A reversible intelligent thermal switch device

Abstract

The present invention discloses a reversible intelligent thermal switch device. An adhesive thermal interface material layer forms a heat conduction path between highly thermally conductive films. A liquid crystal elastomer foam layer expands with increasing temperature and contracts with decreasing temperature, enabling the device to autonomously switch between high and low thermal conductivity levels at different temperatures. The liquid crystal elastomer foam layer serves as an interface control layer, leveraging its large deformation capacity to control the in-plane thermal conductivity of the highly thermally conductive films. Combined with the adhesive thermal interface material layer, this improves the device's thermal switching ratio.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal management, and in particular relates to a reversible intelligent thermal switch device. Background Art

[0002] In today's digital and intelligent era, 5G technology is rapidly developing, and electronic components have achieved tremendous performance breakthroughs. However, this has also led to an increasing focus on heat generation. High heat generation power and density not only affect the stability and reliability of electronic components, but can also lead to performance degradation or even damage. Therefore, efficient thermal management technology is crucial in a variety of application scenarios.

[0003] Traditional static thermal management is a passive heat dissipation method, and the requirement for thermally conductive materials is usually stable thermal conductivity. For example, the cooling systems of microelectronic chips, communication base stations, and mobile phone batteries require high thermal conductivity materials to dissipate heat quickly. As devices and equipment continue to develop in the direction of integration and intelligence, higher requirements are placed on thermally conductive materials. For example, the battery packs in energy storage power stations are usually arranged and stacked together. They will slowly release heat under normal working conditions. High thermal conductivity materials are needed to conduct heat to the heat sink to reduce the temperature of the battery pack. When the battery is damaged and thermal runaway occurs, the heat of the thermal runaway battery pack needs to be isolated to avoid causing other battery packs to burn too quickly. Although some progress has been made in scientific research, such as some materials can achieve a large thermal switching ratio, the switching ratio values ​​of some thermal switching devices are still far from the ideal high-efficiency thermal management requirements. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the purpose of the present invention is to provide a reversible intelligent thermal switch device, in which the adhesive thermal interface material layer is used to form a thermal conduction path between the high thermal conductivity films, and the liquid crystal elastomer foam layer can expand as the temperature increases and contract as the temperature decreases, thereby enabling the reversible intelligent thermal switch device to achieve autonomous switching of thermal conductivity performance at different temperatures.

[0005] The purpose of the present invention is achieved through the following technical solutions.

[0006] A reversible intelligent thermal switch device comprises: an interlayer and two high thermal conductivity films, the interlayer comprising: an adhesive thermal interface material layer and a liquid crystal elastomer foam layer, the two high thermal conductivity films being arranged in parallel and spaced apart, the interlayer being located between the two high thermal conductivity films, the adhesive thermal interface material layer and the liquid crystal elastomer foam layer being arranged side by side and respectively parallel to the high thermal conductivity films; the lower surface of the adhesive thermal interface material layer being fixedly connected to the upper surface of the high thermal conductivity film located therebelow, the lower surface of the liquid crystal elastomer foam layer being fixedly connected to the upper surface of the high thermal conductivity film located therebelow, the lower high thermal conductivity film being used to contact a heat source, the thickness of the adhesive thermal interface material layer being H, and the distance between the two high thermal conductivity films being greater than or equal to H; the high thermal conductivity film located above the interlayer being freely connected to the adhesive thermal interface material layer (i.e., the high thermal conductivity film located above the interlayer can be separated from the adhesive thermal interface material layer), and the high thermal conductivity film located above the interlayer being freely connected or fixedly connected to the liquid crystal elastomer foam layer;

[0007] The thickness of the liquid crystal elastomer foam layer increases as its temperature increases, and the thickness of the liquid crystal elastomer foam layer decreases as its temperature decreases. When the temperature of the liquid crystal elastomer foam layer is greater than Ty°C, the thickness of the liquid crystal elastomer foam layer is greater than H, the upper surface of the liquid crystal elastomer foam layer is connected to the high thermal conductivity film located thereon, and the upper surface of the adhesive thermal interface material layer is not in contact with the high thermal conductivity film located thereon; when the temperature of the liquid crystal elastomer foam layer is less than Tx°C, the thickness of the liquid crystal elastomer foam layer is less than or equal to H, the upper surface of the adhesive thermal interface material layer is in contact with the high thermal conductivity film located thereon (the upper surface of the liquid crystal elastomer foam layer may be in contact with or not in contact with the high thermal conductivity film located thereon), and Tx≤Ty (the values ​​of Tx and Ty are related to the material of the liquid crystal elastomer foam layer and are not limited here).

[0008] In the above technical solution, the right portion of one piece of the high thermal conductivity film is located directly below the left portion of another piece of the high thermal conductivity film, and the interlayer is located between the overlapping portions of the two pieces of the high thermal conductivity film.

[0009] In the above technical solution, H is 0.2 to 5 mm.

[0010] In the above technical solution, the high thermal conductivity film is a graphene film, a graphite film, a carbon nanotube film or a metal film.

[0011] In the above technical solution, the thermal conductivity of the high thermal conductivity film is greater than 100 W / mK.

[0012] In the above technical solution, the sum of the areas of the two high thermal conductivity films is M1, the area of ​​the overlapping portion of the two high thermal conductivity films is M2, and (M2 / M1)*100%=1-50%.

[0013] In the above technical solution, the materials of the two high thermal conductive films are the same or different.

[0014] In the above technical solution, the material forming the adhesive thermal interface material layer is a silicone-based thermal interface material, an acrylic resin-based thermal interface material or a soft elastic thermal interface material, and the silicone-based thermal interface material is thermally conductive silica gel.

[0015] In the above technical solution, the ratio of the liquid crystal elastomer foam layer to the adhesive thermal interface material layer is (1-10):(1-10) by area.

[0016] In the above technical solution, the method for obtaining the liquid crystal elastomer foam layer comprises the following steps:

[0017] Step 1) The NaCl particles are compacted with a mold, and another container is prepared and loaded with water. The mold loaded with the compacted NaCl particles and the container loaded with water (the compacted NaCl particles and the water are not in contact at this time) are placed in the same closed space at the same time, and maintained at 35-50° C. for 10-30 hours to allow the water to wet the compacted NaCl particles. The compacted NaCl particles are taken out and dried to obtain a sintered block as the NaCl salt template.

[0018] In the step 1), the particle size of the NaCl particles is 0.1 to 0.9 mm, preferably 0.45 to 0.6 mm.

[0019] In the step 1), the drying temperature is 50 to 80° C., and the drying time is 2 to 10 hours.

[0020] Step 2) The mixed solution is pressed into the pores of the NaCl salt template by a vacuum-assisted perfusion method, reacted at room temperature for 10 to 20 hours, vacuum dried (for removing the solvent) to obtain a sample, the NaCl salt template is removed with distilled water, and freeze-dried to obtain a pre-crosslinked liquid crystal elastomer foam, wherein the method for obtaining the mixed solution comprises: mixing a liquid crystal monomer, a flexible spacer, a crosslinker, a solvent, and a photoinitiator, stirring at 70 to 90° C. (2 to 5 minutes) until it becomes clear and transparent, removing the mixture, cooling it to 15 to 25° C. (for preventing gelation), adding a catalyst, and mixing uniformly to obtain the mixed solution;

[0021] In the step 2), the ratio of the mixed solution to the NaCl salt template is (1-1.5):2 by volume.

[0022] In the step 2), the liquid crystal monomer is 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene (RM257), the flexible spacer is 3,6-dioxa-1,8-dioctanethiol (EDDET), the crosslinker is pentaerythritol tetrakis(3-mercaptopropionate) (PETMP), the solvent is toluene, the catalyst includes di-n-propylamine, and the photoinitiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (HHMP).

[0023] In step 2), the method of removing the NaCl salt template with distilled water includes: soaking the sample with distilled water for multiple times until the sample floats on the surface of the distilled water.

[0024] In the step 2), the drying temperature is 60 to 90° C., and the drying time is 24 to 48 hours.

[0025] In the step 2), the ratio of the liquid crystal monomer, the flexible spacer and the crosslinking agent is 1:(0.5-0.9):(0.025-0.15) based on the amount of the substances. Preferably, the ratio of the liquid crystal monomer, the flexible spacer and the crosslinking agent is 1:0.7:0.075.

[0026] In the step 2), the catalyst is a mixture of di-n-propylamine and toluene, the concentration of di-n-propylamine in the catalyst is 0.5-2 wt %, and the di-n-propylamine in the catalyst is 0.3-0.7 mol % of the liquid crystal monomer, flexible spacer and cross-linking agent in the catalyst.

[0027] In the step 2), the solvent is 20-40 wt % of the liquid crystal monomer.

[0028] In the step 2), the photoinitiator is 0.5 to 2 wt% of the total weight of the liquid crystal monomer, the flexible spacer and the cross-linking agent.

[0029] Step 3) compressing the pre-crosslinked liquid crystal elastomer foam to 20-50% of its original thickness and irradiating it with ultraviolet light for 10-30 minutes to obtain the liquid crystal elastomer foam layer.

[0030] In the step 3), the compression is constant pressure compression.

[0031] In the step 3), 365 nm ultraviolet light is used for irradiation.

[0032] In step 3), the intensity of the ultraviolet light is 200 to 1000 mW / cm 2 .

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The present invention uses a liquid crystal elastomer foam layer as an interface control layer, and uses its large deformation ability to control the in-plane thermal conductivity of the high thermal conductivity film. It is then combined with an adhesive thermal interface material layer to jointly improve the thermal switching ratio of the reversible intelligent thermal switch device. Specifically, the liquid crystal elastomer foam layer and the adhesive thermal interface material layer are filled between the partially overlapping high thermal conductivity films. Below the critical temperature Tx°C, the adhesive thermal interface material layer connects the high thermal conductivity film to form a thermal conduction path. Heat is transferred across the high thermal conductivity film through the adhesive thermal interface material layer, and the reversible intelligent thermal switch device as a whole exhibits high thermal conductivity. Above the critical temperature Ty°C, the liquid crystal elastomer foam layer expands and separates the adhesive thermal interface material layer from the high thermal conductivity film, hindering heat transfer across the high thermal conductivity film. The reversible intelligent thermal switch device as a whole exhibits low thermal conductivity. Therefore, the reversible intelligent thermal switch device prepared by the present invention can achieve autonomous switching of high and low thermal conductivity at different temperatures. Based on the volume change of the liquid crystal elastomer foam material layer at different temperatures, the present invention achieves dynamic and reversible switching between low-temperature thermal conductivity and high-temperature thermal insulation, which makes up for the shortcomings of traditional static thermal management systems.

[0035] (2) The high thermal conductivity film material and adhesive thermal interface layer material used in the present invention are simple and easy to obtain, and the assembly process is simple and easy to produce, and has good application prospects in the fields of battery management systems and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 (a) Schematic diagram of the temperature of the heat-conducting material sheet during the heating and cooling state, (b) Schematic diagram of the temperature of the reversible intelligent thermal switch device during the heating and cooling state;

[0037] Figure 2 Thermal conductivity tests of the reversible intelligent thermal switch device prepared in Example 1 and the heat transfer material sheet prepared in Comparative Example 1. (a) Infrared thermal imaging of the reversible intelligent thermal switch device prepared in Example 1 at low temperature; (b) Infrared thermal imaging of the heat transfer material sheet prepared in Comparative Example 1 at low temperature; (c) Infrared thermal imaging of the reversible intelligent thermal switch device prepared in Example 1 at high temperature; (d) Infrared thermal imaging of the heat transfer material sheet prepared in Comparative Example 1 at high temperature.

[0038] Figure 3 1 is a curve showing the change of thermal conductivity coefficient inside and outside the liquid crystal elastomer foam layer with temperature in Example 1. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described in detail below with reference to specific embodiments and drawings.

[0040] The method for obtaining the liquid crystal elastomer foam layer is described in: CN117659492A, a method for preparing a thermally expanding and contracting liquid crystal elastomer porous foam material. The method for obtaining the liquid crystal elastomer foam layer in the following embodiment includes the following steps:

[0041] Step 1) NaCl particles (2.8 g) with a particle size of 0.45 to 0.6 mm are manually compressed using a mold (16 mm in diameter and 20 mm in height) to ensure full contact between the NaCl particles. Another container is prepared and loaded with water. The mold loaded with the compressed NaCl particles and the container loaded with water (the compressed NaCl particles and the water are not in contact at this time) are placed in the same enclosed space (the enclosed space is a closed temperature-controlled box) at the same time, maintained at 40°C for 24 hours to allow the water to wet the compressed NaCl particles. The compressed NaCl particles are taken out and dried at 60°C for 5 hours to obtain a sintered block as the NaCl salt template.

[0042] Step 2) 1000 μL of the mixed solution was injected into a 2000 mm 3 The mixture was reacted in the pores of the NaCl salt template at room temperature for 20 hours, the mold was removed, and the mixture was vacuum dried in a vacuum oven at 80°C for 24 hours (for removing the solvent), and cut to a thickness of 5 mm to obtain a sample. The sample was soaked in distilled water several times (replacing the distilled water) until the sample floated on the surface of the distilled water, and freeze-dried to obtain a pre-crosslinked liquid crystal elastomer foam, wherein the method for obtaining the mixed solution comprises: mixing a liquid crystal monomer (1.5 g, 2.546 mmol), a flexible spacer (0.335 g, 1.782 mmol), a crosslinker (0.098 g, 0.191 mmol), a solvent (470 mg) and a photoinitiator (0.0196 g), and stirring in a water bath at 80°C for 3 minutes until a white After the powder is completely dissolved and the liquid becomes clear and transparent, it is immediately taken out and cooled to 20°C in a cold water bath (to prevent gelation), 290 μL of catalyst is added and mixed evenly to obtain a mixed solution; the liquid crystal monomer is 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene (RM257), the flexible spacer is 3,6-dioxa-1,8-dioctanethiol (EDDET), the crosslinker is pentaerythritol tetrakis(3-mercaptopropionic acid)ester (PETMP), the solvent is toluene, the catalyst is a mixture of di-n-propylamine and toluene, the concentration of di-n-propylamine in the catalyst is 1 wt%, and the photoinitiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (HHMP).

[0043] The ratio of the liquid crystal monomer, flexible spacer, and crosslinker is 1:0.7:0.075 by weight. The catalyst comprises 0.5 mol% of di-n-propylamine based on the total weight of the liquid crystal monomer, flexible spacer, and crosslinker. The solvent comprises 31.333 wt% of the liquid crystal monomer. The photoinitiator comprises 1 wt% of the total weight of the liquid crystal monomer, flexible spacer, and crosslinker.

[0044] Step 3) The pre-crosslinked liquid crystal elastomer foam was placed in a cylindrical quartz glass template (16 mm in diameter) and manually compressed to 40% of its original thickness (i.e., to a thickness of 2 mm) using a 365 nm ultraviolet light (the intensity of the ultraviolet light was 400 mW / cm 2 ) and irradiated for 20 min for a second cross-linking to obtain a liquid crystal elastomer foam layer.

[0045]

[0046] According to tests, the thermally reversible deformation range of the liquid crystal elastomer foam layer is 0 to 120%.

[0047] The in-plane and out-of-plane thermal conductivity of the liquid crystal elastomer foam layer itself can affect the thermal switching performance of the reversible intelligent thermal switch device. The in-plane and out-of-plane thermal conductivity of the liquid crystal elastomer foam layer are tested with a thermal conductivity meter as a function of temperature. Figure 3 As shown in Figure 3, when the test temperature increases from 30°C to 150°C, both the in-plane thermal conductivity and the out-of-plane thermal conductivity decrease rapidly.

[0048] Examples 1 to 5

[0049] A reversible intelligent thermal switch device includes: an interlayer and two high thermal conductivity films, both of which are high-purity copper sheets (purity of copper ≥ 99.9%), each of which has a size of 40mm*10mm*0.05mm and a thermal conductivity coefficient of 401W / mK. The interlayer includes: an adhesive thermal interface material layer ( Figure 1 "D") and liquid crystal elastomer foam layer ( Figure 1 The size of the liquid crystal elastomer foam layer is W, and the size of the adhesive thermal interface material layer is N (the size is expressed as length * width * thickness, and the unit of size is mm * mm * mm). The adhesive thermal interface material layer is a commercially available thermal conductive silicone pad. Two high thermal conductive films are set in parallel and spaced apart. One high thermal conductive film ( Figure 1 The right side of "A" is defined as the high thermal conductivity film A) is located on another high thermal conductivity film ( Figure 1 "B" is defined as directly below the left portion of the high thermal conductive film B), the interlayer is located between the overlapping portions of the two high thermal conductive films, the adhesive thermal interface material layer and the liquid crystal elastomer foam layer are arranged side by side and parallel to the high thermal conductive films, respectively; the lower surface of the adhesive thermal interface material layer is fixedly connected to the upper surface of the high thermal conductive film located therebelow, and the lower surface of the liquid crystal elastomer foam layer is fixedly connected to the upper surface of the high thermal conductive film located therebelow, the lower high thermal conductive film is used to contact the heat source, the thickness of the adhesive thermal interface material layer is H, and the high thermal conductive film located above the interlayer is freely connected to the adhesive thermal interface material layer (i.e., the high thermal conductive film located above the interlayer can be separated from the adhesive thermal interface material layer);

[0050] The thickness of the liquid crystal elastomer foam layer increases as its temperature increases, and decreases as its temperature decreases. The distance between the two high thermal conductivity films changes with the thickness of the liquid crystal elastomer foam layer, and the distance between the two high thermal conductivity films is greater than or equal to H; H is 2 mm. When the temperature of the liquid crystal elastomer foam layer is greater than Ty°C, the thickness of the liquid crystal elastomer foam layer is greater than H, the upper surface of the liquid crystal elastomer foam layer is connected to the high thermal conductivity film located thereon, and the upper surface of the adhesive thermal interface material layer does not contact the high thermal conductivity film located thereon. When the temperature of the liquid crystal elastomer foam layer is less than Tx°C, the thickness of the liquid crystal elastomer foam layer is equal to H, and the upper surfaces of the adhesive thermal interface material layer and the liquid crystal elastomer foam layer are both in contact with the high thermal conductivity film located thereon.

[0051] The sum of the areas of the two highly thermally conductive films is M1, the overlapping area of ​​the two highly thermally conductive films is M2, (M2 / M1)*100%=Z%. The ratio of the liquid crystal elastomer foam layer to the adhesive thermal interface material layer is G, calculated by area fraction.

[0052] The W, N, G and Z% of the reversible intelligent thermal switch devices prepared in Examples 1 to 5 are shown in Table 1.

[0053] Table 1

[0054]

[0055]

[0056] The preparation method of a reversible intelligent thermal switch device includes: taking a high thermal conductivity film A and a high thermal conductivity film B, applying an adhesive thermal interface material (thermal conductive silicone) along the edge on the upper surface of the high thermal conductivity film A to form an adhesive thermal interface material layer, cutting a liquid crystal elastomer foam layer to a suitable size, adhering it to the upper surface of the high thermal conductivity film A close to the position of the adhesive thermal interface material layer, placing the high thermal conductivity film B above the high thermal conductivity film A and partially overlapping it, and the adhesive thermal interface material layer and the liquid crystal elastomer foam layer are located in the overlapping area of ​​the high thermal conductivity film B and the high thermal conductivity film A.

[0057] Comparative Example 1

[0058] A heat transfer material sheet is basically the same as that in Example 1, except that the heat transfer material sheet in this comparative example does not include a liquid crystal elastomer foam layer.

[0059] Comparative Example 2

[0060] A heat transfer material sheet is basically the same as that in Example 2, except that the heat transfer material sheet in this comparative example does not include a liquid crystal elastomer foam layer.

[0061] Comparative Example 3

[0062] A heat transfer material sheet is basically the same as that in Example 3, except that the heat transfer material sheet in this comparative example does not include a liquid crystal elastomer foam layer.

[0063] Comparative Example 4

[0064] A heat transfer material sheet is basically the same as that in Example 4, except that the heat transfer material sheet in this comparative example does not include a liquid crystal elastomer foam layer.

[0065] Comparative Example 5

[0066] A heat transfer material sheet is basically the same as that in Example 5, except that the heat transfer material sheet in this comparative example does not include a liquid crystal elastomer foam layer.

[0067] The reversible intelligent thermal switch devices prepared in Examples 1 to 5 and one of the heat transfer material sheets prepared in Comparative Examples 1 to 5 were used as heat conduction devices to conduct a thermal conductivity test: the left portion of the high thermal conductivity film A was marked as the P1 end, and the right portion of the high thermal conductivity film B was marked as the P2 end. Figure 1 As shown, the P1 end of the heat transfer device is attached to the surface of the electric heating platform. When the electric heating platform is operating, the heat generated by the heat transfer device is transferred from the P1 end to the P2 end. The temperature of the electric heating platform is controlled. When the temperature of the P2 end no longer changes significantly, the temperature of the P1 end is measured and recorded as T1 and the temperature of the P2 end as T2 using an infrared thermal imager. The temperature difference ΔT is calculated based on T1 and T2 using the formula ΔT = T1 - T2.

[0068] Figure 1 (a) is a temperature diagram of the thermal conductive material sheet when it is in the state of heating and cooling. Figure 1 (b) is a temperature diagram of the reversible intelligent thermal switch device in the heating and cooling state. Figure 1 The "A" in the middle is high thermal conductivity film A. Figure 1 The "B" in the middle is high thermal conductivity film B, Figure 1 "C" in the middle is the liquid crystal elastomer foam layer, Figure 1 The "D" in the figure is the adhesive thermal interface material layer. Figure 1 The "E" in the middle stands for electric heating table.

[0069] Figure 2 The thermal conductivity test of the reversible intelligent thermal switch device of Example 1 and the heat transfer material sheet of Comparative Example 1. (a) is the infrared thermal imaging of the reversible intelligent thermal switch device of Example 1 at low temperature. (b) is the infrared thermal imaging of the heat transfer material sheet of Comparative Example 1 at low temperature. (c) is the infrared thermal imaging of the reversible intelligent thermal switch device of Example 1 at high temperature. (d) is the infrared thermal imaging of the heat transfer material sheet of Comparative Example 1 at high temperature. Figure 2From (a) and (b), it can be seen that when the temperature T1 on one side of the reversible intelligent thermal switch device of Example 1 is 68.5°C, T2 is 35.3°C, and the temperature difference ΔT is 33.2°C. When the temperature T1 on one side of the heat transfer material sheet of Comparative Example 1 is 69.1°C, T2 is 35.6°C, and the temperature difference ΔT is 33.5°C, indicating that both have good thermal conductivity at lower temperatures. Figure 2 It can be seen from (c) and (d) that when the temperature T1 on one side of the reversible intelligent thermal switch device of Example 1 is 277.0°C, T2 is 45.8°C, and the temperature difference ΔT is 231.2°C. When the temperature T1 on one side of the heat transfer material sheet of Comparative Example 1 is 271.9°C, T2 is 62.1°C, and the temperature difference ΔT is 209.8°C, indicating that the reversible intelligent thermal switch device of Example 1 has better thermal insulation performance than the heat transfer material sheet of Comparative Example 1.

[0070] When the temperature T1 on one side of the reversible intelligent thermal switch device of Example 2 was 67.3°C, T2 was 39.7°C, and the temperature difference ΔT was 27.6°C. When the temperature T1 on the side of the heat transfer material sheet of Comparative Example 2 was 68.4°C, T2 was 40.2°C, and the temperature difference ΔT was 28.2°C, indicating that both devices have good thermal conductivity at lower temperatures. When the temperature T1 on one side of the reversible intelligent thermal switch device of Example 2 was 279.5°C, T2 was 47.2°C, and the temperature difference ΔT was 232.3°C. When the temperature T1 on the side of the heat transfer material sheet of Comparative Example 2 was 272.4°C, T2 was 71.2°C, and the temperature difference ΔT was 201.2°C, indicating that the reversible intelligent thermal switch device of Example 2 has better thermal insulation performance than the heat transfer material sheet of Comparative Example 2.

[0071] When the temperature T1 on one side of the reversible intelligent thermal switch device of Example 3 was 69.2°C, T2 was 32.7°C, and the temperature difference ΔT was 36.5°C. When the temperature T1 on the side of the heat transfer material sheet of Comparative Example 3 was 70.2°C, T2 was 34.1°C, and the temperature difference ΔT was 36.1°C, indicating that both devices have good thermal conductivity at lower temperatures. When the temperature T1 on one side of the reversible intelligent thermal switch device of Example 3 was 272.6°C, T2 was 40.1°C, and the temperature difference ΔT was 232.5°C. When the temperature T1 on the side of the heat transfer material sheet of Comparative Example 3 was 278.4°C, T2 was 63.8°C, and the temperature difference ΔT was 214.6°C, indicating that the reversible intelligent thermal switch device of Example 3 has better thermal insulation performance than the heat transfer material sheet of Comparative Example 3.

[0072] When the temperature T1 on one side of the reversible intelligent thermal switch device of Example 4 was 68.9°C, T2 was 32.1°C, and the temperature difference ΔT was 36.8°C. When the temperature T1 on the side of the heat transfer material sheet of Comparative Example 4 was 70.1°C, T2 was 33.2°C, and the temperature difference ΔT was 36.9°C, indicating that both devices have good thermal conductivity at lower temperatures. When the temperature T1 on one side of the reversible intelligent thermal switch device of Example 4 was 275.3°C, T2 was 44.7°C, and the temperature difference ΔT was 230.6°C. When the temperature T1 on the side of the heat transfer material sheet of Comparative Example 4 was 274.9°C, T2 was 60.4°C, and the temperature difference ΔT was 214.5°C, indicating that the reversible intelligent thermal switch device of Example 4 has better thermal insulation performance than the heat transfer material sheet of Comparative Example 4.

[0073] When the temperature T1 on one side of the reversible intelligent thermal switch device of Example 5 was 70.4°C, T2 was 36.5°C, and the temperature difference ΔT was 33.9°C. When the temperature T1 on the side of the heat transfer material sheet of Comparative Example 5 was 69.8°C, T2 was 36.1°C, and the temperature difference ΔT was 33.7°C, indicating that both devices have good thermal conductivity at lower temperatures. When the temperature T1 on one side of the reversible intelligent thermal switch device of Example 5 was 276.4°C, T2 was 45.1°C, and the temperature difference ΔT was 231.3°C. When the temperature T1 on the side of the heat transfer material sheet of Comparative Example 5 was 273.8°C, T2 was 64.7°C, and the temperature difference ΔT was 209.1°C, indicating that the reversible intelligent thermal switch device of Example 5 has better thermal insulation performance than the heat transfer material sheet of Comparative Example 5.

[0074] When the temperature of the electric heating platform is below 75°C, the liquid crystal elastomer foam layer is in a contracted state. The thermal conductivity path formed by the connection between the high thermal conductivity film and the adhesive thermal interface material layer gives the reversible intelligent thermal switch device a high thermal conductivity, thereby achieving good heat dissipation at low temperatures. When the temperature of the electric heating platform is above 250°C, the liquid crystal elastomer foam layer expands due to heat, stretching the high thermal conductivity film. At this time, the thermal conductivity path formed by the high thermal conductivity film and the adhesive thermal interface material layer is severed. The high thermal conductivity films are connected by the liquid crystal elastomer foam layer, and the thermal conductivity is very low, thus achieving a high-temperature insulation state.

[0075] A heat flux sensor is used to test the heat flux density Q passing through the reversible intelligent thermal switch device. The thermal conductivity of the reversible intelligent thermal switch device is calculated with the help of Fourier's law. The calculation formula is λ = QΔL / ΔT, where ΔL is the distance between P1 and P2, and ΔT is the temperature difference between T1 and T2.

[0076] In the reversible intelligent thermal switch device of Example 1, ΔL is 0.06m, and at low temperature (when the temperature T1 on one side of the reversible intelligent thermal switch device is 68.5°C, T2 is 35.3°C, and the temperature difference ΔT is 33.2°C), the heat flux density Q is 18647.3W / m 2At high temperature (when the temperature T1 on one side of the reversible intelligent thermal switch device is 277℃, T2 is 45.8℃, and the temperature difference ΔT is 231.2℃), the heat flux density Q is 15028.0W / m 2 , the thermal conductivity λ is 33.7W / mK at low temperature, the thermal conductivity λ is 3.9W / mK at high temperature, and the thermal switching ratio is 8.6.

[0077] In the reversible intelligent thermal switch device of Example 2, ΔL is 0.045m, and at low temperature (when the temperature T1 on one side of the reversible intelligent thermal switch device is 67.3°C, T2 is 39.7°C, and the temperature difference ΔT is 27.6°C), the heat flux density Q is 32629.3W / m 2 At high temperature (when the temperature T1 on one side of the reversible intelligent thermal switch device is 279.5℃, T2 is 47.2℃, and the temperature difference ΔT is 232.3℃), the heat flux density Q is 10840.7W / m 2 The thermal conductivity coefficient λ is 53.2W / mK at low temperature, 2.1W / mK at high temperature, and the thermal switching ratio is 25.3.

[0078] The above is an exemplary description of the present invention. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by other skilled in the art without expending creative labor falls within the scope of protection of the present invention.

Claims

1. A reversible intelligent thermal switch device for a battery thermal management system, characterized in that: include: The interlayer and two high thermal conductivity films, the interlayer includes: an adhesive thermal interface material layer and a liquid crystal elastomer foam layer, the two high thermal conductivity films are arranged in parallel and spaced apart, the right part of one high thermal conductivity film is located directly below the left part of the other high thermal conductivity film, the sum of the areas of the two high thermal conductivity films is M1, the area of ​​the overlapping part of the two high thermal conductivity films is M2, (M2 / M1)*100%= 1~50%; the interlayer is located between the overlapping parts of the two high thermal conductivity films, the adhesive thermal interface material layer and the liquid crystal elastomer foam layer are arranged side by side and are parallel to the high thermal conductivity films respectively; the lower surface of the adhesive thermal interface material layer is fixedly connected to the upper surface of the high thermal conductivity film located below it, the lower surface of the liquid crystal elastomer foam layer is fixedly connected to the upper surface of the high thermal conductivity film located below it, the lower high thermal conductivity film is used to contact the heat source, the thickness of the adhesive thermal interface material layer is H, and the distance between the two high thermal conductivity films is greater than or equal to H; the high thermal conductivity film located above the interlayer is freely connected to the adhesive thermal interface material layer, and the high thermal conductivity film located above the interlayer is freely connected or fixedly connected to the liquid crystal elastomer foam layer; wherein the thermal conductivity coefficient of the high thermal conductivity film is greater than 100 W / mK; the material of the adhesive thermal interface material layer is an acrylic resin-based thermal interface material, and the method for obtaining the liquid crystal elastomer foam layer includes: mixing a liquid crystal monomer, a flexible spacer, a crosslinker, a solvent, and a photoinitiator, wherein the liquid crystal monomer is 1,4-bis-[4-(3-acryloxypropoxy)benzoyloxy]-2-methylbenzene, the flexible spacer is 3,6-dioxa-1,8-dioctanethiol, the crosslinker is pentaerythritol tetrakis(3-mercaptopropionic acid), the solvent is toluene, the catalyst includes di-n-propylamine, and the photoinitiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, wherein, based on the amount of the substance, the ratio of the liquid crystal monomer, the flexible spacer, and the crosslinker is 1:(0.5-0.9):(0.025-0.15); and based on the area, the ratio of the liquid crystal elastomer foam layer to the adhesive thermal interface material layer is (1-10):(1-10); The thickness of the liquid crystal elastomer foam layer increases as its temperature increases, and the thickness of the liquid crystal elastomer foam layer decreases as its temperature decreases. When the temperature of the liquid crystal elastomer foam layer is greater than Ty°C, the thickness of the liquid crystal elastomer foam layer is greater than H, the upper surface of the liquid crystal elastomer foam layer is connected to the high thermal conductivity film located thereon, and the upper surface of the adhesive thermal interface material layer is not in contact with the high thermal conductivity film located thereon; when the temperature of the liquid crystal elastomer foam layer is less than Tx°C, the thickness of the liquid crystal elastomer foam layer is less than or equal to H, the upper surface of the adhesive thermal interface material layer is in contact with the high thermal conductivity film located thereon, and Tx≤Ty.

2. The reversible intelligent thermal switch device according to claim 1, characterized in that: The method for obtaining a liquid crystal elastomer foam layer comprises the following steps: Step 1) Compress the NaCl particles with a mold, prepare another container and fill it with water, place the mold loaded with the compressed NaCl particles and the container loaded with water into the same closed space at the same time, maintain them at 35-50°C for 10-30 hours to allow the water to wet the compressed NaCl particles, remove the compressed NaCl particles, and dry them to obtain a sintered block as the NaCl salt template; Step 2), pressing the mixed solution into the pores of the NaCl salt template by a vacuum-assisted perfusion method, reacting at room temperature for 10 to 20 hours, vacuum drying to obtain a sample, removing the NaCl salt template with distilled water, freeze-drying, and obtaining a pre-crosslinked liquid crystal elastomer foam, wherein the method for obtaining the mixed solution comprises: mixing a liquid crystal monomer, a flexible spacer, a crosslinking agent, a solvent, and a photoinitiator, stirring at 70 to 90° C. until it becomes clear and transparent, taking it out, cooling it to 15 to 25° C., adding a catalyst, and mixing it evenly to obtain the mixed solution; In step 3, the pre-crosslinked liquid crystal elastomer foam is compressed to 20-50% of its original thickness and irradiated with ultraviolet light for 10-30 minutes to obtain the liquid crystal elastomer foam layer.

3. The reversible intelligent thermal switch device according to claim 2, characterized in that: In step 2), the catalyst is a mixture of di-n-propylamine and toluene, the concentration of di-n-propylamine in the catalyst is 0.5-2 wt %, and the di-n-propylamine in the catalyst is 0.3-0.7 mol % of the liquid crystal monomer, flexible spacer and cross-linking agent.

4. The reversible intelligent thermal switch device according to claim 2, characterized in that: In step 2), the solvent is 20-40 wt% of the liquid crystal monomer.

5. The reversible intelligent thermal switch device according to claim 2, characterized in that: In step 2), the photoinitiator is 0.5-2 wt% of the liquid crystal monomer, the flexible spacer and the cross-linking agent.

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