JP2024001950A - Carboxymethyl cellulose and/or its salts, electrode composition for non-aqueous electrolyte secondary battery, electrode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide carboxymethyl cellulose and/or its salts capable of obtaining an electrode layer with a small electric resistance and that is used for a binding agent for an electrode of a non-aqueous electrolyte secondary battery.

SOLUTION: Provided is carboxymethyl cellulose and/or its salts used for a binding agent for an electrode of a non-aqueous electrolyte secondary battery, in which a carboxymethyl substitution degree per anhydrous glucose unit is 0.5-1.2. A degree of dispersion measured by using a powder tester is 20-60%.

SELECTED DRAWING: None

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to carboxymethylcellulose and/or a salt thereof used as a binder for an electrode of a non-aqueous electrolyte secondary battery, and an electrode composition for a non-aqueous electrolyte secondary battery using this carboxymethylcellulose and/or a salt thereof. , relates to an electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

In recent years, with the rapid spread of small mobile terminals such as smartphones and tablets, and stationary storage batteries, there has been an increasing demand for small, high-energy-density batteries to power these devices.

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 ), which is currently approaching its limit.

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

Among these materials, silicon can absorb up to 4.4 lithium atoms per 1 silicon atom in terms of molar ratio, and theoretically a capacity about 10 times that of graphite-based carbon materials can be obtained. However, when silicon particles occlude lithium, their volume expands approximately three to four times, so repeated charging and discharging progresses their deterioration and reduces capacity, which is a problem. A detailed analysis of this phenomenon shows that when lithium is inserted into an active material containing silicon, microscopic cracks occur within the electrode due to volumetric expansion, and the electrolyte penetrates into these microscopic cracks, forming a new coating (SEI layer). has been confirmed to be formed. At this time, an irreversible capacity that cannot be restored is generated, resulting in a decrease in battery capacity. This phenomenon appears in changes in charging and discharging efficiency during the cycle. In particular, a decrease in cycle efficiency at the initial stage of the cycle, where the volume change is large, has a large impact on the life of a battery that is combined with a positive electrode that has high charge/discharge efficiency. Therefore, when using an active material containing silicon, it is important to minimize changes in the electrode structure due to this volumetric expansion.

Under these circumstances, Patent Document 1 uses a binder that essentially contains three components: carboxymethyl cellulose or its metal salt, polyacrylic acid or its metal salt, and styrene-butadiene rubber or polyvinidene fluoride to improve battery characteristics. We are trying to However, according to the examples and comparative examples of Patent Document 1, when only two components (carboxymethylcellulose and styrene-butadiene rubber, or carboxymethylcellulose and polyvinidene fluoride) are used as binders, desired battery characteristics can be obtained. It wasn't.

Japanese Patent Application Publication No. 2015-198038

Although Patent Document 1 states that three components including carboxymethyl cellulose or its metal salt are essential as a binder, there is no particular mention of the physical properties of carboxymethyl cellulose or its metal salt. According to studies by the present inventors, it has been found that this physical property affects battery characteristics, particularly the electrical resistance of the obtained electrode layer.

That is, an object of the present invention is to provide carboxymethylcellulose and/or a salt thereof for use in an electrode binder of a non-aqueous electrolyte secondary battery, which can provide an electrode layer with low electrical resistance; An object of the present invention is to provide an electrode composition for a nonaqueous electrolyte secondary battery, an electrode for a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery using methylcellulose and/or a salt thereof.

As a result of intensive studies, the present inventors found that the above problem can be solved by using a material having a predetermined degree of dispersion.

That is, according to the present invention,
(1) Carboxymethylcellulose and/or its salt used as a binder for electrodes of non-aqueous electrolyte secondary batteries, which has a degree of carboxymethyl substitution per anhydroglucose unit of 0.5 to 1.2, and is a powder Carboxymethyl cellulose and/or its salt, the degree of dispersion measured using a tester is 20 to 60%,
(2) The carboxymethyl cellulose and/or its salt according to (1), which has an angle of repose of 42° or more;
(3) The carboxymethylcellulose and/or its salt according to (1) or (2), which has a collapse angle of 19° or more,
(4) The carboxymethyl cellulose and/or according to (1) or (2), wherein the viscosity of a 1% by mass aqueous solution measured with a B-type viscometer (30 rpm) at 25 ° C. is 1,000 to 20,000 mPa s. or its salt;
(5) Prepare 2 liters of a 0.3% by mass aqueous solution of the carboxymethyl cellulose or its salt with a dry mass of m, filter it all through a 250 mesh filter under a reduced pressure condition of -200 mmHg, and remove the residue on the filter after filtration. Carboxymethylcellulose and/or its salt according to (1) or (2), wherein when the dry mass M of the dry mass M is measured, the ratio of the dry mass M to the dry mass M is less than 200 ppm,
(6) An electrode composition for a non-aqueous electrolyte secondary battery, comprising the carboxymethyl cellulose and/or its salt according to (1) or (2), and styrene-butadiene rubber having an average particle size of 50 nm to 300 nm.
(7) The electrode composition for a non-aqueous electrolyte secondary battery according to (6), wherein the styrene-butadiene rubber has a glass transition temperature of -50°C to 50°C. An electrode for non-aqueous electrolyte secondary batteries using an electrode composition for aqueous electrolyte secondary batteries,
(9) A non-aqueous electrolyte secondary battery using the electrode composition for a non-aqueous electrolyte secondary battery according to (6) or (7),
is provided.

According to the present invention, there is provided carboxymethylcellulose and/or a salt thereof that is used as a binder for an electrode of a non-aqueous electrolyte secondary battery that can provide an electrode layer with low electrical resistance. Further, 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 using this carboxymethyl cellulose and/or a salt thereof are provided.

The carboxymethyl cellulose and/or its salt of the present invention will be explained below. The carboxymethyl cellulose and/or its salt of the present invention is carboxymethyl cellulose and/or its salt used as an electrode binder of a non-aqueous electrolyte secondary battery, and has a degree of carboxymethyl substitution per anhydroglucose unit of 0. 5 to 1.2, and the degree of dispersion measured using a powder tester is 20 to 60%.

<Carboxymethylcellulose and/or its salt>
Carboxymethyl cellulose and/or its salt (hereinafter sometimes abbreviated as CMC) contained in the active material layer constituting the present invention has a hydroxyl group in a glucose unit constituting cellulose substituted with a carboxymethyl ether group. Has a structure. Carboxymethylcellulose may be in the form of a salt. Examples of carboxymethylcellulose salts include metal salts such as carboxymethylcellulose sodium salt.

In the present invention, cellulose refers to a polysaccharide having a structure in which D-glucopyranose (simply referred to as "glucose unit" or "anhydroglucose") is linked through β,1-4 bonds. Cellulose is generally classified into natural cellulose, regenerated cellulose, fine cellulose, microcrystalline cellulose excluding non-crystalline regions, etc., depending on its origin, manufacturing method, etc.

Examples of natural cellulose include bleached or unbleached pulp, purified linter, and cellulose produced by microorganisms such as acetic acid bacteria. The raw material for bleached or unbleached pulp is not particularly limited, and examples thereof include wood, cotton, straw, bamboo, and the like. The method for producing bleached or unbleached pulp is not particularly limited, and examples thereof include mechanical methods, chemical methods, and methods that combine mechanical methods and chemical methods. Examples of bleached or unbleached pulp include mechanical pulp, chemical pulp, groundwood pulp, sulfite pulp, kraft pulp, and papermaking pulp. Examples of bleached or unbleached pulp include dissolving pulp, which is chemically refined and used primarily by dissolving in chemicals, and is a main raw material for artificial fibers, cellophane, and the like.

Examples of regenerated cellulose include regenerated cellulose obtained by dissolving cellulose in a solvent such as a cupric ammonia solution, a cellulose xanthate solution, or a morpholine derivative, and spinning the resulting solution again.

Fine cellulose includes fine cellulose and cellulose-based materials obtained by depolymerizing cellulose-based materials such as natural cellulose and regenerated cellulose through acid hydrolysis, alkaline hydrolysis, enzymatic decomposition, blasting treatment, vibrating ball mill treatment, etc. An example is fine cellulose obtained by mechanical treatment.

In manufacturing the CMC used in the present invention, known CMC manufacturing methods can be applied. For example, CMC can be produced by treating cellulose with a mercerizing agent (alkali) to prepare mercerized cellulose (alkali cellulose), then adding an etherifying agent to the mercerized cellulose and causing an etherification reaction. .

As the raw material cellulose, any of the above-mentioned celluloses can be used without particular limitation, but those with high cellulose purity are preferred, and dissolving pulp or linters are more preferred. By using these, highly pure CMC can be obtained.

Examples of the mercerizing agent include alkali metal hydroxide salts such as sodium hydroxide and potassium hydroxide. Examples of the etherification agent include monochloroacetic acid, monochloroacetic acid soda, and the like.

In a general method for producing water-soluble carboxymethylcellulose, the molar ratio of the mercerizing agent to the etherifying agent (mercerizing agent/etherifying agent) is 2.00 to 2.00 when monochloroacetic acid is used as the etherifying agent. 45 is common. The reason for this is that when it is 2.00 or more, the etherification reaction can be carried out sufficiently, and it is possible to prevent unreacted monochloroacetic acid from remaining and being wasted. When it is 2.45 or less, it is possible to prevent side reactions caused by excess mercerizing agent and monochloroacetic acid from proceeding to produce an alkali metal salt of glycolate, which is economical.
In the present invention, CMC may be a commercially available product. Examples of commercially available products include the product name "Sunrose" manufactured by Nippon Paper Industries, Ltd.

In the present invention, the degree of etherification of CMC indicates the proportion of groups substituted with carboxymethyl ether groups (-OCH ₂ COOH) among hydroxyl groups (-OH) in glucose units constituting cellulose.

(degree of substitution of carboxymethyl group)
CMC used in the present invention has a carboxymethyl group substitution degree (hereinafter sometimes referred to as DS value) per anhydroglucose unit of 0.5 to 1.2. By having a DS value of 0.5 or more, good solubility in water can be maintained and generation of undissolved substances can be suppressed. Moreover, by having a DS value of 1.2 or less, increase in stringiness of the liquid can be suppressed and handling can be maintained easily. 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.

The method for measuring the degree of substitution of carboxymethyl groups is as follows:
Weigh approximately 2.0 g of the sample accurately and place it in a 300 mL Erlenmeyer flask with a stopper. Add 100 mL of a solution prepared by adding 100 mL of special grade concentrated nitric acid to 1000 mL of methanol, and shake for 3 hours to convert carboxymethyl cellulose salt (CMC) to H-CMC (hydrogen form carboxymethyl cellulose). Accurately weigh 1.5 to 2.0 g of the bone-dried H-CMC and place it in a 300 mL Erlenmeyer flask with a stopper. Wet H-CMC with 15 mL of 80% methanol, add 100 mL of 0.1N NaOH, and shake at room temperature for 3 hours. Excess NaOH is back titrated with 0.1N--H ₂ SO ₄ using phenolphthalein as an indicator, and the degree of carboxymethyl substitution (DS value) is calculated by the following formula.
A=[(100×F'-0.1N-H ₂ SO ₄ (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-H ₂ SO ₄ F: Factor of 0.1N-NaOH

(viscosity)
Further, the viscosity of a 1% by mass aqueous solution of the carboxymethyl cellulose or its salt of the present invention measured at 25°C with a B-type viscometer (30 rpm) is preferably 1,000 to 20,000 mPa·s, and 1 ,000 to 15,000 mPa·s, and even more preferably 1,000 to 10,000 mPa·s. If this viscosity is too high, there will be problems such as not being able to mix well with the active material and conductive additive when preparing the slurry, and problems such as poor fluidity and being unable to apply the slurry to the current collector. There are problems in that when applied to an electric body, it flows down from the current collector, making it difficult to apply it well, and that the active material and binder such as SBR cause migration, increasing electrical resistance.

The viscosity measurement method is as follows:
Carboxymethyl cellulose or a salt thereof is measured into a 1000 mL glass beaker and dispersed in 900 mL of distilled water to prepare an aqueous dispersion with a solid content of 1% (w/v). The aqueous dispersion is stirred at 25° C. using a stirrer at 600 rpm for 3 hours. Thereafter, the viscosity is measured after 3 minutes at a rotation speed of 30 rpm using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) according to the method of JIS-Z-8803.

(Dispersion degree)
The carboxymethyl cellulose and/or its salt of 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 the above range, CMC exhibits good dispersibility when used as a binder or dispersant in a negative electrode composition, so that the electrical resistance value improves.
On the other hand, if the degree of dispersion is too large, there will be a lot of powder flying, making it impossible to dissolve a predetermined amount of carboxymethyl cellulose, which will reduce its function as a binder and dispersant in the negative electrode, resulting in higher electrical resistance. If it is too small, it cannot be mixed well with other materials, leading to a problem of high electrical resistance.
The method for measuring the degree of dispersion is to use a powder property tester (Powder Tester PT-X (manufactured by Hosokawa Micron)). The degree of dispersion was calculated from the amount of powder that fell using the following formula.
Dispersity (%) = (10 (g) - amount of powder falling on the watch glass (g)) / 10 (g)

(Angle of repose)
The angle of repose of the carboxymethylcellulose and/or its salt of the present invention is preferably 42° or more, more preferably 45° or more. If the angle of repose is too small, the powder will flow out of the feeder outlet without permission, making it impossible to dissolve the specified amount of carboxymethyl cellulose, and reducing its function as a binder and dispersant in the negative electrode. There is a problem that resistance becomes high.
Here, the angle of repose is measured using a powder property testing device (Powder Tester PT-X (manufactured by Hosokawa Micron)) with the angle measurement method set to "Peak Operation" using a sieve with an opening of 710 μm and a linear diameter of 450 μm. did. The moisture content of carboxymethyl cellulose used in the measurement was adjusted to 6.0 to 9.0%.

(collapse angle)
The collapse angle of the carboxymethylcellulose and/or its salt of the present invention is preferably 19° or more, more preferably 21° or more. If the collapse angle is too small, the powder will flow out from the feeder outlet without permission, making it impossible to dissolve the specified amount of carboxymethyl cellulose, and reducing its function as a binder and dispersant in the negative electrode. There is a problem that resistance becomes high.
Here, the collapse angle was measured using a powder property testing device (Powder Tester PT-X (manufactured by Hosokawa Micron)) with the angle measurement method set to "Peak Operation" using a sieve with an opening of 710 μm and a linear diameter of 450 μm. . The moisture content of carboxymethyl cellulose used in the measurement was adjusted to 6.0 to 9.0%.
(difference angle)
Note that the value obtained by subtracting the value of the collapse angle from the value of the above-mentioned angle of repose can be expressed as a difference angle.

(Amount of filtration residue)
Moreover, it is preferable that the amount of filtration residue of the carboxymethyl cellulose and/or its salt of the present invention is within a predetermined range. That is, prepare 2 liters of a 0.3% by mass aqueous solution of the carboxymethyl cellulose or its salt with a dry mass of m, filter it all through a 250 mesh filter under a reduced pressure condition of -200 mmHg, and remove the residue on the filter after filtration. When the dry mass M 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, the electrode slurry will easily become clogged when filtered, and the amount of carboxymethyl cellulose in the filtered slurry will be less than the specified amount, reducing its function as a binder and dispersant. , there is a problem that the electrical resistance becomes high.

(Particle size)
The value obtained by subtracting the particle diameter D10 from the particle diameter D90 of the carboxymethyl cellulose and/or its salt of the present invention (particle diameter D90 - particle diameter D10) is preferably 10 to 50 μm, more preferably 10 to 30 μm, More preferably, it is 20 to 30 μm. If this value is too large, the particles will separate into layers, resulting in a problem that a uniform solution will not be obtained and the electrical resistance will become high.

Further, the value obtained by subtracting the particle diameter D50 from the particle diameter D90 of the carboxymethylcellulose and/or its salt of the present invention (particle diameter D90 - particle diameter D50) is preferably 5 to 30 μm, more preferably 10 to 30 μm. The thickness is more preferably 10 to 20 μm. If this value is too large, the particles will separate into layers, resulting in a problem that a uniform solution will not be obtained and the electrical resistance will become high.

Further, the value obtained by subtracting the particle diameter D10 from the particle diameter D50 of the carboxymethyl cellulose and/or its salt of the present invention (particle diameter D50 - particle diameter D10) is preferably 5 to 20 μm, more preferably 5 to 15 μm. The thickness is more preferably 8 to 12 μm. If this value is too large, there is a problem that the particles will separate into layers and a uniform solution will not be obtained.

Here, D10 is the particle size that includes 10% of the particle size distribution based on the volume average particle size, integrated from the minimum value, and D50 is the particle size that includes 50% of the integrated value from the minimum value. , is the particle size also called the average particle size. Moreover, D90 is a particle diameter that includes 90% of the total value starting from the minimum value. The particle size distribution based on the volume average particle size can be measured using, for example, a laser diffraction/scattering type particle size distribution meter using methanol as a dispersant.

In addition, the particle size D10 of the carboxymethyl cellulose and/or its salt of 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. preferable.

[Crushing process]
In the present invention, carboxymethylcellulose or a salt thereof may be subjected to pulverization treatment. As a method for finely pulverizing carboxymethylcellulose or its salt, select either a dry pulverization method in which it is processed in a powder state or a wet pulverization method in which it is processed in a state in which it is dispersed or dissolved in a liquid. It's okay.

By mechanically dry- or wet-pulverizing carboxymethylcellulose or a salt thereof, gel particles derived from carboxymethylcellulose or a salt thereof that exist as undissolved substances in an aqueous solution are made fine. As a result, it is believed that coarse undissolved substances that cause streak defects, peeling, pinholes, etc. that occur on the surface of the negative electrode can be suppressed.

Examples of the pulverizer that can be used in the present invention include the following.
Examples of the dry crusher include a cutting type mill, an impact type mill, and an air flow type mill. These can be used alone or in combination, and the same model can perform several stages of processing.

Cutting-type mills include mesh mills (manufactured by Horai Co., Ltd.), Atoms (manufactured by Yamamoto Hyakuma Seisakusho Co., Ltd.), knife mills (manufactured by Palman), granulators (manufactured by Herbold), and rotary cutter mills (manufactured by Nara Co., Ltd.). (manufactured by Kikai Seisakusho), etc.

Impact mills include Pulperizer (manufactured by Hosokawa Micron Co., Ltd.), Fine Impact Mill (manufactured by Hosokawa Micron Co., Ltd.), Super Micron Mill (manufactured by Hosokawa Micron Co., Ltd.), Sample Mill (manufactured by Seishin Co., Ltd.), and Bantam Mill (manufactured by Seishin Co., Ltd.). Examples include Seishin Co., Ltd.), an atomizer (Seishin Co., Ltd.), a tornado mill (Nikkiso Co., Ltd.), a turbo mill (Turbo Kogyo Co., Ltd.), and a bevel impactor (Aikawa Tekko Co., Ltd.).

Examples of air flow mills include CGS jet mill (manufactured by Mitsui Mining Co., Ltd.), jet mill (manufactured by Sansho Industry Co., Ltd.), Ebara Jet Micronizer (manufactured by Ebara Corporation), and selenium mirror (Mako Sangyo Co., Ltd.). Co., Ltd.) and a supersonic jet mill (manufactured by Nippon Pneumatic Industries Co., Ltd.).
Examples of the media mill include a vibrating ball mill and the like.

Examples of the wet crusher include a mass colloider (manufactured by Masuko Sangyo Co., Ltd.), and examples of the media mill include a bead mill (manufactured by Imex Co., Ltd.) and a high-pressure homogenizer (manufactured by Sanmaru Kikai Kogyo Co., Ltd.).

In the present invention, a step of classifying the finely pulverized carboxymethyl cellulose or its salt based on the particle size can be provided.
The above-mentioned classification step may be performed during the pulverization step or after the pulverization step. A known method may be used for classification. Examples of the dry classifier include a cyclone classifier, DS separator, turbo classifier, micro separator, and air separator. On the other hand, examples of the wet classifier include a hydrocyclone type, a centrifugal sedimentation machine, and a hydroseparator.

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

<Binder for nonaqueous electrolyte secondary batteries>
The carboxymethyl cellulose and/or its salt of the present invention is used as a binder for electrodes of non-aqueous electrolyte secondary batteries. Usually, an aqueous solution containing carboxymethylcellulose and/or a salt thereof is used as a binder for electrodes of non-aqueous electrolyte secondary batteries.

The concentration of carboxymethylcellulose or its salt in the aqueous solution of carboxymethylcellulose and/or its salt is usually 0.1 to 10% by mass, preferably 0.2 to 4% by mass, and 0.5 to 2% by mass. More preferred.

There are no particular restrictions on the conditions for producing the aqueous solution of carboxymethyl cellulose and/or its salt. For example, it is prepared by adding carboxymethyl cellulose and/or a salt thereof to water (for example, distilled water, purified water, tap water, etc.) and dissolving it by stirring as necessary.

Further, the binder for non-aqueous electrolyte secondary batteries may include other binders in addition to carboxymethyl cellulose and/or its salt. As the binder used in the electrode composition for the negative electrode, a synthetic rubber binder is exemplified. As the synthetic rubber binder, 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 latex of these synthetic rubbers is used. can. Among these, styrene butadiene rubber (SBR) is preferred. Furthermore, examples of the binder used in the electrode composition for the positive electrode include polytetrafluoroethylene (PTFE) in addition to the synthetic rubber binder mentioned as the binder for the negative electrode.

Here, the average particle diameter (D50) of SBR is preferably 50 to 300 nm, more preferably 50 to 200 nm. If the average particle diameter (D50) of SBR is too large, SBR will not adhere uniformly to the active material and the binder function will deteriorate, causing a problem of high electrical resistance. If it is too small, SRB will cover the active material. There is a problem in that the electrical resistance becomes high.

Further, the glass transition temperature (Tg) of SBR is preferably -50°C to 50°C. When the SBR is within the above range, it mixes well with the carboxymethylcellulose and/or its salt of the present invention and has appropriate flexibility when used as a negative electrode layer, so that electrical resistance is unlikely to increase.

<Electrode composition for non-aqueous electrolyte secondary battery>
The electrode composition for non-aqueous electrolyte secondary batteries of the present invention (hereinafter sometimes referred to as "electrode composition") comprises at least the electrode active material and the binder for non-aqueous electrolyte secondary batteries of the present invention. Contains carboxymethylcellulose and/or its salts.

That is, the carboxymethyl cellulose and/or its salt of the present invention can be used as an electrode binder to constitute an electrode composition together with an electrode active material. In this case, the content of carboxymethylcellulose and/or its salt in the electrode composition is preferably 0.1 to 4.0% by mass based on the entire electrode composition.

In addition, when using the above-mentioned other binders, the content of the binder for non-aqueous electrolyte secondary batteries in the electrode composition is preferably 1 to 10% by mass, more preferably 1 to 6% by mass, and further Preferably it is 1 to 2% by mass.

(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 non-aqueous electrolyte secondary battery electrode is for a negative electrode, and a positive electrode active material when it is for a positive electrode. be.

Examples of negative electrode active materials include graphite materials such as graphite (natural graphite, artificial graphite, etc.), coke, and carbon fiber; elements that can form an alloy with lithium, such as silicon-based compounds, Al, Sn, Ag, Elements such as Bi, Mg, Zn, In, Ge, Pb, Ti; Compounds containing elements that can form alloys with lithium; Elements and compounds that can form alloys with lithium, carbon and Examples include/or a composite with the graphite material, a nitride containing lithium, and the like. Among these, graphite materials and silicon-based compounds are preferred, and as graphite and silicon-based compounds, silicon particles or silicon oxide particles are more preferred.

Note that the silicon oxide in the present invention is represented by SiO _x (0<x≦2). Further, in the present invention, a composite of a silicon-based compound and a graphite material is more suitable as the active material layer.

When 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 preferably have a blending ratio of graphite material: silicon-based compound = 10:90 to 90:10, More preferably 50:50 to 80:20.

As the positive electrode active material, LiFePO ₄ , LiMe _x O _y (Me means a transition metal containing at least one of Ni, Co, and Mn. x and y mean arbitrary numbers)-based positive electrode active materials is preferred.

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, even more preferably 95 to 99% by mass, particularly preferably 96% by mass. ~99% by weight, most preferably 98-99% by weight.

Further, the electrode composition may contain a conductive additive, if necessary. 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 to 20% by mass, preferably 0.1 to 10% by mass.

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

A water-soluble organic solvent is an organic solvent that dissolves in water. Examples 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, dimethylsulfoxide (DMSO), acetonitrile, methyl triglycol diester succinate, acetic acid, and combinations thereof.

When using the above mixed solvent 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 even more preferably 70% by mass or more. The upper limit of the amount is not limited, but is preferably 95% by mass or less, more preferably 90% by mass or less. Further, the aqueous solvent may contain a water-insoluble organic solvent within a range that does not impair the effects of the invention.

There are no particular limitations on the manufacturing conditions for the electrode composition. For example, other components constituting the electrode composition are added to an aqueous solution of carboxymethylcellulose and/or its salt, and mixed with stirring as necessary.
Further, the properties of the electrode composition are not particularly limited either. For example, it may be in liquid form, paste form, slurry form, etc., and any of them may be used.

<Electrode for non-aqueous electrolyte secondary battery>
An electrode layer can be formed on the current collector by applying the above electrode composition onto the current collector. Examples of the coating method include blade coating, bar coating, and die coating, with blade coating being preferred. For example, in the case of blade coating, a method of casting the electrode composition onto a current collector using a coating device such as a doctor blade is exemplified. Further, the method of lamination is not limited to the above specific example, and a method may also be used in which the electrode composition is applied by discharging it from an extrusion type liquid injection device having a slot nozzle onto a current collector that is wound around a backup roll and travels. Illustrated. In blade coating, after casting, the electrode layer is obtained by further drying by heating (temperature: 80 to 120°C, heating time: 4 to 12 hours, for example) or applying pressure using a roll press, etc., if necessary. It will be done.

Although the shape of the electrode for a non-aqueous electrolyte secondary battery of the present invention is not particularly limited, it is usually sheet-like. The thickness of a sheet-like electrode plate (thickness of the electrode layer formed from the electrode composition, excluding the current collector part) is difficult to specify as it depends on the composition of the composition and manufacturing conditions. However, it is usually 30 to 150 μm.

(current collector)
Any electrical conductor that does not cause a fatal chemical change in the constructed electrode or battery can be used as the current collector. When the electrode is a negative electrode, a negative electrode current collector can be used, and when the electrode is a positive electrode, a positive electrode current collector can be used.

Examples of the material for the negative electrode current collector include stainless steel, nickel, copper, titanium, carbon, copper, or stainless steel with carbon, nickel, titanium, or silver coated on the surface. Among these, copper or copper alloy is preferable, and copper is more preferable.
Examples of the material for the positive electrode current collector include metals such as aluminum and stainless steel, with aluminum being preferred.
Examples of the shape of the current collector include a net, punched metal, foam metal, and foil processed into a plate shape, with foil processed into a plate shape being preferred.
<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.

That is, the present invention also provides a non-aqueous electrolyte secondary battery. A non-aqueous electrolyte secondary battery may have a structure in which positive electrodes and negative electrodes are alternately stacked with separators interposed therebetween and wound many times. Further, a nonaqueous electrolyte secondary battery can be obtained by placing a multi-turn laminate of a positive electrode, a separator, and a negative electrode in a battery container, injecting a nonaqueous electrolyte, and sealing the container.

The shape of the nonaqueous electrolyte secondary battery is not particularly limited, and may be a cylindrical shape, a square shape, a flat shape, a coin shape, a button shape, a sheet shape, or the like. Further, the material of the battery container is not particularly limited as long as it can achieve the purpose of preventing moisture from entering inside the battery, and examples thereof include metal, laminate of aluminum, and the like.

Note that the separator is usually impregnated with a nonaqueous electrolyte. As the separator, for example, a microporous membrane or nonwoven fabric made of polyolefin such as polyethylene or polypropylene can be used.

Further, the non-aqueous electrolyte usually contains a lithium salt and a non-aqueous solvent. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiBF ₄ , and LiClO ₄ . Further, examples of the nonaqueous solvent include ethylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, butylene carbonate, methyl ethyl carbonate, and the like. The non-aqueous solvents may be used alone or in combination of two or more. The concentration of lithium salt in the non-aqueous electrolyte can be generally 0.5 to 2.5 mol/L.

Electrodes for non-aqueous electrolyte secondary batteries and non-aqueous electrolyte secondary batteries manufactured from an electrode composition using carboxymethyl cellulose and/or a salt thereof of the present invention as a binder for electrodes of non-aqueous electrolyte secondary batteries are Since there is little dissolved gel, the resistance value is low and the battery characteristics are excellent.

Hereinafter, embodiments of the present invention will be described with reference to Examples, but the present invention is not limited thereto.
<Measurement method and evaluation method>
In Examples and Comparative Examples, measurements and evaluations were performed as follows.

(Measurement of carboxymethyl substitution degree (DS value))
Approximately 2.0 g of the sample was accurately weighed and placed in a 300 mL Erlenmeyer flask with a stopper. 100 mL of a solution prepared by adding 100 mL of special grade concentrated nitric acid to 1000 mL of methanol was added and shaken for 3 hours to convert carboxymethyl cellulose salt (CMC) to H-CMC (hydrogen carboxymethyl cellulose). Accurately weigh 1.5 to 2.0 g of the bone-dried H-CMC and place it in a 300 mL Erlenmeyer flask with a stopper. H-CMC was wetted with 15 mL of 80% methanol, 100 mL of 0.1N-NaOH was added, and the mixture was shaken at room temperature for 3 hours. Excess NaOH was back titrated with 0.1N-H ₂ SO ₄ using phenolphthalein as an indicator, and the degree of carboxymethyl substitution (DS value) was calculated using the following formula.
A=[(100×F'-0.1N-H ₂ SO ₄ (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-H ₂ SO ₄ F: Factor of 0.1N-NaOH

(Measurement of 1% by mass viscosity of CMC)
Carboxymethyl cellulose or a salt thereof was measured into a 1000 mL glass beaker and dispersed in 900 mL of distilled water to prepare an aqueous dispersion with a solid content of 1% (w/v). The aqueous dispersion is stirred at 25° C. using a stirrer at 600 rpm for 3 hours. Thereafter, the viscosity was measured after 3 minutes at a rotation speed of 30 rpm using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) according to the method of JIS-Z-8803.

(Particle size)
The particle diameter D10, particle diameter D50, and particle diameter D90 of carboxymethyl cellulose or its salt used in the Examples and Comparative Examples were determined from the particle diameter distribution based on the volume average particle diameter.

The particle size distribution was measured using a laser diffraction/scattering particle size distribution analyzer (Mastersizer 2000E, manufactured by Spectris Co., Ltd.). In the measurement, the sample was dispersed in methanol and then subjected to ultrasonication for at least 1 minute.

(Dispersion degree)
The degree of dispersion of carboxymethyl cellulose or its salt used in Examples and Comparative Examples was measured using a powder tester (Powder Tester PT-X, manufactured by Hosokawa Micron Corporation). Specifically, when 10 g of a sample was placed in the dispersion unit of 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.
Dispersity (%) = (10 (g) - amount of powder falling on the watch glass (g)) / 10 (g)

(Angle of repose)
The angle of repose of carboxymethyl cellulose or its salt used in Examples and Comparative Examples was measured using a powder tester (Powder Tester PT-X, manufactured by Hosokawa Micron Corporation). Specifically, it was measured using a powder property testing device (Powder Tester PT-X (manufactured by Hosokawa Micron Corporation)) with an angle measurement method of "Peak Operation" using a sieve with an opening of 710 μm and a linear size of 450 μm. The moisture content of carboxymethyl cellulose used in the measurement was adjusted to 6.0 to 9.0%.

(collapse angle)
The collapse angle of carboxymethylcellulose or its salt used in Examples and Comparative Examples was measured using a powder tester (Powder Tester PT-X, manufactured by Hosokawa Micron Corporation) under the same conditions as the above-mentioned measurement of the angle of repose.
(difference angle)
Using the angle of repose and angle of collapse measured above, the difference angle was determined as difference angle = angle of repose - angle of collapse.

(impedance)
The electrode compositions obtained in Examples and Comparative Examples were applied onto a current collector (copper foil measuring 320 mm long x 170 mm wide x 17 μm thick (manufactured by Furukawa Electric Co., Ltd., NC-WS)) and heated for 30 minutes at room temperature. After drying for a minute, it was dried at 60° C. for 30 minutes. After drying, it was pressed at 5.0 kN using a small tabletop roll press (manufactured by Tester Sangyo Co., Ltd., SA-602) to obtain a negative electrode plate having a negative electrode active material layer on the current collector. The obtained negative electrode plate and LiCoO ₂ positive electrode plate (manufactured by Hosensha, weight: 227.1 g/m2, effective discharge capacity: 145 mAh/g) were each punched out into a circular shape with a diameter of 16 mm, and the punched negative electrode plate was obtained. 1 and the positive electrode plate were vacuum dried at 120° C. for 12 hours. Similarly, a separator (polypropylene separator manufactured by CS Tech, 20 μm thick) was punched out into a circular shape with a diameter of 17 mm, and vacuum-dried at 60° C. for 12 hours. Thereafter, the negative electrode plate was placed in a stainless steel circular dish-shaped container with a diameter of 20.0 mm, and then the separator, positive electrode plate, spacer (diameter 15.5 mm, thickness 1 mm), and stainless steel washer (manufactured by Hosen Co., Ltd.) were placed. They were laminated in this order, and then 300 μL of an electrolytic solution (1 mol/L LiPF ₆ , 1:1 volume ratio of ethylene carbonate and diethyl carbonate) was added to the circular dish-shaped container. This was covered with a stainless steel cap via a polypropylene packing and sealed using a coin battery caulking machine (Hosen Co., Ltd.) to obtain a coin-shaped nonaqueous electrolyte secondary battery. Using a secondary battery charge/discharge test device (BTS2004, manufactured by Nagano Co., Ltd.), the obtained coin-type battery was subjected to one charge/discharge cycle in which charging and discharging were performed in the order of charging and discharging in a constant temperature bath at 25°C. Next, impedance was measured using an impedance tester (VPS, manufactured by Toyo Technica, Inc.), and a resistance value was calculated using ZView (manufactured by Scribner Associates). The smaller the resistance value, the better the performance of the non-aqueous electrolyte battery when used as a battery.

(Measurement of filtration residue amount of carboxymethyl cellulose or its salt)
Two liters of a 0.3 mass % (mass % based on the dry mass of carboxymethyl cellulose or its salt) aqueous solution of carboxymethyl cellulose or its salt was prepared. Two liters of this aqueous solution was filtered under reduced pressure conditions of -200 mmHg using a filter ("Separoto" manufactured by Kiriyama Seisakusho) through a 250 mesh filter (made of stainless steel, opening 63 μm). The residue remaining on the 250 mesh filter was dried with air at a temperature of 105°C for 16 hours, and then the mass of the dried residue was measured and expressed as a mass percent (ppm) based on the mass of carboxymethylcellulose in the carboxymethylcellulose aqueous solution. .
The above measurement and evaluation results are shown in Table 1.

<Preparation of electrode composition>
(Example 1)
<Manufacture of CMC>
550 parts of isopropanol and 40 parts of sodium hydroxide dissolved in 80 parts of water were added to a twin-screw kneader whose rotational speed was adjusted to 100 rpm, and 100 parts of linter pulp was charged based on the dry weight of drying the linter pulp at 100°C for 60 minutes. is. The mixture was stirred and mixed at 30° C. for 90 minutes to prepare mercerized cellulose. Further, while stirring, 50 parts of monochloroacetic acid was added, and after stirring for 30 minutes, the temperature was raised to 70° C. and a carboxymethylation reaction was carried out for 90 minutes. After the reaction was completed, the mixture was neutralized with acetic acid to a pH of about 7, deliquified, dried, and pulverized to obtain CMC1. The DS value of CMC1 was 0.92, and the 1% viscosity was 1650 mPa·s.
<Manufacture of electrode composition>
1.4 g of 98 mass % graphite powder and 0.6 g of 98 mass % SiO _x powder as the negative electrode active material, 0.01 g of 98 mass % acetylene black as the conductive aid, and an aqueous dispersion of CMC1 (2 mass %) as the binder. 0 g and 63 mg of 48% by mass styrene-butadiene rubber (SBR) and 1.5 g of water were mixed in a Mazerstar (Mazerstar KK-250S, manufactured by Kurashiki Boseki Co., Ltd.) to prepare an electrode composition. In addition, the Tg of SBR was 7° C., and the average particle diameter was 165 nm.

(Example 2)
<Manufacture of CMC>
650 parts of isopropanol and 60 parts of sodium hydroxide dissolved in 100 parts of water were added to a twin-screw kneader whose rotational speed was adjusted to 100 rpm, and 100 parts of linter pulp was charged based on the dry weight of the linter pulp when dried at 100°C for 60 minutes. is. The mixture was stirred and mixed at 30° C. for 90 minutes to prepare mercerized cellulose. Further, while stirring, 70 parts of monochloroacetic acid was added, and after stirring for 30 minutes, the temperature was raised to 70° C. and a carboxymethylation reaction was carried out for 90 minutes. After the reaction was completed, the mixture was neutralized with acetic acid to a pH of about 7, deliquified, dried, and pulverized to obtain CMC2. The DS value of CMC2 was 0.84, and the 1% viscosity was 4580 mPa·s.
<Manufacture of electrode composition>
An electrode composition was prepared in the same manner as in Example 1, except that the type of CMC was changed to CMC2 obtained above.

(Example 3)
<Manufacture of CMC>
600 parts of isopropanol and 55 parts of sodium hydroxide dissolved in 100 parts of water were added to a twin-screw kneader whose rotational speed was adjusted to 100 rpm, and 100 parts of linter pulp was charged based on the dry weight of the linter pulp when dried at 100°C for 60 minutes. is. The mixture was stirred and mixed at 30° C. for 90 minutes to prepare mercerized cellulose. Further, 65 parts of monochloroacetic acid was added while stirring, and after stirring for 30 minutes, the temperature was raised to 70° C. and a carboxymethylation reaction was carried out for 90 minutes. After the reaction was completed, the mixture was neutralized with acetic acid to a pH of about 7, deliquified, dried, and pulverized to obtain CMC3. The DS value of CMC3 was 0.70, and the 1% viscosity was 4900 mPa·s.
<Manufacture of electrode composition>
An electrode composition was prepared in the same manner as in Example 1, except that the type of CMC was changed to CMC3 obtained above.

(Example 4)
<Manufacture of CMC>
600 parts of isopropanol and 38 parts of sodium hydroxide dissolved in 80 parts of water were added to a twin-screw kneader whose rotational speed was adjusted to 100 rpm, and 100 parts of linter pulp was charged based on the dry weight of the linter pulp when dried at 100°C for 60 minutes. is. The mixture was stirred and mixed at 30° C. for 90 minutes to prepare mercerized cellulose. Further, 46 parts of monochloroacetic acid was added while stirring, and after stirring for 30 minutes, the temperature was raised to 70° C. and a carboxymethylation reaction was carried out for 90 minutes. After the reaction was completed, the mixture was neutralized with acetic acid to a pH of about 7, deliquified, dried, and pulverized to obtain CMC4. The DS value of CMC4 was 0.70, and the 1% viscosity was 8980 mPa·s.
<Manufacture of electrode composition>
An electrode composition was prepared in the same manner as in Example 1, except that the type of CMC was changed to CMC4 obtained above.

(Comparative example 1)
<Manufacture of electrode composition>
An electrode composition was prepared in the same manner as in Example 1, except that the type of CMC was changed to CMC5 with a DS value of 0.93 and a 1% viscosity of 3460 mPa·s.

(Comparative example 2)
<Manufacture of electrode composition>
An electrode composition was prepared in the same manner as in Example 1, except that the type of CMC was changed to CMC6 with a DS value of 0.69 and a 1% viscosity of 6340 mPa·S.

As shown in Table 1, carboxymethyl cellulose and/or its salts are used as binders for electrodes of non-aqueous electrolyte secondary batteries, and the degree of carboxymethyl substitution per anhydroglucose unit is 0.5 to 1.2. An electrode layer obtained from an electrode composition using carboxymethyl cellulose and/or its salt, which has a dispersion degree of 20 to 60% as measured using a powder tester, has a low resistance value and has a non-aqueous electrolyte secondary It was shown that the battery performance was good when used as a battery.

Claims (9)

Carboxymethylcellulose and/or its salt used as a binder for electrodes of non-aqueous electrolyte secondary batteries, with a degree of carboxymethyl substitution per anhydroglucose unit of 0.5 to 1.2, using a powder tester. Carboxymethyl cellulose and/or its salt, which has a degree of dispersion of 20 to 60% as measured by The carboxymethylcellulose and/or its salt according to claim 1, having an angle of repose of 42° or more. The carboxymethyl cellulose and/or its salt according to claim 1 or 2, having a collapse angle of 19° or more. The carboxymethyl cellulose and/or its salt according to claim 1 or 2, wherein the viscosity of a 1% by mass aqueous solution measured with a B-type viscometer (30 rpm) at 25° C. is 1,000 to 20,000 mPa·s. Prepare 2 liters of a 0.3% by mass aqueous solution of the carboxymethyl cellulose or its salt with a dry mass of m, filter it all with a 250 mesh filter under a reduced pressure condition of -200 mmHg, and calculate the dry mass of the residue on the filter after filtration. The carboxymethyl cellulose and/or its salt according to claim 1 or 2, wherein when M is measured, the ratio of the dry mass M to the dry mass m is less than 200 ppm. An electrode composition for a non-aqueous electrolyte secondary battery, comprising the carboxymethyl cellulose and/or its salt according to claim 1 or 2, and styrene-butadiene rubber having an average particle size of 50 nm to 300 nm. The electrode composition for a non-aqueous electrolyte secondary battery according to claim 6, wherein the styrene-butadiene rubber has a glass transition temperature of -50°C to 50°C. An electrode for a non-aqueous electrolyte secondary battery, using the electrode composition for a non-aqueous electrolyte secondary battery according to claim 6 or 7. A non-aqueous electrolyte secondary battery using the electrode composition for a non-aqueous electrolyte secondary battery according to claim 6 or 7.