Heat-shrinkable, puncture-resistant polyolefin separator material and method of making same

Abstract

The application discloses a heat-shrinkage-resistant puncture-resistant polyolefin diaphragm material and a preparation method thereof, and belongs to the technical field of polyolefin diaphragms. The application is used for solving the technical problems of low compatibility of a polyolefin composite diaphragm with an electrolyte and poor heat resistance of the polyolefin composite diaphragm in the prior art. The heat-shrinkage-resistant puncture-resistant polyolefin diaphragm material is composed of mixed raw materials including 20-30 parts of modified polyolefin, 10-20 parts of modified ethyl cellulose, 20-30 parts of high-density polyethylene, 0.2-0.4 parts of an antioxidant, 0.1-0.3 parts of a nucleating agent and 0.1-0.2 parts of a dispersing agent according to weight. The application can effectively improve the polarity of the polyolefin composite diaphragm, promote the compatibility between the polyolefin composite diaphragm and the electrolyte, reduce the impedance during ion migration, improve the porosity and puncture strength of the polyolefin composite diaphragm, and reduce the heat shrinkage rate of the polyolefin composite diaphragm.

Description

Technical Field

[0001] This invention relates to the field of polyolefin membrane processing technology, specifically to heat-shrinkable and puncture-resistant polyolefin membrane materials and their preparation methods. Background Technology

[0002] The separator is one of the key internal components of a lithium battery. Its main function is to separate the positive and negative electrodes, preventing short circuits caused by contact between them. It also allows electrolyte ions to pass through. The performance of the separator determines the battery's interface structure and internal resistance, directly affecting its capacity, cycle life, and safety characteristics. A high-performance separator plays a crucial role in improving the overall performance of the battery.

[0003] Lithium-ion battery separators in current technology are typically made from polyolefins such as polyethylene and polypropylene through single-layer, double-layer, or triple-layer composite processes. Polyolefin separators have high mechanical strength and good chemical stability, making them the most widely used separators in commercial applications. However, polyolefin materials lack polar functional groups, resulting in low compatibility between polyolefin separators and highly polar electrolytes, leading to poor wettability and high impedance during ion migration. This severely restricts the long-cycle performance of the battery. PE separators experience cell closure at 135℃, and PP separators at 170℃. Polyolefin separators also have poor thermal stability. When the battery is exposed to high external temperatures or internal abnormalities, the separator shrinks severely, causing short circuits between the positive and negative electrodes, leading to safety accidents such as fires and explosions.

[0004] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a heat-resistant, shrinkage-resistant, and puncture-resistant polyolefin membrane material and its preparation method, which solves the technical problems of low compatibility and poor wettability between polyolefin composite membranes and electrolytes, high impedance during ion migration, and poor heat resistance of existing polyolefin composite membranes. At high temperatures, the membrane pores close, the polyolefin membrane shrinks severely, and short circuits occur between the positive and negative electrodes, posing significant safety hazards.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] The heat-shrinkable and puncture-resistant polyolefin separator material is made from a mixture of 20-30 parts by weight of modified polyolefin, 10-20 parts by modified ethyl cellulose, 20-30 parts by weight of high-density polyethylene, 0.2-0.4 parts by weight of antioxidant, 0.1-0.3 parts by weight of nucleating agent and 0.1-0.2 parts by weight of dispersant. The mixture is extruded by a twin-screw extruder and then pelletized to obtain modified polyolefin granules. These granules are then extruded by a three-layer co-extrusion blown film machine. The composite separator is then cut, heat-treated and stretched according to design requirements to obtain the polyolefin composite separator.

[0008] The modified polyolefin is prepared by free radical reaction of acrylamide and N,N-diethylacrylamide as raw materials. The modified ethyl cellulose is prepared by grafting polyacrylamide onto ethyl cellulose. The antioxidant is one of antioxidant TNP and antioxidant TPP. The dispersant is composed of one or more of zinc stearate, barium stearate, and calcium stearate.

[0009] A method for preparing a heat-shrinkable and puncture-resistant polyolefin membrane material includes the following steps:

[0010] S1. Weigh out the following by weight: 1-3 parts acrylamide, 1-3 parts N,N-diethylacrylamide, 6-18 parts purified water, and 0.1-0.3 parts initiator. Add them to a three-necked flask and stir. Under nitrogen protection, raise the temperature of the three-necked flask to 55-65℃ and react for 15-20 hours. After post-treatment, the modified polyolefin is obtained.

[0011] The synthesis reaction principle of modified polyolefins is as follows:

[0012]

[0013] S2. Weigh out the following components by weight: 20-30 parts modified polyolefin, 10-20 parts modified ethyl cellulose, 20-30 parts high-density polyethylene, 0.2-0.4 parts antioxidant, 0.1-0.3 parts nucleating agent, and 0.1-0.2 parts dispersant. Mix them evenly, add them to a twin-screw extruder, extrude them into strips, cool them in a water cooling tank, and then pulverize them to obtain modified polyolefin granules.

[0014] S3. Add the modified polyolefin particles to a three-layer co-extrusion blown film machine, extrude them through the three-layer co-extrusion blown film machine, and cut, heat treat and stretch the composite membrane raw material according to the design requirements to obtain the polyolefin composite membrane.

[0015] Furthermore, the synthesis of the modified ethyl cellulose includes the following steps:

[0016] A1. Weigh out 2-4 parts by weight of ethyl cellulose, 30-60 parts by weight of N,N-dimethylacetamide, and 10-20 parts by weight of triethylamine. Add them to a three-necked flask and stir until dissolved. Under nitrogen protection, lower the temperature of the three-necked flask to 5-8℃. Weigh out 4-8 parts by weight of toluenesulfonyl chloride and 6-12 parts by weight of dichloromethane. Add them to a beaker and mix to prepare a dropping solution. Add the dropping solution dropwise to the three-necked flask through a constant pressure dropping funnel. After the addition is complete, react for 20-24 hours. After post-processing, obtain intermediate I.

[0017] A2. Weigh out the following by weight: 2-4 parts of intermediate I, 5-10 parts of sodium azide, and 15-30 parts of N,N-dimethylacetamide. Add them to a three-necked flask. Under nitrogen protection, raise the temperature of the three-necked flask to 80-90℃ and react for 20-24 hours. After post-treatment, obtain intermediate II.

[0018] The synthesis reaction principle of intermediate II is as follows:

[0019]

[0020] A3. Weigh out the following by weight: 2-4 parts of intermediate II, 1-2 parts of 3-butynedic acid, and 9-18 parts of tetrahydrofuran. Add them to a three-necked flask and stir until dissolved. Under nitrogen protection, add 0.01-0.02 parts of catalyst to the three-necked flask. Raise the temperature of the three-necked flask to 50-60℃ and react for 20-24 hours. After post-treatment, obtain intermediate III.

[0021] The synthesis reaction principle of intermediate III is as follows:

[0022]

[0023] A4. Weigh out the following by weight: 3-5 parts of intermediate III, 2-4 parts of polyacrylol, 10-20 parts of tetrahydrofuran, and 0.1-0.2 parts of catalyst. Add them to a three-necked flask and stir. Raise the temperature of the three-necked flask to 55-65℃ and react for 8-10 hours. After post-treatment, modified ethyl cellulose is obtained.

[0024] The synthesis reaction principle of modified ethyl cellulose is as follows:

[0025]

[0026] Furthermore, the initiator in step S1 is azobisisobutyronitrile (AIBN), and the post-treatment operation in step S1 is as follows: after the reaction is complete, add 30-90 parts by weight of anhydrous ethanol to a three-necked flask, stir for 15-20 min, filter, add the filter cake and 30-90 parts by weight of ethanol to a beaker, stir for 10-15 min, filter, and place the filter cake in a drying oven at a temperature of 70-80℃ to dry for 8-10 h to obtain modified polyolefin.

[0027] Further, the post-processing operation of step A1 is as follows: weigh 45-90 parts by weight of purified water and add it to a beaker and stir. After the reaction is complete, slowly add the reaction solution from the three-necked flask to the beaker. A large amount of solid precipitates out. Stir for 10-20 minutes, filter, and add the filter cake to the beaker with 45-90 parts by weight of anhydrous ethanol. Stir for 15-30 minutes, filter until no liquid flows out, and place the filter cake in a drying oven at a temperature of 50-60℃ for 5-6 hours to obtain intermediate I.

[0028] Further, the post-processing operation of step A2 is as follows: weigh 90-240 parts by weight of purified water and add it to a beaker and stir. After the reaction is complete, slowly add the reaction solution from the three-necked flask to the beaker. A large amount of solid precipitates out. Stir for 10-20 minutes, filter, and add the filter cake to the beaker with 90-240 parts by weight of anhydrous ethanol. Stir for 15-30 minutes, filter until no liquid flows out, and place the filter cake in a drying oven at a temperature of 50-60℃ for 5-6 hours to obtain intermediate II.

[0029] Furthermore, the catalyst in step A3 is cuprous chloride, and the post-processing steps in step S3 are as follows: after the reaction is complete, add 45-90 parts by weight of methanol to a three-necked flask, stir for 20-30 min, filter, add the filter cake and 20-30 parts by weight of methanol to a beaker, stir for 5-10 min, filter, and place the filter cake in a drying oven at 50-60℃ to dry for 5-6 h to obtain intermediate III.

[0030] Furthermore, the catalyst in step A4 is one of isopropyl zirconate, n-propyl zirconate, and tetraisopropyl titanate. The post-treatment steps in step S4 are as follows: after the reaction is complete, distill under reduced pressure until no liquid flows out, slowly add 40-80 parts by weight of purified water to a three-necked flask, stir for 15-20 min, filter, wash the filter cake with 10-20 parts by weight of anhydrous ethanol, dry it under vacuum, and place the filter cake in a drying oven at 80-90℃ for 10-12 h to obtain modified ethyl cellulose.

[0031] The present invention has the following beneficial effects:

[0032] 1. The modified polyolefin prepared by the present invention through the composite of acrylamide and N,N-diethylacrylamide can modify the polyolefin by grafting a large number of amino groups onto it. Amino groups are highly polar functional groups, which can improve the polarity of the modified polyolefin, thereby improving its compatibility with highly polar electrolytes, reducing the impedance of ions during migration, and promoting the circulation of ions in the electrolyte.

[0033] 2. This invention modifies ethyl cellulose by grafting polyacrylamide onto it. Polyacrylamide, modified polyolefin, and high-density polyethylene are similar and compatible and all have long straight-chain structures, enabling the molecules constituting the polyolefin composite membrane to cross-link with each other, thereby improving the puncture resistance of the polyolefin composite membrane. Furthermore, it generates uniformly distributed pores during stretching, increasing the porosity of the polyolefin composite membrane. The modified ethyl cellulose contains a large number of ether bonds and hydroxyl groups, which promotes the hydrophilic properties of the polyolefin composite membrane and improves its ability to retain electrolyte. Ethyl cellulose has good thermal stability; when the polyolefin composite membrane is heated, ethyl cellulose exhibits excellent thermal stability and will not undergo deformation such as thermal shrinkage at high temperatures, thus ensuring that the polyolefin composite membrane maintains a good thermal shrinkage rate when heated. Detailed Implementation

[0034] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1

[0036] The heat-shrinkable and puncture-resistant polyolefin separator material of this embodiment is composed of a mixture of 30g modified polyolefin, 20g modified ethyl cellulose, 30g high-density polyethylene, 0.4g antioxidant TNP, 0.3g monocyclic carboxylate, and 0.2g barium stearate. The mixture is extruded by a twin-screw extruder and then pelletized to obtain modified polyolefin granules. These granules are then extruded by a three-layer co-extrusion blown film machine. The composite separator is then cut, heat-treated, and stretched according to design requirements to obtain the polyolefin composite separator.

[0037] Example 2

[0038] The method for preparing the heat-shrinkable and puncture-resistant polyolefin membrane material in this embodiment includes the following steps:

[0039] Preparation of modified polyolefins:

[0040] Weigh out the following components by weight: 3g acrylamide, 3g N,N-diethylacrylamide, 18g purified water, and 0.15g azobisisobutyronitrile. Add these components to a three-necked flask and stir. Under nitrogen protection, raise the temperature of the three-necked flask to 55℃ and react for 15 hours. After the reaction is complete, add 90g anhydrous ethanol to the three-necked flask and stir for 15 minutes. Filter the mixture. Add the filter cake and 90g ethanol to a beaker and stir for 10 minutes. Filter the mixture again and place the filter cake in a drying oven at 70℃ for 8 hours to obtain the modified polyolefin.

[0041] Preparation of modified ethyl cellulose:

[0042] Weigh out 6g of ethyl cellulose, 90g of N,N-dimethylacetamide, and 30g of triethylamine by weight, add them to a three-necked flask and stir until dissolved. Under nitrogen protection, lower the temperature of the three-necked flask to 5℃, weigh out 12g of toluenesulfonyl chloride and 18g of dichloromethane, add them to a beaker and mix to prepare a dropping solution. Add the dropping solution dropwise to the three-necked flask through a constant pressure dropping funnel. After the addition is complete, react for 20h. Weigh out 135g of purified water and add it to the beaker and stir. After the reaction is complete, slowly add the reaction solution from the three-necked flask to the beaker. A large amount of solid precipitates out. Stir for 10min, filter, add the filter cake to the beaker with 135g of anhydrous ethanol, stir for 15min, filter until no liquid flows out, place the filter cake in a drying oven at 50℃ and dry for 5h to obtain intermediate I.

[0043] Weigh out the following components by weight: 6g of intermediate I, 15g of sodium azide, and 45g of N,N-dimethylacetamide. Add them to a three-necked flask. Under nitrogen protection, raise the temperature of the three-necked flask to 80℃ and react for 20h. Weigh out 270g of purified water and add it to a beaker. Stir. After the reaction is complete, slowly add the reaction solution from the three-necked flask to the beaker. A large amount of solid precipitates out. Stir for 10min, filter, and add the filter cake to 270g of anhydrous ethanol in the beaker. Stir for 15min, filter until no liquid flows out, and place the filter cake in a drying oven at 50℃ for 5h to obtain intermediate II.

[0044] Weigh out the following components by weight: 6g of intermediate II, 3g of 3-butynedic acid, and 27g of tetrahydrofuran. Add them to a three-necked flask and stir until dissolved. Under nitrogen protection, add 30mg of cuprous chloride to the three-necked flask. Raise the temperature of the three-necked flask to 50℃ and react for 20h. After the reaction is complete, add 135g of methanol to the three-necked flask and stir for 20min. Filter the mixture. Add the filter cake and 60g of methanol to a beaker and stir for 5min. Filter the mixture again. Place the filter cake in a drying oven at 50℃ and dry for 5h to obtain intermediate III.

[0045] Weigh out the following components by weight: 9g of intermediate III, 6g of polyacrylol, 30g of tetrahydrofuran, and 0.3g of isopropyl zirconate. Add these components to a three-necked flask and stir. Raise the temperature of the three-necked flask to 55℃ and react for 8 hours. Once the reaction is complete, distill under reduced pressure until no liquid flows out. Slowly add 120g of purified water to the three-necked flask and stir for 15 minutes. Filter the mixture. Rinse the filter cake with 30g of anhydrous ethanol and dry it under vacuum. Place the filter cake in a drying oven at 80℃ and dry it for 10 hours to obtain modified ethyl cellulose.

[0046] Preparation of modified polyolefin particles:

[0047] Weigh out the following by weight: 20g modified polyolefin, 10g modified ethyl cellulose, 20g high-density polyethylene, 0.2g antioxidant TNP, 0.1g cyclohexylamide, and 0.1g zinc stearate. Mix them evenly, add them to a twin-screw extruder, extrude them into strips, cool them in a water cooling tank, and then pulverize them to obtain modified polyolefin granules.

[0048] Preparation of polyolefin composite membranes:

[0049] Modified polyolefin particles are added to a three-layer co-extrusion blown film machine and extruded. The composite separator preliminary product is cut according to the design requirements and placed between two heating plates. The exterior of the composite separator preliminary product is covered by a metal film on one side. The two heating plates are put together and heated simultaneously. The temperature of the heating plates rises to 135°C and is held for 10 minutes to obtain a rough composite separator product. The rough composite separator product is heated to 120°C and subjected to transverse and longitudinal stretching to stretch it to the designed size to obtain the finished composite separator product.

[0050] Example 3

[0051] The method for preparing the heat-shrinkable and puncture-resistant polyolefin membrane material in this embodiment includes the following steps:

[0052] Preparation of modified polyolefins:

[0053] Weigh out the following components by weight: 6g acrylamide, 6g N,N-diethylacrylamide, 36g purified water, and 0.3g azobisisobutyronitrile. Add these components to a three-necked flask and stir. Under nitrogen protection, raise the temperature of the three-necked flask to 60℃ and react for 17 hours. After the reaction is complete, add 180g of anhydrous ethanol to the three-necked flask and stir for 17 minutes. Filter the mixture. Add the filter cake and 180g of ethanol to a beaker and stir for 12 minutes. Filter the mixture again and place the filter cake in a drying oven at 75℃ for 9 hours to obtain the modified polyolefin.

[0054] Preparation of modified ethyl cellulose:

[0055] Weigh out 9g of ethyl cellulose, 135g of N,N-dimethylacetamide, and 45g of triethylamine by weight, add them to a three-necked flask and stir until dissolved. Under nitrogen protection, lower the temperature of the three-necked flask to 7°C, weigh out 18g of toluenesulfonyl chloride and 27g of dichloromethane, add them to a beaker and mix to prepare a dropping solution. Add the dropping solution dropwise to the three-necked flask through a constant pressure dropping funnel. After the addition is complete, react for 22 hours. Weigh out 202g of purified water and add it to the beaker and stir. After the reaction is complete, slowly add the reaction solution from the three-necked flask to the beaker. A large amount of solid precipitates out. Stir for 15 minutes, filter, add the filter cake to the beaker with 202g of anhydrous ethanol, stir for 28 minutes, filter until no liquid flows out, place the filter cake in a drying oven at 55°C and dry for 5.5 hours to obtain intermediate I.

[0056] Weigh out the following components by weight: 9g of intermediate I, 22.5g of sodium azide, and 67.5g of N,N-dimethylacetamide. Add them to a three-necked flask. Under nitrogen protection, raise the temperature of the three-necked flask to 85℃ and react for 22 hours. Weigh out 495g of purified water and add it to a beaker. Stir. After the reaction is complete, slowly add the reaction solution from the three-necked flask to the beaker. A large amount of solid precipitates out. Stir for 15 minutes and filter. Add the filter cake to the beaker with 495g of anhydrous ethanol and mix. Stir for 28 minutes and filter until no liquid flows out. Place the filter cake in a drying oven at 55℃ and dry for 5.5 hours to obtain intermediate II.

[0057] Weigh out the following components by weight: 9g of intermediate II, 4.5g of 3-butynedic acid, and 39g of tetrahydrofuran. Add them to a three-necked flask and stir until dissolved. Under nitrogen protection, add 45mg of cuprous chloride to the three-necked flask. Raise the temperature of the three-necked flask to 55℃ and react for 22h. After the reaction is complete, add 202g of methanol to the three-necked flask and stir for 25min. Filter the mixture. Add the filter cake and 75g of methanol to a beaker and stir for 8min. Filter the mixture again. Place the filter cake in a drying oven at 55℃ and dry for 5.5h to obtain intermediate III.

[0058] Weigh out the following components by weight: 12g of intermediate III, 9g of polyacrylol, 45g of tetrahydrofuran, and 0.45g of n-propyl zirconate. Add these components to a three-necked flask and stir. Raise the temperature of the three-necked flask to 60℃ and react for 9 hours. Once the reaction is complete, distill under reduced pressure until no liquid flows out. Slowly add 180g of purified water to the three-necked flask and stir for 18 minutes. Filter the mixture. Rinse the filter cake with 45g of anhydrous ethanol and dry it under vacuum. Place the filter cake in a drying oven at 85℃ and dry it for 11 hours to obtain modified ethyl cellulose.

[0059] Preparation of modified polyolefin particles:

[0060] Weigh out the following by weight: 25g modified polyolefin, 15g modified ethyl cellulose, 25g high-density polyethylene, 0.3g antioxidant TPP, 0.2g tricarboxylate, and 0.15g calcium stearate. Mix them evenly, add them to a twin-screw extruder, extrude them into strips, cool them in a water cooling tank, and then pulverize them to obtain modified polyolefin granules.

[0061] Preparation of polyolefin composite membranes:

[0062] Modified polyolefin particles are added to a three-layer co-extrusion blown film machine and extruded. The composite separator preliminary product is cut according to the design requirements and placed between two heating plates. The exterior of the composite separator preliminary product is covered by a metal film on one side. The two heating plates are put together and heated simultaneously. The temperature of the heating plates rises to 135°C and is held for 10 minutes to obtain a rough composite separator product. The rough composite separator product is heated to 120°C and subjected to transverse and longitudinal stretching to stretch it to the designed size to obtain the finished composite separator product.

[0063] Example 4

[0064] The method for preparing the heat-shrinkable and puncture-resistant polyolefin membrane material in this embodiment includes the following steps:

[0065] Preparation of modified polyolefins:

[0066] Weigh out the following components by weight: 9g acrylamide, 9g N,N-diethylacrylamide, 54g purified water, and 0.45g azobisisobutyronitrile. Add these components to a three-necked flask and stir. Under nitrogen protection, raise the temperature of the three-necked flask to 65℃ and react for 20 hours. After the reaction is complete, add 270g anhydrous ethanol to the three-necked flask and stir for 20 minutes. Filter the mixture. Add the filter cake and 270g ethanol to a beaker and stir for 15 minutes. Filter the mixture again and place the filter cake in a drying oven at 80℃ for 10 hours to obtain the modified polyolefin.

[0067] Preparation of modified ethyl cellulose:

[0068] Weigh out 12g of ethyl cellulose, 180g of N,N-dimethylacetamide, and 60g of triethylamine by weight, add them to a three-necked flask and stir until dissolved. Under nitrogen protection, lower the temperature of the three-necked flask to 8℃. Weigh out 24g of toluenesulfonyl chloride and 36g of dichloromethane, add them to a beaker and mix to prepare a dropping solution. Add the dropping solution dropwise to the three-necked flask through a constant pressure dropping funnel. After the addition is complete, react for 24 hours. Weigh out 270g of purified water and add it to the beaker and stir. After the reaction is complete, slowly add the reaction solution from the three-necked flask to the beaker. A large amount of solid precipitates out. Stir for 20 minutes, filter, add the filter cake to the beaker with 270g of anhydrous ethanol, stir for 30 minutes, filter until no liquid flows out, place the filter cake in a drying oven at 60℃ and dry for 6 hours to obtain intermediate I.

[0069] Weigh out 12g of intermediate I, 30g of sodium azide, and 30g of N,N-dimethylacetamide by weight, and add them to a three-necked flask. Under nitrogen protection, raise the temperature of the three-necked flask to 90℃ and react for 24h. Weigh out 720g of purified water and add it to a beaker and stir. After the reaction is complete, slowly add the reaction solution from the three-necked flask to the beaker. A large amount of solid precipitates out. Stir for 20min, filter, and add the filter cake to 720g of anhydrous ethanol and mix. Stir for 30min, filter until no liquid flows out, and place the filter cake in a drying oven at 60℃ for 6h to obtain intermediate II.

[0070] Weigh out the following ingredients by weight: 12g of intermediate II, 6g of 3-butynedic acid, and 54g of tetrahydrofuran. Add them to a three-necked flask and stir until dissolved. Under nitrogen protection, add 60mg of cuprous chloride to the three-necked flask. Raise the temperature of the three-necked flask to 60℃ and react for 24h. After the reaction is complete, add 270g of methanol to the three-necked flask and stir for 30min. Filter the mixture. Add the filter cake and 90g of methanol to a beaker and stir for 10min. Filter the mixture again. Place the filter cake in a drying oven at 60℃ and dry for 6h to obtain intermediate III.

[0071] Weigh out the following components by weight: 15g of intermediate III, 12g of polyacrylamide, 60g of tetrahydrofuran, and 0.6g of tetraisopropyl titanate. Add these components to a three-necked flask and stir. Raise the temperature of the three-necked flask to 65℃ and react for 10 hours. Once the reaction is complete, distill under reduced pressure until no liquid flows out. Slowly add 240g of purified water to the three-necked flask and stir for 20 minutes. Filter the mixture. Rinse the filter cake with 60g of anhydrous ethanol and dry it under vacuum. Place the filter cake in a drying oven at 90℃ and dry it for 10-12 hours to obtain modified ethyl cellulose.

[0072] Preparation of modified polyolefin particles:

[0073] Weigh out the following by weight: 30g of modified polyolefin, 20g of modified ethyl cellulose, 30g of high-density polyethylene, 0.4g of antioxidant TNP, 0.3g of monocyclic carboxylate, and 0.2g of barium stearate. Mix them evenly, add them to a twin-screw extruder, extrude them into strips, cool them in a water-cooling tank, and then pulverize them to obtain modified polyolefin granules.

[0074] Preparation of polyolefin composite membranes:

[0075] Modified polyolefin particles are added to a three-layer co-extrusion blown film machine and extruded. The composite separator preliminary product is cut according to the design requirements and placed between two heating plates. The exterior of the composite separator preliminary product is covered by a metal film on one side. The two heating plates are put together and heated simultaneously. The temperature of the heating plates rises to 135°C and is held for 10 minutes to obtain a rough composite separator product. The rough composite separator product is heated to 120°C and subjected to transverse and longitudinal stretching to stretch it to the designed size to obtain the finished composite separator product.

[0076] Performance testing:

[0077] The porosity, thermal shrinkage rate at 120℃ for 1 hour, ionic conductivity, and puncture strength of the composite separators prepared in Examples 2-4 were tested according to standard GB / T 36363-2018 "Polyolefin Separators for Lithium-ion Batteries". The test results are shown in the table below:

[0078]

[0079] Based on the analysis of the detection data in the table above, the porosity of the polyolefin composite membrane prepared by this invention reached 46%, and the ionic conductivity reached 39 × 10⁻⁶. -3The S / cm conductivity is due to the highly polar amino functional groups grafted onto the modified polyolefin, which promotes the compatibility between the polyolefin composite membrane and the highly polar electrolyte. The lower impedance during ion migration facilitates ion circulation in the electrolyte. The modified ethyl cellulose contains numerous ether bonds and hydroxyl groups, enhancing the hydrophilic properties of the polyolefin composite membrane and effectively improving its ionic conductivity. The polyacrylol grafted onto the modified ethyl cellulose exhibits similar properties to the modified polyolefin and high-density polyethylene. The modified ethyl cellulose, modified polyolefin, and high-density polyethylene possess long carbon linear chains. Under heating, these components cross-link, resulting in improved membrane properties during stretching. The uniform stress distribution prevents tearing and the formation of large pores during stretching, allowing the polyolefin composite membrane to interact with ethyl cellulose and nucleating agents during stretching. This results in uniform pores on the polyolefin composite membrane, increasing its porosity and thus improving its electrolyte retention capacity. Furthermore, the cross-linking between polyolefin composite membrane molecules and the good thermal stability of ethyl cellulose enhance the puncture strength of the polyolefin membrane, achieving a puncture strength of 0.53 N / μm. In a heat shrinkage test at 120°C for 1 hour, its longitudinal shrinkage rate was only 1.09%, and its transverse heat shrinkage rate was only 0.49%, indicating that the polyolefin composite membrane prepared by this invention has excellent heat shrinkage rate and puncture strength.

[0080] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

[0081] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0082] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A heat-shrinkable and puncture-resistant polyolefin membrane material, characterized in that, A mixed raw material consisting of 20-30 parts by weight of modified polyolefin, 10-20 parts of modified ethyl cellulose, 20-30 parts of high-density polyethylene, 0.2-0.4 parts of antioxidant, 0.1-0.3 parts of nucleating agent and 0.1-0.2 parts of dispersant is extruded by a twin-screw extruder and then pelletized to obtain modified polyolefin granules. These granules are then extruded by a three-layer co-extrusion blown film mill. The composite membrane is then cut, heat-treated and stretched according to design requirements to obtain a polyolefin composite membrane. The modified polyolefin is prepared by free radical reaction using acrylamide and N,N-diethylacrylamide as raw materials; the modified ethyl cellulose is prepared by grafting polyacrylamide onto ethyl cellulose; the antioxidant is one of antioxidant TNP and antioxidant TPP; the dispersant is composed of one or more of zinc stearate, barium stearate, and calcium stearate; and the nucleating agent is composed of one or more of monocyclic carboxylates, tricarboxylates, and cyclohexylamide. The method for synthesizing the modified polyolefin is as follows: Weigh out 1-3 parts by weight of acrylamide, 1-3 parts by weight of N,N-diethylacrylamide, 6-18 parts by weight of purified water, and 0.1-0.3 parts by weight of initiator, add them to a three-necked flask and stir. Under nitrogen protection, raise the temperature of the three-necked flask to 55-65℃ and react for 15-20 hours. After post-treatment, the modified polyolefin is obtained. The synthesis of the modified ethyl cellulose includes the following steps: A1. Weigh out 2-4 parts by weight of ethyl cellulose, 30-60 parts by weight of N,N-dimethylacetamide, and 10-20 parts by weight of triethylamine. Add them to a three-necked flask and stir until dissolved. Under nitrogen protection, lower the temperature of the three-necked flask to 5-8℃. Weigh out 4-8 parts by weight of toluenesulfonyl chloride and 6-12 parts by weight of dichloromethane. Add them to a beaker and mix to prepare a dropping solution. Add the dropping solution dropwise to the three-necked flask through a constant pressure dropping funnel. After the addition is complete, react for 20-24 hours. After post-processing, obtain intermediate I. A2. Weigh out the following by weight: 2-4 parts of intermediate I, 5-10 parts of sodium azide, and 15-30 parts of N,N-dimethylacetamide. Add them to a three-necked flask. Under nitrogen protection, raise the temperature of the three-necked flask to 80-90℃ and react for 20-24 hours. After post-treatment, obtain intermediate II. A3. Weigh out the following by weight: 2-4 parts of intermediate II, 1-2 parts of 3-butynedic acid, and 9-18 parts of tetrahydrofuran. Add them to a three-necked flask and stir until dissolved. Under nitrogen protection, add 0.01-0.02 parts of catalyst to the three-necked flask. Raise the temperature of the three-necked flask to 50-60℃ and react for 20-24 hours. After post-treatment, obtain intermediate III. A4. Weigh out the following by weight: 3-5 parts of intermediate III, 2-4 parts of polyacrylol, 10-20 parts of tetrahydrofuran, and 0.1-0.2 parts of catalyst. Add them to a three-necked flask and stir. Raise the temperature of the three-necked flask to 55-65℃ and react for 8-10 hours. After post-treatment, modified ethyl cellulose is obtained.

2. The heat-shrinkable and puncture-resistant polyolefin membrane material according to claim 1, characterized in that, In the synthesis of the modified polyolefin, the initiator is azobisisobutyronitrile (AIBN). The post-treatment operation is as follows: after the reaction is complete, add 30-90 parts by weight of anhydrous ethanol to a three-necked flask, stir for 15-20 min, filter, add the filter cake and 30-90 parts by weight of ethanol to a beaker, stir for 10-15 min, filter, and place the filter cake in a drying oven at 70-80℃ for 8-10 h to obtain the modified polyolefin.

3. The heat-shrinkable and puncture-resistant polyolefin membrane material according to claim 1, characterized in that, The post-processing operation of step A1 is as follows: Weigh 45-90 parts by weight of purified water and add it to a beaker and stir. After the reaction is complete, slowly add the reaction solution from the three-necked flask to the beaker. A large amount of solid precipitates out. Stir for 10-20 minutes, filter, and add the filter cake to the beaker with 45-90 parts by weight of anhydrous ethanol. Stir for 15-30 minutes, filter until no liquid flows out, and place the filter cake in a drying oven at a temperature of 50-60℃ for 5-6 hours to obtain intermediate I.

4. The heat-shrinkable and puncture-resistant polyolefin membrane material according to claim 1, characterized in that, The post-processing operation of step A2 is as follows: Weigh 90-240 parts by weight of purified water and add it to a beaker and stir. After the reaction is complete, slowly add the reaction solution from the three-necked flask to the beaker. A large amount of solid precipitates out. Stir for 10-20 minutes, filter, and add the filter cake to the beaker with 90-240 parts by weight of anhydrous ethanol. Stir for 15-30 minutes, filter until no liquid flows out, and place the filter cake in a drying oven at 50-60℃ for 5-6 hours to obtain intermediate II.

5. The heat-shrinkable and puncture-resistant polyolefin membrane material according to claim 1, characterized in that, The catalyst in step A3 is cuprous chloride. The post-processing steps in step S3 are as follows: After the reaction is complete, add 45-90 parts by weight of methanol to a three-necked flask, stir for 20-30 minutes, filter, add the filter cake and 20-30 parts by weight of methanol to a beaker, stir for 5-10 minutes, filter, and place the filter cake in a drying oven at 50-60℃ for 5-6 hours to obtain intermediate III.

6. The heat-shrinkable and puncture-resistant polyolefin membrane material according to claim 1, characterized in that, The catalyst in step A4 is one of isopropyl zirconate, n-propyl zirconate, and tetraisopropyl titanate. The post-treatment steps in step S4 are as follows: after the reaction is complete, distill under reduced pressure until no liquid flows out, slowly add 40-80 parts by weight of purified water to a three-necked flask, stir for 15-20 min, filter, wash the filter cake with 10-20 parts by weight of anhydrous ethanol, dry it under vacuum, and place the filter cake in a drying oven at 80-90℃ for 10-12 h to obtain modified ethyl cellulose.

7. A method for preparing a heat-shrinkable and puncture-resistant polyolefin membrane material as described in any one of claims 1-6, characterized in that, The following steps are included: S1. Weigh out the following components by weight: 20-30 parts modified polyolefin, 10-20 parts modified ethyl cellulose, 20-30 parts high-density polyethylene, 0.2-0.4 parts antioxidant, 0.1-0.3 parts nucleating agent, and 0.1-0.2 parts dispersant. Mix them evenly, add them to a twin-screw extruder, extrude them into strips, cool them in a water cooling tank, and then extrude them into pellets to obtain modified polyolefin granules. S2. Modified polyolefin particles are added to a three-layer co-extrusion blown film machine, and extruded through the three-layer co-extrusion blown film machine. The composite membrane is then cut, heat-treated, and stretched according to design requirements to obtain a polyolefin composite membrane.

Images