Composite separator for metal ion battery and preparation method and application thereof

Abstract

The present application relates to metal ion battery and diaphragm material technical field, disclose a kind of composite diaphragm for metal ion battery and its preparation method and application, the coating of diaphragm is the mixture of polyurethane-N-isopropyl acrylamide copolymer and polyimide short fiber, with reversible gradient thermal safety protection function and metal ion in situ capture function.Polyurethane-N-isopropyl acrylamide material has temperature-sensitive phase transition characteristics, can accurately control temperature response threshold, realize full-temperature-zone differentiation protection;At the same time, polyurethane-N-isopropyl acrylamide copolymer molecular chain segment contains a large number of polar adsorption sites, can specific adsorption and fixed battery internal dissolved metal ion (for example manganese ion), effectively inhibit metal ion shuttle effect, protect negative electrode interface integrity, stabilize battery electrochemical system, substantially slow down battery capacity attenuation rate, prolong cycle life.

Description

Technical Field

[0001] This invention relates to the field of metal-ion battery and separator material technology, specifically to a composite separator for metal-ion batteries, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, long cycle life, and no memory effect, have been widely used in new energy vehicles, large-scale energy storage, and digital electronics. However, as the industry's requirements for energy density and charge / discharge rate continue to increase, the problem of localized heat accumulation and temperature surges during battery charging and discharging has become increasingly prominent. Localized micro-hot spots can easily lead to thermal runaway, fires, explosions, and other safety accidents. Thermal safety has become a core bottleneck restricting the development of the lithium-ion battery industry.

[0003] As a core insulating component of lithium-ion batteries, the separator plays a crucial role in preventing short circuits by blocking the positive and negative electrodes while simultaneously facilitating lithium-ion transport. Its thermal stability and temperature response characteristics directly determine the battery's safety threshold and cycle life. Currently, the industry commonly achieves thermal protection through temperature-sensitive modified separators, relying on the principle of blocking ion conduction at high temperatures to mitigate safety risks. While this solution addresses some safety issues, existing commercial and patented technologies still suffer from inherent and difficult-to-solve defects, failing to meet the industrialization needs of high-end lithium-ion batteries. Specifically, it faces three major technological challenges: 1) Traditional temperature-sensing separators employ a "one-size-fits-all" passive protection mechanism, lacking flexibility and exhibiting extremely low fault tolerance. Existing conventional temperature-sensing separators only set a single temperature response threshold; once the set temperature is reached, the entire separator closes its pores, thus cutting off ion conduction. In daily battery use, most overheating issues manifest as localized micro-hot spots or precursors to thermal runaway, not overall failure. However, traditional separators directly close all pores, forcing the battery to shut down and become unusable, significantly reducing its effective capacity. Furthermore, current technology cannot achieve gradient responses such as maintaining conduction at low temperatures, adaptive current limiting for localized hot spots, and global high-temperature pore closure, constantly facing the dilemma of "failing due to slight overheating and untimely high-temperature protection."

[0004] 2) Existing safety modification technologies struggle to balance thermal safety and battery cycle performance, failing to achieve synergistic performance improvements. For example, patent CN121885927A modifies the separator by adding a pentafluorocyclic triphosphazene flame-retardant additive, only enhancing the battery's high-temperature fire resistance and heat resistance through the flame-retardant component, addressing only a single safety issue. However, during the charging and discharging process of lithium-ion batteries, especially in high-energy-density batteries using ternary cathode materials, manganese ions dissolve from the material. These free manganese ions migrate to the anode, damaging the SEI film and consuming electrolyte, leading to rapid capacity decay. This patented solution and most existing safety separators lack the ability to capture metal ions, failing to improve cell cycle degradation and thus hindering the simultaneous improvement of safety performance and optimization of battery life. Furthermore, patent CN121885927A uses a PI-based separator, which has a complex manufacturing process and high cost.

[0005] 3) Traditional ceramic-modified separators have poor electrochemical performance and insufficient stability. Most mainstream functional separators on the market are modified with alumina ceramics. Ceramic powder materials are prone to agglomeration and shedding, which not only blocks the inherent pores of the separator, increases the internal resistance of the battery, and reduces the charge and discharge performance, but also reduces the energy density of the battery due to the high density and weight of the ceramic material.

[0006] In summary, existing temperature-sensing separators and safety-modified separators generally suffer from single functionality, performance imbalance, and poor adaptability. They cannot meet the diverse temperature control requirements of batteries, nor can they balance thermal safety and long-cycle performance. Therefore, developing a multifunctional separator that can achieve gradient temperature control, precisely manage local hot spots, and simultaneously ensure cycle performance has become an urgent need for the industry. Summary of the Invention

[0007] This invention aims to provide an integrated composite separator with reversible gradient thermal safety protection and in-situ metal ion capture function. By using existing mature microgravure coating and low-temperature crosslinking equipment, without adding special equipment, a copolymer of polyurethane-N-isopropylacrylamide (PU-NIPAM) and polyimide (PI) nanofibers are coated on the separator surface to form a phase change functional modification layer with gradient thermal management and efficient capture of manganese ions. This simultaneously solves two core pain points: battery temperature warning and avoidance of thermal runaway risk, and battery cycle degradation caused by metal dissolution.

[0008] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a composite separator for metal-ion batteries, characterized by comprising the following steps: S1. Prepare a polyurethane prepolymer with active double bonds at the end groups, and then add deionized water for emulsification to obtain a stable double-bond-terminated waterborne polyurethane prepolymer emulsion. S2. Under an oxygen-free atmosphere, the polyurethane (PU) aqueous prepolymer emulsion obtained in step S1 is mixed with N-isopropylacrylamide (NIPAM) thermosensitive monomer, and an initiator is added to carry out an aqueous free radical copolymerization reaction. After the reaction is completed, the resulting mother liquor is purified by dialysis to obtain polyurethane-N-isopropylacrylamide emulsion. S3. The polyurethane-N-isopropylacrylamide (PU-NIPAM) emulsion obtained in step S2, along with polyimide (PI) nanofibers and an aqueous binder, are dispersed in an aqueous solution to form a stable slurry. Subsequently, the slurry is transferred and coated onto the surface of the base film using a microgravure coating device. After cross-linking and shaping, a composite separator for metal-ion batteries with an ultra-thin organic polymer coating on the surface is obtained.

[0009] As a further preferred technical solution of the present invention, the steps for preparing a polyurethane prepolymer with active double bonds at the end groups specifically include: reacting polyether diol, isocyanate, and hydrophilic chain extender dimethylolpropionic acid (DMPA) under an inert atmosphere to generate an NCO-terminated polyurethane prepolymer; then adding hydroxyethyl methacrylate (HEMA, a double-bond end-capping monomer) for an end-capping reaction to obtain a polyurethane prepolymer with active double bonds at the end groups. The reaction solvent is a polar organic solvent, such as N-methyl-2-pyrrolidone. The inert atmosphere is preferably nitrogen or argon.

[0010] As a further preferred embodiment of the present invention, the polyether diol has a molecular weight of 1000-4000, and preferably contains polyethylene glycol, polypropylene glycol or polytetrahydrofuran diol; and / or, the isocyanate is a polyisocyanate, preferably isophorone diisocyanate (IPDI); and / or, the mass ratio of polyether diol, isocyanate, dimethylolpropionic acid, and hydroxyethyl methacrylate is 100:20-40:1-15:1-20.

[0011] As a further preferred embodiment of the present invention, the reaction temperature for generating the NCO-terminated polyurethane prepolymer is 70~90℃; the end-capping reaction temperature is 50~70℃.

[0012] As a further preferred technical solution of the present invention, the initiator is one or more of azobisisobutyronitrile (AIBN) (V-60), azobisisobutyramidine hydrochloride (AIBA) (V-50), azobiscyanopentanoic acid (ACVA) (V-501), azobisisobutyramidazole hydrochloride (AIBI) (VA-044), and azobisisopropylimidazoline (AIP) (VA-061); and / or, the temperature of the free radical copolymerization reaction is 50~65℃; and / or, the polymerization ratio (mass ratio) of the polyurethane aqueous prepolymer, N-isopropylacrylamide thermosensitive monomer, and initiator is 100:10~50:0.1~1, and the preferred ratio is 100:15~25:0.1~0.5.

[0013] As a further preferred embodiment of the present invention, the diameter of the polyimide (PI) nanofibers is 100~700nm, preferably 100~500nm; and / or, the aqueous binder is at least one of acrylic acid, acrylonitrile, and styrene-butadiene rubber.

[0014] As a further preferred technical solution of the present invention, the cross-linking and shaping temperature is 30~100℃, preferably 50~70℃.

[0015] As a further preferred technical solution of the present invention, the thickness of the organic polymer coating is ≤3µm, preferably 0.5-1.5µm; and / or, the base membrane is a polyolefin membrane, a nonwoven membrane, a fiber membrane, a polyimide membrane, or an aramid membrane.

[0016] According to a second aspect of the present invention, a composite separator for metal-ion batteries is also provided, which is prepared by the method of the first aspect. The coating of the separator is a mixture of polyurethane-N-isopropylacrylamide copolymer and polyimide short fibers, and its surface composite coating is composed of polyurethane-N-isopropylacrylamide copolymer and polyimide short fibers, which has both reversible gradient thermal safety protection function and metal ion in-situ capture function.

[0017] Specifically, the polyurethane molecular chain contains a large number of polar amide groups (-CONH-), which achieve strong adsorption of metal ions through coordination bonds; meanwhile, the temperature-sensitive monomer of N-isopropylacrylamide is selected within the temperature range of 60-70℃. The prepared polyurethane-N-isopropylacrylamide material has temperature-sensitive phase transition characteristics, which can precisely control the temperature response threshold and achieve differentiated protection across the entire temperature range: when the internal temperature of the cell is below 60℃, the material structure is stable, the pores are fully open, and it does not affect the normal operation of the battery; when micro-hot spots of 60℃-70℃ appear locally inside the cell, the coating in the corresponding area undergoes local micro-shrinkage, and the pore size is precisely adjusted to achieve local current limiting and cooling, while non-hot spot areas maintain normal conductivity; when the temperature exceeds 70℃, the coating shrinks and closes the pores, blocking ion conduction, thereby eliminating the risk of thermal runaway. Meanwhile, the polyurethane-N-isopropylacrylamide copolymer molecular chain segments contain a large number of polar adsorption sites, which can specifically adsorb and fix metal ions (such as manganese ions) dissolved inside the battery, effectively suppress the metal ion shuttle effect, protect the integrity of the negative electrode interface, stabilize the battery electrochemical system, significantly slow down the battery capacity decay rate, and extend cycle life.

[0018] Specifically, the polyimide nanofibers can impart high heat resistance (≥260℃) to the separator, ensuring that the separator does not collapse under thermal runaway conditions, thereby further improving battery safety.

[0019] According to a third aspect of the present invention, the present invention also provides the application of the composite separator for metal-ion batteries described in the second aspect in metal-ion batteries. Preferably, the metal-ion battery is a lithium-ion battery, a zinc-ion battery, or a sodium-ion battery.

[0020] This invention utilizes existing mature microgravure coating and low-temperature crosslinking equipment, without requiring additional specialized equipment, to prepare a high-performance separator for metal-ion (such as lithium-ion) batteries with a composite coating of polyurethane-N-isopropylacrylamide copolymer and polyimide short fibers. This achieves a composite separator integrating gradient reversible thermal safety protection and in-situ metal-ion capture. Compared to existing technologies, this invention offers disruptive technological advantages, achieving multiple functional breakthroughs, and specifically providing the following significant benefits: 1. Innovative graded protection mechanism to completely resolve the core contradiction in the industry. This invention is the first to achieve a differentiated protection mode of "full conduction at low temperatures, current limiting and cooling for local hot spots, and closure of the battery at high temperatures." It abandons the traditional passive protection approach of "one-size-fits-all" and can accurately identify and intervene in the early signs of battery thermal runaway, avoiding the problem of the entire battery being scrapped due to slight overheating. While significantly improving battery safety, it effectively reduces the battery scrap rate. The corresponding data is shown in Table 1.

[0021] 2. Achieve dual improvement in safety and cycle performance, breaking through the bottleneck of single function; Unlike existing technologies such as patent application CN121885927A, which can only improve safety performance, this invention can effectively capture metal ions (such as manganese ions) dissolved inside the battery while efficiently preventing the risk of battery thermal runaway, stabilize the electrochemical interface, extend battery cycle life, and achieve synergistic optimization of safety performance and cycle performance.

[0022] 3. This invention adopts a pure organic polymer modification scheme and does not use any nano-ceramic powder materials throughout the process, thus avoiding problems such as powder agglomeration, shedding and pore blockage, as well as high metal impurity content from the root; at the same time, it effectively reduces the weight of the separator, which helps to improve the energy density of the battery. Detailed Implementation

[0023] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0024] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0025] Example 1: This embodiment provides a composite separator for metal-ion batteries, which is prepared according to the following method: (1) 70 g of dimethylolpropionic acid (DMPA) and 150 g of high-purity N-methyl-2-pyrrolidone (NMP) were premixed and heated slightly to 60°C with stirring to dissolve, resulting in a transparent solution for later use. 1 kg of dehydrated polyethylene glycol (PEG1000) was added to the reactor, and stirring was started (200 rpm) while high-purity nitrogen was introduced. After adding the prepared DMPA solution, the temperature was raised to 85°C and stirred for 15 min. Then, 242 g of isophorone diisocyanate (IPDI) was slowly added dropwise to the reactor over 1 h. After the addition was complete, the temperature was maintained at 85±2°C, and the reaction was carried out for 2.5 h to generate NCO-terminated polyurethane prepolymer. Subsequently, the temperature was controlled at 70°C, and 35 g of hydroxyethyl methacrylate (HEMA, double-bond end-capping monomer) was added dropwise at a uniform rate to carry out the end-capping reaction, and the temperature was maintained for 2 h. After the reaction is complete, the temperature is lowered to room temperature, the stirring speed is increased to 1200~1500 rpm, 2 kg of deionized water is slowly added, and stirring is continued for 30 min to obtain a stable double-bond-terminated polyurethane aqueous prepolymer emulsion.

[0026] (2) Place 600g of polyurethane aqueous prepolymer emulsion and 36g of N-isopropylacrylamide thermosensitive monomer in a reaction vessel and stir at room temperature for 30min until uniformly dispersed; bubble high-purity nitrogen gas for 20min to remove oxygen from the system and prevent free radical inactivation; in a closed reaction system, maintain a constant temperature of 60℃ and slowly add 0.72g of initiator azobisisobutyronitrile (AIBN) (V-60) in batches, and continue stirring at a constant temperature for 3-4h; after the reaction is completed, cool to room temperature to obtain polyurethane-N-isopropylacrylamide copolymer mother liquor. Then, put the copolymer mother liquor into a dialysis bag and dialyze continuously with deionized water for 24h, changing the dialysate every 6h to remove unreacted monomers and other residual small molecule byproducts; after dialysis, adjust the solid content of polyurethane-N-isopropylacrylamide emulsion to 10% under low-speed stirring for later use.

[0027] (3) 1000g of the above polyurethane-N-isopropylacrylamide (PU-NIPAM) emulsion was mixed with polyimide (PI) nanofibers (200nm in diameter and 5um in length) at a ratio of 7:3 (mass ratio). The mixture was then dispersed evenly using a high-speed disperser. 40g of polyacrylic acid LA-133 solution (15% solid content) was added and stirred for 2 hours to form a stable slurry. The slurry was then transferred onto the surface of a base film (polyethylene diaphragm) using a microgravure coating machine. After drying in an oven at 60°C, a 1um thick organic polymer coating was formed on the diaphragm surface.

[0028] The above-mentioned diaphragms were subjected to physical property tests and electrical performance tests respectively: 1) Test the ionic conductivity of the diaphragm at different temperatures and the diaphragm temperature resistance at 200℃, and observe the diaphragm integrity after 30 minutes of placement.

[0029] 2) The separator was installed in a 5Ah lithium-ion soft-pack battery, and the cycle performance was tested at a 1C1C charge-discharge rate. The test was terminated when the battery capacity decayed to 80% of the initial capacity. After disassembly and testing, the metal content on the negative electrode surface of the battery was tested.

[0030] Comparative Example 1: A commercially available alumina ceramic was coated onto the surface of a polyethylene separator to prepare a ceramic separator. The ceramic separator was then loaded into a 5Ah lithium-ion pouch battery of the same specifications as in Example 1, and the separator's physical properties and the battery's electrical performance were tested using the same method.

[0031] Comparative Example 2: Polyurethane-N-isopropylacrylamide omitted from the coating 100g of polyimide (PI) nanofibers (200nm in diameter and 5µm in length) were added to 40g of polyacrylic acid LA-133 solution (15% solid content), and stirred for 2 hours to form a stable slurry. The slurry was then transferred onto the surface of a base membrane (polyethylene diaphragm) using a microgravure coating machine and dried in an oven at 60°C to form a 1µm thick coating on the diaphragm surface.

[0032] The separator obtained in Comparative Example 2 was subjected to separator property testing and battery electrical performance testing in the same manner as in Example 1.

[0033] Comparative Example 3: Polyimide nanofibers omitted from the coating (1) 70 g DMPA and 150 g high-purity NMP were premixed and gently heated to 60 °C with stirring to dissolve, resulting in a transparent solution for later use. 1 kg of dehydrated polyether diol was added to the reactor, and stirring was started (200 rpm), with high-purity nitrogen gas introduced. After adding the prepared DMPA solution, the temperature was raised to 80-85 °C and stirred for 15 min. 242 g IPDI was slowly added dropwise to the reactor over 1 h. After the addition was complete, the temperature was maintained at 85±2 °C, and the reaction was carried out for 2.5-3 h to generate NCO-terminated polyurethane prepolymer. Subsequently, the temperature was maintained at 70 °C, and 35 g HEMA was added dropwise at a uniform rate for end-capping reaction, and the temperature was maintained for 2 h. After the reaction was completed, the temperature was lowered to room temperature, the stirring speed was increased to 1200~1500 rpm, 2 kg of deionized water was slowly added, and stirring was continued for 30 min to obtain a stable double-bond-terminated polyurethane aqueous prepolymer emulsion.

[0034] (2) Place 600g of polyurethane aqueous prepolymer emulsion and 36g of N-isopropylacrylamide thermosensitive monomer in a reaction vessel and stir at room temperature for 30min until uniformly dispersed; bubble high-purity nitrogen gas for 20min to remove oxygen from the system and prevent free radical inactivation; in a closed reaction system, maintain a constant temperature of 60℃ and slowly add 0.72g of initiator azobisisobutyronitrile (AIBN) (V-60) in batches, and continue stirring at a constant temperature for 3-4h; after the reaction is completed, cool to room temperature to obtain polyurethane-N-isopropylacrylamide copolymer mother liquor. Then, put the copolymer mother liquor into a dialysis bag and dialyze continuously with deionized water for 24h, changing the dialysate every 6h to remove unreacted monomers and other residual small molecule byproducts; after dialysis, adjust the solid content of polyurethane-N-isopropylacrylamide emulsion to 10% under low-speed stirring for later use.

[0035] (3) Take 1000g of the above polyurethane-N-isopropylacrylamide (PU-NIPAM) emulsion, add 40g of polyacrylic acid LA-133 solution (solid content 15%), and stir for 2h to form a stable slurry. Use a microgravure coating machine to transfer the coating onto the surface of the base film (polyethylene diaphragm), and dry it in an oven at 60-80℃ to form a 1µm thick organic polymer coating on the diaphragm surface.

[0036] The separator obtained in Comparative Example 3 was subjected to separator property testing and battery electrical performance testing in the same manner as in Example 1.

[0037] The test data of Example 1 and Comparative Examples 1-3 are summarized in Tables 1 and 2.

[0038] Table 1 Table 2 As shown in Table 1, the lithium-ion soft-pack battery using the composite separator of the present invention exhibits the following characteristics: when the temperature is 50°C, all separator pores are open, allowing for 100% ion conduction; when the temperature is slightly heated to 60°C-70°C, compared to Comparative Examples 1-3, the separator coating of Example 1 undergoes slight shrinkage, resulting in a decrease in the ionic conductivity of the separator. This means that the separator coating of the present invention achieves current limiting in the slightly heated portion of the battery through pore size micro-adjustment, thereby achieving localized cooling; furthermore, when the temperature exceeds 80°C or higher, the coating shrinks and closes the pores, causing the ionic conductivity to drop sharply to near 0%, helping the battery block ion conduction and thus eliminating the risk of thermal runaway.

[0039] As shown in Table 2, the separator coated with polyurethane-N-isopropylacrylamide copolymer in Example 1 had fewer metal ions on the surface of the negative electrode after cycling performance. This indicates that polyurethane-N-isopropylacrylamide copolymer can effectively adsorb and fix metal ions (such as manganese ions) dissolved inside the battery, effectively suppress the metal ion shuttle effect, protect the integrity of the negative electrode interface, stabilize the battery electrochemical system, significantly slow down the battery capacity decay rate, and extend the cycle life.

[0040] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is defined only by the appended claims.

Claims

1. A method for preparing a composite separator for metal-ion batteries, characterized in that, Includes the following steps: S1. Prepare a polyurethane prepolymer with active double bonds at the end groups, and then add deionized water for emulsification to obtain a stable double-bond-terminated waterborne polyurethane prepolymer emulsion. S2. Under an oxygen-free atmosphere, the polyurethane aqueous prepolymer emulsion obtained in step S1 is mixed with N-isopropylacrylamide thermosensitive monomer, and an initiator is added to carry out an aqueous free radical copolymerization reaction. After the reaction is completed, the resulting mother liquor is purified by dialysis to obtain polyurethane-N-isopropylacrylamide emulsion. S3. The polyurethane-N-isopropylacrylamide emulsion obtained in step S2, along with polyimide nanofibers and an aqueous binder, are dispersed in an aqueous solution to form a stable slurry. Subsequently, the slurry is transferred and coated onto the surface of the base film using a microgravure coating device. After cross-linking and shaping, a composite separator for metal-ion batteries with an ultra-thin organic polymer coating on the surface is obtained.

2. The method for preparing the composite separator for metal-ion batteries according to claim 1, characterized in that, The specific steps for preparing polyurethane prepolymers with active double bonds at the end groups include: reacting polyether diol, isocyanate, and hydrophilic chain extender dimethylolpropionic acid under an inert atmosphere to generate NCO-terminated polyurethane prepolymers; then adding hydroxyethyl methacrylate for end-capping reaction to obtain polyurethane prepolymers with active double bonds at the end groups.

3. The method for preparing the composite separator for metal-ion batteries according to claim 2, characterized in that, The polyether diol has a molecular weight of 1000-4000; and / or, the isocyanate is a polyisocyanate; and / or, the mass ratio of polyether diol, isocyanate, dimethylolpropionic acid, and hydroxyethyl methacrylate is 100:20-40:1-15:1-20.

4. The method for preparing the composite separator for metal-ion batteries according to claim 2 or 3, characterized in that, The reaction temperature for generating the NCO-terminated polyurethane prepolymer is 70~90℃; the end-capping reaction temperature is 50~70℃.

5. The method for preparing the composite separator for metal-ion batteries according to claim 1, characterized in that, The initiator is one or more of azobisisobutyronitrile (AIBN), azobisisobutyramidine hydrochloride (AIBA), azobiscyanopentanoic acid (ACVA), azobisisobutyramidazole hydrochloride (AIBI), and azobisisopropylimidazoline (AIP); and / or, the temperature of the free radical copolymerization reaction is 50-65°C; and / or, the mass ratio of the polyurethane aqueous prepolymer emulsion, N-isopropylacrylamide thermosensitive monomer, and initiator is 100:10-50:0.1-1.

6. The method for preparing the composite separator for metal-ion batteries according to claim 1, characterized in that, The polyimide nanofibers have a diameter of 100-700 nm and a length of 1-30 μm; and / or the aqueous binder is at least one of acrylic acid, acrylonitrile, and styrene-butadiene rubber.

7. The method for preparing the composite separator for metal-ion batteries according to claim 1, characterized in that, The cross-linking and shaping temperature is 30~100℃.

8. The method for preparing the composite separator for metal-ion batteries according to claim 1, characterized in that, The thickness of the organic polymer coating is ≤3µm; and / or the base membrane is a polyolefin membrane, a nonwoven membrane, a fiber membrane, a polyimide membrane, or an aramid membrane.

9. A composite separator for metal-ion batteries, characterized in that, It was prepared by the method described in claim 1.

10. The application of the composite separator for metal-ion batteries according to claim 9 in metal-ion batteries.

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