High-temperature-resistant insulating film for power battery shell and preparation method thereof

Abstract

The application relates to the technical field of PA6 film research and development, and discloses a high-temperature-resistant insulating film for a power battery shell and a preparation method, specifically: benzyl chloride functionalized micro-SiO2 particles are prepared by modifying chloromethyl phenyl triethoxysilane on the surface of micro-SiO2; beta-diketone epoxy functionalized nano-SiO2 particles are prepared by modifying beta-diketone triethoxysilane and KH560 on the surface of nano-SiO2; epoxy functionalized micro-nano SiO2 particles are prepared by taking the micro-SiO2 and the nano-SiO2 as raw materials; and the SiO2 and PA6 are subjected to melt blending and blow molding processes to obtain a functionalized PA film. The film product prepared by the application has the beneficial technical effect of significantly reducing the water absorption rate, and based on this, the dimensional stability of the film product is obviously improved, and the film product exhibits excellent mechanical properties, high-temperature resistance and insulation performance.

Description

Technical Field

[0001] This invention relates to the field of PA6 film research and development technology, and in particular to a high-temperature resistant insulating film for power battery casing and its preparation method. Background Technology

[0002] As a core component in new energy vehicles and energy storage systems, power batteries play a crucial role in energy storage and supply. Currently, power batteries include lithium-ion batteries, sodium-ion batteries, and solid-state batteries. Lithium-ion batteries, as the mainstream choice for power batteries, have various structural forms, such as cylindrical, steel, aluminum, and plastic-cased square structures, and soft-pack structures.

[0003] Currently, the preferred material for soft-pack lithium-ion battery casings is aluminum-plastic film. Its structure, from the outside to the inside, consists of a PA (polyamide) layer, an Al (aluminum foil) layer, and a CPP (cast polypropylene film) layer. The main PA varieties used as outer protective layer materials include PA6, PA66, and PA1010. Among them, PA6 is the preferred choice due to its excellent high-temperature resistance, insulation properties, and low cost.

[0004] However, the amide groups in the PA6 molecular chain have strong polarity. Under high temperature and high humidity conditions, they are prone to forming strong hydrogen bonds with water molecules in the environment, increasing the water absorption rate of the film. At the same time, factors such as the release of internal stress can easily lead to changes in the film size.

[0005] Studies have found that inorganic fillers can improve the water absorption and dimensional stability of PA6. However, the interfacial compatibility between inorganic fillers and PA6 matrix is ​​poor, and phase separation problems are prone to occur, making it impossible to achieve good interfacial bonding. Summary of the Invention

[0006] This invention uses epoxy-functionalized micro / nano SiO2 particles as a functional modification component of PA6 resin, and prepares a functionalized PA film through melt blending and blow molding processes. The film achieves the technical goals of effectively reducing water absorption and significantly improving dimensional stability while possessing excellent mechanical properties, high temperature resistance and insulation properties.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a functionalized PA film includes the following steps: Step 1: Benzyl chloride-functionalized micro-SiO2 particles and β-diketone epoxy-functionalized nano-SiO2 particles are reacted at a mass ratio of 1:0.5-1.5 via a nucleophilic substitution reaction between benzyl chloride and β-diketone to obtain epoxy-functionalized micro / nano-SiO2 particles. Among them, benzyl chloride-functionalized micro-SiO2 particles are obtained by modifying micro-SiO2 particles with chloromethylphenyltriethoxysilane at a mass ratio of 3-7:10. β-Diketone epoxy-functionalized nano-SiO2 particles were obtained by modifying nano-SiO2 particles with β-diketonetriethoxysilane and 3-(2,3-epoxypropoxy)propyltrimethoxysilane at a mass ratio of 1-4:1-3:10. Step 2: Based on the epoxy ring-opening reaction mechanism, epoxy functionalized micro-nano SiO2 particles are melt-blended with PA6 resin to obtain modified PA6 masterbatch, wherein the amount of SiO2 particles is 1-8 wt% of the amount of PA6 resin. The masterbatch is then blow-molded to obtain functionalized PA film.

[0008] Preferably, the method for preparing the chloromethylphenyltriethoxysilane is as follows: Based on the hydrosilylation reaction mechanism, chloromethylphenyltriethoxysilane was prepared using 1 molar equivalent of 4-chloromethylstyrene and 1 molar equivalent of triethoxysilane as raw materials.

[0009] Preferably, the method for preparing the β-diketotriethoxysilane is as follows: Under the action of an alkaline catalyst, the β-diketone group in 1 molar equivalent of acetylacetone undergoes a nucleophilic substitution reaction with the chloromethyl group in 1 molar equivalent of chloromethylphenyltriethoxysilane to prepare β-diketonetriethoxysilane.

[0010] Preferably, the alkaline catalyst is one of potassium carbonate and sodium carbonate.

[0011] Preferably, the temperature of the blow molding process is 180-200℃ in zone one, 220-240℃ in zone two, 230-250℃ in zone three, 240-260℃ in the connecting zone, and 240-250℃ at the die head.

[0012] Preferably, the particle size of the micro-SiO2 particles is 1-10 μm.

[0013] Preferably, the nano-SiO2 particles have a particle size of 50-200 nm.

[0014] A functionalized PA film, wherein the thickness of the functionalized PA film is 20-40 μm.

[0015] Preferably, the functionalized PA film is the outer layer material of an aluminum-plastic film used for encapsulation of lithium-ion batteries.

[0016] The beneficial effects of this invention are as follows: Based on the molecular design mechanism, chloromethylphenyltriethoxysilane was prepared by hydrosilylation reaction using 4-chloromethylstyrene and triethoxysilane as raw materials. Based on the nucleophilic substitution reaction mechanism, β-diketotriethoxysilane was prepared from acetylacetone and chloromethylphenyltriethoxysilane. Benzyl chloride-functionalized micro-SiO2 particles were prepared by modifying the surface of micro-SiO2 particles with chloromethylphenyltriethoxysilane; β-diketotriethoxysilane and 3-(2,3-epoxypropoxy)propyltrimethoxysilane were modified on the surface of nano-SiO2 particles to prepare β-diketoepoxy-functionalized nano-SiO2 particles. By utilizing the nucleophilic substitution reaction between the chloromethyl group on the surface of benzyl chloride-functionalized micro-SiO2 particles and the β-diketone group on the surface of β-diketone epoxy-functionalized nano-SiO2 particles, micro-SiO2 particles and nano-SiO2 particles are covalently linked to each other to obtain epoxy-functionalized micro- and nano-SiO2 particles. By grafting epoxy-functionalized micro / nano SiO2 particles onto the molecular chain of PA6 resin through the epoxy ring-opening reaction mechanism, the modified PA6 masterbatch is used to prepare functionalized PA film through blow molding. Experimental results confirm that the membrane product prepared by this invention has achieved the beneficial technical effect of significantly reducing water absorption rate. Based on this, the dimensional stability of the membrane product has been significantly improved. Furthermore, the membrane product prepared by this invention also exhibits excellent mechanical properties, high temperature resistance, and insulation properties. Detailed Implementation Example 1:

[0017] I. Synthesis of chloromethylphenyltriethoxysilane: The synthetic mechanism is as follows: under the catalysis of chloroplatinic acid-isopropanol, chloromethylphenyltriethoxysilane is prepared by hydrosilylation reaction between the alkenyl functional group in 4-chloromethylstyrene and the silane-hydrogen bond in triethoxysilane. The specific experimental steps are as follows: Under nitrogen protection, 3.1 g of 4-chloromethylstyrene and 3.3 g of triethoxysilane were added to 50 mL of anhydrous toluene and mechanically stirred until homogeneous. Then, 0.05 g of chloroplatinic acid-isopropanol catalyst (0.25 g of chloroplatinic acid was dissolved in 25 mL of anhydrous isopropanol, stirred thoroughly, and allowed to stand for 24 h to obtain chloroplatinic acid-isopropanol) was added. After the addition was complete, the system temperature was raised to 90 °C and the reaction was allowed to proceed for 5 h. After the reaction was completed, the solvent was removed by rotary evaporation to obtain chloromethylphenyltriethoxysilane. The chemical structural formula of chloromethylphenyltriethoxysilane is: ; The 1H NMR spectrum of chloromethylphenyltriethoxysilane is characterized as follows: 1 H NMR (CDCl3, 400MHz) δ: 0.92-1.07 (m, 2H), 1.20-1.23 (t, 9H), 2.55-2.58 (t, 2H), 3.77-3.82(m, 6H), 4.55(s, 2H), 7.02-7.03(d, 2H), 7.24-7.25(d, 2H).

[0018] II. Synthesis of β-diketotriethoxysilane: The synthesis mechanism is as follows: Under the catalysis of potassium carbonate, β-diketotriethoxysilane is obtained by nucleophilic substitution reaction between the chloromethyl group in chloromethylphenyltriethoxysilane and acetylacetone. The specific experimental steps are as follows: 2.7g of potassium carbonate, 2g of acetylacetone and 50mL of anhydrous acetone are added to a 250mL round-bottom flask and mixed well. The system is evacuated and purged with nitrogen, and the temperature of the system is raised to 65℃. 30mL of anhydrous acetone containing 6.3g of chloromethylphenyltriethoxysilane is added dropwise. The reaction is allowed to proceed for 12h. After the reaction is completed, the temperature is lowered to room temperature, and the solvent is removed by rotary evaporation to obtain β-diketotriethoxysilane. The chemical structural formula of β-diketotriethoxysilane is: ; The 1H NMR spectrum of β-diketotriethoxysilane is characterized as follows: 1 H NMR (CDCl3, 400MHz) δ: 0.99-1.13 (m, 2H), 1.24-1.26 (t, 9H), 2.04 (s, 6H), 2.58-2.61 (t, 2H), 2 .94-3.11(m, 2H), 3.62-3.66(t, 1H), 3.78-3.83(m, 6H), 6.93-6.95(d, 2H), 7.05-7.07(d, 2H). Example 2:

[0019] The preparation mechanism of epoxy-functionalized micro- and nano-SiO2 particles is as follows: under the action of triethylamine, the chloromethyl group on the surface of benzyl chloride-functionalized micro-SiO2 particles undergoes a nucleophilic substitution reaction with the β-diketone group on the surface of β-diketone-functionalized nano-SiO2 particles to obtain epoxy-functionalized micro- and nano-SiO2 particles. The specific preparation steps for epoxy-functionalized micro / nano SiO2 particles are as follows: Step 1: Place 10g of micro-SiO2 particles (micron-sized silica, particle size 2μm) in a vacuum drying oven and dry at 100℃ for 24h. Disperse the 10g dried SiO2 particles ultrasonically in 80mL of N-methylpyrrolidone, add 20mL of N-methylpyrrolidone solution containing 5g of chloromethylphenyltriethoxysilane, and stir the reaction for 12h. The entire process is carried out under nitrogen protection. After the reaction is completed, centrifuge to separate the solid material and vacuum dry at 60℃ for 10h to obtain benzyl chloride functionalized micro-SiO2 particles. Step 2: Under nitrogen protection, 10g of nano-SiO2 particles (nano-silica, particle size 100nm) that have been vacuum dried at 100℃ for 24h and 80mL of N-methylpyrrolidone were added to a 250mL round-bottom flask and ultrasonically dispersed for 30min. Then, 20mL of N-methylpyrrolidone solution containing 3g of β-diketotriethoxysilane and 1.9g of 3-(2,3-epoxypropoxy)propyltrimethoxysilane was added and the mixture was stirred for 12h. After the reaction was completed, the mixture was filtered, washed, and dried in a vacuum drying oven at 60℃ for 12h to obtain β-diketoepoxy-functionalized nano-SiO2 particles. Step 3: Add 60 mL of toluene dispersion containing 1 g of β-diketone epoxy-functionalized nano-SiO2 particles to a 250 mL round-bottom flask. While stirring, add 40 mL of toluene dispersion containing 1.5 g of benzyl chloride-functionalized micro-SiO2 particles dropwise, and add 0.8 g of triethylamine. Evacuate the system and purge with nitrogen, and raise the temperature to 60 °C. Then, under reflux, stir and react for 24 h. After the reaction is complete, remove the solvent by rotary evaporation, wash, and vacuum dry at 40 °C for 10 h to obtain epoxy-functionalized micro / nano-SiO2 particles. Example 3:

[0020] The raw material formulation for preparing functionalized PA film I is as follows: 100 parts by weight of PA6 resin (model F136 / NA99001 / 4229D); 1 part by weight of epoxy-functionalized micro / nano SiO2 particles; The preparation method of functionalized PA film I includes the following steps: PA6 resin was dried in a vacuum drying oven at 80°C for 24 hours to obtain dried PA6 resin. The dried PA6 resin was mixed evenly with epoxy functionalized micro-nano SiO2 particles. The mixed material was placed in a twin-screw extruder and melted at 210°C. After extrusion and granulation, the material was dried at 60°C for 10 hours to obtain modified PA masterbatch. The modified PA masterbatch was placed in a blown film machine for blown film formation. The temperature of the blown film formation zone 1 was 190℃, the temperature of the second zone was 230℃, the temperature of the third zone was 244℃, the temperature of the connecting zone was 250℃, and the temperature of the die head was 245℃, resulting in a functionalized PA film I with a thickness of 30μm. Example 4:

[0021] Functionalized PA film II was prepared, and its only difference from functionalized PA film I was that the amount of epoxy-functionalized micro / nano SiO2 particles used was 5 parts by weight. Example 5:

[0022] Functionalized PA film III was prepared, and its only difference from functionalized PA film I was that the amount of epoxy-functionalized micro / nano SiO2 particles used was 8 parts by weight.

[0023] Comparative example:

[0024] The comparative example was prepared, and its only difference from functionalized PA film I was that it did not contain epoxy-functionalized micro / nano SiO2 particles.

[0025] Performance testing:

[0026] I. Mechanical properties and high temperature resistance tests: (1) According to GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets", a universal testing machine was used to conduct tensile tests. The functionalized polyamide film was made into a sample film with a length of 150 mm and a width of 20 mm, with a clamping distance of 50 mm and a testing speed of 100 mm / min. The longitudinal tensile strength of the sample film was tested at room temperature of 25℃. A sample film with a length of 150 mm and a width of 20 mm was placed in an environment with a temperature of 80℃ and a humidity of 85% for 12 hours and then subjected to a tensile test to test the longitudinal tensile strength of the sample film. (2) According to GB / T 37841-2019 "Test Method for Puncture Resistance of Plastic Films and Sheets", functionalized polyamide film was made into a sample film with a length of 100 mm and a width of 100 mm. The puncture speed was 100 mm / min. The puncture resistance of the sample film was tested. II. Insulation performance: According to GB / T 31838.3-2019 "Dielectric and resistive properties of solid insulating materials - Part 3: Resistive properties (DC method) - Surface resistance and surface resistivity", a functionalized polyamide film was made into a sample film with a length of 100 mm and a width of 100 mm. Using electrode device C1, the test voltage was set to 100 V, and the surface resistance of the sample film was tested. III. Dimensional stability and water absorption performance tests: According to GB / T 1034-2008 "Determination of Water Absorption of Plastics", functionalized polyamide film was prepared into a sample film with a length of 60 mm and a width of 60 mm. The sample film was dried in an oven at 50℃ for 24 h, cooled to room temperature, and weighed (recorded as m1, unit: mg). The area of ​​the sample film was also tested (recorded as S1, unit: mm). 2 The sample membrane was then immersed in distilled water at 23°C for 24 hours. After removal, the surface moisture was quickly wiped off with filter paper, and the membrane was weighed again (recorded as m1, unit: mg). The area of ​​the sample membrane was also measured (recorded as S2, unit: mm). 2 The water absorption rate and dimensional change rate of the sample membrane are calculated using the following formulas: water absorption rate = (m2-m1) / m1×100%, dimensional change rate = (S2-S1) / S1×100%. The test results are shown in Table 1 below; Table 1 Performance test results of functionalized polyamide films

[0027] According to the experimental results in Table 1: Conclusion 1: Compared with the comparative example, the functionalized PA film prepared by the present invention significantly reduces the water absorption rate of the film; Conclusion 2: Compared with the comparative example, the functionalized PA film prepared by the present invention has significantly improved in terms of dimensional stability; Conclusion 3: The functionalized PA film prepared by this invention has excellent mechanical properties, high temperature resistance and insulation properties.

Claims

1. A method for preparing a functionalized PA film, characterized in that, Includes the following steps: Step 1: Benzyl chloride-functionalized micro-SiO2 particles and β-diketone epoxy-functionalized nano-SiO2 particles are reacted at a mass ratio of 1:(0.5-1.5) by a nucleophilic substitution reaction between benzyl chloride and β-diketone to obtain epoxy-functionalized micro- and nano-SiO2 particles. The micro-SiO2 particles have a particle size of 2 μm, and the nano-SiO2 particles have a particle size of 100 nm. The benzyl chloride-functionalized micro-SiO2 particles were obtained by modifying micro-SiO2 particles with chloromethylphenyltriethoxysilane at a mass ratio of (3-7):

10. The β-diketone epoxy-functionalized nano-SiO2 particles were obtained by modifying nano-SiO2 particles with β-diketonetriethoxysilane and 3-(2,3-epoxypropoxy)propyltrimethoxysilane at a mass ratio of (1-4):(1-3):

10. The chemical structural formula of chloromethylphenyltriethoxysilane is: ； The chemical structural formula of β-diketotriethoxysilane is: ； Step 2: Based on the epoxy ring-opening reaction mechanism, epoxy functionalized micro / nano SiO2 particles are melt-blended with PA6 resin to obtain modified PA6 masterbatch, wherein the amount of SiO2 particles is 1-8 wt% of the amount of PA6 resin. The masterbatch is then used to produce functionalized PA film through blow molding.

2. The method for preparing a functionalized PA film according to claim 1, characterized in that, The preparation method of the chloromethylphenyltriethoxysilane is as follows: Based on the hydrosilylation reaction mechanism, chloromethylphenyltriethoxysilane was prepared using 1 molar equivalent of 4-chloromethylstyrene and 1 molar equivalent of triethoxysilane as raw materials.

3. The method for preparing a functionalized PA film according to claim 1, characterized in that, The preparation method of the β-diketotriethoxysilane is as follows: Under the action of an alkaline catalyst, the β-diketone group in 1 molar equivalent of acetylacetone undergoes a nucleophilic substitution reaction with the chloromethyl group in 1 molar equivalent of chloromethylphenyltriethoxysilane to prepare β-diketonetriethoxysilane.

4. The method for preparing a functionalized PA film according to claim 3, characterized in that, The alkaline catalyst is either potassium carbonate or sodium carbonate.

5. The method for preparing a functionalized PA film according to claim 1, characterized in that, The blow molding process has the following temperature zones: Zone 1: 180-200℃; Zone 2: 220-240℃; Zone 3: 230-250℃; Connection Zone: 240-260℃; and Head Zone: 240-250℃.

6. A functionalized PA film prepared by the method according to any one of claims 1 to 5, characterized in that, The thickness of the functionalized PA film is 20–40 μm.

7. A functionalized PA film according to claim 6, characterized in that, The functionalized PA film is the outer layer material of the aluminum-plastic film, which is used for the encapsulation of lithium-ion batteries.

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