JP7457228B1 - Method for manufacturing composite for secondary battery electrode - Google Patents

Abstract

[Problem] To provide composite particles that can reduce the drying energy required for removing solvent during electrode production and achieve a homogeneous composite of fibrous carbon with high cohesive strength and active material, and achieve high conductivity even in the electrode. Provided is a composite for secondary battery electrodes. [Solution] A method for producing a composite for a secondary battery electrode containing an electrode active material and fibrous carbon, in which the electrode active material and a fibrous carbon dispersion in which fibrous carbon is dispersed in a solvent are mixed. 1. A method for producing a composite for a secondary battery electrode, the method comprising the steps of: compounding in slurry form using a mechanochemical mixing device; and removing a solvent and drying. [Selection diagram] Figure 1

Description

The present invention relates to a method for manufacturing a composite for secondary battery electrodes.

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, non-aqueous electrolyte secondary batteries using non-aqueous electrolytes, especially lithium ion secondary batteries, are being used in many devices due to their high energy density and high voltage characteristics.

In addition, as the uses of lithium-ion secondary batteries expand, there is a need not only to pursue battery performance such as higher capacity, faster charging, and longer life, but also to reduce battery costs and reduce the environmental impact of production. In particular, there is a growing need to reduce environmental impact by reducing CO2 emissions, and reducing energy consumption related to the production of lithium-ion secondary batteries, which accounts for much of the cost and energy consumption required to manufacture electric vehicles, has become an issue. There is.

To address the above issues, conventional electrode manufacturing methods using composite slurry require a large amount of drying energy to remove the solvent, so a method has been proposed in which electrodes are manufactured by powder molding, which does not require composite slurry. . When manufacturing electrodes by powder molding, improving productivity and making the electrode material uniform are issues, so composite particles of active materials are used, which are expected to improve the fluidity of the material and narrow the particle size distribution.
For example, in Patent Document 1, by controlling the particle size distribution etc. of composite particles produced by spraying and drying a slurry for composite particles containing an electrode active material, a water-soluble polymer, a binder resin, and a dispersion medium, A method for increasing thickness accuracy at low basis weight during powder molding is disclosed.
Further, Patent Document 2 discloses an example in which composite particles having excellent particle strength are manufactured by spraying and granulating a slurry containing a positive electrode active material, carbon black, and cellulose nanofibers.
In addition, active material composite particles are expected to be used not only in powder molding but also in conventional manufacturing processes using composite slurry. In order to increase the capacity of secondary batteries, it is essential to increase the ratio of active materials in the electrodes, so it is necessary to minimize the amount of auxiliary components. Therefore, the use of fibrous carbon, which has a small outer diameter and a large fiber length, is considered promising as a conductive agent because it can form a conductive network with a smaller amount of addition. It becomes difficult to distribute it uniformly in the electrode. Therefore, a method has been proposed that uses composite particles in which fibrous carbon is adsorbed on the surface of an active material in advance.
For example, in Patent Document 3, composite particles in which the materials are uniformly mixed are manufactured by spraying and granulating a slurry in which positive electrode active material particles and fibrous carbon are dispersed in a solvent using an ultrasonic disperser. An example is disclosed in which electrodes are formed after preparing a material slurry.
Further, Patent Document 4 discloses an example in which a positive electrode active material and carbon nanotubes are combined by mechanochemical treatment in a nitrogen atmosphere to produce a positive electrode active material having high electronic conductivity and high mechanical strength.

Patent Publication No. 6954424 Patent No. 6380526 Patent No. 5377946 JP2016-201228A

The methods disclosed in Patent Documents 1 to 3 require a spray granulation step when producing composite particles. It is possible to spray a slurry with uniformly dispersed materials and instantly dry it in a heating tank to produce homogeneous composite particles, but in order to spray it into a spray, it is necessary to reduce the viscosity of the slurry, which requires high solidification. has its limits. Therefore, a larger amount of solvent is required than that used in conventional composite material slurry, and the effect of reducing energy consumption related to electrode production is not large.
In the method disclosed in Patent Document 4, composite particles can be produced without using a solvent because they are mixed in a powder state, but it is difficult to disentangle intertwined fibrous carbon nanotubes during the composite process, and carbon The nanotubes are not uniformly adsorbed onto the surface of the active material and tend to become non-uniform composite particles, making it difficult to form a uniform conductive network in the electrode.

The present invention solves the above-mentioned problems by providing composite particles that can both reduce the drying energy required for removing solvents during electrode production and achieve a homogeneous composite of fibrous carbon with high cohesive strength and an active material. The object of the present invention is to provide a composite for secondary battery electrodes that can obtain conductivity.

The present invention is a method for producing a composite for a secondary battery electrode containing an electrode active material and fibrous carbon, in which the electrode active material and a fibrous carbon dispersion in which fibrous carbon is dispersed in a solvent are prepared in a non-slurry manner. The present invention relates to a method for producing a composite for a secondary battery electrode, which comprises a step of combining the composite material using a mechanochemical mixing device, and a step of removing the solvent and drying it.

The present invention relates to a fibrous carbon dispersion comprising fibrous carbon, a dispersant, and a solvent,
The present invention relates to a method for producing the above composite for a secondary battery electrode, wherein the dispersant comprises a copolymer containing an aliphatic hydrocarbon structural unit and a nitrile group-containing structural unit.

The present invention provides that the copolymer is
Containing a copolymer containing an aliphatic hydrocarbon structural unit, a nitrile group-containing structural unit, and an alkyl group-substituted or unsubstituted carbamoyl group-containing structural unit,
The aliphatic hydrocarbon structural unit includes an alkylene structural unit, the content of the aliphatic hydrocarbon structural unit is 40% by mass or more and less than 85% by mass based on the mass of the copolymer, and the nitrile group The content of the structural unit contained is 15% by mass or more and 50% by mass or less based on the mass of the copolymer, and the content of the alkyl group-substituted or unsubstituted carbamoyl group-containing structural unit is is 10% by mass or less based on the mass of
The total content of the aliphatic hydrocarbon structural unit, the nitrile group-containing structural unit, and the alkyl group-substituted or unsubstituted carbamoyl group-containing structural unit is 80% by mass or more based on the mass of the copolymer. can be,
The present invention relates to the method for producing the composite for a secondary battery electrode, wherein the copolymer has a weight average molecular weight of 5,000 or more and 400,000 or less.

The present invention relates to the method for producing the composite for a secondary battery electrode, wherein the copolymer further contains less than 1 mass % of a carboxyl group-containing structural unit based on the mass of the copolymer.
Regarding.

The present invention relates to the method for producing the composite for a secondary battery electrode, wherein the fibrous carbon dispersion contains a base in an amount of 1% by mass or more and 20% by mass or less based on the mass of the copolymer.

The above secondary battery, wherein the secondary battery electrode composite has an exothermic peak temperature of 520°C or less of fibrous carbon obtained by simultaneous thermogravimetric-differential thermal analysis in an oxygen atmosphere. A method for producing a composite for electrodes.

The present invention relates to the method for producing the composite for secondary battery electrodes, wherein the composite for secondary battery electrodes contains a binder resin.

The present invention relates to a method for producing an electrode film, which includes producing an electrode composite for a secondary battery according to the method described above, and forming an electrode film using the electrode composite for a secondary battery.

The present invention relates to a method for manufacturing a secondary battery, which includes producing an electrode composite for a secondary battery according to the method described above, and forming an electrode film using the electrode composite for a secondary battery.

According to the embodiments of the present invention, by finely controlling the state of dispersion of fibrous carbon on the active material, it is possible to provide a composite for a secondary battery electrode with excellent conductivity. According to still another embodiment of the present invention, it is possible to provide a high-output, long-life nonaqueous electrolyte secondary battery and an electrode film used therein.

FIG. 1 shows the infrared spectra of Copolymer 1, Dispersant 1, and Dispersant 3 in infrared spectroscopic analysis using total reflection measurement. FIG. 2 shows 13C-NMR quantitative spectra of Dispersant 1 and Dispersant 3 obtained using a nuclear magnetic resonance apparatus.

Hereinafter, a method for producing a composite for secondary battery electrodes, which is an embodiment of the present invention, will be described in detail. The present invention is not limited to the following embodiments, and includes embodiments implemented without changing the gist.

In this specification, carbon nanotubes may be referred to as "CNT". Hydrogenated nitrile rubber is sometimes written as "H-NBR", and N-methyl-2-pyrrolidone is sometimes written as "NMP". In addition, in this specification, a carbon nanotube dispersion may be simply referred to as a "CNT dispersion" or a "dispersion liquid." Further, the composite for secondary battery electrodes may be referred to as "composite for electrode" or "composite".

<Method of manufacturing a composite for secondary battery electrode>
The method for producing an electrode composite for a secondary battery of the present invention is characterized by including a step of combining an electrode active material and a fibrous carbon dispersion in which fibrous carbon is dispersed in a solvent in a non-slurry state using a mechanochemical mixer, and a step of removing the solvent and drying the resulting mixture.

In the manufacturing process of the composite for secondary battery electrodes of the present invention, inclusion of the following (1) to (3) is an important element for producing a composite with good resistance characteristics.
(1) Using a dispersion of fibrous carbon (2) Controlling the state of the mixture of the electrode active material and the dispersion in which fibrous carbon is dispersed (3) Combining with a mechanochemical mixing device The reasons for the above will be explained below. .
(1) In order for fibrous carbon to be adsorbed onto the surface of the active material in the form of disintegrated primary particles or bundle particles, it is necessary to disintegrate the fibrous carbon, which has a strong cohesive force, to the above state. Dispersion in a phase state (slurry) is essential. However, if it is combined with an active material in a slurry state, it is not possible to reduce the drying energy of the solvent involved in electrode production. Therefore, it is necessary to use a fibrous carbon dispersion in which fibrous carbon primary particles or bundle particles are uniformly dispersed and stabilized in advance.
(2) By compounding in a non-slurry form with a high solid content concentration, it is possible to make the total amount of drying energy of the solvent smaller than that required for electrode production using a conventional composite material slurry. In addition, if the mixture is in the form of a non-slurry, it will not have fluidity as a liquid, so even if the composition has less resin components than a general composite slurry, the components will separate during drying and the fibrous carbon will not be able to separate from each other. Dry aggregation can be suppressed. The non-slurry mixture preferably has a solid content concentration of 80% by mass or more.
The form of the mixture changes as follows depending on the content of the solvent. In descending order of solvent content, slurry (liquid has fluidity), clay (liquid has no fluidity, viscosity), minced (liquid has no fluidity, no viscosity), and powder (absolutely dry) becomes. In the present invention, the non-slurry state refers to a clay-like or crumbly state. These changes in form greatly affect not only the appearance but also the mixing state of the mixture. As for the form of the mixture in the composite of the present invention, mixing in a crumbly form is more preferable because dry aggregation of fibrous carbon can be suppressed during the solvent removal process.
(3) By mixing in a non-slurry form, dry aggregation can be expected to be suppressed, but since it cannot flow as a liquid, the fibrous carbon dispersion is difficult to wet and spread on the active material surface, making it uneven. easy to become Therefore, by using a mechanochemical mixing device that can apply shear force to press the dispersion of fibrous carbon onto the surface of the active material and promoting wetting and spreading, the fibrous carbon is dissolved and the fibrous carbon is applied to the surface of the active material. It can be expected to have the effect of evenly adsorbing.
By (1) to (3) above, the drying energy during electrode production is reduced, the fibrous carbon is evenly adsorbed to the surface of the active material in a loosened state, and the contained components are separated during the concentration and evaporation process of the solvent. In this way, dry aggregation of fibrous carbon and fibrous carbon hardly occurs, and a highly conductive composite and electrode can be obtained.

<Combined process using mechanochemical mixing equipment>
The mechanochemical mixing device is not particularly limited as long as it can mix a non-slurry mixture by applying shearing force.
For example, high-speed stirrers such as Henschel Mixer and Super Mixer, Hosokawa Micron's particle compounding devices "Nano Cure", "Nobilta", and "Mechano Fusion", Nara Kikai Seisakusho's powder surface modification device, "Mirror", and Primix Co., Ltd. Examples include "Hibismix" and "Hibis Depermix", mixers manufactured by Inoue Manufacturing Co., Ltd., "Planetary Mixer" and "Trimix", and mixing and granulating machines manufactured by Earth Technica, "High Speed Mixer".
Among mechanochemical mixing devices, planetary mixers, trimixes, and mechanofusions that can perform shear composite and uniform mixing of materials are preferred.

<Electrode active material>
The electrode active material is a material that causes a battery reaction necessary to extract electrical energy, and is not particularly limited.
As the positive electrode active material, for example, for secondary battery applications, metal compounds such as metal oxides and metal sulfides that are capable of reversibly doping or intercalating lithium ions can be used. For example, lithium manganese composite oxide (for example, Li _x Mn ₂ O ₄ or Li _x MnO ₂ ), lithium nickel composite oxide (for example, Li _x NiO ₂ ), lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel cobalt Composite oxide (for example, Li _x Ni _1-y Co _y O ₂ ), lithium manganese cobalt composite oxide (for example, Li _{x Mny} Co _1-y O ₂ ), lithium nickel manganese cobalt composite oxide (for example, Li _x Ni _y Co _z Mn _1-y-z O ₂ ), spinel-type lithium manganese nickel composite oxide (e.g. Li _x Mn _2-y Ni _y O ₄ ), and other composite oxide powders of lithium and transition metals, having an olivine structure. Lithium phosphorous oxide powder (e.g. Li _x FePO ₄ , Li _x Fe _{1-y Mny} PO ₄ , Li _x CoPO ₄ etc.), manganese oxide, iron oxide, copper oxide, nickel oxide, vanadium oxide (e.g. V ₂ O ₅ , V ₆ O ₁₃ ), transition metal oxide powders such as titanium oxide, transition metal sulfide powders such as iron sulfate (Fe ₂ (SO ₄ ) ₃ ), TiS ₂ and FeS, and the like. However, x, y, and z are numbers, and 0<x<1, 0<y<1, 0<z<1, and 0<y+z<1. These positive electrode active materials can also be used alone or in combination. Among these active materials, active materials containing Ni and/or Mn (especially when the total amount of Ni and/or Mn in the transition metal is 50 mol% or more) are those containing raw material-derived components or metal ions. Basicity tends to increase due to elution, which tends to cause gelation of the binder resin and deterioration of the dispersion state. Therefore, in the case of batteries containing active materials containing Ni and/or Mn, this implementation The form is particularly effective.

Examples of negative electrode active materials include metal Li, which can reversibly dope or intercalate lithium ions, or alloys thereof, tin alloys, silicon-based materials (metal Si, Si alloys, SiOx, etc.), LiXTiO2, LiXFe2O3, LiXFe3O4. , metal oxides such as LiXWO2, conductive polymers such as polyacetylene and poly-p-phenylene, artificial graphite such as highly graphitized carbon materials, carbonaceous powders such as natural graphite, and resin-sintered carbon materials. can. However, x is a number, and 0<x<1. These negative electrode active materials can also be used singly or in combination. In particular, when using silicon-based materials, although their theoretical capacity is large, their volumetric expansion is extremely large. is preferred.

<Fibrous carbon>
Fibrous carbon is a fibrous carbon material that has a high aspect ratio in the long axis direction, making it easier to form a conductive network compared to particulate carbon such as carbon black.
Examples of fibrous carbon include carbon fiber (CNF) and carbon nanotube (CNT).
CNTs are shaped like planar graphite wound into a cylindrical shape, and include single-walled CNTs, double-walled CNTs, thin-walled (several-walled) CNTs, and multi-walled CNTs, and these may be mixed. Single-walled CNTs have a structure in which one layer of graphite is wound. Multi-walled CNTs have a structure in which two or more layers of graphite are wound. Furthermore, the sidewalls of the CNTs do not have to have a graphite structure. Also, for example, CNTs with sidewalls having an amorphous structure are also CNTs in this specification.

The shape of CNT is not limited. Such shapes include a variety of shapes including needles, cylindrical tubes, fishbones or cup stacks, platelets, and coils. Among these, the shape of the CNT is preferably needle-like or cylindrical tube-like. The CNTs may have a single shape or a combination of two or more shapes.

Examples of the forms of CNT include 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 types.

The average outer diameter of the fibrous carbon is preferably 100 nm or less, more preferably 50 nm or less. If the average outer diameter is too large, it may be difficult to form a composite uniformly. Moreover, it is preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 13 nm or less. Moreover, it is preferably 1 nm or more, and more preferably 3 nm or more. The average outer diameter of fibrous carbon can be determined by observing and imaging fibrous carbon using a transmission electron microscope, selecting 300 arbitrary fibrous carbons from the observation photograph, and measuring the outer diameter of each. It can be calculated by

<Dispersant>
The dispersant for the fibrous carbon dispersion is preferably one that can stabilize the dispersion of fibrous carbon in the fibrous carbon dispersion. As the dispersant, both a resin-type dispersant and a surfactant can be used, but a resin-type dispersant is preferable because it has a strong adsorption power to fibrous carbon and good dispersion stability can be obtained. A suitable type of dispersant can be used in a suitable amount depending on the characteristics required for dispersing the fibrous carbon.

As resin-type dispersants, (meth)acrylic polymers, polymers derived from ethylenically unsaturated hydrocarbons, cellulose derivatives, copolymers thereof, etc. can be used. As polymers derived from ethylenically unsaturated hydrocarbons, polyvinyl alcohol resins, polyvinylpyrrolidone resins, polyacrylonitrile resins, nitrile rubbers, etc. can be used. As polyvinyl alcohol resins, polyvinyl alcohols modified with functional groups other than hydroxyl groups (e.g., acetyl groups, sulfo groups, carboxy groups, carbonyl groups, amino groups), polyvinyl alcohols modified with various salts, other anion-modified or cation-modified polyvinyl alcohols, polyvinyl acetals (polyvinyl acetoacetal, polyvinyl butyral, etc.) modified with acetal (acetoacetal-modified or butyral-modified, etc.) by aldehydes, etc. can be used. The polyacrylonitrile resin may be a homopolymer of polyacrylonitrile, a copolymer of polyacrylonitrile, or a modified product thereof. A polyacrylonitrile resin having at least one selected from the group consisting of active hydrogen groups such as hydroxyl groups, carboxy groups, primary amino groups, secondary amino groups, and mercapto groups, basic groups, (meth)acrylic acid alkyl esters, or alkyl groups derived from α-olefins, etc. is preferred. For example, the acrylonitrile copolymer described in JP-A-2020-163362 can be used. Examples of nitrile rubbers include acrylonitrile butadiene rubber and hydrogenated acrylonitrile butadiene rubber. Examples of cellulose derivatives include cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethyl cellulose, ethyl hydroxyethyl cellulose, nitrocellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, or copolymers thereof. In addition, the dispersants described in International Publication No. 2008/108360, JP 2018-192379 A, JP 2019-087304 A, Japanese Patent No. 6524479 A, and JP 2009-026744 A may be used, but are not limited thereto. In particular, methyl cellulose, ethyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, homopolymer of polyacrylonitrile, copolymer of polyacrylonitrile, and hydrogenated acrylonitrile butadiene rubber are preferred. Polymers in which other substituents have been introduced into a portion of these polymers, modified polymers, and the like may also be used. The weight average molecular weight of the resin-type dispersant is preferably 500,000 or less, more preferably 300,000 or less, and more preferably 3,000 or more, and more preferably 5,000 or more, from the viewpoint of the balance of affinity between the dispersed substance and the dispersion medium and the resistance to the electrolyte. Resin-type dispersants may be used alone or in combination of two or more.

Commercially available polyvinyl alcohol resins are available in various grades under trade names such as Kuraray Poval (polyvinyl alcohol resin manufactured by Kuraray), Gohsenol, and Gohsenex (polyvinyl alcohol resin manufactured by Nippon Gosei Kagaku Kogyo). . Furthermore, modified polyvinyl alcohols having various functional groups are also available. Specific examples of commercially available polyvinylpyrrolidone resins include polyvinylpyrrolidone K30, K90 (Fuji Film Wako), and K120 (DSP Gokei Food & Chemical). Commercially available nitrile rubbers include Therban (hydrogenated nitrile rubber manufactured by Aranxeo), Baymod (nitrile rubber manufactured by Aranxeo), Zetpole (hydrogenated nitrile rubber manufactured by Nippon Zeon), and NipoleNBR (nitrile rubber manufactured by Nippon Zeon). Various grades with different nitrile ratios, hydrogenation rates, molecular weights, etc. are available under trade names such as rubber. Alternatively, those synthesized by a known synthesis method may be used. A surfactant may be used instead of or in addition to the resin-type dispersant described above. Surfactants are classified into anionic, cationic, amphoteric ionic surfactants, and nonionic surfactants.

As the resin type dispersant, a polymer containing at least an aliphatic hydrocarbon structural unit and a nitrile group-containing structural unit may be used. The aliphatic hydrocarbon structural units of the polymer may include alkylene structural units. This polymer may be hydrogenated.

If a dispersant containing a copolymer containing the following aliphatic hydrocarbon structural units, nitrile group-containing units, and carbamoyl group-containing structural units is used, the agglomeration of fibrous carbon during drying of the composite can be prevented. This is preferable because it can be suppressed.
Further, the aliphatic hydrocarbon structural unit includes at least an alkylene structural unit. The content of aliphatic hydrocarbon structural units is 40% by mass or more and less than 85% by mass based on the mass of the copolymer, and the content of nitrile group-containing units is 15% by mass based on the mass of the copolymer. The content of the carbamoyl group-containing structural unit is 10% by mass or less based on the mass of the copolymer. The weight average molecular weight of the copolymer is more preferably 5,000 or more and 400,000 or less because this effectively suppresses the cohesive force of the fibrous carbon and leads to the production of a homogeneous composite.

In this specification, the copolymer may be referred to as "copolymer I". In addition, in this specification, a "substituted or unsubstituted carbamoyl group" (-CO-NR'2 (R' is each independently a hydrogen atom or a substituent)) is sometimes referred to as an "amide group." be.

The aliphatic hydrocarbon structural unit is a structural unit that contains an aliphatic hydrocarbon structure, and is preferably a structural unit that consists only of an aliphatic hydrocarbon structure. The aliphatic hydrocarbon structure contains at least a saturated aliphatic hydrocarbon structure, and may further contain an unsaturated aliphatic hydrocarbon structure. The aliphatic hydrocarbon structure preferably contains at least a linear aliphatic hydrocarbon structure, and may further contain a branched aliphatic hydrocarbon structure.

Examples of aliphatic hydrocarbon structural units include alkylene structural units, alkenylene structural units, alkyl structural units, alkantriyl structural units, alkanetetrayl structural units, and the like. The aliphatic hydrocarbon structural unit includes at least an alkylene structural unit.

The alkylene structural unit is a structural unit that contains an alkylene structure, and is preferably a structural unit that consists only of an alkylene structure. The alkylene structure is preferably a linear alkylene structure or a branched alkylene structure.

It is preferable that the alkylene structural unit includes a structural unit represented by the following general formula (1A).

General formula (1A)

In general formula (1A), n represents an integer of 1 or more. n is preferably an integer of 2 or more, more preferably an integer of 3 or more, particularly preferably an integer of 4 or more. n is preferably an integer of 6 or less, more preferably an integer of 5 or less. In particular, n is preferably 4. In this specification, "*" represents a bonding part with another structure.

It is preferable that the alkylene structural unit includes a structural unit represented by the following general formula (1B).

General formula (1B)

In general formula (1B), n represents an integer of 1 or more. n is preferably an integer of 2 or more, more preferably an integer of 3 or more. n is preferably an integer of 5 or less, more preferably an integer of 4 or less. In particular, n is preferably 3.

The alkylene structural unit preferably includes a structural unit represented by the following general formula (1C).

General formula (1C)

In general formula (1C), n represents an integer of 1 or more. n is preferably an integer of 4 or less, more preferably an integer of 3 or less, and even more preferably an integer of 2 or less. In particular, n is preferably 2.

The method of introducing the alkylene structural unit into the copolymer I is not particularly limited, and examples thereof include the following method (1a) or (1b).

In method (1a), a copolymer is prepared by a polymerization reaction using a monomer composition containing a conjugated diene monomer. The prepared copolymer contains monomer units derived from conjugated diene monomers. In the present invention, a "monomer unit derived from a conjugated diene monomer" is sometimes referred to as a "conjugated diene monomer unit", and monomer units derived from other monomers are similarly omitted. There are cases. Next, by hydrogenating the conjugated diene monomer units, at least a portion of the conjugated diene monomer units are converted into alkylene structural units. Hereinafter, "hydrogenation" may be referred to as "hydrogenation". The copolymer I finally obtained contains a hydrogenated conjugated diene monomer unit as an alkylene structural unit.

Note that the conjugated diene monomer unit includes at least a monomer unit having one carbon-carbon double bond. For example, the 1,3-butadiene monomer unit, which is a conjugated diene monomer unit, includes a monomer unit with a cis-1,4 structure, a monomer unit with a trans-1,4 structure, and a monomer unit with a 1, It contains at least one kind of monomer unit selected from the group consisting of monomer units having two structures, and may contain two or more kinds of monomer units. Further, the conjugated diene monomer unit is a monomer unit having no carbon-carbon double bond, and may further include a monomer unit containing a branch point. As used herein, "branch point" refers to a branch point in a branched polymer, and when the conjugated diene monomer unit contains a monomer unit containing a branch point, the above-prepared copolymer and copolymer I is a branched polymer.

In method (1b), a copolymer is prepared by a polymerization reaction using a monomer composition containing an α-olefin monomer. The prepared copolymer contains alpha-olefin monomer units. The copolymer I finally obtained contains α-olefin monomer units as alkylene structural units.

Among these, method (1a) is preferred because the copolymer can be easily produced. The number of carbon atoms in the conjugated diene monomer is 4 or more, preferably 4 or more and 6 or less. Examples of the conjugated diene monomer include conjugated diene compounds such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Among them, 1,3-butadiene is preferred. The alkylene structural unit preferably includes a structural unit obtained by hydrogenating a conjugated diene monomer unit (hydrogenated conjugated diene monomer unit), and preferably includes a structural unit obtained by hydrogenating a 1,3-butadiene monomer unit. It is more preferable to include a structural unit (hydrogenated 1,3-butadiene monomer unit). The conjugated diene monomers can be used alone or in combination of two or more.

The hydrogenation is preferably a method capable of selectively hydrogenating conjugated diene monomer units. Examples of the hydrogenation method include known methods such as an oil layer hydrogenation method or an aqueous layer hydrogenation method.

Hydrogenation can be carried out by conventional methods. Hydrogenation can be carried out, for example, by treating a copolymer having a conjugated diene monomer unit dissolved in an appropriate solvent with hydrogen gas in the presence of a hydrogenation catalyst. Examples of hydrogenation catalysts include nickel, palladium, platinum, copper, and the like.

In the method (1b), the α-olefin monomer has 2 or more carbon atoms, preferably 3 or more carbon atoms, and more preferably 4 or more carbon atoms. The number of carbon atoms in the α-olefin monomer is preferably 6 or less, more preferably 5 or less. Examples of the α-olefin monomer include α-olefin compounds such as ethylene, propylene, 1-butene, and 1-hexene. The α-olefin monomers can be used alone or in combination of two or more.

The alkylene structural unit preferably contains at least one type selected from the group consisting of a structural unit containing a linear alkylene structure and a structural unit containing a branched alkylene structure, and a structure consisting only of a linear alkylene structure. It is more preferable to include at least one selected from the group consisting of a structural unit consisting only of a branched alkylene structure, a structural unit represented by the above formula (1B), and a structural unit represented by the above formula (1C). It is further preferable that at least one type selected from the group consisting of the structural units shown is included.

The alkylene structural unit may include a structural unit containing a linear alkylene structure and a structural unit containing a branched alkylene structure. When the alkylene structural unit includes a structural unit containing a linear alkylene structure and a structural unit containing a branched alkylene structure, the content of the branched alkylene structure is based on the mass of the alkylene structural unit (i.e., the content of the alkylene structural unit is When the mass of the structural unit is 100% by mass), it is preferably 70% by mass or less, and more preferably 65% by mass or less. In particular, it is preferably 20% by mass or less, more preferably 18% by mass or less, and even more preferably 15% by mass or less. When copolymer I contains a structural unit containing a linear alkylene structure and a structural unit containing a branched alkylene structure, the content of the branched alkylene structure is based on the mass of the alkylene structural unit (i.e., When the mass of the alkylene structural unit is 100% by mass), it is, for example, 1% by mass or more, may be 5% by mass or more, and further may be 10% by mass or more.

In the aliphatic hydrocarbon structural unit, the content of the alkylene structural unit is based on the total mass of the aliphatic hydrocarbon structural unit (i.e., when the mass of the aliphatic hydrocarbon structural unit is 100% by mass), The content is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. The content of the alkylene structural unit is, for example, less than 100% by mass based on the total mass of the aliphatic hydrocarbon structural units (that is, when the mass of the aliphatic hydrocarbon structural units is 100% by mass). , 99.5% by mass or less, 99% by mass or less, or 98% by mass or less. The content of alkylene structural units may be 100% by mass.

The content of aliphatic hydrocarbon structural units is preferably 40% by mass or more, based on the mass of copolymer I (that is, when the mass of copolymer I is 100% by mass), and 50% by mass or more. It is more preferably at least 60% by mass, and even more preferably at least 60% by mass. The content of aliphatic hydrocarbon structural units is preferably less than 85% by mass, based on the mass of copolymer I (i.e., when the mass of copolymer I is 100% by mass), and is preferably less than 75% by mass. It is more preferably at most 70% by mass, even more preferably at most 70% by mass.

The nitrile group-containing structural unit is a structural unit containing a nitrile group, preferably a structural unit containing an alkylene structure substituted with a nitrile group, and more preferably a structural unit consisting only of an alkylene structure substituted with a nitrile group. include. The alkylene structure is preferably a linear or branched alkylene structure. The nitrile group-containing structural unit may further include a structural unit containing (or consisting only of) an alkyl structure substituted with a nitrile group. The number of nitrile groups contained in the nitrile group-containing structural unit is preferably one.

The nitrile group-containing structural unit preferably includes a structural unit represented by the following general formula (2A).

General formula (2A)

In general formula (2A), n represents an integer of 2 or more. n is preferably an integer of 6 or less, more preferably an integer of 4 or less, and still more preferably an integer of 3 or less. In particular, n is preferably 2.

The nitrile group-containing structural unit preferably contains a structural unit represented by the following general formula (2B):

General formula (2B)

In general formula (2B), R represents a hydrogen atom or a methyl group. Preferably, R is a hydrogen atom.

The method for introducing the nitrile group-containing structural unit into the copolymer I is not particularly limited, but a method for preparing a copolymer by polymerization reaction using a monomer composition containing a nitrile group-containing monomer (method (2a)) can be preferably used. The finally obtained copolymer I contains the nitrile group-containing monomer unit as a nitrile group-containing structural unit. Examples of the nitrile group-containing monomer capable of forming the nitrile group-containing structural unit include a monomer containing a polymerizable carbon-carbon double bond and a nitrile group. For example, an α,β-ethylenically unsaturated group-containing compound having a nitrile group can be mentioned, and specifically, acrylonitrile, methacrylonitrile, etc. can be mentioned. In particular, from the viewpoint of increasing the intermolecular force between the copolymers I and/or between the copolymer I and the dispersed substance (adsorbed substance), it is preferable that the nitrile group-containing monomer contains acrylonitrile. The nitrile group-containing monomer can be used alone or in combination of two or more kinds.

The content of the nitrile group-containing structural unit is preferably 15% by mass or more, based on the mass of copolymer I (that is, when the mass of copolymer I is 100% by mass), and 20% by mass. % or more, and even more preferably 30% by mass or more. The content of the nitrile group-containing structural unit is preferably 50% by mass or less, based on the mass of copolymer I (that is, when the mass of copolymer I is 100% by mass), and 46% by mass % or less, and even more preferably 40% by mass or less. By setting the content of the nitrile group-containing structural unit within the above range, adsorption to the object to be dispersed and affinity to the dispersion medium can be controlled, and the object to be dispersed can be stably present in the dispersion medium. Can be done. Furthermore, the affinity of copolymer I to the electrolyte can be controlled, and problems such as copolymer I dissolving in the electrolyte and increasing the resistance of the electrolyte in the battery can be prevented.

The amide group-containing structural unit is a structural unit containing an amide group, preferably a structural unit containing an alkylene structure substituted with an amide group, and more preferably a structural unit consisting only of an alkylene structure substituted with an amide group. include. The alkylene structure is preferably a linear or branched alkylene structure. The amide group-containing structural unit may further include a structural unit containing (or consisting only of) an alkyl structure substituted with an amide group. The number of amide groups contained in the amide group-containing structural unit is preferably one. The amide group is a substituted or unsubstituted carbamoyl group, and examples of the substituent include an alkyl group and a hydroxyalkyl group. By including the amide group-containing structural unit in the copolymer I, the adsorption power to the dispersed material can be significantly improved, and the dispersibility and robustness can be improved. In addition, since amide groups can form strong hydrogen bonds, by including amide group-containing structural units in copolymer I, even if a crosslinked structure due to hydrogen bonds is introduced into the molecules of copolymer I. good. Since the copolymer I having a crosslinked structure introduced therein can be three-dimensionally adsorbed onto the material to be dispersed, the dispersibility and robustness can be further improved.

The amide group-containing structural unit preferably includes a structural unit represented by the following general formula (3A).

General formula (3A)

In general formula (3A), n represents an integer of 2 or more. n is preferably an integer of 6 or less, more preferably an integer of 4 or less, and still more preferably an integer of 3 or less. In particular, n is preferably 2. R' each independently represents a hydrogen atom or a substituent. Preferably, the substituent is an alkyl group or a hydroxyalkyl group. Preferably, at least one R' is a hydrogen atom, and more preferably two R's are hydrogen atoms.

The amide group-containing structural unit preferably includes a structural unit represented by the following general formula (3B).

General formula (3B)

In general formula (3B), R represents a hydrogen atom or a methyl group. Preferably, R is a hydrogen atom. R' each independently represents a hydrogen atom or a substituent. Preferably, the substituent is an alkyl group or a hydroxyalkyl group. Preferably, at least one R' is a hydrogen atom, and more preferably two R's are hydrogen atoms.

The method of introducing the amide group-containing structural unit into the copolymer I is not particularly limited, and examples thereof include the following method (3a) or (3b).

In method (3a), a copolymer is prepared by a polymerization reaction using a monomer composition containing an amide group-containing monomer. The prepared copolymer contains amide group-containing monomer units. The copolymer I finally obtained contains an amide group-containing monomer unit as an amide group-containing structural unit.

In method (3b), a copolymer containing a nitrile group-containing structural unit is prepared. Next, by hydrolyzing the nitrile group contained in the nitrile group-containing structural unit in a basic atmosphere, at least a portion of the nitrile group-containing structural unit is converted into an amide group-containing structural unit. A copolymer containing a nitrile group-containing structural unit can be obtained, for example, by the method (2a) above. The copolymer I finally obtained contains, as an amide group-containing structural unit, a unit in which a nitrile group contained in the nitrile group-containing structural unit is modified by hydrolysis.

When copolymer I is prepared through method (3b), the introduction of amide groups into copolymer I is confirmed by NMR (nuclear magnetic resonance) and/or IR (infrared spectroscopy) measurements. can. In addition, it can be simply confirmed by the change in weight average molecular weight and/or viscosity (viscosity of the solution) that occurs between the copolymer before hydrolysis and Copolymer I. The weight average molecular weight of copolymer I tends to be a smaller value than the weight average molecular weight of the copolymer before hydrolysis (for example, 0.05 to 0.6 times). Furthermore, for example, the viscosity of a solution of copolymer I at a shear stress of 1,000/s tends to be a smaller value than the viscosity of a solution of the copolymer before hydrolysis at a shear stress of 1,000/s. (for example, 0.05 to 0.6 times). Regardless of the method of preparing Copolymer I, the introduction of amide groups into Copolymer I can be confirmed by NMR (nuclear magnetic resonance) and/or IR (infrared spectroscopy) measurements. can.

In the method (3a), examples of the amide group-containing monomer include (meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-isopropyl Monoalkyl (meth)acrylamides such as (meth)acrylamide; dialkyl (meth)acrylamides such as N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, etc.; N-(2-hydroxyethyl )(meth)acrylamide, N-(hydroxyalkyl)(meth)acrylamide such as N-(2-hydroxypropyl)(meth)acrylamide, N-(2-hydroxybutyl)(meth)acrylamide; diacetone(meth)acrylamide ; Examples include acryloylmorpholine. In this specification, "(meth)acrylic" represents acrylic or methacryl. In particular, the amide group-containing monomer preferably contains at least one selected from the group consisting of acrylamide, methacrylamide, and N,N-dimethylacrylamide. The amide group-containing monomers can be used alone or in combination of two or more.

In the method (3b), at least one base selected from the group consisting of inorganic bases and organic hydroxides (organic bases) can be used to create a basic atmosphere.

Inorganic bases include, for example, chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates of alkali metals or alkaline earth metals. or borates; and ammonium hydroxide. Among these, hydroxides of alkali metals or alkaline earth metals are preferred from the viewpoint of easily supplying cations. 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, magnesium hydroxide, and the like. Among these, it is more preferable to use at least one selected from the group consisting of lithium hydroxide, sodium hydroxide, and potassium hydroxide. Note that the metal included in the inorganic base may be a transition metal.

Organic hydroxides are salts containing organic cations and hydroxide ions. Examples of the organic hydroxide include trimethyl-2-hydroxyethylammonium hydroxide, tetramethylammonium hydroxide, cetyltrimethylammonium hydroxide, hexadecyltrimethylammonium hydroxide, trimethylphenylammonium hydroxide, and 3-trifluoromethyl- Examples include phenyltrimethylammonium hydroxide and benzyltrimethylammonium hydroxide. Among these, it is particularly preferable to use at least one selected from the group consisting of trimethyl-2-hydroxyethylammonium hydroxide and tetramethylammonium hydroxide.

The amount of the base used is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, based on the mass of the copolymer. The amount of the base used is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, based on the mass of the copolymer. If the amount used is too small, modification of the nitrile group by hydrolysis tends to be difficult to occur. Using too much can cause corrosion inside the dispersion device and/or battery.

In the method (3b), hydrolysis can be performed by mixing a copolymer containing an alkylene structural unit and a nitrile group-containing monomer unit, a base, and a solvent. Any other components may be mixed. There is no limitation on the order of addition of the copolymer, base, and solvent to the container and the mixing method. They may be added to the container at the same time; the copolymer, base, and solvent may be added to the container separately; or one or both of the copolymer and the base may be mixed with the solvent to prepare a copolymer-containing liquid and/or a base-containing liquid, and the copolymer-containing liquid and/or the base-containing liquid may be added to the container. In particular, since the nitrile group can be efficiently modified, a method in which a base dispersion in which a base is dispersed in a solvent is added to a copolymer solution in which the copolymer is dissolved in a solvent while stirring is preferred. A disperser (dispersing machine) or a homogenizer can be used for stirring. As the solvent, the solvents listed in the description of the dispersant composition described later can be used.

There is no limit to the temperature during mixing, but denaturation can be accelerated by heating to 30°C or higher. Additionally, a small amount of water and/or alcohol may be added to the container to promote denaturation. The water and/or alcohol may be added to the container while mixing the copolymer and base, or may be added to the container before adding the copolymer and base to the container, or the water and/or alcohol may be added to the container while mixing the copolymer and base, or the water and/or alcohol may It may be added to the container at the same time or subsequently. In addition, when the copolymer, base, and optional components used as necessary have high hygroscopicity, water may be contained as absorbed water. The amount of water and/or alcohol is preferably 0.05 to 20% by weight, more preferably 0.05 to 5% by weight, even more preferably 0.05 to 1% by weight, based on the weight of the copolymer.

Examples of the alcohol include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, benzyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, and polypropylene glycol. , butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol and the like. One kind of alcohol can be used alone or two or more kinds can be used in combination. Hydrolysis is preferably carried out in the presence of at least one selected from the group consisting of methanol, ethanol, and water, and particularly preferably in the presence of water.

The content of the amide group-containing structural unit is preferably 10% by mass or less, based on the mass of copolymer I (that is, when the mass of copolymer I is 100% by mass), and 5% by mass or less. It is more preferably 3% by mass or less, even more preferably 1% by mass or less. If the content of the amide group-containing structural unit is below the above range, the problem that the fibrous carbon dispersion gels during storage, which may occur due to the hydrogen bonds between the copolymers I becoming too strong, can be prevented. Can be done. The content of the amide group-containing structural unit is preferably 0.1% by mass or more based on the mass of copolymer I (that is, when the mass of copolymer I is 100% by mass), It is more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, and particularly preferably 0.7% by mass or more. When the content of the amide group-containing structural unit is equal to or higher than the above range, the adsorption power to the object to be dispersed can be sufficiently improved, and a good effect of improving dispersibility and robustness can be obtained.

Copolymer I may contain any structural unit. Examples of the arbitrary structural unit include a carboxyl group-containing structural unit; an alkenylene structural unit; an alkyl structural unit; a structural unit containing a branch point such as an alkantriyl structural unit and an alkanetetrayl structural unit. The structural unit containing a branch point is a structural unit different from the structural unit containing a branched alkylene structure and the structural unit containing a branched alkyl structure.

The carboxyl group-containing structural unit is a structural unit containing a carboxyl group, preferably a structural unit containing an alkylene structure substituted with a carboxyl group, and more preferably a structural unit consisting only of an alkylene structure substituted with a carboxyl group. include. The alkylene structure is preferably a linear or branched alkylene structure. The carboxyl group-containing structural unit may further include a structural unit containing (or consisting only of) an alkyl structure substituted with a carboxyl group. The number of carboxyl groups contained in the carboxyl group-containing structural unit is preferably one or two. By including a carboxyl group-containing structural unit in copolymer I, it is possible to significantly improve the adsorption power to the object to be dispersed, reduce the viscosity of the fibrous carbon dispersion, and improve the dispersion efficiency.

The carboxyl group-containing structural unit preferably includes a structural unit represented by the following general formula (4A).

General formula (4A)

In general formula (4A), n represents an integer of 2 or more. n is preferably an integer of 6 or less, more preferably an integer of 4 or less, and still more preferably an integer of 3 or less. In particular, n is preferably 2.

The carboxyl group-containing structural unit preferably includes a structural unit represented by the following general formula (4B).

General formula (4B)

In general formula (4B), R represents a hydrogen atom or a methyl group. R is preferably a hydrogen atom.

The method of introducing the carboxyl group-containing structural unit is not particularly limited, and examples thereof include the following method (4a) or (4b).

In method (4a), a copolymer is prepared by a polymerization reaction using a composition containing a carboxyl group-containing monomer. The prepared copolymer contains carboxyl group-containing monomer units. The copolymer I finally obtained contains a carboxyl group-containing monomer unit as a carboxyl group-containing structural unit.

In method (4b), a copolymer containing an amide group-containing structural unit is prepared. Next, the amide group contained in the amide group-containing structural unit is hydrolyzed in an acidic atmosphere, thereby converting the amide group-containing structural unit into a carboxyl group-containing structural unit. A copolymer containing an amide group-containing structural unit can be obtained, for example, by the method (3a) or (3b) above. The copolymer I finally obtained contains a unit obtained by modifying the amide group contained in the amide group-containing structural unit by hydrolysis, as a carboxyl group-containing structural unit.

In the method (4a), examples of the carboxyl group-containing monomer include unsaturated monocarboxylic acids such as (meth)acrylic acid, crotonic acid, and isocrotonic acid; maleic acid, fumaric acid, citraconic acid, mesaconic acid, and glutaconic acid; Examples thereof include acids, unsaturated dicarboxylic acids such as itaconic acid, and the like. In particular, the carboxyl group-containing monomer preferably contains at least one selected from the group consisting of acrylic acid and maleic acid. The carboxyl group-containing monomers can be used alone or in combination of two or more.

In the method (4b), at least one acid selected from the group consisting of inorganic acids and organic acids can be used to create an acidic atmosphere.

Examples of inorganic acids include hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, boric acid, and hydrofluoric acid. Examples of organic acids include formic acid, acetic acid, citric acid, oxalic acid, succinic acid, malic acid, benzoic acid, and benzenesulfonic acid. Among these, succinic acid and citric acid are preferred.

The amount of acid used is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, based on the mass of the copolymer. The amount of acid used is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, based on the mass of the copolymer. If the amount used is too small, modification of the amide group by hydrolysis tends to occur less easily. Using too much can cause corrosion inside the dispersion device and/or battery.

The content of the carboxyl group-containing structural unit is preferably less than 1% by mass, based on the mass of copolymer I (that is, when the mass of copolymer I is 100% by mass), and 0.5% by mass. The following is more preferable, and 0.3% by mass or less is still more preferable. If the content of carboxyl group-containing structural units is less than (or below) the above range, the fibrous carbon dispersion described below may gel during storage, which may occur due to the hydrogen bonds between copolymers I becoming too strong. This problem can be avoided. The content of the carboxyl group-containing structural unit is preferably 0.01% by mass or more based on the mass of copolymer I (that is, when the mass of copolymer I is 100% by mass), It is more preferably 0.1% by mass or more, and even more preferably 0.3% by mass or more. When the content of the carboxyl group-containing structural unit is above the above range, it is possible to sufficiently improve the adsorption power to the object to be dispersed, reduce the viscosity of the fibrous carbon dispersion, and improve the dispersion efficiency.

The alkenylene structural unit is a structural unit containing an alkenylene structure, preferably a structural unit consisting only of an alkenylene structure. The alkenylene structure is preferably a linear alkenylene structure or a branched alkenylene structure.

The alkenylene structural unit preferably contains at least one type selected from the group consisting of a structural unit containing a linear alkenylene structure and a structural unit containing a branched alkenylene structure, and a structure consisting only of a linear alkenylene structure. It is more preferable that at least one type selected from the group consisting of a structural unit consisting of only a branched alkenylene structure and a branched alkenylene structure is included.

For example, when copolymer I is obtained through the above method (1a), conjugated diene monomer units having a carbon-carbon double bond within the unit may remain within the molecule of copolymer I without being hydrogenated. The finally obtained copolymer I may contain conjugated diene monomer units having a carbon-carbon double bond within the unit as alkenylene structural units.

An alkyl structural unit is a structural unit containing an alkyl structure (however, other aliphatic hydrocarbon structural units such as a branched alkylene structural unit, a nitrile group-containing structural unit, an amide group-containing structural unit, and a carboxyl group-containing structural unit) ), and is preferably a structural unit consisting only of an alkyl structure. The alkyl structure is preferably a linear alkyl structure or a branched alkyl structure.

The alkyl structural unit preferably contains at least one type selected from the group consisting of a structural unit containing a linear alkyl structure and a structural unit containing a branched alkyl structure, and a structure consisting only of a linear alkyl structure. It is more preferable to include at least one selected from the group consisting of a structural unit consisting only of a branched alkyl structure and a branched alkyl structure.

For example, when copolymer I is obtained via the above method (1a) or (1b), it is preferable that at least a hydrogenated conjugated diene monomer unit or an α-olefin monomer unit is introduced into copolymer I as a terminal group of copolymer I. The finally obtained copolymer I may contain these monomer units as alkyl structural units.

The alkantriyl structural unit is a structural unit containing an alkantriyl structure, preferably a structural unit consisting only of an alkantriyl structure. The alkanetetryl structural unit is a structural unit containing an alkanetetryl structure, preferably a structural unit consisting only of an alkanetetryl structure.

For example, when copolymer I is obtained through the method (1a) above, copolymer I contains conjugated diene monomer units that do not have a carbon-carbon double bond within the unit. It may be introduced into the molecule as a monomer unit containing a branch point. In this case, the copolymer I finally obtained is a branched polymer and contains a conjugated diene monomer unit as an aliphatic hydrocarbon structural unit containing a branch point such as an alkantriyl structural unit or an alkanetetrayl structural unit. But that's fine. Copolymer I is a branched polymer when the aliphatic hydrocarbon structural units include structural units containing branch points. The branched polymer may be a network polymer. Copolymer I containing a structural unit containing a branch point can be three-dimensionally adsorbed onto a material to be dispersed, and therefore can further improve dispersibility and robustness.

Preferred embodiments of copolymer I include the following. - Copolymer I in which the total content of the aliphatic hydrocarbon structural units, nitrile group-containing structural units, and carbamoyl group-containing structural units contained in copolymer I is 80% by mass or more and 100% by mass or less based on the mass of copolymer I. The total content is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more. - Copolymer I in which the total content of the aliphatic hydrocarbon structural units, nitrile group-containing structural units, carbamoyl group-containing structural units, and carboxyl group-containing structural units contained in copolymer I is 80% by mass or more and 100% by mass or less based on the mass of copolymer I. The total content is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more.・Copolymer I containing a structural unit represented by general formula (1A), a structural unit represented by general formula (2A), and a structural unit represented by general formula (3A), and may contain a structural unit represented by general formula (4A) as an optional structural unit, and the total content of the structural units is 80% by mass or more and 100% by mass or less based on the mass of copolymer I. The total content is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more. ・Copolymer I containing a structural unit represented by general formula (1B), a structural unit represented by general formula (2B), and a structural unit represented by general formula (3B), and may contain a structural unit represented by general formula (4B) as an optional structural unit, and the total content of the structural units is 80% by mass or more and 100% by mass or less based on the mass of copolymer I. The total content is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more.

In this specification, the content of structural units can be determined using the amount of monomer used, NMR (nuclear magnetic resonance) and/or IR (infrared spectroscopy) measurements.

Preferred embodiments of the method for producing Copolymer I include the following.・Preparing a copolymer by a polymerization reaction using a monomer composition containing a conjugated diene monomer and a nitrile group-containing monomer (methods (1a) and (2a)), the above copolymer Hydrogenating the conjugated diene monomer unit contained in the copolymer (method of (1a)), and modifying the nitrile group-containing structural unit contained in the copolymer by hydrolysis (method of (3b)) A method for producing copolymer I, comprising: In this method, some or all of the conjugated diene monomer units are hydrogenated. Further, some (but not all) of the nitrile group-containing structural units are modified by hydrolysis so that the copolymer I contains the nitrile group-containing structural units.・Preparing a copolymer by a polymerization reaction using a monomer composition containing a conjugated diene monomer, a nitrile group-containing monomer, and an amide group-containing monomer ((1a), (2a) and method (3a)), and hydrogenating a conjugated diene monomer unit contained in the copolymer (method (1a)). In this method, some or all of the conjugated diene monomer units are hydrogenated.

In the manufacturing method of the above aspect, the monomer composition may further contain a carboxyl group-containing monomer. Alternatively, the manufacturing method of the above embodiment may further include modifying the amide group-containing structural unit by hydrolysis (method of (4b)), and in this method, some of the amide group-containing structural units (not all of them) ) is denatured by hydrolysis.

Copolymer I produced by the method (3b) can be used as a dispersant in the form of a mixture (dispersant-containing liquid) containing Copolymer I, a base, and a solvent after hydrolysis. Alternatively, Copolymer I produced by the method (3b) can be prepared by extracting and removing the base from the hydrolyzed mixture containing Copolymer I, a base, and a solvent (dispersant-containing liquid). It can be used as a dispersant in the form of a mixture (dispersant-containing liquid) containing Coalescence I and a solvent. The method for extracting and removing the base is not particularly limited, but for example, the mixture (dispersant-containing liquid) is dropped into a washing solvent that is a good solvent for the base and a poor solvent for copolymer I, and the precipitated copolymer A method for recovering the coalesce I can be mentioned. The more cleaning solvent there is, the higher the removal efficiency is. Further, the removal efficiency can also be increased by redissolving the precipitated copolymer I and repeatedly washing the copolymer I. A solvent that is a good solvent for a base and a good solvent for copolymer I and a mixture (dispersant-containing liquid) may be thoroughly mixed and then washed in the same manner.

The polymerization reaction used to prepare the copolymer is preferably an emulsion polymerization reaction, and a conventional emulsion polymerization method can be used. The polymerization agents used in emulsion polymerization, such as emulsifiers (surfactants), polymerization initiators, chelating agents, oxygen scavengers, and molecular weight regulators, can be conventionally known agents and are not particularly limited. For example, as the emulsifier, an anionic emulsifier or an anionic and nonionic emulsifier is usually used.

Examples of anionic emulsifiers include fatty acid salts such as potassium tallow fatty acid, partially hydrogenated potassium tallow fatty acid, potassium oleate, and sodium oleate; potassium rosinate, sodium rosinate, hydrogenated potassium rosinate, and hydrogenated sodium rosinate. and alkylbenzenesulfonates such as sodium dodecylbenzenesulfonate. Examples of nonionic emulsifiers include polyethylene glycol ester type emulsifiers, polypropylene glycol ester type emulsifiers, and block copolymer type emulsifiers such as ethylene oxide and propylene oxide.

Examples of the polymerization initiator include thermal decomposition type initiators such as persulfates such as potassium persulfate and ammonium persulfate; t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, octanoyl peroxide, Examples include organic peroxides such as 3,5,5-trimethylhexanoyl peroxide; azo compounds such as azobisisobutyronitrile; and redox initiators consisting of these and a reducing agent such as divalent iron ion. It will be done. Among these, redox initiators are preferred. The amount of initiator used is, for example, in the range of 0.01 to 10% by weight based on the total amount of monomers.

The emulsion polymerization reaction may be continuous or batchwise. The polymerization temperature may be low to high temperature, preferably 0 to 50°C, more preferably 0 to 35°C. Furthermore, the method of adding monomers (all-time addition, divided addition, etc.), polymerization time, polymerization conversion rate, etc. are not particularly limited. The conversion rate is preferably 85% by mass or more, more preferably 90% by mass or more.

The weight average molecular weight of Copolymer I is preferably 5,000 or more, more preferably 10,000 or more, and even more preferably 50,000 or more. The weight average molecular weight of Copolymer I is preferably 400,000 or less, more preferably 350,000 or less, and even more preferably 300,000 or less. When the weight average molecular weight of Copolymer I is 5,000 or more and 400,000 or less, adsorption to the dispersed material and affinity to the dispersion medium are improved, and the stability of the dispersion is improved. There is a tendency to The weight average molecular weight is a weight average molecular weight in terms of polystyrene, and can be measured by gel permeation chromatography (GPC). Specifically, it may be measured by the method described in Examples.

The dispersant contains at least Copolymer I. The dispersant may further contain any polymer, any copolymer, or the like. The content of copolymer I in the dispersant is preferably 50% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The content of copolymer I in the dispersant may be 100% by mass, in which case the dispersant consists only of copolymer I.

<Dispersant composition>
The dispersant composition contains a dispersant, a base of 1% by mass or more and 20% by mass or less based on the mass of copolymer I, and a solvent. That is, the dispersant composition contains Copolymer I, a base of 1% by mass or more and 20% by mass or less based on the mass of Copolymer I, and a solvent. When Copolymer I is obtained through the above-mentioned method (3b), the dispersant composition may contain the base used in the method (3b). The content of the base is 1% by mass or more, preferably 2% by mass or more, and more preferably 3% by mass or more, based on the mass of copolymer I. The content of the base is 20% by mass or less, based on the mass of Copolymer I, from the viewpoint of preventing gelation, thickening over time, and corrosion of the dispersion device and/or inside the battery, and 15% by mass. % or less, more preferably 10% by mass or less. The dispersant composition may contain optional components such as acids.

The dispersant composition contains a solvent. The solvent is preferably a solvent that can dissolve the copolymer I, and is preferably a solvent consisting of any one type of water-soluble organic solvent, or a mixed solvent consisting of two or more types of water-soluble organic solvents. preferable.

Examples of water-soluble organic solvents include amide-based solvents (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N- diethylacetamide, N-methylcaprolactam, etc.), heterocyclics (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.), tetrahydrofuran, urea, acetonitrile, etc. can be used. The water-soluble organic solvent preferably contains an amide organic solvent, and more preferably contains at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone.

The content of copolymer I in the dispersant composition is such that the concentration of the conductive material and/or electrode active material in the fibrous carbon dispersion, binder resin-containing fibrous carbon dispersion, and electrode film slurry is set to a sufficient level. From the viewpoint of this, the content is preferably 2% by mass or more, more preferably 5% by mass or more, based on the mass of the dispersant composition. When the concentration of the conductive material and/or the electrode active material is sufficient, good coating properties can be obtained, and an increase in manufacturing costs due to increases in drying time and transportation costs can be prevented. The content of copolymer I is preferably 15% by mass or less, more preferably 10% by mass or less, based on the mass of the dispersant composition, from the viewpoint of preventing the generation of insoluble matter.

A mixture containing copolymer I, a base, and a solvent (dispersant-containing liquid) obtained through the method (3b) described above may be used as the dispersant composition. Alternatively, a mixture containing copolymer I, a base, an acid, and a solvent (dispersant-containing liquid) obtained through the above-mentioned methods (3b) and (4b) may be used as the dispersant composition. .

<Solvent>
The solvent (dispersion medium) for the fibrous carbon dispersion is not particularly limited, but is preferably a high dielectric constant solvent, and a solvent consisting of any one type of high dielectric constant solvent, or a mixed solvent consisting of two or more types. It is preferable to include. Further, the high dielectric constant solvent may be used alone or in combination with two or more other solvents.

High dielectric constant solvents that can be used include amides (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.), heterocyclics (cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, etc.), sulfoxides (dimethyl sulfoxide, etc.), sulfones (hexamethylphosphorotriamide, sulfolane, etc.), lower ketones (acetone, methyl ethyl ketone, etc.), carbonates (diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, propylene carbonate, ethylene carbonate), water, and others such as tetrahydrofuran, urea, and acetonitrile. The dispersion medium preferably contains an amide-based organic solvent or water, and more preferably contains at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone. The relative dielectric constant of the high dielectric constant solvent can be a value listed in the Solvent Handbook, etc., and is preferably 2.5 or more at 20°C.

<Fibrous carbon dispersion>
The fibrous carbon dispersion contains fibrous carbon and a solvent (dispersion medium), and optionally a dispersant. The fibrous carbon dispersion may contain optional ingredients such as wetting agents, surfactants, pH adjusters, wetting agents, leveling agents, other additives, other conductive materials, and other polymer components, as necessary. may be included as appropriate within a range that does not impede the purpose of the present invention. The optional components can be added at any timing, such as before preparing the dispersion, during dispersion, after dispersion, or a combination thereof.

The dispersibility of the fibrous carbon in the fibrous carbon dispersion can also be evaluated by the median diameter (μm) determined using a laser diffraction/scattering type particle size distribution analyzer. From the median diameter (μm) determined using a laser diffraction/scattering type particle size distribution meter, the particle diameter of the fibrous carbon aggregate particles can be estimated based on the intensity distribution of scattered light by the particles. The median diameter (μm) is preferably 0.4 μm or more, more preferably 5.0 μm or less, and more preferably 2.0 μm or less. By setting it as the said range, the fibrous carbon dispersion of an appropriate dispersion state can be obtained. If it is less than the above range, fibrous carbon in an agglomerated state will exist, and if it exceeds the above range, a large number of finely cut fibrous carbon will be produced, making it difficult to form an efficient conductive network. The median diameter can be measured by the method described in Examples.

The viscosity of the fibrous carbon dispersion is preferably 10 mPa-s or more and less than 10,000 mPa-s, and preferably 10 mPa-s or more and less than 2,000 mPa-s, as measured at 60 rpm at 25° C. using a B-type viscometer. is more preferable, and even more preferably 10 mPa·s or more and less than 1000 mPa·s.

The TI value of the fibrous carbon dispersion can be calculated by dividing the viscosity (mPa·s) at 6 rpm measured at 25°C with a Brookfield viscometer by the viscosity (mPa·s) at 60 rpm. The TI value is preferably 1.0 or more and less than 10.0, more preferably 1.0 or more and less than 5.0, and even more preferably 1.0 or more and less than 3.0. The higher the TI value, the greater the structural viscosity due to the entanglement of the fibrous carbon, dispersant, and other resin components, or their intermolecular forces, and the lower the TI value, the smaller the structural viscosity. By setting the TI value within the above range, it is possible to suppress the entanglement of the fibrous carbon, dispersant, and other resin components while allowing these intermolecular forces to act appropriately.

The average fiber length of the fibrous carbon in the fibrous carbon dispersion is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more. Moreover, it is preferably 20 μm or less, more preferably 10 μm or less. The average fiber length of the fibrous carbon in the fibrous carbon dispersion was determined by scanning a sample obtained by diluting the fibrous carbon dispersion 50 times with a non-aqueous solvent such as NMP and dropping it onto a base material and drying it. It can be calculated by observing with an electron microscope, selecting any 300 fibrous carbons in the observation photograph, and measuring the fiber length of each.

The content of fibrous carbon is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and 0.8% by mass or more based on the total amount of the fibrous carbon dispersion. It is more preferable that there be. Moreover, it is preferably 20% by mass or less, and more preferably 10% by mass or less. By setting it within the above range, fibrous carbon can be satisfactorily and stably present without causing sedimentation or gelation. It is more preferably 0.1 to 20% by mass, and even more preferably 0.5 to 10% by mass. In addition, the content of fibrous carbon is determined depending on the specific surface area of fibrous carbon, affinity for dispersion medium, dispersion ability of dispersant, etc., so that a fibrous carbon dispersion with appropriate fluidity or viscosity can be obtained. It is preferable to adjust it appropriately.

The content of the dispersant is preferably 5 to 200 parts by mass, more preferably 10 to 100 parts by mass, and even more preferably 15 to 80 parts by mass, per 100 parts by mass of fibrous carbon. The content of the dispersant is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, per the total amount of the fibrous carbon dispersion.

The solid content of the fibrous carbon dispersion is preferably 0.2 to 40% by mass, more preferably 0.5 to 20% by mass, and even more preferably 1 to 10% by mass.

The fibrous carbon dispersion may be prepared by separately preparing two or more types of fibrous carbon with different average outer diameters and adding them to a dispersion medium. When two or more types of fibrous carbon with different average outer diameters are used as the fibrous carbon, the average outer diameter of the first fibrous carbon is preferably 1 nm or more and less than 5 nm. The average outer diameter of the second fibrous carbon is preferably 5 nm or more and 30 nm or less, and more preferably 20 nm or less. When two or more types of fibrous carbon with different average outer diameters are used as the fibrous carbon, the mass ratio of the first fibrous carbon to the second fibrous carbon is preferably 1:10 to 1:100, and more preferably 1:10 to 1:50.

The average fiber length of the fibrous carbon is preferably 0.5 μm or more, more preferably 0.8 μm or more, and even more preferably 1.0 μm or more. Moreover, it is preferably 20 μm or less, more preferably 10 μm or less. The average fiber length of fibrous carbon is determined by first observing and imaging fibrous carbon using a scanning electron microscope, selecting 300 arbitrary fibrous carbons from the observation photograph, and measuring the fiber length of each. It can be calculated by

The aspect ratio is the fiber length of fibrous carbon divided by the outer diameter. A representative aspect ratio can be calculated using the average fiber length and the average outer diameter. A conductive material with a higher aspect ratio can provide higher conductivity when formed into an electrode. The aspect ratio of fibrous carbon is preferably 30 or more, more preferably 50 or more, and even more preferably 80 or more. It is also preferably 10,000 or less, more preferably 3,000 or less, and even more preferably 1,000 or less.

The specific surface area of the fibrous carbon is preferably 100 m ² /g or more, more preferably 150 m ² /g or more, and even more preferably 200 m ² /g or more. Moreover, it is preferable that it is 1200 m ^<2> /g or less, and it is more preferable that it is 1000 m ^<2> /g or less. The specific surface area of fibrous carbon is calculated by the BET method using nitrogen adsorption measurement. When the average outer diameter, average fiber length, aspect ratio, and specific surface area of the fibrous carbon are within the above ranges, it becomes easier to form a developed conductive path in the electrode.

The carbon purity of fibrous carbon is expressed by the content (% by mass) of carbon atoms in the fibrous carbon. The carbon purity is preferably 80% by mass or more based on 100% by mass of fibrous carbon.

In order to remove or reduce impurities such as metal catalysts and increase carbon purity, fibrous carbon that has been subjected to a purification treatment may be used.

When fibrous carbon is dispersed in a disperser that uses collisions with media such as a bead mill, or when the carbon is repeatedly passed through a disperser over a long period of time, the fibrous carbon may break and produce short-flaked carbonaceous matter. When short-flaked carbonaceous matter is produced, the viscosity of the fibrous carbon dispersion decreases, and the gloss of the coating film obtained by applying and drying the fibrous carbon dispersion increases. Judging from these evaluation results alone, however, the short-flaked carbonaceous matter has high contact resistance and is difficult to form a conductive network, which may worsen the resistance of the electrode. The degree to which short-flaked carbonaceous matter is produced can be confirmed by diluting the dispersion liquid, dropping it onto a substrate with a smooth surface and good affinity with the dispersion medium, and drying the sample, and observing it with a scanning electron microscope. By adjusting the dispersion conditions and the composition of the dispersion liquid so that carbonaceous matter of 0.1 μm or less is not produced, a highly conductive electrode can be obtained.

The fibrous carbon may be produced by any method. Fibrous carbon 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, fibrous carbon 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. The carbon source may be at least one of hydrocarbons and alcohols.

<Drying process>
The method for removing the solvent and drying is not particularly limited as long as it can remove the solvent from the non-slurry mixture, and examples of the method include drying methods such as hot air drying, vacuum drying, freeze drying, etc. Among these, hot air drying and vacuum drying are preferred from the viewpoint of productivity.

<Composite for secondary battery electrodes>
The secondary battery electrode composite contains an electrode active material and fibrous carbon, and may further optionally contain a binder resin. The electrode composite may further contain optional components.

The fibrous carbon contained in the electrode composite of the present invention has at least a partially crushed form and is attached to the surface of the active material.

The presence of the fibrous carbon in a crushed form on the surface of the active material can efficiently supply electrons required for the battery reaction to the active material, and can also contribute to reducing the contact resistance between active materials when an electrode is fabricated.
Therefore, when the fibrous carbon is crushed and uniformly adsorbed on the surface of the active material, and a certain number of aggregates of fibrous carbon are included, when the electrode is used for a secondary battery, the electrode resistance is reduced and the formation of an electronic conduction path to the active material during the battery reaction is favored, thereby improving the battery rate characteristics and cycle characteristics. In addition, since an efficient conductive path can be formed with a small amount of conductive additive, the amount of conductive additive in the electrode can be reduced, and the battery capacity can be improved.

The form in which fibrous carbon is crushed refers to a form in which secondary particles (agglomerates) of fibrous carbon are interpreted as primary particles or bundles of a plurality of primary particles. The state in which fibrous carbon is crushed and adsorbed on the surface of the active material includes a state in which primary particles and/or bundles are isolated, and a state in which primary particles and/or bundles overlap. From the viewpoint of electron supply to the active material and conductive paths between the composites, it is preferable that the primary particles and/or bundles overlap and are adsorbed in a network shape.

In the present invention, the state in which fibrous carbon is adsorbed on the active material surface in a crushed form means that the area occupied by the fibrous carbon adsorbed on the active material in the crushed state is the surface area of the active material. It refers to 10% or more of the total, preferably 20% or more, and more preferably 50% or more.

The area occupied by the fibrous carbon adsorbed to the active material when the fibers are crushed is determined by the magnification obtained by scanning electron microscopy (SEM) or scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX). It can be measured from the contrast difference between the active material and fibrous carbon from an image observed at a magnification of 5,000 to 50,000 times, and the average value of the area calculated from 20 active materials in the composite was used.

When the combustion temperature of the fibrous carbon in the electrode composite of the present invention is 520°C or lower in an oxygen-containing atmosphere, the fibrous carbon adsorbed on the active material surface becomes loose and uniform.

The temperature of the exothermic peak of the present invention can be determined by TG-DTA (ThermoGravimetry-Differential Thermal Analysis) measurement. Specifically, a TG curve and a DTA curve are obtained by performing TG-DTA measurements under air or oxygen flow conditions. In the obtained DTA curve, the top of the maximum exothermic peak derived from the combustion of fibrous carbon in the vicinity of 300 to 700° C. was read and determined as the temperature of the exothermic peak of fibrous carbon. This represents the combustion temperature of fibrous carbon.
Fibrous carbon generally has thick bundles in which primary particles are strongly aggregated due to van der Waals forces, and large secondary aggregates in which bundles aggregate together. Various physical properties such as thermal stability differ depending on these agglomeration states. Therefore, even if the fibrous carbon is of the same type, the combustion temperature changes depending on the state of aggregation, and the stronger the aggregation, the higher the combustion temperature.

When the combustion temperature of fibrous carbon in an oxygen-containing atmosphere of a secondary battery electrode composite is 520°C or lower, the fibrous carbon on the active material is adsorbed in a more loosened state, and the fibrous carbon is separated from the active material. Formation of an electron conduction path to the active material is advantageous and battery characteristics are improved, which is preferable. The temperature is preferably 480°C or lower, more preferably 450°C or lower.

Since the volume resistivity of the secondary battery electrode composite under a load of 20 kN is 500 Ω・cm or less, the fibrous carbon in the composite does not become unevenly distributed and is adsorbed onto the active material in a more uniform state. Therefore, the electrode resistance can be lowered when used as an electrode for secondary electricity. It is preferably 100 Ω·cm or less, more preferably 50 Ω·cm or less.

The volume resistivity of the electrode composite for secondary batteries can be determined by performing resistivity measurements based on the four-terminal four-probe method. Specifically, four needle-shaped probes (electrodes) are brought into contact with the secondary battery electrode composite to be measured, and the resistance of the test piece is determined from the current passed between the two outer probes and the potential difference generated between the two inner probes. The volume resistivity of the CNTs can then be calculated from the measured resistance and the thickness of the test piece. The measurement is performed using a volume resistivity measuring device (for example, the low-resistance version of the automatic powder resistivity measuring system MCP-PD600 manufactured by Nitto Seiko Analytech Co., Ltd.) under a load of 20 kN.

The electrode composite for a secondary battery is preferably in the form of particles, and the average particle diameter is preferably 0.5 μm or more and 500 μm or less. More preferably, the thickness is 1 μm or more and 200 μm or less.

As mentioned above, when the combustion temperature is 520°C or less and the volume resistivity is 100Ω・cm or less, the fibrous carbon is crushed in the composite and adsorbed finely and uniformly on the active material. When used as an electrode for a next battery, it is preferable because it lowers the electrode resistance and is advantageous in forming an electron conduction path to the active material during battery reaction, improving battery rate characteristics and cycle characteristics. In addition, since an efficient conductive path can be formed with a small amount of conductive aid, the amount of conductive aid in the electrode can be reduced and battery capacity can be improved.

The content of fibrous carbon in the composite is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, based on the mass of the composite for secondary battery electrodes, More preferably, it is 0.05% or more. Further, it is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. If it exceeds the above range, the amount of active material filled in the electrode will decrease, leading to a decrease in battery capacity. In particular, it is preferably 10% by mass or less for high capacity batteries. Also, if it is below the above range, the conductivity of the electrode and battery may become insufficient.

The composite may contain a conductive material other than fibrous carbon. Examples of other conductive materials include carbon materials such as carbon black, fullerene, graphene, multilayer graphene, and graphite. Carbon black may be neutral, acidic, or basic, and oxidation-treated carbon black or graphitized carbon black may be used. Other conductive materials may be used alone or in combination of two or more.

<Binder resin>
The composite of the present invention may contain a binder resin if necessary. The binder resin is not particularly limited as long as it is normally used as a binder resin, and can be appropriately selected depending on the purpose. The binder resin used in the composite is preferably a resin that can bind substances such as active materials and fibrous carbon. The binder resin used in the composite is, for example, a polymer or copolymer containing ethylene, propylene, vinyl chloride, vinyl acetate, maleic acid, acrylic acid, acrylic ester, methacrylic acid, methacrylic ester, styrene, etc. as a structural unit. ; Polyurethane resin, polyester resin, phenolic resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, acrylic resin, formaldehyde resin, silicone resin, fluororesin; Cellulose resin such as carboxymethyl cellulose; styrene-butadiene Examples include elastomers such as rubber and fluororubber; conductive resins such as polyaniline and polyacetylene. Also, modified products, mixtures, and copolymers of these resins may be used. Particularly preferred are fluororesins, such as polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), and modified products thereof. These may be used alone or in combination of two or more. Among these, polymers or copolymers having fluorine atoms in the molecule, such as polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene, etc., resins having these structural units, modified products of these, etc. are recommended from the viewpoint of resistance. preferable.

The content of the binder resin in the composite is preferably 0.1% by mass or more, and preferably 0.3% by mass or more, based on the mass of the active material (assuming the mass of the active material as 100% by mass). It is more preferable. Moreover, it is preferably 20% by mass or less, and more preferably 10% by mass or less.

<Electrodes for secondary batteries>
The secondary battery electrode of the present invention includes a composite for a secondary battery electrode. The electrode may further include optional components such as a binder and a dispersant. In general, the electrode is formed by powder compression molding or by applying a composite slurry onto a current collector and removing volatiles.

The material and shape of the current collector 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. The thickness of the current collector is preferably about 0.5 to 30 μm.

<Method for manufacturing secondary battery electrodes>
Secondary battery electrodes are made by adding a binder etc. to a composite for secondary battery electrodes and press-forming each component into a sheet under dry conditions without using a solvent, or by preparing a composite material slurry and assembling it. It can be formed by coating on an electric body and removing volatile components.
A powder pressure molding method without using a composite material slurry is preferable because energy consumption related to drying the solvent can be reduced.

There are no particular restrictions on the method for press-molding the powder, and any known method can be used.
In addition, when producing an electrode by powder pressure molding without using a composite material slurry, a dry mixture obtained by mixing the electrode composite and a binder in advance, or a dried product after wet mixing may be used.
The method of adding a binder and the like to the secondary battery electrode composite and dry or wet mixing the components is not particularly limited, and various dispersing machines, mixing devices, granulating devices, etc. can be appropriately selected.

When forming an electrode by adding a binder, etc. to a composite for secondary battery electrodes by powder pressure molding and forming each component into a sheet by pressing, etc., each component is prepared by adding a binder, etc. to the composite for secondary battery electrodes. Alternatively, the dry mixture or wet mixture may be directly supplied to the current collector and pressure molded, or each component obtained by adding a binder etc. to the composite for secondary battery electrodes, or the dry mixture or wet mixture may be A self-supporting film made of the dried mixture may be prepared in advance and then laminated on the current collector. Alternatively, the current collector may be prepared using a resin thin film that is a binder component formed in advance on the current collector.

Examples of the powder pressure molding method include a lithographic press and a calendar roll. Among them, it is preferable to use a calender roll because of its productivity and uniform molding.

The method for producing an electrode using the composite slurry is not particularly limited, and any known method can be used. Specific examples include die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, and electrostatic painting. Methods for drying after coating include, but are not limited to, leaving to dry, air blowing dryers, hot air dryers, infrared heaters, and far-infrared heaters.

After coating the composite material slurry, rolling treatment may be performed using a lithographic press, a calendar roll, or the like. The thickness of the electrode film is, for example, 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

<Secondary battery>
The secondary battery includes a positive electrode, a negative electrode, and an electrolyte, and includes an electrode film in which at least one selected from the group consisting of a positive electrode and a negative electrode is made from the composite of the present invention.

As the positive electrode, one in which an electrode film containing a positive electrode active material is formed on a current collector can be used. As the negative electrode, one in which an electrode film containing a negative electrode active material on a current collector is prepared can be used.

The electrolyte may be a liquid electrolyte, a gel electrolyte, or a solid electrolyte. For example, the liquid electrolyte may include an electrolyte salt such as a lithium salt and a non-aqueous solvent. As the electrolyte salt, various conventionally known electrolyte salts 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). It is preferable that the electrolyte salt be dissolved in a non-aqueous solvent and used as an electrolyte.

Examples of non-aqueous solvents include, but are not limited to, carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl 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 1,2 - Glymes such as 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 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 nonwoven fabrics obtained by subjecting these to hydrophilic treatment.

The structure of the secondary battery is not particularly limited, but it usually includes a positive electrode, a negative electrode, and a separator provided as necessary, and can be of various types depending on the purpose of use, such as paper type, cylindrical type, button type, and laminated type. It can be any shape.

Since the composite for secondary battery electrodes of the present invention is an ideal combination of active material and fibrous carbon, it is suitable not only for electrodes made from composite slurry but also for electrodes made by solid or semi-solid processes. It can be used for. Electrodes produced using these solid-state processes can be applied not only to lithium-ion secondary batteries using conventional electrolytes, but also to all-solid-state batteries, semi-solid-state batteries, and the like.

The secondary battery of the present invention can be suitably used as a battery for vehicles such as automobiles, and portable electronic devices such as personal computers and smartphones.

The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples, provided that the gist of the invention is not exceeded. Unless otherwise specified, "parts" refers to "parts by mass" and "%" refers to "% by mass." In addition, in the examples, a "dispersant-containing liquid" that contains a "dispersant" and a solvent may be referred to as a "dispersant solution."

<Preparation of sample for weight average molecular weight (Mw) measurement>
The copolymer was separated and collected from a dispersant-containing liquid (dispersant composition) containing the copolymer, a base, and a solvent using the method described below, and was used as a measurement sample. The dispersant-containing liquid was dropped into purified water to precipitate the copolymer, and the precipitate was collected by filtration with a Buchner funnel. The precipitate was rinsed as it was on a Buchner funnel by sprinkling purified water, and then dissolved in tetrahydrofuran (THF) to obtain a solution. The obtained solution was dropped again into purified water to perform the above-mentioned filtration and washing steps using purified water, and the precipitate was redissolved in THF to prepare a measurement sample. In addition, from the fibrous carbon dispersion containing the copolymer, base, solvent, and conductive material, the conductive material was separated by centrifugation, and the separated supernatant was subjected to the same process as above to prepare a measurement sample. .

<Measurement of weight average molecular weight (Mw)>
The weight average molecular weight (Mw) of the copolymer was measured by gel permeation chromatography (GPC) equipped with an RI detector. HLC-8320GPC (manufactured by Tosoh Corporation) was used as the device, three separation columns were connected in series, and the packing materials were "TSK-GELSUPERAW-4000", "AW-3000", and "AW-" manufactured by Tosoh Corporation in order. 2500", an oven temperature of 40° C., an N,N-dimethylformamide solution of 30 mM triethylamine and 10 mM LiBr as an eluent, and a flow rate of 0.6 mL/min. The concentration of the measurement sample was adjusted to 1% using a solvent consisting of the eluent, and 20 microliters of the sample was injected. The weight average molecular weight is a polystyrene equivalent value.

<Measurement of viscosity of copolymer solution and dispersant-containing liquid>
The copolymer was dissolved to form an 8% solution using NMP as a solvent, and the resulting solution was used as a sample for viscosity measurement. The dispersant-containing liquid (dispersant composition) was diluted with NMP to become an 8% solution to prepare a sample for viscosity measurement. The sample for viscosity measurement was set on a sample stage, and the shear stress was increased from 1/s to 1,000/s using a rheometer (RheoStress 1 rotary rheometer manufactured by ThermoFisher Scientific Co., Ltd.) at 25°C with a 60 mm diameter and 2° cone. The viscosity was measured continuously up to s.

<Infrared spectroscopic analysis using total reflection measurement method>
The solid copolymer was used as it was for measurements. The dispersant-containing liquid (dispersant composition) was treated with hot air at 100° C. for 10 hours to sufficiently dry it, and the obtained solid copolymer was used as a measurement sample. The measurement sample was subjected to IR measurement using an infrared spectrophotometer (Nicoleti S5FT-IR spectrometer manufactured by ThermoFisher Scientific Co., Ltd.).

<Measurement of hydrogenation rate of copolymer>
The hydrogenation rate was determined by performing IR measurement using the same method as the infrared spectroscopic analysis using the total reflection measurement method described above. The double bond derived from the conjugated diene monomer unit has a peak at 970 cm-1, and the hydrogenated single bond has a peak at 723 cm-1, so hydrogenation is determined from the ratio of the heights of these two peaks. calculated the rate.

<Measurement of content of amide group-containing structural unit>
When the amide group-containing structural unit is introduced into the copolymer through a method of hydrolyzing the nitrile group-containing structural unit, the content of the amide group-containing structural unit can be determined using a nuclear magnetic resonance apparatus (ADVANCE 400 Nanobay: manufactured by Bruker Japan Co., Ltd., measurement solvent). From the 13C-NMR quantitative spectrum obtained using CDCl3 (using a 10 mm NMR tube), the modification rate (molar ratio) of the nitrile group was calculated using the formula [A]/([A] + [B]), and the composition ratio ( It was calculated by converting it into mass %). "Amount of amide groups" in the table below means "content of amide group-containing structural units (% by mass)."
[A]: Peak area with chemical shift value of 180.5 to 183.5 ppm
[B]: Peak area with chemical shift value of 121.5 to 123.0 ppm However, since 13C-NMR measurement has low quantitative sensitivity, it cannot be detected unless the content of the amide group-containing structural unit is 1% or more. Therefore, for copolymers for which peaks at about 1570 cm-1 and about 1650 cm-1 derived from amide groups could be detected in IR measurement using the same method as the infrared spectroscopic analysis using the total reflection measurement method described above, The content of the amide group-containing structural unit was determined to be less than 1%. In addition, since a peak could be detected in the same IR measurement as described above, it was determined that the content of the amide group-containing structural unit was 0.3% or more. Furthermore, when the amide group-containing structural unit is introduced through a method of preparing a copolymer using a monomer composition containing an amide group-containing monomer, the content of the amide group-containing structural unit is also less than 1%. In the case of , it was determined to be less than 1% because it could not be quantified. If the content of amide group-containing structural units is 1% or more, the ratio of nitrile group-containing structural units to amide group-containing structural units is confirmed by 13C-NMR quantitative spectrum, and if the content of amide group-containing structural units is 1% or more, synthesis It was confirmed that the content was consistent with the content calculated from the amount of monomer charged at the time.

<Measurement of content of carboxyl group-containing structural unit>
The content of carboxyl group-containing structural units can generally be determined from a 13C-NMR quantitative spectrum using a nuclear magnetic resonance apparatus in the same way as measuring the content of amide group-containing structural units, but the content of carboxyl group-containing structural units If it is less than 1%, it is difficult to quantify. Therefore, in IR measurement using the same method as the infrared spectroscopic analysis using the total reflection measurement method described above, a peak at about 1710 cm-1 derived from the C=O stretching vibration was detected, and a peak at about 1570 cm-1 derived from the amide group was detected. It was determined that a portion of the amide group had been hydrolyzed and a carboxyl group had been introduced into the copolymer, and that the copolymer contained a carboxyl group-containing structural unit. Note that since a peak could be detected in the same IR measurement as described above, it was determined that the content of carboxyl group-containing structural units was 0.3% or more.

<Measurement of moisture in mixture>
The moisture content of the mixture was measured using a Karl Fischer moisture meter (desktop coulometric moisture meter Model CA-200, manufactured by Mitsubishi Chemical Analytech Corporation) by treating the sample at 230°C under a flow of nitrogen gas of 250 ml/min. The value measured by the Fisher method was calculated as the content based on the total mass of the copolymer, base, and solvent.

<Measurement of initial viscosity of fibrous carbon dispersion>
The viscosity value was measured using a B-type viscometer (“BL” manufactured by Toki Sangyo Co., Ltd.) at a temperature of 25°C, after thoroughly stirring the fibrous carbon dispersion with a spatula. , was carried out immediately at a B-type viscometer rotor rotation speed of 60 rpm. The rotor used in the measurement was No. 1 when the viscosity value was less than 100 mPa·s. 1, and if it is 100 or more and less than 500 mPa・s, No. 2, and if it is 500 or more and less than 2,000 mPa・s, No. 3, and if it is 2,000 or more and less than 10,000 mPa・s, No. 4 rotors were used. The lower the viscosity, the better the dispersibility, and the higher the viscosity, the worse the dispersibility. If the obtained fibrous carbon dispersion clearly separated or sedimented, it was judged as having poor dispersibility. Judgment criteria ◎: Less than 500 mPa・s (excellent)
○: 500 mPa・s or more and less than 2,000 mPa・s (good)
△: 2,000 mPa・s or more and less than 10,000 mPa・s (acceptable)
×: 10,000 mPa・s or more, sedimentation or separation (defective)

<Preparation of copolymer 1>
In a stainless steel polymerization reactor, 30 parts of acrylonitrile, 70 parts of 1,3-butadiene, 3 parts of potassium oleate, 0.3 parts of azobisisobutyronitrile, 0.6 parts of t-dodecylmercaptan, and ion exchange. 200 parts of water was added. Polymerization was carried out at 45° C. for 20 hours under a nitrogen atmosphere with stirring, and the polymerization was completed at a conversion rate of 90%. Unreacted monomers were removed by vacuum stripping to obtain an acrylonitrile-conjugated diene rubber latex with a solid content concentration of about 30%. Next, ion-exchanged water was added to the latex to adjust the total solids concentration to 12%, and the latex was placed in a 1L autoclave equipped with a stirrer, and nitrogen gas was passed through it for 10 minutes to remove dissolved oxygen in the contents. Removed. A catalyst solution prepared by dissolving 75 mg of palladium acetate as a hydrogenation catalyst in 180 mL of ion-exchanged water to which 4 times the mole of nitric acid was added to palladium was added to the autoclave. After replacing the inside of the autoclave with hydrogen gas twice, the contents of the autoclave were heated to 50° C. while pressurized with hydrogen gas to 3 MPa, and a hydrogenation reaction was performed for 6 hours. Thereafter, the contents were returned to room temperature, the inside of the autoclave was made into a nitrogen atmosphere, and the solid content was dried to recover Copolymer 1. The hydrogenation rate of Copolymer 1 was 99.5%, and the weight average molecular weight (Mw) was 200,000. In the acrylonitrile-conjugated diene rubber, the content of conjugated diene monomer units is 70%, and the content of nitrile group-containing monomer units is 30%, based on the mass of the acrylonitrile-conjugated diene rubber. Ta. Furthermore, in copolymer 1, the content of aliphatic hydrocarbon structural units containing alkylene structural units is 70%, and the content of nitrile group-containing monomer units is 30%, based on the mass of copolymer 1. %Met. The content of these monomer units and the content of structural units were determined from the amount of monomer used (the same applies hereinafter).

<Synthesis Example 1 Preparation of Dispersant 1>
16 parts of NaOH and 84 parts of NMP were placed in a stainless steel container 1 and stirred for 1 hour using a homogenizer to prepare a NaOH suspension. 9 parts of Copolymer 1 obtained in Synthesis Example 1 and 91 parts of NMP were placed in a stainless steel container 2, and stirred for 1 hour using a homogenizer to prepare a solution of Copolymer 1. Next, a suspension of NaOH and a solution of copolymer 1 were placed in a stainless steel container 3 so that the compositions of NaOH and copolymer 1 were as shown in Table 1, and NMP was further added to adjust the concentration. , a mixture was obtained. The moisture content of the mixture was 0.1%. The mixture was stirred with a homogenizer for 2 hours to modify some of the nitrile groups of Copolymer 1 into amide groups, and the copolymer as Dispersant 1 (in the Examples, the modified Copolymer I was referred to as "Dispersant"). A dispersant 1-containing liquid (dispersant composition) containing NMP and NaOH was obtained. The content of the amide group-containing structural unit and the weight average molecular weight (Mw) of Dispersant 1 were as shown in Table 1. In dispersant 1, the content of aliphatic hydrocarbon structural units containing alkylene structural units is 70%, and the content of nitrile group-containing monomer units is more than 29% and 30%, based on the mass of dispersant 1. The content of the amide group-containing structural unit was less than 1%. The content of these structural units was determined using the amount of monomer used and NMR (nuclear magnetic resonance) and/or IR (infrared spectroscopy) measurements (the same applies hereinafter).

<Preparation of Copolymer 2>
Copolymer 2 was obtained in the same manner as in Synthesis Example 1, except that the monomers used were changed to 20 parts of acrylonitrile, 40 parts of 1,3-butadiene, and 40 parts of 2-methyl-1,3-butadiene. The hydrogenation rate of copolymer 2 was 99.0%, and the weight average molecular weight (Mw) was 300,000. In copolymer 2, the content of aliphatic hydrocarbon structural units including alkylene structural units was 80%, the content of nitrile group-containing monomer units was more than 19% and less than 20%, and the content of amide group-containing structural units was less than 1%, based on the mass of copolymer 2.

<Synthesis Example 2: Preparation of Dispersant 2>
A dispersant 2-containing liquid was obtained in the same manner as in Synthesis Example 1, except that the copolymer used was changed to copolymer 2. The water content of the mixture of the NaOH suspension and the copolymer 2-containing liquid was 1.0%. The content and weight average molecular weight (Mw) of the amide group-containing structural unit of dispersant 2 were as shown in Table 1. In copolymer 2 (dispersant 2), the content of the aliphatic hydrocarbon structural unit containing an alkylene structural unit was 65%, the content of the nitrile group-containing monomer unit was 34.5%, and the content of the amide group-containing monomer unit was 0.5%, based on the mass of the copolymer.

In addition, the abbreviations written in the columns of monomers and bases in Table 1 and Table 2 described below have the following meanings.
BD: 1,3-butadiene MBD: 2-methyl-1,3-butadiene AN: Acrylonitrile AAm: Acrylamide

<Synthesis Examples 3 and 4 Preparation of Dispersants 3 and 4>
Solutions containing dispersants 3 and 4 were obtained in the same manner as in Synthesis Example 1, except that the type and/or amount of the base used was changed according to Table 1. The content of the amide group-containing structural unit and the weight average molecular weight (Mw) of each dispersant were as shown in Table 1.

<Synthesis Example 5 Preparation of Dispersant 5>
To the dispersant 1-containing liquid prepared in Synthesis Example 1, citric acid was further added in an amount of 5% based on dispersant 1 (copolymer 1) to modify some of the amide groups into carboxyl groups, thereby forming dispersant 5. Obtained. The presence of carboxyl groups was confirmed by infrared spectroscopic analysis using total reflection measurement. It was determined that Dispersant 5 contains a carboxyl group-containing structural unit.

<Synthesis Example 6 Preparation of Dispersant 6>
In a stainless steel polymerization reactor, 34.5 parts of acrylonitrile, 65 parts of 1,3-butadiene, 0.5 parts of acrylamide, 3 parts of potassium oleate, 0.3 parts of azobisisobutyronitrile, and t-dodecyl mercaptan. 0.6 parts and 200 parts of ion-exchanged water were added. Polymerization was carried out at 45° C. for 20 hours under a nitrogen atmosphere with stirring, and the polymerization was completed at a conversion rate of 90%. Unreacted monomers were removed by vacuum stripping to obtain an amide group-containing acrylonitrile-conjugated diene rubber latex with a solid content of about 30%. Next, ion-exchanged water was added to the latex to adjust the total solids concentration to 12%, and the latex was placed in a 1L autoclave equipped with a stirrer, and nitrogen gas was passed through it for 10 minutes to remove dissolved oxygen in the contents. Removed. A catalyst solution prepared by dissolving 75 mg of palladium acetate as a hydrogenation catalyst in 180 mL of ion-exchanged water to which 4 times the mole of nitric acid was added to palladium was added to the autoclave. After replacing the inside of the autoclave with hydrogen gas twice, the contents of the autoclave were heated to 50° C. while pressurized with hydrogen gas to 3 MPa, and a hydrogenation reaction was performed for 6 hours. Thereafter, the contents were returned to room temperature, the inside of the autoclave was made into a nitrogen atmosphere, and the solid content was dried to recover the dispersant 6. The hydrogenation rate of Dispersant 6 was 99.5%, and the weight average molecular weight (Mw) was 200,000. In copolymer 6 (dispersant 6), the content of aliphatic hydrocarbon structural units containing alkylene structural units is 65%, based on the mass of copolymer 6, and the content of nitrile group-containing monomer units is 65%. The amount was 34.5%, and the content of amide group-containing monomer units was 0.5%.

FIG. 1 shows the IR spectra of Copolymer 1, Dispersant 1, and Dispersant 3. Comparing the IR spectra of Copolymer 1, Dispersant 1, and Dispersant 3, Dispersant 3 has sharp peaks at about 1570 cm-1 and about 1650 cm-1 that are derived from amide groups, and dispersant It can be confirmed that 1 also has a peak derived from the amide group, although the intensity is low. On the other hand, copolymer 1 does not have this peak because it does not have an amide group. The nearby peak seen at about 1690 cm-1 is derived from the solvent NMP. From this, it was confirmed that amide groups were certainly introduced into Dispersant 1 and Dispersant 3. It was determined that Dispersant 1 and Dispersant 3 contain an amide group-containing structural unit. Further, other dispersants were similarly confirmed.

FIG. 2 shows 13C-NMR spectra of Dispersant 1 and Dispersant 3. The content of amide group-containing structural units calculated from the 13C-NMR spectrum was less than 1% for Dispersant 1 and 3.0% for Dispersant 3.

<Preparation of fibrous carbon dispersion>
(Manufacturing example 1)
A fibrous carbon dispersion was produced as follows according to the materials and composition shown in Table 2. First, NMP was placed in a stainless steel container and heated to 50°C. After adding the dispersant while stirring with a disper, the mixture was stirred for 1 hour to dissolve the dispersant. Next, fibrous carbon was added while stirring with a disper, and a square hole high shear screen was attached to a high shear mixer (L5M-A, manufactured by SILVERSON), and the whole was made uniform at a speed of 8,000 rpm, and the grooves were Batch dispersion was performed using a grind gauge with a maximum depth of 300 μm until the dispersed particle size became 250 μm or less. Subsequently, the liquid to be dispersed was supplied from the stainless steel container via piping to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine), and a 50-pass dispersion process was performed in the high-pressure homogenizer. Fibrous carbon dispersion 1 was obtained. The dispersion treatment was performed using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

(Manufacturing examples 2 to 9)
Fibrous carbon dispersions 2 to 9 were obtained in the same manner as in Production Example 1, except that the materials and compositions were changed according to the materials and compositions shown in Table 2, and the number of passes of the high-pressure homogenizer was changed.

Note that the abbreviations used in Table 2 have the following meanings.
・BT1003: LUCAN BT1003M (manufactured by LG Chem Ltd., multilayer CNT, fiber diameter 13 nm)
・8S: JENOTUBE8S (manufactured by JEIO, multilayer CNT, fiber diameter 6.8 nm)
・H-NBR1: Therban (R) 3406 (manufactured by LANXESS, hydrogenated acrylonitrile-butadiene rubber, acrylonitrile content 34%)
・PVP: Polyvinylpyrrolidone K30 (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.)
・NaOH: Sodium hydroxide (manufactured by Tokyo Kasei Kogyo Co., Ltd., purity >98.0%, granular form)
・KOH: Potassium hydroxide (manufactured by Tokyo Chemical Industry Co., Ltd.)
・NMP: N-methylpyrrolidone (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.)

<Electrode composite for secondary batteries>
(Example 1-1)
According to the composition shown in Table 3, an electrode composite for a secondary battery was produced as follows. First, fibrous carbon dispersion 1 was placed in a stainless steel container, NMP was added while stirring with a disper, and the mixture was stirred for 30 minutes. Next, NMC and the above dispersion were placed in a container of a planetary mixer (Hibismix (R) 2P-1 type, manufactured by Primix), and stirred at a rotation speed (revolution) of 60 rpm for 60 minutes to prepare a mixture. During stirring, the temperature was controlled at 25°C using a temperature control chiller. Thereafter, the resulting mixture was taken out into a stainless steel vat and vacuum dried at 100° C. for 2 hours using a vacuum dryer to completely remove the liquid component. The dried product was coarsely ground in a mortar to obtain electrode composite 1 for secondary batteries.

(Examples 1-2 to 1-8)
Composites 2 to 8 were obtained in the same manner as in Example 1-1 according to the compositions shown in Table 3.

(Example 1-9)
According to the composition shown in Table 3, an electrode composite for a secondary battery was produced as follows. First, the fibrous carbon dispersion 9 was placed in a stainless steel container, NMP was added while stirring with a disper, and the mixture was stirred for 30 minutes. Next, NMC and the above dispersion were placed in a NOB-MINI container (manufactured by Hosokawa Micron), and stirred at a rotational speed of 5000 rpm for 10 minutes to prepare a mixture. During stirring, the temperature was controlled at 25°C using a temperature control chiller. Thereafter, the resulting mixture was taken out into a stainless steel vat and vacuum dried at 100° C. for 2 hours using a vacuum dryer to completely remove the liquid component. The dried product was coarsely ground in a mortar to obtain a secondary battery electrode composite 9.

(Example 1-10)
Composite 10 was obtained according to the composition shown in Table 3 in the same manner as in Example 1-1, except that the rotation speed (revolution) of the planetary mixer was changed to 100 rpm.

(Example 1-11)
According to the composition shown in Table 3, an electrode composite for a secondary battery was produced as follows. First, the fibrous carbon dispersion 2 was placed in a stainless steel container, NMP was added while stirring with a disper, and the mixture was stirred for 30 minutes. Next, NMC and the above-mentioned dispersion were placed in a Mechanofusion (AMS-MINI, manufactured by Hosokawa Micron) container, and stirred at a rotational speed of 3000 rpm for 10 minutes to prepare a mixture. During stirring, the temperature was controlled at 25°C using a temperature control chiller. Thereafter, the resulting mixture was taken out into a stainless steel vat and vacuum dried at 100° C. for 2 hours using a vacuum dryer to completely remove the liquid component. The dried product was coarsely ground in a mortar to obtain a secondary battery electrode composite 11.

(Example 1-12)
According to the composition shown in Table 3, an electrode composite for a secondary battery was prepared as follows. First, the fibrous carbon dispersion 2 was taken in a stainless steel container, and NMP was added while stirring with a disperser, and the mixture was stirred for 30 minutes. Next, NMC and the above dispersion were charged into a Trimix (TX-2L, manufactured by Inoue Seisakusho Co., Ltd.) container, and the mixture was stirred for 30 minutes at a rotation speed (revolution) of 50 rpm to prepare a mixture. During stirring, the temperature was controlled at 25 ° C. with a temperature-controlling chiller. Then, the obtained mixture was taken out into a stainless steel vat and vacuum-dried at 100 ° C. for 2 hours using a vacuum dryer to completely remove the liquid component. The dried product was coarsely crushed in a mortar to obtain an electrode composite for a secondary battery 12.

(Example 1-13)
According to the composition shown in Table 3, an electrode composite for a secondary battery was produced as follows. First, fibrous carbon dispersion 1 was placed in a stainless steel container, NMP was added while stirring with a disper, and the mixture was stirred for 30 minutes. Next, NMC and the above dispersion were placed in a container of a planetary mixer (Hibismix (R) 2P-1 type, manufactured by Primix), and stirred at a rotation speed (revolution) of 60 rpm for 60 minutes to prepare a mixture. During stirring, the temperature was controlled at 25°C using a temperature control chiller. Thereafter, the resulting mixture was taken out into a stainless steel vat and vacuum dried at 100° C. for 2.5 hours using a vacuum dryer to completely remove the liquid component. The dried product was coarsely ground in a mortar to obtain a secondary battery electrode composite 13.

(Example 1-14)
According to the composition shown in Table 3, an electrode composite for a secondary battery was produced as follows. First, fibrous carbon dispersion 1 was placed in a stainless steel container, NMP was added while stirring with a disper, and the mixture was stirred for 30 minutes. Next, NMC and the above dispersion were placed in a container of a planetary mixer (Hibismix (R) 2P-1 type, manufactured by Primix), stirred at a rotation speed (revolution) of 60 rpm for 60 minutes, and then dissolved in NMP in advance. A 10% binder solution (polyvinylidene fluoride resin: KF Polymer #1300) was added thereto, and the mixture was stirred at a rotational speed (revolution) of 60 rpm for 45 minutes to prepare a mixture. During stirring, the temperature was controlled at 25°C using a temperature control chiller. Thereafter, while maintaining the inside of the container at 80° C. using a hot water chiller, the pressure was reduced using a vacuum pump and drying was performed for 3 hours to completely remove the solvent. The dried product was coarsely ground in a mortar to obtain a secondary battery electrode composite 14.

(Example 1-15)
According to the composition shown in Table 3, an electrode composite for a secondary battery was produced as follows. First, fibrous carbon dispersion 1 was placed in a stainless steel container, NMP was added while stirring with a disper, and the mixture was stirred for 30 minutes. Next, NMC and the above dispersion were placed in a container of a high-speed mixer, and stirred for 45 minutes at an agitator rotation speed of 500 rpm and a chopper rotation speed of 1500 rpm. Resin: KF Polymer #1300) was added and stirred at the same rotation speed for 30 minutes to prepare a mixture. During stirring, the temperature was controlled at 25°C using a temperature control chiller. Thereafter, while maintaining the inside of the container at 80° C. using a hot water chiller, the pressure was reduced using a vacuum pump and drying was performed for 3 hours to completely remove the solvent. The dried product was coarsely ground in a mortar to obtain a secondary battery electrode composite 15.

(Comparative example 1-1)
According to the composition shown in Table 3, an electrode composite for a secondary battery was produced as follows. NMC and fibrous carbon were placed in a Mechano Fusion (AMS-MINI, manufactured by Hosokawa Micron Corporation) container, and stirred at a rotation speed of 5000 rpm for 10 minutes to obtain an electrode composite 16 for a secondary battery. During stirring, the temperature was controlled at 25°C using a temperature control chiller.

(Comparative example 1-2)
According to the composition shown in Table 3, NMC and fibrous carbon dispersion 2 were measured into a container and stirred with a spoon for 10 minutes to prepare a mixture. Thereafter, the resulting mixture was taken out into a stainless steel vat and vacuum dried at 100° C. for 2 hours using a vacuum dryer to completely remove the liquid component. The dried product was coarsely ground in a mortar to obtain a secondary battery electrode composite 17.

(Comparative Examples 1-3 and 1-4)
Composites 18 and 19 were obtained in the same manner as in Example 1-1, except that the drying temperature and drying time were changed to 120° C. and 4 hours, according to the composition shown in Table 3.

<Evaluation of the state of fibrous carbon in composites>
The state of dispersion of fibrous carbon in the composite was determined using a scanning electron microscope JSM-7800F manufactured by JEOL.
- Judgment criteria for fibrous carbon aggregates ◎: Contains or does not contain fibrous carbon aggregates of 5 μm or less.
○: Contains fibrous carbon aggregates exceeding 5 μm and 10 μm or less.
△: Contains fibrous carbon aggregates exceeding 10 μm and 50 μm or less ×: Contains fibrous carbon aggregates exceeding 50 μm ・Criteria for determining the state of disintegration of the active material surface of fibrous carbon ◎: Fibers The area occupied by the fibrous carbon adsorbed on the active material in the crushed state is 50% or more of the entire surface of the active material.○: The area occupied by the fibrous carbon adsorbed on the active material in the crushed state is The area occupied is 20% or more and less than 50% of the entire surface of the active material. △: The area occupied by the fibrous carbon adsorbed to the active material in a state where the fibers are crushed is 10% or more of the entire surface of the active material. , less than 20% ×: The fibers are not adsorbed to the active material in a disintegrated state.

<Exothermic peak temperature of fibrous carbon>
The exothermic peak temperature of the fibrous carbon was evaluated using a differential thermometer Thermoplus EV02TG8121 manufactured by Rigaku. The exothermic peak temperature obtained when compressed air was flowed at 200 mL/min and the temperature was raised from 40° C. to 800° C. at 10° C./min was used as an index. The exothermic peak temperature was calculated by reading the temperature at the top of the exothermic peak due to combustion of fibrous carbon in the range of 400 to 700° C. in the DTA curve obtained by measurement.

Note that the abbreviations used in Table 3 have the following meanings.
・NMC: NCM523 (manufactured by Nihon Kagaku Kogyo Co., Ltd., composition: LiNi _0.5 Co _0.2 Mn _0.3 O ₂ )

As shown in Table 3, from the exothermic peak temperature of SEM and TG-DTA, it can be seen that in the example, the fibrous carbon in the composite was appropriately dissolved and adsorbed on the surface of the active material without excessive agglomeration. . On the other hand, in the comparative example, the disintegration of the fibrous carbon agglomeration and the adsorption of the disintegrated material on the surface of the active material were insufficient.

<Preparation of electrode film for positive electrode>
An electrode film for a positive electrode was produced using the electrode composite produced in the example.
Weigh out 1.5 parts of polyvinylidene fluoride resin (KF Polymer #1300) as a binder and 98.5 parts of electrode composite 1 into a plastic container, and use a rotation/revolution mixer (Awatori Rentaro manufactured by Shinky, ARE-310). The mixture was stirred at 2,000 rpm for 15 seconds. The obtained powder mixture was calender-molded into an electrode film on a 20 μm thick aluminum foil serving as a current collector using a powder feeder and a calendar roll (roll temperature 200°C) to form a positive electrode film 1. Obtained. Note that the density of the positive electrode film was 3.0 g/cm ³ .

Positive electrode films 2 to 13 and 16 to 19 were obtained in the same manner as positive electrode film 1 using composites 2 to 13 and 16 to 19.

Weigh out 0.75 parts of polyvinylidene fluoride resin (KF Polymer #1300) as a binder and 99.25 parts of electrode composite 14 into a plastic container, and use a rotation/revolution mixer (Awatori Rentaro manufactured by Shinky, ARE-310). The mixture was stirred at 2,000 rpm for 15 seconds. The obtained powder mixture was calendered into an electrode film on a 20 μm thick aluminum foil serving as a current collector using a powder feeder and a calendar roll (roll temperature 200°C) to form a positive electrode film 14. Obtained. Note that the density of the positive electrode film was 3.0 g/cm ³ .

Using the composite 15, a positive electrode film 15 was obtained in the same manner as the positive electrode film 14.

(Resistance of positive electrode film)
The volume resistivity of the electrode films 1 to 19 was measured according to JIS-K7194 using a four-probe method using Lorester GP (manufactured by Nitto Seiko Analytech). Incidentally, for the resistance measurement, measurement electrodes were used in which the coating base material during the production of each electrode was changed from aluminum foil to a PET base material.
The relative value (%) based on the volume resistivity of the electrode film of Comparative Example 1-3 was determined and evaluated based on the following criteria.
Electrode resistance characteristic judgment criteria ◎: 200% or more (extremely excellent)
○: 150% or more and less than 200% (excellent)
○△: 100% or more and less than 150% (good)
△: 50% or more but less than 100% (defective)
×: Less than 50% (extremely poor)

<Assembly of a cell for evaluating the positive electrode of a lithium-ion secondary battery>
The previously prepared electrode films 1 to 19 were punched out to φ16 mm to be used as the working electrode, and a metallic lithium foil (thickness 0.15 mm) was used as the counter electrode. A separator (porous polypropylene film) was inserted and laminated between the working electrode and the counter electrode, and the cell was filled with an electrolyte (a nonaqueous electrolyte in which LiPF6 was dissolved at a concentration of 1 M in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of _1:1 ) to assemble a bipolar sealed metal cell (HS flat cell manufactured by Hosen Co., Ltd.). The cell was assembled in a glove box substituted with argon gas.

<Evaluation of rate characteristics of lithium ion secondary battery positive electrode>
The produced lithium ion secondary battery positive 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 that charges or discharges the theoretical capacity of the positive 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 1.
(Formula 1) Rate characteristic = 3C discharge capacity / 0.2C discharge capacity x 100 (%)
Relative values (%) based on the rate characteristics of Comparative Example 1-3 were determined and evaluated using the following criteria.
Rate characteristic judgment criteria ◎: 150% or more (extremely excellent)
○: 130% or more and less than 150% (excellent)
○△: 100% or more and less than 130% (good)
×: Less than 100% (defective)

<Evaluation of cycle characteristics of lithium ion secondary battery positive electrode>
The produced lithium ion secondary battery positive 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 60th time, as shown in Equation 2 below.
(Formula 2) Cycle characteristics = 3rd 0.2C discharge capacity / 60th 0.2C discharge capacity x 100 (%)
Relative values (%) based on the cycle characteristics of Comparative Example 1-3 were determined and evaluated using the following criteria.
Cycle characteristic judgment criteria ◎: 180% or more (extremely excellent)
○: 150% or more and less than 180% (excellent)
〇△: 100 or more and less than 150% (good)
×: Less than 100% (defective)

As shown in Table 4, the examples showed superior battery characteristics compared to the comparative examples. The fibrous carbon in the composite of the example was not excessively agglomerated, but was in a state of being unraveled and adsorbed on the surface of the active material. Therefore, it is possible to form conductive paths within the electrodes uniformly, which is presumed to have led to reductions in electrode resistance and improvements in rate characteristics and cycle characteristics. Among them, those in which the adsorption state of fibrous carbon was good showed particularly good performance.
On the other hand, in the comparative example, insufficient disintegration of fibrous carbon during the manufacturing process of the composite and excessive drying agglomeration during the drying process resulted in a decrease in the amount of adsorption on the active material surface and uneven distribution of the material. It is presumed that the formation of conductive paths became non-uniform, leading to an increase in electrode resistance and deterioration of rate characteristics and cycle characteristics.
From the above, it was shown that the electrode composite produced by the production method of the present invention can exhibit excellent battery characteristics.

Claims (8)

A method for producing a composite for a secondary battery electrode containing an electrode active material and fibrous carbon, the method comprising:
A step of combining an electrode active material and a fibrous carbon dispersion in which fibrous carbon is dispersed in a solvent in a non-slurry form using a mechanochemical mixing device, and a step of removing and drying the solvent , The fibrous carbon dispersion includes fibrous carbon, a dispersant, and a solvent,
A method for producing a composite for a secondary battery electrode , wherein the dispersant includes a copolymer containing an aliphatic hydrocarbon structural unit and a nitrile group-containing structural unit . The copolymer is
The copolymer contains an aliphatic hydrocarbon structural unit, a nitrile group-containing structural unit, and an alkyl group-substituted or unsubstituted carbamoyl group-containing structural unit,
the aliphatic hydrocarbon structural unit includes an alkylene structural unit, and the content of the aliphatic hydrocarbon structural unit is 40 mass% or more and less than 85 mass% based on the mass of the copolymer;
the content of the nitrile group-containing structural unit is 15% by mass or more and 50% by mass or less based on the mass of the copolymer, and the content of the alkyl group-substituted or unsubstituted carbamoyl group-containing structural unit is 10% by mass or less based on the mass of the copolymer,
a total content of the aliphatic hydrocarbon structural unit, the nitrile group-containing structural unit, and the alkyl group-substituted or unsubstituted carbamoyl group-containing structural unit is 80 mass% or more based on the mass of the copolymer,
2. The method for producing a composite for a secondary battery electrode in accordance with claim 1 , wherein the weight average molecular weight of the copolymer is from 5,000 to 400,000. The method for producing a composite for a secondary battery electrode according to claim 1 or 2 , wherein the copolymer further contains less than 1 mass % of a carboxyl group-containing structural unit based on the mass of the copolymer. The method for producing a composite for a secondary battery electrode according to claim 1 or 2 , wherein the fibrous carbon dispersion contains a base in an amount of 1% by mass or more and 20% by mass or less based on the mass of the copolymer. Claim 1 or 2, wherein the secondary battery electrode composite has an exothermic peak temperature of 520°C or less of fibrous carbon obtained by simultaneous thermogravimetric-differential thermal analysis in an oxygen atmosphere. A method for producing the composite for secondary battery electrodes described above. The method for producing a composite for secondary battery electrodes according to claim 1 or 2, wherein the composite for secondary battery electrodes contains a binder resin. A method for producing an electrode film, comprising producing an electrode composite for a secondary battery according to the method of claim 1 or 2, and forming an electrode film using the electrode composite for a secondary battery. A method for producing a secondary battery, comprising: preparing an electrode composite for a secondary battery according to the method according to claim 1 or 2; and forming an electrode film using the electrode composite for a secondary battery.