Nonwoven, electrode component, corresponding manufacturing method and apparatus for carrying out the manufacturing method

Abstract

A nonwoven manufactured in a wet-laid or papermaking method, the nonwoven having 70 to 100% carbon fibers of a fiber length between 0.01 and 12 mm.

Description

[0001] Nonwoven fabric, electrode component, manufacturing process therefor and device for carrying out the manufacturing process

[0002] Field of the invention

[0003] The present invention relates to a nonwoven fabric produced by a wet-laid or paper process, which is suitable for the production of electrodes, for example, for fuel cells, gas diffusion layers (GDL), water electrolysis, or other energy-related applications and electrical energy storage devices such as redox flow batteries, as well as other electrical applications. The nonwoven fabric consists primarily of carbon-rich material, in particular carbon fibers, which are inherently electrically conductive or which are made suitably conductive in a subsequent process.

[0004] Background of the invention and prior art

[0005] The storage of renewable energies is a central theme of the energy transition. Hydrogen, as well as its production and conversion, are considered key elements. Hydrogen can be produced sustainably and efficiently using water electrolysis, for example, using proton exchange membrane (PEM) processes. The electrical energy required for production can ideally be provided by photovoltaics (PV) or wind power. However, this requires efficient and cost-effective electrolysis systems. In the PEM electrolysis process, the PTL (Porous Transport Layer) based on precious metals, especially titanium, is located on the anode side, while the cathode side usually contains a PTL based on carbon. The demand-based conversion of the produced hydrogen into electrical energy can, in turn, be achieved using PEM fuel cells.So-called gas diffusion layers (GDL) are used on both the anode and cathode sides, consisting of electrically conductive carbon (carbon paper) and a catalyst layer.

[0006] For storing surplus electrical energy, for example, from PV systems or wind power, stationary energy storage devices such as redox flow batteries (RFBs), such as vanadium RFBs, are now indispensable. Depending on the operating principle, thick or thin carbon-based electrodes on a fleece or felt base are used symmetrically.

[0007] As described above, carbon fiber-based felts, so-called needle felts, are used for some of these applications. The manufacturing process for carbon fiber needle felts is particularly complex because carbon fibers cannot be processed directly into needle felt. Carbon fibers are brittle and fragile when subjected to mechanical stress in their dry state. The potential consequences of improper handling and processing include fiber damage, process deadness, and slow process speeds.

[0008] For this reason, processing methods are currently being pursued, as shown in Fig. 1 as an example, in which it is not the carbon fiber itself that is laid down to form the needle felt, but rather its precursor materials, so-called precursors. For this purpose, virgin polyacrylonitrile or PAN, viscose or cellulose fibers are usually used. Even after their oxidation to a flame-resistant fiber, for example a PANOX fiber as shown in Fig. 1, these still have sufficient textile properties and low brittleness, which means they can be processed into needle felt. After so-called web laying including needling or felting, the needle felt, for example a PANOX felt as shown in Fig. 1, is carbonized and graphitized. However, due to the felting and the resulting fiber structure and high fiber density, slow process conditions are necessary to allow the expulsion of foreign atoms, especially non-carbon atoms, to take place in a controlled manner.Depending on the thickness of the resulting felt, significant limitations in material transport can be expected, which, if uncontrolled, can lead to exothermic reactions and damage to the material. The required system technology is also limiting, as the thermal processes must be carried out under protective gas, necessitating suitable lock systems and seals, which limits the web widths.

[0009] As a result, the resulting felts and products based on them are complex to manufacture and associated with high production costs. The scaling potential of this technology appears to have been exhausted and is limited. Regarding the properties of these needle felts, the desirable high conductivity in the z-direction, achieved through the needling process, is particularly impressive. Overall, however, the conductivity could be increased if the fibers had been subjected to tensile stress during the carbonization process, which the needle felting process does not allow.

[0010] Furthermore, such existing processing methods prevent the use of recycled carbon fibers, whose importance is increasing not only for ecological reasons but also due to rising demand. Demand is driven by the high demand for virgin carbon fibers in the lightweight construction industry, especially the wind energy and aviation industries. Therefore, appropriate processing methods that also allow the use of recycled carbon fibers would be desirable in order to save raw material and material costs while simultaneously protecting the environment.

[0011] Object of the invention

[0012] The object of the present invention is to overcome the above-described problems and disadvantages of the prior art.

[0013] Summary of the invention

[0014] The above-mentioned object and other problems are solved by a nonwoven fabric, semi-finished product, or finished product made of a nonwoven fabric, by an electrode component, by a method for producing a nonwoven fabric, and by a device for carrying out the method according to the main claims. The subclaims relate to preferred embodiments of the invention.

[0015] The nonwoven fabric according to the invention is produced using a wet-laid or paper process, wherein the nonwoven fabric comprises 70 to 100% carbon fibers, preferably >70 to <100% carbon fibers, particularly preferably >75 to <80% carbon fibers, with fiber lengths between 0.01 and 12 mm. This excessively high proportion of carbon fibers results in a significantly higher conductivity of the nonwoven fabric compared to known materials, in particular compared to materials consisting of significantly less than or a maximum of 70% carbon fibers. The nonwoven fabric further preferably comprises carbon fibers with fiber lengths between 0.01 and 12.0 mm, preferably 0.01 to 6 mm, particularly preferably 0.01 to 3 mm. The carbon fibers are optionally made from at least one of the following: polyacrylonitrile, pitch, alternative precursors and / or recycled carbon fibers.More preferably, a nonwoven fabric is present wherein the alternative precursors consist of cellulose, lignin, and / or phenolic resin; and / or wherein the recycled carbon fibers comprise at least one of the following: post-industrial waste carbon fibers, prepreg trim, and carbon fibers exposed by pyrolysis and / or solvolysis. The nonwoven fabric according to the invention is a single-layer nonwoven fabric.

[0016] The nonwoven fabric preferably further comprises carbon fibers with at least 90% carbon. Optionally, the carbon fibers of the nonwoven fabric have an activated surface, graphitized carbon fibers, or a mixture thereof.

[0017] Furthermore, the nonwoven fabric can optionally comprise: 0 to 20% binder, preferably 0 to 15% binder; and / or additives comprising ground fibers, carbon-rich particulate fillers and active substances, and / or activated carbon powder; wherein the additives have particle sizes of 0.01 to 2 mm, preferably 0.005 to 1 mm. The binder is preferably present as binder fibers, spray binders, scatter binders, and / or bulk binders.

[0018] Furthermore, a nonwoven fabric is provided which preferably has an electrical volume resistance and / or an electrical surface resistance of 0.01 to 1000 Ohm / cm 2 has.

[0019] In addition, the nonwoven fabric optionally has a thickness of 0.1 to 10 mm, preferably 0.1 to 6 mm. Optionally, a single layer of the nonwoven fabric has a grammage of 10 to 300 g / m 2 , preferably from 10 to 200 g / m 2 , on.

[0020] The nonwoven fabric may further comprise carbon fibers with at least two average lengths, wherein a distance of at least 0.1 mm, preferably at least 0.2 mm, exists between a first average length and a second average length, or wherein a continuous fiber distribution is present. The nonwoven fabric further preferably has a broad fiber distribution A and a narrow fiber distribution B, wherein the fiber distribution B is preferably monodisperse; and / or wherein a histogrammatically scalable fiber length distribution is preferably present.

[0021] The present invention further provides semi-finished products or finished products each made from the nonwoven fabric according to the invention for the production of electrodes.

[0022] The present invention also provides an electrode component for redox flow batteries, for PEM water electrolysis or for energy and hydrogen-related applications, which is manufactured from the nonwoven fabric according to the invention in one layer or in several superimposed layers.

[0023] Furthermore, the present invention provides a method for producing a nonwoven fabric using a wet-laying process, comprising the following steps: preparing carbon fibers by means of milling and sieving and / or filtering to produce a mixture of carbon fibers with a fiber distribution of carbon fibers having lengths between 0.01 and 12 mm, preferably 0.01 and 6 mm; producing a mixture of the prepared carbon fibers and a liquid, which preferably comprises water; depositing the mixture in a build-up manner; and contact-free drying of the deposited mixture. The method according to the invention for producing a nonwoven fabric preferably provides for producing the nonwoven fabric by depositing the mixture in a single ply or layer.

[0024] The method for producing a nonwoven fabric preferably further comprises: coating and / or impregnating the deposited mixture after nonwoven formation prior to nonwoven drying; or coating and / or impregnating after a pre-drying and / or first consolidation step.

[0025] Optionally, the process for producing a nonwoven fabric is carried out using a paper machine or a wet-laid machine. Also optionally, the carbon fiber processing step additionally includes activating the surface of the carbon fibers.

[0026] The method for producing a nonwoven fabric preferably further comprises the following: introducing a binder as a binding fiber; and / or applying the binder as a spray, scatter, and / or mass binder.

[0027] The present invention further provides an apparatus for carrying out the method of producing a nonwoven fabric according to the invention, comprising: a mill; a screen; and a wet-laid nonwoven machine.

[0028] Short description of the drawings

[0029] The invention, as well as further details and advantages thereof, are explained below using preferred embodiments with reference to the figures. They show:

[0030] Fig. 1 Process steps in needle felt production (state of the art);

[0031] Fig. 2 shows a process chain according to the invention up to the electrode component including the wet nonwoven process;

[0032] Fig. 3 a histogram of a fiber length distribution after fiber processing

[0033] Fig. 4 Relationship between nonwoven thickness and grammage using two different process and fiber preparation settings;

[0034] Fig. 5 shows a carbon fiber-based nonwoven fabric according to the invention; and Fig. 6 shows a distribution of projected angles in the carbon fiber-based nonwoven fabric according to the invention according to Fig. 5.

[0035] Detailed description of the invention

[0036] In this description, the terms top, bottom, right, and left, as well as similar terms, refer to the orientations or arrangements shown in the figures and are used only to describe the exemplary embodiments. These terms may indicate preferred arrangements, but are not to be understood in a limiting sense. Furthermore, the terms "substantially," "approximately," "about," and similar expressions mean that deviations of + / -10%, preferably + / -5%, from the stated value are permissible.

[0037] The value ranges mentioned here are, unless explicitly excluded, always understood in such a way that lower edge ranges are marked with ">", greater than or equal to, and upper edge ranges are marked with less than or equal to the specified value range are considered included. Thus, the peripheral areas themselves are either included in the respective range, but can alternatively also be (unilaterally) excluded.

[0038] The following abbreviations are also used below: The term "wet-laid" stands for a wet-laid nonwoven technology, similar to paper or papermaking technology; "Re-CF" stands for recycled carbon fiber; "ACF" stands for activated carbon fiber; and "PAN" stands for polyacrylonitrile.

[0039] The present invention relates to a carbon fiber-based nonwoven fabric produced by wet-laid or paper processes. Paper processes generally involve short and, if necessary, automatically bonding fibers with fiber lengths in the range of 2 to 3 mm. Wet-laid processes can also work with longer fibers over 3 mm using an open air drying section.

[0040] Nonwoven fabric is defined below as any form of material consisting of fibers of limited length (short or staple fibers), as well as continuous fibers or cut yarns of any type and origin, which have been assembled and bonded together in any way to form a nonwoven fabric (a fiber layer, a fiber web). This does not include the crossing and / or entangling of yarns, as occurs in weaving, knitting, lacemaking, and braiding. The definition here includes the term "paper"; both materials and their production processes are related, but differ primarily in fiber length and fiber material.The nonwoven fabric according to the invention is fundamentally suitable as a substrate for electrodes in energy storage devices and electrolyzers, for example, for fuel cells, gas diffusion layers (GDL), water electrolysis, or other energy-related applications and electrical energy storage devices such as redox flow batteries, as well as other electrical applications. The nonwoven fabric according to the invention, as a semi-finished or finished product, consists primarily of carbon-rich material, in particular carbon fibers, which are electrically conductive or which can be suitably made conductive in a subsequent process.

[0041] Instead of conventional needle felts, the present invention uses a specially designed nonwoven fabric from the so-called wet-laid process. This enables the application of highly scalable and cost-effective paper or wet-laid technology, also known as wet-laid technology, with potentially several hundred meters of process speed. This can reduce the costs of manufacturing the electrodes and the overall costs of the aforementioned energy conversion and storage systems.

[0042] Furthermore, the present invention enables the use of commercially available, already carbonized and / or graphitized fibers. Furthermore, this opens up the unique possibility of using recycled carbon fibers. The rapidly growing recycling market benefits from the increasing use of carbon fibers and structural and, in the medium term, unresolvable capacity bottlenecks for virgin fibers. The special combination of these factors delivers a cost-effective, easily scalable, and, in some applications, technically superior product.

[0043] Carbon, graphite fibers, or particles are laid and bonded to form a nonwoven using wet-laid technology or paper processes. Special fiber processing, for example, through a milling process, as well as process conditions tailored to the specific electrode application, enable the production of a precisely defined, highly porous, open-pore, homogeneous nonwoven. By mixing and grading different fiber types and geometries, which may result from appropriate upstream fiber processing, profiles and specific fiber orientations can be created within nonwovens, which have advantageous functions in finished products such as electrodes. In particular, a controlled orientation of the fibers in the z-direction can be both desirable and advantageous in this case.

[0044] Accordingly, according to the invention, nonwovens with the same material composition can be produced which have an optimized thickness-grammage ratio, for example nonwovens with a high thickness (e.g. 5 mm) and a low grammage (e.g. 100 g / m 2 ) or vice versa. For drying and / or fixing nonwovens produced according to the invention, depending on the application, contact-free drying is preferred to maintain the previously produced volume as well as the previously produced pore size and / or shape.

[0045] Fig. 2 shows a process chain according to the invention for a method for producing a nonwoven fabric according to the invention, which optionally extends to the graphite electrode, including the wet-laying process. Both fresh fibers and recycled fibers can be used as starting materials. Any of the aforementioned carbon- or graphite-based fibers, as well as particulate materials, are possible.

[0046] First, these fibers are processed mechanically, physically, or chemically to obtain advantageous nonwoven structures and properties. Carbon fibers are processed by milling, sieving, and / or filtering to produce a carbon fiber mixture with a fiber distribution of carbon fibers having lengths between 0.01 and 12 mm, preferably 0.01 and 6 mm. Optionally, the surface of the carbon fibers can also be activated during the processing of the carbon fibers. The milling process, in particular, proves to be particularly advantageous in the context of the present invention. This step is used to specifically obtain polydisperse fiber lengths. Despite the potential for brittle fracture behavior of the fiber types used here, it can produce uniform particles having the stated fiber lengths.Using appropriately adjusted grinding tools, uniform fiber lengths can be achieved, even if the initial length of unground fibers is unknown and / or irregular. This is especially true for recycled fibers.

[0047] Subsequently, a mixture of the processed carbon fibers and a liquid, preferably containing water, is created. This is followed by application-specific mixing of the processed fibers with nonwoven fabric additives or other fiber or particulate materials, such as binders, to produce a homogeneous, stable dispersion. One or more binders can optionally be incorporated as binding fibers and / or applied as spray, scatter, and / or bulk binders.

[0048] To produce the nonwoven fabric according to the invention, i.e. a carbon nonwoven fabric as shown by way of example in Fig. 2, further steps are required, namely the build-up deposition of the mixture and contact-free drying of the deposited mixture. Contact-free drying is understood here to mean a drying process in which the nonwoven fabric according to the invention is created as a non-compressed layer, with no pressure being applied to the deposited mixture from above or below. This lows the risk of the deposited mixture sticking to a corresponding deposit or support, for example a so-called web. With contact-free drying, no deposit surface is used that actively dries, but rather one that merely (supports) the deposited mixture during the drying period. Contact-free drying preferably takes place as a one-sided support and / or with a straight and / or flat support surface or guide.The mixture laid down in this way can then, depending on the selected drying parameters, be passed through a dryer in the direction of production. In this case, it is particularly preferred that a maximum of 10% of the laid mixture comes into contact with the corresponding support. Alternatively or additionally, the mixture is laid horizontally or almost horizontally on the corresponding support. Optionally, the drying process of the mixture laid down in this way can be further improved by blowing it through, if necessary with heated air. In this context, however, the use of a suitably air-permeable web is required. In Fig. 2, a wetlaid process with optional impregnation is used as an example, with a process speed of over 100 m / min. The specially prepared fiber material is subjected here, for example, to a wetlaid (or wet-laid) orThe fibers are fed into the paper machine in a manner that prevents segregation, yet maintains a high degree of turbulent flow. A fiber web is formed by dewatering the fiber dispersion on a continuous screen. Depending on the fiber blend and machine settings, deposition and / or build-up structures with an increased proportion of z-oriented fibers are formed. The wet fiber web is fed into a continuous dryer with as little pressure as possible, where water is removed and a potential binder is activated. Depending on the grammage and structure, the nonwoven is removed as sheet material or wound up.

[0049] The deposited mixture can optionally be coated and / or impregnated either before the fleece drying or the coating and / or impregnation can be carried out after an additional step of pre-drying and / or initial consolidation.

[0050] To obtain a carbon electrode as shown in Fig. 2, the produced nonwoven fabric is optionally carbonized at a maximum process speed of 20 m / min. To obtain a graphite electrode as shown in Fig. 2, the produced nonwoven fabric is optionally graphitized alternatively or in parallel at a maximum process speed of 20 m / min.

[0051] An apparatus suitable for producing a nonwoven fabric according to the invention comprises a mill, a screen and a wet-laid nonwoven machine, wherein each of said elements is replaceable by components or parts insofar as they meet the above-mentioned requirements in the manufacturing process.

[0052] The nonwoven fabric according to the invention is produced by the wet-laid or paper process or an equivalent process and comprises 70 to 100% carbon fibers, preferably >70 to <100% carbon fibers, particularly preferably >75 to <80% carbon fibers, with fiber lengths between 0.01 to 12 mm.

[0053] In addition, the nonwoven fabric according to the invention preferably has various characteristics set out below, which can be present in any combination:

[0054] Various carbon fibers or fiber types can be used for the nonwoven fabric according to the invention. These include, for example, common commercially available fiber types such as so-called high-tenacity (HT), intermediate-modulus (IM), and / or high-modulus (HM) fibers. These are based, for example, on polyacrylonitrile but also on pitch, known internationally as pitch, or on variants based on alternative precursors such as cellulose (lyocell, viscose, rayon) and lignin or even phenolic resin, also known under the brand name Kynol. This also includes recycled carbon fibers, which have particular potential as a cost-effective replacement for virgin fibers. Suitable examples in this regard are fibers from so-called post-industrial waste and / or prepreg trimmings, as well as fibers exposed by pyrolysis and / or solvolysis.

[0055] In addition to the basic fiber types mentioned, it is advantageous to use carbon-rich fibers, preferably fibers with at least 90% carbon content, optionally with an activated surface. This can be achieved through a special treatment or purchased directly as so-called activated carbon fibers (ACF). Depending on the application, graphitized carbon fibers can be used additionally or alternatively. Some applications particularly benefit from blends of the aforementioned fiber types.

[0056] In this context, it is noted that an additionally used binding agent, also referred to herein as binder, is also considered to be a “fiber” within the meaning of the present invention, provided that it is or will be added to the nonwoven fabric according to the invention in fiber form.

[0057] Carbon fibers of different geometries, different fiber lengths and / or fiber length distribution(s) can be used for the nonwoven fabric according to the invention. A distinction is made between specific fiber properties before fiber or fiber preparation and the properties of the fibers in the nonwoven fabric as a consequence of a fiber pretreatment or refining process. Before fiber preparation, fibers to be used according to the invention have lengths of 0.1 mm - 25 mm, preferably 0.2 mm - 20 mm. After fiber preparation, i.e. in the finished nonwoven fabric, the fibers used have lengths of 0.01 - 12 mm, preferably 0.01 - 6 mm, very preferably 0.01 - 3 mm, and a fiber length distribution that is broadened towards shorter fibers than before fiber preparation.

[0058] The nonwoven fabric according to the invention optionally comprises carbon fibers with at least two average lengths. Figure 3 shows an exemplary nonwoven fabric in this context. The distance between a first average length and a second average length is at least 0.1 mm, preferably at least 0.2 mm. Alternatively, a continuous fiber distribution can also be present.

[0059] Fig. 3 shows an exemplary fiber dispersion within a nonwoven fabric according to the invention, characterized by a specific fiber length distribution after fiber processing (histogram). The nonwoven fabric according to the invention exhibits a percentage peak at fiber lengths of approximately 1.0 to approximately 3.0 mm. The proportion of longer fibers then decreases rapidly and steadily, as the present histogram shows. The longer fibers serve, in particular, to build strength and reduce electrical conductivity in the plane, while the shorter fibers are responsible for increasing fiber deposition and increased alignment in the z-direction.

[0060] Depending on the application, a nonwoven fabric can simultaneously have several fiber distributions, for example, a broad fiber distribution A and a narrow fiber distribution B. In such a case, the fiber distribution B is preferably monodisperse; and / or preferably, a histogrammatically scalable fiber length distribution is present.

[0061] Furthermore, a wide variety of fiber types or, depending on the application, blends of fibers and particles can be present in application-specific mixing ratios. The technique of so-called additivation, in particular, is a method of choice for adjusting, for example, the structure, conductivity, and / or porosity of the mass to be processed, but also of the final product in the form of a finished nonwoven material.

[0062] Suitable additives include, for example, ground fibers, carbon black, carbon-rich particulate fillers and active substances and / or activated carbon powder, etc. Such particles have a preferred size of 0.01 - 2.0 mm, especially 0.005 - 1.0 mm.

[0063] Furthermore, the bonding of the nonwoven fabric according to the invention or to the nonwoven fabric according to the invention, hereinafter also referred to as nonwoven bonding, can be achieved using various methods, which ultimately affect the product properties of the finished nonwoven fabric. The binder used in this case is preferably present in the finished nonwoven fabric in a weight proportion of 0 to 20%, preferably 0 to 15%.

[0064] The binder can be introduced as a binding fiber, which softens during drying, or applied as a spray binder to a nonwoven web that is not yet dried, partially dried, or fully dried. Additionally or alternatively, the binder can be applied as a scatter binder in the same manner and / or incorporated into the fiber material as a bulk binder by dissolving or dissolving one or more suitable binders in the initial mass. Additionally or alternatively, the binder can be applied or applied using dipping and / or coating processes.

[0065] Suitable binders include thermoplastic binders, reactive binders, such as those from the group of polyvinyl alcohols (PVA) or acrylic polymer systems, as well as systems that have a high carbon residue, such as phenolic resins or polyacrylonitrile.

[0066] Furthermore, for a potential application-specific product performance, it may be advantageous to use binders which, before or after the mostly thermal finishing, have a sufficiently low electrical volume resistance, e.g. < 1000 Ohm / cm 2 , have.

[0067] The nonwoven fabric according to the invention preferably has a volume resistance of about 0.01 to 1000 ohm / cm 2 and / or a surface resistance of approximately 0.01 to 1000 ohm / cm 2 Both values ​​depend on the nonwoven density and the applied measuring pressure. They apply particularly to measurement methods according to DIN 54345-1, DIN EN 1149-1, and DIN EN 1149-2, carried out with a high-resistance measuring electrode TE 50.

[0068] With regard to the parameters of porosity, volume, basis weight and thickness ratio of the nonwoven fabric, it should be noted that the nonwoven fabric according to the invention, depending on the application, has the following properties with regard to the distribution and arrangement of the fibers used:

[0069] The nonwoven fabric according to the invention has a specific gradient across its cross-section / thickness. This gradient is achieved or optionally influenced by strong additional suction during dewatering of the fiber dispersion on the wet-laid nonwoven or paper machine during nonwoven formation and / or by a polydisperse fiber length / geometry distribution and / or by using fibers or additives of different densities and hydrodynamic behavior. In this context, polydisperse refers to having different particle characteristics, such as size. This results in the technical advantage that a finished electrode made from the nonwoven fabric according to the invention can potentially be better contacted by a current collector / supply on the denser side, which faces the more porous side of a cell (e.g., electrolyte). The porosity is preferably determined indirectly via air permeability according to DIN EN ISO 9237: 1995-12.

[0070] Furthermore, during the production of the nonwoven fabric according to the invention, fiber deposition occurs either isotropic (evenly distributed) or anisotropic, depending on the machine settings and stock preparation. Targeted z-orientation of the fiber mixture used is also optionally possible. Preferred isotropic arrangements with respect to the xy plane are explained in more detail below. Depending on the fiber preparation and machine settings, a so-called build-up fiber deposition can be promoted to a greater or lesser extent. In this case, the fibers used are arranged not only planar in cross-section, but also diagonally, i.e. with a corresponding proportion in the z-direction. A framework is formed by mutually building up fibers. This effect can be seen in particular in the desirably high volume or thickness / grammage ratio. The development of a significant z-component is particularly preferred at higher grammages.

[0071] Furthermore, nonwovens according to the invention have thicknesses of 0.1 to 10 mm, preferably 0.1 to 6 mm. Reproducible measurements of these nonwoven thicknesses are carried out in accordance with DIN EN ISO 9073-2: 1997-02. If required, multiple layers of nonwovens according to the invention can optionally be superimposed and processed into an electrode component.

[0072] Furthermore, single-layer nonwovens according to the invention have grammages of 10 to 300 g / m 2 , preferably from 10 to 200 g / m 2 A reproducible measurement of these nonwoven grammages is carried out in accordance with DIN EN 29073-1: 1992-08.

[0073] It should be noted that the above-mentioned orientations and structures, as well as thicknesses and grammages, can be influenced through suitable fiber preparation. In this context, Fig. 4 shows an example of the relationship between the parameters web thickness and grammage based on two different process and fiber preparation settings (setting 1 and setting 2). The associated table provides a comparison of the corresponding values. The graph below provides specific information about the fact that, depending on the machine setting, with increasing grammage, completely different thicknesses can be achieved in the produced nonwoven fabric. The example shown here is characterized by identical fiber pretreatment and web formation processes. As can be seen from Fig. 4, the achievable thickness increases more sharply with increasing grammage, particularly with setting 1 than with setting 2.The specific fiber preparation, in combination with the machine settings used and the type of drying, is therefore crucial for the resulting nonwoven quality.

[0074] Fig. 5 shows a carbon fiber-based nonwoven fabric according to the invention. The image shown in Fig. 5 was created using micro-computed tomography.

[0075] Fig. 6 shows a distribution (histogram) of projected angles determined via micro-CT as evidence of the fiber orientation in the exemplary carbon fiber-based nonwoven fabric according to the invention shown in Fig. 5. The y-axis marks the number of projections, and the x-axis indicates the respective projected angle in degrees [°]. A corresponding peak in this example lies in a range of approximately 85 to 100 degrees.

[0076] Furthermore, it is optionally possible to further refine the nonwoven fabric according to the invention. Depending on the application forms outlined below, the nonwoven fabrics according to the invention are impregnated with resin systems (phenolic resins, acrylonitrile systems, pitch systems, or other systems) for the production of electrodes, for example, and subjected to further thermal processes. These include, for example, additional steps of carbonization, graphitization, and / or activation.

[0077] The nonwoven fabric according to the invention has a wide range of possible applications. It is suitable, for example, for use as a semi-finished product or as a finished product, for example for use in the production of electrodes. It is also suitable for use as a starting material for electrodes for various battery and power storage systems. The nonwoven fabric according to the invention is preferably used as a semi-finished product for the production of electrodes for, for example, redox flow batteries, as a semi-finished product for the production of electrodes for PEM (proton exchange membrane) water electrolysis, for energy technology and hydrogen-related applications in general, and as a semi-finished product or finished product for the production of electrodes of any type, including in fuel cells or electrochemical process technology. The nonwoven fabric according to the invention can be used in one layer or in several superimposed layers.

[0078] The invention has been described with reference to preferred embodiments, whereby the individual features of the described embodiments can be freely combined and / or interchanged, provided they are compatible. Likewise, individual features of the described embodiments can be omitted unless absolutely necessary. Numerous modifications and embodiments are possible and obvious to those skilled in the art without departing from the spirit of the invention.

Claims

Claims 1 . Nonwoven fabric produced by the wet-laid or paper process, the nonwoven fabric comprising: 70 to 100% carbon fibers with fiber lengths between 0.01 to 12 mm.

2. Nonwoven fabric according to claim 1, wherein the nonwoven fabric comprises carbon fibers with fiber lengths between 0.01 to 12.0 mm, preferably 0.01 to 6 mm, particularly preferably 0.01 to 3 mm.

3. Nonwoven fabric according to claim 1 or 2, wherein the carbon fibers are made from at least one of the following: polyacrylonitrile, pitch, alternative precursors and / or recycled carbon fibers.

4. Nonwoven fabric according to claim 3, wherein the alternative precursors consist of cellulose, lignin and / or phenolic resin; and / or wherein the recycled carbon fibers comprise at least one of the following: Post-industrial waste carbon fibers, prepreg trimmings, and carbon fibers exposed by pyrolysis and / or solvolysis.

5. Nonwoven fabric according to one of the preceding claims, wherein the carbon fibers comprise at least 90% carbon.

6. Nonwoven fabric according to one of the preceding claims, wherein the carbon fibers have an activated surface, graphitized carbon fibers or a mixture thereof.

7. Nonwoven fabric according to one of the preceding claims, further comprising: 0 to 20% binder, preferably 0 to 15% binder; and / or additives comprising ground fibers, carbon-rich particulate fillers and active substances and / or activated carbon powder; wherein the additives have particle sizes of 0.01 to 2 mm, preferably 0.005 to 1 mm.

8. Nonwoven fabric according to claim 7, wherein the binder is present as binding fibers, spray binder, scatter binder and / or mass binder.

9. Nonwoven fabric according to one of the preceding claims, wherein the nonwoven fabric has an electrical volume resistance and / or an electrical surface resistance in each case of 0.01 to 1000 ohm / cm 2 has.

10. Nonwoven fabric according to one of the preceding claims, which has a thickness of 0.1 to 10 mm, preferably 0.1 to 6 mm.

11. Nonwoven fabric according to claim 10, wherein a single layer of the nonwoven fabric has a grammage of 10 to 300 g / m 2 , preferably from 10 to 200 g / m 2 , has.

12. Nonwoven fabric according to one of the preceding claims, wherein the nonwoven fabric comprises carbon fibers with at least two average lengths; wherein there is a distance of at least 0.1 mm, preferably at least 0.2 mm, between a first average length and a second average length; or wherein there is a gapless fiber distribution.

13. Nonwoven fabric according to one of the preceding claims, wherein the nonwoven fabric has a broad fiber distribution A and a narrow fiber distribution B; wherein the fiber distribution B is preferably monodisperse; and / or wherein a histogrammatically scalable fiber length distribution is preferably present.

14. Semi-finished product or finished product made from the nonwoven fabric according to one of the preceding claims for the production of electrodes.

15. Electrode component for redox flow batteries, for PEM water electrolysis or for energy and hydrogen-related applications, comprising: Nonwoven fabric according to one of claims 1 to 13 in one layer or in several superimposed layers.

16. A process for producing a nonwoven fabric according to any one of claims 1 to 15 by means of a wet-laying process, comprising the following steps: Processing carbon fibers by grinding and sieving and / or filtering to produce a mixture of carbon fibers having a fiber distribution of carbon fibers having lengths between 0.01 to 12 mm, preferably 0.01 to 6 mm; Creating a mixture of the processed carbon fibers and a liquid, preferably comprising water; depositing the mixture; and contact-free drying of the deposited mixture.

17. A method for producing a nonwoven fabric according to claim 16, further comprising: Coating and / or impregnating the deposited mixture after web formation before web drying; or Coating and / or impregnation after a pre-drying and / or initial solidification step.

18. A process for producing a nonwoven fabric according to claim 16 or 17 using a paper machine or wet-laid machine.

19. A method for producing a nonwoven fabric according to claim 16 to 18, wherein the step of preparing carbon fibers further comprises: activating the surface of the carbon fibers.

20. A process for producing a nonwoven fabric according to any one of claims 16 to 19, further comprising: Introducing a binder as a binding fiber; and / or Application of the binder as a spray, scatter and / or mass binder.

21. An apparatus for carrying out the method for producing a nonwoven fabric according to any one of claims 16 to 20, comprising: a mill; a screen; and a wet-laying machine.

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