Composite for secondary battery electrode

Abstract

The purpose of the present invention is to provide a composite for a secondary battery electrode capable of acquiring high conductivity even in electrodes by a compounding method using an active material and a fibrous carbon. This composite for a secondary battery electrode contains an electrode active material and a fibrous carbon, the composite for a secondary battery electrode characterized by a part of the fibrous carbon having a crushed form and adhering to the surface of the electrode active material, and a part of the fibrous carbon having an aggregate form.

Description

Composite for secondary battery electrodes

[0001] The present invention relates to a composite for a secondary battery electrode, and an electrode, a secondary battery, and a device using the same.

[0002] With the spread of electric vehicles and the trend toward smaller, lighter, and more powerful portable devices, secondary batteries with high energy density and even higher capacity are required. Against this background, non-aqueous electrolyte secondary batteries, particularly lithium-ion secondary batteries, which use a non-aqueous electrolyte solution, are being used in many devices due to their high energy density and high voltage characteristics.

[0003] Secondary battery electrodes are fabricated by coating a current collector with a composite slurry containing a positive or negative electrode active material, a conductive material, a binder resin, and other components. A conductive material dispersion, in which the conductive material is dispersed in a dispersing medium, is prepared. Adding the active material and binder resin to the conductive material dispersion to create a composite slurry results in the conductive material being uniformly dispersed in the electrode film, improving the conductivity of the electrode film. To increase the capacity of secondary batteries, increasing the active material ratio in the electrode is desirable. Carbon nanotubes are considered promising as conductive agents, as they can efficiently form a conductive network even in small amounts and reduce electrode resistance. However, carbon nanotubes with small average outer diameters and long fiber lengths are effective for achieving low resistance with smaller additions. However, their strong cohesion makes it difficult to distribute them uniformly throughout the electrode. To efficiently form a conductive network in the electrode and ensure a conductive path to the active material, a method has been proposed in which a conductive material, such as carbon nanotubes, is pre-adsorbed onto the surface of the active material.

[0004] Patent Document 1 discloses an example of producing a cathode active material having high electronic conductivity and high mechanical strength by combining a cathode active material and acetylene black through mechanochemical treatment under a nitrogen atmosphere. Patent Document 2 discloses an example of producing composite particles with excellent particle strength by spray-granulating a slurry containing a cathode active material, carbon black, and cellulose nanofibers. Patent Document 3 discloses an example of producing a cathode active material having high electronic conductivity and high mechanical strength by combining a cathode active material and carbon nanotubes through mechanochemical treatment under a nitrogen atmosphere. Patent Document 4 discloses an example of producing composite particles in which the materials are uniformly mixed by spray-granulating a slurry in which cathode active material particles and fibrous carbon are dispersed in a solvent using an ultrasonic disperser.

[0005] Japanese Patent Publication No. 2016-201228 Japanese Patent Publication No. 6380526 Japanese Patent Publication No. 2017-142997 Japanese Patent Publication No. 5377946

[0006] The methods disclosed in Patent Documents 1 and 2 use a dispersion of acetylene black as a conductive additive, making it difficult to form an efficient conductive network with a small amount of addition, compared to when fibrous carbon is used as a conductive additive. In the method disclosed in Patent Document 3, it is difficult to disentangle the entangled fibrous carbon nanotubes during the composite formation process, which prevents uniform adsorption of the carbon nanotubes to the active material surface and tends to result in a non-uniform composite, making it difficult to form a uniform conductive network in the electrode. In the method disclosed in Patent Document 4, the carbon nanotubes are present in the composite particles in a network-like disentangled state, resulting in insufficient formation of conductive paths between the composite particles when the electrode is formed.

[0007] In order to solve the above problems, an object of the present invention is to provide a composite for a secondary battery electrode that can achieve high conductivity even in the electrode by a composite method using an active material and fibrous carbon.

[0008] Some embodiments of the present invention are exemplified below. The present invention relates to a composite for a secondary battery electrode, comprising an electrode active material and fibrous carbon, wherein a portion of the fibrous carbon is in a crushed form and adheres to a surface of the electrode active material, and a portion of the fibrous carbon is in the form of an aggregate.

[0009] The present invention relates to the composite for a secondary battery electrode, wherein the average particle size of the aggregates is 0.2 μm or more and 50 μm or less.

[0010] The present invention relates to the composite for a secondary battery electrode, wherein the temperature of the exothermic peak of the fibrous carbon obtained by simultaneous thermogravimetry-differential thermal analysis in the presence of oxygen is 550° C. or less.

[0011] The present invention also relates to the composite for a secondary battery electrode, which further contains a binder resin.

[0012] The present invention also relates to a secondary battery electrode comprising the above-mentioned secondary battery electrode composite.

[0013] The present invention relates to a secondary battery including the electrode for a secondary battery.

[0014] The present invention relates to a vehicle or device equipped with the secondary battery.

[0015] The present invention relates to a method for producing the above-described composite for a secondary battery electrode, comprising the steps of: combining a fibrous carbon dispersion in which fibrous carbon is dispersed in a solvent with an electrode active material using a mixing device; and removing the solvent and drying the resulting mixture.

[0016] Some other embodiments of the present invention are exemplified below: The present invention relates to a composite for a secondary battery electrode comprising an electrode active material and fibrous carbon, wherein the fibrous carbon comprises at least two types of fibrous carbon having different average fiber diameters, the at least two types of fibrous carbon comprising a first fibrous carbon having an average fiber diameter of 1 nm or more and less than 9 nm, and a second fibrous carbon having an average fiber diameter of 9 nm or more and 150 nm or less.

[0017] The present invention relates to a composite for a secondary battery electrode, wherein a portion of the fibrous carbon is in a crushed form and adheres to the surface of the electrode active material, and a portion of the fibrous carbon is in an aggregate form.

[0018] The present invention relates to the composite for a secondary battery electrode, wherein the average particle size of the aggregates is 0.2 μm or more and 50 μm or less.

[0019] The present invention further relates to the above composite for a secondary battery electrode, which contains a binder resin.

[0020] The present invention also relates to a secondary battery electrode comprising the above-mentioned secondary battery electrode composite.

[0021] The present invention relates to a secondary battery including the electrode for a secondary battery.

[0022] The present invention relates to a vehicle or device equipped with the secondary battery.

[0023] The present invention relates to a method for producing the composite for a secondary battery electrode, comprising the steps of: combining a fibrous carbon dispersion and an electrode active material using a dry mixer; and removing the solvent and drying the resulting mixture.

[0024] According to an embodiment of the present invention, by precisely controlling the dispersion state of the fibrous carbon on the active material, a composite for a secondary battery electrode having excellent conductivity can be provided. According to still another embodiment of the present invention, a non-aqueous electrolyte secondary battery having high output and long life and an electrode membrane used therein can be provided.

[0025] Fig. 1 is a diagram showing aggregates of fibrous carbon in the composite of Example 1-1 by SEM. Fig. 2 is an enlarged view showing a state in which the fibrous carbon in the composite of Example 1-1 is adsorbed on the surface of the active material and crushed.

[0026] Hereinafter, a method for producing a composite for a secondary battery electrode according to an embodiment of the present invention will be described in detail. The present invention is not limited to the following embodiment, and the present invention also includes embodiments that are implemented within the scope of the present invention.

[0027] In this specification, carbon nanotubes may be referred to as "CNT." Hydrogenated nitrile rubber may be referred to as "H-NBR," and N-methyl-2-pyrrolidone may be referred to as "NMP." In this specification, a carbon nanotube dispersion may be simply referred to as a "CNT dispersion" or "dispersion." Furthermore, a composite for a secondary battery electrode may be referred to as an "electrode composite" or "composite."

[0028] [First embodiment] <Composite for secondary battery electrode> The composite for secondary battery electrode contains an electrode active material and fibrous carbon, and may further contain, optionally, a dispersant and a binder resin. The composite for electrode may further contain optional components.

[0029] The fibrous carbon contained in the electrode composite of the present invention is partly in a crushed form and adheres to the surface of the active material, and partly in an aggregate form.

[0030] The two forms of fibrous carbon mentioned above are important for achieving excellent battery characteristics. When fibrous carbon is present on the surface of an active material in a crushed form, it can efficiently supply electrons required for the battery reaction to the active material. Furthermore, when fibrous carbon is included in a composite in the form of aggregates, it can contribute to reducing contact resistance between active materials when an electrode is fabricated. Therefore, when fibrous carbon is crushed and uniformly adsorbed on the surface of an active material and contains aggregates of fibrous carbon with an appropriate particle size and number, the electrode resistance is reduced when the electrode is fabricated into a secondary battery, and the formation of an electron conduction path to the active material during the battery reaction is favored, thereby improving 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, thereby improving battery capacity.

[0031] The crushed form of fibrous carbon refers to a form in which secondary particles (aggregates) of fibrous carbon are broken down into primary particles or a bundle state in which multiple primary particles are bundled together. The state in which fibrous carbon is crushed and adsorbed onto the surface of an active material includes a state in which the primary particles and / or bundles are isolated, and a state in which the primary particles and / or bundles are overlapped. From the viewpoint of electron supply to the active material and conductive paths between composites, a state in which the primary particles and / or bundles are overlapped and adsorbed in a network-like form is preferred.

[0032] In the present invention, the state in which the fibrous carbon is adsorbed on the surface of the active material in a crushed form means that the area occupied by the fibrous carbon adsorbed on the active material in a crushed fiber state is 10% or more of the entire surface of the active material, preferably 20% or more, and more preferably 50% or more.

[0033] The area occupied by the fibrous carbon adsorbed on the active material in a state in which the above-mentioned fibers were crushed can be measured from the contrast difference between the active material and the fibrous carbon in an observation image taken at a magnification of 5,000 to 50,000 times using a scanning electron microscope (SEM) or a scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX), and the average value of the above-mentioned areas calculated from 20 pieces of active material in the composite was used.

[0034] The aggregate of fibrous carbon in the present invention is an aggregate having a morphology in which primary particles of fibrous carbon and / or bundles of a plurality of primary particles are entangled.

[0035] The particle diameter of the fibrous carbon aggregates in the present invention can be measured from the length of the major axis of the fibrous carbon aggregates from an observation image taken at a magnification of 5,000 to 50,000 times using a scanning electron microscope (SEM) or a scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX), and the average value of the particle diameters of 10 fibrous carbon aggregates was taken as the average particle diameter of the aggregates.

[0036] The aggregate of fibrous carbon in the present invention refers to one having an average particle size of 0.1 to 100 μm, preferably 0.2 to 10 μm, more preferably 0.2 to 5 μm, and even more preferably 0.2 to 3 μm. If there are agglomerates of fibrous carbon having an average particle size exceeding 100 μm, it may be difficult to form a uniform composite.

[0037] The number of aggregates of the fibrous carbon in the present invention can be measured from the average number of aggregates of the fibrous carbon measured from 10 observation images (observation field area 20 μm × 15 μm) taken at a magnification of 5,000 times by a scanning electron microscope (SEM) or a scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX). The average number of aggregates of the fibrous carbon in the present invention is preferably 1 or more.

[0038] When the combustion temperature of the fibrous carbon in an oxygen-containing atmosphere is 550° C. or less, the electrode composite of the present invention becomes a composite in a homogeneous state in which the fibrous carbon adsorbed on the surface of the active material is loosened.

[0039] The exothermic peak temperature 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 measurement under air or oxygen flow conditions. The top of the exothermic peak of the fibrous carbon, which is located around 400 to 700°C, in the obtained DTA curve is read and defined as the exothermic peak temperature of the fibrous carbon. This represents the combustion temperature of the fibrous carbon. Fibrous carbon generally has thick bundles in which primary particles are strongly aggregated by van der Waals forces, and large secondary aggregates in which bundles aggregate together. Differences in these aggregation states result in different physical properties, such as thermal stability. Therefore, even for the same type of fibrous carbon, the decomposition temperature varies depending on the aggregation state, and the stronger the aggregation, the higher the combustion temperature.

[0040] The combustion temperature of the fibrous carbon in the secondary battery electrode composite in an oxygen-containing atmosphere is preferably 550°C or less, since the fibrous carbon on the active material is adsorbed in a more loosened state, which favors the formation of an electron conduction path from the fibrous carbon to the active material and improves battery characteristics. A temperature of 480°C or less is preferred, and a temperature of 450°C or less is more preferred.

[0041] When the volume resistivity of the electrode composite for secondary batteries under a load of 20 kN is 500 Ω cm or less, the fibrous carbon in the composite is not unevenly distributed and is adsorbed on the active material in a more uniform state, thereby reducing the electrode resistance when used as a secondary battery electrode. A volume resistivity of 100 Ω cm or less is preferable, and 50 Ω cm or less is more preferable.

[0042] The volume resistivity of a secondary battery electrode composite 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 CNT can then be calculated from the measured resistance and the thickness of the test piece. Measurements are performed using a volume resistivity measuring device (e.g., Nitto Seiko Analytech Automatic Powder Resistivity Measurement System, Low Resistance Version, MCP-PD600) under a load of 20 kN.

[0043] The secondary battery electrode composite is preferably in the form of particles, and the average particle size is preferably from 0.5 μm to 500 μm, more preferably from 1 μm to 200 μm.

[0044] As described above, when the combustion temperature is 550°C or lower and the volume resistivity is 100 Ω cm or lower, the fibrous carbon in the composite is crushed and uniformly adsorbed onto the active material, which is preferable because, when used as an electrode for a secondary battery, it reduces the electrode resistance and favors the formation of an electron conduction path to the active material during the battery reaction, thereby improving the battery rate characteristics and cycle characteristics. In addition, because 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, allowing for an improvement in battery capacity.

[0045] <Active Material> The active material is a material that causes a battery reaction required to extract electrical energy, and is not particularly limited. For example, for secondary battery applications, metal compounds such as metal oxides and metal sulfides that can reversibly dope or intercalate lithium ions can be used as the positive electrode active material. For example, lithium manganese composite oxides (e.g., Li ｘ Mn ２ O４ or Li ｘ MnO ２ ), lithium nickel composite oxide (e.g., Li ｘ NiO ２ ), lithium cobalt composite oxide (Li ｘ CoO ２ ), lithium nickel cobalt composite oxide (e.g., Li ｘ Ni １－ｙ Co ｙ O ２ ), lithium manganese cobalt composite oxide (e.g., Li ｘ Mn ｙ Co １－ｙ O ２ ), lithium nickel manganese cobalt composite oxide (e.g., 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 ), lithium phosphate powder having an olivine structure (e.g., Li ｘ FePO ４ , Li ｘ Fe １－ｙ Mn ｙ P.O. 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 powder such as titanium oxide, iron sulfate (Fe ２ (SO ４ ) ３ ), TiS ２and transition metal sulfide powders such as FeS. Here, 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 be used singly 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 metals is 50 mol% or more) tend to become highly basic due to the elution of raw material-derived components or metal ions, which can easily cause gelation of the binder resin or deterioration of the dispersion state. Therefore, this embodiment is particularly effective for batteries containing active materials containing Ni and / or Mn.

[0046] Examples of the negative electrode active material include metal Li, or its alloy, tin alloy, silicon-based material (metal Si, Si alloy, SiO ｘ etc.), LiXTiO ２ , LiXFe ２ O ３ , LiXFe ３ O ４ , LiXWO ２ Examples of materials that can be used include metal oxides such as those listed above, 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-baked carbon materials. Here, x is a number, 0<x<1. These negative electrode active materials can be used alone or in combination. In particular, when silicon-based materials are used, their theoretical capacity is large but their volume expansion is extremely large. Therefore, it is preferable to use them in combination with artificial graphite such as highly graphitized carbon materials, carbonaceous powders such as natural graphite, resin-baked carbon materials, and the like.

[0047] <Fibrous Carbon> Fibrous carbon is a fibrous carbon material that has a high aspect ratio in the longitudinal direction and, compared to particulate carbon such as carbon black, facilitates the formation of a conductive network. Examples of fibrous carbon include carbon fiber (CNF) and carbon nanotubes (CNT). CNTs have a cylindrical shape formed by rolling planar graphite, 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 rolled. Multi-walled CNTs have a structure in which two or more layers of graphite are rolled. Furthermore, the sidewalls of CNTs do not have to have a graphite structure. Furthermore, for example, CNTs having sidewalls with an amorphous structure are also considered CNTs in this specification.

[0048] The shape of the CNTs is not limited. Examples of such shapes include needle-like, cylindrical tubular, fishbone-like (fishbone or cup stacked), trump-like (platelet), and coil-like. Of these, needle-like or cylindrical tubular shapes are preferred. The CNTs may have a single shape or a combination of two or more shapes.

[0049] Examples of the form of CNT include graphite whiskers, filamentous carbon, graphite fibers, ultrafine carbon tubes, carbon tubes, carbon fibrils, carbon microtubes, and carbon nanofibers. The carbon nanotubes may have a single form or a combination of two or more of these forms.

[0050] 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 uniformly combine with the composite. It is also preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 13 nm or less. It is also preferably 1 nm or more, more preferably 3 nm or more. The average outer diameter of the fibrous carbon can be calculated by observing and photographing the fibrous carbon with a transmission electron microscope, randomly selecting 300 pieces of fibrous carbon from the observation photograph, and measuring the outer diameter of each piece.

[0051] The content of fibrous carbon in the composite is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and even more preferably 0.05% by mass or more, based on the mass of the composite for secondary battery electrodes. It is also 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 decreases, resulting in a decrease in battery capacity. For high-capacity batteries in particular, 10% by mass or less is preferable. If it is below the above range, the conductivity of the electrode and battery may be insufficient.

[0052] The composite may contain a conductive material other than fibrous carbon. Examples of the other conductive material include carbon materials such as carbon black, fullerene, graphene, multilayer graphene, and graphite. The carbon black may be neutral, acidic, or basic, and oxidation-treated carbon black or graphitized carbon black may be used. The other conductive materials may be used alone or in combination of two or more.

[0053] <Binder Resin> The composite of the present invention may contain a binder resin as needed. There are no particular limitations on the binder resin, so long as it is typically used as a binder resin, and it can be appropriately selected depending on the purpose. The binder resin used in the composite is preferably a resin capable of bonding materials such as active materials and fibrous carbon. Examples of binder resins used in the composite include polymers or copolymers containing ethylene, propylene, vinyl chloride, vinyl acetate, maleic acid, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, styrene, or the like as structural units; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, and fluororesins; cellulose-based resins such as carboxymethyl cellulose; elastomers such as styrene-butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Modified products, mixtures, and copolymers of these resins are also acceptable. Fluorine resins are particularly preferred, and examples thereof include 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, from the viewpoint of durability, polymers or copolymers having fluorine atoms in the molecule, such as polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene, resins having these structural units, and modified products thereof are preferred.

[0054] The content of the binder resin in the composite is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, based on the mass of the active material (the mass of the active material being 100% by mass), and is preferably 20% by mass or less, more preferably 10% by mass or less.

[0055] <Method for Manufacturing a Composite for a Secondary Battery Electrode> The method for composite of a positive electrode active material and fibrous carbon or the like is not particularly limited. Examples include a dry mixing method for the active material and fibrous carbon or the like, a mixing method with the addition of a solvent, a mixing method using a dispersion in which the active material and fibrous carbon or the like are dispersed in a solvent, and a wet mixing method in which a slurry is prepared by adding the active material, fibrous carbon or the like to a solvent. To produce a more uniform composite, a mixing method using a dispersion in which fibrous carbon or the like is dispersed in a solvent in advance is preferred. Among these, the use of a fibrous carbon dispersion is preferred because it allows the preparation of an electrode composite in which the active material and fibrous carbon are uniformly composited. Even without the use of a fibrous carbon dispersion, the same effect may be obtained by deagglomerating the fibrous carbon using a high-shear force composite machine or the like, which is preferable. In particular, to produce an excellent composite according to the present invention, a method in which the active material and fibrous carbon dispersion are composited using a high-shear force composite machine under high-concentration, non-fluid, non-slurry conditions is preferred.

[0056] Examples of dry mixers include roll mills such as two-roll and three-roll machines, high-speed mixers such as Henschel mixers and super mixers, fluid energy pulverizers such as micronizers and jet mills, attritors, particle composite devices such as "Nanocure," "Nobilta," and "Mechanofusion" manufactured by Hosokawa Micron Corporation, powder surface modification devices such as "Hybridization System," "Mechano Micros," and "Miraro" manufactured by Nara Machinery Manufacturing Co., Ltd., mixers such as "Planetary Mixer" and "Trimix" manufactured by Inoue Manufacturing Co., Ltd., and mixer / granulator "High Speed ​​Mixer" manufactured by EarthTechnica Corporation.

[0057] Furthermore, when using a dry mixer, other raw materials such as fibrous carbon may be added directly in powder form to the active material as a base material. However, to create a more uniform mixture, it is preferable to first disperse or dissolve the other raw materials such as fibrous carbon in a small amount of solvent and then mix them. Among these, the use of a fibrous carbon dispersion is preferred because it allows the preparation of an electrode composite in which the active material and fibrous carbon are uniformly combined. Furthermore, heating may be preferable to increase processing efficiency. Among dry mixers, planetary mixers, Trimix, and Mechanofusion, which are capable of compounding by shearing, are preferred.

[0058] Examples of wet mixing devices include mixers such as a Disper, a Homomixer, or a Planetary Mixer; homogenizers such as "Clearmix" manufactured by M Technique Co., Ltd. or "Filmix" manufactured by PRIMIX; rotation / revolution type mixers such as "Awatori Rentaro" manufactured by THINKYO Corporation; media-type dispersers such as a paint conditioner (manufactured by Red Devil), a ball mill, a sand mill ("Dynomill" manufactured by Shinmaru Enterprises, etc.), an attritor, a pearl mill ("DCP Mill" manufactured by Eirich Corporation, etc.), or a Coball mill; media-less dispersers such as a wet jet mill ("Genus PY" manufactured by Genus, "Starburst" manufactured by Sugino Machine Ltd., "Nanomizer" manufactured by Nanomizer Inc., etc.), "Clear SS-5" manufactured by M Technique Co., Ltd., or "Micros" manufactured by Nara Machinery Manufacturing Co., Ltd.; and other roll mills, kneaders, etc., but are not limited to these. It is preferable to use a wet mixing device that has been treated to prevent metal contamination from the device. Note that when a media-type disperser such as a ball mill is used, there is a risk that the structure of the active material may be destroyed by mixing, so a media-less disperser is preferred.

[0059] <Fibrous Carbon Dispersion> The fibrous carbon dispersion contains fibrous carbon and a dispersion medium, and optionally contains a dispersant. The fibrous carbon dispersion may contain optional components such as other additives (e.g., wetting agents, surfactants, pH adjusters, wetting and penetrating agents, and leveling agents), other conductive materials, and other polymer components, as needed, within a range that does not impair the object 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.

[0060] 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 particle size distribution analyzer. The median diameter (μm) determined using a laser diffraction / scattering particle size distribution analyzer allows the particle size of the fibrous carbon aggregate particles to be estimated from the scattered light intensity distribution by the particles. The median diameter (μm) is preferably 0.4 μm or more, and preferably 5.0 μm or less, and more preferably 2.0 μm or less. By setting the median diameter within the above range, a fibrous carbon dispersion in an appropriately dispersed state can be obtained. If the median diameter is below the above range, the fibrous carbon will be in an aggregated state, and if the median diameter is above the above range, a large amount of finely cut fibrous carbon will be generated, making it difficult to form an efficient conductive network. The median diameter can be measured by the method described in the examples.

[0061] The viscosity of the fibrous carbon dispersion, measured using a Brookfield viscometer at 25°C and 60 rpm, is preferably 10 mPa·s or more and less than 10,000 mPa·s, more preferably 10 mPa·s or more and less than 2,000 mPa·s, and even more preferably 10 mPa·s or more and less than 1,000 mPa·s.

[0062] 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 entanglement of the fibrous carbon, dispersant, and other resin components, or their intermolecular forces, etc., 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 entanglement of the fibrous carbon, dispersant, and other resin components while allowing these intermolecular forces to act appropriately.

[0063] 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. Also, 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 can be calculated by diluting the fibrous carbon dispersion 50 times with a nonaqueous solvent such as NMP, dropping the diluted fibrous carbon dispersion onto a substrate, drying the resulting sample, observing the sample with a scanning electron microscope, and randomly selecting 300 pieces of fibrous carbon from the observation photograph and measuring the fiber length of each piece.

[0064] The content of the fibrous carbon is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 0.8% by mass or more, relative to the total amount of the fibrous carbon dispersion. It is also preferably 20% by mass or less, and more preferably 10% by mass or less. By adjusting the content within the above range, the fibrous carbon can be maintained in a good and stable state 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. It is also preferable to appropriately adjust the content of the fibrous carbon so as to obtain a fibrous carbon dispersion with appropriate fluidity or viscosity, depending on the specific surface area of ​​the fibrous carbon, its affinity for the dispersion medium, the dispersibility of the dispersant, and the like.

[0065] 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, relative to 100 parts by mass of the fibrous carbon. The content of the dispersant is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, relative to the total amount of the fibrous carbon dispersion.

[0066] The solid content of the fibrous carbon dispersion is preferably 0.2 to 40 mass %, more preferably 0.5 to 20 mass %, and even more preferably 1 to 10 mass %.

[0067] The fibrous carbon dispersion may be prepared by separately preparing two or more types of fibrous carbon different in average outer diameter and adding them to a dispersion medium. When two or more types of fibrous carbon different in average outer diameter 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 different in average outer diameter 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.

[0068] 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. Also, it is preferably 20 μm or less, and more preferably 10 μm or less. The average fiber length of the fibrous carbon can be calculated by first observing and photographing the fibrous carbon with a scanning electron microscope, randomly selecting 300 pieces of fibrous carbon from the photograph, and measuring the fiber length of each piece.

[0069] The aspect ratio is the value obtained by dividing the fiber length of fibrous carbon by the outer diameter. A typical aspect ratio can be calculated using the average fiber length and the average outer diameter. A conductive material with a higher aspect ratio can obtain 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.

[0070] The specific surface area of ​​fibrous carbon is 100m ２ / g or more, and ２ / g or more is more preferable, and 200m ２ / g or more is more preferable. ２ / g or less, and ２ / g or less is more preferable. The specific surface area of ​​the 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, a well-developed conductive path is easily formed in the electrode.

[0071] The carbon purity of the fibrous carbon is expressed as the content (mass%) of carbon atoms in the fibrous carbon, and is preferably 80 mass% or more relative to 100 mass% of the fibrous carbon.

[0072] For the purpose of removing or reducing impurities such as metal catalysts and increasing the carbon purity, fibrous carbon that has been subjected to a high-purification treatment may be used.

[0073] When fibrous carbon is dispersed using a disperser that involves collision with media such as a bead mill, or when the fibrous carbon is repeatedly passed through a disperser over a long period of time, the fibrous carbon may be broken, resulting in the formation of short flakes. The formation of short flakes reduces the viscosity of the fibrous carbon dispersion and increases the gloss of the coating film obtained by coating and drying the fibrous carbon dispersion. Judging from these evaluation results alone, the dispersion state may appear to be good. However, the short flakes have high contact resistance and make it difficult to form a conductive network, which may worsen the resistance of the electrode. The extent of the formation of short flakes can be confirmed by diluting the dispersion, dropping it onto a substrate with a smooth surface and good affinity with the dispersion medium, and then observing the dried sample with a scanning electron microscope. By adjusting the dispersion conditions and the formulation of the dispersion to prevent the formation of carbonaceous particles of 0.1 μm or less, a highly conductive electrode can be obtained.

[0074] The fibrous carbon may be produced by any method. Generally, the fibrous carbon can be produced by a laser ablation method, an arc discharge method, a thermal CVD method, a plasma CVD method, or a combustion method, but is not limited to these. For example, the 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 a hydrocarbon and an alcohol.

[0075] <Dispersant> The dispersant for the fibrous carbon dispersion is preferably one that can stabilize the dispersion of the fibrous carbon in the fibrous carbon dispersion. Either a resin-type dispersant or a surfactant can be used as the dispersant, but a resin-type dispersant is preferred because it has a strong adsorption power to the fibrous carbon and can provide good dispersion stability. Depending on the properties required for dispersing the fibrous carbon, an appropriate type of dispersant can be used in an appropriate blending amount.

[0076] Examples of resin-type dispersants that can be used include (meth)acrylic polymers, polymers derived from ethylenically unsaturated hydrocarbons, cellulose derivatives, and copolymers thereof. Examples of polymers derived from ethylenically unsaturated hydrocarbons include polyvinyl alcohol resins, polyvinylpyrrolidone resins, polyacrylonitrile resins, and nitrile rubbers. Examples of polyvinyl alcohol resins include polyvinyl alcohol, modified polyvinyl alcohols having functional groups other than hydroxyl groups (e.g., acetyl groups, sulfo groups, carboxy groups, carbonyl groups, and amino groups), polyvinyl alcohols modified with various salts, other anion- or cation-modified polyvinyl alcohols, and polyvinyl acetals (polyvinyl acetoacetal, polyvinyl butyral, etc.) modified with aldehydes (acetoacetal-modified, butyral-modified, etc.). The polyacrylonitrile resin may be a polyacrylonitrile homopolymer, a polyacrylonitrile copolymer, or a modified product thereof. Preferred examples include polyacrylonitrile resins 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, and alkyl groups derived from (meth)acrylic acid alkyl esters or α-olefins. For example, the acrylonitrile copolymer described in JP 2020-163362 A can be used. Nitrile rubbers include acrylonitrile butadiene rubber and hydrogenated acrylonitrile butadiene rubber. Cellulose derivatives include cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethyl cellulose, ethylhydroxyethyl cellulose, nitrocellulose, methylcellulose, ethylcellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, and copolymers thereof.In addition, 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 to these. In particular, methyl cellulose, ethyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyacrylonitrile homopolymers, polyacrylonitrile copolymers, and hydrogenated acrylonitrile butadiene rubber are preferred. Polymers in which other substituents have been introduced into some of these polymers, modified polymers, etc. may also be used. From the viewpoint of the balance of affinity between the dispersed substance and the dispersion medium and resistance to the electrolyte, the weight average molecular weight of the resin-type dispersant is preferably 500,000 or less, more preferably 300,000 or less, and preferably 3,000 or more, and more preferably 5,000 or more. The resin-type dispersants may be used alone or in combination of two or more.

[0077] Commercially available polyvinyl alcohol resins include various grades under trade names such as Kuraray Poval (polyvinyl alcohol resin manufactured by Kuraray), Gohsenol, and Gohsenex (polyvinyl alcohol resin manufactured by Nippon Synthetic Chemical Industry). Modified polyvinyl alcohols having various functional groups are also available. Commercially available polyvinylpyrrolidone resins include Polyvinylpyrrolidone K30, K90 (manufactured by Fujifilm Wako), and K120 (manufactured by DSP Gokei Food & Chemical). Commercially available nitrile rubbers include Therban (hydrogenated nitrile rubber manufactured by Arlanseo), Baymod (nitrile rubber manufactured by Arlanseo), Zetpole (hydrogenated nitrile rubber manufactured by Nippon Zeon), and Nipole NBR (nitrile rubber manufactured by Nippon Zeon). Various grades with different nitrile ratios, hydrogenation rates, molecular weights, etc. are available. Dispersants synthesized by known synthesis methods may also be used. Surfactants may be used in place of or in addition to the resin-type dispersants described above. Surfactants are classified into anionic, cationic, amphoteric ionic surfactants and nonionic surfactants.

[0078] The resin-type dispersant may be a polymer containing at least an aliphatic hydrocarbon structural unit and a nitrile group-containing structural unit. The aliphatic hydrocarbon structural unit of the polymer may contain an alkylene structural unit. The polymer may be hydrogenated.

[0079] The aliphatic hydrocarbon structural unit is a structural unit containing an aliphatic hydrocarbon structure, and preferably a structural unit consisting solely 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.

[0080] Examples of the aliphatic hydrocarbon structural unit include an alkylene structural unit, an alkenylene structural unit, an alkyl structural unit, an alkanetriyl structural unit, and an alkanetetrayl structural unit. Structural units containing a branch point, such as an alkanetriyl structural unit and an alkanetetrayl structural unit, are structural units different from structural units containing a branched alkylene structure and structural units containing a branched alkyl structure, which will be described later. The aliphatic hydrocarbon structural unit preferably contains at least an alkylene structural unit.

[0081] The alkylene structural unit is a structural unit containing an alkylene structure, and is preferably a structural unit consisting of only an alkylene structure. The alkylene structure is preferably a linear alkylene structure or a branched alkylene structure.

[0082] <Dispersion medium> The dispersion medium for the fibrous carbon dispersion is not particularly limited, but is preferably a high-dielectric solvent, and preferably contains a solvent consisting of any one of high-dielectric solvents or a mixed solvent consisting of two or more of them. In addition, the high-dielectric solvent may be mixed with one or more other solvents.

[0083] Examples of 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 organic solvent or water, and the amide organic solvent more preferably contains at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone. The dielectric constant of the high-dielectric solvent can be a value listed in a solvent handbook or the like, and is preferably 2.5 or more at 20°C.

[0084] Examples of methods for removing the solvent and drying include hot air drying, vacuum drying, spray drying, freeze drying, etc. Among these, hot air drying and vacuum drying are preferred from the viewpoint of productivity.

[0085] <Secondary Battery Electrode Composite Slurry> A secondary battery electrode composite slurry can be prepared using a secondary battery electrode composite. The secondary battery electrode composite slurry can be obtained by adding an electrode composite and a binder resin to a dispersion medium. If necessary, a fibrous carbon dispersion and other optional components may be appropriately contained within a range that does not impair the object of the present invention. The optional components can be added at any timing, such as before preparing the composite slurry, during mixing, after mixing, or a combination thereof. The optional components may be those described above for the fibrous carbon dispersion. The active material may be a positive electrode active material or a negative electrode active material. In this specification, the positive electrode active material and the negative electrode active material may sometimes be simply referred to as "active material."

[0086] The solid content of the composite slurry is preferably 30% by mass or more, more preferably 40% by mass or more, based on the mass of the composite slurry (the mass of the composite slurry being 100% by mass), and is preferably 90% by mass or less, more preferably 85% by mass or less.

[0087] The content of the electrode composite in the composite slurry is preferably 28% by mass or more, more preferably 38% by mass or more, and even more preferably 48% by mass or more, based on the mass of the composite slurry (the mass of the composite slurry being 100% by mass), and is preferably 88% by mass or less, and more preferably 80% by mass or less.

[0088] The content of the binder resin in the composite slurry is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, based on the mass of the active material (the mass of the active material being 100% by mass). It is also preferably 20% by mass or less, more preferably 10% by mass or less. When the electrode composite contains a binder resin, it is preferable to adjust the total amount of the binder resin in the composite slurry to be within the above range.

[0089] The content of fibrous carbon in the composite slurry is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and even more preferably 0.05% by mass or more, based on the mass of the active material (the mass of the active material being 100% by mass). It is also preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and even more preferably 3% by mass or less. Since the electrode composite of the present invention contains fibrous carbon, it is preferable to adjust the total amount of fibrous carbon in the composite slurry to be within the above range. If the content exceeds the above range, the amount of active material filled in the electrode decreases, resulting in a lower battery capacity. If the content is below the above range, the conductivity of the electrode and battery may be insufficient.

[0090] <Method for producing a composite slurry for secondary battery electrodes> In the method for producing a composite slurry, the order in which the electrode composite and binder resin are added to the dispersion medium is not particularly limited. Examples include a method in which a binder resin is added to a dispersion medium to produce a binder resin composition, and then the electrode composite is added to the binder resin composition; a method in which an electrode composite is added to a dispersion medium, and then the binder resin is added; and a method in which the binder resin and the electrode composite are added to the dispersion medium all at once. A preferred method for producing a composite slurry is a method in which a binder resin is added to a dispersion medium to produce a binder resin composition, and then the electrode composite is added to the binder resin composition and stirred. The stirring device used for stirring is not particularly limited. A disperser, a homogenizer, or the like can be used as the stirring device.

[0091] <Secondary Battery Electrode> 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 dispersant. The electrode can be formed by preparing the above-mentioned composite slurry and applying the composite slurry, or by adding a binder or the like to the composite for a secondary battery electrode and pressing the components into a sheet without using the composite slurry. When a composite slurry is not used, a pre-mixed dry mixture or a dried product obtained after wet mixing may be used. When a composite slurry is used, for example, an electrode film can be formed by applying the composite slurry to a current collector and removing volatile components.

[0092] <Method for manufacturing secondary battery electrodes> The material and shape of the current collector are not particularly limited and can be appropriately selected from those suitable for various secondary batteries. Examples of materials for the current collector include metals and alloys such as aluminum, copper, nickel, titanium, and stainless steel. Furthermore, while flat foils are generally used, current collectors with roughened surfaces, perforated foils, and mesh-shaped current collectors can also be used. The thickness of the current collector is preferably about 0.5 to 30 μm.

[0093] The method for applying the composite slurry to the current collector 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 coating. Drying methods after application include, but are not limited to, standing to dry, air dryers, hot air dryers, infrared heaters, and far-infrared heaters.

[0094] The method for dry-mixing or wet-mixing the components by adding a binder or the like to the composite for a secondary battery electrode without using a mixture slurry is not particularly limited, and any known method can be used. Specifically, a dry or wet disperser described in the composite preparation method can be appropriately selected.

[0095] After the composite slurry is applied, it may be rolled using a lithographic press, a calender roll, etc. The thickness of the electrode film is, for example, 1 μm or more and 500 μm or less, and preferably 10 μm or more and 300 μm or less.

[0096] When forming an electrode by adding a binder or the like to a composite for a secondary battery electrode and pressing each component into a sheet without using a composite slurry, the components obtained by adding the binder or the like to the composite for a secondary battery electrode, or a dried product of the dry mixture or wet mixture, may be directly supplied to a current collector and pressure-molded, or a free-standing film made of the components obtained by adding the binder or the like to the composite for a secondary battery electrode, or a dried product of the dry mixture or wet mixture, may be prepared in advance and then laminated on a current collector. Alternatively, a current collector on which a resin thin film serving as a binder component has already been formed may be used or prepared.

[0097] Examples of the pressure molding method include a planographic press, a calendar roll, etc. Among these, the use of a calendar roll is preferred from the viewpoint of productivity and uniform molding.

[0098] <Secondary Battery> The secondary battery includes a positive electrode, a negative electrode, and an electrolyte, and at least one selected from the group consisting of the positive electrode and the negative electrode includes an electrode film made from the composite of the present invention.

[0099] The positive electrode may be formed by forming an electrode film containing a positive electrode active material on a current collector, and the negative electrode may be formed by forming an electrode film containing a negative electrode active material on a current collector.

[0100] The electrolyte may be any of a liquid electrolyte, a gel electrolyte, and a solid electrolyte. For example, the liquid electrolyte may contain an electrolyte salt such as a lithium salt and a non-aqueous solvent. As the electrolyte salt, various conventionally known electrolytes capable of transferring ions may be used. For example, LiBF ４ , LiClO ４ , LiPF ６ , LiAsF ６ , LiSbF ６ , LiCF ３ SO ３ , Li(CF ３ SO ２ ) ２ N, LiC ４ F ９ SO ３ , Li(CF ３ SO ２ ) ３ C, LiI, LiBr, LiCl, LiAlCl, LiHF ２ , LiSCN, or LiBPh ４ (wherein Ph is a phenyl group), etc. The electrolyte salt is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

[0101] The non-aqueous solvent is not particularly limited, but examples thereof include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octanoic lactone; glymes such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. These solvents may be used alone or in combination of two or more.

[0102] The secondary battery preferably includes a separator, such as, but not limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabrics obtained by subjecting these to hydrophilic treatment.

[0103] The structure of the secondary battery is not particularly limited, but it usually comprises a positive electrode, a negative electrode, and a separator that is provided as needed, and can be in various shapes depending on the purpose of use, such as a paper type, a cylindrical type, a button type, or a laminated type.

[0104] The composite for secondary battery electrodes of the present invention is an ideal composite of active material and fibrous carbon, and therefore can be suitably used not only for electrodes made from composite slurries but also for electrodes made by solid or semi-solid processes. These electrodes made by solid processes can be applied not only to lithium ion secondary batteries using conventional electrolyte solutions, but also to all-solid batteries, semi-solid batteries, and the like.

[0105] 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.

[0106] Second Embodiment A second embodiment will now be described. Configurations in the second embodiment that are not specifically described are the same as those in the first embodiment, and descriptions thereof will be omitted.

[0107] In the second embodiment, the composite for a secondary battery electrode includes an electrode active material and fibrous carbon, and may further include, optionally, a dispersant and a binder resin. The composite for an electrode may further include optional components.

[0108] The composite for a secondary battery electrode is characterized in that it contains at least two types of fibrous carbon having different average fiber diameters, and the at least two types of fibrous carbon include a first fibrous carbon having an average fiber diameter of 1 nm or more but less than 9 nm and a second fibrous carbon having an average fiber diameter of 9 nm or more but less than 150 nm.

[0109] In the present invention, the inclusion of at least two types of fibrous carbon having different average fiber diameters is important for achieving excellent battery characteristics. When only the first fibrous carbon having an average fiber diameter of 1 nm or more but less than 9 nm is used, the number of fibers per unit weight increases, which is advantageous for electronic conduction, but the fibers are densely adsorbed onto the active material surface, which is detrimental to ion conduction to the active material. On the other hand, when only the second fibrous carbon having an average fiber diameter of 9 nm or more but less than 150 nm is used, the number of fibers per unit weight is relatively reduced. Therefore, to ensure electronic conduction, it is necessary to increase the content of fibrous carbon in the composite, which is detrimental to energy density. By including at least two types of fibrous carbon having different fiber diameters, it is possible to ensure the number of fibers per unit weight and prevent overcrowding on the active material surface. This is thought to prevent a decrease in energy density and achieve a balance between electron and ion conduction, leading to the development of excellent battery characteristics.

[0110] The average fiber diameter of the fibrous carbon can be calculated by observing and photographing the fibrous carbon with a transmission electron microscope, randomly selecting 300 pieces of fibrous carbon from the photograph, and measuring the outer diameter of each piece. In this specification, "the average fiber diameters are different" means that there is a difference of 2 nm or more between the average fiber diameters of the two, and the difference is preferably 3 to 30 nm, and more preferably 3 to 6 nm.

[0111] The average fiber diameter of the first fibrous carbon is preferably 2 nm or more, more preferably 3 nm or more. It is also preferably 8 nm or less, more preferably 7 nm or less. The average fiber diameter of the second fibrous carbon is preferably 10 nm or more. It is also preferably 100 nm or less, more preferably 50 nm or less. Within the above range, the composite can be more uniformly combined, and the battery characteristics are also improved.

[0112] In the present invention, the content ratio of the at least two types of fibrous carbon having different average fiber diameters is preferably such that the first fibrous carbon accounts for 5 to 90% by weight, more preferably 10 to 60% by weight, and even more preferably 20 to 50% by weight, of the total content of the fibrous carbon.

[0113] It is also preferred that the fibrous carbon contained in the electrode composite of the present invention is partly in a crushed form and adheres to the surface of the active material, and partly in an aggregate form.

[0114] In the second embodiment, the particle diameter of the fibrous carbon aggregate can be measured from the length of the major axis of the fibrous carbon aggregate from an observation image taken at a magnification of 5,000 to 50,000 times using a scanning electron microscope (SEM) or a scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX), and the average value of the particle diameters of 10 fibrous carbon aggregates was taken as the average particle diameter of the aggregate.

[0115] In the second embodiment, the aggregate of fibrous carbon refers to one having an average particle size of 0.1 to 100 μm, preferably 0.2 μm to 50 μm, more preferably 0.2 μm to 10 μm, even more preferably 0.2 μm to 5 μm, and still more preferably 0.2 μm to 3 μm. If there are aggregates of fibrous carbon having an average particle size exceeding 100 μm, it may be difficult to form a uniform composite.

[0116] In the second embodiment, the other configuration of the secondary battery electrode composite is the same as that of the first embodiment described above, and therefore description thereof will be omitted.

[0117] A second embodiment can provide a secondary battery electrode including the above-described secondary battery electrode composite, a secondary battery including this secondary battery electrode, and a vehicle or device including this secondary battery. The second embodiment can provide a method for producing the above-described secondary battery electrode composite, the method comprising the steps of combining a fibrous carbon dispersion and an electrode active material using a dry mixer, and removing the solvent and drying. The second embodiment can provide a method for producing a secondary battery electrode composite including an electrode active material and fibrous carbon, the method using, as the fibrous carbon materials, a first fibrous carbon having an average fiber diameter of 1 nm or more and less than 9 nm and a second fibrous carbon having an average fiber diameter of 9 nm or more and 150 nm or less.

[0118] In the second embodiment, other configurations of the secondary battery electrode, the secondary battery, the vehicle or device, and the method for manufacturing a composite for a secondary battery electrode are common to those of the first embodiment described above, and therefore description thereof will be omitted.

[0119] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples as long as it does not depart from the gist of the invention. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0120] [Experimental Example A] <Production of Dispersant> (Synthesis Example 1 Production of H-NBR) 32 parts of acrylonitrile, 68 parts of 1,3-butadiene, 3 parts of potassium soap oleate, 0.3 parts of azobisisobutyronitrile, 0.48 parts of t-dodecyl mercaptan, and 200 parts of ion-exchanged water were added to a stainless steel polymerization reactor. Under a nitrogen atmosphere, polymerization was carried out at 45°C for 20 hours with stirring, and the polymerization was terminated at a conversion rate of 90%. Unreacted monomers were removed by vacuum stripping, yielding an acrylonitrile-conjugated diene rubber latex with a solids concentration of approximately 30%. Subsequently, ion-exchanged water was added to the latex to adjust the total solids concentration to 12%, and the mixture was placed in a 1 L autoclave equipped with a stirrer. Dissolved oxygen in the contents was removed by flowing nitrogen gas for 10 minutes. A catalyst solution prepared by dissolving 75 mg of palladium acetate as a hydrogenation catalyst in 180 mL of ion-exchanged water containing 4 times the molar amount of nitric acid relative to the palladium was added to an autoclave. The autoclave was purged twice with hydrogen gas, and then the contents of the autoclave were heated to 50°C while pressurized with hydrogen gas to 3 MPa, and a hydrogenation reaction was carried out for 6 hours. The contents were then returned to room temperature, a nitrogen atmosphere was created inside the autoclave, and the solids were dried to obtain a dispersant (H-NBR). The Mooney viscosity (ML1+4, 100°C) of the H-NBR (measured using an L-shaped rotor at 100°C in accordance with Japanese Industrial Standard JIS K6300-1) was 44. The hydrogenation rate (calculated from infrared spectroscopic analysis using total reflectance measurement) was 0.7%. The acrylonitrile-derived structural units determined from the 1H-NMR quantitative spectrum were 32%.

[0121] Synthesis Example 2: Production of Polyacrylonitrile PAN A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 100 parts of acetonitrile and purged with nitrogen gas. The reaction vessel was heated to 70°C, and a mixture of 90.0 parts of acrylonitrile, 10.0 parts of hydroxyethyl acrylate, and 5.0 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (NOF Corporation; V-65) was added dropwise over 3 hours to carry out a polymerization reaction. After completion of the dropwise addition, the reaction was continued for another hour at 70°C, followed by the addition of 0.5 parts of Perbutyl O, and the reaction was continued for another hour at 70°C. Thereafter, measurement of the nonvolatile content confirmed that the conversion rate exceeded 98%, and the dispersion medium was completely removed by vacuum concentration to obtain a dispersant (polyacrylonitrile). The weight average molecular weight (Mw) of the polyacrylonitrile was 15,000.

[0122] In the examples and comparative examples, the following carbon fibers were used: BT1001M: LUCAN BT1001M (manufactured by LG Chem Ltd., multi-walled CNT, fiber diameter 10 nm) 100T: K-Nanos-100T (manufactured by Kumho Petrochemical Co., Ltd., multi-walled CNT, fiber diameter 13.7 nm) 8S: JENOTUBE8S (manufactured by JEIO, multi-walled CNT, fiber diameter 6.8 nm)

[0123] In the examples and comparative examples, the following active materials were used: NMC532: S740 (LiNi ０．５ Mn ０．３ Co ０．２ O ２ , manufactured by RONBAY) SiO ｘ : (SILICONMONOOXIDE, SiO 1.3C 5 μm, manufactured by Osaka Titanium Technology Co., Ltd.)

[0124] <Preparation of Fibrous Carbon Dispersion> (Production Example 1) A fibrous carbon dispersion was prepared as follows according to the materials and composition shown in Table 1. First, NMP was placed in a stainless steel container and heated to 50°C. A dispersant was added while stirring with a disperser, and then the mixture was stirred for 1 hour to dissolve the dispersant. Next, fibrous carbon was added while stirring with a disperser, and a square-hole high-shear screen was attached to a high-shear mixer (L5M-A, manufactured by SILVERSON). Batch dispersion was performed at a speed of 8,000 rpm until the entire mixture became uniform and the dispersion particle size measured using a grind gauge with a maximum groove depth of 300 μm was 250 μm or less. At this time, the dispersion particle size confirmed by the grind gauge was 220 μm. Next, the dispersion liquid was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and a circulation dispersion process was performed. The dispersion treatment was carried out using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. The dispersion was continued until the viscosity of the dispersion liquid measured at 60 rpm with a Brookfield viscometer (manufactured by TOKISANGYO, VISCOMETER, MODEL: BL) reached 3,000 mPa s or less, and then the dispersion was subjected to 50 passes with a high-pressure homogenizer to obtain a fibrous carbon dispersion 1.

[0125] (Production Examples 2 to 4) Fibrous carbon dispersions 2 to 4 were obtained in the same manner as in Production Example 1, except that the materials and compositions were changed according to Table 1.

[0126]

[0127] The dispersants and additives listed in Table 1 are as follows: CMC1: Carboxymethyl cellulose (Sunrose APP-84 manufactured by Nippon Paper Industries Co., Ltd.) NaOH: Sodium hydroxide (Tokyo Chemical Industry Co., Ltd., purity >98.0%, granular) PVA: Polyvinyl alcohol (Poval 203 manufactured by Kuraray Co., Ltd.) PVP: Polyvinylpyrrolidone (K-30 manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0128] (Production Examples 5 to 7) According to the compositions shown in Table 1, fibrous carbon, a dispersant, additives, and a dispersion medium were charged into a glass bottle, and after thoroughly mixing and dissolving or blending, the mixture was dispersed in a paint conditioner for 3 hours using 1.25 mmφ zirconia beads as a medium to obtain each fibrous carbon dispersion.

[0129] <Electrode composite for secondary battery> (Example 1-1) A mixture was prepared by stirring NMC and fibrous carbon dispersion 1 for 60 minutes at a rotation speed of 30 rpm using a planetary mixer according to the composition shown in Table 2. Thereafter, the mixture was dried at 120°C for 2 hours using a hot air oven, thereby obtaining composite 1.

[0130] Example 1-2 Composite 2 was obtained in the same manner as in Example 1-1, except that the rotation speed of the planetary mixer was changed to 50 rpm, according to the composition shown in Table 2.

[0131] (Examples 1-3) According to the composition shown in Table 2, NMC and fibrous carbon dispersion 1 were stirred for 60 minutes using a planetary mixer at a rotation speed of 30 rpm to prepare a mixture, and then, while running 80°C hot water through the jacket of the stirring vessel of the planetary mixer, the inside of the vessel was vacuum-dried for 1 hour to obtain composite 3.

[0132] (Examples 1-4) A mixture of NMC and fibrous carbon dispersion 1 was prepared by stirring at a rotation speed of 3000 rpm for 10 minutes using a high-shear composite machine Mechanofusion manufactured by Hosokawa Micron Corporation according to the composition shown in Table 2. Thereafter, the mixture was dried at 120°C for 2 hours using a hot air oven, thereby obtaining composite 4.

[0133] (Examples 1 to 5) A mixture of NMC and fibrous carbon dispersion 1 was prepared by stirring at a rotation speed of 50 rpm for 15 minutes using a Trimix manufactured by Inoue Seisakusho Co., Ltd., according to the composition shown in Table 2. Thereafter, the mixture was dried at 120°C for 2 hours using a hot air oven, thereby obtaining composite 5.

[0134] (Examples 1-6 to 10) Mixtures were prepared by stirring NMC and fibrous carbon dispersions 2, 3, and 5 to 7 for 60 minutes using a planetary mixer at a rotation speed of 30 rpm according to the compositions shown in Table 2. Then, the mixtures were dried in an oven at 120°C for 2 hours to obtain composites 6 to 10.

[0135] (Examples 1 to 12) SiO was mixed using a planetary mixer according to the composition shown in Table 2. ｘ The mixture was stirred at 50 rpm for 30 minutes and then dried in an oven at 110° C. for 2 hours to obtain composites 11 and 12.

[0136] (Examples 1-13) A mixture was prepared by stirring NMC, fibrous carbon dispersion 1, and an 11% binder solution (polyvinylidene fluoride resin: W#7200) previously dissolved in NMP using a planetary mixer at a rotation speed of 60 rpm for 90 minutes according to the composition shown in Table 2. Thereafter, the mixture was dried for 2 hours under reduced pressure using a vacuum pump while maintaining the temperature inside the container at 80°C using a hot water chiller, thereby obtaining composite 13.

[0137] (Examples 1-14) According to the composition shown in Table 2, a mixture was prepared by stirring NMC, fibrous carbon dispersion 1, and an 11% binder solution (polyvinylidene fluoride resin: W#7200) previously dissolved in NMP for 90 minutes using a high-speed mixer at an agitator rotation speed of 500 rpm and a chopper rotation speed of 1500 rpm. Thereafter, while maintaining the temperature inside the container at 80°C with a hot water chiller, the pressure was reduced with a vacuum pump and the mixture was dried for 2 hours, thereby obtaining composite 14.

[0138] Comparative Example 1-1 According to the composition shown in Table 2, NMC and fibrous carbon BT1001 were stirred for 10 minutes at 1000 rpm using a high-shear composite machine Mechanofusion manufactured by Hosokawa Micron Corporation, to obtain composite 15.

[0139] (Comparative Example 1-2) According to the composition shown in Table 2, NMC and fibrous carbon dispersion 1 were weighed out into a container and stirred with a medicine spoon for 5 minutes to prepare a mixture, which was then dried at 120°C for 2 hours using a hot air oven to obtain composite 16.

[0140] (Comparative Examples 1-3) According to the composition shown in Table 2, fibrous carbon dispersion 1 and a solvent (NMP) were weighed into a stainless steel container, and NMC was added while stirring at 1000 rpm using a homogenizer MARK II 2.5 manufactured by Primix Corporation, followed by stirring for 60 minutes to obtain a slurry. Using this slurry, a composite for a secondary battery electrode was produced using a spray dryer Mini Spray Dryer B-290 manufactured by Nippon Buchi Co., Ltd. The slurry was spray-dried at 220°C under closed system conditions (nitrogen atmosphere) using an inert loop B-295, to obtain composite 17.

[0141] (Comparative Examples 1-4) According to the composition shown in Table 2, SiO ｘ and fibrous carbon BT1001 were stirred for 10 minutes at 1000 rpm using a high shear compound machine Mechanofusion manufactured by Hosokawa Micron Corporation, to obtain Composite 18.

[0142] (Comparative Examples 1-5) According to the composition shown in Table 2, fibrous carbon dispersion 4 and water were weighed out and placed in a stainless steel container, and SiO ｘ After adding the above, the mixture was stirred for 45 minutes to obtain a slurry, which was then spray-dried at 120°C using a Mini Spray Dryer B-290 manufactured by Nippon Buchi Co., Ltd., to obtain Composite 19.

[0143] <Evaluation of the state of fibrous carbon in the composite> The dispersion state of fibrous carbon in the composite was evaluated using a JEOL JSM-7800F scanning electron microscope. - Evaluation criteria for fibrous carbon aggregates [Average particle size of aggregates] ◎: Fibrous carbon aggregates are included, and the average particle size is 0.2 μm or more and 3 μm or less. ○: Fibrous carbon aggregates are included, and the average particle size is less than 0.2 μm or more than 3 μm. ×: Fibrous carbon aggregates are not included. [Average number of aggregates] ◎: Fibrous carbon aggregates are included, and the average number of fibrous carbon aggregates measured from 10 observation images at a magnification of 5,000 times is 2 or more. ○: Fibrous carbon aggregates are included, and the average number of fibrous carbon aggregates measured from 10 observation images at a magnification of 5,000 times is 0.5 or more and less than 2. ×: No aggregates of fibrous carbon are contained. Criteria for determining the state of disintegration of fibrous carbon on the surface of the active material. ◎: The area occupied by fibrous carbon adsorbed on the active material in a state where the fibers are disintegrated is 50% or more of the entire surface of the active material. ○: The area occupied by fibrous carbon adsorbed on the active material in a state where the fibers are disintegrated is 10% or more and less than 50% of the entire surface of the active material. ×: The area occupied by fibrous carbon adsorbed on the active material in a state where the fibers are disintegrated is not adsorbed on the active material.

[0144] <Exothermic Peak Temperature of Fibrous Carbon> The exothermic peak temperature of the fibrous carbon was evaluated using a differential thermobalance Thermoplus EV02TG8121 manufactured by Rigaku Corporation. Compressed air was flowed at 200 mL / min, and the exothermic peak temperature obtained when the temperature was increased from 40°C to 800°C at 10°C / min was used as an index. The exothermic peak temperature was calculated by reading the rise of the exothermic peak of the fibrous carbon in the range of 400 to 700°C in the DTA curve obtained by measurement.

[0145] <Powder Resistivity of Composite> The powder resistivity of the composite was evaluated using a powder resistivity measurement system MCP-PD600 manufactured by Nitto Seiko Analytech Co., Ltd. Measurement was performed using a four-point probe method with a low-resistivity powder probe, and the volume resistivity when a load of 20 kN was applied to each sample was used as an index.

[0146]

[0147] <Preparation of positive electrode mixture slurry and positive electrode film> Capacity 150 cm ３ 14.2 parts of an 8% binder solution (polyvinylidene fluoride resin: W#7200) previously dissolved in NMP and 11.1 parts of a solvent (NMP) were weighed into a plastic container, and then 74.7 parts of electrode composite 1 was added, followed by stirring at 2,000 rpm for 150 seconds using a planetary centrifugal mixer (Thinky's Awatori Rentaro, ARE-310) to obtain composite slurry 1. The nonvolatile content of composite slurry 1 was 76 mass%.

[0148] Composites 2 to 10 and 15 to 17 were treated in the same manner as composite slurry 1 to obtain composite slurries 2 to 10 and 15 to 17.

[0149] Capacity 150cm ３ 7.0 parts of an 8% binder solution (polyvinylidene fluoride resin: W#7200) previously dissolved in NMP and 18.5 parts of a solvent (NMP) were weighed into a plastic container, and then 74.5 parts of electrode composite 1 were added, followed by stirring at 2,000 rpm for 150 seconds using a planetary centrifugal mixer (Thinky's Awatori Rentaro, ARE-310) to obtain composite slurry 13. The nonvolatile content of composite slurry 13 was 75% by mass.

[0150] The composite 14 was prepared in the same manner as the composite slurry 13 to obtain a composite slurry 14.

[0151] The composite slurries 1 to 10 and 13 to 17 were applied to aluminum foil with a thickness of 20 μm using an applicator, and then dried in an electric oven at 120°C ± 5°C for 25 minutes to produce electrode films. The electrode films were then rolled using a roll press (Thank Metal, 3-ton hydraulic roll press) to obtain electrode films 1 to 10 and 13 to 17. The weight per unit area of ​​the composite layer was 20 mg / cm. ２ The density of the composite layer after rolling was 3.2 g / cm ３ It was.

[0152] <Preparation of negative electrode composite slurry and negative electrode film> 12.50 parts by mass of an aqueous solution containing 2% by mass of carboxymethyl cellulose sodium (manufactured by Daicel FineChem Co., Ltd., #1190) and 2.34 parts by mass of ion-exchanged water were weighed into a plastic container. Then, using a rotation / revolution mixer (Thinky Corporation, Awatori Rentaro, ARE-310), the mixture was stirred at 2000 rpm for 1 minute. Then, 2.44 parts by mass of electrode composite 11 was added, and the mixture was stirred at 2000 rpm for 5 minutes using the same rotation / revolution mixer. Furthermore, 21.93 parts by mass of natural graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGB-20) was added, and the mixture was stirred at 2000 rpm for 5 minutes using the same rotation / revolution mixer. Thereafter, 0.78 parts by mass of an aqueous solution in which 48% by mass of styrene-butadiene emulsion was dispersed was added, and the mixture was stirred at 2000 rpm for 30 seconds using a planetary centrifugal mixer (Thinky Corporation's Awatori Rentaro, ARE-310) to obtain composite slurry 11. The nonvolatile content of the composite slurry was 48% by mass.

[0153] Composites 12, 18, and 19 were used to obtain composite slurries 12, 18, and 19 in the same manner as composite slurry 11.

[0154] The composite slurries 11, 12, 18, and 19 were applied to copper foil with a thickness of 18 μm using an applicator, and then dried in an electric oven at 120°C ± 5°C for 25 minutes to produce electrode films. The electrode films were then rolled using a roll press (Thank Metal, 3-ton hydraulic roll press) to obtain electrode films 11, 12, 18, and 19. The weight per unit area of ​​the composite layer was 8 mg / cm. ２ The density of the composite layer after rolling was 1.6 g / cm ３ It was.

[0155] (Resistance of electrode film for positive electrode) The volume resistivities of electrode films 1 to 10 and 13 to 17 were measured by a four-probe method using a Loresta GP (manufactured by Nitto Seiko Analytech Co., Ltd.) in accordance with JIS-K7194. Note that for the resistance measurement, a measurement electrode was used in which the coating substrate used in the preparation of each electrode was changed from aluminum foil to a PET substrate. A relative value (%) was determined based on the volume resistivity of the electrode film of Comparative Example 1-3, and evaluated according to the following criteria. Electrode resistance characteristic evaluation criteria ◎: 200% or more (very excellent) ○: 150% or more and less than 200% (excellent) ○△: 100% or more and less than 150% (good) △: 50% or more and less than 100% (poor) ×: Less than 50% (very poor)

[0156] (Resistance of electrode film for negative electrode) The volume resistivity of the electrode films 11, 12, 18, and 19 was measured by a four-probe method using a Loresta GP (manufactured by Nitto Seiko Analytech Co., Ltd.) in accordance with JIS-K7194. Note that for the resistance measurement, a measurement electrode was used in which the coating substrate used in the preparation of each electrode was changed from copper foil to a PET substrate. A relative value (%) was determined based on the volume resistivity of the electrode film of Comparative Example 1-5, and evaluated according to the following criteria. Electrode resistance characteristic criteria ○: 130% or more (excellent) ○△: 100% or more and less than 130% (good) ×: Less than 100% (poor)

[0157] <Assembly of a cell for evaluating the positive electrode of a lithium-ion secondary battery> The previously prepared electrode films 1 to 10 and 13 to 17 were punched out to a diameter of 16 mm to form a working electrode, and a metallic lithium foil (thickness: 0.15 mm) was used as a 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 prepared by dissolving LiPF6 at a concentration of 1 M in a mixed solvent of ethylene carbonate and diethyl carbonate in 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 purged with argon gas.

[0158] <Evaluation of Rate Characteristics of Lithium-Ion Secondary Battery Positive Electrode> The prepared lithium-ion secondary battery positive electrode evaluation cell was placed in a thermostatic chamber at 25°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Corporation). Constant-current, constant-voltage charging (cutoff current: 0.02C current) was performed at a charge rate of 0.2C with a charge cut-off voltage of 4.2V, followed by constant-current discharging at a discharge rate of 0.2C with a discharge cut-off voltage of 2.5V. This operation was repeated three times, followed by constant-current, constant-voltage charging (cut-off current: 0.02C current) at a charge rate of 0.2C with a charge cut-off voltage of 4.2V, followed by constant-current discharging at a discharge rate of 3C with a discharge cut-off voltage of 2.5V. 1C was defined as the current value required to charge or discharge the theoretical capacity of the positive electrode in one hour. The rate characteristics can be expressed by the ratio of the 0.2C discharge capacity to the 3C discharge capacity, as shown in Equation 1 below. (Formula 1) Rate characteristic = 3C discharge capacity / 0.2C discharge capacity × 100 (%) Relative values ​​(%) based on the rate characteristic of Comparative Examples 1-3 were determined and evaluated according to the following criteria. Rate characteristic evaluation criteria ◎: 150% or more (very good) ○: 130% or more and less than 150% (excellent) ○△: 100% or more and less than 130% (good) ×: Less than 100% (poor)

[0159] <Evaluation of Cycle Characteristics of Lithium-Ion Secondary Battery Positive Electrode> The prepared lithium-ion secondary battery positive electrode evaluation cell was placed in a thermostatic chamber at 25°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Corporation). Constant-current, constant-voltage charging (cutoff current: 0.02C) was performed at a charge rate of 0.2C with a charge cutoff voltage of 4.2V, followed by constant-current discharging at a discharge rate of 0.2C with a discharge cutoff voltage of 2.5V. This procedure was repeated 200 times. 1C was defined as the current value required to charge or discharge the theoretical capacity of the positive electrode in 1 hour. The cycle characteristics can be expressed as the ratio of the 3rd 0.2C discharge capacity to the 200th 0.2C discharge capacity, as shown in Equation 2: (Equation 2) Cycle Characteristics = 200th 0.2C Discharge Capacity / 3rd 0.2C Discharge Capacity × 100 (%). The relative values ​​(%) based on the cycle characteristics of Comparative Examples 1-3 were calculated and evaluated according to the following criteria. Cycle characteristic evaluation criteria ◎: 180% or more (very good) ○: 150% or more and less than 180% (excellent) 〇△: 100% or more and less than 150% (good) ×: Less than 100% (poor)

[0160] <Assembly of a cell for evaluating a negative electrode of a lithium ion secondary battery> The previously prepared electrode films 11, 12, 18, and 19 were punched out to a diameter of 16 mm to serve as working electrodes, and a metallic lithium foil (thickness: 0.15 mm) was used as a counter electrode. A separator (porous polypropylene film) was inserted and laminated between the working electrode and the counter electrode. An electrolyte solution (a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 3:5:2) was prepared, and 1 part by mass of each of VC (vinylene carbonate) and FEC (fluoroethylene carbonate) was added as additives to 100 parts by mass of the mixed solvent, and then LiPF ６ A two-electrode sealed metal cell (HS Flat Cell manufactured by Hosen Co., Ltd.) was assembled by filling the cell with a non-aqueous electrolyte prepared by dissolving 1M of ammonium hydroxide in the electrolyte. The cell was assembled in a glove box purged with argon gas.

[0161] <Evaluation of Rate Characteristics of Lithium-Ion Secondary Battery Negative Electrode> The prepared lithium-ion secondary battery negative electrode evaluation cell was placed in a thermostatic chamber at 25°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Corporation). Constant-current, constant-voltage charging (cutoff current: 0.02C current) was performed at a charge rate of 0.2C with a charge cut-off voltage of 0.05V, followed by constant-current discharging at a discharge rate of 0.2C with a discharge cut-off voltage of 1.5V. This operation was repeated three times, followed by constant-current, constant-voltage charging (cut-off current: 0.02C current) at a charge rate of 0.2C with a charge cut-off voltage of 0.05V, followed by constant-current discharging at a discharge rate of 3C with a discharge cut-off voltage of 1.5V. 1C was defined as the current value required to charge or discharge the theoretical capacity of the negative electrode in one hour. The rate characteristics can be expressed by the ratio of the 0.2C discharge capacity to the 3C discharge capacity, as shown in Equation 2 below. (Formula 2) Rate characteristic = 3C discharge capacity / third 0.2C discharge capacity × 100 (%) Relative values ​​(%) based on the rate characteristic of Comparative Examples 1-5 were determined and evaluated according to the following criteria: ◎: 150% or more (very good) ○: 100% or more and less than 150% (good) ×: Less than 100% (poor)

[0162] <Evaluation of Cycle Characteristics of Lithium-Ion Secondary Battery Negative Electrode> The prepared lithium-ion secondary battery negative electrode evaluation cell was placed in a thermostatic chamber at 25°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Corporation). Constant-current, constant-voltage charging (cutoff current: 0.02C current) was performed at a charge rate of 0.2C with a charge cutoff voltage of 0.05V, followed by constant-current discharging at a discharge rate of 0.2C with a discharge cutoff voltage of 1.5V. This procedure was repeated 20 times. 1C was the current value required to charge or discharge the theoretical capacity of the negative electrode in 1 hour. The cycle characteristics can be expressed as the ratio of the third 0.2C discharge capacity to the 20th 0.2C discharge capacity, as shown in Equation 1 below: (Equation 1) Cycle Characteristics = 20th 0.2C Discharge Capacity / Third 0.2C Discharge Capacity × 100 (%). The relative values ​​(%) based on the cycle characteristics of Comparative Examples 1-5 were calculated and evaluated according to the following criteria. ◎: 150% or more (very good) ○: 100% or more but less than 150% (good) ×: Less than 100% (poor)

[0163] As shown in Table 3, the Examples showed superior battery characteristics compared to the Comparative Examples. This is presumably because, as in the examples shown in Figures 1 and 2, the fibrous carbon in the composite was in an appropriate state, allowing for uniform formation of conductive paths within the electrode, reducing electrode resistance and ensuring that the active material in the electrode was used evenly and uniformly in the charge / discharge reaction, leading to improved rate characteristics and cycle characteristics. From the above, it was demonstrated that electrode composites within the scope of the present invention can exhibit excellent battery characteristics.

[0164] [Experimental Example B]

[0165] <Production of Dispersant>

[0166] Synthesis Example B1: Production of Polyacrylonitrile PAN. A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 100 parts of acetonitrile and purged with nitrogen gas. The reaction vessel was heated to 70°C, and a mixture of 90.0 parts of acrylonitrile, 10.0 parts of hydroxyethyl acrylate, and 5.0 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (NOF Corporation; V-65) was added dropwise over 3 hours to carry out a polymerization reaction. After completion of the dropwise addition, the reaction was continued for another hour at 70°C, followed by the addition of 0.5 parts of Perbutyl O, and the reaction was continued for another hour at 70°C. Thereafter, measurement of the nonvolatile content confirmed that the conversion rate exceeded 98%, and the mixture was concentrated under reduced pressure to completely remove the dispersant, yielding a dispersant (polyacrylonitrile). The weight-average molecular weight (Mw) of the polyacrylonitrile was 15,000.

[0167] In the examples and comparative examples, the following fibrous carbons were used. (First fibrous carbon) 6A: JENOTUBE6A (manufactured by JEIO, multi-walled CNT, fiber diameter 5 nm) 8S: JENOTUBE8S (manufactured by JEIO, multi-walled CNT, fiber diameter 7 nm) (Second fibrous carbon) 10B: JENOTUBE10B (manufactured by JEIO, multi-walled CNT, fiber diameter 10 nm) 100T: K-Nanos-100T (manufactured by KUMHO PETROCHEMICAL, multi-walled CNT, fiber diameter 14 nm) Multi-walled CNT: (manufactured by Fujifilm Wako Co., Ltd., multi-walled CNT, fiber diameter 30 nm)

[0168] In the examples and comparative examples, the following active materials were used: NMC532: S740 (LiNi ０．５ Mn ０．３ Co ０．２ O ２ , manufactured by RONBAY) SiO ｘ : (SILICONMONOOXIDE, SiO 1.3C 5 μm, manufactured by Osaka Titanium Technology Co., Ltd.)

[0169] <Preparation of Fibrous Carbon Dispersion> (Production Example B1) A fibrous carbon dispersion was prepared as follows according to the materials and composition shown in Table B1. First, NMP was placed in a stainless steel container and heated to 50°C. A dispersant was added while stirring with a disperser, and then the mixture was stirred for 1 hour to dissolve the dispersant. Next, fibrous carbon was added while stirring with a disperser, and a square-hole high-shear screen was attached to a high-shear mixer (L5M-A, manufactured by SILVERSON). Batch dispersion was performed at a speed of 8,000 rpm until the entire mixture became uniform and the dispersion particle size was 250 μm or less as measured by a grind gauge with a maximum groove depth of 300 μm. At this time, the dispersion particle size confirmed by the grind gauge was 220 μm. Next, 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 circulation dispersion process was performed. The dispersion treatment was carried out using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. The dispersion was continued until the viscosity of the dispersion liquid measured at 60 rpm with a Brookfield viscometer (manufactured by TOKISANGYO, VISCOMETER, MODEL: BL) reached 3,000 mPa s or less, and then the dispersion was subjected to 25 passes with a high-pressure homogenizer to obtain a fibrous carbon dispersion 1.

[0170] (Production Examples B2 to B5) Fibrous carbon dispersions 2 to 5 were obtained in the same manner as in Production Example B1, except that the materials and compositions were changed according to Table B1.

[0171] (Production Examples B6 and B7) 93.96 parts by mass of ion-exchanged water was added to a stainless steel container, and while stirring with a disperser, 1 part by mass of the PAN prepared in Synthesis Example B1 and 0.04 parts of NaOH were added and dissolved. Thereafter, 2.0 parts by mass of 100T (fibrous carbon) was taken and added while stirring with a disperser. A high-shear mixer (L5M-A, manufactured by SILVERSON) equipped with a square-hole high-shear screen was used, and batch dispersion was carried out at a speed of 8,600 rpm until the entire mixture became uniform and the dispersion particle size measured using a grind gauge reached 250 μm or less. At this time, the dispersion particle size measured using a grind gauge was 180 μm. Next, the dispersion liquid was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and a circulation dispersion process was carried out. The dispersion process was carried out using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. The viscosity of the dispersion liquid measured with a B-type viscometer (TOKISANGYO, VISCOMETER, MODEL: BL) at 60 rpm was dispersed until it was 3,000 mPa s or less, and then 0.5 parts by mass of 100T was further added to the stainless steel container while stirring with a disperser, and a circulation dispersion treatment was again carried out with a high-pressure homogenizer. After circulation dispersion with a high-pressure homogenizer until the viscosity was 3,000 mPa s or less, the work of adding 100T to the stainless steel container while stirring with a disperser was repeated a total of 6 times (the total amount of 100T added was 5.0 parts by mass). Subsequently, a 10-pass dispersion treatment was carried out with a high-pressure homogenizer, and a fibrous carbon dispersion 6 containing 5.0 parts by mass of fibrous carbon was obtained.

[0172] A fibrous carbon dispersion 7 was obtained in the same manner as in Production Example B6, except that the materials and composition were changed according to Table B1.

[0173]

[0174] The dispersants and additives listed in Table B1 are as follows: HNBR: Therban® 3406 (manufactured by LANXESS, hydrogenated acrylonitrile-butadiene rubber, acrylonitrile content 34%) NaOH: sodium hydroxide (manufactured by Tokyo Chemical Industry Co., Ltd., purity >98.0%, granular)

[0175] <Secondary battery electrode composite> (Example B1-1) According to the composition shown in Table B2, NMC, fibrous carbon dispersion 1, and fibrous carbon dispersion 3 were stirred for 45 minutes using a planetary mixer at a rotation speed of 50 rpm to prepare a mixture. Thereafter, the mixture was dried at 120°C for 2 hours using a hot air oven to obtain composite 1.

[0176] Examples B1-2 to B1-7 Composites 2 to 7 were obtained in the same manner as in Example B1-1 according to the compositions shown in Table B2.

[0177] (Examples B1-8) According to the compositions shown in Table B2, fibrous carbon dispersion 2, fibrous carbon dispersion 4, and solvent (NMP) were weighed into a stainless steel container, and NMC was added while stirring at 1000 rpm using a homogenizer MARKII 2.5 manufactured by Primix Corporation, followed by stirring for 60 minutes to obtain a slurry. Using this slurry, a composite for a secondary battery electrode was produced using a spray dryer Mini Spray Dryer B-290 manufactured by Nippon Buchi Co., Ltd. The slurry was spray-dried at 220°C under closed system conditions (nitrogen atmosphere) using an inert loop B-295, to obtain composite 8.

[0178] (Examples B1-9) SiO was mixed using a planetary mixer according to the composition shown in Table B2. ｘ The fibrous carbon dispersion 6 and the fibrous carbon dispersion 7 were stirred at a rotation speed of 50 rpm for 30 minutes to prepare a mixture, which was then dried in an oven at 110°C for 2 hours to obtain a composite 9.

[0179] (Example B1-10) According to the composition shown in Table B2, fibrous carbon dispersion 6, fibrous carbon dispersion 7, and water were weighed and placed in a stainless steel container, and SiO ｘ After adding the above, the mixture was stirred for 45 minutes to obtain a slurry. The slurry was spray-dried at 120°C using a spray dryer, Mini Spray Dryer B-290, manufactured by Nippon Buchi Co., Ltd., to obtain Composite 10.

[0180] Comparative Examples B1-1 and B1-2 Composites 11 and 12 were obtained in the same manner as in Example B1-8 according to the compositions shown in Table B2.

[0181] Comparative Examples B1-3 and B1-4 Composites 13 and 14 were obtained in the same manner as in Comparative Example B1-10 according to the compositions shown in Table B2.

[0182] <Evaluation of the state of fibrous carbon in composite> The dispersion state of fibrous carbon in the composite was evaluated using a scanning electron microscope JSM-7800F manufactured by JEOL Ltd. - Evaluation criteria for aggregates of fibrous carbon [Average particle size of aggregates] ◎: Aggregates of fibrous carbon are included, and the average particle size is 0.2 μm or more and 3 μm or less. ○: Aggregates of fibrous carbon are included, and the average particle size is less than 0.2 μm or more than 3 μm. ×: Aggregates of fibrous carbon are not included. [Average number of aggregates] ◎: Aggregates of fibrous carbon are included, and the number of aggregates of fibrous carbon measured from 10 observation images at a magnification of 5,000 times is 2 or more on average. ○: Aggregates of fibrous carbon are included, and the number of aggregates of fibrous carbon measured from 10 observation images at a magnification of 5,000 times is 0.5 or more and less than 2 on average. ×: Aggregates of fibrous carbon are not included.

[0183] Criteria for determining the crushed state of fibrous carbon on the surface of an active material: ◎: The area occupied by fibrous carbon adsorbed on the active material in a crushed fiber state is 50% or more of the entire surface of the active material. ○: The area occupied by fibrous carbon adsorbed on the active material in a crushed fiber state is 10% or more and less than 50% of the entire surface of the active material. ×: The area occupied by fibrous carbon adsorbed on the active material in a crushed fiber state is not adsorbed on the active material.

[0184]

[0185] <Preparation of positive electrode mixture slurry and positive electrode film> Capacity 150 cm ３ 14.2 parts of an 8% binder solution (polyvinylidene fluoride resin: W#7200) previously dissolved in NMP and 11.1 parts of a solvent (NMP) were weighed into a plastic container, and then 74.7 parts of electrode composite 1 was added, followed by stirring at 2,000 rpm for 150 seconds using a planetary centrifugal mixer (Thinky's Awatori Rentaro, ARE-310) to obtain composite slurry 1. The nonvolatile content of composite slurry 1 was 76 mass%.

[0186] Composites 2 to 8, 11, and 12 were treated in the same manner as composite slurry 1 to obtain composite slurries 2 to 8, 11, and 12.

[0187] The composite slurries 1 to 8, 11, and 12 were applied to aluminum foil with a thickness of 20 μm using an applicator, and then dried in an electric oven at 120°C ± 5°C for 25 minutes to produce electrode films. The electrode films were then rolled using a roll press (Thank Metal, 3-ton hydraulic roll press) to obtain electrode films 1 to 8, 11, and 12. The weight per unit area of ​​the composite layer was 20 mg / cm. ２ The density of the composite layer after rolling was 3.2 g / cm ３ It was.

[0188] <Preparation of negative electrode composite slurry and negative electrode film> 12.50 parts by mass of an aqueous solution containing 2% by mass of carboxymethyl cellulose sodium (manufactured by Daicel FineChem Co., Ltd., #1190) and 2.34 parts by mass of ion-exchanged water 1 were weighed into a plastic container. Then, using a rotation / revolution mixer (Thinky Corporation, Awatori Rentaro, ARE-310), the mixture was stirred at 2000 rpm for 1 minute. Then, 2.44 parts by mass of electrode composite 9 was added, and the mixture was stirred at 2000 rpm for 5 minutes using the same rotation / revolution mixer. Furthermore, 21.93 parts by mass of natural graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGB-20) was added, and the mixture was stirred at 2000 rpm for 5 minutes using the same rotation / revolution mixer. Thereafter, 0.78 parts by mass of an aqueous solution in which 48% by mass of styrene-butadiene emulsion was dispersed was added, and the mixture was stirred at 2000 rpm for 30 seconds using a planetary centrifugal mixer (Thinky Corporation's Awatori Rentaro, ARE-310) to obtain composite slurry 9. The nonvolatile content of the composite slurry was 48% by mass.

[0189] Composites 10, 13 and 14 were used to obtain composite slurries 10, 13 and 14 in the same manner as for the composite slurries.

[0190] The composite slurries 9, 10, 13, and 14 were applied to copper foil with a thickness of 18 μm using an applicator, and then dried in an electric oven at 120°C ± 5°C for 25 minutes to produce electrode films. The electrode films were then rolled using a roll press (Thank Metal, 3-ton hydraulic roll press) to obtain electrode films 9, 10, 13, and 14. The weight per unit area of ​​the composite layer was 8 mg / cm. ２ The density of the composite layer after rolling was 1.6 g / cm ３ It was.

[0191] (Resistance of Positive Electrode Film) The volume resistivities of electrode films 1 to 8, 11, and 12 were measured by a four-probe method using a Loresta GP (manufactured by Nitto Seiko Analytech Co., Ltd.) in accordance with JIS-K7194. Note that for the resistance measurements, a measurement electrode was used in which the coating substrate used in the preparation of each electrode was changed from aluminum foil to a PET substrate. The relative value (%) based on the volume resistivity of the electrode film of Comparative Example B1-2 was determined and evaluated according to the following criteria. Electrode resistance characteristic evaluation criteria ◎: Less than 60% (excellent) ○: 60% or more but less than 100% (good) ×: 100% or more (poor)

[0192] (Resistance of negative electrode film) The volume resistivities of the electrode films 9, 10, 13, and 14 were measured by a four-probe method using a Loresta GP (manufactured by Nitto Seiko Analytech Co., Ltd.) in accordance with JIS-K7194. Note that for the resistance measurement, a measurement electrode was used in which the coating substrate used in the preparation of each electrode was changed from copper foil to a PET substrate. A relative value (%) was determined based on the volume resistivity of the electrode film of Comparative Example B1-4, and evaluated according to the following criteria. Electrode resistance characteristic criteria ◎: Less than 80% (excellent) ○: 80% or more but less than 100% (good) ×: 100% or more (poor)

[0193] <Assembly of a cell for evaluating the positive electrode of a lithium-ion secondary battery> The previously prepared electrode films 1 to 8, 11, and 12 were punched out to a diameter of 16 mm to serve as working electrodes, and a metallic lithium foil (thickness: 0.15 mm) was used as a 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 prepared by dissolving LiPF6 at a concentration of 1 M in a mixed solvent of ethylene carbonate and diethyl carbonate in 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 purged with argon gas.

[0194] <Evaluation of Rate Characteristics of Lithium-Ion Secondary Battery Positive Electrode> The prepared lithium-ion secondary battery positive electrode evaluation cell was placed in a thermostatic chamber at 25°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Corporation). Constant-current, constant-voltage charging (cutoff current: 0.02C current) was performed at a charge rate of 0.2C with a charge cut-off voltage of 4.2V, followed by constant-current discharging at a discharge rate of 0.2C with a discharge cut-off voltage of 2.5V. This operation was repeated three times, followed by constant-current, constant-voltage charging (cut-off current: 0.02C current) at a charge rate of 0.2C with a charge cut-off voltage of 4.2V, followed by constant-current discharging at a discharge rate of 3C with a discharge cut-off voltage of 2.5V. 1C was the current value required to charge or discharge the theoretical capacity of the positive electrode in one hour. The rate characteristics can be expressed by the ratio of the 0.2C discharge capacity to the 3C discharge capacity, as shown in Equation 1 below. (Formula 1) Rate characteristic = 3C discharge capacity / third 0.2C discharge capacity × 100 (%) Relative values ​​(%) based on the rate characteristic of Comparative Example B1-2 were calculated and evaluated according to the following criteria. Rate characteristic evaluation criteria ◎: 130% or more (excellent) ○: More than 100% and less than 130% (good) ×: 100% or less (poor)

[0195] <Evaluation of Cycle Characteristics of Lithium-Ion Secondary Battery Positive Electrode> The prepared lithium-ion secondary battery positive electrode evaluation cell was placed in a thermostatic chamber at 25°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Corporation). Constant-current, constant-voltage charging (cutoff current: 0.02C) was performed at a charge rate of 0.2C with a charge cutoff voltage of 4.2V, followed by constant-current discharging at a discharge rate of 0.2C with a discharge cutoff voltage of 2.5V. This procedure was repeated 100 times. 1C was the current value required to charge or discharge the theoretical capacity of the positive electrode in 1 hour. The cycle characteristics can be expressed as the ratio of the third 0.2C discharge capacity to the 100th 0.2C discharge capacity, as shown in Equation 2 below: (Equation 2) Cycle Characteristics = 100th 0.2C Discharge Capacity / Third 0.2C Discharge Capacity × 100 (%). The relative value (%) based on the cycle characteristics of Comparative Example B1-2 was calculated and evaluated according to the following criteria. Cycle characteristic evaluation criteria ◎: 150% or more (excellent) 〇: More than 100% but less than 150% (good) ×: 100% or less (poor)

[0196] <Assembly of a cell for evaluating a lithium-ion secondary battery negative electrode> The previously prepared electrode films 9, 10, 13, and 14 were punched out to a diameter of 16 mm to serve as working electrodes, and a metallic lithium foil (thickness: 0.15 mm) was used as a counter electrode. A separator (porous polypropylene film) was inserted between the working electrode and the counter electrode and laminated. An electrolyte solution (a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 3:5:2) was prepared, and 1 part by mass of each of VC (vinylene carbonate) and FEC (fluoroethylene carbonate) was added as additives to 100 parts by mass of the mixed solvent, and then LiPF ６ A two-electrode sealed metal cell (HS Flat Cell manufactured by Hosen Co., Ltd.) was assembled by filling the cell with a non-aqueous electrolyte prepared by dissolving 1M of ammonium hydroxide in the electrolyte. The cell was assembled in a glove box purged with argon gas.

[0197] <Evaluation of Rate Characteristics of Lithium-Ion Secondary Battery Negative Electrode> The prepared lithium-ion secondary battery negative electrode evaluation cell was placed in a thermostatic chamber at 25°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Corporation). Constant-current, constant-voltage charging (cutoff current: 0.02C current) was performed at a charge rate of 0.2C with a charge cut-off voltage of 0.05V, followed by constant-current discharging at a discharge rate of 0.2C with a discharge cut-off voltage of 1.5V. This operation was repeated three times, followed by constant-current, constant-voltage charging (cut-off current: 0.02C current) at a charge rate of 0.2C with a charge cut-off voltage of 0.05V, followed by constant-current discharging at a discharge rate of 3C with a discharge cut-off voltage of 1.5V. 1C was the current value required to charge or discharge the theoretical capacity of the negative electrode in 1 hour. The rate characteristics can be expressed by the ratio of the 0.2C discharge capacity to the 3C discharge capacity, as shown in Equation 2 below. (Formula 2) Rate characteristic = 3C discharge capacity / third 0.2C discharge capacity × 100 (%) Relative values ​​(%) based on the rate characteristic of Comparative Example B1-4 were determined and evaluated according to the following criteria: ◎: 150% or more (excellent) ○: More than 100% but less than 150% (good) ×: 100% or less (poor)

[0198] <Evaluation of Cycle Characteristics of Lithium-Ion Secondary Battery Negative Electrode> The prepared lithium-ion secondary battery negative electrode evaluation cell was placed in a thermostatic chamber at 25°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Corporation). Constant-current, constant-voltage charging (cutoff current: 0.02C current) was performed at a charge rate of 0.2C with a charge cut-off voltage of 0.05V, followed by constant-current discharging at a discharge rate of 0.2C with a discharge cut-off voltage of 1.5V. This procedure was repeated 10 times. 1C was the current value required to charge or discharge the theoretical capacity of the negative electrode in 1 hour. The cycle characteristics can be expressed by the ratio of the third 0.2C discharge capacity to the tenth 0.2C discharge capacity, as shown in Equation 1: (Equation 1) Cycle Characteristics = 10th 0.2C Discharge Capacity / Third 0.2C Discharge Capacity × 100 (%). The relative value (%) based on the cycle characteristics of Comparative Example B1-4 was calculated and evaluated according to the following criteria. ◎: 150% or more (excellent) ○: More than 100% but less than 150% (good) ×: 100% or less (poor)

[0199] As shown in Table B3, the Examples showed superior battery characteristics compared to the Comparative Examples. This is presumably because the presence of fibrous carbon of different thicknesses in the composite improved the ion and electron paths necessary for charge / discharge reactions for the active material in the composite, leading to improved rate characteristics and cycle characteristics. From the above, it was demonstrated that electrode composites within the scope of the present invention can exhibit excellent battery characteristics.

[0200] In Examples B1-8 and B1-10, no aggregates of fibrous carbon were observed, and therefore the electrode resistance was lower than in the other Examples. On the other hand, in Examples B1-1 to B1-10, fibrous carbon of different thicknesses was mixed in the composite, and therefore the electrode resistance, rate characteristics, and cycle characteristics were improved compared to the comparative examples.

[0201] Although the present invention has been described with reference to the above-mentioned several embodiments, the present invention is not limited to these several embodiments. Various modifications can be made to the configuration and details of the present invention within the scope of the present invention.

[0202] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-108270 filed on June 30, 2023 and the subject matter described in Japanese Patent Application No. 2023-198578 filed on November 22, 2023, the entire disclosures of which are incorporated herein by reference.

Claims

1. A composite for a secondary battery electrode comprising an electrode active material and fibrous carbon, wherein a portion of the fibrous carbon has a crushed form and is attached to a surface of the electrode active material, and a portion of the fibrous carbon has an aggregate form.

2. The composite for a secondary battery electrode according to claim 1, wherein the average particle size of said aggregates is from 0.2 μm to 50 μm.

3. The composite for a secondary battery electrode according to claim 1, wherein the fibrous carbon has an exothermic peak temperature of 550° C. or less as measured by simultaneous thermogravimetry and differential thermal analysis in the presence of oxygen.

4. A composite for a secondary battery electrode according to claim 1, wherein the average particle size of the aggregates is from 0.2 μm to 50 μm, and the exothermic peak temperature of the fibrous carbon obtained by simultaneous thermogravimetry and differential thermal analysis in the presence of oxygen is 550° C. or less.

5. The composite for a secondary battery electrode according to claim 1, further comprising a binder resin.

6. A composite for a secondary battery electrode according to claim 1, wherein the average particle size of said aggregates is from 0.2 μm to 50 μm, and further contains a binder resin.

7. A composite for a secondary battery electrode according to claim 1, wherein the fibrous carbon comprises at least two types of fibrous carbon having different average fiber diameters, the at least two types of fibrous carbon comprising a first fibrous carbon having an average fiber diameter of 1 nm or more and less than 9 nm, and a second fibrous carbon having an average fiber diameter of 9 nm or more and 150 nm or less.

8. The composite for a secondary battery electrode according to claim 7, wherein the average particle size of said aggregates is from 0.2 μm to 50 μm.

9. The composite for a secondary battery electrode according to claim 7, further comprising a binder resin.

10. The composite for a secondary battery electrode according to claim 7, wherein the average particle size of said aggregates is from 0.2 μm to 50 μm, and further contains a binder resin.

11. A secondary battery electrode comprising the secondary battery electrode composite according to any one of claims 1 to 10.

12. A secondary battery comprising the secondary battery electrode according to claim 11.

13. A vehicle or device equipped with the secondary battery according to claim 12.

14. A method for producing a composite for a secondary battery electrode according to any one of claims 1 to 10, comprising the steps of: combining a fibrous carbon dispersion in which fibrous carbon is dispersed in a solvent with an electrode active material using a mixing device; and removing the solvent and drying the resulting composite for a secondary battery electrode.

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