Graphene / spherical alumina composite aerogel packaged phase change heat storage composite material and preparation method thereof

Abstract

The invention provides a graphene / spherical alumina composite aerogel encapsulated phase change heat storage composite material and a preparation method thereof. The preparation method comprises the following steps: preparing graphene / spherical aluminum oxide composite aerogel with a high-degree double-orientation structure by using a directional freezing technology, and then performing vacuum impregnation on a phase-change material; the out-of-plane heat conductivity of the polyethylene glycol-based heat-conducting phase-change composite material can reach 4.213 W.m <-1 >. K <-1 >, the in-plane heat conductivity of the polyethylene glycol-based heat-conducting phase-change composite material can reach 5.539 W.m <-1 >. K <-1 >, tests show that the highest melting enthalpy (delta Hm) of the polyethylene glycol-based heat-conducting phase-change composite material can reach 186.5 J.g, the highest crystallization enthalpy (delta Hc) of the polyethylene glycol-based heat-conducting phase-change composite material can reach 178.8 J.g, and the polyethylene glycol-based heat-conducting phase-change composite material is stable in structure, low in leakage rate and suitable for industrial production. The application potential in the fields of lithium battery heat management, electronic element heat dissipation, solar heat storage and supply, industrial waste heat recovery and the like is realized.

Description

Technical Field

[0001] The present invention belongs to the field of materials, and specifically relates to a phase change heat storage material, and more specifically relates to a graphene / spherical alumina composite aerogel encapsulated phase change heat storage composite material and a preparation method thereof. Background Art

[0002] With the rapid development of the global economy and the acceleration of industrialization, humanity's demand for energy is growing. Against the backdrop of energy crises and environmental challenges, the development and utilization of renewable energy and improving energy efficiency have become global research focuses. Thermal energy storage technology plays a vital role as a key means of improving energy efficiency and balancing energy supply and demand. It can store excess thermal energy for a specific period of time and release it for use when needed, effectively alleviating the temporal and spatial mismatch between energy supply and demand.

[0003] Phase change thermal storage materials (PCMs) are one of the commonly used technologies for thermal energy storage and are also one of the key factors in promoting the clean energy industrial revolution. They have huge latent heat storage and reversible release characteristics during the phase change process, and have great application development value. Currently developed organic phase change materials generally have poor thermal conductivity. The heat transfer rate within the material is slow, which limits its heat storage and release rates, and thus affects the efficiency of the entire heat storage system. Although inorganic phase change materials have good thermal conductivity, they often suffer from large supercooling and phase separation, which makes their phase change process unstable, shortens their service life, and may cause safety hazards such as leakage in actual applications.

[0004] In order to overcome the defects of single phase change heat storage materials, compounding phase change materials with other materials with specific functions to prepare phase change heat storage composite materials has become a research hotspot in the current heat storage field. Through reasonable composite design, the advantages of different materials can be comprehensively utilized, such as compounding materials with high thermal conductivity with phase change materials to improve the thermal conductivity of phase change materials and accelerate the heat transfer rate; or compounding materials with supporting and encapsulating functions with phase change materials to solve the leakage problem of phase change materials during the phase change process and improve their stability and service life. For example, CN 120059678 A achieves coupling encapsulation of phase change materials through a dense shell plated by magnetron sputtering and a three-dimensional porous graphene aerogel to obtain a low-leakage graphene-based phase change material, but the thermal conductivity of the composite phase change material is not high, only 1.22 W·m -1 ·K -1 .

[0005] In summary, the research and development of new, efficient, stable and safe phase change heat storage composite materials has extremely important practical significance for promoting the development of thermal energy storage technology, promoting the effective use of renewable energy and alleviating energy and environmental problems. Summary of the Invention

[0006] In order to solve the problems of easy leakage and low thermal conductivity of phase change heat storage composite materials in the prior art, the present invention provides a graphene / spherical alumina composite aerogel encapsulated phase change heat storage composite material and a preparation method thereof.

[0007] The technical solution adopted by the present invention is: a method for preparing a graphene / spherical alumina composite aerogel encapsulated phase change heat storage composite material, comprising the following steps: S1. Preparation of polyvinyl alcohol solution; S2. The graphene and graphene oxide are dispersed in the polyvinyl alcohol solution prepared in step S1 to obtain a graphene mixed dispersion; S3 spherical alumina, alumina ethanol dispersion was added to the graphene mixed dispersion prepared in step S2, dialyzed to remove impurities to obtain a graphene / spherical alumina mixed dispersion; S4. The graphene / spherical alumina mixed dispersion prepared in step S3 was poured into a mold, directional frozen, and dried to obtain a composite aerogel; S5. Placing the composite aerogel prepared in step S4 into the liquefied phase change material, vacuum impregnating, and removing the aerogel to obtain a graphene / spherical alumina composite aerogel-encapsulated phase change thermal storage composite material.

[0008] The present invention fills the small gaps between graphene sheets with spherical alumina of different sizes, which can reduce the thermal resistance between fillers and fillers, and between fillers and substrates, thereby improving thermal conductivity and, to a certain extent, leak prevention. Polyvinyl alcohol (PVA) is used as a thermally conductive filler binder to ensure the structural stability of the composite aerogel after freeze-drying. The addition of graphene oxide (GO) can act as a dispersant for uniformly dispersing graphene (GNP) in the PVA solution. Due to the liquid crystal properties of GO, it can also improve the overall viscosity of the graphene mixed dispersion and adjust the flaky fillers for initial orderly arrangement, and prevent the alumina particles from prematurely settling at the bottom of the dispersion. Subsequently, a simple and controllable directional freezing technique ( Figure 3 ) The graphene / spherical alumina mixed dispersion was prepared into a composite aerogel. The growth direction of the ice crystals was controlled from bottom to top and from outside to inside. Under the pressure of the growing ice crystals, the graphene sheets spontaneously formed a regular arrangement, making the prepared graphene / spherical alumina composite aerogel have a distinct orientation structure and good structural stability. ( Figures 1 and 2 Finally, the composite aerogel is placed in the liquefied phase change material for vacuum impregnation, so that the gaps in the composite aerogel are filled with the phase change material. After completion, the composite aerogel is taken out, naturally cooled, and the excess phase change material on the surface is ground to remove, thereby preparing a graphene / spherical alumina composite aerogel encapsulated phase change thermal storage composite material with stable structure and low leakage rate.

[0009] Preferably, in step S1, the polyvinyl alcohol content in the polyvinyl alcohol solution is 15-25 mg / mL.

[0010] Preferably, in step S2, the graphene content in the graphene mixed dispersion is 20-60 mg / mL.

[0011] Preferably, in step S2, the graphene oxide content in the graphene mixed dispersion is 8-12 mg / mL.

[0012] Preferably, in step S3, spherical alumina with particle sizes of 3 μm, 5 μm, 10 μm, and 45 μm are added to the graphene mixed dispersion at a mass ratio of 40-42:7-9:11-13:39-41.

[0013] Preferably, in step S3, the content of nano-α-phase alumina in the alumina ethanol dispersion is 20-30 wt%.

[0014] Preferably, in step S3, the dialysis impurity removal method includes: stirring the mixture of spherical alumina, alumina ethanol dispersion, and graphene mixed dispersion at room temperature, and dialyzing in deionized water after bagging to remove soluble impurities; wherein the stirring time is 10 to 12 hours and the dialysis time is 48 to 72 hours.

[0015] Preferably, in step S4, the temperature of the directional freezing is -80 to -65°C, and the time of the directional freezing is 20 to 40 minutes.

[0016] Preferably, in step S4, the mold is preferably a copper-based mold. In a specific embodiment, the copper-based mold is a half-hollowed cylinder with a hollow cylindrical cavity ( Figure 3 ). The graphene / spherical alumina mixed dispersion is poured into the cylindrical cavity, and then the mold is placed in a pre-cooled low-temperature constant temperature reactor for directional freezing.

[0017] Preferably, in step S5, the phase change material comprises polyethylene glycol, paraffin, fatty acid, inorganic hydrated salt, pentaerythritol, and sucrose, wherein the molecular weight of the polyethylene glycol is preferably 2,000 to 20,000.

[0018] Preferably, in step S5, the vacuum impregnation temperature is 70-80° C., and the vacuum impregnation time is 3-4 h.

[0019] The present invention also provides a graphene / spherical alumina composite aerogel-encapsulated phase-change thermal storage composite material prepared by the method. The graphene / spherical alumina composite aerogel-encapsulated phase-change thermal storage composite material can be used in fields such as lithium battery thermal management, electronic device heat dissipation, solar thermal storage and heating, and industrial waste heat recovery.

[0020] Beneficial effects of the present invention: 1. This invention uses directional freezing technology to prepare highly dual-oriented graphene / spherical alumina composite aerogels. The process is mature and simple. Then, phase change materials are vacuum impregnated to obtain high-performance thermal conductivity and phase change heat storage composite materials with good anti-seepage properties and shape stability. They have strong thermal conductivity and heat storage capabilities, high phase change enthalpy, and high energy storage efficiency. The highest in-plane thermal conductivity of the PEG-based composite phase change material reaches 5.539 W·m -1 ·K -1 The out-of-plane thermal conductivity can reach up to 4.213 W·m -1 ·K -1 , the melting enthalpy can reach up to 186.5 kJ / kg, and the crystallization enthalpy can reach up to 178.8 kJ / kg; 2. The graphene / spherical alumina composite aerogel encapsulated phase change thermal storage composite material prepared by the present invention has a stable structure. The prepared encapsulation aerogel has a rich porous structure and a large specific surface area. It can adsorb phase change materials to solve its leakage problem and exhibits a high phase change material loading rate. At the same time, this special structure gives it good tolerance, long life, high and low temperature resistance, environmental friendliness, and exhibits good thermal stability and good phase change behavior. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic structural diagram of the graphene / spherical alumina composite aerogel encapsulated phase change heat storage composite material provided by the present invention.

[0022] Figure 2 This is an electron microscope image of the graphene / spherical alumina composite aerogel prepared in Example 1 of the present invention.

[0023] Figure 3 This is a schematic diagram of the directional freezing technology used in the present invention. DETAILED DESCRIPTION

[0024] The following describes the embodiments of the present invention by specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. The various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, in the case of no conflict, the features in the following examples and embodiments can be combined with each other. In the embodiments of the present invention, unless otherwise specified, the methods used are all conventional methods, and the reagents used can be obtained from commercial sources.

[0025] Example 1 S1. Preparation of PVA solution: Weigh an appropriate amount of PVA particles, add them to deionized water, and stir at 95°C for 3 h to completely dissolve them. Prepare a transparent PVA solution with a PVA content of 20 mg / mL, and cool it to room temperature before use.

[0026] S2. Preparation of graphene mixed dispersion: Take 30 mL of the PVA solution prepared in S1, add 1.8 g of graphene and 0.6 g of graphene oxide, and disperse under ultrasonication for 30 min before use; S3. Preparation of a graphene / spherical alumina mixed dispersion: Weigh 0.81g, 0.15g, 0.25g, and 0.79g of spherical alumina of different particle sizes (3μm, 5μm, 10μm, and 45μm, respectively). Add 1g of an alumina ethanol dispersion (containing 25 wt% nano-α-phase alumina) to the dispersion in S2. Add the PVA solution in S1 to the final volume of 60 mL. Stir thoroughly at room temperature to prepare a dispersion with a graphene content of 30 mg / mL and a graphene oxide content of 10 mg / mL. After bagging, dialyze in deionized water for 48 hours to remove soluble impurities.

[0027] Preparation of S4, graphene / spherical alumina composite aerogel: The low-temperature constant temperature reactor was adjusted to -75°C, and the graphene / spherical alumina mixed dispersion in S3 was poured into a custom copper mold, placed in the reactor, and subjected to directional freezing for 30 minutes. After that, freeze drying was performed for 72 hours to obtain the composite aerogel. The microstructure of the composite aerogel was observed by electron microscopy. Figure 2 .

[0028] S5. Place the aerogel in the phase change material polyethylene glycol PEG4000 that is liquefied after heating, and vacuum impregnate it in a vacuum oven at 80°C for 3 hours until no bubbles emerge. After completion, take it out, cool it naturally, and grind to remove excess phase change material on the surface to complete the preparation and obtain a graphene / spherical alumina composite aerogel encapsulated phase change thermal storage composite material.

[0029] Example 2 The preparation process was similar to that of Example 1, except that in step S2 of Example 2, 2.4 g of graphene was added, while the amount of graphene oxide remained unchanged. In step S3, a dispersion having a graphene content of 40 mg / mL and a graphene oxide content of 10 mg / mL was prepared. The remaining steps remained unchanged.

[0030] Example 3 The preparation process was different from that of Example 1 except that, in step S2 of Example 3, 3.0 g of graphene was added, while the amount of graphene oxide remained unchanged; and in step S3, a dispersion having a graphene content of 50 mg / mL and a graphene oxide content of 10 mg / mL was prepared. The remaining steps remained unchanged.

[0031] Example 4 The preparation process was different from that in Example 1, except that in step S2 of Example 4, 3.6 g of graphene was added, while the amount of graphene oxide remained unchanged; and in step S3, a dispersion having a graphene content of 60 mg / mL and a graphene oxide content of 10 mg / mL was prepared. The remaining steps remained unchanged.

[0032] Example 5 The preparation process is different from that of Example 4 in that, in step S5 of Example 5, the phase change material used is paraffin wax (PW), and the other steps remain unchanged.

[0033] Comparative Example 1 The preparation process is different from that of Example 4, except that the addition of spherical alumina of different particle sizes and alumina ethanol dispersant in step S3 is not performed in Comparative Example 1, and the thermal conductive filler in the dispersion system contains only 60 mg / mL of graphene and 10 mg / mL of graphene oxide.

[0034] Comparative Example 2 The preparation process is different from that of Example 4 in that, in step S4 of Comparative Example 2, directional freezing is not performed but refrigerator freezing is performed.

[0035]

Performance test

[0036] Table 1 Performance test results of phase change thermal storage composite materials As shown in Examples 1-4 in Table 1, the graphene / spherical alumina composite aerogel-encapsulated phase change thermal storage composite material, prepared by vacuum impregnation and infusion of the phase change material PEG4000, exhibits high in-plane and out-of-plane thermal conductivity, facilitating rapid and efficient heat conduction within the phase change system. It also exhibits a high phase change enthalpy exceeding 150 kJ / kg, facilitating heat storage and release. After 50 cycles of heating and cooling, the material remains stable, with only minor mass loss and a low leakage rate. As can be seen from the above examples, both the in-plane and out-of-plane thermal conductivity of the composite material improves with increasing graphene content.

[0037] Comparing Examples 4 and 5, we conclude that PW, as a phase change material, has a lower phase change enthalpy than PEG4000. PW is suitable for use in electronic devices at temperatures between 0 and 50°C, while PEG4000 is more suitable for higher temperatures, such as industrial waste heat recovery. Comparing Comparative Examples 1 and 2 with Example 4, we conclude that the addition of alumina particles can further fill the larger voids in the aerogel, improving thermal conductivity and, to a certain extent, leak resistance. The thermal conductivity of the composite material prepared by targeted freezing is significantly better than that of random freezing in a refrigerator, and its leak resistance is significantly stronger.

[0038] The embodiments described above are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a graphene / spherical alumina composite aerogel encapsulated phase change thermal storage composite material, characterized in that: The following steps are involved: S1. Preparation of polyvinyl alcohol solution; S2. The graphene and graphene oxide are dispersed in the polyvinyl alcohol solution prepared in step S1 to obtain a graphene mixed dispersion; S3 spherical alumina, alumina ethanol dispersion was added to the graphene mixed dispersion prepared in step S2, dialyzed to remove impurities to obtain a graphene / spherical alumina mixed dispersion; S4. The graphene / spherical alumina mixed dispersion prepared in step S3 was poured into a mold, directional frozen, and dried to obtain a composite aerogel; S5. Placing the composite aerogel prepared in step S4 into the liquefied phase change material, vacuum impregnating, and removing the aerogel to obtain a graphene / spherical alumina composite aerogel-encapsulated phase change thermal storage composite material.

2. The method according to claim 1, wherein In step S1, the polyvinyl alcohol content in the polyvinyl alcohol solution is 15-25 mg / mL.

3. The method according to claim 1, wherein In step S2, the graphene content in the graphene mixed dispersion is 20-60 mg / mL.

4. The method according to claim 1, wherein In step S2, the graphene oxide content in the graphene mixed dispersion is 8-12 mg / mL.

5. The method according to claim 1, wherein In step S3, spherical alumina with particle sizes of 3 μm, 5 μm, 10 μm, and 45 μm are added to the graphene mixed dispersion at a mass ratio of 40-42:7-9:11-13:39-41.

6. The method according to claim 1, wherein In step S3, the content of nano-α-phase alumina in the alumina ethanol dispersion is 20-30 wt%.

7. The method according to claim 1, wherein In step S4, the temperature of the directional freezing is -80 to -65°C, and the time of the directional freezing is 20 to 40 minutes.

8. The method according to claim 1, wherein In step S5, the phase change material includes polyethylene glycol, paraffin, fatty acid, inorganic hydrated salt, pentaerythritol, and sucrose.

9. The method according to claim 1, wherein In step S5, the vacuum impregnation temperature is 70-80° C., and the vacuum impregnation time is 3-4 h.

10. The graphene / spherical alumina composite aerogel encapsulated phase change thermal storage composite material prepared by the method according to any one of claims 1 to 9.

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