WO2012129690A1 - Composites à nanotubes de carbone - Google Patents

Composites à nanotubes de carbone Download PDF

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Publication number
WO2012129690A1
WO2012129690A1 PCT/CA2012/050190 CA2012050190W WO2012129690A1 WO 2012129690 A1 WO2012129690 A1 WO 2012129690A1 CA 2012050190 W CA2012050190 W CA 2012050190W WO 2012129690 A1 WO2012129690 A1 WO 2012129690A1
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Prior art keywords
cnt
metals
cnts
growth
inconel
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PCT/CA2012/050190
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English (en)
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Li Zhang
David Mitlin
Chris HOLT
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The Governors Of The University Of Alberta
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    • 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
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/20—Graphite
    • C01B32/21—After-treatment
    • C01B32/22—Intercalation
    • C01B32/225—Expansion; Exfoliation
    • 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
    • H01G11/22—Electrodes
    • H01G11/26—Electrodes characterised by their structure, e.g. multi-layered, porosity or surface features
    • H01G11/28—Electrodes characterised by their structure, e.g. multi-layered, porosity or surface features arranged or disposed on a current collector; Layers or phases between electrodes and current collectors, e.g. adhesives
    • 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
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/32—Carbon-based
    • H01G11/36—Nanostructures, e.g. nanofibres, nanotubes or fullerenes
    • 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
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/70—Energy storage systems for electromobility, e.g. batteries

Definitions

  • Electrochemical capacitors have attracted wide interest as energy
  • electrochemical capacitors are generally classified into two major types:
  • electrochemical double layer capacitor and pseudocapacitor.
  • the capacitance in the former is electrostatic in origin, arising from charge separation at the interface of the high specific- area electrode and electrolyte.
  • Activated, mesoporous, and carbide-derived carbons, graphene, carbon fabrics, fibers, nanotubes, onions, and nanohorns as well as various nanostructured polymers with high specific surface area and moderate cost have been widely investigated for EDLC applications.
  • transition metal nitrides exhibit superior properties in some respects, such as markedly better electrical conductivity and in some cases excellent chemical stability.
  • Various materials such as
  • MoN and Mo 2 N molybdenum nitrides
  • VN vanadium nitride
  • the capacitance would significantly degrade at high voltage scanning rates/ current densities. For example, the superb capacitance reported in reference 13 degraded by more than 50% when an intermediate scan rate of 100 mV/s was utilized.
  • CNT carbon nanotube
  • 3D three-dimensional
  • loose CNTs may be mixed with a binder and a functional material, and subsequently applied onto a current collector. This approach is more involved and often yields unsatisfactory results.
  • vanadium nitride/carbon nanotube composites were prepared by sonicating nanocrystalline VN with
  • MWCNTs multiwalled carbon nanotubes
  • An A1 2 0 3 barrier layer is also extensively utilized to grow CNTs on a variety of other substrates such as Ni and Fe foils, glassy carbon (GC),
  • a method of creating an energy storage or energy generation device comprising growing anchored carbon nanotubes (CNTs) on an electrically conducting substrate with a spacing suitable for functionalization, and functionalizing the CNTs by conformally coating the CNTs with an energy storage or generation material.
  • CNTs carbon nanotubes
  • the resulting device is also claimed comprising anchored carbon nanotubes (CNTs) extending from an electrically conducting substrate with a spacing suitable for functionalization, and an energy storage or generation material conformally coating the CNTs.
  • the electrically conducting substrate comprises a CNT growth support film with growth catalyst particles deposited onto, built into or forming part of the growth support film.
  • Exemplary bulk substrates include Inconel, copper, stainless steel, glassy and vitreous carbon, graphite, aluminum, magnesium, conventional steel, niobium, titanium,
  • molybdenum molybdenum, tungsten, zirconium, silicon carbide, and tungsten carbide.
  • Exemplary growth support films include oxides of metals, of non-metals and of alloys including oxides of Si, Mg, Fe, Cr, Cr-Ni, Ni, Ir, Zr, Sc, Ti, Mo, and Ta, such as Si0 2 , MgO, Ti0 2 , NbO, Nb0 2 , Nb 2 0 5 , Ti-doped Nb0 2 , Cr 2 0 3 , etc.
  • Support films also include nitrides such as TiN and Ti x V 1-x N (TiVN).
  • Exemplary growth catalysts include metals as Ni, Fe, Cr, Co, Cu, Au, Ag, Pt, Pd,
  • the electrically conducting substrate comprises growth catalyst particles.
  • the electrically conducting substrate comprises a CNT growth support film with the growth catalyst particles deposited onto, built into or forming part of the CNT growth support film.
  • the growth catalyst particles have a wetting angle of 30-90 degrees with the CNT growth support film.
  • the as-deposited thickness of the growth catalyst layer has a thickness of 1-10 nm before it breaks up into growth catalyst particles.
  • the electrically conducting substrate comprises one or more of Inconel, copper, stainless steel, glassy and vitreous carbon, graphite, aluminum, magnesium, conventional steel, niobium, titanium, molybdenum, tungsten, zirconium, silicon carbide, and tungsten carbide.
  • the CNT growth support film comprises one or more of oxides or nitrides of metals, non-metals and alloys.
  • the CNT growth support film comprises one or more of TiN and Ti x Vi -x N and oxides of Si, Mg, Fe, Cr, Cr-Ni, Ni, Ir, Zr, Sc, Ti, Mo, and Ta.
  • the growth catalyst particles comprise one or more of Ni, Fe, Cr, Co, Cu, Au, Ag, Pt, Pd, Mn, Mo, Sn, Mg, alloys that combine two or more of these metals, oxides of these metals, oxides of alloys that combine two or more of these metals, nitrides of these metals, and nitrides of alloys that combine two or more of these metals.
  • the energy storage or generation material comprises a host for Li ions.
  • the energy storage or generation material comprises a provider of reversible faradaic electrochemical oxidation/reduction reactions.
  • the energy storage or generation material comprises one or more of Si, Al, Sn, Co02, Fe203, Mn02, Fe304, FeOOH, MgH2, sulfur, FeS, Ti x Vi -x N, NiCo204, Co304, cobalt hydroxide, iron hydroxide, and VN.
  • the spacing of the CNTs falls within the range of 200 nm to 300 nm.
  • the apparatus is formed as a lithium-ion battery or supercapacitor.
  • Fig. 1A shows an SEM micrograph of an as-grown array of CNT/Inconel/GC.
  • Fig. IB shows TGA (axis on left) and DSC (axis on right) analysis allowing estimation of amorphous carbon fraction.
  • Fig. 2A is an SEM micrograph of VN/GC.
  • Fig. 2B is an X-ray diffraction pattern of VN/Si.
  • Figs. 2C and 2D are increasing magnification SEM micrographs of
  • Fig. 2E is a schematic summarizing the synthesis process and ultimate morphology of the VN/CNT/3D array showing CNTs before coating, Cr-Fe-Ni bases to the CNTs, VN coated CNTs, oxidized Inconel upper substrate, Inconel 600 intermediate substrate and bulk GC or Inconel substrate.
  • the VN mass loading is 0.037 mg per geometrical cm 2 .
  • Fig. 3Aa is a bright-field TEM micrograph on the VN covered CNT tips; Figs. 3B and 3C are bright field and HAADF images of the VN/CNT structure, respectively; and Fig. 3D is an indexed SAED pattern of the VN/CNT structure imaged in Figs. 3B and 3C.
  • Fig. 4A is an SEM micrographs of CNT/A1 2 0 3 ; and Fig. 4B is an SEM micrograph of VN covering only the top surface of CNT/A1 2 0 3 /GC.
  • Fig. 5A is a graph showing a CV curve of CNT/Inconel with data shown at cycle 1 and at cycle 10000;
  • Fig. 5B is a graph showing CV curves of GC and of VN/GC;
  • Fig. 5C is a graph showing CV data for CNT/Inconel, and for the remnant catalyst on Inconel, after the CNTs were removed;
  • Fig. 5D is a graph showing CV data for CNT/Inconel and for VN/CNT/Inconel.
  • Cycling for Fig. 5A was at 50 mV/s, while cyclings for Figs. 5B-5D were at 100 mV/s.
  • Fig 6A shows CV curves of VN/CNT/Inconel/GC in the potential range of -1.0 to
  • Fig. 6B shows the relationship between the specific capacitance versus scan rate for various mass loadings of VN
  • Fig. 6C shows the charge- discharge cycling curves at different current densities
  • Fig. 6D shows the specific capacitance versus current density.
  • Fig. 7A shows Nyquist plots of CNT/Inconel/GC and Fig. 7B shows Nyquist plots for VN/CNT/Inconel/GC electrodes.
  • the insets are the enlarged Nyquist plots in the high frequency region.
  • the electrolyte is 1 M KOH.
  • FIG. 8A shows the relationship between the specific capacitance versus cycle number with different VN mass loading, using a scan rate of at 50 mV/s;
  • Figs. 8B and 8C are SEM micrographs of the pre-cycled and post-cycled (250 cycles) nanostructures.
  • Figs. 9A and 9B are XPS spectra of the VN thin films before electrochemical cycling.
  • Figs. 9C and 9D are XPS spectra after 250 electrochemical cycles.
  • Fig. 10 shows Raman spectra of CNTs grown on Inconel.
  • Fig. 11A shows an HRTEM image of CNTs grown on Inconel and Fig. 1 IB is an
  • Fig. 12A is a graph showing CV curves of GC and of VN/GC and
  • Fig. 12B shows CV data for CNT/Inconel and for VN/CNT/Inconel. Cycling for both Figs. 12A and
  • Fig. 13A shows cyclic voltammogram (CV) curves of CNT/A1203. Data is shown at cycle 1 and at cycle 10000. Cycling was performed at a sweep rate of 50 mV/s.
  • Fig. 13B shows CV data for CNT/A1203and for VN/CNT/A1203 at 20 mV/s.
  • Fig. 14 shows the electrically equivalent circuit used for fitting impedance spectra.
  • a method of creating an energy storage or energy generation device comprising growing anchored carbon nanotubes (CNTs) on an electrically conducting substrate with a spacing suitable for functionalization, and functionalizing the CNTs by conformally coating the CNTs with an energy storage or generation material.
  • the resulting device is also disclosed comprising anchored carbon nanotubes (CNTs) extending from an electrically conducting substrate with a spacing suitable for functionalization, and an energy storage or generation material conformally coating the CNTs.
  • the electrically conducting substrate comprises growth catalyst particles.
  • the electrically conducting substrate may comprise a CNT growth support film with the growth catalyst deposited onto, built into or forming part of the CNT growth support film.
  • the principle of selection of the growth support film and growth catalyst is as follows:
  • the support film should 1) prevent excessive catalyst wetting or dewetting, i.e., have the appropriate film-support interaction to generate a desired catalyst particle size, distribution and spacing, which in turn dictates the CNT size, distribution, spacing and height; 2) prevent or reduce to an acceptable level the interdiffusion of the catalyst into the support film and/or the underlying substrate; 3) be sufficiently electrically conductive and electrochemically stable for the desired application; 4) maintain a strong bond with the bulk substrate, not delaminating or spalling; and 5) maintain a strong bond with the grown CNTs as to prevent CNT delamination or separation from the substrate.
  • the spacing and dimensions of the dewetted catalyst particles and hence of the CNTs may be tailored by the use of the force-balance wetting equation, knowing that the catalyst mass is conserved, and knowing that the as-deposited catalyst thickness is in the 1 - 10 nm range.
  • the wetting angle for the film on the support should be greater than 30° but less than 90°.
  • the predicted utility is based on the disclosed results and application of known principles of vapor and liquid-phase deposition technologies and of supercapacitor and battery materials.
  • the materials for which predictions are provided have been demonstrated to work in bulk or in other nanoscale embodiments. Functionalizing the surfaces of the CNTs with the predicted materials will improve their performance over bulk or other nanoscale embodiments. This is because the CNT supports will provide an excellent electrical conductivity path to the underlying substrate while enabling an ultra-high surface area-to-volume ratio for the battery or supercapacitor material coating. Predictions are also based upon the thermodynamics and phase diagrams of the respective materials systems.
  • Exemplary bulk substrates include Inconel, copper, stainless steel, glassy and vitreous carbon, graphite, aluminum, magnesium, conventional steel, niobium, titanium, molybdenum, tungsten, zirconium, silicon carbide, and tungsten carbide. Each of these materials has excellent electrical conductivity, which is in or near the metallic range. This makes them suitable as electrodes.
  • Exemplary growth support films include oxides of metals, of non-metals and of alloys including oxides of Si, Mg, Fe, Cr, Cr-Ni, Ni, Ir, Zr, Sc, Ti, Mo, and Ta, such as Si0 2 , MgO, Ti0 2 , NbO, Nb0 2 , Nb 2 0 5 , Ti-doped Nb0 2 , Cr 2 0 3 , etc.
  • Support films also include nitrides such as TiN and Ti x Vi_ x N (TiVN). These support growth films would work because 1) they are stable at the CNT growth temperatures (i.e. T meltmg of film » growth temperature), 2) they may be used to block diffusion of the CNT growth catalyst into the substrate, and 3) they have some thermodynamic chemical interaction with the growth catalyst, therefore causing partial wetting and preventing catalyst agglomeration.
  • Exemplary growth catalysts include metals as Ni, Fe, Cr, Co, Cu, Au, Ag, Pt, Pd,
  • These growth catalysts would work because they chemically interact with the precursor hydrocarbon gases (such as ethylene). In addition they all possess some solubility (in solid or liquid phases) for atomic carbon and/or they form carbides, the presence of at least one of the two being a necessary requirement for CNT growth.
  • Exemplary energy storage or generation devices include lithium-ion batteries and supercapacitors.
  • the achieved CNTs may be functionalized with a variety of energy storage materials that either act as hosts for Li ions (batteries) or provide reversible faradaic electrochemical oxidation/reduction reactions and therefore act as supercapacitors.
  • these materials may be used in the positive (cathode) and/or the negative (anode) electrodes.
  • supercapacitors these materials may be used for symmetrical or asymmetrical electrodes.
  • such embodiments include, but are not limited to, elemental materials such as Si, Al, Sn, and their alloys, oxides and hydroxides such as Co0 2 , Fe 2 0 3 , Mn0 2 , Fe 3 0 4 and FeOOH, hydrides such as MgH 2 , sulfur and sulfides such as FeS, and elemental and alloy nitrides such as TiVN.
  • oxides such as NiCo 2 0 4 , Co 3 0 4 , Fe 2 0 3 and Mn0 2
  • hydroxides such as cobalt and/or iron hydroxide
  • nitrides such as VN and TiVN.
  • these materials would work because it is possible to deposit them onto the carbon nanotubes using a variety of techniques such as physical vapor deposition. Furthermore these materials would work because they have been demonstrated to function as an energy storage phase in the CNT-unsupported state. However in the current embodiment we expect these materials to possess improved performance since they are intimately coupled to an electrically conductive skeleton, which would not only accelerate the electronic conductivity but also the ionic conductivity through field effects. Furthermore the CNT arrays provide a natural way for the coating materials to achieve nanoscale dimensions. This would improve the kinetics via a reduction of the diffusion distances of the diffusing species. It would also improve the gravimetric energy density due to a higher surface area-to-volume ratio of the energy storage phase created by the underlying support skeleton.
  • Deposition techniques for depositing a growth support film and growth catalyst include one or a combination of physical vapor deposition (PVD) methods such as sputtering, evaporation, and pulsed laser deposition; chemical vapor deposition (CVD); atomic layer deposition (ALD); electroplating and electroless deposition; and wet chemical techniques.
  • PVD physical vapor deposition
  • CVD chemical vapor deposition
  • ALD atomic layer deposition
  • electroplating and electroless deposition electroless deposition
  • wet chemical techniques wet chemical techniques.
  • CNTS may be carried out by all suitable methods including and related to chemical vapor deposition (CVD) such as conventional CVD, thermal CVD, and plasma- enhanced CVD. These methods would work since they are scientifically established and widely technologically demonstrated methods for CNT growth.
  • CVD chemical vapor deposition
  • Functionalization techniques include one or a combination of physical vapor deposition (PVD) methods such as sputtering (including reactive sputtering), evaporation, and pulsed laser deposition; chemical vapor deposition (CVD); atomic layer deposition (ALD); electroplating and electroless deposition; and wet chemical methods such as precipitation, hydrothermal processing, and ionothermal processing.
  • PVD physical vapor deposition
  • CVD chemical vapor deposition
  • ALD atomic layer deposition
  • electroplating and electroless deposition electroless deposition
  • wet chemical methods such as precipitation, hydrothermal processing, and ionothermal processing.
  • the device may be used, for examples, as a capacitor, battery or a hybrid battery- capacitor.
  • Each of these applications requires a good electrical path from the functional material to the electrode.
  • a significant benefit is achieved when the functional materials and current collectors (dual role of the CNT array as a skeleton support and a current collector) are directly anchored to the underlying substrate (electrode) as they are shown herein.
  • Spacing of the CNTs is preferably greater than 100 nm, more preferably in the range
  • our methodology involves no wet chemical routes and creates in one embodiment 3D arrays of nanostructures that are directly anchored on bulk GC or bulk Inconel electrodes. This is achieved using three steps: First, we use physical vapor deposition (PVD) or other suitable methods disclosed in this document to deposit a CNT growth support film such as an Inconel-based growth support film and a CNT growth catalyst onto a bulk substrate. By this example, we create an electrically conducting substrate with a spacing suitable for functionalization. For a baseline, we also examine the feasibility of using a "conventional" A1 2 0 3 CNT growth support. Second, we grow anchored 3D arrays of CNTs via conventional chemical vapor deposition (CVD) or other suitable methods disclosed in this document.
  • CVD chemical vapor deposition
  • the CNT growth support film may have the growth catalyst particles deposited onto, built into or forming part of a CNT growth support film.
  • ALD atomic layer deposition
  • a CVD-based method has the most potential for industrial -scale production because it is the technique that is capable of growing nanotubes directly on desired substrates.
  • CVD-based techniques for growth of CNTs are also rapidly evolving in their efficiency and process control accuracy, with
  • Recent advances include water-assisted supergrowth of dense and
  • PEM membrane
  • Inconel support films of 150 nm in thickness were synthesized via PVD onto the electrodes. This was achieved via radio frequency (RF) magnetron sputtering (AJA International, Inc.), from an Inconel-600 target (VBM Precision Machine), in ultra-pure argon (99.999%) plasma. Prior to all depositions the sputtering chamber reached a base pressure of less than or equal to 5 ⁇ 10 s Torr. A substrate temperature of 800 °C was used to obtain crystalline Inconel films. The films possessed good adhesion to either electrode. For this PVD step, the sputtering rate was accurately measured in-situ using a crystal monitor at the substrate plane. A deposition rate of 2.5 nm/min was utilized. Inconel-coated electrodes were then placed in the center of a tube furnace (MTI,
  • GSL1100X Oxidation was accomplished by heating the samples to 700 °C at a rate of 15°C/min under a flow of dried air (100 seem total). The sample was held at that temperature for 60 s. Then the furnace was slowly cooled to room temperature under an argon flow (200 seem total). This oxidation process produced roughly a 100 nm thick passivation oxide (blue in color), which acted as the diffusion barrier layer for the CNT growth.
  • a 1 nm Cr/1 nm Fe-30 atom % Ni bilayer CNT growth catalyst was subsequently deposited via direct current (DC) magnetron sputtering and co-sputtering, using elemental targets.
  • CNT growth catalyst was deposited on an A1 2 0 3 support as well. Twenty five nanometers of A1 2 0 3 was reactively sputtered by dc magnetron sputtering from an Al target (99.995% purity) in mixed argon-oxygen plasma. The substrate was held at 350 °C during deposition. The total pressure in the sputtering chamber was maintained at 5 ⁇ 10 "3 Torr for all the experiments, and the volume flow rate ratio of argon to oxygen was 9.5: 1.5 (total 11 seem) . After sputtering, the oxide films were annealed at 400 °C for 60 min.
  • Deposition rate calibration was performed ex situ through the use of a profilometer (KLA-Tencor Alpha-Step IQ) to measure step heights.
  • KLA-Tencor Alpha-Step IQ KLA-Tencor Alpha-Step IQ
  • the 1 nm Cr/1 nm Fe-30 atom % Ni bilayer CNT growth catalyst was subsequently deposited on top.
  • the CNT arrays were synthesized via a commercial CVD reactor (Tystar, Inc.).
  • the mass-production designed system handles up to fifty 150 mm wafers simultaneously, with industry standard process control.
  • the basic process flow is load, heat and reduce, grow, cool, and unload.
  • the electrodes were loaded into the reactor at 550 °C; the reactor was then purged with argon and heated to the growth temperature of 750 °C using a rate of 10 C7min under a flow of 10% hydrogen in argon (3000 seem total).
  • the electrodes were then held at 750 °C for a total time of 40 min. During the growth stage, 15% ethylene and 10% hydrogen in argon (3300 seem total) flowed into the reactor for a time of 4-6 min. The reactor was then cooled to 350 °C under a flow of argon (2700 seem total), and the samples were removed.
  • Vanadium nitride thin films were grown using a similar approach to that by
  • Zasadzinski et al. The methodology consisted of reactive RF magnetron sputtering from an elemental vanadium target (99.995% purity) in mixed argon-nitrogen plasma.
  • the optimum substrate temperature for well-crystallized films was found to be 580 °C. With the heater at temperature, the base pressure in the chamber was less than 5 ⁇ 10 s Torr. High -purity argon and nitrogen were injected directly into the chamber with a volume flow rate ratio of 16.8:3.2 (total 20 seem).
  • the deposition pressure in the sputtering chamber was maintained at 4 ⁇ 10 "3 Torr.
  • VN films were subsequently annealed in the chamber at 610 °C for 60 min in a nitrogen flow (10 seem, 4 ⁇ 10 "3 Torr).
  • Deposition rate calibration was performed ex situ through the use of a profilometer (KLA- Tencor Alpha-Step IQ) to measure the step heights.
  • the deposition rates of VN were on the order of 1 nm/min.
  • the VN mass loading was calculated from the film thickness and the known density of crystalline VN. The loading is presented in units of milligram per geometric (not real) surface area.
  • phase identification was performed on -350 nm thick VN films grown on 4 in. Si substrates. The wafer was oriented to avoid the primary Si reflections in the detector. Sheet electrical resistivity measurements were taken using a four-point probe configuration (Lucas Laboratories). Scanning electron microscopy (SEM) was performed using a Hitachi S-4800 operated at 20 kV accelerating voltage. Transmission electron microscopy (TEM) was performed using a JEOL 2010 operated at 200 kV accelerating voltage. For TEM analysis the structures were mechanically removed from the electrodes and dry-dispersed onto grids. Electron diffraction simulation was performed using the commercial software Desktop MicroscopistTM, with the input of the well-known space group information for the constituent cubic VN phase.
  • XRD glancing angle X-ray diffraction
  • X-ray photoelectron spectroscopy (XPS) measurements were performed using an
  • Axis Ultra spectrometer (Kratos Analytical) with a base pressure of 5 ⁇ 10 "10 Torr. X-rays were generated by an Al mono (K a ) source operated at 210 W. The spectra were collected at a 90° takeoff angle. For the survey spectra, the analyzer pass energy was 160 eV, and for the high -resolution spectra the pass energy was 20 eV. The bonding energy scale in XPS measurements was corrected for the charging effect by assigning a value of 284.6 eV to the C Is peak of adventitious carbon. Peak-fitting identification was performed using the system software and the NIST XPS database as a cross-check.
  • thermogravimetric analysis TGA
  • DSC differential scanning calorimetery
  • Electrochemical impedance spectroscopy (EIS) measurements were carried out to further verify the merit of a 3D CNT/Inconel support on the electrode performance. All the tests were conducted (three-electrode system, with Hg/HgO as reference electrode) on a Solartron 1470 electrochemical test station, applying an alternating current in the frequency range from 1 Hz to 20 kHz, with 5 mV amplitude, around 0 V vs open circuit potential (OCP, around 0.16 V vs reference electrode).
  • EIS Electrochemical impedance spectroscopy
  • Fig. 1 A provides an SEM micrograph of the as-synthesized CNT array on
  • Inconel/GC Inconel/GC.
  • the diameters of the CNTs on Inconel/GC are in the 60 nm range.
  • the nanotubes are relatively coarsely distributed on the substrate, with spacing on the order of 200-300 nm.
  • the height of these CNTs is 45 ⁇ .
  • the number density of the CNTs is (1.01.5) ⁇ 10 9 /cm 2 .
  • Fig. IB shows the results.
  • the decomposition onset temperature for MWCNTs is around 515 °C. All the amorphous carbon was burnt before this onset temperature, with its mass fraction being on the order of 5%. By 710 °C, 98% of the total mass is lost, which indicates that 93% of the material by mass is MWCNT. At higher temperatures only the growth catalyst remains.
  • Fig. 2A presents an SEM micrograph of a 60 nm thick VN film grown on a GC substrate.
  • the film had a mass loading of 0.037 mg/cm 2 by geometric area of the GC substrate.
  • the VN mass loading is that value.
  • the film was continuous and had good electrical conductivity. Its average measured resistivity was 43.5 ⁇ cm. It is well-known that good electrical conductivity is key for fast and reversible redox reactions at high
  • Fig. 2B shows the XRD pattern of the synthesized vanadium nitride thin film. Three strong diffraction peaks are observed at 2 ⁇ value of 38. , 44.3°, and 64.4°. These diffraction peaks can be ascribed to the crystal planes of (111), (200), and (220).
  • VN space group [225] Fm3 m , Joint Committee on Powder Diffraction Standards (JCPDS) Power diffraction File Card No. 25- 1252).
  • Fig. 2C and Fig. 2D highlight the VN/CNT/Inconel/GC system. The case of
  • VN/CNT/Inconel/Inconel is not shown, since the electrochemical capacitor structure (i.e., CNT diameter, height and spacing, VN coverage) is nearly identical to that of VN/CNT/Inconel/GC.
  • the electrochemical capacitor structure i.e., CNT diameter, height and spacing, VN coverage
  • a faceted VN nanocrystallite is not shown, since the electrochemical capacitor structure (i.e., CNT diameter, height and spacing, VN coverage) is nearly identical to that of VN/CNT/Inconel/GC.
  • FIG. 2E provides a summary schematic of the 3D array of the VNCNT nanocomposites, with all the support and catalyst layers included. Conceptually the figure is
  • Figs. 3A-3D show the TEM characterization results of the VN/ CNT/Inconel/GC 3D arrays.
  • Fig. 3A shows a bright field micrograph of the top of the CNTs, highlighting their coverage by the nanocrystalline VN.
  • Figs. 3B and 3C show bright field and high angle annular dark field (HAADF) (Z -contrast) micrographs, respectively.
  • HAADF high angle annular dark field
  • the nanostructures were sheared from the electrode right at the base.
  • the portions imaged in Figs. 3B and 3C were close to the fracture surface, i.e., near the bottom.
  • the CNTs were not fully vertically aligned and hence received somewhat varying levels of coverage depending on their orientation to the atomic flux.
  • SAED selected area electron diffraction
  • CNT arrays grown on A1 2 0 3 /GC are both much denser and much longer compared to those on Inconel (see Figs. 4A and 4B).
  • a typical height and diameter of a CNT is 35 um and 10 nm, respectively.
  • the spacing of CNTs is quite fine, being on the order of 10-15 nm.
  • the coverage of the VN on CNTs grown using the A1 2 0 3 support films is quite different from that of the Inconel case.
  • Carbon nanotubes grown using Inconel are covered by the VN. In the case of the CNTs grown using the A1 2 0 3 support, the VN covers only the very top fraction of the nanotubes.
  • CNT growth is a two-step process. First is the restructuring of a thin film into separated nanoclusters of catalyst particles and subsequent particle coarsening.
  • An A1 2 0 3 support layer is one of the more effective substrates for CNT growth. Its relatively strong chemical interaction with the Fe-based catalyst particles results in a narrow and fine
  • Catalyst substrates with a weak chemical interaction will result in catalyst islands that are widely spaced and dimensionally coarse at elevated temperatures. During CNT growth these particles will also undergo accelerated Ostwald ripening relative to the case of the reactive substrates, e.g., see ref 42 and citations therein. Coarsened catalyst particles will grow CNTs with
  • Fig. 5 A shows the CV curves of CNTs on Inconel at cycle 1 and at cycle 10000 where only minimal degradation is observed.
  • Fig. 5B shows the CV curves for GC and for a VN/GC film tested at a 100 mV/s sweep rate. According to the CV data the specific capacitance of the VN on GC was 84.3 F/g. In the case of exposed GC there is a clear redox peak around -0.25 V.
  • FIG. 5D shows the CV data for the CNT/Inconel/GC vs VN/CNT/Inconel/GC, at 100 mV/s.
  • the geometrical area normalized electrical double layer capacitance for CNT/Inconel is 0.001216 F/cm 2 .
  • the CNTs grown on Inconel were too light to accurately ascertain their mass per geometrical squared centimeter (and hence to obtain specific capacitance per mass).
  • VN/CNT/Inconel is 0.01022 F/cm 2 .
  • the specific capacitance of VN/CNT/Inconel is 276 F/g. Since the VN is conformal to the CNTs, the electrochemically accessible surface areas are similar for both types of structures. Therefore the electric double layer contribution for the VN/CNT/Inconel can be estimated as 12% of the total capacitance.
  • Fig. 6A shows the cyclic voltammetry diagrams of VN/ CNT/Inconel/GC nanostructures.
  • the potential range of -1.0 to 0.06 V is sampled at different scan rates. There is a slight shift of peak positions due to the voltage drop caused by electric resistance at high sweep rates. Otherwise, in the sweep rate range of 20 mV to 1000 mV/s, the shape of all the curves is quite similar.
  • Fig. 6B gives the relationship between the specific capacitance and the scan rate, in the case of VN/CNT/Inconel/ GC, using three different nitride loadings. The specific capacitance, in F/g, degrades with increasing material loading.
  • VN/GC and VN/CNT/Inconel/GC exhibit excellent reversibilities at 100 mV/s, the CV curve is symmetric with respect to zero current, indicating a dominant fast and reversible redox reaction.
  • the capacitances of VN/CNT/Inconel/CNTs are 289 and 276 F/g, respectively.
  • VN/CNT/Inconel composite is a promising material for fast charge-discharge applications.
  • Figs. 7A and 7B show the Nyquist plots of the CNT/Inconel/GC and
  • VN/CNT/Inconel/GC electrodes in 1 M KOH were fitted to the equivalent electronic circuit shown in Fig. 14.
  • the calculated equivalent series resistance (ESR) and charge-transfer resistance (R ct ) of CNT/Inconel/GC are 2.76 and 0.11 ⁇ , respectively.
  • the 0.11 ⁇ for the CNT array probably corresponds to the charge transfer resistance of the oxygen reduction reaction, which, as was already mentioned, is much faster on the carbons than on VN.
  • the ESR and R ⁇ are 2.94 ⁇ and 0.28 ⁇ , respectively.
  • Our value for R; t is almost a
  • VN/CNT/Inconel/ Inconel electrode was subjected to a long-term cycling test. The results are shown in Fig. 8A. After 600 CV cycles at a scan rate of 50 mV/s, the specific capacitance values remain at
  • X-ray photoelectron spectroscopy (XPS) analysis of the post-cycled materials was carried out on 160 nm VN/Si. These planar samples received the same 250 electrochemical cycles. XPS spectra of the VN thin films before and after 250 electrochemical cycles are shown in Figs. 9A- 9D. Besides the experimental peaks (black), the figures also show the model predictions of individual and summation peaks and background fits (lower lines). The peaks were identified using the aforementioned NIST XPS database.
  • Fig. 9A shows the V peaks and O peaks obtained from the as- synthesized film, which was stored at ambient conditions for approximately 24 h prior to analysis.
  • V 2p and V 2p appear to be a sum of the spectral lines from several valence states of
  • V 2p vanadium.
  • the V 2p is fitted with three peaks.
  • the peak at 513.75 eV can be attributed to vanadium
  • V 2 0 3 V (V 2 0 5 ) oxidation states of vanadium, respectively.
  • V 2 0 5 V (V 2 0 5 ) oxidation states of vanadium, respectively.
  • the O Is peak at 530.2 eV is also shown.
  • the O Is spectral line is in the 529.8-530.6 eV range.
  • the O Is spectral peaks are at 530.4, 530.3, and 530.0 eV, respectively. Since these peaks are quite close in energy, it is difficult to ascribe a particular oxidation state from the oxygen peak data.
  • FIG. 9B shows the portion of the spectrum containing the nitrogen peak, before cycling.
  • the nitrogen peak which is at 397.3 eV, is in the position expected for a metal nitride (N spectral line Is: 396.8-398.9 eV). Since both the oxide and the nitride peaks are present in the as-synthesized sample, we can conclude that even prior to electrochemical cycling the VN crystals are at least partially oxidized. Most likely the coverage is uniform, with the nanometer-scale thickness of the mixed oxides still enabling detection of a signal from the underlying VN.
  • Figs. 9C and 9D show XPS results for the post-electrochemically cycled VN films.
  • V curves are different from those of the pre-cycled films.
  • the V 2p line shifts to 515.1 eV (V )
  • OH represents the electrical double layer formed by the hydroxide ions physisorbed on nonspecific sites
  • VN x O y — OH represents chemisorption in the faradaic redox reaction.
  • Impedance measurements in the study by Zhou et al. revealed that a charge transfer reaction is indeed happening. More precise determination of the reaction mechanisms would be possible using spectroscopic techniques such as FTIR and XPS in situ, but that would require a specialized electrochemical setup. Theoretically, a lot of information about the redox processes could be gained from detailed studies of CV peak positions and currents as a function of scan rate, electro-
  • VN/CNT/Inconel nanostructures physically degrading in a way as to reduce that area.
  • VN nanocrystallites are in the form of a continuous shell around a conducting core that directly anchored to a conductive substrate eliminates ohmic losses, resulting in excellent rate capability.
  • the skeleton of multiwalled carbon nanotubes was grown via chemical vapor deposition using an Inconel-based support film.
  • the outer layer of vanadium nitride was subsequently synthesized using physical vapor deposition (reactive sputtering). Transmission electron microscopy analysis indicates that the vanadium nitride layer consists of a shell of interconnected sub-50-nm scale nanocrystallites that conformally cover the nanotubes.
  • X-ray photoelectron spectroscopy analysis was performed on the as-synthesized and the post-electrochemically cycled blanket films of vanadium nitride. Vanadium oxide peaks of several valences and vanadium nitride peaks were present in the as-synthesized and in the post-cycled samples. Hence we conclude that even prior to electrochemical cycling the nitride crystals are at least partially oxidized. Scanning electron microscopy of the post-electrochemically cycled samples revealed minimal morphological changes of the nanocrystalline nitride.
  • a 2000 groove/mm holographic reflection grating was used.
  • the spatial resolution, confocal resolution and spectral resolution are 1 um, 2 ⁇ and 2 cm "1 , respectively.
  • the Raman -scattered light was collected normal to the sample surface where at least five positions were randomly chosen on each sample.
  • the G band is related to the graphite tangential E 2g Raman active mode, which is due to the stretching vibration of 5/J> -hybridized carbon.
  • the D band at -1343 cm “1 , is a breathing mode of Ai g symmetry, which only becomes active in the presence of disorder and defects. Accordingly, the intensity ratio of I G I I D can provide semiquantitative information about the CNT quality.
  • the average value of calculated I G I I D is 1.60, indicating good crystallinity of the as-prepared CNT array, with low levels of disordered
  • Fig. 11 A shows HRTEM image of a CNT grown on Inconel.
  • Fig. 1 IB is an HRTEM image of a CNT grown on A1 2 0 3 .
  • the diameter is much smaller and the resulting packing density much higher (see Figure 4) for the nanotubes grown on A1 2 0 3 .
  • Fig. 12A shows the CV curves of GC and of VN/GC at a slow scan rate of 20 mV/s.
  • Fig. 12B shows the CV data for CNT/Inconel and for VN/CNT/Inconel at a slow scan rate of 20 mV/s. It is clear that the cathodic current is higher than the anodic current.
  • Fig. 13A shows the CV results (scan rate of 50 mV/s) for the case of the CNT/A1 2 0 3 .
  • C sp specific capacitance
  • 13B shows the CV results for CNT/A1 2 0 3 and for VN/CNT/A1 2 0 3 at a sweep rate of 20 mV/s.
  • the total capacitance of the VN- covered array is the sum of the capacitance due to double layer charging and the electrochemical pseudocapacitance of the VN overlayer.
  • the VN covers a relatively small fraction of the CNTs, one can assume that the mass available for double layer charging is about the same in each case.
  • the pseudocapacitive contribution due to the VN surface film can then be obtained from the difference of the two CV curves. This value is calculated to be 131 F/g. This is roughly 50% higher than that of VN/GC, indicating only limited improved utilization of the nitride.
  • the measured impedance spectra were analyzed using the complex nonlinear least- squares (CNLS) fitting method on the basis of the equivalent circuit, 2 which is given in Figure 14.
  • CNLS complex nonlinear least- squares
  • the intercept at real part ( ⁇ ') represents a combined resistance of ionic resistance of electrolyte, intrinsic resistance of substrate, and contact resistance at the active material/current collector interface ( R e or ESR ).
  • R ct represents the charge-transfer resistance caused by the faradaic reactions and C di is the double-layer capacitance on the electrode surface.
  • Z w corresponds to the Warburg resistance, which is a result of the frequency dependence of ion diffusion/ transport in the electrolyte to the electrode surface.
  • C L is the limit capacitance.
  • Cepek, C Knop-Gericke, A.; Milne, S.; Castellarin-Cudia,C; Dolafi, S.; Goldoni, A.; Schloegl, R.; Robertson, J. J. Phys. Chem. C 2008, 112, 12207.

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Abstract

La présente invention concerne la synthèse de réseaux tridimensionnels (3D) rendus supercapacitifs de manière électrochimique. Les réseaux comprennent des nanotubes de carbone à parois multiples recouverts par des matériaux fonctionnels nanocristallins tels que du nitrure de vanadium et ancrés de manière ferme à du carbone vitreux ou à des électrodes en Inconel. Ces nanostructures font preuve d'une capacitance spécifique convenable de 289 F/g, ce qui est réalisé dans 1 M d'électrolyte de KOH à une vitesse de balayage de 20 mV/s. Les structures à conductivité électrique élevée et bien connectées offrent une capacité de vitesse importante ; à une vitesse de balayage très élevée de 1 000 mV/s, la capacitance relative chute de moins de 20 % par rapport à la vitesse de balayage de 20 mV/s. Une telle capacité de vitesse n'a jamais été rapportée pour le VN, et est hautement inhabituelle pour tout autre oxyde ou nitrure. Ces réseaux 3D affichent également des profils de tension triangulaire presque idéaux durant des cycles de charge-décharge de courant.
PCT/CA2012/050190 2011-03-27 2012-03-27 Composites à nanotubes de carbone WO2012129690A1 (fr)

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Cited By (6)

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US20140321027A1 (en) * 2013-04-30 2014-10-30 Ultora, Inc. Rechargeable Power Source For Mobile Devices Which Includes An Ultracapacitor
CN104992847A (zh) * 2015-05-14 2015-10-21 同济大学 一种具有高功率密度的非对称超级电容器及其制备方法
US10600582B1 (en) 2016-12-02 2020-03-24 Fastcap Systems Corporation Composite electrode
CN112053855A (zh) * 2020-08-28 2020-12-08 中南林业科技大学 基于多壁碳纳米管-碳化木材混合支架的电极材料、制备方法和超级电容器
US11270850B2 (en) 2013-12-20 2022-03-08 Fastcap Systems Corporation Ultracapacitors with high frequency response
US11557765B2 (en) 2019-07-05 2023-01-17 Fastcap Systems Corporation Electrodes for energy storage devices

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WO2011005693A1 (fr) * 2009-07-06 2011-01-13 Zeptor Corporation Structures composites à nanotube de carbone et procédés pour leur fabrication

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WO2011005693A1 (fr) * 2009-07-06 2011-01-13 Zeptor Corporation Structures composites à nanotube de carbone et procédés pour leur fabrication

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20140321027A1 (en) * 2013-04-30 2014-10-30 Ultora, Inc. Rechargeable Power Source For Mobile Devices Which Includes An Ultracapacitor
EP3014643A4 (fr) * 2013-04-30 2017-11-01 ZapGo Ltd Source d'alimentation électrique rechargeable incluant un supercondensateur et destinée à des dispositifs mobiles
US20180342357A1 (en) * 2013-04-30 2018-11-29 ZapGo Ltd. Rechargeable power source for mobile devices which includes an ultracapacitor
US11244791B2 (en) 2013-04-30 2022-02-08 Oxcion Limited Rechargeable power source for mobile devices which includes an ultracapacitor
US11270850B2 (en) 2013-12-20 2022-03-08 Fastcap Systems Corporation Ultracapacitors with high frequency response
CN104992847A (zh) * 2015-05-14 2015-10-21 同济大学 一种具有高功率密度的非对称超级电容器及其制备方法
US10600582B1 (en) 2016-12-02 2020-03-24 Fastcap Systems Corporation Composite electrode
US11450488B2 (en) 2016-12-02 2022-09-20 Fastcap Systems Corporation Composite electrode
US11557765B2 (en) 2019-07-05 2023-01-17 Fastcap Systems Corporation Electrodes for energy storage devices
US11848449B2 (en) 2019-07-05 2023-12-19 Fastcap Systems Corporation Electrodes for energy storage devices
CN112053855A (zh) * 2020-08-28 2020-12-08 中南林业科技大学 基于多壁碳纳米管-碳化木材混合支架的电极材料、制备方法和超级电容器
CN112053855B (zh) * 2020-08-28 2022-03-04 中南林业科技大学 基于多壁碳纳米管-碳化木材混合支架的电极材料、制备方法和超级电容器

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