Composite nano thermal insulation sheet for battery cell and preparation method thereof

Abstract

The application discloses a kind of composite nano heat insulation sheet for battery core and preparation method thereof, and relates to the technical field of battery material.The application comprises the following steps: step 1: pine cellulose, modified expanded vermiculite and epichlorohydrin are added to an alkali urea solution composed of sodium hydroxide, urea and water to form a mixed solution, glass fiber felt is impregnated and crosslinked to form a hydrogel, the hydrogel is modified by soaking in boric acid, frozen in liquid nitrogen, vacuum freeze-dried, and a boric acid-cellulose-modified vermiculite aerogel is obtained;step 2: amino phase change microcapsules are prepared by emulsion interfacial polymerization using tetraethyl orthosilicate and 3-aminopropyltriethoxysilane as the silicon source and paraffin as the core material;step 3: the amino phase change microcapsules are dispersed in ethanol, then the boric acid-cellulose-modified vermiculite aerogel is added, and after vacuum-assisted impregnation, the composite nano heat insulation sheet is dried.The application makes the heat insulation sheet have excellent heat insulation, flame retardation and mechanical stability, and meets the thermal protection requirements of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a composite nano-insulating sheet for battery cells and its preparation method. Background Technology

[0002] Power batteries are prone to thermal runaway under abnormal operating conditions. Composite nano-insulation sheets between battery cells are key components for preventing heat spread and ensuring battery pack safety. An ideal insulation sheet must simultaneously possess excellent heat insulation capabilities, reliable insulation and flame retardant properties, and good mechanical stability. It must achieve thermal barrier and electrical insulation at high temperatures, and maintain structural integrity during assembly, extrusion, vibration, and thermal cycling. Currently, aerogels with nanoporous structures are commonly used for insulation, but their skeletons are brittle and prone to pulverization and cracking under stress, resulting in poor heat insulation performance, insulation and flame retardant properties, and mechanical stability.

[0003] In existing technologies, aerogel powder is typically applied as a coating to the surface of a porous fiber matrix. This surface aerogel layer enhances the thermal insulation, electrical insulation, and flame retardancy of the insulation sheet material. However, this process has the following problems: Firstly, the aerogel coating only adheres to the surface of the fiber matrix, resulting in weak interfacial interaction. During long-term use, the coating is prone to powder detachment and interlayer delamination, leading to a significant decrease in the material's thermal insulation performance. Secondly, aerogel is usually improved in terms of insulation and flame retardancy by adding inorganic flame retardant fillers. However, these fillers have poor dispersibility and are prone to agglomeration within the system, resulting in poor insulation and flame retardancy performance. They also cause uneven stress distribution within the material, leading to a decrease in the overall structural mechanical stability.

[0004] In summary, providing a composite nano-insulating sheet for battery cells and its preparation method is of great significance in order to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a composite nano-insulating sheet for battery cells and its preparation method, so as to solve the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for preparing a composite nano-insulating sheet for battery cells includes the following steps: Step 1: (1) Pine cellulose, modified expanded vermiculite, and epichlorohydrin are added sequentially to an alkaline urea solution composed of sodium hydroxide, urea, and water. The mixture is stirred to obtain a mixed solution. Then, glass fiber felt is placed in a mold, and the mixed solution is poured in to impregnate the glass fiber felt. The mixture is allowed to stand and crosslink to form a hydrogel. After washing with water, it is transferred to a boric acid solution for soaking and then washed with water again to obtain a boric acid hydrogel. (2) The boric acid hydrogel is frozen with liquid nitrogen and then freeze-dried under vacuum to obtain a boric acid-cellulose-modified vermiculite aerogel. Step 2: Using tetraethyl orthosilicate and 3-aminopropyltriethoxysilane as silicon sources and paraffin as core material, amino phase change microcapsules were prepared by emulsion interfacial polymerization. Step 3: Disperse the amino phase change microcapsules in ethanol, then add boric acid-cellulose-modified vermiculite aerogel, and impregnate under vacuum-assisted impregnation for 6 to 12 hours at a vacuum degree of -0.07 to -0.09 MPa, and then dry at 50 to 70°C to obtain the composite nano heat insulation sheet.

[0007] In a more optimized manner, in step 1, the raw materials of the mixed solution, by weight, are: 5-7 parts pine cellulose, 200-300 parts alkali urea solution, 1-3 parts modified expanded vermiculite, and 15-25 parts epichlorohydrin.

[0008] In a more optimized manner, the raw materials of the composite nano heat insulation sheet, by weight, have the following composition: amino phase change microcapsules, boric acid-cellulose-modified vermiculite aerogel in a mass ratio of (5~15):(25~45).

[0009] A more optimized method for preparing the modified expanded vermiculite is as follows: Expanded vermiculite is added to a hydrochloric acid solution, the temperature is set to 75-85℃, and the mixture is stirred for 2-4 hours, filtered, and washed with water. Then, it is added to a sodium chloride solution, the temperature is set to 60-70℃, and the mixture is stirred for 3-5 hours, centrifuged at 8000-10000 rpm, and washed with water. Finally, it is added to deionized water, homogenized at 14000-16000 rpm for 20-40 minutes, centrifuged at 8000-10000 rpm, and dried at 60-80℃ for 8-12 hours to obtain the modified expanded vermiculite.

[0010] A more optimized method for preparing the amino phase change microcapsules is as follows: Step 1: Add the polystyrene-maleic anhydride copolymer to an aqueous sodium hydroxide solution and stir to obtain an emulsifier; Step 2: (1) Mix n-hexane, tetraethyl orthosilicate and 3-aminopropyltriethoxysilane to obtain an oil phase solution; (2) Add emulsifier to deionized water and add ammonia dropwise to obtain an aqueous phase solution; (3) Stir the aqueous phase solution to produce foam, add paraffin, continue stirring, then add the oil phase solution, emulsify, stir at 45~55℃ and 300~600rpm for 2~4 hours, finally wash with n-hexane, freeze dry to obtain amino phase change microcapsules.

[0011] In a more optimized manner, the mass ratio of polystyrene-maleic anhydride copolymer to sodium hydroxide aqueous solution in the raw materials of the emulsifier is (10~15):(90~110). In the raw materials of the oil phase solution, the mass ratio of n-hexane, tetraethyl orthosilicate, and 3-aminopropyltriethoxysilane is (10~20):(1~3):(0.2~0.4). In the raw materials of the aqueous solution, the mass ratio of emulsifier to deionized water is (2~4):100; In the raw materials of the amino phase change microcapsules, the mass ratio of aqueous solution, paraffin and oil solution is (15~30):(4~8):(5~15).

[0012] In a more optimized manner, in step 1, the liquid nitrogen freezing time is 4 to 6 minutes; the vacuum freeze-drying temperature is -40 to -30°C, the time is 20 to 30 hours, and the vacuum degree is 4 to 6 Pa.

[0013] Ideally, in step 1, the boric acid solution has a mass fraction of 0.5~1.5 wt%. The temperature for the hydrogel to form during static standing is 20~30℃, and the time is 10~15 hours; The soaking time in the boric acid solution is 1 to 3 hours.

[0014] A method for preparing a composite nano-thermal insulation sheet for battery cells. The composite nano-thermal insulation sheet has a pore size distribution of 20~50nm and a porosity of 92~96%.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are: This application uses glass fiber mat as the fiber matrix, introduces pine cellulose as the skeleton, and combines it with acid-sodium modified expanded vermiculite. A three-dimensional porous network is formed through a two-step crosslinking process using epichlorohydrin and boric acid. The integral molding ensures a strong bond between the crosslinked network and the fiber matrix interface, improving the material's structural integrity. Specifically, epichlorohydrin reacts with the cellulose hydroxyl groups to crosslink the linear pine cellulose molecular chains into a network structure; boric acid further strengthens the crosslinked network through crosslinking with the cellulose hydroxyl groups. After freeze-drying, this network forms numerous micropores, effectively suppressing gas convection heat transfer. Simultaneously, the modified expanded vermiculite, after acid treatment to remove impurities and sodium ion exchange, exhibits improved dispersibility. Its lamellar structure is randomly distributed within the skeleton, reflecting and scattering heat, thus enhancing the material's thermal insulation performance. Furthermore, the thermal decomposition of boric acid releases water vapor to dilute combustible gases, while vermiculite forms a physical barrier. The decomposition of boric acid to generate boron oxide further forms a dense barrier layer. This dual barrier ensures the material rapidly self-extinguishes after being removed from the flame. However, relying solely on the thermal insulation and flame retardant properties of aerogel has limited buffering capacity against thermal runaway of the battery cell. Therefore, the introduction of amino phase change microcapsules further enhances the thermal insulation performance of the material. When the battery cell experiences a rapid temperature rise due to thermal runaway, the microcapsule core material undergoes a solid-liquid phase change, absorbing a large amount of heat and significantly slowing down the rate of temperature rise. At the same time, the amino groups on the surface of the microcapsules form hydrogen bonds with the cellulose hydroxyl groups, preventing the microcapsules from debinding, agglomerating, and migrating. In addition, the amino groups can also form a hydrogen bond network with the silanol groups and boric acid on the surface of modified vermiculite, enabling the microcapsules to be evenly distributed and stably loaded in the aerogel framework, thereby improving the overall thermal insulation performance of the material. Furthermore, to further enhance the long-term structural stability of the material, this application employs liquid nitrogen freezing to induce ice crystal growth through multi-directional temperature gradients, forming a continuous network with hinged nodes. Subsequently, amino phase change microcapsules are attached to the porous surface of the aerogel via vacuum impregnation. This structure improves the overall structural stability of the composite thermal insulation sheet, allows for close fitting of battery cells with different shapes, and accommodates minute volumetric deformations during battery charge-discharge cycles. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] It should be noted that the following proportions are by weight. There are no special restrictions on the manufacturers of the raw materials involved in this invention. Exemplary examples include: pine cellulose of type ARBOCEL BC1000, expanded vermiculite with a particle size of 60 mesh, and glass fiber mat with a thickness of 2 mm and a bulk density of 130 kg / m³. 3 Porosity is 80%; The alkaline urea solution consists of 7% sodium hydroxide, 12% urea, and the balance being water.

[0018] Example 1: A method for preparing a composite nano-thermal insulating sheet for battery cells, comprising the following steps: Pre-preparation: Preparation of modified expanded vermiculite: 12 parts of expanded vermiculite were added to 0.4M hydrochloric acid solution, the temperature was set at 80℃, and the mixture was stirred for 4 hours. After filtration and washing with water, the mixture was added to 2mol / L sodium chloride solution, the temperature was set at 65℃, and the mixture was stirred for 4 hours. After centrifugation at 10000rpm and washing with water, the mixture was added to deionized water and homogenized at 15000rpm for 30 minutes. After centrifugation at 10000rpm and drying at 70℃ for 10 hours, modified expanded vermiculite was obtained.

[0019] Step 1: (1) Add 6 parts of pine cellulose to 250 parts of alkaline urea solution, stir for 30 minutes, set the temperature to -18℃, let stand for 12 hours, then raise to room temperature, add 2 parts of modified expanded vermiculite and 20 parts of epichlorohydrin in sequence, stir for 30 minutes to obtain a mixed solution; put the glass fiber felt into the mold, pour in the mixed solution to impregnate the glass fiber felt, set the temperature to 25℃, let stand for 12 hours to crosslink to form a hydrogel; wash with water until neutral, transfer to 1wt% boric acid solution and soak for 2 hours, wash with water again until neutral to obtain boric acid hydrogel; (2) immerse the boric acid hydrogel in liquid nitrogen and freeze for 6 minutes, then freeze dry under vacuum at -35℃ and 5Pa for 24 hours to obtain boric acid-cellulose-modified vermiculite aerogel; Step 2: (1) Add 13 parts of polystyrene maleic anhydride copolymer to 100 parts of sodium hydroxide aqueous solution and stir to obtain emulsifier; (2) Mix 15 parts of n-hexane, 2 parts of tetraethyl orthosilicate and 0.3 parts of 3-aminopropyltriethoxysilane to obtain oil phase solution; (3) Add 3 parts of emulsifier to 100 parts of deionized water and add ammonia to adjust pH to 10 to obtain aqueous phase solution; (4) Stir 23 parts of aqueous phase solution to produce foam, add 6 parts of paraffin, continue stirring, then add 10 parts of oil phase solution, emulsify and stir at 450 rpm for 3 hours at 50℃, finally wash with n-hexane 3 times, freeze dry to obtain amino phase change microcapsules; Step 3: Disperse 10 parts of amino phase change microcapsules in 100 parts of ethanol, then add 35 parts of boric acid-cellulose-modified vermiculite aerogel, impregnate under vacuum at -0.08 MPa for 8 hours, and dry at 60°C to obtain a composite nano heat insulation sheet.

[0020] Example 2: A method for preparing a composite nano-thermal insulating sheet for battery cells, comprising the following steps: Pre-preparation: Preparation of modified expanded vermiculite: 12 parts of expanded vermiculite were added to 0.4M hydrochloric acid solution, the temperature was set at 80℃, and the mixture was stirred for 4 hours. After filtration and washing with water, the mixture was added to 2mol / L sodium chloride solution, the temperature was set at 65℃, and the mixture was stirred for 4 hours. After centrifugation at 10000rpm and washing with water, the mixture was added to deionized water and homogenized at 15000rpm for 30 minutes. After centrifugation at 10000rpm and drying at 70℃ for 10 hours, modified expanded vermiculite was obtained.

[0021] Step 1: (1) Add 5 parts of pine cellulose to 200 parts of alkaline urea solution, stir for 30 minutes, set the temperature to -18℃, let stand for 12 hours, then raise to room temperature, add 1 part of modified expanded vermiculite and 15 parts of epichlorohydrin in sequence, stir for 30 minutes to obtain a mixed solution; put the glass fiber felt into the mold, pour in the mixed solution to impregnate the glass fiber felt, set the temperature to 25℃, let stand for 12 hours to crosslink to form a hydrogel; wash with water until neutral, transfer to 1wt% boric acid solution and soak for 2 hours, wash with water again until neutral to obtain boric acid hydrogel; (2) immerse the boric acid hydrogel in liquid nitrogen and freeze for 6 minutes, then freeze dry under vacuum at -35℃ and 5Pa for 24 hours to obtain boric acid-cellulose-modified vermiculite aerogel; Step 2: (1) Add 10 parts of polystyrene maleic anhydride copolymer to 90-110 parts of sodium hydroxide aqueous solution and stir to obtain emulsifier; (2) Mix 10 parts of n-hexane, 1 part of tetraethyl orthosilicate and 0.2 parts of 3-aminopropyltriethoxysilane to obtain oil phase solution; (3) Add 2 parts of emulsifier to 100 parts of deionized water and add ammonia to adjust pH to 10 to obtain aqueous phase solution; (4) Stir 15 parts of aqueous phase solution to produce foam, add 4 parts of paraffin, continue stirring, then add 5 parts of oil phase solution, emulsify and stir at 450 rpm for 3 hours at 50℃, finally wash with n-hexane 3 times, freeze dry to obtain amino phase change microcapsules.

[0022] Step 3: Disperse 5 parts of amino phase change microcapsules in 100 parts of ethanol, then add 25 parts of boric acid-cellulose-modified vermiculite aerogel, impregnate under vacuum of -0.08MPa for 8 hours, and dry at 60℃ to obtain composite nano heat insulation sheet.

[0023] Example 3: A method for preparing a composite nano-thermal insulating sheet for battery cells, comprising the following steps: Pre-preparation: Preparation of modified expanded vermiculite: 12 parts of expanded vermiculite were added to 0.4M hydrochloric acid solution, the temperature was set at 80℃, and the mixture was stirred for 4 hours. After filtration and washing with water, the mixture was added to 2mol / L sodium chloride solution, the temperature was set at 65℃, and the mixture was stirred for 4 hours. After centrifugation at 10000rpm and washing with water, the mixture was added to deionized water and homogenized at 15000rpm for 30 minutes. After centrifugation at 10000rpm and drying at 70℃ for 10 hours, modified expanded vermiculite was obtained.

[0024] Step 1: (1) Add 7 parts of pine cellulose to 300 parts of alkaline urea solution, stir for 30 minutes, set the temperature to -18℃, let stand for 12 hours, then raise to room temperature, add 3 parts of modified expanded vermiculite and 25 parts of epichlorohydrin in sequence, stir for 30 minutes to obtain a mixed solution; put the glass fiber mat into the mold, pour in the mixed solution to impregnate the glass fiber mat, set the temperature to 25℃, let stand for 12 hours to crosslink to form a hydrogel; wash with water until neutral, transfer to 1.5wt% boric acid solution, soak for 2 hours, wash with water again until neutral to obtain boric acid hydrogel; (2) immerse the boric acid hydrogel in liquid nitrogen for 6 minutes, then freeze dry under vacuum at -35℃ and 5Pa for 24 hours to obtain boric acid-cellulose-modified vermiculite aerogel; Step 2: (1) Add 15 parts of polystyrene maleic anhydride copolymer to 110 parts of sodium hydroxide aqueous solution and stir to obtain emulsifier; (2) Mix 20 parts of n-hexane, 3 parts of tetraethyl orthosilicate and 0.4 parts of 3-aminopropyltriethoxysilane to obtain oil phase solution; (3) Add 4 parts of emulsifier to 100 parts of deionized water and add ammonia to adjust pH to 10 to obtain aqueous phase solution; (4) Stir 30 parts of aqueous phase solution to produce foam, add 8 parts of paraffin, continue stirring, then add 15 parts of oil phase solution, emulsify and stir at 450 rpm for 3 hours at 50℃, finally wash with n-hexane 3 times, freeze dry to obtain amino phase change microcapsules.

[0025] Step 3: Disperse 15 parts of amino phase change microcapsules in 100 parts of ethanol, then add 45 parts of boric acid-cellulose-modified vermiculite aerogel, impregnate under vacuum of -0.08MPa for 8 hours, and dry at 60℃ to obtain composite nano heat insulation sheet.

[0026] Comparative Example 1: Based on Example 1, the boric acid-cellulose-modified vermiculite aerogel was replaced with cellulose-modified vermiculite aerogel; the rest was the same as in Example 1; the difference was: Step 1: Add 6 parts of pine cellulose to 250 parts of alkali urea solution, stir for 30 minutes, set the temperature to -18℃, let stand for 12 hours, then raise to room temperature, add 2 parts of modified expanded vermiculite and 20 parts of epichlorohydrin in sequence, stir for 30 minutes to obtain a mixed solution; place glass fiber mat in a mold, pour in the mixed solution to impregnate the glass fiber mat, set the temperature to 25℃, let stand for 12 hours to crosslink to form a hydrogel; wash with water until neutral, then immerse in liquid nitrogen to freeze for 6 minutes, and then freeze-dry under vacuum at -35℃ and 5Pa for 24 hours to obtain cellulose-modified vermiculite aerogel.

[0027] Comparative Example 2: Based on Example 1, the modified expanded vermiculite was not modified, and all other aspects remained the same as in Example 1; the difference was: Step 1: (1) Add 6 parts of pine cellulose to 250 parts of alkaline urea solution, stir for 30 minutes, set the temperature to -18℃, let stand for 12 hours, then raise to room temperature, add 2 parts of expanded vermiculite and 20 parts of epichlorohydrin in sequence, stir for 30 minutes to obtain a mixed solution; put the glass fiber felt into the mold, pour the mixed solution into the mold, so that the mixed solution impregnates the glass fiber felt, set the temperature to 25℃, and let stand for 12 hours to form a hydrogel.

[0028] Comparative Example 3: Based on Example 1, the amino phase change microcapsules were replaced with phase change microcapsules, and the rest remained the same as in Example 1; the difference was: Step 2: (1) Add 13 parts of polystyrene maleic anhydride copolymer to 100 parts of sodium hydroxide aqueous solution and stir to obtain emulsifier; (2) Mix 15 parts of n-hexane and 2 parts of tetraethyl orthosilicate to obtain oil phase solution; (3) Add 3 parts of emulsifier to 100 parts of deionized water and add ammonia to adjust pH to 10 to obtain aqueous phase solution; (4) Stir 23 parts of aqueous phase solution to produce foam, add 6 parts of paraffin, continue stirring, then add 10 parts of oil phase solution, emulsify and stir at 50°C for 3 hours, finally wash with n-hexane 3 times, freeze dry to obtain phase change microcapsules.

[0029] Comparative Example 4: Based on Example 1, 35 parts of amino phase change microcapsules and 10 parts of boric acid-cellulose-modified vermiculite aerogel were added to the composite nano-insulation sheet; the difference is: Step 3: Disperse 35 parts of amino phase change microcapsules in 100 parts of ethanol, then add 10 parts of boric acid-cellulose-modified vermiculite aerogel, impregnate under vacuum of -0.08MPa for 8 hours, and dry at 60℃ to obtain composite nano heat insulation sheet.

[0030] Comparative Example 5: Based on Example 1, liquid nitrogen freezing was replaced with unidirectional freezing; the difference is: Step 1: (1) Add 6 parts of pine cellulose to 250 parts of alkaline urea solution, stir for 30 minutes, set the temperature to -18℃, let stand for 12 hours, then raise to room temperature, add 2 parts of modified expanded vermiculite and 20 parts of epichlorohydrin in sequence, stir for 30 minutes to obtain a mixed solution; put the glass fiber felt into the mold, pour in the mixed solution to impregnate the glass fiber felt, set the temperature to 25℃, let stand for 12 hours to crosslink to form a hydrogel; wash with water until neutral, transfer to 1wt% boric acid solution and soak for 2 hours, wash with water again until neutral to obtain boric acid hydrogel; (2) attach the bottom of the boric acid hydrogel to a liquid nitrogen cold stage pre-cooled to -196℃ and freeze continuously in one direction for 6 minutes, then freeze dry in vacuum at -35℃ and 5Pa for 24 hours to obtain boric acid-cellulose-modified vermiculite aerogel.

[0031] Performance testing: The composite nano-insulation sheets prepared in the examples and comparative examples were used as samples for the following tests; (1) Thermal conductivity test: According to GB / T10295-2008 "Determination of steady-state thermal resistance and related properties of thermal insulation materials by heat flow meter method", a thermal conductivity meter was used. The test parameters were: the temperature of the hot plate was 70℃, the temperature of the cold plate was 30℃, and the clamping load was 0.1MPa. The thermal conductivity of the sample was tested.

[0032] (2) Thermal insulation performance test: The sample was cut into 100×100×1.2mm pieces. 3 Specifications: A thermocouple is attached to the upper and lower surfaces of the device, which is then placed on a heating platform. The heating temperature is set to 600℃, and a pressure of 0.9MPa is applied continuously for 10 minutes. The temperature difference between the cold and hot surfaces is recorded to characterize the thermal insulation performance.

[0033] (3) Mechanical property test: The sample was cut into 2×2×1cm pieces. 3 Specifications: At room temperature, the deformation and stress after applying force along its length were tested using a universal testing machine at a compression rate of 3 mm / min, with a compressive strain rate of 40%.

[0034] (4) Limiting oxygen index test: According to the ASTM D2863 test standard, the oxygen index tester is used. The sample is cut into strips of 100×10×10mm, fixed vertically in the equipment and ignited. The flame is observed to burn downwards. The combustion judgment is based on the sample burning to the 5cm mark from the top and continuing to burn for no less than 180s. The combustion time is recorded and the oxygen concentration is adjusted to obtain the limiting oxygen index of the material.

[0035]

[0036] Conclusion: As can be seen from the data in the table above, the heat insulation sheet formed by liquid nitrogen freezing in the embodiment forms an interlocking heat insulation skeleton. This structure can disperse compressive stress in multiple dimensions and retain air in the pores to a high degree, ultimately achieving low thermal conductivity, high temperature difference between hot and cold surfaces, high compressive modulus and high limiting oxygen index, which significantly improves the heat insulation, mechanical properties and flame retardant safety performance of the heat insulation sheet.

[0037] Comparative Examples and Examples: In Comparative Example 1, after omitting the boric acid crosslinking treatment, the cellulose network became unstable, and the aerogel channels collapsed and densified over a large area during the freeze-drying process, resulting in a significant increase in thermal conductivity and a substantial decrease in compressive modulus and flame retardant properties. In Comparative Example 2, when unmodified virgin expanded vermiculite was used, the bonding force between the filler and the matrix was weak, and multiple microscopic thermal short circuits were formed internally, significantly weakening the reinforcing effect of the filler and its ability to prevent high-temperature charring. In Comparative Example 3, after replacing the amino phase change microcapsules with phase change microcapsules, the phase change microcapsules could not form chemical bonds with the aerogel matrix, and were prone to agglomeration and detachment after impregnation, making it difficult to fully utilize the phase change heat storage and insulation function, and compromising structural integrity. In Comparative Example 4, adjusting the ratio of boric acid-cellulose aerogel to amino phase change microcapsules resulted in excessive organic paraffin microcapsules clogging the porous thermal insulation framework, leading to a sharp deterioration in thermal conductivity and a significant drop in compressive modulus. In Comparative Example 5, replacing liquid nitrogen freezing with unidirectional directional freezing resulted in the formation of only parallel layered through-channels within the material. Under pressure in the thickness direction, the interlayers were prone to slippage, buckling, and collapse, causing a significant decrease in compressive modulus. Simultaneously, the through-channels exacerbated internal air convection, further deteriorating the thermal insulation effect. However, since the freezing method only changed the physical pore morphology and its chemical flame-retardant components remained unchanged, its limiting oxygen index only fluctuated slightly. In summary, this application achieves a composite nano-thermal insulation sheet for battery cells that combines low thermal conductivity, structural stability, and high flame retardancy by forming a three-dimensional network through boric acid crosslinking, modifying expanded vermiculite to optimize interfacial heat transfer efficiency and improve flame retardancy, synergistically introducing amino phase change microcapsules to achieve phase change heat storage and temperature control, and employing a liquid nitrogen multidirectional freezing process.

[0038] Insulation performance test: The composite nano-insulation sheet prepared in Example 1 was cut into 100×100×2mm pieces. 3 Volume resistivity test: According to GB / T31838.2-2019 "Test methods for volume resistivity and surface resistivity of solid insulating materials", the composite nano heat insulation sheet was placed at 500℃ for 10 minutes and cooled to room temperature before its volume resistivity was tested.

[0039]

[0040] As shown in the test data in the table above, the composite nano-insulation sheet prepared in Example 1 has a volume resistivity of 1.3 × 10⁻⁶ after aging at 500℃. 14 The Ω·cm reading proves that it has reliable insulation performance and can meet the isolation requirements between battery cells.

[0041] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a composite nano-thermal insulating sheet for battery cells, characterized in that: Includes the following steps: Step 1: (1) Pine cellulose, modified expanded vermiculite and epichlorohydrin are added to an alkaline urea solution composed of sodium hydroxide, urea and water in sequence, and stirred to obtain a mixed solution; then glass fiber felt is placed in a mold, the mixed solution is poured in to impregnate the glass fiber felt, and it is allowed to stand for cross-linking to form a hydrogel; After being washed with water, the solution was transferred to a boric acid solution for soaking, and then washed with water again to obtain boric acid hydrogel; (2) the boric acid hydrogel was frozen with liquid nitrogen and then freeze-dried under vacuum to obtain boric acid-cellulose-modified vermiculite aerogel; Step 2: Using tetraethyl orthosilicate and 3-aminopropyltriethoxysilane as silicon sources and paraffin as core material, amino phase change microcapsules were prepared by emulsion interfacial polymerization. Step 3: Disperse the amino phase change microcapsules in ethanol, then add boric acid-cellulose-modified vermiculite aerogel, and impregnate under vacuum-assisted impregnation for 6 to 12 hours at a vacuum degree of -0.07 to -0.09 MPa, and then dry at 50 to 70°C to obtain the composite nano heat insulation sheet.

2. The method for preparing a composite nano-thermal insulating sheet for a battery cell according to claim 1, characterized in that: In step 1, the raw materials of the mixed solution, by weight, are: 5-7 parts pine cellulose, 200-300 parts alkali urea solution, 1-3 parts modified expanded vermiculite, and 15-25 parts epichlorohydrin.

3. The method for preparing a composite nano-thermal insulating sheet for a battery cell according to claim 1, characterized in that: The raw materials of the composite nano heat insulation sheet, by weight, have the following composition: amino phase change microcapsules, boric acid-cellulose-modified vermiculite aerogel in a mass ratio of (5~15):(25~45).

4. The method for preparing a composite nano-thermal insulating sheet for a battery cell according to claim 2, characterized in that: The modified expanded vermiculite is prepared as follows: expanded vermiculite is added to hydrochloric acid solution, the temperature is set at 75~85℃, stirred for 2~4 hours, filtered, washed with water, then added to sodium chloride solution, the temperature is set at 60~70℃, stirred for 3~5 hours, centrifuged at 8000~10000 rpm, washed with water, and finally added to deionized water, homogenized at 14000~16000 rpm for 20~40 minutes, centrifuged at 8000~10000 rpm, and dried at 60~80℃ for 8~12 hours to obtain modified expanded vermiculite.

5. The method for preparing a composite nano-thermal insulating sheet for a battery cell according to claim 1, characterized in that: The preparation method of the amino phase change microcapsules is as follows: Step 1: Add the polystyrene-maleic anhydride copolymer to an aqueous sodium hydroxide solution and stir to obtain an emulsifier; Step 2: (1) Mix n-hexane, tetraethyl orthosilicate and 3-aminopropyltriethoxysilane to obtain an oil phase solution; (2) Add emulsifier to deionized water and add ammonia dropwise to obtain an aqueous phase solution; (3) Stir the aqueous phase solution to produce foam, add paraffin, continue stirring, then add the oil phase solution, emulsify, stir at 45~55℃ and 300~600rpm for 2~4 hours, finally wash with n-hexane, freeze dry to obtain amino phase change microcapsules.

6. The method for preparing a composite nano-thermal insulating sheet for a battery cell according to claim 5, characterized in that: In the raw materials of the emulsifier, the mass ratio of polystyrene maleic anhydride copolymer to sodium hydroxide aqueous solution is (10~15):(90~110). In the raw materials of the oil phase solution, the mass ratio of n-hexane, tetraethyl orthosilicate, and 3-aminopropyltriethoxysilane is (10~20):(1~3):(0.2~0.4). In the raw materials of the aqueous solution, the mass ratio of emulsifier to deionized water is (2~4):100; In the raw materials of the amino phase change microcapsules, the mass ratio of aqueous solution, paraffin and oil solution is (15~30):(4~8):(5~15).

7. The method for preparing a composite nano-thermal insulating sheet for a battery cell according to claim 1, characterized in that: In step 1, the liquid nitrogen freezing time is 4 to 6 minutes; the vacuum freeze-drying temperature is -40 to -30°C, the time is 20 to 30 hours, and the vacuum degree is 4 to 6 Pa.

8. The method for preparing a composite nano-thermal insulating sheet for a battery cell according to claim 1, characterized in that: In step 1, the boric acid solution has a mass fraction of 0.5~1.5 wt%. The temperature for the hydrogel to form during static standing is 20~30℃, and the time is 10~15 hours; The soaking time in the boric acid solution is 1 to 3 hours.

9. The composite nano-thermal insulating sheet prepared by the method for preparing a composite nano-thermal insulating sheet for a battery cell according to any one of claims 1 to 8, characterized in that: The composite nano-insulation sheet has a pore size distribution of 20~50nm and a porosity of 92~96%.

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