Composite phase change material based on PEG, PEO and MXene derived skeleton and preparation method and application thereof

Abstract

The invention belongs to the technical field of composite phase-change materials and electric heating energy storage, and provides a composite phase-change material based on a PEG, PEO and MXene derived skeleton as well as a preparation method and application of the composite phase-change material. The preparation method comprises the following steps: by taking PEG as a phase change material, etching Ti3AlC2 with hydrofluoric acid to prepare MXene, freeze-drying an ice template to prepare an MXene / PEO aerogel three-dimensional framework material, and then preparing PEG (at) MXene / PEO from the PEG and the MXene / PEO aerogel three-dimensional framework material through a vacuum impregnation method. The composite phase change material has thermal management performance and an electromagnetic shielding function. According to the invention, PEG is packaged in an MXene-based aerogel skeleton by directional growth and vacuum impregnation methods, and the prepared composite phase change material has good shape stability, thermal management performance and electromagnetic interference shielding efficiency, and has huge potential in integration of excellent electromagnetic interference shielding and advanced thermal energy management application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of composite phase change materials and electrothermal energy storage materials for photothermal, energy storage and electronic devices, and particularly relates to a composite phase change material based on PEG, PEO and MXene derived skeleton as well as a preparation method and application thereof. The composite phase change material is a novel composite phase change material with electrothermal conversion, photothermal conversion, heat management performance, electromagnetic interference shielding performance and energy storage. BACKGROUND

[0002] In the modern wave of scientific and technological development, the trend of miniaturization and high power of electronic devices is obvious, although it brings many conveniences, but also produces serious problems. Miniaturization increases the integration level of components, and heat is concentrated. High power makes the heat production increase dramatically per unit time. Heat accumulation will affect the performance and stability of electronic devices, leading to chip operation errors, slow operation and even burning. At the same time, miniaturization and high power require higher energy management for electronic devices. In addition, with the widespread application of electronic devices, the problem of electromagnetic pollution is becoming increasingly serious. Electronic devices will generate electromagnetic waves during operation. These electromagnetic waves not only interfere with the normal work of surrounding electronic devices, but also may cause potential harm to human health. Under this background, phase change materials (PCM) are expected to become the key to solving the problems of electronic device heat dissipation and energy management due to their characteristics of absorbing or releasing a large amount of latent heat during phase change, and provide strong support for the development of miniaturization and high power of electronic devices. However, traditional phase change materials have some limitations in practical application, for example, some organic phase change materials have the problems of easy leakage, easy volatilization and poor thermal conductivity, while inorganic phase change materials often have the problems of supercooling phenomenon, low phase change enthalpy and poor compatibility with matrix materials, which limits their wide application in the field of electronic device heat management. SUMMARY

[0003] The application provides a composite phase change material based on PEG, PEO and MXene derived skeleton as well as a preparation method and application thereof to solve the problem that current composite phase change materials cannot stably play the heat management and electromagnetic shielding performance. The composite phase change material is a novel composite phase change material with electrothermal conversion, photothermal conversion, heat management performance, electromagnetic interference shielding performance and energy storage.

[0004] The application is implemented by the following technical scheme: a composite phase change material based on PEG, PEO and MXene derived skeleton, the composite phase change material takes polyethylene glycol (PEG) as a phase change material, MXene is prepared by etching Ti3AlC2 with hydrofluoric acid, the MXene / PEO aerogel three-dimensional skeleton material is prepared by ice template freeze-drying directional growth, the skeleton material is used as a heat conductor and an electrically conductive filler, then the PEG and the MXene / PEO aerogel three-dimensional skeleton material are prepared into the composite phase change material based on PEG, PEO and MXene derived skeleton (PEG@MXene / PEO) by a vacuum impregnation method.

[0005] The method for preparing the composite phase change material based on PEG, PEO and MXene derived skeleton comprises the following steps: (1) preparing a MXene solution: 2g of LiF and 30mL of 12M hydrochloric acid are uniformly mixed and stirred for 30min, then 2g of Ti3AlC2 is added, and stirring is performed for 24h; (2) the reaction liquid obtained in step (1) is evenly divided into four parts and centrifuged at a speed of 3500rpm for 10min, after centrifugation, the supernatant is discarded, 40mL of deionized water is added to the precipitate, and the precipitate is mixed with the deionized water uniformly by using a vortex mixer, then 750W ultrasonic is performed for 10min, and the liquid is taken out and centrifuged at a speed of 3500rpm for 10min, the operation is repeated several times until the pH value of the liquid discarded after centrifugation is 5; (3) 40mL of ethanol is added to the precipitate obtained in step (2) and ultrasonic is performed for 1h, then 10min of centrifugation is performed at a speed of 3500rpm, and the lower precipitate is collected; (4) collecting the upper dispersion liquid: 20mL of deionized water is added to the centrifugal precipitate in step (3), and the mixture is uniformly mixed by using a vortex mixer, then 750W ultrasonic is performed for 10min, 3min of centrifugation is performed at a speed of 3500rpm, and the black upper liquid is collected as the upper dispersion liquid; the suspension, ultrasonic and centrifugation are repeated, and the upper dispersion liquid is maximally collected, that is, the MXene solution is obtained; (5) Preparation of MXene-based aerogel: 0.1g, 0.3g, 0.5g PEO was dissolved in 10mL deionized water respectively, and stirred vigorously at room temperature for 4h, to obtain PEO aqueous solution with concentration of 1wt%, 3wt% or 5wt% respectively; 32mL MXene solution obtained in step (4) was used to prepare MXene / PEO three-dimensional skeleton by ice template freeze-drying method: the MXene solution, 1.2mL PEO aqueous solution was mixed at room temperature for 1h to obtain a uniform MXene / PEO hybrid hydrogel; then, the obtained MXene / PEO hybrid hydrogel was placed in a cylindrical mold with copper sheet at the bottom and polytetrafluoroethylene at the four sides, pre-frozen with liquid nitrogen for 30min, and then freeze-dried at-64℃ for 72h to convert into MXene / PEO aerogel three-dimensional skeleton; According to the initial concentration of the PEO solution, the prepared MXene / PEO aerogel three-dimensional skeleton is named as MXene / (1%PEO), MXene / (3%PEO) and MXene / (5%PEO). The three-dimensional skeleton is a black gray cylinder with an average gram weight of 0.11g; According to the initial concentration of the PEO solution, the prepared MXene / PEO aerogel three-dimensional skeleton is named as MXene / (1%PEO), MXene / (3%PEO) and MXene / (5%PEO); (6) Preparation of final product: PEG and MXene / PEO aerogel three-dimensional skeleton material were placed in a small box with a capacity of 50g, and the flaky PEG completely covered the MXene / PEO aerogel three-dimensional skeleton, then treated in a vacuum oven at 80℃ and a relative vacuum degree of-70kPa for 360min, to prepare PEG@MXene / PEO composite phase change material by vacuum impregnation, which is recorded as PEG@MXene / (1%PEO), PEG@MXene / (3%PEO) and PEG@MXene / (5%PEO).

[0006] The application also provides the application of the PEG, PEO and MXene derived skeleton based composite phase change material or the PEG, PEO and MXene derived skeleton based composite phase change material obtained by the preparation method in electromagnetic interference shielding system, light-heat conversion system and battery thermal management system.

[0007] The PEG, PEO and MXene derived skeleton based composite phase change material prepared by the application is tested for electromagnetic shielding efficiency by a vector network analyzer VNA, the light-heat conversion capacity of the composite phase change material is obtained by irradiating the composite phase change material with an incandescent lamp, and a battery thermal management test platform is built to test the battery thermal management performance.

[0008] The application prepares a composite phase change material PEG@MXene / PEO with stable shape, high thermal conductivity and high latent heat by introducing PEG into the MXene-based aerogel skeleton, and the composite material also has EMI shielding function and photothermal conversion capacity. Through the change of the content of PEO in the skeleton, the thermal conductivity of PEG@MXene / (5% PEO) can reach 0.37 W / m·K at most, and the melting enthalpy is 184.85 J / g. The EMI shielding effectiveness (SE) of PEG@MXene / (1% PEO) is as high as 30.16 dB, which is much higher than the commercial standard (20 dB). In terms of comprehensive performance, the combination of the prepared performance diversified aerogel and PEG can further protect the human body and electronic equipment from electromagnetic pollution in addition to heat runaway, and has wide application prospect in photothermal, energy storage and electronic equipment thermal management, and is a potential electronic packaging material. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 It is a material synthesis step diagram; Figure 2 It is a sample SEM and EDS diagram; in the figure: (a) is the SEM image of MXene / PEO; (b) is the SEM image of PEG@MXene / PEO; (c) is the EDS element mapping analysis of PEG@MXene / PEO: corresponding to C, N, O, F, Ti respectively; Figure 3 It is a sample DSC, loading rate and leakage rate test diagram; in the figure: (a) is the DSC image of PEG and PEG@MXene / PEO; (b) is the loading rate (y-axis) and leakage rate (z-axis) of PEG@MXene / PEO; Figure 4 It is a sample thermal conductivity coefficient diagram; Figure 5 It is a sample TG test diagram; in the figure: (a) is the TG image of MXene / PEO; (b) is the TG image of PEG@MXene / PEO; Figure 6 It is a sample infrared thermal imaging test diagram; in the figure: (a) is the infrared thermal imaging time-temperature curve of PEG@MXene / PEO; (b) is the infrared thermal imaging test schematic diagram (upper), test process record diagram (lower); Figure 7 It is a sample photothermal conversion device diagram; Figure 8 It is a sample photothermal conversion curve diagram; in the figure: (a) is the photothermal conversion time-temperature curve of PEG@MXene / PEO; (b) is the absorbance test result of PEG and PEG@MXene / PEO; Figure 9 It is a sample battery thermal management device diagram; Figure 10Figure 4 is a graph of battery thermal management test data for the sample at 0.5C charge-discharge rate; in the figure: (a) is a comparison of the temperature of the battery without CPCM wrapping and the battery with CPCM wrapping at 0.5C charge-discharge rate; (b) is the 5th cycle in 0.5C cycle; Figure 11 Figure 5 is a graph of battery thermal management test data for the sample at 1C charge-discharge rate; in the figure: (a) is a comparison of the temperature of the battery without CPCM wrapping and the battery with CPCM wrapping at 1C charge-discharge rate; (b) is the 5th cycle in 1C cycle; Figure 12 Figure 6 is a graph of battery thermal management test data for the sample at 2C charge-discharge rate; in the figure: (a) is a comparison of the temperature of the battery without CPCM wrapping and the battery with CPCM wrapping at 2C charge-discharge rate; (b) is the 5th cycle in 2C cycle; Figure 13 Figure 7 is a graph of electromagnetic shielding test for the sample; in the figure: (a) is a graph of electromagnetic shielding mechanism; (b) is a graph of electromagnetic interference shielding effectiveness; (c) is a graph of electromagnetic interference shielding effectiveness in 12-18 GHz band; (d) is a graph of total shielding effectiveness and electromagnetic parameters comparison. DETAILED DESCRIPTION

[0010] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0011] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs, and the materials referred to in this disclosure are incorporated by reference.

[0012] The equivalent techniques of the described specific embodiments, which can be realized by those skilled in the art through routine experiments, are included in the present application.

[0013] In the following examples, the experimental methods are all routine methods unless otherwise specified. In the following examples, the instrument equipment used is all routine laboratory instrument equipment unless otherwise specified; in the following examples, the experimental materials used are all purchased from routine biochemical reagent stores unless otherwise specified.

[0014] Materials: MAX (Ti3AlC2, purity about 99%) powder, 200 mesh, purchased from China Jilin No. 11 Science and Technology Co., Ltd. Polyethylene oxide PEO (CH2CH2O, average metering, Mv600,000, powder), polyethylene glycol PEG (HO (CH2CH2O) nH, average metering, Mn8000), titanium aluminum carbide (TiAlC2), lithium fluoride (LiF) were purchased from Shanghai Aldrin Chemical Reagent Co., Ltd. Hydrochloric acid (HCl), anhydrous ethanol (CH3CH2OH) were purchased from Tianjin Gaoyu Fine Chemical Co., Ltd.

[0015] The preparation of the composite phase change material based on the PEG, PEO, MXene derived skeleton is as follows: (1) Preparation of MXene solution: 2g LiF and 30mL, 12M hydrochloric acid were mixed uniformly and stirred for 30min, then 2g Ti3AlC2 was added and stirred for 24h; (2) The reaction liquid obtained in step (1) was evenly divided into 4 parts and centrifuged at 3500rpm for 10min. After centrifugation, the supernatant was discarded, and 40mL of deionized water was added to the precipitate, which was mixed uniformly by vortex mixer, and then ultrasonic was performed for 10min at 750W. The liquid was taken out and centrifuged at 3500rpm for 10min. Repeat several times until the pH value of the liquid poured out after centrifugation is 5; (3) In the precipitate obtained in step (2), 40mL of ethanol was added and ultrasonic was performed for 1h, and then centrifugation was performed at 3500rpm for 10min, and the lower precipitate was collected; (4) Collect the upper dispersion liquid: add 20mL of deionized water to the centrifugal precipitate in step (3) and mix uniformly by vortex mixer, then put it into the ultrasonic machine and perform ultrasonic for 10min at 750W, and then centrifuge at 3500rpm for 3min. The black upper liquid is collected as the upper dispersion liquid. Repeat the suspension, ultrasonic centrifugation, and the maximum amount of upper dispersion liquid is collected, which is the MXene solution; (5) Preparation of MXene-based aerogel: 0.1g, 0.3g, 0.5g PEO was dissolved in 10mL deionized water respectively, and stirred vigorously at room temperature for 4h to obtain PEO aqueous solution with concentration of 1wt%, 3wt% and 5wt% respectively. Take 32mL MXene solution obtained in step (4), and prepare MXene / PEO three-dimensional skeleton by ice template freeze-drying method: mix the MXene solution and 1.2mL PEO aqueous solution uniformly at room temperature for 1h to obtain a homogeneous MXene / PEO hybrid hydrogel. Then, the obtained MXene / PEO hybrid hydrogel is placed in a cylindrical mold with copper sheet at the bottom and polytetrafluoroethylene at the four sides. Pre-freeze with liquid nitrogen for 30min, then freeze-dry at-64℃ for 72h to convert into MXene / PEO aerogel three-dimensional skeleton. The three-dimensional skeleton is black and gray cylinder with an average weight of 0.11g; According to the initial concentration of the PEO solution, the prepared MXene / PEO aerogel three-dimensional skeleton is named MXene / (1%PEO), MXene / (3%PEO) and MXene / (5%PEO); (6) Preparation of final product: PEG and MXene / PEO aerogel three-dimensional skeleton material are placed in a small box with a capacity of 50 g, and the flaky PEG completely covers the MXene / PEO aerogel three-dimensional skeleton. Then, in a vacuum oven at 80°C and a relative vacuum degree of -70 kPa, the PEG@MXene / PEO composite phase change material is prepared by vacuum impregnation for 360 min, and is recorded as PEG@MXene / (1%PEO), PEG@MXene / (3%PEO) and PEG@MXene / (5%PEO).

[0016] The specific implementation is as follows: Example 1: Preparation of PEG@MXene / (1%PEO): First, 32 mL of MXene suspension and 1.2 mL of 1wt% PEO powder are mixed in a beaker and uniformly stirred in a magnetic stirrer for 1 h to uniformly disperse the mixed solution. In the second step, the prepared mixed solution is poured into a polytetrafluoroethylene mold and directionally frozen on a copper sheet immersed in liquid nitrogen. Finally, the polytetrafluoroethylene mold is placed in a vacuum drying machine for vacuum drying for 72 h to prepare MXene / PEO. By vacuum impregnation, the MXene / PEO adsorbs PEG in a vacuum oven at 80°C, and the vacuum is performed three times during this period. Finally, the excess PEG is removed on filter paper to obtain a stable composite phase change material PEG@MXene / (1%PEO).

[0017] The obtained composite phase change material: its electromagnetic shielding efficiency is tested by a vector network analyzer VNA, a commercial 18650 type lithium ion battery with sufficient electricity is pasted with a thermocouple, the PEG@MXene / (1%PEO) composite material is wrapped outside the battery, and in the same environment, the charging and discharging cycle is carried out, and a data acquisition device connected with the thermocouple is used to record the change of the battery surface temperature. To characterize the battery thermal management performance.

[0018] Example 2: Preparation of PEG@MXene / (3%PEO): 1wt% PEO in Example 1 is replaced with 3wt% PEO, and the rest is the same as described in Example 1.

[0019] The obtained PEG@MXene / (3%PEO) is detected: PEG@MXene / (1%PEO) in Example 1 is replaced with PEG@MXene / (3%PEO), and the other methods are the same as described in Example 1.

[0020] Example 3: Preparation of PEG@MXene / (5%PEO): Replace 1wt% PEO in Example 1 with 5wt% PEO, the rest of the method is the same as described in Example 1.

[0021] Test of the obtained PEG@MXene / (5%PEO): Replace PEG@MXene / (1%PEO) in Example 1 with PEG@MXene / (5%PEO), the rest of the method is the same as described in Example 1.

[0022] Preparation of MXene / (1%PEO) in Comparative Example 1: No PEG is added, and the rest of the method is the same as described in Example 1.

[0023] Test of the obtained MXene / (1%PEO): Replace PEG@MXene / (1%PEO) in Example 1 with MXene / (1%PEO), the rest of the method is the same as described in Example 1.

[0024] Preparation of MXene / (3%PEO) in Comparative Example 2: No PEG is added, and the rest of the method is the same as described in Example 1.

[0025] Preparation of MXene / (5%PEO) in Comparative Example 3: No PEG is added, and the rest of the method is the same as described in Example 1.

[0026] Characterization of the relevant properties of the new composite phase change materials obtained in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3: Example 1: The material synthesis steps are as shown in Figure 1 The material micro-morphology characterization results are as shown in Figure 2 Figure 2 The SEM image of (a) shows the microstructure of MXene / PEO aerogel framework at different magnifications, and a large number of irregular pores and sheet structures can be seen, which interweave to form a three-dimensional porous network. The formation of this porous network is due to the directional growth method used in the preparation of MXene / PEO. This method is to quickly act liquid nitrogen on the copper sheet at the bottom of the mold, and the instantaneous low temperature is conducted to the copper bottom plate, which makes the ice crystals inside the MXene / PEO hydrogel rapidly generate from bottom to top. These ice crystals promote the vertical arrangement of MXene sheet layers, and PEO forms connecting points between independent MXene sheet layers, finally forming the three-dimensional porous network in the figure. This porous structure shows the strong adsorption of aerogel.

[0027] The SEM image of PEG@MXene / PEO composite material reveals the multi-level structure characteristics of the material, as shown in Figure 2 ​(b) shown. Under the action of vacuum impregnation, a large amount of PEG was adsorbed on the MXene / PEO skeleton, so the sheet structure of MXene / PEO was filled in the SEM image, but the texture of the layered structure could still be observed, indicating that the three-dimensional channel formed by the synthesized MXene / PEO skeleton was relatively dense and had good stability.

[0028] By Figure 2 (c) It can be seen that the C element is widely and uniformly distributed in the MXene / PEO system. The source of C element mainly includes the structure of MXene itself and the carbon chain structure of PEO. This uniform distribution indicates that during the material preparation process, the carbon-containing components achieve good dispersion in the system, without obvious carbon enrichment or carbon-poor areas, ensuring the uniformity of the material composition. N element has a certain degree of distribution, but compared with C, Ti and other main elements, its bright spot number and density are obviously lower. N element may come from a small amount of nitrogen-containing impurities in MXene material. O element is widely distributed and has high density. This is mainly due to two aspects: on the one hand, the rich -OH, -O and other functional groups on the surface of MXene are an important source of O element; on the other hand, PEO molecular structure also contains oxygen atoms, so O element exists widely in MXene / PEO material. In the preparation process of MXene, hydrofluoric acid (HF) is often used for etching, so that MXene surface has -F functional groups. Ti element, as one of the main components of MXene, has a relatively obvious bright spot in the distribution image. The distribution of Ti element is closely related to the structure distribution of MXene, further confirming the existence state of MXene in the material.

[0029] Example 2: In order to further understand the heat absorption and release capacity of the material, the material was tested by differential scanning calorimetry. The DSC curve of PEG@MXene / PEO was measured by TA Q20 of USA with a temperature rising and falling rate of 4 ℃ / min in nitrogen atmosphere. The results are as follows Figure 3 (a) Among them, the melting enthalpy of PEG@MXene / (1% PEO) and PEG@MXene / (3% PEO) is 176.06 J / g and 182.66 J / g, respectively, reaching 92.77% and 96.24% of the melting enthalpy of PEG. The melting enthalpy of PEG@MXene / (5% PEO) is 184.85 J / g, reaching 97.40% of the melting enthalpy of PEG, with excellent phase change energy storage capacity.

[0030] Figure 3(b) Leakage rate test and loading rate test results of PEG and PEG@MXene / PEO. In the leakage rate test, after the sample was weighed, it was placed in a petri dish with filter paper. Then it was moved into an electric heating oven at 80°C, and a photo was taken every 20 min. After one hour, it was removed from the oven and cooled, the leaked PEG was scraped off, and the mass of the sample at that time was recorded to calculate the leakage rate. All the PEG leaked after 60 min, while under the action of MXene / PEO, only a small amount of PEG leaked, and the leakage rates of the three samples were 10.04%, 7.89%, and 3.90%, respectively. The loading rates were 98.06%, 98.35%, and 98.60%, respectively.

[0031] Example 3: The thermal conductivity of the samples was collected using a thermal conductivity instrument (HotDisk), and the results are shown in Figure 4 . Among them, the thermal conductivities of PEG@MXene (1% PEO) and PEG@MXene (3% PEO) were 0.33 W / (m·K) and 0.36 W / (m·K), respectively, and the thermal conductivity of PEG@MXene (5% PEO) reached 0.37 W / (m·K), which was 1.48 times that of pure PEG.

[0032] The TGA curve was tested by Japan HITACHI STA200. The temperature was raised at a rate of 10°C / min under nitrogen atmosphere from room temperature to 800°C. The results are shown in Figure 5 . The TG image of MXene / PEO is shown in Figure 5 (a), and the three samples all started to lose weight significantly at around 200°C, indicating that high PEO content accelerated the decomposition of the polymer. In the high temperature stage (>450°C), the oxidation decomposition of MXene, Ti3C2T x was dominated by the conversion of Ti3C2T Figure 5 x to TiO2 and the release of CO2. The TG image of PEG@MXene / PEO is shown in Figure 5 (b), and the mass loss trend of the composite phase change material is the same as that of pure PEG. All samples started to decompose at around 320°C. Due to the generation of thermally stable residues during the decomposition of the skeleton material, the composite phase change materials did not show complete weight loss, and the final residual mass corresponded to the residual mass of the skeleton material. Pure PEG material showed complete weight loss, and the final residual mass tended to zero.

[0033] Example 4: The infrared thermal imaging performance test results of the composite phase change materials obtained in Examples 1-3 are shown in Figure 6(a) is the infrared thermal imaging data diagram of PEG@MXene / PEO. is the data collected by the infrared thermal imager to collect the temperature change of PEG@MXene / PEO and the heating plate with time. Under the heating of the heating table, the temperature of PEG@MXene / PEO rises slowly, and after about 1000s of heating, the temperature of all samples reaches a stable state, the temperature of PEG@MXene / (1%PEO)composite material is about 55℃, the temperature of PEG@MXene / (3%PEO)composite material is about 53℃, and the temperature of PEG@MXene / (5%PEO)composite material is about 48℃, which is significantly lower than the temperature of the heating plate of 100℃, which shows that the polyethylene glycol PEG in the composite material absorbs heat, and PEG has excellent heat absorption capacity.

[0034] Example 5: In order to further study the light-heat conversion ability of PEG@MXene / PEO, a device as shown in Figure 7 is built. PEG@MXene / PEO is placed in a lightproof black box, a light source of 130mW / cm 2 is set above the box to simulate sunlight. A thermocouple is placed on the upper surface of PEG@MXene / PEO to collect temperature change data, which is transmitted to the computer and recorded after data collection. Figure 8 (a) is the light-heat conversion data diagram. As can be seen from the image, the temperature of PEG@MXene / (1%PEO)sample rises slowly, while the temperature of PEG@MXene / (3%PEO)and PEG@MXene / (5%PEO)samples rises rapidly, and the temperature of PEG@MXene / (5%PEO)sample can reach 70℃. In the cooling stage after the light source is turned off, the cooling curves of the three samples are highly coincident. It can be seen that the light-heat storage capacity of PEG@MXene / (5%PEO)sample is good. In order to verify this point, the absorbance test of pure PEG and three kinds of PEG@MXene / PEO materials is carried out, and the ultraviolet-visible-near infrared absorption spectrum of pure PEG and three kinds of composite phase change materials is shown in Figure 8 (b). The absorbance test of PEG@MXene / PEO is carried out by Japanese Hitachi UH4150, and the integral sphere mode is tested by diffuse reflection / absorption. PEG has little absorbance, and all the composite phase change materials show significant light absorption characteristics in the range of 200-800nm, and the intensity increases with the increase of PEO content, and all of them are >1, indicating that the introduction of PEO has a significant regulation effect on the optical properties of the composite material. Overall, PEG@MXene / PEO has good light absorption capacity in the range of 200~800nm.

[0035] Example 6:Figure 9 The battery test system shown, the thermal management performance of PEG@MXene / PEO battery was tested under different charge-discharge rates (0.5C, 1C, 2C), and the surface of the commercial 18650 type lithium ion battery with sufficient power was pasted with a thermocouple. The PEG@MXene / PEO composite material with different PEO content was wrapped outside the battery. In the same environment, charge-discharge cycle was carried out, and data acquisition device connected with thermocouple was used to record the change of battery surface temperature. The temperature change of blank battery control group and battery samples wrapped with PEG@MXene / PEO composite material with different PEO content under different rate charge-discharge cycle is shown in Figures 10-12 It can be observed that the surface temperature of the battery wrapped with composite phase change material is significantly lower than that of the battery without wrapping composite phase change material, which shows that the composite phase change material has excellent ability in battery thermal management. And no matter at 0.5C, 1C or 2C charge-discharge rate, with the increase of PEO content, the temperature of the battery during charge-discharge cycle is lower, because the increase of PEO makes more MXene layers connected, the network channel in the three-dimensional skeleton increases, and the thermal conductivity rises, which can help the battery to dissipate heat quickly, reduce the battery surface temperature, prolong the battery life and reduce the probability of thermal runaway.

[0036] Example 7: EMI shielding performance test of composite phase change material: with the development of electronic products, electromagnetic wave radiation (EMW) not only affects the performance of electronic equipment, but also endangers health. It is also important to prepare multifunctional composite phase change materials with electromagnetic shielding while meeting thermal management. As shown in Figure 13 The electromagnetic interference shielding performance in the frequency range of 12-18 GHz was studied. Figure 13 (a) gives the mechanism diagram of the propagation process of incident electromagnetic wave in PEG@MXene / PEO. When the incident electromagnetic wave propagates to the surface of PEG@MXene / PEO, due to the impedance mismatch between PEG@MXene / PEO and air, the electromagnetic wave is reflected and propagates into the internal structure of PEG@MXene / PEO, respectively. By directional freezing, MXene nanosheets form a tight and continuous electron transmission channel, and the electromagnetic wave repeatedly reflects and scatters in the skeleton to dissipate. And due to the characteristics of MXene surface containing rich functional groups (-OH and -F) and local defect phenomenon, the incident electromagnetic wave is dissipated. Through the above phenomena, it is shown that PEG@MXene / PEO has excellent electromagnetic shielding performance, which provides an efficient and feasible idea for the synthesis of multifunctional high-performance electromagnetic shielding materials.

[0037] In Figure 13(b) shows that PEG@MXene (1%PEO) has good electromagnetic interference shielding effect in Ku band (12-18GHz), and the SE A T of the three composite phase change materials is large, and the SE R gradually decreases and the maximum value is less than 3, so it can be inferred that the main mechanism of electromagnetic interference shielding of the composite phase change material is absorption. As shown in Figure 13 (c), the electromagnetic shielding performance of PEG@MXene (1%PEO) is excellent, and the maximum reaches 30.16dB in the whole process of Ku band (12-18GHz), which is much larger than the commercial application requirement of 20dB. Figure 13 The gradual decrease of R value in (d) also shows that the EMI shielding mechanism of the composite phase change material is absorption, and the T value of PEG@MXene (1%PEO) tends to 0, so the material surface has good shielding performance.

[0038] Finally, it should be pointed out that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.​

Claims

1. A composite phase change material based on a PEG, PEO, and MXene-derived framework, characterized in that: This composite phase change material uses polyethylene glycol (PEG) as the phase change material. MXene is prepared by etching Ti3AlC2 with hydrofluoric acid. MXene / PEO aerogel three-dimensional framework material is prepared by freeze-drying with an ice template and then used as a thermal and conductive filler. Finally, PEG and MXene / PEO aerogel three-dimensional framework material are used to prepare a composite phase change material based on PEG, PEO, and MXene-derived framework, namely PEG@MXene / PEO, by vacuum impregnation.

2. The method for preparing the composite phase change material based on the PEG, PEO, and MXene-derived framework as described in claim 1, characterized in that: The synthesis pathway includes the following steps: (1) Preparation of MXene solution: Mix 2g LiF and 30mL of 12M hydrochloric acid evenly and stir for 30min, then add 2g Ti3AlC2 and stir for 24h; (2) Divide the reaction solution obtained in step (1) into 4 equal parts and centrifuge at 3500 rpm for 10 min. After centrifugation, discard the supernatant, add 40 mL of deionized water to each precipitate, shake to mix, and mix the precipitate and deionized water evenly. Then sonicate at 750 W for 10 min, take it out and continue to centrifuge at 3500 rpm for 10 min. Repeat several times until the pH value of the liquid poured out after centrifugation reaches 5. (3) Add 40 mL of ethanol to the precipitate obtained in step (2) and sonicate for 1 h. Centrifuge at 3500 rpm for 10 min and collect the lower precipitate. (4) Collect the upper dispersion: Add 20 mL of deionized water to the centrifuged precipitate in step (3), shake it with a vortex mixer to mix it evenly, place it in an ultrasonic machine at 750W for 10 min, centrifuge at 3500 rpm for 3 min, and collect the dark brown upper liquid as the low-layer dispersion; repeat the suspension and ultrasonic centrifugation to collect the maximum amount of upper dispersion, which is the MXene solution; (5) Preparation of MXene-based aerogel: Dissolve 0.1g, 0.3g, and 0.5g of PEO in 10mL of deionized water and stir vigorously at room temperature for 4h to obtain PEO aqueous solutions with concentrations of 1wt%, 3wt%, or 5wt%, respectively; Take 32mL of the MXene solution obtained in step (4) and prepare the MXene / PEO three-dimensional framework by ice template freeze-drying method: Mix the MXene solution and 1.2mL of PEO aqueous solution at room temperature for 1 hour to obtain a uniform MXene / PEO hybrid hydrosol; Then, place the obtained MXene / PEO hybrid hydrosol in a mold with a copper sheet at the bottom and polytetrafluoroethylene around the edges, pre-freeze with liquid nitrogen for 30min, and then freeze-dry at -64℃ for 72h to transform into a black-gray solid MXene / PEO aerogel three-dimensional framework with an average basis weight of 0.11g; Based on the initial concentration of the PEO solution, the prepared MXene / PEO aerogel three-dimensional frameworks were named MXene / (1%PEO), MXene / (3%PEO), and MXene / (5%PEO). (6) Preparation of final products: The sheet-like PEG was completely covered on the MXene / PEO aerogel three-dimensional framework material, and then treated in a vacuum oven at 80°C and a relative vacuum of -70 kPa for 360 min. The PEG@MXene / PEO composite phase change materials were prepared by vacuum impregnation and were denoted as PEG@MXene / (1%PEO), PEG@MXene / (3%PEO) and PEG@MXene / (5%PEO).

3. The application of the composite phase change material based on the PEG, PEO, and MXene-derived framework as described in claim 1, or the composite phase change material based on the PEG, PEO, and MXene-derived framework obtained by the preparation method described in claim 2, in electromagnetic interference shielding systems, photothermal conversion systems, and battery thermal management systems.

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