Composite phase change material with wide temperature range as well as preparation method and application of composite phase change material

Abstract

The invention discloses a wide-temperature-range composite phase change material and a preparation method and application thereof. Comprising the following steps: mixing a hydrogenated styrene-butadiene block copolymer and a non-polar solvent, and stirring to form an SEBS solution; mixing and stirring paraffin and polyethylene glycol, adding expanded graphite, and uniformly stirring and mixing to obtain a mixture; the mixture is dried, and a PA-PEG-EG compound is obtained; the PA-PEG-EG compound and an SEBS solution are mixed and stirred, then the mixture is put into a vacuum drying oven to be dried, and a PA-PEG-EG-SEBS compound is obtained; and placing the PA-PEG-EG-SEBS compound in a steel mold, placing the steel mold on a hot press for hot pressing, naturally cooling, and demolding to obtain the wide-temperature-range composite phase change material. The material has strong cycle stability, can be used in long-term battery thermal management, and has the effects of low-temperature preheating, working cooling, thermal runaway delay and protection.

Description

Technical Field

[0001] The present invention relates to the technical field of phase change materials, and in particular to a composite phase change material with a wide temperature range, a preparation method thereof, and applications thereof. Background Art

[0002] As a high-energy-density energy storage device, lithium-ion batteries have become the core power source for electric vehicles, renewable energy storage, and portable electronic devices. However, the temperature limitations of their efficient operating temperature range (20-45°C) and the critical temperature for thermal runaway (>60°C) severely restrict their application in extreme environments. Under low-temperature conditions, the increased viscosity of the electrolyte hinders lithium-ion migration, triggering the growth of lithium dendrites and the risk of internal short circuits. At high temperatures or high-rate charge and discharge, heat generation is concentrated within the battery. If heat is not dissipated in time, the local temperature rise can quickly exceed the critical threshold, triggering a thermal runaway chain reaction, accompanied by safety accidents such as fire and explosion. Traditional thermal management technologies rely on active battery thermal management systems such as liquid cooling, air cooling, and heat pipe circulation. Although these can partially alleviate the temperature rise problem, they have drawbacks such as complex systems, high energy consumption, and large size and weight, making them difficult to adapt to the lightweight and high-integration requirements in extreme environments.

[0003] Solid-liquid phase change materials (PCMs) have become a research hotspot for battery thermal management due to their higher enthalpy values compared to solid-solid phase change materials and lower volume expansion rates than liquid-gas phase change. Traditional solid-liquid phase change materials face multiple limitations in the solid-liquid phase change process in lithium-ion battery thermal management applications:

[0004] (i) The inherent low thermal conductivity of the material significantly prolongs the heat transfer cycle, leading to uneven temperature distribution in the battery pack and increased risk of thermal runaway;

[0005] (ii) The mechanical stress caused by phase change volume expansion can easily cause damage to the battery cell structure;

[0006] (iii) Material collapse leads to problems such as thermal enthalpy decay, fluid leakage and interface contact failure.

[0007] To address insufficient thermal conductivity, research focuses on material composite modification and process innovation. By incorporating highly conductive components (such as carbon nanotubes and copper foam) to construct multiscale heat transfer networks, these materials are combined with strategies such as crosslinking constraints (such as hydrogen bonding), porous adsorption, and spinning strategies (such as electrospinning and melt spinning) to improve morphological stability and reduce or eliminate mechanical issues associated with material collapse and excessive expansion. These enhancements have further expanded their application in battery thermal management. However, most PCMs have a single phase transition temperature, which limits their ability to store and release large amounts of heat within a specific temperature range. Consequently, most PCMs are designed for specific applications: low-temperature insulation (<0°C), process cooling (20-45°C), and high-temperature insulation protection against thermal runaway (>60°C). Relying solely on PCMs to achieve thermal management across the entire temperature range from extremely low temperatures (-40°C) to high temperatures remains a significant challenge. This challenge lies in regulating the responsiveness of PCM thermal properties, such as thermal conductivity and heat storage, across different temperature ranges. Summary of the Invention

[0008] The present invention aims to overcome the shortcomings of the prior art by providing a composite phase-change material with a wide temperature range, as well as its preparation method and application. The composite phase-change material of the present invention exhibits efficient electrical preheating in low-temperature environments and robust cooling during operation. It also maintains excellent stability in various operating environments and conditions, and possesses both high shape stability and high thermal conductivity.

[0009] To achieve the above purpose, the technical solution designed by the present invention is as follows:

[0010] The present invention provides a method for preparing a composite phase change material with a wide temperature range, comprising the following steps:

[0011] (1) According to weight percentage, 5-15 wt% of expanded graphite, 30-50 wt% of paraffin wax, 30-50 wt% of polyethylene glycol and 5-15 wt% of hydrogenated styrene-butadiene block copolymer are weighed;

[0012] (2) mixing the weighed hydrogenated styrene-butadiene block copolymer and a non-polar solvent, and stirring to form a SEBS solution;

[0013] (3) mixing the weighed paraffin wax and polyethylene glycol, adding the weighed expanded graphite, and stirring and mixing uniformly to obtain a mixture;

[0014] (4) drying the mixture in a vacuum drying oven to obtain a PA-PEG-EG complex;

[0015] (5) mixing the PA-PEG-EG complex with the SEBS solution, and then drying the mixture in a vacuum drying oven to obtain a PA-PEG-EG-SEBS complex;

[0016] (6) The PA-PEG-EG-SEBS composite was placed in a steel mold and placed on a hot press for hot pressing, cooled naturally, and demolded to obtain a composite phase change material with a wide temperature range.

[0017] Furthermore, in the step (1), the volume of the expanded graphite is larger than 40-60 mesh and smaller than 20-35 mesh, and the expanded graphite is dried at 80-100° C. for 24-36 hours before use;

[0018] The volumes of the paraffin wax and polyethylene glycol are smaller than 200-300 meshes and larger than 500-635 meshes.

[0019] Furthermore, in step (1), the mass percentages of expanded graphite, paraffin wax, polyethylene glycol and hydrogenated styrene-butadiene block copolymer are 10 wt%, 42.5 wt%, 42.5 wt% and 5 wt% respectively.

[0020] Furthermore, in step (1), the mass percentages of expanded graphite, paraffin wax, polyethylene glycol and hydrogenated styrene-butadiene block copolymer are 15 wt%, 40 wt%, 40 wt% and 5 wt% respectively.

[0021] Furthermore, in step (2), the non-polar solvent is any one of cyclohexane, toluene and benzene; the mass volume ratio of the hydrogenated styrene-butadiene block copolymer to the non-polar solvent is 1:12-20 g / mL;

[0022] The stirring condition is 500-800 r / min, 0.5-1 h.

[0023] Furthermore, in the step (3), the paraffin wax and polyethylene glycol are mixed and stirred at 500-600 r / min for 20-30 min; and the stirring condition after adding the expanded graphite is 200-300 r / min for 8-10 min.

[0024] Furthermore, in step (4), the drying conditions are 75 to 85° C., -0.08 to -0.1 MPa, and 2 to 3 hours.

[0025] Furthermore, in step (5), the mixing and stirring conditions are 200-300 r / min, 4-6 min; and the drying conditions are 75-85° C., -0.08-0.1 MPa, 24-36 h.

[0026] Furthermore, in step (6), the hot pressing conditions are 120-140° C., 4-5 MPa, and 8-10 min; and the pressure is maintained at 4-5 MPa during natural cooling.

[0027] The present invention also provides a composite phase change material with a wide temperature range prepared by the preparation method. The expanded graphite adsorbs paraffin and polyethylene glycol on the surface, and the hydrogenated styrene-butadiene block copolymer is wrapped around the surface of the expanded graphite adsorbed with paraffin and polyethylene glycol to encapsulate the expanded graphite.

[0028] The present invention also provides an application of the wide-temperature-range composite phase change material in the thermal management of lithium-ion batteries, wherein the thermal management of lithium-ion batteries includes low-temperature preheating, operating cooling, and thermal runaway protection of lithium-ion batteries.

[0029] Principle of the present invention:

[0030] The present invention first screens paraffin wax (PA), polyethylene glycol (PEG), and expanded graphite (EG) of appropriate sizes through material pretreatment, then preliminarily mixes them by stirring. The melted PA and PEG are then fully absorbed by the EG in a vacuum drying oven. A hydrogenated styrene-butadiene block copolymer (SEBS) solution is then added and stirred until the surface of the PA-PEG-EG complex is substantially wetted. The solvent is then vacuum dried to evaporate, and the SEBS forms a thin film on the surface of the PA-PEG-EG complex, encapsulating the PA-PEG-EG complex. After drying, hot pressing is performed. The technical principles underlying each step of the preparation method are as follows:

[0031] (1) The pretreated sample is stirred and evenly mixed before vacuum adsorption. PA and PEG are adsorbed based on the capillary action of the porous structure inside EG. This process is physical adsorption.

[0032] (2) After the SEBS solution wets the surface of the PA-PEG-EG complex, the SEBS will cover the surface of the PA-PEG-EG complex during the drying process for further encapsulation of PA and PEG.

[0033] (3) During the hot pressing process at 120-140°C, the shape of SEBS will be reconstructed and show a certain viscosity, which will enhance the adhesion at the interface, thereby enhancing the shape stability of the material and improving the problem of loose material after traditional EG packaging molding.

[0034] (4) PA is made of a mixture of non-polar alkanes, and its melting point can be adjusted by adjusting the type and molecular weight of the alkanes. PEG itself is a polar organic compound, and its melting point can be controlled by adjusting the degree of polymerization. PA and PEG differ in polarity and non-polarity. During the adsorption and evaporation process without physical effects such as catalysts, the difference in their chemical properties ensures that they will not dissolve in each other or undergo side reactions, ensuring the synthesis of dual-phase transition point composite phase change materials. The first phase transition point is used for cooling during the normal operation of the battery, and the second phase transition point is used to delay and protect against thermal runaway.

[0035] (5) Under the pressure induction of 4-5 MPa, large-sized EGs will be arranged and assembled in an orderly manner to form a high-speed thermal conductivity network, further enhancing the thermal conductivity of the composite phase change material.

[0036] Beneficial effects of the present invention:

[0037] 1. The wide-temperature-range composite phase-change material PCM-EGx@SEBS of the present invention (x represents the weight percentage of expanded graphite) uses EG and SEBS as packaging materials, achieves a leakage-free effect through the physical adsorption of EG and the surface coating and packaging of SEBS, and constructs a dual phase-change point using non-polar PA and polar PEG as the base phase-change materials.

[0038] 2. By regulating the pyrolysis characteristics of the material so that its pyrolysis temperature corresponds to the battery thermal runaway temperature range, the battery thermal runaway process can be cooled by pyrolysis and endothermic cooling. This construction method is suitable for thermal management of batteries with different characteristic temperatures.

[0039] 3. Simply regulating the melting point and thermal stability of the base materials PA and PEG can effectively enhance the thermal response characteristics of the composite phase change material in different temperature ranges during battery thermal management. During the synthesis process, large-scale EG is orderly assembled under pressure induction, enhancing the material's thermal conductivity. The PA and PEG also undergo micro-migration during the thermal induction process. In the node area, the PA and PEG diffuse and migrate to the surrounding area under the action of heat, reducing the node thermal resistance and further enhancing the material's thermal conductivity. The SEBS interface adhesion under thermal induction further enhances the material's shape stability and reduces the interfacial thermal resistance. The material is prepared using PA and PEG with strong cyclic stability, and the synthesis process does not involve chemical reactions between PA and PEG. Therefore, the material has strong cyclic stability and can be used in long-term battery thermal management. Its active and passive thermal management performance covers the range from -40°C to thermal runaway, so it can provide thermal management and protection for batteries in harsh environments and extreme operating conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the SEM image of PCM-EG10@SEBS prepared in Example 2;

[0041] Figure 2 This is an SEM image of the SEBS structure of the cross section of PCM-EG10@SEBS prepared in Example 2;

[0042] Figure 3 This is an SEM image of the cross-section of SEBS of PCM-EG15@SEBS prepared in Example 3;

[0043] Figure 4 This is the DSC curve of PCM-EG10@SEBS, paraffin and polyethylene glycol prepared in Example 2.

[0044] Figure 5 The overall thermal conductivity curve of PCM-EGx@SEBS prepared in Example 1, Example 2, and Example 3;

[0045] Figure 6 This is a comparison chart of the anti-leakage performance of the composite phase change material prepared in Example 2 and Comparative Example 1;

[0046] Figure 7 This is a cross-sectional SEM image of the composite phase change material of Comparative Example 1;

[0047] Figure 8 This is a temperature rise curve of the PCM-EG10@SEBS prepared in Example 2 when the battery is electrically preheated in a low-temperature environment of -40°C;

[0048] Figure 9 This is a graph showing the cooling effect of PCM-EG10@SEBS prepared in Example 2 during the 1C battery charge and discharge process;

[0049] Figure 10 TG test curve of PCM-EG10@SEBS prepared in Example 2;

[0050] Figure 11 This is a diagram showing the cooling effect of PCM-EG10@SEBS prepared in Example 2 during the battery thermal runaway process. DETAILED DESCRIPTION

[0051] The present invention is further described in detail below with reference to specific embodiments so that those skilled in the art can understand.

[0052] Example 1

[0053] The preparation method of the composite phase change material with a wide temperature range comprises the following specific steps:

[0054] 1. Material pretreatment:

[0055] (1) Screening out expanded graphite (EG) with a volume larger than 40 mesh and smaller than 30 mesh, drying it in an oven at 80-100° C. for 24-36 hours until it is anhydrous, and setting aside for use;

[0056] (2) Use a crusher to crush paraffin wax (PA) and polyethylene glycol (PEG) into fine powder, and screen out PA and PEG with a volume smaller than 300 mesh and larger than 500 mesh for later use.

[0057] 2. According to weight percentage, weigh 5 wt% expanded graphite (EG), 45 wt% paraffin (PA), 45 wt% polyethylene glycol (PEG) and 5 wt% hydrogenated styrene-butadiene block copolymer (SEBS).

[0058] 3. SEBS was mixed with cyclohexane at a ratio of 1:20 g / mL and stirred at a speed of 600 r / min for 30 min to form a SEBS solution.

[0059] 4. Add the weighed PA and PEG into a beaker and stir at 600 r / min for 25 min. Add the weighed EG and mix them. Slowly mix them evenly by mechanical stirring at 300 r / min for 10 min to obtain a mixture without adsorption.

[0060] 5. Place the above mixture in a vacuum drying oven with a temperature set at 80°C and an air pressure maintained at -0.1 MPa (the negative pressure environment helps EG adsorb the melted PA and PEG). This process lasts for 2 hours to obtain a PA-PEG-EG complex.

[0061] 6. The PA-PEG-EG complex and SEBS solution were mixed at a mechanical stirring rate of 300 r / min for 5 min to allow the SEBS solution to fully wet the surface of the PA-PEG-EG complex, and then placed in a vacuum drying oven at 80°C and -0.1 MPa for 30 h to obtain a PA-PEG-EG-SEBS complex.

[0062] 7. The PA-PEG-EG-SEBS complex was placed in a steel mold and placed on a hot press. The hot press temperature was set to 135°C and hot pressing was performed at a pressure of 4.5 MPa. The hot pressing process was 8 minutes, and then the temperature was turned off and the pressure of 4.5 MPa was maintained until natural cooling, and then demolding was performed to obtain PCM-EG5@SEBS with a thermal conductivity of 5.96 W / (m·K).

[0063] Example 2

[0064] The preparation method of the composite phase change material with a wide temperature range comprises the following specific steps:

[0065] 1. Material pretreatment:

[0066] (1) Screen out EG with a volume larger than 60 mesh and smaller than 30 mesh, and dry it in an oven at 80-100°C for 24-36 hours until it is dry and ready for use;

[0067] (2) Use a crusher to crush PA and PEG into fine powder, and screen out PA and PEG with a volume smaller than 200 mesh and larger than 635 mesh for later use.

[0068] 2. According to weight percentage, weigh 10 wt% EG, 42.5 wt% PA, 42.5 wt% PEG and 5 wt% SEBS.

[0069] 3. SEBS was mixed with toluene at a ratio of 1:15 g / mL and stirred at 600 r / min for 40 min to form a SEBS solution.

[0070] 4. Add the weighed PA and PEG into a beaker and stir at 600 r / min for 25 min. Add the weighed EG and mix them. Slowly mix them evenly by mechanical stirring at 300 r / min for 10 min to obtain a mixture without adsorption.

[0071] 5. Place the above mixture in a vacuum drying oven with a temperature set at 80°C and an air pressure maintained at -0.1 MPa (the negative pressure environment helps EG adsorb the melted PA and PEG). This process lasts for 2 hours to obtain a PA-PEG-EG complex.

[0072] 6. The PA-PEG-EG complex and SEBS solution were mixed at a mechanical stirring rate of 300 r / min for 5 min to allow the SEBS solution to fully wet the surface of the PA-PEG-EG complex, and then placed in a vacuum drying oven at 80°C and -0.1 MPa for 30 h to obtain a PA-PEG-EG-SEBS complex.

[0073] 7. The PA-PEG-EG-SEBS complex was placed in a steel mold and placed on a hot press. The hot press temperature was set to 130°C and hot pressing was performed at a pressure of 4.5 MPa. The hot pressing process was 8 minutes, and then the temperature was turned off and the pressure of 4.5 MPa was maintained until natural cooling, and then demolding was performed to obtain PCM-EG10@SEBS with a thermal conductivity of 6.52 W / (m·K).

[0074] Example 3

[0075] The preparation method of the composite phase change material with a wide temperature range comprises the following specific steps:

[0076] 1. Material pretreatment:

[0077] (1) Screen out EG with a volume larger than 60 mesh and smaller than 35 mesh, and dry it in an oven at 80-100°C for 24-36 hours until it is dry and ready for use;

[0078] (2) Use a crusher to crush PA and PEG into fine powder, and screen out PA and PEG with a volume smaller than 300 mesh and larger than 635 mesh for later use.

[0079] 2. According to weight percentage, weigh 15 wt% EG, 40 wt% PA, 40 wt% PEG and 5 wt% SEBS.

[0080] 3. SEBS was mixed with benzene at a ratio of 1:12 g / mL and stirred at a speed of 600 r / min for 45 minutes to form a SEBS solution.

[0081] 4. Add the weighed PA and PEG into a beaker and stir at a speed of 550 r / min for 25 minutes. Add the weighed EG and mix them. Slowly mix them evenly by mechanical stirring at 250 r / min for 9 minutes to obtain a mixture without adsorption.

[0082] 5. The above mixture was placed in a vacuum drying oven with the temperature set at 85°C and the air pressure maintained at -0.1 MPa (the negative pressure environment helps EG adsorb the melted PA and PEG). The process lasted for 2.5 hours to obtain a PA-PEG-EG complex.

[0083] 6. The PA-PEG-EG complex and SEBS solution were mixed at a mechanical stirring rate of 300 r / min for 5 min to allow the SEBS solution to fully wet the surface of the PA-PEG-EG complex, and then placed in a vacuum drying oven at 85°C and -0.08 MPa for 28 h to obtain a PA-PEG-EG-SEBS complex.

[0084] 7. The PA-PEG-EG-SEBS complex was placed in a steel mold and placed on a hot press. The hot press temperature was set to 140°C and hot pressing was performed at a pressure of 5 MPa. The hot pressing process was 8 minutes, and then the temperature was turned off and the pressure of 5 MPa was maintained until natural cooling, and then demolding was performed to obtain PCM-EG15@SEBS with a thermal conductivity of 10.73 W / (m·K).

[0085] Example 4

[0086] The preparation method of the composite phase change material with a wide temperature range comprises the following specific steps:

[0087] 1. Material pretreatment:

[0088] (1) Screen out EG with a volume larger than 60 mesh and smaller than 30 mesh, and dry it in an oven at 80-100°C for 24-36 hours until it is dry and ready for use;

[0089] (2) Use a crusher to crush PA and PEG into fine powder, and screen out PA and PEG with a volume smaller than 300 mesh and larger than 500 mesh for later use.

[0090] 2. According to weight percentage, weigh 5 wt% EG, 30 wt% PA, 50 wt% PEG and 15 wt% SEBS.

[0091] 3. SEBS was mixed with benzene at a ratio of 1:12 g / mL and stirred at a speed of 500 r / min for 60 min to form a SEBS solution.

[0092] 4. Add the weighed PA and PEG into a beaker and stir at a speed of 500 r / min for 30 minutes. Add the weighed EG and mix them. Slowly mix them evenly by mechanical stirring at 200 r / min for 10 minutes to obtain a mixture without adsorption.

[0093] 5. The above mixture was placed in a vacuum drying oven with the temperature set at 75°C and the air pressure maintained at -0.08 MPa (the negative pressure environment helps EG adsorb the melted PA and PEG). The process lasted for 3 hours to obtain a PA-PEG-EG complex.

[0094] 6. The PA-PEG-EG complex and SEBS solution were mixed at a mechanical stirring rate of 200 r / min for 6 min to allow the SEBS solution to fully wet the surface of the PA-PEG-EG complex, and then placed in a vacuum drying oven at 75°C and -0.08 MPa for 36 h to obtain a PA-PEG-EG-SEBS complex.

[0095] 7. The PA-PEG-EG-SEBS complex was placed in a steel mold and placed on a hot press. The hot press temperature was set to 120°C and hot pressing was performed at a pressure of 5 MPa. The hot pressing process was carried out for 10 minutes, and then the temperature was turned off and the pressure of 5 MPa was maintained until natural cooling, and then demolding was performed to obtain PCM-EG5@SEBS with a thermal conductivity of 2.13 W / (m·K).

[0096] Example 5

[0097] The preparation method of the composite phase change material with a wide temperature range comprises the following specific steps:

[0098] 1. Material pretreatment:

[0099] (1) Screen out EG with a volume larger than 60 mesh and smaller than 20 mesh, and dry it in an oven at 80-100°C for 24-36 hours until it is dry and ready for use;

[0100] (2) Use a crusher to crush PA and PEG into fine powder, and screen out PA and PEG with a volume smaller than 300 mesh and larger than 635 mesh for later use.

[0101] 2. According to weight percentage, weigh 15 wt% EG, 50 wt% PA, 30 wt% PEG and 5 wt% SEBS.

[0102] 3. SEBS was mixed with benzene at a ratio of 1:12 g / mL and stirred at 800 r / min for 30 min to form a SEBS solution.

[0103] 4. Add the weighed PA and PEG into a beaker and stir at a speed of 600 r / min for 20 minutes. Add the weighed EG and mix them. Slowly mix them evenly by mechanical stirring at 300 r / min for 8 minutes to obtain a mixture without adsorption.

[0104] 5. Place the above mixture in a vacuum drying oven with the temperature set at 85°C and the air pressure maintained at -0.1 MPa (the negative pressure environment helps EG adsorb the melted PA and PEG). This process lasts for 2 hours to obtain a PA-PEG-EG complex.

[0105] 6. The PA-PEG-EG complex and SEBS solution were mixed at a mechanical stirring rate of 300 r / min for 4 min to allow the SEBS solution to fully wet the surface of the PA-PEG-EG complex, and then placed in a vacuum drying oven at 85°C and -0.08 MPa for 28 h to obtain a PA-PEG-EG-SEBS complex.

[0106] 7. The PA-PEG-EG-SEBS complex was placed in a steel mold and placed on a hot press. The hot press temperature was set to 140°C and hot pressing was performed at a pressure of 4 MPa. The hot pressing process was 8 minutes, and then the temperature was turned off and the pressure of 4 MPa was maintained until natural cooling, and then demolding was performed to obtain PCM-EG15@SEBS with a thermal conductivity of 10.91 W / (m·K).

[0107] Comparative Example 1

[0108] The composite phase change material is prepared by a melt stirring method, comprising the following steps:

[0109] Weigh 8.5g PA and 8.5g PEG into a beaker, place it in an 80℃ oil bath stirring pot to fully heat and melt it, then weigh 3g of untreated EG and add it, and then start mechanical stirring at a speed of 600r / min for 2h. After cooling, die-casting is carried out in a mold at a pressure of 4MPa to obtain a composite phase change material.

[0110] Compared with the PCM-EG10@SEBS prepared in Example 2, the composite phase change material of this comparative example showed leakage of PA and PEG in the anti-leakage test, which could not achieve a leakage-free effect, and showed a broken internal EG grid in the SEM image, which was the main reason why it could not be completely encapsulated.

[0111] Example 6

[0112] Performance testing of PCM-EGx@SEBS composite phase change material with wide temperature range

[0113] 1. SEM analysis of PCM-EG10@SEBS prepared in Example 2 was performed. The results are as follows: Figure 1 As shown, the layered stacking structure of expanded graphite can be seen.

[0114] 2. The SEBS structure of the cross section of PCM-EG10@SEBS prepared in Example 2 was analyzed by SEM. The results are as follows: Figure 2 As shown, the surface of expanded graphite is a SEBS layer;

[0115] 3. The SEBS at the cross section of PCM-EG15@SEBS prepared in Example 3 was analyzed by SEM. The results are as follows: Figure 3 As shown, SEBS is attached and grown on the surface of expanded graphite.

[0116] 4. PCM-EG10@SEBS, paraffin and polyethylene glycol prepared in Example 2 were subjected to DSC analysis. The results are as follows: Figure 4 As shown in Figure 3, PCM-EG10@SEBS exhibits dual phase transition points. The two phase transition temperature ranges of PCM-EG10@SEBS correspond to the working cooling and thermal runaway critical temperature management of lithium batteries.

[0117] 5. The overall thermal conductivity of PCM-EGx@SEBS prepared in Example 1, Example 2 and Example 3 was analyzed. The results are as follows: Figure 5 As shown in the figures, in the embodiments, with the increase of expanded graphite content and the improvement of the process, the thermal conductivity can be significantly improved.

[0118] 6. The anti-leakage performance of the composite phase change material prepared in Example 2 and the comparative example 1 was analyzed. The results are as follows: Figure 6 As shown, it can be seen that the method of Example 2 can achieve good packaging and show a leakage-free effect.

[0119] 7. The cross section of the composite phase change material of Comparative Example 1 was subjected to SEM analysis. The results are as follows: Figure 7 As shown in the figure, the expanded graphite of the material is severely broken and no complete large-sized expanded graphite particles can be observed.

[0120] 8. The electrical preheating performance of the PCM-EG10@SEBS prepared in Example 2 was analyzed in a low temperature environment of -40°C. The results are as follows: Figure 8 As shown in the figure, the preheating rate is 14.81℃ / min, and the preheating effect is strong.

[0121] 9. The cooling effect of PCM-EG10@SEBS prepared in Example 2 during the 1C battery charge and discharge process was analyzed. The results are as follows: Figure 9 As shown in Figure 2, the maximum temperature drop in this process is 11.05℃.

[0122] 10. The PCM-EG10@SEBS prepared in Example 2 was subjected to TG test. The results are as follows: Figure 10 As shown in the figure, the test results show that the material weight loss temperature range is 120℃~425℃.

[0123] 11. The PCM-EG10@SEBS prepared in Example 2 was tested for its thermal runaway cooling effect. The blank group used foam as the material. The maximum temperature during the thermal runaway process of the blank control group was 801.1°C, while the maximum temperature of the experimental group in Example 2 was 477.1°C. Compared with the TG test results, the heat absorption capacity of the material PCM-EG10@SEBS can absorb most of the heat released by the thermal runaway of the battery, thereby achieving a cooling effect.

[0124] Although the above embodiments have been described in detail, they are only a part of the embodiments of the present invention, not all of them. People can also obtain other embodiments based on this embodiment without inventiveness, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a composite phase change material with a wide temperature range, characterized by: The following steps are involved: (1) According to weight percentage, 5-15 wt% of expanded graphite, 30-50 wt% of paraffin wax, 30-50 wt% of polyethylene glycol and 5-15 wt% of hydrogenated styrene-butadiene block copolymer are weighed; (2) mixing the weighed hydrogenated styrene-butadiene block copolymer and a non-polar solvent, and stirring to form a SEBS solution; (3) mixing the weighed paraffin wax and polyethylene glycol, adding the weighed expanded graphite, and stirring and mixing uniformly to obtain a mixture; (4) drying the mixture in a vacuum drying oven to obtain a PA-PEG-EG complex; (5) mixing the PA-PEG-EG complex with the SEBS solution, and then drying the mixture in a vacuum drying oven to obtain a PA-PEG-EG-SEBS complex; (6) The PA-PEG-EG-SEBS composite was placed in a steel mold and placed on a hot press for hot pressing, cooled naturally, and demolded to obtain a composite phase change material with a wide temperature range.

2. The preparation method according to claim 1, wherein: In the step (1), the volume of the expanded graphite is greater than 40 to 60 meshes and less than 20 to 35 meshes, and the expanded graphite is dried at 80 to 100° C. for 24 to 36 hours before use; The volumes of the paraffin wax and polyethylene glycol are smaller than 200-300 meshes and larger than 500-635 meshes.

3. The preparation method according to claim 1, wherein: In the step (1), the mass percentages of expanded graphite, paraffin wax, polyethylene glycol and hydrogenated styrene-butadiene block copolymer are 10 wt%, 42.5 wt%, 42.5 wt% and 5 wt% respectively.

4. The preparation method according to claim 1, wherein: In the step (2), the non-polar solvent is any one of cyclohexane, toluene and benzene; the mass volume ratio of the hydrogenated styrene-butadiene block copolymer to the non-polar solvent is 1:12-20 g / mL; The stirring condition is 500-800 r / min, 0.5-1 h.

5. The preparation method according to claim 1, wherein: In the step (3), the paraffin wax and polyethylene glycol are mixed and stirred at a speed of 500 to 600 r / min for 20 to 30 minutes; and the stirring condition after adding the expanded graphite is 200 to 300 r / min for 8 to 10 minutes.

6. The preparation method according to claim 1, wherein: In the step (4), the drying conditions are 75 to 85° C., -0.08 to -0.1 MPa, and 2 to 3 hours.

7. The preparation method according to claim 1, wherein: In the step (5), the mixing and stirring conditions are 200-300 r / min, 4-6 min; and the drying conditions are 75-85° C., -0.08-0.1 MPa, 24-36 h.

8. The preparation method according to claim 1, wherein: In the step (6), the hot pressing conditions are 120-140° C., 4-5 MPa, and 8-10 min; and the pressure is maintained at 4-5 MPa during natural cooling.

9. A composite phase change material with a wide temperature range prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The expanded graphite adsorbs paraffin and polyethylene glycol on the surface, and the hydrogenated styrene-butadiene block copolymer wraps the surface of the expanded graphite adsorbed with paraffin and polyethylene glycol to encapsulate the surface.

10. Use of the wide temperature range composite phase change material according to claim 9 in thermal management of lithium-ion batteries, characterized in that: The thermal management of lithium-ion batteries includes low-temperature preheating, operating cooling, and thermal runaway protection of lithium-ion batteries.

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