WO2020081409A1 - Matériaux actifs d'anode protégés par des particules de graphène poreux pour batteries au lithium - Google Patents

Matériaux actifs d'anode protégés par des particules de graphène poreux pour batteries au lithium Download PDF

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Publication number
WO2020081409A1
WO2020081409A1 PCT/US2019/056031 US2019056031W WO2020081409A1 WO 2020081409 A1 WO2020081409 A1 WO 2020081409A1 US 2019056031 W US2019056031 W US 2019056031W WO 2020081409 A1 WO2020081409 A1 WO 2020081409A1
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graphene
anode
carbon
lithium
porous
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PCT/US2019/056031
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English (en)
Inventor
Sheng-yi LU
Wen Y. CHIU
Bor Z. Jang
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Global Graphene Group, Inc.
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Publication date
Priority claimed from US16/163,955 external-priority patent/US20200127277A1/en
Priority claimed from US16/163,964 external-priority patent/US11152620B2/en
Application filed by Global Graphene Group, Inc. filed Critical Global Graphene Group, Inc.
Publication of WO2020081409A1 publication Critical patent/WO2020081409A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/184—Preparation
    • C01B32/19—Preparation by exfoliation
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/194—After-treatment
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/198—Graphene oxide
    • 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
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2204/00—Structure or properties of graphene
    • C01B2204/02—Single layer graphene
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2204/00—Structure or properties of graphene
    • C01B2204/20—Graphene characterized by its properties
    • C01B2204/22—Electronic properties
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/14—Pore volume
    • 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
    • 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 disclosure relates generally to the field of rechargeable lithium battery and, more particularly, to the lithium battery anode containing a new group of porous graphene particulate-protected anode active material particles and the process for producing same.
  • a unit cell or building block of a lithium-ion battery is typically composed of an anode active material layer, an anode or negative electrode layer (containing an anode active material responsible for storing lithium therein, a conductive additive, and a resin binder), an electrolyte and porous separator, a cathode or positive electrode layer (containing a cathode active material responsible for storing lithium therein, a conductive additive, and a resin binder), and a separate cathode current collector.
  • the electrolyte is in ionic contact with both the anode active material and the cathode active material.
  • a porous separator is not required if the electrolyte is a solid- state electrolyte.
  • the binder in the binder layer is used to bond the anode active material (e.g. graphite or Si particles) and a conductive filler (e.g. carbon black or carbon nanotube) together to form an anode layer of structural integrity, and to bond the anode layer to a separate anode current collector, which acts to collect electrons from the anode active material when the battery is discharged.
  • anode active material e.g. graphite or Si particles
  • a conductive filler e.g. carbon black or carbon nanotube
  • the most commonly used anode active materials for lithium-ion batteries are natural graphite and synthetic graphite (or artificial graphite) that can be intercalated with lithium and the resulting graphite intercalation compound (GIC) may be expressed as Li x C 6 , where x is typically less than 1.
  • Graphite or carbon anodes can have a long cycle life due to the presence of a protective solid-electrolyte interface layer (SEI), which results from the reaction between lithium and the electrolyte (or between lithium and the anode surface/edge atoms or functional groups) during the first several charge-discharge cycles.
  • SEI solid-electrolyte interface layer
  • the lithium in this reaction comes from some of the lithium ions originally intended for the charge transfer purpose.
  • the SEI As the SEI is formed, the lithium ions become part of the inert SEI layer and become irreversible, i.e. these positive ions can no longer be shuttled back and forth between the anode and the cathode during charges/discharges. Therefore, it is desirable to use a minimum amount of lithium for the formation of an effective SEI layer.
  • the irreversible capacity loss Q n can also be attributed to graphite exfoliation caused by electrolyte/solvent co-intercalation and other side reactions.
  • inorganic materials that have been evaluated for potential anode applications include metal oxides, metal nitrides, metal sulfides, and the like, and a range of metals, metal alloys, and intermetallic compounds that can accommodate lithium atoms/ions or react with lithium.
  • lithium alloys having a composition formula of Li a A are of great interest due to their high theoretical capacity, e.g., Li 4 Si (3,829 mAh/g), Li 4.4 Si (4,200 mAh/g), Li 4.4 Ge (1,623 mAh/g), Li 4.4 Sn (993 mAh/g), Li 3 Cd (715 mAh/g), Li 3 Sb (660 mAh/g), Li 44 Pb (569 mAh/g), LiZn (410 mAh/g), and Li 3 Bi (385 mAh/g).
  • A is a metal or semiconductor element, such as Al and Si, and "a" satisfies 0 ⁇ a ⁇ 5
  • Li 4 Si 3,829 mAh/g
  • Li 4.4 Ge (1,623 mAh/g
  • Li 3 Sb 660 mAh/g
  • Li 44 Pb 569
  • a composite composed of small electrode active particles protected by (dispersed in or encapsulated by) a less active or non-active matrix e.g., carbon-coated Si particles, sol gel graphite-protected Si, metal oxide-coated Si or Sn, and monomer-coated Sn nanoparticles.
  • the protective matrix provides a cushioning effect for particle expansion or shrinkage, and prevents the electrolyte from contacting and reacting with the electrode active material.
  • anode active particles are Si, Sn, and Sn0 2 .
  • an active material particle such as Si particle, expands (e.g.
  • the protective coating is easily broken due to the mechanical weakness and/o brittleness of the protective coating materials.
  • the coating or matrix materials used to protect active particles are carbon, sol gel graphite, metal oxide, monomer, ceramic, and lithium oxide. These protective materials are all very brittle, weak (of low strength), and/or non conducting (e.g., ceramic or oxide coating).
  • the protective material should meet the following requirements: (a) The coating or matrix material should be of high strength and stiffness so that it can help to refrain the electrode active material particles, when lithiated, from expanding to an excessive extent (b) The protective material should also have high fracture toughness or high resistance to crack formation to avoid disintegration during repeated cycling (c) The protective material must be inert (inactive) with respect to the electrolyte, but be a good lithium ion conductor (d) The protective material must not provide any significant amount of defect sites that irreversibly trap lithium ions (e) The protective material must be lithium ion-conducting as well as electron-conducting. The prior art protective materials all fall short of these requirements.
  • the resulting anode typically shows a reversible specific capacity much lower than expected.
  • the first-cycle efficiency is extremely low (mostly lower than 80% and some even lower than 60%).
  • the electrode was not capable of operating for a large number of cycles. Additionally, most of these electrodes are not high-rate capable, exhibiting unacceptably low capacity at a high discharge rate.
  • the prior art has not demonstrated a composite material that has all or most of the properties desired for use as an anode material in a lithium-ion battery.
  • a new anode for the lithium-ion battery that has a high cycle life, high reversible capacity, low irreversible capacity, and compatibility with commonly used electrolytes.
  • Another object of the present disclosure is to provide a porous graphene particulate- protected anode active material. These particulates contain anode active material particles residing in the pores of these particulates. Another object of the present disclosure is to provide a cost-effective process for producing highly conductive, mechanically robust porous graphene particulates in large quantities.
  • the disclosure provides an anode or negative electrode for a lithium battery.
  • the anode comprises multiple porous graphene-containing particulates
  • porous graphene particulates comprises multiple pores (having a total volume Vpp), pore walls (containing graphene or carbon bonded graphene sheets), and primary particles of an anode active material (having a total volume Va, disposed in the pores), wherein
  • the pore walls contain a graphene material selected from a pristine graphene, graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, boron-doped graphene, nitrogen-doped graphene, chemically functionalized graphene, or a combination thereof;
  • the primary particles of anode active material are in an amount from 0.5% to 95% by weight based on the total porous graphene particulate weight;
  • the volume ratio Vpp/Va is from 1.3/1.0 to 5.0/1.0 and the pores in the particulate have a sufficient amount of free space to accommodate the volume expansion of the primary particles of anode active material when the lithium battery is charged without inducing a volume expansion of the anode electrode by more than 20% (preferably from 0% to 10%).
  • the porous graphene particulate excluding particles of anode active material, has a density from 0.1 to 1.5 g/cm and a specific surface area from 50 to 2,000 m /g. There is no restriction on the shape of such a porous graphene particulate.
  • the porous graphene particulate typically has a dimension (e.g. diameter, major axis, etc.) from 100 nm to 50 mih, preferably from 0.5 pm to 20 pm, and most preferably from 1 pm to 10 pm.
  • the largest dimension of the particulate typically is less than 1 mm, more typically less than 100 pm, and most typically 50 pm.
  • the porous graphene particulate can assume practically any shape: spherical, ellipsoidal, potato-shaped, rod-shape, irregular shape, etc.
  • the present disclosure provides a new anode electrode composition wherein primary particles of an anode active material (e.g. Si, Li, or Sn0 2 particles) are naturally lodged in pores of a porous graphene particulate.
  • an anode active material e.g. Si, Li, or Sn0 2 particles
  • These porous graphene particulates are in a powder form containing isolated, individual particulates that are not formed into a sheet of graphene foam; the latter graphene foam (in a large sheet form being typically 10-100 cm wide and 1-100 meters long) is described in one of our earlier applications (Aruna Zhamu and Bor Z. Jang, “Graphene Foam- Protected Anode Active Materials for Lithium Batteries,” U.S. Patent
  • the particulate has an adequate room to accommodate the expanded volume of the anode active material particles when the battery is charged.
  • the cell walls of the presently invented porous graphene particulate are elastic, of good structural integrity, highly electrically conducting and thermally conducting.
  • the volume expansion is accommodated by the surrounding pores without inducing a significant volume change of the graphene particulate and with a minimal volume expansion (0% to 20%, typically ⁇ 10%) of the entire anode layer (hence, not exerting internal pressure to the battery).
  • these particles shrink; yet the local cell walls shrink or snap back in a congruent manner, maintaining a good contact between cell walls and the anode active particles (remaining capable of accepting Li + ions and electrons during the next charge cycle).
  • the porous graphene particulate further comprises a carbon material that chemically bonds sheets of a graphene material together to form an integral 3D network of electron-conducting pathways interposed between pores inside the particulate.
  • the exterior surface of the porous graphene particulate is naturally sealed with a thin layer of graphene, carbon, or a graphene-carbon combination (e.g. graphene sheets bonded by a carbon material) when the particulates are made by using the presently invented process (described in a later portion of this section).
  • the exterior surface may also be sealed with an electrically conducting material, such as an intrinsically conducting polymer, a conducting polymer composite (e.g. having graphene sheets, CNTs, expanded graphite flakes, etc. dispersed in or bonded by a polymer), or a conducting metal oxide (e.g. indium-tin oxide).
  • the pristine graphene material has essentially zero % of non-carbon elements ( ⁇ 0.02%).
  • a non-pristine graphene material has from 0.02% to 20% by weight of non-carbon elements, wherein the non-pristine graphene is selected from graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, boron-doped graphene, nitrogen-doped graphene, chemically functionalized graphene, or a combination thereof.
  • the anode active material is selected from the group consisting of: (a) silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti), nickel (Ni), cobalt (Co), and cadmium (Cd); (b) alloys or intermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Ni, Co, or Cd with other elements; (c) oxides, carbides, nitrides, sulfides, phosphides, selenides, and tellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, V, or Cd, and their mixtures, composites, or lithium-containing composites; (d) salts and hydroxides of Sn; (e) lithium titanate, lithium manganate, lithium aluminate,
  • the prelithiated version of a high-capacity anode active material means an anode active material that is intercalated or inserted with a desired amount of lithium before this anode active material is introduced into the foam pores, or before this anode active material is mixed with the graphene material to form a foamed structure.
  • the anode active material is in a form of nanoparticle, nanowire, nanofiber, nanotube, nanosheet, nanobelt, nanoribbon, or nanocoating having a thickness or diameter less than 100 nm. More preferably, the anode active material has a dimension less than 20 nm.
  • the porous graphene particulate further comprises a carbon or graphitic material therein, wherein the carbon or graphite material is in electronic contact with or deposited onto the anode active material particle surface.
  • this carbon or graphite material embraces the particles of the anode active material and the embraced particles are then lodged in the pores of the porous graphene particulate.
  • the carbon or graphite material may be selected from polymeric carbon, amorphous carbon, chemical vapor deposition carbon (CVD carbon), coal tar pitch, petroleum pitch, mesophase pitch, carbon black, coke, acetylene black, activated carbon, fine expanded graphite particle with a dimension smaller than 100 nm, artificial graphite particle, natural graphite particle, or a combination thereof.
  • CVD carbon chemical vapor deposition carbon
  • coal tar pitch coal tar pitch
  • petroleum pitch mesophase pitch
  • carbon black carbon black
  • coke coke
  • acetylene black acetylene black
  • individual primary particles of the anode active material are coated with a conductive protective coating, selected from a carbon material, electronically conductive polymer, conductive metal oxide, conductive metal coating, or a lithium-conducting material.
  • a conductive protective coating selected from a carbon material, electronically conductive polymer, conductive metal oxide, conductive metal coating, or a lithium-conducting material.
  • the pore walls contain stacked graphene planes having an inter-plane spacing doo2 from 0.3354 nm to 0.36 nm as measured by X-ray diffraction.
  • the pore walls can contain a pristine graphene and the porous graphene particulate has a density from 0.1 to 1.5 g/cm (when measured in the absence of the anode active material particles).
  • the non-pristine graphene material contains a content of non-carbon elements from 0.01% to 2.0% by weight.
  • the pore walls contain graphene fluoride and the porous graphene particulate contains a fluorine content from 0.01% to 2.0% by weight.
  • the pore walls contain graphene oxide and the porous graphene particulate contains an oxygen content from 0.01% to 2.0% by weight.
  • the non-carbon elements include an element selected from oxygen, fluorine, chlorine, bromine, iodine, nitrogen, hydrogen, or boron.
  • the porous graphene foam has a specific surface area from 200 to 2,000 m /g or a density from 0.3 to 1.3 g/cm .
  • the porous graphene particulate has an oxygen content or non-carbon content less than 0.01% by weight and the pore walls contain stacked graphene planes having an inter-graphene spacing less than 0.34 nm.
  • the porous graphene particulate has an oxygen content or non-carbon content no greater than 0.01% by weight and the pore walls contain stacked graphene planes having an inter- graphene spacing less than 0.336 nm, and a mosaic spread value no greater than 0.7.
  • the porous graphene particulate has pore walls containing stacked graphene planes having an inter-graphene spacing less than 0.336 nm, and a mosaic spread value no greater than 0.4.
  • the pore walls may contain stacked graphene planes having an inter-graphene spacing less than 0.337 nm and a mosaic spread value less than 1.0.
  • the porous graphene particulate exhibits a degree of graphitization no less than 80% and/or a mosaic spread value less than 0.4. More preferably, the porous graphene particulate exhibits a degree of graphitization no less than 90% and/or a mosaic spread value no greater than 0.4.
  • the pore walls typically contain a 3D network of interconnected graphene planes.
  • the present disclosure also provides a powder mass of an anode active material comprising multiple porous graphene particulates, wherein at least one of said porous graphene particulates comprises multiple pores, having a total volume Vpp, pore walls, and primary particles of said anode active material, having a total volume Va, disposed in the pores, wherein
  • the pore walls contain a graphene material selected from a pristine graphene, graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, boron-doped graphene, nitrogen-doped graphene, chemically functionalized graphene, or a combination thereof;
  • the primary particles of anode active material are in an amount from 0.5% to 95% by weight based on the total porous graphene particulate weight
  • the graphene particulate is embraced or encapsulated by a thin encapsulating layer of electrically conducting material having a thickness from 1 nm to 10 pm, an electric conductivity from 10 6 S/cm to 20,000 S/cm and a lithium ion conductivity from 10 8 S/cm to 5 x 10 2 S/cm; and
  • the volume ratio Vpp/Va is from 1.3/1.0 to 5.0/1.0.
  • the present disclosure also provides a lithium battery containing the anode or negative electrode as defined above, a cathode or positive electrode, and an electrolyte in ionic contact with the anode and the cathode.
  • This lithium battery can further contain a cathode current collector in electronic contact with the cathode.
  • the lithium battery further contains an anode current collector in electronic contact with the anode.
  • the graphene foam operates as an anode current collector to collect electrons from the anode active material during a charge of the lithium battery, which contains no separate or additional current collector.
  • the lithium battery can be a lithium-ion battery, lithium metal battery, lithium- sulfur battery, or lithium-air battery.
  • the disclosure also provides a process for producing the multiple porous graphene particulates as a powder mass for the anode layer as described above.
  • the process comprises:
  • the dispersion contains a blowing agent having a blowing agent-to-graphene material weight ratio from 0.01/1.0 to 1.0/1.0;
  • the process may further include a step of combining these multiple porous graphene particulates, along with a resin binder and an optional conductive additive, into an anode electrode, preferably on an anode current collector (e.g. Cu foil).
  • the graphene material contains pristine graphene and the dispersion contains a blowing agent having a blowing agent-to-pristine graphene weight ratio from 0.01/1.0 to 1.0/1.0.
  • the blowing agent is a physical blowing agent, a chemical blowing agent, a mixture thereof, a dissolution-and-leaching agent, or a mechanically introduced blowing agent.
  • the step of dispensing, forming and drying includes operating a procedure selected from pan-coating, air-suspension coating, centrifugal extrusion, vibration- nozzle encapsulation, spray-drying, coacervation-phase separation, interfacial polycondensation and interfacial cross-linking, in-situ polymerization, matrix polymerization, or a combination thereof.
  • the dispersion further comprises a polymer dissolved or dispersed in the liquid medium, wherein the polymer-to-graphene weight ratio is from 1/100 to 100/1.
  • the graphene material is selected from the group of non-pristine graphene materials consisting of graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, and combinations thereof, and wherein the heat treatment temperature is less than 2,500°C and the porous graphene particulate contains a content of non-carbon elements from 0.01% to 2.0% by weight.
  • the first heat treatment temperature is selected from l00°C to l,500°C.
  • the process further comprises a step of coating or embracing the porous graphene particulates with a thin encapsulating layer of a polymer or a polymer composite containing a carbonaceous or graphitic material dispersed in or bonded by a polymer to form polymer- or polymer composite-encapsulated porous graphene particulates.
  • the process may further comprise a step of heat-treating the polymer- or polymer composite-encapsulated porous graphene particulates to obtain carbon- or graphite-encapsulated porous graphene particulates.
  • the amount of blowing agent may be reduced if the graphene material has a content of non-carbon elements (e.g. O, H, N, B, F, Cl, Br, I, etc.) no less than 5% by weight (preferably no less than 10%, further preferably no less than 20%, even more preferably no less than 30% or 40%, and most preferably up to 55%).
  • the subsequent high temperature treatment serves to remove a majority of these non-carbon elements from the graphene material, generating volatile gas species that produce pores or cells in the solid graphene material structure.
  • these non-carbon elements play the role of a blowing agent.
  • the use of a blowing agent can provide added flexibility in regulating or adjusting the porosity level and pore sizes for a desired application.
  • the blowing agent is typically required if the non-carbon element content is less than 5%, such as pristine graphene that is essentially all-carbon.
  • this process comprises: (A) preparing a graphene dispersion having multiple primary particles of an anode active material and multiple sheets of a graphene material dispersed in a liquid medium, wherein the graphene material is selected from graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, or a combination thereof and wherein the graphene contains a non-carbon element proportion of from 20% to 55% by weight of the graphene material; (B) dispensing, forming and drying the graphene dispersion into multiple droplets containing therein graphene sheets and particles of the anode active material; and (C) heat treating the droplets at a heat treatment temperature selected from 80°C to 3,200°C (typically
  • the porous graphene particulate minus the anode active material, has a specific surface area from 200 to 2,000 m /g. In one embodiment, the porous graphene particulate has a density from 0.1 to 1.5 g/cm .
  • the graphene dispersion has at least 3% by weight of graphene oxide dispersed in the liquid medium to form a liquid crystal phase.
  • the graphene dispersion contains a graphene oxide dispersion prepared by immersing a graphitic material in a powder or fibrous form in an oxidizing liquid in a reaction vessel at a reaction temperature for a length of time sufficient to obtain the graphene dispersion wherein the graphitic material is selected from natural graphite, artificial graphite, mesophase carbon, mesophase pitch, mesocarbon microbead, soft carbon, hard carbon, coke, carbon fiber, carbon nanofiber, carbon nanotube, or a combination thereof and wherein the graphene oxide has an oxygen content no less than 5% by weight.
  • the heat treatment temperature contains a temperature in the range from 80°C-300°C and, as a result, the porous graphene particulate has an oxygen content or non carbon element content less than 5%, and the pore walls have an inter-graphene spacing less than 0.40 nm.
  • the heat treatment temperature contains a temperature in the range from 300°C-l,500°C and, as a result, the porous graphene particulate has an oxygen content or non-carbon content less than 1%, and the pore walls have an inter-graphene spacing less than 0.35 nm.
  • the porous graphene particulate When the heat treatment temperature contains a temperature in the range from l,500°C- 2,l00°C, the porous graphene particulate has an oxygen content or non-carbon content less than 0.01% and pore walls have an inter- graphene spacing less than 0.34 nm.
  • the porous graphene particulate When the heat treatment temperature contains a temperature greater than 2,l00°C, the porous graphene particulate has an oxygen content or non-carbon content no greater than 0.001% and pore walls have an inter-graphene spacing less than 0.336 nm, and a mosaic spread value no greater than 0.7.
  • the porous graphene particulate has pore walls containing stacked graphene planes having an inter-graphene spacing less than 0.336 nm, and a mosaic spread value no greater than 0.4.
  • the pore walls contain stacked graphene planes having an inter graphene spacing less than 0.337 nm and a mosaic spread value less than 1.0.
  • the solid wall portion of the porous graphene particulate exhibits a degree of graphitization no less than 80% and/or a mosaic spread value less than 0.4.
  • the solid wall portion of the porous graphene particulate exhibits a degree of graphitization no less than 90% and/or a mosaic spread value no greater than 0.4.
  • the pore walls in a porous graphene particulate contain a 3D network of interconnected graphene planes that are electron-conducting pathways.
  • the cell walls contain graphitic domains or graphite crystals having a lateral dimension (L a , length or width) no less than 20 nm, more typically and preferably no less than 40 nm, still more typically and preferably no less than 100 nm, still more typically and preferably no less than 500 nm, often greater than 1 pm, and sometimes greater than 10 pm.
  • the graphitic domains typically have a thickness from 1 nm to 200 nm, more typically from 1 nm to 100 nm, further more typically from 1 nm to 40 nm, and most typically from 1 nm to 30 nm.
  • the pore walls comprise carbon- bonded graphene sheets.
  • FIG. 1 Schematic illustrating the notion that expansion of Si particles, upon lithium
  • intercalation can lead to pulverization of Si particles, interruption of the conductive paths formed by the conductive additive, and loss of contact with the current collector.
  • FIG. 2 Schematic of a porous graphene particulate-protected anode active material according to an embodiment of instant disclosure. Multiple particulates are then bonded together by a resin binder to make an anode electrode.
  • FIG. 3(A) Schematic of a prior art lithium-ion battery cell, wherein the anode layer is a thin coating of an anode active material itself;
  • FIG. 3(B) Schematic of another lithium-ion battery; the anode layer being composed of particles of an anode active material, a conductive additive (not shown) and a resin binder (not shown).
  • FIG. 4 A possible mechanism of chemical linking between graphene oxide sheets, which
  • FIG. 5 The specific capacity of a lithium battery having a porous pristine graphene particulate- protected Si and that of a graphene paper-protected Si as an electrode material (lithium metal as the counter-electrode in a half-cell configuration) plotted as a function of the number of charge-discharge cycles.
  • FIG. 6 Specific capacities of two anode layers: the presently invented GO-derived porous
  • FIG. 7 Specific capacities of two anode layers: the presently invented porous graphene
  • FIG. 8 Specific capacities of two anode layers: the presently invented porous graphene
  • particulate-protected Sn0 2 particles and solid, pore-free graphene particulate-protected Sn0 2 particles.
  • FIG. 9 Specific capacities of two anode layers: the presently invented porous graphene
  • particulate-protected Si nanowires and solid, pore-free graphene particulate -protected Si nanowires.
  • This disclosure is directed at the anode (negative electrode layer) containing a high- capacity anode active material for the lithium secondary battery, which is preferably a secondary battery based on a non-aqueous electrolyte, a polymer gel electrolyte, an ionic liquid electrolyte, a quasi-solid electrolyte, or a solid-state electrolyte.
  • the shape of a lithium secondary battery can be cylindrical, square, button-like, etc.
  • the present disclosure is not limited to any battery shape or configuration. For convenience, we will use Si, Co 3 0 4 , Sn, or Sn0 2 as illustrative examples of a high-capacity anode active material. This should not be construed as limiting the scope of the disclosure.
  • a lithium-ion battery cell is typically composed of an anode current collector (e.g. Cu foil), an anode or negative electrode (anode layer containing an anode active material, conductive additive, and binder), a porous separator and/or an electrolyte component, a cathode electrode (cathode active material, conductive additive, and resin binder), and a cathode current collector (e.g. Al foil).
  • the anode layer is composed of primary particles of an anode active material (e.g.
  • This anode layer is typically 50-300 pm thick (more typically 100-200 pm) to give rise to a sufficient amount of current per unit electrode area.
  • the anode active material is deposited in a thin film form directly onto an anode current collector, such as a sheet of copper foil.
  • an anode current collector such as a sheet of copper foil.
  • an anode current collector such as a sheet of copper foil.
  • Such a thin-film battery has very limited scope of application.
  • a Si layer thicker than 100 nm has been found to exhibit poor cracking resistance during battery charge/discharge cycles. It takes but a few cycles to get such a thick film fragmented.
  • a desirable electrode thickness is at least 100 pm.
  • These thin-film electrodes (with a thickness ⁇ 100 nm) fall short of the required thickness by three (3) orders of magnitude.
  • Si or Si0 2 film-based anode layers cannot be too thick either since these materials are not conductive to transport of both electrons and lithium ions.
  • a large layer thickness implies an excessively high internal resistance.
  • the present disclosure provides an anode or negative electrode for a lithium battery.
  • the anode comprises multiple porous graphene particulates, wherein at least one of the porous graphene particulates comprises multiple pores (having a total volume Vpp), pore walls, and primary particles of an anode active material (having a total volume Va, disposed in the pores), wherein (A) the pore walls contain a graphene material selected from a pristine graphene, graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, boron-doped graphene, nitrogen-doped graphene, chemically functionalized graphene, or a combination thereof; (B) the primary particles of anode active material are in an amount from 0.5% to 95% by weight based on the total porous graphene particulate weight; (C) the graphene particulate is
  • the essential material, graphene, in the invented particulate (secondary particle) is briefly discussed as follows:
  • Bulk natural graphite is a 3-D graphitic material with each graphite particle being composed of multiple grains (a grain being a graphite single crystal or crystallite) with grain boundaries (amorphous or defect zones) demarcating neighboring graphite single crystals.
  • Each grain is composed of multiple graphene planes that are oriented parallel to one another.
  • a graphene plane in a graphite crystallite is composed of carbon atoms occupying a two-dimensional, hexagonal lattice.
  • the graphene planes are stacked and bonded via van der Waal forces in the crystallographic c-direction (perpendicular to the graphene plane or basal plane). Although all the graphene planes in one grain are parallel to one another, typically the graphene planes in one grain and the graphene planes in an adjacent grain are inclined at different orientations. In other words, the orientations of the various grains in a graphite particle typically differ from one grain to another.
  • the constituent graphene planes of a graphite crystallite in a natural or artificial graphite particle can be exfoliated and extracted or isolated to obtain individual graphene sheets of carbon atoms provided the inter-planar van der Waals forces can be overcome.
  • An isolated, individual graphene sheet of carbon atoms is commonly referred to as single-layer graphene.
  • a stack of multiple graphene planes bonded through van der Waals forces in the thickness direction with an inter-graphene plane spacing of approximately 0.3354 nm is commonly referred to as a multi layer graphene.
  • a multi-layer graphene platelet has up to 300 layers of graphene planes ( ⁇ 100 nm in thickness), but more typically up to 30 graphene planes ( ⁇ 10 nm in thickness), even more typically up to 20 graphene planes ( ⁇ 7 nm in thickness), and most typically up to 10 graphene planes (commonly referred to as few-layer graphene in scientific community).
  • Single-layer graphene and multi-layer graphene sheets are collectively called“nano graphene platelets” (NGPs).
  • NGPs are a class of carbon nanomaterial (a 2-D nanocarbon) that is distinct from the 0-D fullerene, the l-D CNT, and the 3- D graphite.
  • the solid graphene foam typically has a density from 0.1 to 1.5 g/cm , (more typically from 0.2 to 1.3 g/cm 3 , and more desirably from 0.3 to 1.2 g/cm 3 ) and a specific surface area from 50 to 2,000 m /g.
  • these porous graphene structures When these porous graphene structures are made into centimeter-sized discs for conductivity measurement purposes (instead of into micron-scaled particulates) under comparable heat treatment conditions, they exhibit a thermal conductivity of at least 100 W/mK per unit of specific gravity, and/or an electrical conductivity no less than 1,000 S/cm per unit of specific gravity. It may be noted that these ranges of physical densities are not arbitrarily selected ranges.
  • these densities are designed so that the internal pore amount (level of porosity) is sufficiently large to accommodate the maximum expansion of an anode active material, which varies from one anode active material to another (e.g. approximately 300% - 380% maximum volume expansion for Si and approximately 200% for Sn0 2 ).
  • the pore amount cannot be too large (or physical density being too low); otherwise, the pore walls of the graphene particulate cannot be sufficiently elastic (or, not capable of undergoing a large deformation that is fully recoverable or reversible).
  • the anode active material may be selected from the group consisting of: (a) silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti), nickel (Ni), cobalt (Co), and cadmium (Cd); (b) alloys or intermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Ni, Co, or Cd with other elements; (c) oxides, carbides, nitrides, sulfides, phosphides, selenides, and tellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, V, or Cd, and their mixtures, composites, or lithium-containing composites; (d) salts and hydroxides of Sn; (e) lithium titanate, lithium manganate, lithium aluminate, lithium-containing
  • Li or Li alloy particularly surface-stabilized Li particles (e.g. wax-coated Li particles), were found to be good anode active material per se or an extra lithium source to compensate for the loss of Li ions that are otherwise supplied only from the cathode active material.
  • the presence of these Li or Li- alloy particles was found to significantly improve the cycling performance of a lithium-ion cell.
  • the anode active material may include particles of natural graphite or artificial graphite, prelithiated or non-lithiated.
  • the particles of the anode active material may be in the form of a nanoparticle, nanowire, nanofiber, nanotube, nanosheet, nanobelt, nanoribbon, or nanocoating.
  • the nanoparticle, nanowire, nanofiber, nanotube, nanosheet, nanobelt, nanoribbon, or nanocoating is prelithiated.
  • the particles are embraced by an electron-conducting and/or lithium-conducting coating, such as an amorphous carbon produced by chemical vapor deposition (CVD) or pyrolization of a resin.
  • the porous graphene particulate further comprises a carbon or graphitic material therein, wherein the carbon or graphite material is in electronic contact with or deposited onto the anode active material particle surface.
  • this carbon or graphite material embraces the particles of the anode active material and the embraced particles are then lodged in the pores of the porous graphene particulate.
  • the carbon or graphite material may be selected from polymeric carbon, amorphous carbon, chemical vapor deposition carbon (CVD carbon), coal tar pitch, petroleum pitch, mesophase pitch, carbon black, coke, acetylene black, activated carbon, fine expanded graphite particle with a dimension smaller than 100 nm, artificial graphite particle, natural graphite particle, or a combination thereof.
  • CVD carbon chemical vapor deposition carbon
  • coal tar pitch coal tar pitch
  • petroleum pitch mesophase pitch
  • carbon black carbon black
  • coke coke
  • acetylene black acetylene black
  • individual primary particles of the anode active material are coated with a conductive protective coating, selected from a carbon material, electronically conductive polymer, conductive metal oxide, conductive metal coating, or a lithium-conducting material.
  • a conductive protective coating selected from a carbon material, electronically conductive polymer, conductive metal oxide, conductive metal coating, or a lithium-conducting material.
  • the process for producing the invented powder mass of porous graphene particulates comprises the following steps:
  • heat treating the droplets at a heat treatment temperature selected from 80°C to 3,200°C (typically ⁇ 2,500°C, more typically ⁇ 2,l00°C, and further more typically ⁇ l,500°C) at a desired heating rate sufficient to induce volatile gas molecules from the non-carbon elements or to activate the blowing agent for producing the multiple porous graphene particulates.
  • a heat treatment temperature selected from 80°C to 3,200°C (typically ⁇ 2,500°C, more typically ⁇ 2,l00°C, and further more typically ⁇ l,500°C) at a desired heating rate sufficient to induce volatile gas molecules from the non-carbon elements or to activate the blowing agent for producing the multiple porous graphene particulates.
  • a polymer may be added into the dispersion in step (A).
  • the multiple droplets in step (B) also contain polymer therein. When heated, the polymer is converted to carbon and pores.
  • the process may further include a step of combining these multiple porous graphene particulates, along with a resin binder and an optional conductive additive, into an anode electrode, preferably on an anode current collector (e.g. Cu foil).
  • anode current collector e.g. Cu foil
  • the pores in the porous graphene particulate are formed slightly before, during, or after sheets of a graphene material are (1) chemically linked/merged together (edge-to-edge and/or face-to-face) typically at a temperature from 100 to l,500°C and/or (2) re-organized into larger graphite crystals or domains (herein referred to as re-graphitization) along the pore walls at a high temperature (typically > 2,l00°C and more typically > 2,500°C).
  • the particles of the anode active material may be in the form of small particulate, wire, rod, sheet, platelet, ribbon, tube, etc. with a size of ⁇ 20 pm (preferably ⁇ 10 pm, more preferably ⁇ 5 pm, further preferably ⁇ 1 pm, still more preferably ⁇ 300 nm, and most preferably ⁇ 100 nm).
  • a blowing agent or foaming agent is a substance which is capable of producing a cellular or foamed structure via a foaming or pore-forming process in a variety of materials that undergo hardening or phase transition, such as polymers (plastics and rubbers), glass, and metals. They are typically applied when the material being foamed is in a liquid state. It has not been previously known that a blowing agent can be used to create a foamed material while in a solid state. More significantly, it has not been taught or hinted that an aggregate of sheets of a graphene material in a secondary particle (particulate) form can be converted into a porous graphene particulate via a blowing agent.
  • the cellular structure in a matrix is typically created for the purpose of reducing density, increasing thermal resistance and acoustic insulation, while increasing the thickness and relative stiffness of the original polymer.
  • Blowing agents or related pore-forming mechanisms to create pores or cells (bubbles) in a structure for producing a porous or cellular material can be classified into the following groups:
  • Physical blowing agents e.g. hydrocarbons (e.g. pentane, isopentane, cyclopentane), chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and liquid C0 2 .
  • the bubble/foam-producing process is endothermic, i.e. it needs heat (e.g. from a melt process or the chemical exotherm due to cross-linking), to volatize a liquid blowing agent.
  • thermoplastic foams materials (for thermoplastic and elastomeric foams), sodium bicarbonate (e.g. baking soda, used in thermoplastic foams).
  • gaseous products and other by-products are formed by a chemical reaction, promoted by process or a reacting polymer's exothermic heat. Since the blowing reaction involves forming low molecular weight compounds that act as the blowing gas, additional exothermic heat is also released.
  • Powdered titanium hydride is used as a foaming agent in the production of metal foams, as it decomposes to form titanium and hydrogen gas at elevated temperatures.
  • Zirconium (II) hydride is used for the same purpose. Once formed the low molecular weight compounds will never revert to the original blowing agent(s), i.e. the reaction is irreversible.
  • Mechanically injected agents involve methods of introducing bubbles into liquid polymerizable matrices (e.g. an unvulcanized elastomer in the form of a liquid latex). Methods include whisking-in air or other gases or low boiling volatile liquids in low viscosity lattices, or the injection of a gas into an extruder barrel or a die, or into injection molding barrels or nozzles and allowing the shear/mix action of the screw to disperse the gas uniformly to form very fine bubbles or a solution of gas in the melt. When the melt is molded or extruded and the part is at atmospheric pressure, the gas comes out of solution expanding the polymer melt immediately before solidification.
  • liquid polymerizable matrices e.g. an unvulcanized elastomer in the form of a liquid latex.
  • the graphene material in the dispersion is selected from pristine graphene, graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, or a combination thereof.
  • the starting graphitic material for producing any one of the above graphene materials may be selected from natural graphite, artificial graphite, mesophase carbon, mesophase pitch, mesocarbon microbead, soft carbon, hard carbon, coke, carbon fiber, carbon nanofiber, carbon nanotube, or a combination thereof.
  • the graphene oxide (GO) may be obtained by immersing powders or filaments of a starting graphitic material (e.g. natural graphite powder) in an oxidizing liquid medium (e.g. a mixture of sulfuric acid, nitric acid, and potassium permanganate) in a reaction vessel at a desired temperature for a period of time (typically from 0.5 to 96 hours, depending upon the nature of the starting material and the type of oxidizing agent used).
  • the resulting graphite oxide particles may then be subjected to thermal exfoliation or ultrasonic wave-induced exfoliation to produce GO sheets.
  • Pristine graphene may be produced by direct ultrasonication (also known as liquid phase production) or supercritical fluid exfoliation of graphite particles. These processes are well- known in the art. Multiple pristine graphene sheets and primary particles of an anode active material may be dispersed in water or other liquid medium with the assistance of a surfactant to form a suspension. A chemical blowing agent may then be dispersed into the dispersion. This suspension is then spray-dried to form particulates. When heated to a desired temperature, the chemical blowing agent is activated or decomposed to generate volatile gases (e.g. N 2 or C0 2 ), which act to form bubbles or pores in an otherwise mass of solid graphene sheets, forming a pristine graphene-based porous particulates having primary particles of anode active material residing therein.
  • volatile gases e.g. N 2 or C0 2
  • Fluorinated graphene or graphene fluoride is herein used as an example of the halogenated graphene material group.
  • fluorination of presynthesized graphene This approach entails treating graphene prepared by mechanical exfoliation or by CVD growth with fluorinating agent such as XeF 2 , or F-based plasmas;
  • exfoliation of multilayered graphite fluorides Both mechanical exfoliation and liquid phase exfoliation of graphite fluoride can be readily accomplished [F.
  • the process of liquid phase exfoliation includes ultra sonic treatment of a graphite fluoride in a liquid medium.
  • the nitrogenation of graphene can be conducted by exposing a graphene material, such as graphene oxide, to ammonia at high temperatures (200°C -400°C). Nitrogenated graphene could also be formed at lower temperatures by a hydrothermal method; e.g. by sealing GO and ammonia in an autoclave and then increased the temperature to l50°C -250°C. Other methods to synthesize nitrogen doped graphene include nitrogen plasma treatment on graphene, arc- discharge between graphite electrodes in the presence of ammonia, ammonolysis of graphene oxide under CVD conditions, and hydrothermal treatment of graphene oxide and urea at different temperatures.
  • a graphene material such as graphene oxide
  • Nitrogenated graphene could also be formed at lower temperatures by a hydrothermal method; e.g. by sealing GO and ammonia in an autoclave and then increased the temperature to l50°C -250°C.
  • Step (B) of forming droplets may be conducted by using a micro-encapsulation process.
  • micro-encapsulation methods There are three broad categories of micro-encapsulation methods that can be implemented to produce encapsulated particulates: physical methods, physico-chemical methods, and chemical methods.
  • the physical methods include pan-coating, air-suspension coating, centrifugal extrusion, vibration nozzle, and spray-drying methods.
  • the physico-chemical methods include ionotropic gelation and coacervation-phase separation methods.
  • chemical methods include interfacial
  • Pan-coating method The pan coating process involves tumbling the active material particles, graphene sheets, and a blowing agent in a pan or a similar device while the
  • encapsulating material e.g. monomer/oligomer, polymer melt, polymer/solvent solution
  • encapsulating material e.g. monomer/oligomer, polymer melt, polymer/solvent solution
  • Air-suspension coating method In the air suspension coating process, the solid particles (core materials, including anode active material particles, graphene sheets, a blowing agent) are dispersed into the supporting air stream in an encapsulating chamber. A controlled stream of a polymer- solvent solution (polymer or its monomer or oligomer dissolved in a solvent; or its monomer or oligomer alone in a liquid state) is concurrently introduced into this chamber, allowing the solution to hit and coat the suspended particles. These suspended particles are encapsulated (fully coated) with polymers while the volatile solvent is removed, leaving a very thin layer of polymer (e.g. elastomer or its precursor, which is cured/hardened subsequently) on surfaces of these particles.
  • a polymer- solvent solution polymer or its monomer or oligomer dissolved in a solvent; or its monomer or oligomer alone in a liquid state
  • This process may be repeated several times until the required parameters, such as full-coating thickness (i.e. encapsulating shell or wall thickness), are achieved.
  • the air stream which supports the particles also helps to dry them, and the rate of drying is directly proportional to the temperature of the air stream, which can be adjusted for optimized shell thickness.
  • the particles in the encapsulating zone portion may be subjected to re-circulation for repeated coating.
  • the encapsulating chamber is arranged such that the particles pass upwards through the encapsulating zone, then are dispersed into slower moving air and sink back to the base of the encapsulating chamber, enabling repeated passes of the particles through the encapsulating zone until the desired encapsulating shell thickness is achieved.
  • Anode active materials may be encapsulated using a rotating extrusion head containing concentric nozzles.
  • a stream of core fluid slurry containing particles of an anode active material and other ingredients dispersed in a solvent
  • the suspension/slurry also contains a blowing agent and graphene sheets.
  • the device rotates and the stream moves through the air it breaks, due to Rayleigh instability, into droplets of core, each coated with the shell solution. While the droplets are in flight, the molten shell may be hardened or the solvent may be evaporated from the shell solution. If needed, the capsules can be hardened after formation by catching them in a hardening bath.
  • Vibrational nozzle encapsulation method Core-shell encapsulation or matrix- encapsulation of an anode active material (along with a blowing agent, for instance) can be conducted using a laminar flow through a nozzle and vibration of the nozzle or the liquid. The vibration has to be done in resonance with the Rayleigh instability, leading to very uniform droplets.
  • the liquid can consist of any liquids with limited viscosities (1-50,000 mPa-s):
  • the solidification can be done according to the used gelation system with an internal gelation (e.g. sol-gel processing, melt) or an external (additional binder system, e.g. in a slurry).
  • an internal gelation e.g. sol-gel processing, melt
  • an external binder system e.g. in a slurry
  • Spray drying may be used to encapsulate particles of an active material when the active material is dissolved or suspended in a melt or polymer solution to form a suspension.
  • the suspension may also contain a sacrificial material and an optional conducting material.
  • the liquid feed solution or suspension
  • the liquid feed is atomized to form droplets which, upon contacts with hot gas, allow solvent to get vaporized and thin polymer shell to fully embrace the solid particles of the active material.
  • Coacervation-phase separation This process consists of three steps carried out under continuous agitation:
  • the core material is dispersed in a solution of the encapsulating polymer (elastomer or its monomer or oligomer).
  • the encapsulating material phase which is an immiscible polymer in liquid state, is formed by (i) changing temperature in polymer solution, (ii) addition of salt, (iii) addition of non-solvent, or (iv) addition of an incompatible polymer in the polymer solution.
  • shell material being immiscible in vehicle phase and made rigid via thermal, cross-linking, or dissolution techniques.
  • Interfacial polycondensation entails introducing the two reactants to meet at the interface where they react with each other. This is based on the concept of the Schotten-Baumann reaction between an acid chloride and a compound containing an active hydrogen atom (such as an amine or alcohol), polyester, polyurea, polyurethane, or urea-urethane condensation. Under proper conditions, thin flexible encapsulating shell (wall) forms rapidly at the interface. A solution of the anode active material and a diacid chloride are emulsified in water and an aqueous solution containing an amine and a polyfunctional isocyanate is added.
  • an active hydrogen atom such as an amine or alcohol
  • a base may be added to neutralize the acid formed during the reaction.
  • Condensed polymer shells form instantaneously at the interface of the emulsion droplets.
  • Interfacial cross-linking is derived from interfacial polycondensation, wherein cross- linking occurs between growing polymer chains and a multi-functional chemical groups to form an elastomer shell material.
  • In-situ polymerization In some micro-encapsulation processes, active materials particles are fully coated with a monomer or oligomer first. Then, direct polymerization of the monomer or oligomer is carried out on the surfaces of these material particles.
  • Matrix polymerization This method involves dispersing and embedding a core material in a polymeric matrix during formation of the particles. This can be accomplished via spray drying, in which the particles are formed by evaporation of the solvent from the matrix material. Another possible route is the notion that the solidification of the matrix is caused by a chemical change.
  • the powder mass of droplets (e.g. containing GF or GO sheets, primary particles of an anode active material, and a blowing agent) is then subjected to a heat treatment to activate the blowing agent and/or the thermally-induced reactions that remove the non-carbon elements (e.g. F, O, etc.) from the graphene sheets to generate volatile gases as by products.
  • the non-carbon elements e.g. F, O, etc.
  • the non-carbon elements in the graphene material preferably occupy at least 10% by weight of the graphene material (preferably at least 20%, and further preferably at least 30%).
  • the first (initial) heat treatment temperature is typically greater than 80°C, preferably greater than l00°C, more preferably greater than 300°C, further more preferably greater than 500°C and can be as high as l,500°C.
  • the blowing agent is typically activated at a temperature from 80°C to 300°C, but can be higher.
  • the foaming procedure formation of pores, cells, or bubbles
  • the chemical linking or merging between graphene planes (GO or GF planes) in an edge-to-edge and face-to-face manner can occur at a relatively low heat treatment temperature (e.g. even as low as from l50°C to 300°C).
  • a properly programmed heat treatment procedure can involve just a single heat treatment temperature or a range of heat treatment temperatures (e.g. first temperature for a period of time and then raised to a second temperature and maintained at this second temperature for another period of time), or any other combination of heat treatment temperatures (HTT) that involve an initial treatment temperature (first temperature) and a final HTT (second), higher than the first.
  • HTT heat treatment temperatures
  • first temperature initial treatment temperature
  • second final HTT
  • the highest or final HTT that the dried graphene layer experiences may be divided into four distinct HTT regimes:
  • the presently invented porous graphene particulates containing an anode active material therein can be obtained by heat-treating the dried GO or GF layer with a temperature program that covers at least the first regime (typically requiring 1-4 hours in this temperature range if the temperature never exceeds 500°C), and more commonly covers the first two regimes (1-2 hours preferred); but less commonly the first three regimes (preferably 0.5-2.0 hours in Regime 3), and seldom cover all the 4 regimes (including Regime 4 for 0.2 to 1 hour, may be implemented to achieve the highest conductivity).
  • a temperature program that covers at least the first regime (typically requiring 1-4 hours in this temperature range if the temperature never exceeds 500°C), and more commonly covers the first two regimes (1-2 hours preferred); but less commonly the first three regimes (preferably 0.5-2.0 hours in Regime 3), and seldom cover all the 4 regimes (including Regime 4 for 0.2 to 1 hour, may be implemented to achieve the highest conductivity).
  • the graphene material is selected from the group of non-pristine graphene materials consisting of graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, or a combination thereof, and wherein the maximum heat treatment temperature (e.g. both the first and second heat treatment temperatures) is (are) less than 2,500°C, then the resulting porous graphene particulates typically contain a content of non carbon elements in the range from 0.01% to 2.0% by weight (non-pristine graphene foam).
  • the maximum heat treatment temperature e.g. both the first and second heat treatment temperatures
  • the pore walls of the porous graphene particulate having a i/002 higher than 0.3440 nm reflects the presence of oxygen- or fluorine-containing functional groups (such as -F, -OH, >0, and -COOH on graphene molecular plane surfaces or edges) that act as a spacer to increase the inter-graphene spacing.
  • oxygen- or fluorine-containing functional groups such as -F, -OH, >0, and -COOH on graphene molecular plane surfaces or edges
  • Another structural index that can be used to characterize the degree of ordering of the stacked and bonded graphene planes in the pore walls of graphene and conventional graphite crystals is the“mosaic spread,” which is expressed by the full width at half maximum of a rocking curve (X-ray diffraction intensity) of the (002) or (004) reflection.
  • This degree of ordering characterizes the graphite or graphene crystal size (or grain size), amounts of grain boundaries and other defects, and the degree of preferred grain orientation.
  • a nearly perfect single crystal of graphite is characterized by having a mosaic spread value of 0.2-0.4. Most of our graphene walls have a mosaic spread value in this range of 0.2-0.4 (if produced with a heat treatment temperature (HTT) no less than 2,500°C). However, some values are in the range from 0.4-0.7 if the HTT is between l,500°C and 2,500°C, and in the range from 0.7- 1.0 if the HTT is between 300°C and l,500°
  • FIG. 4 Illustrated in FIG. 4 is a plausible chemical linking mechanism where only 2 aligned GO molecules are shown as an example, although a large number of GO molecules can be chemically linked together to form a pore wall. Further, chemical linking could also occur face- to-face, not just edge-to-edge for GO, GF, and chemically functionalized graphene sheets. These linking and merging reactions proceed in such a manner that the molecules are chemically merged, linked, and integrated into one single entity.
  • the graphene sheets (GO or GF sheets) completely lose their own original identity and they no longer are discrete sheets/platelets/flakes.
  • the resulting product is not a simple aggregate of individual graphene sheets, but a single entity that is essentially a network of interconnected giant molecules with an essentially infinite molecular weight. This may also be described as a graphene poly-crystal (with several grains, but typically no discernible, well-defined grain boundaries). All the constituent graphene planes are very large in lateral dimensions (length and width) and, if the HTT is sufficiently high (e.g. > l,500°C or much higher), these graphene planes are essentially bonded together with one another.
  • the porous graphene particulates of the presently invented anode layer have the following unique and novel features that have never been previously taught or hinted:
  • the graphene pore wall is not made by gluing or bonding discrete flakes/platelets together with a resin binder, linker, or adhesive. Instead, GO sheets (molecules) from the GO dispersion or the GF sheets from the GF dispersion are merged through joining or forming of covalent bonds with one another, into an integrated graphene entity, without using any externally added linker or binder molecules or polymers.
  • non-active materials such as a resin binder or a conductive additive, which are incapable of storing lithium. This implies a reduced amount of non-active materials or increased amount of active materials in the anode, effectively increasing the specific capacity per total anode weight, mAh/g (of composite).
  • the graphene pore walls can comprise graphene sheets bonded by a carbon material
  • Graphene sheets and the bonding carbon together form a 3D network of electron-conducting pathways inside a particulate.
  • the GO- or GF-derived graphene particulates have a unique combination of outstanding thermal conductivity, electrical conductivity, mechanical strength, and stiffness (elastic modulus).
  • porous graphene particulates produced by using the presently invented process may contain some small voids or gaps on the exterior surface of the particulate. These gaps or voids may be sealed off by coating or encapsulating the heat-treated porous graphene particulates with a thin layer of conducting polymer, conducting material-reinforced polymer, carbon, or graphene-reinforced carbon (or expanded graphite flake- or CNT -reinforced carbon).
  • the process may further comprise a step of coating the porous graphene particulates with a thin encapsulating layer of a polymer (e.g.
  • This process may further comprise a step of heat-treating the polymer- or polymer composite-encapsulated porous graphene particulates to obtain carbon- or carbon matrix composite-encapsulated porous graphene particulates.
  • the disclosure also provides a process for producing multiple porous graphene particulates for a lithium battery anode without using a blowing agent.
  • the process comprises: (A) preparing a graphene dispersion having multiple primary particles of an anode active material and multiple sheets of a graphene material dispersed in a liquid medium, wherein the graphene material is selected from graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, or a combination thereof and wherein the graphene material contains a non-carbon element proportion of from 20% to 55% by weight of the graphene material; (B) dispensing, forming and drying the graphene dispersion into multiple droplets containing therein graphene sheets and particles of the anode active material; and (C) heat treating the droplets at a heat treatment temperature selected from 80°C to 3,200°C
  • the dispersion may further comprise a polymer dissolved or dispersed in said liquid medium and the polymer-to-graphene weight ratio is from 1/100 to 100/1.
  • the process further comprises a step of coating the multiple porous graphene particulates (after step C), with a thin encapsulating layer of a polymer or a polymer composite containing a carbonaceous or graphitic material dispersed in or bonded by a polymer to form polymer- or polymer composite-encapsulated porous graphene particulates.
  • the process may further comprise a step of heat-treating said polymer- or polymer composite- encapsulated porous graphene particulates to obtain carbon- or carbon composite-encapsulated porous graphene particulates.
  • the step of dispensing, forming and drying includes operating a procedure selected from pan-coating, air-suspension coating, centrifugal extrusion, vibration-nozzle encapsulation, spray drying, coacervation-phase separation, interfacial polycondensation and interfacial cross-linking, in-situ polymerization, matrix polymerization, or a combination thereof.
  • any anode active material that can be made into fine particles ( ⁇ 20 pm in size, preferably ⁇ 1 pm, and further preferably ⁇ 100 nm) can be similarly incorporated into a graphene suspension (containing graphene sheets, a blowing agent, and an optional polymer) and made into porous graphene particulate-protected anode particles in a similar manner.
  • any chemical blowing agent e.g. in a powder or pellet form
  • the chemical blowing agent may be dispersed in the liquid medium to become a second dispersed phase (sheets of graphene material being the first dispersed phase) in the suspension, which can be deposited onto the solid supporting substrate to form a wet layer. This wet layer of graphene material may then be dried and heat treated to activate the chemical blowing agent.
  • CFAs Chemical foaming agents
  • CFAs can be organic or inorganic compounds that release gasses upon thermal decomposition.
  • CFAs are typically used to obtain medium- to high-density foams, and are often used in conjunction with physical blowing agents to obtain low-density foams.
  • CFAs can be categorized as either endothermic or exothermic, which refers to the type of decomposition they undergo. Endothermic types absorb energy and typically release carbon dioxide and moisture upon decomposition, while the exothermic types release energy and usually generate nitrogen when decomposed.
  • Endothermic CFAs are generally known to decompose in the range from l30°C to 230°C (266°F -446°F), while some of the more common exothermic foaming agents decompose around 200°C (392°F).
  • CFAs can be reduced by addition of certain compounds.
  • activation (decomposition) temperatures of CFAs fall into the range of our heat treatment temperatures.
  • suitable chemical blowing agents include sodium bi-carbonate (baking soda), hydrazine, hydrazide, azodicarbonamide (exothermic chemical blowing agents), nitroso compounds (e.g. N, N-dinitroso pentamethylene tetramine), hydrazine derivatives (e.g. 4, 4’-oxybis (benzenesulfonyl hydrazide) and hydrazo dicarbonamide), and hydrogen carbonate (e.g. Sodium hydrogen carbonate).
  • baking soda hydrazine
  • hydrazide azodicarbonamide
  • nitroso compounds e.g. N, N-dinitroso pentamethylene tetramine
  • hydrazine derivatives e.g. 4, 4’-oxybis (benzenesulfonyl hydrazide) and
  • blowing agents include carbon dioxide (C0 2 ), nitrogen (N 2 ), isobutane (C4H10), cyclopentane (C5H10), isopentane (C S H I2 ), CFC-l l (CFCI3), HCFC-22 (CHF 2 CI), HCFC-l42b (CF 2 CICH 3 ), and HCFC-l34a (CH 2 FCF 3 ).
  • C0 2 carbon dioxide
  • N 2 isobutane
  • C4H10 cyclopentane
  • C5H10 isopentane
  • C S H I2 CFC-l l
  • CFC-22 CHF 2 CI
  • HCFC-l42b HCFC-l42b
  • HCFC-l34a CH 2 FCF 3
  • chlorofluorocarbons are also not environmentally safe and therefore already forbidden in many countries.
  • the alternatives are hydrocarbons, such as isobutane and pentane, and the gases such as C0 2 and nitrogen.
  • blowing agent amount introduced into the suspension is defined as a blowing agent-to-graphene material weight ratio, which is typically from 0/1.0 to 1.0/1.0.
  • Chopped graphite fibers with an average diameter of 12 pm and natural graphite particles were separately used as a starting material, which was immersed in a mixture of concentrated sulfuric acid, nitric acid, and potassium permanganate (as the chemical intercalate and oxidizer) to prepare graphite intercalation compounds (GICs).
  • the starting material was first dried in a vacuum oven for 24 h at 80°C. Then, a mixture of concentrated sulfuric acid, fuming nitric acid, and potassium permanganate (at a weight ratio of 4: 1:0.05) was slowly added, under appropriate cooling and stirring, to a three-neck flask containing fiber segments.
  • the acid-treated graphite fibers or natural graphite particles were filtered and washed thoroughly with deionized water until the pH level of the solution reached 6. After being dried at l00°C overnight, the resulting graphite intercalation compound (GIC) or graphite oxide fiber was re-dispersed in water and/or alcohol to form a slurry.
  • GIC graphite intercalation compound
  • the resulting suspension was then spray-dried to form droplets, which were then subjected to heat treatments that typically involve an initial thermal reduction temperature of 80°C -350°C for 1-2 hours, followed by heat-treating at a second temperature of 500°C -l,50°C for 0.5 to 5 hours.
  • MCMBs Mesocarbon microbeads
  • MCMB 10 grams were intercalated with an acid solution (sulfuric acid, nitric acid, and potassium permanganate at a ratio of 4:1:0.05) for 48-96 hours. Upon completion of the reaction, the mixture was poured into deionized water and filtered. The intercalated MCMBs were repeatedly washed in a 5% solution of HC1 to remove most of the sulfate ions. The sample was then washed repeatedly with deionized water until the pH of the filtrate was no less than 4.5.
  • the slurry was then subjected ultrasonication for 10-100 minutes to produce GO suspensions.
  • TEM and atomic force microscopic studies indicate that most of the GO sheets were single-layer graphene when the oxidation treatment exceeded 72 hours, and 2- or 3-layer graphene when the oxidation time was from 48 to 72 hours.
  • the GO sheets contain oxygen proportion of approximately 35%-47% by weight for oxidation treatment times of 48-96 hours.
  • GO sheets and primary particles of an anode active material Si nanowires, Ge, Sn0 2 , etc. were suspended in water to form suspension (slurry) samples.
  • Sodium hydrogen carbonate (5%-20% by weight), as a chemical blowing agent, was added to the suspension just prior to droplet formation.
  • the graphene droplets were then subjected to heat treatments that involve a thermal reduction temperature of 80°C-l,500°C for 1-5 hours. This heat treatment led to the production of porous graphene particulates.
  • Comparative EXAMPLE 4-1 Pristine Graphene Particulate-Protected Anode vs. Prior Art Pristine Graphene Paper/Film-Protected Anode
  • a graphene film (paper) containing 61% by weight of Si particles (without any blowing agent) was cast and heat treated up to l,500°C to obtain a layer of graphene paper protected anode active material.
  • Graphite oxide was prepared by oxidation of graphite flakes with an oxidizer liquid consisting of sulfuric acid, sodium nitrate, and potassium permanganate at a ratio of 4:1:0.05 at 30°C.
  • an oxidizer liquid consisting of sulfuric acid, sodium nitrate, and potassium permanganate at a ratio of 4:1:0.05 at 30°C.
  • the reacting mass was rinsed with water 3 times to adjust the pH value to at least 3.0.
  • a final amount of water was then added to prepare a series of GO-water suspensions. We observed that GO sheets form a liquid crystal phase when GO sheets occupy a weight fraction > 3% and typically from 5% to 15%.
  • a chemical blowing agent and anode active material particles were then added into this GO liquid crystal dispersion.
  • the resulting slurry was then formed into droplets using a vibration nozzle procedure.
  • Several GO particulate samples were then subjected to different heat treatments, which typically include a thermal reduction treatment at a first temperature of l00°C to 500°C for 1-3 hours, and at a second temperature of 500°C-2,l50°C for 0.5-5 hours. With these heat treatments, the droplets were turned into porous graphene particulates having anode active material residing in the pores of the particulates.
  • HEG highly exfoliated graphite
  • FHEG fluorinated highly exfoliated graphite
  • FHEG FHEG
  • an organic solvent methanol, ethanol, 1 -propanol, 2-propanol, 1 -butanol, ieri-butanol, isoamyl alcohol
  • an ultrasound treatment 280 W
  • Five minutes of sonication was enough to obtain a relatively homogenous dispersion, but longer sonication times ensured better stability.
  • Particles of an anode active material and a blowing agent were then added to the dispersion to form a slurry, which was then spray-dried to form droplets.
  • Graphene oxide (GO), synthesized in Example 2 was finely ground with different proportions of urea and the pelletized mixture heated in a microwave reactor (900 W) for 30 s. The product was washed several times with deionized water and vacuum dried. In this method graphene oxide gets simultaneously reduced and doped with nitrogen.
  • the products obtained with graphene : urea mass ratios of 1 : 0.5, 1 : 1 and 1 : 2 are designated as NGO-l, NGO-2 and NGO-3 respectively and the nitrogen contents of these samples were 14.7, 18.2 and 17.5 wt% respectively as found by elemental analysis. These nitrogenated graphene sheets remain dispersible in water.
  • the resulting suspensions containing added anode active material particles and a blowing agent, were then spray-dried to form droplets, which were heat-treated initially at 200°C-350°C as a first heat treatment temperature and subsequently treated at a second temperature of l,500°C.
  • the resulting nitrogenated graphene foams exhibit physical densities from 0.45 to 1.28 g/cm .
  • EXAMPLE 8 Porous Graphene Particulate-Protected Cobalt Oxide (C0 3 O 4 ) Anode
  • Co(OH) 2 precursor suspension was calcined at 450°C in air for 2 h to form particles of the layered Co 3 0 4 .
  • Some of the Co 3 0 4 particles were combined with GO sheets to form porous graphene particulates each comprising a carbon shell-encapsulated core of Co 3 0 4 particles and blowing agent-induced pores.
  • the shell thickness was varied from 115 nm to 1.2 pm.
  • the working electrodes were prepared by mixing 85 wt. % active material (porous graphene particulate -protected Co 3 0 4 and non-porous graphene ball- wrapped Co 3 0 4 , separately), 7 wt. % acetylene black (Super-P), and 8 wt. % polyvinylidene fluoride (PVDF) binder dissolved in N-methyl-2-pyrrolidinoe (NMP) to form a slurry of 5 wt. % total solid content. After coating the slurries on Cu foil, the electrodes were dried at l20°C in vacuum for 2 h to remove the solvent before pressing.
  • active material porous graphene particulate -protected Co 3 0 4 and non-porous graphene ball- wrapped Co 3 0 4 , separately
  • Super-P 7 wt. % acetylene black
  • PVDF polyvinylidene fluoride
  • NMP N-methyl-2
  • Electrochemical measurements were carried out using CR2032 (3V) coin-type cells with lithium metal as the counter/reference electrode, Celgard 2400 membrane as separator, and 1 M LiPF 6 electrolyte solution dissolved in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC-DEC, 1:1 v/v).
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • the cell assembly was performed in an argon-filled glove-box.
  • the CV measurements were carried out using a CH-6 electrochemical workstation at a scanning rate of 1 mV/s.
  • the electrochemical performance of the particulates of carbon/graphene-encapsulated Co 3 0 4 particles having pores created by-design and those having no pores were evaluated by galvanostatic charge/discharge cycling at a current density of 50 mA/g, using a LAND electrochemical workstation.
  • the first-cycle lithium insertion capacity is 765 mAh/g, which is higher than the theoretical values of graphite (372 mAh/g). Both cells exhibit some first-cycle irreversibility.
  • the initial capacity loss might have resulted from the incomplete conversion reaction and partially irreversible lithium loss due to the formation of solid electrolyte interface (SEI) layers.
  • SEI solid electrolyte interface
  • the cycle life of the cell containing the non-encapsulated anode active material is approximately 150 cycles.
  • the cycle life of the presently invented cells is typically from 1,000 to 4,000.
  • Tin oxide (Sn0 2 ) nanoparticles were obtained by the controlled hydrolysis of
  • SnC -5H 2 0 with NaOH using the following procedure: SnC -5H 2 0 (0.95 g, 2.7 m-mol) and NaOH (0.212 g, 5.3 m-mol) were dissolved in 50 mL of distilled water each. The NaOH solution was added drop-wise under vigorous stirring to the tin chloride solution at a rate of 1 mL/min. This solution was homogenized by sonication for 5 m in. Subsequently, the resulting hydrosol was reacted with H 2 S04. To this mixed solution, few drops of 0.1 M of H 2 S04 were added to flocculate the product. The precipitated solid was collected by centrifugation, washed with water and ethanol, and dried in vacuum. The dried product was heat-treated at 400°C for 2 h under Ar atmosphere to obtain Sn0 2 particles.
  • FIG. 8 shows that the anode prepared according to the presently invented approach of porous graphene particulate protection having a high level of internal porosity offers a significantly more stable and higher reversible capacity compared to the Sn0 2 particle-based particulates having no internal pores.
  • Si nanowires were supplied from Angstron Energy Co. (Dayton, Ohio). In a first series of samples, Si nanowires (approximately 63% by weight based on the final particulate weight), oxidized expanded graphite flakes (5% by weight) and a blowing agent were dispersed into water (containing 0.5% by weight of polyethylene oxide or PEO dissolved therein) to form a slurry.
  • the slurry was then spray-dried to form droplets containing a core of Si nanowires, expanded graphite flakes, and the blowing agent being embraced by an encapsulating shell of expanded graphite flake-PEO composite.
  • Some of the particulates were then subjected to heat treatments that convert the polymer (PEO) into carbon and pores in the core region and carbon-bonded graphite flakes in the encapsulating shell.
  • the converted carbon along with the expanded graphite flakes in the encapsulating shell on the exterior surface of the particulate somehow form a relatively pore-free skin layer and yet, in contrast, the volume of the droplet is significantly expanded (25% to 88% by volume of pores, depending upon the proportion of the blowing agent used) with some residual carbon that serves as an electron-conducting material for the Si nanowires.
  • the Si nanowires occupy approximately 18% to 33% by volume in these samples.
  • a second series of samples were prepared in a similar manner, but did not contain a blowing agent in the slurry. As such, the resulting particulates after heat treatments do not contain any significant amount of pores (typically ⁇ 5%).
  • FIG. 9 shows the specific capacities of 2 lithium-ion cells having a core of Si nanowires (SiNW) and expanded graphite flakes dispersed in a carbon matrix derived from PEO and an encapsulating shell of expanded graphite flakes-carbon: one having pores (76% by volume) derived from carbonized PEO and the blowing agent and the other having no artificially created pores.
  • SiNW Si nanowires
  • FIG. 9 shows the specific capacities of 2 lithium-ion cells having a core of Si nanowires (SiNW) and expanded graphite flakes dispersed in a carbon matrix derived from PEO and an encapsulating shell of expanded graphite flakes-carbon: one having pores (76% by volume) derived from carbonized PEO and the blowing agent and the other having no artificially created pores.
  • the presently invented strategy of implementing blowing agent- induced pores or free space in the anode particulates is very effective in reducing the rapid capacity decay issues commonly associated with high-capacity anode active

Abstract

L'invention concerne une anode pour une batterie au lithium, comprenant de multiples particules de graphène poreux, au moins l'une des particules comprenant de multiples pores (volume total Vpp), des parois de pore et des particules primaires d'un matériau actif d'anode (volume total Va), disposées dans les pores, (a) les parois de pores contenant un matériau de graphène ; (b) les particules primaires étant en une quantité de 0,5 % à 95 % en poids sur la base du poids particulaire total ; (c) la particule étant entourée ou encapsulée par une couche d'encapsulation mince de matériau électroconducteur ayant une épaisseur de 1 nm à 10 µm, une conductivité électrique de 10-6 S/cm à 20 000 S/cm et une conductivité des Ions lithium de 10-8 S/cm à 5 x 10-2 S/cm ; et (d) le rapport volumétrique Vpp/Va étant de 1,3/1,0 à 5,0/1,0. L'invention concerne également un procédé de production de multiples particules de graphène poreux pour une anode de batterie au lithium.
PCT/US2019/056031 2018-10-18 2019-10-14 Matériaux actifs d'anode protégés par des particules de graphène poreux pour batteries au lithium WO2020081409A1 (fr)

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US16/163,964 US11152620B2 (en) 2018-10-18 2018-10-18 Process for producing porous graphene particulate-protected anode active materials for lithium batteries
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