Curable heat-conducting composition and its use for forming a thermal interface

Abstract

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

Description

[0001] The invention relates to a curable thermally conductive composition and its use for forming a thermal interface.

[0002] It is known from the prior art that energy storage systems, in particular high-voltage battery storage systems for electrically powered vehicles, have a temperature management system for optimal operation and performance and to prevent premature aging. A battery storage system for an electrically powered vehicle typically consists of several battery modules, each containing several battery cells. The battery modules are housed in a battery casing or inserted into compartments in the chassis that function as battery casings. Cooling and / or temperature control systems are located in or under their base plate to maintain the battery cells within an optimized temperature range. The temperature control system can, for example,The base plate has fluid channels for the passage of a thermofluid and serves in particular to remove the heat generated during the charging and discharging of the modules, but can also be used to condition the modules in cold weather.

[0003] Due to the manufacturing process, a gap between the battery modules containing the battery cells and the base plate of the battery housing is unavoidable. Therefore, so-called thermal interface materials (TI materials) are inserted into this gap to facilitate heat transfer (heat dissipation 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 to the base plate via the TI material and dissipated by the temperature control system. TI materials are primarily used in the form of so-called "gappads," pre-cut viscoelastic thermally conductive mats that are inserted into the battery housing, or as "gap fillers" in the form of thermally conductive pastes or adhesives. In both cases, complete filling of the gap without gas or other gas leakage is essential.Air inclusions or defects due to unfilled gaps are important for optimal heat transfer.

[0004] Thermal pastes are dispersions of thermally conductive particles in a viscous carrier material, while thermal adhesives contain the thermally conductive particles in a curable matrix that is flowable in its uncured state, so thermal adhesives are also pasty before curing. The pasty thermal interface material is applied to the thermally coupled surface of the respective battery module and / or to the thermal coupling surfaces of the battery housing. When the battery modules are installed in the battery housing, the thermal coupling surfaces are wetted by pressing the pasty thermal interface material into place, thus compensating for different gap dimensions. This is only possible to a limited extent with pre-cut thermal interface mats. Thermal pastes remain viscous, which can lead to material flowing out of the gap during operation, resulting in unfilled gap areas if the coupling surfaces have different coefficients of thermal expansion.Thermally conductive adhesives, on the other hand, harden after application, so that such flow-through associated with gap formation cannot occur, but due to the matrix material they generally have a lower thermal conductivity than thermal pastes.

[0005] 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.

[0006] From DE 10 2021 106 551 A1, a thermally inert material (TI) is known that enables efficient connection to a cooling system and meets stricter safety requirements in the event of a fire. The TI material consists of a silicone matrix and a filler made of ceramic particles, such that it becomes a ceramic when cured and heated above a specific temperature.

[0007] 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, aluminium nitride, graphite, etc.

[0008] 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 mean particle size is between 10 and 30 µm, with at least 20–50 vol.% not larger than 10 µm and at least 10 vol.% larger than 30–50 µm.

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

[0010] WO 2019 / 120924 A1 concerns a similar composition, wherein the first component comprises two different thermally conductive fillers, one of which has a thermal conductivity of not more than 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, or oxides.

[0011] WO 2020 / 176612 A1 describes a thermally conductive, curable composition, the first component of which comprises a catalyst, a ceramic filler mixture, a low-volatility organic liquid, and water. A second component of the composition comprises a silyl-modified reactive polymer, a low-volatility organic liquid, and a ceramic filler mixture. The proportion of the low-volatility 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 ceramic particles with 2.4 µm, 40 µm, and 0.3 µm.

[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. Fraunhofer, 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, increased conductivity can be achieved through improved particle sphericity, a narrower particle 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 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 for electromobility, cost is a crucial factor. Therefore, in practical applications, aluminum oxide is predominantly used as a cost-effective thermally conductive filler particle in a polymer-based matrix for gap fillers. Although higher conductivities could be achieved by using particles with higher conductivity, such as aluminum nitride or boron nitride, or by increasing the particle fraction, 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 machinery, resulting in more frequent and costly replacement of the corresponding dosing and application components.

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

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

[0017] This problem is solved by a curable, heat-conducting composition having the features of claim 1.

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

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

[0020] 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. The composition comprises the following components: 20 to 50% by mass ettringite-forming cement, based on the total mass of the composition, 10 to 65% by mass of thermally conductive fillers, based on the total mass of the composition, 6 to 30% by mass of polymer particles, based on the total mass of the composition, and Added water in an amount that is tailored to the mass fraction of the ettringite-forming cement, so that the added water is bound after the composition has hardened.

[0021] The ettringite formed ensures that the added water remains completely bound and that no water escapes or is released from the composition according to the invention after hardening. Therefore, it is possible for the cement-containing composition according to the invention to be used to form a thermal interface in an electrical device such as an energy storage device, since the hardened composition is thermally conductive but not electrically conductive.

[0022] Ettringite belongs to the mineral class of hydrous sulfates and has the chemical composition Ca6Al2(SO4)3(OH) 12·26 H2O or the oxide formula 3CaO · Al2O3 · 3CaSO4 · 32H2O. With a water content of approximately 46% by mass, ettringite has a very high water content. Ettringite is formed by the hydration of Ye'elimit (anhydrous calcium sulfoaluminate, 4CaO·3Al2O3·SO4) in the presence of readily soluble sulfate. The hydration reaction 4CaO·3Al2O3·SO3 + 2 CaSO4 + 32 H2O → 3CaO·Al2O3·3CaSO4·32H2O + 4 Al(OH)3 The curing process is very rapid, resulting in fast hardening within approximately two hours. The curing time of the composition according to the invention depends primarily on the curing time of the ettringite-forming cement, but is also influenced by the proportion of polymer particles contained in the composition, which slightly increases the curing time. However, the curing time can be shortened or lengthened accordingly by the optional addition of an accelerator or liquefier, and can thus be tailored to the manufacturing process of the electrical device. Before curing, the composition is in a paste-like state, allowing application, for example, by injection or pouring, so that the composition can be applied to, for example, a housing component to form the thermal interface and brought into contact with an electrical component.In its cured state, the composition is relatively soft and possesses a degree of elasticity similar to hard or solid rubber, allowing for manual processing such as cutting with a utility knife or inserting a screw without pre-drilling. These material properties not only permit easy processing of the thermal interface even after curing, but also ensure contact between the thermally joined components (e.g., electrical component and housing), as they can compensate for vibrations or thermal expansion effects to a certain extent. The ettringite-forming cement not only ensures rapid setting with minimal shrinkage, but also acts as a reactive filler, contributing to matrix formation with the polymer dispersion and to heat conduction through the thermally conductive fillers, since the cement has a higher thermal conductivity than the polymer.

[0023] The thermal conductivity of the cured composition, at least 1.4 W / mK, corresponds at least to the thermal conductivity of conventional gap fillers used in battery manufacturing. Depending on the embodiment of the composition according to the invention and depending on 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.

[0024] 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 the range of 0.2 to 0.8, preferably 0.3 to 0.6. The amount of added water is then such that it is completely consumed in the hydration reaction.

[0025] Further embodiments of the composition according to the invention relate to the fact that the polymer particles are redispersible polymer particles, so that the composition can be provided as a storable dry mix without the addition of water. Thus, a dry mix comprising the ettringite-forming cement, the thermally conductive fillers, and the redispersible polymer particles, which forms the composition according to the invention when combined with water, is also an object of the invention.

[0026] Alternatively, the polymer particles can be provided as an aqueous polymer dispersion. A polymer dispersion is defined as a colloidally stable dispersion of polymer particles in an aqueous phase. This dispersion water of the polymer dispersion constitutes at least a portion of the added water; that is, when adjusting the amount of added water to the mass fraction of the 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, it may be possible to completely omit additional added water to supplement the dispersion water if the dispersion water contained in the polymer dispersion is sufficient for the proportion of ettringite-forming cement present in the composition according to the invention.For storage purposes, the composition according to the invention can be provided as a set comprising a base dry mix, which includes the ettringite-forming cement and the thermally conductive fillers, and a polymer dispersion. The composition according to the invention is formed by mixing the polymer dispersion with the base dry mix and, optionally, an additional proportion of water, so that the set of base dry mix and polymer dispersion also constitutes part of the invention. Both the dry mix and the base dry mix with the polymer dispersion can further be formulated according to the other embodiments of the composition according to the invention, which are described below.

[0027] According to a further embodiment, the ettringite-forming cement may have the following composition: - 45 to 90 mass-% Ye'elimit or 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 additional 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 the sum of the proportions of at least one further cement clinker phase and the cementitious material does not exceed 40 mass-% of the ettringite-forming cement.

[0028] In a preferred embodiment, the ettringite-forming cement may contain 50 to 70 wt% calcium sulfoaluminate and 15 to 25 wt%, in particular 20 wt%, calcium sulfate, based on the total mass of the ettringite-forming cement. The calcium sulfate, in the form of anhydrite, gypsum, or bassanite, may preferably be micronized, i.e., have a significantly smaller average particle size compared to commercially available gypsum.

[0029] Further developments of the composition according to the invention relate to the fact that the optional additional 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 cement-like material optionally contained in the ettringite-forming cement can be selected from latent hydraulic materials and / or natural or artificial pozzolanic materials, comprising latent hydraulic slags such as blast furnace slag, lime-rich and / or lime-poor fly ashes, calcined clays or shales, trass, brick dust, artificial glasses, microsilica, and silicon-rich combustion residues of organic materials such as rice hull ash, and combinations thereof.

[0030] The cement-like material contributes to hardening and improves the grain structure in the fines range. Latent hydraulic materials such as granulated blast furnace slag harden hydraulically in the presence of an accelerator 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-like hardening products.

[0031] Furthermore, according to a further embodiment, the composition according to the invention can comprise up to 40% by mass of at least one inactive additive to influence the processability and vary the consistency and strength before or after curing, based on the total mass of the composition. The inactive additive(s) are selected from a group that includes at least sand, rock flour, e.g., quartz flour or limestone flour, and pigments.

[0032] Inactive additives are substances that do not react with either cement or water and therefore have no effect on the cement's hydration reactions. The aggregate size of the inactive additives influences the workability before hardening and the strength or hardness after hardening. Smaller grain sizes allow for easier processing of the mixture but are associated with lower strength after hardening. 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 composition. By adding rock flour such as quartz flour (typical grain size up to 0.25 mm), the flour content is increased to the finest grain size range of 0.125 mm.The flour 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 of metal oxides with a size of 0.1 to 1.0 µm, which primarily serve for coloring.

[0033] 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 expandable 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 expandable graphite can preferably be between 10 and 45% of the composition. The thermally conductive fillers can have a particle size in the range of 100 to 1,000 µm, preferably 100 to 500 µm.

[0034] 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 conductivity in the composition according to the invention but also serves as fire protection. Due to the increase in volume of the expanded graphite, which occurs when the temperature rises above the starting temperature, the thermal interface initially expands into existing gaps in the electrical device before it oozes out of the electrical device or inflates its structure. This separates the electrical components from one another, particularly thermally, in order to prevent or at least delay the spread of thermal runaway from one cell to neighboring cells.Furthermore, the oxygen supply is cut off, thus preventing, reducing, or extinguishing fires in the electrical device. Expandable graphite is produced from graphite by intercalation using acids, usually sulfuric acid, whereby water-insoluble salts are introduced into its layered structure. Under the influence of heat, these salts evaporate, causing the graphite layers to separate. After further development, the expandable graphite can achieve an expansion rate of at least 100 cm³. 3 / g or at least 200 cm 3 / g or at least 300 cm 3 The expanded graphite has a starting temperature in the range of 140 °C to 270 °C, preferably 180 °C to 240 °C. Furthermore, the expanded graphite can have a particle size distribution in which 70% of the expanded graphite particles are larger than 300 µm or 80% of the particles are larger than 250 µm. In particular, 80% of the particles can be larger than 300 µm.

[0035] Furthermore, according to another 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 the 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.

[0036] When using a polymer dispersion with a solids content in the defined range, the composition according to the invention, according to yet another embodiment, can comprise the ettringite-forming cement, the polymer dispersion and the thermally conductive fillers, in particular made of graphite or expandable graphite, in a mass ratio of 1:1:1.

[0037] In 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 at -38 °C, so that the thermal interfaces formed by the composition, which are exposed to the ambient temperature, do not become brittle in freezing conditions. This is particularly important for electrical devices such as energy storage devices, which may be installed in vehicles.

[0038] Suitable redispersible or dispersion-based polymer particles are cement-compatible and, 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 wt%. 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. Butyl or ethylhexyl acrylate are non-exclusive examples of suitable alkyl acrylates.

[0039] Further embodiments of the composition according to the invention relate to the fact that the composition may optionally include further components in order to optimize the properties of the composition for processing and / or after curing. Thus, the composition according to the invention may further comprise up to 5% by mass of accelerator and / or up to 2% by mass of liquefier. The accelerator may be selected from a group comprising salts, in particular chlorides, oxides, hydroxides, carbonates, and nitrates, of alkali, alkaline earth, 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, and magnesium sulfate. If calcium oxide and calcium hydroxide are chosen as accelerators, which may also be included as an optional additional cement clinker phase in the composition according to the invention, their proportion as accelerators is credited against the proportion of the optional additional cement clinker phase, so that the proportion of the optional additional cement clinker phase, including the proportion of the calcium oxide or calcium hydroxide used as accelerators, should not exceed 30% by mass.

[0040] A liquefier can be selected from sulfonates, polycarboxylates, and polycarboxylate ethers. Suitable sulfonates include, for example, lignosulfonates, naphthalene formaldehyde sulfonates, and melamine formaldehyde sulfonates.

[0041] Optionally, a composition according to the invention may include further additives to modify its properties. Examples include defoamers or degassing agents to prevent the formation of gas or air pores that could impair thermal conductivity after curing. Silicone-based and silicone-free defoamers are known for this purpose. Alternative examples of additives include foaming agents to create gas or air pores in the composition that are retained during the curing of the thermal interface, thereby reducing its weight. Preferably, the air pore content of such a lightweight interface is at most 20% so that the thermal conductivity of the thermal interface does not decrease significantly. Surfactants and / or proteins can be used as foaming agents. Lignosulfonates, which act as liquefiers, can also be used as foaming agents.

[0042] One 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 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 thermally connects the electrical component to the housing component and has a thermal conductivity of at least 1.4 W / mK after curing of the composition.

[0043] The composition according to the invention is cost-effective both in terms of material and processing, and can also be applied and cured reliably. These properties, combined with the thermal and mechanical material properties achievable after curing, make the composition according to the invention suitable for mass production as a thermally conductive adhesive or gap filler for creating a thermal interface in an electrical device.

[0044] For the purposes of this invention, an electrical device is understood to be a device comprising at least one electrical component arranged in or on a housing component designed for heat conduction, i.e., heat dissipation or heat input. Housing components include not only the housing walls that define the external boundaries of the device, but also support components, wall or base elements, which may be located within a housing between other housing components and / or may be part of a heat sink or heat exchanger. The composition according to the invention is intended to be applied to the housing or support component before curing, or inserted between the housing or support component and the electrical component, in order to form the thermal interface after curing that thermally connects the electrical component to the housing or support component.Electrical components are defined as all components used in electrotechnical or electronic circuits, including energy storage devices, in particular chemical energy storage devices or electrical energy storage devices such as battery cells. The composition according to the invention can, in particular, also be used to form a thermal interface in an energy storage device comprising a battery housing and a plurality of battery cells, wherein the thermal interface connects the battery cells thermally to the housing components of the battery housing or a heat exchanger or cooling sink provided for heat supply or dissipation.

[0045] 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 connected to the housing component via a thermal interface provided by a composition according to the invention in a cured state. This allows, for example, the heat generated by the electrical component during operation to be transferred to the housing component via the thermal interface, which accordingly consists of a thermally conductive material or incorporates a temperature control system. Conversely, at excessively low ambient temperatures, heat can be supplied to the electrical component from the housing component via the thermal interface to heat the electrical component to an optimal operating temperature.

[0046] The housing component of the electrical device can have at least one fluid channel for conveying a thermofluid in the area of ​​the thermal interface as a temperature control system.

[0047] The electrical device can 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 input, or a heat exchanger. Typically, an energy storage device contains a plurality of battery cells, which may, but need not, be grouped into battery modules, with each battery cell being thermally connected to the battery housing via a thermal interface that is broadened by the composition according to the invention in its cured state.

[0048] Further embodiments of the composition and use according to the invention, as well as some of the advantages associated with these and further embodiments, will become clearer and more easily understood through the following detailed description with reference to the accompanying figures. Items or parts thereof that are essentially 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.

[0049] This shows: Fig. 1 a schematic cross-sectional view of an energy storage device, Fig. 2 a detailed view D from Fig. 1.

[0050] The invention relates to a curable, thermally conductive composition suitable for forming a thermal interface. Fig.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 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 typically includes several such battery housings 4 to accommodate multiple battery modules 2. Each battery module 2 has a plurality of battery cells 3, whereby 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 to form 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 into modules. In principle, the thermally conductive composition can be used in any electrical device to form a thermal interface between an electrical component requiring temperature control and a housing component designed for heat dissipation or input, such as a housing or partition wall, a housing base, a support component, or a heat sink or heat exchanger.

[0051] In the energy storage device 1 shown in the figures, a thermal interface 5 made of the cured thermally conductive composition thermally connects the battery cells 3 of the battery module 2, which are to be temperature-controlled, to the base 4'' of the battery housing 4. The base 4'' contains a temperature control / cooling system consisting of a cooling channel 4' through which a thermofluid 6 flows to dissipate heat transferred from the battery cells 3 to the base 4'' via the thermal interface 5 during charging or discharging. Naturally, a temperature control / cooling system can also have multiple cooling channels.

[0052] Contrary to what is shown, it is also possible that a thermal interface between the battery cells, or more generally, an electrical component requiring temperature control, and a side wall of a housing, an internal partition, or a support plate can be designed as a housing component capable of dissipating or supplying heat. Similar to the housing base, this interface can also contain cooling channels for the passage of a thermofluid. These cooling channels are part of a cooling circuit, which may include a heat exchanger, located outside the housing, to dissipate the heat absorbed by the thermofluid, for example, to the environment. Conversely, such a temperature control system can also be used in cold weather to heat the electrical component for optimal operation by warming the thermofluid outside the housing and transferring the heat to the electrical component via the thermal interface.

[0053] The curable, thermally conductive composition intended for the formation of the thermal interface comprises, based on the total mass of the composition, 20 to 50 wt% ettringite-forming cement, 10 to 45 wt% thermally conductive fillers, and 6 to 30 wt% polymer particles and added water in an amount that is adjusted to the mass fraction of the ettringite-forming cement and is in the range of 0.2 to 0.8, preferably 0.3 to 0.6, such that the added water is completely bound after curing of the composition. Optionally, the curable, thermally conductive composition may further comprise, based on the total mass of the composition, up to 40 wt% of at least one inactive additive such as sand, rock flour, or pigments, up to 5 wt% accelerator, and / or up to 2 wt% plasticizer.By varying the proportions of the components within the specified ranges, the properties of the composition can be adjusted before and after curing. This applies not only to 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 to processing-related parameters such as viscosity, curing time, and, after curing, material parameters such as strength, hardness, and elasticity.

[0054] Due to the rapid setting time resulting from the hydration reaction of the cement formed by the ettringite, the composition is prepared by mixing the components immediately before application. This can be done by mixing a dry mix of the composition, containing the ettringite-forming cement, thermally conductive fillers, water-redispersible polymer particles, and optionally one or more of the optional components, with water. Alternatively, the composition can be prepared from a base dry mix containing the ettringite-forming cement, thermally conductive fillers, and optionally one or more of the optional components, and a polymer dispersion containing the polymer particles dispersed in water.In this set consisting of base dry mix and polymer dispersion, the dispersion water, with a solids content of 50 to 70% by mass relative to the total mass of the polymer dispersion, provides at least part, and possibly all, of the added water.

[0055] Carbon particles made of graphite or expandable 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 µm. Larger particle sizes up to 1,000 µm are advantageous because the composition can incorporate a higher proportion of coarser particles, which have better thermal conductivity, than finer particles. Depending on the type of application, however, particle sizes up to 500 µm may be advantageous for good application and dosing of the composition or for reducing wear on the application device. Expandable graphite particles can be used preferentially as thermally conductive fillers when the fire protection of an electrical device also needs to be improved.

[0056] The ettringite-forming cement contains, based on the total mass of the ettringite-forming cement, 45 to 90 wt% calcium sulfoaluminate (cement chemical English short formula C4A3S or Ye'elimitl4CaO·3Al20). 3'' SO4), 10 to 30 mass-% calcium sulfate (CS or anhydrite / CaSO4 or CSH2 or gypsum / CaSO4·2H2O or CSH 0.5 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.

[0057] The optional at least one further cement clinker phase can consist of dicalcium silicate (C2S or belite / CaO·SiO2), calcium aluminate ferrite (C2(A,F) or ferrite / 2CaO(Al2O3, Fe2O3)), calcium aluminates (CA, C3A, CA2, C 12A7 or aluminates / CaO·Al2O3, 3CaO·Al2O3, CaO·2Al2O3, 12CaO·7Al2O3), calcium aluminate silicate (C2AS or Gehlenite / Ca2Al[AlSiO7]), tricalcium silicate (C3S or alite / 3CaO·SiO2), calcium hydroxide (CH or portlandite / Ca(OH)2), calcium sulfate silicate (C5S2S or ternesite / Ca5(SiO4)2(SO4)) or calcium oxide (C or free lime / CaO).

[0058] Ettringite-forming cements usable in the composition according to the invention, which contain calcium sulfoaluminate from ground calcium sulfoaluminate clinker and (added) calcium sulfate within the specified mass proportions, 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) may optionally contain or be supplemented with cement-like material from latent hydraulic and / or natural or artificial pozzolanic materials such as granulated blast furnace slag, fly ash, calcined clays or shales, 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.

[0059] Two examples of commercially available CSA cement that can be used as an ettringite-forming cement in a composition according to the invention are i.tech® ALI CEM from HeidelbergCement AG, Germany, and Duzzi Unicem Next Base from Dyckerhoff GmbH, Germany.

[0060] i.tech® ALI CEM from HeidelbergCement AG is a mixture of a CSA cement (i.tech® ALI PRE from HeidelbergCement AG) and 20% by mass added calcium sulfate. According to the manufacturer, the CSA cement ALI PRE has as its main phases at least 58% by mass C4A3S (calcium sulfoaluminate), at most 25% by mass C2S (dicalcium silicate), and at most 5% by mass CS (calcium sulfate). Therefore, the ALI CEM mixture, used as an ettringite-forming cement, contains at least 46.4% by mass calcium sulfoaluminate, at most 20% by mass dicalcium silicate, and a total of 20 to 24% by mass calcium sulfate. The main components of the CSA cement i.tech® ALI PRE are 36 to 41 wt% CaO, at most 9 wt% SiO2, 27 to 33 wt% Al2O3, at most 1.5 wt% Fe2O3, 10 to 14 wt% SO3, and at most 5 wt% MgO.

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

[0062] Advantageously, the commercially available cements mentioned as examples 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 cements in a composition according to the invention by adding a corresponding amount of calcium sulfate.

[0063] An exemplary composition according to one embodiment of the invention comprises, in equal parts (i.e., in a mass ratio of 1:1:1), 33.3 wt% each of an ettringite-forming cement, a polymer dispersion with 60 wt% solids content and a glass transition temperature (Tg) of -38 °C, and expandable graphite particles with a particle size of at least 100 µm. 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 hardened state, the composition exhibits a thermal conductivity of over 2 W / mK and presents itself as a comparatively soft material similar to hard or solid rubber, which can be cut, for example, by hand with a utility knife and into which screws can be driven without pre-drilling.

[0064] When manufacturing the composition, gentle mixing of the components is advantageous to avoid particle crushing, which would require more water. Gentle mixing involves the shortest possible mixing time at a moderate temperature and speed. A vacuum mixer is advantageous for mixing because it prevents the introduction of air, which would significantly reduce the thermal conductivity of the cured composition. Centrifugal mixers are also suitable. REFERENCE MARK LIST 1 Energy storage device 2 battery modules 3 battery cells 4 battery cases 4' Fluid channel 4'' case base 4''' side walls 5 Thermal interface 6 Thermofluid

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, wherein the composition has: 20 to 50 mass-% ettringite-forming cement, based on the total mass of the composition, 10 to 65% by mass of thermally conductive fillers, based on the total mass of the composition, 6 to 30% by mass of polymer particles, based on the total mass of the composition, and Added water in an amount that is tailored 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 the mass ratio of the added water to the ettringite-forming cement is in the 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 part 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 additional cement clinker phase based on the total mass of the ettringite-forming cement, - 0 to 40 mass-% of a cement-like material based on the total mass of the ettringite-forming cement, wherein the sum of the proportions of at least one further cement clinker phase and the cement-like material does not exceed 40 mass-% of the ettringite-forming cement. [5] Composition according to claim 4, wherein - which is at least one further cement clinker phase selected from a group containing 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, comprising latent hydraulic slags, lime-rich and / or lime-poor fly ashes, calcined clays or shales, trass, brick dust, artificial glasses, microsilica and silicon-rich combustion residues of organic matter and combinations thereof. [6] Composition according to at least one of claims 1 to 5, wherein the composition further comprises up to 40 wt% 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 graphite or expandable graphite, and / or have a particle size in the range of 100 to 1,000 µm, preferably 100 to 500 µm. [8] Composition according to at least one of claims 3 to 7, wherein the polymer dispersion is a solvent-free, saponification-resistant polymer dispersion with a solids content in the range of 50 to 70 wt% 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 thermally conductive 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) 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, the alkyl side chain of which has at least four carbon atoms. [12] Composition according to at least one of claims 1 to 11, wherein the composition, in relation to the total mass of the composition, further comprises: - up to 5% by 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 aluminium, and / or - up to 2% by mass of liquefier 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 tempered 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) thermally connects the electrical component (3) to the housing component (4) and has a thermal conductivity of at least 1.4 W / mK after curing of the composition. [14] Use of the composition according to claim 13, wherein the housing component (4) has at least one fluid channel (4') in the area of ​​the thermal interface (5) for conveying a thermofluid (6). [15] Use of the composition according to claim 13 or 14, 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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