Curable thermally conductive ettringite forming compositions and their use for forming thermal interfaces in electrical devices

Abstract

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

Description

[0001] The present invention relates to a curable thermally conductive composition for use in forming a thermal interface, and an electrical device having a thermal interface formed from the composition in a cured state.

[0002] As is known from existing technology, energy storage systems, particularly high-voltage battery energy storage systems for electrically powered motor vehicles, have temperature management systems for optimal operation and performance, as well as to prevent premature aging. Battery energy storage systems for electrically powered motor vehicles typically consist of multiple battery modules, each containing multiple battery cells. The battery modules are housed in battery casings within a chassis, or individually inserted into slots that act as battery casings. Cooling or temperature control systems are located in or below their base plates to maintain the battery cells within an optimized temperature range. The temperature control system may, for example, have fluid channels in the base plate for guiding hot fluid through, and is specifically designed to dissipate heat generated during module loading and unloading, but can also be used to regulate the modules in cold weather.

[0003] However, for manufacturing reasons, a gap between the battery module containing the battery cells and the base plate of the battery casing is unavoidable. This is why a so-called thermal interface material (TI material) is introduced into the gap to establish heat transfer (either for heat dissipation or heating) between the battery cells and the base plate. For example, heat generated during loading and unloading processes can be transferred from the battery cells of the battery module to the base plate via the TI material and dissipated by a temperature control system. TI material is primarily used in the form of a so-called "gap pad" (a pre-cut viscoelastic thermally conductive pad) inserted into the battery casing, or as a so-called "gap filler" in the form of thermal paste or thermally conductive adhesive. In both cases, complete filling of the gap without gas or air inclusions, or without defects caused by unfilled gap areas, is important for optimal heat transfer.

[0004] Thermal paste is a dispersion of thermally conductive particles in a viscous carrier material, while thermally conductive adhesives have thermally conductive particles in a curable matrix that is free-flowing in its uncured state, making the thermally conductive adhesive also paste-like before curing. Applying a paste-like thermally conductive material to the thermally coupled surfaces of the respective battery modules and / or battery housings allows the thermally coupled surfaces to be wetted by pressing the paste-like thermally conductive material during the installation of the battery module into the battery housing, compensating for different gap sizes. This is only possible to a limited extent for thermally conductive pad pre-cuts. The viscous nature of the thermal paste allows material to leak from the gaps during operation when the coupled surfaces exhibit different thermal expansion behaviors, thus creating unfilled gap areas. In contrast, thermally conductive adhesives cure after application, preventing this gap-forming-related loss, but they typically have lower thermal conductivity than thermal pastes due to their matrix materials.

[0005] The thermal conductivity of a curable thermally conductive composition depends on the thermal conductivity of the filler particles used, their fraction in the composition, particle size and distribution, and the heat transfer between the filler particles and the matrix.

[0006] A TI material is known from DE 10 2021 106 551 A1, which provides an effective connection to a cooling device and meets more stringent safety requirements regarding fire. This TI material is formed from a silicone matrix and ceramic particle fillers, such that it becomes ceramic in the cured state and in response to heating above a certain temperature.

[0007] EP 1 816 175 B1 relates to a thermally conductive composition comprising 2 to 20% by weight of an acrylic polymer having a glass transition temperature in the range of 30°C to -40°C, 2 to 30% by weight of a liquid resin and optionally one or more solid resins, and 50 to 95% by weight of thermally conductive particles selected from metals, metal oxides, boron nitride, aluminum nitride, graphite, etc.

[0008] WO 2021 / 074734 A1 discloses a composition having a thermal conductivity of at least 1 W / mK after curing, comprising a cyclic olefin, a ring-opening catalyst, and at least 40% by weight of thermally conductive particles with a defined particle size distribution, said thermally conductive particles being selected from alumina, aluminum hydroxide, silicon carbide, boron nitride, aluminum nitride, graphite, and zinc oxide. The average particle size is between 10 and 30 μm, wherein at least 20-50% by volume is not greater than 10 μm, and at least 10% by volume is greater than 30-50 μm.

[0009] WO 2021 / 115810 A1 discloses a composition having a first component and a second component, the first component having a polyol, a chain extender and a surface-treated thermally conductive filler, the thermally conductive filler being a metal oxide, metal hydroxide, metal silicate or metal sulfide having isocyanate reactive groups on its surface, and the second component having an isocyanate-terminated compound.

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

[0011] WO 2020 / 176612 A1 describes a curable thermally conductive composition, the first component of which comprises a catalyst, a ceramic filler mixture, a low-volatility organic liquid, and water. The second component of the composition comprises a silane-modified reactive polymer, a low-volatility organic liquid, and the ceramic filler mixture. The low-volatility organic liquid in the composition comprises 50% by weight of the total weight of the silane-modified reactive polymer. The ceramic filler mixture has a defined particle size distribution of ceramic particles of 2.4 μm, 40 μm, and 0.3 μm.

[0012] The article "Optimized Heat Dissipation of Energy Storage Systems" by M. Frauenhofer, M. Gormanns, M. Simon, M. Rütters, and H. Fricke (from Adhesion: Adhesives + Sealants, The Trade Journal for Industrial Adhesives and Sealants, 3 / 2020, volume 17, 12-17) specifically describes methods for improving the conductivity of interstitial fillers in polymer matrices. Regarding alumina-based interstitial fillers, increased conductivity can be achieved through improved particle sphericity, narrower size distribution, and particle surface coatings that match the polymer matrix. The conductivity of interstitial fillers with aluminum filler particles is limited by the high thermal transition resistance between aluminum and the polymer matrix. When using carbon-based fillers, the achievable thermal conductivity depends not only on the fraction of filler particles but also on the type of carbon.

[0013] Further general prior art consists of DE 10 2017 127 337 A1; DE 10 2022 104 035 A1; EP3 318 538 A1 and JP 2019-163 176 A.

[0014] Cost is a critical factor for the mass production of battery energy storage in the electric mobility sector, which is why cost-effective alumina is primarily used as the thermally conductive filler particle in polymer-based matrices. Even though higher conductivity particles (such as aluminum nitride or boron nitride, for example) or higher conductivity could be achieved by increasing the particle fraction, this has been forgone for cost reasons. This is because using aluminum nitride or boron nitride particles would significantly increase material costs, and high particle concentrations lead to increased wear on processing machinery, which is associated with more frequent and expensive replacements of the corresponding metering and application components.

[0015] Thermally conductive compositions used to form thermal interfaces and for mass production of battery energy storage should therefore not only be cost-effective, but also be process-reliable to apply during the process and be curable both in terms of materials and processing.

[0016] Based on the existing technology, the purpose of this invention is to provide an improved thermal interface material.

[0017] This objective is achieved by a curable thermally conductive composition having the features of claim 1.

[0018] The use of the curable thermally conductive composition as a thermal interface is disclosed in accordance with the features of independent claim 13.

[0019] Further developments or preferred embodiments of the composition and its use are specified in the dependent claims.

[0020] According to a first embodiment, the curable thermally conductive composition for forming a thermal interface according to the present invention has a thermal conductivity of at least 1.4 W / mK after curing. The composition thus has the following components: Based on the total mass of the composition, 20 to 50% by mass of ettringite forms cement. Based on the total mass of the composition, 10 to 65% by weight of thermally conductive filler, Based on the total mass of the composition, 6 to 30% by mass of polymer particles, and The added water, the amount of which is matched to the mass fraction of the ettringite forming cement, is such that the added water exists in a bound form after the composition has cured.

[0021] The resulting ettringite ensures that the added water remains fully 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 for forming thermal interfaces can be used in electrical devices, such as, for example, energy storage devices, because the cured composition is thermally conductive but not electrically conductive.

[0022] Electrite belongs to the category of hydrous sulfate minerals and has the chemical composition Ca6Al2(SO4)3(OH). 12 • 26 H2O or the oxidized molecular formula 3CaO·Al2O3·3CaSO4·32 H2O. Etnacite has a water content of approximately 46% by mass, exhibiting a very high water of crystallization content. Etnacite is formed by the hydration of Ye'elimite (anhydrous calcium sulfoaluminate, 4CaO·3Al2O3·SO4) in the presence of readily soluble sulfates. The hydration reaction 4CaO·3Al2O3·SO3 + 2 CaSO4 + 32 H2O → 3CaO·Al2O3·3CaSO4·32H2O + 4 Al(OH)3 proceeds very rapidly, resulting in rapid solidification within approximately two hours.

[0023] The curing time of the composition according to the invention depends essentially on the curing time of the ettringite-formed cement, but is also affected by the fraction of polymer particles also contained in the composition, which results in a slight increase in curing time. However, the curing time can be shortened or lengthened accordingly by optionally adding an accelerator or a water-reducing agent, and thus can be matched to applications in the production process of electrical devices. Before curing, the composition exists in a paste state, which allows application, for example, by spraying or casting, so that the composition can be applied, for example, to housing components and can come into contact with electrical components to form a thermal interface. In the cured state, the composition is relatively soft and has a certain elasticity similar to hard rubber or solid rubber, making manual processing (such as grooving or screwing in screws, for example, with a cutter) possible without pre-drilling. These material properties not only allow for simple processing of the thermal interface even after curing, but also ensure contact between components to be thermally connected (e.g., electrical components and housing), as vibration or thermal expansion effects can be compensated to some extent. Etnacite cement not only ensures rapid curing and low shrinkage, but also participates in the matrix formation of polymer dispersions as a reactive filler, and in the matrix formation of thermally conductive fillers during heat conduction, because cement has a higher thermal conductivity than polymers.

[0024] The thermal conductivity of the cured composition, at least 1.4 W / mK, corresponds at least to the thermal conductivity of conventional interstitial fillers used during battery production. Depending on the embodiment of the composition according to the invention, and depending on the material and size of the thermally conductive filler used, the thermal conductivity of the cured composition may be higher than 1.4 W / mK, for example 2 W / mK or 3 W / mK, or even higher.

[0025] In another embodiment of the composition according to the invention, the mass ratio of added water to ettringite forming cement is in the range of 0.2 to 0.8, preferably in the range of 0.3 to 0.6. The added water is then metered so that it is completely consumed in the hydration reaction.

[0026] Further embodiments of the compositions according to the invention involve the fact that the polymer particles are redispersible polymer particles, such that the composition without added water can be provided as a storable dry mixture. Therefore, it is also an object of the invention to have ettringite forming cement, thermally conductive filler, and redispersible polymer particles, and to form a dry mixture with added water that conforms to the compositions according to the invention.

[0027] Alternatively, polymer particles can be provided as an aqueous polymer dispersion. A colloidal stable dispersion of polymer particles in an aqueous phase is referred to as a polymer dispersion. This dispersion water of the polymer dispersion thus constitutes at least a portion of the added water, i.e., the amount of dispersion water of the polymer dispersion is taken into account when matching the amount of added water to the mass fraction of ettringite-forming cement. Depending on the solids content of the polymer dispersion, additional water for supplementing the dispersion water may be entirely omitted when the dispersion water contained in the polymer dispersion is sufficient for the fraction of ettringite-forming cement contained in the composition according to the invention. For storability purposes, the composition according to this embodiment of the invention can be provided as a kit consisting of a base dry mixture (which has ettringite-forming cement and thermally conductive filler) and a polymer dispersion. The composition according to the invention is formed during the mixing of the polymer dispersion with the base dry mixture and optionally a supplementary fraction of added water, such that the kit of the base dry mixture and the polymer dispersion also represents the purpose of the invention. The dry mixture and the base dry mixture and polymer dispersion can be further formed according to other embodiments of the composition according to the invention described below.

[0028] According to another embodiment of the composition of the present invention, ettringite-formed cement may have: - Based on the total mass of the cement formed from the ettringite, 45% to 90% by mass of Ye'elimite or calcium sulfoaluminate. - Based on the total mass of the cement formed from the ettringite, 10 to 30% calcium sulfate by mass. - Based on the total mass of the cement formed from the ettringite, at least one other cement clinker phase, by mass, comprising 0 to 30% of the total mass. - Based on the total mass of the cement formed from the ettringite, 0 to 40% by mass of cement-like materials, The sum of the fractions of the at least one other cement clinker phase and the cement-like material shall not exceed 40% by mass of the ettringite-formed cement.

[0029] In a preferred embodiment, based on the total mass of the ettringite-formed cement, the ettringite-formed cement may contain 50 to 70% calcium sulfoaluminate and 15 to 25%, particularly 20%, calcium sulfate by mass. The calcium sulfate, in the form of anhydrite, gypsum, or calcined gypsum, may preferably be micronized, i.e., have a significantly reduced average particle size compared to commercially available gypsum.

[0030] Further development of the compositions according to the invention relates to the fact that optional other cement clinker phases in the ettringite-forming cement are selected from at least the group consisting of: dicalcium silicate, calcium aluminoferrite, calcium aluminate, calcium aluminosilicate, tricalcium silicate, calcium hydroxide, calcium sulfosilicate, and calcium oxide. Cement-like materials optionally included in the ettringite-forming cement may be selected from potential hydraulic materials and / or natural or artificial pozzolanic materials, including potential hydraulic slag (such as slag sand), calcium-rich and / or calcium-poor fly ash, calcined clay or shale, trast tuff, brick powder, artificial glass, silica powder, and silica-rich combustion residues of organic matter (such as rice husk ash), and combinations thereof.

[0031] Cement-like materials facilitate curing and improve the particle structure within the powder range. Potentially hydraulic materials, such as slag sand, undergo hydraulic curing in the presence of stimulants such as, for example, calcium hydroxide or calcium sulfate. Natural volcanic ash materials (such as rough tuff) and artificial volcanic ash materials (such as fly ash or silica powder) react with calcium hydroxide in response to hydration and form a hardened cement paste-like curing product.

[0032] In order to influence processability and changes in consistency and strength before or after curing, the composition according to the invention in another embodiment may further include, based on the total mass of the composition, at least 40% by weight of at least one inactive additive. One or more inactive additives are selected from at least the group consisting of: sand, stone powder (e.g., quartz powder or limestone powder), and pigments.

[0033] Substances that neither react with cement nor with water and therefore have no effect on the hydration reaction of cement are considered inactive additives. Aggregates containing inactive additives affect workability before curing and, respectively, strength or hardness after curing. Smaller particle sizes allow for easier processing of the composition and are associated with lower strength after curing. Sand thus refers to aggregates with a particle size of 0.063 to 2 mm, and is mostly composed of quartz particles, but may also contain particles of other mineral compositions. By adding stone powder, such as quartz powder (typically up to 0.25 mm in size), the powder content in the ultrafine particle range increases to 0.125 mm. Powder content not only affects workability and strength / hardness but also ensures a dense structure and contributes to the fact that the composition does not release water during and after curing. Pigments are fine-grained, mostly inorganic metal oxide particles with a size of 0.1 to 1.0 μm, which are specifically used for coloring.

[0034] In another embodiment of the composition according to the invention, the thermally conductive filler may be composed of metallic, ceramic, or carbon materials, preferably graphite or expandable graphite. Due to its high density, the thermally conductive filler can be used in a higher mass fraction than carbon particles. The mass fraction of the thermally conductive filler of graphite or expandable graphite is preferably 10 to 45% of the composition. The thermally conductive filler can thus have a particle size in the range of 100 to 1,000 μm, preferably 100 to 500 μm.

[0035] In a preferred embodiment, the thermally conductive filler may be expandable graphite particles with a particle size in the range of 100 to 1,000 μm, preferably 100 to 500 μm. In the composition according to the invention, expandable graphite not only ensures thermal conductivity but also serves a fire-resistant purpose. Due to the volume increase that occurs when the temperature of expandable graphite rises above the initial temperature, the thermal interface initially expands into the available intermediate space of the electrical device, and then overflows from the electrical device or causes its structure to expand. The electrical components are thus separated from each other, particularly thermally separated from each other, to prevent or at least delay the spread of, for example, "thermal penetration" of a battery cell to adjacent battery cells. Furthermore, the oxygen supply is blocked, making it possible to prevent or reduce fires in the electrical device, or to extinguish them, respectively. Expandable graphite is produced by intercalating graphite with an acid (usually sulfuric acid), wherein a water-insoluble salt is introduced into its layer structure, which expands the graphite layers by evaporation under heating. According to a further development, expandable graphite may have a thickness of at least 100 cm. 3 / g or at least 200 cm 3 / g or at least 300 cm 3The expandable graphite has an expansion rate of / g, wherein the expandable graphite may have an initial temperature in the range of 140°C to 270°C, preferably 180°C to 240°C. The expandable graphite may further have a particle size distribution, in which case 70% of the expandable graphite particles may be larger than 300 μm or 80% of the particles may be larger than 250 μm. In particular, 80% of the particles may be larger than 300 μm.

[0036] In another embodiment of the composition according to the invention, the polymer dispersion may be a solvent-free, saponification-resistant polymer dispersion having a solids content in the range of 50% to 70% by weight, 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 may have a solids content of 60% by weight.

[0037] When using a polymer dispersion with a solid content within a defined range, the composition according to the invention according to yet another embodiment may contain ettringite forming cement, polymer dispersion and thermally conductive filler, particularly graphite or expandable graphite, in a mass ratio of 1:1:1.

[0038] A further development of the composition according to the invention provides that the polymer particles are composed of polymers with a glass transition temperature (Tg) below 0°C, preferably below -10°C, particularly preferably below -20°C, for example at -38°C, such that the thermal interface formed by the composition and subjected to ambient temperatures does not become brittle in cold weather conditions. This is particularly important in the case of electrical devices, such as energy storage devices that can be installed in vehicles.

[0039] Suitable polymer particles, which are redispersible or exist as a dispersion, are cement-compatible, and, for example, according to another embodiment of the composition according to the invention, may consist of ethylene vinyl acetate copolymers or alkyl acrylate-based polyacrylate or acrylate copolymers, wherein the alkyl side chains of the alkyl acrylate-based polyacrylate or acrylate copolymers have at least four carbon atoms. The vinyl acetate fraction of the ethylene vinyl acetate copolymer depends on the desired low glass transition temperature and can be in the range of 7 to 20% by mass. With respect to alkyl acrylate-based polyacrylate or acrylate copolymers, the desired low glass transition temperature is achieved by a correspondingly high fraction of alkyl acrylates, whose alkyl side chains have at least four carbon atoms. Butyl acrylate or ethylhexyl acrylate are non-exclusive examples of suitable alkyl acrylates.

[0040] Further embodiments of the compositions according to the invention involve the fact that the compositions may optionally contain other components to optimize the properties of the compositions after processing and / or curing. Therefore, based on the total mass of the composition, the compositions according to the invention may further contain up to 5% by mass of an accelerator and / or up to 2% by mass of a water-reducing agent. The accelerator may be selected from the group containing salts, particularly chlorides, oxides, hydroxides, carbonates, and nitrates of alkali metals, alkaline earth metals, and earth metals, especially 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, and magnesium sulfate. If calcium oxide and calcium hydroxide are chosen as accelerators, they may also be included as optional other cement clinker phases in the composition according to the invention. In this case, the applicable ratio of their accelerators to the ratio of optional other cement clinker phases is such that the ratio of optional other cement clinker phases, including the ratio of calcium oxide or calcium hydroxide used as accelerators respectively, does not exceed 30% by mass.

[0041] Water-reducing agents can be selected from sulfonates, polycarboxylate groups, and polycarboxylate ethers. For example, lignin sulfonate, naphthaldehyde sulfonate, and melamine formaldehyde sulfonate are suitable sulfonates.

[0042] The compositions according to the invention, according to other embodiments, may optionally also contain other additives for modifying properties. Examples of such additives are defoamers or degassing agents to prevent the formation of gas or air pores, which can affect thermal conductivity after curing. Silicone-based and silicone-free defoamers are known for this purpose. Alternatively, another example of an additive is a foaming agent to create gas or air pores in the composition, which are retained during curing of the thermal interface to reduce its weight. The air pore fraction 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 water-reducing agents, can also be used as foaming agents.

[0043] The use of the composition according to the invention relates to forming a thermal interface in an electrical device between at least one electrical component and at least one housing component, the at least one housing component providing or being connected to or capable of being connected to a heat sink or 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 the composition has been cured.

[0044] The compositions according to the invention are thus cost-effective in terms of both materials and processing, and can be applied and cured in a process-reliable manner. With these properties, coupled with the thermal and mechanical material properties achievable after curing, the compositions according to the invention are suitable for mass production as thermally conductive adhesives or gap fillers for forming thermal interfaces in electrical devices.

[0045] In this context, an electrical device is understood as a device having at least one electrical component arranged within a housing or on a housing component formed for heat conduction, i.e., heat dissipation or heating. In this context, not only the housing wall defining the device externally, but also the carrier component, wall, or bottom element (which may also be located between other housing components within the housing and / or may be part of a cooling element or heat exchanger) are all part of the housing component. The composition according to the invention is then provided for application to the housing component or carrier component separately before curing, or for introduction between the housing component or carrier component and the electrical component, to form a thermal interface after curing that thermally connects the electrical component to the housing component or carrier component. All components used in electrical or electronic circuits, including energy storage devices, particularly chemical or electrical energy storage devices such as battery cells, are referred to as electrical components. Therefore, the compositions according to the invention can particularly provide for forming a thermal interface in an energy storage device having a battery housing and a plurality of battery cells, wherein the thermal interface thermally connects the battery cells to the battery housing or one or more housing components provided with heat exchangers or cooling elements for heating or cooling.

[0046] Such an electrical device may accordingly have at least one electrical component and at least one housing component as defined above, wherein the electrical component is thermally connected to the housing component via a thermal interface provided by the composition according to the invention in a cured state. For example, heat generated by the electrical component during operation can thus be dissipated to the housing component, for example, through the thermal interface, which is correspondingly composed of a thermally conductive material or has a temperature control system. Conversely, in cases where the ambient temperature is too low, heat can be supplied from the housing component to the electrical component through the thermal interface to heat the electrical component to its optimal operating temperature.

[0047] In the thermal interface region, which serves as a temperature control system, the housing component of the electrical device may have at least one fluid channel for guiding hot fluid through.

[0048] The electrical device can be an energy storage device, wherein the electrical components are battery cells, and the housing components are either battery housings or part of a heat exchanger for heat dissipation or heating. The energy storage device typically comprises multiple battery cells, which may, but need not, be grouped in a battery module, wherein each battery cell is thermally connected to the battery housing via a thermal interface provided by the composition according to the invention in a cured state.

[0049] Further embodiments of the compositions and uses according to the invention, and some advantages associated with these and further embodiments, become clear and can be more readily understood through the following detailed description with reference to the accompanying drawings. Essentially identical or similar objects or portions thereof may be provided with the same reference numerals. The drawings are merely schematic diagrams of embodiments of the invention, in which: Figure 1 A schematic cross-sectional view of the energy storage device is shown. Figure 2 It shows Figure 1 Detailed view D.

[0050] This invention relates to a curable thermally conductive composition suitable for forming a thermal interface. Figure 1 This thermal interface 5 in an energy storage device 1 is illustrated by way of example. The energy storage device 1 has a battery housing 4 having a housing bottom 4” and sidewalls 4”', in which battery modules 2 are arranged. The battery housing 4 may be part of a vehicle chassis, which typically includes multiple battery housings of this type 4 to accommodate multiple battery modules 2. Each battery module 2 has multiple battery cells 3, wherein the number of battery cells per module and the number of modules per vehicle may vary depending on the manufacturer or desired vehicle capacity. However, the use of thermally conductive compositions for forming thermal interfaces is not limited to energy storage devices with battery modules. Thermally conductive compositions can also be used to form thermal interfaces in energy storage devices with battery cells that are not grouped within modules. Thermally conductive compositions can generally be used in any electrical device to form a thermal interface between electrical components whose temperature is to be controlled and housing components (e.g., housing walls or intermediate walls, housing bottom, carrier components, or separate cooling elements or heat exchangers) for heat dissipation or supply, respectively.

[0051] In the energy storage device 1 shown in the figure, a thermal interface 5 from a cured thermally conductive composition thermally connects the battery cells 3 of the battery module 2, whose temperature is to be controlled, to the bottom 4" of the battery housing 4 in a thermally conductive manner. A temperature control or cooling system is located in the bottom 4" of the housing, and this system consists of cooling channels 4' through which a hot fluid 6 is guided to dissipate the heat transferred from the battery cells 3 to the bottom 4" of the housing via the thermal interface 5 during loading or unloading. It goes without saying that the temperature control or cooling system may also have multiple cooling channels.

[0052] In contrast to the example shown, it is further possible that thermal interfaces can be formed between the battery cell or, generally, the electrical component whose temperature is to be controlled, and the housing sidewalls, inner partition walls, or carrier plates, respectively serving as housing components for heat dissipation or heating. Similar to the bottom of the housing, corresponding cooling channels for guiding the hot fluid can also be located therein. These cooling channels are part of a cooling circuit, which may have a heat exchanger, for example, outside the housing, to dissipate the heat absorbed from the hot fluid, for example, into the environment. Furthermore, this temperature control system can be used conversely to heat the electrical components for optimal operation in cold weather, since the hot fluid is heated outside the housing to output heat to the electrical components through the thermal interfaces.

[0053] Based on the total mass of the composition, a curable thermally conductive composition for forming a thermal interface is provided, comprising 20 to 50% by mass of ettringite-forming cement, 10 to 45% by mass of thermally conductive filler, and 6 to 30% by mass of polymer particles, and added water in an amount matched to the mass fraction of the ettringite-forming cement and in the range of 0.2 to 0.8, preferably 0.3 to 0.6, such that the added water is present in a fully bound form after the composition has cured. Based on the total mass of the composition, the curable thermally conductive composition may optionally further comprise up to 40% by mass of at least one inactive additive, such as sand, stone powder, or pigment, up to 5% by mass of accelerator, and / or up to 2% by mass of water-reducing agent. The properties of the composition can be adjusted before and after curing by varying the component fractions within a specified fractional range. This involves not only thermal conductivity, which is primarily affected by the type, fraction, size, and shape of the thermally conductive filler and the cement-to-polymer ratio, but also process-related parameters such as viscosity, curing time, and post-curing material parameters such as strength, hardness, and elasticity.

[0054] Due to the rapid curing time resulting from the hydration reaction of ettringite-forming cement, the composition is produced immediately before application by mixing the components. For this purpose, a dry mixture of the composition, having ettringite-forming cement, a thermally conductive filler, and water-redispersible polymer particles, and optionally one or more other optional components, can be mixed with added water. Alternatively, the composition can be produced from a base dry mixture (having ettringite-forming cement and a thermally conductive filler, and optionally one or more other optional components) and a polymer dispersion containing polymer particles dispersed in dispersion water. In the case of this combination of base dry mixture and polymer dispersion, at least a portion of the added water is provided based on the total mass of the polymer dispersion, having a dispersion water content of 50 to 70% by mass of solids; optionally, all of the added water is provided.

[0055] Carbon particles of graphite or expandable graphite are preferably used as thermally conductive fillers, but particles of other thermally conductive materials, such as metals or ceramics, can also be used. The particle size used is at least 100 μm. Larger particle sizes, up to 1,000 μm, are advantageous because the composition can absorb a higher fraction of coarse particles than fine particles, which is associated with improved thermal conductivity. However, depending on the type of application, particle sizes up to 500 μm can respectively benefit good suitability of the composition and less wear on the metering or application device. Expandable graphite particles are preferably used as thermally conductive fillers when the fire resistance of electrical installations also needs improvement.

[0056] Based on the total mass of ettringite-formed cement, ettringite-formed cement contains 45 to 90% calcium sulfoaluminate (C4A3) by mass. Or Ye'elimite / 4CaO·3Al2O3·SO4), calcium sulfate at 10 to 30% by mass (C respectively) Or anhydrite / CaSO4, or C respectively H2 or gypsum / CaSO4·2H2O, or C H 0.5 The cement consists of calcined gypsum / CaSO4·0.5H2O, 0 to 30% by weight of at least one other cement clinker phase and 0 to 40% by weight of cement-like materials, wherein the sum of the fractions of at least one other cement clinker phase and cement-like materials does not exceed 40% by weight of cement formed from ettringite.

[0057] At least one other optional cement clinker phase may be dicalcium silicate (C2S or belite / CaO·SiO2, respectively), calcium aluminoferrite (C2(A,F) or ferrate / 2CaO(Al2O3, Fe2O3), respectively), or calcium aluminate (CA, C3A, CA2, C...). 12 A7 or aluminate / CaO·Al2O3, 3CaO·Al2O3, CaO·2Al2O3, 12CaO·7Al2O3), calcium aluminosilicate (C2AS or calcium aluminum feldspar / Ca2Al[AlSiO7] respectively), tricalcium silicate (C3S or alite / 3CaO·SiO2 respectively), calcium hydroxide (CH or calcium hydroxide / Ca(OH)2 respectively), calcium sulfosilicate (C5S2 respectively) Or ternesite / Ca5(SiO4)2(SO4)) or calcium oxide (C or free lime / CaO respectively).

[0058] Electrite-forming cements, comprising ground calcium sulfoaluminate clinker and (added) calcium sulfate in specified mass fractions, which can be used in the compositions according to the invention, are known and are commercially available in different compositions with respect to the fractions of calcium sulfoaluminate, calcium sulfate, and optional other cement clinker phases. These commercially available calcium sulfoaluminate cements (CSA cements) may optionally contain cementitious materials with potential hydraulic properties and / or natural or artificial pozzolanic materials, such as slag sand, fly ash, calcined clay or shale, rough tuff, brick powder, artificial glass, silica fume, and silica-rich combustion residues of organic matter, or may be supplemented thereto form ettringite-forming cements that can be used in the compositions according to the invention.

[0059] Two commercially available CSA cements that can be used as cement-forming ettringite in the compositions according to the present invention are i.tech® ALI CEM from HeidelbergCement AG, Germany, and DuzziUnicem Next Base from Dyckerhoff GmbH, Germany.

[0060] HeidelbergCement AG's i.tech® ALI CEM is a mixture of CSA cement (HeidelbergCement AG's i.tech® ALI PRE) and 20% by weight of added calcium sulfate. According to the manufacturer's specifications, the CSA cement ALI PRE, as the main phase, has at least 58% by weight of C4A3. (Calcium sulfoaluminate), up to 25% by weight of C2S (dicalcium silicate) and up to 5% by weight of C (Calcium sulfate) makes the mixture used as the cement-forming agent for ettringite, ALI CEM, contain at least 46.4% calcium sulfoaluminate, up to 20% dicalcium silicate, and – in total – 20 to 24% calcium sulfate by mass. The main components of the CSA cement i.tech® ALI PRE are thus 36 to 41% CaO, up to 9% SiO2, 27 to 33% Al2O3, up to 1.5% Fe2O3, 10 to 14% SO3, and up to 5% MgO by mass.

[0061] Dyckerhoff GmbH's Duzzi Unicem Next Base consists of 82% by weight of ground calcium sulfoaluminate clinker and 18% by weight of added anhydrite (calcium sulfate), and contains approximately 50% by weight of calcium sulfoaluminate. Chemically, this CSA cement consists of 41 to 45% by weight of CaO, 22 to 36% by weight of Al2O3, 8 to 9% by weight of SiO2, and 17 to 19% by weight of SO3.

[0062] Commercially available cements mentioned as examples advantageously contain added calcium sulfate. However, it goes without saying that commercially available CSA cements containing no or insufficient calcium sulfate can be used as ettringite-forming cements in the compositions according to the invention by adding appropriate amounts of calcium sulfate.

[0063] An exemplary composition according to embodiments of the invention comprises equal parts, i.e., in a 1:1:1 mass ratio, thus in each case being 33.3% by mass of ettringite-forming cement, a polymer dispersion having a 60% by mass solids fraction and a glass transition temperature (Tg) of -38°C, and expandable graphite particles with a particle size of at least 100 μm. No water is required because 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, is used as the ettringite-forming cement. In the cured state, the composition has a thermal conductivity exceeding 2 W / mK and exhibits a relatively soft material form similar to hard rubber or solid rubber. The composition can be cut, for example by hand with a cutter, and screws can be driven into it without pre-drilling.

[0064] During the production of the composition, careful mixing of the components is advantageous to avoid particle breakage, which is associated with higher water consumption. Careful mixing involves mixing for the shortest possible time at moderate temperatures and speeds. Vacuum mixers are advantageous for mixing because they prevent the introduction of air, which significantly reduces the thermal conductivity of the cured composition. Centrifugal mixers are also suitable for this purpose.

[0065] List of reference numerals 1. Energy storage device 2 Battery Module 3 Battery Units 4. Battery casing 4' Fluid Channel 4” Bottom of the casing 4”' sidewall 5. Thermal Interface 6. Thermal fluids.

Claims

1. A curable thermally conductive composition for forming a thermal interface, said composition having a thermal conductivity of at least 1.4 W / mK after curing. in, The composition has: Based on the total mass of the composition, 20 to 50% by mass of ettringite is used to form cement. Based on the total mass of the composition, 10 to 65% by weight of thermally conductive filler, Based on the total mass of the composition, 6 to 30% by mass of polymer particles, and The added water, the amount of which is matched to the mass fraction of the ettringite forming cement, is such that the added water exists in a bound form after the composition has cured.

2. The composition according to claim 1, wherein, The mass ratio of the added water to the cement formed by the ettringite is in the range of 0.2 to 0.8, preferably in the range of 0.3 to 0.

6.

3. The composition according to claim 1 or 2, wherein, The polymer particles are redispersible polymer particles or exist as an aqueous dispersion, wherein the dispersion water provides at least a portion of the added water.

4. The composition according to at least one of claims 1 to 3, wherein, The ettringite forming cement has the following properties: - Based on the total mass of the cement formed from the ettringite, 45% to 90% calcium sulfoaluminate by mass. - Based on the total mass of the cement formed from the ettringite, 10 to 30% calcium sulfate by mass. - Based on the total mass of the cement formed from the ettringite, at least one other cement clinker phase, by mass, comprising 0 to 30% of the total mass. - Based on the total mass of the cement formed from the ettringite, 0 to 40% by mass of cement-like materials, The sum of the fractions of the at least one other cement clinker phase and the cement-like material shall not exceed 40% by mass of the ettringite-formed cement.

5. The composition according to claim 4, wherein, - The at least one other cement clinker phase is selected from at least the group consisting of: dicalcium silicate, calcium aluminoferrite, calcium aluminate, calcium aluminosilicate, tricalcium silicate, calcium hydroxide, calcium sulfosilicate, calcium oxide; and / or - The cement-like material is selected from potential hydraulic materials and / or natural or artificial volcanic ash materials, including potential hydraulic slag, calcium-rich and / or calcium-poor fly ash, calcined clay or shale, rough tuff, brick powder, artificial glass, silica powder and silica-rich combustion residues of organic matter, and combinations thereof.

6. The composition according to at least one of claims 1 to 5, wherein, The composition further comprises at least one inactive additive in a weight of up to 40% based on the total mass of the composition, wherein the at least one inactive additive is selected from the group consisting of at least sand, stone powder and pigment.

7. The composition according to at least one of claims 1 to 6, wherein, The thermally conductive filler is composed of metallic, ceramic, or carbon materials, preferably graphite or expandable graphite, and / or has a particle size in the range of 100 to 1,000 μm, preferably 100 to 500 μm.

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

9. The composition according to claim 8, wherein, The composition comprises the ettringite cement, the polymer dispersion, and the thermally conductive filler in a 1:1:1 mass ratio.

10. The composition according to at least any one of claims 1 to 9, wherein, The polymer particles are composed of polymers with a glass transition temperature (Tg) below 0°C, preferably below -10°C, and particularly preferably below -20°C.

11. The composition according to at least any one of claims 1 to 10, wherein, The polymer particles are composed of ethylene vinyl acetate copolymer or alkyl acrylate-based polyacrylate or acrylate copolymer, wherein the alkyl side chain of the alkyl acrylate-based polyacrylate or acrylate copolymer has at least four carbon atoms.

12. The composition according to at least one of claims 1 to 11, wherein, Based on the total mass of the composition, the composition further comprises: - Up to 5% by weight of an accelerator, said accelerator being selected from the group consisting of salts, particularly chlorides, oxides, hydroxides, carbonates, nitrates, sulfates, and / or chlorides of alkali metals, alkaline earth metals, and earth metals, particularly lithium, sodium, potassium, calcium, magnesium, and aluminum. - Up to 2% by weight of water-reducing agent, said water-reducing agent being selected from the group consisting of sulfonates, polycarboxylic acid compounds and polycarboxylic acid ethers.

13. Use of the composition according to at least any one of claims 1 to 12 for forming a thermal interface (5) in an electrical device (1) between at least one electrical component (3) and at least one housing component (4) at a temperature to be controlled, said at least one housing component providing or being connected to or capable of being connected to a heat sink or heat source, wherein said thermal interface (5) connects said electrical component (3) to said housing component (4) in a thermally conductive manner and has a thermal conductivity of at least 1.4 W / mK after the composition has been cured.

14. Use of the composition according to claim 13, wherein, The electrical device (1) has at least one electrical component (3) and at least one housing component (4), wherein the electrical component (3) is thermally connected to the housing component (4) via the thermal interface (5), the thermal interface being provided by curing a composition according to at least any one of claims 1 to 12.

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

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 (4).

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