Preparation method of a shell-core type silica / inorganic phase change material microcapsule

Abstract

A method for preparing shell-core silica / inorganic phase change material microcapsules belongs to the technical field of phase change energy storage materials. The microcapsules are made from inorganic hydrated salt phase change materials that are inexpensive, readily available, have high phase change latent heat, and are non-flammable, and inorganic sodium silicate that is stable, non-toxic, and environmentally friendly. The coated inorganic hydrated salt phase change material is synthesized based on microcapsule coating technology; the mass ratio of inorganic hydrated salt to deionized water in the inorganic phase change material is 1:(0.5~1). The preparation method of the microcapsules is: using the oil-in-water emulsion template method and the sol-gel method, by strictly controlling the amount of surfactant, water content, shell-core raw material ratio, stirring rate and other reaction conditions, the microcapsules are formed in situ. Compared with traditional phase change materials, the microcapsules of the present invention have higher phase change enthalpy values and thermal response rates and lower supercooling, and can effectively achieve the dual-temperature thermal management effect of latent heat energy storage and thermochemical energy storage, reducing energy consumption.

Description

Technical Field

[0001] The present invention relates to a phase change energy storage material microcapsule, in particular to a silicon dioxide / inorganic phase change material microcapsule with a "shell-core" structure and a preparation method thereof, belonging to the technical field of phase change energy storage materials. Background Art

[0002] In recent years, energy, as one of the three major resource pillars of human society, has been continuously developed and utilized, significantly improving people's living standards and driving social development. Currently, traditional fossil fuels, represented by oil, coal, and natural gas, still dominate the energy consumption structure due to their low cost and ease of use. However, the increasing demand for traditional fossil fuels and the rapid growth of global consumption have put the global energy supply in a critical position. Furthermore, while providing energy, fossil fuels also emit acidic pollutants such as sulfur dioxide and carbon dioxide into the air, leading to irreversible greenhouse effects and environmental pollution. Currently, China attaches great importance to the development of new energy industries. Finding green, reliable alternative energy sources to meet global energy needs as fossil fuels become depleted has become a critical issue that humanity must address.

[0003] With support from national policies and energy transformation, new energy sources, represented by lithium-ion batteries, are experiencing a broader market development outlook. In practical applications, the electrochemical performance of lithium-ion batteries is closely related to operating temperature. The optimal operating temperature for lithium-ion batteries is 20-50°C. Temperatures too high or too low are detrimental to their performance. As a chemical power source, lithium-ion batteries undergo complex electrochemical reactions during the charge and discharge process. During normal operation, the heat generated by the battery dissipates naturally over time, keeping the battery temperature within a manageable range. However, under abnormal conditions such as mechanical damage, high external temperatures, overcharging, and internal short circuits caused by rapid charging, the heat generated by the battery exceeds the upper limit of natural heat dissipation, causing heat accumulation in the central region, uneven temperature distribution within the battery, and significant temperature differences between cells, impacting the overall performance of the battery system. Research has shown that the capacity decay of lithium-ion batteries increases with increasing temperature. At 55°C, a battery exhibited approximately 70% capacity loss after 490 cycles. High temperatures hinder heat dissipation, leading to a gradual increase in battery temperature and a high risk of thermal runaway within the battery cells. To ensure the stability and safety of battery performance, a reasonable battery thermal management system must be designed to reduce the temperature differences within single cells and battery packs, solve the problems of thermal dissipation or thermal runaway caused by batteries operating in low or high temperature environments, and improve the overall performance of the battery.

[0004] Common battery thermal management technologies are categorized as active and passive. Active cooling, using air or liquid as a cooling medium, is currently the most common battery thermal management method. Thermal management using gas as a heat transfer medium is known as air cooling, or simply air cooling. While traditional air cooling systems offer advantages such as simple structure, ease of maintenance, and relatively mature technology, they lack sufficient temperature control in high-temperature environments and under conditions such as rapid charging due to air's low thermal conductivity and specific heat capacity. Furthermore, forced air cooling systems create large temperature gradients within the battery pack, making it difficult to ensure uniform temperature distribution. Compared to air, liquid cooling technology offers higher specific heat capacity and convective heat transfer coefficients, compensating for the poor temperature control performance of air cooling. However, liquid cooling systems are complex in structure, and in practical applications, the heat exchange area between the battery cells and the heat exchange tubes is extremely limited. Furthermore, to prevent coolant leakage, piping sealing, insulation, and layout must be considered during the design phase. This significantly increases the volume, weight, and cost of the battery system, resulting in a lower specific energy density of the battery pack and negating the inherent specific energy advantage of high-energy batteries.

[0005] Passive thermal management systems based on phase change materials (PCMs) offer advantages such as compact structure, simple process, excellent cooling performance, and minimal temperature fluctuations. They also require no additional energy consumption, holding great potential for cost-effective thermal management and energy storage, attracting considerable research interest. PCMs, with their high energy storage density, constant phase transition temperature, and low contact thermal resistance, act as a thermal storage medium, absorbing or releasing large amounts of heat during phase transitions, maintaining temperature uniformity within battery systems. Inorganic PCMs are naturally non-flammable, possess high latent heat of phase change and thermal conductivity, and are low-cost. Some studies have further enhanced the thermal conductivity of PCMs by increasing the heat transfer area, significantly improving their thermophysical properties. However, this reduces the relative mass of the PCMs, thus weakening the thermal storage capacity of the PCM system. Numerous studies have focused on improving the overall performance of these materials, exploring the optimal balance between energy storage density and thermal performance. Using PCMs for sensible and latent heat storage is a common thermal energy management strategy, and numerous studies have demonstrated the excellent temperature control capabilities of PCMs in thermal management. However, thermochemical heat storage with greater energy storage density is rarely reported in the literature. Summary of the Invention

[0006] The purpose of this invention is to conduct detailed experimental and theoretical research on non-flammable inorganic phase change materials, designing low-cost, safe, and fast-response thermal runaway protection materials. The invention also provides a silica / inorganic phase change material microcapsule with a "core-shell" structure and a preparation method. This microcapsule utilizes the combined thermal storage potential of inorganic hydrated salts for phase change and thermochemical heat storage, improving the performance of phase change materials in thermal energy storage. The invention designs a microcapsule with a typical "core-shell" structure, consisting of an inorganic hydrated salt core and a dense silica shell.

[0007] The microcapsules are made of inorganic hydrated salt phase change materials that are cheap, readily available, have high latent heat of phase change, and are non-flammable, and inorganic sodium silicate that is stable, non-toxic, and environmentally friendly. They not only provide a large specific surface area for the loaded inorganic phase change material to transfer heat, but also produce a heterogeneous nucleation effect on the inorganic phase change material, prompting the phase change material to rapidly undergo phase transition to achieve thermal energy storage and release, thereby effectively reducing the supercooling of the phase change material and significantly enhancing its heat conduction and thermal response rate. At the same time, by forming a dense silica shell layer on the outside of the microcapsule, the inorganic phase change material is tightly sealed and effectively protected, thereby preventing leakage and loss of the phase change material and significantly improving the working life of the phase change material. The present invention provides a method for preparing a "core-shell" type silica / inorganic phase change material microcapsule. The preparation method first uses a surfactant, an inorganic phase change material, and an organic phase to establish an emulsion template system. Then, using oxalic acid as an initiator, an emulsion template self-assembly method and a sol-gel method are used to finally form a dense silica shell and an inorganic phase change material core. By strictly controlling the amount of surfactant, core / shell raw material ratio, stirring rate and other synthesis conditions, silica / inorganic phase change material microcapsules with dense surface morphology can be successfully prepared.

[0008] Compared to traditional phase change materials, the present invention's "core-shell" silica / inorganic phase change material microcapsules provide a large contact area for the loaded phase change material. This not only enables the phase change material to achieve a faster thermal response and higher thermal conductivity, but also significantly reduces supercooling, resulting in superior, more stable and reliable thermal management performance. Using an inorganic phase change material as the core material and inorganic sodium silicate as the coating material, the present invention effectively achieves a dual-temperature thermal management effect of latent heat storage and thermochemical energy storage, reducing energy consumption. It is suitable for applications in energy storage power stations, aerospace, solar energy utilization, industrial waste heat recovery, and other fields.

[0009] In order to achieve the above technical objectives, the technical solutions adopted by the present invention are as follows:

[0010] A "core-shell" type silica / inorganic phase change material microcapsule, characterized in that the microcapsule is a microcapsule with dense silica as the shell and an inorganic phase change material as the core, and has a typical "shell-core" structure, and the mass ratio of inorganic hydrated salt to deionized water in the inorganic phase change material is 1:(0.5~1).

[0011] Furthermore, the microcapsules have higher phase change enthalpy value and thermal response rate and lower supercooling, which can effectively achieve the dual-temperature thermal management effect of latent heat energy storage-thermochemical energy storage.

[0012] A method for preparing the "core-shell" type silica / inorganic phase change material microcapsules, the preparation method comprising the following steps:

[0013] (1) Preparation of "water-in-oil" emulsion

[0014] In reaction flask A, the surfactant and inorganic phase change material were mixed and ultrasonically dispersed. The mixing temperature was adjusted to 10°C higher than the melting point of the inorganic phase change material and stirred continuously for 30 minutes to obtain a stable and uniform aqueous phase solution. At the same temperature, a certain amount of n-butanol and n-hexane were added respectively and vigorously stirred at a speed of 500-1500 rpm for 30 minutes to obtain a stable "water-in-oil" emulsion.

[0015] (2) Silicon source hydrolysis, self-assembly and polycondensation

[0016] At the same temperature, in another reaction flask B, an appropriate amount of sodium metasilicate nonahydrate was weighed and dissolved in deionized water according to the desired shell-core ratio. An acidic solution was slowly added dropwise. After the acidic solution was added, stirring was continued for 30 minutes to obtain a silica precursor solution. This solution was then poured into reaction flask A and the reaction continued for 6 hours. After stirring was stopped, the solution was aged at the same reaction temperature for 2 hours to allow the precursor to complete the polycondensation reaction on the droplet surface, resulting in a suspension of phase change microcapsules. The target product was then filtered to obtain the target product. After washing several times with deionized water and alcohol, the target product was dried until the washing solvent was completely evaporated, resulting in silica / inorganic phase change material microcapsules with a "shell-core" structure.

[0017] Furthermore, the inorganic phase change material uses an inorganic hydrated salt and water, and the inorganic hydrated salt includes one or more of sodium acetate trihydrate, sodium thiosulfate pentahydrate, sodium sulfate decahydrate, and disodium hydrogen phosphate dodecahydrate, preferably sodium acetate trihydrate.

[0018] Furthermore, the silicon source is any one of sodium metasilicate nonahydrate and tetraethyl orthosilicate, preferably sodium metasilicate nonahydrate.

[0019] Furthermore, in step (1), the mass ratio of the inorganic hydrated salt to deionized water is 1:(0.5-1), preferably 1:0.8.

[0020] Furthermore, in step (1), the mass ratio of the inorganic phase change material to the silicon source is 1:(0.4-1), preferably 5:4, and every 15g of the inorganic phase change material corresponds to 0.5-1.5g of surfactant and 30-150mL of organic solvent.

[0021] Furthermore, the acidic solution in step (2) is any one of oxalic acid and acetic acid, preferably oxalic acid solution.

[0022] Furthermore, the reaction speed in step (2) is 500-1500 rpm, preferably 1000 rpm.

[0023] Furthermore, the drying temperature in step (3) is 40° C. to 80° C., preferably 60° C. The drying time is 12 to 48 hours, preferably 12 to 18 hours.

[0024] The beneficial effects of adopting the technical solution of the present invention are:

[0025] (1) In view of the defects of traditional phase change materials such as low thermal conductivity, slow thermal response rate, and high supercooling, the "shell-core" type silica / inorganic phase change material microcapsules prepared in the present invention can not only provide a huge specific surface area for the loaded inorganic phase change material, but also produce a significant heterogeneous nucleation effect, thereby effectively suppressing the supercooling phenomenon of the phase change material and greatly improving the thermal conductivity and thermal response rate of the phase change material.

[0026] (2) The "shell-core" type silica / inorganic phase change material microcapsules prepared by the present invention are coated with dense silica on the outside. This new "shell-core" structure can effectively solve the volume change and liquid leakage problems during the phase change process of the traditional phase change material core material, significantly improve the phase change cycle stability of the loaded phase change material, and extend its working life.

[0027] (3) The "shell-core" type silica / inorganic phase change material microcapsules of the present invention, although their structure is complex, can be prepared by an in-situ one-step method. The preparation method is simple, no toxic or harmful substances are generated during the production process, the preparation process is green and environmentally friendly, and it is easy to industrialize. The prepared microcapsules can achieve highly sensitive thermal management and thermal temperature regulation, and are suitable for energy storage power stations, aerospace, solar energy utilization, industrial waste heat recovery and other fields. Its potential application fields are very wide.

[0028] (4) Differential scanning calorimetry curves of “shell-core” silica / inorganic phase change material microcapsules at different water contents. It can be seen that increasing the water content in the core material appropriately is beneficial to improving the phase change properties of the composite material and increasing the coating efficiency of silica. Because adding water helps prevent the dehydration of the hydrated salt, the composition of the hydrated salt can still be maintained after being coated. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the FT-IR Fourier transform infrared spectrum of the "shell-core" type silica / inorganic phase change material microcapsules.

[0030] Figure 2 This is a scanning electron microscope photo of the "shell-core" type silica / inorganic phase change material microcapsule.

[0031] Figure 3 Differential scanning calorimetry curves of "shell-core" silica / inorganic phase change material microcapsules at different water contents.

[0032] Figure 4 Differential scanning calorimetry curves of "shell-core" silica / inorganic phase change material microcapsules at different core-to-wall ratios.

[0033] Figure 5 The differential scanning calorimeter curves of "shell-core" silica / inorganic phase change material microcapsules at different rotation speeds.

[0034] Figure 6 This is the temperature change curve of the thermal platform experiment of "shell-core" type silica / inorganic phase change material microcapsules. DETAILED DESCRIPTION

[0035] The following examples are implemented based on the technical solution of the present invention, and provide detailed synthesis methods and implementation processes, but these examples are not intended to limit the scope of protection of the present invention. "One embodiment" or "embodiment" referred to herein refers to a specific feature, structure or characteristic that may be included in at least one implementation of the present invention. The "in one embodiment" that appears in different places in this specification does not refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments. The present invention is further described below in conjunction with the examples.

[0036] Example 1

[0037] (1) Preparation of "water-in-oil" emulsion

[0038] Weigh 8.3 g of sodium acetate trihydrate and 6.8 g of deionized water and heat to melt. In reaction flask A, mix 0.5 g of CTAB (cetyltrimethylammonium bromide) and the inorganic phase change material. Ultrasonic dispersion is performed. Stir continuously in a 60°C oil bath for 30 min to obtain a stable and uniform aqueous phase solution. At the same temperature, add 1 g of n-butanol and 75 mL of n-hexane, respectively, and vigorously stir at 1000 rpm for 30 min to obtain a stable "water-in-oil" emulsion.

[0039] (2) Silicon source hydrolysis, self-assembly and polycondensation

[0040] At the same temperature, 11.82g of sodium metasilicate nonahydrate was weighed into a beaker, followed by 100mL of deionized water and stirring at 600rpm for 30 minutes. Then, 7.67g of oxalic acid was slowly added to adjust the solution's pH to approximately 3-4. Stirring was continued for 30 minutes to obtain a stable, uniform, and transparent silica precursor solution. This solution was then added dropwise to reaction flask A and the reaction continued for 6 hours. Stirring was then turned off, and the mixture was aged at the same temperature for 2 hours to allow the precursor to complete the polycondensation reaction on the droplet surface, resulting in a suspension of phase change microcapsules. The target product was then filtered and washed several times with deionized water and then ethanol, yielding silica / inorganic phase change material microcapsules with a "shell-core" structure.

[0041] Examples 2 to 5

[0042] (1) Preparation of "water-in-oil" emulsion

[0043] Weigh 8.3 g of sodium acetate trihydrate and 6.8 g of deionized water and heat to melt. In reaction flask A, mix 0.5 g of CTAB and the inorganic phase change material, disperse them ultrasonically, and stir continuously in a 60°C oil bath for 30 minutes to obtain a stable and uniform aqueous phase solution. At the same temperature, add 1 g of n-butanol and 75 mL of n-hexane, respectively, and stir vigorously at 1000 rpm for 30 minutes to obtain a stable "water-in-oil" emulsion.

[0044] (2) Silicon source hydrolysis, self-assembly and polycondensation

[0045] At the same temperature, according to different core-to-wall ratios (core-to-wall ratio in Example 2 is 1:0.5, in Example 3 it is 1:0.6, in Example 4 it is 1:0.8, and in Example 5 it is 1:0.9), 7.11g, 8.68g, 11.82g, and 13.4g of sodium metasilicate nonahydrate were weighed into a beaker, 100mL of deionized water was added, and the mixture was stirred at 600rpm for 30min. Oxalic acid was slowly added to adjust the pH of the solution to about 3-4, and stirring was continued for 30min to obtain a stable, uniform, and transparent silica precursor solution, which was then added dropwise to reaction flask A and the reaction was continued for 6h. Subsequently, stirring was turned off and the mixture was aged at the reaction temperature for 2h to allow the precursor to complete the polycondensation reaction on the surface of the droplets to obtain a suspension of phase change microcapsules. The target product was then obtained by filtration, and then washed several times with deionized water and alcohol to obtain silica / inorganic phase change material microcapsules with a "shell-core" structure.

[0046] Examples 6 to 8

[0047] (1) Preparation of "water-in-oil" emulsion

[0048] 8.3 g of sodium acetate trihydrate and 6.8 g of deionized water were weighed and heated to melt. 0.5 g of CTAB and the inorganic phase change material were mixed in reaction flask A, ultrasonically dispersed, and stirred continuously in a 60°C oil bath for 30 min to obtain a stable and uniform aqueous phase solution. At the same temperature, 1 g of n-butanol and 75 mL of n-hexane were respectively added, and the mixture was vigorously stirred at a set speed (500 rpm in Example 6, 1000 rpm in Example 7, and 1500 rpm in Example 8) for 30 min to obtain a stable "water-in-oil" emulsion.

[0049] (2) Silicon source hydrolysis, self-assembly and polycondensation

[0050] At the same temperature, 11.82g of sodium metasilicate nonahydrate was weighed into a beaker, followed by 100mL of deionized water and stirring at 600rpm for 30 minutes. Then, 7.68g of oxalic acid was slowly added to adjust the solution's pH to approximately 3-4. Stirring was continued for 30 minutes to obtain a stable, uniform, and transparent silica precursor solution. This solution was then added dropwise to reaction flask A and the reaction continued for 6 hours. Stirring was then turned off, and the mixture was aged at the same temperature for 2 hours to allow the precursor to complete the polycondensation reaction on the droplet surface, resulting in a suspension of phase change microcapsules. The target product was then filtered and washed several times with deionized water and then ethanol, yielding silica / inorganic phase change material microcapsules with a "shell-core" structure.

[0051] Example 9

[0052] (1) Preparation of "water-in-oil" emulsion

[0053] Weigh 12.67 g of disodium hydrogen phosphate dodecahydrate and 3.98 g of deionized water and heat to melt. In reaction flask A, mix 0.5 g of CTAB and the inorganic phase change material, disperse them ultrasonically, and stir continuously in a 50°C oil bath for 30 minutes to obtain a stable and uniform aqueous phase solution. At the same temperature, add 1 g of n-butanol and 75 mL of n-hexane, respectively, and stir vigorously at 1000 rpm for 30 minutes to obtain a stable "water-in-oil" emulsion.

[0054] (2) Silicon source hydrolysis, self-assembly and polycondensation

[0055] At the same temperature, 11.82g of sodium metasilicate nonahydrate was weighed into a beaker, followed by 100mL of deionized water and stirring at 600rpm for 30 minutes. Then, 7.68g of oxalic acid was slowly added to adjust the solution's pH to approximately 3-4. Stirring was continued for 30 minutes to obtain a stable, uniform, and transparent silica precursor solution. This solution was then added dropwise to reaction flask A and the reaction continued for 6 hours. Stirring was then turned off, and the mixture was aged at the same temperature for 2 hours to allow the precursor to complete the polycondensation reaction on the droplet surface, resulting in a suspension of phase change microcapsules. The target product was then filtered and washed several times with deionized water and then ethanol, yielding silica / inorganic phase change material microcapsules with a "shell-core" structure.

[0056] Test Example 1

[0057] The physical and chemical properties of the composite phase change materials in Examples 1-9 were measured, and the specific results are shown in Table 1.

[0058] Table 1 Phase change properties of “shell-core” silica / inorganic phase change material microcapsules

[0059] Example Sample name Phase transition temperature (℃) Enthalpy change (J / g) 1 <![CDATA[SAT@SiO2-H2O]]> 73.00 625.84 2 Si-1 78.59 723.04 3 Si-2 77.30 625.84 4 Si-3 80.04 918.17 5 Si-4 79.77 845.87 6 500rpm 82.66 1314.10 7 1000rpm 80.04 918.17 8 1500rpm 89.43 1335.70 9 <![CDATA[DSP@SiO2]]> 73.24 800.12

[0060] From Table 1, Figure 1 and Figure 2 It can be seen that the silica / inorganic phase change material microcapsules prepared by the present invention have good physical and chemical properties and an elliptical microscopic morphology. The chemical structures of the three materials SAT, H2O@SiO2, and SAT@SiO2 were detected by Fourier transform infrared spectroscopy. As shown in the figure, for SAT, 3650~3200cm -1 The broad absorption band is the stretching vibration peak of -OH, ~2986cm -1 The characteristic absorption peak at 1700~1400cm corresponds to the stretching vibration of -CH3 -1 The four-finger absorption peak at 1049 cm corresponds to the characteristic peak of -C=O. -1 The characteristic absorption peak of -CO appears. In addition, 1500~400cm -1 There are multiple absorption peaks in the region, which may be corresponding to the lattice vibration of sodium salt. For H2O@SiO2, ~3394cm -1 and ~965cm -1 The absorption peaks appearing at 1052 cm-1 belong to the stretching vibration peak and bending vibration peak of Si-OH, respectively. -1 It is the asymmetric stretching vibration peak of Si-O-Si, ~440cm -1 The absorption peaks nearby belong to the bending vibration peaks of the Si-O-Si group. The infrared spectrum of the SAT@SiO2 composite material shows the infrared characteristic peaks of SAT and SiO2, indicating that the composite material contains two substances and no new groups are generated.

[0061] Figure 3 Differential scanning calorimetry (DSC) curves of "shell-core" silica / inorganic phase change material microcapsules at different water contents are presented. It can be seen that appropriately increasing the water content of the core material can enhance the phase change properties of the composite material and improve the silica encapsulation efficiency. This is because the addition of water helps prevent dehydration of the hydrated salt, maintaining its composition after encapsulation. In other words, a certain water content can effectively prevent phase separation of the hydrated salt.

[0062] Figure 4 Differential scanning calorimetry (DSC) curves of core-shell silica / inorganic phase change material microcapsules at different core-to-wall ratios are presented. The overall changes in peak shape for the four materials are nearly identical. As the core-to-wall ratio increases from 1:0.9 to 1:0.8, the surface area of the peak increases, indicating that the heat of reaction increases with the core-to-wall ratio. This is because SiO2 does not undergo a phase change; only the hydrated salt participates in the reaction. Further increasing the core-to-wall ratio to 1:0.6 decreases the phase change enthalpy of the prepared material. This suggests that excessive amounts of hydrated salt are added, resulting in thin microcapsule walls coated with the wall material. These walls are easily broken during subsequent reactions, causing core material leakage, which in turn is detrimental to the improvement of the material's phase change properties.

[0063] Figure 5 The differential scanning calorimeter curves of "shell-core" silica / inorganic phase change material microcapsules at different rotational speeds are given. Due to the wrapping effect of the wall material, a certain temperature difference effect is formed between the phase change material and the wall material. After microencapsulation, the effective content of the phase change material decreases, causing the total phase change enthalpy of the composite material to decrease. With the increase of the rotational speed, the area of the first peak first increases and then decreases, and the area of the second peak first decreases and then increases, indicating that the rotational speed affects the coating effect of the material and its ability to bind water molecules. When the stirring speed is too low, it is not conducive to the dispersion uniformity of the emulsion system, so that part of the core material is not coated by the emulsifier molecules and is lost during the subsequent filtration process. If the stirring speed is too high, there is a risk of demulsification and wall material rupture.

[0064] Figure 6Figure 3 shows the temperature curves of a thermal platform experiment for a core-shell silica / inorganic phase change material microcapsule. To determine the material's response speed to heat and thermal management effectiveness, three experimental conditions were compared: (a) air cooling; (b) H2O@SiO2 as a thermal protection material; and (c) SAT@SiO2, with a phase change temperature range of 70-100°C, as a thermal protection material. It can be seen that under air cooling alone, the cold-end temperature rapidly rose to 99.26°C within 5 minutes and remained at around 101.9°C. The H2O@SiO2 material primarily absorbs heat through the small amount of water encapsulated within the SiO2. Compared to air, silica has relatively low thermal conductivity. Under this condition, a stable plateau period of 10 minutes appeared at approximately 70°C. After 40 minutes, the surface temperature of the material remained at around 91.7°C. The SAT@SiO2 material showed a temperature drop trend at 10 minutes, and water droplets appeared at 5 minutes. The rapid cooling effect of the cold end was achieved by utilizing the decomposition process of crystalline water converted into free water and the heat absorption capacity during vaporization. After 40 minutes of continuous heating, the cold end temperature rose to 79.8°C, which was 22.2°C lower than the unprotected Air group. As the temperature gradually increased, the crystalline water of sodium acetate trihydrate gradually decomposed and vaporized. In addition, the surrounding air was atomized by heat, and a small amount of white mist appeared on the inner wall of the beaker. This is because sodium acetate trihydrate will exchange materials with the environment during the heating process, and water molecules will tend to be dissipated into the environment in the direction of entropy increase. SiO2 encapsulates the hydrated salt, which has a certain effect of blocking water and delaying the volatilization of water, thereby ensuring the stability of the thermochemical energy storage capacity and showing a better cooling effect.

[0065] The focus of the present invention is to select inorganic hydrated salts that are cheap, easily available, have high phase change latent heat, and are non-flammable, and inorganic sodium silicate that is stable, non-toxic and environmentally friendly as raw materials, and synthesize coated inorganic hydrated salt phase change materials based on microencapsulation technology, thereby obtaining silica / inorganic hydrated salt microcapsules with high phase change enthalpy, low supercooling and high thermal stability, thereby achieving a dual-temperature heat storage effect of latent heat storage and thermochemical energy storage.

Claims

1. A method for preparing core-shell silica / inorganic phase change material microcapsules, characterized in that: The microcapsule has a typical shell-core structure with silicon dioxide as the shell and an inorganic phase change material as the core; the mass ratio of the inorganic hydrated salt to deionized water in the inorganic phase change material is 1:(0.5-1); The specific steps include: (1) Preparation of water-in-oil emulsion The surfactant and the inorganic phase change material are mixed, ultrasonically dispersed, and continuously stirred to obtain a stable and uniform aqueous phase solution; an organic solvent is added, wherein the organic solvent is n-butanol and n-hexane, and stirred to obtain a stable water-in-oil emulsion; (2) Preparation of silica precursor Dissolve the silicon source in deionized water, slowly add the acidic solution dropwise, adjust the pH to 3-4, and continue stirring after the addition is complete to obtain a silicon dioxide precursor solution; (3) Shell polycondensation and shell-core self-assembly The silica precursor solution is added dropwise to the water-in-oil emulsion and the reaction is continued for 4-8 hours. After stopping stirring, the mixture is aged at the reaction temperature for 1-3 hours to allow the precursor to complete the polycondensation reaction on the surface of the droplets to obtain a suspension of phase change microcapsules; after filtering, washing and drying, silica / inorganic phase change material microcapsules are obtained.

2. The method for preparing a core-shell silica / inorganic phase change material microcapsule according to claim 1, characterized in that: The inorganic phase change material is prepared using inorganic hydrated salt and water. The specific preparation method is: weigh the inorganic hydrated salt phase change material, dissolve it in deionized water, and continue stirring for 5-20 minutes; the inorganic phase change material refers to a solution obtained by uniformly mixing inorganic hydrated salt and deionized water in a mass ratio of 1: (0.5-1); the inorganic hydrated salt includes one or more of sodium acetate trihydrate, sodium thiosulfate pentahydrate, sodium sulfate decahydrate, and disodium hydrogen phosphate dodecahydrate.

3. The method for preparing a core-shell silica / inorganic phase change material microcapsule according to claim 1, characterized in that: The silicon source is sodium metasilicate nonahydrate and / or tetraethyl orthosilicate.

4. The method for preparing a core-shell silica / inorganic phase change material microcapsule according to claim 1, wherein: The acidic solution is a weak acid selected from oxalic acid and / or acetic acid.

5. The method for preparing a core-shell silica / inorganic phase change material microcapsule according to claim 1, characterized in that: The mass ratio of the inorganic phase change material to the silicon source is 1:(0.4-1).

6. The method for preparing a core-shell silica / inorganic phase change material microcapsule according to claim 1, characterized in that: The mass ratio of the inorganic phase change material to the surfactant is 1:(0.03-0.1), and the mass ratio of the inorganic phase change material to the organic solvent is 1g:(2-10)mL.

7. Use of the microcapsules prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The microcapsule realizes the dual-temperature thermal management effect of latent heat storage and thermochemical energy storage, and is applied to energy storage power stations, aerospace, solar energy utilization, etc. Use and industrial waste heat recovery.

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