Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/15—Nano-sized carbon materials
  • C01B32/158—Carbon nanotubes
  • C01B32/159—Carbon nanotubes single-walled
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/15—Nano-sized carbon materials
  • C01B32/158—Carbon nanotubes
  • C01B32/168—After-treatment
  • C01B32/174—Derivatisation; Solubilisation; Dispersion in solvents
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
  • H01B1/20—Conductive material dispersed in non-conductive organic material
  • H01B1/24—Conductive material dispersed in non-conductive organic material the conductive material comprising carbon-silicon compounds, carbon or silicon
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/22—Electrodes
  • H01G11/24—Electrodes characterised by structural features of the materials making up or comprised in the electrodes, e.g. form, surface area or porosity; characterised by the structural features of powders or particles used therefor
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/22—Electrodes
  • H01G11/30—Electrodes characterised by their material
  • H01G11/32—Carbon-based
  • H01G11/36—Nanostructures, e.g. nanofibres, nanotubes or fullerenes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/22—Electrodes
  • H01G11/30—Electrodes characterised by their material
  • H01G11/48—Conductive polymers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
  • H01M4/621—Binders
  • H01M4/622—Binders being polymers
  • H01M4/623—Binders being polymers fluorinated polymers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
  • H01M4/624—Electric conductive fillers
  • H01M4/625—Carbon or graphite
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2202/00—Structure or properties of carbon nanotubes
  • C01B2202/02—Single-walled nanotubes
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2202/00—Structure or properties of carbon nanotubes
  • C01B2202/20—Nanotubes characterized by their properties
  • C01B2202/28—Solid content in solvents
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2202/00—Structure or properties of carbon nanotubes
  • C01B2202/20—Nanotubes characterized by their properties
  • C01B2202/36—Diameter
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/021—Physical characteristics, e.g. porosity, surface area
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present disclosure relates to a carbon nanotube dispersion composition. More specifically, the present disclosure relates to a carbon nanotube dispersion composition, a composite slurry containing the carbon nanotube dispersion composition and an active material, an electrode film formed from the composite slurry, and a nonaqueous electrolyte secondary battery including the electrode film.
• non-aqueous electrolyte secondary batteries that use non-aqueous electrolytes, and in particular lithium-ion secondary batteries, are being used in many devices due to their characteristics of high energy density and high voltage.
• the capacity of a lithium-ion secondary battery depends heavily on the main materials, the positive and negative electrode active materials, various materials for use in these electrode active materials are being actively researched.
• the charging capacity when using electrode active materials in practical use is close to the theoretical value in all cases, and improvements to electrode active materials are close to their limit. Therefore, since the charging capacity can be simply increased by increasing the amount of electrode active material filled in the electrode film, attempts are being made to reduce the amount of conductive material and binder resin added, which do not directly contribute to the charging capacity.
• Fine carbon materials are generally used as conductive materials, and carbon nanotubes have been used more frequently in recent years.
• single-walled carbon nanotubes have very strong cohesive forces and are difficult to use, so various studies are being conducted.
• Patent Documents 1 to 3 propose a method of providing a nonaqueous electrolyte secondary battery with good characteristics by first finely dispersing carbon nanotubes using various dispersants and then producing an electrode composite slurry.
• Patent Document 4 describes an electrode including a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other, and a battery including the electrode.
• Patent documents 1 to 3 use a dispersant as an essential component, and can obtain a dispersion composition that has good fluidity and storage stability even at high concentrations.
• a dispersant as an essential component, and can obtain a dispersion composition that has good fluidity and storage stability even at high concentrations.
• Patent Document 4 single-walled carbon nanotubes are mixed with polyvinylidene fluoride resin without using a dispersant with high dispersing ability, and it is presumed that the original length of the carbon nanotubes is adequately maintained.
• storage stability such as a low carbon nanotube concentration, high viscosity and poor fluidity, and the carbon nanotubes aggregate and settle during storage, causing phase separation.
• a dispersion composition with a low carbon nanotube concentration has problems such as low design freedom when mixing materials such as active materials, and high transportation costs per non-volatile content.
• poor fluidity makes it difficult to remove from a tank during transportation or storage, and poor storage stability can result in a short shelf life or poor quality stability.
• the problem that the present invention aims to solve is to provide a carbon nanotube dispersion composition that has high conductivity and good fluidity and storage stability, and to provide a nonaqueous electrolyte secondary battery that has excellent rate characteristics and cycle characteristics by using an electrode composite slurry and an electrode film that use the carbon nanotube dispersion composition.
• the inventors have studied the relationship between the dispersion state of carbon nanotubes and rate characteristics, and have found that maintaining the state of a bundle structure of carbon nanotubes with an average outer diameter of 3 nm or less and dispersing them without shortening the fiber length leads to a reduction in contact resistance and is effective in improving rate characteristics and cycle characteristics.
• the inventors have found that by making the particle size D90 of the dispersion composition 2.0 ⁇ m or more and less than 20.0 ⁇ m and the pH 7.5 or more, the storage stability and fluidity are dramatically improved and the sedimentation of carbon nanotubes can be suppressed.
• the carbon nanotube dispersion composition includes carbon nanotubes having an average outer diameter of 3 nm or less, a polymer component, and a solvent, the polymer component including, as a main component, a polyvinylidene fluoride resin which may have a substituent, and the carbon nanotube dispersion composition has a particle size D 90 at 90% cumulative volume of a particle size distribution measured by a laser diffraction method of 2.0 ⁇ m or more and less than 20.0 ⁇ m, and a pH of 7.5 or more, thereby providing a dispersion composition with excellent storage stability and fluidity, and enabling the formation of a good conductive network in an electrode.
• a carbon nanotube dispersion composition comprising carbon nanotubes having an average outer diameter of 3 nm or less, a polymer component, and a solvent, the polymer component comprising, as a main component, a polyvinylidene fluoride resin which may have a substituent, the carbon nanotube dispersion composition having a particle size D90 at a cumulative 90% volume of a particle size distribution measured by a laser diffraction method of 2.0 ⁇ m or more and less than 20.0 ⁇ m, and a pH of 7.5 or more.
• the carbon nanotube dispersion composition according to ⁇ 1> wherein the content of the polyvinylidene fluoride resin which may have a substituent is 30 parts by mass or more and 270 parts by mass or less per 100 parts by mass of the carbon nanotubes having an average outer diameter of 3 nm or less.
• ⁇ 3> Further containing a basic compound, The carbon nanotube dispersion composition according to ⁇ 1> or ⁇ 2>, wherein the content of the basic compound is 0.01 mass % or more and 0.2 mass % or less based on the mass of the carbon nanotube dispersion composition.
• ⁇ 4> The carbon nanotube dispersion composition according to any one of ⁇ 1> to ⁇ 3>, wherein the total content of the carbon nanotubes having an average outer diameter of 3 nm or less and the polymer component is 80 mass% or more based on the total mass of the non-volatile components of the carbon nanotube dispersion composition.
• ⁇ 5> The carbon nanotube dispersion composition according to any one of ⁇ 1> to ⁇ 4>, wherein the content of the polyvinylidene fluoride resin which may have a substituent is 87 mass% or more based on the mass of the polymer component.
• a composite slurry comprising the carbon nanotube dispersion composition according to any one of ⁇ 1> to ⁇ 5> and an active material.
• a nonaqueous electrolyte secondary battery including a positive electrode and a negative electrode, at least one of the positive electrode and the negative electrode having the electrode film according to ⁇ 7>.
• a carbon nanotube dispersion composition has high electrical conductivity and good storage stability, and a composite slurry using the carbon nanotube dispersion composition makes it possible to provide a nonaqueous electrolyte secondary battery with excellent rate characteristics and cycle characteristics.
• FIG. 1 is a photograph (30,000 times) of a positive electrode 10 observed by a scanning electron microscope.
• FIG. 2 is a photograph (30,000 times) of the comparative positive electrode 6 observed with a scanning electron microscope.
• the dispersion composition, composite slurry, and nonaqueous electrolyte secondary battery which are embodiments of the present disclosure, are described in detail below.
• the present disclosure is not limited to the following embodiments, and the present invention also includes embodiments that are implemented within the scope that does not change the gist of the present disclosure.
• carbon nanotubes may be referred to as "CNT”
• carbon nanotube dispersion compositions may be referred to as “dispersion compositions” or “CNT dispersion compositions”
• polyvinylidene fluoride resins which may have substituents may be referred to as “polyvinylidene fluoride resins” or “PVdF”.
• the carbon nanotube dispersion composition of the present embodiment contains carbon nanotubes having an average outer diameter of 3 nm or less, a polymer component, and a solvent, and has a particle size D90 at 90% cumulative volume of a particle size distribution measured by a laser diffraction method of 2.0 ⁇ m or more and less than 20.0 ⁇ m, and a pH of 7.5 or more, and the polymer component contains, as a main component, a polyvinylidene fluoride resin which may have a substituent.
• the dispersion composition of this embodiment does not contain an active material.
• an active material if contained, it is defined as a composite slurry.
• the dispersion composition of the embodiment of the present disclosure refers to the state before the active material is added.
• the dispersion composition is distinguished from a composite slurry that contains an active material.
• the dispersion composition does not substantially contain active material.
• This concept excludes a state in which an active material is intentionally added to the dispersion composition, and the active material may be 1 mass % or less, 0.5 mass % or less, or 0.1 mass % or less relative to the total mass of the dispersion composition, or it may be 0 mass %.
• the active material is described below.
• the dispersion composition can be suitably used for electrodes for non-aqueous electrolyte secondary batteries.
• it is not limited to applications for non-aqueous electrolyte secondary batteries, and can also be used for power storage devices other than non-aqueous electrolyte secondary batteries, such as electrodes for electric double layer capacitors and electrodes for non-aqueous electrolyte capacitors, or as antistatic materials for IC trays for plastic or rubber products, molded bodies of electronic component materials, electronic components, transparent electrode (ITO film) replacements, electromagnetic wave shielding, etc.
• ITO film transparent electrode
• the average outer diameter of the carbon nanotubes is 3 nm or less, preferably 1 nm or more and 3 nm or less, and more preferably 1 nm or more and 2 nm or less.
• the average outer diameter of the carbon nanotubes is in the above range, the specific surface area is increased, so that a conductive network can be efficiently formed.
• the average outer diameter of the carbon nanotubes may be 0.5 nm or more and 3 nm or less, 0.8 nm or more and 2.8 nm or less, 1 nm or more and 2.5 nm or less, or 1 nm or more and 2 nm or less.
• the average outer diameter of the carbon nanotubes can be calculated by observing the morphology of the carbon nanotubes using a transmission electron microscope (manufactured by JEOL Ltd.), measuring the lengths of the minor axes of 100 tubes, and averaging the measured values.
• the carbon nanotubes of this embodiment preferably contain single-walled carbon nanotubes, and may be a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes.
• Single-walled carbon nanotubes alone are more preferable.
• Single-walled carbon nanotubes are preferable because they have a small average outer diameter and a large specific surface area, allowing a conductive network to be formed efficiently.
• Single-walled carbon nanotubes may be produced by mixing with multi-walled carbon nanotubes during synthesis.
• Single-walled carbon nanotubes have a structure in which one layer of graphite is wrapped around them, and multi-walled carbon nanotubes have a structure in which two or three or more layers of graphite are wrapped around them.
• the main component is the component with the highest mass content.
• the BET specific surface area of the carbon nanotubes of this embodiment is preferably 550 m2 /g or more and 1200 m2 /g or less, more preferably 600 m2 /g or more and 1200 m2 /g or less, even more preferably 700 m2 /g or more and 1200 m2 /g or less, and even more preferably 800 m2 /g or more and 1200 m2 /g or less.
• the BET specific surface area of the carbon nanotubes is in the above range, the carbon nanotubes tend to be evenly entangled with the electrode active material, and therefore a conductive network can be efficiently formed.
• the G/D ratio is preferably 5 to 100, more preferably 10 to 90, and even more preferably 20 to 80.
• the crystallinity is high and good electrical conductivity is easily obtained.
• the volume resistivity of the carbon nanotube of this embodiment is preferably 1.0 ⁇ 10 ⁇ 3 ⁇ cm or more and 3.0 ⁇ 10 ⁇ 2 ⁇ cm or less, and more preferably 1.0 ⁇ 10 ⁇ 3 ⁇ cm or more and 1.0 ⁇ 10 ⁇ 2 ⁇ cm or less.
• the volume resistivity of the carbon nanotube can be measured using a powder resistivity measuring device (Loresta GP Powder Resistivity Measuring System MCP-PD-51, manufactured by Mitsubishi Chemical Analytech Co., Ltd.). When the volume resistivity of the carbon nanotube is in the above range, the electron transfer resistance between the carbon nanotube and the active material can be reduced.
• the carbon purity of the carbon nanotubes of this embodiment is expressed as the content (%) of carbon atoms in the carbon nanotubes.
• the carbon purity is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, relative to 100% by mass of the carbon nanotubes.
• the carbon purity of the carbon nanotubes is within the above range, it is possible to prevent problems such as short circuits caused by the formation of dendrites due to impurities such as metal catalysts.
• the amount of metal contained in the carbon nanotubes of this embodiment is preferably less than 20% by mass, more preferably less than 10% by mass, and even more preferably less than 5% by mass, relative to 100% by mass of the carbon nanotubes.
• Metals contained in the carbon nanotubes include metals and metal oxides used as catalysts when synthesizing the carbon nanotubes, and metal powders that have been mixed in due to wear of the equipment, etc. Specific examples include metals such as cobalt, nickel, aluminum, magnesium, silica, manganese, and molybdenum, alloys of these metals, metal oxides, and composite oxides of these metals.
• the carbon nanotubes of this embodiment may be surface-treated carbon nanotubes.
• the carbon nanotubes may be carbon nanotube derivatives to which functional groups, such as carboxy groups, have been added.
• Carbon nanotubes that encapsulate substances such as organic compounds and metal atoms may also be used.
• the carbon nanotubes of this embodiment may be pulverized carbon nanotubes.
• the pulverization process is performed by using a pulverizer containing pulverization media such as beads or steel balls to pulverize the carbon nanotubes without the use of any liquid substance, and is also called dry pulverization.
• the pulverization is performed by utilizing the pulverizing force or destructive force caused by the collision of pulverization media.
• the pulverization mainly has the effect of reducing the size of the secondary particles of the carbon nanotubes, and can improve the dispersibility of the carbon nanotubes.
• a dry pulverization device a known method such as a dry attritor, ball mill, vibration mill, or bead mill can be used, and the pulverization time can be set as desired depending on the device.
• the carbon nanotubes of this embodiment may be carbon nanotubes produced by any method.
• Carbon nanotubes can generally be produced by, but are not limited to, the laser ablation method, the arc discharge method, the thermal CVD method, the plasma CVD method, and the combustion method.
• the polymer component of the present embodiment contains a polyvinylidene fluoride resin, which may have a substituent, as a main component.
• a polymer component other than the polyvinylidene fluoride resin may be contained.
• the term "polymer” refers to a molecule having a weight average molecular weight of 1,000 or more
• the term "main component" refers to a component having the highest mass content.
• the content of the polyvinylidene fluoride resin in the polymer component is preferably 87% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, and may be 100% by mass, based on the total amount of the polymer component.
• any conventionally known surfactant or polymer dispersant can be used without any particular limitation.
• the content of the polymer component other than polyvinylidene fluoride resin is preferably 13 mass% or less, more preferably 10 mass% or less, even more preferably 5 mass% or less, based on the total amount of the polymer components, and even more preferably none.
• polyvinylidene fluoride resin optionally having a substituent
• examples of polyvinylidene fluoride resins include homopolymers of polyvinylidene fluoride, copolymers of vinylidene fluoride with hexafluoropropylene, tetrafluoroethylene, etc., and copolymers are preferred.
• polyvinylidene fluoride resins do not have the dispersing ability to disperse carbon nanotubes at a high concentration, for example, down to individual tubes, but by containing polyvinylidene fluoride resin and adjusting the pH to 7.5 or more, the state of the bundle structure of carbon nanotubes can be maintained and the fiber length can be dispersed without shortening.
• the polyvinylidene fluoride resin has a substituent.
• a substituent with low elimination ability is preferable, and for example, an acidic functional group such as a carboxy group is more preferable.
• an acidic functional group is present, it can be ionized or polarized, and the effect of dispersion stabilization due to electrostatic repulsion can be obtained.
• the concerted dehydrofluorination reaction caused by the basic compound is stopped by the presence of some heterogeneous bonds, which is preferable as it can suppress viscosity increase and gelation.
• polyvinylidene fluoride resins that do not have a substituent (i.e., homopolymers) include, for example, the KF Polymer series (W#7300, W#7200, W#1700, W#1300, W#1100, L#7305, L#7208, L#1710, L#1320, L#1120) manufactured by Kureha Corporation, and the Solef series (6008, 6010, 6012, 1015, 6020, 9007, 460, 41308) manufactured by Solvay.
• KF Polymer series W#7300, W#7200, W#1700, W#1300, W#1100, L#7305, L#7208, L#1710, L#1320, L#1120
• Solef series 6008, 6010, 6012, 1015, 6020, 9007, 460, 41308 manufactured by Solvay.
• polyvinylidene fluoride resins which are copolymers, include the Solef series (21216, 11010, 21510, 31508, 60512) manufactured by Solvay.
• substituted polyvinylidene fluoride resins include, for example, KF Polymer series "W#9700, W#9300, W#9100” manufactured by Kureha Corporation, and Solef series "5130" manufactured by Solvay.
• the polyvinylidene fluoride resin is contained in the carbon nanotube dispersion composition.
• the polyvinylidene fluoride resin may be further added after the dispersion composition is produced or when the composite slurry is produced. The composite slurry will be explained in detail later.
• the dispersion composition of the present embodiment contains a solvent.
• the solvent is not particularly limited, but is preferably a solvent capable of dissolving polyvinylidene fluoride resin.
• “capable of dissolving polyvinylidene fluoride resin” means that when 0.5 g of polyvinylidene fluoride resin is dissolved in 100 g of a solvent at 25° C., no insoluble matter can be visually confirmed and the solution is clear and transparent.
• the solvent preferably includes a solvent consisting of any one of the high dielectric constant solvents, or a mixed solvent consisting of two or more of them.
• the high dielectric constant solvent may also be used by mixing one or more other solvents.
• the "high dielectric constant solvent” has a relative dielectric constant value described in the Solvent Handbook (Teruzo Asahara, Jinichiro Tokura, Makoto Okawara, Keiju Kumano, Manabu Senoo, Solvent Handbook, 14th Edition, Kodansha, 1996, p. 936) of preferably 25 to 60 at 20°C, more preferably 25 to 50.
• polyvinylidene fluoride resin By using a solvent with a dielectric constant in the above range, polyvinylidene fluoride resin can be stably dissolved, and in particular when a basic compound is contained, the storage stability and fluidity of the dispersion composition can be improved by polarization of the solvent.
• 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, ⁇ -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), and others such as
• the solvent is substantially free of water.
• Polyvinylidene fluoride resins tend to have low solubility in water.
• hydrogen fluoride may be eliminated to form conjugated double bonds in the main chain, causing gelation, or hydrogen fluoride may corrode other materials or devices.
• the adsorption of polyvinylidene fluoride resin to carbon nanotubes may decrease, making it difficult for carbon nanotubes to exist stably in the solvent.
• “Substantially free” means that water is not intentionally added in excess of the amount that is contained due to moisture absorption or the like.
• the water content based on the total mass of the solvent is preferably 5 mass% or less, more preferably 1 mass% or less, and even more preferably 0.5 mass% or less.
• the dispersion composition preferably contains a basic compound.
• the strong polarization of the polyvinylidene fluoride resin and the basic compound interact with each other, and the fluidity and storage stability of the dispersion composition can be further improved.
• the basic compound to be added can be at least one selected from the group consisting of inorganic bases, inorganic metal salts, organic bases, and organic base salts.
• inorganic bases and inorganic metal salts include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, borates, and ammonium hydroxide of alkali metals or alkaline earth metals.
• hydroxides or alkoxides of alkali metals which are strong bases, are preferred because they easily interact with polyvinylidene fluoride resin.
• hydroxides of alkali metals examples include lithium hydroxide, sodium hydroxide, and potassium hydroxide.
• hydroxides of alkaline earth metals include calcium hydroxide and magnesium hydroxide. Among these, it is more preferable to use at least one selected from the group consisting of lithium hydroxide, sodium hydroxide, and potassium hydroxide.
• the metal contained in the inorganic base may be a transition metal.
• alkali metal alkoxides include lithium methoxide, lithium ethoxide, lithium n-butoxide, lithium t-butoxide, potassium methoxide, potassium ethoxide, potassium n-butoxide, potassium t-butoxide, sodium methoxide, sodium ethoxide, sodium n-butoxide, and sodium t-butoxide.
• the number of carbon atoms in the alkoxide may be 5 or more.
• Sodium t-butoxide is particularly preferred.
• alkaline earth metal alkoxides examples include magnesium methoxide, magnesium ethoxide, magnesium n-butoxide, magnesium t-butoxide, etc.
• the number of carbon atoms in the alkoxide may be 5 or more.
• lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, lithium t-butoxide, potassium t-butoxide, and sodium t-butoxide are more preferred, sodium hydroxide and sodium t-butoxide are even more preferred, and sodium hydroxide is even more preferred.
• the metal contained in the inorganic base and inorganic metal salt of this embodiment may be a transition metal.
• organic bases include primary, secondary, and tertiary amine compounds (alkylamines, amino alcohols, etc.) having 1 to 40 carbon atoms, which may have a substituent, and organic hydroxides.
• the content of the basic compound is preferably 0.01 mass% or more, more preferably 0.02 mass% or more based on the mass of the dispersion composition. Moreover, it is preferably 0.2 mass% or less, more preferably 0.15 mass% or less, and even more preferably 0.10 mass% or less.
• the content of the basic compound may be 0.01 mass% or more and 0.2 mass% or less, 0.02 mass% or more and 0.15 mass% or less, or 0.04 mass% or more and 0.10 mass% or less based on the mass of the dispersion composition.
• the content of the basic compound is equal to or higher than the lower limit, the effect of storage stability tends to be easily obtained.
• the content of the basic compound is equal to or lower than the upper limit, the gelation of the polyvinylidene fluoride resin can be suppressed, and further, the corrosion of the dispersion device and/or the inside of the battery can be prevented, which is preferable.
• the dispersion composition is preferably produced, for example, by dispersing carbon nanotubes, a polyvinylidene fluoride resin which may have a substituent, and a solvent, to finely disperse them using a dispersing device.
• the dispersion process can be a multi-stage process of two or more steps, with the timing of adding the materials being arbitrarily adjusted.
• the timing of adding the basic compound is not particularly limited, but it is preferable to add the basic compound after dispersing the mixture of the solvent, the polyvinylidene fluoride resin, and the carbon nanotubes, which makes it easier to obtain a dispersion composition with excellent storage stability and flowability.
• a preferred method for producing a carbon nanotube dispersion composition includes a step of producing a carbon nanotube dispersion containing carbon nanotubes, a polymer component, and a solvent, and then mixing a basic compound with the carbon nanotube dispersion to obtain a carbon nanotube dispersion composition having a particle size D90 at 90% cumulative volume of particle size distribution measured by a laser diffraction method of 2.0 ⁇ m or more and less than 20.0 ⁇ m, and a pH of 7.5 or more.
• Examples of the dispersion device include a kneader, a two-roll mill, a three-roll mill, a planetary mixer, a ball mill, a horizontal sand mill, a vertical sand mill, an annular bead mill, an attritor, a high shear mixer, a high pressure homogenizer, an ultrasonic homogenizer, and the like.
• a high shear mixer in order to finely disperse the CNTs in the dispersion composition and obtain suitable dispersibility, it is preferable to use a high shear mixer, a high pressure homogenizer, an ultrasonic homogenizer, or a combination of these.
• the high shear mixer in the initial dispersion step, and then to use a high pressure homogenizer from the viewpoint of dispersing the CNTs while maintaining their aspect ratio.
• the pressure when using the high pressure homogenizer is preferably 50 to 150 MPa, and more preferably 70 to 150 MPa.
• Dispersion methods using a dispersion device include batch dispersion, pass dispersion, and circulation dispersion, and any of these methods may be used, or two or more methods may be combined.
• Batch dispersion is a method in which dispersion is performed using only the dispersion device itself, without using piping or the like. It is easy to handle, so it is preferable for small-scale production.
• Pass dispersion is a dispersion method in which the dispersion device itself is equipped with a tank that supplies the dispersion liquid (a mixture containing dispersoid and dispersion medium, which is a precursor of the dispersion composition) via piping, and a tank that receives the dispersion liquid, and the dispersion liquid is passed through the dispersion device itself.
• circulation dispersion is a method in which the dispersion liquid that has passed through the dispersion device itself is returned to the tank that supplies the dispersion liquid, and dispersion is performed while circulating.
• the longer the processing time the more the dispersion progresses, so it is sufficient to repeat the pass or circulation until the desired dispersion state is achieved, and the processing volume can be increased by changing the size of the tank or the processing time.
• Pass dispersion is preferable in that it is easier to homogenize the dispersion state than circulation dispersion.
• Circulation dispersion is preferable in that the work and manufacturing equipment are simpler than pass dispersion.
• the disintegration of agglomerated particles, the loosening, wetting, and stabilization of the conductive material proceed sequentially or simultaneously, and the final dispersion state differs depending on how the process proceeds, so it is preferable to manage the dispersion state in each dispersion process by using various evaluation methods.
• the pH of the dispersion composition of this embodiment is 7.5 or more.
• the pH of the dispersion composition is preferably 7.7 or more, and more preferably 8.0 or more. Also, it is preferably 13.0 or less, more preferably 12.0 or less, and even more preferably 11.0 or less. If the pH exceeds the above-mentioned preferred upper limit, problems such as corrosion of various raw materials and exterior materials in the battery, or gelation of polyvinylidene fluoride resin may occur. Also, if the pH is below the above-mentioned lower limit, it is difficult to obtain the effect of storage stability.
• the pH may be in the range of 7.5 or more, and may be 7.5 to 13.0, 7.7 to 12.0, 8.0 to 12.0, or 8.0 to 11.0.
• the "pH" of the dispersion composition in this specification is the value of the pH of a "pH measurement sample" prepared by diluting the dispersion composition with water, measured using a general pH meter.
• the pH measurement sample is adjusted by adding water so that the mass of the non-volatile content of the pH measurement sample is 40 parts by mass when the mass of the non-volatile content of the dispersion composition is 100 parts by mass.
• water is added so that the non-volatile content concentration of the dispersion composition is 0.8% by mass, and this can be measured by the method described in the Examples.
• the particle size D 90 at 90% cumulative volume measured by the laser diffraction method of the dispersion composition of this embodiment is preferably 2.0 ⁇ m or more, more preferably 2.2 ⁇ m or more, even more preferably 2.4 ⁇ m or more, and even more preferably 2.5 ⁇ m or more. Also, it is preferably 20.0 ⁇ m or less, more preferably 15.0 ⁇ m or less, and even more preferably 10.0 ⁇ m or less.
• the particle size D 90 may be 2.0 ⁇ m to 20.0 ⁇ m, 2.2 ⁇ m to 15.0 ⁇ m, 2.3 ⁇ m to 15.0 ⁇ m, 2.4 ⁇ m to 10.0 ⁇ m, or 2.5 ⁇ m to 10.0 ⁇ m.
• the particle size D90 can be determined by using a dispersion liquid that has been subjected to ultrasonic operation as a pretreatment, and using a general laser diffraction measuring device. If the pretreatment is not performed, the measured values may vary, making accurate evaluation difficult. More specifically, the particle size D90 can be measured by the method described in the Examples. In this specification, the particle size D90 at 90% of the cumulative size may be referred to as " D90 ".
• the viscosity of the dispersion composition of this embodiment is preferably 8,000 mPa ⁇ s or more and less than 11,000 mPa ⁇ s, more preferably 6,000 mPa ⁇ s or more and less than 8,000 mPa ⁇ s, and even more preferably less than 6,000 mPa ⁇ s.
• the viscosity of the dispersion composition is within the above range, it can be easily handled.
• the content of carbon nanotubes having an average outer diameter of 3 nm or less is preferably 0.4 mass% or more, more preferably 0.5 mass% or more, even more preferably 0.8 mass% or more, and even more preferably 1.1 mass% or more, relative to 100 mass% of the dispersion composition. Also, it is preferably 3.0 mass% or less, preferably 2.0 mass% or less, more preferably 1.6 mass% or less, and even more preferably 1.3 mass% or less.
• the content of carbon nanotubes having an average outer diameter of 3 nm or less may be 0.4 mass% or more and 3.0 mass% or less, 0.5 mass% or more and 2.0 mass% or less, 0.8 mass% or more and 1.6 mass% or less, or 1.1 mass% or more and 1.3 mass% or less, relative to 100 mass% of the dispersion composition.
• the content of the polyvinylidene fluoride resin is preferably 30 parts by mass or more, more preferably 70 parts by mass or more, relative to 100 parts by mass of carbon nanotubes having an average outer diameter of 3 nm or less. Also, it is preferably 270 parts by mass or less, more preferably 200 parts by mass or less, and even more preferably 150 parts by mass or less. If it exceeds the above upper limit, the viscosity of the dispersion composition increases with an increase in the polyvinylidene fluoride resin not adsorbed to the carbon nanotubes, and handling properties may be impaired.
• the content of the polyvinylidene fluoride resin may be 30 parts by mass or more and 270 parts by mass or less, 50 parts by mass or more and 250 parts by mass or less, 60 parts by mass or more and 200 parts by mass or less, or 70 parts by mass or more and 150 parts by mass or less, relative to 100 parts by mass of carbon nanotubes having an average outer diameter of 3 nm or less.
• the resistance of the electrode can be improved, resulting in more excellent rate characteristics.
• the total mass of the carbon nanotubes having an average outer diameter of 3 nm or less and the polyvinylidene fluoride resin which may have a substituent may be 100% by mass or less, preferably 80% by mass or more, more preferably 82.5% by mass or more, and even more preferably 85% by mass or more, relative to the total mass of the non-volatile components in the dispersion composition.
• the carbon nanotubes having an average outer diameter of 3 nm or less, the polyvinylidene fluoride resin which may have a substituent, and the basic compound can interact uniformly, so that a dispersion composition which is more well dispersed can be obtained.
• the total mass of the carbon nanotubes having an average outer diameter of 3 nm or less and the polyvinylidene fluoride resin which may have a substituent may be 80% by mass or more and 100% by mass or less, 82.5% by mass or more and 99.5% by mass or less, or 85% by mass or more and 99% by mass or less, relative to the total mass of the non-volatile components in the dispersion composition.
• the total mass of non-volatile components in a dispersion composition refers to the mass of the residue (solid content) after the dispersion composition is heated to volatilize the solvent.
• the dispersion composition of this embodiment may be produced, for example, by mixing and dispersing carbon nanotubes having an average outer diameter of 3 nm or less, a polymer component containing, as a main component, polyvinylidene fluoride resin which may have a substituent, and a solvent, either together or in portions.
• other components may be used additionally, but it is preferable to use carbon nanotubes having an average outer diameter of 3 nm or less alone as the carbon nanotubes.
• polyvinylidene fluoride resin which may have a substituent alone as the polymer component.
• the obtained carbon nanotube dispersion composition should have a particle size D90 at 90% cumulative volume of the particle size distribution measured by laser diffraction method of 2.0 ⁇ m or more and less than 20.0 ⁇ m, and a pH of 7.5 or more.
• the composite slurry of the present embodiment can be obtained by adding an active material to the dispersion composition, and can be used for electrodes for non-aqueous electrolyte secondary batteries.
• the composite slurry may further include a polyvinylidene fluoride resin or/and other polymer components that may have a substituent added to the dispersion composition for the purpose of further binding the active material, etc.
• the polyvinylidene fluoride resin or/and other polymer components that may have a substituent added to the dispersion composition for the purpose of further binding the active material, etc. may be referred to as a "binder resin".
• the active material may be a positive electrode active material or a negative electrode active material.
• the positive electrode active material and the negative electrode active material may be simply referred to as "active material".
• An active material is a material that is the basis of a battery reaction. Active materials are divided into positive electrode active materials and negative electrode active materials based on electromotive force.
• a positive electrode active material can be used to make a positive electrode mixture slurry, and a negative electrode active material can be used to make a negative electrode mixture slurry.
• the composite slurry is preferably in a slurry form in order to improve uniformity and processability.
• the binder resin added for the purpose of better binding the active material, etc. is not particularly limited as long as it is a polymer component that is normally used as a binder resin for batteries, and can be appropriately selected according to the purpose.
• the aforementioned polyvinylidene fluoride resin, which may have a substituent, may be used, and other polymer components may include, for example, polymers or copolymers having ethylene, propylene, vinyl chloride, vinyl acetate, maleic acid, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, styrene, etc.
• polyurethane resins as constituent components; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins; elastomers such as styrene-butadiene rubber and fluororubber; conductive resins such as polyaniline and polyacetylene, etc.
• Modified bodies, mixtures, and copolymers of these resins may also be used, and one type may be used alone, or two or more types may be used in combination.
• the CNT content in the composite slurry is preferably 0.01 parts by mass or more, more preferably 0.03 parts by mass or more, and even more preferably 0.05 parts by mass or more, per 100 parts by mass of active material. Also, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less. If it exceeds the upper limit, the amount of active material filled in the electrode may decrease, resulting in a lower capacity of the battery. Also, if it falls below the lower limit, the conductivity of the electrode and battery may be insufficient.
• the content of the polymer component in the composite slurry is preferably 0.01 parts by mass or more, and more preferably 0.02 parts by mass or more, per 100 parts by mass of active material. By keeping it within the above range, the adhesion of the conductive film can be further improved. Also, it is preferably 20 parts by mass or less, and more preferably 10 parts by mass or less. By keeping it within the above range, the active material concentration of the conductive film can be increased, and a higher capacity can be achieved.
• the positive electrode active material is not particularly limited.
• metal compounds such as metal oxides and metal sulfides capable of reversibly doping or intercalating lithium ions can be used.
• lithium and transition metal composite oxide powders such as lithium manganese composite oxide (e.g., Li x Mn 2 O 4 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 ), and spinel-type lithium manganese nickel composite oxide (e.g., Li x Mn 2-y Ni y O 4 ), lithium phosphate powders having an olivine structure (e.g., Li x FePO 4 , Li x
• the positive electrode active material include powders of transition metal oxides such as Fe1 - yM
• V2O5 , V6O13 titanium oxide
• powders of transition metal sulfides such as iron sulfate ( Fe2 ( SO4 ) 3 ), TiS2 , and FeS.
• x, y, and z are numbers, and 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1, 0 ⁇ z ⁇ 1, and 0 ⁇ y+z ⁇ 1.
• the negative electrode active material is not particularly limited, but may be, for example, a metal Li capable of reversibly doping or intercalating lithium ions, or an alloy thereof, a tin alloy, a silicon alloy negative electrode, a metal oxide system such as Li x TiO 2 , Li x Fe 2 O 3 , Li x Fe 3 O 4 , or Li x WO 2, a conductive polymer such as polyacetylene or poly-p-phenylene, an artificial graphite such as a highly graphitized carbon material, or a carbonaceous powder such as natural graphite, or a resin-sintered carbon material.
• x is a number, and 0 ⁇ x ⁇ 1.
• negative electrode active materials may be used alone or in combination.
• a silicon alloy negative electrode when used, the theoretical capacity is large, but the volume expansion is extremely large, so it is preferable to use it in combination with an artificial graphite such as a highly graphitized carbon material, or a carbonaceous powder such as natural graphite, or a resin-sintered carbon material.
• the order of adding the binder resin and the active material is not particularly limited.
• a method of preparing the composite slurry by adding the binder resin to the dispersion composition and then adding the active material a method of preparing the composite slurry by adding the active material to the dispersion composition and then adding the binder resin; a method of preparing the composite slurry by adding the binder resin and the active material all at once, and the like can be mentioned.
• the binder resin may be added after being dissolved in advance.
• a method of adding the binder resin to the dispersion composition and then further adding the active material and performing a stirring process is preferable.
• the stirring device used for stirring is not particularly limited.
• the stirring device can be a disperser, a homogenizer, or the like.
• the amount of non-volatile matter in the composite slurry is preferably 30% by mass or more, and more preferably 40% by mass or more, based on the mass of the composite slurry (mass of the composite slurry being 100% by mass). Also, it is preferably 90% by mass or less, and more preferably 85% by mass or less.
• a nonaqueous electrolyte 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 is made from the composite slurry according to the present embodiment.
• the positive electrode and the negative electrode may further include a current collector.
• one of the electrode films of the positive electrode and the negative electrode is an electrode film using the dispersion composition according to the present embodiment.
• the electrode film of the other electrode is not particularly limited and may be a conventionally known electrode film.
• the structure of the nonaqueous electrolyte secondary battery of one embodiment is not particularly limited, but typically includes a positive electrode, a negative electrode, an electrolyte, and a separator that is provided as needed, and can be in a variety of shapes depending on the intended use, such as a paper type, a cylindrical type, a button type, or a laminated type.
• the positive electrode or negative electrode has an electrode film formed from a composite slurry using the dispersion composition of this embodiment, and a current collector.
• the electrode film can be formed, for example, by applying the dispersion composition onto a current collector and drying it.
• the electrode film formed using the positive electrode composite slurry can be used as a positive electrode.
• the electrode film formed using the negative electrode composite slurry can be used as a negative electrode.
• the film formed using the dispersion composition containing an active material may be referred to as an "electrode composite layer".
• the material and shape of the current collector used to form the electrode film are not particularly limited, and can be appropriately selected from those suitable for various non-aqueous electrolyte secondary batteries.
• Examples of materials for the current collector include conductive metals or alloys such as aluminum, copper, nickel, titanium, or stainless steel. In terms of shape, a flat foil is generally used, but current collectors with a roughened surface, perforated foil current collectors, and mesh current collectors can also be used.
• the thickness of the current collector is preferably about 0.5 to 30 ⁇ m.
• the method for applying the dispersion composition onto 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 painting. Drying methods include, but are not limited to, leaving to dry, or drying using a blower dryer, hot air dryer, infrared heater, far-infrared heater, etc.
• a rolling process may be performed using a lithographic press, a calendar roll, or the like.
• the thickness of the formed film is, for example, 1 ⁇ m or more and 500 ⁇ m or less, and preferably 10 ⁇ m or more and 300 ⁇ m or less.
• the film formed using the dispersion composition can also be used as a base layer for the electrode mixture layer to improve adhesion between the electrode mixture layer and the current collector, or to improve the conductivity of the electrode film.
• electrolyte various conventionally known electrolytes capable of moving ions can be used.
• Non-aqueous solvents include, but are not limited to, carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as ⁇ -butyrolactone, ⁇ -valerolactone, and ⁇ -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.
• the non-aqueous electrolyte secondary battery preferably has a separator.
• separators include, but are not limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabrics that have been subjected to a hydrophilic treatment.
• TNSR Single-wall carbon nanotube (manufactured by Timensnano, average outer diameter 1.5 nm, carbon purity 95%, specific surface area 610 m 2 /g)
• TNSAR Single-wall carbon nanotube (manufactured by Timensnano, average outer diameter 1.5 nm, carbon purity 95%, specific surface area 950 m 2 /g)
• TUBALL Single-wall carbon nanotube (OCSiAl, average outer diameter 1.6 nm, carbon purity 99%, specific surface area 980 m 2 /g)
• TUBALL Single-wall carbon nanotube (OCSiAl, average outer diameter 1.8 nm, carbon purity 80%, specific surface area 520 m 2 /g)
• Example 1-1 ⁇ Preparation of Dispersion Composition> (Example 1-1) According to the materials and compositions shown in Table 1, a dispersion composition was prepared as follows. First, NMP was taken in a stainless steel container. Next, a standard round hole type head was attached to a high shear mixer (L5M-A, manufactured by SILVERSON), and polyvinylidene fluoride resin was added while stirring at a speed of 3,000 rpm, and then stirred for 1 hour to dissolve the polyvinylidene fluoride resin. Next, CNT was added while stirring with a high shear mixer, and batch dispersion was performed at a speed of 6,000 rpm for 1 hour.
• L5M-A high shear mixer
• the liquid to be dispersed was supplied from the stainless steel container through a pipe to a high pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine), and a circulation type dispersion treatment was performed according to the number of passes shown in Table 1.
• the dispersion treatment was performed using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa.
• the liquid to be dispersed was supplied from the high pressure homogenizer through a pipe to a stainless steel container, and a basic compound was added while stirring at a speed of 3,500 rpm with a high shear mixer. After stirring for 30 minutes, dispersion composition 1 was obtained.
• the carbon nanotube content based on the dispersion composition 1 was 1.0 mass%
• the polymer component was 1.0 mass% (the polyvinylidene fluoride resin content based on the polymer component was 100 mass%)
• the basic compound content was 0.04 mass%
• the solvent was 97.96 mass%.
• the total content of the carbon nanotubes and the polymer component was 98 mass% based on the total mass of the non-volatile components of the dispersion composition 1.
• Example 2 to 30 Each dispersion composition 2 to 30 was obtained in the same manner as in Example 1-1, except that the materials, compositions, and number of passes were changed according to those shown in Table 1.
• Examples 1-31 to 1-37 According to the materials and compositions shown in Table 1, the dispersion compositions were prepared as follows. First, NMP was placed in a stainless steel container. Next, a standard round-hole head was attached to a high shear mixer (L5M-A, manufactured by SILVERSON), and polyvinylidene fluoride resin and other polymeric components were added while stirring at a speed of 3,000 rpm, and then the mixture was stirred for 1 hour to dissolve the polyvinylidene fluoride resin and other polymeric components. Thereafter, a circulation-type dispersion treatment was performed using a high-pressure homogenizer in the same manner as in the working process of the dispersion composition of Example 1-1, and each of the dispersion compositions 31 to 37 was obtained.
• L5M-A high shear mixer
• Comparative dispersion compositions 1 to 3 were obtained in the same manner as in Example 1-1, except that the materials, compositions, and number of passes were changed according to those shown in Table 1.
• Comparative dispersion composition 4 was obtained in the same manner as in Example 1-31, except that the materials and compositions were changed according to those shown in Table 1.
• a dispersion composition was prepared as follows. First, NMP was placed in a stainless steel container. Next, a standard round-hole head was attached to a high shear mixer (L5M-A, manufactured by SILVERSON), and the polymer component and basic compound were added while stirring at a speed of 3,000 rpm, and then the mixture was stirred for 1 hour to dissolve the polymer component and basic compound. Next, CNT was added while stirring with a high shear mixer, and batch dispersion was performed at a speed of 6,000 rpm for 1 hour.
• L5M-A high shear mixer
• the liquid to be dispersed was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) through a pipe, and a circulation dispersion process was performed according to the number of passes shown in Table 1.
• the dispersion process was performed using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa.
• the liquid to be dispersed was supplied from the high-pressure homogenizer through piping to the stainless steel container, and the polyvinylidene fluoride resin was completely dissolved while stirring with a disperser, whereby a comparative dispersion composition 5 was obtained.
• the basic compounds listed in Table 1 are as follows: NaOH: Sodium hydroxide (Tokyo Chemical Industry Co., Ltd., purity >98.0%, granular) LiOH: Lithium hydroxide (Tokyo Chemical Industry Co., Ltd., purity >98.0%) KOH: Potassium hydroxide (Tokyo Chemical Industry Co., Ltd., purity >86.0%) Na2CO3 : Sodium carbonate (Tokyo Chemical Industry Co. , Ltd., purity >99.0%) C 2 H 5 NH 2 : 2-aminoethanol (Tokyo Chemical Industry Co., Ltd., purity >99.0%)
• H-NBR1 Therban® 3406 (manufactured by ARLANXEO, hydrogenated acrylonitrile-butadiene rubber)
• H-NBR2 Therban® AT 3404 (manufactured by ARLANXEO, hydrogenated acrylonitrile-butadiene rubber)
• H-NBR3 Zetpole 2000L (manufactured by Zeon Corporation, hydrogenated acrylonitrile-butadiene rubber)
• PVP Polyvinylpyrrolidone K-15 (manufactured by ISP)
• PVA Kuraray Poval 3-86SD (manufactured by Kuraray, modified polyvinyl alcohol)
• D 90 was measured using a particle size distribution analyzer (Partial LA-960V2, manufactured by HORIBA).
• the circulation/ultrasonic operation conditions were: circulation speed: 3, ultrasonic intensity: 7, ultrasonic time: 1 minute, stirring speed: 1, stirring mode: continuous.
• ultrasonic operation was performed with ultrasonic intensity 7 and ultrasonic time 5 seconds.
• the refractive index of water was 1.333, and the refractive index of the carbon material was 1.92.
• the measurement was performed by diluting the measurement sample so that the transmittance of the red laser diode was 70 to 90%, and ultrasonic operation was performed under the conditions of ultrasonic intensity: 7 and ultrasonic time: 1 minute, and the particle size standard was volume.
• the values in Table 1 indicate that the particle size D 90 is in the following range. 1: Less than 2.0 ⁇ m 2: 2.0 ⁇ m or more and less than 2.3 ⁇ m 3: 2.3 ⁇ m or more and less than 2.5 ⁇ m 4: 2.5 ⁇ m or more and less than 10.0 ⁇ m 5: 10.0 ⁇ m or more and less than 15.0 ⁇ m 6: 15.0 ⁇ m or more and less than 20.0 ⁇ m 7: 20.0 ⁇ m or more
• the pH measurement sample was adjusted by dropping water while stirring the dispersion composition with a disperser so that the non-volatile content of the pH measurement sample was 40 parts when the mass of the non-volatile content of the dispersion composition was 100 parts.
• the measurement was performed at a temperature of 25°C using a tabletop pH meter (Seven Compact S200 Expert Pro, manufactured by Mettler Toledo).
• Table 1 indicate that the pH is in the following range. 1: Less than 7.5 2: 7.5 or more and less than 7.7 3: 7.7 or more and less than 8.0 4: 8.0 or more and less than 11.0 5: 11.0 or more and less than 12.0 6: 12.0 or more and less than 13.0 7: 13.0 or more
• the viscosity of the dispersion composition was measured at 25°C using a Brookfield viscometer ("BL" manufactured by Toki Sangyo Co., Ltd.) immediately after thorough stirring with a spatula at a rotor speed of 12 rpm. The viscosity measured at 12 rpm was taken as the initial viscosity. From the viewpoint of fluidity, the lower the initial viscosity, the better, and evaluation criteria A to C indicate good handling.
• the storage stability was evaluated by determining whether or not phase separation occurred after the dispersion composition was left to stand at 40°C for storage.
• the determination method is as follows. 1.5 g to 2.0 g of the supernatant of the dispersion composition was placed in an aluminum dish with a diameter of 7.5 cm and a height of 1 cm, and dried in an electric oven at 120°C ⁇ 5°C for 1 hour. Thereafter, the weight of the solid content was measured, and if it was reduced by 0.10% or more from the theoretical solid content, it was determined that phase separation had occurred.
• B Phase separation occurred after 1 week.
• C Phase separation occurred after 3 days.
• D Phase separation occurred after 1 day.
• a positive electrode composite slurry and a positive electrode were prepared as follows according to the combination and composition ratio shown in Table 3.
• the dispersion composition, the positive electrode active material, and NMP were added to a plastic container having a capacity of 150 cm3 , and the mixture was stirred at 2,000 rpm for 150 seconds using a rotation/revolution mixer (Thinky's Awatori Rentaro, ARE-310) to obtain a positive electrode composite slurry.
• the non-volatile content of the positive electrode composite slurry was 78 mass%.
• the positive electrode mixture slurry was applied onto an aluminum foil having a thickness of 20 ⁇ m using an applicator, and then dried in an electric oven at 120° C. ⁇ 5° C. for 25 minutes to prepare an electrode film.
• the electrode film was then rolled using a roll press (3 ton hydraulic roll press, manufactured by Sunk Metals) to obtain positive electrodes (positive electrodes 1 to 32, comparative positive electrodes 1 to 3).
• the weight per unit area of the electrode mixture layer was 20 mg/cm 2 , and the density of the electrode mixture layer after the rolling process was 3.2 g/cc.
• ⁇ NMC1 S800 (LiNi 0.8 Mn 0.1 Co 0.1 O 2 , manufactured by Kinwa)
• Photographs (30,000x magnification) of the obtained positive electrode observed by a scanning electron microscope are shown in Figures 1 and 2.
• Figure 1 is a photograph (30,000x magnification) of Example 2-10 (positive electrode 10)
• Figure 2 is a photograph (30,000x magnification) of Comparative Example 2-6 (comparative positive electrode 6).
• the carbon nanotubes are defibrated one by one and in contact with the positive electrode active material
• Fig. 1 it can be seen that they are maintained in a bundled structure. It is presumed that the fiber length of the bundled structure is longer than that of an individual carbon nanotube, which reduces the contact resistance between the carbon nanotubes.
• the above-mentioned standard negative electrode composite slurry was applied to a copper foil having a thickness of 20 ⁇ m as a current collector using an applicator, and then dried in an electric oven at 80° C. ⁇ 5° C. for 25 minutes to adjust the weight per unit area of the electrode to 10 mg/cm 2. Further, a rolling process was performed using a roll press (3 t hydraulic roll press, manufactured by Sun Metals) to produce a standard negative electrode with an electrode composite layer density of 1.6 g/cm 3 .
• electrolyte a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1 was prepared, and 1 mass % of vinylene carbonate was further added as an additive to 100 mass %, and then LiPF 6 was dissolved at a concentration of 1 M to prepare a non-aqueous electrolyte solution) was injected, and the aluminum laminate was sealed to prepare a non-aqueous electrolyte secondary battery.
• the obtained secondary battery 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). After constant-current constant-voltage charging (cutoff current 2.5mA (0.05C)) at a charge current of 25mA (0.5C) and a charge end voltage of 4.3V, constant-current discharging was performed at a discharge current of 25mA (0.5C) and a discharge end voltage of 3V. This operation was repeated 200 times.
• SM-8 charge/discharge device
• cycle characteristics can be expressed by the ratio of the third 0.5C discharge capacity at 25°C to the 200th 0.5C discharge capacity, as shown in the following formula 2.
• Cycle characteristic 200th 0.5C discharge capacity / 3rd 0.5C discharge capacity x 100 (%)
• the carbon nanotube dispersion composition of this embodiment has high conductivity and good fluidity and storage stability, and it was confirmed that an electrode composite slurry and an electrode film using this carbon nanotube dispersion composition can provide a non-aqueous electrolyte secondary battery with excellent rate characteristics and cycle characteristics.
• the comparative example had problems with either the initial viscosity, storage stability, conductivity, adhesion, rate characteristics, or cycle characteristics, and it was not possible to achieve both the storage stability of the dispersion composition and the rate characteristics and cycle characteristics when made into a non-aqueous electrolyte secondary battery.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Electrochemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Nanotechnology (AREA)
• Organic Chemistry (AREA)
• Power Engineering (AREA)
• Inorganic Chemistry (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Manufacturing & Machinery (AREA)
• Physics & Mathematics (AREA)
• Crystallography & Structural Chemistry (AREA)
• Dispersion Chemistry (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Battery Electrode And Active Subsutance (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Carbon And Carbon Compounds (AREA)
• Electric Double-Layer Capacitors Or The Like (AREA)
• Conductive Materials (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=89534391

Family Applications (1)

Country Status (5)

Families Citing this family (1)

Citations (10)

Family Cites Families (1)

• 2023
  • 2023-03-10 JP JP2023037367A patent/JP7414171B1/ja active Active
  • 2023-12-06 JP JP2023205825A patent/JP2024128933A/ja active Pending
• 2024
  • 2024-01-12 CN CN202480005286.4A patent/CN120322873A/zh active Pending
  • 2024-01-12 WO PCT/JP2024/000580 patent/WO2024190056A1/ja not_active Ceased
  • 2024-01-12 KR KR1020257016831A patent/KR20250093379A/ko active Pending
  • 2024-01-12 EP EP24770178.2A patent/EP4679537A4/en active Pending

Patent Citations (10)

Non-Patent Citations (2)

Also Published As

Similar Documents

Legal Events