Polyolefin elastomer modified co-extrusion diaphragm core layer material as well as preparation method and application thereof

Abstract

The invention discloses a polyolefin elastomer modified co-extrusion diaphragm core layer material and a preparation method and application thereof, and relates to the technical field of diaphragms.The polyolefin elastomer modified co-extrusion diaphragm core layer material is adopted, the core layer material is applied to processing of a co-extrusion diaphragm, the mechanical property of the diaphragm can be effectively improved, and the service life of the diaphragm is prolonged. The diaphragm has high tensile strength, especially tensile strength and puncture-resistant strength, the high tensile strength can ensure that the diaphragm is not easy to deform or damage in the battery assembly and use process, and the high puncture-resistant strength can resist the risk that lithium dendrites in the battery grow to puncture the diaphragm, so that the safety of the lithium battery is enhanced, and the cycle service life of the lithium battery is prolonged.

Description

Technical Field

[0001] This invention relates to the field of membrane technology, specifically to a polyolefin elastomer modified co-extruded membrane core material, its preparation method, and its application. Background Technology

[0002] With the explosive growth of the new energy vehicle and energy storage markets, higher demands are being placed on power / energy storage lithium batteries for high energy density, long cycle life, and high safety. The separator is a key inner component of lithium batteries, manufactured from polyolefin materials such as polypropylene and polyethylene using dry or wet processes. Its main functions are to separate the positive and negative electrodes, prevent short circuits, and facilitate lithium-ion transport through its microporous structure. The separator's thickness uniformity, mechanical strength, permeability, and thermal stability directly affect battery performance. However, traditional single-layer / double-layer separators suffer from bottlenecks such as excessive thickness, insufficient mechanical strength, and high thermal shrinkage, making it difficult to meet the safety requirements of lithium batteries and hindering the improvement of lithium battery energy density and safety optimization.

[0003] The mechanical properties of the separator are key factors determining the safety and reliability of lithium batteries, affecting their short-circuit withstand capability, assembly stability, and safety under abnormal conditions. Specifically, the mechanical properties of the separator are mainly reflected in two aspects: tensile strength and puncture resistance. Tensile strength reflects the separator's ability to maintain structural integrity under tensile force. During battery assembly and use, the separator may be subjected to mechanical stress. If the tensile strength is insufficient, the separator is prone to deformation or breakage, leading to electrode misalignment or contact, and thus causing a short circuit. Puncture resistance refers to the separator's ability to resist penetration by sharp objects. If the puncture resistance is insufficient, the positive and negative electrodes may come into direct contact due to the separator being punctured, leading to an internal short circuit, causing overheating, fire, or even explosion. Therefore, improving the tensile strength and puncture resistance of the separator is of great significance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a polyolefin elastomer modified co-extruded separator core layer material and its preparation method, and to apply the core layer material to the processing of co-extruded separators, which can effectively improve the mechanical properties of the separator, thereby enhancing the safety of lithium batteries and extending the cycle life of lithium batteries.

[0005] The technical problem to be solved by this invention is achieved by the following technical solution:

[0006] One of the objectives of this invention is to provide a polyolefin elastomer-modified co-extruded membrane core material, including modified POE.

[0007] Furthermore, the core layer material also includes PP or PE. That is, the core layer material can be composed of PP and modified POE, or it can be composed of PE and modified POE.

[0008] Furthermore, the modified POE accounts for 10~40wt% of the core material.

[0009] Furthermore, the modified POE is prepared by grafting POE with bis(1-vinylimidazol-2-)one.

[0010] Further, the modified POE is prepared by adding POE, bis(1-vinylimidazol-2-)one and an initiator to toluene, refluxing the mixture, cooling the reaction solution to room temperature after the reaction is completed, adding acetone to precipitate the mixture, filtering, washing, and drying to obtain the modified POE.

[0011] Furthermore, the POE exhibits a melt flow rate of 0.5~3 g / 10min under test conditions of 190℃ / 2.16 kg.

[0012] Furthermore, the initiator includes, but is not limited to, at least one of benzoyl peroxide (BPO), dicumyl peroxide (DCP), and bis-tert-butylperoxyisopropylbenzene (BIPB).

[0013] Furthermore, the mass ratio of POE, bis(1-vinylimidazol-2-)one and initiator is 100 : (10~20) : (0.1~1).

[0014] Furthermore, the core material also includes monostearate-polyethylene glycol-maleimide.

[0015] Furthermore, the monostearate-polyethylene glycol-maleimide accounts for 5-10 wt% of the core material.

[0016] The second objective of this invention is to provide a method for preparing the core layer material of the polyolefin elastomer-modified co-extruded membrane, wherein modified POE is added to PP or PE and mixed evenly to obtain the core layer material.

[0017] This invention also provides the application of the polyolefin elastomer-modified co-extruded separator core material in lithium batteries. Using PP as the outer layer material, a base film is obtained through three-layer co-extrusion casting, and a lithium battery separator is produced through processes such as annealing, stretching, and heat setting.

[0018] The beneficial effects of this invention are as follows: This invention uses polyolefin elastomer modified co-extruded separator core material and applies this core material to the processing of co-extruded separators, which can effectively improve the mechanical properties of the separator, especially tensile strength and puncture resistance. High tensile strength can ensure that the separator is not easily deformed or damaged during battery assembly and use, and high puncture resistance can resist the risk of lithium dendrite growth inside the battery puncturing the separator, thereby enhancing the safety of lithium batteries and extending the cycle life of lithium batteries. Detailed Implementation

[0019] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0020] The following descriptions of the raw materials used in the examples and comparative examples are as follows:

[0021] POE 8150 was purchased from Dow Chemical Company, USA, with a melt flow rate of 0.5 g / 10 min under test conditions of 190℃ / 2.16 kg; POE 8480 was purchased from Dow Chemical Company, USA, with a melt flow rate of 1 g / 10 min under test conditions of 190℃ / 2.16 kg; POE 6120 was purchased from ExxonMobil, with a melt flow rate of 3 g / 10 min under test conditions of 190℃ / 2.16 kg; PP 7011L1 was purchased from ExxonMobil, with a melt flow rate of 1 g / 10 min under test conditions of 230℃ / 2.16 kg; PP 7032E3 was purchased from ExxonMobil, with a melt flow rate of 4 g / 10 min under test conditions of 230℃ / 2.16 kg; LDPE 2420D was purchased from Maoming Petrochemical, with a melt flow rate of 0.3 g / 10 min under test conditions of 190℃ / 2.16 kg. g / 10 min; LDPE A6220 was purchased from Borealis, with a melt flow rate of 2.1 g / 10 min under test conditions of 190℃ / 2.16 kg; monostearate-polyethylene glycol-maleimide was purchased from Xi'an Qiyue Biotechnology Co., Ltd., with a PEG molecular weight of 1000.

[0022] Example 1

[0023] 1. Preparation of modified POE:

[0024] 100 g of POE 8150, 10 g of bis(1-vinylimidazol-2-)one and 0.3 g of BPO were added to 500 mL of toluene and refluxed for 3 h. After the reaction was completed, the reaction solution was cooled to room temperature, and then 500 mL of acetone was added to precipitate the product. The product was filtered, washed with water, and dried under vacuum at 50 °C for 8 h to obtain modified POE.

[0025] 2. Preparation of core layer material:

[0026] Modified POE was added to PP 7011L1 and mixed evenly to obtain the core layer material. The modified POE accounted for 30 wt% of the core layer material.

[0027] 3. Preparation of the three-layer co-extruded diaphragm:

[0028] Using PP 7011L1 as the outer layer material, the outer layer material and the core layer material were fed into two separate twin-screw extruders. After melting and plasticizing, they were extruded through a co-extrusion die (extrusion temperature 180~230℃), followed by traction cooling (cooling temperature 80℃, traction speed 80 m / min) to obtain a cast sheet. The cast sheet was annealed at 125℃ for 12 h, longitudinally stretched 1.5 times at 60℃, longitudinally stretched 2.5 times at 140℃, and heat-set at 130℃ for 3 min to obtain a PP / PP+POE / PP three-layer co-extruded separator. The separator thickness was 12 μm, with the core layer thickness being 5 μm.

[0029] Example 2

[0030] 1. Preparation of modified POE:

[0031] 100 g of POE 6120, 15 g of bis(1-vinylimidazol-2-)one and 0.5 g of DCP were added to 500 mL of toluene and refluxed for 5 h. After the reaction was completed, the reaction solution was cooled to room temperature, and then 500 mL of acetone was added to precipitate the product. The product was filtered, washed with water, and dried under vacuum at 50 °C for 8 h to obtain modified POE.

[0032] 2. Preparation of core layer material:

[0033] Modified POE was added to PP 7011L1 and mixed thoroughly to obtain the core layer material. The modified POE accounted for 20 wt% of the core layer material.

[0034] 3. Preparation of the three-layer co-extruded diaphragm:

[0035] Using PP 7011L1 as the outer layer material, the outer layer material and the core layer material were fed into two separate twin-screw extruders. After melting and plasticizing, they were extruded through a co-extrusion die (extrusion temperature 180~230℃), followed by traction cooling (cooling temperature 90℃, traction speed 60 m / min) to obtain a cast sheet. The cast sheet was annealed at 120℃ for 24 h, longitudinally stretched 1.2 times at 50℃, longitudinally stretched 1.5 times at 150℃, and heat-set at 140℃ for 2 min to obtain a PP / PP+POE / PP three-layer co-extruded separator. The separator thickness was 13 μm, with the core layer thickness being 5 μm.

[0036] Example 3

[0037] 1. Preparation of modified POE:

[0038] 100 g of POE 8480, 18 g of bis(1-vinylimidazol-2-)one and 0.6 g of DCP were added to 500 mL of toluene and refluxed for 4 h. After the reaction was completed, the reaction solution was cooled to room temperature, and then 500 mL of acetone was added to precipitate the product. The product was filtered, washed with water, and dried under vacuum at 50 °C for 8 h to obtain modified POE.

[0039] 2. Preparation of core layer material:

[0040] Modified POE was added to LDPE 2420D and mixed thoroughly to obtain the core material. The modified POE accounted for 10 wt% of the core material.

[0041] 3. Preparation of the three-layer co-extruded diaphragm:

[0042] Using PP 7032E3 as the outer layer material, the outer layer material and the core layer material were fed into two separate twin-screw extruders. After melting and plasticizing, they were extruded through a co-extrusion die (extrusion temperature 180~230℃), followed by traction cooling (cooling temperature 80℃, traction speed 100 m / min) to obtain a cast sheet. The cast sheet was annealed at 150℃ for 8 h, longitudinally stretched 1.5 times at 80℃, longitudinally stretched 3 times at 130℃, and heat-set at 150℃ for 3 min to obtain a PP / PE+POE / PP three-layer co-extruded separator. The separator thickness was 15 μm, with the core layer thickness being 6 μm.

[0043] Example 4

[0044] 1. Preparation of modified POE:

[0045] 100 g of POE 8480, 20 g of bis(1-vinylimidazol-2-)one and 0.8 g of BPO were added to 500 mL of toluene and refluxed for 5 h. After the reaction was completed, the reaction solution was cooled to room temperature, and then 500 mL of acetone was added to precipitate the product. The product was filtered, washed with water, and dried under vacuum at 50 °C for 8 h to obtain modified POE.

[0046] 2. Preparation of core layer material:

[0047] Modified POE was added to LDPE A6220 and mixed thoroughly to obtain the core layer material. The modified POE accounted for 40 wt% of the core layer material.

[0048] 3. Preparation of the three-layer co-extruded diaphragm:

[0049] Using PP 7032E3 as the outer layer material, the outer layer material and the core layer material were fed into two separate twin-screw extruders. After melting and plasticizing, they were extruded through a co-extrusion die (extrusion temperature 180~230℃), followed by traction cooling (cooling temperature 100℃, traction speed 60 m / min) to obtain a cast sheet. The cast sheet was annealed at 135℃ for 10 h, longitudinally stretched 1.3 times at 70℃, longitudinally stretched 2 times at 140℃, and heat-set at 120℃ for 5 min to obtain a PP / PE+POE / PP three-layer co-extruded separator. The separator thickness was 13 μm, with the core layer thickness being 5 μm.

[0050] Example 5

[0051] The method is the same as in Example 1, except that monostearate-polyethylene glycol-maleimide is added to the core material.

[0052] 1. Preparation of modified POE:

[0053] 100 g of POE 8150, 10 g of bis(1-vinylimidazol-2-)one and 0.3 g of BPO were added to 500 mL of toluene and refluxed for 3 h. After the reaction was completed, the reaction solution was cooled to room temperature, and then 500 mL of acetone was added to precipitate the product. The product was filtered, washed with water, and dried under vacuum at 50 °C for 8 h to obtain modified POE.

[0054] 2. Preparation of core layer material:

[0055] Modified POE and monostearate-polyethylene glycol-maleimide were added to PP 7011L1 and mixed evenly to obtain the core layer material. The modified POE accounted for 30 wt% of the core layer material, and the monostearate-polyethylene glycol-maleimide accounted for 5 wt%.

[0056] 3. Preparation of the three-layer co-extruded diaphragm:

[0057] Using PP 7011L1 as the outer layer material, the outer layer material and the core layer material were fed into two separate twin-screw extruders. After melting and plasticizing, they were extruded through a co-extrusion die (extrusion temperature 180~230℃), followed by traction cooling (cooling temperature 80℃, traction speed 80 m / min) to obtain a cast sheet. The cast sheet was annealed at 125℃ for 12 h, longitudinally stretched 1.5 times at 60℃, longitudinally stretched 2.5 times at 140℃, and heat-set at 130℃ for 3 min to obtain a PP / PP+POE / PP three-layer co-extruded separator. The separator thickness was 12 μm, with the core layer thickness being 5 μm.

[0058] Example 6

[0059] The method is the same as in Example 2, except that monostearate-polyethylene glycol-maleimide is added to the core material.

[0060] 1. Preparation of modified POE:

[0061] 100 g of POE 6120, 15 g of bis(1-vinylimidazol-2-)one and 0.5 g of DCP were added to 500 mL of toluene and refluxed for 5 h. After the reaction was completed, the reaction solution was cooled to room temperature, and then 500 mL of acetone was added to precipitate the product. The product was filtered, washed with water, and dried under vacuum at 50 °C for 8 h to obtain modified POE.

[0062] 2. Preparation of core layer material:

[0063] Modified POE and monostearate-polyethylene glycol-maleimide were added to PP 7011L1 and mixed evenly to obtain the core layer material. The modified POE accounted for 20 wt% of the core layer material, and the monostearate-polyethylene glycol-maleimide accounted for 10 wt%.

[0064] 3. Preparation of the three-layer co-extruded diaphragm:

[0065] Using PP 7011L1 as the outer layer material, the outer layer material and the core layer material were fed into two separate twin-screw extruders. After melting and plasticizing, they were extruded through a co-extrusion die (extrusion temperature 180~230℃), followed by traction cooling (cooling temperature 90℃, traction speed 60 m / min) to obtain a cast sheet. The cast sheet was annealed at 120℃ for 24 h, longitudinally stretched 1.2 times at 50℃, longitudinally stretched 1.5 times at 150℃, and heat-set at 140℃ for 2 min to obtain a PP / PP+POE / PP three-layer co-extruded separator. The separator thickness was 13 μm, with the core layer thickness being 5 μm.

[0066] Example 7

[0067] The method is the same as in Example 3, except that monostearate-polyethylene glycol-maleimide is added to the core material.

[0068] 1. Preparation of modified POE:

[0069] 100 g of POE 8480, 18 g of bis(1-vinylimidazol-2-)one and 0.6 g of DCP were added to 500 mL of toluene and refluxed for 4 h. After the reaction was completed, the reaction solution was cooled to room temperature, and then 500 mL of acetone was added to precipitate the product. The product was filtered, washed with water, and dried under vacuum at 50 °C for 8 h to obtain modified POE.

[0070] 2. Preparation of core layer material:

[0071] Modified POE and monostearate-polyethylene glycol-maleimide were added to LDPE 2420D and mixed evenly to obtain the core layer material. The modified POE accounted for 10 wt% of the core layer material, and the monostearate-polyethylene glycol-maleimide accounted for 8 wt%.

[0072] 3. Preparation of the three-layer co-extruded diaphragm:

[0073] Using PP 7032E3 as the outer layer material, the outer layer material and the core layer material were fed into two separate twin-screw extruders. After melting and plasticizing, they were extruded through a co-extrusion die (extrusion temperature 180~230℃), followed by traction cooling (cooling temperature 80℃, traction speed 100 m / min) to obtain a cast sheet. The cast sheet was annealed at 150℃ for 8 h, longitudinally stretched 1.5 times at 80℃, longitudinally stretched 3 times at 130℃, and heat-set at 150℃ for 3 min to obtain a PP / PE+POE / PP three-layer co-extruded separator. The separator thickness was 15 μm, with the core layer thickness being 6 μm.

[0074] Example 8

[0075] The method is the same as in Example 4, except that monostearate-polyethylene glycol-maleimide is added to the core material.

[0076] 1. Preparation of modified POE:

[0077] 100 g of POE 8480, 20 g of bis(1-vinylimidazol-2-)one and 0.8 g of BPO were added to 500 mL of toluene and refluxed for 5 h. After the reaction was completed, the reaction solution was cooled to room temperature, and then 500 mL of acetone was added to precipitate the product. The product was filtered, washed with water, and dried under vacuum at 50 °C for 8 h to obtain modified POE.

[0078] 2. Preparation of core layer material:

[0079] Modified POE and monostearate-polyethylene glycol-maleimide were added to LDPE A6220 and mixed evenly to obtain the core layer material. The modified POE accounted for 40 wt% of the core layer material, and the monostearate-polyethylene glycol-maleimide accounted for 10 wt%.

[0080] 3. Preparation of the three-layer co-extruded diaphragm:

[0081] Using PP 7032E3 as the outer layer material, the outer layer material and the core layer material were fed into two separate twin-screw extruders. After melting and plasticizing, they were extruded through a co-extrusion die (extrusion temperature 180~230℃), followed by traction cooling (cooling temperature 100℃, traction speed 60 m / min) to obtain a cast sheet. The cast sheet was annealed at 135℃ for 10 h, longitudinally stretched 1.3 times at 70℃, longitudinally stretched 2 times at 140℃, and heat-set at 120℃ for 5 min to obtain a PP / PE+POE / PP three-layer co-extruded separator. The separator thickness was 13 μm, with the core layer thickness being 5 μm.

[0082] Comparative Example 1

[0083] The core material and the three-layer co-extruded separator were prepared according to the method of Example 1, except that the modified POE was replaced with POE.

[0084] 1. Preparation of core layer material:

[0085] POE 8150 was added to PP 7011L1 and mixed thoroughly to obtain the core layer material. The proportion of POE 8150 in the core layer material was 30 wt%.

[0086] 2. Preparation of the three-layer co-extruded diaphragm:

[0087] Using PP 7011L1 as the outer layer material, the outer layer material and the core layer material were fed into two separate twin-screw extruders. After melting and plasticizing, they were extruded through a co-extrusion die (extrusion temperature 180~230℃), followed by traction cooling (cooling temperature 80℃, traction speed 80 m / min) to obtain a cast sheet. The cast sheet was annealed at 125℃ for 12 h, longitudinally stretched 1.5 times at 60℃, longitudinally stretched 2.5 times at 140℃, and heat-set at 130℃ for 3 min to obtain a PP / PP+POE / PP three-layer co-extruded separator. The separator thickness was 12 μm, with the core layer thickness being 5 μm.

[0088] Comparative Example 2

[0089] The core material and the three-layer co-extruded separator were prepared according to the method of Example 2, except that the modified POE was replaced with POE.

[0090] 1. Preparation of core layer material:

[0091] POE 6120 was added to PP 7011L1 and mixed thoroughly to obtain the core layer material. The proportion of POE 6120 in the core layer material was 20 wt%.

[0092] 2. Preparation of the three-layer co-extruded diaphragm:

[0093] Using PP 7011L1 as the outer layer material, the outer layer material and the core layer material were fed into two separate twin-screw extruders. After melting and plasticizing, they were extruded through a co-extrusion die (extrusion temperature 180~230℃), followed by traction cooling (cooling temperature 90℃, traction speed 60 m / min) to obtain a cast sheet. The cast sheet was annealed at 120℃ for 24 h, longitudinally stretched 1.2 times at 50℃, longitudinally stretched 1.5 times at 150℃, and heat-set at 140℃ for 2 min to obtain a PP / PP+POE / PP three-layer co-extruded separator. The separator thickness was 13 μm, with the core layer thickness being 5 μm.

[0094] Comparative Example 3

[0095] The core material and the three-layer co-extruded separator were prepared according to the method of Example 3, except that the modified POE was replaced with POE.

[0096] 1. Preparation of core layer material:

[0097] POE 8480 was added to LDPE 2420D and mixed thoroughly to obtain the core layer material. The proportion of POE 8480 in the core layer material was 10 wt%.

[0098] 2. Preparation of the three-layer co-extruded diaphragm:

[0099] Using PP 7032E3 as the outer layer material, the outer layer material and the core layer material were fed into two separate twin-screw extruders. After melting and plasticizing, they were extruded through a co-extrusion die (extrusion temperature 180~230℃), followed by traction cooling (cooling temperature 80℃, traction speed 100 m / min) to obtain a cast sheet. The cast sheet was annealed at 150℃ for 8 h, longitudinally stretched 1.5 times at 80℃, longitudinally stretched 3 times at 130℃, and heat-set at 150℃ for 3 min to obtain a PP / PE+POE / PP three-layer co-extruded separator. The separator thickness was 15 μm, with the core layer thickness being 6 μm.

[0100] Comparative Example 4

[0101] The core material and the three-layer co-extruded separator were prepared according to the method of Example 4, except that the modified POE was replaced with POE.

[0102] 1. Preparation of core layer material:

[0103] POE 8480 was added to LDPE A6220 and mixed thoroughly to obtain the core layer material. The proportion of POE 8480 in the core layer material was 40 wt%.

[0104] 2. Preparation of the three-layer co-extruded diaphragm:

[0105] Using PP 7032E3 as the outer layer material, the outer layer material and the core layer material were fed into two separate twin-screw extruders. After melting and plasticizing, they were extruded through a co-extrusion die (extrusion temperature 180~230℃), followed by traction cooling (cooling temperature 100℃, traction speed 60 m / min) to obtain a cast sheet. The cast sheet was annealed at 135℃ for 10 h, longitudinally stretched 1.3 times at 70℃, longitudinally stretched 2 times at 140℃, and heat-set at 120℃ for 5 min to obtain a PP / PE+POE / PP three-layer co-extruded separator. The separator thickness was 13 μm, with the core layer thickness being 5 μm.

[0106] Comparative Example 5

[0107] Modified POE, core material, and three-layer co-extruded separator were prepared according to the method of Example 4, except that maleic anhydride was used instead of bis(1-vinylimidazol-2-)one in the preparation of modified POE.

[0108] 1. Preparation of modified POE:

[0109] 100 g of POE 8480, 20 g of maleic anhydride and 0.8 g of BPO were added to 500 mL of toluene and refluxed for 5 h. After the reaction was completed, the reaction solution was cooled to room temperature and 500 mL of acetone was added to precipitate the product. The product was then filtered, washed with water, and dried under vacuum at 50 °C for 8 h to obtain modified POE.

[0110] 2. Preparation of core layer material:

[0111] Modified POE was added to LDPE A6220 and mixed thoroughly to obtain the core layer material. The modified POE accounted for 40 wt% of the core layer material.

[0112] 3. Preparation of the three-layer co-extruded diaphragm:

[0113] Using PP 7032E3 as the outer layer material, the outer layer material and the core layer material were fed into two separate twin-screw extruders. After melting and plasticizing, they were extruded through a co-extrusion die (extrusion temperature 180~230℃), followed by traction cooling (cooling temperature 100℃, traction speed 60 m / min) to obtain a cast sheet. The cast sheet was annealed at 135℃ for 10 h, longitudinally stretched 1.3 times at 70℃, longitudinally stretched 2 times at 140℃, and heat-set at 120℃ for 5 min to obtain a PP / PE+POE / PP three-layer co-extruded separator. The separator thickness was 13 μm, with the core layer thickness being 5 μm.

[0114] Comparative Example 6

[0115] Modified POE, core material, and three-layer co-extruded separator were prepared according to the method of Example 4, except that bis(1-vinylimidazol-2-)one was replaced with silane coupling agent KH570 when preparing modified POE.

[0116] 1. Preparation of modified POE:

[0117] 100 g of POE 8480, 20 g of silane coupling agent KH570 and 0.8 g of BPO were added to 500 mL of toluene and refluxed for 5 h. After the reaction was completed, the reaction solution was cooled to room temperature, and then 500 mL of acetone was added to precipitate the product. The product was filtered, washed with water, and dried under vacuum at 50 °C for 8 h to obtain modified POE.

[0118] 2. Preparation of core layer material:

[0119] Modified POE was added to LDPE A6220 and mixed thoroughly to obtain the core layer material. The modified POE accounted for 40 wt% of the core layer material.

[0120] 3. Preparation of the three-layer co-extruded diaphragm:

[0121] Using PP 7032E3 as the outer layer material, the outer layer material and the core layer material were fed into two separate twin-screw extruders. After melting and plasticizing, they were extruded through a co-extrusion die (extrusion temperature 180~230℃), followed by traction cooling (cooling temperature 100℃, traction speed 60 m / min) to obtain a cast sheet. The cast sheet was annealed at 135℃ for 10 h, longitudinally stretched 1.3 times at 70℃, longitudinally stretched 2 times at 140℃, and heat-set at 120℃ for 5 min to obtain a PP / PE+POE / PP three-layer co-extruded separator. The separator thickness was 13 μm, with the core layer thickness being 5 μm.

[0122] Comparative Example 7

[0123] A three-layer co-extruded separator was prepared according to the method in Example 4, except that PE was used as the core material when preparing the three-layer co-extruded separator.

[0124] Preparation of three-layer co-extruded membrane:

[0125] Using PP 7032E3 as the outer layer material and LDPE A6220 as the core layer material, the outer and core layer materials were fed into two separate twin-screw extruders. After melting and plasticizing, they were extruded through a co-extrusion die (extrusion temperature 180~230℃), followed by traction cooling (cooling temperature 100℃, traction speed 60 m / min) to obtain a cast sheet. The cast sheet was annealed at 135℃ for 10 h, longitudinally stretched 1.3 times at 70℃, longitudinally stretched 2 times at 140℃, and heat-set at 120℃ for 5 min to obtain a PP / PE / PP three-layer co-extruded separator. The separator thickness was 13 μm, with the core layer thickness being 5 μm.

[0126] The three-layer co-extruded diaphragms prepared in Examples 1-8 and Comparative Examples 1-7 were cut into samples with a size of 200 mm × 15 mm. The tensile strength and puncture resistance of the samples were tested using a universal testing machine. The tensile speed was 200 mm / min and the puncture speed was 50 mm / min. The test results are shown in Table 1.

[0127] Table 1 Tensile strength and puncture resistance of three-layer co-extruded separators

[0128] Longitudinal tensile strength (MPa) Puncture resistance (gf) Example 1 228 846 Example 2 204 823 Example 3 193 804 Example 4 219 835 Example 5 237 908 Example 6 220 876 Example 7 205 853 Example 8 231 891 Comparative Example 1 190 794 Comparative Example 2 173 770 Comparative Example 3 165 758 Comparative Example 4 184 782 Comparative Example 5 153 736 Comparative Example 6 146 712 Comparative Example 7 137 695

[0129] As shown in Table 1, the present invention improves the tensile strength and puncture resistance of the three-layer co-extruded diaphragm by adding an appropriate amount of modified POE to the core layer material; and further improves the tensile strength and puncture resistance of the three-layer co-extruded diaphragm by adding an appropriate amount of monostearate-polyethylene glycol-maleimide to the core layer material.

[0130] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A polyolefin elastomer-modified co-extruded membrane core layer material, characterized in that: Including modified POE.

2. The polyolefin elastomer modified co-extruded membrane core material according to claim 1, characterized in that: The core material also includes PP or PE.

3. The polyolefin elastomer modified co-extruded membrane core material according to claim 1, characterized in that: The modified POE accounts for 10~40wt% of the core material.

4. The polyolefin elastomer modified co-extruded membrane core material according to claim 1, characterized in that: The modified POE was prepared by grafting POE with bis(1-vinylimidazol-2-)one.

5. The polyolefin elastomer-modified co-extruded membrane core material according to claim 4, characterized in that, The modified POE is prepared by adding POE, bis(1-vinylimidazol-2-)one and an initiator to toluene, refluxing the mixture, cooling the reaction solution to room temperature after the reaction is complete, adding acetone to precipitate the mixture, filtering, washing, and drying to obtain the modified POE.

6. The polyolefin elastomer modified co-extruded membrane core material according to claim 5, characterized in that: The melt flow rate of the POE under the test conditions of 190℃ / 2.16 kg was 0.5~3 g / 10 min.

7. The polyolefin elastomer modified co-extruded membrane core material according to claim 5, characterized in that: The initiator is at least one of benzoyl peroxide, dicumyl peroxide, and bis-tert-butylperoxyisopropylbenzene.

8. The polyolefin elastomer modified co-extruded membrane core material according to claim 5, characterized in that: The mass ratio of POE, bis(1-vinylimidazol-2-)one and initiator is 100 : (10~20) : (0.1~1).

9. A method for preparing the polyolefin elastomer modified co-extruded membrane core material according to any one of claims 1 to 8, characterized in that: Modified POE is added to PP or PE and mixed evenly to obtain the core material.

10. The application of the polyolefin elastomer modified co-extruded separator core material according to any one of claims 1 to 8 in lithium batteries.