A phase-change waterproof and air-permeable packaging film of a lithium battery cell interval thermal aerogel and a preparation method and application thereof

Abstract

The application relates to the field of film materials, and discloses a phase-change waterproof and air-permeable packaging film for lithium battery cells and a spacer thermal aerogel and a preparation method and application thereof. The phase-change waterproof and air-permeable packaging film comprises the following raw materials: 50-85 parts of polytetrafluoroethylene emulsion; 5-15 parts of tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer emulsion; 8-15 parts of phase-change microcapsules; 15-30 parts of PLGA microsphere pore-forming agent; and pore-forming solvent. The packaging film takes polytetrafluoroethylene emulsion as the main raw material, contains a suitable pore structure in the film, after the spacer thermal aerogel is packaged, the expansion gas in the cell spacing thermal material can be moderately promoted to diffuse to avoid the packaging film from being inflated and bulged, and the thermal insulation property of the thermal insulation material can be greatly reduced. The phase-change microcapsules in the packaging film can prevent heat diffusion to the adjacent cells to cause thermal runaway in cooperation with the thermal insulation material, and can inhibit the thermal expansion of the gas, further reducing the risk of the packaging film being inflated and bulged.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of film materials, in particular to a phase change waterproof and breathable packaging film for lithium battery cell interval thermal aerogel and a preparation method and application thereof. BACKGROUND

[0002] The thermal management of new energy automobile lithium battery pack, especially the thermal runaway management, has become an important research object to ensure the safety of new energy automobile driving and riding. With the continuous improvement of the energy density of lithium batteries, the thermal insulation material in the lithium battery pack, especially the cell interval thermal material, has become the mainstream solution to prevent the spread of thermal runaway caused by heat transfer between cells.

[0003] At present, the cell interval thermal material mainly adopts aerogel material, for example, aerogel felt, which has become a commonly used cell interval thermal material due to its small density, low thermal conductivity and certain compressibility. However, the aerogel felt also has obvious shortcomings, that is, the aerogel powder is easy to fall out of the felt and pollute the internal environment of the battery pack. The falling of the aerogel powder will also cause a significant loss of the thermal insulation performance of the aerogel felt. Therefore, the thermal insulation material of the aerogel type usually needs to be packaged with a packaging film.

[0004] At present, ordinary packaging films generally use PET or other plastic films. However, ordinary packaging films will cause the overall thermal conductivity of the material to increase, thereby reducing the thermal insulation performance. In addition, ordinary packaging films are also prone to bulging and gasification when the temperature rises rapidly due to the rapid expansion of air and the high-temperature vaporization of organic matter in the cell interval thermal material. The generation of bulging and gasification will cause uneven pressure between cells, which will easily lead to more serious secondary thermal runaway damage.

[0005] In summary, at present, the use of ordinary packaging films to package aerogel materials generally has the technical problems of deteriorated thermal insulation performance and negative thermal runaway risk caused by bulging and gasification under high temperature conditions. SUMMARY

[0006] In order to solve the above technical problems, the present application provides a phase change waterproof and breathable packaging film for lithium battery cell interval thermal aerogel and a preparation method and application thereof. The packaging film of the present application uses polytetrafluoroethylene emulsion as the main raw material, and the film prepared by flow casting contains suitable pore structures. After packaging the thermal insulation aerogel, the expansion of the gas in the cell interval thermal material can be moderately promoted to avoid the bulging and gasification of the packaging film, while the thermal insulation performance of the thermal insulation material can be avoided from being significantly reduced. The packaging film of the present application contains phase change microcapsules, which can prevent the spread of heat to adjacent cells and cause thermal runaway, and can also inhibit the thermal expansion of gas, thereby further reducing the risk of bulging and gasification of the packaging film.

[0007] The specific technical scheme of the present application is:

[0008] In a first aspect, the present invention provides a phase change waterproof and breathable encapsulation film for a thermal aerogel spacer in lithium battery cells, comprising the following raw materials in parts by weight: 50-85 parts of polytetrafluoroethylene emulsion; 5-15 parts of tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer (PFA) emulsion; 8-15 parts of phase change microcapsules (with paraffin as the core material, chitosan as the inner wall material, and silica modified with aluminum hydroxide as the outer wall material); 15-30 parts of PLGA microsphere pore-forming agent with a particle size of 100-500 nm; and pore-forming solvent.

[0009] (1) The encapsulation film of the present invention uses polytetrafluoroethylene emulsion as the main raw material. At the same time, PLGA microspheres with a specific content and a specific particle size range are used as pore-forming agents during the film-making process. After the film is formed, the pore-forming agent is dissolved by the pore-forming solvent, which can form a uniformly dispersed and appropriately sized pore structure in the encapsulation film. When the cell temperature rises, it can provide a diffusion channel for the gas that expands in volume. Therefore, it can effectively solve the problem that conventional encapsulation films are prone to bulging and swelling after being heated.

[0010] It is important to note that the particle size and content of the pore-forming agent determine the pore size and porosity, respectively. Therefore, the particle size and content of the pore-forming agent have a significant impact on the thermal insulation and gas diffusion capabilities of the encapsulation film. If the particle size is too small or the content is too low, the encapsulation film will have low gas permeability, hindering the diffusion of expanding gas and causing the encapsulation film to easily bulge or bubble. If the particle size is too large or the content is too high, the encapsulation film will have excessive gas permeability, leading to a significant reduction in the thermal insulation performance of the encapsulated thermal insulation material, and also resulting in a deterioration in waterproof performance. Ultimately, we found that within the above-mentioned content and particle size range of this invention, the formed pores can both moderately promote the diffusion of expanding gas to avoid bulging or bubble formation in the encapsulation film and avoid a significant reduction in the thermal insulation and waterproof performance of the thermal insulation material.

[0011] (2) The encapsulation film of the present invention is mainly made of polytetrafluoroethylene and a portion of tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer. The hot melt softening point of tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer is lower than that of polytetrafluoroethylene. Therefore, this characteristic can be used to facilitate the heat sealing of aerogel materials after the encapsulation film is formed.

[0012] (3) In the encapsulation film of the present invention, phase change microcapsules are also uniformly dispersed, and the core material is paraffin wax. When the temperature of the battery cell rises, the paraffin wax can absorb heat and melt, storing a large amount of heat. On the one hand, it can be used in conjunction with aerogel insulation material to further lock the heat within a specific range, preventing the heat from spreading to adjacent battery cells and causing thermal runaway; on the other hand, after absorbing the heat, the paraffin wax can also inhibit the thermal expansion of the gas, thereby further reducing the risk of the encapsulation film bulging and swelling.

[0013] The phase change microcapsules of this invention have a dual-wall structure (the inner wall material is chitosan, and the outer wall material is aluminum hydroxide-modified silica). The reason for this dual-wall structure is that, as discovered, using a silica layer as a single wall material has the following drawbacks: Firstly, the encapsulation rate of the paraffin core material by the silica single-wall layer is not ideal, failing to completely encapsulate the paraffin, resulting in a high risk of leakage after the paraffin melts. Secondly, the volume expansion of paraffin after absorbing heat and melting, combined with the brittleness of the silica layer, increases the risk of paraffin leakage. Therefore, this invention employs the aforementioned dual-wall structure. On the one hand, it significantly improves the paraffin encapsulation rate to prevent leakage; on the other hand, the inner wall material, chitosan, has better toughness, which can buffer the volume expansion after paraffin melts, while the outer wall material, silica, has better heat resistance, compensating for the poor heat resistance of chitosan, thereby extending the material's service life in high-temperature environments. In addition, modifying the surface of the silicon dioxide layer with aluminum hydroxide can further improve the heat resistance and mechanical properties of the encapsulation film.

[0014] Preferably, the pore-forming solvent is tetrahydrofuran.

[0015] Preferably, the concentration of the polytetrafluoroethylene emulsion is 55-70 wt%, and the solvent is water; the concentration of the tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer emulsion is 35-50 wt%, and the solvent is water.

[0016] Preferably, the phase change waterproof and breathable sealing film further includes the following raw materials in parts by weight: 0.05-0.3 parts of dispersant; 0.1-0.5 parts of suspending agent; and 0.01-0.1 parts of thickener.

[0017] Preferably, the dispersant is BYK-9810; the suspending agent is PVP K25; and the thickener is sodium polyacrylate with a molecular weight of 4000-6000.

[0018] Preferably, the preparation method of the phase change microcapsules is as follows:

[0019] A: Add melted paraffin wax and emulsifier to water at a temperature higher than the melting point of paraffin wax, stir and emulsify to obtain a paraffin wax emulsion; add the paraffin wax emulsion to a chitosan acetic acid solution at a temperature higher than the melting point of paraffin wax and disperse evenly, add alkali to adjust pH ≥ 7, let stand, chitosan gradually precipitates out with paraffin wax particles as the core, after chitosan no longer precipitates, filter, wash and dry to obtain chitosan-encapsulated paraffin wax microcapsules.

[0020] In step A, the present invention adds paraffin emulsion to chitosan acetate solution and adjusts pH ≥ 7. Since chitosan is only soluble in acidic aqueous solution and not in neutral or alkaline aqueous solution, chitosan will gradually precipitate out with the paraffin emulsion particles dispersed in the system as the core and form a coating layer, thereby obtaining chitosan-encapsulated paraffin microcapsules.

[0021] B: Chitosan-encapsulated paraffin microcapsules were dispersed in water, p-azidobenzoic acid was added, and the mixture was allowed to stand, filtered, and dried to obtain chitosan-encapsulated paraffin microcapsules with p-azidobenzoic acid adsorbed on the surface.

[0022] In step B, since chitosan is positively charged in solution and para-azidobenzoic acid is negatively charged, para-azidobenzoic acid can rapidly aggregate on the surface of chitosan-encapsulated paraffin microcapsules and form an electrostatic adsorption layer of para-azidobenzoic acid.

[0023] C: Chitosan-encapsulated paraffin microcapsules with azidobenzoic acid adsorbed on the surface were dispersed in an alkaline ethanol aqueous solution. Tetraethyl orthosilicate was added dropwise under stirring. The mixture was allowed to stand, filtered, washed and dried. The resulting product was then subjected to ultraviolet irradiation treatment to obtain silica / chitosan-encapsulated paraffin microcapsules with internal pores.

[0024] In step C, the present invention forms a bilayer wall structure by in-situ hydrolysis of chitosan-encapsulated paraffin microcapsules with adsorbed p-azidobenzoic acid on their surface to generate a silica layer. Based on this, p-azidobenzoic acid decomposes under ultraviolet irradiation to produce nitrogen gas, thereby creating localized voids between the chitosan and silica layers. The purpose of these voids is to provide sufficient space for the volume expansion of the chitosan layer, further ensuring that the silica layer does not break (if the chitosan and silica layers are tightly bonded without sufficient space, the silica layer is still prone to breakage when the chitosan layer expands).

[0025] D: Disperse paraffin microcapsules encapsulated with silica / chitosan in water, add aluminum chloride, adjust the pH to alkaline by adding alkali, heat the reaction, filter, wash and dry to obtain phase change microcapsules with paraffin as the core material, chitosan as the inner wall material, and silica modified with aluminum hydroxide as the outer wall material.

[0026] In step D, aluminum hydroxide is generated in situ on the surface of the silica / chitosan-coated paraffin microcapsules. Specifically, since silica carries a negative charge in an alkaline environment, positively charged aluminum ions accumulate on the surface of the silica / chitosan-coated paraffin microcapsules under electrostatic attraction and are converted into aluminum hydroxide under alkaline conditions, thereby obtaining phase change microcapsules with aluminum hydroxide surface modification.

[0027] Secondly, the present invention provides a method for preparing a phase change waterproof and breathable encapsulation film of thermal aerogel for lithium battery cells, comprising the following steps:

[0028] S1: Mix polytetrafluoroethylene emulsion and tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer emulsion, add dispersant and suspending agent to obtain a mixture.

[0029] S2: Under stirring conditions, add phase change microcapsules and PLGA microsphere porogens to the mixture, and finally add thickener and stir evenly to obtain coating liquid.

[0030] S3: The vertical tower casting coating process is adopted, in which the continuously driven base film is immersed in the coating tank containing the coating liquid, and after coating, it is vertically passed through the drying device; after continuous coating and drying multiple times, the base film is peeled off to obtain a semi-finished film.

[0031] S4: The semi-finished film is immersed in an impregnation tank containing a pore-forming solvent for pore-forming treatment, and then washed with water and dried to obtain a phase change waterproof and breathable encapsulation film.

[0032] This invention uses a vertical tower casting coating process to form a thin film on the surface of a base film. Compared with conventional coating processes, the vertical tower casting coating method can make the coating more stable for films with high filler content.

[0033] Preferably, in S3, the base film is a PI film.

[0034] Preferably, in S3, the film thickness formed after each coating and drying is 0.2-0.5 mm, and the coating and drying are repeated 2-5 times.

[0035] Thirdly, the present invention provides the application of the above-mentioned phase change waterproof and breathable encapsulation film in the thermal aerogel for encapsulating lithium battery cells.

[0036] Fourthly, the present invention provides a thermal insulation material for lithium battery cells, comprising:

[0037] Aerogel; and phase change waterproof and breathable encapsulation film encapsulated on the surface of aerogel.

[0038] Preferably, the aerogel is a silica aerogel.

[0039] Silica aerogel itself has excellent thermal insulation properties. When encapsulated with the phase change waterproof and breathable encapsulation film specially made in this invention, it can effectively block heat and prevent the spread of thermal runaway effect of the battery cell.

[0040] Compared with the prior art, the beneficial effects of the present invention are:

[0041] (1) The encapsulation film of the present invention uses polytetrafluoroethylene emulsion as the main raw material. During the film-making process, a specific amount and a specific particle size range of pore-forming agent are added. After the film is formed, the pore-forming agent is dissolved by the pore-forming solvent, which can form a uniformly dispersed and appropriately sized pore structure in the encapsulation film. When the cell temperature rises, it can provide a diffusion channel for the gas that expands in volume. Therefore, it can effectively solve the problem that conventional encapsulation films are prone to bulging and swelling after being heated.

[0042] (2) The encapsulation film of the present invention contains a portion of tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, whose hot melt softening point is lower than that of polytetrafluoroethylene, and this characteristic can be used to facilitate the heat sealing process of the encapsulation film.

[0043] (3) The encapsulation film of this invention uniformly disperses phase change microcapsules. On the one hand, this can work with aerogel insulation materials to further lock heat within a specific range, preventing heat from diffusing to adjacent cells and causing thermal runaway. On the other hand, paraffin absorbs heat and inhibits the thermal expansion of the gas, thereby further reducing the risk of bulging and swelling of the encapsulation film. The phase change microcapsules of this invention have a double-walled layer structure, which not only has a high paraffin coating rate, but also has an inner chitosan layer with excellent toughness, which can buffer the volume expansion after the paraffin melts. The outer silica layer has excellent heat resistance, which can extend the service life of the material in high-temperature environments. The aluminum hydroxide modified on the surface of the silica layer can further improve the material's resistance to photoaging and mechanical properties.

[0044] (4) The present invention uses a vertical tower casting coating process to form a thin film on the surface of the base film. Compared with conventional coating processes, the coating can be more stable and is especially suitable for the preparation of high-filling films. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the vertical tower casting coating process of the present invention;

[0046] Figure 2 This is a schematic diagram of the pore-forming process of the present invention. Detailed Implementation

[0047] The present invention will be further described below with reference to embodiments.

[0048] General Implementation Examples

[0049] A phase change waterproof and breathable encapsulation film for a thermal aerogel separator in lithium battery cells, comprising the following raw materials in parts by weight: 50-85 parts of polytetrafluoroethylene emulsion, 5-15 parts of tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer emulsion, 8-15 parts of phase change microcapsules with a particle size of 100-350 micrometers, 15-30 parts of PLGA microsphere porogen with a particle size of 100-500 nm, 0.05-0.3 parts of dispersant, 0.1-0.5 parts of suspending agent, 0.01-0.1 parts of thickener, and porogen solvent.

[0050] Preferably, the concentration of the polytetrafluoroethylene emulsion is 55-70 wt%, and the solvent is water; the concentration of the PFA emulsion is 35-50 wt%, and the solvent is water; the pore-forming solvent is tetrahydrofuran; the dispersant is BYK-9810; the suspending agent is PVP K25; and the thickener is sodium polyacrylate with a molecular weight of 4000-6000.

[0051] Phase change microcapsules use paraffin wax with a melting point of 50-60℃ as the core material, chitosan as the inner wall material, and silica modified with aluminum hydroxide as the outer wall material. The preparation method is as follows:

[0052] A: Add melted paraffin wax and emulsifier to water at 65-80℃ and emulsify by stirring at 300-700 rpm to obtain a paraffin wax emulsion (paraffin wax and emulsifier concentrations are 1-2 wt% and 0.3-0.7 wt%, respectively). Add the paraffin wax emulsion to a chitosan acetate solution heated in a water bath at 65-80℃ at a mass ratio of 1:(1.5-2.5) and disperse evenly. Adjust the pH to ≥7 with alkali, let stand, and chitosan will gradually precipitate out with paraffin wax particles as the core. After the chitosan stops precipitating, filter, wash and dry to obtain chitosan-encapsulated paraffin wax microcapsules.

[0053] B: Chitosan-encapsulated paraffin microcapsules were dispersed in water, p-azidobenzoic acid was added, the mixture was allowed to stand, filtered, and dried to obtain chitosan-encapsulated paraffin microcapsules with p-azidobenzoic acid adsorbed on the surface. The mass ratio of chitosan-encapsulated paraffin microcapsules, p-azidobenzoic acid, and water was 1:(0.1-0.3):(80-120).

[0054] C: Chitosan-encapsulated paraffin microcapsules with surface adsorbed p-azidobenzoic acid were dispersed in an alkaline ethanol aqueous solution (80-90 wt%) with pH 8-10. Ethyl orthosilicate was added dropwise under stirring, allowed to stand, filtered, washed, and dried. The resulting product was then subjected to ultraviolet irradiation for 5-10 min to obtain silica / chitosan-encapsulated paraffin microcapsules with internal pores. The mass ratio of chitosan-encapsulated paraffin microcapsules with surface adsorbed p-azidobenzoic acid, ethyl orthosilicate, and alkaline ethanol aqueous solution was 1:(0.6-0.8):(80-120).

[0055] D: Disperse silica / chitosan-encapsulated paraffin microcapsules in water, add aluminum chloride, adjust the pH to alkaline (preferably 8-9) with alkali, heat to 40-45℃ for reaction, filter, wash and dry to obtain phase change microcapsules with paraffin (melting point 50-60℃) as core material, chitosan as inner wall material, and silica modified with aluminum hydroxide as outer wall material; the mass ratio of silica / chitosan-encapsulated paraffin microcapsules, aluminum chloride and water is 1∶(0.6-0.8)∶(80-120).

[0056] A method for preparing a phase change waterproof and breathable encapsulation film for lithium battery cell spacer thermal aerogel includes the following steps:

[0057] S1: Mix polytetrafluoroethylene emulsion and tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer emulsion, add dispersant and suspending agent to obtain a mixture.

[0058] S2: Under stirring conditions, add phase change microcapsules and PLGA microsphere porogens to the mixture, and finally add thickener and stir evenly to obtain coating liquid.

[0059] S3: As Figure 1 As shown, a vertical tower casting coating process is used, in which a continuously driven base film (preferably a PI film) is immersed in a coating tank containing a coating solution, and then vertically passed through a drying device after coating; after multiple consecutive coating and drying cycles, the base film is peeled off to obtain a semi-finished film. Preferably, in step S3, the film thickness formed after each coating and drying cycle is 0.2-0.5 mm, and the coating and drying cycles are repeated 2-5 times.

[0060] S4: As Figure 2 As shown, the semi-finished film is immersed in an impregnation tank containing a pore-forming solvent for pore-forming treatment, and then washed with water and dried to obtain a phase change waterproof and breathable encapsulation film.

[0061] A thermal insulation material for lithium battery cells includes an aerogel and a phase change waterproof and breathable encapsulation film encapsulated on the surface of the aerogel. Preferably, the aerogel is a silica aerogel.

[0062] Example 1

[0063] A thermal insulation material for lithium-ion battery cells includes a silica aerogel felt and a phase change waterproof and breathable encapsulation film encapsulated on the surface of the silica aerogel felt. The phase change waterproof and breathable encapsulation film comprises the following raw materials in parts by weight: 60 parts (60 wt%) of polytetrafluoroethylene aqueous emulsion, 10 parts (40 wt%) of tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer aqueous emulsion, 10 parts (average particle size 200 μm) of phase change microcapsules, 20 parts (average particle size 300 nm) of PLGA microsphere pore-forming agent, 0.15 parts of dispersant (BYK-9810), 0.3 parts of suspending agent (PVP K25), 0.05 parts of thickener (sodium polyacrylate with a molecular weight of 5000), and a pore-forming solvent (based on the amount used to immerse the semi-finished film).

[0064] The preparation method of the thermal insulation material for lithium battery cells is as follows:

[0065] (1) Preparation of phase change microcapsules:

[0066] (1.1) 100g of melted paraffin 56 (melting point 56℃) and emulsifier Tween-80 were added to deionized water at 70℃ and emulsified by stirring at 500rpm to obtain a paraffin emulsion (paraffin concentration 1.5wt%, emulsifier concentration 0.5wt%). 1000g of paraffin emulsion was added to 2000g of chitosan acetate solution heated in a 70℃ water bath (chitosan concentration 2.5wt%, acetic acid concentration 2.0wt%) and dispersed evenly. The pH was adjusted to 7.5 by adding alkali and allowed to stand. Chitosan gradually precipitated out with paraffin emulsion particles as the core. After the chitosan stopped precipitating, the mixture was filtered, washed and dried to obtain chitosan-encapsulated paraffin microcapsules.

[0067] (1.2) Take 10g of chitosan-coated paraffin microcapsules and disperse them in 1000mL of deionized water. Add 2g of p-azidobenzoic acid, let stand, filter, and dry to obtain chitosan-coated paraffin microcapsules with p-azidobenzoic acid adsorbed on the surface.

[0068] (1.3) Take 5g of chitosan-encapsulated paraffin microcapsules with azidobenzoic acid adsorbed on the surface and disperse them in 500mL of alkaline ethanol aqueous solution with pH 9 (ethanol concentration 85wt%). Add 3.5g of tetraethyl orthosilicate dropwise under stirring, let stand, filter, wash and dry, and irradiate the obtained product with ultraviolet light for 8min to obtain silica / chitosan-encapsulated paraffin microcapsules with internal pores.

[0069] (1.4) Take 5g of silica / chitosan-encapsulated paraffin microcapsules and disperse them in 500mL of deionized water. Add 3.5g of aluminum chloride, adjust the pH to 8.5 with alkali, heat at 42℃ to react, filter, wash and dry to obtain phase change microcapsules.

[0070] (2) Preparation of phase change waterproof and breathable sealing film:

[0071] (2.1) Mix the polytetrafluoroethylene aqueous emulsion and the tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer emulsion according to the formula, add the prescribed amount of dispersant and suspending agent, and disperse evenly to obtain a mixture.

[0072] (2.2) Under stirring conditions, add the formulated amount of phase change microcapsules and pore-forming agent to the mixture, and finally add the formulated amount of thickener, stir evenly, and obtain the coating liquid.

[0073] (2.3) The vertical tower casting coating process is adopted. The continuously driven base film (PI film) is immersed in a coating tank containing coating liquid. After coating, it is vertically passed through an oven with openings at the top and bottom (the thickness of the newly formed film after each drying is 0.3 mm). After continuous coating and drying twice, the base film is peeled off to obtain a semi-finished film.

[0074] (2.4) The semi-finished film is immersed in an impregnation tank containing a pore-forming solvent for pore-forming treatment, and then washed with water and dried to obtain a phase change waterproof and breathable encapsulation film.

[0075] (3) Preparation of thermal insulation material for lithium battery cell: Silica aerogel felt is used as thermal insulation material and encapsulated with phase change waterproof and breathable encapsulation film to obtain the finished product.

[0076] Examples 2-8 and Comparative Examples 1-5

[0077] The differences between the formulations of the phase change waterproof and breathable sealing films of Examples 2-8 and Comparative Examples 1-5 and those of Example 1 are as follows (all parts by weight):

[0078] Raw materials PTFE emulsion PFA emulsion Pore former Phase change microcapsule Category / characteristics Daikin D210 3M 6910GZ PLGA microspheres Average particle size 200 microns Example 1 60 10 20 (average particle size 300 nm) 10 Comparative Example 1 70 10 10 (average particle size 300 nm) 10 Example 2 65 10 15 (average particle size 300 nm) 10 Example 3 55 10 25 (average particle size 300 nm) 10 Example 4 50 10 30 (average particle size 300 nm) 10 Comparative Example 2 45 10 35 (average particle size 300 nm) 10 Comparative Example 3 60 10 20 (average particle size 50 nm) 10 Example 5 60 10 20 (average particle size 100 nm) 10 Example 6 60 10 20 (average particle size 500 nm) 10 Comparative Example 4 60 10 20 (average particle size 600 nm) 10 Comparative Example 5 65 10 20 (average particle size 300 nm) 5 Example 7 62 10 20 (average particle size 300 nm) 8 Example 8 55 10 20 (average particle size 300 nm) 15 Comparative Example 6 52 10 20 (average particle size 300 nm) 18

[0079] In the table above, the phase change microcapsules used in each embodiment and comparative example are the same as those in Example 1.

[0080] Performance testing

[0081] Performance test data for samples from each embodiment and comparative example:

[0082] (1) Heat absorption test: Take the 3mm thick heat insulation material obtained from each case (the thickness of the phase change waterproof and breathable sealing film on the upper and lower sides of the silica aerogel felt is 0.6mm respectively), place it on a hot plate at 80℃, and test the highest temperature of the other side (cold side) within 20 minutes.

[0083] (2) Inflation and bulging test: After assembling the insulation material and battery cell obtained in each case, draw a square grid (100 grids in total) on its surface and place it in a sealed environment at 150℃ for 5 minutes. Count the number of grids occupied by inflation and bulging.

[0084]

[0085]

[0086] The data comparison in the table above shows that:

[0087] Thermal insulation materials encapsulated with conventional non-porous PET film do not contain phase change microcapsules, so they rely solely on the thermal insulation effect of silica aerogel felt, which is not ideal. At the same time, due to poor air permeability, severe bulging occurs in the bulging test.

[0088] The difference between Comparative Example 1, Example 2, Example 1, Example 3, Example 4, and Comparative Example 2 lies in the gradually increasing content of the pore-forming agent. The results showed that the proportion of bulging area was generally negatively correlated with the pore-forming agent content. This is because a higher pore-forming agent content results in better gas permeability of the encapsulation film, making bulging less likely. However, in the heat absorption test, the heat absorption effect was generally positively correlated with the pore-forming agent content. Therefore, considering both the heat absorption test and the bulging test results, the optimal pore-forming agent content is between 20 and 30 parts.

[0089] The difference between Comparative Example 3, Example 5, Example 1, Example 6, and Comparative Example 4 lies in the increasing particle size of the porogen. The results showed that in the bulging test, Comparative Example 3 exhibited a larger area of ​​bulging, Example 5 showed 6%, while Examples 6 and 4 showed virtually no bulging. However, similarly, in the endothermic test, Comparative Example 4, due to its larger pore size, resulted in less than ideal endothermic performance. Therefore, considering all factors, the optimal particle size range for the porogen is 100-500 nm.

[0090] The difference between Comparative Example 5, Example 7, Example 1, Example 8, and Comparative Example 6 lies in the increasing content of phase change microcapsules. Data shows that in endothermic testing, the endothermic effect gradually improves with increasing phase change microcapsule content; however, when the content reaches approximately 15 parts, further increases in content no longer result in a significant temperature decrease, indicating that a bottleneck has been reached. Furthermore, excessive addition of phase change microcapsules can affect the rheological properties of the liquid, thus negatively impacting the coating process and the mechanical properties of the final encapsulated film. Therefore, the optimal content range is 8-15 parts.

[0091] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0092] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a phase change waterproof and breathable encapsulation film of thermal aerogel for lithium battery cells, characterized in that... include: S1: Mix 50-85 parts by weight of polytetrafluoroethylene emulsion and 5-15 parts by weight of tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer emulsion, add dispersant and suspending agent to obtain a mixture; S2: Add 8-15 parts of phase change microcapsules with paraffin as the core material, chitosan as the inner wall material, and silica modified with aluminum hydroxide as the outer wall material, and 15-30 parts of PLGA microsphere pore maker with a particle size of 100-500nm to the mixture under stirring, add thickener and stir well to obtain coating liquid. S3: The vertical tower casting coating process is adopted. The continuously driven base film is immersed in the coating tank containing the coating liquid, and after coating, it is vertically passed through the drying device. After continuous coating and drying multiple times, the base film is peeled off to obtain a semi-finished film. S4: The semi-finished film is immersed in an impregnation tank containing a pore-forming solvent for pore-forming treatment, and then washed with water and dried to obtain a phase change waterproof and breathable encapsulation film.

2. The preparation method according to claim 1, characterized in that: The pore-forming solvent is tetrahydrofuran.

3. The preparation method according to claim 1, characterized in that: The concentration of the polytetrafluoroethylene emulsion is 55-70 wt%, and the solvent is water; The concentration of the tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer emulsion is 35-50 wt%, and the solvent is water.

4. The preparation method according to claim 1, characterized in that: The dispersant is present in an amount of 0.05-0.3 parts by weight; The suspending agent has a weight ratio of 0.1-0.5 parts; The thickener is present in parts by weight of 0.01-0.1 parts.

5. The preparation method according to claim 1, characterized in that: The preparation method of the phase change microcapsules is as follows: A: Add melted paraffin and emulsifier to water at a temperature higher than the melting point of paraffin, stir and emulsify to obtain paraffin emulsion; add the paraffin emulsion to a preheated chitosan acetic acid solution at a temperature higher than the melting point of paraffin and disperse evenly, add alkali to adjust pH ≥ 7, let stand, filter, wash and dry to obtain chitosan-encapsulated paraffin microcapsules. B: Chitosan-encapsulated paraffin microcapsules were dispersed in water, p-azidobenzoic acid was added, and the mixture was allowed to stand, filtered, and dried to obtain chitosan-encapsulated paraffin microcapsules with p-azidobenzoic acid adsorbed on the surface. C: Chitosan-encapsulated paraffin microcapsules with azidobenzoic acid adsorbed on the surface were dispersed in an alkaline ethanol aqueous solution, and tetraethyl orthosilicate was added dropwise under stirring. The mixture was allowed to stand, filtered, washed and dried, and the resulting product was subjected to ultraviolet irradiation treatment to obtain silica / chitosan-encapsulated paraffin microcapsules with internal pores. D: Disperse silica / chitosan-encapsulated paraffin microcapsules in water, add aluminum chloride, adjust the pH to alkaline with alkali, heat the reaction, filter, wash and dry to obtain phase change microcapsules.

6. The preparation method according to claim 1, characterized in that: In S3, the base film is a PI film; In S3, the film thickness formed after each coating and drying is 0.2-0.5 mm, and the coating and drying are repeated 2-5 times.

7. A phase change waterproof and breathable encapsulation film for lithium battery cell spacer thermal aerogel, characterized in that: Obtained by the preparation method described in any one of claims 1-6.

8. The application of the phase change waterproof and breathable encapsulation film obtained by the preparation method according to any one of claims 1-6 in the thermal aerogel for encapsulating lithium battery cells.

9. A thermal insulation material for lithium battery cells, characterized in that: include: Aerogel; A phase change waterproof and breathable encapsulating film encapsulated on the surface of the aerogel; the phase change waterproof and breathable encapsulating film is obtained by the preparation method according to any one of claims 1-6.

10. The cell heat-insulating material as described in claim 9, characterized in that: The aerogel is a silica aerogel.

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