Graphite-PTFE composite film capable of adaptively switching heat transfer resistance along with temperature

Abstract

The invention provides a graphite-PTFE composite film capable of adaptively switching heat transfer resistance along with temperature. The graphite-PTFE composite film can be applied to scenes of low-temperature heat conduction and high-temperature heat insulation. Two layers of graphite films are taken, one layer of graphite film is tightly attached to an object needing heat dissipation, and a layer of radiation refrigeration material is sprayed on the surface of the other layer of graphite film; pTFE film interlayers are placed on the inner sides of the two layers of graphite films, liquid-gas phase change materials are contained in the interlayers, and meanwhile the PTFE film interlayers and the graphite films are attached and packaged through heat conduction silicone grease; under the low-temperature working condition, heat can be quickly transferred to the radiation refrigeration coating through the graphite film and the PTFE interlayer so as to be dissipated in a heat radiation mode, under the high-temperature working condition, heat can pass through the graphite film and the PTFE interlayer for a long time, much heat can be transferred to the phase change material in the period, liquid-gas phase change is caused, the PTFE film interlayer is opened, and the heat dissipation effect is achieved. Therefore, self-adaptive conversion of heat conduction and heat resistance is achieved, and then the effects of heat dissipation under the low-temperature normal working condition and heat insulation under the high-temperature abnormal working condition are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite films, and specifically, relates to a graphite-PTFE composite film capable of adaptively switching heat transfer thermal resistance with temperature. Background Art

[0002] With the development of new power technologies, the usage scale of various power-related devices has gradually increased. Especially under the current background of the country's promotion of new energy, the large-scale popularization of new energy vehicles and the construction of renewable energy storage stations have sharply increased the demand for new heat dissipation materials. In order to prevent the occurrence of extreme situations such as high-temperature thermal runaway of power equipment, the importance of thermal management materials has become even more prominent. In addition, using efficient thermal management materials can not only improve the performance and lifespan of power equipment, but also ensure safety and stability. Currently, the main function of the widely used thermal management materials is to conduct heat away from the battery or electronic components to maintain the normal operating temperature of the equipment. With a single function and limitations, in the event of thermal runaway, the relatively low heat transfer thermal resistance will instead increase the risk of fire.

[0003] Among various power equipment, taking power batteries as an example, due to chemical reactions and current flow during the charge and discharge process, a large amount of heat is easily generated. If this heat cannot be effectively dissipated, it will cause the battery temperature to rise, thereby affecting the battery's performance, charge and discharge efficiency, and service life; in extreme cases, thermal runaway will occur, leading to a fire accident. When thermal runaway occurs, an effective thermal insulation design can slow down the spread speed of the fire and give surrounding personnel enough time to escape. With the popularization of electric vehicles and clean energy equipment, the demand for power battery thermal management materials will further increase, and the industry will face new challenges and opportunities. Developing more efficient thermal management materials will play a crucial role in the application safety, economy, and environmental protection of power batteries. Therefore, researching and developing a new thermal management technology capable of intelligently switching thermal resistance has become an urgent need in the new energy industry. Summary of the Invention

[0004] In view of the above problems, in order to solve the technical problems existing in the above technical background, the present invention proposes to prepare a graphite-PTFE composite film with intelligent switching heat transfer resistance. Under normal working conditions, a layer of radiation cooling coating and two layers of graphite film and thermal conductive silicone grease and a PTFE film sandwich containing liquid-gas phase change material sealed with a high thermal conductivity adhesive form a sandwich structure. The phase change material is in a low temperature state and behaves as a liquid state. At this time, the thermal resistance is a low thermal conductivity thermal resistance. The graphite film has excellent thermal conductivity. This excellent thermal conductivity makes the graphite-PTFE composite film also have good thermal conductivity, which can quickly and effectively extract heat from the heat source, thereby effectively dissipating heat from the battery under normal working conditions and controlling the average temperature of the battery. On the other hand, when the battery is in a high temperature condition of thermal runaway, the continuous heat transfer causes the comprehensive temperature of the phase change material to rise and reach the phase change temperature, thereby vaporizing, causing the PTFE film sandwich to expand, and the resulting volume deformation can form a high thermal resistance convection heat exchange insulation gas layer between the two layers of graphite film, thereby realizing the conduction behavior of controlling the temperature.

[0005] Technical solution, in order to achieve the above-mentioned purpose, the present invention proposes a graphite-PTFE composite membrane with intelligent switching heat transfer resistance, the graphite-PTFE composite membrane comprises a first graphite film, a second graphite film, and a PTFE film interlayer; wherein, a radiation cooling coating is sprayed on the outer side of the first graphite film, and the inner sides of the first graphite film and the second graphite film are coated with silicone grease; a PTFE film interlayer sealed with a thermally conductive adhesive is arranged between the first graphite film and the second graphite film; the PTFE film interlayer contains liquid-gas phase change material.

[0006] Among them, thermally conductive silicone grease is applied between the PTFE film interlayer and the graphite film to fill the gap and bond the PTFE film interlayer to the graphene film; the liquid-gas phase change material in the PTFE film interlayer plays the role of intelligently converting thermal resistance under different working conditions.

[0007] Under normal operating conditions, the PTFE film interlayer is in a tightly attached thin layer state with a small thermal resistance. The heat of the battery can be quickly transferred to the outside through the graphite film and thermal grease. At the same time, the radiation cooling coating can reduce the heat radiated from the outside to the battery while increasing the heat released to the outside.

[0008] When the battery temperature is too high and thermal runaway occurs, heat is continuously transferred to the phase change material through the graphite film and the PTFE film. The phase change material absorbs enough latent heat to vaporize, causing the volume of the PTFE film interlayer to change. At the same time, the two graphite films are stretched apart, thereby transforming heat conduction into a composite heat transfer of conduction and convection, increasing the thermal resistance of the interlayer, and thus controlling the thermal runaway of the battery.

[0009] As an implementation method, in the composite film, the graphite film used is a polyimide-based thermally conductive graphite film.

[0010] The in-plane thermal conductivity of this thermally conductive graphite film is 1275 ± 20 W / (m·K), the tensile strength reaches 232 ± 5 MPa, and the thickness is 50 to 170 μm.

[0011] As an implementation method, the PTFE film is a polytetrafluoroethylene (PTFE) / SiO2 thermally conductive composite film material, with a mechanical strength of 17.3 ± 0.05 MPa and a thermal conductivity of 0.98 ± 0.02 W / (m·K).

[0012] As an implementation method, the thermal grease is Prolimatech PK-3, with a thermal conductivity of 16 W / (m·K), being non-toxic, non-irritating, and having good viscosity at the same time.

[0013] As an implementation method, the adhesive is an epoxy resin-based MasterBond EP29LPA-1, with a thermal conductivity of 1.1 W / m·K.

[0014] As an implementation method, the radiative cooling coating is a composite radiative cooling coating based on bamboo fiber mixed with SiO2 particles. The solar spectral reflectivity of the bamboo fiber / SiO2 composite film is 90.1%, and the infrared emissivity is 97.9%.

[0015] As an implementation method, the phase change material is 3F-50 electronic coolant. This material is colorless, odorless, transparent, highly insulating, and has good chemical inertness. The phase change temperature is 47.5 °C, and the thermal conductivity is 0.063 W / (m·K).

[0016] Advantages: Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0017] The present invention combines graphite film, silicone grease, PTFE film, liquid-gas phase change material and radiation cooling coating to manufacture a composite film with intelligent conversion mode. Graphite film has strong thermal conductivity and good toughness, and effectively dissipates heat for the battery under normal application conditions. Silicone grease has strong thermal conductivity and viscosity, and can evenly transfer the heat between the graphite film and the PTFE interlayer and play the role of encapsulating the PTFE interlayer and the graphite film. The PTFE film interlayer contains liquid-gas phase change material. Under normal low-temperature conditions, the PTFE interlayer is in a thinner state of bonding, and the heat conduction distance at this time is small, which can reduce the thermal interface thermal resistance; when the battery has thermal runaway temperature higher than the normal condition, the phase change material can continuously absorb heat and then undergo liquid-gas phase change to expand the volume of the PTFE interlayer, expand the PTFE film interlayer, increase the heat conduction distance, and add a convective heat exchange process to the heat conduction, increase the thermal resistance of the thermal interface, and reduce the thermal conductivity. PTFE film has good thermal conductivity, heat resistance and mechanical strength, and can act as a good encapsulated liquid-gas phase change material. In addition, the radiation cooling coating can reduce the input of external radiation heat and radiate heat to the outside, thereby achieving the effect of suppressing battery thermal runaway. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments are briefly introduced below.

[0019] Figure 1 Schematic diagram of the overall structure of the composite membrane for intelligent conversion of heat transfer resistance;

[0020] Figure 2 Schematic diagram of the low-temperature structure of the PTFE sandwich in the composite membrane for intelligent conversion of heat transfer resistance;

[0021] Figure 3 Schematic diagram of the high-temperature deformation state of the PTFE interlayer in the composite membrane for intelligent conversion of heat transfer resistance;

[0022] Figure 4 Thermal resistance change diagram before and after phase change;

[0023] In the figure: 1. Graphite film; 2. Thermal grease; 3. PTFE film; 4. Phase change material; 5. Thermal conductive adhesive; 6. Radiant cooling coating. DETAILED DESCRIPTION

[0024] like Figure 1As shown in the figure, this embodiment provides a graphite-PTFE composite film with an intelligently switchable heat transfer thermal resistance. The graphite-PTFE composite film includes a first graphite thin film, a second graphite thin film, and a PTFE film interlayer. Among them, a radiation cooling coating is sprayed on the outer side of the first graphite thin film, and thermal conductive silicone grease is coated on the inner sides of both the first graphite thin film and the second graphite thin film; the PTFE film interlayer is located between the first graphite thin film and the second graphite thin film, and the PTFE film interlayer is formed by sealing two layers of PTFE films with a thermal conductive adhesive; the PTFE film interlayer contains a liquid-gas phase change material.

[0025] As Figure 2 shown in the figure, the partial structural schematic diagram of the PTFE film interlayer of the composite film provided in this embodiment includes a PTFE film 3, a phase change material 4, and an adhesive 5.

[0026] In this embodiment, a method for preparing the graphite thin film is proposed. The method includes the following steps:

[0027] (1) Add 4,4'-diaminodiphenyl ether (ODA):p-phenylenediamine (PDA) to a three-necked flask in a molar ratio of 70:30. At the same time, add N,N-dimethylacetamide (DMAc), and control the solid content of polyamic acid PAA in the flask to be in the range of 15% - 20%. During the preparation process, N2 protection is introduced, and stirring and dispersion are carried out until the diamine is completely dissolved;

[0028] (2) Add pyromellitic dianhydride PMDA to the flask in equal molar batches. When the viscosity of PAA reaches 100 - 120 Pa·S, stop adding PMDA;

[0029] (3) Add a micron-sized calcium carbonate solution and control its content to be 1.5% (the micron-sized calcium carbonate solution is prepared by using a shearing and grinding process and dispersing with KH550 as a dispersing aid). Continue stirring for 2 h to completely disperse and homogenize the calcium carbonate in PAA, and perform a defoaming treatment to finally obtain a polyamic acid slurry;

[0030] (4) Bake and cool the completely defoamed polyamic acid slurry to obtain a polyimide carbon-based film. Heat the polyimide carbon-based film from 0°C to 1300°C at a constant rate of 3°C / min for carbonization treatment, then cool it to room temperature first, and then heat it from 1000°C to 2700°C at a constant rate of 3°C / min under the environmental conditions of argon and normal pressure for graphitization treatment to finally obtain the graphite thin film.

[0031] The thermal conductivity of the graphite thin film is as high as 1275 ± 20 W / (m·K), the tensile strength of the graphite thin film is 232 ± 5 MPa, the thermal conductivity is 1275 ± 20 W / (m·K), and the thickness is 50μm - 170μm.

[0032] In this example, the material that fills the gap and acts as a bond between the PTFE interlayer and the graphite film is a high-performance thermal conductive silicone grease, Prolimatech PK-3, which has a thermal conductivity of up to 16 W / (m·K), good electrical insulation, good viscosity, and adaptability to a wide temperature range.

[0033] When in a high-temperature thermal runaway condition, the phase change material will vaporize. Therefore, the selection of PTFE film needs to ensure its sealing. To prevent leakage, high-performance adhesives are used for sealing. In addition, the PTFE film also needs to have a certain ductility and strain recovery ability so that when the upper and lower layers are stretched apart, the phase change gas can form an insulating layer.

[0034] In this embodiment, the PTFE film interlayer needs to be sealed with an adhesive. The selection of a high-performance thermally conductive adhesive needs to consider good thermal conductivity and good chemical resistance. Therefore, the epoxy resin-based MasterBond EP29LPA-1 is selected, and the thermal conductivity is 1.1 W / m·K.

[0035] In this embodiment, a method for preparing the PTFE film is proposed, which comprises the following steps:

[0036] (1) At room temperature, weigh a silane coupling agent, a surfactant, ethanol, formic acid and a PTFE emulsion in appropriate proportions, place them in a flask and stir them evenly.

[0037] (2) Al2O3 ceramic powder and SiO2 ceramic powder are added to the flask in sequence, and stirred evenly to obtain a mixed glue solution.

[0038] (3) The glass fiber cloth material is impregnated with a silane coupling agent surface modification liquid, and then air-dried and baked at 110-120° C. for 10 min to obtain a glass fiber cloth for use.

[0039] (4) Pour the mixed adhesive solution after stirring evenly into a clean impregnation tank, immerse the glass fiber cloth treated in step (3) in the adhesive solution, dry it at 70° C. to remove the adhesive solvent, and continue to bake it at 180° C. for 5 minutes to obtain a PTFE / SiO2 composite film material containing Al2O3 filler.

[0040] According to the required resin content, multiple impregnations can be carried out, and finally the composite film is rolled up when the thickness requirement is reached. The film has high thermal conductivity while ensuring the mechanical properties and air tightness of the composite film.

[0041] At the same time, in order to control the battery temperature and dissipate heat to the outside world under various working conditions, a radiation cooling coating is used. The radiation cooling coating uses natural bamboo as raw material, uses a two-step method to carry out delignification treatment, introduces SiO2 particles by spraying, and prepares a cooling material bamboo fiber / SiO2 composite film with daytime passive radiation cooling performance based on the multi-level structure and radiation characteristics of cellulose and SiO2 particles. The film has a solar spectrum reflectivity of 90.1% and an infrared emissivity of 97.9%.

[0042] The PTFE film interlayer in the graphite-PTFE composite film undergoes phase change when the film is at different temperatures, and the liquid-gas phase change material filled therein undergoes phase change, resulting in a change in heat transfer thermal resistance. The thermal resistance calculation formula is:

[0043]

[0044] Among them, when the temperature is lower than 47.5℃,

[0045] When the temperature is higher than 47.5℃, is the thermal resistance of the phase change material;

[0046] is the thermal resistance of graphite film;

[0047] is the thermal resistance of PTFE interlayer;

[0048] Thermal resistance of thermal conductive silicone grease;

[0049] Rtotal is the thermal resistance of the composite film, in K / W; L1 is the thickness of the phase change material, L2 is the thickness of the graphite film, L3 is the thickness of the PTFE film, and L4 is the thickness of the silicone grease, in m; k1 is the thermal conductivity of the phase change material, in W / m·K; k2 is the convection heat transfer coefficient of the phase change material, in W / m 2 ·K; k3 is the graphite heat transfer coefficient, unit is W / m·K; k4 is the PTFE film heat transfer coefficient, unit is W / m·K; k5 is the silicone grease heat transfer coefficient, unit is W / m·K; A1 is the cross-sectional area of ​​PTFE interlayer, A2 is the cross-sectional area of ​​graphite film, A3 is the cross-sectional area of ​​PTFE film, A4 is the cross-sectional area of ​​silicone grease layer, unit is m 2 .

[0050] The overall thermal resistance of the composite film before and after the phase change liquid continues to exceed the phase change temperature and absorbs heat to expand the PTFE film is as follows: Figure 4 As shown, it can be seen that the thermal resistance of the composite film before the phase change temperature is 0.1K / W, which reflects good thermal conductivity. Under high temperature conditions, the thermal resistance of the composite film changes to 1.2K / W, which is 12 times that before the phase change temperature. It can be seen that the composite film achieves the effect of converting heat transfer thermal resistance.

[0051] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which does not affect the essence of the present invention.

Claims

1. A graphite-PTFE composite membrane capable of adaptively switching heat transfer resistance according to temperature, characterized in that: The graphite-PTFE composite film comprises a first graphite film, a second graphite film, and a PTFE film interlayer, wherein a radiation cooling coating is sprayed on the outer side of the first graphite film, and the inner sides of the first graphite film and the second graphite film are coated with thermal conductive silicone grease; the PTFE film interlayer is located between the first graphite film and the second graphite film, and the PTFE film interlayer is formed by two layers of PTFE films sealed by a thermal conductive adhesive; the PTFE film interlayer contains a liquid-gas phase change material.

2. The graphite-PTFE composite membrane capable of adaptively switching heat transfer resistance according to temperature according to claim 1, characterized in that: The first graphite film and the second graphite film are polyimide-based thermally conductive graphite films, and the thermally conductive graphite films have an in-plane thermal conductivity of 1275±20 W / (m·K), a tensile strength of 232±5 MPa, and a thickness of 50 to 170 μm.

3. The graphite-PTFE composite membrane capable of adaptively switching heat transfer resistance according to temperature according to claim 1, characterized in that: The PTFE film is a polytetrafluoroethylene (PTFE) / SiO2 thermal conductive composite film material, with a mechanical strength of 17.3±0.05 MPa and a thermal conductivity of 0.98±0.02 W / (m·K).

4. The graphite-PTFE composite membrane capable of adaptively switching heat transfer resistance according to temperature according to claim 1, characterized in that: The thermal conductive silicone grease is Prolimatech PK-3, and the thermal conductivity is 16 W / (m·K).

5. The graphite-PTFE composite membrane capable of adaptively switching heat transfer resistance according to temperature according to claim 1, characterized in that: The thermally conductive adhesive is epoxy resin-based MasterBond EP29LPA-1, and has a thermal conductivity of 1.1 W / m·K.

6. The graphite-PTFE composite membrane capable of adaptively switching heat transfer resistance according to temperature according to claim 1, characterized in that: The radiation cooling coating is a composite radiation cooling coating based on bamboo fiber and mixed with SiO2 particles. The solar spectrum reflectivity of the bamboo fiber / SiO2 composite film is 90.1%, and the infrared emissivity is 97.9%.

7. The graphite-PTFE composite membrane capable of adaptively switching heat transfer resistance according to temperature according to claim 1, characterized in that: The phase change material is 3F-50 electronic coolant, with a phase change temperature of 47.5° C. and a thermal conductivity of 0.063 W / (m·K).

8. The graphite-PTFE composite membrane capable of adaptively switching heat transfer resistance according to temperature according to claim 1, characterized in that: The preparation method of the PTFE film is as follows: (1) Weigh a silane coupling agent, a surfactant, ethanol, formic acid and a PTFE emulsion in proportion at room temperature, place them in a flask and stir them evenly; (2) adding Al2O3 ceramic powder and SiO2 ceramic powder into a flask in sequence, and stirring evenly to obtain a mixed glue solution; (3) using a silane coupling agent surface modification liquid to impregnate the glass fiber cloth material, then air-drying it and baking it at 110-120° C. for 10 min, and the obtained glass fiber cloth is ready for use; (4) Pour the mixed adhesive solution after being stirred evenly into a clean dipping tank, immerse the glass fiber cloth treated in step (3) in the adhesive solution, dry it at 70° C. to remove the adhesive solvent, and continue baking at 180° C. for 5 minutes to obtain a PTFE / SiO2 composite film containing Al2O3 filler.

9. The graphite-PTFE composite membrane capable of adaptively switching heat transfer resistance according to temperature according to claim 1, characterized in that: The first graphite film and the second graphite film are prepared by the following method: (1) Adding 4,4′-diaminodiphenyl ether (ODA) and p-phenylenediamine (PDA) in a molar ratio of 70:30 into a three-necked flask, and simultaneously adding N,N-dimethylacetamide (DMAc), and controlling the solid content of polyamic acid (PAA) in the flask to be in the range of 15% to 20%, introducing N2 protection during the preparation process, and stirring and dispersing until the diamine is completely dissolved; (2) adding pyromellitic anhydride (PMDA) in equal molar batches into a flask, and stopping adding PMDA when the viscosity of PAA reaches 100-120 Pa·S; (3) adding a micron-sized calcium carbonate solution and controlling its content to 1.5%, continuing stirring for 2 hours to allow the calcium carbonate to be completely dispersed in the PAA, and performing a degassing treatment to obtain a polyamic acid slurry; (4) The completely degassed polyamic acid slurry is baked and cooled to obtain a polyimide carbon-based film, and the polyimide carbon-based film is carbonized by heating the film from 0°C to 1300°C at a constant rate of 3°C / min under vacuum conditions, first cooled to room temperature, and then heated from 1000°C to 2700°C at a constant rate of 3°C / min under argon gas and normal pressure conditions to obtain the graphite film.

10. The graphite-PTFE composite membrane capable of adaptively switching heat transfer resistance according to temperature according to claim 9, characterized in that: The micron-sized calcium carbonate solution is prepared by using a shearing and grinding process and KH550 as a dispersing aid.

Images