Preparation method of high-thermal-conductivity phase change energy storage material based on bubble jet oriented graphene nanosheet layer

Abstract

The application relates to a preparation method of a high-thermal-conductivity phase change energy storage material based on bubble jet orientation of graphene nanosheet layers. By introducing high-pressure expanded microspheres into graphene, air jets are generated when the microspheres break, the graphene sheet layers are deflected, a highly oriented graphene skeleton is prepared, high-thermal-conductivity graphene skeletons are obtained through high-temperature graphitization treatment, the phase change energy storage material is filled multiple times through a vacuum-assisted filling method, and a high-thermal-conductivity graphene phase change energy storage composite material is obtained. The high-thermal-conductivity graphene phase change energy storage material has the characteristics of fast response and high heat storage, the response time is shortened by 1 / 2 compared with traditional commercial materials, the thermal conductivity is up to 152 W / (m*K), the bulk phase change enthalpy value is up to 249 kJ / L, and the thermal conductivity and the phase change enthalpy value can be adjusted according to different requirements. Therefore, the novel graphene phase change energy storage material has great application prospect.

Description

Technical Field

[0001] This invention relates to the field of composite materials, and specifically to a method for preparing a high thermal conductivity phase change energy storage material based on bubble jet-oriented graphene nanosheets. Background Technology

[0002] Research on phase change energy storage technology began in the 20th century, initially focusing primarily on solar energy utilization and thermal storage in residential heating systems. With technological advancements, the application scope of this material has gradually expanded, encompassing multiple fields such as construction, transportation, and electronics manufacturing. This is because phase change energy storage materials possess significant advantages in energy conservation, emission reduction, and improved energy efficiency, effectively supporting the goals of sustainable development. Furthermore, the non-renewable nature and polluting characteristics of petroleum resources have led to serious environmental problems and concerns about resource depletion, such as global warming and air pollution, and this unsustainable energy model urgently needs to be transformed. Therefore, developing efficient and clean energy storage and conversion technologies is an urgent task.

[0003] Among the many energy storage technologies available today, thermal energy storage technology demonstrates enormous potential and prospects. This technology can store thermal energy in a high-capacity and large-scale manner. Thanks to the rapid development of materials science in recent years, thermal energy storage not only boasts high energy density and high conversion efficiency but also achieves relatively low costs. In particular, the application of phase change energy storage composite materials is especially important. These materials utilize the heat absorption or release properties during phase change processes, allowing the stored heat to be released during peak electricity demand periods and the excess heat to be stored during off-peak periods. This not only helps balance the supply and demand of thermal energy but also significantly improves the overall energy utilization efficiency.

[0004] A major technical challenge in current research on phase change energy storage composite materials is improving their thermal conductivity, as these materials typically exhibit low thermal conductivity. The key to solving this problem lies in optimizing the support structure of the composite material to achieve a faster thermal response. In this regard, graphene, a popular two-dimensional material, shows great potential due to its extremely high in-plane thermal conductivity (between 2000 and 5000 W / m·K). This material has been extensively studied and applied in improving thermal conductivity. However, graphene's unique two-dimensional structure causes its thermal conductivity to differ from conventional materials, requiring a high degree of orientation in the graphene framework structure to fully utilize its excellent thermal conductivity properties. Summary of the Invention

[0005] Addressing the urgent need for high thermal conductivity phase change energy storage composite materials, this invention provides a method for preparing a high thermal conductivity phase change energy storage material based on bubble jet-oriented graphene nanosheets. First, expanded microspheres are modified to encapsulate graphene sheets onto the expanded microspheres. A hot-pressing device generates high-pressure bubbles in the expanded microspheres. Upon rapid depressurization, the bubbles rupture, generating a jet. The jet possesses a strong impact force, which can deflect the graphene nanosheets, resulting in a highly oriented graphene framework with high in-plane thermal conductivity. The phase change material is then infused using a vacuum-assisted infusion method to obtain a high thermal conductivity graphene-based phase change energy storage composite material. Specifically, the process is carried out according to the following steps:

[0006] 1) Modification of expanded microspheres: The expanded microspheres were prepared into a dispersion with a mass fraction of 10%, placed in a water bath and heated to 50°C. Triethylbenzylammonium chloride, octadecyldimethylbenzylammonium chloride, benzalkonium chloride, etc. (one or more of them can be used) were added dropwise and the mixture was kept at the temperature for 3 hours and stirred and heated to react.

[0007] 2) Preparation of graphene / expanded microsphere composite solid: The concentration of graphene slurry is 1wt%-10wt% and modified expanded microspheres (the weight ratio of graphene to expanded microspheres is 1:1) are placed in a planetary stirrer and stirred at a rate of 500-2000 r / min for 1 h to allow the graphene sheets and modified expanded microspheres to form a nano-dispersion in the aqueous solution. Then, the mixed dispersion is filtered to obtain the graphene / expanded microsphere composite solid and dried in an oven at 50℃.

[0008] 3) Preparation of highly oriented graphene framework: The dried graphene / expanded microsphere composite solid was sieved into powder using a 500-mesh sieve. The powdered graphene / expanded microsphere composite solid was placed in a temperature-controlled molding device for heat preservation, causing the liquid in the microsphere to undergo a phase change, thereby causing the microsphere to expand and generate high-pressure bubbles. Then, the bubbles were rapidly pressed down through the mold, generating a high-speed jet, which caused the graphene nanosheets to deflect, thereby obtaining a highly oriented graphene framework.

[0009] 4) Graphitization treatment of highly oriented graphene framework: The highly oriented graphene / expanded microsphere framework obtained in 3) is placed in a graphitization furnace and graphitized for 10-14 hours in an inert gas atmosphere to remove the internal expanded microspheres and repair the defects of the graphene nanosheets themselves. The graphitization treatment temperature is 2500℃-3200℃.

[0010] 5) Secondary densification of highly oriented graphene framework: The highly oriented graphene framework obtained in 4) is placed in the molding die of 3) and molded again to re-overlap the originally non-overlapping graphene nanosheets, further reducing the micro-interface thermal resistance.

[0011] 6) Injecting phase change energy storage material into graphene framework: Place graphene framework on solid phase change material and put it into vacuum oven. After the vacuum oven is evacuated to -0.1MPa, the temperature is raised to melt the phase change material. After melting, it is injected into the interior of graphene framework under vacuum negative pressure. After natural cooling, high thermal conductivity graphene phase change energy storage material is obtained.

[0012] Preferably, the amount of expanded microspheres used in step 1) above is 10-50g, and the amount of triethylbenzylammonium chloride is 1-5g; (the expanded microspheres are polymer microspheres (such as methyl methacrylate) containing volatile liquid (such as butane) inside, which can generate bubbles inside the microspheres by heating to above the phase change temperature of the liquid, thereby expanding.

[0013] Preferably, the concentration of the graphene slurry in step 2) above is 1wt%-10wt%;

[0014] Preferably, the temperature control range of the molding device in step 3) above is 90-140°C, the heat holding time is 5-30 min, and the molding rate is 200-1000 mm / min;

[0015] Preferably, the molding rate used for the secondary densification of the graphene framework in step 5) above is 1-5 mm / min;

[0016] Preferably, the phase change material mentioned in step 6) above includes, but is not limited to, highly refined paraffin wax, heptadecane, tetradecane, dioctadecane, tridecane, oxidized polyethylene wax, etc., and one or more of them can be used.

[0017] The beneficial effects of this invention are as follows: 1. The process of preparing graphene framework using this invention is simpler than traditional methods: Compared with methods for preparing carbon foam, this method only requires stirring, drying, and hot pressing to prepare highly anisotropic graphene foam, and the cost is lower. Traditional methods require high temperatures and long processing times to prepare carbon foam, and the resulting carbon foam is isotropic, making it difficult to meet anisotropic application requirements. 2. This invention achieves high orientation of graphene foam through gas explosion: This invention implants expandable microspheres inside graphene sheets, fills them with gas through heating, and then uses pressure to cause the microspheres to rupture laterally, generating a strong airflow, thereby achieving radial orientation of the graphene nanosheets. 3. The samples prepared by this invention can be mass-produced and are more flexible: This invention prepares highly oriented graphene foam using only stirring, drying, and hot pressing, thus allowing for the preparation of graphene foams of different sizes according to different sample requirements, and with higher uniformity of orientation, which is a significant improvement over traditional preparation methods. Attached Figure Description

[0018] Figure 1This is a simulation diagram of expanded microsphere-oriented graphene sheets;

[0019] Figure 2 These are SEM images of the graphene / expanded microsphere composite solid from Example 1;

[0020] Figure 3 This is an optical photograph of the high thermal conductivity graphene framework of Example 1. Detailed Implementation

[0021] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0022] Example 1:

[0023] The preparation method of the fast-response, high-orientation phase change energy storage composite material described in this embodiment is carried out according to the following steps:

[0024] 1) 20g of expanded microspheres (methyl methacrylate microspheres encapsulated with butane) were prepared into a dispersion with a mass fraction of 10%, placed in a water bath and heated to 50°C. 2g of triethylbenzylammonium chloride was added dropwise and kept at the temperature for 3h. The reaction did not occur after stirring and heating.

[0025] 2) 5 wt% of graphene slurry and modified expanded microspheres (the weight ratio of graphene to expanded microspheres is 1:1) were placed in a planetary stirrer and stirred at a rate of 500 r / min for 1 h to allow the graphene sheets and modified expanded microspheres to form a nano-dispersion in the aqueous solution. The mixed dispersion was then filtered to obtain a graphene / expanded microsphere composite solid, which was then dried in an oven at a temperature of 50 °C.

[0026] 3) Using a 500-mesh sieve, the dried graphene / expanded microsphere composite solid is sieved into powder. The powdered graphene / expanded microsphere composite solid is placed in a temperature-controlled molding device and kept at 110°C for 10 minutes. It is then pressed at a speed of 500 mm / min using a bidirectional press head.

[0027] 4) The highly oriented graphene / expanded microsphere framework obtained in 3) is placed in a graphitization furnace and graphitized for 12 hours in an inert gas atmosphere to remove the internal polymeric dispersant and expanded microspheres and repair the defects of the graphene nanosheets themselves. The graphitization temperature is 3000℃.

[0028] 5) The highly oriented graphene framework obtained in 4) is placed in the molding die of 3) and molded at a speed of 3 mm / min to obtain a highly thermally conductive graphene framework with a porosity of 80%. Re-molding can re-overlap the originally non-overlapping graphene nanosheets, further reducing the micro-interface thermal resistance.

[0029] 6) Place the graphene skeleton on polyoxyethylene paraffin and put it into a vacuum oven. After the vacuum oven is evacuated to -0.1MPa, the temperature is raised to melt the polyoxyethylene paraffin. After melting, it is injected into the interior of the graphene skeleton under the action of vacuum negative pressure. After natural cooling, a high thermal conductivity graphene phase change energy storage material is obtained.

[0030] The graphene phase change energy storage material prepared in this embodiment has a height of 20 mm and a diameter of 200 mm.

[0031] This embodiment, through testing the in-plane thermal conductivity of the sample, yielded an in-plane thermal conductivity of 113 W / (m·K), a bulk latent heat of phase change of 230 kJ / L, an open area ratio of 95%, and an orientation factor of 0.66 for the fast-response, highly oriented phase change energy storage composite material. This represents a 159% improvement in thermal conductivity and a two-fold increase in orientation factor compared to traditional graphene / organic phase change energy storage materials. Compared to commercial phase change composite materials, it shows a 15% increase in open area ratio and a 40% improvement in response speed. Furthermore, this energy storage material can be processed into phase change energy storage materials of different shapes for application in complex environments.

[0032] Example 2:

[0033] The preparation method of the highly oriented phase change energy storage composite material described in this embodiment is the same as that in Example 1, except that the amount of expanded microspheres in step 1) is changed to 30g.

[0034] The graphene phase change energy storage material prepared in this embodiment has a height of 20 mm and a diameter of 200 mm. This embodiment increases the amount of expanded microspheres, thereby increasing the number of bubbles and generating more jets at different locations, causing more graphene nanosheets to deflect and improving their orientation. By testing the in-plane thermal conductivity of the sample, the in-plane thermal conductivity of the high thermal conductivity, high orientation phase change energy storage composite material was found to be 141 W / (m·K), the bulk latent heat of phase change was 233 kJ / L, the orientation factor was 0.78, and the porosity reached 95%. The increased amount of expanded microspheres in step 1) causes more graphene nanosheets to deflect, increasing the orientation of the graphene framework and thus increasing the in-plane thermal conductivity of the high thermal conductivity, high orientation phase change energy storage composite material.

[0035] Example 3:

[0036] The preparation method of the highly oriented phase change energy storage composite material described in this embodiment is the same as that in Embodiment 1, except that the heat preservation temperature in step 3) is changed to 140℃.

[0037] The graphene phase change energy storage material prepared in Example 3 has a height of 20 mm and a diameter of 200 mm. This example increases the internal pressure of the expanded microspheres by increasing the insulation temperature, thereby enhancing the impact force of the jet generated when the expanded microspheres rupture. This results in a greater degree of deflection of the graphene nanosheets, a higher orientation of the graphene framework, and a high thermal conductivity, high orientation phase change energy storage composite material with an in-plane thermal conductivity of 121 W / (m·K), a latent heat of phase change of 231 kJ / L, an orientation factor of 0.69, and an open porosity of 95%. The reason why increasing the temperature does not significantly improve the thermal conductivity may be that the expanded microspheres rupture prematurely at excessively high temperatures.

[0038] Example 4:

[0039] The preparation method of the high thermal conductivity and high orientation phase change energy storage composite material described in this embodiment is the same as that in Embodiment 1, except that the pressing speed in step 3) is changed to 700 mm / min.

[0040] The graphene phase change energy storage material prepared in Example 4 has a height of 20 mm and a diameter of 200 mm. By increasing the downward pressure speed, the impact force on the expanded microspheres is increased, resulting in a faster and stronger jet velocity and a larger deflection angle of the graphene nanosheets. Testing the in-plane thermal conductivity of the sample revealed that the high thermal conductivity and high heat storage capacity phase change energy storage composite material has an in-plane thermal conductivity of 125 W / (m·K), a latent heat of phase change of 223 kJ / L, an orientation factor of 0.70, and an open porosity of 95%.

[0041] Example 5:

[0042] The preparation method of the high thermal conductivity and high orientation phase change energy storage composite material described in this embodiment is the same as that in Embodiment 1, except that the heat treatment time in step 4) is changed to 14 hours.

[0043] The graphene phase change energy storage material prepared in Example 5 has a height of 20 mm and a diameter of 200 mm. By testing the in-plane thermal conductivity of the sample, the in-plane thermal conductivity of the high thermal conductivity, high orientation phase change energy storage composite material was found to be 142 W / (m·K), with a phase change latent heat of 226 kJ / L, an orientation factor of 0.62, and an open porosity of 95%. Changing the heat treatment temperature in step 4) was to verify the effect of graphitization temperature on removing residual groups on the graphene surface and on the rearrangement of the carbon structure on the graphene surface.

[0044] Example 6:

[0045] The preparation method of the high thermal conductivity and high orientation phase change energy storage composite material described in this embodiment only changes the pressing speed in step 5) by 50 mm / min, and the remaining steps are the same as in Embodiment 1.

[0046] The graphene phase change energy storage material prepared in Example 6 has a height of 20 mm and a diameter of 200 mm. By testing the in-plane thermal conductivity of the sample, the in-plane thermal conductivity of the high thermal conductivity, high orientation phase change energy storage composite material was found to be 121 W / (m·K), with a phase change latent heat of 232 kJ / L, an orientation factor of 0.62, and an open porosity of 95%. Changing the pressing rate in step 5) was to fill the pores sintered in step 4), allowing the graphene nanosheets to overlap and the framework to become denser, thereby improving the in-plane thermal conductivity of the phase change energy storage composite material. With increasing pressing speed, less normal deflection occurs in the graphene sheets, thus improving the thermal conductivity.

[0047] Comparative Example 1:

[0048] The preparation method of the fast-response, highly oriented phase change energy storage composite material described in this comparative example is the same as that in Example 1, except that triethylbenzylammonium chloride in step 1) is replaced with Tween 80.

[0049] The graphene phase change energy storage material prepared in Comparative Example 1 has a height of 20 mm and a diameter of 200 mm. This example changed the type of modifier, thereby altering the surface charge of the expanded microspheres and consequently the number of graphene nanosheets adsorbed on the surface. By testing the in-plane thermal conductivity of the samples, the high thermal conductivity oriented phase change energy storage composite material was found to have an in-plane thermal conductivity of 102 W / (m·K), a bulk latent heat of phase change of 232 kJ / L, an orientation factor of 0.67, and an open porosity of 95%.

[0050] Comparative Example 2:

[0051] The preparation method of the fast-response, highly oriented phase change energy storage composite material described in this comparative example only changes the heat treatment temperature in step 4) to 2200℃, while the remaining steps are the same as in Example 1.

[0052] The graphene phase change energy storage material prepared in Comparative Example 2 has a height of 20 mm and a diameter of 200 mm. By testing the in-plane thermal conductivity of the sample, the in-plane thermal conductivity of the fast-response, high-heat-storage phase change energy storage composite material was found to be 91 W / (m·K), with a latent heat of phase change of 226 kJ / L and an orientation factor of 0.67. Increasing the heat treatment temperature was intended to provide more energy to the six-membered carbon rings, allowing more carbon atoms to complete the rearrangement reaction, reducing defects in the graphene sheets, and improving its thermal conductivity.

[0053] Comparative Example 3:

[0054] The preparation method of the high thermal conductivity and high orientation phase change energy storage composite material described in this comparative example is the same as that in Example 1, except that the oxidized polyethylene wax in step 6) is replaced with vinyl acetate.

[0055] The graphene phase change energy storage material prepared in Comparative Example 3 has a height of 20 mm and a diameter of 200 mm. By testing the in-plane thermal conductivity of the sample, the in-plane thermal conductivity of the high thermal conductivity, high orientation phase change energy storage composite material was found to be 110 W / (m·K), with a latent heat of phase change of 249 kJ / L, an orientation factor of 0.67, and an open porosity of 95%. Different phase change materials have different enthalpy values, and different phase change materials can be used according to different requirements.

[0056] Comparative Example 4:

[0057] The steps in this comparative example are the same as in Example 1, except that no expanded microspheres are added.

[0058] In this embodiment, by testing the in-plane thermal conductivity of the sample, the in-plane thermal conductivity of the fast-response, highly oriented phase change energy storage composite material was found to be 43 W / (m·K), the bulk latent heat of phase change was 211 kJ / L, the porosity was 67%, and the orientation factor was 0.21.

Claims

1. A method for preparing a high thermal conductive phase change energy storage material based on bubble jet oriented graphene nanoplatelets, characterized in that: The method comprises the following steps: 1) modification of expanded microspheres: the expanded microspheres containing volatile liquid inside are configured into a dispersion liquid with a mass fraction of 10%, placed in a water bath kettle and heated to 50℃, and then triethylbenzylammonium chloride, octadecyldimethylbenzylammonium chloride or benzalkonium chloride is added dropwise, and the mixture is heated and stirred for 3h; 2) preparation of graphene / expanded microsphere composite solid: graphene slurry with a concentration of 1wt%-10wt% is placed in a planetary mixer with the modified expanded microspheres, and the mixture is stirred at a rate of 500-2000r / min for 1h, the weight ratio of graphene to expanded microspheres is 1:1, and the graphene layers and the modified expanded microspheres form nanodispersion in the aqueous solution, then the mixed dispersion liquid is obtained by suction filtration to obtain graphene / expanded microsphere composite solid, and the graphene / expanded microsphere composite solid is dried in an oven at a temperature of 50℃; 3) preparation of high-oriented graphene skeleton: the dried graphene / expanded microsphere composite solid is sieved into powder using a 500-mesh sieve, and the powder is placed in a heating mold device for heat preservation, so that the liquid in the microspheres undergoes phase change, the microspheres expand to generate high-pressure bubbles, and then the mold is rapidly pressed down, the bubbles break, a high-speed jet stream is generated, the graphene nanosheets are deflected, and a high-oriented graphene skeleton is obtained; 4) graphitization treatment of the high-oriented graphene skeleton: the high-oriented graphene / expanded microsphere skeleton obtained in step 3) is placed in a graphitization furnace and subjected to graphitization treatment for 10-14h in an inert gas atmosphere, the internal expanded microspheres are removed, and the defects of the graphene nanosheets are repaired, the graphitization treatment temperature is 2500℃-3200℃; 5) secondary densification of the high-oriented graphene skeleton: the high-oriented graphene skeleton obtained in step 4) is placed in the mold of step 3) for secondary molding, so that the originally non-overlapping graphene nanosheets are overlapped again, and the micro-interface thermal resistance is further reduced; 6) pouring phase change energy storage material into the graphene skeleton: the graphene skeleton is placed on a solid phase change material and placed in a vacuum oven, the vacuum oven is pumped to -0.1MPa, and then heated to melt the phase change material, the phase change material is poured into the graphene skeleton under the action of vacuum negative pressure after melting, and a high-thermal-conductivity graphene phase change energy storage material is obtained after natural cooling.

2. The preparation method of the high thermal conductive phase change energy storage material based on bubble jet oriented graphene nanosheet layers according to claim 1, characterized in that: The amount of the expanded microspheres used in step 1) is 10-50g, and the amount of triethylbenzylammonium chloride is 1-5g.

3. The method of claim 1, wherein the method comprises: providing a graphene nanoplatelet layer; providing a bubble jet; and orienting the graphene nanoplatelet layer with the bubble jet. The expanded microspheres are made of methyl methacrylate, and the volatile liquid contained inside is butane.

4. The method of claim 1, wherein the method is characterized by: The temperature control range of the mold pressing device in step 3) is 90-140℃, and the mold pressing rate is 200-1000mm / min.

5. The method of claim 1, wherein the method is characterized by: The mold pressing rate used in the secondary densification of the graphene skeleton in step 5) is 1-5mm / min.

6. The method of claim 1, wherein the method is characterized by: The phase change material used in step 6) includes at least one of high-refined paraffin, heptacosane, tetradecane, dioctadecane, dodecane, and oxidized polyethylene wax.

7. The high-thermal-conductivity phase change energy storage material of oriented graphene nanosheets prepared by the method of any one of claims 1-6.

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