WO2017134653A1 - Tissu de nanotubes de carbone utilisé comme collecteur de courant d'électrode dans une batterie lithium-ion - Google Patents

Tissu de nanotubes de carbone utilisé comme collecteur de courant d'électrode dans une batterie lithium-ion Download PDF

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Publication number
WO2017134653A1
WO2017134653A1 PCT/IL2017/050109 IL2017050109W WO2017134653A1 WO 2017134653 A1 WO2017134653 A1 WO 2017134653A1 IL 2017050109 W IL2017050109 W IL 2017050109W WO 2017134653 A1 WO2017134653 A1 WO 2017134653A1
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fabric
cnt
electrode
μιη
carbon nanotubes
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PCT/IL2017/050109
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English (en)
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Yair Ein-Eli
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Technion Research & Development Foundation Limited
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-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
    • 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
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/32—Carbon-based
    • H01G11/36—Nanostructures, e.g. nanofibres, nanotubes or fullerenes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/50—Electrodes characterised by their material specially adapted for lithium-ion capacitors, e.g. for lithium-doping or for intercalation
    • 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
    • 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
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention in some embodiments thereof, relates to material and electrochemical sciences, and more particularly, but not exclusively, to a lightweight and highly conductive carbonaceous material.
  • Li-ion batteries are powering portable electronic devices, ranging from small- scale electronic devices to electric vehicles, due to their high energy density and long cycle life. There is a growing need for a battery flexibility and shape adaptation in order to meet the consumers' needs and demands.
  • the positive and negative active materials are coated onto metal foils current collectors,
  • Li-ion battery typically copper (about 13 mg/cm ) at the anode and aluminum (about 5- 10 mg/cm ) at the cathode, whereas the copper anode current collector is considered as the heavy and costly one.
  • the active materials in Li-ion battery account for only less than 55 % of the total weight, while the copper current collector alone, is responsible for about 10 % of the total cell's weight.
  • CNT fabric is most suitable and a key component in the growing market of thin, flexible energy storage devices for emerging foldable electronic devices [Landi, B.J. et al., Energy Environ. Sci., 2009, 2, pp. 638-654] .
  • the SEI layer is composed of mixed Li+ ion organic and inorganic salts formed because of electrolyte's components reduction.
  • the SEI layer contains various products, such as inorganic Li-salts L1 2 CO 3 , LiF and other Li-carbonaceous (organic) compounds originating from the first charging process of the battery. This is an energy consuming process, which causes irreversible capacity loss, since Li ions are exhausted from the cathode containing material and are consumed at the anode side for the SEI build-up and thus, do not contribute to the overall battery capacity.
  • Graphene/CNT composite “paper” was reported as a candidate for current collector material in anodes of Li-ion batteries [Yuhai, H. et al., J. Power Sources, 2013, 237, pp. 41-46] .
  • the CNTs are randomly dispersed between the graphene sheets (GNS), and hence the hybrid papers exhibit high mechanical strength and flexibility even after being annealed at 800 °C.
  • Electrochemical properties of the hybrid papers are strongly dependent on the CNT/GN ratios. Highest lithium ion storage capacities were obtained in the paper with a CNT/GN ratio of 2: 1.
  • the initial reversible specific capacities are about 375 mAh g _1 at 100 mA g _1 ; however, this material did not performed acceptably in a rechargeable cell due to exceedingly high first irreversible capacity of 75 % to 100 %.
  • U.S. Patent No. 8,785,053 discloses a current collector that includes a support and at least one carbon nanotube layer.
  • the support includes two surfaces, and the carbon nanotube layer is located on one of the two surfaces of the support, namely at least one CNT layer is located on one of two surfaces.
  • the carbon nanotube layer includes a number of uniformly distributed carbon nanotubes.
  • a lithium ion battery includes a cathode electrode and an anode electrode, and at least one of the cathode electrode and the anode electrode includes the disclosed current collector.
  • U.S. Patent No. 9,005,807 discloses a bipolar secondary battery current collector having electrical conductivity, and an expansion section that expands in a thickness direction of the current collector at a temperature equal to or higher than a prescribed temperature, wherein the bipolar plate current collectors are made of composite polymers.
  • U.S. Patent No. 9,331,362 discloses a battery that includes an electrode having an active medium on a current collector.
  • the active medium includes one or more active materials
  • the current collector includes or consists of carbon nanotubes immobilized on a collector support. The electrical conductivity and weight of carbon nanotubes permit the weight of the battery to be reduced while the energy density and the power density of the battery are increased.
  • U.S. Patent No. 9,537,153 discloses a current collector for a lithium electrochemical accumulator that includes an electronically-insulating viscoelastic foam associated with an electroconductive polymer film.
  • U.S. Patent Application Publication No. 20150311532 discloses cathodes containing active materials and carbon nanotubes, whereas the use of carbon nanotubes in cathode materials can provide a battery having increased longevity and volumetric capacity over batteries that contain a cathode that uses conventional conductive additives such as carbon black or graphite.
  • U.S. Patent No. 8,734,996 discloses an anode of a lithium battery that includes a supporting member and a carbon nanotube woven film disposed on a surface of the support member.
  • the semi-woven carbon nanotube film is a cross ⁇ stacked CNT sheet that includes at least two overlapped and intercrossed layers of unidirectional carbon nanotubes, wherein each layer includes a plurality of successive carbon nanotube bundles aligned in the same direction.
  • the rather complex and costly method for fabricating the provided anode includes (a) providing an array of carbon nanotubes; (b) pulling out, by using a tool, at least two carbon nanotube films from the array of carbon nanotubes; and (c) providing a supporting member and disposing the carbon nanotube films to the supporting member along different directions and overlapping with each other to achieving the anode of lithium battery.
  • Additional exemplary prior art documents include U.S. Patent Nos. 9,001,495, 8,734,996, 9,257,704, 8,790,826, 8,911,905, 8,492,029, 8,017,272, 8,822,059, 8,956,765, 8,859, 165, 9,276,260, 8,974,967, 9,105,932, 8,810,995, 9,325,041, 9,397,330, 9,269,959, 8,252,069, 9,350,028, 8,475,961, 9,537,151, 7,061,749, 8,679,677, 8,861, 183, 7,531,267, 8,597,832, 6,703, 163, 8,518,229, 9, 105,921, 9,397,341, 8,007,650, 7, 108,773, 8,920,979, 7,993,794, 8,526,166, 9,455,469, 8,802,304, 8,415,072, 7,029,794, 8,603, 195, 9,118,084, 8,709,
  • a light-weight, flexible and highly conductive free-standing fabric comprising carbon nanotube is provided herewith, suitable for serving as a current collector in Li- ion batteries.
  • the CNT fabric may be also coated with a thin metal layer on one or two faces thereof, while maintaining its light weight and flexibility, and increasing its conductivity and compatibility with the chemistry of a Li-ion battery.
  • an electrode which includes a current collector and an active material disposed thereon, wherein the current collector includes a carbon nanotubes (CNT) fabric, the carbon nanotubes fabric is unilamellar.
  • the carbon nanotubes fabric is a treated CNT fabric.
  • the carbon nanotubes fabric is a free-standing fabric.
  • the carbon nanotubes fabric is a non-woven fabric characterized by a non-directional CNT structure.
  • the carbon nanotubes fabric is characterized by a conductance of at least 2.5xl0 5 S per m ( ⁇ ).
  • the carbon nanotubes fabric is characterized by a density of at least 0.5 grams per cm .
  • the carbon nanotubes fabric is having a thickness that ranges from 1 ⁇ to 30 ⁇ .
  • the carbon nanotubes fabric is having an average thickness greater than 4 ⁇ .
  • the carbon nanotubes fabric is characterized by a
  • the carbon nanotubes fabric is characterized by a
  • the carbon nanotubes fabric is characterized by a conductance of at least 2.5x105 S per m and is having a thickness that ranges from 1 ⁇ to 30 ⁇ .
  • the carbon nanotubes fabric is characterized by at least one of:
  • a thickness that ranges from 1 ⁇ to 30 ⁇ ; and is coated with a metal layer over at least one surface thereof, the metal layer is less than 2 ⁇ thick.
  • the metal layer is less than 1 ⁇ thick.
  • any of the treated CNT fabrics presented herein is further coated with a metal layer over at least one surface thereof.
  • the metal layer is less than 2 ⁇ thick. In some embodiments, the metal layer is less than 1 ⁇ thick.
  • any of the treated CNT fabrics presented herein is coated with a metal layer over a top surface and a bottom surface thereof (composite metal- CNT-metal "sandwich").
  • the metal is selected from the group consisting of copper, aluminum, gold and platinum.
  • the electrode presented herein is an anode. In some embodiments, the electrode presented herein is a cathode.
  • the electrode presented herein forms a part of an electrochemical cell.
  • an electrochemical cell that includes an electrode as presented herein.
  • the electrochemical cell is a lithium ion battery.
  • an electrical device that includes an electrochemical cell as presented herein, wherein the electrochemical cell includes an electrode as presented herein, and the electrode includes a current collector based on a treated and optionally metal coated CNT fabric, as presented herein.
  • the electrical device presented herein is selected from the group consisting of a disposable electric power source device, a rechargeable electric power source device, a portable electric power source device, a terrestrial vehicle, an aerial vehicle, a marine vehicle, a space vehicle, a satellite, a computer, a cellular device, a camera, a detector, a robotic system and an illumination device.
  • a flexible light-weight material comprising a unilamellar carbon nanotubes fabric fabricated so as to exhibit a conductance of at least 2.5xl0 5 S per m, wherein the fabric is characterized by a density of at least 0.5 grams per cm .
  • the carbon nanotubes fabric of the material is coated with a metal layer over at least one surface thereof.
  • the carbon nanotubes fabric of the material is coated with a metal layer over a top surface and a bottom surface thereof.
  • the metal layer on the carbon nanotubes fabric of the material is less than 2 ⁇ thick. In some embodiments, the layer is less than 1 ⁇ thick.
  • the metal optionally coating the CNT fabric of the material presented herein is selected from the group consisting of copper, aluminum, gold and platinum.
  • a process of manufacturing the material presented herein includes: contacting a pristine carbon nanotubes fabric with an organic solvent; and removing the organic solvent from the fabric by drying, to thereby obtain a flexible light-weight material that includes a unilamellar carbon nanotubes fabric that is characterized by a conductance of at least 2.5xl0 5 S per m, and a density of at least 0.5 grams per cm 3 .
  • the process further includes, subsequent to the removing, heating the solvent-contacted CNT fabric.
  • the process further includes, subsequent to the heating step, repeating at least once a cycle that includes the solvent contacting, the removal of the solvent and the heating steps, sequentially.
  • the organic solvent is an alcohol
  • the alcohol is represented by general Formula I:
  • each of R4-R 3 is independently an alkyl or H, and at least two of R4-R 3 is a Ci_6 linear or branched alkyl.
  • At least one of R 1 -R 3 is a C 2 -6 branched alkyl.
  • each of R 1 -R 3 a C 1-6 linear or branched alkyl.
  • each of R 1 -R 3 a Ci_ 6 is methyl (CO.
  • At least one of R 1 -R 3 is further substituted by one of more hydroxyl (-OH) group.
  • the alcohol is selected from the group consisting of isopropyl alcohol, propylene glycol, butane-2,3-diol, 2-methylbutane-2,3-diol, t- butanol, 2,3,4-trimethylpentan-3-ol, 3-methylpentane-l,2-diol, hexane-3,4-diol and any mixture thereof.
  • the alcohol is isopropyl alcohol and/or t-butanol (each used alone or in a mixture).
  • the IPA:tBuOH mixture is a 20:80 mixture, respectively.
  • the process further includes, subsequent to the removal of the solvent or the heating step, if present, coating at least one surface of the fabric with a metal layer.
  • the metal coating is effected by any method known in the art, such as electroless deposition in acidic media, electroless deposition in alkaline media, electroplating, physical vapor deposition, chemical vapor deposition, ion plating, thin-film deposition, and sputtering.
  • FIGs. 1A-E present micrographs of the MCMB graphite active material layer loaded on the surface of the CNT fabric, wherein FIG. 1A is a top view SEM image of the layer, and FIGs. 1B-E are HR-SEM cross section images of the continuous MCMB layers obtained on-top of the surfaces of about 10 ⁇ Cu foil (FIG. IB), about 5-10 ⁇ CNT fabric (FIG. 1C), about 50 ⁇ CNT fabric (FIG. ID), and about 120 ⁇ CNT fabric (FIG. IE);
  • FIGs. 2A-H present HRSEM micrographs of a conductive CNT fabric, according to some embodiments of the present invention, showing a pristine CNT fabric as received and having original thickness of about 5-10 ⁇ (FIG. 2A), after washing the CNT fabric in water (FIG. 2B, after washing in acetone (FIG. 2C), after washing in methanol (FIG. 2D), after washing in ethanol (FIG. 2E), after washing in propanol (FIG. 2F), after washing in isopropanol (IPA) (FIG. 2G), and after washing in IPA and heating at 250 °C in ambient air atmosphere for 6 hours (FIG. 2H);
  • FIGs. 3A-B present FIB cross section micrographs of a pristine-as received CNT fabric (FIG. 3A), and after IPA washing (FIG. 3B);
  • FIGs. 4A-B present plots of slow scan cyclic voltammetries (SSCV) measurements conducted in a cell comprising a CNT fabric current collector, according to some embodiments of the present invention, or a Cu foil current collector, wherein FIG. 4A presents the 1 st cycle and the inset therein presents a close view of the SEI formation peak, and FIG. 4B presents the 3 cycle, whereas experiments were conducted in 3 electrodes cells at a scan rate of 5 ⁇ s "1 ; Li metal serves as both counter and reference electrodes; FIGs. 5A-C present plots of charge-discharge profiles measured in carbon vs. Li metal half-cells, wherein FIG.
  • SSCV slow scan cyclic voltammetries
  • FIG. 5A shows a first and second cycle charge-discharge profiles of a cell comprising 5 ⁇ CNT fabrics, having been pre-treated, according to some embodiments of the present invention, as active material and as current collector (no MCMB material was loaded)(capacity is expressed in mAh g "1 and is related only to the mass of the CNT fabric)
  • FIG. 5B shows first charge-discharge profiles of half-cells (graphite vs. Li metal) analysis measured with different pre-treatments to the CNT fabric current collector (originally 5- 10 ⁇ ) while a cell utilizing Cu foil current collector is presented as a standard for comparison (capacity is expressed in mAh g "1 and is related only to the mass of the loaded graphite)
  • FIG. 5C shows capacity retention profile for cells utilizing IPA washed 5- 10 ⁇ CNT fabric current collector compared in the inset with data collected from cells utilizing Cu foil as a current collector;
  • FIGs. 6 A-E present HRSEM micrographs of samples of CNT fabric surface, as taken before and after densification treatment, according to some embodiments of the present invention, wherein FIG. 6A shows top view of a pristine (as received, untreated) CNT fabric; FIG. 6B shows FIB cross section of a pristine CNT tissue, FIG. 6C shows top view of a CNT fabric after immersion and drying in isopropanol (IPA), FIG. 6D shows FIB cross section of a CNT fabric after bundling and densification in IPA (immersion and heating to 250 °C), FIG. 6E shows a top view of a CNT fabric after immersion and drying in 80:20 tBuOH IPA, and FIG. 6F shows a cross section of a CNT tissue after bundling and densification in 80:20 tBuOH:IPA;
  • IPA isopropanol
  • FIG. 6E shows a top view of a CNT fabric after immersion and drying in 80:20 t
  • FIG. 7 A presents first cycle charge-discharge profiles of half-cell (graphite vs. Li metal) recorded with different thicknesses of CNT fabric as the current collectors.
  • Cell utilizing Cu foil current collector in half-cell configuration is presented for comparison, wherein the inset shows a close view of the SEI formation "step";
  • FIG. 7B presents a summary of the accumulated reversible and the consumed irreversible capacities associated with the utilization of CNT' s current collector fabrics, wherein the capacity is expressed in mAh g "1 and is related only to the mass of the loaded graphite;
  • FIG. 8 presents a schematic illustration of coating of a CNT fabric with thin layers of copper to afford a composite structure, according to some embodiments of the present invention, that can serve as a replacement of copper current collector in Li-ion batteries, wherein a presently known copper foil current collector is presented on the right side, and an exemplary Cu-coated CNT fabric, according to embodiments of the present invention, is depicted on the right being used as a Li-ion battery anode configuration;
  • FIG. 9 presents plots of the potentiodynamic profiles of a 90 ⁇ thick CNT fabric electrode in copper sulfate and copper pyrophosphate electrolytes, whereas the inset presents the potential-time transients obtained from the CNT fabric electrode exposed at OCP in the two copper ion solutions;
  • FIGs. 10A-B present current- time transient plots for copper electrodeposition obtained from CNT fabric electrode polarized to a several applied potentials in an acid copper solution (FIG. 10A), and an alkaline copper solution (FIG. 10B);
  • FIGs. 11A-J present HRSEM micrographs of top view of copper nucleation and deposition at different cathodic potentials, in an acid copper electrolyte for a period of 60 sec, wherein FIGs.11 A-B are of nucleation and deposition at -20 mV, FIGs.11 C-D at -70 mV, FIGs.11 E-F at -120 mV, FIGs.11 G-H at - 170 mV, and FIGs.11 I-J at -220 mV;
  • FIGs. 12A-I present HRSEM micrographs of top view of copper nucleation and deposition at different potentials, in an alkaline copper electrolyte for a period of 60 sec, wherein FIG. 12A is of nucleation and deposition at -20 mV, FIGs. l2B-C at -70 mV, FIGs. 12D-E at - 120 mV, FIGs. 12F-G at - 170 mV, and FIGs.12H-I at -220 mV;
  • FIGs. 13A-F present results of copper electrodeposition on a CNT fabric, wherein FIG. 13 A shows a current-time transient profile obtained from copper electrodeposition on a CNT fabric in a copper sulfate electrolyte at a potential of -0.28 V, FIG. 13B shows a copper pyrophosphate electrolyte at a potential of -1.3V, FIG. 13C shows a surface morphology, FIG. 13D shows a cross section of a copper layer deposited from a copper sulfate electrolyte, FIG. 13E shows a surface morphology, and FIG. 13F shows a cross section of a copper layer deposited from a copper pyrophosphate electrolyte;
  • FIGs. 14A-D present results of cathodic behavior of the CNT fabrics in two electrolytic baths, whereas potentiodynamic profiles of CNT tissues having different thicknesses obtained from a copper sulfate electrolyte (FIG. 14A), a copper pyrophosphate electrolyte (FIG. 14A), wherein the insets present potential-time transients for the different thickness of CNT fabrics electrodes exposure at OCP, and further show surface morphology of the deposited copper layer onto a 90 ⁇ CNT tissue in a copper sulfate solution (-0.28 V) (FIG. 14C) and in the inset copper crystals decorating the coarse copper grains, and a copper pyrophosphate (-1.3 V) (FIG. 14D) and in the inset a crater zoom-in showing a continuous Cu film deposited onto the CNT tissue tracking morphology changes; and
  • FIGs. 15A-B show cyclic voltammetry scans obtained from a tree-electrode cell having Li metal serving as both counter and reference electrodes
  • FIG. 15A shows a slow scan cyclic voltammetry (SSCV) measurement (scan rate of 5 ⁇ s "1 at the 3 cycle) obtained from the 5 ⁇ Cu-coated CNT fabric electrodeposited from a copper sulfate electrolyte
  • FIG. 15B shows 2 nd galvanostatic (0.1 mA cm "2 ) charge- discharge profiles of half-cells (MCMB graphite vs. Li metal) analysis measured with a Cu coated CNT fabric and a Cu foil current collector and: 1 st cycle in the inset, whereas capacity is expressed in mAh g "1 and is related only to the mass of the loaded graphite.
  • SSCV slow scan cyclic voltammetry
  • the present invention in some embodiments thereof, relates to material and electrochemical sciences, and more particularly, but not exclusively, to a lightweight and highly conductive carbonaceous material.
  • the present inventor has surprisingly found that a single layered (unilamellar), non-woven free-standing CNT fabric, which is treated by soaking or washing in certain organic solvents, and particularly certain alcohols, is rendered more conductive and thus more suitable for use as a current collector.
  • the microstructural and chemical properties of the treated CNT fabrics is particularly suitable to electrode current collectors in Li-ion batteries, in that these treated CNT fabrics exhibit minimal irreversible first cycle loss of capacity.
  • Electrodes having CNT fabric as a current collector are not necessarily limited in its application to the details set forth in the following description or exemplified by the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways. Electrodes having CNT fabric as a current collector:
  • an electrode which includes a current collector and an active material disposed thereon, wherein the current collector comprises a unilamellar carbon nanotubes (CNT) fabric.
  • the electrode is an anode, and in some embodiments the electrode is a cathode, each having an anode- suitable active material or a cathode-suitable active material disposed thereon, respectively.
  • the electrodes presented herein may serve as electrodes of an electrochemical cell, including primary batteries, secondary (rechargeable) batteries, metal-air batteries, and any other type of battery.
  • electrochemical cell refers to a device capable of storing and generating electrical energy from chemical reactions, or facilitating chemical reactions through the introduction of electrical energy.
  • the electrodes presented herein are particularly useful as anodes and/or cathodes of Li-ion batteries, as these electrochemical cells are known in the art.
  • fabric refers to an essentially two-dimensionally shaped material made from fibrous elements and resembles cloth.
  • the term “fabric” may be used interchangeably with the term “tissue” to refer to a single layered cloth made of CNT filaments, strands or bundles.
  • the CNTs in the fabric take the role of fibers, and are characterized by a high aspect ratio, namely the length of an individual CNT is hundreds and/or thousands of times greater than the diameter of an individual CNT.
  • the term CNT fabric refers to a non-woven fabric comprising or consisting of CNT.
  • unilamellar refers to a fabric having a single layer or lamella of CNTs, namely the fabric is not made of several distinguishable layers or lamellas stacked one over the other, and but is rather made of a uniform bulk thin film.
  • the fabric is further non-woven and thus characterized by a non-directional CNT structure.
  • non-woven fabrics are broadly defined as sheet or web structures bonded together by mechanical entanglement of fibers or filaments, which may or may not be reinforced by thermal and/or chemical bonding.
  • non-woven fabrics are flat sheets that are made directly from separate filaments or fibers, without any steps or processes of weaving or specific directional arrangement of the fibers.
  • the non-directionality of the CNTs in the unilamellar, non-woven, felt-like fabric is advantageous for exhibiting isotropic electrical and mechanical properties at least in the plane of the fabric, which may be referred to as the X and Y axes of the fabric.
  • the CNT fabric is a free-standing sheet-like structure.
  • free-standing refers to a fabric which is not bound to a substrate or any other form of support, and can be handled as any other staple fabric.
  • the active material disposed over the unilamellar CNT fabric presented herein can be any anode or cathode active material, as these are known in the art.
  • Exemplary anode active materials of a Li-ion battery include, without limitation, natural graphite, artificial graphite, amorphous-based carbon, silicon, silicon dioxide, elemental (red and black) phosphorous, tin and its oxides, and other active materials as known in the art.
  • Exemplary cathode active materials of a Li-ion battery include, without limitation, lithium nickel cobalt aluminum oxide (LiNiCoA10 2 ) and its derivatives, lithium nickel cobalt manganese oxide (LiNiCoMn0 2 ) and its derivatives, lithium iron phosphate (LiFeP0 4 ), lithium manganese oxide (LiMn 2 0 4 ) and its derivatives, lithium cobalt oxide (LiCo0 2 ), LiMn 1.5 Nio.5O t.
  • Exemplary cathode active materials of Li metal primary and rechargeable batteries include Mn0 2 , copper oxides, and elemental sulfur.
  • the electrode presented herein may further include binder materials that assist in adhering the active material to the CNT fabric.
  • electrode binders include styrene butadiene copolymer (SBR), polyvinylidene fluoride (PVDF), poly-tetra-fluoro-ethylene (PTFE, TeflonTM), ethylene propylene diene monomers (EPDM) rubber, CMC (carboxy-methyl cellulose), polyacrylic acid and its alkaline salts derivatives, and polycarboimide, and any mixtures thereof.
  • the CNT fabric is made suitable for serving as an effective current collector in battery electrode by a treatment (process) discussed hereinbelow.
  • a CNT fabric which has not undergone the required process is referred to herein as a "pristine CNT fabric", and the CNT fabric which has been treated is referred to simply as “CNT fabric” or "treated CNT fabric”.
  • CNT fabric or "treated CNT fabric”.
  • the unilamellar CNT fabric presented herein is capable of serving as an effective current collector due to its notably improved conductance compared to the pristine fabric, which is presumably associated with its notably higher density, compared to the pristine fabric.
  • the electric conductance of the treated CNT fabric is at least 2.5xl0 5 S per m, or 2.5xl0 5 ⁇ conductance units.
  • the electric conductance of the treated CNT fabric is greater than 1.5xl0 5 ⁇ , 2xl0 5 ⁇ , 2.5xl0 5 ⁇ , 3xl0 5 ⁇ , 3.5xl0 5 ⁇ , or greater than 4xl0 5 ⁇ .
  • This level of electric conductivity is notably higher than the conductance of a comparably shapes and sized pristine CNT fabric, which is about 8.4 xlO 4 S per m for a 10 ⁇ thick pristine CNT fabric.
  • the density of the CNT fabric is at least 0.5 grams per cm .
  • the density of the treated CNT fabric is
  • the conductance of the CNT fabric correlates to the density of the fabric, and the density of the fabric is somewhat dependent of the thickness of the pristine CNT fabric which is used to produce the treated CNT fabric.
  • the average thickness of the unilamellar treated CNT fabric presented herein ranges from 1 micron to 30 microns.
  • the average thickness of the unilamellar treated CNT fabric is greater than 1 ⁇ , 2 ⁇ , 3 ⁇ , 4 ⁇ , 5 ⁇ , 6 ⁇ , 7 ⁇ , 8 ⁇ , 9 ⁇ , 10 ⁇ , 15 ⁇ , 20 ⁇ , 25 ⁇ , 30 ⁇ , 35 ⁇ , 40 ⁇ , 45 ⁇ , or greater than 50 ⁇ .
  • a unilamellar, nonwoven, free-standing carbon nanotubes fabric having an average width of 4-5 ⁇ , represents the width of about 200 individual CNTs stacked tightly one on top of the other.
  • the average thickness of the CNT fabric presented herein is greater than the width of a stack of 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300 or more single-CNT-thick layers.
  • the increased density of the CNT fabric increases the electric conductance of the fabric such that it is more suitable for serving as a current collection in electrodes of batteries.
  • the present inventor has successfully added a thin layer of a metal on the surface of a treated CNT fabric.
  • the resulting composite metal-coated-CNT fabric exhibited exceptional performance as efficient current collectors in secondary Li-ion batteries, as demonstrated in the Examples section that follows below.
  • the CNT fabric is metal-coated on one side (surface) thereof, or metal-coated both top and bottom sides (surfaces) thereof.
  • a composite metal-coated CNT fabric having a layer of metal on both sides thereof is referred to herein as a metal-CNT-metal "sandwich".
  • the metal layer disposed on the surface(s) of the treated CNT fabric is sufficiently thin so as not to limit the flexibility of the CNT fabric, and still not to increase its weigh to the weight of an all-metal functionally comparable current collector presently used in Li-ion batteries.
  • the weight of a copper coated CNT fabric having an original thickness of 5-6 microns and having a 1 micron thick copper coat on each side is about 2.2 mg per cm , which is less than 25 % of the functionally comparable 10 microns copper foil, currently being used in commercial Li- ion cells.
  • the average thickness of a single metal layer, disposed over one surface of the CNT fabric presented herein is less than 0.1 ⁇ , 0.2 ⁇ , 0.3 ⁇ , 0.4 ⁇ , 0.5 ⁇ , 0.6 ⁇ , 0.7 ⁇ , 0.8 ⁇ , 0.9 ⁇ , 1 ⁇ , 2 ⁇ , 3 ⁇ , 4 ⁇ , or less than 5 ⁇ thick.
  • the metal coating the CNT fabric is selected from the group consisting of copper, aluminum, gold and platinum; however, other metals are also contemplated within the scope of the present invention.
  • the CNT fabric is coated on top and bottom surfaces thereof by a thin layer of copper, having an average thickness of about 1 micron.
  • an electrode that includes a current collector and an active material disposed thereon, wherein the current collector comprises a carbon nanotubes fabric coated with a layer of a metal.
  • the carbon nanotubes fabric is a unilamellar fabric, and having the properties presented hereinabove.
  • a flexible light-weight material comprising a carbon nanotubes fabric and having a conductance of at least 2.5xl0 5 S per m and a density of at least 0.5 grams per cm .
  • the flexible light-weight material presented herein is a free-standing sheet-shaped structural element, as described in the foregoing.
  • the flexible light-weight material presented herein is based on a carbon nanotubes fabric which is coated with a layer of a metal over at least one surface thereof, and the metal layer is as described in the foregoing.
  • the CNT fabric of the flexible light-weight material presented herein is coated with a layer of a metal over a top surface and a bottom surface thereof, and the metal layers are as described in the foregoing.
  • an electrical device that is capable of storing, producing or is powered by electricity, comprising an electrochemical cell that includes at least one electrode based on or comprising a CNT fabric, as provided herein.
  • the electrical device may be any one of a disposable electric power source device, a rechargeable electric power source device, a portable electric power source device, a terrestrial vehicle, an aerial vehicle, a marine vehicle, a space vehicle, a satellite, a computer, a cellular device, a camera, a detector, a robotic system, and/or an illumination device.
  • a process of manufacturing the flexible and light-weight material comprising a carbon nanotubes fabric as described in the foregoing includes:
  • the process further includes, subsequent to the removal of the organic solvent, heating the fabric.
  • the heating serves to further remove residues of the organic solvent and/or to facilitate in the densification of the pristine CNT fabric.
  • the process further includes, subsequent to the removal of the organic solvent, and the optional heating of the fabric, reiterating the cycle of contacting with the solvent and heating the fabric sequentially. This reiteration may be repeated once, twice or more.
  • the organic solvent is an alcohol.
  • the alcohol is represented by general formula I:
  • each of R4-R 3 is independently an alkyl or H, and at least two of R4-R 3 is a Ci-6 linear or branched alkyl.
  • At least one of R 1 -R 3 is a C 2 -6 branched alkyl.
  • each of R 1 -R 3 a Ci_ 6 linear or branched alkyl. In some embodiments, each of R 1 -R 3 a Ci_ 6 is methyl (CO.
  • At least one of R 1 -R 3 is further substituted by one of more hydroxyl (-OH) group.
  • alkyl refers to an all aliphatic hydrocarbon residue which can be linear, branched or cyclic.
  • Non-limiting examples of alcohols suitable in the context of preparing the CNT fabric presented herein include, isopropyl alcohol (IPA), propylene glycol, butane-2,3- diol, 2-methylbutane-2,3-diol, t-butanol (tBuOH)), 2,3,4-trimethylpentan-3-ol, 3- methylpentane- l,2-diol, hexane-3,4-diol and any mixture thereof.
  • the alcohol is isopropyl alcohol and/or t-butanol in a mixture.
  • the alcohol in cases the alcohol is not a liquid at room temperature, the alcohol maybe molten at elevated temperatures, up to 250-300 °C or higher, as long as the CNT fabric is not damaged at the elevated temperature.
  • the alcohol may be mixed with another organic solvent so as to obtain a liquid solution wherein the alcohol is at a concentration ranging from 50 % to 99 %.
  • the alcohol can be heated and mixed with another organic solvent to afford a liquid CNT fabric treatment media.
  • the process of manufacturing the flexible and light-weight material presented herein further includes, subsequent to the foregoing treatment with an organic solvent, , coating at least one surface of the CNT fabric with a layer of a metal.
  • the metal layer can be deposited on the treated CNT fabric by any method known in the art, including electroless deposition (plating) in acidic media, electroless deposition (plating) in alkaline media, electroplating, physical vapor deposition, chemical vapor deposition, ion plating, thin-film deposition, and sputtering.
  • CNT-based current collector It is expected that during the life of a patent maturing from this application many relevant CNT -based current collectors will be developed and the scope of the term CNT- based current collector is intended to include all such new technologies a priori.
  • compositions, method or structure may include additional ingredients, steps and/or parts, but only if the additional ingredients, steps and/or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.
  • the phrases “substantially devoid of” and/or “essentially devoid of” in the context of a certain substance refer to a composition that is totally devoid of this substance or includes less than about 5, 1, 0.5 or 0.1 percent of the substance by total weight or volume of the composition.
  • the phrases "substantially devoid of” and/or “essentially devoid of” in the context of a process, a method, a property or a characteristic refer to a process, a composition, a structure or an article that is totally devoid of a certain process/method step, or a certain property or a certain characteristic, or a process/method wherein the certain process/method step is effected at less than about 5, 1, 0.5 or 0.1 percent compared to a given standard process/method, or property or a characteristic characterized by less than about 5, 1, 0.5 or 0.1 percent of the property or characteristic, compared to a given standard.
  • exemplary is used herein to mean “serving as an example, instance or illustration”. Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments and/or to exclude the incorporation of features from other embodiments.
  • a compound or “at least one compound” may include a plurality of compounds, including mixtures thereof.
  • range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.
  • process and “method” refer to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of the chemical, material, mechanical, computational and digital arts.
  • alkyl describes an aliphatic hydrocarbon including straight chain and branched chain groups.
  • the alkyl group may exhibit 1 to 20 carbon atoms, and preferably 8-20 carbon atoms. Whenever a numerical range; e.g., "1-20", is stated herein, it implies that the group, in this case the alkyl group, may contain 1 carbon atom, 2 carbon atoms, 3 carbon atoms, etc., up to and including 20 carbon atoms.
  • the alkyl can be substituted or unsubstituted, and/or branched or unbranched (linear).
  • the substituent can be, for example, an alkyl, an alkenyl, an alkynyl, a cycloalkyl, an aryl, a heteroaryl, a halo, a hydroxy, an alkoxy and a hydroxyalkyl as these terms are defined herein.
  • alkyl also encompasses saturated or unsaturated hydrocarbon, hence this term further encompasses alkenyl and alkynyl.
  • alkenyl describes an unsaturated alkyl, as defined herein, having at least two carbon atoms and at least one carbon-carbon double bond.
  • the alkenyl may be branched or unbranched (linear), substituted or unsubstituted by one or more substituents, as described herein.
  • alkynyl is an unsaturated alkyl having at least two carbon atoms and at least one carbon-carbon triple bond.
  • the alkynyl may be branched or unbranched (linear), and/or substituted or unsubstituted by one or more substituents, as described herein.
  • alicyclic and cycloalkyl refer to an all-carbon monocyclic or fused ring (i.e., rings which share an adjacent pair of carbon atoms), branched or unbranched group containing 3 or more carbon atoms where one or more of the rings does not have a completely conjugated pi-electron system, and may further be substituted or unsubstituted.
  • the cycloalkyl can be substituted or unsubstituted by one or more substituents, as described herein.
  • aryl describes an all-carbon aromatic monocyclic or fused-ring polycyclic (i.e., rings which share adjacent pairs of carbon atoms) groups having a completely conjugated pi-electron system.
  • the aryl group may be substituted or unsubstituted.
  • Substituted aryl may have one or more substituents as described for alkyl herein.
  • heteroaryl describes a monocyclic or fused ring (i.e., rings which share an adjacent pair of atoms) group having in the ring(s) one or more atoms, such as, for example, nitrogen, oxygen and sulfur and, in addition, having a completely conjugated pi-electron system.
  • Representative examples of heteroaryls include, without limitation, furane, imidazole, indole, isoquinoline, oxazole, purine, pyrazole, pyridine, pyrimidine, pyrrole, quinoline, thiazole, thiophene, triazine, triazole and the like.
  • the heteroaryl group may be substituted or unsubstituted as described for alkyl herein.
  • halo refers to -F, -CI, -Br or -I.
  • hydroxy refers to an -OH group.
  • alkoxy and hydroxy alkyl refer to a -OR group, wherein R is alkyl. It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.
  • modified CNT fabrics were used to construct a current of an anode in a Li battery.
  • the CNT fabric treatment in, for example, IPA, followed the procedure described below:
  • CNT fabrics were obtained and used as received from Tortech Nano-Fibers Ltd., Israel, or washed with isopropyl alcohol (IPA) and dried at ambient air atmosphere.
  • IPA isopropyl alcohol
  • MCMB meso-carbon micro-beads graphite powder
  • NMP N-methyl- 2-pyrrolidone
  • FIGs. 1A-E present micrographs of the MCMB graphite active material layer loaded on the surface of the CNT fabric, wherein FIG. 1A is a top view SEM image of the layer, and FIGs. 1B-E are HR-SEM cross section images of the continuous MCMB layers obtained on-top of the surfaces of about 10 ⁇ Cu foil (FIG. IB), about 5- 10 ⁇ CNT fabric (FIG. 1C), about 50 ⁇ CNT fabric (FIG. ID), and about 120 ⁇ CNT fabric (FIG. IE).
  • a continuous layer of about 15 ⁇ spherical particles films were obtained on-top of the surfaces of the flexible CNT fabrics (5- 120 ⁇ in thickness) and the Cu current collectors.
  • FIGs. 2A-H present HRSEM micrographs of a conductive CNT fabric, according to some embodiments of the present invention, showing a pristine CNT fabric as received and having original thickness of about 5- 10 ⁇ (FIG. 2A), after washing the CNT fabric in water (FIG. 2B, after washing in acetone (FIG. 2C), after washing in methanol (FIG. 2D), after washing in ethanol (FIG. 2E), after washing in propanol (FIG. 2F), after washing in isopropanol (IPA) (FIG. 2G), and after washing in IPA and heating at 250 °C in ambient air atmosphere for 6 hours (FIG. 2H).
  • the pristine CNT fabric appears as a web of elongated curved continuous nanotubes having 20-30 nm width.
  • Immersing the fabrics in different solvents water, ethanol, methanol, acetone, propanol and iso-propanol
  • FIG. 2A the pristine CNT fabric appears as a web of elongated curved continuous nanotubes having 20-30 nm width.
  • Immersing the fabrics in different solvents water, ethanol, methanol, acetone, propanol and iso-propanol
  • FIG. 2E When ethanol was used (FIG. 2E), CNT bundles appear in some areas on the fabric and this effect is intensified when propanol was used (FIG.
  • FIGs. 3A-B present FIB cross section micrographs of a pristine-as received CNT fabric (FIG. 3A), and after IPA washing (FIG. 3B).
  • Loosening of the bundled CNT's in the fabric is partially possible via a thermal treatment, weakening the adhesive forces: upon heating the IPA treated fabric, (possessing elongated bundled CNT's), some areas are reconstructed back to the original pristine fabric structure and thickness, while other zones maintained their dense and bundled characteristics, as shown in FIG. 2H.
  • This phenomena suggests that densification of the bundles and the thinning of the CNT fabric is afforded by an alcohol assisted annealing process, suggesting that a repeated heat-cool treatment may lead to even tighter and more compact (dense) fabric.
  • Two-electrode configuration T-cell type were assembled in order to study the CNT fabric current collector.
  • Cells were constructed inside an Argon filled glovebox using the MCMB coated onto CNT fabric as the working electrode, a glass microfiber separator (Whatman), and Li metal foil (Sigma-Aldrich) as a counter electrode.
  • Cu copper
  • Arbin BT2000 battery test system For comparison analysis, copper (Cu) current collector (about 10 ⁇ thickness) loaded with the same MCMB weight and composition were used. Charge-discharge cycles experiments were performed at a current density of 0.1 mA cm " at room temperature, using an Arbin BT2000 battery test system.
  • FIGs. 4A-B present plots of slow scan cyclic voltammetries (SSCV) measurements conducted in a cell comprising a CNT fabric current collector, according to some embodiments of the present invention, or a Cu foil current collector, wherein FIG. 4A presents the 1 st cycle and the inset therein presents a close view of the SEI formation peak, and FIG. 4B presents the 3 cycle, whereas experiments were conducted in 3 electrodes cells at a scan rate of 5 ⁇ s "1 ; Li metal serves as both counter and reference electrodes.
  • SSCV slow scan cyclic voltammetries
  • the plot reveals a broaden reduction peak at 0.7-1 V for the cell assembled with CNT fabric as a current collector, according to some embodiments of the present invention.
  • this peak is also presented in the SSCV originating from the cell utilizing Cu current collector; albeit, this peak is quite minimal.
  • This peak is related to the formation of the electrically insulating SEI layer on the surface of the CNT fabric, since no oxidation peak in the reverse direction appears.
  • the formation of the SEI layer on graphite surface in this voltage range is well known; furthermore, it has been shown previously that SEI is formed also on the surface of carbon nanotubes.
  • the layer on the composite CNT anode material originated from the access of electrolyte to both the MCMB graphite and the CNT fabric surface area, where it is being reduced and transformed into Li-salts, as electrolyte's decomposition products. Due to the relatively large surface area of the long carbon nanotubes, the layer formation process is noticeable in the SSCV plot. As can be seen in FIGs. 4A-B, presenting for example the third SSCV cycle, all cathodic and anodic peaks related to complete Li-ions intercalation/de-intercalation processes are clearly present in both half-cells. This result demonstrates that the CNT fabric can function as the current collector for Li + intercalation/de-intercalation processes while free from the adverse effects of SEI layer formation.
  • FIGs. 5A-C present plots of charge-discharge profiles measured in carbon vs. Li metal half-cells, wherein FIG. 5A shows a first and second cycle charge-discharge profiles of a cell comprising 5 ⁇ CNT fabrics, having been pre-treated, according to some embodiments of the present invention, as active material and as current collector (no MCMB material was loaded)(capacity is expressed in mAh g "1 and is related only to the mass of the CNT fabric), FIG. 5B shows first charge-discharge profiles of half-cells (graphite vs.
  • FIG. 5C shows capacity retention profile for cells utilizing IPA washed 5- 10 ⁇ CNT fabric current collector compared in the inset with data collected from cells utilizing Cu foil as a current collector.
  • the intercalation/de-intercalation process was substantiated by the 67+2.9 % reversible capacity obtained at the second cycle, and by a linear shape of the charge curve that has been also reported previously for CNT.
  • the smoothly varying curve is related to the presence of multiple sites for lithium ions. Nonetheless, results show that the CNT fabric is less suitable to serve as the major active material; the high active surface area of the CNT causes an enormous irreversible capacity of 88+0.5 % at the first cycle.
  • Li ions can intercalate to the inner core of the CNT and into the outer surfaces of the nanotubes, while de-intercalation is possible only from the nanotubes outer surfaces.
  • Li ions intercalated into the inner core of the nanotubes do not de-intercalate and therefore, contribute to a high irreversible capacity value.
  • Copper foil and untreated CNT fabric were used as current collector for comparison purposes as presented hereinabove.
  • Galvanostatic curves obtained during the first charge-discharge cycles (Li-ion intercalation and de-intercalation, respectively) are shown in FIG. 5B and summarized in Table 2.
  • Table 2 presents a summary of the reversible and irreversible capacities associated with the utilization of the Cu foil, the as receives CNT fabric and the treated CNT fabrics current collectors.
  • the acetone washed CNT fabric current collector did not show any decreasing in the irreversible capacity (about 116+4.8 mAh g "1 , equivalent to about 32+1.1 %), while ethanol washed CNT fabric current collector showed a minor reduction of the irreversible capacity (about 70+5.5 mAh g "1 , equivalent to about 19+1.3 %).
  • This irreversible capacity is related to the potential step observed at around 0.8 V (well observed also in the SSCV, shown in FIGs.
  • Irreversible loss of capacity is considered to be a fundamental obstacle en route to achieving practical application of CNT fabric in lithium-based electrical storage devices.
  • reducing the irreversible capacity of the CNT fabric is a prime challenge that is mitigated by the high-density CNT fabrics provided herein.
  • the use of IPA washed CNT fabric reduces the irreversible capacity (about 13+1.3 %) to a value comparable to the irreversible capacity recorded for a copper current collector cell (14+1.1 %), and demonstrates high reversibility during cycling, as presented in FIG. 5C.
  • the recorded reversible capacity during 30 cycles between 1.5 to 0.02 V vs.
  • Li/Li+ shows highly stable and efficient cycling, even when compared to a "traditional" cell utilizing a Cu foil current collector, as seen in the inset of FIG. 5C.
  • IPA washing not only removes organic residues from the CNT fabric, as being naturally anticipated, but also changes the surface morphology of the CNT fabric. Thus, IPA washing seems as a beneficial step toward an implementation of a stable CNT fabric in a light-weight, flexible high energy density advanced Li-ion batteries.
  • the reversible capacity recorded for the IPA treated CNT current collector remarkablyd to as high as about 305+3.3 mAh g "1 , compared with about 230+2.9 and about 280+2.7 mAh g "1 recorded for the cell utilizing pristine CNT and copper foil as current collectors, respectively. It is suggested that the CNT fabric takes an active role in the Li + intercalation/de-intercalation process and therefore, contributes to a higher reversible capacity values than the capacity recorded for the copper foil coated graphite electrode.
  • Tert-butanol (t-butanol; tBuOH) exhibits three methyl moieties that can contribute to the binding and strapping capabilities of neighboring tubes. Since t- butanol is a solid at room temperature (melting point of about 25 °C), it was mixed with 20 % by volume of IPA to form a CNT fabric washing solution. The obtained surface morphology, after treating the CNT fabric with T-butanol (20 % IPA) is shown in FIGs 6E-F.
  • FIGs. 6 A-E present HRSEM micrographs of samples of CNT fabric surface, as taken before and after densification treatment, according to some embodiments of the present invention, wherein FIG. 6A shows top view of a pristine (as received, untreated)
  • FIG. 6B shows FIB cross section of a pristine CNT tissue
  • FIG. 6C shows top view of a CNT fabric after immersion and drying in isopropanol (IPA)
  • FIG. 6D shows FIB cross section of a CNT fabric after bundling and densification in IPA (immersion and heating to 250 °C)
  • FIG. 6E shows a top view of a CNT fabric after immersion and drying in 80:20 tBuOH IPA
  • FIG. 6F shows a cross section of a
  • FIGs. 6A-F a more pronounce bundling effect has been observed using t-butanol.
  • the web of elongated curved continuous nano-tubes seems to create an aligned structure of bundles on the surface of the CNT fabric.
  • a significant densification of the fabric was observed, reflected in a reduction of the total thickness of the sample from 5-10 ⁇ to 2-3 ⁇ .
  • the densification is vividly demonstrated in the cross sectional image (FIG. 6F), showing a denser structure of the tBuOH-treated fabric relatively to the IPA-treated fabric (FIG. 6D), particularly near the exterior (top/bottom) surfaces.
  • the CNT volumetric density analysis was conducted by the following procedure:
  • the highly conductive CNT fabric material was characterized by ultra-light weight. It is noted herein that following the treatment with IPA, the electrical conductivity as well as the density of the CNT fabric increased with CNT fabric thinning, as shown in Table 3. Table 3
  • IPA treatment includes immersing the CNT fabric in IPA, withdrawing it from the solvent and allowing it to dry at ambient atmosphere.
  • the pristine CNT fabric appears as a web of disoriented continuous curved nanotubes, with an average diameter of 20-30 nm. Fe residues are also detected on the CNT surface, since they are used as the catalytic precursor in the manufacture procedure.
  • a notable densification and reduction in the CNT fabric thickness was observed, due to an overall surface CNT bundling.
  • the densification of the CNT fabric, induced by IPA treatment is demonstrated in the cross section images of the pristine and IPA treated CNT fabrics presented in FIG. 6B and FIG. 6D, respectively.
  • this densification phenomenon is being ascribed to a merging of neighboring tubes due to enhanced capillary forces.
  • the effect is intensified with IPA owing to its molecular structure, having two methyl moieties to connect two neighboring CNTs.
  • a substantial support to this assumption is given once IPA is being replaced by tBuOH, exhibiting three methyl groups.
  • tBuOH would act on three neighboring tubes.
  • the use of the tBuOH allows the formation of a complete compact and densified CNT fabric surface, as shown in FIG. 6E and FIG. 6F.
  • FIG. 7 A presents first cycle charge-discharge profiles of half-cell (graphite vs. Li metal) recorded with different thicknesses of CNT fabric as the current collectors.
  • Cell utilizing Cu foil current collector in half-cell configuration is presented for comparison, wherein the inset shows a close view of the SEI formation "step";
  • FIG. 7B presents a summary of the accumulated reversible and the consumed irreversible capacities associated with the utilization of CNT' s current collector fabrics, wherein the capacity is expressed in mAh g "1 and is related only to the mass of the loaded graphite.
  • Table 5 presents a summary of the reversible and irreversible capacities associated with the utilization of the Cu foil and different CNT thickness current collectors.
  • This phenomenon is likely to be directly related to a substantially lower surface area of the thin CNT fabric that can interact with the electrolyte, forming the SEI layer.
  • a very thick CNT fabric (about 120 ⁇ ) demonstrated the highest reversible capacity, higher than the theoretical one for a graphitic anode (372 mAh g "1 ). This is probably related to the capability of the CNT to accommodate Li-ion, as was shown in FIG. 5A.
  • the weight per area of the current collector is 9- 13 mg cm "
  • the CNT fabric is in a thickness of less than 5 ⁇ (in, for example, its IPA-treated form the thickness stands on only 3-5 ⁇ ) and has a weight per area of less than 0.3 mg cm " .
  • CNT fabric current collector can save up to 97 % of the current collector weight and therefore, improves Li-ion gravimetric energy density significantly.
  • the above-presented improvement, afforded by the modified CNT fabric current collectors, according to embodiments of the present invention, allows loading more active anode MCMB and cathode materials per the free volume being cleared, due to the substantial minimization in the anode current collector thickness. It is also suggested that the CNT fabric is electroactive and has an active role in Li+ intercalation/de-intercalation. This phenomenon is well observed when a thick and dense CNT fabric (for example, in the 120 ⁇ CNT fabric) is utilized as a current collector.
  • Copper electrodeposited CNT fabrics as anode current collectors in Li-ion battery A distinct electrodeposition of copper on the external surface of CNT fabrics has been demonstrated in two copper electrolytic baths: acid copper sulfate (pH 0.5) and alkaline copper pyrophosphate (pH 8.6). Copper nucleation and growth on the CNT fabric was investigated while applying cathodic polarizations and current transients in a single-step and cost-effective processes. The established copper films were characterized with high uniformity, planarity and excellent adhesion to the densified and bundled CNT fabric substrates, while the surface morphology varies with the chemical composition of the electrolytic bath. In addition, the capability of the copper- coated CNT fabrics to function as anode current collectors in a Li-ion battery was shown below.
  • CNT-copper composite materials exhibit 100 times higher current carrying capacity than common electrical conductors, such as Cu and Au [Subramaniam; C. et al., Nature Communications, 2013, Vol. 4] .
  • Other researches presented CNT reinforced copper nanocomposites, fabricated by electroless deposition process, presenting homogeneous distribution of the CNTs in the metal matrix that enhances both physical and mechanical properties [Walid, D.M. et al., Materials Science & Engineering A, 2009, 513, pp.247- 253] .
  • the example below presents a simple single-step electrochemical process, enabling the fabrication of layered CNT-Cu composite structures, obtaining an electrical conductivity, which is one order of magnitude higher than pristine CNT fabric.
  • this example presents the capabilities to distinctively electrodeposit a thin Cu film on the exterior surface of the CNT fabrics.
  • the simple and cost effective process permits a deposition of uniform copper films, particularly over the CNT fabric in acid or alkaline aqueous solutions.
  • Copper nucleation and growth on the CNT fabric was investigated in cathodic polarization and current transient experiments.
  • the study presents the cathodic electrochemical behavior of CNT fabric electrodes in both acid and alkaline aqueous Cu solutions, Cu distinct nucleation and growth on the CNT fabric, as well as the characteristics of the obtained copper thin layer on various CNT fabrics possessing different thicknesses and densities.
  • this working example demonstrates the ability of the Cu coated CNT fabrics to function as Li-ion battery anode current collector.
  • the layered Cu-CNT-Cu composite structure can function as a conductive material in various applications.
  • a Li-ion battery as the copper coated CNT fabric may be a fine substitution to the heavy 10-12 ⁇ commercial Cu foil current collector, being used in presently known Li-ion cells.
  • the Cu-CNT-Cu sandwich fabrics is therefore highly conductive, having substantial lower densities than copper.
  • the thin copper layers on the external (side) surfaces of the CNT fabric would allow higher conductivity, relatively to a bare CNT fabric current collector (about 106 vs.
  • FIG. 8 presents a schematic illustration of coating of a CNT fabric with thin layers of copper to afford a composite structure, according to some embodiments of the present invention, that can serve as a replacement of copper current collector in Li-ion batteries, wherein a presently known copper foil current collector is presented on the right side, and an exemplary Cu-coated CNT fabric, according to embodiments of the present invention, is depicted on the right being used as a Li-ion battery anode configuration.
  • CNT fabrics were obtained from Tortech Nano-Fibers Ldt. (Israel). Prior to any use, the fabrics were washed with isopropyl alcohol (IPA) or IPA-tBuOH mixture, followed by drying in ambient air, as discussed and presented hereinabove.
  • IPA isopropyl alcohol
  • IPA-tBuOH IPA-tBuOH
  • the electrochemical measurements related to the copper plating were performed with a PARSTAT 2273a potentiostat (EG&G) in a three-electrode electrochemical cell equipped with a saturated calomel reference electrode (SCE) and a Pt-wire counter electrode.
  • the reference electrode was installed in the solution through a Luggin-Haber capillary tip assembly. All the potentials presented and discussed in the electrochemical measurements are vs. SCE.
  • the application of the three-layered Cu-CNT-Cu sandwich composite structure as a battery current collector was performed by casting with doctor blade a graphite slurry [90 % MCMB graphite (Targray): 10 % polyvinyldene fluoride (PVDF, Aldrich) binder] onto the coated CNT.
  • the casted film was dried in a vacuum oven at a temperature of 120 °C for 2 hours.
  • Charge-discharge cycles of ⁇ CNT-Cu/graphite ⁇ /Li metal half-cells were carried out at a current density of 0.1 mA cm " at room temperature using an Arbin BT2000 battery test system.
  • Copper electrodeposition over the CNT fabric electrode surface was performed in an acid sulfate solution containing Cu +2 ions and in an alkaline pyrophosphate solution containing the complex [Cu(P 2 0 7 ) 2 ] 6 ions.
  • Cathodic polarization studies of copper deposition on a 90 ⁇ CNT fabric electrode were performed in the two electroplating baths. The cathodic behavior of the CNT electrodes upon immersion in the two solutions is shown in FIG. 9.
  • FIG. 9 presents plots of the potentiodynamic profiles of a 90 ⁇ thick CNT fabric electrode in copper sulfate and copper pyrophosphate electrolytes, whereas the inset presents the potential-time transients obtained from the CNT fabric electrode exposed at OCP in the two copper ion solutions.
  • the cathodic current onset for the CNT fabric electrode in the alkaline electrolyte is initiated at -0.13 V, a more negative potential than the +0.20 V, detected for the acid electrolyte.
  • the acid copper sulfate solution presents an onset in the cathodic currents at 0.2 V.
  • the cathodic current increases and reaches the maximal current value with a peak at -0.15 V.
  • the reaction responsible for the peak is represented by Eq. 1, below: Eq. 1: Cu +2 + 2e ⁇ ⁇ Cu
  • the onset of the cathodic current in this solution is located more negatively, at a potential value near -0.13 V.
  • the current increases and reaches values of about 8 mA cm " at potentials below -0.9 V.
  • the increase in the current densities values at potentials below -0.7 V in the acid electrolyte, and below -1.0 V in the alkaline solution, is associated with an accelerated hydrogen evolution rates.
  • FIGs. 10A-B present current- time transient plots for copper electrodeposition obtained from CNT fabric electrode polarized to a several applied potentials in an acid copper solution (FIG. 10A), and an alkaline copper solution (FIG. 10B).
  • the current-time profiles evaluate the nucleation and growth of copper in a potential range between -20 and -220 mV.
  • the cathodic current is higher at the beginning of the cathodic polarization, and then gradually decreases until a stabilization is achieved after 10- 15 seconds.
  • the copper electrodeposition rate is drastically increased by a negative shift in the applied potential to -220 mV.
  • FIG. 10B presents current transients in an alkaline copper pyrophosphate electrolyte under applied potentials of -300 to -500 mV. Similar to the current profiles obtained in the acid electrolyte, higher currents were obtained at the beginning of the copper electrodeposition, followed by a decrease and stabilization during further 5- 10 seconds. Also, the copper deposition rate is gradually increased by a negative shift in the applied potential, as indicated by the increased measured cathodic current density. These results are in agreement with HRSEM observation of the CNT fabric surface subsequent to copper deposition in pyrophosphate solution at applied potential range of -0.3 V to -0.5 V for 60 seconds.
  • FIGs. 11A-J present HRSEM micrographs of top view of copper nucleation and deposition at different cathodic potentials, in an acid copper electrolyte for a period of 60 sec, wherein FIGs.11 A-B are of nucleation and deposition at -20 mV, FIGs.11 C-D at -70 mV, FIGs.11 E-F at -120 mV, FIGs.11 G-H at - 170 mV, and FIGs.11 I-J at -220 mV.
  • FIGs. 12A-I present HRSEM micrographs of top view of copper nucleation and deposition at different potentials, in an alkaline copper electrolyte for a period of 60 sec, wherein FIG. 12A is of nucleation and deposition at -20 mV, FIGs. l2B-C at -70 mV, FIGs. 12D-E at - 120 mV, FIGs. 12F-G at - 170 mV, and FIGs. l2H-I at -220 mV.
  • FIGs. 13A-F present results of copper electrodeposition on a CNT fabric, wherein FIG. 13 A shows a current-time transient profile obtained from copper electrodeposition on a CNT fabric in a copper sulfate electrolyte at a potential of -0.28 V, FIG. 13B shows a copper pyrophosphate electrolyte at a potential of -1.3V, FIG. 13C shows a surface morphology, FIG. 13D shows a cross section of a copper layer deposited from a copper sulfate electrolyte, FIG. 13E shows a surface morphology, and FIG. 13F shows a cross section of a copper layer deposited from a copper pyrophosphate electrolyte.
  • FIGs. 13A-B these transient currents are presented for the first 10 minutes at potentials of -0.28 and -1.3V, for the acid and the alkaline electrolytes, respectively.
  • FIG. 13C presents the evolved surface morphology of the copper film electrodeposited over the CNT fabric surface at an applied potential of - 0.28 V during 10 minutes in the copper sulfate acid electrolyte.
  • the obtained copper film on top of the CNT fabric surface presents a homogeneous structure, constructed via a coarse agglomeration of copper crystals.
  • FIG. 13D illustrates a cross-sectional view of the CNT fabric having a 5 ⁇ uniform copper film formed on top of its surface (- 0.28 V, 30 minutes).
  • FIG. 13E presents the homogeneous metal film, formed within the selected parameters, with fine copper crystals, tracking the fabrics' texture.
  • FIG. 13F presents the uniform 2 ⁇ thin copper film, formed on the external surface of the CNT fabric. In both electrolytes, no delamination or pull-out of the electrodeposited copper from the coated CNT fabric was observed, while performing adhesion tests (180 0 bending of the coated CNT fabrics).
  • FIGs. 14A-D present results of cathodic behavior of the CNT fabrics in two electrolytic baths, whereas potentiodynamic profiles of CNT tissues having different thicknesses obtained from a copper sulfate electrolyte (FIG. 14A), a copper pyrophosphate electrolyte (FIG. 14A), wherein the insets present potential-time transients for the different thickness of CNT fabrics electrodes exposure at OCP, and further show surface morphology of the deposited copper layer onto a 90 ⁇ CNT tissue in a copper sulfate solution (-0.28 V) (FIG. 14C) and in the inset copper crystals decorating the coarse copper grains, and a copper pyrophosphate (-1.3 V) (FIG. 14D) and in the inset a crater zoom-in showing a continuous Cu film deposited onto the CNT tissue tracking morphology changes.
  • FIGs. 14A-B potentiodynamic polarization of each fabric electrode was performed subsequent to a potential transient measurement in each solution.
  • FIGs. 14A-B insets show potential transients obtained from CNT fabric electrodes exposed at OCP in the electrolytes.
  • Results of the potentiodynamic plot in the acid solution show that the cathodic current is initiated at a potential of +0.25 V, with a rather low shift in the current onset.
  • a maximal cathodic current value peak was observed at a potential of -0.15 V, while in the range of -0.2 to - 0.7 V, the cathodic current remained nearly constant.
  • the current onset in the copper pyrophosphate solution FIG.
  • FIGs. 14C-D show the surface morphology of copper films electrodepo sited onto the CNT fabrics at applied potentials -0.28 V during 30 minutes in acid electrolyte and - 1.3 V during 10 minutes in alkaline electrolyte. In both solutions, a continuous uniform copper film was electrodeposited on the surface of the CNT fabrics.
  • Performance of copper-coated CNT fabrics as anode current collector in a Li- ion battery configuration The copper-coated CNT fabric performance, as a lightweight highly conductive anode current collector in Li-ion batteries, was evaluated at this stage in order to demonstrate the capability of the Cu-CNT-Cu tri-layered structure to function as a conductive component, and specifically as a current collector.
  • the Cu-CNT-Cu tri- layered material may be considered an excellent candidate to replace Cu foil anode current collector, proven it functions at least as good as a Cu foil.
  • FIGs. 15A-B show cyclic voltammetry scans obtained from a tree-electrode cell having Li metal serving as both counter and reference electrodes
  • FIG. 15A shows a slow scan cyclic voltammetry (SSCV) measurement (scan rate of 5 ⁇ s "1 at the 3 rd cycle) obtained from the 5 ⁇ Cu-coated CNT fabric electrodeposited from a copper sulfate electrolyte
  • FIG. 15B shows 2 nd galvanostatic (0.1 mA cm "2 ) charge- discharge profiles of half-cells (MCMB graphite vs. Li metal) analysis measured with a Cu coated CNT fabric and a Cu foil current collector and: 1 st cycle in the inset, whereas capacity is expressed in mAh g "1 and is related only to the mass of the loaded graphite.
  • SSCV slow scan cyclic voltammetry
  • the 5 ⁇ tri-layered Cu-CNT-Cu sandwich composite structure current collector composed of a 3 ⁇ bundled and densified CNT fabric, subsequent to IPA immersion and wash, according to some embodiments of the present invention, and an additional of about 1 ⁇ of electrodeposited copper on each side, performed at high standards. Results obtained from utilizing a 10 ⁇ copper foil as a current collector are shown for a comparison, as well. As can be seen in FIG. 15 A, all cathodic and anodic peaks related to a complete Li-ions intercalation/de-intercalation stages are clearly presented in both half-cells. Thus, a copper-coated CNT fabric can function as a current collector, enabling Li + intercalation/de-intercalation processes. As can be seen in FIG.
  • the above working example presents two simple techniques to electrodeposit a thin and continuous copper layer only on the external surfaces of modified CNT fabrics, according to some embodiments of the present invention.
  • Two copper solutions were studied and evaluated as copper deposition electrolytic baths: an acidic copper sulfate and an alkaline copper pyrophosphate.
  • the cathodic potentiodynamic behavior of the modified CNT fabrics in the solutions revealed different characteristics.
  • the electrodepo sited copper films surface morphologies under pre-selected electrochemical conditions were significantly different; while the film deposited in the acid electrolyte demonstrated agglomerated copper deposits having coarse crystals, the thin-deposited layers obtained from the alkaline electrolyte possess fine grains, tracking and tracing the CNT fabric texture.
  • the lightweight Cu-CNT fabric based on densified CNT fabrics, according to embodiments of the present invention, is highly conductive and as such, it may function as a conductive component in various applications, replacing commonly used relatively heavy copper foil as well as enabling a substantial reduction (of up to 50 %) in the overall thickness of conductive substrate.
  • This working example demonstrates the suitability and capability of Cu-coated densified CNT fabrics to function as a lightweight anode current collector in advanced Li-ion batteries, replacing the commonly and traditional used copper foil.

Abstract

L'invention concerne un tissu auto-supporté, léger, souple et de haute conductivité comprenant un nanotube de carbone, ledit tissu étant approprié pour servir de collecteur de courant dans des batteries lithium-ion. Le tissu de NTC peut également être revêtu d'une mince couche métallique sur une ou deux de ses faces, tout en conservant sa légèreté et sa souplesse et en accroissant sa conductivité et sa compatibilité avec la chimie d'une batterie lithium-ion. L'invention concerne également des électrodes à base du tissu de NTC selon l'invention, des batteries et des dispositifs mettant en oeuvre lesdites électrodes, et un procédé pour leur fabrication.
PCT/IL2017/050109 2016-02-03 2017-01-30 Tissu de nanotubes de carbone utilisé comme collecteur de courant d'électrode dans une batterie lithium-ion WO2017134653A1 (fr)

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US20200266492A1 (en) * 2017-10-02 2020-08-20 Saft Lithium ion electrochemical cell operating at a high temperature
WO2019239408A1 (fr) * 2018-06-13 2019-12-19 Tortech Nano Fibers Ltd Produits composites nanotubes de carbone (ntc)-métal et leurs procédés de production
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WO2022094767A1 (fr) * 2020-11-03 2022-05-12 智能容电(北京)科技有限公司 Condensateur variable flexible et son procédé de préparation
CN114497569A (zh) * 2022-01-10 2022-05-13 湖南大晶新材料有限公司 一种锂离子电池用高分子集流体及其制备方法
CN114497569B (zh) * 2022-01-10 2024-05-07 湖南大晶新材料有限公司 一种锂离子电池用高分子集流体及其制备方法

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