A pi diaphragm containing lithium-conducting ceramic and a preparation method and application thereof

Abstract

The application belongs to the technical field of lithium ion battery separator preparation and application, and relates to a PI separator containing lithium-conducting ceramic and a preparation method and application thereof. The preparation method comprises three core steps of preparing electrospinning solution, electrospinning and high-temperature amination. In the process of preparing the electrospinning solution, lithium-conducting ceramic powder with ultrahigh melting point and thermal inertia is added to uniformly disperse in the PI fiber to form a "physical support skeleton". The ceramic particles do not soften and shrink at high temperature, can limit the thermal motion of the PI fiber, enhance the physical bonding force between the fibers, make the thermal shrinkage rate of the separator significantly lower than that of pure PI, and even close to 0, thereby avoiding the explosion risk caused by short circuit in the lithium battery. The ceramic powder can promote heat conduction, build a unique "heat conduction channel" in the separator, quickly conduct the local heat generated in the battery cycle process, reduce heat accumulation, and delay the occurrence of thermal runaway. At the same time, the wettability and liquid retention capacity of the separator are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery separator preparation technology, and relates to a PI separator containing lithium-conducting ceramics, its preparation method and application. Background Technology

[0002] Electrochemical energy storage technology is one of the most important methods for integrating and developing intermittent (wind power, solar power) new energy sources. Lithium-ion battery systems, as the core energy carrier of energy storage systems, have advantages such as being unrestricted by geographical conditions, fast response time, and ease of large-scale integration, and have gained a huge application market. By the end of 2023, China had a cumulative installed capacity of 86.5 GW for operational power storage projects, accounting for 30% of the global market. Unfortunately, since 2020, several accidents have occurred at energy storage power stations in my country, causing huge economic losses and casualties. This shows that although battery manufacturers have done a lot of work in core materials and system management, the intrinsic safety of batteries remains a serious issue. Therefore, research on the safety of energy storage batteries is urgently needed.

[0003] In reality, with the expansion of application scenarios and the pursuit of high energy density, high-rate charging and discharging, and wide-temperature-range operation, the safety issues of lithium-ion batteries have become increasingly prominent, becoming a bottleneck for their large-scale application. This is because lithium-ion batteries use flammable and explosive organic electrolytes, resulting in a narrow safe operating temperature range. When internal heat distribution is uneven, thermal runaway can easily occur, especially under overcharging and high-temperature environments. The internal separator can rupture due to thermal and mechanical stress, further triggering electrode short circuits, leading to a chain of exothermic reactions and posing a fire risk.

[0004] Currently, research on the safety of energy storage batteries is developing in multiple dimensions, including materials, structure, and system management technologies. By integrating multiple disciplines, the aim is to create a multi-level safety guarantee based on materials, combined with system design and thermal management optimization, and intelligent monitoring and early warning technologies. Comparatively, material safety is the fundamental guarantee for the safety of energy storage batteries. Improvements in material-level safety demonstrate direct, fundamental, and precise protection, and are also an important prerequisite and foundation for effectively integrating thermal management technologies and safety early warning systems. Among these, research on high-safety separators, with its economic efficiency and ease of implementation, has become an important research direction for effectively addressing the safety issues of energy storage batteries. China's domestic lithium battery separator industry started relatively late, but in recent years, it has developed rapidly with the continuous growth of my country's lithium battery industry. Currently, domestic lithium battery separator technology continues to innovate, and companies such as Qingtao, Xingyuan Material, and Enjie have strong competitiveness in terms of production capacity, product quality, and technology research and development. In contrast, the foreign lithium battery separator industry started earlier and has relatively deep technological accumulation. Companies such as Asahi Kasei of Japan, SKI of South Korea, and Toray Industries of Japan occupy important positions in the global lithium battery separator market.

[0005] With the development of lithium-ion battery technology, domestic and foreign separator companies and research institutions have continuously promoted technological innovation, improving the thermal stability and mechanical strength of separators and reducing the risk of battery thermal runaway by improving processes (such as ceramic powder coating) and adopting new materials (such as polyimide). However, overall progress has been slow. In summary, although some progress has been made in the research of high-safety separators for energy storage batteries, there are still problems such as unsatisfactory material performance and immature technology, which require further research. Summary of the Invention

[0006] Based on this, the purpose of this invention is to address the problem of low intrinsic safety of lithium-ion batteries. By innovating the battery separator material and structure, a PI separator containing lithium-conducting ceramics is provided. Applying the separator to lithium-ion batteries can alleviate the risk of short circuits in lithium battery electrodes, enhance the thermal stability of battery operation, reduce the risk of thermal runaway under extreme conditions such as thermal abuse and overcharging, and ensure the thermal safety of lithium battery cycles.

[0007] This invention also provides a method for preparing a PI separator containing lithium-conducting ceramics. The method mainly includes three core steps: preparing an electrospinning solution, electrospinning, and high-temperature decomposition. The raw materials are readily available, the process is simple, and it is easy to scale up production.

[0008] The present invention also provides an application of a PI separator containing lithium-conducting ceramics in a lithium-ion battery and a lithium-ion battery.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing a PI separator containing lithium-conducting ceramic, comprising the following steps: S1, organic diamine, organic acid anhydride, and lithium-conducting ceramic particles are added to an organic solvent and mixed thoroughly to obtain a spinning precursor solution; S2, electrospinning the spinning precursor solution described in S1 to obtain a spun film; S3, the spun membrane described in S2 is first dried, then subjected to programmed temperature rise heat treatment, and finally cooled to obtain the PI separator containing lithium-conducting ceramic.

[0010] Further, the organic diamine includes 4,4'-diaminodiphenyl ether, the organic anhydride includes 4,4'-biphenyl ether dianhydride, the organic solvent includes N,N-dimethylacetamide, and the lithium-conducting ceramic particles include lithium lanthanum zirconium tantalum oxide particles, the molecular formula of which is Li. 6.4 La3Zr 1.4 Ta 0.6 O 12 Its particle size is <100nm; Furthermore, the lithium lanthanum zirconium tantalum oxide particles are prepared by a solid-state reaction process; the preparation process includes the following steps: (1) Mix Li2CO3, La2O3, ZrO2 and Ta2O5 in stoichiometric ratio, grind them and heat them at 850~950℃ for 5~7 hours to obtain solid powder; (2) The solid powder is ground and mixed with Al2O3, and then cold isostatically pressed at a pressure of 320~340 MPa for 1~3 minutes to obtain a green body; the amount of Al2O3 added accounts for 1.1~1.3% of the mass of the solid powder; (3) The blank is annealed at 1130~1150°C for 14~18 hours in an atmosphere covered with the same master powder to obtain the lithium lanthanum zirconium tantalum oxide particles.

[0011] Further, in S1, the molar ratio of the organic diamine and the organic anhydride is 0.995~1.005:1, and the added mass of the lithium-conducting ceramic particles is 1~5wt% of the total mass of the organic diamine, the organic anhydride and the lithium-conducting ceramic particles; the organic anhydride is added in batches, including a first batch of organic anhydride and a second batch of organic anhydride, and the mass ratio of the first batch of organic anhydride and the second batch of organic anhydride is 1~1.02:1.

[0012] Furthermore, the preparation of the spinning precursor solution in S1 includes the following steps: S11, at 25±5℃, the organic diamine is added to the organic solvent and stirred at 400~600r / min for 20~40 minutes to obtain solution A; In step S12, at 25±5℃, the first batch of organic acid anhydride and the lithium-conducting ceramic particles are added together to solution A in step S11 and mixed to obtain solution B. Then, the second batch of organic acid anhydride is added to solution B, and after stirring and dissolving, the spinning precursor solution is obtained. The stirring is preferably magnetic stirring at a speed of 500±50 r / min for 1~2 h.

[0013] Furthermore, the electrospinning parameters described in S2 are: positive pressure of 20~30KV, negative pressure of -10~-14V, pushing speed of 0.1~0.3mL / min, and translation distance of 180~190cm.

[0014] Furthermore, the drying conditions described in S3 are: a temperature of 55~65℃ and a time of 4~5 hours.

[0015] Furthermore, the conditions for the programmed temperature rise heat treatment described in S3 are as follows: the initial temperature is 25~35℃, the temperature is increased to 95~105℃ for 35~45 minutes and held for 55~65 minutes, the temperature is further increased to 190~210℃ for 45~55 minutes and held for 55~65 minutes, and finally the temperature is increased to 290~310℃ for 45~55 minutes and held for 110~130 minutes.

[0016] The present invention further provides a PI separator containing lithium-conducting ceramic, which is prepared by the above-described method for preparing a PI separator containing lithium-conducting ceramic.

[0017] The present invention further provides an application of the above-mentioned PI separator containing lithium-conducting ceramics in lithium-ion batteries.

[0018] The present invention further provides a lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the separator is the aforementioned PI separator containing lithium-conducting ceramic.

[0019] The beneficial effects of this invention are: The present invention provides a method for preparing a PI separator containing lithium-conducting ceramics, comprising three core steps: preparing an electrospinning solution, electrospinning, and high-temperature decomposition. By adding pre-ground lithium-conducting ceramic powder during the preparation of the electrospinning solution, the ceramic powder, possessing an ultra-high melting point and thermal inertness, can form a "physical support framework" when uniformly dispersed within the PI fibers. At high temperatures, the ceramic particles do not soften or shrink, thus limiting the thermal movement of the PI fibers. The resulting separator exhibits a significantly lower thermal shrinkage rate compared to pure PI, even approaching zero, avoiding the risk of explosion caused by short circuits. The ceramic powder composite promotes the thermal conductivity of the fiber membrane, rapidly conducting localized heat generated during battery cycling by constructing "heat conduction channels" within the separator, reducing heat accumulation and delaying thermal runaway. Applying this separator to lithium-ion batteries can mitigate the risk of short circuits in lithium battery electrodes, enhance battery thermal stability, reduce the risk of thermal runaway under extreme conditions such as thermal abuse and overcharging, and ensure the thermal safety of lithium battery cycling. Simultaneously, the wettability and liquid retention capacity of this separator are significantly improved. Attached Figure Description

[0020] To more clearly illustrate the technical solution of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the preparation process of the PI separator containing lithium-conducting ceramics in this invention; Figure 2 The images show SEM images of the diaphragms prepared in Examples 1, 2, 1, and 5 of this invention at high magnification. In the images, a is the morphology of the diaphragm in Example 2, b is the morphology of the diaphragm in Example 1, c is the morphology of the diaphragm in Comparative Example 1, and d is the morphology of the diaphragm in Comparative Example 5. The scale bar is 3 μm. Figure 3 The images show SEM test results of the composite nanoscale silica polyimide fiber membrane material in Comparative Example 4 of this invention. In the images, the scale bar of image a is 5 μm and the scale bar of image b is 20 μm. Figure 4 The images show SEM images of the diaphragm prepared in Example 1 of this invention at low magnification. In the images, a shows the surface morphology with a scale bar of 20 μm, and b shows the cross-sectional morphology with a scale bar of 80 μm. Figure 5 The figures show the electrolyte wettability test results of the diaphragms in Examples 1, 2, and 3 of this invention; in the figures, PI+ceramic powder is the diaphragm in Example 1, PI is the diaphragm in Comparative Example 3, and PP / PE / PP is the diaphragm in Comparative Example 2. Figure 6 The figures show the test results of the thermal shrinkage performance of the diaphragms in Example 1 and Comparative Example 2 of this invention. In the figures, PI+ceramic powder is the diaphragm in Example 1, and PP / PE / PP is the diaphragm in Comparative Example 2. The temperature in Figure a is 100℃, the temperature in Figure b is 150℃, the temperature in Figure c is 180℃, and the temperature in Figure d is 200℃. Figure 7 The figures show the thermogravimetric test results of the diaphragms in Example 1 and Comparative Example 2 of this invention. In the figures, PI+ceramic powder is the diaphragm in Example 1, and PP / PE / PP is the diaphragm in Comparative Example 2. Figure a is the thermogravimetric test curve of the PI+ceramic powder diaphragm, Figure b is the thermogravimetric test curve of the PP / PE / PP diaphragm, and Figure c is the heat absorption curve of the two diaphragm materials. Figure 8 The figures show the tensile strength test results of the diaphragms in Example 1 and Comparative Example 2 of this invention. In the figures, PI+ceramic powder is the diaphragm in Example 1, and PP / PE / PP is the diaphragm in Comparative Example 2. Figure 9 The figures show the tensile strength test results of the diaphragms in Example 1 and Comparative Example 2 of this invention. In the figures, PI+ceramic powder is the diaphragm in Example 1, and PP / PE / PP is the diaphragm in Comparative Example 2. Figure a shows the mercury intrusion porosimetry curve corresponding to the composite diaphragm, Figure b shows the mercury intrusion porosimetry curve corresponding to the commercial three-layer diaphragm, Figure c shows the pore size distribution curve, and Figure d shows the pore size distribution density function. Figure 10 The figures show the thermal stability test results of lithium-ion batteries containing the separators in Example 1 and Comparative Example 2 of this invention. Figure a shows the test results of the battery containing the separator in Example 1, and Figure b shows the test results of the battery containing the separator in Comparative Example 2. Figure 11 The lithium-ion transference number calculation results are for lithium-ion batteries containing the separator in Example 1 of this invention; Figure 12The lithium-ion transference number is calculated for the lithium-ion battery containing the separator in Comparative Example 2 of this invention. Figure 13 The lithium-ion transference number is calculated for a lithium-ion battery containing the separator in Comparative Example 4 of this invention. Figure 14 The figures show the thermal runaway performance test results of lithium-ion pouch batteries (with a capacity of approximately 1.5 Ah) containing the separators from Examples 1 and 2 of this invention. In the figures, figure a is the thermal runaway temperature curve of the separator in Comparative Example 2, figure b is the thermal runaway temperature curve of the separator in Example 1, figure c is the thermal runaway scene diagram of the separator in Comparative Example 2, and figure d is the thermal runaway scene diagram of the separator in Example 1. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All mentioned embodiments are implemented based on the technical solutions of the present invention, and detailed implementation processes are given. However, it should be stated that the scope of protection of the present invention is not limited to the following embodiments.

[0023] like Figure 1 The schematic diagram shown illustrates the preparation process. This invention provides a method for preparing a PI separator containing lithium-conducting ceramics. The method mainly includes three core steps: preparing an electrospinning solution, performing electrospinning, and high-temperature decomposition. First, a PAA precursor solution (i.e., a spinning precursor solution) is prepared by magnetic stirring. Then, the PAA solution is poured into a syringe, and a suitable needle is selected. The syringe is placed in an electrospinning apparatus, and parameters are set (positive pressure 20~30KV, negative pressure -10~-14V, pushing speed 0.1~0.3mL / min, translation distance 180~190cm) for spinning. Finally, the spun separator is placed in a drying oven. After drying in a medium temperature range (55-65℃ for 4-5 hours), the polyimide (PI) nanofiber separator containing lithium-conducting ceramics is cut and clamped with a metal mesh for high-temperature calcination (initial temperature 25-35℃, heating for 35-45 minutes to 95-105℃ and holding for 55-65 minutes, continuing to heat for 45-55 minutes to 190-210℃ and holding for 55-65 minutes, and finally heating for 45-55 minutes to 290-310℃ and holding for 110-130 minutes). Finally, a usable polyimide (PI) separator containing lithium-conducting ceramics is obtained, which is a nanofiber membrane.

[0024] The following embodiments provide detailed implementation procedures for the technical solutions of the present invention. Unless otherwise specified, the experimental methods used in the following experimental examples are conventional methods; unless otherwise specified, the materials and reagents used are commercially available.

[0025] Example 1

[0026] (1) Preparation of spinning precursor solution Weigh 1.108 g of 4,4'-diaminodiphenyl ether into a beaker, add 10 mL of N,N-dimethylacetamide solvent, and stir at 500 r / min for 30 min at a constant temperature of 25℃. After the 4,4'-diaminodiphenyl ether is completely dissolved, weigh 0.841 g of 4,4'-biphenyl ether dianhydride and 0.1 g of ground lithium lanthanum zirconium tantalum oxide ceramic powder (Li). 6.4 La3Zr 1.4 Ta 0.6 O 12 The particles (particle size <100nm) were added together with the solvent, and then 0.82g of 4,4'-biphenyl ether dianhydride was weighed and added to the solvent and stirred at a constant temperature (magnetic stirring, speed 500r / min, 1h) until completely dissolved to obtain a uniform spinning precursor solution; the amount of ceramic powder added was 3.49% of the total amount of raw materials.

[0027] The lithium-lanthanum-zirconium-tantalum-oxygen ceramic powder was prepared via a solid-state reaction process. Specifically, Li₂CO₃ (Sinopharm Chemical Reagent Co., Ltd., purity 99.99%, excess 20%), La₂O₃ (Sinopharm Chemical Reagent Co., Ltd., purity 99.99%), ZrO₂ (Aladdin Company, purity 99.99%), and Ta₂O₅ (Sinopharm Chemical Reagent Co., Ltd., purity 99.99%) were mixed in stoichiometric proportions, thoroughly ground using an agate mortar and pestle, and then heated at 900°C for 6 hours. The resulting powder was ball-milled with 1.2% (by mass) Al₂O₃ and cold isostatically pressed at 330 MPa for 2 minutes. The prepared green body was annealed at 1140°C for 16 hours in an atmosphere covered with the same masterbatch powder.

[0028] (2) Electrospinning Pour the uniform spinning precursor solution obtained in step (1) into a clean disposable syringe, remove air bubbles from the syringe, place the syringe on the electrospinning device and fix it, adjust the injection position so that it can just push the syringe, wrap the aluminum foil around the roller to receive the spun filament, and clamp the alligator clip in the middle of the syringe needle. Then set the parameters: positive pressure to 24KV, negative pressure to -12V, injection speed to 0.2ml / min, translation distance to 180-190cm, save and click start, divide the spinning time on the control panel by 2, pause when half the time has elapsed, replace the second aluminum foil and continue the second spinning. The electrospinning device used in this invention is: ET-2535X electrospinning machine (brand: Beijing Yongkang Leyue).

[0029] (3) Heat treatment forming The tin foil that underwent spinning in step (2) was placed in a drying oven at 60°C and dried for 4-5 hours. Then, the polyimide nanofiber separator containing lithium lanthanum zirconium tantalum oxide ceramic powder was peeled off and cut. After cutting, it was placed in a muffle furnace and a heating program was executed: first, the initial temperature in the furnace was set to 30°C, then the temperature was increased to 100°C for 40 minutes and held at this temperature for 60 minutes; then the temperature was increased to 200°C for 50 minutes and held at this temperature for 60 minutes; finally, the temperature was increased to 300°C for 50 minutes and held at this temperature for 120 minutes to complete the entire heat treatment process. After the heat treatment was completed, the PI separator containing lithium-conducting ceramic was removed after the temperature dropped to room temperature.

[0030] Example 2

[0031] The difference between this embodiment and embodiment 1 is that the amount of ceramic powder added in step (1) is 1.77%.

[0032] Comparative Example 1 The difference between this comparative example and Example 1 is that the amount of ceramic powder added in step (1) is 6.74%.

[0033] Comparative Example 2 It uses a commercially available three-layer PP / PE / PP separator (brand: Celgard). Comparative Example 3 Pure PI nanofiber membrane Comparative Example 4 The difference between this comparative example and Example 1 is that the lithium lanthanum zirconium tantalum oxide ceramic powder in step (1) is replaced with silicon oxide (SiO2).

[0034] Comparative Example 5 The difference between this comparative example and Example 1 is that the amount of ceramic powder added in step (1) is 9.78%.

[0035] Implementation effect analysis

[0036] (1) Surface morphology test The morphology of the membranes prepared in Examples 1 and 2, and Comparative Examples 1 and 4 was measured using scanning electron microscopy. The SEM results are shown below. Figures 2-4 As shown.

[0037] from Figure 2 As can be seen from the data, the PI separators containing lithium-conducting ceramics in Examples 1 and 2 (with ceramic powder addition amounts of 3.49% and 1.77%, respectively) exhibit clearly visible fiber surface particles and good morphological uniformity. Figure 2(See Figures a and b in the original text). However, the PI membranes in Comparative Examples 1 and 5 (with ceramic powder content of 6.74% and 9.87%, respectively) exhibited fiber breakage and structural collapse after heat treatment due to the excessively high amount of ceramic powder. Figure 2 (Figures c and d in the diagram).

[0038] from Figure 3 As can be seen from the above, the composite nanoscale silica polyimide fiber membrane material in Comparative Example 4 exhibits non-uniformity in fiber diameter of the composite silica particles under high-magnification electron microscopy. Figure 3 (Figure a in the image) This also affects the surface smoothness of the film at the microscopic level; under low-magnification scanning electron microscopy, droplets are easily observed. Figure 3 (Figure b in the text).

[0039] The overall surface morphology and cross-sectional morphology of the PI separator containing lithium-conducting ceramic in Example 1 were further tested, and the test results are as follows: Figure 4 As shown. From Figure 4 As can be seen, the diaphragm presents a continuous three-dimensional network-like fiber skeleton, forming an interconnected porous structure; the nano-sized ceramic particles are uniformly dispersed and tightly attached to the surface and pores of the PI fibers, without obvious agglomeration or phase separation. It retains the high porosity structure of the PI matrix and achieves uniform composite of the ceramic phase. The interface is tightly bonded and does not damage the network skeleton of PI. This structure takes into account both the porosity characteristics required for electrolyte wetting and the mechanical and thermal stability potential enhanced by the ceramic phase.

[0040] (2) Electrolyte wettability test A lithium-ion battery electrolyte (model: KLD-TF05, a high-performance lithium-ion electrolyte using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the solute, which uses ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) mixed in a 1:1:1 volume ratio as the solvent) was dropped onto the surface of the separators in Example 1, Comparative Example 2, and Comparative Example 3, respectively. The contact angles were then measured using a contact angle meter, and the results are shown below. Figure 4 As shown.

[0041] from Figure 5As can be seen, in Comparative Example 2, the electrolyte contact angle of the traditional commercial PP / PE / PP membrane remained consistently between 47° and 50°, with almost no significant decrease, indicating poor wettability of the electrolyte. In Comparative Example 3, the electrolyte contact angle of the commercial pure PI nanofiber membrane gradually decreased from an initial 36°, reaching 0° at 3 seconds (when the droplet was fully spread), demonstrating superior wettability compared to the traditional PP / PE / PP membrane. In Example 1, the electrolyte contact angle of the PI membrane (PI + ceramic powder) composite membrane containing lithium-conducting ceramics was initially only 27°, and it dropped to 0° within 2 seconds, indicating a faster droplet spreading speed. This is because the hydrophilic groups (such as hydroxyl groups) on the surface of the ceramic powder enhance the interfacial affinity between the membrane and the electrolyte. The results clearly demonstrate that the electrolyte wettability of the PI membrane containing lithium-conducting ceramics is significantly better than that of pure PI and traditional PP / PE / PP membranes. The superior wettability helps the electrolyte to quickly fill the membrane pores, creating a more stable ion transport channel for the battery.

[0042] (3) Thermal stability test The PI separator containing lithium-conducting ceramics prepared in Example 1 and the commercial PP / PE / PP separator from Comparative Example 2 were respectively cut to the size required for CR2032 button cells and placed in the battery case. Then, the separators were heated to the battery case using a heating device, and the thermal shrinkage of the separators was observed and recorded. The results are as follows: Figure 6 As shown.

[0043] from Figure 6 As can be seen, at 100℃, both types of diaphragms maintained their initial circular shape without significant deformation. Figure 6 (Figure a in the diagram); at 150℃, both maintained structural stability and showed no significant changes. Figure 6 (See Figure b in the original text); When the temperature rises to 180°C, the commercial PP / PE / PPI separator in Comparative Example 2 begins to shrink and develops surface wrinkles, while the PI separator containing lithium-conducting ceramics in Example 1 maintains a flat, circular structure. Figure 6 (See Figure c in the original text); at 200°C, the shrinkage and deformation of the commercial PP / PE / PP separator in Comparative Example 2 were further aggravated, and the structural integrity was damaged, while the PI separator containing lithium-conducting ceramics in Example 1 only slightly changed color and still maintained good morphology and structural stability. Figure 6 (See Figure d in the diagram). This result clearly demonstrates that the PI separator containing lithium-conducting ceramics has superior high-temperature stability compared to commercial PP / PE / PP separators, maintaining structural integrity at higher temperatures and improving the thermal safety performance of the battery.

[0044] To investigate the reasons for the changes in thermal stability, this invention used a thermogravimetric analyzer to perform thermogravimetric tests on the PI membrane containing lithium-conducting ceramics prepared in Example 1 and the commercially pure PI membrane in Comparative Example 2. The test results are as follows: Figure 7 As shown.

[0045] Figure 7 Figures a and b in the figure are thermogravimetric test curves, where the black curve corresponds to the change in total material weight on the left vertical axis, and the red curve corresponds to the right vertical axis, representing the relationship between the rate of weight change and temperature. The red curve directly reflects the main temperature of material weight loss. The PI membrane material containing lithium-conducting ceramics in Example 1 decomposes and loses weight at around 600℃, while the commercial PP / PE / PP membrane in Comparative Example 2 decomposes and loses weight at around 270℃. Its thermal stability is far inferior to that of the PI membrane material containing lithium-conducting ceramics in Example 1. Figure 7 Figure c shows the endothermic curves for the two membrane materials. It can be seen from the figure that the commercial PP / PE / PP membrane exhibits a phase transition peak between polymers PP and PE between 100 and 160℃. At 200-210℃, both substances undergo an oxidation reaction, which is exothermic. In contrast, the PI membrane containing lithium-conducting ceramics shows no significant phase transition throughout the entire temperature curve.

[0046] (4) Mechanical strength test The PI separator containing lithium-conducting ceramics prepared in Example 1 and the commercial PP / PE / PP separator in Comparative Example 2 were tested using an electronic universal testing machine. The test results are as follows: Figure 8 As shown.

[0047] from Figure 8 As can be seen, the tensile properties of the PI separator containing lithium-conducting ceramics are comparable to those of commercial PP / PE / PP separators, which can meet the requirements of lithium batteries for the tensile properties of separators.

[0048] (5) Pore structure test The pore structures of the PI membrane containing lithium-conducting ceramics prepared in Example 1 and the commercial PP / PE / PP membrane in Comparative Example 2 were tested using mercury intrusion porosimetry. The test results are as follows: Figure 9 test.

[0049] Figure 9In Figures a and b, the horizontal axis represents the pore size (as pressure gradually increases, the indentable pore size decreases), and the vertical axis represents the cumulative mercury ingress volume during the pressure increase process. The red line is the mercury ingress curve, and the black line is the mercury regress curve; mercury cannot completely regress. In Figure c, the horizontal axis represents the pore size, and the vertical axis represents the pore volume corresponding to the pore size. This figure shows the pore volume distribution curve for the corresponding material pore size. In Figure d, the horizontal axis represents the pore size, and the vertical axis represents the pore volume divided by the pore size. Taking a cylindrical pore as an example, the pore volume divided by the cross-sectional area is the pore length. The area and diameter of the circle are positively correlated. As can be seen from the figure, the pore size of the PI separator containing lithium-conducting ceramics exhibits a multi-level distribution.

[0050] (6) Lithium-ion battery performance testing The PI separator containing lithium-conducting ceramics prepared in Example 1 and the commercial PP / PE / PP separator in Comparative Example 2 were applied to lithium-ion batteries to prepare lithium-ion batteries. This experiment used a button cell (CR2032) packaging method to prepare a lithium symmetric battery. The specific steps are as follows: Material preparation: In an argon-filled glove box (water and oxygen content <0.1 ppm), prepare 16 mm diameter lithium metal sheets as positive and negative electrodes, 19 mm diameter PI diaphragms containing lithium-conducting ceramics and commercial PP / PE / PP diaphragms, as well as KLD-TF series electrolytes (taking KLD-TF05 as an example). Also prepare CR2032 button cell casings, gaskets, spring contacts, and other components.

[0051] Assembly Process: Place a clean positive electrode shell in a glove box, then place a 16 mm diameter lithium metal sheet as the positive electrode and a 19 mm diameter separator in sequence. Slowly add KLD-TF05 electrolyte (1.0 M LiTFSI in EC:DMC:DEC=1:1:1 vol%) to the separator, using approximately 50-70 μL, ensuring complete wetting of the separator. Next, place the 16 mm diameter lithium metal sheet as the negative electrode, followed by the gasket and spring clip. Cover with the negative electrode shell and seal using a button cell sealing machine under 5-10 MPa pressure. After sealing, allow the battery to stand at room temperature for 4-6 hours to allow the electrolyte to fully wet the electrodes and separator before testing.

[0052] Battery safety was tested as follows: Both types of batteries were first charged to 3.65V. Then, they were placed in an oven and heated sequentially from 25℃ to 50℃, 100℃, 150℃, and 180℃ at a rate of 3℃ / min, and held at each temperature for 30 minutes to test battery safety. The test results are as follows. Figure 10 As shown.

[0053] Figure 10The results show that the coin cell based on the PI separator containing lithium-conducting ceramic exhibits high thermal stability with a slight decrease in voltage throughout the temperature rise from 25℃ to 180℃. In contrast, the coin cell based on the commercial PP / PE / PP separator, while maintaining a stable voltage at 150℃, rapidly drops below 1V when the temperature rises to 180℃. This trend clearly demonstrates that the commercial PP / PE / PP separator completely melts at 180℃, accompanied by structural shrinkage, causing a short circuit between the positive and negative electrodes and resulting in a rapid voltage drop.

[0054] (7) Lithium-ion transference number test Lithium-ion batteries were prepared by applying the PI separator containing lithium-conducting ceramics prepared in Example 1, the commercial PP / PE / PP separator in Comparative Example 2, and the separator in Comparative Example 4 to lithium-ion batteries. The battery preparation method was the same as that used in the lithium-ion battery performance testing. Impedance testing was performed on the lithium-ion batteries, and the lithium-ion transference number was calculated based on the test results. The calculation formula is: ( In the formula, I0 and I s R0 and Rs represent the currents under the initial and steady-state conditions, respectively; R0 and Rs represent the AC resistances under the initial and steady-state conditions, respectively; ΔV represents the constant polarization potential (10 mV). The test results are as follows: Figures 11-13 As shown.

[0055] from Figures 11-13 As can be seen from the example, the lithium ion transference number of the membrane material obtained by the preparation method provided by the present invention in Example 1 is 0.42, which is much higher than the lithium ion transference number (0.25) of the fiber membrane based on silicon oxide support and the lithium ion transference number (0.35) of the commercial PP / PE / PP membrane.

[0056] (8) Battery thermal runaway performance test The PI separator containing lithium-conducting ceramics prepared in Example 1 and the commercial PP / PE / PP separator in Comparative Example 2 were respectively applied to lithium-ion soft-pack batteries. The positive and negative electrodes of the soft-pack batteries were commercial lithium iron phosphate and graphite, manufactured by Tianmu Lake Advanced Energy Storage Metal Research Institute Co., Ltd. The electrolyte used was 1M LiPF6 dissolved in an equal volume ratio of EC+DEC+DMC. The thermal runaway test method was mainly constant current charging with a charging current of 1A. The test results are as follows. Figure 14 As shown.

[0057] from Figure 14 As can be seen, the highest detected temperature of thermal runaway in pouch cells based on commercial PP / PE / PP separators exceeds 200℃. Figure 14 Figure a in the diagram shows the thermal runaway phenomenon observed at the same time. Figure 14(Figure c in the figure), while the soft-pack battery assembled based on the composite separator in this invention has a maximum temperature of less than 80°C ( Figure 14 (See Figure d in the diagram), and no thermal runaway occurred during the entire process.

[0058] In summary, the preparation method of the PI separator containing lithium-conducting ceramics provided by this invention includes three core steps: preparing an electrospinning solution, electrospinning, and high-temperature decomposition. By adding pre-ground lithium-conducting ceramic powder during the preparation of the electrospinning solution, the ceramic powder, with its ultra-high melting point and thermal inertia, can form a "physical support framework" when uniformly dispersed in the PI fibers. At high temperatures, the ceramic particles do not soften or shrink, limiting the thermal movement of the PI fibers. This significantly reduces the thermal shrinkage rate of the separator compared to pure PI, even approaching zero, thus avoiding the risk of explosion caused by short circuits. The ceramic powder has high thermal conductivity, which can construct "heat conduction channels" within the separator, rapidly conducting localized heat generated during battery cycling, reducing heat accumulation, and delaying thermal runaway. Applying this separator to lithium-ion batteries can alleviate the risk of short circuits in lithium battery electrodes, enhance battery thermal stability, reduce the risk of thermal runaway under extreme conditions such as thermal abuse and overcharging, and ensure the thermal safety of lithium battery cycling. Simultaneously, the wettability and liquid retention capacity of this separator are significantly improved.

[0059] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a PI separator containing lithium-conducting ceramic, characterized in that, Includes the following steps: S1, add organic diamine, organic acid anhydride and lithium-conducting ceramic particles to an organic solvent and mix well to obtain a spinning precursor solution; S2, electrospinning the spinning precursor solution described in S1 to obtain a spun film; S3, the spun membrane described in S2 is first dried, then subjected to programmed temperature rise heat treatment, and finally cooled to obtain the PI separator containing lithium-conducting ceramic.

2. The method for preparing a PI separator containing lithium-conducting ceramic according to claim 1, characterized in that, The organic diamine includes 4,4'-diaminodiphenyl ether, the organic acid anhydride includes 4,4'-biphenyl ether dianhydride, the organic solvent includes N,N-dimethylacetamide, and the lithium-conducting ceramic particles include lithium lanthanum zirconium tantalum oxide particles, the molecular formula of which is Li. 6.4 La3Zr 1.4 Ta 0.6 O 12 Its particle size is <100nm.

3. The method for preparing a PI separator containing lithium-conducting ceramic according to claim 1, characterized in that, The molar ratio of the organic diamine and the organic anhydride in S1 is 0.995~1.005:1, and the added mass of the lithium-conducting ceramic particles is 1~5wt% of the total mass of the organic diamine, organic anhydride and lithium-conducting ceramic particles; the organic anhydride is added in batches, including a first batch of organic anhydride and a second batch of organic anhydride, and the mass ratio of the first batch of organic anhydride and the second batch of organic anhydride is 1~1.02:

1.

4. The method for preparing a PI separator containing lithium-conducting ceramic according to claim 3, characterized in that, The preparation of the spinning precursor solution described in S1 includes the following steps: S11, at 25±5℃, the organic diamine is added to the organic solvent and stirred at 400~600r / min for 20~40 minutes to obtain solution A; S12, at 25±5℃, the first batch of organic acid anhydride and the lithium-conducting ceramic particles are first added to solution A in S11 and mixed to obtain solution B. Then, the second batch of organic acid anhydride is added to solution B, and after stirring and dissolving, the spinning precursor solution is obtained.

5. The method for preparing a PI separator containing lithium-conducting ceramic according to claim 1, characterized in that, The electrospinning parameters described in S2 are: positive pressure of 20~30KV, negative pressure of -10~-14V, pushing speed of 0.1~0.3mL / min, and translation distance of 180~190cm.

6. The method for preparing a PI separator containing lithium-conducting ceramic according to claim 1, characterized in that, The drying conditions described in S3 are: temperature of 55~65℃ and time of 4~5 hours.

7. The method for preparing a PI separator containing lithium-conducting ceramic according to claim 1, characterized in that, The conditions for the programmed temperature rise heat treatment described in S3 are as follows: the initial temperature is 25~35℃, the temperature is increased to 95~105℃ for 35~45 minutes and held for 55~65 minutes, the temperature is further increased to 190~210℃ for 45~55 minutes and held for 55~65 minutes, and finally the temperature is increased to 290~310℃ for 45~55 minutes and held for 110~130 minutes.

8. A PI separator containing lithium-conducting ceramic, characterized in that, It is prepared using the method for preparing the PI separator containing lithium-conducting ceramic as described in any one of claims 1 to 7.

9. The application of the PI separator containing lithium-conducting ceramic as described in claim 8 in a lithium-ion battery.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, characterized in that, The separator is the PI separator containing lithium-conducting ceramic as described in claim 8.

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