Anti-puncture lithium battery composite diaphragm, preparation method and application

Abstract

The application provides an anti-puncture lithium battery composite diaphragm, a preparation method and application, relates to the field of lithium battery diaphragms, and comprises upper and lower surface layers, which are composed of cross-linked furan-based polyamide electrostatic spinning nanofibers; a core layer, which is composed of furan ring-containing porous / hollow polyimide microspheres and a polyolefin-based film, wherein at least one side surface of the polyolefin-based film has a homologous transition layer; the microspheres retain part of amide acid / anhydride groups on the surface, and covalent bonding and physical interpenetrating networks are formed between the nanofibers of the surface layer and the microspheres through hot pressing. The anti-puncture lithium battery composite diaphragm, the preparation method and the application have the advantages that raw materials are easy to obtain, the process is controllable, and large-scale production can be realized by using existing electrostatic spinning and coating equipment. The obtained composite diaphragm is suitable for lithium ion batteries, especially for high-safety and high-energy-density power batteries, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of lithium battery separators, and in particular to a puncture-resistant lithium battery composite separator, its preparation method, and its application. Background Technology

[0002] The separator in a lithium-ion battery is a crucial component located between the positive and negative electrodes, and its performance directly affects the battery's safety, cycle life, and rate performance. Currently, commercially available lithium-ion battery separators are mainly made of polyolefin (PE, PP) microporous membranes, which have advantages such as low cost, good mechanical properties, and thermally closed-cell characteristics. However, they also have problems such as poor heat resistance, insufficient electrolyte wettability, and low porosity. When a battery experiences thermal runaway, the polyolefin separator shrinks severely at high temperatures, which can easily lead to direct contact and short circuit between the positive and negative electrodes, causing a safety accident.

[0003] To improve the heat resistance and wettability of polyolefin separators, existing technologies often employ coating modification methods, such as coating the surface of the polyolefin-based membrane with inorganic ceramic particles (e.g., Al2O3, SiO2) or heat-resistant polymers (e.g., polyimide, aramid). However, the adhesion between these coatings and the polyolefin-based membrane is relatively weak, and the coating is prone to peeling or detachment during battery charging and discharging due to volume changes or thermal cycling, affecting the long-term reliability of the separator. Furthermore, while ceramic coatings can improve heat resistance, they often increase the separator thickness, reduce ionic conductivity, and exhibit poor interfacial compatibility between inorganic particles and the organic matrix.

[0004] Electrospun nanofiber membranes possess high porosity, high specific surface area, and good electrolyte wettability, and have been widely studied for use as the surface layer of lithium-ion battery separators or composite separators. For example, combining electrospun nanofiber membranes such as polyvinylidene fluoride (PVDF), polyimide (PI), and polyamide (PA) with polyolefin-based membranes can yield composite separators that combine high wettability with certain heat resistance. However, in existing composite separators, the surface nanofibers and the core layer (especially polyolefin-based membranes or coatings) are mainly bonded by physical adhesion or simple hot-pressing, resulting in limited interfacial bonding strength and a tendency to delaminate under long-term use or high-temperature conditions. Furthermore, when the core layer is a polyimide microsphere coating, the significant difference in chemical structure between the surface polyamide and the core polyimide leads to poor interfacial compatibility, making it difficult to form a robust, integrated structure.

[0005] Therefore, there is an urgent need to develop a composite membrane that combines high heat resistance, high interfacial bonding strength, excellent electrolyte wettability, and good safety. Summary of the Invention

[0006] The purpose of this invention is to provide a puncture-resistant lithium-ion battery composite separator, its preparation method, and its applications. The raw materials are readily available, the process is controllable, and it can be mass-produced using existing electrospinning and coating equipment. The resulting composite separator is suitable for lithium-ion batteries, especially for high-safety, high-energy-density power batteries, and has promising prospects for industrial applications.

[0007] To achieve the above objectives, the present invention provides a puncture-resistant lithium battery composite separator comprising an upper surface layer and a lower surface layer, which is composed of cross-linked furanyl polyamide electrospun nanofibers. The core layer consists of porous / hollow polyimide microspheres containing furan rings and a polyolefin-based membrane, wherein the polyolefin-based membrane has a homologous transition layer on at least one side surface. The surface of the microspheres retains some amyl acid / anhydride groups, and the surface nanofibers and the microspheres are covalently bonded and physically interpenetrating network formed by hot pressing. The surface of the polyolefin-based film has a 50-500 nm homologous furanyl polyamic acid imidized transition layer.

[0008] Preferably, the crosslinked furanyl polyamide is formed by the condensation polymerization of a diamine and 2,5-furandicarboxyl chloride, wherein the diamine is selected from at least one of p-phenylenediamine, m-phenylenediamine, and 4,4'-diaminodiphenyl ether.

[0009] Preferably, the diameter of the electrospun nanofibers is 80~300 nm, the porosity of the upper and / or lower surface layers is 75%~85%, and the average pore size is 0.05~0.15 μm; The thickness of the upper and lower surface layers is independently 2-6 μm, and the thickness of the core layer is 8-16 μm.

[0010] Preferably, the porous or hollow polyimide microspheres have a D50 of 0.3~1.2μm and a specific surface area ≥100 m². 2 / g, with an imidization degree of 70%~95%, and a surface-active amic acid group and / or anhydride group content of 0.2~1.0 mmol / g; In the porous or hollow polyimide microspheres containing furan rings, the molar fraction of furan ring monomers is ≥20 mol%; The porous or hollow polyimide microspheres form medium-sized pores, which, together with the small pores in the upper and lower surface layers and the micropores in the polyolefin-based film, constitute a gradient pore structure.

[0011] Preferably, the polyolefin-based membrane is a polyethylene microporous membrane or a polypropylene microporous membrane.

[0012] A method for preparing a puncture-resistant lithium battery composite separator includes the following steps: (1) Prepare cross-linked furanyl polyamide electrospun nanofiber membranes as upper and lower surface layers; (2) Prepare porous or hollow polyimide microspheres containing furan rings, form a homologous transition layer on the surface of a polyolefin-based membrane, and coat the microspheres onto the homologous transition layer to obtain a modified core layer; (3) The upper surface layer, the modified core layer and the lower surface layer are stacked in sequence and hot-pressed at 110~140℃ and 2~4 MPa to form a covalent bond and physical interpenetrating network between the surface nanofibers and the core microspheres.

[0013] Preferably, in step (1), diamine, 2,5-furandicarboxyl chloride and optional monomers containing active side groups are subjected to low-temperature solution polycondensation in an organic solvent to obtain a furanyl polyamide solution; the solution is electrospun with a spinning voltage of 18~32 kV, a receiving distance of 25~35 cm, a temperature of 20~30℃, and a humidity of 25%~40% to obtain a nanofiber membrane with a fiber diameter of 80~300 nm; The monomer containing the active side group is selected from at least one of 3,5-diaminobenzoic acid and 2,5-dihydroxyterephthalic acid, and is used to introduce carboxyl or hydroxyl groups into the molecular chain.

[0014] Preferably, in step (2), a polyamic acid solution is obtained by low-temperature polycondensation of a furan ring-containing dianhydride or diamine with conventional dianhydride and / or diamine in an organic solvent; a pore-forming agent is added to the polyamic acid solution, and porous or hollow polyimide microspheres are obtained by emulsification, solvent replacement and thermal imidization; the thermal imidization temperature is controlled at 180~250℃ and the time is 0.5~2 h, so that the degree of imidization is 70%~95%; Forming a homologous transition layer on the surface of a polyolefin-based film includes: subjecting the polyolefin-based film to plasma treatment or ultraviolet grafting modification, then immersing it in a 0.5-3 wt% furanyl polyamic acid solution, drying it at 80-120°C, and imidizing it at 150-200°C for 10-30 min to form a homologous transition layer with a thickness of 50-500 nm. The porous or hollow polyimide microspheres are mixed with a homologous ammonium polyaminate aqueous binder, surfactant, and wetting agent to prepare an aqueous slurry with a solid content of 5-25 wt%. This slurry is then coated onto one or both sides of a polyolefin-based membrane with a homologous transition layer and dried at 60-90°C. The microsphere coating amount is 0.5-3.0 g / m³. 2 .

[0015] Preferably, in step (3), before hot pressing, a solution of homologous furanyl polyamic acid oligomer is rolled or sprayed onto the inner surfaces of the upper and lower surfaces or the surface of the modified core layer, wherein the weight average molecular weight of the oligomer is 2000-10000. While hot-pressing composite, ultrasonic assistance of 20~40 kHz is applied to embed the surface nanofibers between the core microspheres and promote the formation of covalent bonds. It also includes a post-processing step: hot air or infrared treatment at 150~180℃ for 5~30 min to further imidize the residual ammonium acid and eliminate internal stress.

[0016] Application of a puncture-resistant lithium battery composite separator in the preparation of lithium-ion batteries.

[0017] Therefore, the present invention employs the above-mentioned puncture-resistant lithium battery composite separator, preparation method, and application, and the technical effects are as follows: Significantly improved interfacial bonding: The surface furan-based polyamide nanofibers and the core furan-ring-containing polyimide microspheres form covalent bonds through the ring-opening reaction of amide acid / anhydride, while also combining a physical interpenetrating network. The peel strength is more than twice that of traditional physically bonded composite membranes, and there is no delamination after thermal cycling.

[0018] True chemical homology: The core microspheres are synthesized using furan ring monomers, which have the same furan ring structure as the surface furan-based polyamide, resulting in good interfacial compatibility and avoiding phase separation.

[0019] Excellent heat resistance and dimensional stability: The homologous transition layer on the surface of the polyolefin-based film provides chemical anchoring, with a thermal shrinkage rate of ≤2% at 150℃. The structure remains intact after closing the pores, effectively preventing thermal runaway.

[0020] High porosity and electrolyte wettability: The porous or hollow microsphere structure increases the core porosity and electrolyte absorption rate by 15% to 30%, improves ionic conductivity, and enhances battery cycle and rate performance.

[0021] The gradient pore structure balances safety and transport: the surface pores block particles, the core pores store liquid and conduct ions, and the base film micropores achieve thermal closure, resulting in excellent overall performance. Attached Figure Description

[0022] Figure 1 This is a comparison graph showing the ionic conductivity performance of this method with that of Comparative Examples 1, 2, and 7. Figure 2 This is a comparison chart of the electrolyte contact angle performance of the proposed method with that of Comparative Examples 1, 2, 6, and 7. Figure 3 This is a performance comparison chart of the capacity retention rate at 1C / 500 cycles between this method and Comparative Examples 1, 2, 3, 4, 5 and 7. Figure 4 This is a comparison chart of the puncture resistance performance of our method with that of Comparative Examples 1, 2, 3, 4, and 6. Detailed Implementation

[0023] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0025] The organic solvent used in preparing cross-linked furanyl polyamide electrospun nanofiber membranes is selected from N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), or dimethyl sulfoxide (DMSO).

[0026] The organic solvents used in preparing porous or hollow polyimide microspheres containing furan rings are selected from tetrahydrofuran (THF), ethyl acetate, acetone, NMP, and DMAc.

[0027] The pore-forming agent is selected from polyethylene glycol (PEG, Mw=2000~20000), polyvinylpyrrolidone (PVP, Mw=10000~100000), polypropylene glycol (PPG), ammonium bicarbonate, urea, sodium chloride, ammonium nitrate, n-hexane, cyclohexane, and petroleum ether.

[0028] The surfactants are selected from Triton X-100 (octylphenol polyoxyethylene ether), Tween-80 (polysorbate 80), Span-80 (sorbitan oleate), OP-10, alkyl glycoside (APG)), sodium dodecyl sulfate (SDS), and sodium dodecylbenzene sulfonate (SDBS).

[0029] The wetting agent is selected from ethanol, isopropanol, n-butanol, ethylene glycol butyl ether, propylene glycol methyl ether, BYK-346, BYK-348, Tego Wet 270, 3M FC-4430, and DuPont Capstone FS-3100.

[0030] The specific preparation steps of the homologous polyamic acid ammonium salt water-based adhesive are as follows: p-Phenylenediamine (or 4,4'-diaminodiphenyl ether) and 2,5-furandicarboxyl chloride (or furanyl dianhydride) are polycondensed at low temperature in NMP to obtain a polyamic acid solution with a solid content of 10-20 wt%. Ammonia (25-28 wt%) or triethylamine is slowly added dropwise to the polyamic acid solution under stirring to adjust the pH to 7.0-8.5, so that the carboxyl groups are converted into ammonium salts, and the system becomes water-soluble or water-dispersible. Stirring is continued for 0.5-2 h, and then deionized water or a water / isopropanol mixture is added to dilute to a solid content of 5-15 wt%, thus obtaining a homologous polyamic acid ammonium salt water adhesive.

[0031] Specific steps for plasma treatment or UV grafting modification of polyolefin-based membranes: Cut the polyolefin-based membrane to the required size, ultrasonically clean it with ethanol for 5 min, and dry it. Lay the membrane flat on the sample holder inside the plasma chamber and close the chamber door. Turn on the vacuum pump and evacuate to a background pressure <10 Pa. Introduce high-purity O2 (purity ≥99.9%) or Ar / N2 mixture and adjust the flow rate to stabilize the chamber pressure at 20~80 Pa. Turn on the radio frequency power supply, set the power to 100~300 W, and the processing time to 1~5 min. Turn off the radio frequency power supply and gas, restore atmospheric pressure, and remove the membrane. The treated membrane should be immediately used for the next dip coating step or stored in a desiccator to prevent the deactivation of surface active groups.

[0032] Example 1 Step 1: Preparation of the surface layer of cross-linked furanyl polyamide nanofibers Under dry nitrogen protection, 0.1 mol of p-phenylenediamine and 0.02 mol of 3,5-diaminobenzoic acid were dissolved in 200 mL of N-methylpyrrolidone (NMP) and cooled to 0–5 °C. 0.122 mol of 2,5-furandicarboxylic acid chloride was slowly added, maintaining the temperature below 10 °C, and the reaction was continued for 2 h, then heated to room temperature for another 4 h. The reaction solution was poured into deionized water to precipitate the product, which was then filtered, washed, and dried to obtain furanyl polyamide containing carboxyl side groups. The obtained polymer was dissolved in NMP to prepare a spinning solution with a solid content of 15 wt% and an intrinsic viscosity of 1.1 dL / g.

[0033] Uniaxial electrospinning was employed with a spinning voltage of 25 kV, a receiving distance of 30 cm, a temperature of 25℃, a humidity of 30%, a solution flow rate of 0.6 mL / h, and a receiving time of 2 h. This yielded a furanyl polyamide nanofiber membrane with an average fiber diameter of approximately 180 nm, a thickness of approximately 4 μm, a porosity of 82%, and an average pore size of 0.10 μm.

[0034] Step 2: Preparation of the core layer modified with furan ring-containing porous polyimide microspheres 0.08 mol of 2,5-furandicarboxylic anhydride (containing furan ring dianhydride) and 0.02 mol of 4,4'-oxophthalic anhydride were dissolved in 150 mL of tetrahydrofuran to obtain a dianhydride solution. 0.1 mol of 4,4'-diaminodiphenyl ether was dissolved in 200 mL of tetrahydrofuran to obtain a diamine solution. The dianhydride solution was slowly added dropwise to the diamine solution under ultrasonic oscillation, and the reaction was carried out in an ice bath for 3 h to obtain a polyamic acid solution. 10 g of polyethylene glycol (Mw=6000) was added as a pore-forming agent, and after stirring until homogeneous, the solution was added dropwise to cyclohexane containing 1 wt% Span-80, and stirred at high speed to form an emulsion. After solvent displacement, the emulsion was thermally imidized at 220 °C for 1 h to obtain porous polyimide microspheres containing furan rings, with a D50 of approximately 0.8 μm and a specific surface area of ​​approximately 135 m². 2 / g, with an imidization degree of approximately 88% and a surface-active ammonium acid / anhydride group content of approximately 0.45 mmol / g.

[0035] A polyethylene (PE) microporous membrane (12 μm thick, 40% porosity) was treated with O2 plasma for 3 min, then dipped in a 2 wt% homologous furanyl polyamic acid solution (prepared by polycondensation of p-phenylenediamine and 2,5-furandicarboxylic acid chloride), dried at 80 °C, and then imidized at 180 °C for 20 min to form a homologous transition layer of about 200 nm on each side of the PE membrane.

[0036] The porous microspheres were mixed with a homologous ammonium polyamic acid aqueous binder (5 wt% solids content), a nonionic surfactant (Triton X-100), and a wetting agent to prepare an aqueous slurry with a solids content of 12 wt%. The slurry was coated onto both sides of a PE base film with a homologous transition layer and dried at 80°C. The microsphere coating amount was approximately 1.5 g / m². 2 A modified core layer with a total thickness of approximately 14 μm was obtained.

[0037] Step 3: Homovalent Covalent Composite A 0.5 wt% NMP / water mixture of homologous furanyl polyamic acid oligomer (Mw≈5000) was roll-coated onto the inner side of the surface nanofiber membrane. The upper surface layer, modified core layer, and lower surface layer were then sequentially stacked and hot-pressed at 125℃ and 3 MPa for 40 s, simultaneously with 25 kHz ultrasonic assistance. Afterward, infrared treatment at 160℃ for 20 min further imidized the residual amic acid, yielding a three-layer homologous composite membrane with a total thickness of approximately 22 μm.

[0038] Example 2 The procedure is essentially the same as in Example 1, except that: in step one, p-phenylenediamine is replaced with m-phenylenediamine; the monomer containing the active side group is 2,5-dihydroxyterephthalic acid; in step two, the monomer containing the furan ring is 5,5'-oxobis(2-benzofuran-1,3-dione), with a molar fraction of 30 mol%; and in step three, the hot-pressing temperature is 135°C, the pressure is 4 MPa, and the time is 20 s. The total thickness of the resulting composite membrane is approximately 20 μm.

[0039] Example 3 The procedure is essentially the same as in Example 1, except that: in step one, p-phenylenediamine is replaced with 4,4'-diaminodiphenyl ether, and 3,5-diaminobenzoic acid is not added to prepare furanyl polyamide without carboxyl side groups; in step two, the imidization degree of the microspheres is controlled to be 75%, and the content of surface active groups is approximately 0.8 mmol / g; in step three, no infrared post-treatment is performed after hot pressing. The total thickness of the resulting composite membrane is approximately 24 μm.

[0040] Comparative Example 1 The ordinary polyimide microspheres prepared in Example 1 of patent CN109817870B (made by polymerization of ODA and BTDA in ethyl acetate and imidization in toluene, solid structure, without furan ring) are used instead of the furan ring-containing porous / hollow polyimide microspheres in this scheme.

[0041] Ordinary PI microspheres lack the polar oxygen atoms of the furan ring, resulting in decreased electrolyte wettability and ion transport capacity; they also lack a porous / hollow structure, significantly reducing their specific surface area (<50 m²). 2 / g vs ≥100 m 2 The ability to capture metal ions and construct lithium ion transport channels is weakened; the surface of the microspheres lacks active amyl acid / anhydride groups (content ≈ 0 vs 0.2~1.0 mmol / g), and the ability to covalently bond with the surface fibers is lost.

[0042] Comparative Example 2 The surface electrospinning material was replaced with the conventional aromatic polyamide (polymer product of m-phenylenediamine and isophthaloyl chloride) in Comparative Example 1 or the ordinary polyimide in patent CN109817870B. Specifically, m-phenylenediamine and isophthaloyl chloride were polymerized in NMP and then electrospinned. The remaining components (including furan ring porous PI microsphere core layer, homologous transition layer, and hot pressing process) remained unchanged.

[0043] Conventional polyamides lack polar sites of furan rings, resulting in an increased contact angle of the surface electrolyte (from <30° to >32°); strong hydrogen bonding between molecular chains, leading to decreased solubility and processability; poor fiber diameter uniformity; weakened compatibility with furan ring-containing microspheres; and reduced covalent bonding reactivity.

[0044] Comparative Example 3 The plasma treatment or UV grafting modification step for the polyolefin-based membrane is eliminated, as are the dip-coating of furan-based polyamic acid solution and subsequent imidization treatment steps. Instead, an aqueous slurry containing furan ring porous PI microspheres is directly coated onto the surface of an unmodified PE or PP microporous membrane. All other components and processes remain unchanged.

[0045] Without a homologous transition layer, the polyolefin-based film (PE / PP) has a strong surface inertness and poor interfacial adhesion with the PI microsphere coating; the coating peel strength decreases significantly (from >6 N / m to <3 N / m); the microsphere coating is prone to detachment and pulverization during battery cycling; interfacial defects appear between the base film and the core layer, affecting the uniformity of ion transport.

[0046] Comparative Example 4 The upper surface layer, modified core layer, and lower surface layer are simply laminated or composited at room temperature under low pressure (<1 MPa), without hot pressing at 110~140℃ and 2~4 MPa, and without applying ultrasonic assistance at 20~40 kHz. The remaining components and processes remain unchanged.

[0047] Without hot pressing, effective covalent bonding (amidation reaction requires temperature drive) and physical interpenetration cannot be formed between the surface nanofibers and the core microspheres; the interlayer peel strength is significantly reduced; the lack of ultrasonic assistance results in insufficient fiber embedding between microspheres, and macroscopic voids exist at the interface; the interlayers are prone to separation during battery cycling, and the overall structural stability of the separator decreases.

[0048] Comparative Example 5 The thermal imidization temperature of the furan ring-containing porous PI microspheres was increased to above 300℃ and the time was extended to above 4 h, resulting in an imidization degree of >99% and a reduction in the content of surface-active ammonium acid / anhydride groups to near 0 mmol / g. The remaining components and processes remained unchanged.

[0049] When there are no active groups on the surface of the microspheres, covalent bonds cannot be formed between them and the surface furanyl polyamide fibers and the homologous transition layer (amidation reaction requires the reaction of carboxyl groups / anhydrides with amino groups); the interlayers are only bound by physical entanglement and van der Waals forces, and the bonding strength is significantly lower than that of covalently bonded networks; the interfacial bonding force is insufficient after hot pressing, and the long-term cycling stability decreases.

[0050] Comparative Example 6 Referring to the method of Comparative Example 2 in patent CN109817870B, cross-linked furanyl polyamide was directly formulated into a slurry with an aqueous adhesive, surfactant, etc., and then coated onto the core layer surface using a blade coating or gravure coating method to form a coating, replacing the electrospun nanofiber membrane. The remaining components (including the furan ring porous PI microsphere core layer and the homologous transition layer) remained unchanged.

[0051] The coating formed by solution coating is a dense or semi-dense structure, which cannot form the high porosity (75%~85%) and uniform pore size distribution (0.05~0.15 μm) of the nanofiber network; the wettability of electrolyte and ionic conductivity decrease; the coating is prone to clogging the pores of the base film, and the air permeability (Gurley value) increases significantly; the lack of physical barrier effect of the fiber network reduces the puncture resistance.

[0052] Comparative Example 7 Polyimide microspheres were prepared using conventional dianhydride (BTDA) and diamine (ODA) as described in patent CN109817870B, without introducing any furan ring-containing monomers; however, the porous / hollow structure (achieved through a pore-forming agent) and partial imidization (retaining active groups on the surface) were preserved. The remaining components (furan-based polyamide electrospinning surface layer, homologous transition layer, and hot-pressing process) remained unchanged.

[0053] The absence of furan rings in the microspheres reduces chemical compatibility with the furan-based polyamide surface and homologous transition layer; the lack of polar oxygen atoms in the furan rings weakens electrolyte wettability and lithium-ion transport capacity; effective π-π interactions and hydrogen bond synergy cannot be formed with the surface furan-based polyamide; and the overall structural integration is reduced.

[0054] Combination Figure 1 , Figure 2 , Figure 3 and Figure 4 It is evident that the various technological innovations of this solution (furan-ring porous / hollow microspheres, furan-based polyamide electrospun surface layer, homologous transition layer, hot-pressing + ultrasonic-assisted composite process, partial imidization of microsphere surface, etc.) all make irreplaceable contributions to the overall performance of the membrane. The absence or replacement of any component will lead to a significant decrease in the membrane's ionic conductivity, electrolyte wettability, cycle stability, mechanical properties, or interlayer bonding strength, fully demonstrating the synergistic effect among the components of this solution.

[0055] Therefore, the present invention employs the aforementioned puncture-resistant lithium battery composite separator, its preparation method, and its application. The raw materials are readily available, the process is controllable, and it can be mass-produced using existing electrospinning and coating equipment. The resulting composite separator is suitable for lithium-ion batteries, especially for high-safety, high-energy-density power batteries, and has promising prospects for industrial application.

[0056] 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 preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A puncture-resistant composite separator for lithium batteries, characterized in that, It includes an upper and lower surface layer, which are composed of cross-linked furanyl polyamide electrospun nanofibers; The core layer consists of porous / hollow polyimide microspheres containing furan rings and a polyolefin-based membrane, wherein the polyolefin-based membrane has a homologous transition layer on at least one side surface. The surface of the microspheres retains some amyl acid / anhydride groups, and the surface nanofibers and the microspheres are covalently bonded and physically interpenetrating network formed by hot pressing. The surface of the polyolefin-based film has a 50-500 nm homologous furanyl polyamic acid imidized transition layer.

2. The puncture-resistant lithium battery composite separator according to claim 1, characterized in that, The cross-linked furanyl polyamide is formed by the condensation of a diamine with 2,5-furandicarboxylic acid chloride, wherein the diamine is selected from at least one of p-phenylenediamine, m-phenylenediamine, and 4,4'-diaminodiphenyl ether.

3. The puncture-resistant lithium battery composite separator according to claim 1, characterized in that, The electrospun nanofibers have a diameter of 80~300 nm, and the porosity of the upper and / or lower surface layers is 75%~85%, with an average pore size of 0.05~0.15 μm. The thickness of the upper and lower surface layers is independently 2-6 μm, and the thickness of the core layer is 8-16 μm.

4. The puncture-resistant lithium battery composite separator according to claim 1, characterized in that, The porous or hollow polyimide microspheres have a D50 of 0.3~1.2μm and a specific surface area ≥100 m². 2 / g, with an imidization degree of 70%~95%, and a surface-active amic acid group and / or anhydride group content of 0.2~1.0 mmol / g; In the porous or hollow polyimide microspheres containing furan rings, the molar fraction of furan ring monomers is ≥20 mol% The porous or hollow polyimide microspheres form medium-sized pores, which, together with the small pores in the upper and lower surface layers and the micropores in the polyolefin-based film, constitute a gradient pore structure.

5. The puncture-resistant lithium battery composite separator according to claim 1, characterized in that, The polyolefin-based membrane is a polyethylene microporous membrane or a polypropylene microporous membrane.

6. The method for preparing a puncture-resistant lithium battery composite separator according to claim 1, characterized in that, Includes the following steps: (1) Prepare cross-linked furanyl polyamide electrospun nanofiber membranes as upper and lower surface layers; (2) Prepare porous or hollow polyimide microspheres containing furan rings, form a homologous transition layer on the surface of a polyolefin-based membrane, and coat the microspheres onto the homologous transition layer to obtain a modified core layer; (3) The upper surface layer, the modified core layer and the lower surface layer are stacked in sequence and hot-pressed at 110~140℃ and 2~4 MPa to form a covalent bond and physical interpenetrating network between the surface nanofibers and the core microspheres.

7. The puncture-resistant lithium battery composite separator according to claim 1, characterized in that, In step (1), diamine, 2,5-furandicarboxyl chloride and optional monomers containing active side groups are subjected to low-temperature solution polycondensation in an organic solvent to obtain a furanyl polyamide solution; the solution is electrospun with a spinning voltage of 18~32 kV, a receiving distance of 25~35 cm, a temperature of 20~30℃, and a humidity of 25%~40% to obtain a nanofiber membrane with a fiber diameter of 80~300 nm; The monomer containing the active side group is selected from at least one of 3,5-diaminobenzoic acid and 2,5-dihydroxyterephthalic acid, and is used to introduce carboxyl or hydroxyl groups into the molecular chain.

8. The puncture-resistant lithium battery composite separator according to claim 1, characterized in that, In step (2), a polyamic acid solution is obtained by low-temperature polycondensation of a furan ring-containing dianhydride or diamine with conventional dianhydride and / or diamine in an organic solvent; a pore-forming agent is added to the polyamic acid solution, and porous or hollow polyimide microspheres are obtained by emulsification, solvent replacement and thermal imidization; the thermal imidization temperature is controlled at 180~250℃ and the time is 0.5~2 h to make the degree of imidization 70%~95%; Forming a homologous transition layer on the surface of a polyolefin-based film includes: subjecting the polyolefin-based film to plasma treatment or ultraviolet grafting modification, then immersing it in a 0.5-3 wt% furanyl polyamic acid solution, drying it at 80-120°C, and imidizing it at 150-200°C for 10-30 min to form a homologous transition layer with a thickness of 50-500 nm. The porous or hollow polyimide microspheres are mixed with a homologous ammonium polyaminate aqueous binder, surfactant, and wetting agent to prepare an aqueous slurry with a solid content of 5-25 wt%. This slurry is then coated onto one or both sides of a polyolefin-based membrane with a homologous transition layer and dried at 60-90°C. The microsphere coating amount is 0.5-3.0 g / m³. 2 .

9. The puncture-resistant lithium battery composite separator according to claim 1, characterized in that, In step (3), before hot pressing, a solution of homologous furanyl polyamic acid oligomer is rolled or sprayed onto the inner surfaces of the upper and lower surfaces or the surface of the modified core layer. The weight average molecular weight of the oligomer is 2000-10000. While hot-pressing composite, ultrasonic assistance of 20~40 kHz is applied to embed the surface nanofibers between the core microspheres and promote the formation of covalent bonds. It also includes a post-processing step: hot air or infrared treatment at 150~180℃ for 5~30 min to further imidize the residual ammonium acid and eliminate internal stress.

10. The application of the puncture-resistant lithium battery composite separator according to claim 1 in the preparation of lithium-ion batteries.

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