JP7337616B2 - Binder for non-aqueous electrolyte secondary battery, electrode composition for non-aqueous electrolyte secondary battery, electrode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a binder for nonaqueous electrolyte secondary batteries, an electrode composition for nonaqueous electrolyte secondary batteries, an electrode for nonaqueous electrolyte secondary batteries, and a nonaqueous electrolyte secondary battery.

2. Description of the Related Art In recent years, with the rapid spread of small portable terminals such as smartphones and tablets, there is an increasing demand for small batteries with high energy density to drive them.

Graphite-based materials are generally used for negative electrodes of lithium-ion secondary batteries, and the theoretical capacity of graphite-based materials 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 obtained by alloying lithium with silicon, tin, or the like, which have a low potential and a large specific capacity next to carbon and lithium, are attracting attention.

Among these materials, silicon can occlude up to 4.4 lithium atoms per 1 silicon atom in terms of molar ratio, theoretically yielding a capacity about 10 times that of graphite-based carbon materials. However, when silicon particles absorb lithium, their volume expands about three to four times. Therefore, repeated charging and discharging progresses deterioration, resulting in a decrease in capacity. A detailed analysis of this phenomenon reveals that when lithium is inserted into an active material containing silicon, fine cracks occur within the electrode due to volume expansion, and the electrolyte penetrates into these fine cracks, forming a new film (SEI layer). is confirmed to be formed. At this time, an irreversible capacity that does not return to its original state is generated, resulting in a decrease in battery capacity. This phenomenon appears in changes in charge-discharge efficiency during cycles. In particular, the decrease in cycle efficiency at the initial stage of the cycle when the volume change is large greatly affects the life of the battery in combination with the positive electrode with high charge-discharge efficiency. Therefore, when using an active material containing silicon, it is an important issue to minimize the change in the electrode structure due to this volume expansion.

Under these circumstances, in Patent Document 1, by using a negative electrode material in which carbon particles are modified with a silane coupling agent, it is possible to obtain an electrode that has excellent durability and excellent charge-discharge cycles even when a silicon-based compound is used. is proposed.
Further, Patent Document 2 proposes to attach niobium oxide to a silicon-based compound to improve durability.

Japanese Patent No. 5599527 JP 2017-174829 A

In Patent Documents 1 and 2, the negative electrode active material is improved, but further improvement is required for the binder used for the negative electrode.

SUMMARY OF THE INVENTION An object of the present invention is to provide a binder for non-aqueous electrolyte secondary batteries that can provide a battery having excellent performance even when an active material containing silicon is used. To provide an electrode composition for a non-aqueous electrolyte secondary battery containing a binder for an electrolyte secondary battery; It is to provide a water electrolyte secondary battery.

As a result of intensive studies, the present inventors have found that the above problems can be solved by setting the charge density of the binder to a specific range.

That is, according to the present invention,
(1) A binder for a non-aqueous electrolyte secondary battery containing at least carboxymethyl cellulose and/or a salt thereof, in 1 g of the binder for a non-aqueous electrolyte secondary battery measured by a titration method using a flow current meter A binder for a non-aqueous electrolyte secondary battery, characterized in that the degree of anionization indicated by milliequivalents (meq/g) of the anion is 5 meq/g or more;
(2) The carboxymethyl cellulose and/or its salt has a degree of carboxymethyl substitution in the range of 0.5 to 1.5, and a viscosity ( 30 rpm, 25° C.) is in the range of 100 to 20000 mPa s, the binder for a non-aqueous electrolyte secondary battery according to (1),
(3) The binder for a nonaqueous electrolyte secondary battery according to (1) or (2), further comprising a water-soluble polymer having a weight average molecular weight of 1,000,000 or more.
(4) The binder for a non-aqueous electrolyte secondary battery according to (3), wherein the water-soluble polymer is polyacrylic acid;
(5) An electrode composition for non-aqueous electrolyte secondary batteries, comprising the binder for non-aqueous electrolyte secondary batteries according to any one of (1) to (4),
(6) The electrode composition for a non-aqueous electrolyte secondary battery according to (5), characterized in that the content of the silicon-based active material is 10% by mass or more with respect to 100% by mass of the active material;
(7) an electrode for a non-aqueous electrolyte secondary battery using the electrode composition for a non-aqueous electrolyte secondary battery according to (5) or (6);
(8) A nonaqueous electrolyte secondary battery using the electrode composition for a nonaqueous electrolyte secondary battery according to (5) or (6) is provided.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a binder for a non-aqueous electrolyte secondary battery that enables a battery having excellent performance to be obtained even when an active material containing silicon is used. Electrode composition for non-aqueous electrolyte secondary battery containing binder for non-aqueous electrolyte secondary battery, and electrode and non-aqueous electrolyte for non-aqueous electrolyte secondary battery using this electrode composition for non-aqueous electrolyte secondary battery A secondary battery can be provided.

A binder for a non-aqueous electrolyte secondary battery, 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 according to embodiments of the present invention will be described below.

The binder for a non-aqueous electrolyte secondary battery of the present invention is a binder for a non-aqueous electrolyte secondary battery containing at least carboxymethylcellulose and/or a salt thereof, and has a weight of 1 g measured by a titration method using a flow current meter. The degree of anionization in the binder for a non-aqueous electrolyte secondary battery is 5 meq/g or more, expressed as milliequivalents (meq/g) of the anion.

<Binder for Nonaqueous Electrolyte Secondary Battery>
The binder for non-aqueous electrolyte secondary batteries of the present invention contains at least carboxymethylcellulose and/or a salt thereof.

<Carboxymethylcellulose and/or its salt>
Carboxymethyl cellulose and/or its salt (hereinafter sometimes abbreviated as CMC) used in the present invention has a structure in which hydroxyl groups in glucose units constituting cellulose are substituted with carboxymethyl ether groups. 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 means a polysaccharide having a structure in which D-glucopyranose (also referred to simply as “glucose unit” or “anhydroglucose”) is linked with β,1-4 bonds. Cellulose is generally classified into natural cellulose, regenerated cellulose, fine cellulose, microcrystalline cellulose excluding non-crystalline regions, etc., according to its origin, production method, and the like.

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

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

As fine cellulose, fine cellulose and cellulosic materials obtained by depolymerizing cellulosic materials such as natural cellulose and regenerated cellulose by acid hydrolysis, alkaline hydrolysis, enzymatic decomposition, blasting treatment, vibrating ball mill treatment, etc. are used. Fine cellulose obtained by mechanical treatment is exemplified.

In manufacturing the CMC used in the present invention, a 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 for an etherification reaction. .

As the raw material cellulose, any of the celluloses described above can be used without particular limitation, but cellulose with high purity is preferred, and dissolving pulp or linter is more preferred. By using these, CMC with high purity can be obtained.

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

In the 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 the ratio is 2.00 or more, the etherification reaction can be sufficiently carried out, and unreacted monochloroacetic acid can be prevented from remaining and being wasted. When it is 2.45 or less, it is possible to prevent the formation of an alkali metal glycolate due to a side reaction caused by excess mercerizing agent and monochloroacetic acid, which is economical.
In the present invention, CMC may be a commercial product. Commercially available products include, for example, Nippon Paper Industries Co., Ltd.'s trade name "Sunrose".

Further, the ratio of groups substituted with carboxymethyl ether groups (-OCH ₂ COOH) among hydroxyl groups (-OH) in glucose units constituting cellulose can be expressed as the degree of etherification of CMC.

The CMC used in the present invention has a degree of substitution of carboxymethyl groups per glucose unit (hereinafter sometimes referred to as "CM-DS" or "DS value") in the range of 0.5 to 1.5. is preferred. When the CM-DS is 0.5 or more, good solubility in water can be maintained, and generation of undissolved substances can be suppressed. Further, when the CM-DS is 1.5 or less, it is possible to suppress an increase in the spinnability of the liquid and maintain easy handling. CM-DS can be calculated by the method shown in Examples. Therefore, the CM-DS of the CMC of the present invention is preferably 0.5 to 1.5, more preferably 0.7 to 1.5, and particularly preferably 1.0 to 1.5.

The method for measuring the degree of substitution of carboxymethyl groups is as follows:
About 2.0 g of the sample is precisely weighed and placed in a 300 mL Erlenmeyer flask with a common stopper. Add 100 mL of a solution obtained 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 carboxymethyl cellulose). Accurately weigh 1.5 to 2.0 g of the absolute dry H-CMC and put it in a 300 mL Erlenmeyer flask with a common stopper. Wet the H-CMC with 15 mL of 80% methanol, add 100 mL of 0.1 N 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 equation.
A = [(100 x F'-0.1N-H ₂ SO ₄ (mL) x F) x 0.1]/(absolute dry mass of H-CMC (g))
Carboxymethyl substitution degree = 0.162 × A / (1-0.058 × A)
F′: factor of 0.1N—H ₂ SO ₄ F: factor of 0.1N—NaOH

Further, the viscosity of the aqueous dispersion of CMC having a solid content of 1% (w/v) at 25° C., measured using a Brookfield viscometer, is preferably 100 to 20,000 mPa·s.

The viscosity measurement method is as follows:
Carboxymethylcellulose or a salt thereof is weighed into a 1000 mL glass beaker and dispersed in 900 mL of distilled water to prepare an aqueous dispersion having a solid content of 1% (w/v). The aqueous dispersion is stirred at 25° C. with a stirrer at 600 rpm for 3 hours. After that, according to the method of JIS-Z-8803, using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.), No. The viscosity is measured after 3 minutes at 1 rotor/rotation speed of 30 rpm.
The CMC used in the present invention may be of one type, or may be a combination of two or more types of CMC having different degrees of etherification, CM-DS, viscosity, molecular weight and the like.

<Water-soluble polymer>
The binder for non-aqueous electrolyte secondary batteries of the present invention preferably contains a water-soluble polymer in addition to carboxymethylcellulose and/or a salt thereof.
The weight average molecular weight (Mw) of the water-soluble polymer is preferably 1,000,000 or more, more preferably 4,000,000 or more.

Examples of water-soluble polymers include crosslinked polyacrylic acid, uncrosslinked polyacrylic acid, alginic acid, xanthan gum, etc. Among these, polyacrylic acid is preferred.

The water-soluble polymer is preferably 1 to 200% by mass, more preferably 20 to 180% by mass, even more preferably 50 to 150% by mass, based on 100% by mass of carboxymethylcellulose and/or a salt thereof.

<Degree of anionization>
The degree of anionization (also referred to as anion charge density) of the binder for non-aqueous electrolyte secondary batteries of the present invention is 5 meq/g or more. As used herein, the term “anionization degree” refers to the equivalent of electric charge per unit mass of chemically modified cellulose fiber, and is a value (unit: meq/g) measured by a titration method using a flow current meter. be.

In addition, in the present invention, the method for measuring the degree of anionization is as follows:
The binder for non-aqueous electrolyte secondary batteries of the present invention is dispersed in water to prepare an aqueous dispersion having a solid content of 10 g/L, and the dispersion is stirred at 1000 rpm all day and night using a magnetic stirrer. After diluting the resulting slurry to 0.1 g/L, 10 mL was sampled and titrated with 1/1000 normality diallyldimethylammonium chloride (DADMAC) using a streaming current detector (Mutek Particle Charge Detector 03). Using the amount of DADMAC added until the flowing current becomes zero, the degree of anionization is calculated by the following formula:
q=(V×c)/m
q: degree of anionization (meq/g)
V: Amount of DADMAC added until flowing current becomes zero (L)
c: concentration of DADMAC (meq/L)
m: Mass (g) of binder for non-aqueous electrolyte secondary batteries in the measurement sample.

As used herein, the term "anionization degree" refers to the equivalent of DADMAC required to neutralize anionic groups in a unit mass binder for a non-aqueous electrolyte secondary battery, as can be seen from the above measurement method. and corresponds to the anion equivalent per unit mass of binder for non-aqueous electrolyte secondary batteries.

The degree of anionization of the binder for non-aqueous electrolyte secondary batteries of the present invention is 5 meq/g or more, preferably 20 meq/g or less, more preferably 15 meq/g or less, and even more preferably 10 meq/g or less. Binders for non-aqueous electrolyte secondary batteries having an anionization degree within such a range have improved adhesive strength due to ester bonds, and have better battery characteristics than binders for non-electrolyte secondary batteries having a low degree of anionization. It can be improved.

In addition, the strength of the film produced using the binder for non-aqueous electrolyte secondary batteries of the present invention is preferably 50 MPa or more, more preferably 60 MPa or more, and 100 MPa or more in elastic modulus. is more preferred. When the elastic modulus is within the above range, it is possible to obtain a non-aqueous electrolyte secondary battery having excellent battery performance such as capacity retention rate.
Elastic modulus can be measured as follows.
The elastic modulus was measured using a dynamic ultra-micro hardness tester DUH-W201S (Shimadzu Corporation). The measurement conditions were as follows, and the elastic modulus was calculated by analysis using the attached software.
・Test mode: Load-unload
・Test force: 2.000mN
・Loading speed: 5
・Hold time: 1sec
・Depth scale: 10.00 µm

Here, a film produced using the binder for non-aqueous electrolyte secondary batteries of the present invention can be obtained by coating the binder for non-aqueous electrolyte secondary batteries of the present invention on a substrate and drying. . Although the substrate is not particularly limited, for example, substrates made of polyethylene, polypropylene, polytetrafluoroethylene, glass, and the like can be used. In addition, as the drying conditions, it is preferable to dry at room temperature to 60° C. under normal pressure until it becomes a film, and then to dry at 150° C. to 200° C. under vacuum conditions for 2 hours or more. It is more preferable to dry at ~60°C to form a film, followed by drying at 150°C for 2 hours under vacuum conditions.

<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") contains the binder for non-aqueous electrolyte secondary batteries, and may further contain an electrode active material. It may contain other components such as a conductive aid, which are preferably and optionally used.

That is, in the present invention, the binder for non-aqueous electrolyte secondary batteries can constitute the electrode composition together with the electrode active material. In this case, the binder for non-aqueous electrolyte secondary batteries in the electrode composition is preferably 1 to 15% by mass with respect to the entire electrode composition.

<Electrode active material>
The electrode active material contained in the electrode composition is a negative electrode active material when used for a negative electrode for a non-aqueous electrolyte secondary battery, and is a positive electrode when used for a positive electrode for a non-aqueous electrolyte secondary battery. Active material.

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

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 negative electrode active material.

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 to 90:90 to 10, 50-80: 50-20 is more preferred. In addition, the content of the silicon-based active material is preferably 10% by mass or more, more preferably 20% by mass or more, based on 100% by mass of the negative electrode active material.

As the positive electrode active material, LiFePO ₄ or _{LiMexO y} (Me means a transition metal containing at least one of Ni, Co, and Mn, and x and y are arbitrary numbers)-based positive electrode active material. is preferred.

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

<Other ingredients>
In addition, the electrode composition may contain binders other than the binder for non-aqueous electrolyte secondary batteries of the present invention. Synthetic rubber-based binders are exemplified as other binders used in the electrode composition for the negative electrode. As the synthetic rubber binder, at least one selected from the group consisting of styrene-butadiene rubber (SBR), nitrile-butadiene rubber, methyl methacrylate-butadiene rubber, chloroprene rubber, carboxy-modified styrene-butadiene rubber, and latexes of these synthetic rubbers is used. can. Of these, styrene-butadiene rubber (SBR) is preferred. Further, examples of other binders used in the positive electrode composition include the synthetic rubber-based binders mentioned above as the binders for the negative electrode, and polytetrafluoroethylene (PTFE). It is preferred to use tetrafluoroethylene (PTFE).
The content of other binders in the electrode composition is usually 1 to 10% by mass, preferably 1 to 6% by mass, more preferably 1 to 2% by mass.

Moreover, the electrode composition may contain a conductive aid as needed. Examples of conductive aids include conductive carbons 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 the electrode composition, an aqueous solvent is preferable. Although the type of aqueous solvent is not particularly limited, it is preferably water, a water-soluble organic solvent, or a mixed solvent thereof, and more preferably water.

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 the mixed solvent is used as the aqueous solvent, the amount of the water-soluble organic solvent in the mixed solvent is preferably 10% by mass or more, more preferably 50% by mass or more, and even more preferably 70% by mass or more. Although the upper limit of the amount is not limited, it is preferably 95% by mass or less, more preferably 90% by mass or less. In addition, the aqueous solvent may contain a water-insoluble organic solvent as long as the effects of the invention are not impaired.

The manufacturing conditions for the electrode composition are not particularly limited. For example, other components constituting the electrode composition are added to an aqueous solution of carboxymethylcellulose and/or a salt thereof, and mixed with stirring as necessary.
Also, the properties of the electrode composition are not particularly limited. For example, it may be liquid, paste, slurry, or the like, and any of them may be used.

<Electrodes for non-aqueous electrolyte secondary batteries>
The electrode for non-aqueous electrolyte secondary batteries of the present invention can be obtained by applying the electrode composition for non-aqueous electrolyte secondary batteries obtained above onto a current collector. Examples of coating methods 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 for non-aqueous electrolyte secondary batteries of the present invention 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 examples, and a method of applying the electrode composition by discharging it from an extrusion liquid injector having a slot nozzle onto a current collector that is wound around a backup roll and running is also possible. exemplified. In blade coating, after casting, if necessary, drying by heating (temperature is, for example, 80 to 120 ° C., heating time is, for example, 4 to 12 hours), etc. By performing pressure such as roll press, the non-container of the present invention is applied. An electrode for a water electrolyte secondary battery is obtained.

<Current collector>
As a current collector, any electrical conductor can be used as long as it does not cause a fatal chemical change in the constructed electrode or battery. A negative electrode current collector can be used when the electrode is a negative electrode, and a positive electrode current collector can be used when the electrode is a positive electrode.

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

<Non-aqueous electrolyte secondary battery>
The electrode for a nonaqueous electrolyte secondary battery of the present invention is used as an electrode (at least one of a negative electrode and a positive electrode) of a nonaqueous electrolyte secondary battery. That is, the present invention also provides a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery of the present invention can have a structure in which positive electrodes and negative electrodes are alternately laminated via separators and wound many times. A non-aqueous electrolyte secondary battery can be obtained by putting a laminate of a positive electrode, a separator, and a negative electrode wound many times into a battery container, injecting a non-aqueous electrolyte, and sealing the container.

The shape of the non-aqueous electrolyte secondary battery is not particularly limited, and cylindrical, rectangular, flat, coin-shaped, button-shaped, sheet-shaped and the like can be adopted. The material of the battery container is not particularly limited as long as it can achieve the purpose of preventing moisture from penetrating into the inside of the battery.

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

Also, the non-aqueous electrolyte usually comprises a lithium salt and a non-aqueous solvent. Lithium salts include, for example, LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiClO ₄ and the like. Examples of non-aqueous solvents include ethylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, butylene carbonate, and methyl ethyl carbonate. The non-aqueous solvent may be used singly or in combination of two or more. The concentration of the lithium salt in the non-aqueous electrolyte is usually 0.5 to 2.5 mol/L.

[EXAMPLES] Hereafter, although an Example demonstrates embodiment of this invention, this invention is not limited by this.
(Example 1)
(Preparation of binder)
Carboxymethyl cellulose (A350SH, DS value: 1.34, 1% viscosity: 1239 mPa s) aqueous dispersion (2% by mass) 5 g, uncrosslinked polyacrylic acid (hereinafter sometimes referred to as "uncrosslinked PAA") (Weight average molecular weight (Mw): 1 million, viscosity of water dispersion with solid content 1% (w / v) (30 rpm, 25 ° C.): 100 mPa s) 5 g of water dispersion (2% by mass) Mazerustar ( The mixture was mixed with Mazerustar KK-250S manufactured by Kurashiki Boseki Co., Ltd. to obtain binder 1 for non-aqueous electrolyte secondary battery.

(Example 2)
(Preparation of binder)
Except for changing the type of uncrosslinked polyacrylic acid to one with a weight average molecular weight (Mw) of 4 million (viscosity of aqueous dispersion with a solid content of 1% (w/v) (30 rpm, 25°C): 10153 mPa s) prepared a binder in the same manner as in Example 1 to obtain a binder 2 for a non-aqueous electrolyte secondary battery.

(Example 3)
(Preparation of binder)
A binder was prepared in the same manner as in Example 1, except that the type of carboxymethylcellulose was changed to MAC500LC (DS value: 0.65, 1% viscosity: 4700 mPa s). got 3.

(Preparation of negative electrode plate)
1.0 g of 98% by mass graphite powder (artificial graphite) and 1.0 g of 98% by mass SiO _x powder as the negative electrode active material, 0.01 g of 98% by mass acetylene black (hereinafter sometimes referred to as AB) as a conductive aid, As a binder, 20 mg of the binder 3 for non-aqueous electrolyte secondary batteries in terms of solid content, 63 mg of 48% by mass styrene-butadiene rubber (hereinafter sometimes referred to as SBR), and 1.5 g of water were mixed with Mazerustar (manufactured by Kurashiki Boseki Co., Ltd.). , Mazerustar KK-250S) to obtain an electrode composition for a non-aqueous electrolyte secondary battery. After that, the obtained electrode composition was applied to a current collector (320 mm long × 170 mm wide × 17 μm thick copper foil (manufactured by Furukawa Electric Co., Ltd., NC-WS)) with a 130 μm applicator, and applied at room temperature for 30 minutes. After drying for 1 minute, it was dried at 60° C. for 30 minutes. After drying, press at 5.0 kN using a small tabletop roll press (manufactured by Tester Sangyo Co., Ltd., SA-602) and dry at 120 ° C. for 2 hours under vacuum conditions to form a negative electrode active material layer on the current collector. Thus, a negative electrode plate 1 was obtained.

(Production of coin-type non-aqueous electrolyte secondary battery)
The obtained negative electrode plate 1 and LiCoO ₂ positive electrode plate 1 (manufactured by Hosen Co., basis weight: 227.1 g/m ² , discharge effective capacity: 145 mAh/g) were each punched out into a circle with a diameter of 16 mm. The resulting negative electrode plate 1 and positive electrode plate 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 into 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 is placed in a stainless steel circular dish-shaped container with a diameter of 20.0 mm, followed by a separator, a positive electrode plate, a spacer (15.5 mm in diameter, 1 mm in thickness), and a stainless steel washer (manufactured by Hosen Co., Ltd.). were stacked in this order, and then 300 μL of an electrolytic solution (1 mol/L of LiPF ₆ , ethylene carbonate and diethyl carbonate at a volume ratio of 1:1) was added to the circular dish-shaped container. This was covered with a stainless steel cap via a polypropylene packing and sealed with a coin battery crimping machine (Hosen Co., Ltd.) to obtain a coin-shaped non-aqueous electrolyte secondary battery 1 .

(Comparative example 1)
(Preparation of binder)
A binder 4 for a non-aqueous electrolyte secondary battery was prepared using only an aqueous dispersion (2% by mass) of carboxymethyl cellulose (A350SH) without using uncrosslinked polyacrylic acid.

<Evaluation method>
<Degree of anionization>
Each of the binders 1 to 4 for non-aqueous electrolyte secondary batteries obtained in Examples and Comparative Examples was dispersed in water to prepare an aqueous dispersion having a solid content of 10 g/L, and stirred at 1000 rpm all day and night using a magnetic stirrer. Stirred. After diluting the resulting slurry to 0.1 g/L, 10 mL was sampled and titrated with 1/1000 normality diallyldimethylammonium chloride (DADMAC) using a streaming current detector (Mutek Particle Charge Detector 03). Using the amount of DADMAC added until the flowing current became zero, the degree of anionization was calculated by the following formula:
q=(V×c)/m
q: degree of anionization (meq/g)
V: Amount of DADMAC added until flowing current becomes zero (L)
c: concentration of DADMAC (meq/L)
m: Mass (g) of binder for non-aqueous electrolyte secondary batteries in the measurement sample.

<Elastic modulus>
Each of the non-aqueous electrolyte secondary battery binders 1 to 4 obtained in Examples and Comparative Examples was applied to a polytetrafluoroethylene petri dish substrate, dried at 60° C. under normal pressure until it became a film, and then dried. A film was obtained by vacuum drying at 150° C. for 2 hours.
The elastic modulus of the obtained film was measured using a dynamic ultra-micro hardness tester DUH-W201S (Shimadzu Corporation). The measurement conditions were as follows, and the elastic modulus was calculated by analysis using the attached software.
・Test mode: Load-unload
・Test force: 2.000mN
・Loading speed: 5
・Hold time: 1sec
・Depth scale: 10.00 µm

<Discharge capacity>
A charge-discharge rate test was performed using a secondary battery charge-discharge test device (BTS2004, manufactured by Nagano Co., Ltd.) in a constant temperature bath at 25 ° C., using the coin-shaped non-aqueous electrolyte secondary battery 1 produced in Example 3. 52 cycles were carried out, with charging and discharging performed in the order of charging and discharging as one cycle.

The charging process conditions were a constant current constant voltage (CC-CV) system (CC current 0.2 C, CV voltage 4.2 V, final current 0.02 C) in all cycles. Moreover, as a condition of the discharge treatment, the end voltage was set to 3.0V. In the first cycle, the discharge treatment was performed at a constant current of 0.2 C, and the discharge capacity A (mAh/g) after one cycle was measured after discharge.

Until the subsequent 52nd cycle, the constant current for the discharge treatment was set as described below, and the discharge capacity B (mAh/g) was measured after 52 cycles of discharge.
・(Constant current for discharge treatment in each cycle)
2 to 10 cycles: constant current 0.2C for discharge treatment
11 to 20 cycles: constant current 1C for discharge treatment
21 cycles: constant current 0.2C for discharge treatment
22-31 cycles: constant current 2C for discharge treatment
32 cycles: constant current 0.2C for discharge treatment
33-42 cycles: constant current 3C for discharge treatment
43-52 cycles: constant current 0.2C for discharge treatment

<Capacity retention rate>
From the discharge capacity A and B in each cycle test described above, the capacity retention rate is
Capacity retention rate (%) = Discharge capacity B after 52 cycles (mAh/g)/Discharge capacity A after 1 cycle (mAh/g) x 100
It was calculated from the formula of
The results of the above measurements are shown in Table 1 below.

As shown in Table 1, 1 g of a binder for a non-aqueous electrolyte secondary battery containing at least carboxymethyl cellulose and/or a salt thereof, measured by a titration method using a flow current meter. A binder for a non-aqueous electrolyte secondary battery in which the degree of anionization indicated by milliequivalents (meq/g) of the anion in the binder for a non-aqueous electrolyte secondary battery is 5 meq/g or more has a high elastic modulus when formed into a film. It was found that the capacity retention rate of the secondary battery using such a binder was good.

Claims (8)

An electrode composition for a non-aqueous electrolyte secondary battery containing an active material that is a composite of a graphite material and a silicon-based compound and has a blending ratio of graphite material: silicon-based compound = 10 to 90:90 to 10 A binder for a non-aqueous electrolyte secondary battery containing at least carboxymethyl cellulose and/or a salt thereof and a water-soluble polymer, wherein 1 g of the non-aqueous electrolyte is measured by a titration method using a flow current meter. 1. A binder for non-aqueous electrolyte secondary batteries, characterized in that the degree of anionization in the binder for secondary batteries is 5 meq/g or more, as expressed by milliequivalents (meq/g) of the anions. The carboxymethyl cellulose and/or its salt has a degree of carboxymethyl substitution in the range of 0.5 to 1.5, and a viscosity (30 rpm, 25 °C) is in the range of 100 to 20000 mPa·s. 3. The binder for a non-aqueous electrolyte secondary battery according to claim 1 , wherein the water-soluble polymer has a weight average molecular weight of 1,000,000 or more. 4. The binder for a non-aqueous electrolyte secondary battery according to claim 3, wherein said water-soluble polymer is polyacrylic acid. An electrode composition for a non-aqueous electrolyte secondary battery, comprising the binder for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4. 6. The electrode composition for a non-aqueous electrolyte secondary battery according to claim 5, wherein the content of said silicon-based active material is 10% by mass or more in 100% by mass of said active material. An electrode for a non-aqueous electrolyte secondary battery using the electrode composition for a non-aqueous electrolyte secondary battery according to claim 5 or 6. A non-aqueous electrolyte secondary battery using the electrode composition for a non-aqueous electrolyte secondary battery according to claim 5 or 6.