Layered composite phase change material based on structural degree regulation and control and preparation method thereof

Abstract

The invention discloses a layered composite phase change material based on structural degree regulation and a preparation method thereof, and belongs to the technical field of heat energy storage materials. The material comprises a heat conduction layer and a heat storage layer which are alternately stacked, the heat conduction layer is composed of a first high heat conduction component, and the heat storage layer is formed by mixing a phase change matrix and a second high heat conduction component; the degree R of the layered structure meets 0 lt; r is less than or equal to 1.0, and R is the ratio of the mass of the first high-thermal-conductivity component in the thermal conductive layer to the total mass of all the high-thermal-conductivity components in the material. The active regulation and control of the anisotropy of the heat conductivity can be realized by regulating and controlling the R value. The method comprises the following steps: providing raw material powder; distributing heat-conducting components according to a designed R value; alternately laying and pre-pressing a heat conduction layer and a heat storage layer in the mold; and finally performing compression molding. According to the invention, collaborative optimization of high in-plane heat conductivity and high energy storage density is realized under the condition of low filler content, and the problems of low heat conduction improvement efficiency and uncontrollable anisotropy of a traditional uniform composite material are solved.

Description

Technical Field

[0001] This invention relates to the field of thermal energy storage materials technology, specifically to a composite phase change material with an adjustable macroscopic layered structure and anisotropic thermal conductivity, and its preparation method. It belongs to the category of composite design and manufacturing technology of medium-temperature thermal storage materials and functional thermal conductive materials, and is applicable to directional thermal energy regulation application scenarios such as industrial waste heat recovery, energy system thermal management, and electronic device heat dissipation. Background Technology

[0002] Against the backdrop of continuous energy structure transformation and increasing industrial energy conservation demands, medium-temperature phase change thermal energy storage technology has become an important technical route in fields such as industrial waste heat recovery, renewable energy peak shaving, and electronic thermal management due to its advantages such as high energy storage density, reusability, and environmental friendliness.

[0003] Among various phase change materials, molten salt inorganic phase change materials (such as lithium nitrate-sodium chloride eutectic salt) are widely regarded as the preferred materials for medium-temperature thermal storage due to their high latent heat of phase change, moderate phase change temperature (generally 200~300℃) and excellent thermal stability.

[0004] However, these materials are usually ionic crystal structures with low intrinsic thermal conductivity, generally less than 0.5 W / (m·K). In practical applications, this often leads to slow heat transfer rates and significant thermal hysteresis during heat storage / release processes, which in turn limits the response speed and power density of the heat storage system, becoming a core bottleneck in engineering applications.

[0005] To improve the overall thermal conductivity of materials, researchers have proposed a composite reinforcement strategy that introduces highly thermally conductive fillers into a phase change matrix. This type of technology uses high thermal conductivity materials such as graphene, expanded graphite, carbon nanotubes, and boron nitride as building blocks for the thermally conductive network, enhancing the material's thermal conductivity through physical doping or compression-induced configuration. For example, patent CN114656939A discloses a composite method that uniformly mixes inorganic salts with expanded graphite and achieves partial filler orientation alignment through compression.

[0006] However, traditional composite strategies still have the following significant shortcomings: 1. The filler is prone to agglomeration or uneven dispersion: In order to obtain an effective heat conduction network, it is often necessary to heat and melt the matrix and mix it with the filler. This process is not only complicated, but may also cause oxidation, decomposition or component segregation of molten salt. 2. High filler content affects energy storage density: In order to improve thermal conductivity, 10~30 wt% of thermally conductive components are usually added, which significantly reduces the content of phase change matrix and causes a decrease in energy storage capacity; 3. Lack of design initiative in the orientation of the thermal conduction structure: Traditional pressing can only induce the directionality of some fillers at the microscale, and the thermal conduction path is uncontrollable, making it difficult to achieve the structural regulation of anisotropic thermal properties at the macroscale.

[0007] Therefore, it is urgent to break through the existing material design method of "uniform composite + passive arrangement", and propose a new composite phase change material and its construction method that can construct a macroscopically ordered thermal conduction structure at a low filler addition amount, achieve controllable anisotropy of thermal conductivity, and have both high energy storage density and high thermal response efficiency. Summary of the Invention

[0008] The purpose of the present invention is to overcome the technical problems existing in the existing uniform composite phase change materials, such as low thermal conduction enhancement efficiency, large loss of energy storage density, and uncontrollable anisotropy of thermal conductivity, and propose a layered composite phase change material based on structure degree regulation and its preparation method with clear structure design, adjustable anisotropy, and strong process adaptability. By constructing a layered structure with alternating stacking of thermal conduction layers and heat storage layers, and introducing "structure degree R" as the core quantitative parameter, the directional improvement of thermal conductivity is achieved at a low filler addition amount while maintaining a high energy storage density.

[0009] To achieve the above purpose, the present invention provides the following technical solutions: In the first aspect, the present invention provides a layered composite phase change material based on structure degree regulation, which includes a plurality of alternating thermal conduction layers and a plurality of heat storage layers.

[0010] The thermal conduction layer is composed of a first high thermal conductivity component, forming an efficient thermal conduction path continuous in the in-plane direction.

[0011] The heat storage layer is composed of a phase change matrix and a second high thermal conductivity component, and has both a heat storage function and a transverse auxiliary thermal conduction function.

[0012] The present invention introduces "layered structure degree R" as the core structure parameter to characterize the interlayer distribution degree of the thermal conduction filler. The layered structure degree R satisfies 0 < R ≤ 1.0, and is defined as the ratio of the total mass m1 of the first high thermal conductivity component in the thermal conduction layer to the total mass (m1 + m2) of all high thermal conductivity components in the material, that is: where m2 is the total mass of the second high thermal conductivity component in the heat storage layer. When R = 0, it represents a traditional uniform composite structure; when R = 1, it means that all high thermal conductivity components are concentrated in the thermal conduction layer, and the heat storage layer does not contain thermal conduction fillers.

[0013] Preferably, the first and second high thermal conductivity components can be the same material, selected from sheet-like or fibrous materials with high intrinsic thermal conductivity such as graphene, expanded graphite, boron nitride, carbon nanotubes, etc.

[0014] The phase change matrix is ​​a molten salt or an organic phase change material. Preferably, the molten salt is a nitrate, chloride, carbonate, or a eutectic thereof. The organic material can be paraffin wax, fatty acids, etc., suitable for medium- and low-temperature thermal storage applications.

[0015] Preferably, the total mass of the high thermal conductivity component accounts for 2 wt% to 15 wt% of the total mass of the composite phase change material, more preferably 4 wt% to 10 wt%. Within this range, the in-plane thermal conductivity can be significantly improved without significantly reducing the energy storage density through structural control.

[0016] Preferably, the ratio of the in-plane thermal conductivity to the out-of-plane thermal conductivity of the composite phase change material is greater than 1.5, more preferably 2.0 or more, and even more preferably 3.0 or more, thereby achieving directional selective conduction of heat flow.

[0017] More preferably, the structural density R ranges from 0.3 ≤ R ≤ 0.7. Experimental results show that the optimal synergistic performance of thermal conductivity and thermal storage can be obtained within this range.

[0018] Secondly, the present invention also provides a method for preparing the above-mentioned layered composite phase change material, comprising the following steps: S1: Provides phase change matrix powder and high thermal conductivity component powder. The powder can be obtained by grinding, ball milling, etc.

[0019] S2: Based on the designed structural density R, a portion of the high thermal conductivity component is used as the thermally conductive layer material, and the remaining portion is mixed with all the phase change matrix powder to form the heat storage layer material. This step is crucial for achieving the target R value.

[0020] S3: Alternately lay the heat-conducting layer material and the heat-storing layer material in the mold, and pre-press (e.g., 50~150 MPa) after each or every two layers to maintain structural stability and form a layered preform.

[0021] S4: The preform is finally pressed and molded, preferably with a pressure of 50 MPa to 300 MPa, more preferably 200 MPa to 250 MPa, to obtain a dense layered composite phase change material.

[0022] Preferably, the thickness ratio of the thermal conductive layer to the thermal storage layer is controlled to be 2:1 to 4:1 during the laying process, more preferably 3:1, in order to optimize the synergistic performance of thermal conductivity and thermal storage density.

[0023] Based on the above technical solution, the layered composite phase change material of the present invention, based on structure degree control, achieves active design and precise control of thermal conductivity anisotropy under low thermal conductivity filler content by constructing alternating stacked thermally conductive and thermally storing layers and introducing a quantifiable layered structure degree R. This structure enables the composite material to have significantly improved thermal conductivity in the in-plane direction while maintaining a high energy storage density, thereby effectively solving the problems of low thermal conductivity enhancement efficiency, large energy storage density loss, and difficulty in controlling thermal conductivity anisotropy in existing homogeneous composite phase change materials.

[0024] Compared to traditional homogeneous phase change materials, this invention employs a composite structure of a "thermal conductive layer + thermal storage layer," forming a macroscopically controllable anisotropic heat conduction path within the material. This breaks through the existing microstructural models that rely solely on uniform powder dispersion and pressing processes. In particular, by defining the key parameter "layered structure degree R," the material's performance is transformed from passive process control to active structural design control, significantly improving the material's engineering applicability and adjustability.

[0025] Furthermore, the preparation method of this invention is simple and easy to scale up for mass production. By distributing a portion of the thermally conductive filler to the thermally conductive layer, and mixing the remaining filler with the phase change matrix to form a heat storage layer, and then employing a layered layup and pressing process, a composite material with a clear hierarchical structure and anisotropic thermal conductivity can be obtained. This method significantly reduces the amount of thermally conductive filler used while ensuring the thermal conductivity of the material, balancing both high thermal conductivity and high energy storage density, thus overcoming the traditional contradiction between "thermal conductivity" and "energy storage" in material design.

[0026] Furthermore, by adjusting parameters such as pressing pressure and the thickness ratio of each layer, the material can be flexibly adapted to the specific requirements of thermal conductivity and heat storage capacity in different application scenarios. For example, in the fields of industrial waste heat utilization, power battery thermal management, or high-power electronic device thermal regulation, the material of this invention can provide targeted thermal management solutions.

[0027] Therefore, the layered composite phase change material with structure degree control capability and its preparation method provided by this invention not only achieve structural optimization and functional synergy in terms of performance, but also show broad engineering application prospects and industrial promotion value in terms of preparation process, material versatility and application adaptability. Attached Figure Description

[0028] To more clearly illustrate the technical solution of the present invention, the embodiments of the present invention will be described below in conjunction with the accompanying drawings. These drawings do not constitute a limitation on the scope of protection of the present invention. Figure 1 This is a schematic diagram of the structural preparation process of the layered composite phase change material of the present invention, showing the overall process of alternately laying and pressing the thermally conductive layer and the thermally storing layer.

[0029] Figure 2 The images show cross-sectional scanning electron microscope (SEM) images and elemental distribution diagrams of the composite phase change material prepared in Example 2 (structure degree R = 0.5), used to illustrate the structural characteristics of the alternating layered distribution of thermally conductive components and phase change matrix on a macroscopic scale.

[0030] Figure 3 The diagram shows a comparison of the in-plane thermal conductivity of composite phase change materials with different layered structure degrees (R) prepared in Comparative Example 1 and Examples 1-4, illustrating the influence trend of structure degree regulation on in-plane thermal conductivity.

[0031] Figure 4 The diagram shows a comparison of the out-of-plane thermal conductivity of composite phase change materials with different structure degrees (R) prepared in Comparative Example 1 and Examples 1-4, illustrating the suppressive effect of structural design on vertical thermal conductivity.

[0032] Figure 5 This is a schematic diagram of a typical layered structure of the layered composite phase change material of the present invention, illustrating the alternating stacking arrangement of the heat-conducting layer and the heat-storing layer in the thickness direction. Detailed Implementation

[0033] To more clearly illustrate the technical features and implementation path of the present invention, the following describes in detail the structural design, preparation method, and performance of the layered composite phase change material of the present invention through several preferred embodiments and in conjunction with the accompanying drawings. The specific contents include: raw material selection and general process flow, typical sample construction schemes under different structure degrees (R) conditions, experimental verification results of material structure and thermal conductivity, and related comparisons and conclusions. Through these embodiments, the practical feasibility and technical advantages of the "structure degree regulation" mechanism proposed in this invention in constructing anisotropic thermal conductivity networks can be fully demonstrated.

[0034] It should be noted that the following embodiments are merely preferred embodiments of the present invention and are used to assist in understanding the technical essence of the present invention. They should not be construed as limiting the scope of protection. All equivalent adjustments, substitutions, or functional optimizations made based on the disclosure of the present invention should be included within the scope of protection of the present invention.

[0035] I. Overview of Implementation Methods The technical solution of the present invention will be further described below with reference to specific embodiments. It should be noted that the types of raw materials, proportions, process parameters, and structural designs (such as layered structure degree R, number of layers, thickness ratio, etc.) used in the embodiments are all for the purpose of more clearly demonstrating the core solution and technical effects of the present invention, and should not be construed as limiting the present invention.

[0036] The essence of this invention lies in defining and controlling the layered structure degree R to distribute high thermal conductivity components to the thermally conductive layer and the thermal storage layer in a set ratio, thereby constructing a composite material with a macroscopically ordered layered structure. This design significantly improves the in-plane thermal conductivity of the material while reducing the amount of filler used and maintaining a high energy storage density, achieving synergistic optimization of thermal conductivity anisotropy and thermal storage performance.

[0037] In practical implementation, those skilled in the art can adjust the following aspects according to actual application needs without departing from the concept of the present invention: High thermal conductivity components: In addition to expanded graphite, materials with high thermal conductivity and orientation properties such as graphene, boron nitride, and carbon nanotubes can also be selected; Phase change matrix: Organic phase change materials (such as paraffin, fatty acids) or molten salts and their eutectics of different systems can be selected according to the operating temperature range; Structural parameters such as layered structure degree R, pressing pressure, layer thickness ratio, and number of layers can all be adaptively adjusted according to the required thermal conductivity and structural strength. Molding process: In addition to the pressing process, hot pressing, interlayer melt composite, hot rolling and other methods can also be used to achieve the integration of layered structures.

[0038] The above embodiments are merely illustrative examples, and the scope of protection of this invention is defined by the claims. All equivalent substitutions or reasonable modifications made based on the concept of this invention should be included within the scope of protection of this invention.

[0039] II. Material Preparation and General Manufacturing Process The layered composite phase change material described in this invention achieves the design-controlled anisotropy of thermal conductivity by constructing an alternating stacked system of thermally conductive and thermally stored layers with an adjustable layered structure degree R. Figure 1 The typical preparation process of this material is demonstrated, including raw material preparation, structure distribution, alternating layup and pre-compression, and final pressing and molding, as detailed below: 1. Raw material preparation This invention uses inorganic molten salt and high thermal conductivity carbon material to form a composite phase change thermal storage system.

[0040] Phase change matrix: A lithium nitrate (LiNO3) and sodium chloride (NaCl) eutectic molten salt with a mass ratio of 87:13 is preferred, as it has a moderate melting point and good thermal stability, making it suitable for medium-temperature thermal storage scenarios. After initial crushing of the eutectic salt, the particle size is refined by ball milling.

[0041] Ball milling conditions: Zirconia balls were used as the grinding media, the ball-to-material ratio was 15:1, the rotation speed was set to 400 rpm, and ball milling was carried out for 4 hours using alternating forward and reverse rotation. After ball milling, the powder is sieved through a 300-mesh sieve and vacuum dried at 60°C for 2 hours to obtain a phase change matrix powder with uniform particle size distribution and good flowability.

[0042] High thermal conductivity component: Expanded graphite is preferred as a filler due to its flake structure, high intrinsic thermal conductivity, and good compactability, which facilitates the formation of an in-plane thermally conductive network during the pressing process. The total amount of expanded graphite added accounts for 10 wt% of the composite material mass, and the specific distribution ratio between the thermally conductive layer and the thermal storage layer is determined based on the structure degree R value.

[0043] 2. Structural density R design and filler distribution To achieve controllability of the thermally conductive structure, this invention introduces "layered structure degree R" as a structural quantification parameter. R is defined as the ratio of the mass m1 of the first high thermal conductivity component in the thermally conductive layer to the total mass (m1 + m2) of all high thermal conductivity components in the material, i.e.: Where m2 is the mass of the second highest thermal conductivity component in the thermal storage layer. By setting the R value, a primary-secondary structural relationship of thermal conductivity distribution can be established between the pure thermal conductivity layer and the hybrid thermal storage layer.

[0044] The packing distribution method is as follows: Determine m1 and m2 based on the target R value; m1 parts of expanded graphite were used alone as the thermal conductive layer material; m2 parts of expanded graphite were mixed evenly with the dried molten salt matrix to serve as the heat storage layer material. The mixing method employs mechanical stirring or dry high-speed mixing to ensure that the thermally conductive filler is uniformly dispersed in the matrix and to avoid agglomeration.

[0045] 3. Layered laying and preloading (corresponding to) Figure 1 Intermediate layer steps) The heat-conducting layer material and the heat-storing layer material are sequentially laid into the mold and stacked alternately. The preferred laying method is as follows: After each layer of heat-conducting or heat-storing layer is laid, pre-compression pressure is applied to ensure tightness and interlayer bonding. The pre-compression pressure is preferably 100 MPa to ensure stable positioning of the powder in the mold; The total number of stacked layers can be set to an odd number (such as 7 layers) depending on the sample size, and the thermal conductive layers are located at the top and bottom to enhance the continuity of the in-plane thermal conductive network.

[0046] The thickness ratio of the heat storage layer to the heat conduction layer is preferably set between 2:1 and 4:1. The specific value can be selected according to the performance balance requirements, with a preferred value of 3:1.

[0047] The above-mentioned structure, in which the heat-conducting layer and the heat storage layer are laid alternately, is as follows: Figure 5As shown in the figure, the layered stacking configuration of the typical composite material of the present invention is illustrated. The heat-conducting layer and the heat-storing layer are arranged sequentially along the thickness direction, forming a layered structure with directional heat-conducting channels, which provides a continuous physical basis for improving in-plane thermal conductivity.

[0048] 4. Final pressing and shaping After alternating layering and pre-compression, the preform is pressed into shape as a whole in a mold: The pressing pressure setting range is 50 MPa to 300 MPa, preferably 200 MPa to 250 MPa; Setting the pressure holding time to 2 minutes helps to build a dense and stable layered structure; After pressing, the pressure is slowly released and the sample is demolded and allowed to cool naturally to room temperature to obtain a layered composite phase change material block with a clear structure and consistent thickness.

[0049] III. Implementation Examples and Comparative Examples Example 1 (partially layered structure, R = 0.3) The composite phase change material in this embodiment is made from the following raw materials: 90 parts of binary eutectic molten salt and 10 parts of expanded graphite, of which 3.0 parts of expanded graphite are used to construct the thermally conductive layer and the remaining 7.0 parts are mixed with the phase change matrix to form a heat storage layer. Its layered structure degree R=0.3, representing a composite structure in which the thermally conductive components are partially concentrated in the thermally conductive layer.

[0050] Preparation method: The binary eutectic molten salt block was pre-crushed and then placed in a planetary ball mill with zirconia grinding balls at a ball-to-material ratio of 15:1. The ball milling was carried out at 400 rpm in alternating forward and reverse rotation mode for 4 hours. The milled material was passed through a 300-mesh sieve and then vacuum dried at 60℃ for 2 hours to obtain a dry phase change matrix powder.

[0051] 7.0 parts of expanded graphite were mixed evenly with all the molten salt powder in a mechanical stirrer to form a heat storage layer material; the remaining 3.0 parts of expanded graphite were used separately as a heat conduction layer material.

[0052] The thermally conductive layer and the thermally stored layer are alternately laid in the mold, for a total of 7 layers, starting and ending with the thermally conductive layer. After each layer is laid, a pre-pressure of 100 MPa is applied to ensure a dense structure. After the layup is completed, the material is pressed and molded under a pressure of 250 MPa and held for 2 minutes. After demolding and cooling, a composite phase change material with a partially layered structure is obtained.

[0053] Example 2 (Collaborative optimization structure, R = 0.5) The composite phase change material in this embodiment is made from the following raw materials: 90 parts of binary eutectic molten salt and 10 parts of expanded graphite, of which 5.0 parts of expanded graphite are used to construct the thermally conductive layer and the remaining 5.0 parts are mixed with the phase change matrix to form a heat storage layer. Its layered structure degree R=0.5, which represents the structural form in which the thermally conductive components are equally distributed in the thermally conductive layer and the heat storage layer.

[0054] Preparation method: The binary eutectic molten salt block was pre-crushed and then placed in a planetary ball mill with zirconia grinding balls at a ball-to-material ratio of 15:1. The ball milling was carried out at 400 rpm in alternating forward and reverse rotation mode for 4 hours. The milled material was passed through a 300-mesh sieve and then vacuum dried at 60℃ for 2 hours to obtain a dry phase change matrix powder.

[0055] 5.0 parts of expanded graphite were mixed evenly with all the molten salt powder in a mechanical stirrer to form a heat storage layer material; the remaining 5.0 parts of expanded graphite were used separately as a heat conduction layer material.

[0056] In a mold, thermally conductive and heat-storing layers are alternately laid in sequence, for a total of 7 layers, starting and ending with the thermally conductive layer. After each layer is laid, a pre-pressure of 100 MPa is applied to initially densify the powder and form a stable layered structure. After laying, the material is finally pressed and molded under a pressure of 250 MPa, held for 2 minutes, demolded, and cooled to obtain a layered composite phase change material with optimized structure.

[0057] Scanning electron microscopy (SEM) revealed that the thermally conductive components and the matrix were regularly alternating, with clear layered interfaces, validating the effectiveness of the macroscopic structural design. This structure exhibits optimal synergistic performance in balancing high in-plane thermal conductivity and high heat storage density.

[0058] Example 3 (emphasis on thermally conductive structure, R = 0.7) The composite phase change material in this embodiment is made from the following raw materials: 90 parts of binary eutectic molten salt and 10 parts of expanded graphite, of which 7.0 parts of expanded graphite are used to construct the thermally conductive layer and the remaining 3.0 parts are mixed with the phase change matrix to form a heat storage layer. Its layered structure degree R=0.7, which represents a structural form in which a large proportion of the thermally conductive components are concentrated in the thermally conductive layer.

[0059] Preparation method: The binary eutectic molten salt block was pre-crushed and then placed in a planetary ball mill with zirconia grinding balls at a ball-to-material ratio of 15:1. The ball milling was carried out at 400 rpm with alternating forward and reverse rotation for 4 hours. After ball milling, the powder was passed through a 300-mesh sieve and vacuum dried at 60℃ for 2 hours to obtain a phase change matrix powder with uniform particle size.

[0060] 3.0 parts of expanded graphite were mixed evenly with all the dried molten salt powder in a mechanical stirrer to form a heat storage layer material; the remaining 7.0 parts of expanded graphite were used separately as a heat conduction layer material.

[0061] Seven layers of thermally conductive and heat-storing materials were alternately laid in a mold, with the thermally conductive layers located at the top and bottom. A pre-pressure of 100 MPa was applied after each layer to maintain good contact and structural stability between layers. After all layers were laid, the entire structure was pressed and molded under 250 MPa pressure, held under pressure for 2 minutes, and then demolded and cooled to obtain a layered composite phase change material with high structural density.

[0062] In this sample structure, the thermally conductive filler is highly enriched in the thermally conductive layer, forming a continuous thermally conductive network. However, due to the reduced proportion of thermally conductive components in the heat storage layer, the interconnectivity of the interlayer thermally conductive network is relatively weakened, making it suitable for application scenarios with higher requirements for internal thermal conductivity.

[0063] Example 4 (Completely layered structure, R = 1.0) The composite phase change material in this embodiment is made from the following raw materials: 90 parts of binary eutectic molten salt and 10 parts of expanded graphite. All 10.0 parts of expanded graphite are used to construct the thermally conductive layer. The heat storage layer is composed only of pure phase change matrix and does not contain thermally conductive components. Its layer structure degree R=1.0, which represents a completely separated structure in which all thermally conductive fillers are concentrated in the thermally conductive layer.

[0064] Preparation method: The binary eutectic molten salt block was pre-crushed and then placed in a planetary ball mill with zirconia grinding balls at a ball-to-material ratio of 15:1. The ball milling was carried out at 400 rpm in alternating forward and reverse rotation mode for 4 hours. After ball milling, the powder was sieved through a 300-mesh sieve and then vacuum dried at 60℃ for 2 hours to obtain a dry phase change matrix powder.

[0065] Since the heat storage layer does not contain any thermally conductive fillers, all dry molten salt powder is used directly as the heat storage layer material; 10.0 parts of expanded graphite are used separately as the thermally conductive layer material.

[0066] Seven layers of thermally conductive and thermally storing materials were alternately laid in a mold, with four thermally conductive layers and three thermally storing layers, forming a symmetrical structure. The thermally conductive layers were located on the outermost layer. A pre-pressure of 100 MPa was applied after each layer to fix the structural layers. After laying, the entire structure was pressed and molded under a pressure of 250 MPa for 2 minutes, then cooled and demolded to obtain a fully layered composite phase change material.

[0067] In this sample structure, all the thermally conductive components are concentrated in the pure thermally conductive layer, resulting in a clear and highly directional thermal conduction path. However, the thermal conduction channel between the heat storage layer and the thermally conductive layer is blocked by the interface, leading to a large interlayer thermal resistance and the lowest out-of-plane thermal conductivity. This structure is suitable for applications requiring extremely high directional heat flow, such as directional insulation or in-plane rapid heat dissipation systems.

[0068] Figure 5This illustration shows a typical alternating structural layout of the heat-conducting layer and the heat storage layer constructed in this embodiment. The interlayer distribution is clear, and the different design schemes with contrasting structural degree R values ​​are representative.

[0069] IV. Performance Testing and Structural Analysis To evaluate the effect of different structures R on the thermal conductivity of the composite phase change material, the samples prepared in Comparative Example 1 and Examples 1-4 were subjected to microstructural observation and thermal conductivity testing. All test samples were bulk materials obtained by pressing, with dimensions of approximately 10 mm × 10 mm × 8 mm.

[0070] 1. Microstructure analysis Taking the composite phase change material sample prepared in Example 2 (structure degree R = 0.5) as an example, its cross-sectional structure was analyzed by energy dispersive spectroscopy (EDS). The analysis results are as follows: Figure 2 As shown: Figure 2 The elemental distribution diagram of the sample clearly shows that the material exhibits a typical layered structure along the thickness direction, with alternating stacked thermal conductive and thermal storage layers, smooth interfaces, and good interlayer bonding. C element (expanded graphite) is mainly enriched in the thermally conductive layer, exhibiting a continuous and dense distribution, which constitutes a good in-plane thermal conduction path. The Na element (eutectic salt) was uniformly distributed in the heat storage layer area, the filler was well dispersed, and no obvious agglomeration was observed. The above microstructure characterization results fully verify that the layered thermal conductive structure achieved by the present invention through structural degree R design has been effectively constructed on a macroscopic scale. This structure helps to significantly improve in-plane thermal conductivity while maintaining the stability of the overall material structure, providing a structural basis and physical support for achieving anisotropic thermal management performance.

[0071] 2. Thermal conductivity test The in-plane and out-of-plane thermal conductivity of the samples were tested using the steady-state heat flow method (instrument model: DRL-VI thermal conductivity meter, Xiangtan Xiangyi Instrument Co., Ltd.). The heat flow direction was set as follows: In-plane thermal conductivity test: The direction of heat flow is parallel to the arrangement direction of the layered structure (thermal conductive layer); Out-of-plane thermal conductivity test: The direction of heat flow is perpendicular to the layered structure, that is, through multiple layer interfaces.

[0072] Each sample group was tested three times, and the average value was taken as the final result. Test data are as follows: Figure 3 and Figure 4 As shown, the specific analysis is as follows: Figure 3 In-plane thermal conductivity vs. R-value The in-plane thermal conductivity of the Comparative Example 1 (R=0) sample is 19.20 W / (m·K), which is uniformly distributed. As the R value increases, the in-plane thermal conductivity increases significantly; It reaches its peak value of approximately 27.67 W / (m·K) at R = 0.5 (Example 2); When R continues to increase to 0.7 and 1.0, the in-plane thermal conductivity decreases slightly because the thermally conductive components in the thermal storage layer are insufficient, affecting the network interconnection.

[0073] Figure 4 Out-of-plane thermal conductivity vs. R value Comparative Example 1 (R=0) has the highest out-of-plane thermal conductivity, approximately 9.83 W / (m·K); As the R value increases, the out-of-plane thermal conductivity continues to decrease; It decreased to the lowest level, approximately 4.57 W / (m·K), when R=1.0 (Example 4); The reason is that under high R values, the heat-conducting layer and the heat storage layer are completely separated, and the heat flow passes through multiple interfaces in the vertical direction, resulting in significant superposition of interface thermal resistance.

[0074] 3. Summary of Results and Analysis of Patterns This invention achieves the directional designability of the thermal conductivity of composite materials by adjusting the structure degree R value; Within the R=0.3~0.7 range, the material achieves an excellent synergy between high in-plane thermal conductivity and reasonable out-of-plane control; Especially around R=0.5, the material's thermal conductivity network forms an "interconnected + interlocked" structure, achieving the optimal balance of thermal performance; Compared with the traditional uniform structure (R=0), the present invention significantly improves performance without changing the total filler content; This demonstrates that the design concept of "structure-driven thermal performance" is superior to the traditional model of "uniform composite + random arrangement".

[0075] In summary, this invention, by constructing a macroscopic layered structure with adjustable structural density R, enables composite phase change materials to achieve synergistic optimization of high in-plane thermal conductivity and high energy storage density with low filler content, overcoming the technical bottlenecks of low efficiency in improving thermal conductivity and uncontrollable structure in traditional homogeneous composite materials. Combining reasonable raw material selection, structural design parameters, and pressing processes, this invention proposes a composite material construction approach that synergistically evolves structural design and thermal conductivity, providing a novel material solution for medium-temperature thermal energy management systems, and possessing significant engineering application value and promising prospects for widespread application.

[0076] The technical solution disclosed in this invention has been verified through comparative embodiments under multiple structural conditions, demonstrating significant feasibility and stability. The disclosed design method also has reference value for other thermal storage systems with directional heat conduction requirements.

[0077] It should be understood that the specific embodiments described above are only used to illustrate the principles and technical solutions of the present invention, and are intended to help those skilled in the art understand and implement the present invention, rather than to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements or variations made without departing from the spirit and substance of the present invention should be covered within the scope of protection defined by the claims of the present invention.

Claims

1. A layered composite phase change material based on structure degree regulation, characterized in that, It includes multiple thermally conductive layers and multiple thermal storage layers that are stacked alternately; The thermally conductive layer is composed of a first high thermal conductivity component; The thermal storage layer is composed of a phase change matrix and a second high thermal conductivity component; The material has a layered structure degree R, and satisfies 0 < R ≤ 1.0, where R is the ratio of the total mass m1 of the first high thermal conductivity component constituting all the thermally conductive layers to the total mass (m1 + m2) of all high thermal conductivity components in the material, calculated by the following formula: Where m2 is the total mass of the second high thermal conductivity component that constitutes all of the heat storage layers.

2. The layered composite phase change material according to claim 1, characterized in that, The first high thermal conductivity component and the second high thermal conductivity component are made of the same material.

3. The layered composite phase change material according to claim 1, characterized in that, The high thermal conductivity component is selected from at least one of graphene, carbon nanotubes, boron nitride, or expanded graphite.

4. The layered composite phase change material according to claim 1, characterized in that, The phase change matrix is ​​a molten salt or an organic phase change material.

5. The layered composite phase change material according to claim 4, characterized in that, The molten salt is at least one of nitrate, chloride, carbonate, or a eutectic mixture thereof.

6. The layered composite phase change material according to claim 1, characterized in that, The total mass of the high thermal conductivity component accounts for 2 wt% to 15 wt% of the total mass of the composite phase change material.

7. The layered composite phase change material according to claim 1, characterized in that, The ratio of the in-plane thermal conductivity to the out-of-plane thermal conductivity of the composite phase change material is greater than 1.

5.

8. A method for preparing a layered composite phase change material as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1: Provides phase change matrix powder and high thermal conductivity component powder; S2: Based on the target layered structure degree R, a portion of the high thermal conductivity component powder is used as a thermally conductive layer material, and the remaining high thermal conductivity component powder is mixed with all of the phase change matrix powder to serve as a heat storage layer material. S3: In the mold, the heat-conducting layer material and the heat-storing layer material are alternately laid layer by layer and pre-pressed to form a layered preform; S4: Press the layered preform to obtain the layered composite phase change material; The layered structure degree R is adjusted by controlling the mass of the high thermal conductivity component laid in the thermally conductive layer.

9. The preparation method according to claim 8, characterized in that, The compression molding pressure is from 50 MPa to 300 MPa.

10. The preparation method according to claim 8, characterized in that, The thickness ratio of the heat storage layer to the heat-conducting layer is 2:1 to 4:1.

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