Preparation process of cold-pressed battery diaphragm

Abstract

The invention discloses a preparation process of a cold-pressed battery diaphragm. The preparation process comprises the following steps: coating a GO film, coating a pseudo-boehmite film, crystallizing boehmite to form a film, and preparing a self-repairing boehmite film. The GO, the pseudo-boehmite and the boehmite are sequentially coated on the PP microporous membrane to prepare a PP / boehmite multi-layer composite membrane structure, so that the multi-layer composite structure is formed, and the mechanical strength of the diaphragm is enhanced; according to the preparation method, graphene oxide and mercaptopyridine-polyethylene glycol-amino are subjected to a grafting reaction, mercaptopyridine-polyethylene glycol-amino is further added into an adhesive, disulfide bonds, mercaptopyridine and other functional groups can chemically react with polysulfide ions, conversion of the polysulfide ions to Li2S is promoted, shuttling of polysulfide in the diaphragm is effectively inhibited, and the performance of the diaphragm is improved. The cycling stability of the battery is improved; meanwhile, the pore structure of the boehmite layer can be repaired by utilizing the self-repairing function of the disulfide bond, so that the diaphragm damage and battery short circuit risk caused by high temperature are avoided, and the safety of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery materials, and particularly relates to a preparation process of a cold-pressed battery separator. Background Art

[0002] Cold pressing is an important step in battery manufacturing. It usually occurs after electrode coating and drying. The dried electrode sheet is fed into a cold press, and the pressure of the cold press is used to compact the electrode sheet to ensure closer contact between the electrode material and the current collector, increase the density of the electrode sheet, thereby reducing the internal resistance of the battery and improving its electrochemical performance. In the cold pressing process, the electrode sheet is compressed without heating, which can avoid material property changes or damage caused by thermal effects.

[0003] The cold-pressed battery separator needs to have good chemical stability, a high porosity, be as thin and light as possible, have electronic insulation, good electrolyte wettability, and high mechanical strength. The cold-pressed lithium battery separator is generally a polypropylene (PP) or polyethylene (PE) microporous separator.

[0004] However, the PP or PE microporous separator has obvious thermal shrinkage. Therefore, a commonly used solution is to coat the microporous separator with a ceramic slurry. For example, in the "Preparation method of an aqueous ceramic slurry for coating" disclosed in Chinese Patent CN 114057430 A, different grinding processes are used to obtain boehmite with different particle size distributions, and through the compounding of components such as a dispersant, a binder, and a thickener, a ceramic slurry is obtained. After coating and drying and dehydrating to form pores, the obtained PP / boehmite composite film has an effect of low thermal shrinkage rate.

[0005] However, in the further application process, cracking occurs due to out-of-control temperature and humidity during the drying process; or after being placed in the battery for a period of time, due to the high wettability characteristics of boehmite, thermal cracking phenomena occur in the ceramic coating, resulting in a significant reduction in the number of battery uses and the heat-resistant life. Therefore, this coating process needs to be improved; in addition, the retention ability of the existing PP / boehmite composite film for polysulfide ions also needs to be improved. Summary of the Invention

[0006] The purpose of the present invention is to solve the deficiencies existing in the prior art, and to propose a preparation process of a cold-pressed battery separator.

[0007] In order to achieve the above purpose, the present invention adopts the following technical solutions: The present invention first proposes a preparation process of a cold-pressed battery separator, including the following steps: S1. GO Coating: Pour the graphene oxide suspension above the PP microporous membrane, and leak to obtain a transparent film A with light black spots; Pour the mercaptopyridine-polyethylene glycol-amine aqueous solution above the transparent film A, filter by suction after the reaction of leakage, and obtain the light black transparent film B; S2. Coating of pseudo-boehmite: Pour the pseudo-boehmite seed slurry above the transparent film B, introduce CO2 for reaction, and filter by suction after aging to obtain the composite film C with an aging layer; S3. Crystallization and film formation of boehmite: Pour the acidolysis solution above the composite film C for reaction. The aging layer of the composite film C gradually becomes a fluffy flocculent layer. Introduce ammonia gas for reaction below the composite film C, and finally introduce water vapor for in-situ hydrothermal reaction, aging, and suction filtration to obtain the composite film D with a fluffy boehmite layer; S4. Preparation of self-healing boehmite film: Pour the adhesive solution above the composite film D. The adhesive solution contains mercaptopyridine-polyethylene glycol-amine. After suction filtration, dry it in ventilation to obtain the finished product of the battery separator.

[0008] Preferably, S1 includes the following steps: S101. Place the PP microporous membrane above the wire mesh. The size of the square holes of the wire mesh is 1 mm × 1 mm. Pour the graphene oxide suspension with a mass concentration of 1 mg / ml above it. The input amount of the graphene oxide suspension is: stop adding when the liquid height is 3 - 5 mm. The graphene oxide suspension contains sulfuric acid with a weight concentration of about 8 wt%. Filter naturally. At this time, the water slowly leaks (the leakage speed is 0.03 s / drop) until no liquid drops out from the bottom surface of the wire mesh, and the PP microporous membrane presents the transparent film A with light black spots; S102. Prepare an aqueous solution of mercaptopyridine-polyethylene glycol-amine with a weight concentration of 5 wt% and pour it above the transparent film A. The input amount of the mercaptopyridine-polyethylene glycol-amine aqueous solution is: stop adding when the liquid height is 3 - 5 mm. React naturally for 30 - 60 min under low leakage (the leakage speed is 0.08 s / drop), and then perform suction filtration under a low pressure of 1 - 5 kPa below the wire mesh to obtain a relatively uniform light black transparent film B; The molecular formula of OPSS-PEG-Amino is:

[0009] By reacting the amino group in OPSS-PEG-Amino with the carboxyl group on the surface of GO, a microporous membrane with functional groups such as PEG, disulfide bonds, and mercaptopyridine is obtained. By suction filtration, part of the molecular chain of OPSS-PEG-Amino passes through the micropores of the PP microporous membrane, which plays a role in plugging the pores on the one hand, and on the other hand, promotes the conversion of polysulfur in the positive electrode region by using disulfide bonds and the mercaptopyridine dissociated from them, inhibiting the shuttle of polysulfides in the microporous membrane from both physical and chemical barriers. The mechanism is as follows: According to previous studies, disulfide bonds are prone to thiol exchange reactions with polysulfide ions in an electrochemical environment, and the dissociated mercaptopyridine has the effect of promoting the conversion of polysulfides to Li2S (Teng Deng, etc. Dynamically Regulating Polysulfide Degradation via Organic Sulfur Electrolyte Additives in Lithium-Sulfur Batteries. Adv. Energy Mater. 2024, 2402319); In addition, during the natural reaction process, GO forms a dissolution-sedimentation equilibrium. After grafting OPSS-PEG-Amino, PEG acts as a binder, enabling GO to adhere tightly to the PP microporous membrane. At the same time, the dissolution-sedimentation equilibrium also makes the originally unevenly distributed GO spread on the surface of the microporous membrane in a more uniform manner, playing a role in plugging large pores and leaving micropores.

[0010] Preferably, S2 includes the following steps: S201, Preparation of pseudo-boehmite seed slurry: The pseudo-boehmite seed slurry is prepared by stirring sodium aluminate, pseudo-boehmite seeds, and water in a weight ratio of 10-20:1-3:100; S202, Remove the vacuum pressure below the transparent film B, and continue to pour the pseudo-boehmite seed slurry above the transparent film B. The input amount of the pseudo-boehmite seed slurry is: when the liquid height reaches 3-5 mm, stop adding. Then, introduce 0.3 MPa of pure CO2 gas below the transparent film B, and let the gas pass through the micropores of the transparent film B into the pseudo-boehmite seed slurry, react for 15-20 min, remove the pure CO2 gas below, and carry out aging for 2-3 h under normal pressure with low leakage (leakage rate is 0.56 s / drop). Then, filter by suction to remove the clear liquid, and obtain a composite film C with a 4-5 μm thick aging layer; By reacting sodium aluminate with CO2 and inducing crystallization through seeds, pseudo-boehmite is obtained, that is, sodium aluminate reacts with CO2 to produce aluminum hydroxide colloid:

[0011] The aluminum hydroxide colloid crystallizes under the induction of crystals to obtain boehmite:

[0012] Preferably, S3 includes the following steps: S301. Prepare an acidolysis solution: Mix water and cetyltrimethylammonium chloride in a weight ratio of 100:3 - 4, add an aqueous hydrochloric acid solution with a weight concentration of 5wt%, and adjust the pH to 4 to obtain the acidolysis solution; S302. Pour the acidolysis solution above the composite membrane C. The input amount of the acidolysis solution is: stop adding when the liquid height reaches 3 - 5 mm, and react for 20 - 30 min. The aging layer of the composite membrane C gradually becomes a fluffy flocculent layer, and the thickness of the flocculent layer is about 7 - 9 μm; S303. At this time, introduce ammonia gas at 0.3 MPa below the composite membrane C. At this time, the leakage is significantly enhanced (the leakage rate is 1.89 s / drop, which may be due to the back - suction phenomenon of ammonia gas), and the ammonia gas continues to react for 30 min through the flocculent layer; S304. Remove the ammonia gas, introduce steam at 0.2 MPa and 100 °C below the composite membrane C, continuously react for 2 - 3 h, then remove the steam. After cooling to room temperature, age for 3 - 4 h; S305. Perform suction filtration at a low pressure of 1 - 5 kPa to obtain a boehmite crystallization layer. Through the mass transfer and heat conduction of steam and the heat conduction of the heat transfer wall, the alkaline flocculent layer adhering to ammonia undergoes a hydrothermal reaction, and crystallization is controlled in a narrow space to form a composite membrane D with a fluffy boehmite layer (the thickness of the boehmite layer after suction filtration is 2.5 - 3.5 μm).

[0013] Preferably, S4 includes the following steps: S401. Prepare an adhesive solution: Mix sodium carboxymethylcellulose, polyacrylate adhesives, wetting agents, mercapto - pyridine - polyethylene glycol - amino and water in a weight ratio of 2 - 3:7 - 9:1 - 2:5 - 6:100. After stirring and dissolving at 70 °C, cool to room temperature to obtain the adhesive solution; By adding adhesives and disulfides, the bonding effect is further improved. Moreover, disulfide bonds can self - repair under certain conditions (such as when the battery is short - circuited and generates heat), which can ensure the stability of the pore structure of the boehmite layer, and can convert polysulfur through reactions, thereby blocking the passage of polysulfide ions, and thus repairing and avoiding some risks of short - circuit high temperature; S402. Pour the adhesive solution above the composite membrane D. The input amount of the adhesive solution is: stop adding when the liquid height reaches 1 - 1.5 mm, and perform suction filtration until no liquid droplets flow down from the composite membrane D; S403. Introduce dry air at 0.2 MPa and 70 °C below the composite membrane D, and continuously dry for 30 - 40 min to obtain the finished product of the battery separator, and the thickness of the boehmite layer is about 2.5 - 3.5 μm.

[0014] The present invention also provides an application of the battery separator finished product obtained by the foregoing preparation process in a lithium-sulfur battery, which is characterized in that a cold pressing process is adopted, and the positive electrode material, the battery separator finished product and the negative electrode material are compacted by a cold press. After compaction, an electrolyte solution is infiltrated to obtain a battery. It is also possible to adopt the method of a wound-core battery, in which the positive electrode material, the battery separator finished product and the negative electrode material are alternately laid, wound into a wound core after cold pressing, and impregnated with an electrolyte solution to obtain a battery.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention first uses the method of in-situ deposition on the surface of a PP microporous separator to prepare a PP / boehmite composite membrane structure. By sequentially coating GO, pseudo-boehmite and boehmite on the PP microporous membrane, a multi-layer composite structure is formed, enhancing the mechanical strength of the separator. At the same time, components such as sodium carboxymethylcellulose and polyacrylate adhesives in the adhesive solution further improve the adhesion and stability of the boehmite layer, enabling the separator to withstand greater pressure during cold pressing without damage.

[0016] 2. The present invention conducts a grafting reaction between graphene oxide and mercapto-pyridine-polyethylene glycol-amine, and further adds mercapto-pyridine-polyethylene glycol-amine to the adhesive to form a microporous membrane with functional groups such as disulfide bonds and mercapto-pyridine. These functional groups can chemically react with polysulfide ions to promote their conversion to Li2S, thereby effectively inhibiting the shuttle of polysulfides in the separator and improving the cycle stability of the battery.

[0017] 3. The present invention produces a pseudo-boehmite layer from sodium aluminate, then prepares a fluffy flocculent layer through acidolysis, and finally converts it into a boehmite layer through an alkalization hydrothermal reaction. This in-situ reaction has stronger thermal shrinkage resistance compared to the separators in the prior art (the "Preparation method of an aqueous ceramic slurry for coating" disclosed in the applicant's CN114057430 A). And through multiple suction filtration treatments, the existence of large pores is avoided, thereby avoiding thermal cracking at high temperatures and improving the thermal stability of the battery during use.

[0018] 4. The present invention contains disulfide bonds in the adhesive solution. Under conditions such as battery short circuit and heat generation, the disulfide bonds can undergo a self-healing reaction to repair the pore structure of the boehmite layer, avoiding diaphragm damage and battery short circuit risks caused by high temperatures and improving the safety of the battery.

[0019] 5. In summary, the process of the present invention solves the problems of cracking of the existing PP / boehmite composite membrane caused by out-of-control temperature and humidity during drying and thermal cracking after being used in the battery for a period of time. At the same time, it improves the interception ability of polysulfide ions, providing a new technical solution for the preparation and application of cold-pressed battery separators, and having good market prospects and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a test diagram of the cycle current capacity of a battery using a cold-pressed battery diaphragm proposed by the present invention. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0022] 1. Preparation of diaphragm: Embodiment 1: A preparation process of a cold-pressed battery separator comprises the following steps: S1, GO coating: S101, placing a PP microporous membrane on top of a wire mesh, the square hole size of the wire mesh is 1mm×1mm, pouring a graphene oxide suspension with a mass concentration of 1mg / ml on top (Shenzhen Turing New Materials Co., Ltd., the original factory is 5mg / ml, and then adding dilute sulfuric acid with a weight concentration of 10wt% to dilute the suspension to increase the volume five times), the input amount of the graphene oxide suspension is: when the liquid height is 3mm, stop adding, the graphene oxide suspension contains sulfuric acid with a weight concentration of about 8wt%, and naturally filter, at this time, water slowly leaks (leakage rate is 0.03s / drop), until no liquid drips out from the bottom of the wire mesh, and the PP microporous membrane presents a transparent film A with light black spots; S102, prepare OPSS-PEG-Amino (customized by Xi'an Qiyue Biotechnology Co., Ltd., wherein PEG is PEG2000) into an aqueous solution with a weight concentration of 5wt%, and pour it on the transparent film A. The amount of OPSS-PEG-Amino aqueous solution added is: when the liquid height is 3mm, the addition is stopped, and the reaction is allowed to proceed naturally for 30-60min under low leakage (leakage rate is 0.08s / drop), and then the low pressure of 1-5kPa is used for suction filtration under the wire mesh to obtain a relatively uniform light black transparent film B; In the natural reaction process, GO forms a dissolution-sedimentation equilibrium. After being grafted with OPSS-PEG-Amino, PEG acts as a binder, making GO adhere more firmly to the PP microporous membrane. At the same time, the dissolution-sedimentation equilibrium also makes the originally unevenly distributed GO spread on the surface of the microporous membrane in a more uniform manner, playing the role of blocking large pores and leaving micropores. The adhesion effect can be judged by the bonding strength.

[0023] Adhesion test: The GO side of the dried transparent film A and transparent film B was adhered with tape (3M Scotch transparent tape) respectively (pressing firmly at a pressure of 10 N / mm and then tearing the film). The result was that after tearing the film once, the black spots on the tape of transparent film A were more obvious, while there were basically no black spots on the tape of transparent film B, proving that the adhesion of GO was significantly improved after grafting.

[0024] S2. Coating with pseudoboehmite: Refer to the method for preparing pseudoboehmite proposed in Patent CN 117735581 A: S201. Preparation of pseudoboehmite seed slurry: The pseudoboehmite seed slurry was prepared by stirring sodium aluminate (analytical pure, Macklin Shanghai), pseudoboehmite seeds (pseudoboehmite, 100 nm, Macklin Shanghai) and water in a weight ratio of 10:3:100. S202. Remove the vacuum pressure below transparent film B, and continue to pour the pseudoboehmite seed slurry above transparent film B. The input amount of the pseudoboehmite seed slurry is: stop adding when the liquid height reaches 5 mm. Then, introduce pure CO2 gas at 0.3 MPa below transparent film B to make the gas permeate through the micropores of transparent film B into the pseudoboehmite seed slurry, react for 15 - 20 min, remove the pure CO2 gas below, and carry out aging for 2 - 3 h under normal pressure with low leakage (leakage rate is 0.56 s / drop). Filter out the supernatant to obtain composite film C with an aging layer 4 - 5 μm thick. S3. Crystallization and film formation of boehmite: S301. Refer to the method for preparing boehmite from pseudoboehmite proposed in Patent CN 115140753 A: Prepare the acidolysis solution: Mix water and cetyltrimethylammonium chloride (dispersant, Sigma - Aldrich) in a weight ratio of 100:4, and add a hydrochloric acid aqueous solution with a weight concentration of 5 wt% to adjust the pH to 4 to obtain the acidolysis solution. S302. Pour the acidolysis solution above composite film C. The input amount of the acidolysis solution is: stop adding when the liquid height reaches 5 mm. React for 20 - 30 min, and the aging layer of composite film C gradually becomes a fluffy flocculent layer with a thickness of about 7 - 9 μm. S303. At this time, introduce ammonia gas at 0.3 MPa below composite film C. At this time, the leakage is significantly enhanced (leakage rate is 1.89 s / drop, probably due to the back - suction phenomenon of ammonia gas), and the ammonia gas permeates through the flocculent layer and continues to react for 30 min. S304. Remove the ammonia gas, introduce steam at 0.2 MPa and 100 °C below composite film C, and continue to react for 2 - 3 h. Then remove the steam, and after cooling to room temperature, carry out aging for 3 - 4 h. S305. Perform suction filtration at a low pressure of 1 - 5 kPa to obtain a boehmite crystal layer. Through water vapor mass transfer heat conduction and heat transfer wall heat conduction, the alkaline flocculent layer adhering with ammonia undergoes a hydrothermal reaction, and crystallization is controlled in a narrow space to form a composite membrane D with a flocculent and fluffy boehmite layer (the thickness of the boehmite layer after suction filtration is 2.5 - 3.5 μm).

[0025] S4. Preparation of the self - healing boehmite membrane: S401. Prepare the adhesive solution: Sodium carboxymethyl cellulose (CMC thickener, substitution degree 0.8 - 1.0, Sigma - Aldrich), polyacrylate adhesive (CHMEITAC6 polyacrylate rubber adhesive, Dalton, composed of a mixture of water, 2 - methyl - 2 - acrylic acid, butyl acrylate, and methyl 2 - methyl - 2 - acrylate, with a solid content of 20% - 48% and a viscosity of 800 - 4000 mPa·s), wetting agent (wetting agent P - 40, Guide Chemical), mercapto - pyridine - polyethylene glycol - amine, and water are mixed according to a weight ratio of 2:7:2:6:100. After stirring and dissolving at 70 °C, it is cooled to room temperature to obtain the adhesive solution; by adding the adhesive and disulfide, the bonding effect is further improved, and the disulfide bond can self - heal under certain conditions (such as when the battery short - circuits and heats up), which can ensure the stability of the pore structure of the boehmite layer, and can convert polysulfur through reaction, thereby blocking the passage of polysulfide ions, thus repairing and avoiding some risks of short - circuit high temperature; S402. Pour the adhesive solution above the composite membrane D. The input amount of the adhesive solution is: stop adding when the liquid height reaches 1.5 mm, and perform suction filtration until no liquid droplets flow down from the composite membrane D; S403. Pass dry air at 0.2 MPa and 70 °C below the composite membrane D and continuously dry for 30 - 40 min to obtain the finished product of the battery separator, and the thickness of the boehmite layer is about 2.5 - 3.5 μm.

[0026] Example 2: A preparation process of a cold - pressed battery separator includes the following steps: S1. GO coating: S101. Place the PP microporous membrane above the wire mesh, and pour the graphene oxide suspension with a mass concentration of 1 mg / ml above it. The input amount of the graphene oxide suspension is: stop adding when the liquid height reaches 4 mm. The graphene oxide suspension contains sulfuric acid with a weight concentration of about 8 wt%. Perform natural filtration. At this time, water slowly leaks (the leakage speed is 0.03 s / drop) until no liquid drips from the bottom surface of the wire mesh, and the PP microporous membrane presents a transparent membrane A with light black spots; S102. Prepare an aqueous solution of mercaptopyridine-polyethylene glycol-amine with a weight concentration of 5 wt%, pour it above the transparent film A, and the input amount of the mercaptopyridine-polyethylene glycol-amine aqueous solution is: stop adding when the liquid height reaches 4 mm, and under the condition of low leakage (the leakage rate is 0.08 s / drop), react naturally for 30 - 60 min, and then perform suction filtration under a low pressure of 1 - 5 kPa below the wire mesh to obtain a relatively uniform light black transparent film B; S2. Coating of pseudo-boehmite: S201. Preparation of pseudo-boehmite seed slurry: The pseudo-boehmite seed slurry is prepared by stirring sodium aluminate, pseudo-boehmite seeds and water according to a weight ratio of 15:2:100; S202. Remove the vacuum pressure below the transparent film B, continue to pour the pseudo-boehmite seed slurry above the transparent film B, and the input amount of the pseudo-boehmite seed slurry is: stop adding when the liquid height reaches 4 mm, and introduce 0.3 MPa of pure CO₂ gas below the transparent film B to make the gas permeate into the pseudo-boehmite seed slurry through the micropores of the transparent film B, react for 15 - 20 min, remove the pure CO₂ gas below, and age for 2 - 3 h under normal pressure and low leakage conditions (the leakage rate is 0.56 s / drop), and suction filter to remove the supernatant to obtain a composite film C with an aged layer 4 - 5 μm thick; S3. Crystallization and film formation of boehmite: S301. Prepare an acidolysis solution: Mix water and cetyltrimethylammonium chloride according to a weight ratio of 100:3.5, add a hydrochloric acid aqueous solution with a weight concentration of 5 wt%, and adjust the pH to 4 to obtain an acidolysis solution; S302. Pour the acidolysis solution above the composite film C, and the input amount of the acidolysis solution is: stop adding when the liquid height reaches 3 - 5 mm, react for 20 - 30 min, and the aged layer of the composite film C gradually becomes a fluffy flocculent layer, and the thickness of the flocculent layer is about 7 - 9 μm; S303. At this time, introduce 0.3 MPa of ammonia gas below the composite film C. At this time, the leakage is significantly enhanced (the leakage rate is 1.89 s / drop, probably due to the backflow phenomenon of ammonia gas), and the ammonia gas continues to react through the flocculent layer for 30 min; S304. Remove the ammonia gas, introduce steam at 0.2 MPa and 100 °C below the composite film C, continue to react for 2 - 3 h, remove the steam, and after cooling to room temperature, age for 3 - 4 h; S305. Perform suction filtration under a low pressure of 1 - 5 kPa to obtain a boehmite crystal layer. Through steam mass transfer and heat conduction and heat transfer wall heat conduction, the alkaline flocculent layer adhering to ammonia undergoes a hydrothermal reaction, and crystallization is controlled in a narrow space to form a composite film D with a fluffy boehmite layer (the thickness of the boehmite layer after suction filtration is 2.5 - 3.5 μm).

[0027] S4. Preparation of self-healing boehmite film: S401. Preparation of adhesive solution: Sodium carboxymethylcellulose, polyacrylate adhesive, wetting agent, mercapto pyridine-polyethylene glycol-amine and water are mixed in a weight ratio of 2.5:8:1.5:5.5:100, stirred and dissolved at 70 °C, and then cooled to room temperature to obtain the adhesive solution. S402. Pour the adhesive solution above the composite film D. The input amount of the adhesive solution is: stop adding when the liquid height reaches 1.3 mm, and filter by suction until no liquid droplets flow down from the composite film D. S403. Pass dry air at 0.2 MPa and 70 °C below the composite film D and continuously dry for 30 - 40 min to obtain the finished battery separator, and the thickness of the boehmite layer is about 2.5 - 3.5 μm.

[0028] Example 3: A preparation process of a cold-pressed battery separator includes the following steps: S1. GO coating: S101. Place the PP microporous membrane above the wire mesh, and pour the graphene oxide suspension with a mass concentration of 1 mg / ml above it. The input amount of the graphene oxide suspension is: stop adding when the liquid height reaches 5 mm. The graphene oxide suspension contains sulfuric acid with a weight concentration of about 8 wt%. Filter naturally. At this time, water leaks slowly (the leakage rate is 0.03 s / drop) until no liquid drips from the bottom surface of the wire mesh, and the PP microporous membrane presents a transparent film A with light black spots. S102. Prepare an aqueous solution of mercapto pyridine-polyethylene glycol-amine with a weight concentration of 5 wt% and pour it above the transparent film A. The input amount of the mercapto pyridine-polyethylene glycol-amine aqueous solution is: stop adding when the liquid height reaches 5 mm. React naturally for 30 - 60 min under low leakage (the leakage rate is 0.08 s / drop), and then perform suction filtration under a low pressure of 1 - 5 kPa below the wire mesh to obtain a relatively uniform light black transparent film B. S2. Boehmite-like coating: S201. Preparation of boehmite-like seed slurry: The boehmite-like seed slurry is prepared by stirring sodium aluminate, boehmite-like seeds and water in a weight ratio of 15:2:100. S202. Remove the vacuum pressure below the transparent film B, and continue to pour the boehmite seed slurry above the transparent film B. The input amount of the boehmite seed slurry is: stop adding when the liquid height reaches 4 mm. Then, introduce pure CO2 gas at 0.3 MPa below the transparent film B to allow the gas to permeate through the micropores of the transparent film B into the boehmite seed slurry, and react for 15 - 20 min. Then, remove the pure CO2 gas below. Under the condition of low leakage at normal pressure (the leakage rate is 0.56 s / drop), carry out aging for 2 - 3 h, and filter to remove the supernatant to obtain the composite film C with an aging layer 4 - 5 μm thick. S3. Crystallization and film formation of boehmite: S301. Prepare the acidolysis solution: Mix water and cetyltrimethylammonium chloride according to a weight ratio of 100:3, add a hydrochloric acid aqueous solution with a weight concentration of 5 wt%, and adjust the pH to 4 to obtain the acidolysis solution. S302. Pour the acidolysis solution above the composite film C. The input amount of the acidolysis solution is: stop adding when the liquid height reaches 3 mm. React for 20 - 30 min, and the aging layer of the composite film C gradually becomes a fluffy flocculent layer with a thickness of about 7 - 9 μm. S303. At this time, introduce ammonia gas at 0.3 MPa below the composite film C. At this time, the leakage is significantly enhanced (the leakage rate is 1.89 s / drop, possibly due to the back - suction phenomenon of ammonia gas), and the ammonia gas permeates through the flocculent layer and continues to react for 30 min. S304. Remove the ammonia gas, introduce water vapor at 0.2 MPa and 100 °C below the composite film C, and continue to react for 2 - 3 h. Then, remove the water vapor. After cooling to room temperature, carry out aging for 3 - 4 h. S305. Carry out suction filtration under a low pressure of 1 - 5 kPa to obtain the boehmite crystallization layer. Through water vapor mass transfer and heat conduction and heat transfer wall heat conduction, carry out hydrothermal reaction on the alkaline flocculent layer adhering to ammonia gas, and control crystallization in a narrow space to form a composite film D with a fluffy boehmite layer (the thickness of the boehmite layer after suction filtration is 2.5 - 3.5 μm).

[0029] S4. Preparation of the self - healing boehmite film: S401. Prepare the adhesive solution: Mix sodium carboxymethylcellulose, polyacrylate adhesives, wetting agents, mercapto - pyridine - polyethylene glycol - amine, and water according to a weight ratio of 3:9:1:5:100. After stirring and dissolving at 70 °C, cool to room temperature to obtain the adhesive solution. S402. Pour the adhesive solution above the composite film D. The input amount of the adhesive solution is: stop adding when the liquid height reaches 1 mm, and filter until no liquid droplets flow down from the composite film D. S403. Pass dry air at 0.2 MPa and 70 °C below the composite film D and continuously dry for 30 - 40 min to obtain the finished battery separator. The thickness of the boehmite layer is about 2.5 - 3.5 μm.

[0030] Comparative Example 1: A preparation process of a cold-pressed battery separator includes the following steps: S1. GO coating: Place the PP microporous membrane above the wire mesh. At the same time, pour a graphene oxide suspension with a mass concentration of 1 mg / ml and mercapto pyridine - polyethylene glycol - amino into an aqueous solution with a weight concentration of 5 wt% above the wire mesh. The liquid height is 8 mm, and react naturally for 30 - 60 min under low leakage conditions. Then, perform suction filtration at a low pressure of 1 - 5 kPa below the wire mesh to obtain a relatively uniform light black transparent film B. S2. Boehmite coating: S201. Preparation of boehmite seed slurry: The boehmite seed slurry is prepared by stirring sodium aluminate, boehmite seeds and water according to a weight ratio of 15:2:100. S202. Remove the vacuum pressure below the transparent film B, and continue to pour the boehmite seed slurry above the transparent film B. The input amount of the boehmite seed slurry is: stop adding when the liquid height reaches 4 mm. Pass pure CO2 gas at 0.3 MPa below the transparent film B to allow the gas to penetrate into the boehmite seed slurry through the micropores of the transparent film B, react for 15 - 20 min, remove the pure CO2 gas below, and age for 2 - 3 h under normal pressure and low leakage conditions (leakage rate is 0.56 s / drop). Filter out the clear liquid to obtain a composite film C with a 4 - 5 μm thick aged layer. S3. Crystallization film formation of boehmite: S301. Prepare the acidolysis solution: Mix water and cetyltrimethylammonium chloride according to a weight ratio of 100:3.5, add a hydrochloric acid aqueous solution with a weight concentration of 5 wt%, and adjust the pH to 4 to obtain the acidolysis solution. S302. Pour the acidolysis solution above the composite film C. The input amount of the acidolysis solution is: stop adding when the liquid height reaches 3 - 5 mm, and react for 20 - 30 min. The aged layer of the composite film C gradually becomes a fluffy flocculent layer, and the thickness of the flocculent layer is about 7 - 9 μm. S303. At this time, pass ammonia gas at 0.3 MPa below the composite film C. At this time, the leakage is significantly enhanced (the leakage rate is 1.89 s / drop, which may be due to the back suction phenomenon of ammonia gas), and the ammonia gas penetrates through the flocculent layer and continues to react for 30 min. S304. Remove ammonia gas, introduce steam at 0.2 MPa and 100 °C below the composite membrane C, and continue the reaction for 2 - 3 h. Then remove the steam. After cooling to room temperature, age for 3 - 4 h; S305. Perform suction filtration under a low pressure of 1 - 5 kPa to obtain a boehmite crystal layer. Through steam mass transfer heat conduction and heat transfer wall heat conduction, the alkaline flocculent layer adhering with ammonia gas undergoes a hydrothermal reaction, and crystallization is controlled in a narrow space to form a composite membrane D with a flocculent and fluffy boehmite layer (the thickness of the boehmite layer after suction filtration is 2.5 - 3.5 μm).

[0031] S4. Preparation of the self - healing boehmite membrane: S401. Prepare the adhesive solution: Sodium carboxymethylcellulose, polyacrylate adhesive, wetting agent, mercapto - pyridine - polyethylene glycol - amine, and water are mixed according to a weight ratio of 2.5:8:1.5:5.5:100. After stirring and dissolving at 70 °C, cool to room temperature to obtain the adhesive solution; S402. Pour the adhesive solution above the composite membrane D. The input amount of the adhesive solution is: stop adding when the liquid height reaches 1.3 mm, and then perform suction filtration until no liquid droplets flow down from the composite membrane D; S403. Introduce dry air at 0.2 MPa and 70 °C below the composite membrane D, and continue drying for 30 - 40 min to obtain the finished battery separator membrane, and the thickness of the boehmite layer is about 2.5 - 3.5 μm.

[0032] Comparative Example 2: A preparation process of a cold - pressed battery separator membrane includes the following steps: S1. GO coating: S101. Place the PP microporous membrane above the wire mesh, and pour the graphene oxide suspension with a mass concentration of 1 mg / ml above it. The input amount of the graphene oxide suspension is: stop adding when the liquid height reaches 4 mm. The graphene oxide suspension contains sulfuric acid with a weight concentration of about 8 wt%. Perform natural filtration. At this time, water slowly leaks (the leakage rate is 0.03 s / drop) until no liquid droplets drip from the bottom surface of the wire mesh, and the PP microporous membrane presents a transparent membrane A with light black spots; S102. Prepare an aqueous solution of mercapto - pyridine - polyethylene glycol - amine with a weight concentration of 5 wt%, and pour it above the transparent membrane A. The input amount of the mercapto - pyridine - polyethylene glycol - amine aqueous solution is: stop adding when the liquid height reaches 4 mm. React naturally for 30 - 60 min under low leakage (the leakage rate is 0.08 s / drop), and then perform suction filtration under a low pressure of 1 - 5 kPa below the wire mesh to obtain a relatively uniform light - black transparent membrane B; S2. Pseudoboehmite coating: S201. Preparation of pseudo-boehmite seed slurry: The pseudo-boehmite seed slurry is prepared by stirring sodium aluminate, pseudo-boehmite seeds and water in a weight ratio of 15:2:100; S202. Remove the vacuum pressure below the transparent film B, and continue to pour the pseudo-boehmite seed slurry above the transparent film B. The input amount of the pseudo-boehmite seed slurry is: when the liquid height reaches 4 mm, stop adding. Directly introduce pure CO2 gas at 0.3 MPa into the pseudo-boehmite seed slurry, so that the gas permeates into the pseudo-boehmite seed slurry through the micropores of the transparent film B, react for 15 - 20 min, remove the pure CO2 gas below, and carry out aging for 2 - 3 h under normal pressure with low leakage (leakage rate is 0.56 s / drop). Filter by suction to remove the clear liquid, and obtain a composite film C with an aging layer 4 - 5 μm thick; S3. Crystallization and film formation of boehmite: S301. Prepare the acidolysis solution: Mix water and cetyltrimethylammonium chloride in a weight ratio of 100:3.5, add a hydrochloric acid aqueous solution with a weight concentration of 5 wt%, and adjust the pH to 4 to obtain the acidolysis solution; S302. Pour the acidolysis solution above the composite film C. The input amount of the acidolysis solution is: when the liquid height reaches 3 - 5 mm, stop adding, and react for 20 - 30 min. The aging layer of the composite film C gradually becomes a fluffy flocculent layer, and the thickness of the flocculent layer is about 7 - 9 μm; S303. At this time, introduce ammonia gas at 0.3 MPa below the composite film C. At this time, the leakage is significantly enhanced (the leakage rate is 1.89 s / drop, which may be due to the back suction phenomenon of ammonia gas), and the ammonia gas continues to react for 30 min through the flocculent layer; S304. Remove the ammonia gas, introduce steam at 0.2 MPa and 100 °C below the composite film C, and continue to react for 2 - 3 h. Remove the steam, and after cooling to room temperature, age for 3 - 4 h; S305. Carry out suction filtration under a low pressure of 1 - 5 kPa to obtain a boehmite crystal layer. Through steam mass transfer and heat conduction and heat transfer wall heat conduction, carry out hydrothermal reaction on the alkaline flocculent layer adhering to ammonia gas, and control crystallization in a narrow space to form a composite film D with a fluffy boehmite layer (the thickness of the boehmite layer after suction filtration is 2.5 - 3.5 μm);

[0033] S4. Preparation of self-healing boehmite film: S401. Prepare the adhesive solution: Mix sodium carboxymethylcellulose, polyacrylate adhesives, wetting agents, mercapto pyridine - polyethylene glycol - amino and water in a weight ratio of 2.5:8:1.5:5.5:100, stir and dissolve at 70 °C, and then cool to room temperature to obtain the adhesive solution; S402. Pour the adhesive solution above the composite film D. The input amount of the adhesive solution is as follows: when the liquid height reaches 1.3 mm, stop adding, and perform suction filtration until no liquid droplets flow down from the composite film D. S403. Pass dry air at 0.2 MPa and 70 °C below the composite film D, and continuously dry for 30 - 40 min to obtain the finished battery separator. The thickness of the boehmite layer is about 2.5 - 3.5 μm.

[0034] Comparative Example 3: A preparation process of a cold - pressed battery separator includes the following steps: S1. GO coating: S101. Place the PP microporous membrane above the wire mesh, and pour the graphene oxide suspension with a mass concentration of 1 mg / ml above it. The input amount of the graphene oxide suspension is as follows: when the liquid height reaches 4 mm, stop adding. The graphene oxide suspension contains sulfuric acid with a weight concentration of about 8 wt%. Perform natural filtration. At this time, water slowly leaks (the leakage speed is 0.03 s / drop) until no liquid drips from the bottom surface of the wire mesh, and the PP microporous membrane presents a transparent film A with light black spots. S102. Prepare an aqueous solution of mercapto - pyridine - polyethylene glycol - amine with a weight concentration of 5 wt% and pour it above the transparent film A. The input amount of the mercapto - pyridine - polyethylene glycol - amine aqueous solution is as follows: when the liquid height reaches 4 mm, stop adding. React naturally for 30 - 60 min under low leakage (the leakage speed is 0.08 s / drop), and then perform suction filtration at a low pressure of 1 - 5 kPa below the wire mesh to obtain a relatively uniform light - black transparent film B. S2. Boehmite coating: S201. Preparation of the boehmite seed slurry: The boehmite seed slurry is prepared by stirring sodium aluminate, boehmite seeds and water in a weight ratio of 15:2:100. S202. Remove the vacuum pressure below the transparent film B, and continue to pour the boehmite seed slurry above the transparent film B. The input amount of the boehmite seed slurry is as follows: when the liquid height reaches 4 mm, stop adding. Pass pure CO2 gas at 0.3 MPa below the transparent film B to make the gas permeate into the boehmite seed slurry through the micropores of the transparent film B, and react for 15 - 20 min. Then remove the pure CO2 gas below, and perform aging for 2 - 3 h under normal pressure and low leakage (the leakage speed is 0.56 s / drop). Filter out the clear liquid to obtain a composite film C with a 4 - 5 μm thick aging layer. S3. Crystallization and film - formation of boehmite: S301. Prepare the acid - hydrolysis solution: Mix water and cetyltrimethylammonium chloride in a weight ratio of 100:3.5, add an aqueous hydrochloric acid solution with a weight concentration of 5 wt%, and adjust the pH to 4 to obtain the acid - hydrolysis solution. S302. Pour the acidolysis solution above the composite membrane C. The input amount of the acidolysis solution is such that when the liquid height reaches 3 - 5 mm, stop adding. React for 20 - 30 min. The aging layer of the composite membrane C gradually becomes a fluffy flocculent layer, and the thickness of the flocculent layer is about 7 - 9 μm. S303. Directly introduce ammonia gas at 0.3 MPa into the acidolysis solution and continue to react for 30 min. S304. Remove the ammonia gas. Directly introduce steam at 0.2 MPa and 100 °C into the acidolysis solution and continuously react for 2 - 3 h. Then remove the steam. After cooling to room temperature, age for 3 - 4 h. S305. Perform suction filtration under a low pressure of 1 - 5 kPa to obtain a boehmite crystal layer. Through steam mass transfer and heat conduction and heat transfer wall heat conduction, the alkaline flocculent layer adhering with ammonia gas undergoes hydrothermal reaction, and crystallization is controlled in a narrow space to form a composite membrane D with a fluffy boehmite layer (the thickness of the boehmite layer after suction filtration is 2.5 - 3.5 μm).

[0035] S4. Preparation of the self - healing boehmite membrane: S401. Prepare the adhesive solution: Sodium carboxymethylcellulose, polyacrylate adhesives, wetting agents, mercapto - pyridine - polyethylene glycol - amine, and water are mixed according to a weight ratio of 2.5:8:1.5:5.5:100. After stirring and dissolving at 70 °C, cool to room temperature to obtain the adhesive solution. S402. Pour the adhesive solution above the composite membrane D. The input amount of the adhesive solution is such that when the liquid height reaches 1.3 mm, stop adding. Perform suction filtration until no liquid droplets flow from the composite membrane D. S403. Introduce dry air at 0.2 MPa and 70 °C below the composite membrane D and continuously dry for 30 - 40 min to obtain the finished product of the battery separator, and the thickness of the boehmite layer is about 2.5 - 3.5 μm.

[0036] Comparative Example 4: A preparation process of a cold - pressed battery separator includes the following steps: S1. GO coating: S101. Place the PP microporous membrane above the iron wire mesh. Pour the graphene oxide suspension with a mass concentration of 1 mg / ml above it. The input amount of the graphene oxide suspension is such that when the liquid height reaches 4 mm, stop adding. The graphene oxide suspension contains sulfuric acid with a weight concentration of about 8 wt%. Perform natural filtration. At this time, water slowly leaks (the leakage speed is 0.03 s / drop) until no liquid droplets drip from the bottom surface of the iron wire mesh, and the PP microporous membrane presents a transparent membrane A with light black spots. S102. Prepare an aqueous solution of mercaptopyridine-polyethylene glycol-amine with a weight concentration of 5 wt%, pour it above the transparent film A, and the input amount of the mercaptopyridine-polyethylene glycol-amine aqueous solution is: stop adding when the liquid height reaches 4 mm. Under the condition of low leakage (the leakage rate is 0.08 s / drop), react naturally for 30 - 60 min, and then perform suction filtration under a low pressure of 1 - 5 kPa below the wire mesh to obtain a relatively uniform light black transparent film B; S2. Coating of pseudo-boehmite: S201. Preparation of pseudo-boehmite seed slurry: The pseudo-boehmite seed slurry is prepared by stirring sodium aluminate, pseudo-boehmite seeds and water according to a weight ratio of 15:2:100; S202. Remove the vacuum pressure below the transparent film B, continue to pour the pseudo-boehmite seed slurry above the transparent film B, and the input amount of the pseudo-boehmite seed slurry is: stop adding when the liquid height reaches 4 mm. Pass 0.3 MPa of pure CO₂ gas below the transparent film B to make the gas permeate into the pseudo-boehmite seed slurry through the micropores of the transparent film B, react for 15 - 20 min, remove the pure CO₂ gas below, and age for 2 - 3 h under the condition of low leakage at normal pressure (the leakage rate is 0.56 s / drop), and filter to remove the supernatant to obtain a composite film C with an aged layer 4 - 5 μm thick; S3. Crystallization and film formation of boehmite: S301. Prepare an acidolysis solution: Mix water and cetyltrimethylammonium chloride according to a weight ratio of 100:3.5, add an aqueous hydrochloric acid solution with a weight concentration of 5 wt%, and adjust the pH to 4 to obtain an acidolysis solution; S302. Pour the acidolysis solution above the composite film C, and the input amount of the acidolysis solution is: stop adding when the liquid height reaches 3 - 5 mm. React for 20 - 30 min, and the aged layer of the composite film C gradually becomes a fluffy flocculent layer with a thickness of about 7 - 9 μm; S303. At this time, pass 0.3 MPa of ammonia gas below the composite film C. At this time, the leakage is significantly enhanced (the leakage rate is 1.89 s / drop, which may be due to the back suction phenomenon of ammonia gas), and the ammonia gas continues to react for 30 min through the flocculent layer; S304. Remove the ammonia gas, pass 0.2 MPa of steam at 100 °C below the composite film C, and continue to react for 2 - 3 h. Remove the steam, and after cooling to room temperature, age for 3 - 4 h; S305. Perform suction filtration under a low pressure of 1 - 5 kPa to obtain a boehmite crystallization layer. Through steam mass transfer and heat conduction and heat transfer wall heat conduction, the basic flocculent layer adhering to ammonia gas undergoes a hydrothermal reaction, and crystallization is controlled in a narrow space to form a composite film D with a fluffy boehmite layer (the thickness of the boehmite layer after suction filtration is 2.5 - 3.5 μm).

[0037] S4. Preparation of Self-healing Boehmite Film: S401. Preparation of Adhesive Solution: Sodium carboxymethylcellulose, polyacrylate adhesive, wetting agent, mercapto-pyridine-polyethylene glycol-amine and water are mixed in a weight ratio of 2.5:8:1.5:5.5:100, stirred and dissolved at 70 °C, and then cooled to room temperature to obtain the adhesive solution; S402. Pour the adhesive solution above the composite film D. The input amount of the adhesive solution is: stop adding when the liquid height reaches 1.3 mm, and filter until no liquid droplets flow down from the composite film D; S403. Pass dry air at 0.2 MPa and 70 °C above the composite film D and dry continuously for 30 - 40 min to obtain the finished battery separator membrane, and the thickness of the Boehmite layer is about 2.5 - 3.5 μm.

[0038] II. Performance Testing of the Separator: 1. Testing Standards: Air Permeability Increase: T / SEN 001 - 2007; Transverse (MD) Thermal Shrinkage Rate: GB / T 2027 - 2004; 150 °C / h, take the average of two measurements; Longitudinal (TD) Thermal Shrinkage Rate: GB / T 2027 - 2004: 150 °C / h, take the average of two measurements.

[0039] 2. Test Results Table 1. Air Permeability and Thermal Shrinkage Resistance Performance of the Separator

[0040] As can be seen from Table 1, comparing Examples 1 - 3, with the increase in the amounts of graphene oxide suspension and mercapto-pyridine-polyethylene glycol-amine aqueous solution, the air permeability increase gradually decreases, indicating that the formation of the GO filtration membrane and the increase in its thickness reduce the air permeability, and in the balance relationship between lithium ion permeability and polysulfide ion blocking. Therefore, the input amounts of each reagent in Example 2 have relatively superior effects; with the increase in the amounts of pseudoboehmite seed slurry and acidolysis solution used, the thermal shrinkage resistance first increases and then decreases.

[0041] Compared with Example 2, in Comparative Example 1, a mixture of graphene oxide suspension and mercapto-pyridine-polyethylene glycol-amine aqueous solution is selected, and the air permeability slightly increases, but the thermal shrinkage resistance decreases, which may be due to the non-uniformity of GO on the porous membrane.

[0042] Compared with Example 2, in Comparative Example 2, an excessive amount of CO2 gas is directly introduced into the pseudoboehmite seed slurry, resulting in the formation of large crystals, and a relatively thick inorganic layer is formed without aging. It is easy to understand that both the air permeability and the thermal shrinkage resistance are poor; Comparative Example 3, compared with Example 2, chose to directly introduce ammonia gas into the acidolysis solution and then directly introduce water vapor after the reaction. Since the slow reaction through the microporous ventilation was not utilized, the crystals were larger and its performance was worse than that of Comparative Example 2. Comparative Example 4, compared with Example 2, chose to introduce dry air above Composite Membrane D. Its performance was slightly different from that of Example 2. This difference might stem from the fact that the pore size of the bottom surface of Composite Membrane D was larger than that of the top surface, resulting in a slower drying rate. The volatile components for pore formation by membrane volatilization were not easily transferred from top to bottom, causing a decrease in the porosity of the top surface.

[0043] III. Battery Assembly: Comparative Example 5: In S1 of Example 2, the aqueous solution of mercapto pyridine - polyethylene glycol - amino was not added.

[0044] Comparative Example 6: In the adhesive solution of S4 of Example 2, mercapto pyridine - polyethylene glycol - amino was not added.

[0045] Comparative Example 7: In S1 of Example 2, the aqueous solution of mercapto pyridine - polyethylene glycol - amino was not added, and in the adhesive solution of S4 of Example 2, mercapto pyridine - polyethylene glycol - amino was not added.

[0046] The diaphragms obtained from Examples 1 - 3 and Comparative Examples 5 - 7 were assembled into batteries. The preparation of the batteries referred to Patent CN 117895182A, a preparation method of a high - entropy alloy - modified lithium - sulfur battery diaphragm and a lithium - sulfur battery diaphragm: 10 grams of sulfur, 2 grams of mesoporous carbon, 0.5 gram of Super P (conductive carbon black), 10 grams of CMC (carboxymethyl cellulose) - 2000 (solid content 1.5%), and 1 gram of SBR (styrene - butadiene rubber) (solid content 50%) were mixed, with water as the solvent to form a slurry, stirred for 12 h, and coated on aluminum foil as the positive electrode; metallic lithium was used as the negative electrode, the diaphragms obtained from Examples 1 - 3 and Comparative Examples 5 - 7 were used, 1 mo1 / L of LiTFSI (lithium trifluoromethanesulfonimide) dissolved in DOL / DME (volume ratio 1:1) solvent was used as the electrolyte, and 1 mo1 / L of LiNO3 (lithium nitrate) was used as an additive; button batteries were assembled in a glove box. A blue - electric test system was used for constant - current charge - discharge testing. The charge - discharge current was 0.05C, the charge - discharge voltage range was 1.8 - 2.8 volts, and the capacity retention rate of the lithium - sulfur battery after 100 cycles was 82%. DOL is a small cyclic ether molecule and DME is dimethyl ether.

[0047] Refer to Figure 1 , after 400 cycles at 1C, the capacity was tested. Refer to Figure 1 , after 400 cycles at 1C for Examples 1 - 3, it still maintained > 550 mAh·g -1capacity, while the capacities of Comparative Examples 5-7 decreased sharply after 50 cycles at 1C, and only about 100 mAh·g remained after 400 cycles. -1 or so.

[0048] As described above, only the preferred specific embodiments of the present invention are provided, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solutions and inventive concepts of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A preparation process of a cold-pressed battery separator, characterized in that, It includes the following steps: S1. GO coating: Pour the graphene oxide suspension above the PP microporous membrane, and leak to obtain a transparent film A with light black spots; Pour the mercaptopyridine-polyethylene glycol-amine aqueous solution above the transparent film A, leak and react, then filter by suction to obtain a light black transparent film B; S2. Boehmite coating: Pour the boehmite seed slurry above the transparent film B, and introduce CO2 for reaction. After aging, filter by suction to obtain a composite film C with an aging layer; S3. Crystallization and film formation of boehmite: Pour the acidolysis solution above the composite film C for reaction. The aging layer of the composite film C gradually becomes a fluffy flocculent layer. Introduce ammonia gas below the composite film C for reaction, and finally introduce water vapor for in-situ hydrothermal reaction, aging, and filtration by suction to obtain a composite film D with a fluffy boehmite layer; S4. Preparation of self-healing boehmite film: Pour the adhesive solution containing mercaptopyridine-polyethylene glycol-amine above the composite film D, filter by suction and dry in ventilation to obtain the finished product of the battery separator.

2. The preparation process of a cold-pressed battery separator according to claim 1, characterized in that, The S1 includes the following steps: S101. Place the PP microporous membrane above the wire mesh. The size of the square holes of the wire mesh is 1 mm×1 mm. Pour the graphene oxide suspension with a mass concentration of 1 mg / ml above it. The input amount of the graphene oxide suspension is: stop adding when the liquid height is 3 - 5 mm. The graphene oxide suspension contains sulfuric acid with a weight concentration of about 8 wt%. Filter naturally. At this time, the water slowly leaks until no liquid drips from the bottom surface of the wire mesh, and the PP microporous membrane presents a transparent film A with light black spots; S102. Prepare an aqueous solution of mercaptopyridine-polyethylene glycol-amine with a weight concentration of 5 wt%, pour it above the transparent film A. The input amount of the mercaptopyridine-polyethylene glycol-amine aqueous solution is: stop adding when the liquid height is 3 - 5 mm. React naturally for 30 - 60 min under low leakage conditions, and then perform suction filtration at a low pressure of 1 - 5 kPa below the wire mesh to obtain a relatively uniform light black transparent film B.

3. The preparation process of a cold-pressed battery separator according to claim 1, characterized in that, The S2 includes the following steps: S201. Preparation of boehmite seed slurry: The boehmite seed slurry is prepared by stirring sodium aluminate, boehmite seeds and water in a weight ratio of 10 - 20:1 - 3:100; S202. Remove the vacuum pressure below the transparent film B, and continue to pour the boehmite seed slurry above the transparent film B. The input amount of the boehmite seed slurry is: stop adding when the liquid height is 3 - 5 mm. Introduce pure CO2 gas with a pressure of 0.3 MPa below the transparent film B to make the gas penetrate into the boehmite seed slurry through the micropores of the transparent film B, react for 15 - 20 min, remove the pure CO2 gas below, and age for 2 - 3 h under low leakage at normal pressure, then filter by suction to remove the clear liquid to obtain a composite film C with an aging layer 4 - 5 μm thick.

4. The preparation process of a cold-pressed battery separator according to claim 1, characterized in that The S3 includes the following steps: S301. Prepare the acidolysis solution: Mix water and cetyltrimethylammonium chloride in a weight ratio of 100:3 - 4, add a hydrochloric acid aqueous solution with a weight concentration of 5 wt%, and adjust the pH to 4 to obtain the acidolysis solution; S302. Pour the acidolysis solution above the composite film C. The input amount of the acidolysis solution is such that when the liquid height reaches 3 - 5 mm, stop adding. React for 20 - 30 min. The aging layer of the composite film C gradually becomes a fluffy flocculent layer, and the thickness of the flocculent layer is about 7 - 9 μm. S303. At this time, introduce ammonia gas at 0.3 MPa below the composite film C. At this time, the leakage is significantly enhanced, and the ammonia gas passes through the flocculent layer and continues to react for 30 min. S304. Remove the ammonia gas. Introduce steam at 0.2 MPa and 100 °C below the composite film C and continuously react for 2 - 3 h. Then remove the steam. After cooling to room temperature, age for 3 - 4 h. S305. Perform suction filtration at a low pressure of 1 - 5 kPa to obtain a boehmite crystal layer. Through steam mass transfer heat conduction and heat transfer wall heat conduction, the alkaline flocculent layer adhering with ammonia gas undergoes a hydrothermal reaction, and crystallization is controlled in a narrow space to form a composite film D with a fluffy boehmite layer.

5. The preparation process of a cold-pressed battery separator according to claim 1, characterized in that, The said S4 includes the following steps: S401. Prepare an adhesive solution: Sodium carboxymethylcellulose, polyacrylate adhesive, wetting agent, mercapto - pyridine - polyethylene glycol - amino, and water are mixed according to a weight ratio of 2 - 3:7 - 9:1 - 2:5 - 6:

100. After stirring and dissolving at 70 °C, cool to room temperature to obtain the adhesive solution. S402. Pour the adhesive solution above the composite film D. The input amount of the adhesive solution is such that when the liquid height reaches 1 - 1.5 mm, stop adding. Suction filter until no liquid droplets flow down from the composite film D. S403. Introduce dry air at 0.2 MPa and 70 °C below the composite film D and continuously dry for 30 - 40 min to obtain the finished product of the battery separator. The thickness of the boehmite layer is about 2.5 - 3.5 μm.

6. Use of the battery separator finished product obtained by the preparation process according to any one of claims 1-5 in a lithium-sulfur battery, characterized in that, Adopt a cold pressing process to compact the positive electrode material, the finished product of the battery separator, and the negative electrode material through a cold press. After compaction, infiltrate the electrolyte solution to obtain the battery.

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