An aramid-coated separator, its preparation method and application
By introducing a three-dimensional cross-linked network of styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer into the aramid-coated separator, the problem of insufficient temperature resistance and ion conductivity of the aramid-coated separator was solved, and a synergistic improvement in high heat resistance and high ion conductivity was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- TAYHO BATTERY MATERIALS TECH CO LTD
- Filing Date
- 2026-06-17
- Publication Date
- 2026-07-21
AI Technical Summary
Existing aramid-coated separators cannot simultaneously possess both high temperature resistance and high ion conductivity, resulting in insufficient safety and electrochemical performance of lithium-ion batteries at high temperatures.
A three-dimensional covalent cross-linked network was formed by mixing styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer with aramid solution and cross-linking reaction. The balance between cross-linking density and ion conduction channels was optimized to prepare aramid-coated separators.
The heat resistance and mechanical strength of the separator were improved, the membrane rupture temperature was increased to over 250℃, the thermal shrinkage rate was reduced to below 2.5%, and the ionic conductivity reached 0.44mS/cm, thus enhancing the high-temperature safety and lithium-ion conduction performance of the battery.
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Figure CN122436664A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to an aramid-coated separator, its preparation method, and its application, belonging to the field of battery separator technology. Background Technology
[0002] Thermal runaway in lithium-ion batteries is a core cause of fires and explosions, seriously threatening personal safety and property. As a critical battery component, insufficient mechanical strength of the separator can easily lead to short circuits in the electrodes, while excessively low separator rupture temperatures can cause large-area shrinkage and melting at high temperatures. Therefore, improving these two parameters is of paramount importance for enhancing the thermal dimensional stability of batteries and preventing internal short circuits and thermal runaway.
[0003] Aramid-coated separators, due to their polymer structure, significantly improve the mechanical strength and rupture temperature of the separator, effectively enhancing battery safety. Patent application CN110444714A discloses a ceramic aramid-coated separator and its preparation method; however, its heat resistance is limited by the aramid material itself, making it difficult to meet increasingly stringent requirements for thermal runaway protection. Patent application CN119253192A discloses a composite coated separator for lithium-ion batteries and its preparation method, which improves the separator's temperature resistance by forming a cross-linked structure with a meta-aramid polymer solution and an isocyanate-based inducing agent. However, the cross-linked network makes the polymer structure denser, leading to a decrease in lithium-ion conductivity. Although this disclosed technology uses a pore-forming agent to establish a porous structure, it still cannot effectively achieve a good balance between temperature resistance and lithium-ion conductivity. Patent application CN112421046A discloses a method for preparing a single-ion conductive polymer composite material for lithium anode protection in lithium metal secondary batteries. The method involves synthesizing an organic polymer through crosslinking techniques using 4-styrenesulfonyltrifluoromethanesulfonylimide lithium-based single-ion conductive organic monomers, hydroxyl-containing poly(ethylene glycol) methacrylate (PEGMA), or PEGMA and methyl-containing ethylene glycol monoethyl ether acrylate, or PEGMA and acrylonitrile, etc. This organic polymer is then mixed with conductive ceramic powder to obtain the single-ion conductive polymer composite material. This method aims to reduce concentration polarization caused by lithium salt electrolytes and inhibit lithium dendrite growth. However, this technique does not significantly improve the heat resistance and ionic conductivity of the secondary battery.
[0004] Developing an aramid membrane that simultaneously possesses high temperature resistance and high ion conductivity is of great value for obtaining lithium-ion batteries with excellent electrochemical performance and high safety performance. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this invention provides an aramid-coated diaphragm, its preparation method, and its application. The aramid-coated diaphragm exhibits high temperature resistance and high ion conductivity.
[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a method for preparing an aramid-coated separator, wherein the preparation method is as follows: S1. Dissolve the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer in a solvent to obtain a copolymer solution; mix the copolymer solution with the aramid solution evenly to obtain a coating slurry; S2. The coating slurry is coated onto the surface of the base film, heated to carry out a cross-linking reaction and dried to obtain the aramid coated diaphragm; The structure of the styrenesulfonyl (trifluoromethanesulfonyl)imine lithium-chloromethylstyrene copolymer is as follows: ; The ratio of m to n is (2-10):1, and n≥2.
[0007] Further, in step S1, the mass ratio of the styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer to the aramid polymer in the coating slurry is 1:(4-19).
[0008] Furthermore, the solvent for dissolving styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer is selected from at least one of N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, dimethylacetamide, tetrahydrofuran, acetonitrile, and acetone.
[0009] Furthermore, the solvent in the aramid solution is selected from at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide; the aramid solution contains lithium chloride as a co-solvent.
[0010] Furthermore, in step S2, the heating temperature during the crosslinking reaction and drying is 40-80℃, and the heating time is 12-72h.
[0011] Furthermore, the preparation method of the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer is as follows: Under deoxygenated conditions, monomers A and B are dissolved in a solvent, and an initiator is added to initiate polymerization. After the reaction is complete, the polymer in the reaction solution is separated and placed in an ion exchange solution containing lithium ions for full ion exchange until the content of potassium or sodium ions in the polymer is <100ppm. After rinsing and drying, styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer is obtained. The monomer A is either potassium 4-styrenesulfonyl(trifluoromethylsulfonyl)imide or sodium 4-styrenesulfonyl(trifluoromethylsulfonyl)imide; the monomer B is chloromethylstyrene.
[0012] Furthermore, the molar ratio of monomer A to monomer B is (2-10):1; the amount of initiator is 0.5-2% of the total molar amount of monomer A and monomer B. The polymerization reaction temperature is 60-80℃.
[0013] Furthermore, the initiator is selected from at least one of benzoyl peroxide and azobisisobutyronitrile; The ion exchange solution includes solute C and solvent D, wherein solute C is any one of LiCl, LiTFSI, and LiOH, and solvent D is at least one of water, methanol, or a DOL-DME mixture.
[0014] The present invention also discloses an aramid-coated separator, wherein the aramid-coated separator is prepared according to the preparation method described in the present invention.
[0015] The present invention also discloses an application of an aramid-coated separator, which is used in lithium-ion batteries.
[0016] The beneficial effects of this invention are: The aramid-coated separator of this invention achieves significant improvements in heat resistance, mechanical strength, and lithium-ion conductivity. The membrane rupture temperature is not lower than 250°C, the thermal shrinkage rate at 130°C is not higher than 2.5%, and the ionic conductivity reaches above 0.44 mS / cm. At the same time, the puncture strength is significantly enhanced. After being assembled into a battery, it exhibits excellent rate charge-discharge performance and high-temperature safety performance, thus effectively solving the technical problem that existing aramid-coated separators cannot simultaneously achieve both temperature resistance and ion conductivity.
[0017] In the preparation method of the aramid-coated separator of the present invention, a styrene-sulfonyl(trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer containing both chloromethyl crosslinking active groups and sulfonyl(trifluoromethanesulfonyl)imide lithium ion-conducting groups is introduced into the aramid coating system. The chloromethyl group is then subjected to a heating and drying process to induce alkylation of the amide groups or benzene rings of the aramid, forming a three-dimensional covalent crosslinked network. This crosslinked structure significantly improves the glass transition temperature and thermal decomposition temperature of the coating, enabling the separator to maintain dimensional stability and resist melt-rupture at high temperatures, while also enhancing the coating's puncture resistance. More importantly, during the crosslinking process, the sulfonyl(trifluoromethanesulfonyl)imide lithium groups on the copolymer side chains are firmly anchored to the aramid backbone through covalent bonds, preventing the functional groups from separating and detaching from the coating during long-term cyclic charging and discharging, thus ensuring the long-term stability of ion conduction performance.
[0018] In the preparation method of the aramid-coated separator described in this invention, a good balance is achieved between the crosslinking density and the ion conduction channel density by precisely controlling the molar ratio of ion-conducting units to crosslinking units in the copolymer, as well as the mixing ratio of the copolymer to aramid. While increasing the crosslinking density alone can further improve temperature resistance, excessively dense structures can hinder lithium-ion migration. Conversely, increasing the content of ion-conducting groups alone without sufficient crosslinking results in limited improvement in temperature resistance and easy swelling of the coating. This invention, through the synergistic optimization of the above multiple parameters, enables the crosslinking network to provide sufficient thermomechanical constraint while retaining sufficient free volume and continuous ion transport paths, thereby achieving a synergistic improvement in both temperature resistance and ion conductivity.
[0019] This invention employs a process in the copolymer preparation stage where potassium or sodium monomers are polymerized followed by ion exchange until the residual ion content is below 100 ppm. This avoids interference from residual potassium and sodium ions on the electrochemical performance of the battery and prevents side reactions caused by incompletely exchanged impurity groups during crosslinking. Simultaneously, by using appropriate crosslinking and drying conditions, the crosslinking reaction can proceed fully under mild and controllable conditions, resulting in a uniform and continuous three-dimensional network structure within the coating. This avoids both the brittleness caused by excessive crosslinking and the performance defects caused by insufficient crosslinking, ultimately yielding an aramid-coated separator with excellent overall performance. Attached Figure Description
[0020] Figure 1 Flowchart for the preparation of aramid-coated separators; Figure 2 This is an electron microscope image of the aramid-coated diaphragm prepared in Example 1. Detailed Implementation
[0021] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.
[0022] Unless otherwise defined, all technical and scientific terms used herein are consistent with the technical field to which this invention pertains. like Figure 1 As shown, a method for preparing an aramid-coated separator is described, wherein the preparation method is as follows: S1. Dissolve the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer in a solvent to obtain a copolymer solution; mix the copolymer solution with the aramid solution evenly to obtain a coating slurry; S2. The coating slurry is coated onto the surface of the base film, heated to carry out a cross-linking reaction and dried to obtain the aramid coated diaphragm; The structure of the styrenesulfonyl (trifluoromethanesulfonyl)imine lithium-chloromethylstyrene copolymer is as follows: ; The ratio of m to n is (2-10):1, and n≥2.
[0023] Preferably, the ratio of m to n is (4-8):1.
[0024] Specifically, the preparation method of the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer is as follows: (1) Under deoxygenation conditions, monomer A and monomer B are dissolved in a solvent; The monomer A is either potassium 4-styrenesulfonyl(trifluoromethylsulfonyl)imide or sodium 4-styrenesulfonyl(trifluoromethylsulfonyl)imide; the monomer B is chloromethylstyrene. The solvent is selected from any one of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), and dimethylacetamide (DMAc); The molar ratio of monomer A to monomer B is (2-10):1, and the total mass of monomer A and monomer B accounts for 3-20% of the solvent mass. Preferably, the molar ratio of monomer A to monomer B is (4-8):1.
[0025] (2) Add an initiator to the system solution of step (1) to initiate polymerization, and stop the reaction when the conversion rate is ≥95%; The initiator is selected from at least one of benzoyl peroxide and azobisisobutyronitrile; The amount of initiator used is 0.5-2% of the total molar amount of monomer A and monomer B; The polymerization reaction temperature is 60-80℃.
[0026] The method for testing the conversion rate of the polymer at a specific time is as follows: record the total mass m1 of monomer A and monomer B. When the reaction reaches a specific time, pour the reaction solution into diethyl ether or n-hexane to precipitate the polymer. Wash the polymer with n-hexane and water in sequence, then dry and weigh it. Record the mass of the dried polymer as m2, and the conversion rate is m2 / m1.
[0027] (3) Pour the reaction solution from step (2) into a poor solvent to precipitate the polymer and wash and dry it to obtain styrenesulfonyl (trifluoromethanesulfonyl)imide potassium-chloromethylstyrene copolymer or styrenesulfonyl (trifluoromethanesulfonyl)imide sodium-chloromethylstyrene copolymer; The unsuitable solvent is diethyl ether or n-hexane.
[0028] (4) The above-mentioned potassium styrene sulfonyl (trifluoromethanesulfonyl)imide-chloromethylstyrene copolymer or sodium styrene sulfonyl (trifluoromethanesulfonyl)imide-chloromethylstyrene copolymer is repeatedly immersed in ion exchange solution until the content of potassium ions or sodium ions in the polymer is <100ppm (confirmed by ICP-OES), rinsed with water or methanol and dried to obtain lithium styrene sulfonyl (trifluoromethanesulfonyl)imide-chloromethylstyrene copolymer; The ion exchange liquid includes solute C and solvent D. Solute C is any one of LiCl, LiTFSI, and LiOH. Solvent D is at least one of water, methanol, or a DOL-DME mixture, wherein the DOL-DME mixture is a mixture of 1,3-dioxolane and ethylene glycol dimethyl ether. In the embodiments of the present invention, the ion exchange liquid used is a saturated solution of solute C in solvent D.
[0029] Specifically, in step S1, the mass ratio of the styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer to the aramid polymer in the coating slurry is 1:(4-19).
[0030] Preferably, in step S1, the mass ratio of the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer to the aramid polymer in the coating slurry is 1:12.
[0031] Specifically, the solvent for dissolving lithium styrenesulfonyl (trifluoromethanesulfonyl)imide-chloromethylstyrene copolymer is selected from at least one of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), tetrahydrofuran (THF), acetonitrile, and acetone.
[0032] Specifically, the solvent in the aramid solution is selected from at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide; the aramid solution contains lithium chloride as a co-solvent, and the amount of lithium chloride added is 1%-4% of the solvent mass.
[0033] More specifically, the mass percentage of the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer in the copolymer solution is 1%-30%; The aramid polymer in the aramid solution accounts for 1%-30% by mass.
[0034] The solid content of the coating slurry is 4%-20%.
[0035] There are no major restrictions on the mass ratio of styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer in the copolymer solution, or the mass ratio of aramid polymer in the aramid solution. It is sufficient that the copolymer is uniformly dispersed to facilitate the coating process.
[0036] Specifically, in step S2, the heating temperature during the crosslinking reaction and drying is 40-80℃, and the heating time is 12-72h.
[0037] Preferably, in step S2, gradient heating is used during the crosslinking reaction and drying: heating at 40-60°C for 8-12 hours; then heating at 65-80°C for 4-8 hours.
[0038] The alkylation reaction between chloromethyl groups and aramid groups or benzene rings requires a solvent environment. Solvent molecules, on the one hand, allow the polymer chains to fully extend, ensuring effective collisions between reactive sites; on the other hand, they act as a reaction medium to promote the crosslinking process. If a one-step high-temperature drying method is used, the solvent evaporates rapidly, the coating surface cures quickly, and the residual solvent inside is insufficient to maintain the necessary reaction environment, leading to incomplete crosslinking and affecting the mechanical properties and heat resistance of the membrane. Conversely, if the temperature is maintained at a low level for an extended period, the crosslinking reaction time is too long, easily leading to over-crosslinking and low drying efficiency. Gradient heating first slowly removes some of the solvent at a lower temperature, allowing the coating to retain an appropriate amount of solvent medium while providing sufficient reaction time and a mild reaction environment for chloromethyl and aramid, promoting the uniform and complete formation of the crosslinked network. After the crosslinking reaction reaches a high conversion rate, the temperature is increased to a higher level to further remove residual solvent and promote deeper crosslinking of the remaining active sites, while simultaneously improving the density and structural stability of the coating. This gradient heating process effectively avoids the decline in mechanical properties and insufficient heat resistance caused by insufficient crosslinking, and also prevents the blockage of ion transport channels caused by excessive crosslinking or rapid solvent evaporation. It achieves the optimal balance between crosslinking density and ion conductivity, thereby maintaining excellent lithium-ion conductivity while ensuring high membrane rupture temperature, low thermal shrinkage and high puncture strength of the membrane.
[0039] Specifically, the base membrane is selected from any one of polyethylene diaphragm, polypropylene diaphragm, and polyethylene / polypropylene composite diaphragm. The base membrane used in this embodiment is selected from Xingyuan, model SW807I, but this does not constitute a limitation of the invention.
[0040] Specifically, the aramid solution is a para-aramid solution or a meta-aramid solution; in this embodiment of the invention, a meta-aramid solution is used, but this does not constitute a limitation of the invention.
[0041] More specifically, the meta-aramid solution solvent used in the embodiments of the present invention is DMAC, the polymer mass percentage is 20%, and the viscosity (25°C) is 100000 mPa·s.
[0042] An aramid-coated separator, wherein the aramid-coated separator is prepared according to the preparation method described in this invention.
[0043] An application of an aramid-coated separator, wherein the aramid-coated separator is used in a lithium-ion battery.
[0044] Example 1: Preparation of aramid-coated diaphragm.
[0045] A method for preparing an aramid-coated separator with high temperature resistance and high ion conductivity includes the following steps: (1) Under deoxygenation conditions, monomer A and monomer B are dissolved in a solvent; The monomer A is potassium 4-styrenesulfonyl (trifluoromethylsulfonyl)imide, and the monomer B is chloromethylstyrene; The solvent is N,N-dimethylformamide (DMF); The molar ratio of monomer A to monomer B is 6:1, and the total mass of monomer A and monomer B accounts for 10% of the solvent mass.
[0046] (2) Add benzoyl peroxide to the system solution in step (1) to initiate polymerization. The amount of benzoyl peroxide is 2 mol% (mole fraction) of the total amount of monomer A and monomer B. The polymerization temperature is 70℃. The reaction ends when the conversion rate is ≥95%. (3) Pour the reaction solution from step (2) into diethyl ether to precipitate the polymer and wash and dry it to obtain styrene sulfonyl (trifluoromethanesulfonyl) imine potassium-chloromethylstyrene copolymer.
[0047] (4) The above styrene sulfonyl (trifluoromethanesulfonyl)imide potassium-chloromethylstyrene copolymer was repeatedly immersed in ion exchange solution until the potassium ion content was <100ppm (confirmed by ICP-OES), rinsed with water and dried to obtain styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer. The ion exchange solution is a LiCl solution in water.
[0048] (5) Preparation of aramid coating slurry: The above-mentioned styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer was prepared into a styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer solution, and then mixed with meta-aramid solution to prepare aramid coating slurry; The styrenesulfonyl (trifluoromethanesulfonyl)imine lithium-chloromethylstyrene copolymer has the following chemical structure: The ratio of m to n is 6:1, and n≥2; The mass ratio of styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer to aramid polymer in the aramid coating slurry is 1:12. The solvent in the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer solution is N,N-dimethylformamide (DMF); The mass percentage of the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer in the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer solution is 15%. The solvent for the meta-aramid solution is a mixture of N,N-dimethylacetamide and lithium chloride (wherein the amount of lithium chloride added is 3% of the solvent mass). The meta-aramid polymer accounts for 15% of the mass of the meta-aramid solution.
[0049] (6) Preparation of aramid-coated diaphragm: The aramid coating slurry is coated on both sides of the base membrane and dried to obtain the aramid-coated diaphragm; The base film is selected from Xingyuan, model SW807I; The drying process involves heating at 40°C for 72 hours.
[0050] Example 2: Preparation of aramid-coated diaphragm.
[0051] A method for preparing an aramid-coated separator with high temperature resistance and high ion conductivity includes the following steps: (1) Under deoxygenation conditions, monomer A and monomer B are dissolved in a solvent; The monomer A is sodium 4-styrenesulfonyl (trifluoromethylsulfonyl)imide, and the monomer B is chloromethylstyrene; The solvent is N-methylpyrrolidone (NMP); The molar ratio of monomer A to monomer B is 4:1, and the total mass of monomer A and monomer B accounts for 10% of the solvent mass.
[0052] (2) Add benzoyl peroxide to the system solution in step (1) to initiate polymerization. The amount of initiator is 2 mol% (mole fraction) of the total amount of monomer A and monomer B. The polymerization temperature is 70℃. The reaction ends when the conversion rate is ≥95%.
[0053] (3) Pour the reaction solution from step (2) into diethyl ether to precipitate the polymer and wash and dry it to obtain sodium styrenesulfonyl (trifluoromethanesulfonyl)imide-chloromethylstyrene copolymer.
[0054] (4) The above-mentioned sodium styrene sulfonyl (trifluoromethanesulfonyl)imide-chloromethylstyrene copolymer was repeatedly immersed in ion exchange solution until the sodium ion content was <100ppm (confirmed by ICP-OES), rinsed with methanol and dried to obtain lithium styrene sulfonyl (trifluoromethanesulfonyl)imide-chloromethylstyrene copolymer. The ion exchange solution is a solution of solute LiCl in water.
[0055] (5) Preparation of aramid coating slurry: The above-mentioned styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer was prepared into a styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer solution, and then mixed with meta-aramid solution to prepare aramid coating slurry; The styrenesulfonyl (trifluoromethanesulfonyl)imine lithium-chloromethylstyrene copolymer has the following chemical structure: The ratio of m to n is 4:1, and n≥2; The mass ratio of styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer to aramid polymer in the aramid coating slurry is 1:12. The solvent in the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer solution is selected from N,N-dimethylformamide (DMF).
[0056] The mass percentage of the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer in the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer solution is 15%.
[0057] The solvent for the meta-aramid solution is selected from a mixture of N,N-dimethylacetamide and lithium chloride (wherein the amount of lithium chloride added is 3% of the solvent mass). The meta-aramid polymer accounts for 15% of the mass of the meta-aramid solution.
[0058] (6) Preparation of aramid-coated diaphragm: The aramid coating slurry is coated on both sides of the base membrane and dried to obtain the aramid-coated diaphragm; The base film is selected from Xingyuan, model SW807I; The drying process involves heating at 60°C for 24 hours.
[0059] Example 3: Preparation of aramid-coated diaphragm.
[0060] A method for preparing an aramid-coated separator with high temperature resistance and high ion conductivity includes the following steps: (1) Under deoxygenation conditions, monomer A and monomer B are dissolved in a solvent; The monomer A is potassium 4-styrenesulfonyl (trifluoromethylsulfonyl)imide, and the monomer B is chloromethylstyrene; The solvent is selected from N,N-dimethylformamide (DMF); The molar ratio of monomer A to monomer B is 8:1, and the total mass of monomer A and monomer B accounts for 10% of the solvent mass.
[0061] (2) Add benzoyl peroxide as an initiator to the system solution of step (1) to initiate polymerization. The amount of initiator is 2 mol% (mole fraction) of the total amount of monomer A and monomer B. The polymerization temperature is 70℃. The reaction ends when the conversion rate reaches 98%.
[0062] (3) Pour the reaction solution from step (2) into diethyl ether to precipitate the polymer and wash and dry it to obtain styrene sulfonyl (trifluoromethanesulfonyl) imine potassium-chloromethylstyrene copolymer.
[0063] (4) The above styrene sulfonyl (trifluoromethanesulfonyl)imide potassium-chloromethylstyrene copolymer was repeatedly immersed in ion exchange solution until the potassium ion content was <100ppm (confirmed by ICP-OES), rinsed with water and dried to obtain styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer. The ion exchange solution is a solution of solute LiCl in solvent water.
[0064] (5) Preparation of aramid coating slurry: The above-mentioned styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer was prepared into a styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer solution, and then mixed with meta-aramid solution to prepare aramid coating slurry; The styrenesulfonyl (trifluoromethanesulfonyl)imine lithium-chloromethylstyrene copolymer has the following chemical structure: The ratio of m to n is 8:1, and n≥2; The mass ratio of styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer to aramid polymer in the aramid coating slurry is 1:12. The solvent in the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer solution is selected from N,N-dimethylformamide (DMF); The mass percentage of the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer in the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer solution is 15%. The solvent for the meta-aramid solution is selected from a mixture of N,N-dimethylacetamide and lithium chloride (wherein the amount of lithium chloride added is 3% of the solvent mass). The meta-aramid fiber accounts for 15% of the mass of the meta-aramid fiber solution.
[0065] (6) Preparation of aramid-coated diaphragm: The aramid coating slurry is coated on both sides of the base membrane and dried to obtain the aramid-coated diaphragm; The base film is selected from Xingyuan, model SW807I; The drying process involves heating at 80°C for 12 hours.
[0066] Example 4: Preparation of aramid-coated diaphragm.
[0067] A method for preparing an aramid-coated separator with high temperature resistance and high ion conductivity includes the following steps: (1) Under deoxygenation conditions, monomer A and monomer B are dissolved in a solvent; The monomer A is potassium 4-styrenesulfonyl (trifluoromethylsulfonyl)imide, and the monomer B is chloromethylstyrene; The solvent is N,N-dimethylformamide (DMF); The molar ratio of monomer A to monomer B is 6:1, and the total mass of monomer A and monomer B accounts for 10% of the solvent mass.
[0068] (2) Add benzoyl peroxide to the system solution in step (1) to initiate polymerization. The amount of benzoyl peroxide is 2 mol% (mole fraction) of the total amount of monomer A and monomer B. The polymerization temperature is 70℃. The reaction ends when the conversion rate is ≥95%. (3) Pour the reaction solution from step (2) into diethyl ether to precipitate the polymer and wash and dry it to obtain styrene sulfonyl (trifluoromethanesulfonyl) imine potassium-chloromethylstyrene copolymer.
[0069] (4) The above styrene sulfonyl (trifluoromethanesulfonyl)imide potassium-chloromethylstyrene copolymer was repeatedly immersed in ion exchange solution until the potassium ion content was <100ppm (confirmed by ICP-OES), rinsed with water and dried to obtain styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer. The ion exchange solution is a solution of LiTFSI in a DOL-DME mixture (where the volume ratio of DOL to DME is 1:1).
[0070] (5) Preparation of aramid coating slurry: The above-mentioned styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer was prepared into a styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer solution, and then mixed with meta-aramid solution to prepare aramid coating slurry; The styrenesulfonyl (trifluoromethanesulfonyl)imine lithium-chloromethylstyrene copolymer has the following chemical structure: The ratio of m to n is 6:1, and n≥2; The mass ratio of styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer to aramid polymer in the aramid coating slurry is 1:12. The solvent in the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer solution is N,N-dimethylformamide (DMF); The mass percentage of the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer in the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer solution is 15%. The solvent for the meta-aramid solution is a mixture of N,N-dimethylacetamide and lithium chloride (wherein the amount of lithium chloride added is 3% of the solvent mass). The meta-aramid polymer accounts for 15% of the mass of the meta-aramid solution.
[0071] (6) Preparation of aramid-coated diaphragm: The aramid coating slurry is coated on both sides of the base membrane and dried to obtain the aramid-coated diaphragm; The base film is selected from Xingyuan, model SW807I; The drying process is as follows: heat at 40°C for 12 hours, then raise the temperature to 80°C and heat for 5 hours.
[0072] Example 5: Preparation of aramid-coated diaphragm.
[0073] A method for preparing an aramid-coated separator with high temperature resistance and high ion conductivity includes the following steps: (1) Under deoxygenation conditions, monomer A and monomer B are dissolved in a solvent; The monomer A is sodium 4-styrenesulfonyl (trifluoromethylsulfonyl)imide, and the monomer B is chloromethylstyrene; The solvent is N-methylpyrrolidone (NMP); The molar ratio of monomer A to monomer B is 4:1, and the total mass of monomer A and monomer B accounts for 10% of the solvent mass.
[0074] (2) Add benzoyl peroxide to the system solution in step (1) to initiate polymerization. The amount of initiator is 2 mol% (mole fraction) of the total amount of monomer A and monomer B. The polymerization temperature is 70℃. The reaction ends when the conversion rate is ≥95%.
[0075] (3) Pour the reaction solution from step (2) into diethyl ether to precipitate the polymer and wash and dry it to obtain sodium styrenesulfonyl (trifluoromethanesulfonyl)imide-chloromethylstyrene copolymer.
[0076] (4) The above-mentioned sodium styrene sulfonyl (trifluoromethanesulfonyl)imide-chloromethylstyrene copolymer was repeatedly immersed in ion exchange solution until the sodium ion content was <100ppm (confirmed by ICP-OES), rinsed with methanol and dried to obtain lithium styrene sulfonyl (trifluoromethanesulfonyl)imide-chloromethylstyrene copolymer. The ion exchange solution is a solution of solute LiCl in water.
[0077] (5) Preparation of aramid coating slurry: The above-mentioned styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer was prepared into a styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer solution, and then mixed with meta-aramid solution to prepare aramid coating slurry; The styrenesulfonyl (trifluoromethanesulfonyl)imine lithium-chloromethylstyrene copolymer has the following chemical structure: The ratio of m to n is 4:1, and n≥2; The mass ratio of styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer to aramid polymer in the aramid coating slurry is 1:12. The solvent in the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer solution is selected from N,N-dimethylformamide (DMF).
[0078] The mass percentage of the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer in the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer solution is 15%.
[0079] Specifically, the solvent for the meta-aramid solution is selected from a mixture of N,N-dimethylacetamide and lithium chloride (wherein the amount of lithium chloride added is 3% of the solvent mass). The meta-aramid polymer accounts for 15% of the mass of the meta-aramid solution.
[0080] (6) Preparation of aramid-coated diaphragm: The aramid coating slurry is coated on both sides of the base membrane and dried to obtain the aramid-coated diaphragm; The base film is selected from Xingyuan, model SW807I; The drying process is as follows: heat at 60°C for 8 hours, then raise the temperature to 70°C and heat for another 8 hours.
[0081] Comparative Example 1: Preparation of aramid-coated diaphragm.
[0082] The aramid-coated separator was prepared using the same method as in Example 1, except that styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer was not added in Comparative Example 1. The specific preparation process is as follows: (1) Preparation of aramid coating slurry: meta-aramid solution is aramid coating slurry; The meta-aramid solution is the same as in Example 1.
[0083] (2) Preparation of aramid-coated diaphragm: The aramid coating slurry is coated on the base film and dried to obtain the aramid-coated diaphragm; The base film is selected from Xingyuan, model SW807I; The thickness of the aramid coating slurry coated on both sides of the base film is the same as in Example 1.
[0084] The drying process involves heating at 40°C for 72 hours.
[0085] Comparative Example 2: Preparation of aramid-coated diaphragm.
[0086] Aramid-coated separators were prepared using the same method as in Example 1, except that the amount of styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer was increased in Comparative Example 2. The specific preparation process is as follows: Steps (1)-(4) are the same as in Example 1.
[0087] In step (5), the mass ratio of styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer to aramid polymer is 1:3, and other process conditions are the same as in Example 1.
[0088] Step (6) is the same as in Example 1.
[0089] Comparative Example 3: Preparation of aramid-coated diaphragm.
[0090] The aramid-coated separator was prepared using the same method as in Example 1, except that in the preparation of the styrenesulfonyl (trifluoromethanesulfonyl)imide potassium-chloromethylstyrene copolymer in Comparative Example 3, the molar ratio of monomer A to monomer B was 1:1, i.e., the amount of monomer B was increased. Other process conditions were the same as in Example 1.
[0091] Comparative Example 4: Preparation of aramid-coated diaphragm.
[0092] The aramid-coated separator was prepared using the same method as in Example 1, except that in Comparative Example 4, when preparing the potassium styrenesulfonyl (trifluoromethanesulfonyl)imide-chloromethylstyrene copolymer, the molar ratio of monomer A to monomer B was 15:1, i.e., the amount of monomer B was reduced and the amount of monomer A was increased. Other process conditions were the same as in Example 1.
[0093] Comparative Example 5: Preparation of aramid-coated diaphragm.
[0094] The aramid-coated separator was prepared using the same method as in Example 1, except that the drying process in Comparative Example 5 was as follows: heating at 35°C for 84 hours (i.e., lowering the drying temperature and extending the drying time). Other process conditions were the same as in Example 1.
[0095] Comparative Example 6: Preparation of aramid-coated diaphragm.
[0096] The aramid-coated separator was prepared using the same method as in Example 1, except that the drying process in Comparative Example 6 was as follows: heating at 90°C for 12 hours (i.e., increasing the drying temperature). Other process conditions were the same as in Example 1.
[0097] The membranes prepared in the above embodiments and comparative examples were subjected to performance tests, and the test methods involved are as follows.
[0098] (1) Heat shrinkage rate test: The diaphragms were placed in an oven at 130°C for 30 min to study the dimensional changes of the diaphragms before and after heat treatment.
[0099] (2) Ionic conductivity test: Ionic conductivity was determined using the AC impedance method. A coin cell (SS / separator / SS) was assembled by placing the membrane material between two stainless steel electrodes (SS). The electrolyte was LBED8-240421. Testing was performed using a CHI760E, with a frequency range of 0.01-106 Hz and an AC signal amplitude of 5 mV. The ionic conductivity σ was calculated using formula (1). σ = d / (Rb×S) (1); Where d is the thickness of the diaphragm (μm), the bulk resistance Rb (Ω) of the diaphragm can be obtained from the intersection of the real and imaginary axes of the corresponding EIS spectrum, and S represents the effective contact area between the diaphragm and the electrode (cm²). 2 ).
[0100] (3) Membrane rupture temperature test: The diaphragm rupture temperature was tested using a thermomechanical analyzer (TMA). The diaphragm sample was flatly clamped in the upper and lower fixtures of the TMA, ensuring that the sample was vertical, without slack or eccentric force. A constant preload of 0.1N was set, and the temperature was increased after the baseline was stabilized. The instrument acquired the thermal deformation displacement-temperature curve of the sample in real time. As the temperature increased, the diaphragm first underwent micropore closure and thermal shrinkage deformation. As the temperature continued to rise, the diaphragm melted and collapsed, the structure fractured, and the displacement abruptly changed and dropped. The temperature corresponding to the inflection point of this abrupt change was determined to be the diaphragm rupture temperature.
[0101] (4) Puncture strength: Cut the diaphragm into strips measuring 10cm × 20cm. Place the strips flat in the testing instrument and clamp them with a special clamp. Once ready, turn on the testing instrument and move the needle at a speed of 10mm / min. The strength value at which the needle punctures the diaphragm is the puncture strength of the diaphragm.
[0102] (5) Charge and discharge performance test: The separator was assembled into a pouch cell, with the positive electrode made of NCM811 material and the negative electrode made of graphite material. The electrolyte type was LBED8-240421. The assembled cells were subjected to room temperature charge-discharge rate and high temperature discharge rate performance tests, which were conducted according to the methods specified in GB / T 31486-2015.
[0103] Table 1 Performance test results of the diaphragm
[0104] Table 2 Battery performance test results
[0105] As can be seen from the data in Tables 1 and 2 above, Examples 1-5 are membranes prepared using the method described in this invention. These membranes achieve a good balance between the temperature resistance and lithium-ion conductivity of the coated membrane. The chloromethyl active sites in the lithium styrenesulfonyl (trifluoromethanesulfonyl)imide-chloromethylstyrene copolymer can undergo alkylation reactions with amide groups, benzene rings, or benzene rings on the aramid backbone to form covalent bonds, thereby forming a cross-linked polymer. On the one hand, the introduction of the cross-linked structure improves the temperature resistance and strength of the polymer, thus improving the heat resistance, rupture temperature, and puncture strength of the coated membrane. On the other hand, the introduction of the cross-linked structure improves the compatibility between the lithium styrenesulfonyl (trifluoromethanesulfonyl)imide-chloromethylstyrene copolymer and aramid, thereby introducing functional lithium sulfonyl (trifluoromethanesulfonyl)imide groups into the aramid, reducing the influence of the cross-linked structure on the lithium-ion conductivity of the membrane, and significantly improving the lithium-ion conductivity of the membrane. In summary, the resulting product exhibits superior strength, temperature resistance, and ion conductivity, demonstrating better electrochemical and safety performance when assembled into a battery. Furthermore, comparisons of the results from Examples 1 and 4, and Examples 2 and 5, show that gradient heating during the crosslinking reaction and drying process is more conducive to obtaining a separator with excellent overall performance. This effectively avoids the decline in mechanical properties and insufficient heat resistance caused by insufficient crosslinking, and also prevents ion transport channel blockage caused by excessive crosslinking or rapid solvent evaporation. It achieves an optimal balance between crosslinking density and ion conductivity, thus maintaining excellent lithium-ion conductivity while ensuring a high membrane rupture temperature, low thermal shrinkage, and high puncture strength. Figure 2 This is an electron microscope image of the aramid-coated diaphragm prepared in Example 1. Figure 2 It can be seen that the surface of the aramid-coated diaphragm has uniform pores.
[0106] A comparison of the results from Comparative Example 1 and Example 1 shows that the membrane rupture temperature of Comparative Example 1 is significantly lower, the thermal shrinkage rate at 130℃ is significantly higher, the puncture strength is also lower, and the ionic conductivity is slightly lower. Although the pure aramid coating possesses certain heat resistance and mechanical strength, due to the lack of chloromethyl crosslinking active sites provided by the copolymer, the aramid molecular chains cannot form a covalent crosslinking network, and the coating relies solely on intermolecular forces (such as hydrogen bonds and π-π stacking) to maintain its structure. Under high-temperature conditions, these non-covalent interactions are easily disrupted, leading to relative slippage and thermal shrinkage of the aramid molecular chains, resulting in poor dimensional stability and a lower rupture temperature. Furthermore, the pure aramid coating lacks sulfonyl (trifluoromethanesulfonyl)imide lithium functional groups, and lithium-ion conduction relies solely on the coating's own pore structure and electrolyte wettability, resulting in relatively low ionic conductivity. Therefore, it can be seen that the introduction of the copolymer in this invention plays a crucial role in balancing high temperature resistance and high ionic conductivity.
[0107] A comparison of the results from Comparative Example 2 and Example 1 shows that in Comparative Example 2, increasing the amount of lithium styrenesulfonyl (trifluoromethanesulfonyl)imide-chloromethylstyrene copolymer significantly decreased the membrane rupture temperature, significantly increased the thermal shrinkage rate at 130°C, and also decreased the ionic conductivity. The increased copolymer content resulted in a significant reduction in the aramid content, leading to insufficient amide groups and benzene ring sites on the aramid backbone in the coating layer that could participate in alkylation crosslinking. This resulted in a significantly reduced crosslinking density, preventing the formation of a complete and continuous three-dimensional covalent crosslinked network. Consequently, the thermal dimensional stability and mechanical strength of the membrane decreased. Simultaneously, insufficient crosslinking reduced the compatibility between the copolymer and aramid, and some functional lithium sulfonyl (trifluoromethanesulfonyl)imide groups failed to be effectively anchored by covalent bonds. These groups were prone to migration or aggregation during subsequent use, impairing the continuity and stability of the ion conduction channels and leading to a decrease in ionic conductivity.
[0108] A comparison of the results of Comparative Example 3 and Example 1 shows that in the preparation of the styrenesulfonyl (trifluoromethanesulfonyl)imide potassium-chloromethylstyrene copolymer in Comparative Example 3, the molar ratio of monomer A (ion-conducting unit) to monomer B (crosslinking unit) was adjusted to 1:1, which significantly increased the proportion of chloromethylstyrene monomer and decreased the proportion of ion-conducting unit. The ionic conductivity of the membrane decreased sharply, and the coating became brittle, with a slight decrease in puncture strength. The increased proportion of monomer B significantly increased the density of chloromethyl active sites in the copolymer, leading to over-crosslinking with aramid during the drying crosslinking process, forming an excessively dense three-dimensional network structure. Although the excessively dense crosslinking network further restricted the thermal motion of the aramid molecular chains, increasing the membrane rupture temperature, it also severely compressed the free volume inside the coating, blocking the lithium ion migration channels. More importantly, due to the reduced proportion of monomer A, the number of functional sulfonyl (trifluoromethanesulfonyl)imide lithium groups on the copolymer side chains decreased, resulting in a decline in intrinsic ion conduction capability. The excessive cross-linking leads to structural densification, which in turn reduces the number of ion-conducting groups, resulting in a cumulative effect that causes a severe deterioration in ion conductivity.
[0109] A comparison of the results from Comparative Example 4 and Example 1 shows that when preparing the styrenesulfonyl (trifluoromethanesulfonyl)imide potassium-chloromethylstyrene copolymer, reducing the proportion of chloromethylstyrene monomer and increasing the proportion of ion-conducting units significantly lowers the membrane rupture temperature, significantly increases the thermal shrinkage rate at 130°C, and significantly reduces the puncture strength. The reduction in the proportion of monomer B results in a severe deficiency of chloromethyl active sites in the copolymer, preventing the formation of sufficient covalent cross-links with aramid during the drying cross-linking process, leading to a sparse and incomplete cross-linking network. Insufficient cross-linking results in a lack of sufficient chemical bond constraints between aramid molecular chains, making them prone to relative slippage and thermal shrinkage at high temperatures, thus significantly reducing the membrane's thermal dimensional stability and puncture resistance. Although the sparse cross-linking network provides less physical obstruction to ion conduction channels, and the abundant sulfonyl (trifluoromethanesulfonyl)imide lithium groups provide sufficient ion transport sites, maintaining a high level of ion conductivity, this approach of sacrificing temperature resistance for ion conductivity cannot meet the comprehensive requirements of high-safety lithium-ion batteries for the membrane.
[0110] A comparison of the results from Comparative Example 5 and Example 1 shows that the crosslinking reaction needs to reach the ideal crosslinking density within appropriate temperature and time. Excessive time leads to over-alkylation between chloromethyl and aramid fibers, resulting in an overly dense three-dimensional covalent crosslinked network. Excessive crosslinking severely compresses the free volume within the coating, significantly reducing the mobility of polymer chains and obstructing the spatial channels for lithium ion migration. Furthermore, excessive crosslinking may also cause some sulfonyl (trifluoromethanesulfonyl)imide lithium functional groups to be embedded or the crosslinking network to be distorted, preventing them from effectively participating in ion conduction and further reducing ionic conductivity. In addition, excessive crosslinking increases the rigidity and decreases the flexibility of the coating, making it more prone to brittle fracture under puncture force, thus reducing puncture strength.
[0111] A comparison of the results from Comparative Example 6 and Example 1 shows that increasing the drying temperature significantly reduces the puncture strength and ionic conductivity of the diaphragm. Excessively high drying temperatures lead to rapid solvent evaporation, causing the coating surface to solidify quickly and form a dense "skin." Residual solvent inside the coating cannot escape in time, generating internal stress at high temperatures and causing the coating to crack. Simultaneously, the rapid solvent evaporation causes the alkylation crosslinking reaction between chloromethyl and aramid fibers to occur in a lack of a suitable medium, resulting in poor reaction uniformity, with some areas exhibiting excessive crosslinking while others are under-crosslinked. Over-crosslinked areas become too dense and brittle, easily developing microcracks under stress; under-crosslinked areas cannot provide sufficient thermomechanical confinement. Furthermore, coating cracks disrupt the continuity of ion conduction channels, leading to a decrease in the overall performance of the diaphragm.
[0112] This invention achieves optimal matching between crosslinking density and ion conduction channel density by precisely controlling the copolymer structure, addition ratio, and drying process, thereby realizing a synergistic improvement in temperature resistance, mechanical strength, and ion conductivity.
[0113] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0114] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.
Claims
1. A method for preparing an aramid-coated diaphragm, characterized in that, The preparation method is as follows: S1. Dissolve the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer in a solvent to obtain a copolymer solution; mix the copolymer solution with the aramid solution evenly to obtain a coating slurry; S2. The coating slurry is coated onto the surface of the base film, heated to carry out a cross-linking reaction and dried to obtain the aramid coated diaphragm; The structure of the styrenesulfonyl (trifluoromethanesulfonyl)imine lithium-chloromethylstyrene copolymer is as follows: ； The ratio of m to n is (2-10):1, and n≥2.
2. The method for preparing an aramid-coated separator according to claim 1, characterized in that, In step S1, the mass ratio of the styrene sulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer to the aramid polymer in the coating slurry is 1:(4-19).
3. The method for preparing an aramid-coated separator according to claim 1, characterized in that, The solvent for dissolving styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer is selected from at least one of N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, dimethylacetamide, tetrahydrofuran, acetonitrile, and acetone.
4. The method for preparing an aramid-coated separator according to claim 1, characterized in that, The solvent in the aramid solution is selected from at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide; the aramid solution contains lithium chloride as a co-solvent.
5. The method for preparing an aramid-coated separator according to claim 1, characterized in that, In step S2, the heating temperature during the crosslinking reaction and drying is 40-80℃, and the heating time is 12-72h.
6. The method for preparing an aramid-coated separator according to claim 1, characterized in that, The preparation method of the styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer is as follows: Under deoxygenated conditions, monomers A and B are dissolved in a solvent, and an initiator is added to initiate polymerization. After the reaction is complete, the polymer in the reaction solution is separated and placed in an ion exchange solution containing lithium ions for full ion exchange until the content of potassium or sodium ions in the polymer is <100ppm. After rinsing and drying, styrenesulfonyl (trifluoromethanesulfonyl)imide lithium-chloromethylstyrene copolymer is obtained. The monomer A is either potassium 4-styrenesulfonyl(trifluoromethylsulfonyl)imide or sodium 4-styrenesulfonyl(trifluoromethylsulfonyl)imide; the monomer B is chloromethylstyrene.
7. The method for preparing an aramid-coated separator according to claim 6, characterized in that, The molar ratio of monomer A to monomer B is (2-10):1; the amount of initiator used is 0.5-2% of the total molar amount of monomer A and monomer B. The polymerization reaction temperature is 60-80℃.
8. The method for preparing an aramid-coated separator according to claim 6, characterized in that, The initiator is selected from at least one of benzoyl peroxide and azobisisobutyronitrile; The ion exchange solution includes solute C and solvent D, wherein solute C is any one of LiCl, LiTFSI, and LiOH, and solvent D is at least one of water, methanol, or a DOL-DME mixture.
9. An aramid-coated diaphragm, characterized in that, The aramid-coated diaphragm is prepared according to the preparation method described in any one of claims 1-8.
10. An application of the aramid-coated separator according to claim 9, characterized in that, The aramid-coated separator is used in lithium-ion batteries.