Complex Network Structure

Abstract

The present invention relates to a composite network structure comprising at least a first layer and a second layer, wherein the first layer comprises a porous metal structure that is electrically conductive, and the second layer is an electrically conductive layer onto which the first layer is fixed, and the first and second layers are mechanically and electrically conductively connected to each other.

Description

[Technical Field]

[0001] The present invention relates to a composite network structure having at least two layers, a method for producing the network structure, and a method for preparing an electrode using the network structure. [Background technology]

[0002] Three-dimensional (3D) structures, such as metal fiber networks and metal foams, have advantageous properties in several technical fields, such as filters and electrodes, particularly battery electrodes. In particular, ultrafine fibers, such as microfibers, having thicknesses and / or widths in the 50 μm and below range, offer very large surface-to-volume ratios and corresponding surface areas, which have been found to be advantageous for electrode applications. Furthermore, when such thin fibers have a noncircular cross-section, e.g., a ribbon-like cross-section, the surface area is even greater. Furthermore, in filter applications, such networks using fibers with noncircular cross-sections, e.g., ribbon-like cross-sections, have been found to have better filtration properties, likely due to the turbulence caused by the shape of the fibers with such noncircular cross-sections.

[0003] To produce such a network, metal fibers can be laid into a conductive, high-strength nonwoven fabric using various processes (dry and wet) known to those skilled in the art. Such nonwoven fabrics can be bonded using processes such as sintering at temperatures close to or above the melting point. The production of such metal fiber networks is known to those skilled in the art, for example, from International Publication No. WO 2020 / 016240 A1, the entire contents of which are incorporated herein by reference. Metal fibers can be produced by melt spinning, as described, for example, in International Publication No. WO 2016 / 020493 A1 and International Publication No. WO 2020 / 229400 A1, the entire contents of which are incorporated herein by reference.

[0004] However, the stability of 3D networks of metal fibers with such noncircular cross sections against compression, such as during preparation or filling of the network with electrode active material, may not be sufficient to prevent shrinkage of the network thickness (z-axis). In particular, such nonwoven networks, when made from relatively short and thin fibers, cannot be handled without very careful precautions to prevent them from falling apart or shrinking in the web thickness (z-axis) during sintering or coating with electrode active material. This hampers the roll-to-roll process for fabricating 3D networks of metal fine fibers.

[0005] Furthermore, even after completing the 3D network by sintering the nonwoven metal fibers together, the resulting network may have problems with mechanical stability. Especially for microfiber networks with thicknesses and / or widths in the 50 μm and below range, even after sintering the metal fibers together, the stability is not sufficient for large-scale production processes, such as roll-to-roll processes, to fill the metal fiber network with electrode active materials. Similar difficulties are observed with other porous structures, such as metal foams.

[0006] The 3D network of metal fibers with conductive interconnects used as electron current collectors in lithium-ion batteries allows for very thick electrodes with high active material loading. Such thick electrodes can reach capacities of 100 mAh / cm. 2 Such electrodes constructed with a 3D metal fiber network not only allow for high current flow in three dimensions toward the power socket, but also allow for high current flow in terms of ion mobility within the electrode itself (as described in unpublished patent application PCT / EP2021 / 062443, filed May 11, 2021, the entire contents of which are incorporated herein by reference). This is of particular interest when the electrode is a battery electrode and the battery is subjected to rapid charge or discharge cycles.

[0007] Especially when using ultra-fine fibers, each fiber can only handle a certain current due to its small conductor cross-section. If the current is too high, individual fibers may be destroyed. Repeated use can cause more and more damage to the metal fiber network, which can gradually reduce its functionality. Furthermore, when used in batteries, high current loads can cause high temperatures in individual fibers. This can lead to degradation of the active material and / or electrolyte. Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, existing network structures have a limited lifespan when repeatedly exposed to electric current, such as in battery electrodes, and when manufacturing such metal fiber networks or filling such metal fiber networks with electrode active materials, there is a problem in that the metal fiber networks are brittle and difficult to process using a roll-to-roll process or the like. [Means for solving the problem]

[0009] This problem is solved by the present application by providing a composite network structure as set forth in claim 1. In particular, the composite network structure of the present invention comprises at least a first layer and a second layer, the first layer comprising a porous metal structure that is electrically conductive, the second layer being an electrically conductive layer onto which the first layer is fixed, and the first layer and the second layer being mechanically and electrically conductively connected to each other.

[0010] The second layer has the dual purpose of providing mechanical and electrical support for the 3D network of the first layer. Mechanical support is achieved through the mechanical connection between the porous material of the first layer and the second layer. This avoids mechanical stress on individual parts, such as foam struts or fibers. Instead, the second layer acts as a carrier for the porous structure, absorbing mechanical stresses, thereby preventing damage to individual foam struts or metal fibers during handling of the porous structure, such as during the manufacture of electrodes containing such a network. Thanks to the electrical connection between the first and second layers, current conducted along the thickness of the network, i.e., the porous structure, only needs to traverse the z-plane through the metal network, while the second layer acts as a surface current collector in the x-y plane, i.e., the first and second layers are in surface contact with each other. This reduces the electrical stress on individual parts of the porous structure, such as foam struts or fibers. Thus, the present invention provides a composite network structure with improved mechanical strength and electrical stability, since the second layer is in surface contact with the first layer and provides mechanical and electrical stabilization.

[0011] Furthermore, the improved mechanical stability makes it easier to further process the network structure, such as for the purpose of incorporating electrically active materials into the porous structure. The mechanical strength is high enough to allow roll-to-roll processing.

[0012] The present invention provides a method for producing a network structure, comprising the steps of: Step A: Providing a first layer of a porous metal structure that is electrically conductive; Step B: providing a second layer that is electrically conductive; Step C: placing the first layer on the second layer; Step D: Fixing the layer of porous metal structure on the second layer by sintering; The present invention further relates to a method comprising:

[0013] This produces a network structure in which the first layer is in surface contact with the second layer. The first and second layers are electrically and mechanically bonded to each other through sintering. Therefore, when a network structure is produced according to the present invention, the above-described stabilization with respect to mechanical and electrical loads can be achieved. This allows for large-scale production, such as in the form of a roll-to-roll process.

[0014] The present invention provides a method for manufacturing an electrode, comprising the steps of: Step E: Providing a network structure according to the present invention; Step F: Filling the network structure provided in step E with an electrode active material; The present invention further relates to a method comprising:

[0015] The mechanical stabilization achieved by the surface-to-surface contact of the first and second layers allows for easier filling of the network structure, particularly the porous metal structure of the first layer, without compressing the porous structure through its thickness, i.e., in the z-axis direction, for example, through the second layer if the second layer is porous. Furthermore, the mechanical stabilization by the second layer provides the possibility of realizing large-scale production, such as in the form of a roll-to-roll process.

[0016] Furthermore, the present invention relates to a battery comprising at least one electrode having a network structure according to the present invention.

[0017] The combination of mechanical and electrical stabilization reduces the mechanical and current loads on the individual fibers, which can extend the life of the battery, especially when subjected to rapid charge and discharge cycles.

[0018] In the following, preferred embodiments of the present invention are described.

[0019] In the network structure of the present invention, the porous structure may be a metal foam structure with open pores, or a network of metal fibers with open pores between the metal fibers. In the case of an open-porous foam, the network is formed by the struts of the foam. In the case of metal fibers, the fibers are the connections of the network. In particular, the porous structure is composed of a plurality of metal fibers fixed to each other, particularly a plurality of metal fibers sintered or soldered to each other, and preferably has a width and / or thickness of 80 μm or less. The plurality of metal fibers forms a three-dimensional network of metal fibers fixed to each other, particularly sintered to each other.

[0020] According to the present invention, the first layer preferably includes a plurality of metal fibers having a thickness of 50 μm or less, more preferably 30 μm or less, even more preferably 10 μm or less, and most preferably 5.0 μm or less. Such thin fibers provide a large surface area, resulting in advantageous electrochemical properties and suppressing lithium dendrite growth when the network structure is used as an electrode in a lithium-ion battery. In the network structure of the present invention, the lower limit of the thickness of the metal fibers in the first layer is not particularly limited. In a preferred embodiment of the present invention, the lower limit of the thickness may be 1.0 μm or more. Thinner fibers may be difficult to produce by melt spinning or the like and may be difficult to handle.

[0021] In the network structure of the present invention, the metal fibers in the first layer preferably have a width of 80 μm or less, more preferably 70 μm or less, even more preferably 40 μm or less, and most preferably 5.0 μm or less. Such thin fibers provide a large surface area, resulting in advantageous electrochemical properties and suppressing the growth of lithium dendrites when the network structure is used as an electrode in a lithium-ion battery. In the network structure of the present invention, the lower limit of the thickness of the metal fibers in the first layer is not particularly limited. In a preferred embodiment of the present invention, the lower limit of the thickness may be 1.0 μm or more. Thinner fibers may be difficult to produce by melt spinning or the like and may be difficult to handle.

[0022] The first and second types of metal fibers preferably have lengths of 2.0 mm or greater, more preferably 10 mm or greater, even more preferably 20 mm or greater, and even more preferably 70 mm or greater. Metal fiber lengths that meet the above length specifications improve the mechanical stability of the 3D metal fiber network because, as the metal fiber length increases, each metal fiber can have several contact points with other metal fibers in the network, where each metal fiber is anchored to each of the other metal fibers to form electrically conductive connections with high mechanical strength. Therefore, if one connection between metal fibers is severed, several other connections between fibers are available to hold the network together and provide the desired electrical conductivity, preventing the overall structural integrity of the network from being compromised or the metal fibers from separating from the network. Preferably, the fiber length should be in the range of 1.0 to 20 cm, more preferably 3.0 to 15 cm, and even more preferably 4.0 to 10.0 cm, since this allows for easier fiber placement by carding.

[0023] The cross section of the metal fiber is not particularly limited. In a preferred embodiment, the plurality of metal fibers includes metal fibers having a non-circular cross section, particularly a ribbon-like cross section. Such a non-circular cross section provides a large surface area, which may be advantageous in filtration applications because the non-circular cross section induces turbulence in the fluid flowing through the filter. When used in battery electrodes, fibers having a non-circular cross section increase the surface area of ​​the electrode material, thereby improving the electrochemical properties of the electrode and improving the suppression of lithium dendrite growth in lithium-ion batteries, for example.

[0024] It is particularly preferred that metal fibers be sintered to other metal fibers, most preferably directly sintered to other metal fibers without the need for an additional binder, such as a polymer binder. Most preferably, the fixation of one metal fiber to another is achieved by the material of the metal fibers. Thus, it is even more preferred that the metal fibers are fixed to each other without a polymer binder, as such polymer binders often have poor electrical conductivity and high-temperature performance. When the metal fibers are sintered directly to each other, it is also possible to omit solder materials, etc., in the network according to the present invention.

[0025] It is further preferred that the porous structure, particularly a 3D network of metal fibers, be directly fixed to the second layer without the need for an additional binder, such as a polymer binder. Most preferably, the porous material, such as the metal fibers, is fixed to the second layer by the porous structure and the material of the second layer. Therefore, it is further preferred that the metal fibers be fixed to the second layer without a polymer binder, since such polymer binders often have poor electrical conductivity and high-temperature performance. When the metal fibers are directly sintered to the second layer, it is also possible to omit solder materials, etc., from the network structure of the present invention.

[0026] According to a further preferred embodiment of the network structure, the porous structure is based on copper or aluminum. In particular, the porous structure is made of metal fibers based on copper or aluminum. In this specification, "based on copper" indicates that the material contains copper to an extent of at least 80 wt.-%, in particular at least 90 wt.-%. In this specification, "based on aluminum" indicates that the material contains aluminum to an extent of at least 80 wt.-%, in particular at least 90 wt.-%. In both cases, the remainder may be other elements.

[0027] According to a particularly preferred embodiment of the present invention, the material of the porous metal structure of the first layer and the material of the second layer are substantially the same. When both the first and second layers are made of substantially the same material, a stable fixation is achieved by sintering the layers together. As used herein, "substantially the same material" means that these materials are based on the same element, for example, copper or aluminum. In this context, "based on the same element" indicates that the material contains at least 80 wt.-%, particularly at least 90 wt.-%, of the element, the remainder of which may be other elements, and may differ between the first and second layers and / or between the first and second types of metal fibers if the 3D network contains two different types of metal fibers. The material of the first layer and the material of the second layer may be the same, and / or the material of the first and second types of metal fibers may be the same.

[0028] According to another preferred embodiment of the present invention, the first layer comprises a plurality of metal fibers of a first type and a plurality of metal fibers of a second type, the first type being different from the second type. The first type may be considered a stabilizing type of fiber, while the second type may be considered a functional type of fiber. The second type may have a higher surface area per weight of metal fiber compared to the first type. This means that the first type of metal fibers may also provide a desired functionality, such as available surface area for electrochemical processes or a filtering effect, albeit to a lesser extent.

[0029] Due to the use of different types of metal fibers, one type of metal fiber, i.e., the first type mentioned above, can function as a mechanical stabilizing component and as a more elastic conductor along the thickness of the 3D network of the second type of metal fibers, most importantly in the z-axis direction. In particular, the first type of metal fibers and the second type of metal fibers form an integral network of metal fibers, meaning that the first type of metal fibers and the second type of metal fibers are preferably sintered directly to each other to form a single 3D network containing both types of metal fibers. In other words, the first type of metal fibers and the second type of metal fibers do not form separate networks. Furthermore, due to the use of different types of metal fibers, they constitute a hierarchically structured network, in which thin fibers form a fine mesh and are supported by stronger fibers, for example, to collect current within a small volume element, while thicker fibers ensure further transport of locally collected electrons by maintaining a higher current due to their higher conductive cross-section, thereby functioning as a conductive path not only in the x-y plane of the network but also in the z-axis of the porous network of metal fibers. As a result, the use of two different types of metal fibers allows for even further reduction of the electrical load on each individual fiber: one type of metal fiber provides a current path in the z-axis direction, while the second layer collects the current in the xy plane.

[0030] In addition to providing electrical stabilization, a mixture of two different fiber types protects the metal fiber network from undesired densification in the z-direction, particularly when the metal fibers are sintered together, as well as when the 3D network is filled with active material to prepare a functional electrode for a Li-ion battery. It has been observed that combining two different fiber types, particularly during sintering of metal fibers to form a network, results in thickness shrinkage, i.e., shrinkage in the z-axis, compared with using only one type of metal fiber, particularly when these metal fibers have a thickness and / or width of 80 μm or less. Such shrinkage can be reduced or even completely avoided by using two different types of metal fibers. In this way, one of the two types, i.e., the first type mentioned above, acts as a mechanical stabilizer and prevents shrinkage. When preparing metal fibers for sintering, they are typically first deposited on a support, for example, to form a web-like nonwoven fabric. The weight of the fibers can cause compression, leading to undesirable porosity gradients. Such compression can occur, particularly when the fibers soften due to elevated temperatures during sintering. Also, when fibers are deposited from a dispersion and the liquid drains from the porous support structure, hydrodynamic pressure causes web compression in the z-axis. This can be improved by incorporating bulkier fibers with greater mechanical stability, i.e., thicker fibers, fibers with different melting points, or corrugated fibers.

[0031] Each of the first and second types of metal fibers may have a distribution of properties such as width, thickness, length, etc. This difference in meaning means that such distributions of the first and second types are different from each other. The second type should not be understood as part of the distribution of the first type. Mixing the second type with the first type should result in at least a bimodal distribution of these properties.

[0032] More preferably, the first and second types of metal fibers have different cross-sectional morphologies, and / or different melting points before sintering, and / or different longitudinal shapes, and / or different widths and / or thicknesses, and / or different metal alloys, particularly with respect to alloy additions to the same base metal. The longitudinal shape refers to how the fibers extend along their length, e.g., wavy or straight. Wavy refers to abrupt changes in fiber direction, while straight refers to no changes or only smooth changes. Abrupt changes in direction are considered when the change in direction is observed over a length shorter than the fiber width. A smooth change in direction is considered when the change in direction extends over a distance greater than the fiber width.

[0033] Preferably, the second type of metal fibers have a non-circular cross-sectional shape, i.e., the second type of metal fibers are ribbon-shaped, while the first type of fibers have a substantially circular cross-section. Ribbon-shaped fibers have a large surface area per mass, providing the desired functionality. In contrast, circular fibers have a smaller surface area per mass, but are more mechanically stable. However, even though the circular fibers have a smaller surface area per mass, they still contribute to the desired functionality by providing such a surface.

[0034] The first type of metal fibers preferably have a thickness at least 1.50 times, more preferably at least 2.0 times, and even more preferably at least 2.5 times the width of the second type of metal fibers. Also preferably, the width of the first type of metal fibers is at least 1.50 times, more preferably at least 2.0 times, and even more preferably at least 2.5 times the width of the second type of metal fibers. A stabilizing effect can be achieved when the thickness and / or width of the first type of metal fibers is at least 1.5 times that of the second type of metal fibers. Therefore, the thickness and / or width of the first type of metal fibers is at least 50% (at least 1.50 times), and especially at least 100% (at least 2.0 times) greater than the thickness and / or width of the second type of metal fibers. This facilitates mechanical and electrical stabilization.

[0035] Furthermore, it is preferred that the ratio of the difference in the arithmetic mean values ​​of the thickness and / or width of the first type of metal fibers and the second type of metal fibers to the product of the variances of the first type of metal fibers and the second type of metal fibers is at least 5, in particular at least 7, and even more in particular at least 10.

[0036] The thickness, width and length of each type of metal fiber may follow a distribution, in which case the values ​​given herein refer to arithmetic mean values.

[0037] According to a preferred embodiment of the present invention, the first type of metal fibers and the second type of metal fibers are made of different metal alloys, particularly with respect to alloy additions to the same base metal. Small differences in alloy additions can have a significant effect on the melting temperature. Therefore, fibers with a higher melting point alloy can stabilize the network structure during sintering. During sintering, fibers with a lower melting point are heated near or even above their melting point, which significantly softens these fibers. However, fibers with a higher melting point, such as a different alloy of the same base metal, can reduce or even avoid shrinkage of the entire network structure in the z-axis direction.

[0038] In a preferred embodiment, at least the second type of metal fiber has a non-circular cross-section, particularly a ribbon-like shape. Such a non-circular cross-section provides a large surface area, which may be advantageous in filtration applications because the non-circular cross-section induces turbulence in the fluid flowing through the filter. When used in battery electrodes, fibers with a non-circular cross-section increase the surface area of ​​the electrode material, thereby improving the electrochemical properties of the electrode and improving the suppression of lithium dendrite growth, such as in lithium metal batteries.

[0039] Preferably, the second type of metal fibers have a non-circular cross-sectional shape, i.e., the second type of metal fibers are ribbon-shaped, while the first type of fibers have a substantially circular cross-section. Ribbon-shaped fibers have a large surface area per mass, providing the desired functionality. In contrast, circular fibers have a smaller surface area per mass, but are more mechanically stable. However, even though the circular fibers have a smaller surface area per mass, they still contribute to the desired functionality by providing such a surface.

[0040] In a further preferred embodiment, the first type of metal fiber and the second type of metal fiber have different melting points. This is possible even if these types of metal fibers are made of the same material. When metal fibers are produced by melt spinning, the melt of the fiber material cools rapidly. This causes the melt to solidify so quickly that the material cannot settle into a thermodynamically favorable state, as explained in detail in WO 2020 / 016240 A1. After production by melt spinning, the metal fibers can be subjected to an annealing or aging treatment, which allows the material to relax and settle into a thermodynamically favorable state. It has been observed that after such an annealing treatment, the melting point of the metal fibers increases, even if the material composition remains unchanged. The difference in melting point between the first type of metal fiber and the second type of metal fiber can be at least 1 K, preferably at least 5 K, more preferably at least 6 K, even more preferably at least 7 K, and even more preferably at least 8 K. Another measure of the difference between the first and second types of fibers resulting from rapid cooling during melt spinning is the degree of recrystallization that can be observed when the fiber is heated to melt, as a measure of metastable conditions. For example, the onset of recrystallization can occur several hundred degrees below the melting point.

[0041] There is no particular upper limit to the melting point difference. For practical reasons only, the melting point difference is typically 20 K or less, preferably 15 K or less.

[0042] It is particularly preferred that the metal fibers be sintered directly to one another without the need for an additional binder, such as a polymer binder. Most preferably, the fixation of one metal fiber to another is achieved by the material of the metal fibers. Therefore, it is even more preferred that the metal fibers be fixed to one another without a polymer binder, as such polymer binders often have poor electrical conductivity and high-temperature performance. When the metal fibers are sintered directly to one another, it is also possible to omit solder materials, etc., in the network according to the present invention.

[0043] As already mentioned above, the first and second types of metal fibers are preferably made of substantially the same material, i.e., have substantially the same elemental composition. This allows the first and second types of metal fibers to be easily bonded to each other, facilitating the production of an integrated metal fiber network. According to a preferred embodiment of the present invention, the first and second types of metal fibers differ in metal alloy, particularly with respect to alloy additions to the same base metal. Small differences in alloy additions can have a significant effect on the melting temperature. Thus, fibers with a higher melting point alloy can stabilize the network structure during sintering. During sintering, fibers with a lower melting point are heated near or even above their melting point, which significantly softens these fibers. However, fibers with a higher melting point, such as a different alloy of the same base metal, can reduce or even avoid shrinkage of the entire network structure in the z-axis direction.

[0044] Furthermore, it is preferred if the first type of metal fiber can be obtained from the second type of metal fiber by, for example, heat treatment. In this context, the second type of metal fiber can preferably be obtained by melt spinning, and the first type of metal fiber can preferably be obtained by heat treatment of the second type of metal fiber. Heat treatment can increase the melting point by allowing the metal fiber material to approach its thermodynamic equilibrium. Furthermore, heat treatment can change the cross-sectional shape of the second type of metal fiber to a non-circular cross section, i.e., from a ribbon-like cross section to a substantially circular cross section.

[0045] The ratio of the first type of metal fibers to the second type of metal fibers can vary depending on the degree of electrical and mechanical stabilization required. The weight ratio of the first type to the second type is preferably in the range of 0.10:99.90 to 99.90:0.10, more preferably in the range of 15:85 to 85:15, even more preferably in the range of 30:70 to 70:30, and even more preferably in the range of 40:60 to 60:40. The weight portion of the stabilizing fibers, i.e., the first type, may exceed the weight portion of the second type of fibers. However, the larger surface area of ​​the second type of fibers still provides the desired functionality. The desired functionality can also be provided, although perhaps to a lesser extent, by the first type. Preferably, the ratio of the first type of metal fibers to the second type of metal fibers is set so that the amount of the first type exceeds the percolation threshold. This allows the first type of metal fibers in the sintered 3D network to extend throughout the entire network structure, improving mechanical and electrical stabilization not only in the z-axis direction but also in the xy plane.

[0046] According to another preferred embodiment, the first layer has a different structure compared to the second layer. In particular, the second layer can have a two-dimensional (2D) structure and can be non-porous, in particular a foil. A 2D structure is one that is substantially devoid of functional pores in the thickness direction, i.e., the z-axis direction. Functional pores are pores that contribute to the essential technical function of the network structure, i.e., filtration in filter applications or participation in the electrochemical process of a battery electrode. In a further preferred aspect of this embodiment, the second layer has a porous structure, such as a randomly laid layer or woven mesh of sintered metal fibers, which has higher mechanical stability compared to the first layer, or a perforated polymer sheet. The pores or perforations in the second layer allow the first layer to be filled with active material, which then penetrates through the second layer into the first layer. By introducing the active material through the second layer, the first layer is protected from mechanical loads during the introduction of the active material. The active material is, in particular, an electrode active material.

[0047] The porous structure of the second layer is preferably a metal mesh or expanded metal. The pore size of the second layer is not particularly limited, especially when the porous metal structure of the first layer is already completed even before contacting the second layer. From a manufacturing standpoint, it is possible to deposit multiple discrete metal fibers on the porous second layer, even if the pores of the second layer are larger than the length of the metal fibers. However, it is preferable that the pore size of the second layer is equal to or smaller than the length of the metal fibers. In this specification, the pore size corresponds to the opening size of the pores at the surface of the second layer that is in contact with the first layer. In the case of a metal mesh, the pore size corresponds to the mesh width.

[0048] More preferably, in the network structure of the present invention, the thickness of the first layer is greater than the thickness of the second layer. The primary functionality of the network structure is provided by the first layer. By making the thickness of the first layer greater than the thickness of the second layer, the weight contribution of the second layer is minimized, thereby increasing the weight capacity of the network structure when the network is used as a battery electrode. Preferably, the first layer has a thickness of at least 200 μm, more preferably at least 500 μm, even more preferably greater than 550 μm, even more preferably at least 750 μm, and even more preferably at least 1,000 μm. The thickness of the first layer can even be 2,000 μm or more. The upper limit of the thickness of the first layer is not particularly limited, and may be 10,000 μm or less, 8,000 μm or less, 6,000 μm or less, or 4,000 μm or less.

[0049] A network structure can be understood as a composite structure of a 3D structure and a 2D substrate (such as a film, a screen cloth, or a 2D mesh structure).

[0050] Preferably, the network structure of the present invention is part of a battery electrode.

[0051] All preferred embodiments and features described above or claimed herein for the network structure itself apply mutatis mutandis to the method for producing the network structure as well as to the method for producing the electrodes.

[0052] For example, in the method for manufacturing a network structure of the present invention, it is also preferable that the porous metal structure and the second layer are made of at least substantially the same material, thereby obtaining a stable bond between the two layers. Further details of the first and second layers are described in detail above.

[0053] Furthermore, in the method of the present invention for producing a network structure, the porous metal structure is preferably composed of a plurality of metal fibers having a width and / or thickness of 80 μm or less, and which form a three-dimensional network of metal fibers in which the metal fibers are fixed to each other at least after step D.

[0054] In the method of the present invention for producing a network structure, the metal fibers are already fixed to one another before step C. Therefore, a network of sintered metal fibers is first prepared and then placed on the support structure of the second layer. This approach allows for greater freedom in choosing the structure of the second layer. The structure can be porous or non-porous, and in particular, non-porous structures can be used, since it is not necessary to remove the carrier liquid that may be required to deposit the individual fibers.

[0055] According to another embodiment, it is preferred if the first layer is disposed in the form of loose metal fibers on the second layer in step C. In such a case, the second layer preferably has a porous structure, which allows the carrier liquid for depositing the loose metal fibers to be removed through the second layer.

[0056] Regardless of whether the metal fiber network is already sintered before being disposed on the second layer, the second layer is preferably a porous structure, which can be advantageous in subsequent processing steps where compression of the first layer should be avoided.

[0057] According to the present invention, it is preferable to carry out steps A to D as a roll-to-roll process, which allows large-scale production to be achieved.

[0058] Most preferably, the network structure obtained after step D is a network structure according to the present invention.

[0059] As already mentioned above, the present invention further relates to a method for producing an electrode, which comprises the use of a network structure according to the present invention, in which, in step F, the electrode material is provided as a slurry, preferably having thixotropic behavior.

[0060] In a preferred embodiment of the method for producing an electrode of the present invention, the second layer is porous. This allows the first layer to be filled with an active material, particularly an electrode active material, by passing the active material through the pores of the second layer. Those skilled in the art can select the pore size of the second layer depending on the particle size and / or fluid behavior of the active material.

[0061] Preferably, the active material is introduced into the first layer in the form of a slurry, particularly a thixotropic slurry. The viscosity of the thixotropic slurry decreases when subjected to a shear force. After the shear force is no longer acting on the slurry, its viscosity increases again. To adjust this rheological behavior as needed, those skilled in the art can add commercially available rheological additives. In this context, it is preferable for the thixotropic slurry to be filled into the network structure, i.e., the first layer, through the porous second layer. This can be achieved by using a doctor blade. The thixotropic slurry is subjected to a shear force when it comes into contact with the doctor blade. This reduces the viscosity of the slurry, allowing it to flow through the pores of the second layer into the first layer. This prevents mechanical stress on the first layer and its compression. After penetrating the first layer, the thixotropic slurry is no longer subjected to a shear force, and therefore its viscosity increases, so it remains there instead of flowing out of the first layer. Furthermore, it is still possible to introduce the slurry directly into the pores of the network structure. This may be done in addition to filling the pores through the second layer.

[0062] In a preferred embodiment of the present invention, at least step F is carried out as a roll-to-roll process. Even more preferably, step E includes a method for producing a network structure of the present invention, i.e., a method having at least steps A to D.

[0063] The present invention also relates to a battery comprising at least one electrode having a composite network structure according to the present invention, particularly a 3D network of metal fibers. The composite structure of the present invention can be used in many different types of batteries. However, particularly when the 3D network of metal fibers has a thickness of 200 μm or more, as described above as preferred herein, the battery can be a single-cell battery. The single-cell battery referred to herein is not a stack of many battery cells, but rather a single battery cell having one anode, one cathode, and a separator therebetween. Of course, the battery can also be a multi-cell battery.

[0064] Furthermore, the invention relates to a filter comprising at least one composite network structure according to the invention.

[0065] The present invention will now be described in more detail, by way of example only, with reference to the accompanying drawings and figures and by way of various examples of networks and methods of the present invention. [Brief explanation of the drawings]

[0066] [Figure 1] FIG. 1 is a schematic diagram showing the layers of the network structure of the present invention and the names of the z-axis and xy-planes. [Figure 2] 1 is a schematic diagram illustrating a method for manufacturing a network structure according to the present invention. [Figure 3] 1 is a schematic diagram illustrating a method for manufacturing an electrode according to the present invention. [Figure 4] 1 is a scanning electron microscope image of a metal fiber network according to Example 1. [Figure 5] 1 is a scanning electron microscope image of a metal fiber network according to Example 2. [Figure 6] 10 illustrates a network structure according to a third embodiment of the present invention. [Figure 7] 10 shows a network structure according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0067] For clarity, not all or no reference signs are shown in some figures.

[0068] FIG. 1 shows a schematic representation of a network structure 1 of the present invention. The illustrated network structure 1 includes a porous first layer 10 and a conductive second layer 20. The first and second layers each extend in the xy plane, as shown in the coordinate system of FIG. 1. The first layer 10 and the second layer 20 are in direct surface contact with each other. In the drawing of FIG. 1, the surface contact between these layers extends parallel to the xy plane. The first layer 10, as shown in FIG. 1, is a network of metal fibers sintered together. In the drawing of FIG. 1, this network is shown only schematically, and therefore individual fibers 12 (see FIG. 2) are not labeled. The second layer 20 is a support layer to which the fibers of the network of the first layer 10 are directly fixed by sintering. This allows the fibers in the network to be in direct electrical contact with the conductive second layer 20. When an electrochemical process provides electrons in the first layer, these electrons only need to travel through the network in the z-axis direction before reaching the second layer 20, which can act as a current collector. This reduces the electrical load on the individual fibers, as the electrons do not have to pass through the network of metal fibers in the xy plane to reach the electrical connection (not shown in the drawings).

[0069] FIG. 2 illustrates a process for preparing a network structure. In step A, a conductive porous metal structure is provided. In the schematic diagram of FIG. 2, this structure is provided by a plurality of metal fibers 14 fixed to one another. While only seven metal fibers are shown in FIG. 2, it should be understood that in reality, the number of metal fibers is much greater. A conductive second layer is provided from roll 21, which rotates in the direction indicated by the white arrow. In step C, a first layer 10, i.e., a network of metal fibers, is disposed on second layer 20. In step D, the first layer 10 is fixed on second layer 20 by sintering. The network structure 1 is then wound onto roll 22, which rotates in the direction indicated by the white arrow. This illustrates how the present invention for producing a network structure can be realized as a roll-to-roll process.

[0070] A schematic diagram of the fabrication of an electrode 30 according to the present invention is shown in FIG. 3. In step E, a network structure 1 according to the present invention is provided from a roll 23 rotating in the direction indicated by the white arrow. The network structure 1 has a first layer 10 and a second layer 20, as described above. The first layer 10 comprises a network of metal fibers 14 sintered together. The second layer 20 is a porous layer. The network structure 1 is conveyed from the roll 23 to a doctor blade 40, where a thixotropic slurry 42 of the electrode active material is subjected to a shear force and forced through the second layer 20 and into the first layer 10, thereby forming the electrode 30 after a drying step (not shown in FIG. 3). Because the doctor blade acts only on the second layer 20, the first layer is not subjected to any pressure, thereby avoiding undesired compression of the first layer 10. The drying step may be performed immediately after filling the pores with the slurry 42 or at a separate stage, or, if circumstances permit, may be omitted entirely. 3, the electrode is then wound onto a roll 24 rotating in the direction indicated by the white arrow, thereby realizing the manufacture of the electrode according to the present invention as a roll-to-roll process.

[0071] In principle, each of the roll-to-roll processes of Figures 2 and 3 can be performed as a single integrated process instead of winding the network structure 1 onto a roll 22 and directing it to a doctor blade 40 as shown in Figure 3.

[0072] The following examples further illustrate the present invention.

[0073] Examples 1 and 2 and Comparative Examples 1 and 2 illustrate the preparation of networks of metal fibers that can be utilized as the first layer of a composite network structure according to the present invention.

[0074] Example 1: In this example, ribbon-shaped flat fibers (approximately 100 μm wide, 5 μm thick, equivalent radius of approximately 12.6 μm) obtained by melt spinning were mixed 50:50 with approximately circular fibers (radius of approximately 45 μm) of the same material composition.

[0075] The fibers were sintered at 620 °C (average heating rate of 200 K / min, argon atmosphere, 60 s holding time, natural cooling, i.e., removed from the furnace and allowed to cool to room temperature). Scanning electron microscope images in Figure 4 show that the fibers were bonded together and that the fiber shape remained unchanged. The network was 950 μm thick after sintering.

[0076] Comparative Example 1 was carried out in the same manner as Example 1, except that only ribbon-shaped flat fibers were used without using circular fibers. The thickness of the network after sintering was only about 300 μm.

[0077] Comparison of Example 1 and Comparative Example 1 shows that the use of two different types of fibers, one with a ribbon-like shape with a non-circular cross section and the other with a circular cross section, improves the mechanical stabilization during the sintering process, thereby avoiding compression of the metal fibers.

[0078] Example 2: In this example, ribbon-like flat fibers (approximately 80 × 5 μm) obtained by melt spinning were used. Half of the fibers (by weight) were aged at 400 °C for 60 minutes under inert gas and sintered with untreated fibers at 620 °C as described above for Example 1. As shown in Figure 5, the fibers were firmly bonded together after sintering, and the thickness of the sintered network was 750 μm.

[0079] After aging, the shape of the aged fibers did not change, but DSC measurements showed that the aged fibers had a melting temperature about 7 K higher than that of the unaged fibers.

[0080] Comparative Example 2 was carried out in the same manner as Example 2, except that only untreated ribbon-like flat fibers were used, i.e., without aged fibers, and the final network thickness was only 250 μm.

[0081] Comparison of Example 2 and Comparative Example 2 shows that the use of two types of fibers with different melting points improves the mechanical stabilization during the sintering process, thereby avoiding compaction of the metal fibers.

[0082] Examples 3 and 4 demonstrate the preparation of composite network structures according to the present invention.

[0083] Example 3: An already sintered metal fiber network (sintered at 920°C (average heating rate of 200 K / min, argon atmosphere, 60 s holding time, natural cooling, i.e., removed from the furnace and allowed to cool to room temperature) was placed on a copper foil (99.9+, 10 μm thick) and sintered together using the same 920°C temperature program used for the initial sintering of the metal fiber network. A photograph of the resulting composite network structure is shown in Figure 6.

[0084] Example 4: Unsintered fibers were placed loosely on a fine copper mesh and sintered at 920°C (average heating rate of 200 K / min, argon atmosphere, 60 s holding time, natural cooling, i.e., removed from the furnace and allowed to cool to room temperature). The fibers are firmly sintered together within themselves and to the copper network. A photograph of the resulting composite network structure is shown in Figure 7.

[0085] The thickness and width of the metal fibers referred to herein can be determined either by scanning electron microscopy or micro-CT. The melting point of the metal fibers can be determined by DSC.

[0086] The following summarizes embodiments of the present invention and preferred aspects thereof, but it should be understood that these embodiments and preferred aspects are disclosed in combination with the claims and any of the additional features described herein.

[0087] Embodiments: 1. Comprising at least a first layer (10) and a second layer (20); The first layer (10) comprises a porous metal structure that is electrically conductive; The second layer (20) is a conductive layer onto which the first layer (10) is fixed; The first layer (10) and the second layer (20) are mechanically and conductively connected to each other. Composite network structure (1).

[0088] 2. The porous structure is one in which a plurality of metal fibers (14) fixed to each other and having a width and / or thickness of 80 μm or less form a three-dimensional network of metal fibers (14) in which the metal fibers (14) are fixed to each other; A composite network structure (1) according to embodiment 1.

[0089] 3. The first layer (10) includes a plurality of metal fibers (14) having a thickness of 50 μm or less; A composite network structure (1) according to embodiment 1 or 2.

[0090] 4. The first layer (10) includes a plurality of metal fibers (14) having a thickness of 1.0 μm or more. 10. The composite network structure (1) of any of the preceding embodiments.

[0091] 5. The first layer (10) includes a plurality of metal fibers (14) having a width of 70 μm or less; 10. The composite network structure (1) of any of the preceding embodiments.

[0092] 6. The first layer (10) includes a plurality of metal fibers (14) having a width of 1.0 μm or more. 10. The composite network structure (1) of any of the preceding embodiments.

[0093] 7. At least a portion of the metal fibers (14) have a non-circular cross section, in particular a ribbon-like cross section; 10. The composite network structure (1) of any of the preceding embodiments.

[0094] 8. The metal fibers (14) are based on copper or aluminum, 10. The composite network structure (1) of any of the preceding embodiments.

[0095] 9. The metal fibers (14) are in direct contact with each other; 10. The composite network structure (1) of any of the preceding embodiments.

[0096] 10. The first layer (10) comprises a plurality of metal fibers (14) of a first type and a plurality of metal fibers (14) of a second type, and the first metal fibers (14) and the second metal fibers (14) differ from each other in terms of mechanical properties; 10. The composite network structure (1) of any of the preceding embodiments.

[0097] 11. The first type of metal fibers (14) and the second type of metal fibers (14) have different cross-sectional shapes. 10. The composite network structure (1) of any of the preceding embodiments.

[0098] 12. The first type of metal fibers (14) and the second type of metal fibers (14) have different melting points before being sintered together. 10. The composite network structure (1) of any of the preceding embodiments.

[0099] 13. The first type of metal fibers (14) and the second type of metal fibers (14) have different melting points before being sintered together. 10. The composite network structure (1) of any of the preceding embodiments.

[0100] 14. The first type of metal fibers (14) and the second type of metal fibers (14) have different widths and / or thicknesses; the thickness and / or width of the first type of metal fibers is at least 10% greater, in particular at least 15% greater, than the thickness and / or width of the second type of metal fibers (14); and / or The first type of metal fibers (14) and the second type of metal fibers (14) are of different metal alloys, particularly with respect to alloying additions to the same base metal; 10. The composite network structure (1) of any of the preceding embodiments.

[0101] 15. The weight ratio of the first type to the second type is in the range of 1:99 to 99:1, more preferably in the range of 15:85 to 85:15, even more preferably in the range of 30:70 to 70:30, and even more preferably in the range of 40:60 to 60:40; 10. The composite network structure (1) of any of the preceding embodiments.

[0102] 16. The first type of metal fibers (14) and the second type of metal fibers (14) are of substantially the same material; 10. The composite network structure (1) of any of the preceding embodiments.

[0103] 17. The first layer (10) has a different structure compared to the second layer (20); 10. The composite network structure (1) of any of the preceding embodiments.

[0104] 18. The second layer (20) has a two-dimensional structure and is non-porous, in particular a foil; 10. The composite network structure (1) of any of the preceding embodiments.

[0105] 19. The second layer (20) has a porous structure, such as a layer or mesh of sintered metal fibers (14), which has a higher mechanical stability compared to the first layer (10); 10. The composite network structure (1) of any of the preceding embodiments.

[0106] 20. The first layer (10) is thicker than the second layer (20); 10. The composite network structure (1) of any of the preceding embodiments.

[0107] 21. The metal fibers (14) of the first layer (10) and the metal component of the second layer (20) are of at least substantially the same material; 10. The composite network structure (1) of any of the preceding embodiments.

[0108] 22. A method for producing a composite network structure, comprising: Step A: Providing a first layer (10) of a porous metal structure that is electrically conductive; Step B: Providing a second layer (20) that is electrically conductive; Step C: placing the first layer (10) on the second layer (20); Step D: Fixing the layer of porous metal structure on the second layer (20) by sintering; A method comprising:

[0109] 23. The porous metal structure and the second layer (20) are of at least substantially the same material; 23. The method of embodiment 22.

[0110] 24. The porous metal structure is composed of a plurality of metal fibers (14) having a width and / or thickness of 80 μm or less, and at least after step D, the metal fibers (14) are fixed to each other to form a three-dimensional network of metal fibers (14); 24. The method of embodiment 22 or 23.

[0111] 25. The metal fibers (14) are already fixed to each other before step C. 25. The method according to any one of embodiments 22 to 24.

[0112] 26. The second layer (20) is a porous or non-porous structure, in particular a non-porous structure; 26. The method of embodiment 25.

[0113] 27. In step C, the first layer (10) is placed on the second layer (20) in the form of discrete metal fibers (14); 25. The method according to any one of embodiments 22 to 24.

[0114] 28. The second layer (20) is a porous structure. 28. The method of embodiment 27.

[0115] 29. Steps A to D are performed as a roll-to-roll process. The method according to any one of embodiments 22 to 28.

[0116] 30. The network structure obtained after step D is the network structure according to at least one of embodiments 1 to 21. The method according to any one of embodiments 22 to 29.

[0117] 31. A method for manufacturing an electrode, comprising: Step E: Providing a network structure according to at least one of embodiments 1 to 21; Step F: Filling the network structure provided in step E with an electrode active material; A method comprising:

[0118] 32. In step F, the electrode material is provided as a slurry having thixotropic behavior; The second layer (20) is porous, The thixotropic slurry is filled into the network structure through the porous second layer (20), and / or The thixotropic slurry is directly filled into the pores of the network structure. 32. The method of embodiment 31.

[0119] 33. At least step F is performed as a roll-to-roll process; 33. The method of embodiment 32.

[0120] 34. Step E comprises the method of any one of embodiments 22 to 30. The method of embodiment 32 or 33.

[0121] 35. A battery comprising at least one electrode having a network structure according to at least one of embodiments 1 to 21.

[0122] 36. The battery is a single cell battery. 36. The battery of claim 35.

[0123] 37. The battery is a multi-cell battery. 36. The battery of claim 35.

[0124] 38. A filter comprising at least one composite network structure according to any one of embodiments 1 to 21, in particular wherein the second layer has a porous structure. [Explanation of symbols]

[0125] 1 Network Structure 10 1st layer 14 Metallic Fibers 20 2nd layer 21 rolls 22 rolls 23 rolls 24 rolls 30 electrodes 40 Doctor Blade 42 Slurry

Claims

1. comprising at least a first layer (10) and a second layer (20); The first layer (10) comprises a porous metal structure that is electrically conductive; The second layer (20) is a conductive layer on which the first layer (10) is fixed, The first layer (10) and the second layer (20) are mechanically and conductively connected to each other. Composite network structure (1).

2. The porous structure is one in which a plurality of metal fibers (14) are fixed to each other and have a width and / or thickness of 80 μm or less, and form a three-dimensional network of metal fibers (14) in which the metal fibers (14) are fixed to each other. A composite network structure (1) according to claim 1.

3. The first layer (10) includes a plurality of metal fibers (14) having a thickness of 50 μm or less and / or a width of 70 μm or less. A composite network structure (1) according to claim 1 or 2.

4. At least a portion of the metal fibers (14) have a non-circular cross section, in particular a ribbon-like cross section. A composite network structure (1) according to claim 1 or 2.

5. The metal fibers (14) are based on copper or aluminum, A composite network structure (1) according to claim 1 or 2.

6. The first layer (10) comprises a plurality of metal fibers (14) of a first type and a plurality of metal fibers (14) of a second type, the first type of metal fibers (14) and the second type of metal fibers (14) being different from each other, particularly with respect to mechanical properties; The first type of metal fibers (14) and the second type of metal fibers (14) are preferably made of substantially the same material. A composite network structure (1) according to claim 1 or 2.

7. The first type of metal fibers (14) and the second type of metal fibers (14) have different cross-sectional shapes, and / or The first type of metal fibers (14) and the second type of metal fibers (14) have different melting points before being sintered together, and / or the first type of metal fibers (14) and the second type of metal fibers (14) differ in width and / or thickness, the thickness and / or width of the first type of metal fibers being at least 10% greater, in particular at least 15% greater, than the thickness and / or width of the second type of metal fibers (14); and / or the first type of metal fibers (14) and the second type of metal fibers (14) are of different metal alloys, particularly with respect to alloying additions to the same base metal; A composite network structure (1) according to claim 1 or 2.

8. the weight ratio of said first type to said second type is in the range of 1:99 to 99:1, more preferably in the range of 15:85 to 85:15, even more preferably in the range of 30:70 to 70:30, and even more preferably in the range of 40:60 to 60:40; A composite network structure (1) according to claim 1 or 2.

9. The first layer (10) is thicker than the second layer (20), The thickness of said first layer (10) is at least 200 μm, preferably at least 500 μm, more preferably more than 550 μm, even more preferably at least 750 μm, and even more preferably at least 1,000 μm; A composite network structure (1) according to claim 1 or 2.

10. The second layer (20) has a porous structure. A composite network structure (1) according to claim 1 or 2.

11. The second layer (20) has a non-porous structure. A composite network structure (1) according to claim 1 or 2.

12. 1. A method for producing a composite network structure, comprising: Step A: Providing a first layer (10) of a porous metal structure that is electrically conductive; Step B: Providing a second layer (20) that is electrically conductive; Step C: placing the first layer (10) on the second layer (20); Step D: fixing the layer of the porous metal structure onto the second layer (20) by sintering; A method comprising:

13. The porous metal structure and the second layer (20) are of at least substantially the same material. The method of claim 12.

14. The metal fibers (14) are already fixed to each other before step C.

14. The method of claim 12 or 13.

15. The second layer (20) is a porous structure.

14. The method of claim 12 or 13.

16. The second layer (20) is a non-porous structure.

14. The method of claim 12 or 13.

17. In step C, the first layer (10) is disposed on the second layer (20) in the form of discrete metal fibers (14); The second layer (20) is a porous structure.

14. The method of claim 12 or 13.

18. Steps A to D are performed as a roll-to-roll process.

14. The method of claim 12 or 13.

19. The network structure obtained after step D is the network structure according to claim 1 or 2.

14. The method of claim 12 or 13.

20. A method for manufacturing an electrode (30), comprising the steps of: Step E: Providing a composite network structure (1) according to claim 1; Step F: Filling the composite network structure (1) provided in Step E with an electrode active material; A method comprising:

21. In step F, the electrode material is provided as a slurry having thixotropic behavior; The second layer (20) is porous, The thixotropic slurry is filled into the network structure through the porous second layer (20), and / or The thixotropic slurry is directly filled into the pores of the network structure, and / or At least step F is performed as a roll-to-roll process; 21. The method of claim 20.

22. Step E comprises the method of claim 12 or 13, The method according to any one of claims 20 to 21.

23. A battery comprising at least one electrode (30) having a composite network structure (1) according to claim 1 or 2.

24. 3. A filter comprising at least one composite network structure according to claim 1 or 2, in particular said second layer having a porous structure.

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