Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
  • H01M4/0402—Methods of deposition of the material
  • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/133—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
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/134—Electrodes based on metals, Si or alloys
• • 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
  • H01M4/362—Composites
  • H01M4/366—Composites as layered products
• • 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
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
• • 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
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
  • H01M4/386—Silicon or alloys based on silicon
• • 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
• • 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
• • 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
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/021—Physical characteristics, e.g. porosity, surface area
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/027—Negative electrodes
• • 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 a negative electrode active material and a secondary battery containing the negative electrode active material.
• the present invention also relates to a method for producing the negative electrode active material.
• Non-aqueous electrolyte secondary batteries are used in mobile devices, hybrid vehicles, electric vehicles, household storage batteries, etc., and are required to have well-balanced characteristics such as electrical capacity, safety, and operational stability. ing.
• a lithium intercalation compound that releases lithium ions from between layers is mainly used as a negative electrode material, and lithium ions can be intercalated and released between crystal plane layers during charging and discharging.
• various lithium ion batteries using a carbonaceous material such as graphite as a negative electrode active material have been developed and put to practical use.
• Patent Documents 1 and 2 disclose a soft carbon material for lithium ion secondary battery negative electrode material comprising a nanomaterial coating supported on the surface layer of soft carbon powder particles and a conductive carbon layer covering the outer surface of the nanomaterial coating. disclosed. However, it is conceivable that many voids are present in soft carbon on which nanomaterials are supported.
• Patent Document 3 discloses a negative electrode material containing composite particles in which amorphous carbon containing specific nanosilicon is attached to the surface of graphite particles.
• Patent Document 4 discloses a negative electrode material for a lithium ion battery in which a granular active material made of graphite and a network structure having a plurality of CO-Si bonds are provided on a part of the surface of the granular active material. are doing.
• JP 2015-128045 A Japanese Patent Publication No. 2017-526118 WO2020/088248 JP 2020-64876 A
• an object of the present invention is to provide a negative electrode active material that provides a secondary battery having high initial discharge capacity, high capacity retention rate and high charge/discharge capacity and having an excellent balance of these properties.
• A represents the average grain size of the granular structure
• B represents the penetration depth of the surface layer into the concave portion.
• Step (1) A step of obtaining a surface layer forming precursor
• Step (2) A step of applying the surface layer forming precursor to the surface of a granular structure mainly composed of graphite having an uneven surface
• Inactive A step [14] of obtaining a negative electrode active material by high-temperature firing at a firing temperature of 1000 to 1300 ° C. in an atmosphere [14].
• a secondary battery comprising the negative electrode active material according to any one of [1] to [14].
• a negative electrode active material that provides a secondary battery having high initial discharge capacity, capacity retention rate, and charge/discharge capacity, and having an excellent balance of these characteristics, and a secondary battery using the negative electrode active material are provided.
• the negative electrode active material of the present invention (hereinafter also referred to as “the present negative electrode active material”) comprises a granular structure (hereinafter also referred to as “the present granular structure”) mainly composed of graphite and having an uneven surface on the surface, At least part of the surface of the present granular structure has a surface layer in which silicon particles having an average particle size of 20 nm to 200 nm are dispersed in a matrix phase.
• the combined use of silicon which has a higher theoretical capacity than graphite, has conventionally been investigated.
• silicon expands up to about 3 to 4 times in volume as lithium is inserted, self-destructs, or separates from the electrode.
• the resulting lithium secondary battery has poor cycle characteristics.
• Patent Documents 1 to 4 In order to suppress the volume expansion, a method of coating or adhering the surface of graphite with silicon particles as described in Patent Documents 1 to 4, a method of introducing a three-dimensional network structure, and the like have been proposed.
• the present negative electrode active material uses a granular structure mainly composed of graphite having an uneven surface, and has a surface layer in which silicon particles are dispersed in a matrix phase on at least a part of the surface of the present granular structure. It is believed that the strength between graphite and silicon particles was improved. As a result, it is believed that the initial discharge capacity, capacity retention rate, and charge/discharge capacity of the secondary battery using this negative electrode active material were improved.
• the granular structure is mainly composed of graphite. Assuming that the mass of the present granular structure is 100% by mass, the content of graphite is preferably more than 50% by mass, more preferably 80% by mass or more.
• Graphite which is the main component, includes amorphous carbon such as natural graphite, artificial graphite, and hard carbon or soft carbon. Graphite is preferably natural graphite or artificial graphite from the viewpoint of initial discharge capacity or charge/discharge capacity.
• the granular structure may contain carbon nanotubes, carbon fibers, or a small amount of binder used during the granulation process.
• the graphite When the graphite is natural graphite or artificial graphite, the graphite has an average particle size of 1 ⁇ m to 25 ⁇ m and a specific surface area of 0.5 m 2 /g to 20 m 2 /g. This is preferable from the viewpoint of simultaneously suppressing side effects on the surface of graphite during charging and discharging.
• the average particle size is a D50 value that can be measured using a laser diffraction particle size analyzer or the like. D50 can be measured by a dynamic light scattering method using a laser particle size analyzer or the like.
• the average particle diameter is the particle diameter at which the volume cumulative distribution curve is drawn from the small diameter side in the particle diameter distribution, and the cumulative volume reaches 50%.
• the average particle size means D50.
• the specific surface area is the BET specific surface area determined by the BET formula using a specific surface area measuring device from nitrogen gas adsorption measurement.
• the specific surface area means the BET specific surface area.
• the present granular structure has an uneven portion on its surface.
• the uneven portion may be formed on a part of the surface of the present granular structure, and may be formed on the entire surface.
• the irregularities may be formed continuously or intermittently on the surface of the present granular structure. Further, the uneven portion may be formed regularly or irregularly.
• the irregularities may be formed, for example, by roughening the surface of the present granular structure, or may be formed by forming a plurality of holes on the surface. When forming a plurality of holes, the holes may be open holes or communicating holes.
• the unevenness depth which is the average of the distances between the deepest part and the highest part of the adjacent uneven part, is the ratio of the unevenness depth to the grain size of the present granular structure from the viewpoint of the adhesive strength between the surface layer and the present granular structure, which will be described later. is preferably 0.01 or more, more preferably 0.05 or more.
• the mechanical performance of the granular structure may be deteriorated, and the surface layer becomes difficult to enter the irregularities of the granular structure, and voids are generated in the active material, resulting in charging and discharging. Occasionally, there is a possibility of performance deterioration due to permeation of the electrolyte.
• the cross-sectional shape of the uneven portion includes, for example, triangular, rectangular, semi-circular, and semi-elliptical shapes, and a plurality of these shapes may be mixed.
• the average particle size of the present granular structure is preferably 1 ⁇ m to 30 ⁇ m, more preferably 3 ⁇ m to 20 ⁇ m.
• the specific surface area of the present granular structure is preferably 1 m 2 /g to 30 m 2 /g, more preferably 3 m 2 /g to 20 m 2 /g. When the specific surface area is within the above range, appropriate surface voids can be maintained in order to maintain adhesion to the surface layer.
• the cumulative pore volume of pore diameters in the range of 3 nm to 300 nm is preferably 0.001 cm 3 /g or more from the viewpoint of maintaining adhesion to the surface layer.
• the cumulative pore volume of the pore diameter is the cumulative pore volume of pores having a pore diameter in the range of 2 nm or more and 100 nm or less, among the pores measured by the mercury porosimetry.
• the mercury intrusion method is to inject mercury into the hardened body and measure the pore size distribution from the relationship between the pressure and the intrusion amount at that time, assuming that the shape of the pores is cylindrical. calculated by
• the cumulative pore volume is more preferably 0.01 cm 3 /g or more.
• the upper limit of the accumulated pore volume is usually 0.5 cm 3 /g.
• the present negative electrode active material has a surface layer in which silicon particles having an average particle size of 20 nm to 200 nm (hereinafter also referred to as "present silicon particles") are dispersed in a matrix phase on at least part of the surface of the present granular structure. .
• the average particle diameter of the present silicon particles is the value of D50. From the viewpoint of improving cycle performance, the average particle size of the present silicon particles is preferably 100 nm or less, more preferably 80 nm or less.
• the average particle size of the present silicon particles is preferably 20 nm or more, more preferably 30 nm or more, from the viewpoint of maintaining good dispersibility of the silicon nanoparticles.
• the particle size of the present silicon particles is preferably distributed over a wide range of 5 nm to 300 nm within the range satisfying the average particle size.
• silicon particles having different particle diameters over a wide range it is easy to increase the packing density of the silicon particles in the present active material.
• the expression "widely distributed" means that the shape of the particle size distribution is not particularly limited as long as the particles exist within the range of the particle size.
• the particle size of the present silicon particles is distributed over a wide range, the particles may be concentrated in a part of the particle size range, and a normal distribution is preferred. Silicon particles with a broad distribution of particle sizes can be produced, for example, by dry or wet mechanical comminution methods.
• the present silicon particles are composed of zero-valent silicon, and for example, a mass of silicon can be pulverized into particles such that the average particle size falls within the above range.
• crushers used for crushing silicon lumps include crushers such as ball mills, bead mills, and jet mills.
• the pulverization may be wet pulverization using an organic solvent, and as the organic solvent, for example, alcohols, ketones, etc. can be preferably used. Group hydrocarbon solvents can also be used.
• the present silicon particles can be obtained by appropriately controlling the pulverization conditions of the silicon particles so that the average particle size falls within the above range, and finally performing classification or the like.
• the shape of the present silicon particles may be granular, needle-like, or flaky as long as it satisfies the above-mentioned average particle size, but the flaky shape is preferable from the viewpoint of improving the performance of the active material.
• the silicon particles are flaky, they are crystalline, and if the crystallite size obtained from the peak at 28.4° in the X-ray diffraction spectrum is 40 nm or less, the initial coulombic efficiency and the capacity retention rate can be improved. preferable.
• the crystallite size is more preferably 30 nm or less. Further, the crystallite size is more preferably 10 nm or more.
• the compound that constitutes the matrix phase is preferably a compound containing silicon, oxygen, and carbon, and the compound containing silicon, oxygen, and carbon preferably has a three-dimensional network structure of silicon-oxygen-carbon skeleton and a structure containing free carbon.
• free carbon is carbon that is not contained in the three-dimensional skeleton of silicon-oxygen-carbon. Free carbon includes carbon present as a carbon phase, carbon bonded between carbon phase carbons, and carbon bonded between a silicon-oxygen-carbon skeleton and a carbon phase.
• the silicon-oxygen-carbon skeleton in the matrix phase is chemically It is highly stable and has a composite structure with free carbon, which facilitates the diffusion of lithium ions along with the reduction in electronic transition resistance. Direct contact between the silicon particles and the electrolytic solution is prevented by tightly enveloping the silicon particles in the composite structure of the silicon-oxygen-carbon skeleton and free carbon.
• the present silicon particles in the negative electrode play a role of being the main component for the expression of charge-discharge performance, while avoiding a chemical reaction between silicon and the electrolyte during charge-discharge. As a result, deterioration of the performance of the present silicon particles can be prevented to the maximum.
• the electron distribution inside the silicon-oxygen-carbon skeleton changes due to the approach of lithium ions, causing electrostatic bonding and coordination between the silicon-oxygen-carbon skeleton and lithium ions. Positional bonds and the like are formed. Lithium ions are stored in the silicon-oxygen-carbon skeleton by this electrostatic bond and coordinate bond. On the other hand, since the coordination bond energy is relatively low, the desorption reaction of lithium ions easily occurs. In other words, it is considered that the silicon-oxygen-carbon skeleton can reversibly cause intercalation and deintercalation reactions of lithium ions during charging and discharging.
• the free carbon is preferably amorphous carbon.
• the matrix phase preferably contains silicon oxycarbide represented by the following formula (2).
• SiOx Cy (2) In formula (2), x represents the molar ratio of oxygen to silicon, and y represents the molar ratio of carbon to silicon.
• x represents the molar ratio of oxygen to silicon
• y represents the molar ratio of carbon to silicon.
• the compound constituting the matrix phase may contain nitrogen in addition to silicon, oxygen and carbon.
• Nitrogen is a functional group in the raw material used in the manufacturing method of the active material described later, such as phenolic resin, dispersant, polysiloxane compound, other nitrogen compounds, and nitrogen gas used in the firing process. By having an atomic group containing it, it can be introduced into the matrix phase.
• the matrix phase contains nitrogen, the charge/discharge performance and the capacity retention rate tend to be excellent when using the present negative electrode active material.
• the compound constituting the matrix phase is a compound containing silicon, oxygen, carbon and nitrogen
• the matrix phase preferably contains a compound represented by the following formula (3).
• SiOxCyNz (3) In formula (3), x and y have the same meanings as above, and z represents the molar ratio of nitrogen to silicon.
• the matrix phase contains the compound represented by the formula (3), 1 ⁇ x ⁇ 2, 1 ⁇ y ⁇ 20, 0 ⁇ z ⁇ 0.5 are preferable, and 1.1 ⁇ x ⁇ 1.8, 1.2 ⁇ y ⁇ 15, and 0 ⁇ z ⁇ 0.4 are more preferable.
• the above x, y and z can be obtained by measuring the mass content of each element and then converting to a molar ratio (atomic number ratio).
• the content of oxygen and carbon can be quantified by using an inorganic elemental analyzer, and the content of silicon can be quantified by using an ICP optical emission spectrometer (ICP-OES).
• ICP-OES ICP optical emission spectrometer
• the present active material is locally analyzed, and a large number of measurement points for the content ratio data obtained thereby is obtained. It is also possible to analogize the content ratio of the entire negative electrode active material. Local analysis includes, for example, Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Electron Probe Microanalyzer (EPMA).
• the surface layer of the present negative electrode active material on at least part of the present granular structure includes the present silicon particles, the silicon oxycarbide as a matrix phase in which the present silicon particles are dispersed, and amorphous carbon as the free carbon. It is preferable that the surface layer contains 1 to 80% by mass of the present silicon particles based on 100% by mass of the total mass of the surface layer. Examples of amorphous carbon include carbon generated by thermal decomposition of organic substances such as aromatic resins.
• the surface layer preferably contains nitrogen from the viewpoint of Si--O--C skeleton stability.
• the matrix phase preferably contains the compound represented by the formula (3).
• the surface layer more preferably contains the present silicon particles in an amount of 10% by mass or more, more preferably 15% by mass or more.
• the surface layer preferably contains the present silicon particles in an amount of 80% by mass or less, more preferably 70% by mass or less.
• the negative electrode active material preferably contains 1 to 80% by mass of the surface layer based on 100% by mass of the total mass of the negative electrode active material.
• the present negative electrode active material preferably contains the surface layer in an amount of 5% by mass or more, more preferably 10% by mass or more, based on 100% by mass of the total mass of the present negative electrode active material.
• the negative electrode active material preferably contains 70% by mass or less of the surface layer, more preferably 60% by mass or less, based on 100% by mass of the total mass of the negative electrode active material. preferable.
• the total mass of the present negative electrode active material is the total mass of the present granular structure and the surface layer that constitute the present negative electrode active material. When the matrix phase contains nitrogen, it is the total amount including nitrogen. When the present negative electrode active material contains a coating layer to be described later, the total mass of the present negative electrode active material is the total mass including the mass of the coating layer in addition to the above.
• the present negative electrode active material has the surface layer on at least a part of the surface of the present granular structure, but from the viewpoint of suppressing the specific surface area and rationalizing the fine structure, 80% or more of the surface of the present granular structure has the above-mentioned surface layer. It is preferable to have a surface layer, and more preferably 90% or more of the surface of the present granular structure has the surface layer.
• the penetration depth of the surface layer into the recesses of the granular structure preferably satisfies the formula (1). 0.01 ⁇ B/A ⁇ 0.3 (1)
• A represents the average grain size of the present granular structure
• B represents the penetration depth of the surface layer into the recess.
• A is the aforementioned D50
• B is measured by SEM observation of the cross section of the particle.
• a and B more preferably satisfy the following formula (4), and more preferably satisfy the following formula (5).
• the present negative electrode active material may contain other necessary third components in addition to the above.
• the surface of the present negative electrode active material may be coated with a coating material.
• a coating material a substance that can be expected to have electronic conductivity, lithium ion conductivity, and an effect of suppressing decomposition of the electrolytic solution is preferable.
• the average thickness of the coating is preferably 10 nm or more and 300 nm or less.
• the average thickness of the coating is preferably 20 nm or more and 200 nm or less. Since the present negative electrode active material has a film having the above average thickness, it is possible to protect the present silicon particles exposed on the surface of the granular structure. Stability and thermal stability are improved. It is possible to further suppress the deterioration of the charge/discharge performance of the secondary battery obtained as a result.
• the content of the coating is 100 mass of the total mass of the present negative electrode active material from the viewpoint of improving the chemical stability and thermal stability of the negative electrode active material. % is preferably 1 to 30% by mass, more preferably 3 to 25% by mass.
• the total mass of the present negative electrode active material is the same as described above.
• the coating examples include electron conductive materials such as carbon, titanium, and nickel. Among these, from the viewpoint of improving the chemical stability and thermal stability of the negative electrode active material, carbon is preferable, and low-crystalline carbon is more preferable.
• the coating is carbon
• the average thickness of the carbon coating is preferably 10 nm or more and 300 nm or less, or the content of carbon is preferably 1 to 10% by mass based on 100% by mass of the total amount of the present negative electrode active material.
• the total amount of the present negative electrode active material is the same as described above.
• the coating is preferably produced by chemical vapor deposition (CVD).
• the scattering peak intensity ratio I (G band/D band) of the Raman spectrum is preferably in the range of 0.9 to 1.1. It is preferable that the specific surface area by the BET method is 3.5 m 2 /g or less and the true density is 1.9 g/cm 3 or more.
• the present negative electrode active material has a high initial discharge capacity, a high capacity retention rate, and a high charge/discharge capacity, and is excellent in the balance of these characteristics. Exhibits charge-discharge characteristics.
• a slurry comprising the present negative electrode active material, an organic binder, and, if necessary, other components such as a conductive aid is applied in the form of a thin film onto the current collector copper foil. It can be a negative electrode.
• a negative electrode can also be produced by adding a carbon material such as graphite to the slurry. Carbon materials include natural graphite, artificial graphite, amorphous carbon such as hard carbon or soft carbon, and the like.
• the present negative electrode active material and a binder that is an organic binder are kneaded together with a solvent using a dispersing device such as a stirrer, ball mill, super sand mill, pressure kneader, etc. to prepare a negative electrode material slurry, which is then collected. It can be obtained by applying it to an electric body to form a negative electrode layer.
• the negative electrode layer can also be obtained by forming a paste-like negative electrode material slurry into a shape such as a sheet or pellet and integrating this with a current collector.
• organic binder examples include styrene-butadiene rubber copolymer (hereinafter also referred to as "SBR"); methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylonitrile , and ethylenically unsaturated carboxylic acid esters such as hydroxyethyl (meth)acrylate, and ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid (meth)acrylic copolymerization
• Unsaturated carboxylic acid copolymers such as coalescence; A high molecular compound is mentioned.
• these organic binders can be dispersed or dissolved in water, or dissolved in an organic solvent such as N-methyl-2-pyrrolidone (NMP).
• NMP N-methyl-2-pyrrolidone
• the content ratio of the organic binder in the negative electrode layer of the lithium ion secondary battery negative electrode is preferably 1% by mass to 30% by mass, more preferably 2% by mass to 20% by mass, and 3% by mass. to 15% by mass is more preferable.
• the present negative electrode active material has high chemical stability and can be used with an aqueous binder, which makes it easy to handle in terms of practical use.
• the negative electrode material slurry may be mixed with a conductive aid, if necessary.
• conductive aids include carbon black, graphite, acetylene black, oxides and nitrides exhibiting conductivity, and the like.
• the amount of the conductive aid used may be about 1% by mass to 15% by mass with respect to the negative electrode active material of the present invention.
• the material and shape of the current collector for example, copper, nickel, titanium, stainless steel, etc. may be used in the form of a foil, a perforated foil, a mesh, or the like in a strip shape.
• Porous materials such as porous metal (foamed metal) and carbon paper can also be used.
• Examples of the method for applying the negative electrode material slurry to the current collector include a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, and a screen printing method. etc. After coating, it is preferable to carry out a rolling treatment using a flat plate press, calendar rolls, or the like, if necessary.
• the negative electrode material slurry can be made into a sheet or pellet form, and integrated with the current collector by, for example, rolling, pressing, or a combination thereof.
• the negative electrode layer formed on the current collector or the negative electrode layer integrated with the current collector is preferably heat-treated according to the organic binder used.
• heat treatment may be performed at 100 to 130°C
• heat treatment is performed at 150 to 450°C. is preferred.
• This heat treatment removes the solvent and hardens the binder to increase the strength, improving the adhesion between particles and between the particles and the current collector.
• These heat treatments are preferably performed in an inert atmosphere such as helium, argon, or nitrogen, or in a vacuum atmosphere in order to prevent oxidation of the current collector during the treatment.
• the negative electrode using the present negative electrode active material preferably has an electrode density of 1 g/cm 3 to 1.8 g/cm 3 , more preferably 1.1 g/cm 3 to 1.7 g/cm 3 , More preferably from 1.2 g/cm 3 to 1.6 g/cm 3 .
• the electrode density there is a tendency that the higher the electrode density, the higher the adhesion and the volume capacity density of the electrode.
• the electrode density is too high, the voids in the electrode are reduced, which weakens the effect of suppressing the volume expansion of silicon or the like, and the capacity retention rate may decrease. Therefore, an optimum range of electrode densities is selected.
• the secondary battery of the present invention includes the present negative electrode active material in the negative electrode.
• a secondary battery having a negative electrode containing the present negative electrode active material a non-aqueous electrolyte secondary battery and a solid electrolyte secondary battery are preferable, and excellent performance is exhibited particularly when used as a negative electrode of a non-aqueous electrolyte secondary battery. It is something to do.
• a positive electrode and a negative electrode containing the negative electrode active material of the present invention are placed facing each other with a separator interposed therebetween, and an electrolytic solution is injected. It can be configured by
• the positive electrode can be obtained by forming a positive electrode layer on the surface of the current collector in the same manner as the negative electrode.
• the current collector may be a strip-shaped one made of a metal or alloy such as aluminum, titanium, or stainless steel in the form of foil, foil with holes, mesh, or the like.
• the positive electrode material used for the positive electrode layer is not particularly limited.
• a metal compound, a metal oxide, a metal sulfide, or a conductive polymer material capable of doping or intercalating lithium ions should be used.
• lithium cobalt oxide LiCoO 2
• lithium nickel oxide LiNiO 2
• lithium manganate LiMnO 2
• lithium manganese spinel LiMn 2 O 4
• lithium vanadium compounds V2O5 , V6O13 , VO2 , MnO2 , TiO2 , MoV2O8 , TiS2 , V2S5 , VS2 , MoS2 , MoS3 , Cr3O8 , Cr 2 O 5
• olivine-type LiMPO 4 (where M is Co, Ni, Mn or Fe), conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene and polyacene, porous carbon, etc. can be used.
• the separator for example, a non-woven fabric, cloth, microporous film, or a combination of them can be used, the main component of which is polyolefin such as polyethylene or polypropylene.
• the positive electrode and the negative electrode of the non-aqueous electrolyte secondary battery to be manufactured are structured such that they do not come into direct contact with each other, there is no need to use a separator.
• electrolytes examples include lithium salts such as LiClO 4 , LiPF 6 , LiAsF 6 , LiBF 4 and LiSO 3 CF 3 , ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, cyclopentanone, sulfolane.
• the structure of the secondary battery of the present invention is not particularly limited, but usually, a positive electrode, a negative electrode, and an optional separator are wound into a flat spiral to form a wound electrode plate group. It is common to have a structure in which flat plates are laminated to form a laminated electrode plate group, and these electrode plate groups are enclosed in an outer package.
• the half-cell used in the examples of the present invention has a negative electrode composed mainly of the present active material and a simple evaluation using metallic lithium as the counter electrode. for comparison.
• a secondary battery using this negative electrode active material is used, for example, as a paper-type battery, a button-type battery, a coin-type battery, a laminate-type battery, a cylindrical battery, a square-type battery, or the like.
• the present negative electrode active material can also be applied to general electrochemical devices having a charging/discharging mechanism of intercalating and deintercalating lithium ions, such as hybrid capacitors and solid lithium secondary batteries.
• the present negative electrode active material can be produced, for example, by a method including the following steps (1) to (3).
• Step (1) A step of obtaining a surface layer forming precursor
• Step (2) A step of applying the surface layer forming precursor to the surface of a granular structure mainly composed of graphite having an uneven surface
• Step (3) Inactive A process of obtaining a negative electrode active material by high temperature firing at a firing temperature of 1000 to 1300°C in an atmosphere.
• a surface layer-forming precursor that provides the surface layer in which silicon particles are dispersed in a matrix phase is prepared by the following method.
• Silicon particles can be obtained, for example, by using an organic solvent and pulverizing silicon lumps with a wet powder pulverizer.
• a dispersant may be used to facilitate the crushing of the silicon lumps in the organic solvent.
• Commercially available silicon powder, large-sized silicon particles, and the like are used as the silicon lumps.
• the wet pulverizer is not particularly limited, and includes roller mills, high-speed rotary pulverizers, container-driven mills, bead mills, and the like. In wet pulverization, it is preferable to pulverize until the silicon particles have the particle size of the present silicon particles.
• Organic solvents used in the wet method include those that do not chemically react with silicon. Examples thereof include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and diisobutyl ketone; alcohols such as ethanol, methanol, normal propyl alcohol and isopropyl alcohol; aromatic benzene, toluene and xylene.
• ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and diisobutyl ketone
• alcohols such as ethanol, methanol, normal propyl alcohol and isopropyl alcohol
• aromatic benzene, toluene and xylene include those that do not chemically react with silicon. Examples thereof include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and diisobutyl ketone; alcohols such as ethanol, methanol, normal
• Types of the dispersant include aqueous and non-aqueous dispersants. Use of a non-aqueous dispersant is preferred in order to suppress excessive oxidation of the surface of the silicon particles.
• Types of non-aqueous dispersants include polymer types such as polyethers, polyalkylene polyamines, polycarboxylic acid partial alkyl esters, low molecular types such as polyhydric alcohol esters and alkylpolyamines, and polyphosphates. is exemplified by the inorganic type of
• the concentration of silicon in wet grinding is not particularly limited, but when the solvent and optionally a dispersant are included, the total amount of the dispersant and silicon is 100% by mass, and the amount of silicon is 5% to 40% by mass. is preferable, and 10% by mass to 30% by mass is more preferable.
• silicon particles whose particle diameters are broadly distributed from 5 nm to 300 nm as the present silicon particles
• silicon particles can be produced by the following method.
• a wet bead mill is used to control multiple grinding conditions such as the amount of dispersant added, the bead diameter, the number of revolutions, and the grinding time.
• a polysiloxane compound can be used as a raw material for the matrix phase in which the present silicon particles are dispersed.
• the polysiloxane compound is a resin containing at least one of a polycarbosilane structure, a polysilazane structure, a polysilane structure and a polysiloxane structure.
• a resin containing only these structures may be used, or a composite resin having at least one of these structures as a segment and chemically bonded to another polymer segment may be used.
• Forms of composite include graft copolymerization, block copolymerization, random copolymerization, alternating copolymerization, and the like.
• composite resins that have a graft structure in which polysiloxane segments and side chains of polymer segments are chemically bonded
• composite resins that have a block structure in which polysiloxane segments are chemically bonded to the ends of polymer segments. mentioned.
• the polysiloxane segment preferably has a structural unit represented by the following general formula (S-1) and/or the following general formula (S-2).
• the polysiloxane compound more preferably has a carboxy group, an epoxy group, an amino group, or a polyether group at the side chain or end of the siloxane bond (Si--O--Si) main skeleton.
• R 1 represents an optionally substituted aromatic hydrocarbon group, an alkyl group, an epoxy group, a carboxy group, or the like.
• R 2 and R3 represents an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group, an epoxy group, a carboxy group, etc.
• Alkyl groups include, for example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, isopentyl group, neopentyl group, tert-pentyl group, 1 -methylbutyl group, 2-methylbutyl group, 1,2-dimethylpropyl group, 1-ethylpropyl group, hexyl group, isohesyl group, 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl group, 1,1 -dimethylbutyl group, 1,2-dimethylbutyl group, 2,2-dimethylbutyl group, 1-ethylbutyl group, 1,1,2-trimethylpropyl group, 1,2,2-trimethylpropyl group, 1-ethyl- 2-methylpropyl group, 1-ethyl-1-methylpropyl group
• aryl groups include phenyl, naphthyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-vinylphenyl, and 3-isopropylphenyl groups.
• the aralkyl group includes, for example, a benzyl group, a diphenylmethyl group, a naphthylmethyl group and the like.
• polymer segments other than the polysiloxane segment possessed by the polysiloxane compound include vinyl polymer segments such as acrylic polymers, fluoroolefin polymers, vinyl ester polymers, aromatic vinyl polymers, and polyolefin polymers, Examples include polymer segments such as polyurethane polymer segments, polyester polymer segments, and polyether polymer segments. Among them, a vinyl polymer segment is preferred.
• the polysiloxane compound may be a composite resin in which polysiloxane segments and polymer segments are bonded in a structure represented by the following structural formula (S-3), or may have a three-dimensional network-like polysiloxane structure.
• the carbon atom is the carbon atom that constitutes the polymer segment, and the two silicon atoms are the silicon atoms that constitute the polysiloxane segment
• the polysiloxane segment of the polysiloxane compound may have a functional group capable of reacting by heating, such as a polymerizable double bond, in the polysiloxane segment.
• a functional group capable of reacting by heating such as a polymerizable double bond
• the cross-linking reaction proceeds and the polysiloxane compound becomes solid, thereby facilitating the thermal decomposition treatment.
• polymerizable double bonds examples include vinyl groups and (meth)acryloyl groups. Two or more polymerizable double bonds are preferably present in the polysiloxane segment, more preferably 3 to 200, and even more preferably 3 to 50. In addition, by using a composite resin having two or more polymerizable double bonds as the polysiloxane compound, the cross-linking reaction can be facilitated.
• the polysiloxane segment may have silanol groups and/or hydrolyzable silyl groups.
• Hydrolyzable groups in hydrolyzable silyl groups include, for example, halogen atoms, alkoxy groups, substituted alkoxy groups, acyloxy groups, phenoxy groups, mercapto groups, amino groups, amido groups, aminooxy groups, iminooxy groups, alkenyloxy and the like, and the hydrolyzable silyl group becomes a silanol group by hydrolysis of these groups.
• a hydrolytic condensation reaction proceeds between the hydroxyl group in the silanol group and the hydrolyzable group in the hydrolyzable silyl group, thereby obtaining a solid polysiloxane compound. can.
• a silanol group as used in the present invention is a silicon-containing group having a hydroxyl group directly bonded to a silicon atom.
• the hydrolyzable silyl group referred to in the present invention is a silicon-containing group having a hydrolyzable group directly bonded to a silicon atom, specifically, for example, a group represented by the following general formula (S-4) are mentioned.
• R4 represents a monovalent organic group such as an alkyl group, an aryl group or an aralkyl group
• R5 represents a halogen atom, an alkoxy group, an acyloxy group, an allyloxy group, a mercapto group, an amino group, an amido group, an aminooxy group, iminooxy group or alkenyloxy group
• b is an integer of 0 to 2.
• Alkyl groups include, for example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, isopentyl group, neopentyl group, tert-pentyl group, 1 -methylbutyl group, 2-methylbutyl group, 1,2-dimethylpropyl group, 1-ethylpropyl group, hexyl group, isohesyl group, 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl group, 1,1 -dimethylbutyl group, 1,2-dimethylbutyl group, 2,2-dimethylbutyl group, 1-ethylbutyl group, 1,1,2-trimethylpropyl group, 1,2,2-trimethylpropyl group, 1-ethyl- 2-methylpropyl group, 1-ethyl-1-methylpropyl group
• aryl groups include phenyl, naphthyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-vinylphenyl, and 3-isopropylphenyl groups.
• the aralkyl group includes, for example, a benzyl group, a diphenylmethyl group, a naphthylmethyl group and the like.
• the halogen atom includes, for example, fluorine atom, chlorine atom, bromine atom, iodine atom and the like.
• alkoxy groups include methoxy, ethoxy, propoxy, isopropoxy, butoxy, sec-butoxy, and tert-butoxy groups.
• acyloxy groups include formyloxy, acetoxy, propanoyloxy, butanoyloxy, pivaloyloxy, pentanoyloxy, phenylacetoxy, acetoacetoxy, benzoyloxy, and naphthoyloxy groups. mentioned.
• allyloxy groups include phenyloxy groups and naphthyloxy groups.
• alkenyloxy groups include vinyloxy, allyloxy, 1-propenyloxy, isopropenyloxy, 2-butenyloxy, 3-butenyloxy, 2-petenyloxy, 3-methyl-3-butenyloxy, 2 -hexenyloxy group and the like.
• Examples of the polysiloxane segment having the structural unit represented by the above general formula (S-1) and/or the above general formula (S-2) include those having the following structures.
• the polymer segment may have various functional groups as necessary to the extent that the effects of the present invention are not impaired.
• Such functional groups include, for example, carboxyl group, blocked carboxyl group, carboxylic anhydride group, tertiary amino group, hydroxyl group, blocked hydroxyl group, cyclocarbonate group, epoxy group, carbonyl group, primary amide group, secondary An amide group, a carbamate group, a functional group represented by the following structural formula (S-5), and the like can be used.
• polymer segment may have polymerizable double bonds such as vinyl groups and (meth)acryloyl groups.
• the above polysiloxane compound is preferably produced, for example, by the methods shown in (4) to (6) below.
• a polymer segment containing a silanol group and/or a hydrolyzable silyl group is prepared in advance, and the polymer segment and the silanol group and/or the hydrolyzable silyl group are and a method of mixing with a silane compound having a polymerizable double bond and carrying out a hydrolytic condensation reaction.
• a polymer segment containing a silanol group and/or a hydrolyzable silyl group is prepared in advance.
• Polysiloxane is also prepared in advance by subjecting a silane compound having both a silanol group and/or a hydrolyzable silyl group and a polymerizable double bond to a hydrolytic condensation reaction. Then, a method of mixing the polymer segment and polysiloxane and performing a hydrolytic condensation reaction.
• a polysiloxane compound is obtained by the method described above.
• Examples of the polysiloxane compound include the Ceranate (registered trademark) series (organic/inorganic hybrid type coating resin; manufactured by DIC Corporation) and the Compoceran SQ series (silsesquioxane type hybrid; manufactured by Arakawa Chemical Industries, Ltd.). .
• a carbon source resin is used as another raw material for the matrix phase.
• the carbon source resin it is preferable to use a synthetic resin or a natural chemical raw material that has good miscibility with the polysiloxane compound, is carbonized by firing at high temperature in an inert atmosphere, and has an aromatic functional group.
• Synthetic resins include thermoplastic resins such as polyvinyl alcohol and polyacrylic acid, and thermosetting resins such as phenol resin and furan resin.
• Natural chemical raw materials include heavy oils, especially tar pitches such as coal tar, light tar oil, medium tar oil, heavy tar oil, naphthalene oil, anthracene oil, coal tar pitch, pitch oil, mesophase pitch, and oxygen-crosslinked petroleum pitch. , heavy oil, etc., but the use of phenolic resin is more preferable from the viewpoint of inexpensive availability and removal of impurities.
• the carbon source resin is preferably a resin containing an aromatic hydrocarbon moiety
• the resin containing an aromatic hydrocarbon moiety is preferably a phenolic resin, an epoxy resin, or a thermosetting resin.
• the phenolic resin is preferably of resol type. Examples of phenolic resins include the Sumilite Resin series (resol-type phenolic resin, manufactured by Sumitomo Bakelite Co., Ltd.).
• the obtained slurry of silicon particles is mixed with the polysiloxane compound and the carbon source resin to obtain a suspension in which the silicon particles, the polysiloxane compound and the carbon source resin are uniformly dispersed.
• the resulting suspension is subjected to solvent removal and drying to obtain a precursor for forming a surface layer.
• the mixture containing the polysiloxane compound and the carbon source resin is preferably in a state in which the polysiloxane compound and the carbon source resin are uniformly mixed.
• the mixing is performed using a device having a dispersing/mixing function. For example, a stirrer, an ultrasonic mixer, a premix disperser and the like can be used.
• a dryer, a reduced-pressure dryer, a spray dryer, or the like can be used for solvent removal and drying for the purpose of distilling off the organic solvent.
• the surface layer-forming precursor contains 3% to 50% by mass of the present silicon particles, 15% to 85% by mass of the solid content of the polysiloxane compound, and 3% to 70% by mass of the solid content of the carbon source resin.
• the solid content of the silicon particles is 8% to 40% by mass
• the solid content of the polysiloxane compound is 20 to 70% by mass
• the solid content of the carbon source resin is 3% to 60% by mass. is more preferable.
• step (2) the precursor for forming a surface layer obtained in step (1) is applied to the surface of the present granular structure.
• the coating method for example, the present particulate structure is added to a slurry containing the surface layer-forming precursor, and after mixing, the solvent is removed and the mixture is dried. Mixing, desolvation and drying are the same as in step (1) above.
• a granular structure mainly composed of graphite having surface irregularities is prepared by, for example, uniformly mixing graphite with a pore-forming agent or a small amount of a resin binder, and using, for example, a pressing machine or the like, to form pellets, granules, or flakes. etc. Thereafter, the pore-forming agent or resin binder can be removed to produce a granular structure having surface irregularities.
• the pore-forming agent is used to form holes in the molded body by being removed from the molded body by baking, etching, washing, or the like after the molding.
• the material of the pore-forming agent is appropriately selected depending on the method of removing the pore-forming agent.
• Step (3) the present negative electrode active material is fired at a high temperature of 1000° C. to 1300° C. in an inert atmosphere, to which the precursor for forming the surface layer obtained in the above step (2) is applied. substance is obtained.
• the thermally decomposable organic component is completely decomposed, and the other main components are made into a fired product suitable for the negative electrode active material by precisely controlling the firing conditions.
• the raw material polysiloxane compound and carbon source resin are converted into a silicon-oxygen-carbon skeleton and free carbon by the energy of the high-temperature treatment.
• the present granular structure coated with the precursor for forming the surface layer obtained in the step (2) is fired in an inert atmosphere within the above temperature range, thereby forming a microstructure of the present negative electrode active material.
• the present granular structure coated with the precursor for forming the surface layer obtained in the step (2) is fired in an inert atmosphere within the above temperature range, thereby forming a microstructure of the present negative electrode active material.
• the calcination method is not particularly limited, but a reaction apparatus having a heating function may be used in an inert atmosphere, and continuous and batch processes are possible.
• a fluidized bed reactor, a rotary furnace, a vertical moving bed reactor, a tunnel furnace, a batch furnace, a rotary kiln, or the like can be appropriately selected as the firing apparatus according to the purpose.
• the present negative electrode active material obtained in the step (3) may be pulverized and classified as necessary. Pulverization may be performed with a bead mill, a jet mill, or the like. Classification may be performed using a wind classifier, a wet classifier, or the like. The pulverization step can be omitted if the precursor mixture is controlled to have a shape near the target particle size by spray drying or the like before firing in step (3), and firing is performed in that shape.
• the present negative electrode active material obtained in steps (1) to (3) is subjected to, for example, a thermally decomposable carbon source gas and carrier nitrogen in a chemical vapor deposition apparatus.
• a thermally decomposable carbon source gas and carrier nitrogen in a chemical vapor deposition apparatus.
• the present negative electrode active material when used as a negative electrode active material for a secondary battery, the secondary battery is excellent in initial coulombic efficiency and capacity retention rate.
• the present active material can be used as a negative electrode by the method described above to form a secondary battery having the negative electrode.
• the present negative electrode active material the secondary battery including the present negative electrode active material in the negative electrode, and the method for producing the present negative electrode active material have been described above, the present invention is not limited to the configurations of the above embodiments. In the configuration of the present embodiment and the secondary battery containing the present active material in the negative electrode, any other configuration may be added, or any configuration that exhibits the same function may be substituted. good. Moreover, in the structure of the said embodiment, the manufacturing method of this negative electrode active material may additionally have another arbitrary process, and may replace it with the arbitrary processes which produce a similar effect
• the present invention will be described in detail below with reference to Examples, but the present invention is not limited to these.
• the half-cell used in the examples of the present invention has a negative electrode composed mainly of the silicon-containing active material of the present invention, and a simple evaluation using metallic lithium as the counter electrode. This is to clearly compare the cycle characteristics.
• Synthesis Example 1 Preparation of Silicon Particles Zirconia beads with a particle size of 0.1 mm to 0.2 mm and 100 ml of methyl ethyl ketone solvent (MEK) were put into a container of a small bead mill apparatus of 150 ml at a filling rate of 60%. After that, silicon powder (commercially available) with an average particle size of 5 ⁇ m and a cationic dispersant liquid (BYK-Chemie Japan Co., Ltd.: BYK145) are added, and wet milling is performed under the conditions shown in Table 1 to obtain a solid. Dark brown liquid silicon slurries Si1 to Si6 having a concentration of 30% by mass were obtained. The morphology and size of the pulverized silicon products were confirmed by TEM observation.
• MEK methyl ethyl ketone solvent
• Synthesis Example 2 Treatment for imparting unevenness to the surface of graphite particles was added, and after mixing for 30 minutes with a desktop mixer, it was molded into a cylindrical shape with a pressure of 40 to 80 MPa as shown in Table 2 with a molding machine.
• the molded product was pulverized in a mortar, and the pulverized product was immersed in a 10% by mass sulfuric acid solution for 24 hours at room temperature to dissolve and remove copper. After filtering the mixed liquid, it was dried under reduced pressure at 110° C. for 12 hours to give voids to the surface of the graphite powder.
• the depth of irregularities on the graphite surface was measured by cross-sectional observation with an SEM, and the average particle size, specific surface area, pore volume, and the like of the graphite particles were obtained using a light scattering particle size measuring device and a specific surface area measuring device. Table 2 shows the results.
• Graphite 8 is obtained by pulverizing 15 ⁇ m spherical graphite powder with zirconia balls having a particle size of 5 mm for 10 hours under ball mill conditions to obtain an average graphite particle size of 1.5 ⁇ m, and further using copper particles having an average particle size of 1 ⁇ m. After vacancies were provided, the copper was removed by dissolution.
• Graphite 9 was obtained by molding 15 ⁇ m spherical graphite powder and copper particles with an average particle size of 1 ⁇ m into a cylindrical shape with a molding machine at a pressure of 35 MPa, and then dissolving and removing the copper under the above conditions to provide voids.
• Graphite 10 is obtained by molding spherical graphite powder with an average particle size of 2.5 ⁇ m and copper particles with an average particle size of 1 ⁇ m into a cylindrical shape with a molding machine at a pressure of 70 MPa. made the grant.
• Table 2 shows the conditions for providing voids in graphites 1 to 10.
• Synthesis Example 3 Preparation of Polysiloxane Compound (Synthesis of Condensate of Methyltrimethoxysilane) 1,421 parts by mass of methyltrimethoxysilane (hereinafter abbreviated as "MTMS”) was charged into a reaction vessel equipped with a stirrer, thermometer, dropping funnel, condenser and nitrogen gas inlet, and the temperature was raised to 60°C. I warmed up. Then, a mixture of 0.17 parts by mass of iso-propyl acid phosphate ("Phoslex A-3" manufactured by SC Organic Chemical Co., Ltd.) and 207 parts by mass of deionized water was dropped into the reaction vessel over 5 minutes.
• MTMS methyltrimethoxysilane
• the condensate obtained by the above hydrolytic condensation reaction was distilled at a temperature of 40 to 60 ° C. and a reduced pressure of 40 to 1.3 kPa to remove the methanol and water produced in the reaction process, resulting in a number average molecular weight of 1. 1,000 parts by mass of a liquid having an active ingredient content of 70% by mass and containing a condensate of MTMS from 1,000 to 5,000 was obtained.
• the effective ingredient is a value obtained by dividing the theoretical yield (parts by mass) when all the methoxy groups of the silane monomer such as MTMS are condensed by the actual yield (parts by mass) after the condensation reaction [methoxy of the silane monomer] Theoretical yield (parts by mass) when all groups are subjected to condensation reaction/Actual yield after condensation reaction (parts by mass)].
• MMA methyl methacrylate
• BMA butyl methacrylate
• BA butyric acid
• MPTS methacryloyloxypropyltrimethoxysilane
• BuOH butylperoxy-2-ethylhexanoate
• Example 1 The composition weight ratio after baking the polysiloxane resin (curable resin (1)) having an average molecular weight of 3500 and the phenolic resin having an average molecular weight of 3000 prepared as in Synthesis Example 3 is SiOC/C of 50/50. and the silicon slurry of Si3 obtained in Synthesis Example 1 so that the content of silicon particles in the product after high-temperature firing is 50% by weight, and an appropriate amount of Methyl ethyl ketone solvent was added and mixed well in a stirrer. As a result, a silicon particle-containing resin mixture suspension having a solid concentration of 10% by mass was obtained.
• Graphite 2 treated in Synthesis Example 2 was added to 100 parts by mass of the silicon particle-containing resin mixed suspension so as to be 94% by mass after high-temperature firing, and after thorough mixing, the mixture was placed in an oil bath at 120°C under nitrogen flow. Desolvation was performed under the following conditions. Then, it was dried under reduced pressure at 110° C. for 10 hours using a vacuum dryer, and finally baked at a high temperature of 1100° C. for 4 hours in a nitrogen atmosphere to obtain composite particles of a black solid. After pulverizing with a planetary ball mill, an active material was produced. The average particle diameter was about 16 ⁇ m in D50, and the specific surface area by the BET method was 3.1 m 2 /g.
• the crystallite was obtained by the Scherrer formula. The size was 21 nm.
• 80 parts of the obtained active material powder, 10 parts of acetylene black as a conductive aid, and 10 parts of a mixture of CMC and SBR as a binder were mixed to prepare a slurry and form a film on a copper foil.
• a half cell of a coin-type lithium secondary battery was prepared using a Li metal foil as a counter electrode, and the charge/discharge characteristics were evaluated using a secondary battery charge/discharge test device (manufactured by Hokuto Co., Ltd.). rice field.
• the cutoff voltage range was 0.005 to 1.5V.
• the charge/discharge measurement results were an initial discharge capacity of 403 mAh/g and an initial coulombic efficiency of 90%.
• a single-layer sheet using LiCoO 2 as a positive electrode active material and aluminum foil as a current collector was used to prepare a positive electrode film, and graphite powder was used at a discharge capacity design value of 400 mAh / g. and the active material powder were mixed to prepare a negative electrode film.
• a non-aqueous electrolyte solution prepared by dissolving lithium hexafluorophosphate in a mixture of ethylene carbonate and diethyl carbonate at a volume ratio of 1/1 at a concentration of 1 mol/L was used as the non-aqueous electrolyte, and polyethylene having a thickness of 30 ⁇ m was used as the separator.
• a laminate-type lithium-ion secondary battery was fabricated using a microporous film made by A laminated lithium ion secondary battery is charged at room temperature at a constant current of 1.2 mA (0.25c based on the positive electrode) until the voltage of the test cell reaches 4.2 V, and after reaching 4.2 V, Charging was performed by decreasing the current so as to keep the cell voltage at 4.2 V, and the discharge capacity was determined.
• the capacity retention rate after 300 cycles at 25°C was 91%. Table 3 shows the results.
• Examples 2 to 9 In the same manner as in Example 1, the amount of graphite 2 treated in Synthesis Example 2 was added to 100 parts by mass of the Si3 silicon particle-containing resin mixed suspension obtained in Synthesis Example 1 having a solid concentration of 10 mass%. was adjusted to 90% by mass to 50% by mass after firing as shown in Table 3, and after thorough mixing, desolvation was performed in an oil bath at 120° C. under nitrogen gas flow conditions. Other conditions were the same as in Example 1 to obtain an active material. A secondary battery using a negative electrode active material containing the obtained active material was evaluated. Table 3 shows the results.
• Examples 10 to 17 Using a curable resin (2) having an average molecular weight of 3200, 100 parts by mass of the Si3 silicon particle-containing resin mixed suspension obtained in Synthesis Example 1 having a solid concentration of 10% by mass was treated in Synthesis Example 2.
• Graphite 1 (Example 10), Graphite 3 (Example 11), Graphite 4 (Example 12), Graphite 5 (Example 13), Graphite 6 (Example 14), Graphite 7 (Example 15), Graphite 8 (Example 16) and graphite 3 (Example 17) were added so as to be 85% by mass each after firing. After thorough mixing, the solvent was removed in an oil bath at 120° C. under nitrogen gas flow conditions. Other conditions were the same as in Example 1 to obtain an active material. A secondary battery using a negative electrode active material containing the obtained active material was evaluated. Table 4 shows the results.
• Examples 18-20 Synthesized into a silicon particle-containing resin mixture suspension of Si1 (Example 18), Si2 (Example 19) and Si4 (Example 20) obtained in Synthesis Example 1 with a solid concentration of 10% by mass and 100 parts by mass Graphite 2 treated in Example 2 was added to the high temperature firing at 85% by weight each and mixed well. Thereafter, the solvent was removed in an oil bath at 120° C. under nitrogen gas flow conditions. Other conditions were the same as in Example 1 to obtain an active material.
• Example 21 Using commercially available monodisperse spherical silicon particles (manufactured by Alfa Aesar) having an average D50 particle size of 50 nm, a resin mixture suspension containing 10 parts by mass of solids was prepared under the same conditions as in Example 1. was prepared. Graphite 2 treated in Synthesis Example 2 was added to 100 parts by mass of the resin mixed suspension so that it became 85% by mass after high-temperature firing, and after sufficiently mixing, in an oil bath at 120 ° C. under nitrogen gas flow conditions. Solvent was removed by Other conditions were the same as in Example 1 to obtain an active material. A secondary battery using a negative electrode active material containing the obtained active material was evaluated. Table 4 shows the results.
• Example 22 Using the silicon particles of Si3 obtained in Synthesis Example 1, under the same conditions as in Example 1, a resin mixture suspension containing 10 parts by mass of solids was prepared. Graphite 9 treated in Synthesis Example 2 was added to 100 parts by mass of the above resin mixture suspension so that it became 85% by mass after high-temperature firing, and after thorough mixing, in an oil bath at 120 ° C. under nitrogen gas flow conditions. Solvent was removed by Other conditions were the same as in Example 1 to obtain an active material. A secondary battery using a negative electrode active material containing the obtained active material was evaluated. Table 4 shows the results.
• Example 23 Graphite 10 treated in Synthesis Example 2 was added to 100 parts by mass of the silicon particle-containing resin mixture suspension of Si3 obtained in Synthesis Example 1 with a solid concentration of 10 mass%, and 85 mass% after high temperature firing. After being thoroughly mixed, the solvent was removed in an oil bath at 120° C. under nitrogen gas flow conditions. Other conditions were the same as in Example 1 to obtain an active material. A secondary battery using a negative electrode active material containing the obtained active material was evaluated. Table 4 shows the results.
• Comparative example 1 Using spherical graphite having an average D50 particle size of 15 ⁇ m, the particle size distribution and specific surface area were measured, and then an active material was obtained in the same manner as in Example 1. A secondary battery using a negative electrode active material containing the obtained active material was evaluated. Table 4 shows the results.
• Comparative example 2 Commercially available graphite particles having a D50 average particle size of 15 ⁇ m were added to 100 parts by mass of the Si5 silicon particle-containing resin mixture suspension obtained in Synthesis Example 1 with a solid concentration of 10 mass %, and 85 mass % after high temperature firing. and mixed well. After that, the solvent was removed in an oil bath at 120° C. under nitrogen gas flow conditions. Other conditions were the same as in Example 1 to obtain an active material. A secondary battery using a negative electrode active material containing the obtained active material was evaluated. Table 4 shows the results.
• Comparative example 3 Commercially available graphite particles having a D50 average particle size of 15 ⁇ m were added to 100 parts by mass of the Si6 silicon particle-containing resin mixture suspension obtained in Synthesis Example 1 with a solid concentration of 10 mass %, and 85 mass % after high temperature firing. and mixed well. After that, the solvent was removed in an oil bath at 120° C. under nitrogen gas flow conditions. Other conditions were the same as in Example 1 to obtain an active material. A secondary battery using a negative electrode active material containing the obtained active material was evaluated. Table 4 shows the results.
• each evaluation method is as follows.
• D50 Measured using a laser diffraction particle size distribution analyzer (Mastersizer 3000, manufactured by Malvern Panalytical).
• Specific surface area Measured by BET method from nitrogen adsorption measurement using a specific surface area measuring device (BELSORP-mini manufactured by BEL JAPAN).
• 29 Si-NMR JNM-ECA600 manufactured by JEOL RESONANCE was used.
• Crystallite size Measured with an X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation) and calculated by the Scherrer formula.
• Specific surface area Measured with a specific surface measuring device (BELSORP VAC3, manufactured by Microtrack Bell).
• Battery characteristics evaluation Battery characteristics are measured using a secondary battery charge-discharge test device (manufactured by Hokuto Denko Co., Ltd.), room temperature 25 ° C., cutoff voltage range from 0.005 to 1.5 V, charge / discharge rate is 0
• the charging/discharging characteristics were evaluated under conditions of constant current/constant voltage charging/constant current discharging at 0.2 C (after 4 cycles) and 1 C (1 to 3 times). At the time of switching between charging and discharging, the battery was left in an open circuit for 30 minutes.
• the initial discharge capacity, initial charge/discharge efficiency, and capacity retention rate after 300 cycles were determined as follows.
• the secondary battery using the present negative electrode active material has an initial discharge capacity of 400 or more, an initial efficiency of 80% or more, and a capacity retention rate after 300 cycles of 80% or more, all of which are high. It also has a good balance of these. The reason for this is thought to be that, compared to commercially available graphite, the graphite having the uneven surface has improved adhesion strength to the surface layer, and as a result, secondary battery characteristics such as initial discharge capacity have been improved. .

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