TWI750759B - Electrode for non-aqueous electrolyte secondary battery, and manufacturing method thereof - Google Patents

Abstract

An electrode for a non-aqueous electrolyte secondary battery, which has an active material layer containing carboxymethyl cellulose and/or a salt thereof on a current collector, and has an active material layer from a surface layer of the active material layer to the current collector Brightness derived from carboxymethyl cellulose and/or its salt obtained by electron dyeing the active material layer with _{ruthenium tetroxide (RuO 4} ) in the image analysis of the scanning electron microscope in the depth direction of the body The average is above 85.

Description

Electrode for non-aqueous electrolyte secondary battery, and method for producing the same

The present invention relates to an electrode for a non-aqueous electrolyte secondary battery and a method for producing the same.

In recent years, with the rapid spread of small portable terminals represented by smartphones, tablet computers, and the like, there has been an increasing demand for small and high-energy-density batteries for driving them.

Generally, a graphite-based material is used for the negative electrode of a lithium ion secondary battery, but the theoretical capacity of the graphite-based material is 372 mAh/g (LiC ₆ ), and the current situation is close to the limit.

In order to further improve the energy density of lithium-ion secondary batteries, new materials need to be selected. Therefore, following carbon and lithium, materials obtained by alloying silicon, tin, and the like, which have a low potential and a large specific capacity, and lithium have attracted attention.

Among these materials, silicon can store lithium atoms up to 4.4 with respect to silicon atom 1 in terms of molar ratio, and theoretically, a capacity about 10 times that of graphite-based carbon materials can be obtained. However, when the silicon particles occlude lithium, the volume expands to about 3 times to 4 times. Therefore, there is a problem in that the deterioration progresses due to repeated charge and discharge, and the capacity decreases. When this phenomenon was analyzed in detail, it was confirmed that when lithium was inserted into an active material containing silicon, fine cracks were generated in the electrode due to volume expansion, and the electrolyte solution penetrated into the fine cracks. Cracks, forming a new film (solid electrolyte interface (solid electrolyte interface, SEI) layer). At this time, irreversible capacity that cannot be restored occurs, resulting in a decrease in battery capacity. This phenomenon appears when the charge-discharge efficiency changes in the middle of the cycle. In particular, the decrease in cycle efficiency in the initial stage of the cycle where the volume change is large has a great influence on the life of a battery that is combined with a positive electrode with high charge-discharge efficiency. Therefore, when an active material containing silicon is used, it is an important issue to minimize the change in the electrode structure due to the volume expansion.

In view of this situation, Patent Document 1 proposes that by using a negative electrode material in which carbon particles are modified with a silane coupling agent, it is possible to obtain an anode material which is excellent in durability and excellent in charge-discharge cycles even when a silicon-based compound is used. electrode.

In addition, Patent Document 2 proposes to improve durability by attaching niobium oxide to a silicon-based compound.

[Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 5599527

[Patent Document 2] Japanese Patent Laid-Open No. 2017-174829

However, both of Patent Document 1 and Patent Document 2 aim to improve the adhesion force in the electrode composition, and when the content of the silicon-based compound in the electrode composition is further increased, the electrode layer will deteriorate due to a change in volume expansion or the like. Adhesion is deteriorated, and there is battery life reduce worry.

In addition, if the crosslinking points are not uniformly dispersed in the electrode composition, there is a fear that the desired effect may not be exhibited, and improvement of the manufacturing method is required.

Therefore, an object of the present invention is to obtain an electrode for a non-aqueous electrolyte secondary battery that contains a large amount of a silicon-based active material without using components such as a cross-linking agent, and a method for producing the same. The maintenance of battery performance is also excellent.

The inventors of the present invention have made diligent studies and found that the above-mentioned problems can be solved by uniformly presenting carboxymethyl cellulose and/or a salt thereof in the active material layer.

That is, according to the present invention, there is provided the following: (1) An electrode for a non-aqueous electrolyte secondary battery having an active material layer containing carboxymethyl cellulose and/or a salt thereof on a current collector, wherein the non-aqueous electrolyte is The electrode for an electrolyte secondary battery is characterized by using ruthenium tetroxide (RuO ₄ ) The average brightness of the carboxymethyl cellulose and/or its salt obtained by electronically dyeing the active material layer is 85 or more; (2) The electrode for a non-aqueous electrolyte secondary battery according to (1) , wherein in the active material layer, the content of carboxymethyl cellulose and/or its salt is more than 1 mass % and 15 mass % or less; (3) the non-aqueous electrolyte according to (1) or (2) An electrode for a secondary battery, wherein the degree of substitution of the carboxymethyl group per glucose unit of the carboxymethylcellulose and/or its salt is more than 0.3 and less than 1.5; (4) as in (1) to (3) The electrode for a non-aqueous electrolyte secondary battery according to any one of the above, wherein the viscosity at 25° C. of a 1 mass % aqueous solution of the carboxymethyl cellulose and/or its salt measured by a Brookfield viscometer is 10 mPa. s~50000mPa. s; (5) A method for producing an electrode for a non-aqueous electrolyte secondary battery, the electrode for a non-aqueous electrolyte secondary battery having an active material layer containing carboxymethyl cellulose and/or a salt thereof on a current collector, The manufacturing method of the electrode for a non-aqueous electrolyte secondary battery is characterized by comprising: the following steps (1) to (2), and step (1): coating the current collector with a non-aqueous non-aqueous material containing at least an electrode active material An electrode composition for an electrolyte secondary battery, a step of obtaining an active material coating body; step (2): further coating a solution containing carboxymethyl cellulose and/or its salt on the obtained active material coating body step; (6) The method for producing an electrode for a non-aqueous electrolyte secondary battery according to (5), wherein scanning electrons in the depth direction from the surface layer of the active material layer to the current collector In the image analysis of the microscope, the average brightness of the carboxymethyl cellulose and/or its salt obtained by electron-dying the active material layer with _{ruthenium tetroxide (RuO 4 ) was 85 or more.}

According to the present invention, there can be obtained an electrode for a non-aqueous electrolyte secondary battery, and a method for producing the same, wherein the electrode for a non-aqueous electrolyte secondary battery has high battery performance even when a silicon-based active material is contained in a large amount without using components such as a cross-linking agent. The maintenance is also excellent.

FIG. 1 is a diagram showing a scanning electron microscope (SEM) mapping image of an example.

Hereinafter, the electrode for non-aqueous electrolyte secondary batteries of the present invention will be described. In the present invention, unless otherwise specified, "~" includes terminal values. That is, "X~Y" includes the values X and Y at both ends.

The electrode for a non-aqueous electrolyte secondary battery of the present invention has an active material layer containing carboxymethyl cellulose and/or a salt thereof on the current collector, and the electrode for a non-aqueous electrolyte secondary battery is characterized in that: In the image analysis of the scanning electron microscope in the depth direction from the surface layer of the active material layer to the current collector, the result is obtained by electron dyeing the active material layer with _{ruthenium tetroxide (RuO 4 ).} The average brightness of the carboxymethyl cellulose and/or its salt is 85 or more.

Moreover, the manufacturing method of the electrode for non-aqueous electrolyte secondary batteries of this invention is a method for manufacturing the electrode for non-aqueous electrolyte secondary batteries which has a carboxymethyl fiber on a current collector The active material layer of the element and/or its salt, the manufacturing method preferably includes the following steps (1) to (2).

Step (1): coating the current collector with an electrode composition for a non-aqueous electrolyte secondary battery containing at least an electrode active material to obtain an active material-coated body; Step (2): coating the obtained active material The cloth body is further coated with a solution containing carboxymethyl cellulose and/or its salt.

<active material layer>

The active material layer constituting the electrode for a non-aqueous electrolyte secondary battery of the present invention contains carboxymethyl cellulose and/or a salt thereof. In addition, the active material layer contains an electrode active material.

<Carboxymethylcellulose and/or its salt>

Carboxyl methyl cellulose and/or its salts (hereinafter, abbreviated as CMC (Carboxyl Methyl Cellulose, carboxymethyl cellulose)) contained in the active material layer constituting the present invention have glucose units constituting cellulose. A structure in which a hydroxyl group is substituted with a carboxymethyl ether group. Carboxymethylcellulose may be in the form of a salt. As a salt of carboxymethyl cellulose, metal salts, such as carboxymethyl cellulose sodium salt, etc. are illustrated.

In the present invention, the term cellulose refers to a polysaccharide having a structure in which D-glucopyranose (also simply referred to as "glucose unit" and "anhydroglucose") is linked by β-1,4 bonds. Cellulose is generally classified into natural cellulose, regenerated cellulose, fine cellulose, microcrystalline cellulose from which amorphous regions have been removed, and the like according to sources, production methods, and the like.

Examples of natural cellulose include cellulose produced by microorganisms such as bleached or unbleached pulp, purified cotton linters, and acetic acid bacteria. The raw material of bleached or unbleached pulp is not particularly limited, and examples thereof include wood, cotton, straw, bamboo, and the like. The manufacturing method of bleached or unbleached pulp is also not particularly limited, and a mechanical method, a chemical method, or a method in which a mechanical method and a chemical method are combined can be exemplified. As bleached or unbleached pulp, mechanical pulp, chemical pulp, groundwood pulp, sulfite pulp, kraft pulp, and pulp for papermaking can be exemplified. In addition, as bleached or unbleached pulp, there may be exemplified: Dissolving pulp used as a main raw material of rayon, cellophane, etc., which is chemically purified and mainly dissolved in chemicals.

Examples of regenerated cellulose include regenerated cellulose obtained by dissolving cellulose in a solvent such as a cuprammonium solution, a cellulose xanthate solution, and a morpholine derivative, and spinning again.

As fine cellulose, fine cellulose obtained by depolymerizing cellulose-based raw materials such as natural cellulose and regenerated cellulose by acid hydrolysis, alkali hydrolysis, enzymatic hydrolysis, blasting treatment, vibration ball milling treatment, etc., can be exemplified. ; Fine cellulose obtained by mechanically treating cellulose-based raw materials.

When manufacturing the CMC used by this invention, a well-known CMC manufacturing method can be applied. 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 perform an etherification reaction .

As the raw material cellulose, if it is the above-mentioned cellulose, it can be used without particular limitation, but cellulose with high cellulose purity is preferable, and dissolving pulp or cotton lint is more preferable. By using these, CMC with high purity can be obtained.

As a mercerizing agent, alkali metal hydroxides, such as sodium hydroxide and potassium hydroxide, can be illustrated. As an etherifying agent, monochloroacetic acid, sodium monochloroacetate, etc. can be illustrated.

In the production method of common water-soluble carboxymethyl cellulose, the molar ratio of the mercerizing agent and the etherifying agent (mercerizing agent/etherifying agent) is usually 2.00~2.45 when using monochloroacetic acid as the etherifying agent. . The reason for this is that by being 2.00 or more, the etherification reaction can sufficiently proceed, and unreacted monochloroacetic acid can be prevented from remaining and being wasted. By being 2.45 Hereinafter, the excess mercerizing agent and monochloroacetic acid can be prevented from side-reacting to generate an alkali metal glycolic acid salt, which is very economical.

In the present invention, CMC may be a commercially available product. As a commercial item, the brand name "Sunrose" by Nippon Paper Co., Ltd. is mentioned, for example.

In the present invention, the degree of etherification of CMC refers to the ratio of groups _{substituted with carboxymethyl ether groups (—OCH 2 COOH) among hydroxyl groups (—OH) in glucose units constituting cellulose.}

The CMC used in the present invention preferably has a degree of substitution of the carboxymethyl group per glucose unit (hereinafter, abbreviated as CM-DS) in the range of more than 0.3 and less than 1.5. When the CM-DS exceeds 0.3, the solubility in water can be well maintained, and the generation of undissolved substances can be suppressed. In addition, since the CM-DS is less than 1.5, the increase in the stringiness of the liquid can be suppressed, and the handling is ensured. CM-DS can be calculated by the method shown in the Example. Therefore, the CM-DS of the CMC of the present invention is preferably more than 0.3 and less than 1.5, more preferably more than 0.4 and less than 1.2, particularly preferably more than 0.45 and less than 1.1.

In addition, the measurement method of the substitution degree of a carboxymethyl group is as follows: About 2.0 g of a sample is accurately weighed, and it put into a 300 mL conical flask with a stopper. 100 mL of a liquid prepared by adding 100 mL of super concentrated nitric acid to 1000 mL of methanol was added and shaken for 3 hours to convert the salt of carboxymethyl cellulose (CMC) into H-CMC (hydrogen carboxymethyl cellulose). Accurately weigh 1.5g~2.0g of the absolutely dry H-CMC and put it into a 300mL conical flask with a stopper. The H-CMC was wetted 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 H 2} SO ₄ , and the carboxymethyl substitution degree (DS value) was calculated by the following formula.

A=[(100×F'-(0.1N H ₂ SO ₄ )(mL)×F)×0.1]/(Absolute dry mass of H-CMC(g))

Degree of substitution of carboxymethyl group=0.162×A/(1-0.058×A)

F ': 0.1N factor of H ₂ SO ₄ is

F: Factor of 0.1N NaOH

Moreover, it is preferable that the viscosity measured using the Brookfield viscometer of the CMC 1 mass % aqueous solution at 25 degreeC is 10 mPa. s~50,000mPa. s.

Furthermore, the viscosity measurement method is as follows: take the amount of carboxymethyl cellulose or its salt into a glass beaker with a capacity of 1000 mL, disperse it in 900 mL of distilled water, and make the solid content as 1% (w/v). way to prepare an aqueous dispersion. The aqueous dispersion was stirred for 3 hours at 25°C using a stirrer at 600 rpm. Then, according to the method of Japanese Industrial Standards (JIS)-Z-8803, using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.), the viscosity after 3 minutes was measured at No. 1 rotor/revolution number 30 rpm. Determination.

The CMC used in the present invention may be one type, or may be a combination of two or more types of CMCs having different degrees of etherification, CM-DS, viscosity, molecular weight, and the like.

<Electrode Active Material>

Regarding the electrode active material contained in the active material layer constituting the present invention, when the electrode for a non-aqueous electrolyte secondary battery is an electrode for a negative electrode, it is a negative electrode active material. The substance is a positive electrode active material when the electrode for a non-aqueous electrolyte secondary battery is an electrode for a positive electrode.

Examples of the negative electrode active material include graphite (natural graphite, artificial graphite, etc.), coke, carbon fiber, and other graphite materials; elements that can form alloys with lithium, such as silicon-based compounds, Al, Sn, Ag, Bi, Mg, Elements such as Zn, In, Ge, Pb, Ti, etc.; compounds containing elements that can form alloys with lithium; elements that can form alloys with lithium and composites of said compounds, and carbon and/or said graphitic materials, or Nitride containing lithium, etc. Among them, graphite materials and silicon-based compounds are preferred, and graphite and silicon particles or silicon oxide particles as silicon-based compounds are more preferred.

In addition, the silicon oxide of the present invention refers to _{a compound represented by SiO x} (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 further suitable.

In the case where the negative electrode active material is a composite of a graphite material and a silicon-based compound, the graphite material and the silicon-based compound are preferably a blending ratio of graphite material: silicon-based compound=10~90:90~10, More preferably, it is 50-80:50-20.

As the positive electrode active material, preferably _{LiFePO 4, LiMe x O y (} Me refers to a Ni, Co, at least one transition metal of Mn; x, y refers to any number) of the positive electrode active material lines.

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

<Electrode for Nonaqueous Electrolyte Secondary Battery>

The method for producing an electrode for a non-aqueous electrolyte secondary battery of the present invention preferably includes: step (1): coating the current collector with an electrode composition for a non-aqueous electrolyte secondary battery (hereinafter, the following: abbreviated as "electrode composition"), the step of obtaining an active material coating body; step (2): further coating a solution comprising carboxymethyl cellulose and/or its salt on the obtained active material coating body step.

<Electrode composition>

The electrode composition contains at least an electrode active material. As the electrode active material, the above-mentioned materials can be exemplified.

Moreover, in this invention, carboxymethyl cellulose and/or its salt can constitute an electrode composition together with an electrode active material as a binder for electrodes. In this case, the content of the carboxymethyl cellulose and/or its salt in the electrode composition is preferably 0.1% by mass to 4.0% by mass relative to the entire electrode composition.

In addition, a binder other than the aqueous solution of carboxymethylcellulose and/or its salt may be contained in the electrode composition. As the binder used in the electrode composition for negative electrodes, a synthetic rubber-based binder can be exemplified. As the synthetic rubber-based binder, one selected from the group consisting of styrene butadiene rubber (SBR), nitrile butadiene rubber, methyl methacrylate butadiene rubber, chloroprene rubber, and carboxyl modified One or more of the group consisting of styrene butadiene rubber and latex of these synthetic rubbers. Among them, styrene butadiene rubber (SBR) is preferred. In addition, as the binder used in the electrode composition for positive electrodes, in addition to the synthetic rubber-based binders exemplified as the binder for negative electrodes, polytetrafluoroethylene can also be exemplified. (Polytetrafluoroethylene, PTFE) Among them, polytetrafluoroethylene (PTFE) is preferably used.

The content of the binder in the electrode composition is usually 1% by mass to 10% by mass, preferably 1% by mass to 6% by mass, and more preferably 1% by mass to 2% by mass.

In addition, the electrode composition may contain a conductive aid as needed. Examples of the conductive aid include conductive carbon such as carbon black, acetylene black, and Ketjen black. The content of the conductive aid in the electrode composition is usually 0.01% by mass to 20% by mass, preferably 0.1% by mass to 10% by mass.

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

The so-called water-soluble organic solvent refers to an organic solvent dissolved in water. Examples thereof include methanol, ethanol, 2-propanol, butanol, glycerol, acetone, methyl ethyl ketone, 1,4-dioxane, N-methyl-2-pyrrolidone, tetrahydrofuran ( tetrahydrofuran (THF), N,N-dimethylformamide (N,N-dimethylformamide, DMF), N,N-dimethylacetamide, dimethyl sulfoxide (DMSO), acetonitrile, Methyl triethylene glycol succinate, acetic acid, combinations of these, and the like.

When the mixed solvent is used as an 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 still more preferably 70% by mass or more. The upper limit of the amount is not particularly limited, but is preferably 95% by mass or less, more preferably 90% by mass or less. In addition, without prejudice to the effect of the invention The water-based solvent may also include a water-insoluble organic solvent within the scope of the present invention.

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 and/or its salt, and mixed as necessary while stirring.

In addition, the properties of the electrode composition are also not particularly limited. For example, a liquid state, a paste form, a slurry form, etc. are mentioned, and any one may be sufficient.

<Active material coating body>

By applying the electrode composition on the current collector, an active material-coated body can be obtained. As a coating method, for example, blade coating, bar coating, and die coating are mentioned, and blade coating is preferable. For example, in the case of doctor blade coating, a method of casting the electrode composition on the current collector using a coating device such as a doctor blade can be exemplified. In addition, the method of lamination is not limited to the above-mentioned specific example, and a method may be exemplified in which the electrode composition is ejected from an extrusion-type liquid injector having a slit nozzle onto a current collector that is wound around a backup roll and travels material and coated. In doctor blade coating, after casting, drying by heating (for example, 80° C. to 120° C., and heating time, for example, 4 hours to 12 hours), etc., and pressing by roll pressing, etc. can be performed as necessary. An active material-coated body is obtained.

<Current collector>

As the current collector, any conductor can be used as long as it does not cause a fatal chemical change in the electrode or battery to be formed. When an electrode is a negative electrode, the current collector for negative electrodes can be used, and when an electrode is a positive electrode, the current collector for positive electrodes can be used.

As a material of the current collector for negative electrodes, stainless steel, nickel, copper, titanium, carbon, a material in which carbon, nickel, titanium, or silver is adhered to the surface of copper or stainless steel, and the like can be exemplified. Among these, copper or a copper alloy is preferable, and copper is more preferable.

As a material of the current collector for positive electrodes, metals such as aluminum and stainless steel can be exemplified, and aluminum is preferred.

As the shape of the current collector, a mesh, a punched metal, a foamed metal, a foil processed into a plate shape, etc. can be exemplified, and a foil processed into a plate shape is preferred.

<Solution containing carboxymethylcellulose and/or its salt>

In the electrode for a nonaqueous electrolyte secondary battery of the present invention, it is preferable that a solution containing carboxymethyl cellulose and/or a salt thereof is further coated on the active material-coated body formed on the current collector.

As such a solution containing carboxymethylcellulose and/or a salt thereof, an aqueous solvent in which carboxymethylcellulose is dissolved may be used as a solvent, and it is generally preferable to use water as a solvent. In addition, the above-mentioned solvent is mentioned as an aqueous solvent.

The production conditions of the aqueous solution of carboxymethylcellulose and/or its salt are not particularly limited. For example, carboxymethylcellulose and/or its salt are added to water (for example, distilled water, purified water, tap water, etc.), and if necessary, it is prepared by stirring or the like to dissolve it. The concentration of carboxymethyl cellulose and/or its salt in the carboxymethyl cellulose solution thus obtained is usually 0.1% by mass to 10% by mass, preferably 0.2% by mass to 4% by mass, more preferably 0.5% by mass ~2 mass %.

The method for coating the active material coating body with the solution containing carboxymethyl cellulose and/or its salt is not particularly limited, for example, the active material coating body can be selected By the same method as the lamination method of the present invention, an electrode for a non-aqueous electrolyte secondary battery suitable for the present invention can be obtained.

For the electrode for a nonaqueous electrolyte secondary battery of the present invention obtained in the manner described above, it is important that, in a scanning electron microscope (SEM) image analysis, the activity _{derived from the use of ruthenium tetroxide (RuO 4 )} The average brightness of the carboxymethyl cellulose and/or its salt obtained by electronically dyeing the material layer is 85 or more.

In addition, the measurement conditions of the said brightness are as follows.

The electrode for a non-aqueous electrolyte secondary battery was vacuum degassed and electron-dyed with _{osmium tetroxide (OsO 4 ).} Then, vacuum degassing was performed again, and after removing osmium tetroxide from the processing space, electron dyeing was performed with _{ruthenium tetroxide (RuO 4 ).} For the electron-dyed active material layer, a scanning electron microscope (product name: JSM IT-300 (manufactured by JEOL Ltd.) was used, and measurement conditions: acceleration voltage 10 Kv, number of lines of irradiation current 20,000 cps, double time 1 mSec, scanning (sweep times 100), mapping measurements were performed, and the obtained mapping data were extracted using image analysis software (product name: Image J) derived from carboxymethyl groups obtained by electron staining with ruthenium tetroxide. The color development of cellulose and/or its salt is green (Green), and the luminance in the depth direction from the surface layer of the active material layer to the current collector is measured. The average value was obtained by removing the luminance within 5 pixels from the interface with the current collector. Furthermore, the brightness is represented by a numerical value of 8 bits (0~255) and has no unit.

In the active material layer, when the average brightness of carboxymethylcellulose and/or its salt satisfies the above-mentioned range, the effect of the present invention can be obtained at a high level. As the principle, it is presumed that the carboxymethyl cellulose added to the electrode composition is in the electrode composition It exhibits excellent effects such as binding properties and thickening properties, but is affected by the active material when it is applied to the current collector to form the active material layer. Even if the electronic dyeing is performed, the brightness derived from carboxymethyl cellulose is The color rendering is also limited. In this state, when a silicon-based compound with high expansion and shrinkage is used in the active material layer, cracks are likely to be generated in the active material layer during charge and discharge.

On the other hand, it is presumed that the electrode for a non-aqueous electrolyte secondary battery satisfying the structure of the present invention is, for example, by coating an electrode containing carboxymethyl cellulose and/or a salt thereof after the active material coating body is formed. solution, etc., to obtain a state in which carboxymethyl cellulose and/or its salts are uniformly present in the active material layer, so that even if a silicon-based compound with high expansion and shrinkage is used in the active material layer, the The active material layer exhibits a buffering effect, and thus exhibits the excellent effects of the present invention. Furthermore, it is considered that carboxymethyl cellulose and/or its salt permeate into the active material-coated body by applying a solution containing carboxymethyl cellulose and/or its salt after the active material-coated body is formed. . Moreover, similarly, the effect of this invention can be exhibited if it is a state in which carboxymethylcellulose and/or its salt are uniformly distributed in an active material coating body.

The shape of the electrode for a nonaqueous electrolyte secondary battery of the present invention is not particularly limited, but is usually a sheet shape. The thickness in the case of a sheet-like electrode plate (thickness of the mixture layer formed of the electrode composition excluding the current collector portion) is difficult to specify because it also depends on the composition of the composition, manufacturing conditions, etc., but is usually 30 μm to 150 μm .

<Non-aqueous electrolyte secondary battery>

The electrode for a nonaqueous electrolyte secondary battery of the present invention can be used as an electrode of a nonaqueous electrolyte secondary battery. Non-aqueous electrolyte secondary batteries can be alternately positive and negative It is a structure formed by stacking and winding multiple times with a spacer in between. In addition, a non-aqueous electrolyte secondary battery can be obtained by putting the laminated body of the positive electrode, the separator, and the negative electrode wound many times into a battery container, pouring a non-aqueous electrolyte, and sealing.

The shape of the non-aqueous electrolyte secondary battery is not particularly limited, and a cylindrical type, a square type, a flat type, a coin type, a button type, a sheet type, and the like can be used. In addition, the material of the battery container is not particularly limited as long as the purpose of preventing the intrusion of moisture into the battery can be achieved, and laminates of metals, aluminum, and the like are exemplified.

Furthermore, the separator is usually impregnated with a non-aqueous electrolyte. As the separator, for example, a microporous film or nonwoven fabric made of polyolefin such as polyethylene and polypropylene can be used.

In addition, the non-aqueous electrolyte usually contains a lithium salt and a non-aqueous solvent. As the lithium salt, and examples thereof _{include: LiPF 6, LiAsF 6, LiBF} 4, LiClO 4 and the like. Moreover, as a non-aqueous solvent, ethylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, butyl carbonate, methyl ethyl carbonate, etc. are mentioned. The non-aqueous solvent may be used alone or in combination of two or more. The concentration of the lithium salt in the non-aqueous electrolyte is usually used at a concentration of 0.5 mol/L to 2.5 mol/L.

[Example]

Hereinafter, embodiments of the present invention will be described by way of examples, but the present invention is not limited to the examples.

(Example 1)

<Production of negative electrode plate>

_{1.0 g of 98 mass % graphite powder and 1.0 g of 98 mass % SiO x} powder as negative electrode active materials were prepared by Mazerustar (manufactured by Kurabo Industries, Ltd., Mazerustar KK-250S). 0.01 g of 98% by mass acetylene black as a conductive aid, CMC (trade name Sunrose (manufactured by Nippon Paper Co., Ltd.), MAC500LC, DS=0.67, 1% viscosity 4700 mPa·s) water as a binder 1.0 g of the dispersion liquid (2 mass %), 63 mg of 48 mass % styrene butadiene rubber (SBR), and 1.5 g of water were mixed to obtain an electrode composition for a negative electrode. Then, the obtained electrode composition for negative electrodes was applied on a current collector (copper foil of 320 mm in length x 170 mm in width x 17 μm in thickness (manufactured by Furukawa Electric Co., Ltd., NC-WS)), dried at room temperature for 30 minutes, thereby forming an active material coating body on the current collector.

After forming the active material coating body on the current collector, using an applicator, CMC ( A carboxymethyl group obtained by mixing 2 g of an aqueous dispersion (2 mass %) and 2.9 g of water with a trade name of Sunrose (manufactured by Nippon Paper Co., Ltd., MAC500LC, DS=0.67, 1% viscosity 4700 mPa.s) The cellulose solution was applied to the active material-coated body, and dried at 120° C. for 30 minutes. After drying, it pressed at 5.0 kN using a small table-top roll press (manufactured by Tester Sangyo Co., Ltd., SA-602), and the negative electrode plate 1 was obtained.

<Production of Coin-Type Nonaqueous Electrolyte Secondary Battery>

_{The obtained negative electrode plate 1 and LiCoO 2} positive electrode plate (manufactured by Baoquan Co., Ltd., unit area weight 227.1 g/m ² , effective discharge capacity 145 mAh/g) were punched out so as to form a circle with a diameter of 16 mm, respectively. The blanked negative and positive plates were vacuum dried at 120° C. for 12 hours.

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

After that, the negative electrode plate 1 was placed in a stainless steel circular disk-shaped container with a diameter of 20.0 mm, and a separator, a positive electrode plate, a spacer (15.5 mm in diameter, 1 mm in thickness), and a stainless steel gasket (Baoquan) were laminated in this order. Co., Ltd.), and then 300 μl of an electrolytic solution (1 mol/L LiPF ₆ , a volume ratio of ethylene carbonate to diethyl carbonate: 1:1) was added to a circular disc-shaped container. A lid made of stainless steel was covered with a polypropylene gasket therebetween, and sealed with a coin cell caulking machine (Baoquan Co., Ltd.) to obtain a coin-type non-aqueous electrolyte secondary battery 1 .

(Comparative Example 1)

An electrode composition for a negative electrode was prepared in the same manner as in Example 1. Next, the obtained electrode composition for negative electrodes was coated on a current collector (320 mm in length x 170 mm in width x 17 μm in thickness copper foil (manufactured by Furukawa Electric Co., Ltd., NC) using an applicator so that the thickness at the time of coating was 130 μm. -WS)) at 120°C after drying at room temperature for 30 minutes. Dry at °C for 30 minutes. After drying, it pressed at 5.0 kN using a small table roll press (manufactured by Tester Sangyo Co., Ltd., SA-602) to obtain a negative electrode plate 2 having an active material layer on a current collector.

Next, a coin-type nonaqueous electrolyte secondary battery 2 was produced by the same procedure as in Example 1 except that the negative electrode plate 2 was used instead of the negative electrode plate 1 .

<Evaluation method>

<Carboxymethylcellulose in the active material layer derived from electro-dyeing and/or determination of the brightness of its salt>

The electrodes for non-aqueous electrolyte secondary batteries obtained in Examples and Comparative Examples were cut out in a size of 5 mm in length x 10 mm in width, and used as test pieces. The obtained test piece was attached to a glass slide using a double-sided tape, the test piece was degassed under reduced pressure together with the slide glass, and then _{steam-dyed with osmium tetroxide (OsO 4} ) for 5 hours.

Next, the test piece was degassed under reduced pressure for half a day, and steam-stained with _{ruthenium tetroxide (RuO 4 ) for 1 hour together with the glass slide.} After standing under reduced pressure for about half a day to disperse unreacted RuO ₄ , an electronically dyed test piece was obtained.

The electron-dyed test piece was subjected to mapping measurement using a scanning electron microscope (JSM-IT300, manufactured by JEOL Ltd.) (pressing voltage 10 kV, irradiation current: line count 20,000 cps, double time 1 mSec, scanning count 100), Get mapping information.

The obtained mapping data was image-saved with a 24-bit mapping setting, and the image was imported into an image analysis software (product name: Image J).

RGB color separation was performed to extract the color derived from carboxymethyl cellulose and/or its salt after electron dyeing with ruthenium tetroxide, i.e. green, and the content from the surface layer of the active material layer to the current collector was measured. The brightness of the range including the depth direction. Then, the luminance within 5 pixels from the interface with the current collector was removed, and the average value was obtained, and the luminance was defined as the luminance derived from carboxymethyl cellulose and/or its salt. The SEM mapping images of Example 1 and Comparative Example 1 are shown in FIG. 1 . Furthermore, the brightness is represented by a numerical value of 8 bits (0~255) and has no unit.

<Discharge capacity>

For the charge-discharge rate test, a secondary battery charge-discharge tester (BTS2004, manufactured by Nagano Co., Ltd.) was used in a constant temperature bath at 25°C. For the water electrolyte secondary battery, 52 cycles were performed with one cycle of charge and discharge performed in this order of charge treatment and discharge treatment.

In addition, as the conditions of the charging process, in all the cycles, a constant current constant voltage (CC-CV (constant current-constant voltage)) method (CC current 0.2C, CV voltage 4.2V, termination current 0.02) was used. C). In addition, as a condition of the discharge treatment, the termination voltage was set to 3.0V. A constant current of the discharge treatment was applied at 0.2 C for the first cycle, and the discharge capacity A (mAh/g) after one cycle was measured after the discharge.

The constant current of the discharge treatment was set as follows until the 52nd cycle thereafter, and the measurement of the discharge capacity B (mAh/g) was performed after the 52th cycle of discharge.

. (Constant current of discharge treatment in each cycle)

2 cycles ~ 10 cycles: constant current 0.2C for discharge treatment

11 cycles ~ 20 cycles: constant current 1C for discharge treatment

21 cycles: constant current 0.2C for discharge treatment

22 cycles ~ 31 cycles: constant current 2C for discharge treatment

32 cycles: constant current 0.2C for discharge treatment

33 cycles ~ 42 cycles: constant current 3C for discharge treatment

43 cycles ~ 52 cycles: constant current 0.2C for discharge treatment

<Capacity retention rate>

The capacity retention rate is based on the discharge capacity A and the discharge capacity B in each cycle test described above, and the capacity retention rate (%)=discharge capacity B after 52 cycles (mAh/g)/discharge capacity after 1 cycle A (mAh/g) × 100 formula to calculate.

Table 1 shows the measurement results of brightness, discharge capacity, and capacity retention rate derived from carboxymethylcellulose and/or its salt.

From the results shown in Table 1, it was shown that the obtained non-aqueous electrolyte secondary battery was excellent in the capacity retention rate of the electrode for a non-aqueous electrolyte secondary battery having the following electrode for a non-aqueous electrolyte secondary battery Scanning electron microscope view of the current collector having an active material layer containing carboxymethyl cellulose and/or a salt thereof, and in the depth direction from the surface layer of the active material layer to the current collector In the image analysis, the average brightness derived from carboxymethyl cellulose and/or its salt obtained by electronically dyeing the active material layer with _{ruthenium tetroxide (RuO 4 ) was 85 or more.}

Claims (5)

An electrode for a non-aqueous electrolyte secondary battery, which has an active material layer containing carboxymethyl cellulose and/or a salt thereof on a current collector, wherein the electrode for a non-aqueous electrolyte secondary battery is characterized in that: In the image analysis of the scanning electron microscope in the depth direction from the surface layer of the active material layer to the current collector, it is derived from the carboxymethyl group obtained by electron dyeing the active material layer with ruthenium tetroxide. The average brightness of the cellulose and/or its salt is 85 or more, and the degree of substitution of the carboxymethyl group per glucose unit in the carboxymethyl cellulose and/or its salt is more than 0.3 and less than 1.5. The electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the content of carboxymethyl cellulose and/or its salt in the active material layer is more than 1 mass % and 15 mass % or less. The electrode for a non-aqueous electrolyte secondary battery according to claim 1 or claim 2, wherein the carboxymethyl cellulose and/or its salt has a 1 mass % aqueous solution at 25°C measured by a Brookfield viscometer. The viscosity is 10mPa. s~50000mPa. s. A method for producing an electrode for a non-aqueous electrolyte secondary battery, the electrode for a non-aqueous electrolyte secondary battery having an active material layer containing carboxymethyl cellulose and/or a salt thereof on a current collector, the non-aqueous electrolyte secondary battery The method for producing an electrode for a secondary battery is characterized by comprising the following steps (1) to (2), and step (1): coating a current collector with at least an electrode active material for a non-aqueous electrolyte secondary battery an electrode composition, and a step of obtaining an active material coating body; Step (2): A step of further coating a solution containing carboxymethyl cellulose and/or a salt thereof on the obtained active material coating body. The method for producing an electrode for a non-aqueous electrolyte secondary battery according to claim 4, wherein image analysis by scanning electron microscopy in the depth direction from the surface layer of the active material layer to the current collector Among them, the average of the brightness derived from carboxymethyl cellulose and/or a salt thereof obtained by electronically dyeing the active material layer using ruthenium tetroxide is 85 or more.

Images