Composite multifunctional battery diaphragm as well as preparation method and application thereof

Abstract

The invention provides a composite multifunctional battery diaphragm as well as a preparation method and application thereof, and belongs to the field of new energy batteries. The composite multifunctional battery diaphragm comprises a polyolefin base membrane and a composite coating positioned on at least one side surface of the polyolefin base membrane, the composite coating is prepared from the following raw materials: an alpha-crystal-form aluminum oxide raw material, a sodium-containing boehmite raw material, a ZIF-8 metal organic framework raw material, a water-based adhesive, a sodium polycarboxylate dispersant, disodium ethylene diamine tetraacetate, polyvinyl alcohol and a water-based polyether modified organic silicon wetting agent. The problems of dissolution of manganese ions in an LMFP battery system and poor stability of a high-energy-density battery system are synchronously solved, the interface resistance can be effectively reduced, the pore structure is optimized, the high-temperature resistance of the diaphragm is improved, the growth and thermal runaway of lithium dendrites are inhibited, the affinity of the diaphragm to an electrolyte is improved while the side reaction of the electrolyte is reduced, and the service life of the diaphragm is prolonged. Meanwhile, the industrial cost advantage is realized.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology and relates to a composite multifunctional battery separator, its preparation method, and its application. Background Technology

[0002] In applications in the 3C consumer electronics and energy storage industries, especially for energy storage applications requiring long cycle times, existing separators in lithium manganese iron phosphate battery systems have the following key defects: Manganese ion dissolution disrupts interfacial stability: Manganese ion dissolution easily occurs at the LMFP cathode during charge and discharge. After migrating to the anode, free manganese ions catalyze the decomposition of the electrolyte interphase (SEI), initiating irreversible capacity decay and exacerbating electrode side reactions (such as Jahn-Teller distortion and disproportionation), resulting in a significant decrease in cycle life.

[0003] Insufficient high temperature resistance and mechanical strength: Traditional diaphragms have a high thermal shrinkage rate at high temperatures, which can easily cause short circuits at electrode contacts; at the same time, their puncture strength and tensile strength are insufficient to suppress lithium dendrite penetration, posing a safety hazard.

[0004] Low electrolyte wettability and low ion transport efficiency: Due to the high viscosity of the electrolyte, the electrolyte is easily unevenly distributed on the surface of the traditional separator, resulting in poor interfacial wettability, which increases the resistance to lithium ion transport, exacerbates the uneven local lithium deposition, and leads to dendrite growth and increased interfacial impedance.

[0005] Lack of manganese ion adsorption mechanism: Existing membranes lack the ability to actively capture dissolved manganese ions, cannot block their migration path to the negative electrode, and cannot inhibit manganese ion diffusion through charge balance.

[0006] The aforementioned problems severely restrict the application of LMFP batteries in high energy density and long cycle life scenarios, and there is an urgent need to develop a new composite separator that combines manganese ion adsorption, high temperature stability enhancement, interface wettability optimization and dendrite suppression synergistic functions. Summary of the Invention

[0007] The purpose of this invention is to address the aforementioned problems in existing technologies by proposing a composite multifunctional battery separator, its preparation method, and its application.

[0008] The objective of this invention can be achieved through the following technical solution: a composite multifunctional battery separator, comprising a polyolefin base membrane and a composite coating located on at least one side surface of the polyolefin base membrane; the raw materials for preparing the composite coating include: α-crystalline alumina raw material, sodium-containing boehmite raw material, ZIF-8 metal-organic framework raw material, an aqueous binder containing lithium carboxylate functional group side chains and ester functional group side chains, a sodium polycarboxylate dispersant, disodium ethylenediaminetetraacetate, polyvinyl alcohol, and an aqueous polyether-modified organosilicon wetting agent; the aqueous binder: lithium acrylate monomer and acrylate monomer are chemically bonded to the main chain of the aqueous binder, respectively serving as a side chain containing -COOLi functional group and a side chain containing -COOR functional group; the main chain of the aqueous binder is a carbon chain. The acrylate monomer is at least one of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, and ethyl methacrylate monomers. The polyolefin-based film is specifically a PE-based film; the sodium polycarboxylate dispersant is specifically a sodium polyacrylate dispersant; the α-crystalline alumina raw materials include alumina raw material A and alumina raw material B; the water-based polyether-modified silicone wetting agent is specifically BYK347 wetting agent; the water-based adhesives include adhesive NAL46 and adhesive NAL28; adhesive NAL28: viscosity 910 mPa·s, solid content 15.2%, pH value 7.5; adhesive NAL46: viscosity 790 mPa·s, solid content 15.2%, pH value 7.0.

[0009] The following parameters are required for sodium-containing boehmite raw materials: Microstructure: rhombic platy; Particle size: 0.1μm≤D10<0.5μm, 0.6μm≤D50<1.1μm, 1.3μm≤D90<1.8, 1.9μm≤D99<5.0μm; Specific surface area: 5.0-10.0m² / g; Sodium content: 0.03-0.05%; The parameters for alumina raw material A are as follows: particle size: 0.1μm≤D10<0.25μm, 0.3μm≤D50<0.5μm, 0.6μm≤D90<0.85μm; specific surface area is 6.0-10.0m² / g; The parameters for alumina raw material B are as follows: particle size: 0.25μm≤D10<0.4μm, 0.5μm≤D50<0.7μm, 0.85μm≤D90<1.5μm; specific surface area is 5.5-9.0m² / g; The raw material parameters for ZIF-8 metal-organic framework are as follows: specific surface area ≥ 1500 m² / g; particle size: 500-700 nm; pore size: 0.9-1.8 nm; The PE base film parameters are as follows: Structural parameters: Pore size distribution range: 30-50nm, average pore size 35-40nm; Air permeability: 160±70s / 100cc; Porosity: 39%-50%; Mechanical properties: Puncture strength: ≥300gf; Longitudinal tensile strength: ≥1500kgf / cm 2 Transverse tensile strength: ≥1200 kgf / cm 2 Longitudinal elongation at break: ≥50%; Transverse elongation at break: ≥50%; Thermal stability: Under a thermal environment of 90℃: CMD thermal shrinkage rate ≤1.5%, CTD transverse thermal shrinkage rate ≤0.5%; Under a thermal environment of 105℃: CMD longitudinal thermal shrinkage rate ≤5%, CTD transverse thermal shrinkage rate ≤3%; Under a thermal environment of 120℃: CMD longitudinal thermal shrinkage rate ≤6%, CTD transverse thermal shrinkage rate ≤5.5%; Areal density: 5.4±1.0g / m².

[0010] Preferably, the parameters of alumina raw material A also have the following requirements: calcium content <300ppm; iron content <100ppm; copper content <5ppm; The parameters for alumina raw material B also have the following requirements: calcium content < 300 ppm; iron content < 100 ppm; copper content < 5 ppm.

[0011] The parameters for boehmite raw materials also include the following requirements: iron content < 50 ppm, copper content < 5 ppm, and calcium content < 300 ppm.

[0012] The purity of the ZIF-8 metal-organic framework raw material is greater than 98%.

[0013] Preferably, the weight ratio of BYK347 wetting agent: α-crystalline alumina raw material: sodium-containing boehmite raw material: ZIF-8 metal-organic framework raw material: disodium EDTA: polyvinyl alcohol: water-based binder: sodium polycarboxylate dispersant is 0.3-0.6:68-76:10-15:8-10:3-5:0.2-0.3:4-6:0.4-1; in the α-crystalline alumina raw material, the ratio of alumina raw material A to alumina raw material B is 1:1.2-1.5; in the water-based binder, the ratio of binder NAL46 to binder NAL28 is 7-8:2-3.

[0014] Sodium-containing boehmite raw material, alumina raw material A, alumina raw material B, and PE base film are all custom raw materials. Among MOFs materials that meet the ZIF-8 metal-organic framework raw material parameters, market testing revealed that Carbon Language's KAR-F02 MOFs material matches the required parameters. It can also be customized through Blue Shell Clean Energy and Sichuan Indile.

[0015] The requirements for water-based adhesives are as follows: lithium acrylate monomers and acrylate monomers are chemically bonded to the main chain of the water-based adhesive as functional side chains; the water-based adhesive contains -COOLi and -COOR functional groups, and the main chain has a common carbon chain bonding structure on the market. After market research and comparison, it was found that the NAL series water-based adhesives produced by Chengdu Yiang Technology Co., Ltd. meet the requirements. The side chain structure meets the requirements of this invention for the side chain of water-based adhesives, and the main chain meets the bonding requirements. Combining the parameters of the above-mentioned customized raw materials and ZIF-8 metal-organic framework raw materials, after multiple experiments, it was found that the adhesive performance of the combination of NAL46 and adhesive NAL28 is the best. Of course, other companies' products can also be used, as long as the side chain contains -COOLi and -COOR functional groups and the main chain meets the bonding requirements.

[0016] In diaphragm design, the strict setting of various parameters is not an isolated requirement, but rather a means to achieve multi-level synergy between materials, structure, and function: Alumina A, alumina B, and boehmite raw materials, as inorganic particles, can achieve a denser packing by mixing particles of different sizes. Fine particles fill the gaps between coarse particles, while coarse particles form the framework. The multi-peaked particle size distribution significantly increases the packing density of inorganic particles in the coating. The advantages are as follows: dense packing reduces excessively large voids, resulting in a more uniform and denser microporous structure, improving the coating's porosity; increased contact points between particles lead to tighter bonding, contributing to improved coating hardness and puncture resistance, enhancing the high-temperature dimensional stability and puncture and dendrite-blocking properties of the composite multifunctional membrane; denser packing itself reduces the total pore volume, but more importantly, it optimizes the pore size distribution, reducing macropores and increasing micropores. Uniform micropores are generally more conducive to ion conduction stability than a small number of macropores, thus reducing coating porosity (optimized pore size distribution); mixed use can balance the overall specific surface area of ​​the slurry, placing it within a more suitable range. This helps balance specific surface area and slurry rheology: improves slurry dispersion stability, reduces particle agglomeration, and ensures uniform dispersion of inorganic fillers in the slurry. It controls slurry viscosity, preventing excessive slurry thickness and maintaining good flowability and coating performance. It optimizes binder dosage, reducing the amount of binder needed due to excessive adsorption by high specific surface area particles. In summary, particle gradation achieves a denser and more uniform buildup of inorganic coatings, improving mechanical strength and thermal stability, optimizing pore structure, balancing the overall specific surface area of ​​the slurry, improving dispersion stability and rheology, and facilitating coating processing. Alumina, boehmite, and ZIF-8 work synergistically to construct a multi-level, porous composite structure, maximizing the advantages of each component (high hardness and good wettability of boehmite, high thermal stability and strength of alumina, and ultra-high specific surface area and improved ionic conductivity of ZIF-8), ultimately resulting in a composite ceramic membrane with excellent overall performance. This design embodies the complementary nature of different component properties in material formulation to achieve performance optimization that is difficult to achieve with a single component. Impurity limits (Fe / Cu / Ca < specific ppm): Basic principle: The active metals in the positive electrode are quantitative and controllable, while the impurity metals in the auxiliary materials are quantitative and uncontrollable. The presence of the latter will disrupt the redox balance inside the battery and must be strictly limited; Synergistic goal: Avoid parasitic reaction chains caused by impurities; Impurity Fe, especially trivalent iron: catalyzes electrolyte decomposition → generates HF → corrodes the positive electrode → exacerbates Mn dissolution; Cu: reduces and deposits at the negative electrode → forms copper dendrites → punctures the separator; The core reason for limiting calcium content: forms insoluble calcium salt precipitates, which easily block ion channels. The reason for requiring boehmite raw materials to be rhomboid flakes is: Kinetic level: acute angle drives rotational diffusion, resisting sedimentation; Interfacial level: directional adsorption of wetting agents, reducing the dispersion energy barrier; Structural level: capillary force guides self-assembly, ensuring coating homogeneity.

[0017] ZIF-8 metal-organic framework material: Its highly ordered pore structure and extremely large specific surface area provide a large number of manganese ion adsorption sites. Van der Waals forces and electrostatic interactions within the pores can rapidly capture manganese ions dissolved from the lithium manganese iron phosphate electrode during cycling. Furthermore, the extremely large specific surface area of ​​MOFs effectively improves the affinity of this composite multifunctional battery separator for the electrolyte, enabling the separator to quickly adsorb and uniformly distribute the electrolyte. It can precisely adsorb manganese ions within the required pore size while allowing free lithium ion transport; forming continuous lithium ion transport channels, reducing lithium ion transport resistance, significantly lowering the battery's internal resistance. Simultaneously, it effectively shortens the lithium ion diffusion path, thus meeting the fast-charging requirements. Furthermore, the sufficient wetting of the separator by the electrolyte effectively reduces side reactions at the electrode-electrolyte interface, improves interface stability, promotes uniform lithium ion distribution, and inhibits lithium dendrite growth, thereby mitigating capacity decay. The choice of zinc ions, rather than other ions, as the MOF material is based on the fact that zinc ions represent the optimal solution for balancing "ion sieving ability - electrochemical inertness - structural stability" in MOF materials: its d¹ 0 The electronic configuration fundamentally avoids the risks of reduction / oxidation; the moderate coordination strength enables dynamic capture of manganese ions, and zinc ions can replace manganese ions through ion exchange mechanisms. Since the radii of Mn ions and zinc ions are close, they can partially occupy zinc sites in the ZIF-8 framework, thereby immobilizing manganese ions; the rigid pore structure provides a dedicated diffusion path for lithium ions. This choice is essentially to avoid the side reaction chain caused by the activity of transition metals at the atomic scale.

[0018] The effects of polyvinyl alcohol (PVA): 1. The hydrogen bond network and cross-linking structure formed between PVA molecular chains significantly improve its glass transition temperature and enhance thermal stability; 2. PVA-containing separators can reduce thermal shrinkage at high temperatures (150℃), effectively preventing short circuits caused by battery thermal runaway; 3. PVA is rich in hydroxyl groups (-OH), which can reduce the electrolyte contact angle, improve electrolyte wettability and affinity; 4. The coating with added PVA forms a three-dimensional network porous structure, which can improve the liquid absorption and retention rate, while also improving mechanical strength and dendrite inhibition, enhancing puncture strength and effectively blocking lithium dendrite penetration.

[0019] Aqueous binders: Side-chain functional groups are the chemical foundation for the function of aqueous binders. Their core value lies in: 1. Forming coordination structures with manganese ions in lithium manganese iron phosphate electrodes, participating in the formation of a more stable electrode-electrolyte interface film in the electrolyte, thereby inhibiting the dissolution of manganese ions in lithium manganese iron phosphate. 2. To a certain extent, it compensates for the problem of reduced specific surface area of ​​MOFs due to coating issues when using MOF materials alone, thus reducing the adsorption capacity for manganese ions. At the same time, it can effectively supplement the free lithium ion content in the battery system, thereby improving electrochemical performance. 3. It has a dendrite inhibition synergistic effect, repels anions, reduces space charge layer distortion, and homogenizes lithium ion flux density. 4. System synergy: It forms a multi-level protective network with ZIF-8 (physical adsorption), EDTA (strong chelation), and sodium ions (charge balance).

[0020] The disodium EDTA added to the separator acts as a strong chelating agent. Through its four carboxylic acid groups and two amino groups, it forms a stable hexadecimal complex (e.g., [Mn-EDTA]⁻) with dissolved manganese ions (Mn²⁺ / Mn³⁺), inhibiting the migration of manganese ions to the negative electrode and damaging the SEI film during LMFP charge-discharge due to the Jahn-Teller effect, thereby improving cycle stability. Its strong coordination field also restricts the solvation structure of Mn²⁺, preventing Mn³⁺ from forming MnO₂ precipitate through disproportionation reactions, reducing side reactions on the electrode surface. Simultaneously, when used in conjunction with an aqueous binder, it maintains the ionic conductivity of the electrolyte and participates in the formation of a stable interfacial film on the electrode surface, further inhibiting manganese ion dissolution. The synergistic effect of both is manifested in the following ways: EDTA preferentially immobilizes free metal ions (such as Mn²⁺ and Fe³⁺) in the electrolyte, while the aqueous binder reduces side reactions by optimizing the lithium-ion transport pathway, jointly enhancing the stability of the electrode-electrolyte interface and further optimizing battery performance.

[0021] In the composite separator design of lithium manganese iron phosphate batteries, the fundamental reason for choosing BYK-347 wetting agent over other wetting agents lies in its unique material composition (polyether-modified organosilicon) and its derived functional properties, which are highly compatible with the separator slurry system and the electrochemical requirements of the battery. The following is a comprehensive analysis from four dimensions: component characteristics, functional adaptability, system compatibility, and electrochemical impact: I. Material Composition Characteristics: The Irreplaceability of Polyether-Modified Organosilicon: The chemical composition of BYK-347 is polyether-modified siloxane (polyether segments + organosilicon backbone). Its molecular structure has dual characteristics: Hydrophilic end (polyether chain): Contains ether bonds (-O-) and hydroxyl groups (-OH), forming hydrogen bonds with water molecules, significantly improving the hydrophilicity of the slurry. Effectively reduces surface tension, promoting the spreading and wetting of the slurry on the polyolefin-based membrane (PE). Hydrophobic end (organosilicon): Siloxane chains (-Si-O-Si-) are oriented to the coating surface, reducing interfacial energy without increasing slippage (preventing delamination between coatings). Compared to other wetting agents: Non-silicone wetting agents (such as fluorocarbons): Although they can strongly reduce surface tension, they easily migrate to the interface, resulting in excessive slippage, which affects subsequent coating or electrode bonding. Traditional organosilicon wetting agents (such as BYK-333): Introduce slippage, weakening the interfacial adhesion between the diaphragm coating and the electrolyte. II. Functional compatibility: Meeting the stringent requirements of diaphragm slurry processes: 1. Recoating compatibility of thin coatings: BYK-347 exhibits excellent recoating properties in thin coatings (such as 1-4μm coatings on one side of the diaphragm), allowing for multi-layer coating without affecting interlayer adhesion; other wetting agents (such as BYK-345) cause interfacial energy mismatch due to residual migration during multiple coatings, leading to pinholes or peeling. 2. Weak foam stability ensures slurry stability: BYK-347 produces only slight foam stability, which can be efficiently removed by magnetic filtration / screen filtration (200–400 mesh); alternatives (such as fluorinated wetting agents) often result in air-filled pores in the slurry due to strong foam stability, forming an ion transport barrier after curing. 3. Compatibility: Avoids organic solvent contamination of electrodes or side reactions; some wetting agents (such as XT-3037) contain dipropylene glycol monomethyl ether solvent, which can swell the PE base film or reduce thermal stability. III. System Compatibility: Synergistic effect with battery components: 1. Synergy with water-based binders (NAL46 / NAL28): The polyether chains of BYK-347 form a hydrogen bond network with the carboxyl groups of the water-based binder, enhancing the mechanical strength of the coating. If BYK-333 (containing hydrophobic silane) is used, it will hinder the interfacial bonding between the binder and ZIF-8 / MOFs, reducing the manganese ion adsorption efficiency. 2. pH Stability Matches Electrolyte Environment: BYK-347 remains stable at pH 4–10, compatible with the electrolyte of lithium manganese iron phosphate batteries. Some wetting agents (such as amine-containing agents) decompose in acidic environments, releasing impurity ions and catalyzing manganese dissolution. IV. Electrochemical Performance: Directly Related to Battery Life and Safety: 1. Suppressing Interfacial Side Reactions: BYK-347 enhances the hydrophilicity of the separator, enabling the electrolyte to quickly form continuous Li⁺ channels and reduce internal resistance.Insufficient wetting agents (such as BYK-349) can lead to uneven electrolyte distribution and localized lithium dendrite growth. 2. Thermal stability assurance: Superior high-temperature resistance compared to low-flash-point wetting agents (such as alcohol-based ones), preventing volatilization or decomposition during coating (58–65℃). Synergistically with the PE base film, it prevents separator deformation and short circuits at high temperatures. BYK-347, with its polyether-modified silicone molecular design, achieves an irreplaceable balance in wetting, recoatability, purity, and electrochemical compatibility. Replacing it with other wetting agents will disrupt the component synergy of the separator coating (e.g., introducing slippage, impurities, or solvents), leading to decreased manganese ion adsorption efficiency, increased interfacial impedance, or deteriorated thermal stability, ultimately affecting battery cycle life and safety.

[0022] The reason for choosing sodium polyacrylate dispersant is not only to achieve good dispersion, but also to consider the synergistic functional extension of the carboxylic acid groups. The carboxylic acid groups can reduce the lithium ion desolvation energy barrier and inhibit lithium dendrite nucleation, thus optimizing the lithium ion transport channel.

[0023] The sodium content in the composite multifunctional battery separator is increased by using sodium polyacrylate dispersant, sodium-containing boehmite, and disodium EDTA. The reasons are as follows: 1. Sodium ions compete with manganese ions for migration in the electrolyte. Due to the smaller Stokes radius and lower charge density of sodium ions, they preferentially occupy transport sites in the separator pores, thus blocking the diffusion path of manganese ions. Sodium ions form a positively charged barrier layer, repelling positively charged manganese ions through Coulomb repulsion, reducing their migration rate and inhibiting SEI film damage caused by manganese dissolution at the source. 2. Homogenizing lithium-ion flow: Maintaining interfacial order through charge balance ensures efficient lithium-ion transport. Sodium ions have a lower migration rate than lithium ions and can form a temporary electrostatic shielding layer at the interface, making lithium-ion deposition / deintercalation more uniform, suppressing dendrites, and reducing interfacial impedance, thus reducing the lithium-ion desolvation barrier and improving fast-charging capability. Allowing boehmite to contain a certain amount of sodium is also a cost consideration. Natural boehmite raw materials typically contain a certain amount of sodium as an impurity. Industrially used boehmite is mainly an intermediate product in the Bayer process for alumina production or is specially synthesized. The Bayer process uses a concentrated sodium hydroxide solution to dissolve bauxite under high temperature and pressure. Although subsequent processes wash away most of the sodium, trace amounts of sodium ions remain on the surface or in the structure of the boehmite particles. Because higher purity boehmite is more expensive, utilizing sodium, which would normally be considered an "impurity," as part of the raw material effectively reduces the cost of the boehmite used.

[0024] Reasons for choosing PE-based membranes: Compared to ordinary batteries, batteries in the 3C consumer electronics and energy storage industries have higher electrolyte viscosity, greater interfacial pressure, and higher requirements for protection against thermal runaway. Mechanical performance parameters require resistance to interfacial stress in the electrolyte, preventing short circuits between the positive and negative electrodes due to separator damage. Thermal stability parameters require maintaining structural integrity during localized battery heating, delaying thermal runaway. Pore characteristics require providing channels for lithium ions in the electrolyte (ion conduction depends on pore structure) while preventing particle blockage of pores. Industrial selection logic: Batteries are extremely cost-sensitive. PE-based membranes, with their mature supply chain and large-scale production advantages, achieve low separator unit prices while meeting performance requirements, providing cost space for the functionalization of composite coatings. Meeting application design requirements: The temperature threshold and closed-cell characteristics of PE-based membranes can block thermal runaway currents, and its pore size distribution and permeability balance ion conduction. The composite coating in this invention can precisely compensate for defects in thermal stability, wettability, and mechanical strength; if replaced with PP base film: excessive heat shrinkage rate → risk of high-temperature short circuit; if PI base film is used: cost increases dramatically → loss of competitiveness in the energy storage market.

[0025] When selecting a coating method, experiments were conducted on microgravure coating, wire rod coating, and slit coating, and it was found that microgravure coating yielded the best results.

[0026] In composite multifunctional battery separators, when the polyolefin-based membrane is coated with a composite coating on only one side, the side with the composite coating is positioned facing the positive electrode of the lithium manganese iron phosphate battery to achieve the best technical effect.

[0027] A method for preparing a composite multifunctional separator, specifically comprising the following steps: S1: Mix sodium polycarboxylate dispersant and deionized water evenly and disperse to obtain mixture A; S2: Add α-crystalline alumina raw material, sodium-containing boehmite raw material and ZIF-8 metal-organic framework raw material to mixture A, stir evenly to obtain mixture B; S3: Add disodium ethylenediaminetetraacetate, polyvinyl alcohol and water-based binder to mixture B, and stir until homogeneous to obtain mixture C; S4: Add water-based polyether-modified organosilicon wetting agent to mixture C, stir evenly, and obtain mixture D; S5: Perform magnetic filtration and screen filtration on mixture D sequentially to obtain the target slurry; S6: At a preset temperature, the target slurry is coated onto at least one side of the surface of the polyolefin-based membrane and then cured to obtain a composite multifunctional membrane. In the composite multifunctional membrane, the thickness of the composite coating is 1-4 μm.

[0028] In this method for preparing a composite multifunctional diaphragm, the order of material addition is not randomly set, but rather based on a multi-level logical design considering dispersion stability, component compatibility, functional synergy, and process feasibility. The entire material addition sequence follows a progressive logic of "dispersion priority → particle synergy → functional enhancement → coating optimization," with each step laying the foundation for subsequent processes while avoiding negative interactions between components: First, a dispersant is added to solve the fundamental problem of "particle agglomeration," which is a prerequisite for the realization of all subsequent functions; then, inorganic particles are added to utilize the dispersion environment to achieve particle size distribution and structural synergy, ensuring the mechanical / thermal stability of the coating; next, a chelating agent / binder is added to achieve functional synergy of "manganese ion capture," "interfacial bonding," and "thermal stability network" on the basis of dispersion stability, avoiding competition with the dispersant; finally, a wetting agent is added to optimize coating performance after the system stabilizes, avoiding interfacial migration failure; and post-filtration ensures slurry cleanliness and retains all functional components. Arbitrarily adjusting the order (such as adding particles before dispersants, or adding wetting agents before binders) can lead to slurry agglomeration and stratification, functional component failure, and coating structural defects. Ultimately, this will prevent the diaphragm from achieving its multifunctionality or even meeting the requirements of industrial coating. The specific principle is as follows: Prioritize the addition of dispersants: This lays the foundation for uniform dispersion of inorganic particles. The core purpose is to ensure that dispersant molecules fully dissolve in water and form a stable "dispersant-water" system, creating an "instant dispersion environment" for the subsequent addition of inorganic particles (α-alumina, boehmite, ZIF-8) and preventing particle agglomeration. The mechanism of action of dispersants: The carboxylate groups of sodium polycarboxylate adsorb onto the surface of inorganic particles through electrostatic repulsion and steric hindrance, preventing particles from agglomerating due to van der Waals forces. If the order is reversed (particles added first, then dispersant), the particles will first form loose aggregates in the water. Dispersant molecules cannot penetrate into the aggregates and can only coat the surface, leading to "false dispersion"—the slurry is prone to stratification after settling, and the coating may show particle accumulation or uneven porosity after coating, directly affecting the ion transport efficiency and mechanical strength of the membrane. Targeted adaptation: The inorganic particles in this invention contain bimodal alumina (A / B), rhombic platy boehmite, and nano-sized ZIF-8. The particle size range is large (0.1μm-5μm) and the specific surface area varies significantly (5.5-1500m² / g). Therefore, the dispersant needs to be "pre-activated" in advance to ensure that particles of different sizes are uniformly suspended and to avoid the sedimentation of large particles or the agglomeration of nano-sized ZIF-8.

[0029] Inorganic particles are added after the dispersant to avoid the risk of irreversible agglomeration. The addition of α-alumina, sodium-containing boehmite, and ZIF-8 to the dispersant-water system is based on the logic of "building the environment first, then adding the materials," ensuring that the particles are encapsulated by dispersant molecules as soon as they enter the system, inhibiting agglomeration from the source. Key contradiction resolved: If inorganic particles are added first, they will quickly form "primary agglomerates" in water. In particular, ZIF-8 has a specific surface area ≥1500m² / g and extremely high surface energy, making it difficult to disperse the agglomerates through subsequent stirring. If the rhombic plate-like structure of boehmite agglomerates, it will lose its "directional self-assembly" ability, resulting in an uneven coating structure and affecting high-temperature resistance. Particle size distribution coordination requirement: This invention achieves "close packing" through the gradation of alumina A (fine particles), alumina B (medium particles), and boehmite (flaky particles). The three types of particles need to be uniformly mixed under the action of a dispersant so that the fine particles can fill the gaps between the coarse particles and the flaky particles can be oriented. If the order is disordered, the uneven distribution of particles will destroy the packing structure, resulting in a decrease in the mechanical strength of the coating (such as insufficient puncture strength) and uncontrolled porosity.

[0030] Delayed addition of chelating agents / binders: To avoid competition for adsorption with dispersants and ensure functional effectiveness, disodium ethylenediaminetetraacetate (EDTA), polyvinyl alcohol, and water-based binders are added after the inorganic particles are dispersed and stabilized. The core principle is to avoid "component competition for adsorption" and "functional interference," ensuring that each component performs its function effectively. Avoiding competition between dispersants and binders: Water-based binders (NAL46 / NAL28) contain lithium carboxylate and ester functional groups, which compete with the carboxylate groups of the sodium polycarboxylate dispersant for adsorption sites. If the binder is added before the dispersant, the binder will preferentially adsorb onto the surface of the inorganic particles, occupying the adsorption sites of the dispersant, leading to dispersant failure and particle agglomeration. Conversely, if the dispersant adsorbs first, the binder can synergistically work with the dispersant through intermolecular forces (such as hydrogen bonds), neither compromising dispersion stability nor hindering the formation of a three-dimensional network of "dispersant-binder-particles," thus improving coating adhesion. Ensuring the chelating activity of EDTA: Only after the particles are stably dispersed can EDTA be uniformly dispersed in the slurry, and after the diaphragm is formed, it can exert its "manganese ion capture" function, preventing it from reacting with the dispersant prematurely and becoming ineffective. PVA network construction requirements: PVA needs to be added after the inorganic particles are dispersed in order to form hydrogen bonds with the hydroxyl groups on the particle surface (such as Al-OH in boehmite) through hydroxyl groups, constructing a three-dimensional cross-linked network, improving the coating's thermal stability (reducing high-temperature shrinkage) and liquid retention. If PVA is added first, its molecular chains are easily entangled with undispersed particles, forming "particle-PVA agglomerates," which destroy the coating's pore structure.

[0031] Finally, a wetting agent is added to prevent "interface migration failure" and ensure coating uniformity. A water-based polyether-modified silicone wetting agent (BYK347) is added after the slurry system has stabilized. The core principle is to utilize the "surface activity" of the wetting agent to avoid "interface migration" or "functional loss" caused by premature addition. If added prematurely (e.g., before the dispersant or particles), the wetting agent will preferentially migrate to the slurry surface or container wall, resulting in insufficient wetting agent concentration inside the slurry and causing "pinholes" or "missing coatings" during coating. Simultaneously, if the wetting agent mixes with the dispersant too early, it may form a "complex" due to intermolecular forces, losing its ability to reduce surface tension. Process compatibility requirements: This invention uses microgravure coating technology, requiring the slurry to have stable surface tension (ensuring uniform coating thickness, 1-4μm ultrathin coating). Adding the wetting agent last allows for immediate adjustment of the slurry surface tension to the optimal range (adapting to the surface energy of the PE base film), avoiding surface tension fluctuations caused by premature addition, and ensuring uniform coating thickness and no bubbles after coating (subsequent magnetic filtration can further remove bubbles).

[0032] Post-filtration process: To ensure slurry cleanliness and avoid loss of functional components; the final slurry undergoes magnetic filtration and 200-400 mesh filtration, which must be performed after all materials have been added for two reasons: First, to remove impurities and agglomerates: After mixing materials in the first four steps, trace metal impurities or incompletely dispersed small agglomerates (such as ZIF-8 nanoparticle agglomerates) may be introduced. Magnetic filtration can adsorb metal impurities, and mesh filtration can remove agglomerates (preventing scratching of the base film or pore blockage during coating). Second, to avoid loss of functional components: ZIF-8 has a small particle size, and PVA molecular chains are relatively long. If these components are filtered before addition, subsequently added functional components may be trapped by the mesh (e.g., ZIF-8 clogging the mesh), or the PVA molecular chains may be damaged, affecting their cross-linking function. Post-filtration ensures that all functional components are retained in the slurry, removing only impurities and agglomerates.

[0033] If the order is arbitrarily adjusted (such as adding particles before dispersants, or adding wetting agents before binders), it may lead to slurry agglomeration and stratification, failure of functional components, and defects in the coating structure. Ultimately, the diaphragm will be unable to achieve its core functions of "inhibiting manganese ion dissolution, high temperature resistance, and low interfacial impedance", and may even fail to meet the requirements of industrial coating.

[0034] Preferably, a 200-400 mesh filter is used in the filter filtration process.

[0035] Preferably, in step S6, the preset temperature is 58-65°C, and the target slurry is coated onto at least one side surface of the polyolefin-based film using microgravure coating technology.

[0036] Preferably, the deionized water accounts for 15-30% of the solid content in the target slurry.

[0037] An application of a composite multifunctional separator, which is used in lithium manganese iron phosphate battery systems in the 3C consumer electronics and energy storage industries.

[0038] The battery separator of this invention is designed for the application scenarios of lithium manganese iron phosphate batteries in the 3C consumer electronics and energy storage industries, especially for energy storage applications with long cycle requirements. The specific beneficial effects are as follows: 1. Highly Effective Inhibition of Manganese Ion Dissolution and Enhanced Cycle Life: Manganese Ion Adsorption Mechanism: The ZIF-8 metal-organic framework provides numerous physical adsorption sites, capturing dissolved manganese ions through van der Waals forces and electrostatic interactions. Disodium EDTA, as a strong chelating agent, forms a stable hexadecate complex with Mn²⁺ / Mn³⁺, inhibiting manganese ion migration to the negative electrode and its damage to the SEI film. The side-chain functional groups (-COOLi / -COOR) of the aqueous binder coordinate with manganese ions, participating in the formation of a stable interfacial film and further reducing dissolution. Synergistic Protection Network: The triple mechanism of physical adsorption (ZIF-8), chemical chelation (EDTA), and coordination fixation (binder) blocks the migration pathway of manganese ions, significantly reducing Jahn-Teller distortion and disproportionation reactions. Results: Effectively alleviates irreversible capacity decay and extends battery cycle life (especially meeting the long-cycle requirements of energy storage scenarios).

[0039] 2. Enhanced High-Temperature Stability and Mechanical Strength: Improved Heat Resistance: α-alumina (A / B bimodal gradation) and boehmite (rhombic lamellar structure) provide high thermal conductivity and thermal stability, suppressing high-temperature shrinkage. PVA's high glass transition temperature enhances the coating's heat resistance and reduces high-temperature deformation. Optimized Mechanical Properties: The close packing of alumina / boehmite (particle size gradation design) improves coating hardness and puncture resistance; the PE-based film synergistic composite coating reduces thermal shrinkage to 0.5% at 130℃, far superior to traditional separators. Result: Prevents short circuits at high-temperature electrode contacts, improving battery safety.

[0040] 3. Optimization of Electrolyte Wetting and Ion Transport Efficiency: Enhanced Wetting: BYK-347 wetting agent significantly reduces the surface tension of the slurry, improving its spreadability on the PE-based film. The ultra-high specific surface area of ​​ZIF-8 and the hydroxyl groups of PVA synergistically enhance the hydrophilicity of the separator, accelerating electrolyte wetting. Optimized Ion Transport: The rigid channels of ZIF-8 form continuous lithium-ion channels, shortening the diffusion path. Sodium ions (introduced by boehmite / EDTA / dispersant) homogenize the lithium-ion flow, reducing interfacial impedance and desolvation barrier. Results: Reduced internal resistance, supporting fast charging requirements, and suppressing dendrite growth caused by uneven local lithium deposition.

[0041] 4. Synergistic Suppression of Lithium Dendrites and Side Reactions: Physical Dendrite Barrier: The close-packed structure of alumina / boehmite and the high hardness of the coating effectively block dendrite penetration. Electrochemical Regulation: Sodium ions repel manganese ions through Coulomb repulsion and form an electrostatic shielding layer at the interface, promoting uniform lithium ion deposition. Binder side chains (-COOLi) optimize the lithium ion transport path and reduce space charge distortion. Results: Reduced short-circuit risk caused by dendrites and improved interface stability.

[0042] 5. Cost and industrialization compatibility: Raw material cost optimization: Reduce production costs by utilizing sodium-containing boehmite; Process compatibility: Microgravure coating technology enables uniform application of ultra-thin coatings (1-4μm), compatible with large-scale production. A mature PE base film supply chain ensures low cost, while coating overcomes defects. Result: A balance between high performance and cost, suitable for the 3C consumer electronics and energy storage markets.

[0043] In summary, this invention, through multi-component synergistic design and precise parameter control, simultaneously addresses the issues of manganese ion dissolution and poor stability in high-energy-density battery systems within LMFP battery systems, thereby significantly improving battery energy density and cycle life. It effectively reduces interfacial resistance, optimizes pore structure, and enhances the high-temperature resistance of the separator, suppressing lithium dendrite growth and thermal runaway. While reducing electrolyte side reactions, it also improves the separator's affinity for the electrolyte and offers industrial cost advantages. Designed for lithium manganese iron phosphate batteries in the 3C consumer electronics and energy storage industries, the core logic is to address the battery's requirements for high safety, high ion conductivity, and high interfacial compatibility through a polyolefin-based membrane + composite coating structure, particularly effective for energy storage applications with long cycle requirements. Detailed Implementation

[0044] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments. Example 1

[0045] A composite multifunctional battery separator for lithium manganese iron phosphate batteries includes a polyolefin-based membrane and a composite coating coated on at least one side of the polyolefin-based membrane. The raw materials for preparing the composite coating include: α-crystalline alumina raw material, sodium-containing boehmite raw material, ZIF-8 metal-organic framework raw material, aqueous binder, sodium polycarboxylate dispersant, disodium ethylenediaminetetraacetate, polyvinyl alcohol, and aqueous polyether-modified organosilicon wetting agent. The waterborne polyether-modified silicone wetting agent is BYK347. The weight ratio of BYK347 wetting agent: α-crystalline alumina raw material: boehmite raw material: ZIF-8 metal-organic framework raw material: disodium EDTA: polyvinyl alcohol: waterborne adhesive: sodium polycarboxylate dispersant is 0.4:72:13:9.5:4.3:0.25:5:0.65. In the α-crystalline alumina raw material, the mass ratio of alumina raw material A to alumina raw material B is 1:1.4. In the waterborne adhesive, the mass ratio of adhesive NAL46: adhesive NAL28 is 8:2. The waterborne adhesive is the NAL series waterborne adhesive produced by Chengdu Yiang Technology Co., Ltd. Specifically, adhesive NAL28 has a viscosity of 910 mPa·s, a solid content of 15.2%, and a pH of 7.5; adhesive NAL46 has a viscosity of 790 mPa·s, a solid content of 15.2%, and a pH of 7.0. Example 2

[0046] A method for preparing a composite multifunctional battery separator for lithium manganese iron phosphate batteries, specifically comprising the following steps: S1: After uniformly mixing sodium polycarboxylate dispersant and deionized water, mixture A is obtained; Sodium polycarboxylate dispersant: DA-10 (Changzhou Rongtuo Trading Co., Ltd.); (Sodium polyacrylate) colorless or light yellow liquid (anionic); viscosity 200-300 mPa·s; solid content 40 ± 1%; S2: Add α-crystalline alumina raw material, sodium-containing boehmite raw material and ZIF-8 metal-organic framework raw material to mixture A, stir evenly to obtain mixture B; α-crystalline alumina raw material includes alumina raw material A and alumina raw material B; The parameters of sodium-containing boehmite raw material are shown in Table 1, the parameters of alumina raw material A are shown in Table 2, the parameters of alumina raw material B are shown in Table 3, and the raw material for ZIF-8 metal-organic framework is KAR-FO2 from Carbon Talk.

[0047] Table 1

[0048] Table 2

[0049] Table 3 S3: Add disodium ethylenediaminetetraacetate, polyvinyl alcohol and water-based binder to mixture C, stir evenly to obtain mixture D; S4: Add BYK347 wetting agent to mixture D, stir well to obtain mixture E; S5: Perform magnetic filtration and screen filtration on mixture E in sequence to obtain the target slurry.

[0050] S6: At a preset temperature, the target slurry is coated onto at least one side of the PE base film and then cured to obtain a composite multifunctional battery separator. The parameters of the PE base film are shown in Table 4.

[0051]

[0052] Table 4 Performance testing: The nickel chloride solution adsorption experiment was used. Since the solution of manganese chloride is transparent after dissolving in anhydrous ethanol, the adsorption effect cannot be judged by the color change. Therefore, nickel chloride, which is also a transition metal chloride, was used instead of manganese chloride to evaluate the adsorption capacity for metal ions. The test results are shown in Table 5.

[0053]

[0054] Table 5 Thermal stability testing: Thermal stability was tested at 130℃, and the results are shown in Table 6.

[0055] Table 6 The above are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite multifunctional battery separator, characterized in that, Includes a polyolefin-based film and a composite coating located on at least one surface of the polyolefin-based film; The raw materials for preparing the composite coating include: α-crystalline alumina raw material, sodium-containing boehmite raw material, ZIF-8 metal-organic framework raw material, waterborne binder containing lithium carboxylic acid functional group side chains and ester functional group side chains, sodium polycarboxylate dispersant, disodium ethylenediaminetetraacetate, polyvinyl alcohol and waterborne polyether modified organosilicon wetting agent.

2. The composite multifunctional battery separator as described in claim 1, characterized in that, The polyolefin-based film is specifically a PE-based film; the sodium polycarboxylate dispersant is specifically a sodium polyacrylate dispersant; the α-crystalline alumina raw materials include alumina raw material A and alumina raw material B; the water-based polyether-modified silicone wetting agent is specifically BYK347 wetting agent; the thickness of the composite coating is 1-4 μm; The following parameters are required for sodium-containing boehmite raw materials: Microstructure: rhombic platy; Particle size: 0.1μm≤D10<0.5μm, 0.6μm≤D50<1.1μm, 1.3μm≤D90<1.8, 1.9μm≤D99<5.0μm; Specific surface area: 5.0-10.0m² / g; Sodium content: 0.03-0.05%; The parameters for alumina raw material A are as follows: particle size: 0.1μm≤D10<0.25μm, 0.3μm≤D50<0.5μm, 0.6μm≤D90<0.85μm; specific surface area is 6.0-10.0m² / g; The parameters for alumina raw material B are as follows: particle size: 0.25μm≤D10<0.4μm, 0.5μm≤D50<0.7μm, 0.85μm≤D90<1.5μm; specific surface area is 5.5-9.0m² / g; The raw material parameters for ZIF-8 metal-organic framework are as follows: specific surface area ≥ 1500 m² / g; particle size: 500-700 nm; pore size: 0.9-1.8 nm; The PE base film parameters are as follows: Structural parameters: pore size distribution range: 30-50nm, average pore size 35-40nm; air permeability: 160±70s / 100cc; porosity: 39%-50%; Mechanical properties: Puncture strength: ≥300gf; Longitudinal tensile strength: ≥1500kgf / cm 2 Transverse tensile strength: ≥1200 kgf / cm 2 Longitudinal elongation at break: ≥50%; Transverse elongation at break: ≥50%; Thermal stability: At 90℃: CMD thermal shrinkage rate ≤1.5%, CTD transverse thermal shrinkage rate ≤0.5%; At 105℃: CMD longitudinal thermal shrinkage rate ≤5%, CTD transverse thermal shrinkage rate ≤3%; At 120℃: CMD longitudinal thermal shrinkage rate ≤6%, CTD transverse thermal shrinkage rate ≤5.5%; Surface density: 5.4±1.0g / m².

3. The composite multifunctional battery separator as described in claim 2, characterized in that, The parameters for alumina raw material A also have the following requirements: calcium content < 300 ppm; iron content < 100 ppm; copper content < 5 ppm; The parameters for alumina raw material B also have the following requirements: calcium content < 300 ppm; iron content < 100 ppm; copper content < 5 ppm.

4. The composite multifunctional battery separator as described in claim 2, characterized in that, The parameters for boehmite raw materials also include the following requirements: iron content < 50 ppm, copper content < 5 ppm, and calcium content < 300 ppm.

5. The composite multifunctional battery separator as described in claim 2, characterized in that, The purity of the ZIF-8 metal-organic framework raw material is greater than 98%.

6. The composite multifunctional battery separator as described in claim 2, characterized in that, The weight ratio of BYK347 wetting agent: α-crystalline alumina raw material: sodium-containing boehmite raw material: ZIF-8 metal-organic framework raw material: disodium EDTA: polyvinyl alcohol: water-based binder: sodium polycarboxylate dispersant is 0.3-0.6:68-76:10-15:8-10:3-5:0.2-0.3:4-6:0.4-1; in the α-crystalline alumina raw material, the ratio of alumina raw material A to alumina raw material B is 1:1.2-1.5; the water-based binder includes binder NAL46 and binder NAL28; the weight ratio of binder NAL46 to binder NAL28 is 7-8:2-3.

7. A method for preparing a composite multifunctional battery separator, used to prepare the composite multifunctional battery separator according to any one of claims 1-6, characterized in that, The specific preparation method includes the following steps: S1: Mix sodium polycarboxylate dispersant and deionized water evenly and disperse to obtain mixture A; S2: Add α-crystalline alumina raw material, sodium-containing boehmite raw material and ZIF-8 metal-organic framework raw material to mixture A, stir evenly to obtain mixture B; S3: Add disodium ethylenediaminetetraacetate, polyvinyl alcohol and water-based binder to mixture B, and stir until homogeneous to obtain mixture C; S4: Add water-based polyether-modified organosilicon wetting agent to mixture C, stir evenly, and obtain mixture D; S5: Perform magnetic filtration and screen filtration on mixture D sequentially to obtain the target slurry; S6: At a preset temperature, the target slurry is coated onto at least one side of the polyolefin-based membrane and then cured to obtain a composite multifunctional membrane.

8. The method for preparing the composite multifunctional battery separator as described in claim 7, characterized in that, In step S5, a 200-400 mesh filter is used; in step S6, the preset temperature is 58-65℃.

9. The method for preparing the composite multifunctional battery separator as described in claim 7, characterized in that, The deionized water content is 15-30% of the solid content in the target slurry.

10. An application of a composite multifunctional battery separator, wherein the composite multifunctional battery separator is any one of the composite multifunctional battery separators described in claims 1-6, characterized in that, Composite multifunctional battery separators are used in lithium manganese iron phosphate batteries in the 3C consumer electronics and energy storage industries.

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