WO2023027191A1 - 導電材複合粒子の提供方法 - Google Patents
導電材複合粒子の提供方法 Download PDFInfo
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- WO2023027191A1 WO2023027191A1 PCT/JP2022/032301 JP2022032301W WO2023027191A1 WO 2023027191 A1 WO2023027191 A1 WO 2023027191A1 JP 2022032301 W JP2022032301 W JP 2022032301W WO 2023027191 A1 WO2023027191 A1 WO 2023027191A1
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- conductive material
- composite particles
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- 229940082509 xanthan gum Drugs 0.000 description 1
- UHVMMEOXYDMDKI-JKYCWFKZSA-L zinc;1-(5-cyanopyridin-2-yl)-3-[(1s,2s)-2-(6-fluoro-2-hydroxy-3-propanoylphenyl)cyclopropyl]urea;diacetate Chemical compound [Zn+2].CC([O-])=O.CC([O-])=O.CCC(=O)C1=CC=C(F)C([C@H]2[C@H](C2)NC(=O)NC=2N=CC(=CC=2)C#N)=C1O UHVMMEOXYDMDKI-JKYCWFKZSA-L 0.000 description 1
Images
Classifications
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- 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
-
- 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
- H01B1/04—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of carbon-silicon compounds, carbon or silicon
-
- 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
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B13/00—Apparatus or processes specially adapted for manufacturing conductors or cables
-
- 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
- H01G11/38—Carbon pastes or blends; Binders or additives therein
-
- 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
- H01G11/84—Processes for the manufacture of hybrid or EDL capacitors, or components thereof
- H01G11/86—Processes for the manufacture of hybrid or EDL capacitors, or components thereof specially adapted for 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
- H01M4/04—Processes of manufacture in general
-
- 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
-
- 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 invention has high dispersibility when mixed with an electrode active material and a binder (binder) and high uniformity in the electrode coating film, while containing coarse particles and foreign matter that may cause short circuits during operation.
- the present invention relates to a method for producing conductive material composite particles from which dispersion media such as water and organic solvents have been removed and which can be suitably used for power storage devices such as batteries and capacitors.
- Electrodes use positive and negative electrodes in which an electrode active material is coated on a belt-shaped metal foil, which are wound together with a separator and then housed in a battery can.
- the positive electrode uses a lithium transition metal composite oxide or the like as an electrode active material.
- These electrode active materials alone used in the positive electrode have poor electronic conductivity, that is, electrical conductivity. Therefore, conductive carbon black with a highly developed structure to impart conductivity, and graphite with crystals that exhibit significant anisotropy are used.
- a carbon material such as is added as a conductive material, and dispersed in a non-aqueous solvent such as N-methyl-2-pyrrolidone together with a binder to prepare an electrode paste.
- a film is formed to produce a positive electrode.
- Carbon-based materials such as graphite, as well as low-conductivity materials such as silicon, are mainly used as electrode active materials for negative electrodes.
- Carbon-based materials have conductivity, but depending on the size, gaps may occur between the active materials, and electron conduction paths may not be sufficiently formed by themselves. It is effective to improve In this way, the conductive material plays an important role in lithium-ion secondary batteries. There is a need for a highly dispersible and uniform conductive material that spreads evenly around the periphery and imparts conductivity.
- the conductive carbon material which is mainly used as a conductive material, is a fine powder with a small primary particle size, and is a material that has a strong cohesive force and is extremely difficult to uniformly disperse. Therefore, when preparing an electrode paste by mixing it with a material such as an electrode active material, unless the agglomeration is sufficiently loosened by stirring for a long time or the like, the conductive material is unevenly distributed in the electrode coating film. As a result, a portion of the positive electrode plate with poor conductivity is generated locally, and the electrode active material is not effectively used due to insufficient electron transfer, resulting in low charge/discharge capacity. This was cited as a drawback (Patent Document 1).
- a conductive material-dispersed paste in which a conductive material is dispersed in a solvent in advance to form a liquid or paste-like conductive material to improve dispersibility (Patent Documents 2 to 10, etc.).
- Patent Documents 2 to 10 for the purpose of reducing the environmental load, after preparing the conductive material dispersion paste, the solvent is removed by drying to prepare conductive material fine particles with a reduced amount of organic solvent.
- Patent Document 11 A technique for manufacturing a secondary battery has been proposed (Patent Document 11).
- Patent Document 12 after filtering and drying the prepared conductive material dispersion paste to remove the solvent, it was crushed in an agate mortar and passed through a sieve with an opening diameter of 45 ⁇ m. Powdered carbon black composition and A lithium ion secondary battery electrode using the carbon black composition has been proposed.
- Patent Documents 2 to 10 it is necessary to use a large amount of an organic solvent with a high environmental load during production. There were some shortcomings such as lack of sexuality.
- Patent Document 11 by making powder from which the solvent has been removed, it has succeeded in reducing the environmental load, improving long-term stability, and handling such as storage and transportation. Since the uniformity of the conductive material in the electrode paste and electrode coating film is not sufficient, the electronic conductivity imparted to the active material is insufficient and the ability is not fully utilized, so the effect of improving battery performance is limited. was there.
- the carbon black composition of Patent Document 12 the electron conductivity imparted to the active material is insufficient, and the lithium ion secondary battery using the carbon black composition does not have sufficient battery performance. This was clarified as a result of examination by the inventors.
- the purpose of the present invention is to solve these problems found in the prior art and to overcome the problems.
- it is a new dry powder that is effective in reducing environmental load and improving long-term stability, and has high dispersibility and uniformity in the electrode coating film that realizes improvement in battery performance.
- An object of the present invention is to provide a conductive material and a method for manufacturing the same.
- the present invention (1) Particles containing at least a conductive material and a dispersant, having a particle size distribution D50 of 15 ⁇ m or more and a sieved particle size of 150 ⁇ m or less, and a DBP oil absorption of the conductive material of 550 ml/100 g or less, Conductive material composite particles characterized by containing 1 to 10 parts by weight of a dispersant with respect to 100 parts by weight of the conductive material, (2) Particles containing at least a conductive material and a dispersant, having a particle size distribution D50 of 15 ⁇ m or more and an upper limit of particle size of 300 ⁇ m or less, a DBP oil absorption of the conductive material of 550 ml/100 g or less, and a conductive material Conductive material composite particles characterized by containing 1 to 10 parts by weight of a dispersant with respect to 100 parts by weight of the material, (3) The conductive material composite particles according to either (1) or (2) above, which have an OD value of 3.
- a method for producing conductive material composite particles comprising a step of preparing a conductive material-dispersed paste containing at least a conductive material, a dispersant, and a dispersion medium, and a step of removing the dispersion medium from the conductive material-dispersed paste, A method for producing conductive material composite particles, wherein the conductive material composite particles in the material-dispersed paste have a particle diameter of 50 ⁇ m or less, (10) The method for producing conductive material composite particles according to (9) above, wherein the conductive material-dispersed paste does not contain foreign matter having a particle size of more than 50 ⁇ m, (11) The method for producing the conductive material composite particles according to (9) or (10), which includes a drying step of heating the conductive material dispersed paste at 80° C.
- a method for producing an electrode comprising mixing the conductive material composite particles according to (1) or (2) above with at least an active material and a binder, and applying the mixture to a substrate;
- a method for producing an electrode comprising mixing the conductive material composite particles obtained by the production method according to (9) or (10) with at least an active material and a binder, and applying the mixture to a substrate;
- the conductive material composite particles obtained by the present invention have a particle size distribution that is adjusted so that secondary aggregation is easily crushed during the kneading process during the preparation of the electrode paste, and the particles contain a dispersant. shows high dispersibility for Therefore, since it is not necessary to knead for a long period of time when preparing the electrode paste, there is no risk of deterioration in conductivity due to reaggregation due to excessive miniaturization. Furthermore, since the conductive material composite particles of the present invention easily form conductive paths in the electrode coating film, they are excellent in conductivity and can dramatically improve battery performance such as charge/discharge capacity.
- the conductive material can be dispersed without being unevenly distributed in the paste, and can be uniformly distributed around the active material to provide sufficient electronic conductivity. It is possible to form an electrode coating film that achieves charge/discharge capacity.
- the occurrence of problems such as thermal runaway and early deterioration of charge / discharge capacity of the battery can be suppressed, and battery performance can be maintained for a long time. it is conceivable that.
- the conductive material composite particles obtained by the present invention are dry powders that do not substantially contain a solvent, there is no fear of deterioration over time due to sedimentation or solidification compared to liquid or paste-like conductive materials. In addition to being stable enough to be stored at room temperature for a long period of time, it is possible to reduce the amount of organic solvent used during manufacturing, thereby reducing the burden on the environment.
- conductive material composite particles having excellent long-term stability can be produced while suppressing the load on the environment, and the conductive material composite particles of the present invention are used as an electrode paste for producing positive and negative plates.
- a lithium ion secondary battery having excellent battery performance such as high charge/discharge capacity and long-term stability of charge/discharge ability can be produced.
- FIG. 1 is a diagram showing a flow chart for explaining the method for producing conductive material composite particles of the present invention.
- FIG. 2 is a view showing a SEM (scanning electron microscope) photograph of a cross section of the coating film produced in Example 1.
- FIG. 3 is a diagram showing an EDS (energy dispersive X-ray spectroscope) analysis image of the cross section of the coating film produced in Example 1.
- FIG. 4 is a diagram showing a SEM photograph of a cross section of the coating film produced in Example 2.
- FIG. 5 is a diagram showing an EDS analysis image of a cross section of the coating film produced in Example 2.
- FIG. FIG. 6 is a diagram showing a SEM photograph of a cross section of the coating film produced in Example 3.
- FIG. 1 is a diagram showing a flow chart for explaining the method for producing conductive material composite particles of the present invention.
- FIG. 2 is a view showing a SEM (scanning electron microscope) photograph of a cross section of the coating film produced in
- FIG. 7 is a diagram showing an EDS analysis image of a cross section of the coating film produced in Example 3.
- FIG. 8 is a diagram showing a SEM photograph of a cross section of the coating film produced in Example 4.
- FIG. 9 is a diagram showing an EDS analysis image of a cross section of the coating film produced in Example 4.
- FIG. 10 is a diagram showing a SEM photograph of a cross section of the coating film produced in Comparative Example 1.
- FIG. 11 is a diagram showing an EDS analysis image of a cross section of the coating film produced in Comparative Example 1.
- FIG. 12 is a diagram showing a SEM photograph of a cross section of the coating film produced in Comparative Example 2.
- FIG. 13 is a diagram showing an EDS analysis image of a cross section of the coating film produced in Comparative Example 2.
- FIG. 14 is a diagram showing a SEM photograph of a cross section of the coating film produced in Comparative Example 3.
- FIG. 15 is a diagram showing an EDS analysis image of a cross section of the coating film produced in Comparative Example 3.
- FIG. 16 is a diagram showing a SEM photograph of a cross section of the coating film produced in Comparative Example 4.
- FIG. 17 is a diagram showing an EDS analysis image of a cross section of the coating film produced in Comparative Example 4.
- the conductive material composite particles of the present invention refer to particles containing at least a conductive material and a dispersant. A detailed description will be given below.
- Carbon black, carbon nanotubes, carbon nanofibers, graphite, graphene, hard carbon, and the like can be suitably used as the conductive material used in the present invention.
- carbon black is preferable because it can efficiently form a conductive path in the electrode by structure and improve conductivity.
- ketjen black, furnace black, acetylene black, thermal black, etc. are used as carbon black.
- acetylene black is particularly preferable because of its high conductivity, low impurity content, and excellent heavy overload characteristics.
- one type of these conductive materials can be used alone, or two or more types can be used in combination.
- the average primary particle size of the conductive material is preferably 10 nm or more and 50 nm or less, more preferably 45 nm or less, and even more preferably 40 nm or less. Moreover, 10 nm or more is more preferable, and 15 nm or more is still more preferable. If the average primary particle size of the conductive material is larger than 50 nm, the conductivity of the coating film obtained from the electrode paste may be lowered. If the thickness is less than 10 nm, the viscosity of the conductive material-dispersed paste and the electrode paste will be high, which may make it difficult to disperse the conductive material depending on the equipment used, and may also deteriorate handling properties. As used herein, the average primary particle size refers to an arithmetic average particle size measured using a transmission electron microscope according to ASTM: D3849-14.
- the conductive material has a DBP oil absorption of 550 ml/100 g or less. Preferably 170-240ml/100g, most preferably 170-230ml/100g. If the DBP oil absorption of the conductive material is more than 550 ml/g, the viscosity of the conductive material-dispersed paste and the electrode paste increases, making it difficult to disperse the paste and causing uneven distribution of the conductive material, which may result in failure to exhibit sufficient conductivity.
- the DBP oil absorption of the conductive material can be measured according to JIS6217-4.
- the purity of the conductive material is preferably 99.9% or more, more preferably 99.95 to 100% by mass. By setting the purity of the conductive material within the above range, it is possible to prevent short-circuiting of the battery due to impurities and reduce the defect rate.
- the purity of carbon black can be calculated based on the amount of impurities, with ash measured according to JIS K1469 or JIS K6218 as impurities.
- conductive materials suitable for satisfying the above conditions include carbon blacks such as Denka Black powder, Denka black granular, Denka black FX-35, Denka black HS-100, and Denka black Li Li-100. , Denka Black Li Li-250, Denka Black Li Li-400, Denka Black Li Li-435, etc. (product names, manufactured by Denka Co., Ltd.), LITX 50, LITX 66, LITX 60R, LITX 200, LITX 300, LITX- HP, etc.
- carbon blacks such as Denka Black powder, Denka black granular, Denka black FX-35, Denka black HS-100, and Denka black Li Li-100.
- Denka Black Li Li-250, Denka Black Li Li-400, Denka Black Li Li-435, etc. product names, manufactured by Denka Co., Ltd.
- LITX 50, LITX 66, LITX 60R, LITX 200, LITX 300, LITX- HP etc.
- the dispersant as used in the present invention means an additive used for uniformly dispersing an inorganic or organic pigment in a dispersion medium to prepare a stable dispersion. It is roughly divided into nonionic and amphoteric.
- any dispersing agent can be used as long as it has the effect of preventing reaggregation of the conductive material particles after loosening the conductive material particles and uniformly distributing the conductive material particles in the solvent. can.
- a nonionic dispersant having no ionic functional group is suitable because it does not inhibit the movement of lithium ions.
- nonionic dispersant one that acts as a binder after film formation and does not affect the electrical properties, or one that has a low decomposition temperature and is removed by heat treatment during electrode production is preferably used.
- Dispersants with these characteristics include polyvinylpyrrolidone, polyvinylbutyral, polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, polyvinyl alcohol, polyvinylacetal, polyvinylether, polyether, polyhydric alcohol ester, cellulose acetate, Cellulose acetate butyrate, methylcellulose, ethylcellulose, hydroxyethylcellulose, ethylhydroxyethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose. Most preferred of these are methylcellulose and polyvinylpyrrolidone.
- the nonionic dispersant preferably has a weight average molecular weight of 1,000 or more and 1,000,000 or less. It is more preferably 5,000 or more and 300,000 or less, and still more preferably 5,000 or more and 200,000 or less. If the weight-average molecular weight exceeds 1,000,000, the viscosity of the conductive material-dispersed paste becomes high, and the fluidity is lost, resulting in poor dischargeability and poor handling. On the other hand, if the weight-average molecular weight is less than 1,000, the dispersibility is poor, making it difficult to produce the conductive material-dispersed paste. These nonionic dispersants can be used alone or in combination of two or more. The weight average molecular weight can be measured using gel permeation chromatography (GPC).
- the method for producing the composite particles of the present invention is not particularly limited, but as an example of the preferred embodiment disclosed herein, the above materials are mixed with a dispersion medium and an additive, stirred, and the resulting mixed solution is subjected to a wet process.
- a conductive material-dispersed paste is produced by performing a pulverization treatment, and the conductive material composite particles are produced by removing the dispersion medium of the conductive material-dispersed paste by drying.
- the conductive material-dispersed paste in the present invention refers to a paste in which the conductive material is pulverized in a liquid dispersion medium and uniformly stabilized.
- the dispersion medium used for the conductive material-dispersed paste is not particularly limited as long as it can disperse the conductive material and can be removed in the subsequent drying step, but it is preferable to uniformly dissolve the dispersant used.
- Solvents capable of uniformly dissolving the dispersant used in the present invention include water, methanol, ethanol, N-methyl-2-pyrrolidone, methyl ethyl ketone, and the like. When used for lithium-ion secondary batteries, water and N-methyl-2-rollidone are generally selected, but water is preferred from the viewpoint of safety and convenience in the subsequent drying process, as well as consideration for the environment. is.
- the content of the dispersion medium is preferably in the range of 99.0 to 50.0% by mass, more preferably 99.0 to 60.0% by mass, still more preferably 99.0% to 70.0% by mass. %. If the amount of the dispersion medium is less than 50% by mass, the conductive material dispersion paste will have poor fluidity, and it may be difficult to keep the maximum particle size and viscosity within the preferred ranges in the wet pulverization process.
- Additives can be arbitrarily selected and included according to necessity when the conductive material dispersion paste is produced. Additives include pH adjusters, binders, solvents, thickeners, antifoaming agents, surfactants, preservatives, antifungal agents, and the like. As long as the effects of the present invention are not hindered, it may be contained in an arbitrary amount depending on the performance required for the electrode, the amount of dispersion medium blended, and the like.
- pH adjusters examples include potassium hydroxide, sodium hydroxide, and triethanolamine.
- the above pH adjusters may be contained singly or in combination of two or more.
- the content of the pH adjuster can be appropriately adjusted according to the desired pH.
- binders examples include water-soluble polymers and emulsion resins. Binders may be natural, semi-synthetic or synthetic. Specifically, cellulose, starch and modified products thereof, natural rubber, rosin and modified products thereof, polyvinyl alcohols, acrylic resins, epoxy resins, urethane resins, melamine resins and the like may be used as binders. The above binders may be contained singly or in combination of two or more.
- a solvent may be contained as an additive in order to adjust the drying property and the film forming property of the coating film.
- solvent means a substance different from the dispersion medium used for wet pulverization, and means the following substances used as modifiers.
- alcohols alkyl ether alcohols, glycols, diols, and the like may be used.
- alcohols include methanol, ethanol, and isopropyl alcohol.
- alkyl ether alcohols include ethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether and propylene glycol monobutyl ether.
- glycols examples include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, and polyethylene glycol having a number average molecular weight of 2000 or less.
- Diols include, for example, glycerin.
- the solvent may be contained singly or in combination of two or more.
- thickeners include natural polysaccharides and synthetic polymer thickeners.
- natural polysaccharides include guar gum, locust bin gum, galactomannan, pectin and its derivatives, psyllium pseudogum, tamarind gum, microbial xanthan gum, rheozan gum, rhamzan gum, welan gum, gellan gum, carrageenan of seaweed polysaccharides, alginic acid and Derivatives thereof, gum tarraganth of resinous polysaccharides, cellulose and derivatives thereof may be mentioned.
- Synthetic polymer-based thickeners include water active agents of polyacrylic acid and its crosslinked copolymers, polyvinyl alcohol, polyvinylpyrrolidone and its derivatives, polyvinyl methyl ether and its derivatives, polyether acrylic resins and silicon acrylic resins. Examples include emulsifying emulsions, self-emulsifying in water emulsions, and core-shell emulsions in water.
- the above thickeners may be contained singly or in combination of two or more.
- the dispersant is weighed so that the weight ratio to the conductive material is the ratio described later, added to the dispersion medium and stirred to dissolve sufficiently.
- an additive it is added at the same time as the dispersant depending on the application to an extent that does not hinder the function of each material.
- the method of stirring the material is not particularly limited, and a commercially available stirrer, kneader, mixer, or the like can be used.
- a conductive material is added to this dispersant solution and stirred to obtain a conductive material mixture.
- a wet pulverization process is applied to the conductive material mixed liquid, and pulverization and dispersion are performed until a predetermined viscosity and maximum particle size are obtained to obtain a predetermined conductive material dispersed paste described below.
- wet pulverization treatment commercially available wet pulverizers and wet dispersers can be used. As long as it can grind to a predetermined viscosity and maximum particle size, the method, type, etc.
- ball mills are not limited at all, and ball mills, sand grinders, dyno mills, spike mills, DCP mills, basket mills, paint Medialess dispersers such as wet media dispersers such as conditioners, nanomizers, agitzers, ultrasonic dispersers, thin-film rotating high-speed mixers, roll mills, colloid mills, high-pressure dispersers, homogenizers, and in-line mixers can be selected.
- the maximum particle size of carbon black in the conductive material-dispersed paste is preferably 50 ⁇ m or less, preferably less than 50 ⁇ m, more preferably 40 ⁇ m or less, and particularly preferably 30 ⁇ m or less. If the maximum particle size of the paste exceeds 50 ⁇ m, the distribution of the active material and the conductive material in the electrode coating film of the battery may become non-uniform, impairing the battery performance.
- the maximum particle size may be measured using a grind gauge in accordance with JIS K5600-2-5.
- the viscosity of the conductive material-dispersed paste is preferably 3000 mPa ⁇ s or less, more preferably 2000 mPa ⁇ s or less, and still more preferably 1000 mPa ⁇ s or less.
- the electrically conductive material composite particles of the present invention are produced by drying the electrically conductive material-dispersed paste prepared by the above method, removing part or all of the dispersion medium, and granulating.
- the method for removing the dispersion medium is not particularly limited, and commercially available dryers such as freeze dryers, spray dryers, flash dryers, thermal dryers and fluidized bed dryers can be used.
- Spray drying which can form particles and adjust the particle size at the same time as drying, and has the merits of shortening the process and simplifying equipment.
- Various spray dryers can be used in the spray drying method, and examples include centrifugal atomization and spray atomization. It is not particularly limited as long as it is one of When a spray dryer is used, the diameter of droplets can be reduced by increasing the feeding amount of conductive material dispersion paste, the supply amount of compressed air, and the number of revolutions of the disk. By this operation, the particle size after drying can be adjusted within a predetermined range described later, and the conductive material composite particles of the present invention can be obtained.
- the drying speed can be increased by raising the heating temperature, and the water content after drying can be further reduced.
- the heating temperature during drying can be arbitrarily finely adjusted from the temperature at which each material dries, but if it is less than 80 ° C. for all conductive materials, moisture tends to remain in the powder after drying, and the temperature exceeds 300 ° C.
- the temperature is preferably 80 to 300°C, more preferably 100 to 150°C, because deterioration and decomposition of the material tend to occur easily.
- the moisture content of the conductive material composite particles after drying is preferably 4% by weight or less, more preferably 1% by weight or less.
- the dispersion medium such as water remaining in the conductive material composite particles reduces the solubility of polyvinylidene fluoride, which is most often used as a binder when making an electrode paste, and prevents the formation of a uniform coating film.
- the remaining water is decomposed during the first charge of the lithium ion secondary battery, and the generated hydrogen and oxygen are released into the battery members.
- the moisture content is measured, and if the remaining moisture content is large, the drying time is extended until the remaining moisture content reaches a predetermined value or less.
- the water content can be measured using a commercially available moisture meter such as a halogen lamp heating moisture meter (manufactured by Shinko Denshi Co., Ltd., MA-120).
- the dried conductive material-dispersed paste is pulverized until a powder having a predetermined particle size, which will be described later, is obtained.
- the pulverization method is not particularly limited, and commonly used methods such as hammer mills, crushers, mixers, mortars, and ball mills can be suitably selected according to the equipment conditions and production volume.
- the conductive material composite particles from which the dispersion medium has been removed can be classified by sieving to obtain conductive material composite particles having a specific particle size range.
- the sieving operation is not particularly limited, it can be performed as follows. Of the multiple sieves with different nominal openings conforming to JIS8801-1, the one with the larger opening is stacked in order, and the conductive material composite particles are placed in the top sieve, and then shaken by an electromagnetic sieve. Shake for 30 minutes with a machine (manufactured by Fritsch Japan Co., Ltd.) to classify the conductive material composite particles by particle size. By taking out the particles that have passed through the desired openings and the particles that have not passed through, it is possible to obtain conductive material composite particles that have been classified to have a predetermined particle size.
- the conductive material composite particles obtained by these operations have the following characteristics and favorable properties.
- the conductive material composite particles of the present invention are characterized by having a particle size distribution D50 of 15 ⁇ m or more. It is preferably 20 ⁇ m or more, more preferably 25 ⁇ m or more. As a result of studies by the present inventors, it was found that when the particle size distribution D50 is smaller than 15 ⁇ m, the battery charge/discharge capacity and cycle characteristics are lowered. Further, it was found that when kneading for 10 minutes or longer when mixing with the active material to form an electrode paste, the electrical conductivity is greatly impaired. The mechanism is not completely clear, but the inventors speculate as follows.
- the conductive material contributes to the improvement of conductivity and battery performance by connecting the electrode and the active material and between the active materials in the electrode coating film to form a conductive path.
- a force is also applied to the conductive material, but the effect of the force differs depending on whether the particle size is large or small.
- the conductive material is carbon black
- carbon black generally forms a structure in which primary particles are connected by chemical bonds, and the structures are further van der Waals bonds, simple adhesion, entanglement, etc.
- the structure is dispersed in the paste while the bonds between the structures are maintained to some extent, so that conductive paths are easily formed, and the conductivity and battery performance are improved.
- the development of secondary aggregates is small and a large force is not required to loosen them. It is thought that it is also often used in For this reason, single structures with broken bonds and small aggregates in which only a few structures are bonded are dispersed in the paste, making it difficult to form conductive paths, and high conductivity and battery performance can be exhibited. Can not.
- the particle size distribution D10 As an index showing the range of the particle size that can maintain the bond between structures even after the electrode paste is made by the above action and express high conductivity and battery performance, in addition to the particle size distribution D50, the particle size distribution D10, Particle size distribution D90, average particle size, etc. can also be used.
- the particle size distribution D10 is used as an indicator, the particle size is preferably 10 ⁇ m or more, particularly preferably 15 ⁇ m or more.
- the particle size distribution D90 is used as an index, the particle size is preferably 30 ⁇ m or more, particularly preferably 40 ⁇ m or more.
- the particle size distributions D10, D50 and D90 are obtained by photographing a group of dispersed particles using a scanning electron microscope and measuring the maximum diameter passing through the center point of each particle.
- D10 is 10%
- D50 is 50%
- D90 is the value corresponding to the particle diameter at which the volume accumulation when drawn from .
- the particle size distributions D10, D50 and D90 of the conductive material composite particles can be measured by the following methods, but the measurement methods are not limited to these as long as the same results can be obtained. First, a conductive sample stage is used for antistatic purposes, and conductive material composite particles are dispersed on the sample stage so that the particles do not overlap each other.
- the conductive material composite particles preferably have a particle size of 150 ⁇ m or less as determined by sieving.
- the particle size obtained by sieving is more preferably 100 ⁇ m or less, particularly preferably 75 ⁇ m or less. Coarse particles are removed by sieving to a particle size of 150 ⁇ m or less, and battery performance can be improved. If the particle size obtained by sieving is larger than 150 ⁇ m, the conductive material is unevenly distributed in the electrode coating film, and sufficient electronic conductivity cannot be imparted to the active material.
- the particle size obtained by sieving as used herein refers to the minimum opening through which the target particles can pass, among the nominal openings of the sieve conforming to JIS8801-1.
- the sieving operation is not particularly limited as long as it is a sieve conforming to JIS8801-1, but by using the method disclosed in 0039, it is possible to pass through sieves of different sizes in one measurement, and measure the particle size. , classification of particles, and extraction of particles having a desired particle size can be performed at the same time.
- the second invention of the present application is characterized in that the upper limit of the particle diameter of the conductive material composite particles is 300 ⁇ m or less.
- the upper limit of the particle size is preferably 200 ⁇ m or less, particularly preferably 100 ⁇ m or less.
- coarse particles can be removed and the composite particles can obtain sufficient dispersing power.
- the electrode paste is applied, the conductive material is uniformly dispersed in the paste and in the electrode coating film, and sufficient conductivity can be imparted to the active material, thereby improving the charge/discharge capacity of the battery. can be done.
- the upper limit of the particle size refers to a measured value obtained by the following method. However, the measurement method is not limited to this as long as the same result can be obtained. First, a conductive sample stage is used for antistatic purposes, and conductive material composite particles are dispersed on the sample stage so that the particles do not overlap each other.
- the conductive material composite particles of the present invention preferably have an average particle size of 20 ⁇ m to 80 ⁇ m. More preferably 25 ⁇ m to 60 ⁇ m or less, most preferably 25 ⁇ m to 40 ⁇ m or less.
- the average particle size is the arithmetic mean of the largest diameters passing through the center point of each particle, and can be obtained as follows. It is not limited to this.
- a conductive sample stage is used for antistatic purposes, and conductive material composite particles are dispersed on the sample stage so that the particles do not overlap each other.
- a scanning electron microscope manufactured by Hitachi High-Tech Co., Ltd., FlexSEM1000
- AZtec manufactured by Oxford Instruments Co., Ltd., particle analysis software
- the conductive material composite particles of the present invention can contain 9% or more of particles having an aspect ratio of less than 1.2. Compared to particles having an aspect ratio of less than 1.2 and less than 9%, such conductive material composite particles have excellent handling properties during powder feeding, storage, etc., and excellent dispersibility when used as a conductive paste. ing. Furthermore, it may contain 55% or more of particles having an aspect ratio of less than 1.2 and 85% or more of particles having an aspect ratio of less than 1.5. When particles with an aspect ratio of less than 1.2 or less than 1.5 are contained in the above ratio or more, the dispersibility when used as an electrode paste is particularly improved, and the handling during powder feeding, storage, etc. is also improved. Therefore, it is highly preferable.
- the aspect ratio of the conductive material composite particles of the present invention refers to the ratio (a/b) between the maximum diameter (a) and the minimum diameter (b) passing through the center point of each particle, and can be obtained as follows.
- the measurement method is not limited to this as long as the same result can be obtained. First, a conductive sample stage is used for antistatic purposes, and conductive material composite particles are dispersed on the sample stage so that the particles do not overlap each other.
- the aspect ratio of each particle is measured, and from the measured value of 300 or more particles can be calculated.
- the aspect ratio of the conductive material composite particles can be within the above range, but by using spray drying in particular during drying, more particles with an aspect ratio close to 1 can be produced. can do.
- the conductive material composite particles of the present invention preferably have an angle of repose of less than 45°. More preferably, the angle of repose is less than 38°.
- the angle of repose referred to here is the mountain naturally formed by gently depositing powder on a horizontal surface, according to the measurement method specified in Japanese Industrial Standard JIS 9301-2-:2:1999. It can be obtained by reading the angle formed by the slope and the horizontal plane, but the measurement method is not limited to this as long as the same result can be obtained.
- the conductive material composite particles are characterized by containing 1 to 10 parts by weight of a dispersant with respect to 100 parts by weight of the conductive material. More preferably, it contains 4-10 parts by weight of dispersant, most preferably 6-10 parts by weight.
- a dispersant By using a dispersant, the conductive material can be uniformly pulverized and dispersed in the dispersion medium during the wet pulverization process.
- the presence of the dispersant in the conductive material composite particles after drying improves the dispersibility in the solvent. If the amount of the dispersant is less than 1 part by weight, there is a problem that a sufficient dispersing effect in the dispersion medium cannot be obtained in the wet pulverization treatment.
- the dispersant exceeds 10 parts by weight, there is a problem that the resistance value increases and the battery performance is adversely affected when the electrode coating film is formed.
- the decomposition temperature of the dispersant is not exceeded, and the dispersant is hardly removed even after the material mixing, wet dispersion, dispersion medium removal, and pulverization steps, or is coated with the conductive material.
- the weight ratio of the dispersant added during material mixing and stirring is within the above-mentioned range, so that the weight ratio of the conductive material composite particles is also within that range. can be done.
- the dispersant content in the conductive material composite particles after production can be measured and confirmed as necessary by the following method.
- the conductive material composite particles are heated until the dispersant is completely decomposed at a temperature at which the dispersant thermally decomposes and the weight of the conductive material does not change, and the weight of the dispersant is obtained from the weight difference before and after heating. can do things When the dispersant is dissolved or dispersed in another solvent or the like, the weight of the dispersant is converted to the amount of the active ingredient.
- a TG-DTA thermogravimetry/differential thermal analyzer
- the conductive material composite particles are held at 100 ° C. for 1 hour to completely remove moisture, and then heated to 300 ° C. at a rate of 5 ° C. per minute. and then maintained for an additional hour to decompose the dispersant.
- the weight after holding at 300° C. is the weight of only the conductive material, and the difference between the weight after holding at 100° C. and the weight after holding at 300° C. is the amount of dispersant in the conductive material composite particles.
- the bulk density of the conductive material composite particles is preferably 0.04 g/ml or more. More preferably 0.10 g/ml or more, still more preferably 0.20 g/ml or more. By setting the bulk density to the above numerical value or more, the particles are less likely to scatter in the production factory, and the cost for transportation and storage can be suppressed because dust collection equipment and the like are not required. Bulk density can be measured by measuring the initial bulk density according to R-1627-1997.
- the arithmetic mean roughness (Ra) when formed into a coating film is 0.4 or less. It is more preferably 0.3 or less, still more preferably 0.2 or less.
- Arithmetic mean roughness (Ra) is defined as the absolute value of the distance from the reference line in the interval measured from the unevenness in the height direction of the surface in a certain reference length (section). It is the numerical value which calculated the average.
- a high numerical value for arithmetic mean roughness (Ra) means that there are many irregularities. In other words, the main causes of irregularities on the coating film are aggregation and uneven distribution of the conductive material, coarse particles, and foreign matter. means likely.
- the arithmetic mean roughness means a numerical value specified by the following method, but the method is not limited to this as long as the same result can be obtained.
- conductive material composite particles were added to a solution obtained by diluting commercially available polyvinylidene fluoride ("KF Polymer W#7200" manufactured by Kureha Corporation) as a binder to 8.0% with N-methyl-2-pyrrolidone as a solvent.
- a paste is prepared by weighing and adding so that it becomes 8.3% of the whole, and kneading for 1 minute at 2000 rpm with a rotation-revolution mixer (manufactured by Thinky Co., Ltd., Awatori Mixer). This paste was applied to a glass plate using an applicator so that the film thickness after drying was 7.5 to 8.5 ⁇ m, and dried in a hot air dryer at 100 ° C. for 30 minutes to remove the solvent.
- the surface roughness of the coating film for dispersibility evaluation is measured using a contact-type surface roughness meter (Surfcom 130A, manufactured by Tokyo Seimitsu Co., Ltd.), and the arithmetic mean roughness is calculated.
- the conductive material composite particles are characterized by having an optical density OD value of 3.0 or more when dispersion is evaluated. It is more preferably 3.5 or more, still more preferably 4.0 or more.
- the OD value at the time of dispersion evaluation here is a numerical value obtained by measuring the above-mentioned dispersibility evaluation coating film using a spectrodensitometer (manufactured by Videojet X-Rite Co., Ltd., x-rite). The measurement method is not limited to this as long as the same result can be obtained.
- the OD value is obtained by measuring the spectral transmittance of the coating film and expressing the degree of light absorption in logarithm. .
- the conductive material composite particles of the present invention satisfying the above properties exhibit the following performances and effects.
- the shear viscosity when making into an electrode paste is low, so it is excellent in coatability and has an appropriate viscosity gradient at low and high shear. It is possible to suppress sedimentation of the active material and prevent uneven distribution of the conductive material when it is formed into a coating film.
- agglomeration is easily loosened in the kneading process when making the electrode paste, the film thickness becomes uniform when the film is formed, and it is difficult for the film thickness to locally become thinner or the film is not formed, resulting in a higher yield. rises.
- the paste becomes uniform in a shorter stirring time than the powdery conductive material, so that cost merits can be obtained by shortening the process time.
- the conductive material is less likely to be unevenly distributed in the coating film, so the conductive material is evenly dispersed among more active materials in the electrode coating film, giving electronic conductivity. It is considered that the charge/discharge capacity can be increased as a result, and the occurrence of early capacity decrease due to local current concentration at the positive and negative electrodes can be reduced.
- the conductive material composite particles do not contain a solvent, it is possible to reduce the amount of organic solvent used during manufacturing compared to a slurry-like conductive material dispersed paste, thereby reducing the burden on the environment. In addition, it can be used regardless of the type and presence of the solvent used when making the electrode paste.
- the lithium ion secondary battery of the present invention is an electrode paste prepared by dispersing the conductive material composite particles of the present invention together with an electrode active material and a binder in a non-aqueous solvent such as N-methyl-2-pyrrolidone on a metal substrate.
- a positive electrode prepared by coating and drying, or an electrode paste prepared by dispersing the conductive material composite particles of the present invention together with an electrode active material and a binder in a solvent such as water is coated and dried on a metal substrate. It can be produced by winding the produced negative electrode around a separator and housing it in a battery can together with an electrolytic solution.
- a fuse In order to prevent pressure rise inside the battery, overcharge/discharge, and the like, a fuse, an overcurrent prevention element such as a PTC element, an expanded metal, a lead plate, and the like may be provided as necessary.
- the shape of the battery can be, for example, coin-shaped, button-shaped, sheet-shaped, cylindrical, rectangular, or flat.
- the characteristics of the conductive material composite particles of the present invention are not limited to lithium ion secondary batteries, but also when used in other power storage devices. It is effective for improvement, cost reduction, and reduction of environmental load.
- the conductive material composite particles of the present invention can be suitably used as a substitute for these existing conductive materials. .
- primary batteries such as alkaline manganese dry batteries and nickel-manganese batteries
- secondary batteries such as nickel-hydrogen batteries, nickel-cadmium batteries, sodium-sulfur batteries, and sodium-ion batteries
- other electrochemical elements such as capacitors.
- the electrically conductive material already used may be replaced with the electrically conductive material composite particles of the present invention. If the existing conductive material is a particulate conductive material such as carbon black, it can be substituted as it is.
- a slurry-like conductive material such as a carbon black dispersion
- it can be used by replacing the conductive material with the conductive material composite particles of the present invention and adjusting the solid content of the electrode paste to achieve an appropriate viscosity.
- Example 1 To 84 parts by weight of ion-exchanged water used as a dispersion medium, 1 part by weight of methyl cellulose polymer (weight average molecular weight 35,000 as measured by GPC) was added as a dispersant, and thoroughly dissolved with a commercially available stirrer to obtain a dispersant solution. rice field. Next, in 85 parts by weight of the resulting dispersant solution, 15 acetylene black (manufactured by Denka Co., Ltd., "Denka Black Granular") having an average primary particle diameter of 35 nm as a conductive material measured according to ASTM: D3849-14. A conductive material mixture was obtained by adding weight parts and mixing and stirring with a commercially available stirrer.
- acetylene black manufactured by Denka Co., Ltd., "Denka Black Granular
- the resulting conductive material mixture was subjected to wet pulverization using a commercially available horizontal bead mill to refine the conductive material until there were no particles of 50 ⁇ m or more as evaluated by a grind gauge, thereby obtaining a conductive material dispersed paste.
- the obtained conductive material-dispersed paste was filtered through a mesh with an opening of 50 ⁇ m to remove foreign matter, and a conductive material-dispersed paste 1 was obtained.
- the conductive material dispersion paste 1 is dried using a commercially available spray nozzle type spray dryer at an inlet temperature of 160 ° C. and a spray pressure of 0.03 MPa, and an electromagnetic sieve shaker (manufactured by Fritsch Japan Co., Ltd.).
- Conductive material composite particles 1 having a particle size of 75 ⁇ m or less and 45 ⁇ m or more were obtained by sieving in the classification used.
- Example 2 To 84 parts by weight of ion-exchanged water used as a dispersion medium, 1 part by weight of polyvinylpyrrolidone (weight-average molecular weight measured by GPC: 66,800) was added as a dispersant, and thoroughly dissolved with a commercially available stirrer. A conductive material-dispersed paste 2 was obtained by performing the same operation. Except for using this conductive material dispersion paste 2, the subsequent operations were performed in the same manner as in Example 1, and the particle size was determined by sieving by classification using an electromagnetic sieve shaker (manufactured by Fritsch Japan Co., Ltd.). Conductive material composite particles 2 having a size of 75 ⁇ m or less and 45 ⁇ m or more were obtained.
- Example 3 The conductive material dispersion paste 1 obtained by performing the same operation as in Example 1 was dried at 100° C. for 12 hours using a commercially available hot air dryer, and the resulting dried body was pulverized with a commercially available cutter mixer. After that, by classifying using an electromagnetic sieve shaker (manufactured by Fritsch Japan Co., Ltd.), conductive material composite particles 3 having a particle size of 75 ⁇ m or less and 45 ⁇ m or more by sieving were obtained.
- an electromagnetic sieve shaker manufactured by Fritsch Japan Co., Ltd.
- Example 4 The conductive material dispersion paste 1 obtained by performing the same operation as in Example 1 was dried at 100 ° C. for 12 hours using a commercially available hot air dryer, and the obtained dried body was pulverized with a commercially available cutter mixer. After that, by performing classification using an electromagnetic sieve shaker (manufactured by Fritsch Japan Co., Ltd.), conductive material composite particles 4 having a particle size of 150 ⁇ m or less and 75 ⁇ m or more by sieving were obtained.
- an electromagnetic sieve shaker manufactured by Fritsch Japan Co., Ltd.
- Example 1 The conductive material dispersion paste 1 obtained by performing the same operation as in Example 1 was dried at 100 ° C. for 12 hours using a commercially available hot air dryer, and the obtained dried body was pulverized with a commercially available cutter mixer. After that, by classifying using an electromagnetic sieve shaker (manufactured by Fritsch Japan Co., Ltd.), conductive material composite particles 5 having a particle size of 250 ⁇ m or less and 150 ⁇ m or more by sieving were obtained.
- an electromagnetic sieve shaker manufactured by Fritsch Japan Co., Ltd.
- Example 2 The conductive material dispersion paste 1 obtained by performing the same operation as in Example 1 was dried at 100 ° C. for 12 hours using a commercially available hot air dryer, and the obtained dried body was pulverized with a commercially available cutter mixer. After that, by classifying using an electromagnetic sieve shaker (manufactured by Fritsch Japan Co., Ltd.), conductive material composite particles 6 having a particle size of 500 ⁇ m or less and 250 ⁇ m or more by sieving were obtained.
- an electromagnetic sieve shaker manufactured by Fritsch Japan Co., Ltd.
- Example 3 The conductive material dispersion paste 1 obtained by performing the same operation as in Example 1 was dried at 100 ° C. for 12 hours using a commercially available hot air dryer, and the obtained dried body was pulverized with a commercially available cutter mixer. After that, by performing classification using an electromagnetic sieve shaker (manufactured by Fritsch Japan Co., Ltd.), conductive material composite particles 7 having a particle size of 45 ⁇ m or less by sieving were obtained.
- an electromagnetic sieve shaker manufactured by Fritsch Japan Co., Ltd.
- the DBP oil absorption of acetylene black used as a conductive material in each example and comparative example was measured according to JIS6217-4. The measured value was 360ml/100g.
- the viscosities of conductive material dispersed pastes 1 and 2 were measured using a B-type viscometer (TVB10 M-type viscometer manufactured by Toki Sangyo Co., Ltd.).
- the moisture content of the conductive material composite particles 1, 2, 3, 4, 5, 6, and 7 and the conductive material base 1 was measured using a halogen lamp heating moisture meter (manufactured by Shinko Denshi Co., Ltd., MA-120). .
- the arithmetic mean roughness of the conductive material composite particles 1, 2, 3, 4, 5, 6 and 7 and the conductive material raw material 1 was measured by the following method.
- Conductive material composite particles or conductive The materials were weighed and mixed so that the material raw material was 8.3% of the whole, and kneaded at 2000 rpm for 1 minute with a rotation/revolution mixer (manufactured by Thinky Co., Ltd., Awatori Mixer) to prepare a paste.
- This paste was applied to a glass plate using an applicator so that the film thickness after drying was 7.5 to 8.5 ⁇ m, and dried in a hot air dryer at 100 ° C. for 30 minutes to remove the solvent.
- the coating film obtained here be the "coating film for dispersibility evaluation.”
- the arithmetic mean roughness (Ra) and the arithmetic mean height (Sa) of this dispersibility evaluation coating film were measured and calculated using a contact-type surface roughness meter (Surfcom 130A, manufactured by Tokyo Seimitsu Co., Ltd.). Further, the OD value of the coating film for evaluation of dispersibility was measured using a spectral densitometer (x-rite, manufactured by Videojet X-Rite Co., Ltd.).
- Li Ni 1/3 Co 1/3 M n 1 as a commercially available active material HED NCM111 1100 (manufactured by BASF Toda Battery Materials LLC) (referred to as B), which is a composition of / 3 O 2 , and PVdF (Solef 5130 manufactured by Solvay Japan Co., Ltd.) as a binder (referred to as C), and the solid content of each
- B Li Ni 1/3 Co 1/3 M n 1 as a commercially available active material HED NCM111 1100 (manufactured by BASF Toda Battery Materials LLC)
- B which is a composition of / 3 O 2 , and PVdF (Solef 5130 manufactured by Solvay Japan Co., Ltd.) as a binder
- C binder
- evaluation electrode paste A was obtained by kneading for 2 minutes at 2000 rpm in a rotation/revolution mixer. Further, “evaluation electrode paste B” was obtained in the same manner as the coating film evaluation paste A, except that the kneading time by the rotation/revolution mixer was changed to 10 minutes.
- the dispersant contained in the composite particles acts as a binder on the electrode coating film, so the amount of the dispersant is Considered as the amount of binder, in calculating the compounding ratio, divide the amount of dispersant contained in the conductive material composite particles from A, add this amount of dispersant to C, and then A, B, and C are each 2 parts by weight,
- the conductive material composite particles, the active material, and the binder were weighed to 97 parts by weight and 1 part by weight. After applying the above evaluation electrode paste A and evaluation electrode paste B onto the PET film using an applicator, it was dried at 100 ° C. for 30 minutes using a hot air dryer to remove NMP and the film thickness was 100 ⁇ m.
- Electrode paste evaluation coating film A and “electrode paste evaluation coating film B”, respectively.
- the electrode paste evaluation coating film A was exposed in cross section using a cross-section cutter for SEM sample preparation, and a scanning electron microscope (FlexSEM1000 manufactured by Hitachi High-Tech Co., Ltd.) and an energy dispersive X-ray spectrometer (Oxford) - Using AZtecEnergy x-act (manufactured by Instruments Co., Ltd.), the dispersion state of the conductive material in the coating film was photographed at a magnification of 500 times.
- the coating film resistance was measured by the following method. First, the coating film was cut into pieces of 2 cm in width and 3 cm in length, and the volume resistivity of the coating film was measured at an applied voltage of 10 V using a resistivity meter (manufactured by Nitto Seiko Analytic Tech Co., Ltd., Loresta-GP MCP-T610). Table 1 shows the results of each measurement test described above.
- CR2032 type (diameter 20 mm height 3.2 mm ) was fabricated, and its performance was evaluated.
- the secondary battery disclosed below and the method for producing the same are merely examples for evaluating the conductive material composite particles of the present invention, and do not limit the usage and embodiments of the conductive material composite particles of the present invention. not a thing
- the conductive material composite particles of the present invention are not limited to each material, battery manufacturing method, battery form, and other conditions disclosed below, and are suitably used as electrode materials for a wide range of power storage devices including lithium ion secondary batteries. be able to.
- Positive electrode active material HED NCM111 1100 manufactured by BASF Toda Battery Materials LLC, theoretical capacity: 160 mAh / g
- binder PVdF (Solef 5130 manufactured by Solvay Japan)
- conductive material conductive material composite particle 1
- the binder is dissolved in a solvent (N-methyl-2-pyrrolidone)
- the positive electrode active material and the conductive material are mixed, and the solid content of the coating liquid is 70 to 75 with the solvent.
- This electrode paste was applied to an aluminum foil having a thickness of 20 ⁇ m so that the basis capacity (battery capacity per unit area) was 3.0 to 4.0 mAh/cm 2 .
- the positive electrode coated plate obtained here the electrode paste is dried and formed into a film on the aluminum foil that is the current collector.
- This positive electrode coating plate is pressed so that the electrode density (positive electrode mixture layer mass/positive electrode mixture layer volume) is 2.9 to 3.4 g/cm 3
- a ⁇ 14 mm piece was punched out by a coin-shaped punching machine to obtain a positive electrode.
- the positive electrode mixture layer mass is obtained by subtracting the aluminum foil mass from the positive electrode coating plate weight
- the positive electrode mixture layer volume is obtained by subtracting the aluminum foil thickness from the positive electrode coating plate thickness. After setting the height, ⁇ 14 mm was determined as the bottom area.
- a separator (“Seillon P2010”, material: polypropylene, ⁇ 17 mm, manufactured by CS Tech) is inserted between the positive electrode obtained as described above and the negative electrode (lithium foil, thickness 200 ⁇ m, ⁇ 16 mm, manufactured by Honjo Metal Co., Ltd.), and electrolysis is performed.
- a CR2032 type coin cell filled with a liquid (1.0M LiPF6 EC:DEC (1:1 v/v%), manufactured by Kishida Chemical Co., Ltd.) was assembled to prepare a battery for evaluation.
- charge/discharge tester Model 580 high-performance charge/discharge system manufactured by Scribner Associates
- charge/discharge and actual discharge capacity of the resulting battery for evaluation were measured as follows. Charging and discharging was carried out at room temperature (25° C.) by constant current/constant voltage charging at 1C to full charge with an upper limit voltage of 4.3V, and then discharging to 3.0V at a constant current of 1C. A total of 30 cycles were performed with this as one cycle, and the actual discharge capacity at the 30th cycle was measured. A rest period of 10 minutes was provided from the completion of full charge to the start of discharge in each cycle and between each cycle.
- the effective capacity refers to the ratio of the actual discharge capacity when the theoretical capacity (mass (g) of the positive electrode mixture layer ⁇ active material mixture ratio ⁇ theoretical capacity of the active material per 1 g) is taken as 100%. Also, the effective capacity in the first cycle was taken as the initial effective capacity.
- the capacity retention rate is a value indicating the ratio of the effective capacity at the 30th cycle to the initial effective capacity of 100%.
- Batteries were produced in the same manner as in Example 1 except that the conductive material was changed to each of the composite particles and conductive material raw materials shown in Table 1, and the performance thereof was evaluated. Table 1 shows the results.
- the conductive material composite particles of Examples had an OD value of 3.0 or more after coating, indicating that the conductive material was uniformly dispersed in the coating. .
- the optical density of the coating film exceeded 4.0, indicating that the uniformity was very excellent.
- Comparing Examples 3 and 4 which differ only in the upper limit of the particle size, with Comparative Examples 1 and 2, the optical density is lowered in the comparative example in which the particle size of the composite particles is large, indicating a decrease in uniformity.
- the surfaces of Comparative Examples 1 and 2 are rougher than those of Examples, indicating that many coarse particles are present in the coating film.
- Comparative Example 4 has a low OD value, and the surface roughness of the coating film is not good.
- the white spherical substance is the active material, and is attached around it.
- the gray haze indicates the conductive material.
- carbon which is a conductive material, is visualized in white. From these figures, in the example, the conductive material is evenly distributed between the active materials, but in the comparative example, there are places where it is concentrated and places where it is almost absent. It can be seen that they are unevenly distributed.
- the EDS analysis images of Comparative Examples 1, 2 and 4 show the presence of coarse particles or aggregates (white lumps in the images).
- FIG. 1 shows the presence of coarse particles or aggregates (white lumps in the images).
- Comparative Examples 1, 2 and 3 have low effective capacity and low capacity retention rate. Also, in Comparative Example 4, the capacity retention rate at the 30th cycle is significantly reduced.
- the conductive material is uniformly dispersed between the active materials in the coating film, and sufficient electronic conductivity is obtained for many active materials. It is possible to impart properties, and it is possible to improve the charge-discharge capacity when made into a battery. In addition, there is no uneven distribution or agglomeration of the conductive material, and there are no coarse particles or foreign matter. Low compared to technology, battery performance can be maintained for a long time.
- a lithium ion secondary battery using the present invention can be suitably used as a power source for an electric motor mounted on an electric vehicle or the like.
- the conductive material composite particles of the present invention can be stored at room temperature for a long period of time, and the amount of solvent used during production is suppressed, so that the environmental load and production costs can be reduced.
- the conductive material composite particles of the present invention as a substitute for existing conductive materials such as carbon black, performance is improved not only in lithium ion secondary batteries but also when used in other power storage devices. It can contribute to cost reduction.
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Abstract
Description
このうち、正極は電極活物質としてリチウム遷移金属複合酸化物等を用いる。正極で用いられるこれらの電極活物質単独では電子伝導性、即ち導電性に乏しいため、導電性を付与するために高度にストラクチャーが発達した導電性カーボンブラックや、結晶が著しい異方性を示すグラファイト等の炭素材料を導電材として添加し、バインダーとともにN-メチル-2-ピロリドン等の非水系溶媒に分散させて電極ペーストを作製し、この電極ペーストを金属箔上に塗布・乾燥して電極塗膜を形成し、正極を作製する。
負極においてはシリコン等の導電性の低い材料のほか、グラファイトなどの炭素系材料が電極活物質として主に用いられる。炭素系材料は導電性を有しているが、大きさによっては活物質間に間隙が生じ単独では電子伝導パスを十分に形成できない場合があるため、正極と同じく導電材を用いて導電性を向上させることが有効である。
このように、導電材はリチウムイオン二次電池において重要な役割をしており、高い充放電容量、充放電能力の長期安定性といった電池性能の向上のためには、容易に分散し、活物質周辺へ満遍なくいきわたり導電性を付与することができる分散性・均一性の高い導電材が必要とされる。
(1) 少なくとも導電材及び分散剤を含有する粒子であって、粒度分布D50が15μm以上かつふるい分けによる粒子径が150μm以下の粒子であり、導電材のDBP吸油量が550ml/100g以下であり、導電材100重量部に対して分散剤を1~10重量部含むことを特徴とする導電材複合粒子、
(2)少なくとも導電材及び分散剤を含有する粒子であって、粒度分布D50が15μm以上かつ粒子径上限が300μm以下の粒子であり、導電材のDBP吸油量が550ml/100g以下であり、導電材100重量部に対して分散剤を1~10重量部含むことを特徴とする導電材複合粒子、
(3) 分散評価時のOD値が3.0以上であることを特徴とする上記(1)または(2)のいずれかに記載の導電材複合粒子、
(4) 前記分散剤が、非イオン性分散剤であることを特徴とする、上記(1)または(2)に記載の導電材複合粒子、
(5) 前記非イオン性分散剤の重量平均分子量が1,000~1,000,000であることを特徴とする、上記(4)に記載の導電材複合粒子、
(6) 前記導電材の純度が99.9%以上であることを特徴とする、上記(1)または(2)に記載の導電材複合粒子、
(7) 前記導電材の平均一次粒子径が10nm以上50nm以下であることを特徴とする、上記(1)または(2)に記載の導電材複合粒子、
(8) 電池電極用の導電材である、上記(1)または(2)に記載の導電材複合粒子、
(10) 前記導電材分散ペーストに粒子径50μmを超える異物を含まないことを特徴とする、上記(9)記載の導電材複合粒子の製造方法、
(11) 前記導電材分散ペーストを、80℃以上300℃以下で加熱する乾燥工程を含むことを特徴とする、前記(9)又は(10)に記載の導電材複合粒子の製造方法、
(12) 上記(1)または(2)に記載の導電材複合粒子を少なくとも活物質及びバインダーと混合し、基板に塗布することを特徴とする電極の製造方法、
(13) 上記(9)または(10)に記載の製造方法により得られた導電材複合粒子を少なくとも活物質及びバインダーと混合し、基板に塗布することを特徴とする電極の製造方法、
(14) 上記(12)に記載の方法により得られた電極を用いたリチウムイオン二次電池、
(15) 上記(1)または(2)に記載の導電材複合粒子を用いた蓄電装置、
(16) 上記(12)に記載の方法により得られた電極を用いた蓄電装置、
にある。
加えて、粗大粒子や異物が除去されているため、導電材がペースト内で偏在することなく分散し、活物質周辺に均一に分布し十分な電子導電性を付与することができるため、優れた充放電容量を実現する電極塗膜を形成することができる。また、粗大粒子や導電材の偏在による局所的な通電、短絡が起こりにくいため、電池の熱暴走や、早期の充放電能力低下といった不具合の発生を抑え、長期にわたり電池性能を維持することができると考えられる。
また、本発明によって得られる導電材複合粒子は、溶媒を実質的に含まない乾燥した粉体であるため、液状又はペースト状の導電材と比較して沈降や固化による経時劣化の恐れがなく、常温で長期に保管することができる安定性を有しているほか、製造時の有機溶剤使用量を削減し環境への負荷を軽減させることができる。
本発明に用いる導電材としては、カーボンブラック及びカーボンナノチューブ、カーボンナノファイバー、黒鉛、グラフェン、ハードカーボン等を好適に用いることができる。この中では、ストラクチャーにより電極内で効率的に導電パスを形成し導電性を向上させる事ができるカーボンブラックが好ましく、カーボンブラックとしては、ケッチェンブラック、ファーネスブラック、アセチレンブラック、サーマルブラック等が使用できるが、導電性が高く不純物が少ない点と、重過負荷特性が優れる点で、アセチレンブラックが特に好ましい。また、これらの導電材1種を単独で又2種以上を併せて用いることができる。
ここでいう、平均一次粒子径とは、ASTM:D3849-14に準拠して、透過型電子顕微鏡を用いて測定された算術平均粒子径を示す。
導電材のDBP吸油量は、JIS6217-4に準拠して測定すれば良い。
なお、カーボンブラックの純度は、JIS K1469又はJIS K6218に準拠して測定した灰分を不純物とし、その不純物量に基づき算出できる。
中でも好ましくはデンカブラック粉状品、デンカブラック粒状品、デンカブラックFX-35、デンカブラックHS-100、デンカブラックLi Li-100、デンカブラックLi Li-250、デンカブラックLi Li-400、デンカブラックLi Li-435であり、より好ましくはデンカブラック粒状品、デンカブラックFX-35、デンカブラックLi Li-100、デンカブラックLi Li-435であり、特に好ましくはデンカブラック粒状品、デンカブラックFX-35である。
本発明でいう分散剤とは無機、有機顔料を分散媒体中に均一に分散させ安定な分散体を調整するために使用される添加剤を意味し、そのイオン性により、アニオン性、カチオン性、非イオン性、両性に大別される。本発明に用いる分散剤としては、導電材の凝集をほぐした後、導電材粒子の再凝集を防ぐとともに溶媒中に導電材粒子を均一に分布させる効果があれば、任意のものを用いる事ができる。その中でもリチウムイオンの移動を阻害しないので、イオン性官能基を有さない非イオン性分散剤が適している。
非イオン性分散剤としては、皮膜形成後にバインダーとして作用して、電気特性に影響を及ぼさないもの、あるいは、電極作製時に加熱処置で除去される分解温度が低いものが好適に使用される。これらの特徴を持つ分散剤としては、ポリビニルピロリドン、ポリビニルブチラール、ポリフッ化ビニリデン、ポリテトラフルオロエチレン、ポリヘキサフルオロプロピレン、ポリビニルアルコール、ポリビニルアセタール、ポリビニルエーテル、ポリエーテル、多価アルコールエステル、セルロースアセテート、セルロースアセテートブチレート、メチルセルロース、エチルセルロース、ヒドロキシエチルセルロース、エチルヒドロキシエチルセルロース、ヒドロキシエチルセルロース、ヒドロキシプロピルセルロース、ヒドロキシプロピルメチルセルロースが挙げられる。中でも最も好ましいのはメチルセルロース又はポリビニルピロリドンである。
重量平均分子量は、ゲルろ過クロマトグラフィー(GPC)を用いて測定する事ができる。ゲルろ過クロマトグラフィーでの測定条件の例を以下に記す。
装置:高速液体クロマトグラフ(島津製作所株式会社製、Prominence)
カラム:Shodex株式会社製、OHpakSB-802.5HQ
Shodex株式会社製、OHpakSB-804HQ
検出器:RI
溶離液:0.5M NaCl水溶液
流量:1.0ml/min
試料濃度:0.2wt/vol%
カラム温度:40℃
本発明の複合粒子を製造する方法は特に限定されないが、ここで開示する好適な実施形態の一例としては、以上の材料を分散媒及び添加剤と混合して攪拌し、得た混合液に湿式粉砕処理を行うことで導電材分散ペーストを作製し、その導電材分散ペーストの分散媒を乾燥により除去することで導電材複合粒子を作製する。なお、本発明における導電材分散ペーストとは、導電材が液状の分散媒中に解砕され、均一に安定化された状態のものをいう。
前記導電材分散ペーストに使用する分散媒としては、導電材が分散でき、後の乾燥工程で除去可能な分散媒であれば特に限定されないが、使用する分散剤を均一に溶解させるものが好ましい。本発明で使用する分散剤を均一に溶解させる事ができる溶媒としては、水、メタノール、エタノール、N-メチル-2-ピロリドン、メチルエチルケトン等がある。リチウムイオン二次電池用に使用する場合は一般に水やN-メチル-2-ロリドンが選択されるが、後の乾燥工程での安全性や利便性、環境面への配慮の観点から水が好適である。
分散媒の配合量としては、99.0~50.0質量%の範囲で有る事が好ましく、より好ましくは99.0~60.0質量%、更に好ましくは99.0%~70.0質量%である。分散媒量が50質量%より少ない場合、導電材分散ペーストが流動性に乏しくなり、湿式粉砕処理工程において最大粒子径と粘度を好ましい範囲とする事が難しい場合がある。
導電材分散ペースト作製時には、必要性に応じて添加剤を任意で選択し含む事ができる。添加剤としては、pH調整剤、バインダー、溶剤、増粘剤、消泡剤、界面活性剤、防腐剤、防かび剤等が挙げられる。本発明の効果を妨げない範囲であれば、電極で所望される性能要求や分散媒配合量等に応じて任意の量を含有して良い。
例として、アルコール類、アルキルエーテルアルコール類、グリコール類、ジオール類などを使用してよい。アルコール類としては、例えばメタノール、エタノール、イソプロピルアルコールなどが挙げられる。アルキルエーテルアルコール類としては、例えばエチレングルコールモノメチルエーテル、ジエチレングリコールモノエチルエーテル、ジエチレングルコールモノブチルエーテル、トリエチレングリコールモノブチルエーテル、プロピレングリコールモノブチルエーテルなどが挙げられる。グリコール類としては、例えばエチレングリコール、ジエチレングリコール、トリエチレングリコール、テトラエチレングリコール、プロピレングリコール、ジプロピレングリコール、トリプロピレングリコール、数平均分子量2000以下のポリエチレングリコールなどが挙げられる。ジオール類としては、例えばグリセリンなどが挙げられる。上記の溶剤を単独で含有してもよいし、2種以上を組み合わせて含有してもよい。
まず、導電材に対する重量比が後述する比率になるように分散剤を秤量し、分散媒に加えて攪拌し充分に溶解させる。添加剤を加える場合は、分散剤と同時に、用途に応じて各材料の機能を阻害しない程度に加える。材料を攪拌する方法は特に限定されず、市販の撹拌機、混錬機、ミキサー等を用いることができる。次いで、この分散剤溶解液に導電材を加えて攪拌し、導電材混合液を得る。
前記導電材混合液に湿式粉砕処理を加え、所定の粘度、最大粒子径となるまで粉砕・分散し、以下に説明する所定の導電材分散ペーストを得る。湿式粉砕処理には、市販の湿式粉砕装置、湿式分散装置を用いることができる。所定の粘度、最大粒子径まで粉砕を行うことができる装置であれば、その方式、種類等は何ら限定されるものではなく、ボールミル、サンドグラインダー、ダイノミル、スパイクミル、DCPミル、バスケットミル、ペイントコンディショナーなどの湿式メディア分散機、ナノマイザー、アルチマイザー、超音波分散機、薄膜旋回型高速ミキサー、ロールミル、コロイドミル、高圧分散機、ホモジナイザー、インラインミキサーなどのメディアレス分散機を選択することができる。
ペーストの最大粒子径が50μmを超えると、電池の電極塗膜中での活物質と導電材の分布が不均一化し電池性能を損なう場合がある。最大粒子径は、JIS K5600-2-5に準拠し、グラインドゲージを用いて測定すればよい。
前記のグラインドゲージによる最大粒子径の測定では、50μmを超える粒子を完全に除去することはできないため、導電材分散ペーストを作製した後、50μmを超える異物、粗大粒子を除去する工程を含む事が好ましい。ここでいう異物とは、分散ペーストに含まれる50μmを超える導電材を含むあらゆる物質をいう。異物、粗大粒子を除去しておく事により、電極ペーストとして用いた際に電極塗膜上で粗大粒子同士が接触して短絡回路を形成することを防ぎ、電池に内部短絡が発生するリスクを軽減する事ができる。異物除去の方法は特に限定されないが、送液ポンプ等を用いて導電材分散ペーストを送液し、経路上にセットしたフィルターや磁選機を通液させる事によって、所定のサイズ以上の異物を除去する事ができる。
以上の方法で作製した導電材分散ペーストを乾燥させ、その分散媒の一部又は全部を除去し、粒子化することで、本発明の導電材複合粒子を作製する。分散媒の除去方法は特に限定されず、凍結乾燥機、噴霧乾燥機、気流乾燥機、温熱乾燥機、流動層乾燥機など市販の乾燥機を用いる事ができる。
これらの乾燥方法の中では、乾燥と同時に粒子の形成と粒径の調整を行うことができ、工程の短縮や設備簡素化のメリットがある噴霧乾燥を用いることが特に好ましい。噴霧乾燥法には各種の噴霧乾燥機を用いることができ、例えば遠心噴霧式やスプレー噴霧式が例として挙げられるが、液体又は固体と液体の混合物等を、気体中に噴霧して乾燥させる方式のものであれば特に限定されない。噴霧乾燥機を用いた場合には、材料である導電材分散ペーストの送液量や圧縮エアの供給量、ディスクの回転数を増加させる事で液滴径を小粒径化させる事ができる。この操作によって、乾燥後の粒子径を後述する所定の範囲内に調整することができ、本発明の導電材複合粒子を得ることができる。
導電材分散ペーストの乾燥時には、加熱温度を上げる事で乾燥速度を早くする事ができ、乾燥後の水分量をさらに低減させる事ができる。乾燥時の加熱温度はそれぞれの材料が乾燥する温度から任意に微調整することができるが、すべての導電材について80℃を下回ると乾燥後の粉体に水分が残りやすくなり、300℃を超えると材料の劣化、分解が発生しやすくなるため、80~300℃とするのが好ましく、100~150℃とするのがより好ましい。
分散媒除去においては、乾燥後の導電材複合粒子の水分量が4重量%以下である事が好ましく、1重量%以下で有ることがより好ましい。導電材複合粒子中に残存する水などの分散媒は、電極ペースト化時のバインダーとして最もよく用いられているポリフッ化ビニリデンの溶解性を低下させ、均一な塗膜を作製できず合材層内の強度の低下、及び合材層と金属箔との密着性の低下を引き起こすほか、リチウムイオン二次電池にした際の初回充電時に残存水が分解され、発生した水素と酸素が電池内の部材を劣化させる要因となる。水分量が4重量%を超える場合は、これらの作用の影響が大きくなり電池性能が低減するおそれがある。乾燥後に水分量を測定し、残存している水分量が多い場合は乾燥時間を延ばして所定の数値以下になるまで乾燥させる。水分量の測定は、ハロゲンランプ加熱式水分計(新光電子株式会社製、MA-120)等の市販の水分計を用いて測定する事ができる。
前記分散媒除去工程において噴霧乾燥以外の乾燥方法を用いた場合は、乾燥後の導電材分散ペーストを後述する所定の粒子径を有する粉体が得られるまで粉砕する。粉砕の方法は特に限定されず、設備状況や作製量に合わせてハンマーミル、クラッシャー、ミキサー、乳鉢、ボールミル等の一般的に用いられているものを好適に選択することができる。
分散媒を除去した導電材複合粒子は、ふるい分けにより分級を行うことで、特定の粒子径範囲を有する導電材複合粒子を得ることができる。
ふるい分けの操作は特に限定されないが、以下の様にして行う事ができる。
JIS8801-1に準拠した公称目開きの異なる複数のふるいのうち、目開きの大きいものを上にして順番に重ね、導電材複合粒子を一番上部のふるいに入れた後、電磁式ふるい振とう機(フリッチュ・ジャパン株式会社製)で30分間振とうし、導電材複合粒子をその粒子径毎に分級する。所望の目開きを通過した粒子、及び通過しなかった粒子を取り出すことで、所定の粒子径に分級された導電材複合粒子を得ることができる。
本発明者らの検討の結果、粒度分布D50が15μmより小さい場合は、電池充放電容量及びサイクル特性が低下することが見出された。また、活物質と混合し電極ペーストとする際に、10分以上の混錬を行った場合において導電性が大きく損なわれることも見出された。その機序は完全には明らかではないが、発明者らは以下のように推測する。
前述のとおり、導電材は電極塗膜内で電極と活物質、及び活物質同士をつなげ、導電パスを形成することで、導電性・電池性能の向上に寄与している。
ここで、電極ペーストを混錬する際に導電材にも力がかかるが、その力が及ぼす影響は、粒子径が大きい場合と小さい場合で異なる。具体的には、例えば、導電材がカーボンブラックの場合、カーボンブラックは一般的に一次粒子が化学結合により連結したストラクチャーを形成し、ストラクチャー同士がさらにファンデルワールス結合や、単なる付着、絡み合いなどにより強く凝集した数十ミクロンから数百ミクロンの二次凝集体(アグロメレート)を形成しており、導電材複合粒子内においても、カーボンブラックは主に二次凝集体の状態で存在している。電極ペースト作製時の混錬により複合粒子に力がかかると、この力は当然に複合粒子内の二次凝集体にもかかるが、大きい粒子の場合は、力の大半は二次凝集体をほぐすことに使われ、凝集をほぐした後さらにストラクチャー同士の結合を切断するまでには使われにくい。したがって、混錬後もストラクチャー同士の結合がある程度保持された状態でペースト内に分散されるため、導電パスが形成されやすく、導電性及び電池性能が向上する。
しかし、小さい粒子の場合は、二次凝集体の発達が小さく、ほぐすために大きな力を必要としないため、混錬によりかかる力は、凝集をほぐしたあと、さらにストラクチャー同士の結合を切断するためにも多く使われると考えられる。このため、結合を断たれた単独のストラクチャーや、ストラクチャーが少数のみ結合した小さな凝集体がペースト内に分散された状態となり、導電パスが形成されにくく、高い導電性及び電池性能を発揮することができない。
粒度分布D10を指標として用いる場合は、10μm以上であることが好ましく、15μm以上であることが特に好ましい。また、粒度分布D90を指標として用いる場合は、30μm以上であることが好ましく、40μm以上であることが特に好ましい。
導電材複合粒子の粒度分布D10、D50及びD90は、以下の方法により測定することができるが、同一の結果が得られるのであればその測定方法はこれに限られない。
まず、帯電防止のために導電性の試料台を用い、導電材複合粒子を粒子同士が重ならない様に試料台上に散布する。次に走査電子顕微鏡(株式会社日立ハイテク社製、FlexSEM1000)とAZtec(オックスフォード・インスツルメンツ株式会社製、粒子解析ソフト)を用いて、300個以上の粒子を解析した直径の数値から算出する事ができる
ふるい分けによる粒子径を150μm以下とすることで粗大粒子が除去され、電池性能を向上させることができる。ふるい分けによる粒子径が150μmより大きいと、電極塗膜中での導電材の偏在が発生し活物質に十分な電子導電性を付与することができない。
ここでいうふるい分けによる粒子径とは、JIS8801-1に準拠したふるいの公称目開きのうち、対象の粒子が通過する最小の目開きをいう。JIS8801-1に準拠したふるいであれば、ふるい分けの操作は特に限定されないが、0039にて開示した方法を用いることで一度の測定で異なるサイズのふるいを通過させることができ、粒子径の測定と、粒子の分級、所望の粒子径の粒子の取り出しを同時に行うことができる。
本発明において粒子径上限とは、以下の方法により求められる測定値をいう。ただし、同一の結果が得られるのであればその測定方法はこれに限られない。
まず、帯電防止のために導電性の試料台を用い、導電材複合粒子を粒子同士が重ならない様に試料台上に散布する。次に走査電子顕微鏡(株式会社日立ハイテク社製、FlexSEM1000)とAZtec(オックスフォード・インスツルメンツ株式会社製、粒子解析ソフト)を用いて、約300個の粒子について、各粒子の中心点を通る最大の直径を測定し、それらの測定値のうち最大のものとして求めることができる。
平均粒子径を上記範囲内とすることで、導電材の偏在が起きにくいほか、ハンドリング性も向上する。また、前述の作用により導電パスが形成されやすいため、導電性及び電池性能の向上に貢献する。ここでいう平均粒子径は、各粒子の中心点を通る直径のうち最大のものの算術平均であり、以下のようにして求めることができるが、同一の結果が得られるのであればその測定方法はこれに限られない。
まず、帯電防止のために導電性の試料台を用い、導電材複合粒子を粒子同士が重ならない様に試料台上に散布する。次に走査電子顕微鏡(株式会社日立ハイテク社製、FlexSEM1000)と、AZtec(オックスフォード・インスツルメンツ株式会社製、粒子解析ソフト)を用いて、300個以上の粒子を解析した直径の数値から算出する事ができる。
本発明の導電材複合粒子のアスペクト比は、各粒子の中心点を通る最大の直径(a)と最小の直径(b)の比(a/b)をいい、以下のようにして求めることができるが、同一の結果が得られるのであればその測定方法はこれに限られない。
まず、帯電防止のために導電性の試料台を用い、導電材複合粒子を粒子同士が重ならない様に試料台上に散布する。次に走査電子顕微鏡(株式会社日立ハイテク社製、FlexSEM1000)とAZtec(オックスフォード・インスツルメンツ株式会社製、粒子解析ソフト)を用いて、各粒子のアスペクト比を測定し、粒子300個以上の測定値から算出することができる。
前述の各材料及び製造方法を用いることで導電材複合粒子のアスペクト比を上記範囲内とすることができるが、乾燥時に特に噴霧乾燥を用いることで、アスペクト比が1に近い粒子をより多く作製することができる。
ここでいう安息角とは、日本工業規格 JIS 9301-2-:2:1999に規定されている測定方法に準じ、水平な面上に粉体を静かに堆積させて自然に形成された山の斜面と水平面とがなす角度を読み取る事で求める事ができるが、同一の結果が得られるのであればその測定方法はこれに限られない。
上記に開示した製造方法であれば、分散剤の分解温度を超えることはなく、材料混合、湿式分散、分散媒除去、粉砕工程を経ても分散剤はほとんど除去されない、若しくは導電材に被覆されるとともに除去され導電材に対する比率を維持するため、材料混合・攪拌時にて添加する分散剤の重量比を前述の範囲内にすることで、導電材複合粒子における重量比についてもその範囲内とすることができる。
分散剤が熱分解し、かつ導電材の重量が変化しない温度で分散剤が完全に分解し得る時間まで導電材複合粒子を加熱し、加熱前、加熱後の重量差から分散剤の重量を求める事ができる。
なお、分散剤の重量は、分散剤が他の溶剤などに溶解又は分散している場合は有効成分の量で換算する。複合粒子中の各成分の含有比を求めるためには、TG-DTA(熱重量・示差熱分析装置)により、分散剤が分解し導電材が分解しない温度範囲で継続的に加熱し分散剤の熱重量変化を測定する事で、容易に確認する事ができる。
具体的な一例としては、TG-DTA(ブルカージャパン株式会社製)を用い、導電材複合粒子を100℃で1時間保持して完全に水分を除去した後、毎分5℃の速度で300℃まで昇温させ、その後さらに1時間保持し分散剤を分解させることにより、測定することができる。300℃保持後の重量が導電材のみの重量であり、100℃保持後の重量と300℃保持後の重量の差分が導電材複合粒子中の分散剤量である。
本発明において、算術平均粗さとは以下の方法により特定される数値をいうが、同一の結果が得られるのであればその方法はこれに限られない。まずバインダーである市販のポリフッ化ビニリデン(クレハ株式会社製、「KFポリマーW#7200」)を溶媒であるN-メチル-2-ピロリドンで8.0%に希釈した溶液に、導電材複合粒子が全体の8.3%になるように秤量して加え、自転公転ミキサー(シンキー株式会社製、あわとり練太郎)にて2000rpmで1分間混練する事によりペーストを作製する。このペーストを、アプリケーターを用いて乾燥後の膜厚で7.5~8.5μmとなる様にガラス板上へ塗布し、100℃の温風乾燥機で30分間乾燥させ溶媒を除去した塗膜を得る。得られた塗膜を、「分散性評価用塗膜」とする。接触式の表面粗度計(株式会社東京精密製、Surfcom130A)を用いて分散性評価用塗膜の表面粗さを測定し、算術平均粗さを算出する。
OD値とは、塗膜の分光透過率を測定し、光の吸収度合を対数で表示したものであり、塗膜を透過する光が少なくなるほど数値が大きくなるものであることが知られている。本発明者らの検討の結果、OD値と電気特性との間には相関があり、導電材複合粒子を塗膜化した際のOD値を所定の範囲内に調整することにより、電池材料として優れた性能を得ることができることが判明した。より具体的には、塗膜時のOD値が3.0以上を示す導電材複合粒子は、電極塗膜化した際に導電材が均一に分散し、その結果充放電容量が上昇する事が判明した。また、塗膜時のOD値が3.0未満の導電材複合粒子を用いて電池化した場合には導電材の分散の均一性が低い傾向にあり、充放電容量が低下し易いことがあることも分かった。
この理由としては次のようなものが考えられる。導電材の分散の均一性が十分でなく、塗膜中で多くの導電材が凝集、偏在していると、局所的に導電材が存在しない部分が不均一に発生することとなる。そうした部分は光を吸収しないため、塗膜全体として透過する光が増大し、その結果OD値が低下する。塗膜中で導電材が均一に分散していないことは、活物質へ十分な電子導電性を付与できず、電池化した際の充放電容量が低下すること、局所的な通電により早期に容量が低下することにつながるため、OD値が低下していることは導電材の分散性が不十分であり、電池化した際の性能が低下していることを示していると考えることができる。
加えて、従来の導電材複合粒子と比較して塗膜中で導電材が偏在しにくいため、電極塗膜内で導電材がより多くの活物質間に均一に分散し電子導電性を付与して充放電容量が上がることや、正負極の局所的な電流集中による早期の容量低下の発生を少なくすることができると考えられる。
また、導電材複合粒子中に溶媒を含まないため、スラリー状の導電材分散ペーストと比較して、製造時の有機溶媒の使用量を抑えられることができ、環境への負荷を低減することができるほか、電極ペースト化時に使用される溶媒の種類や有無によらず使用する事ができる。
本発明のリチウムイオン二次電池は、本発明の導電材複合粒子を電極活物質、バインダーとともにN-メチル-2-ピロリドン等の非水系溶媒に分散させることで作製した電極ペーストを金属基板上に塗布・乾燥することで作製した正極、または、本発明の導電材複合粒子を電極活物質、バインダーと共に水などの溶媒に分散させることで作製した電極ペーストを金属基板上に塗布・乾燥することで作製した負極を、セパレータととに巻回し、電解液と併せて電池缶に収納することで作製することができる。電池内部の圧力上昇、過充放電等の発生を防止するために、必要に応じて、ヒューズ、PTC素子等の過電流防止素子、エキスパンドメタル、リード板などを設けてもよい。また、電池缶の形状は、例えば、コイン型、ボタン型、シート型、円筒型、角形、扁平型など、何れであってもよい。
本発明の導電材複合粒子の有する分散時の均一性、溶媒を実質的に含まないといった特徴は、リチウムイオン二次電池に限らず、その他の蓄電装置に用いられた場合についても充放電性能の向上やコストダウン、環境負荷の低減等に有効である。
特に、カーボンブラックやカーボンナノチューブ、グラファイト等の炭素材料及びそれらを用いたスラリーを導電材として用いる蓄電装置において、本発明の導電材複合粒子はそれら既存の導電材の代替として好適に用いることができる。
例えば、アルカリマンガン乾電池、ニッケルマンガン電池等の一次電池、ニッケル水素電池、ニッケルカドミウム電池、ナトリウム硫黄電池、ナトリウムイオン電池等の二次電池や、コンデンサ(キャパシタ)等、その他電気化学素子において、好適に用いることができる。
これらの蓄電装置に使用する場合には、既に用いられている導電材を本発明の導電材複合粒子に置換すればよい。既存の導電材がカーボンブラック等の粉粒体状の導電材である場合には、そのまま置換することができる。カーボンブラック分散体等のスラリー状の導電材である場合には、導電材を本発明の導電材複合粒子に置換し電極ペーストの固形分を調整し適切な粘度に仕上げることで用いることができる。
分散媒として用いるイオン交換水84重量部に、分散剤としてメチルセルロースポリマー(GPCによる測定で重量平均分子量35,000)1重量部を添加し、市販の攪拌機で十分に溶解させ、分散剤溶液を得た。次いで、得られた分散剤溶液85重量部に、導電材としてASTM:D3849-14に準拠した測定方法による平均一次粒子径が35nmであるアセチレンブラック(デンカ株式会社製、「デンカブラック粒状」)15重量部を添加し、市販の攪拌機で混合攪拌する事で導電材混合液を得た。得られた導電材混合液を、市販の横型ビーズミルを用いた湿式粉砕処理によりグラインドゲージによる評価で50μm以上の粒子が無くなるまで導電材の微細化を進め、導電材分散ペーストを得た。得られた導電材分散ペーストを目開き50μmのメッシュで濾過して異物の除去を行い、導電材分散ペースト1とした。
前記導電材分散ペースト1を市販のスプレーノズル式噴霧乾燥機を用いて乾燥機の入口温度160℃、噴霧圧力0.03MPaで乾燥し、電磁式ふるい振とう機(フリッチュ・ジャパン株式会社製)を用いた分級でふるい分けによる粒子径が75μm以下、45μm以上の導電材複合粒子1を得た。
分散媒として用いるイオン交換水84重量部に、分散剤としてポリビニルピロリドン(GPCによる測定で重量平均分子量66,800)を1重量部添加し、市販の攪拌機で充分に溶解させ、以降は実施例1と同様の操作を行い導電材分散ペースト2を得た。
この導電材分散ペースト2を用いる以外は、その後の操作についても実施例1と同様の操作を行い、電磁式ふるい振とう機(フリッチュ・ジャパン株式会社製)を用いた分級でふるい分けによる粒子径が75μm以下、45μm以上の導電材複合粒子2を得た。
実施例1と同様の操作を行うことで得られた導電材分散ペースト1を、市販の温風乾燥機を用いて100℃で12時間乾燥し、得られた乾燥体を市販のカッターミキサーにより粉砕したのちに電磁式ふるい振とう機(フリッチュ・ジャパン株式会社製)を用いた分級を行うことで、ふるい分けによる粒子径が75μm以下、45μm以上である導電材複合粒子3を得た。
実施例1と同様の操作を行うことで得られた導電材分散ペースト1を、市販の温風乾燥機を用いて100℃で12時間乾燥し、得られた乾燥体を市販のカッターミキサーにより粉砕したのちに電磁式ふるい振とう機(フリッチュ・ジャパン株式会社製)を用いた分級を行うことで、ふるい分けによる粒子径が150μm以下、75μm以上である導電材複合粒子4を得た。
実施例1と同様の操作を行うことで得られた導電材分散ペースト1を、市販の温風乾燥機を用いて100℃で12時間乾燥し、得られた乾燥体を市販のカッターミキサーにより粉砕したのちに電磁式ふるい振とう機(フリッチュ・ジャパン株式会社製)を用いた分級を行うことで、ふるい分けによる粒子径が250μm以下、150μm以上である導電材複合粒子5を得た。
実施例1と同様の操作を行うことで得られた導電材分散ペースト1を、市販の温風乾燥機を用いて100℃で12時間乾燥し、得られた乾燥体を市販のカッターミキサーにより粉砕したのちに電磁式ふるい振とう機(フリッチュ・ジャパン株式会社製)を用いた分級を行うことで、ふるい分けによる粒子径が500μm以下、250μm以上である導電材複合粒子6を得た。
実施例1と同様の操作を行うことで得られた導電材分散ペースト1を、市販の温風乾燥機を用いて100℃で12時間乾燥し、得られた乾燥体を市販のカッターミキサーにより粉砕したのちに電磁式ふるい振とう機(フリッチュ・ジャパン株式会社製)を用いた分級を行うことで、ふるい分けによる粒子径が45μm以下である導電材複合粒子7を得た。
市販のアセチレンブラック(デンカ株式会社製、「デンカブラック粉状」)を導電材原体1とした。なお、このアセチレンブラックは各実施例及び比較例で導電材として用いるアセチレンブラックと同種のものである。
以上の各実施例及び比較例に開示した方法で準備した各分散ペースト、導電材複合粒子及び導電材原体について以下の操作により物性測定、性能評価を行った。
導電材分散ペースト1、2について、B型粘度計(東機産業株式会社製、TVB10M形粘度計)を用いて粘度を測定した。
導電材複合粒子1、2、3、4、5、6、7及び導電材原体1について、ハロゲンランプ加熱式水分計(新光電子株式会社製、MA-120)を用いて水分率を測定した。
導電材複合粒子1、2、3、4、5、6、及び7について、走査電子顕微鏡(株式会社日立ハイテク社製、FlexSEM1000)とAZtec(オックスフォード・インスツルメンツ株式会社製、粒子解析ソフト)を用いて、粒子径上限、平均粒子径、粒子径下限、粒度分布D10、D50、D90、D95、及びアスペクト比を測定、算出した。また、JIS 9301-2-:2:1999に準じ安息角を測定した。各測定結果は表1に示す。
ここで得られた塗膜を「分散性評価用塗膜」とする。この分散性評価用塗膜を、接触式の表面粗度計(株式会社東京精密製、Surfcom130A)を用いて算術平均粗さ(Ra)及び算術平均高さ(Sa)を測定、算出した。
また、前記分散性評価用塗膜について、分光濃度計(ビデオジェットエックスライト株式会社製、x-rite)を用いてOD値を測定した。
なお、導電材複合粒子1、2、3、4、5、6、7については、複合粒子が含有している分散剤が電極塗膜上でバインダーの役割をするため、ここでは分散剤量をバインダー量とみなし、配合比の計算においてはAから導電材複合粒子に含まれる分散剤量を除算し、この分散剤量をCに加算したうえで、A、B、Cがそれぞれ2重量部、97重量部、1重量部になるように導電材複合粒子、活物質、バインダーを秤量した。
上記の評価用電極ペーストA及び評価用電極ペーストBを、アプリケーターを用いてPETフィルム上へ塗布した後、温風乾燥機を用いて100℃で30分間乾燥しNMPを除去して膜厚が100μm~120μmの範囲内にある塗膜を得た。ここで得られた塗膜を、それぞれ「電極ペースト評価用塗膜A」、「電極ペースト評価用塗膜B」とする。
このうち、電極ペースト評価用塗膜AをSEM試料作製用の断面カッターを使用して断面を露出させ、走査電子顕微鏡(株式会社日立ハイテク社製、FlexSEM1000)とエネルギー分散型X線分光器(オックスフォード・インスツルメンツ株式会社製、AZtecEnergy x-act)を用いて塗膜中の導電材の分散状態を倍率500倍で撮影した。
また、電極ペースト評価用塗膜A、B双方を用いて、以下の方法により塗膜抵抗を測定した。
まず、塗膜を幅2cm長さ3cmに切り出し、抵抗率計(日東精工アナリテック株式会社製、ロレスタ-GP MCP-T610)を用いて、印加電圧 10Vで塗膜の体積抵抗率を測定した。
上記各測定試験の結果を、表1に示す。
次に、導電材複合粒子1、2、3、4、5、6、7及び導電材原体1、並びに以下の各材料を用いて、以下の方法によりCR2032タイプ(直径20mm 高さ3.2mm)のコイン型の二次電池を作製し、その性能を評価した。
なお、以下に開示する二次電池、及びその作製方法は、本発明の導電材複合粒子を評価するための一例にすぎず、本発明の導電材複合粒子の使用方法及び実施形態を何ら限定するものではない。本発明の導電材複合粒子は、以下に開示する各材料、電池製造方法、電池の形態、その他条件に限らず、リチウムイオン二次電池をはじめとする幅広い蓄電装置向けの電極材料として好適に用いることができる。
正極活物質(HED NCM111 1100 BASF戸田バッテリーマテリアルズ合同会社製、理論容量:160mAh/g)と、バインダー(PVdF (ソルベイジャパン社製 Solef5130)と導電材(導電材複合粒子1)を97:1:2(重量比)の割合で秤量し、バインダーを溶媒(N―メチルー2ピロリドン)に溶解したものに、正極活物質と導電材とを混合し、溶媒で塗工液の固形分が70~75質量%となるように希釈し、電極ペースト化した。この電極ペーストを厚さ20μmのアルミ箔上に目付容量(単位面積当たりの電池容量)が3.0~4.0mAh/cm2となるように塗布して100℃のオーブンで30分間乾燥し、正極塗膜板を得た。ここで得られた正極塗膜板において、集電体であるアルミ箔上の、電極ペーストが乾燥・成膜した部分を「正極合材層」とする。この正極塗膜板を、電極密度(正極合材層質量/正極合材層体積)が2.9~3.4g/cm3となるようにプレスした後、コイン型打ち抜き機でΦ14mmに打ち抜き、正極とした。
なお、電極密度の算出においては、正極合材層質量は正極塗膜板質量からアルミ箔の質量を引くことにより、また、正極合材層体積は正極塗膜版厚みからアルミ箔厚みを引いて高さとしたあと、Φ14mmを底面積としてもとめた。
前記のとおり得た正極と、負極(リチウム箔、厚み200μm、φ16mm、本城金属社製)の間にセパレータ(「Seillon P2010」、材質;ポリプロピレン、Φ17mm、CS Tech社製)を挿入し、電解液(1.0M LiPF6 EC : DEC(1:1 v/v%)、キシダ化学社製)を満たしたCR2032型コインセルを組み立て、評価用電池を作製した。
得られた評価用電池について、充放電試験機(580型 高性能充放電システム Scribner Associates社製)を用いて以下のとおり充放電及び実放電容量の測定を行った。
充放電は、室温(25℃)で1Cの定電流・定電圧充電により4.3Vを上限電圧として満充電させ、その後1Cの定電流で3.0Vまで放電を行った。これを1サイクルとして合計30サイクル行い、30サイクル目の実放電容量を測定した。なお、各サイクル中の満充電完了から放電開始まで、及び各サイクル間には10分間の休止時間を設けた。得られた実放電容量(mAh)をもとに、初期有効容量、30サイクル目の有効容量及び容量維持率を求めた。その結果を表1に示す。
ここで、有効容量とは、理論容量(正極合材層の質量(g)×活物質配合割合×1gあたりの活物質の理論容量)を100%とした場合の実放電容量の比率をいう。また、第1サイクル目の有効容量を初期有効容量とした。
また、容量維持率は、初期有効容量を100%として、30サイクル目の有効容量の比率を示した値である。
導電材を表1に示す各複合粒子及び導電材原体に変更し、そのほかは実施例1と同様にして電池を作製し、その性能を評価した。結果を表1に示す。
粒子径上限のみが異なる実施例3、4と比較例1、2を比較すると、複合粒子の粒子径が大きい比較例では光学濃度が低下しており、均一性の低下が示されている。また、比較例1、2は実施例と比較して表面が粗くなっており、塗膜中に粗大粒子が多く存在していることが示されている。
比較例4はOD値が低く、塗膜の表面粗さも良好でない。
図3、図5、図7、図9、図11、図13、図15、図17のEDS解析画像内では、導電材であるカーボンが白く可視化されている。
これらの図から、実施例は導電材が活物質間に満遍なく均一に分布しているが、比較例では集中して存在している箇所や、ほとんど存在していない箇所があり、塗膜内で偏在していることが分かる。また、比較例1、2及び4のEDS解析画像では粗大粒子又は凝集(画像内の白い塊)が存在していることが読みとれる。図15は大きな塊は確認できないが、白いもやもほとんどみえない。これはペースト混錬過程で二次凝集体が過度にほぐされ、ストラクチャー同士の結合が切断されていることを示していると考えられる。このような状態では、導電パスが形成されにくく、高い電池性能を発揮することはできない。
この様に、本発明の通り作製された複合粒子を使用する事で、比較例と比べて良好な分散性を持ち、導電材が均一に分散した電極塗膜を得る事ができることが分かる。
また、本発明の導電材複合粒子は、カーボンブラック等の既存の導電材の代替品として用いることで、リチウムイオン二次電池に限らず、その他の蓄電装置に用いられた場合についても性能向上やコストダウンに貢献することができる。
Claims (16)
- 少なくとも導電材及び分散剤を含有する粒子であって、粒度分布D50が15μm以上かつふるい分けによる粒子径が150μm以下である粒子であり、導電材のDBP吸油量が550ml/100g以下であり、導電材100重量部に対して分散剤を1~10重量部含むことを特徴とする導電材複合粒子。
- 少なくとも導電材及び分散剤を含有する粒子であって、粒度分布D50が15μm以上かつ粒子径上限が300μm以下の粒子であり、導電材のDBP吸油量が550ml/100g以下であり、導電材100重量部に対して分散剤を1~10重量部含むことを特徴とする導電材複合粒子。
- 少なくとも導電材及び分散剤を含有する粒子であることを特徴とする請求項1又は2のいずれかに記載の導電材複合粒子。
- 前記分散剤が、非イオン性分散剤であることを特徴とする、請求項1又は2に記載の導電材複合粒子。
- 前記非イオン性分散剤の重量平均分子量が1,000以上1,000,000以下であることを特徴とする、請求項4に記載の導電材複合粒子。
- 前記導電材の純度が99.9%以上であることを特徴とする、請求項1または2に記載の導電材複合粒子。
- 前記導電材の平均一次粒子径が10nm以上50nm以下であることを特徴とする、請求項1または2に記載の導電材複合粒子。
- 電池電極用の導電材である、請求項1または2に記載の導電材複合粒子。
- 少なくとも導電材、分散剤及び分散媒を含有する導電材分散ペーストを作製する工程、並びに導電材分散ペーストの分散媒を除去する工程を含む導電材複合粒子の製造方法であって、導電材分散ペースト中の導電材複合粒子の粒子径が50μm以下であることを特徴とする、導電材複合粒子の製造方法。
- 前記導電材分散ペーストに50μmを超える異物を含まないことを特徴とする、請求項9記載の導電材複合粒子の製造方法。
- 前記導電材分散ペーストを、80℃以上300℃以下で加熱する乾燥工程を含むことを特徴とする、請求項9又は10に記載の導電材複合粒子の製造方法。
- 請求項1または2に記載の導電材複合粒子を少なくとも活物質及びバインダーと混合し、基板に塗布することを特徴とする電極の製造方法。
- 請求項9または10に記載の製造方法により得られた導電材複合粒子を少なくとも活物質及びバインダーと混合し、基板に塗布することを特徴とする電極の製造方法。
- 請求項12に記載の方法により得られた電極を用いたリチウムイオン二次電池。
- 請求項1または2に記載の導電材複合粒子を用いた蓄電装置。
- 請求項12に記載の方法により得られた電極を用いた蓄電装置。
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