Composite diaphragm for battery as well as preparation method and application of composite diaphragm

Abstract

The invention discloses a composite diaphragm for a battery as well as a preparation method and application of the composite diaphragm. The composite diaphragm is formed by interweaving micro-nano-scale core-shell fibers, and a fiber core layer is composed of a first polymer insoluble in an electrolyte and is loaded with a cross-linking agent; the shell layer is composed of a second polymer soluble in an electrolyte and embeds an initiator. The diaphragm is assembled in a battery, an electrolyte precursor containing ether monomers is injected, and synchronous triggering can be achieved through one-time heating: the shell layer dissolves and releases the initiator, and the monomers are initiated to be subjected to in-situ polymerization to form a gel electrolyte; meanwhile, a core layer cross-linking agent is activated, so that in-situ cross-linking enhancement of a diaphragm framework and chemical bonding of the diaphragm framework and gel are realized. According to the invention, the function integration of physical isolation, polymerization initiation and autonomous enhancement is realized, the interface stability, mechanical strength, thermal safety and cycle life of the battery are remarkably improved, and the preparation method is suitable for high-energy-density lithium metal, magnesium metal and other secondary battery systems.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage device technology, specifically relating to a composite separator for batteries, particularly metal batteries (such as lithium metal batteries and magnesium metal batteries). More specifically, this invention relates to a functional integrated composite separator prepared by coaxial electrospinning, having a core-shell structure and capable of simultaneously triggering in-situ polymerization of the electrolyte and enhancing the cross-linking of the separator itself, its preparation method, and its application in high-safety, high-energy-density batteries. Background Technology

[0002] With the rapid development of consumer electronics, electric vehicles, and large-scale energy storage systems, unprecedented demands have been placed on the energy density and safety performance of rechargeable batteries. Using metals such as lithium and magnesium as anodes is an effective way to improve battery energy density. However, the poor compatibility between traditional liquid electrolytes and highly active metal anodes easily leads to dendrite growth, interfacial side reactions, and electrolyte decomposition, resulting in short battery cycle life and high safety risks.

[0003] Solid-state or gel polymer electrolytes (SPE / GPE) are considered key materials for next-generation high-energy-density batteries due to their excellent interfacial compatibility, dendrite suppression, and higher safety. Among them, gel electrolytes prepared by in-situ polymerization can be formed directly inside the battery, maintaining close contact with the electrodes, and have unique advantages. Existing technologies typically involve pre-mixing the initiator in the electrolyte or simply loading it into a porous membrane, injecting a precursor solution containing monomers, and then heating to initiate polymerization.

[0004] Despite some progress, existing technologies still face the following core challenges: The membrane function is passive: commercial membranes (such as Celgard) or ordinary porous membranes only serve as physical isolation layers or inert supports, and cannot actively participate in and optimize the electrolyte solidification process, resulting in weak bonding with the final gel electrolyte interface.

[0005] Limited performance improvement: Simple physical loading of initiators cannot simultaneously address the problem of insufficient mechanical strength of the membrane itself. After gelation, micro-gaps still exist at the membrane-electrolyte interface, resulting in high interfacial impedance and insufficient mechanical strength to effectively suppress metal dendrite puncture.

[0006] Complex processes or pollution: Some methods require pre-modification of the membrane (such as coating or grafting), which is a complicated process; while some in-situ polymerization systems still require the use of large amounts of organic solvents, which does not conform to the trend of green manufacturing.

[0007] The structural design is too simple: it lacks precise functional zoning design at the fiber scale, making it difficult to achieve the controllable, orderly release and synergistic effect of multiple functional components.

[0008] Therefore, developing a novel, structurally active composite separator that can not only serve as a physical barrier but also as a "reactor" and "reinforcer" to guide and participate in the solidification and structural strengthening process of the electrolyte inside the battery is of great significance for realizing the commercial application of metal batteries. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a structure-function integrated composite separator and its green, efficient preparation method and applications. The core concept of this separator lies in utilizing coaxial electrospinning technology to construct micro / nanofibers with a "non-soluble core-soluble shell" partitioning function. The core layer is responsible for mechanical support and subsequent cross-linking enhancement, while the shell layer is responsible for carrying and controlling the release of polymerization initiators. After battery assembly, only one heating step is needed to simultaneously and orderly trigger the in-situ gelation of the electrolyte and the in-situ cross-linking of the separator framework, thereby achieving deep fusion and synergistic enhancement of the electrolyte and separator at the molecular / fiber scale.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a composite separator for batteries.

[0011] The composite membrane is made of interwoven micro- and nano-scale core-shell fibers; The core-shell fibers include: The inner core layer is formed of a first polymer that is insoluble in the battery electrolyte and contains a crosslinking agent; The outer shell is formed of a second polymer that is soluble in the battery electrolyte and contains an initiator; The core layer and the shell layer are combined through a coaxial electrospinning process to form a continuous coating structure.

[0012] In this invention, "non-soluble" means that the first polymer maintains its solid fibrous morphology within the battery operating temperature range and the liquid electrolyte precursor used, without dissolving, melting, or significantly swelling to avoid structural damage, thereby providing a durable and stable three-dimensional porous framework. "Soluble" means that the second polymer, under specific battery activation conditions (such as heating to a certain temperature), can dissolve or rapidly swell in the injected liquid electrolyte precursor, thereby releasing its encapsulated functional components.

[0013] Preferably, the crosslinking agent is an epoxy-containing crosslinking agent and / or inorganic nanoparticles with a surface modified by an epoxy silane coupling agent. The initiator is an initiator capable of initiating cationic ring-opening polymerization of ether monomers in the electrolyte.

[0014] More preferably, the first polymer is selected from at least one of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), and polysulfone (PSU). These materials exhibit good electrochemical stability and mechanical properties. The second polymer is selected from at least one of polyethylene oxide (PEO), polyvinylpyrrolidone (PVP), polyvinyl butyral (PVB), polyacrylonitrile (PAN), and polyethylene glycol (PEG). More preferably, these polymers exhibit good solubility in ether solvents.

[0015] More preferably, the first polymer is a polyvinylidene fluoride-hexafluoropropylene copolymer or polyphenylene sulfide, polyether ether ketone; the second polymer is polyethylene oxide, a blend of polyethylene oxide and polyvinylpyrrolidone, or a blend of polyvinyl butyral and polyethylene glycol.

[0016] More preferably, the epoxy-containing crosslinking agent is selected from at least one of trimethylolpropane triglycidyl ether, γ-glycidyl etheroxysilyl sesquioxane, tri(4-hydroxyphenyl)methane triglycidyl ether, trifunctional aziridine crosslinking agent, N,N,N,N-tetragoxypropyl-4,4-diaminodiphenylmethane, and glycerol triglycidyl ether. The inorganic nanoparticles are preferably silica (SiO2) nanoparticles or boron nitride (BN) nanosheets modified with γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560). The initiator is selected from at least one of aluminum trifluoromethanesulfonate (Al(OTf)3), boron trifluoride diethyl ether complex (BF3·Et2O), and diphenyliodonium hexafluorophosphate (DPI-PF6).

[0017] More preferably, the amount of the crosslinking agent (including modified inorganic nanoparticles) added is 0-50% relative to the mass of the first polymer, more preferably 10%-30%, and even more preferably 24%-32%. The amount of the initiator added is 0-50% relative to the mass of the second polymer, more preferably 20%-35%, and even more preferably 25%-30%.

[0018] Secondly, the present invention provides a method for preparing the above-mentioned composite diaphragm.

[0019] The method employs coaxial electrospinning technology and includes the following steps: (1) Preparation of inner layer spinning solution: Dissolve or disperse the first polymer and the crosslinking agent in a first solvent to form a uniform solution or dispersion; (2) Preparation of outer spinning solution: Dissolve the second polymer and the initiator in a second solvent to form a homogeneous solution; (3) Coaxial electrospinning: The inner spinning solution and the outer spinning solution are used as the core layer and the sheath layer, respectively, and spinning is performed by a coaxial electrospinning device. Under the action of a high-voltage electrostatic field, the composite droplets are stretched, split, and the solvent evaporates, and finally solidify and deposit on the receiving device to form a nascent fiber membrane composed of interwoven core and shell fibers; this step realizes the composite and spatial positioning of the "insoluble skeleton" and the "soluble functional layer" at the scale of a single fiber in one step.

[0020] (4) Post-treatment: The nascent fiber membrane is dried to completely remove residual solvent. Heat treatment may be performed if necessary.

[0021] As a preferred embodiment of the present invention, the following process conditions are included, but are not limited to: The first solvent may be selected from N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), or a mixture thereof with acetone; the second solvent may be selected from acetonitrile, ethanol, isopropanol, or a mixture thereof with water. Preferably, the mass-to-volume ratio of the first polymer to the first solvent is 5-6:100, in g / mL; the mass-to-volume ratio of the second polymer to the second solvent is 4:80-100, in g / mL. The preferred process parameters for coaxial electrospinning are: voltage 15-30 kV, receiving distance 15-25 cm, inner layer flow rate 0.5-1.5 mL / h, outer layer flow rate 1.0-2.0 mL / h, and ambient humidity controlled at 5-40%.

[0022] Thirdly, the present invention provides a battery.

[0023] The battery includes a positive electrode, a negative electrode, and a separator located therebetween, characterized in that the separator is a composite separator provided in the first aspect of the present invention; and the battery contains an electrolyte precursor capable of being polymerized by the initiator.

[0024] Preferably, the electrolyte precursor comprises an ether-based polymerizable monomer and an electrolyte salt. The ether-based polymerizable monomer is preferably at least one selected from 1,3-dioxolane (DOL) and 1,3,5-trioxane (TXE). More preferably, the ether-based polymerizable monomer is a mixture of 1,3-dioxolane and 1,3,5-trioxane; even more preferably, the molar ratio of 1,3-dioxolane and 1,3,5-trioxane is 1:9 to 9:1, and more preferably 3 to 4:6 to 7.

[0025] The electrolyte salt is preferably a magnesium salt (such as magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2) or magnesium perchlorate (Mg(ClO4)2)) or a lithium salt (such as lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)), with a concentration of 0.1 to 2 mol / L.

[0026] Preferably, the electrolyte precursor may further contain 1-20% by mass of a flame retardant and / or plasticizer to further improve performance. The flame retardant is one or more of trimethyl phosphate (TMP), triethyl phosphate (TEP), tributyl phosphate (TBP), tris(2-butoxyethyl) phosphate (TBEP), tri(2,2,2-trifluoroethyl) phosphate (TFEP), and tris(2,2-difluoroethyl) phosphate. The plasticizer is one of ethylene glycol dimethyl ether (DME), succinate (SN), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0027] The battery fabrication and functionalization process is as follows: The composite separator and positive and negative electrode sheets are assembled sequentially into a battery cell, the electrolyte precursor is injected, and the cell is sealed. Subsequently, the battery is activated by heating (e.g., at 60-80°C for 10-25 hours). During this process, the following synergistic reactions occur: Dissolution and release: The fiber shell (second polymer) dissolves in the electrolyte precursor, uniformly releasing the initiator embedded inside.

[0028] In-situ gelation: The released initiator (such as aluminum trifluoromethanesulfonate) initiates cationic ring-opening polymerization of ether monomers (such as 1,3-dioxolane and 1,3,5-trioxane) in the electrolyte, forming a three-dimensional cross-linked gel polymer electrolyte network in the pores of the membrane, on the fiber surface and at the electrode interface.

[0029] In-situ crosslinking enhancement: Simultaneously, the acidic environment created by the initiator (or the initiator itself) activates active sites such as epoxy groups on the crosslinking agent in the core layer. These groups undergo hydrolysis and further react with each other, forming chemical crosslinks on two levels: a) Covalent cross-linking points are formed inside the core layer fibers and between adjacent fibers, which significantly improves the mechanical strength of the membrane body (such as tensile strength and puncture resistance). b) Partial cross-linking reactions may occur at the interface between the growing gel electrolyte and the fiber skeleton, forming a “membrane-gel” interpenetrating covalent network, achieving strong chemical bonding between the two and greatly reducing interfacial impedance.

[0030] The battery is particularly suitable for high-energy-density battery systems that use lithium or magnesium metal as the negative electrode and Chevrell phase (Mo6S8), molybdenum disulfide (MoS2), or sulfur as the positive electrode active material.

[0031] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: Functional integration and spatiotemporal synergy: This innovative design integrates the "initiation center" (shell layer) and the "reinforcement center" (core layer) into a single fiber, achieving precise spatial positioning through coaxial spinning. During battery activation, the two work synergistically in a sequence of "first dissolution and release, then synchronous initiation and cross-linking," realizing a leap from a "passive separator" to an "active reaction platform."

[0032] Interface fusion and impedance reduction: The in-situ formed gel electrolyte and the cross-linked reinforced fiber skeleton are tightly bonded by chemical bonds and physical interpenetration, forming a seamless ion transport channel and a stable mechanical support. The electrode / electrolyte interface impedance is significantly reduced and the interface stability is greatly improved.

[0033] Excellent mechanical and safety performance: The core layer insoluble polymer provides basic toughness, and the covalent network constructed by in-situ crosslinking provides additional reinforcement, giving the composite membrane excellent puncture resistance and thermal stability, effectively inhibiting metal dendrite penetration and widening the battery safety window.

[0034] Simplified and environmentally friendly process: The battery manufacturing process is simplified to a standard three-step process of "stacking - electrolyte injection - heating". Complex chemical processes (polymerization, cross-linking) are all completed automatically inside the sealed battery, without any additional solvent treatment, coating or post-curing steps. The process is short, energy-efficient, and environmentally friendly, making it suitable for large-scale continuous production.

[0035] Universal design and adjustable performance: By flexibly selecting the core / shell polymer, crosslinking agent / initiator type and electrolyte formulation, this composite membrane system can be adapted to various metal battery systems such as lithium, magnesium, and sodium, meeting the specific performance requirements of different application scenarios. Attached Figure Description

[0036] Figure 1 The image shows the scanning electron microscope (SEM) image of the diaphragm prepared in Example 1.

[0037] Figure 2 The impedance spectrum of the battery assembled in Example 1 is shown.

[0038] Figure 3 The electrochemical oxidation window is determined by linear scanning voltammetry of the assembled battery in Example 1. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to specific embodiments, but this does not limit the present invention in any way. Any modifications or improvements made based on the teachings of the present invention shall fall within the protection scope of the present invention.

[0040] The processes, conditions, reagents, and experimental methods used in implementing this invention, except as specifically mentioned below, are all common knowledge and general knowledge in the field, and this invention does not have any particular limitations. Experimental methods in the embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer.

[0041] Unless otherwise stated, all technical terms and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. However, in the event of any conflict, the specification containing the definitions shall prevail.

[0042] Example 1: Preparation of PVDF-HFP / SiO2@KH-560 core-shell composite separator and its application in magnesium batteries 1. Preparation of composite membranes Preparation of the inner layer spinning solution: Weigh 5.0 g of polyvinylidene fluoride-hexafluoropropylene copolymer and dissolve it in 100 mL of a mixed solvent composed of N,N-dimethylformamide and acetone (volume ratio 1:1). Stir in a 50 °C water bath until completely dissolved. Then, add 1.2 g of silica nanoparticles (SiO2@KH-560) modified with γ-(2,3-epoxypropoxy)propyltrimethoxysilane and ultrasonically disperse in an ice-water bath for 2 hours to obtain a uniform and stable milky white inner layer spinning solution.

[0043] Preparation of outer spinning solution: Weigh 4.0 g of polyethylene oxide (Mw≈600,000) and dissolve it in 100 mL of acetonitrile. Stir at room temperature until transparent. Add 1.0 g of aluminum trifluoromethanesulfonate and continue stirring until completely dissolved to obtain a homogeneous outer spinning solution.

[0044] Coaxial electrospinning: Inject the inner and outer spinning solutions into two separate syringes, which are then mounted on a coaxial spinneret (inner diameter 0.8 mm, outer diameter 1.6 mm). Set the inner layer flow rate to 0.6 mL / h and the outer layer flow rate to 1.0 mL / h. Apply a 20 kV DC voltage between the spinneret and the aluminum foil receiver, with a receiving distance of 18 cm and an ambient humidity of <10%. Spin for 5-6 hours and collect the nascent fiber membrane.

[0045] Post-processing: The fiber membrane was dried in a vacuum drying oven at 55℃ for 24 hours to completely remove residual solvent, yielding a composite membrane, denoted as M-1. Its scanning electron microscope image is shown below. Figure 1 .

[0046] 2. Battery assembly Electrolyte precursor preparation: In an argon glove box, 1,3-dioxolane and 1,3,5-trioxane were mixed at a molar ratio of 3:7. Magnesium bis(trifluoromethanesulfonyl)imide was added to a concentration of 1.0 mol / L, followed by the addition of 6 wt% tris(2,2,2-trifluoroethyl) phosphate as a flame retardant, and the mixture was stirred until homogeneous.

[0047] Electrode and battery assembly: Using Chevrell phase Mo6S8 as the positive electrode and magnesium foil as the negative electrode, the separator M-1 is placed between them, and the electrolyte precursor is injected to assemble a CR2032 coin cell.

[0048] In-situ activation: The battery was placed in a 65°C oven and left to stand for 20 hours to complete in-situ polymerization and cross-linking, resulting in battery B-1.

[0049] Example 2: Preparation of PPS / BN@KH-560 core layer and PEO-PVP blended shell composite membrane and its application in high-safety magnesium batteries 1. Preparation of composite membranes Inner layer spinning solution preparation: 5.0 g of polyphenylene sulfide was dissolved in 100 mL of N-methylpyrrolidone, and 1.6 g of boron nitride (BN) nanosheets (BN@KH-560) modified with γ-(2,3-epoxypropoxy)propyltrimethoxysilane were added and ultrasonically dispersed for 3 hours.

[0050] Preparation of outer spinning solution: Weigh 3.0 g of polyethylene oxide (Mw≈200,000) and 1.0 g of polyvinylpyrrolidone (Mw≈1,300,000), and dissolve them together in 80 mL of a mixed solvent consisting of anhydrous ethanol and deionized water (volume ratio 9:1). Add 1.2 g of aluminum trifluoromethanesulfonate and stir until completely dissolved.

[0051] Coaxial electrospinning: inner layer flow rate 0.8 mL / h, outer layer flow rate 1.2 mL / h, voltage 25 kV, receiving distance 20 cm. Other conditions are the same as in Example 1. Collect the nascent fiber membrane.

[0052] Post-processing: The fiber membrane was placed in a vacuum drying oven at 55°C and dried for 24 hours to completely remove residual solvent, resulting in a composite membrane, denoted as M-2.

[0053] 2. Battery assembly Electrolyte precursor: Mix 1,3-dioxolane and 1,3,5-trioxane in a molar ratio of 4:6, add magnesium bis(trifluoromethanesulfonyl)imide to a concentration of 1.2 mol / L, then add 8 wt% tri(2,2,2-trifluoroethyl) phosphate and 5 wt% succinate, and stir until homogeneous.

[0054] Electrode and battery assembly: The composite separator is cut into a circular piece with a diameter of 16 mm, placed between the molybdenum disulfide positive electrode and the magnesium foil negative electrode, and the above electrolyte is injected to assemble a CR2032 type button magnesium battery.

[0055] In-situ polymerization and crosslinking process: The assembled battery was placed in a 70°C environment and left to stand for 18 hours to obtain battery B-2. During this process: Outer layer dissolution and initiator release: The outer layer of polyethylene oxide / polyvinylpyrrolidone gradually dissolves in the 1,3-dioxolane / 1,3,5-trioxane electrolyte, releasing aluminum trifluoromethanesulfonate initiator.

[0056] In-situ polymerization: Aluminum trifluoromethanesulfonate initiates the ring-opening polymerization of ether monomers to form polyether-based gel electrolytes.

[0057] Enhanced inner layer crosslinking: At the same time, the acidic environment provided by aluminum trifluoromethanesulfonate activates the epoxy groups on the surface of the KH-560 modified boron nitride nanosheets in the inner layer fibers, causing them to hydrolyze and participate in crosslinking, further enhancing the bond between the gel network and the polyphenylene sulfide backbone.

[0058] Example 3: Preparation of a composite separator with a PEEK / BN@KH core layer and a PVB-PEG blended shell layer and its application in a high-load sulfur cathode magnesium battery. 1. Preparation of composite membranes Inner layer spinning solution preparation: Measure 6.0 g of polyetheretherketone, dissolve it in 100 mL of N,N-dimethylformamide, add 1.6 g of KH-560 modified boron nitride nanosheets, and ultrasonically disperse for 3 hours.

[0059] Preparation of outer spinning solution: Weigh 2.0 g of polyvinyl butyral and 2.0 g of polyethylene glycol (Mw=2000) and dissolve them together in 100 mL of isopropanol. Add 1.2 g of diphenyliodonium hexafluorophosphate and stir in the dark until dissolved.

[0060] Coaxial electrospinning: inner layer flow rate 0.7 mL / h, outer layer flow rate 1.0 mL / h, voltage 25 kV, receiving distance 20 cm. Other conditions are the same as in Example 1. Collect the nascent fiber membrane.

[0061] Post-processing: The fiber membrane was placed in a vacuum drying oven at 55°C and dried for 24 hours to completely remove residual solvent, resulting in a composite membrane, namely membrane M-3.

[0062] 2. Battery assembly Electrolyte precursor: Mix 1,3-dioxolane and 1,3,5-trioxane in a molar ratio of 4:6, add magnesium perchlorate to a concentration of 0.8 mol / L, and then add 10 wt% fluoroethylene carbonate.

[0063] Electrode and battery assembly: Utilizing an areal capacity > 3.0 mAh / cm² 2 A high-load sulfur positive electrode and a magnesium foil negative electrode are assembled by placing a separator M-3 between them, injecting an electrolyte precursor, and then assembling it into a CR2032 coin cell.

[0064] In-situ activation: The assembled battery was placed at 70°C and left to stand for 15 hours to obtain battery B-3.

[0065] Example 4: Application of PVDF-HFP / PEO core-shell membrane with single DOL monomer Composite membrane M-1 was prepared according to the method in Example 1.

[0066] Electrolyte precursor: 1,3-dioxolane was used as the sole polymerization monomer, with the addition of 1.0 mol / L magnesium bis(trifluoromethanesulfonyl)imide and 6 wt% tri(2,2,2-trifluoroethyl) phosphate.

[0067] The battery assembly and activation steps are the same as in Example 1.

[0068] Comparative Example 1 (Traditional Liquid Electrolyte System) Membrane and electrolyte: Commercial Celgard 2400 polypropylene membrane was used. The electrolyte was a 3:7 mixture of 1,3-dioxolane and 1,3,5-trioxane, containing 1.0 M magnesium bis(trifluoromethanesulfonyl)imide and 6% tri(2,2,2-trifluoroethyl) phosphate, and contained no initiator.

[0069] Battery assembly: Mo6S8 is used as the positive electrode and magnesium foil is used as the negative electrode. No heating activation is performed after the battery is assembled.

[0070] Comparative Example 2 (Simple gelation system, without core-shell partitioning functional design) Membrane preparation: A monolayer nanofiber membrane was prepared by dispersing polyvinylidene fluoride-hexafluoropropylene copolymer and silica nanoparticles modified with γ-(2,3-epoxypropoxy)propyltrimethoxysilane in a mixed solvent of N,N-dimethylformamide / acetone using conventional uniaxial electrospinning.

[0071] Battery assembly: The electrolyte precursor was the same as in Example 1 (containing aluminum trifluoromethanesulfonate). The battery was assembled using this monolayer membrane as the separator, Mo6S8 as the positive electrode, and magnesium foil as the negative electrode, and heated at 65°C for 20 hours.

[0072] Test Example 1: Performance Testing Methods and Results 1. Testing Methods Ionic conductivity: Room temperature (25°C) ionic conductivity was calculated using an electrochemical workstation via electrochemical impedance spectroscopy (EIS) of the blocked electrode (SS|polymer@diaphragm|SS).

[0073] LSV electrochemical window testing: Assembled Li / polymer@separator / SS cell at 1 mV S -1 At the specified scan speed, the scan range is 2-6V.

[0074] Interface stability: Assembled magnesium symmetric cells (Mg|polymer@separator|Mg) at 0.1 mA / cm 2 Constant current deposition / stripping cycles were performed at current density, and the time until short circuit was recorded.

[0075] Full battery cycle performance: Constant current charge-discharge test was performed at room temperature, and the capacity retention rate was recorded after a specific number of cycles.

[0076] Thermal stability: The diaphragm was heat-treated at different temperatures for 1 hour, and its macroscopic dimensional changes were observed.

[0077] Mechanical properties: Tensile strength was tested using a universal testing machine, and puncture strength was tested using a standard puncture strength tester.

[0078] Safety testing: The entire battery was placed in a high-temperature oven for thermal shock testing to observe whether fire, leakage, or other phenomena occurred.

[0079] 2. Test Results Test results are available Figure 2-3 And Table 1.

[0080] Table 1 Performance test results of Examples 1-3 and Comparative Examples 1-2

[0081] As can be seen from the data comparison in the table above, the composite separators prepared in Examples 1-4 of this invention and the batteries assembled from them systematically and significantly outperform Comparative Example 1 (traditional liquid electrolyte system) and Comparative Example 2 (simple gelation system) in several key performance aspects, including ionic conductivity, interfacial stability, long cycle life, LSV electrochemical window, high-temperature dimensional stability, and mechanical strength. This fully verifies the technical superiority of the proposed "insoluble core-soluble shell" functional partitioning design and one-step heating in-situ synergistic triggering mechanism (gelation + crosslinking). This design effectively solves the core problems of high interfacial impedance, uncontrolled dendrite growth, and poor thermomechanical stability in metal batteries, providing an innovative and efficient solution for the development of high-safety, high-energy-density secondary batteries.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite separator for batteries, characterized in that, The composite membrane is made of interwoven micro- and nano-scale core-shell fibers; The core-shell fibers include: The inner core layer is formed of a first polymer that is insoluble in the battery electrolyte and contains a crosslinking agent; The outer shell is formed of a second polymer that is soluble in the battery electrolyte and contains an initiator; The core layer and the shell layer are combined through a coaxial electrospinning process to form a continuous coating structure.

2. The composite diaphragm according to claim 1, characterized in that, The crosslinking agent is an epoxy-containing crosslinking agent and / or inorganic nanoparticles with an epoxy silane coupling agent on the surface; the initiator is a cationic initiator capable of initiating the ring-opening polymerization of ether monomers in the electrolyte.

3. The composite diaphragm according to claim 1, characterized in that, The first polymer is selected from at least one of polyvinylidene fluoride-hexafluoropropylene copolymer, polyphenylene sulfide, polyether ether ketone, and polysulfone; the second polymer is selected from at least one of polyethylene oxide, polyvinylpyrrolidone, polyvinyl butyral, polyacrylonitrile, and polyethylene glycol.

4. The composite diaphragm according to claim 2, characterized in that, The epoxy-containing crosslinking agent is selected from at least one of trimethylolpropane triglycidyl ether, γ-glycidyl etheroxysilylpropyl sesquioxane, tri(4-hydroxyphenyl)methane triglycidyl ether, trifunctional aziridine crosslinking agent, N,N,N,N-tetragoxypropyl-4,4-diaminodiphenylmethane, or glycerol triglycidyl ether; the inorganic nanoparticles are at least one of silica or boron nitride nanosheets modified with an epoxysilane coupling agent.

5. The composite diaphragm according to claim 2, characterized in that, The initiator is selected from at least one of aluminum trifluoromethanesulfonate, boron trifluoride diethyl ether complex, or diphenyliodonium hexafluorophosphate.

6. A method for preparing a composite separator as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Preparation of inner layer spinning solution: Dissolve or disperse the first polymer and the crosslinking agent in a first solvent; the first solvent is selected from any one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; (2) Preparation of outer spinning solution: Dissolve the second polymer and the initiator in a second solvent; the second solvent is selected from any one of ethanol, methanol, and isopropanol; (3) Coaxial electrospinning: The inner spinning solution and the outer spinning solution are used as the core layer and the sheath layer, respectively. Electrospinning is performed by a coaxial spinning device to collect the nascent fiber membrane. (4) Post-processing: The nascent fiber membrane is dried to obtain the composite membrane.

7. A battery comprising a positive electrode, a negative electrode, and a separator located therebetween, characterized in that, The separator is a composite separator as described in any one of claims 1-5; the battery contains an electrolyte precursor that can be polymerized by the initiator.

8. The battery according to claim 7, characterized in that, The electrolyte precursor comprises an ether polymerizable monomer and an electrolyte salt; the ether polymerizable monomer is selected from at least one of 1,3-dioxolane and 1,3,5-trioxane.

9. The battery according to claim 8, characterized in that, The electrolyte salt is a magnesium salt or a lithium salt; the battery is activated by heating, which dissolves the shell layer to release the initiator, thereby initiating the in-situ polymerization of the ether monomer to form a gel electrolyte, and triggering the crosslinking reaction of the crosslinking agent in the core layer.

10. The battery according to any one of claims 7-9, characterized in that, The electrolyte precursor also contains 1-20% by mass of flame retardant and / or plasticizer.

Images