A Cu-NC based phase change composite material with battery thermal management function and its preparation method

Abstract

The present invention discloses a Cu-NC-based phase change composite material with battery thermal management function, which is composed of expanded graphite EG, paraffin wax PW, and Cu-NC. Among them, Cu-NC is obtained by calcining Cu-MOF; EG is an encapsulating material and a heat-conducting material; PW is a phase change material, providing phase change heat storage and temperature control performance; Cu-NC is a heat-conducting material; the role of the obtained Cu-MOF by calcination is to enhance the dispersion and compatibility of Cu metal nanoparticles, thereby improving the heat conduction performance and stability; the thermal conductivity is 0.92 - 1.29 W / (m·K), the crystallization latent heat value is 233.20 - 276.64 J / g, and the melting latent heat is 233.68 - 277.78 J / g. Its preparation method includes the following steps: 1. Preparation of expanded graphite EG; 2. Preparation of Cu-NC heat-conducting material; 3. Preparation of molten mixture; 4. Preparation of composite phase change material with battery thermal management function. As an application of battery thermal management material, it has heat conduction performance, encapsulation performance and anti-leakage performance; when wrapping a lithium battery, the rising speed of the battery charging and discharging temperature slows down, and the battery surface temperature decreases by 10.7 - 23.3 °C.

Description

Technical Field

[0001] The present invention relates to the fields of phase change energy storage materials and electronic and electrical thermal management technologies, and specifically relates to a Cu-NC based phase change composite material with battery thermal management function and a preparation method thereof. Background Art

[0002] The performance of electronic devices is significantly affected by temperature. Too high or too low temperature will affect the performance of electronic devices, and even cause safety problems such as thermal runaway and internal short circuit of the battery. In order to improve the use performance and thermal safety of electronic devices and extend their cycle life, it is necessary to perform thermal management on electronic devices.

[0003] Phase change materials have the property of absorbing or releasing heat under near-constant temperature conditions and can be used as temperature control materials for electronic devices. As described in the existing literature 1, in the previous work of the research group of the present inventor (CN115895283A, a thermally induced flexible composite material with battery thermal management function and its preparation method and application [P]), a thermally induced flexible composite material with battery thermal management function was prepared by a melt blending method using expanded graphite, paraffin wax, and olefin block copolymer as raw materials. Compared with a lithium battery without thermal management, the technical effect that the surface temperature of the lithium battery decreased by 10-18°C was achieved after coating the thermally induced flexible composite material. In addition, the porous structure of expanded graphite and the olefin block copolymer form a double three-dimensional network structure, effectively solving the problem of easy leakage of the phase change material. Moreover, the two form graphite-interconnected sheets during the subsequent hot pressing process, which not only improves the thermal conductivity of the composite material (0.92W / (m·K)), but also improves the mechanical properties of the material, making the material have thermal induced flexibility for easy installation and use of the phase change material.

[0004] However, the above technical solution still has the following technical problems:

[0005] Problem 1: The enthalpy value is relatively low. Among them, the crystallization latent heat value is 144.72-175.70J / g, and the melting latent heat is 142.53-172.04J / g, which cannot meet the application requirements.

[0006] Problem 2: The thermal management performance of the phase change composite material for the battery is relatively low, and the surface temperature of the battery only decreases by 10-18°C.

[0007] Regarding the cause of Problem 1, through subsequent research by the inventor, it was found that the low enthalpy value was due to the invention purpose of this technical solution being to enhance the encapsulation performance and mechanical properties of the composite material. Therefore, the technical feature of adding a macromolecular material, olefin block copolymer, was selected. The negative effect directly caused by this technical feature is that after adding the olefin block copolymer, the enthalpy value of the paraffin decreased from 212.76 J / g to 166.13 J / g. Subsequent research showed that the principle of the enthalpy value decrease is as follows: Although XRD tests indicated that adding the olefin block copolymer does not affect the crystallization behavior of the paraffin, however, since adding the olefin block copolymer restricts the movement of the paraffin, it leads to a reduction in the latent heat and enthalpy value of the composite phase change material. Therefore, to solve the problem of the olefin block copolymer causing a reduction in the latent heat and enthalpy value of the composite phase change material, there are the following two solutions: 1. Use a phase change material with a higher enthalpy value to increase the latent heat and enthalpy value of the composite material. However, this solution cannot fundamentally solve this technical problem, and the enthalpy value of the newly added phase change material will still decrease due to the addition of the olefin block copolymer; 2. Do not use the olefin block copolymer as the encapsulation material and achieve the encapsulation performance through other materials.

[0008] Regarding the cause of Problem 2, in addition to being a carrier, when expanded graphite is used as a thermal conductive material, its own thermal conductivity is relatively low. Compared with pure phase change materials, its thermal conductivity is only increased by 1 - 2 times, resulting in a smaller battery thermal management range for the composite material.

[0009] To improve the thermal conductivity of the composite material, it can be achieved by additionally introducing a thermal conductive material with higher thermal conductivity. Currently, common thermal conductive materials mainly include carbon materials, conventional metal materials, etc.

[0010] Adding carbon materials is one of the conventional methods to improve thermal conductivity. For example, the existing literature 2 (Gong Shengqin. Research on Octadecanol / Al2O3(SiC) / Expanded Graphite Composite Phase Change Heat Storage Materials [D]. Wuhan University of Technology, 2021.) provides octadecanol / SiC / expanded graphite composite materials. Although this technical solution significantly improves the thermal conductivity of the composite material by adding the high - thermal - conductivity material SiC - the thermal conductivity of octadecanol composite with 9wt% SiC / EG is more than four times that of pure octadecanol, however, the following two conclusions can be obtained from its encapsulation performance test:

[0011] 1. When using pure expanded graphite, there is an obvious leakage situation in the composite material, that is, the encapsulation effect cannot be achieved;

[0012] 2. When adding SiC, there is no obvious improvement in the encapsulation performance of the composite material;

[0013] Through the above analysis, it can be seen that the technical problem of this technical solution is that adding SiC can only improve the thermal conductivity and cannot improve the encapsulation performance at the same time.

[0014] Adding metal materials is also one of the conventional methods to improve thermal conductivity. For example, in the existing literature 3 (He Linhan, Ling Kaili, Ren Ruiqing, etc. Research on the properties of wood-based composite phase change energy storage materials reinforced with Cu particles for thermal conductivity [J]. Journal of Beijing Forestry University, 2022, 44(12): 132-141.), dispersed metal Cu particles were prepared in the balsa wood matrix by chemical reduction method, increasing the thermal conductivity of the composite material by 1.76 times. Due to the use of the chemical reduction method in this technical solution, the size of its Cu particles reached 2.5 μm, which blocked the pores of the balsa wood matrix and seriously affected the encapsulation effect of the composite material.

[0015] From the above two existing technologies, it can be seen that although current conventional thermal conductive materials can effectively improve the thermal conductivity, and avoid the problem of the phase change material being restricted by the olefin block copolymer and the enthalpy value decreasing, none of them can achieve the improvement of the encapsulation performance by the olefin block copolymer. Summary of the Invention

[0016] The purpose of the present invention is to provide a Cu-NC-based phase change composite material with battery thermal management function and its preparation method.

[0017] In view of the technical problems existing in the prior art, the present invention achieves the above technical effects by introducing materials that can not only improve thermal conductivity but also improve encapsulation performance. The specific principle is as follows:

[0018] 1. The porous skeleton encapsulation method is adopted instead of the macromolecular olefin block copolymer to solve the encapsulation problem of the phase change material. Because of the capillary force of the pores in the porous skeleton encapsulation technology and the strong interfacial adhesion between the pore surface and the phase change medium, the leakage of the phase change material can be effectively avoided, and the stability of the composite phase change material can be improved. At the same time, functional fillers can be doped into the porous matrix to endow the composite phase change material with multifunctionality, thereby increasing the enthalpy value and thermal conductivity of the phase change material;

[0019] 2. Expandable graphite that is easy to synthesize is selected as the porous skeleton encapsulation material. Because expandable graphite can provide a worm-like porous structure, which can effectively encapsulate the phase change material. At the same time, its porous structure can uniformly disperse the high thermal conductivity material and solve the problems of easy shedding and agglomeration of the thermal conductivity material, thereby improving the problem of uneven heat conduction caused by the shedding and agglomeration of the thermal conductivity material. In addition, expandable graphite also has thermal conductivity. Selecting expandable graphite with thermal conductivity as the encapsulation material can further improve the thermal conductivity of the composite phase change material and improve the material utilization rate;

[0020] 3. Cu has high thermal conductivity and can be used as a thermal conductive material. However, direct addition of metal nanoparticles is prone to agglomeration. Therefore, Cu-NC with high thermal conductivity is used as the copper source, that is, the thermal conductive material. The principle of anti-agglomeration is as follows: The metal organic framework carbide is used to restrict Cu metal nanoparticles, thereby achieving the effect of improving the dispersibility and atomic utilization efficiency of Cu metal nanoparticles. At the same time, the restriction by the metal organic framework can effectively reduce the size of metal particles, making them uniformly dispersed in the pores of the porous material without blocking the pores, and solving the problem of the decline in encapsulation performance caused by metal particles blocking the matrix material. Moreover, the graphite carbon in Cu-NC has high compatibility with paraffin, which can improve its compatibility with expanded graphite and paraffin, and further improve the encapsulation performance, thermal conductivity and stability of the composite material, enhancing the thermal management performance of the composite phase change material.

[0021] In order to achieve the above-mentioned invention purpose, the technical solution adopted by the present invention is as follows:

[0022] A Cu-NC-based phase change composite material with battery thermal management function is composed of expanded graphite EG, paraffin PW, and Cu-NC. Among them, Cu-NC is a graphite carbon sheet loaded with Cu nanoparticles obtained by calcining Cu-MOF;

[0023] The function of the expanded graphite is to serve as one of the encapsulation materials and thermal conductive materials;

[0024] The function of the paraffin is to serve as a phase change material, providing phase change heat storage and temperature control performance;

[0025] The function of the Cu-NC is to serve as one of the thermal conductive materials;

[0026] The function of the Cu-MOF is to restrict Cu metal nanoparticles through the metal organic framework, thereby effectively enhancing the dispersibility of Cu metal nanoparticles, and improving the compatibility between Cu metal nanoparticles and expanded graphite and paraffin, and further improving the thermal conductivity and stability of the composite material;

[0027] The thermal conductivity is 0.92 - 1.29 W / (m·K), the crystallization latent heat value is 233.20 - 276.64 J / g, and the melting latent heat is 233.68 - 277.78 J / g.

[0028] A preparation method of a Cu-NC-based phase change composite material with battery thermal management function includes the following steps:

[0029] Step 1, preparation of expanded graphite EG. Expandable graphite is heated and expanded under certain conditions to obtain expanded graphite with a worm-like porous structure, simply referred to as EG;

[0030] In the said step 1, the conditions for thermal expansion are that the heating temperature is 900 - 1000 °C and the heating time is 30 - 120 s;

[0031] Step 2: Preparation of Cu-NC thermal conductive material. First, 2-aminoterephthalic acid and copper nitrate hexahydrate satisfy a certain molar ratio. 2-aminoterephthalic acid and copper nitrate hexahydrate are dispersed in a mixed solution of N,N-dimethylformamide and methanol and stirred evenly to obtain mixture A. Then, under certain conditions, mixture A is subjected to a hydrothermal reaction. After the reaction is completed, it is naturally cooled to room temperature. The obtained product is centrifuged, washed, and vacuum dried to obtain the MOF material. Finally, under certain conditions, the MOF material is calcined to obtain the Cu-NC thermal conductive material, abbreviated as Cu-NC;

[0032] In the said step 2, the molar ratio of 2-aminoterephthalic acid and copper nitrate hexahydrate is 1:1 - 1:6, and the volume ratio of N,N-dimethylformamide and methanol is 9:1; the conditions for the hydrothermal reaction are that the hydrothermal temperature is 120 - 160 °C and the hydrothermal time is 15 - 24 h; the conditions for the calcination are that under the condition of an argon-hydrogen mixed gas, the calcination temperature is 500 - 700 °C and the calcination time is 1 - 3 h;

[0033] Step 3: Preparation of the molten mixture. First, EG obtained in step 1 and Cu-NC obtained in step 2 satisfy a certain mass ratio. EG and Cu-NC are dispersed in deionized water to obtain mixture B. Then, under the condition that the drying temperature is 60 °C, mixture B is dried. Cu-NC is evenly dispersed into EG to achieve adsorption, and the EG-Cu composite material, abbreviated as EG-Cu, is obtained. Finally, with a certain addition amount of EG-Cu, PW and EG-Cu are mixed to obtain mixture C. Then, under certain conditions, mixture C is vacuum dried at a heating temperature of 60 °C, so that the completely melted PW enters the pores of EG, and the molten mixture can be obtained;

[0034] In the said step 3, the mass ratio of EG and Cu-NC is 1:1; the addition amount of EG-Cu is 15 - 30 wt%;

[0035] Step 4: Preparation of the composite phase change material with battery thermal management function. Under certain conditions, the molten blend obtained in step 3 is hot pressed, and after cooling, the Cu-NC-based phase change composite material with battery thermal management function, abbreviated as EG-PW-Cu, can be obtained;

[0036] In the said step 4, the conditions for hot pressing are that the temperature is 40 - 60 °C, the pressure is 5 - 10 MPA, and the hot pressing time is 15 - 60 s.

[0037] As an application of battery thermal management materials, it has thermal conductivity, encapsulation performance and anti-leakage performance; when wrapping a lithium battery, the rising speed of the battery charging and discharging temperature slows down, and the battery surface temperature decreases by 10.7 - 23.3 °C.

[0038] The technical effects of the present invention can be known through tests:

[0039] The FT-IR test results show that the infrared characteristic peaks of industrial paraffin, expandable graphite, and the thermal conductive material Cu-NC appear in the composite phase change material with battery thermal management function, and no new peaks appear, proving that the composite phase change material with battery thermal management function prepared by the present invention is a physical adsorption effect and no chemical reaction occurs;

[0040] The XRD test results show that the characteristic diffraction peaks of industrial paraffin, expandable graphite, and the thermal conductive material Cu-NC appear in the composite phase change material with battery thermal management function, and no new peaks appear, indicating that the component structures of each material have not changed, which proves that the composite phase change material with battery thermal management function prepared by the present invention is successfully prepared and does not affect the performance of each material;

[0041] The SEM test results show that in the composite phase change material with battery thermal management function, EG shows an irregular network structure formed by extremely thin graphite nanosheets, which can improve the heat transfer efficiency and provide effective support for the attachment and dispersion of the thermal conductive material Cu-NC, and provide opportunities for the adsorption and filling of paraffin EG;

[0042] The DSC test results show that in the range of 20 - 80 °C, the composite phase change material with battery thermal management function shows melting peaks and crystallization peaks respectively. After adding expandable graphite, the crystallization latent heat value is 233.20 - 276.64 J / g, and the melting latent heat is 233.68 - 277.78 J / g. The prepared composite phase change material with battery thermal management function has a high latent heat storage capacity;

[0043] The temperature control test results show that the composite phase change material with battery thermal management function has good temperature control function;

[0044] The thermal conductivity test results show that the composite phase change material with battery thermal management function has high thermal conductivity, and the thermal conductivity is 0.92 - 1.29 W / (m·K);

[0045] The anti-leakage performance test results show that the composite phase change material with battery thermal management function has good anti-leakage performance.

[0046] The battery management system test results show that the composite phase change material with battery thermal management function has good thermal management performance for electronic devices.

[0047] Therefore, compared with the prior art, the composite phase change material with battery thermal management function of the present invention has the following advantages:

[0048] 1. The high thermal conductivity material Cu-NC prepared by the present invention not only effectively improves the thermal conductivity of the composite phase change material, but also improves its compatibility with expanded graphite and paraffin, thereby improving the encapsulation performance, thermal conductivity and stability of the composite material, and enhancing the thermal management performance of the composite phase change material;

[0049] 2. The present invention has a good thermal management function for electronic devices, effectively reduces the operating temperature of the battery, increases the thermal management temperature range of the battery, and reduces the risk of thermal runaway;

[0050] 3. Selecting expanded graphite instead of olefin block copolymer as the encapsulating material effectively retains the high enthalpy value of the phase change material;

[0051] 4. The expandable graphite of the present invention is rapidly heated and expanded at high temperature to form expanded graphite with a worm-like porous structure, which effectively adsorbs and disperses the high thermal conductivity material Cu-NC, and at the same time adsorbs the phase change material, and further forms a flaky material with graphite interconnection during the subsequent hot pressing process, and constitutes an irregular network structure, effectively improving the anti-leakage performance and cyclic stability of the composite phase change material. Description of the Drawings

[0052] Figure 1 FT-IR spectra of the materials prepared in Example 1, Comparative Example 1, Comparative Example 2, and Example 2;

[0053] Figure 2 XRD spectra of the materials prepared in Example 1, Comparative Example 1, Comparative Example 2, and Example 2;

[0054] Figure 3 Field emission scanning images of the materials prepared in Example 1, Comparative Example 1, Comparative Example 2, and Example 2;

[0055] Figure 4 DSC curves of the materials prepared in Example 1, Comparative Example 2, and Example 2;

[0056] Figure 5 200-cycle DSC test results of Example 1;

[0057] Figure 6 Thermal conductivity diagrams of the materials prepared in Example 1, Comparative Example 1, Comparative Example 2, and Example 2;

[0058] Figure 7 Encapsulation performance test diagrams of the materials prepared in Example 1, Comparative Example 1, Comparative Example 2, and Example 2;

[0059] Figure 8Temperature control test diagrams of the materials prepared in Example 1, Comparative Example 1, Comparative Example 2, and Example 2;

[0060] Figure 9 Battery thermal management performance test diagram of the material prepared in Example 1. Detailed implementation manners

[0061] The present invention further elaborates on the content of the present invention through examples in combination with the accompanying drawings of the specification, but it is not a limitation to the present invention.

[0062] Example 1

[0063] A preparation method of a Cu-NC-based phase change composite material with battery thermal management function, comprising the following steps:

[0064] Step 1, preparation of expanded graphite EG. Expandable graphite is heated and expanded at a heating temperature of 950 °C and a heating time of 60 s to obtain expanded graphite with a worm-like porous structure, simply referred to as EG;

[0065] Step 2, preparation of Cu-NC thermal conductive material. First, 2-aminoterephthalic acid and copper nitrate hexahydrate are in a molar ratio of 1:4. 8 mM of 2-aminoterephthalic acid and 2 mM of copper nitrate hexahydrate are dispersed in a mixed solution of 45 mL of N,N-dimethylformamide and 5 mL of methanol and stirred evenly to obtain mixture A. Then, mixture A is subjected to a hydrothermal reaction at a hydrothermal temperature of 150 °C and a hydrothermal time of 20 h. After the reaction is completed, it is naturally cooled to room temperature. The obtained product is centrifuged, washed, and vacuum dried to obtain a MOF material. Finally, under the condition of an argon-hydrogen mixed gas, the MOF material is calcined at a calcination temperature of 500 °C and a calcination time of 2 h to obtain a Cu-NC thermal conductive material, simply referred to as Cu-NC;

[0066] Step 3, preparation of the molten mixture. First, EG obtained in step 1 and Cu-NC obtained in step 2 are in a mass ratio of 1:1. EG and Cu-NC are dispersed in deionized water to obtain mixture B. Then, mixture B is dried at a drying temperature of 60 °C to adsorb Cu-NC evenly into EG to obtain an EG-Cu composite material, simply referred to as EG-Cu. Finally, with the addition amount of EG-Cu being 17.5 wt%, PW and EG-Cu are mixed to obtain mixture C, and then mixture C is vacuum dried at a heating temperature of 60 °C to allow the completely melted PW to enter the pores of EG, and a molten mixture can be obtained;

[0067] Step 4: Preparation of the composite phase change material with battery thermal management function. Under the conditions of a hot pressing temperature of 60 °C, a hot pressing pressure of 7 MPA, and a hot pressing time of 30 s, the molten blend obtained in Step 3 is hot pressed, and after cooling, the Cu-NC-based phase change composite material with battery thermal management function can be obtained, simply referred to as EG-PW-Cu. Among them, the material obtained in Example 1 is named EG-PW-Cu-2.

[0068] To prove the composition of EG-PW-Cu-2, FT-IR tests were carried out. The test results are as Figure 1 shown. EG-PW-Cu-2 contains all the infrared characteristic peaks of EG, PW, and Cu-NC simultaneously. Among them, there is no obvious difference between the infrared characteristic peaks of PW in EG-PW-Cu-2 and those of pure PW. The test results show that EG-PW-Cu-2 was successfully prepared, and the binding mode between the components is physical binding, that is, no chemical reaction occurred during the preparation process.

[0069] To further verify the composition of EG-PW-Cu-2, XRD tests were carried out. The test results are as Figure 2 shown. EG-PW-Cu-2 contains all the diffraction characteristic peaks of EG, PW, and Cu-NC simultaneously. Among them, there is no obvious difference between the characteristic diffraction peaks of PW in EG-PW-Cu-2 and those of pure PW. The test results show that the conclusion obtained from the XRD test is consistent with that of the FT-IR test, and the preparation process has no effect on the crystallization behavior of PW, that is, it does not affect the good heat storage capacity of the composite phase change material.

[0070] To prove the microscopic morphology of EG-PW-Cu-2, SEM tests were carried out on EG obtained in Step 1, EG-Cu obtained in Step 3, and EG-PW-Cu-2 obtained in Step 5, respectively.

[0071] The test results of EG are as Figure 3 shown. EG presents a significant worm-like porous structure;

[0072] The test results of EG-Cu are as Figure 3 shown. Cu-NC is successfully and uniformly distributed inside the EG porous structure;

[0073] The test results of EG-PW-Cu-2 are as Figure 3 shown. In EG-PW-Cu-2, the graphite-interconnected flaky materials formed by EG constitute an irregular network, and paraffin is uniformly wrapped on the surface of the EG-Cu material;

[0074] The test results show that PW was successfully adsorbed inside and on the surface of the EG-Cu material without destroying the porous interconnected structure of EG.

[0075] To prove the phase change performance of EG-PW-Cu-2, differential scanning calorimetry (DSC) tests were conducted. The test results are as Figure 4 shown in Table 1. The test results indicate that within the test temperature range of 20 - 80 °C, there is an endothermic peak at 44.88 °C during the melting process of EG-PW-Cu-2, with a latent heat value of 233.87 J / g, and an exothermic peak at 36.92 °C during the crystallization process, with a latent heat value of 233.57 J / g. The test results show that EG-PW-Cu-2 has good phase change behavior and heat storage capacity.

[0076] Table 1 Phase change enthalpy values and temperatures of different samples

[0077]

[0078] To prove the cycle stability of EG-PW-Cu-2, 200 cycle tests were conducted. The test results are as Figure 5 shown. During the 200 cycles, there is no obvious change in the thermal cycle curve of EG-PW-Cu-2, that is, the phase change performance of EG-PW-Cu-2 remains unchanged before and after cycling. The test results show that EG-PW-Cu-2 has good cycle stability.

[0079] To prove the thermal conductivity of EG-PW-Cu-2, thermal conductivity tests were conducted. And for comparison, PW was also tested. The test results are as Figure 6 shown.

[0080] The thermal conductivity of PW is 0.20 W / (m·K);

[0081] The thermal conductivity of EG-PW-Cu-2 is 1.19 W / (m·K), indicating that EG-PW-Cu-2 has significant thermal conductivity;

[0082] The test results show that the thermal conductivity of EG-PW-Cu-2 is increased by 595% compared to PW, that is, adding EG and Cu-NC can significantly improve the thermal conductivity of PW.

[0083] Table 2 Thermal conductivity of composite phase change materials of different samples

[0084]

[0085] To prove the encapsulation performance of the prepared EG-PW-Cu-2, anti-leakage tests were conducted on EG-PW-Cu-2 and PW respectively. The specific test method is to heat EG-PW-Cu-2 and PW at a heating temperature of 60 °C for 10 minutes and observe the material state.

[0086] The test results of PW are as Figure 7 shown. PW completely melted and flowed around;

[0087] The test results of EG-PW-Cu-2 are as follows Figure 7 shown, and there is no obvious change in EG-PW-Cu-2;

[0088] The test results show that the addition of EG effectively improves the leakage problem of PW, that is, EG-PW-Cu-2 has excellent encapsulation performance and can effectively prevent the leakage of PW.

[0089] To prove the temperature control performance of EG-PW-Cu-2, a temperature control test was carried out in a high and low temperature test chamber. The results are as follows Figure 8 shown. EG-PW-Cu-2 shows an obvious temperature control platform at 43-44 °C, corresponding to the melting endotherm during the heating stage and the crystallization exotherm during the cooling stage respectively. The test results show that EG-PW-Cu-2 has good temperature control function.

[0090] To prove that EG-PW-Cu-2 has the thermal management performance of electronic devices, a simulated lithium battery charge and discharge test was carried out, and the surface temperature data of the battery was measured and recorded. For comparison, ordinary lithium batteries and lithium batteries wrapped with EG-PW-Cu-2 were tested respectively.

[0091] The test results of ordinary lithium batteries are as follows Figure 9 shown. During the charge and discharge process, the temperature rises sharply;

[0092] The test results of lithium batteries wrapped with EG-PW-Cu-2 are as follows Figure 9 shown. The temperature rise is significantly slowed down, and the temperature is significantly lower than the discharge temperature of lithium batteries. The maximum temperature difference reaches 23.3 °C;

[0093] [[ID=2,8]]The experimental results show that wrapping EG-PW-Cu-2 can control the temperature rise of the battery and effectively reduce the working temperature of electronic devices, that is, it has the thermal management function of electronic devices.

[0094] To prove the influence of Cu-NC as a thermal conductive filler on the properties of the composite phase change material, Comparative Example 1, an EG-PW composite material without adding Cu-NC, is provided.

[0095] Comparative Example 1

[0096] A preparation method of an EG-PW composite material without adding Cu-NC. Unless otherwise specified, the steps are the same as those in Example 1. The differences are as follows: Steps 2 and 3 are not carried out, and in Step 4, EG is used instead of EG-Cu. The obtained material is named EG-PW.

[0097] To prove the composition of EG-PW, an FT-IR test was carried out. The test results are as follows Figure 1As shown, EG-PW contains all the infrared characteristic peaks of both EG and PW. Among them, there is no obvious difference between the infrared characteristic peaks of PW in EG-PW and those of pure PW. The test results show that EG-PW has been successfully prepared, and it can be proved that no chemical reaction occurred during the preparation process.

[0098] To further verify the composition of EG-PW, XRD tests were carried out. The test results are as Figure 2 shown. EG-PW contains all the characteristic diffraction peaks of both EG and PW. Among them, there is no obvious difference between the diffraction characteristic peaks of PW in PW-GE and those of pure PW. The test results show that the conclusion obtained from the XRD test is consistent with that obtained from the FT-IR test, and the preparation process has no effect on the crystallization behavior of PW, that is, it does not affect the good heat storage capacity of PW.

[0099] To prove the thermal conductivity of EG-PW, thermal conductivity tests were carried out. The test results are as Figure 6 and Table 2 shown. The thermal conductivity of EG-PW is 0.32 W / (m·K). By comparing the test results with those of Example 1, it can be seen that the thermal conductivity of EG-PW-Cu-2 has increased by 372% compared with that of EG-PW. The experimental results show that adding Cu-NC can effectively enhance the thermal conductivity of EG-PW-Cu-2.

[0100] To prove the influence of the EG addition amount on the properties of the composite phase change material, Comparative Example 2 and Example 2 were provided, with the EG addition amounts being 10 wt% and 30 wt% respectively.

[0101] Comparative Example 2

[0102] A preparation method of a composite phase change material with a battery thermal management function and an EG addition amount of 10 wt%. The steps not specifically described are the same as those in Example 1, except that: in step 4, the EG addition amount is 10 wt%, and the obtained material is a phase change composite material with an EG addition amount of 10 wt%, abbreviated as EG-PW-Cu-1.

[0103] The XRD test results of EG-PW-Cu-1 are as Figure 2 shown. The characteristic diffraction peaks of EG-PW-Cu-1 have no obvious difference from those of EG-PW-Cu-2 in Example 1, which proves that the composite phase change material has been successfully prepared and does not affect the good heat storage capacity of PW.

[0104] The SEM test results of EG-PW-Cu-1 are as Figure 3As shown, the SEM image of EG-PW-Cu-1 is basically the same as that of EG-PW-Cu-1 in Example 1; however, due to the decrease in the addition amount of EG, the paraffin on the surface of EG-PW-Cu-1 significantly increases, and the irregular network structure of EG significantly decreases compared to the surface of EG-PW-Cu-2.

[0105] The DSC test results of EG-PW-Cu-1 are as Figure 4 shown in Table 1. In the test temperature range of 20 - 80 °C, there is an endothermic peak at 44.7 °C during the melting process of EG-PW-Cu-1, with a latent heat value of 233.72 J / g, and there is an exothermic peak at 37.39 °C during the crystallization process, with a latent heat value of 235.53 J / g. The test results show that there is no obvious difference in the phase change behavior and heat storage capacity between EG-PW-Cu-1 and EG-PW-Cu-2.

[0106] The thermal conductivity test results of EG-PW-Cu-1 are as Figure 6 shown in Table 2. The thermal conductivity of EG-PW-Cu-1 is 0.92 W / (m·K); compared with EG-PW-Cu-2 obtained in Example 1, the thermal conductivity has decreased by 23%. Combining with the SEM test results, it can be seen that the irregular network structure formed by EG and its addition amount has a direct impact on the thermal conductivity of the composite phase change material.

[0107] The encapsulation performance test results of EG-PW-Cu-1 are as Figure 7 shown. Leakage occurs in EG-PW-Cu-1 after heating for 10 minutes. The test results show that when the addition amount of EG is less than the required addition range, the encapsulation effect cannot be achieved.

[0108] The temperature control test results of EG-PW-Cu-1 are as Figure 8 shown. An obvious temperature control platform appears in EG-PW-Cu-1 at 43 - 44 °C. The test results show that there is no obvious difference in the temperature control function between EG-PW-Cu-1 and EG-PW-Cu-2.

[0109] Example 2

[0110] A preparation method of a Cu-NC-based phase change composite material with a battery thermal management function and an EG addition amount of 30 wt%, the steps not specifically described are the same as those in Example 1, and the difference lies in that: in step 4, the addition amount of EG is 30 wt%, and the obtained material is a Cu-NC-based phase change composite material with a battery thermal management function and an EG addition amount of 30 wt%, abbreviated as EG-PW-Cu-3.

[0111] The XRD test results of EG-PW-Cu-3 are as Figure 2As shown, the characteristic diffraction peaks of EG-PW-Cu-3 have no obvious difference from those of EG-PW-Cu-2 in Example 1, which proves that the composite phase change material was successfully prepared and did not affect the good heat storage capacity of PW.

[0112] The SEM test results of EG-PW-Cu-3 are as Figure 3 shown. The SEM image of EG-PW-Cu-3 is basically the same as that of EG-PW-Cu-1 in Example 1. However, due to the increase in the addition amount of EG, the paraffin on the surface of EG-PW-Cu-1 significantly decreases, and the irregular network structure of EG is significantly enhanced compared to the surface of EG-PW-Cu-2.

[0113] The DSC test results of EG-PW-Cu-3 are as Figure 4 and Table 1 show that in the test temperature range of 20 - 80 °C, there is an endothermic peak at 44.88 °C during the melting process of EG-PW-Cu-1, with a latent heat value of 233.68 J / g, and there is an exothermic peak at 36.86 °C during the crystallization process, with a latent heat value of 233.50 J / g. The test results show that there is no obvious difference in the phase change behavior and heat storage capacity between EG-PW-Cu-3 and EG-PW-Cu-2.

[0114] The thermal conductivity test results of EG-PW-Cu-3 are as Figure 6 and Table 2 show that the thermal conductivity of EG-PW-Cu-3 is 1.29 W / (m·K). Compared with EG-PW-Cu-2 obtained in Example 1, the thermal conductivity has increased by 108%.

[0115] The encapsulation performance test results of EG-PW-Cu-3 are as Figure 7 shown. The test results are as Figure 7 shown. There is no obvious change in EG-PW-Cu-3. The test results show that EG has excellent encapsulation ability and can effectively prevent PW leakage.

[0116] The temperature control test results of EG-PW-Cu-3 are as Figure 8 shown. An obvious temperature control platform appears in EG-PW-Cu-3 at 43 - 44 °C. The test results show that there is no obvious difference in the temperature control function between EG-PW-Cu-3 and EG-PW-Cu-2.

[0117] The temperature control test curve of EG-PW-Cu-1 has no obvious difference from the temperature control curve in Example 1, and an obvious temperature control platform appears at 43 - 44 °C. The test results show that EG-PW-Cu-3 has good temperature control function.

[0118] From Comparative Example 2, Example 1, and Example 2, the following conclusions can be obtained:

[0119] 1. Expanded graphite EG has thermal conductivity and can effectively improve the thermal conductivity of the composite phase change material. As the addition amount of EG increases, the thermal conductivity of the composite phase change material gradually enhances. However, when the addition amount of EG is too large, the proportion of paraffin in the phase change composite material is significantly reduced, resulting in that the expanded graphite is not filled with paraffin. This directly leads to a large number of pores in the composite phase change material during the subsequent hot pressing process, causing serious uneven heat conduction, and thus resulting in a serious decline in the thermal conductivity and heat storage performance.

[0120] 2. Different addition amounts of expanded graphite EG have a decisive impact on the encapsulation performance of the composite phase change material. When the addition amount of expanded graphite EG is less than the required range, the composite phase change material will leak. However, within the required addition range, the composite phase change material has good encapsulation performance.

Claims

1. Preparation method of a Cu-NC-based phase change composite material with battery thermal management function, characterized in that It includes the following steps: Step 1: Preparation of expanded graphite EG. Expandable graphite is heated and expanded under certain conditions to obtain expanded graphite with a worm-like porous structure, simply referred to as EG. Step 2: Preparation of Cu-NC thermal conductive material. First, 2-aminoterephthalic acid and copper nitrate hexahydrate are in a certain molar ratio. 2-aminoterephthalic acid and copper nitrate hexahydrate are dispersed in a mixed solution of N,N-dimethylformamide and methanol and stirred evenly to obtain mixture A. Then, mixture A is subjected to a hydrothermal reaction under certain conditions. After the reaction is completed, it is naturally cooled to room temperature. The obtained product is centrifuged, washed, and vacuum dried to obtain the MOF material. Finally, under certain conditions, the MOF material is calcined to obtain the Cu-NC thermal conductive material, simply referred to as Cu-NC. Step 3: Preparation of the molten mixture. First, EG obtained in Step 1 and Cu-NC obtained in Step 2 are in a certain mass ratio. EG and Cu-NC are dispersed in deionized water to obtain mixture B. Then, mixture B is dried at a drying temperature of 60 °C to evenly disperse Cu-NC into EG for adsorption to obtain the EG-Cu composite material, simply referred to as EG-Cu. Finally, with a certain addition amount of EG-Cu, PW and EG-Cu are mixed to obtain mixture C. Then, under certain conditions, mixture C is vacuum dried at a heating temperature of 60 °C to allow the completely melted PW to enter the pores of EG, and the molten mixture can be obtained. Step 4: Preparation of the composite phase change material with battery thermal management function. Under certain conditions, the molten blend obtained in Step 3 is hot pressed and cooled to obtain the Cu-NC-based phase change composite material with battery thermal management function, simply referred to as EG-PW-Cu.

2. The preparation method according to claim 1, characterized in that: In Step 1, the conditions for heating and expansion are: the heating temperature is 900 - 1000 °C, and the heating time is 30 - 120 s. In Step 2, the molar ratio of 2-aminoterephthalic acid and copper nitrate hexahydrate is 1:1 - 1:6, and the volume ratio of N,N-dimethylformamide and methanol is 9:

1. The conditions for the hydrothermal reaction are: the hydrothermal temperature is 120 - 160 °C, and the hydrothermal time is 15 - 24 h. The conditions for calcination are: under an argon-hydrogen mixed gas condition, the calcination temperature is 500 - 700 °C, and the calcination time is 1 - 3 h. In Step 3, the mass ratio of EG and Cu-NC is 1:1; the addition amount of EG-Cu is 15 - 30 wt%. In Step 4, the conditions for hot pressing are: the temperature is 40 - 60 °C, the pressure is 5 - 10 MPA, and the hot pressing time is 15 - 60 s.

3. The preparation method according to claim 1, characterized in that: The obtained Cu-NC-based phase change composite material is composed of expanded graphite EG, paraffin wax PW, and Cu-NC. Among them, Cu-NC is a graphite carbon sheet loaded with Cu nanoparticles obtained by calcining Cu-MOF. The function of the expanded graphite is to be one of the encapsulation materials and thermal conductive materials. The function of the paraffin wax is to be a phase change material, providing phase change heat storage and temperature control performance. The function of the Cu-NC is to be one of the thermal conductive materials. The function of the Cu-MOF is to confine Cu metal nanoparticles through a metal-organic framework, thereby effectively enhancing the dispersion of the Cu metal nanoparticles and improving the compatibility between the Cu metal nanoparticles, expanded graphite, and paraffin, and further improving the thermal conductivity and stability of the composite material; The obtained Cu-NC-based phase change composite material has a thermal conductivity of 0.92 - 1.29 W / (m·K), a crystallization latent heat value of 233.20 - 276.64 J / g, and a melting latent heat of 233.68 - 277.78 J / g.

4. The preparation method according to claim 1, characterized in that: When the obtained Cu-NC-based phase change composite material is used as a battery thermal management material, it has thermal conductivity, encapsulation performance, and anti-leakage performance. When wrapping a lithium battery, the rising speed of the battery charging and discharging temperature slows down, and the battery surface temperature decreases by 10.7 - 23.3 °C.

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