High-thermal-conductivity composite phase change material as well as preparation method and application thereof

Abstract

The invention discloses a high-thermal-conductivity composite phase change material as well as a preparation method and application thereof, and belongs to the technical field of thermal management materials. The preparation method of the high-thermal-conductivity composite phase change material comprises the following steps: S1, mixing a thermal conductive filler with a solvent, adding an interface regulator, mixing, and freeze-drying to obtain a first filler; s2, heating and mixing a phase-change material and a styrene elastomer, adding a first filler for mixing and dipping, and then carrying out horizontal orientation treatment on the dipped first filler, so that the heat-conducting filler in the first filler is distributed in a horizontal orientation manner to obtain the high-heat-conductivity composite phase-change material, the heat-conducting filler is a three-dimensional heat-conducting filler, a one-dimensional heat-conducting filler and a zero-dimensional heat-conducting filler. Through the constructed three-dimensional continuous heat conduction network, the heat conduction coefficient is improved under the condition of lower filling amount, so that the composite phase change material shows excellent heat conduction capability and heat management performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal management materials, and specifically relates to a high thermal conductivity composite phase change material and a preparation method and application thereof. Background Art

[0002] Phase change material is a kind of energy storage material that can absorb or release a large amount of latent heat during the phase change process while maintaining a nearly constant temperature. Therefore, phase change materials have good energy storage and temperature control characteristics. In recent years, phase change materials have attracted the attention of many domestic and foreign researchers and are widely used in building energy conservation, photovoltaics, refrigeration equipment, electronic equipment and battery thermal management. Solid-liquid phase change materials are widely used in practical engineering fields due to their high phase change latent heat, small volume change during the phase change process and good cycle stability. However, the thermal conductivity of pure phase change materials is relatively low, generally only about 0.2W / m·K. Traditional phase change materials have the disadvantages of low thermal conductivity, high rigidity and easy leakage, which limits their application in scenarios with high heat load. Therefore, providing a phase change material with high thermal conductivity, flexibility and non-leakage is a technical problem that needs to be solved urgently.

[0003] At present, most researchers increase the thermal conductivity of phase change materials by adding a single or two thermally conductive fillers, but the added filler content is often very high, which will greatly reduce the excellent performance of the phase change material itself. For example, patent CN113388237A discloses a method for preparing a flexible composite phase change material, in which paraffin-expanded graphite-thermoplastic copolyester elastomer is melt blended to prepare a composite phase change material. This method has simple steps and low cost. With the increase of expanded graphite, the thermal conductivity increases from 0.23W / (m·K) to 2.73W / (m·K), but the latent heat value decreases from 237.9J / g to 71.2J / g. Although the thermal conductivity of the phase change material is improved, the latent heat value decreases too much. The low latent heat of this type of phase change material may lead to insufficient temperature regulation ability. When it is applied to the battery heat dissipation layer, it cannot effectively maintain the required temperature range, resulting in reduced thermal management performance of the phase change material. Summary of the invention

[0004] In order to solve the above problems in the prior art, the purpose of the present invention is to provide a method for preparing a high thermal conductivity composite phase change material.

[0005] Another object of the present invention is to provide a high thermal conductivity composite phase change material.

[0006] Another object of the present invention is to provide a high thermal conductivity composite phase change material for use in the preparation of photovoltaic equipment, refrigeration equipment, electronic and energy storage equipment.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing a high thermal conductivity composite phase change material comprises the following steps:

[0009] S1. The thermally conductive filler is mixed with a solvent, an interface modifier is added, and the mixture is freeze-dried to obtain a first filler;

[0010] S2. The phase change material and the styrene elastomer are heated and mixed, a first filler is added and mixed, and then the first filler after impregnation is horizontally oriented so that the thermal conductive filler in the first filler is horizontally oriented and distributed to obtain the high thermal conductivity composite phase change material;

[0011] The thermally conductive filler is a three-dimensional thermally conductive filler, a one-dimensional thermally conductive filler and a zero-dimensional thermally conductive filler.

[0012] The present invention uses heat-conducting fillers of different dimensions and freeze drying to construct a three-dimensional heat-conducting network structure with vertical orientation, uses high-temperature impregnation to adsorb molten phase-change materials and styrene elastomers in the three-dimensional heat-conducting network structure, and then combines hot pressing and rolling to achieve horizontal orientation of the heat-conducting fillers, so that the composite phase-change material forms a horizontally oriented heat-conducting structure, reduces the gaps inside the filler, and makes the three-dimensional dual-carbon heat-conducting network of the composite phase-change material more compact, increasing the heat conduction path. The prepared composite phase-change material has the properties of high thermal conductivity, high latent heat value, stable shape and adjustable phase change temperature.

[0013] Thermally conductive fillers of different dimensions are interconnected through π-π stacking to construct a three-dimensional thermally conductive network structure, and then the solvent is removed through freeze drying to form a three-dimensional thermally conductive network structure with a vertical orientation. The three-dimensional thermally conductive network structure constructed by the present invention enriches the thermally conductive branches and thermally conductive paths of the composite phase change material, improves the thermal conductivity rate of the composite phase change, improves the thermal conductivity and heat dissipation capacity of the composite phase change material, and reduces the interface thermal resistance between the phase change material and the thermally conductive filler. In addition, the present invention utilizes interface regulator modification and freeze drying to improve the dispersibility of the thermally conductive filler, reduce the agglomeration of the thermally conductive filler, and enable the composite phase change material to maintain its own high latent heat and mechanical properties (such as flexibility and elasticity).

[0014] Specifically, the high thermal conductivity composite phase change material includes the following components in parts by mass: 2.2 to 10.5 parts of thermal conductive filler, 0.025 to 0.1 parts of interface regulator, 32 to 40 parts of phase change material, and 5 to 10 parts of styrene elastomer.

[0015] Preferably, the high thermal conductivity composite phase change material comprises the following components in parts by mass: 2.5 to 10 parts of thermal conductive filler, 0.025 to 0.1 parts of interface regulator, 32 to 40 parts of phase change material, and 5 to 10 parts of styrene elastomer.

[0016] More specifically, the thermally conductive filler includes the following components in parts by mass: 1.5 to 7.5 parts of a three-dimensional thermally conductive filler, 0.25 to 1.2 parts of a one-dimensional thermally conductive filler, and 0.45 to 1.8 parts of a zero-dimensional thermally conductive filler.

[0017] Specifically, the horizontal alignment process includes heat pressing and roll pressing.

[0018] The molten composite phase change material is induced by pressure during the hot pressing process, causing the thermally conductive filler to form a segregated structure in the phase change material, thereby achieving a horizontally oriented arrangement of the thermally conductive filler. After roller pressing, the thermally conductive filler is arranged from disordered to ordered in the thermal conductive network, reducing the voids inside the thermally conductive filler and forming a tighter three-dimensional cross-linked network structure, providing more thermal conductive pathways and significantly improving the thermal conductivity of the material.

[0019] More specifically, the temperature of the hot pressing is 80-120°C.

[0020] More specifically, the heat pressing time is 5 to 15 minutes.

[0021] More specifically, the hot pressing pressure is 0.5-2.0 MPa.

[0022] More specifically, the rolling is performed 3 to 10 times.

[0023] Specifically, the three-dimensional thermal conductive filler is at least one of expanded graphite, graphene sponge, foamed nickel, foamed copper, and diamond.

[0024] Preferably, the three-dimensional thermally conductive filler is expanded graphite.

[0025] More preferably, the three-dimensional thermally conductive filler is expanded graphite obtained by microwave puffing treatment.

[0026] Specifically, the one-dimensional thermal conductive filler is at least one of carbon nanotubes, carbon fibers, carbon nanorods, tubular aluminum nitride and boron nitride nanotubes.

[0027] Preferably, the one-dimensional thermally conductive filler is carbon nanotube.

[0028] Specifically, the zero-dimensional thermal conductive filler is at least one of aluminum nitride, aluminum oxide, silicon carbide, boron carbide, beryllium oxide, silicon carbide, and diamond.

[0029] More specifically, the zero-dimensional thermally conductive filler is a phosphoric acid-modified ceramic filler.

[0030] Specifically, the solvent is at least one of anhydrous ethanol, deionized water, and tert-butanol.

[0031] In the present invention, pre-freezing is required before freeze drying, and the solvent is frozen and crystallized and sublimated at low temperature and low pressure, leaving a three-dimensional structure with the shape of the solvent crystal as a template. Since the crystals formed by the solvent grow vertically, a vertically oriented three-dimensional heat conductive network structure is formed after freeze drying.

[0032] Specifically, the phase change material is at least one of paraffin, stearic acid, lauric acid, pentadecanoic acid, eicosanoic acid, polyvinyl alcohol, n-hexadecane, n-octadecane and n-docosane.

[0033] Preferably, the phase change material is paraffin.

[0034] Specifically, the styrene elastomer is at least one of styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-butadiene block copolymer (SBS), and polystyrene-ethylene-butylene-polystyrene block copolymer (SEBS).

[0035] Preferably, the styrene elastomer is styrene-ethylene-propylene-styrene block copolymer (SEPS).

[0036] Specifically, the interface regulator is at least one of 3-aminopropyltrimethoxysilane, vinyltrimethoxysilane, and 3-methacryloxypropyltrimethoxysilane.

[0037] Preferably, the interface regulator is 3-methacryloxypropyltrimethoxysilane.

[0038] Specifically, in step S1, the temperature for adding the interface regulator and mixing is 60-70° C., and the mixing time is 1-3 hours.

[0039] Specifically, in step S1, the freeze-drying temperature is -90 to -50°C.

[0040] Specifically, in step S1, the freeze-drying time is 10 to 24 hours.

[0041] Specifically, in step S1, the freeze-drying pressure is less than 1 MPa.

[0042] Specifically, in step S2, the temperature of heating and mixing is 120-180°C.

[0043] Specifically, in step S2, the heating and mixing time is 20 to 60 minutes.

[0044] Specifically, in step S2, the time for adding the first filler and mixing is 5 to 15 minutes.

[0045] Specifically, in step S2, the first filler is added and the impregnation time is 0.5 to 2 hours.

[0046] The present invention also protects a high thermal conductivity composite phase change material prepared by the above preparation method.

[0047] The present invention also protects the use of the above-mentioned high thermal conductivity composite phase change material in the preparation of photovoltaic equipment, refrigeration equipment, electronic and energy storage equipment.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) The present invention uses thermally conductive fillers of different dimensions and freeze-drying to construct a three-dimensional thermally conductive network structure with a vertical orientation, and then realizes the horizontal orientation arrangement of the thermally conductive fillers through a combination of hot pressing and rolling, so that the composite phase change material forms a horizontally oriented thermally conductive structure, and makes the three-dimensional dual-carbon thermally conductive network of the composite phase change material more compact, thereby increasing the thermal conduction path. The constructed three-dimensional thermally conductive network structure enriches the thermally conductive branches and thermally conductive paths of the composite phase change material, improves the thermal conductivity rate of the composite phase change material, improves the thermal conductivity and heat dissipation capacity of the composite phase change material, and can greatly reduce the interface thermal resistance. The present invention improves the thermal conductivity coefficient under the condition of a relatively low filling amount, so that the prepared composite phase change material exhibits excellent thermal conductivity and thermal management performance.

[0050] (2) The present invention utilizes interface regulator modification and freeze drying to improve the dispersibility of the thermal conductive filler and reduce the agglomeration of the thermal conductive filler, so that the composite phase change material maintains its own high latent heat and mechanical properties (such as flexibility and elasticity).

[0051] (3) The composite phase change material prepared by the present invention has a phase change temperature controlled at about 40-50°C. The temperature control range of the phase change material meets the requirements for normal operation of the battery and can improve the temperature uniformity of the battery pack under high temperature and high rate discharge conditions. The material has a good thermal management effect in high rate discharge of the battery and can still maintain excellent temperature uniformity under high rate 5C cycle discharge; and the prepared composite phase change material has a large phase change enthalpy value and a stable phase change temperature, and is also suitable for the field of solar photovoltaics.

[0052] (4) The preparation method provided by the present invention is simple to operate and is conducive to industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 This is a scanning electron microscope image of Example 3.

[0054] Figure 2 The dynamic thermomechanical test diagrams of Example 3(b) and Comparative Example 1(a) at 30-80°C.

[0055] Figure 3 It is a leakage test diagram of pure paraffin, Example 3, Comparative Example 1 and Comparative Example 2 at 70°C.

[0056] Figure 4 The temperature change curves of the lithium iron phosphate soft-pack battery under 1C charging, 2C, 3C, and 5C discharge rates and the 5C cycle charge and discharge temperature curve (c) are shown based on the high thermal conductivity composite phase change material heat dissipation (a) of Example 3 and based on air heat dissipation (b).

[0057] Figure 5 This is a scanning electron microscope image of the horizontal orientation of the thermally conductive filler formed in Example 3. DETAILED DESCRIPTION

[0058] The present invention is further described below in conjunction with examples. These examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods in the following examples that do not specify specific conditions are usually carried out according to conventional conditions in the art or according to the conditions recommended by the manufacturer; the raw materials, reagents, etc. used, unless otherwise specified, are all raw materials and reagents that can be obtained from commercial channels such as conventional markets. Any non-substantial changes and substitutions made by those skilled in the art on the basis of the present invention belong to the scope of protection claimed by the present invention.

[0059] Preparation of modified aluminum nitride:

[0060] Take 50g of aluminum nitride and mix it with anhydrous ethanol, stir it at a speed of 300rmp for 15min, and then ultrasonically disperse it for 10min to form a dispersion. Then, place the dispersion in a 60℃ oil bath and stir it, and add 1.5g of phosphoric acid dropwise for modification. After modification for 2h, filter the mixture, remove the excess solvent, and dry it in a 105℃ oven for 2h. Grind the dried powder to obtain phosphoric acid-modified aluminum nitride.

[0061] Example 1

[0062] S1. Weigh 1.79g of expanded graphite, 0.27g of carbon nanotubes, and 0.45g of modified aluminum nitride, mix and place in a beaker, add an appropriate amount of anhydrous ethanol, stir at a speed of 300rmp for 10min, and ultrasonically disperse for 10min to form a dispersion, add 0.025g of 3-methacryloxypropyltrimethoxysilane, stir in an oil bath at 65°C for 2h, and then place the dispersion at low temperature for pre-freezing. Finally, freeze-dry at -86°C and <1MPa for 12h to obtain a composite thermal conductive filler (first filler).

[0063] S2. Weigh 40g of paraffin wax and melt it in an oil bath at 80℃, add 7.5g of SEPS, and stir it in an oil bath at 150℃ for 30min to make the mixture molten; then add 2.5g of composite thermal conductive filler, stir it at a speed of 150rmp for 10min, and then immerse it at high temperature for 1h; then hot press it at 85℃ and 1MPa for 10min to form it, and then roll it 5 times (hot pressing and rolling make the thermal conductive filler horizontally oriented) to obtain a high thermal conductivity composite phase change material.

[0064] Example 2

[0065] S1. Weigh 3.57g of expanded graphite, 0.54g of carbon nanotubes, and 0.89g of modified aluminum nitride, mix and place in a beaker, add an appropriate amount of anhydrous ethanol, stir at a speed of 300rmp for 10min, and ultrasonically disperse for 10min to form a dispersion, add 0.05g of 3-methacryloxypropyltrimethoxysilane, stir in an oil bath at 65°C for 2h, and then place the dispersion at low temperature for pre-freezing. Finally, freeze-dry at -86°C and <1MPa for 12h to obtain a composite thermal conductive filler (first filler).

[0066] S2. Weigh 37.5g of paraffin wax and melt it in an oil bath at 80℃, add 7.5g of SEPS, and stir it in an oil bath at 150℃ for 30min to melt the mixture; then add 5g of composite thermal conductive filler, stir it at a speed of 150rmp for 10min, and then immerse it at high temperature for 1h; then hot press it at 85℃ and 1MPa for 10min to form it, and then roll it 5 times (hot pressing and rolling make the thermal conductive filler horizontally oriented) to obtain a high thermal conductivity composite phase change material.

[0067] Example 3

[0068] S1. Weigh 5.36g of expanded graphite, 0.8g of carbon nanotubes, and 1.34g of modified aluminum nitride, mix and place in a beaker, add an appropriate amount of anhydrous ethanol, stir at a speed of 300rmp for 10min, and ultrasonically disperse for 10min to form a dispersion, add 0.075g of 3-methacryloxypropyltrimethoxysilane, stir in an oil bath at 65°C for 2h, and then place the dispersion at low temperature for pre-freezing. Finally, freeze-dry at -86°C and <1MPa for 12h to obtain a composite thermal conductive filler (first filler).

[0069] S2. Weigh 35g of paraffin wax and melt it in an oil bath at 80℃, add 7.5g of SEPS, and stir it in an oil bath at 150℃ for 30min to melt the mixture; then add 7.5g of composite thermal conductive filler, stir it at a speed of 150rmp for 10min, and then immerse it at high temperature for 1h; then hot press it at 85℃ and 1MPa for 10min to form it, and then roll it 5 times (hot pressing and rolling make the thermal conductive filler horizontally oriented) to obtain a high thermal conductivity composite phase change material.

[0070] Example 4

[0071] S1. Weigh 7.14g of expanded graphite, 1.07g of carbon nanotubes, and 1.79g of modified aluminum nitride, mix and place in a beaker, add an appropriate amount of anhydrous ethanol, stir at a speed of 300rmp for 10min, and ultrasonically disperse for 10min to form a dispersion, add 0.1g of 3-methacryloxypropyltrimethoxysilane, stir in an oil bath at 65°C for 2h, and then place the dispersion at low temperature for pre-freezing. Finally, freeze-dry at -86°C and <1MPa for 12h to obtain a composite thermal conductive filler (first filler).

[0072] S2. Weigh 32.5g of paraffin wax and melt it in an oil bath at 80℃, add 7.5g of SEPS, and stir it in an oil bath at 150℃ for 30min to melt the mixture; then add 10g of composite thermal conductive filler, stir it at a speed of 150rmp for 10min, and then immerse it at high temperature for 1h; then hot press it at 85℃ and 1MPa for 10min to form it, and then roll it 5 times (hot pressing and rolling press make the thermal conductive filler horizontally oriented) to obtain a high thermal conductivity composite phase change material.

[0073] Comparative Example 1

[0074] Compared with Example 3, this comparative example is different in that step S1 is omitted, that is, the composition does not contain the composite thermal conductive filler, and the rest is the same as Example 3.

[0075] Comparative Example 2

[0076] The difference between this comparative example and Example 3 is that step S2 does not contain styrene elastomer SEPS, and the rest is the same as Example 3.

[0077] Comparative Example 3

[0078] Weigh 35g of paraffin wax and melt it in an 80℃ oil bath, add 7.5g of SEPS, and stir it in a 150℃ oil bath for 30min to make the mixture molten; weigh 5.36g of expanded graphite, 0.8g of carbon nanotubes, and 1.34g of modified aluminum nitride, stir them at a speed of 150rmp for 10min, and then immerse them at high temperature for 1h; then hot press them at 85℃ and 1MPa for 10min to form them, and then roll press them 5 times (hot pressing and rolling press make the thermal conductive filler horizontally oriented) to obtain a high thermal conductivity composite phase change material.

[0079] Comparative Example 4

[0080] S1. Weigh 5.36 g of expanded graphite, 0.8 g of carbon nanotubes, and 1.34 g of modified aluminum nitride, mix and place in a beaker, add an appropriate amount of anhydrous ethanol, stir at a speed of 300 rpm for 10 min, and ultrasonically disperse for 10 min to form a dispersion. After adding 0.075 g of 3-methacryloxypropyltrimethoxysilane, stir in an oil bath at 65°C for 2 h, and then place the dispersion in an oven at 105°C and dry for 2 h to obtain a composite thermally conductive filler (first filler).

[0081] S2. Weigh 35g of paraffin wax and melt it in an oil bath at 80℃, add 7.5g of SEPS, and stir it in an oil bath at 150℃ for 30min to melt the mixture; then add 7.5g of composite thermal conductive filler, stir it at a speed of 150rmp for 10min, and then immerse it at high temperature for 1h; then hot press it at 85℃ and 1MPa for 10min to form it, and then roll it 5 times (hot pressing and rolling make the thermal conductive filler horizontally oriented) to obtain a high thermal conductivity composite phase change material.

[0082] Comparative Example 5

[0083] The difference between this comparative example and Example 3 is that step S1 does not contain expanded graphite and carbon nanotubes, and the rest is the same as Example 3.

[0084] Comparative Example 6

[0085] Compared with Example 3, this comparative example is different in that step S1 does not contain expanded graphite and modified aluminum nitride, and the rest is the same as Example 3.

[0086] Comparative Example 7

[0087] The difference between this comparative example and Example 3 is that step S1 does not contain carbon nanotubes and modified aluminum nitride, and the rest is the same as Example 3.

[0088] Performance Testing

[0089] Test Method

[0090] SEM test: After the sample is sprayed with gold, it is placed in a scanning electron microscope and photographed at different magnifications at a voltage of 5.00 kV or 10.00 kV.

[0091] DMA test: Place the sample in a dynamic mechanical analyzer and test it using a tensile fixture, setting the test range to 30-70°C.

[0092] Thermal conductivity test: The samples were cut into discs with a diameter of 3 cm and tested according to the method in ASTM D5470-2006.

[0093] Melting enthalpy and solidification enthalpy test: Weigh an appropriate amount of sample into a differential scanning calorimeter, set the test atmosphere to N2, increase the test temperature from 25°C to 80°C, and then decrease the temperature from 80°C to 25°C, with a heating and cooling rate of 5°C / min.

[0094] Leakage test: paraffin, Example 3, Comparative Example 1 and Comparative Example 2 were placed in a 70° C. oven for a leakage test, and the morphological changes of each sample were observed.

[0095] Thermal conductivity test, melting enthalpy test and solidification enthalpy test were performed on Examples 1 to 4 and Comparative Examples 1 to 7. The results are shown in Table 1.

[0096] Table 1 Performance test results

[0097]

[0098]

[0099] As can be seen from Table 1, the melting enthalpy of paraffin is 206.6 J / g, but the thermal conductivity is very low, only 0.27 W / (m·K). In order to compensate for the low thermal conductivity of the phase change material, it is necessary to add a thermally conductive filler to enhance the thermal conductivity. The thermal conductivity of Example 1 is 2.58 W / (m·K), the melting enthalpy is 167.5 J / g, and the solidification enthalpy is 144.5 J / g; the thermal conductivity of Example 4 is increased to 4.51 W / (m·K), the melting enthalpy is 151.6 J / g, and the solidification enthalpy is 124.1 J / g. Under the condition of relatively low filling amount (i.e., the amount of thermally conductive filler added), by adding thermally conductive fillers of different dimensions and constructing a three-dimensional thermally conductive structure, the thermal conductivity of the composite phase change material is significantly increased and a good latent heat value (latent heat value refers to melting enthalpy or solidification enthalpy) is maintained, so that the prepared composite phase change material exhibits excellent thermal conductivity and thermal management performance.

[0100] From the thermal conductivity of Example 3 and Comparative Example 3, it can be seen that the thermal conductivity of Comparative Example 3 is only 2.47W / (m·K), which shows that directly mixing the raw materials not only leads to internal agglomeration of the filler, but also has poor compatibility with the phase change material, resulting in uneven distribution of the thermal conductive filler inside the material, making it difficult to form a continuous three-dimensional thermal conductive network. Therefore, after the composite thermal conductive filler is modified with a coupling agent and freeze-dried, it can not only increase the internal dispersion and interface compatibility of the filler, but also be more conducive to the construction of a three-dimensional thermal conductive network.

[0101] From the thermal conductivity of Example 3 and Comparative Example 4, it can be seen that the thermal conductivity of Comparative Example 4 is 2.81W / (m·K). This is because the thermal conductive filler is not freeze-dried, so its orientation in the matrix is ​​low, and it is difficult to form an orderly arranged thermal conductive network, resulting in the heat flow being hindered during the transfer process, reducing the thermal conductivity of the material. The thermal conductivity of Example 3 reaches 4.29W / (m·K). This shows that the orientation of the composite filler is improved by the driving effect of ice crystal growth during freeze drying, and it is easier to construct a relatively complete three-dimensional thermal conductive path.

[0102] From the comparison of thermal conductivity between Example 3 and Comparative Examples 5 to 7, it can be seen that the use of a single thermally conductive filler to construct a thermally conductive network will result in limited distribution and connection of the thermally conductive filler in the matrix, resulting in a discontinuous thermally conductive network structure, so that heat needs to bypass these discontinuous points during transmission, increasing thermal resistance, thereby causing the thermal conductivity of the composite phase change material to decrease. The three-dimensional thermally conductive network constructed using multi-dimensional thermally conductive fillers can reduce the scattering of phonons at the interface and defects between the thermally conductive filler particles during transmission, avoid interruption of the phonon transmission path, and greatly improve the thermal conductivity.

[0103] SEM test was carried out on Example 3, and the results were as follows Figure 1 As shown. Figure 1 It can be seen that the expanded graphite, carbon nanotubes and aluminum nitride in the composite thermal conductive filler are interconnected between paraffin and SEPS to form a three-dimensional network structure.

[0104] DMA test was performed on Example 3 and Comparative Example 1. Figure 2 (a) and Figure 2(b) The dynamic mechanical properties of comparative example 1 and example 3 in the temperature range of 30°C to 70°C, respectively. As can be seen from the figure, the storage modulus of example 3 decreased from 50.4MPa to 0.68MPa; the loss modulus decreased from 30.4MPa to 0.08MPa. The storage modulus of comparative example 1 decreased from 48.9MPa to 0.67MPa; the loss modulus decreased from 16.1MPa to 0.03MPa. The results of the storage modulus Eˋ show that with the increase of temperature, the smaller the rigidity of the material, the better the flexibility; the loss modulus Eˋˋ also decreases with the increase of temperature, which also shows that the flexibility of the material is better. The overall trend of the storage modulus and loss modulus of example 3 decreases with the increase of temperature, indicating that the prepared material has good flexibility and elasticity.

[0105] Leakage tests were performed on Example 3, Comparative Example 1, Comparative Example 2, and pure paraffin. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that paraffin and comparative example 2 melted and leaked at 70°C in just 5 minutes, and comparative example 1 gradually became transparent, indicating that the phase change material had slight leakage; while example 3 not only did not leak, but also maintained a stable shape. This shows that the addition of SEPS effectively limits the leakage of paraffin, and further shows that the addition of thermal conductive fillers and the formation of a three-dimensional thermal conductive structure can further improve the anti-leakage ability of the phase change material.

[0106] Figure 4 The temperature change curves of the lithium iron phosphate soft-pack battery at 1C charging, 2C, 3C, and 5C discharge rates and the 5C cycle charge and discharge temperature curve (c) are shown based on the high thermal conductivity composite phase change material heat dissipation of Example 3 (a) and based on air heat dissipation (b). Figure 4 As can be seen in (a), the discharge temperatures of 2C, 3C and 5C under the high thermal conductivity composite phase change material are 34.4℃, 35.8℃ and 39.4℃ respectively; Figure 4 (b) The 2C, 3C and 5C discharge temperatures without high thermal conductivity phase change material heat dissipation are 36.9℃, 40.2℃ and 46.7℃ respectively. Figure 4 Compared with (a), the temperature difference is 2.5℃, 4.4℃ and 7.3℃. Figure 4(c) The 5C cycle discharge temperature curve also shows that the temperature of the battery with high thermal conductivity phase change material is basically maintained at around 39°C. From the above analysis, it can be seen that the constructed three-dimensional thermal conductive network provides a large number of heat paths, which effectively accelerates the heat transfer generated by the battery. As the discharge rate increases, the heat dissipation effect of the battery becomes more and more obvious; it also further illustrates that the three-dimensional thermal conductive network can more evenly distribute the heat on the surface of the battery, avoid local overheating, and prevent the battery from thermal runaway when working under high load. The highest temperature point of the battery after 10 cycles of charge and discharge also shows that the three-dimensional thermal conductive network can effectively reduce the degradation of the material under high temperature and high load, and improve the cycle durability of the material. This shows that the thermal management system based on the heat dissipation of the high thermal conductivity composite phase change material in Example 3 has a good thermal management effect on the high rate discharge of the battery and has excellent temperature control performance. Therefore, the high thermal conductivity composite phase change material prepared by the present invention has excellent thermal management performance.

[0107] Figure 5 This is a scanning electron microscope image of the horizontally oriented structure of the thermal conductive filler. Figure 5 (a) and Figure 5 (b) are the plan and cross-sectional structural diagrams of Example 3, and it can be clearly seen that the expanded graphite, carbon nanotubes and aluminum nitride are interconnected and arranged in a horizontal direction, indicating that the thermal conductive filler forms a horizontally oriented structure inside the material. This shows that hot pressing and rolling can form a horizontally oriented thermal conductive structure for the thermal conductive filler, which can further increase the thermal conductive path of the thermal conductive filler inside the material and improve the thermal transfer performance of the material.

[0108] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled 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 list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a high thermal conductivity composite phase change material, characterized in that: The following steps are involved: S1. The thermally conductive filler is mixed with a solvent, an interface modifier is added, and the mixture is freeze-dried to obtain a first filler; S2. The phase change material and the styrene elastomer are heated and mixed, a first filler is added and mixed, and then the first filler after impregnation is horizontally oriented so that the thermal conductive filler in the first filler is horizontally oriented and distributed to obtain the high thermal conductivity composite phase change material; The thermally conductive filler is a three-dimensional thermally conductive filler, a one-dimensional thermally conductive filler and a zero-dimensional thermally conductive filler.

2. The preparation method according to claim 1, characterized in that: The high thermal conductivity composite phase change material comprises the following components in parts by weight: 2.2 to 10.5 parts of thermal conductive filler, 0.025 to 0.1 parts of interface regulator, 32 to 40 parts of phase change material, and 5 to 10 parts of styrene elastomer.

3. The preparation method according to claim 1, characterized in that: The horizontal alignment process includes heat pressing and roll pressing.

4. The preparation method according to claim 1, characterized in that: The three-dimensional thermal conductive filler is at least one of expanded graphite, graphene sponge, nickel foam, and copper foam.

5. The preparation method according to claim 1, characterized in that: The one-dimensional thermal conductive filler is at least one of carbon nanotubes, carbon fibers, carbon nanorods, tubular aluminum nitride and boron nitride nanotubes.

6. The preparation method according to claim 1, characterized in that: The zero-dimensional thermal conductive filler is at least one of aluminum nitride, aluminum oxide, boron carbide, beryllium oxide, silicon carbide, and diamond.

7. The preparation method according to claim 1, characterized in that: The phase change material is at least one of paraffin, stearic acid, lauric acid, pentadecanoic acid, eicosanoic acid, polyvinyl alcohol, n-hexadecane, n-octadecane and n-docosane.

8. The preparation method according to claim 1, characterized in that: The styrene-based elastomer is at least one of styrene-ethylene-propylene-styrene block copolymer, styrene-butadiene block copolymer, and polystyrene-ethylene-butylene-polystyrene block copolymer.

9. A high thermal conductivity composite phase change material prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the high thermal conductivity composite phase change material as claimed in claim 9 in the preparation of photovoltaic equipment, refrigeration equipment, electronic and energy storage equipment.

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