Safe and high-performance lithium ion battery diaphragm and preparation method thereof

Abstract

The invention discloses a safe and high-performance lithium ion battery diaphragm and a preparation method thereof, and belongs to the technical field of battery diaphragms. The safe and high-performance lithium ion battery diaphragm prepared by the invention is prepared by the following steps: by taking eight-arm vinyl polyhedral oligomeric silsesquioxane as an assistant cross-linking agent, mixing, melting and grafting functionalized amphiphilic polyethylene, linear polyethylene and a cross-linking agent, adding a solvent, melting and mixing, and extruding and casting to form a casting sheet; and performing two-way stretching on the casting piece at high temperature to obtain a film blank, then putting the film blank into an extraction tank filled with an extraction agent for extraction, and finally performing heat setting to obtain the safe and high-performance lithium ion battery diaphragm. Wherein the functionalized amphiphilic polyethylene is obtained by inclusion of amphiphilic polyethylene with modified cyclodextrin; the modified cyclodextrin is cyclodextrin containing unsaturated double bonds; the amphiphilic polyethylene is obtained by reaction of highly linear polyethylene containing terminal group double bonds and dimercapto polyethylene glycol.

Description

Technical Field

[0001] The present invention relates to a safe and high-performance lithium-ion battery separator and a preparation method thereof. Background Art

[0002] In recent years, due to characteristics such as high energy density, long cycle life, and environmental friendliness, lithium-ion batteries have been widely used in fields such as portable electronic devices, electric vehicles, and energy storage systems. However, with the increasing demand for high-energy-density batteries, their safety issues have become increasingly prominent. For example, short-circuit and thermal runaway accidents caused by thermal shrinkage of the separator or lithium dendrite puncture in the battery (such as the combustion of Tesla electric vehicles and the explosion of Samsung Note 7). As one of the key components of the battery, the separator plays the role of isolating the positive and negative electrodes and preventing short circuits, but its performance directly determines the thermal stability and electrochemical performance of the battery.

[0003] Currently, the mainstream commercial polyolefin separators (such as PP, PE, and multi-layer composite separators) have significant limitations due to material characteristics: First, poor thermal stability, low melting points of polyolefins (135°C for PE and 165°C for PP), and easy melting and shrinkage at high temperatures, resulting in internal short circuits in the battery; Second, strong hydrophobicity, poor wettability with polar electrolytes, and low liquid absorption rate (usually 100% - 200%), which limits the ionic conductivity (for example, the ionic conductivity of Celgard 2325 separator is only 3.5×10 -4 S·cm -1 ), thereby affecting the rate performance and cycle life; Third, insufficient mechanical strength, making it difficult to effectively inhibit lithium dendrite puncture. These problems have seriously hindered the development of high-safety and high-power lithium-ion batteries.

[0004] Therefore, the applicant has prepared a safe and high-performance lithium-ion battery separator. Summary of the Invention

[0005] The object of the present invention is to provide a safe and high-performance lithium-ion battery separator and a preparation method thereof to solve the technical problems mentioned in the above background art.

[0006] The technical solution to achieve the object of the present invention is as follows:

[0007] In a first aspect, the present invention provides a safe and high-performance lithium-ion battery separator. The safe and high-performance lithium-ion battery separator is obtained by melt grafting octa-armed vinyl polyhedral oligomeric silsesquioxane as a co-crosslinking agent, functionalized amphiphilic polyethylene, linear polyethylene, and a crosslinking agent, then adding a solvent and melt mixing, followed by extrusion and casting into a cast film, then biaxially stretching the cast film at high temperature to obtain a film blank, subsequently placing it in an extraction tank filled with an extractant for extraction, and finally performing heat setting.

[0008] Further, the functionalized amphiphilic polyethylene is obtained by inclusion of amphiphilic polyethylene with modified cyclodextrin.

[0009] Further, the modified cyclodextrin is obtained by graft reaction of unsaturated acyl chloride and cyclodextrin.

[0010] Further, the amphiphilic polyethylene is obtained by thiol-ene click reaction of highly linear polyethylene with terminal double bonds and bis-mercapto polyethylene glycol, and then graft-capped with dimethyldiallylammonium chloride through thiol-ene click reaction.

[0011] Second, a preparation method of the safe and high-performance lithium-ion battery separator as described in the first aspect is as follows:

[0012] (1) Weigh and proportion each raw material component.

[0013] (2) Stir and mix evenly the octa-armed vinyl polyhedral oligomeric silsesquioxane, functionalized amphiphilic polyethylene, linear polyethylene, and cross-linking agent dicumyl peroxide weighed in step (1), then use a single-screw extruder to carry out melt grafting at 160-210 °C, extrude and pelletize, dry, then melt-mix with the weighed solvent, then extrude and cast into a film, and then perform biaxial stretching, extraction, and heat setting on the film at high temperature to obtain a safe and high-performance lithium-ion battery separator.

[0014] Further, in step (1), each raw material component by weight includes: 0.8-1.2 parts by mass of octa-armed vinyl polyhedral oligomeric silsesquioxane, 7-9 parts by mass of functionalized amphiphilic polyethylene, 11-13 parts by mass of linear polyethylene, 0.04-0.06 parts by mass of cross-linking agent dicumyl peroxide, and 80 parts by mass of solvent.

[0015] Further, the preparation steps of the functionalized amphiphilic polyethylene are as follows: Mix the amphiphilic polyethylene block copolymer and deionized water at a mass ratio of 1:5-5.5, then stir at 300-500 rpm for 50-70 min, then add an aqueous solution of modified cyclodextrin while stirring at 1000-2000 rpm, stir at room temperature for 55-65 min, then leave overnight in an environment of 6-8 °C, and then perform freeze-drying to obtain functionalized amphiphilic polyethylene.

[0016] Further, the mass of the modified cyclodextrin is 2.1-2.3 times that of the amphiphilic polyethylene block copolymer, and the concentration of the aqueous solution of the modified cyclodextrin is 180-220 mg / mL.

[0017] Further, the modified cyclodextrin uses mono-(6-p-vinylbenzenesulfonyl)-β-cyclodextrin.

[0018] Further, the preparation steps of the amphiphilic polyethylene are as follows: Under the protection of nitrogen, 5 parts by mass of highly linear polyethylene with terminal double bonds after vacuum drying is mixed with 52 - 53 parts by mass of toluene and stirred thoroughly to dissolve. Subsequently, 4 - 4.4 parts by mass of bis-mercapto polyethylene glycol and 0.8 - 1.2 parts by mass of azobisisobutyronitrile are added. The reaction is carried out at 75 - 85 °C for 3.5 - 4.5 h. Then, 2 - 2.2 parts by mass of dimethyldiallylammonium chloride is added, and the reaction continues for 3.5 - 4.5 h. It is washed 2 - 4 times with anhydrous methanol, filtered, and dried at 40 °C for 11 - 13 h to obtain amphiphilic polyethylene.

[0019] Adopting the above technical solution, the present invention has the following beneficial effects:

[0020] (1) The safe and high-performance lithium-ion battery separator of the present invention is prepared by melt grafting octa-arm vinyl polyhedral oligomeric silsesquioxane as a co-crosslinking agent, functionalized amphiphilic polyethylene, linear polyethylene, and a crosslinking agent, then adding a solvent for melt mixing and extruding and casting into a sheet. The sheet is then subjected to biaxial stretching at a high temperature to obtain a film blank, which is then placed in an extraction tank filled with an extractant for extraction, and finally heat-set. The safe and high-performance lithium-ion battery separator prepared by the present invention has good thermal stability, ionic conductivity, and mechanical properties.

[0021] (2) The battery separator of the present invention uses octa-arm vinyl polyhedral oligomeric silsesquioxane as a co-crosslinking agent. The addition of the rigid cubic silsesquioxane octa-arm vinyl polyhedral oligomeric silsesquioxane can crosslink with functionalized amphiphilic polyethylene and linear polyethylene under the action of a crosslinking agent, effectively improving the mechanical properties of the battery separator.

[0022] (3) The functionalized amphiphilic polyethylene of the present invention is obtained by inclusion of amphiphilic polyethylene with modified cyclodextrin; wherein, the modified cyclodextrin is obtained by grafting reaction of unsaturated acyl chloride and cyclodextrin; the amphiphilic polyethylene is obtained by thiol-ene click reaction of highly linear polyethylene with terminal double bonds and one thiol group of bis-mercapto polyethylene glycol, and then grafting and capping with dimethyldiallylammonium chloride and the other thiol group of bis-mercapto polyethylene glycol through thiol-ene click reaction; the inner cavity of cyclodextrin is hydrophobic, while the surface is hydrophilic due to a large number of hydroxyl groups. This property enables the amphiphilic polyethylene to penetrate into the inner cavity of cyclodextrin in a polar medium. The hydrophobic part of the amphiphilic polyethylene will stay in the cavity of cyclodextrin, and the hydrophilic part extends outside, thus forming an inclusion complex. Then, the functionalized amphiphilic polyethylene, octavinyl polyhedral oligomeric silsesquioxane, and linear polyethylene are melt-grafted under the action of a cross-linking agent. The octavinyl polyhedral oligomeric silsesquioxane caps the functionalized amphiphilic polyethylene through unsaturated bond polymerization, preventing the cyclodextrin from re-detaching from the molecular chain when slipping on the molecular chain of the functionalized amphiphilic polyethylene. Without changing the cross-linking density, the problem of restricting the movement of molecular chains caused by the addition of octavinyl polyhedral oligomeric silsesquioxane is improved, thereby ensuring the migration of ions. When the battery separator is impacted, the impact can be buffered by the slipping of cyclodextrin, enhancing the mechanical properties of the battery separator; at the same time, introducing modified cyclodextrin, bis-mercapto polyethylene glycol, and dimethyldiallylammonium chloride into the functionalized amphiphilic polyethylene can endow the separator with the property of being hydrophilic to the electrolyte, significantly reducing the contact angle with the electrolyte and increasing the liquid absorption rate. The free ions of the functionalized amphiphilic polyethylene after being infiltrated by the electrolyte can form a synergistic transport channel with Li + in the electrolyte, and together with the porous structure of the battery separator, provide a continuous electrolyte phase to jointly improve the overall ionic conductivity. Detailed implementation manners

[0023] In order to better understand the above technical solution, the following will specifically describe the above technical solution in detail in combination with specific implementation manners.

[0024] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0025] The following embodiments are only used to more clearly illustrate the technical solution of the present invention and should not be used to limit the protection scope of the present invention.

[0026] The following are some raw materials of the examples and comparative examples:

[0027] Highly linear polyethylene with terminal double bonds: Mn GPC = 390 g / mol, the relative molecular mass distribution coefficient is 1.34, M NMR=690g / mol, end group selectivity greater than 91%, obtained by ethylene oligomerization catalyzed by a pyridine diimine iron catalyst. The preparation steps are described in Chinese invention patent CN111718382B, "Imine metal complex catalyst, preparation method thereof, and application thereof in ethylene polymerization."

[0028] Eight-arm vinyl polyhedral oligomeric silsesquioxane was purchased from Beijing Huawei Raycus Chemical Co., Ltd.

[0029] The bismercapto polyethylene glycol used is bismercapto polyethylene glycol-2000.

[0030] For the preparation method of mono-(6-p-vinylbenzenesulfonyl)-β-cyclodextrin, please refer to Chinese invention patent 201410839508.0, mono-(6-p-vinylbenzenesulfonyl)-β-cyclodextrin functional monomer and preparation method thereof.

[0031] (Example 1)

[0032] A method for preparing a safe and high-performance lithium-ion battery separator, the preparation steps are as follows:

[0033] (1) Weighing and mixing the following raw materials: 0.8 parts by mass of octa-arm vinyl polyhedral oligomeric silsesquioxane, 7 parts by mass of functionalized amphiphilic polyethylene, 13 parts by mass of linear polyethylene, 0.04 parts by mass of cross-linking agent diisopropyl peroxide, and 80 parts by mass of solvent liquid paraffin;

[0034] (2) The eight-arm vinyl polyhedral oligomeric silsesquioxane, functionalized amphiphilic polyethylene, linear polyethylene, and crosslinking agent diisopropylbenzene peroxide weighed in step (1) are stirred and mixed uniformly, and then melt-grafted at 160° C. using a single-screw extruder, extruded into granules, and dried. Subsequently, the mixture is mixed with a weighed solvent and placed in a single-screw extruder and melt-blended at 190° C. to form a homogeneous melt. The melt is then extruded from the extruder die head onto a cooling roller at 35° C., drawn into a sheet, and sliced into a cubic sheet. The sheet is then stretched at a stretching ratio of 5*5 at 125° C. to obtain a film blank, which is immersed in dichloromethane for extraction for 30 minutes, then taken out and naturally air-dried, and then heat-set at 120° C. for 5 minutes to obtain a 35 μm thick safe and high-performance lithium-ion battery separator.

[0035] The preparation steps of the functionalized amphiphilic polyethylene are as follows: an amphiphilic polyethylene block copolymer and deionized water are mixed in a mass ratio of 1:5, followed by stirring at 300 rpm for 50 minutes, then adding an aqueous solution of modified cyclodextrin while stirring at 1000 rpm, stirring at room temperature for 55 minutes and then at 6°C overnight, followed by freeze-drying to obtain the functionalized amphiphilic polyethylene.

[0036] The mass of the modified cyclodextrin is 2.1 times that of the amphiphilic polyethylene block copolymer, and the concentration of the aqueous solution of the modified cyclodextrin is 180 mg / mL.

[0037] The modified cyclodextrin used is mono-(6-vinylbenzenesulfonyl)-β-cyclodextrin.

[0038] The preparation steps of the amphiphilic polyethylene are as follows: Under the protection of nitrogen, 5 parts by mass of highly linear polyethylene with terminal double bonds after vacuum drying and 52 parts by mass of toluene are mixed and stirred thoroughly to dissolve. Subsequently, 4 parts by mass of bis-mercapto polyethylene glycol and 0.8 part by mass of azobisisobutyronitrile are added, and the reaction is carried out at 75 °C for 3.5 h. Then, 2 parts by mass of dimethyldiallylammonium chloride are added, and the reaction continues for 3.5 h. It is washed twice with anhydrous methanol, filtered, and dried at 40 °C for 11 h to obtain amphiphilic polyethylene.

[0039] (Example 2)

[0040] A preparation method of a safe and high-performance lithium-ion battery separator, and the preparation steps are as follows:

[0041] (1) Weigh and mix the raw material components: 1 part by mass of octa-armed vinyl polyhedral oligomeric silsesquioxane, 8 parts by mass of functionalized amphiphilic polyethylene, 12 parts by mass of linear polyethylene, 0.05 part by mass of crosslinking agent dicumyl peroxide, and 80 parts by mass of solvent liquid paraffin;

[0042] (2) Stir and mix evenly the octa-armed vinyl polyhedral oligomeric silsesquioxane, functionalized amphiphilic polyethylene, linear polyethylene, and crosslinking agent dicumyl peroxide weighed in step (1). Subsequently, use a single-screw extruder to carry out melt grafting at 185 °C, extrude and pelletize, and dry. Then, mix with the weighed solvent and put it into a single-screw extruder to carry out melt blending at 200 °C to form a homogeneous melt. Then, extrude the melt from the die head of the extruder onto a cooling roll at 35 °C, draw it into a sheet and cut it into cube-shaped sheets. Then, stretch it at a stretching ratio of 5×5 at 125 °C to obtain a film blank. Immerse the film blank in dichloromethane for extraction for 30 min, then take it out and air-dry it naturally, and then carry out heat setting at 120 °C for 5 min to obtain a 35-μm-thick safe and high-performance lithium-ion battery separator.

[0043] The preparation steps of the functionalized amphiphilic polyethylene are as follows: Mix the amphiphilic polyethylene block copolymer and deionized water at a mass ratio of 1:5.3, then stir at 400 rpm for 60 min. Then, add the aqueous solution of the modified cyclodextrin under stirring at 1500 rpm, stir at room temperature for 60 min, and then stay overnight in an environment at 7 °C. Subsequently, carry out freeze-drying to obtain functionalized amphiphilic polyethylene.

[0044] The mass of the modified cyclodextrin is 2.2 times that of the amphiphilic polyethylene block copolymer, and the concentration of the aqueous solution of the modified cyclodextrin is 200 mg / mL.

[0045] The modified cyclodextrin used is mono-(6-vinylbenzenesulfonyl)-β-cyclodextrin.

[0046] The preparation steps of the amphiphilic polyethylene are as follows: Under the protection of nitrogen, 5 parts by mass of highly linear polyethylene with terminal double bonds after vacuum drying and 52.5 parts by mass of toluene are mixed and stirred thoroughly until dissolved, then 4.2 parts by mass of bis-mercapto polyethylene glycol and 1 part by mass of azobisisobutyronitrile are added, and the reaction is carried out at 80 °C for 4 h. Then 2.1 parts by mass of dimethyldiallylammonium chloride is added, and the reaction continues for 4 h. It is washed 3 times with anhydrous methanol, filtered, and dried at 40 °C for 12 h to obtain amphiphilic polyethylene.

[0047] (Example 3)

[0048] A preparation method of a safe and high-performance lithium-ion battery separator, the preparation steps are as follows:

[0049] (1) Weigh and mix the raw material components: 1.2 parts by mass of octa-armed vinyl polyhedral oligomeric silsesquioxane, 9 parts by mass of functionalized amphiphilic polyethylene, 11 parts by mass of linear polyethylene, 0.06 parts by mass of crosslinking agent dicumyl peroxide, and 80 parts by mass of solvent liquid paraffin;

[0050] (2) Stir and mix the octa-armed vinyl polyhedral oligomeric silsesquioxane, functionalized amphiphilic polyethylene, linear polyethylene, and crosslinking agent dicumyl peroxide weighed in step (1) evenly, then use a single-screw extruder to carry out melt grafting at 210 °C, extrude and granulate, dry, and then mix with the weighed solvent and put it into a single-screw extruder to carry out melt blending at 210 °C to form a homogeneous melt. Then extrude the melt from the die head of the extruder onto a cooling roll at 35 °C, pull it into a sheet and cut it into cube-shaped sheets. Then stretch it at a stretching ratio of 5×5 at 125 °C to obtain a film blank. Immerse the film blank in dichloromethane for extraction for 30 min, then take it out and air-dry it naturally, and then carry out heat setting at 120 °C for 5 min to obtain a 35-μm-thick safe and high-performance lithium-ion battery separator.

[0051] The preparation steps of the functionalized amphiphilic polyethylene are as follows: Mix the amphiphilic polyethylene block copolymer and deionized water according to a mass ratio of 1:5.5, then stir at 500 rpm for 70 min, then add the aqueous solution of the modified cyclodextrin under stirring at 2000 rpm, stir at room temperature for 65 min and then overnight in an 8 °C environment, and then carry out freeze-drying to obtain functionalized amphiphilic polyethylene.

[0052] The mass of the modified cyclodextrin is 2.3 times that of the amphiphilic polyethylene block copolymer, and the concentration of the aqueous solution of the modified cyclodextrin is 220 mg / mL.

[0053] The modified cyclodextrin used is mono-(6-vinylbenzenesulfonyl)-β-cyclodextrin.

[0054] The preparation steps of the amphiphilic polyethylene are as follows: Under the protection of nitrogen, 5 parts by mass of highly linear polyethylene with terminal double bonds after vacuum drying are mixed with 53 parts by mass of toluene and stirred thoroughly to dissolve. Subsequently, 4.4 parts by mass of bis-mercapto polyethylene glycol and 1.2 parts by mass of azobisisobutyronitrile are added, and the reaction is carried out at 85 °C for 4.5 h. Then, 2.2 parts by mass of dimethyldiallylammonium chloride are added, and the reaction continues for 4.5 h. It is washed 4 times with anhydrous methanol, filtered, and dried at 40 °C for 13 h to obtain amphiphilic polyethylene.

[0055] (Comparative Example 1)

[0056] The difference between Comparative Example 1 and Example 2 is that the high-safety and high-performance lithium-ion battery separator in Comparative Example 1 does not add the crosslinking aid octavinyl polyhedral oligomeric silsesquioxane, and the remaining steps and components are the same as those in Example 2.

[0057] (Comparative Example 2)

[0058] The difference between Comparative Example 2 and Example 2 is that the functionalized amphiphilic polyethylene in Comparative Example 2 does not use modified cyclodextrin to include amphiphilic polyethylene, that is, amphiphilic polyethylene is added as the functionalized amphiphilic polyethylene, that is, modified cyclodextrin is not added, and the remaining steps and components are the same as those in Example 2.

[0059] (Comparative Example 3)

[0060] The difference between Comparative Example 3 and Example 2 is that the functionalized amphiphilic polyethylene in Comparative Example 3 is obtained by including amphiphilic polyethylene with cyclodextrin, and the remaining steps and components are the same as those in Example 2.

[0061] (Comparative Example 4)

[0062] The difference between Comparative Example 4 and Example 2 is that the high-safety and high-performance lithium-ion battery separator in Comparative Example 4 does not add functionalized amphiphilic polyethylene, and the remaining steps and components are the same as those in Example 2.

[0063] (Comparative Example 5)

[0064] The difference between Comparative Example 5 and Example 2 is that the amphiphilic polyethylene in Comparative Example 5 is obtained by a thiol-ene click reaction between highly linear polyethylene with terminal double bonds and one thiol group of bis-mercapto polyethylene glycol, and the remaining steps and components are the same as those in Example 2.

[0065] (Effect Example)

[0066] Thermal stability: The safety high-performance lithium-ion battery separators of Examples 1 to 3 and Comparative Examples 1 to 5 were placed in an oven and heat-treated at 90 °C for 1 h, and then their dimensional thermal shrinkage rates were tested to reflect the thermal stability of the composite separators.

[0067] Liquid uptake: It was determined by the differential weight method. The safety high-performance lithium-ion battery separators of Examples 1 to 3 and Comparative Examples 1 to 5 were immersed in the electrolyte for 30 min (until saturated), and the weights of the membrane before and after infiltration were recorded as Wa and Wb respectively. The liquid uptake was calculated according to the formula:

[0068] Liquid uptake(%)=(Wb-Wa) / Wa×100%.

[0069] Ionic conductivity test: The membrane was cut into circular pieces with a diameter of 16 mm using a slicing machine, and the separator was infiltrated with the electrolyte in an argon glove box, and then assembled into a button-type blocking battery with both the positive and negative electrodes being stainless steel circular pieces (14 mm); an electrochemical workstation (CS350, Wuhan KOST Instrument Co., Ltd.) was used to conduct the AC impedance test of the battery, and the test frequency was 0.01 Hz to 100 KHz. The bulk impedance R b was obtained through data fitting, and the ionic conductivity was calculated according to the formula:

[0070]

[0071] where S represents the membrane area and D represents the membrane thickness.

[0072] The following Table 1 shows the performance data results of the safety high-performance lithium-ion battery separators of Examples 1 to 3 and Comparative Examples 1 to 5:

[0073] Table 1

[0074]

[0075] It can be seen from the comparison of the performance data in Table 1 above that the safety high-performance lithium-ion battery separators prepared in Examples 1 to 3 have better thermal stability, ionic conductivity, and mechanical properties.

[0076] The difference between Comparative Example 1 and Example 2 is that the safety high-performance lithium-ion battery separator of Comparative Example 1 did not add the crosslinking aid octavinyl polyhedral oligomeric silsesquioxane, and its crosslinking degree was lower than that of Example 2, and there were fewer micropores, which affected the thermal stability, ionic conductivity, and mechanical properties of the safety high-performance lithium-ion battery separator.

[0077] The difference between Comparative Example 2 and Example 2 lies in that in Comparative Example 2, the functionalized amphiphilic polyethylene did not use modified cyclodextrin to include the amphiphilic polyethylene. That is, the amphiphilic polyethylene was added as the functionalized amphiphilic polyethylene, i.e., no modified cyclodextrin was added. It was impossible to utilize the slippage of the modified cyclodextrin on the molecular chain of the functionalized amphiphilic polyethylene to buffer the impact, which affected the liquid absorption rate and mechanical properties of the separator for safe and high-performance lithium-ion batteries.

[0078] The difference between Comparative Example 3 and Example 2 lies in that the functionalized amphiphilic polyethylene in Comparative Example 3 was obtained by including amphiphilic polyethylene with cyclodextrin. Cyclodextrin could not crosslink with the polymer network, and it was impossible to utilize the slippage of the modified cyclodextrin on the molecular chain of the functionalized amphiphilic polyethylene to buffer the impact, which affected the mechanical properties of the separator for safe and high-performance lithium-ion batteries.

[0079] The difference between Comparative Example 4 and Example 2 lies in that the separator for safe and high-performance lithium-ion batteries in Comparative Example 4 did not add functionalized amphiphilic polyethylene, which affected the ionic conductivity and mechanical properties of the separator for safe and high-performance lithium-ion batteries.

[0080] The difference between Comparative Example 5 and Example 2 lies in that the amphiphilic polyethylene in Comparative Example 5 was obtained by the thiol-ene click reaction of highly linear polyethylene with terminal double bonds and one thiol group of polyethylene glycol with double thiol groups, which affected the ionic conductivity and mechanical properties of the separator for safe and high-performance lithium-ion batteries.

[0081] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A safe and high-performance lithium-ion battery separator, characterized in that: The described safe and high-performance lithium-ion battery separator is prepared by taking octa-armed vinyl polyhedral oligomeric silsesquioxane as a co-crosslinking agent, mixing and melt-grafting functionalized amphiphilic polyethylene, linear polyethylene, and a crosslinking agent, adding a solvent for melt mixing, then extruding and casting into a sheet, biaxially stretching the sheet at a high temperature to obtain a film blank, subsequently placing it in an extraction tank filled with an extractant for extraction, and finally performing heat setting.

2. The safety high-performance lithium-ion battery separator according to claim 1, wherein The described functionalized amphiphilic polyethylene is obtained by encapsulating amphiphilic polyethylene with modified cyclodextrin.

3. The safe and high-performance lithium-ion battery separator according to claim 2, characterized in that: The described modified cyclodextrin is obtained by reacting unsaturated acyl chloride with cyclodextrin for grafting.

4. The safety and high-performance lithium-ion battery separator according to claim 2, characterized in that, The described amphiphilic polyethylene is obtained by reacting highly linear polyethylene with terminal double bonds and bis-mercapto polyethylene glycol, and then grafting and capping with dimethyldiallylammonium chloride.

5. A method for preparing a safe and high-performance lithium-ion battery separator according to any one of claims 1 to 4, characterized in that: The preparation steps are as follows: (1) Weigh and proportion each raw material component. (2) Stir and mix evenly the octa-armed vinyl polyhedral oligomeric silsesquioxane, functionalized amphiphilic polyethylene, linear polyethylene, and crosslinking agent dicumyl peroxide weighed in step (1), then use a single-screw extruder to perform melt grafting at 160 - 210 °C, extrude and pelletize, dry, then melt mix with the weighed solvent, then extrude and cast into a sheet, and then biaxially stretch, extract, and heat set the sheet at a high temperature to obtain a safe and high-performance lithium-ion battery separator.

6. The preparation method of the safe and high-performance lithium-ion battery separator according to claim 5, characterized in that, In step (1), each raw material component by weight includes: 0.8 - 1.2 parts by mass of octa-armed vinyl polyhedral oligomeric silsesquioxane, 7 - 9 parts by mass of functionalized amphiphilic polyethylene, 11 - 13 parts by mass of linear polyethylene, 0.04 - 0.06 parts by mass of crosslinking agent dicumyl peroxide, and 80 parts by mass of solvent.

7. The preparation method of the safe and high-performance lithium-ion battery separator according to claim 5, characterized in that The preparation steps of the described functionalized amphiphilic polyethylene are as follows: Mix the amphiphilic polyethylene block copolymer and deionized water at a mass ratio of 1:5 - 5.5, then stir at 300 - 500 rpm for 50 - 70 min, then add an aqueous solution of modified cyclodextrin while stirring at 1000 - 2000 rpm, stir at room temperature for 55 - 65 min, then stay overnight in an environment of 6 - 8 °C, and then perform freeze-drying to obtain functionalized amphiphilic polyethylene.

8. The preparation method of the safe and high-performance lithium-ion battery separator according to claim 7, characterized in that, The mass of the described modified cyclodextrin is 2.1 - 2.3 times that of the amphiphilic polyethylene block copolymer, and the concentration of the aqueous solution of modified cyclodextrin is 180 - 220 mg / mL.

9. The preparation method of the safe and high-performance lithium-ion battery separator according to claim 7, characterized in that The described modified cyclodextrin uses mono-(6-vinylbenzenesulfonyl)-β-cyclodextrin.

10. The preparation method of the safe and high-performance lithium-ion battery separator according to claim 7, wherein, The preparation steps of the described amphiphilic polyethylene are as follows: Under the protection of nitrogen, mix 5 parts by mass of highly linear polyethylene with terminal double bonds after vacuum drying and 52 - 53 parts by mass of toluene and stir to dissolve fully, then add 4 - 4.4 parts by mass of bis-mercapto polyethylene glycol and 0.8 - 1.2 parts by mass of azobisisobutyronitrile, react at 75 - 85 °C for 3.5 - 4.5 h, then add 2 - 2.2 parts by mass of dimethyldiallylammonium chloride, continue to react for 3.5 - 4.5 h, wash with anhydrous methanol 2 - 4 times, filter, and dry at 40 °C for 11 - 13 h to obtain amphiphilic polyethylene.

Images