A biaxially stretched flame-retardant reinforced nylon film for lithium ion battery packaging and a preparation method thereof
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- QUANZHOU NORMAL UNIV
- Filing Date
- 2026-04-08
- Publication Date
- 2026-07-03
Smart Images
Figure SMS_1
Abstract
Description
Technical Field
[0001] This invention relates to the field of nylon film technology, specifically to a biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery packaging and its preparation method. Background Technology
[0002] Lithium-ion batteries are widely used in new energy vehicles, consumer electronics, and energy storage devices due to their high energy density, long cycle life, and environmental friendliness. Encapsulation materials, acting as a "protective barrier" for lithium-ion batteries, directly affect the battery's safety, cycle life, and reliability. Among these, biaxially oriented nylon film (BOPA), with its excellent mechanical strength, barrier properties, and puncture resistance, has become one of the core substrates for both soft-pack and hard-shell encapsulation of lithium-ion batteries. It is primarily used for inner layer protection and buffering, preventing electrolyte leakage and damage to the battery core from external impacts.
[0003] However, traditional nylon films used for lithium-ion battery packaging still have many technical drawbacks: First, their flame retardant properties are poor. Lithium-ion batteries are prone to thermal runaway under extreme conditions such as overcharging, short circuits, and compression, resulting in high-temperature open flames. The limiting oxygen index of traditional nylon films is only 21% to 23%, and their vertical flammability rating is only UL94. The V-2 rating indicates that the nylon film is flammable and produces molten droplets, failing to effectively prevent flame spread and exacerbating battery safety hazards. Secondly, its resistance to electrolyte corrosion is insufficient. The carbonate electrolytes commonly used in lithium-ion batteries are corrosive, and traditional nylon films are prone to swelling and cracking after prolonged contact with the electrolyte, leading to encapsulation failure and electrolyte leakage. Thirdly, its mechanical properties still need improvement. Lithium-ion batteries must withstand tensile, folding, and puncture forces during encapsulation, and the puncture resistance and tensile strength of traditional nylon films are insufficient to meet the stringent requirements of high-end power batteries. Fourthly, the additives exhibit poor dispersibility. Existing flame retardants and reinforcing agents used for modification are mostly added alone or in simple compound formulations, resulting in poor compatibility with the nylon matrix, easy agglomeration, uneven film performance, and impacted encapsulation quality.
[0004] To address the aforementioned issues, existing technologies often employ the addition of flame retardants and electrolyte-resistant modifiers to modify nylon films. Regarding flame retardants, commonly used halogen-based flame retardants offer good flame retardancy, but they produce toxic and harmful gases during combustion, polluting the environment and potentially reacting with lithium-ion battery electrolytes, affecting battery performance. Phosphorus-based and nitrogen-based halogen-free flame retardants are environmentally friendly, but their flame retardant efficiency is low when used alone, and high addition amounts can lead to a decrease in the film's mechanical properties. As for reinforcing agents, inorganic nanomaterials such as carbon nanotubes and titanium dioxide can improve the film's mechanical properties, but their surface polarity differs significantly from the nylon matrix, leading to easy aggregation within the matrix and an inability to simultaneously maintain electrolyte resistance. Furthermore, existing modification methods for flame retardancy, reinforcement, and electrolyte resistance lack synergy, making it difficult to simultaneously meet the multi-dimensional performance requirements of lithium-ion battery packaging materials. Summary of the Invention
[0005] The purpose of this invention is to provide a biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery packaging and its preparation method. By adding two inorganic modifying compounds, the flame-retardant properties, mechanical properties, and electrolyte corrosion resistance of the nylon film are synergistically improved. At the same time, the problems of poor additive dispersibility and insufficient aging resistance are solved, which meets the application requirements of high-end lithium-ion battery packaging and improves the safety and service life of the battery.
[0006] To achieve the above objectives, the solution of the present invention is: A biaxially oriented flame-retardant reinforced nylon film for lithium-ion battery encapsulation comprises, by weight, the following raw materials: 80-95 parts nylon matrix, 1-5 parts mesoporous silica-coated carbon nanotube hybrid (MSCNT), 2-8 parts phosphorus-nitrogen synergistic flame-retardant reinforced titanium dioxide nanorods (PN-TNR), 0.2-2 parts antioxidant, 0.3-2 parts lubricant, 0.5-3 parts dispersant, and 0.3-1.5 parts electrolyte-resistant modifier. The mesoporous silica-coated carbon nanotube hybrid (MSCNT) is prepared by surface-modifying carbon nanotubes and then coating the surface of the carbon nanotubes with mesoporous silica using a sol-gel method. The mesoporous silica has a pore size of 2-5 nm and a coating thickness of 10-30 nm. nm; The phosphorus-nitrogen synergistic flame-retardant enhanced titanium dioxide nanorods (PN-TNR) are prepared by hydrothermal reaction of titanium source to prepare titanium dioxide nanorods, followed by grafting phosphorus-nitrogen flame-retardant groups with a silane coupling agent. The diameter of the titanium dioxide nanorods is 20~50 nm, the length is 100~300 nm, and the grafting amount of phosphorus in the phosphorus-nitrogen synergistic flame-retardant enhanced titanium dioxide nanorods (PN-TNR) is 3. wt %~8 wt The grafting amount of nitrogen is 5%. wt %~12 wt %.
[0007] The nylon matrix is one or more blends of nylon 6, nylon 66, nylon 11 and nylon 12. The nylon matrix is preferably a blend of nylon 6 and nylon 66 in a mass ratio of 1 to 3:1. The relative viscosity of the nylon matrix is 2.0 to 3.0, which is suitable for the electrolyte resistance and puncture resistance requirements of lithium-ion battery packaging materials.
[0008] The antioxidant is one or two of hindered phenolic antioxidants and phosphite antioxidants; the lubricant is one or more of stearic acid, stearamide, and ethylene bis-stearamide; the dispersant is one or more of polyethylene wax, polypropylene wax, and silane coupling agent; and the electrolyte-resistant modifier is vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP).
[0009] The hindered phenolic antioxidants are antioxidant 1010 and antioxidant 1076, and the phosphite antioxidants are antioxidant 168.
[0010] A method for preparing a biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation includes the following steps: Step 1: First, according to the formula ratio, add 80-95 parts of nylon matrix, 1-5 parts of MSCNT, 2-8 parts of PN-TNR, 0.2-2 parts of antioxidant, 0.3-2 parts of lubricant, 0.5-3 parts of dispersant, and 0.3-1.5 parts of electrolyte-resistant modifier into a high-speed mixer and mix for 10-20 minutes at a temperature of 80-100℃ and a speed of 1000-1500 r / min to ensure uniform mixing of all components. Then, add the mixture into a twin-screw extruder, melt extrude, and pelletize to obtain composite masterbatch. Step 2: Then, place the composite masterbatch in a vacuum drying oven and dry it at 80~100℃ for 4~8 hours until the moisture content of the composite masterbatch is ≤0.05%. wt To avoid air bubbles during melt extrusion and prevent leakage after lithium-ion battery encapsulation, the dried composite masterbatch is then added to a single-screw extruder, melt-extruded, cast through a T-die, and then cooled and shaped by cooling rollers to obtain a casting with a thickness of 0.8~1.5 mm. The surface of the casting must be flat, free of air bubbles and scratches to ensure the quality of subsequent stretching and encapsulation. Step 3: The cast sheet is then fed into a biaxial stretching machine for longitudinal and transverse stretching. The longitudinal stretching process parameters are: stretching temperature 70~90℃, stretching ratio 2.5~4.0 times, and stretching speed 5~10 m / min, to ensure uniform stretching of the cast sheet in the longitudinal direction and improve the longitudinal mechanical properties and puncture resistance of the film. The transverse stretching process parameters are: stretching temperature 90~110℃, stretching ratio 3.0~4.5 times, and stretching speed 3~8 m / min, to ensure uniform stretching of the cast sheet in the transverse direction and make the longitudinal and transverse mechanical properties of the film more consistent, adapting to the multi-directional stress requirements in the lithium-ion battery packaging process. Step 4: Then, the biaxially stretched film is placed in a setting oven and set with hot air at a temperature of 120~140℃ for 5~15 seconds to eliminate internal stress, improve dimensional stability, and prevent shrinkage after lithium-ion battery encapsulation, which could lead to encapsulation failure. The set film is then cooled by cooling rollers, edge defects are removed by trimming, and finally it is wound up by a winding machine to obtain the biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation with a thickness of 15~50 μm.
[0011] In step 1, the preparation process of the MSCNT is as follows: S1, Surface modification of carbon nanotubes: First, 1–5 g of carbon nanotubes with a diameter of 10–20 nm and a length of 1–5 μm were added to 200–500 mL of a mixed acid solution and ultrasonically dispersed for 30–60 min to ensure uniform dispersion of the carbon nanotubes in the mixed acid solution, wherein the volume ratio of concentrated nitric acid to concentrated sulfuric acid in the mixed acid solution was 1:3. Then, the mixed solution was placed in an oil bath and heated under reflux at 80–100 °C for 4–8 h to graft carboxyl groups onto the surface of the carbon nanotubes. After the reaction was complete, the mixed solution was cooled to room temperature and repeatedly washed with deionized water until the filtrate was neutral. Then, it was placed in a vacuum drying oven and dried at 80–100 °C for 12–24 h to obtain a carboxyl grafting amount of 5. wt %~10 wt % carboxylated carbon nanotubes, the introduction of carboxyl groups can improve the bonding stability between carbon nanotubes and mesoporous silica, and further improve the compatibility with nylon matrix; S2, Coating with mesoporous silica: Then, 0.5–2 g of carboxylated carbon nanotubes were dispersed in 100–200 mL of a mixed solvent and ultrasonically dispersed for 20–40 min to obtain a homogeneous dispersion. The volume ratio of ethanol to deionized water in the mixed solvent was 3:1. Next, 5–15 mL of 25%–28% ammonia solution was added to the dispersion to adjust the pH to 9–11, and the mixture was stirred for 10–20 min. Subsequently, 2–8 mL of tetraethyl orthosilicate (TEOS) was slowly added dropwise at a rate of 1–2 drops / second. After the addition was complete, the mixture was kept at a constant temperature of 30–50 °C and stirred for 6–12 h to allow the tetraethyl orthosilicate to hydrolyze and condense on the surface of the carboxylated carbon nanotubes, forming a mesoporous silica shell. After the reaction was complete, the reaction solution was centrifuged at 3000–5000 r / min for 10–20 minutes. After 3 min, the precipitate was collected and washed 3-5 times alternately with ethanol and deionized water. Finally, it was placed in a vacuum drying oven and dried at 80-100℃ for 12-24 h to obtain mesoporous silica-coated carbon nanotube hybrid (MSCNT), wherein the mesoporous silica has a mesopore size of 2-5 nm and a coating thickness of 10-30 nm.
[0012] In step 1, the preparation process of the PN-TNR is as follows: Preparation of S1, titanium dioxide nanorods: Add 5-15 mL of titanium source to 100-200 mL of deionized water and stir for 10-20 min to form a homogeneous titanium source solution, wherein the titanium source is one of tetrabutyl titanate and isopropyl titanate. Add 20-50 mL of 1-5 mol / L sodium hydroxide solution to the titanium source solution and stir for 30-60 min to ensure thorough mixing of the titanium source and sodium hydroxide solution. Then transfer the mixed solution to a hydrothermal reactor and perform a hydrothermal reaction at 120-160℃ for 12-24 h. After cooling to room temperature, adjust the pH of the solution to 6-7 with 1-2 mol / L dilute hydrochloric acid. Filter, collect the precipitate, wash with deionized water until neutral, and then place it in an oven to dry at 80-100℃ for 12-24 h. Then place it in a muffle furnace and calcine at 400-600℃ for 2-4 h to obtain a diameter of 20-50 nm and a length of 100-300 nm. Titanium dioxide nanorods of nm size can improve the mechanical properties of thin films without affecting their processability. S2, Surface grafting modification: Then, 1-3 g of titanium dioxide nanorods were dispersed in 100-200 mL of anhydrous ethanol and ultrasonically dispersed for 20-40 min to obtain a uniform dispersion. Next, 0.5-2 g of silane coupling agent was added to the dispersion, and the mixture was placed in an oil bath and heated under reflux at 60-80 °C for 2-4 h to graft the silane coupling agent onto the surface of the titanium dioxide nanorods. The silane coupling agent was one of KH550 or KH560. Subsequently, 2-6 g of phosphorus-nitrogen flame retardant was added, and the reaction was continued at 60-80 °C for 4-8 h to graft phosphorus-nitrogen flame retardant groups onto the surface of the titanium dioxide nanorods via the silane coupling agent. The phosphorus-nitrogen flame retardant was one or two of ammonium dihydrogen phosphate, melamine cyanurate, and phosphate ester amine. After the reaction was complete, the mixture was centrifuged at 3000-5000 r / min for 10-20 minutes. The precipitate was collected after 3 min of drying time and washed 3-5 times alternately with anhydrous ethanol and deionized water. Finally, it was placed in a vacuum drying oven and dried at 80-100℃ for 12-24 h to obtain PN-TNR, in which the phosphorus grafting amount was 3%. wt %~8 wt The grafting amount of nitrogen is 5%. wt %~12 wt %.
[0013] In step 1, the process parameters of the twin-screw extruder are as follows: barrel temperature is 230~260℃, with the feeding section at 230~240℃, the compression section at 240~250℃, and the discharge section at 250~260℃; screw speed is 150~250 r / min; and feeding speed is 20~50 kg / h. This ensures that the material is fully melted and plasticized, and that MSCNT and PN-TNR are uniformly dispersed in the nylon matrix. At the same time, it avoids the decomposition of the electrolyte-resistant modifier and ensures the electrolyte resistance of the film.
[0014] In step 2, the process parameters of the single-screw extruder are as follows: barrel temperature is 240~270℃, with the feeding section at 240~250℃, the compression section at 250~260℃, and the discharge section at 260~270℃; screw speed is 80~150 r / min; and die temperature is 260~270℃. This ensures good melt flowability, stable casting, and avoids film thickness deviation caused by uneven melt flow.
[0015] In step 2, the temperature of the cooling roller is 20~40℃. In step 4, the temperature of the cooling roller is 25~40℃, and the winding speed is 4~8 m / min.
[0016] After adopting the above technical solution, the biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery packaging of the present invention has the following beneficial effects: 1. Two novel inorganic modified compounds (MSCNT and PN-TNR) were designed and synthesized to meet the encapsulation requirements of lithium-ion batteries and achieve synergistic effects of flame retardancy, reinforcement, and electrolyte corrosion resistance. MSCNT, with carbon nanotubes as the core and mesoporous silica as the shell, not only improves compatibility with the nylon matrix but also leverages the reinforcing effect of carbon nanotubes and the electrolyte-resistant auxiliary effect of the mesoporous structure (adsorption of electrolyte impurities). PN-TNR, by grafting phosphorus and nitrogen flame-retardant groups onto the surface of titanium dioxide nanorods, can rapidly form a flame-retardant carbon layer during thermal runaway of lithium-ion batteries, preventing flame spread and achieving integrated functions of reinforcement, flame retardancy, aging resistance, and electrolyte corrosion resistance. The synergistic effect of these two compounds solves the technical challenge of simultaneously achieving flame retardancy, mechanical properties, and electrolyte resistance in traditional nylon films used for lithium-ion battery encapsulation.
[0017] 2. Excellent dispersibility of additives and uniform film performance: The mesoporous silica shell of MSCNT and the silane coupling agent modification of PN-TNR effectively improve the compatibility with the nylon matrix and avoid the agglomeration problem of inorganic additives. At the same time, the newly added electrolyte-resistant modifier works synergistically with the components to ensure that MSCNT, PN-TNR and electrolyte-resistant modifier are uniformly dispersed in the nylon matrix, giving full play to their respective functions, while ensuring the transparency and processing performance of the film, and ensuring the consistency and reliability of lithium-ion battery packaging.
[0018] 3. Product performance fully adapts to lithium-ion battery packaging requirements: The prepared biaxially oriented nylon film not only has excellent flame retardant properties (UL94 V-0 rating), high mechanical strength and puncture resistance, but also has good resistance to electrolyte corrosion and aging. It shows no obvious damage after being immersed in electrolyte, which can effectively prevent electrolyte leakage, improve the safety and service life of lithium-ion batteries, and meet the high-end lithium-ion battery packaging requirements in fields such as new energy vehicles, consumer electronics, and energy storage equipment. Detailed Implementation
[0019] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.
[0020] Example 1 1. Preparation of MSCNTs: S1, Surface modification of carbon nanotubes: First, 3 g of carbon nanotubes with a diameter of 15 nm and a length of 3 μm were added to 230 mL of a mixed acid solution and ultrasonically dispersed for 35 min to ensure uniform dispersion of the carbon nanotubes in the mixed acid solution. The volume ratio of concentrated nitric acid to concentrated sulfuric acid in the mixed acid solution was 1:3. Then, the mixed solution was placed in an oil bath and heated under reflux at 85 °C for 5 h to graft carboxyl groups onto the surface of the carbon nanotubes. After the reaction was complete, the mixed solution was cooled to room temperature and repeatedly washed with deionized water until the filtrate was neutral. Then, it was placed in a vacuum drying oven and dried at 90 °C for 12 h to obtain a carboxyl grafting amount of 5... wt % carboxylated carbon nanotubes, the introduction of carboxyl groups can improve the bonding stability between carbon nanotubes and mesoporous silica, and further improve the compatibility with nylon matrix; S2, Coating with mesoporous silica: Then, 0.5 g of carboxylated carbon nanotubes were dispersed in 100 mL of a mixed solvent and ultrasonically dispersed for 30 min to obtain a uniform dispersion. The volume ratio of ethanol to deionized water in the mixed solvent was 3:1. Next, 8 mL of 25% ammonia water was added to the dispersion to adjust the pH to 10, and the mixture was stirred for 15 min. Subsequently, 5 mL of TEOS was slowly added dropwise at a rate of 2 drops / second. After the addition was complete, the mixture was stirred at 40 °C for 8 h to allow TEOS to hydrolyze and condense on the surface of the carboxylated carbon nanotubes, forming a mesoporous silica shell. After the reaction was completed, the reaction solution was centrifuged at 3000 r / min for 15 min, the precipitate was collected, and washed three times alternately with ethanol and deionized water. Finally, the precipitate was placed in a vacuum drying oven and dried at 85 °C for 12 h to obtain MSCNTs, in which the mesoporous silica had a mesopore size of 3 nm and a coating thickness of 20 nm.
[0021] 2. Preparation of PN-TNR: Preparation of S1, titanium dioxide nanorods: 8 mL of tetrabutyl titanate was added to 120 mL of deionized water and stirred for 15 min to form a homogeneous tetrabutyl titanate solution. 30 mL of 2 mol / L sodium hydroxide solution was added to the tetrabutyl titanate solution and stirred for 40 min to ensure thorough mixing of the tetrabutyl titanate and sodium hydroxide solution. The mixture was then transferred to a hydrothermal reactor and subjected to a constant temperature hydrothermal reaction at 140 °C for 12 h. After cooling to room temperature, the pH of the solution was adjusted to 6 with 1 mol / L dilute hydrochloric acid. The solution was filtered, the precipitate was collected, washed with deionized water until neutral, and then placed in an oven and dried at 90 °C for 12 h. Finally, it was placed in a muffle furnace and calcined at 500 °C for 2 h to obtain titanium dioxide nanorods with a diameter of 35 nm and a length of 200 nm. Titanium dioxide nanorods of this size improve the mechanical properties of the film without affecting its processability. S2, Surface grafting modification: Then, 2 g of titanium dioxide nanorods were dispersed in 150 mL of anhydrous ethanol and ultrasonically dispersed for 30 min to obtain a uniform dispersion. Next, 1 g of silane coupling agent KH550 was added to the dispersion, and the mixture was placed in an oil bath and refluxed at 70 °C for 2 h to graft the silane coupling agent KH550 onto the surface of the titanium dioxide nanorods. Subsequently, 3 g of phosphorus-nitrogen flame retardant was added, and the reaction was continued at 70 °C for 4 h to graft phosphorus-nitrogen flame retardant groups onto the surface of the titanium dioxide nanorods via the silane coupling agent. The phosphorus-nitrogen flame retardant was a mixture of ammonium dihydrogen phosphate and melamine cyanurate in a 1:1 mass ratio. After the reaction was complete, the mixture was centrifuged at 3000 r / min for 15 min, the precipitate was collected, and washed four times alternately with anhydrous ethanol and deionized water. Finally, it was placed in a vacuum drying oven and dried at 80 °C for 12 h to obtain PN-TNR, in which the phosphorus grafting amount was 5%. wt The grafting amount of nitrogen was 8%. wt %.
[0022] 3. Formulation of biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation The composition consists of 90 parts nylon matrix, 2.5 parts MSCNT, 3 parts PN-TNR, 0.8 parts antioxidant 1010, 0.7 parts EBS lubricant, 1.5 parts polyethylene wax dispersant, and 1.5 parts PVDF-HFP electrolyte-resistant modifier. The nylon matrix is a blend of nylon 6 and nylon 66 in a mass ratio of 2:1, with a relative viscosity of 2.5.
[0023] 4. Preparation of biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery packaging A method for preparing a biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation includes the following steps: Step 1: First, according to the formula ratio, add 90 parts of nylon matrix, 2.5 parts of MSCNT, 3 parts of PN-TNR, 0.8 parts of antioxidant 1010, 0.7 parts of EBS lubricant, 1.5 parts of polyethylene wax dispersant, and 1.5 parts of PVDF-HFP electrolyte-resistant modifier into a high-speed mixer and mix for 15 minutes at a temperature of 90℃ and a speed of 1200 r / min to ensure uniform mixing of all components. Then, add the mixture to a twin-screw extruder, melt extrude, and pelletize to obtain composite masterbatch. Step 2: Then, place the composite masterbatch in a vacuum drying oven and dry it at 90℃ for 6 hours until the moisture content of the composite masterbatch is ≤0.05%. wt To avoid air bubbles during melt extrusion and prevent leakage after lithium-ion battery encapsulation, the dried composite masterbatch is then added to a single-screw extruder, melt-extruded, cast through a T-die, and then cooled and shaped by cooling rollers to obtain a 1.2 mm thick casting. The surface of the casting must be flat, free of air bubbles and scratches to ensure the quality of subsequent stretching and encapsulation. Step 3: The cast sheet is then fed into a biaxial stretching machine for longitudinal and transverse stretching. The longitudinal stretching process parameters are: stretching temperature 80℃, stretching ratio 3.2 times, and stretching speed 8 m / min, to ensure uniform stretching of the cast sheet in the longitudinal direction and improve the longitudinal mechanical properties and puncture resistance of the film. The transverse stretching process parameters are: stretching temperature 100℃, stretching ratio 3.8 times, and stretching speed 5 m / min, to ensure uniform stretching of the cast sheet in the transverse direction and make the longitudinal and transverse mechanical properties of the film more consistent, adapting to the multi-directional stress requirements in the lithium-ion battery packaging process. Step 4: Then, the biaxially stretched film is placed in a setting oven and set with hot air at a temperature of 130°C for 10 seconds. This is to eliminate internal stress in the film, improve its dimensional stability, and prevent shrinkage after lithium-ion battery encapsulation, which could lead to encapsulation failure. The set film is then cooled by cooling rollers, edge defects are removed by trimming, and finally it is wound up by a winding machine to obtain a 30 μm thick biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation.
[0024] In step 1, the process parameters of the twin-screw extruder are as follows: barrel temperature is 230~260℃, with the feeding section at 230℃, the compression section at 250℃, and the discharge section at 260℃; screw speed is 200 r / min; and feeding speed is 35 kg / h. This ensures that the material is fully melted and plasticized, and that MSCNT and PN-TNR are uniformly dispersed in the nylon matrix. At the same time, it avoids the decomposition of electrolyte-resistant modifiers and ensures the electrolyte resistance of the film.
[0025] In step 2, the process parameters of the single-screw extruder are as follows: barrel temperature is 240~265℃, with the feeding section at 240℃, the compression section at 255℃, and the discharge section at 265℃; screw speed is 120 r / min; and die temperature is 265℃. This ensures good melt flowability, stable casting, and avoids film thickness deviations caused by uneven melt flow.
[0026] In step 2, the temperature of the cooling roller is 30℃. In step 4, the temperature of the cooling roller is 30℃, and the winding speed is 6 m / min.
[0027] Example 2 1. Preparation of MSCNTs: S1, Surface modification of carbon nanotubes: First, 3 g of carbon nanotubes with a diameter of 12 nm and a length of 2 μm were added to 300 mL of a mixed acid solution and ultrasonically dispersed for 30 min to ensure uniform dispersion of the carbon nanotubes in the mixed acid solution. The volume ratio of concentrated nitric acid to concentrated sulfuric acid in the mixed acid solution was 1:3. Then, the mixed solution was placed in an oil bath and heated under reflux at 90 °C for 5 h to graft carboxyl groups onto the surface of the carbon nanotubes. After the reaction was complete, the mixed solution was cooled to room temperature and repeatedly washed with deionized water until the filtrate was neutral. Then, it was placed in a vacuum drying oven and dried at 90 °C for 12 h to obtain a carboxyl grafting amount of 6. wt % carboxylated carbon nanotubes, the introduction of carboxyl groups can improve the bonding stability between carbon nanotubes and mesoporous silica, and further improve the compatibility with nylon matrix; S2, Coating with mesoporous silica: Then, 1 g of carboxylated carbon nanotubes were dispersed in 150 mL of mixed solvent and ultrasonically dispersed for 30 min to obtain a uniform dispersion. The volume ratio of ethanol to deionized water in the mixed solvent was 3:1. Then, 10 mL of 25% ammonia water was added to the dispersion to adjust the pH to 10, and the mixture was stirred for 15 min. Subsequently, 4 mL of TEOS was slowly added dropwise at a rate of 2 drops / second. After the addition was complete, the mixture was stirred at 40 °C for 8 h to allow TEOS to hydrolyze and condense on the surface of the carboxylated carbon nanotubes, forming a mesoporous silica shell. After the reaction was completed, the reaction solution was centrifuged at 4000 r / min for 15 min, the precipitate was collected, and washed 4 times alternately with ethanol and deionized water. Finally, it was placed in a vacuum drying oven and dried at 90 °C for 15 h to obtain MSCNTs, in which the mesoporous silica had a mesopore diameter of 4 nm and a coating thickness of 25 nm.
[0028] 2. Preparation of PN-TNR: Preparation of S1, titanium dioxide nanorods: 8 mL of isopropyl titanate was added to 150 mL of deionized water and stirred for 20 min to form a homogeneous isopropyl titanate solution. 40 mL of a 2 mol / L sodium hydroxide solution was added to the isopropyl titanate solution and stirred for 40 min to ensure thorough mixing. The mixture was then transferred to a hydrothermal reactor and subjected to a constant-temperature hydrothermal reaction at 140 °C for 15 h. After cooling to room temperature, the pH of the solution was adjusted to 7 with 2 mol / L dilute hydrochloric acid. The solution was filtered, the precipitate was collected, washed with deionized water until neutral, and then placed in an oven and dried at 90 °C for 15 h. Finally, it was placed in a muffle furnace and calcined at 500 °C for 3 h to obtain titanium dioxide nanorods with a diameter of 40 nm and a length of 250 nm. These titanium dioxide nanorods improved the mechanical properties of the film without affecting its processability. S2, Surface grafting modification: Then, 2 g of titanium dioxide nanorods were dispersed in 150 mL of anhydrous ethanol and ultrasonically dispersed for 30 min to obtain a uniform dispersion. Next, 1.5 g of silane coupling agent KH560 was added to the dispersion, and the mixture was placed in an oil bath and refluxed at 70 °C for 3 h to graft the silane coupling agent KH560 onto the surface of the titanium dioxide nanorods. Subsequently, 4 g of phosphate ester amine was added, and the reaction was continued at 70 °C for 5 h to graft phosphorus and nitrogen flame retardant groups onto the surface of the titanium dioxide nanorods via the silane coupling agent. After the reaction was completed, the mixture was centrifuged at 4000 r / min for 15 min, the precipitate was collected, and washed four times alternately with anhydrous ethanol and deionized water. Finally, it was placed in a vacuum drying oven and dried at 90 °C for 15 h to obtain PN-TNR, in which the phosphorus grafting amount was 7%. wt The grafting amount of nitrogen was 10%. wt %.
[0029] 3. Formulation of biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation The composition consists of 90 parts nylon matrix, 3 parts MSCNT, 5 parts PN-TNR, 0.5 parts antioxidant 168, 0.5 parts stearic acid lubricant, 0.6 parts KH570 dispersant, and 0.4 parts PVDF-HFP electrolyte-resistant modifier. The nylon matrix is nylon 66 with a relative viscosity of 2.8.
[0030] 4. Preparation of biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery packaging A method for preparing a biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation includes the following steps: Step 1: First, according to the formula ratio, add 90 parts of nylon matrix, 3 parts of MSCNT, 5 parts of PN-TNR, 0.5 parts of antioxidant 168, 0.5 parts of stearic acid lubricant, 0.6 parts of KH570 dispersant, and 0.4 parts of PVDF-HFP electrolyte-resistant modifier to a high-speed mixer and mix for 12 minutes at a temperature of 85℃ and a speed of 1400 r / min to ensure uniform mixing of all components. Then, add the mixture to a twin-screw extruder, melt extrude, and pelletize to obtain composite masterbatch. Step 2: Then, place the composite masterbatch in a vacuum drying oven and dry it at 95℃ for 5 hours until the moisture content of the composite masterbatch is ≤0.05%. wt To avoid air bubbles during melt extrusion and prevent leakage after lithium-ion battery encapsulation, the dried composite masterbatch is then added to a single-screw extruder, melt-extruded, cast through a T-die, and then cooled and shaped by cooling rollers to obtain a 1.4 mm thick casting. The surface of the casting must be flat, free of air bubbles and scratches to ensure the quality of subsequent stretching and encapsulation. Step 3: The cast sheet is then fed into a biaxial stretching machine for longitudinal and transverse stretching. The longitudinal stretching process parameters are: stretching temperature 85℃, stretching ratio 3.5 times, and stretching speed 9 m / min, to ensure uniform stretching of the cast sheet in the longitudinal direction and improve the longitudinal mechanical properties and puncture resistance of the film. The transverse stretching process parameters are: stretching temperature 105℃, stretching ratio 4.2 times, and stretching speed 6 m / min, to ensure uniform stretching of the cast sheet in the transverse direction, so that the longitudinal and transverse mechanical properties of the film tend to be consistent, adapting to the multi-directional stress requirements in the lithium-ion battery packaging process. Step 4: The biaxially stretched film is then placed in a setting oven and set with hot air at 135°C for 8 seconds to eliminate internal stress, improve dimensional stability, and prevent shrinkage after lithium-ion battery encapsulation, which could lead to encapsulation failure. The set film is then cooled by cooling rollers, edge defects are removed by trimming, and finally it is wound up by a winding machine to obtain a 40 μm thick biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation.
[0031] In step 1, the process parameters of the twin-screw extruder are as follows: barrel temperature is 235~260℃, with the feeding section at 235℃, the compression section at 255℃, and the discharge section at 260℃; screw speed is 220 r / min; and feeding speed is 40 kg / h. This ensures that the material is fully melted and plasticized, and that MSCNT and PN-TNR are uniformly dispersed in the nylon matrix. At the same time, it avoids the decomposition of electrolyte-resistant modifiers and ensures the electrolyte resistance of the film.
[0032] In step 2, the process parameters of the single-screw extruder are as follows: barrel temperature is 245~270℃, with the feeding section at 245℃, the compression section at 260℃, and the discharge section at 270℃; screw speed is 130 r / min; and die temperature is 265℃. This ensures good melt flowability, stable casting, and avoids film thickness deviations caused by uneven melt flow.
[0033] In step 2, the temperature of the cooling roller is 35℃. In step 4, the temperature of the cooling roller is 35℃, and the winding speed is 7 m / min.
[0034] Comparative Example 1 The difference from Example 1 is that: Comparative Example 1 prepared a conventional biaxially oriented nylon film for lithium-ion battery packaging without adding MSCNT, PN-TNR and electrolyte-resistant modifier. The components, by weight, included 97 parts nylon matrix, 0.8 parts antioxidant 1010, 0.7 parts EBS lubricant and 1.5 parts polyethylene wax dispersant. The preparation method was the same as in Example 1.
[0035] In the above embodiments and comparative examples, the nylon matrix was purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd., the carbon nanotubes from Wuhan Carbon Technology Co., Ltd., the mesoporous silica from Sinoma High-Tech Materials Co., Ltd., and the tetraethyl orthosilicate from Hubei Xingfa Chemical Group Co., Ltd.; tetrabutyl titanate and isopropyl titanate were purchased from Sigma-Aldrich; silane coupling agents KH550 and KH560 and dispersant KH570 were purchased from Jiangxi Chenguang New Materials Co., Ltd.; ammonium dihydrogen phosphate, melamine cyanurate, and phosphate ester amine were purchased from Shandong Longhui Chemical Co., Ltd.; antioxidant 1010 and antioxidant 168 were purchased from Tianjin Lianlong New Materials Co., Ltd.; EBS lubricant, stearic acid lubricant, and polyethylene wax dispersant were purchased from Croda Chemicals (Shanghai) Co., Ltd., and the electrolyte-resistant modifier was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.
[0036] Performance testing 1. Testing method: Flame retardant performance: Limiting oxygen index was tested according to the method specified in GB / T 2406.3-2022; Vertical flammability rating UL94 was tested according to the method specified in GB 5169.16-2017. Mechanical strength properties: tested according to the methods specified in GB / T 1040.3-2006; Strength retention rate: Calculation method: Strength after electrolyte immersion (aging) / Strength before immersion (aging) * 100% 2. Test Results Table 1 Performance test results of biaxially stretched nylon film for lithium-ion battery packaging
[0037] As can be seen from the data in Table 1, by comparing Example 1, Example 2 and Comparative Example 1, it can be seen that after the present invention combines MSCNT with the nylon matrix, the puncture resistance of the film can be increased by more than 30%, and the tensile strength retention rate is ≥95% after soaking in lithium-ion battery electrolyte for 72 hours; after the present invention combines PN-TNR with the nylon matrix, the limiting oxygen index of the film can be increased to more than 32%, the vertical burning rating reaches UL94 V-0, and there is no obvious swelling or cracking after soaking in lithium-ion battery electrolyte for 72 hours.
[0038] This invention significantly improves the flame retardant properties, mechanical properties, and electrolyte corrosion resistance of nylon films by adding two core inorganic modifying compounds, MSCNT and PN-TNR, along with an electrolyte-resistant modifier. This solves the core technical pain points of traditional nylon films used in lithium-ion battery packaging, and the prepared film can stably adapt to the usage requirements of different packaging scenarios such as soft packs and hard shells for lithium-ion batteries.
[0039] The above embodiments are not intended to limit the product form and style of the present invention. Any appropriate changes or modifications made by those skilled in the art should be considered as not departing from the patent scope of the present invention.
Claims
1. A biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation, characterized in that: The raw materials, by weight, include the following amounts: 80-95 parts nylon matrix, 1-5 parts MSCNT, 2-8 parts PN-TNR, 0.2-2 parts antioxidant, 0.3-2 parts lubricant, 0.5-3 parts dispersant, and 0.3-1.5 parts electrolyte-resistant modifier. The MSCNT is prepared by surface-modifying carbon nanotubes and then coating the surface of the carbon nanotubes with mesoporous silica via a sol-gel method. The mesoporous silica has a pore size of 2-5 nm and a coating thickness of 10-30 nm. The PN-TNR is prepared by preparing titanium dioxide nanorods from a titanium source via a hydrothermal reaction, followed by grafting phosphorus and nitrogen flame-retardant groups onto the nanorods using a silane coupling agent. The titanium dioxide nanorods have a diameter of 20-50 nm and a length of 100-300 nm. The amount of phosphorus grafted into the PN-TNR is 3... wt %~8 wt The grafting amount of nitrogen is 5%. wt %~12 wt %.
2. The biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation according to claim 1, characterized in that: The nylon matrix is one or more blends of nylon 6, nylon 66, nylon 11 and nylon 12. The nylon matrix is preferably a blend of nylon 6 and nylon 66 with a mass ratio of 1 to 3:
1. The relative viscosity of the nylon matrix is 2.0 to 3.
0.
3. The biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation according to claim 1, characterized in that: The antioxidant is one or two of hindered phenolic antioxidants and phosphite antioxidants; the lubricant is one or more of stearic acid, stearamide, and ethylene bis-stearamide; the dispersant is one or more of polyethylene wax, polypropylene wax, and silane coupling agent; and the electrolyte-resistant modifier is PVDF-HFP.
4. The biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation according to claim 3, characterized in that: The hindered phenolic antioxidants are antioxidant 1010 and antioxidant 1076, and the phosphite antioxidants are antioxidant 168.
5. A method for preparing a biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation as described in claim 1, characterized in that: Includes the following steps: Step 1: First, according to the formula ratio, add 80-95 parts of nylon matrix, 1-5 parts of MSCNT, 2-8 parts of PN-TNR, 0.2-2 parts of antioxidant, 0.3-2 parts of lubricant, 0.5-3 parts of dispersant, and 0.3-1.5 parts of electrolyte-resistant modifier into a high-speed mixer and mix for 10-20 minutes at a temperature of 80-100℃ and a speed of 1000-1500 r / min to ensure uniform mixing of all components. Then, add the mixture into a twin-screw extruder, melt extrude, and pelletize to obtain composite masterbatch. Step 2: Then, place the composite masterbatch in a vacuum drying oven and dry it at 80~100℃ for 4~8 hours until the moisture content of the composite masterbatch is ≤0.05%. wt %, and then the dried composite masterbatch is added to a single screw extruder, melt-extruded and cast through a T-die, and then cooled and shaped by a cooling roller to obtain a casting sheet with a thickness of 0.8~1.5 mm; Step 3: Then, the casting is fed into a biaxial stretching machine for longitudinal and transverse stretching. The process parameters for longitudinal stretching are: stretching temperature 70~90℃, stretching ratio 2.5~4.0 times, and stretching speed 5~10 m / min; the process parameters for transverse stretching are: stretching temperature 90~110℃, stretching ratio 3.0~4.5 times, and stretching speed 3~8 m / min. Step 4: Then, the biaxially stretched film is sent into a setting oven for hot air setting at a temperature of 120-140°C for 5-15 seconds. The set film is then cooled by cooling rollers, edge defects are removed by trimming, and finally it is wound up by a winding machine to obtain the biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation with a thickness of 15-50 μm.
6. The method for preparing a biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation according to claim 5, characterized in that: In step 1, the preparation process of the MSCNT is as follows: S1, Surface modification of carbon nanotubes: First, 1–5 g of carbon nanotubes with a diameter of 10–20 nm and a length of 1–5 μm were added to 200–500 mL of a mixed acid solution and ultrasonically dispersed for 30–60 min to ensure uniform dispersion of the carbon nanotubes in the mixed acid solution, wherein the volume ratio of concentrated nitric acid to concentrated sulfuric acid in the mixed acid solution was 1:
3. Then, the mixed solution was placed in an oil bath and heated under reflux at 80–100 °C for 4–8 h to graft carboxyl groups onto the surface of the carbon nanotubes. After the reaction was complete, the mixed solution was cooled to room temperature and repeatedly washed with deionized water until the filtrate was neutral. Then, it was placed in a vacuum drying oven and dried at 80–100 °C for 12–24 h to obtain a carboxyl grafting amount of 5. wt %~10 wt % carboxylated carbon nanotubes; S2, Coating with mesoporous silica: Then, 0.5–2 g of carboxylated carbon nanotubes were dispersed in 100–200 mL of a mixed solvent and ultrasonically dispersed for 20–40 min to obtain a homogeneous dispersion. The volume ratio of ethanol to deionized water in the mixed solvent was 3:
1. Next, 5–15 mL of 25%–28% ammonia solution was added to the dispersion to adjust the pH to 9–11, and the mixture was stirred for 10–20 min. Subsequently, 2–8 mL of TEOS was slowly added dropwise at a rate of 1–2 drops / second. After the addition was complete, the mixture was stirred at a constant temperature of 30–50 °C for 6–12 h to allow tetraethyl orthosilicate to hydrolyze and condense on the surface of the carboxylated carbon nanotubes, forming a mesoporous silica shell. After the reaction was complete, the reaction solution was centrifuged at 3000–5000 r / min for 10–20 min, the precipitate was collected, and washed alternately with ethanol and deionized water 3–5 times. Finally, the precipitate was placed in a vacuum drying oven and dried at 80–100 °C for 12–24 hours. h, MSCNT is obtained, wherein the mesoporous silica has a mesopore size of 2~5 nm and a coating thickness of 10~30 nm.
7. The method for preparing a biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation according to claim 5, characterized in that: In step 1, the preparation process of the PN-TNR is as follows: Preparation of S1, titanium dioxide nanorods: Add 5-15 mL of titanium source to 100-200 mL of deionized water and stir for 10-20 min to form a homogeneous titanium source solution, wherein the titanium source is one of tetrabutyl titanate and isopropyl titanate; add 20-50 mL of sodium hydroxide solution with a concentration of 1-5 mol / L to the titanium source solution and stir for 30-60 min to fully mix the titanium source and sodium hydroxide solution. The mixed solution was then transferred to a hydrothermal reactor and subjected to a constant-temperature hydrothermal reaction at 120-160℃ for 12-24 h. After cooling to room temperature, the pH of the solution was adjusted to 6-7 with 1-2 mol / L dilute hydrochloric acid. The solution was filtered, the precipitate was collected, washed with deionized water until neutral, and then placed in an oven to dry at 80-100℃ for 12-24 h. Finally, it was placed in a muffle furnace and calcined at 400-600℃ for 2-4 h to obtain titanium dioxide nanorods with a diameter of 20-50 nm and a length of 100-300 nm. S2, Surface grafting modification: Then, 1-3 g of titanium dioxide nanorods were dispersed in 100-200 mL of anhydrous ethanol and ultrasonically dispersed for 20-40 min to obtain a uniform dispersion. Next, 0.5-2 g of silane coupling agent was added to the dispersion, and the mixture was placed in an oil bath and heated under reflux at 60-80℃ for 2-4 h to graft the silane coupling agent onto the surface of the titanium dioxide nanorods. The silane coupling agent was one of KH550 or KH560. Subsequently, 2-6 g of phosphorus-nitrogen flame retardant was added, and the reaction was continued at 60-80℃ for 4-8 h. The phosphorus-nitrogen flame retardant was one or two of ammonium dihydrogen phosphate, melamine cyanurate, and phosphate ester amine. After the reaction was complete, the mixture was centrifuged at 3000-5000 r / min for 10-20 min, the precipitate was collected, and washed alternately with anhydrous ethanol and deionized water 3-5 times. Finally, the precipitate was placed in a vacuum drying oven and dried at 80-100℃ for 12-24 hours. h, PN-TNR was obtained, in which the grafting amount of phosphorus was 3. wt %~8 wt The grafting amount of nitrogen is 5%. wt %~12 wt %.
8. The method for preparing a biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery packaging according to claim 5, characterized in that: In step 1, the process parameters of the twin-screw extruder are as follows: barrel temperature is 230~260℃, of which the feeding section is 230~240℃, the compression section is 240~250℃, the discharge section is 250~260℃, the screw speed is 150~250 r / min, and the feeding speed is 20~50 kg / h.
9. The method for preparing a biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation according to claim 5, characterized in that: In step 2, the process parameters of the single-screw extruder are as follows: barrel temperature is 240~270℃, of which the feeding section is 240~250℃, the compression section is 250~260℃, the discharge section is 260~270℃, the screw speed is 80~150 r / min, and the die temperature is 260~270℃.
10. The method for preparing a biaxially stretched flame-retardant reinforced nylon film for lithium-ion battery encapsulation according to claim 5, characterized in that: In step 2, the temperature of the cooling roller is 20~40℃. In step 4, the temperature of the cooling roller is 25~40℃, and the winding speed is 4~8 m / min.