Lithium ion battery flame-retardant diaphragm coating as well as preparation method and application thereof

Abstract

The invention discloses a lithium ion battery flame-retardant diaphragm coating and a preparation method and application thereof, and belongs to the technical field of battery diaphragms, the coating comprises a base membrane and a coating layer, the coating layer contains 10%-20% of an APP-coated Co-MOF composite material, 1%-5% of a fluororesin binder and the balance of an N-methyl pyrrolidone solvent, and the base membrane is a polypropylene diaphragm. The preparation method comprises the following steps: preparing the APP (at) Co-MOF composite material, preparing coating slurry, coating with a micro gravure roller, and drying at 60 DEG C. Through a physical barrier-chemical flame retardant-ion regulation triple synergistic mechanism, the diaphragm is kept stable in structure at 150 DEG C, the flame retardance is remarkably improved, meanwhile, the cycle life is prolonged by more than 5 times, the charge transfer impedance is reduced by 30%, and the ionic conductivity reaches 1.2 * 10 <-3 > S / cm. The coating is suitable for portable electronic products, energy storage facilities and lithium ion batteries for new energy automobiles, the contradiction between the thermal runaway hidden danger and electrochemical performance of a traditional diaphragm is solved, the process is easy to industrialize, and the application prospect is wide.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, specifically relating to a flame-retardant separator coating for lithium-ion batteries, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, due to their high energy density and long cycle life, have been widely used in portable electronic devices, electric vehicles, and large-scale energy storage systems. However, their safety issues, especially the risk of fire or even explosion caused by thermal runaway, remain a key hidden danger restricting their further development. Currently, most commercial lithium-ion batteries use carbonate-based organic liquid electrolytes and polyolefin (such as polyethylene PE and polypropylene PP) microporous membranes. Although these membranes have good electrochemical stability and low resistance, their melting point is low (PP is about 165°C), and they will experience severe thermal shrinkage at temperatures far below their melting point (such as above 130°C). When abnormal heat is generated inside the battery, the shrinkage or melting of the membrane can easily lead to direct contact between the positive and negative electrodes, causing an internal short circuit. This instantly generates a large amount of heat and ignites the flammable liquid electrolyte, thereby inducing a violent thermal runaway chain reaction.

[0003] To improve the safety of diaphragms, the industry has tried various methods, such as: 1) Develop ceramic coated membranes to improve thermal stability by coating with inorganic particles such as Al2O3 and SiO2, but often face problems such as easy coating peeling, poor wettability with electrolyte, and limited improvement in ionic conductivity. 2) Flame retardants are introduced by surface modification or blending, but they are often difficult to put into practical use due to poor compatibility between the flame retardant and the matrix, easy migration, or negative impact on electrochemical performance (such as increased impedance and catalytic side reactions). 3) Research on solid electrolytes or high heat-resistant polymer membranes (such as polyimide PI) is being conducted, but challenges such as high cost, high interfacial impedance, or insufficient mechanical properties are being faced.

[0004] Therefore, designing and preparing a novel modified separator that is compatible with existing battery systems, significantly improves the flame retardancy and thermal dimensional stability of the separator, and does not impair or even improve its ion conductivity and electrochemical cycling stability has become a technical bottleneck that urgently needs to be overcome in this field. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a flame-retardant separator coating for lithium-ion batteries, its preparation method and application, to solve the technical problems of existing polyolefin separators having poor heat resistance and being prone to shrinkage and melting at high temperatures, resulting in a high risk of battery thermal runaway, and existing improvement solutions being unable to simultaneously achieve excellent flame retardancy, high thermal stability and good electrochemical performance.

[0006] The present invention adopts the following technical solution: A flame-retardant separator coating for lithium-ion batteries includes a base film and a coating layer coated on the base film; the coating layer contains APP@Co-MOF composite material.

[0007] Preferably, by weight fraction, the coating layer comprises the following components: 10% to 20% APP@Co-MOF composite material, 1% to 5% binder, and the balance being a solvent, wherein the solvent is N-methylpyrrolidone.

[0008] Preferably, the adhesive is a fluoropolymer adhesive.

[0009] Preferably, the base membrane is a polypropylene diaphragm.

[0010] Another technical solution of the present invention is a method for preparing a flame-retardant separator coating for lithium-ion batteries, comprising the following steps: S1. Cobalt nitrate pentahydrate and ammonium polyphosphate are dissolved in methanol, 2-methylimidazole is added, and after stirring and dissolving, the mixture is aged at room temperature, filtered, washed, and dried to obtain a flame retardant. The flame retardant and binder are dissolved in N-methylpyrrolidone and stirred to obtain a mixed solution. The mixed solution is coated on a base film and dried to obtain an APP@Co-MOF composite material coating. S2. Add the APP@Co-MOF composite material and binder to an N-methylpyrrolidone solution and stir to obtain a coating slurry; S3. The coating slurry obtained in step S2 is uniformly coated onto the base film, dried and rolled up to obtain the flame-retardant separator coating for lithium-ion batteries.

[0011] Preferably, in step S1, the stirring and dissolving time is 5 to 10 minutes, the drying temperature is 60 to 90°C, and the time is 10 to 12 hours.

[0012] Preferably, in step S1, the flame retardant and binder are dissolved in N-methylpyrrolidone and then stirred for 20 to 24 hours.

[0013] Preferably, in step S1, after the mixed solution is coated onto the base film, it is dried at 60–90°C for 5–7 hours.

[0014] Preferably, in step S2, the stirring time is 20 to 25 hours and the rotation speed is 100 to 1200 rpm.

[0015] Another technical solution of the present invention is a lithium-ion battery that uses the aforementioned lithium-ion battery flame-retardant separator coating or the lithium-ion battery flame-retardant separator coating prepared by the aforementioned preparation method.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: A novel flame-retardant separator coating for lithium-ion batteries combines ammonium polyphosphate (APP) with a cobalt-based metal-organic framework (Co-MOF) to form a novel functional material (APP@Co-MOF). This breakthrough overcomes the performance limitations of existing single-polymer separators by constructing a dual protection system of physical barrier and chemical flame retardancy through the synergistic effect of APP and Co-MOF. APP decomposes upon heating to produce phosphoric acid, which catalyzes the formation of char, while Co-MOF promotes the flame-retardant reaction through metal ion catalysis. The combination of these two technologies addresses the shortcomings of traditional separators, such as low ignition point and high-temperature failure. Simultaneously, this structure does not sacrifice the ion transport channels of the separator, ensuring that the basic electrochemical functions of the battery remain unaffected. Compared to traditional separators without a coating, this design achieves a unified approach of flame retardant protection and electrochemical compatibility at the structural level, representing a key structural design for solving the thermal runaway problem in lithium-ion batteries.

[0017] Furthermore, an APP@Co-MOF content of 10%~20% ensures sufficient flame-retardant active components to form an effective flame-retardant barrier, while avoiding clogging of the base film pores and affecting ion conduction due to excessive content; a binder content of 1%~5% ensures a firm bond between the coating layer and the base film, preventing coating peeling during cycling, while also preventing increased ion transport resistance due to excessive binder; N-methylpyrrolidone, as a solvent, has excellent solubility for all components, ensuring uniform dispersion of the slurry and providing a good foundation for subsequent coating processes.

[0018] Furthermore, fluoropolymer binders (especially PVDF) exhibit excellent chemical stability and electrochemical compatibility with lithium-ion battery systems, and do not undergo side reactions with the electrolyte. Simultaneously, PVDF possesses good adhesion and film-forming properties, ensuring that APP@Co-MOF particles firmly adhere to the base film surface, forming a stable, uniform coating structure with a certain porosity. This structure neither completely blocks the original pores of the base film, affecting ion passage, nor hinders the formation of an effective functional layer. In addition, PVDF itself also possesses a certain degree of heat resistance, further enhancing the thermal stability of the entire coating system.

[0019] Furthermore, the coating technology of this invention is a modification specifically targeting the core weakness of PP membranes: poor heat resistance. Applying the APP@Co-MOF coating of this invention to PP membranes can significantly improve their safety shortcomings while retaining their original advantages such as low cost and easy processing, endowing them with excellent flame retardant and high-temperature resistance properties, and achieving a performance leap for older platforms.

[0020] A method for preparing a flame-retardant separator coating for lithium-ion batteries is disclosed. This method ensures high purity and thorough compounding of the flame retardant through methanol dissolution, room temperature aging, and directional washing and drying. Prolonged stirring ensures uniform dispersion of the slurry components, preventing agglomeration. The coating and drying process is gentle and does not damage the structure of the base film or composite material. The entire process involves no harsh reaction conditions, and all equipment used is conventional chemical production equipment, making operation simple and easy to control. The performance of the products from the preceding steps directly guarantees the effectiveness of subsequent processes; for example, high-purity flame retardants ensure the flame-retardant efficiency of the slurry, and uniform slurry ensures consistent coating thickness. This method solves the problems of complex processes, high costs, and large performance fluctuations in traditional flame-retardant separator preparation, achieving a balance between efficient preparation and stable performance.

[0021] Furthermore, the stirring time is sufficient to ensure that the raw materials are fully mixed and react to form the APP@Co-MOF composite structure. A drying temperature of 60-90℃ is a mild and effective range, which thoroughly removes solvents such as methanol while avoiding premature decomposition of APP or destruction of the Co-MOF structure due to excessively high temperatures. A drying time of 10-12 hours ensures complete drying of the material, resulting in a free-flowing powdered flame retardant (APP@Co-MOF precursor).

[0022] Furthermore, the flame retardant and binder are stirred in NMP for 20-24 hours to ensure that the APP@Co-MOF composite particles and PVDF binder achieve thorough mixing and dissolution at the molecular level in the NMP solvent. Prolonged and vigorous stirring helps break up particle agglomeration, allowing the PVDF molecular chains to fully extend and coat or connect the composite material particles, forming a uniform, stable slurry system with suitable viscosity.

[0023] Furthermore, the drying conditions following the application of the mixed solution to the base film allow for the gentle and complete evaporation of the NMP solvent at a specific temperature, while the PVDF binder cures, firmly fixing the APP@Co-MOF composite material to the base film surface and forming a dense and porous functional coating. A drying time of 5-7 hours ensures complete solvent removal, preventing residual solvent from affecting battery performance.

[0024] Furthermore, the rotation speed range of 100-1200 rpm provides flexibility, allowing adjustment based on the slurry viscosity and solids content. Low-speed stirring facilitates initial dispersion and prevents splashing; high-speed shear stirring further deagglomerates particles, achieving better dispersion and ensuring uniform coating thickness, smooth surface, and consistent performance.

[0025] A new lithium-ion battery technology has been developed that solves the thermal runaway problem in various scenarios and improves key performance aspects such as cycle life and charge-discharge stability, meeting the differentiated needs of different applications. Furthermore, this coating is compatible with existing lithium-ion battery production systems, requiring no significant modifications to the battery structure and directly replacing traditional separators, making it easy to apply and widely adopted. Its application not only expands the safe usage boundaries of lithium-ion batteries but also provides crucial material support for the commercialization of high-energy-density batteries, demonstrating significant market value.

[0026] In summary, this invention achieves a synergistic improvement in thermal stability and flame retardancy through the APP@Co-MOF composite system, optimizes component ratios and process parameters to ensure electrochemical performance, adapts to existing substrates and production systems to reduce costs, covers multiple application scenarios, and solves the core contradiction between safety and performance in lithium-ion batteries.

[0027] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the following description of the relative embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 SEM comparison images of PP separator and APP@Co-MOF@PP separator; Figure 2 A comparison of the thermal stability of PP separator and APP@Co-MOF@PP separator; Figure 3 The image shows a comparison of the flame retardant properties of different diaphragms, where (a) is a PP diaphragm and (b) is an APP@Co-MOF@PP diaphragm. Figure 4 The graph shows a comparison of the cycle capacity of different membranes, where (a) is a PP membrane and (b) is an APP@Co-MOF@PP membrane. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0032] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0033] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0034] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0035] In this invention, unless otherwise specified, the numerical range "a~b" represents an abbreviation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" means that all real numbers between "6~22" have been listed in this document, and "6~22" is just an abbreviation of these numerical combinations.

[0036] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0037] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0038] In this invention, unless otherwise stated, the various reaction or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0039] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0040] This invention provides a flame-retardant separator coating for lithium-ion batteries, its preparation method, and its application. Through the structural design and optimized process of the base film + APP@Co-MOF composite coating layer, a breakthrough improvement in the performance of lithium-ion battery separators is achieved. In terms of thermal stability, the separator maintains its shape at 150℃ without significant shrinkage or curling, solving the problem of high-temperature failure of traditional polypropylene separators. Flame retardancy is significantly enhanced, and shrinkage is greatly reduced, effectively suppressing the risk of fire caused by thermal runaway. Excellent electrochemical performance is achieved, with cycle life extended by more than 5 times, specific capacity maintained at 450mAh / g with only 13.5% capacity decay, charge transfer impedance reduced by 30%, and ionic conductivity reaching 1.2×10⁻⁶. -3The battery exhibits a high energy density (S / cm), stable charge and discharge process, and low diffusion resistance. Furthermore, its fabrication process is simple and controllable, with moderate cost, compatible with existing production systems, and applicable to a wide range of scenarios. It successfully balances high energy density and safety performance, providing key technological support for the next generation of high-performance lithium-ion batteries.

[0041] The present invention provides a flame-retardant separator coating for lithium-ion batteries, comprising a base film and a coating layer; the coating layer comprises APP@Co-MOF composite material.

[0042] A method for preparing a flame-retardant separator coating for lithium-ion batteries includes the following steps: S1. Cobalt nitrate pentahydrate and ammonium polyphosphate are dissolved in methanol; 2-methylimidazole is added and stirred vigorously for 5-10 minutes to fully dissolve; after aging the solution at room temperature, it is washed 3-5 times in methanol and dried at 60-90℃ for 10-12 hours to obtain a flame retardant; the flame retardant is added to polyvinylidene fluoride and stirred for 20-24 hours to dissolve in N-methylpyrrolidone, coated on both sides of a polypropylene separator, and dried at 60-90℃ for 5-7 hours to obtain the APP@Co-MOF composite material; The coating layer comprises, by weight fraction, the following components: The mixture consists of 10%–20% APP@Co-MOF composite material, 1%–5% binder, and N-methylpyrrolidone solution.

[0043] The adhesive is a fluoropolymer.

[0044] The base membrane is a polypropylene diaphragm.

[0045] S2. The coating slurry containing the APP@Co-MOF composite material prepared in step S1 is uniformly coated on the base film as a coating layer; dried and wound up to obtain a flame-retardant separator coating for lithium-ion batteries.

[0046] The preparation process of the coating slurry is as follows: The APP@Co-MOF composite material and binder were added sequentially to an N-methylpyrrolidone solution and stirred for 20–25 hours at a speed of 100–1200 rpm to obtain a coating slurry containing the APP@Co-MOF composite material.

[0047] This invention provides a flame-retardant separator coating for lithium-ion batteries that can be applied in various applications.

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0049] Example 1 A method for preparing a flame-retardant separator coating for lithium-ion batteries includes the following steps: Step 1: Dissolve 1.49 g of 5 mmol cobalt nitrate pentahydrate and 1 g of ammonium polyphosphate in 100 mL of methanol. Stir magnetically at room temperature for 3 hours. Then add 1.64 g of 20 mmol 2-methylimidazole and stir vigorously for 5 minutes until fully dissolved. After aging the solution at room temperature for 12 hours, filter the precipitate and wash it thoroughly with methanol. After washing, vacuum dry at 80 °C for 12 hours to obtain the flame retardant. Take 1.08 g of the flame retardant and add it to 0.12 g of polyvinylidene fluoride. Dissolve the precipitate in 10 mL of N-methylpyrrolidone and stir for 24 hours. Coat the resulting solution on both sides of a polypropylene separator and vacuum dry at 60 °C for 6 hours to obtain the APP@Co-MOF composite material.

[0050] Step 2: By mass fraction, 10.8% of the above-prepared APP@Co-MOF composite material and 1.2% of the binder are stirred in an N-methylpyrrolidone solution for 24 hours at a speed of 800 rpm to obtain a coating slurry containing the APP@Co-MOF composite material.

[0051] Step 3: Using a micro-gravure roller coating process, the prepared coating slurry is evenly roller-coated onto the polypropylene separator using a coating machine. After baking in a 60℃ oven, it is rolled up for later use, thus obtaining the flame-retardant separator.

[0052] Example 2 A method for preparing a flame-retardant separator coating for lithium-ion batteries includes the following steps: Step 1: Dissolve 1.49g of cobalt nitrate pentahydrate and 1g of ammonium polyphosphate in 100mL of methanol, stir magnetically at room temperature for 3 hours, then add 1.64g of 2-methylimidazole, stir vigorously for 10 minutes to fully dissolve; after aging the solution at room temperature for 12 hours, filter the precipitate, wash the precipitate three times with methanol, and dry it under vacuum at 60℃ for 10 hours to obtain the flame retardant.

[0053] Step 2: Add 1.20g of flame retardant to 0.05g of polyvinylidene fluoride (as a binder), dissolve in 10mL of N-methylpyrrolidone, stir for 20 hours, and coat the resulting solution evenly on both sides of the polypropylene diaphragm. After vacuum drying at 90℃ for 5 hours, the APP@Co-MOF composite material coating is obtained. The composition of the coating layer corresponding to this step is approximately: 10.0wt% APP@Co-MOF composite material, 0.4wt% binder, and the balance of NMP solvent (calculated based on 12.25g of slurry, of which 1.25g is solid and approximately 10.3g is NMP in 10mL).

[0054] Step 3: Treat the flame retardant prepared in Step 1 as the APP@Co-MOF composite material. Weigh 10.0% of the composite material and 1.0% of the polyvinylidene fluoride binder by mass fraction, add them to sufficient N-methylpyrrolidone to prepare a slurry with a solid content of 11%, stir for 20 hours at a speed of 100 rpm to obtain the coating slurry.

[0055] Step 4: Using a micro-gravure roller coating process, the prepared coating slurry is evenly roller-coated onto another clean polypropylene diaphragm. After baking in a 90℃ oven, it is rolled up to obtain the flame-retardant diaphragm.

[0056] Testing showed that its thermal stability was significantly improved compared to the comparative example; after heat treatment at 150℃, it maintained its shape without significant shrinkage. Electrochemical testing indicated that its ionic conductivity reached approximately 1.0 × 10⁻³ S / cm, and its cycling performance was stable, proving that even at the lower limit of the parameter range, this invention can still effectively improve the flame retardancy and electrochemical compatibility of the diaphragm.

[0057] Example 3 A method for preparing a flame-retardant separator coating for lithium-ion batteries includes the following steps: Step 1: Same as Step 1 in Example 1, to obtain the flame retardant (APP@Co-MOF composite material precursor).

[0058] Step 2: Add 0.90g of flame retardant to 0.45g of polyvinylidene fluoride, dissolve in 10mL of N-methylpyrrolidone, stir for 24 hours, and coat the resulting solution evenly on both sides of the polypropylene diaphragm. After vacuum drying at 60℃ for 7 hours, the APP@Co-MOF composite material coating is obtained. The composition of the coating layer corresponding to this step is approximately: 15.0 wt% APP@Co-MOF composite material, 7.5 wt% binder, and the remainder NMP solvent (total calculated based on 11.35g of slurry, of which 1.35g is solids).

[0059] Step 3: Weigh 20.0% of the flame retardant obtained in Step 1 (as a composite material) and 5.0% of the polyvinylidene fluoride binder according to the mass fraction, add them to sufficient N-methylpyrrolidone to prepare a slurry with a solid content of 25%, stir for 25 hours at a speed of 1200 rpm to obtain the coating slurry.

[0060] Step 4: Using the same coating process, the coating slurry is evenly coated onto the polypropylene diaphragm, dried at 60°C and then rolled up to obtain the flame-retardant diaphragm (referred to as sample E3).

[0061] The membrane coating obtained in this embodiment is dense, with a high APP@Co-MOF loading. Performance tests show that the membrane exhibits superior flame retardant properties and extremely low thermal shrinkage. Simultaneously, its charge transfer resistance is further reduced, and its ionic conductivity is increased to approximately 1.3 × 10⁻⁶. -3 The S / cm ratio indicates that the high-load composite coating not only improves safety but also significantly promotes ion transport.

[0062] Example 4 A method for preparing a flame-retardant separator coating for lithium-ion batteries includes the following steps: Step 1: Referring to Step 1 of Example 1, the drying conditions were changed to 90°C and dried for 12 hours to obtain the flame retardant.

[0063] Step 2: Take 1.00g of flame retardant and add it to 0.20g of polyvinylidene fluoride, dissolve it in 10mL of N-methylpyrrolidone, stir for 22 hours, coat the resulting solution onto a polypropylene diaphragm, and vacuum dry at 80℃ for 6 hours to obtain a pretreated coating.

[0064] Step 3: Weigh 15.0% of the flame retardant obtained in Step 1 and 3.0% of the polyvinylidene fluoride binder by mass fraction, add them to N-methylpyrrolidone to prepare a slurry, stir for 22 hours at a speed of 500 rpm to obtain the coating slurry.

[0065] Step 4: Using the same coating process, the coating slurry is evenly coated onto the polypropylene separator, dried at 80°C, and then rolled up to obtain the flame-retardant separator.

[0066] Test results show that its thermal stability, flame retardancy, cycle capacity retention rate and impedance characteristics are all better than the comparative example, and its performance is comparable to that of Example 1. It has good repeatability, which proves the stability and universality of the process within the parameter range described in this invention.

[0067] Comparative example: The same polypropylene diaphragm as described above was used as a comparison, but without any coating.

[0068] The flame-retardant membranes prepared in the above embodiments and the polypropylene membranes in the comparative example were subjected to relevant performance tests, and the results are shown in the table below:

[0069] As shown in the table above, the APP@Co-MOF@PP composite membrane achieves synergistic improvement in multiple properties through its unique structural design. Its surface has an irregular microstructure, increasing the specific surface area and reactive sites, which is beneficial for flame retardant reactions and enhanced physical adsorption. In terms of performance, this membrane exhibits significantly improved thermal stability and flame retardancy, with temperature resistance exceeding 150℃.

[0070] The electrochemical performance is also excellent: cycle life is extended by more than 5 times, capacity retention is better, and charge / discharge voltage characteristics are more stable; charge transfer impedance is reduced by about 30%, and ionic conductivity is increased to about 1.2 × 10⁻⁶. -3 S / cm; At high scan rates, capacitive behavior accounts for a larger proportion, making it suitable for rapid charging and discharging, and the electrode process is dominated by capacitive behavior with low diffusion resistance.

[0071] The success of the flame-retardant separator coating for lithium-ion batteries in this invention stems from a triple synergistic mechanism of physical barrier, chemical flame retardancy, and ion regulation. Structurally, it provides a functional basis for flame retardancy, catalysis, and ion transport, thereby achieving a comprehensive breakthrough in thermal safety and electrochemical performance.

[0072] Please see Figure 1 The image on the left shows an uncoated PP (polypropylene) membrane with a smooth surface and regular pore structure, typical characteristics of traditional polypropylene membranes. However, this structure leads to a low ignition point and easy shrinkage at high temperatures. The image on the right shows an APP@Co-MOF@PP composite membrane with an irregular, rough surface structure, and a uniformly covered coating layer visible in the cross-section. This rough structure increases the membrane's specific surface area and reactive sites, which is beneficial for flame-retardant reactions and provides more channels for ion transport, visually demonstrating the structural design advantages of the coating in this invention. Please see Figure 2 PP separators exhibit significant thermal shrinkage below 150°C and severe curling and loss of structural integrity upon temperature increases. In contrast, the APP@Co-MOF@PP composite separator maintains structural stability at temperatures of 150°C and above, with a significantly lower thermal shrinkage rate than PP separators. This figure demonstrates, through a clear comparison of thermal behavior, that the coating layer of this invention effectively inhibits high-temperature shrinkage and melting of the base film, significantly improving the thermal stability of the separator and ensuring battery safety at high temperatures.

[0073] Please see Figure 3(a) is a PP diaphragm, which exhibited severe shrinkage, rapid combustion, and lack of self-extinguishing properties during testing, easily leading to flame spread; (b) is an APP@Co-MOF@PP composite diaphragm, which showed low shrinkage during testing, rapidly forming a dense char layer to block the flame during combustion, and exhibiting good self-extinguishing properties. This figure directly verifies the highly efficient flame-retardant effect of the coating of this invention, solving the core defect of traditional diaphragms' flammability through physical barrier (char layer) and chemical flame retardancy (synergistic effect of APP and Co-MOF).

[0074] Please see Figure 4 (a) shows a PP membrane battery, whose specific capacity decreased to 225 mAh / g after 10 cycles, a decrease of approximately 14%, and exhibited significant capacity fluctuations; (b) shows an APP@Co-MOF@PP composite membrane battery, whose specific capacity remained at 450 mAh / g after multiple cycles, with a decrease of only 13.5%, and a stable capacity curve. This figure demonstrates that the coating of this invention improves flame retardancy and thermal stability without sacrificing the battery's electrochemical performance. Instead, it optimizes cycle stability and capacity retention, resolving the inherent contradiction between flame retardancy and electrochemical performance in traditional flame-retardant membranes.

[0075] In summary, this invention provides a flame-retardant separator coating for lithium-ion batteries, its preparation method, and its application. The coating significantly improves the thermal stability of the base film, enabling it to maintain its shape integrity even at 150°C, greatly mitigating the short-circuit risk caused by high-temperature shrinkage. It exhibits excellent flame retardancy and extremely low thermal shrinkage. Benefiting from the porous structure and potential catalytic effect of the APP@Co-MOF composite material, the coated separator demonstrates lower charge transfer impedance, higher ionic conductivity, and excellent cycle stability. It achieves an effective synergy of "physical barrier-chemical flame retardancy-ionic regulation." Experiments have shown that, within the broad process parameter range defined in the claims, products with significantly superior performance compared to uncoated separators can be stably prepared. The technical solution is robust and possesses excellent prospects for industrial application.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A flame-retardant separator coating for lithium-ion batteries, characterized in that, It includes a base film and a coating layer coated on the base film; the coating layer contains APP@Co-MOF composite material.

2. The flame-retardant separator coating for lithium-ion batteries according to claim 1, characterized in that, The coating comprises, by weight fraction, the following components: 10% to 20% of APP@Co-MOF composite material, 1% to 5% of binder, and the balance being a solvent, wherein the solvent is N-methylpyrrolidone.

3. The lithium-ion battery flame-retardant separator coating according to claim 2, characterized in that, The adhesive is a fluoropolymer adhesive.

4. The flame-retardant separator coating for lithium-ion batteries according to claim 1, characterized in that, The base membrane is a polypropylene diaphragm.

5. A method for preparing a flame-retardant separator coating for lithium-ion batteries, characterized in that, Includes the following steps: S1. Cobalt nitrate pentahydrate and ammonium polyphosphate are dissolved in methanol, 2-methylimidazole is added, and after stirring and dissolving, the mixture is aged at room temperature, filtered, washed, and dried to obtain a flame retardant. The flame retardant and binder are dissolved in N-methylpyrrolidone and stirred to obtain a mixed solution. The mixed solution is coated on a base film and dried to obtain an APP@Co-MOF composite material coating. S2. Add the APP@Co-MOF composite material and binder to an N-methylpyrrolidone solution and stir to obtain a coating slurry; S3. The coating slurry obtained in step S2 is uniformly coated onto the base film, dried and rolled up to obtain the flame-retardant separator coating for lithium-ion batteries.

6. The method for preparing a flame-retardant separator coating for lithium-ion batteries according to claim 5, characterized in that, In step S1, the stirring and dissolving time is 5 to 10 minutes, the drying temperature is 60 to 90°C, and the time is 10 to 12 hours.

7. The method for preparing a flame-retardant separator coating for lithium-ion batteries according to claim 5, characterized in that, In step S1, the flame retardant and binder are dissolved in N-methylpyrrolidone and stirred for 20 to 24 hours.

8. The method for preparing a flame-retardant separator coating for lithium-ion batteries according to claim 5, characterized in that, In step S1, after the mixed solution is coated onto the base film, it is dried at 60–90°C for 5–7 hours.

9. The method for preparing a flame-retardant separator coating for a lithium-ion battery according to claim 5, characterized in that, In step S2, the stirring time is 20 to 25 hours and the stirring speed is 100 to 1200 rpm.

10. A lithium-ion battery, characterized in that, The flame-retardant separator coating for lithium-ion batteries according to any one of claims 1 to 4 or the flame-retardant separator coating for lithium-ion batteries prepared by any one of claims 5 to 9.

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