Coating diaphragm and preparation method thereof

Abstract

The invention provides a coating diaphragm and a preparation method thereof, and belongs to the technical field of lithium ion battery diaphragms. The coating diaphragm provided by the invention comprises a diaphragm base material and a heat-resistant flexible coating coated on the surface of at least one side of the diaphragm base material, the heat-resistant flexible coating comprises an organic-inorganic functional coating or an organic functional coating. The raw materials for preparing the organic functional coating comprise a flexible heat-resistant organic material, so that the heat resistance of the coating diaphragm can be improved. Raw materials for preparing the organic-inorganic functional coating comprise an organic-inorganic material, and the organic-inorganic material is composed of an inorganic material and a flexible heat-resistant organic material coating or partially coating the outer surface of the inorganic material. The inorganic material is a gas source type inorganic flame-retardant material and can be decomposed to release inert gas, so that on one hand, the flame-retardant safety characteristic is improved; and on the other hand, gas released by the inorganic material can enable the heat-resistant flexible coating to foam and expand, so that buffering and insulating effects are achieved, and the safety characteristic of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery separator technology, and in particular to a coated separator and its preparation method. Background Technology

[0002] Lithium-ion batteries have garnered significant attention due to their advantages such as high energy density, long cycle life, low self-discharge, good safety performance, and fast charge / discharge rates. The battery separator is a crucial material in lithium-ion batteries, separating the positive and negative electrodes and preventing short circuits. Currently, mainstream separator products are wet-process PE separators and dry-process PP separators, or products with conventional ceramic and PVDF coatings on the surface of PE or PP separators, offering high maturity and cost-effectiveness. However, as the market demands increasingly higher performance from lithium-ion batteries in terms of capacity, energy density, cycle life, and fast charge / discharge, for example, the new national standard mandates that batteries "not catch fire or explode" after thermal runaway. One of the main causes of lithium battery fires and explosions is separator shrinkage caused by internal or external factors leading to puncture short circuits or thermal runaway, which in turn triggers large-area heat release and chain reactions, resulting in safety accidents. Therefore, the separator, as the core material inside lithium batteries, must undergo further improvements in safety performance.

[0003] Currently, the needle penetration and impact tests are key safety tests for lithium batteries under the new national standard. The needle penetration test uses a steel needle (usually 5mm) with a diameter of 3-8mm to vertically pierce the battery, observing whether it catches fire, explodes, or leaks. The impact test places the battery on a platform and drops a 9.1kg weight from a height of 610mm onto a steel column above the battery to test for fire or explosion. Currently, conventional wet-process PE, dry-process PP, and products with conventional ceramic and PVDF coatings on the separator surface cannot guarantee 100% pass rates in both the needle penetration and impact tests, posing safety hazards and failing to meet the requirements of the new national standard. The main reasons for the low pass rates of needle penetration and heavy object impact tests on lithium batteries are: first, the heat resistance of the separator is insufficient, making it unable to maintain dimensional stability under rapid temperature rise inside the battery; second, during the needle penetration test, especially the heavy object impact test, the high hardness of the ceramic-coated separator allows the high-hardness ceramic particles to puncture the separator under pressure and impact, causing the separator to break inside the battery, triggering an internal short circuit, which in turn leads to a rapid temperature rise and combustion or explosion.

[0004] Currently, the main technology to improve the heat resistance of the separator is to coat the surface with inorganic coatings such as alumina or boehmite, which provide support through the heat resistance stability of inorganic materials. However, inorganic materials generally have high hardness and irregular shape, which can easily damage the separator during processing and use. Under cell safety testing, especially under heavy impact, the separator is easily punctured, which reduces the pass rate of safety testing and fails to meet the requirements of the "new national standard". Summary of the Invention

[0005] The purpose of this invention is to provide a coated diaphragm with good heat resistance and high safety, and a method for preparing the same.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: The present invention provides a coated diaphragm, comprising a diaphragm substrate and a heat-resistant flexible coating coated on at least one surface of the diaphragm substrate; The heat-resistant flexible coating includes an organic-inorganic functional coating or an organic functional coating. The raw materials for preparing the organic-inorganic functional coating, by weight, include: 100 parts of organic-inorganic material, 0.5-10 parts of wetting and dispersing agent, 0.1-10 parts of crosslinking agent, 1-15 parts of film-forming substance, and 0.1-5 parts of anti-pinhole agent; the organic-inorganic material is composed of inorganic material and flexible heat-resistant organic material that coats or partially coats the outer surface of the inorganic material; The inorganic material is a gas-source type inorganic flame retardant material; The mass ratio of the gas-source inorganic flame-retardant material to the flexible heat-resistant organic material is 10:1~100; The raw materials for preparing the organic functional coating, by weight, include: 100 parts of flexible heat-resistant organic material, 0.5-10 parts of wetting and dispersing agent, 0.1-10 parts of crosslinking agent, 1-15 parts of film-forming substance, and 0.1-5 parts of anti-pinhole agent.

[0007] Preferably, the Mohs hardness of the gas-source inorganic flame retardant material is ≤4.

[0008] Preferably, the gas-source inorganic flame retardant material includes one or more of aluminum hydroxide, magnesium hydroxide, basic magnesium carbonate, zinc hydroxide, basic zinc carbonate, zinc borate, and ammonium polyphosphate.

[0009] Preferably, the softening temperature or glass transition temperature of the flexible heat-resistant organic material is 40~100℃.

[0010] Preferably, the flexible heat-resistant organic material includes one or more of acrylate copolymers, modified polystyrene (SAN), EVA, epoxy resin, polyurethane, modified SBR, and modified SAR.

[0011] Preferably, the crosslinking agent includes one or more of organic peroxides, diisocyanates, polyisocyanates, epoxy group-containing crosslinking agents, and silane coupling agents.

[0012] Preferably, the film-forming substance includes one or more of acrylamide copolymer, acrylonitrile copolymer, methacrylamide copolymer, methyl methacrylate copolymer, and (meth)acrylic acid copolymer.

[0013] Preferably, the diaphragm substrate includes a PP diaphragm, a PE diaphragm, or a non-woven fabric diaphragm.

[0014] This invention also provides a method for preparing the coated diaphragm described in the above technical solution. When the heat-resistant flexible coating is an organic-inorganic functional coating, the preparation method of the coated diaphragm includes: mixing a gas-source inorganic flame-retardant material, a flexible heat-resistant organic material, and an adhesive, followed by granulation to obtain an organic-inorganic material; mixing the organic-inorganic material, a wetting and dispersing agent, a crosslinking agent, a film-forming substance, and an anti-pinhole agent to obtain an organic-inorganic functional slurry; coating the organic-inorganic functional slurry onto at least one surface of the diaphragm substrate, and drying it to obtain the coated diaphragm; Alternatively, an organic-inorganic functional slurry is coated onto a release film, dried to obtain an organic-inorganic functional coating, and the organic-inorganic functional coating is transferred to one or both sides of the diaphragm substrate, followed by hot pressing to obtain a coated diaphragm. When the heat-resistant flexible coating is an organic functional coating, the preparation method of the coating membrane includes: A flexible heat-resistant organic material, a wetting and dispersing agent, a crosslinking agent, a film-forming substance, and an anti-pinhole agent are mixed to obtain an organic functional slurry; the organic functional slurry is coated on at least one surface of a diaphragm substrate and dried to obtain a coated diaphragm; Alternatively, an organic functional slurry can be coated onto a release film, dried to obtain an organic functional coating, and then the organic functional coating can be transferred to one or both sides of a diaphragm substrate and subjected to hot pressing to obtain a coated diaphragm.

[0015] Preferably, the adhesive is a compound containing one or more functional groups, namely hydroxyl, carboxyl, or ester groups.

[0016] This invention provides a coated diaphragm, comprising a diaphragm substrate and a heat-resistant flexible coating coated on at least one surface of the diaphragm substrate; the heat-resistant flexible coating comprises an organic-inorganic functional coating or an organic functional coating; by weight, the raw materials for preparing the organic-inorganic functional coating include: 100 parts of organic-inorganic material, 0.5-10 parts of wetting and dispersing agent, 0.1-10 parts of crosslinking agent, 1-15 parts of film-forming substance, and 0.1-5 parts of anti-pinhole agent; the organic-inorganic material is composed of... The coating is composed of an inorganic material and a flexible, heat-resistant organic material that coats or partially coats the outer surface of the inorganic material. The inorganic material is a gas-source inorganic flame-retardant material. The mass ratio of the gas-source inorganic flame-retardant material to the flexible, heat-resistant organic material is 10:1 to 100. By weight, the raw materials for preparing the organic functional coating include: 100 parts of flexible, heat-resistant organic material, 0.5 to 10 parts of wetting and dispersing agent, 0.1 to 10 parts of crosslinking agent, 1 to 15 parts of film-forming substance, and 0.1 to 5 parts of anti-pinhole agent. The coated diaphragm provided by this invention includes a diaphragm substrate and a heat-resistant flexible coating applied to at least one surface of the diaphragm substrate. The heat-resistant flexible coating includes an organic-inorganic functional coating or an organic functional coating. Including a flexible, heat-resistant organic material in the raw materials for preparing the organic functional coating can improve the heat resistance of the coated diaphragm. The raw materials for preparing the organic-inorganic functional coating include organic-inorganic materials, which consist of inorganic materials and flexible heat-resistant organic materials that coat or partially coat the outer surface of the inorganic materials. The inorganic materials are gas-source inorganic flame-retardant materials that can decompose and release inert gases, thereby improving flame-retardant safety characteristics. Furthermore, because the inorganic materials are coated or partially coated by the flexible heat-resistant organic materials, the released gases can cause the heat-resistant flexible coating to foam and expand, providing buffering and insulation effects and improving battery safety characteristics. The results of the embodiments show that the air permeability of the coating membrane provided by this invention increases by more than 10%; the stab strength reduction rate can reach 0%; the thermal shrinkage rate is significantly reduced at 130℃ for 1 hour; and after the coating membrane is used to prepare a lithium-ion battery, the needle penetration test and heavy object impact pass rate can both reach 100%. Detailed Implementation

[0017] The present invention provides a coated diaphragm, comprising a diaphragm substrate and a heat-resistant flexible coating coated on at least one surface of the diaphragm substrate; The heat-resistant flexible coating includes an organic-inorganic functional coating or an organic functional coating. The raw materials for preparing the organic-inorganic functional coating, by weight, include: 100 parts of organic-inorganic material, 0.5-10 parts of wetting and dispersing agent, 0.1-10 parts of crosslinking agent, 1-15 parts of film-forming substance, and 0.1-5 parts of anti-pinhole agent; the organic-inorganic material is composed of inorganic material and flexible heat-resistant organic material that coats or partially coats the outer surface of the inorganic material; The inorganic material is a gas-source type inorganic flame retardant material; The mass ratio of the gas-source inorganic flame-retardant material to the flexible heat-resistant organic material is 10:1~100; The raw materials for preparing the organic functional coating, by weight, include: 100 parts of flexible heat-resistant organic material, 0.5-10 parts of wetting and dispersing agent, 0.1-10 parts of crosslinking agent, 1-15 parts of film-forming substance, and 0.1-5 parts of anti-pinhole agent.

[0018] The coated diaphragm provided by this invention includes a diaphragm substrate. In this invention, the diaphragm substrate preferably includes a PP diaphragm, a PE diaphragm, or a non-woven fabric diaphragm. This invention does not specifically limit the source of the PP diaphragm, PE diaphragm, or non-woven fabric diaphragm; dry-process PP, wet-process PE, or non-woven fabric diaphragm substrates available to those skilled in the art can be used.

[0019] The coated diaphragm provided by the present invention includes a heat-resistant flexible coating applied to at least one surface of the diaphragm substrate.

[0020] In one embodiment of the present invention, the heat-resistant flexible coating includes an organic-inorganic functional coating.

[0021] The raw materials for preparing the organic-inorganic functional coating include 100 parts by weight of organic-inorganic materials.

[0022] In this invention, the organic-inorganic material is composed of an inorganic material and a flexible, heat-resistant organic material that covers or partially covers the outer surface of the inorganic material.

[0023] In this invention, the secondary particle size D50 of the organic-inorganic powder is preferably 2~10μm.

[0024] In this invention, the inorganic material is a gas-source inorganic flame-retardant material, and the Mohs hardness of the gas-source inorganic flame-retardant material is preferably ≤4. This invention uses a gas-source inorganic flame-retardant material with the aforementioned Mohs hardness, which has a low Mohs hardness. After the flexible heat-resistant coating material is transferred to the substrate surface, it forms an integral structure with the diaphragm substrate, effectively improving the heat resistance and safety performance of the diaphragm and reducing damage to the diaphragm during processing and use.

[0025] In this invention, the gas-source inorganic flame-retardant material is preferably in the form of flakes, oblate spheroids, or fibers. The use of gas-source inorganic flame-retardant materials with the aforementioned morphologies in this invention is more conducive to forming a supporting structure within a heat-resistant flexible coating.

[0026] In this invention, the gas-source inorganic flame retardant material preferably includes one or more of aluminum hydroxide, magnesium hydroxide, basic magnesium carbonate, zinc hydroxide, basic zinc carbonate, zinc borate, and ammonium polyphosphate. This invention utilizes the above-mentioned gas-source inorganic flame retardant material, which can decompose and release inert gas at relatively low temperatures (≤400℃). This improves flame retardant safety characteristics on the one hand; on the other hand, the released gas can cause the heat-resistant flexible coating to foam and expand, providing buffering and insulation effects, thus improving battery safety characteristics.

[0027] In this invention, the softening temperature or glass transition temperature of the flexible heat-resistant organic material is preferably 40~100℃. As one embodiment of the invention, the softening temperature or glass transition temperature of the flexible heat-resistant organic material can be 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, or 100℃. The flexible heat-resistant organic material used in this invention has a softening temperature or glass transition temperature within the above-mentioned temperature range and low molecular chain motion barriers, which allows it to maintain flexibility and deformability at lower temperatures, exhibiting good toughness.

[0028] In this invention, the flexible heat-resistant organic material preferably includes one or more of acrylate copolymers, modified polystyrene (SAN), EVA, epoxy resin, polyurethane, modified SBR, and modified SAR. In this invention, the acrylate copolymer is preferably an acrylate copolymer with a crosslinking degree not exceeding 50%. The crosslinking degree is evaluated by testing the mass swelling rate after immersion in the electrolyte; 100% crosslinking results in a mass swelling rate of 0%, while no crosslinking results in a mass swelling rate of 100%. This invention does not have a specific limitation on the source of the flexible heat-resistant organic material; conventional commercially available products are acceptable. In an embodiment of this invention, the flexible heat-resistant organic material can be sourced from Sichuan Yindile Technology Co., Ltd., and the model can be LCP32.

[0029] In this invention, the mass ratio of the gas-source inorganic flame-retardant material to the flexible heat-resistant organic material is 10:1 to 100. As one embodiment of this invention, the mass ratio of the gas-source inorganic flame-retardant material to the flexible heat-resistant organic material can be 10:1, 10:10, 10:20, 10:30, 10:40, 10:50, 10:60, 10:70, 10:80, 10:90, or 10:100. By controlling the mass ratio of the gas-source inorganic flame-retardant material to the flexible heat-resistant organic material within the above range, this invention makes it more advantageous for the flexible heat-resistant organic material to coat or partially coat the outer surface of the inorganic material.

[0030] The raw materials for preparing the organic-inorganic functional coating, based on 100 parts by weight of the organic-inorganic material, include 0.5 to 10 parts by weight of a wetting and dispersing agent. In one embodiment of the invention, the wetting and dispersing agent can be 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 parts by weight. The present invention uses a wetting and dispersing agent to achieve wetting, dispersion, suspension stabilization, and adhesion.

[0031] In this invention, the wetting and dispersing agent is preferably a medium-molecular-weight / high-molecular-weight wetting and dispersing agent, more preferably one or more of polyurethane block copolymers, hydroxyl-terminated polyacrylates, hydroxyl-terminated polyesters, polyether-modified organosiloxanes, modified polyacrylates, and polyvinyl alcohol-ammonium acrylate copolymers; the modified polyacrylate is preferably a polyacrylamide-acrylate-isooctyl ester copolymer. This invention selects medium-molecular-weight or high-molecular-weight wetting and dispersing agents because, on the one hand, the molecular chain segments contain hydrophilic groups such as hydroxyl, carboxyl, or amide groups, which adsorb onto the particle surface, forming electrostatic charge repulsion and providing excellent particle dispersion performance; on the other hand, the chain-like or branched molecular structure coated on the particle surface prevents particle agglomeration through steric hindrance, playing a role in dispersion and stabilization, and slowing down sedimentation; furthermore, the medium-molecular-weight / high-molecular-weight wetting and dispersing agent itself can form a film, interact with the particles, and provide a certain degree of adhesion, improving the adhesion of particles to the membrane substrate surface.

[0032] Based on 100 parts by weight of organic-inorganic materials, the raw materials for preparing the organic-inorganic functional coating include 0.1 to 10 parts by weight of a crosslinking agent. In one embodiment of the invention, the weight of the crosslinking agent can be 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 parts. By controlling the amount of crosslinking agent within the above range, the invention can prevent insufficient crosslinking from achieving the desired effect; it can also prevent excessive crosslinking agent usage. Firstly, excessive crosslinking agent may not react completely, leading to residual crosslinking agent that can easily cause side reactions in downstream battery applications. Secondly, excessive crosslinking can cause material agglomeration, making it brittle and hard, affecting the coating thickness and the safety performance of battery applications.

[0033] In this invention, the crosslinking agent preferably comprises one or more of organic peroxides, diisocyanates, polyisocyanates, epoxy-containing crosslinking agents, and silane coupling agents. In this invention, the organic peroxide preferably comprises dicumyl peroxide (DCP), di-tert-butyl peroxide (DTBP), benzoyl peroxide (BPO), or tert-butyl peroxide (TBPB); the diisocyanate preferably comprises MDI (4,4'-diphenylmethane diisocyanate), TDI (toluene diisocyanate), or HDI (hexamethylene diisocyanate); the polyisocyanate preferably comprises trimer (HDI) or blocked isocyanate; the epoxy-containing crosslinking agent... The crosslinking agent preferably includes bisphenol A diglycidyl ether (DGEBA), epichlorohydrin derivatives, alicyclic epoxy resins, or multifunctional epoxy curing agents; the silane coupling agent preferably includes KH-550 (γ-aminopropyltriethoxysilane), KH-560 (γ-glycidyl etheroxypropyltrimethoxysilane), KH-570 (γ-methacryloyloxypropyltrimethoxysilane), vinyltrimethoxysilane (VTMS), or methyltriethoxysilane (MTES). In this invention, since the flexible heat-resistant organic material may contain one or more polar or active functional groups for further reaction, such as amino, carboxyl, hydroxyl, double bonds, triple bonds, etc., it can further crosslink to improve the coating's structural strength and heat resistance. The addition of the crosslinking agent can promote crosslinking reactions on the surface of the material particles, reduce the conditions for curing and crosslinking, and improve the efficiency and effect of crosslinking. The present invention uses the above-mentioned crosslinking agent, which can further crosslink and cure under the action of crosslinking agent and temperature, and can achieve rapid crosslinking at a low temperature of 60~120℃, shortening the crosslinking time to less than 0.5h.

[0034] The raw materials for preparing the organic-inorganic functional coating include 1 to 15 parts of film-forming substance, based on 100 parts by weight of organic-inorganic materials. In one embodiment of the invention, the weight of the film-forming substance can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 parts. In this invention, the film-forming substance preferably includes one or more of acrylamide copolymer, acrylonitrile copolymer, methacrylamide copolymer, methyl methacrylate copolymer, and (meth)acrylic acid copolymer. The film-forming substance selected in this invention is a polymer material with excellent heat resistance, a high Tg value or softening temperature (Tg or Tf ≥ 100℃), film-forming properties, and good heat resistance and toughness after film formation. It can connect organic-inorganic materials into a whole and firmly adhere to the surface or interior of the diaphragm substrate.

[0035] The raw materials for preparing the organic-inorganic functional coating include 0.1 to 5 parts of an anti-pinhole agent, calculated based on 100 parts by weight of the organic-inorganic material. In one embodiment of the invention, the anti-pinhole agent can be 0.1, 0.5, 1, 2, 3, 4, or 5 parts by weight. In this invention, the anti-pinhole agent is preferably a wetting type, more preferably one or more of acetylenic diol ethoxylates, modified polysiloxanes, and modified polyether siloxane polymers. The use of the above-mentioned anti-pinhole agent (or anti-pinhole agent) in this invention can assist the functional slurry in wetting, spreading, and penetrating the surface, improving coating uniformity, providing coating adhesion, and preventing defects such as pinholes, white spots, and missed coatings.

[0036] In another embodiment of the present invention, the heat-resistant flexible coating includes an organic functional coating.

[0037] The raw materials for preparing the organic functional coating include 100 parts by weight of a flexible heat-resistant organic material. In this invention, the softening temperature or glass transition temperature of the flexible heat-resistant organic material is preferably 40-100°C. As one embodiment of this invention, the softening temperature or glass transition temperature of the flexible heat-resistant organic material can be 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C. The flexible heat-resistant organic material used in this invention has a softening temperature or glass transition temperature within the above-mentioned temperature range and a low molecular chain motion barrier, which allows it to maintain flexibility and deformability at lower temperatures, exhibiting good toughness.

[0038] In this invention, the flexible heat-resistant organic material preferably includes one or more of acrylate copolymers, modified polystyrene (SAN), EVA, epoxy resin, polyurethane, modified SBR, and modified SAR. In this invention, the acrylate copolymer is preferably an acrylate copolymer with a crosslinking degree not exceeding 50%. The crosslinking degree is evaluated by testing the mass swelling rate after immersion in the electrolyte; 100% crosslinking results in a mass swelling rate of 0%, while no crosslinking results in a mass swelling rate of 100%. This invention does not have a specific limitation on the source of the flexible heat-resistant organic material; conventional commercially available products can be used.

[0039] The raw materials for preparing the organic functional coating, with 100 parts by weight of flexible heat-resistant organic material, also include 0.5-10 parts of a wetting and dispersing agent, 0.1-10 parts of a crosslinking agent, 1-15 parts of a film-forming substance, and 0.1-5 parts of an anti-pinhole agent. In this invention, the types of wetting and dispersing agent, crosslinking agent, film-forming substance, and anti-pinhole agent are the same as those described in the above technical solutions, and will not be repeated here.

[0040] The coated separator provided by this invention includes a separator substrate and a heat-resistant flexible coating coated on at least one surface of the separator substrate; the heat-resistant flexible coating includes an organic-inorganic functional coating or an organic functional coating. The raw materials for preparing the organic functional coating include a flexible heat-resistant organic material, which can improve the heat resistance of the coated separator. The raw materials for preparing the organic-inorganic functional coating include an organic-inorganic material, which is composed of an inorganic material and a flexible heat-resistant organic material covering or partially covering the outer surface of the inorganic material; the inorganic material is a gas-source inorganic flame-retardant material, capable of decomposing and releasing inert gas, thereby improving flame-retardant safety characteristics; on the other hand, because the inorganic material is covered or partially covered by the flexible heat-resistant organic material, the gas released by the inorganic material can cause the heat-resistant flexible coating to foam and expand, playing a buffering and insulating role, and improving battery safety characteristics.

[0041] This invention also provides a method for preparing the coated diaphragm described in the above technical solution. When the heat-resistant flexible coating is an organic-inorganic functional coating, the preparation method of the coated diaphragm includes: mixing a gas-source inorganic flame-retardant material, a flexible heat-resistant organic material, and an adhesive, followed by granulation to obtain an organic-inorganic material; mixing the organic-inorganic material, a wetting and dispersing agent, a crosslinking agent, a film-forming substance, and an anti-pinhole agent to obtain an organic-inorganic functional slurry; coating the organic-inorganic functional slurry onto at least one surface of the diaphragm substrate, and drying it to obtain the coated diaphragm; Alternatively, an organic-inorganic functional slurry is coated onto a release film, dried to obtain an organic-inorganic functional coating, and then the organic-inorganic functional coating is transferred to one or both sides of the diaphragm substrate and subjected to hot pressing to obtain a coated diaphragm.

[0042] This invention involves mixing gas-source inorganic flame-retardant materials, flexible heat-resistant organic materials, and adhesives, followed by granulation to obtain an organic-inorganic material.

[0043] In this invention, the type of gas-source inorganic flame retardant material is the same as that described in the above technical solution, and will not be repeated here.

[0044] In this invention, the secondary particle size D50 of the gas-source inorganic flame retardant material is preferably 5~30μm.

[0045] In this invention, the type of flexible heat-resistant organic material is the same as that described in the above technical solution, and will not be repeated here.

[0046] In this invention, the flexible heat-resistant organic material can be granular, or it can be spherical, ellipsoidal, irregular polyhedral, disc-shaped, needle-shaped, sheet-like, comb-like, dendritic, or mesh-like. In this invention, the secondary particle size D50 of the flexible heat-resistant organic material is preferably 10~50 μm.

[0047] In this invention, the adhesive is preferably a compound containing one or more functional groups, including hydroxyl, carboxyl, or ester groups, more preferably polyvinyl alcohol, ethylene vinyl acetate copolymer, aqueous acrylate copolymer, or sodium carboxymethyl cellulose. In this invention, the degree of alcoholysis of the polyvinyl alcohol is preferably 80-99%; the VA content of the ethylene vinyl acetate copolymer is preferably 20-40%; and the Tg of the aqueous acrylate copolymer is preferably 40-100°C. In this invention, the aqueous acrylate copolymer can be prepared by combining methyl methacrylate, styrene, and other hard monomers with a small amount of butyl acrylate (to obtain a polymethyl methacrylate-styrene-butyl acrylate copolymer with a Tg of approximately 60°C). The degree of substitution of the sodium carboxymethyl cellulose can be 0.5 ≤ DS ≤ 1.0. In this invention, the adhesive can be sourced from Kuraray PVA-420H (Japan). This invention, by adding the aforementioned adhesive, can be a liquid, solid, or powder. During the granulation process, it undergoes high-speed collision, friction, and mixing to form a relatively uniform blend. The adhesive acts as a bridge, connecting the gas-source inorganic flame-retardant material and the flexible heat-resistant organic material. Of course, after softening, the flexible heat-resistant organic material can also directly coat and adhere to the inorganic material. After the blending is completed and cooled, an organic-inorganic composite material is formed, realizing the inorganic material being coated or partially coated by the organic material.

[0048] In this invention, the mass percentage of the adhesive aid in the total mass of the gas-source inorganic flame retardant material and the flexible heat-resistant organic material is preferably 0.1-10%, more preferably 1-5%.

[0049] In this invention, the granulation method is preferably a dry blending method; the dry blending method is preferably carried out in the grinding chamber of an air jet mill. In this invention, the air pressure in the grinding chamber of the air jet mill is preferably 0.6~1.0 MPa, more preferably 0.8~1.0 MPa; the air velocity is preferably 2~4 times the speed of sound; and the hot air temperature is preferably 40~100℃, more preferably 50~80℃.

[0050] After obtaining the organic-inorganic material, the present invention mixes the organic-inorganic material, wetting and dispersing agent, crosslinking agent, film-forming substance and anti-pinhole agent to obtain organic-inorganic functional slurry.

[0051] In this invention, the preferred method for mixing the organic-inorganic material, wetting and dispersing agent, crosslinking agent, film-forming substance, and anti-pinhole agent is as follows: the organic-inorganic material is first mixed with a mixed solvent to obtain a dispersion, and the wetting and dispersing agent, crosslinking agent, film-forming substance, and anti-pinhole agent are added to the dispersion for a second mixing to obtain an organic-inorganic functional slurry.

[0052] In this invention, the mixed solvent preferably includes one or a combination of several of the following: water, ethanol, isopropanol, butanol, ethyl acetate, butyl acetate, N-methylpyrrolidone, N,N-dimethylacetamide, and DMSO. In this invention, the amount of the mixed solvent is preferably sufficient to achieve a solid content of 5-50% in the organic-inorganic functional slurry.

[0053] In this invention, the preferred rotational speed for the first mixing is 200-1000 rpm, more preferably 500-800 rpm; the preferred mixing time is 0.1-2 h, more preferably 0.5-1 h; and the preferred flow rate for the first mixing is 1-10 kg / min, more preferably 5-10 kg / min. In this invention, the preferred apparatus for the first mixing is a horizontal sand mill, a vertical mill, a double planetary ball mill, or a conical mill. By performing the first mixing under the above parameters, this invention can obtain a dispersion with uniform performance.

[0054] The present invention does not have a specific time limit for the second mixing, as long as the wetting and dispersing agent, crosslinking agent, film-forming substance and anti-pinhole agent are uniformly dispersed in the dispersion.

[0055] After obtaining the organic-inorganic functional slurry, the present invention coats the organic-inorganic functional slurry onto at least one side of the membrane substrate and dries it to obtain a coated membrane.

[0056] In this invention, the coating method is preferably microgravure roller reverse transfer coating or wire rod coating. This invention does not specifically limit the specific operating parameters of the microgravure roller reverse transfer coating or wire rod coating, as long as a uniform coating thickness can be formed on the diaphragm substrate.

[0057] In this invention, the drying temperature is preferably 60-90°C, more preferably 70-80°C. This invention does not have a particular limitation on the drying time, as long as it is sufficient to completely remove the solvent from the coating.

[0058] As one embodiment of the present invention, the method for preparing the coated diaphragm includes: coating an organic-inorganic functional slurry onto a release film, drying it to obtain an organic-inorganic functional coating, transferring the organic-inorganic functional coating to one or both sides of a diaphragm substrate, and then performing a hot-pressing treatment to obtain a coated diaphragm.

[0059] In this invention, the drying temperature is preferably 60-90°C, more preferably 70-80°C. This invention does not have a particular limitation on the drying time, as long as it is sufficient to completely remove the solvent from the coating.

[0060] In this invention, the temperature of the hot pressing process is preferably 40~100℃, more preferably 50~80℃; the pressure of the hot pressing process is preferably 5~10 kgf. By performing hot pressing at the above temperatures, this invention can achieve the softening temperature or glass transition temperature of organic materials and adhesives.

[0061] In this invention, when the heat-resistant flexible coating is an organic functional coating, the preparation method of the coating membrane includes: mixing a flexible heat-resistant organic material, a wetting and dispersing agent, a crosslinking agent, a film-forming substance, and an anti-pinhole agent to obtain an organic functional slurry.

[0062] In this invention, the preferred method for mixing the flexible heat-resistant organic material, wetting and dispersing agent, crosslinking agent, film-forming substance, and anti-pinhole agent is as follows: the flexible heat-resistant organic material is first mixed with a mixed solvent to obtain a dispersion; the wetting and dispersing agent, crosslinking agent, film-forming substance, and anti-pinhole agent are added to the dispersion, and a second mixing is performed to obtain an organic functional slurry.

[0063] In this invention, the mixed solvent preferably includes one or a combination of several of the following: water, ethanol, isopropanol, butanol, ethyl acetate, butyl acetate, N-methylpyrrolidone, N,N-dimethylacetamide, and DMSO. In this invention, the amount of the mixed solvent is preferably sufficient to achieve a solid content of 5-50% in the organic functional slurry.

[0064] In this invention, the preferred rotational speed for the first mixing is 200-1000 rpm, more preferably 500-800 rpm; the preferred mixing time is 0.1-2 h, more preferably 0.5-1 h; and the preferred flow rate for the first mixing is 1-10 kg / min, more preferably 5-10 kg / min. In this invention, the preferred apparatus for the first mixing is a horizontal sand mill, a vertical mill, a double planetary ball mill, or a conical mill. By performing the first mixing under the above parameters, this invention can obtain a dispersion with uniform performance.

[0065] The present invention does not have a specific time limit for the second mixing, as long as the wetting and dispersing agent, crosslinking agent, film-forming substance and anti-pinhole agent are uniformly dispersed in the dispersion.

[0066] After obtaining the organic functional slurry, the present invention coats the organic functional slurry onto at least one side of the membrane substrate and dries it to obtain a coated membrane.

[0067] In this invention, the parameters for coating and drying are the same as those for coating and drying in the above-described technical solutions, and will not be repeated here.

[0068] As one embodiment of the present invention, the method for preparing the coated diaphragm includes: coating an organic functional slurry onto a release film, drying it to obtain an organic functional coating, transferring the organic functional coating to one or both sides of a diaphragm substrate, and then performing a hot pressing treatment to obtain the coated diaphragm.

[0069] In this invention, the parameters for the drying and hot-pressing processes are the same as those for the drying and hot-pressing processes described in the above technical solutions, and will not be repeated here.

[0070] The method provided by this invention is simple to operate and easy to control, and can produce coated diaphragms with excellent safety.

[0071] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0072] Example 1 A coated diaphragm comprises a diaphragm substrate and a heat-resistant flexible coating coated on one side surface of the diaphragm substrate; the heat-resistant flexible coating is an organic-inorganic functional coating. The raw materials for preparing the organic-inorganic functional coating, by weight, are: 100 parts organic-inorganic material, 0.5 parts wetting and dispersing agent (polyether-modified organosiloxane), 10 parts crosslinking agent (benzoyl peroxide), 1 part film-forming substance (acrylonitrile copolymer emulsion with 40% solid content), and 0.1 parts anti-pinhole agent (modified polysiloxane anti-pinhole agent, German BYK brand 20990). The organic-inorganic material is composed of inorganic material and flexible heat-resistant organic material coated on the outer surface of the inorganic material. The gas-source inorganic flame retardant material (flake magnesium hydroxide, D50=5μm) and the flexible heat-resistant organic material are modified SAR (styrene-acrylate copolymer) spherical organic powders (D50=10μm, Tg=40℃, crosslinking degree 40%). The mass ratio of the gas-source inorganic flame retardant material to the flexible heat-resistant organic material is 10:100.

[0073] The method for preparing the coated diaphragm is as follows: (1) Organic-inorganic material pretreatment: 100 parts of modified SAR (styrene-acrylate copolymer) spherical organic powder (D50=10μm, Tg=40℃, crosslinking degree 40%), 10 parts of flake magnesium hydroxide (D50=5μm), and 0.11 parts of PVA particles with a degree of alcoholysis of 98% were added to the feed pipe and conveyed to the air jet mill for air jet milling. The air pressure was 0.6MPa, the air flow rate was twice the speed of sound, and the hot air temperature was 40℃. After air jet milling for 10min, the output particle size D50=2μm was obtained, and irregular polyhedral material B was obtained, which is the organic-inorganic material. (2) Add 50 parts of material B obtained in step (1) to a mixed solvent consisting of 50 parts of water and 50 parts of ethanol, add 0.25 parts of polyether modified organosiloxane, disperse by vertical grinding process, dispersion speed 400 rpm, grinding for 0.5 h, flow rate 3 kg / min to obtain material B dispersion, add 5 parts of benzoyl peroxide, 1.25 parts of acrylonitrile copolymer emulsion (40% solid content), 0.05 parts of modified polysiloxane anti-pinhole agent, mix evenly to obtain an organic-inorganic functional slurry with a solid content of 35.6%, which is denoted as the functional slurry of material B; (3) The functional slurry of material B obtained in step (2) is coated on one side of the diaphragm substrate by reverse transfer coating with a micro-gravure roller at a coating speed of 50 m / min. Then, it is dried in an oven at 60°C for 24 s to remove the solvent and obtain the coated diaphragm.

[0074] Test Results: The diaphragm substrate used in this embodiment is uniaxially stretched PP material with a thickness of 12.5 μm and a porosity of 42%. The coating thickness of the diaphragm prepared in this embodiment is 2.5 ± 0.5 μm, the air permeability increase rate is 10%, at 130℃ for 1 h, MD=2.5%, TD=0%, the diaphragm electrical weakness test voltage is 100V / μ, the number of electrical weaknesses is 2 / 50m, the puncture strength decrease rate is 4%, the mass swelling rate of the coating organic material is 50%, the Mohs hardness of the coating material is 2.5, and the coated diaphragm applied to the battery has a 100% pass rate in the needle penetration test and heavy object impact test.

[0075] Example 2 A coated diaphragm comprises a diaphragm substrate and a heat-resistant flexible coating coated on one side surface of the diaphragm substrate; the heat-resistant flexible coating is an organic-inorganic functional coating. The raw materials for preparing the organic-inorganic functional coating, by weight, are: 100 parts organic-inorganic material, 10 parts wetting and dispersing agent (polyacrylamide-isooctyl acrylate copolymer), 0.1 parts crosslinking agent (tert-butyl peroxide), 15 parts film-forming substance (40% solid content methacrylamide copolymer emulsion), and 5 parts anti-pinhole agent (acetylenic diol ethoxylate anti-pinhole agent Tianjin Hepufele FS-204H); the organic-inorganic material is composed of inorganic material and flexible heat-resistant organic material coating the outer surface of the inorganic material; the gas-source inorganic flame retardant material (flattened spherical aluminum hydroxide D50=30μm) and the flexible heat-resistant organic material are modified SAN (styrene-acrylonitrile copolymer) ellipsoidal organic powder (D50=50μm, Tg=100℃, crosslinking degree 10%); the mass ratio of the gas-source inorganic flame retardant material to the flexible heat-resistant organic material is 10:1.

[0076] The method for preparing the coated diaphragm is as follows: (1) 10 parts of modified SAN (styrene-acrylonitrile copolymer) ellipsoidal organic powder (D50=50μm, Tg=100℃, crosslinking degree 10%), 100 parts of flattened spherical aluminum hydroxide (D50=30μm), and 11 parts of sodium carboxymethyl cellulose powder with a degree of substitution DS=0.85 were added to the feed pipe and conveyed to an air jet mill for air jet milling. The air pressure was 1.0MPa, the air flow rate was 4 times the speed of sound, and the hot air temperature was 100℃. After air jet milling for 30min, the output particle size D50=10μm was obtained, and a spherical organic-inorganic material was obtained, which was denoted as material B. (2) 100 parts of material B obtained in step (1) are added to a mixed solvent consisting of 97.6 parts of water and 10 parts of isopropanol, and 10 parts of polyacrylamide-acrylate-isooctyl ester copolymer are added. The mixture is dispersed by horizontal grinding at a speed of 1000 rpm for 2 hours and a flow rate of 10 kg / min to obtain a dispersion of material B. 0.1 parts of tert-butyl peroxide, 37.5 parts of methacrylamide copolymer emulsion (40% solid content), and 5 parts of acetylacetonate ethoxylate anti-pinhole agent are added and mixed evenly to obtain an organic-inorganic functional slurry with a solid content of 50%, which is referred to as the functional slurry of material B. (3) The functional slurry of material B obtained in step (2) is coated on one side of the diaphragm substrate by reverse transfer coating with a micro-gravure roller at a coating speed of 100 m / min. Then, it is dried in an oven at 90°C for 12 seconds to remove the solvent, thereby obtaining the coated diaphragm. Test Results: The diaphragm substrate used in this embodiment is a non-woven fabric substrate with a thickness of 12μm and a porosity of 60%. The coating thickness of the coated diaphragm prepared in this embodiment is 4±0.5μm, the air permeability increase rate is 20%, MD=0.5%, TD=0.1% at 130℃ for 1h, the diaphragm electrical weakness test voltage is 100V / μ, the number of electrical weaknesses is 5 / 50m, the puncture strength decrease rate is 0%, the mass swelling rate of the coating organic material is 10%, the Mohs hardness of the coating material is 3.0, and the coated diaphragm applied to the battery has a 100% pass rate in needle penetration test and heavy object impact test.

[0077] Example 3 A coated diaphragm comprises a diaphragm substrate and a heat-resistant flexible coating coated on one side surface of the diaphragm substrate; the heat-resistant flexible coating is an organic-inorganic functional coating. The raw materials for preparing the organic-inorganic functional coating, by weight, are: 100 parts organic-inorganic material, 5 parts wetting and dispersing agent (hydroxyl-terminated polyacrylate), 5 parts crosslinking agent (KH-550), 8 parts film-forming substance (40% solid content methyl methacrylate copolymer emulsion), and 2.5 parts anti-pinhole agent (modified polyether siloxane polymer anti-pinhole agent Tu Yi Le® Superwet4000); the organic-inorganic material is composed of inorganic material and flexible heat-resistant organic material coating the outer surface of the inorganic material; the gas-source inorganic flame retardant material is oblate ammonium polyphosphate (D50=10μm), and the flexible heat-resistant organic material is acrylate copolymer cake-shaped organic powder (D50=20μm, Tg=60℃, crosslinking degree 30%); the mass ratio of the gas-source inorganic flame retardant material to the flexible heat-resistant organic material is 10:10.

[0078] The method for preparing the coated diaphragm is as follows: (1) 100 parts of acrylate copolymer cake-shaped organic powder (D50=20μm, Tg=60℃, crosslinking degree 30%), 100 parts of oblate ammonium polyphosphate (D50=10μm), and 10 parts of ethylene vinyl acetate copolymer with VA content of 20-40% were added to the feed pipe and conveyed to the air jet mill for air jet milling. The air pressure was 0.8MPa, the air flow rate was 3 times the speed of sound, and the hot air temperature was 80℃. After air jet milling for 20min, the output particle size D50=6μm was obtained, and ellipsoidal organic-inorganic material B was obtained, which was denoted as material B. (2) Add 10 parts of material B obtained in step (1) to a mixed solvent consisting of 200 parts of water and 27.6 parts of N-methylpyrrolidone, add 0.5 parts of hydroxyl-terminated polyacrylate, disperse by conical milling process, disperse at 8000 rpm, grind for 1 h, flow rate 5 kg / min to obtain material B dispersion, add 0.5 parts of silane coupling agent KH-550, 2 parts of methyl methacrylate copolymer emulsion (40% solid content), 0.25 parts of modified polyether siloxane polymer anti-pinhole agent, mix evenly to obtain an organic-inorganic functional slurry with a solid content of 5%, denoted as the functional slurry of material B; (3) The functional slurry of material B obtained in step (2) is coated on one side of a 50μm release paper substrate by a gravure roller forward transfer coating method. The coating speed is 30m / min. Then, it is dried in an oven at 70℃ for 20s to remove the solvent. After drying, the coating is transferred to the surface of the diaphragm substrate by hot pressing (pressure 8kg, temperature 60℃) to obtain a heat-resistant, safe, flexible coated diaphragm. Test Results: The membrane substrate used in this embodiment is a wet-process PE substrate with a thickness of 12 μm and a porosity of 35%. The coating thickness of the coated membrane prepared in this embodiment is 2 ± 0.5 μm, the air permeability increase rate is 10%, at 130℃ for 1 h, MD=2.8%, TD=2.5%, the membrane electrical weak current test voltage is 100V / μm, the number of electrical weak points is 0 / 50m, the puncture strength decrease rate is 1%, the mass swelling rate of the coating organic material is 30%, the Mohs hardness of the coating material is 1.2, and the coated membrane applied to the battery has a 100% pass rate in the needle penetration test and heavy object impact test.

[0079] Example 4 The difference between Example 4 and Example 1 is that: no inorganic materials are added in step (1) organic-inorganic material pretreatment, and the remaining components and preparation methods are the same as in Example 1.

[0080] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that no organic material is added in step (1) organic-inorganic material pretreatment, and the remaining components and preparation methods are the same as in Example 1.

[0081] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in step (1) organic-inorganic material pretreatment, all organic and inorganic materials are replaced with alumina materials (Mohs hardness = 9), and the remaining components and preparation methods are the same as in Example 1.

[0082] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that step (1) is omitted, and modified SAR (styrene-acrylate copolymer) spherical organic powder (D50=10μm, Tg=40℃, crosslinking degree 40%) and flake magnesium hydroxide are directly added in step (2). The remaining components and preparation methods are the same as in Example 1.

[0083] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that no wetting and dispersing agent is added in step (2), while the remaining components and preparation methods are the same as in Example 1.

[0084] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that no crosslinking agent is added in step (2), while the remaining components and preparation methods are the same as in Example 1.

[0085] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that no anti-pinhole agent is added in step (2), while the remaining components and preparation methods are the same as in Example 1.

[0086] Comparative Example 7 Using the dry PP substrate of Example 1, without any coating process, the substrate thickness is 12.5 μm and the porosity is 42%.

[0087] Test case The separators prepared in Examples 1-4 and Comparative Examples 1-7 were used to fabricate cylindrical batteries with a rated capacity of 2 Ah. The positive electrode was NCM622, and the negative electrode was graphite. The electrolyte consisted of EC / EMC = 3 / 7 (v / v), 1 M LiPF6, and 2% VC. The lithium-ion battery separators of Examples 1-4 and Comparative Examples 1-7 were measured for coating thickness, air permeability increase rate at 130°C for 1 hour, MD / TD thermal shrinkage rate, number of electrical weak points, puncture strength reduction rate, coating material mass swelling rate, coating material Mohs hardness, and puncture strength. After the separators were made into batteries, the needle penetration test and heavy object impact pass rate of the batteries were measured. The results are shown in Table 1. Table 1. Test results of the separators and batteries prepared in the examples and comparative examples.

[0088] As can be seen from Table 1, the coated separator prepared in Example 1, through a superior formulation and process, exhibits the best overall physicochemical properties: moderate coating thickness, small increase in air permeability, low MD / TD thermal shrinkage rate at 130℃ for 1 hour, few electrical weaknesses, low puncture strength reduction rate, moderate swelling rate of organic materials, and low Mohs hardness. The battery prepared from the heat-resistant, safe, flexible coated dry-process PP separator prepared in Example 1 achieved a 100% pass rate in the needle penetration test and heavy object impact test.

[0089] The results from Example 2 show that as the coating thickness increases to 4 μm, the rate of increase in air permeability doubles. This is because the nonwoven fabric substrate has high porosity, allowing the functional slurry to penetrate into the substrate after coating, causing slight pore blockage. Thanks to the use of a nonwoven fabric substrate, the heat-resistant, safe, and flexible coated nonwoven fabric separator exhibits very low MD / TD thermal shrinkage at 130°C for 1 hour. The number of electrical weak points increases to the upper limit of 5 per 50m, the puncture strength decreases by 0%, the organic material swelling rate reaches the lower limit of 10%, the Mohs hardness is 3.0, and the needle penetration test and heavy object impact test pass rates of the battery manufactured using the separator from Example 2 are both 100%. The results of Example 3 show that using a wet-process PE substrate, the coating thickness is reduced to 2μm, the increase in air permeability is small, and the MD / TD thermal shrinkage rate at 130℃ for 1h is slightly larger. This is due to the high strength of the wet-process membrane, the number of electrical weak points is 0, the puncture strength decrease rate is only 1%, the swelling rate of organic materials is 30%, which is moderate; the Mohs hardness is low, at 1.2; the battery prepared by the separator of Example 3 also has a 100% pass rate in the needle penetration test and heavy object impact test.

[0090] As can be seen from the results of Example 4, based on Example 1, the inorganic material was reduced while the coating thickness remained unchanged. Because the organic material was packed more densely, its heat resistance was slightly lower than that of the inorganic material, resulting in a slightly larger increase in air permeability after coating and a slightly larger MD / TD thermal shrinkage rate at 130°C for 1 hour. Thanks to the low Mohs hardness of the organic material (only 1.2), the number of electrical weak points in the separator after coating was only 1, and the puncture strength reduction rate was only 2%. The battery prepared with the separator of Example 4 also achieved a 100% pass rate in both the needle penetration test and the heavy object impact test.

[0091] Compared with Example 1, in step (1) organic-inorganic material pretreatment, no organic material was added. The lack of organic material resulted in an excessive number of electrical weak points, reaching 8, and the puncture strength reduction rate reached 10%. The swelling rate of organic material was only 5%, which was significantly low. The battery prepared by the separator of Comparative Example 1 passed the needle penetration test with a rate of only 70% and the heavy object impact test with a rate of only 60%.

[0092] Compared with Example 1, in step (1) organic-inorganic material pretreatment, all organic and inorganic materials were replaced with alumina materials (Mohs hardness = 9), which is equivalent to using a conventional alumina ceramic slurry scheme. The prepared coating membrane had more than 15 electrical weaknesses, a puncture strength reduction rate of 30%, an organic material swelling rate of only 4%, and a Mohs hardness of 9, making the coating very hard and easy to damage the membrane substrate. The battery prepared from the membrane of Comparative Example 2 passed the needle penetration test with only 75% pass and the heavy object impact pass rate was as low as 40%.

[0093] Compared with Example 1, Comparative Example 3, the organic-inorganic material pretreatment in step (1) was directly added before grinding in the functional slurry preparation process in step (2). Due to the lack of organic-inorganic material pretreatment, the organic and inorganic materials were poorly bonded, the coating thickness increased to 2.8 μm, the air permeability increased by 13%, the MD / TD thermal shrinkage rate increased at 130℃ for 1 hour, the MD exceeded the standard by 3.5%, the number of electrical weak points exceeded the standard by 6, and the puncture strength decreased by 7%. The battery prepared by the separator of Comparative Example 3 only passed the needle penetration test by 80%, and the heavy object impact pass rate was only 70%.

[0094] Compared with Example 1, Comparative Example 4 did not add a wetting and dispersing agent in step (2). Due to the lack of a highly efficient wetting and dispersing agent, the organic and inorganic materials were poorly dispersed, the coating thickness increased to 3 μm, the air permeability increased by 11%, the MD / TD thermal shrinkage rate increased at 130°C for 1 hour, the MD exceeded the standard by 4%, the number of electrical weak points exceeded the standard by 7, and the puncture strength decreased by 8%. The battery prepared by the separator of Comparative Example 4 only passed the needle penetration test by 72%, and the heavy object impact pass rate was only 65%.

[0095] Compared with Example 1, no crosslinking agent was added in step (2) of Comparative Example 5. Due to the lack of crosslinking agent, the organic material was further crosslinked to improve the heat resistance. As a result, the MD / TD heat shrinkage rate increased at 130°C for 1 hour, and the MD exceeded the standard to 3.8%, which reduced the heat resistance safety performance. The battery prepared by the separator of Comparative Example 5 passed the needle penetration test 85% and the heavy object impact test 95%, which did not reach the 100% pass rate.

[0096] Compared with Example 1, Comparative Example 6 did not add anti-pinhole agent in step (2). Due to the lack of anti-pinhole agent, the slurry was poorly wetted and penetrated on the surface and inside of the substrate, resulting in uneven spreading and substandard coverage. This led to an increase in the MD / TD thermal shrinkage rate at 130℃ for 1 hour, with MD exceeding the standard by 3.9%, and a decrease in heat resistance and safety performance. The battery prepared by the separator of Comparative Example 6 passed the needle penetration test with a pass rate of 75% and the heavy object impact test with a pass rate of 85%, failing to reach 100% pass rate.

[0097] Compared with Example 1, Comparative Example 7 used the dry PP substrate of Example 1 without any coating process. Due to the lack of necessary coating, the substrate did not have an additional coating to provide heat resistance support, resulting in a significant increase in the MD / TD thermal shrinkage rate at 130°C for 1 hour, with MD exceeding the standard by 4.5%, and a significant decrease in heat resistance safety performance. The battery prepared with the separator of Comparative Example 7 only passed the needle penetration test by 50%, the heavy object impact test by 50%, and the core safety test by only half.

[0098] As can be seen from the test results of the diaphragms prepared in the above embodiments and comparative examples, the functional coating of a heat-resistant, safe, and flexible coating diaphragm has a significant impact on the performance of the diaphragm substrate. The coating provided by this invention is mainly composed of heat-resistant organic (material A) or organic-inorganic composite material (material B). The raw materials of the functional coating diaphragm also include crosslinking agents, film-forming substances, and anti-pinhole agents. This invention, by preparing a unique functional slurry containing material A or material B, can form a functional layer on the diaphragm surface, or partially or completely penetrate into the porous structure inside the diaphragm, thereby forming a 2D (surface coating) or 3D (coating from the surface to the interior) structure coating on the diaphragm. The particle surface may contain polar or active functional groups, which can further undergo chemical reactions under certain conditions, increasing the chemical interaction strength between coating particles and forming a tightly connected integral structure, thereby improving the heat resistance and dimensional stability of the coating at high temperatures. The coating endows the diaphragm with heat-resistant and safe performance: low thermal shrinkage rate, high flexibility, and dimensional stability at high temperatures. The coating material has low Mohs hardness, certain elasticity, and excellent heat resistance. After being coated or hot-pressed onto the substrate surface, the flexible heat-resistant coating material forms an integral structure with the separator substrate, which can effectively improve the heat resistance and safety performance of the separator material, reduce damage to the separator during processing and use, solve problems such as difficulty in passing safety tests such as needle penetration and heavy object impact, meet the battery testing requirements of the "new national standard", and help the large-scale application of heat-resistant and safe flexible coating separators in power and energy storage batteries.

[0099] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A coated diaphragm, comprising a diaphragm substrate and a heat-resistant flexible coating applied to at least one surface of the diaphragm substrate; The heat-resistant flexible coating includes an organic-inorganic functional coating or an organic functional coating. The raw materials for preparing the organic-inorganic functional coating, by weight, include: 100 parts of organic-inorganic material, 0.5-10 parts of wetting and dispersing agent, 0.1-10 parts of crosslinking agent, 1-15 parts of film-forming substance, and 0.1-5 parts of anti-pinhole agent; the organic-inorganic material is composed of inorganic material and flexible heat-resistant organic material that coats or partially coats the outer surface of the inorganic material; The inorganic material is a gas-source type inorganic flame retardant material; The mass ratio of the gas-source inorganic flame-retardant material to the flexible heat-resistant organic material is 10:1~100; The raw materials for preparing the organic functional coating, by weight, include: 100 parts of flexible heat-resistant organic material, 0.5-10 parts of wetting and dispersing agent, 0.1-10 parts of crosslinking agent, 1-15 parts of film-forming substance, and 0.1-5 parts of anti-pinhole agent.

2. The coated diaphragm according to claim 1, characterized in that, The Mohs hardness of the gas-source inorganic flame-retardant material is ≤4.

3. The coated diaphragm according to claim 1, characterized in that, The gas-source inorganic flame retardant material includes one or more of aluminum hydroxide, magnesium hydroxide, basic magnesium carbonate, zinc hydroxide, basic zinc carbonate, zinc borate, and ammonium polyphosphate.

4. The coated diaphragm according to claim 1, characterized in that, The softening temperature or glass transition temperature of the flexible heat-resistant organic material is independently 40~100℃.

5. The coated diaphragm according to claim 4, characterized in that, The flexible heat-resistant organic material includes one or more of acrylate copolymers, modified polystyrene (SAN), EVA, epoxy resin, polyurethane, modified SBR, and modified SAR.

6. The coated diaphragm according to claim 1, characterized in that, The crosslinking agent includes one or more of organic peroxides, diisocyanates, polyisocyanates, epoxy group-containing crosslinking agents, and silane coupling agents.

7. The coated diaphragm according to claim 1, characterized in that, The film-forming substance includes one or more of acrylamide copolymer, acrylonitrile copolymer, methacrylamide copolymer, methyl methacrylate copolymer, and (meth)acrylic acid copolymer.

8. The coated diaphragm according to claim 1, characterized in that, The diaphragm substrate includes PP diaphragm, PE diaphragm or non-woven fabric diaphragm.

9. A method for preparing the coated diaphragm according to any one of claims 1 to 8, characterized in that, When the heat-resistant flexible coating is an organic-inorganic functional coating, the preparation method of the coated diaphragm includes: mixing a gas-source inorganic flame-retardant material, a flexible heat-resistant organic material, and an adhesive, followed by granulation to obtain an organic-inorganic material; mixing the organic-inorganic material, a wetting and dispersing agent, a crosslinking agent, a film-forming substance, and an anti-pinhole agent to obtain an organic-inorganic functional slurry; coating the organic-inorganic functional slurry onto at least one surface of the diaphragm substrate, and drying it to obtain the coated diaphragm; Alternatively, an organic-inorganic functional slurry is coated onto a release film, dried to obtain an organic-inorganic functional coating, and the organic-inorganic functional coating is transferred to one or both sides of the diaphragm substrate, followed by hot pressing to obtain a coated diaphragm. When the heat-resistant flexible coating is an organic functional coating, the preparation method of the coating membrane includes: A flexible heat-resistant organic material, a wetting and dispersing agent, a crosslinking agent, a film-forming substance, and an anti-pinhole agent are mixed to obtain an organic functional slurry; the organic functional slurry is coated on at least one surface of a diaphragm substrate and dried to obtain a coated diaphragm; Alternatively, an organic functional slurry can be coated onto a release film, dried to obtain an organic functional coating, and then the organic functional coating can be transferred to one or both sides of a diaphragm substrate and subjected to hot pressing to obtain a coated diaphragm.

10. The preparation method according to claim 9, characterized in that, The adhesive is a compound containing one or more functional groups, namely hydroxyl, carboxyl, or ester groups.

Images