A rigid-flexible conversion composite phase change material suitable for battery thermal management and a preparation method and application thereof

Abstract

The application relates to a rigid-flexible conversion composite phase change material suitable for battery thermal management and a preparation method and application thereof, and belongs to the technical field of lithium ion battery materials. The rigid-flexible conversion composite phase change material is composed of n-octadecane 70-90 wt%, polymer high molecular fixed phase change support material 5 wt% and expanded graphite 10%-25% in percentage by mass. The rigid-flexible conversion composite phase change material is stable in shape, can be converted between rigid materials and flexible materials with the change of temperature, can be used for heat preservation of lithium batteries in cold environments, and the required cold start time is shorter after the automobile is parked in the cold environment for a long time. The synthesis process of the material is simple, the material is convenient to apply, and the material has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to a rigid-flexible conversion composite phase change material suitable for battery thermal management and its preparation method and application, and belongs to the technical field of lithium ion battery materials. BACKGROUND

[0002] Currently, the development of green energy storage and the use of electric vehicles using renewable energy have become an inevitable trend in the future. However, the performance of lithium batteries is greatly affected by temperature, especially in cold environments. Studies have shown that when the temperature drops to 10℃ or below, the initial discharge voltage of lithium batteries will decrease significantly, and the discharge capacity will also be greatly reduced. This will affect the life and performance of lithium batteries, and in severe cases, it will cause internal micro-short circuits, and eventually cause fires and explosions. Therefore, it is necessary to protect lithium batteries reliably.

[0003] Phase change materials have attracted much attention due to their simple structure, stable performance, low price and no additional consumption. Phase change materials can absorb or release a large amount of latent heat during the phase change process, while their own temperature remains almost unchanged. In this process, the latent heat absorbed or released by the phase change is large, and the change in temperature and volume is small, which can control the temperature within a certain range and thus protect the lithium battery. Ling et al. studied the temperature maintaining ability of phase change materials at low temperatures through experiments. They found that when the battery is cooled from 40℃ to 10℃, RT28 / silica can maintain the temperature of the battery above 5℃ for about 1 hour [Z. Ling, X. Wen, Z. Zhang, X. Fang, T. Xu, Warming-Up Effects of Phase Change Materials on Lithium-Ion Batteries Operated at Low Temperatures, Energy Technol. 4(9) (2016) 1071-1076.]. However, the inherent crystalline rigidity of phase change materials and the problem that the preheating time of lithium batteries wrapped with phase change materials will be prolonged after long-term placement in cold environments limit their application in battery thermal management systems. SUMMARY

[0004] In order to solve the problems in the prior art, the application provides a rigid-flexible conversion composite phase change material suitable for battery thermal management and a preparation method and application thereof, so as to solve the problems of inherent crystalline rigidity of the phase change material in the prior art and the problem that the phase change material wrapped around a lithium battery will prolong the start-up preheating time when placed in a cold environment for a long time. The material introduces n-octadecane into a polymer skeleton and adds expanded graphite, so that the energy storage material with adjustable phase change temperature, stable shape and rigid-flexible conversion with temperature change can be obtained, can be used for heat preservation of the lithium battery in a cold environment, and the required cold start-up time is short after the automobile is parked in a cold environment for a long time. The synthesis process of the material is simple, the application is convenient, and the material has a wide application prospect.

[0005] A rigid-flexible conversion composite phase change material suitable for battery thermal management, the rigid-flexible conversion composite phase change material is composed of n-octadecane 70-90 wt%, polymer macromolecular shaped phase change support material 5 wt% and expanded graphite 10%-25% in terms of mass percentage.

[0006] Preferably, the rigid-flexible conversion composite phase change material is composed of n-octadecane 70 wt%, polymer macromolecular shaped phase change support material 5 wt% and expanded graphite 25% in terms of mass percentage.

[0007] Preferably, the polymer macromolecular shaped phase change support material is one of SIS, SBS, SEBS and SEPS.

[0008] The composite phase change material has a rigid-flexible conversion characteristic, and the conversion temperature from rigidity to flexibility is 30 DEG C.

[0009] Another object of the application is to provide a preparation method of the rigid-flexible conversion composite phase change material suitable for battery thermal management.

[0010] A preparation method of a rigid-flexible conversion composite phase change material suitable for battery thermal management, comprising the following process steps:

[0011] (1) n-octadecane, expanded graphite and polymer macromolecular shaped phase change support material are vacuum dried at 80 DEG C for 48 h;

[0012] (2) the polymer macromolecular shaped phase change support material is dissolved in cyclohexane at a molar ratio of 1:15 at 50 DEG C to obtain a uniform solution;

[0013] (3) n-octadecane and expanded graphite are added to the solution obtained in step (2), stirred to ensure uniform mixing, and then the mixture is placed in a vacuum drying box for two hours;

[0014] (4) Pour the mixture obtained in step (3) into a mold, and place it in air for 48 h to volatilize the solvent; finally, place it in a vacuum drying oven for 24 h to remove the residual solvent, to obtain the rigid-flexible conversion composite phase change material.

[0015] Preferably, in step (2), the solvent is 1-3 of tetrahydrofuran, dioxane, petroleum ether, acetone, butanone, chloroform, dichloromethane, carbon tetrachloride, carbon disulfide, DMF, DMSO, benzene, toluene, xylene, nitrobenzene, chlorobenzene, cyclohexane or n-hexane.

[0016] Another object of the present application is to provide a battery thermal management device comprising the rigid-flexible conversion composite phase change material.

[0017] A battery thermal management device comprises a battery and the rigid-flexible conversion composite phase change material, wherein the rigid-flexible conversion composite phase change material is attached to at least part of the surface of the battery.

[0018] Preferably, the rigid-flexible conversion composite phase change material is attached to the two sides with the largest area of the battery.

[0019] Preferably, the battery is a single soft-pack lithium ion battery.

[0020] Preferably, the device is applied in a cold environment in a low temperature state.

[0021] Further, the device is applied in a temperature range of -20℃ to 0℃.

[0022] The present application has the following beneficial effects: the rigid-flexible conversion composite phase change material disclosed in the present application for battery thermal management in a cold environment is composed of n-octadecane, polymer high molecular fixed phase change support material and expanded graphite. The n-octadecane provides a heat preservation effect due to its low freezing point. The polymer high molecular fixed phase change support material endows the rigid-flexible conversion composite phase change material with the function of rigid-flexible conversion with temperature and prevents leakage of n-octadecane. The expanded graphite has a large specific surface area and also has a synergistic packaging function and improves the thermal conductivity. When applied to battery thermal management in a cold environment, the rigid-flexible conversion composite phase change material is attached to the two sides with the largest area of the single battery. The rigid-flexible conversion composite phase change material releases heat to keep the battery temperature within the optimal working temperature range of the lithium battery. In addition, due to the high thermal conductivity of the rigid-flexible conversion composite phase change material, the time for restarting after long-time placement in a cold environment is also short. The present application makes full use of the latent heat storage characteristics of phase change materials to meet the safe and efficient use of lithium ion batteries in a low temperature environment, and therefore can be widely applied to battery thermal management systems to ensure the performance and service life of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The infrared spectrum of the material in Example 1;

[0024] wherein: a, n-octadecane, b, SEBS, c, expanded graphite, d, n-octadecane / SEBS, e, n-octadecane / SEBS / expanded graphite.

[0025] Figure 2 DSC curve of the material in Example 1.

[0026] Figure 3 DSC curve of the material in Example 1.

[0027] wherein: a, n-octadecane, b, n-octadecane / SEBS, c, n-octadecane / SEBS / expanded graphite.

[0028] Figure 4 Shaping performance of the material involved in Example 1 after heating at 50℃ for 0-60min, wherein (a) n-octadecane, (b) n-octadecane / SEBS / expanded graphite.

[0029] Figure 5 Conversion of the rigid material to the flexible material of n-octadecane / SEBS / expanded graphite involved in Example 1 at 10-40℃.

[0030] Figure 6 Time required for cold start and heat preservation performance of the material in Example 1, wherein (a) time required for cold start of the bare battery from -20℃ to 10℃ after being placed at -20℃ for 6h, (b) time required for cold start of the battery wrapped with n-octadecane / SEBS / expanded graphite rigid-flexible conversion composite phase change material from -20℃ to 10℃ after being placed at -20℃ for 6h, (c) time required for the battery without wrapping and the battery wrapped with n-octadecane / SEBS / expanded graphite rigid-flexible conversion composite phase change material to cool down from 50℃ to 10℃, (d) comparison of discharge capacity of the battery without wrapping and the battery wrapped with n-octadecane / SEBS / expanded graphite rigid-flexible conversion composite phase change material after being placed at -20℃ for 30min. DETAILED DESCRIPTION

[0031] The following non-limiting examples can make those skilled in the art more fully understand the present application, but in no way limit the present application.

[0032] In the following examples, the test methods described are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0033] One of the embodiments:

[0034] A rigid-flexible conversion composite phase change material suitable for battery thermal management in cold environment, the rigid-flexible conversion composite phase change material is composed of the following components in mass percentage:

[0035] n-octadecane: 70-90 wt%;

[0036] polymer macromolecular shape-stabilized phase change support material: 5 wt%;

[0037] expanded graphite: 10-25 wt%.

[0038] Preferably, the rigid-flexible conversion composite phase change material according to the present application is composed of the following components by mass percentage:

[0039] n-octadecane: 70 wt%;

[0040] polymer macromolecular shape-stabilized phase change support material: 5 wt%;

[0041] expanded graphite: 25 wt%.

[0042] Preferably, the polymer macromolecular shape-stabilized phase change support material of the rigid-flexible conversion composite phase change energy storage material according to the present application is one of SIS, SBS, SEBS, and SEPS.

[0043] A method for preparing a rigid-flexible conversion composite phase change material suitable for battery thermal management in a cold environment, comprising the following process steps: first, dissolve the macromolecular shape-stabilized phase change support material in a solvent at 50℃ for half an hour to obtain a uniform solution. Second, add n-octadecane and expanded graphite to the solution and stir with a glass rod to ensure uniform mixing. Then, place the mixture in a vacuum drying box for two hours of adsorption. Subsequently, pour the prepared phase change material emulsion into a specific mold, and let it stand in the air for a period of time to volatilize the solvent. Finally, place it in a vacuum drying box for 24h to remove the residual solvent, obtaining a rigid-flexible conversion composite phase change material suitable for battery thermal management.

[0044] In the above technical solution, the solvent is preferably one to three of tetrahydrofuran, dioxane, petroleum ether, acetone, butanone, chloroform, dichloromethane, carbon tetrachloride, carbon disulfide, DMF, DMSO, benzene, toluene, xylene, nitrobenzene, chlorobenzene, cyclohexane, or n-hexane.

[0045] A battery thermal management device made of a rigid-flexible conversion composite phase change material suitable for battery thermal management in a cold environment, comprising a battery, and the rigid-flexible conversion composite phase change material suitable for battery thermal management is attached to the two sides of the battery with the largest area.

[0046] The application range of the above battery thermal management device is in a cold environment under low temperature conditions.

[0047] Preferably, the battery is a single soft-pack lithium ion battery.

[0048] The above-mentioned rigid-flexible conversion composite phase change materials suitable for battery thermal management are used in the preparation of temperature control materials for lithium-ion single-cell batteries.

[0049] After the aforementioned rigid-flexible phase change composite material suitable for battery thermal management is used to encapsulate lithium-ion cells, the required cold start time is shorter when restarting in a cold environment after a long period of storage.

[0050] Example 1

[0051] (1) The n-octadecane, expanded graphite and SEBS were vacuum dried at 80°C for 48 h.

[0052] (2) At 50°C, SEBS and cyclohexane were dissolved in cyclohexane at a molar ratio of 1:15 to obtain a homogeneous solution.

[0053] (3) Add n-octadecane and expanded graphite to the solution obtained in step (2), stir with a glass rod to ensure uniform mixing, and then place the mixture in a vacuum drying oven for two hours for adsorption. The amount of n-octadecane added is 70wt%, the amount of SEBS added is 5wt%, and the amount of expanded graphite added is 25wt%.

[0054] (4) Subsequently, the prepared mixture was poured into a mold (100*60*60mm) and left in the air for 48 hours to allow the solvent cyclohexane to evaporate. Finally, it was placed in a vacuum drying oven for 24 hours to remove the residual cyclohexane, and a rigid-flexible phase change composite material with a size of 100*60*4mm was obtained.

[0055] From the infrared spectrum of the material (attached) Figure 1 As can be seen from the XRD characterization, the infrared spectrum (curve e) of the obtained rigid-flexible phase change material (n-octadecane / SEBS / expanded graphite) does not show any new characteristic peaks compared to the infrared spectra (curves a-d) of the other three, indicating that the two are physically mixed. Figure 2 As can be seen, the crystallization peak of the obtained rigid-flexible conversion composite phase change energy storage material is the same as the characteristic peak of n-octadecane, indicating that it has crystallization characteristics. The DSC curve of the obtained rigid-flexible conversion composite phase change energy storage material is attached. Figure 3 In the study, the phase change enthalpy of the resulting octadecane / SEBS / expanded graphite rigid-flexible conversion composite phase change energy storage material was lower than that of octadecane. This is because the physically added SEBS and expanded graphite do not possess phase change properties. However, the phase change enthalpy of octadecane / SEBS / expanded graphite reached 142.3 J / g, exhibiting good phase change thermal storage characteristics. (Appendix) Figure 4It shows that when the temperature is heated to 50℃, the heating time is 15min, and n-octadecane is close to complete melting, and the obtained n-octadecane / SEBS / expanded graphite rigid-flexible conversion composite phase change energy storage material still remains solid state without flowing even if the heating time is 60min, which shows that the material has excellent shape-stabilized phase change characteristics. Figure 5 It can be seen that at 10℃, the n-octadecane / SEBS / expanded graphite shows very high rigidity; while at 20℃, it shows weaker rigidity. At 30℃ and 40℃, the n-octadecane / SEBS / expanded graphite can realize a large degree of bending and show flexibility. This temperature-dependent change can freely realize the conversion of rigid and flexible materials, which helps to realize the compactness of the device in limited space and improve the thermal management efficiency. Figure 6 a-b shows that after being placed in a cold environment at -20℃ for 6h, the time required for the bare battery to naturally warm up from 20℃ to 10℃ is 655s, while the battery wrapped with n-octadecane / SEBS / expanded graphite rigid-flexible conversion composite phase change energy storage material has a warming time of 668s, which is almost the same as that of the bare battery. This can meet the demand for fast preheating of lithium batteries after long-time placement in a cold environment. Figure 6 c-d shows that the battery wrapped with n-octadecane / SEBS / expanded graphite rigid-flexible conversion composite phase change energy storage material has a significantly improved heat preservation time and discharge capacity compared with the unwrapped battery. This shows that the phase change material can meet the demand for safe and efficient use of lithium ion batteries in a cold environment, and therefore can be widely used in battery thermal management systems to ensure the performance and service life of the battery.

[0056] Example 2

[0057] n-octadecane: 90wt%; polymer macromolecular shape-stabilized phase change support material: 5wt%; expanded graphite: 5%. Other conditions are consistent with Example 1.

[0058] Example 3

[0059] n-octadecane: 85wt%; polymer macromolecular shape-stabilized phase change support material: 5wt%; expanded graphite: 10%. Other conditions are consistent with Example 1.

[0060] Example 4

[0061] n-octadecane: 80wt%; polymer macromolecular shape-stabilized phase change support material: 5wt%; expanded graphite: 15%. Other conditions are consistent with Example 1.

[0062] Examples 5-8

[0063] SIS is used instead of SEBS as a polymer macromolecular shape-stabilized phase change support material to obtain the corresponding rigid-flexible conversion composite phase change energy storage material, and other conditions are consistent with Examples 1-4.

[0064] Examples 9-12

[0065] SBS is used instead of SIS as the polymer macromolecular setting phase change support material to obtain the corresponding rigid-flexible conversion composite phase change energy storage material, and other conditions are consistent with examples 1-4.

[0066] Examples 13-16

[0067] SEPS is used instead of SIS as the polymer macromolecular setting phase change support material to obtain the corresponding rigid-flexible conversion composite phase change energy storage material, and other conditions are consistent with examples 1-4.

Claims

1. A rigid-flexible transition composite phase change material suitable for battery thermal management, characterized in that, The rigid-flexible conversion composite phase change material is composed of n-octadecane 70wt%, polymer macromolecular shape-stabilized phase change support material SEBS 5wt% and expanded graphite 25% by mass percentage.

2. The material of claim 1, wherein, The composite phase change material has rigid-flexible conversion characteristics, and the conversion temperature from rigid to flexible is 30°C.

3. A method for preparing a rigid-flexible transition composite phase change material suitable for battery thermal management, characterized in that, The method comprises the following steps: (1) vacuum drying n-octadecane, expanded graphite and polymer macromolecular shape-stabilized phase change support material at 80°C for 48h; (2) dissolving the polymer macromolecular shape-stabilized phase change support material and solvent in cyclohexane at a molar ratio of 1:15 at 50°C to obtain a uniform solution; (3) adding n-octadecane and expanded graphite to the solution obtained in step (2) and stirring to ensure uniform mixing, and then placing the mixture in a vacuum drying box for adsorption for two hours; (4) pouring the mixture obtained in step (3) into a mold, placing it in air for 48h to volatilize the solvent, and finally placing it in a vacuum drying box for 24h to remove the residual solvent, thereby obtaining the rigid-flexible conversion composite phase change material.

4. The method of claim 3, wherein, In step (2), the solvent is 1-3 kinds of tetrahydrofuran, dioxane, petroleum ether, acetone, butanone, chloroform, dichloromethane, carbon tetrachloride, carbon disulfide, DMF, DMSO, benzene, toluene, xylene, nitrobenzene, chlorobenzene, cyclohexane or n-hexane.

5. A battery thermal management device comprising a battery and the rigid-flexible transition composite phase change material of claim 1, wherein, The rigid-flexible conversion composite phase change material is attached to at least part of the surface of the battery.

6. The apparatus of claim 5, wherein, The rigid-flexible conversion composite phase change material is attached to the two sides with the largest area of the battery.

7. The apparatus of claim 5, wherein, The battery is a single soft-pack lithium ion battery.

8. The apparatus of claim 5, wherein, The application range of the device is in a low-temperature cold environment.

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