High-performance flexible composite phase change energy storage film and preparation method thereof

Abstract

The application discloses a kind of high-performance flexible composite phase change energy storage films and preparation method thereof, belong to phase change energy storage material technical field.Its technical scheme is: S1 is added to the solution containing polyvinylidene fluoride carboxyl-rich carbon-boron nitride compound, mixed to obtain black viscous solution;S2 is added to the black viscous solution, stirs to make it uniformly dispersed to obtain black viscous mixture, after removing solvent, flexible composite phase change energy storage film is obtained.The flexible composite phase change energy storage film prepared by the application has excellent light-heat conversion capacity, heat conduction performance and mechanical strength;In addition, it can maintain shape stability in solid phase and aqueous environment, has excellent heat conduction capacity and light-heat conversion storage efficiency.

Description

Technical Field

[0001] This invention relates to the field of phase change energy storage materials technology, specifically to a high-performance flexible composite phase change energy storage membrane and its preparation method. Background Technology

[0002] Among renewable energy sources, solar energy is the most abundant on Earth. However, solar radiation is susceptible to seasonality, diurnal variation, and weather conditions, leading to intermittent fluctuations in energy supply systems. Furthermore, the direct utilization rate of solar energy is very low; it must be converted into other forms of energy for effective use. Therefore, exploring efficient solar energy conversion and storage technologies using flexible and adaptable methods to meet energy supply and demand balance is imperative. Latent heat storage (LHEST) technology utilizes phase change materials (PCMs) to store thermal energy by absorbing / releasing heat during phase change while maintaining a constant temperature. Therefore, the application of LHEST in the solar energy field can effectively improve solar energy utilization efficiency.

[0003] Polyethylene glycol (PEG) is a typical organic phase change material (PCM) due to its high energy density and excellent temperature control performance. However, inherent problems such as PEG's weak light absorption, high rigidity, poor thermal conductivity, and easy leakage in the molten state severely limit its practical application in the solar energy field. To solve these problems, researchers have turned their attention to preparing composite PCMs by adding photothermal conversion agents, thermally conductive fillers, and supporting materials to PEG, and have achieved some results. However, most of the composite PCMs prepared with high photothermal conversion, high heat storage capacity, and high thermal conductivity are highly rigid, and currently, most composite PCMs are only suitable for solid-phase environments. Once exposed to an aqueous environment, the supporting material loses its ability to encapsulate the PCM, and its high photothermal conversion and high thermal conductivity properties are rendered ineffective. Therefore, it is imperative to prepare a thermally enhanced flexible phase change composite membrane that maintains shape stability in both solid and aqueous environments to expand the practical application of PCMs in the field of solar thermal management. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the difficulties of traditional phase change energy storage materials, such as high rigidity and instability in water, and to provide a flexible composite phase change energy storage membrane with high photothermal conversion and storage efficiency, high heat storage capacity and high thermal conductivity, as well as its preparation method. The prepared flexible composite phase change energy storage membrane has excellent photothermal conversion capability, thermal conductivity and mechanical strength; in addition, it can maintain shape stability in both solid and aqueous environments, and has excellent thermal conductivity and photothermal conversion and storage efficiency.

[0005] The technical solution of this invention is as follows:

[0006] On the one hand, the present invention provides a method for preparing a high-performance flexible composite phase change energy storage membrane, comprising the following steps:

[0007] S1 adds a carboxyl-rich boron carbon nitride (RHTC-BN) compound to a solution containing polyvinylidene fluoride (PVDF) and mixes to obtain a black viscous solution;

[0008] S2 adds polyethylene glycol to the above black viscous solution and stirs. As the stirring process continues, the viscosity of the black viscous solution increases significantly. After the polyethylene glycol is uniformly dispersed by the hydrogen bonding and capillary action between the carboxyl-rich carbon and polyethylene glycol, a black viscous mixture is obtained. After removing the solvent, a flexible composite phase change energy storage membrane is obtained.

[0009] This invention ingeniously utilizes the pores and effective functional groups of polyvinylidene fluoride (PVDF). Not only does it enable boron nitride to be uniformly dispersed in PVDF through the key bridging effect of carboxyl-rich carbon, but it also allows polyethylene glycol to be adsorbed in the pores of PVDF. This not only achieves the purpose of encapsulation but also provides a thermally conductive network framework, improving thermal conductivity.

[0010] The polyethylene glycol used in this invention has a single melting point (common polyethylene glycol melting points are 35℃, 47℃, 52℃, 56℃, 59℃, 60℃, 61℃, and 62℃), and a single temperature control range. The polyethylene glycol described in this invention has a melting point of 57-60℃. As the molecular weight of polyethylene glycol increases, its melting point and heat storage capacity also increase. However, with the increase of the molecular weight of polyethylene glycol, the content of hydroxyl groups at the molecular chain ends gradually decreases, leading to a weakening of the intermolecular interaction between polyethylene glycol and other groups. Therefore, to enable polyethylene glycol to possess both high heat storage capacity and strong intermolecular interaction, polyethylene glycol with a melting point of 57-60℃ is selected as the phase change material.

[0011] Preferably, in step S1, the preparation method of the carboxyl-rich carbon-boron nitride compound is as follows:

[0012] 1) Prepare a glucose solution by adding glucose to secondary water, and then add acrylic acid to the glucose solution to obtain a mixture;

[0013] 2) The above mixture is ultrasonically treated and then subjected to hydrothermal reaction to obtain carboxyl-rich carbon. The carboxyl-rich carbon has a petal-like structure and its surface is rich in oxygen-containing groups (hydroxyl and carboxyl groups). It can form hydrogen bonds with polyethylene glycol and also has π-π conjugation with boron nitride, thus acting as a photothermal conversion medium and a key bridge.

[0014] 3) Add carboxyl-rich carbon and boron nitride to deionized water and then sonicate and centrifuge them in sequence. After thorough drying, carboxyl-rich carbon-boron nitride compound is obtained, which can be used together as a photothermal conversion medium and a high thermal conductivity filler.

[0015] Preferably, in step 1), the concentration of the glucose solution is 0.8-1.5 wt%; and the amount of acrylic acid added is 10-16% based on the mass of the glucose solution.

[0016] Preferably, in step 2), the hydrothermal reaction temperature is 170-190℃. The hydrothermal reaction temperature has a significant impact on the morphology and properties of carboxyl-rich carbon. When the temperature is below 170℃, the resulting carbon microstructure is an interconnected spherical structure, which affects both subsequent modification and thermal conductivity. When the temperature is above 190℃, the spherical structure of the carboxyl-rich carbon begins to break down, and the number of grafted carboxyl functional groups is significantly reduced. Therefore, the hydrothermal reaction temperature affects the strength of the intermolecular forces between the carboxyl-rich carbon, polyethylene glycol, and boron nitride, thereby affecting the photothermal conversion efficiency and thermal conductivity of the finally prepared flexible composite phase change energy storage membrane.

[0017] Preferably, in step 3), the mass ratio of carboxyl-rich carbon to boron nitride is 1:(2-9); preferably, the mass ratio of carboxyl-rich carbon to boron nitride is 1:4.

[0018] Preferably, in step S1, the mixing temperature is 35-45℃; in step S2, the mixing temperature is 45-55℃.

[0019] Preferably, in step S1, the solvent in the solution containing polyvinylidene fluoride is methylpyrrolidone, N,N-dimethylformamide (DMF), acetone, or dimethyl sulfoxide.

[0020] Preferably, in step S1, based on the mass of polyvinylidene fluoride, the amount of carboxyl-rich carbon-boron nitride added is 20-60%, and the amount of polyethylene glycol added is 50-90%.

[0021] Preferably, in step S2, the solvent removal method is as follows: the obtained black viscous mixture is dried to obtain a black flexible composite film, which is then fully immersed in secondary water and dried repeatedly to ensure complete solvent removal. The resulting black flexible composite film exhibits good mechanical properties, with a stress reaching 2.53 MPa (e.g., ...). Figure 9 (as shown in b).

[0022] On the other hand, the present invention also provides a high-performance flexible composite phase change energy storage membrane prepared by the above preparation method.

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

[0024] 1. This invention uses polyethylene glycol as the phase change energy storage material, boron nitride as the high thermal conductivity filler, polyvinylidene fluoride as the flexible support material, and carboxyl-rich carbon as the photothermal conversion agent and key bridge to prepare a flexible composite phase change membrane, which significantly improves the heat transfer rate of polyethylene glycol (e.g., ...). Figure 12As shown, it has defects such as 400% increase, easy leakage in the molten state, weak light absorption capacity, and high rigidity.

[0025] 2. The flexible composite phase change membrane prepared by the present invention using polyvinylidene fluoride flexible support material not only maintains shape stability in a solid phase environment and has excellent thermal conductivity and photothermal conversion and storage efficiency, but also maintains the morphology of the composite membrane in an aqueous phase environment and has excellent photothermal conversion and storage performance and heat transfer rate.

[0026] 3. The flexible composite membrane prepared by this invention is simple to operate, low in cost, and has high chemical and thermal stability, which can further broaden the application of phase change materials in the field of solar thermal management. Attached Figure Description

[0027] Figure 1 The tensile stress-strain curves of the composite energy storage membrane VP1 prepared in Comparative Example 1, the composite energy storage membrane VP2 prepared in Comparative Example 2, the composite energy storage membrane VP3 prepared in Comparative Example 3, the composite energy storage membrane VP4 prepared in Comparative Example 4, and pure polyvinylidene fluoride (PVDF) are shown.

[0028] Figure 2 The shape stability tests of the pure PEG membrane (I), the flexible composite energy storage membrane (II) prepared in Example 1, the flexible composite energy storage membrane (III) prepared in Example 2, and the flexible composite energy storage membrane (IV) prepared in Example 3 are shown in Figure a, which shows the test at 30°C; Figure b shows the test at 70°C for 2 hours.

[0029] Figure 3 The diagram shows the thermal conductivity of the flexible composite energy storage membrane V1BP prepared in Comparative Example 5, the flexible composite energy storage membrane V1RP prepared in Comparative Example 6, and the flexible composite energy storage membrane V1RBP prepared in Example 1.

[0030] Figure 4 The figures show the temperature-time curves of the flexible composite energy storage membrane V1BP prepared in Comparative Example 5, the flexible composite energy storage membrane V1RP prepared in Comparative Example 6, and the flexible composite energy storage membrane V1RBP prepared in Example 1 under simulated sunlight irradiation.

[0031] Figure 5 The images show the temperature-time curves of the flexible composite energy storage membrane V1RBP prepared in Example 1, the flexible composite energy storage membrane V2RBP prepared in Example 4, the flexible composite energy storage membrane V3RBP prepared in Example 5, and polyethylene glycol (PEG) under simulated sunlight irradiation.

[0032] Figure 6 The images show the DSC curves of the flexible composite energy storage membrane V1RBP prepared in Example 1, the flexible composite energy storage membrane V2RBP prepared in Example 4, the flexible composite energy storage membrane V3RBP prepared in Example 5, polyethylene glycol (PEG), and the flexible composite energy storage membrane VP2 prepared in Comparative Example 2.

[0033] Figure 7 The images show SEM images of the carboxyl-rich carbon prepared in Comparative Example 7 (a), the carboxyl-rich carbon prepared in Example 1 (b), and the carboxyl-rich carbon prepared in Comparative Example 8 (c).

[0034] Figure 8 The thermal conductivity is that of the flexible composite energy storage membrane prepared in Example 1 and the flexible composite energy storage membrane prepared in Comparative Example 9.

[0035] Figure 9 The stress-strain curves are those of the flexible composite energy storage membrane M1RBP(a) prepared in Comparative Example 12 and the flexible composite energy storage membrane V1RBP(b) prepared in Examples 1 and 4-5.

[0036] Figure 10 The figures show the mass changes of the flexible composite energy storage membrane M1RBP prepared in Comparative Example 12 and the flexible composite energy storage membrane V1RBP prepared in Example 1 after multiple immersion-drying cycles in water. The numbers 1-4 in the bar chart correspond to the initial mass, the mass after one cycle, the mass after two cycles, and the mass after three cycles, respectively.

[0037] Figure 11 These are SEM images of the carboxyl-rich carbons prepared in Comparative Example 13(a), Example 1(b), and Comparative Example 14(c).

[0038] Figure 12 The thermal conductivity diagrams are of the flexible composite energy storage membrane V1RBP prepared in Example 1 and the composite energy storage membrane VP1 prepared in Comparative Example 1.

[0039] Figure 13 These are macroscopic images of the carboxyl-rich carbon prepared in Example 1 and the carboxyl-rich carbon prepared in Comparative Example 14. Detailed Implementation

[0040] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this invention.

[0041] Comparative Example 1

[0042] The preparation method of the flexible composite phase change energy storage membrane in Comparative Example 1 includes the following steps:

[0043] (1) Disperse 0.1g of polyvinylidene fluoride into 5.0g of methylpyrrolidone solvent, and stir the mixture continuously in a 45℃ water bath for 12h to form a light orange viscous solution;

[0044] (2) Add 0.05g of polyethylene glycol to the above viscous solution, stir continuously for 4 hours, and then place it in a 70℃ forced-air drying oven for 24 hours to remove the solvent and obtain a white crude membrane product; place the crude membrane product in deionized water to fully soak, remove the remaining impurities, and then dry it in a 70℃ forced-air drying oven to obtain a light orange flexible composite energy storage membrane VP1.

[0045] Comparative Example 2

[0046] The difference between Comparative Example 2 and Comparative Example 1 is that in step (2), the amount of polyethylene glycol added is 0.07g, resulting in a light orange flexible composite energy storage membrane VP2.

[0047] Comparative Example 3

[0048] The difference between Comparative Example 3 and Comparative Example 1 is that in step (2), the amount of polyethylene glycol added is 0.09g, resulting in a light orange flexible composite energy storage membrane VP3.

[0049] Comparative Example 4

[0050] The difference between Comparative Example 4 and Comparative Example 1 is that in step (2), the amount of polyethylene glycol added is 0.10g, resulting in a light orange flexible composite energy storage membrane VP4.

[0051] Since the phase change material polyethylene glycol has a rigid structure and the flexible supporting material polyvinylidene fluoride has no heat storage capacity, in order to ensure that the prepared flexible composite membrane has excellent heat storage capacity while maintaining mechanical properties, the mechanical properties of the flexible supporting material polyvinylidene fluoride were analyzed in Comparative Examples 1-4. The results are as follows: Figure 1 As shown. By Figure 1 It is known that when the doping amount of polyethylene glycol (PEG) is too high, the heat storage capacity of the light orange composite film increases accordingly. However, excessive doping with rigid polyethylene glycol will cause the flexibility (mechanical strength) of the composite film to gradually decrease or even disappear. When the doping amount of polyethylene glycol is too low, although the light orange composite film has high flexibility, its heat storage capacity is too low. The amount of heat energy that can be absorbed / released per unit area of ​​the composite film is too small, which is not conducive to large-scale application.

[0052] Example 1

[0053] The preparation method of the flexible composite phase change energy storage membrane in Example 1 includes the following steps:

[0054] (1) Glucose solution (concentration of 1 wt%) was prepared by adding glucose to secondary water. Based on the mass of the glucose solution, 10 wt% acrylic acid was added to the glucose solution to obtain a mixture. The mixture was ultrasonically treated and then subjected to hydrothermal reaction at 180°C to obtain carboxyl-rich carbon.

[0055] (2) Add 0.2g of carboxyl-rich carbon and 0.8g of boron nitride to 100mL of deionized water and sonicate at 800W for 24h; then centrifuge and dry overnight in an 80℃ drying oven to remove solvent, and obtain gray-black carboxyl-rich carbon-boron nitride compound powder.

[0056] (3) Disperse 0.1g of polyvinylidene fluoride into 5.0g of methylpyrrolidone solvent, and stir the mixture continuously in a 45℃ water bath for 12h to form a light orange viscous solution;

[0057] (4) 0.02g of carboxyl-rich boron nitride compound was slowly added to the above viscous solution and stirred continuously at 40°C for 5h to make the carboxyl-rich boron nitride compound evenly distributed in the polyvinylidene fluoride solution to obtain a black viscous mixed solution.

[0058] (5) Add 0.05g of polyethylene glycol to the above viscous mixed solution, stir continuously at 50°C for 4h, and then place in a 70°C forced-air drying oven for 24h to remove the solvent and obtain the crude membrane product; place the crude membrane product in deionized water to fully soak, remove the remaining impurities, and then dry in a 70°C forced-air drying oven to obtain the black flexible composite energy storage membrane V1RBP.

[0059] Example 2

[0060] The preparation method of the flexible composite phase change energy storage membrane in Example 2 includes the following steps:

[0061] (1) Glucose solution (concentration of 0.8 wt%) was prepared by adding glucose to secondary water. Based on the mass of the glucose solution, 15 wt% acrylic acid was added to the glucose solution to obtain a mixture. The mixture was ultrasonically treated and then subjected to hydrothermal reaction at 170°C to obtain carboxyl-rich carbon.

[0062] (2) Add 0.3g of carboxyl-rich carbon and 0.7g of boron nitride to 100mL of deionized water and sonicate at 800W for 24h; then centrifuge and dry overnight in an 80℃ drying oven to remove solvent, and obtain gray-black carboxyl-rich carbon-boron nitride compound powder.

[0063] (3) Disperse 0.1g of polyvinylidene fluoride into 5.0g of DMF solvent, and stir the mixture continuously in a 45℃ water bath for 12h to form a light orange viscous solution;

[0064] (4) 0.04 g of carboxyl-rich carbon-boron nitride compound was slowly added to the above viscous solution and stirred continuously at 35°C for 5 h to make the carboxyl-rich carbon-boron nitride compound evenly distributed in the polyvinylidene fluoride solution to obtain a black viscous mixed solution.

[0065] (5) Add 0.07g of polyethylene glycol to the above viscous mixed solution, stir continuously at 45°C for 4 hours, and then place it in a 70°C forced-air drying oven for 24 hours to remove the solvent and obtain the crude membrane product; place the crude membrane product in deionized water to fully soak, remove the remaining impurities, and then dry it in a 70°C forced-air drying oven to obtain a black flexible composite energy storage membrane.

[0066] Example 3

[0067] The preparation method of the flexible composite phase change energy storage membrane in Example 3 includes the following steps:

[0068] (1) Glucose solution (concentration of 1.5 wt%) was prepared by adding glucose to secondary water. Based on the mass of the glucose solution, 16 wt% acrylic acid was added to the glucose solution to obtain a mixture. The mixture was ultrasonically treated and then subjected to hydrothermal reaction at 190°C to obtain carboxyl-rich carbon.

[0069] (2) Add 0.1g of carboxyl-rich carbon and 0.9g of boron nitride to 100mL of deionized water and sonicate at 800W for 24h; then centrifuge and dry overnight in an 80℃ drying oven to remove solvent, and obtain gray-black carboxyl-rich carbon-boron nitride compound powder.

[0070] (3) Disperse 0.1g of polyvinylidene fluoride into 5.0g of dimethyl sulfoxide solvent, and stir the mixture continuously in a 45℃ water bath for 12h to form a light orange viscous solution;

[0071] (4) 0.04 g of carboxyl-rich carbon-boron nitride compound was slowly added to the above viscous solution and stirred continuously at 45°C for 5 h to make the carboxyl-rich carbon-boron nitride compound evenly distributed in the polyvinylidene fluoride solution to obtain a black viscous mixed solution.

[0072] (5) Add 0.09g of polyethylene glycol to the above viscous mixed solution, stir continuously at 55°C for 4 hours, and then place it in a 70°C forced-air drying oven for 24 hours to remove the solvent and obtain the crude membrane product; place the crude membrane product in deionized water to fully soak, remove the remaining impurities, and then dry it in a 70°C forced-air drying oven to obtain a black flexible composite energy storage membrane.

[0073] Shape stability of the flexible composite energy storage membrane and pure PEG membrane tested in solid-state environment (Examples 1-3): The membrane was placed on a heating plate and heated at 30°C and above the phase transition temperature (70°C) for 2 hours, and the shape change of the membrane was observed. Results are as follows: Figure 2As shown, the flexible composite energy storage membranes and pure PEG membranes of Examples 1-3 maintain their original shape at 30°C; while the phase change material of the pure PEG membrane completely turns into a liquid state after heating at 70°C, losing its shape stability. The flexible composite energy storage membranes prepared in Examples 1-3 maintain excellent shape stability above the phase change temperature without any leakage. This further proves that polyvinylidene fluoride is an excellent flexible support material. Furthermore, with the increase of carboxyl-rich carbon-boron nitride compound doping, the color of the composite membrane becomes significantly darker and more uniform, indicating that the carboxyl-rich carbon-boron nitride compound is uniformly dispersed in the composite membrane, which is beneficial to improving its thermal conductivity and photothermal conversion performance.

[0074] Comparative Example 5

[0075] The difference between Comparative Example 6 and Example 1 is that in step (4), 0.02g of boron nitride was used instead of 0.02g of carboxyl-rich carbon-boron nitride compound in Example 1, and a white flexible composite energy storage membrane V1BP was finally obtained.

[0076] Comparative Example 6

[0077] The difference between Comparative Example 6 and Example 1 is that in step (4), 0.02g of carboxyl-rich carbon was used instead of 0.02g of carboxyl-rich carbon-boron nitride compound in Example 1, and the black flexible composite energy storage membrane V1RP was finally obtained.

[0078] In Examples 1 and Comparative Examples 5-6, different fillers (carboxyl-rich carbon-boron nitride, boron nitride, and carboxyl-rich carbon) were used to prepare three different types of flexible composite membranes. Figure 3 and Figure 4 The thermal conductivity and photothermal conversion performance of these three flexible composite films were characterized. The results showed that the V1BP composite film, prepared by doping only with thermally conductive boron nitride filler, had poor light absorption and could not effectively utilize solar energy; the V1RP composite film, doped only with carboxyl-rich carbon, had a slow heat transfer rate; while the V1RBP prepared in Example 1, containing carboxyl-rich carbon-boron nitride compounds, exhibited both excellent photothermal conversion capability (92.1%) and excellent thermal conductivity (0.9 W / m·K).

[0079] Example 4

[0080] The difference between Example 4 and Example 1 is that in step (4), the amount of carboxyl-rich carbon-boron nitride compound added is 0.04g, and the black flexible composite energy storage membrane V2RBP is finally obtained.

[0081] Example 5

[0082] The difference between Example 5 and Example 1 is that in step (4), the amount of carboxyl-rich carbon-boron nitride compound added is 0.06g, and the black flexible composite energy storage membrane V3RBP is finally obtained.

[0083] To fully demonstrate that a thermally conductive and photothermal conversion network has been formed within polyvinylidene fluoride / (carboxyl-rich carbon-boron nitride) / polyethylene glycol (VRBP), the photothermal conversion performance was studied using Examples 4-5 as comparisons. Figure 5 As shown, the thermal conductivity and photothermal conversion storage efficiency of the polyvinylidene fluoride / (carboxyl-rich boron carbon nitride) / polyethylene glycol (V2RBP) prepared in Example 4 and the polyvinylidene fluoride / (carboxyl-rich boron carbon nitride) / polyethylene glycol (V3RBP) prepared in Example 5 are similar, and higher than those of the polyvinylidene fluoride / (carboxyl-rich boron carbon nitride) / polyethylene glycol (V1RBP) prepared in Example 1. This proves that a complete thermal conductivity and photothermal conversion network is formed in the V2RBP prepared in Example 4, and further doping with carboxyl-rich boron carbon nitride compounds has little impact on its thermal conductivity and photothermal conversion performance. Furthermore, since carboxyl-rich boron carbon nitride has no heat storage capacity, excessive addition will only negatively affect the heat storage capacity of the polyvinylidene fluoride / (carboxyl-rich boron carbon nitride) / polyethylene glycol (VRBP) flexible composite film. Therefore, the heat storage capacity of the three VRBP composite films was analyzed, and the results are as follows. Figure 6 As shown. Compared to polyvinylidene fluoride / polyethylene glycol (VP), the three VRBP flexible composite films have different T values. m The significant reduction is due to the fact that the addition of RHTC-BN effectively improves the heat transfer rate of PEG, enabling the solid-liquid phase change process to be achieved rapidly at lower temperatures. Figure 6 In b, compared to PEG, the T values ​​of the three VRBP flexible composite films are... c All showed a significant increase. This is because the heat transfer rate of the composite increased, allowing it to reach T0 more quickly. c Furthermore, the faster the heat transfer rate, the higher the temperature at which the composite begins to crystallize.

[0084] Table 1 shows the DSC parameters of polyethylene glycol (PEG), the flexible composite energy storage membrane VP2 prepared in Comparative Example 2, the flexible composite energy storage membrane V1RBP prepared in Example 1, the flexible composite energy storage membrane V2RBP prepared in Example 4, and the flexible composite energy storage membrane V3RBP prepared in Example 5. From the sample parameters summarized in Table 1, it can be seen that the heat storage capacity of V1RBP is 114.9 J / g, that of V2RBP is 113.2 J / g, and that of V3RBP is 112.5 J / g. This indicates that excessive doping with carboxyl-rich boron nitride compounds will affect the heat storage capacity of the VRBP composite membrane. Therefore, the doping with carboxyl-rich boron nitride compounds should be minimized while ensuring the formation of a complete thermally conductive network.

[0085] Table 1

[0086]

[0087] Comparative Example 7

[0088] The difference from Example 1 is that in step (1), the hydrothermal reaction temperature is 150°C.

[0089] like Figure 7 As shown in Figure a, at this temperature, the carboxyl-rich carbon spheres adhere to each other and aggregate in one place. When the same amount of acrylic acid is added as in Example 1, the interaction between the carboxyl-rich carbon and polyethylene glycol is significantly weakened, making it unable to act as a high photothermal conversion agent and key bridge.

[0090] Comparative Example 8

[0091] The difference from Example 1 is that in step (1), the hydrothermal reaction temperature is 220°C.

[0092] like Figure 7 As shown in c, at this temperature, carboxyl-rich carbon begins to break down or even disintegrate, fusing into large, shapeless structures. Furthermore, when modified with acrylic acid, surface modification with acrylic acid becomes difficult.

[0093] In summary, as shown in Example 1 and Comparative Examples 7-8, the hydrothermal reaction temperature significantly affects the morphology and properties of carboxyl-rich carbon. When the temperature is between 170-190℃, the carboxyl-rich carbon exhibits a uniform, petal-like spherical structure with no obvious adhesion. Furthermore, the oxygen-containing functional groups (carboxyl and hydroxyl groups) on its surface facilitate interaction with polyethylene glycol and polyvinylidene fluoride, resulting in uniform dispersion within the flexible composite membrane. When the temperature is below 170℃, the resulting carbon microstructure consists of mutually adhered spherical structures, which affects subsequent modification and reduces thermal conductivity. When the temperature exceeds 190℃, the spherical structure of the carboxyl-rich carbon begins to break down, and the number of grafted carboxyl functional groups decreases significantly. Therefore, the hydrothermal reaction temperature affects the strength of the intermolecular forces between carboxyl-rich carbon, polyethylene glycol, and boron nitride, thereby influencing the photothermal conversion efficiency and thermal conductivity of the final flexible composite phase change energy storage membrane.

[0094] Comparative Example 9

[0095] The difference from Example 1 is that in step (4), the amount of carboxyl-rich carbon-boron nitride compound added is 0.006g.

[0096] As the doping amount of RHTC-BN increases, the color of the flexible composite film gradually deepens; when the addition amount is only 0.006g, the color of the flexible composite film is almost white. Figure 8As shown in the thermal conductivity diagram, when the RHTC-BN doping amount is 0.006g, the thermal conductivity of the flexible composite film is only 0.37W / m·K. Moreover, as the RHTC-BN doping amount increases, the thermal conductivity of the composite film increases rapidly. This indicates that at this time, too little RHTC-BN in the flexible composite film does not form a thermally conductive network, and the prepared flexible composite film has poor thermal conductivity and cannot be put into application.

[0097] Comparative Example 10

[0098] The difference from Example 1 is that in step (3), the mass ratio of carboxyl-rich carbon to boron nitride is 1:1.

[0099] At this point, the interaction forces between the oxygen-containing functional groups of excessive carboxyl-rich carbons are enhanced, causing the carboxyl-rich carbons to attract and aggregate with each other, while the interaction forces with boron nitride are weakened, which is not conducive to the formation of carboxyl-rich carbon-boron nitride compounds.

[0100] Comparative Example 11

[0101] The difference from Example 1 is that in step (3), the mass ratio of carboxyl-rich carbon to boron nitride is 1:12.

[0102] At this point, the amount of carboxyl-rich carbon doping is too small, and it can only interact with some boron nitride to form carboxyl-rich carbon-boron nitride compounds. The remaining boron nitride still has problems such as chemical inertness and poor dispersibility.

[0103] Comparative Example 12

[0104] The difference from Example 1 is that melamine foam is used instead of polyvinylidene fluoride to prepare melamine foam / (carboxyl-rich carbon-boron nitride) / polyethylene glycol flexible composite phase change material M1RBP (melamine foam is from Huizhi Yang, Yufeng Bai, Chunhua Ge, Chunxue Ma, Weiyue Liang, Xiangdong Zhang. Modified Melamine Foam-Based Flexible Phase Change Composites: Enhanced Photothermal Conversion and Shape Memory Properties. ACS Applied Polymer Materials. 2021, 3, 3321-3333).

[0105] The shape stability of the flexible composite material (membrane) prepared in Example 1 and Comparative Example 12 in water was analyzed by three cycles: the flexible composite material was immersed in water for 24 hours and then completely dried in an oven at 70°C for one cycle. Figure 10 The mass changes of the samples before and after immersion were recorded. After three immersion-drying cycles in water, the flexible composite material M1RBP prepared in Comparative Example 12 showed significant mass loss compared to before the cycles, indicating it could not remain stable in water. However, the flexible composite membrane V1RBP prepared in Example 1 showed no significant mass change compared to before the cycles after three immersion-drying cycles in water, exhibiting excellent shape stability in water. This indicates that the flexible composite phase change material prepared in Comparative Example 12 can only remain stable in a solid-state environment; once it comes into contact with an aqueous environment, it will disintegrate and lose its original high thermal conductivity and high photothermal conversion performance.

[0106] At the same time, such as Figure 9 As shown, the flexible composite phase change material obtained using melamine sponge as the supporting material has a block structure and a maximum stress of 0.22 MPa, which is much lower than the flexible composite phase change film obtained using polyvinylidene fluoride as the supporting material, whose stress is 2.6 MPa (e.g., Figure 9(as shown in b). In addition, the literature has reported the use of expanded graphite (Giang Tien Nguyen, Tan Nhiem Ly, Nhung Thi Tran, Huynh Nguyen Anh Tuan, Nguyen Huu Hieu, Trung HuuBui. Glutaric acid / expanded graphite composites as highly efficient shape-stabilized phase change materials at medium-temperature. Journal of Energy Storage. 2023, 63, 107038), multi-walled carbon nanotubes (ASSathishkumar, K. Arun Balasubramanian, T. Investigations on thermal properties of MWCNT-NBN Paraffin Wax phase change material for thermal storage applications. Ramkumar. Journal of Thermal Analysis and Calorimetry. 2023. DOI:10.1007 / s10973-022-11931-2), and multi-layered porous network structures composed of silicon carbide nanowires and silicon carbide fibers (Xiangfei Kong, Ruiming). Nie,JianjuanYuan.Shape stabilized three-dimensional porous SiC-based phase changematerials for thermal management of electronic components.ChemicalEngineering Journal.2023,462,142168), activated carbon with dendritic pore structure (Jianuo Xu,JingmengSun,Junqi Zhao,Weiye Zhang,Jun Zhou,Liang Xu,Hongwu Guo,Yi Liu,DaihuiZhang.Eco-friendly wood-plastic composites with biomass-activated carbon-based form-stable phase change material for building energy conversion. Industrial Crops and Products. 2023, 197, 116573. These materials, along with others, have been used as support materials to prepare composite phase change materials, effectively improving the problem of easy leakage of molten phase change materials in solid-phase environments. However, some of these composite phase change materials lack flexibility and cannot exist stably in aqueous environments. This indicates that the polyvinylidene fluoride (PVDF) used in this invention has excellent flexibility (mechanical strength), providing a longer service life and wider application range as a flexible support framework for phase change materials.

[0107] Comparative Example 13

[0108] The difference from Example 1 is that in step (1), the amount of acrylic acid added is 2%.

[0109] like Figure 11 As shown, the carboxyl-rich carbon prepared in Example 1 has a petal-like spherical structure with an uneven surface. Its surface is rich in carboxyl functional groups, resulting in stronger interactions with polyethylene glycol and boron nitride. In contrast, the carboxyl-rich carbon prepared in Comparative Example 13 has a smooth spherical structure. Due to the insufficient addition of acrylic acid, the modification of the carbon material is weak, and the carbon surface has too few carboxyl functional groups, resulting in extremely weak interactions with boron nitride and preventing the formation of a carboxyl-rich carbon-boron nitride compound. Furthermore, the insufficient carboxyl functional groups on the carbon surface also weaken its interactions with polyethylene glycol and polyvinylidene fluoride, preventing it from acting as a crucial bridge between boron nitride and polyvinylidene fluoride. Consequently, the thermally conductive filler boron nitride cannot be uniformly dispersed in the flexible composite film.

[0110] Comparative Example 14

[0111] The difference from Example 1 is that in step (1), the amount of acrylic acid added is 25%.

[0112] like Figure 11 As shown, the carboxyl-rich carbon petal-like spherical structure prepared in Comparative Example 14 completely collapsed, with the carbon materials adhering to each other in one place, exhibiting no obvious structure. This is because excessive acrylic acid cannot participate in the modification of the carbon materials, instead forming polyacrylic acid microspheres that adhere to the surface of the carbon materials. Furthermore, as... Figure 13 As shown, the carboxyl-rich carbon prepared in Comparative Example 14 has formed a blocky structure and cannot be used.

Claims

1. A method for preparing a high-performance flexible composite phase change energy storage membrane, characterized in that, Includes the following steps: S1. A carboxyl-rich boron carbon nitride compound is added to a solution containing polyvinylidene fluoride (PVDF) and mixed to obtain a black viscous solution; the amount of carboxyl-rich boron carbon nitride added is 20-60% based on the mass of PVDF. S2 adds polyethylene glycol to the above black viscous solution, stirs to disperse it evenly to obtain a black viscous mixture, and removes the solvent to obtain a flexible composite phase change energy storage membrane. In step S1, the preparation method of the carboxyl-rich carbon-boron nitride compound is as follows: 1) Prepare a glucose solution by adding glucose to deionized water, and then add acrylic acid to the glucose solution to obtain a mixture; the amount of acrylic acid added is 10-16% based on the mass of the glucose solution. 2) After ultrasonic treatment, the above mixture is subjected to hydrothermal reaction at a temperature of 170-190℃ to obtain carboxyl-rich carbon. 3) Add carboxyl-rich carbon and boron nitride to deionized water and then sonicate and centrifuge them in sequence, and then dry them thoroughly to obtain carboxyl-rich carbon-boron nitride compound; the mass ratio of carboxyl-rich carbon to boron nitride is 1:(2-9).

2. The method for preparing the high-performance flexible composite phase change energy storage membrane as described in claim 1, characterized in that, In step 1), the concentration of the glucose solution is 0.8-1.5 wt%.

3. The method for preparing the high-performance flexible composite phase change energy storage membrane as described in claim 1, characterized in that, In step 3), the mass ratio of carboxyl-rich carbon to boron nitride is 1:

4.

4. The method for preparing the high-performance flexible composite phase change energy storage membrane as described in claim 1, characterized in that, In step S1, the mixing temperature is 35-45℃; in step S2, the mixing temperature is 45-55℃.

5. The method for preparing the high-performance flexible composite phase change energy storage membrane as described in claim 1, characterized in that, In step S1, the solvent in the solution containing polyvinylidene fluoride is methylpyrrolidone, N,N-dimethylformamide, acetone, or dimethyl sulfoxide.

6. The method for preparing the high-performance flexible composite phase change energy storage membrane as described in claim 1, characterized in that, In step S2, based on the mass of polyvinylidene fluoride, the amount of polyethylene glycol added is 50-90%.

7. The method for preparing the high-performance flexible composite phase change energy storage membrane as described in claim 1, characterized in that, In step S2, the solvent removal method is as follows: the obtained black viscous mixture is dried to obtain a black flexible composite film, which is then fully immersed in deionized water and dried. This process is repeated multiple times to ensure that the solvent is completely removed.

8. A high-performance flexible composite phase change energy storage membrane prepared by the preparation method according to any one of claims 1-7.

Images