Intelligent responsive functional separator and method for preparing the same

Abstract

The application discloses an intelligent response type functional diaphragm and a preparation method thereof, and relates to the technical field of lithium batteries. In order to overcome the defects that the response mechanism of the existing safety diaphragm is single, has no self-repairing function, and has poor ion conductivity in normal working conditions, a double-response composite coating is arranged on the surface of a polyolefin base diaphragm to obtain the intelligent response type functional diaphragm. In the battery cycle process, the functional diaphragm can be self-repaired and self-blocked according to temperature and voltage, realizes high ion conductivity in normal working conditions, realizes rapid blocking in dangerous working conditions, realizes self-repairing performance in working condition recovery, and thus comprehensively improves the battery safety and cycle stability.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a smart responsive functional separator and its preparation method. Background Technology

[0002] Lithium-ion batteries are prone to overheating and overvoltage under abnormal operating conditions such as high-rate charging and discharging, high-temperature environments, or overcharging. This can lead to problems such as electrolyte decomposition and electrode material failure, ultimately resulting in thermal runaway and seriously threatening battery safety. Existing safety separators are mostly single-response type, such as those that only respond to temperature, and are often one-time melt-off structures that cannot be recovered after being triggered, causing the battery to be directly scrapped. At the same time, traditional separators are prone to developing microcracks during cycling, leading to unstable ion transport and even the risk of internal short circuits.

[0003] In existing technologies, temperature-sensitive or voltage-responsive separator modification schemes are used to improve battery safety, but they have the following drawbacks: First, a single response mechanism cannot fully cover the two core safety risks of over-temperature and over-voltage, leaving loopholes in protection; second, they lack self-healing function, and micro-cracks generated in the separator cannot be repaired, resulting in poor long-term cycle stability; third, some responsive coatings can increase ion transport resistance under normal operating conditions, affecting the battery rate performance.

[0004] Therefore, developing a separator that combines dual-response blocking and self-healing functions without affecting normal operating performance is of great significance for improving the safety performance and service life of lithium-ion batteries. Summary of the Invention

[0005] To overcome the shortcomings of existing safety diaphragms, such as a single response mechanism, lack of self-repair function, and poor ion conductivity under normal operating conditions, this invention provides an intelligent responsive functional diaphragm and its preparation method. The functional diaphragm can self-repair and self-block according to temperature and voltage. Under normal operating conditions, it achieves a synergistic effect of high ion conductivity, rapid blocking under dangerous conditions, and self-repair during recovery, thus comprehensively improving battery safety and cycle stability.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows: A method for preparing a smart responsive functional membrane includes the following steps: Step 1: Immerse the polyolefin substrate membrane in a silane coupling agent solution and dry it to form a transition bonding layer; obtain a substrate membrane with a transition bonding layer; Step 2: Thermosensitive polymer microspheres, voltage-responsive ionic liquid, lithium-ion conductor particles and elastic binder are added to deionized water in sequence and stirred to obtain a composite slurry; the composite slurry is coated on the surface of the pretreated substrate membrane with a transition adhesive layer, dried and annealed to form a dual-response composite coating; thus, a smart responsive functional membrane is obtained. In the raw materials of the dual-response composite coating, the mass ratio of thermosensitive polymer microspheres, voltage-responsive ionic liquid, lithium-ion conductor particles and elastic binder is (2.8~3.2):(1.8~2.2):1:(0.4~0.6).

[0007] The silane coupling agent comprises a 2 wt% KH550 ethanol solution; the thickness of the transition bonding layer is 2-5 nm; the coating method is blade coating, the coating rate is 7-9 mm / s, the wet film thickness is 70-90 μm, and the thickness of the dual-response composite coating is 30-40 nm; the annealing process parameters are: working atmosphere is nitrogen, temperature is 100-150℃, and time is 1-2 hours. The dual-response composite coating is loaded within the gaps between the transition adhesive layer and the polyolefin substrate membrane.

[0008] More preferably, the temperature-sensitive polymer microspheres are poly(N-isopropylacrylamide) microspheres, and the preparation method is as follows: using N-isopropylacrylamide as monomer, ammonium persulfate as initiator, and N,N'-methylenebisacrylamide as crosslinking agent, polymerize at 55~65℃ for 4~6 hours, and obtain poly(N-isopropylacrylamide) microspheres after centrifugation, washing, and drying. In the raw materials for the poly(N-isopropylacrylamide) microspheres, the mass ratio of N-isopropylacrylamide, ammonium persulfate, and N,N'-methylenebisacrylamide is (9.8~10.2):(0.2~0.4):(0.4~0.6).

[0009] Ideally, the particle size of the poly(N-isopropylacrylamide) microspheres is 0.1~0.3 μm.

[0010] The poly(N-isopropylacrylamide) microspheres have a minimum critical dissolution temperature of 65-80°C. When the temperature is below the minimum critical dissolution temperature, they are in a contracted state and do not affect ion transport. When the temperature is above the minimum critical dissolution temperature, they expand rapidly in volume with an expansion rate of ≥300%, thereby blocking the pores of the substrate.

[0011] More preferably, the voltage-responsive ionic liquid comprises 1-butyl-3-methylimidazolium azobenzene sulfonate, and the lithium-ion conductor particles comprise Li3PO4 nanoparticles with a particle size of 20~50 nm.

[0012] Specifically, within the normal battery voltage range, when the voltage is ≤4.5V, 1-butyl-3-methylimidazolium azobenzenesulfonate exhibits a cis structure and good ion conductivity. When the voltage is >4.5V, it undergoes cis-trans isomerization, transforming into a trans structure, resulting in a sharp drop in ion conductivity. The Li3PO4 nanoparticles are used to improve ion conductivity efficiency under normal operating conditions.

[0013] More preferably, the elastic adhesive is a waterborne polyurethane, and the preparation method of the waterborne polyurethane is as follows: under a nitrogen atmosphere, polytetrahydrofuran ether diol-1000 and polyethylene glycol-1000 are added sequentially to toluene diisocyanate and stirred, the temperature is raised to 65~75℃ and stirred for 2 hours; then the temperature is lowered to 55~65℃ and sulfonate-amine chain extender, dibutyltin dilaurate and acetone are added sequentially, and stirring is continued for 1.5~2.5 hours; the temperature is lowered to 35~45℃ and allyloxyisomeric alcohol ether sulfate ammonium salt is added, and the mixture is stirred and emulsified to obtain waterborne polyurethane; The raw materials of the waterborne polyurethane, by weight, are: 6-8 parts polytetrahydrofuran ether diol-1000, 2-4 parts polyethylene glycol-1000, 3-4 parts toluene diisocyanate, 1-2 parts sulfonate-amine chain extender, 0.02-0.04 parts dibutyltin dilaurate, and 0.1-0.3 parts allyloxyisomeric alcohol ether sulfate ammonium salt.

[0014] A more optimized method for preparing the sulfonate-amine chain extender is as follows: Step 1: Toluenesulfonic acid monohydrate, sodium benzaldehyde-2,4-disulfonate, and 2,2'-(ethylenedioxy)bis(ethylamine) in a mass ratio of (0.2~0.3):(10~15):(2.5~3.5) were added sequentially to DMSO. The mixture was stirred at room temperature for 20~30 hours, then quenched with methanol, and then precipitated, purified, and dried in ethyl acetate to obtain an imine intermediate. Step 2: Add the imine intermediate and sodium borohydride in a mass ratio of (24~26):(2~4) to methanol in sequence, stir, transfer to ethyl acetate for precipitation and drying to obtain the chain extender intermediate; then perform cation exchange to obtain the sulfonate-amine chain extender.

[0015] In a more optimized manner, the cation exchange method is as follows: Step 1: Wash the 732 type sodium cation exchange resin sequentially with ethanol, methanol and deionized water, then pack it into a chromatography column, slowly pass a methanol / water mixture of tetrabutylammonium bromide into the column at a flow rate of 3-4 seconds / drop, and then rinse the resin with the methanol / water mixture. Step 2: Dissolve the chain extender intermediate in a methanol / water mixture and slowly pass it through the pre-treated chromatography column at a flow rate of 3-4 seconds / drop. Collect the eluent, concentrate it, redissolve it in acetone, centrifuge to collect the supernatant, and dry it.

[0016] Ideally, the solid content of the composite slurry is 10-20%; and the thickness of the coated wet film is 50-100 μm.

[0017] More preferably, the polyolefin-based membrane includes one of a polypropylene porous membrane and a polyethylene porous membrane, with a porosity of 35-50%, an average pore size of 0.1-0.5 μm, and a thickness of 12-20 μm.

[0018] A method for preparing a smart responsive functional membrane.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. The functional membrane prepared in this application has both temperature and voltage response mechanisms. Under over-temperature conditions of 65~80℃, it can achieve pore blockage within 10~30s and block ion transport; under over-voltage conditions above 4.5V, the ion conductivity drops sharply within 5~10s, fully covering the core safety risks of the battery and effectively avoiding thermal runaway. 2. The functional separator prepared in this application, after the working conditions return to normal, has a temperature below the minimum critical dissolution temperature and a voltage returning to the safe range. The composite coating can reversibly recover to its initial state within 30~60s, and the self-repair cycle count is ≥50 times. This solves the problem of battery scrapping after traditional disposable safety separators are triggered, and improves battery life. 3. The functional separator prepared in this application has excellent performance under normal operating conditions. The composite coating does not block the substrate pores under normal operating conditions. The lithium ion transference number is ≥0.65. The battery's 1C rate discharge capacity retention rate is ≥97.2%, and the 5C rate discharge capacity retention rate is ≥85%. It does not affect the battery's normal performance. 4. The functional separator prepared in this application has a simple preparation process, using mature processes such as solution coating, without the need for complex equipment, and the coating thickness and response threshold can be precisely controlled. It is compatible with existing lithium-ion battery production lines and is easy to mass-produce industrially. 5. This invention employs a sulfonate-amine chain extender in synergy with an emulsifier in waterborne polyurethane, effectively overcoming the limitations of conventional waterborne polyurethanes in terms of insulation and poor ion conductivity. On one hand, the sulfonic acid groups in the sulfonate-amine chain extender structure possess lithium-philic properties, allowing lithium ions to migrate and transport between sulfonic acid groups via electrostatic interactions, thus enhancing ion conductivity in conjunction with the liquid electrolyte. Simultaneously, the sulfonic acid groups can fill the interfacial voids between Li3PO4 nanoparticles, reducing interfacial contact resistance and capturing residual water that is difficult to completely remove from the battery system, thus assisting lithium ion migration. Furthermore, due to the low solubility of sodium ions in organic solvents, the chain extender undergoes cation exchange treatment, exchanging sodium ions for larger tetrabutylammonium ions. This improves the solubility of the chain extender in organic solvents, resulting in a more uniform chain extension reaction. Simultaneously, the larger tetrabutylammonium ions increase the steric hindrance between sulfonic acid groups, promoting local aggregation of ionic groups, enhancing emulsion stability, and improving the water resistance of the cured film. On the other hand, the removal of sodium ions from the chain extender effectively prevents sodium ion migration and subsequent damage to the SEI (Sediment Injection).

[0020] On the other hand, waterborne polyurethane incorporates allyloxyisomeric alcohol ether sulfate ammonium salt as an emulsifier. The sulfate groups in the allyloxyisomeric alcohol ether sulfate ammonium salt structure form a synergistic hydrophilic network with the sulfonic acid groups in the sulfonate-amine chain extender, significantly improving the stability of the waterborne polyurethane emulsion in high-temperature, high-humidity, and electrolyte environments, and enhancing the long cycle life of the dual-response composite coating membrane. Furthermore, allyloxyisomeric alcohol ether sulfate ammonium salt possesses low surface tension and excellent wetting and dispersing properties, effectively promoting the uniform dispersion of Li3PO4 nanoparticles in the coating, avoiding the problems of ion transport channel blockage and reduced utilization caused by filler agglomeration in traditional coatings. Meanwhile, waterborne polyurethane exhibits good compatibility with coating components, enabling it to form a uniform and dense composite coating on the surface of a polyolefin substrate. It can also fill cracks through molecular chain peristalsis, synergistically driving the redistribution of temperature-sensitive polymer microspheres and ionic liquids, restoring the integrity of the coating. The flexibility it provides allows the temperature-sensitive microspheres to expand freely to achieve thermal shut-off. At the same time, its ion conduction and self-healing properties synergistically enhance the mechanical integrity and ion conductivity of the coating, significantly extending the battery cycle life. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention are described in detail and completely below. It should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other equivalent embodiments obtained by those skilled in the art based on the embodiments disclosed in this invention without creative effort are within the protection scope of this invention.

[0022] It should be noted that there are no special restrictions on the manufacturers of the raw materials involved in this invention. Exemplary examples include: allyloxyisomeric alcohol ether sulfate ammonium salt with model number SR-1025, poly-N-isopropylacrylamide microspheres with a particle size of 0.3 μm, and Li3PO4 nanoparticles with a particle size of 35 nm.

[0023] Pre-preparation: I. Preparation of sulfonate-amine chain extenders: Step 1: Add 0.25 parts of toluenesulfonic acid monohydrate and 12.5 parts of sodium benzaldehyde-2,4-disulfonate to 50 parts of DMSO in sequence, stir, then add 3 parts of 2,2'-(ethylenedioxy)bis(ethylamine), stir at room temperature for 24 hours, then quench with methanol, then precipitate in ethyl acetate, purify, and dry to obtain an imine intermediate; Step 2: (1) Add 25 parts imine intermediate and 3 parts sodium borohydride by mass ratio to 100 parts methanol, stir, transfer to ethyl acetate for precipitation and dry to obtain chain extender intermediate; (2) Wash 0.063 mol of 732 type sodium cation exchange resin with ethanol, methanol and deionized water in sequence, and then pack it into a chromatography column. Dissolve 0.1 mol tetrabutylammonium bromide in a mixed solution of 50 mL methanol and 50 mL deionized water and slowly pass it through the chromatography column at a flow rate of 3 seconds / drop. Then wash the resin 3 times with a methanol / water mixed solution with a volume ratio of 1:1; Dissolve the chain extender intermediate in a mixed solution of 20 mL methanol / water with a volume ratio of 1:1 and slowly pass it through the above-treated chromatography column at a flow rate of 3 seconds / drop. Collect the eluent, concentrate it and redissolve it in acetone, centrifuge to obtain the supernatant and dry it to obtain sulfonate-amine chain extender.

[0024] II. Preparation of waterborne polyurethane: Under a nitrogen atmosphere, 7 parts of polytetrahydrofuran ether diol-1000 and 3 parts of polyethylene glycol-1000 were added sequentially to 3.5 parts of toluene diisocyanate and stirred. The mixture was heated to 70°C and stirred for 2 hours. Then, the temperature was lowered to 60°C and 1.5 parts of sulfonate-amine chain extender, 0.03 parts of dibutyltin dilaurate, and 50 parts of acetone were added sequentially. The mixture was stirred for another 2 hours. The temperature was then lowered to 40°C and 0.2 parts of allyloxyisomeric alcohol ether sulfate ammonium salt were added. The mixture was stirred and emulsified to obtain waterborne polyurethane.

[0025] Example 1: A method for preparing a smart responsive functional membrane, the specific steps of which are as follows: Step 1: A polypropylene porous membrane with a porosity of 42%, an average pore size of 0.3 μm, and a thickness of 16 μm was ultrasonically cleaned with ethanol for 12 minutes, then rinsed three times with deionized water, and vacuum dried at 60°C for 2 hours; then it was immersed in a 2% wt% KH550 ethanol solution, soaked at room temperature for 45 minutes, and dried at 100°C for 1 hour to form a 3.5 nm thick transition bonding layer; thus, a substrate membrane with a transition bonding layer was obtained. Step 2: Add 3 parts of poly(N-isopropylacrylamide) microspheres, 2 parts of 1-butyl-3-methylimidazolium azobenzene sulfonate, 1 part of Li3PO4 nanoparticles, and 0.5 parts of waterborne polyurethane to 43.5 parts of deionized water in sequence, and stir at high speed for 2.5 hours to obtain a composite slurry with a solid content of 15%. Use a doctor blade coating method to coat the composite slurry onto the surface of the substrate diaphragm with a transition adhesive layer at a coating rate of 8 mm / s to form an 80 μm wet film. Dry the film in a 60℃ oven for 4 hours, and anneal it at 130℃ for 1.5 hours in a nitrogen atmosphere to form a 35 nm thick dual-response composite coating; thus, a smart responsive functional diaphragm is obtained.

[0026] Example 2: A method for preparing a smart responsive functional membrane, the specific steps of which are as follows: Step 1: A polypropylene porous membrane with a porosity of 42%, an average pore size of 0.3 μm, and a thickness of 16 μm was ultrasonically cleaned with ethanol for 12 minutes, then rinsed three times with deionized water, and vacuum dried at 60°C for 2 hours; then it was immersed in a 2% wt% KH550 ethanol solution, soaked at room temperature for 45 minutes, and dried at 100°C for 1 hour to form a 3.5 nm thick transition bonding layer; thus, a substrate membrane with a transition bonding layer was obtained.

[0027] Step 2: 2.8 parts of poly(N-isopropylacrylamide) microspheres, 1.8 parts of 1-butyl-3-methylimidazolium azobenzene sulfonate, 1 part of Li3PO4 nanoparticles, and 0.4 parts of waterborne polyurethane were added sequentially to 43.5 parts of deionized water and stirred at high speed for 2.5 hours to obtain a composite slurry with a solid content of 15%. Using a doctor blade coating method, the coating rate was controlled at 8 mm / s, and the composite slurry was coated onto the surface of the substrate diaphragm with a transition adhesive layer to form an 80 μm wet film. The film was dried in a 60℃ oven for 4 hours and annealed at 130℃ for 1.5 hours in a nitrogen atmosphere to form a 35 nm thick dual-response composite coating; thus, the intelligent responsive functional diaphragm was obtained.

[0028] Example 3: A method for preparing a smart responsive functional membrane, the specific steps of which are as follows: Step 1: A polypropylene porous membrane with a porosity of 42%, an average pore size of 0.3 μm, and a thickness of 16 μm was ultrasonically cleaned with ethanol for 12 minutes, then rinsed three times with deionized water, and vacuum dried at 60°C for 2 hours; then it was immersed in a 2% wt% KH550 ethanol solution, soaked at room temperature for 45 minutes, and dried at 100°C for 1 hour to form a 3.5 nm thick transition bonding layer; thus, a substrate membrane with a transition bonding layer was obtained. Step 2: 3.2 parts of poly(N-isopropylacrylamide) microspheres, 2.2 parts of 1-butyl-3-methylimidazolium azobenzene sulfonate, 1 part of Li3PO4 nanoparticles, and 0.6 parts of aqueous polyurethane were added sequentially to 43.5 parts of deionized water and stirred at high speed for 2.5 hours to obtain a composite slurry with a solid content of 15%. Using a doctor blade coating method, the coating rate was controlled at 8 mm / s, and the composite slurry was coated onto the surface of the substrate diaphragm with a transition adhesive layer to form an 80 μm wet film. The film was dried in a 60℃ oven for 4 hours and annealed at 130℃ for 1.5 hours in a nitrogen atmosphere to form a 35 nm thick dual-response composite coating; thus, the intelligent responsive functional diaphragm was obtained.

[0029] Example 4: Based on Example 1, no annealing treatment was performed after the composite slurry was dried, and the rest was the same as in Example 1.

[0030] Example 5: Based on Example 1, the particle size of the poly(N-isopropylacrylamide) microspheres is 0.2 μm, and the rest is the same as in Example 1.

[0031] Comparative Example 1, based on Example 1, has a particle size of 0.4 μm for poly(N-isopropylacrylamide) microspheres, and the rest is the same as in Example 1.

[0032] Comparative Example 2: Based on Example 1, the emulsifier of the waterborne polyurethane was adjusted, and distilled water was added to replace allyloxyisomeric alcohol ether sulfate ammonium salt as the emulsifier, while the rest remained the same as in Example 1.

[0033] Comparative Example 3: Based on Example 1, the preparation of the sulfonate-amine chain extender was adjusted, ion exchange was not performed, and the rest remained the same as in Example 1.

[0034] Comparative Example 4: Using commercial Celgard 2400 diaphragm.

[0035] Comparative Example 5: Using a traditional PP membrane with an average pore size of 100nm.

[0036] Performance testing experiments: The functional separators prepared in Examples 1-5 and Comparative Examples 1-5 were stacked in the order of "positive electrode - functional separator - negative electrode" to assemble CR2032 coin cells. The positive electrode was a ternary system with a Ni / Co / Mn molar ratio of 1:1:1, the negative electrode was graphite, and the electrolyte was 1 mol / L lithium hexafluorophosphate dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate. The following performance testing experiments were conducted: (1) Pore blockage rate: The prepared intelligent responsive functional diaphragm is cut into a sample of a preset size and placed in a water-filled sample pool in a water pressurizer. The test temperature is gradually increased to 70℃. The porosity of the diaphragm in the sample pool is recorded every 15s. When the temperature reaches 70℃, the pore blockage rate is calculated according to the following formula: Pore blockage rate (%) = (initial porosity - porosity at 70℃) / initial porosity × 100%.

[0037] (2) Ionic conductivity: The membrane sample was immersed in 1.0 mol / L LiPF6 electrolyte, the membrane was sandwiched between two stainless steel electrodes, and heated to 70°C at a constant heating rate of 2°C / min. The changes in temperature and resistance were recorded. When the temperature reached 70°C, the ionic conductivity of the membrane (unit: S / cm) was measured by electrochemical impedance spectroscopy. The thermal shutdown response time was recorded as the time required for the ionic conductivity to drop to the set threshold from the start of heating to 70°C.

[0038] (3) Battery capacity retention rate: The CR2032 button cell battery was tested for rate performance at 25℃±2℃. The testing method was as follows: the battery was charged to 100% SOC, then stored at 25℃ for 28 days, and then discharged to 0% SOC. The capacity retention rate was calculated according to the following formula: Capacity retention rate (%) = (Amount discharged after storage / Amount fully charged before storage) × 100%.

[0039] (4) Capacity retention rate after 500 cycles: Under a temperature environment of 25℃, constant current charge-discharge cycles were performed with a current of 1C. The charge-discharge voltage range was set (2.8V~4.3V). The discharge capacity was recorded for each cycle. After 500 cycles, the discharge capacity was recorded every 100 cycles. The capacity retention rate after the cycles was calculated according to the following formula: Capacity retention rate (%) after 500 cycles = Discharge capacity at 500th cycle / Initial discharge capacity × 100%.

[0040]

[0041] Conclusion: As can be seen from the data in the table, in Examples 1-5, the pore blockage rate reached over 92% within 15 seconds at 70℃, and the ionic conductivity rapidly decreased to 8.0 × 10⁻⁶. -5 ~8.3×10 -5 S / cm; ionic conductivity decreased to 9.3 × 10⁻⁶ within 8 seconds when a voltage of 4.6 V was applied. -5 ~9.7×10 -5 S / cm; ion conductivity recovered to 94%~97% of initial value within 35s after stimulation removal; 1C capacity retention ≥97.5%, 5C capacity retention ≥85.3%, and capacity retention ≥86% after 500 cycles; although Example 4 did not undergo annealing treatment, its thermal shutdown and rate performance remained at a good level. Therefore, this separator combines pore shut-off and damage repair functions, significantly improving the overall performance of the battery.

[0042] A comparison of Comparative Examples 1-5 with Example 1 shows that Comparative Example 1, using poly-N-isopropylacrylamide microspheres with a particle size of 0.4 μm, achieved a pore blockage rate of only 45% and an ionic conductivity reduction of only 5.5 × 10⁻⁶. -5S / cm indicates that excessively large microsphere size leads to severe degradation of the thermal shutdown function. Comparative Example 2 uses distilled water instead of emulsifier. Due to the lack of synergistic emulsification, the slurry dispersion is poor, the coating uniformity is insufficient, the ion conduction recovery rate is only 55%, and the cycle retention rate drops to 78%. Comparative Example 3 does not perform cation exchange, and the chain extender used is still in sodium salt form. This chain extender has low solubility in the organic solvent acetone, resulting in uneven chain extension reaction during the preparation of waterborne polyurethane. Consequently, the coating structure is not dense, and the dispersion of functional components is poor. Therefore, its recovery rate and cycle stability are further reduced, with a recovery rate of less than 40% and a 500-cycle retention rate of 76%. Comparative Examples 4 and 5 are uncoated commercial diaphragms and traditional PP diaphragms, which do not have thermal shutdown, voltage response, or self-healing functions at all. Although the rate performance reduction is not significant, they cannot achieve intelligent response. In summary, this invention introduces sulfonate-amine chain extenders into aqueous polyurethane and employs techniques such as cation exchange treatment, reversible hydrogen bonding, and microsphere particle size control to enable the functional membrane to self-repair / self-block based on dual temperature / voltage responses. This achieves a synergistic effect of high ion conduction under normal operating conditions, rapid blocking under hazardous conditions, and self-repair during recovery, thereby comprehensively improving battery safety and cycle stability.

[0043] Those skilled in the art should understand that the present invention is not limited to the details of the exemplary embodiments described above. Other specific embodiments may be adopted without departing from the spirit and essential characteristics of the invention. Therefore, the above embodiments should be considered exemplary only and not restrictive, and the scope of protection of the present invention is defined by the appended claims, not by the foregoing description. All changes within the meaning and scope of the claims and their equivalents should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a smart responsive functional membrane, characterized in that: Includes the following steps: Step 1: Immerse the polyolefin substrate membrane in a silane coupling agent solution and dry it to form a transition bonding layer; obtain a substrate membrane with a transition bonding layer; Step 2: Thermosensitive polymer microspheres, voltage-responsive ionic liquid, lithium-ion conductor particles and elastic binder are added to deionized water in sequence and stirred to obtain a composite slurry; the composite slurry is coated on the surface of the substrate membrane with a transition adhesive layer, dried and annealed to form a dual-response composite coating; thus, a smart responsive functional membrane is obtained. In the raw materials of the dual-response composite coating, the mass ratio of thermosensitive polymer microspheres, voltage-responsive ionic liquid, lithium-ion conductor particles and elastic binder is (2.8~3.2):(1.8~2.2):1:(0.4~0.6).

2. The method for preparing a smart responsive functional membrane according to claim 1, characterized in that: The temperature-sensitive polymer microspheres are poly(N-isopropylacrylamide) microspheres, and the preparation method is as follows: using N-isopropylacrylamide as monomer, ammonium persulfate as initiator, and N,N'-methylenebisacrylamide as crosslinking agent, polymerize at 55~65℃ for 4~6 hours, and obtain poly(N-isopropylacrylamide) microspheres after centrifugation, washing, and drying. In the raw materials for the poly(N-isopropylacrylamide) microspheres, the mass ratio of N-isopropylacrylamide, ammonium persulfate, and N,N'-methylenebisacrylamide is (9.8~10.2):(0.2~0.4):(0.4~0.6).

3. The method for preparing a smart responsive functional membrane according to claim 2, characterized in that: The particle size of the poly(N-isopropylacrylamide) microspheres is 0.1~0.3 μm.

4. The method for preparing a smart responsive functional membrane according to claim 1, characterized in that: The voltage-responsive ionic liquid includes 1-butyl-3-methylimidazolium azobenzene sulfonate, and the lithium-ion conductor particles include Li3PO4 nanoparticles with a particle size of 20~50nm.

5. The method for preparing a smart responsive functional membrane according to claim 1, characterized in that: The elastic adhesive is a waterborne polyurethane, and the preparation method of the waterborne polyurethane is as follows: under a nitrogen atmosphere, polytetrahydrofuran ether diol-1000 and polyethylene glycol-1000 are added sequentially to toluene diisocyanate and stirred, the temperature is raised to 65~75℃ and stirred for 2 hours; then the temperature is lowered to 55~65℃ and sulfonate-amine chain extender, dibutyltin dilaurate and acetone are added sequentially, and stirring is continued for 1.5~2.5 hours; the temperature is lowered to 35~45℃ and allyloxyisomeric alcohol ether sulfate ammonium salt is added, and the mixture is stirred and emulsified to obtain waterborne polyurethane; The raw materials of the waterborne polyurethane, by weight, are: 6-8 parts polytetrahydrofuran ether diol-1000, 2-4 parts polyethylene glycol-1000, 3-4 parts toluene diisocyanate, 1-2 parts sulfonate-amine chain extender, 0.02-0.04 parts dibutyltin dilaurate, and 0.1-0.3 parts allyloxyisomeric alcohol ether sulfate ammonium salt.

6. The method for preparing a smart responsive functional membrane according to claim 5, characterized in that: The preparation method of the sulfonate-amine chain extender is as follows: Step 1: Toluenesulfonic acid monohydrate, sodium benzaldehyde-2,4-disulfonate, and 2,2'-(ethylenedioxy)bis(ethylamine) in a mass ratio of (0.2~0.3):(10~15):(2.5~3.5) were added sequentially to DMSO. The mixture was stirred at room temperature for 20~30 hours, then quenched with methanol, and then precipitated, purified, and dried in ethyl acetate to obtain an imine intermediate. Step 2: Add the imine intermediate and sodium borohydride in a mass ratio of (24~26):(2~4) to methanol in sequence, stir, transfer to ethyl acetate for precipitation and drying to obtain the chain extender intermediate; then perform cation exchange to obtain the sulfonate-amine chain extender.

7. The method for preparing a smart responsive functional diaphragm according to claim 6, characterized in that: The cation exchange method is as follows: Step 1: Wash the 732 type sodium cation exchange resin sequentially with ethanol, methanol and deionized water, then pack it into a chromatography column, slowly pass a methanol / water mixture of tetrabutylammonium bromide into the column at a flow rate of 3-4 seconds / drop, and then rinse the resin with the methanol / water mixture. Step 2: Dissolve the chain extender intermediate in a methanol / water mixture and slowly pass it through the pre-treated chromatography column at a flow rate of 3-4 seconds / drop. Collect the eluent, concentrate it, redissolve it in acetone, centrifuge to collect the supernatant, and dry it.

8. The method for preparing a smart responsive functional membrane according to claim 1, characterized in that: The solid content of the composite slurry is 10-20%; the thickness of the coated wet film is 50-100 μm.

9. The method for preparing a smart responsive functional diaphragm according to claim 1, characterized in that: The polyolefin-based membrane includes one of a polypropylene porous membrane and a polyethylene porous membrane, with a porosity of 35-50%, an average pore size of 0.1-0.5 μm, and a thickness of 12-20 μm.

10. The smart responsive functional membrane prepared by the method of preparing a smart responsive functional membrane according to any one of claims 1 to 9.

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