Wide-temperature-range flexible composite phase change material and preparation method thereof

Abstract

The invention relates to the technical field of composite material preparation, and discloses a wide-temperature-range flexible composite phase-change material and a preparation method thereof.The preparation method comprises the steps that paraffin, an ethylene-octylene copolymer elastomer, a powdery polyurethane porous solid-solid phase-change framework and expanded graphite are prepared according to the formula mass percent, the paraffin is melted into liquid paraffin, and the liquid paraffin is prepared; the preparation method comprises the following steps: heating an ethylene-octylene copolymer elastomer to a softened state, dropwise adding molten liquid paraffin into a beaker filled with the ethylene-octylene copolymer elastomer according to a mass ratio of 11: 9 to form a mixture, adding a powdery cross-linked polyurethane solid-solid phase change skeleton into the mixture, adjusting the temperature and continuously stirring to obtain a mixture; after stirring is completed, the mixture is subjected to high-speed shearing through a homogenizer, after the paraffin / ethylene-octylene copolymer elastomer and the polyurethane framework form a uniform mixture, the expanded graphite is added, the temperature is adjusted, continuous stirring is conducted, and the obtained composite multi-phase-change material has the advantages of being high in enthalpy value, good in heat conduction performance, wide in temperature range and flexible.

Description

Technical Field

[0001] The present invention relates to the technical field of composite material preparation, and particularly to a wide-temperature-range flexible composite phase change material and a preparation method thereof. Background Technique

[0002] With the rapid development of the new energy electric vehicle market, as the core component of the vehicle, the performance and stability of the power battery directly affect the overall performance of the vehicle. However, if the heat generated during the operation of the power battery cannot be dissipated in a timely and effective manner, it will lead to a decline in battery performance, a shortening of the service life, and even potential safety hazards. Therefore, the thermal management problem of the power battery has become a key technical challenge that needs to be solved urgently. Research shows that by controlling the operating temperature of the battery module within a suitable range (20°C to 55°C) through efficient thermal management technology, the service life of the battery and the vehicle performance can be significantly improved.

[0003] Due to the advantages of high efficiency, compactness, and light weight, the thermal management system based on phase change materials has been widely used in the field of new energy electric vehicles. However, with the continuous improvement of the energy density of lithium-ion power batteries, the heat generated during their operation has increased significantly, posing higher requirements for thermal management materials. Existing phase change materials generally have problems such as low enthalpy value, poor thermal conductivity, and strong rigidity, making it difficult to meet the actual application requirements. In particular, traditional shaped composite phase change materials are difficult to adapt to the volume change of the battery during charging and discharging due to their large rigidity and high contact thermal resistance, which limits their thermal management effect.

[0004] To solve the above problems, flexible composite phase change materials have gradually become a research hotspot. However, current research mainly focuses on thermally induced flexible materials, whose flexibility significantly decreases when the temperature is lower than the phase change temperature, making it difficult to meet the installation requirements of the battery at room temperature. In addition, existing flexible composite phase change materials usually rely on a large amount of flexible matrices to achieve wide-temperature-range flexibility, but these matrices do not have phase change functions, resulting in a decrease in the overall enthalpy value of the material and limited thermal management capabilities. Therefore, developing a composite phase change material with both wide-temperature-range flexibility, high phase change enthalpy value, and excellent thermal conductivity is of great significance for improving the thermal management performance of power batteries and also provides technical support for the further development of new energy electric vehicles.

[0005] By combining the excellent mechanical properties of ethylene-octene copolymer elastomer and the phase change characteristics of polyurethane porous solid-solid phase change framework, and utilizing the support and adsorption effects of its cross-linked network structure, the present invention constructs a multi-component composite phase change material with both wide-temperature-range flexibility, high phase change enthalpy value, and excellent thermal conductivity, so as to improve the applicability and thermal management efficiency of the material in the thermal management system of power batteries. Summary of the Invention

[0006] (I) Technical Problems to be Solved

[0007] In view of the deficiencies of the prior art, the present invention provides a wide-temperature-range flexible composite phase change material and a preparation method thereof, which have the advantages of wide-temperature-range flexibility, high phase change enthalpy value and excellent thermal conductivity, and solve the technical problems of weakened flexibility, low phase change enthalpy value and poor thermal conductivity of existing flexible composite phase change materials below the phase change temperature.

[0008] (II) Technical Solution

[0009] To achieve the above object, the present invention provides the following technical solution: a wide-temperature-range flexible composite phase change material, and the components and mass percentages of the composite phase change material are: paraffin wax 35% - 70%; ethylene-octene copolymer elastomer 30% - 50%; powdery polyurethane porous solid-solid phase change skeleton 0% - 20%; expanded graphite 0% - 20%.

[0010] Preferably, the phase change temperature of the paraffin wax is 40 - 45°C, and the phase change enthalpy value is 230 - 250 kJ / kg. When the paraffin wax and the ethylene-octene copolymer elastomer are synthesized according to a mass ratio of 11:9, a composite flexible matrix of paraffin wax-ethylene-octene copolymer elastomer can be obtained and used as the matrix of the composite phase change material. Its phase change temperature is 38 - 40°C, the phase change enthalpy value is 120 - 170 kJ / kg, the elongation at break is 4% - 600%, the tensile strength is 0.7 - 5 MPa, and the Young's modulus is 30 - 170 MPa.

[0011] Preferably, the preparation process of the powdery polyurethane porous solid-solid phase change skeleton is: dispersing polyethylene glycol in an organic solvent, and slowly injecting a N,N-dimethylformamide solution of hexamethylene diisocyanate biuret under nitrogen protection for reaction, and then drying, curing and grinding to obtain the powdery polyurethane porous solid-solid phase change skeleton.

[0012] Preferably, the number-average molecular weight of the polyethylene glycol is 7000 - 9000, the organic solvent is N,N-dimethylformamide, the reaction is carried out at 50°C - 70°C, and the drying is carried out at 80°C - 100°C.

[0013] Preferably, the phase change temperature of the powdery polyurethane porous solid-solid phase change skeleton is 55°C - 60°C, and the phase change enthalpy value is 160 kJ / kg - 180 kJ / kg.

[0014] Preferably, the powdery polyurethane porous solid-solid phase change skeleton is made by reacting polyethylene glycol and hexamethylene diisocyanate biuret according to a molar ratio of 1:1 - 2:1.

[0015] Preferably, the mesh number of the expanded graphite is 40 - 60 meshes, and the expansion degree is 200 - 300 times. A preparation method of a wide-temperature-range flexible composite phase change material is prepared according to the components and their mass percentages of the above-mentioned wide-temperature-range flexible composite phase change material, including the following preparation steps:

[0016] Step 1. Raw material preparation: Prepare paraffin wax, ethylene-octene copolymer elastomer, powdery polyurethane porous solid-solid phase change skeleton and expanded graphite according to the mass percentages of the formula.

[0017] Step 2. Raw material pretreatment: Melt the paraffin wax at a temperature of 40 - 45 °C to form liquid paraffin.

[0018] Step 3. Melt blending: Add the ethylene-octene copolymer elastomer into a glass beaker, heat it to a soft state on a flat magnetic stirrer heater at 110 - 120 °C, and drop the melted liquid paraffin into the beaker containing the ethylene-octene copolymer elastomer according to a mass ratio of 11:9. Keep the temperature of the flat heater and melt blend for 55 - 60 min under continuous stirring to form a mixture.

[0019] Step 4. Mixture homogenization: Add the powdery crosslinked polyurethane solid-solid phase change skeleton into the above mixture, adjust the temperature of the flat magnetic stirrer heater to 135 - 140 °C, and continuously stir for 25 - 30 min. After stirring, homogenize the mixture by high-speed shearing with a homogenizer for 2 - 3 min.

[0020] Step 5. Add expanded graphite: After the paraffin / ethylene-octene copolymer elastomer and polyurethane skeleton form a uniform mixture, add expanded graphite. Adjust the temperature of the flat magnetic stirrer heater to 145 - 150 °C and stir evenly for 15 - 20 min to obtain a composite multi-phase change material.

[0021] Preferably, the phase change temperature of the composite multi-phase change material is 39 - 44 °C, the phase change enthalpy value is 100 - 150 kJ / kg, and the thermal conductivity is 2 W / (m·K) - 8 W / (m·K).

[0022] Preferably, the components and their mass percentages of the composite phase change material in the raw material preparation are: paraffin wax 44%; ethylene-octene copolymer elastomer 36%; powdery polyurethane porous solid-solid phase change skeleton 15%; expanded graphite 5%.

[0023] Compared with the prior art, the present invention provides a wide-temperature-range flexible composite phase change material and a preparation method thereof, having the following beneficial effects:

[0024] 1. The wide-temperature flexible multi-component composite phase change material of the present invention is made by combining the raw material formula and the preparation method. Among them, a powdery polyurethane porous solid-solid phase change skeleton is added to the phase change material, which has a cross-linked spatial network structure. It can adsorb paraffin on the polyurethane skeleton chains and fill the voids between the polyurethane skeleton chains, so that the paraffin cannot flow freely during the phase change, showing a shaped phase change macroscopically. The prepared material can have a high energy density while having good thermal stability and chemical stability. Not only there is no liquid leakage after the phase change process, but also after the mechanical property test, the elongation at break of the composite material is much higher than the strain definition value of the flexible material. It also has relatively good apparent bending flexibility at -10°C to 40°C. Moreover, the phase change temperature and phase change enthalpy value of the wide-temperature flexible multi-component composite phase change material can vary with the different molecular weights of polyethylene glycol and the R value in the polyurethane porous solid-solid phase change skeleton. Therefore, the phase change temperature range of this phase change material is wide and can be freely regulated.

[0025] 2. Compared with the prior art, the preparation method provided by the present invention is characterized by using the in-situ polymerization method, the melt blending method and the molding method. Among them, an ethylene-octene copolymer elastomer is added to the phase change material and used as a flexible substrate, which can reduce the rigidity of the single paraffin phase change material (for example: the elongation at break of the blend obtained by mixing paraffin and ethylene-octene copolymer elastomer according to the mass ratio of 11:9 is as high as 204.9%). It can effectively solve the problem of strong rigidity of the single paraffin phase change material. The phase change material prepared by the present invention has both a high phase change enthalpy value and excellent thermal conductivity, and at the same time has wide-temperature flexibility, thus overcoming the technical defects such as low enthalpy value, poor thermal conductivity and thermally induced flexibility commonly existing in the existing flexible phase change materials. Since its preparation method is simple, the raw materials are pollution-free and the production cost is low, it is suitable for large-scale industrial production. Description of the Drawings

[0026] Figure 1 SEM image of the phase change material of Example 1;

[0027] Figure 2 DSC test result graph of the phase change material of Example 4;

[0028] Figure 3 SEM image of the phase change material of Example 4;

[0029] Figure 4 Deformation characteristic test result graph of the phase change material of Example 4 at different temperatures.

[0030] Figure 5 Stress-strain test result graph of the phase change material of Example 4. Detailed Description of the Invention

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] Please refer to Figure 1 - Figure 4 , a wide-temperature flexible composite phase change material. The components and their mass percentages of the composite phase change material are as follows: paraffin wax 35% - 70%; ethylene-octene copolymer elastomer 30% - 50%; powdered polyurethane porous solid-solid phase change skeleton 0% - 20%; expanded graphite 0% - 20%.

[0033] Specifically, the phase change temperature of the paraffin wax is 40 - 45°C, and the phase change enthalpy value is 230 - 250 kJ / kg. When the paraffin wax and the ethylene-octene copolymer elastomer are synthesized according to a mass ratio of 11:9, a composite flexible matrix of paraffin wax-ethylene-octene copolymer elastomer can be obtained and used as the matrix of the composite phase change material. Its phase change temperature is 38 - 40°C, the phase change enthalpy value is 120 - 170 kJ / kg, the elongation at break is 4% - 600%, the tensile strength is 0.7 - 5 MPa, and the Young's modulus is 30 - 170 MPa.

[0034] Advantages: By adding an ethylene-octene copolymer elastomer to the phase change material of the present invention and using it as a flexible substrate, the rigidity of the single paraffin wax phase change material can be reduced (for example: the elongation at break of the blend obtained by mixing paraffin wax and ethylene-octene copolymer elastomer according to a mass ratio of 11:9 is as high as 204.9%), thus effectively solving the problem of strong rigidity of the single paraffin wax phase change material.

[0035] Specifically, polyethylene glycol with a molecular weight of 8000 that has been vacuum-dried is mixed uniformly with anhydrous N,N-dimethylformamide and placed in a three-necked flask. Then, in a 60°C water bath, with the magnetic stirring speed maintained at 300 r / min, under nitrogen protection, a solution of hexamethylene diisocyanate biuret in N,N-dimethylformamide is slowly injected dropwise with a syringe. After reacting for 1 h, it is poured into a polytetrafluoroethylene petri dish and cured in a vacuum drying oven at 90°C until the mass remains unchanged to remove the solvent to obtain a polyurethane skeleton, which is ground into powder and reserved for use.

[0036] Advantages: The powdered polyurethane porous solid-solid phase change skeleton is added to the phase change material of the present invention. It has a cross-linked spatial network structure, which can adsorb paraffin wax on the polyurethane skeleton chains and fill the voids between the polyurethane skeleton chains. This makes it impossible for paraffin wax to flow freely when it undergoes a phase change, and it shows a shaped phase change macroscopically.

[0037] Specifically, the mesh number of the expanded graphite is 40 - 60 mesh, and the expansion degree is 200 - 300 times.

[0038] The advantages are as follows: Expanded graphite is added to the phase change material of the present invention. It has a large specific surface area and a rich porous structure, and can construct a heat conduction channel in the material system without structural modification, which can significantly improve the heat conduction performance of the phase change material.

[0039] Specifically, a preparation method of a wide - temperature - range flexible composite phase change material is prepared according to the components and their mass percentages of the above - mentioned wide - temperature - range flexible composite phase change material, and includes the following preparation steps:

[0040] Step 1. Raw material preparation: Prepare paraffin wax, ethylene - octene copolymer elastomer, powdery polyurethane porous solid - solid phase change skeleton and expanded graphite according to the mass percentages of the formula;

[0041] Step 2. Raw material pretreatment: Melt paraffin wax at a temperature of 40 - 45 °C to form liquid paraffin;

[0042] Step 3. Melting and blending: Add ethylene - octene copolymer elastomer into a glass beaker, heat it to a softening state on a flat magnetic stirrer heater at 110 - 120 °C, and drop the melted liquid paraffin into the beaker containing ethylene - octene copolymer elastomer according to a mass ratio of 11:9. Keep the flat heating temperature, and melt - blend for 55 - 60 min under continuous stirring to form a mixture;

[0043] Step 4. Homogenization of the mixture: Add the powdery cross - linked polyurethane solid - solid phase change skeleton into the above - mentioned mixture, adjust the temperature of the flat magnetic stirrer heater to 135 - 140 °C, and continuously stir for 25 - 30 min. After stirring is completed, shear the mixture through a homogenizer at high speed for 2 - 3 min;

[0044] Step 5. Adding expanded graphite: After the paraffin / ethylene - octene copolymer elastomer and polyurethane skeleton form a uniform mixture, add expanded graphite. Adjust the temperature of the flat magnetic stirrer heater to 145 - 150 °C, and stir evenly for 15 - 20 min to obtain a composite multi - phase change material.

[0045] The advantages are as follows: The phase change material of the present invention has a higher phase change enthalpy value and stronger cycle stability compared with other flexible phase change materials. This is because the added polyurethane porous solid - solid phase change skeleton can provide a considerable phase change enthalpy value while adsorbing paraffin wax, and does not affect the flexibility and thermal conductivity of the material.

[0046] Specifically, the phase change temperature of the composite multi - phase change material is 39 - 44 °C, the phase change enthalpy value is 100 - 150 kJ / kg, and the thermal conductivity is 2 W / (m·K) - 8 W / (m·K).

[0047] The advantages are as follows: The thermal conductivity of the phase change material of the present invention can reach 2 W / (m·K) to 8 W / (m·K), and the phase change enthalpy value can reach 100 kJ / kg to 150 kJ / kg, fully meeting the application requirements of the phase change material in the field of power battery thermal management.

[0048] Specifically, in the preparation of raw materials in step one, the components and their mass percentages of the composite phase change material are as follows: paraffin wax 44%; ethylene-octene copolymer elastomer 36%; powdery polyurethane porous solid-solid phase change skeleton 15%; expanded graphite 5%. The composite phase change material prepared according to the above preparation method is used to improve the service life of power batteries.

[0049] Example 1:

[0050] A phase change material, whose composition is shown in the following table:

[0051] Table 1 Composition table of a phase change material

[0052]

[0053]

[0054] Note:

[0055] The above-mentioned powdery polyurethane porous solid-solid phase change skeleton is prepared by the following method: 12 g to 20 g of polyethylene glycol with a number average molecular weight of 8000 is vacuum dried and then added to 15 mL to 25 mL of N,N-dimethylformamide. It is stirred and dispersed at 60 °C under nitrogen protection, and then 1.0 g to 2.1 g of hexamethylene diisocyanate biuret is added dropwise. After adding, it is continuously stirred for 1 h, vacuum dried and cured at 60 °C, and then ground to obtain the powdery polyurethane porous solid-solid phase change skeleton (phase change temperature is 55 °C to 60 °C, phase change enthalpy value is 160 kJ / kg to 180 kJ / kg).

[0056] The preparation method of the above-mentioned phase change material includes the following steps:

[0057] (1) According to the above mass percentages, 8.8 g of paraffin wax and 7.2 g of ethylene-octene copolymer elastomer are mixed, and then stirred at 120 °C with a stirring speed of 200 to 1000 r / min for 60 min until in a molten state;

[0058] (2) After adding the powdery polyurethane porous solid-solid phase change skeleton, continue to stir for 30 min, and then obtain a blend by high-speed shearing with a homogenizer at a rotation speed of 10000 r / min for 2 min;

[0059] (3) Place the blend in a molding die and hot press it in a flat vulcanizing machine. The hot pressing temperature is 135 °C, the pressure is 10 MPa, and the hot pressing time is 30 min;

[0060] (4) Cure the hot-pressed die at room temperature to obtain a paraffin / ethylene-octene copolymer elastomer / polyurethane porous solid-solid phase change skeleton multi-component composite phase change material.

[0061] Performance test:

[0062] (1) Use a differential scanning calorimeter (DSC) to measure the phase change temperature and phase change enthalpy value of the phase change material in this example.

[0063] The phase change starting temperature of the phase change material in this example is 43.13 °C, the peak temperature is 46.51 °C, the phase change enthalpy value is 137.6 kJ / kg, and the thermal conductivity is 0.33 W / (m·K). It can be seen that the phase change temperature of this phase change material meets the requirements of the power battery thermal management field, has a high phase change enthalpy value, and there is no leakage phenomenon during the cold and hot cycling process, so it has broad application prospects.

[0064] (2) The scanning electron microscope (SEM) image of the phase change material in this example is as Figure 1 shown.

[0065] It can be seen from Figure 1 that there are many cracks on the material surface, enabling paraffin / POE to be well adsorbed on the surface of the polyurethane porous solid-solid phase change skeleton and filling the voids between the three-dimensional grid structures.

[0066] Example 2:

[0067] A phase change material, the composition of which is shown in the following table:

[0068] Table 2 Composition table of a phase change material

[0069]

[0070] The preparation method of the above phase change material includes the following steps:

[0071] (1) According to the above mass percentages, mix 8.8 g of paraffin and 7.2 g of ethylene-octene copolymer elastomer, and at 120 °C, with a stirring speed of 200 - 1000 r / min, continuously stir for 60 min until it reaches the molten state;

[0072] (2) Then add 3.8 g of powdered polyurethane porous solid-solid phase change skeleton and continue stirring for 30 min. Then, use a homogenizer to perform high-speed shearing at a rotational speed of 10000 r / min for 2 min, add 0.2 g of expanded graphite, and stir with a glass rod every 5 min until it is uniform to obtain a blend;

[0073] (3) Place the blend in a molding die and hot press it in a flat vulcanizing machine. The hot pressing temperature is 135 °C, the pressure is 10 MPa, and the hot pressing time is 30 min.

[0074] (4) Cure the hot-pressed die at room temperature to obtain the paraffin / ethylene-octene copolymer elastomer / polyurethane porous solid-solid phase change skeleton / expanded graphite multi-component composite phase change material.

[0075] After testing (the testing method is the same as that in Example 1), the phase change starting temperature of the phase change material in this example is 41.4 °C, the peak temperature is 48.68 °C, the phase change enthalpy value is 134.4 kJ / kg, and the thermal conductivity is 0.52 W / (m·K), meeting the requirements of the power battery thermal management field.

[0076] Example 3:

[0077] A phase change material, the composition of which is shown in the following table:

[0078] Table 3 Composition table of a phase change material

[0079]

[0080] The preparation method of the above phase change material includes the following steps:

[0081] (1) According to the above mass percentages, mix 8.8 g of paraffin and 7.2 g of ethylene-octene copolymer elastomer, and then at 120 °C, with a stirring speed of 200 - 1000 r / min, continuously stir for 60 min until it reaches the molten state.

[0082] (2) Then add 3.4 g of powdered polyurethane porous solid-solid phase change skeleton and continue stirring for 30 min. Then, use a homogenizer to perform high-speed shearing at a speed of 10000 r / min for 2 min, add 0.6 g of expanded graphite, and stir with a glass rod every 5 min until it is uniform to obtain a blend.

[0083] (3) Place the blend in a molding die and hot press it in a flat vulcanizing machine. The hot pressing temperature is 135 °C, the pressure is 10 MPa, and the hot pressing time is 30 min.

[0084] (4) Cure the hot-pressed die at room temperature to obtain the paraffin / ethylene-octene copolymer elastomer / polyurethane porous solid-solid phase change skeleton / expanded graphite multi-component composite phase change material.

[0085] After testing (the testing method is the same as that in Example 1), the phase change starting temperature of the phase change material in this example is 40.93 °C, the peak temperature is 47.62 °C, the phase change enthalpy value is 133.1 kJ / kg, and the thermal conductivity is 0.80 W / (m·K), meeting the requirements of the power battery thermal management field. Moreover, its microscopic morphology and deformation characteristics are very close to those of the phase change material in Example 2.

[0086] Example 4:

[0087] A phase change material, the composition of which is shown in the following table:

[0088] Table 4 Composition table of a phase change material

[0089]

[0090] The preparation method of the above phase change material includes the following steps:

[0091] (1) According to the above mass percentages, 8.8 g of paraffin wax and 7.2 g of ethylene-octene copolymer elastomer are mixed and then stirred at 120 °C with a stirring speed of 200 - 1000 r / min for 60 min until in a molten state;

[0092] (2) Then 3 g of powdered polyurethane porous solid-solid phase change skeleton is added and stirring continues for 30 min. Then, it is sheared at a high speed of 10000 r / min by a homogenizer for 2 min, and 1 g of expanded graphite is added. Stir with a glass rod every 5 min until a homogeneous blend is obtained;

[0093] (3) The blend is placed in a molding die and hot-pressed in a flat vulcanizer. The hot-pressing temperature is 135 °C, the pressure is 10 MPa, and the hot-pressing time is 30 min;

[0094] (4) The die after hot-pressing is cured at room temperature to obtain the paraffin / ethylene-octene copolymer elastomer / polyurethane porous solid-solid phase change skeleton / expanded graphite multi-component composite phase change material.

[0095] After testing (the testing method is the same as that in Example 1), the phase change starting temperature of the phase change material in this example is 40.76 °C, the peak temperature is 46.51 °C, the phase change enthalpy value is 132.9 kJ / kg, and the thermal conductivity is 1.784 W / (m·K). It can be seen that the phase change temperature of this phase change material meets the requirements of the power battery thermal management field, has a high phase change enthalpy value, and there is no leakage phenomenon during the cold and hot cycling process, with broad prospects for popularization and application.

[0096] The scanning electron microscope (SEM) image of the phase change material in this example is as Figure 3 shown.

[0097] By Figure 3It can be known that the addition of expanded graphite enables the molten mixture of the polyurethane porous solid-solid phase change skeleton and paraffin to adhere to its porous structure. The components are well compatible, and the cross-linked network of the polyurethane porous solid-solid phase change skeleton and the porous structure of expanded graphite can play a synergistic role in the shaping of paraffin.

[0098] In addition, take 3 phase change material samples (dumbbell-shaped) of this embodiment, place them in a constant temperature and humidity chamber at -10°C, 25°C, and 40°C for 1 h respectively (to ensure thermal equilibrium), then apply a certain external force to the samples, and observe and photograph the deformation characteristics of the samples.

[0099] The bending deformation diagrams of the phase change material of this embodiment at different temperatures are as Figure 4 shown.

[0100] As can be seen from Figure 4 a-c: The materials of Example 4 can withstand a certain external force and deform without breaking at -10°C, 25°C, and 40°C. In addition, it can be clearly felt that as the temperature increases, the specimen is more likely to bend at the same angle, indicating that the flexibility performance improves with the increase of temperature, and it can fit more closely to the surface of the battery core in the battery thermal management system, thereby reducing the contact thermal resistance and enhancing the temperature control performance.

[0101] Example 5:

[0102] A phase change material, the composition of which is shown in the following table:

[0103] Table 5 Composition table of a phase change material

[0104]

[0105] The preparation method of the above phase change material includes the following steps:

[0106] (1) According to the above mass percentages, mix 8.8 g of paraffin and 7.2 g of ethylene-octene copolymer elastomer, and at 120°C, with a stirring speed of 200 - 1000 r / min, continuously stir for 60 min until it reaches the molten state;

[0107] (2) Then add 2 g of powdery polyurethane porous solid-solid phase change skeleton and continue stirring for 30 min, then use a homogenizer to shear at a high speed of 10,000 r / min for 2 min, add 2 g of expanded graphite, and stir with a glass rod every 5 min until it is uniform to obtain a blend;

[0108] (3) Place the blend in a molding die and put it in a flat vulcanizing machine for hot pressing and forming. The hot pressing temperature is 135°C, the pressure is 10 MPa, and the hot pressing time is 30 min;

[0109] (4) Demold the hot-pressed mold at room temperature to obtain the paraffin / ethylene-octene copolymer elastomer / polyurethane porous solid-solid phase change skeleton / expanded graphite multi-component composite phase change material.

[0110] After testing (the testing method is the same as that in Example 1), the phase change starting temperature of the phase change material in this example is 40.61 °C, the peak temperature is 47.87 °C, the phase change enthalpy value is 123.4 kJ / kg, and the thermal conductivity is 4.55 W / (m·K), meeting the requirements of the power battery thermal management field, and its microscopic morphology and deformation characteristics are very close to those of the phase change material in Example 4.

[0111] Example 6:

[0112] A phase change material, the composition of which is shown in the following table:

[0113] Table 6 Composition table of a phase change material

[0114]

[0115] The preparation method of the above-mentioned phase change material includes the following steps:

[0116] (1) According to the above mass percentages, mix 8.8 g of paraffin and 7.2 g of ethylene-octene copolymer elastomer, and at 120 °C, with a stirring speed of 200 - 1000 r / min, continuously stir for 60 min until it reaches the molten state;

[0117] (2) Then add 4 g of expanded graphite, and stir with a glass rod every 5 min until it is uniform to obtain a blend;

[0118] (3) Place the blend in a molding mold and hot-press it in a flat vulcanizing machine. The hot-pressing temperature is 135 °C, the pressure is 10 MPa, and the hot-pressing time is 30 min;

[0119] (4) Demold the hot-pressed mold at room temperature to obtain the paraffin / ethylene-octene copolymer elastomer / polyurethane porous solid-solid phase change skeleton multi-component composite phase change material.

[0120] After testing (the testing method is the same as that in Example 1), the phase change starting temperature of the phase change material in this example is 39.89 °C, the peak temperature is 47.73 °C, the phase change enthalpy value is 104.0 J / kg, and the thermal conductivity is 7.54 W / (m·K), meeting the requirements of the power battery thermal management field.

[0121] Example 7:

[0122] A phase change material, the composition of which is shown in the following table:

[0123] Table 7 Composition table of a phase change material

[0124]

[0125] The preparation method of the above-mentioned phase change material comprises the following steps:

[0126] (1) According to the above mass percentages, after mixing 11 g of paraffin wax and 9 g of ethylene-octene copolymer elastomer, at 120 °C with a stirring speed of 200 - 1000 r / min, continuously stir for 60 min until in a molten state;

[0127] (2) Place the blend in a molding die and hot press it in a flat vulcanizing machine. The hot pressing temperature is 135 °C, the pressure is 10 MPa, and the hot pressing time is 30 min;

[0128] (3) Cure and demold the hot-pressed die at room temperature to obtain a paraffin / ethylene-octene copolymer elastic composite flexible matrix.

[0129] After testing (the testing method is the same as that in Example 1), the phase change starting temperature of the phase change material in this example is 39.40 °C, the peak temperature is 47.49 °C, the phase change enthalpy value is 134.0 J / kg, and the thermal conductivity is 0.31 W / (m·K).

[0130] In addition, use a universal testing machine to conduct a tensile property test on the standard specimen of this example.

[0131] The stress-strain curve of the phase change material in this example is as Figure 5 shown. As can be Figure 5 seen, its elongation at break is as high as 204.9%, and the tensile strength is 2.70 MPa, indicating that the paraffin / ethylene-octene copolymer elastomer flexible composite phase change matrix has excellent mechanical properties, thus laying a good foundation for the next step of preparing a wide-temperature-range flexible multi-component composite phase change material.

[0132] 1. The wide-temperature-range flexible multi-component composite phase change material prepared by the present invention through the combination of raw material formula and preparation method can have a relatively high energy density while having good thermal stability and chemical stability. Not only is there no liquid leakage after the phase change process, and after mechanical property testing, the elongation at break of the composite material is much higher than the defined minimum value of the elongation at break for flexible materials, but also it has relatively good apparent bending flexibility at -10 °C - 40 °C. Moreover, the phase change temperature and phase change enthalpy value of the wide-temperature-range flexible multi-component composite phase change material can be different with the different molecular weights of polyethylene glycol and R value in the polyurethane porous solid-solid phase change skeleton. Therefore, the phase change temperature range of this phase change material is relatively wide and can be freely regulated.

[0133] 2. Compared with the prior art, the preparation method provided by the present invention is characterized by the adoption of in-situ polymerization method, melt blending method and molding method. Moreover, the phase change material prepared by the present invention has the advantages of high enthalpy value, good thermal conductivity, no leakage of paraffin, etc. In addition, its preparation method is simple, the raw materials are pollution-free, and the production cost is low, which is suitable for large-scale industrial production and application.

[0134] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A wide temperature range flexible composite phase change material, characterized in that: The components and mass percentages of the composite phase change material are: 35% to 70% paraffin; 30% to 50% ethylene-octene copolymer elastomer; 0% to 20% powdered polyurethane porous solid-solid phase change skeleton; and 0% to 20% expanded graphite.

2. The wide temperature range flexible composite phase change material according to claim 1, characterized in that: The phase change temperature of the paraffin wax is 40-45°C, and the phase change enthalpy value is 230-250kJ / kg. The paraffin wax and ethylene-octene copolymer elastomer are synthesized in a mass ratio of 11:9 to obtain a composite flexible matrix of the paraffin wax-ethylene-octene copolymer elastomer, which is used as a composite phase change material matrix. The phase change temperature is 38-40°C, the phase change enthalpy value is 120-170kJ / kg, the elongation at break is 4% to 600%, the tensile strength is 0.7-5MPa, and the Young's modulus is 30-170MPa.

3. The wide temperature range flexible composite phase change material according to claim 1, characterized in that: The preparation process of the powdered polyurethane porous solid-solid phase change skeleton is as follows: polyethylene glycol is dispersed in an organic solvent, and an N,N-dimethylformamide solution of hexamethylene diisocyanate biuret is slowly injected with a syringe under nitrogen protection for reaction, and then dried, cured and ground to obtain a powdered polyurethane porous solid-solid phase change skeleton.

4. The wide temperature range flexible composite phase change material according to claim 3, characterized in that: The number average molecular weight of the polyethylene glycol is 7000-9000, the organic solvent is N,N-dimethylformamide, the reaction is carried out at 50°C-70°C, and the drying is carried out at 80°C-100°C.

5. The wide temperature range flexible composite phase change material according to claim 3, characterized in that: The phase change temperature of the powdered polyurethane porous solid-solid phase change skeleton is 55° C. to 60° C., and the phase change enthalpy value is 160 kJ / kg to 180 kJ / kg.

6. The wide temperature range flexible composite phase change material according to claim 3, characterized in that: The powdery polyurethane porous solid-solid phase change skeleton is prepared by reacting polyethylene glycol and hexamethylene diisocyanate biuret in a molar ratio of 1:1 to 2:

1.

7. The wide temperature range flexible composite phase change material according to claim 1, characterized in that: The mesh number of the expanded graphite is 40-60 meshes, and the expansion degree is 200-300 times.

8. A method for preparing a wide temperature range flexible composite phase change material, characterized in that: The components and mass percentages of a wide temperature range flexible composite phase change material according to claim 1 are prepared, comprising the following preparation steps: Step 1, raw material preparation: prepare paraffin wax, ethylene-octene copolymer elastomer, powdered polyurethane porous solid-solid phase change skeleton and expanded graphite according to the formula mass percentage; Step 2: Pretreatment of raw materials: Melting the paraffin at a temperature of 40-45°C to form liquid paraffin; Step 3, melt blending: add ethylene-octene copolymer elastomer into a glass beaker, heat it on a flat magnetic heater at 110-120° C. to a softened state, dropwise add melted liquid paraffin into the beaker containing ethylene-octene copolymer elastomer at a mass ratio of 11:9, maintain the flat heating temperature, and melt blend for 55-60 minutes under continuous stirring to form a mixture; Step 4: homogenizing the mixture: adding the powdered cross-linked polyurethane solid-solid phase change skeleton to the above mixture, adjusting the temperature of the flat magnetic heater to 135-140°C, and stirring continuously for 25-30 minutes. After stirring, the mixture is sheared at high speed by a homogenizer for 2-3 minutes; Step 5, adding expanded graphite: After the paraffin wax / ethylene-octene copolymer elastic and polyurethane skeleton form a uniform mixture, add expanded graphite, adjust the temperature of the flat magnetic heater to 145-150° C., and stir evenly for 15-20 minutes to obtain a composite multi-phase change material.

9. The method for preparing a wide temperature range flexible composite phase change material according to claim 8, characterized in that: The phase change temperature of the composite multi-phase change material is 39-44° C., the phase change enthalpy value is 100-150 kJ / kg, and the thermal conductivity is 2W / (m·K)-8W / (m·K).

10. The method for preparing a wide temperature range flexible composite phase change material according to claim 8, characterized in that: The components and mass percentages of the composite phase change material in the raw material preparation are: 44% paraffin; 36% ethylene-octene copolymer elastomer; 15% powdered polyurethane porous solid-solid phase change skeleton; and 5% expanded graphite.

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