Porous carbon enhanced heat conduction solid-solid composite phase change material and preparation method and application thereof

Abstract

The invention provides a preparation method of a porous carbon enhanced heat-conducting solid-solid composite phase change material, which comprises the following steps: preparing a solution from sodium bicarbonate and hydroxypropyl methyl cellulose, and sequentially sintering, washing and drying to obtain a three-dimensional layered porous carbon-based material; the preparation method comprises the following steps: dissolving polyethylene glycol and hexamethylene diisocyanate in N, N-dimethylformamide, and reacting to obtain a polyurethane prepolymer solution; and 3, adding the three-dimensional layered porous carbon-based material prepared in the step 1 into the polyurethane prepolymer solution, quickly pouring the obtained material into a mold after reaction, putting the mold into a drying oven for curing, and cooling and demolding after curing to obtain the porous carbon reinforced heat conduction solid-solid composite phase change material. According to the preparation method, hydroxypropyl methyl cellulose is taken as a carbon source, sodium bicarbonate is taken as an activating agent, a three-dimensional layered porous carbon-based material is prepared, and the three-dimensional layered porous carbon-based material and a polyethylene glycol molecular chain are crosslinked in a three-dimensional structure of an interpenetrating network, so that the stability of the phase-change material is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of phase change energy storage materials, and particularly relates to a porous carbon enhanced heat conduction solid-solid composite phase change material, a preparation method thereof and an application thereof. Background Art

[0002] Solid-solid phase change materials store and release thermal energy through the transformation between solid phases and no liquid or gas phase is generated during the phase change process. Therefore, no container encapsulation is required during actual use. Especially solid-solid phase change materials with polymers as carriers have small volume changes, long service lives and good application development prospects. For example, in the existing literature 2 (Shi J, Aftab W, Liang Z, et al. Tuning the flexibility and thermal storage capacity of solid–solid phase change materials towards wearable applications [J]. J. Mater. Chem. A, 2022, 8, 20133-20140.).

[0003] Currently, polymer-based solid-solid phase change materials generally have defects such as low thermal conductivity, poor thermal stability and low phase change enthalpy values, which limit their applications in higher fields. For example, in the existing literature 3 (Yang Y, Cai X, Kong W. A novel intrinsic photothermal and flexible solid–solid phase change materials with super mechanical toughness and multi-recyclability [J]. Appl. Energy, 2023, 332, 120564.). Yang et al. introduced benzoquinone dioxime during the preparation of polyurethane by chemical crosslinking based on PEG to prepare an intrinsic photothermal phase change material, which improved the photo-thermal conversion performance of polyurethane. However, due to the presence of the oxime-urethane bond formed by introducing benzoquinone dioxime in the crosslinked network, the movement of molecular chains may be restricted, resulting in a decrease in the phase change enthalpy value, and its maximum phase change latent heat is only 92.35 J / g.

[0004] For example, in the existing literature 4 (Du X, Qiu J, Deng S, et al. Ti3C2T x@PDA-Integrated Polyurethane Phase Change Composites with Superior Solar-Thermal Conversion Efficiency and Improved Thermal Conductivity[J], ACS Sustain. Chem. Eng. 2020, 5799–5806.) Du et al. prepared polyurethane phase change materials using polyethylene glycol 6000 and 4,4'-diphenylmethane diisocyanate. The phase change enthalpy value of pure polyethylene glycol 6000 was 182.1 J / g. However, the phase change enthalpy value of the prepared polyurethane phase change material was only 128.2 J / g. Moreover, the thermal conductivity of polyurethane was only 0.27 W / m·K, close to that of pure polyethylene glycol (0.27 W / m·K). Although the addition of polydopamine-modified MXene improved the thermal conductivity and photo-thermal conversion efficiency of the composite phase change material, the phase change enthalpy value of the composite phase change material decreased with the increase in the addition amount of MXene. This may be because the addition of MXene may interfere with the crystallization behavior of polyurethane during the preparation process, resulting in a decrease in the enthalpy value of the composite phase change material.

[0005] Therefore, the technical problems existing in the prior art are to improve the thermal conductivity of polymer-based solid-solid phase change materials, further increase their latent heat of phase change, and endow them with good thermal cycle stability, so as to continuously enhance their application potential in the field of phase change energy storage. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a porous carbon-reinforced solid-solid composite phase change material aiming at the deficiencies of the above-mentioned prior art. The solid-solid composite phase change material reacts with the cyanate ester group in the cross-linking agent with the hydroxyl group at the end of polyethylene glycol to obtain modified polyethylene glycol with cyanate ester at the end, uses hydroxypropyl methylcellulose as the carbon source, and sodium bicarbonate as the activator. Sodium bicarbonate plays a key pore-forming role during the activation process and is the decisive factor for obtaining a three-dimensional layered porous carbon-based material with interconnected pores. During the phase change process of the material, due to the cross-linking of polyethylene glycol molecular chains in the three-dimensional structure of the interpenetrating network, the stability of the phase change material is ensured. At the same time, due to the good template provided by the layered interconnected porous carbon-based material for the polyethylene glycol molecular chains, the thermal conductivity and heat storage capacity of the polyurethane-based solid-solid phase change material are improved.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is: A preparation method of a porous carbon-reinforced solid-solid composite phase change material, characterized in that the method is as follows:

[0008] Step 1: The raw material formula of the porous carbon-based material is sodium bicarbonate and hydroxypropyl methylcellulose. Prepare a solution of sodium bicarbonate and hydroxypropyl methylcellulose in proportion, and then successively carry out drying, curing, sintering, and pickling to obtain a three-dimensional layered porous carbon-based material.

[0009] Step 2: Dissolve polyethylene glycol and hexamethylene diisocyanate in N,N-dimethylformamide and react to obtain a polyurethane prepolymer solution; then add the three-dimensional layered porous carbon-based material prepared in Step 1 to the polyurethane prepolymer solution. After the reaction, quickly pour the obtained material into a mold, place the mold in an oven for curing, and after curing is completed, cool and demold to obtain a solid-solid composite phase change material with enhanced heat conduction by porous carbon.

[0010] Preferably, the mass ratio of sodium bicarbonate to hydroxypropyl methylcellulose in Step 1 is 1-3:1.

[0011] Preferably, the sintering temperature condition in Step 1 is 800 °C. During washing, use a 1M hydrochloric acid solution to wash multiple times to remove excess sodium bicarbonate, and then wash with deionized water until neutral. During drying, place it in a blast drying oven at 80 °C for drying.

[0012] Preferably, the molar ratio of polyethylene glycol to hexamethylene diisocyanate in Step 2 is 2:1.

[0013] Preferably, the reaction conditions for dissolving polyethylene glycol and hexamethylene diisocyanate in N,N-dimethylformamide in Step 2 are: under a nitrogen atmosphere, the temperature is 70 °C, and the reaction time is 4 h.

[0014] Preferably, the three-dimensional layered porous carbon-based material in Step 2 is dispersed in an N,N-dimethylformamide solution and then dropped into the polyurethane prepolymer solution.

[0015] Preferably, the curing temperature in Step 2 is 100 °C and the time is 12 h.

[0016] The present invention also discloses a solid-solid composite phase change material with enhanced heat conduction by porous carbon, which is a solid-solid composite phase change material with enhanced heat conduction by porous carbon prepared by the above preparation method.

[0017] The present invention also discloses an application of the solid-solid composite phase change material with enhanced heat conduction by porous carbon. The solid-solid composite phase change material with enhanced heat conduction by porous carbon is used as a temperature control material during the charge and discharge process of a lithium-ion battery.

[0018] The present invention has the following advantages compared with the prior art:

[0019] 1. The hydroxyl groups at the ends of the polyethylene glycol in the present invention react with the cyanate ester groups in the crosslinking agent to obtain modified polyethylene glycol with cyanate ester at the ends. Using hydroxypropyl methylcellulose as the carbon source and sodium bicarbonate as the activator, where sodium bicarbonate plays a key pore-forming role during the activation process and is a decisive factor in obtaining an interconnected porous structure carbon-based material. During the phase change process of the material, since the polyethylene glycol molecular chains are crosslinked in the three-dimensional structure of the interpenetrating network, the stability of the phase change material is ensured. At the same time, due to the good template provided by the hierarchically interconnected porous structure for the polyethylene glycol molecular chains, the thermal conductivity of the polyurethane-based solid-solid phase change material is improved. Moreover, the ordered porous structure template enables the heat storage capacity of the polyurethane-based solid-solid phase change material to be increased.

[0020] 2. The latent heat of phase change values of the solid-solid composite phase change material prepared in the present invention are in the range of 158.93 - 174.80 J / g. Compared with the latent heat of phase change value of pure PEG (187.05 J / g), the latent heat retention rate of the composite phase change material prepared in the present invention is 85.0% - 93.5%. The thermal conductivity is in the range of 0.30 - 0.43 W / m·K. Compared with the thermal conductivity of pure PEG (0.224 W / m·K), the thermal conductivity of the composite phase change material prepared in the present invention is increased by 132.6% - 192.9%. Therefore, compared with the prior art, the present invention has a higher latent heat of phase change and better thermal conductivity, thereby improving the thermal response rate and energy utilization efficiency of the material, and having broad application prospects in the fields of phase change heat storage and electronic device heat dissipation.

[0021] The technical solution of the present invention will be further described in detail below through the drawings and embodiments. Description of the Drawings

[0022] Figure 1 SEM image of the material prepared in Example 1 of the present invention;

[0023] Figure 2 SEM image of the material prepared in Comparative Example 1 of the present invention;

[0024] Figure 3 SEM image of the material prepared in Comparative Example 2 of the present invention;

[0025] Figure 4 SEM image of the material prepared in Comparative Example 3 of the present invention;

[0026] Figure 5 XRD pattern of the material prepared in Example 1 of the present invention;

[0027] Figure 6 XRD pattern of the material prepared in Comparative Example 1 of the present invention;

[0028] Figure 7XRD pattern of the material prepared in Comparative Example 2 of the present invention;

[0029] Figure 8 XRD pattern of the material prepared in Comparative Example 3 of the present invention;

[0030] Figure 9 Infrared spectrum of the material prepared in Example 1 of the present invention;

[0031] Figure 10 Test photos of the leakage prevention ability of the material prepared in Example 1 of the present invention. Detailed implementation manners

[0032] Example 1

[0033] This example discloses a preparation method of a porous carbon-based solid-solid composite phase change material with enhanced thermal conductivity. The specific steps are as follows:

[0034] Step 1: Sodium bicarbonate (activator) and hydroxypropyl methylcellulose (carbon source) are thoroughly ground and mixed in a mass ratio of 3:1. Then, under an argon atmosphere, it is calcined at 800 °C for 2 h to achieve carbonization. After the obtained product is cooled to room temperature, it is washed several times with 1 M hydrochloric acid solution to remove excess sodium bicarbonate, and then washed with deionized water until neutral, and placed in a blast drying oven at 80 °C for drying to obtain a three-dimensional layered porous carbon-based material, named PC2 respectively.

[0035] In order to prove the morphology of the porous carbon obtained in Step 1, SEM tests were carried out. The test results are as Figure 1 shown. PC2 is a porous structure, with an interconnected pore structure while maintaining a layered structure, and the surface is relatively smooth.

[0036] Step 2: Functional modification of the end of the polyethylene glycol molecular chain. Weigh 18 g of polyethylene glycol with a weight average molecular weight (Mw) of 8000 and place it in a three-necked flask, add 50 mL of DMF solution, heat to 75 °C, and stir magnetically until it is completely dissolved to obtain a polyethylene glycol-DMF solution. Weigh hexamethylene diisocyanate (HDI) with a molar ratio of 2:1 to polyethylene glycol, dissolve it in 25 mL of DMF solution to obtain an HDI-DMF solution, and slowly add it to the polyethylene glycol-DMF solution under magnetic stirring, and react at 75 °C under an argon atmosphere for 6 h to obtain a polyurethane prepolymer solution.

[0037] Step 3, grafting of carbon-based material with poly(ethylene glycol): Weigh PC2, which is 10% of the mass of the polyurethane prepolymer, and add it to 50 mL of DMF solution. Place it in an ultrasonic disperser and ultrasonically disperse it until it is completely dispersed. Then, drop it into the polyurethane prepolymer solution obtained in Step 2 and react it under an argon atmosphere at 75 °C for 12 h. Distill the obtained mixed solution under reduced pressure, then dry it in a forced-air drying oven at 100 °C for 24 h, and finally dry it in a vacuum drying oven at 60 °C until constant weight is achieved, obtaining a solid-solid composite phase change material with enhanced thermal conductivity by hierarchical porous carbon-based material, named PC2-PU.

[0038] To prove the phase composition of PC2-PU obtained in Step 3, XRD test was carried out on PC2-PU. The test results are as Figure 5 shown. The two strong characteristic peaks of polyethylene glycol and PC2-PU at 19° and 23° respectively correspond to the (120) and (112) crystal planes of polyethylene glycol. The strong diffraction peaks of PC2-PU and polyethylene glycol are almost exactly the same, indicating that PC2-PU and polyethylene glycol have the same crystal structure.

[0039] To further verify the structural characteristics of PC2-PU obtained in Step 3, Fourier transform infrared spectroscopy analysis test was carried out. The test results are as Figure 9 shown. The -NCO band of hexamethylene diisocyanate at 2274 cm -1 and the -OH characteristic band of PEG at 3464 cm -1 have disappeared, confirming the synthesis of -NHCOO in PC2-PU.

[0040] PC2-PU prepared by the present invention has phase change energy storage performance and can be used as a temperature control material during the charge and discharge process of lithium-ion batteries.

[0041] To prove the phase change energy storage performance of PC2-PU obtained in Step 3, differential scanning calorimetry test was carried out: with a nitrogen gas flow rate of 20 mL / min, a heating and cooling rate of 5 °C / min, and a temperature test range of -10 - 100 °C for testing. The test results are shown in Table 1. The phase change enthalpy value of PC2-PU is 174.8 J / g, proving the phase change energy storage function of the solid-solid composite phase change material obtained by the present invention.

[0042] To prove the thermal conductivity of PC2-PU obtained in Step 3, thermal conductivity test was carried out. And, for comparison, PEG 8000 was tested. The test results are shown in Table 2.

[0043] The thermal conductivity of PEG 8000 is 0.22 W / m·K, and the thermal conductivity of HPC2-PU is 0.44 W / m·K, indicating that the thermal conductivity of PC2-PU is significantly improved compared with PEG 8000;

[0044] Meanwhile, the phase change heat storage performance of the organic phase change material also needs to meet the anti-leakage requirement. To prove the anti-leakage effect of PC2-PU of the present invention, a heating comparison experiment was carried out: pure polyethylene glycol and PC2-PU were simultaneously placed in an oven at 100 °C, and the samples before and after heating were observed. The experimental results are as Figure 10 shown that PC2-PU is a stable solid at room temperature and remains in the initial solid state after being heated at 100 °C for 12 h; while pure polyethylene glycol is a solid at 25 °C and has completely turned into a liquid state at 100 °C. This experimental phenomenon indicates that PC2-PU remains in a stable solid state after phase change, that is, it meets the anti-leakage requirement.

[0045] Comparative Example 1

[0046] This comparative example discloses a preparation method of a solid-solid composite phase change material added with porous carbon. The steps are not particularly described as the same as those in Example 1, and the differences are as follows: in Steps 1 and 3, cellulose acetate is selected as the carbon source and KOH is used as the activator in Step 1, and the obtained material is named LC. And in Step 3, LC is used instead of PC2, and the obtained solid-solid composite phase change material is named LC-PU.

[0047] To prove the morphology of LC, SEM test was carried out. The test results are as Figure 2 shown that LPC exhibits a typical two-dimensional sheet structure.

[0048] To prove the phase composition of LC-PU, XRD test was carried out on LC-PU. The test results are as Figure 6 shown that the two strong characteristic peaks of PEG and LC-PU at 19° and 23° correspond to the (120) and (112) crystal planes of PEG respectively. The strong diffraction peaks of LC-PU and PEG are almost exactly the same, indicating that LC-PU and PEG have the same crystal structure.

[0049] To prove the phase change energy storage performance of LPC-PU, differential scanning calorimetry test was carried out: with a nitrogen gas flow rate of 20 mL / min, a heating and cooling rate of 5 °C / min, and a temperature test range of: -10 - 100 °C for testing. The test results are shown in Table 1 that the phase change enthalpy value of LC-PU is 158.6 J / g.

[0050] To prove the thermal conductivity of the obtained LC-PU, thermal conductivity test was carried out, and the test results are shown in Table 2. It can be seen from the comparison with Example 1 that the thermal conductivity of LC-PU is only 63.1% of that of PC2-PU. This experimental result shows that the effect of adding LC to enhance the thermal conductivity is not as good as that of PC2.

[0051] Comparative Example 2

[0052] This comparative example discloses a preparation method of a solid-solid composite phase change material with enhanced thermal conductivity by porous carbon. The steps not specifically described are the same as those in Example 1. The differences are as follows: In steps 1 and 3, in step 1, sodium bicarbonate and hydroxypropyl methylcellulose are in a mass ratio of 1:1, and the obtained material is named PC1. And in step 3, PC1 is used instead of PC2, and the obtained solid-solid composite phase change material is named PC1-PU.

[0053] To prove the morphology of PC1, SEM tests were carried out. The test results are as Figure 3 shown. PC1 exhibits a porous structure, with an interconnected pore structure while maintaining a layered structure, and the surface is relatively smooth.

[0054] To prove the phase composition of PC1-PU, XRD tests were carried out on PC1-PU. The test results are as Figure 7 shown. The two strong characteristic peaks of PEG and PC1-PU at 19° and 23° correspond to the (120) and (112) crystal planes of PEG respectively. The strong diffraction peaks of PC1-PU and PEG are almost exactly the same, indicating that PC1-PU and PEG have the same crystal structure.

[0055] To prove the phase change energy storage performance of PC1-PU, differential scanning calorimetry tests were carried out: with a nitrogen gas flow rate of 20 mL / min, a heating and cooling rate of 5 °C / min, and the temperature test range was:

[0056] Tested from -10 to 100 °C. The test results are shown in Table 1. The phase change enthalpy value of PC1-PU is 158.9 J / g.

[0057] To prove the thermal conductivity of the obtained PC1-PU, thermal conductivity tests were carried out. And for comparison, PEG8000 was tested. The test results are shown in Table 2. Comparing the test results with those in Example 1, it can be seen that the thermal conductivity of PC1-PU is only 67.4% of that of PC2-PU. This experimental result shows that the effect of adding PC1 to enhance the thermal conductivity is not as good as that of PC2.

[0058] Comparative Example 3

[0059] This comparative example discloses a preparation method of a solid-solid composite phase change material with enhanced thermal conductivity by porous carbon. The steps not specifically described are the same as those in Example 1. The differences are as follows: In steps 1 and 3, in step 1, sodium bicarbonate and hydroxypropyl methylcellulose are in a mass ratio of 4:1, and the obtained material is named PC3. And in step 3, PC3 is used instead of PC2, and the obtained solid-solid composite phase change material is named PC3-PU.

[0060] To prove the morphology of PC3, SEM tests were carried out. The test results are as Figure 4As shown, PC3 exhibits a porous structure with interconnected pore structures while maintaining a layered structure and a relatively smooth surface.

[0061] To prove the phase composition of PC3-PU, XRD tests were carried out on PC3-PU. The test results are as Figure 8 shown. The two strong characteristic peaks of PEG and PC3-PU at 19° and 23° correspond to the (120) and (112) crystal planes of PEG respectively. The strong diffraction peaks of PC3-PU and PEG are almost exactly the same, indicating that PC3-PU and PEG have the same crystal structure.

[0062] To prove the phase change energy storage performance of PC3-PU, differential scanning calorimetry tests were carried out: with a nitrogen gas flow rate of 20 mL / min, a heating and cooling rate of 5 °C / min, and a temperature test range of:

[0063] -10 - 100 °C for testing. The test results are shown in Table 1. The phase change enthalpy value of PC3-PU is 161.4 J / g.

[0064] Table 1 Test data of the phase change energy storage performance of the prepared materials

[0065]

[0066] To prove the thermal conductivity of the obtained PC3-PU, thermal conductivity tests were carried out. The test results are shown in Table 2. It can be seen from the comparison with Example 1 that the thermal conductivity of PC3-PU is 98% of that of PC2-PU.

[0067] Table 2 Test data of the thermal conductivity of the prepared materials

[0068]

[0069] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent variations made to the above embodiments according to the technical essence of the invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a porous carbon-enhanced thermally conductive solid-solid composite phase change material, characterized in that: The method is: Step 1, preparing a solution of sodium bicarbonate and hydroxypropyl methylcellulose, and sequentially sintering, washing, and drying to obtain a three-dimensional layered porous carbon-based material; Step 2: dissolving polyethylene glycol and hexamethylene diisocyanate in N,N-dimethylformamide to react to obtain a polyurethane prepolymer solution; then adding the three-dimensional layered porous carbon-based material prepared in step 1 to the polyurethane prepolymer solution, quickly pouring the obtained material into a mold after the reaction, placing the mold in an oven for curing, cooling and demolding after curing, and obtaining a porous carbon-enhanced thermally conductive solid-solid composite phase change material.

2. The method for preparing a porous carbon enhanced thermal conductive solid-solid composite phase change material according to claim 1, characterized in that: The mass ratio of sodium bicarbonate to hydroxypropyl methylcellulose in step 1 is 1-3:

1.

3. The method for preparing a porous carbon enhanced thermal conductive solid-solid composite phase change material according to claim 1, characterized in that: The sintering temperature in step 1 is 800° C. The excess sodium bicarbonate is removed by washing with 1M hydrochloric acid solution for multiple times, and then washed with deionized water until neutral. The product is dried in an 80° C. forced air drying oven.

4. The method for preparing a porous carbon enhanced thermal conductive solid-solid composite phase change material according to claim 1, characterized in that: The molar ratio of polyethylene glycol to hexamethylene diisocyanate in step 2 is 2:

1.

5. The method for preparing a porous carbon enhanced thermal conductive solid-solid composite phase change material according to claim 1, characterized in that: In step 2, the polyethylene glycol and hexamethylene diisocyanate are dissolved in N,N-dimethylformamide and the reaction conditions are: under a nitrogen atmosphere, a temperature of 70° C., and a reaction time of 4 hours.

6. The method for preparing a porous carbon enhanced thermal conductive solid-solid composite phase change material according to claim 1, characterized in that: The three-dimensional layered porous carbon-based material described in step 2 is dispersed in an N,N-dimethylformamide solution and then added dropwise to the polyurethane prepolymer solution.

7. The method for preparing a porous carbon enhanced thermal conductive solid-solid composite phase change material according to claim 1, characterized in that: The curing temperature in step 2 is 100° C. and the curing time is 12 h.

8. A porous carbon enhanced thermal conductive solid-solid composite phase change material, characterized in that: A porous carbon enhanced thermally conductive solid-solid composite phase change material prepared by the preparation method described in any one of claims 1 to 8.

9. An application of the porous carbon enhanced thermal conductive solid-solid composite phase change material as claimed in claim 8, characterized in that: The porous carbon enhanced thermally conductive solid-solid composite phase change material is used as a temperature control material in the charging and discharging process of a lithium ion battery.

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