Phase change energy storage composite material and preparation method and application thereof

Abstract

The application provides a phase change energy storage composite material, which is twisted from a strip-shaped composite film; the composite film comprises at least one carbon film layer and at least one phase change material film layer; the carbon film layer and the phase change material film layer are arranged alternately, and the number of layers of the carbon film layer is equal to the number of layers of the phase change material film layer or the number of layers of the carbon film layer is one more than the number of layers of the phase change material film layer. The application further provides a preparation method and application of the phase change energy storage composite material.

Description

Technical Field

[0001] This invention relates to the field of phase change energy storage, specifically to a phase change energy storage composite material, its preparation method, and its application. Background Technology

[0002] Helical materials possess high strength and stiffness, making all-carbon helical materials an ideal choice for reinforcement, significantly improving the mechanical properties of composite materials, including strength, stiffness, and durability. They also exhibit excellent electrical and thermal conductivity, showing great potential in electronic, electrical, and thermal management applications. Combining helical materials with phase change materials can significantly enhance the electrical and thermal conductivity of the materials, thereby expanding the application range of composite materials, such as in electromagnetic shielding, sensors, and thermal conductive materials. Furthermore, the low density of composite helical fibers makes them widely applicable in lightweight and multifunctional materials, such as in aerospace, automotive, medical, and energy industries.

[0003] Patent CN116768642A discloses a helical fiber-flexible substrate combined stretchable sensor, its preparation method, and its application. Helical conductive fibers are fixed onto a flexible substrate, which is then configured as a partially conductive structure. The combination of the helical conductive fibers and the partially conductive flexible substrate forms a conductive path. During stretching, the resistance difference between the helical conductive fibers and the conductive portion of the flexible substrate creates different conductive paths, continuously altering the current flow path and thus changing the resistance value during stretching, thereby achieving the sensing function.

[0004] Patent CN115323580B discloses a heat-driven deformable fabric based on superspiral composite fibers and its preparation method. The preparation method includes the following steps: forming an organic polymer coating layer on the circumferential surface of conductive fibers to obtain composite fibers; twisting the composite fibers to obtain superspiral composite fibers; and weaving the superspiral composite fibers to obtain the heat-driven deformable fabric. Under heat-driven conditions, this fabric can undergo dimensional shrinkage, resulting in a denser fabric structure and reduced air permeability, moisture permeability, light transmittance, and transparency. After the heat-driven process is removed, the fabric returns to its original size, the fabric structure returns to its original looser state, the size increases, and the air permeability, moisture permeability, light transmittance, and transparency recover.

[0005] However, existing phase change energy storage materials have shortcomings in terms of thermal conductivity, leakage risk, energy storage density, and structural stability. Summary of the Invention

[0006] The first objective of this invention is to provide a phase change energy storage composite material with a high heat storage coefficient, low leakage rate and three-dimensional thermal conductivity.

[0007] The second objective of this invention is to provide a method for preparing the phase change energy storage composite material.

[0008] A third objective of this invention is to provide an application of the aforementioned phase change energy storage composite material.

[0009] This invention is achieved through the following technical solution:

[0010] A phase change energy storage spiral composite material, wherein the spiral composite material is obtained by twisting a strip composite film;

[0011] The composite film includes at least one carbon film layer and at least one phase change material film layer;

[0012] The carbon film layer and the phase change material film layer are alternately arranged, and the number of carbon film layers is equal to the number of phase change material film layers or the number of carbon film layers is one more than the number of phase change material film layers.

[0013] During the twisting process, the twisting direction of the strip-shaped composite film is oriented along the circumferential direction of the carbon film layer;

[0014] The carbon film layer includes a carbon nanotube film or a graphene film;

[0015] The phase change material includes paraffin, fatty acids, or polyethylene glycol.

[0016] The phase change material film layer is doped with a polymer elastomer;

[0017] In the phase change material film, the weight ratio of polymer elastomer to phase change material is 1-3:7-9;

[0018] The polymeric elastomer includes thermoplastic elastomers or thermosetting elastomers;

[0019] The thermoplastic elastomer includes polyurethane or olefin block copolymer methyl ester;

[0020] The thermosetting elastomer includes dimethylsiloxane;

[0021] The olefin block copolymers include Infuse 9530, Infuse 9100, Infuse 9807, Infuse 9107 or Infuse 9817.

[0022] The width of the composite film is 5~20mm;

[0023] The thickness of the phase change material film is 50-100 micrometers.

[0024] The thickness of the carbon film layer is 5-10 micrometers;

[0025] The thermal conductivity of the carbon film is 50-1000 W / (m·K).

[0026] The preparation method of the phase change energy storage composite material includes the following steps:

[0027] Liquid phase change material is loaded onto the surface of a substrate and cooled to obtain a phase change material film.

[0028] A composite film is obtained by hot pressing alternating layers of phase change material film and carbon film.

[0029] The composite film is cut and twisted to obtain the phase change energy storage composite material.

[0030] The preparation method of the phase change energy storage composite material includes the steps of incorporating a polymeric elastomer into the phase change material, melting it, and loading it onto the surface of a matrix.

[0031] The melting temperature is the melting temperature of the polymer elastomer plus 20~50℃;

[0032] The melting heating rate is 1~10℃ / min;

[0033] The holding time for melting is 20-60 minutes.

[0034] The substrate includes copper foil;

[0035] The substrate surface is also coated with a release agent;

[0036] The release agent includes mineral oil.

[0037] The hot pressing temperature is 100-200℃.

[0038] The holding time for hot pressing is 60~360s.

[0039] The holding pressure of the hot pressing is 0.1~1MPa.

[0040] The twisting speed is 50~200r.

[0041] The twisting time is 10~40 minutes.

[0042] The aforementioned phase change energy storage composite material is used in the preparation of energy storage systems; or

[0043] Applications include the preparation of temperature control materials; or

[0044] It is used in the manufacture of thermal protection systems.

[0045] The thermal protection system includes clothing incorporating the phase change energy storage composite material.

[0046] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0047] The phase change energy storage composite material provided by this invention has high thermal conductivity, low leakage risk, high energy storage density, and strong structural stability.

[0048] The preparation method of the phase change energy storage composite material provided by this invention is simple and can be mass-produced.

[0049] The phase change energy storage composite material provided by this invention can be widely used in the preparation of energy storage systems, temperature control materials and thermal protection systems to achieve safe and efficient energy storage and conversion. Attached Figure Description

[0050] Figure 1 A transverse SEM image of the phase change energy storage composite material prepared in Example 1 is shown;

[0051] Figure 2 A longitudinal SEM image of the phase change energy storage composite material prepared in Example 1 is shown. Detailed Implementation

[0052] Traditional phase change materials (PCMs) suffer from low heat transfer efficiency due to their low thermal conductivity, which in turn affects their energy storage and release efficiency. Furthermore, the volume change during the phase change process can lead to leakage as the encapsulation structure may rupture during melting or solidification. This leakage not only reduces energy storage efficiency but can also pollute the environment and equipment. In addition, existing PCM technologies struggle to achieve high energy density, limiting their potential for application in compact spaces. This is because energy density refers to the energy stored per unit mass or unit volume of a substance; traditional PCM composites typically add a significant amount of thermally conductive material to improve thermal conductivity, resulting in a reduced proportion of PCM mass and consequently lower energy density.

[0053] This invention provides a phase change energy storage composite material to solve the problems of high thermal conductivity, high leakage risk, and low energy storage density of phase change energy storage materials disclosed in the prior art.

[0054] Specifically, this invention provides a phase change energy storage composite material, which is obtained by twisting a strip-shaped composite film. The strip-shaped composite film consists of at least one carbon film layer and at least one phase change material film layer. The carbon film layer and the phase change material film layer are alternately arranged, and the number of carbon film layers is equal to the number of phase change material film layers, or the number of carbon film layers is one more than the number of phase change material film layers. After twisting along the circumferential direction of the carbon film layer, the phase change material is sealed within a space formed by the twisting of the carbon film layer. This enhances the structural stability of the composite material, enabling it to withstand repeated phase change processes without losing its structural performance. Simultaneously, the phase change material is also encapsulated within this space, effectively preventing leakage and improving the material's sealing and safety. Furthermore, because the carbon film layer is very thin and the thickness of the phase change material film layer is adjustable, the alternating arrangement of the carbon film layer and the phase change material film layer, along with increasing the number of phase change material film layers, can increase the loading of phase change material while maintaining structural stability, thereby increasing the overall energy storage density of the phase change energy storage composite material and thus enhancing its application potential in compact spaces. Furthermore, the twisting process creates a helical structure in the carbon film layer, resulting in a high radial thermal conductivity coefficient perpendicular to the composite material's axial direction. This accelerates the transfer of heat stored in the phase change material. Simultaneously, the large contact area between the phase change material and the carbon film layer in this composite material also contributes to improved thermal conductivity between them.

[0055] Specifically, during twisting, the twisting direction of the strip composite film is oriented along the circumferential direction of the carbon film layer, so that the carbon film layer is located on the outer layer of the phase change composite material, and the phase change material is encapsulated in the spiral structure formed by the carbon film layer.

[0056] Preferably, the carbon film layer can be a carbon nanotube film or a graphene film. However, it is evident that other types of high thermal conductivity carbon films can also achieve the present invention.

[0057] Preferably, the phase change material is paraffin, fatty acid, or polyethylene glycol. Obviously, other types of phase change materials can also achieve this invention.

[0058] Furthermore, a polymeric elastomer is doped into the phase change material film layer; due to the adsorption effect of the polymeric elastomer on the phase change material, it can improve the structural stability of the phase change material, thereby enabling the phase change material to maintain a film structure during repeated phase changes, while further reducing the leakage rate of the phase change material in the phase change composite material.

[0059] Specifically, in the phase change material film layer, the weight ratio of the polymeric elastomer to the phase change material is 1-3:7-9. Preferably, the polymeric elastomer is a thermoplastic elastomer or a thermosetting elastomer; wherein the thermoplastic elastomer is preferably polyurethane or olefin block copolymer methyl ester; the thermosetting elastomer is preferably dimethylsiloxane; the olefin block copolymer is preferably Infuse 9530, Infuse 9100, Infuse 9807, Infuse 9107, or Infuse 9817. Olefin block copolymers (OBCs) consist of hard segments and soft blocks, wherein the hard blocks aggregate into a dispersed phase, while the soft blocks aggregate into a continuous phase. The two combine to form a three-dimensional network structure, where the hard segments act as the connection points of the physically cross-linked network structure. The phase change material crystals are dispersed in the amorphous phase of the OBC, and the volume growth of the phase change material during melting is constrained by the OBC network. Therefore, OBCs can be used to limit the flowability of molten phase change materials.

[0060] Furthermore, the width of the composite film can vary between 5 and 20 mm, the thickness of the phase change material film layer can vary between 50 and 100 micrometers, and the thickness of the carbon film layer can vary between 5 and 10 micrometers. By simply modifying the preparation process, these dimensions can be controlled, resulting in phase change composite materials of different specifications to meet the application needs in various fields.

[0061] Furthermore, the present invention can be achieved with carbon film layers having a thermal conductivity between 50 and 1000 W / (m·K).

[0062] The present invention also provides a method for preparing the phase change energy storage composite material. The method is simple to operate. First, liquid phase change material is loaded onto the surface of a substrate and cooled to obtain a phase change material film. Then, the phase change material film is removed from the substrate surface. Next, the phase change material film and carbon film are stacked alternately and hot-pressed to obtain a composite film. Finally, the composite film is cut and twisted to obtain the phase change energy storage composite material.

[0063] To better shape the cooled phase change material, in the process of phase change energy storage composite materials, a polymer elastomer can be incorporated into the phase change material and then melted before the phase change material is loaded onto the surface of the matrix.

[0064] Specifically, setting the melting temperature to a range of 20-50°C higher than the melting temperature of the polymer elastomer allows the polymer elastomer to melt fully and makes it easier to mix evenly with the phase change material.

[0065] Setting the melting heating rate to 1~10℃ / min and holding it at the melting temperature for 20~60min after reaching the melting temperature can ensure that the polymer elastomer is fully melted.

[0066] Preferably, the substrate comprises copper foil; the function of the substrate is as a bottom pressure film, therefore, the present invention can also be achieved using other metal foils.

[0067] To facilitate the removal of the cooled phase change material, a release agent can be applied to the substrate surface;

[0068] Preferably, the release agent can be mineral oil.

[0069] When hot pressing, the temperature can be set to 100-200℃. When the temperature reaches the set value, maintain the pressure at 0.1~1MPa for 60~360s.

[0070] During twisting, the twisting speed can be set to 50~200 rpm, and the twisting time can be set to 10~40 min. After twisting the composite film, a phase change energy storage composite material can be obtained. At this time, the space formed by the carbon film layer will encapsulate the phase change material.

[0071] The present invention also provides applications of the aforementioned phase change energy storage composite material.

[0072] The phase change energy storage composite material can be used to prepare energy storage systems. In the energy storage system, the composite material can effectively store and release thermal energy. Through the phase change process of the phase change material, it absorbs and releases a large amount of heat within a certain temperature range, thereby achieving effective energy storage and regulation.

[0073] The phase change energy storage composite material can be used to prepare temperature control materials for regulating indoor or electronic device temperatures. By incorporating phase change materials into building materials, indoor temperature fluctuations can be reduced, comfort improved, and energy consumption lowered. In electronic devices, this material can serve as a thermal interface material, improving temperature uniformity, preventing overheating, and extending device lifespan. The phase change energy storage composite material can also be used to prepare thermal protection systems. In these systems, the composite material can protect equipment from extreme temperatures. By using phase change materials in critical parts of the system, heat can be absorbed when the temperature rises to prevent overheating, and released when the temperature drops to maintain system temperature stability.

[0074] Specifically, the thermal protection system may be clothing that integrates the phase change energy storage composite material.

[0075] The present invention will be further described below with reference to specific embodiments.

[0076] Example 1

[0077] 1. OBC and paraffin particles in a ratio of 2:8 were mixed by mechanical stirring. The mixture was then placed in a heating vessel and heated to 150°C at a rate of 10°C / min. The temperature was then maintained for 40 min. Mechanical stirring was performed during both the heating and maintenance processes to obtain the blended solution A.

[0078] 2. Coat one side of the copper foil with mineral oil, place the copper foil on a coating machine, and adjust the coating spacing of the coating machine's squeegee to 80μm. Pour solution A onto the copper foil coated with mineral oil, start the coating machine, and the squeegee will coat solution A onto the copper foil. After cooling to room temperature, remove the formed film from the copper foil to obtain coated film B.

[0079] 3. The coated film B and the 8μm thick CNT film are stacked on top of each other in a hot press mold. The hot press equipment is heated to 150℃ for hot pressing, the hot pressing pressure is 0.6MPa, and the hot pressing state is maintained for 60s. After cooling to room temperature, the composite film C is taken out.

[0080] 4. Cut the composite film C into strips 20mm wide. Fix one end of the strip to the motor and the other end to the movable slider. Adjust the twisting direction so that the side with the composite film faces the inside of the spiral structure. Start the motor to twist at 140 rpm for 20 minutes to obtain the spiral fiber D.

[0081] 5. Lay the spiral fiber D flat in an oven for low-temperature heat treatment. Heat the temperature to 60℃ and heat for 10 minutes. After cooling to room temperature, remove the fiber to obtain the final composite spiral fiber material.

[0082] Example 2

[0083] The difference between this embodiment and Embodiment 1 is that in step 1, OBC and paraffin particles in a ratio of 3:7 are mixed by mechanical stirring. The remaining steps and parameters are the same as in Embodiment 1.

[0084] Example 3

[0085] The difference between this embodiment and Embodiment 1 is that in step 1, OBC and paraffin particles in a ratio of 1:9 are mixed by mechanical stirring. The remaining steps and parameters are the same as in Embodiment 1.

[0086] Example 4

[0087] The difference between this embodiment and Embodiment 1 is that in step 2, the coating spacing of the coating machine blade is adjusted to 50μm, while the remaining steps and parameters are the same as in Embodiment 1.

[0088] Example 5

[0089] The difference between this embodiment and Embodiment 1 is that in step 2, the coating spacing of the coating machine blade is adjusted to 100μm, while the remaining steps and parameters are the same as in Embodiment 1.

[0090] Example 6

[0091] The difference between this embodiment and embodiment 1 is that in step 3, the coating film B and the 8μm thick CNT film are stacked alternately, and another 8μm thick CNT film is stacked on one side of the coating film B. The middle layer formed is the coating film B, and the three layers of the coating film B and the CNT film on the top and bottom are placed in the hot press mold. The remaining steps and parameters are the same as in embodiment 1.

[0092] Example 7

[0093] The difference between this embodiment and Embodiment 1 is that in step 3, the coating film B and the 8μm thick CNT film are stacked alternately, and the stacking of coating film B and CNT film is repeated once. The two stacked films are then stacked together to form a stacking pattern of 4 layers, one CNT film and one coating film. Finally, another CNT film is stacked on the outermost coating film to form a 5-layer stacked structure of CNT film-coating film-CNT film-coating film-CNT film. The 5-layer stacked film is placed in a hot press mold, and the remaining steps and parameters are the same as in Embodiment 1.

[0094] Example 8

[0095] The difference between this embodiment and Embodiment 1 is that in step 4, the composite film C is cut into strips with a width of 5mm. The remaining steps and parameters are the same as in Embodiment 1.

[0096] Example 9

[0097] The difference between this embodiment and Embodiment 1 is that in step 4, the twisting speed is 200 rpm, while the remaining steps and parameters are the same as in Embodiment 1.

[0098] Example 10

[0099] The difference between this embodiment and Embodiment 1 is that in step 4, the twisting speed is 50 rpm, while the remaining steps and parameters are the same as in Embodiment 1.

[0100] Example 11

[0101] The difference between this embodiment and embodiment 1 is that in step 3, the hot pressing equipment is heated to 100°C for hot pressing and maintained in the hot pressing state for 360 seconds. The remaining steps and parameters are the same as in embodiment 1.

[0102] Example 12

[0103] The difference between this embodiment and embodiment 1 is that in step 2, silicone oil is applied to one side of the copper foil; the remaining steps and parameters are the same as in embodiment 1.

[0104] Example 13

[0105] The difference between this embodiment and embodiment 1 is that in step 3, the hot pressing pressure is 1 MPa, while the remaining steps and parameters are the same as in embodiment 1.

[0106] Example 14

[0107] The difference between this embodiment and embodiment 1 is that in step 3, the hot pressing pressure is 0.1 MPa, while the remaining steps and parameters are the same as in embodiment 1.

[0108] Example 15

[0109] The difference between this embodiment and Embodiment 1 is that in step 4, the twisting time is 40 minutes, while the remaining steps and parameters are the same as in Embodiment 1.

[0110] Example 16

[0111] The difference between this embodiment and Embodiment 1 is that in step 4, the twisting time is 10 minutes, while the remaining steps and parameters are the same as in Embodiment 1.

[0112] Example 17

[0113] The difference between this embodiment and Embodiment 1 is that in step 3, a CNT film with a thickness of 10 μm is used; the remaining steps and parameters are the same as in Embodiment 1.

[0114] Example 18

[0115] The difference between this embodiment and Embodiment 1 is that in step 3, a CNT film with a thickness of 5 μm is used; the remaining steps and parameters are the same as in Embodiment 1.

[0116] Comparative Example 1

[0117] The difference between this comparative example and Example 1 is that in step 2, OBC and paraffin particles in a ratio of 1:20 are mixed by mechanical stirring. Other steps and parameters are the same as in Example 1.

[0118] Comparative Example 2

[0119] The difference between this comparative example and Example 1 is that step 5 is omitted, while the other steps and parameters remain the same as in Example 1.

[0120] Comparative Example 3

[0121] The difference between this comparative example and Example 1 is that in step 2, solution A is poured directly onto the copper foil; the other steps and parameters are the same as in Example 1.

[0122] Comparative Example 4

[0123] The difference between this comparative example and Example 1 is that in step 2, the copper foil is placed on the coating machine and the coating spacing of the coating machine blade is adjusted to 130μm. Other steps and parameters are the same as in Example 1.

[0124] Comparative Example 5

[0125] The difference between this comparative example and Example 1 is that in step 2, the copper foil is placed on the coating machine and the coating spacing of the coating machine blade is adjusted to 30μm. The remaining steps and parameters are the same as in Example 1.

[0126] Comparative Example 6

[0127] The difference between this comparative example and Example 1 is that in step 3, the hot pressing pressure is 1.5 MPa, while the other steps and parameters are the same as in Example 1.

[0128] Comparative Example 7

[0129] The difference between this comparative example and Example 1 is that in step 3, the hot pressing pressure is 0.05 MPa, while the remaining steps and parameters are the same as in Example 1.

[0130] In this invention, the samples prepared in the examples and comparative examples can be tested using the following methods, and the results are listed in Table 1:

[0131] 1. The frontal and cross-sectional views of the sample were observed using a Japanese scanning electron microscope (JSM-7610). The measurement functions of the scanning electron microscope were used to measure the angle α (°) between the helical knot and the horizontal line, the diameter of the helical fiber a1 (μm), and the width of the helical knot a2 (μm).

[0132] 2. The thermal conductivity is calculated from the resistivity using the formula K1=440000 / (ρ+258)-295, where K1 is the thermal conductivity (W / (m·K)) and ρ is the resistivity (μΩ·cm) measured by the four-point method on a circuit board.

[0133] 3. The radial thermal conductivity of the sample was obtained by heat flow method and is denoted as K2.

[0134] 4. Tensile strength test, conducted in accordance with standard ISO 11566:1996.

[0135] 5. Latent heat is obtained by DCS testing.

[0136] 6. Leakage rate test: Take a section of composite spiral fiber as a sample and weigh it, recording it as m0 (g). Place the sample in a 90℃ oven and heat it, weighing it every 2 hours, recording the weight as m. n(g) The fiber leakage rate (%) is calculated according to the following formula.

[0137] Leakage rate = [(m0-m n ) / m0]×100%

[0138] Comparative Examples 3, 5, and 6 were not tested because they failed to form a coating film due to the lack of a release agent, the coating thickness was too small for easy demolding, and the hot pressing pressure was too high, causing the film to rupture.

[0139] Table 1:

[0140]

[0141] As demonstrated in the examples, enclosing phase change materials (PCMs) within a helical structure improves the latent heat and thermal conductivity of the composite material, enhancing its temperature regulation capabilities. The helical structure, composed of carbonaceous materials, possesses flexibility and plasticity, providing good mechanical properties and shape controllability within the composite material. This makes PCMs easier to fabricate into various shapes and sizes, suitable for diverse applications. Furthermore, the helical structure helps accelerate the phase change process and heat transfer. The helical structure also increases the material's surface area, allowing more heat to be transferred through the fiber surface, thus improving out-of-plane thermal conductivity. This structure also enables PCMs to absorb or release heat more quickly, improving their thermal efficiency. Simultaneously, the helical fiber structure provides stronger structural support and stability, helping to prevent the flow or spillage of PCMs, increasing durability and cycle stability, which is beneficial for long-term use and multiple cycles. Setting multiple layers of carbonaceous film and PCM film can form a multi-layered helical structure within the composite material, further reducing the leakage rate of the PCMs. Simultaneously, this design can significantly increase the PCM content in the composite material, thereby enhancing its heat storage capacity. Meanwhile, the multi-layered carbonaceous film can also greatly improve the thermal conductivity of the composite material. The diameter of the composite material increases with the number of stacked layers. The alternating arrangement of carbon film layers and phase change material film results in higher tensile strength of the prepared helical fiber with more layers.

[0142] To reduce the leakage rate of phase change materials (PCMs), polymeric elastomers are added. These elastomers possess excellent flexibility and toughness, and the resulting blends are more likely to form softer, easier-to-process films, facilitating subsequent processing into helical structures. Furthermore, polymeric elastomers can improve the surface roughness of the film and enhance its adhesion properties, making it easier to bond with carbonaceous films. Therefore, PCMs exhibit low leakage rates, good mechanical properties, and excellent morphological stability. The addition of polymeric elastomers makes the composite material more morphologically stable during processing and use, reducing the possibility of deformation and shrinkage, and preventing the coated film from crumbling, thus extending its service life.

[0143] As shown by the data from Examples 1, 2, and 3, the paraffin content directly affects the phase transition temperature, latent heat, mechanical properties, and stability of the composite material. Paraffin has low thermal conductivity, therefore, the thermal conductivity decreases with increasing paraffin content. The paraffin addition ratio in Example 3 is higher than in Examples 1 and 2, resulting in increased brittleness and decreased tensile strength. A suitable paraffin addition ratio can lead to a low leakage rate and maintain good cycle performance. A decrease in paraffin content is accompanied by an increase in OBC content. OBC has excellent flexibility and toughness; blends containing more OBC are more likely to form softer, easier-to-process films, which is beneficial for subsequent processing into helical structures. OBC can improve the surface roughness of the film, and an appropriate amount of OBC addition improves the film's adhesion properties, making it easier to bond with the carbon film layer. However, OBC has lower thermal conductivity than paraffin; a suitable OBC to paraffin addition ratio can improve the overall performance of the material.

[0144] Data from Examples 1, 4, and 5 show that, under the same preparation process, the coating thickness affects the final diameter of the spiral fiber and the overall content of OBC and paraffin in the spiral fiber. A thicker coating results in a larger spiral fiber diameter, a longer distance perpendicular to the spiral fiber direction, a longer spirally wound film length, and a longer path along the spiral direction and perpendicular to the spiral fiber direction during heat transfer. Consequently, K1 and K2 are lower than those of spiral fibers with smaller diameters. A thicker coating thickness results in a higher overall content of OBC and paraffin compared to a thinner coating thickness; therefore, the latent heat of Example 5 is higher than that of Example 4.

[0145] As can be seen from the data of Examples 1, 6, and 7, the diameter of the spiral fiber increases with the increase of the number of stacked layers. The CNT film and the phase change material film are alternately arranged. The more layers there are, the higher the tensile strength of the prepared spiral fiber.

[0146] Data from Examples 1, 9, 10, 15, and 16 show that increasing the twisting speed or twisting time helps to enhance the cohesion of the yarn, prevent loosening, and form a stable helical structure. This structure not only enhances the mechanical strength of the fiber, but the tensile strength of Example 9 is also higher than that of Example 10.

[0147] Data from Examples 1 and 17 and 18 show that the presence of intrinsic and interfacial thermal resistance induces strong phonon scattering, resulting in a thermal conductivity of CNT films typically one order of magnitude lower than that of monomeric CNTs. As the thickness of the thermally conductive material increases, the thermal resistance does not increase linearly with thickness; it may be a curve with a steeper slope. Therefore, the thickness of the CNT film is directly proportional to its thermal resistance; the thicker the material, the greater the thermal resistance, leading to a decrease in thermal conductivity.

[0148] As shown by the data from Example 1 and Comparative Example 1, OBC possesses good flexibility and toughness, which can enhance the mechanical properties of the material. Too low an OBC content reduces the flexibility of the helical fibers, leading to a decrease in the tensile strength of the material. The addition of OBC improves the morphological stability of the composite material, reducing the possibility of deformation and shrinkage. Excessively low OBC content causes morphological instability of the helical fibers during processing or use, resulting in powdering of the coating film and thus affecting the material's service life. Simultaneously, the reduction in OBC decreases the stability of paraffin wax, leading to a narrower phase change temperature range or decreased phase change performance of the phase change material, and an increased leakage rate.

[0149] As shown by the data from Example 1 and Comparative Example 2, the tensile strength, latent heat, and thermal conductivity of the material after low-temperature heat treatment are superior to those of the material without low-temperature heat treatment. This is because the low-temperature heat treatment process can repair defects such as cracks and fissures formed during the twisting of the composite film into a spiral structure. During coating, twisting, and other processing, defects such as cracks and fissures will occur in the phase change material film layer. These defects will form thermal bridges, reduce thermal conductivity, and cause uneven heat conduction in the material, thereby reducing the overall thermal conductivity of the material. In addition, defects can also cause some areas of the phase change material to lose its phase change material properties. Low-temperature heat treatment can cause the phase change material layer to melt slightly for self-repair.

[0150] As can be seen from the data of Example 1 and Comparative Example 3, if no coating agent is added during the coating process, the blend cannot be removed from the copper foil after the coating has cooled. Therefore, a release agent must be added to the copper foil to facilitate demolding later.

[0151] Data from Example 1 and Comparative Examples 4 and 5 show that when the phase change material (PCM) film layer is too thick, uneven thickness, bending, and cracking are more likely to occur during thick coating than with thin coating. These problems affect the flatness of the PCM film. The twisting process is carried out at room temperature. Paraffin wax is more brittle and hard at higher temperatures. A thicker PCM film has a higher paraffin wax content than a thinner one, resulting in higher overall brittleness, lower flatness, and higher cracking during the spiral process. A thicker PCM film is also difficult to spiral, and the resulting spiral fiber material has low thermal conductivity and tensile strength. After hot pressing, the PCM film layer is removed from the copper foil. When the PCM film layer is too thin, its tensile strength is too low, easily causing the film to crack and making demolding impossible.

[0152] Data from Example 1 and Comparative Examples 6 and 7 show that excessive hot-pressing pressure during the preparation of the phase change material (PCM) membrane can easily lead to the rupture of the PCM membrane, thus preventing the formation of a composite membrane of the PCM membrane and the CNT membrane. When the hot-pressing pressure is too low, the contact between the PCM membrane and the CNT membrane is low, resulting in low bonding strength of the composite membrane. During the twisting process to prepare the spiral fiber, the composite membrane delaminates and cracks, leading to a decrease in thermal conductivity and tensile strength, and an increase in leakage rate.

Claims

1. A phase change energy storage composite material, characterized in that: The composite material is obtained by twisting a strip-shaped composite film; The strip-shaped composite film includes at least one carbon film layer and at least one phase change material film layer; the phase change material film layer is doped with a polymer elastomer; the carbon film layer and the phase change material film layer are alternately arranged, and the number of carbon film layers is equal to the number of phase change material film layers or the number of carbon film layers is one more than the number of phase change material film layers.

2. The phase change energy storage composite material as described in claim 1, characterized in that: During twisting, the twisting direction of the strip composite film is oriented along the circumferential direction of the carbon film layer; The carbon film layer includes a carbon nanotube film or a graphene film; The phase change material includes paraffin, fatty acids, or polyethylene glycol.

3. The phase change energy storage composite material as described in claim 1, characterized in that: In the phase change material film, the weight ratio of polymer elastomer to phase change material is 1-3:7-9; The polymeric elastomer is a thermoplastic elastomer; The thermoplastic elastomer is a polyurethane or an olefin block copolymer; The olefin block copolymer is Infuse9530, Infuse9100, Infuse9807, Infuse9107 or Infuse817.

4. The phase change energy storage composite material as described in claim 1, characterized in that: The width of the strip-shaped composite film is 5~20mm; The thickness of the phase change material film is 50~100 micrometers; The thickness of the carbon film layer is 5-10 micrometers; The thermal conductivity of the carbon film is 50-1000 W / (m·K).

5. The method for preparing the phase change energy storage composite material as described in claim 1, characterized in that: Includes the following steps: Liquid phase change material is loaded onto the surface of a substrate and cooled to obtain a phase change material film. A composite film is obtained by hot pressing the alternating stacking of phase change material film layers and carbon film layers; The composite film is cut and twisted to obtain the phase change energy storage composite material.

6. The method for preparing the phase change energy storage composite material as described in claim 5, characterized in that: This includes the steps of incorporating a polymeric elastomer into a phase change material, then melting and loading it onto the surface of a matrix; The melting temperature is the melting temperature of the polymer elastomer plus 20~50℃; The melting heating rate is 1~10℃ / min; The melting and holding time is 20-60 minutes; The substrate includes copper foil; The substrate surface is also coated with a release agent; The release agent includes mineral oil.

7. The method for preparing the phase change energy storage composite material as described in claim 5, characterized in that: The hot pressing temperature is 100-200℃; The holding time for the hot pressing is 60~360s; The holding pressure of the hot pressing is 0.1~1MPa.

8. The method for preparing the phase change energy storage composite material as described in claim 5, characterized in that: The twisting speed is 50~200r; The twisting time is 10~40 minutes.

9. The application of the phase change energy storage composite material as described in claim 1, characterized in that: Applications in the preparation of energy storage systems; or Applications include the preparation of temperature control materials; or It is used in the manufacture of thermal protection systems.

10. The application of the phase change energy storage composite material as described in claim 9, characterized in that: The thermal protection system includes clothing incorporating the phase change energy storage composite material.

Images