Patent Description:
The increase in the cost of fuels, exhaustion of non-renewable energy sources, pollution, and a large increase in the use of portable electronic devices requires other energy storage technologies and devices to fulfil the energy needs beyond current consumer requirements. As a result, there is a growing interest in high-power and high-energy-density storage systems. Electrochemical energy devices form an indispensable part of the transition to green energy. Supercapacitors, batteries and fuel cells are energy devices based on an electrochemical energy conversion mechanism. An electrochemical supercapacitor is an energy storage device with high specific capacitance, long cycle life, high power density, and no memory effect. A supercapacitor can store <NUM> to <NUM> times more energy per unit mass than electrolytic capacitors and can deliver charge much faster than commonly used batteries, with a fast charge-discharge process. Thus, supercapacitors can function as a bridge for the power-energy difference that exists between electrolytic capacitors (higher power density) and batteries (high energy storage). Being small, light-weight, and easy to handle makes supercapacitors attractive components for portable electronic devices. Moreover, supercapacitors can be used in hybrid electric vehicles to offer sufficient power for rapid acceleration and energy recuperation during braking.

As energy storage devices, supercapacitors are dependent on direct current (DC) power. Additionally, the complex microporous structures in a carbon-based electrode exhibit large electrochemical resistance and can rarely be charged and discharged at high frequencies (above <NUM>). This unsatisfactory frequency response of supercapacitors is one of the bottlenecks in the conversion of alternating current (AC) to DC and thus for increasing power demand. Conventional AC filter capacitors are based on aluminium electrolytic capacitors, which are bulky in size and have small capacitance. Electrodes for filtering applications in a supercapacitor demand highly conductive thin (<NUM>-<NUM>) electrode material in an intimate interconnect format, with minimum contact resistance with the current collector.

Most of the currently available energy storage devices use carbon-based electrodes for the charge-storage mechanism. Commercially available carbon-based electrodes do not meet the requirements for high-energy-density applications due to their low theoretical capacity. Alternatives to carbon-based materials are tin oxide and silicon-based materials that are capable of providing high specific capacity and energy density. Nevertheless, some of the high capacity electrodes have been found unsuitable due to capacity fading after initial charge-discharge cycles and due to large volume expansions. The large volume expansions and structural changes can damage the electrode material and thereby lower the cycling stability.

To meet the above-mentioned characteristics for supercapacitors with excellent filtering properties, direct growth of carbon-based materials on a conductive substrate (current collector) can be used as a suitable technique, which can allow an intimate interconnect format and minimum contact resistance with the current collector.

<CIT> discloses a method for the manufacture of carbon nanofibers on nickel foam for supercapacitor applications. A two-step process for the synthesis of carbon nanofibers is disclosed, including chemical vapour deposition at a temperature of <NUM>.

<CIT> discloses the application of metal nitrides for electrical energy storage devices. A multi-step process for fabricating the electrode material at high temperatures is disclosed.

A method for graphene-carbon-nanotube-based hybrid-material-based electrodes for supercapacitor applications with high-frequency performance was given in <CIT>. The method comprises different stages, which include the growth of graphene by chemical vapour deposition, depositing catalyst material onto the graphene, and the growth of carbon nanotubes at high temperatures.

<CIT> discloses a preparation method for nitrogen-doped graphene cladding nickel sulphide composite electrode materials. The method of <CIT> includes high-temperature annealing for the preparation of the electrode material. High-temperature synthesis conditions are not a suitable option for the large scale growth of electrode materials due to large energy consumption and critical treatment conditions.

<CIT> reveals the application of metal nitride-containing electrodes for supercapacitors. The active materials were fabricated by an ammonothermal process using supercritical ammonia with alkali mineralizers. The active materials are mixed with conductive carbon agents and binders and coated onto a current collector to fabricate the electrode.

A multi-step method, including chemical vapour deposition, atomic layer deposition, and electrochemical deposition, for fabricating noble-metal-atoms-coated carbon-nanostructure-based electrodes for supercapacitors was given in <CIT>.

A method for fabricating thin-film carbon-based electrodes for flexible and transparent supercapacitors was disclosed in <CIT>. The active material was fabricated on a porous template using a chemical vapour deposition process.

<CIT> discloses a preparation method for graphene-based electrodes for AC line filtering applications. The electrodes were fabricated by an electrochemical reduction method, including numerous chemical reactions.

An electric double-layer capacitor with a high-frequency response is disclosed in <CIT>. The active material was carbon nanotubes directly grown on the current collector using a catalyst-assisted technique at a heating environment. In some embodiments, binder materials were also used for preparing the electrode materials.

<CIT> discloses electrophoretic deposition of CNTs on a metal substrate for high-density supercapacitors.

<CIT> illustrates carbon nanosheets as an electrode material for supercapacitors. The carbon nanosheets were deposited directly onto conductive substrates using radio frequency plasma-assisted techniques.

<CIT> discloses methods for developing nitride, carbon nitride, and oxynitride-based electrodes for supercapacitors applications using a sol-gel process. The synthesis procedure comprises different steps, including chemical reactions, sintering, and hydrolysis.

<CIT> discloses a method for preparing a metal sulphide/graphene/nickel sulphide composite thin-film material. The procedure involves multiple steps and a long treatment time (~<NUM> hours) for the fabrication of the composite.

<CIT> discloses a method for the fabrication of electrode material comprised of fine carbon powder coated with metal oxide, metal nitride, or metal carbide for supercapacitors. The procedure involves multiple steps, including chemical reactions and ultrasonic irradiation dehydration treatment for preparing the active material. Further, the active material was mixed with polymeric binders to prepare the electrodes.

<CIT> discloses a method for manufacturing carbon nanotube-metal sulphide composites. The method includes post-synthetic ultra-centrifugation purification techniques for the selective area functionalization. The metal sulphide compounds are deposited onto the carbon nanotubes by atomic layer deposition techniques. The manufacturing of the carbon nanotube-metal sulphide nanostructure involves multiple steps, including purification and separation.

<CIT> and <CIT> disclose the application of array-type nickel-disulphide-carbon nanotube composite electrodes. The electrodes were designated as a Ni/Ni<NUM>S<NUM>/carbon nanotube-based structure or as a Ni/carbon nanotube/Ni<NUM>S<NUM> based structure. A hydrothermal curing technique for the direct fabrication of electroactive material on a conductive substrate was used for the preparation of the electrode material. However, electrode fabrication involves multiple chemical processing steps and long processing time (more than <NUM> hours).

<CIT> discloses a method for manufacturing supercapacitor electrodes comprising the steps of applying a buffer layer, a catalytic bed, a dielectric layer, an insulating layer in the dielectric layer of the window matrix to a catalytic bed, deposition in the windows of arrays of vertically oriented carbon nanotubes, the functionalization of the surface of carbon nanotubes by oxygen-containing groups, the layer formation of polyaniline containing the isotope C-<NUM>, on vertically oriented carbon nanotubes by electrochemical deposition and annealing. <CIT> discloses a composite material including carbon nanotubes and/or nanofibers and composite intrinsic and doped silicon structures. The method includes depositing a catalytic layer on a surface of a substrate in a first processing chamber, processing the catalytic layer to form a plurality of nanoislands, forming a plurality of graphitic nanofilaments over the nanoislands in a second processing chamber. <CIT> discloses highly-orientated, multi-walled carbon nanotubes grown on an outer surface of a substrate initially disposed with a catalyst film or catalyst nano-dot by plasma enhanced hot film chemical vapour deposition. <CIT> discloses carbon nanotubes manufactured by chemical vapour phase growth by using fine particles of a sulfur compound of nickel as a catalyst and introducing hydrocarbon gas at high temperature. <CIT> discloses a method for preparing a nickel sulfide-doped three-dimensional carbon nanotube foam composite material. The method comprises synthesizing a nickel-doped 3D carbon nanotube net as a substrate and using a hydrothermal reaction to form the nickel sulfide-soped 3D carbon nanotube foam composite. Rangom et al. disclose a method for the synthesis of carbon-nanotube-based electrodes for AC line-filtering applications [<NUM>]. The authors have used commercially available carbon nanotubes for preparing the active materials interfaced with an additional metal current collector.

disclose a method for preparing carbon-nanotube-film-based electrodes for AC line filtering applications [<NUM>]. The active material preparation disclosed by Yoo et al. involves several chemical reactions and purifications, and the electrode is prepared using a binder.

Miller et al. disclose a graphene double layer capacitor for AC line-filtering applications. Graphene was directly deposited on the metal substrates using plasma-assisted deposition techniques at relatively high-temperature [<NUM>].

Zhang et al. [<NUM>] disclose a one-step synthesis of reduced graphene oxide/Ni<NUM>S<NUM>-based electrodes for high-performance supercapacitors, wherein the active materials are prepared by chemical methods. Chen et al. [<NUM>] demonstrate the preparation of sponge-like NiS/Ni<NUM>S<NUM> hybrid nanosheets for supercapacitors using chemical treatment techniques. Tian et al. [<NUM>] disclose a method for constructing Ni<NUM>S<NUM> wrapped by reduced graphene oxide on carbon cloth for a supercapacitor application. Anil Kumar et al. disclose a method for the direct growth of Ni<NUM>S<NUM> on a current collector using chemical treatments [<NUM>]. Namdarian et al. disclose a chemical-treatment-assisted technique for the synthesis of reduced graphene oxide-Ni<NUM>S<NUM> nanocubes for supercapacitor applications [<NUM>].

Dai Chao-Shuan et al. [<NUM>] discloses Ni<NUM>S<NUM> nanoparticles with the diameters ranging from <NUM> to <NUM> are grown on the backbone of conductive multiwalled carbon nanotubes (MWCNTs). The method for the preparation of nanoparticles is a glucose-assisted hydrothermal method.

In all these cases, the preparation of the electrode material involves multiple process steps, a variety of different chemicals, and long processing time (more than <NUM> hours).

Among all these methods disclosed in the prior art, Ni<NUM>S<NUM>-based metal sulphides combined with a conductive carbon structure used as an electrode for energy storage devices provided higher capacity, better stability, and higher energy density compared to plain carbon-based electrodes. In these cases, the electrode preparation takes long (more than <NUM> hours), involves multiple processing steps, requires various chemical/binders/additives and/or requires high-temperature.

There is a need for an improved and/or a simplified process for the manufacture of hybrid binder-free electrodes for electrochemical energy storage devices, such as for electrochemical supercapacitors. Moreover, there is a need for hybrid binder-free electrodes that have improved properties when used in electrochemical supercapacitors.

The inventors have found a novel method for the preparation of hybrid binder-free electrodes for electrochemical energy storage devices, preferably for electrochemical supercapacitors, that meets the above needs. The preparation method has the advantages of being simple, fast, low in energy consumption, and suitable for large-scale industrial production. The resulting hybrid binder-free electrodes have advantageous properties for application in both electrochemical energy storage devices and high-frequency filtering applications.

The scope of the present invention is defined by the appended set of claims. Accordingly, in a first aspect, the invention concerns a method for manufacturing a first hybrid binder-free electrode for electrochemical energy storage devices, preferably for electrochemical supercapacitors, said first hybrid binder-free electrode comprising, preferably consisting of, a conductive metal substrate (e.g. nickel) and carbon nanotubes attached to the conductive metal substrate, wherein each carbon nanotube has only one single-crystal metal nanoparticle positioned at its tip with a metal nitride top layer, the method comprising the following subsequent steps:.

wherein no binder is applied during the process.

In a second aspect, the disclosure, not part of the claims, concerns the first hybrid binder-free electrode for electrochemical energy storage devices, preferably for electrochemical supercapacitors, obtainable by or obtained by steps (a) - (g) of the method as defined hereinbefore.

In a third aspect, the disclosure, not part of the claims, provides a first hybrid binder-free electrode for electrochemical energy storage devices, preferably for electrochemical supercapacitors, said first hybrid binder-free electrode comprising, preferably consisting of, a conductive metal substrate with carbon nanotubes having an average length of preferably <NUM> to <NUM> and an average diameter of preferably <NUM> to <NUM> attached thereto, wherein each carbon nanotube has only one single-crystal metal nanoparticle positioned at its tip with a metal nitride top layer,.

In a fourth aspect, the invention concerns the use of the first hybrid binder-free electrode as defined hereinbefore or the first hybrid binder-free electrode obtainable by or obtained by steps (a) - (g) of the method as defined hereinbefore as an electrode for an electrochemical supercapacitor for high-frequency filtering applications, wherein said electrode preferably shows a phase angle above -<NUM>° and a capacitance above <NUM>µF at high frequencies (above <NUM>) with a cut-off frequency above <NUM>.

In a preferred embodiment, the process as defined hereinbefore comprises additional steps that convert the first hybrid binder-free electrode for electrochemical energy storage devices, preferably for electrochemical supercapacitors, obtained in step (g), to a second hybrid binder-free electrode, comprising, preferably consisting of, a conductive metal substrate (e.g. nickel) and carbon nanotubes attached to the conductive metal substrate, wherein each carbon nanotube has only one single-crystal metal nanoparticle positioned at its tip with a metal sulphide top layer, a single-crystal metal nanoparticle core and a metal nitride layer in between the metal sulphide top layer and the single-crystal metal nanoparticle core, the method comprising the following additional subsequent steps following step (g):.

In a fifth aspect, the disclosure, not part of the claims, concerns the second hybrid binder-free electrode for electrochemical energy storage devices, preferably for electrochemical supercapacitors, obtainable by or obtained by steps (a) - (l) of the methods as defined hereinbefore.

In a sixth aspect, the disclosure, not part of the claims, provides a second hybrid binder-free electrode for electrochemical energy storage devices, preferably for electrochemical supercapacitors, said second hybrid binder-free electrode comprising, preferably consisting of, a conductive metal substrate with carbon nanotubes having an average length of preferably <NUM> to <NUM> and an average diameter of preferably <NUM> to <NUM> attached thereto, wherein each carbon nanotube has only one single-crystal metal nanoparticle positioned at its tip with a metal sulphide top layer, a single-crystal metal nanoparticle core and a metal nitride layer in between the metal sulphide top layer and the single-crystal metal nanoparticle core,.

In a seventh aspect, the invention concerns the use of the second hybrid binder-free electrode as defined hereinbefore or the second hybrid binder-free electrode obtainable by or obtained by steps (a) - (l) of the methods as defined hereinbefore as an electrode for a supercapacitor for electrochemical energy storage devices, wherein during charge-discharge cycling at a current density above <NUM> A·g-<NUM> said electrode after many cycles (more than <NUM>) preferably delivers a specific capacity of above <NUM> C·g-<NUM>, and wherein the specific capacity retains above <NUM> % of the initial specific capacity (more than <NUM> C·g-<NUM>) at higher current densities (more than <NUM> A·g-<NUM>).

In another aspect of the disclosure, not part of the claims, the composite material is directly grown onto the conductive substrate, and the use of this material as a binder-free electrode for electrochemical energy storage devices, preferably for electrochemical supercapacitors, addresses the current challenges related to electrode fabrication.

In another aspect, the invention provides a first hybrid binder-free electrode for electrochemical energy storage devices obtained by the method of the present invention, preferably for electrochemical supercapacitors, said first hybrid binder-free electrode comprising, preferably consisting of, a conductive metal substrate with carbon nanotubes having an average length of preferably <NUM> to <NUM> and an average diameter of preferably <NUM> to <NUM> attached thereto, wherein each carbon nanotube has only one single-crystal metal nanoparticle positioned at its tip with a metal nitride top layer,.

In another aspect, the disclosure, not part of the claims, concerns the use of the first hybrid binder-free electrode as defined hereinbefore or the first hybrid binder-free electrode obtainable by or obtained by steps (a) - (g) of the method as defined hereinbefore in an electrode for an electrochemical supercapacitor for high-frequency filtering applications, wherein said electrode preferably shows a phase angle above -<NUM>° and a capacitance above <NUM>µF at high frequencies (above <NUM>) with a cut-off frequency above <NUM>.

In another aspect, the invention provides a second hybrid binder-free electrode for electrochemical energy storage devices obtained by the method of the invention, preferably for electrochemical supercapacitors, said second hybrid binder-free electrode comprising, preferably consisting of, a conductive metal substrate with carbon nanotubes having an average length of preferably <NUM> to <NUM> and an average diameter of preferably <NUM> to <NUM> attached thereto, wherein each carbon nanotube has only one single-crystal metal nanoparticle positioned at its tip with a metal sulphide top layer, a single-crystal metal nanoparticle core and a metal nitride layer in between the metal sulphide top layer and the single-crystal metal nanoparticle core,.

In another aspect, the disclosure, not part of the claims, concerns the use of the second hybrid binder-free electrode as defined hereinbefore or the second hybrid binder-free electrode obtainable by or obtained by steps (a) - (l) of the methods as defined hereinbefore in an electrode for a supercapacitor for electrochemical energy storage devices, wherein during charge-discharge cycling at a current density above <NUM> A·g-<NUM> said electrode after many cycles (more than <NUM>) preferably delivers a specific capacity of above <NUM> C·g-<NUM>, and wherein the specific capacity retains above <NUM> % of the initial specific capacity (more than <NUM> C·g-<NUM>) at higher current densities (more than <NUM> A·g-<NUM>).

Compared with the prior art, the present invention provides the following advantages:.

The term 'sccm' as used in the context of the present invention is an abbreviation of 'standard cubic centimetre per minute' and concerns a volumetric unit of flow measurement defined at the following standard conditions: a temperature of <NUM> and a pressure of <NUM> Pa.

The term 'binder' as used herein means material that is responsible for holding the active material within the electrode together and maintaining a good contact, physical and electrical, between the active material and current collector. The binder typically is an inert, flexible, in electrolyte insoluble and electrochemically stable material, often a polymer.

The expression 'binder-free electrode' is to be construed as an electrode that has been produced without the use of a binder and that does, therefore, not contain any binder.

The term 'conductive' in 'conductive metal substrate' and in 'conductive metal coil' as used herein concerns the electrical conductivity.

In a first aspect, the invention concerns a method for manufacturing a first hybrid binder-free electrode for electrochemical energy storage devices, preferably for electrochemical supercapacitors, said first hybrid binder-free electrode comprising, preferably consisting of, a conductive metal substrate (e.g. nickel) and carbon nanotubes attached to the conductive metal substrate, wherein each carbon nanotube has only one single-crystal metal nanoparticle positioned at its tip with a metal nitride top layer, the method comprising the following subsequent steps:.

In step (g), the first hybrid binder-free electrode is obtained.

The numbers between brackets (. ) correspond to the numbers in <FIG>, wherein (<NUM>) represents a processing chamber, (<NUM>) represents carbon nanotubes on the conductive metal substrate, (<NUM>) represents (means for supplying) sulphur-containing gas, (<NUM>) represents a heating element, such as an external heating coil, (<NUM>) represents a pressure gauge, (<NUM>) represents a vacuum pump, (<NUM>) represents another processing chamber, (<NUM>) represents a substrate holder, (<NUM>) represents a high-frequency plasma generator, such as a radio-frequency (RF) plasma generator, (<NUM>) represents a conductive metal coil, (25a) represents a conductive metal substrate, (25b) represents a conductive metal substrate with carbon nanotubes thereon, (<NUM>) represents means for supplying gas, (26a) represents carbon-containing gas, (26b) represents nitrogen-containing gas, (<NUM>) represents a pressure gauge and (<NUM>) represents a vacuum pump.

In a second aspect, the disclosure, not part of the claims, concerns the first hybrid binder-free electrode for electrochemical energy storage devices, preferably for electrochemical supercapacitors, obtainable by or obtained by steps (a) - (g) of the methods as defined hereinbefore.

In a fourth aspect, the invention concerns the use of the first hybrid binder-free electrode as defined hereinbefore or the first hybrid binder-free electrode obtainable by or obtained by steps (a) - (g) of the methods as defined hereinbefore as an electrode for an electrochemical supercapacitor for high-frequency filtering applications, wherein said electrode preferably shows a phase angle above -<NUM>° and a capacitance above <NUM>µF at high-frequencies (above <NUM>) with a cut-off frequency above <NUM>.

In a preferred embodiment, the process as defined hereinbefore comprises additional steps that convert the first hybrid binder-free electrode obtained in step (g) to a second hybrid binder-free electrode for electrochemical energy storage devices, preferably for electrochemical supercapacitors, comprising, preferably consisting of, a conductive metal substrate (e.g., nickel) and carbon nanotubes attached to the conductive metal substrate, wherein each carbon nanotube has only one single-crystal metal nanoparticle positioned at its tip with a metal sulphide top layer, a single-crystal metal nanoparticle core and a metal nitride layer in between the metal sulphide top layer and the single-crystal metal nanoparticle core, the method comprising the following additional subsequent steps following step (g):.

In a seventh aspect, the invention concerns the use of the second hybrid binder-free electrode as defined hereinbefore or the second hybrid binder-free electrode obtainable by or obtained by steps (a) - (l) of the methods as defined hereinbefore as or in an electrode for a supercapacitor for electrochemical energy storage devices, wherein during charge-discharge cycling at a current density above <NUM> A·g-<NUM> said electrode after many cycles (more than <NUM>) preferably delivers a specific capacity of above <NUM> C·g-<NUM>, and wherein the specific capacity retains above <NUM> % of the initial specific capacity (more than <NUM> C·g-<NUM>) at higher current densities (more than <NUM> A·g-<NUM>).

In a preferred embodiment, steps (b) - (g) are performed in the same processing chamber (<NUM>) as used in step (a). Accordingly, in a preferred embodiment, the invention concerns the method for manufacturing the first or second hybrid binder-free electrode for electrochemical energy storage devices, as defined hereinbefore, comprising the following subsequent steps:.

In another aspect, the disclosure, not part of the claims, concerns the use of the first hybrid binder-free electrode as defined hereinbefore or the first hybrid binder-free electrode obtainable by or obtained by steps (a) - (g) of the methods as defined hereinbefore in an electrode for an electrochemical supercapacitor for high-frequency filtering applications, wherein said electrode preferably shows a phase angle above -<NUM>° and a capacitance above <NUM>µF at high-frequencies (above <NUM>) with a cut-off frequency above <NUM>.

wherein the metal sulphide layer on top of the metal nitride layer on the single-crystal metal nanoparticle core is preferably in the form of single-crystalline nanostructures, with individual crystallite size of between <NUM> to <NUM>.

The carbon nanotubes grown in step (a) are preferably multi-walled carbon nanotubes. These carbon nanotubes have a length (largest dimension) and a diameter (smallest dimension). The carbon nanotubes are grown in a direction perpendicular to the surface of the conductive metal substrate. This means that the central axis of the carbon nanotubes, along the length or the largest dimension, points in a direction perpendicular to the surface of the conductive metal substrate.

The average length of the carbon nanotubes grown in step (a) is preferably larger than <NUM>. More preferably, the average length of the carbon nanotubes grown in step (a) is between <NUM> and <NUM>. The average diameter of the carbon nanotubes grown in step (a) is preferably <NUM> or smaller. More preferably, the average diameter of the carbon nanotubes grown in step (a) is between <NUM> and <NUM>.

The carbon nanotubes grown in step (a) have only one single-crystal metal nanoparticle positioned at their tips. This means a single-crystal metal nanoparticle positioned at the outer end of the carbon nanotube that is not attached to the conductive metal substrate.

The metal nitride top layer formed in step (e) on the single-crystal metal nanoparticle preferably is in the form of thin layer nanostructures with a total layer thickness of between <NUM> to <NUM>, preferably between <NUM> and <NUM>, such as about <NUM>.

The metal sulphide top layer formed in step (k) on the single-crystal metal nanoparticle preferably is in the form of single-crystalline nanostructures with individual crystallite sizes of between <NUM> and <NUM>.

Without wishing to be bound by any theory, the inventors believe that the metal nitride layer serves as a diffusion layer for the metal from the single-crystal metal nanoparticle during the formation of the metal sulphide top layer. Accordingly, the metal sulphide is formed on top of the metal nitride instead of from conversion of the metal nitride to metal sulphide. Moreover, again without wishing to be bound by any theory, the inventors believe that the metal nitride layer serves as a single-crystal template, enabling the subsequent epitaxial growth of a single-crystal metal sulphide structure.

The metal of the conductive metal substrate is preferably catalytic towards carbon nanotube synthesis. In a preferred embodiment, the metal of the conductive metal substrate has (substantial) carbon solubility. In a very preferred embodiment, the metal of the conductive metal substrate is chosen from the group consisting of nickel, cobalt and copper.

In a very preferred embodiment, the metal of the conductive metal substrate is nickel and the metal nitride is nickel nitride (Ni<NUM>N). In another very preferred embodiment, the metal of the conductive metal substrate is nickel, the metal nitride is nickel nitride (Ni<NUM>N) and the metal sulphide is trinickel disulphide (Ni<NUM>S<NUM>). The thickness of the conductive metal substrate is preferably <NUM> or more, more preferably about <NUM>.

The conductive metal substrate can be a solid substrate, a porous substrate or a foam.

In a typical embodiment, processing chamber (<NUM>) is a long cylindrical quartz tube attached to a heating system, preferably an external heating coil.

The metal of the single-crystal metal nanoparticles and the metal of the conductive metal substrate are the same. The metal nitride is formed in step (e) by contacting the metal of the single crystal metal nanoparticle with a nitrogen-containing plasma. The metal sulphide is formed in step (k) by contacting the metal of the single-crystal metal nanoparticles with a sulphur-containing gas. As appreciated by the skilled person, the metal in the metal sulphide and in the metal nitride is therefore also identical to the metal of the single-crystal metal nanoparticles and the metal of the conductive metal substrate.

In a preferred embodiment, the nitrogen-containing gas applied in step (c) is selected from the group consisting of nitrogen, ammonia, and nitrogen dioxide. More preferably, the nitrogen-containing gas applied in step (c) is molecular nitrogen (N<NUM>). Most preferably, the nitrogen-containing gas applied in step (c) is molecular nitrogen with a purity greater than <NUM> %, wherein the partial pressure of the molecular nitrogen inside the processing chamber is between <NUM> and <NUM> Pa, preferably between <NUM> and <NUM> Pa. Best results in terms of uniformity are obtained when only one gas is used.

In a preferred embodiment, the interaction time in step (e) is between <NUM> and <NUM>, preferably between <NUM> and <NUM>, such as about <NUM>, preferably applied in increments of <NUM> with intermediate cooling.

In an embodiment, the plasma inside the processing chamber, e.g. processing chamber (<NUM>), is created in step (d) at low power, preferably at a power of between <NUM> and <NUM> W, such as about <NUM> W.

The high-frequency plasma generator (<NUM>), preferably a radio-frequency (RF) plasma generator (such as at <NUM>), applied in step (d) is coupled, preferably using inductive coupling, to a conductive metal coil or antenna (<NUM>), preferably a copper coil or copper antenna, wrapped around the processing chamber (<NUM>).

As depicted in <FIG>, the processing chamber (<NUM>) preferably takes the form of a cross-type glass tube. Preferably, the processing chamber (<NUM>) is a dielectric chamber with tubes made of borosilicate glass.

In a preferred embodiment, the sulphur-containing gas (<NUM>) applied in step (i) is hydrogen sulphide (H<NUM>S) and the partial pressure of the sulphur-containing gas is between <NUM>·<NUM><NUM> and <NUM>·<NUM><NUM> Pa. Best results in terms of uniformity are obtained when only one gas is used.

In a preferred embodiment, the interaction time in step (k) is between <NUM> and <NUM> minutes, preferably between <NUM> and <NUM> minutes.

In a preferred embodiment, the carbon nanotubes are grown in step (a) using a vapour deposition tip-growth method.

In a very preferred embodiment, the carbon nanotubes are grown in step (a) using a plasma vapour deposition tip-growth method comprising the following steps:.

In an embodiment, the growth of the carbon nanotubes in step (V) is performed continuously for a duration of between <NUM> and <NUM> minutes, preferably about <NUM> minutes.

The carbon-containing gas (26a) applied in step (III) is preferably selected from the group consisting of methane, carbon dioxide, ethylene, and acetylene. More preferably, the carbon-containing gas (26a) in step (III) is methane. Most preferably, the carbon-containing gas (26a) in step (III) is methane with a purity greater than <NUM> % wherein the partial pressure of the methane inside the processing chamber (<NUM>) is between <NUM> and <NUM> Pa after the methane supply.

In an embodiment, the plasma inside the processing chamber (<NUM>) is created in step (IV) at high power, preferably between <NUM>-<NUM> W.

The high-frequency plasma generator (<NUM>), preferably a radio-frequency (RF) plasma generator (such as at <NUM>), applied in step (IV) is coupled, preferably using inductive coupling, to a conductive metal coil or antenna (<NUM>), preferably a copper coil or copper antenna, wrapped around the processing chamber (<NUM>).

In a typical embodiment, the plasma vapour deposition tip-growth method is performed as follows. The conductive metal substrate (25a) is placed on a conductive substrate holder (<NUM>), which is electrically grounded during the process. The processing chamber (<NUM>) is evacuated to a pressure of below <NUM> Pa using a rotary vacuum pump (<NUM>). The pressure inside the processing chamber (<NUM>) is measured using a pressure gauge (<NUM>). Carbon-containing gas (26a) is supplied to the processing chamber (<NUM>) for the growth process and is fed through a mass flow controller (<NUM>) at a flow rate not less than <NUM> sccm. The plasma is created at a power typically not higher than <NUM> W for the growth of the carbon nanotubes. The plasma vapour deposition tip-growth process typically lasts not less than <NUM>. The processing chamber (<NUM>) and the conductive substrate holder (<NUM>) are not subjected to any external heating step during the growth process. The conductive substrate holder is heated due to the plasma heating effects during the growth itself. The conductive substrate holder (<NUM>) is taken out after the plasma vapour deposition tip-growth process and after the temperature of the substrate holder has dropped below a threshold temperature of below <NUM>.

Thus, the invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art.

Furthermore, for a proper understanding of this document and its claims, it is to be understood that the verb 'to comprise' and its conjugations are used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. In addition, reference to an element by the indefinite article 'a' or 'an' does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article 'a' or 'an' thus usually means 'at least one'.

The following examples serve to demonstrate the preferred embodiments of the present invention and should not be interpreted as limiting the scope of the invention.

The method of the invention was applied to prepare a first hybrid binder-free electrode according to the invention. This example relates to the preparation of a binder-free electrode for electrochemical supercapacitors for high-frequency applications. In this example, metallic nickel foil with a thickness of <NUM> and a diameter of <NUM> was used as the conductive metal substrate.

In a first step, multi-walled carbon nanotubes, wherein each carbon nanotube has only one single-crystal nickel nanoparticle positioned at its tip, were grown on the nickel foil using a plasma-assisted deposition system via a tip-growth mechanism. A setup as depicted in <FIG> was used.

The nickel foil as the conductive metal substrate (25a) was placed on a conductive substrate holder (<NUM>) inside a plasma processing chamber (<NUM>) made of borosilicate glass in the middle of a conductive metal coil (<NUM>) wrapped around the processing chamber (<NUM>). The conductive substrate holder (<NUM>) was electrically grounded during the growth. Then, the processing chamber (<NUM>) was evacuated with a rotary vacuum pump (<NUM>) and a pressure gauge (<NUM>) to a pressure below <NUM> Pa. Subsequently, methane gas (26a) was leaked into the processing chamber (<NUM>) as the carbon precursor at a flow rate of <NUM> sccm through a mass flow controller (<NUM>). After supply of the methane gas (26a), the pressure inside the processing chamber was <NUM> Pa.

After establishing the atmosphere for carbon nanotube growth, an RF (<NUM>) plasma generator (<NUM>) was turned on at power <NUM> W. The RF plasma generator (<NUM>) was inductively coupled to the conductive metal coil (<NUM>). After <NUM> minutes, the RF plasma generator and the methane supply were turned off. The temperature of the sample holder reached <NUM>-<NUM> during the growth process due to the plasma heating effects. After an additional <NUM> minutes, the temperature of the sample holder (<NUM>) was cooled to below a threshold temperature of <NUM>. In this first step, a nickel foil with carbon nanotubes thereon (25b), wherein each carbon nanotube has only one single-crystal metal nanoparticle positioned at its tip, was obtained.

In a second step, the nickel foil with the grown carbon nanotubes thereon (25b) was exposed to nitrogen plasma-treatment in the same plasma processing chamber (<NUM>) in the middle of the conductive metal coil (<NUM>) wrapped around the processing chamber (<NUM>). At this stage, the conductive substrate holder (<NUM>) was not electrically grounded. The processing chamber (<NUM>) was evacuated with a rotary vacuum pump (<NUM>) using a pressure gauge (<NUM>) to a pressure below <NUM> Pa. Subsequently, molecular nitrogen (N<NUM>) gas (26b) was leaked into the processing chamber (<NUM>) as the treatment gas. After the supply of the nitrogen gas (26b), the pressure inside the processing chamber was <NUM> Pa. Then the RF (<NUM>) plasma generator (<NUM>) was turned on at a power <NUM> W and turned off after <NUM>. After a cooling period of <NUM>, the plasma generator (<NUM>) was turned on again at a power <NUM> W and turned off after <NUM>. This process was repeated once again, and the nitrogen supply was turned off. Accordingly, the total effective plasma treating time was <NUM>. After an additional <NUM> minutes, the processing chamber was vented and opened to take out the sample. Thus, a first hybrid binder-free electrode according to the invention was obtained.

<FIG> presents a TEM micrograph of an individual carbon nanotube obtained after the nitrogen plasma-treatment in the second step. The structure of the product is similar to the structure obtained after the first step, however, a layer of single-crystalline nickel nitride (Ni<NUM>N) was observed on top of the nickel nanoparticle.

The resulting first hybrid binder-free electrode was used in an electrochemical setup for a supercapacitor and tested as an electrode for high-frequency filtering applications, and exhibited a phase angle above -<NUM>° and a capacitance above <NUM>µF at high-frequencies (above <NUM>) with a cut-off frequency above <NUM>.

The method of the invention was applied to prepare a second hybrid binder-free electrode according to the invention. This second example relates the preparation of a hybrid-binder-free electrode for electrochemical energy storage devices. The first hybrid binder-free electrode obtained in the second step of Example <NUM> was subjected to a third step. In the third step, the nickel foil with the nitrogen plasma-treated carbon nanotubes (<NUM>), wherein each carbon nanotube has only one single-crystal metal nanoparticle covered with a single-crystalline nickel nitride layer positioned at its tip, was placed in a thermal treatment processing chamber (<NUM>), as depicted in <FIG>, for the growth of nickel sulphide. The processing chamber (<NUM>) was evacuated to a pressure of below <NUM> Pa using a vacuum pump (<NUM>) and a pressure gauge (<NUM>). Then, hydrogen sulphide (H<NUM>S) gas was leaked into the processing chamber as the sulphur-containing gas (<NUM>), and the pressure inside the processing chamber (<NUM>) was kept at about <NUM>·<NUM><NUM> Pa. The temperature of the chamber was elevated to <NUM> at a rate of <NUM>/minutes using an external heating coil (<NUM>), and annealed for <NUM> minutes. Afterwards, the processing chamber (<NUM>) was let to cool down to room temperature, and the H<NUM>S gas was pumped out using the vacuum pump (<NUM>). During the third step, the nickel sulphide successfully formed on top of the nickel nitride layer from the single-crystal nickel nanoparticle. The process resulted in a top layer of nickel sulphide on a single-crystal nickel nanoparticle core with a nickel nitride layer in between, without destroying the underlying carbon nanotubes.

<FIG> shows a TEM micrograph of the material obtained after the three steps. The nickel sulphide is only attached to the single-crystal nickel nanoparticle core covered with nickel nitride. The composite material consists of nickel sulphide, a nickel core and nickel nitride in between, carbon nanotubes and a nickel foil. There were no other sulphur-containing nanoparticles observed on the backbone of the carbon nanotube. As the nickel substrate was completely covered with carbon structures, it was not affected by the H<NUM>S gas. The nickel sulphide was formed from the single-crystal nickel nanoparticle on top of the nickel nitride layer in the form of single-crystalline nanostructures of Ni<NUM>S<NUM>. The obtained hybrid binder-free electrode is therefore confirmed as having a Ni<NUM>S<NUM>/Ni<NUM>N/Ni/carbon nanotube hybrid hierarchical structure.

Claim 1:
A method for manufacturing a first hybrid binder-free electrode for electrochemical energy storage devices, preferably for electrochemical supercapacitors, said first hybrid binder-free electrode comprising, preferably consisting of, a conductive metal substrate and carbon nanotubes attached to the conductive metal substrate, wherein each carbon nanotube has only one single-crystal metal nanoparticle positioned at its tip with a metal nitride top layer, the method comprising the following subsequent steps:
a) growing carbon nanotubes, preferably multi-walled carbon nanotubes, in a processing chamber (<NUM>) using a tip-growth mechanism, wherein each carbon nanotube has only one single-crystal metal nanoparticle positioned at its tip, on a conductive metal substrate (25a) in a direction perpendicular to the surface of the conductive metal substrate, wherein the metal of the single-crystal metal nanoparticles and the metal of the conductive metal substrate are the same;
b) providing the conductive metal substrate with the carbon nanotubes thereon, as obtained in step (a), in a processing chamber wherein the conductive metal substrate with the carbon nanotubes thereon is arranged on a conductive substrate holder that is not grounded, and evacuating said processing chamber to a pressure below <NUM> Pa;
c) supplying nitrogen-containing gas to the evacuated processing chamber of step (b) to obtain a partial pressure of the nitrogen-containing gas of between <NUM> Pa and <NUM> Pa;
d) creating a plasma inside the processing chamber using a high-frequency plasma generator;
e) allowing the single-crystal metal nanoparticles at the tips of the carbon nanotubes to interact with the nitrogen-containing plasma inside the processing chamber for a time period of between <NUM> and <NUM>, leading to the formation of a metal nitride layer on top of the single-crystal metal nanoparticles;
f) turning off the high-frequency plasma generator; and
g) assuring that the temperature of the processing chamber drops below a threshold value, preferably below <NUM>, and subsequently venting the processing chamber to atmospheric pressure,
wherein no binder is applied during the process.