Bionic Janus composite film for thermal management of energy automobile as well as preparation method and application of bionic Janus composite film

Abstract

The invention belongs to the technical field of material science, and particularly relates to a bionic Janus composite film for heat management of an energy automobile as well as a preparation method and application of the bionic Janus composite film. The thermal management bionic Janus composite film has various properties such as high thermal conductivity, high insulation, high electromagnetic shielding and good mechanical properties. The thermal management bionic Janus composite film comprises a lower CNF / TPU coated Al2O3 / f-BN insulating film layer and an upper CNF / TPU coated AgNF / CNT conductive film layer. The CNF / TPU coated Al2O3 / f-BN thin film layer is prepared from cellulose nanofibers, modified boron nitride and TPU coated Al2O3. The insulating CNF / TPU-coated AgNF / CNT conductive film layer is prepared from cellulose nanofibers, multi-walled carbon nanotubes and TPU-coated AgNF, and the upper and lower layers of composite films both have a three-dimensional dual-channel heat-conducting network structure similar to onion epidermal cells.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of high polymer-based multifunctional composite materials, and particularly relates to an energy vehicle thermal management biomimetic Janus composite film as well as a preparation method and application thereof. The energy vehicle thermal management biomimetic Janus composite film has multiple properties such as high thermal conductivity, high insulation, high electromagnetic shielding, etc. BACKGROUND

[0002] With the rapid development of new energy vehicles and intelligent vehicle technologies, the electronic system of a vehicle is becoming increasingly complex, and its thermal management, electromagnetic compatibility and electrical safety have become important factors restricting the development of the industry. In the field of vehicles, the battery pack of the power system, the central control system of the vehicle-mounted electronic device, the automatic driving sensor and the communication module, etc., as well as the vehicle lamp, etc., will generate a large amount of heat during operation. If not cooled in time, the internal temperature of the battery will continue to rise, which will damage the diaphragm inside the battery and cause the semiconductor PN junction in the circuit to fail, short circuit, cause fire and combustion accidents, and seriously affect the safety and reliability of the vehicle. Thermal management is crucial to ensuring the functionality, reliability and safety of electronic components and batteries, and therefore thermal interface materials for new energy vehicle thermal management are highly valued. The main function of the thermal interface material is to fill the interface gap between the heat-generating element and the heat sink in the longitudinal direction, reduce the thermal resistance in the longitudinal direction, and thus improve the heat dissipation capacity of the electronic device and the battery pack, and ensure the thermal stability and reliability of the device. If these heat cannot be effectively conducted and dissipated in time, it will seriously affect the performance, service life and safety of the device. At the same time, the vehicle electronic device will be subject to electromagnetic interference when operating at high power, which will affect its normal signal transmission and even may cause safety hazards. Therefore, the thermal interface material needs to have high out-of-plane thermal conductivity, insulation and high electromagnetic shielding performance.

[0003] Cellulose nanofiber, abbreviated as CNF. After molding, the layered structure of CNF has excellent mechanical properties and multi-layer designability, and is an excellent polymer matrix. However, its low intrinsic thermal conductivity of 0.2 W / mK~0.4 W / mK limits its practical application. At present, cellulose-based composites for thermal management generally introduce boron nitride, aluminum oxide and other high-thermal-conductivity insulating fillers or metal materials, carbon materials and other high-thermal-conductivity conductive fillers into the cellulose matrix and construct a layered structure to enhance the thermal conductivity of the cellulose matrix. Patent CN109627471A proposes a preparation idea of a high-thermal-conductivity flexible film: first, make hydroxylated boron nitride nanosheets and nanocellulose into aqueous dispersions, respectively, then mix, stir and ultrasonic them to obtain a uniform composite dispersion. Subsequently, water is removed by suction filtration, and the film is dried at room temperature to obtain a layered hydroxylated boron nitride / nanocellulose composite film. The in-plane thermal conductivity of the film can be as high as 22.67 W / mK, but its out-of-plane thermal conductivity is only 1.08 W / mK. Patent CN201610315269 introduces graphene into cellulose to obtain a layered graphene / nanocellulose composite film by vacuum suction filtration. The in-plane thermal conductivity of the film can reach 9.62 W / mK, but its out-of-plane thermal conductivity is only 0.08 W / mK. Whether high-thermal-conductivity insulating fillers or high-thermal-conductivity conductive fillers are introduced, the low out-of-plane thermal conductivity of these layered cellulose-based thermal interface materials cannot meet the actual heat dissipation requirements of battery and electric core of energy vehicles. Although the layered structure cannot meet the heat dissipation requirements, the addition of these conductive fillers can significantly enhance the electromagnetic shielding performance of the matrix. These conductive fillers form an efficient in-plane conductive network in the matrix, so that electromagnetic waves can be reflected, absorbed and attenuated multiple times inside the material, thereby effectively improving the electromagnetic shielding efficiency. Patent CN202211003472 introduces MXene into cellulose to obtain a layered MXene / nanocellulose composite film by vacuum suction filtration. The electromagnetic shielding efficiency of the film can reach 45 dB. In summary, it can be found that this high-density in-plane conductive network of the layered structure performs well in electromagnetic shielding and in-plane heat conduction, but sacrifices the insulation performance and out-of-plane heat conduction performance of the material, thereby limiting its use in some special scenarios, such as new energy battery modules and electric core thermal management.

[0004] Currently, researchers have explored various methods to optimize the insulating properties of materials. One common strategy is to combine insulating layers with conductive layers to form alternating multilayers or double-layer Janus structures. The design of such structures is intended to enable CNF-based composites to simultaneously possess multiple properties such as thermal conductivity, insulation, and electromagnetic shielding by designing the alternating stacking of insulating and conductive layers in the longitudinal direction. According to the patent CN202411323549, a thermally conductive and electromagnetic shielding multilayer composite film is prepared by sequentially stacking insulating and conductive layers, electromagnetic shielding layers, and insulating and conductive layers. The electromagnetic shielding efficiency of this insulating film can reach 42 dB, but its out-of-plane thermal conductivity is only 0.9 W / mK. Although this strategy of combining insulating layers with conductive layers has made progress in insulation and electromagnetic shielding, it has obvious limitations. Specifically, in this strategy, the structure of the fillers in the insulating and conductive layers is a layered structure. Although the alternating stacking of this layered structure is beneficial for forming an efficient in-plane conductive network in cellulose-based composites, thereby effectively improving the electromagnetic shielding efficiency, the limited fillers are used to build a rich in-plane thermal and conductive network, which cannot balance the network density in the in-plane and out-of-plane directions, and to some extent, the out-of-plane thermal conductivity of the material is reduced. This reduction in out-of-plane thermal conductivity may limit the use of the material in some applications that require full-range thermal management, such as in complex battery systems, where the lack of out-of-plane thermal conductivity may lead to heat accumulation, thereby affecting the performance and lifespan of the device.

[0005] Therefore, the existing technology has the problem of not being able to simultaneously meet the needs in terms of out-of-plane thermal conductivity, insulation, and electromagnetic shielding. High molecular materials such as cellulose have good insulation but poor thermal conductivity, and alternating multilayer or double-layer Janus structures have good insulation and electromagnetic shielding but poor out-of-plane thermal conductivity, making it difficult to meet the triple demands of high-efficiency heat conduction, insulation protection, and electromagnetic shielding for automotive electronic components. SUMMARY

[0006] To solve the above technical problems, the present application provides an energy automobile thermal management biomimetic Janus composite film and its preparation method and application.

[0007] To facilitate understanding of the present application, the materials used in the present application and their abbreviations are listed as follows: Ag nanoflower, AgNF for short, is the English name of nanosilver flower particles. Thermoplastic polyurethane elastomer rubber, TPU for short, is the English name of thermoplastic polyurethane elastomer rubber. TPU@AgNF is the English name of TPU ball coated with nanosilver flower particles. TPU@Al2O3 is the English name of TPU ball coated with Al2O3. Functionalized boron nitride, f-BN for short, is the English name of alkali modified boron nitride. Carbon nanotube, CNT for short, is the English name of multi-walled carbon nanotube. Dimethylacetamide, DMAc for short, is the English name of dimethylacetamide. Cellulose nanofiber, CNF for short. Polyvinyl alcohol, PVA for short.

[0008] CNF / TPU@Al2O3 / f-BN is the English name of the alumina with bionic structure and the modified boron nitride reinforced nanofiber-based insulating film layer. CNF / TPU@AgNF / CNT is the English name of the nanosilver flower particle with bionic structure and the multi-walled carbon nanotube reinforced nanofiber-based conductive film layer.

[0009] The first object of the present application is to provide a bionic Janus composite film for energy vehicle thermal management, which comprises a lower CNF / TPU@Al2O3 / f-BN insulating film layer and an upper CNF / TPU@AgNF / CNT conductive film layer.

[0010] The CNF / TPU@Al2O3 / f-BN insulating film layer is made of CNF, f-BN and TPU@Al2O3, has a three-dimensional double-channel heat conduction network structure similar to onion epidermal cells, insulation and out-of-plane thermal conductivity.

[0011] The TPU@Al2O3 is a "rigid-flexible" spherical micromaterial with core-shell structure, which is made of flexible TPU ball as core and rigid Al2O3 as shell by high-temperature mechanical surface micro-melting method.

[0012] The CNF / TPU@AgNF / CNT conductive film layer is made of CNF, CNT and TPU@AgNF, has a three-dimensional double-channel heat conduction network structure similar to onion epidermal cells, out-of-plane thermal conductivity, conductivity and electromagnetic shielding property.

[0013] The TPU@AgNF is a "rigid-flexible" spherical micromaterial with core-shell structure, which is made of flexible TPU ball as core and rigid AgNF as shell by high-temperature mechanical surface micro-melting method.

[0014] The thickness ratio of the CNF / TPU@Al2O3 / f-BN insulating film layer to the CNF / TPU@AgNF / CNT conductive film layer is 0.5-2:1; wherein the thickness of the CNF / TPU@Al2O3 / f-BN insulating film layer is 50 µm-200 µm, and the thickness of the CNF / TPU@AgNF / CNT conductive film layer is 50 µm-100 µm.

[0015] Preferably, the thickness of the CNF / TPU@Al2O3 / f-BN insulating film layer is 75 µm, and the thickness of the CNF / TPU@AgNF / CNT conductive film layer is 75 µm.

[0016] A second object of the present application is to provide a preparation method of the energy automobile thermal management biomimetic Janus composite film, comprising the following steps: Preparation of TPU balls: TPU is dissolved in DMAc to obtain a TPU solution, then PVA aqueous solution is added dropwise, stirring is performed until white flocculation appears, and then the dropwise addition is immediately stopped, 5 times the volume of PVA buffer solution is added to stabilize the phase inversion system, a TPU ball suspension is obtained, washing is performed, normal temperature drying is performed, and screening is performed to obtain TPU balls.

[0017] Preparation of TPU@AgNF and TPU@Al2O3: TPU balls are mixed with AgNF at room temperature, heating is performed until the TPU softens, high-temperature mechanical surface micro-melting coating is performed to obtain TPU@AgNF. TPU balls are mixed with spherical Al2O3 at room temperature, heating is performed until the TPU softens, high-temperature mechanical surface micro-melting coating is performed to obtain TPU@Al2O3.

[0018] Preparation of the CNF / TPU@Al2O3 / f-BN insulating film layer: f-BN is added to deionized water, ultrasonic treatment is performed to obtain an f-BN dispersion liquid, the f-BN dispersion liquid is mixed with a CNF diluent liquid, TPU@Al2O3 is added, uniform mixing is performed, then suction filtration, demolding and pressure drying are performed to obtain the CNF / TPU@Al2O3 / f-BN insulating film layer.

[0019] Preparation of the biomimetic Janus composite film: CNT is added to deionized water, ultrasonic treatment is performed to obtain a CNT dispersion liquid, the CNT dispersion liquid is mixed with a CNF diluent liquid, TPU@AgNF is added, uniform mixing is performed, the CNF / TPU@Al2O3 / f-BN insulating film layer is overlaid and suction filtered above, the CNF / TPU@AgNF / CNT conductive film layer is obtained, demolding is performed, and pressure drying is performed to obtain the energy automobile thermal management biomimetic Janus composite film.

[0020] Preferably, the preparation method of the AgNF is as follows: silver nitrate and diammonium hydrogen citrate are added to water in a molar ratio of 0.3-0.4:0.15-0.2, and a silver citrate complex is generated by reacting at 50°C for 90-110s; ammonia water is added until the silver citrate complex is dissolved, boric acid is added to adjust the pH to 7.4-7.6, an L-ascorbic acid solution is added to generate an AgNF suspension, which is filtered and dried at 25-60°C for 4-24h to obtain AgNF.

[0021] Preferably, the concentration of the silver nitrate solution is 0.2-0.8mol / L, and the volume is 30-100mL; the concentration of the diammonium hydrogen citrate solution is 0.05-0.4mol / L, and the volume is 30-100mL; the concentration of the ammonia water is 10-14mol / L, and the volume is 50-100mL; the concentration of the L-ascorbic acid solution is 0.1-0.7mol / L, and the volume is 30-100mL.

[0022] Preferably, the mass ratio of the TPU and PVA is 0.3-0.5:1-2.

[0023] Preferably, the injection temperature is 65-80°C, the speed is 0.5-1mL / min, and the stirring speed is 250-300rpm.

[0024] Preferably, the concentration of the PVA buffer solution is 0.01-0.05g / mL, and the volume is 500-600mL.

[0025] Preferably, the diameter of the TPU balls is 25-35μm and 50-70μm, and the mesh size during sieving is 625-1000mesh.

[0026] Preferably, the concentration of the TPU solution is 0.03-0.05g / mL, and the volume is 50-30mL; the concentration of the PVA solution is 0.1-0.5g / mL, and the volume is 50-100mL.

[0027] Preferably, the PVA buffer solution is a PVA aqueous solution with a concentration of 0.01-0.05g / mL.

[0028] Preferably, the diameter of the TPU balls in the TPU@Al2O3 is 50-70μm, the mass ratio of the TPU balls and AgNF is 1:1-5, and the temperature during coating is 70-100°C.

[0029] Preferably, in the TPU@AgNF, the diameter of the TPU ball is 25-35 mu m, the volume ratio of the spherical Al2O3 to the TPU ball with a diameter of 60 mu m is 1:1-5, and the heating temperature is 70-100 DEG C.

[0030] Preferably, the TPU@AgNF is used together with the TPU ball with a diameter of 25-35 mu m, and the TPU@Al2O3 is used together with the TPU ball with a diameter of 50-70 mu m, and the two different diameters of the TPU ball cannot be used interchangeably.

[0031] Preferably, the preparation method of the f-BN is as follows: BN and NaOH are mixed and dispersed into water in a mass ratio of 0.5-2:0.16-2, hydrothermal reaction is carried out at 110-120 DEG C for 16-18 h to obtain a f-BN suspension, filtration, washing, drying at 40-80 DEG C for 2-6 h to obtain f-BN.

[0032] Preferably, 0.3-1.0 g of BN is dispersed into 100-200 mL of 0.02-0.06 mol / L NaOH solution.

[0033] Preferably, the volume ratio of the f-BN, TPU@Al2O3 and CNF is 1:2:2-4.

[0034] Preferably, the volume ratio of the CNT, TPU@AgNF and CNF is 2:1-4:4-8, the ultrasonic power is 100-250 W, the time is 1-3 h, the drying temperature is 25-70 DEG C, and the time is 8-10 h.

[0035] Preferably, the TPU can be expanded to other thermoplastic elastomer rubbers, such as thermoplastic polyester elastomer, thermoplastic copolyester elastomer, thermoplastic vulcanized rubber, etc.

[0036] The spherical Al2O3 can be expanded to other insulating fillers, such as spherical boron nitride, flaky aluminum nitride, diamond, spherical aluminum nitride, flaky aluminum oxide, spherical silicon oxide, etc.

[0037] The third object of the application is to provide an application of the energy automobile thermal management bionic Janus composite film in energy automobile thermal management.

[0038] Compared with the prior art, the application has the following beneficial effects: 1. The energy automobile thermal management bionic Janus composite film of the application comprises a lower CNF / TPU@Al2O3 / f-BN insulating film layer and an upper CNF / TPU@AgNF / CNT conductive film layer. The lower CNF / TPU@Al2O3 / f-BN film layer is made of CNF, f-BN and TPU@Al2O3, has a three-dimensional double-channel heat conduction network structure similar to onion skin cells, has high out-of-plane thermal conductivity and insulation, and can separate electronic devices from the environment. The TPU@Al2O3 is a "rigid-flexible" spherical micromaterial with a core-shell structure, with a flexible thermoplastic polyurethane rubber ball as the core and a rigid Al2O3 shell, made by high-temperature mechanical surface micro-melting method. The upper CNF / TPU@AgNF / CNT conductive film layer is made of CNF, CNT and TPU@AgNF, has a three-dimensional double-channel heat conduction network structure similar to onion skin cells, has high out-of-plane thermal conductivity, conductivity and electromagnetic shielding. The TPU@AgNF is a "rigid-flexible" spherical micromaterial with a core-shell structure, with a flexible TPU as the core and a rigid AgNF as the shell, made by high-temperature mechanical surface micro-melting method. CNF is used as a polymer matrix, filled with TPU@AgNF or TPU@Al2O3, to build a CNF-based composite system with a bionic structure similar to onion skin cells, to achieve efficient in-plane and out-of-plane heat conduction. The thickness ratio of the CNF / TPU@Al2O3 / f-BN insulating film layer to the CNF / TPU@AgNF / CNT conductive film layer is 0.5-2:1. The thickness of the CNF / TPU@Al2O3 / f-BN insulating film layer is 50-200 µm, and the thickness of the CNF / TPU@AgNF / CNT conductive film layer is 50-100 µm. The thickness of the thermal management CNF-based composite film of the application is 0.075-1.5 mm. Under the combined action of thickness and two-layer film structure, the thermal management CNF-based composite film has an out-of-plane thermal conductivity of 2.86 W / m·K, an in-plane thermal conductivity of 8.86 W / m·K, an electromagnetic shielding effectiveness of about 35 dB in the X band when the thickness is 0.15 mm, an electromagnetic shielding of 233 dB / mm, an electromagnetic shielding efficiency of 99.968%, and a resistivity of 1.32 x 10 9 Ω·cm.

[0039] The present application utilizes the template effect of TPU and the volume exclusion effect under pressure, so that CNTs are isolated by TPU balls, showing obvious 3D structural characteristics. In the CNF / TPU@AgNF / CNT conductive film layer, the core-shell structure of TPU@AgNF shows obvious stacking structure, and the gap is filled by CNF matrix and CNT. When the filling amount of TPU@AgNF core-shell structure reaches 40vol%, the supporting effect of TPU core makes the TPU@AgNF core-shell structure closely contact to form an effective Ag-Ag interconnected network structure. The TPU@AgNF core-shell structure forms Ag-Ag conductive main channels between TPU balls. CNTs are inserted into the gap of TPU@AgNF core-shell structure under the volume exclusion effect, and are further densified to form a 3D connected CNT-CNT conductive sub-channel similar to the onion skin cell biomimetic structure under the shrinkage extrusion effect during drying. Under the joint action of Ag-Ag conductive main channel and CNT-CNT conductive sub-channel, the CNF / TPU@AgNF / CNT conductive film layer has good conductive performance, electromagnetic shielding efficiency and out-of-plane thermal conductivity. Similar template effect of TPU and volume exclusion effect under pressure make f-BN be isolated by TPU balls, showing obvious 3D structural characteristics. Under the joint action of Al2O3-Al2O3 thermal main channel and BN-BN thermal sub-channel, the CNF / TPU@Al2O3 / f-BN insulating film layer has good out-of-plane thermal conductivity. Therefore, under the joint action of the lower insulating film layer and the upper conductive film layer, the CNF-based biomimetic Janus composite film for thermal management has high-efficiency electromagnetic shielding efficiency, out-of-plane thermal conductivity and insulation performance, and other multifunctional properties.

[0040] 2、The preparation method of the bionic Janus composite film for energy automobile thermal management of the application comprises the following steps: dissolving TPU in DMAc to obtain a TPU solution, then injecting a PVA aqueous solution, stirring, generating white flocculation, then stopping immediately, adding 5 times the volume of PVA buffer solution to terminate the reaction, obtaining a TPU ball suspension, washing, drying at room temperature, screening, and obtaining TPU balls with a diameter of 25-35 microns and a diameter of 50-70 microns by adjusting the process. The diameter of AgNF is relatively small, can form a uniform AgNF layer on the surface of the TPU ball with a diameter of 25-35 microns, and the amount of AgNF required is relatively small, and the arrangement is compact. Al2O3 has a larger diameter, and can form a uniform core-shell structure on the surface of the TPU ball with a diameter of 50-70 microns. If the larger diameter Al2O3 is combined with the TPU ball with a diameter of 25-35 microns, a larger gap will be formed between the Al2O3, making the core-shell structure unstable and not compact. The TPU ball is mixed with AgNF, heated, and coated by high-temperature mechanical surface micro-melting method to obtain TPU@AgNF. The TPU ball is mixed with spherical Al2O3, heated, and coated by high-temperature mechanical surface micro-melting method to obtain TPU@Al2O3. f-BN is added to deionized water, ultrasonic, to obtain a f-BN dispersion liquid, the f-BN dispersion liquid is mixed with a CNF diluent liquid, TPU@Al2O3 is added and mixed uniformly, then suction filtration, demolding and pressure drying are performed to obtain a CNF / TPU@Al2O3 / f-BN film layer with insulation, thermal conductivity and certain tensile strength. CNT is added to deionized water, ultrasonic, to obtain a CNT dispersion liquid, the CNT dispersion liquid is mixed with a CNF diluent liquid, TPU@AgNF is added and mixed uniformly, and the CNF / TPU@Al2O3 / f-BN film is suction filtered on top, demolded, dried to obtain a bionic Janus composite film for energy automobile thermal management. TPU@AgNF, CNT and CNF are stacked on top of the CNF / TPU@Al2O3 / f-BN film to form a conductive layer film, AgNF and CNT form a conductive channel under the volume exclusion effect of TPU and pressure, so that the thermal management composite film has electromagnetic shielding property. The high-density electron network of the conductive film layer cannot be connected in the out-of-plane direction of the bionic Janus composite film, and at the same time, the existence of the CNF / TPU@Al2O3 / f-BN film layer does not affect the complete conductive network of the bionic Janus composite film in the plane.

[0041] Therefore, the bionic Janus composite film for energy automobile thermal management of the application not only has excellent out-of-plane conductivity and insulation, but also has excellent electromagnetic shielding performance, which can significantly improve the anti-electromagnetic interference ability of electronic products, thereby ensuring the stable operation of microelectronic devices in complex environments.

[0042] 3、Other benefits The energy automobile thermal management biomimetic Janus composite film of the present application constructs a three-dimensional double-channel structure through a volume exclusion mechanism, and successfully obtains a CNF-based Janus multifunctional film with a double-channel structure. The three-dimensional double-channel structure in the Janus structure significantly improves the thermal conductivity of the thermal management CNF-based Janus composite film in the out-of-plane direction, while also having excellent electromagnetic shielding effect and good insulation performance, thereby effectively solving the contradiction between insulation and conduction, heat dissipation and electromagnetic shielding that is difficult to balance in the prior art.

[0043] The energy automobile thermal management biomimetic Janus composite film of the present application has certain insulation performance and mechanical properties in addition to the thermal conductivity and electromagnetic shielding property described above, which can meet the use requirements of more scenes, and provides a new solution for the thermal management and electromagnetic shielding of automobiles. The thickness of the energy automobile thermal management biomimetic Janus composite film can be artificially controlled, the preparation method is simple, the cost is low, and large-scale industrial production can be easily realized. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The preparation flow chart of the energy automobile thermal management biomimetic Janus composite film of the present application.

[0045] Figure 2 The actual photo of the energy automobile thermal management biomimetic Janus composite film of the present application.

[0046] Figure 3 The morphology scanning diagram of the TPU@AgNF core-shell structure material of the present application, wherein (a) is a full view diagram of the TPU@AgNF core-shell structure, and (b) is a detailed enlarged view diagram.

[0047] Figure 4 The cross-sectional morphology scanning diagram of the energy automobile thermal management biomimetic Janus composite film of the present application.

[0048] Figure 5 The conductive layer of the energy automobile thermal management biomimetic Janus composite film of the present application and the thermal conductivity comparison diagram of different materials.

[0049] In order for those skilled in the art to better understand the technical solutions of the present application and to implement them, the technical solutions in the embodiments of the present application are described clearly and completely in combination with the preferred embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0050] It should be noted that all the professional terms used in the present application are only for the purpose of describing the specific embodiments and are not intended to limit the protection scope of the present application. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the following embodiments of the present application can be purchased from the market or prepared by the existing method.

[0051] Example 1 A preparation method of an energy automobile thermal management bionic Janus composite film, comprising the following steps: (1) Preparation of AgNF 50 mL of 0.3 mol / L silver nitrate solution and 50 mL of 0.15 mol / L diammonium citrate solution were mixed at 50°C for 100 s to generate white flocculent silver citrate complex. Then 50 mL of 12 mol / L ammonia water was added dropwise until the silver citrate complex was completely dissolved, and the solution was clear. Boric acid was added to adjust the pH value to 7.5, and finally 50 mL of 0.3 mol / L L-ascorbic acid solution was injected to generate a silver-gray AgNF suspension. After filtration, washing and drying at 50°C for 5 h, AgNF was obtained.

[0052] (2) Preparation of TPU balls TPU was dissolved in DMAc to obtain 50 mL of 0.04 g / mL TPU solution. Then, 50 mL of 0.15 g / mL PVA solution was injected at a rate of 1 mL / min at 75°C, while stirring at a speed of 275 rpm. After the formation of white flocculation, 100 mL of 0.02 g / mL PVA buffer was added to terminate the reaction, and the TPU balls were collected, washed and dried. TPU microspheres with an average particle size of 30 μm were obtained. By changing the concentration of TPU in the preparation process to 0.05 g / mL and the stirring speed to 200 rpm, TPU microspheres with an average particle size of 60 μm were obtained.

[0053] (3) Preparation of TPU@AgNF and TPU@Al2O3 30 μm TPU balls were mixed with spherical AgNF at a mass ratio of 1:1 at 92.5°C to coat TPU@AgNF.

[0054] 60 μm TPU balls were mixed with spherical Al2O3 at a volume ratio of 1.5:1 at 92.5°C to coat TPU@Al2O3.

[0055] (4) Preparation of f-BN 1 g of BN was dispersed in 200 mL of 0.05 mol / L NaOH solution, and hydrothermal treatment was carried out at 120°C for 18 h. The f-BN suspension was collected by filtration and washed with deionized water until neutral. f-BN was obtained.

[0056] (5) Preparation of CNF / TPU@Al2O3 / f-BN insulating film layer 100 mL, 20 vol% f-BN dispersion liquid was mixed with 100 mL, 40 vol% CNF liquid, 40 mL TPU@Al2O3 was added, then vacuum-assisted filtration was carried out under the condition of 0.1 MPa, after water was extracted, demolding and drying were carried out, and CNF / TPU@Al2O3 / f-BN insulating film layer was obtained. The thickness of the CNF / TPU@Al2O3 / f-BN insulating film layer was 0.075 mm, and the out-of-plane thermal conductivity was 2.07 W / m·K.

[0057] (6) Preparation of energy automobile thermal management biomimetic Janus composite film CNT was dispersed in deionized water for 6 h to obtain a 20 vol% CNT dispersion liquid, 100 mL, 20 vol% CNT dispersion liquid was mixed with 100 mL, 40 vol% CNF diluent liquid, 40 mL TPU@AgNF was added, and after mixing, CNF / TPU@Al2O3 / f-BN film was stacked and extracted, to obtain CNF / TPU@AgNF / CNT conductive film layer. After demolding and oven drying, an energy automobile thermal management biomimetic Janus composite film was obtained. The thickness of the CNF / TPU@AgNF / CNT conductive film layer was 0.075 mm. The out-of-plane thermal conductivity of the energy automobile thermal management biomimetic Janus composite film was 2.86 W / m·K, the in-plane thermal conductivity was 8.86 W / m·K, the electromagnetic shielding effectiveness of the energy automobile thermal management biomimetic Janus composite film with a thickness of 0.15 mm in the X wave band was 35 dB, the electromagnetic shielding property was 233 dB / mm, the electromagnetic shielding efficiency was as high as 99.968%, and the resistivity could reach 1.32×10 9 Ω·cm.

[0058] Example 2 A method for preparing an energy automobile thermal management biomimetic Janus composite film, comprising the following steps: (1) Preparation of TPU balls 0.03 g / mL TPU was dissolved in DMAc to obtain 60 mL TPU solution. Then, 60 mL, 0.1 g / mL PVA solution was injected at a rate of 0.5 mL / min at 65°C, while stirring at a speed of 250 rpm. After white flocculation was generated, 120 mL, 0.01 g / mL PVA buffer was added to terminate the reaction, and TPU balls were collected, washed and dried. A sieve was used to separate TPU balls with diameters of 35 μm and 70 μm.

[0059] (4) Preparation of TPU@Al2O3 TPU balls of 70 pm were mixed with spherical Al2O3 at a volume ratio of 1:1 at 80 °C to coat to obtain TPU@Al2O3.

[0060] 0.5 g of BN was dispersed in 100 mL of 0.06 mol / L NaOH solution, and hydrothermal treatment was carried out at 110 °C for 16 h, and f-BN suspension was collected by filtration and washed with deionized water until neutral. f-BN was obtained.

[0061] (5) Preparation of CNF / TPU@Al2O3 / f-BN insulating film layer 100 mL of 20 vol% f-BN dispersion liquid was mixed uniformly with 100 mL of 60 vol% CNF diluent liquid, and 40 mL of TPU@Al2O3 was added, followed by vacuum-assisted filtration at 0.1 MPa, and after the water was extracted, demolding and oven drying were carried out to obtain CNF / TPU@Al2O3 / f-BN insulating film layer. The thickness of the CNF / TPU@Al2O3 / f-BN insulating film layer was 0.1 mm.

[0062] (6) Preparation of energy automobile thermal management biomimetic Janus composite film CNT was dispersed in deionized water and ultrasonicated for 4 h to obtain a 20 vol% CNT dispersion liquid. 100 mL of 20 vol% CNT dispersion liquid was mixed uniformly with 100 mL of 60 vol% CNF diluent liquid, and 30 mL of TPU@AgNF was added. After mixing uniformly, CNF / TPU@Al2O3 / f-BN film was stacked and extracted to obtain CNF / TPU@AgNF / CNT conductive film layer. The thickness of the CNF / TPU@AgNF / CNT conductive film layer was 0.075 mm. After demolding and oven drying, an energy automobile thermal management biomimetic Janus composite film was prepared. The out-of-plane thermal conductivity of the energy automobile thermal management biomimetic Janus composite film was 1.42 W / m·K, and the resistivity could reach 10 9 Ω·cm.

[0063] Example 3 A method for preparing an energy automobile thermal management biomimetic Janus composite film, comprising the following steps: (1) Preparation of AgNF The 55 mL, 0.4 mol / L silver nitrate solution was mixed with the 55 mL, 0.2 mol / L diammonium hydrogen citrate solution at 50°C for 110 s to generate white flocculent silver citrate complex. Subsequently, 55 mL, 10 mol / L ammonia water was added dropwise until the silver citrate complex was completely dissolved, and the solution was clear. Boric acid was then added to adjust the pH value to 7.6. Finally, 55 mL, 0.4 mol / L L-ascorbic acid solution was injected to generate a silver gray AgNF suspension. After filtration, washing, and drying, AgNF was obtained.

[0064] (2) Preparation of TPU balls The 55 mL, 0.05 g / mL TPU solution was prepared by dissolving TPU in DMAc. Subsequently, 55 mL, 0.1 g / mL PVA solution was injected at a rate of 1 mL / min at 80°C while stirring at a speed of 250 rpm. After the white flocculent material was generated, the reaction was terminated by adding an equal volume of 0.015 g / mL PVA buffer solution. The TPU balls were collected, washed, and dried. A sieve was used to separate the TPU balls with diameters of 25 μm and 50 μm.

[0065] (3) Preparation of TPU@AgNF The 25 μm TPU balls were mixed with spherical AgNF at a mass ratio of 1:4 at 95°C to obtain TPU@AgNF.

[0066] (4) Preparation of TPU@Al2O3 The 50 μm TPU balls were mixed with spherical Al2O3 at a volume ratio of 4:1 at 95°C to obtain TPU@Al2O3.

[0067] The 1 g BN was dispersed in 200 mL, 0.04 mol / L NaOH solution, and subjected to hydrothermal treatment at 120°C for 20 h. The f-BN suspension was collected by filtration and washed with deionized water until neutral. The f-BN was obtained.

[0068] (5) Preparation of CNF / TPU@Al2O3 / f-BN insulating film layer The 100 mL, 20 vol% f-BN dispersion liquid was mixed with 100 mL, 80 vol% CNF liquid, and 40 mL TPU@Al2O3 was added. Subsequently, vacuum-assisted filtration was performed at 0.1 MPa. After the water was removed, the CNF / TPU@Al2O3 / f-BN insulating film layer was obtained by demolding and oven drying. The thickness of the CNF / TPU@Al2O3 / f-BN insulating film layer was 0.150 mm.

[0069] (6) Preparation of energy automobile thermal management biomimetic Janus composite film The CNTs were dispersed in deionized water for 4 h to obtain a 20 vol% CNT dispersion. 100 mL of the 20 vol% CNT dispersion was mixed with 100 mL of a 60 vol% CNF diluent, and then 20 mL of TPU@AgNF was added. The CNF / TPU@AgNF / CNT conductive film layer was obtained by stacking and filtering on the basis of the CNF / TPU@Al2O3 / f-BN film. The thickness of the CNF / TPU@AgNF / CNT conductive film layer was 0.075 mm. After the water was drained, the energy automobile thermal management biomimetic Janus composite film was prepared after demolding and oven drying. The out-of-plane thermal conductivity of the energy automobile thermal management biomimetic Janus composite film was 0.93 W / m·K, the electromagnetic shielding efficiency was as high as 99.968%, and the resistivity could reach 10 9 Ω·cm.

[0070] Example 4 A preparation method of an energy automobile thermal management biomimetic Janus composite film, the volume fraction of TPU@AgNF in Example 1 was adjusted to 10 vol%, the thickness of the CNF / TPU@AgNF / CNT conductive film layer was adjusted to 0.1 mm, and the thickness of the CNF / TPU@Al2O3 / f-BN insulating film layer was adjusted to 0.15 mm. The other conditions were the same as in Example 1. The out-of-plane thermal conductivity of the obtained energy automobile thermal management biomimetic Janus composite film was 0.82 W / m·K, and the resistivity could reach 10 9 Ω·cm.

[0071] Example 5 A preparation method of an energy automobile thermal management biomimetic Janus composite film, the thickness of the CNF / TPU@AgNF / CNT conductive film layer in Example 1 was adjusted to 0.1 mm, and the thickness of the CNF / TPU@Al2O3 / f-BN insulating film layer was adjusted to 0.2 mm. The other conditions were the same as in Example 1. The out-of-plane thermal conductivity of the obtained energy automobile thermal management biomimetic Janus composite film was 0.64 W / m·K, and the resistivity could reach 10 9 Ω·cm.

[0072] Comparative Example 1 A preparation method of an energy automobile thermal management biomimetic Janus composite film, the volume fraction of TPU@AgNF in Example 1 was adjusted to 0 vol%, the thickness of the CNF / TPU@AgNF / CNT conductive film layer was adjusted to 0.1 mm, and the thickness of the CNF / TPU@Al2O3 / f-BN insulating film layer was adjusted to 0.05 mm. The other conditions were the same as in Example 1. The out-of-plane thermal conductivity of the obtained energy automobile thermal management biomimetic Janus composite film was 2.41 W / m·K, and the resistivity could reach 109 Ω·cm.

[0073] Comparative Example 2 A preparation method of an energy automobile thermal management biomimetic Janus composite film, the volume fraction of TPU@AgNF and TPU@Al2O3 in Example 1 is adjusted to 0vol%, the thickness of the conductive layer is adjusted to 0.15mm, the thickness of the insulating layer is adjusted to 0.2mm, and the other conditions remain the same as in Example 1. The out-of-plane thermal conductivity of the obtained energy automobile thermal management biomimetic Janus composite film is 0.84W / m·K, and the resistivity can reach 10 9 Ω·cm.

[0074] Comparative Example 3 A preparation method of an energy automobile thermal management biomimetic Janus composite film, the volume fraction of TPU@AgNF in Example 1 is adjusted to 4.18vol% of AgNF, the thickness of the conductive layer is adjusted to 0.15mm, the thickness of the insulating layer is adjusted to 0.15mm, and the other conditions remain the same as in Example 1. The out-of-plane thermal conductivity of the obtained energy automobile thermal management biomimetic Janus composite film is 1.17W / m·K, and the resistivity can reach 10 9 Ω·cm.

[0075] Comparative Example 4 A preparation method of an energy automobile thermal management biomimetic Janus composite film, the volume fraction of TPU@AgNF and TPU@Al2O3 in Example 1 is adjusted to 0vol%, the thickness of the conductive layer is adjusted to 0.2mm, and the thickness of the insulating layer is adjusted to 0.2mm. The other conditions remain the same as in Example 1. The out-of-plane thermal conductivity of the obtained energy automobile thermal management biomimetic Janus composite film is 1.05W / m·K, and the resistivity can reach 10 9 Ω·cm.

[0076] In order to illustrate the beneficial effects of the energy automobile thermal management biomimetic Janus composite film of the present application, the following experiments are also carried out.

[0077] I. Materials and equipment 1. Experimental materials The main materials used in the present application include TPU, PVA and CNF.

[0078] Among them, the TPU is an industrial grade thermoplastic polyurethane rubber purchased from Shanghai Qianxin New Material Development Co., Ltd. The CNF is a nanocellulose purchased from Zhongshan Nafang New Material Co., Ltd., with model NFC1904H. The degree of polymerization of PVA is 1700, and the alcoholysis degree is 88%.

[0079] II. Experimental method 1. Structure characterization of TPU@AgNF and energy automobile thermal management biomimetic Janus composite film In order to study the coating effect of Ag on TPU balls and the microstructure of the surface of the energy automobile thermal management biomimetic Janus composite film, the structure of the TPU@AgNF structure and the energy automobile thermal management biomimetic Janus composite film was characterized by using a JEOL JSM-IT700HR / LA scanning electron microscope at a voltage of 12kV~15kV.

[0080] 2. Thermal conductivity, electromagnetic shielding rate and resistivity of composite films prepared by different materials The thermal conductivity is systematically evaluated or calculated by the formula k = aCPp, wherein k, a, CP and p represent the thermal conductivity, thermal diffusivity, specific heat capacity and density, respectively. The specific heat capacity is determined by differential scanning calorimetry at a speed of 10℃ / min, the thermal diffusivity is measured by laser flash analysis at 30℃, the resistivity is measured using a four-point probe system, and the electromagnetic shielding effectiveness is measured using a waveguide method vector network analyzer.

[0081] III. Experimental results 1. Morphology characterization of TPU@AgNF and energy automobile thermal management biomimetic Janus composite film The characterization of TPU@AgNF of the present application is shown in Figure 3 The effect of AgNF coating on the surface of the TPU core can be seen from Figure 3 , Ag presents a typical close-packed distribution, which confirms the reliability of the high-temperature mechanical surface micro-melting method.

[0082] The double-channel structure characterization of the energy automobile thermal management biomimetic Janus composite film of the present application is shown in Figure 4 The details of the double-channel structure of the onion skin cells, the TPU@AgNF and TPU@Al2O3 core-shell structure form a close-packed structure, forming Ag-Ag and Al2O3-Al2O3 conductive and thermal main channels. CNT and f-BN are inserted into the gap between TPU@AgNF and TPU@Al2O3 core-shell structure under the action of volume exclusion, and are further densified under the action of shrinkage and extrusion during drying, which forms 3D connected CNT-CNT and BN-BN conductive and thermal secondary channels.

[0083] 2. Thermal conductivity, electromagnetic shielding rate and resistivity of composite films prepared by different materials The thermal conductivity of different materials and the conductive layer in the energy automobile thermal management biomimetic Janus composite film is shown in Figure 5The results show that the temperature rising rate of the pure CNF film is the slowest, followed by the randomly dispersed CNT-filled CNF film between 0 s and 6.5 s. The temperature of the thermal management composite film rises to above 70℃ within 3.5 s, and the temperature distribution is uniform, while the temperature of the other films is still rising, and the temperature distribution is not uniform. This shows that the heat transfer speed of the conductive layer in the energy automobile thermal management bionic Janus composite film is faster than that of the film. This is due to the increase in thermal conductivity of the 3D interconnected Ag-Ag and CNT-CNT heat conduction channels formed in the conductive layer. The CNF / TPU@AgNF / CNT conductive film layer with a double-channel structure formed by introducing CNT into the stacking gap of TPU@AgNF shows the best temperature rising rate and the upper surface temperature after steady state. The maximum temperature of the upper surface of the double-channel film is 73.1℃, which is 15.2℃ higher than that of the pure CNF film. These results show that the double-channel structure similar to the onion epidermal cell has a significant improvement on the thermal conductivity of the CNF-based thermal conductive film.

[0084] The thermal conductivity, electromagnetic shielding rate and insulation of the composite films prepared by different materials are shown in Table 1. The results show that the composite film prepared by using TPU@AgNF as the filler of the conductive layer has good out-of-plane thermal conductivity, and the composite film prepared by using AgNF and CNT as the filler of the conductive layer has poor out-of-plane thermal conductivity. The results show that the composite film prepared by using TPU@Al2O3 as the filler of the insulating layer has good out-of-plane thermal conductivity, and the composite film prepared by using Al2O3 and f-BN as the filler of the insulating layer has poor out-of-plane thermal conductivity. The energy automobile thermal management bionic Janus composite film prepared by introducing 40vol% of TPU@AgNF and TPU@Al2O3 has the best out-of-plane thermal conductivity and electromagnetic shielding properties. It has an out-of-plane thermal conductivity of 2.86W / m·K, an in-plane thermal conductivity of 8.86W / m·K, and the electromagnetic shielding efficiency of the thermal management bionic Janus composite film with an insulating layer and a conductive layer thickness of 75μm is about 35dB, i.e. the electromagnetic shielding property is 233dB / mm.

[0085] Table 1 Thermal conductivity, electromagnetic shielding rate and insulation of composite films prepared by different materials “-” in the table indicates no such item.

[0086] The preparation flow chart of the energy automobile thermal management bionic Janus composite film of Example 1 of the present application is shown in Figure 1 The actual picture of the energy automobile thermal management bionic Janus composite film is shown in Figure 2The thermal conductivity experiment results of different materials show that the temperature of the conductive layer in the energy automobile thermal management bionic Janus composite film rises above 70 DEG C within 3.5 s, and the temperature distribution is uniform. The temperature of other films is still rising, and the temperature distribution is not uniform. The highest temperature on the surface of the conductive layer of the final energy automobile thermal management bionic Janus composite film reaches 73.1 DEG C, which is 15.2 DEG C higher than that of the pure CNF film. The energy automobile thermal management bionic Janus composite film has good out-of-plane thermal conductivity, and the composite film prepared by using AgNF and CNT as conductive layer filler has poor out-of-plane thermal conductivity. The composite film prepared by using TPU@Al2O3 as insulating layer filler has good out-of-plane thermal conductivity, and the composite film prepared by using Al2O3 and f-BN as insulating layer filler has poor out-of-plane thermal conductivity. The composite film prepared by using 40vol% TPU@AgNF and TPU@Al2O3 has the best thermal conductivity and electromagnetic shielding properties. It has an out-of-plane thermal conductivity of 2.86 W / m·K, an in-plane thermal conductivity of 8.86 W / m·K, and an electromagnetic shielding efficiency of 35 dB, i.e. an electromagnetic shielding property of 233 dB / mm, and a resistivity of 1.32*10 9 Ω·cm. Therefore, the energy automobile thermal management bionic Janus composite film of the application has good out-of-plane thermal conductivity, electromagnetic shielding property and insulation performance.

[0087] The application constructs a three-dimensional double-channel structure through a volume exclusion mechanism, and successfully obtains a CNF-based Janus multifunctional film with a three-dimensional double-channel structure. This unique structure design significantly improves the thermal conductivity of the material in the out-of-plane direction. Specifically, the Janus structure innovatively constructs a double-channel out-of-plane thermal conductivity three-dimensional structure on a single-layer film, which not only optimizes the heat conduction path, but also greatly enhances the thermal conductivity of the material. At the same time, this carefully designed structure endows the CNF-based composite film with multiple properties, enabling it to have excellent electromagnetic shielding effect and good insulation performance on the basis of efficient heat conduction, thereby effectively solving the contradiction between insulation and conductivity, heat dissipation and shielding in the prior art, and providing a new solution for the thermal management and electromagnetic shielding of automobiles.

[0088] The application focuses on the technical field of filler-filled polymer matrix composites, especially for the application of automotive electronic equipment thermal management field, aiming to develop a multifunctional thermal interface material with high thermal conductivity, high electromagnetic shielding and insulation and other excellent properties. The material is constructed by filling specific fillers in the polymer matrix to form a CNF-based composite system with a bionic structure similar to the onion skin cells. Further, the application focuses on the preparation process of the three-dimensional double-channel thermal and electrical conduction network structure formed by the filler-filled polymer material, realizing the construction of efficient heat conduction and electrical conduction channels. This structure provides a new structure design idea to meet the current application requirements of high thermal conductivity, insulation and high electromagnetic shielding performance, and is expected to promote the technical progress and development of thermal interface materials in the key fields of electronic equipment heat dissipation and electromagnetic compatibility.

[0089] It should be noted that when numerical ranges are involved in the present application, both endpoints of each numerical range and any number between the two endpoints can be selected. Since the same steps and examples are used, the preferred embodiments of the present application are described to prevent redundancy. Although the preferred embodiments of the present application have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the inventive concept of the present application, and these changes and modifications all fall within the scope of the present application.

[0090] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. If these modifications and variations of the present application fall within the scope of the equivalent technology of the present application, the present application also intends to include these modifications and variations.

Claims

1. A bionic Janus composite film for thermal management of energy vehicles, characterized in that, The CNF / TPU@Al2O3 / f-BN insulating film layer and the CNF / TPU@AgNF / CNT conductive film layer are stacked to form the CNF / TPU@Al2O3 / f-BN@AgNF / CNT film. The CNF / TPU@Al2O3 / f-BN insulating film layer is made of cellulose nanofiber, modified boron nitride and TPU@Al2O3, has a three-dimensional double-channel heat conduction network structure similar to the onion skin cell, insulation and out-of-plane thermal conductivity. The TPU@Al2O3 is a spherical micromaterial with core-shell structure, with a flexible thermoplastic polyurethane rubber ball as the core and a rigid Al2O3 shell, prepared by high-temperature mechanical surface micro-melting coating. The CNF / TPU@AgNF / CNT conductive film layer is made of cellulose nanofiber, multi-walled carbon nanotube and TPU@AgNF, has a three-dimensional double-channel heat conduction network structure similar to the onion skin cell, conductivity, out-of-plane thermal conductivity and electromagnetic shielding property. The TPU@AgNF is a spherical micromaterial with core-shell structure, with a flexible thermoplastic polyurethane rubber ball as the core and a rigid nano-silver flower particle as the shell, prepared by high-temperature mechanical surface micro-melting coating. The thickness ratio of the CNF / TPU@Al2O3 / f-BN insulating film layer to the CNF / TPU@AgNF / CNT conductive film layer is 0.5-2:1, wherein the thickness of the CNF / TPU@Al2O3 / f-BN insulating film layer is 50µm-200µm, and the thickness of the CNF / TPU@AgNF / CNT conductive film layer is 50µm-100µm. 2.The method for preparing a bionic Janus composite film for thermal management of an energy vehicle according to claim 1, characterized in that, The preparation method comprises the following steps: Preparation of thermoplastic polyurethane rubber balls: dissolve thermoplastic polyurethane rubber in dimethylacetamide to obtain a thermoplastic polyurethane solution, then dropwise add the solution into a polyvinyl alcohol solution, stir, stop dropping immediately after white flocculation is generated, add 5 times the volume of polyvinyl alcohol buffer to terminate the reaction, obtain a thermoplastic polyurethane rubber ball suspension, wash, filter, dry at room temperature, screen, and obtain two kinds of thermoplastic polyurethane rubber balls with different particle sizes by adjusting the process; Preparation of TPU@AgNF and TPU@Al2O3: mix thermoplastic polyurethane rubber balls with one particle size and nano-silver flower particles, heat, and perform high-temperature mechanical surface micro-melting coating to obtain TPU@AgNF; mix thermoplastic polyurethane rubber balls with another particle size and spherical Al2O3, and perform high-temperature mechanical surface micro-melting coating to obtain TPU@Al2O3; Preparation of the CNF / TPU@Al2O3 / f-BN insulating film layer: uniformly mix alkali-modified boron nitride dispersion liquid and cellulose nanofiber liquid, add TPU@Al2O3, uniformly mix, then perform suction filtration demolding, and dry to obtain a CNF / TPU@Al2O3 / f-BN film layer; Preparation of the CNF / TPU@AgNF / CNT conductive film layer: uniformly mix cellulose nanofiber liquid and multi-walled carbon nanotube dispersion liquid, add TPU@AgNF, uniformly mix, then perform suction filtration demolding, and dry to obtain a CNF / TPU@AgNF / CNT film layer. Preparation of high-molecular-based thermal management bionic Janus composite film: the multi-walled carbon nanotube dispersion liquid is mixed with the cellulose nanofiber liquid, TPU@AgNF is added and uniformly mixed, and is stacked on the CNF / TPU@Al2O3 / f-BN film by suction filtration to obtain a CNF / TPU@AgNF / CNT conductive film layer, and then demolding, drying, and obtaining the energy automobile thermal management bionic Janus composite film.

3. The method according to claim 2, wherein the method is characterized by, The preparation method of the nano-silver flower particles is as follows: silver nitrate and hydrogen diammonium citrate are added to water in a mass ratio of 1-2.4:0.5-1.2, a silver citrate complex is generated by reacting at 50 DEG C for 90-110 seconds, ammonia water is added until the silver citrate complex is dissolved, boric acid is added to adjust the pH to 7.4-7.6, an L-ascorbic acid solution is added, and a nano-silver flower particle suspension is generated, which is filtered and dried to obtain the nano-silver flower particles. 4.The method for preparing the energy vehicle thermal management biomimetic Janus composite film according to claim 2, characterized in that, The mass ratio of the thermoplastic polyurethane elastomer rubber and the polyvinyl alcohol is 0.3-0.5:1-2; The injection temperature is 65-80 DEG C, and the speed is 0.5-1 mL / min; The polyvinyl alcohol buffer solution concentration is 0.01-0.02 g / mL; The thermoplastic polyurethane rubber ball diameter is 25-35 mu m and 50-70 mu m.

5. The method of claim 2, wherein the method further comprises: In the TPU@Al2O3, the thermoplastic polyurethane rubber ball diameter is 50-70 mu m, the mass ratio of the thermoplastic polyurethane elastomer rubber ball and the spherical Al2O3 is 1:1-4, and the heating temperature is 80-95 DEG C. 6.The method for preparing the energy vehicle thermal management biomimetic Janus composite film according to claim 2, characterized in that, In the TPU@AgNF, the thermoplastic polyurethane rubber ball diameter is 25-35 mu m, the volume ratio of the nano-silver flower particles and the thermoplastic polyurethane elastomer rubber ball is 1:1-4, and the heating temperature is 80-95 DEG C.

7. The method of claim 2, wherein the method further comprises the steps of: providing a Janus composite film; and coating the Janus composite film with a hydrophobic material. The preparation method of the modified boron nitride is as follows: boron nitride and NaOH are mixed and dispersed into water in a mass ratio of 0.5-1:0.16-0.96, and a hydrothermal reaction is carried out at 110-120 DEG C for 16-18 hours to obtain an alkali-modified boron nitride suspension, which is filtered, washed, and dried to obtain the alkali-modified boron nitride. 8.The method for preparing the energy vehicle thermal management biomimetic Janus composite film according to claim 2, characterized in that, The volume ratio of the modified boron nitride, TPU@Al2O3, and cellulose nanofiber is 1:2:2-4; The volume ratio of the multi-walled carbon nanotube, TPU@AgNF, and cellulose nanofiber is 2:1-4:4-8. 9.The method of claim 1, wherein the method further comprises the steps of: coating a first layer of the Janus composite film on a substrate; and coating a second layer of the Janus composite film on the first layer. The TPU can be extended to other thermoplastic elastomer rubbers, such as thermoplastic polyester elastomers, thermoplastic copolyester elastomers, and thermoplastic vulcanized rubbers. The spherical Al2O3 can be extended to other insulating fillers, such as spherical boron nitride, flaky aluminum nitride, diamond, spherical aluminum nitride, flaky aluminum oxide, and spherical silicon oxide.

10. The energy automobile thermal management bionic Janus composite film according to claim 1 is applied to energy automobile thermal management.

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