CARBON MATERIALS

Abstract

There is described a carbon material comprising sp.sup.2 and sp.sup.3 hybridised carbon. Also described is a method of making a carbon material the method comprising: exposing a substrate to a flux of at least 10.sup.11 carbon ions per cm.sup.2 of substrate per 1 ms, a majority of the carbon ions having a kinetic energy of at least 10 eV. Further, electrodes comprising the carbon material are described. The electrodes may operate as an anode in Li ion battery characterised with improved specific capacity and operation life-time.

Claims

1. A carbon material formed by exposing a substrate to a flux of at least 10.sup.11 carbon ions per cm.sup.2 of substrate per 1 ms, a majority of the carbon ions having a kinetic energy of at least 10 eV to provide a carbon material comprising sp.sup.2 and sp.sup.3 hybridised carbon having a hierarchical porosity to provide a specific lithium storage capacity of at least 400 mAh/g and wherein the percentage of sp.sup.2 type carbon is at least 25 w % based on the total weight of the material and the percentage of sp.sup.3 type carbon is at least 20 w % based on the total weight of the carbon material.

2. The carbon material of claim 1 wherein the carbon material is deposited on the substrate without any binders to adhere the carbon to the substrate.

3. The carbon material of claim 1, wherein the carbon material comprises graphite-like nanocrystals of regularly arranged layers of carbon embedded in amorphous carbon.

4. The carbon material of claim 3, wherein the inter-layer spacing between individual layers in areas of regularly arranged carbon being greater than 0.335 nm.

5. The carbon material of claim 1 wherein the material is electrically conductive, optionally with an electrical conductivity of at least 1 S/m.

6. The carbon material of claim 1, wherein the carbon material has an initial specific lithium storage capacity of at least 1000 mAh/g at a first charge cycle.

7. The carbon material of claim 1 wherein the material has a surface area of at least 1000 m.sup.2/g.

8. The carbon material of claim 1, wherein the carbon material comprises from 0.1 w % to 30 w % of one or more additives or dopants, optionally selected from Si, P, Fe, Cu, Li, Al, N, O, S, P, B, Ti, Co, Ni, Na, Ka or combinations thereof, the additive or dopant being co-deposited with the carbon or incorporated into the carbon material as particles or layers.

9. A method of making a carbon material the method comprising: exposing a substrate to a flux of at least 10.sup.11 carbon ions per cm.sup.2 of substrate per 1 ms, a majority of the carbon ions having a kinetic energy of at least 10 eV.

10. The method of claim 9 wherein the flux is provided by a virtual cathode deposition (VCD) process.

11. The method of claim 9, further comprising co-depositing one or more dopants or additives to form part of the carbon material or incorporating the dopant or additives into the carbon material as particles or layers.

12. The method of claim 9, further comprising separating the carbon material from the substrate to provide a free-standing carbon material film.

13. An electrode for an electrochemical cell, the electrode comprising an electrode substrate bearing a carbon material according to claim 1.

14. The electrode of claim 13, wherein the electrode substrate comprises a current collector, the current collector optionally comprising a metal foil.

15. The electrode of claim 13, the electrode substrate comprising a current collector, comprising an interlayer between the current collector and the carbon material, the interlayer optionally comprising Si, P, Fe, Cu, Li, Al, S, P, B, Ti, Co, Ni, Na, Ka or a combination thereof.

16. The electrode of claim 13, wherein the electrode substrate comprises a polymeric support to support the carbon material and the carbon material bears a current collector layer.

17. The electrode of claim 13, wherein the electrode substrate comprises a polymeric substrate which is non-current collecting to provide a battery separator.

18. The electrochemical cell comprising the electrode of claim 13 in an electrochemical cell.

19. The electrochemical cell comprising the electrode of claim 13 in an electrochemical cell, being selected from the group consisting of a lithium ion cell, a lithium metal cell, a sodium ion cell, a sulphur cell, a fuel cell, and a supercapacitor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0112] One or more non-limiting embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0113] FIG. 1 is a schematic drawing showing an apparatus for carrying out a virtual cathode deposition process;

[0114] FIG. 2 is a series of graphs showing time-of-flight measurements of the carbon ion plume generated in the VCD process of Example 1, taken at various distances from the graphite target;

[0115] FIG. 3 is a graph showing a non-normalised energy distribution of the carbon ions generated in the VCD process of Example 1;

[0116] FIG. 4 is a series of graphs showing energy-dispersive X-ray spectroscopy (EDX) results for selected samples from Example 3. (A): Sample 3; (B): Sample 4; (C): Sample 5; (D): Sample 7;

[0117] FIG. 5 is a series of scanning electron microscope (SEM) images of the cross-section of carbon material sample C7 of Example 3;

[0118] FIG. 6 is high resolution Focused ion beam (FIB) SEM image of sample C51 of Example 3;

[0119] FIGS. 7(a)-(c) are XPS spectra of the carbon material samples I-K, respectively, of Example 13;

[0120] FIG. 8(a) is a transmission electron microscope (TEM) image of the carbon material sample of Example 8; FIG. 8(b) is an enlarged image of zone 1 of FIG. 8(a); FIG. 8(c) is a graph showing the pixel intensity along the arrow in FIG. 8(b);

[0121] FIG. 9 is a Raman spectrum of carbon material sample C51 of Example 3;

[0122] FIG. 10 is a graph showing the X-ray diffraction spectroscopy (XRD) spectra of the carbon material samples C21, C22 and C23 of Example 3, along with that of an aluminium substrate;

[0123] FIG. 11 is a series of X-ray photoelectron spectroscopy (XPS) spectra of the carbon material samples 3, 4, 5 and 7 of Example 3;

[0124] FIG. 12 is a series of SEM images of free-standing films of a carbon material sample of Example 13;

[0125] FIG. 13 is the Raman spectra of free-standing films of the carbon material samples of Example 13;

[0126] FIG. 14 is a photograph of a strip of iron-doped carbon-containing material with a gradually increasing of iron content along the length of the strip;

[0127] FIGS. 15(a) and (b) are Raman spectra of three different areas of the strip of iron-doped carbon-containing material of FIG. 14;

[0128] FIGS. 16(a) and (b) are graphs showing XPS analysis of the carbon (FIG. 16(a)) and Fe content (FIG. 16(b)) in areas 1, 2, and 3 of the iron-doped film strip of FIG. 14;

[0129] FIG. 17 shows the outcome of the electrochemical test of Example 15. FIG. 17(a) is a graph showing the cyclability of the coin cell test battery with the carbon material on copper electrode. FIG. 17(b) is a graph showing potential versus specific capacity of the cell; and

[0130] FIGS. 18(a) and (b) are graphs showing the results of tests on the cycle life of the carbon material on copper electrode as anode in a lithium ion half-cell setup.

EXAMPLES

[0131] In various embodiments, the invention provides a method of making a carbon material using a VCD process.

[0132] With reference to FIG. 1, the VCD process comprises providing a hollow cathode, a substrate and a carbon target, the substrate and the target being located on opposite sides of the hollow cathode. A plasma is supplied to the interior of the hollow cathode at an end of the hollow cathode nearest the target. A high voltage pulse is then supplied to the hollow cathode, such that a virtual plasma cathode is formed and such that the virtual plasma cathode generates an electron beam, directed towards the target. A plume of ablated target material comprising carbon ions passes through the hollow cathode towards the substrate and is deposited thereon.

[0133] The VCD process thus utilizes a Virtual Plasma Cathode (VPC) as a pulsed electron beam source. Prior to each pulse of the electron beam, a new plasma cathode is generated by fast (e.g. 100 ns) ionization of an operational gas. The plasma cathode acquires negative high voltage potential with respect to a target due to the application to the plasma of a high-voltage and high-current pulse (e.g. 100-10000 ns) generated by a Pulsed Power Generator (PPG). This causes the VPC to form in the vicinity of the target and an electron beam is extracted from the plasma boundary. The electron beam ablates the target and then the VPC decays, leaving a space for ablated target material in the form of a plasma plume to propagate toward a substrate, where it condenses forming a carbon material.

[0134] Repetition of the pulse, which starts with the formation of a new VPC and ends with the condensing of the target material on the substrate, allows a material to grow on the substrate with controlled growth rate and properties.

[0135] Deposited material properties, such as the crystal structure (formation of chemical bonds between the atoms of the film) or the lack of it, adhesion (formation of the bonds between the film and substrate), electrical conductivity (energy gap between conduction and valence band) and roughness (surface crystal state or structure and the number of phases), are dependent on the target material plume plasma kinetic energy, ionization level, temperature, and density. The plasma plume parameters in turn depend on the electron beam parameters.

Example 1Deposition of Carbon Material

[0136] A VCD tool generally as described in WO2016042530 with reference to FIG. 5 thereof was used to generate a carbon ion flux and deposit a carbon material. The disclosure of WO2016042530 is incorporated herein by reference. FIG. 5 of WO2016042530 is reproduced herein as FIG. 1.

[0137] The deposition process was performed with some key modifications of the teaching of WO2016042530. In particular, the total VCD pulse energy was raised to >2.5 J and the pulsed power source was modified to have an internal impedance of 10 Ohm or lower. The triggering pulse parameters and gas supply were modified to further improve electron beam focusing. This increased the overall energy density of the electrons beam on the target surface, which in turn improved the energy delivered to the plume plasma and increased the kinetic energy of the deposited carbon ions above 20 eV. The modifications are explained below in more detail.

[0138] With reference to FIG. 1, the apparatus 1 was provided with a graphite target 117 (99% purity), and an aluminium substrate 125. The chamber 127 was pumped down to 10.sup.5 mbar (10.sup.3 Pa) initial pressure. Then argon gas was introduced from sources 123, 503 to increase the pressure in the chamber up to 4.Math.10.sup.4-8.Math.10.sup.4 mbar (3.Math.10.sup.2-8.Math.10.sup.2 Pa), with the gas supply from source 503 providing 60% to 80% of the total gas flow.

[0139] Pulsed power source 119 had an internal impedance of 10 Ohm or lower, and was operated to generate pulses of >15 kV voltage at 20 Hz-200 Hz repetition rate. The total pulse energy per pulse was greater than 2.5 J, preferably 4 J or 4.5 J. The duration of the pulses was 10-20 s.

[0140] When a pulse reached its maximal voltage, a trigger pulse was supplied by the trigger pulse generators 121, 502. The trigger pulse voltages were in the range of +5 to +15 kV and had a duration of 2 s. A first trigger pulse was generated by trigger pulse generator 502 and a second pulse by trigger pulse generator 121, with no delay between the first and second pulses beginnings. The trigger pulse generators 121 and 502 were modified to have an internal impedance of 100 Ohm and total energy of 0.05 J per pulse each. This allowed the simultaneous energy injection from 121 and 502 into the initial plasma 127 increasing its temperature and density by at least 20% compared with the previous setup of a short non-simultaneous trigger pulses.

[0141] The electrical pulses caused the formation of a virtual plasma cathode, which in turn generated an electron beam to ablate the target. The denser virtual cathode accompanied with the lower impedance of the pulsed power source led to a higher electron beam current (increase on 20%) and energy density of the electron beam on the target. A plasma plume was formed and condensed on the substrate which was placed at 20 cm distance from the target. A carbon material was formed on the substrate.

[0142] The substrate temperature did not exceed 60 C. The deposition rate at a distance of 25 cm from the target was measured with a quartz-crystal microbalance (QCM) and was determined to be 0.01 nm/pulse for 4 J total energy of the pulse.

Example 2Characterisation of Deposition

[0143] The plasma plume ablated from the graphite target in the deposition of Example 1 was investigated with a well-known Time-Of-Flight method, for example described in publication D. Yarmolich et. al, Plasma Sources Sci. Technol. 17 (2008) 035002. In particular, the ion current of the plasma plume was measured with a biased Faraday Cup at distances 30-50 cm from the ablation point on the target. The results are shown in FIG. 2.

[0144] The delay of an ion current peak increase with distance was transformed to the linear velocity. The lines in FIG. 2 show the delay of the Faraday Cup (I.sub.FC) depending on distance. The velocity of the plasma front was found to be of 4.5.10.sup.6 cm/s and the carbon ion maximum flux propagated with velocity of 2.10.sup.6 cm/s.

[0145] The carbon ion flux (number of ions arriving to the substrate per unit of surface area per unit of time) can be estimated by integrating the Faraday Cup current over unit of time that provides the total charge of arrived ions and dividing it by the ion charge (1.6.Math.10.sup.19 C) and the area of the Faraday Cup current collector.

[0146] With reference to FIG. 3, the velocity of the carbon ions can be transformed to a non-normalized Energy Distribution. Most of the ions have an energy in the range of from 10 eV to 150 eV, and significant amount of the ions have energy above 100 eV. There is some amount of the ions that have energies above 150 eV. However, Faraday Cup measurements of the ions having an energy above 150 eV are not precise enough to quantify amounts accurately, due to the high secondary electron and ion emission.

Example 3Deposition of Further Carbon Materials

[0147] Further depositions of carbon material were performed using VCD, generally as described hereinabove, in accordance with the parameters set out in Table 1:

TABLE-US-00001 TABLE 1 Pulse Example Substrate Film Thickness Energy (J) 1 Aluminium 100 nm 4.5 2 Aluminium 60 nm 4.5 3 Aluminium 40 nm 4.0 4 Aluminium 0.8 m 4.0 5 Aluminium ca. 1 m 4.0 6 Aluminium ca. 1.3 m 4.5 7 Aluminium ca. 5 m 4.0 C7 Free-standing ca. 10 m 4.5 C21 Aluminium ca. 1 m 4.5 C22 Aluminium ca. 4 m 4.5 C23 Aluminium ca. 10 m 4.5 C51 Copper ca. 5 m. 4.5

Example 4Characterisation EDX

[0148] FIG. 4 shows energy-dispersive X-ray spectroscopy (EDX) results for samples 3, 4, 5 and 7 from Example 3. EDX analysis of the carbon material in each sample revealed the presence of three elements only: carbon (film); aluminium (substrate); and oxygen (oxide layer formed on the aluminium substrate). The signal strength of the oxygen and aluminium decreased with increasing thickness, confirming that the films are pure carbon. The aluminium peaks almost disappear in the EDX spectrum for sample 7, which has the thickest layer of carbon material.

Example 5SEM Images

[0149] FIG. 5 shows scanning electron microscope (SEM) images of a cross-section of sample C7. FIG. 5a shows two clearly distinguishable zones, which correspond to different growing modes of the film during VCD deposition. The upper surface and its adjacent zone is dense and representing the initial stage of the film growth. The second one starting at 1 m thickness from the upper surface is largely granular. SEM analysis shows the complex hierarchical morphology of the carbon material which consists of grains with sizes 10-100 nm (FIG. 5c), 100-1000 nm (FIG. 5b) and above 1 micron (FIG. 5a). Grains with the size 100-1000 nm have a characteristic repeatable shape (see FIG. 5b-c). One can also estimate the pore size between the grains that is 20-100 nm from FIG. 5c, 100-1000 nm from FIG. 5b and above 1 micron (FIG. 5a).

Example 6FIB-SEM Image

[0150] In order to check the porosity below 20 nm a (Focused ion beam) FIB SEM was employed. FIG. 6 shows a FIB SEM image of sample C51 containing the pores in the range 1-20 nm.

Example 7XPS and sp2/sp3 Hybridization Ratio

[0151] FIGS. 7 a to 7 c show XPS spectra of Examples I to K from Table 4, respectively. A near ambient pressure (NAP) X-ray photoemission spectroscopy (XPS) system (Thermo Scientific ESCALAB 250Xi) was used for elemental and carbon bonding analysis. The system provides the following complementary capabilities: [0152] X-ray photoemission spectroscopy (XPS) for chemical analysis of surfaces under inert/UHV conditions (sensitivity to the chemical structure near the outmost of the surface (0.5-8 nm)); [0153] Depth profiling x-ray photoemission spectroscopy (DPXPS) which combines a sequence of argon ion gun etch cycles (The sputter rate estimate: Ta.sub.2O.sub.5=0.1 nm/sec) with XPS analysis

[0154] XPS analysis of the free-standing carbon material films shows a rather unusual ratio between sp.sup.2 and spa hybridized bonds.

[0155] The significant amount of sp.sup.2 bonds are in line with the TEM, Raman and XRD results suggesting the existence of ordered strands of 2D sheets of carbon.

Example 8TEM Images of Carbon Material on a Copper Grid

[0156] FIG. 8a shows transmission electron microscope (TEM) images of the carbon material deposited on a copper grid, in accordance with the general method outlined above.

[0157] STEM studies have been performed in a state-of-the-art analytical instrument (FEI Tecnai Osiris) designed for easy TEM imaging and fast chemical mapping in scanning transmission electron microscope (STEM) configuration using energy dispersive X-ray and electron energy loss spectroscopies (EDX and EELS) with primary beam energy of 200 keV. TEM imaging is accommodated with a Gatan UltraScan1000XP (2048 by 2048 pixel) camera with high-speed upgrade. Four STEM detectors (HAADF, DF4, DF2 and BF) allow angular integration over a wide range of collection angles and are compatible with the EEL spectrometer. EDX detectors are FEIs Super-X system employing 4 Bruker silicon drift detectors (SDD) for high collection efficiency (>0.9 sr solid angle) and high count rates (>250 kcps). EELS is performed using Gatan's Enfinium ER 977 spectrometer with electrostatic shuttering and fast Voltage Scan Module for Dual EELS (sequential low-loss and high-loss spectrum acquisition) and Range EELS.

[0158] The TEM images show that there are a few nanocrystals with a size of about 10 nm embedded in the amorphous carbon. The nanocrystals shown in FIG. 8a appear to represent parallel sheets of graphene or Net W or another 2D carbon allotrope packed at the structure with the d.sub.002 spacing larger than that of graphite (0.335 nm). Five different zones of FIG. 8a designated by rectangles were analysed on the nanocrystals d.sub.002 spacing.

[0159] FIG. 8b shows zone 1 of FIG. 8a. There are clear black and white strips representing nine 2D carbon layers. The pixels intensity along the arrow shown in FIG. 8b are shown in FIG. 8c. Averaging the distance between the peaks in FIG. 8c provides the d.sub.002 spacing for the nanocrystal in the zone 1 as 0.352 nm. The d.sub.002 spacings obtained in the same way of five zones selected in FIG. 8a are shown in Table 2.

TABLE-US-00002 TABLE 2 Interlayer distance nm d.sub.1 0.352 d.sub.2 0.348 d.sub.3 0.353 d.sub.4 0.358 d.sub.5 0.366 average 0.355

Example 9Raman Spectra

[0160] In order to further confirm the structure, the carbon material film was investigated using Raman spectroscopy.

[0161] For Raman measurements a Renishaw Ramascope-1000 was used, with a 30 mW 514.5 nm Ar excitation laser operated with the holographic Notch-filter with cut-off at 150 cm.sup.1. The data collection was calibrated against a silicon standard. The instrument offers spectral resolution of 0.1 cm.sup.1 and spatial resolution of 1 m. Variable laser power levels (1-100%) were used at an integration time of 10 s. Spectra were normally collected at 5 different randomly selected point of the sample surfaces in the range of 100-3200 cm.sup.1 Raman shift. The spectra background was subtracted with the Bio-Rad KnowItAll software and the peaks were de-convoluted using Origin software.

[0162] All samples showed the typical structure of disordered nanostructured carbon. An exemplar Raman spectra with G band at around 1340 cm.sup.1, D band at around 1600 cm.sup.1 and 2D band at around 2680 cm.sup.1 of sample C51 can be found in FIG. 9. The ratio and shape of the bands depend on the VCD parameters as well as thickness of the film. The intermixed graphitic content with sp.sup.2 (graphitic) and sp.sup.3 (diamond) carbon bonds was further confirmed by deconvolution of the first order Raman spectra.

Example 10XRD and Allotropic Structure

[0163] FIG. 10 shows the XRD spectra in Bragg-Brentano geometry for samples C21, C22 and C23 and Al substrate.

[0164] X-ray diffraction (XRD) was performed with a D8 Advance Bruker diffractometer (position sensitive detector (LynxEye EX)6.5% energy resolution, moving slit to reduce background scattering at low angles, best instrumental resolution 0.06 in 2theta & 0.03 in omega) equipped with Cu K . The 2 angle was varied with a step size of 0.02-0.04. In order to achieve reasonable intensity, long counting times (up to 14 s/step) were utilized. With the same intention, the use of Ni-filters was avoided.

[0165] For all samples a broad peak around 20 deg is observed that most probably corresponds to agglomerates of 2D carbon monolayers. The peak was found to be shifted towards smaller angles than reported in the literature for hard carbon (Mechanism of lithium insertion in hard carbons prepared by pyrolysis of epoxy resins, doi: 10.1016/0008-6223(96)00177-7). The peak at around 26.5 deg indexed as 002 of graphite-like unit cell and indicates the presence of the nanocrystals. This observation is in agreement with the TEM data.

[0166] The presence of these two characteristic peaks on the same XRD pattern has never been reported in the literature.

Example 11XPS Spectra

[0167] The X-ray photoelectron spectroscopy (XPS) spectra for samples 3, 4, 5 and 7 of Example 3 are shown in FIG. 11. A near ambient pressure (NAP) X-ray photoemission spectroscopy (XPS) system (Thermo Scientific ESCALAB 250Xi) was used.

[0168] The XPS results are in good agreement with both XRD and Raman. The film is pure carbon, with a mixture of sp.sup.2 and sp.sup.3 bonds and some carbon-oxygen bonds were observed, however the amount of oxygen is lower comparing to the free-standing films of example 7. The oxygen was absorbed after the samples were extracted from the vacuum chamber and the free standing carbon nanomaterial absorbs more than deposited on the Al substrate.

Discussion of Examples 1 to 11

[0169] Without wishing to be bound by theory, it appears that the structural features of the carbon materials were formed due to the high kinetic energy and flux of the carbon ions during the deposition. It is posited that the processes during the deposition may be understood as follows: [0170] 1. The pure carbon ions in significant amount (>10.sup.12 ions per cm.sup.2 of the substrate) arrive to the substrate during short time <50 us (see FIG. 2) with high kinetic energies (see FIG. 3) [0171] 2. The incoming ions collide with the previously deposited film or substrate losing their energy (usually <10 eV per collision) so a few collisions are required before the incoming ion will stop somewhere under the surface. [0172] 3. Those high-energy ions (>20 eV) are sub-planted into the substrate or previously deposited film on a depth of few atomic layers (see Y. Lifshitz et. all, Diamond and Related Materials 4 (1995) 318, and references within it). Lifshitz did not obtain the same structure of materials probably because of low flux of the carbon ions (100 times lower than in various embodiments of the invention) and his process was not pulsed. [0173] 4. Then there is a relaxation time (between pulses) when the internal stress generated within the film due to the sub-plantation is relaxed. This is a temperature-dependent process and in our case the temperature is <60 degrees C. [0174] 5. Next pulse comes in at least 100 us after all the processes in the film are finished

[0175] The overall process can be imagined as implanting carbon ions with high energy inside the film, the film thus growing from inside. This process of the material formation can be considered as the formation of carbon material with exceeding energy brought with the carbon ions. The energy of the ions goes into the formation of a crystal stricture which preferably should have as much internal energy as possible. Structures with high surface area usually have more internal energy, hence the favourable structure obtained with the high-energy and high-intensity ion beam should have a morphology with a high surface area. The presence of spa bonds suggests additional way to accommodate the high internal energies per carbon atom.

Example 12Conductivity of Carbon Material Deposited on Glass

[0176] The conductivity of carbon material films deposited over glass at various thicknesses was investigated. Samples A to H were prepared according to the general method outlined above by depositing carbon onto a glass substrate according to the general method of Example 1 with a pulse energy of 4.5 J. The carbon layer thickness and the deposition process parameters were varied between the samples.

[0177] Resistance and resistivity were determined with a 2-point probe method using a Keithley 2002 multimeter.

[0178] The properties of samples A to H are shown in Table 3 below.

[0179] The conductivity and resistivity of the carbon material films was found to be dependent upon the thickness that corresponds to the number of VDC pulses applied to form the film.

TABLE-US-00003 TABLE 3 Number of Resistance Resistivity Conductivity Example pulses (1000) (M) ( .Math. m) (S/m) A 25 25.94 0.99769 1.00231303 B 50 7.320 0.56308 1.775956284 C 100 1.800 0.27692 3.611111111 D 150 0.828 0.19108 5.233494364 E 10 29.72 0.57154 1.749663526 F 30 3.810 0.21981 4.549431321 G 70 0.656 0.08831 11.32404181 H 260 0.269 0.12415 8.054522924

[0180] The conductivity of the carbon material film is due to the sp.sup.2 bonds which can be metallic type for net W carbon allotrope, semi-metallic type for graphene or graphite, while the diamond bonds spa favour a non-conductive material behaviour. The conductivity can be improved with use of metal doping.

Example 13Free Standing Carbon Materials

[0181] In samples I to K relatively thick (>200 nm) carbon material films were separated from their substrates to provide a free-standing carbon material film. In each case, deposition of the carbon material film was carried out according to the general method outlined above, and then the film was mechanically separated from the substrate. Example J was carried out with a polyethylene terephthalate (PET) substrate onto which a thin film of stainless steel was deposited prior to the deposition of carbon. The deposition process parameters and substrates used in each sample are shown in Table 3 below.

TABLE-US-00004 TABLE 4 Number of Approx. Example pulses (1000) thickness (nm) Substrate I 50 800 Stainless steel J 30 500 Stainless steel on PET K 50 800 Stainless steel

[0182] SEM images showed the bottom side of the free-standing films to be smooth; similar to the smoothness of the stainless steel foil substrate to which is was previously attached. FIG. 12 shows the top side of the free-standing film was rough, similar to the roughness observed in the SEM images of the film adhered to an aluminium substrate.

[0183] FIG. 13 shows a comparison of the Raman spectra of Examples I to K (top line: example I; middle line: example J; bottom line: example K) taken from the upper side. The Raman spectra of the upper side of all three spectra has a signal at D: 1350 cm.sup.1 and G: 1580 cm.sup.1 of the carbon. Also there are peaks in the area between 200-1100 cm.sup.1 that that suggests the presence of some of the removed substrate material integrated into the carbon film. This confirms the formation of strong bonds between the film and the substrate.

Example 14: Doping/Mixing with Iron

[0184] A strip of iron-doped carbon-containing material was prepared with a gradually increasing gradient of iron content along the length of the strip, as shown in FIG. 14.

[0185] In order to prepare the strip of carbon material doped/mixed with iron, a vacuum chamber was set up having a first VCD source with a graphite target (deposition process was the same as the sample I of example 11) and a second VCD source with an iron target. The iron target was ablated in such a way that the ablated iron material arrived at the same aluminium substrate as the ablated carbon.

[0186] The experiment was initially performed with independent control of the second VCD source so that the parameters of the ablated iron plasma could be adjusted to provide the required different energies, timing of pulses, densities etc of the iron ions arriving at the substrate. This allowed the structure and abundance of dopant material to be precisely controlled. The pulses of carbon and other material plasmas can be arranged to arrive at the substrate simultaneously, alternating pulse by pulse, or alternating a number of pulses of the first material and then a number of pulses of the second material.

[0187] The iron-doped carbon material was prepared such that the centre of deposition of carbon was towards the left side of the as strip, whilst the centre of deposition of iron was on the right of the strip. Hence, the iron-doped material was prepared in such a way that there was a gradual increase in carbon content and a gradual decrease in iron content from left to right across the strip.

[0188] Raman analysis was performed on three different areas of the strip of iron-doped film prepared above, as shown in FIG. 15a and FIG. 15b. Area 1 of the strip (on the far left of the strip) corresponds to approximately 90% iron and 10% carbon film. Area 2 of the strip (in the centre of the strip) corresponds to approximately 50% iron and 50% carbon film. Area 3 of the strip (on the far right of the strip) corresponds to approximately 10% iron and 90% carbon film. The Raman spectra confirmed the abundance of material in each area of the strip.

[0189] For Fe samples, Fe peak intensity increased as the thickness increased. For C samples, all samples showed a crystalline and amorphous mixed structure.

[0190] FIG. 16a shows XPS analysis of the carbon content in areas 1, 2, and 3 of the strip. There is a noticeable shift in the character of the carbon bonds from spa to sp.sup.2 as the carbon content of the strip increases. FIG. 16b shows XPS analysis of the iron content in areas 1, 2, and 3 of the strip.

[0191] In conclusion, this study demonstrates the possibility of doping carbon-containing films with iron. This technology can be used to dope carbon-containing materials with any other material.

Example 15: Battery Test

[0192] Electrodes were formed by depositing carbon material (0.1 mg) on standard copper over an area of about 1.13 cm.sup.2 without any additional material interlayers, i.e. the carbon material was deposited directly onto the copper foil.

[0193] The deposition conditions for the carbon material were the same as sample 6 of Example 3.

[0194] The electrochemical properties of the electrodes as anodes in lithium ion cells were investigated using 2032-type coin cells with a lithium foil counter electrode and 1M LiPF.sub.6 in ethylene carbonate/dimethyl carbonate (EC/DMC) (1:1 v/v) as the electrolyte, and separator [Celgard 25 m Trilayer polypropylene-polyethylene-polypropylene membrane].

[0195] The specific capacities of the electrodes were calculated from the total masses of active materials, and their electrochemical characteristics were examined by charge-discharge curves using a galvanostat (CT2001A, LAND) within a 0.01-3 V range.

[0196] An electrochemical test of the coin cell test battery with the carbon material on copper electrode was performed over 200 cycles. FIG. 17a show the cycleability (200 cycles) of the carbon material on copper electrode. The specific capacity of the 200th cycle was observed to be 716 mAh/g at a current of 0.5 A/g. This shows that carbon material has a higher specific capacity than graphite (theoretical specific capacity of 372 mAh/g) at relatively high current density and that this capacity is stably retained over 200 cycles with insignificant losses. The first cycle capacity of 1700 mAh/g was found to become irreversible and it is thought that this is related to the formation of Solid-Electrolyte Interface (SEI) during first 20 cycles. The SEI formation requires further investigation.

[0197] With reference to FIG. 17b, since at full capacity the potential against lithium is zero volts, all available lithium sites appear to be utilised during discharge, which is reproducible even after 200 cycles.

Discussion of Examples 13 to 15

[0198] The battery performance of the examined embodiments of carbon material is postulated to originate from their structure, which defines metal or semi-metal conductivity, and a Li ion intercalation mechanism between the 2D layers of carbon. It is thought the 2D layers consist of the net W carbon allotrope or other similar to graphene 2D structure which provides both the electronic conductivity and an intercalation mechanism. The distance between the 2D layers are slightly larger than in graphite, providing the space for the Li ion intercalation. The hierarchical porosity of the carbon materials is also beneficial for the battery performance.

[0199] In summary, the examined carbon materials' benefits for batteries can be summarised as follows: [0200] 1. Crystalline areas with 2D structures which provides metallic electrical conductivity. [0201] 2. Larger-than-graphite distance between 2D layer enables higher capacity of Li ions intercalated into the carbon material. [0202] 3. Hierarchical porosity of carbon material enhances electrolyte penetration and increases specific capacity. [0203] 4. Presence of spa bonds improves mechanical hardness of the carbon material, which enhances cyclability. [0204] 5. Formation of chemical bonds with the substrate/current collector improves contact/battery impedance. [0205] 6. Possibility to dope the carbon materials with materials (Si, for example which have high specific capacity) which can improve further the battery performance. [0206] 7. Possibility to deposit carbon material on the battery components without use of binder improves further the battery weight hence improving energy density of the cell. [0207] 8. Combination of the material conductivity with good contact/adhesion to the substrate and with the good penetration of electrolyte into the carbon material through the hierarchically arranged pores provides a high rate of charging/discharging currents (up to 10 C) of the battery cell.

[0208] In conclusion it was found that the carbon material can be used as an electrode material in batteries or supercapacitors. The application for energy storage can be achieved with different setups, using different electrolytes and/or second electrode materials.