Classifications

• • 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
• • 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
  • 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
  • H01M4/04—Processes of manufacture in general
  • H01M4/0402—Methods of deposition of the material
  • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
• • 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
  • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
• • 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
  • H01M4/139—Processes of manufacture
  • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
• • 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
• • 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
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/028—Positive electrodes
• • 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
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
  • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
• • 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 conductive material dispersion, a positive electrode slurry containing the conductive material dispersion, a method for manufacturing a positive electrode for a non-aqueous electrolyte secondary battery using the positive electrode slurry, and a non-aqueous electrolyte secondary battery manufactured using the positive electrode slurry.
• the present invention relates to a positive electrode for a secondary battery, and a non-aqueous electrolyte secondary battery including the positive electrode.
• nonaqueous electrolyte secondary batteries such as lithium ion batteries have been widely used in applications that require high durability and high energy density, such as various electronic devices and automotive applications.
• DCIR direct current resistance
• Electrodes which are the main components of non-aqueous electrolyte secondary batteries, greatly affect their performance, and therefore many studies have been conducted on electrodes.
• Electrodes particularly positive electrodes, generally contain a conductive material to form a conductive path within the electrode plate. Electrodes are manufactured by applying a slurry containing an active material, a binder, and a conductive material onto a core material such as metal foil, and compressing the coating to form a composite material layer on both sides of the core material.
• the slurry is prepared using a conductive material dispersion liquid in which a conductive material is dispersed in advance. It is also known that the performance of the conductive material dispersion greatly affects the DCIR of the electrode finally obtained.
• Patent Document 1 discloses a conductive material dispersion using carbon nanotubes (CNT) as a conductive material.
• the dispersion liquid of Patent Document 1 is characterized in that the particle size distribution of CNTs has a D50 of 3 to 10 ⁇ m.
• Patent Document 1 discloses that by producing an electrode using the dispersion liquid, the DCIR becomes low when the depth of charge (SOC) of the battery is 50%.
• a conductive material dispersion according to the present disclosure is a conductive material dispersion containing a conductive material, a dispersant, and an aprotic polar solvent, the conductive material having carbon nanotubes as a main component, and the dispersing agent comprising: It is characterized in that the volume-based median diameter of the electrically conductive material containing nitrile rubber and dispersed in a polar solvent is less than 3 ⁇ m.
• a positive electrode slurry for a non-aqueous electrolyte secondary battery according to the present disclosure includes the above-mentioned conductive material dispersion and a lithium-containing transition metal oxide.
• a method for manufacturing a positive electrode for a non-aqueous electrolyte secondary battery according to the present disclosure is a method for manufacturing a positive electrode for a non-aqueous electrolyte secondary battery using a positive electrode slurry, in which the positive electrode slurry is applied to the surface of a positive electrode core material. The membrane is dried to form a positive electrode composite layer.
• a nonaqueous electrolyte secondary battery including a positive electrode manufactured using the conductive material dispersion according to the present disclosure has a DCIR not only when the SOC is 50% but also when the SOC is as low as 10%. can be kept low and has a high discharge capacity retention rate.
• the conductive material dispersion liquid of Patent Document 1 in which the DCIR increases in a low SOC state, still has room for improvement from the viewpoint of increasing battery durability.
• the volume-based median diameter of the conductive material (CNT) in a state of being dispersed in a polar solvent containing nitrile rubber as a dispersant is controlled to be less than 3 ⁇ m.
• CNT conductive material
• the following describes a conductive material dispersion, a positive electrode slurry, and a method for manufacturing a positive electrode according to the present disclosure, and an example of an embodiment of a positive electrode and a nonaqueous electrolyte secondary battery manufactured using a conductive material dispersion according to the present disclosure.
• a conductive material dispersion a positive electrode slurry, and a method for manufacturing a positive electrode according to the present disclosure
• an example of an embodiment of a positive electrode and a nonaqueous electrolyte secondary battery manufactured using a conductive material dispersion according to the present disclosure are included in the present disclosure.
• a non-aqueous electrolyte secondary battery includes an electrode, a non-aqueous electrolyte, and an exterior body that houses the electrode and the non-aqueous electrolyte.
• the exterior body is, for example, a bottomed cylindrical metal exterior can.
• a sealing body is attached to the opening of the outer can via a gasket.
• the non-aqueous electrolyte secondary battery according to the present disclosure is not limited to a cylindrical battery having a cylindrical outer can, but may also include a prismatic battery having a prismatic outer can or a coin-shaped battery having a coin-shaped outer can.
• the battery may be a laminate battery having an exterior body made of a laminate sheet including a metal layer and a resin layer.
• the electrode of the non-aqueous electrolyte secondary battery is manufactured using the conductive material dispersion liquid of this embodiment (hereinafter referred to as "dispersion liquid (D)").
• the electrode includes a positive electrode and a negative electrode, and both the positive electrode and the negative electrode may be manufactured using the dispersion (D), but it is particularly preferable that the positive electrode is manufactured.
• the positive electrode is manufactured using a positive electrode slurry containing the dispersion liquid (D) and a lithium-containing transition metal oxide.
• a non-aqueous electrolyte secondary battery generally includes an electrode body that includes a positive electrode, a negative electrode, and a separator, and the positive electrode and the negative electrode are arranged facing each other with the separator interposed therebetween.
• the electrode body may have a spirally wound structure, or may have a laminated structure in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked with separators in between.
• the positive electrode includes a positive electrode core material and a positive electrode composite material layer formed on the surface of the positive electrode core material.
• a positive electrode core material a metal foil such as aluminum or an aluminum alloy that is stable in the positive electrode potential range, a film with the metal disposed on the surface, or the like can be used.
• the positive electrode composite material layer includes a positive electrode active material, a conductive material, and a binder, and is preferably formed on both sides of the positive electrode core material.
• An example of the thickness of the positive electrode composite material layer is 50 to 150 ⁇ m on one side of the positive electrode core material.
• a positive electrode slurry containing a positive electrode active material, a conductive material, a binder, etc. is applied onto the positive electrode core material, the coating is dried, and then compressed to form a positive electrode composite layer on both sides of the positive electrode core material. It can be produced by
• the positive electrode composite layer contains a particulate lithium-containing transition metal oxide as a positive electrode active material.
• the lithium-containing transition metal oxide is a composite oxide containing metal elements such as Co, Mn, Ni, and Al in addition to Li.
• Metal elements constituting the lithium-containing transition metal oxide include, for example, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Sn, It is at least one selected from Sb, W, Pb, and Bi. Among these, it is preferable to contain at least one selected from Co, Ni, and Mn.
• suitable composite oxides include lithium-containing transition metal oxides containing Ni, Co, and Mn, and lithium-containing transition metal oxides containing Ni, Co, and Al.
• the volume-based median diameter (D50) of the positive electrode active material is, for example, 1 to 25 ⁇ m, preferably 3 to 20 ⁇ m.
• D50 means a particle size at which the cumulative frequency is 50% from the smallest particle size in the volume-based particle size distribution, and is also called the median diameter.
• the particle size distribution of the positive electrode active material can be measured using a laser diffraction type particle size distribution measuring device (for example, MT3000 manufactured by Microtrac) using water as a dispersion medium.
• the content of the positive electrode active material is, for example, 90 to 99.5% by mass based on the mass of the positive electrode composite material layer.
• the positive electrode composite material layer contains at least CNTs as a conductive material. When added in a small amount, CNT forms a good conductive path in the positive electrode composite layer, reduces the DCIR of the battery, and is suitable for increasing durability and increasing energy density.
• the positive electrode composite material layer may contain a conductive material other than CNT, such as carbon black such as acetylene black and Ketjen black, carbon fiber other than CNT such as graphite, carbon nanofiber, and graphene.
• the main component of the conductive material is preferably CNT, and the positive electrode composite layer may substantially contain only CNT as the conductive material.
• a suitable content of the conductive material is, for example, 0.01 to 10% by mass, more preferably 0.2 to 1% by mass, based on the mass of the positive electrode composite material layer.
• binder included in the positive electrode composite layer examples include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide, acrylic resin, and polyolefin. Furthermore, these resins may be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like.
• the content rate of the binder is, for example, 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, based on the mass of the positive electrode composite material layer 31.
• the negative electrode includes a negative electrode core material and a negative electrode composite material layer formed on the surface of the negative electrode core material.
• a foil of a metal such as copper or copper alloy that is stable in the potential range of the negative electrode, a film in which the metal is disposed on the surface layer, or the like can be used.
• the negative electrode composite material layer contains a negative electrode active material, a binder, and, if necessary, a conductive material, and is preferably formed on both sides of the negative electrode core material.
• the thickness of the negative electrode composite material layer is, for example, 30 to 150 ⁇ m on one side of the negative electrode core material.
• the negative electrode is produced by applying a negative electrode slurry containing a negative electrode active material, a binder, etc. onto the negative electrode core material, drying the coating film, and then compressing it to form a negative electrode composite layer on both sides of the negative electrode core material. It can be made.
• the negative electrode composite material layer contains, as a negative electrode active material, a carbon-based active material that reversibly occludes and releases lithium ions.
• Suitable carbon-based active materials include natural graphite such as flaky graphite, lumpy graphite, and earthy graphite, and graphite such as artificial graphite such as massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB).
• MAG massive artificial graphite
• MCMB graphitized mesophase carbon microbeads
• a Si-based active material containing Si may be used as the negative electrode active material.
• the binder contained in the negative electrode composite material layer for example, PAN, polyimide, acrylic resin, polyolefin, styrene-butadiene rubber (SBR), etc. can be used.
• the negative electrode composite material layer may contain CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like.
• a conductive material such as CNT may be added to the negative electrode composite material layer, especially when using a Si-based active material.
• a negative electrode slurry containing dispersion D can be used to manufacture the negative electrode.
• the non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.
• the non-aqueous solvent for example, esters, ethers, nitriles, amides, mixed solvents of two or more of these, and the like are used.
• the non-aqueous solvent may contain a halogen-substituted product in which at least some of the hydrogen atoms of these solvents are replaced with halogen atoms such as fluorine.
• nonaqueous solvents include ethylene carbonate (EC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC), and mixed solvents thereof.
• a lithium salt such as LiPF 6 is used as the electrolyte salt.
• the non-aqueous electrolyte is not limited to a liquid electrolyte, and may be a solid electrolyte.
• the dispersion liquid (D) contains a conductive material, a dispersant, and an aprotic polar solvent.
• the dispersion (D) is added to a positive electrode slurry used for manufacturing a positive electrode for a non-aqueous electrolyte secondary battery, and the conductive material contained in the dispersion (D) constitutes a composite material layer of the positive electrode. forming conductive paths in the layers;
• the dispersant is dissolved in a polar solvent, and the conductive material is dispersed in the polar solvent by the action of the dispersant.
• the solid content (conductive material and dispersant) concentration of the dispersion liquid (D) is, for example, 0.1 to 20% by mass, and preferably 0.2 to 20% from the viewpoint of achieving both CNT dispersibility and productivity.
• the content is 15% by mass, more preferably 1 to 10% by mass.
• the conductive material contains CNT as a main component, and the dispersant contains nitrile rubber.
• the volume-based median diameter of the conductive material dispersed in the polar solvent is less than 3 ⁇ m.
• CNTs tend to aggregate, and if a positive electrode is manufactured using a dispersion containing aggregated CNTs, the CNTs will be aggregated even in the positive electrode composite layer, making it difficult to form a good conductive path.
• the dispersion liquid (D) it is thought that a good dispersion state of CNTs is stably maintained until the time of manufacturing the positive electrode. Therefore, when the positive electrode is manufactured using the dispersion liquid (D), the DCIR of the battery is can be effectively reduced.
• the main component of the conductive material means the component having the highest mass ratio among the components constituting the conductive material.
• CNT forms a good conductive path in the positive electrode composite layer and reduces the DCIR of the battery, but the mass ratio of CNT to the conductive material is preferably 50 mass% or more.
• the conductive material contains at least CNT and has CNT as a main component.
• the conductive material may contain conductive carbon particles such as carbon black, and conductive fibrous carbon materials other than CNTs such as graphene and carbon fibers, but the mass of CNTs in the conductive material The ratio is preferably 50% by mass or more, more preferably 66% or more.
• the dispersion liquid (D) may contain substantially only CNTs as the conductive material.
• CNTs are conductive carbon fibers with a diameter (outer diameter) of 100 nm or less, and have an extremely large aspect ratio (ratio of fiber length to fiber diameter).
• the aspect ratio of CNT is, for example, 20 times or more, preferably 50 times or more. According to CNTs having a high aspect ratio, the contact between the active material and the core material is not a point contact but a linear contact. Therefore, a good conductive path can be formed with a small amount of addition.
• the average fiber diameter (outer diameter) of CNT is, for example, 20 nm or less, and may be 15 nm or less. Note that the fiber diameter means the length in the direction perpendicular to the fiber length direction. When the average fiber diameter is 20 nm or less, DCIR is reduced more effectively. Although the lower limit of the average fiber diameter of CNT is not particularly limited, one example is 1 nm.
• the average fiber diameter of CNTs is determined by image analysis using a transmission electron microscope (TEM). The average fiber diameter of the CNTs is determined by arbitrarily selecting 100 CNTs, measuring the fiber diameters, and taking the arithmetic mean of the measured values.
• the average fiber length of CNT is, for example, 0.5 ⁇ m or more, and may be 1 ⁇ m or more. Note that the fiber length means the length when CNTs are stretched linearly. If the average fiber length is 0.5 ⁇ m or more, DCIR can be reduced more effectively. Although the upper limit of the average fiber length of CNT is not particularly limited, one example is 100 ⁇ m.
• the average fiber length of CNTs is determined by image analysis using a scanning electron microscope (SEM). The average fiber length of CNTs is determined by arbitrarily selecting 100 CNTs, measuring their lengths, and taking the arithmetic average of the measured values.
• the CNTs may be either single-walled CNTs (SWCNTs) or multi-walled CNTs (MWCNTs), and SWCNTs and MWCNTs may be used together as the conductive material.
• SWCNTs have a structure in which a single layer of graphite sheets is formed into a tube shape
• multilayer CNTs have a structure in which multilayer graphite sheets are formed in a tube shape.
• An example of multi-walled CNTs is double-walled CNTs that have a two-layered structure.
• the preferred BET specific surface area of CNTs varies somewhat depending on the type of CNTs, but as an example, it is 200 m 2 /g or more, more preferably 500 m 2 /g or more.
• the upper limit of the BET specific surface area is not particularly limited, but an example is 1500 m 2 /g.
• the BET specific surface area is measured according to the BET method (nitrogen adsorption method) described in JIS R1626.
• the content of CNT in the dispersion (D) is preferably 0.05 to 20% by mass, more preferably 0.1 to 10% by mass. Even when a conductive material other than CNT is added, the content of the conductive material is preferably within the range. If the content of CNT (conductive material) is within the range, the dispersibility of CNT will be better while ensuring good productivity of the dispersion (D), and the effect of reducing DCIR will be more pronounced. .
• the preferred content varies somewhat depending on the type of CNT, but for example, in the case of SWCNT, 0.1 to 5% by mass is particularly preferred, and in the case of MWCNT, 2 to 7% by mass is particularly preferred.
• CNTs are dispersed in a polar solvent due to the function of a dispersant, but the CNT fibers do not extend straight; instead, one or more CNT fibers are entangled and dispersed in a particle-like state. . Therefore, like the particles of the positive electrode active material, the CNTs are dispersed in a polar solvent with a predetermined particle size distribution. In the positive electrode slurry, the positive electrode active material and CNT coexist, but the volume-based median diameter (D50) of the CNT is smaller than the D50 of the positive electrode active material.
• D50 volume-based median diameter
• the D50 of the conductive material dispersed in the polar solvent is less than 3 ⁇ m.
• the D50 of the conductive material is adjusted to be less than 3 ⁇ m, the DCIR of the battery can be effectively reduced.
• the particle size distribution of the conductive material can be measured using a laser diffraction type particle size distribution measuring device (manufactured by Microtrac, MT3000).
• the dispersion liquid (D) can be used as it is as a measurement sample.
• the D50 of the conductive material in the dispersion (D) is more preferably less than 0.8 ⁇ m. In this case, the effect of reducing DCIR becomes more significant.
• the D50 of the CNTs is at least less than 3 ⁇ m, and more preferably less than 0.8 ⁇ m.
• the lower limit of D50 of the conductive material (CNT) is not particularly limited, and varies depending on the fiber length of the CNT, but is 0.1 ⁇ m as an example.
• the dispersion liquid (D) is prepared by mixing a conductive material, a dispersant, and an aprotic polar solvent.
• a conventionally known dispersing machine or mixer (hereinafter referred to as "mixer etc.") can be used.
• the D50 of the conductive material changes depending on, for example, the type and amount of the dispersant added, and generally, as the amount of the dispersant added increases, the dispersibility of the conductive material improves and the D50 tends to become smaller.
• Examples of the above-mentioned mixers include planetary mixers, homomixers, pin mixers, high-speed mixers, dispers, roll mills, ball mills, jet mills, kneaders, and the like. Among these, it is preferable to use a ball mill.
• the D50 of the conductive material also changes depending on the mixing conditions, and generally, the stronger the stirring force of a mixer or the like and the longer the mixing time, the smaller the D50 tends to be. However, if the shearing force acting on the CNTs is too strong, the fibers may be cut. Apply shear force to dispersion (D).
• the dispersant contains at least nitrile rubber. Even if the D50 of CNTs is controlled to be less than 3 ⁇ m, if the dispersion liquid (D) does not contain nitrile rubber, it is considered difficult to ensure good dispersibility of CNTs throughout the positive electrode manufacturing process, and the DCIR No improvement effect can be obtained.
• the nitrile rubber is a copolymer of monomers containing unsaturated nitrile and conjugated diene as raw materials, and may be a copolymer of substantially only unsaturated nitrile and conjugated diene. The molar ratio of unsaturated nitrile to conjugated diene is, for example, 10:90 to 50:50.
• the weight average molecular weight of the nitrile rubber is not particularly limited, but is, for example, 5,000 to 2,000,000.
• the nitrile rubber may be a hydrogenated nitrile rubber.
• the hydrogenated nitrile rubber includes, for example, a structural unit derived from an unsaturated nitrile, a structural unit derived from a conjugated diene, and a structural unit derived from a hydrogenated conjugated diene.
• An example of a suitable hydrogenated nitrile rubber is a partially hydrogenated nitrile rubber in which 80 mol% or more of the structural units derived from a conjugated diene are hydrogenated.
• An example of an unsaturated nitrile is acrylonitrile or methacrylonitrile, preferably acrylonitrile.
• An example of the conjugated diene is a conjugated diene having 3 to 6 carbon atoms, preferably butadiene.
• the nitrile rubber is preferably contained in an amount of 10 to 100 parts by mass based on 100 parts by mass of CNTs. More preferably, it is 10 to 80 parts by weight, particularly preferably 20 to 50 parts by weight. In this case, it becomes easy to maintain a good dispersion state of CNTs over a long period of time.
• the dispersion liquid (D) may contain only nitrile rubber as a dispersant, or may contain other dispersants in combination.
• the mass ratio of the nitrile rubber in the dispersant is preferably 30% by mass or more, more preferably 40% by mass or more.
• PVP polyvinyl alcohol
• PVP polyvinylpyrrolidone
• PVP polyalkylene oxide
• polyvinyl acetal polyvinyl ether
• cellulose chitins
• chitosan starch
• PVP polyvinyl ether
• cellulose chitins
• chitosan starch
• PVP polyvinyl alcohol
• PVP polyvinylpyrrolidone
• PVP polyalkylene oxide
• polyvinyl acetal polyvinyl acetal
• PVP polyvinyl ether
• cellulose chitins
• chitosan starch
• derivatives it is preferable to use PVP or its derivatives (PVPs).
• PVPs PVP or its derivatives
• the mass ratio of nitrile rubber and PVPs is, for example, 40:60 to 60:40.
• the weight average molecular weight of PVPs is not particularly limited, but is, for example, 5,000 to 1,000,000
• At least a portion of the dispersant may function as a binder for the positive electrode composite layer.
• the dispersion liquid (D) may contain PVdF or the like that is added to the positive electrode slurry as a binder.
• the dispersion liquid (D) contains an aprotic polar solvent as a dispersion medium.
• the aprotic polar solvent may be any solvent as long as it can dissolve the dispersant and disperse the CNTs. Since the dispersion liquid (D) is added to the positive electrode slurry, the polar solvent is preferably one that is miscible with the solvent of the positive electrode slurry, and may be the same type of solvent as the solvent of the positive electrode slurry.
• aprotic polar solvents examples include N-methyl-2-pyrrolidone (NMP), methyl ethyl ketone, tetrahydrofuran, dimethyl formamide, acetone, ethyl acetate, dimethyl sulfoxide, and the like. Among them, it is preferable to use NMP.
• the aprotic polar solvent one type of solvent may be used alone, or two or more types of solvents may be used in combination.
• the mass ratio of NMP to the polar solvent is 50% by mass or more, and may be 100% by mass.
• the polar solvent may consist essentially only of NMP.
• the content of the polar solvent is, for example, 80% by mass or more of the mass of the dispersion (D), preferably 85 to 99.5% by mass, more preferably 90 to 99% by mass.
• the positive electrode slurry of this embodiment includes a dispersion liquid (D) and the above-mentioned lithium-containing transition metal oxide, which is a positive electrode active material. Furthermore, the positive electrode slurry includes a binder and a dispersion medium. The positive electrode slurry may be prepared by mixing these raw materials at once. For example, the positive electrode active material and the binder powder are dry blended and added to the dispersion medium, and then the dispersion liquid (D) is mixed. It may also be prepared by The solid content concentration of the positive electrode slurry is, for example, 70 to 90% by mass.
• the proportion of the positive electrode active material in the solid content of the positive electrode slurry is, for example, 90% by mass or more, preferably 90 to 99.5% by mass, and more preferably 95 to 99% by mass.
• the proportion of the conductive material in the solid content of the positive electrode slurry is, for example, 0.05 to 10% by mass, preferably 0.1 to 8% by mass, and more preferably 0.5 to 5% by mass. Note that the amount of the dispersion liquid (D) added is adjusted so that the content of the conductive material is within the range.
• the proportion of the binder in the solid content of the positive electrode slurry is, for example, 0.1 to 5% by mass.
• the dispersion medium for example, disperses the positive electrode active material and the conductive material and dissolves the binder.
• water, lower alcohols such as ethanol, etc. can be used as the dispersion medium, but generally an aprotic polar solvent is used as in the case of dispersion liquid (D). used.
• the dispersion medium include NMP, methyl ethyl ketone, dimethyl formamide, and the like. Among them, it is preferable to use NMP.
• NMP dispersion medium
• the same type of dispersion medium (NMP) is used in the dispersion liquid (D) and the positive electrode slurry.
• a conventionally known mixer or the like can be used for mixing (kneading) the positive electrode active material, dispersion liquid (D), binder, and dispersion medium.
• mixers include planetary mixers, homomixers, pin mixers, high-speed mixers, dispersers, roll mills, ball mills, jet mills, kneaders, and the like.
• planetary mixer is a rotation-revolution type stirring mixer that can apply strong shearing force to slurry by planetary motion of the blades.
• Example 1 [Preparation of conductive material dispersion] MWCNT (average fiber diameter: 10 nm, average fiber length: 1 ⁇ m) was used as the conductive material, and hydrogenated nitrile rubber (H-NBR) in which a copolymer of acrylonitrile and butadiene was substituted with hydrogen and polyvinylpyrrolidone were used as the dispersant. (PVP) mixed at a mass ratio of 1:1 was used. A powder obtained by dry blending a conductive material and a dispersant at a mass ratio of 2:1 is added to N-methyl-2-pyrrolidone (NMP) and kneaded using a ball mill, so that the conductive material is approximately 5% by mass. , a conductive material dispersion having a D50 of 0.74 ⁇ m was obtained. The particle size distribution of the conductive material in the conductive material dispersion was measured using MT3000.
• a lithium transition metal oxide represented by the general formula LiNi 0.9 Co 0.05 Al 0.05 O 2 was used as the positive electrode active material, and polyvinylidene fluoride (PVdF) was used as the binder.
• PVdF polyvinylidene fluoride
• a powder obtained by dry blending the positive electrode active material and the binder at a mass ratio of 100:1 was added to NMP.
• the above conductive material dispersion is added and kneaded so that the mass ratio of the positive electrode active material and the conductive material is 100:0.5, thereby creating a positive electrode slurry containing the positive electrode active material, the conductive material, and the binder. I got it.
• Graphite was used as the negative electrode active material.
• a negative electrode active material, a dispersion of styrene butadiene rubber (SBR), and sodium salt of carboxymethylcellulose (CMC-Na) were mixed at a solid content mass ratio of 98:1:1, and water was used as a dispersion medium.
• a negative electrode slurry was prepared. Next, the negative electrode slurry is applied to both sides of the negative electrode core material made of copper foil, and after drying and compressing the coating film, the negative electrode core material is cut into a predetermined electrode size, and the negative electrode composite material is applied to both sides of the negative electrode core material. A negative electrode with a layer formed thereon was obtained.
• a nonaqueous electrolyte was obtained by dissolving LiPF 6 at a concentration of 1.2 mol/L in a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a volume ratio of 3:7 (25° C.).
• Examples 2 to 5> The procedure was the same as in Example 1, except that the kneading conditions using the ball mill were changed to prepare conductive material dispersions with D50s of 0.86 ⁇ m, 0.94 ⁇ m, 1.04 ⁇ m, and 2.86 ⁇ m, respectively. A test cell was prepared.
• Test cells were produced in the same manner as in Example 1, except that the kneading conditions were changed to set the D50 of the conductive material to 4.47 ⁇ m and 8.98 ⁇ m, respectively.
• the test cells of the examples all have lower DCIR at low SOC than the test cells of the comparative example.
• the D50 of the CNTs in the dispersion was less than 0.8 ⁇ m (see Example 1), the effect of reducing DCIR was more remarkable.
• the SOC was 50%, for example, there was no significant difference in DCIR between the test cells of each example and the test cells of Comparative Examples 2 and 4 prepared using dispersions containing H-NBR. It wasn't done.

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