Composite phase change heat storage material coupled with solid-liquid polydisperse phase self-assembly structure as well as preparation method and application of composite phase change heat storage material

Abstract

The invention relates to the technical field of energy storage materials, and discloses a composite phase change heat storage material coupled with a solid-liquid polydisperse phase self-assembly structure and a preparation method and application thereof. The phase change heat storage material comprises the following components in percentage by weight: 15-35% of a liquid water phase, 1-10% of modified silicon carbide, 1.5-3% of a surfactant and the balance of a paraffin-based phase change material. The composite phase change material is coupled with phase change latent heat characteristics of paraffin and water, and collaborative storage and release of heat energy and cold energy are achieved; silicon carbide is subjected to interface modification by adopting a surface hydrophilic and oleophylic modification technology, so that the interface compatibility of the modified silicon carbide and a water phase is effectively improved, and the heat-conducting property of the composite material is remarkably enhanced; the composite phase change material can meet the temperature regulation requirements of wide temperature ranges including high temperature and low temperature in battery thermal management.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage materials, and in particular to a composite phase change heat storage material with a coupled solid-liquid multi-dispersed phase self-assembly structure, and a preparation method and application thereof, providing a reliable phase change material for the efficient storage and utilization of heat and cold energy. Background Art

[0002] Phase change energy storage materials have shown broad application prospects in the fields of industrial waste heat recovery, building energy conservation and electric vehicle thermal management due to their advantages such as high latent heat storage density and small temperature fluctuation. Traditional phase change materials are mainly divided into organic (such as paraffin) and inorganic (such as inorganic salts). Among them, paraffin-based phase change energy storage materials have been widely studied due to their good chemical stability and low cost, but their inherent defects limit their practical applications. These mainly include: (1) The thermal conductivity of paraffin is low. The thermal conductivity of pure paraffin is only 0.2~0.24 W / (m·K), which leads to slow heat transfer during the phase change process and affects the energy storage efficiency; (2) The singleness of the heat storage temperature range. Existing materials are usually only designed for a single temperature range of high temperature (>50℃). It is difficult to adjust to a wide temperature range including low temperature (<0℃), so it is difficult to meet the energy storage needs of periodic hot and cold alternation of equipment; (3) The structural stability is poor. Phase separation or performance degradation is easy to occur during multiple phase change cycles, especially under extreme temperature conditions. The reliability is insufficient.

[0003] Although thermal conductivity can be improved by adding thermal conductive fillers such as metal particles and graphite, traditional composite materials have the following technical difficulties: (1) Low-temperature heat loss: High thermal conductive fillers accelerate the heat loss of phase change materials in low-temperature environments, and cannot effectively cope with energy storage applications under wide temperature ranges including low-temperature sections; (2) High thermal resistance of the material: Inorganic fillers have poor compatibility with organic matrices, and some inorganic fillers will aggregate and settle, resulting in a discontinuous thermal network, and the effect of improving heat conduction is not significant.

[0004] Therefore, there is an urgent need to develop a composite phase change material that has both high thermal conductivity and wide temperature range adaptability. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a composite phase change heat storage material with a coupled solid-liquid multi-dispersed phase self-assembly structure, as well as its preparation method and application. The present invention aims to break through the performance bottlenecks of low-temperature heat loss and large material thermal resistance of traditional phase change materials by constructing a composite material with a three-dimensional thermal conductive network coupled with solid and liquid phases and a synergistic dual-phase change system, and meet the energy storage needs of high-temperature and efficient heat storage and low-temperature stable cold storage under wide temperature range conditions.

[0006] The technical solution adopted by the present invention to solve its technical problem is: A composite phase change heat storage material having a coupled solid-liquid multi-dispersed phase self-assembly structure, comprising the following components in percentage by mass: Liquid water phase 15~35wt.% Modified silicon carbide 1~10wt.% Surfactant 1.5~3wt.% Paraffin-based phase change material balance.

[0007] This composite phase-change energy storage material consists of paraffin wax as the continuous phase, which absorbs high-temperature heat energy, and solid modified silicon carbide and liquid water as the dispersed phases. Specifically, the solid-liquid polydispersed phases are liquid water and solid modified silicon carbide, respectively. Both are dispersed in paraffin wax. Paraffin wax has a high melting point (35-50°C), allowing for phase change to store and utilize heat energy over a wide temperature range (>50°C). Water is the liquid dispersed phase. Due to its low freezing point (0°C), it can store and utilize cold energy over a wide temperature range (<0°C). Furthermore, since water is liquid at room temperature, to prevent leakage of the phase-change material during room-temperature storage, a surfactant is added to encapsulate the water phase as dispersed micro-nano droplets within the solid paraffin wax matrix. The solid dispersed phase is interface-modified silicon carbide, chosen for its high thermal conductivity, which improves the thermal conductivity of the paraffin-based phase-change material. However, since silicon carbide may aggregate and settle in paraffin, an appropriate amount of interfacial modifier is added to enhance the oil-water amphiphilicity of silicon carbide at the phase interface, promote its interaction with dispersed water droplets, and promote the formation of a self-assembled network structure between silicon carbide and water droplets. This self-assembled structure can become an efficient heat conduction channel, preventing silicon carbide from aggregating and settling, while further improving the thermal conductivity of the material.

[0008] The liquid water phase has a low freezing point (0℃). At low temperatures (<0℃), water can store and utilize cold energy through phase change, which corresponds to the storage and utilization of high-temperature thermal energy by paraffin through phase change at high temperatures (>50℃). The prepared composite phase change material can realize thermal energy consumption within a wide temperature range that takes into account both high-temperature heat and low-temperature cooling.

[0009] Furthermore, the paraffin-based phase change material is solid, and the paraffin-based phase change material includes normal alkanes (with carbon numbers of 16 to 30 in the carbon chain), isoalkanes, or a mixture of normal and isoalkanes with different carbon chain lengths.

[0010] Furthermore, the phase change temperature of the paraffin-based phase change material from solid to liquid is 35-50° C., and the phase change latent heat is 150-220 kJ / kg.

[0011] Furthermore, the surfactant includes one or more of Span60, Span80, and glyceryl monostearate.

[0012] Furthermore, the preparation method of the modified silicon carbide specifically comprises the following steps: Step (a), adding water to a container, heating the water to 70-80° C., adding glyceryl monostearate to the hot water, and stirring at a speed of 300-350 rpm for 10-15 minutes to ensure that the glyceryl monostearate is completely dissolved in the hot water to obtain a hot water solution; Step (b), adding silicon carbide powder to the hot water solution, with the mass ratio of glyceryl monostearate to silicon carbide powder being (1-1.2): (8.8-9), stirring at 300-350 rpm for 20-30 minutes to promote full contact between glyceryl monostearate and silicon carbide particles, to obtain a mixed solution; Step (c), pouring the mixed solution into an evaporation container, placing the evaporation container in a drying oven preheated to a temperature ≥100°C and drying for 18 to 24 hours to ensure that the water in the mixed solution is completely evaporated to obtain dry particles; Step (d), pouring the dried particles into a grinding container and grinding them thoroughly for 15 to 20 minutes to obtain silicon carbide particles modified with glyceryl monostearate; Step (e) characterizes the hydrophilicity and lipophilicity of the silicon carbide particles before and after modification. Appropriate amounts of silicon carbide before and after modification are placed on a glass slide, water droplets are added, and the contact angle between the silicon carbide particles and the water droplets is measured. Based on the size of the contact angle θ, if θ<90°, the material is characterized as hydrophilic, and if θ>90°, the material is characterized as lipophilic.

[0013] Silicon carbide particles have high thermal conductivity. Adding them to paraffin-based phase change materials significantly improves the wax's thermal conductivity, facilitating heat transfer and storage. In this study, untreated silicon carbide particles were heated and mixed with a high-melting-point interfacial modifier (glycerol monostearate) to produce interfacially active silicon carbide particles.

[0014] In the present invention, the silicon carbide particles with interfacial activity serve as the solid dispersed phase in the paraffin wax and self-assemble with the liquid water droplets to form a spatial network of heat conduction channels, which can further improve the efficiency of heat conduction and storage of the composite phase change material.

[0015] Furthermore, in step (b), the diameter of the silicon carbide powder is 50 nm to 1 μm.

[0016] Preferably, the preparation method of modified silicon carbide is as follows: after heating water to 75°C, add an appropriate amount of glyceryl monostearate, and stir at 300 rpm for 15 minutes to ensure that the glyceryl monostearate is completely dissolved in the hot water. Subsequently, an appropriate amount of silicon carbide powder with a size of 50 nm is weighed at a mass ratio of glyceryl monostearate to silicon carbide of 1:9, poured into the above hot water solution, and continued to stir at 300 rpm for 30 minutes to promote full contact between the glyceryl monostearate and the silicon carbide particles. The above mixture is poured into an evaporating dish, and the evaporating dish is placed in a drying oven preheated to 100°C and dried for 24 hours. Ensure that the water in the mixture is completely evaporated, and pour the dried particles into a grinding dish for grinding to obtain silicon carbide particles modified with glyceryl monostearate.

[0017] A method for preparing the composite phase change heat storage material having the coupled solid-liquid multi-dispersed phase self-assembly structure as described above specifically comprises the following steps: Step S1, weighing the materials in the above mass percentage; Step S2: placing the paraffin-based phase change material in a heating box and heating it to melt at a temperature of 50-60° C., then adding a surfactant, continuing to stir and mix evenly to obtain a molten paraffin system; Step S3: adding deionized water to the molten paraffin system under stirring, and obtaining a dispersed aqueous phase after the aqueous phase is added dropwise. The aqueous phase dispersion can promote the dispersion of the aqueous phase into micro-nano-sized water droplets in the liquid paraffin, so that the water droplets can be better dispersed and contacted in the molten paraffin system; Step S4, adding the modified silicon carbide to the high-temperature paraffin solution of the emulsified water droplets, applying stirring at 300-350 rpm for 10-15 minutes to promote the interaction between the interface-modified silicon carbide and the emulsified droplets, so that the solid interface-modified silicon carbide particles can spontaneously adhere to the liquid water droplets and self-assemble to form a spatial network structure of modified silicon carbide-emulsified water droplets coupled; taking a small amount of the fully stirred mixture and observing it under a polarizing microscope to clarify the distribution morphology of the modified silicon carbide and the water droplets in the paraffin and the spatial network structure formed by the interaction, thereby verifying the autonomous assembly process between the modified silicon carbide and the water droplets; Step S5: After the stirring is completed, the mixture is cooled and cooled until the paraffin wax is completely solidified, thereby obtaining a finished composite phase change heat storage material with a coupled solid-liquid multi-dispersed phase self-assembly structure.

[0018] Furthermore, in step S3, the aqueous phase is dispersed into liquid water droplets using a combination of dropwise addition and emulsification. Specifically, the water is divided into 4 to 6 equal portions by volume, and one portion is slowly added dropwise to the paraffin wax. After the dropwise addition is completed, the aqueous phase is fully emulsified in the liquid paraffin wax for 1 to 2 minutes. This process is repeated until the water sample is completely added to the liquid paraffin wax. The size of the dispersed aqueous phase droplets ranges from 10 nm to 50 μm.

[0019] Furthermore, in step S5, the cooling temperature is 25±0.5°C.

[0020] An application of the aforementioned coupled solid-liquid multi-disperse phase self-assembly composite phase change thermal storage material is described. The material's application in energy storage over a wide temperature range combines high-temperature (>50°C) heat storage with low-temperature (<0°C) cold storage. Specifically, the prepared composite phase change material was studied for wide-temperature energy storage applications in battery thermal management, specifically high-power discharge overheating (>50°C) and low-temperature (<0°C) battery storage. Lithium batteries of various specifications, including 18650, 21700, and 26650, as well as prismatic and pouch cells, were used to study battery overheating control under high charge and discharge power conditions of 2-5C. This simulated the temperature rise of an electric vehicle during high-temperature discharge, and the heat absorption capacity and efficiency of the composite phase change material coated on the battery surface were characterized at high temperatures. The battery was then placed in a low-temperature environment (-10--20°C) to simulate the temperature drop of an electric vehicle parked for an extended period in cold weather. The cold storage capacity and efficiency of the composite phase change material coated on the battery surface were further characterized at low temperatures. The energy storage application potential of composite phase change materials is evaluated by regulating the temperature of batteries in a wide temperature range including high and low temperatures.

[0021] The beneficial effects of the present invention are: the present invention has a reasonable design, a simple preparation method, and has the following advantages: (1) Compared with the traditional phase change materials that can only achieve single heat storage or cold storage, the phase change material prepared by the present invention fully utilizes the phase change latent heat of paraffin and water, realizes the comprehensive utilization of both heat and cold energy, enriches the levels and methods of energy transmission and storage, and meets the energy storage and release requirements of the equipment in periodic hot and cold alternation; (2) Due to the low thermal conductivity of paraffin, the energy storage efficiency of paraffin in the high-temperature heat storage process is low. Therefore, by adding modified silicon carbide with high thermal conductivity to the phase change material, the thermal conductivity of paraffin is enhanced, and heat is transferred more quickly. Since the surface of silicon carbide is hydrophilic, it is not easy to disperse in paraffin. Therefore, the oil-soluble surfactant glycerol monostearate is used to perform lipophilic and hydrophilic interface modification on the silicon carbide raw material particles to increase the contact angle between silicon carbide and the water phase and enhance the interfacial activity of silicon carbide particles. The modified silicon carbide can be dispersed in paraffin. In addition, the interfacial activity of silicon carbide can make it spontaneously adsorbed around water droplets. The solid silicon carbide and the liquid water droplets form a spatial network structure to reduce the interfacial thermal resistance between paraffin and water, thereby further improving the thermal conductivity of the phase change material. At the same time, it also takes into account the stability of silicon carbide to prevent it from aggregating and settling in paraffin. (3) Considering that the ambient temperature of the material is mostly at room temperature, paraffin is solid at room temperature and water is liquid, a surfactant is added to the paraffin to emulsify the water phase into micro-nanoscale water droplets and disperse them in the solid paraffin, which facilitates the transportation and storage of the composite phase change material; (4) Based on the thermal management requirements of electric vehicle batteries under high and low temperature conditions, the energy storage application of the composite phase change material prepared by the present invention under wide temperature range conditions is explored. This includes two aspects: heat storage during high-power discharge of the battery and absorption of cold energy to prevent the battery temperature from being too low in a low-temperature environment. The composite phase change material prepared by the present invention can reduce the power consumption caused by high-temperature cooling and low-temperature heating of the battery in active battery thermal management, and effectively improve the battery's efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 This is a product display diagram of the composite phase change heat storage material with coupled solid-liquid multi-dispersed phase self-assembly structure prepared in Example 1; Figure 2 1 is a comparison of the contact angles of silicon carbide with water droplets before and after modification in Example 1; Figure 3 This is a microscopic morphology of the composite phase change heat storage material with coupled solid-liquid multi-dispersed phase self-assembly structure obtained in Example 1 observed under a polarizing microscope; Figure 4 This is a diagram of a device for conducting battery thermal management tests using the invented composite phase change material; Figure 5 The temperature change curves of high-temperature heat storage and heat release experiments of Examples 1 to 5 and Comparative Examples 1 to 2 are shown; Figure 6 It is the temperature change curve of the low-temperature cold storage and cold release experiment of Example 1 to Example 5 and Comparative Example 1 to Comparative Example 2. DETAILED DESCRIPTION

[0024] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0025] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular also includes the plural. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0026] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] Unless otherwise specified, the raw materials used in the present invention are all commercially available.

[0028] Example 1 This embodiment provides a method for preparing a composite phase change heat storage material having a coupled solid-liquid multi-dispersed phase self-assembly structure, specifically: (1) Place the paraffin-based phase change material with a phase change temperature of 45°C in a heating box and heat it to melt. After heating to 50°C and keeping the temperature constant for 2 hours, add 2 wt.% of the surfactant Span80 and stir at 300 rpm for 15 minutes. (2) Add 15 wt.% of deionized water at 50°C to the above solution, divide the deionized water into 4 equal volumes, take 1 portion and drop it into the liquid paraffin, continue stirring and emulsifying for 2 minutes after the addition is completed, so as to promote the surfactant Span80 to emulsify the aqueous phase into micro-nano-scale water droplets, and use the same combination of dropwise addition and emulsification for the subsequent 3 portions of aqueous phase. After the addition of the aqueous phase is completed, a dispersed aqueous phase can be obtained. The aqueous phase dispersion can promote the dispersion and contact of water droplets in the molten paraffin system; (3) Add 5 wt.% of modified silicon carbide particles to the above mixture and stir at 300 rpm for 15 minutes; (4) After the stirring is completed, the emulsion is placed in a constant temperature box at 25°C to cool down until the paraffin is completely solidified, and finally a composite phase change heat storage material with a coupled solid-liquid multi-dispersed phase self-assembly structure is obtained.

[0029] Figure 1 This is a product display diagram of the composite phase change heat storage material with coupled solid-liquid multi-dispersed phase self-assembly structure prepared in this embodiment.

[0030] Figure 2This is a comparison of the contact angles of silicon carbide with water droplets before and after modification in this embodiment. The contact angle of the modified silicon carbide with water droplets increases significantly, from being completely hydrophilic before modification (contact angle θ=43°) to having certain lipophilic properties (contact angle θ=122°), that is, it has an amphiphilic interface activity.

[0031] Figure 3 This is a microscopic morphology of the composite phase change heat storage material with a coupled solid-liquid multi-dispersed phase self-assembly structure obtained in this embodiment under polarizing microscope observation. In order to better show the distribution of dispersed water droplets and modified silicon carbide in paraffin wax, the phase change energy storage material is heated to 50°C to allow the paraffin wax to completely melt, so as to avoid the wax crystals of the paraffin wax affecting the observation effect during the polarizing microscope observation process. In the figure, 301 is the dispersed water droplets formed by emulsification, and 302 is the modified silicon carbide particles. It can be seen that while silicon carbide is dispersed in the paraffin wax, it also adheres to the surface of the water droplets, and self-assembles to form a three-dimensional spatial network structure, which helps stabilize the two dispersed phases of silicon carbide and water and prevents them from aggregating and settling.

[0032] Example 2 The difference between this embodiment and embodiment 1 is that in step (2), the proportion of the added aqueous phase is adjusted to 25 wt.%, and the rest of the preparation process is the same as that of embodiment 1, to obtain a composite phase change heat storage material with a coupled solid-liquid multi-dispersed phase self-assembly structure.

[0033] Example 3 The difference between this embodiment and embodiment 1 is that in step (2), the proportion of the added aqueous phase is adjusted to 35 wt.%, and the rest of the preparation process is the same as that of embodiment 1, to obtain a composite phase change heat storage material with a coupled solid-liquid multi-dispersed phase self-assembly structure.

[0034] Example 4 The difference between this embodiment and embodiment 1 is that in step (3), the proportion of modified silicon carbide added is adjusted to 1 wt.%, and the rest of the preparation process is the same as that of embodiment 1, to obtain a composite phase change heat storage material with a coupled solid-liquid multi-dispersed phase self-assembly structure.

[0035] Example 5 The difference between this embodiment and embodiment 1 is that in step (3), the proportion of modified silicon carbide added is adjusted to 10 wt.%, and the rest of the preparation process is the same as that of embodiment 1, to obtain a composite phase change heat storage material with a coupled solid-liquid multi-dispersed phase self-assembly structure.

[0036] The composite phase change heat storage material with coupled solid-liquid multi-dispersed phase self-assembly structure prepared in Examples 1 to 5 was tested for its energy storage application under wide temperature range conditions. Figure 4The measurement device shown in the figure, marked 401 is a computer for data collection, 402 is a charging and discharging device, which can charge and discharge the battery at different powers of 0.5~5C, 403 is a temperature sensor, which measures the temperature of the battery surface, and 404 is a battery-composite phase change material module. The composite phase change material is wrapped around the battery to study the energy storage application under the battery's wide temperature range conditions.

[0037] First, a high-temperature heat storage test was conducted. The high-temperature conditions were as follows: the composite phase change material was wrapped around a 26650 rechargeable lithium battery (basic battery parameters: diameter: 26mm, height: 65mm, shape: cylindrical, rated voltage: 3.7V, full-charge voltage: 4.2V, rated capacity: 5000mAh). The battery was discharged at a high discharge power of 2C. At this discharge rate, the battery would generate high temperature and enter an overheating state. The temperature rise process of the battery surface wrapped with the composite phase change material of the five embodiments was recorded. The temperature rise rate K from room temperature to the phase change temperature stage (25℃~45℃), the heat storage time, and the final temperature T of the battery surface after discharge were measured. max The size of represents the high-temperature heat transfer efficiency and heat storage capacity of the composite phase change material. The high-temperature heat storage test results of Examples 1 to 5 are shown in Table 1.

[0038] Table 1 High temperature heat storage test results of Examples 1 to 5 Moisture content wt.% Modified silicon carbide content wt.% Heating rate K℃ / min Heat storage time min <![CDATA[Final temperature T max °C]]> Example 1 15 5 2.88 10.1 47.5 Example 2 25 5 2.60 9.5 46.5 Example 3 35 5 2.37 9.1 45.8 Example 4 15 1 3.26 10.5 20.1 Example 5 15 10 2.57 9.8 46.9 High temperature heat storage process: Figure 5 The temperature change curves of the high-temperature heat storage and heat release experiments of Examples 1 to 5 are shown in the table above. Combined with the above table, it can be seen that the heat storage process of the composite phase change energy storage material in absorbing the discharge of the 2C high-power battery and preventing the battery from entering an overheating state is divided into three stages: (1) At 25℃~45℃, the temperature of the battery surface does not reach the phase transition temperature of solid paraffin at this stage, and the battery surface temperature rises rapidly; the difference in the material heating rate K is related to the thermal conductivity of the material. For Example 1 and Examples 4 and 5 with the same water content, it is shown that as the modified silicon carbide increases, the material heating rate K decreases, indicating that the thermal conductivity of the material has been enhanced and can more quickly take away the heat generated by the battery during the 2C discharge process; In addition, from Table 1 and Figure 3 It can be seen that water droplets can participate in the self-organizing three-dimensional spatial network structure formed by modified silicon carbide, forming a heat conduction path and promoting heat transfer. Therefore, for Examples 1 to 3 containing the same modified silicon carbide, it is also shown that as the water content increases, the heating rate K of the material decreases, that is, the self-organizing spatial heat conduction network formed by the coupling of the solid-liquid dispersed phase in the material is strengthened. (2) At 45°C, the temperature rise curves of the battery surface temperature of the five embodiments become gentle. At this time, the temperature reaches the melting point of solid paraffin. The paraffin phase changes and melts, absorbing a large amount of heat released from the battery surface. This delays the temperature rise of the material. The material exhibits the ability to store heat, and the heat is stored in the material in the form of the latent heat of the phase change of paraffin. In this heat storage process, for the embodiments 1, 2, and 3 containing the same silicon carbide, the heat absorption phase change time is 10.1 min, 9.5 min, and 9.1 min, respectively. That is, as the water content increases, the proportion of paraffin in the phase change material gradually decreases, and the heat storage time also decreases accordingly. For the embodiments 1, 4, and 5 with the same water content, the heat absorption phase change time is 10.1 min, 10.5 min, 9.8 min, respectively. min, and the heat storage time also satisfies the positive correlation between the proportion of paraffin in the composite phase change material. In Example 4, the modified silicon carbide content is the lowest, the proportion of paraffin is the highest, and the heat storage time is the longest. In Example 5, the modified silicon carbide content is the highest, the proportion of paraffin decreases accordingly, and the heat storage time is the shortest. (3) 45℃~T max When the paraffin wax in the composite phase change material of the five embodiments has been completely melted, the temperature of the battery surface continues to rise, and the final temperature of the material is T max The difference is also due to the different thermal conductivity of the five embodiments; the final temperature T of Examples 1 to 3 is max As the moisture content increases, the T decreases gradually, as shown by the T of Example 3 with the highest moisture content. max The final temperature of Example 1, Example 4, and Example 5 gradually decreases with the increase of modified silicon carbide content, as shown in the T of Example 5 with the highest content of modified silicon carbide. max It is 46.9℃.

[0039] The composite phase-change thermal storage materials, featuring coupled solid-liquid polydisperse phase self-assembly structures, prepared in Examples 1 through 5, were tested for their low-temperature cold storage performance. Batteries coated with the materials from each of the five examples were placed in a -15°C refrigerator. The temperature change from 25°C to -15°C was measured, and the cold storage capacity of the five examples was characterized by the phase-change temperature and cold storage duration. The low-temperature cold storage test results for Examples 1 through 5 are shown in Table 2.

[0040] Table 2 Low temperature cold storage test results of Examples 1 to 5 Moisture content wt.% Modified silicon carbide content wt.% Response temperature ℃ Cold storage time min Example 1 15 5 -5.0 8.2 Example 2 25 5 -4.8 9.5 Example 3 35 5 -4.7 10.3 Example 4 15 1 -5.0 8.4 Example 5 15 10 -5.0 8.3 like Figure 6 As shown in the figure, the cooling and heat release process from 25℃ to -15℃ is also divided into three stages: (1) 25℃~phase transition temperature, at this time the temperature drops rapidly, and the liquid water droplets dispersed in the phase change material have not yet reached the phase transition temperature; (2) Phase change temperature ~ 0℃. Since the dispersed water droplets are supercooled, the phase change response temperature is lower than 0℃. As can be seen from Table 2, for Examples 1 to 3 with different water contents, as the water content increases, the phase change temperature of the examples increases slightly. This is related to the water content. At higher water contents, the size of the water droplets is larger. Large-sized water droplets reduce the energy barrier required for nucleation through non-uniform nucleation and are easier to crystallize. For Example 1 and Examples 4 and 5 with the same water content, the response temperature of the three examples has almost no change. After the water phase changes and crystallizes, the phase change material absorbs the cold energy of the environment and transfers the phase change heat to the battery, causing the temperature of the battery surface to rise to 0℃. In addition, as the water content increases, the battery surface temperature is maintained at 0℃ for a longer time. The cold storage time of Examples 1, 2, and 3 is 8.2, 9.5, and 10.3 minutes, respectively. However, the cold storage time of Examples 1 and Examples 4 and 5 with the same water content does not change much and is maintained at about 8.3 minutes. (3) 0℃~-15℃, when the water phase of the phase change materials of the five embodiments is completely crystallized, the temperature of the battery surface is further reduced until the temperature is consistent with the ambient temperature.

[0041] Through the above-mentioned high-temperature heat storage and low-temperature cold storage experiments in a wide temperature range, it can be found that Examples 1 to 5 show different advantages in heat storage and cold storage, which is due to the effects of paraffin wax, water and added modified silicon carbide. The specific summary is as follows: (1) In the high-temperature heat storage link, in terms of heat storage time, the composite phase change material of Example 4 has the largest wax content, so it has the longest heat storage time of 10.5 minutes among the five examples. For processes that require heat storage, the heat storage capacity of Example 4 is more advantageous; (2) In the high-temperature heat storage link, in terms of thermal conductivity efficiency, the composite phase change material of Example 3 has the highest thermal conductivity coefficient. The source of this high thermal conductivity is the spatial thermal conduction path formed by the modified silicon carbide and dispersed water droplets in the paraffin wax ( Figure 3 ); Therefore, it has the highest thermal conductivity among the five embodiments, as shown by the lowest heating rate K value of 2.37. In addition, Example 5 with the highest modified silicon carbide content also shows a high thermal conductivity, with a heating rate K value of 2.57, which is close to the heating rate of Example 3. If the cold storage aspect is not considered, Examples 3 and 5 have advantages over the other embodiments; (3) In the low-temperature cold storage link, in terms of cold storage response temperature and cold storage time, for Examples 1, 2, and 3 with different water contents, Example 3 with the highest water content has more advantages, and has the highest response temperature of -4.7°C and the longest cold storage time of 10.3 min. This is because its water content is higher, the degree of supercooling in the cold storage process is lower, and the cold storage capacity is larger. Compared with Examples 1, 4, and 5 with different silicon carbide contents, its water content of only 15 wt.% makes it more obviously inferior to Examples 2 and 3 with water contents of 25 wt.% and 35 wt.% respectively in terms of cold storage.

[0042] In summary, Examples 1 to 5 are applicable to both high-temperature heat storage and low-temperature cold storage in a wide temperature range. In specific use, the appropriate embodiment can be selected according to the degree of demand for heat storage or cold storage under actual working conditions.

[0043] Comparative Example 1 Solid paraffin wax with a phase change temperature of 45°C is placed in a high-temperature heating box to melt it, heated to 50°C and kept at a constant temperature for 2 hours, and then the molten paraffin is placed in a 25°C constant temperature box to cool down. After the paraffin is completely solidified, a typical paraffin phase change heat storage material is finally prepared.

[0044] Conventional paraffin-based phase change energy storage materials mostly only consider the material heat storage process, that is, only paraffin is used as the phase change material.

[0045] Comparative Example 2 Solid paraffin wax with a phase change temperature of 45°C was placed in a high-temperature heating chamber to melt. After heating to 50°C and maintaining the temperature for 2 hours, 2 wt.% of the surfactant Span 80 and 5 wt.% of modified silicon carbide particles were added and stirred at 300 rpm for 15 minutes. The mixture was then cooled in a 25°C constant temperature chamber until the paraffin wax completely solidified, resulting in a conventional paraffin wax + silicon carbide phase change thermal storage material.

[0046] Comparative Example 3 The difference between this comparative example and Example 1 is that 5 wt.% of unmodified silicon carbide is added to paraffin wax, and the rest of the preparation process is the same as that of Example 1 to obtain a phase change energy storage material.

[0047] The material obtained in the above comparative example was Figure 4 The performance test was carried out using the measuring device shown in the figure, and the comparison results with those of the embodiment are shown in Table 3, Table 4 and Table 5.

[0048] Table 3 Thermal conductivity of Examples 1 to 5 and Comparative Examples 1 to 2

[0049] Table 3 shows the thermal conductivity of Examples 1 to 5 and Comparative Examples 1 to 3 obtained from the test. It can be seen from the table that the addition of modified silicon carbide significantly enhances the thermal conductivity of paraffin wax. The thermal conductivity of Example 1 and Examples 4 and 5 are 3.9, 5.4 and 6.3 times that of the pure paraffin wax in Comparative Example 1, respectively. Figure 3 It can be found that the thermal conductivity of Examples 1 to 3 in which modified silicon carbide and water droplets are self-assembled to form a spatial network structure is 5.4, 6.0, and 7.0 times that of pure paraffin in Example 1. By comparing the components of Example 3 and Example 5, it can be found that Example 5 uses 10 wt.% of modified silicon carbide to increase the thermal conductivity of the composite phase change material to 1.51 W (m·K), while the modified silicon carbide content of Example 3 is only 50% of that of Example 5. However, because the modified silicon carbide and water droplets form a spatial self-assembled network structure, the structure becomes a microscopic channel for heat conduction, which further enhances the thermal conductivity of the system to 1.68 W (m·K). This shows that the multi-dispersed phase in the composite system has a stronger effect on improving the thermal conductivity of the phase change material than the single dispersed phase in the system.

[0050] Table 4 High temperature heat storage test results of Example 1, Comparative Example 1 and Comparative Example 2 Moisture content wt.% Modified silicon carbide content wt.% Heating rate K℃ / min Heat storage time min <![CDATA[Final temperature T max °C]]> Example 1 15 5 2.88 10.1 47.5 Comparative Example 1 0 0 3.71 11.0 50.4 Comparative Example 2 0 5 3.23 -10.5 49.2 Table 5 Low temperature cold storage test results of Example 1, Comparative Example 2 and Comparative Example 3 Moisture content wt.% Modified silicon carbide content wt.% Response temperature ℃ Cold storage time min Example 1 15 5 -5.0 8.2 Comparative Example 2 0 5 0 0 Comparative Example 3 0 5 (unmodified silicon carbide) 0 0 It can be seen from Tables 4 and 5 that, compared with Example 1, Comparative Example 1 contains only one phase change material, paraffin, without the participation of the water phase change, and cannot achieve the low-temperature cold storage function, that is, there is no corresponding response temperature and cold storage time, and it can only achieve a single high-temperature heat storage effect. Compared with Example 1, Comparative Example 2 also has no water phase and relies only on modified silicon carbide to enhance thermal conductivity. It can be found that its heating rate K value is 3.23, which is still greater than that of Example 1. As with the comparison of Examples 3 and 5 above, it also shows that relying solely on modified silicon carbide, the degree of enhancement of the thermal conductivity of paraffin is not as good as the structure of modified silicon carbide coupled with water droplets. The comparison of these two comparative materials highlights the dual role and efficacy of water droplets in low-temperature cold storage and enhanced thermal conductivity.

[0051] Furthermore, in Comparative Example 3, unmodified silicon carbide was used to prepare a composite phase-change energy storage material. After the phase-change material was prepared, it was found that the unmodified silicon carbide did not disperse well in the paraffin wax, resulting in the silicon carbide settling at the bottom of the phase-change material. This resulted in a difference in overall thermal conductivity. Therefore, its thermal conductivity was not measured in Table 3, and subsequent high-temperature heat storage and low-temperature cold storage experiments could not be carried out properly.

[0052] In summary, the present invention makes full use of the latent heat of phase change of paraffin and water, and disperses liquid water droplets at room temperature in solid paraffin with the help of surfactants, thereby facilitating the storage and transportation of composite phase change materials. By modifying silicon carbide to be hydrophilic and lipophilic, the coupling between silicon carbide and water droplets is promoted, further enhancing the thermal conductivity of the composite phase change material. In combination with the actual needs of heat storage and cold storage, the appropriate composition ratio of paraffin and water can be selected according to the corresponding heat storage and cold storage indicators obtained from the above tests, so as to efficiently realize the comprehensive utilization of both heat and cold energy.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite phase change heat storage material with a coupled solid-liquid multi-dispersed phase self-assembly structure, characterized by: The following components are included in mass percentage: Liquid water phase 15~35wt.% Modified silicon carbide 1~10wt.% Surfactant 1.5~3wt.% Paraffin-based phase change material balance.

2. The composite phase change thermal storage material of the coupled solid-liquid multi-dispersed phase self-assembly structure according to claim 1, characterized in that: The paraffin-based phase change material is solid and includes normal alkanes, isoalkanes, or a mixture of normal alkanes and isoalkanes with different carbon chain lengths.

3. The composite phase change thermal storage material of the coupled solid-liquid multi-dispersed phase self-assembly structure according to claim 1, characterized in that: The phase change temperature of the paraffin-based phase change material from solid to liquid is 35-50° C., and the phase change latent heat is 150-220 kJ / kg.

4. The composite phase change thermal storage material of the coupled solid-liquid multi-dispersed phase self-assembly structure according to claim 1, characterized in that: The surfactant includes one or more of Span 60, Span 80, and glyceryl monostearate.

5. The composite phase change heat storage material with coupled solid-liquid multi-dispersed phase self-assembly structure according to claim 1, characterized in that: The preparation method of the modified silicon carbide specifically comprises the following steps: Step (a), adding water to a container, heating the water to 70-80° C., adding glyceryl monostearate to the hot water, and stirring at a speed of 300-350 rpm for 10-15 minutes to ensure that the glyceryl monostearate is completely dissolved in the hot water to obtain a hot water solution; Step (b), adding silicon carbide powder to the hot water solution, with the mass ratio of glyceryl monostearate to silicon carbide powder being (1-1.2): (8.8-9), stirring at 300-350 rpm for 20-30 minutes to promote full contact between glyceryl monostearate and silicon carbide particles, to obtain a mixed solution; Step (c), pouring the mixed solution into an evaporation container, placing the evaporation container in a drying oven preheated to a temperature ≥100°C and drying for 18 to 24 hours to ensure that the water in the mixed solution is completely evaporated to obtain dry particles; Step (d), pouring the dried particles into a grinding container and grinding them thoroughly for 15 to 20 minutes to obtain silicon carbide particles modified with glyceryl monostearate; Step (e) characterizes the hydrophilicity and lipophilicity of the silicon carbide particles before and after modification. Appropriate amounts of silicon carbide before and after modification are placed on a glass slide, water droplets are added, and the contact angle between the silicon carbide particles and the water droplets is measured. Based on the size of the contact angle θ, if θ<90°, the material is characterized as hydrophilic, and if θ>90°, the material is characterized as lipophilic.

6. The composite phase change heat storage material with coupled solid-liquid multi-dispersed phase self-assembly structure according to claim 5, characterized in that: In the step (b), the diameter of the silicon carbide powder is 50 nm to 1 μm.

7. A method for preparing a composite phase change thermal storage material having a coupled solid-liquid multi-dispersed phase self-assembly structure according to any one of claims 1 to 6, characterized in that: The specific steps include: Step S1, weighing the materials in the above mass percentage; Step S2: placing the paraffin-based phase change material in a heating box and heating it to melt at a temperature of 50-60° C., then adding a surfactant, continuing to stir and mix evenly to obtain a molten paraffin system; Step S3: adding deionized water to the molten paraffin system under stirring, and obtaining a dispersed aqueous phase after the aqueous phase is added dropwise. The aqueous phase dispersion can promote the dispersion of the aqueous phase into micro-nano-scale water droplets in the liquid paraffin; Step S4, adding the modified silicon carbide to the high-temperature paraffin solution of the emulsified water droplets, applying stirring at 300-350 rpm for 10-15 minutes to promote the interaction between the interface-modified silicon carbide and the emulsified droplets, so that the solid interface-modified silicon carbide particles can spontaneously adhere to the liquid water droplets and self-assemble to form a spatial network structure of modified silicon carbide-emulsified water droplets coupled; taking a small amount of the fully stirred mixture and observing it under a polarizing microscope to clarify the distribution morphology of the modified silicon carbide and the water droplets in the paraffin and the spatial network structure formed by the interaction, thereby verifying the autonomous assembly process between the modified silicon carbide and the water droplets; Step S5: After the stirring is completed, the mixture is cooled and cooled until the paraffin wax is completely solidified, thereby obtaining a finished composite phase change heat storage material with a coupled solid-liquid multi-dispersed phase self-assembly structure.

8. The method for preparing a composite phase change thermal storage material having a coupled solid-liquid multi-dispersed phase self-assembly structure according to claim 7, characterized in that: In step S3, the aqueous phase is dispersed into liquid water droplets by combining dropwise addition and emulsification. The specific operation is as follows: the water is divided into 4 to 6 equal parts by volume, and one part is slowly added dropwise to the paraffin. After the dropwise addition is completed, the aqueous phase is fully emulsified in the liquid paraffin for 1 to 2 minutes, and this process is repeated until the water sample is completely added to the liquid paraffin.

9. The method for preparing a composite phase change thermal storage material having a coupled solid-liquid multi-dispersed phase self-assembly structure according to claim 7, characterized in that: In step S5, the cooling temperature is 25±0.5°C.

10. Use of the composite phase change heat storage material having a coupled solid-liquid multi-dispersed phase self-assembly structure according to any one of claims 1 to 6, characterized in that: The material can be used for energy storage in a wide temperature range, taking into account both high-temperature heat storage and low-temperature cold storage.

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