Diaphragm and lithium ion battery

Abstract

This invention relates to the field of lithium-ion battery materials and manufacturing technology, specifically to separators and lithium-ion batteries. The separator comprises a porous base membrane and a composite coating; the dry raw materials of the composite coating, by mass percentage, include: 30%-50% polar inorganic ceramic framework, 20%-40% mesoporous metal-organic framework, 10%-25% polar hot-melt closed-cell micropowder, and 2%-8% room-temperature crosslinking binder. The preparation method includes: pre-filling the MOF pores with polyethylene glycol, slurrying, coating onto the base membrane, drying at no higher than 60°C, then eluting the PEG with an organic solvent, and crosslinking and curing at room temperature. This separator utilizes the polar closed-cell micropowder melting at around 110°C and densely filling the pores through capillary action of the ceramic framework, achieving early pore closure; simultaneously, the mesopores of the MOF are activated, with its Zr6O4(OH)4 clusters adsorbing HF and SO3Li groups to exchange heavy metal ions, synergistically improving the high-temperature safety and cycle life of high-nickel batteries with electrolyte additives.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials and manufacturing technology, specifically to separators and lithium-ion batteries. Background Technology

[0002] With the rapid development of new energy vehicles and energy storage systems, high-nickel ternary cathode lithium-ion batteries (such as NCM811) have attracted much attention due to their high energy density. However, the safety and cycle life issues of high-nickel systems are becoming increasingly prominent. As a key safety component of the battery, the performance of the separator directly affects the risk of thermal runaway and electrochemical stability. Existing technologies mainly have the following shortcomings.

[0003] To improve membrane safety, a common practice is to coat polyolefin-based membranes with ceramic particles (such as boehmite or alumina) to enhance heat resistance. To interrupt ion transport in the early stages of thermal runaway, some studies incorporate low-melting-point polymers into the coating as closing-cell materials. For example, Chinese patent application CN111509173A, published on August 7, 2020, discloses a functional coated membrane in which polyethylene emulsion or ethylene-vinyl acetate copolymer emulsion is added to a ceramic slurry, utilizing the high-temperature melting of the polymer to block the membrane pores. However, the polymers used in this approach, such as polyethylene and EVA, are non-polar or weakly polar materials with extremely poor interfacial affinity to polar ceramic frameworks (such as boehmite). When the temperature rises to the melting point, the molten polymer is prone to agglomeration or slippage, failing to be effectively guided by the ceramic framework to densely fill the pores, leading to delayed or even failed pore-closing. Similarly, Chinese patent application CN118367305A, published on November 25, 2025, discloses a membrane containing core-shell structured microspheres, with the outer shell being polyethylene. The pore-closing mechanism still relies on the natural melting of non-polar polymers and also lacks a polarity matching design with the ceramic skeleton, resulting in insufficient pore-closing reliability.

[0004] To suppress the dissolution of transition metal ions in high-nickel cathodes and improve ion conduction, researchers have attempted to introduce metal-organic framework (MOF) materials. Chinese patent application CN121529116A, published on February 13, 2026, discloses an asymmetric bifunctional coated separator. This membrane forms MOF layers (such as ZIF-8) on both sides of a base film through in-situ growth to suppress metal ion dissolution and homogenize lithium-ion flow. While in-situ growth avoids binder pore blockage, the process is complex and requires stringent conditions (specific solvents and reaction conditions). Furthermore, its MOF function is mainly limited to physical sieving, lacking chemical adsorption capacity for hydrofluoric acid (HF) and ion exchange capture capacity for transition metal ions. If a more economical aqueous coating process is used to directly mix MOFs and binders, serious problems arise: aqueous binders (such as polyurethane and polyacrylate) densely coat the surface of MOF particles during demulsification and film formation, while small-molecule additives penetrate the pores, permanently blocking the mesopores. Existing technologies lack effective solutions to this problem, causing MOFs to become dead volumes and unable to perform adsorption and ion exchange functions.

[0005] In most of the aforementioned coating membrane preparation processes, high-temperature (>100℃) baking and curing are required after coating. However, when the coating contains low-melting-point closed-cell micropowder with a melting point of only 100-120℃, high-temperature baking will directly cause it to melt and fail prematurely, and will also cause thermal shrinkage damage to the polyolefin-based membrane. Chinese patent application CN108963164A (published on 2018.12.07) and others all use high-temperature curing processes without considering compatibility with heat-sensitive closed-cell materials.

[0006] Lithium difluorophosphate (LiDFP) is often added to high-nickel batteries to build a stable interfacial film. However, LiDFP is prone to hydrolysis, producing HF, which corrodes the cathode and exacerbates the dissolution of transition metals. Existing ceramic-coated separators only provide physical heat resistance and cannot actively remove HF or capture metal ions. Therefore, they cannot form an effective synergy with additives such as LiDFP, and the problems of high-temperature gas generation and metal ion shuttle remain serious.

[0007] In summary, existing technologies suffer from irreconcilable contradictions regarding early-stage pore closure reliability, MOF pore protection, process compatibility, and chemical synergy. This invention aims to provide a novel membrane structure and its fabrication process to systematically address these issues. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the purpose of this invention is to provide a separator that aims to solve the comprehensive problems of high-energy-density lithium-ion batteries in terms of high-temperature safety, interface stability and long cycle life through material matching and microstructure design of composite coatings.

[0009] Another object of the present invention is to provide a lithium-ion battery that employs the above-mentioned separator and works synergistically with a specific electrolyte system to achieve excellent high-temperature safety, low gas generation characteristics and long cycle life.

[0010] This invention is achieved using the following technical solution: The diaphragm includes a porous base membrane and a composite coating applied to at least one side thereof; By mass percentage, the dry raw materials of the composite coating comprise: 30%-50% polar inorganic ceramic framework, 20%-40% mesoporous metal-organic framework, 10%-25% polar hot-melt closed-cell micro powder, and 2%-8% room-temperature crosslinking binder; the sum of the mass percentages of all components of the dry raw materials of the composite coating is 100%. The diaphragm is prepared by the following steps: (1) The mesoporous metal-organic framework is dispersed in an aqueous solution containing polyethylene glycol, so that the polyethylene glycol fills its pores, and then dried to obtain a pretreated powder; (2) Aqueous slurry is prepared by dispersing polar inorganic ceramic skeleton, pretreated powder, polar hot melt closed-cell micro powder and room temperature crosslinking binder in water; (3) The slurry is coated onto the porous base membrane and dried at a temperature not exceeding 60°C to obtain the initial membrane; (4) The initial state membrane is eluted with an organic extraction solvent to remove the polyethylene glycol in the mesopores. Then the solvent is evaporated at room temperature and crosslinked and matured to obtain the membrane.

[0011] Specifically, a first aspect of the present invention provides a lithium-ion battery separator, comprising a porous base membrane and a composite coating coated on at least one side thereof. The dry raw materials of the composite coating, by weight percentage, comprise: 30%-50% polar inorganic ceramic framework, 20%-40% mesoporous metal-organic framework, 10%-25% polar hot-melt closed-cell micropowder, and 2%-8% room-temperature crosslinking binder.

[0012] To achieve the structure and function of the above coating, the diaphragm is prepared by the following steps: dispersing the mesoporous metal-organic framework in an aqueous solution containing polyethylene glycol, allowing the polyethylene glycol to fill its pores, and drying to obtain a pretreated powder; subsequently, dispersing the polar inorganic ceramic framework, the pretreated powder, the polar hot-melt closed-cell micro powder, and the room-temperature crosslinking binder in water to prepare an aqueous slurry, which is then coated onto a porous base membrane and gently dried at a temperature not exceeding 60°C to obtain a nascent diaphragm; finally, eluting the nascent diaphragm with an organic extraction solvent to remove the polyethylene glycol from the mesopores, and evaporating the solvent and crosslinking at room temperature.

[0013] Mesoporous metal-organic frameworks (MOFs) possess excellent ion sieving and adsorption capabilities. However, in traditional slurry coating processes, polymeric binders easily penetrate and permanently block their nanoscale pores. This invention employs a "pre-occupation, then elution" process route. Polyethylene glycol molecules act as a "pore protectant" to pre-liquidate / solidify the MOF pores, preventing binder intrusion. After the coating is essentially formed, a specific solvent is used to elute the binder, thus perfectly preserving and activating the unobstructed nanoscale active pores within the formed membrane.

[0014] In a preferred embodiment of the present invention, the polar inorganic ceramic framework is boehmite with hydroxyl content on its surface, and its particle size D50 is 0.1μm-0.5μm; the polar hot-melt closed-cell micro powder is copolyester micro powder, with a melting point of 100℃-120℃ and a particle size D50 of 1μm-5μm.

[0015] The polar hydroxyl groups abundant on the boehmite surface synergize highly with the polar groups of the copolyester. When the battery experiences an internal short circuit and abnormally heats up to around 110°C, the copolyester micropowder rapidly melts into a polar liquid. Under the surface tension of the boehmite's polar three-dimensional framework, a strong "capillary suction effect" is triggered. The liquid polyester is drawn in and fills the gaps between the base film and the coating, forming a dense insulating wall. This allows the separator to achieve irreversible physical pore closure 15°C-20°C before the polyolefin base film undergoes thermal shrinkage and collapse (typically above 130°C), thus blocking the thermal runaway chain.

[0016] Furthermore, the mesoporous metal-organic framework is preferably a zirconium-based mesoporous material HP-UiO-66-SO3Li containing -SO3Li groups, with an average pore size ranging from 2.0 nm to 5.0 nm. This achieves microscopic-level chemical safety and ion control: on the one hand, the pore size of 2.0-5.0 nm allows for rapid penetration of solvated lithium ions (approximately 0.8 nm) while simultaneously creating steric hindrance for bulky anions; on the other hand, its exposed Zr6O4(OH)4 cluster core can strongly chemically adsorb trace amounts of moisture and HF, while the -SO3Li groups embedded within the pores interact with heavy metal ions (such as Ni) shuttling from the positive electrode. 2+ Mn 2+ Irreversible ion exchange occurs, anchoring pathogenic ions within the pores, while simultaneously releasing Li in situ. + To compensate for the battery's initial efficiency.

[0017] Preferably, the polyethylene glycol in the pretreatment step is PEG-400 or PEG-600, which is liquid or semi-solid at room temperature. Liquid PEG with a very small molecular weight is rich in ether bonds and terminal hydroxyl groups, which can spontaneously and densely penetrate and adsorb into the pores of mesoporous MOF through strong hydrogen bonding, achieving perfect site protection, and is easily eluted subsequently.

[0018] Preferably, the room-temperature crosslinking adhesive comprises an aqueous aliphatic polyurethane emulsion containing free carboxyl groups and a multifunctional aqueous carbodiimide crosslinking agent.

[0019] The use of this binder system is crucial for ensuring the compatibility of the preparation process with the formulation characteristics. Because the formulation contains polyester micropowder with a melting point of only 110℃, traditional high-temperature heat setting processes above 100℃ would directly cause the micropowder to melt prematurely and become unusable. This invention utilizes the ring-opening crosslinking reaction between the free carboxyl groups and carbodiimide groups of aliphatic waterborne polyurethane at room temperature (20℃-30℃), eliminating the need for high-temperature baking. This protects the physical state of the closed-cell micropowder and prevents thermodynamic tensile damage to the base film. The multifunctional carbodiimide crosslinking agent is chemically inert to primary alcohols (such as ethanol) at room temperature and specifically targets the free carboxyl groups for ring-opening reactions. Therefore, the ethanol elution process does not consume the crosslinking agent, ensuring the integrity of the subsequent network curing.

[0020] Furthermore, in the elution step, the organic extraction solvent is anhydrous ethanol or isopropanol. This invention cleverly utilizes the principle of "selective dissolution." Anhydrous ethanol is an excellent solvent for PEG-400, capable of efficiently extracting PEG from the pores. However, the porous base membrane (polyolefin), polar hot-melt closed-cell micropowder (copolyester), and room-temperature crosslinking binder (waterborne polyurethane crosslinking network) are all insoluble in anhydrous ethanol. Therefore, the elution process only selectively opens the MOF pores, without damaging the macroscopic morphology, adhesion, or base membrane structure of the coating.

[0021] This invention resolves the chemical conflict between pore elution and binder crosslinking. It employs a waterborne polyurethane (WPU) containing free carboxyl groups in combination with a waterborne carbodiimide crosslinking agent. During gentle drying at 60°C, moisture evaporates, and the high molecular weight WPU forms a physically dry film insoluble in ethanol. In the subsequent anhydrous ethanol elution step, the carbodiimide crosslinking agent is extremely stable to alcohols (no side reactions occur), and ethanol causes slight swelling of the WPU network, allowing for the smooth diffusion extraction of small molecule PEG. After ethanol evaporation, the carbodiimide slowly undergoes a crosslinking reaction with the carboxyl groups during standing at room temperature (confirmed by FTIR spectroscopy, the -N=C=N- characteristic peak completely disappears after 24 hours), ultimately forming a dense network that locks in all components.

[0022] The copolyester micropowder is highly crystalline, remaining completely solid below 90°C (without the risk of softening and sticking), but melting instantaneously at its melting point of 110°C, with extremely low melt viscosity (<500 Pa·s at 115°C). This allows it to rapidly undergo capillary pumping on the polar surface of boehmite and fill the pores.

[0023] Furthermore, there is no competition between MOF materials when they exert their dual protective functions: the adsorption of HF by the Zr6O4(OH)4 cluster is a surface acid-base Lewis interaction (with extremely fast kinetics), while the adsorption of Ni by -SO3Li is different. 2+ The capture of ions is a thermodynamic exchange of ions within the pores. Both operate in parallel at different spatial sites, working together to protect the battery.

[0024] A second aspect of the present invention provides a high-safety, long-life lithium-ion battery comprising a positive electrode, a negative electrode, a non-aqueous organic electrolyte, and the aforementioned separator disposed between the positive and negative electrodes.

[0025] Furthermore, the non-aqueous organic electrolyte contains the additives lithium difluorophosphate and 1,3-propanesulfonate lactone. Preferably, based on the total mass of the non-aqueous organic electrolyte, the mass percentage of lithium difluorophosphate is 0.5%-2.0%, and the mass percentage of 1,3-propanesulfonate lactone is 0.2%-1.0%.

[0026] While lithium difluorophosphate (LiDFP) possesses excellent interfacial film-forming capabilities, it is highly susceptible to hydrolysis or thermal decomposition, producing highly corrosive hydrofluoric acid (HF). This leads to severe high-temperature gas generation and rapid cycle deterioration in conventional batteries. In this invention, however, specific MOF channels in the separator have been eluted and activated, and their strong fluoride-loving sites act as "proton acid sponges," instantly neutralizing and locking up nascent HF in the electrolyte. The separator thus functions as a "local pH regulator," creating an ideal "local zero-acid environment" for the electrolyte. Under this acid-free environment, LiDFP and 1,3-propanesulfonic acid lactone can undergo perfect self-assembly and polymerization on the positive and negative electrode surfaces, constructing a robust and low-resistance interfacial film. This reduces high-temperature gas generation in the battery by more than 90%, achieving chemical defense gains through the combined application of the separator and a specific electrolyte.

[0027] In a preferred battery system, the active material of the positive electrode comprises a layered high-nickel transition metal oxide, LiNi. x Co y Mn z O2 or LiNi x Co y Al z O2, where x≥0.6, x+y+z=1. High-nickel systems are extremely sensitive to HF corrosion and transition metal dissolution. The separator of this invention, through the dual-effect mechanism of "acid removal and film formation protection" and "pore ion exchange capture", eliminates the surface structure phase transition of high-nickel cathode and the poisoning shuttle effect of anode, thus greatly improving the high-temperature long cycle life of high-nickel batteries.

[0028] Compared with the prior art, the beneficial effects of the present invention are: (1) In this invention, polar copolyester micropowder with a specific melting point is matched with a polar boehmite framework. When the battery is abnormally heated to 110°C, the copolyester micropowder melts and rapidly wets and fills the pores of the base film and coating under the capillary action of the polar boehmite framework. This mechanism effectively cuts off the ion transport channels before the polyolefin base film undergoes significant thermal shrinkage, reducing the risk of thermal runaway.

[0029] (2) This invention retains the active Zr6 oxygen clusters in the MOF material through a specific process. This structure can effectively adsorb trace amounts of water and free HF generated by the decomposition of lithium difluorophosphate in the electrolyte, reducing local acidity. Under low-acid conditions, additives such as LiDFP and 1,3-propanesulfonic acid lactone can form films more stably on the electrode surface, significantly reducing the interfacial gas generation expansion rate of high-nickel / high-voltage batteries under high-temperature conditions.

[0030] (3) The membrane coating retains the unobstructed mesoporous channels of the MOF. The -SO3Li groups grafted onto the inner walls of these channels can undergo ion exchange reactions with the transition metal ions dissolved from the positive electrode, retaining them on the membrane side and reducing metal deposition on the negative electrode surface. Simultaneously, the displaced Li... + It enters the electrolyte, compensating for the capacity and improving the battery's high-temperature cycle life.

[0031] (4) The process of “polyethylene glycol prefilling-room temperature crosslinking-organic solvent elution” was adopted. The objective data of specific surface area before and after elution confirmed that the method effectively blocked the physical blockage of the pores on the MOF surface by the demulsification and film formation of waterborne polyurethane. At the same time, the room temperature crosslinking process avoided the premature melting of low melting point closed-cell materials and thermal shrinkage damage to porous base films caused by traditional high temperature baking. Detailed Implementation

[0032] To make the objectives, technical solutions, and technical effects of this invention clearer, the invention will be further described in detail below with reference to principle analysis and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0033] This invention proposes a lithium-ion battery separator with multiple safety protections and improved cycle life, which is composed of a specific composite coating coated on a porous base membrane (such as a polyethylene (PE) or polypropylene (PP) microporous membrane). The dry-state formulation of this composite coating comprises the following interacting components by weight percentage: 30wt%-50wt% polar inorganic ceramic framework: This framework utilizes inorganic particles with polar hydroxyl groups (-OH) on their surface, preferably nano-sized boehmite (γ-AlOOH) with a particle size D50 of 0.1μm-0.5μm. It primarily serves as a physical support in the coating, reducing the high-temperature thermal shrinkage rate of the base film; simultaneously, its polar surface characteristics provide surface tension conditions for the subsequent flow of the polyester melt.

[0034] 20wt%-40wt% mesoporous metal-organic framework (MOF): preferably a zirconium-based mesoporous material containing -SO3Li groups (HP-UiO-66-SO3Li). This material must possess the following structural features to achieve specific functions: ① a strongly fluorine-loving Zr6O4(OH)4 cluster core for complexing free water and hydrogen fluoride (HF) in the electrolyte; ② a mesoporous structure of 2.0nm-5.0nm, allowing solvated lithium ions to pass through and generating certain steric hindrance; ③ -SO3Li groups grafted onto the inner walls of the pores for interaction with free transition metal ions (such as Ni) in the electrolyte. 2+ Mn 2+ An ion exchange reaction occurs, releasing Li. + .

[0035] 10wt%-25wt% of polar hot-melt closed-cell micro powder: preferably copolyester micro powder, with a melting point controlled between 100℃ and 120℃ and a particle size D50 of 1μm-5μm. This micro powder needs to contain polar groups such as ester groups, terminal hydroxyl groups, or terminal carboxyl groups so that it can wet and capillary with the boehmite skeleton after reaching the melting point.

[0036] 2wt%-8wt% room temperature crosslinking adhesive: including aqueous aliphatic polyurethane (WPU) emulsions containing free carboxyl groups and multifunctional carbodiimide crosslinking agents. This system can form a stable three-dimensional adhesive network through a ring-opening crosslinking reaction between the cyclopropylamine groups of carbodiimide and the carboxyl groups of polyurethane at room temperature (20℃-30℃).

[0037] Since direct aqueous pulping can cause polymeric binders to enter and clog the mesoporous channels of MOFs, resulting in their loss of chemical activity, this invention employs a specific "pretreatment site-occupancy" method for MOF raw materials: Aqueous dispersion and pore filling: The synthesized HP-UiO-66-SO3Li powder was dispersed in an aqueous solution containing small-molecule polyethylene glycol (such as PEG-400 or PEG-600, which is liquid or semi-solid at room temperature), and stirred at room temperature for 1-3 hours. PEG molecules contain ether bonds and terminal hydroxyl groups, which can enter and occupy the mesoporous channels of MOF through hydrogen bonding.

[0038] Drying and curing: The above mixture is filtered and gently dried at around 60°C to obtain pretreated MOF powder with PEG-filled pores. In this state, the pores are occupied, preventing the intrusion of polymer binders during subsequent pulping.

[0039] Based on the completion of raw material pretreatment, the preparation of the diaphragm includes the following steps. This process system is compatible with low-melting-point closed-cell materials and avoids high-temperature damage: Slurry preparation: The above-mentioned polar inorganic ceramic skeleton (boehmite), pretreated MOF powder, and polar hot-melt closed-cell micro powder (copolyester) are dispersed in deionized water in a certain proportion, and then room temperature crosslinking binder (WPU and carbodiimide crosslinking agent) are added. The mixture is stirred and dispersed in a conventional manner to obtain a uniform aqueous slurry.

[0040] Coating and Low-Temperature Drying: The slurry is coated onto a porous base membrane with a thickness of 5μm-12μm. The slurry is dried in an oven at 40℃-60℃ to remove moisture, yielding the initial membrane state. The drying temperature must be below the melting point of the copolyester micropowder (100℃-120℃) to maintain its particle morphology.

[0041] Solvent extraction elution: The nascent membrane is immersed in an organic extraction solvent (such as anhydrous ethanol or isopropanol) for elution for 1-10 minutes. Anhydrous ethanol has good solubility for PEG, but no significant solubility for porous base membranes (polyolefins), copolyester micropowders, and cross-linked cured WPU. Therefore, the elution process can specifically remove PEG occupying the MOF pores and reopen the active pores.

[0042] Room temperature crosslinking and curing: The washed diaphragm is removed and allowed to evaporate any residual ethanol on the surface at room temperature (20℃-30℃) for 12-48 hours. During this period, the binder system fully completes the room temperature crosslinking reaction, yielding the final diaphragm.

[0043] This invention further provides a method for applying the above-mentioned separator to a lithium-ion battery, specifically requiring the separator to be used in conjunction with an electrolyte and a positive electrode of a specific composition to achieve systematic technical effects: Application Method: Using the membrane prepared above, a positive electrode (preferably a layered high-nickel transition metal oxide, such as NCM811 or NCA) and a conventional negative electrode (such as graphite or silicon-carbon electrode sheets) are combined, and a specific non-aqueous organic electrolyte is injected to assemble a full cell. This electrolyte, based on conventional solvents and lithium salts, contains 0.5%-2.0% by mass of lithium difluorophosphate (LiDFP) and 0.2%-1.0% by mass of 1,3-propanesulfonic acid lactone (PS).

[0044] The above application method generates the following synergistic mechanism within the battery: While lithium difluorophosphate (LiDFP) possesses excellent interfacial film-forming capabilities, it is prone to side reactions that generate hydrofluoric acid (HF), leading to gas production and degradation. The active MOF channels (Zr6O4(OH)4 cluster cores) within the separator can adsorb and consume free water and trace amounts of HF in the electrolyte, reducing localized acidity in the battery. Under low-acidity conditions, the decomposition side reactions of LiDFP and PS are suppressed, allowing for more stable polymerization on the electrode surface to form a solid-state ion-exchange membrane (SEI / CEI), thus significantly reducing gas production under high temperature and high pressure conditions. During cycling, the high-nickel cathode may leach Ni. 2+ Transition metal ions are present. When these ions diffuse into the membrane with the electrolyte, the -SO3Li groups on the inner wall of the MOF channels immobilize them within the membrane through an ion exchange reaction, reducing metal deposition on the negative electrode side. Simultaneously, the displaced Li... + Entering the electrolyte system can replenish the active lithium consumed during cycling to some extent. When the battery temperature rises abnormally to around 110°C, the copolyester micropowder in the coating melts. Guided by the capillary action of the boehmite polar framework, the liquid polyester flows in and fills the pores of the base film, preemptively sealing the ion transport channels before the base film undergoes significant thermal shrinkage due to higher temperatures, thus reducing the risk of thermal runaway.

[0045] In the following examples and comparative examples, unless otherwise stated, all raw materials used are commercially available and all equipment used is conventional in the art.

[0046] I. Main Raw Materials, Reagents, Manufacturers, Specifications, and Grades Boehmite (polar inorganic ceramic framework): Nabaltec, Germany, Apyral® 40AOHD50: 0.2-0.4μm, surface -OH content ≥12%, purity ≥99.5% ceramic framework; Copolyester hot melt micro powder (polar closed-cell material): Swiss EMS-Griltech, Griltex® D1616E, melting point 110-120℃ (DSC measured), D50: 2-5μm, melt viscosity <500Pa·s@115℃; Polyethylene glycol: Sinopharm Chemical Reagent Co., Ltd., PEG-400, AR grade, molecular weight 360-440, hydroxyl value 268-295 mgKOH / g, moisture ≤1%; Waterborne polyurethane emulsion: Covestro, Dispercoll® U54, anionic aliphatic, free carboxyl groups 2-4 meq / g, solid content 49-51%, room temperature crosslinking component A; Multifunctional carbodiimide crosslinking agent: Nisshinbo, Carbodilite® V-02-L2, multifunctional waterborne carbodiimide, stable to ethanol, solid content 40%, room temperature crosslinking component B; Porous PE base membrane: Shanghai Enjie New Material Technology Co., Ltd., SE9-389μm thick, porosity 38%, Gurley value 130s / 100mL, TD shrinkage <5%@130℃; Ethylene carbonate (EC): Shida Shenghua, battery grade EC, purity ≥99.99%, moisture ≤20ppm; Diethyl carbonate (DEC): Shida Shenghua battery-grade DEC, purity ≥99.99%, moisture ≤20ppm, main solvent for electrolyte, EC:DEC=3:7; Lithium difluorophosphate (LiDFP): Guangzhou Tinci Advanced Materials Co., Ltd., TinciLiDFP-01, purity ≥99.9%; 1,3-Propanesulfonate lactone (PS): Xinzhoubang (Jiangsu Hankang), PS-EL purity ≥99.9%; NCM811: Ningbo Ronbay New Energy Technology Co., Ltd., NCM811-S01B, Ni≥80%, D50=10±2μm, initial efficiency≥88%, high nickel cathode, x≥0.6; NCA: GEM Co., Ltd., NCA-80Ni≥80%, Co≤15%, Al≤5%, D50=10±2μm; Artificial graphite: BTR New Materials Group Co., Ltd. SG-18D50=15±2μm, initial efficiency ≥93%, capacity ≥350mAh / g; 2-Sulfono-1,4-Phenylacetic acid monosodium salt: Aladdin, S108456, purity ≥98%, CAS: 190523-68-5; Zirconium tetrachloride (anhydrous): Aladdin, A11638, purity ≥99.9%, CAS: 10026-11-6; Lauryl acid (lauric acid, pore expander): Sinopharm Group, AR grade, purity ≥99%, CAS: 143-07-7; Lithium hydroxide: Aladdin, L11633, purity ≥99%, CAS: 1310-65-2; N,N-Dimethylformamide (DMF, solvent): Sinopharm Group, AR grade, anhydrous, purity ≥99.9%, moisture ≤0.05%, CAS: 68-12-2; Polyethylene wax (non-polar): Honeywell, AC®316A, melting point 140℃, D50=5μm, oxidized polyethylene wax; UiO-66 Bailingwei / Xianfeng Nano: UiO-66 standard product pore size -0.6nm, no -SO3Li groups; Anhydrous ethanol (organic extraction solvent): Sinopharm Chemical Reagent Co., Ltd., analytical grade (AR), moisture ≤0.3%, CAS: 64-17-5.

[0047] II. Preparation method of core self-made raw material (HP-UiO-66-SO3Li) Ligand preparation: Weigh out the monosodium 2-sulfono-1,4-phthalic acid as the ligand containing -SO3. - Organic ligands.

[0048] Pore-expanding synthesis (HP-UiO-66-SO3H): The above ligand and zirconium tetrachloride (ZrCl4) were dissolved in N,N-dimethylformamide (DMF) at a molar ratio of 1:1. Lauric acid (lauric acid) was added to this system as a pore-expanding regulator (the ratio of regulator to Zr was 30:1). The mixture was placed in a polytetrafluoroethylene-lined reactor at 120°C and subjected to a solvothermal reaction for 24 hours. After the reaction, the solid was collected by centrifugation, washed repeatedly with DMF and methanol, and then vacuum dried at 150°C for 12 hours to completely remove reaction residues and the regulator from the pores, obtaining mesoporous UiO-66-SO3H (proton state) with a pore size of approximately 3.0 nm.

[0049] Lithification exchange (HP-UiO-66-SO3Li): The above protonated MOF powder is dispersed in a methanol / water mixed solution containing lithium chloride (LiCl) or lithium carbonate (Li2CO3), and ion exchange occurs under stirring at room temperature. The powder is recovered by centrifugation, washed with anhydrous methanol until neutral, and dried under vacuum at 80°C to obtain an active powder with a strong affinity for fluorinated Zr4O clusters and -SO3Li groups embedded in the pores.

[0050] III. Standards for Physical and Electrochemical Testing Methods To ensure the accuracy and comparability of the effectiveness data of this invention, the testing process strictly follows national standards or industry-recognized rigorous evaluation methods: 1. Specific surface area (BET) test of coating powder: Method: Refer to GB / T19587-2017 "Determination of specific surface area of ​​solid substances by gas adsorption BET method".

[0051] Sampling: Carefully scrape off the coating powder from the diaphragm surface using a flexible ceramic scraper.

[0052] Test procedure: The scraped powder was placed in the Mack Instrument ASAP2460 fully automatic specific surface area analyzer and degassed under vacuum at 80℃ for 6 hours. Then, nitrogen adsorption-desorption isotherm test was performed at liquid nitrogen temperature (77K) to calculate the BET specific surface area.

[0053] 2. Tests on the air permeability of the diaphragm at room temperature and its closed-cell air permeability at 110℃: Room temperature test: Referring to GB / T36363-2018 "Polyolefin separator for lithium-ion batteries" standard, the time required for 100cc of air to pass through a 1 square inch separator under a fixed pressure (s / 100cc) was tested using a Gurley air permeability meter.

[0054] 110℃ Closure Trigger Test (Custom-made, for verifying capillary pore-closure mechanism): The membrane sample is flattened and sandwiched between two flat Teflon heating plates preheated to 110℃ and maintained at a constant temperature. A uniform pressure of 0.1MPa is applied, and the holding time is precisely controlled to 1 minute. The sample is then removed and allowed to cool naturally at room temperature. After cooling, it is transferred to a Gurley instrument to test permeability. If the test value is greater than 10000s / 100cc, the pores are considered to be completely and densely filled by the physical material. The uniform pressure of 0.1MPa is intended to simulate the normal assembly stress of the internal electrodes of a pouch cell on the membrane, to realistically reflect the spreading and pore-closure behavior of polyester after melting under interfacial compression and capillary action.

[0055] 3. High-temperature heat shrinkage test of the diaphragm: Method: Refer to GB / T36363-2018.

[0056] Procedure: Cut a 10cm × 10cm diaphragm sample and mark the machine orientation (MD) and transverse direction (TD). Sandwich the sample between two layers of release paper and bake in a constant temperature forced-air drying oven at 130℃ for 1 hour. After cooling, measure the dimensional changes and calculate the transverse (TD) heat shrinkage rate.

[0057] 4. Battery high-temperature (45℃) long cycle life test: Method: Refer to GB / T31484-2015.

[0058] Procedure: The assembled pouch cells were placed in a 45°C constant temperature chamber on a Neware battery testing system. Constant current-constant voltage (CC-CV) mode was used, and charge-discharge cycles were performed at a rate of 1C (i.e., full load current) within a voltage range of 2.8V to 4.4V. The discharge capacity after the 1000th cycle was recorded, and the capacity retention rate was calculated by comparing it with the initial discharge capacity.

[0059] 5. Battery full charge (60℃) high temperature storage gas expansion test: Method: The industry-standard Archimedes displacement method (volume displacement method).

[0060] Procedure: The full battery was charged to 4.4V at 0.5C at room temperature. The buoyancy of the battery in silicone oil (or deionized water) before storage was measured, and the initial volume V0 was calculated. The battery was then stored in a 60℃ constant temperature chamber for 30 days. After cooling, the final volume V1 was measured again using the same method. The volume expansion rate was calculated as (V1 - V0) / V0 × 100%.

[0061] 6. Detection of transition metal (Ni) deposition on the negative electrode surface (ICP-OES): Method: Quantitative analysis of microscopic chemistry.

[0062] Procedure: The battery, after undergoing 1000 cycles at 45℃, was disassembled in a discharged state. The negative electrode was removed, and its surface was repeatedly rinsed three times with high-purity dimethyl carbonate (DMC) to remove residual electrolyte, and then dried under vacuum. Approximately 0.5g of the negative electrode active material powder was precisely scraped from the surface of the negative electrode and placed in a polytetrafluoroethylene digestion vessel. Aqua regia (concentrated hydrochloric acid to concentrated nitric acid, volume ratio 3:1) was added, and the mixture was thoroughly digested in a microwave digester. The digestion solution was then brought to a final volume, and the mass concentration of nickel (Ni) (ppm, i.e., micrograms per gram of negative electrode powder) was measured using an inductively coupled plasma optical emission spectrometer (ICP-OES, such as an Agilent 720).

[0063] Example 1 The diaphragm is prepared by the following steps: (1) Pre-filling: Take 300g of mesoporous ion exchange MOF (HP-UiO-66-SO3Li, mesopore size 3.0nm, median particle size 200nm, pure powder BET specific surface area 1850m²) 2 Add PEG-400 (g) to an aqueous solution containing 300g PEG-400, sonicate for 2 hours, filter and dry to obtain an intermediate product in which the internal mesopores are completely blocked by PEG-400.

[0064] (2) Slurry preparation and coating: 500g of nano-boehmite (surface rich in polar -OH), 300g of the above intermediate product (based on MOF net weight), 150g of polar polyester hot melt powder (Griltex® D1616E, median particle size 5μm, melting point 110℃), 50g of aqueous polyurethane emulsion (WPU, solid content based on 49.5g) and 0.5g of carbodiimide crosslinking agent were dispersed in deionized water and stirred to form a uniform slurry. The slurry was coated on one side of a porous PE base film with a thickness of 9μm and gently dried at 50℃ to obtain the initial coating.

[0065] (3) Elution and crosslinking: The above-mentioned coated diaphragm was immersed in anhydrous ethanol and ultrasonically eluted for 5 minutes to extract PEG-400 in the pores. Then it was taken out and left to stand at room temperature (25°C) for 24 hours to allow WPU and carbodiimide to spontaneously crosslink and mature, thus obtaining the diaphragm of the present invention. The dry coating thickness was 4 μm.

[0066] Example 2: The coating formulation was adjusted to: 40wt% boehmite + 40wt% MOF + 15wt% polyester powder + 5wt% WPU binder. The rest is the same as in Example 1.

[0067] Example 3: The coating formulation was adjusted to: 45wt% boehmite + 30wt% MOF + 20wt% polyester powder + 5wt% WPU binder. The rest is the same as in Example 1.

[0068] Example 4: The pore size of HP-UiO-66-SO3Li was adjusted to 2.5nm, and the rest was the same as in Example 1.

[0069] Example 5: Step (1) Replace PEG-400 with PEG-600, and the rest is the same as in Example 1.

[0070] Comparative Example 1 Steps (1) and (3) in Example 1 are omitted. Pure HP-UiO-66-SO3Li powder, boehmite, polyester hot melt powder, WPU and crosslinking agent are directly mixed to form a slurry and coated, and then allowed to dry at room temperature. The same electrolyte as in Example 1 is used to assemble the full cell.

[0071] Comparative Example 2 In step (2) of Example 1, no polar polyester hot melt powder is added (the formulation ratio is adjusted to 65wt% boehmite + 30wt% MOF + 5wt% WPU). Everything else is the same as in Example 1.

[0072] Comparative Example 3 In step (2) of Example 1, the "polar polyester hot melt powder" is replaced in equal amounts with "non-polar PE wax micro powder" of the same particle size and the same melting point (110°C). All other steps are the same as in Example 1.

[0073] Comparative Example 4 In step (1) of Example 1, conventional mesoporous UiO-66 (without -SO3Li functional groups) of the same pore size is used instead of HP-UiO-66-SO3Li. All other steps are the same as in Example 1.

[0074] Comparative Example 5 The most common ceramic separator on the market is prepared by coating alumina (Al2O3) onto a PE base film using PVDF binder (baking and drying at 100℃). An electrolyte containing 1.0 wt% LiDFP is used when assembling the battery.

[0075] Comparative Example 6 The "anhydrous ethanol elution" in step (3) of Example 1 is changed to the "heat treatment template removal method" commonly used for mesoporous materials: the coated diaphragm is placed in a vacuum oven at 150°C and heated for 2 hours to volatilize PEG.

[0076] The test data for Examples 1-5 and Comparative Examples 1-6 are shown in Table 1.

[0077] Table 1: Test data of Examples 1-5 and Comparative Examples 1-6

[0078] As shown in Table 1, the BET values ​​of the coatings in Examples 1-5 all remained at 410 μm. 2 The result was above / g, consistent with theoretical expectations, confirming that the "PEG pre-filling + ethanol room temperature elution" process effectively opened the MOF channels. Conversely, Comparative Example 1, using conventional direct slurry coating, saw its BET value plummet to 35m. 2 The / g value demonstrates that the waterborne polyurethane, during demulsification and film formation, coats the MOF surface, blocking the pores and causing complete failure of the internal channels. Furthermore, Comparative Example 7 shows that the traditional high-temperature template removal method directly leads to the melting and destruction of the PE base film and polyester micropowder, making it unsuitable for membrane preparation. Examples 1-5 exhibited normal permeability at room temperature (-200s / 100mL), but after heat treatment at 110℃, the permeability became unmeasurable (closed-cell density), confirming effective physical pore filling after the copolyester melts. In contrast, Comparative Example 2 (without polyester) showed a delayed pore-closing temperature of 134℃, relying on the shrinkage of the base film itself; Comparative Example 3, replacing the polyester with a non-polar PE wax of the same melting point, failed to achieve capillary wetting and spreading on the boehmite surface due to the lack of polarity matching, resulting in poorer permeability and a delayed pore-closing temperature of 128℃. The comparison of the above macroscopic physical data confirms the necessity of polarity matching in achieving early dense pore closing.

[0079] Battery assembly and application examples: Battery specifications: Standardized 1Ah pouch cell. The negative electrode uses artificial graphite.

[0080] Application Example 1: Using the separator from Example 1 + positive electrode NCM811 (LiNi) 0.8 Co 0.1 Mn 0.1 O2) + electrolyte (containing 1.0% LiDFP + 0.5% PS).

[0081] Application Example 2: Using the separator from Example 1 + positive electrode NCA (LiNi) 0.8 Co 0.15 Al 0.05O2) + electrolyte (containing 1.0% LiDFP + 0.5% PS).

[0082] Application Example 3: Using the membrane from Example 2 + NCM811 positive electrode + electrolyte (containing 1.0% LiDFP + 0.5% PS).

[0083] Application Comparative Example 1: The membrane of Comparative Example 1 + NCM811 positive electrode + electrolyte (containing 1.0% LiDFP + 0.5% PS) was used.

[0084] Comparative Example 2: The membrane of Comparative Example 4 (without -SO3Li) + positive electrode NCM811 + electrolyte (containing 1.0% LiDFP + 0.5% PS) was used.

[0085] Application Comparative Example 3: The membrane from Example 1 + NCM811 positive electrode + basic electrolyte (excluding LiDFP and PS) was used.

[0086] Application Comparative Example 4: Using ordinary alumina ceramic membrane + positive electrode NCM811 + electrolyte (containing 1.0% LiDFP).

[0087] Supplementary notes on battery testing conditions: Aging and formation process: After electrolyte injection and sealing, all pouch cells were left at room temperature for 24 hours, followed by step formation at a low current of 0.05C. After formation, the cells were aged in a 45°C high-temperature chamber for 24 hours to ensure the stability of the SEI / CEI membrane.

[0088] High-temperature gas generation test definition: High-temperature storage fully charged state is defined as constant current and constant voltage charging at 0.5C to the set cutoff voltage (4.2V for NCM811). Test data are the average value ± standard deviation (SD) of 3 parallel samples from the same batch.

[0089] The test results of Application Examples 1-3 and Application Comparative Examples 1-4 are shown in Table 2.

[0090] Table 2: Test results of application examples 1-3 and application comparative examples 1-4 (Note: All data are the average of 3 parallel samples ± SD)

[0091] Table 2 shows that in Application Examples 1 and 2, which used high-nickel cathode systems, the volume expansion rate at 60°C was controlled below 3.8%. A horizontal comparison revealed that Application Comparative Example 4, using only an electrolyte containing LiDFP and a conventional membrane, experienced an expansion rate as high as 28.5% due to acid production side reactions; Application Comparative Example 3, using the membrane of this invention but without LiDFP, had an expansion rate of 15.2%. Only when the membrane of this invention was used in conjunction with LiDFP did the gas production rate drop to 3.5%. This confirms that the activated Zr6 oxygen clusters in the membrane effectively removed free HF, providing a stable low-acid polymerization environment for the film-forming additives. The amount of Ni deposited on the negative electrode surface is a quantitative indicator reflecting the transition metal shuttle effect. Application Comparative Example 2 used conventional UiO-66 (containing Zr6 oxygen clusters but not -SO3Li groups), which had a low expansion rate, but due to the lack of ion exchange function, the amount of Ni deposited on the negative electrode was as high as 320 ppm, and the cycle life to 80% was only 850 cycles. In contrast, the Ni deposition amount in Application Example 1 was reduced to 45 ppm, with a cycle life of 1250 cycles. The comparison of controlled variables confirmed that the -SO3Li group is a key structure for capturing transition metal ions. Application Comparative Example 1 used a separator with pores blocked by a binder, which showed significant deterioration in gas production rate and negative electrode Ni deposition amount during battery testing, exhibiting performance levels similar to conventional MOF-free ceramic separators. This, from an electrochemical perspective, indirectly confirms that retaining an open and accessible mesoporous network in the coating is a fundamental prerequisite for achieving the aforementioned dual chemical functions of acid removal and ion exchange.

Claims

1. A diaphragm, characterized in that, Includes a porous base membrane and a composite coating applied to at least one side thereof; By mass percentage, the dry raw materials of the composite coating comprise: 30%-50% polar inorganic ceramic framework, 20%-40% mesoporous metal-organic framework, 10%-25% polar hot-melt closed-cell micro powder, and 2%-8% room-temperature crosslinking binder; the sum of the mass percentages of all components of the dry raw materials of the composite coating is 100%. The diaphragm is prepared by the following steps: (1) The mesoporous metal-organic framework is dispersed in an aqueous solution containing polyethylene glycol, so that the polyethylene glycol fills its pores, and then dried to obtain a pretreated powder; (2) Aqueous slurry is prepared by dispersing polar inorganic ceramic skeleton, pretreated powder, polar hot melt closed-cell micro powder and room temperature crosslinking binder in water; (3) The slurry is coated onto the porous base membrane and dried at a temperature not exceeding 60°C to obtain the initial membrane; (4) The initial state membrane is eluted with an organic extraction solvent to remove the polyethylene glycol in the mesopores. Then the solvent is evaporated at room temperature and crosslinked and matured to obtain the membrane.

2. The diaphragm according to claim 1, characterized in that, The polar inorganic ceramic framework is boehmite with hydroxyl content on its surface, and its particle size D50 is 0.1μm-0.5μm; the polar hot-melt closed-cell micro powder is copolyester micro powder, with a melting point of 100℃-120℃ and a particle size D50 of 1μm-5μm.

3. The diaphragm according to claim 1, characterized in that, The mesoporous metal-organic framework is a zirconium-based mesoporous material HP-UiO-66-SO3Li containing -SO3Li groups, and its average pore size ranges from 2.0 nm to 5.0 nm.

4. The diaphragm according to claim 1, characterized in that, In step (1), the polyethylene glycol is PEG-400 or PEG-600, which is liquid or semi-solid at room temperature.

5. The diaphragm according to claim 1, characterized in that, The room-temperature crosslinking adhesive includes an aqueous aliphatic polyurethane emulsion containing free carboxyl groups and a multifunctional aqueous carbodiimide crosslinking agent.

6. The diaphragm according to claim 1 or 5, characterized in that, In step (4), the organic extraction solvent is anhydrous ethanol or isopropanol; the porous base membrane, polar hot-melt closed-pore micro powder and room temperature crosslinking binder are all insoluble in the organic extraction solvent.

7. A lithium-ion battery, characterized in that, It comprises a positive electrode, a negative electrode, a non-aqueous organic electrolyte, and a membrane disposed between the positive electrode and the negative electrode; the membrane is the membrane as described in any one of claims 1-6.

8. The lithium-ion battery according to claim 7, characterized in that, The non-aqueous organic electrolyte contains additives lithium difluorophosphate and 1,3-propanesulfonic acid lactone.

9. The lithium-ion battery according to claim 8, characterized in that, Based on the total mass of the non-aqueous organic electrolyte, the lithium difluorophosphate has a mass percentage of 0.5%-2.0%, and the 1,3-propanesulfonic acid lactone has a mass percentage of 0.2%-1.0%.

10. The lithium-ion battery according to claim 7, characterized in that, The active material of the positive electrode comprises a layered high-nickel transition metal oxide, LiNi. x Co y Mn z O2 or LiNi x Co y Al z O2, where x≥0.6, x+y+z=1.

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