Composite phase change material and preparation method thereof
By introducing metal-organic gel and expanded graphite into phase change materials, a three-dimensional thermally conductive network was constructed, which solved the problems of thermal conductivity and stability of phase change materials, realized a composite phase change material with high thermal conductivity and leakage resistance, and improved the thermal management effect of battery modules.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-11
- Publication Date
- 2026-04-14
AI Technical Summary
Existing phase change materials have problems such as low thermal conductivity and easy leakage in battery thermal management systems, which affect the heat dissipation effect and stability of battery modules.
A blend of polyethylene glycol, organometallic gel, and expanded graphite was used. The porous structure and hydrogen bonding of the organometallic gel anchored the polyethylene glycol, and the expanded graphite was combined to construct a three-dimensional thermally conductive network, thereby improving stability and thermal conductivity.
It achieves high thermal conductivity (up to 4.32 W/mK) and good leakage resistance, significantly improving the thermal management performance of the battery module and ensuring stable operation of the battery at high charge and discharge rates.
Smart Images
Figure CN121851998A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of phase change materials technology, and in particular to a composite phase change material and its preparation method. Background Technology
[0002] In the automotive sector, new energy electric vehicles are favored by consumers worldwide due to their advantages such as not consuming fossil fuels, producing no carbon dioxide or pollutant emissions, and having low operating costs. The market demand for fast charging is increasing, but the core component, the battery module, generates a large amount of heat at high charge and discharge rates. Coupled with the spatial accumulation effect, the unevenness worsens with increasing usage time, leading to adverse effects such as capacity reduction and shortened lifespan, and in severe cases, battery thermal runaway. Therefore, it is essential to construct a battery thermal management system that provides timely heat dissipation and ensures thermal uniformity for the battery module.
[0003] Currently, battery thermal management systems can be categorized into air-cooled, liquid-cooled, phase change material (PCM)-cooled, and heat pipe-cooled systems based on the heat transfer medium. Among these, passive battery thermal management systems, which primarily utilize PCM cooling, have garnered widespread attention due to their low-carbon and energy-saving nature, eliminating the need for an additional power system. However, PCM (such as polyethylene glycol) cooling still suffers from drawbacks, including the easy leakage of phase change components and the low thermal conductivity of solid-liquid PCMs. Summary of the Invention
[0004] The purpose of this invention is to provide a composite phase change material and its preparation method. The composite phase change material provided by this invention possesses both good thermal conductivity and leak resistance.
[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:
[0006] The present invention provides a composite phase change material comprising a blend of polyethylene glycol, a metal organogel, and expanded graphite; wherein the metal organogel is a chelate of citric acid and metal ions; and the polyethylene glycol is dispersed within and on the surface of the expanded graphite and the metal organogel.
[0007] Preferably, the composite phase change material contains 3-5 wt% expanded graphite and 20-30 wt% metal-organic gel.
[0008] Preferably, the metal ions include Zn. 2+ Cu 2+ and Fe 3+ One or more of them.
[0009] Preferably, the polyethylene glycol includes polyethylene glycol 2000.
[0010] Preferably, the thermal conductivity of the composite phase change material is 2.26 to 4.32 W / mK.
[0011] This invention provides a method for preparing the composite phase change material described above, comprising the following steps:
[0012] Citric acid, water-soluble metal salt, and alkaline solution are mixed and chelated to obtain an aqueous solution of metal-organic gel.
[0013] The metal-organic gel aqueous solution, molten polyethylene glycol and expanded graphite are mixed, and the resulting mixture is dried and cured to obtain the composite phase change material.
[0014] Preferably, the molar ratio of citric acid to the metal ions in the water-soluble metal salt is (0.5-2):1.
[0015] Preferably, the alkaline solution includes one or more of sodium hydroxide solution, sodium carbonate solution, and sodium acetate solution; the amount of alkaline solution used satisfies the molar ratio required for the acid-base neutralization reaction between the alkali and citric acid in the alkaline solution.
[0016] Preferably, mixing the metal organogel aqueous solution, molten polyethylene glycol, and expanded graphite comprises: adding the metal organogel aqueous solution to the molten polyethylene glycol, performing a first stirring, and then adding expanded graphite to the resulting mixture and performing a second stirring.
[0017] Preferably, the drying temperature is 60–80°C.
[0018] This invention provides a composite phase change material comprising a blend of polyethylene glycol, a metal-organic gel, and expanded graphite; the metal-organic gel is a chelate of citric acid and metal ions; the polyethylene glycol is dispersed within and on the surface of the expanded graphite and the metal-organic gel. This invention utilizes the capillary action and hydrogen bonding of the porous structure of the metal-organic gel to anchor the phase change material component (polyethylene glycol), improving the stability of the composite phase change material and making it less prone to leakage; the tight bonding between the expanded graphite and the metal-organic gel constructs a three-dimensional thermally conductive network, providing a continuous heat transfer path for phonon transport, increasing the mean free path of phonon transport, effectively reducing interfacial thermal resistance, and improving thermal conductivity.
[0019] The results of the embodiments show that the composite phase change material provided by the present invention, under the premise of sufficient latent heat, has a thermal conductivity of up to 4.32 W / mK, which is much higher than the thermal conductivity of pure polyethylene glycol 2000 (0.4 W / mK). Furthermore, it can maintain its original shape without collapsing when placed on a constant temperature heating table at 70°C for 5 hours, with a mass loss rate of less than 1%. Attached Figure Description
[0020] Figure 1SEM images of expanded graphite, polyethylene glycol 2000, the organometallic gel of Example 1, and various composite phase change materials;
[0021] Figure 2 Thermal conductivity results for different composite phase change materials prepared from polyethylene glycol 2000, Examples 1-5 and Comparative Example 1;
[0022] Figure 3 Leakage of polyethylene glycol 2000 and different composite phase change materials prepared according to Examples 1-5 and Comparative Example 1 after heating at 70°C for 4 hours;
[0023] Figure 4 The graph shows the mass loss rate of different composite phase change materials prepared according to Examples 1-5 and Comparative Example 1 after heating at 70°C for 4 hours. Detailed Implementation
[0024] The present invention provides a composite phase change material comprising a blend of polyethylene glycol, a metal organogel, and expanded graphite; wherein the metal organogel is a chelate of citric acid and metal ions; and the polyethylene glycol is dispersed within and on the surface of the expanded graphite and the metal organogel.
[0025] In this invention, the polyethylene glycol preferably includes polyethylene glycol 2000.
[0026] In this invention, the metal ions preferably include Zn. 2+ Cu 2+ and Fe 3+ One or more of the following, more preferably Zn 2+ .
[0027] In this invention, the content of expanded graphite in the composite phase change material is preferably 3-5 wt%, and in the embodiments of this invention, it can be 4 wt%; the content of the metal-organic gel is preferably 20-30 wt%, and in the embodiments of this invention, it can be 22 wt%, 25 wt%, and 27 wt%; the balance is polyethylene glycol.
[0028] This invention utilizes the capillary action and hydrogen bond interaction of the porous structure of metal-organic gel to anchor the phase change material component (polyethylene glycol), thereby improving the stability of the composite phase change material and making it less prone to leakage. By using the tight bonding between expanded graphite and metal-organic gel to construct a three-dimensional heat-conducting network, a continuous heat transfer path is provided for phonon transport, increasing the mean free path of phonon transport, effectively reducing interfacial thermal resistance, and improving thermal conductivity.
[0029] In this invention, the thermal conductivity of the composite phase change material is preferably 2.26 to 4.32 W / mK. In specific embodiments of this invention, the thermal conductivity of the composite phase change material is 2.26 W / mK, 2.84 W / mK, 2.85 W / mK, or 4.32 W / mK.
[0030] In this invention, the latent heat of phase change of the composite phase change material is preferably 100-140 J / g, more preferably 105-135 J / g.
[0031] This invention provides a method for preparing the composite phase change material described above, comprising the following steps:
[0032] Citric acid, water-soluble metal salt, and alkaline solution are mixed and chelated to obtain an aqueous solution of metal-organic gel.
[0033] The metal-organic gel aqueous solution, molten polyethylene glycol and expanded graphite are mixed, and the resulting mixture is dried and cured to obtain the composite phase change material.
[0034] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.
[0035] This invention involves mixing citric acid, a water-soluble metal salt, and an alkaline solution to perform a chelation reaction, thereby obtaining an aqueous solution of a metal-organic gel.
[0036] In this invention, the citric acid is preferably monohydrated citric acid; this invention does not have special requirements for the water-soluble metal salt, and any water-soluble metal salt well-known in the art is acceptable, especially when the metal ion is Zn. 2+ In this case, the water-soluble metal salt is preferably zinc acetate dihydrate.
[0037] In this invention, the preferred molar ratio of citric acid to the metal ions in the water-soluble metal salt is (0.5–2):1. In specific embodiments of this invention, the molar ratio of citric acid to the metal ions in the water-soluble metal salt can be 1:1, 1:2, 2:1, 2:3, or 3:2. In this invention, when the molar ratio of citric acid to the metal ions in the water-soluble metal salt is 3:2, the resulting composite phase change material exhibits higher thermal conductivity and good stability while ensuring the latent heat of phase change.
[0038] In this invention, the alkaline solution preferably includes one or more of sodium hydroxide solution, sodium carbonate solution, and sodium acetate solution. This invention does not have specific requirements regarding the concentration of the alkaline solution. In this invention, the amount of the alkaline solution preferably satisfies the molar ratio required for the acid-base neutralization reaction between the alkali and citric acid in the alkaline solution.
[0039] In this invention, the chelation reaction is preferably carried out under stirring conditions, and the chelation reaction time is preferably 1 hour.
[0040] After obtaining the metal-organic gel aqueous solution, the present invention mixes the metal-organic gel aqueous solution, molten polyethylene glycol and expanded graphite, and dries and solidifies the resulting mixture to obtain the composite phase change material.
[0041] In this invention, the preparation of the molten polyethylene glycol preferably includes: placing polyethylene glycol in an oil bath and heating it to 70-80°C until the polyethylene glycol is completely melted to obtain molten polyethylene glycol.
[0042] In this invention, mixing the metal organogel aqueous solution, molten polyethylene glycol, and expanded graphite comprises: adding the metal organogel aqueous solution to the molten polyethylene glycol, performing a first stirring, and then adding expanded graphite to the resulting mixture for a second stirring.
[0043] In this invention, the first stirring time is preferably 0.5 h, and the stirring speed is preferably 400-500 rad / min; the second stirring time is preferably 2-3 h, and the stirring speed is preferably 700-800 rad / min.
[0044] In this invention, the drying temperature is preferably 70–80°C, and the drying is preferably carried out in a vacuum drying oven. This invention does not have special requirements for the drying time, as long as the moisture in the mixture is removed.
[0045] In this invention, the curing is preferably carried out in a mold. Preferably, the dried material is placed into the mold, pressed using a press, and cured to obtain the composite phase change material. This invention does not impose specific limitations on the curing conditions, as long as the curing effect is achieved.
[0046] The following detailed description of the composite phase change material and its preparation method provided by the present invention, with reference to the embodiments, should not be construed as limiting the scope of protection of the present invention.
[0047] Example 1
[0048] (1) Citric acid monohydrate and zinc acetate dihydrate were added to an alkaline solution in a molar ratio of 3:2. The alkaline solution was a sodium hydroxide solution with a solute content of 10% and a molar ratio of sodium hydroxide to citric acid of 3:1. The mixture was magnetically stirred for 1 hour to obtain an aqueous solution of metal-organic gel.
[0049] (2) A 71 wt% (w / w) polyethylene glycol 2000 phase change substrate was placed in an oil bath at 80°C. After the polyethylene glycol was completely melted, a metal-organic gel aqueous solution (equivalent to a 25 wt% (w / w) metal gel in the composite phase change material) was poured in and stirred at 400 rad / min for 30 min. Then, 4 wt% (w / w) expanded graphite was slowly added and stirred at 800 rad / min for 4 h to ensure thorough mixing. The mixture was then placed in a vacuum drying oven at 80°C and dried for 48 h to remove excess moisture. Finally, it was poured into a custom mold for curing to obtain a high thermal conductivity composite phase change material, labeled PCZ5.
[0050] Comparative Example 1
[0051] (1) Citric acid monohydrate and zinc acetate dihydrate were added to an alkaline solution in a molar ratio of 3:2. In this example, the alkaline solution was a sodium hydroxide solution with a solute content of 10%. The solution was magnetically stirred for 1 hour to obtain an aqueous solution of metal-organic gel.
[0052] (2) A 71 wt% (w / w) polyethylene glycol 2000 phase change substrate was placed in an oil bath at 80°C. After the polyethylene glycol was completely melted, an aqueous solution of a metal-organic gel (equivalent to a 29 wt% (w / w) metal gel in the composite phase change material) was poured into it and stirred at 400 rad / min to ensure thorough mixing. The mixture was then placed in a vacuum drying oven at 80°C and dried for 48 hours to remove excess moisture. Finally, it was poured into a custom mold for curing to obtain a high thermal conductivity composite phase change material, labeled PCZ0.
[0053] Example 2
[0054] The preparation process is the same as in Example 1, except that the molar ratio of citric acid monohydrate and zinc acetate dihydrate in the organometallic gel solution in Example 1 is changed to 1:1 to prepare a high thermal conductivity composite phase change material, which is labeled as PCZ1.
[0055] Example 3
[0056] The preparation process is the same as in Example 1, except that the molar ratio of citric acid monohydrate and zinc acetate dihydrate in the organometallic gel solution in Example 1 is changed to 2:1 to prepare a high thermal conductivity composite phase change material, which is labeled as PCZ2.
[0057] Example 4
[0058] The preparation process is the same as in Example 1, except that the alkaline solution in Example 1 is replaced with a sodium carbonate solution with a solute content of 10% to prepare a high thermal conductivity composite phase change material, which is labeled as PCZ3.
[0059] Example 5
[0060] The preparation process is the same as in Example 1, except that the alkaline solution in Example 1 is replaced with a sodium acetate solution with a solute content of 10% to prepare a high thermal conductivity composite phase change material, which is labeled as PCZ4.
[0061] Characterization and performance testing
[0062] (1) The microstructure of the composite phase change material was observed using a cold field emission scanning electron microscope (SEM, Hitachi TM3030) at an accelerating voltage of 10 kV. Figure 1 SEM images of expanded graphite (EG), polyethylene glycol 2000 (PEG), the organometallic gel (MOF1) of Example 1, and various composite phase change materials are shown. EG exhibits a lamellar honeycomb structure, while the MOF1 shows a spherical porous structure. In the composite phase change materials, lamellar PEG fills the spaces between EG and MOF1, and its surface is relatively smooth, although lamellar and spherical protrusions are still visible. This is mainly due to the aggregation of PEG and MOF1. PCZ5 shows less surface aggregation and smaller pores, indicating better dispersion of PEG and MOF1 in this composite phase change material, which is more conducive to forming a dense thermally conductive network.
[0063] (2) The phase change properties of pure polyethylene glycol 2000 and different composite phase change materials prepared according to Examples 1-5 and Comparative Example 1 were measured by differential scanning calorimetry (DSC). The heating range was 0℃ to 80℃. The latent heat of phase change ΔH and the peak phase change temperature T were also measured. p As shown in Table 1:
[0064] Table 1. Latent heat of phase change ΔH and peak temperature of phase change for different phase change materials. p
[0065] Phase change materials ΔH(J / g) <![CDATA[T p (℃)]]> PEG 157.96 55.02 PCZ0 110.45 58.61 PCZ1 114.85 54.1 PCZ2 131.61 53.8 PCZ3 108.04 47.53 PCZ4 107.91 48.77 PCZ5 114.24 49.27
[0066] As shown in Table 1, the latent heat of phase change (LCH) of the composite phase change materials prepared using the above examples and comparative examples is lower than that of pure polyethylene glycol 2000. This is mainly because the addition of thermally conductive and supporting components to the composite phase change materials reduces the mass percentage of polyethylene glycol 2000 as a phase change component. Since the mass percentage of the phase change components in the composite phase change materials prepared in the above examples and comparative examples is consistent, their LCH is not significantly different, generally remaining around 111 J / g, which is consistent with the theoretically calculated LCH (112.18 J / g). Among them, the LCH of the composite phase change material PCZ2 reaches 131 J / g, making it the component with the highest LCH value among the examples and all comparative examples, indicating stronger energy storage capacity.
[0067] (3) The thermal conductivity of different products was tested using a hot disk thermal constant analyzer. Figure 2 The graph shows the thermal conductivity results for different composite phase change materials prepared from polyethylene glycol 2000, Examples 1-5, and Comparative Example 1. Figure 2 It can be seen that, comparing samples PCZ1, PCZ2, and PCZ5 with different molar ratios of citric acid monohydrate and zinc acetate dihydrate in the organometallic gel, the thermal conductivity is 2.85 W / mK, 1.75 W / mK, and 4.32 W / mK, respectively. Compared to samples PCZ3, PCZ4, and PCZ5 in an alkaline environment created by alkaline solutions with the same molar ratio of 3:2 but different pH values, the thermal conductivity is 2.85 W / mK, 2.26 W / mK, and 4.32 W / mK, respectively. The thermal conductivity of the samples increases with increasing alkalinity. Therefore, PCZ5 in Example 1 has the highest thermal conductivity of 4.32 W / mK, which is 980% higher than the 0.40 W / mK thermal conductivity of ordinary polyethylene glycol 2000. This can effectively improve the thermal management performance of battery modules when applied to a power battery thermal management system.
[0068] (4) The composite phase change materials prepared using Examples 1-5 and Comparative Example 1 were placed on a digital display constant temperature heating platform at 70°C and heated continuously for 5 hours. The mass and leakage of the samples were recorded every 1 hour. Before this, the mass of each sample and a picture at room temperature were recorded. Figure 3 The figures show the leakage of different composite phase change materials prepared according to Examples 1-5 and Comparative Example 1 after heating at 70°C for 4 hours. As can be seen from the figures, polyethylene glycol 2000 (PEG) showed serious leakage after only 2 minutes of heating. After continuous heating at 70°C for 5 hours, although all composite phase change materials showed varying degrees of leakage, they maintained their original shape without collapsing during the heating process, indicating that the composite phase change materials have good shape stability and leakage resistance. Figure 3 In the diagram, areas circled for composite phase change materials indicate obvious leakage, with diffusion boundaries visible on the filter paper; areas not circled indicate no obvious leakage. Figure 4 Table 2 shows the mass loss rate of different composite phase change materials prepared according to Examples 1-5 and Comparative Example 1 after heating at 70°C for 4 hours. Specific data are also shown in Table 2. Figure 4 As shown in Table 2, the mass loss rate of the composite phase change materials after adding expanded graphite is all below 3%.
[0069] Table 2. Mass loss rate of different composite phase change materials (heating for 4 hours)
[0070] Composite phase change materials Quality loss rate (%) PEG 100％ PCZ0 7.15％ PCZ1 0.62％ PCZ2 0.68％ PCZ3 0.89％ PCZ4 2.43％ PCZ5 0.71％
[0071] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A composite phase change material, characterized in that, It includes a blend of polyethylene glycol, a metal organogel, and expanded graphite; the metal organogel is a chelate of citric acid and metal ions; the polyethylene glycol is dispersed inside and on the surface of the expanded graphite and the metal organogel.
2. The composite phase change material according to claim 1, characterized in that, The composite phase change material contains 3-5 wt% expanded graphite and 20-30 wt% metal-organic gel.
3. The composite phase change material according to claim 1, characterized in that, The metal ions include Zn. 2+ Cu 2+ and Fe 3 + One or more of them.
4. The composite phase change material according to claim 1, characterized in that, The polyethylene glycol includes polyethylene glycol 2000.
5. The composite phase change material according to any one of claims 1 to 4, characterized in that, The thermal conductivity of the composite phase change material is 2.26–4.32 W / mK.
6. The method for preparing the composite phase change material according to any one of claims 1 to 5, characterized in that, Includes the following steps: Citric acid, water-soluble metal salt, and alkaline solution are mixed and chelated to obtain an aqueous solution of metal-organic gel. The metal-organic gel aqueous solution, molten polyethylene glycol and expanded graphite are mixed, and the resulting mixture is dried and cured to obtain the composite phase change material.
7. The preparation method according to claim 6, characterized in that, The molar ratio of citric acid to the metal ions in the water-soluble metal salt is (0.5–2):
1.
8. The preparation method according to claim 6 or 7, characterized in that, The alkaline solution includes one or more of sodium hydroxide solution, sodium carbonate solution, and sodium acetate solution; the amount of the alkaline solution used satisfies the molar ratio required for the acid-base neutralization reaction between the alkali and citric acid in the alkaline solution.
9. The preparation method according to claim 6, characterized in that, The mixing of the metal organogel aqueous solution, molten polyethylene glycol, and expanded graphite comprises: adding the metal organogel aqueous solution to the molten polyethylene glycol, performing a first stirring, and then adding expanded graphite to the resulting mixture for a second stirring.
10. The preparation method according to claim 6, characterized in that, The drying temperature is 60–80°C.