A fire-retardant thermal barrier material for an electrical cell and a method of making the same

Abstract

The present application relates to the technical field of thermal insulation materials, and discloses a flame-retardant thermal insulation material for an electric core and a preparation method thereof. The flame-retardant thermal insulation material for the electric core is obtained through cellulose dissolution, crosslinking and flame-retardant modification, gel forming and drying. The active intermediates released by the oxazine ring during ring-opening polymerization at high temperature can catalyze the crosslinking reaction between molecular chains, forming a three-dimensional network structure and improving the flame-retardant performance of the material. Borate ester decomposes into boron oxide or boric acid at high temperature, and forms a transparent glassy coating after melting, which tightly covers the surface of the material, physically blocks the transmission of oxygen and heat, and has a flame-retardant effect. The phosphoric acid ester decomposes to generate phosphorus-containing free radicals, which can combine with active free radicals in the flame to interrupt the combustion chain reaction, reduce the flame temperature, and further improve the flame-retardant performance of the material. The silane decomposes to generate non-combustible or difficult-to-combust substances such as silicon dioxide, which form a dense protective layer on the surface of the material, thereby preventing the spread of the flame and having a flame-retardant effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thermal insulation materials, in particular to a flame-retardant thermal insulation material for battery cells and a preparation method thereof. BACKGROUND

[0002] With the rapid development of the new energy industry, the safety requirements of energy storage devices such as lithium ion batteries are increasingly stringent, and the fire accidents caused by thermal runaway of power batteries have become a key problem restricting the development of the industry. As a core component for blocking heat spread and delaying thermal runaway, the performance of high-efficiency thermal insulation materials directly affects the safety and reliability of battery cells. Thermal insulation materials are mainly divided into traditional thermal insulation materials and aerogels, and traditional thermal insulation materials include foam boards, glass fiber cotton, vacuum insulation boards, etc., but their thermal insulation performance, physical properties and environmental protection performance are difficult to meet the requirements. In recent years, cellulose aerogels have been considered as ideal green thermal insulation materials due to their low density, high porosity, low thermal conductivity and biodegradability, etc. However, the inherent flammability of cellulose aerogels has seriously limited their application between power battery cells. SUMMARY

[0003] (I) Technical problems solved

[0004] In view of the deficiencies of the prior art, the present application provides a flame-retardant thermal insulation material for battery cells and a preparation method thereof to solve the problem of poor flame-retardant performance of cellulose aerogels.

[0005] (II) Technical solutions

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solutions: a preparation method of a flame-retardant thermal insulation material for battery cells, wherein the preparation method of the flame-retardant thermal insulation material for battery cells is as follows: sodium hydroxide, urea and water are added to a reactor, stirred and mixed, and pre-cooled to -14 to -10℃ to obtain a cellulose dissolving agent, cotton cellulose with a mass fraction of 5.8%-6.2% is dispersed in the cellulose dissolving agent, and a transparent sol is obtained after stirring for 25-35min, a crosslinking agent with a mass fraction of 4.5%-5.5% is added to the transparent sol, and reacted for 1-1.5h, then a borate modified benzoxazine flame retardant with a mass fraction of 10%-12% and sodium-based montmorillonite with a mass fraction of 2.4%-3.2% are sequentially added thereto, and ultrasonic dispersion is performed for 30-40min, then the gel is poured into a mold, and after curing at 48-52℃ for 8-14h, gradient replacement with ethanol and tert-butyl alcohol is performed, and after freeze-drying at -50 to -45℃ for 20-24h and drying at 55-65℃ for 42-48h, the flame-retardant thermal insulation material for battery cells is obtained.

[0007] Preferably, the mass ratio of sodium hydroxide, urea and water is 1:1.6-1.8:11.3-11.9.

[0008] Preferably, the preparation method of the borate-modified benzoxazine flame retardant, comprising the following steps:

[0009] (1) 4.55-4.85 g of 4-aminopyridine, 3-3.2 g of polyformaldehyde are added to 40-60 mL of toluene solvent, and reacted at 32-36°C for 1-2 h, 8.3-8.9 g of 4-bromophenol is added, and the temperature is raised to 78-84°C for continuous reaction for 4-6 h, after the reaction is completed, it is washed with 4%-4.5% sodium hydroxide solution, and the solvent is removed by rotary evaporation to obtain a benzoxazine intermediate;

[0010] (2) 5.4-6.3 g of the benzoxazine intermediate, 6-6.2 g of pinacol diboron are dissolved in 80-100 mL of 1,4-dioxane solvent, 1.45-1.55 g of catalyst, 8-8.2 g of potassium carbonate are added, and the temperature is raised to 90-110°C for reaction under nitrogen atmosphere for 3.5-5.5 h, after the reaction is completed, the solvent is removed by rotary evaporation, washed and vacuum dried to obtain the borate-modified benzoxazine flame retardant.

[0011] Preferably, the catalyst in step (2) is [1,1-bis(diphenylphosphino)ferrocene] palladium dichloride.

[0012] Preferably, the preparation method of the epoxy crosslinking agent, comprising the following steps:

[0013] S1. 2.9-3 g of N-methyldiethanolamine is added to 60-80 mL of anhydrous ethanol solvent, stirred and dissolved, 5.1-5.3 g of 3-chloropropyltrimethoxysilane is added dropwise, after the dropwise addition is completed, the temperature is raised to 75-85°C for reflux reaction for 13-16 h, after the reaction is completed, the solvent is removed by rotary evaporation to obtain a silane quaternary ammonium salt intermediate;

[0014] S2. Under nitrogen atmosphere, 4.4-4.5 g of the silane quaternary ammonium salt intermediate, 0.8-1.2 mL of an acid binding agent are added to 40-50 mL of dichloromethane solvent, stirred and dissolved at 6-12°C, 1.62-1.72 g of phenylphosphoryl dichloride is added dropwise, the dropwise addition time is 20-30 min, after the dropwise addition is completed, the reaction is carried out for 10-14 h, after the reaction is completed, the solvent is removed by rotary evaporation, washed and vacuum dried to obtain a phosphonate-modified silane quaternary ammonium salt;

[0015] S3. 7.2-7.9g of phosphonate-modified silane quaternary ammonium salt, 18.4-18.6g of epichlorohydrin, and 0.78-0.82g of sodium hydroxide were added into 80-90mL of isopropyl alcohol solvent, and the temperature was raised to 48-54℃, and nitrogen was introduced for protection, and after stirring and dissolving, the temperature was raised to 65-70℃, and 0.78-0.82g of sodium hydroxide was added, and the reaction was continued for 3-4h, and after the reaction was completed, the solvent was removed by vacuum filtration, and then washed and vacuum dried to obtain an epoxy crosslinking agent.

[0016] Preferably, the dropping time of 3-chloropropyl trimethoxysilane in S1 is 40-50min.

[0017] Preferably, the acid-binding agent in S2 is triethylamine.

[0018] The application provides a flame-retardant thermal insulation material for an electric core prepared by the preparation method.

[0019] (Three) beneficial technical effects

[0020] The application obtains a flame-retardant thermal insulation material for an electric core through cellulose dissolution, crosslinking and flame-retardant modification, gel forming and drying.

[0021] In the borate-modified benzoxazine flame retardant, the active intermediates released by the ring-opening polymerization of the oxazine ring at high temperature can catalyze the crosslinking reaction between molecular chains, forming a three-dimensional network structure. This structure is not easy to decompose into small molecular combustible substances during combustion, but promotes the formation and stability of the carbon layer, thereby improving the flame-retardant performance of the material. The borate decomposes into boron oxide or boric acid at high temperature, and forms a transparent glassy coating after melting, which tightly covers the surface of the material, physically blocks the transmission of oxygen and heat, and prevents the escape of flammable gas, thereby achieving the effect of flame retardation. In the epoxy crosslinking agent, the phosphorus-containing radicals produced by the decomposition of the phosphate can combine with active radicals in the flame, interrupt the combustion chain reaction, and reduce the flame temperature, thereby further improving the flame-retardant performance of the material. The non-combustible or difficult-to-combust substances such as silicon dioxide produced by the decomposition of silane will form a dense protective layer on the surface of the material, thereby preventing the spread of the flame and achieving the effect of flame retardation. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is the synthesis reaction formula of the borate-modified benzoxazine flame retardant.

[0023] Figure 2 is the synthesis reaction formula of the epoxy crosslinking agent. DETAILED DESCRIPTION

[0024] In order to make the purposes, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application are described clearly and completely. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0025] In order to better understand the above technical solutions, the above technical solutions will be described in detail below in combination with the drawings in the specification and specific embodiments.

[0026] Embodiment 1

[0027] (1) 4.55 g of 4-aminopyridine, 3 g of polyformaldehyde were added into 40 mL of toluene solvent, and reacted at 32°C for 1 h, 8.3 g of 4-bromophenol was added, and the temperature was increased to 78°C for continuous reaction for 4 h. After the reaction was completed, the reaction solution was washed with 4% sodium hydroxide solution, and the solvent was removed by rotary evaporation to obtain a benzoxazine intermediate;

[0028] (2) 5.4 g of the benzoxazine intermediate and 6 g of pinacol diboronic acid were dissolved in 80 mL of 1,4-dioxane solvent, 1.45 g of [1,1-bis(diphenylphosphine)ferrocene] palladium dichloride catalyst and 8 g of potassium carbonate were added, and the temperature was increased to 90°C for reaction under nitrogen atmosphere for 3.5 h. After the reaction was completed, the solvent was removed by rotary evaporation, washed and vacuum dried to obtain a borate-modified benzoxazine flame retardant;

[0029] (3) 2.9 g of N-methyldiethanolamine was added into 60 mL of anhydrous ethanol solvent and stirred and dissolved, 5.1 g of 3-chloropropyltrimethoxysilane was added dropwise, the dropwise addition time was 40 min, after the dropwise addition was completed, the temperature was increased to 75°C for reflux reaction for 13 h. After the reaction was completed, the solvent was removed by rotary evaporation to obtain a silane quaternary ammonium salt intermediate;

[0030] (4) 4.4 g of the silane quaternary ammonium salt intermediate and 0.8 mL of triethylamine acid acceptor were added into 40 mL of dichloromethane solvent and stirred and dissolved at 6°C, 1.62 g of phenylphosphoryl dichloride was added dropwise, the dropwise addition time was 20 min, and the reaction was carried out for 10 h. After the reaction was completed, the solvent was removed by rotary evaporation, washed and vacuum dried to obtain a phosphate-modified silane quaternary ammonium salt;

[0031] (5) 7.2 g of phosphonate-modified silane quaternary ammonium salt, 18.4 g of epichlorohydrin, and 0.78 g of sodium hydroxide were added to 80 mL of isopropyl alcohol solvent, and the mixture was stirred and dissolved under nitrogen protection, and then the temperature was raised to 65°C. After 3 hours of continuous reaction, the solvent was removed by vacuum filtration, washed, and vacuum dried to obtain an epoxy crosslinking agent;

[0032] (6) Sodium hydroxide, urea, and water were added to a reactor, stirred and mixed, and pre-cooled to -14°C. The mass ratio of sodium hydroxide, urea, and water was 1:1.6:11.3, and a cellulose dissolving agent was obtained. Cotton cellulose with a mass fraction of 5.8% was dispersed in the cellulose dissolving agent, and a transparent sol was obtained after stirring for 25 min. An epoxy crosslinking agent with a mass fraction of 4.5% was added to the transparent sol, and the reaction was carried out for 1 h. Then, a borate-modified benzoxazine flame retardant with a mass fraction of 10% and sodium-based montmorillonite with a mass fraction of 2.4% were sequentially added, and ultrasonic dispersion was carried out for 30 min. The gel was poured into a mold, and after curing at 48°C for 8 h, gradient replacement with ethanol→tert-butyl alcohol was carried out, and freeze-drying was carried out at -50°C for 20 h, and then drying was carried out at 55°C for 42 h to obtain a flame-retardant thermal insulation material for battery cells.

[0033] Example 2

[0034] (1) 4.85 g of 4-aminopyridine and 3.2 g of paraformaldehyde were added to 60 mL of toluene solvent, and the mixture was reacted at 36°C for 2 h. Then, 8.9 g of 4-bromophenol was added, and the temperature was raised to 84°C for continuous reaction for 6 h. After the reaction was completed, the mixture was washed with a 4.5% mass fraction sodium hydroxide solution, and the solvent was removed by rotary evaporation to obtain a benzoxazine intermediate;

[0035] (2) 6.3 g of the benzoxazine intermediate and 6.2 g of pinacol diboronic acid were dissolved in 100 mL of 1,4-dioxane solvent, and 1.55 g of [1,1-bis(diphenylphosphino)ferrocene]palladium dichloride catalyst and 8.2 g of potassium carbonate were added. The mixture was reacted at 110°C for 5.5 h under a nitrogen atmosphere. After the reaction was completed, the solvent was removed by rotary evaporation, and the mixture was washed and vacuum dried to obtain a borate-modified benzoxazine flame retardant;

[0036] (3) 3 g of N-methyldiethanolamine was added to 80 mL of anhydrous ethanol solvent, and the mixture was stirred and dissolved. Then, 5.3 g of 3-chloropropyltrimethoxysilane was added dropwise, and the dropwise addition was carried out for 50 min. After the dropwise addition was completed, the temperature was raised to 85°C for reflux reaction for 16 h. After the reaction was completed, the solvent was removed by rotary evaporation to obtain a silane quaternary ammonium salt intermediate;

[0037] (4) Under a nitrogen atmosphere, 4.5 g of silane quaternary ammonium salt intermediate and 1.2 mL of triethylamine acid binder were added to 50 mL of dichloromethane solvent and stirred and dissolved at 12 °C. 1.72 g of phenylphosphodichloro was added dropwise over a period of 30 min. After the addition was complete, the reaction was allowed to proceed for 14 h. After the reaction was completed, the solvent was removed by rotary evaporation, and the product was washed and dried under vacuum to obtain phosphate-modified silane quaternary ammonium salt.

[0038] (5) Add 7.9 g of phosphate-modified silane quaternary ammonium salt and 18.6 g of epichlorohydrin to 90 mL of isopropanol solvent, heat to 54 °C, purge with nitrogen for protection, stir to dissolve and continue heating to 70 °C, add 0.82 g of sodium hydroxide and continue reaction for 4 h. After the reaction is completed, remove the solvent by vacuum filtration, wash and vacuum dry to obtain epoxy crosslinking agent;

[0039] (6) Add sodium hydroxide, urea and water to the reactor, stir and mix and pre-cool to -10℃, wherein the mass ratio of sodium hydroxide, urea and water is 1:1.8:11.9 to obtain cellulose solvent. Disperse cotton cellulose with a mass fraction of 6.2% in the cellulose solvent and stir for 35 min to obtain transparent sol. Add epoxy crosslinking agent with a mass fraction of 5.5% to the transparent sol and react for 1.5 h. Then add borate ester modified benzoxazine flame retardant with a mass fraction of 12% and sodium montmorillonite with a mass fraction of 3.2% in sequence. After ultrasonic dispersion for 40 min, pour the gel into the mold and cure at 52℃ for 14 h. Then use ethanol → tert-butanol gradient replacement, freeze dry at -45℃ for 24 h, and dry at 65℃ for 48 h to obtain flame retardant and heat insulation material for battery cells.

[0040] Example 3

[0041] (1) Add 4.7 g of 4-aminopyridine and 3.1 g of paraformaldehyde to 50 mL of toluene solvent, react at 34 °C for 1.5 h, add 8.6 g of 4-bromophenol, raise the temperature to 81 °C and continue the reaction for 5 h. After the reaction is completed, wash with 4.25% sodium hydroxide solution and remove the solvent by rotary evaporation to obtain benzoxazine intermediate;

[0042] (2) Dissolve 5.85 g of benzoxazine intermediate and 6.1 g of pinacol diborate in 90 mL of 1,4-dioxane solvent, add 1.5 g of [1,1-bis(diphenylphosphine)ferrocene]palladium dichloride catalyst and 8.1 g of potassium carbonate, and react at 100 °C for 4.5 h under nitrogen atmosphere. After the reaction is completed, remove the solvent by rotary evaporation, wash and vacuum dry to obtain borate ester modified benzoxazine flame retardant;

[0043] (3) Add 2.95 g of N-methyldiethanolamine to 70 mL of anhydrous ethanol solvent, stir to dissolve, add 5.2 g of 3-chloropropyltrimethoxysilane dropwise over a period of 45 min, and after the addition is complete, heat to 80 °C and reflux for 14.5 h. After the reaction is complete, remove the solvent by rotary evaporation to obtain the silane quaternary ammonium salt intermediate.

[0044] (4) Under a nitrogen atmosphere, 4.45 g of silane quaternary ammonium salt intermediate and 1 mL of triethylamine acid binder were added to 45 mL of dichloromethane solvent and stirred at 9 °C to dissolve. 1.67 g of phenylphosphodichloro was added dropwise over a period of 25 min. After the addition was complete, the reaction was allowed to proceed for 12 h. After the reaction was completed, the solvent was removed by rotary evaporation, and the product was washed and dried under vacuum to obtain phosphate-modified silane quaternary ammonium salt.

[0045] (5) Add 7.55g of phosphate-modified silane quaternary ammonium salt and 18.5g of epichlorohydrin to 85mL of isopropanol solvent, heat to 51℃, purge with nitrogen for protection, stir to dissolve and continue heating to 68℃, add 0.8g of sodium hydroxide, continue reaction for 3.5h, after the reaction is completed, remove solvent by vacuum filtration, wash and vacuum dry to obtain epoxy crosslinking agent;

[0046] (6) Add sodium hydroxide, urea and water to the reactor, stir and mix and pre-cool to -12°C, wherein the mass ratio of sodium hydroxide, urea and water is 1:1.7:11.6 to obtain cellulose solvent. Disperse 6% cotton cellulose in the cellulose solvent and stir for 30 min to obtain transparent sol. Add 5% epoxy crosslinking agent to the transparent sol and react for 1.2 h. Then add 11% borate ester modified benzoxazine flame retardant and 2.8% sodium montmorillonite to it in sequence. After ultrasonic dispersion for 35 min, pour the gel into the mold and cure at 50°C for 11 h. Then use ethanol → tert-butanol gradient replacement, freeze dry at -48°C for 22 h, and dry at 60°C for 45 h to obtain flame retardant and heat insulation material for battery cells.

[0047] Example 4

[0048] (1) Add 4.55 g of 4-aminopyridine and 3 g of paraformaldehyde to 40 mL of toluene solvent, react at 32 °C for 1 h, add 8.3 g of 4-bromophenol, raise the temperature to 78 °C and continue the reaction for 4 h. After the reaction is completed, wash with 4% sodium hydroxide solution and remove the solvent by rotary evaporation to obtain benzoxazine intermediate;

[0049] (2) 5.4 g of benzoxazine intermediate, 6 g of bisphenol A, 80 mL of 1,4-dioxane solvent, 1.45 g of [1,1-bis(diphenylphosphine)ferrocene] dichloropalladium catalyst, 8 g of potassium carbonate, under nitrogen atmosphere, heated to 90°C for 3.5 h, after the reaction is completed, the solvent is removed by rotary evaporation, washed and vacuum dried to obtain borate modified benzoxazine flame retardant;

[0050] (3) 3 g of N-methyldiethanolamine is added to 80 mL of anhydrous ethanol solvent, stirred and dissolved, 5.3 g of 3-chloropropyltrimethoxysilane is added dropwise, the dropwise addition time is 50 min, after the dropwise addition is completed, it is heated to 85°C and refluxed for 16 h, after the reaction is completed, the solvent is removed by rotary evaporation to obtain a silane quaternary ammonium salt intermediate;

[0051] (4) Under a nitrogen atmosphere, 4.5 g of silane quaternary ammonium salt intermediate, 1.2 mL of triethylamine acid acceptor is added to 50 mL of dichloromethane solvent, stirred and dissolved at 12°C, 1.72 g of phenylphosphonic dichloride is added dropwise, the dropwise addition time is 30 min, after the dropwise addition is completed, it is reacted for 14 h, after the reaction is completed, the solvent is removed by rotary evaporation, washed and vacuum dried to obtain a phosphate modified silane quaternary ammonium salt;

[0052] (5) 7.55 g of phosphate modified silane quaternary ammonium salt, 18.5 g of epichlorohydrin is added to 85 mL of isopropanol solvent, heated to 51°C, protected by nitrogen, stirred and dissolved, then heated to 68°C, 0.8 g of sodium hydroxide is added, and the reaction is continued for 3.5 h, after the reaction is completed, the solvent is removed by vacuum filtration, washed and vacuum dried to obtain an epoxy crosslinking agent;

[0053] (6) Sodium hydroxide, urea, water are added to the reactor, stirred and mixed and pre-cooled to negative 12°C, the mass ratio of sodium hydroxide, urea and water is 1:1.7:11.6, a cellulose dissolving agent is obtained, cotton cellulose with a mass fraction of 6% is dispersed in the cellulose dissolving agent, stirred for 30 min to obtain a transparent sol, an epoxy crosslinking agent with a mass fraction of 5% is added to the transparent sol, reacted for 1.2 h, then an borate modified benzoxazine flame retardant with a mass fraction of 11% and sodium montmorillonite with a mass fraction of 2.8% are added in turn, ultrasonic dispersion is carried out for 35 min, then the gel is poured into a mold, cured at 50°C for 11 h, gradient displacement is carried out using ethanol→tert-butyl alcohol, frozen and dried at negative 48°C for 22 h, then dried at 60°C for 45 h to obtain a flame-retardant thermal insulation material for battery cells.

[0054] Example 5

[0055] (1) 4.7 g of 4-aminopyridine, 3.1 g of paraformaldehyde were added into 50 mL of toluene solvent, and reacted at 34°C for 1.5 h, 8.6 g of 4-bromophenol was added, and the reaction was continued at 81°C for 5 h. After the reaction was completed, the reaction solution was washed with 4.25% by mass sodium hydroxide solution, and the solvent was removed by rotary evaporation to obtain a benzoxazine intermediate;

[0056] (2) 5.85 g of the benzoxazine intermediate, 6.1 g of pinacol diboronic acid were dissolved in 90 mL of 1,4-dioxane solvent, 1.5 g of [1,1-bis(diphenylphosphino)ferrocene] palladium dichloride catalyst, 8.1 g of potassium carbonate were added, and the reaction was continued at 100°C for 4.5 h under nitrogen atmosphere. After the reaction was completed, the solvent was removed by rotary evaporation, washed and vacuum dried to obtain a borate-modified benzoxazine flame retardant;

[0057] (3) 2.9 g of N-methyldiethanolamine was added into 60 mL of anhydrous ethanol solvent, and stirred and dissolved. 5.1 g of 3-chloropropyltrimethoxysilane was added dropwise, and the dropwise addition was continued for 40 min. After the dropwise addition was completed, the reaction was continued at 75°C for 13 h. After the reaction was completed, the solvent was removed by rotary evaporation to obtain a silane quaternary ammonium salt intermediate;

[0058] (4) 4.4 g of the silane quaternary ammonium salt intermediate, 0.8 mL of triethylamine acid acceptor were added into 40 mL of dichloromethane solvent, and stirred and dissolved at 6°C. 1.62 g of phenylphosphoryl dichloride was added dropwise, and the dropwise addition was continued for 20 min. After the dropwise addition was completed, the reaction was continued for 10 h. After the reaction was completed, the solvent was removed by rotary evaporation, washed and vacuum dried to obtain a phosphate-modified silane quaternary ammonium salt;

[0059] (5) 7.9 g of the phosphate-modified silane quaternary ammonium salt, 18.6 g of epichlorohydrin were added into 90 mL of isopropanol solvent, and stirred and dissolved under nitrogen protection at 54°C. 0.82 g of sodium hydroxide was added, and the reaction was continued at 70°C for 4 h. After the reaction was completed, the solvent was removed by reduced pressure filtration, washed and vacuum dried to obtain an epoxy crosslinking agent;

[0060] (6) adding sodium hydroxide, urea and water into the reactor, stirring and mixing and pre-cooling to minus 10℃, wherein the mass ratio of sodium hydroxide, urea and water is 1:1.8:11.9, obtaining a cellulose dissolving agent, dispersing cotton cellulose with a mass fraction of 6.2% in the cellulose dissolving agent, obtaining a transparent sol after stirring for 35 min, adding an epoxy crosslinking agent with a mass fraction of 5.5% into the transparent sol, reacting for 1.5 h, then adding borate modified benzoxazine flame retardant with a mass fraction of 12% and sodium-based montmorillonite with a mass fraction of 3.2% into the transparent sol in sequence, ultrasonic dispersing for 40 min, then pouring the gel into a mold, curing at 52℃ for 14 h, using ethanol→tert-butyl alcohol gradient replacement, freezing and drying at minus 45℃ for 24 h, and drying at 65℃ for 48 h, obtaining the flame-retardant thermal insulation material for the battery cell.

[0061] Comparative Example 1

[0062] The present comparative example is different from Example 5 in that the step (6) does not contain borate modified benzoxazine flame retardant.

[0063] Comparative Example 2

[0064] The present comparative example is different from Example 5 in that the step (6) uses epichlorohydrin instead of the epoxy crosslinking agent.

[0065] The flame-retardant thermal insulation material for the battery cell in Examples 1-5 and Comparative Examples 1-2 is subjected to vertical burning test according to UL94 burning test method, and the limiting oxygen index test of the flame-retardant thermal insulation material for the battery cell in Examples 1-5 and Comparative Examples 1-2 is performed by using an oxygen index tester. The test results are shown in Table 1.

[0066] Table 1: Flame-retardant property test.

[0067] Item Burning class Limiting oxygen index (%) Example 1 V0 46.3 Example 2 V0 45.7 Example 3 V0 46.1 Example 4 V0 45.9 Example 5 V0 46.4 Comparative Example 1 V1 39.2 Comparative Example 2 V1 41.7

[0068] As shown in Table 1, the flame-retardant thermal insulation material in Examples 1-5 has better flame-retardant property compared with the flame-retardant thermal insulation material in Comparative Examples 1-2.

[0069] It should be noted that in this document, the terms “comprising”, “containing” or any other variant thereof are intended to cover non-exclusive inclusions, so that a process, method, article or device that includes a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such a process, method, article or device. Without more limitations, the element defined by the statement “comprising a…” does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0070] The above examples are only used to illustrate the technical solutions of the present application, but not limit the present application; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

[0071] Those skilled in the art should understand that the above only describes several specific embodiments of the present application, but not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications and improvements that do not exceed the scope of the claims should be considered as the protection scope of the present application.

Claims

1. A method for preparing a flame-retardant and heat-insulating material for battery cells, characterized in that, The preparation method of the flame-retardant and heat-insulating material used in the battery cell is as follows: Sodium hydroxide, urea, and water are added to a reactor, stirred and mixed, and pre-cooled to -14 to -10°C to obtain a cellulose solvent. Cotton cellulose with a mass fraction of 5.8%-6.2% is dispersed in the cellulose solvent, and after stirring for 25-35 minutes, a transparent sol is obtained. An epoxy crosslinking agent with a mass fraction of 4.5%-5.5% is added to the transparent sol, and the reaction is carried out for 1-1.5 hours. Then, the reaction is carried out sequentially... Add 10%-12% by mass of borate-modified benzoxazine flame retardant and 2.4%-3.2% sodium montmorillonite, ultrasonically disperse for 30-40 minutes, pour the gel into a mold, cure at 48-52℃ for 8-14 hours, then use ethanol → tert-butanol gradient displacement, freeze dry at -50--45℃ for 20-24 hours, and then dry at 55-65℃ for 42-48 hours to obtain a flame-retardant and heat-insulating material for battery cells; The mass ratio of sodium hydroxide, urea, and water is 1:1.6-1.8:11.3-11.9; The preparation method of the borate ester modified benzoxazine flame retardant includes the following steps: (1) Add 4.55-4.85g of 4-aminopyridine and 3-3.2g of paraformaldehyde to 40-60mL of toluene solvent, react at 32-36℃ for 1-2h, add 8.3-8.9g of 4-bromophenol, raise the temperature to 78-84℃ and continue the reaction for 4-6h. After the reaction is completed, wash with 4%-4.5% sodium hydroxide solution and remove the solvent by rotary evaporation to obtain benzoxazine intermediate; (2) Dissolve 5.4-6.3g of benzoxazine intermediate and 6-6.2g of pinacol diborate in 80-100mL of 1,4-dioxane solvent, add 1.45-1.55g of catalyst and 8-8.2g of potassium carbonate, and react at 90-110℃ for 3.5-5.5h under nitrogen atmosphere. After the reaction is completed, remove the solvent by rotary evaporation, wash and vacuum dry to obtain borate ester modified benzoxazine flame retardant; The preparation method of the epoxy crosslinking agent includes the following steps: S1. Add 2.9-3g of N-methyldiethanolamine to 60-80mL of anhydrous ethanol solvent, stir to dissolve, and add 5.1-5.3g of 3-chloropropyltrimethoxysilane dropwise. After the addition is complete, heat to 75-85℃ and reflux for 13-16h. After the reaction is complete, remove the solvent by rotary evaporation to obtain the silane quaternary ammonium salt intermediate. S2. Under a nitrogen atmosphere, 4.4-4.5 g of silane quaternary ammonium salt intermediate and 0.8-1.2 mL of acid-binding agent are added to 40-50 mL of dichloromethane solvent and stirred to dissolve at 6-12 °C. 1.62-1.72 g of phenylphosphodichlorophosphate is added dropwise over 20-30 min. After the addition is complete, the reaction is allowed to proceed for 10-14 h. After the reaction is complete, the solvent is removed by rotary evaporation, and the product is washed and dried under vacuum to obtain phosphate-modified silane quaternary ammonium salt. S3. Add 7.2-7.9 g of phosphate-modified silane quaternary ammonium salt and 18.4-18.6 g of epichlorohydrin to 80-90 mL of isopropanol solvent, heat to 48-54 °C, purge with nitrogen for protection, stir to dissolve, and continue heating to 65-70 °C. Add 0.78-0.82 g of sodium hydroxide and continue the reaction for 3-4 h. After the reaction is complete, remove the solvent by vacuum filtration, wash and vacuum dry to obtain the epoxy crosslinking agent.

2. The method for preparing the flame-retardant and heat-insulating material for battery cells according to claim 1, characterized in that, The catalyst in step (2) is [1,1-bis(diphenylphosphine)ferrocene]palladium dichloride.

3. The method for preparing the flame-retardant and heat-insulating material for battery cells according to claim 1, characterized in that, The addition time of 3-chloropropyltrimethoxysilane in S1 is 40-50 min.

4. The method for preparing the flame-retardant and heat-insulating material for battery cells according to claim 1, characterized in that, The acid-binding agent in S2 is triethylamine.

5. A flame-retardant and heat-insulating material for battery cells prepared by the method described in any one of claims 1-4.

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