Preparation method of polyurethane-based flexible phase change material and battery thermal management device

Abstract

The invention relates to a preparation method of a polyurethane-based flexible phase-change material and a battery heat management device. Polyethylene glycol is used as a phase-change material, and adipic dihydrazide (ADH) and 4, 4 '-diphenyltetracarboxylic dianhydride (ADH) are integrated at a condensation end of a heat pipe; at least one of 4, 4 '-diaminobenzanilide (DABA) is used as a cross-linking agent, and at least one of HMDI or IPDI is used as a chain extender to prepare the polyurethane-based flexible phase change material with enthalpy value, flexible rigidity and appropriate phase change temperature. The material not only has excellent mechanical strength and thermal stability, but also has healing property, recoverability and shape memory function. The polyurethane-based flexible phase change material serves as an energy storage film and forms a sealing structure with the condensation end through mechanical pressing. When the temperature rises, the energy storage film B1 absorbs heat and expands, the contact area with the outside is increased, the heat dissipation power is improved, and the heat dissipation efficiency and the heat load management capacity are remarkably improved by maximizing the heat transfer area and utilizing the high latent heat characteristic.

Description

Technical Field

[0001] The present invention relates to the field of battery thermal management, and particularly to a preparation method of a polyurethane-based flexible phase change material and a battery thermal management device. Background Art

[0002] Heat pipes achieve efficient heat conduction through liquid evaporation and condensation, and are filled with working liquid inside. It can evenly distribute heat, prevent the battery from overheating, and improve the stability and lifespan of the battery. However, the heat dissipation performance of the condensation end of the heat pipe cannot be dynamically adjusted, resulting in a large difference in heat dissipation efficiency under different working conditions. Traditional heat dissipation structures are prone to heat dissipation bottlenecks when dealing with sudden high heat flux densities, leading to system overheating and performance degradation. Therefore, the existing technology has problems such as limited heat dissipation efficiency, inability to dynamically adjust, poor adaptability, and high system cost in the heat management of the condensation end of battery heat pipes, and innovative solutions are urgently needed.

[0003] Phase change materials (PCMs) absorb or release thermal energy through phase transitions to maintain a constant temperature, and are widely used in battery cooling and temperature control. However, in practical applications, they often face problems such as easy leakage, poor thermal conductivity, and high rigidity. Especially when in rigid contact with the battery, the effective contact area is limited, reducing the thermal management efficiency. The limitations of traditional covalent cross-linking strategies are obvious, and modern application requirements demand materials with advanced properties such as thermal energy storage, healability, shape memory, and recyclability. Existing technologies such as CN115073909B introduce a flexible phase change composite material with adjustable dielectric constant, which has good encapsulation and flexibility, but the enthalpy value is only 52.1 J / g, and the heat dissipation efficiency under high-power conditions is insufficient. While CN116875034 A proposes a flexible composite phase change material with a honeycomb structure dual thermal conduction network, the phase change enthalpy value is as high as 96.88 kJ / kg, but the flexibility is insufficient, and it may crack under extreme stress conditions. Neither of them has advanced properties such as healability, shape memory, and recyclability.

[0004] Therefore, researchers urgently need to use a simple and easy-to-operate process to prepare flexible thermal management materials with high flexibility and high enthalpy values. These materials should have excellent thermal conductivity and the above-mentioned advanced properties to meet the heat dissipation requirements of electronic devices. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to propose a battery thermal management device based on a flexible phase change material. The device adopts an L-shaped heat pipe and integrates a layer of flexible phase change material at its condensation end, and utilizes the high latent heat characteristic of the flexible phase change material to absorb and release heat, so as to improve the heat transfer efficiency, thereby enhancing the overall heat dissipation performance and achieving effective management and regulation of the heat load at the condensation end.

[0006] Another object of the present invention is to provide a preparation method of a polyurethane-based flexible phase change material, which has both high flexibility and heat enthalpy value and has advanced properties such as healability, shape memory and recyclability.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] In a first aspect, the present invention provides a preparation method of a polyurethane-based flexible phase change material. The process of the preparation method is as follows:

[0009] 1) In an inert atmosphere, dissolve the phase change substrate polyethylene glycol and the chain extender in a co-solvent, and then add the catalyst 2-lauric acid-2-butyltin, and uniformly stir and mix at a temperature of 70-80 °C to obtain a prepolymer solution;

[0010] The mass ratio of the phase change material to the co-solvent is 1:2-10, and the molar ratio of the phase change material to the chain extender is 1:2-2.1; the addition amount of the catalyst is 2-3 drops;

[0011] 2) Then add a crosslinking agent under an inert atmosphere, and uniformly stir and mix at a temperature of 30-45 °C in an inert atmosphere to obtain a polyurethane phase change energy storage polymer solution; the crosslinking agent is at least one of 4,4-diaminobenzanilide and adipic dihydrazide;

[0012] 3) Put the polyurethane phase change energy storage polymer solution into a container, and place it in a vacuum drying oven to fully dry and cure to obtain a polyurethane-based flexible phase change material.

[0013] Furthermore, the polyurethane-based flexible phase change material can be curled 360° without breaking, the enthalpy value is not less than 70 J / g, the elongation at break is greater than 550%, the phase change temperature is 30-50 °C, and it has shape memory ability.

[0014] Furthermore, the crosslinking agent is a mixture composed of 4,4-diaminobenzanilide and adipic dihydrazide, the chain extender is at least one of HMDI or IPDI, and the polyurethane-based flexible phase change material has self-healing ability.

[0015] Furthermore, the 4,4-diaminobenzanilide and adipic dihydrazide are mixed according to a molar ratio of 1:1; the chain extender is HMDI, the maximum stress of the phase change material exceeds 10 MPa, the elongation at break is 1200%-1500%, and the phase change temperature is 36-42.69 °C.

[0016] Furthermore, the reaction chemicals are pretreated for water removal: dry N,N-dimethylformamide with 5A molecular sieve for one week, dry polyethylene glycol in a vacuum drying oven (-0.1 MPa, 120 °C) for 3 h, and all glass instruments involved in the experiment are dried in advance.

[0017] Further, the number-average molecular weight of the polyethylene glycol is 4000 - 6000, preferably 5000 - 6000.

[0018] Further, in step 1), the rotation speed of the stirring and mixing is 500 - 700 rad / min, and the stirring time is 2 - 3 h; after adding the crosslinking agent, the rotation speed is 200 - 300 rad / min, and the stirring time is 2 - 3 h to prevent the polymer from agglomerating.

[0019] In a second aspect, the present invention provides an application of the polyurethane-based flexible phase change material obtained by the above preparation method, and the polyurethane-based flexible phase change material is used in battery thermal management.

[0020] In a third aspect, the present invention provides a battery thermal management device, which uses the polyurethane-based flexible phase change material obtained by the above preparation method as an energy storage film. The device includes a battery box A0, a cylindrical battery module A1, an L-shaped heat pipe A2, a heat conducting plate A3, and an energy storage film B1; inside the battery box A0, the cylindrical battery modules A1 are regularly arranged. The cylindrical battery modules A1 are fixed by a battery fixing mechanism and a heat sink B2. The heat conducting plate A3 is closely attached to the cylindrical battery module A1, so that the heat generated is transferred to the evaporation section of the L-shaped heat pipe A2 through the heat conducting plate A3. Among them, the L-shaped heat pipes A2 are equidistantly arranged between the gaps of each cylindrical battery A1. The L-shaped heat pipe A2 is L-shaped and includes a vertically arranged evaporation section and a horizontally arranged condensation section. There are several L-shaped heat pipes A2, which are distributed in an array. All the L-shaped heat pipes A2 in the same row are divided into two parts, and the condensation sections at the top of each part are combined into the same branch. There are two branches, left and right, arranged in the same row, and the end of each branch forms a sealed structure with the energy storage film B1 through mechanical pressing; the L-shaped heat pipe A2 is a gravity heat pipe, and the inside of the heat pipe is filled with a working medium. The condensation section of the L-shaped heat pipe A2 is in full contact with the heat sink B2.

[0021] Further, the process of the device thermal management is as follows: The heat generated by the heat-generating cylindrical battery module A1 is transferred to the evaporation section of the L-shaped heat pipe through the heat conducting plate A3. The working medium inside the L-shaped heat pipe is vaporized into steam after being heated and moves upward to the end of the condensation section of the L-shaped heat pipe located at the top of the cylindrical battery module A1, which is the condensation end; at the condensation end, the temperature rises, and the energy storage film B1 plays a role: after absorbing heat and expanding, it expands the heat dissipation area; then it releases heat and contracts to store the excess energy;

[0022] When the steam reaches the condensation section, heat is transferred by heat flow drive. The coolant condenses in the condensation section, and the condensed working medium then flows back along the inner wall of the heat pipe to the evaporation section to complete a cooling cycle. At the same time, the energy storage film expands again during the backflow of the coolant and resumes its heat absorption capacity. Through such continuously repeated cycles, efficient heat dissipation and battery cooling effects are achieved, thereby keeping the battery within the ideal operating temperature range.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The polyurethane-based flexible phase change material obtained by the preparation method of the present invention selects at least one of adipic dihydrazide (ADH) and 4,4'-diaminobenzanilide (DABA) as a cross-linking agent, which synergistically acts with specific types of phase change substrates and chain extenders, endowing the material with excellent mechanical strength, thermal stability, shape memory and recyclability.

[0025] In the present invention, the combination of adipic dihydrazide (ADH) and 4,4'-diaminobenzanilide (DABA) as a cross-linking agent can form a dynamic cross-linking network, which serves as a rigid framework. Utilizing the high-density hydrogen bond network and π-π stacking interactions, and synergistically acting with the phase change substrate and chain extender, endows the material with excellent mechanical strength, thermal stability, healability, shape memory and recyclability. This material can achieve unbroken 360°, and due to its shape memory property, it can return to its original shape even after deformation, greatly enhancing its adaptability and reliability in practical applications. The experimental data of the examples show that when the strain of this flexible phase change material reaches an astonishing 1342.78%, it can still maintain its structural integrity and does not break until the maximum stress of 21.22 MPa, having excellent tensile fracture ability and shape memory property. At the same time, the phase change temperature is 42.69 °C and the enthalpy value is 107.2 J / g. These properties together ensure its excellent thermal stability.

[0026] In the present invention, the obtained polyurethane-based flexible phase change material is used in battery heat management, and this polyurethane-based flexible phase change material is innovatively integrated in the battery thermal management device, effectively optimizing the heat transfer and heat dissipation performance.

[0027] In the present invention, one or more layers of light yellow semi - transparent flexible phase - change material films with a thickness of about 2 mm are provided at the condensation end of the heat pipe as energy - storage films. By utilizing the high flexibility and phase - change characteristics of the flexible phase - change material, the effective contact area between the vapor and the material is maximized during the endothermic expansion process, thus greatly improving the heat transfer efficiency. This not only effectively reduces the temperature at the condensation end of the heat pipe, but also comprehensively improves the overall heat dissipation performance of the battery, providing a solid guarantee for the efficient and stable operation of the battery. This innovative structure of the present invention effectively solves the problem of a large amount of heat generated during the charging and discharging process of the battery, avoiding problems such as battery performance degradation, safety accidents, and shortened lifespan. In addition, the high latent heat characteristic of the flexible phase - change material enables it to automatically absorb and release heat with temperature changes, effectively managing and regulating the heat load at the condensation end, overcoming the heat dissipation bottleneck problem caused by the rigidity and thermal conductivity limitations of traditional heat - dissipation materials, and improving the overall heat - dissipation efficiency and adaptability of the system. Brief Description of the Drawings

[0028] Figure 1 Fig. is a schematic diagram of the application of the battery thermal management device based on flexible phase - change material in a cylindrical battery module;

[0029] Figure 2 Fig. is a schematic diagram of the working state of the battery thermal management device based on flexible phase - change material applied in a cylindrical battery module;

[0030] Figure 3 Fig. is a schematic diagram of the working process of the energy - storage film in the battery thermal management device based on flexible phase - change material of the present invention;

[0031] Figure 4 Fig. is a dynamic process diagram of heating the deformed material to 80 °C to gradually restore it to its original shape.

[0032] Figure 5 Fig. is the healability test of Example 1.

[0033] Figure 6 Fig. is the mechanical property test after healing of Example 1.

[0034] Table 1 shows the elongation at break and tensile strength of samples with PU6000 as the phase - change substrate, using different chain extenders and different ratios of cross - linkers.

[0035] Table 2 shows the phase - change temperature and enthalpy value of samples with PU6000 as the phase - change substrate, using different chain extenders and different ratios of cross - linkers.

[0036] In the figures: A1, cylindrical battery; A2, heat pipe; A3, heat - conducting plate; B1, energy - storage film; B2, heat sink. Detailed Description of the Embodiments

[0037] The present invention will be further explained below in conjunction with embodiments and the accompanying drawings, but this is not intended to limit the protection scope of the present application.

[0038] Example 1

[0039] (1) 15 g of polyethylene glycol (PEG6000) was pre-dried at 120 °C for 2 h. The chain extender dicyclohexylmethane diisocyanate (HMDI) ester was dissolved in N,N-dimethylformamide (DMF), and then the catalyst dibutyltin dilaurate was added. The reaction was fully stirred at 80 °C for 2 h in a nitrogen atmosphere to obtain a prepolymer solution.

[0040] (2) 0.28 g of 4,4-diaminobenzanilide and adipic dihydrazide (ADH) were added to the product obtained in (1). The reaction was stirred at 40 °C for 3 h in a nitrogen environment to obtain a polyurethane phase change energy storage polymer solution.

[0041] (3) The polyurethane phase change energy storage polymer solution obtained in step (2) was placed in a vacuum drying oven for sufficient drying for 24 h. After removing the solvent, a polyurethane flexible phase change energy storage film was obtained. The polyurethane flexible phase change energy storage film is a light yellow semi-transparent film about 2 mm thick, can be curled 360° without breakage, and has good flexibility; the phase change temperature is 42.69 °C; the enthalpy value is 107.2 J / g.

[0042] When applied to a heat pipe, it has excellent thermal performance, indicating that the material has very high ductility and toughness, and exhibits good shape memory ability in experiments.

[0043] The normal operating temperature of the battery is between 20 and 40 °C. The phase change temperature of the sample in Example 1 is 42.69 °C, and it has good temperature control ability, which is very suitable for battery thermal management.

[0044] Figure 5 In, the sample was divided into two parts and marked respectively, and then the two samples were bonded together and heated at 100 °C for 15 minutes. As a result, it can be seen that the two samples were successfully healed, indicating that the material has good healability, is not easy to break, and can be used for a long time at high temperature.

[0045] Figure 6 In, the healed sample was suspended with a 200 g weight for mechanical testing. The results showed that even at the healed part, the sample still had good mechanical properties.

[0046] By heating the film under an electric heating film, the experiment shows that the curling height of the flexible phase change material film in this example is significant under heating conditions, indicating the good shape memory characteristics of the material.

[0047] Examples 2 - 6

[0048] In this example, compared with Example 1, the molar ratio of the two substances in the crosslinking agent (0:1, 2:1, 1:2, 1:0) and whether a chain extender is added (DABA:ADH = 1:1) are changed.

[0049] The samples of Examples 2-6 were subjected to relevant stress-strain tests, and the test results are shown in Table 1. In Table 1, "I" represents that the chain extender is IPDI, "H" represents that the chain extender is HMDI, "D" and "A" respectively represent 4,4-diaminobenzanilide DABA and adipic dihydrazide ADH, and the subscript numbers represent the ratio of the two. The elongation at break of all five materials is less than 900%. In the case of no DABA or no ADH and when ADH is in excess, the elongation at break cannot reach 800%, and the tensile strength is higher than 14 MPa. When a chain extender is added, the elongation at break is the largest, exceeding 800%, and the maximum tensile stress is greater than 25 MPa. Compared with Example 1, different types of chain extenders have a greater impact on the performance effect. Example 1 is preferred, which can achieve an elongation at break of more than 1000%.

[0050] In addition, it was found through testing that in the case of no DABA or no ADH, the self-healing ability of the material is poor, but it still has the shape memory function.

[0051] Table 1

[0052]

[0053] As can be seen from the above table, although the tensile strength is relatively high at 35.02 MPa when DABA:ADH = 1:0, its elongation at break is less than 800%. When DABA:ADH = 1:1 and the chain extender IPDI is added, and when DABA:ADH = 2:1 and the chain extender HMDI is added, the tensile strength of the material (>21.22 MPa) is better than that of the sample in Example 1 (21.22 MPa), but the elongation at break of the sample in Example 1 (1342.78%) is significantly higher than that of other materials. Since this device mainly relies on thermal expansion and contraction and steam pressure to increase the volume of the heat dissipation material at the condensation end, thereby improving the heat dissipation efficiency, and the steam pressure is small, the requirement for the tensile strength of the material is relatively low, but the requirement for the elongation at break is relatively high to achieve a greater volume expansion. Based on this characteristic, the sample in Example 1 is more suitable as the heat dissipation material at the condensation end of the heat pipe.

[0054] The test results were obtained by differential scanning calorimetry (DSC) and are shown in Table 2.

[0055] Table 2

[0056]

[0057] As can be seen from Table 3, the lower phase change temperatures of Examples 2-6 are relatively lower than that of Example 1, and the enthalpy values can be controlled above 70 J / g, indicating that the materials of the present invention have excellent elongation at break and also take into account relatively high enthalpy values. Moreover, the enthalpy value (107.2 J / g) of the sample in Example 1 is significantly higher than that of other materials, indicating that it can absorb more heat and has a more significant improvement in the heat dissipation efficiency of the heat pipe. Therefore, the sample in Example 1 is more suitable as the heat dissipation material for the condensation end of the heat pipe.

[0058] Example 7

[0059] (1) 20 g of polyethylene glycol (PEG4000) was pre-dried at 120 °C for 2 h, 2.62 g of diphenylmethane diisocyanate (HMDI) dissolved in N,N-dimethylformamide (DMF) was added, and then the catalyst dibutyltin dilaurate (DBDTL) was added. The reaction was fully stirred at 80 °C for 2 h in a nitrogen atmosphere to obtain a prepolymer solution.

[0060] (2) 0.56 g of 4,4-diaminobenzanilide (DABA) and 0.44 g of adipic dihydrazide (ADH) were added to the product obtained in (1), and the reaction was stirred at 40 °C for 3 h in a nitrogen environment to obtain a polyurethane phase change energy storage polymer solution.

[0061] (3) The polyurethane phase change energy storage polymer solution obtained in step (2) was placed in a vacuum drying oven for sufficient drying for 24 h. After removing the solvent, a polyurethane flexible phase change energy storage film was obtained. The polyurethane flexible phase change energy storage film is a light yellow semi-transparent film about 2 mm thick, can be curled 360° without breaking, and has good flexibility; the phase change temperature is 36.09 °C, the enthalpy value is 79.35 J / g, the maximum stress is about 18.35 MPa, and the material breaks only when the strain reaches 1245%, indicating that the material has very high ductility and toughness. And it showed good shape memory ability in the experiment.

[0062] Example 8

[0063] In this example, polyethylene glycol PEG5000 was used on the basis of Example 1, and the elongation at break was 1315%.

[0064] After relevant tests, the maximum stress (tensile strength) of the phase change materials of the present invention all exceed 10 MPa. The maximum stress in multiple tests is about 12-24 MPa, and the elongation at break is greater than 550%, preferably above 1100%, especially in the range of 1200%-1500%, indicating that the material has very high ductility and flexibility, achieving a balance between rigidity and flexibility.

[0065] Example 9

[0066] Figure 1This is a schematic diagram of the battery thermal management device based on flexible phase change materials in this embodiment, which is applied to a cylindrical battery module, including a battery box A0, a cylindrical battery module A1, an L-shaped heat pipe A2, a heat conduction plate A3, a storage thin film B1 (the material of which is the flexible phase change material prepared in Embodiment 1), and a heat sink B2. Inside the battery box A0, the cylindrical battery modules A1 are arranged regularly. The cylindrical battery modules A1 are fixed to the heat sink B2 by a battery fixing mechanism. The heat conduction plate A3 is closely attached to the cylindrical battery module A1, so that the heat generated by it is transferred to the evaporation section of the L-shaped heat pipe A2. Among them, the L-shaped heat pipes A2 are arranged at equal distances between the gaps of each cylindrical battery A1. The L-shaped heat pipe A2 is L-shaped, including a vertically arranged evaporation section and a horizontally arranged condensation section. There are a number of L-shaped heat pipes A2, which are distributed in an array. All the L-shaped heat pipes A2 in the same row are divided into two parts, and the condensation sections at the top of each part are combined into the same branch. There are two branches, left and right, arranged in the same row. The end of each branch is hermetically connected to the storage thin film, and a sealed structure is formed with the storage thin film B1 by mechanical pressing at the end; the L-shaped heat pipe A2 is a gravity heat pipe, and the heat pipe is filled with a working medium. The condensation section of the L-shaped heat pipe A2 is in full contact with the heat sink B2 to further improve the heat dissipation capacity, and finally realize the efficient heat dissipation of the condensation section.

[0067] As the temperature of the storage thin film B1 rises, it absorbs heat and expands, increasing the contact area with the outside world, improving the heat dissipation power, and then releases heat and contracts, storing the excess energy. By using the high latent heat characteristics of the flexible phase change material, it absorbs and releases heat, realizing the effective management and regulation of the heat load at the condensation end.

[0068] See Figure 2 This is a schematic diagram of the working process of the battery thermal management device based on flexible phase change materials of the present invention. For the cylindrical battery module A1 that generates heat, the heat generated by it is transferred to the evaporation section of the L-shaped heat pipe through the heat conduction plate A3. The working medium inside the L-shaped heat pipe is vaporized by heat to form steam and moves upward to the end (condensation end) of the condensation section of the L-shaped heat pipe located at the top of the cylindrical battery module A1. At the condensation end, the temperature rises, and the storage thin films B1 play a role: after absorbing heat and expanding, they increase the heat dissipation area; then they release heat and contract, storing the excess energy. When the steam reaches the condensation section, the heat is transferred by heat flow drive, and the coolant condenses in the condensation section. The condensed working medium then flows back along the inner wall of the heat pipe to the evaporation section, completing a cooling cycle. At the same time, the storage thin film becomes larger again during the process of the coolant flowing back, restoring the heat absorption ability. Through such continuous repetition of the cycle in the whole system, efficient heat dissipation and battery cooling effects are achieved, so as to keep the battery within the ideal working temperature range. This process utilizes the characteristics of the heat pipe and the flexible phase change material, which is both efficient and ensures the light and compact design of the system.

[0069] Figure 3This is a schematic diagram of the working process of the flexible phase change material in the battery thermal management device based on the flexible phase change material of the present invention. As the temperature inside the heat pipe increases, the heat transferred by the heat pipe increases, causing the surface of the energy storage film B1 to rapidly heat up. Since the energy storage film B1 absorbs heat and expands during heating, the heat dissipation area is increased and the heat dissipation speed is accelerated. When the temperature of the condensation end of the L-shaped heat pipe gradually decreases, due to the shape memory function of the energy storage film B1, the energy storage film B1 will return to its original size, thus realizing flexible temperature management.

[0070] The present invention also provides a method for controlling the shape memory behavior of a polyurethane-based phase change material (PU-PCMs). This method utilizes the dynamic characteristics of the polyurethane molecular chain to enable the material to exhibit programmable shape memory behavior at different temperatures. Specifically, it includes: when the temperature is below the glass transition temperature (Tg), the molecular chain is in a frozen state and the material maintains its pre-set shape; when the temperature is above Tg, the molecular chain thaws and triggers the material to return to its original configuration. The polyurethane-based phase change material (PU-PCMs) is subjected to an initial deformation treatment at room temperature. The deformed material is heated to 80 °C to gradually restore it to its original shape, and the whole process takes 330 seconds. As Figure 4 shown, by utilizing the dynamic characteristics of the polyurethane molecular chain, the programmable shape memory behavior of the material is realized.

[0071] The present invention maximizes the heat transfer area between steam and the flexible phase change material, improves the heat transfer efficiency, and thus enhances the overall heat dissipation performance; utilizes the high latent heat characteristic of the flexible phase change material to absorb and release heat, and realizes effective management and regulation of the heat load at the condensation end.

[0072] Obviously, the above are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

[0073] Matters not described in the present invention are applicable to the prior art.

Claims

1. A preparation method of a polyurethane-based flexible phase change material, characterized in that, The process of the preparation method is as follows: 1) In an inert atmosphere, dissolve the phase change substrate polyethylene glycol and the chain extender in a cosolvent, and then add the catalyst 2-butyltin dilaurate. Stir and mix uniformly at a temperature of 70-80 °C to obtain a prepolymer solution; The mass ratio of the phase change material to the cosolvent is 1:2-10, and the molar ratio of the phase change material to the chain extender is 1:2-2.1; the addition amount of the catalyst is 2-3 drops; 2) Then add a crosslinking agent under an inert atmosphere and stir and mix uniformly at a temperature of 30-45 °C in an inert atmosphere to obtain a polyurethane phase change energy storage polymer solution; the crosslinking agent is at least one of 4,4-diaminobenzanilide and adipic dihydrazide; 3) Place the polyurethane phase change energy storage polymer solution in a container and place it in a vacuum drying oven to fully dry and cure to obtain a polyurethane-based flexible phase change material.

2. The preparation method according to claim 1, characterized in that, The polyurethane-based flexible phase change material can be curled 360° without fracture, the enthalpy value is not less than 70 J / g, the elongation at break is greater than 550%, the phase change temperature is 30-50 °C, and it has shape memory ability.

3. The preparation method according to claim 1, wherein The crosslinking agent is a mixture composed of 4,4-diaminobenzanilide and adipic dihydrazide, the chain extender is at least one of HMDI (dicyclohexylmethane diisocyanate) or IPDI (isophorone diisocyanate), and the polyurethane-based flexible phase change material has self-healing ability.

4. The preparation method according to claim 3, characterized in that, The 4,4-diaminobenzanilide and adipic dihydrazide are mixed according to a molar ratio of 1:1; the chain extender is HMDI, the maximum stress of the phase change material exceeds 10 MPa, the elongation at break is 1200%-1500%, and the phase change temperature is 36-42.69 °C.

5. The preparation method according to claim 1, characterized in that, Perform dehydration pretreatment on the reaction chemicals: dry N,N-dimethylformamide with 5A molecular sieve for one week, dry polyethylene glycol in a vacuum drying oven (-0.1 MPa, 120 °C) for 3 h, and dry all glass instruments involved in the experiment in advance.

6. The preparation method according to claim 1, characterized in that, The number average molecular weight of the polyethylene glycol is 4000-6000.

7. The preparation method according to claim 1, characterized in that, In step 1), the rotation speed of the stirring and mixing is 500-700 rad / min, and the stirring time is 2-3 h; after adding the crosslinking agent, the rotation speed is 200-300 rad / min, and the stirring time is 2-3 h.

8. Use of the polyurethane-based flexible phase change material obtained by the preparation method according to any one of claims 1-7, characterized in that, The polyurethane-based flexible phase change material is used in battery thermal management.

9. A battery heat management device uses a polyurethane-based flexible phase change material obtained by the preparation method described in any one of claims 1-7 as an energy storage thin film, characterized in that, The device includes a battery box body, a cylindrical battery module, an L-shaped heat pipe, a heat conducting plate and an energy storage film; inside the battery box body, the cylindrical battery modules are arranged regularly, the cylindrical battery modules are fixed by a battery fixing mechanism and a heat sink, the heat conducting plate is closely attached to the cylindrical battery module, so that the heat generated by it is transferred to the evaporation section of the L-shaped heat pipe through the heat conducting plate, wherein the L-shaped heat pipes are arranged equidistantly between the gaps of each cylindrical battery, the L-shaped heat pipe is L-shaped, including a vertically arranged evaporation section and a horizontally arranged condensation section, there are a number of L-shaped heat pipes, which are distributed in an array, all the L-shaped heat pipes in the same row are divided into two parts, the condensation sections at the top of each part are combined into the same branch, there are two left and right branches arranged in the same row, and the end of each branch forms a sealed structure with the energy storage film through mechanical pressing; the L-shaped heat pipe is a gravity heat pipe, the inside of the heat pipe is filled with a working medium, and the condensation section of the L-shaped heat pipe is in full contact with the heat sink.

10. The battery heat management device according to claim 9, characterized in that, The process of the device thermal management is as follows: the heat generated by the heat-generating cylindrical battery module is transferred to the evaporation section of the L-shaped heat pipe through the heat conducting plate, the working medium inside the L-shaped heat pipe is vaporized to form steam after being heated, and moves upward to the end of the condensation section of the L-shaped heat pipe located at the top of the cylindrical battery module, that is, the condensation end; at the condensation end, the temperature rises, and the energy storage film plays a role: after absorbing heat and expanding, it expands the heat dissipation area; then it releases heat and contracts, storing the excess energy; When the steam reaches the condensation section, the heat is transferred by heat flow drive, the coolant condenses in the condensation section, and the condensed working medium flows back along the inner wall of the heat pipe to the evaporation section to complete a cooling cycle; at the same time, the energy storage film becomes larger again during the process of the coolant flowing back, restoring the heat absorption ability; through such continuous repetition of the cycle, an efficient heat dissipation and battery cooling effect are achieved, so as to keep the battery within an ideal working temperature range.

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