A kaolin-modified PVA aerogel / paraffin-shaped composite phase change material for lithium battery thermal management and its preparation method

Abstract

This invention discloses a method for preparing a kaolin-modified PVA aerogel / paraffin-shaped composite phase change material for lithium battery thermal management. The method includes the following steps: Step 1, adding PVA to deionized water and stirring until homogeneous to obtain a PVA solution; Step 2, adding kaolin to the PVA solution obtained in Step 1, adding boric acid solution, and stirring until homogeneous to obtain a mixture; Step 3, pouring the mixture into a silicone mold and freeze-drying to obtain a kaolin / PVA composite aerogel; Step 4, molten paraffin, placing it into the composite aerogel, and preparing the composite phase change material using a vacuum impregnation method. This invention solves the problems of easy leakage, poor shape stability, low thermal conductivity, and insufficient cycle stability of paraffin phase change materials. It also optimizes the structure and performance of the aerogel carrier, improves the mechanical properties of the composite phase change material, and provides reliable material support for thermal management applications.

Description

Technical Field

[0001] This invention relates to a phase change energy storage material, specifically to a kaolin-modified PVA aerogel / paraffin-shaped composite phase change material for lithium battery thermal management and its preparation method. Background Technology

[0002] With the escalating global energy crisis and increasing demands for energy conservation and emission reduction, latent heat storage technology has received widespread attention. Phase change materials (PCMs), due to their ability to store and release large amounts of heat during phase change processes and their stable temperature, are widely used in thermal energy storage, building energy conservation, and battery thermal management. Based on chemical composition, PCMs can be divided into three categories: organic, inorganic, and eutectic. Among them, organic PCMs are chemically stable, exhibit no phase separation, and have suitable phase change temperatures, making them the mainstream research choice. Paraffin wax, as the most representative organic PCM, boasts high heat storage density, good thermochemical stability, low cost, and non-toxicity, leading to extensive research and application. However, paraffin wax has significant drawbacks: it is prone to leakage during phase change, has poor shape stability, and low thermal conductivity, making it difficult to directly meet practical requirements. To address these issues, researchers have modified it by adding nanoparticles and microencapsulation, which has improved thermal conductivity and leak-proof performance, but still suffers from limited encapsulation effectiveness and complex processes.

[0003] Aerogels are low-density, high-specific-surface-area three-dimensional porous materials with strong adsorption capacity, effectively solving the leakage problem of phase change materials. They also possess excellent thermal insulation properties, making them suitable for applications such as thermal insulation and flame retardant materials. In lithium-ion battery thermal management, aerogels can block heat transfer and delay thermal runaway, making them ideal encapsulation carriers. Polyvinyl alcohol (PVA) aerogels are highly water-soluble, biodegradable, and their porous structure allows for the loading of paraffin wax and improved shape stability, making them a preferred composite carrier for phase change materials. Existing research has shown that modifying PVA aerogels with crosslinking agents and inorganic minerals significantly improves their mechanical strength, porosity, and thermal insulation performance, enabling efficient encapsulation of paraffin wax.

[0004] However, existing systems still have key shortcomings: paraffin itself is flammable, the composite material has poor flame retardancy, and it is easily combustible at high temperatures, limiting its application in high-risk scenarios such as batteries. Current modification strategies involve adding flame retardants and nanofillers, such as calcium silicate, carbon nanotubes, and phytic acid, to PVA aerogels. This can improve the material's flame retardancy, mechanical properties, and thermal insulation, with some systems showing a significant increase in limiting oxygen index and a significant decrease in heat release rate.

[0005] Kaolin is a natural layered silicate mineral with abundant reserves and low cost. At high temperatures, it can form a dense barrier layer that blocks the transfer of heat and oxygen, combining physical barrier and free radical fixation. It has been proven to effectively improve the flame retardant properties of polymer materials such as polypropylene and epoxy resin, reducing the heat release rate and increasing the oxygen index. It is an environmentally friendly and efficient inorganic flame retardant material. Summary of the Invention

[0006] This invention provides a kaolin-modified PVA aerogel / paraffin-shaped composite phase change material for lithium battery thermal management and its preparation method. It aims to solve the problems of easy leakage, poor shape stability, low thermal conductivity and insufficient cycle stability of paraffin phase change materials. At the same time, it optimizes the structure and performance of the aerogel carrier, improves the mechanical properties of the composite phase change material, and provides reliable material support for thermal management applications.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A kaolin-modified PVA aerogel / paraffin-based shaped composite phase change material for lithium battery thermal management is disclosed. The material uses polyvinyl alcohol (PVA) aerogel as the matrix, kaolin as the inorganic modifier, and paraffin (PA) as the phase change functional material. The shaped composite phase change material is prepared via vacuum impregnation. The specific preparation method is as follows:

[0009] Step 1: PVA solution preparation: Add 6-10g of PVA to 90-94g of deionized water, stir well, and obtain a PVA solution with a mass concentration of 6-10%.

[0010] Step 2, Preparation of the mixture: Add 1-4g of kaolin to the PVA solution obtained in Step 1, add 10ml of boric acid solution with a mass concentration of 0.5-1.0%, stir evenly to obtain the mixture;

[0011] Step 3, preparation of composite aerogel: The mixture is poured into a silicone mold and freeze-dried to obtain kaolin / PVA composite aerogel. The freeze-drying conditions are: first pre-freezing at -20~-10℃ for 10~15h, and then freeze-drying at -80℃ for 70~75h.

[0012] Step 4: Preparation of composite phase change material: Molten paraffin is placed in composite aerogel, and composite phase change material is prepared by vacuum impregnation method. The impregnation temperature is controlled at 40~60℃ and the impregnation time is 0.5~1.5h.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] 1. Mechanical properties: Kaolin improves the mechanical properties of aerogel by 49.91%; the best sample can withstand 1kg of material without deformation.

[0015] 2. Leakage prevention performance: With a paraffin loading of 405.08%, the leakage rate is only 1.37% after 1 hour of heat preservation at 50℃, demonstrating excellent sealing effect.

[0016] 3. Thermal properties: The thermal conductivity is as low as 0.032 W / (m·K) (aerogel) and 0.23 W / (m·K) (composite material), which is 32.4% lower than that of the pure system; the latent heat of phase change reaches 159.7 J / g, and the heat storage performance is good.

[0017] 4. Cyclic stability: After 600 cycles of heating and cooling, the mass loss is 4.83%, the enthalpy retention rate is 99.31%, and the cycle life is excellent.

[0018] 5. Safety performance: The material is self-extinguishing when the flame is removed, with an afterflame time of <180s, and possesses basic flame-retardant and self-extinguishing characteristics. Attached Figure Description

[0019] Figure 1 This is a flowchart of the preparation process for shaped phase change materials;

[0020] Figure 2 SEM images of composite aerogels and composite phase change materials;

[0021] Figure 3 The pore size distribution of the composite aerogel;

[0022] Figure 4 The compressibility of the composite aerogel;

[0023] Figure 5 The thermal conductivity of the composite aerogel and the composite phase change material;

[0024] Figure 6 The energy storage density of the phase change material;

[0025] Figure 7 The corresponding DSC endothermic and exothermic curves of SSPCM3 after 600 thermal cycles are shown. Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0027] This invention provides a method for preparing a kaolin-modified PVA aerogel / paraffin-shaped composite phase change material for lithium battery thermal management, such as... Figure 1 As shown, the specific preparation steps are as follows:

[0028] 8g of PVA was added to 92g of deionized water and stirred at 90℃ for 1 hour to prepare an 8% PVA solution. Different masses of kaolin (0g, 1g, 2g, 3g, and 4g) were added to five 20ml portions of the PVA solution, and the mixtures were magnetically stirred at 60℃ for 1 hour to obtain homogeneous solutions with different proportions. Then, 10ml of a 0.8% boric acid solution was added and stirred at 60℃ for 30 minutes to obtain a mixed solution. The mixed solution was poured into a silicone mold, pre-frozen at -20℃ for 12 hours, and freeze-dried for 72 hours to obtain five types of kaolin / PVA aerogels. Composite phase change materials were prepared using a vacuum impregnation method. Excess paraffin was heated on a 50℃ heating stage. After the paraffin was completely melted, the five composite aerogels with different proportions were placed in beakers containing molten paraffin and transferred together to a vacuum drying oven. The oven was maintained at 50℃ under vacuum for 1 hour to allow the liquid paraffin to penetrate the aerogel matrix. The composite PCMs were then placed in an oven at 50°C and placed on filter paper for 4 hours to remove excess paraffin, resulting in five composite phase change materials. The composition of the five composite phase change materials is shown in Table 1.

[0029] Table 1

[0030]

[0031] Performance verification:

[0032] Compression tests were conducted on the aerogel using an electronic universal testing machine, and its microstructure was observed using a scanning electron microscope. The pore structure of the aerogel was observed using a mercury porosimeter. The phase transition temperature and latent heat of the phase change material were measured using differential scanning calorimetry (DSC). The thermal conductivity of the phase change material was measured using a thermal conductivity meter. The flame retardant properties of the material were tested using a critical oxygen index analyzer. Heating and cooling cycle experiments were conducted on the samples using a thermal cycling instrument.

[0033] Depend on Figure 2 It can be seen that as the kaolin content increases, the pore structure of the aerogel gradually strengthens. When a small amount of kaolin is added, the pore structure of K1 / PVA ((b)) tends to be dense, while having a small number of pores. However, with the increase of kaolin content, K2 / PVA clearly exhibits a porous network structure with a large number of interconnected pores ((c)). Similarly, the structure of K3 / PVA ((d)) clearly shows a uniformly distributed three-dimensional porous structure and a large number of tiered pore structures. In contrast, K4 / PVA ((e)) shows local agglomeration of pores due to excessive kaolin, resulting in irregular pore morphology and reduced pore structure integrity. In summary, the K3 / PVA composite aerogel has the optimal microstructure—a uniformly distributed three-dimensional porous structure that ensures high porosity, which is beneficial for paraffin loading, and enhances the mechanical properties of the aerogel through the synergistic effect of kaolin and PVA.

[0034] Depend on Figure 3 It can be seen that the pore size distribution curves of the composite aerogels have roughly the same trend, with two peaks in the 1000~10000nm range. With the increase of kaolin content, the nano-sized pore size peaks shift slightly towards smaller sizes, while the micron-sized peaks gradually decrease. In particular, K3 / PVA has a distinct single peak in the 1000nm~10000nm range, and its pore size distribution is uniform. However, K4 / PVA shows an abnormally high peak at around 10μm, indicating that kaolin agglomeration leads to the formation of a large number of micron-sized macropores, which disrupts the uniformity of pore distribution.

[0035] Figure 4 The stress-strain curves of kaolin / PVA aerogels show that the stress at 80% strain initially increases and then decreases with increasing kaolin content. The K3 / PVA composite aerogel exhibits strong compressive stress, demonstrating excellent mechanical properties. This enhancement can be attributed to the formation of hydrogen bonds between the hydroxyl groups on the kaolin surface and the hydroxyl groups on the PVA molecular chains, resulting in a robust three-dimensional porous structure through strong hydrogen bond interaction. In contrast, the compressive properties of the K4 / PVA composite aerogel decrease significantly, mainly due to a decrease in porosity, disruption of the pore structure, reduced stability, and consequently, decreased mechanical properties.

[0036] Figure 5The figures show the thermal conductivity of the composite aerogel and the phase change material, respectively. With increasing kaolin content, the thermal conductivity of the composite aerogel gradually decreases to 0.032 W / (m·K) for K3 / PVA. When the kaolin content is further increased to K4 / PVA, the thermal conductivity increases to approximately 0.040 W / (m·K), which is attributed to the numerous pores within the composite aerogel. These pores force heat to transfer along tortuous paths, effectively hindering rapid heat conduction. The addition of an appropriate amount of kaolin can cross-link with the PVA matrix to form a uniform porous three-dimensional network structure. The increased proportion of still air in the aerogel pores further inhibits heat convection and conduction, resulting in a decrease in thermal conductivity. However, when the kaolin content is too high (K4 / PVA), excessive kaolin particles tend to agglomerate in the PVA matrix, not only disrupting the porous network structure of the aerogel but also forming continuous heat conduction channels in the agglomerated areas. Simultaneously, the insulating effect of still air is weakened, ultimately leading to an increase in thermal conductivity. The thermal conductivity of SSPCMs decreased significantly after paraffin adsorption, and the overall trend was completely consistent with that of the aerogel matrix: the thermal conductivity continued to decrease with increasing kaolin content, reaching a minimum of approximately 0.23 W / (m·K) in SSPCM3. After further increasing the kaolin content (SSPCM4), the thermal conductivity rebounded to approximately 0.25 W / (m·K). This result indicates that the porous structure of the aerogel matrix and the kaolin modification effect can still effectively regulate the thermal conductivity of the composite phase change material after paraffin adsorption, with SSPCM3 achieving the best thermal insulation effect.

[0037] Figure 6 The thermal storage density of the phase change material (PCM) decreases further with the addition of kaolin. This is mainly because kaolin itself lacks thermal storage capacity and occupies part of the adsorption space within the PVA aerogel, thus leading to a decrease in thermal storage density. However, with the increase of kaolin content in the PVA aerogel, the thermal storage density increases slightly, reaching its maximum at SSPCM3. This is primarily because K3 / PVA aerogel has the highest porosity and contains a relatively high proportion of PA compared to other PCMs, thus exhibiting stronger thermal storage capacity.

[0038] Figure 7 The corresponding DSC endothermic and exothermic curves of SSPCM3 after 600 thermal cycles show that its mass loss is only 4.83% after 600 cycles, and its melting enthalpy and crystallization enthalpy decrease by only 0.69% and 0.78% respectively, demonstrating excellent cycle stability.

[0039] Based on the above characterization, the composite phase change material (SSPCM3) with the best performance was selected. This material has a leakage rate of only 1.37%, a thermal conductivity of 0.23 W / (m·K), a latent heat of phase change of 159.7 J / g, a mass loss of 4.83% after 600 cycles, and an enthalpy retention rate of 99.31%, making it the best in terms of overall performance.

Claims

1. A method for preparing a kaolin-modified PVA aerogel / paraffin-shaped composite phase change material for lithium battery thermal management, characterized in that... The method includes the following steps: Step 1: PVA solution preparation: Add 6-10g of PVA to 90-94g of deionized water, stir well, and obtain a PVA solution with a mass concentration of 6-10%. Step 2, Preparation of the mixture: Add 1-4g of kaolin to the PVA solution obtained in Step 1, add 10ml of boric acid solution with a mass concentration of 0.5-1.0%, stir evenly to obtain the mixture; Step 3, preparation of composite aerogel: The mixture is poured into a silicone mold and freeze-dried to obtain kaolin / PVA composite aerogel; Step 4: Preparation of composite phase change material: Molten paraffin is placed in composite aerogel and composite phase change material is prepared by vacuum impregnation.

2. The preparation method of the kaolin-modified PVA aerogel / paraffin-shaped composite phase change material for lithium battery thermal management according to claim 1, characterized in that... In step 1, the mass concentration of the PVA solution is 8%.

3. The preparation method of the kaolin-modified PVA aerogel / paraffin-shaped composite phase change material for lithium battery thermal management according to claim 1, characterized in that... In step 2, the mass concentration of the boric acid solution is 0.8%.

4. The preparation method of the kaolin-modified PVA aerogel / paraffin-shaped composite phase change material for lithium battery thermal management according to claim 1, characterized in that... In step 3, the freeze-drying conditions are as follows: first, pre-freeze at -20~-10℃ for 10~15h, and then freeze-dry at -80℃ for 70~75h.

5. The preparation method of the kaolin-modified PVA aerogel / paraffin-shaped composite phase change material for lithium battery thermal management according to claim 1, characterized in that... In step 4, the immersion temperature is controlled at 40~60℃ and the immersion time is 0.5~1.5h.

6. A kaolin-modified PVA aerogel / paraffin-shaped composite phase change material prepared by the method of any one of claims 1-5.

7. The application of a kaolin-modified PVA aerogel / paraffin-shaped composite phase change material prepared by the method of any one of claims 1-5 in the thermal management of lithium batteries.

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