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

Abstract

To provide a binder for an electrode of a non-aqueous electrolyte secondary battery that has a desired adhesive strength between an active material and a current collector and that exhibits good dispersibility of the active material and a conductive additive, and also to provide an electrode composition for a non-aqueous electrolyte secondary battery, an electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery that use the binder for an electrode of a non-aqueous electrolyte secondary battery.SOLUTION: A binder for an electrode of a non-aqueous electrolyte secondary battery includes a component A: carboxymethyl cellulose and / or a salt thereof, the viscosity of a 1 mass% aqueous solution of which is 1,000 to 20,000 mPa s as measured at 25°C with a Brookfield viscometer (30 rpm), and a component B: nucleic acid having a weight-average molecular weight of 1,000 to 20,000, and the blending ratio of the components A and B in the binder for an electrode of a non-aqueous electrolyte secondary battery is component A / component B=99 / 1 to 40 / 60.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In recent years, the rapid spread of small portable devices such as smartphones and tablets, as well as stationary storage batteries, has led to an increasing demand for small, high-energy-density batteries to power them.

[0003] Generally, graphite-based materials are used for the negative electrodes of lithium-ion secondary batteries, but the theoretical capacity of graphite-based materials is 372 mAh / g (LiC6), which is currently approaching its limit.

[0004] Furthermore, in order to improve the energy density of lithium-ion secondary batteries, it is necessary to select new materials. Therefore, materials made by alloying lithium with silicon, tin, etc., which have the second lowest potential and large specific capacity after carbon and lithium, are attracting attention.

[0005] Among these materials, silicon can absorb up to 4.4 lithium atoms per 1 silicon atom in molar ratio, theoretically providing approximately 10 times the capacity of graphite-based carbon materials. However, silicon particles expand in volume approximately three to four times when they absorb lithium, leading to degradation and capacity loss with repeated charge-discharge cycles. Detailed analysis of this phenomenon has revealed that when lithium is inserted into silicon-containing active materials, the volume expansion causes microcracks to form within the electrode, allowing the electrolyte to penetrate these microcracks and form a new coating (SEI layer). This creates irreversible capacity loss, resulting in a decrease in battery capacity. This phenomenon manifests itself in changes in charge-discharge efficiency during cycling. The decrease in cycle efficiency, especially during the early stages of cycling when volume change is large, significantly impacts the battery's lifespan when combined with a positive electrode with high charge-discharge efficiency. Therefore, minimizing changes in electrode structure due to this volume expansion is a key challenge when using silicon-containing active materials.

[0006] In view of these circumstances, Patent Document 1 aims to improve battery characteristics by using a binder containing three essential components: carboxymethyl cellulose or a metal salt thereof, polyacrylic acid or a metal salt thereof, and styrene-butadiene rubber or polyvinylidene fluoride. However, according to the examples and comparative examples of Patent Document 1, when only two components (carboxymethyl cellulose and styrene-butadiene rubber, or carboxymethyl cellulose and polyvinylidene fluoride) were used as the binder, desired battery characteristics were not obtained. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-198038 Summary of the Invention [Problem to be solved by the invention]

[0008] According to the investigations of the present inventors, it has been found that a composition containing carboxymethyl cellulose or a salt thereof and nucleic acid affects the adhesive strength between the active material and the current collector, as well as the dispersibility of the active material and the conductive additive. Furthermore, when the adhesive strength between the active material and the current collector and the dispersibility of the active material and the conductive additive are improved, the battery characteristics are also improved.

[0009] That is, an object of the present invention is to provide a binder for electrodes of non-aqueous electrolyte secondary batteries that has a desired adhesive strength between an active material and a current collector and that exhibits good dispersibility of the active material and a conductive additive, and to provide an electrode composition for non-aqueous electrolyte secondary batteries, an electrode for non-aqueous electrolyte secondary batteries, and a non-aqueous electrolyte secondary battery that use the binder for electrodes of non-aqueous electrolyte secondary batteries. [Means for solving the problem]

[0010] As a result of extensive efforts, the present inventors have found that the problems can be solved by the following [1] to [6]. [1] A binder for electrodes of non-aqueous electrolyte secondary batteries, comprising: component A: carboxymethyl cellulose and / or a salt thereof, the viscosity of a 1% by mass aqueous solution of which, as measured at 25°C with a Brookfield viscometer (30 rpm), is 1,000 to 20,000 mPa s; and component B: nucleic acid having a weight-average molecular weight of 1,000 to 20,000, wherein the blending ratio of components A and B in the binder for electrodes of non-aqueous electrolyte secondary batteries is component A / component B=99 / 1 to 40 / 60. [2] The binder for a non-aqueous electrolyte secondary battery electrode according to [1], wherein the degree of carboxymethyl substitution per anhydroglucose unit of the component A is 0.5 to 1.2. [3] The binder for a non-aqueous electrolyte secondary battery electrode according to [1], wherein the component B is a ribonucleic acid (RNA) derived from yeast. [4] An electrode composition for a non-aqueous electrolyte secondary battery, using the binder for a non-aqueous electrolyte secondary battery electrode according to [1]. [5] An electrode for a non-aqueous electrolyte secondary battery, using the binder for a non-aqueous electrolyte secondary battery electrode according to [1]. [6] A non-aqueous electrolyte secondary battery using the binder for a non-aqueous electrolyte secondary battery electrode according to [1]. [Effects of the Invention]

[0011] According to the present invention, there are provided a binder for electrodes of non-aqueous electrolyte secondary batteries that has a desired adhesive strength between an active material and a current collector and that exhibits good dispersibility of the active material and a conductive additive, as well as an electrode composition for non-aqueous electrolyte secondary batteries, an electrode for non-aqueous electrolyte secondary batteries, and a non-aqueous electrolyte secondary battery that use the binder for electrodes of non-aqueous electrolyte secondary batteries. DETAILED DESCRIPTION OF THE INVENTION

[0012] The binder for electrodes of non-aqueous electrolyte secondary batteries of the present invention will be described below. The binder for electrodes of non-aqueous electrolyte secondary batteries of the present invention comprises component A: carboxymethyl cellulose and / or a salt thereof, the viscosity of a 1% by mass aqueous solution of which, as measured at 25°C with a Brookfield viscometer (30 rpm), is 1,000 to 20,000 mPa·s, and component B: nucleic acid having a molecular weight of 1,000 to 20,000, wherein the blending ratio of components A and B in the binder for electrodes of non-aqueous electrolyte secondary batteries is component A / component B=99 / 1 to 40 / 60.

[0013] <Component A: Carboxymethyl cellulose and / or a salt thereof having a viscosity of 1,000 to 20,000 mPa s in a 1% by mass aqueous solution> (viscosity) The viscosity of a 1% by mass aqueous solution of carboxymethyl cellulose or a salt thereof (hereinafter sometimes abbreviated as CMC) constituting the present invention, measured at 25°C using a Brookfield viscometer (30 rpm), is preferably 1,000 to 20,000 mPa·s, more preferably 1,000 to 15,000 mPa·s, and even more preferably 1,000 to 10,000 mPa·s. A viscosity of 1,000 to 20,000 mPa·s allows for the preparation of a slurry with a viscosity suitable for coating. This also prevents the structure of the coating layer from being damaged by expansion and contraction of the coating layer during charge and discharge.

[0014] The viscosity in the present invention is measured by the following method: Carboxymethylcellulose or its salt was weighed into a 1000 mL glass beaker and dispersed in 900 mL of distilled water to prepare an aqueous dispersion with a solids content of 1% (w / v). The aqueous dispersion was stirred at 600 rpm for 3 hours at 25°C using a stirrer. The viscosity was then measured after 3 minutes using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) with a No. 1 rotor at 30 rpm according to the method of JIS-Z-8803.

[0015] The carboxymethyl cellulose and / or its salts constituting the present invention have a structure in which the hydroxyl groups in the glucose units constituting the cellulose are substituted with carboxymethyl ether groups. The carboxymethyl cellulose may be in the form of a salt. Examples of the salt of carboxymethyl cellulose include metal salts such as sodium carboxymethyl cellulose.

[0016] (cellulose raw material) In the present invention, cellulose refers to a polysaccharide having a structure in which D-glucopyranose units (also simply referred to as "glucose units" or "anhydroglucose") are linked together via β,1-4 bonds. Cellulose is generally classified into native cellulose, regenerated cellulose, fine cellulose, microcrystalline cellulose (which is cellulose obtained by removing the amorphous region), etc., based on its origin and manufacturing method.

[0017] Examples of natural cellulose include bleached or unbleached pulp, purified linters, and cellulose produced by microorganisms such as acetic acid bacteria. The raw materials for bleached or unbleached pulp are not particularly limited, and examples include wood, cotton, straw, bamboo, etc. The method for producing bleached or unbleached pulp is also not particularly limited, and examples include mechanical methods, chemical methods, and methods that combine mechanical and chemical methods. Examples of bleached or unbleached pulp include mechanical pulp, chemical pulp, groundwood pulp, sulfite pulp, kraft pulp, and papermaking pulp. Another example of bleached or unbleached pulp is dissolving pulp, which is chemically refined and used primarily by dissolving it in chemicals, and is used as a main raw material for artificial fibers, cellophane, etc.

[0018] Examples of regenerated cellulose include regenerated cellulose obtained by dissolving cellulose in a solvent such as a cuprammonium solution, a cellulose xanthate solution, or a morpholine derivative, and then spinning the resulting solution.

[0019] Examples of fine cellulose include fine cellulose obtained by depolymerizing cellulosic materials such as natural cellulose and regenerated cellulose through acid hydrolysis, alkali hydrolysis, enzymatic decomposition, blasting treatment, vibrating ball mill treatment, etc., and fine cellulose obtained by mechanically treating cellulosic materials.

[0020] The carboxymethyl cellulose or one of its salts constituting the present invention can be produced by a known CMC production method. For example, CMC can be produced by treating cellulose with a mercerizing agent (alkali) to prepare mercerized cellulose (alkali cellulose), and then adding an etherifying agent to the mercerized cellulose to cause an etherification reaction.

[0021] The cellulose raw material can be any of the above-mentioned celluloses, but those with high cellulose purity are preferred, and dissolving pulp or linter are more preferred. By using these, CMC with high purity can be obtained.

[0022] Examples of the mercerizing agent include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, etc. Examples of the etherifying agent include monochloroacetic acid, sodium monochloroacetate, etc.

[0023] In a typical method for producing water-soluble carboxymethyl cellulose, the molar ratio of the mercerizing agent to the etherifying agent (mercerizing agent / etherifying agent) is generally 2.00 to 2.45 when monochloroacetic acid is used as the etherifying agent. A ratio of 2.00 or more allows the etherification reaction to proceed sufficiently, preventing unreacted monochloroacetic acid from being wasted. A ratio of 2.45 or less prevents a side reaction between the excess mercerizing agent and monochloroacetic acid from progressing, resulting in the production of an alkali metal glycolate, which is economical. In the present invention, the CMC may be a commercially available product, for example, a product under the trade name "Sunrose" manufactured by Nippon Paper Industries Co., Ltd.

[0024] (Degree of substitution of carboxymethyl group) The carboxymethyl cellulose or salt thereof constituting the present invention has a degree of substitution of carboxymethyl groups per anhydroglucose unit (hereinafter sometimes referred to as DS value) of 0.5 to 1.2. A DS value of 0.5 or more can maintain good solubility in water and suppress the generation of undissolved matter. Furthermore, a DS value of 1.2 or less can suppress an increase in spinnability of the liquid and maintain easy handling. Therefore, the DS value of the CMC of the present invention is 0.5 to 1.2, preferably 0.5 to 1.0, and more preferably 0.6 to 1.0.

[0025] The degree of substitution of carboxymethyl groups is measured as follows: Weigh out approximately 2.0 g of sample and place it in a 300 mL Erlenmeyer flask with a stopper. Add 100 mL of a solution of 1000 mL of methanol and 100 mL of concentrated nitric acid, and shake for 3 hours to convert carboxymethyl cellulose salt (CMC) to H-CMC (hydrogen-form carboxymethyl cellulose). Weigh out 1.5 to 2.0 g of the bone-dry H-CMC and place it in a 300 mL Erlenmeyer flask with a stopper. Wet the H-CMC with 15 mL of 80% methanol, add 100 mL of 0.1 N NaOH, and shake for 3 hours at room temperature. Using phenolphthalein as an indicator, back-titrate the excess NaOH with 0.1 N H2SO4, and calculate the degree of carboxymethyl substitution (DS value) using the following formula: A = [(100 × F' - 0.1N-H2SO4 (mL) × F) × 0.1] / (bone-dry mass of H-CMC (g)) Carboxymethyl substitution degree = 0.162 x A / (1 - 0.058 x A) F': Factor of 0.1N-H2SO4 F: Factor of 0.1N-NaOH

[0026] (Dispersion degree) The carboxymethyl cellulose or salt thereof constituting the present invention has a degree of dispersion measured using a powder tester of 20 to 60%, preferably 25 to 55%, and more preferably 30 to 50%. When the degree of dispersion is within this range, CMC exhibits good dispersibility when used as a binder or dispersant in a negative electrode composition, resulting in low electrical resistance. On the other hand, if the degree of dispersion is too high, there is a problem of excessive dusting, making it impossible to dissolve a predetermined amount of carboxymethyl cellulose, and therefore reducing its function as a binder or dispersant in the negative electrode, resulting in high electrical resistance. On the other hand, if the degree of dispersion is too low, it is difficult to mix well with other materials, resulting in high electrical resistance. Here, the degree of dispersion was measured using a powder tester (Powder Tester PT-X (manufactured by Hosokawa Micron Corporation)). 10 g of the sample was placed in the dispersion unit of the PT-X and dropped. The degree of dispersion was calculated from the amount of powder that fell onto the watch glass using the following formula. Dispersibility (%) = (10 (g) - amount of powder dropped onto the watch glass (g)) / 10 (g)

[0027] (Amount of filtration residue) The carboxymethyl cellulose or salt thereof constituting the present invention preferably has a filtration residue amount within a predetermined range. That is, when 2 L of a 0.3% by mass aqueous solution of the carboxymethyl cellulose or salt thereof with a dry mass m is prepared and completely filtered through a 250-mesh filter under reduced pressure conditions of -200 mmHg, and the dry mass M of the residue on the filter after filtration is measured, the ratio of the dry mass M to the dry mass m is preferably less than 200 ppm, more preferably less than 50 ppm. If this value is too large, clogging occurs easily during filtration of the electrode slurry, the amount of carboxymethyl cellulose in the filtered slurry is less than the predetermined amount, and the function as a binder and dispersant is reduced, resulting in problems such as high electrical resistance.

[0028] (particle size) The particle size D10 of the carboxymethyl cellulose or salt thereof constituting the present invention is preferably 1 to 10 μm, the particle size D50 is preferably 10 to 20 μm, and the particle size D90 is preferably 20 to 40 μm.

[0029] Here, D10 is the particle size that contains 10% of the particles when calculated from the minimum value in the particle size distribution based on the volume average particle size, D50 is the particle size that contains 50% of the particles when calculated from the minimum value, and is also called the average particle size. Furthermore, D90 is the particle size that contains 90% of the particles when calculated from the minimum value. The particle size distribution based on the volume average particle size can be measured using a laser diffraction / scattering particle size distribution analyzer, for example, using methanol as a dispersant.

[0030] Furthermore, the value obtained by subtracting the particle diameter D10 from the particle diameter D90 of the carboxymethyl cellulose or salt thereof constituting the present invention (particle diameter D90 - particle diameter D10) is preferably 10 to 50 μm, more preferably 10 to 30 μm, and even more preferably 20 to 30 μm. If this value is too large, coarse undissolved matter in the particles may cause hole defects in the negative electrode layer.

[0031] Furthermore, the value obtained by subtracting the particle diameter D50 from the particle diameter D90 of carboxymethyl cellulose and / or its salt (particle diameter D90 - particle diameter D50) is preferably 5 to 30 μm, more preferably 10 to 30 μm, and even more preferably 10 to 20 μm. If this value is too large, coarse undissolved matter in the particles may cause hole defects in the negative electrode layer.

[0032] Furthermore, the value obtained by subtracting the particle diameter D10 from the particle diameter D50 of carboxymethyl cellulose and / or its salt (particle diameter D50 - particle diameter D10) is preferably 5 to 20 μm, more preferably 5 to 15 μm, and even more preferably 8 to 12 μm. If this value is too large, there is a problem that undissolved matter in the particles may cause hole defects in the negative electrode layer.

[0033] (Crushing process) In the present invention, carboxymethyl cellulose or a salt thereof may be finely pulverized. As a method for finely pulverizing carboxymethyl cellulose or a salt thereof, either a dry pulverization method in which the carboxymethyl cellulose or a salt thereof is treated in a powder state or a wet pulverization method in which the carboxymethyl cellulose or a salt thereof is treated in a dispersed or dissolved state in a liquid may be selected.

[0034] By subjecting carboxymethyl cellulose or a salt thereof to mechanical dry or wet grinding, gel particles derived from carboxymethyl cellulose or a salt thereof that exist as undissolved matter in an aqueous solution are reduced in size, which is thought to prevent the formation of coarse undissolved matter that can cause streak defects, peeling, pinholes, and the like on the surface of the negative electrode.

[0035] The following types of milling devices can be used in the present invention. Dry mills include cutting mills, impact mills, and airflow mills. These can be used alone or in combination, and the same type of mill can be used for multiple stages of processing.

[0036] Examples of cutting-type mills include Mesh Mill (manufactured by Horai Co., Ltd.), Atoms (manufactured by Yamamoto Hyakuma Seisakusho Co., Ltd.), Knife Mill (manufactured by Parman Co., Ltd.), Granulator (manufactured by Herbolt Co., Ltd.), and Rotary Cutter Mill (manufactured by Nara Machinery Works Co., Ltd.).

[0037] Examples of impact mills include Pulperizer (manufactured by Hosokawa Micron Corporation), Fine Impact Mill (manufactured by Hosokawa Micron Corporation), Super Micron Mill (manufactured by Hosokawa Micron Corporation), Sample Mill (manufactured by Seishin Corporation), Bantam Mill (manufactured by Seishin Corporation), Atomizer (manufactured by Seishin Corporation), Tornado Mill (Nikkiso Co., Ltd.), Turbo Mill (Turbo Kogyo Co., Ltd.), and Bevel Impactor (Aikawa Iron Works Co., Ltd.).

[0038] Examples of airflow mills include a CGS-type jet mill (manufactured by Mitsui Mining Co., Ltd.), a jet mill (manufactured by Sansho Industry Co., Ltd.), an Ebara Jet Micronizer (manufactured by Ebara Corporation), a Selenium Mirror (manufactured by Masuko Sangyo Co., Ltd.), and a supersonic jet mill (manufactured by Nippon Pneumatic Mfg. Co., Ltd.). An example of a media mill is a vibrating ball mill.

[0039] Examples of the wet mill include Masscolloider (manufactured by Masuko Sangyo Co., Ltd.), and examples of the media mill include Bead Mill (manufactured by Imex Co., Ltd.) and High Pressure Homogenizer (manufactured by Sanmaru Machinery Industry Co., Ltd.).

[0040] In the present invention, a step of classifying the pulverized carboxymethyl cellulose or a salt thereof based on particle size can be provided. The classification step may be performed during or after the pulverization step. Any known method may be used for classification. Examples of dry classifiers include cyclone classifiers, DS separators, turbo classifiers, microseparators, and air separators. Examples of wet classifiers include liquid cyclone type, centrifugal settlers, and hydroshield separators.

[0041] <Component B: Nucleic acid having a weight-average molecular weight of 1,000 to 20,000> (Weight average molecular weight) The nucleic acid constituting the present invention preferably has a weight-average molecular weight (Mw) of 1,000 to 20,000, more preferably 1,000 to 15,000, and even more preferably 5,000 to 15,000. When the weight-average molecular weight (Mw) is 1,000 to 20,000, battery materials such as acetylene black can be easily dispersed. The molecular weight distribution of the nucleic acid referred to here can be determined, for example, by GPC (gel permeation chromatography).

[0042] The type of sugar constituting nucleic acid may be either deoxyribose or ribose. In other words, nucleic acid may be either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA). The types of bases constituting nucleic acid mainly include adenine, guanine, thymine, cytosine, and uracil, that is, the types of nucleosides constituting nucleic acid include adenosine, guanosine, cytidine, uridine, and thymidine. The phosphate constituting nucleotide may be monophosphate or may be composed of multiple phosphates. Commercially available products may be used as nucleic acids. One type of nucleic acid may be formulated alone, or multiple types may be formulated in combination. Ribonucleic acid and nucleotides may preferably be used as nucleic acids.

[0043] The origin of the nucleic acid is not particularly limited, and it may be artificially synthesized or derived from a natural product, and it is particularly preferable to use nucleic acids extracted or purified from microorganisms such as yeast.

[0044] <Binder for non-aqueous electrolyte secondary batteries> The binder for non-aqueous electrolyte secondary batteries of the present invention (hereinafter sometimes referred to as "battery binder") preferably contains carboxymethyl cellulose and / or a salt thereof as component A and nucleic acid as component B in a blending ratio of component A / component B of 99 / 1 to 40 / 60, more preferably 95 / 5 to 50 / 50. When component A / component B is 99 / 1 to 40 / 60, not only are the active material and conductive additive uniformly dispersed in the slurry, but also an electrode plate having excellent adhesive strength between the active material and the current collector can be obtained.

[0045] The binder for non-aqueous electrolyte secondary batteries of the present invention can also be prepared as an aqueous solution. The conditions for producing such an aqueous solution are not particularly limited. For example, the electrode binder can be added to water (e.g., distilled water, purified water, tap water, etc.) and dissolved by stirring, etc., as necessary. Alternatively, carboxymethyl cellulose or a salt thereof can be dissolved in water, etc., and then a borate can be added and dissolved by stirring, etc. Similarly, a borate can be dissolved in water, etc., and then carboxymethyl cellulose or a salt thereof can be dissolved by stirring, etc.

[0046] The aqueous solution of such a binder for a non-aqueous electrolyte secondary battery preferably has a pH in the range of 1 to 8, more preferably in the range of 2 to 8, even more preferably in the range of 3 to 8, and particularly preferably in the range of 6 to 8. If the pH of the aqueous solution is too acidic, it becomes difficult for the aqueous solution to exhibit the viscosity expected of the aqueous solution. Therefore, if the pH is in the range of 6 to 8, a particularly good balance between viscosity and solubility can be achieved, making it possible to obtain an aqueous solution with excellent coatability.

[0047] In the mixed aqueous solution of carboxymethylcellulose and / or a salt thereof with nucleic acid, the combined concentration of carboxymethylcellulose or a salt thereof and nucleic acid is usually 0.1 to 10 mass %, preferably 0.2 to 4 mass %, more preferably 0.5 to 2 mass %.

[0048] Furthermore, the viscosity of a 1% by mass aqueous solution of the binder for non-aqueous electrolyte secondary batteries, measured at 25°C with a Brookfield viscometer (30 rpm), is preferably 400 mPa·s or more, more preferably 800 mPa·s or more, and is preferably 15,000 mPa·s or less, more preferably 10,000 mPa·s or less, and even more preferably 8,000 mPa·s or less. When the aqueous solution of the binder for non-aqueous electrolyte secondary batteries has a viscosity within the above range, it can exhibit suitable dispersibility, thickening properties, and binding properties when added to an electrode composition.

[0049] The binder for a non-aqueous electrolyte secondary battery may contain other binders in addition to carboxymethyl cellulose and / or its salt as component A and nucleic acid as component B. Examples of binders used in electrode compositions for negative electrodes include synthetic rubber binders. Examples of synthetic rubber binders that can be used 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. Examples of binders used in electrode compositions for positive electrodes include the synthetic rubber binders listed above as binders for negative electrodes, as well as polytetrafluoroethylene (PTFE).

[0050] The average particle size (D50) of the SBR is preferably 50 to 300 nm, and more preferably 50 to 200 nm. If the average particle size (D50) of the SBR is too large, the SBR will not adhere uniformly to the active material, reducing its binder function and resulting in a problem of high electrical resistance. If the average particle size (D50) of the SBR is too small, the SBR will cover the active material, resulting in a problem of high electrical resistance.

[0051] The glass transition temperature (Tg) of the SBR is preferably −50° C. to 50° C. When the SBR is within the above range, it mixes well with the carboxymethyl cellulose and / or salt thereof of the present invention and has appropriate flexibility when used in the negative electrode layer, making it less likely to have high electrical resistance.

[0052] <Electrode composition for nonaqueous electrolyte secondary batteries> The electrode composition for a non-aqueous electrolyte secondary battery of the present invention (hereinafter sometimes referred to as "electrode composition") contains at least an electrode active material and two types of carboxymethyl cellulose and / or salts thereof as the binder for the non-aqueous electrolyte secondary battery.

[0053] The content of the mixture of carboxymethyl cellulose and / or a salt thereof and nucleic acid in the electrode composition is preferably 0.1 to 4.0% by mass based on the total amount of the electrode composition.

[0054] When the other binders are used, the content of the binder for a non-aqueous electrolyte secondary battery in the electrode composition is preferably 1 to 10 mass %, more preferably 1 to 6 mass %, and even more preferably 1 to 2 mass %.

[0055] (electrode active material) The electrode active material contained in the active material layer constituting the present invention is a negative electrode active material when the electrode for a nonaqueous electrolyte secondary battery is a negative electrode, and is a positive electrode active material when the electrode is a positive electrode.

[0056] Examples of negative electrode active materials include graphite materials such as graphite (natural graphite, artificial graphite, etc.), coke, and carbon fiber; elements capable of forming an alloy with lithium, i.e., silicon-based compounds, elements such as Al, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, and Ti; compounds containing elements capable of forming an alloy with lithium; composites of elements and compounds capable of forming an alloy with lithium with carbon and / or the graphite materials, or nitrides containing lithium. Among these, graphite materials and silicon-based compounds are preferred, and silicon particles or silicon oxide particles are more preferred as graphite and silicon-based compounds.

[0057] In addition, the silicon oxide in the present invention is represented by SiOx (0 < x ≤ 2). Further, in the present invention, as the active material layer, a composite of a silicon-based compound and a graphite material is more preferable.

[0058] When the negative electrode active material is a composite of a graphite material and a silicon-based compound, the mixing ratio of the graphite material to the silicon-based compound is preferably 10:90 to 90:10, and more preferably 50:50 to 80:20.

[0059] As the positive electrode active material, a positive electrode active material of the LiFePO4, LiMexOy (Me means a transition metal containing at least one of Ni, Co, and Mn. x and y mean arbitrary numbers.) system is preferable.

[0060] The content of the electrode active material in the electrode layer is usually 90 to 99% by mass, preferably 91 to 99% by mass, more preferably 92 to 99% by mass, still more preferably 95 to 99% by mass, particularly preferably 96 to 99% by weight, and most preferably 98 to 99% by mass.

[0061] Further, the electrode composition may contain a conductive assistant as necessary. Examples of the conductive assistant include conductive carbons such as carbon black, acetylene black, and ketjen black. The content of the conductive assistant in the electrode composition is usually 0.01 to 20% by mass, preferably 0.1 to 10% by mass.

[0062] In addition, as the solvent used in the electrode composition, an aqueous solvent is preferable. The type of the aqueous solvent is not particularly limited, but it is preferably water, a water-soluble organic solvent, or a mixed solvent thereof, and more preferably water.

[0063] The water-soluble organic solvent is an organic solvent that dissolves in water. Examples of water-soluble organic solvents include methanol, ethanol, 2-propanol, butanol, glycerin, acetone, methyl ethyl ketone, 1,4-dioxane, N-methyl-2-pyrrolidone, tetrahydrofuran (THF), N,N-dimethylformamide (DMF), N,N-dimethylacetamide, dimethyl sulfoxide (DMSO), acetonitrile, methyl succinate triglycol diester, acetic acid, and combinations thereof.

[0064] When the mixed solvent is used as the aqueous solvent, the amount of the water-soluble organic solvent in the mixed solvent is preferably 10% by mass or more, more preferably 50% by mass or more, and even more preferably 70% by mass or more. There is no upper limit to this amount, but it is preferably 95% by mass or less, more preferably 90% by mass or less. Furthermore, the aqueous solvent may contain a water-insoluble organic solvent as long as it does not impair the effects of the invention.

[0065] The conditions for producing the electrode composition are not particularly limited. For example, other components constituting the electrode composition are added to an aqueous solution of carboxymethyl cellulose and / or a salt thereof, and mixed with stirring as necessary. The form of the electrode composition is not particularly limited, and may be, for example, a liquid, a paste, a slurry, or any other form.

[0066] <Nonaqueous electrolyte secondary battery electrode> An electrode layer can be formed on a current collector by applying the electrode composition to the current collector. Examples of application methods include blade coating, bar coating, and die coating, with blade coating being preferred. For example, blade coating can be achieved by casting the electrode composition onto the current collector using a coating device such as a doctor blade. The lamination method is not limited to the specific example described above, and can also be achieved by discharging the electrode composition from an extrusion-type injector having a slot nozzle onto a running current collector wound around a backup roll. In blade coating, after casting, the electrode layer can be obtained by further drying, such as by heating (for example, at a temperature of 80 to 120°C, for example, for 4 to 12 hours) or by applying pressure using a roll press, as needed.

[0067] The shape of the electrode for a non-aqueous electrolyte secondary battery of the present invention is not particularly limited, but is usually a sheet. The thickness of the sheet-shaped electrode plate (the thickness of the electrode layer formed from the electrode composition, excluding the current collector portion) is difficult to specify because it depends on the composition and production conditions of the composition, but is usually 30 to 150 μm.

[0068] (current collector) Any electrical conductor that does not cause a fatal chemical reaction in the constructed electrode or battery can be used as the current collector. If the electrode is a negative electrode, a negative electrode current collector can be used, and if the electrode is a positive electrode, a positive electrode current collector can be used.

[0069] Examples of materials for the negative electrode current collector include stainless steel, nickel, copper, titanium, carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium or silver, etc. Among these, copper or a copper alloy is preferred, and copper is more preferred. Examples of materials for the positive electrode current collector include metals such as aluminum and stainless steel, with aluminum being preferred. The current collector may be in the form of a mesh, punched metal, foam metal, or foil processed into a plate shape, with foil processed into a plate shape being preferred.

[0070] <Nonaqueous electrolyte secondary battery> The electrode for a non-aqueous electrolyte secondary battery of the present invention is used as an electrode for a non-aqueous electrolyte secondary battery.

[0071] That is, the present invention also provides a nonaqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery can have a structure in which positive electrodes and negative electrodes are alternately stacked with separators interposed therebetween and wound many times. The nonaqueous electrolyte secondary battery can be obtained by placing the wound stack of positive electrodes, separators, and negative electrodes in a battery container, injecting a nonaqueous electrolyte, and sealing the container.

[0072] The shape of the nonaqueous electrolyte secondary battery is not particularly limited, and may be a cylindrical shape, a prismatic shape, a flat shape, a coin shape, a button shape, a sheet shape, etc. The material of the battery container is not particularly limited as long as it can prevent moisture from entering the battery, and examples thereof include a laminate of metal, aluminum, etc.

[0073] The separator is usually impregnated with a non-aqueous electrolyte. The separator may be, for example, a microporous membrane or nonwoven fabric made of polyolefin such as polyethylene or polypropylene.

[0074] The non-aqueous electrolyte typically contains a lithium salt and a non-aqueous solvent. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, and LiClO4. Examples of non-aqueous solvents include ethylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, butylene carbonate, and methyl ethyl carbonate. One type of non-aqueous solvent may be used alone, or two or more types may be used in combination. The concentration of the lithium salt in the non-aqueous electrolyte is typically 0.5 to 2.5 mol / L.

[0075] When the binder for a non-aqueous electrolyte secondary battery of the present invention is added to an electrode composition, it not only uniformly disperses the active material and conductive additive, but also provides strong binding between the active material and the current collector foil, so that the electrode for a non-aqueous electrolyte secondary battery and the non-aqueous electrolyte secondary battery produced by the present invention have excellent battery characteristics. [Example]

[0076] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

[0077] In the present examples and comparative examples, the indices for carboxymethylcellulose or a salt thereof and nucleic acids are measured by the following methods.

[0078] <Method for measuring the degree of carboxymethyl substitution (CM-DS)> Approximately 2.0 g of pulverized carboxymethylcellulose sample was weighed and placed in a 300 mL Erlenmeyer flask with a stopper. 100 mL of methanol (1000 mL of methanol plus 100 mL of concentrated nitric acid) was added and the mixture was shaken for 3 hours to convert the carboxymethylcellulose salt (CMC salt) to H-CMC (carboxymethylcellulose). 1.5-2.0 g of bone-dried H-CMC was weighed and placed in a 300 mL Erlenmeyer flask with a stopper. The 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, excess NaOH was back-titrated with 0.1 N H2SO4. The CM-DS was calculated using the following equation. (Formula 1) A = [(100 × F - (0.1 N HSO (mL)) × F') × 0.1] / (bone-dry weight of H-CMC (g)) Carboxymethyl substitution degree (CM-DS) = 0.162 × A / (1-0.058 × A) A: Amount of 1N NaOH (mL) required to neutralize 1g of H-CMC F': Factor of 0.1N H2SO4 F: Factor of 0.1N NaOH

[0079] <Viscosity> Carboxymethylated cellulose or its salt was weighed into a 1000 mL glass beaker and dispersed in 900 mL of distilled water to prepare an aqueous dispersion with a solids content of 1% (w / v). The aqueous dispersion was stirred at 600 rpm for 3 hours at 25°C using a stirrer. The viscosity after 3 minutes was then measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) at 30 rpm according to the method of JIS-Z-8803.

[0080] <Dispersion> The dispersibility of carboxymethyl cellulose or its salt was measured using a powder tester (Powder Tester PT-X, manufactured by Hosokawa Micron Corporation). Specifically, a 10 g sample was placed in the dispersion unit of the PT-X and dropped, and the dispersibility was calculated from the amount of powder that fell onto a watch glass using the following formula: Dispersibility (%) = (10 (g) - amount of powder dropped onto the watch glass (g)) / 10 (g)

[0081] <Measurement of the mass ratio of the mass of the filtration residue to the dry mass of carboxymethyl cellulose dissolved in an aqueous solution> Two liters of an aqueous solution containing 0.3% by mass (mass % based on the dry mass of carboxymethyl cellulose or its salt) of carboxymethyl cellulose or its salt was prepared. This 2 liters of aqueous solution was filtered through a 250-mesh filter (stainless steel, 63 μm mesh) using a filter ("Separote," manufactured by Kiriyama Seisakusho) under a reduced pressure of -200 mmHg. The residue remaining on the 250-mesh filter was dried with air at 105°C for 16 hours, and the mass of the dried residue was measured and expressed as a percentage by mass (ppm) relative to the mass of carboxymethyl cellulose in the aqueous carboxymethyl cellulose solution.

[0082] <Weight average molecular weight (nucleic acid)> The weight-average molecular weight (Mw) of the nucleic acid can be measured by gel permeation chromatography (GPC). GPC measurement can be performed using a known pullulan-equivalent method under the following conditions. Measuring device: Tosoh Columns used: Shodex Column OH-pak SB-806HQ, SB-804HQ, SB-802.5HQ Eluent: 1.0% sodium tetraborate, 0.3% isopropyl alcohol aqueous solution Eluent flow rate: 1.00ml / min Column temperature: 50℃ Measurement sample concentration: 0.2% by mass Standard material: Pullulan (Shodex) Detector: RI detector (manufactured by Tosoh) Calibration curve: pullulan standard

[0083] The adhesive strength of the negative electrode plates 1 to 7 using the battery binders 1 to 7 obtained in the examples and comparative examples was evaluated as follows.

[0084] <Adhesion strength evaluation> The negative electrode plates obtained in the examples and comparative examples were cut with a cutter to a width of 250 mm, and the coated surface of the negative electrode plate was attached to a wooden board (300 mm long x 200 mm wide x 3 mm thick) with double-sided tape (manufactured by Nitto Denko Corporation). The force required to peel the copper foil from the coating layer using a TENSILON RTC-1210A (manufactured by A&D Corporation) was determined as the adhesion strength.

[0085] The dispersibility of the active material and the conductive additive in battery binders 1 to 7 was evaluated as follows.

[0086] <Evaluation of dispersibility of active materials> 5 g of SiOx was added to 125 g of a 0.2% by mass mixed solution of carboxymethylcellulose and nucleic acid, and the mixture was stirred at 2,500 rpm for 30 minutes. The resulting dispersion was diluted 100 times with water, and the particle size was measured using a ZETASIZER 3000 HSA (Malvern Instruments).

[0087] <Evaluation of the dispersibility of conductive additives> 0.1 g of acetylene black (Stream Chemical) was added to 125 g of a 0.2% by mass mixed solution of carboxymethylcellulose and nucleic acid, and the mixture was stirred at 2,500 rpm for 30 minutes. The resulting dispersion was diluted 100-fold with water, and the particle size was measured using a ZETASIZER 3000 HSA (Malvern Instruments).

[0088] Example 1 (Production of CMC(a)) A twin-screw kneader with the rotation speed adjusted to 100 rpm was charged with 600 parts of isopropanol and 38 parts of sodium hydroxide dissolved in 80 parts of water. The resulting mixture was then mixed and stirred for 90 minutes at 30°C to prepare mercerized cellulose. While stirring, 46 parts of monochloroacetic acid was added. After stirring for 30 minutes, the mixture was heated to 70°C and carboxymethylated for 90 minutes. After the reaction was completed, the mixture was neutralized with acetic acid to a pH of approximately 7, deliquored, dried, and pulverized to obtain carboxymethylcellulose sodium salt (a) (hereinafter sometimes referred to as "CMC(a)"), which had a carboxymethyl substitution degree of 0.70, a viscosity of a 1% by weight aqueous solution of 7,900 mPa·s measured at 25°C using a Brookfield viscometer, a filter residue of 48 ppm relative to the dry mass of carboxymethylcellulose dissolved in the aqueous solution, and a dispersity of 36.1%.

[0089] A yeast-derived RNA preparation (product name "RNA-FN", manufactured by Nippon Paper Industries Co., Ltd.) was used as nucleic acid (1). The weight-average molecular weight of "RNA-FN" was 11,000.

[0090] (Preparation of Battery Binder 1) The above-mentioned CMC (a) and nucleic acid (1) were mixed so that the weight ratio was CMC (a) / nucleic acid (1) = 95 / 5, and an electrode binder 1 was obtained, in which the viscosity of a 1 mass% aqueous solution measured with a Brookfield viscometer at 25°C was 3,130 mPa s.

[0091] (Creating the negative electrode plate) As the negative electrode material, SiOx, acetylene black (manufactured by Stream Chemical Co.), electrode binder 1, and styrene butadiene rubber (SBR, manufactured by JSR Corporation, product number S2910(E)-12-Na) were mixed so that the solids weight ratio was 100:0.5:1.0:1.5, water was added so that the slurry concentration was 45.6 mass%, and the mixture was thoroughly stirred using a Mazerustar (manufactured by Kurabo Industries, Ltd., KK-250S) to obtain slurry 1. This slurry was applied with an applicator to a copper foil (manufactured by Furukawa Electric Co., Ltd., NC-WS) measuring 320 mm in length, 170 mm in width, and 17 μm in thickness, and then air-dried for 30 minutes, followed by drying in a dryer at 60 ° C. for 30 minutes. Furthermore, using a small tabletop roll press (SA-602 manufactured by Tester Sangyo Co., Ltd.), the plate was pressed at 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 an effective discharge capacity of 2100 mAh / g.

[0092] Example 2 An electrode binder 2 and a negative electrode plate 2 using the same with the binder were obtained in the same manner as in Example 1, except that the compounding ratio of CMC (a) and nucleic acid (1) was changed to 90 / 10 and the basis weight was changed to 19.7 / m2.

[0093] Example 3 An electrode binder 3 and a negative electrode plate 3 using the same were obtained in the same manner as in Example 1, except that the compounding ratio of CMC (a) and nucleic acid (1) was changed to 80 / 20.

[0094] Example 4 An electrode binder 4 and a negative electrode plate 4 using the same were obtained in the same manner as in Example 1, except that the compounding ratio of CMC (a) and nucleic acid (1) was changed to 50 / 50.

[0095] (Comparative Example 1) An electrode binder 5 and a negative electrode plate 5 using the same were obtained in the same manner as in Example 1, except that the compounding ratio of CMC (a) and nucleic acid (1) was changed to 20 / 80.

[0096] (Comparative Example 2) An electrode binder 6 and a negative electrode plate 6 using the same were obtained in the same manner as in Example 1, except that CMC(a) was used alone.

[0097] (Comparative Example 3) An electrode binder 7 and a negative electrode plate 7 using the same were obtained in the same manner as in Example 1, except that nucleic acid (1) was used alone instead of CMC.

[0098] The evaluation results of adhesive strength and dispersibility in the examples and comparative examples are shown in Table 1 below.

[0099] [Table 1]

[0100] As shown in Table 1, Examples 1 to 4, which used the electrode binder of the present invention, had superior adhesion strength to Comparative Examples 1 and 3. Furthermore, Examples 1 to 4 had improved dispersibility (decreased particle size) compared to Comparative Example 2. It is believed that by mixing CMC, which has high adhesion strength, with nucleic acid, which has high dispersibility, both adhesion strength and dispersion effect were achieved. From the above, the electrode binder of the present invention was found to be excellent in adhesive strength between the active material and the current collector, and further, was also excellent in dispersibility of the active material and the conductive additive.

Claims

1. Component A: carboxymethyl cellulose and / or a salt thereof having a viscosity of 1,000 to 20,000 mPa s in a 1% by mass aqueous solution measured at 25°C with a Brookfield viscometer (30 rpm), Component B: a nucleic acid having a weight average molecular weight of 1,000 to 20,000; wherein a blending ratio of component A to component B in the binder for a non-aqueous electrolyte secondary battery electrode is component A / component B=99 / 1 to 40 / 60.

2. 2. The binder for a non-aqueous electrolyte secondary battery electrode according to claim 1, wherein the degree of carboxymethyl substitution per anhydroglucose unit of said component A is 0.5 to 1.

2.

3. 2. The binder for a non-aqueous electrolyte secondary battery electrode according to claim 1, wherein the component B is ribonucleic acid (RNA) derived from yeast.

4. An electrode composition for a non-aqueous electrolyte secondary battery, which uses the binder for a non-aqueous electrolyte secondary battery electrode according to claim 1.

5. An electrode for a non-aqueous electrolyte secondary battery, which uses the binder for a non-aqueous electrolyte secondary battery electrode according to claim 1.

6. A non-aqueous electrolyte secondary battery using the binder for electrodes of a non-aqueous electrolyte secondary battery according to claim 1.

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