Alkali-activated metakaolin composite molten salt phase change heat storage material and preparation method thereof

Abstract

The invention relates to the technical field of phase change heat storage materials, in particular to an alkali-activated metakaolin composite molten salt phase change heat storage material and a preparation method thereof. The preparation method comprises the following steps: uniformly mixing metakaolin and a fused salt phase change material, adding an aqueous solution of an alkali activator, uniformly stirring, and carrying out compression molding to obtain a raw material blank; and curing and drying the raw material green body at 50-90 DEG C under a sealing condition to obtain the alkali-activated metakaolin composite molten salt phase change heat storage material. The alkali-activated metakaolin is used as a matrix, the fused salt is used as a phase change medium, the fused salt can be packaged in the alkali-activated metakaolin through normal-temperature pressing, and the fused salt phase change heat storage material with excellent mechanical strength and a stable structure is obtained; in the alkali-activated metakaolin composite molten salt phase change heat storage material, an N-A-S-H framework can be generated through reaction in a low-temperature interval of 50-90 DEG C, the excitation reaction is mild, energy consumption procedures such as traditional sintering or cold pressing-high-temperature sintering are not needed, the process route is greatly shortened, and energy consumption is remarkably reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of phase change heat storage materials, in particular to an alkali-activated metakaolin composite molten salt phase change heat storage material and a preparation method thereof. BACKGROUND

[0002] With the growth of global energy demand and the highlighting of environmental problems, the sustainable development of energy has become a major challenge, and it is crucial to develop and utilize renewable energy such as solar energy and wind energy. However, renewable energy such as solar energy and wind energy has intermittency and instability, and needs to be combined with heat storage technology to improve its utilization efficiency and stability.

[0003] Molten salt phase change heat storage technology has great advantages in the field of heat storage due to its high temperature stability, high heat storage density, nearly constant temperature in the charging and discharging process, easy access to raw materials and low cost. However, traditional molten salt phase change heat storage materials have the disadvantages of corrosion, morphological change at high temperature and low thermal conductivity, which limit their wide application. In order to solve these problems, researchers use porous ceramics, expanded graphite, foam metals and other matrix materials to encapsulate them, but the process is complex, high-temperature adsorption is required, and the cost is high, which makes it difficult to be applied on a large scale.

[0004] In recent years, the technology of preparing molten salt composite phase change materials by cold pressing-sintering method has developed rapidly, and the matrix materials used are mostly solid waste such as steel slag and red mud, which has the advantages of simple process and low cost. However, this technology does not consider the mechanical stability at high temperature, and the encapsulation amount of phase change materials is small, which has the risk of cracking and leakage after multiple thermal cycles. In addition, the double-tank molten salt phase change energy storage technology commonly used in solar thermal power generation technology has the problem of limited application on small energy storage facilities, while the single-tank energy storage technology has the advantages of low initial investment cost and small space occupation, but has the problems of thermocline control difficulty, reliability problem under high temperature gradient and heat collection efficiency.

[0005] Therefore, it is urgent to develop a new type of molten salt phase change heat storage material. SUMMARY

[0006] The present application provides an alkali-activated metakaolin composite molten salt phase change heat storage material and a preparation method thereof, which aims to solve the technical problems of poor structural stability, easy leakage and low thermal conductivity of existing molten salt phase change materials.

[0007] In order to achieve the above purpose, the following technical solutions are adopted.

[0008] The first aspect of the present application provides a preparation method of an alkali-activated metakaolin composite molten salt phase change heat storage material, comprising:

[0009] S1, mix metakaolin and molten salt phase change material evenly, then add an aqueous solution of alkali activator and stir evenly, then press and shape to obtain raw material blank;

[0010] S2, the raw material blanks are cured and dried at 50~90 ℃ under sealed conditions to obtain alkali-activated metakaolin composite molten salt phase change thermal storage material.

[0011] Preferably, the molten salt phase change material includes any one of sodium nitrate, potassium nitrate, lithium nitrate, sodium chloride, potassium chloride, calcium chloride, or magnesium chloride;

[0012] The alkaline activator is sodium hydroxide or sodium silicate.

[0013] Preferably, the mass ratio of metakaolin, molten salt phase change material and alkali activator is 20~50:50~80:9~15;

[0014] The total mass fraction of metakaolin, phase change material and alkali activator is 100 parts.

[0015] Preferably, the concentration of the aqueous solution of the alkaline activator is 6~16 mol / L.

[0016] Preferably, the particle size of the molten salt phase change material is less than 0.1 mm.

[0017] Preferably, the pressing pressure is 1~40 MPa and the time is 1~10 min.

[0018] Preferably, the curing time is 10~48 h.

[0019] Preferably, the drying temperature is 60~150 ℃ and the drying time is 10~48 h.

[0020] A second aspect of this application provides a composite molten salt phase change thermal storage material prepared by the above-described preparation method.

[0021] A third aspect of this application provides the application of the aforementioned composite molten salt phase change thermal storage material in the field of phase change energy storage.

[0022] Compared with the prior art, the beneficial effects of this application are as follows:

[0023] This application uses alkali-activated metakaolin as the matrix and molten salt as the phase change medium. Molten salt is encapsulated within the alkali-activated metakaolin through room-temperature pressing, resulting in a molten salt phase change thermal storage material with excellent mechanical strength and structural stability. In this application, the NASH gel generated from the alkali-activated metakaolin reaction exhibits excellent high-temperature resistance and chemical stability. It maintains structural integrity even during molten salt liquefaction and retains its framework without collapsing at 700-800 °C. The matrix and molten salt have good chemical compatibility and excellent interfacial bonding. Its thermal storage performance remains undiminished after multiple thermal cycles, demonstrating high thermal storage capacity. Furthermore, the alkali-activated metakaolin matrix of this application has a porous structure, which buffers the volume expansion during the solid-liquid phase change of the molten salt and provides a channel for residual water vapor to escape, preventing internal pressure cracking. The structure remains intact after repeated thermal cycles, further improving structural stability.

[0024] In the alkali-activated metakaolin composite molten salt phase change thermal storage material of this application, the NASH framework can be generated in a low temperature range of 50-90 ℃. The alkali activation reaction is mild and does not require energy-consuming processes such as traditional sintering or cold pressing-high temperature sintering. The process route is greatly shortened and energy consumption is significantly reduced. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the mechanism of the alkali-activated metakaolin composite molten salt phase change thermal storage material of this application; the figures are labeled as follows: 1. metakaolin; 2. molten salt phase change material; 3. alkali activator; 4. polymerization product NASH gel;

[0027] Figure 2 This is a photograph of the composite molten salt phase change thermal storage material of Example 1 after thermal cycling testing;

[0028] Figure 3 This is a DSC test curve of the composite molten salt phase change thermal storage material after thermal cycling in Example 1;

[0029] Figure 4 The images show the XRD patterns of the composite molten salt phase change thermal storage materials before and after thermal cycling in the examples and comparative examples. Detailed Implementation

[0030] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0031] In the following description of this embodiment, the terms "including", "comprising", "having", and "containing" are all open-ended terms, meaning that they include but are not limited to.

[0032] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0033] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0034] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0035] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0036] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood as each intermediate value between the upper and lower limits of the specifically disclosed range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0037] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0038] In a first aspect, this application provides a method for preparing an alkali-activated metakaolin composite molten salt phase change thermal storage material, comprising:

[0039] S1, mix metakaolin and molten salt phase change material evenly, then add an aqueous solution of alkali activator and stir evenly, then press and shape to obtain raw material blank;

[0040] In this application, the molten salt phase change material includes any one of sodium nitrate, potassium nitrate, lithium nitrate, sodium chloride, potassium chloride, calcium chloride, or magnesium chloride, preferably sodium nitrate; wherein, the particle size of the molten salt phase change material is preferably less than 0.1 mm.

[0041] The alkaline activator can be sodium hydroxide or sodium silicate; in this application, it is preferred to dissolve the alkaline activator in water to prepare a solution with a concentration of 6~16 mol / L to improve the alkaline activation effect.

[0042] In this application, the mass ratio of metakaolin, molten salt phase change material and alkali activator is 20~50:50~80:9~15; wherein the sum of the mass parts of metakaolin, phase change material and alkali activator is 100 parts.

[0043] In this application, it is preferred that the raw material is pressed into a rectangular or cylindrical shape, and the pressing pressure is 1~40 MPa and the time is 1~10 min.

[0044] S2, the raw material blank is cured at 50~90 ℃ and under sealed conditions for 10~48 h and then dried to obtain alkali-activated metakaolin composite molten salt phase change thermal storage material.

[0045] The alkali-activated metakaolin framework structure formation process described in this application involves dissolving and repolymerizing the active components in metakaolin through an alkali activation reaction (alkali-activation process) to form a gel with a three-dimensional network structure, which serves as the matrix material. The specific reaction mechanism is as follows: the main components of metakaolin are silicates (SiO2) and aluminates (Al2O3), as well as small amounts of metal oxides such as titanium, iron, calcium, and potassium. Under the action of the activator NaOH, the silicates and aluminates of metakaolin first undergo a dissolution reaction to form soluble silicate ions (SiO4).4- ) and aluminate (AlO4) 5- In an alkaline environment, dissolved silicate and aluminate ions recombine through polymerization to form a three-dimensional network structure NASH (sodium-aluminum-silicon-water) gel. This NASH gel possesses a three-dimensional network structure, which provides the material's skeletal support and exhibits good mechanical strength and thermal stability. The silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra in the NASH gel are connected by oxygen bridges, forming a stable framework, while sodium ions exist as cations balancing the charge within the network structure. This application uses alkali-activated metakaolinite as the matrix and molten salt as the phase change medium. Molten salt can be encapsulated within alkali-activated metakaolinite through room-temperature pressing, resulting in a molten salt phase change thermal storage material with excellent mechanical strength and structural stability. The mechanism is as follows: Figure 1 As shown, 1 is metakaolin, 2 is molten salt phase change material, 3 is alkali activator, and 4 is the polymer product NASH gel.

[0046] The purpose of this application for curing under sealed conditions is to block carbon dioxide in the air, prevent carbon dioxide from reacting with the activator, and reduce the evaporation of moisture at high temperatures. Since moisture is the solvent for dissolving metakaolin as an activator and the medium for final polymerization, sealed curing is necessary.

[0047] In this application, the purpose of drying is to remove free water and prevent structural damage caused by sudden boiling of moisture during high-temperature heat storage. The drying temperature is preferably 60~150 ℃, and the drying time is preferably 10~48 h.

[0048] In the alkali-activated metakaolin composite molten salt phase change thermal storage material of this application, the NASH framework can be generated in a low temperature range of 50-90 ℃. The activation reaction is mild and does not require energy-consuming processes such as traditional sintering or cold pressing-high temperature sintering. The process route is greatly shortened and energy consumption is significantly reduced.

[0049] The composite molten salt phase change thermal storage material prepared in this application exhibits excellent mechanical strength and high structural stability. The NASH gel generated by the alkali-activated metakaolin reaction possesses outstanding high-temperature resistance and chemical stability, maintaining structural integrity even during molten salt liquefaction and preventing framework collapse at 700-800 °C. The matrix and molten salt exhibit good chemical compatibility and excellent interfacial bonding, with no degradation in thermal storage performance after multiple thermal cycles, demonstrating high thermal storage capacity. Furthermore, the alkali-activated metakaolin matrix of this application has a porous structure, which can buffer the volume expansion during the solid-liquid phase change of molten salt and provide a channel for residual water vapor to escape, preventing internal pressure cracking. The structure remains intact after repeated thermal cycles, further improving structural stability.

[0050] Based on the excellent mechanical strength, high structural stability and high thermal storage performance of the composite molten salt phase change thermal storage material of this application, it can be widely used in the field of phase change energy storage.

[0051] The present application will be further illustrated by the following examples.

[0052] Example 1

[0053] This embodiment provides a method for preparing an alkali-activated metakaolin composite molten salt phase change thermal storage material, wherein each component is specified by weight. Specifically, it includes:

[0054] S1. Weigh 9 parts of NaOH and add it to 6.15 parts of water. Stir to dissolve and obtain the activator solution. Let it stand for 24 hours before use. Weigh 50 parts of sodium nitrate and 41 parts of metakaolin. Mix the metakaolin and sodium nitrate evenly to form a dry mixture. Then add the activator solution to the dry mixture and stir in a stirring device for 6 minutes.

[0055] Using a pressing mold, 3 g of the well-mixed material is pressed in the mold at a pressure of 10 MPa for 2 minutes to form a cylindrical raw material blank.

[0056] S2, the raw material blank is isolated from the outside air and sealed and cured at 80 ℃ for 24 h, and the cured material blank is dried at 105 ℃ for 24 h to obtain alkali-activated metakaolin composite molten salt phase change thermal storage material.

[0057] Example 2

[0058] This embodiment provides a method for preparing an alkali-activated metakaolin composite molten salt phase change thermal storage material, wherein each component is specified by weight. Specifically, it includes:

[0059] S1. Weigh 15 parts of NaOH and add it to 5.25 parts of water. Stir to dissolve and obtain the activator solution. Let it stand for 24 hours before use. Weigh 50 parts of sodium nitrate and 35 parts of metakaolin. Mix the metakaolin and sodium nitrate evenly to form a dry mixture. Then add the activator solution to the dry mixture and stir in a stirring device for 6 minutes.

[0060] Using a pressing mold, 3 g of the well-mixed material is pressed in the mold at a pressure of 10 MPa for 2 minutes to form a cylindrical raw material blank.

[0061] S2, the raw material blank is isolated from the outside air and sealed and cured at 80 ℃ for 24 h, and the cured material blank is dried at 105 ℃ for 24 h to obtain alkali-activated metakaolin composite molten salt phase change thermal storage material.

[0062] Example 3

[0063] This embodiment provides a method for preparing an alkali-activated metakaolin composite molten salt phase change thermal storage material, wherein each component is specified by weight. Specifically, it includes:

[0064] S1. Weigh 15 parts of NaOH and add it to 5.25 parts of water. Stir to dissolve and obtain the activator solution. Let it stand for 24 hours before use. Weigh 60 parts of sodium nitrate and 25 parts of metakaolin. Mix the metakaolin and sodium nitrate evenly to form a dry mixture. Then add the activator solution to the dry mixture and stir in a stirring device for 6 minutes.

[0065] Using a pressing mold, 3 g of the well-mixed material is pressed in the mold at a pressure of 10 MPa for 2 minutes to form a cylindrical raw material blank.

[0066] S2, the raw material blank is isolated from the outside air and sealed and cured at 80 ℃ for 24 h, and the cured material blank is dried at 105 ℃ for 24 h to obtain alkali-activated metakaolin composite molten salt phase change thermal storage material.

[0067] Comparative Example 1

[0068] This embodiment provides a method for preparing an alkali-activated metakaolin composite molten salt phase change thermal storage material, wherein each component is specified by weight. Specifically, it includes:

[0069] S1, change the amount of NaOH to 3 parts and the amount of water to 7.05 parts; the rest are the same as in Example 1.

[0070] S2 is the same as in Example 1.

[0071] Comparative Example 2

[0072] This embodiment provides a method for preparing an alkali-activated metakaolin composite molten salt phase change thermal storage material, wherein each component is specified by weight. Specifically, it includes:

[0073] S1, the amount of sodium nitrate was changed to 80 parts, and the rest was the same as in Example 1.

[0074] S2 is the same as in Example 1.

[0075] The composite molten salt phase change thermal storage material samples (φ18mm) prepared in the examples and comparative examples were tested as follows:

[0076] 1. The samples were subjected to thermal cycling tests in a muffle furnace at 250 ℃~350 ℃, with a heating and cooling rate of 5 ℃ / min and a holding time of 30 min. The thermal cycles were 0, 1 and 50 times.

[0077] 2. The mechanical strength of the sample after thermal cycling was tested using an electronic universal testing machine, with a loading rate of 0.5 MPa / s.

[0078] 3. High-temperature cyclic thermal storage performance test, the specific method is as follows: DSC test is performed on the samples after 0 and 50 cycles in the above thermal cycling test.

[0079] 4. High-temperature cyclic chemical stability test, the specific method is as follows: XRD test is performed on the samples after 0 and 50 cycles in the above thermal cycling test.

[0080] Table 1 Performance test results of composite molten salt phase change thermal storage materials

[0081]

[0082] As shown in Table 1, the composite molten salt phase change thermal storage materials of this application all exhibit high compressive strength and good structural stability under high-temperature conditions. The composite molten salt phase change thermal storage material of Example 1 possesses good compressive strength and thermal storage capacity, with latent heats of phase change of 79.84 J / g and 81.47 J / g after 0 and 50 thermal cycles, respectively, demonstrating excellent thermal cycling stability. Example 2 increased the content of the alkali activator, improving its mechanical properties. Example 3 increased the molten salt content, improving its thermal storage performance, but slightly reducing its compressive strength; the latent heat of phase change after 0 thermal cycles was 94.70 J / g, indicating good thermal cycling stability.

[0083] The sample in Comparative Example 1 leaked after thermal cycling, and its mechanical strength was too low to be effectively measured after the cycling. This is because the activator content in Comparative Example 1 was too low, resulting in insufficient NASH gel formation and the inability to form a complete framework material, leading to a significant reduction in the material's mechanical properties and a substantial weakening of its encapsulation capability. Specifically, the OH content in the system... - Insufficient concentration prevents the Al-O and Si-O bonds in metakaolinite from being fully broken, leading to a sharp drop in the dissolution-rearrangement rate. This results in a significant decrease in NASH gel yield and incomplete polymerization, with the skeleton exhibiting a loose, "incompletely grown" state. The large number of unreacted particles remain only in physical stacking, with few interfacial bonding points. This causes shrinkage cracks to appear in the preform during the drying stage. Upon entering a high-temperature environment, the low-strength porous structure cannot withstand the osmotic pressure of the molten salt phase and the solid-liquid phase change volume expansion. The skeleton particles are gradually pushed and rearranged, macroscopically manifested as collapse, bulging, or even fragmentation. At the same time, due to the low gel content, the matrix's ability to wet and bind the molten salt decreases, making it prone to salting out and leakage during thermal cycling. The heat storage performance rapidly declines with increasing cycle count, ultimately resulting in the loss of morphological stability and encapsulation function.

[0084] In Comparative Example 2, the sample experienced severe leakage after thermal cycling, resulting in a significant loss of compressive strength. When the phase change molten salt content was too high, the NASH gel network in the matrix was interrupted by excessive salt, the originally continuous skeleton became loose, and the effective encapsulation capacity was sharply reduced.

[0085] The actual images of the composite molten salt phase change thermal storage material of Example 1 after 0, 1, and 50 thermal cycles are shown below. Figure 2 As shown. From Figure 2 It can be seen that the shape remained intact after 50 thermal cycles, without molten salt leakage or structural damage, indicating that the metakaolin particles can achieve effective chemical bonding between particles under alkaline activation conditions, resulting in a good encapsulation effect for the phase change material. The thermal cycling results show that the alkaline-activated metakaolin framework support material can effectively encapsulate the phase change material under high temperature conditions, thereby maintaining the morphological stability of the material.

[0086] The DSC test results of the composite molten salt phase change thermal storage material sample in Example 1 after 0 and 50 cycles are as follows: Figure 3 As shown. From Figure 3 It can be seen that after 50 thermal cycles, the phase transition temperature decreased slightly from 306.49 ℃ to 303.29 ℃, indicating that the thermal cycling had a limited effect on the phase transition temperature; the latent heat of phase transition decreased from 79.84 J·g -1 It rose to 81.47 J·g -1 After 50 thermal cycles, it still exhibits good thermal stability, and its phase change energy storage capacity is not significantly weakened, providing performance assurance for its long-term service.

[0087] The XRD test results of the composite molten salt phase change thermal storage material samples of the examples and comparative examples after 0 and 50 cycles are as follows: Figure 4 As shown. Figure 4 In this context, for example, "NaNO3-50%-15%-0 cycle" indicates that the composite molten salt phase change thermal storage material contains 50% sodium nitrate and 15% sodium hydroxide, and undergoes 0 thermal cycles. Specifically, "NaNO3-50%-9%-0 cycle" and "NaNO3-50%-9%-50 cycle" represent 0 and 50 thermal cycles respectively for the composite molten salt phase change thermal storage material of Example 1; "NaNO3-50%-15%-0 cycle" and "NaNO3-50%-15%-50 cycle" represent 0 and 50 thermal cycles respectively for the composite molten salt phase change thermal storage material of Example 2; and "NaNO3-50%-3%-0 cycle" and "NaNO3-50%-3%-50 cycle" represent 0 and 50 thermal cycles respectively for the composite molten salt phase change thermal storage material of Comparative Example 1.

[0088] from Figure 4It can be seen that after 50 thermal cycles, the mineral phase is mainly sodium nitrate molten salt, the same as in the first cycle, followed by the mullite phase contained in metakaolinite. No new phases are formed, indicating that its chemical properties are stable and it has good chemical compatibility.

[0089] The above tests show that, in this embodiment, alkali-activated metakaolin is used as the encapsulation aggregate to prepare phase change thermal storage material. The high-temperature phase change thermal storage material of alkali-activated metakaolin composite molten salt can still maintain good mechanical properties, thermal storage capacity and chemical stability after multiple thermal cycles.

[0090] Although this application has been described in detail in this specification with general descriptions and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, such modifications or improvements made without departing from the spirit of this application are all within the scope of protection claimed in this application.

Claims

1. A method for preparing an alkali-activated metakaolin composite molten salt phase change thermal storage material, characterized in that, include: S1, mix metakaolin and molten salt phase change material evenly, then add an aqueous solution of alkali activator and stir evenly, then press and shape to obtain raw material blank; S2, the raw material blanks are cured and dried at 50~90 ℃ under sealed conditions to obtain alkali-activated metakaolin composite molten salt phase change thermal storage material.

2. The preparation method according to claim 1, characterized in that, The molten salt phase change material includes any one of sodium nitrate, potassium nitrate, lithium nitrate, sodium chloride, potassium chloride, calcium chloride, or magnesium chloride; The alkaline activator is sodium hydroxide or sodium silicate.

3. The preparation method according to claim 1, characterized in that, The mass ratio of metakaolin, molten salt phase change material and alkali activator is 20~50:50~80:9~15; The total mass fraction of metakaolin, phase change material and alkali activator is 100 parts.

4. The preparation method according to claim 1, characterized in that, The concentration of the aqueous solution of the alkaline activator is 6~16 mol / L.

5. The preparation method according to claim 1, characterized in that, The particle size of the molten salt phase change material is less than 0.1 mm.

6. The preparation method according to claim 1, characterized in that, The pressing pressure is 1~40 MPa, and the time is 1~10 min.

7. The preparation method according to claim 1, characterized in that, The maintenance time is 10~48 hours.

8. The preparation method according to claim 1, characterized in that, The drying temperature is 60~150 ℃, and the drying time is 10~48 h.

9. The composite molten salt phase change thermal storage material prepared by the preparation method according to any one of claims 1-8.

10. The application of the composite molten salt phase change thermal storage material according to claim 9 in the field of phase change energy storage.

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