High-thermal-conductivity flexible composite phase change film based on AZC-coated LDH

Abstract

The invention relates to a high-thermal-conductivity flexible composite phase change film based on AZC-coated LDH and a preparation method and application thereof, and belongs to the technical field of composite phase change materials and thermal safety regulation and control. The composite phase-change film is prepared from a flexible self-supporting film framework and ACZ-coated LDH nano heat-conducting filler uniformly dispersed in the flexible self-supporting film framework through a simple process of one-step blending and solution casting, and the flexible self-supporting film framework is a PEI / CMC three-dimensional network matrix loaded and confined with a polyethylene glycol phase-change material; the ACZ (at) LDH nano heat conduction filler is a core-shell structure nano hybrid filler formed by growing layered double hydroxide nanosheets on the surface of a ZIF-8 derived porous carbon material. The composite phase change film has excellent flexibility, shape stability and high thermal conductivity, integrates efficient photo-thermal conversion / energy storage and active thermal runaway inhibition functions, and is suitable for the fields of battery thermal management, solar photo-thermal utilization, microelectronic thermal protection and the like.

Description

Technical Field

[0001] This invention belongs to the field of advanced thermal management functional composite materials technology, and relates to a composite phase change material that combines photothermal conversion / energy storage and thermal runaway suppression functions. In particular, it relates to a composite phase change film material with high thermal conductivity, flexibility and flame retardancy and its preparation method. Background Technology

[0002] With the continuous development of information technology, portable electronic devices, wearable devices, and high-energy-density batteries are increasingly evolving towards thinner, lighter, smaller, and higher-power designs. This trend leads to a dramatic increase in the heat generated per unit volume during device operation, resulting in a significant rise in heat flux density. Abnormal increases in device temperature can cause a series of serious problems. First, overheating poses a fire hazard, endangering user safety. Second, high temperatures accelerate the aging of internal electronic components, shortening the lifespan of the device. Therefore, developing efficient thermal management technologies and materials to achieve rapid heat dissipation and maintain appropriate operating temperature ranges for electronic devices or batteries has become a critical technical challenge that urgently needs to be addressed.

[0003] Phase change materials (PCMs), with their reversible phase change behavior and high energy storage density under small temperature differences, have shown great application potential in the field of thermal management. The main function of PCMs is to act as a transfer station during the reversible phase change process, storing and releasing energy, achieving efficient heat "time shifting" under near-isothermal conditions. This is beneficial for energy saving and peak load transfer, providing an ideal solution for maintaining equipment operation within a suitable temperature range. Among them, solid-liquid PCMs, compared to other PCMs, achieve relatively efficient energy storage capacity within a small temperature difference range while ensuring relatively stable volume changes during the phase change process, thus overcoming limitations in more application scenarios. However, solid-liquid PCMs, especially the most widely used organic PCM material polyethylene glycol (PEG), have significant technical drawbacks: firstly, leakage is prone to occur during the solid-liquid transition, affecting the stability and safety of the device; secondly, their intrinsic thermal conductivity is generally low, limiting their heat absorption / release rates; and thirdly, their flexibility and photothermal conversion capabilities are insufficient. These shortcomings in flexibility, thermal conductivity, leakage sensitivity, and photothermal conversion capability severely limit its widespread application in the thermal safety management of advanced electronic equipment.

[0004] Existing technologies primarily address the aforementioned leakage and poor thermal conductivity issues through strategies such as microencapsulation, porous carrier adsorption, or polymer network encapsulation. However, while microencapsulation technology or loading PEG onto porous materials (such as expanded graphite or porous silica) can suppress leakage to some extent, the preparation processes are often complex, production costs are high, and environmentally unfriendly substances may be introduced, contradicting the principles of green and sustainable development. While constructing a three-dimensional polymer network encapsulation of PCM through chemical cross-linking can effectively improve shape stability and leak-proof performance, the dense and irreversible cross-linked network makes the material difficult to recycle and reuse, and also poses a challenge to the orderly arrangement of molecular chains. Furthermore, while physical encapsulation using thermoplastic elastomers through microphase separation structures is relatively simple, it suffers from low phase change material loading rates, significantly reduced latent heat storage capacity, and limited biocompatibility, and also faces difficulties in recycling after disposal.

[0005] Jing et al. (Flexible electrospun porous carbon nanofiber@PEG phase changenanofibrous membrane for advanced solar- / electro-thermal energy conversion and storage[J]. Journal of Energy Storage (2024, 104: 114608.) PEG was encapsulated in robust, flexible, porous carbon nanofibers (PCNFs) derived from electrospun polyacrylonitrile / polystyrene (PAN / PS) composite nanofibers. The resulting PCNF@PEG had latent heats of melt and freeze of 71.9 J g / g. -1 Its thermal conductivity is only 0.4575 W / m·K. Its preparation process is complex and its thermal conductivity is insufficient, making it difficult to meet the needs of complex battery thermal management scenarios.

[0006] Liu et al. (Flexible MoS2 / CNF / PEG phase change film with superior photothermal conversion and thermal energy storage[J]. Solar Energy Materials and Solar Cells(2025, 282: 113376.) A flexible film was prepared by self-assembling cellulose nanofibers (CNF) and molybdenum disulfide (MoS2) and encapsulating it with PEG to obtain a MoS2 / CNF / PEG phase change film. This phase change film has excellent solar energy collection capabilities. In solar-thermal-electric conversion applications, the output voltage of PEG / CNF / MoS2 can reach 147.9mV. However, it exhibits a certain degree of phase change leakage at the phase change temperature of 80℃.

[0007] Carboxymethyl cellulose (CMC), as a water-soluble biopolymer, possesses excellent film-forming properties and biocompatibility. A simple mixture of CMC and PEG has been studied for encapsulation, but the low loading rate and easy PEG precipitation resulted in less than ideal performance. Furthermore, polyethyleneimine (PEI), rich in amine groups, may form a cross-linked network with CMC through interactions such as hydrogen bonding, potentially improving its encapsulation effect on PEG. However, relying solely on the CMC / PEI network, the thermal conductivity and flame retardant properties of the composite material still fall short of meeting the thermal management requirements of high-performance electronic devices.

[0008] In summary, existing technologies lack a composite phase change material that simultaneously achieves excellent leak-proof performance, high thermal conductivity, good flexibility, and is simple to prepare, environmentally friendly, and easily recyclable. Therefore, developing a novel thermal management material with superior overall performance that aligns with sustainable development strategies is of great significance for advancing the development of next-generation electronic devices. Summary of the Invention

[0009] The purpose of this invention is to provide a high thermal conductivity flexible composite phase change film based on AZC@LDH that combines photothermal conversion performance and thermal management performance, as well as its preparation method and application, in order to overcome the limitations of existing composite phase change materials in terms of flexibility, thermal conductivity and leakage sensitivity, and improve their application effect in battery thermal management systems (BTMS).

[0010] To achieve the above objectives, this invention provides a high thermal conductivity flexible composite phase change film based on AZC@LDH, which consists of a flexible self-supporting film skeleton and ACZ@LDH nano-thermal conductive fillers uniformly dispersed therein, wherein:

[0011] The flexible self-supporting film skeleton includes a PEI / CMC three-dimensional network matrix formed by cross-linking of polyethyleneimine and sodium carboxymethyl cellulose through intermolecular forces, and a polyethylene glycol phase change material uniformly dispersed and confined in the three-dimensional network matrix;

[0012] The ACZ@LDH nano thermally conductive filler is a core-shell structured nano-hybrid filler composed of ZIF-8-derived porous carbon material as the core and layered bimetallic hydroxide nanosheets grown and loaded on the core surface.

[0013] The composite phase change film exhibits flexibility and self-support at room temperature and maintains shape stability within the phase change temperature range of polyethylene glycol.

[0014] Specifically, the composite phase change film of the present invention is composed of 50-70 wt% polyethylene glycol phase change material, 25-40 wt% PEI / CMC three-dimensional network matrix and 5-10 wt% ACZ@LDH nano thermally conductive filler.

[0015] More specifically, the composite phase change film of the present invention is further preferably composed of 55-65 wt% polyethylene glycol phase change material, 30-38 wt% PEI / CMC three-dimensional network matrix, and 8-10 wt% ACZ@LDH nano thermally conductive filler.

[0016] ZIF-8 derived porous carbon material is an advanced functional carbon material with a uniform nitrogen-doped, well-ordered morphology, characterized by high specific surface area, tunable pore structure, and high thermal conductivity, obtained through high-temperature carbonization derivatization using a zeolite imidazole framework (ZIF-8) as a precursor. Therefore, it is an ideal thermal conductivity-enhancing framework, possessing unique advantages in effectively improving the thermal conductivity of composite phase change materials and preventing phase change material leakage. Preferably, the ZIF-8 derived porous carbon material used in this invention is a KOH-activated porous carbon material.

[0017] Layered bimetallic hydroxide nanosheets, as a two-dimensional anionic clay material, possess environmentally friendly, low-cost, and inherently flame-retardant properties. When loaded onto the surface of carbon materials, they can effectively enhance the flame-retardant performance of composite film materials. Furthermore, the layered bimetallic hydroxide nanosheets described in this invention specifically refer to magnesium aluminum hydrotalcite (MgAl-LDH).

[0018] Furthermore, the polyethylene glycol phase change material selected in this invention has an average molecular weight of 2000–10000 and a phase change temperature in the range of 60–80°C, which matches the operating temperature range of most electronic devices. A more preferred polyethylene glycol phase change material in this invention is PEG-8000.

[0019] This invention also provides a method for preparing the aforementioned AZC@LDH-based high thermal conductivity flexible composite phase change film, specifically including:

[0020] Polyethyleneimine and sodium carboxymethyl cellulose were dissolved in water, and polyethylene glycol was added and mixed evenly to obtain a PEG-PC precursor solution.

[0021] Using ZIF-8-derived porous carbon material as the core, layered bimetallic hydroxide nanosheets were grown in situ on its surface by hydrothermal method to obtain ACZ@LDH nano thermally conductive filler with core-shell structure.

[0022] ACZ@LDH nano-thermal conductive filler was dispersed in a PEG-PC precursor solution to obtain a composite slurry, which was then cast into a film using a solution casting method and dried to obtain the PEG-PC high thermal conductivity flexible composite phase change film based on AZC@LDH.

[0023] The present invention employs a simple and low-energy blending strategy to prepare the PEG-PC precursor solution, and obtains a uniformly mixed precursor solution by stirring for no less than 2 hours.

[0024] Furthermore, the ACZ@LDH nano-thermal conductive filler of the present invention is specifically prepared by adding ZIF-8 derived porous carbon material to a urea aqueous solution containing water-soluble magnesium salt and water-soluble aluminum salt, and carrying out a hydrothermal reaction at 100-120°C to grow layered bimetallic hydroxide nanosheets in situ on the surface of the ZIF-8 derived porous carbon material.

[0025] Furthermore, the hydrothermal reaction time is preferably 12 to 15 hours.

[0026] Furthermore, after casting the composite slurry into a film using a solution casting method, the present invention preferably dries it at 55-65°C for 12-15 hours to obtain the final composite phase change film PEG-PC.

[0027] The ZIF-8 derived porous carbon material can be prepared using any conventionally reported method, and the present invention does not limit the specific preparation method thereto.

[0028] Preferably, the ZIF-8 derived porous carbon material of the present invention is prepared by reacting 2-methylimidazole and zinc acetate in an aqueous solution at room temperature to prepare ZIF-8 crystals, carbonizing them at high temperature under an inert atmosphere to obtain carbon framework ZC, and then activating them with KOH to obtain ZIF-8 derived porous carbon material AZC with high specific surface area.

[0029] Furthermore, the sodium carboxymethyl cellulose used in this invention preferably has a molecular weight (M) of [missing information]. W The molecular weight range is 600,000 to 800,000, the degree of substitution ranges from 0.6 to 0.9, and the corresponding viscosity of a 2 wt% aqueous solution at 25°C is 800 to 1200 mPa·s. This specification system ensures that CMC possesses both good water solubility and suitable processing viscosity, and can form a stable three-dimensional cross-linked network with polyethyleneimine through electrostatic interactions, providing a structural basis for composite phase change films. The selected polyethyleneimine has a molecular weight (M... W The range is 1500 to 2000 to ensure the strength and uniformity of the constructed three-dimensional cross-linked network.

[0030] This invention prepares a high thermal conductivity flexible composite phase change film based on AZC@LDH through a simple one-step blending and solution casting process. It has excellent flexibility, shape stability and high thermal conductivity, and integrates efficient photothermal conversion / energy storage and active thermal runaway suppression functions. It is suitable for applications in battery thermal management, solar photothermal utilization and microelectronic thermal protection.

[0031] Therefore, the present invention further provides the application of the high thermal conductivity flexible composite phase change film based on AZC@LDH in the preparation of integrated thermal management devices that combine thermal energy storage and thermal runaway suppression functions.

[0032] Furthermore, the integrated thermal management device is selected from any of the following: a thermal management device for rechargeable battery modules to simultaneously realize battery waste heat storage / utilization and thermal runaway propagation suppression; a thermal management device for solar thermal systems to simultaneously realize photothermal conversion, thermal energy storage and self-overheat protection; and a flexible thermal buffer material for microelectronic packaging or intelligent building envelope structures to simultaneously realize thermal buffering regulation and fire safety protection.

[0033] Furthermore, the present invention also provides the application of the composite phase change film in the preparation of flame-retardant and heat-insulating protective materials.

[0034] This invention successfully constructs a high-performance composite phase change membrane through ingenious material design and a simple preparation process. First, an effective three-dimensional cross-linked encapsulation network is formed based on the hydrogen bonding between CMC and PEI. Utilizing intermolecular forces such as van der Waals interactions between the PEG melt and this network, a high-load, low-leakage flexible composite phase change material is prepared via a simple one-step blending method. Second, an AZC porous framework structure is introduced. Capillary forces and surface tension physically lock the liquid state of PEG during its solid-liquid phase transition, ensuring that PEG will not leak even when it melts. Furthermore, MgAl-LDH nanosheets are grown in situ on the AZC surface as fillers and added to the flexible composite phase change material. This significantly improves the material's thermal conductivity, endowing it with excellent light absorption and photothermal conversion capabilities, achieving efficient thermal management and solar energy storage. It also possesses inherent flame-retardant safety, overcoming the flammability hazards of traditional organic phase change materials. Finally, the composite material is fabricated into a flexible membrane using solution casting, maintaining high thermal conductivity, leak-proof properties, and flame retardancy while possessing good flexibility and conformability, greatly expanding its application potential on curved surfaces or dynamic components.

[0035] In summary, the high thermal conductivity flexible composite phase change membrane based on AZC@LDH prepared in this invention ingeniously integrates high heat storage density, excellent leak-proof performance, rapid thermal management, intrinsic flame retardancy, good flexibility, and recyclability. Its simple and green preparation process and multifunctional characteristics make it promising for applications in fields such as thermal management of electronic devices, thermal protection of wearable device batteries, and solar thermal utilization. Attached Figure Description

[0036] Figure 1 This is a flowchart illustrating the preparation process of the high thermal conductivity flexible composite phase change film based on AZC@LDH according to the present invention.

[0037] Figure 2 These are SEM topographic images of ZC, AZC, and AZC@LDH.

[0038] Figure 3 These are SEM images of the composite phase change film and its C / N / O elemental distribution diagrams, as well as the Mg / Al elemental distribution diagram of AZC@LDH.

[0039] Figure 4 These are XRD and FTIR spectra of different materials.

[0040] Figure 5 These are physical images of leakage conditions of different phase change materials and corresponding leakage rate curves as a function of temperature.

[0041] Figure 6 It is a schematic diagram of complex deformations of composite phase change films, such as bending, curved surface bonding and torsion, and a comparison diagram of the elastic modulus of different materials.

[0042] Figure 7 It contains complete DSC curves, solidification curves, and melting curves for different materials.

[0043] Figure 8 These are the TGA curves of different materials under a nitrogen atmosphere.

[0044] Figure 9 This is a comparison chart of the thermal conductivity of different materials.

[0045] Figure 10 These are the test results of the photothermal conversion performance of different composite phase change films.

[0046] Figure 11 These are the thermal management time-temperature curves of batteries with different composite phase change films at different rate of increase.

[0047] Figure 12 These are test charts showing the flame retardant properties of different composite phase change films. Implementation

[0049] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings and specific examples. It should be noted that the embodiments are merely illustrative and are intended to provide a thorough understanding of the technical solutions of the present invention and to provide guidance for those skilled in the art to implement and apply the present invention. It should be understood that these descriptions do not constitute any limitation on the scope of protection of the present invention.

[0050] Unless otherwise expressly stated, the production processes, experiments, tests or analysis methods involved in the embodiments of the present invention are all considered to be conventional methods known to those skilled in the art, and only need to be implemented in accordance with conventional conditions or relevant product instructions. The steps and names involved are also generally clear and unambiguous in the art.

[0051] The instruments, equipment, raw materials, reagents, or samples used in the embodiments are not subject to any special restrictions on their source. They are all conventional products that can be purchased through regular commercial channels or prepared by known methods, and their source does not have a substantial impact on the implementation results of the present invention.

[0052] Unless otherwise expressly defined, the scientific and technical terms used in this invention have the meanings commonly understood by one of ordinary skill in the art. In case of any conflict, the definitions in this specification shall prevail.

[0053] The terms “comprising,” “including,” “having,” etc., used in this invention should be understood as open-ended, meaning “including but not limited to.” The term “and / or” includes any and all combinations of one or more of the associated listed items. Quantitative terms such as “a,” “one,” etc., do not exclude multiples; “multiple” or “a variety” refers to quantities greater than or equal to two.

[0054] The terms "preferred", "better", and "exemplary" used in this invention are only used to describe specific solutions or effects and are not intended to limit the necessary scope of the solution or the scope of protection.

[0055] This invention relates to the description of numerical parameters (such as quantity, concentration, temperature, time, etc.), and it should be understood that reasonable deviations naturally exist due to measuring instruments, operational errors, statistical fluctuations, etc. The range of such deviations should be within limits acceptable to those skilled in the art based on common sense.

[0056] The following specific embodiments of the present invention are in accordance with Figure 1 The process flow shown for preparing the AZC@LDH-based high thermal conductivity flexible composite phase change film specifically includes:

[0057] 1) Preparation of PEG-PC: PEG was added to deionized water containing PEI and CMC, and stirred evenly at room temperature to obtain a mixed solution of phase change composite material PEG-PC.

[0058] 2) Preparation of AZC: Zinc acetate and 2-methylimidazole were dispersed in deionized water, stirred and dried to obtain ZIF-8 powder. ZIF-8-derived carbon ZC was prepared by high-temperature carbonization at 900℃ under nitrogen atmosphere. After mixing with KOH, ZIF-8-derived porous carbon material AZC was prepared by high-temperature activation at 900℃ under nitrogen atmosphere.

[0059] 3) Preparation of AZC@LDH: Add AZC, MgCl2·6H2O, AlCl3·H2O and urea to deionized water and mix evenly. Then carry out hydrothermal reaction in a high-pressure reactor to prepare AZC@LDH.

[0060] 4) Preparation of PEG-PC-AZC / LDH: Add AZC@LDH to the PEG-PC mixed solution and mix evenly to obtain a composite slurry. Cast the slurry into a film using the solution casting method and dry it to obtain a high thermal conductivity flexible composite phase change film PEG-PC-AZC / LDH based on AZC@LDH. Example

[0061] Example 1

[0062] Weigh out polyethyleneimine (PEI, M) W =1800) 1.0g, sodium carboxymethyl cellulose (CMC, M W =700000)0.4g, together with 20mL of deionized water, stirred to dissolve, and obtained a uniform, transparent, viscous solution as the carrier solution.

[0063] 2.2 g of PEG-8000 was added to the carrier solution and the mixture was magnetically stirred at room temperature for 2 h to prepare a homogeneous PEG-PC mixed solution.

[0064] The obtained mixed solution was poured into a glass petri dish with a diameter of 60 mm and dried in a drying oven at 65 °C for 12 h to prepare the phase change composite membrane material PEG-PC.

[0065] Example 2

[0066] Weigh 15g of zinc acetate and 56g of 2-methylimidazole and add them to 500mL of deionized water. Stir the mixture at room temperature for 12h, centrifuge, wash and dry to prepare ZIF-8 powder.

[0067] ZIF-8 powder was placed in a quartz boat and heated to 900°C at a heating rate of 5°C / min under a nitrogen atmosphere, and held at this temperature for 3 hours for high-temperature carbonization. After cooling, the carbonized product was washed with 2M hydrochloric acid solution to remove residual Zn components, then washed with deionized water and dried to prepare ZIF-8 derived carbon, denoted as ZC.

[0068] Figure 2Images (a, b) in the figure show scanning electron microscope (SEM) images of ZC at different magnifications. The images reveal that ZC exhibits a rhombic dodecahedral structure, a typical morphological feature of ZIF-8, indicating that ZC was formed by the shrinkage of the original morphology retained after high-temperature carbonization of ZIF-8. Furthermore, image (b) shows that the ZC surface is relatively smooth, without obvious pores, and the carbon skeleton shows no significant collapse.

[0069] Example 3

[0070] The ZC powder prepared in Example 2 was uniformly mixed with KOH solid at a mass ratio of 1:1, impregnated with deionized water for 12 hours, dried, and then placed in a nitrogen atmosphere. The mixture was heated to 900°C at a heating rate of 5°C / min and held at this temperature for 3 hours for high-temperature activation. The activated product was washed sequentially with 2M hydrochloric acid solution and deionized water, and dried to obtain the activated ZIF-8 derived porous carbon material, denoted as AZC.

[0071] Figure 2 Images (c, d) in the middle show scanning electron microscope images of AZC at different magnifications. Compared to ZC, AZC shows obvious etching marks on its surface, with abundant pores and irregular structures, indicating that KOH activation led to the local collapse of the carbon framework and the formation of mesopores.

[0072] The formation of pores in AZC is primarily due to the synergistic physicochemical reaction of KOH activation. KOH reacts with carbon at 900℃ to produce K₂CO₃ and K₂ vaporizes and escapes, creating high-pressure gas channels within the carbon framework, leading to… Figure 2 In (a), the bulk structure breaks down into smaller particles, while the strong alkalinity of KOH etches ZC carbon lattice defect sites, generating micropores; and K2CO3, acting as a template agent, decomposes at high temperature to produce CO2, further expanding the pores to form mesopores / macropores, ultimately from... Figure 2 (b) Dense, non-porous ZC transforms into Figure 2 (d) The high specific surface area and porous structure of AZC significantly improve the exposure of its active sites; furthermore, the activation process also introduces a large number of oxygen-containing functional groups (such as -COOH, -OH, C=O, etc.) on the surface of AZC, providing active sites for the subsequent heterogeneous nucleation of LDH.

[0073] Example 4

[0074] Weigh 0.5g of AZC prepared in Example 3, 1.62g of MgCl2·6H2O, 0.9g of AlCl3·H2O, and 2.4g of urea, and dissolve each in 20mL of deionized water. Stir magnetically for 30min, then pour the solutions into a 200mL beaker and stir magnetically for 1h. Pour the resulting mixed solution into a high-pressure reactor and heat to 100℃ for hydrothermal reaction for 12h. After cooling to room temperature, remove the reaction product, centrifuge, wash, and dry to obtain AZC@LDH.

[0075] Figure 2 Images (e, f) in the figure show scanning electron microscope (SEM) images of AZC@LDH at different magnifications. The nanoflower structure of AZC@LDH can be directly observed in the images. It consists of an AZC polyhedron core and Mg-Al LDH nanosheets as a shell. This is because the -COOH / -OH groups on the AZC surface are deprotonated and negatively charged. The Mg-Al complex preferentially nucleates on the AZC surface through electrostatic attraction, forming LDH sheet structures. The LDH sheets grow vertically or obliquely, and in some areas, they stack in a petal-like shape, forming the rose-like structure shown in the image. This structure retains the porosity of AZC while introducing the ordered layered structure of LDH. The large interlayer distance of LDH provides more adsorption space for the phase change material.

[0076] Example 5

[0077] Weigh 0.36g of AZC@LDH prepared in Example 4 and add it to the PEG-PC mixed solution in Example 1. After mixing evenly, pour it into a glass petri dish with a diameter of 60mm and dry it in a drying oven at 65℃ for 12h to prepare a high thermal conductivity flexible composite phase change film PEG-PC-AZC / LDH based on AZC@LDH.

[0078] Figure 3 (a, b) show SEM images of the composite phase change membrane PEG-PC-AZC / LDH at different magnifications. The images show a uniformly distributed flexible membrane structure with a smooth, crack-free surface, no visible phase separation, and tight interfacial bonding, indicating that PEG, CMC, and PEI have been successfully composited with AZC@LDH into a single unit.

[0079] Figure 3 The EDS elemental spectra of C, N, and O of PEG-PC-AZC / LDH shown in (c-e) also help to confirm the network distribution of PEI, PEG, and CMC in the composite phase change film. The EDS elemental spectra of Mg and Al shown in (f, g) indicate that AZC@LDH has been uniformly composited into the composite phase change film.

[0080] Comparative Example 1

[0081] Weigh 0.36g of ZC prepared in Example 2 and add it to the PEG-PC mixed solution in Example 1. After mixing evenly, pour it into a glass petri dish with a diameter of 60mm and dry it in a drying oven at 65℃ for 12h to prepare the composite phase change film PEG-PC-ZC.

[0082] Comparative Example 2

[0083] Weigh 0.36g of AZC prepared in Example 3 and add it to the PEG-PC mixed solution in Example 1. After mixing evenly, pour it into a glass petri dish with a diameter of 60mm and dry it in a drying oven at 65℃ for 12h to obtain the composite phase change film PEG-PC-AZC.

[0084] Application Example 1

[0085] Figure 4 In (a), X-ray diffraction (XRD) patterns of the raw material PEG, the composite phase change film PEG-PC prepared in Example 1, ZC and AZC prepared in Examples 2 and 3, the composite phase change film PEG-PC-AZC / LDH prepared in Example 5, and the PEG-PC-ZC and PEG-PC-AZC prepared in Comparative Examples 1 and 2 are provided respectively.

[0086] After carbonization, ZC and AZC exhibited two characteristic broad diffraction peaks at approximately 25° and 44°, respectively, corresponding to the (002) crystal plane diffraction of the graphite structure and the (101) crystal plane diffraction of the amorphous carbon structure, indicating the successful formation of the graphitized structure. Compared to ZC, the peak intensity of the activated AZC was slightly enhanced. This is because the defect sites in the carbon framework were etched during the activation process, resulting in an increase in crystallite size and improved crystallinity.

[0087] PEG exhibits typical diffraction peaks at 2θ = 19.24° and 23.45°. Characteristic PEG peaks are also present in PEG-PC, PEG-PC-ZC, PEG-PC-AZC, and PEG-PC-AZC / LDH. In PEG-PC-ZC, the PEG characteristic peak is retained, while the ZC characteristic peak is weakened, indicating that ZC is dispersed in the PEG matrix, and some crystal planes are encapsulated by amorphous PEG. PEG-PC-AZC also retains the PEG peak, but the AZC peak is weaker. This is because the high specific surface area and porous structure of AZC lead to a decrease in crystal plane diffraction intensity. In contrast, the PEG characteristic peak in PEG-PC-AZC / LDH shifts to the left due to the incorporation of Mg. 2+ Al 3+ These large-diameter ions cause lattice stretching. Overall, no new characteristic peaks appeared in the diffraction patterns of all composite phase change films; instead, the diffraction patterns mainly showed the superposition of characteristic peaks of each component. No new chemical phase formation was observed, which verifies the high chemical compatibility among the components within the composite phase change film.

[0088] Figure 4 Figure (b) provides the Fourier Transmission Infrared (FT-IR) spectra of each material. The FT-IR spectrum of the raw material PEG is shown at 1108 cm⁻¹. -1 and 2888cm -1 The absorption peaks at 1360 cm⁻¹ belong to the stretching vibrations of COC and CH, respectively, while those at 1360 cm⁻¹ belong to the stretching vibrations of COC and CH, respectively. -1 and 1470cm -1 The absorption peak at 1611 cm⁻¹ belongs to the -CH₂ bond; the CMC of the raw material is at 1611 cm⁻¹. -1 A strong peak was observed at 3423 cm⁻¹, originating from carboxylic acid groups (-COOH). Various phase change composite membrane materials showed peak values ​​at 3423 cm⁻¹. -1 The broad peaks observed nearby correspond to the superposition of the tensile vibration peaks of the hydroxyl groups in CMC and the NH amino groups in PEI, while the peaks at 3200 to 3700 cm⁻¹ are... -1 The slowdown of the characteristic peak is mainly attributed to the cross-linking reaction between CMC and PEI, in which the carboxyl groups form peptide bonds and are consumed. Meanwhile, compared with the OH absorption peak in PEG, the absorption peaks of each composite phase change film showed a slight shift. The broadening of the absorption peaks to reduce the frequency is the main manifestation of hydrogen bond formation, thus proving the formation of a hydrogen bond network within the composite phase change film.

[0089] Based on the combined XRD and FT-IR results, the composite phase change film successfully and uniformly bonded the raw materials used together without any chemical reaction occurring during the bonding process.

[0090] Application Example 2

[0091] The leakage rate of PEG phase change material and various composite phase change films at high temperature was tested. The samples were placed in a forced-air drying oven at 20℃, 40℃, 60℃ and 80℃ for 30 min, respectively. Their macroscopic morphology was recorded and the mass change before and after heating was measured. Figure 5 (a) shows the macroscopic morphology of the sample, while the leakage rate data over time are summarized in Figure 5 (b) in.

[0092] In the figure, PEG showed slight leakage at 60℃ and complete leakage at 80℃; in contrast, no leakage was detected in PEG-PC-ZC, PEG-PC-AZC, and PEG-PC-AZC / LDH at either 60℃ or 80℃. Although PEG-PC underwent partial melting at 60℃ and 80℃, the molten PEG was effectively bound to the matrix due to hydrogen bonding and intermolecular forces, and the mass loss was negligible.

[0093] Application Example 3

[0094] Figure 6Figure (a) shows a schematic diagram of the flexible composite phase change film PEG-PC-AZC / LDH prepared by the present invention, indicating that the material can undergo complex deformations such as bending, curve bonding and twisting, and the material has excellent flexibility and mechanical adaptability. Figure 6 (b) Further demonstration of the mechanical flexibility of the composite phase change film at room temperature through practical operation, showing that the material can be easily bent, twisted and rolled without breaking, proving its high flexibility and excellent mechanical properties.

[0095] At room temperature, the bending stress of composite phase change films PEG-PC, PEG-PC-ZC, PEG-PC-AZC and PEG-PC-AZC / LDH was tested using an electronic universal testing machine to explore the flexibility of different composite phase change films and to calculate their elastic modulus.

[0096]

[0097] Table 1 shows the specific data of elastic modulus and bending stress of different composite phase change films. It can be seen that, compared with pure PEG, the elastic modulus and bending stress of the different composite phase change films prepared are significantly reduced, indicating that all composite phase change films are flexible films.

[0098] Furthermore from Figure 6 (c) The bar chart of elastic modulus of different composite phase change films shows that the elastic modulus of PEG-PC-AZC / LDH is only 5.88 MPa, which is much lower than that of other materials, indicating that it has extremely strong flexibility and deformability. Compared with other materials, PEG-PC-AZC / LDH exhibits the lowest values ​​in both elastic modulus and bending stress, two key factors affecting flexibility. This comprehensive advantage makes its flexibility performance the most outstanding.

[0099] Application Example 4

[0100] Differential scanning calorimetry (DSC) was used to test pure PEG and different composite phase change films to further understand the heat absorption / release capabilities of different composite phase change films and characterize the latent heat storage capacity of the materials. The relevant phase change enthalpy and phase change temperature data are summarized in Table 2.

[0101]

[0102] Figure 7 (a) shows the complete DSC curves for each material, visually illustrating its phase transition behavior. Figure 7 (b) and (c) are local curves of the melting and solidification processes, respectively.

[0103] Based on the analysis in Table 2, pure PEG exhibits a distinct melting peak at 43.64℃ and a crystallization peak at 62.91℃, demonstrating typical phase transition behavior and possessing the highest phase transition enthalpy. H m =168.0 J / g, H c =170.0 J / g).

[0104] In comparison, the melting and crystallization peaks of PEG-PC decreased to 40.32℃ and 55.88℃, respectively, and the phase transition enthalpy also decreased significantly. This is because the addition of non-phase transition components such as PEI and CMC occupies some space and mass, reducing the relative content of PEG and thus lowering the phase transition enthalpy. Furthermore, the cross-linking network formed by PEI, CMC, and PEG interferes with the orderly arrangement and crystallization process of PEG molecular chains, restricting the movement of PEG molecular chains and reducing the driving force for crystallization. As a result, the phase transition process of PEG is more likely to be initiated at a lower temperature, thus lowering the phase transition temperature.

[0105] The phase transition enthalpy of PEG-PC-AZC / LDH is the highest among the four phase change composite film materials. This phenomenon can be attributed to the fact that the LDH layered structure loaded on the AZC@LDH surface provides a larger interlayer spacing, offering more ample space for PEG molecules to adsorb and arrange in an orderly manner, thereby increasing the energy storage density per unit mass of the composite material and thus enhancing the phase transition enthalpy. Therefore, although the absolute enthalpy of PEG-PC-AZC / LDH is lower than that of pure PEG, the introduction of AZC@LDH filler successfully achieved the highest relative phase transition enthalpy in the composite phase change film, maintaining good thermal energy storage and release capabilities while ensuring high encapsulation loading.

[0106] Application Example 5

[0107] Thermogravimetric analysis (TGA) was used to characterize the thermal stability of pure PEG and different composite phase change films.

[0108] Figure 8 The TGA curves of pure PEG and different composite phase change films are shown under N2 atmosphere. It can be clearly seen from the figure that PEG-PC-ZC has the most residual ZC at 800℃. This is because ZC has a high degree of graphitization and a stable carbon skeleton, and hardly undergoes thermal decomposition at high temperature. On the other hand, the residual weight of PEG-PC-AZC at 800℃ is close to 0. This is because the KOH activation process destroys the graphitization structure of ZC. The destroyed carbon skeleton is more easily thermally decomposed during high-temperature calcination, resulting in a carbon residue close to 0.

[0109] The residual weight of PEG-PC-AZC / LDH at high temperature is second only to PEG-PC-ZC. Figure 8The magnified image shows that PEG-PC-AZC / LDH exhibits the best thermal stability between 340 and 380°C, with the slowest decomposition process and the least weight loss. This is because LDH is loaded on the surface of AZC, preventing the pyrolysis of AZC at high temperatures. The layered structure of LDH also significantly delays the thermal decomposition of PEG, providing the best thermal shielding effect and increasing the pyrolysis temperature of the composite phase change film.

[0110] Overall, the composite phase change membrane exhibits significantly better thermal stability than pure PEG, with PEG-PC-AZC / LDH showing the best thermal stability. Combined thermogravimetric analysis and differential scanning calorimetry results indicate that PEG-PC-AZC / LDH possesses good thermal stability and practicality, and also demonstrates potential for thermal management and energy storage.

[0111] Application Example 6

[0112] Figure 9 The thermal conductivity of pure PEG and different composite phase change films was demonstrated. The thermal conductivity of PEG, PEG-PC, PEG-PC-ZC, PEG-PC-AZC and PEG-PC-AZC / LDH were 0.374, 0.860, 1.052, 1.851 and 1.793 W / m·K, respectively.

[0113] The thermal conductivity of PEG-PC is significantly enhanced compared to pure PEG, attributed to the extensive hydrogen bonding and electrostatic network formed between PEG, PEI, and CMC, which promotes phonon transport compared to pure PEG. The introduction of high-performance porous carbon material ZC as a thermally conductive filler significantly improved thermal conductivity. Subsequent activation treatment of AZC further reduced interfacial thermal resistance, resulting in a significant increase in thermal conductivity of 0.799 W / m·K compared to the unactivated material. The slight decrease in thermal conductivity after adding AZC@LDH is attributed to the increased interfacial thermal resistance between LDH and PEG.

[0114] Application Example 7

[0115] Figure 10 (a) shows a schematic diagram of the photothermal conversion testing device, which mainly consists of a sealed black box and a 130mW / cm² thermal conductivity meter. 2 It consists of simulated lighting and a data acquisition unit (7018 temperature acquisition unit).

[0116] Different composite phase change films were placed in sealed black boxes. Under simulated light illumination, the surface temperature of the materials changed. The temperature changes of the sample surface were sampled by a temperature acquisition device and stored in a computer. Detailed experimental data are as follows: Figure 10 As shown in (b).

[0117] Under simulated light illumination, the surface temperature of PEG-PC, PEG-PC-ZC, PEG-PC-AZC, and PEG-PC-AZC / LDH rose rapidly. As the temperature difference between the material and the air increased, the material's heat dissipation capacity also increased, thus the rate of temperature rise gradually slowed down. Figure 10 As shown in (b), the temperature of PEG-PC-AZC / LDH rises the fastest, reaching about 71°C before starting to decrease. Moreover, the temperature decrease rate in the high-temperature region is slower than that of other materials, indicating that the addition of AZC@LDH further enhances the photothermal conversion performance of the composite phase change film, making it exhibit excellent photothermal stability and conversion efficiency.

[0118] Calculated as 130mW / cm 2 Under simulated lighting, 1.48cm 2 The photothermal conversion efficiencies of different bilayer phase change composite film materials are as follows: η PEG-PC =50.3%, η PEG-PC-ZC =74.9%, η PEG-PC-AZC =76.7%, η PEG-PC-AZC / LDH =92.3%. These results indicate that introducing AZC@LDH with high photothermal effect can improve the photothermal conversion and storage efficiency of composite phase change films.

[0119] To further explain the temperature change of the composite phase change film, the absorbance of each material was tested in the range of 200–800 nm. The results are as follows: Figure 10 As shown in (c).

[0120] The light absorption capacity of PEG-PC, PEG-PC-ZC, PEG-PC-AZC, and PEG-PC-AZC / LDH shows an increasing trend. This is because ZC is a porous carbon material with good light absorption capacity, and its introduction can significantly improve the light absorption capacity of PEG-PC. The light absorption capacity of PEG-PC-AZC is better than that of PEG-PC-ZC because the activated AZC has a larger specific surface area and a larger light absorption area. Due to its unique layered structure, LDH reflects incident light multiple times between layers, which improves its light absorption capacity. Therefore, the maximum absorbance of PEG-PC-AZC / LDH can reach 1.48 L / (g·cm).

[0121] Application Example 8

[0122] To evaluate the application potential of composite phase change films in the thermal management of lithium-ion batteries (LIBs), a blank battery pack without any phase change material coating was used as an Air control. The surface temperature changes of batteries coated with different composite phase change films were tested at discharge rates of 1C, 2C, and 3C. The tests were conducted at room temperature, and the results are as follows: Figure 11 As shown.

[0123] Observing the information in the figure, it can be seen that the temperature curves of PEG-PC at all expansion rates are similar to those of the Air control, indicating that its thermal management effect is limited. Compared with PEG-PC, PEG-PC-ZC shows slightly better temperature control at high expansion rates (2C and 3C), with slightly lower temperature peaks. However, at all expansion rates, the temperature curves of PEG-PC-AZC are more stable than those of PEG-PC and PEG-PC-ZC, especially at the 3C expansion rate, showing better thermal stability.

[0124] Compared to the above, the temperature curve of PEG-PC-AZC / LDH was the most stable at all test rates, especially at the 3C rate, showing the best thermal management effect. This further proves that the introduction of AZC@LDH filler plays a decisive role in improving the overall thermal management performance of the composite phase change film.

[0125] Quantitative analysis showed that the peak temperatures of the blank battery pack without phase change material coating were 40℃, 51.5℃, and 63.4℃ under multiple charge-discharge cycles at different rates. Compared to the Air control, the surface temperature of the battery coated with the composite phase change film was significantly reduced. The peak temperatures of PEG-PC were 39.4℃, 50.1℃, and 61.8℃, representing decreases of 1.5%, 2.7%, and 2.5%, respectively. However, the peak temperature reduction of PEG-PC-AZC / LDH was more significant, at 36.7℃, 45℃, and 53.8℃, representing decreases of 3.3%, 12.6%, and 15.1%, respectively. Compared with the other three composite phase change films, PEG-PC-AZC / LDH exhibited the greatest cooling effect at all three charge-discharge rates, which can improve battery safety and lifespan.

[0126] Application Example 9

[0127] PEG-PC, PEG-PC-ZC, PEG-PC-AZC, and PEG-PC-AZC / LDH were ignited directly on an alcohol lamp to test the flame retardant properties of different composite phase change films.

[0128] Equal weights of different composite phase change films were taken and directly ignited using an alcohol lamp flame, with the ignition time recorded. The materials were then removed from the flame, and their combustion time and behavior were recorded. After extinguishing the flame, the remaining material was weighed, and the residual amount was calculated. Different materials exhibited significantly different combustion processes. Figure 12 The specific combustion process was recorded, and the combustion data is shown in Table 3.

[0129]

[0130] Among them, PEG-PC burned severely within 2 seconds after ignition and continued to burn even after being removed; PEG-PC-ZC and PEG-PC-AZC ignited after 3 seconds and continued to burn even after being removed; PEG-PC-AZC / LDH was ignited after 5 seconds and extinguished rapidly after the flame was removed. This is because the interlayer water of MgAl-LDH precipitated at high temperature, which can prevent the flammable gas generated by the decomposition and cooling of PEG, reduce the flame propagation speed, and also block oxygen, thus inhibiting further combustion of the material.

[0131] The above ignition tests show that PEG-PC-AZC / LDH has both high thermal conductivity and certain flame retardancy. In addition, the PEG-PC-AZC / LDH PEG composite phase change film did not drip during combustion, and the film structure remained intact before and after ignition, which further proves that it has great leakage prevention potential.

[0132] Application Example 10

[0133] PEG-PC, PEG-PC-ZC, PEG-PC-AZC, and PEG-PC-AZC / LDH were tested for oxygen index (LOI) at 23℃ and 50%RH according to the standard GB / T 2406.3-2022. The sample size was 120mm×6.5mm×0.20mm, the ignition gas was a mixture of 97%O2 / 3%N2, and the ignition time was 15s. The flame retardant performance of the four composite phase change films was evaluated, and the synergistic effect of AZC@LDH nano thermally conductive filler on the flame retardant effect of the composite phase change film was verified. The test data are shown in Table 4.

[0134]

[0135] PEG-PC has an LOI value of 27.1%, indicating that it continues to burn after being removed from the flame and exhibits severe dripping, classifying it as a flammable material. PEG-PC-ZC has an LOI value of 28.4%, while PEG-PC-AZC further increases its LOI value to 32.1%, forming a continuous and dense char layer after combustion. PEG-PC-AZC / LDH has a significantly increased LOI value of 38.1%, which is 37.5% higher than PEG-PC. This material self-extinguishes within 2 seconds after being removed from the flame, does not continue to burn after secondary ignition, and exhibits very little dripping, demonstrating excellent flame retardant properties.

[0136] The oxygen index test data above show that the introduction of AZC@LDH can significantly improve the flame retardancy of the composite phase change film. The PEG-PC-AZC / LDHPEG composite phase change film has good application prospects in battery thermal management, solar thermal utilization and microelectronic thermal protection.

[0137] The above embodiments of the present invention do not describe all details exhaustively, nor do they limit the present invention to the embodiments described above. Various changes, modifications, substitutions, and variations made by those skilled in the art to these embodiments without departing from the principles and spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A highly thermally conductive flexible composite phase change film based on AZC@LDH, comprising a flexible self-supporting film framework and uniformly dispersed ACZ@LDH nano-thermal conductive fillers therein, wherein: The flexible self-supporting film skeleton includes a PEI / CMC three-dimensional network matrix formed by cross-linking of polyethyleneimine and sodium carboxymethyl cellulose through intermolecular forces, and a polyethylene glycol phase change material uniformly dispersed and confined in the three-dimensional network matrix; The ACZ@LDH nano thermally conductive filler is a core-shell structured nano-hybrid filler composed of ZIF-8-derived porous carbon material as the core and layered bimetallic hydroxide nanosheets grown and loaded on the core surface. The composite phase change film exhibits flexibility and self-support at room temperature and maintains shape stability within the phase change temperature range of polyethylene glycol.

2. The high thermal conductivity flexible composite phase change film based on AZC@LDH according to claim 1, characterized in that... The ZIF-8 derived porous carbon material is a porous carbon material activated by KOH.

3. The high thermal conductivity flexible composite phase change film based on AZC@LDH according to claim 1, characterized in that... The layered bimetallic hydroxide nanosheets are magnesium aluminum hydrotalcite (MgAl-LDH).

4. The high thermal conductivity flexible composite phase change film based on AZC@LDH according to claim 1, 2 or 3, characterized in that: The composite phase change film consists of 50–70 wt% polyethylene glycol phase change material, 25–40 wt% PEI / CMC three-dimensional network matrix, and 5–10 wt% ACZ@LDH nano thermally conductive filler.

5. The high thermal conductivity flexible composite phase change film based on AZC@LDH according to claim 4, characterized in that... The components of the composite phase change film are: polyethylene glycol phase change material 55-65 wt%, PEI / CMC three-dimensional network matrix 30-38 wt%, and ACZ@LDH nano thermally conductive filler 8-10 wt%.

6. The high thermal conductivity flexible composite phase change film based on AZC@LDH according to claim 1, characterized in that... The average molecular weight of the polyethylene glycol phase change material is 2000-10000.

7. The method for preparing the high thermal conductivity flexible composite phase change film based on AZC@LDH as described in claim 1, comprising: Polyethyleneimine and sodium carboxymethyl cellulose were dissolved in water, and polyethylene glycol was added and mixed evenly to obtain a PEG-PC precursor solution. Using ZIF-8-derived porous carbon material as the core, layered bimetallic hydroxide nanosheets were grown in situ on its surface by hydrothermal method to obtain ACZ@LDH nano thermally conductive filler with core-shell structure. ACZ@LDH nano-thermal conductive filler was dispersed in a PEG-PC precursor solution to obtain a composite slurry, which was then cast into a film using a solution casting method and dried to obtain the high thermal conductivity flexible composite phase change film based on AZC@LDH.

8. The application of the high thermal conductivity flexible composite phase change film based on AZC@LDH as described in claim 1 in the preparation of an integrated thermal management device that combines thermal energy storage and thermal runaway suppression functions.

9. The application according to claim 8, wherein the integrated thermal management device is selected from any one of the following: a thermal management device for rechargeable battery modules to simultaneously realize battery waste heat storage / utilization and thermal runaway propagation suppression; a thermal management device for solar thermal systems to simultaneously realize photothermal conversion, thermal energy storage and self-overheat protection; a flexible thermal buffer material for microelectronic packaging or intelligent building envelope structures to simultaneously realize thermal buffering regulation and fire safety protection.

10. The application of the high thermal conductivity flexible composite phase change film based on AZC@LDH as described in claim 1 in the preparation of flame-retardant and heat-insulating protective materials.

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