WO2018038764A1 - Collecteur de courant à film de feuille métallique lié à de l'acide humique et batterie et super-condensateur le contenant - Google Patents

Collecteur de courant à film de feuille métallique lié à de l'acide humique et batterie et super-condensateur le contenant Download PDF

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WO2018038764A1
WO2018038764A1 PCT/US2017/018708 US2017018708W WO2018038764A1 WO 2018038764 A1 WO2018038764 A1 WO 2018038764A1 US 2017018708 W US2017018708 W US 2017018708W WO 2018038764 A1 WO2018038764 A1 WO 2018038764A1
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graphene
current collector
film
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PCT/US2017/018708
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English (en)
Inventor
Aruna Zhamu
Bor Z. Jang
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Nanotek Instruments, Inc.
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Priority claimed from US15/243,589 external-priority patent/US10014519B2/en
Priority claimed from US15/243,606 external-priority patent/US10597389B2/en
Application filed by Nanotek Instruments, Inc. filed Critical Nanotek Instruments, Inc.
Priority to JP2019510304A priority Critical patent/JP6959328B2/ja
Priority to KR1020197007640A priority patent/KR20190040261A/ko
Priority to CN201780060219.2A priority patent/CN109792055B/zh
Publication of WO2018038764A1 publication Critical patent/WO2018038764A1/fr

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/665—Composites
    • H01M4/667—Composites in the form of layers, e.g. coatings
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/04—Carbon
    • C08K3/042—Graphene or derivatives, e.g. graphene oxides
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/16—Nitrogen-containing compounds
    • C08K5/34—Heterocyclic compounds having nitrogen in the ring
    • C08K5/35—Heterocyclic compounds having nitrogen in the ring having also oxygen in the ring
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/66—Current collectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/66—Current collectors
    • H01G11/68—Current collectors characterised by their material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/66—Current collectors
    • H01G11/70—Current collectors characterised by their structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/84—Processes for the manufacture of hybrid or EDL capacitors, or components thereof
    • 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/661—Metal or alloys, e.g. alloy coatings
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/663—Selection of materials containing carbon or carbonaceous materials as conductive part, e.g. graphite, carbon fibres
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M12/00—Hybrid cells; Manufacture thereof
    • H01M12/08—Hybrid cells; Manufacture thereof composed of a half-cell of a fuel-cell type and a half-cell of the secondary-cell type
    • 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
    • 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
    • Y02E60/13—Energy storage using capacitors

Definitions

  • the present invention provides a current collector for a lithium battery or supercapacitor.
  • the current collector is a metal foil bonded with a thin film of highly oriented humic acid or humic acid-derived highly conducting graphitic film.
  • This patent application is directed at a current collector that works with an anode electrode (anode active material layer) or a cathode electrode (cathode active material layer) of a lithium cell (e.g. lithium-ion cell, lithium-metal cell, or lithium-ion capacitor), a supercapacitor, a non-lithium battery (such as the zinc-air cell, nickel metal hydride battery, sodium-ion cell, and magnesium-ion cell), and other electrochemical energy storage cells.
  • a lithium cell e.g. lithium-ion cell, lithium-metal cell, or lithium-ion capacitor
  • a supercapacitor e.g. lithium-ion cell, lithium-metal cell, or lithium-ion capacitor
  • a non-lithium battery such as the zinc-air cell, nickel metal hydride battery, sodium-ion cell, and magnesium-ion cell
  • This application is not part of the anode active material layer or the cathode active material layer per se.
  • the lithium-metal cell includes the conventional lithium-metal rechargeable cell (e.g. using a lithium foil as the anode and Mn0 2 particles as the cathode active material), lithium-air cell (Li-Air), lithium-sulfur cell (Li-S), and the emerging lithium-graphene cell (Li-graphene, using graphene sheets as a cathode active material), lithium-carbon nanotube cell (Li-CNT, using CNTs as a cathode), and lithium-nano carbon cell (Li-C, using nano carbon fibers or other nano carbon materials as a cathode).
  • the anode and/or the cathode active material layer can contain some lithium, or can be prelithiated prior to or immediately after cell assembly.
  • Li-ion Rechargeable lithium-ion
  • Li-ion Li-ion
  • Li metal Li-sulfur, and Li metal-air batteries are considered promising power sources for electric vehicle (EV), hybrid electric vehicle (HEV), and portable electronic devices, such as lap-top computers and mobile phones.
  • Lithium as a metal element has the highest lithium storage capacity (3,861 mAh/g) compared to any other metal or metal-intercalated compound as an anode active material (except Li 4 4 Si, which has a specific capacity of 4,200 mAh/g).
  • Li metal batteries having a lithium metal anode
  • conventional lithium-ion batteries having a graphite anode).
  • rechargeable lithium metal batteries were produced using non-lithiated compounds having relatively high specific capacities, such as TiS 2 , MoS 2 , Mn0 2 , Co0 2 , and V 2 0 5 , as the cathode active materials, which were coupled with a lithium metal anode.
  • non-lithiated compounds having relatively high specific capacities such as TiS 2 , MoS 2 , Mn0 2 , Co0 2 , and V 2 0 5
  • the cathode active materials When the battery was discharged, lithium ions were transferred from the lithium metal anode to the cathode through the electrolyte and the cathode became lithiated.
  • the lithium metal resulted in the formation of dendrites at the anode that ultimately caused internal shorting, thermal runaway, and explosion.
  • Li metal batteries e.g. Lithium-sulfur and Lithium-transition metal oxide cells
  • lithium-ion secondary batteries in which pure lithium metal sheet or film was replaced by carbonaceous materials (e.g. natural graphite particles) as the anode active material.
  • the carbonaceous material absorbs lithium (through intercalation of lithium ions or atoms between graphene planes, for instance) and desorbs lithium ions during the re-charge and discharge phases, respectively, of the lithium-ion battery operation.
  • the carbonaceous material may comprise primarily graphite that can be intercalated with lithium and the resulting graphite intercalation compound may be expressed as Li x C 6 , where x is typically less than 1 (with graphite specific capacity ⁇ 372 mAh/g).
  • Li-ion batteries are promising energy storage devices for electric drive vehicles
  • state-of-the-art Li-ion batteries have yet to meet the cost, safety, and performance targets (such as high specific energy, high energy density, good cycle stability, and long cycle life).
  • Li-ion cells typically use a lithium transition-metal oxide or phosphate as a positive electrode (cathode) that de/re-intercalates Li at a high potential with respect to the carbon negative electrode (anode).
  • the specific capacity of lithium transition-metal oxide or phosphate based cathode active material is typically in the range of 140-170 mAh/g.
  • the specific energy (gravimetric energy density) of commercially available Li-ion cells featuring a graphite anode and a lithium transition-metal oxide or phosphate based cathode is typically in the range of 120-220 Wh/kg, most typically 150-200 Wh/kg.
  • the corresponding typical range of energy density (volumetric energy density) is from 400 to 550 Wh/L.
  • the energy densities are even lower under high charge-discharge rate conditions.
  • a typical battery cell is composed of (a) an anode current collector, (b) an anode electrode (also referred to as the anode active material layer, typically including an anode active material, a conductive filler, and a binder resin component) bonded to the anode current collector with a binder resin, (c) an electrolyte/separator, (d) a cathode electrode (also referred to as the cathode active material layer, typically including a cathode active material, a conductive filler, and a binder resin), (e) a cathode current collector bonded to the cathode electrode with a binder resin, (f) metal tabs that are connected to external wiring, and (g) casing that wraps around all other components except for the tabs.
  • an anode electrode also referred to as the anode active material layer, typically including an anode active material, a conductive filler, and a binder resin component
  • the current collectors are crucially important for cost, weight, safety, and performance of a battery.
  • graphene or graphene-coated solid metal or plastic has been considered as a potential current collector material, as summarized in the references listed below:
  • graphene current collectors come in three different forms: graphene-coated substrate [Ref. 1-4], free-standing graphene paper [Ref. 5], and monolayer graphene film produced by transition metal (Ni, Cu)-catalyzed chemical vapor deposition (CVD) followed by metal etching [Ref. 6].
  • graphene-coated substrate small isolated sheets or platelets of graphene oxide (GO) or reduced graphene oxide (RGO) are spray-deposited onto a solid substrate (e.g. plastic film or Al foil).
  • a solid substrate e.g. plastic film or Al foil.
  • the building blocks are separated graphene sheets/platelets (typically 0.5 - 5 ⁇ in length/width and 0.34-30 nm in thickness) that are typically bonded by a binder resin, such as PVDF [Refs. 1, 3, and 4].
  • the resulting graphene-binder resin composite layer is relatively poor in electrical conductivity (typically ⁇ 100 S/cm and more typically ⁇ 10 S/cm).
  • another purpose of using a binder resin is to bond the graphene-binder composite layer to the substrate (e.g. Cu foil); this implies that there is a binder resin (adhesive) layer between Cu foil and the graphene-binder composite layer.
  • this binder resin layer is electrically insulating and the resulting detrimental effect seems to have been totally overlooked by prior workers.
  • a trace amount of H 2 0 in this electrolyte can trigger a series of chemical reactions that involve formation of HF (a highly corrosive acid) that readily breaks up the aluminum oxide layer and continues to corrode the Al foil and consume electrolyte.
  • HF a highly corrosive acid
  • the capacity decay typically becomes much apparent after 200-300 charge-discharge cycles.
  • Free-standing graphene paper is typically prepared by vacuum-assisted filtration of GO or RGO sheets/platelets suspended in water. In a free-standing paper, the building blocks are separated graphene sheets/platelets that are loosely overlapped together.
  • the quantity of intercalation solution retained on the flakes after draining may range from 20 to 150 parts of solution by weight per 100 parts by weight of graphite flakes (pph) and more typically about 50 to 120 pph.
  • the residual intercalate species retained by the flakes decompose to produce various species of sulfuric and nitrous compounds (e.g., NO x and SO x ), which are undesirable.
  • the effluents require expensive remediation procedures in order not to have an adverse environmental impact.
  • the catalyzed CVD process for graphene production involves introduction of a hydrocarbon gas into a vacuum chamber at a temperature of 500-800°C. Under these stringent conditions, the hydrocarbon gas gets decomposed with the decomposition reaction being catalyzed by the transition metal substrate (Ni or Cu). The Cu/Ni substrate is then chemically etched away using a strong acid, which is not an environmentally benign procedure. The whole process is slow, tedious, and energy-intensive, and the resulting graphene is typically a single layer graphene or few-layer graphene (up to 5 layers maximum since the underlying Cu/Ni layer loses its effectiveness as a catalyst).
  • Bhardwaj, et al [Ref. 6] suggested stacking multiple CVD-graphene films to a thickness of 1 ⁇ or a few ⁇ ; however, this would require hundreds or thousands of films stacked together (each film being typically 0.34 nm to 2 nm thick).
  • Bhardwaj, et al claimed that "The graphene may reduce the manufacturing cost and/or increase the energy density of a battery cell," no experimental data was presented to support their claim. Contrary to this claim, the CVD graphene is a notoriously expensive process and even a single-layer of CVD graphene film would be significantly more expensive than a sheet of Cu or Al foil given the same area (e.g. the same 5 cm x 5 cm).
  • a stack of hundreds or thousands of mono-layer or few-layer graphene films as suggested by Bhardwaj, et al would mean hundreds or thousands times more expensive than a Cu foil current collector. This cost would be prohibitively high. Further, the high contact resistance between hundreds of CVD graphene films in a stack and the relatively low conductivity of CVD graphene would lead to an overall high internal resistance, nullifying any potential benefit of using thinner films (1 ⁇ of graphene stack vs. 10 ⁇ of Cu foil) to reduce the overall cell weight and volume. It seems that the patent application of Bhardwaj, et al [Ref. 6], containing no data whatsoever, is nothing but a concept paper.
  • the present invention is directed at a new class of materials, herein referred to as a highly oriented film of humic acid (HA), alone or in combination with graphene, which is chemically bonded to metal foil surface.
  • HA humic acid
  • Graphene used herein includes pristine graphene, graphene oxide, graphene fluoride, nitrogenated graphene, hydrogenated graphene, boron-doped graphene, any other type of doped graphene, and other type of chemically functionalized graphene. Quite unexpectedly and significantly, this highly oriented film of HA or HA/graphene mixture can be thermally converted to a highly conducting graphitic film.
  • HA is an organic matter commonly found in soil and can be extracted from the soil using a base (e.g. KOH). HA can also be extracted, with a high yield, from a type of coal called leonardite, which is a highly oxidized version of lignite coal. HA extracted from leonardite contains a number of oxygenated groups (e.g. carboxyl groups) located around the edges of the graphene-like molecular center (SP 2 core of hexagonal carbon structure). This material is slightly similar to graphene oxide (GO) which is produced by strong acid oxidation of natural graphite. HA has a typical oxygen content of 5% to 42% by weight (other major elements being carbon and hydrogen).
  • GO graphene oxide
  • HA after chemical or thermal reduction, has an oxygen content of 0.01% to 5% by weight.
  • humic acid refers to the entire oxygen content range, from 0.01% to 42% by weight.
  • the reduced humic acid is a special type of HA that has an oxygen content of 0.01% to 5% by weight.
  • humic acid when brought in intimate contact with a surface of a metal foil, can chemically bond to the metal foil. It is further surprising to discover that, when properly aligned and packed together, humic acid molecules can chemically link with one another to obtain longer and wider humic acid sheets. These humic acid molecules are also capable of chemically linking or bonding with graphene sheets, if present and properly aligned and packed.
  • the resulting humic acid- or graphitic film-bonded thin metal foil is electrolyte- compatible, non-reactive, corrosion-protective, of low contact resistance, thermally and electrically conductive, ultra-thin, and light-weight, enabling a battery or capacitor to deliver a higher output voltage, higher energy density, high rate-capability, and much longer cycle life.
  • the present invention provides a highly oriented humic acid-bonded metal foil current collector for use in a battery or supercapacitor.
  • the invention also provides a current collector composed of a metal foil and a humic acid-derived highly conducting graphitic film bonded to one or two primary surfaces of the metal foil.
  • the invention also provides processes for producing these current collectors.
  • the invented current collector comprises: (a) a thin metal foil having a thickness from 1 ⁇ to 30 ⁇ (preferably from 4 ⁇ to 12 ⁇ ) and two opposed but substantially parallel primary surfaces; and (b) at least one thin film of highly oriented humic acid (HA) or a mixture of HA and graphene sheets (or a highly conducting graphitic film derived from this thin film) being chemically bonded to at least one of the two opposed primary surfaces of the metal foil.
  • HA highly oriented humic acid
  • graphene sheets or a highly conducting graphitic film derived from this thin film
  • the thin film of HA or HA/graphene mixture or the derived graphitic film has a thickness from 10 nm to 10 ⁇ , an oxygen content from 0.01% to 10% by weight, a physical density from 1.3 to 2.2 g/cm 3 , hexagonal carbon planes being oriented substantially parallel to each other and parallel to the primary surfaces, an inter-planar spacing of 0.335 to 0.50 nm between hexagonal carbon planes, a thermal conductivity greater than 250 W/mK (more typically >500 W/mK), and an electrical conductivity greater than 800 S/cm (more typically >1,500 S/cm) when measured alone without said thin metal foil.
  • each of the two opposed primary surfaces is chemically bonded with such a thin film of humic acid or HA/graphene mixture or a graphitic film derived from this thin film produced through heat treatments.
  • one or both thin films of HA or both HA and graphene (or the derived graphitic film) are chemically bonded to one or both opposed primary surfaces of the metal foil without using a binder or adhesive. If a binder is used, this binder is an electrically conductive material selected from an intrinsically conductive polymer, pitch, amorphous carbon, or carbonized resin (polymeric carbon).
  • the thin metal foil has a thickness from 4 to 12 ⁇ .
  • the thin film of humic acid or HA/graphene mixture or the graphitic film has a thickness from 20 nm to 2 ⁇ .
  • the metal foil is selected from Cu, Ti, Ni, stainless steel, Al foil, or a combination thereof.
  • the primary surface does not contain a layer of passivating metal oxide thereon (e.g. no alumina, A1 2 0 3 , on Al foil surface).
  • the thin film of HA or HA/graphene mixture or the graphitic film derived therefrom has an oxygen content from 1% to 5% by weight. Further preferably, the thin film or the graphitic film derived therefrom has an oxygen content less than 1%, an inter-planar spacing less than 0.345 nm, and an electrical conductivity no less than 3,000 S/cm. More preferably, the thin film or the graphitic film derived therefrom has an oxygen content less than 0.1%, an inter- planar spacing less than 0.337 nm, and an electrical conductivity no less than 5,000 S/cm.
  • the thin film or the graphitic film derived therefrom has an oxygen content no greater than 0.05%, an inter-planar spacing less than 0.336 nm, a mosaic spread value no greater than 0.7, and an electrical conductivity no less than 8,000 S/cm. Even more preferably, the thin film or the graphitic film derived therefrom has an inter-planar spacing less than 0.336 nm, a mosaic spread value no greater than 0.4, and an electrical conductivity greater than 10,000 S/cm.
  • the thin film of HA or HA/graphene mixture or the graphitic film derived therefrom exhibits an inter-planar spacing less than 0.337 nm and a mosaic spread value less than 1.0.
  • the thin film e or the graphitic film derived therefrom exhibits a degree of graphitization no less than 80% and/or a mosaic spread value no greater than 0.4.
  • the thin film of HA or HA/graphene mixture is obtained by depositing a suspension of HA or a mixture of HA and graphene sheets onto said at least one primary surface under the influence of an orientation-controlling stress to form a layer of HA or a mixture of HA and graphene sheets and then heat-treating said layer at a heat treatment temperature from 80°C to 1,500°C. More preferably, the heat treatment temperature is from 80°C to 500°C and further more preferably from 80°C to 200°C.
  • the highly oriented thin film of HA or HA/graphene or the graphitic film derived therefrom bonded to the underlying current collector typically contains chemically bonded humic acid molecules or chemically merged humic acid and graphene planes that are parallel to one another, as illustrated in FIG. 3(C).
  • the thin film is a continuous length film having a length no less than 5 cm and a width no less than 1 cm and this thin film is made by a roll-to-roll process.
  • the thin film of HA or HA/graphene mixture or the graphitic film derived therefrom when measured alone (as a free-standing layer without the presence of a metal foil), has a physical density greater than 1.6 g/cm3, and/or a tensile strength greater than 30 MPa. More preferably, the thin film or the graphitic film derived therefrom, when measured alone, has a physical density greater than 1.8 g/cm3, and/or a tensile strength greater than 50 MPa. Most preferably, the thin film or the graphitic film derived therefrom, when measured alone, has a physical density greater than 2.0 g/cm 3 , and/or a tensile strength greater than 80 MPa.
  • the present invention also provides a rechargeable lithium battery or lithium-ion battery containing the presently invented current collector as an anode current collector and/or a cathode current collector.
  • the rechargeable lithium battery may be a lithium-sulfur cell, a lithium- selenium cell, a lithium sulfur/selenium cell, a lithium-air cell, a lithium-graphene cell, or a lithium-carbon cell.
  • the present invention also provides a capacitor containing the invented current collector as an anode current collector or a cathode current collector, which capacitor is a symmetric ultracapacitor, an asymmetric ultracapacitor cell, a hybrid supercapaci tor-battery cell, or a lithium-ion capacitor cell.
  • the invention also provides a process for producing a highly oriented humic acid film- bonded metal foil current collector for use in a battery or supercapacitor.
  • the process comprises: (a) preparing a dispersion of humic acid (HA) or chemically functionalized humic acid (CHA) sheets dispersed in a liquid medium, wherein the HA sheets contain an oxygen content higher than 5 % by weight or the CHA sheets contain non-carbon element content higher than 5% by weight; (b) dispensing and depositing the HA or CHA dispersion onto at least one primary surface of a metal foil to form a wet layer of HA or CHA on the surface, wherein the dispensing and depositing procedure includes subjecting the dispersion to an orientation-inducing stress;
  • the process may further comprise a step of compressing the humic acid film of merged or reduced HA or CHA after said step (d).
  • the process may comprise an additional step (e) of further heat-treating the humic acid film-bonded metal foil at a second heat treatment temperature higher than the first heat treatment temperature for a sufficient period of time to produce a graphitic film-bonded metal foil current collector, wherein the graphitic film has an inter-planar spacing d 0 02 less than 0.4 nm and an oxygen content or non-carbon element content less than 5% by weight; and (f) compressing the graphitic film to produce a highly conducting graphitic film having a physical density no less than 1.3 g/cm 3 , a thermal conductivity of at least 500 W/mK, and/or an electrical conductivity no less than 1,000 S/cm.
  • the highly conductive graphitic film preferably has a thickness from 5 nm to 20 ⁇ , but more preferably from 10 nm to 2 ⁇ .
  • the HA or CHA dispersion may further contain graphene sheets or molecules dispersed therein and the HA-to-graphene or CHA-to-graphene ratio is from 1/100 to 100/1 wherein the graphene is selected from pristine graphene, graphene oxide, reduced graphene oxide, graphene fluoride, graphene bromide, graphene iodide, boron-doped graphene, nitrogen-doped graphene, chemically functionalized graphene, or a combination thereof.
  • the process may include additional step (e) of further heat-treating the humic acid film of merged or reduced HA or CHA at a second heat treatment temperature higher than the first heat treatment temperature for a sufficient period of time to produce a graphitic film having an inter-planar spacing d 0 02 less than 0.4 nm and an oxygen content or non-carbon element content less than 5% by weight; and step (f) of compressing the graphitic film to produce a highly conducting graphitic film having a physical density no less than 1.6 g/cm 3 , a thermal conductivity of at least 700 W/mK, and/or an electrical conductivity no less than 1,500 S/cm.
  • the HA or CHA sheets are in an amount sufficient to form a liquid crystal phase in the liquid medium.
  • the dispersion contains a first volume fraction of HA or CHA dispersed in the liquid medium that exceeds a critical volume fraction (V c ) for a liquid crystal phase formation and the dispersion is concentrated to reach a second volume fraction of HA or CHA, greater than the first volume fraction, to improve a HA or CHA sheet orientation.
  • the first volume fraction is equivalent to a weight fraction of from 0.05% to 3.0%) by weight of HA or CHA in the dispersion.
  • the dispersion may be concentrated to contain higher than 3.0% but less than 15%> by weight of HA or CHA dispersed in thed liquid medium prior to said step (b).
  • the dispersion further contains a polymer dissolved in said liquid medium or attached to HA or CHA.
  • the CHA may contain a chemical functional group selected from a polymer, S0 3 H, COOH, H 2 , OH, R'CHOH, CHO, CN, COC1, halide, COSH, SH, COOR', SR', SiR 3 , Si(-OR- ) y R 3 -y, Si( ⁇ 0 ⁇ SiR 2 ⁇ )OR, R", Li, A1R 2 , Hg-X, T1Z 2 and Mg-X; wherein y is an integer equal to or less than 3, R is hydrogen, alkyl, aryl, cycloalkyl, or aralkyl, cycloaryl, or poly(alkylether), R" is fluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl or cycloaryl, X is halide, and Z is carboxylate or trifluoroacetate, or a combination thereof.
  • a chemical functional group selected from a polymer,
  • the graphene sheets may contain chemically functionalized graphene containing a chemical functional group selected from a polymer, S0 3 H, COOH, H 2 , OH, R'CHOH, CHO, CN, COC1, halide, COSH, SH, COOR, SR, SiR 3 , Si(-OR-) y R 3 -y, Si(-0- SiR 2 ⁇ )OR, R", Li, A1R 2 , Hg— X, T1Z 2 and Mg— X; wherein y is an integer equal to or less than 3, R is hydrogen, alkyl, aryl, cycloalkyl, or aralkyl, cycloaryl, or poly(alkyl ether), R" is fluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl or cycloaryl, X is halide, and Z is carboxylate or trifluoroacetate, or a combination thereof.
  • the liquid medium consists of water or a mixture of water and an alcohol.
  • the liquid medium contains a non-aqueous solvent selected from polyethylene glycol, ethylene glycol, propylene glycol, an alcohol, a sugar alcohol, a polyglycerol, a glycol ether, an amine based solvent, an amide based solvent, an alkylene carbonate, an organic acid, or an inorganic acid.
  • the second heat treatment temperature may be higher than 1,500°C for a length of time sufficient for decreasing an inter-plane spacing doo 2 to a value less than 0.36 nm and decreasing the oxygen content or non-carbon element content to less than 0.1% by weight.
  • the second heat treatment temperature may be from 1,500°C to 3,200°C.
  • the process is preferably a roll-to-roll or reel-to-reel process, wherein step (b) includes feeding a sheet of the metal foil from a roller to a deposition zone, depositing a layer of HA or CHA dispersion onto at least one primary surface of the metal foil to form a wet layer of HA or CHA dispersion thereon, drying the HA or CHA dispersion to form a dried HA or CHA layer deposited on metal foil surface, and collecting the HA or CHA layer-deposited metal foil on a collector roller.
  • step (b) includes feeding a sheet of the metal foil from a roller to a deposition zone, depositing a layer of HA or CHA dispersion onto at least one primary surface of the metal foil to form a wet layer of HA or CHA dispersion thereon, drying the HA or CHA dispersion to form a dried HA or CHA layer deposited on metal foil surface, and collecting the HA or CHA layer-deposited metal foil on a collector roller.
  • the first heat treatment temperature contains a temperature in the range of 100°C-1,500°C and the highly oriented humic acid film has an oxygen content less than 2.0 %, an inter-planar spacing less than 0.35 nm, a physical density no less than 1.6 g/cm 3 , a thermal conductivity of at least 800 W/mK, and/or an electrical conductivity no less than 2,500 S/cm.
  • the first heat treatment temperature contains a temperature in the range of 1,500°C- 2, 100°C and the highly oriented humic acid film, becoming a highly conducting graphitic film, has an oxygen content less than 1.0 %, an inter-planar spacing less than 0.345 nm, a thermal conductivity of at least 1,000 W/mK, and/or an electrical conductivity no less than 5,000 S/cm.
  • the first and/or second heat treatment temperature contains a temperature greater than 2,100°C and the highly conducting graphitic film has an oxygen content no greater than 0.1%, an inter-graphene spacing less than 0.340 nm, a mosaic spread value no greater than 0.7, a thermal conductivity of at least 1,300 W/mK, and/or an electrical conductivity no less than 8,000 S/cm.
  • the second heat treatment temperature contains a temperature no less than 2,500°C
  • the highly conducting graphitic film has an inter-graphene spacing less than 0.336 nm, a mosaic spread value no greater than 0.4, a thermal conductivity greater than 1,500 W/mK, and/or an electrical conductivity greater than 10,000 S/cm.
  • the degree of graphitization may be no less than 80% and a mosaic spread value less than 0.4.
  • the HA or CHA sheets have a maximum original length and the highly oriented humic acid film contains HA or CHA sheets having a length larger than the maximum original length. This implies that some humic acid molecules have merged with other HA molecules in an edge-to-edge manner to increase the length or width of the planar molecules or sheets.
  • the step (e) of heat-treating induces chemical linking, merging, or chemical bonding of HA or CHA sheets with other HA or CHA sheets, or with graphene sheets to form a graphitic structure.
  • the highly conducting graphitic film is a poly-crystal graphene structure having a preferred crystalline orientation as determined by said X-ray diffraction method.
  • the process typically results in the formation of a highly oriented graphitic film having an electrical conductivity greater than 5,000 S/cm, a thermal conductivity greater than 800 W/mK, a physical density greater than 1.9 g/cm 3 , a tensile strength greater than 80 MPa, and/or an elastic modulus greater than 60 GPa.
  • the highly oriented graphitic film has an electrical conductivity greater than 8,000 S/cm, a thermal conductivity greater than 1,200 W/mK, a physical density greater than 2.0 g/cm 3 , a tensile strength greater than 100 MPa, and/or an elastic modulus greater than 80 GPa.
  • the highly oriented graphitic film has an electrical conductivity greater than 12,000 S/cm, a thermal conductivity greater than 1,500 W/mK, a physical density greater than 2.1 g/cm 3 , a tensile strength greater than 120 MPa, and/or an elastic modulus greater than 120 GPa.
  • FIG.1(A) A flow chart illustrating various prior art processes for producing exfoliated graphite products (flexible graphite foils and flexible graphite composites) and pyrolytic graphite (bottom portion).
  • FIG.1(B) Process for producing isolated graphene sheets and aggregates of graphene or graphene oxide sheets in the form of a graphene paper or membrane.
  • FIG.1(C) Process for producing isolated graphene sheets and aggregates of graphene or graphene oxide sheets in the form of a graphene paper or membrane.
  • FIG.2 An SEM image of a cross-section of a flexible graphite foil, showing many graphite
  • FIG.3 A SEM image of a HA liquid crystal-derived HOGF, wherein multiple hexagonal carbon planes are seamlessly merged into continuous-length graphene-like sheets or layers that can run for tens of centimeters wide or long (only a 50 ⁇ width of a 10-cm wide HOGF being shown in this SEM image);
  • FIG.3(B) A SEM image of a cross-section of a conventional graphene paper prepared from
  • discrete reduced graphene oxide sheets/platelets using a paper-making process (e.g. vacuum-assisted filtration).
  • the image shows many discrete graphene sheets being folded or interrupted (not integrated), with orientations not parallel to the film/paper surface and having many defects or imperfections;
  • FIG.3(C) Schematic of a film of highly oriented humic acid molecules being chemically merged together to form a highly ordered and conducting graphitic film.
  • FIG.4(A) Thermal conductivity values of the HA/GO-derived HOGF, GO-derived HOGF, HA- derived HOGF, and FG foil plotted as a function of the final heat treatment temperature;
  • FIG.4(B) Thermal conductivity values of the HA/GO-derived HOGF, HA-derived HOGF, and polyimide-derived HOPG, all plotted as a function of the final HTT;
  • FIG.4(C) Electric conductivity values of the HA/GO-derived HOGF, GO-derived HOGF, HA- derived HOGF, and FG foil plotted as a function of the final heat treatment temperature.
  • FIG.5(A) Inter-graphene plane spacing in HA-derived HOGF measured by X-ray diffraction
  • FIG.5(B) The oxygen content in the HA-derived HOGF
  • FIG.5(C) The correlation between inter-graphene spacing and the oxygen content
  • FIG.5(D) Thermal conductivity values of the HA/GO-derived HOGF, GO-derived HOGF, HA- derived HOGF, and FG foil plotted as a function of the final heat treatment temperature.
  • FIG.6 Thermal conductivity of HOGF samples plotted as a function of the proportion of GO sheets in a HA/GO suspension.
  • FIG.7(A) Tensile strength values of HA/GO-derived HOGF, GO-derived HOGF, HA-derived
  • FIG.7(B) Tensile modulus of the HA/GO-derived HOGF, GO-derived HOGF, and HA-derived HOGF, plotted as a function of the final heat treatment temperature.
  • FIG.8 Thermal conductivity of three HA-derived highly oriented films; one obtained by heat- treating a HA film that was peeled off from a glass surface, one deposited on and bonded to Ti surface while being heat-treated, and one deposited on and bonded to a Cu foil surface while being heat-treated.
  • FIG.9(A) The discharge capacity values of three Li-S cells each as a function of the
  • first cell having HA-bonded Cu foil and HA-bonded Al foil as the anode and cathode current collectors, respectively; second cell having
  • GO/resin-coated Cu foil and GO-coated Al foil (no pre-etching) as the anode and cathode current collector, respectively (a prior art cell); third cell having a Cu foil anode current collector and Al foil cathode current collector (a prior art cell).
  • FIG.9(B) Ragone plots of the three cells: first cell having HA-bonded Cu foil and HA-bonded Al foil as the anode and cathode current collectors, respectively; second cell having
  • GO/resin-coated Cu foil and GO-coated Al foil (no pre-etching) as the anode and cathode current collector, respectively (a prior art cell); third cell having a Cu foil anode current collector and Al foil cathode current collector (a prior art cell).
  • FIG.10 The cell capacity values of three magnesium metal cells; first cell having HA-bonded Cu foil and HA-bonded Al foil as the anode and cathode current collectors, respectively; second cell having GO/resin-coated Cu foil and GO-coated Al foil (no pre-etching) as the anode and cathode current collector, respectively (a prior art cell); third cell having a Cu foil anode current collector and Al foil cathode current collector (a prior art cell).
  • the present invention provides a humic acid-bonded metal foil thin-film current collector (e.g. as schematically shown in FIG. 1(C)) for use in a battery or supercapacitor.
  • the current collector comprises: (a) a free-standing, non-supported thin metal foil (214 in FIG.1(C)) having a thickness from 1 ⁇ to 30 ⁇ and two opposed but substantially parallel primary surfaces; and (b) a thin film 212 of humic acid (HA) or HA/graphene mixture chemically bonded to at least one of the two opposed primary surfaces (without using a binder or adhesive).
  • FIG. 1(C) only shows one primary surface of the metal foil 214 being bonded with a thin film 212 of HA or HA/graphene mixture. However, preferably, the opposite primary surface is also bonded with a thin film of HA or HA/graphene mixture (not shown in FIG.1(C)).
  • a metal tab 218 is typically welded or soldered to the metal foil 214.
  • a preferred embodiment of the present invention is a HA- bonded metal foil current collector, wherein no binder resin layer or passivating aluminum oxide layer is present between the film of HA or HA/graphene mixture and the Cu foil or Al foil.
  • the prior art graphene-coated metal foil current collector typically and necessarily requires a binder resin layer between the graphene layer (a graphene-resin composite) and the metal foil (e.g. Cu foil).
  • a passivating aluminum oxide (alumina) layer is naturally present between the graphene layer and the Al metal foil.
  • HA molecules can be well -bonded to these metal foils under the presently invented processing conditions, without using an external resin binder or adhesive (hence, no dramatically increased contact resistance).
  • processing conditions include well-aligning HA (or a mixture of HA and graphene) molecules or sheets on the metal foil surface and then heat-treating the two-layer structure at a temperature in the range of 80°C-1,500°C (more typically and desirably of 80°C- 500°C, and most typically and desirably of 80°C-200°C).
  • the heat treatment temperature can be as high as 1, 500-3, 000°C (provided the metal foil can withstand such a high temperature).
  • These processing conditions in the cases of aluminum foil -based current collectors, preferably include chemically etching off the passivating aluminum oxide layer prior to being coated with and bonded by HA, followed by a heat treatment under comparable temperature conditions described above.
  • the HA molecules may be prepared in an acidic state, which is characterized by having high oxygen contents, reflecting high amounts of -OH and - COOH groups and having a pH value less than 5.0 (preferably ⁇ 3.0 and even more preferably ⁇ 2.0).
  • the Al foil may be allowed to get immersed in a bath of HA solution, wherein the acidic environment naturally removes the passivating A1 2 0 3 layer.
  • the resulting thin film of HA or HA/graphene mixture in the presently invented HA-bonded metal foil has a thickness from 10 nm to 10 ⁇ , an oxygen content from 0.1% to 10% by weight, an inter-graphene plane spacing of 0.335 to 0.50 nm, a physical density from 1.3 to 2.2 g/cm 3 , all HA and graphene sheets (if present) being oriented substantially parallel to each other and parallel to the primary surfaces, exhibiting a thermal conductivity greater than 500 W/mK, and/or electrical conductivity greater than 1,500 S/cm when measured alone without the thin metal foil.
  • This thin film of HA or HA/graphene is chemically inert and provides a highly effective protective layer against corrosion of the underlying metal foil.
  • a graphene-coated current collector containing a binder or passivating metal oxide layer may be viewed as a three-layer structure (FIG. 1(B)) with the graphene film, interfacial binder resin layer (or passivating alumina layer), and metal foil layer electrically connected in series.
  • the thickness-direction resistivity pi of graphene layer 0.1 ohm-cm
  • the binder or alumina layer resistivity p 2 l x 10 14 ohm-cm
  • lithium batteries and supercapacitors featuring the presently invented graphene oxide-bonded metal foil current collectors always exhibit a higher voltage output, higher energy density, higher power density, more stable chare- discharge cycling response, and last longer without capacity decay or corrosion issues as compared to prior art graphene-based current collectors
  • Bulk natural flake graphite is a 3-D graphitic material with each 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. In a given grain or single crystal, 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).
  • 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 different in orientation. In other words, the orientations of the various grains in a graphite particle typically differ from one grain to another.
  • a graphite single crystal (crystallite) per se is anisotropic with a property measured along a direction in the basal plane (crystallographic a- or b-axis direction) being dramatically different than the property measured along the crystallographic c-axis direction (thickness direction).
  • the thermal conductivity of a graphite single crystal can be up to approximately 1,920 W/mK (theoretical) or 1,800 W/mK (experimental) in the basal plane (crystallographic a- and b- axis directions), but that along the crystallographic c-axis direction is less than 10 W/mK
  • the multiple grains or crystallites in a graphite particle are typically all oriented along different directions. Consequently, a natural graphite particle composed of multiple grains of different orientations exhibits an average property between these two extremes (i.e. typically ⁇ 100 W/mK).
  • the constituent graphene planes (typically 30 nm - 2 ⁇ wide/long) of a graphite crystallite can be exfoliated and extracted or isolated from the graphite crystallite 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 hexagonal 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 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).
  • Graphene sheets/platelets or NGPs are a new class of carbon nano material (a 2-D nano carbon) that is distinct from the 0-D fullerene, the 1-D CNT, and the 3-D graphite.
  • Our research group pioneered the development of pristine graphene materials, isolated graphene oxide sheets, and related production processes as early as 2002: (1) B. Z. Jang and W. C. Huang, "Nano-scaled Graphene Plates," U.S. Pat. No. 7,071,258 (07/04/2006), application submitted on October 21, 2002; (2) B. Z. Jang, et al. "Process for Producing Nano-scaled Graphene Plates," U.S. Patent Application No.
  • NGPs are typically obtained by intercalating natural graphite particles 100 with a strong acid and/or oxidizing agent to obtain a graphite intercalation compound 102 (GIC) or graphite oxide (GO).
  • GIC graphite intercalation compound 102
  • GO graphite oxide
  • the presence of chemical species or functional groups in the interstitial spaces between graphene planes serves to increase the inter-graphene spacing (d 02 , as determined by X-ray diffraction), thereby significantly reducing the van der Waals forces that otherwise hold graphene planes together along the c-axis direction.
  • the GIC or GO is most often produced by immersing natural graphite powder in a mixture of sulfuric acid, nitric acid (an oxidizing agent), and another oxidizing agent (e.g.
  • the resulting GIC (102) is actually some type of graphite oxide (GO) particles.
  • This GIC or GO is then repeatedly washed and rinsed in water to remove excess acids, resulting in a graphite oxide suspension or dispersion, which contains discrete and visually discernible graphite oxide particles dispersed in water.
  • Route 1 involves removing water from the suspension to obtain "expandable graphite,” which is essentially a mass of dried GIC or dried graphite oxide particles.
  • expandable graphite essentially a mass of dried GIC or dried graphite oxide particles.
  • the GIC undergoes a rapid volume expansion by a factor of 30-300 to form “graphite worms” (104), which are each a collection of exfoliated, but largely un-separated graphite flakes that remain interconnected.
  • these graphite worms can be re-compressed to obtain flexible graphite sheets or foils (106) that typically have a thickness in the range of 0.1 mm (100 ⁇ ) - 0.5 mm (500 ⁇ ).
  • flexible graphite sheets or foils 106 that typically have a thickness in the range of 0.1 mm (100 ⁇ ) - 0.5 mm (500 ⁇ ).
  • These expanded graphite flakes may be made into a paper-like graphite mat (110).
  • Exfoliated graphite worms, expanded graphite flakes, and the recompressed mass of graphite worms are all 3-D graphitic materials that are fundamentally different and patently distinct from either the 1 -D nano carbon material (CNT or CNF) or the 2-D nano carbon material (graphene sheets or platelets, NGPs).
  • Flexible graphite (FG) foils can be used as a heat spreader material, but exhibiting a maximum in-plane thermal conductivity of typically less than 500 W/mK (more typically ⁇ 300 W/mK) and in-plane electrical conductivity no greater than 1,500 S/cm.
  • the exfoliated graphite is subjected to high-intensity mechanical shearing (e.g. using an ultrasonicator, high-shear mixer, high-intensity air jet mill, or high-energy ball mill) to form separated single-layer and multi-layer graphene sheets (collectively called NGPs, 112), as disclosed in our US Application No. 10/858,814.
  • Single-layer graphene can be as thin as 0.34 nm, while multi-layer graphene can have a thickness up to 100 nm, but more typically less than 20 nm.
  • Graphene sheets or platelets may then be made into a graphene paper or membrane (114).
  • Route 2 entails ultrasonicating the graphite oxide suspension for the purpose of separating/isolating individual graphene oxide sheets from graphite oxide particles. This is based on the notion that the inter-graphene plane separation bas been increased from 0.3354 nm in natural graphite to 0.6-1.1 nm in highly oxidized graphite oxide, significantly weakening the van der Waals forces that hold neighboring planes together. Ultrasonic power can be sufficient to further separate graphene plane sheets to form separated, isolated, or discrete graphene oxide (GO) sheets.
  • GO graphene oxide
  • RGO reduced graphene oxides
  • NGPs include discrete sheets/platelets of single-layer and multi-layer pristine graphene, graphene oxide, or reduced graphene oxide (RGO).
  • Pristine graphene has essentially 0% oxygen.
  • RGO typically has an oxygen content of 0.001%-5% by weight.
  • Graphene oxide can have 0.001%- 50% by weight of oxygen. It may be noted that flexible graphite foils (obtained by compressing or roll-pressing exfoliated graphite worms) for electronic device thermal management applications (e.g.
  • flexible graphite (FG) foils exhibit a relatively low thermal conductivity, typically ⁇ 500 W/mK and more typically ⁇ 300 W/mK. By impregnating the exfoliated graphite with a resin, the resulting composite exhibits an even lower thermal conductivity (typically « 200 W/mK, more typically ⁇ 100 W/mK).
  • Flexible graphite foils without a resin impregnated therein or coated thereon, are of low strength, low rigidity, and poor structural integrity. The high tendency for flexible graphite foils to get torn apart makes them difficult to handle in the process of making a heat sink. As a matter of fact, the flexible graphite sheets (typically 50-200 ⁇ thick) are so
  • solid NGPs including discrete sheets/platelets of pristine graphene, GO, and RGO
  • a film, membrane, or paper sheet (114) of non-woven aggregates using a paper-making process typically do not exhibit a high thermal conductivity unless these sheets/platelets are closely packed and the film/membrane/paper is ultra-thin (e.g. ⁇ 1 ⁇ , which is mechanically weak).
  • ultra-thin film or paper sheets ( ⁇ 10 ⁇ ) are difficult to produce in mass quantities, and difficult to handle when one tries to incorporate these thin films as a heat sink material.
  • a paper-like structure or mat made from platelets of graphene, GO, or RGO exhibit many defects, wrinkled or folded graphene sheets, interruptions or gaps between platelets, and non- parallel platelets (e.g. SEM image in FIG. 3(B)), leading to relatively poor thermal conductivity, low electric conductivity, and low structural strength.
  • These papers or aggregates of discrete NGP, GO or RGO platelets alone (without a resin binder) also have a tendency to get flaky, emitting conductive particles into air.
  • Another prior art graphitic material is the pyrolytic graphite film, typically thinner than 100 ⁇ . The process begins with carbonizing a polymer film (e.g.
  • This thickness-related problem is inherent to this class of materials due to their difficulty in forming into an ultra-thin ( ⁇ 10 ⁇ ) and thick film (> 100 ⁇ ) while still maintaining an acceptable degree of polymer chain orientation and mechanical strength that are required of proper carbonization and graphitization.
  • a second type of pyrolytic graphite is produced by high temperature decomposition of hydrocarbon gases in vacuum followed by deposition of the carbon atoms to a substrate surface.
  • This vapor phase condensation of cracked hydrocarbons is essentially a chemical vapor deposition (CVD) process.
  • CVD chemical vapor deposition
  • HOPG highly oriented pyrolytic graphite
  • HOPG highly oriented pyrolytic graphite
  • This entails a thermo-mechanical treatment of combined and concurrent mechanical compression and ultra-high temperature for an extended period of time in a protective atmosphere; a very expensive, energy-intensive, time-consuming, and technically challenging process.
  • the process requires ultra-high temperature equipment (with high vacuum, high pressure, or high compression provision) that is not only very expensive to make but also very expensive and difficult to maintain. Even with such extreme processing conditions, the resulting HOPG still possesses many defects, grain boundaries, and mis- orientations (neighboring graphene planes not parallel to each other), resulting in less-than- satisfactory in-plane properties.
  • the best prepared HOPG sheet or block typically contains many poorly aligned grains or crystals and a vast amount of grain boundaries and defects.
  • the most recently reported graphene thin film ( ⁇ 2 nm) prepared by catalytic CVD of hydrocarbon gas (e.g. C 2 H 4 ) on Ni or Cu surface is not a single-grain crystal, but a poly- crystalline structure with many grain boundaries and defects.
  • hydrocarbon gas e.g. C 2 H 4
  • carbon atoms obtained via decomposition of hydrocarbon gas molecules at 800-l,000°C are deposited onto Ni or Cu foil surface to form a sheet of single-layer or few-layer graphene that is poly-crystalline.
  • the grains are typically much smaller than 100 ⁇ in size and, more typically, smaller than 10 ⁇ in size.
  • graphene thin films being optically transparent and electrically conducting, are intended for applications such as the touch screen (to replace indium- tin oxide or ITO glass) or semiconductor (to replace silicon, Si).
  • the Ni- or Cu- catalyzed CVD process does not lend itself to the deposition of more than 5 graphene planes (typically ⁇ 2 nm) beyond which the underlying Ni or Cu catalyst can no longer provide any catalytic effect.
  • CVD graphene layer thicker than 5 nm is possible. Both CVD graphene film and HOPG are extremely expensive.
  • HA is an organic matter commonly found in soil and can be extracted from the soil using a base (e.g. KOH). HA can also be extracted from a type of coal called leonardite, which is a highly oxidized version of lignite coal. HA extracted from leonardite contains a number of oxygenated groups (e.g. carboxyl groups) located around the edges of the graphene- like molecular center (SP 2 core of hexagonal carbon structure). This material is slightly similar to graphene oxide (GO) which is produced by strong acid oxidation of natural graphite. HA has a typical oxygen content of 5% to 42% by weight (other major elements being carbon, hydrogen, and nitrogen).
  • GO graphene oxide
  • Non-aqueous solvents for humic acid include polyethylene glycol, ethylene glycol, propylene glycol, an alcohol, a sugar alcohol, a polyglycerol, a glycol ether, an amine based solvent, an amide based solvent, an alkylene carbonate, an organic acid, or an inorganic acid.
  • the present invention also provides a process for producing a highly oriented humic acid film (with or without externally added graphene sheets) and humic acid-derived graphitic film with a thickness from 2 nm to 30 ⁇ (more typically and preferably from 5 nm to 10 ⁇ , even more typically from 10 nm to 2 ⁇ ) and a physical density no less than 1.3 g/cm 3 (up to 2.2 g/cm 3 ).
  • This film is chemically bonded to metal foil surfaces.
  • the process comprises:
  • HA humic acid
  • CHA chemically functionalized humic acid
  • the HA or CHA dispersion further contains graphene sheets or molecules dispersed therein and the HA-to-graphene or CHA-to-graphene ratio is from 1/100 to 100/1.
  • These graphene sheets may be selected from pristine graphene, graphene oxide, reduced graphene oxide, graphene fluoride, graphene bromide, graphene iodide, boron-doped graphene, nitrogen-doped graphene, chemically functionalized graphene, or a combination thereof.
  • a metal foil e.g. a Cu foil
  • the dispensing and depositing procedure includes subjecting the dispersion to an orientation-inducing stress;
  • This orientation-controlling stress typically including a shear stress, enables the HA/CHA sheets (or sheet-like molecules) and graphene sheets (if present) to get aligned along planar directions of the metal foil substrate surface (e.g. Cu foil).
  • Proper alignment of the HA/CHA and graphene sheets is essential to the chemical linking or merging between two or multiple HA/CHA sheets, or between HA/CHA sheets and graphene sheets during subsequent heat treatments.
  • the process can comprise an additional step (e) of further heat-treating the humic acid film of merged and reduced HA or CHA at a second heat treatment temperature higher than the first heat treatment temperature for a sufficient period of time to produce a graphitic film having an inter-planar spacing doo 2 less than 0.4 nm and an oxygen content or non-carbon element content less than 5% by weight; and (f) compressing the graphitic film (e.g. against the Cu foil) to produce a highly conducting graphitic film bonded to the metal foil.
  • step (e) includes heat-treating the highly oriented humic acid film at a second heat treatment temperature higher than the first heat treatment temperature (typically > 300°C) for a length of time sufficient for decreasing an inter-plane spacing d 0 02 to a value of from 0.3354 nm to 0.36 nm and decreasing the oxygen content or non-carbon content to less than 0.5% by weight.
  • the second (or final) heat treatment temperature includes at least a temperature selected from (A) 100-300°C, (B) 300 - 1,500°C, (C) 1,500- 2,500°C, and/or (D) 2,500-3, 200°C.
  • the second heat treatment temperature includes a temperature in the range of 300 - 1,500°C for at least 1 hour and then a temperature in the range of 1,500-3,200°C for at least another hour.
  • the highly oriented humic acid (HOHA) film still contains planar molecules that are characteristic of humic acid molecules.
  • the highly oriented humic acid (HOHA) film contains chemically bonded and merged hexagonal carbon planes, which are HA/CHA or combined HA/CHA-graphene planes. These planes (hexagonal structured carbon atoms having a small amount of oxygen- containing group) are parallel to one another.
  • This HOHA film if exposed to a heat treatment temperature (HTT) of 1,500°C or higher for a sufficient length of time, typically no longer contains any significant amount of humic acid molecules and essentially all HA/CHA sheets/molecules have been converted to graphene- or graphene oxide-like hexagonal carbon planes that are parallel to one another.
  • the lateral dimensions (length or width) of these planes are huge, typically several times or even orders of magnitude larger than the maximum dimensions (length/width) of the starting HA/CHA sheets.
  • the presently invented HOHA is essentially a "giant hexagonal carbon crystal" or "giant planar graphene-like layer" having all constituent graphene-like planes being essentially parallel to one another. This is a unique and new class of material that has not been previously discovered, developed, or suggested to possibly exist.
  • the oriented HA/CHA layer (HOHA film with no HTT > 1,500°C) is itself a very unique and novel class of material that surprisingly has great cohesion power (self-bonding, self- polymerizing, and self-crosslinking capability). These characteristics have not been previously taught or hinted in the prior art.
  • Type-A current collector This type of current collector can be heat-treated up to a maximum temperature close to the melting point of the underlying metal foil.
  • certain metal foil e.g.
  • Cu, Ti, and steel appears to be capable of catalyzing the chemical linking between HA sheets or between HA and graphene, enabling the formation of larger HA/graphene domains and fewer defects and leading to higher thermal and electrical conductivity and structural integrity that otherwise could not be achieved without invoking a much higher heat treatment temperature.
  • Type-B current collector The preparation of Type-B current collector is described in the following two paragraphs:
  • the above procedures from (a) to (d) or (e), can be conducted by depositing the dispersion of HA or HA/graphene mixture onto a plastic film or glass surface and, upon liquid removal, the resulting dried film is peeled off from the plastic film or glass so that the film can be subsequently heat treated at any desired temperature.
  • the highly oriented HA film (after a heat treatment at a temperature from 80 to 1,500°C) or the derived graphitic film (after a heat treatment at a temperature from 1,500 to 3,200°C), as a free-standing film, is then bonded to one or both primary surfaces of a metal foil (e.g. Cu or Al foil) using a binder resin or adhesive.
  • Type-B current collector In comparison with Type-A current collector (wherein the highly oriented HA film or highly conducting graphitic film derived therefrom is prepared by directly depositing the thin film of HA or HA/graphene to a surface of a metal foil and chemically bonding to this surface without using a binder), such a Type-B current collector (obtained at a comparable final heat treatment temperature) has a lower in-plane thermal conductivity, lower in-plane electrical conductivity, higher contact resistance between layers, and less durable (easier to get
  • binder materials that are more conducting than the typical binder resins (e.g. PVDF, SBR, etc. commonly used in lithium battery and supercapacitor industries). These include intrinsically conductive polymers (e.g. polyaniline, polypyrrole, polythiophene, etc.), pitch (e.g. isotropic pitch, meso-phase pitch, etc.), amorphous carbon (e.g. via chemical vapor infiltration), or a carbonized resin (heat-treating the current collector after the free-standing graphitic layer is bonded to the metal foil, converting resing binder to carbon binder in situ).
  • PVDF polyaniline
  • polypyrrole polypyrrole
  • polythiophene etc.
  • pitch e.g. isotropic pitch, meso-phase pitch, etc.
  • amorphous carbon e.g. via chemical vapor infiltration
  • a carbonized resin heat-treating the current collector after the free-standing graphitic layer is bonded to the metal foil,
  • Step (a) entails dispersing HA/CHA sheets or molecules in a liquid medium, which can be water or a mixture of water and an alcohol, for certain HA or CHA molecules that contain a significant amount of -OH and/or -COOH groups at the edges and/or on the planes of the HA/CHA sheets (e.g. having an oxygen content between 20% and 47% by weight, preferably between 30% and 47%).
  • a liquid medium which can be water or a mixture of water and an alcohol
  • the HA/CHA suspension contains an initial volume fraction of HA/CHA sheets that exceeds a critical or threshold volume fraction for the formation of a liquid crystal phase prior to step (b).
  • a critical volume fraction is typically equivalent to a HA/CHA weight fraction in the range of from 0.2% to 5.0% by weight of HA/CHA sheets in the dispersion.
  • such a range of low HA/CHA contents is not particularly amenable to the formation of the desired thin films using a scalable process, such as casting and coating.
  • the HA/CHA sheets in a liquid crystal state containing 4% to 16% by weight of HA/CHA sheets have the highest tendency to get readily oriented under the influence of a shear stress created by a commonly used casting or coating process.
  • the HA/CHA suspension is formed into a thin-film layer preferably under the influence of a shear stress that promotes a laminar flow.
  • a shearing procedure is casting or coating a thin film of HA/CHA suspension using a slot-die coating machine. This procedure is similar to a layer of polymer solution being coated onto a solid substrate.
  • the roller, "doctor's blade", or wiper creates a shear stress when the film is shaped, or when there is a relative motion between the roller/blade/wiper and the supporting substrate at a sufficiently high relative motion speed.
  • such a shearing action enables the planar HA/CHA sheets to well align along, for instance, a shearing direction.
  • a molecular alignment state or preferred orientation is not disrupted when the liquid components in the HA/CHA suspension are subsequently removed to form a well-packed layer of highly aligned HA/CHA sheets that are at least partially dried.
  • the dried layer has a high birefringence coefficient between an in-plane direction and the normal-to- plane direction.
  • the present invention includes the discovery of a facile amphiphilic self-assembly approach to fabricate HA/CHA-based thin films with desired hexagonal plane orientation.
  • HA containing 5-46% by weight of oxygen may be considered a negatively charged amphiphilic molecule due to its combination of hydrophilic oxygen-containing functional groups and a hydrophobic basal plane.
  • the functional groups can be made to be hydrophilic or hydrophobic.
  • the successful preparation of the HA/CHA films with unique hexagonal, graphene-like plane orientations does not require complex procedures. Rather, it is achieved by tailoring HA/CHA synthesis and manipulating the liquid crystalline phase formation and deformation behaviors to enable the self-assembly of HA/CHA sheets in a liquid crystalline phase.
  • the HA/CHA suspension was characterized using atomic force microscopy (AFM), Raman spectroscopy, and FTIR to confirm its chemical state. Finally, the presence of lyotropic meso-morphism of HA sheets (liquid crystalline HA phase) in aqueous solution was assessed for aqueous solution.
  • HA or CHA sheets feature high anisotropy, with monatomic or few-atom thickness (t) and normally micrometer-scale lateral width (w). According to Onsager's theory, high aspect ratio 2D sheets can form liquid crystals in dispersions, when their volume fraction exceeds a critical value:
  • HA or CHA can be made to exhibit good dispersibility in water and polar organic solvents, such as alcohol, ⁇ , ⁇ -dimethyl formamide (DMF) and NMP, due to the numerous oxygen-containing functional groups attached to its edges.
  • Naturally occurring HA e.g. that from coal
  • non-aqueous solvents for humic acid include polyethylene glycol, ethylene glycol, propylene glycol, an alcohol, a sugar alcohol, a polyglycerol, a glycol ether, an amine based solvent, an amide based solvent, an alkylene carbonate, an organic acid, an inorganic acid, or a mixture thereof.
  • HA/CHA samples were prepared using a pH-assisted selective sedimentation technique. The lateral sizes of HA/CHA sheets were assessed by dynamic light scattering (DLS) via three different measurement modes, as well as AFM.
  • DLS dynamic light scattering
  • HA/CHA liquid crystals During the investigation of HA/CHA liquid crystals we made an unexpected but highly significant discovery: The liquid crystalline phase of HA/CHA sheets in water and other solvents can be easily disrupted or destroyed with mechanical disturbances (e.g. mechanical mixing, shearing, turbulence flow, etc.). The mechanical stability of these liquid crystals can be significantly improved if the concentration of HA/CHA sheets is gradually increased to above 5%) (preferably from 5% to 16% by weight) by carefully removing (e.g. vaporizing) the liquid medium without mechanically disturbing the liquid crystalline structure.
  • concentration of HA/CHA sheets is gradually increased to above 5%) (preferably from 5% to 16% by weight) by carefully removing (e.g. vaporizing) the liquid medium without mechanically disturbing the liquid crystalline structure.
  • HA/CHA weight fraction in this range of 5-16%, HA/CHA sheets are particularly amenable to forming desired orientations during casting or coating to form thin films.
  • HA/CHA aspect ratio effect could be the structural corrugation of HA/CHA sheets in solvent as the restoring force originated from bending the sheets is much weaker than that along the sheet. It was found that the degree of HA/CHA corrugated morphology in solvent could be further enhanced if its aspect ratio is increased. This corrugated configuration will significantly affect both the intra and intermolecular interactions of HA/CHA in suspension.
  • HA/CHA sheets still contain a considerable portion of hydrophobic domains, attractive ⁇ - ⁇ interactions and van der Waals forces can be effectively overcome by adjusting the long-range electrostatic repulsive forces
  • the chemical composition of HA/CHA plays an important role in tailoring the electrostatic interaction in an aqueous or organic solvent dispersion.
  • the increase of surface charge density will lead to an increase in the strength of the electrostatic repulsion against the attractive forces.
  • the ratio of the aromatic and oxygenated domains can be easily tuned by the level of hexagonal carbon plane oxidation or chemical modification.
  • the Fourier transform infrared spectroscopy under attenuated total reflectance mode (FTIR-ATR) results of the HA/CHA indicate that oxidized species (hydroxyl, epoxy, and carboxyl groups) exist on the HA/CHA surfaces.
  • Thermogravimetric analysis (TGA) in nitrogen was used to probe the oxygen functional group density on the HA/CHA surface.
  • TGA Thermogravimetric analysis
  • XPS X-ray photoelectron spectroscopy
  • the colloidal interaction between HA sheets can be significantly influenced by the ionic strength, because the Debye screening length ( ⁇ -1) can be effectively increased by reducing the concentration of free ions surrounding HA sheets.
  • the electrostatic repulsion of the HA liquid crystal in water could decrease as the salt concentration increases. As a result, more water is expelled from the HA interlamellar space with an accompanying reduction in d spacing.
  • ionic impurities in the HA dispersions should be sufficiently removed, as it is a crucial factor influencing the formation of HA liquid crystal structure.
  • the dried HA/CHA layer may then be subjected to heat treatments.
  • a properly programmed heat treatment procedure can involve at least two heat treatment temperatures (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 at least two heat treatment temperatures (HTT) that involve an initial treatment temperature (first temperature) and a final HTT, higher than the first.
  • HTT heat treatment temperatures
  • the first heat treatment temperature is for chemical linking and thermal reduction of HA/CHA and is conducted at the first temperature of > 80°C (can be up to 1,000°C, but preferably up to 700°C, and most preferably up to 300°C). This is herein referred to as Regime 1 :
  • HA/CHA sheets are packed and chemically bonded together side by side and edge to edge to form an integrated layer of graphene oxide-like entity.
  • a HA/CHA layer primarily undergoes thermally-induced reduction reactions, leading to a reduction of oxygen content to
  • the oxygen content is essentially eliminated, typically 0.01% - 0.1%.
  • the inter-graphene spacing is reduced to down to approximately 0.3354 nm (degree of graphitization from 80% to nearly 100%), corresponding to that of a perfect graphite single crystal.
  • the graphene poly-crystal has all the graphene planes being closely packed and bonded, and all the planes are aligned along one direction, a perfect orientation. Such a perfectly oriented structure has not been produced even with the HOPG that was produced by subjecting pyrolytic graphite concurrently to an ultra-high temperature
  • the highly oriented graphene structure can achieve such a highest degree of perfection with a significantly lower temperature and an ambient (or slightly higher compression) pressure.
  • the structure thus obtained exhibits an in- plane thermal conductivity from 1,500 up to slightly >1,700 W/mK, and in-plane electrical conductivity to a range from 15,000 to 20,000 S/cm.
  • the presently invented highly oriented HA-derived structure can be obtained by heat-treating the HA/CHA layer with a temperature program that covers at least the first regime (typically requiring 1-24 hours in this temperature range), more commonly covers the first two regimes (1- 10 hours preferred), still more commonly the first three regimes (preferably 0.5-5 hours in Regime 3), and most commonly all the 4 regimes (Regime 4, for 0.5 to 2 hour, may be implemented to achieve the highest conductivity).
  • a temperature program that covers at least the first regime (typically requiring 1-24 hours in this temperature range), more commonly covers the first two regimes (1- 10 hours preferred), still more commonly the first three regimes (preferably 0.5-5 hours in Regime 3), and most commonly all the 4 regimes (Regime 4, for 0.5 to 2 hour, may be implemented to achieve the highest conductivity).
  • the HOHA having a i3 ⁇ 402 higher than 0.3440 nm reflects the presence of oxygen-containing functional groups (such as -OH, >0, and -COOH on graphene-like plane surfaces) that act as a spacer to increase the inter-graphene spacing.
  • oxygen-containing functional groups such as -OH, >0, and -COOH on graphene-like plane surfaces
  • Another structural index that can be used to characterize the degree of ordering of the presently invented HOHA-derived graphitic film 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 HOHA-derived graphitic samples 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).
  • HTT heat treatment temperature
  • some values are in the range of 0.4-0.7 if the HTT is between 1,500 and 2,500°C, and in the range of 0.7-1.0 if the HTT is between 300 and 1,500°C.
  • HA or graphene may be functionalized through various chemical routes.
  • the resulting functionalized HA or functionalized graphene (collectively denoted as Gn) may broadly have the following formula(e): [Gn] ⁇ R m
  • R is selected from S0 3 H, COOH, H 2 , OH, R'CHOH, CHO, CN, COCl, halide, COSH, SH, COOR, SR', SiR * 3 , Si(-OR-) y R 3 -y, Si(-0-SiR 2 ⁇ )OR, R", Li, A1R 2 , Hg-X, T1Z 2 and Mg-X;
  • R is hydrogen, alkyl, aryl, cycloalkyl, or aralkyl, cycloaryl, or poly(alkylether), R" is fluoroalkyl, fluoroaryl, fluorocycloalkyl, fluoroaralkyl or cycloaryl, X is halide, and Z is carboxylate or trifluoroacetate.
  • a polymer such as epoxy resin, and HA or graphene sheets can be combined to make a coating composition
  • X is halide
  • Z is carboxylate or trifluoroacetate.
  • One of the - H 2 groups may be bonded to the edge or surface of a graphene sheet and the remaining un-reacted - H 2 groups will be available for reacting with epoxy resin later.
  • Such an arrangement provides a good interfacial bonding between the HA (or graphene) sheet and the resin additive.
  • Other useful chemical functional groups or reactive molecules may be selected from the group consisting of amidoamines, polyamides, aliphatic amines, modified aliphatic amines, cycloaliphatic amines, aromatic amines, anhydrides, ketimines, diethylenetriamine (DETA), tri ethyl ene-tetramine (TETA), tetraethylene-pentamine (TEPA), polyethylene polyamine, polyamine epoxy adduct, phenolic hardener, non-brominated curing agent, non-amine curatives, and combinations thereof.
  • These functional groups are multi-functional, with the capability of reacting with at least two chemical species from at least two ends. Most importantly, they are capable of bonding to the edge or surface of graphene or HA using one of their ends and, during subsequent curing stage, are able to react with a resin at one or two other ends.
  • the above-described [Gn] ⁇ R m may be further functionalized.
  • compositions of the invention also include CHAs upon which certain cyclic compounds are adsorbed. These include compositions of matter of the formula: [Gn]— [X— RJ m
  • X is a polynuclear aromatic, polyheteronuclear aromatic or metallopolyheteronuclear aromatic moiety and R is as defined above.
  • Preferred cyclic compounds are planar. More preferred cyclic compounds for adsorption are porphyrins and phthalocyanines. The adsorbed cyclic compounds may be functionalized. Such compositions include compounds of the formula: [Gn]— [X— A a ] m
  • the functionalized HA or graphene of the instant invention can be directly prepared by sulfonation, electrophilic addition to deoxygenated GO surfaces, or metallation.
  • the graphene or HA sheets can be processed prior to being contacted with a functionalizing agent. Such processing may include dispersing the graphene or HA sheets in a solvent. In some instances the sheets may then be filtered and dried prior to contact.
  • One particularly useful type of functional groups is the carboxylic acid moieties, which naturally exist on the surfaces of HAs if they are prepared from acid intercalation route discussed earlier. If an additional amount of carboxylic acid is needed, the HA sheets may be subjected to chlorate, nitric acid, or ammonium persulfate oxidation.
  • Carboxylic acid functionalized graphene sheets are particularly useful because they can serve as the starting point for preparing other types of functionalized graphene or HA sheets.
  • alcohols or amides can be easily linked to the acid to give stable esters or amides. If the alcohol or amine is part of a di- or poly-functional molecule, then linkage through the O- or H- leaves the other functionalities as pendant groups.
  • These reactions can be carried out using any of the methods developed for esterifying or aminating carboxylic acids with alcohols or amines as known in the art. Examples of these methods can be found in G. W. Anderson, et al., J. Amer. Chem. Soc. 96, 1839 (1965), which is hereby incorporated by reference in its entirety.
  • Amino groups can be introduced directly onto graphitic fibrils by treating the fibrils with nitric acid and sulfuric acid to obtain nitrated fibrils, then chemically reducing the nitrated form with a reducing agent, such as sodium dithionite, to obtain amino-functionalized fibrils.
  • a reducing agent such as sodium dithionite
  • the aforementioned functional groups can be attached to HA or graphene sheet surfaces or edges for one or several of the following purposes: (a) for improved dispersion of graphene or HA in a desired liquid medium; (b) enhanced solubility of graphene or HA in a liquid medium so that a sufficient amount of graphene or HA sheets can be dispersed in this liquid that exceed the critical volume fraction for liquid crystalline phase formation; (c) enhanced film-forming capability so that thin film of otherwise discrete sheets of graphene or HA can be coated or cast; (d) improved capability of graphene or HA sheets to get oriented due to modifications to the flow behaviors; and (e) enhanced capability for graphene or HA sheets to get chemically linked and merged into larger or wider graphene planes.
  • the present invention also provides a rechargeable battery that contains a presently invented graphene oxide thin film-bonded metal foil as an anode current collector and/or a cathode current collector.
  • This can be any rechargeable battery, such as a zinc-air cell, a nickel metal hydride cell, a sodium-ion cell, a sodium metal cell, a magnesium-ion cell, or a magnesium metal cell, just to name a few.
  • This invented battery can be a rechargeable lithium battery containing the unitary graphene layer as an anode current collector or a cathode current collector, which lithium battery can be a lithium-sulfur cell, a lithium-selenium cell, a lithium
  • Another embodiment of the invention is a capacitor containing the current collector of the present invention as an anode current collector or a cathode current collector, which capacitor is a symmetric ultracapacitor, an asymmetric ultracapacitor cell, a hybrid
  • the present invention provides a rechargeable lithium-metal cell composed of a current collector at the anode, a lithium film or foil as the anode, a porous separator/electrolyte layer, a cathode containing a cathode active material (e.g. lithium-free V 2 0 5 and Mn0 2 ), and a current collector.
  • a current collector at the anode, a lithium film or foil as the anode, a porous separator/electrolyte layer, a cathode containing a cathode active material (e.g. lithium-free V 2 0 5 and Mn0 2 ), and a current collector.
  • Either or both the anode current collector and cathode current collector can be a HA-based current collector of the present invention (i.e. derived from highly oriented thin film of HA or a HA/graphene mixture).
  • Another example of the present invention is a lithium-ion capacitor (or hybrid supercapacitor) composed of a current collector at the anode, a graphite or lithium titanate anode, a porous separator soaked with liquid or gel electrolyte, a cathode containing a cathode active material (e.g. activated carbon having a high specific surface area), and a current collector.
  • a lithium-ion capacitor or hybrid supercapacitor
  • either or both the anode current collector and cathode current collector can be a HA-based current collector of the present invention.
  • Yet another example of the present invention is another lithium-ion capacitor or hybrid supercapacitor, which is composed of a current collector at the anode, a graphite anode (and a sheet of lithium foil as part of the anode), a porous separator soaked with liquid electrolyte, a cathode containing a cathode active material (e.g. activated carbon having a high specific surface area), and a current collector.
  • a current collector at the anode a graphite anode (and a sheet of lithium foil as part of the anode), a porous separator soaked with liquid electrolyte, a cathode containing a cathode active material (e.g. activated carbon having a high specific surface area), and a current collector.
  • a cathode active material e.g. activated carbon having a high specific surface area
  • Still another example of the present invention is a lithium-graphene cell composed of a current collector at the anode, a porous, nano-structured anode (e.g. comprising graphene sheets having high surface areas upon which returning lithium ions can deposit during cell recharge, which are mixed with surface-stabilized lithium powder particles, or having a sheet of lithium foil attached to the nano-structure), a porous separator soaked with liquid electrolyte, a cathode containing a graphene-based cathode active material (e.g. graphene, graphene oxide, or graphene fluoride sheets having high specific surface areas to capture lithium ions during cell discharge), and a cathode current collector.
  • the anode current collector and cathode current collector can be a HA-based current collector of the present invention.
  • Humic acid can be extracted from leonardite by dispersing leonardite in a basic aqueous solution (pH of 10) with a very high yield (in the range of 75%). Subsequent acidification of the solution leads to precipitation of humic acid powder.
  • leonardite was dissolved by 300 ml of double deio ized water containing 1M KOH (or NH 4 OH) solution under magnetic stirring. The pH value was adjusted to 10. The solution was then filtered to remove any big particles or any residual impurities.
  • the resulting humic acid dispersion containing HA alone or HA with the presence of graphene oxide sheets (GO prepared in Example 3 described below), was coated onto a Cu foil or Ti foil surface form a series of HA-bonded Cu foil or Ti foil films for subsequent heat treatments to obtain Type-A current collectors.
  • EXAMPLE 2 Preparation of humic acid from coal and HA-bonded metal foil current collectors
  • 300 mg of coal was suspended in concentrated sulfuric acid (60 ml) and nitric acid (20 ml), and followed by cup sonication for 2 h.
  • the reaction was then stirred and heated in an oil bath at 100 or 120°C for 24 h.
  • the solution was cooled to room temperature and poured into a beaker containing 100 ml ice, followed by a step of adding NaOH (3M) until the pH value reached 7.
  • the neutral mixture was then filtered through a 0.45-mm
  • Natural graphite from Ashbury Carbons was used as the starting material.
  • GO was obtained by following the well-known modified Hummers method, which involved two oxidation stages.
  • the first oxidation was achieved in the following conditions: 1100 mg of graphite was placed in a 1000 mL boiling flask. Then, 20 g of K 2 S 2 0 8 , 20 g of P 2 0 5 , and 400 mL of a concentrated aqueous solution of H 2 S0 4 (96%) were added in the flask. The mixture was heated under reflux for 6 hours and then let without disturbing for 20 hours at room temperature. Oxidized graphite was filtered and rinsed with abundant distilled water until a pH value > 4.0 was reached. A wet cake-like material was recovered at the end of this first oxidation.
  • the previously collected wet cake was placed in a boiling flask that contains 69 mL of a concentrated aqueous solution of H 2 S0 4 (96%).
  • the flask was kept in an ice bath as 9 g of KMn0 4 was slowly added. Care was taken to avoid overheating.
  • the resulting mixture was stirred at 35°C for 2 hours (the sample color turning dark green), followed by the addition of 140 mL of water. After 15 min, the reaction was halted by adding 420 mL of water and 15 mL of an aqueous solution of 30 wt % H 2 0 2 . The color of the sample at this stage turned bright yellow.
  • the mixture was filtered and rinsed with a 1 : 10 HC1 aqueous solution.
  • the collected material was gently centrifuged at 2700g and rinsed with deionized water.
  • the final product was a wet cake that contained 1.4 wt % of GO, as estimated from dry extracts. Subsequently, liquid dispersions of GO platelets were obtained by lightly sonicating wet-cake materials, which were diluted in deionized water.
  • water suspensions containing mixtures of GO and humic acid at various GO proportions were prepared and slot-die coated to produce thin films of various compositions.
  • the suspension after ultrasoni cation contains pristine graphene sheets dispersed in water and s surfactant dissolved therein. Humic acid was then added into the suspension and the resulting mixture suspension was further ultrasoni cated for 10 minutes to facilitate uniform dispersion and mixing. The dispersion was then coated onto Cu and Ti foil and, for comparison, onto glass and PET films, prior to heat treatments.
  • HOG highly exfoliated graphite
  • F£EG was further fluonnated by vapors of chlorine trifluoride to yield fluonnated highly exfoliated graphite (FFIEG).
  • FMIEG fluonnated highly exfoliated graphite
  • Pre-cooled Teflon reactor was filled with 20-30 mL of liquid pre-cooled C1F 3 , the reactor was closed and cooled to liquid nitrogen temperature. Then, no more than 1 g of F£EG was put in a container with holes for C1F 3 gas to access and situated inside the reactor. In 7 days a gray -beige product with approximate formula C 2 F was formed.
  • FHEG FHEG
  • an organic solvent methanol and ethanol, separately
  • an ultrasound treatment 280 W
  • 280 W ultrasound treatment
  • the dispersions were then made into thin films supported by Cu foil using comma coating.
  • the highly oriented HA films were then heat-treated to various extents to obtain highly conducting graphitic films.
  • Graphene oxide (GO), synthesized in Example 3, 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 wre obtained with graphene/urea mass ratios of 1 : 0.5, 1 : 1 and 1 : 2. and the nitrogen contents of these samples were 14.7, 18.2 and 17.5 wt. % respectively as fdetermined by elemental analysis. These nitrogenataed graphene sheets remain dispersible in water. Various amounts of HA, having oxygen contents of 20.5% to 45%, were added into the suspensions.
  • the resulting suspension of nitrogenated graphene-HA dispersions were then coated onto a plastic film substrate to form wet films, which were then dried and peeled off from the plastic film and subjected to heat treatments at various heat treatment temperatures, from 80 to 2,900°C to obtain highly oriented humic acid (HOHA) films (if final HTT ⁇ 1,500°C) or highly ordered and conducting graphitic films (if 1,500°C or higher). These films were then bonded to Ti and Cu surfaces, using a resin binder, to make Type-B current collectors. Additionally, for comparison purposes, some amounts of suspension of nitrogenated graphene-HA dispersions were also coated onto Ti and Cu foil surfaces to form wet films, which were then dried and heat-treated up to 1,500°C and 1,250°C, respectively.
  • HOHA highly oriented humic acid
  • Example 7 Preparation of nematic liquid crystals from humic acid sheets and highly conducting films produced therefrom
  • Humic acid aqueous dispersions were prepared by dispersing HA sheets in deionized water by mild sonication. Any acidic or ionic impurities in the dispersions were removed by dialysis, which is a crucial step for liquid-crystal formation.
  • a low-concentration dispersion typically 0.05-0.6 wt.% immobilized for a sufficiently long time (usually more than 2 weeks) macroscopically phase-separated into two phases.
  • the low-density top phase was optically isotropic
  • the high-density bottom phase demonstrated prominent optical birefringence between two crossed polarizers.
  • a typical nematic schlieren texture consisting of dark and bright brushes was observed in the bottom phase.
  • the compositional range for the biphase was significantly broad because of the large polydispersity of the HA molecules.
  • ionic strength and pH values significantly influence the stability of HA liquid crystals.
  • the electrostatic repulsion from the dissociated surface functional groups such as carboxylate plays a crucial role in the stability of HA liquid crystals. Thus, reducing repulsive interaction by increasing ionic strength or lowering pH values increased the coagulation of HA sheets.
  • HA sheets form a liquid crystal phase when HA sheets occupy a weight fraction of 1.1%, and the liquid crystals can be preserved by gradually increasing the concentration of HA to the range of from 6% to 16%.
  • the prepared humic acid dispersion exhibited an inhomogeneous, chocolate-milk-like appearance to the naked eye. This milky appearance can be mistaken for aggregation or precipitation of the graphene oxide but, in fact, it is a nematic liquid crystal.
  • HA suspension was peeled off from the PET film to become a free-standing film prior to heat treating. Additionally, HA suspension was also coated on Cu foil or Ti surfaces and then dried. Each film (both the free-standing film peeled off from PET and the Ti- or Cu-supported film) was then subjected to different heat treatments, which typically include a chemical linking and thermal reduction treatment at a first temperature of 80°C to 300°C for 1- 10 hours, and at a second temperature of 1,500°C-2,850°C for 0.5-5 hours. The Cu-supported film and Ti-supported film were heat-treated up to only 1,250°C and 1,500°C, respectively. With these heat treatments, also under a compressive stress, the HOHA films were transformed into highly conducting graphitic films (HOGF).
  • HOGF highly conducting graphitic films
  • the internal structures (crystal structure and orientation) of several dried HA layers (HOHA films), and the HOGF at different stages of heat treatments were investigated.
  • X-ray diffraction curves of a layer of dried HOHA prior to the heat treatment, a HOHA film thermally treated at 150°C for 5 hours, and the resultant HOGF were obtained.
  • the dried film exhibits the formation of a hump centered at 22°, indicating that it has begun the process of decreasing the inter-planar spacing, indicating the beginning of chemical linking and ordering processes.
  • the doo 2 spacing of the films has decreased to approximately 0.336, close to 0.3354 nm of a graphite single crystal.
  • the d 0 o 2 spacing of the films not bonded to metal surfaces is decreased to approximately to 0.3354 nm, identical to that of a graphite single crystal.
  • the (004) peak intensity relative to the (002) intensity on the same diffraction curve, or the 7(004)//(002) ratio, is a good indication of the degree of crystal perfection and preferred orientation of graphene planes.
  • the (004) peak is either non-existing or relatively weak, with the 7(004)//(002) ratio ⁇ 0.1, for all conventional graphitic materials heat treated at a temperature lower than 2,800°C.
  • the 7(004)//(002) ratio for the graphitic materials heat treated at 3,000-3,250°C e.g., highly oriented pyrolytic graphite, HOPG
  • HOPG highly oriented pyrolytic graphite
  • the 7(004)//(002) ratio for all tens of flexible graphite foil compacts investigated are all « 0.05, practically non-existing in most cases.
  • the 7(004)//(002) ratio for all graphene paper/membrane samples prepared with a vacuum-assisted filtration method is ⁇ 0.1 even after a heat treatment at 3,000°C for 2 hours.
  • FIG. 5(A) HOGF samples obtained by heat treating at various temperatures over a wide temperature range are summarized in FIG. 5(A). Corresponding oxygen content values are shown in FIG. 5(B). In order to show the correlation between the inter-graphene spacing and the oxygen content, the data in FIG. 5(A) and FIG. 5(B) are re-plotted in FIG. 5(C). A close scrutiny of FIG. 5(A) to FIG.5(C) indicate that there are four HTT ranges (100-300°C; 300-l,500°C; 1,500-2,000°C, and > 2,000°C) that lead to four respective oxygen content ranges and inter-graphene spacing ranges. The thermal conductivity of the HA liquid crystal-derived HOGF specimens and the
  • the resulting highly oriented HA film exhibits a thermal conductivity of 756 W/mK (from HA alone) and 1, 105 W/mK (from a HA-GO mixture), respectively. This is in stark contrast to the observed 268 W/mK of the flexible graphite foil with an identical heat treatment temperature.
  • the flexible graphite foil only shows a thermal conductivity lower than 600 W/mK.
  • the presently invented HOGF layer delivers a thermal conductivity of 1,745 W/mK for a layer derived from a mixture of HA and GO (FIG.
  • SEM scanning electron microscopy
  • TEM transmission electron microscopy
  • SAD selected-area electron diffraction
  • BF bright field
  • DF dark-field
  • FIG. 2 A close scrutiny and comparison of FIG. 2, FIG. 3(A), and FIG. 3(B) indicates that the graphene-like layers in a HOGF are substantially oriented parallel to one another; but this is not the case for flexible graphite foil and graphene oxide paper.
  • the inclination angles between two identifiable layers in the highly conducting graphitic film are generally less than 10 degrees and mostly less than 5 degrees.
  • there are so many folded graphite flakes, kinks, and mis- orientations in flexible graphite that many of the angles between two graphite flakes are greater than 10 degrees, some as high as 45 degrees (FIG. 2).
  • the mis- orientations between graphene platelets in NGP paper (FIG. 3(B)) are also high and there are many gaps between platelets.
  • the HOGF entity is essentially gap-free.
  • FIG.4 (A) shows the thermal conductivity values of the HA/GO-derived film, GO- derived film, HA suspension-derived HOGF, and flexible graphite (FG) foil, respectively, all plotted as a function of the final HTT.
  • the HA/GO liquid crystal suspension-derived HOGF appears to be superior to the GO gel- derived HOGF in thermal conductivity at comparable final heat treatment temperatures.
  • the heavy oxidation of graphene sheets in GO gel might have resulted in high defect populations on graphene surfaces even after thermal reduction and re-graphitization.
  • the presence of HA molecules seem to be capable of helping to heal the defects or bridging the gaps between GO sheets.
  • HA is one order of magnitude less expensive than natural graphite (a raw material for GO) and 2-4 orders of magnitude less expensive than GO.
  • HOPG polyimide
  • FIG. 4(B) shows the thermal conductivity values of the HA/GO suspension-derived
  • HOGF the HA suspension-derived HOGF, and the polyimide-derived HOPG, all plotted as a function of the final heat treatment temperature.
  • PI carbonized polyimide
  • the conventional HOPG produced by using the carbonized polyimide (PI) route, exhibits a consistently lower thermal conductivity as compared to the HA/GO-derived HOGF, given the same HTT for the same length of heat treatment time.
  • the HOPG from PI exhibits a thermal conductivity of 820 W/mK after a graphitization treatment at 2,000°C for 1 hour.
  • the HA/GO-derived HOGF exhibits a thermal conductivity value of 1,586 W/mK.
  • PI is also orders of magnitude more expensive than HA and the production of PI involves the use of several environmentally undesirable organic solvents.
  • the thermal conductivity is always lower than that of a HA/GO liquid crystal-derived HOGF. It is also surprising to discover that humic acid molecules are capable of chemically linking with one another to form strong and highly conducting graphitic films. It is clear that, the highly oriented HA film (including highly oriented HA/GO film), and the subsequently heat-treated versions are fundamentally different and patently distinct from the flexible graphite (FG) foil, graphene/GO/RGO paper/membrane, and pyrolytic graphite (PG) in terms of chemical composition, crystal and defect structure, crystal orientation, morphology, process of production, and properties.
  • FG flexible graphite
  • PG pyrolytic graphite
  • conductivity values of the HA/GO suspension-derived and HA suspension-derived HOGF HOGF are far superior to those of the FG foil sheets over the entire range of final HTTs investigated.
  • Example 8 The effect of graphene addition on the properties of HA-based highly oriented graphitic films and graphitic films derived therefrom
  • FIG. 7(A) For comparison, some tensile strength data of RGO paper and flexible graphite foil are also summarized in FIG. 7(A).
  • the HA/GO and HA dispersion contains highly oriented/aligned, chemically active HA/GO and HA sheets/molecules that are capable of chemical linking and merging with one another during the heat treatment, while the graphene platelets in the conventional GO paper and the graphite flakes in the FG foil are essentially dead platelets.
  • the HA or HA/GO-based highly oriented films and the subsequently produced graphitic films is a new class of material by itself.
  • the film obtained by simply spraying HA-solvent solution onto a glass surface and drying the solvent, does not have any strength (it is so fragile that you can break the film by simply touch the film with a finger). After heat treating at a temperature > 100°C, this film became fragmented (broken into a huge number of pieces).
  • the highly oriented HA film (wherein all HA molecules or sheets are highly oriented and packed together), upon heat treatment at 150°C for one hour, became a film of good structural integrity, having a tensile strength > 24 MPa.
  • Example 10 The novel effect of metal foil on heat-induced chemical linking of humic acid molecules
  • Shown in FIG.8 are the thermal conductivity values of three HA-derived highly oriented films.
  • the first one was obtained by heat-treating a HA film peeled off from a glass surface.
  • the second one was coated on Ti surface and the film was bonded to Ti surface during the heat- treatment.
  • the third one was coated on a Cu foil surface and was bonded to the Cu foil surface during the heat treatment.
  • the metal foil-supported HA films exhibit significantly higher thermal conductivity values as compared to those of the films peeled off from PET film surface prior to heat treating.
  • the Cu and Ti foil appear to be capable of providing some kind of catalytic effect on the heat-induced chemical linking or merging between humic acid molecules in intimate contact with Cu or Ti. This is truly unexpected.
  • Example 11 Li-S Cell Containing a Humic Acid-Bonded Metal Foil Current Collector at the Anode and at the Cathode
  • Li-S cells Three (3) Li-S cells were prepared and tested, each one having a lithium foil as the anode active material, a sulfur/expanded graphite composite (75/25 wt. ratio) as the cathode active material, 1M of LiN(CF 3 S02)2 in DOL as the electrolyte, and a Celgard 2400 as the separator.
  • the first cell (a baseline cell for comparison) contains a 10- ⁇ thick Cu foil as the anode current collector and a 20- ⁇ thick Al foil as the cathode current collector.
  • the second cell (another baseline cell for comparison) has a 10- ⁇ thick GO-resin layer as the anode current collector and a sheet of 14- ⁇ RGO-coated Al foil as the cathode current collector.
  • the third cell has a HA-bonded Cu foil (totally 12- ⁇ thick) of the present invention as the anode current collector and a sheet of a 20- ⁇ thick HA-coated Al foil as the cathode current collector.
  • Charge storage capacities were measured periodically and recorded as a function of the number of cycles.
  • the specific discharge capacity herein referred to is the total charge inserted into the cathode during the discharge, per unit mass of the composite cathode (counting the weights of cathode active material, conductive additive or support, and the binder, but excluding the current collectors).
  • the specific energy and specific power values presented in this section are based on the total cell weight (including anode and cathode, separator and electrolyte, current collectors, and packaging materials).
  • the morphological or micro-structural changes of selected samples after a desired number of repeated charging and recharging cycles were observed using both transmission electron microscopy (TEM) and scanning electron microscopy (SEM).
  • FIG. 9(A) shows the discharge capacity values of the three cells each as a function of the charge/discharge cycle number.
  • Each cell was designed to have an initial cell capacity of 100 mAh to facilitate comparison. It is clear that the Li-S cell featuring the presently invented HA- bonded current collector at both the anode and the cathode exhibits the most stable cycling behavior, experiencing a capacity loss of 6% after 50 cycles.
  • the cell containing GO/resin- coated Cu and GO-coated Al current collector suffers from a 23% capacity decay after 50 cycles.
  • the cell containing a Cu foil anode current collector and an Al foil cathode current collector suffers from a 26% capacity decay after 50 cycles. Post-cycling inspection of the cells indicate that the Al foil in all prior art electrodes suffered a severe corrosion problem. In contrast, the presently invented humic acid oxide-bonded Al current collectors remain intact.
  • FIG. 9(B) shows the Ragone plots (gravimetric power density vs. gravimetric energy density) of the three cells. It is of interest to note that our HA-bonded metal foil current collectors surprisingly impart both higher energy density and higher power power density to the Li-S cell compared to prior art graphene/resin-coated current collector at the anode (with GO- coated Al foil at the cathode), and Cu/Al current collectors. This is quite unexpected considering that Cu foil has an electrical conductivity that is more than one order of magnitude higher than that of the graphene film and HA film.
  • Example 12 Magnesium-Ion Cell Containing a HA-enabled Current Collector at the Anode and at the Cathode
  • a cathode active material Magnetic Manganese Silicate, Mgi.03Mn 0. 7SiO 4
  • the starting materials were magnesium oxide (MgO), manganese (II) carbonate (MnC0 3 ) and silicon dioxide (Si0 2 , 15-20 nm) powder.
  • the stoichiometric amounts for the precursor compounds were controlled with the molar ratio of 1.03 :0.97: 1 for Mg:Mn:Si.
  • the electrodes were typically prepared by mixing 85 wt% of an electrode active material (e.g. Mg 1.03 Mn 0 .9 7 SiO 4 particles, 7 wt% acetylene black (Super- P), and 8 wt% polyvinylidene fluoride binder (PVDF, 5 wt % solid content dissolved in N- methyl-2-pyrrolidinoe ( MP)) to form a slurry-like mixture. After coating the slurry on an intended current collector, the resulting electrode was dried at 120°C in vacuum for 2 h to remove the solvent before pressing.
  • an electrode active material e.g. Mg 1.03 Mn 0 .9 7 SiO 4 particles, 7 wt% acetylene black (Super- P), and 8 wt% polyvinylidene fluoride binder (PVDF, 5 wt % solid content dissolved in N- methyl-2-pyrrolidinoe ( MP)
  • PVDF polyvinylidene flu
  • first cell having HA-bonded Cu foil and HA-bonded Al foil as the anode and cathode current collectors, respectively; second cell having GO/resin-coated Cu foil and GO- coated Al foil (no pre-etching) as the anode and cathode current collector, respectively (a prior art cell); third cell having a Cu foil anode current collector and Al foil cathode current collector (a prior art cell).
  • a thin sheet of magnesium foil was attached to the anode current collector surface, and a piece of porous separator (e.g., Celgard 2400 membrane) was, in turn, stacked on top of the magnesium foil.
  • a piece of cathode disc coated on a cathode current collector was used as a cathode and stacked over the separator layer to form a CR2032 coin-type cell.
  • the electrolyte used was 1 M of Mg(AlCl 2 EtBu) 2 in THF.
  • the cell assembly was performed in an argon-filled glove-box.
  • the CV measurements were carried out using a CHI-6 electrochemical workstation at a scanning rate of 1 mV/s.
  • the electrochemical performance of the cells was also evaluated by galvanostatic charge/discharge cycling at a current density of from 50 mA/g to 10 A/g (up to 100 A/g for some cells), using an Arbin and/or a LAND electrochemical workstation.
  • FIG. 10 shows the cell discharge specific capacity values of the three cells each as a function of the charge/discharge cycle number.
  • Example 13 Chemical and Mechanical Compatibility Testing of Various Current Collectors for Various Intended Batteries or Supercapacitors
  • each current collector must be connected to a tab that is, in turn, connected to an external circuit wire.
  • the current collector must be mechanically compatible with the tab, being readily or easily fastened or bonded thereto.
  • CVD graphene films just cannot be mechanically fastened to the tab without being easily broken or fractured. Even with the assistance of adhesive, the CVD film is easily fractured during the procedures of connecting to a tab or battery cell packaging.

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Abstract

Cette invention concerne un collecteur de courant à feuille métallique lié à de l'acide humique dans une batterie ou un super-condensateur, comprenant : (a) une feuille métallique mince ayant deux surfaces principales opposées mais parallèles ; et (b) un film mince d'acide humique (HA) ou un mélange de HA et de graphène, ayant des plans de carbone hexagonaux, l'HA ou le HA et le graphène étant chimiquement liés à au moins l'une des deux surfaces principales, le film mince ayant une épaisseur de 10 nm à 10 µm, une teneur en oxygène de 0,01 à 10 % en poids, un espacement entre plans de 0,335 à 0,50 nm entre des plans de carbone hexagonaux, une densité physique de 1,3 à 2,2 g/cm3, tous les plans de carbone hexagonaux étant orientés sensiblement parallèlement les uns aux autres et parallèles aux surfaces principales, présentant une conductivité thermique supérieure à 500 W/mK, et/ou une conductivité électrique supérieure à 1500 S/cm lorsqu'elle est mesurée sans la feuille métallique.
PCT/US2017/018708 2016-08-22 2017-02-21 Collecteur de courant à film de feuille métallique lié à de l'acide humique et batterie et super-condensateur le contenant WO2018038764A1 (fr)

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KR1020197007640A KR20190040261A (ko) 2016-08-22 2017-02-21 휴믹산-결합 금속 포일 필름 집전체 및 이를 함유한 배터리 및 슈퍼커패시터
CN201780060219.2A CN109792055B (zh) 2016-08-22 2017-02-21 结合腐殖酸的金属箔膜集流体以及含有其的电池和超级电容器

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US15/243,589 US10014519B2 (en) 2016-08-22 2016-08-22 Process for producing humic acid-bonded metal foil film current collector
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US15/243,606 US10597389B2 (en) 2016-08-22 2016-08-22 Humic acid-bonded metal foil film current collector and battery and supercapacitor containing same
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CN115732702A (zh) * 2022-12-06 2023-03-03 武汉理工大学 一种高导热集流体及基于该集流体的高安全性锂离子电池

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KR102495668B1 (ko) * 2020-11-02 2023-02-06 포항공과대학교 산학협력단 2차원 물질의 액정상을 이용한 나노시트 제조 방법

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CN115732702A (zh) * 2022-12-06 2023-03-03 武汉理工大学 一种高导热集流体及基于该集流体的高安全性锂离子电池

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