Thermal interface material, energy storage devices with a thermal interface material and methods for their production

Abstract

Thermal Interface Material (TIM) (1), in particular for an energy storage device, comprising a plate (2) of expanded graphite, wherein a reinforcement (3) is embedded in the plate (2), wherein the reinforcement (3) is an expanded metal of aluminium or copper or wherein the reinforcement (3) comprises a metallized hook tape or a metallized spacer fabric or a metallized velour or a metallized pole fabric or a metallized woven fabric.

Description

[0001] The present invention relates to a thermal interface material (TIM), in particular for an energy storage device. It further relates to an energy storage device and to a method for producing such a thermal interface material (TIM) and an energy storage device. The invention is particularly advantageous in the field of electromobility.

[0002] In the context of electrical applications, especially modern energy storage systems used in electromobility, the demands on thermal management increase with increasing performance.

[0003] During the charging and discharging processes of energy storage systems in electric vehicles, heat is generated, which must be dissipated by appropriate thermal management systems. Typically, heat is transferred to a battery tray located below a battery module, where cooling channels may be present. A gap is created between the battery tray and the battery module due to the manufacturing process. This gap should be bridged by a thermal interface material (TIM). Currently, gap filler pastes are used for this purpose. These pastes typically offer a thermal conductivity of around 3 W / mK and, due to their flow properties, are able to bridge the gap. However, gap filler pastes are relatively heavy and expensive.

[0004] EP 2 745 348 B1 discloses a heat sink comprising a graphite expanded metal forming element having two main surfaces, wherein a plastic layer is arranged on at least one main surface, wherein the at least one plastic layer is perforated and has a hole structure, a strip and / or a meander structure.

[0005] Publication US 3 404 061 A shows a flexible graphite material made of expanded, compressed particles.

[0006] Document US 2005 / 0175838A1 discloses a thermal interface material consisting of a flexible graphite sheet with two parallel, flat surfaces, the first flat surface of the TIM being in contact with the outer surface of a heat source and the second flat surface being in contact with a cooling module. The graphite sheet contains oil.

[0007] In light of the state of the art, the object of the present invention is to propose a high-performance thermal management system that can maximize the lifespan of a battery while being easy to manufacture and handle.

[0008] This problem is solved by a thermal interface material (TIM) according to claim 1. It is also solved by an energy storage device according to claim 17 or by a method according to claim 21 or 23. Advantageous embodiments will become apparent from the dependent claims as well as from the following description and the figures.

[0009] Accordingly, a Thermal Interface Material (TIM) is proposed comprising a sheet of expanded graphite with reinforcement embedded in the sheet.

[0010] The TIM offers the advantage of optimized stability while simultaneously enabling good heat dissipation. Furthermore, it allows compression at low, defined forces, thus preventing damage to adjacent structures.

[0011] In the present application, "compacting" refers in particular to the densification of an expanding graphite during the production of a plate, while "compressing" typically refers to the densification of the expanding graphite during installation between the module and the tub.

[0012] An energy storage device according to the invention, to which this document also refers, contains the TIM.

[0013] In the manufacturing process according to the invention, a TIM is produced by providing expanded graphite flakes. Reinforcement is provided between the expanded graphite flakes. The graphite flakes are then compacted into a plate in which the reinforcement is embedded. The process, which can be used in particular for the production of all embodiments of the TIM described herein, will be described in more detail later. It should be emphasized that features described herein only for the TIM or the energy storage device can also be claimed for the process and vice versa.

[0014] The reinforcement can, for example, be made of a thermally conductive material whose thermal conductivity is at least equal to that of the expandable graphite. The expandable graphite, for example, has a conductivity of approximately 4 W / mK.

[0015] In TIM specifications, the reinforcement has a thermal conductivity of at least 2 W / mK, 4 W / mK, 15 W / mK, or 150 W / mK. In particular, the reinforcement can have a conductivity of approximately 200 W / mK. As will be explained in more detail later, the reinforcement can be made of aluminum. For example, by being made of aluminum, the reinforcement can have a thermal conductivity of 190–230 W / mK.

[0016] In one possible design, the reinforcement has a mesh structure. This allows the weight of the reinforcement, and therefore of the TIM, to be kept low, while also making it advantageous to embed the reinforcement in the expandable graphite during the manufacturing process, as the expandable graphite can pass through the mesh.

[0017] The reinforcement can be designed, for example, as a mesh, a textile structure, or expanded metal.

[0018] The reinforcement can be made of materials such as aluminum, copper, carbon, or ceramic.

[0019] The reinforcement can be, for example, a mesh structure, particularly a braid, made of aluminum, copper, carbon, or ceramic. It is also possible to provide reinforcement made of a polymer, for example, in the form of a mesh structure, particularly a braid.

[0020] The reinforcement is expanded metal made of aluminum or copper, or it comprises, in particular, a metallized hook tape, a metallized spacer fabric, a metallized velour, a metallized pile fabric, or a metallized woven fabric. The reinforcement may, in particular, be or comprise a copper-plated or silver-plated hook tape, spacer fabric, velour, pile fabric, or woven fabric.

[0021] The mesh size of the reinforcement can be, for example, at least 1 mm, 3 mm, or 5 mm. Alternatively or additionally, the mesh size can be at most 15 mm or 10 mm. This allows the expandable graphite to pass through the mesh particularly well, while simultaneously minimizing weight and sufficiently improving handling strength.

[0022] It may be stipulated that the reinforcement is free of plastic. In particular, it may be stipulated that the entire TIM is free of plastic.

[0023] The plate has two opposing main surfaces, each of which can typically contact an adjacent structure.

[0024] The TIM can be designed such that the reinforcement is flush with one of the main surfaces, i.e., the upper or lower main surface of the panel. Alternatively, the reinforcement can be completely covered by the expanded graphite of the panel on both the upper and lower main surfaces, and can be positioned centrally or off-center. Alternatively or additionally, the reinforcement can be flush with the panel laterally. The reinforcement can also be completely enclosed laterally by the panel, extending, for example, to within less than 1 cm of the panel's edge. This can increase stability even at the edges of the TIM. The reinforcement can also extend laterally beyond the panel. This can be advantageous, for example, for handling.

[0025] Because the reinforcement is embedded in the plate and the reinforcement preferably has good thermal conductivity itself, good heat transfer across the main surfaces can be achieved.

[0026] The panel can, for example, have lateral dimensions of at least 10 cm x 10 cm or at least 10 cm x 20 cm. The overall dimensions are typically no more than 50 cm x 50 cm. In one example, the panel has lateral dimensions of 35 cm x 15 cm.

[0027] The TIM, in a relaxed state where the plate is not compressed by the pressure of other components, can have a thickness of, for example, 2 mm or less. The plate thickness can be selected according to the desired application and can also be greater than 2 mm, e.g., up to 3 mm or up to 4 mm.

[0028] In one example, the plate can have overall dimensions of approximately 35 cm x 15 cm x 0.2 cm when the expanded graphite is relaxed.

[0029] The TIM can, for example, be compressed to a thickness of 1 mm.

[0030] The TIM can be designed or manufactured in such a way that the expanded graphite has a density of at least 0.05 g / cm³ in the relaxed state. 3 and / or of no more than 0.1 g / cm³ 3 exhibits. In particular, the expandable graphite can have a density of 0.07 g / cm³. 3 This is achieved in the manufacturing process by controlling the compaction of the graphite flakes to produce a plate with a density of less than 0.1 g / cm³. 3 to produce.

[0031] These types of TIMs are lightweight, which is particularly advantageous in the field of electromobility. Furthermore, by selecting such densities, the pressure exerted by the TIM on adjacent structures can be kept to a minimum.

[0032] In some versions, the expanded graphite of the plate is impregnated with an impregnating agent. This allows the plate's properties to be modified. For example, it can further stabilize the plate and / or extend its service life by improving corrosion resistance. In particular, it can help prevent contact corrosion. The impregnating agent can, for example, contain or be silicone oil.

[0033] It may be provided that the pores of the expanded graphite are filled with the impregnating agent to a maximum of 50% or a maximum of 40%.

[0034] To produce a saturated plate, the process can be carried out by placing the plate containing the reinforcement onto a reservoir of the impregnating medium so that its underside makes contact with the medium. This can be done in such a way that the plate is not completely immersed. The impregnation can be carried out without pressure, particularly by using capillary action. Alternatively, the impregnation can be carried out by first evacuating the pores of the plate by subjecting it to a vacuum, and then bringing the plate into contact with the impregnating medium.

[0035] The TIM can be designed to consist of the board and the reinforcement and have no other components. The expandable graphite of the board can be impregnated, or it can be unimpregnated expandable graphite.

[0036] As mentioned, this also reveals an energy storage device. It comprises a battery module and a battery tray, with a TIM (transformational insulation module) arranged between the battery module and the battery tray. This TIM comprises a plate of expanded graphite in which reinforcement is embedded.

[0037] The TIM described herein can be used in all described versions as TIM in this energy storage device.

[0038] The energy storage device could be a drive battery for an electric vehicle, especially an electric car.

[0039] In the energy storage system, there is a gap between the battery module and the battery tray. Such a gap is typically unavoidable due to manufacturing processes. The gap is preferably completely filled by the thermal interface material (TIM). Preferably, the TIM makes full-surface contact, thus optimizing heat transfer between the battery module and the battery tray.

[0040] In the energy storage system, the gap between the battery module and the battery tray can have a height of between 0.3 mm and 2 mm.

[0041] The pressure exerted on the battery tray and / or battery module by the TIM, especially by the compressed TIM, is, for example, a maximum of 2.5 bar. With the densities specified above for the TIM, this pressure threshold is advantageously not exceeded until maximum compression is reached at, for example, a thickness of 1 mm, thus preventing damage to battery components, such as the battery module or battery tray.

[0042] The reinforcement can be arranged decentrally, for example, particularly near one of the main surfaces or flush with one of the main surfaces. Specifically, the reinforcement can be arranged decentrally in the direction of the battery tray, i.e., particularly in the direction of the lower main surface. However, it is also possible to arrange the reinforcement centrally or near the upper main surface.

[0043] A possible impregnating agent could, for example, be located on the side of the battery tray.

[0044] The energy storage device can be manufactured by first producing the TIM (thermoelectric module) as described above. The TIM can then be placed in a battery tray. Vacuum gripping technology, for example, can be used for this purpose. The battery module is then placed onto the TIM, causing the latter to deform. The battery module is then secured in its intended position relative to the battery tray.

[0045] The invention is explained below using figures as an example.

[0046] It shows: Fig. 1. an energy storage device with a Thermal Interface Material (TIM), Fig. 2a The TIM in a top view, Fig. 2b a section through the TIM according to a first execution, in a relaxed state, Fig. 2c the section through the TIM according to the first execution, in a compressed state, Fig. 2d the section through the TIM according to a second execution, in a relaxed state, Fig. 2e the section through the TIM according to the second execution, in a compressed state, and Fig. 3a-3d different reinforcements for the TIM.

[0047] Fig. Figure 1 schematically depicts an energy storage device in a side view. The energy storage device comprises a battery module 10, which is arranged above a battery tray 20, with a thermal interface material (TIM) 1 arranged between the battery module 10 and the battery tray 20. The TIM 1 and its components will be explained in detail in connection with the following figures. The TIM 1 comprises a plate 2 made of expanded graphite in which a reinforcement 3 is embedded (see, e.g., Figure 1). Fig. 2a-2e).

[0048] The energy storage from Fig. 1 is designed as a drive battery for an electric car.

[0049] In the battery storage system, heat transfer between battery module 10 and the battery tray is facilitated by the TIM 1. The battery tray 20 and the battery module 10 are matched components. Due to the manufacturing process, a gap between the battery tray 20 and the battery module 10 is generally unavoidable. This gap is bridged by the TIM 1, which completely fills it, thus enabling thermal exchange. During component manufacturing, the gap is set to, for example, 1.5 mm ± 0.5 mm.

[0050] The expandable graphite of TIM 1 is compressible. TIM 1 is designed such that, in a relaxed, i.e., uncompressed state, it has a thickness of, for example, 2 mm and can be compressed to 1 mm.

[0051] The TIM 1 is inserted into the battery tray 20, and then the battery module 10 is pressed onto it, at least partially compressing the TIM 1. Finally, the battery module is fixed in its intended position relative to the battery tray 10. Due to the dimensions of the gap and the TIM 1, the gap is now completely filled by the TIM 1. The density and deformability of the TIM 1 are selected such that the pressure exerted by the TIM 1 on the battery tray 20 and the battery module 10 does not exceed 2.5 bar, and the thickness of the TIM 1 is not less than one millimeter. For this purpose, a density of less than 0.1 g / cm³ is used for the TIM 1. 3 selected, e.g. 0.07 g / cm² 3 .

[0052] The expanded graphite has a thermal conductivity of approximately 4 W / mK and a thermal conductivity of the reinforcement contained within it (su, Fig. 2a - 3d) is even higher, thus enabling an overall advantageous heat transfer. At the same time, the device is robust and lightweight.

[0053] Fig. 2a shows the one in Fig. 1 drawn section AA through the TIM 1, i.e. a horizontal section in a top view.

[0054] The lateral dimensions of plate 2 and thus of TIM 1, which are in the Fig. The dimensions 2a, which are recognizable, can be larger than 10 x 20 cm. For example, they can be 15 cm x 35 cm.

[0055] The cut of the Fig. Figure 2a discloses the reinforcement 3, which has a mesh structure. It also discloses the expanded graphite formed by the plate 2, which extends between the meshes. The reinforcement 3 terminates laterally flush with the expanded graphite of the plate 2.

[0056] The mesh structure is formed by an aluminum mesh. Aluminum has a thermal conductivity higher than that of expanded graphite. With a thermal conductivity between 190 and 230 W / mK and a relatively low density, the entire TIM 1 system is advantageous in terms of weight and thermal conductivity.

[0057] The aluminum mesh has mesh sizes ranging from 1 mm to a maximum of 15 mm.

[0058] TIM 1 is produced by creating expanded graphite flakes. This is achieved by heating a puffy base graphite in the form of platelets, which are, for example, many molecular layers thick, in an oven (to about 600°C) so that it expands and forms the expanded graphite flakes.

[0059] The expanded graphite flakes are poured into a compaction device, into which, either before or after, the reinforcement 3 is also placed.

[0060] Due to the mesh dimensions, the expanded graphite flakes can penetrate and fill the meshes of the reinforcement 3.

[0061] Using the compaction device, the expanded graphite flakes are pressed so that they interlock under deformation, forming plate 2, which contains the reinforcement 3 located between the graphite flakes. The reinforcement 3 stabilizes plate 2 and facilitates its handling.

[0062] Compaction occurs to such an extent that the density of the resulting plate 2 in the relaxed state is less than 0.1 g / cm³. 3 is, for example, 0.07 g / cm² 3 .

[0063] The expanded graphite structure of plate 2 is porous and deformable.

[0064] Fig. 2b and Fig. 2c show the in Fig. 2a shows the section through the TIM 1, i.e. a front view in which the position of the reinforcement in relation to the plate 2 is recognizable. Fig. Figure 2b shows plate 2 in its uncompressed state, in which its thickness is 2 mm. Fig. Figure 2c shows the plate in its compressed state, e.g. after installation, where its thickness is only 1 mm.

[0065] The reinforcement 3 is shown in the first version of the Fig. 2b and Fig. 2c is positioned on the lower main surface and is flush with it. That is, the reinforcement is shifted towards the battery tray 20 and / or contacts sections of the battery tray 20.

[0066] Fig. 2d and Fig. 2e show the same cut as the Fig. 2b and Fig. 2c - also before and after compression - where plate 2 is in a second version. Accordingly, the reinforcement 3 is offset towards the lower main surface and thus towards the battery tray 20; however, the reinforcement 3 does not terminate flush with plate 2 at the bottom but is completely covered at the bottom by the expanded graphite of plate 2, so that the reinforcement 3 does not directly contact the battery tray.

[0067] In both the first and second versions, the pores of the TIM 1 can optionally be partially filled with an impregnating agent, particularly silicone oil, e.g., up to 40%. Additionally or alternatively, other impregnating agents or reactive resins can also be used. The impregnating agent can be located, for example, near the lower main surface, i.e., on the side facing the battery tray 20.

[0068] Fig. Figures 3a-3d illustrate various possible reinforcements that can be used in the TIM 1.

[0069] Fig. Figure 3a shows a reinforcement designed as a mesh. This can be made of aluminum, as described above. It can also be made of copper, carbon, or ceramic.

[0070] Fig. Figures 3b to 3d show copper-plated textile structures that can be used as reinforcement 3.

Claims

[1] Thermal Interface Material (TIM) (1), in particular for an energy storage device, comprising a plate (2) of expanded graphite, wherein a reinforcement (3) is embedded in the plate (2), wherein the reinforcement (3) is an expanded metal of aluminium or copper or wherein the reinforcement (3) comprises a metallised hook tape or a metallised spacer fabric or a metallised velour or a metallised pole fabric or a metallised woven fabric. [2] TIM (1) according to claim 1, wherein the reinforcement (3) is formed from a thermally conductive material, wherein the thermal conductivity of the reinforcement (3) in particular corresponds to at least a thermal conductivity of the expandable graphite and / or wherein the reinforcement (3) has a thermal conductivity of at least 2 W / mK or of at least 15 W / mK or of at least 150 W / mK. [3] TIM (1) according to one of the preceding claims, wherein the reinforcement (3) has meshes. [4] TIM (1) according to any of the preceding claims, wherein the reinforcement (3) is designed as a mesh or as a textile structure or as expanded metal. [5] TIM (1) according to any of the preceding claims, wherein the reinforcement (3) is a mesh of aluminium or of copper or of carbon or of ceramic. [6] TIM (1) according to any of the preceding claims, wherein the reinforcement (3) comprises a copper-plated or silver-plated hook tape or a copper-plated or silver-plated spacer fabric or a copper-plated or silver-plated velour or a copper-plated or silver-plated pile fabric or a copper-plated or silver-plated woven fabric. [7] TIM (1) according to claim 3 or any one of claims 4 to 6, insofar as it relates back to claim 3, wherein the mesh size of the reinforcement (3) is at least 1 mm and / or at most 15 mm. [8] TIM (1) according to any of the preceding claims, wherein the reinforcement (3) is free of plastic and in particular the TIM (1) is free of plastic. [9] TIM (1) according to any of the preceding claims, wherein the TIM (1) has a thickness of 2 mm or less than 2 mm in a relaxed state. [10] TIM (1) according to any of the preceding claims, wherein the TIM (1) is compressible to a thickness of 1 mm. [11] TIM (1) according to any of the preceding claims, wherein the plate (2) has lateral dimensions of at least 10 cm x 10 cm or of at least 10 cm x 20 cm, wherein the plate (2) in particular has lateral dimensions of 15 cm x 35 cm. [12] TIM (1) according to any of the preceding claims, wherein the expanded graphite in the relaxed state has a density of at least 0.05 g / cm³ 3 and / or of no more than 0.1 g / cm³ 3 exhibits, in particular a density of 0.07 g / cm³ 3 . [13] TIM (1) according to any of the preceding claims, wherein the reinforcement (3) is flush with an upper main surface or lower main surface of the plate (2), or wherein the reinforcement (3) is completely covered by the expandable graphite of the plate (2) towards the upper main surface and the lower main surface and / or wherein the reinforcement (3) is laterally flush with the plate (2) or laterally completely enclosed by the plate (2). [14] TIM (1) according to one of the preceding claims, wherein the expanded graphite of the plate (2) is impregnated with an impregnating agent. [15] TIM (1) according to any of the preceding claims, wherein the TIM (1) consists of the plate (2) of impregnated or unimpregnated expanded graphite and the reinforcement (3). [16] TIM (1) according to claim 14 or 15, wherein the impregnating agent is or contains silicone oil and / or wherein the pores of the expandable graphite are filled to a maximum of 50% or a maximum of 40%. [17] Energy storage device comprising a battery module (10) and a battery tray (20), wherein a thermal interface material (TIM) (1) is arranged between the battery module (10) and the battery tray (20), in particular the TIM (1) according to one of the preceding claims, wherein the TIM (1) comprises a plate (2) made of expanded graphite in which a reinforcement (3) is embedded. [18] Energy storage device according to claim 17, wherein a gap between the battery module (10) and the battery tray (20) has a height of between 0.3 mm and 2 mm and the gap is completely filled by the TIM (1). [19] Energy storage device according to claim 17 or 18, wherein the pressure exerted by the TIM (1) on the battery tray (20) and / or the battery module (10) is at most 2.5 bar. [20] Energy storage device according to one of claims 17 to 19, wherein it is a traction battery for an electric vehicle, in particular for an electric car. [21] Method for producing a thermal interface material (TIM) (1) according to any one of claims 1 to 16, for an energy storage device, wherein expanded graphite flakes are provided and the reinforcement (3) is provided between the expanded graphite flakes, wherein the graphite flakes are compacted to form a plate (2) in which the reinforcement (3) is embedded. [22] Method according to claim 21, wherein the graphite flakes form a plate (2) with a density of less than 0.1 g / cm³ 3 be compacted. [23] Method for manufacturing an energy storage device, wherein a TIM (1) is manufactured according to a method of one of claims 21 or 22, wherein the TIM (1) is placed in a battery tray (20), in particular using vacuum gripping technology, wherein a battery module (10) is pressed onto the TIM (1) by deforming the TIM (1) and the battery module (10) is fixed relative to the battery tray (20).

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