A high heat-resistant, high liquid-absorbing ceramic diaphragm, its preparation method and application

Abstract

This invention relates to the field of battery separators, specifically to a high-heat-resistant, high-absorbency ceramic separator, its preparation method, and its application. The invention introduces hydroxyl-containing polymers into the coating. Because hydroxyl-containing polymers have good affinity for electrolytes, the ceramic separator exhibits excellent liquid absorption performance, thereby effectively improving the cycle performance of the battery cell. Furthermore, by introducing a boron-containing crosslinking agent into the coating, the borate ions in the inorganic boric acid aqueous solution can act as crosslinking agents to form hydrogen bonds with the hydroxyl-containing polymers, resulting in a crosslinking reaction. Additionally, the copolymerization of 4-vinylphenylboronic acid and ethylene glycol diethylene ether in the organic boric acid solution can form a six-membered ring at high temperatures. Therefore, a three-dimensional network structure is formed within the system over a wide temperature range, improving the skeletal strength of the ceramic separator coating and ensuring both high liquid absorption and improved temperature resistance of the ceramic separator.

Description

Technical Field

[0001] This invention relates to the field of battery separators, and more particularly to a high heat-resistant, high liquid-absorbing ceramic separator, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries have become a hot topic in power technology research in recent years due to their advantages such as high specific energy, long cycle life, no memory effect (compared to nickel-cadmium batteries), safety, reliability, and ability to withstand rapid re-discharge. They play an irreplaceable role in widely used electronic devices such as mobile phones and laptops, as well as in the emerging fields of electric and hybrid vehicles.

[0003] The main components of a lithium-ion battery include positive / negative electrode materials, electrolyte, battery separator, and battery casing. The battery separator is a crucial element of a lithium-ion battery, structurally acting to directly separate the positive and negative electrodes and prevent short circuits. The performance of the battery separator directly determines the battery's interface performance, cycle performance, and safety performance. Therefore, a high-performance separator plays a vital role in improving the overall performance of the battery.

[0004] Because ceramics can be dispersed in water and are environmentally friendly, they are now widely used in membrane coating to prepare high-temperature resistant ceramic-coated membranes with good thermal stability. Electrolyte wettability is an important indicator for evaluating membranes. Excellent electrolyte wettability is beneficial to improving the ionic conductivity of the battery. To further improve the ability of lithium battery membranes to absorb electrolytes, polymeric adhesives containing polar hydrophilic groups are usually introduced into the membrane coating. For example, patent document CN108305972B discloses a ceramic-coated membrane, its preparation method, and its application. This ceramic-coated membrane includes a base membrane and a ceramic coating. The ceramic coating is formed by coating inorganic particles grafted with polyethylene glycol. The inorganic particles are grafted with polyethylene glycol containing hydroxyl groups. Although this achieves a fast liquid absorption rate and high liquid absorption rate, it exhibits large thermal shrinkage under high-temperature conditions, resulting in poor mechanical strength and temperature resistance of the ceramic-coated membrane at high temperatures.

[0005] To address the aforementioned issues, a crosslinkable polymer adhesive can be introduced into the separator coating to form a three-dimensional network structure on the separator surface, thereby increasing the mechanical strength and temperature resistance of the ceramic-coated separator. For example, patent document CN113964450A discloses a battery separator coating liquid and its preparation method, as well as a battery separator and a battery. In this battery separator coating liquid, due to the interaction forces or hydrogen bonds between ceramics, adhesives, nanowires, and coupling agents, a structure of ... ceramic-coupling agent-nanowire-ceramic-coupling agent-nanowire... is formed, thus giving the final battery separator good heat resistance. However, since hydrogen bonds are unstable, they may be destroyed at a certain temperature. Therefore, this method has limited effectiveness in improving the mechanical strength of the separator at high temperatures.

[0006] Therefore, in response to the aforementioned technologies, there is an urgent need to develop a high heat-resistant, high liquid-absorbing ceramic diaphragm, its preparation method, and its applications. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a high heat resistance and high liquid absorption ceramic diaphragm, its preparation method and application, so as to solve the problem of poor liquid absorption performance of ceramic diaphragms in the prior art.

[0008] To achieve the above objectives, the present invention provides a high heat-resistant, high liquid-absorbing ceramic diaphragm, its preparation method, and its application.

[0009] A high heat-resistant and high liquid-absorbing ceramic diaphragm includes a coating and a substrate. The coating is prepared from the following raw materials in parts by weight: 80-120 parts ceramic particles, 4-8 parts hydroxyl-containing polymer, 3-5 parts binder, 30-50 parts boron-containing crosslinking agent, 0.1-0.5 parts additives, and 1-2 parts dispersant.

[0010] The substrate is composed of any one of polyethylene, polypropylene and polymethylpentene;

[0011] The preparation method of the boron-containing crosslinking agent is as follows:

[0012] S1. Dissolve a boron-containing inorganic compound in water, then add an inorganic alkaline compound to obtain an aqueous solution of inorganic boric acid;

[0013] S2. Mix 4-vinylphenylboronic acid, ethylene glycol diethylene ether, 3-chloro-2-hydroxypropyltrimethylammonium chloride, azobisisobutyronitrile, tetrahydrofuran and water evenly, and react at 75-85℃ for 22-24h to obtain an organoboronic acid solution.

[0014] S3. Mix the inorganic boric acid aqueous solution and the organic boric acid solution evenly to obtain a boron-containing crosslinking agent.

[0015] Preferably, the hydroxyl-containing polymer is one or more of nano bamboo charcoal powder, nano cellulose, polyvinyl alcohol, and polyethylene glycol, and the binder is one or more of styrene-butadiene rubber, polymethyl acrylate, polybutyl acrylate, polyvinyl alcohol, and polyvinylidene fluoride.

[0016] Preferably, the additive is one or more of succinic acid, fluoroalkyl methoxy ether alcohol, sodium polyacrylate, ethynyl glycol vinyl ether, fatty acid polyoxyethylene ether, and polyether-modified siloxane, and the dispersant is one or more of sodium polyacrylate, ammonium polyacrylate, carboxylates, and sulfonates.

[0017] Preferably, the boron-containing inorganic compound in step S1 is one or more of sodium borate, potassium tetraborate, lithium tetraborate, and ammonium borate.

[0018] Preferably, the mass ratio of the boron-containing inorganic compound, water, and inorganic alkaline compound in step S1 is 1-4:28-42:1-4.

[0019] Preferably, the inorganic alkaline compound in step S1 is one or more inorganic oxides such as nano-alumina, aluminum hydroxide, magnesium hydroxide, boehmite, and silicon dioxide, and the concentration of the borate ion aqueous solution in step S1 is 1%-10%.

[0020] Preferably, the ratio of 4-vinylphenylboronic acid, ethylene glycol diethylene ether, 3-chloro-2-hydroxypropyltrimethylammonium chloride, azobisisobutyronitrile, tetrahydrofuran, and water in step S2 is 20-40g: 30-50g: 220-240mg: 18-20mg: 95-100mL: 2-3mL.

[0021] Preferably, the mass ratio of the inorganic boric acid aqueous solution and the organic boric acid aqueous solution in step S3 is 30-50:10-15.

[0022] A method for preparing a high heat-resistant, high liquid-absorbing ceramic diaphragm includes the following steps:

[0023] S11. Mix the dispersant and deionized water evenly, add ceramic particles, stir evenly, and grind for 10-50 minutes to obtain dispersion 1;

[0024] S12. Add a binder to dispersion 1, stir for 30-60 min, then add a hydroxyl-containing polymer, stir for 30-60 min, and obtain mixture 2;

[0025] S13. Add the additive to mixture 2, stir for 30-60 minutes, then pass it through a magnetic filter device, stir for 5-20 minutes, and filter with a 250-mesh filter to obtain the slurry;

[0026] S14. The slurry is coated onto the substrate using a microgravure plate, dried, and then immersed in a boron-containing crosslinking agent for 10-20 minutes to cure, thus obtaining a ceramic diaphragm.

[0027] An application of a high heat-resistant, high liquid-absorbing ceramic separator, which can be used in new types of secondary batteries such as lithium-ion batteries and sodium-ion batteries.

[0028] The beneficial effects of this invention are:

[0029] This invention provides a high heat-resistant, high liquid-absorbing ceramic diaphragm, its preparation method, and its application. By introducing hydroxyl-containing polymers into the coating, the ceramic diaphragm exhibits good liquid absorption performance due to the good affinity of hydroxyl-containing polymers for electrolytes, thereby effectively improving the cycle performance of the battery cell.

[0030] This invention provides a high-heat-resistant, high-liquid-absorption ceramic diaphragm, its preparation method, and its application. By introducing a boron-containing crosslinking agent into the coating, the borate ions in the inorganic boric acid aqueous solution can act as crosslinking agents and undergo crosslinking reactions with hydroxyl-containing polymers. Meanwhile, the 4-vinylphenylboronic acid and ethylene glycol diethylene ether in the organic boric acid solution copolymerize to form a copolymer, which can form a six-membered ring at high temperatures, thus forming a three-dimensional network structure inside the coating. This improves the skeletal strength of the ceramic diaphragm and significantly enhances its temperature resistance. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0032] Example 1: A method for preparing a high heat-resistant, high liquid-absorbing ceramic diaphragm, comprising the following steps:

[0033] S1. Dissolve 1g of sodium borate in 28g of water, and then add 1g of nano-alumina to obtain an inorganic boric acid aqueous solution with a concentration of 1%;

[0034] S2. Mix 20g of 4-vinylphenylboronic acid, 30g of ethylene glycol diethylene ether, 220mg of 3-chloro-2-hydroxypropyltrimethylammonium chloride, 18mg of azobisisobutyronitrile, 95mL of tetrahydrofuran and 2mL of water evenly, and react at 75℃ for 22h to obtain an organoboronic acid solution.

[0035] S3. Add 10g of organic boric acid solution to 30g of 1% inorganic boric acid aqueous solution to obtain a boron-containing crosslinking agent;

[0036] S4. Mix 1g of sodium polyacrylate and deionized water evenly, add 80g of ceramic particles, stir evenly and grind for 10min to obtain dispersion 1;

[0037] S5. Add 3g of styrene-butadiene rubber to dispersion 1, stir for 30min, then add 4g of nano bamboo charcoal powder, stir for 30min to obtain mixture 2;

[0038] S6. Add 0.1g of succinic acid to mixture 2, stir for 30min, then pass through a magnetic filter, stir for 5min, and filter with a 250-mesh filter to obtain a slurry;

[0039] S7. The slurry is coated onto one side of the polyethylene substrate using a microgravure plate, dried, and then soaked in a boron-containing crosslinking agent for 10 minutes to cure, thus obtaining a ceramic diaphragm.

[0040] Example 2: A method for preparing a high heat-resistant, high liquid-absorbing ceramic diaphragm, comprising the following steps:

[0041] S1. Dissolve 2g of potassium tetraborate in water, then add 2g of aluminum hydroxide to obtain an inorganic boric acid aqueous solution with a concentration of 2.5%;

[0042] S2. Mix 27g of 4-vinylphenylboronic acid, 37g of ethylene glycol diethylene ether, 227mg of 3-chloro-2-hydroxypropyltrimethylammonium chloride, 18.7mg of azobisisobutyronitrile, 97.2mL of tetrahydrofuran and 2.4mL of water evenly, and react at 78℃ for 22.8h to obtain an organoboronic acid solution;

[0043] S3. Add 12g of organic boric acid aqueous solution to 35g of 2.5% inorganic boric acid aqueous solution to obtain a boron-containing crosslinking agent;

[0044] S4. Mix 1.25g of ammonium polyacrylate and deionized water evenly, add 90g of ceramic particles, stir evenly and grind for 20min to obtain dispersion 1;

[0045] S5. Add 3.5g of polymethyl acrylate to dispersion 1, stir for 37.5min, then add 5g of nanocellulose, stir for 37.5min to obtain mixture 2;

[0046] S6. Add 0.2g of fluoroalkyl methoxy ether alcohol to mixture 2, stir for 37.5min, then pass through a magnetic filter, stir for 10min, and filter with a 250-mesh filter to obtain a slurry;

[0047] S7. The slurry is coated onto one side of the polypropylene substrate using a microgravure plate, dried, and then immersed in a boron-containing crosslinking agent for 12.5 minutes to cure, thus obtaining a ceramic diaphragm.

[0048] Example 3: A method for preparing a high heat-resistant, high liquid-absorbing ceramic diaphragm, comprising the following steps:

[0049] S1. Dissolve 3g of lithium tetraborate in water, then add 3g of magnesium hydroxide to obtain an 8% inorganic boric acid aqueous solution;

[0050] S2. Mix 34g of 4-vinylphenylboronic acid, 44g of ethylene glycol diethylene ether, 234mg of 3-chloro-2-hydroxypropyltrimethylammonium chloride, 19.4mg of azobisisobutyronitrile, 98.5mL of tetrahydrofuran and 2.8mL of water evenly, and react at 82℃ for 23.6h to obtain an organoboronic acid solution;

[0051] S3. Add 14g of organic boric acid solution to 45g of 8% inorganic boric acid aqueous solution to obtain a boron-containing crosslinking agent;

[0052] S4. Mix 1.8g sodium carboxylate and deionized water evenly, add 110g ceramic particles, stir evenly and grind for 40min to obtain dispersion 1;

[0053] S5. Add 4.5g of polybutyl acrylate to dispersion 1, stir for 50min, then add 7g of polyvinyl alcohol, stir for 50min to obtain mixture 2;

[0054] S6. Add 0.4g of sodium polyacrylate to mixture 2, stir for 50min, then pass it through a magnetic filter, stir for 16min, and filter with a 250-mesh filter to obtain slurry;

[0055] S7. The slurry is coated onto one side of the polymethylpentene substrate using a microgravure plate, dried, and then immersed in a boron-containing crosslinking agent for 18 minutes to cure, thus obtaining a ceramic diaphragm.

[0056] Example 4: A method for preparing a high heat-resistant, high liquid-absorbing ceramic diaphragm, comprising the following steps:

[0057] S1. Dissolve 4g of lithium tetraborate in water, then add 4g of magnesium hydroxide to obtain an inorganic boric acid aqueous solution with a concentration of 10%;

[0058] S2. Mix 40g of 4-vinylphenylboronic acid, 50g of ethylene glycol diethylene ether, 240mg of 3-chloro-2-hydroxypropyltrimethylammonium chloride, 20mg of azobisisobutyronitrile, 100mL of tetrahydrofuran and 3mL of water evenly, and react at 85℃ for 24h to obtain an organoboronic acid solution.

[0059] S3. Add 15g of organic boric acid solution to 50g of 10% inorganic boric acid aqueous solution to obtain a boron-containing crosslinking agent;

[0060] S4. Mix 2g of sodium carboxylate and deionized water evenly, add 120g of ceramic particles, stir evenly and grind for 50min to obtain dispersion 1;

[0061] S5. Add 5g of polybutyl acrylate to dispersion 1, stir for 60min, then add 8g of polyvinyl alcohol, stir for 60min to obtain mixture 2;

[0062] S6. Add 0.5g of sodium polyacrylate to mixture 2, stir for 60min, then pass it through a magnetic filter, stir for 20min, and filter with a 250-mesh filter to obtain slurry;

[0063] S7. The slurry is coated onto one side of the polymethylpentene substrate using a microgravure plate, dried, and then immersed in a boron-containing crosslinking agent for 20 minutes to cure, thus obtaining a ceramic diaphragm.

[0064] Comparative Example 1:

[0065] This comparative example uses a 12μm thick polyethylene substrate as a reference.

[0066] Comparative Example 2:

[0067] Compared with Example 1, this comparative example only replaces "ethylene glycol diethylene ether" with "4-vinylphenylboronic acid". All other steps and parameters are the same, and will not be repeated here. The final ceramic diaphragm is obtained.

[0068] Comparative Example 3:

[0069] Compared with Example 1, this comparative example only replaces "4-vinylphenylboronic acid" with "ethylene glycol diethylene ether". All other steps and parameters are the same, and will not be repeated here. The final ceramic diaphragm is obtained.

[0070] Comparative Example 4:

[0071] Compared with Example 1, this comparative example did not add "organoboric acid solution" in the preparation process of the ceramic diaphragm. All other steps and parameters were the same, and will not be repeated here. The ceramic diaphragm was finally obtained.

[0072] Comparative Example 5:

[0073] Compared with Example 1, this comparative example did not add "inorganic boric acid aqueous solution" in the preparation process of ceramic diaphragm. All other steps and parameters were the same, and will not be repeated here. Finally, a ceramic diaphragm was obtained.

[0074] Performance testing

[0075] Referring to GB / T6672-2001 "Mechanical Measurement Method for Determination of Thickness of Plastic Films and Sheets", the thickness (μm) of each group of samples in Examples 1-4 and Comparative Examples 1-5 was tested using a THI-1801 thickness gauge.

[0076] Referring to GB / T135I9-2016 standard, the heat shrinkage rate (%) of each group of samples in Examples 1-4 and Comparative Examples 1-5 after being placed at 150℃ for 1h was measured using an FST-3102 film heat shrinkage performance tester.

[0077] According to ISO 15105-1:2007 "Plastics - Film and Sheeting Part 1: Differential pressure Methods", the air permeability values ​​(s / 100ml) of each group of samples in Examples 1-4 and Comparative Examples 1-5 were measured using a GTR-704R air permeability meter.

[0078] Referring to QB / T2303.11-2008 "Battery Pulp Paper Part 11: Determination of Liquid Absorption Rate" standard, the liquid absorption rate of each group of samples in Examples 1-4 and Comparative Examples 1-5 was measured by weighing. Each group of samples was immersed in electrolyte for 120 minutes to obtain the liquid absorption rate. The formula for calculating the liquid absorption rate is as follows:

[0079] ε(%)=[(M1-M0)] / M0×100%

[0080] Where ε is the liquid absorption rate (%); M0 is the dry film mass (g); M1 is the wet film mass (g);

[0081] Referring to GB / T30447-2013 standard, the contact angle of each group of samples in Examples 1-4 and Comparative Examples 1-5 with the electrolyte was measured using a JC2000D1 contact angle tester.

[0082] Referring to GB / T36363-2018 standard, the tensile strength of each group of samples in Examples 1-4 and Comparative Examples 1-5 at 25℃ and 80℃ was measured using an AGS-J universal tensile testing machine. The results are shown in Table 1 below:

[0083] Table 1

[0084]

[0085]

[0086] Data Analysis:

[0087] As shown in Table 1, the ceramic diaphragm prepared in this invention has a high liquid absorption rate, a low thermal shrinkage rate, and high tensile strength at both high and low temperatures. By introducing hydroxyl-containing polymers and boron-containing crosslinking agents into the coating, the hydroxyl-containing polymers have good affinity for the electrolyte, giving the ceramic diaphragm good liquid absorption performance, thereby effectively improving the cycle performance of the battery cell. The borate ions in the inorganic boric acid aqueous solution can act as crosslinking agents and undergo crosslinking reactions with the hydroxyl-containing polymers. The copolymerization of 4-vinylphenylboronic acid and ethylene glycol diethylene ether in the organic boric acid solution forms a copolymer of alternating phenylboronic acid and ether bonds. The phenylboronic acid portion can form a six-membered ring at high temperatures, and the presence of flexible ether bonds allows the phenylboronic acid to rotate, making the participation of phenylboronic acid in the formation of the six-membered ring more thorough. This allows the formation of a three-dimensional network structure inside the coating, improving the skeletal strength of the ceramic diaphragm and thus significantly improving the temperature resistance of the ceramic diaphragm. As a result, the prepared ceramic diaphragm has high mechanical properties over a wide temperature range.

[0088] In Comparative Example 2, ethylene glycol diethylene ether was used instead of 4-vinylphenylboronic acid, and the system contained only the homopolymer of 4-vinylphenylboronic acid. Similarly, no organic boric acid solution was added in Comparative Example 4. In this case, hydrogen bonds formed between borate ions in the inorganic boric acid aqueous solution and hydroxyl-containing polymers. However, as the temperature increased, these hydrogen bonds became unstable, leading to a decrease in the performance of the ceramic membrane. In Comparative Example 3, 4-vinylphenylboronic acid was used instead of ethylene glycol diethylene ether. The hydrogen bonds between borate ions and hydroxyl-containing polymers became unstable at elevated temperatures, but the homopolymer of 4-vinylphenylboronic acid could form a six-membered ring within the system, which was beneficial for the coating. The internal three-dimensional network structure increases the heat resistance of the ceramic separator and provides space for the electrolyte, which improves the electrolyte retention of the battery separator and further enhances the cycle performance of the battery. In Comparative Example 5, no inorganic boric acid aqueous solution was added to the system. Therefore, at low temperatures, the system exists in the form of hydroxyl-containing polymers and copolymers of 4-vinylphenylboronic acid and ethylene glycol diethylene ether. When the temperature rises, six-membered rings are formed between the copolymers of 4-vinylphenylboronic acid and ethylene glycol diethylene ether, forming a three-dimensional network structure inside the system. Therefore, the mechanical properties of the ceramic separator are better after the temperature rises.

[0089] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A high heat-resistant, high liquid-absorbing ceramic diaphragm, characterized in that, The product includes a coating and a substrate. The coating is prepared from the following raw materials in parts by weight: 80-120 parts ceramic particles, 4-8 parts hydroxyl-containing polymer, 3-5 parts binder, 30-50 parts boron-containing crosslinking agent, 0.1-0.5 parts additives, and 1-2 parts dispersant. The substrate is composed of any one of polyethylene, polypropylene and polymethylpentene; The preparation method of the boron-containing crosslinking agent is as follows: S1. Dissolve a boron-containing inorganic compound in water, then add an inorganic alkaline compound to obtain an aqueous solution of inorganic boric acid; S2. Mix 4-vinylphenylboronic acid, ethylene glycol diethylene ether, 3-chloro-2-hydroxypropyltrimethylammonium chloride, azobisisobutyronitrile, tetrahydrofuran and water evenly, and react at 75-85℃ for 22-24h to obtain an organoboronic acid solution. S3. Mix the inorganic boric acid aqueous solution and the organic boric acid solution evenly to obtain a boron-containing crosslinking agent.

2. The high heat resistance and high liquid absorption ceramic diaphragm according to claim 1, characterized in that, The hydroxyl-containing polymer is one or more of nano bamboo charcoal powder, nano cellulose, polyvinyl alcohol, and polyethylene glycol, and the binder is one or more of styrene-butadiene rubber, polymethyl acrylate, polybutyl acrylate, polyvinyl alcohol, and polyvinylidene fluoride.

3. The high heat resistance and high liquid absorption ceramic diaphragm according to claim 1, characterized in that, The additive is one or more of succinic acid, fluoroalkyl methoxy ether alcohol, sodium polyacrylate, ethynyl glycol vinyl ether, fatty acid polyoxyethylene ether, and polyether-modified siloxane, and the dispersant is one or more of sodium polyacrylate, ammonium polyacrylate, carboxylates, and sulfonates.

4. The high heat resistance and high liquid absorption ceramic diaphragm according to claim 1, characterized in that, The boron-containing inorganic compound mentioned in step S1 is one or more of sodium borate, potassium tetraborate, lithium tetraborate, and ammonium borate.

5. The high heat resistance and high liquid absorption ceramic diaphragm according to claim 1, characterized in that, The mass ratio of the boron-containing inorganic compound, water, and inorganic alkaline compound in step S1 is 1-4:28-42:1-4.

6. The high heat resistance and high liquid absorption ceramic diaphragm according to claim 1, characterized in that, The inorganic alkaline compound mentioned in step S1 is one or more of nano-alumina, aluminum hydroxide, magnesium hydroxide, boehmite, and silica inorganic oxides, and the concentration of the borate ion aqueous solution in step S1 is 1%-10%.

7. The high heat resistance and high liquid absorption ceramic diaphragm according to claim 1, characterized in that, In step S2, the ratio of 4-vinylphenylboronic acid, ethylene glycol diethylene ether, 3-chloro-2-hydroxypropyltrimethylammonium chloride, azobisisobutyronitrile, tetrahydrofuran, and water is 20-40g: 30-50g: 220-240mg: 18-20mg: 95-100mL: 2-3mL.

8. The high heat resistance and high liquid absorption ceramic diaphragm according to claim 1, characterized in that, The mass ratio of the inorganic boric acid aqueous solution and the organic boric acid aqueous solution in step S3 is 30-50:10-15.

9. A method for preparing a high-heat-resistant, high-absorbency ceramic diaphragm according to any one of claims 1-8, characterized in that, Includes the following steps: S11. Mix the dispersant and deionized water evenly, add ceramic particles, stir evenly, and grind for 10-50 minutes to obtain dispersion 1; S12. Add a binder to dispersion 1, stir for 30-60 min, then add a hydroxyl-containing polymer, stir for 30-60 min, and obtain mixture 2; S13. Add the additive to mixture 2, stir for 30-60 minutes, then pass it through a magnetic filter device, stir for 5-20 minutes, and filter with a 250-mesh filter to obtain the slurry; S14. The slurry is coated onto the substrate using a microgravure plate, dried, and then immersed in a boron-containing crosslinking agent for 10-20 minutes to cure, thus obtaining a ceramic diaphragm.

10. An application of a high heat-resistant, high liquid-absorbing ceramic diaphragm according to any one of claims 1-8, characterized in that, The ceramic separator is used in lithium-ion batteries and sodium-ion batteries.

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