Nonwoven fabric, electrode assembly, method for manufacturing the same, and apparatus for performing the manufacturing method

Abstract

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

Description

Technical Field

[0001] This invention relates to a nonwoven fabric manufactured by wet web forming or papermaking processes. The nonwoven fabric is suitable for producing electrodes, such as gas diffusion layers (GDLs) for fuel cells, water electrolysis, or other energy technology applications, and energy storage devices such as redox flow batteries, but also suitable for other electrical applications. The nonwoven fabric is primarily composed of carbon-rich materials, particularly carbon fibers, that are initially conductive or are made to have appropriate conductivity during subsequent processes. Background Technology

[0002] Hydrogen can be produced sustainably and efficiently via water electrolysis, for example, using a proton exchange membrane (PEM) process. Ideally, the electricity required for this production can be supplied by photovoltaic (PV) or wind power generation. However, this requires an efficient and cost-effective electrolysis system. In a PEM electrolysis process, the anode side is characterized by a porous transport layer (PTL) based on a noble metal, particularly titanium, while the cathode side is typically characterized by a carbon-based PTL. A PEM fuel cell can then be used to convert the produced hydrogen into electricity as needed. In this context, a so-called gas diffusion layer (GDL) consisting of conductive carbon (carbon paper) and a catalyst layer is used on both the anode and cathode sides.

[0003] Today, stationary energy storage devices, such as redox flow batteries (RFBs) (e.g., vanadium RFBs), are indispensable for storing surplus electrical energy (e.g., from PV systems or wind power). Depending on the operating principle, thick or thin carbon-based electrodes based on fiber mesh or felt are used symmetrically.

[0004] As mentioned above, carbon fiber-based felt (known as needle-punched felt) is used in some of these applications. The manufacturing process for carbon fiber needle-punched felt is particularly complex because carbon fiber cannot be directly processed into needle-punched felt. Carbon fiber is brittle and fragile when subjected to mechanical stress in a dry state. The potential consequences of improper handling and processing include fiber damage, processing dust, and slow processing speeds.

[0005] Therefore, such as Figure 1As shown, a processing method is currently being sought in which, instead of laying the carbon fiber itself, it is laid with its precursor material (also known as the precursor) to form needle-punched felt. Polyacrylonitrile (PAN) or PAN fiber, viscose fiber, or virgin fiber are commonly used for this purpose. Even when oxidized into flame-retardant fibers (e.g., according to...) Figure 1 After processing with PANOX fibers, these fibers still retain sufficient textile properties and low fragility, meaning they can be processed into needle-punched felt. Following so-called web laying (including needling or felting), needle-punched felt (e.g., according to...) Figure 1 The PANOX felt is carbonized and graphitized. However, due to the felting process and the resulting fibrous structure and high fiber density, slow processing conditions are required to allow for the controlled removal of foreign atoms, particularly non-carbon atoms. Depending on the thickness of the resulting felt, mass transfer is expected to be significantly limited, which, if left uncontrolled, could lead to exothermic reactions and damage to the material. Furthermore, the required production equipment technology is also a limiting factor, as hot processing must be carried out under a protective gas atmosphere, necessitating a suitable locking system and sealing, which limits the web width.

[0006] Therefore, the manufactured felt and products based on said felt are complex to manufacture and involve high manufacturing costs. The potential for expansion of this technology appears to have been exhausted and is limited. Regarding the properties of these needle-punched felts, the desired high electrical conductivity in the z-direction produced by the needle-punching process is particularly impressive. However, in general, electrical conductivity can increase if the fibers have been subjected to tensile stress during the carbonization process, which is not allowed to occur in the needle-punching felting process.

[0007] Furthermore, this known processing method has hindered the use of recycled carbon fiber (Re-CF), whose importance stems not only from ecological reasons but also from increasing demand. The high demand for fresh carbon fiber from the lightweight construction industry, particularly the wind power and aerospace industries, is driving this need. Therefore, suitable processing methods that also allow the use of recycled carbon fiber are desired in order to save on raw materials and material costs while protecting the environment.

[0008] Purpose of the invention

[0009] The purpose of this invention is to overcome the above-mentioned problems and the shortcomings of the prior art. Summary of the Invention

[0010] The aforementioned tasks and other problems are solved by nonwoven fabrics, semi-finished or finished products made from nonwoven fabrics, by electrode assemblies, by methods for manufacturing nonwoven fabrics, and by apparatus for carrying out the methods according to the independent claims. The dependent claims relate to preferred embodiments of the invention.

[0011] The nonwoven fabric according to the invention is manufactured using a wet-laid or paperprocess, wherein the nonwoven fabric comprises 70% to 100% carbon fiber, preferably ≥70% to ≤100% carbon fiber, particularly preferably ≥75% to ≤80% carbon fiber, wherein the fiber length is between 0.01 mm and 12 mm. This disproportionately high proportion of carbon fiber results in a significantly higher electrical conductivity in the nonwoven fabric compared to known materials, particularly compared to materials containing significantly less than 70% carbon fiber. The nonwoven fabric also preferably comprises carbon fibers with a fiber length between 0.01 mm and 12.0 mm, preferably 0.01 mm to 6 mm, and particularly preferably 0.01 mm to 3 mm. The carbon fibers are optionally made from at least one of: polyacrylonitrile, pitch, alternative precursors, and / or recycled carbon fibers. Even more preferably, a nonwoven fabric is provided, wherein the alternative precursor consists of cellulose, lignin, and / or phenolic resin; and / or wherein the recycled carbon fibers comprise at least one of: post-industrial waste carbon fiber, prepreg scrap, and carbon fibers exposed through pyrolysis and / or solvent decomposition. The nonwoven fabric according to the invention is a single-layer nonwoven fabric.

[0012] The nonwoven fabric also preferably comprises carbon containing at least 90% carbon. Optionally, the carbon fibers of the nonwoven fabric include activated surfaces, graphitized carbon fibers, or mixtures thereof.

[0013] In addition, the nonwoven fabric may optionally contain the following components: 0% to 20% binder, preferably 0% to 15% binder; and / or additives including milled fibers, carbon-rich microparticle fillers, and activators and / or activated carbon powder; wherein the additives have a particle size of 0.01 mm to 2 mm, preferably 0.005 mm to 1 mm. The binder is preferably present in the form of bonding fibers, spray binder, scatter binder, and / or mass binder.

[0014] In addition, a nonwoven fabric is provided, wherein in each case the nonwoven fabric preferably comprises an electrical volume resistance of 0.01 ohms / cm² to 1000 ohms / cm² and / or an electrical surface resistance.

[0015] Furthermore, the nonwoven fabric optionally has a thickness of 0.1 mm to 10 mm, preferably 0.1 mm to 6 mm. Optionally, the single-layer nonwoven fabric has a thickness of 10 g / m². 2 Up to 300 g / m 2 Preferably 10 g / m 2 Up to 200 g / m 2 The weight in grams.

[0016] Nonwoven fabrics may also contain carbon fibers of at least two average lengths, wherein there is a distance of at least 0.1 mm, preferably at least 0.2 mm, between the first average length and the second average length, or wherein there is a continuous fiber distribution.

[0017] The nonwoven fabric also preferably includes a wide 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.

[0018] The present invention also provides semi-finished or finished products made of nonwoven fabric according to the invention for manufacturing electrodes.

[0019] The present invention also provides an electrode assembly for redox flow batteries, for PEM water electrolysis, or for energy technology and hydrogen-related applications, said electrode assembly being made of a nonwoven fabric according to the present invention in the form of a single layer or in the form of several layers superimposed on each other.

[0020] Furthermore, the present invention provides a method for manufacturing nonwoven fabrics by a wet web-forming process, the method comprising the steps of: preparing carbon fibers by grinding and screening and / or filtering to produce a mixture of carbon fibers, the mixture comprising a fiber distribution of carbon fibers with lengths between 0.01 mm and 12 mm, preferably between 0.01 mm and 6 mm; generating a mixture of the prepared carbon fibers and a liquid, preferably water; depositing the mixture in a stacked manner; and non-contact drying of the deposited mixture. The method for manufacturing nonwoven fabrics according to the present invention preferably provides for manufacturing nonwoven fabrics by depositing the mixture into a single layer or sheet.

[0021] The method for manufacturing nonwoven fabrics preferably further includes the steps of: coating and / or impregnating the deposited mixture after the formation of the nonwoven fabric and before drying the nonwoven fabric; or coating and / or impregnating after the pre-drying and / or initial consolidation steps.

[0022] Optionally, the method for manufacturing nonwoven fabrics is carried out using a paper machine or a wet web forming machine.

[0023] Optionally, the steps for preparing carbon fibers may further include: activating the surface of the carbon fibers.

[0024] The method for manufacturing nonwoven fabrics further preferably includes: introducing an adhesive as a bonding fiber; and / or applying an adhesive as a spray adhesive, a dispersion adhesive, and / or a block adhesive.

[0025] The present invention also provides an apparatus for carrying out the method for manufacturing nonwoven fabrics according to the present invention, the apparatus comprising: a grinding mill; a screen; and a wet web forming machine. Attached Figure Description

[0026] The present invention, and its further details and advantages, are explained below with reference to the accompanying drawings using preferred embodiments. The drawings show:

[0027] Figure 1 The technological steps in the production of needle-punched felt (current technical level);

[0028] Figure 2 According to the present invention, the process chain up to the electrode assembly includes a wet web process;

[0029] Figure 3 Histogram of fiber length distribution after fiber preparation;

[0030] Figure 4 The relationship between web thickness and basis weight based on two different process settings and fiber preparation settings;

[0031] Figure 5 Nonwoven fabrics based on carbon fibers according to the present invention; and

[0032] Figure 6 according to Figure 5 The distribution of projection angles in the carbon fiber-based nonwoven fabric according to the present invention. Detailed Implementation

[0033] In this description, the terms "above," "below," "right," and "left," and similar terms refer to the orientation or arrangement shown in the figures and are used only to describe embodiments. These terms may indicate preferred arrangements but should not be construed as limiting.

[0034] In addition, the terms “essentially,” “approximately,” “about,” and similar terms mean that a deviation of + / -10%, preferably + / -5%, relative to the stated value is permissible.

[0035] Unless explicitly excluded, the numerical ranges mentioned herein should always be understood to mean that within the specified numerical range, the lower limit is included by "≥" (greater than or equal to) and the upper limit is included by "≤" (less than or equal to). Therefore, the limit itself is either included in the corresponding range, or, alternatively, the limit itself may be excluded (on one side).

[0036] The following abbreviations are also used in this article: “wet-laid” refers to wet fiber web technology similar to paper or papermaking technology; “Re-CF” refers to recycled carbon fiber; “ACF” refers to activated carbon fiber; and “PAN” refers to polyacrylonitrile.

[0037] This invention relates to a carbon fiber-based nonwoven fabric manufactured by wet web forming or a papermaking process. The papermaking process typically refers to short fibers, and if necessary, to self-bonding fibers with a fiber length ranging from 2 mm to 3 mm. The wet web forming process can also use an open air drying section to process longer fibers exceeding 3 mm.

[0038] The term "nonwoven fabric" is understood below to refer to any form of material consisting of fibers (short fibers or staple fibers) of finite length and of any kind and origin, either continuous fibers or cut yarns, which have been assembled in a certain way to form a nonwoven fabric (fiber layers, fiber piles) and have been bound together in a certain way. This does not include the crossing and / or winding of yarns, as seen in weaving, knitting, lace making, and braiding. The definition here includes the term "paper"; the two materials and their manufacture are related, but the main difference lies in the fiber length and fiber material.

[0039] The nonwoven fabrics according to the invention are fundamentally suitable as substrates for electrodes in energy storage devices and electrolyzers, such as for gas diffusion layers (GDLs) in fuel cells, water electrolysis or other energy technology applications, and electrical energy storage devices such as redox flow batteries, and are also suitable for other electrical applications. The nonwoven fabrics according to the invention, as semi-finished or finished products, are primarily composed of carbon-rich materials, particularly carbon fibers, which are conductive or are made appropriately conductive in subsequent processes.

[0040] Instead of known needle-punched felt, this invention uses a special type of nonwoven fabric derived from a so-called wet web forming process. This enables the use of highly scalable and cost-effective paper or wet web forming techniques (also known as wet web forming technology) with potential processing speeds of several hundred meters. This reduces the cost of manufacturing electrodes and lowers the overall cost of the aforementioned energy conversion and storage system.

[0041] Furthermore, this invention enables the use of commercially available pre-carbonized and / or graphitized fibers. It also opens up unique possibilities for the use of recycled carbon fiber. The rapidly growing recycled market is benefiting from the increasing use of carbon fiber and the structural and medium-term capacity bottleneck of fresh fiber. This particular combination of factors results in a cost-effective, highly scalable product that is technologically superior in certain applications.

[0042] Carbon and graphite fibers or particles are laid and bonded into nonwoven fabrics using wet web forming techniques or papermaking processes. Specialized fiber preparation through milling processes and process conditions tailored for electrode applications, for example, enable the production of precisely defined, highly porous, open-cell, homogeneous nonwoven fabrics. By mixing and grading different types of fibers and geometries (which may be achieved through prior fiber preparation, etc.), it is also possible to create profiles and specific fiber orientations within the nonwoven fabric that have advantageous functions in finished products such as electrodes. In particular, the controlled orientation of the fibers in the z-direction can be both desirable and advantageous in this case.

[0043] Therefore, the present invention enables the manufacture of nonwoven fabrics with the same material composition and an optimized thickness-to-weight ratio, such as high thickness (e.g., 5 mm) and low weight (e.g., 100 g / m²). 2 Nonwoven fabrics according to the invention, and vice versa. For drying and / or fixing of nonwoven fabrics manufactured according to the invention, depending on the application, non-contact drying is preferred in order to maintain the previously generated volume and the previously generated pore size and / or shape.

[0044] Figure 2 A process chain according to the invention for manufacturing a nonwoven fabric according to the invention is shown, the process chain optionally extending to a graphite electrode including a wet nonwoven process. Both virgin and regenerated fibers can be used as starting materials. Any of the aforementioned carbon-based or graphite-based fibers and particulate materials can be used.

[0045] First, these fibers are processed mechanically, physically, or chemically to obtain a favorable nonwoven fabric structure and properties. The carbon fibers are processed by grinding and screening and / or filtering to produce a mixture of carbon fibers comprising a fiber distribution of carbon fibers with lengths between 0.01 mm and 12 mm, preferably 0.01 mm to 6 mm. Optionally, the surface of the carbon fibers may also be activated during carbon fiber processing. In conjunction with the invention, the grinding process has proven particularly advantageous. This step is used to obtain specific polydisperse fiber lengths. Although the fiber types used herein have potentially fragile breakage behavior, this process can be used to produce uniform particles containing specified fiber lengths. Uniform fiber lengths can be achieved by using properly adjusted grinding tools, even if the initial length of the undrinded fibers is unknown and / or irregular. This is especially true for regenerated fibers.

[0046] In the next step, a mixture of processed carbon fibers and a liquid (preferably water) is produced. If necessary, the processed fibers are mixed with additives for forming a web or with other fibers or particulate materials (e.g., adhesives), resulting in a homogeneous, stable dispersion. One or more adhesives may optionally be introduced as bonding fibers and / or applied as a spray adhesive, dispersion adhesive, and / or block adhesive.

[0047] To manufacture the nonwoven fabric according to the present invention, i.e., as Figure 2The carbon nonwoven fabric shown requires further steps, namely, layering the mixture and non-contact drying of the layered mixture. Non-contact drying in this context is understood as a drying process in which the nonwoven fabric according to the invention is formed as a non-compressible layer, thereby applying no pressure from above or below to the deposited mixture. This minimizes the risk of the deposited mixture adhering to the corresponding deposit or support (e.g., a so-called web). Therefore, in non-contact drying, instead of actively drying the deposition surface, a surface is used to support the deposited mixture only during drying. Preferably, non-contact drying is carried out with unilateral support and / or using straight and / or flat support surfaces or guiding devices. Depending on the selected drying parameters, the mixture deposited in this manner can then be guided through the drying process in the direction of production. Particularly preferred is that up to 10% of the deposited mixture is in contact with the corresponding support. Alternatively, or additionally, the mixture is deposited horizontally or almost horizontally on the corresponding support. Optionally, the drying process of the mixture deposited in this manner can be further improved by blowing air (using hot air if necessary) through the mixture. However, in this context, a correspondingly breathable mesh will be required.

[0048] exist Figure 2 In this example, a wet web-forming process utilizing optional impregnation is used, where the processing speed exceeds 100 m / min. For instance, a specially prepared fibrous material is fed into a wet web-forming or papermaking machine in a manner that prevents separation but introduces a high proportion of turbulence. A fiber web is formed by dewatering the fiber dispersion on a continuous screen. Depending on the fiber mixture and machine settings, a deposition and / or construction structure with an increased proportion of z-oriented fibers is formed. The wet fiber web is fed into a continuous dryer at the lowest possible pressure, where water is removed and potential binders are activated. Depending on the basis weight and structure, the nonwoven fabric is removed as a sheet or rolled up.

[0049] The deposited mixture may optionally be coated and / or impregnated before the nonwoven fabric is dried, or the coating and / or impregnation may be carried out after the additional steps of pre-drying and / or initial consolidation.

[0050] In order to progress to such Figure 2 The carbon electrode shown, and the optional carbonization of the manufactured nonwoven fabric, are carried out at a maximum processing speed of 20 m / min. To optionally obtain... Figure 2 The graphite electrode shown is used as an alternative to optionally graphitize the manufactured nonwoven fabric at the same maximum processing speed of 20 m / min.

[0051] Apparatus suitable for manufacturing nonwoven fabrics according to the invention includes a grinding mill, a screen, and a wet web forming machine, each of which may be replaced by a component or assembly that meets the above requirements in the manufacturing process.

[0052] The nonwoven fabric according to the invention is manufactured using a wet web forming or papermaking process or an equivalent process, and contains 70% to 100% carbon fiber, preferably ≥70% to ≤100% carbon fiber, particularly preferably ≥75% to ≤80% carbon fiber, wherein the carbon fiber comprises fiber lengths between 0.01 mm and 12 mm.

[0053] Furthermore, the nonwoven fabrics according to the invention preferably include the various properties described herein below, which may be present in any combination:

[0054] Various carbon fibers or fiber types can be used in the nonwoven fabrics according to the invention. These fiber types include, for example, commercially available fiber types such as high-tenacity (HT) fibers, intermediate-modulus (IM) fibers, and / or high-modulus (HM) fibers. These fiber types are based, for example, on polyacrylonitrile, but also on pitch (internationally known as bitumen), or on variants of alternative precursors such as cellulose (lyocell, viscose, rayon) and lignin or phenolic resins (also known by the trademark Kynol). This also includes recycled carbon fibers, which have particular potential as a cost-effective alternative to virgin fibers. Examples include fibers from so-called post-industrial waste and / or prepreg waste, as well as fibers released through pyrolysis and / or solvent decomposition.

[0055] In addition to the basic fiber types mentioned above, it is advantageous to use carbon-rich fibers, preferably fibers with a carbon content of at least 90% (and, if necessary, activated surfaces). This can be achieved through additional treatment or by directly purchasing activated carbon fiber (ACF). Depending on the application, the use of graphitized carbon fiber may also be preferable. Some applications particularly benefit from mixtures of the fiber types mentioned above.

[0056] In this context, it should be noted that additional adhesives (also referred to herein as binders) are also considered "fibers" within the meaning of this invention, provided that the additional adhesives are added to or will be added to the nonwoven fabric according to the invention in the form of fibers.

[0057] Carbon fibers with different geometries, fiber lengths, and / or fiber length distributions can be used in the nonwoven fabrics according to the invention. There is a difference between the specific fiber properties prior to fiber or fiber raw material preparation and the fiber properties in the nonwoven fabric obtained due to fiber pretreatment or milling processes. Prior to fiber processing, the fibers intended for use according to the invention comprise lengths of 0.1 mm to 25 mm, preferably 0.2 mm to 20 mm. After fiber processing, i.e., in the finished nonwoven fabric, the fibers used comprise lengths of 0.01 mm to 12 mm, preferably 0.01 mm to 6 mm, most preferably 0.01 mm to 3 mm, and a wider fiber length distribution towards shorter fibers than before fiber processing.

[0058] The nonwoven fabric according to the invention optionally contains carbon fibers having at least two average lengths. Figure 3 Examples of nonwoven fabrics in this context are shown. The first average length and the second average length differ from each other by at least 0.1 mm, preferably at least 0.2 mm. Alternatively, a continuous fiber distribution may be present.

[0059] Figure 3 An exemplary fiber dispersion within a nonwoven fabric according to the invention is shown, characterized by a specific fiber length distribution (histogram) after fiber preparation. The nonwoven fabric according to the invention has a peak percentage at fiber lengths of about 1.0 mm to about 3.0 mm. As shown in the histogram, the proportion of longer fibers thereafter decreases rapidly and steadily. The longer fibers are particularly useful for enhancing strength and reducing electrical conductivity in the plane, while the shorter fibers cause constructive fiber deposition and increased alignment in the z-direction.

[0060] Depending on the application, nonwoven fabrics may simultaneously have several fiber distributions, such as a wide fiber distribution A and a narrow fiber distribution B. In this case, fiber distribution B is preferably monodisperse; and / or preferably has a fiber length distribution that can be expanded in a histogram manner.

[0061] Furthermore, various fiber types may be present, or a mixture of fibers and granules may exist depending on the application and a specific mixing ratio. In particular, so-called additive technology is a selective means of adjusting, for example, the structure, electrical conductivity, and / or porosity of the material to be processed and the final product in the form of a finished nonwoven material.

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

[0063] Furthermore, the bonding of the nonwoven fabric according to the invention, or the bonding with the nonwoven fabric according to the invention (hereinafter also referred to as nonwoven bonding), can be achieved by various methods, which are ultimately reflected in the product properties of the finished nonwoven fabric. The adhesive used herein is preferably present in the finished nonwoven fabric at a weight ratio of 0% to 20%, preferably 0% to 15%.

[0064] The adhesive can be introduced as a bonding fiber softened during drying, or as a spray adhesive applied to undried, partially dried, or fully dried nonwoven fabric webs. Alternatively, the adhesive can be applied in the same manner as a dispersion adhesive and / or introduced into the fibrous material as a bulk adhesive by properly dissolving or dispersing one or more suitable adhesives in the starting material. Alternatively, the adhesive can be applied or coated using immersion and / or coating processes.

[0065] Thermoplastic adhesives and reactive adhesives (such as adhesives from the group consisting of polyvinyl alcohol (PVA) or acrylic polymer systems) as well as systems with high carbon residues (such as phenolic resins or polyacrylonitrile) are all suitable as adhesives.

[0066] Furthermore, for potential application-specific product performance, it may be advantageous to use an adhesive with sufficiently low resistivity (e.g., <1000 ohms / cm²) before or after the main thermal finishing process.

[0067] The nonwoven fabric according to the invention preferably has a volume resistivity of about 0.01 ohms / cm² to 1000 ohms / cm² and / or a surface resistivity of about 0.01 ohms / cm² to 1000 ohms / cm². Both values ​​depend on the density of the nonwoven fabric and the applied measurement pressure. It is particularly suitable for measurement methods implemented using the high-resistance measuring electrode TE 50 according to German Standards Institut fur Normung (DIN) 54345-1, DIN European Standard (EN) (DIN EN) 1149-1, and DIN EN 1149-2.

[0068] Regarding the parameters of porosity, volume, weight per unit area, and thickness ratio of the nonwoven fabric, it should be noted that, depending on the application, the nonwoven fabric according to the invention has the following properties in terms of the distribution and arrangement of the fibers used:

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

[0070] Furthermore, depending on the machine settings and fabric preparation, the fiber deposition during the manufacture of the nonwoven fabric according to the invention is isotropic (uniformly distributed) or anisotropic. Optionally, a targeted z-orientation of the fiber mixture used may also be present. The preferred isotropic arrangement relative to the xy plane is explained in more detail below.

[0071] Depending on the fiber preparation and machine settings, so-called constructive fiber deposition can be promoted to a greater or lesser extent. Here, the fibers used are arranged not only planarly in cross-section but also diagonally, i.e., with a corresponding proportion in the z-direction. This generates a framework composed of mutually reinforcing fibers. This effect is particularly pronounced at desired high volumetric or thickness / basis weight ratios. At higher basis weights, significant development of the z-component is especially preferred.

[0072] Furthermore, the nonwoven fabric according to the invention has a thickness of 0.1 mm to 10 mm, preferably 0.1 mm to 6 mm. Reproducible measurements of these nonwoven fabric thicknesses are performed according to DIN EN ISO 9073-2:1997-02. If necessary, several layers of nonwoven fabric according to the invention can optionally be stacked on top of each other and processed into electrode assemblies.

[0073] Furthermore, at the aforementioned thickness, the single-layer nonwoven fabric according to the present invention has a density of 10 g / m². 2 Up to 300 g / m 2 Preferably 10 g / m 2 Up to 200 g / m 2The weight per unit area (gb) of these nonwoven fabrics was measured reproducibly according to DIN EN 29073-1: 1992-08.

[0074] It should be noted that the aforementioned orientation and structure, as well as thickness and basis weight, can be affected by appropriate fiber preparation. In this context, Figure 4 Examples are shown illustrating the relationship between parameters for nonwoven fabric thickness and basis weight based on two different processes and fiber preparation settings (Setting 1 and Setting 2). A table is provided for comparison of the corresponding values. The figure below provides specific information showing that, depending on the machine settings, entirely different thicknesses can be achieved in the manufactured nonwoven fabric as the basis weight increases. The examples shown here are characterized by the same fiber pretreatment and nonwoven fabric formation process. (See figure below for details.) Figure 4 As can be seen, in setting 1, the achievable thickness increases more significantly with increasing basis weight compared to setting 2. Therefore, the specific fiber preparation combined with the machine settings and drying type is crucial to the quality of the resulting nonwoven fabric.

[0075] Figure 5 A carbon fiber-based nonwoven fabric according to the present invention is shown. Figure 5 The images shown were generated using micro-computed tomography (micro-CT).

[0076] Figure 6 The distribution of projection angles (histogram) is shown, which was determined by microcomputer tomography as a basis for... Figure 5 Evidence of fiber orientation in an exemplary nonwoven fabric according to the invention, showing the carbon fibers. The y-axis marks the number of projections, and the x-axis represents the corresponding projection angle in degrees [°]. In this example, the corresponding peak is in the range of approximately 85 to 100 degrees.

[0077] Furthermore, optionally, the nonwoven fabric according to the invention can be further refined. According to the applications described below, the nonwoven fabric according to the invention is impregnated, for example, with a resin system (phenolic resin, acrylonitrile system, pitch system, or other system) for the manufacture of electrodes, and subjected to further thermal processing. These thermal processing steps include, for example, additional steps of carbonization, graphitization, and / or activation.

[0078] The nonwoven fabric according to the invention has a wide range of applications. For example, the nonwoven fabric is suitable as a semi-finished product or as a finished product, such as for manufacturing electrodes. The nonwoven fabric is also suitable as a starting material for electrodes used in various batteries and energy storage systems. The nonwoven fabric according to the invention is preferably used as a semi-finished product for manufacturing electrodes for example, redox flow batteries, as a semi-finished product for manufacturing electrodes for proton exchange membrane (PEM) water electrolysis, for general energy technologies and hydrogen-related applications, and as a semi-finished or finished product for manufacturing any kind of electrode, including in fuel cells or electrochemical process technologies. The nonwoven fabric according to the invention can be used in single-layer form or in several layers stacked on top of each other.

[0079] The invention has been described based on preferred embodiments, wherein the individual features of the described embodiments can be freely combined and / or interchanged with each other, provided that the features are compatible. Similarly, if an individual feature of the described embodiments is not absolutely necessary, it may be omitted. Many modifications and designs will be possible and apparent to those skilled in the art without departing from the concept of the invention.

Claims

1. A nonwoven fabric manufactured by wet web forming or papermaking processes, wherein the nonwoven fabric comprises: 70% to 100% carbon fiber, including fiber lengths between 0.01 mm and 12 mm.

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

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

4. The nonwoven fabric according to claim 3, wherein the alternative precursor is composed of cellulose, lignin, and / or phenolic resin; and / or The recycled carbon fiber mentioned above includes at least one of the following: Post-industrial waste carbon fiber, prepreg waste, and carbon fiber released through pyrolysis and / or solvent decomposition.

5. The nonwoven fabric according to any one of the preceding claims, wherein the carbon fiber contains at least 90% carbon.

6. The nonwoven fabric according to any one of the preceding claims, wherein the carbon fiber comprises an activated surface, graphitized carbon fiber, or a mixture thereof.

7. The nonwoven fabric according to any one of the preceding claims further comprises: 0% to 20% adhesive, preferably 0% to 15% adhesive; and / or Including milled fibers, carbon-rich microparticle fillers, and additives such as activators and / or activated carbon powder; The additive has a particle size of 0.01 mm to 2 mm, preferably 0.005 mm to 1 mm.

8. The nonwoven fabric of claim 7, wherein the adhesive is present in the form of bonding fibers, spray adhesive, dispersion adhesive and / or block adhesive.

9. The nonwoven fabric according to any one of the preceding claims, wherein the nonwoven fabric has an electrical volume resistivity of 0.01 ohms / cm² and / or an electrical surface resistivity of 1000 ohms / cm² in each case.

10. The nonwoven fabric according to any one of the preceding claims, comprising a thickness of 0.1 mm to 10 mm, preferably 0.1 mm to 6 mm.

11. The nonwoven fabric of claim 10, wherein a single layer of the nonwoven fabric comprises 10 g / m². 2 Up to 300g / m 2 Preferably 10 g / m 2 Up to 200 g / m 2 The weight in grams.

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

13. The nonwoven fabric according to any one of the preceding claims, The nonwoven fabric includes a wide fiber distribution A and a narrow fiber distribution B; The fiber distribution B is preferably monodisperse; and / or Preferably, there exists a fiber length distribution that can be expanded in a histogram manner.

14. A semi-finished or finished product, each made of a nonwoven fabric as described in any of the preceding claims, for use in manufacturing electrodes.

15. An electrode assembly for use in redox flow batteries, proton exchange membrane water electrolysis, or energy technologies and hydrogen-related applications, comprising the following: The nonwoven fabric as described in any one of claims 1 to 13, wherein the nonwoven fabric is in the form of a single layer or in the form of several layers superimposed on each other.

16. A method for manufacturing a nonwoven fabric as described in any one of claims 1 to 15 by a wet web-forming process, comprising the following steps: Carbon fibers are prepared by grinding and screening and / or filtering to produce a mixture of carbon fibers, the mixture comprising a fiber distribution of carbon fibers with lengths between 0.01 mm and 12 mm, preferably between 0.01 mm and 6 mm. A mixture of the prepared carbon fiber and a liquid, preferably water, is generated; The mixture is deposited in a stacked manner; as well as The deposited mixture is then dried without contact.

17. The method for manufacturing a nonwoven fabric according to claim 16, further comprising: After the nonwoven fabric is formed and before the nonwoven fabric is dried, the deposited mixture is coated and / or impregnated. or Coating and / or impregnation are performed after the pre-drying and / or initial consolidation steps.

18. The method for manufacturing nonwoven fabrics according to claim 16 or 17, using a paper machine or a wet web forming machine.

19. The method for manufacturing nonwoven fabrics according to claims 16 to 18, wherein the step of preparing carbon fibers further comprises: The surface of the carbon fiber is activated.

20. The method for manufacturing a nonwoven fabric according to any one of claims 16 to 19, further comprising: Introducing adhesives as bonding fibers; and / or The adhesive is applied as a spray adhesive, dispersion adhesive, and / or block adhesive.

21. An apparatus for carrying out the method for manufacturing a nonwoven fabric as claimed in any one of claims 16 to 20, comprising: Grinding machine; sieve; as well as Wet web forming machine.

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