JP2023153456A - Non-aqueous electrolyte secondary battery electrode and non-aqueous electrolyte secondary battery - Google Patents

Abstract

To provide an electrode that can maintain its structure before and after charging and discharging, and to provide a non-aqueous electrolyte secondary battery with high cycle characteristics and high rate characteristics.SOLUTION: In a non-aqueous electrolyte secondary battery electrode including at least a composite material layer, the composite material layer includes a conductive additive, an active material, and a binder, the conductive additive includes carbon nanotubes, and the composite material layer has an elastic deformation power of 45% or more in an indentation test.SELECTED DRAWING: None

Description

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

BACKGROUND OF THE INVENTION With the spread of electric vehicles and the miniaturization, weight reduction, and performance improvement of portable devices, there is a demand for secondary batteries with high energy density and higher capacity of the secondary batteries. Against this background, nonaqueous electrolyte secondary batteries using nonaqueous electrolytes, especially lithium ion secondary batteries, are used in many devices because of their high energy density and high voltage characteristics.

As negative electrode materials used in these lithium ion secondary batteries, carbon materials typified by graphite, which have a base potential close to lithium (Li) and a large charge/discharge capacity per unit mass, are used. The theoretical capacity of graphite is 372 mAhg ^-1 , and it is used to a point close to the theoretical value. In contrast, alloy-based negative electrode materials such as Si and SiO have been attracting attention in recent years as active materials that exhibit a capacity exceeding that of graphite. The theoretical capacity of Si is 4200 mAhg ^-1 , which is 11 times higher than that of graphite. However, Si has a risk of breaking the conductive path of the electrode, peeling off the current collector and the mixture layer, etc. due to the large volume change accompanying charging and discharging. This becomes a factor that deteriorates the cycle characteristics of the lithium ion secondary battery.

In recent years, maintenance of electrode structure and improvement of cycle characteristics have been reported by applying various polymer binders. Examples include carboxymethylcellulose, polyamideimide, polyacrylic acid, and sodium alginate. In Patent Document 1, a high molecular weight crosslinked sodium polyacrylate is used as a main binder, and a low molecular weight non-crosslinked acrylic acid is used as an auxiliary binder. The main binder is responsible for maintaining the structure, and the auxiliary binder is responsible for adhesion to the active material. Patent Document 2 reports that by using polyvinyl acetal resin as a binder, cycle characteristics are improved not only in the negative electrode but also in the positive electrode. Thus, it has been reported that improving the binder properties is effective in improving the cycle properties of lithium ion secondary batteries.

On the other hand, in order to maintain the electrode structure stably, the electrode structure itself must have durability against volume changes. In Patent Document 3, by using a crosslinked polymer containing an ethylenically unsaturated carboxylic acid compound as a repeating unit as a binder, the composite elastic modulus and hardness of the electrode are controlled, and the electrode is stabilized during charging and discharging. It has been reported that it suppresses the volume change of.

International Publication No. 2016/051811 International Publication No. 2018/079200 JP2018-107060

The problem to be solved by the present invention is to provide an electrode that can maintain its structure before and after charging and discharging, and to provide a non-aqueous electrolyte secondary battery with high cycle characteristics and high rate characteristics.

The inventors of the present invention have made extensive studies to solve the above problems. The inventors found that by having the composite material layer have an elastic deformation power of 45% or more in an indentation test, an electrode that can maintain its structure before and after charging and discharging can be obtained, and has excellent cycle characteristics and rate characteristics. It has been discovered that a non-aqueous electrolyte secondary battery can be obtained.

The present invention provides an electrode for a non-aqueous electrolyte secondary battery that includes at least a composite material layer, wherein the composite material layer includes a conductive additive, an active material, and a binder, the conductive additive includes carbon nanotubes, and the composite material layer includes a conductive additive, an active material, and a binder. The composite material layer relates to an electrode for a non-aqueous electrolyte secondary battery that has an elastic deformation power of 45% or more in an indentation test.

The present invention relates to the electrode for a non-aqueous electrolyte secondary battery, in which the composite material layer has an indentation creep of 4.0% or less.

The present invention relates to the electrode for a non-aqueous electrolyte secondary battery, wherein the carbon nanotubes include carbon nanotubes dispersed with a dispersant.

The present invention relates to the electrode for a non-aqueous electrolyte secondary battery, wherein the content of the dispersant is 10 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the carbon nanotubes.

The present invention relates to the electrode for a non-aqueous electrolyte secondary battery, in which the dispersant includes a triazine derivative having an acidic functional group.

The present invention relates to the electrode for a non-aqueous electrolyte secondary battery, wherein the content of the carbon nanotubes is 2 parts by mass or less based on 100 parts by mass of the composite material layer.

The present invention relates to the electrode for a non-aqueous electrolyte secondary battery, wherein the active material includes a silicon-based active material.

The present invention relates to a non-aqueous electrolyte secondary battery using the above electrode.

(1) Composite material layer The electrode film of the electrode for a non-aqueous electrolyte secondary battery includes at least a composite material layer, and for example, a configuration in which the composite material layer is provided on a current collector is exemplified. Further, the composite material layer includes a conductive additive, an active material, and a binder, and is obtained by forming a composite material slurry containing a conductive additive, an active material, a binder, and a solvent into a layer, for example.

The material and shape of the current collector used in the electrode film are not particularly limited, and one suitable for various secondary batteries can be selected as appropriate. For example, examples of the material of the current collector include metals and alloys such as aluminum, copper, nickel, titanium, and stainless steel. Further, as for the shape, a flat foil is generally used, but a current collector with a roughened surface, a foil with holes, and a mesh-like current collector can also be used.

There are no particular limitations on the method for coating the composite material slurry on the current collector, and any known method can be used. Specifically, die coating method, dip coating method, roll coating method, doctor coating method, knife coating method, spray coating method,
Gravure coating method, screen printing method, electrostatic coating method, etc. can be mentioned, and as a drying method, leaving drying, blow dryer, hot air dryer, infrared heating device, far infrared heating device, etc. can be used, but especially It is not limited to these.

Further, after coating, rolling treatment may be performed using a lithographic press, a calendar roll, or the like. The thickness of the electrode mixture layer is generally 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

The composite material layer of this embodiment contains carbon nanotubes as a conductive aid, and has an elastic deformation power of 45% or more in an indentation test. By employing a composite material layer with such elastic deformation power, when a volume change occurs due to charging and discharging, elastic deformation becomes dominant and the deformation easily returns to its original state. In other words, the adhesion between particles within the composite layer, the adhesion between the composite layer and the current collector, and the conductive path created by the conductive additive are maintained, making this a non-aqueous electrolyte with excellent cycle and rate characteristics. A secondary battery is obtained. The elastic deformation power is more preferably 50% or more, and even more preferably 60% or more.

The composite material layer of this embodiment preferably has an indentation creep of 4.0% or less, more preferably 3.5% or less, as determined by an indentation test. By employing such an indentation creep composite material layer, it is able to withstand loads due to internal stress, so structural changes due to charging and discharging can be suppressed. In other words, the adhesion between particles within the composite layer, the adhesion between the composite layer and the current collector, and the conductive path created by the conductive additive are maintained, making this a non-aqueous electrolyte with excellent cycle and rate characteristics. A secondary battery is obtained.

There are empirical rules such as the 5x rule and the 10x rule for push-in strength measurement methods. That is, since the influence of indentation extends to a region 5 to 10 times deeper than the indentation depth, it is desirable that the indentation depth does not exceed 1/10 of the film thickness.
In this specification, the elastic deformation power and indentation creep of the composite material layer are determined by measuring using an indentation tester (manufactured by Fisher Instruments, FISCHERSCOPE H100), and in the present invention, a dedicated test piece is used. By using this method, information on the strength of not only the surface layer but also the inside of the composite material layer can be obtained.
Special test pieces can be made by dropping a composite slurry into a silicone mold, drying it, taking it out, and pressing it. A Vickers indenter was used as the indenter, and measurements were taken at 100 locations at a load of 300 mN, a loading rate of 15 mN/s, and a creep time of 5 s, and the average values were taken as the elastic deformation power and creep strength.

Methods for adjusting the elastic deformation power and indentation creep within the above ranges include changing the electrode density, changing the type and amount of binder added, and changing the type, amount, and dispersion state of carbon nanotubes. can be mentioned.
Methods for changing the electrode density include changing the composition of the composite slurry, coating method, drying conditions, type of press, press pressure, press temperature, etc. In the case of roll press, changing the feed rate, Another method is to change the gap distance.
Methods for changing the type and amount of binder added include changing the main chain of the binder, changing the side chain or crosslinked structure of the binder, increasing or decreasing the amount added, and changing the combination or ratio of binders. Examples include methods.
Examples of methods for changing the type and amount of carbon nanotubes added include changing the length, diameter, specific surface area, G/D ratio, and surface condition of carbon nanotubes, and increasing or decreasing the amount added. Examples of the method of changing the dispersion state of carbon nanotubes include changing the method of dispersing carbon nanotubes, the type of dispersant, the dispersion conditions, and the method of mixing with the composite material.

However, if the density of the electrode and the type and amount of binder added are changed from the appropriate values, even if the elastic deformation power and indentation creep are adjusted to the above range, the energy density, cycle characteristics, and rate characteristics will change due to other factors. There is a risk of a decline. For example, adding a large amount of binder may impede the conduction of lithium ions, leading to a decrease in rate characteristics and energy density. On the other hand, compared to binders, carbon nanotubes can adjust elastic deformation power and indentation creep by adding small amounts, and addition can also be expected to increase electronic conductivity, so it is possible to adjust cycle characteristics while maintaining energy density. This is suitable for improving performance and rate characteristics.

(2) Conductive auxiliary agent The conductive auxiliary agent contains at least carbon nanotubes. Carbon nanotubes form good conductive paths in the electrode film. As a conductive aid other than carbon nanotubes, acetylene black, Ketjen black, etc. may be used in combination.
From the viewpoint of conductive path formation effect and cost, carbon nanotubes are preferably contained in an amount of 0.025 parts by mass or more and 2.0 parts by mass or less based on 100 parts by mass of the composite layer, and in the negative electrode, 0.025 parts by mass. More preferably, the amount is 1.0 parts by mass or less, and in the case of the positive electrode, it is more preferably 0.10 parts by mass or more and 2.0 parts by mass or less.

Carbon nanotubes have the shape of planar graphite rolled into a cylindrical shape. The carbon nanotubes may include a mixture of single-walled carbon nanotubes. Single-walled carbon nanotubes have a structure in which a single layer of graphite is wound. Multi-walled carbon nanotubes have a structure in which two or more layers of graphite are wound. Furthermore, the sidewalls of the carbon nanotubes do not need to have a graphite structure. For example, a carbon nanotube with a side wall having an amorphous structure can also be used as the carbon nanotube.

The shape of carbon nanotubes is not limited. Such shapes include a variety of shapes including needles, cylindrical tubes, fishbones (fishbone or stacked cup types), and coils. Alternatively, it may be a plate-shaped or platelet-shaped secondary aggregate obtained by dry-processing cylindrical tube-shaped carbon nanotubes. In this embodiment, the shape of the carbon nanotube is preferably needle-like or cylindrical tube-like. The carbon nanotubes may have a single shape or a combination of two or more shapes.

Examples of the form of carbon nanotubes include, but are not limited to, graphite whiskers, filamentous carbon, graphite fibers, ultrafine carbon tubes, carbon tubes, carbon fibrils, carbon microtubes, and carbon nanofibers. Carbon nanotubes may have a single form or a combination of two or more of these forms.

The average outer diameter of the carbon nanotubes is preferably 1 nm or more and 25 nm or less, more preferably 1 nm or more and 20 nm or less, and even more preferably 1 nm or more and 15 nm or less. When the average outer diameter of the carbon nanotubes is within the above range, the surface of the active material described below is likely to be covered with carbon nanotubes, and the conductivity and adhesion of the electrode film are improved.

The outer diameter and average outer diameter of carbon nanotubes are determined as follows. First, carbon nanotubes are observed and imaged using a transmission electron microscope. Next, 300 arbitrary carbon nanotubes were selected from the observation photograph and the outer diameter of each was measured. Next, the average outer diameter (nm) of the carbon nanotubes is calculated as the number average of the outer diameters.

The BET specific surface area of carbon nanotubes is preferably 150 to 1500 m ² /g, more preferably 200 to 1300 m ² /g.

The product of the amount of carbon nanotubes added in the composite material layer and the specific surface area of the carbon nanotubes is preferably 10 to 1000, more preferably 40 to 700.

Carbon nanotubes usually exist as secondary particles. The shape of the secondary particles may be, for example, a state in which carbon nanotubes, which are common primary particles, are intricately entangled. It may be an aggregate of linear carbon nanotubes. Secondary particles, which are aggregates of linear carbon nanotubes, are easier to unravel than those that are entangled. Furthermore, linear carbon nanotubes have better dispersibility than tangled carbon nanotubes, so they can be suitably used as carbon nanotubes.

The carbon nanotubes may be surface-treated carbon nanotubes. Further, the carbon nanotubes may be carbon nanotube derivatives to which functional groups such as carboxyl groups are added. Furthermore, carbon nanotubes containing an organic compound, a metal atom, or a substance typified by fullerene can also be used.

The carbon nanotubes may be carbon nanotubes manufactured by any method. Carbon nanotubes can generally be produced by a laser ablation method, an arc discharge method, a thermal CVD method, a plasma CVD method, and a combustion method, but are not limited thereto. For example, carbon nanotubes can be produced by catalytically reacting a carbon source with a catalyst at 500 to 1000° C. in an atmosphere with an oxygen concentration of 1% by volume or less.

Any conventionally known raw material gas can be used as a carbon source for carbon nanotubes. For example, hydrocarbons such as methane, ethylene, propane, butane, and acetylene, carbon monoxide, and alcohol can be used as the carbon-containing raw material gas, but are not limited thereto. Particularly from the viewpoint of ease of use, it is desirable to use at least one of hydrocarbons and alcohol as the source gas.

Commercially available carbon nanotubes include, for example, VGCF-H, VGCF-X manufactured by Showa Denko; carbon nanotubes manufactured by Meijo Nano Carbon; NTP3003, NTP3021, NTP3121, NTP8012, NTP8022, NTP9012, NTP9112, etc. manufactured by NTP; and JEIO. 10B, 6A; TUBALL, manufactured by OCSiAl; and the like.

(3) Dispersant The carbon nanotubes are preferably contained in the composite layer in the form of carbon nanotubes dispersed by a dispersant. For example, by preparing a carbon nanotube dispersion containing carbon nanotubes, a dispersant, and a solvent, and preparing a composite material slurry using this carbon nanotube dispersion, the carbon nanotubes dispersed by the dispersant can be added to the composite material layer. , and can form a good conductive path.
The dispersant is preferably used in an amount of 10 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of carbon nanotubes. It is more preferably 20 parts by mass or more and 100 parts by mass or less, and even more preferably 20 parts by mass or more and 80 parts by mass or less.

The dispersant is not particularly limited as long as it can stabilize the dispersion of carbon nanotubes, and surfactants, resin-type dispersants, and triazine derivatives having acidic functional groups can be used. Surfactants are mainly classified into anionic, cationic, nonionic and amphoteric. Depending on the characteristics required for dispersing carbon nanotubes, a suitable type of dispersant can be used in a suitable amount.

When selecting an anionic surfactant, its type is not particularly limited. Specifically, fatty acid salts, polysulfonates, polycarboxylate salts, alkyl sulfate ester salts, alkylaryl sulfonates, alkylnaphthalene sulfonates, dialkyl sulfonates, dialkyl sulfosuccinates, alkyl phosphates, polyoxy ethylene alkyl ether sulfate,
Examples include, but are not limited to, polyoxyethylene alkylaryl ether sulfates, naphthalene sulfonic acid formalin condensates, polyoxyethylene alkyl phosphoric acid sulfonates, glycerol borate fatty acid esters, and polyoxyethylene glycerol fatty acid esters. Further, specific examples include sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium polyoxyethylene lauryl ether sulfate, polyoxyethylene nonylphenyl ether sulfate salt, and sodium salt of β-naphthalenesulfonic acid formalin condensate. , but not limited to.

Cationic surfactants include alkylamine salts and quaternary ammonium salts. Specifically, stearylamine acetate, trimethylyacyanmonium chloride, trimethyltallow ammonium chloride, dimethyldioleylammonium chloride, methyloleyldiethanol chloride, tetramethylammonium chloride, laurylpyridinium chloride, laurylpyridinium bromide, laurylpyridinium disulfate, cetylpyridinium bromide. , 4-alkylmercaptopyridine, poly(vinylpyridine)-dodecyl bromide and dodecylbenzyltriethylammonium chloride. Examples of amphoteric surfactants include aminocarboxylic acid salts, but are not limited thereto.

Examples of nonionic surfactants include, but are not limited to, polyoxyethylene alkyl ethers, polyoxyalkylene derivatives, polyoxyethylene phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and alkyl allyl ethers. Specific examples include polyoxyethylene lauryl ether, sorbitan fatty acid ester, and polyoxyethylene octylphenyl ether,
Not limited to these.

The surfactant selected is not limited to a single surfactant. For this reason, it is also possible to use two or more types of surfactants in combination. For example, a combination of an anionic surfactant and a nonionic surfactant, or a combination of a cationic surfactant and a nonionic surfactant can be used. The blending amount at that time is preferably a blending amount suitable for each surfactant component. As for the combination, a combination of an anionic surfactant and a nonionic surfactant is preferred. Preferably, the anionic surfactant is a polycarboxylate. Preferably, the nonionic surfactant is polyoxyethylene phenyl ether.

Specific examples of resin-type dispersants include cellulose derivatives (cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethylcellulose, ethylhydroxyethylcellulose, nitrocellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose) , carboxymethylcellulose, etc.), polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyacrylonitrile polymers, and the like.
Particularly preferred are methylcellulose, ethylcellulose, carboxymethylcellulose, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, and polyacrylonitrile polymers.

Carboxymethylcellulose can be used in the form of a salt such as a sodium salt of carboxymethylcellulose in which the hydroxyl group of carboxymethylcellulose is replaced with a carboxymethyl sodium group.

The weight average molecular weight of the dispersant in terms of pullulan is preferably 5,000 or more and 300,000 or less, more preferably 10,000 or more and 100,000 or less, and even more preferably 10,000 or more and 50,000 or less. When a dispersant having an appropriate weight average molecular weight is used, adsorption to CNTs is improved, and the stability of the carbon nanotube dispersion is further improved. Additionally, if a dispersant exceeding the above range is used, the viscosity of the carbon nanotube dispersion will increase, and if a dispersing machine in which the liquid to be dispersed passes through a narrow channel, such as a nozzle-type high-pressure homogenizer, is used, the dispersion efficiency will decrease. It may decrease.

Further, the dispersant is preferably a triazine derivative having an acidic functional group, and more preferably a triazine derivative represented by the following general formula (1).

General formula (1)

X ₁ represents -NH-, -O-, -CONH-, -SO ₂ NH-, -CH ₂ NH-, -CH ₂ NHCOCH ₂ NH- or -X ₃ -Y-X ₄ -, and X ₂ and X ₄ each independently represents -NH- or -O-, and X ₃ represents -CONH-, -SO ₂ NH-, -CH ₂ NH-,
-NHCO- or -NHSO ₂ -, Y is an alkylene group that may have a substituent, an alkenylene group that may have a substituent, or an alkenylene group that may have a substituent and has 1 to 20 carbon atoms. Z represents -SO ₃ M or -COOM, or -P(O)(-OM) 2 , M represents one equivalent of a mono- to trivalent cation, and R ₁ represents an organic Represents a dye residue, a heterocyclic residue that may have a substituent, an aromatic ring residue that may have a substituent, or a group represented by the following general formula (2), and Q is - O-R ₂ , -NH-R ₂ represents a halogen group, -X ₁ -R ₁ or -X ₂ -Y-Z, R ₂ is a hydrogen atom, an alkyl group that may have a substituent, or a substituent represents an alkenyl group which may have

General formula (2)

X ₅ represents -NH- or -O-, and X ₆ and X ₇ each independently represent -NH-, -O-
, -CONH-, -SO ₂ NH-, -CH ₂ NH- or -CH ₂ NHCOCH ₂ NH-
, R ₃ and R ₄ each independently represent an organic dye residue, a heterocyclic residue which may have a substituent, an aromatic ring residue which may have a substituent, or -Y- represents Z, and Y and Z have the same meaning as in general formula (1).

The organic dye residues represented by R ₁ in general formula (1) and R ₃ and R ₄ in general formula (2) are as follows:
For example, diketopyrrolopyrrole dyes, azo dyes such as azo, disazo, and polyazo, phthalocyanine dyes, diaminodianthraquinone, anthrapyrimidine, flavanthrone, anthranthrone, indanthrone, pyrantrone, anthraquinone dyes such as violanthrone, and quinacridone dyes. Examples include dyes, dioxazine dyes, perinone dyes, perylene dyes, thioindigo dyes, isoindoline dyes, isoindolinone dyes, quinophthalone dyes, threne dyes, metal complex dyes, and the like. In particular, in order to enhance the effect of suppressing short circuits in batteries caused by metals, it is preferable to use organic dye residues other than metal complex dyes, including azo dyes, diketopyrrolopyrrole dyes, metal-free phthalocyanine dyes, Quinacridone dyes and dioxazine dyes are preferably used because they have excellent dispersibility.

Examples of the heterocyclic residue and aromatic ring residue represented by R ₁ in general formula (1) and R ₃ and R ₄ in general formula (2) include thiophene, furan, pyridine, pyrazole, pyrrole, and imidazole. , isoindoline, isoindolinone, benzimidazolone, benzthiazole, benztriazole, indole, quinoline, carbazole, acridine, benzene,
Examples include naphthalene, anthracene, fluorene, phenanthrene, and anthraquinone. In particular, it is preferable to use a heterocyclic residue containing at least one of S, N, and O heteroatoms because of its excellent dispersibility.

Y in the general formulas (1) and (2) represents an alkylene group, an alkenylene group, or an arylene group which may have a substituent having 20 or less carbon atoms, preferably an optionally substituted phenylene group. group, biphenylene group, naphthylene group, or alkylene group which may have a side chain having 10 or less carbon atoms.

The optionally substituted alkyl group or alkenyl group represented by R ₂ contained in Q of the general formula (1) preferably has 20 or less carbon atoms, and more preferably has 10 carbon atoms. Examples include alkyl groups that may have the following side chains. An alkyl group or alkenyl group having a substituent is one in which the hydrogen atom of an alkyl group or alkenyl group is substituted with a halogen group such as a fluorine atom, chlorine atom, or bromine atom, a hydroxyl group, a mercapto group, or the like.

In the general formula (1), M represents one equivalent of a mono- to trivalent cation, and represents, for example, a hydrogen atom (proton), a metal cation, or a quaternary ammonium cation. Further, when the dispersant structure has two or more M, M may be one of protons, metal cations, and quaternary ammonium cations, or a combination thereof.
Examples of metals include lithium, sodium, potassium, calcium, barium, magnesium, aluminum, nickel, and cobalt.
The quaternary ammonium cation is a single compound or a mixture having a structure represented by general formula (3).

General formula (3)

R ₅ , R ₆ , R ₇ , and R ₈ are any of hydrogen, an alkyl group that may have a substituent, an alkenyl group that may have a substituent, or an aryl group that may have a substituent. represents something.

R ₅ , R ₆ , R ₇ and R ₈ in general formula (3) may be the same or different. Further, when R ₅ , R ₆ , R ₇ and R ₈ have carbon atoms, the number of carbon atoms is 1 to 40, preferably 1 to 30, and more preferably 1 to 20. When the number of carbon atoms exceeds 40, the conductivity of the electrode may decrease.

Specific examples of quaternary ammonium include dimethylammonium, trimethylammonium, diethylammonium, triethylammonium, hydroxyethylammonium, dihydroxyethylammonium, 2-ethylhexylammonium, dimethylaminopropylammonium, lauryl ammonium, stearyl ammonium, etc.
Not limited to these.

(4) Carbon nanotube dispersion As a dispersion device for preparing a carbon nanotube dispersion, a dispersion machine commonly used for dispersing pigments and the like can be used.
For example, mixers such as dispers, homomixers, and planetary mixers, homogenizers (Advanced Digital Sonifer (registered trademark) manufactured by BRANSON, MODEL 450DA, ``Creamix'' manufactured by M Techniques, ``Filmix'' manufactured by PRIMIX, etc., manufactured by Silverson, etc.) "Abramix" etc.), paint conditioner (manufactured by Red Devil Co., Ltd.), colloid mill ("PUC Colloid Mill" made by PUC Co., Ltd.)
, "Colloid Mill MK" manufactured by IKA), Corn mill ("Cone Mill MKO" manufactured by IKA)
etc.), ball mills, sand mills (such as "Dyno Mill" manufactured by Shinmaru Enterprises), attritor, pearl mills (such as "DCP Mill" manufactured by Eirich), media-type dispersion machines such as Koball Mill, wet jet mills (such as "Dyno Mill" manufactured by Genus), Genus PY, Sugino Machine Co., Ltd.'s "Starburst," Nanomizer Co., Ltd.'s "Nanomizer," etc.), M Technique Co., Ltd.'s "Claire SS-5," Nara Kikai Co., Ltd.'s "MICROS," and other medialess dispersion machines, and other roll mills. etc., but are not limited to these.

The amount of carbon nanotubes in the carbon nanotube dispersion is preferably 0.2 to 20 parts by mass, preferably 0.5 to 10 parts by mass, and 0.2 to 20 parts by mass, preferably 0.5 to 10 parts by mass, based on 100 parts by mass of the carbon nanotube dispersion. More preferably 5 to 7.0 parts by mass.

The pH of the carbon nanotube dispersion is preferably 6 to 11, more preferably 7 to 11, even more preferably 8 to 11, particularly preferably 9 to 11. The pH of the carbon nanotube dispersion can be measured using a pH meter (manufactured by Horiba, Ltd., pHMETERF-52).

Moreover, in addition to the dispersant, an inorganic base and a metal-free salt may be included. The inorganic base and inorganic metal salt are preferably compounds containing at least one of an alkali metal and an alkaline earth metal. Examples include salts, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, and borates. Moreover, among these, chlorides, hydroxides, and carbonates of alkali metals and alkaline earth metals are preferable from the viewpoint that cations can be easily supplied. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, and the like. Examples of alkaline earth metal hydroxides include calcium hydroxide and magnesium hydroxide. Examples of alkali metal carbonates include lithium carbonate, lithium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate, and the like. Examples of alkaline earth metal carbonates include calcium carbonate and magnesium carbonate. Among these, lithium hydroxide, sodium hydroxide, lithium carbonate, and sodium carbonate are more preferred.

Moreover, in addition to the dispersant, an antifoaming agent may be included. Any antifoaming agent can be used as long as it has an antifoaming effect, such as commercially available antifoaming agents, wetting agents, hydrophilic organic solvents, and water-soluble organic solvents. Good too.
For example, alcohol-based; ethanol, propanol, isopropanol, butanol, octyl alcohol, hexadecyl alcohol, acetylene alcohol, ethylene glycol monobutyl ether, methyl cellosolve, butyl cellosolve, propylene glycol monomethyl ether, acetylene glycol, polyoxyalkylene glycol, propylene glycol, etc. Glycols, etc.
Fatty acid esters; diethylene glycol laurate, glycerin monoricinolate, alkenyl succinic acid derivatives, sorbitol monolaurate, sorbitol trioleate, polyoxyethylene monolaurate, polyoxyethylene sorbitol monolaurate, natural wax, etc.
Amide type; polyoxyalkylene amide, acrylate polyamine, etc.
Phosphate esters; tributyl phosphate, sodium octyl phosphate, etc.
Metal soaps; aluminum stearate, calcium oleate, etc.
Fats and oils; animal and vegetable oils, sesame oil, castor oil, etc.
Mineral oil: Kerosene, paraffin, etc.
Silicone type; Examples include dimethyl silicone oil, silicone paste, silicone emulsion, organically modified polysiloxane, and fluorosilicone oil.

The solvent is not particularly limited as long as the carbon nanotubes can be dispersed therein, but it is preferably a mixed solvent consisting of one or more of water and/or a water-soluble organic solvent, and may contain water. is more preferable. When water is included, it is preferably 95 parts by mass or more, more preferably 98 parts by mass or more based on the entire solvent.

Water-soluble organic solvents include alcohols (methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, benzyl alcohol, etc.), polyhydric alcohols (ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol, etc.), polyhydric alcohol ethers (ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene Glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, etc.), amines (ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine) , ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone) (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.), heterocyclic systems (cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2 -imidazolidinone, γ-butyrolactone, etc.), sulfoxides (dimethylsulfoxide, etc.), sulfones (hexamethylphosphorotriamide, sulfolane, etc.), lower ketones (acetone, methyl ethyl ketone, etc.), others, tetrahydrofuran, urea, acetonitrile, etc. can be used.

(5) Active material An active material is a material that becomes the basis of a battery reaction. Active materials are divided into positive electrode active materials and negative electrode active materials based on electromotive force.

The positive electrode active material is not particularly limited, but metal compounds such as metal oxides and metal sulfides that can be doped with or intercalated with lithium ions, conductive polymers, and the like can be used. Examples include oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium, and inorganic compounds such as transition metal sulfides. Specifically, transition metal oxide powders such as MnO, V ₂ O ₅ , V ₆ O ₁₃ , and TiO ₂ , lithium nickelate with a layered structure, lithium cobalt oxide, lithium manganate, lithium manganate with a spinel structure, etc. Examples include composite oxide powder of lithium and transition metal, lithium iron phosphate material which is a phosphoric acid compound having an olivine structure, and transition metal sulfide powder such as TiS ₂ and FeS. Furthermore, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Further, the above inorganic compounds and organic compounds may be used in combination.

The negative electrode active material is not particularly limited as long as it is capable of doping or intercalating lithium ions. For example, metal Li, its alloys such as tin alloys, silicon alloys, lead alloys, Li x Fe ₂ O ₃ , Li _x Fe ₃ O ₄ , Li _x WO ₂ (x is a number of 0<x<1) ), metal oxides such as lithium titanate, lithium vanadate, and lithium silicate, conductive polymers such as polyacetylene and poly-p-phenylene, amorphous carbonaceous materials such as soft carbon and hard carbon, Examples include carbonaceous materials such as artificial graphite such as highly graphitized carbon materials, carbonaceous powders such as natural graphite, carbon black, mesophase carbon black, resin-sintered carbon materials, vapor grown carbon fibers, and carbon fibers. These negative electrode active materials can also be used singly or in combination.

As the negative electrode active material, a silicon-based negative electrode active material is preferable, and examples thereof include silicon, silicon alloy, lithium silicate, and the like.

Examples of silicon include so-called metallurgical grade silicon, which is produced by reducing silicon dioxide with carbon, industrial grade silicon, which is produced by reducing impurities by treating metallurgical grade silicon with acid or unidirectional solidification, and silicon obtained by reacting silicon. At the same time, high-purity silicon with different crystal states such as high-purity single crystal, polycrystalline, and amorphous produced from silane, and industrial-grade silicon are made to high purity using sputtering method or EB evaporation (electron beam evaporation) method. Examples include silicon whose crystal state and precipitation state have been adjusted.

Other examples include silicon oxide, which is a compound of silicon and oxygen, silicon and various alloys, and silicon compounds whose crystal states are adjusted by a rapid cooling method or the like. Among these, a silicon-based negative electrode active material having a structure in which silicon nanoparticles are dispersed in silicon oxide and whose outside is coated with a carbon film is preferable.

As the negative electrode active material, in addition to silicon-based negative electrode active materials, amorphous carbonaceous materials such as soft carbon and hard carbon, artificial graphite such as highly graphitized carbon materials, or carbonaceous powder such as natural graphite may be used. is preferred. Among these, it is preferable to use carbonaceous powder such as artificial graphite or natural graphite.

The amount of the silicon-based negative electrode active material is preferably 3 to 50% by mass, more preferably 5 to 25% by mass, based on 100% by mass of carbonaceous powder such as artificial graphite or natural graphite.

The BET specific surface area of the active material is preferably 0.1 to 10 m ² /g, more preferably 0.2 to 5 m ² /g, even more preferably 0.3 to 3 m ² /g.

The average particle size of the active material is preferably within the range of 0.5 to 50 μm, more preferably 2 to 20 μm. The average particle diameter of the active material as used herein is the average value of the particle diameters of the active material measured using an electron microscope.

(6) Binder A binder is a resin for binding substances such as active materials and carbon nanotubes.

Examples of the binder include ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic ester, methacrylic acid, methacrylic ester, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc. Polymers or copolymers contained as structural units; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, fluorine resins; carboxymethyl cellulose Examples include cellulose resins such as; rubbers such as styrene-butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Also, modified products, mixtures, and copolymers of these resins may be used. Among these, carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid are preferred.

The type and quantity ratio of the binder are appropriately selected depending on the properties of coexisting substances such as carbon nanotubes and active materials. For example, regarding the amount of carboxymethylcellulose used, when the mass of the active material is 100% by mass, the proportion of carboxymethylcellulose is preferably 0.5 to 3.0% by mass, and 1.0 to 2.0% by mass. More preferred.

The carboxymethylcellulose is preferably a sodium salt of carboxymethylcellulose in which the hydroxyl group of carboxymethylcellulose is replaced with a carboxymethyl sodium group.

Carboxymethyl cellulose preferably has a viscosity of 500 to 6000 mPa·s, more preferably 1000 to 3000 mPa·s when a 1% aqueous solution is prepared. The viscosity of a 1% carboxymethylcellulose aqueous solution can be measured at 25° C. using a B-type viscometer at a rotor rotation speed of 60 rpm.

The degree of etherification of carboxymethylcellulose is preferably 0.6 to 1.5, more preferably 0.8 to 1.2.

As the styrene-butadiene rubber, any oil-in-water emulsion that is generally used as a binder for electrodes can be used. Regarding the amount of styrene-butadiene rubber used, when the mass of the active material is 100% by mass, the proportion of styrene-butadiene rubber is preferably 0.5 to 3.0% by mass, and 1.0 to 2.0% by mass. More preferred.

(7) Composite material slurry Composite material slurry contains at least a conductive additive, an active material, a binder, and a solvent.

The composite material slurry can be produced by various conventionally known methods. Preferably, the carbon nanotube dispersion, the binder, and the active material are mixed, but the order in which they are mixed is not particularly limited, and each may be added sequentially, or two or more of them may be added. They may be added at the same time. For example, the active material may be added after adding a binder to a carbon nanotube dispersion to produce a carbon nanotube resin composition, or the active material may be added to a carbon nanotube dispersion and then a binder is added. You may.

In order to obtain a composite slurry, it is preferable to add the active material to the carbon nanotube resin composition and then perform a dispersion process. The dispersion device used to perform such processing is not particularly limited. The composite material slurry can be obtained using the dispersion device described for the carbon nanotube dispersion.

The amount of active material in the composite slurry is preferably 20 to 85 parts by mass, more preferably 30 to 80 parts by mass, and 40 to 75 parts by mass based on 100 parts by mass of the composite slurry. It is even more preferable.

The amount of carbon nanotubes in the composite slurry is preferably 0.01 to 10 parts by mass, more preferably 0.02 to 5 parts by mass, and 0.01 to 10 parts by mass, more preferably 0.02 to 5 parts by mass, based on 100 parts by mass of the active material. More preferably, the amount is 0.02 to 3 parts by mass.

The amount of binder in the composite slurry is preferably 0.5 to 30% by mass, more preferably 1 to 25% by mass, and 2 to 20% by mass based on 100% by mass of the active material. It is even more preferable.

The amount of solids in the composite slurry is preferably 30 to 90% by mass, more preferably 35 to 85% by mass, and 40 to 80% by mass based on 100% by mass of the composite slurry. It is even more preferable.

(8) Nonaqueous electrolyte secondary battery A nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and an electrolyte.
As the positive electrode, an electrode film prepared by applying and drying a composite slurry containing a positive electrode active material onto a current collector can be used.
As the negative electrode, an electrode film prepared by applying and drying a composite slurry containing a negative electrode active material on a current collector can be used.

As the electrolyte, various conventionally known electrolytes that allow movement of ions can be used.
For example, _{LiBF4 , LiClO4} , LiPF6 _{, LiAsF6} , _{LiSbF6 , LiCF3SO3} , _Li ( _{CF3SO2 ) 2N} , _{LiC4F9SO3 ,} Li( _CF3SO2 ) _3C , LiI , LiBr, LiCl, LiAlCl, LiHF ₂ , LiSCN, or LiBPh ₄ (where Ph is a phenyl group), etc., but are not limited to these, and include sodium salts and calcium salts. can also be used. It is preferable that the electrolyte be dissolved in a non-aqueous solvent and used as an electrolytic solution.

Examples of non-aqueous solvents include, but are not limited to, carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethylmethyl carbonate, and diethyl carbonate; γ-butyrolactone, γ-valerolactone, and γ. - Lactones such as octanoic lactone; tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1, Examples include glymes such as 2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. These solvents may be used alone or in combination of two or more.

Preferably, the non-aqueous electrolyte secondary battery includes a separator. Examples of the separator include, but are not limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and those subjected to hydrophilic treatment.

The structure of a non-aqueous electrolyte secondary battery is not particularly limited, but it usually consists of a positive electrode, a negative electrode, and a separator provided as necessary, and can be of a paper type, cylindrical type, button type, laminated type, etc. depending on the purpose of use. It can be made into various shapes depending on the requirements.

The present invention will be explained in more detail with reference to Examples below. The present invention is not limited to the following examples unless it exceeds the gist thereof. In addition, unless otherwise specified, "parts" represent "parts by mass" and "%" represent "% by mass." In examples, "carbon nanotube" is sometimes abbreviated as "CNT".

The compounds used in Examples and Comparative Examples are shown below.
<Carbon nanotubes>
・JENOTUBE 10B (manufactured by JEIO)
・JENOTUBE 6A (manufactured by JEIO)
・TUBALL SWCNT 93% (manufactured by OCSiAL)
<Binder resin>
・CMC #1190: Carboxymethylcellulose (manufactured by Daicel Millize)
・PVDF#5130: Polyvinylidene fluoride (manufactured by Solvey)
・SBR TRD2001: Styrene butadiene emulsion (manufactured by JSR Corporation)
<Solvent>
・NMP: N-methyl-2-pyrrolidone (manufactured by Kishida Chemical Co., Ltd.)
<Negative electrode active material>
・SiO: Silicon monoxide (manufactured by Osaka Titanium Technology Co., Ltd., SILICONMONOOXIDE)
<Cathode active material>
・NCM: Nickel-based positive electrode material (manufactured by BASF Toda Battery Materials LLC, HED (registered trademark) NCM-111 1100)

<Dispersant>
Table 1 shows the dispersants used in Examples and Comparative Examples.

(Example 1)
96.25 parts of ion-exchanged water and 0.75 parts of dispersant X were placed in a glass bottle, and after sufficiently mixing and dissolving, 3.00 parts of CNT (JENOTUBE 10B, manufactured by JEIO) was added. Next, 200 parts of 0.8 mm diameter zirconia beads were added as a media, the bottle was sealed, and the mixture was dispersed in a paint shaker for 4 hours to obtain a dispersion liquid (A).
In a plastic container, we weighed 0.42 parts by mass of CNT dispersion (A), 12.50 parts by mass of an aqueous solution in which 2% by mass of carboxymethyl cellulose (manufactured by Daicel Millize Co., Ltd., #1190) and 11.95 parts by mass of ion-exchanged water were weighed. . Thereafter, the mixture was stirred for 1 minute at 2000 rpm using a rotation/revolution mixer (Awatori Rentaro, ARE-310, manufactured by Shinky Co., Ltd.) to obtain a CNT resin composition. Thereafter, 2.44 parts by mass of silicon monoxide (manufactured by Osaka Titanium Technology Co., Ltd., SILICON MONOOXIDE, SiO 1.3C 5 μm) as a negative electrode active material was added, and the mixture was stirred at 2000 rpm for 5 minutes using the above-mentioned autorotation/revolution mixer. Furthermore, 21.93 parts by mass of natural graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGB-20) was added, and the mixture was stirred at 2000 rpm for 5 minutes using the above-mentioned rotation/revolution mixer. Thereafter, 0.78 parts by mass of styrene-butadiene emulsion (manufactured by JSR Corporation, TRD2001) with a solid content concentration of 48% by mass was added, and the mixture was stirred at 2000 rpm for 30 seconds using the above-mentioned rotation/revolution mixer to form a negative electrode mixture. Got slurry.
After applying the negative electrode composite slurry onto the copper foil using an applicator so that the area weight per unit of electrode was 8 mg/cm ² , it was heated in an electric oven at 120°C ± 5°C for 30 minutes. The coating was allowed to dry. Next, the coating film was rolled using a roll press (manufactured by Thank Metal Co., Ltd., 3t hydraulic roll press) to obtain an electrode film with a composite layer density of 1.6 g/cm ³ .

<Preparation of test piece exclusively for indentation test>
The negative electrode composite slurry was dropped into a rectangular silicone mold, dried on a hot plate at 40°C for 5 hours, and then dried in an electric oven at 120°C±5°C for 30 minutes. Next, the dried product was taken out of the silicone mold and rolled using a roll press (manufactured by Thank Metal Co., Ltd., 3t hydraulic roll press) to obtain a thickness of 0.8 mm and a density of 1.6 g/cm ³ for a special test. Got a piece.

<Measurement by indentation test>
Using an indentation tester (manufactured by Fisher Instruments, FISCHERSCOPE H100), the elastic deformation power and indentation creep of the test piece exclusively for indentation tests were measured. A Vickers indenter was used as the indenter, and measurements were taken at 100 locations at a load of 300 mN, a loading rate of 15 mN/s, and a creep time of 5 s, and the average values were taken as the elastic deformation power and creep strength.

Table 2 shows the CNT dispersions used in Examples and Comparative Examples.

ＣＮＴ分散液（Ｆ）は、ペイントシェーカーで４時間分散した際の粘度が高く、分散液とビーズを分離することができなかった。

The CNT dispersion liquid (F) had a high viscosity when dispersed in a paint shaker for 4 hours, and the dispersion liquid and beads could not be separated.

Table 3 shows the composition of the composite material layer used in the Examples and Comparative Examples.

(Examples 2 to 14)
An electrode film and a test piece exclusively for the indentation test were obtained in the same manner as in Example 1, except that the compositions of the dispersant, CNT dispersion, and composite material layer listed in Tables 1 to 3 were changed.

(Example 15)
96.25 parts of NMP and 0.75 parts of dispersant Z were placed in a glass bottle, thoroughly mixed and dissolved, and then 3.00 parts of CNT (JENOTUBE 10B, manufactured by JEIO) was added. Next, 200 parts of zirconia beads having a diameter of 0.8 mm were added as a media, the bottle was sealed, and the mixture was dispersed in a paint shaker for 4 hours to obtain a dispersion (E).
In a plastic container, 4.17 parts by mass of CNT dispersion (E), 6.25 parts by mass of an NMP solution in which 8% by mass of PVDF (manufactured by Solvey, #5130) had been dissolved, and 15.22 parts by mass of NMP were weighed. Thereafter, the mixture was stirred for 1 minute at 2000 rpm using a rotation/revolution mixer (Awatori Rentaro, ARE-310, manufactured by Shinky Co., Ltd.) to obtain a CNT resin composition. Thereafter, 24.38 parts by mass of a positive electrode active material (manufactured by BASF Toda Battery Materials LLC, HED (registered trademark) NCM-111 1100) was added, and the mixture was stirred for 5 minutes at 2000 rpm using the rotation/revolution mixer. A composite material slurry was obtained.
After applying the positive electrode composite slurry onto aluminum foil using an applicator so that the weight per unit of electrode was 20 mg/cm ² , it was heated in an electric oven at 120°C ± 5°C for 30 minutes. The coating was allowed to dry. Next, the coating film was rolled using a roll press (manufactured by Thank Metal Co., Ltd., 3t hydraulic roll press) to obtain an electrode film with a composite layer density of 3.1 g/cm ³ .
<Preparation of test piece exclusively for indentation test>
The positive electrode composite slurry was dropped into a rectangular silicone mold, dried on a hot plate at 40°C for 5 hours, and then dried in an electric oven at 120°C±5°C for 30 minutes. Next, the dried product was taken out of the silicone mold and rolled using a roll press (manufactured by Thank Metal Co., Ltd., 3t hydraulic roll press) to obtain a thickness of 0.8 mm and a density of 3.1 g/cm ³ for a special test. Got a piece.

(Examples 16 to 18)
An electrode film and a test piece exclusively for the indentation test were obtained in the same manner as in Example 15, except that the composition of the composite layer listed in Table 3 was changed.

(Comparative example 1)
In a plastic container, 12.50 parts by mass of an aqueous solution in which 2% by mass of carboxymethyl cellulose (manufactured by Daicel Millize Co., Ltd., #1190) was dissolved and 12.34 parts by mass of ion-exchanged water were weighed. Thereafter, the mixture was stirred for 1 minute at 2000 rpm using a rotation/revolution mixer (Awatori Rentaro, ARE-310, manufactured by Shinky Co., Ltd.). Thereafter, 2.44 parts by mass of silicon monoxide (manufactured by Osaka Titanium Technology Co., Ltd., SILICON MONOOXIDE, SiO 1.3C 5 μm) as a negative electrode active material was added, and the mixture was stirred at 2000 rpm for 5 minutes using the same rotation/revolution mixer. Furthermore, 21.93 parts by mass of natural graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGB-20) was added and stirred for 5 minutes at 2000 rpm using the same rotation/revolution mixer. Then, 0.78 parts by mass of styrene-butadiene emulsion (manufactured by JSR Corporation, TRD2001) was added and stirred for 30 seconds at 2000 rpm using a rotation/revolution mixer (Awatori Rentaro, ARE-310, manufactured by Shinky Corporation), A negative electrode composite material slurry was obtained.
After applying the negative electrode composite slurry onto the copper foil using an applicator so that the area weight per unit of electrode was 8 mg/cm ² , it was heated in an electric oven at 120°C ± 5°C for 30 minutes. The coating was allowed to dry. Next, the coating film was rolled using a roll press (manufactured by Thank Metal Co., Ltd., 3t hydraulic roll press) to obtain an electrode film with a composite layer density of 1.6 g/ ^cm3 , and a special test piece was prepared. Created.

(Comparative Examples 2-3)
An electrode film and a test piece exclusively for the indentation test were obtained in the same manner as in Example 1, except that the compositions of the CNT dispersion liquid and composite material layer listed in Tables 1 and 2 were changed.

(Comparative example 4)
In a plastic container, 12.50 parts by mass of an aqueous solution in which 2% by mass of carboxymethyl cellulose (manufactured by Daicel Millize Co., Ltd., #1190) was dissolved, 12.34 parts by mass of ion-exchanged water, and 0.08 parts of CNT (JENOTUBE 10B, manufactured by JEIO Corporation). Weighed. Thereafter, the mixture was stirred for 1 minute at 2000 rpm using a rotation/revolution mixer (Awatori Rentaro, ARE-310, manufactured by Shinky Co., Ltd.) to obtain a CNT resin composition. Thereafter, 2.43 parts by mass of silicon monoxide (SILICONMONOOXIDE, SiO 1.3C 5 μm, manufactured by Osaka Titanium Technology Co., Ltd.) as a negative electrode active material was added, and the mixture was stirred at 2000 rpm for 5 minutes using the same rotation/revolution mixer. Furthermore, 21.87 parts by mass of natural graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGB-20) was added and stirred for 5 minutes at 2000 rpm using the same rotation/revolution mixer. Then, 0.78 parts by mass of styrene-butadiene emulsion (manufactured by JSR Corporation, TRD2001) was added and stirred for 30 seconds at 2000 rpm using a rotation/revolution mixer (Awatori Rentaro, ARE-310, manufactured by Shinky Corporation), A negative electrode composite slurry was obtained.
After applying the negative electrode composite slurry onto the copper foil using an applicator so that the area weight per unit of electrode was 8 mg/cm ² , it was heated in an electric oven at 120°C ± 5°C for 30 minutes. The coating was allowed to dry. Next, the coating film was rolled using a roll press (manufactured by Thank Metal Co., Ltd., 3t hydraulic roll press) to obtain an electrode film with a composite layer density of 1.6 g/ ^cm3 , and a special test piece was prepared. Created.

(Comparative example 5)
An electrode film and a test piece exclusively for the indentation test were obtained in the same manner as in Example 15, except that the composition of the composite layer listed in Table 2 was changed.

<Assembling cell for evaluating lithium ion secondary battery negative electrode>
The previously produced electrode films (Examples 1 to 14, Comparative Examples 1 to 4) were punched out to a diameter of 16 mm to serve as a working electrode, metal lithium foil (thickness 0.15 mm) was used as a counter electrode, and a separator ( A mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate was mixed at a ratio of 3:5:2 (volume ratio) was prepared by inserting and laminating a porous polypropylene film, and VC ( After adding 1 part by mass of each of vinylene carbonate (vinylene carbonate) and FEC (fluoroethylene carbonate) to 100 parts by mass of the mixed solvent, a non-aqueous electrolyte (in which LiPF6 was dissolved at a concentration of 1M) was added to form a two-electrode sealed metal cell. (HS flat cell manufactured by Hosensha) was assembled. Cell assembly was performed in a glove box purged with argon gas.

<Cycle characteristic evaluation of lithium ion secondary battery negative electrode>
The prepared lithium ion secondary battery negative electrode evaluation cell was placed in a constant temperature room at 25° C., and charging and discharging was measured using a charging and discharging device (manufactured by Hokuto Denko Co., Ltd., SM-8). After performing constant current constant voltage charging (cutoff current: 0.02C current) at a charge rate of 0.2C and a charge end voltage of 0.05V, constant current is charged at a discharge rate of 0.2C and a discharge end voltage of 1.5V. Discharge was performed. This operation was repeated 20 times. 1C is the current value for charging or discharging the theoretical capacity of the negative electrode in 1 hour. The cycle characteristics can be expressed by the ratio of the 3rd 0.2C discharge capacity to the 20th 0.2C discharge capacity, as shown in Equation 1 below.

(Formula 1) Cycle characteristics = 3rd 0.2C discharge capacity / 20th 0.2C discharge capacity x 100 (%)

4: 95.0% or more 3: 90.0% or more and less than 95.0% 2: 80.0% or more and less than 90.0% 1: 60.0% or more and less than 80.0% 0: Less than 60.0%

<Evaluation of rate characteristics of lithium ion secondary battery negative electrode>
The prepared lithium ion secondary battery negative electrode evaluation cell was placed in a constant temperature room at 25° C., and charging and discharging was measured using a charging and discharging device (manufactured by Hokuto Denko Co., Ltd., SM-8). After performing constant current constant voltage charging (cutoff current: 0.02C current) at a charge rate of 0.2C and a charge end voltage of 0.05V, constant current is charged at a discharge rate of 0.2C and a discharge end voltage of 1.5V. Discharge was performed. After repeating this operation three times, perform constant current and constant voltage charging (cutoff current: 0.02C current) at a charge rate of 0.2C and a charge end voltage of 0.05V, and then perform constant current and constant voltage charging (cutoff current: 0.02C current) at a charge rate of 0.2C and a discharge end voltage of 1 Constant current discharge was performed at .5V. 1C is the current value for charging or discharging the theoretical capacity of the negative electrode in 1 hour. The rate characteristic can be expressed by the ratio of 0.2C discharge capacity to 3C discharge capacity, and the following equation 2.

(Formula 2) Rate characteristic = 3C discharge capacity / 3rd 0.2C discharge capacity x 100 (%)

3: 80.0% or more 2: 65.0% or more and less than 80.0% 1: 50.0% or more and less than 65.0% 0: Less than 50.0%

<Assembling cell for evaluating lithium ion secondary battery positive electrode>
The previously prepared electrode films (Examples 15 to 18, Comparative Example 5) were punched to a diameter of 16 mm to serve as a working electrode, metal lithium foil (thickness 0.15 mm) was used as a counter electrode, and a separator (porous Polypropylene film) is inserted and laminated, and an electrolyte solution (a non-aqueous electrolyte solution in which LiPF ₆ is dissolved at a concentration of 1M in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1:1) is inserted to form a two-electrode closed system. A metal cell (HS flat cell manufactured by Hosensha) was assembled. Cell assembly was performed in a glove box purged with argon gas.

<Cycle characteristic evaluation of lithium ion secondary battery positive electrode>
The prepared lithium ion secondary battery negative electrode evaluation cell was placed in a constant temperature room at 25° C., and charging and discharging was measured using a charging and discharging device (manufactured by Hokuto Denko Co., Ltd., SM-8). After performing constant current and constant voltage charging (cutoff current: 0.02C current) at a charge rate of 0.2C and a charge end voltage of 4.2V, constant current is charged at a discharge rate of 0.2C and a discharge end voltage of 2.5V. Discharge was performed. This operation was repeated 200 times. 1C is the current value that charges or discharges the theoretical capacity of the positive electrode in 1 hour. The cycle characteristics can be expressed by the ratio of the 0.2C discharge capacity at the third time and the 0.2C discharge capacity at the 200th time, and the following equation 3.

(Formula 3) Cycle characteristics = 3rd 0.2C discharge capacity/200th 0.2C discharge capacity x 100 (%)

4: 95.0% or more 3: 90.0% or more and less than 95.0% 2: 80.0% or more and less than 90.0% 1: 60.0% or more and less than 80.0% 0: Less than 60.0%

<Evaluation of rate characteristics of lithium ion secondary battery positive electrode>
The prepared lithium ion secondary battery negative electrode evaluation cell was placed in a constant temperature room at 25° C., and charging and discharging was measured using a charging and discharging device (manufactured by Hokuto Denko Co., Ltd., SM-8). After performing constant current and constant voltage charging (cutoff current: 0.02C current) at a charge rate of 0.2C and a charge end voltage of 4.2V, constant current is charged at a discharge rate of 0.2C and a discharge end voltage of 2.5V. Discharge was performed. After repeating this operation three times, constant current and constant voltage charging (cutoff current: 0.02C current) is performed at a charge rate of 0.2C and a charge end voltage of 4.2V, and a discharge rate of 3C is performed at a discharge end voltage of 2V. Constant current discharge was performed at .5V. 1C is the current value for charging or discharging the theoretical capacity of the negative electrode in 1 hour. The rate characteristic can be expressed by the ratio of 0.2C discharge capacity to 3C discharge capacity, and the above equation 2.

3: 80.0% or more 2: 65.0% or more and less than 80.0% 1: 50.0% or more and less than 65.0% 0: Less than 50.0%

Table 4 shows the evaluation results of the electrode films and lithium ion secondary batteries produced in Examples 1 to 18 and Comparative Examples 1 to 5.

From Table 4, lithium ion secondary batteries with excellent cycle characteristics and rate characteristics were obtained in the examples as compared to the comparative examples. This is thought to be because conductive paths were formed in the electrode film by the carbon nanotubes, and the electrode structure was maintained before and after charging and discharging.

Claims (8)

An electrode for a non-aqueous electrolyte secondary battery including at least a composite material layer, the composite material layer containing a conductive additive, an active material, and a binder, the conductive additive containing carbon nanotubes, and the composite material layer comprising: An electrode for a nonaqueous electrolyte secondary battery having an elastic deformation power of 45% or more in an indentation test. The electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the composite material layer has an indentation creep of 4.0% or less. The electrode for a nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the carbon nanotubes include carbon nanotubes dispersed with a dispersant. The electrode for a non-aqueous electrolyte secondary battery according to claim 3, wherein the content of the dispersant is 10 parts by mass or more and 100 parts by mass or less based on 100 parts by mass of the carbon nanotubes. The electrode for a non-aqueous electrolyte secondary battery according to claim 3, wherein the dispersant includes a triazine derivative having an acidic functional group. The electrode for a nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the content of the carbon nanotubes is 2 parts by mass or less based on 100 parts by mass of the composite material layer. The electrode for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the active material includes a silicon-based active material. A nonaqueous electrolyte secondary battery using the electrode according to claim 1 or 2.