A poly-m-phenylene isophthalamide-based electrospun flame-retardant separator and application thereof

Abstract

The application belongs to the technical field of lithium ion batteries, and discloses a poly-m-phenylene isophthalamide-based electrostatic spinning flame-retardant separator and application thereof. The m-phenylene isophthalamide-based electrostatic spinning separator, namely PMIA-based electrostatic spinning separator, is prepared by mixing modified PZS microspheres, PMIA and an organic solvent, and then adopting an electrostatic spinning method. The modified PZS microspheres are prepared by in-situ growth of an inorganic layer SiO2 on the surface of polyphosphazene PZS microspheres with flame-retardant properties. The polyphosphazene PZS microspheres are prepared by a polymerization reaction between tannic acid and hexachlorocyclotriphosphazene. The spinning separator prepared by the application has very excellent porosity, liquid absorption rate and ionic conductivity, and good thermal stability and flame retardancy.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to a poly(m-phenylene isophthalamide) electrospun flame-retardant separator and its application. Background Technology

[0002] Lithium-ion batteries (LIBs) possess significant advantages such as high energy density, long lifespan, fast charging, and environmental friendliness, leading to their widespread application in portable devices, electric vehicles, and energy storage power stations. However, under abusive conditions, the chemical energy stored within LIBs can be suddenly released in the form of fire or explosion, causing catastrophic accidents. The battery separator, a thin film separating the positive and negative electrodes and allowing for the rapid transport of ionic charge carriers, is considered one of the most critical components affecting the safety of LIBs.

[0003] Currently, the most widely used separators in lithium-ion secondary batteries are mainly composed of polyethylene (PE), polypropylene (PP), and composites of both. While these separators offer relatively high mechanical strength and thermal shutdown capability, they still suffer from low porosity, poor electrolyte wettability, and low thermal stability. When the internal temperature of the battery rises and approaches its melting point, the dimensions of commercially available separators shrink until they melt. Once the separator melts, the positive and negative electrodes of the battery come into contact, leading to an internal short circuit, inducing thermal runaway or a fire. Furthermore, the exothermic reaction of traditional polyolefin separators during combustion exacerbates the fire hazard. The poor thermal stability and flammability of commercially available polyolefin separators pose a serious threat to the safety performance of lithium-ion batteries.

[0004] Poly(m-phenylene isophthalamide) (PMIA) exhibits a regularly arranged serrated molecular chain, and its main chain is composed of numerous phenyl cyclic amide bonds. Due to the absence of conjugation effects within its molecular structure, its cohesive behavior is relatively low, resulting in good flexibility and superior physical and chemical properties in the fibers produced. PMIA has a thermal decomposition temperature between 400 and 430°C, making it a promising alternative to traditional polyolefin materials and a potential ideal membrane material.

[0005] Although PMIA has certain advantages in high-temperature resistance as a membrane substrate material, its inherent flame retardancy is far from sufficient in the event of thermal runaway. Therefore, to further improve the flame retardancy of PMIA-based membrane materials, adding flame retardants or flame-retardant coatings is a common modification method. For example, patent CN115911752A discloses a method for coating meta-aramid lithium-ion battery membranes with sodium alginate. This method involves droplets of sodium alginate coating onto a dried PMIA porous membrane, with a coating thickness of 20-200 μm, followed by static drying to obtain a Na-Alg / PMIA composite membrane. However, the Na-Alg / PMIA composite separator prepared by this invention has a porosity of only 40-60% and a specific capacity of 168.8 mAh / g during the first discharge. Similarly, patent CN115241606A discloses an aramid resin-based composite coated lithium battery separator and its preparation method. This invention selects PMIA as a high-temperature resistant substrate material and coats the separator surface with a mixture of polymer and inorganic ceramics. The porosity of this separator is only 25%-85%. While these modification methods improve the flame retardant properties of PMIA-based separator materials to some extent, they have adverse effects on the electrochemical performance of the separator. Summary of the Invention

[0006] The main objective of this invention is to provide a poly(m-phenylene isophthalamide) membrane material that can improve its flame retardancy and safety while maintaining good electrochemical performance.

[0007] To achieve the above objectives, in a first aspect, this application provides a poly(m-phenylene isophthalamide)-based electrospun flame-retardant separator, hereinafter referred to as PMIA-based electrospun separator. The PMIA-based electrospun separator is prepared by mixing modified PZS microspheres with PMIA and an organic solvent, followed by electrospinning. The modified PZS microspheres are prepared by in-situ growth of an inorganic SiO2 layer on the surface of flame-retardant polyphosphazene PZS microspheres. The inorganic SiO2 layer has the effect of inhibiting lithium dendrite growth. The polyphosphazene PZS microspheres are prepared by polymerization reaction between tannic acid and hexachlorocyclotriphosphazene.

[0008] Preferably, the preparation process of the polyphosphazene PZS microspheres includes: dissolving tannic acid in acetonitrile until completely dissolved to obtain a first solution, wherein the mass ratio of tannic acid to acetonitrile is 1:(250-300); then adding hexachlorocyclotriphosphazene, wherein the mass ratio of the added hexachlorocyclotriphosphazene to the first solution is 1:(300-350), and continuing ultrasonic stirring for 30-60 min to obtain a second solution; then slowly adding pyridine solution dropwise to the second solution within 1 h, wherein the mass ratio of the added pyridine solution to the second solution is 1:(20-30), maintaining the reaction at room temperature for 12 h, finally collecting the product by centrifugation at 8000 rpm, washing with acetonitrile and deionized water, and finally freeze-drying.

[0009] Further preferably, the preparation process of the modified PZS microspheres includes: ultrasonically dispersing polyphosphazene PZS microspheres in ethanol as a third solution, wherein the mass ratio of the polyphosphazene PZS microspheres to ethanol is 1:(180-240), ultrasonicating for 30-45 min, then adding the precursor sodium metasilicate, wherein the mass ratio of the added sodium metasilicate to the third solution is 1:(15-20), and ultrasonicating with stirring for 30-45 min to obtain a fourth solution, then adding a catalyst, wherein the catalyst is one of hydrofluoric acid, nitric acid, hydrochloric acid, ammonia, triethylamine, or ethylenediamine, and the mass ratio of the added catalyst to the fourth solution is 1:(200-250), ultrasonicating for 10-15 min, transferring to a hydrothermal reactor, and reacting at 180°C for 24 h, finally collecting the product by centrifugation at 8000 rpm, and drying at 80°C to obtain the product modified PZS microspheres SiO2@PZS.

[0010] Further preferably, the preparation process of the spun membrane obtained by electrospinning the modified PZS microspheres with PMIA and an organic solvent includes: taking modified PZS microsphere powder, dispersing it in N,N-dimethylacetamide as a fifth solution, wherein the mass ratio of the modified PZS microsphere powder to N,N-dimethylacetamide is 1:(70-75), and more preferably 1:72; after ultrasonic stirring and dispersion for 1 hour, adding PMIA, wherein the mass ratio of the fifth solution to PMIA is 1:(1.3-1.5), and more preferably 73:100; continuing ultrasonic stirring and dispersion for 10 hours, the resulting mixture is the spinning solution; and taking an appropriate amount using a disposable syringe. The spinning solution was prepared using an 18-gauge needle with a positive voltage of 20–30 kV, a negative voltage of -1.5–-2 kV, a pushing speed of 1.2–1.5 mL / h, a needle distance of 15–20 cm from the receiver, and a stroke of 10–12 mm. More preferred electrospinning parameters were: a positive voltage of 20 kV, a negative voltage of -1.5 kV, a pushing speed of 1.2 mL / h, a needle distance of 20 cm from the receiver, and a needle stroke of 10 mm. This resulted in a PMIA-based spun diaphragm. After electrospinning, the PMIA-based spun diaphragm was placed in a vacuum oven for vacuum drying for 24 h to prepare the poly(m-phenylene isophthalamide)-based electrospun flame-retardant diaphragm SiO2@PZS@PMIA.

[0011] Secondly, this application provides the application of electrospun separators in the fabrication of lithium-ion battery separators, and further provides their application in the fabrication of lithium-ion batteries. PMIA-based spun separators have a distinct porous fiber structure, thus possessing excellent porosity, liquid absorption rate, and ionic conductivity. After adding modified flame-retardant materials, the SiO2@PZS@PMIA separator exhibits even better thermal stability and flame retardancy, making it suitable for assembling lithium-ion batteries.

[0012] The technical principle is as follows:

[0013] The electrospun separator SiO2@PZS@PMIA provided in this application is generated by decomposing the precursor to produce silicon dioxide, which is then coated onto pre-prepared polyphosphazene PZS microspheres to form SiO2@PZS microspheres, and then incorporated into the PMIA separator by electrospinning to obtain the PMIA-based separator.

[0014] The nitrogen and phosphorus elements in the polyphosphazene (PZS) microsphere structure release non-combustible gases, such as ammonia and phosphine, during pyrolysis. These gases dilute the concentration of combustible gases, thereby reducing the flammability of the flame. At high temperatures, PZS decomposes to generate phosphoric acid or polyphosphoric acid. These substances promote the formation of a glassy or viscous protective layer on the material surface, effectively isolating heat and oxygen. During combustion, phosphorus generates phosphorus oxides, which capture free radicals produced during combustion, interrupting the combustion chain reaction and inhibiting flame propagation. PZS also promotes the formation of a char layer during combustion. This char layer forms a protective film on the material surface, isolating air, preventing further combustion, and reducing heat transfer.

[0015] PMIA, as a high-temperature resistant fiber material, works synergistically with SiO2@PZS after incorporation. Through various mechanisms such as the coating layer effect, gas dilution effect, and heat absorption effect, it inhibits combustion and effectively improves the flame retardant performance of PMIA-based spun separators. When thermal runaway occurs inside the battery, it works synergistically to interrupt and inhibit the chain reaction. Traditional electrospun fibers, due to their micro-nano structure, usually have low mechanical properties and are easily damaged during bending, folding, and other operations, making them prone to puncture and causing short circuits inside the battery. In-situ growth of an inorganic SiO2 layer on the PZS surface, which can inhibit lithium dendrite growth, can give the separator a better effect in inhibiting lithium dendrite growth and further improve the safety performance of the battery.

[0016] The beneficial effects of this invention are:

[0017] (1) In the patent with publication number CN115911752A, the lithium-ion battery assembled with a Na-Alg / PMIA composite separator has an initial specific capacity of 168 mAh / g, which decreases to 129 mAh / g after 50 charge-discharge cycles. The lithium-ion battery assembled with the SiO2@PZS@PMIA separator prepared in this invention has an initial specific capacity of 229 mAh / g, which decreases to 220 mAh / g after 50 charge-discharge cycles. The difference in specific capacity after multiple charge-discharge cycles indicates that the Na-Alg / PMIA separator does not inhibit lithium dendrite growth. However, the SiO2@PZS microspheres in the novel separator prepared in this application have excellent lithium dendrite growth inhibition function. Therefore, the separator prepared in this application can effectively inhibit lithium dendrite growth, reduce the loss of active material, and extend the battery's service life and performance.

[0018] (2) In patent publication CN115241606A, the porosity of an aramid resin-based composite coated lithium battery separator is only 25% to 85%. The SiO2@PZS@PMIA separator prepared by this invention has a liquid absorption rate of 322.01%. The novel separator prepared in this application can provide more transport channels for lithium ions, significantly improving the electrochemical performance of the battery.

[0019] (3) In patent CN118909296A, a lithium-ion battery assembled with a PDA-BN and PMIA composite porous membrane is disclosed. Its first-cycle specific capacity at different rate cycles of 0.1C, 0.2C, 0.5C, 1C, and 2C is 150, 148, 139, 128, and 109 mAh / g, respectively. The discharge specific capacity of the battery assembled with the SiO2@PZS@PMIA separator of this invention is 229, 219, 210, 199, 177, and 161 mAh / g. -1 This indicates that the new separator can adapt well to cycling tests under high-density current, and suppresses lithium dendrite growth, reduces battery polarization, and reduces capacity decay.

[0020] (4) In patent CN118496498A, a PMIA separator modified with a 9-phenoxy-10-phenylanthracene structure is disclosed with a melting point of 350°C. The novel separators prepared by this invention all have melting points above 550°C, thus giving the battery higher thermal stability and safety.

[0021] (5) After testing, the battery equipped with a commercial separator experienced SEI film decomposition at 174℃, with a maximum thermal runaway temperature of 220℃, a thermal runaway initiation time of 300 min, and an activation energy of 0.64 eV. However, the SEI film decomposition temperatures of the batteries equipped with PMIA separators and SiO2@PZS@PMIA separators were 182℃ and 189℃, respectively, with maximum thermal runaway temperatures of 452℃ and 509℃, and activation energies of 0.77 eV and 0.83 eV, respectively. The novel separator of this invention can effectively delay battery thermal runaway and improve the activation energy of the thermal runaway reaction. Attached Figure Description

[0022] Figure 1 This is a SEM image of the PZS microspheres prepared in Example 1 of this application;

[0023] Figure 2 This is a SEM image of the SiO2@PZS material prepared in Example 1 of this application;

[0024] Figure 3 This is a scanning electron microscope (SEM) image of the SiO2@PZS@PMIA spinning diaphragm in Example 1 of this application;

[0025] Figure 4 Comparison of residues after combustion tests for commercial diaphragms and SiO2@PZS@PMIA prepared in Example 1;

[0026] Figure 5 Thermal shrinkage test of commercial membrane and SiO2@PZS@PMIA membrane prepared in Example 1;

[0027] Figure 6 Comparison of porosity between commercial membranes and SiO2@PZS@PMIA membranes prepared in Example 1;

[0028] Figure 7 Comparison of liquid absorption rates between commercial membranes and SiO2@PZS@PMIA membranes prepared in Example 1;

[0029] Figure 8 The image shows the results of cycling the battery with the separator for 50 cycles at a current density of 0.1C.

[0030] Figure 9 The image shows the results of cycling the battery with the separator for 50 cycles at a current density of 0.5C.

[0031] Figure 10 A graph showing the rate test results for a battery with a separator installed.

[0032] Figure 11 Cyclic diagram of a battery with a separator under different operating voltage conditions;

[0033] Figure 12 SEM images of lithium-ion cells after cycling at different operating voltages for batteries with separators assembled.

[0034] Figure 13 Cycling diagram of a battery with a separator at high voltage;

[0035] Figure 14 SEM image of lithium-ion cells after cycling at high voltage for a battery with a separator assembled;

[0036] Figure 15 The results of thermal insulation tests on batteries with assembled separators;

[0037] Figure 16 Activation energy diagram for a battery with a separator assembled;

[0038] Figure 17 Radar chart for safety assessment of batteries with diaphragms. Detailed Implementation

[0039] To further illustrate the technical solution of the present invention, preferred embodiments are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0040] Furthermore, all raw materials or reagents mentioned below that are not specifically described are commercially available products, and all process steps or methods not specifically mentioned are process steps or methods known to those skilled in the art.

[0041] The sources of some of the raw materials and reagents used in the following examples, comparative examples, and test cases are shown below:

[0042] PMIA is derived from Ningbo Taihe Company, with a molecular weight of 200,000 and a solid content of 20%.

[0043] The solute in the pyridine solution is pyridine, the solution is water, and the concentration is 0.5 mol / L.

[0044] The conventional commercial diaphragm was purchased from Celgard Corporation in the United States, model number Celgard 2325;

[0045] The hexachlorotriphosphazene was purchased from Maclean Biotech, model AR, 99 wt%.

[0046] Example 1

[0047] Step S1: Weigh 0.6 g of tannic acid and dissolve it in 210 ml (165 g) of acetonitrile until completely dissolved, forming a homogeneous and stable solution. Then, precisely add 0.51 g of hexachlorocyclotriphosphazene to this solution and ultrasonically stir to ensure thorough mixing. Immediately afterward, over 1 hour, slowly and uniformly add 7 ml (7 g) of pyridine solution dropwise to the above solution, strictly controlling the dropping rate to ensure a stable reaction. The reaction system is allowed to stand at room temperature for 12 hours. After the reaction is complete, the product is collected by centrifugation at 8000 rpm, washed successively with acetonitrile and deionized water to remove impurities, and finally freeze-dried to obtain polyphosphazene microspheres (PZS) with a diameter of approximately 120 nm.

[0048] In step S2, 0.2 g of PZS was placed in 50 ml (39.5 g) of ethanol and ultrasonically dispersed for 30 min to form a stable system. Then, 1 ml (2.4 g) of sodium metasilicate was added, stirred, and ultrasonicated for 30 min to ensure thorough mixing and initial reaction with the PZS. Next, 0.2 ml (0.18 g) of ammonia was added, and ultrasonication was performed for 1 h to promote reaction fusion. The system was then transferred to a hydrothermal reactor and reacted at 180 °C for 24 h to generate the target product. After the reaction was complete, the product was collected by centrifugation at 8000 r / min and dried at 80 °C to obtain SiO2@PZS.

[0049] In step S3, 0.1 g of SiO2@PZS powder was placed in 7.2 g of DMAC and ultrasonically stirred for 1 h until a uniform and stable dispersion system was formed. Then, 10 g of PMIA was slowly added, and ultrasonically stirred for 10 h to obtain a homogeneous mixture, completing the pre-spinning preparation. Afterwards, the spinning solution was drawn up using a disposable syringe equipped with an 18-gauge needle, and the spinning equipment parameters were set as follows: positive voltage 20 kV, negative voltage -1.5 kV, push speed 1.2 mL / h, needle-receiver distance 20 cm, needle stroke 10 mm. The SiO2@PZS@PMIA membrane was successfully prepared.

[0050] The materials prepared in Example 1 were characterized, such as... Figure 1 SEM images of the PZS microspheres prepared in Example 1 at different magnifications; Figure 2 SEM image of SiO2@PZS microspheres prepared in Example 1; as shown Figure 3 The SiO2@PZS@PMIA membrane prepared in Example 1 was examined by transmission electron microscopy, which showed that the membrane had dense pores after electrospinning.

[0051] The following uses traditional commercial diaphragms Celgard and PMIA as Comparative Examples 1 and 2, respectively, to perform performance tests and comparisons with the diaphragm prepared in Example 1 of this invention. Specifically, combustion tests, thermal shrinkage tests, porosity tests, and liquid absorption rate tests were conducted.

[0052] Test Example 1: Combustion Test

[0053] like Figure 4 As shown, the Celgard membrane has a very short burning time, lasting less than 2 seconds, while the PMIA membrane has a significantly longer burning time. The burning time of the PMIA membrane with added modified flame retardant material SiO2@PZS@PMIA membrane is further extended, and there are still obvious residues after it is extinguished. This shows that the addition of SiO2@PZS does indeed improve the flame retardant effect of the PMIA-based spinning membrane.

[0054] Test Example 2: Heat Shrinkage Test

[0055] like Figure 5As shown, traditional commercial separators Celgard, PMIA, and SiO2@PZS@PMIA were subjected to a heat shrinkage experiment under the same temperature gradient. The Celgard separator began to deform severely at only 140℃, while the PMIA and SiO2@PZS@PMIA separators showed almost no change at the same temperature. Subsequently, at 160℃, the Celgard separator had already pyrolyzed, while the PMIA and SiO2@PZS@PMIA separators maintained a relatively good morphology. Between 180℃ and 200℃, the Celgard separator continued to pyrolyze and completely lost its original morphology, while the PMIA separator also showed significant deformation at 200℃. The SiO2@PZS@PMIA separator, however, maintained a relatively intact morphology at 200℃ without significant deformation. This demonstrates that the spun separator prepared by this invention has excellent heat resistance and strong thermal stability, far exceeding that of ordinary commercial separators.

[0056] Test Example 3: Porosity Test

[0057] Porosity is the volume ratio of membrane pores to membrane volume. The pores in the membrane are the pathways for ion flow during the charging and discharging of a lithium-ion battery. High porosity improves ionic conductivity, and a sufficiently high porosity also enhances the liquid absorption rate. The membrane is cut into 17mm diameter discs, and its weight and thickness are measured. The discs are then immersed in a beaker containing n-butanol solution for 1 hour. After immersion, excess n-butanol is wiped off with filter paper, and the weight of the membrane is measured again. The porosity is calculated by dividing the mass difference of the membrane before and after immersion by the mass of n-butanol.

[0058] like Figure 6 As shown, the Celgard membrane has a porosity of only 73.51%, while the PMIA and SiO2@PZS@PMIA membranes have porosities of 318.74% and 322.04%, respectively, which are much higher than the Celgard membrane.

[0059] Test Example 4: Liquid Absorption Rate Test

[0060] The liquid absorption rate of the diaphragm can indirectly indicate its ability to store electrolyte. The test procedure for the liquid absorption rate of the diaphragm is as follows: Cut the diaphragm into 17mm diameter circular pieces and measure the weight of the diaphragm. Then, immerse the diaphragm in a beaker containing electrolyte solution for one hour. After immersion, wipe off the excess electrolyte with filter paper and weigh the diaphragm after immersion. The porosity is calculated by dividing the mass difference of the diaphragm before and after immersion by the mass of the diaphragm before immersion.

[0061] like Figure 7As shown, the Celgard membrane's liquid absorption rate was only 128.53%, while the liquid absorption rates of PMIA and SiO2@PZS@PMIA were 1132.11% and 1071.34%, respectively. Therefore, even with the addition of modified flame-retardant materials to the polyimide (PMIA)-based membrane with a spun structure in this experiment, its liquid absorption rate did not change significantly. This result indicates that the unique structure of the membrane imparted by electrospinning in this application largely determines its excellent liquid absorption rate. Therefore, for this application, the liquid absorption rate of the spun membrane is mainly determined by its unique structure, rather than the addition of flame retardants.

[0062] Example 2: Battery Assembly

[0063] The prepared separators were assembled into batteries in a glove box: First, the Celgard separator, PMIA separator, and the separator prepared in Example 1 were cut into circles with a diameter of 16 mm, and then assembled with the positive electrode and lithium sheet negative electrode of the NCM811 battery, respectively. 1 M LiPF6 and EMC / EC (v / v = 1 / 1) electrolyte were added. The battery assembly sequence was: negative electrode casing—lithium sheet—separator—80 μL electrolyte—positive electrode sheet—stainless steel gasket—spring sheet—positive electrode casing. Finally, the battery was placed in a packaging machine and subjected to a pressure of 5 MPa for 5 seconds to complete the battery assembly. Test Example 5: Cycle test after battery assembly.

[0064] The batteries assembled with different separators in Example 2 were subjected to cycle tests, and the discharge specific capacity change curves of the cycle tests are shown in the figure. Figure 8 and Figure 9 As shown, Figure 8 The figures show the discharge specific capacity variation curves of the batteries at a current density of 0.1C. The first-cycle discharge specific capacities of the batteries equipped with Celgard separators, PMIA separators, and SiO2@PZS@PMIA separators are 220.7, 211.5, and 229.8 mAh g, respectively. -1 Batteries using Celgard separators began to show capacity decay after 30 cycles, with discharge specific capacities of 205.1, 196.8, and 189.1 mAh g at the 30th, 40th, and 50th cycles, respectively. -1 The batteries using PMIA and SiO2@PZS@PMIA separators showed significantly higher discharge specific capacities at the same number of cycles. The SiO2@PZS@PMIA separator battery exhibited discharge specific capacities of 221.2, 214.7, and 220.0 mAh g at 30, 40, and 50 cycles, respectively. -1 .

[0065] Figure 9The discharge specific capacity of batteries equipped with different separators at 0.5C was demonstrated. After the first five activation cycles, the current density decreased to 0.5C starting from the sixth cycle, resulting in a significant decrease in the battery's discharge specific capacity. The Celgard separator battery achieved a discharge specific capacity of 158.9 mAh g at the 0.5C current density in the sixth cycle. -1 The capacity briefly increased to 170mAh g during the 20th lap. -1 The capacity was around 100 mAh / g, but it continued to decrease in subsequent cycles, reaching a discharge specific capacity of 165.4 mAh / g at the 50th cycle. -1 Batteries using PMIA separators and SiO2@PZS@PMIA separators exhibited higher discharge specific capacity, with discharge specific capacities of 199.3 and 210.7 mAh g⁻¹ respectively in the sixth cycle. -1 This is significantly higher than that of Celgard membrane batteries. The discharge specific capacities of PMIA membrane batteries at 10, 30, and 50 cycles are 197.6, 189.9, and 184.5 mAh g, respectively. -1 The battery using the SiO2@PZS@PMIA separator exhibited discharge specific capacities of 208.2, 198.8, and 197.8 mAh g at the 10th, 30th, and 50th cycles, respectively. -1 It exhibits extremely high stability. Therefore, it is evident that the SiO2@PZS@PMIA membrane battery has a higher charge / discharge capacity than the PMIA membrane battery, regardless of whether the current density is 0.1C or 0.5C.

[0066] Test Example 6: Rate Test After Battery Assembly

[0067] The battery was assembled following the same cyclic testing steps, and the battery rate performance test results were obtained. Figure 10 As shown. Due to polarization, the discharge specific capacity of batteries using different separators decreases with increasing rate. The capacity decay of Celgard separator batteries is more pronounced, with discharge specific capacities of 192.7, 180.1, 166.6, 151.1, 127.9, and 104.3 mAh g at 0.1, 0.2, 0.5, 1, 2, and 5C, respectively. -1 The batteries using PMIA separators and SiO2@PZS@PMIA separators showed significantly improved discharge specific capacities at 0.1, 0.2, 0.5, 1, 2, and 5C rates. Especially at high rates, the SiO2@PZS@PMIA batteries exhibited discharge specific capacities of 229.8, 219.3, 210.7, 199.3, 177.3, and 161.3 mAh g at the same current density. -1Both are far superior to Celgard and PMIA batteries. Furthermore, when the current density recovers to 0.1C, the discharge specific capacity of the SiO2@PZS@PMIA battery can still recover to a relatively high level, indicating that these two separators can reduce the polarization of the battery and reduce capacity decay.

[0068] Test Example 7: Lithium Dendrite Growth Test

[0069] The batteries were assembled following the same cyclic testing procedure, but the positive and negative electrodes were replaced with lithium plates, and the batteries were divided into two groups. One group was used to study the batteries under different operating voltage conditions (1 mAh / cm²). 2 1mA / cm 2 2mAh / cm 2 2mA / cm 2 3mAh / cm 2 3mA / cm 2 4mAh / cm 2 4mA / cm 2 5mAh / cm 2 5mA / cm 2 The changes in lithium dendrites, another group of studies the battery at high voltage 5mAh / cm 2 5mA / cm 2 Changes in lithium dendrites.

[0070] Figure 11 The graph shows the cycling of the battery under different operating voltage conditions. It can be seen that as the voltage increases, the battery voltage of the SiO2@PZS@PMIA separator rises steadily and the voltage fluctuation range is stable, while the voltage fluctuation range of the Celgard separator battery is large, and the voltage drops sharply at 180h. The voltage of the PMIA separator battery is relatively stable in the first 180h, and the voltage starts to fluctuate significantly at 240h.

[0071] Figure 12 The image shows the SEM image of the lithium sheet after cycling. It can be seen that the lithium sheet of the SiO2@PZS@PMIA separator battery exhibits a relatively smooth surface at magnifications of 50μm and 10μm, with relatively fine and uniformly distributed particles on the surface.

[0072] Figure 13 The graph shows the battery cycling under high voltage conditions. It can be seen that the SiO2@PZS@PMIA membrane battery can cycle stably for 550 hours under high voltage conditions, while the Celgard membrane battery showed voltage instability in the early stage of cycling. The PMIA membrane battery was relatively stable in voltage for the first 300 hours, after which voltage instability occurred.

[0073] Figure 14This is a SEM image of the lithium wafers after cycling, showing the lithium dendrite ratio of the Celgard separator and the PMIA separator. Figure 12 The lithium dendrite structure of commercially available separators is coarser, exhibiting an irregular granular structure with varying particle sizes and a relatively random distribution at magnifications of 50μm and 10μm. In contrast, the lithium sheet surface of the SiO2@PZS@PMIA separator battery retains a relatively smooth morphology, with finer and more uniformly distributed particles. The addition of flame-retardant microparticles improves the uniformity of the electrode surface, reduces lithium dendrite growth, and facilitates uniform diffusion and deposition of lithium ions, thereby enhancing battery performance and stability.

[0074] Test Example 8: Thermal Runaway Test. The test used a THT-ARC adiabatic accelerated calorimeter to test batteries with three different separators. During the test, the THT-ARC operated in a "heat-wait-search" mode, gradually increasing the battery temperature. Heating was stopped when the battery exhibited self-heating and the temperature rise rate exceeded 0.02℃ / min. The activation energy of the battery was calculated based on the Arrhenius equation using the data obtained from the ARC experiment, thus assessing the risk of thermal runaway. Figure 15 The following table shows the ARC experimental results for three types of separators, and Table 1 below shows the temperature characteristic points of the battery: Table 1 Temperature characteristic points of the battery

[0075] Separator T0 (°C) [T1 (°C)] [T2 (°C)] Celgard 174.9 220.4 505.1 PMIA 182.4 291.0 452.6 SiO2@PZS@PMIA 189.7 240.8 509.9

[0076] pass Figure 15As shown in Table 1, the T0 of the Celgard separator battery is 174.9℃, the PMIA separator battery is 182.41℃, and the SiO2@PZS@PMIA separator battery is 189.7℃. The T0 is due to the SEI film decomposing under heat during battery cycling, causing the battery to release heat. The Celgard separator's T0 is significantly lower than other separators, indicating that the new separator has excellent thermal stability. In terms of time, during the test, the self-heating time of batteries using PMIA and SiO2@PZS@PMIA separators was significantly slower than that of the Celgard separator battery, indicating that the new spun separators can make the batteries safer. The T1 of the Celgard separator battery was 220.4℃, that of the PMIA separator battery was 291.0℃, and that of the SiO2@PZS@PMIA separator battery was 240.8℃, with corresponding times of 300.5 min, 400.2 min, and 573.9 min, respectively. This demonstrates that the SiO2@PZS@PMIA separator significantly improves the battery's heat resistance and flame retardancy. The separator remains stable under heat, without deformation or collapse, greatly delaying the time to thermal runaway. Using the Celgard separator, the times to reach the highest thermal runaway temperature for the PMIA separator and the SiO2@PZS@PMIA separator were 573.4 min, 442.8 min, and 680.7 min, respectively. This time comparison also shows that the PMIA-based separator reduces the battery's risk at high temperatures.

[0077] Figure 16 The diagram shows the activation energies of the three membranes. It can be seen that the activation energies of Celgard membrane, PMIA membrane and SiO2@PZS@PMIA membrane are 0.64, 0.77 and 0.83 eV, respectively. It can be seen that the novel PMIA-based membrane improves the activation energy of the battery in the event of thermal runaway.

[0078] Figure 17 The radar diagrams for the thermal runaway safety of the three separators show that the area of ​​the SiO2@PZS@PMIA separator is larger than that of the commercial separator and the PMIA separator. This indicates that the PMIA-based novel separator reduces the risk of battery failure at high temperatures and improves battery safety.

Claims

1. A poly(m-phenylene isophthalamide)-based electrospun flame-retardant separator, namely a PMIA-based electrospun separator, wherein the PMIA-based electrospun separator is prepared by electrospinning after mixing modified PZS microspheres with PMIA and an organic solvent; wherein the modified PZS microspheres are prepared by in-situ growth of an inorganic SiO2 layer on the surface of flame-retardant polyphosphazene PZS microspheres; wherein the polyphosphazene PZS microspheres are prepared by polymerization reaction between tannic acid and hexachlorocyclotriphosphazene. The preparation process of the polyphosphazene PZS microspheres includes: Tannic acid was dissolved in acetonitrile until completely dissolved to obtain a first solution, wherein the mass ratio of tannic acid to acetonitrile was 1:(250~300); then hexachlorocyclotriphosphazene was added, with the mass ratio of the added hexachlorocyclotriphosphazene to the first solution being 1:(300~350), and the mixture was stirred ultrasonically for 30~60 min to obtain a second solution; then, pyridine solution was slowly added dropwise to the second solution over 1 h, with the mass ratio of the added pyridine solution to the second solution being 1:(20~30), and the reaction was maintained at room temperature for 12 h. Finally, the product was collected by centrifugation at 8000 rpm, washed with acetonitrile and deionized water, and then freeze-dried. The preparation process of the modified PZS microspheres includes: ultrasonically dispersing polyphosphazene PZS microspheres in ethanol as a third solution, wherein the mass ratio of polyphosphazene PZS microspheres to ethanol is 1:(180~240), ultrasonicating for 30~45 min, then adding sodium metasilicate as a precursor, wherein the mass ratio of added sodium metasilicate to the third solution is 1:(15~20), and ultrasonicating with stirring for 30~45 min as a fourth solution, then adding a catalyst, wherein the catalyst is one of hydrofluoric acid, nitric acid, hydrochloric acid, ammonia, triethylamine, or ethylenediamine, and the mass ratio of added catalyst to the fourth solution is 1:(200~250), ultrasonicating for 10~15 min, then transferring to a hydrothermal reactor, maintaining the reaction at 180 ℃ for 24 h, finally collecting the product by centrifugation at 8000 rpm, and drying at 80 ℃ to obtain the product modified PZS microspheres SiO2@PZS; The preparation process of the modified PZS microspheres, PMIA, and organic solvent mixed and electrospun to obtain the spun membrane includes: taking modified PZS microsphere powder, dispersing it in N,N-dimethylacetamide as the fifth solution, the mass ratio of the modified PZS microsphere powder to N,N-dimethylacetamide is 1:(70~75), ultrasonically stirring and dispersing for 1 h, adding PMIA, the mass ratio of the fifth solution to PMIA is 1:(1.3~1.5), continuing ultrasonic stirring and dispersing for 10 h, the obtained mixture is the spinning solution, an appropriate amount of the spinning solution is drawn with a disposable syringe for electrospinning, to obtain the PMIA-based spun membrane; after the electrospinning is completed, the PMIA-based spun membrane is placed in a vacuum oven for vacuum drying for 24 h, thus obtaining the poly(m-phenylene isophthalamide)-based electrospun flame-retardant membrane SiO2@PZS@PMIA.

2. The poly(m-phenylene isophthalamide) electrospun flame-retardant separator as described in claim 1, characterized in that, The electrospinning steps include: using an 18-gauge needle, a positive voltage of 20~30 kV, a negative voltage of -1.5~-2 kV, a pushing speed of 1.2~1.5 mL / h, a needle distance of 15~20 cm from the receiver, and a stroke of 10~12 mm.

3. The poly(m-phenylene isophthalamide) electrospun flame-retardant separator as described in claim 1, characterized in that, The electrospinning steps include: a positive voltage of 20 kV, a negative voltage of -1.5 kV, a pushing speed of 1.2 mL / h, a needle-receiver distance of 20 cm, and a needle stroke of 10 mm.

4. The poly(m-phenylene isophthalamide) electrospun flame-retardant separator as described in claim 1, characterized in that, The mass ratio of the modified PZS microsphere powder to N,N-dimethylacetamide is 1:

72.

5. The poly(m-phenylene isophthalamide) electrospun flame-retardant separator as described in claim 1, characterized in that, The mass ratio of the fifth solution to PMIA was 73:

100.

6. The application of the poly(m-phenylene isophthalamide) electrospun flame-retardant separator as described in claim 1 in the manufacture of lithium-ion battery separators.

7. A lithium-ion battery, the lithium-ion battery comprising the poly(m-phenylene isophthalamide) electrospun flame-retardant separator as described in claim 1.

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