Ceramic composite diaphragm for lithium battery and preparation method of ceramic composite diaphragm

Abstract

The invention discloses a ceramic composite diaphragm for a lithium battery and a preparation method of the ceramic composite diaphragm, and belongs to the technical field of lithium ion battery diaphragms. The ceramic composite diaphragm for the lithium battery comprises a base membrane and a composite ceramic coating coated on the surface of the base membrane, the composite ceramic coating is prepared from the following raw material components in parts by mass: 30 to 40 parts of modified flaky aluminum oxide, 0.2 to 0.8 part of a dispersing agent, 2 to 4 parts of an adhesive, 6 to 12 parts of a thickening agent, 0.1 to 0.5 part of a wetting agent and 42 to 60 parts of water; the modified flake alumina is obtained by modifying flake alumina with a silane coupling agent; wherein p-(triethoxysilyl) acetophenone is adopted as the silane coupling agent; the flaky aluminum oxide is a two-dimensional aluminum oxide nanosheet prepared by a template method; the thickening agent is obtained by compounding an antioxidant and lithium polyacrylate; 3, 5-di-tert-butyl-4-hydroxybenzoic acid methyl ester is adopted as the antioxidant; the ceramic composite diaphragm for the lithium battery prepared by the preparation method disclosed by the invention is relatively good in high temperature resistance, wettability and ionic conductivity.

Description

Technical Field

[0001] This invention relates to a ceramic composite separator for lithium batteries and its preparation method. Background Technology

[0002] With the rapid development of portable electronic devices, electric vehicles, and large-scale energy storage systems, lithium-ion batteries have become one of the most important electrochemical energy storage devices due to their high energy density, long cycle life, and low self-discharge rate. The separator, a key component of lithium-ion batteries, is located between the positive and negative electrodes. Its main function is to isolate the electrodes to prevent short circuits while allowing lithium ions to pass through smoothly during charging and discharging. Therefore, the performance of the separator directly affects the battery's safety, cycle stability, and rate performance.

[0003] Currently, commercial lithium-ion batteries widely use polyolefin microporous membranes, such as polyethylene (PE) and polypropylene (PP) and their composite membranes. These membranes possess good mechanical strength, chemical stability, and ionic conductivity, but exhibit significant performance defects at high temperatures. When the battery operates at high temperatures or under abnormal conditions, the thermal stability of polyolefin membranes is poor; they typically begin to shrink at around 130°C and may melt above 160°C, leading to direct contact between the positive and negative electrodes, causing internal short circuits and seriously threatening battery safety. Furthermore, polyolefin membranes have poor wettability to the electrolyte and are prone to aging and deformation during long-term cycling, affecting the uniform transport of lithium ions, exacerbating lithium dendrite growth, and thus reducing the battery's cycle stability and lifespan.

[0004] To address these challenges, researchers are dedicated to developing novel membrane materials with excellent high-temperature resistance and good electrochemical stability. Among these, ceramic composite membranes have attracted significant attention due to their outstanding thermal stability and mechanical strength. By coating a polyolefin substrate with a layer of inorganic ceramic particles (such as alumina, silica, boehmite, etc.), the heat resistance of the membrane can be significantly improved, thermal shrinkage at high temperatures can be suppressed, and the membrane's affinity for the electrolyte and its electrolyte retention capacity can be enhanced, thereby improving the battery's cycle performance and safety.

[0005] However, existing ceramic composite separators still have some shortcomings. For example, the weak bonding between ceramic particles and the polymer substrate may cause the coating to detach during battery cycling, affecting the long-term stability of the battery. In addition, the uniformity and pore structure of the coating are difficult to control precisely, which may affect ion transport efficiency. Therefore, developing a ceramic composite separator for lithium batteries that combines excellent high-temperature resistance, good ionic conductivity, and high cycle stability, and providing a scalable and cost-effective preparation method, is of great significance for improving the overall performance and safety of lithium-ion batteries. Summary of the Invention

[0006] The purpose of this invention is to provide a ceramic composite separator for lithium batteries and its preparation method, so as to solve the technical problems mentioned in the background art.

[0007] The technical solution to achieve the objective of this invention is: In a first aspect, the present invention provides a ceramic composite separator for lithium batteries, comprising a base film and a composite ceramic coating applied to the surface of the base film; the raw material components of the composite ceramic coating, by mass parts, include 30-40 parts of modified flake alumina, 0.2-0.8 parts of dispersant, 2-4 parts of binder, 6-12 parts of thickener, 0.1-0.5 parts of wetting agent, and 42-60 parts of water.

[0008] Furthermore, the modified lamellar alumina is obtained by modifying lamellar alumina with a silane coupling agent.

[0009] Furthermore, the sheet-like alumina is a two-dimensional alumina nanosheet prepared by a template method.

[0010] Furthermore, the silane coupling agent is p-(triethoxysilyl)acetophenone.

[0011] Furthermore, the thickener is obtained by combining an antioxidant and lithium polyacrylate.

[0012] In a second aspect, the present invention provides a method for preparing a ceramic composite separator for lithium batteries as described in the first aspect, comprising the following preparation steps: S1. Preparation of composite ceramic coating slurry: S1.1. Weigh and prepare each raw material component; S2.1. Under nitrogen protection, the modified flake alumina is added to 200-300 parts by weight of tetrahydrofuran and mixed and stirred. Then, 0.08-0.12 times the mass of the modified flake alumina of sodium hydride is added and stirred at room temperature. Thickener is added and stirred to react. After the reaction is completed, the mixture is cooled to room temperature, poured into ice-cold ultrapure water, and the pH is adjusted to acidic with hydrochloric acid. The mixture is filtered, washed, and dried to obtain the premix. S2.2 Add the premix and dispersant to ultrapure water, and uniformly disperse the slurry system using a planetary ball mill. Then add the binder, add the wetting agent after ball milling, and continue ball milling to obtain the composite ceramic coating slurry. S3. Coat the prepared slurry onto the base film and dry it to obtain an alumina-coated diaphragm.

[0013] Further, the preparation steps of the modified flake alumina are as follows: 0.5~0.7 parts by mass of silane coupling agent are added to 200 parts by mass of anhydrous ethanol aqueous solution with a volume ratio of 19:1, and after stirring at 60°C for 30 min, 20 parts by mass of flake alumina are added, stirred for 8 h, filtered, and dried to obtain modified flake alumina.

[0014] Furthermore, the specific surface area of ​​the lamellar alumina is 125.8~228.1 m². 2 / g.

[0015] Further, the preparation steps of the thickener are as follows: Lithium hydroxide monohydrate and deionized water are mixed and stirred until dissolved at a mass ratio of 0.04~0.05:1, and then 1~1.2 parts by mass of 0.1g / L polyacrylic acid solution are added and stirred thoroughly to obtain a lithium polyacrylate solution, wherein the mass ratio of lithium hydroxide monohydrate to polyacrylic acid is 0.4~0.5:1; the lithium polyacrylate solution is mixed with an antioxidant and heated and stirred at 60°C for 5~7h to obtain the thickener.

[0016] Furthermore, the mass ratio of lithium polyacrylate to antioxidant is 2~4:1.

[0017] By adopting the above technical solution, the present invention has the following beneficial effects: (1) The ceramic composite separator for lithium batteries of the present invention is obtained by coating a composite ceramic coating on the surface. The raw material components of the composite ceramic coating include 30-40 parts by mass of modified lamellar alumina, 0.2-0.8 parts by mass of dispersant, 2-4 parts by mass of binder, 6-12 parts by mass of thickener, 0.1-0.5 parts by mass of wetting agent, and 42-60 parts by mass of water. The lamellar alumina has a large specific surface area and highly interconnected gaps between its lamellar structures, thereby forming a well-developed porous structure. By modifying and improving dispersibility, a relatively uniform porous structure is formed in the composite ceramic coating, which is conducive to the uniform penetration of liquid electrolyte and the transport of lithium ions, and helps to improve the performance of the battery.

[0018] (2) The addition of antioxidants to the thickener of the present invention can help lithium-ion batteries remove free radicals during charge-discharge cycles and improve the cycle stability of lithium-ion batteries.

[0019] (3) In the preparation of the slurry of the composite ceramic coating of the present invention, the modified alumina obtained by modifying the (triethoxysilyl)acetophenone with a silane coupling agent is first subjected to a composite reaction with a thickener. The methyl benzoate on the modified alumina undergoes a Claisen condensation reaction with the acetophenone in the thickener to form a β-diketone compound. The thickener is stably dispersed and wrapped on the surface of the modified alumina, which can effectively prevent the alumina from falling off in the composite ceramic coating. At the same time, the β-diketone can undergo enolization and can undergo a reversible coordination-dissociation process with lithium ions, which can selectively promote lithium ion transport and inhibit anion migration, thereby improving ionic conductivity. Detailed Implementation

[0020] To better understand the above technical solution, the following will provide a detailed explanation of the technical solution in conjunction with specific implementation methods.

[0021] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0022] The following embodiments are only used to illustrate the technical solutions of the present invention more clearly, and should not be used to limit the scope of protection of the present invention.

[0023] The preparation method of sheet-like alumina is as follows: Potassium carbonate, lithium carbonate, and titanium oxide are mixed in a molar ratio of 0.8:0.27:3.46, placed in an alumina crucible, and then placed in a muffle furnace. The temperature is first raised to 1150°C at a rate of 5°C / min and held for 24 hours. After natural cooling, the material is removed and ground to obtain layered K. 0.8 Li 0.27 Ti 1.73 O4 powder; layered K 0.8 Li 0.27 Ti 1.73 O4 powder was added to 1M HCl for acid treatment, wherein layered K 0.8 Li 0.27 Ti 1.73 O4 powder and HCl were mixed at a ratio of 1g:100mL, and then stirred continuously on a magnetic stirrer for three days. Filtering was performed daily, with the solution replaced with fresh 1M HCl. After three days, excess HCl was filtered off, and the filter cake was washed multiple times with deionized water until the washing solution was neutral. The washed filter cake was then allowed to air dry to obtain H2O. 1.07 Ti 1.73 O4·nH2O; in TBA + :H + In an aqueous solution of tetrabutylammonium hydroxide with a molar ratio of 4:1, 0.1 g of the prepared H was added. 1.07 Ti 1.73 O4·nH2O was stirred in a magnetic stirrer for seven days to obtain Ti with a concentration of 5 g / L. 0.87 O2 nanosheet suspension, Ti was prepared using the Langmuir-Blodgett (LB) method. 0.87 The deposition of O2 nanosheets resulted in a Ti substrate with a relatively smooth surface and a thickness of approximately 2 nm. 0.87 O2 nanosheets; take 100 mL of Al 3+A 0.1M aluminum chloride solution was prepared. Separately, 20 mL of a 5 g / L Ti0.87O2 nanosheet suspension was diluted to 500 mL with deionized water. A 0.04M tetrabutylammonium hydroxide aqueous solution was added and stirred until homogeneous. This mixture was then added dropwise to the aluminum chloride solution. After the addition was complete, the solution was allowed to stand. The solution separated into layers, and the supernatant was removed using a dropper. Deionized water was then added again, and the solution was allowed to stand for further separation. The supernatant was removed, and this process was repeated five times to remove impurity ions from the solution. The product was then freeze-dried to obtain flake aluminum hydroxide. The prepared flake aluminum hydroxide was calcined at 800℃ to obtain a specific surface area of ​​228.1 m². 2 / g of flake alumina.

[0024] The silane coupling agent used is p-(triethoxysilyl)acetophenone.

[0025] The antioxidant used is methyl 3,5-di-tert-butyl-4-hydroxybenzoate.

[0026] Example 1 A method for preparing a ceramic composite separator for lithium batteries includes the following preparation steps: S1. Preparation of composite ceramic coating slurry: S1.1. Weigh and prepare the following raw materials: 30 parts by weight of modified flake alumina, 0.2 parts by weight of dispersant, 2 parts by weight of binder, 6 parts by weight of thickener, 0.1 parts by weight of wetting agent, and 60 parts by weight of water; S2.1. Under nitrogen protection, the modified flake alumina was added to 200 parts by weight of tetrahydrofuran and mixed. Then, sodium hydride with a mass of 0.08 times that of the modified flake alumina was added and stirred at room temperature for 60 min. After dispersing the modified flake alumina for 30 min, the mixture was reacted at 70 °C for 24 h. After the reaction was completed, the mixture was cooled to room temperature, poured into ice-cold ultrapure water, and the pH was adjusted to acidic with hydrochloric acid. The mixture was then filtered, washed, and dried to obtain the premix. S2.2 Add the premix and dispersant to ultrapure water, and uniformly disperse the slurry system in a planetary ball mill for 60 min. Then add the binder and ball mill for 30 min. Next, add the wetting agent and ball mill for 30 min to obtain the composite ceramic coating slurry. The ball mill parameters are set to 400 rpm / min. S3. The prepared slurry is coated onto a 9μm PE film to obtain an alumina-coated diaphragm. The diaphragm is coated using a small coating machine and dried at 60℃ to obtain a 9+2μm coated diaphragm.

[0027] The preparation steps of the modified flake alumina are as follows: 0.5 parts by mass of silane coupling agent are added to 200 parts by mass of anhydrous ethanol aqueous solution with a volume ratio of 19:1, and after stirring at 60°C for 30 min, 20 parts by mass of flake alumina are added, stirred for 8 h, filtered, and dried to obtain modified flake alumina.

[0028] The preparation steps of the thickener are as follows: Lithium hydroxide monohydrate and deionized water are mixed and stirred until dissolved at a mass ratio of 0.04:1. Then, 1 part by mass of 0.1 g / L polyacrylic acid solution is added and stirred thoroughly to obtain a lithium polyacrylate solution, wherein the mass ratio of lithium hydroxide monohydrate to polyacrylic acid is 0.4:1. The lithium polyacrylate solution is mixed with an antioxidant and heated and stirred at 60°C for 6 hours to obtain the thickener, wherein the mass ratio of lithium polyacrylate to antioxidant is 2:1.

[0029] Example 2 A method for preparing a ceramic composite separator for lithium batteries includes the following preparation steps: S1. Preparation of composite ceramic coating slurry: S1.1. Weigh and prepare the following raw materials: 35 parts by mass of modified flake alumina, 0.6 parts by mass of dispersant, 3 parts by mass of binder, 9 parts by mass of thickener, 0.3 parts by mass of wetting agent, and 51 parts by mass of water; S2.1. Under nitrogen protection, the modified flake alumina was added to 200 parts by weight of tetrahydrofuran and mixed. Then, sodium hydride with a mass of 0.1 times that of the modified flake alumina was added and stirred at room temperature for 60 min. After dispersing the modified flake alumina for 30 min, the mixture was reacted at 70 °C for 24 h. After the reaction was completed, the mixture was cooled to room temperature, poured into ice-cold ultrapure water, and the pH was adjusted to acidic with hydrochloric acid. The mixture was then filtered, washed, and dried to obtain the premix. S2.2 Add the premix and dispersant to ultrapure water, and uniformly disperse the slurry system in a planetary ball mill for 60 min. Then add the binder and ball mill for 30 min. Next, add the wetting agent and ball mill for 30 min to obtain the composite ceramic coating slurry. The ball mill parameters are set to 400 rpm / min. S3. The prepared slurry is coated onto a 9μm PE film to obtain an alumina-coated diaphragm. The diaphragm is coated using a small coating machine and dried at 60℃ to obtain a 9+2μm coated diaphragm.

[0030] The preparation steps of the modified flake alumina are as follows: 0.6 parts by mass of silane coupling agent are added to 200 parts by mass of anhydrous ethanol aqueous solution with a volume ratio of 19:1, and after stirring at 60°C for 30 min, 20 parts by mass of flake alumina are added, stirred for 8 h, filtered, and dried to obtain modified flake alumina.

[0031] The preparation steps of the thickener are as follows: Lithium hydroxide monohydrate and deionized water are mixed and stirred until dissolved at a mass ratio of 0.046:1. Then, 1.1 parts by mass of 0.1 g / L polyacrylic acid solution are added and stirred thoroughly to obtain a lithium polyacrylate solution, wherein the mass ratio of lithium hydroxide monohydrate to polyacrylic acid is 0.46:1. The lithium polyacrylate solution is mixed with an antioxidant and heated and stirred at 60°C for 6 hours to obtain the thickener, wherein the mass ratio of lithium polyacrylate to antioxidant is 3:1.

[0032] Example 3 A method for preparing a ceramic composite separator for lithium batteries includes the following preparation steps: S1. Preparation of composite ceramic coating slurry: S1.1. Weigh and prepare the following raw materials: 40 parts by weight of modified flake alumina, 0.8 parts by weight of dispersant, 4 parts by weight of binder, 12 parts by weight of thickener, 0.5 parts by weight of wetting agent, and 42 parts by weight of water; S2.1. Under nitrogen protection, the modified flake alumina was added to 300 parts by weight of tetrahydrofuran and mixed. Then, sodium hydride with a mass of 0.12 times that of the modified flake alumina was added and stirred at room temperature for 60 min. After dispersing the modified flake alumina for 30 min, the mixture was reacted at 70°C for 24 h. After the reaction was completed, the mixture was cooled to room temperature, poured into ice-cold ultrapure water, and the pH was adjusted to acidic with hydrochloric acid. The mixture was then filtered, washed, and dried to obtain the premix. S2.2 Add the premix and dispersant to ultrapure water, and uniformly disperse the slurry system in a planetary ball mill for 60 min. Then add the binder and ball mill for 30 min. Next, add the wetting agent and ball mill for 30 min to obtain the composite ceramic coating slurry. The ball mill parameters are set to 400 rpm / min. S3. The prepared slurry is coated onto a 9μm PE film to obtain an alumina-coated diaphragm. The diaphragm is coated using a small coating machine and dried at 60℃ to obtain a 9+2μm coated diaphragm.

[0033] The preparation steps of the modified flake alumina are as follows: 0.7 parts by mass of silane coupling agent are added to 200 parts by mass of anhydrous ethanol aqueous solution with a volume ratio of 19:1, and after stirring at 60°C for 30 min, 20 parts by mass of flake alumina are added, stirred for 8 h, filtered, and dried to obtain modified flake alumina.

[0034] The preparation steps of the thickener are as follows: Lithium hydroxide monohydrate and deionized water are mixed and stirred until dissolved at a mass ratio of 0.05:1. Then, 1.2 parts by mass of 0.1 g / L polyacrylic acid solution are added and stirred thoroughly to obtain a lithium polyacrylate solution, wherein the mass ratio of lithium hydroxide monohydrate to polyacrylic acid is 0.5:1. The lithium polyacrylate solution is mixed with an antioxidant and heated and stirred at 60°C for 6 hours to obtain the thickener, wherein the mass ratio of lithium polyacrylate to antioxidant is 4:1.

[0035] Comparative Example 1 The only difference between Comparative Example 1 and Example 2 is that flake alumina was used instead of modified alumina.

[0036] A method for preparing a ceramic composite separator for lithium batteries includes the following preparation steps: S1. Preparation of composite ceramic coating slurry: S1.1. Weigh and prepare the following raw materials: 35 parts by weight of flake alumina, 0.6 parts by weight of dispersant, 3 parts by weight of binder, 9 parts by weight of thickener, 0.3 parts by weight of wetting agent, and 51 parts by weight of water; S2.1. Under nitrogen protection, the modified flake alumina was added to 200 parts by weight of tetrahydrofuran and mixed. Then, sodium hydride with a mass of 0.1 times that of the modified flake alumina was added and stirred at room temperature for 60 min. After the flake alumina was added and dispersed for 30 min, the mixture was reacted at 70 °C for 24 h. After the reaction was completed, the mixture was cooled to room temperature, poured into ice-cold ultrapure water, and the pH was adjusted to acidic with hydrochloric acid. The mixture was then filtered, washed, and dried to obtain the premix. S2.2 Add the premix and dispersant to ultrapure water, and uniformly disperse the slurry system in a planetary ball mill for 60 min. Then add the binder and ball mill for 30 min. Next, add the wetting agent and ball mill for 30 min to obtain the composite ceramic coating slurry. The ball mill parameters are set to 400 rpm / min. S3. The prepared slurry is coated onto a 9μm PE film to obtain an alumina-coated diaphragm. The diaphragm is coated using a small coating machine and dried at 60℃ to obtain a 9+2μm coated diaphragm.

[0037] The preparation steps of the thickener are as follows: Lithium hydroxide monohydrate and deionized water are mixed and stirred until dissolved at a mass ratio of 0.046:1. Then, 1.1 parts by mass of 0.1 g / L polyacrylic acid solution are added and stirred thoroughly to obtain a lithium polyacrylate solution, wherein the mass ratio of lithium hydroxide monohydrate to polyacrylic acid is 0.46:1. The lithium polyacrylate solution is mixed with an antioxidant and heated and stirred at 60°C for 6 hours to obtain the thickener, wherein the mass ratio of lithium polyacrylate to antioxidant is 3:1.

[0038] Comparative Example 2 The only difference between Comparative Example 2 and Example 2 is that the thickener used is lithium polyacrylate without added antioxidants.

[0039] A method for preparing a ceramic composite separator for lithium batteries includes the following preparation steps: S1. Preparation of composite ceramic coating slurry: S1.1. Weigh and prepare the following raw materials: 35 parts by mass of modified flake alumina, 0.6 parts by mass of dispersant, 3 parts by mass of binder, 9 parts by mass of thickener, 0.3 parts by mass of wetting agent, and 51 parts by mass of water; S2.1. Under nitrogen protection, the modified flake alumina was added to 200 parts by weight of tetrahydrofuran and mixed. Then, sodium hydride with a mass of 0.1 times that of the modified flake alumina was added and stirred at room temperature for 60 min. After dispersing the modified flake alumina for 30 min, the mixture was reacted at 70 °C for 24 h. After the reaction was completed, the mixture was cooled to room temperature, poured into ice-cold ultrapure water, and the pH was adjusted to acidic with hydrochloric acid. The mixture was then filtered, washed, and dried to obtain the premix. S2.2 Add the premix and dispersant to ultrapure water, and uniformly disperse the slurry system in a planetary ball mill for 60 min. Then add the binder and ball mill for 30 min. Next, add the wetting agent and ball mill for 30 min to obtain the composite ceramic coating slurry. The ball mill parameters are set to 400 rpm / min. S3. The prepared slurry is coated onto a 9μm PE film to obtain an alumina-coated diaphragm. The diaphragm is coated using a small coating machine and dried at 60℃ to obtain a 9+2μm coated diaphragm.

[0040] The preparation steps of the modified flake alumina are as follows: 0.6 parts by mass of silane coupling agent are added to 200 parts by mass of anhydrous ethanol aqueous solution with a volume ratio of 19:1, and after stirring at 60°C for 30 min, 20 parts by mass of flake alumina are added, stirred for 8 h, filtered, and dried to obtain modified flake alumina.

[0041] The thickener used is lithium polyacrylate.

[0042] Comparative Example 3 The only difference between Comparative Example 3 and Example 2 is that the raw material components were directly mixed without premixing.

[0043] A method for preparing a ceramic composite separator for lithium batteries includes the following preparation steps: S1. Preparation of composite ceramic coating slurry: S1.1. Weigh and prepare the following raw materials: 35 parts by mass of modified flake alumina, 0.6 parts by mass of dispersant, 3 parts by mass of binder, 9 parts by mass of thickener, 0.3 parts by mass of wetting agent, and 51 parts by mass of water; S2.1. Dissolve the thickener in ultrapure water, then add the dispersant and stir for 30 min. Add the modified flake alumina and disperse the slurry system evenly in a planetary ball mill for 60 min. Then add the binder and ball mill for 30 min. Next, add the wetting agent and ball mill for 30 min to obtain the composite ceramic coating slurry. The ball mill parameters are set to 400 rpm / min. S3. The prepared slurry is coated onto a 9μm PE film to obtain an alumina-coated diaphragm. The diaphragm is coated using a small coating machine and dried at 60℃ to obtain a 9+2μm coated diaphragm.

[0044] The preparation steps of the modified flake alumina are as follows: 0.6 parts by mass of silane coupling agent are added to 200 parts by mass of anhydrous ethanol aqueous solution with a volume ratio of 19:1, and after stirring at 60°C for 30 min, 20 parts by mass of flake alumina are added, stirred for 8 h, filtered, and dried to obtain modified flake alumina.

[0045] The preparation steps of the thickener are as follows: Lithium hydroxide monohydrate and deionized water are mixed and stirred until dissolved at a mass ratio of 0.046:1. Then, 1.1 parts by mass of 0.1 g / L polyacrylic acid solution are added and stirred thoroughly to obtain a lithium polyacrylate solution, wherein the mass ratio of lithium hydroxide monohydrate to polyacrylic acid is 0.46:1. The lithium polyacrylate solution is mixed with an antioxidant and heated and stirred at 60°C for 6 hours to obtain the thickener, wherein the mass ratio of lithium polyacrylate to antioxidant is 3:1.

[0046] Example of effect Thermal stability: The ceramic composite separators for lithium batteries prepared in the examples and comparative examples were placed in an environment of 150°C for 30 min and then removed. The dimensional changes of the separator before and after heat treatment were observed and the thermal shrinkage rate (%) was calculated. The thermal shrinkage rate (%) = (area of ​​separator before heat treatment - area of ​​separator after heat treatment) * 100% / area of ​​separator before heat treatment.

[0047] Ionic conductivity: The lithium batteries prepared in the examples and comparative examples were immersed in electrolyte with ceramic composite membranes sandwiched between stainless steel sheets. SS / Separator / SS batteries were assembled and the membrane impedance was measured. The measurement frequency range was 1×10⁻⁶. 6 Hz-10Hz, AC amplitude of 10 mV, the intercept of the curve on the X-axis in the Nyquist spectrum obtained by electrochemical impedance spectroscopy is the impedance of the diaphragm after being soaked in electrolyte. The ionic conductivity of the diaphragm = diaphragm thickness / (area of ​​stainless steel sheet * diaphragm impedance).

[0048] Cyclic performance: The high-temperature resistant lithium batteries prepared in the examples and comparative examples were assembled with composite separators to form LiFePO4 / separator / Li half-cells. Cyclic charge-discharge tests were conducted at a current density of 1 C. The cycle performance of the batteries was measured by comparing the capacity retention rate of the batteries after cycling.

[0049] Table 1 below shows the performance test results of the ceramic composite separators for lithium batteries obtained in the examples and comparative examples: Table 1

[0050] As shown in Table 1, the ceramic composite separators for lithium batteries in Examples 1-3 have good thermal stability, high ionic conductivity, and the prepared batteries have good cycle stability.

[0051] The only difference between Comparative Example 1 and Example 2 is that sheet alumina was used instead of modified alumina. The resulting ceramic composite separator for lithium batteries has weaker thermal stability, lower ionic conductivity, and weaker cycle stability.

[0052] The only difference between Comparative Example 2 and Example 2 is that the thickener used is lithium polyacrylate without the addition of antioxidants. The resulting ceramic composite separator for lithium batteries has weaker thermal stability, lower ionic conductivity, and weaker cycle stability.

[0053] The only difference between Comparative Example 3 and Example 2 is that the raw material components were directly mixed without premixing. The resulting ceramic composite separator for lithium batteries had weaker thermal stability, lower ionic conductivity, and weaker cycle stability.

[0054] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A ceramic composite separator for lithium batteries, characterized in that, It includes a base film and a composite ceramic coating applied to the surface of the base film; the raw material components of the composite ceramic coating include, by mass parts, 30-40 parts modified flake alumina, 0.2-0.8 parts dispersant, 2-4 parts binder, 6-12 parts thickener, 0.1-0.5 parts wetting agent, and 42-60 parts water.

2. The ceramic composite separator for lithium batteries according to claim 1, characterized in that, The modified lamellar alumina is obtained by modifying lamellar alumina with a silane coupling agent.

3. The ceramic composite separator for lithium batteries according to claim 2, characterized in that, The sheet-like alumina is a two-dimensional alumina nanosheet prepared by a template method.

4. The ceramic composite separator for lithium batteries according to claim 2, characterized in that, The silane coupling agent used is p-(triethoxysilyl)acetophenone.

5. The ceramic composite separator for lithium batteries according to claim 1, characterized in that, The thickener is obtained by combining an antioxidant and lithium polyacrylate.

6. A method for preparing a ceramic composite separator for lithium batteries as described in any one of claims 1 to 5, characterized in that, The preparation steps include the following: S1. Preparation of composite ceramic coating slurry: S1.

1. Weigh and prepare each raw material component; S2.

1. Under nitrogen protection, the modified flake alumina is added to 200-300 parts by weight of tetrahydrofuran and stirred to disperse. Then, 0.08-0.12 times the mass of the modified flake alumina of sodium hydride is added and stirred at room temperature. Thickener is added and stirred to react. After the reaction is completed, the mixture is cooled to room temperature, poured into ice-cold ultrapure water, and the pH is adjusted to acidic with hydrochloric acid. The mixture is filtered, washed, and dried to obtain the premix. S2.2 Add the premix and dispersant to ultrapure water, and uniformly disperse the slurry system using a planetary ball mill. Then add the binder, add the wetting agent after ball milling, and continue ball milling to obtain the composite ceramic coating slurry. S3. Coat the prepared slurry onto the base film and dry it to obtain an alumina-coated diaphragm.

7. The method for preparing a ceramic composite separator for lithium batteries according to claim 6, characterized in that, The preparation steps of the modified flake alumina are as follows: 0.5-0.7 parts by mass of silane coupling agent are added to 200 parts by mass of anhydrous ethanol aqueous solution with a volume ratio of 19:1, and after stirring at 60°C for 30 min, 20 parts by mass of flake alumina are added, stirred for 8 h, filtered, and dried to obtain modified flake alumina.

8. The method for preparing a ceramic composite separator for lithium batteries according to claim 7, characterized in that, The specific surface area of ​​the lamellar alumina is 125.8~228.1 m². 2 / g.

9. The method for preparing a ceramic composite separator for lithium batteries according to claim 6, characterized in that, The preparation steps of the thickener are as follows: Lithium hydroxide monohydrate and deionized water are mixed and stirred until dissolved at a mass ratio of 0.04~0.05:1, and then 1~1.2 parts by mass of polyacrylic acid solution are added and stirred thoroughly to obtain a lithium polyacrylate solution, wherein the mass ratio of lithium hydroxide monohydrate to polyacrylic acid is 0.4~0.5:1; the lithium polyacrylate solution is mixed with an antioxidant and heated to obtain the thickener.

10. The method for preparing a ceramic composite separator for lithium batteries according to claim 9, characterized in that, The mass ratio of lithium polyacrylate to antioxidant is 2~4:1.

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