Classifications

• • 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
  • C01B32/20—Graphite
  • C01B32/21—After-treatment
• • 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
  • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
• • 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
• • 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
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
  • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
  • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
• • 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 relates to an organic compound-coated carbon material, a method for producing the same, a negative electrode, and a secondary battery.
• lithium ion secondary batteries which have higher energy densities and superior large-current charge/discharge characteristics than nickel-cadmium batteries and nickel-hydrogen batteries.
• increasing the capacity of lithium-ion secondary batteries has been widely studied.
• there has been an increasing demand for higher performance of lithium-ion secondary batteries, and higher capacity, higher input/output, longer life, and other property improvements are being demanded.
• Patent Document 1 discloses that as a negative electrode material for lithium ion secondary batteries capable of improving characteristics such as initial efficiency, cycle characteristics, and rapid charge/discharge characteristics, spheroidized graphite is isotropically pressurized to obtain a high-density electrode material.
• a negative electrode material for a lithium ion secondary battery containing highly isotropic graphite that has been denatured has been proposed.
• Patent Document 2 discloses a carbon material (A) having a surface functional group content O/C value of 1% or more and 4% or less as a negative electrode material for a non-aqueous secondary battery having high capacity and good charge/discharge load characteristics.
• a carbon material (C) for a non-aqueous secondary battery has been proposed in which a water-soluble polymer (B) is attached to the
• the negative electrode material disclosed in Patent Document 1 is inferior in initial efficiency because it is not coated with an organic compound. Since the carbon material disclosed in Patent Document 2 is not pressurized, the internal pores are not reduced, resulting in poor high-speed charging characteristics.
• an organic compound-coated carbon material which is obtained by coating a carbon material with an organic compound and has a specific pore diameter and an accumulated pore volume of a predetermined value or less, can solve the above problems, and completed the present invention. came to.
• the reason why the organic compound-coated carbon material according to the present invention exhibits the above effects is considered as follows.
• the area of contact between the carbon material and the electrolytic solution is reduced, and the initial charging and discharging efficiency is improved.
• the gist of the present invention is as follows.
• the organic compound-coated carbon material of the present invention is an organic compound-coated carbon material obtained by coating a carbon material with an organic compound, and has a cumulative pore volume of 0 within a pore diameter range of 10 nm or more and 800 nm or less as measured by a mercury porosimeter. .10 mL/g or less.
• the organic compound-coated carbon material of the present invention is preferably produced through the following steps (1) and (2) according to the method for producing an organic compound-coated carbon material of the present invention.
• Step (1) A step of pressurizing the carbon material (hereinafter sometimes referred to as “raw carbon material”)
• Step (2) The carbon material obtained in step (1) )”.) and the step of mixing the organic compound raw material
• the organic compound-coated carbon material of the present invention will be described below according to the method for producing the organic compound-coated carbon material of the present invention.
• the organic compound-coated carbon material of the present invention is not limited to those produced by the method for producing an organic compound-coated carbon material of the present invention.
• the organic compound-coated carbon material of the present invention may be any organic compound-coated carbon material that satisfies the above cumulative pore volume.
• the raw carbon material is not particularly limited, but examples thereof include the following.
• raw carbon materials include raw carbon materials having various degrees of graphitization ranging from graphite to amorphous.
• Graphite or raw material carbon with a low degree of graphitization is particularly preferable from the viewpoint of being readily commercially available.
• amorphous carbon graphite or graphite with a small degree of graphitization (amorphous carbon) is used as the raw carbon material, the charge/discharge characteristics at high current densities are significantly higher than when other negative electrode active materials are used, which is preferable. .
• Natural graphite is preferable because it has a large specific surface area and is highly effective in improving the initial efficiency by coating with an organic compound. Graphite with few impurities is preferable, and it is used after being subjected to various purification treatments as necessary.
• natural graphite examples include flake graphite, flake graphite, and soil graphite.
• artificial graphite examples include graphite particles such as coke, needle coke, and high-density carbon materials, which are produced by subjecting pitch raw materials to high-temperature heat treatment. Spherical natural graphite is preferable from the viewpoint of low cost and ease of electrode production.
• artificial graphite include coal tar pitch, coal-based heavy oil, atmospheric residual oil, petroleum-based heavy oil, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polyphenylene, polyvinyl chloride, Baking organic materials such as polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymers, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, imide resin, etc. at a temperature usually in the range of 2500°C or higher and 3200°C or lower. and graphitized.
• the raw carbon material may be used by appropriately mixing particles such as metal particles and metal oxide particles in an arbitrary combination with the raw carbon material.
• the raw carbon material may be one in which a plurality of materials are mixed in individual particles. For example, carbonaceous particles having a structure in which the surface of graphite is coated with a carbon material having a low degree of graphitization, or particles obtained by aggregating a carbon material with an appropriate organic substance and re-graphitizing it may be used.
• the raw carbon material may contain metals such as Sn, Si, Al, and Bi that can be alloyed with Li in the composite particles.
• the raw carbon material preferably has the following physical properties or characteristics.
• the d value (interlayer distance) of the lattice plane (002) determined by X-ray diffraction of the raw material carbon material according to the Gakushin method is usually 0.335 nm or more and less than 0.340 nm.
• the d value is preferably 0.339 nm or less, more preferably 0.337 nm or less.
• the crystallinity is moderately high, and there is a tendency to suppress an increase in the initial irreversible capacity.
• 0.335 nm, which is the lower limit of the d value is the theoretical value of graphite.
• the d value of the lattice plane (002) is the value determined by X-ray diffraction according to the Gakushin method.
• the surface functional group content O/C value represented by the following formula (A) of the raw carbon material is usually 1% or more and 4% or less, preferably 2% or more and 3.6% or less, and 2.6% or more. 3% or less is more preferable.
• the surface functional group amount O/C value is equal to or higher than the lower limit, the interaction between the surface of the raw carbon material and the organic compound tends to be strong, making it difficult for the organic compound to come off.
• the surface functional group amount O/C value is equal to or less than the upper limit, the O/C value can be easily adjusted by oxidation treatment or the like, the manufacturing process can be performed in a short time, the number of steps does not need to be increased, and productivity is improved. and cost reduction.
• O / C value (%) ⁇ O atom concentration determined based on the peak area of O1s spectrum in X-ray photoelectron spectroscopy (XPS) analysis / C atom determined based on the peak area of C1s spectrum in XPS analysis concentration ⁇ 100
• the surface functional group amount O/C value is a value measured using X-ray photoelectron spectroscopy (XPS). Specifically, using an X-ray photoelectron spectrometer, the object to be measured is placed on a sample stage so that the surface is flat, K ⁇ rays of aluminum are used as the X-ray source, and C1s (280 to 300 eV) is measured by multiplex measurement. A spectrum of O1s (525-545 eV) is measured. The peak top of the obtained C1s is corrected to 284.3 eV, and the peak areas of the spectra of C1s and O1s are obtained. Furthermore, the surface atomic concentrations of C and O are calculated by multiplying by the apparatus sensitivity coefficient. The obtained atomic concentration ratio O/C (O atomic concentration/C atomic concentration) of O and C is taken as the surface functional group amount O/C value.
• XPS X-ray photoelectron spectroscopy
• the volume-based average particle size d50 of the raw carbon material is usually 1 ⁇ m or more, preferably 4 ⁇ m or more, and more preferably 10 ⁇ m or more. Also, it is usually 50 ⁇ m or less, preferably 30 ⁇ m or less, more preferably 25 ⁇ m or less.
• the volume-based average particle diameter d50 is at least the lower limit, the surface area does not become too large, and there is a tendency to suppress the activity with respect to the electrolytic solution.
• the volume-based average particle diameter d50 is equal to or less than the upper limit, there is a tendency to suppress process problems such as streaking when the electrode plate is formed.
• the volume-based average particle diameter d50 is the value of the volume-based median diameter measured with a laser diffraction/scattering particle size distribution analyzer. Specifically, 0.01 g of a carbon material is suspended in 10 mL of a 0.2% by mass aqueous solution of polyoxyethylene sorbitan monolaurate, which is a surfactant, and introduced into a laser diffraction/scattering particle size distribution analyzer, After irradiating ultrasonic waves of 28 kHz with an output of 60 W for 1 minute, the volume-based median diameter is measured by the measuring device.
• the specific surface area (SA) of the raw carbon material measured by the BET method is usually 4 m 2 /g or more, preferably 5 m 2 /g or more. Also, it is usually 13 m 2 /g or less, preferably 12 m 2 /g or less, more preferably 11 m 2 /g or less.
• the specific surface area is equal to or higher than the lower limit value, it is possible to sufficiently secure a portion through which Li enters and exits, resulting in excellent high-speed charge/discharge characteristics and output characteristics.
• the specific surface area is equal to or less than the upper limit, the activity of the active material with respect to the electrolytic solution can be moderately suppressed, an increase in the initial irreversible capacity can be suppressed, and there is a tendency that a high-capacity battery can be produced.
• the specific surface area is a value measured by the BET method. Specifically, using a specific surface area measuring device, the sample was preliminarily dried under reduced pressure at 100 ° C. under nitrogen flow for 30 minutes, then cooled to liquid nitrogen temperature, and using nitrogen gas, by the BET one-point method. Measure.
• the abundance ratio (3R/2H) of hexagonal crystals to rhombohedral crystals obtained from X-ray diffraction structure analysis (XRD) of the raw carbon material is usually 0.20 or more, preferably It is 0.25 or more, more preferably 0.30 or more.
• 3R/2H is equal to or higher than the lower limit, there is a tendency to suppress deterioration in high-speed charge/discharge characteristics.
• 3R/2H is a value determined by X-ray diffraction structure analysis (XRD). Specifically, a sample plate of 0.2 mm is filled with a carbon material so as not to be oriented, and is measured with an X-ray diffractometer using CuK ⁇ rays at an output of 30 kV and 200 mA. After subtracting the background from both peaks of 3R(101) near 43.4° and 2H(101) near 44.5° obtained, the intensity ratio 3R(101)/2H(101) is calculated.
• XRD X-ray diffraction structure analysis
• the tap density of the raw carbon material is usually 0.7 g/cm 3 or more, preferably 0.8 g/cm 3 or more, more preferably 1 g/cm 3 or more. It is usually 1.3 g/cm 3 or less, preferably 1.2 g/cm 3 or less, more preferably 1.1 g/cm 3 or less.
• the tap density is equal to or higher than the lower limit, high-speed charge/discharge characteristics are excellent.
• the tap density is equal to or less than the upper limit, there is a tendency to suppress an increase in the carbon density in the particles, suppress a decrease in rollability, and easily form a high-density negative electrode sheet.
• the tap density is measured by using a powder density measuring instrument, passing the carbon material through a sieve with an opening of 300 ⁇ m through a cylindrical tap cell with a diameter of 1.6 cm and a volume capacity of 20 cm 3 , and filling the cell to the full. After that, tapping is performed 1000 times with a stroke length of 10 mm, and the density value obtained from the volume and mass of the sample at that time is taken as the density value.
• the Raman R value of the raw carbon material is usually 0.1 or more, preferably 0.15 or more, and more preferably 0.2 or more. Also, it is usually 0.6 or less, preferably 0.5 or less, and more preferably 0.4 or less.
• the Raman R value is equal to or higher than the lower limit, the crystallinity of the particle surface is difficult to increase, and when the density is increased, it becomes difficult to orient the crystals in the direction parallel to the negative electrode plate, and there is a tendency to avoid deterioration in load characteristics. .
• the Raman R value is at least the upper limit, the crystallinity of the particle surface is less likely to be disturbed, the reactivity with the electrolytic solution is suppressed, and there is a tendency to avoid a decrease in charge-discharge efficiency and an increase in gas generation.
• the Raman R value is obtained by measuring the intensity I A of the peak P A near 1580 cm ⁇ 1 and the intensity I B of the peak P B near 1360 cm ⁇ 1 in the Raman spectrum obtained by Raman spectroscopy, A value calculated as the intensity ratio (I B /I A ).
• near 1580 cm ⁇ 1 refers to the range from 1580 to 1620 cm ⁇ 1 .
• Around 1360 cm ⁇ 1 refers to the range from 1350 to 1370 cm ⁇ 1 .
• a Raman spectrum is measured with a Raman spectrometer.
• the carbon material is filled into the measurement cell by allowing it to fall naturally, and while the measurement cell is irradiated with an argon ion laser beam, the measurement cell is rotated in a plane perpendicular to the laser beam for measurement. conduct.
• the measurement conditions are as follows. Argon ion laser light wavelength: 514.5 nm Laser power on sample: 25mW Resolution: 4 cm -1 Measurement range: 1100 cm -1 to 1730 cm -1 Peak intensity measurement, peak half width measurement: background processing, smoothing processing (convolution 5 points by simple average)
• the raw carbon material is not particularly limited as long as it is graphitized carbon particles.
• natural graphite, artificial graphite, coke powder, needle coke powder, and graphitized powder such as resin can be used.
• natural graphite is preferable, and spherical natural graphite that has been subjected to a spheroidizing treatment is particularly preferable from the viewpoint that the effect of coating with an organic compound is likely to appear.
• a method for producing spherical natural graphite will be described below as an example.
• an apparatus that spheroidizes carbon particles by repeatedly applying mechanical actions such as compression, friction, and shearing force, mainly impact force, including particle interaction, can be used.
• it has a rotor with a large number of blades installed inside the casing, and when the rotor rotates at high speed, mechanical impact such as impact compression, friction, and shear force is applied to the coking carbon material introduced inside.
• Apparatus for applying the action and surface treatment is preferred.
• it is preferable to have a mechanism for repeatedly applying a mechanical action by circulating the raw carbon material.
• Preferred devices include, for example, Hybridization System (manufactured by Nara Machinery Works), Crypton (manufactured by Earthtechnica), CF Mill (manufactured by Ube Industries), Mechanofusion System (manufactured by Hosokawa Micron), Theta Composer (Tokuju Kosakusho). company) and the like.
• Hybridization System manufactured by Nara Machinery Works
• Crypton manufactured by Earthtechnica
• CF Mill manufactured by Ube Industries
• Mechanofusion System manufactured by Hosokawa Micron
• Theta Composer Yamaju Kosakusho
• the scaly natural graphite is folded into a spherical shape, or the peripheral edge portion of the raw carbon material is made spherical by performing the spheroidization step by the surface treatment described above. It is pulverized into a spherical shape, and fine powder mainly of 5 ⁇ m or less generated by the pulverization adheres to the base particles.
• the raw carbon material is subjected to pressure treatment before mixing the raw carbon material and the organic compound raw material.
• the internal voids of the raw carbon material are compressed.
• the density of the raw carbon material crushed after the pressure treatment is increased, the high-speed charging characteristics can be improved, and the organic compound raw material is not excessively absorbed into the internal pores of the raw carbon material. , the raw carbon material is efficiently coated.
• isotropic pressure treatment is preferable because flattening of the particles is less likely to occur, the spherical shape can be maintained, and a drop in fluidity when slurried can be prevented.
• a roll compactor, a roll press, a briquette machine, a cold isostatic press (CIP), a uniaxial molding machine, a tablet machine, etc. can be used as the pressurizing means.
• a cold isostatic pressurizing device is preferable because it can reduce the internal pores while maintaining the particle shape.
• the raw carbon material can be pressed and shaped at the same time according to the pattern engraved on the roll.
• a method of evacuating the air existing between the raw carbon material particles and performing vacuum pressing can also be applied.
• the pressure for pressurizing the raw carbon material is usually 50 kgf/cm 2 or higher, preferably 100 kgf/cm 2 or higher, more preferably 300 kgf/cm 2 or higher, and most preferably 1000 kgf/cm 2 or higher. Also, it is usually 3000 kgf/cm 2 or less, preferably 2500 kgf/cm 2 or less.
• the pressure is equal to or higher than the lower limit, firm granulation is achieved and internal voids tend to decrease.
• the pressure is equal to or lower than the upper limit, there is a tendency to lead to cost reduction in the process.
• the temperature at which the raw carbon material is pressurized is usually 0° C. or higher, preferably 5° C. or higher, and more preferably 10° C. or higher. Moreover, it is usually 60° C. or lower, preferably 50° C. or lower, and more preferably 40° C. or lower. When the temperature is equal to or higher than the lower limit, there is no need for cooling, and the amount of energy required during production can be reduced. When the temperature is equal to or lower than the upper limit, the surface functional group content of the raw carbon material can be maintained.
• the time for pressurizing the raw carbon material is usually 0.1 second or longer, preferably 3 seconds or longer, and more preferably 1 minute or longer. Moreover, it is usually 30 minutes or less, preferably 10 minutes or less, and more preferably 3 minutes or less. If the time is at least the lower limit, firm granulation will be achieved and internal voids will tend to decrease. When the time is equal to or less than the upper limit, there is a tendency to lead to cost reduction in the process.
• the raw carbon material (a) after the pressure treatment preferably has the following physical properties or characteristics.
• the intra-particle porosity of the raw carbon material (a) is usually 10% or more, preferably 15% or more, and more preferably 20% or more. Also, it is usually 40% or less, preferably 35% or less, and more preferably 30% or less.
• the organic compound raw material to be mixed is present in an appropriate amount, suppressing aggregation of the raw carbon material (a) with each other, and efficiently converting the raw carbon material (a) into an organic compound. It tends to be coated with compounds.
• the organic compound raw material to be mixed is suppressed from being excessively absorbed in the internal voids of the raw carbon material (a), and the raw carbon material (a) is efficiently converted into an organic compound. tend to be coated with
• the internal porosity be the value calculated
• the internal porosity is determined from the obtained intra-particle pore volume and the true density of the carbon material. As the true density of the carbon material, 2.26 g/cm 3 which is the true density of general graphite is used.
• the organic compound raw material to be mixed with the raw carbon material (a) preferably has a plurality of hydroxyl groups or groups capable of self-crosslinking by heat or light in the molecule from the viewpoint of forming a strong film.
• organic compound raw materials include polyol resins such as polyvinyl alcohol resins, acrylic polyol resins, polyester polyol resins and polyether polyol resins, silicone resins, epoxy resins, and acrylic resins and polyester resins having hydrolyzable silyl groups. It is mentioned as a preferable one.
• polyvinyl alcohol-based resins acrylic polyol resins, polyester polyol resins, acrylic resins and polyester resins having a hydrolyzable silyl group are more preferable, and polyvinyl alcohol-based resins, acrylic polyol resins, and polyester polyol resins are more preferable.
• Polyvinyl alcohol-based resins are particularly preferable from the viewpoint of excellent solvent resistance of the active material layer formed using the organic compound-coated carbon material.
• PVOH resin Polyvinyl alcohol resin
• the specific structure of the polyvinyl alcohol-based resin (hereinafter referred to as "PVOH-based resin" as appropriate) is not particularly limited as long as it is a resin having a vinyl alcohol structural unit.
• the PVOH-based resin is typically obtained by saponifying polycarboxylic acid vinyl ester obtained by polymerizing a carboxylic acid vinyl ester monomer such as vinyl acetate, but is not limited thereto.
• PVOH-based resins examples include unmodified PVOH-based resins and modified PVOH-based resins.
• the modified PVOH-based resin may be a copolymerized modified PVOH-based resin synthesized by copolymerizing a monomer other than a vinyl ester-based monomer that provides a PVOH structural unit.
• it may be a modified PVOH-based resin obtained by modifying the side chain with a compound.
• copolymerizable monomers examples include olefins such as ethylene, propylene, isobutylene, ⁇ -octene, ⁇ -dodecene, and ⁇ -octadecene; Hydroxy group-containing ⁇ -olefins such as buten-1-ol, 4-penten-1-ol, 5-hexene-1-ol, or derivatives such as acylated products thereof; acrylic acid, methacrylic acid, crotonic acid, maleic acid, Unsaturated acids such as maleic anhydride, itaconic acid and undecylenic acid or salts thereof; monoesters or dialkyl esters; amides such as diacetone acrylamide, acrylamide and methacrylamide; ethylenesulfonic acid, allylsulfonic acid, methallylsulfonic acid olefin sulfonic acids
• Examples of copolymerized modified PVOH-based resins include PVOH-based resins having primary hydroxyl groups in side chains.
• Examples of such PVOH-based resins include side chain 1,2-diol-modified PVOH-based resins obtained by copolymerizing 3,4-diacetoxy-1-butene, vinylethylene carbonate, glycerin monoallyl ether, and the like; -Diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, 1,3-dibutyronyloxy-2-methylenepropane, etc. are copolymerized with hydroxymethylvinylidene diacetate and saponified. a PVOH-based resin having a hydroxymethyl group in the side chain obtained;
• a method for post-modifying the post-modified PVOH-based resin a method of acetoacetic esterification, acetalization, urethanization, etherification, grafting, phosphate esterification, and oxyalkylenation of unmodified PVOH or the modified PVOH-based resin is performed. etc.
• Both the above-mentioned unmodified PVOH-based resin and modified PVOH-based resin can be used as the organic compound raw material in step (2). Even a PVOH-based resin that is easily eluted when it is made into a water slurry for electrode plate coating becomes slightly soluble by cross-linking, and can be suitably used as a film for a carbon material. As a result, in the case of the unmodified PVOH-based resin, it is possible to use a partially saponified product that has good wettability to the hydrophobic surface of the carbon material and does not easily increase the viscosity of the aqueous solution even at low temperatures.
• anion-containing PVOH-based resins having functional groups with excellent lithium conductivity in side chains such as carboxylic acid groups and sulfonic acid groups, and nonion-modified PVOH resins having hydroxyalkyl groups and oxyethylene groups, etc.
• a group-containing PVOH-based resin can also be used, and the resistance of the film can be lowered.
• the solubility of PVOH resin differs depending on the degree of saponification and polymerization. Since the degree of saponification of the PVOH-based resin can be rendered insoluble by the crosslinked structure, a wide range of degrees of saponification can be selected.
• the degree of saponification of the unmodified PVOH resin is usually 70 mol % or more, preferably 78 to 100 mol %, more preferably 85 to 99.8 mol %.
• the saponification degree of the modified PVOH resin is usually 85 mol % or more, preferably 90 to 100 mol %, and 98 to 99.8 mol %.
• PVOH-based resin When using a PVOH-based resin in a solvent system, PVOH with a degree of saponification of 38 to 55 mol% and a cross-linking agent can be used in combination.
• the degree of saponification is a value measured according to ISO 15023-2.
• the average degree of polymerization is usually 200-3000, preferably 250-2800, more preferably 300-2600. In the case of the modified PVOH resin, the average degree of polymerization is usually 100-4000, preferably 200-3500, more preferably 250-2800. When the average degree of polymerization is within the above range, the solubility is in a suitable range. As used herein, the average degree of polymerization is a value measured by an aqueous solution viscosity measurement method based on ISO 15023-2.
• the PVOH-based resin only one resin may be used, or two or more resins may be blended and used.
• the structural units may differ, the degree of saponification may differ, and the average degree of polymerization may differ.
• the saponification degree, the average degree of polymerization, and the like should be within the above ranges for the average values of all the PVOH-based resins.
• the PVOH-based resin may be partially modified.
• the modification rate is 90% within 60 minutes after dispersing 10 g of the resin particles in 100 g of water with stirring at 20° C., raising the temperature to 90° C. at 1° C./min under stirring.
• a range in which the mass % or more is dissolved is preferable.
• the solvent is not particularly limited as long as it dissolves the organic compound raw material.
• the solvent is preferably water, ethyl methyl ketone, toluene, acetone, methyl isobutyl ketone, ethanol or methanol, more preferably water, ethyl methyl ketone, acetone, methyl isobutyl ketone, ethanol or methanol, still more preferably is water.
• Additives may be added to the solution.
• additives cross-linking agents that contribute to cross-linking of organic compound raw materials; surfactants and silane coupling agents that contribute to imparting wettability and adhesion to negative electrode active materials and binder resins; inorganic oxidation that contributes to reducing the resistance of coatings.
• lithium compound particles conductive polymers such as polyaniline sulfonic acid; and compounds that form complex ions with lithium ions, such as polyethylene oxide and complex hydrides.
• the basal surface of the raw material carbon material (a) can be uniformly coated with the organic compound material.
• a method is preferred.
• Examples of the mixing method include a method of stirring using a stirring blade in a fixed container, a method of mixing by rotating the container itself to tumble the contents, and a method of fluidizing by air flow for mixing. .
• a method of stirring using a stirring blade in a fixed container is preferable.
• Fixed containers include inverted cone type, vertical cylindrical type, horizontal cylindrical type, and U-shaped trough.
• the horizontally placed cylindrical type is preferable from the viewpoint of adhesion in the container and uniform mixing.
• the shape of the stirring blade if it is a horizontal shaft type, it can be ribbon type, screw type, single shaft paddle type, double shaft paddle type, anchor type, and plow type.
• Vertical shaft type includes ribbon type, screw type, planetary type, conical screw type, lower high speed rotating blade. From the viewpoint of uniform mixing, the horizontal axis system is preferable, and the horizontal plow type system is more preferable.
• a mixer that is a horizontally placed cylindrical container and that has a plow-shaped stirring blade with a horizontal axis.
• the peripheral speed of the stirring blade is preferably 0.1 m/sec or more, more preferably 1 m/sec or more, still more preferably 2 m/sec or more, and particularly preferably 3 m/sec. seconds or more. Also, it is preferably 100 m/sec or less, more preferably 80 m/sec or less, and still more preferably 50 m/sec or less.
• the treatment time is preferably 0.5 minutes or longer, more preferably 1 minute or longer, and still more preferably 5 minutes or longer. Also, it is preferably 300 minutes or less, more preferably 60 minutes or less, and even more preferably 20 minutes or less. When the treatment time is within the above range, more uniform mixing can be achieved while maintaining the throughput.
• the mixing temperature is preferably 1° C. or higher, more preferably 10° C. or higher. Also, it is preferably 100° C. or lower, more preferably 80° C. or lower.
• the mixing temperature is within the above range, an increase in the viscosity of the solution of the organic compound raw material can be suppressed, and the mixture can be mixed more uniformly. Also, the cost for temperature control can be suppressed.
• the concentration of the organic compound raw material in the organic compound raw material solution is preferably 0.01% by mass or more, more preferably 0.03% by mass, and still more preferably 0% by mass in 100% by mass of the organic compound raw material solution. 05% by mass or more. Also, it is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. When the concentration is within the above range, the organic compound raw material can be uniformly present on the basal surface of the raw carbon material (a), and the effects of the present invention can be obtained efficiently.
• the amount of the organic compound raw material mixed is usually 0.05 parts by mass or more, preferably 0.1 parts by mass or more, and more preferably 0.15 parts by mass with respect to 100 parts by mass of the raw carbon material (a). That's it. Also, it is usually 2 parts by mass or less, preferably 1.5 parts by mass or less, and more preferably 0.8 parts by mass or less.
• the mixing amount is equal to or higher than the lower limit, the carbon material is uniformly coated with the organic compound, which tends to improve the initial efficiency of the battery.
• the mixing amount is equal to or less than the upper limit, the amount of the organic compound coated on the carbon material is not too large, and the reversible capacity of the battery tends not to decrease.
• the mixing amount of the solution of the organic compound raw material may be appropriately set according to the concentration of the organic compound raw material described above and the mixing amount of the organic compound raw material described above. parts or more, more preferably 5 parts by mass or more. Also, it is preferably 300 parts by mass or less, more preferably 250 parts by mass or less. When the mixing amount is within the above range, uniform mixing can be achieved, and the drying time in the post-process can be shortened.
• the heating temperature for drying is usually higher than the boiling point of the solvent and lower than the decomposition temperature of the organic compound raw material, preferably 50 to 300°C, more preferably 100 to 250°C.
• the heating temperature for drying is within the above range, the drying efficiency is sufficient, and deterioration of battery performance due to residual solvent can be avoided.
• the organic compound raw material can be crosslinked, so that the decomposition of the organic compound raw material can be easily prevented, and the effect can be easily prevented from being reduced due to weakening of the interaction between the raw carbon material (a) and the organic compound.
• the pressure When drying is performed under reduced pressure, the pressure is usually -0.2 MPa or higher, preferably -0.15 MPa or higher, in terms of gauge pressure (difference from atmospheric pressure). Also, it is usually 0 MPa or less, preferably -0.03 MPa or less. When the pressure is within the above range, drying can be performed relatively efficiently.
• uniform coating is preferred from the viewpoint of suppressing the initial amount of gas and the amount of stored gas.
• the uniform coating allows the organic compound to be efficiently adsorbed onto the specific mesopore surfaces, and the effect of suppressing gas generation is likely to be obtained.
• the heat transfer method includes a convection heat transfer method that dries by directly applying hot air, and a conduction heat transfer method that transfers heat from the heat medium through a conduction heating plate. From the viewpoint of yield, conductive heat transfer is preferred.
• Examples of the mode of movement of the material to be dried include stationary drying in which the material is left to stand still to dry, hot air transport type drying in which the material to be dried is dispersed in hot air or sprayed with hot air and dried, and agitation drying in which the material is dried while being agitated. Agitation drying is preferable from the viewpoint of uniformly drying the material to be dried.
• the drying step may be carried out in the same equipment as step (2) as long as mixing uniformity and drying capacity are maintained.
• Agitation drying methods include a method in which the mixture is dried while stirring using an agitating blade in a fixed container, a method in which the container itself rotates to tumble the powder while drying, and a method in which hot air is blown in from the bottom.
• a method of drying while fluidizing and agitating is mentioned. From the viewpoint of uniformity and yield, it is preferable to dry the mixture while stirring it with a stirring blade in a fixed container.
• the stirring tank includes an inverted cone type, a vertical cylindrical type, a horizontal cylindrical type, and a U-shaped trough. From the viewpoint of yield, workability, and installation space, a horizontal cylindrical type is preferable.
• the shape of the stirring impeller is ribbon type, screw type, single shaft paddle type, double shaft paddle type, anchor type, plow type, and hollow wedge type in the case of the horizontal axis method.
• Vertical shaft type includes ribbon type, screw type, conical screw type, and lower high speed rotating blade.
• a horizontal shaft type stirring blade is preferable, and a horizontal shaft type single-shaft paddle type or plow type is more preferable.
• the peripheral speed of the stirring blade is preferably 0.01 m/sec or more, more preferably 0.2 m/sec or more, still more preferably 1 m/sec or more, and particularly preferably 2 m/sec. / second or more. Also, it is preferably 40 m/sec or less, more preferably 20 m/sec or less, and still more preferably 10 m/sec or less.
• the types of heat medium include heat medium oil, steam, and electric heaters. Steam is preferred for cost reasons.
• the heat medium can transfer heat to the material to be dried via the heat transfer surface by flowing the heat medium through the agitation tank jacket, the agitation blade, and the agitation shaft. From the viewpoint of heat transfer efficiency, it is preferable to flow the heat medium through all of the stirring tank jacket, the stirring blades and the stirring shaft.
• Examples of devices capable of flowing a heat medium through a stirring vessel jacket, stirring blades, and stirring shafts include the following.
• a horizontally placed cylindrical agitation vessel that can be heated by flowing a heat medium through the agitation vessel jacket.
• CD dryer Karl, Ltd.
• a horizontally placed cylindrical stirring tank that can be heated by flowing a heat medium through the stirring tank jacket and the stirring blades.
• a ribocon with a vertical shaft type ribbon-shaped stirring blade that can be heated by flowing Amixon (Toyo Hitec) is a vertically placed cylindrical stirring vessel that can be heated by flowing a heat medium through the stirring vessel jacket and stirring blades.
• a step of filtering the mixture of the raw carbon material (a) and the organic compound raw material, and a step of washing the resulting residue with water may be included prior to drying.
• a step of filtering the mixture of the raw carbon material (a) and the organic compound raw material, and a step of washing the resulting residue with water may be included prior to drying.
• this step it is possible to remove the excess organic compound raw material that is not directly attached to the raw material carbon material (a), and it is possible to suppress the decrease in capacity and the increase in resistance due to the adhesion of the excess organic compound raw material. can.
• a solution is prepared by dissolving the other components in a solvent in the same manner as the organic compound raw material, and the solution is used as the raw material carbon material (a). After mixing, it is preferable to dry by heating and/or under reduced pressure.
• a solution of the other components may be prepared separately from the solution of the raw material of the organic compound, or a solution may be prepared in addition to the same solvent as the solution of the raw material of the organic compound. good.
• the organic compound-coated carbon material obtained through the above steps may be subjected to powder processing such as pulverization, pulverization, and classification, if necessary.
• Examples of coarse pulverizers include shearing mills, jaw crushers, impact crushers, cone crushers and the like.
• Examples of intermediate pulverizers include roll crushers and hammer mills.
• Examples of fine pulverizers include ball mills, vibration mills, pin mills, stirring mills, jet mills, and the like.
• the organic compound-coated carbon material of the present invention is characterized by having a cumulative pore volume of 0.10 mL/g or less in a pore diameter range of 10 nm or more and 800 nm or less measured with a mercury porosimeter.
• This integrated pore volume is preferably 0.09 mL/g or less, more preferably 0.08 mL/g or less.
• the cumulative pore volume in the pore diameter range of 10 nm or more and 800 nm or less is preferably 0.01 mL/g or more, more preferably 0.02 mL/g or more, from the viewpoint of the contact area with the electrolytic solution, More preferably, it is 0.03 mL/g or more.
• the integrated pore volume in the pore diameter range of 10 nm or more and 800 nm or less is a value measured with a mercury porosimeter.
• the carbon material was weighed to a value of about 0.2 g, sealed in a powder cell, and pretreated by deaeration at 25° C. and 50 ⁇ mHg or less for 10 minutes. do.
• a vacuum of 4 psia is then applied to introduce mercury into the cell and the pressure is stepped from 4 psia to 40,000 psia and then decreased to 25 psia.
• the number of steps during pressure increase is set to 80 or more, and the amount of mercury intrusion is measured after an equilibrium time of 10 seconds at each step.
• the Washburn equation is used to calculate the pore size distribution, and the cumulative pore volume of pore diameters of 10 nm or more and 800 nm or less is obtained.
• the surface tension ( ⁇ ) of mercury is calculated as 485 dyne/cm and the contact angle ( ⁇ ) as 140°.
• the organic compound preferably coats the basal surface of the carbon material, preferably the starting carbon material (a), from the viewpoint of suppressing an increase in resistance.
• An organic compound-coated carbon material in which the basal surface of the carbon material is coated with an organic compound is preferable because the initial efficiency can be improved without increasing the resistance.
• An organic compound-coated carbon material in which the basal surface of the carbon material is coated with an organic compound can be produced by the above-described method for producing an organic compound-coated carbon material of the present invention.
• the basal surface of the carbon material is coated with an organic compound can be confirmed by simultaneously measuring the adsorption isotherm and the heat of adsorption using toluene gas.
• the surface of a carbon material having a heat of adsorption of 67 kJ/mol or more and having a high affinity for toluene is defined as a basal surface.
• the basal surface is coated with an organic compound.
• the carbon material is preferably natural graphite, and the organic compound coating the carbon material is preferably a crosslinked PVOH resin.
• organic compound-coated carbon material of the present invention preferably has the following physical properties or characteristics.
• DBP dibutyl phthalate
• oil absorption of the organic compound-coated carbon material of the present invention is preferably 48 mL/100 g or less, more preferably 47 mL/100 g or less, still more preferably 46.5 mL/100 g or less, Particularly preferably, it is 46 mL/100 g or less. Also, it is preferably 40 mL/100 g or more, more preferably 42 mL/100 g or more.
• the DBP oil absorption is less than the upper limit, it means that the internal pores can be reduced while maintaining the particle shape by pressurization, and the high-speed charging characteristics are excellent.
• the DBP oil absorption is equal to or higher than the lower limit, there is a pore structure in the particles, so there is a tendency to avoid lowering the reaction surface.
• the DBP oil absorption is a value measured according to ISO 4546. Specifically, 40 g of the carbon material is added, and the measurement is made at a drip rate of 4 mL/min, a rotation speed of 125 rpm, and a set torque of 500 N ⁇ m.
• a measuring device for example, an absorbometer E type manufactured by Brabender can be used.
• a carbon material preferably a raw carbon material (a)
• the coating amount is usually 0.05 parts by mass or more, preferably 0.1 parts by mass or more, and more preferably 0.15 parts by mass or more with respect to 100 parts by mass of the raw carbon material (a). . Also, it is usually 2 parts by mass or less, preferably 1.5 parts by mass or less, and more preferably 0.8 parts by mass or less.
• the coating amount is at least the lower limit, the carbon material is uniformly coated with the organic compound, which tends to improve the initial efficiency of the battery.
• the amount of coating is equal to or less than the upper limit, the amount of the organic compound coated on the carbon material is not too large, and there is a tendency that a decrease in reversible capacity and an increase in resistance of the battery can be suppressed.
• the coating amount of the organic compound of the organic compound-coated carbon material of the present invention means the weight at 200° C. to 700° C. when the organic compound-coated carbon material is heated in nitrogen using a TG-DTA apparatus. Decrease rate value.
• the volume-based average particle diameter d50 of the organic compound-coated carbon material of the present invention is preferably 1 ⁇ m or more, more preferably 3 ⁇ m or more, still more preferably 5 ⁇ m or more, particularly preferably 10 ⁇ m or more, and most preferably. is 15 ⁇ m or more. Also, it is preferably 50 ⁇ m or less, more preferably 45 ⁇ m or less, still more preferably 40 ⁇ m or less, particularly preferably 35 ⁇ m or less, and most preferably 30 ⁇ m or less.
• the circularity of the organic compound-coated carbon material of the present invention is preferably 0.88 or more, more preferably 0.90 or more, and still more preferably 0.91 or more. Also, it is preferably 1 or less, more preferably 0.98 or less, and still more preferably 0.97 or less. When the degree of circularity is 1, it becomes a theoretical perfect sphere. When the degree of circularity is within the above range, there is a tendency that deterioration in high-current-density charge-discharge characteristics of a secondary battery obtained by using the organic compound-coated carbon material of the present invention as a negative electrode material can be suppressed.
• the degree of circularity is a value determined by the following formula (C). Specifically, about 0.2 g of a carbon material is dispersed in 50 mL of a 0.2% by mass aqueous solution of polyoxyethylene sorbitan monolaurate, which is a surfactant, and ultrasonic waves of 28 kHz are applied to the dispersion for 1 minute at an output of 60 W. After irradiation, the detection range is assigned from 0.6 to 400 ⁇ m, and particles ranging in size from 1.5 to 40 ⁇ m are measured using a flow particle image analyzer.
• Formula (C) Circularity (perimeter of equivalent circle with same area as particle projection shape)/(actual perimeter of particle projection shape)
• the spheroidizing treatment includes, for example, a method of mechanically approximating a spherical shape by applying a shearing force and a compressive force, a mechanical/physical treatment method of granulating a plurality of carbon materials by the adhesive force of the binder or the particles themselves, and the like. is mentioned.
• the tap density of the organic compound-coated carbon material of the present invention is preferably 0.7 g/cm 3 or more, more preferably 0.8 g/cm 3 or more, and still more preferably 0.85 g/cm 3 or more. , particularly preferably 0.9 g/cm 3 or more, most preferably 0.95 g/cm 3 or more. Also, it is preferably 1.3 g/cm 3 or less, more preferably 1.2 g/cm 3 or less, and still more preferably 1.1 g/cm 3 or less.
• the tap density is within the above range, when the electrode plate is formed, problems in the process such as streaking are suppressed, and high-speed charge/discharge characteristics are excellent. In addition, it tends to suppress an increase in the carbon density in the particles, suppress a decrease in rollability, and easily form a high-density negative electrode sheet.
• the d value (interlayer distance) of the lattice plane (002 plane) obtained by X-ray diffraction by the Gakushin method of the organic compound-coated carbon material of the present invention is usually 0.335 nm or more and less than 0.340 nm, preferably 0. 0.339 nm or less, more preferably 0.337 nm or less.
• the d value is less than 0.340, the crystallinity is moderately high, and there is a tendency to suppress an increase in the initial irreversible capacity.
• 0.335 nm, which is the lower limit of the d value is the theoretical value of graphite.
• Crystallite size of organic compound-coated carbon material The crystallite size (Lc) of the organic compound-coated carbon material of the present invention determined by X-ray diffraction according to the Gakushin method is preferably 1.5 nm or more, more preferably 3.0 nm or more.
• the lower limit of the crystallite size is the theoretical value of graphite. When the crystallite size is within the above range, the particles are not too low in crystallinity, and a decrease in reversible capacity when used as a secondary battery can be suppressed.
• the ash contained in the organic compound-coated carbon material of the present invention is preferably 0.0001% by mass or more in 100% by mass of the organic compound-coated carbon material. Also, it is preferably 1% by mass or less, more preferably 0.5% by mass or less, and still more preferably 0.1% by mass or less.
• the ash content is within the above range, deterioration of the battery performance due to the reaction between the organic compound-coated carbon material as the negative electrode material and the electrolyte during charge/discharge can be suppressed to a negligible extent in the case of a secondary battery.
• the production of the negative electrode material does not require a large amount of time, energy, and equipment for preventing contamination, it is possible to suppress an increase in cost.
• the specific surface area (SA) of the organic compound-coated carbon material of the present invention measured by the BET method is preferably 1 m 2 /g or more, more preferably 2 m 2 /g or more, and still more preferably 2.5 m 2 /g. g or more, particularly preferably 2.8 m 2 /g or more, most preferably 3 m 2 /g or more. Also, it is preferably 11 m 2 /g or less, more preferably 9 m 2 /g or less, still more preferably 8 m 2 /g or less, particularly preferably 7 m 2 /g or less, most preferably 6 m 2 / g or less.
• the specific surface area is within the above range, enough sites for Li to enter and exit can be secured, so that high-speed charge/discharge characteristics and output characteristics are excellent, and the activity of the active material with respect to the electrolyte can be moderately suppressed. For this reason, an increase in initial irreversible capacity can be suppressed, and there is a tendency to manufacture high-capacity batteries.
• the specific surface area is within the above range, when a negative electrode is formed using the organic compound-coated carbon material as a negative electrode material, an increase in reactivity with the electrolyte can be suppressed, and gas generation can be suppressed.
• a secondary battery can be provided.
• the total pore volume of the organic compound-coated carbon material of the present invention is preferably 0.1 mL/g or more, more preferably 0.2 mL/g or more, still more preferably 0.25 mL/g or more, Particularly preferably, it is 0.5 mL/g or more. Also, it is preferably 10 mL/g or less, more preferably 5 mL/g or less, still more preferably 2 mL/g or less, and particularly preferably 1 mL/g or less.
• the total pore volume is within the above range, there is no need to use an excessive amount of binder when forming an electrode plate, and the effect of dispersing the thickening agent and binder can be easily obtained.
• the average pore diameter of the organic compound-coated carbon material of the present invention is preferably 0.03 ⁇ m or more, more preferably 0.05 ⁇ m or more, still more preferably 0.1 ⁇ m or more, and particularly preferably 0.5 ⁇ m or more. is. Also, it is preferably 80 ⁇ m or less, more preferably 50 ⁇ m or less, and still more preferably 20 ⁇ m or less.
• the average pore diameter is within the above range, there is no need to use an excessive amount of binder when forming an electrode plate, and there is a tendency to avoid deterioration in high current density charge/discharge characteristics of the battery.
• the total pore volume and average pore diameter are values measured with a mercury porosimeter. Specifically, using a mercury porosimeter, the carbon material was weighed to a value of about 0.2 g, sealed in a powder cell, and pretreated by deaeration at 25° C. and 50 ⁇ mHg or less for 10 minutes. do. A vacuum of 4 psia is then applied to introduce mercury into the cell and the pressure is stepped from 4 psia to 40,000 psia and then decreased to 25 psia. The number of steps during pressure increase is set to 80 or more, and the amount of mercury intrusion is measured after an equilibrium time of 10 seconds at each step.
• the Washburn equation is used to calculate the pore size distribution and determine the total pore volume.
• the average pore diameter is the pore diameter when the cumulative pore volume is 50%.
• the surface tension ( ⁇ ) of mercury is calculated as 485 dyne/cm and the contact angle ( ⁇ ) as 140°.
• the true density of the organic compound-coated carbon material of the present invention is preferably 1.9 g/cm 3 or more, more preferably 2 g/cm 3 or more, still more preferably 2.1 g/cm 3 or more, particularly It is preferably 2.2 g/cm 3 or more.
• the upper limit of true density is 2.26 g/cm 3 which is the theoretical value of graphite.
• the powdery aspect ratio of the organic compound-coated carbon material of the present invention is 1 or more, preferably 1.1 or more, and more preferably 1.2 or more. Also, it is preferably 10 or less, more preferably 8 or less, even more preferably 5 or less, and particularly preferably 3 or less.
• the aspect ratio is within the above range, the slurry containing the organic compound-coated carbon material is less likely to streak when formed into an electrode plate, and a uniform coated surface can be obtained, resulting in high current density charge-discharge characteristics of the secondary battery. tend to avoid a decline in
• the aspect ratio is determined by A/B, where A is the longest diameter of the organic compound-coated carbon material particles when observed three-dimensionally, and B is the shortest diameter among the diameters perpendicular to it. value.
• Observation of the organic compound-coated carbon material particles is performed with a scanning electron microscope capable of magnified observation. Select any 50 particles fixed to the end surface of a metal with a thickness of 50 ⁇ m or less, rotate and tilt the stage on which the sample is fixed for each, measure A and B, and obtain the average value of A / B Ask for
• the Raman R value of the organic compound-coated carbon material of the present invention is preferably 0.1 or more, more preferably 0.15 or more, and still more preferably 0.2 or more. Also, it is preferably 0.6 or less, more preferably 0.5 or less, and still more preferably 0.4 or less.
• the Raman R value is within the above range, the crystallinity of the surface of the organic compound-coated carbon material particles is less likely to be high, and when the density is increased, the crystals are less likely to be oriented in the direction parallel to the negative electrode plate, resulting in a decrease in load characteristics. tend to avoid.
• the Raman R value is within the above range, the crystallinity of the particle surface is less likely to be disturbed, the reactivity with the electrolytic solution is suppressed, and there is a tendency to avoid a decrease in charge-discharge efficiency and an increase in gas generation.
• the maximum particle size dmax of the organic compound-coated carbon material of the present invention is preferably 200 ⁇ m or less, more preferably 150 ⁇ m or less, even more preferably 120 ⁇ m or less, and particularly preferably 100 ⁇ m or less.
• dmax is within the above range, there is a tendency to suppress process problems such as streaking when the electrode plate is formed.
• the maximum particle size dmax is the value of the largest particle size measured in the particle size distribution obtained when measuring the volume-based average particle size d50.
• the particle diameter d10 corresponding to the cumulative 10% of the smaller particle diameter measured on the volume basis of the organic compound-coated carbon material of the present invention is preferably 1 ⁇ m or more, more preferably 2 ⁇ m or more, still more preferably 3 ⁇ m or more, especially It is preferably 5 ⁇ m or more, most preferably 7 ⁇ m or more. Also, it is preferably 30 ⁇ m or less, more preferably 20 ⁇ m or less, and even more preferably 17 ⁇ m or less.
• the particle diameter d10 is within the above range, the tendency of the particles to aggregate is not too strong, and the occurrence of process problems such as an increase in slurry viscosity, a decrease in electrode strength in a secondary battery, and a decrease in initial charge-discharge efficiency can be avoided. can.
• the particle diameter d10 is within the above range, there is a tendency to avoid deterioration of high current density charge/discharge characteristics and deterioration of low temperature input/output characteristics.
• the particle size d10 is a value obtained by accumulating 10% from the particle size with the smallest particle frequency % in the particle size distribution obtained when the volume-based average particle size d50 is measured.
• the particle size d90 corresponding to cumulative 90% from the small particle side measured on a volume basis of the organic compound-coated carbon material of the present invention is preferably 15 ⁇ m or more, more preferably 18 ⁇ m or more, and even more preferably. It is 20 ⁇ m or more, and particularly preferably 25 ⁇ m or more. Also, it is preferably 100 ⁇ m or less, more preferably 70 ⁇ m or less, still more preferably 60 ⁇ m or less, particularly preferably 50 ⁇ m or less, and most preferably 45 ⁇ m or less.
• the particle size d90 is defined as a value obtained by accumulating 90% from the particle size with the smallest particle frequency % in the particle size distribution obtained when the volume-based average particle size d50 is measured.
• the amount of organic compounds eluted from the organic compound-coated carbon material of the present invention is preferably 20% by mass or less, more preferably 15% by mass or less, based on 100% by mass of the organic compounds contained in the organic compound-coated carbon material. , more preferably 10% by mass or less, and particularly preferably 5% by mass or less.
• the organic compound is less likely to come off during high-temperature storage or charge-discharge cycles, and deterioration in storage characteristics and charge-discharge cycle characteristics can be effectively suppressed.
• Electrode sheet The negative electrode of the present invention (hereinafter referred to as “electrode sheet” as appropriate) includes a current collector and an active material layer formed on the current collector, wherein the active material layer comprises at least the organic compound of the present invention. Includes coated carbon material.
• the active material layer preferably further contains a binder.
• the binder preferably has an olefinic unsaturated bond in the molecule from the viewpoint of reducing the swelling property of the active material layer against the electrolyte.
• Specific examples thereof include styrene-butadiene rubber, styrene/isoprene/styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene/propylene/diene copolymer.
• styrene-butadiene rubber is preferable from the viewpoint of availability.
• the strength of the negative electrode plate can be increased.
• the strength of the negative electrode is high, deterioration of the negative electrode due to charging and discharging can be suppressed, and the cycle life can be lengthened.
• a binder having an olefinically unsaturated bond in its molecule preferably has a large molecular weight or a large proportion of unsaturated bonds from the viewpoint of mechanical strength and flexibility.
• the weight average molecular weight is preferably 10,000 or more, more preferably 50,000 or more. Also, it is preferably 1,000,000 or less, and more preferably 300,000 or less.
• the number of moles of olefinic unsaturated bonds per 1 g of the binder is preferably 2.5 ⁇ 10 ⁇ 7 mol or more, more preferably 8 ⁇ 10 ⁇ 7 mol or more. is.
• the binder may satisfy at least one of the weight-average molecular weight and the proportion of unsaturated bonds, but it is preferable to satisfy both of them at the same time.
• the degree of unsaturation of the binder having olefinic unsaturated bonds is preferably 15% or more, more preferably 20% or more, and still more preferably 40% or more. Also, it is preferably 90% or less, more preferably 80% or less. As used herein, the degree of unsaturation is defined as the ratio (%) of double bonds to the repeating units of the polymer.
• a binder having no olefinic unsaturated bond can also be used together.
• the amount of the binder having no olefinically unsaturated bond is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, with respect to 100 parts by mass of the binder having olefinically unsaturated bonds. Coatability can be improved by using a binder having no olefinic unsaturated bond.
• Binders having no olefinic unsaturated bonds include, for example, thickening polysaccharides such as methylcellulose, carboxymethylcellulose, starch, carrageenan, pullulan, guar gum and xanthan gum (xanthan gum); polyethers such as polyethylene oxide and polypropylene oxide; Vinyl alcohols such as polyvinyl alcohol and polyvinyl butyral; polyacids such as polyacrylic acid and polymethacrylic acid; metal salts of these polymers; fluorine-containing polymers such as polyvinylidene fluoride; A polymer etc. are mentioned.
• the negative electrode of the present invention is formed by dispersing the organic compound-coated carbon material of the present invention and a binder in a dispersion medium to form a slurry, which is then applied to a current collector.
• a dispersion medium an organic solvent such as alcohol or water can be used.
• a conductive agent may be added to this slurry if desired.
• the conductive agent include carbon black such as acetylene black, ketjen black, and furnace black, and fine powders of Cu, Ni, or alloys thereof having an average particle size of 1 ⁇ m or less.
• the amount of the conductive agent added is preferably 10 parts by mass or less with respect to 100 parts by mass of the organic compound-coated carbon material of the present invention.
• Examples of current collectors to which the slurry is applied include metal thin films such as rolled copper foil, electrolytic copper foil, and stainless steel foil.
• the thickness of the current collector is preferably 4 ⁇ m or more, more preferably 6 ⁇ m or more. Moreover, it is preferably 30 ⁇ m or less, and more preferably 20 ⁇ m or less.
• This slurry is applied, for example, to a width of 5 cm using a doctor blade so that 10.0 ⁇ 0.3 mg/cm 2 of the negative electrode material adheres to a copper foil having a thickness of 20 ⁇ m as a current collector.
• the electrode sheet After drying at °C for 30 minutes, the electrode sheet can be obtained by roll-pressing with a roller having a diameter of 20 cm and adjusting the density of the active material layer to 1.60 ⁇ 0.03 g/cm 3 .
• the slurry on the current collector After coating the slurry on the current collector, it is preferably dried at a temperature of 60° C. or higher, more preferably 80° C. or higher, preferably 200° C. or lower, more preferably 195° C. or lower in dry air or an inert atmosphere. , to form the active material layer.
• the thickness of the active material layer is preferably 5 ⁇ m or more, more preferably 20 ⁇ m or more, still more preferably 30 ⁇ m or more. Also, it is preferably 200 ⁇ m or less, more preferably 100 ⁇ m or less, and even more preferably 75 ⁇ m or less. When the thickness of the active material layer is within the above range, it is excellent in practicality as a negative electrode because of the balance with the particle size of the organic compound-coated carbon material, and the function of absorbing and releasing Li is sufficient for high-density current values. Obtainable.
• the density of the organic compound-coated carbon material in the active material layer varies depending on the application. For applications where capacity is important, this density is preferably 1.45 g/cm 3 or more, more preferably 1.5 g/cm 3 or more, even more preferably 1.55 g/cm 3 or more, and particularly preferably is 1.6 g/cm 3 or more. Moreover, it is preferably 1.9 g/cm 3 or less. When the density is within the above range, the capacity of the battery per unit volume can be sufficiently secured, and the rate characteristics are less likely to deteriorate.
• the organic compound-coated carbon material of the present invention described above is used to produce a negative electrode for a non-aqueous secondary battery
• the method and selection of other materials are not particularly limited.
• a lithium ion secondary battery is produced using this negative electrode, there are no particular restrictions on the selection of members necessary for the battery configuration, such as the positive electrode and the electrolytic solution that constitute the lithium ion secondary battery.
• a secondary battery usually includes a positive electrode, a negative electrode, and an electrolyte capable of intercalating and deintercalating lithium ions.
• the negative electrode the negative electrode of the present invention described above is used.
• the positive electrode is obtained by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector.
• positive electrode active materials include metal chalcogen compounds capable of intercalating and deintercalating alkali metal cations such as lithium ions during charging and discharging.
• metal chalcogen compounds include transition metal oxides such as vanadium oxide, molybdenum oxide, manganese oxide, chromium oxide, titanium oxide, tungsten oxide, vanadium sulfide, molybdenum sulfides of titanium, sulfides of titanium, transition metal sulfides such as CuS, phosphorus-sulfur compounds of transition metals such as NiPS 3 and FePS 3 , selenium compounds of transition metals such as VSe 2 and NbSe 3 , Fe 0.25 V Composite oxides of transition metals such as 0.75 S 2 and Na 0.1 CrS 2 , composite sulfides of transition metals such as LiCoS 2 and LiNiS 2 and the like are included.
• These positive electrode active materials may be used singly or in combination.
• V2O5 , V5O13 , VO2 , Cr2O5 , MnO2 , TiO2 , MoV2O8 , LiCoO2 , LiNiO2 , LiMn2O4 , TiS2 , V2S5 , Cr 0.25 V 0.75 S 2 and Cr 0.5 V 0.5 S 2 are preferable, LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , lithium obtained by substituting a part of these transition metals with other metals Transition metal composite oxides are more preferred.
• the binder that binds the positive electrode active material examples include inorganic compounds such as silicate and water glass, and resins that do not have unsaturated bonds such as polytetrafluoroethylene and polyvinylidene fluoride. Among them, a resin having no unsaturated bond is preferable. When a resin having no unsaturated bond is used as the resin that binds the positive electrode active material, decomposition during the oxidation reaction can be suppressed.
• the weight average molecular weight of these resins is usually 10,000 or more, preferably 100,000 or more. Moreover, it is usually 3 million or less, preferably 1 million or less.
• a conductive material may be contained in the positive electrode active material layer in order to improve the conductivity of the electrode.
• Examples of conductive materials include carbon powder such as acetylene black, carbon black, and graphite, and fibers, powders, and foils of various metals.
• the positive electrode plate is formed by slurrying a positive electrode active material and a binder with a dispersion medium, applying the slurry on a current collector, and drying the slurry, in the same manner as in manufacturing the negative electrode.
• positive electrode current collectors include aluminum, nickel, and stainless steel (SUS).
• a non-aqueous electrolytic solution obtained by dissolving a lithium salt in a non-aqueous solvent, or a gel-like, rubber-like, or solid sheet-like form of this non-aqueous electrolytic solution with an organic polymer compound or the like is used.
• Non-aqueous solvents used in the non-aqueous electrolytic solution include, for example, chain carbonates such as diethyl carbonate, dimethyl carbonate and ethyl methyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate; Chain ethers such as dimethoxyethane; Cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, and 1,3-dioxolane; Chain esters such as methyl formate, methyl acetate, and methyl propionate; ⁇ -butyrolactone, ⁇ - cyclic esters such as valerolactone; Any one of these non-aqueous solvents may be used alone, or two or more thereof may be mixed and used.
• chain carbonates such as diethyl carbonate, dimethyl carbonate and ethyl methyl carbonate
• cyclic carbonates such as ethylene carbonate, propylene
• a mixed solvent a combination of a mixed solvent containing a cyclic carbonate and a chain carbonate is preferred.
• the cyclic carbonate in the mixed solvent is a mixed solvent of ethylene carbonate and propylene carbonate from the viewpoint that high ionic conductivity can be expressed even at low temperatures and low-temperature charging characteristics are improved.
• the proportion of propylene carbonate is preferably 2% by mass or more and 80% by mass or less, more preferably 5% by mass or more and 70% by mass or less, and even more preferably 10% by mass or more and 60% by mass or less in 100% by mass of the non-aqueous solvent. .
• the proportion of propylene carbonate is at least the lower limit, it is possible to suppress a decrease in ionic conductivity at low temperatures. If the proportion of propylene carbonate is equal to or less than the upper limit, delamination deterioration of the graphite-based negative electrode active material due to co-insertion of propylene carbonate solvated with lithium ions into graphite phases can be suppressed when a graphite-based electrode is used. , sufficient capacity is obtained.
• Lithium salts used in the non-aqueous electrolyte include, for example, halides such as LiCl and LiBr; perhalates such as LiClO4 , LiBrO4 and LiClO4 ; inorganic fluorides such as LiPF6 , LiBF4 and LiAsF6 ; Inorganic lithium salts such as compound salts, perfluoroalkanesulfonates such as LiCF 3 SO 3 and LiC 4 F 9 SO 3 , perfluoroalkanesulfonic acids such as Li trifluorosulfonimide ((CF 3 SO 2 ) 2 NLi) fluorine-containing organic lithium salts such as imide salts; Lithium salts may be used alone or in combination of two or more. Among them, LiClO 4 , LiPF 6 and LiBF 4 are preferred.
• the concentration of the lithium salt in the non-aqueous electrolytic solution is usually 0.5 mol/L or more and 2.0 mol/L or less.
• the non-aqueous electrolytic solution described above contains an organic polymer compound and is used in the form of a gel, a rubber or a solid sheet
• specific examples of the organic polymer compound include poly(polyethylene) such as polyethylene oxide and polypropylene oxide.
• Ether-based polymer compound Crosslinked polymer of polyether-based polymer compound; Vinyl alcohol-based polymer compound such as polyvinyl alcohol and polyvinyl butyral; Insolubilized vinyl alcohol-based polymer compound; Polyepichlorohydrin; vinyl-based polymer compounds such as polyvinylpyrrolidone, polyvinylidene carbonate, and polyacrylonitrile; poly( ⁇ -methoxyoligooxyethylene methacrylate), poly( ⁇ -methoxyoligooxyethylene methacrylate-co-methyl methacrylate), poly(hexafluoropropylene) -vinylidene fluoride) and the like.
• Vinyl alcohol-based polymer compound such as polyvinyl alcohol and polyvinyl butyral
• Insolubilized vinyl alcohol-based polymer compound Polyepichlorohydrin
• vinyl-based polymer compounds such as polyvinylpyrrolidone, polyvinylidene carbonate, and polyacrylonitrile
• the non-aqueous electrolytic solution described above may further contain a film-forming agent.
• film-forming agents include carbonate compounds such as vinylene carbonate, vinyl ethyl carbonate and methylphenyl carbonate; alkene sulfides such as ethylene sulfide and propylene sulfide; sultone compounds; acid anhydrides such as maleic anhydride and succinic anhydride;
• the non-aqueous electrolytic solution may further contain an overcharge inhibitor such as diphenyl ether or cyclohexylbenzene.
• the content is usually 10% by mass or less, preferably 8% by mass or less, more preferably 5% by mass or less, and still more preferably 100% by mass of the non-aqueous electrolytic solution. is 2% by mass or less.
• the content of the additive is within the above range, adverse effects on other battery characteristics such as an increase in initial irreversible capacity, deterioration in low-temperature characteristics, deterioration in rate characteristics, and the like can be reduced.
• a polymer solid electrolyte which is a conductor of alkali metal cations such as lithium ions, can also be used as the electrolyte.
• solid polymer electrolytes include those obtained by dissolving a lithium salt in the aforementioned polyether-based polymer compound, polymers in which terminal hydroxyl groups of polyether are substituted with alkoxides, and the like.
• a porous separator such as a porous membrane or non-woven fabric is usually interposed between the positive electrode and the negative electrode to prevent a short circuit between the electrodes.
• the non-aqueous electrolytic solution is used by impregnating a porous separator.
• materials for the separator include polyolefins such as polyethylene and polypropylene, and polyethersulfone. Among them, polyolefin is preferred.
• the form of the secondary battery of the present invention is not particularly limited. Examples thereof include a cylinder type in which a sheet electrode and a separator are spirally formed, a cylinder type with an inside-out structure in which a pellet electrode and a separator are combined, a coin type in which a pellet electrode and a separator are laminated, and the like.
• a cylinder type in which a sheet electrode and a separator are spirally formed
• a cylinder type with an inside-out structure in which a pellet electrode and a separator are combined a coin type in which a pellet electrode and a separator are laminated, and the like.
• the procedure for assembling the secondary battery of the present invention may be an appropriate procedure according to the structure of the battery.
• a negative electrode is placed on an exterior case, an electrolytic solution and a separator are provided thereon, a positive electrode is placed so as to face the negative electrode, and a gasket and a sealing plate are crimped together to form a battery.
• a mercury porosimeter (model name "Autopore 9520", manufactured by Micromeritex) is used, and the carbon material is weighed to a value of about 0.2 g, sealed in a powder cell, Pretreatment was carried out by degassing for 10 minutes at 25° C. under vacuum (50 ⁇ mHg or less). Then, the pressure was reduced to 4 psia (about 28 kPa), mercury was introduced into the cell, and the pressure was increased stepwise from 4 psia (about 28 kPa) to 40000 psia (about 280 MPa), and then decreased to 25 psia (about 170 kPa).
• the number of steps during the pressure increase was set to 80 or more, and the intrusion amount of mercury was measured after an equilibrium time of 10 seconds at each step. From the mercury intrusion curve thus obtained, the Washburn equation was used to calculate the pore size distribution, and the cumulative pore volume of pore diameters of 10 nm or more and 800 nm or less was determined.
• the surface tension ( ⁇ ) of mercury was calculated as 485 dyne/cm, and the contact angle ( ⁇ ) as 140°.
• SA specific surface area
• Example 1 Natural graphite flakes were subjected to a mechanical action using a spheronizing device having a pulverizing rotor to obtain spheroidized graphite having a volume-based average particle size d50 of 16.3 ⁇ m. The obtained spheroidized graphite was subjected to isotropic pressure treatment using a CIP molding machine at a pressure of 2000 kgf/cm 2 and 25° C. for 1 minute, and then pulverized to obtain a raw carbon material (a). .
• Tables 1 and 2 show the cumulative pore volume, DBP oil absorption, and BET specific surface area of the spheroidized graphite used in Example 1 before the isotropic pressure treatment.
• Comparative Example 2 An organic compound-coated carbon material (X-1) of Comparative Example was obtained in the same manner as in Example 1, except that the spheroidized graphite was mixed with the polyvinyl alcohol aqueous solution without isotropic pressure treatment. Table 1 shows the measurement results of the cumulative pore volume, DBP oil absorption and BET specific surface area of the obtained organic compound-coated carbon material (X-1).
• Tables 1 and 2 show the measurement results of the integrated pore volume, DBP oil absorption, and BET specific surface area of the raw carbon material (a) obtained by subjecting the spheroidized graphite to isotropic pressure treatment in Example 1. show.
• Example 2 An organic compound-coated carbon material (A-2) of the present invention was obtained in the same manner as in Example 1, except that the polyvinyl alcohol was changed to polyallylamine (average molecular weight: 15,000). Table 2 shows the measurement results of the cumulative pore volume, DBP oil absorption and BET specific surface area of the obtained organic compound-coated carbon material (A-2).
• the basal surface of the raw carbon material (a) was coated with a polyvinyl alcohol-based resin-derived compound and a polyvinyl alcohol-based resin. It was confirmed by simultaneously measuring the adsorption isotherm and the heat of adsorption using toluene gas that each compound derived from the allylamine resin was coated.
• an electrode plate having an active material layer with a density of 1.60 ⁇ 0.03 g/cm 3 was produced. Specifically, 20.00 ⁇ 0.02 g of the negative electrode material, 20.00 ⁇ 0.02 g of 0.7 mass% carboxymethylcellulose sodium salt aqueous solution (0.14 g in terms of solid content) and styrene-butadiene rubber aqueous dispersion 0.42 ⁇ 0.02 g (0.2 g in terms of solid content) was mixed, stirred for 5 minutes with "Awatori Mixer" (manufactured by Thinky), and defoamed for 30 seconds to obtain a slurry.
• “Awatori Mixer” manufactured by Thinky
• This slurry is applied to a 10 cm thick copper foil as a current collector using a die coating machine so that 10.10 ⁇ 0.3 mg/cm 2 of the negative electrode material adheres to a width of 10 cm and a diameter of 20 cm. rollers to adjust the density of the active material layer to 1.60 ⁇ 0.03 g/cm 3 to obtain an electrode sheet.

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• 2023
  • 2023-02-03 JP JP2024501284A patent/JPWO2023157670A1/ja active Pending
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