Current collector, device or system including current collector, and method for manufacturing current collector

Abstract

The present invention relates to a current collector (1) for an electrical energy storage or power generation system, comprising a conductive substrate (2), a non-conductive polymer matrix (4), and carbon nanotubes, the nanotubes having a first end (31), called the transfer end (31), which enables them to transfer current to the substrate, and a second end (32) opposite the first end, called the current collecting end, which enables them to collect current from an external active material, in particular an electrode, thereby forming a layer on the surface of the conductive substrate (2) comprising a plurality of current collecting regions electrically isolated from each other by intercalated regions of the non-conductive polymer matrix, each current collecting region comprising a plurality of carbon nanotubes, the second ends of the carbon nanotubes in each current collecting region all protruding beyond the surface of the non-conductive polymer matrix.

Description

[Technical Field]

[0001] The present invention relates to the field of electrochemical devices, more precisely to the field of electrochemical devices for the storage and generation of electrical energy.

[0002] More specifically, the present invention relates to current collectors that can be used in electrochemical systems and devices that generate electrical energy, such as fuel cells, and in electrochemical systems and devices that store electrical energy, such as batteries (more specifically, lithium-ion and lithium-air batteries) and supercapacitors. These current collectors have a special shape that, when used in energy storage devices, allows for optimized adhesion between the active material of the electrode and the current collector while limiting interfacial resistance. The present invention also relates to a method for producing such current collectors with a novel structure that provides excellent electrical conductivity. [Background technology]

[0003] Electrodes for energy storage devices, particularly electrochemical systems, are typically fabricated by depositing active materials onto thin, conductive films called current collectors. The current collectors provide mechanically robust support for the active materials while allowing current to flow to and / or from the active materials. The primary current collectors used in these energy storage devices are sheets of aluminum, copper, stainless steel, or nickel, less than 40 pm thick.

[0004] The electrodes of these energy storage devices are generally composed of active material particles, a binder that ensures mechanical cohesion of the electrode, and conductive particles that ensure electrical conductivity within the electrode.

[0005] Adequate adhesion of the active material to the current collector is desirable to ensure electrode processability during assembly processes in electrochemical systems, such as cutting and winding. This adhesion is also recommended to optimize the life of the energy storage device containing it. Because the materials used to manufacture the current collector are different from those used in the electrode, the binder selection may be limited, as it must ensure not only good adhesion of the active material but also good adhesion between the active material and the current collector. Furthermore, the proportion of binder in the active material must be adjusted to ensure adequate adhesion to the current collector. To optimize system operation, electron transfer between the current collector and the active material must be as efficient as possible. Contact between the current collector and the particulate active material creates interfacial electrical resistance. This electrical resistance contributes to the device's series resistance and is even more important due to the importance of the amount of binder in the active material. Therefore, a compromise must be made between the need to ensure adhesion between the active material and the current collector and the need to limit interfacial resistance.

[0006] Increasing the ratio of binder to conductive particles in the active material ensures good adhesion and reduces interfacial resistance. However, these factors do not contribute to the active material's primary purpose: its ability to store electrical energy. To obtain the most efficient energy storage system possible while reducing production and raw material costs, it is desirable to maintain the active particle content in the active material as high as possible. [Prior art documents] [Patent documents]

[0007] Various types of current collectors have been developed to provide excellent performance for electrical energy storage devices. European Patent No. 2 500 969 A1 discloses the use of an aluminum sheet containing 0.01 to 3.0 mass % dispersed support carbon particles as a current collector to reduce interfacial resistance. U.S. Patent No. 8,785,053 B2 discloses the use of a current collector comprising a support and a layer of uniformly dispersed carbon nanotubes disposed on the support to provide high corrosion resistance.

[0008] In order to limit corrosion or prevent oxidation of the current collector, even when the operating potential of the electrical energy storage device is equal to or greater than the oxidation potential of the material forming the current collector, it is known from EP 3 716 378 A1 to coat the current collector of an electrical energy storage device with an interfacial layer. This interfacial layer consists of a binder and a conductive material, such as carbon particles, in particular in the form of carbon black, graphite, graphene or even carbon nanotubes. From US Patent Publication No. 2012 / 0121974 it is also known to protect the cathode current collector with a porous protective conductive coating comprising conductive carbon or graphite.

[0009] However, this interfacial layer still creates electrical contact resistance both between the interfacial layer and the substrate and between the interfacial layer and the active material. Furthermore, the small contact surface between the active material and the current collector necessitates the use of a substantial amount of carbon particles in this interfacial layer. Summary of the Invention [Problem to be solved by the invention]

[0010] SUMMARY OF THE INVENTION The object of the present invention is to at least partially remedy the above-mentioned drawbacks of the prior art.

[0011] In particular, the aim is to propose a current collector that can be used in any electrochemical energy storage system and that effectively ensures adhesion of the active material while limiting the interfacial resistance.

[0012] In particular, the aim is to propose a process that allows for the simple, reliable and rapid production of current collectors with a very long service life.

[0013] It is also an object to propose an energy storage device, preferably an electrochemical energy storage system such as a battery, a supercapacitor or a fuel cell, with a very long lifetime. [Means for solving the problem]

[0014] At least one of the above-mentioned objects can be achieved by at least one of the following aspects of the present invention, which provide a current collector, a method for manufacturing the same, and an energy storage device such as a battery, as set forth in the appended claims. [Effects of the Invention]

[0015] As a first object, the present invention provides a current collector for an electrochemical energy storage system or an electrochemical power generation system, the current collector comprising: a. a conductive substrate; b. a non-conductive polymer matrix; and c. carbon nanotubes, the carbon nanotubes having a first end, called a transfer end, which enables current to be transferred to the substrate, the first end being fixed on and electrically connected to the surface of the conductive substrate (2), and a second end (32) opposite the first end, the second end being called a current collecting end, which enables current to be collected from an external active material, in particular an electrode, thereby forming a layer on the surface of the conductive substrate (2) comprising a plurality of current collecting areas electrically insulated from each other by intercalated areas of the non-conductive polymer matrix, each of the current collecting areas comprising a plurality of carbon nanotubes, the second ends of the carbon nanotubes in each of the current collecting areas all protruding beyond the surface of the non-conductive polymer matrix.

[0016] Other features of the current collector according to the invention, which may be adopted individually or according to technically suitable features, include that the carbon nanotubes in the current collecting region have an average tube spacing of less than 100 nm in top view, and the minimum distance between the outer edges of the current collecting region is 1 μm or more, preferably greater than 10 μm, the conductive substrate is selected from copper, aluminum, nickel, stainless steel, heavily doped silicon, carbon, and composite materials containing carbon, preferably composite materials containing carbon and a resin selected from polyester, vinyl ester, epoxy, phenolic, polyimide, polyamide, polypropylene, polyether ether ketone resins, or mixtures of one or more thereof, the conductive substrate is selected from flat substrates, lattice substrates, fibrous substrates, and felt substrates, and the carbon nanotubes electrically connected to the surface of the conductive substrate have a thickness of less than 10 μm, preferably less than 1 μm, and / or a thickness of less than 100 μm. 2 / g, preferably above 250m 2 / g and the volume ratio of said non-conductive polymer matrix to said carbon nanotubes is less than 300%, preferably less than 200%, more preferably less than 70%.

[0017] The present invention also relates to devices for storing or generating electrical energy, such as batteries, supercapacitors, fuel cells, etc., which comprise a current collector according to the present invention.

[0018] The present invention also relates to an electrochemical system for storing or generating electrical energy comprising a current collector according to the present invention.

[0019] The present invention ultimately relates to a method for producing a current collector comprising a conductive substrate, carbon nanotubes fixed at one end to the surface of the conductive substrate, and a non-conductive polymer matrix, the method comprising the following successive steps: (a) forming a carpet of vertically aligned carbon nanotubes on the conductive substrate, preferably by chemical vapor deposition, or transferring aligned nanotubes synthesized on another substrate to the conductive substrate; and (b) depositing the non-conductive polymer matrix on the carbon nanotubes by any suitable means, preferably by liquid deposition, to form a layer on the surface of the conductive substrate comprising a plurality of current collecting areas electrically isolated from one another by intercalated areas of the non-conductive polymer matrix, each of the current collecting areas comprising a plurality of the carbon nanotubes, all of whose second ends protrude beyond the surface of the non-conductive polymer matrix. Advantageously, the deposition of the non-conductive polymer matrix in step (b) is carried out by a method selected from the group consisting of coating, spraying, dipping, extrusion, and impregnation in one or more steps.

[0020] The present invention will now be described with reference to the accompanying drawings, which are given by way of non-limiting example only. Figures 1 to 10 illustrate certain aspects of the invention. Figures 1 to 3 show diagrammatically current collectors according to the invention. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 shows a longitudinal cross-section of a current collector (1) of the present invention, which comprises a conductive substrate (2), vertically aligned carbon nanotubes (3) forming a current collecting region (33), and a non-conductive polymer matrix (4) forming an intermediate region (41).

[0022] [Figure 2]FIG. 2 is a top view similar to FIG. 1 showing a current collector (1) according to the present invention, more specifically showing the circular shape of the current collecting regions (33), each containing a plurality of vertically aligned carbon nanotubes (3), and the minimum distance (d) between the outer edges of the current collecting regions.

[0023] [Figure 3] FIG. 3 shows a longitudinal cross-section of an electrode (10) of an energy storage system, including a current collector (1) according to the present invention and an active material (5) disposed on the current collector.

[0024] [Figure 4] FIG. 4 is a schematic representation of a three-dimensional exploded perspective view of a standardized Swagelok®-type cell that enabled evaluation of wet supercapacitor components, showing a central separator, electrodes positioned on either end of the central separator, and current collectors positioned at the ends of the electrodes opposite the separator.

[0025] [Figure 5] FIG. 5 is a schematic representation of a three-dimensional exploded perspective view of a standardized Swagelok®-type cell that allows evaluation of supercapacitor components in a dry process, showing a central separator, free-standing electrodes positioned on either end of the central separator, and current collectors positioned on the ends of the free-standing electrodes opposite the separator.

[0026] [Figure 6] Figure 6 is a schematic 3D exploded view of a half-cell of a standardized "Coin Cell 2032" type battery, allowing evaluation of the battery components, showing the central separator (Celgard 3501 impregnated with 1M LiPF electrolyte in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC), EC / DEC ratio (1:1)), the electrodes located on either end of the central separator, and the current collectors located on the ends of the electrodes opposite the separator.

[0027] [Figure 7] FIG. 7 is a schematic exploded view of an open cell device, showing a substrate / separator / substrate structure formed by assembling a substrate, such as a current collector according to the present invention, with a separator (Celgard 3501) impregnated with ionic liquid EMITFSI 99.5% (Solvionic), and tightening the screws of the pressure plate with a torque driver to apply pressure of 1 N.

[0028] [Figure 8] FIG. 8 shows Nyquist diagrams obtained from current collectors of the present invention with different SBR / C volume ratios (%), specifically for current collectors with SBR / C volume ratios of 153% (x), 191% (points marked with triangles), 298% (points marked with diamonds), and 687% (points marked with squares), and for a commercially available current collector of type NPC-055D Korea JCC supplied by Samwha (dashed line), as well as details of these same diagrams.

[0029] [Figure 9] FIG. 9 shows the equivalent series resistance (ESR) evaluated from the Nyquist diagram shown in FIG. 8 for different current collectors with different SBR / C volume ratios, specifically, a commercially available current collector of type NPC-055D Korea JCC supplied by Samwha (dashed line), a current collector of the present invention containing 0.15 mg / cm to 0.43 mg / cm of SBR prepared in Example 3 (marked with black circles), a VACNT layer without a polymer coating prepared in Example 1 (marked with triangles), and a current collector of the present invention containing more than 1 mg / cm of SBR prepared in Example 3 (marked with squares).

[0030] [Figure 10] FIG. 10 shows the results of visual evaluation of the mechanical strength of a commercial current collector of type NPC-055D Korea JCC manufactured by Samwha, a supported VACNT layer prepared in Example 1 without a polymer coating, and a current collector according to the present invention at different SBR / C volume ratios. DETAILED DESCRIPTION OF THE INVENTION

[0031] A current collector according to the present invention will now be described with reference to Figures 1, 2 and 3. The present invention relates to a current collector (1) for an electrochemical system or device for storing or generating electrical energy, comprising: a. a conductive substrate (2); b. a non-conductive polymer matrix (4); and c. carbon nanotubes (hereinafter referred to as "Vertically Aligned Carbon NanoTubes" or VACNTs), advantageously vertically aligned nanotubes (3), which have a first end, called a transfer end (31), that allows them to transfer current to the substrate, and a second end, called a current collecting end (32), that allows them to collect current from an external active material (5), in particular an electrode, so that on the surface of the conductive substrate (2) a layer is formed comprising a plurality of current collecting areas electrically isolated from each other by intercalated regions of the non-conductive polymer matrix, each current collecting area comprising a plurality of the carbon nanotubes, the second ends of the carbon nanotubes of each collecting area all protruding beyond the surface of the non-conductive polymer matrix.

[0032] The present invention will be described below primarily in relation to vertically aligned carbon nanotubes, which are a particularly advantageous embodiment. However, this does not limit the scope of the present invention to vertically aligned nanotubes. For example, the nanotubes may be aligned in a direction other than vertical while remaining parallel to each other (e.g., tilted), or may not be aligned with respect to each other. Furthermore, the nanotubes may be synthesized on this conductive substrate (i.e., deposited by a chemical process, typically in the vapor phase) or may be synthesized on another substrate and then mechanically transferred to the conductive substrate. Transferring vertically aligned nanotubes from one substrate to another can be achieved using techniques known to those skilled in the art, as exemplified below. The presence of vertically aligned carbon nanotubes (3) on a conductive substrate (2) (hereinafter referred to as a vertically aligned carbon nanotube layer or VACNT carpet) provides multiple electrical contact points for the active material (5) due to their large specific surface area and vertical orientation. Synthesizing VACNTs on a conductive substrate (2) allows for direct electrical contact between the conductive substrate (2) and the active material (5) via the VACNT unit tubes. This not only limits the amount of conductive particles in the active material, but also makes it possible to significantly reduce the interfacial resistance between the active material (5) and the conductive substrate (2).

[0033] The presence of the non-conductive polymer matrix (4) improves the adhesion of the VACNTs to the substrate. This provides a purely polymeric attachment area for the electrode's active material (5), freeing the choice of binder to ensure the electrode's mechanical bond. The use of such a non-conductive polymer matrix (4) makes it possible to significantly reduce the amount of binder in the electrode. The non-conductive polymer matrix (4) is preferably a non-conductive material, advantageously with good ionic conductivity.

[0034] The inventors have noted that coating VACNTs synthesized directly on a conductive substrate (2) with a non-conductive polymer matrix (4) can produce a bimodal pore structure particularly suited to the intended application. Indeed, the synthesized VACNT carpet advantageously has a regular tube spacing of less than 100 nm, preferably in the range of 5 nm to 50 nm, depending on the synthesis conditions. The non-conductive polymer matrix (4) is advantageously made from any suitable non-conductive polymer or mixture of suitable non-conductive polymers, such as poly(styrene / butadiene), known by the abbreviation SBR (Styrene-Butadiene Rubber), carboxymethyl cellulose, known by the abbreviation CMC, or poly(acrylic acid), known by the abbreviation PAA.

[0035] The non-conductive polymer matrix, and in particular the polymer that constitutes this polymer matrix, is selected depending on the end use of the current collector according to the present invention, the energy storage device containing it, in particular the heat resistance that the device is expected to achieve during operation, and the various materials that constitute the device, such as the active material of the electrodes, etc. Poly(styrene / butadiene) is particularly used as the polymer matrix because it has excellent heat resistance, good chemical and electrochemical compatibility with the active materials and binders used in battery electrodes, and is inexpensive.

[0036] When a non-conductive polymer matrix (4) is deposited on a conductive substrate (2) that has been pre-coated with vertically aligned carbon nanotubes (3), regardless of the deposition method, a layer is formed on the surface of the conductive substrate (2) that includes multiple current collecting regions (33) electrically separated from each other by intermediate regions (41) of the non-conductive polymer matrix, each current collecting region (33) including multiple vertically aligned carbon nanotubes (3).

[0037] Advantageously, the vertically aligned carbon nanotubes of the current collecting region (33) have an average tube spacing of less than 100 nm to ensure sufficient direct electrical contact between the conductive substrate (2) and the active material (5), particularly the electrode. The current collecting region (33) is advantageously circular, and the minimum distance (d) between the outer edges of the current collecting region is 1 μm or more, preferably greater than 10 μm, and preferably between 1 μm and 50 μm. This distance is comparable to the particle size of active material typically used in electrodes of electrochemical energy storage systems. This particular structure of the current collector according to the present invention has both regions highly suitable for the attachment of active material (i.e., intermediate regions of the non-conductive polymer matrix) and regions highly suitable for electrical conduction (i.e., the current collecting region). The current collecting region (33) and intermediate regions (41) of the non-conductive polymer matrix are uniformly distributed on the surface of the current collector, preventing adhesion or electrical conductivity non-uniformities that could adversely affect the operation of an energy storage device including such a current collector according to the present invention.

[0038] The current collector according to the present invention makes it possible to effectively ensure adhesion of the active material in an optimal manner while limiting the interfacial resistance in the following cases: the vertically aligned carbon nanotubes in the current collecting region (33) have an average tube spacing of less than 100 nm, and the current collecting region (33) is circular, and the minimum distance (d) between the outer edges of the current collecting region is 1 μm or more, preferably greater than 10 μm, and preferably 1 μm to 50 μm.

[0039] The vertically aligned carbon nanotubes (3) electrically connected to the surface of the conductive substrate (2) advantageously have a thickness of less than 10 μm, preferably less than 1 μm, which allows the mass increase associated with the use of these vertically aligned carbon nanotubes (3) to be minimized, i.e., the final weight of the current collector according to the present invention to be minimized, and ultimately allows the optimization of an electrochemical energy storage system comprising such a current collector according to the present invention.

[0040] The vertically aligned carbon nanotubes (3) electrically connected to the surface of the conductive substrate (2) are preferably spaced apart from each other by a distance of 100 m to maximize contact between the external active material (5), in particular the electrode, and the carbon nanotubes, preferably the so-called current collecting ends (32) of the carbon nanotubes. 2 / g, preferably above 250m 2 / g.

[0041] The volume ratio of non-conductive polymer matrix to carbon nanotubes (hereinafter also referred to as polymer matrix / C volume ratio) of the current collector according to the present invention is advantageously less than 300%, preferably less than 200%, and more preferably less than 70%. This volume ratio is determined as a function of the amount of carbon nanotubes present in the current collector according to the present invention, the amount of polymer constituting the non-conductive polymer matrix, and their respective theoretical densities. A polymer matrix / C volume ratio of less than 300%, preferably less than 200%, and more preferably less than 70% advantageously limits the interfacial resistance between the conductive substrate and the active material of the electrode, regardless of the chemical nature of the non-conductive polymer matrix, while effectively ensuring adhesion of the active material.

[0042] The polymer matrix / C volume ratio is advantageously selected depending on the end use of the energy storage device comprising the current collector according to the invention.

[0043] The shape of the conductive substrate is advantageously adapted to the structure of the energy storage device containing it. Therefore, the conductive substrate can be selected from flat substrates, grid-like substrates, fibrous substrates, and felt-like substrates. The chemical nature of the conductive substrate is selected depending, inter alia, on the operating conditions of the energy storage device containing it and the processes used during the manufacture of this energy storage device. The conductive substrate may be a metal, a metal alloy, or a carbon-containing composite material (hereinafter referred to as a carbon material). The conductive substrate is preferably selected from copper, aluminum, nickel, stainless steel, heavily doped silicon, carbon, and carbon-containing composite materials, preferably a composite material containing carbon and a resin selected from polyester, vinyl ester, epoxy, phenolic, polyimide, polyamide, polypropylene, polyether ether ketone resin, or a mixture of one or more thereof.

[0044] Here, we describe the fabrication of vertically aligned carbon nanotubes in the form of a carpet, which is virtually free of by-products, exhibits controlled physicochemical properties (length, diameter, and density of carbon nanotubes), can be produced by any means on a conductive substrate, and is advantageously synthesized by a chemical vapor deposition (CVD) process.

[0045] This process allows a carpet or layer of vertically aligned carbon nanotubes to be formed on the surface of a conductive substrate in one or two steps. The carbon nanotubes obtained by either of these processes advantageously have a diameter of 5 nm to 50 nm, which ensures a good balance between the developed surface area (which should be large to improve electrical contact) and the intrinsic conductivity of the nanotubes.

[0046] A one-step aerosol-based chemical vapor deposition process, preferably using a solution of ferrocene in toluene, allows for the synthesis of vertically aligned carbon nanotubes with tunable physicochemical properties for specific applications, regardless of substrate type. This process allows for wide-ranging control of the diameter, length, and density of the carbon nanotubes. In this one-step process, a carbon precursor and a catalyst precursor are simultaneously injected into a reactor and treated at temperatures ranging from 550°C to 850°C to promote the nucleation and growth of carbon nanotubes. The synthesis temperature is preferably around 800°C. This is a low-cost, easily industrialized process. This process allows for the synthesis of nanotubes with densities up to 10 9 carbon nanotubes / cm 2 In this case, carbon nanotubes with diameters between 20 nm and 40 nm are advantageously obtained, and more generally with a density of 10 8 ~10 12 nanotubes / cm 2 In this case, carbon nanotubes with diameters of 5 nm to 50 nm can be obtained.

[0047] In a two-step chemical vapor deposition process, a layer of catalytic material is deposited prior to the carbon nanotube nucleation and growth step from a gaseous carbon source such as acetylene. The use of acetylene allows the synthesis temperature to be reduced to below 650°C. This may allow carbon nanotubes to be grown on substrates with low melting points, such as aluminum. This process advantageously allows for the growth of carbon nanotubes (with a density of 10 11 carbon nanotubes / nm 2 This results in carbon nanotubes with diameters of less than 5 nm, which are denser than conventional nanotubes (or higher).

[0048] Furthermore, the growth rate and thickness of the carbon nanotube film can be adjusted by controlling the reaction temperature and adjusting the acetylene concentration in the reactor. By adjusting the catalyst particle size, catalyst material used, type of reactants and / or additives, temperature, pressure, and other parameters, the morphology and density of vertically aligned carbon nanotubes in these VACNT layers or carpets can be appropriately controlled using methods known to those skilled in the art.

[0049] The conductive substrate may be heavily doped silicon, a metal or metal alloy, or a carbonaceous material, as previously described. In the case of growth on a metal or carbon substrate, a SiO 2 layer is preferably used prior to the growth of carbon nanotubes by chemical vapor deposition to prevent carbon diffusion into the substrate or to promote catalytic reactivity. x It may be necessary to deposit a barrier sublayer such as a SiO2 layer. In a one-step process, this deposition precedes the supply of catalyst and carbon precursors to the reactor required for carbon nanotube growth; in a two-step process, this deposition precedes the deposition of the catalyst. For deposition on aluminum substrates, it is not necessary to deposit a barrier sublayer, since the native oxide already serves as a barrier sublayer.

[0050] Next, a method for producing a current collector according to the present invention will be described.

[0051] On the carpet or layer of supported vertically aligned carbon nanotubes, a non-conductive polymer matrix is deposited by any suitable means, preferably a liquid deposition process, to obtain a current collector according to the present invention. The deposition of this polymer matrix makes it possible to form on the surface of a conductive substrate a layer comprising a plurality of current collecting regions electrically separated from one another by intermediate regions of the non-conductive polymer matrix, each current collecting region comprising a plurality of the vertically aligned carbon nanotubes, and all second ends of the vertically aligned carbon nanotubes of each current collecting region protruding beyond the surface of the non-conductive polymer matrix.

[0052] Advantageously, the deposition of said non-conductive polymer matrix is carried out by any suitable means, preferably by a method chosen from among coating, spraying, and immersion removal in a liquid phase in which the polymer is dissolved in a suitable solvent, which is then removed, in particular by evaporation. The deposition of the polymer matrix can also be carried out by extrusion, by infiltration in one or more stages, or by injection in one or more stages. After the deposition of the polymer matrix, the current collector according to the invention can also be subjected to a hot pressing or lamination process to strengthen its mechanical structure.

[0053] These deposition methods are simple and quick to implement. The method used to deposit the polymer matrix is selected depending, inter alia, on the chemical nature of the polymer matrix used.

[0054] <Example> The present invention will now be described with reference to examples, but is not limited to these examples. These examples relate to the preparation of a current collector according to the present invention and its evaluation in comparison with a commercially available current collector. The commercially available current collector used for comparison is a sheet designated NPC-055D Korea JCC, supplied by Samwha. This commercially available current collector is composed of a 50 μm thick aluminum sheet, two opposite sides of which are coated with a 1 μm to 2 μm thick carbon coating, and carbon black particles with an average diameter of 160 μm are embedded in a polymer binder.

[0055] Example 1: Single-step fabrication of VACNT carpet using chemical vapor deposition

[0056] Vertically aligned carbon nanotubes were formed on aluminum substrates by chemical vapor deposition (CVD) from ferrocene dissolved in toluene, hydrogen, and acetylene.

[0057] To achieve this, a 20 μm thick aluminum substrate is continuously fed into a roll-to-roll reactor. The reaction chamber is supplied with argon, acetylene, hydrogen, ferrocene, and toluene vapors. The substrate temperature in the reaction chamber is 615 °C. The pressure in the reaction chamber is atmospheric pressure (±15 Pa). The scroll speed of the aluminum substrate is adjusted so that the substrate's transit time through the reaction chamber is 2 minutes. At the exit of the roll-to-roll reactor, the substrate is covered with a 2 μm thick layer of VACNTs.

[0058] Example 2: Two-step VACNT carpet fabrication using chemical vapor deposition A 6-inch silicon wafer (p-type, 1-10 Ω cm, Silicon Quest International) was prepared and cleaned using a standard "piranha" solution consisting of one part hydrogen peroxide and three parts sulfuric acid. Next, a 1 / 10 nm Fe / Al2O3 patterned catalyst film was deposited on this cleaned silicon wafer by electron beam evaporation using a Temescal VES-2550 coupled with an FDC-8000 film deposition controller in a single pump cycle. The catalyst pattern was fabricated by lift-off of a 1 μm-thick image-reversal photoresist layer (AZ-5214E) patterned by photolithography. The catalyst was deposited over the entire surface of the silicon wafer. The catalyst-deposited portion on the photoresist was then removed by immersion in an acetone bath for 5 minutes followed by gentle sonication. The thickness of the catalyst film was measured during deposition using a quartz crystal monitor and subsequently confirmed by Rutherford backscattering spectroscopy (RBS).

[0059] The silicon wafer coated with the Fe / Al2O3 patterned film was introduced into a single-zone atmospheric pressure quartz tube furnace (Lindberg) with an inner diameter of 22 mm on a 30 cm long heating plate. The furnace then reached the set temperature of 700 °C in 30 min, and then heated at 400 cm 3The argon flow rate was maintained at 1 / min for another 15 min. Then, a mixture of argon (Ar, 99.999%, Airgas), ethylene (C2H4, 99.5%, Airgas), and hydrogen (H2, 99.999%, BOC) was added at 100 / 500 / 200 cm3 to induce carbon nanotube growth. 3 A flow rate of C2H4 / H2 / Ar was introduced into the tube furnace at standard / min. This flow was maintained for 1 min to allow for carbon nanotube growth.

[0060] Next, the flow of H2 and C2H4 was discontinued and 400 cm3 of argon was added to displace the gaseous reactants from the tube furnace. 3 The standard / min flow was maintained for an additional 10 minutes, then reduced to a nominal flow rate while the furnace cooled to below 100°C.

[0061] A layer of carbon nanotubes mainly aligned perpendicular to the substrate, i.e., a VACNT layer with a thickness of approximately 5 μm, was obtained.

[0062] Example 3: Preparation of a current collector according to the present invention The previously obtained supported VACNT layers prepared in Examples 1 and 2 were coated with a copolymer of butadiene and styrene (known by the acronym SBR for Styrene-Butadiene Rubber) by dip coating. For this purpose, a toluene solution containing 20 mg of SBR per ml was prepared. The previously obtained VACNT layers were immersed in this solution at a dipping speed of 10 mm / s, then left in this solution for 10 seconds and removed at a speed of 10 mm / s.

[0063] To evaluate the effect of the polymer matrix / C volume ratio (abbreviated as SBR / C volume ratio in the following examples), a current collector according to the present invention was produced by performing several immersion-immersion-hold-removal cycles as described above in a toluene solution containing 20 mg of SBR per ml.

[0064] 1cm 2To prepare a current collector of the present invention containing 4.5 mg of SBR per ml, a toluene solution containing 100 mg of SBR per ml was prepared and then pipetted onto the supported VACNT layer prepared in Example 1.

[0065] In this way, a 1 cm 2 film was fabricated from the supported VACNT layer synthesized in Example 1. 2 Current collectors according to the invention containing 0.15 mg to 4.5 mg of SBR per layer were obtained. The properties of these current collectors were compared, particularly by impedance spectroscopy, with those of the supported VACNT layer developed in Example 1 without a polymer coating, with those of the aluminum substrate, and with those of a commercially available current collector NPC-055D Korea JCC supplied by Samwha Corporation.

[0066] Example 4: Evaluation of current collectors according to the present invention 4.1: Swagelok®-type supercapacitor cell with wet activated carbon electrodes In a mortar, 85% by mass of activated carbon (hereinafter referred to as CA) as a binder, 10% by mass of polyvinylidene fluoride (Kynar 3103) used as a binder, and 10% by mass of carbon black (Timcal®) were mixed with N-methyl-2-pyrrolidone (hereinafter referred to as NMP). The resulting viscous solution was poured into a 1 cm 2 The electrode was deposited by doctor blade coating to a thickness of 200 μm on a current collector according to the present invention prepared in Example 3 containing an average of 0.23 mg of SBR per electrode, and also on an aluminum substrate and a commercially available current collector for comparison. After drying in an oven, the current collector disks and electrodes were cut out and assembled in a glove box with a separator (Celgard EPP 1208) impregnated with NEtBF1M(ABCR) electrolyte to form a Swagelok®-type supercapacitor cell, as shown in Figure 4.

[0067] Impedance spectroscopy measurements were performed in potentiostatic mode with the constant voltage set at 0.02 V and the frequency swept in the range of 400 kHz to 100 mHz. The equivalent series resistance (commonly abbreviated as ESR) was evaluated from the impedance spectroscopy measurements and is shown in Table 1 below.

[0068] [Table 1]

[0069] 4.2: Swagelok®-type supercapacitor cell with free-standing electrodes 95% by weight of reference CA YP80F (Kuraray) and 5% by weight of an aqueous solution containing 60% polytetrafluoroethylene (PTFE) (Sigma Aldrich) were mixed in ethanol under magnetic stirring and heating. The resulting paste was flattened to a thickness of approximately 150 μm, and disks were cut from the resulting film and dried in an oven. The free-standing electrode (also called the "dry" electrode) thus obtained was assembled in a glovebox with a substrate serving as a current collector and a separator (Celgard EPP 1208) impregnated with ACN NEtBF 1 M (ABCR) electrolyte, as shown in Figure 5, to form a Swagelok®-type supercapacitor cell.

[0070] For comparison, Swagelok® type supercapacitor cells were fabricated using a different substrate, i.e., an aluminum substrate, developed in Example 3, which served as the current collector, with an average SBR content of 0.23 mg SBR / cm. 2 The current collectors were fabricated using the current collectors of the present invention, including the present invention, and the commercially available current collectors described above. The equivalent series resistance (ESR) was evaluated from impedance spectroscopy measurements and is shown in Table 2 below.

[0071] [Table 2]

[0072] 4.3: Half cell of "Coin Cell 2032" type battery cell Fabricate a cathode layer of LiFePO4 on a substrate that acts as a current collector In a mortar, 75% by weight of LiFePO4 (hereafter referred to as LFP, Sigma Aldrich), 5% by weight of polyvinylidene fluoride (PVdF) used as a binder (Kynar 1810), and 20% by weight of carbon black (Norit) were mixed with N-methyl-2-pyrrolidone, known as NMP for short. The resulting viscous solution had an average viscosity of 0.23 mg SBR / cm as prepared in Example 3. 2 A cathode layer was obtained by doctor blade coating to a thickness of 100 μm on a current collector of the present invention containing ethylenediaminetetraacetic acid (EC) and an aluminum substrate for comparison. After drying in an oven, the current collector and electrode disk were cut out and assembled in a glove box with a separator (Celgard 3501) impregnated with 1M LiPF6 electrolyte in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) in an EC / DEC ratio of 1:1 (Sigma Aldrich) to form a half-battery cell, as shown in Figure 6.

[0073] Impedance spectroscopy measurements were performed in potentiostatic mode with the constant voltage set at 0 V and the frequency swept between 10 kHz and 100 mHz. The equivalent series resistance (ESR) was evaluated from the impedance spectroscopy measurements and is shown in Table 3 below.

[0074] [Table 3]

[0075] LiNi on the substrate acting as a current collector 0.8 Mn 0.1 Co 0.1 Fabricating the O2 cathode layer On a substrate that can function as a current collector, LiNi 0.8 Mn 0.1 Co 0.1A coating of O2 (hereafter referred to as NMC811) was applied. In a mortar, 222.5 g of NMC811, 3.18 g of polyvinylidene fluoride (PVdF) as a binder, and 1.36 g of carbon black were mixed with 74.1 g of N-methyl-2-pyrrolidone (NMP). The resulting solution had a solids content of 75.1% and a viscosity of 2919 mPa at 25°C. This viscous solution was then doctor blade coated to an average thickness of 0.23 mg SBR / cm. 2 The cathode layer was deposited to a thickness of 100 μm on a current collector according to the present invention developed in Example 3, which contained NMP. For comparison, it was also deposited on an aluminum substrate. After drying in an oven to remove the NMP, the current collecting disk and electrode were cut out. In a glove box, a separator (Celgard 3501) impregnated with 40 μL of 1M LiPF6 electrolyte in ethyl carbonate (EC) and diethyl carbonate (DEC) at an EC / DEC ratio of 1:1 (Sigma Aldrich) was assembled with the metallic lithium disk to form a half-battery cell, as shown in FIG. 6.

[0076] The produced electrode contained 98 mass % of NMC811, 0.6 mass % of conductive carbon, and 1.4 mass % of PVdF as active materials.

[0077] The fabricated electrodes were characterized by power pulse tests and resistance drop measurements under the same operating conditions.

[0078] 4.4: Evaluation of the current collector of the present invention by impedance spectroscopy 0.15 mg / cm prepared in Example 3 2 ~4.5mg / cm 2 The current collector of the present invention containing SBR, the VACNT layer without polymer coating prepared in Example 1, an aluminum substrate, and a commercially available current collector, NPC-055D Korea JCC (Samwha), were evaluated by impedance spectroscopy.

[0079] To do this, each of these substrates was introduced into an “open” cell device as shown in Figure 7 and assembled with a separator (Celgard 3501) impregnated with the ionic liquid EMITFSI 99.5% (Solvionic) as the electrolyte to form a substrate / separator / substrate structure.

[0080] Impedance spectroscopy measurements were carried out in potentiostatic mode, with the constant voltage set at 0.02 V and the frequency swept from 400 kHz to 100 mHz.

[0081] The Nyquist diagrams obtained for these different substrates are shown in Figure 8. These allow evaluation of not only the equivalent series resistance (ESR) but also the additional parallel resistance associated with ion diffusion, as shown in Chapter 13 of D. Larcher et al.'s publication "Energy storage in the world of transport," Chemistry and transport, EDP Science (2014). The equivalent series resistance (ESR) was evaluated from measurements performed by impedance spectroscopy and is shown in Table 4 below and depicted in Figure 9 below as a function of the SBR / C volume ratio for the current collector according to the present invention, compared to the commercial current collector NPC-055D Korea JCC (Samwha).

[0082] [Table 4]

[0083] The mechanical resistance of different current collectors according to the present invention was evaluated visually by rubbing with a finger (left side of the sample) and scratching with pliers (right side of the sample), as shown in Figure 10. The current collectors according to the present invention, especially those with SBR / C volume ratios of 49% and 687%, have better mechanical resistance than the supported VACNT layer prepared in Example 1 or the commercial current collector NPC-055D Korea JCC (Samwha).

[0084] The properties of the current collector according to the present invention are summarized in Table 5 below.

[0085] [Table 5]

[0086] Example 5: Transfer of vertically aligned nanotubes from a growth substrate to another substrate A sample of vertically aligned nanotubes (approximately 30 μm thick carpet) was prepared on a stainless steel substrate instead of an aluminum substrate, following Example 1. The sample was then mechanically compressed against an uncoated copper current collector (12 μm thick) using a laboratory calender with a stainless steel roller (TOB-JS-300) with a gap of 30 μm and a maximum pressure of 500 N / mm.

Claims

1. A current collector (1) for an electrical energy storage system or power generation system, a. Conductive substrate (2) and b. A non-conductive polymer matrix and c. Contains carbon nanotubes, The carbon nanotube mentioned above is It includes a first end called a transfer end (31) that enables the transfer of current to the substrate, the first end being fixed on the surface of the conductive substrate (2) and electrically connected thereto. Furthermore, it includes a second end (32) on the opposite side of the first end, the second end being called the current collecting end, which can collect current from external active material, particularly electrodes. This forms a layer on the surface of the conductive substrate (2) that includes a plurality of current-collecting regions which are electrically insulated from each other by the insertion regions of the non-conductive polymer matrix. Each of the current-collecting regions includes a plurality of carbon nanotubes, A current collector in which the second ends of the carbon nanotubes in each of the current-collecting regions all protrude beyond the surface of the non-conductive polymer matrix.

2. A current collector according to claim 1, The carbon nanotubes are aligned, preferably substantially perpendicular to the substrate. These nanotubes, which are aligned substantially perpendicular to the substrate, are characterized by being called "vertically aligned carbon nanotubes" and thus make up the current collector.

3. A current collector according to claim 2, In a top view, a. The multiple vertically aligned carbon nanotubes in the current collection region have an average tube spacing of less than 100 nm, and / or b. A current collector characterized in that the current collection area is circular, and the minimum distance between the outer edges of the current collection area is 1 μm or more, preferably greater than 10 μm.

4. A current collector according to any one of claims 1 to 3, The conductive substrate is selected from copper, aluminum, nickel, stainless steel, highly doped silicon, carbon, and carbon-containing composite materials. Preferably, the current collector is characterized by being selected from a composite material comprising carbon and a resin selected from polyester, vinyl ester, epoxy, phenol, polyimide, polyamide, polypropylene, polyetheretherketone resin, or a mixture of one or more thereof.

5. A current collector according to any one of claims 1 to 3, The current collector is characterized in that the conductive substrate is selected from a flat substrate, a grid-like substrate, a fibrous substrate, and a felt-like substrate.

6. A current collector according to any one of claims 1 to 3, The vertically aligned carbon nanotubes electrically connected to the surface of the conductive substrate are a. Having a thickness of less than 10 μm, preferably less than 1 μm, and / or, b. 100m ２ Exceeding / g, preferably 250m ２ A current collector characterized by having an unfolded surface area exceeding / g.

7. A current collector according to any one of claims 1 to 3, A current collector characterized in that the volume ratio of the nonconductive polymer matrix to the carbon nanotubes is less than 300%, preferably less than 200%, and more preferably less than 70%.

8. An apparatus or system for storing or generating electrical energy such as a battery, supercapacitor, or fuel cell, comprising a current collector as described in any one of claims 1 to 3.

9. A method for manufacturing a current collector comprising a conductive substrate, a carbon nanotube with one end fixed to the surface of the conductive substrate, and a non-conductive polymer matrix, The aforementioned manufacturing method is The following sequence of steps, namely, a. On the conductive substrate, a carpet is formed by vertically aligned carbon nanotubes, preferably by a deposition technique using chemical vapor deposition, or aligned nanotubes synthesized on another substrate are transferred onto the conductive substrate. b. The nonconductive polymer matrix is ​​deposited on the carbon nanotubes by any suitable means, preferably by a liquid-phase deposition method, to form a layer on the surface of the conductive substrate that includes a plurality of current-collecting regions electrically insulated from each other by the insertion regions of the nonconductive polymer matrix, Each of the current-collecting regions includes a plurality of carbon nanotubes, A method for manufacturing a current collector, wherein all of the second ends of the carbon nanotubes in each of the current-collecting regions protrude beyond the surface of the non-conductive polymer matrix.

10. A method for manufacturing a current collector according to claim 9, A method for manufacturing a current collector, characterized in that the deposition of the nonconductive polymer matrix in step b is carried out by a method selected from coating, spray application, immersion removal, extrusion, and impregnation in one or more steps.

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