carboxymethyl cellulose or its salt with high purity can be obtained.

[0027] As the mercerizing agent, alkali metal hydroxide salts such as sodium hydroxide and potassium hydroxide can be used. As the etherifying agent, monochloroacetic acid, sodium monochloroacetate, etc. can be used.

[0028] In the case of the production method of general water-soluble carboxymethyl cellulose, the molar ratio of the mercerizing agent to the etherifying agent is generally 2.00 to 2.45 when monochloroacetic acid is used as the etherifying agent. The reason is that if it is less than 2.00, the etherification reaction may not proceed sufficiently, so unreacted monochloroacetic acid may remain and waste may occur, and if it exceeds 2.45, side reactions due to the excess mercerizing agent and monochloroacetic acid may proceed to produce alkali metal glycolate, which may be uneconomical.

[0029] In the present invention, carboxymethyl cellulose or its salt may be used as it is a commercially available product, or after being treated as necessary. Examples of commercially available products include the product named "Sun Rose" (sodium salt of carboxymethyl cellulose) manufactured by Nippon Paper Industries Co., Ltd.

[0030] [Grinding treatment] In the present invention, carboxymethyl cellulose or its salt may be used as it is the carboxymethyl cellulose or its salt as described above, or it may be further subjected to a grinding treatment (ground product). The grinding treatment is usually a mechanical grinding treatment using a machine. Examples of the method for grinding carboxymethyl cellulose or its salt include a dry grinding method for treating in a powder state and a wet grinding method for treating in a state of being dispersed or dissolved in a liquid. In the present invention, any of these may be selected.

[0031] When an aqueous solution of carboxymethyl cellulose or a salt thereof is prepared, gel particles derived from carboxymethyl cellulose or a salt thereof remain in the aqueous solution as undissolved matter. By mechanically dry or wet grinding carboxymethyl cellulose or a salt thereof, in an aqueous solution of the mechanically ground product of carboxymethyl cellulose or a salt thereof, the above gel particles are refined. As a result, when an electrode is formed using an aqueous solution of the mechanically ground product of carboxymethyl cellulose or a salt thereof, it is considered that coarse undissolved matter that causes streak-like defects (streaks), peeling, pinholes, etc. generated on the surface of the electrode can be further suppressed.

[0032] Examples of the grinding device that can be used for mechanical grinding treatment in the present invention include the following dry grinders and wet grinders.

[0033] Examples of the dry grinder include a cutting mill, an impact mill, a pneumatic mill, and a media mill. These can be used alone or in combination, and further, can be processed in multiple stages with the same model, but a pneumatic mill is preferred.

[0034] Examples of the cutting mill include a mesh mill (manufactured by Horai Co., Ltd.), an atoms (manufactured by Yamamoto Hyakuba Seisakusho Co., Ltd.), a knife mill (manufactured by Pallmann), a granulator (manufactured by Herbold), a rotary cutter mill (manufactured by Nara Kikai Seisakusho Co., Ltd.), etc.

[0035] Examples of the impact mill include a pulpizer (manufactured by Hosokawa Micron Corporation), a fine impact mill (manufactured by Hosokawa Micron Corporation), a super micron mill (manufactured by Hosokawa Micron Corporation), a sample mill (manufactured by Seishin Co., Ltd.), a bantam mill (manufactured by Seishin Co., Ltd.), an atomizer (manufactured by Seishin Co., Ltd.), a tornado mill (manufactured by Nikkiso Co., Ltd.), a turbo mill (manufactured by Turbo Kogyo Co., Ltd.), a bevel impactor (manufactured by Aikawa Tekko Co., Ltd.), etc.

[0036] Examples of the pneumatic mill include CGS type jet mill (manufactured by Mitsui Mining Co., Ltd.), jet mill (manufactured by Sanjo Industries Co., Ltd.), Ebara jet micronizer (manufactured by Ebara Corporation), Selen mirror (manufactured by Masayuki Sangyo Co., Ltd.), supersonic jet mill (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and the like.

[0037] Examples of the media mill include vibration ball mill and the like.

[0038] Examples of the wet grinder include Mascoloider (manufactured by Masayuki Sangyo Co., Ltd.), high-pressure homogenizer (manufactured by Sanmaru Kikai Kogyo Co., Ltd.), and media mill. Examples of the media mill include bead mill (manufactured by Aimex Co., Ltd.) and the like.

[0039] <Molybdate> It is important that the binder for the electrode of the present invention contains molybdate. The molybdate in the present invention includes potassium molybdate, sodium molybdate, calcium molybdate, lithium molybdate, ammonium molybdate, and the like. Among these, lithium molybdate and ammonium molybdate are preferred.

[0040] When such molybdate is used as a binder for the electrode together with carboxymethyl cellulose, the hydroxy group in the molybdate forms a cross-linked structure through hydrogen bonding with the carboxy group of carboxymethyl cellulose. In this cross-linked structure, more hydroxy groups and carboxyl groups are contained in the molecule than in carboxymethyl cellulose alone. Therefore, the reactivity with the negative electrode material such as SiOx dispersed in the negative electrode slurry through hydrogen bonding is increased. As a result, it is presumed that a stable oxide film can be formed on the surface of the negative electrode material such as SiOx, the decomposition of the electrolytic solution is suppressed, and the excessive thickness of the SEI film (Solid Electrolyte Interface) on the electrode surface is prevented, leading to an improvement in battery characteristics.

[0041] Further, when using lithium molybdate, molybdic acid can exhibit neutral or weak alkalinity when added to a binder for an electrode. When molybdic acid is not in the state of a lithium salt, the electrode composition in the form of an aqueous solution becomes strongly acidic, resulting in a decrease in the viscosity of the electrode composition and uneven distribution of polarity, which causes unevenness when applying the electrode composition to a current collector, so this is not preferable. Furthermore, since molybdic acid is a lithium salt, the incorporation of impurities is reduced when using a lithium-based active material, making it easier to exhibit electrical performance.

[0042] <Binder for electrode> The binder for a non-aqueous electrolyte secondary battery electrode of the present invention importantly contains at least carboxymethyl cellulose having a carboxymethyl substitution degree of 0.5 to 1.2 per anhydrous glucose unit as described above and / or a salt thereof, and a molybdate. Such a binder for an electrode preferably contains a molybdate in the range of 30 to 200% by weight, more preferably in the range of 40 to 170% by weight, and even more preferably in the range of 50 to 150% by weight, based on carboxymethyl cellulose or a salt thereof. When the blending ratio is within this range, it is presumed that the formation of the cross-linked structure of carboxymethyl cellulose and molybdate described above occurs more effectively.

[0043] The binder for an electrode of the present invention can also be made into an aqueous solution. The production conditions for such an aqueous solution are not particularly limited. For example, the binder for an electrode can be added to water (such as distilled water, purified water, tap water, etc.) and dissolved by stirring or the like as necessary. Also, after dissolving carboxymethyl cellulose or a salt thereof in water or the like, a molybdate can be added and dissolved by stirring or the like. Similarly, after dissolving a molybdate in water or the like, carboxymethyl cellulose or a salt thereof can be dissolved by stirring or the like.

[0044] The aqueous solution of such a binder for an electrode preferably has a pH in the range of 1 to 8, more preferably in the range of pH 2 to 8, still more preferably in the range of pH 3 to 8, and particularly preferably in the range of pH 6 to 8. When the pH of the aqueous solution is biased toward the acidic side, it becomes difficult to exhibit the expected viscosity of the aqueous solution. Therefore, when the pH is in the range of 6 to 8, an aqueous solution with an excellent balance of viscosity and solubility and excellent coatability can be obtained.

[0045] Further, the aqueous solution of the binder for an electrode preferably has a viscosity of 5 mPa·s or more, more preferably 250 mPa·s or more, preferably 15,000 mPa·s or less, more preferably 10,000 mPa·s or less, and still more preferably 8,000 mPa·s or less for a 1 mass% aqueous solution measured with a B-type viscometer (30 rpm) at 25°C. When the aqueous solution of the binder for an electrode is within the above viscosity range, suitable thickening properties and binding properties can be exhibited when added to the electrode composition.

[0046] The binder for an electrode of the present invention can also contain components constituting other electrode compositions as long as the effects of the present invention are not inhibited. Examples of such additive components include inorganic salts that ionize into cations in an aqueous solution. The presence of cations reinforces the cross-linked structure of carboxymethyl cellulose, so that an excellent effect on electrical properties can be exhibited. As such cations, monovalent, divalent, trivalent and other cations can be appropriately used, and specifically, those containing Fe ions and the like are preferable.

[0047] <Electrode composition> The binder for an electrode of the present invention can constitute an electrode composition together with the active material of the electrode. The properties of the electrode composition are not particularly limited and may be either slurry-like or paste-like.

[0048] In the present invention, the content of carboxymethyl cellulose or a salt thereof in the electrode composition is preferably 0.1 to 4.0 mass% based on the whole electrode composition.

[0049] The electrode composition may contain various components depending on whether the electrode formed by the composition is either the negative electrode or the positive electrode.

[0050] In the case of the electrode composition for the negative electrode, usually, a negative electrode active material is contained. As the negative electrode active material, graphite materials such as graphite (natural graphite, artificial graphite), coke, and carbon fiber; elements capable of forming an alloy with lithium, that is, for example, elements such as Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Ti, etc.; compounds containing elements capable of forming an alloy with lithium; composites of elements capable of forming an alloy with lithium and the compounds with carbon and / or the graphite materials; nitrides containing lithium can be used. Among these, graphite materials and / or silicon-based compounds are preferred, more preferably containing graphite and / or silicon-based compounds, and preferably containing at least silicon-based compounds.

[0051] In the case of the electrode composition for the positive electrode, usually, a positive electrode active material is contained. As the positive electrode active material, a positive electrode active material of the LiMexOy (Me means a transition metal containing at least one of Ni, Co, and Mn. x and y mean arbitrary numbers.) system is preferred. The positive electrode active material of the LiMexOy system is not particularly limited, but positive electrode active materials of the LiMn2O4 system, LiCoO2 system, and LiNiO2 system are preferred. Examples of the positive electrode active materials of the LiMn2O4 system, LiCoO2 system, and LiNiO2 system include compounds in which various metal elements are substituted with, for example, LiMnO2, LiMn2O4, LiCoO2, and LiNiO2 as the main framework. The positive electrode active materials of the LiMn2O4 system, LiCoO2 system, and LiNiO2 system are excellent in performance as positive electrode active materials, such as excellent diffusion performance of electrons and lithium ions, so that a lithium ion secondary battery having high charge-discharge efficiency and good cycle characteristics can be obtained. Among these, the positive electrode active material of the LiCoO2 system is preferred, and LiCoO2 is more preferred. On the other hand, from the viewpoint of low material cost, it is preferable to use a positive electrode active material of the LiMn2O4 system.

[0052] The content of the active material in the electrode composition is usually 90 to 99% by mass, preferably 91 to 99% by mass, more preferably 92 to 99% by mass.

[0053] In the case of the electrode composition for the positive electrode, the electrode composition preferably has a conductive material. By having a conductive material in the electrode composition, the characteristics of the produced positive electrode are improved. Further, the conductive material can ensure the electrical conductivity of the positive electrode. Examples of the conductive material include a mixture of one or more carbon materials such as carbon black, acetylene black, and graphite. Among these, carbon black is preferred.

[0054] In addition, the electrode composition may contain a binder other than an aqueous solution of carboxymethyl cellulose or its salt. Examples of the binder in the case of the electrode composition for the negative electrode include synthetic rubber-based binders. Examples of the synthetic rubber-based binder include one or more selected from the group consisting of styrene-butadiene rubber (SBR), nitrile-butadiene rubber, methyl methacrylate-butadiene rubber, chloroprene rubber, carboxy-modified styrene-butadiene rubber, and latexes of these synthetic rubbers. Among these, styrene-butadiene rubber (SBR) is preferred. In addition, examples of the binder in the case of the electrode composition for the positive electrode include, in addition to the synthetic rubber-based binders mentioned as the binders for the negative electrode, polytetrafluoroethylene (PTFE), and among these, polytetrafluoroethylene (PTFE) is preferred.

[0055] The content of the binder in the electrode composition is usually 0.5 to 5% by mass, preferably 0.5 to 3% by mass, more preferably 0.5 to 2% by mass.

[0056] The production conditions of the electrode composition are not particularly limited. For example, other components constituting the electrode composition are added to an aqueous solution of carboxymethyl cellulose or its salt, and mixed while stirring as necessary.

[0057] The properties of the electrode composition are not particularly limited either. For example, liquid, paste, slurry, etc. can be mentioned, and any of them may be used.

[0058] The electrode composition is used for manufacturing an electrode for a non-aqueous electrolyte secondary battery. The manufacturing of the electrode for a non-aqueous electrolyte secondary battery may be carried out by a method of laminating the electrode composition on a current collector substrate (current collector). Examples of the lamination method include blade coating, bar coating, and die coating, and blade coating is preferred. For example, in the case of blade coating, a method of casting the electrode composition on the current collector substrate using a coating device such as a doctor blade is exemplified. Further, the lamination method is not limited to the above specific examples, and a method of discharging and applying the electrode composition from an extrusion type injector having a slot nozzle onto a current collector substrate wound around a backup roll and running is also exemplified. In blade coating, after casting, drying by heating (temperature is, for example, 80 to 120 °C, heating time is, for example, 4 to 12 hours) etc. as necessary, and pressurization by roll pressing etc. can be carried out.

[0059] As the current collector substrate, any electrical conductor that does not cause a fatal chemical change in the constructed battery can be used.

[0060] As the current collector substrate for the negative electrode active material, stainless steel, nickel, copper, titanium, carbon, those obtained by attaching carbon, nickel, titanium or silver to the surface of copper or the stainless steel, etc. can be used. Among these, copper or a copper alloy is preferred, and copper is most preferred.

[0061] Examples of the material of the current collector substrate for the positive electrode include metals such as aluminum and stainless steel, and aluminum is preferred. As the shape of the current collector substrate, a net, punched metal, foam metal, a foil processed into a plate shape, etc. can be used, and a foil processed into a plate shape is preferred.

[0062] The shape of the electrode for a non-aqueous electrolyte secondary battery formed by the electrode composition is not particularly limited, but is usually sheet-like. The thickness (the thickness of the mixture layer formed from the electrode composition, excluding the current collector substrate portion) in the case of a sheet-like electrode plate is difficult to define univocally because it is also appropriately selected according to the composition of the composition, manufacturing conditions, etc., but is usually 30 to 150 μm.

[0063] The electrode formed by the composition is used as an electrode of a non-aqueous electrolyte secondary battery. That is, the present invention provides an electrode formed by the composition, and a non-aqueous electrolyte secondary battery can be manufactured using this electrode. The non-aqueous electrolyte secondary battery may have a structure in which a positive electrode and a negative electrode are alternately stacked via a separator and wound multiple times. The separator is usually impregnated with a non-aqueous electrolyte. As this negative electrode and / or positive electrode, a negative electrode and / or positive electrode formed by the above-described electrode composition can be used. Such a non-aqueous electrolyte secondary battery uses carboxymethyl cellulose or a salt thereof having excellent solubility, can omit processes such as filtration by a filter, is excellent in productivity, has a significantly improved initial irreversible capacity, and can exhibit high battery characteristics.

Examples

[0064] Hereinafter, embodiments of the present invention will be described by way of examples, but the present invention is not limited thereto.

[0065] In this example and comparative examples, each index of carboxymethyl cellulose or a salt thereof was measured by the following method. <Measurement method of carboxymethyl substitution degree (CM-DS)> Approximately 2.0 g of a sample of carboxymethyl cellulose pulverized product was precisely weighed and placed in a 300 mL Erlenmeyer flask with a stopper. 100 mL of methanol (a solution prepared by adding 100 mL of special grade concentrated nitric acid to 1000 mL of methanol) was added, and the mixture was shaken for 3 hours to convert carboxymethyl cellulose salt (CMC salt) to H-CMC (carboxymethyl cellulose). 1.5 - 2.0 g of absolutely dry H-CMC was precisely weighed and placed in a 300 mL Erlenmeyer flask with a stopper. H-CMC was moistened with 15 mL of 80% methanol, 100 mL of 0.1 N NaOH was added, and the mixture was shaken at room temperature for 3 hours. Using phenolphthalein as an indicator, the excess NaOH was back-titrated with 0.1 N H2SO4. CM-DS was calculated by the following formula 1. (Formula 1) A = [(100×F - (0.1 N of H2SO4 (mL))×F')×0.1] / (dry weight of H-CMC (g)) Degree of carboxymethyl substitution (CM-DS) = 0.162×A / (1 - 0.058×A) A: Amount of 1 N NaOH (mL) required for neutralization of 1 g of H-CMC F': Factor of 0.1 N H2SO4 F: Factor of 0.1 N NaOH

[0066] <Viscosity> Carboxymethylated cellulose or its salt was weighed into a 1000 mL glass beaker, dispersed in 900 mL of distilled water, and an aqueous dispersion was prepared to a solid content of 1% (w / v). The aqueous dispersion was stirred at 25 °C using a stirrer at 600 rpm for 3 hours. Then, in accordance with the method of JIS-Z-8803, using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.), the viscosity after 3 minutes at No. 1 rotor / rotation speed of 30 rpm was measured.

[0067] <Measurement of mass ratio of filtration residue to dry mass of carboxymethyl cellulose dissolved in aqueous solution> 2 liters of a 0.3 mass% (mass% based on the dry mass of carboxymethyl or its salt) aqueous solution of carboxymethyl cellulose or its salt was prepared. 2 liters of this aqueous solution was filtered using a filter (manufactured by Kiriyama Seisakusho, "Separate") under a reduced pressure condition of -200 mmHg with a 250 mesh filter (made of stainless steel, aperture 63 μm). The residue remaining on the 250 mesh filter was dried by blowing air at a temperature of 105 °C for 16 hours, and then the mass of the dried residue was measured and expressed as mass percentage (ppm) with respect to the mass of carboxymethyl cellulose in the carboxymethyl cellulose aqueous solution.

[0068] Also, using the coin-type non-aqueous electrolyte secondary batteries obtained in the examples and comparative examples, the batteries were evaluated as follows.

[0069] <Battery evaluation> (Discharge capacity (charge-discharge rate test)) The charge-discharge rate test of the coin-type non-aqueous electrolyte secondary battery obtained in the examples and comparative examples was carried out using BTS2004 of Nagano Corporation. In a constant temperature bath at 25 °C, using the coin-type non-aqueous electrolyte secondary battery, the charge-discharge performed in the order of charge treatment - discharge treatment was defined as one cycle, and 52 cycles were carried out. As the conditions for the charge treatment, in all cycles, a constant current constant voltage (CC-CV) method (CC current 0.2C, CV voltage 4.2V, termination current 0.02C) was adopted. As the conditions for the discharge treatment, the termination voltage was set to 3.0V. In the first cycle, the constant current of the discharge treatment was carried out at 0.2C, and after the discharge, the discharge capacity (mAh / g) after one cycle was measured. Up to the 52nd cycle thereafter, the constant current of the discharge treatment was set as follows, and the discharge capacity (mAh / g) was measured after the discharge of each cycle. (Constant current of discharge treatment in each cycle) 2 - 10 cycles: Constant current of discharge treatment 0.2C 11 - 20 cycles: Constant current of discharge treatment 1C 21st cycle: Constant current of discharge treatment 0.2C 22 - 31 cycles: Constant current of discharge treatment 2C 32nd cycle: Constant current of discharge treatment 0.2C 33 - 42 cycles: Constant current of discharge treatment 3C 43 - 52 cycles: Constant current of discharge treatment 0.2C

[0070] (Capacity retention rate) The capacity retention rate was calculated from the discharge capacity (mAh / g) in each of the above-described cycle tests by the formula "Capacity retention rate = Discharge capacity (mAh / g) after one cycle / Discharge capacity (mAh / g) after 52 cycles × 100".

[0071] (Example 1) (Preparation of binder for electrode) To a twin-screw kneader with the rotation speed adjusted to 100 rpm, 2720 g of isopropyl alcohol, 170 g of sodium monochloroacetate, and 58 g of sodium hydroxide dissolved in 480 g of water were added, and 160 g of lint pulp was charged based on the dry weight when dried at 30 °C for 60 minutes. After stirring and mixing at 30 °C for 90 minutes to prepare mercerized cellulose, the temperature was raised to 70 °C and a carboxymethylation reaction was carried out for 90 minutes. After the reaction was completed, it was neutralized with acetic acid to a pH of about 7, de-liquored, dried, and pulverized to obtain a sodium salt of carboxymethyl cellulose (hereinafter sometimes referred to as "CMC1") with a degree of carboxymethyl substitution of 0.70, a viscosity of 7,900 mPa·s for a 1 mass% aqueous solution measured with a B-type viscometer at 25 °C, and a filtration residue of 48 ppm based on the dry mass of the carboxymethyl cellulose dissolved in the aqueous solution. 150 mass% of ammonium hexa-molybdate tetrahydrate (manufactured by Fujifilm Wako Pure Chemical Corporation) with respect to the above-mentioned sodium carboxymethyl cellulose and sodium carboxythyl cellulose was weighed into a 300 mL glass beaker, and distilled water was added to prepare an aqueous dispersion so that the solid content concentration of the carboxymethyl cellulose was 2% (w / v). The aqueous dispersion was stirred at 500 rpm for 2 hours at 25 °C using a stirrer to obtain a binder 1 for electrodes.

[0072] <Fabrication of negative electrode plate> SiOx, acetylene black (manufactured by Stream Chemical), binder 1 for electrodes, and styrene-butadiene rubber (SBR, manufactured by JSR, product number S2910(E)-12-Na) were mixed so that the solid content weight ratio was 97:0.5:1.0:1.5, water was added so that the slurry concentration was 45.6 mass%, and it was stirred well using a Mazersstar (manufactured by Kurashiki Boseki, KK-250S) to obtain slurry 1. This slurry was coated on a copper foil (manufactured by Furukawa Electric Co., Ltd., NC-WS) with a size of 320 mm in length × 170 mm in width × 17 μm in thickness using an applicator, air-dried for 30 minutes, and then dried in a dryer at 60 °C for 30 minutes. Further, using a small bench-top roll press (manufactured by Tester Sangyo Co., Ltd., SA-602), it was pressed under the conditions of 5 kN and a roll peripheral speed of 50 m / min to obtain a negative electrode plate 1 with a basis weight of 19.7 g / m2 and a discharge effective capacity of 2100 mAh / g.

[0073] <Fabrication of Coin-Type Non-Aqueous Electrolyte Secondary Battery> The obtained negative electrode plate 1 and a LiCoO2 positive electrode plate (manufactured by Takizawa Shoten, basis weight 110.2 g / m2, effective discharge capacity 145 mAh / g) were punched out into a circular shape with a diameter of 16 mm, and the punched negative electrode plate and positive electrode plate were vacuum dried at 120 °C for 12 hours.

[0074] Similarly, a separator (a polypropylene separator manufactured by CS Tech, thickness 20 μm) was punched out into a circular shape with a diameter of 17 mm and vacuum dried at 60 °C for 12 hours.

[0075] Thereafter, the negative electrode plate 1 was placed in a stainless steel circular dish-shaped container with a diameter of 20.0 mm, and then a separator, a positive electrode plate, a spacer (diameter 15.5 mm, thickness 1 mm), and a stainless steel washer (manufactured by Takizawa Co., Ltd.) were laminated in this order. Thereafter, 300 μL of an electrolytic solution (1 mol / L LiPF6, volume ratio of ethylene carbonate to diethyl carbonate 1:1) was added to the circular dish-shaped container. A stainless steel cap was placed over this through a polypropylene packing and sealed with a coin battery caulking machine (manufactured by Takizawa Co., Ltd.) to obtain a coin-type non-aqueous electrolyte secondary battery 1.

[0076] (Example 2) An electrode binder 2 was obtained in the same manner as in Example 1, except that lithium molybdate (manufactured by Fujifilm Wako Pure Chemical Corporation) was used at 50% by mass with respect to sodium carboxymethyl cellulose instead of ammonium hexaammonium heptamolybdate tetrahydrate.

[0077] A slurry, a negative electrode plate, and a coin-type non-aqueous electrolyte secondary battery were fabricated in the same manner as in Example 1, except that electrode binder 2 was used instead of electrode binder 1.

[0078] (Comparative Example 1) An electrode binder 3 was obtained in the same manner as in Example 1, except that molybdate was not added. Also, a slurry, a negative electrode plate, and a coin-type non-aqueous electrolyte secondary battery were fabricated in the same manner as in Example 1, except that electrode binder 3 was used instead of electrode binder 1.

[0079] The measurement and evaluation results in the examples and comparative examples are shown in Table 1 below.

[0080]

Table 1

[0081] As shown in Table 1, the non-aqueous electrolyte secondary battery using a binder for a non-aqueous electrolyte secondary battery electrode containing at least carboxymethyl cellulose and / or a salt thereof having a degree of carboxymethyl substitution of 0.5 to 1.2 per anhydrous glucose unit and a molybdate was excellent in battery capacity retention rate.

Claims

1. A binder for a non-aqueous electrolyte secondary battery electrode, comprising at least carboxymethyl cellulose and / or a salt thereof having a degree of carboxymethyl substitution of 0.5 to 1.2 per anhydrous glucose unit, and a molybdate, wherein the molybdate contains at least one selected from ammonium molybdate and lithium molybdate.

2. The binder for a non-aqueous electrolyte secondary battery electrode according to Claim 1, wherein the molybdate is contained in a range of 30 to 200% by weight based on 100% by weight of the solid content of the carboxymethyl cellulose or a salt thereof.

3. The binder for an electrode of a non-aqueous electrolyte secondary battery according to Claim 1 or 2, wherein, when preparing 2 liters of a 0.3% by mass aqueous solution of the carboxymethyl cellulose or a salt thereof having a dry mass B, filtering all of it through a 250-mesh filter under a reduced pressure condition of -200 mmHg, and measuring the dry mass A of the residue on the filter after filtration, the ratio of the dry mass A to the dry mass B is less than 50 ppm.

4. The binder for a non-aqueous electrolyte secondary battery electrode according to any one of Claims 1 to 3, wherein the carboxymethylated cellulose or a salt thereof has a viscosity of 1,000 to 20,000 mPa·s in a 1% by mass aqueous solution measured with a B-type viscometer (30 rpm) at 25°C.

5. An electrode composition for a non-aqueous electrolyte secondary battery, comprising the binder for a non-aqueous electrolyte secondary battery electrode according to any one of Claims 1 to 4 and a silicon-based compound.

6. An electrode for a non-aqueous electrolyte secondary battery, using the electrode composition for a non-aqueous electrolyte secondary battery according to Claim 5.

7. A non-aqueous electrolyte secondary battery, using the electrode composition for a non-aqueous electrolyte secondary battery according to Claim 5.

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