Curable thermally conductive ettringite-forming composition and use thereof for forming a thermal interface in an electrical device

Abstract

The present invention provides a curable thermally conductive composition and the use thereof for forming a thermal interface that has a thermal conductivity of at least 1.4 W / mK after curing. The composition has, based on the total mass of the composition, 20 to 50% by mass of ettringite-forming cement, 10 to 65% by mass of thermally conductive fillers, 6 to 30% by mass of polymer particles, and added water in an amount which is matched to the mass fraction of the ettringite-forming cement, such that the added water is present in bound form after curing of the composition. The invention further relates to the use of the thermally conductive composition for forming a thermal interface, and to an electrical device (1) having a thermal interface formed from the thermally conductive composition.

Description

[0001] Curable thermally conductive composition, its use for forming a thermal interface and electrical device

[0002] The invention relates to a curable thermally conductive composition, its use for forming a thermal interface and an electrical device having a thermal interface made of the composition in the cured state.

[0003] It is known from the prior art that energy storage systems, in particular high-voltage battery storage systems for electrically powered motor vehicles, have a temperature management system for optimal operation and performance and to prevent premature aging. A battery storage system for an electrically powered motor vehicle typically consists of several battery modules, each containing several battery cells. The battery modules are housed in a battery housing or inserted into slots in the chassis that function as battery housings. Cooling or temperature control systems are located in or under their base plate to keep the battery cells in an optimized temperature range. The temperature control system can, for example,Fluid channels in the base plate for the passage of a thermal fluid and are used in particular to dissipate the heat generated when charging and discharging the modules, but can also be used to condition the modules in cold weather.

[0004] For manufacturing reasons, however, a gap between the battery modules with the battery cells and the base plate of the battery housing is unavoidable. For this reason, so-called thermal interface materials (TI materials for short) are introduced into the gap to provide heat transfer (heat removal or supply) between the battery cells and the base plate. For example, the heat generated during charging and discharging processes can be transferred from the battery cells of the battery modules via the TI material to the base plate and dissipated by the temperature control system. TI materials are mainly used in the form of so-called “gappads,” pre-cut viscoelastic heat-conducting mats that are inserted into the battery housing, or as “gap fillers” in the form of thermal pastes or thermal adhesives. In both cases, the gap can be completely filled without the use of gas or liquid.Air inclusions or defects caused by unfilled gaps are important for optimal heat transfer.

[0005] Thermal pastes are dispersions of thermally conductive particles in a viscous carrier material, whereas thermally conductive adhesives contain the thermally conductive particles in a curable matrix that is flowable in its uncured state, so that the thermally conductive adhesive is also pasty before curing. The pasty thermal conductive material is applied to the surface of the respective battery module to be thermally coupled and / or to the thermal coupling surfaces of the battery housing. When the battery modules are installed in the battery housing, the pasty thermal conductive material is pressed into the thermal coupling surfaces to wet them, thus compensating for different gap sizes. This is only possible to a limited extent with pre-cut thermal mats. Thermal pastes remain viscous, which can lead to the material flowing out of the gap during operation and thus to the formation of unfilled gap areas if the coupling surfaces exhibit different thermal expansion behaviors.Thermally conductive adhesives, on the other hand, harden after application, so that such flow-off, which would result in gaps, cannot occur. However, due to the matrix material, they generally have a lower thermal conductivity than thermal pastes.

[0006] The thermal conductivity of the curable thermal conductivity composition depends on the thermal conductivity of the filler particles used, their proportion in the composition, the particle size and distribution and the heat transfer between the filler particles and the matrix.

[0007] DE 10 2021 106 551 A1 discloses a Tl material that enables efficient connection to a cooling system and meets stricter safety requirements in the event of a fire. The Tl material is formed with a silicone matrix and a filler made of ceramic particles, so that it becomes a ceramic when cured and heated above a certain temperature.

[0008] EP 1 816 175 B1 relates to a thermally conductive composition comprising 2 to 20 wt.% acrylic polymer with a glass transition temperature in the range of 30°C to -40°C, 2 to 30 wt.% liquid resins and optionally one or more solid resins, and 50 to 95 wt.% thermally conductive particles selected from metals, metal oxides, boron nitride, aluminum nitride, graphite, and others. WO 2021 / 074734 A1 discloses a composition with a thermal conductivity of at least 1 W / mK after curing, comprising a cyclic olefin, a ring-opening catalyst, and at least 40 wt.% thermally conductive particles with a specific particle size distribution selected from aluminum oxide, aluminum hydrate, silicon carbide, boron nitride, aluminum nitride, graphite, and zinc oxide. The average particle size is between 10 and 30 µm, with at least 20 - 50 vol% being no larger than 10 µm and at least 10 vol% being larger than 30 - 50 µm.

[0009] WO 2021 / 1 15810 A1 discloses a composition with a first component comprising a polyol, a chain extender and a surface-treated thermally conductive filler made of metal oxide, metal hydroxide, metal silicate, metal sulfide with isocyanate-reactive groups on the surface, and with a second component comprising an isocyanate-terminated compound.

[0010] WO 2019 / 120924 A1 relates to a similar composition, wherein the first component comprises two different thermally conductive fillers, one of which has a thermal conductivity of at most 50 W / mK, e.g., metal oxides, hydroxides, silicates, and sulfides, and the other of at least 80 W / mK, e.g., graphite, expandable graphite, graphene, carbon fibers or nanotubes, metal nitrides, flakes, oxides.

[0011] WO 2020 / 176612 A1 describes a thermally conductive curable composition whose first component comprises a catalyst, a ceramic filler mixture, a low-volatile organic liquid, and water. A second component of the composition comprises a silyl-modified reactive polymer, a low-volatile organic liquid, and a ceramic filler mixture. The proportion of the low-volatile organic liquid in the composition is 50 wt.% of the total weight of the silyl-modified reactive polymer. The ceramic filler mixture has a defined particle size distribution of the ceramic particles with 2.4 pm, 40 pm, and 0.3 pm.

[0012] The article "Optimized Heat Dissipation of Energy Storage Systems" (from Adhesion: Adhesives + Sealants, The Trade Journal for Industrial Adhesives and Sealants, 3 / 2020, Volume 17, 12-17) by M. Frauenhofer, M. Gormanns, M. Simon, M. Rütters, and H. Fricke describes, among other things, approaches to improving gap fillers made of conductive filler particles in a polymer matrix. With regard to aluminum oxide-based gap fillers, an increase in conductivity can be achieved through improved particle sphericity, narrower size distribution, and a surface coating of the particles tailored to the polymer matrix. The conductivity of gap fillers with aluminum filler particles is limited by the high thermal contact resistance between the aluminum and the polymer matrix. When using carbon-based fillers, the achievable thermal conductivity depends not only on the proportion of filler particles, but also on the type of carbon.

[0013] Further general prior art is formed by DE 10 2017 127 337 A1 ; DE 10 2022 104 035 A1 ; EP 3 318 538 A1 and JP 2019 - 163 176 A.

[0014] In the mass production of battery storage systems in the field of electromobility, cost is a key factor, which is why the gap fillers used in practice predominantly use cost-effective aluminum oxide as thermally conductive filler particles in a polymer-based matrix. Although higher conductivities could be achieved by using particles with higher conductivity, such as aluminum nitride or boron nitride, or by increasing the particle content, this is avoided for cost reasons. The use of aluminum nitride or boron nitride particles would significantly increase material costs, while high particle concentrations would lead to increased wear on the processing machines, which would be associated with costly, more frequent replacement of the corresponding dosing and application components.

[0015] A thermally conductive composition suitable for use in mass production of battery storage systems to form a thermal interface should therefore not only be cost-effective in terms of both the material and processing, but also be reliably applicable and curable.

[0016] Based on this prior art, it is the object of the present invention to provide an improved thermal interface material.

[0017] This object is achieved by a curable thermally conductive composition having the features of claim 1. A use of the curable thermally conductive composition as a thermal interface is disclosed by the features of independent claim 13.

[0018] Further developments or preferred embodiments of the composition and its use are set out in the subclaims.

[0019] According to a first embodiment, a curable thermally conductive composition according to the invention for forming a thermal interface has a thermal conductivity of at least 1.4 W / mK after curing of the composition. The composition comprises the following components:

[0020] 20 to 50 mass% ettringite-forming cement, based on the total mass of the composition,

[0021] 10 to 65 mass% of thermally conductive fillers, based on the total mass of the composition,

[0022] 6 to 30 mass% polymer particles, based on the total mass of the composition, and

[0023] Add water in an amount that is adjusted to the mass fraction of the ettringite-forming cement, so that the added water is bound after the composition has hardened.

[0024] The formed ettringite ensures that the added water remains completely bound and that no water escapes or is released from the composition according to the invention after curing. Therefore, it is possible that the cementitious composition according to the invention can be used to form a thermal interface in an electrical device, such as an energy storage device, since the cured composition is thermally conductive but not electrically conductive.

[0025] Ettringite belongs to the mineral class of hydrous sulfates and has the chemical composition Ca6AI2(SO4)3(OH)12-26H2O, or the oxidic molecular formula 3CaO ■ AI2O3 ■ 3CaSO4 ■ 32H2O. With a water content of approximately 46% by mass, ettringite has a very high crystal water content. Ettringite is formed by the hydration of ye'elimite (anhydrous calcium sulfoaluminate, 4CaO-3Al2O3 SO4) in the presence of readily soluble sulfate. The hydration reaction

[0026] 4CaO-3AI2O3SO3 + 2 CaSO4 + 32 H2O 3CaO AI2O3-3CaSO4-32H2O + 4 AI(OH)3 proceeds very quickly, which leads to rapid curing within approximately two hours. The curing time of the composition according to the invention depends essentially on the curing time of the ettringite-forming cement, but is also influenced by the proportion of polymer particles also contained in the composition, which lead to a slight increase in the curing time. However, the curing time can be shortened or extended accordingly by the optional addition of accelerator or plasticizer and can thus be tailored to the application of the manufacturing process of the electrical device. Before curing, the composition is in a pasty state, which allows application, for example, by spraying or pouring, so that the composition can be used to form the thermal interface, for example.It can be applied to a housing component and brought into contact with an electrical component. When cured, the compound is comparatively soft and has a certain elasticity similar to hard or solid rubber, allowing manual processing such as cutting with a utility knife or screwing in a screw without pre-drilling. These material properties not only allow for easy processing of the thermal interface even after curing, but also ensure contact between the components to be thermally connected (e.g., electrical component and housing), as vibrations or thermal expansion effects can be compensated to a certain extent.The ettringite-forming cement not only ensures rapid setting with low shrinkage, but also acts as a reactive filler material, both in matrix formation with the polymer dispersion and in heat conduction through the heat-conducting fillers, since the cement has a higher thermal conductivity than the polymer.

[0027] The thermal conductivity of the cured composition of at least 1.4 W / mK corresponds at least to the thermal conductivity of conventional gap fillers used in battery production. Depending on the embodiment of the composition according to the invention and the material and size of the thermally conductive fillers used, the thermal conductivity of the cured composition can be more than 1.4 W / mK, e.g., 2 W / mK or 3 W / mK, or even higher.

[0028] According to a further embodiment of the composition according to the invention, the mass ratio of the added water to the ettringite-forming cement is in a range from 0.2 to 0.8, preferably from 0.3 to 0.6. The added water is then measured such that it is completely consumed for the hydration reaction. Further embodiments of the composition according to the invention relate to the polymer particles being redispersible polymer particles, so that the composition can be provided as a storable dry mixture without the added water. Thus, a dry mixture comprising the ettringite-forming cement, the heat-conducting fillers, and the redispersible polymer particles, and which forms the composition according to the invention with added water, is also an object of the invention.

[0029] Alternatively, the polymer particles can be provided as an aqueous polymer dispersion. A polymer dispersion is a colloidally stable dispersion of polymer particles in an aqueous phase. This dispersion water of the polymer dispersion makes up at least a portion of the added water, i.e., when adjusting the amount of added water to the mass fraction of ettringite-forming cement, the amount of dispersion water of the polymer dispersion is taken into account. Depending on the solids content of the polymer dispersion, additional added water to supplement the dispersion water may be completely unnecessary if the dispersion water contained in the polymer dispersion is sufficient for the proportion of ettringite-forming cement contained in the composition according to the invention.For storage stability, the composition according to the invention can be provided according to this embodiment as a set comprising a base dry mix, which comprises the ettringite-forming cement and the heat-conducting fillers, and a polymer dispersion. The composition according to the invention is formed by mixing the polymer dispersion with the base dry mix and, if appropriate, a supplementary portion of added water, so that the set comprising the base dry mix and the polymer dispersion also constitutes a subject matter of the invention. Both the dry mix and the base dry mix with the polymer dispersion can also be formed according to the other embodiments of the composition according to the invention, which are described below.

[0030] According to a further embodiment of the composition according to the invention, the ettringite-forming cement may comprise:

[0031] - 45 to 90 mass% of ye'elimite or calcium sulfoaluminate, based on the total mass of the ettringite-forming cement,

[0032] - 10 to 30 mass% calcium sulfate, based on the total mass of the ettringite-forming cement, - 0 to 30 mass% of at least one further cement-clinker phase, based on the total mass of the ettringite-forming cement,

[0033] - 0 to 40 mass% of a cementitious material, based on the total mass of the ettringite-forming cement, wherein the sum of the proportions of the at least one further cement clinker phase and the cementitious material does not exceed 40 mass% of the ettringite-forming cement.

[0034] In a preferred embodiment, the ettringite-forming cement can contain 50 to 70 mass% calcium sulfoaluminate and 15 to 25 mass%, in particular 20 mass% calcium sulfate, based on the total mass of the ettringite-forming cement. Calcium sulfate, in the form of anhydrite, gypsum, or bassanite, can preferably be micronized, i.e., have a significantly reduced average particle size compared to commercially available gypsum.

[0035] Further developments of the composition according to the invention relate to the fact that the optional further cement-clinker phase in the ettringite-forming cement is selected from a group comprising at least dicalcium silicate, calcium aluminate ferrite, calcium aluminates, calcium aluminate silicate, tricalcium silicate, calcium hydroxide, calcium sulfate silicate, and calcium oxide. The cementitious material optionally contained in the ettringite-forming cement can be selected from latent-hydraulic materials and / or natural or artificial pozzolanic materials, which include latent-hydraulic slags such as granulated blast furnace slag, lime-rich and / or lime-poor fly ash, calcined clays or slates, trass, brick dust, artificial glasses, microsilica, and silicon-rich combustion residues of organic substances such as rice husk ash, and combinations thereof.

[0036] The cementitious material contributes to hardening and improves the grain structure in the powder area. Latent-hydraulic materials such as granulated blast furnace slag harden hydraulically in the presence of an activator such as calcium hydroxide or calcium sulfate. Natural pozzolanic materials such as trass and artificial pozzolanic materials such as fly ash or microsilica react with calcium hydroxide upon hydration and form cement paste-like hardening products. Furthermore, according to a further embodiment, the composition according to the invention can contain up to 40% by mass of at least one inactive additive, based on the total mass of the composition, to influence the workability and vary the consistency and strength before or after hardening. The inactive additive(s) are selected from a group comprising at least sand, rock flour, e.g., quartz flour or limestone flour, and pigments.

[0037] Inactive additives are substances that react neither with cement nor with water and therefore have no effect on the hydration reactions of the cement. The aggregate size of the inactive additives influences the processing before curing and the strength or hardness after curing. Smaller grain sizes allow for easier processing of the composition and are associated with lower strength after curing. Sand refers to an aggregate with a grain size of 0.063 to 2 mm and usually consists predominantly of quartz grains, but can also contain grains of other mineral compositions. By adding rock flour such as quartz flour (typical grain size up to 0.25 mm), the fines content is increased in the finest grain range up to 0.125 mm.The fine-grain content not only influences workability and strength / hardness, but also ensures a closed structure and helps prevent the composition from releasing water during and after curing. Pigments are fine-grained, mostly inorganic particles made of metal oxides with a size of 0.1 to 1.0 pm, which are primarily used for coloring.

[0038] According to a further embodiment of the composition according to the invention, the thermally conductive fillers can consist of a metal, ceramic, or carbon material, preferably graphite or expanded graphite. Due to their high density, thermally conductive fillers can be used in higher mass fractions than carbon particles. The mass fraction of the thermally conductive fillers made of graphite or expanded graphite can preferably be 10 to 45% of the composition. The thermally conductive fillers can have a particle size in a range of 100 to 1,000 μm, preferably 100 to 500 μm.

[0039] In a preferred embodiment, the thermally conductive fillers can be expanded graphite particles with a particle size in the range of 100 to 1,000 μm, preferably 100 to 500 μm. Expandable graphite, also known as expandable graphite, not only provides thermal conduction in the composition according to the invention but also serves as fire protection. Due to the volume increase of the expandable graphite, which occurs when the temperature rises above the starting temperature, the thermal interface initially expands into existing gaps in the electrical device before bulging out of the electrical device or expanding its structure. This separates the electrical components from one another, in particular thermally, in order to, for example, prevent or at least delay the propagation of a "thermally runaway" cell to neighboring cells.In addition, the oxygen supply is blocked, so that fires in the electrical device can be prevented, reduced, or extinguished. Expandable graphite is produced by intercalation of graphite using acids, usually sulfuric acid. Water-insoluble salts are introduced into the layered structure, which, under the influence of heat, force the graphite layers apart through evaporation. According to a further development, the expandable graphite can have an expansion rate of at least 100 cm³. 3 / g or at least 200 cm 3 / g or at least 300 cm 3 / g, wherein the expandable graphite can have a starting temperature in a range from 140 °C to 270 °C, preferably from 180 °C to 240 °C. Furthermore, the expandable graphite can have a particle size distribution in which 70% of the expandable graphite particles can be larger than 300 pm or 80% of the particles can be larger than 250 pm. In particular, 80% of the particles can be larger than 300 pm.

[0040] Furthermore, according to a further embodiment of the composition according to the invention, the polymer dispersion can be a solvent-free, saponification-resistant polymer dispersion with a solids content in a range of 50 to 70% by mass, wherein the solids content is based on the total mass of the polymer dispersion. For example, the polymer dispersion of the composition according to the invention can have a solids content of 60% by mass.

[0041] When using a polymer dispersion with the solids content in the defined range, the composition according to the invention can, according to yet another embodiment, comprise the ettringite-forming cement, the polymer dispersion and the heat-conducting fillers, in particular made of graphite or expandable graphite, in a mass ratio of 1:1:1.

[0042] According to a further development of the composition according to the invention, the polymer particles consist of a polymer with a glass transition temperature (Tg) below 0 °C, preferably below -10 °C, particularly preferably below -20 °C, for example -38 °C, so that the thermal interfaces formed from the composition, which are exposed to the ambient temperature, do not become brittle in frost. This is particularly important for electrical devices such as energy storage devices that may be installed in vehicles.

[0043] Suitable redispersible or dispersed polymer particles are cement-compatible and, for example, according to a further embodiment of the composition according to the invention, can consist of an ethylene-vinyl acetate copolymer or an alkyl acrylate-based polyacrylate or acrylate copolymer whose alkyl side chain has at least four carbon atoms. The vinyl acetate content of an ethylene-vinyl acetate copolymer depends on the desired low glass transition temperature and can range from 7 to 20% by mass. With regard to the alkyl acrylate-based polyacrylate or acrylate copolymer, the desired low glass transition temperature is achieved by a correspondingly high proportion of the alkyl acrylate whose alkyl side chain has at least four carbon atoms. Non-exclusive examples of a suitable alkyl acrylate are butyl or ethylhexyl acrylate.

[0044] Further embodiments of the composition according to the invention relate to the fact that the composition can optionally comprise further components in order to optimize the properties of the composition for processing and / or after curing. Thus, the composition according to the invention can further comprise up to 5% by mass of accelerator and / or up to 2% by mass of plasticizer, based on the total mass of the composition. The accelerator can be selected from a group comprising salts, in particular chlorides, oxides, hydroxides, carbonates, and nitrates, of alkali metals, alkaline earth metals, and earth metals, in particular lithium, sodium, potassium, calcium, magnesium, and aluminum.Examples of accelerators include aluminum sulfate, calcium oxide, calcium hydroxide, calcium chloride, calcium nitrate, potassium hydroxide, potassium sulfate, potassium carbonate, sodium hydroxide, sodium sulfate, sodium carbonate, sodium nitrate, lithium hydroxide, lithium chloride, lithium carbonate, magnesium chloride, magnesium sulfate. If calcium oxide and calcium hydroxide are selected as accelerators, which can also be included as an optional additional cement-clinker phase in the composition according to the invention, their proportion as accelerators is counted towards the proportion of the optional additional cement-clinker phase, so that the proportion of the optional additional cement-clinker phase, including the proportion of calcium oxide or calcium hydroxide used as an accelerator, should not exceed 30% by mass. A plasticizer can be selected from sulfonates, polycarboxylates, and polycarboxylate ethers.Suitable sulfonates include ligninsulfonates, naphthaleneformaldehydesulfonates and melamineformaldehydesulfonates.

[0045] Optionally, according to further embodiments, a composition according to the invention can comprise further additives to modify its properties. Examples of these are defoamers or degassing agents to prevent the formation of gas or air pores that can impair thermal conduction after curing. Silicone-based and silicone-free defoamers are known for this purpose. Further alternative examples of additives are foaming agents to create gas or air pores in the composition that are retained during the curing of the thermal interface in order to reduce its weight. The air void content of such a lightweight interface is preferably at most 20% so that the thermal conductivity of the thermal interface is not significantly reduced. Surfactants and / or proteins can be used as foaming agents. Lignosulfonates, which act as plasticizers, can also be used as foaming agents.

[0046] An inventive use of the composition according to the invention relates to the formation of a thermal interface in an electrical device between at least one electrical component and at least one housing component which provides a heat sink or a heat source or is connected or connectable to a heat sink or a heat source, wherein the thermal interface connects the electrical component to the housing component in a thermally conductive manner and has a thermal conductivity of at least 1.4 W / mK after curing of the composition.

[0047] The composition according to the invention is cost-effective both in terms of material and processing, and can also be applied and cured reliably. Due to these properties, in conjunction with the thermal and mechanical material properties achievable after curing, the composition according to the invention is suitable for use in mass production as a thermally conductive adhesive or gap filler for forming a thermal interface in an electrical device. In the present case, an electrical device is understood to mean a device with at least one electrical component that is arranged in a housing or on a housing component that is designed for heat conduction, i.e. heat dissipation or heat supply.In the present case, the housing components include not only the housing walls that delimit the device to the outside, but also support components, wall or floor elements, which can also be located within a housing between other housing components and / or can be part of a heat sink or heat exchanger. The composition according to the invention is then intended to be applied to the housing or support component before curing or to be introduced between the housing or support component and the electrical component in order to form the thermal interface after curing, which connects the electrical component to the housing or support component in a thermally conductive manner. Electrical components are all components that are used in electrotechnical or electronic circuits, including energy storage devices, in particular chemical energy storage devices or storage devices for electrical energy such as battery cells.Thus, the composition according to the invention can in particular also be provided for forming a thermal interface in an energy storage device which has a battery housing and a plurality of battery cells, wherein the thermal interface connects the battery cells in a thermally conductive manner to the housing component(s) of the battery housing or of a heat exchanger or heat sink provided for heat supply or dissipation.

[0048] Accordingly, such an electrical device can comprise at least one electrical component and at least one housing component as defined above, wherein the electrical component is thermally conductively connected to the housing component by a thermal interface provided by a composition according to the invention in the cured state. Thus, for example, the heat generated by the electrical component during operation can be dissipated via the thermal interface to the housing component, which accordingly consists of a thermally conductive material or has a temperature control system. Conversely, if the ambient temperature is too low, heat can be supplied to the electrical component from the housing component via the thermal interface in order to heat the electrical component to an optimal operating temperature.The housing component of the electrical device can have at least one fluid channel for the passage of a thermal fluid in the region of the thermal interface as a temperature control system.

[0049] The electrical device may be an energy storage device, wherein the electrical component is a battery cell and the housing component is a part of a battery housing designed for heat dissipation or supply, or a heat exchanger. Typically, an energy storage device contains a plurality of battery cells, which may or may not be grouped into battery modules, each battery cell being thermally connected to the battery housing by a thermal interface provided by the composition according to the invention in the cured state.

[0050] Further embodiments of the composition and use according to the invention, as well as some of the advantages associated with these and other embodiments, will become clear and better understood from the following detailed description with reference to the accompanying figures. Items or parts thereof that are substantially the same or similar may be provided with the same reference numerals. The figures are merely a schematic representation of one embodiment of the invention.

[0051] Showing:

[0052] Fig. 1 is a schematic cross-sectional view of an energy storage device, Fig. 2 is a detailed view D from Fig. 1 .

[0053] The invention relates to a curable, thermally conductive composition suitable for forming a thermal interface. Figure 1 shows a schematic example of such a thermal interface 5 in an energy storage device 1. The energy storage device 1 has a battery housing 4 with a housing base 4" and side walls 4'", in which a battery module 2 is arranged. The battery housing 4 can be part of a vehicle chassis, which usually comprises several such battery housings 4 in order to accommodate several battery modules 2. Each battery module 2 has a plurality of battery cells 3, wherein the number of cells per module and the number of modules per vehicle can vary depending on the manufacturer or the desired vehicle capacity. However, the use of the thermally conductive composition for forming a thermal interface is not limited to energy storage devices with battery modules.The thermally conductive composition can also be used to form a thermal interface in energy storage devices with battery cells that are not grouped in modules. In principle, the thermally conductive composition can be used in any electrical device to form a thermal interface between an electrical component to be temperature-controlled and a housing component designed for heat dissipation or supply, such as a housing or partition wall, a housing base, a support component, or a heat sink or heat exchanger.

[0054] In the energy storage device 1 shown in the figures, a thermal interface 5 made of the cured thermally conductive composition connects the battery cells 3 of the battery module 2, which are to be tempered, to the housing base 4" of the battery housing 4 in a thermally conductive manner. Located in the housing base 4" is a temperature control or cooling system consisting of a cooling channel 4' through which a thermal fluid 6 is passed in order to dissipate heat that was transferred from the battery cells 3 to the housing base 4" via the thermal interface 5 during charging or discharging. Of course, it is also possible for a temperature control or cooling system to have multiple cooling channels.

[0055] Contrary to what is shown, it is also possible for a thermal interface between the battery cells or, in general, an electrical component to be temperature-controlled and a side wall of a housing, an inner partition wall, or carrier plate to be designed as a heat-dissipating or heat-dissipating housing component. Analogous to the housing base, corresponding cooling channels for the passage of a thermal fluid can also be located therein. The cooling channels are part of a cooling circuit which, for example, can have a heat exchanger outside the housing to dissipate the heat absorbed by the thermal fluid, for example to the environment. Furthermore, such a temperature control system can conversely be used in cold weather to heat the electrical component for optimal operation by heating the thermal fluid outside the housing in order to transfer the heat to the electrical component via the thermal interface.

[0056] The curable, thermally conductive composition intended to form the thermal interface comprises, based on the total mass of the composition, 20 to 50 mass% of ettringite-forming cement, 10 to 45 mass% of thermally conductive fillers, and 6 to 30 mass% of polymer particles, as well as added water in an amount that is adjusted to the mass fraction of the ettringite-forming cement and lies in a range of 0.2 to 0.8, preferably 0.3 to 0.6, so that the added water is completely bound after the composition has cured. Optionally, the curable, thermally conductive composition can further comprise, based on the total mass of the composition, up to 40 mass% of at least one inactive additive such as sand, rock flour, or pigments, up to 5 mass% of accelerator, and / or up to 2 mass% of plasticizer.By varying the proportions of the components within the specified ranges, the properties of the composition before and after curing can be adjusted. This affects not only the thermal conductivity, which is primarily influenced by the type, proportion, size, and shape of the thermally conductive fillers, but also by the cement-to-polymer ratio, but also processing-relevant parameters such as viscosity, curing time, and post-curing material parameters such as strength, hardness, and elasticity.

[0057] Due to the rapid setting time caused by the hydration reaction of the ettringite-forming cement, the composition is prepared by mixing the components immediately prior to application. For this purpose, a dry mix of the composition, which comprises the ettringite-forming cement, the thermally conductive fillers, and water-redispersible polymer particles, as well as one or more of the optional components, can be mixed with added water. Alternatively, the composition can be prepared from a base dry mix, which comprises the ettringite-forming cement and the thermally conductive fillers, as well as one or more of the optional components, and a polymer dispersion containing the polymer particles dispersed in dispersion water.In this set of base dry mix and polymer dispersion, the dispersion water, with a solids content of 50 to 70 mass% based on the total mass of the polymer dispersion, provides at least part of the addition water, if necessary all of the addition water.

[0058] Carbon particles made of graphite or expanded graphite are preferably used as thermally conductive fillers, but particles made of other thermally conductive materials such as metal or ceramic can also be used. The particle size of the particles used is at least 100 pm. Large particle sizes of up to 1,000 pm are advantageous because the composition can absorb a higher proportion of coarser particles, which is associated with better thermal conductivity, than fine particles. Depending on the type of application, however, particle sizes of up to 500 pm can be advantageous for good applicability and metering of the composition or for reduced wear on the application device. Expanded graphite particles are preferably used as thermally conductive fillers if the fire protection of an electrical device also needs to be improved.

[0059] The ettringite-forming cement comprises, based on the total mass of the ettringite-forming cement, 45 to 90 mass% calcium sulfoaluminate (cement chemical abbreviation C4A3S or Ye'elimit CaO'SAhOs SC ), 10 to 30 mass% calcium sulfate (CS or anhydrite / CaSC or CSH2 or gypsum / CaSO4'2H2O or CSH0.5 bassanite / CaSO4'0.5H2O), 0 to 30 mass% of at least one further cement clinker phase and 0 to 40 mass% of a cement-like material, wherein the sum of the proportions of the at least one further cement clinker phase and the cement-like material does not exceed 40 mass% of the ettringite-forming cement.

[0060] The optional at least one further cement clinker phase can be dicalcium silicate (C2S or belite / CaO-SiO2), calcium aluminate ferrite (C2(A,F) or ferrite / 2CaO(AI2O3, Fe2O3)), calcium aluminates (C1A, C3A, C12, C12A7 or aluminates / CaO-AI2O3, 3CaO-AI2O3, CaO-2AI2O3, 12CaO-7AI2O3), calcium aluminate silicate (C2A5 or gehlenite / Ca2AI[AISiO?]), tricalcium silicate (C3S or alite / 3CaO-SiO2), calcium hydroxide (CH or portlandite / Ca(OH)2), calcium sulfate silicate (CsS2S or ternesite / Ca5(SiO4)2(SO4)) or calcium oxide (C or free Lime / CaO).

[0061] Ettringite-forming cements usable in the composition according to the invention, which contain calcium sulfoaluminate from ground calcium sulfoaluminate clinkers and (added) calcium sulfate within the specified mass fractions, are known and commercially available in various compositions with respect to the proportions of calcium sulfoaluminate, calcium sulfate, and optionally other cement-clinker phases. These commercially available calcium sulfoaluminate cements (CSA cements) can optionally contain, or be supplemented with, cementitious material from latent-hydraulic and / or natural or artificial pozzolanic materials such as granulated blast furnace slag, fly ash, calcined clays or slates, trass, brick dust, artificial glasses, microsilica, and silicon-rich combustion residues of organic substances to form the ettringite-forming cement usable in the composition according to the invention.Two examples of commercially available CSA cement that can be used as ettringite-forming cement in a composition according to the invention are i.tech® ALI CEM from HeidelbergCement AG, Germany, and Duzzi llnicem Next Base from Dyckerhoff GmbH, Germany.

[0062] i.tech® ALI CEM from HeidelbergCement AG is a mixture of a CSA cement (i.tech® ALI PRE from HeidelbergCement AG) and 20 mass% added calcium sulfate. According to the manufacturer's specifications, the CSA cement ALI PRE contains as its main phases at least 58 mass% C4A3S (calcium sulfoaluminate), at most 25 mass% C2S (dicalcium silicate), and at most 5 mass% CS (calcium sulfate). Thus, the ALI CEM mixture used as an ettringite-forming cement contains at least 46.4 mass% calcium sulfoaluminate, at most 20 mass% dicalcium silicate, and – in total – 20 to 24 mass% calcium sulfate. The main components of the CSA cement i.tech® ALI PRE are 36 to 41 mass% CaO, maximum 9 mass% SiO2, 27 to 33 mass% AI2O3, maximum 1.5 mass% Fe2O3, 10 to 14 mass% SO3, and maximum 5 mass% MgO.

[0063] Duzzi Unicem Next Base from Dyckerhoff GmbH consists of 82% by mass of ground calcium sulfoaluminate clinker and 18% by mass of added anhydrite (calcium sulfate) and contains approximately 50% by mass of calcium sulfoaluminate. Chemically, this CSA cement is composed of 41 to 45% by mass CaO, 22 to 36% by mass Al2O3, 8 to 9% by mass SiO2, and 17 to 19% by mass SO3.

[0064] The commercially available cements mentioned as examples advantageously already contain added calcium sulfate. Of course, commercially available CSA cements that contain no or insufficient calcium sulfate can also be used as ettringite-forming cement in a composition according to the invention by adding an appropriate amount of calcium sulfate.

[0065] An exemplary composition according to an embodiment of the invention comprises in equal parts, i.e. in a mass ratio of 1:1:1, i.e. 33.3 mass% each of an ettringite-forming cement, a polymer dispersion with 60 mass% solids content and a glass transition temperature (Tg) of -38°C, and expandable graphite particles with a particle size of at least 100 pm. The addition of water is not necessary, as the water contained in the polymer dispersion is sufficient for the reaction of the ettringite-forming cement. i.tech® ALI CEM from HeidelbergCement AG, Germany, was used as the ettringite-forming cement. In the cured state, the composition has a thermal conductivity of over 2 W / mK and is a comparatively soft material similar to hard or solid rubber, which can be cut by hand with a utility knife, for example, and into which screws can be screwed without pre-drilling.

[0066] During the preparation of the composition, gentle mixing of the components is advantageous to avoid particle size reduction, which would require a higher water requirement. Gentle mixing involves the shortest possible mixing time at a moderate temperature and rotational speed. A vacuum mixer is advantageous for mixing, as it avoids the introduction of air, which would significantly reduce the thermal conductivity of the cured composition. Centrifugal mixers are also suitable.

[0067] LIST OF REFERENCE SYMBOLS

[0068] 1 energy storage device

[0069] 2 battery module

[0070] 3 battery cells

[0071] 4 battery housings

[0072] 4' fluid channel

[0073] 4" case back

[0074] 4'“ side walls

[0075] 5 Thermal interface

[0076] 6 Thermofluid

Claims

PATENT CLAIMS 1 . A curable thermally conductive composition for forming a thermal interface which, after curing, has a thermal conductivity of at least 1.4 W / mK, the composition comprising: 20 to 50 mass% ettringite-forming cement, based on the total mass of the composition, 10 to 65 mass% of thermally conductive fillers, based on the total mass of the composition, 6 to 30 mass% polymer particles, based on the total mass of the composition, and Add water in an amount that is adjusted to the mass fraction of the ettringite-forming cement, so that the added water is bound after the composition has hardened.

2. Composition according to claim 1, wherein a mass ratio of the added water to the ettringite-forming cement is in a range of 0.2 to 0.8, preferably 0.3 to 0.

6.

3. Composition according to claim 1 or 2, wherein the polymer particles are redispersible polymer particles or are present as an aqueous polymer dispersion, wherein the dispersion water provides at least a portion of the addition water.

4. Composition according to at least one of claims 1 to 3, wherein the ettringite-forming cement comprises: - 45 to 90 mass% calcium sulfoaluminate based on the total mass of the ettringite-forming cement, - 10 to 30 mass% calcium sulfate based on the total mass of the ettringite-forming cement, - 0 to 30 mass% of at least one further cement-clinker phase based on the total mass of the ettringite-forming cement, - 0 to 40 mass% of a cementitious material based on the total mass of the ettringite-forming cement, wherein a sum of the proportions of the at least one further cement-clinker phase and the cementitious material does not amount to more than 40 mass% of the ettringite-forming cement.

5. Composition according to claim 4, wherein - the at least one further cement clinker phase is selected from a group comprising at least dicalcium silicate, calcium aluminate ferrite, calcium aluminate, calcium aluminate silicate, tricalcium silicate, calcium hydroxide, calcium sulfate silicate, calcium oxide; and / or - the cementitious material is selected from latent hydraulic materials and / or natural or artificial pozzolanic materials, including latent hydraulic slags, lime-rich and / or lime-poor fly ash, calcined clays or slates, trass, brick dust, artificial glasses, microsilica and silicon-rich combustion residues of organic substances and combinations thereof.

6. Composition according to at least one of claims 1 to 5, wherein the composition further comprises up to 40% by mass of at least one inactive additive, based on the total mass of the composition, wherein the at least one inactive additive is selected from a group comprising at least sand, rock flour and pigments.

7. Composition according to at least one of claims 1 to 6, wherein the thermally conductive fillers consist of a metal, ceramic or carbon material, preferably of graphite or expandable graphite, and / or have a particle size in a range of 100 to 1,000 pm, preferably 100 to 500 pm.

8. Composition according to at least one of claims 3 to 7, wherein the polymer dispersion is a solvent-free, saponification-resistant polymer dispersion having a solids content in a range of 50 to 70 mass% based on the total mass of the polymer dispersion.

9. Composition according to claim 8, wherein the composition comprises the ettringite-forming cement, the polymer dispersion and the heat-conducting fillers in a mass ratio of 1 :1 :

1.

10. Composition according to at least one of claims 1 to 9, wherein the polymer particles consist of a polymer having a glass transition temperature (Tg) which is below 0 °C, preferably below -10 °C, particularly preferably below -20 °C.

11. Composition according to at least one of claims 1 to 10, wherein the polymer particles consist of an ethylene-vinyl acetate copolymer or an alkyl acrylate-based polyacrylate or acrylate copolymer whose alkyl side chain has at least four C atoms.

12. Composition according to at least one of claims 1 to 11, wherein the composition further comprises, based on the total mass of the composition: - up to 5 mass% of accelerator selected from a group comprising salts, in particular chlorides, oxides, hydroxides, carbonates, nitrates, sulfates of alkali, alkaline earth and earth metals, in particular lithium, sodium, potassium, calcium, magnesium and aluminum, and / or - up to 2% by mass of plasticizer selected from a group comprising sulfonates, polycarboxylates and polycarboxylate ethers.

13. Use of a composition according to at least one of claims 1 to 12 for forming a thermal interface (5) in an electrical device (1) between at least one electrical component (3) to be temperature-controlled and at least one housing component (4) which provides a heat sink or a heat source or is connected or connectable to a heat sink or a heat source, wherein the thermal interface (5) connects the electrical component (3) to the housing component (4) in a heat-conducting manner and has a thermal conductivity of at least 1.4 W / mK after the composition has cured.

14. Use of the composition according to claim 13, wherein the electrical device (1) comprises at least one electrical component (3) and at least one housing component (4), wherein the electrical component (3) is thermally conductively connected to the housing component (4) by the thermal interface (5) which is formed by the Composition according to at least one of claims 1 to 12 is provided by curing.

15. Use of the composition according to claim 14, wherein the housing component (4) has at least one fluid channel (4') for the passage of a thermal fluid (6) in the region of the thermal interface (5).

16. Use of the composition according to claim 14 or 15, wherein the electrical device (1) is an energy storage device (1 ), and the electrical component (3) is a battery cell (3) and the housing component (4) is a battery housing

Images