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

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a lithium ion battery coating diaphragm as well as a preparation method and application thereof. According to the invention, the polymer conductive material is coated on the surfaces of the solid electrolyte particles, and the polymer conductive material and the flexible material with a specific content are compounded through an optimized one-step mixing process, so that a coating structure with ionic conduction, interface adaptation and stress buffering functions is constructed. The diaphragm can synergistically improve the ionic conductivity, significantly reduce the interface contact resistance, endow the battery with excellent long-cycle stability and high-temperature safety performance, and is suitable for the lithium ion battery with high requirements on energy density and reliability.

Description

Technical Field

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

[0002] With the increasing demands for energy density, cycle life, and safety and reliability of lithium-ion batteries from electric vehicles and large-scale energy storage systems, the stability and compatibility of the interfaces between various components within the battery have become crucial in determining the overall battery performance. Among these, the separator, as the core component that isolates the positive and negative electrodes and ensures ion transport, has a particularly critical physical contact interface with the porous electrodes. During long-term charge-discharge cycles, the active materials of the electrodes inevitably undergo volume changes, and the battery may face the risk of localized overheating under abnormal conditions. Traditional polyolefin separators have chemically inert surfaces and poor compatibility with the electrode interfaces, easily leading to increased interfacial contact resistance and uneven current distribution, thus affecting battery power characteristics and even causing interface failure under thermal stress, posing a safety hazard. Therefore, developing a novel separator that can actively adapt to dynamic changes in the electrode interface, maintain low impedance, and possess excellent thermal stability is of great significance for the development of next-generation high-performance, high-safety lithium-ion batteries.

[0003] To improve membrane performance, existing technologies have evolved primarily in two directions: one is to coat the base membrane surface with inorganic ceramic particles (such as alumina or solid electrolytes) to enhance thermal stability and ionic conductivity; the other is to introduce organic polymer coatings (such as PVDF) onto the base membrane to enhance electrolyte wetting and adhesion. Furthermore, to endow the coating with more functions, surface coating of inorganic fillers with conductive polymers is also a known technical approach, typically aimed at improving the electronic conductivity or mechanical strength of the composite material.

[0004] However, the existing solutions mentioned above still have significant shortcomings in addressing the deep-seated problem of "dynamic interface stability." First, regardless of whether inorganic or organic-inorganic composite coatings are used, the material systems often exhibit rigid or brittle characteristics in terms of mechanical properties, making it difficult to adapt to the volume deformation of the electrode during cycling. This leads to a reduction in physical contact points at the interface or stress concentration, causing a continuous increase in contact resistance. Second, and more critically, the polymer components used to improve the interface or act as binders in these solutions are mostly conventional general-purpose polymer materials (such as common polyurethanes and acrylate resins). These materials lack specific design in their chemical structure and electrochemical system, resulting in weak interfacial interactions with the solid electrolyte and conductive polymers. Consequently, they cannot effectively maintain the overall structural integrity of the coating under complex electrochemical environments and thermal stresses for extended periods. As a result, microscopic separation easily occurs between the components within the coating and between the coating and the electrode after long-term service, leading to the failure of the ion transport network and an increase in interfacial impedance, ultimately limiting the battery's cycle life and safety performance.

[0005] Therefore, developing solutions that can significantly improve the stability of coating integration and the ability of interfaces to adhere for a long time is crucial for realizing the next generation of high-performance, high-safety lithium-ion batteries. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes a lithium-ion battery coated separator, its preparation method, and its application. This invention provides an innovative solution to the problems of insufficient interfacial stability and mechanical compatibility of coated separators by using a polymer conductive material to coat a solid electrolyte and then combining it with a flexible material.

[0007] The first objective of this invention is achieved through the following technical solution:

[0008] A lithium-ion battery coated separator includes a base film and a coating layer coated on at least one surface of the base film. The coating layer is composed of a polymer conductive material, a solid electrolyte, and a flexible material. The flexible material is one or more selected from polyurethane elastomer, silicone rubber, and polyether-type thermoplastic elastomer. The preparation method of the coating layer includes the following steps:

[0009] A) Mix and stir the solid electrolyte dispersion, the polymer conductive material solution, and the flexible material dispersion to form a coated dispersion;

[0010] B) Coat the coating dispersion onto the base film and dry.

[0011] Preferably, the flexible material accounts for 5%-20% of the mass of the coating layer.

[0012] Preferably, the flexible material is a polyurethane elastomer, and the polyurethane elastomer is a cyano-grafted polyurethane elastomer.

[0013] More preferably, the cyano-grafted polyurethane elastomer is prepared by a method comprising the following steps:

[0014] (1) Synthesis of prepolymer: Under an inert atmosphere, polyether polyol and diisocyanate are reacted at 70-85°C for 2-4 hours to generate isocyanate-terminated prepolymer; wherein, the polyether polyol is preferably polytetrahydrofuran ether diol with a molecular weight of 1000-2000 g / mol; the diisocyanate is selected from diphenylmethane diisocyanate, toluene diisocyanate or hexamethylene diisocyanate;

[0015] (2) Cyano grafting: The prepolymer obtained in step (1) is subjected to a graft copolymerization reaction with a cyano-containing vinyl monomer at 65-80°C for 8-12 hours in the presence of a free radical initiator to obtain a cyano-grafted modified prepolymer; the cyano-containing vinyl monomer is selected from acrylonitrile or methacrylonitrile; the free radical initiator can be selected from azobisisobutyronitrile, and its amount is 0.5-1% of the monomer mass;

[0016] (3) Chain extension and curing: The cyano-grafted modified prepolymer obtained in step (2) is mixed with a chain extender and reacted at 40-60°C for 1-3 hours to extend the chain. Then, it is vacuum cured at 75-85°C for 12-36 hours to obtain the cyano-grafted polyurethane elastomer. The chain extender is selected from one or more of 1,4-butanediol, ethylene glycol, and diethylene glycol.

[0017] Preferably, the polymer conductive material is one or more of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid, polyaniline, and polypyrrole.

[0018] More preferably, the polymer conductive material is poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid. It possesses the dual advantages of electronic conductivity and ion permeability. The conductivity of pure poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid films can reach 100-500 S / cm, and it exhibits good chemical stability in lithium battery electrolytes, showing no adverse reactions with various solid electrolytes. Its glass transition temperature is above 150°C, and it maintains structural stability during battery operating temperatures and thermal tests below 140°C. Commercially available aqueous solutions of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid are inexpensive and require no additional polymerization equipment, making them more environmentally friendly.

[0019] Preferably, the solid electrolyte is one or more of lithium lanthanum zirconium oxide, lithium phosphorus oxynitrogen, and sulfide solid electrolytes.

[0020] More preferably, the solid electrolyte is lithium lanthanum zirconium oxide. It is a garnet-type oxide solid electrolyte with high ionic conductivity, good lithium stability, and excellent thermal stability.

[0021] Preferably, the drying process includes the following steps: first, a first stage of drying is carried out at 60-80°C, and then a second stage of drying is carried out at 80-120°C.

[0022] Preferably, the base film is one or more of the following: polyethylene film, polypropylene film, polypropylene / polyethylene / polypropylene multilayer composite film, polyvinylidene fluoride film, and polyvinylidene fluoride-hexafluoropropylene copolymer film.

[0023] This solution constructs a novel coated separator by integrating a polymer conductive material, a solid electrolyte, and a flexible material. The polymer conductive material coats the solid electrolyte particles, aiming to optimize interfacial charge distribution and enhance electron-assisted conduction; its high-temperature stability provides a rigid framework for the coating. The introduction of the flexible material, particularly a polyurethane with enhanced polarity through molecular design, aims to utilize its elasticity and strong interfacial forces to fill the gaps between composite particles and buffer stress, thereby improving dynamic contact with the electrodes. This composite coating system simultaneously and significantly improves the ionic conductivity of the separator, substantially reduces its contact resistance with the electrodes, and significantly improves the battery's cycle life and high-temperature safety performance.

[0024] The second objective of this invention is achieved through the following technical solution:

[0025] A method for preparing a lithium-ion battery coated separator as described above includes the following steps:

[0026] A) Mix and stir the solid electrolyte dispersion, the polymer conductive material solution, and the flexible material dispersion to form a coated dispersion;

[0027] B) Coating the coating dispersion onto the base film;

[0028] C) Perform two-stage drying on the coated base film: first, perform the first stage of drying at 60-80℃, and then perform the second stage of drying at 80-120℃.

[0029] Preferably, in step A), the mixing and stirring speed is 500-1000 rpm, and the stirring time is 1-2 hours. This speed range can provide sufficient fluid shear force to ensure that the polymer conductive material is fully and uniformly adsorbed and coated on the surface of the solid electrolyte particles to form a complete shell structure. Too low a speed may lead to uneven coating, while too high a speed may cause agglomeration or damage to the flexible material structure.

[0030] Preferably, in step A), based on 1 part by weight of the flexible material, the solid electrolyte comprises 4-6 parts by weight, and the polymer conductive material comprises 0.1-0.2 parts by weight. This ratio range ensures that there is sufficient polymer conductive material to completely cover the surface of the solid electrolyte particles. Too low a ratio may result in incomplete coating, while too high a ratio will waste material and may affect other properties of the coating.

[0031] Preferably, the solid electrolyte dispersion is prepared by: placing solid electrolyte powder in an organic solvent, stirring at 300-600 rpm for 1-2 hours for initial dispersion, and then ultrasonically dispersing at 200-500W for 15-30 minutes to obtain a uniform and stable dispersion; the organic solvent is selected from N-methylpyrrolidone, dimethylformamide or ethanol.

[0032] Preferably, the preparation method of the flexible material dispersion is as follows: dissolving or dispersing the flexible material in acetone or ethyl acetate, and stirring at 300-500 rpm for 1-2 hours.

[0033] Preferably, the preparation method of the flexible material dispersion is as follows: dissolving or dispersing the flexible material in acetone or ethyl acetate, and ultrasonically dispersing it for 10-20 minutes at a power of 200-400W.

[0034] In a further preferred embodiment, when the flexible material is a cyano-grafted polyurethane elastomer, it can be further homogenized under high pressure to form a more uniform nanoscale dispersion in the dispersion liquid.

[0035] Preferably, in step B), the coating method is scraping, spraying, or roller coating.

[0036] In a further preferred embodiment, when using a scraper coating method, the thickness is adjusted by controlling the distance between the scraper and the base film, and the base film moving speed is 0.5-2 m / min.

[0037] Preferably, in step B), the coating thickness is 5-15 μm.

[0038] Preferably, in step C), the drying time for the first stage is 1-2 hours, and the drying time for the second stage is 1-2 hours. In the two-stage drying process, the initial lower temperature is used to gently evaporate most of the solvent, avoiding the formation of pores or cracks in the coating due to rapid solvent evaporation; the subsequent higher temperature is used to fully cure the coating, promote a stronger bond between the components, and fully crosslink the flexible material elastomer, thereby firmly adhering to the surface of the base film.

[0039] This method provides an efficient and controllable approach to preparing the composite-coated separator. The principle lies in optimizing the blending and drying processes to promote the formation of a uniform, dense, and stable composite structure among the solid electrolyte, the polymer conductive material, and the flexible material. During the blending step, the components do not simply coexist in the liquid phase. Instead, under specific hydrodynamic conditions, intermolecular forces and physical adsorption cause the polymer conductive material to preferentially and uniformly adhere to the surface of the solid electrolyte particles, while the flexible material is fully dispersed and embedded into the voids of the forming composite network. The subsequent two-stage drying process simulates the ideal path for coating curing: first, most of the solvent is removed under mild conditions to prevent structural defects; then, a higher temperature promotes complete curing of the coating and tight bonding between the components, thereby forming a dense, robust, and functionally integrated coating layer on the base film. This method, with its consistent process and well-defined conditions, is key to achieving the aforementioned high-performance composite-coated separator structure.

[0040] The third objective of this invention is achieved through the following technical solution:

[0041] A lithium-ion battery, characterized in that it comprises a lithium-ion battery coated separator as described above.

[0042] Preferably, the lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and the coated separator located between the positive and negative electrodes.

[0043] More preferably, the coating layer of the coated diaphragm is disposed facing the positive and / or negative electrode.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] 1. This invention creatively combines a polymer conductive material-coated solid electrolyte with a flexible material, achieving a synergistic improvement in ionic conductivity, interfacial contact performance, and mechanical compatibility compared to existing solutions that simply employ a coating structure or a simple physical mixture coating. This composite system not only retains the promoting and enhancing effect of the coating structure on ion transport but also significantly improves the dynamic adhesion between the coating and the rough electrode surface through the introduction of the flexible material. This reduces interfacial resistance while enhancing the coating's resistance to strain fatigue, resolving the contradiction between high conductivity and flexibility in traditional technologies.

[0046] 2. By optimizing the content of the flexible material, this invention has found a formulation window that achieves optimal overall performance. This design ensures that the flexible material is sufficient to play its key role in improving the interface and buffering stress, while avoiding its excessive introduction from hindering ion transport or occupying too much active volume. This results in a superior balance between electrochemical and physicomechanical properties in the final product, achieving comprehensive benefits far exceeding those of conventional formulations.

[0047] 3. The specific flexible material used in this invention, particularly the cyano-grafted polyurethane elastomer designed with a molecular structure, exhibits an interface reinforcement effect that surpasses that of conventional polymers. Its unique chemical structure endows it with stronger interaction forces with other components in the coating, thereby significantly improving the structural integrity and cohesive strength of the composite coating. This enables the separator to more effectively resist interfacial delamination and structural degradation under long-term cycling and temperature variations, significantly improving the long-term cycle life and reliability of the battery.

[0048] 4. The method of this invention employs a one-step mixing process and solves the key challenges of uniform dispersion and effective composite of multiple components by optimizing and controlling the stirring speed and time. This parameter window provides the necessary fluid shear force, ensuring that the solid electrolyte, polymer conductive material, and flexible material can fully collide and interact in the liquid phase, thereby forming a precursor with uniform component distribution and a dense structure.

[0049] 5. The two-stage drying process employed in this invention ensures complete curing of the coating. The gentle drying in the first stage prevents coating cracking or porosity caused by rapid solvent evaporation; the temperature-curing in the second stage promotes the final shaping of the coating's internal structure and strengthens the bonding between components. This process design helps obtain a final product with a complete structure and strong adhesion, and is a crucial step in ensuring the quality of the finished product within the entire preparation method. Attached Figure Description

[0050] Figure 1 This is a SEM image of the composite coated diaphragm in Example 1. Detailed Implementation

[0051] The following will provide a clear and complete description of the concept, specific structure, and technical effects of the present invention in conjunction with embodiments and accompanying drawings, so as to fully understand the purpose, solution, and effects of the present invention. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0052] Example 1

[0053] The method for preparing the composite coated diaphragm in Example 1 includes the following steps:

[0054] (1) Weigh 5.0g of lithium lanthanum zirconium oxide powder and add it to 50mL of N-methylpyrrolidone solvent. Stir at 400 rpm for 1.5 hours, then ultrasonically disperse at 300W for 20 minutes to obtain a solid electrolyte dispersion.

[0055] (2) Weigh 2.0g of polyurethane elastomer (Zhejiang Huafeng, brand: HF-1095A) and add it to 20mL of acetone. Stir at 400 rpm for 1.5 hours to obtain a flexible material dispersion.

[0056] (3) Under stirring, the solid electrolyte dispersion obtained in step (1), 10 mL of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid aqueous solution (manufacturer: Heraeus, brand name: Clevios) and the flexible material dispersion from step (2) are simultaneously added to a mixing container. The mixture is stirred continuously at 750 rpm for 1.2 hours to obtain the coated dispersion.

[0057] (4) The coating dispersion is coated onto the surface of the polypropylene base film by scraping method, and the target dry film thickness is controlled to be 10 μm and the base film moving speed is 1 m / min.

[0058] (5) Place the coated wet film in a forced-air drying oven, dry it at 70°C for 1.5 hours, and then heat it to 90°C for 1 hour to obtain a composite coated diaphragm.

[0059] Example 2

[0060] In the composite coating membrane preparation method of Example 2, steps (1) and (3)-(5) are the same as in Example 1, except for step (2).

[0061] Step (2) is as follows: Weigh 0.8g of polyurethane elastomer and add it to 20mL of acetone. Stir at 400 rpm for 1.5 hours to obtain a flexible material dispersion.

[0062] Example 3

[0063] In the composite coating membrane preparation method of Example 3, steps (1) and (3)-(5) are the same as in Example 1, except for step (2).

[0064] Step (2) is as follows: Weigh 4.0g of polyurethane elastomer and add it to 20mL of acetone. Stir at 400 rpm for 1.5 hours to obtain a flexible material dispersion.

[0065] Example 4

[0066] In the composite coating membrane preparation method of Example 4, steps (1) and (3)-(5) are the same as in Example 1, except for step (2).

[0067] Step (2) involves preparing a cyano-grafted polyurethane (CN-PU) elastomer dispersion. Under nitrogen protection, 100g of polytetrahydrofuran ether diol (PTMEG, Mn=2000) and 35g of diphenylmethane diisocyanate (MDI) were stirred at 80°C for 3 hours to obtain an end-NCO prepolymer. After cooling to 70°C, 10g of acrylonitrile and 0.05g of azobisisobutyronitrile (AIBN) were added, and the mixture was reacted at 70°C for 10 hours. Subsequently, 8g of 1,4-butanediol (BDO) was added, and after stirring for 2 hours, the product was cured in a vacuum drying oven at 80°C for 24 hours to obtain cyano-grafted polyurethane elastomer blocks. 2.0g of this elastomer was dissolved in 20mL of acetone and stirred at 400 rpm for 2 hours to obtain a CN-PU elastomer dispersion.

[0068] Example 5

[0069] In the composite coating membrane preparation method of Example 5, steps (1), (2), (4)-(5) are the same as in Example 1, except for step (3).

[0070] Step (3) involves simultaneously adding the solid electrolyte dispersion obtained in step (1), 10 mL of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid aqueous solution, and the flexible material dispersion from step (2) into a mixing container while stirring. The mixture is stirred continuously at 900 rpm for 1.2 hours to obtain the coated dispersion.

[0071] Example 6

[0072] In the composite coating membrane preparation method of Example 6, steps (1), (2), (4)-(5) are the same as in Example 1, except for step (3).

[0073] Step (3) involves simultaneously adding the solid electrolyte dispersion obtained in step (1), 10 mL of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid aqueous solution, and the flexible material dispersion from step (2) into a mixing container while stirring. The mixture is stirred continuously at 600 rpm for 1.2 hours to obtain the coated dispersion.

[0074] Comparative Example 1

[0075] In the membrane preparation method of Comparative Example 1, steps (1) and (4)-(5) are the same as in Example 1, except that no flexible material is added to the system. Specifically, the method includes the following steps:

[0076] (1) Weigh 5.0g of lithium lanthanum zirconium oxide powder and add it to 50mL of N-methylpyrrolidone solvent. Stir at 400 rpm for 1.5 hours, then ultrasonically disperse at 300W for 20 minutes to obtain a solid electrolyte dispersion.

[0077] (2) While stirring, the solid electrolyte dispersion obtained in step (1) and 10 mL of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid aqueous solution were simultaneously added to a mixing container. The mixture was stirred continuously at 600 rpm for 1.2 hours to obtain the coated dispersion.

[0078] (3) The coating dispersion was coated onto the surface of the polypropylene base film by scraping method, and the target dry film thickness was controlled to be 10 μm and the base film moving speed was 1 m / min.

[0079] (4) Place the coated wet film in a forced-air drying oven, dry it at 70°C for 1.5 hours, and then heat it to 90°C for 1 hour to obtain a composite coated diaphragm.

[0080] Comparative Example 2

[0081] In the membrane preparation method of Comparative Example 2, steps (1), (2), (4), and (5) are the same as in Example 1, except for step (3).

[0082] Step (3) involves simultaneously adding the solid electrolyte dispersion obtained in step (1), 10 mL of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid aqueous solution, and the flexible material dispersion from step (2) into a mixing container while stirring. The mixture is stirred continuously at 300 rpm for 1.2 hours to obtain the coated dispersion.

[0083] Comparative Example 3

[0084] In the membrane preparation method of Comparative Example 3, steps (1), (2), (4), and (5) are the same as in Example 1, except for step (3).

[0085] Step (3) involves simultaneously adding the solid electrolyte dispersion obtained in step (1), 10 mL of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid aqueous solution, and the flexible material dispersion from step (2) into a mixing container while stirring. The mixture is stirred continuously at 1200 rpm for 1.2 hours to obtain the coated dispersion.

[0086] Comparative Example 4

[0087] In the comparative membrane preparation method of Comparative Example 4, steps (1), (2), (4), and (5) are the same as in Example 1, except for step (3).

[0088] Step (3) involves a two-step mixing process. First, the solid electrolyte dispersion obtained in step (1) is mixed with 10 mL of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid aqueous solution and stirred continuously at 600 rpm for 1 hour. Then, the flexible material dispersion from step (2) is added to this mixture, and stirring is continued at 600 rpm for 0.2 hours, for a total stirring time of 1.2 hours, to obtain the dispersion.

[0089] The composite coated membrane samples prepared according to Examples 1-6 and Comparative Examples 1-4 were subjected to systematic performance testing and characterization. The specific methods and conditions for each test item are as follows:

[0090] 1. Observation of coating morphology and thickness

[0091] Scanning electron microscopy (SEM) was used to observe the surface and cross-sectional morphology of the diaphragm coating. Diaphragm samples were cut to appropriate sizes, sputter-coated with gold, and then placed under an SEM to observe the uniformity and density of the coating particles and the presence of defects such as cracks. The actual thickness of the coating was measured using cross-sectional samples and compared with the target thickness.

[0092] 2. Electrochemical performance testing

[0093] The separators prepared in each embodiment and comparative example were assembled into CR2032 coin-type lithium-ion batteries for testing. The battery configuration was as follows: the positive electrode was lithium iron phosphate, the negative electrode was lithium metal sheet, and the electrolyte was a 1 mol / L LiPF6 EC / DMC (volume ratio 1:1) solution.

[0094] First charge / discharge specific capacity test: Charge and discharge tests were conducted at a rate of 0.5C, with a voltage range of 2.5-4.2V, and the discharge specific capacity of the first cycle was recorded.

[0095] Cyclic performance test: Constant current charge-discharge cycle test was performed at 1C rate, the discharge capacity after 500 cycles was recorded, and its retention rate relative to the first discharge capacity was calculated.

[0096] 3. Interface contact resistance test

[0097] The four-probe method was used to test the contact resistance between the diaphragm and the simulated electrode. The diaphragm was sandwiched between two stainless steel sheets, a certain pressure was applied, and the resistance value between them was measured using an electrochemical workstation or a high-precision resistance meter. The resistance value was then converted into the contact resistance per unit area based on the contact area.

[0098] 4. Ionic conductivity test

[0099] The ionic conductivity of the separator was tested using AC impedance spectroscopy. The separator was sandwiched between two blocking electrodes to form a symmetrical cell, and AC impedance spectroscopy was performed within a specific frequency range using an electrochemical workstation. The bulk resistance was obtained from the spectral analysis, and the lithium-ion conductivity was calculated by combining the separator thickness and electrode area.

[0100] 5. Thermal stability test

[0101] The assembled button cells were placed in a forced-air drying oven and kept at a constant temperature of 120°C for 1 hour. The cells were then removed, allowed to cool to room temperature, and their appearance was observed for signs of bulging or leakage. The voltage was measured, and a simple charge-discharge test was performed to determine if an internal short circuit had occurred.

[0102] The above test methods are a unified standard and are applicable to the performance comparison and evaluation of all embodiments and comparative samples.

[0103] The membrane samples prepared in Examples 1-6 and Comparative Examples 1-4 were subjected to the above-mentioned performance tests, and the results are summarized in the table below.

[0104] Table 1 Performance test results of the examples and comparative examples

[0105]

[0106] The surface of the composite coated diaphragm prepared in Example 1 was observed using a scanning electron microscope, and the results were as follows: Figure 1 The SEM image shown is an example of a continuous, porous matrix framework formed by polyurethane curing. Numerous fine LLZO particles, ranging in size from 0.1 to 0.5 micrometers, are uniformly attached to the surface and pores. A light gray continuous phase fills the interface between the matrix and the particles, as well as the pores. This microstructure directly confirms the core improvement of this invention: the continuous porous flexible framework provides crucial mechanical support and buffering, forming the structural basis for excellent mechanical adaptability and resistance to strain fatigue; the uniformly dispersed and non-agglomerated LLZO particles demonstrate the effectiveness of the one-step mixing process in achieving uniform distribution of active components, ensuring efficient and uniform ion transport channels; and the PEDOT:PSS continuous phase filling the interface visually demonstrates the coating and bridging effect of the conductive polymer on the active particles. It not only enhances the interfacial bonding force of each component and improves structural integrity to resist delamination, but also constructs a continuous conductive network, thereby synergistically reducing interfacial impedance and achieving a synergistic improvement in ionic conductivity, interfacial contact performance, and mechanical flexibility.

[0107] As shown in Table 1, the composite coated diaphragm prepared by this invention achieves significant synergistic improvements in key performance aspects such as ionic conductivity, interfacial contact, cycle life, and thermal safety. Among them, Example 4 (using cyano-grafted polyurethane) exhibits the best overall performance, with an ionic conductivity of 3.2 × 10⁻⁶. -1 S / cm, contact resistance as low as 21Ω·cm 2 The capacity retention rate reached 91% after 500 cycles, and it passed the 120°C thermal test, which proves that specific molecular structure design of flexible materials can bring unexpected outstanding effects.

[0108] By comparing Example 1 and Comparative Example 1, it can be seen that without the addition of flexible material, the diaphragm contact resistance increases significantly to 52 Ω·cm. 2 The cycle retention rate was only 79%, and a short circuit occurred at 120°C. This directly demonstrates the indispensability of flexible materials in constructing stable interfaces and ensuring cycle life and thermal safety.

[0109] By comparing Examples 1 (flexible material content approximately 10%), 2 (approximately 4%), and 3 (approximately 17%), it can be seen that when the flexible material content is in the range of 5%-20%, the prepared membranes all exhibit significantly better overall performance than Comparative Example 1, which does not contain flexible material. Specifically, Example 1 achieves the best balance of various properties within this range, demonstrating that this formulation window ensures that the flexible material can fully exert its role in improving the interface and buffering stress, while avoiding hindering ion transport. This is a key design feature for achieving a synergistic improvement in high ionic conductivity, low contact resistance, and long cycle life.

[0110] By comparing Example 1 and Comparative Example 4, it can be seen that although conventional understanding suggests that preparing the coating structure of the solid electrolyte and conductive polymer first (two-step method) should facilitate the formation of a more regular interface, the test results unexpectedly show that the membrane prepared by directly mixing the three components in one step (Example 1) is superior to the two-step process (Comparative Example 4) in all key indicators, including initial capacity, cycle retention, interfacial contact, and thermal stability. This counterintuitive result strongly demonstrates that the one-step mixing process used in this invention can promote a more complete and uniform interaction between the solid electrolyte, conductive polymer, and flexible material in the liquid phase, thereby forming a denser, more stable, and more interfacially bonded composite microstructure. This is the key process innovation of this invention.

[0111] Comparative studies of Examples 1, 5, and 6 show that when the mixing speed is 750, 900, and 600 rpm, respectively—that is, within the 500-1000 rpm parameter window described in this invention—the prepared membranes all exhibit excellent and stable overall performance. This result contrasts sharply with the performance degradation caused by excessively low (Comparative Example 2, 300 rpm) or excessively high (Comparative Example 3, 1200 rpm) speeds, clearly demonstrating that the aforementioned speed range is a necessary process condition to ensure effective dispersion and uniform compounding of the components, ultimately resulting in a high-performance coating.

[0112] Of particular importance, a comparison of Example 4 and Example 1 reveals that, under the same process conditions, simply replacing ordinary polyurethane with cyano-grafted polyurethane further and simultaneously improves the ionic conductivity, contact resistance, and cycle retention rate of the membrane. This conclusively demonstrates that the cyano-grafting modification endows the flexible material with stronger interfacial interactions, thereby achieving additional enhancements to the coating structure integrity and electrochemical performance at the molecular level. This is one of the key innovations of this invention.

[0113] In summary, this invention solves the problems of high rigidity and poor interfacial compatibility of traditional coatings by synergistically combining polymer-coated solid electrolytes, a specific amount of flexible material, and a one-step high-speed mixing process. Systematic comparisons of the embodiments and comparative examples confirm that this technical solution is not obvious overall and achieves a significant comprehensive improvement.

[0114] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A lithium-ion battery coated separator, comprising a base film and a coating layer coated on at least one surface of the base film, characterized in that, The coating layer is composed of a polymer conductive material, a solid electrolyte, and a flexible material; the flexible material is one or more of polyurethane elastomer, silicone rubber, and polyether-type thermoplastic elastomer; the preparation method of the coating layer includes the following steps: A) Mix and stir the solid electrolyte dispersion, the polymer conductive material solution, and the flexible material dispersion to form a coated dispersion; B) Coat the coating dispersion onto the base film and dry.

2. The coated diaphragm according to claim 1, characterized in that, The flexible material accounts for 5%-20% of the mass of the coating layer.

3. The coated diaphragm according to claim 1, characterized in that: The polymer conductive material is one or more of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid, polyaniline, and polypyrrole. And / or, the solid electrolyte is one or more of lithium lanthanum zirconium oxide, lithium phosphorus oxynitrogen, and sulfide solid electrolytes.

4. The coated diaphragm according to claim 1, characterized in that, The flexible material is a polyurethane elastomer, which is a cyano-grafted polyurethane elastomer.

5. The coated diaphragm according to claim 4, characterized in that, The method for preparing the cyano-grafted polyurethane elastomer includes the following steps: (1) Under an inert atmosphere, the polyether polyol and diisocyanate are reacted at 70-85°C for 2-4 hours to generate isocyanate-terminated prepolymer. (2) The prepolymer obtained in step (1) is subjected to graft copolymerization with a cyano-containing vinyl monomer at 65-80°C in the presence of a free radical initiator for 8-12 hours to obtain a cyano-grafted modified prepolymer. (3) The cyano-grafted modified prepolymer obtained in step (2) is mixed with a chain extender and reacted at 40-60°C for 1-3 hours to extend the chain. Then, it is vacuum cured at 75-85°C for 12-36 hours to obtain the cyano-grafted polyurethane elastomer.

6. The coated diaphragm according to claim 5, characterized in that: In step (1), the diisocyanate is selected from one or more of diphenylmethane diisocyanate, toluene diisocyanate, and hexamethylene diisocyanate; And / or, in step (2), the cyano-containing vinyl monomer is selected from acrylonitrile or methacrylonitrile; And / or, in step (3), the chain extender is selected from one or more of 1,4-butanediol, ethylene glycol, and diethylene glycol.

7. A method for preparing a coated diaphragm as described in any one of claims 1-6, characterized in that, Includes the following steps: A) Mix and stir the solid electrolyte dispersion, the polymer conductive material solution, and the flexible material dispersion to form a coated dispersion; B) Coating the coating dispersion onto the base film; C) Perform two-stage drying on the coated base film: first, perform the first stage of drying at 60-80℃, and then perform the second stage of drying at 80-120℃.

8. The method according to claim 7, characterized in that: The mixing speed is 500-1000 rpm, and the mixing time is 1-2 hours; And / or, based on 1 part by weight of the flexible material, the solid electrolyte is 4-6 parts by weight, and the polymer conductive material is 0.1-0.2 parts by weight.

9. The method according to claim 7, characterized in that, The coating thickness is 5-15μm.

10. A lithium-ion battery, characterized in that, It includes the coated diaphragm as described in any one of claims 1-6.

Images