Preparation method and application of solid-state lithium battery diaphragm

Abstract

The invention provides a preparation method of a solid-state lithium battery diaphragm, which comprises the following steps: preparing diaphragm slurry, uniformly coating a substrate with the diaphragm slurry to form a wet diaphragm, covering the wet diaphragm with a high polymer material plate, then covering the high polymer material plate with a quartz glass cover plate, and carrying out static pressure to obtain a diaphragm assembly; after the diaphragm assembly is cured, the glass cover plate and the high polymer material plate are removed in sequence, the cured diaphragm is stripped from the substrate, and a formed diaphragm is obtained; and extracting, drying and rolling the formed diaphragm to obtain the solid-state lithium battery diaphragm. The invention also provides application of the solid-state lithium battery diaphragm prepared by the preparation method, and the solid-state lithium battery diaphragm is used for preparing a lithium battery. The preparation method of the solid-state lithium battery diaphragm is simple in process and low in cost; the thickness of the prepared battery diaphragm is determined by the mechanical thickness of the high polymer material plate, so that the ultrathin diaphragm can be realized; the performance is excellent, and the porosity and the air permeability are good.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, specifically relating to a method for preparing a solid-state lithium battery separator and its application. Background Technology

[0002] Solid-state lithium battery separators are one of the key internal components of lithium-ion batteries, and their performance (such as thickness uniformity, porosity, mechanical strength, and thermal stability) directly determines the battery's capacity, cycle life, and safety. Currently, fabricating ultra-thin, uniform solid-state lithium battery separators (especially wet-process separators) is a technological challenge.

[0003] Traditional methods for controlling diaphragm thickness mainly include: ① Blade coating: This method uses a blade to smooth the slurry, but it requires extremely high precision and flatness of the blade, easily resulting in scratches, uneven thickness, and other problems, and it is difficult to produce ultra-thin (e.g., <50μm) diaphragms. ② Casting: The slurry flows out through a slit mold and forms on a substrate. Thickness control depends on the precision of the mold slit and the rheological properties of the slurry, and it also suffers from edge effects and thickness fluctuations. ③ Roll calendering: The formed substrate film is calendered to control thickness and porosity, but this method involves high pressure, which can easily damage the microporous structure of the diaphragm, leading to decreased porosity and performance degradation. These traditional methods generally suffer from technical bottlenecks such as poor control of diaphragm thickness uniformity, difficulty in achieving ultra-thin diaphragms, and easy damage to the diaphragm's microstructure during production. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing a solid lithium battery separator and its application, which addresses the shortcomings of the prior art. The method is simple and low in cost. The thickness of the prepared solid lithium battery separator is determined by the mechanical thickness of the polymer material plate, which can achieve ultra-thin separator with excellent performance, including good porosity, air permeability and mechanical properties.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing a solid-state lithium battery separator, the method being as follows: S1. Preparation of diaphragm slurry: Polyvinylidene fluoride-hexafluoropropylene was dissolved in N-methylpyrrolidone, and then a pore-forming agent was added. After stirring and dispersing, a diaphragm slurry was obtained. S2, Lamination thickness control: The diaphragm slurry obtained in S1 is uniformly coated on the substrate to form a wet diaphragm. A polymer material plate is then covered on the wet diaphragm, and a quartz glass cover plate is then covered on the polymer material plate. After static pressing, a diaphragm assembly is obtained. Using polymer material plates as thickness control spacers: Unlike the dynamic scraping of a scraper or the strong pressure of rollers, using static, precisely thick polymer material plates as physical limits fundamentally ensures the accuracy and consistency of the prepared thickness. The unique combination of "rigid pressure plate + flexible spacer" ensures absolute uniformity of pressure across the entire plane by utilizing the rigidity of the glass cover plate and the flexibility of the polymer material plate to perfectly fit the slurry surface. This not only transmits pressure but also avoids adhesion or damage to the film surface due to its non-stickiness. This is the ingenuity of the invention. S3, Curing and Molding: The diaphragm assembly obtained in S2 is cured and cooled. The glass cover plate and the polymer material plate are removed in sequence, and the cured diaphragm is peeled off from the substrate to obtain the formed diaphragm. Due to the excellent non-stick properties of the polymer material plate, it can be peeled off from the cured diaphragm surface without any damage; S4. Post-processing: The shaped separator obtained in S3 is immersed in ethanol for extraction, dried, and wound up to obtain a solid lithium battery separator.

[0006] Preferably, the pore-forming agent in S1 is silica, lithium aluminum titanium phosphate, lithium difluorosulfonyl imide, lithium lanthanum zirconium oxide, or tantalum-doped lithium lanthanum zirconium oxide; the stirring conditions are: stirring at a speed of 1500 rpm to 2000 rpm for 30 min to 60 min; the mass ratio of polyvinylidene fluoride-hexafluoropropylene to the pore-forming agent is 4:3.

[0007] Preferably, the coating method in S2 is spin coating, blade coating, or casting; the size of the substrate is 300mm×300mm; the thickness of the polymer material plate is selected according to the final required thickness of the solid-state lithium battery separator; and the static pressing time is 60s.

[0008] Preferably, the substrate in S2 is a glass plate, a stainless steel plate, a silicon wafer plate, or a silicon wafer plate; the polymer material plate is a polytetrafluoroethylene plate, a fluoroethylene-propylene copolymer plate, a soluble polytetrafluoroethylene plate, or an ethylene-tetrafluoroethylene copolymer plate.

[0009] Preferably, the curing conditions in S3 are: curing at a temperature of 60℃~80℃ for 1min~5min; and cooling to a temperature of 20℃~25℃.

[0010] Preferably, the extraction time in S4 is 10h to 12h; the drying conditions are: drying at a temperature of 50℃ to 60℃ for 10h to 12h.

[0011] Preferably, the solid-state lithium battery separator in S4 has an average thickness of 19μm to 30μm, a porosity of 40% to 60%, and an air permeability of 200s / 100cc to 300s / 100cc.

[0012] The present invention also provides the application of the solid lithium battery separator prepared by the above preparation method, wherein the solid lithium battery separator is used to prepare lithium batteries.

[0013] Compared with the prior art, the present invention has the following advantages: 1. The solid-state lithium battery separator of the present invention has extremely high thickness accuracy and good uniformity. The thickness of the separator is determined by the mechanical thickness of the polymer material plate such as PTFE / FEP / PFA / ETFE, so a separator with extremely small thickness tolerance (such as within ±0.5μm) can be prepared.

[0014] 2. This invention can achieve ultra-thin solid-state lithium battery separators. By selecting ultra-thin polymer material plates, ultra-thin separators can be easily prepared with a high yield rate.

[0015] 3. The solid-state lithium battery separator of the present invention has excellent performance. Due to the gentle molding process and the absence of strong extrusion, the microporous structure that has been formed or is about to be formed in the wet separator is protected to the maximum extent, and its porosity and air permeability (Gurley value) are well maintained.

[0016] 4. The solid lithium battery separator of the present invention has a simple preparation process and low cost. It does not require a high-precision scraper or slit mold. The cost of the main consumable material, polymer material plate, is controllable and can be reused multiple times, which is conducive to large-scale industrial production.

[0017] 5. The solid-state lithium battery separator of the present invention has good surface quality. The non-adhesiveness of the polymer material plates such as PTFE / FEP / PFA / ETFE ensures that the separator surface is smooth, without scratches, and without adhering contaminants.

[0018] 6. The unique combination of "rigid pressure plate + flexible spacer" in this invention: The rigidity of the quartz glass cover plate is used to ensure the absolute uniformity of pressure throughout the entire plane, and the flexibility of polymer materials such as PTFE / FEP / PFA / ETFE is used to perfectly fit the surface of the slurry. It not only transmits pressure, but also does not stick or damage the film surface due to its non-stickiness.

[0019] The present invention will be further described in detail below with reference to the embodiments. Detailed Implementation

[0020] Example 1 This embodiment describes a method for preparing a solid-state lithium battery separator with a thickness of 24 μm. The method is as follows: S1. Preparation of diaphragm slurry: Polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was dissolved in N-methylpyrrolidone (NMP), and then lithium titanium aluminum phosphate (LATP) was added. After stirring at 1500 rpm for 40 min, the membrane slurry was obtained. The mass ratio of PVDF-HFP to LATP is 4:3; S2, Lamination thickness control: The diaphragm slurry obtained in S1 was uniformly coated onto a stainless steel plate with a size of 300mm×300mm using a spin coating method to form a wet diaphragm with an initial thickness of 50μm. A fluorinated ethylene propylene copolymer (FEP) plate with a thickness of 30μm was then covered on the wet diaphragm, and then a glass cover plate of the same size was covered on the FEP plate. After applying a slight additional pressure of 0.1kgf / cm2 and statically pressing for 60s, the diaphragm assembly was obtained. Using FEP polymer material plates as thickness control spacers: Unlike the dynamic scraping of a doctor blade or the strong pressure rolling of rollers, using static, thickness-precise FEP polymer material plates as physical limits fundamentally ensures the accuracy and consistency of the prepared thickness. The unique combination of "rigid pressure plate + flexible spacer" ensures absolute uniformity of pressure across the entire plane by utilizing the rigidity of the glass cover plate and the flexibility of the polymer material plate to perfectly fit the slurry surface. This not only transmits pressure but also avoids adhesion or damage to the film surface due to its non-stickiness. This is the ingenuity of the invention. S3, Curing and Molding: The diaphragm assembly obtained in S2 is heated and cured in an oven at 60°C for 5 minutes to allow NMP to initially evaporate and the diaphragm to initially take shape. After cooling to 20°C, the glass cover plate and the FEP plate are removed in sequence, and the cured diaphragm is peeled off from the stainless steel plate to obtain the formed diaphragm. Due to the excellent non-stick properties of the FEP polymer material sheet, it can be peeled off from the cured diaphragm surface without any damage; S4. Post-processing: The shaped separator obtained in S3 was immersed in an ethanol solution for 10 hours to remove the pore-forming agent and residual NMP. After drying at 50°C for 12 hours and winding, a solid lithium battery separator with a thickness of 24 μm was obtained.

[0021] This embodiment also tested the performance of the solid-state lithium battery separator prepared above.

[0022] The thickness of the solid-state lithium battery separator was measured using a micrometer. The measurement showed that the thickness of the solid-state lithium battery separator prepared in this embodiment was 24 μm, with a thickness tolerance within ±0.3 μm; the porosity reached 40%, and the air permeability Gurley value was 200s / 100cc.

[0023] In summary, the 24μm thick solid-state lithium battery separator prepared in this embodiment uses an FEP polymer material plate as the thickness control spacer, fundamentally ensuring the accuracy and consistency of the thickness. The unique combination of "rigid pressure plate + flexible spacer" utilizes the rigidity of the glass cover to ensure absolute uniformity of pressure throughout the entire plane, and utilizes the flexibility of the polymer material plate to perfectly fit the slurry surface, transmitting pressure while avoiding adhesion or damage to the membrane surface due to its non-stickiness. The pressure is low and uniform throughout the preparation process, without the use of strong external extrusion, thus maximizing the protection of the microporous structure that has formed or is about to form in the wet separator. This is beneficial for obtaining a product with high porosity and air permeability, achieving a porosity of 40% and an air permeability Gurley value of 200s / 100cc, which can be used to prepare high-performance lithium batteries.

[0024] Example 2 This embodiment describes a method for preparing a solid-state lithium battery separator with a thickness of 19 μm. The method is as follows: S1. Preparation of diaphragm slurry: PVDF-HFP was dissolved in NMP, and then silica was added. The mixture was stirred and dispersed at 1700 rpm for 35 min to obtain the diaphragm slurry. The mass ratio of PVDF-HFP to silica is 4:3; S2, Lamination thickness control: The diaphragm slurry obtained in S1 is uniformly coated onto a glass plate with a size of 300mm×300mm using a doctor blade to form a wet diaphragm with an initial thickness of 50μm. A polytetrafluoroethylene (PTFE) plate with a thickness of 25μm is then covered on the wet diaphragm, and then a glass cover plate of the same size is covered on the PTFE plate. After static pressure is applied by the weight of the glass cover plate for 60s, the diaphragm assembly is obtained. S3, Curing and Molding: The diaphragm assembly obtained in S2 is heated and cured in an oven at 70°C for 3 minutes to allow NMP to initially evaporate and the diaphragm to initially take shape. After cooling to 23°C, the glass cover plate and the PTFE plate are removed in sequence, and the cured diaphragm is peeled off from the glass plate to obtain the formed diaphragm. S4. Post-processing: The shaped separator obtained in S3 was immersed in an ethanol solution for 11 hours to remove the pore-forming agent and residual NMP. After drying at 55°C for 11 hours and then winding, a solid lithium battery separator with a thickness of 19 μm was obtained.

[0025] This embodiment also tested the performance of the solid-state lithium battery separator prepared above.

[0026] The thickness of the solid-state lithium battery separator was measured using a micrometer. The measurement showed that the thickness of the solid-state lithium battery separator prepared in this embodiment was 19 μm, with a thickness tolerance within ±0.3 μm; the porosity reached 60%, and the air permeability Gurley value was 300s / 100cc.

[0027] Example 3 This embodiment describes a method for preparing a solid-state lithium battery separator with a thickness of 26 μm. The method is as follows: S1. Preparation of diaphragm slurry: PVDF-HFP was dissolved in NMP, and then lithium lanthanum zirconium oxide (LLZO) was added. After stirring at 2000 rpm for 30 min, the membrane slurry was obtained. The mass ratio of PVDF-HFP to LLZO is 4:3; S2, Lamination thickness control: The diaphragm slurry obtained in S1 is uniformly coated onto a silicon wafer with a size of 300mm×300mm using a casting method to form a wet diaphragm with an initial thickness of 50μm. A soluble polytetrafluoroethylene (PFA) plate with a thickness of 35μm is then covered on the wet diaphragm, and then a glass cover plate of the same size is covered on the PFA plate. After static pressure is applied by the weight of the glass cover plate for 60s, the diaphragm assembly is obtained. S3, Curing and Molding: The diaphragm assembly obtained in S2 is heated and cured in an oven at 80°C for 1 minute to allow NMP to initially evaporate and the diaphragm to initially take shape. After cooling to 25°C, the glass cover plate and the PFA plate are removed in sequence, and the cured diaphragm is peeled off from the silicon wafer to obtain the formed diaphragm. S4. Post-processing: The shaped separator obtained in S3 was immersed in an ethanol solution for 12 hours to remove the pore-forming agent and residual NMP. After drying at 60°C for 10 hours and then winding, a solid lithium battery separator with a thickness of 26 μm was obtained.

[0028] This embodiment also tested the performance of the solid-state lithium battery separator prepared above.

[0029] The thickness of the solid-state lithium battery separator was measured using a micrometer. The measurement showed that the thickness of the solid-state lithium battery separator prepared in this embodiment was 26 μm, with a thickness tolerance within ±0.3 μm; the porosity reached 45%, and the air permeability Gurley value was 240s / 100cc.

[0030] Example 4 This embodiment describes a method for preparing a solid-state lithium battery separator with a thickness of 30 μm. The method is as follows: S1. Preparation of diaphragm slurry: PVDF-HFP was dissolved in NMP, and then tantalum-doped lithium lanthanum zirconium oxide (LLZTO, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) was added. After stirring at 2000 rpm for 30 min, the diaphragm slurry was obtained. The mass ratio of PVDF-HFP to LLZTO is 4:3; The tantalum-doped lithium lanthanum zirconium oxide can also be a lithium bis(fluorosulfonyl)imide salt; S2, Lamination thickness control: The diaphragm slurry obtained in S1 is uniformly coated onto a silicon wafer with a size of 300mm×300mm using a doctor blade to form a wet diaphragm with an initial thickness of 50μm. An ethylene-tetrafluoroethylene copolymer (ETFE) plate with a thickness of 40μm is then covered on the wet diaphragm, and then a glass cover plate of the same size is covered on the ETFE plate. After static pressure is applied by the weight of the glass cover plate for 60s, the diaphragm assembly is obtained. S3, Curing and Molding: The diaphragm assembly obtained in S2 is heated and cured in an oven at 80°C for 10 minutes to allow NMP to initially evaporate and the diaphragm to initially take shape. After cooling to 20°C, the glass cover plate and the ETFE plate are removed in sequence, and the cured diaphragm is peeled off from the silicon wafer to obtain the formed diaphragm. S4. Post-processing: The shaped separator obtained in S3 was immersed in an ethanol solution for 10 hours to remove the pore-forming agent and residual NMP. After drying at 50°C for 12 hours and then winding, a solid lithium battery separator with a thickness of 30 μm was obtained.

[0031] This embodiment also tested the performance of the solid-state lithium battery separator prepared above.

[0032] The thickness of the solid-state lithium battery separator was measured using a micrometer. The measurement showed that the thickness of the solid-state lithium battery separator prepared in this embodiment was 30 μm, with a thickness tolerance within ±0.3 μm; the porosity reached 50%, and the air permeability Gurley value was 220s / 100cc.

[0033] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method of preparing a solid-state lithium battery separator, characterized by, The method comprises: S1, preparation of a diaphragm slurry: Dissolve polyvinylidene fluoride-hexafluoropropylene in N-methyl pyrrolidone, then add a pore-forming agent, stir and disperse to obtain a diaphragm slurry; S2, control of the lamination thickness: Uniformly coat the diaphragm slurry obtained in S1 on a substrate to form a wet diaphragm, cover a polymer material plate on the wet diaphragm, then cover a quartz glass cover plate on the polymer material plate, and obtain a diaphragm assembly after static pressure; S3, curing and forming: Cure the diaphragm assembly obtained in S2, remove the glass cover plate and the polymer material plate in sequence after cooling, and peel off the cured diaphragm from the substrate to obtain a formed diaphragm; S4, post-treatment: Immerse the formed diaphragm obtained in S3 in ethanol for extraction, dry and wind up to obtain a solid-state lithium battery diaphragm.

2. The method of claim 1, wherein the solid-state lithium battery separator is prepared by the steps of: The pore-forming agent in S1 is silicon dioxide, lithium aluminum titanium phosphate, lithium bisfluorosulfonylimide, lithium lanthanum zirconium oxide, or tantalum-doped lithium lanthanum zirconium oxide; the stirring conditions are: stirring at a speed of 1500 rpm to 2000 rpm for 30 min to 40 min; the mass ratio of polyvinylidene fluoride-hexafluoropropylene to pore-forming agent is 4:

3.

3. The method of claim 1, wherein the solid-state lithium battery separator is prepared by the steps of: The coating method in S2 is spin coating, blade coating or casting; the size of the substrate is 300 mm x 300 mm; the thickness of the polymer material plate is selected according to the final required thickness of the solid-state lithium battery diaphragm; the static pressure time is 60 s.

4. The method of claim 1, wherein the solid-state lithium battery separator is prepared by the steps of: The substrate in S2 is a glass plate, a stainless steel plate, a silicon sheet plate, or a silicon wafer plate; the polymer material plate is a polytetrafluoroethylene plate, a fluorinated ethylene propylene copolymer plate, a soluble polytetrafluoroethylene plate, or an ethylene-tetrafluoroethylene copolymer plate.

5. The method of claim 1, wherein the solid-state lithium battery separator is prepared by the steps of: The curing conditions in S3 are: curing at a temperature of 60°C to 80°C for 1 min to 5 min; the cooling temperature is 20°C to 25°C.

6. The method of claim 1, wherein the solid-state lithium battery separator is prepared by the steps of: The extraction time in S4 is 10 h to 12 h; the drying conditions are: drying at a temperature of 50°C to 60°C for 10 h to 12 h.

7. The method of claim 1, wherein the solid-state lithium battery separator is prepared by the steps of: The average thickness of the solid-state lithium battery diaphragm in S4 is 19 μm to 30 μm, the porosity is 40% to 60%, and the air permeability is 200 s / 100 cc to 300 s / 100 cc.

8. Use of a solid-state lithium battery separator prepared according to the preparation method of any one of claims 1 to 7, characterized in that The solid-state lithium battery diaphragm is used to prepare a lithium battery.