Process for preparing electrolyte-resistant etched separator for lithium-ion batteries

Abstract

The present application relates to the technical field of lithium ion battery separator, and discloses a preparation process of electrolyte corrosion resistant lithium ion battery etching separator, which uses a bidirectional stretching three-layer co-extruded polyolefin-based film as a substrate, removes impurities through three-stage gradient cleaning, removes moisture through vacuum drying, etches through a three-stage liquid-phase etching of a composite oxidizing solution, constructs multiple levels of micropores through a mixed gas source plasma gas-phase etching, coats a ternary corrosion resistant coating on both sides, performs ultraviolet hot air coupling curing and constant temperature roller pressing and shaping, and performs vacuum constant temperature aging after laser cutting to obtain the target etching separator. The process precisely constructs uniform micropores, improves the coating adhesion, and the prepared separator is excellent in electrolyte corrosion resistance, mechanical and dimensional stability, can prolong the lithium battery cycle life, improve the use safety, and is suitable for large-scale industrial production and high-end lithium battery application.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery separator technology, and particularly relates to the preparation process of lithium-ion battery etched separators resistant to electrolyte corrosion. Background Technology

[0002] Lithium-ion batteries, as core components for new energy storage and power supply, are widely used in power batteries, energy storage power stations, consumer electronics and other fields. The separator is a key inner component of lithium-ion batteries, which mainly undertakes the core functions of electronic insulation, lithium-ion conduction and preventing direct contact between electrodes. Its resistance to electrolyte corrosion, pore stability and interfacial bonding strength directly determine the battery's cycle life, high-temperature stability and safety.

[0003] Currently, biaxially oriented polyolefin (BEO) membranes are the mainstream substrate for commercial lithium-ion battery separators. Polyolefin materials have advantages such as excellent mechanical strength, low production cost, and moderate ion conductivity. However, they also have significant technical drawbacks under conditions of long-term immersion in lithium salt electrolytes, high-voltage charging and discharging, and high-temperature operation. Polyolefin molecular chains have weak resistance to electrolyte corrosion, making them prone to chain segment degradation, pore swelling, and structural collapse. This leads to separator failure, which in turn causes a surge in battery internal resistance, accelerated cycle degradation, and even the risk of thermal runaway and short circuits.

[0004] Current membrane etching modification processes still have many technical shortcomings. Traditional liquid-phase etching often uses a single etching system without segmented and precise control, which easily leads to uneven pore size distribution, poor pore connectivity, and strong surface inertness of the pore walls, making it impossible to provide a stable bonding interface for subsequent coatings. Vapor-phase plasma etching has rudimentary process parameter control, low grafting efficiency of active groups, and limited improvement in the surface energy of the base film, resulting in insufficient interfacial bonding between the modified coating and the base film. After long-term immersion in the electrolyte, coating peeling and delamination are prone to occur.

[0005] Most membrane modification coatings use single organic or inorganic materials. Organic coatings have weak resistance to electrolyte corrosion, while inorganic coatings are brittle and lack flexibility, making it impossible to simultaneously achieve corrosion resistance, mechanical properties, and ion conductivity. Furthermore, existing preparation processes do not employ coupled curing and vacuum aging synergistic treatments, resulting in insufficient coating crosslinking density, poor membrane dimensional stability, and susceptibility to thermal shrinkage after high-temperature cycling. This batch-to-batch consistency fails to meet the requirements for large-scale applications in power and energy storage batteries.

[0006] The industry urgently needs an integrated manufacturing process that combines multi-stage liquid-phase etching, plasma vapor-phase grafting, ternary corrosion-resistant coating application, coupled curing and shaping, and vacuum aging quality control. This process would address the industry pain points of polyolefin separators, such as poor electrolyte corrosion resistance, weak coating adhesion, insufficient porosity, and easy shrinkage at high temperatures. The goal is to produce highly corrosion-resistant, highly stable, and highly consistent lithium-ion battery etched separators that meet the long-cycle, high-safety, and wide-temperature-range application requirements of high-end lithium-ion batteries. Summary of the Invention

[0007] To address the shortcomings of existing polyolefin separators, such as poor resistance to electrolyte corrosion, uneven pore size during etching, weak coating adhesion, insufficient curing crosslinking, poor dimensional stability, easy shrinkage at high temperatures, and low batch consistency, this invention provides a process for preparing an electrolyte-resistant lithium-ion battery etched separator.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A process for preparing an etched separator for lithium-ion batteries resistant to electrolyte corrosion includes the following steps: S1. Select a biaxially stretched multilayer co-extruded polyolefin base film as the diaphragm substrate, and sequentially pass it through a three-stage gradient cleaning process of alkaline degreasing liquid spray cleaning, anhydrous ethanol immersion rinsing, and ultrapure water rinsing to remove oil, dust and weak interface bonding layer on the surface of the substrate. S2. The polyolefin base film that has completed gradient cleaning is sent into a vacuum drying equipment and dried in a constant temperature and pressure mode to remove residual moisture inside and on the surface of the base film. S3. The dried base film is introduced into the liquid phase etching equipment and a three-stage liquid phase etching process is carried out using a composite oxidation chemical etching solution. After etching, the base film is rinsed with five-stage ultrapure water in a countercurrent manner until the pH value of the base film surface reaches the neutral range. S4. The washed base film is sent into the radio frequency plasma etching chamber and vapor phase etching is performed in a vacuum environment using a mixed gas source to construct a through-and-uniform multi-level microporous topology on the surface and inside of the base film. S5. A micro-gravure reverse coating equipment is used to simultaneously coat the upper and lower surfaces of the base film after plasma etching with a ternary electrolyte corrosion-resistant modified coating to control the uniformity of coating thickness and surface density. S6. The coated base film is sent into a UV light and hot air coupled curing equipment for multi-stage gradient curing treatment, so that the modified coating forms a dense and stable covalent cross-linked network structure. S7. The cured base film is introduced into a constant temperature roller press for continuous hot pressing and shaping to stabilize the pore structure, flatness and dimensional stability of the diaphragm. S8. The hot-pressed base film is cut to length using a high-precision laser cutting device. After cutting, it is sent to a vacuum constant temperature aging device for aging treatment. After completion, the target etched diaphragm is obtained through performance testing.

[0009] Preferably, the process also includes a polyolefin chain segment directional oxidation pyrolysis etching reaction during the three-stage liquid phase etching process in S3. This reaction can precisely etch polyolefin molecular chains and regulate the pore size distribution, pore connectivity and pore wall roughness of the base film substrate micropores.

[0010] Preferably, the process also includes a grafting reaction between active hydroxyl and carboxyl groups during the vapor-phase etching process in S4, which significantly improves the surface energy of the base film after grafting modification, thereby strengthening the interfacial bonding strength between the modified coating and the base film.

[0011] Preferably, in S1, the biaxially oriented multilayer co-extruded polyolefin base film is a PP / PE / PP three-layer composite structure with a total base film thickness of 18μm-32μm, an initial porosity of 32%-52%, and an initial average pore size of 0.04μm-0.22μm. The alkaline degreasing solution is a mixture of sodium hydroxide and anionic surfactant with a pH of 9.5-11.5, and the total time for the three-stage gradient cleaning is 8min-20min.

[0012] Preferably, the vacuum drying temperature in S2 is 60℃-80℃, the equipment vacuum degree is -0.09MPa to -0.07MPa, the drying time is 20min-40min, the drying process adopts a segmented heating mode, and after drying, the moisture content inside the base film is less than 0.08%, and the base film is free from curling, deformation and heat damage.

[0013] Preferably, the composite oxidative chemical etching solution in S3 is a compound system of sulfuric acid, potassium permanganate, oxalic acid and deionized water. The mass fraction of sulfuric acid is 15%-28%, the mass fraction of potassium permanganate is 2%-4.5%, and the mass fraction of oxalic acid is 0.8%-2.5%. The three-stage liquid phase etching is divided into pre-etching, main etching and fine etching. The total etching time is 60s-210s, the etching temperature is 35℃-55℃, and the etching process is continuously stirred to ensure uniform etching solution concentration.

[0014] Preferably, in S4, the mixed gas source for radio frequency plasma etching is a mixture of oxygen, argon, and nitrogen in a certain proportion, with a total gas flow rate of 100 sccm-220 sccm, a radio frequency plasma power of 200 W-450 W, a vacuum degree of 3 Pa-25 Pa in the etching chamber, a gas phase etching time of 120 s-270 s, and an average pore size of 0.1 μm-0.35 μm for the multi-level micropores on the substrate surface after etching, with a pore uniformity deviation of less than 4%.

[0015] Preferably, in S5, the ternary electrolyte corrosion-resistant modified coating is a slurry composed of nano-alumina, PVDF-HFP copolymer, fluoroalkylsilane and conductive carbon dots, with a single-sided coating thickness of 3.5μm-6.5μm, a microgravure reverse coating speed of 2m / min-7m / min, and a coating surface density deviation of ≤0.2g / ㎡; in S6, the UV curing power is 250W-600W, the hot air gradient curing is divided into three stages of heating, with a temperature range of 75℃-135℃, and a total curing time of 4min-10min. During the curing process, an organic-inorganic covalent cross-linking reaction of the coating occurs.

[0016] Preferably, in S7, the constant temperature roller pressing hot pressing temperature is 90℃-115℃, the roller pressing line pressure is 1.0MPa-2.5MPa, the roller pressing line speed is 1m / min-5m / min, the overall thickness deviation of the diaphragm after hot pressing is ≤0.25μm, the porosity retention deviation is ≤2.5%, and the diaphragm flatness is ≤0.3μm; in S8, the laser cutting power is 60W-150W, the cutting positioning accuracy is ≤0.08mm, and the cutting edge is free of burrs, shrinkage cavities, and coating peeling.

[0017] Preferably, the vacuum constant temperature aging temperature in S8 is 50℃-65℃, the vacuum degree is -0.08MPa to -0.06MPa, the aging time is 36h-72h, and after aging, the finished diaphragm does not swell, delaminate, peel off the coating, or suffer structural damage after being immersed in lithium salt electrolyte for 480h. The electrolyte corrosion rate is ≤0.006mg / h, the tensile strength is ≥110MPa, the interfacial bonding force is ≥6N / m, the porosity retention rate is ≥98.5%, and the dimensional shrinkage rate after high temperature cycling is ≤0.5%.

[0018] The present invention has the following beneficial effects: This invention utilizes a synergistic process of three-stage gradient cleaning, three-stage liquid-phase etching, and radio-frequency plasma vapor-phase etching to remove impurities and weak bonding layers from the substrate film surface, constructing a continuous and uniform multi-level microporous structure. Simultaneously, a large number of active groups are grafted onto the substrate film surface, enhancing surface energy and interfacial adhesion, resulting in a tighter bond between subsequent coatings and the substrate film, effectively preventing coating peeling and delamination. The entire process parameters are highly controllable, with smooth flow connections, ensuring stable micropore distribution, pore size uniformity, and structural consistency in the diaphragm, improving batch stability, and making it suitable for large-scale continuous industrial production.

[0019] This invention employs a ternary corrosion-resistant modified coating combined with a UV light and hot air coupled curing process, which enables the coating to form a dense and stable covalent cross-linked network structure. This significantly enhances the membrane's resistance to electrolyte corrosion, preventing swelling, damage, and structural degradation even after long-term exposure to an electrolyte environment. The coating combines the corrosion resistance of inorganic materials with the flexibility of organic materials, while also offering excellent mechanical strength, ion conductivity, and interfacial compatibility. Furthermore, constant-temperature rolling and vacuum aging treatments stabilize the membrane's dimensions and pore structure, reducing thermal shrinkage during high-temperature use and improving the membrane's structural stability over a wide temperature range.

[0020] The separator prepared by this invention exhibits significantly improved overall performance. Its stable microporous structure ensures efficient and smooth lithium-ion transport, while its excellent corrosion resistance and mechanical properties extend its service life, thereby enhancing the cycle life and safety of lithium-ion batteries. The separator is adaptable to various application scenarios, including power batteries, energy storage power stations, and high-end consumer electronics, effectively reducing the risk of short circuits and thermal runaway caused by separator failure. It broadens the operating conditions of lithium-ion batteries, providing reliable support for the safe and stable operation of high-end lithium-ion batteries, and possesses significant technological value and advantages for industrial application. Attached Figure Description

[0021] Figure 1 This invention provides a process flow diagram for preparing an etched separator for lithium-ion batteries that is resistant to electrolyte corrosion; Figure 2 This invention provides a comparison of the tensile strength of the diaphragms in the embodiments and comparative examples. Figure 3 This invention presents the relationship between plasma power and pore uniformity deviation. Figure 4 This is a comparison of the overall performance of Embodiment 2 and Comparative Example 1 proposed in this invention; Figure 5 This invention presents the relationship between curing time and electrolyte corrosion rate. Detailed Implementation

[0022] The entire preparation process of this specific embodiment was carried out in a Class 10,000 cleanroom, with the ambient temperature controlled at 22℃-26℃ and the relative humidity controlled at 40%-50%. The entire process was conducted in a light-proof and dust-proof environment to prevent impurities from contaminating the separator. The core chemical reaction of this invention is clearly defined, and the process parameters are quantifiable and replicable. This embodiment includes three preferred examples and one comparative example of a conventional process. All preparation steps are fully described, and performance testing is performed in accordance with the national standards for lithium-ion battery separators.

[0023] Core chemical reaction formula: Directional oxidative pyrolysis etching reaction of polyolefin segments: (C2H4) n +3nO2 2nCO2↑+2nH2O Grafting reaction of active hydroxyl groups with carboxyl groups: 2R-CH2-CH2-R'+3O2 2R-COOH + 2R'-CH2OH Organic-inorganic covalent crosslinking reaction of coating: (CF2-CH2-)n+R-Si-(OCH2CH3)3 Corrosion-resistant cross-linked network structure + 3CH3CH2OH.

[0024] Example 1 S1. A biaxially oriented polyolefin (PP / PE / PP) three-layer co-extruded polyolefin membrane was selected as the membrane substrate. The total thickness of the membrane was 18 μm, the initial porosity was 32%, and the initial average pore size was 0.04 μm. A three-stage gradient cleaning process was adopted, consisting of alkaline degreasing solution spray cleaning, anhydrous ethanol immersion rinsing, and ultrapure water rinsing. The alkaline degreasing solution was a mixture of sodium hydroxide and anionic surfactant with a pH of 9.5. The total cleaning time for the three stages was 8 minutes to remove oil, dust, and weak interfacial bonding layers from the substrate surface.

[0025] S2. The polyolefin base film that has completed gradient cleaning is sent to a vacuum drying equipment and dried using a constant temperature and pressure segmented heating mode. The vacuum drying temperature is 60℃, the equipment vacuum degree is -0.09MPa, and the drying time is 20min. The residual moisture inside and on the surface of the base film is removed. After drying, the moisture content inside the base film is less than 0.08%, and the base film is free from curling, deformation, and heat damage.

[0026] S3. The dried base film is introduced into a liquid phase etching device. A three-stage liquid phase etching process is performed using a composite oxidative chemical etching solution made of sulfuric acid, potassium permanganate, oxalic acid, and deionized water. The mass fraction of sulfuric acid is 15%, potassium permanganate is 2%, and oxalic acid is 0.8%. The three-stage liquid phase etching consists of pre-etching, main etching, and fine etching, with a total etching time of 60 seconds and an etching temperature of 35°C. Continuous stirring is maintained during the etching process to ensure uniform concentration of the etching solution. After etching, the base film is rinsed countercurrently with five stages of ultrapure water until the pH value of the base film surface reaches the neutral range.

[0027] S4. The washed base film is sent into the radio frequency plasma etching chamber. Under a vacuum atmosphere, a mixed gas source of oxygen, argon and nitrogen is used for vapor phase etching. The total gas flow rate is 100 sccm, the radio frequency plasma power is 200W, the vacuum degree of the etching chamber is 3Pa, and the vapor phase etching time is 120s. A multi-level microporous topology structure with uniform penetration is constructed on the surface and inside of the base film. After etching, the average pore size of the multi-level micropores on the surface of the base film is 0.1μm, and the pore uniformity deviation is less than 4%.

[0028] S5. Using a micro-gravure reverse coating equipment, a ternary electrolyte-resistant modified coating is simultaneously coated on both sides of the base film after plasma etching. The coating is a composite slurry of nano-alumina, PVDF-HFP copolymer, fluoroalkyl silane and conductive carbon dots. The coating thickness on one side is 3.5μm. The micro-gravure reverse coating speed is 2m / min, and the coating surface density deviation is ≤0.2g / ㎡.

[0029] S6. The coated base film is sent into a UV light and hot air coupled curing equipment for multi-stage gradient curing. The UV curing power is 250W, and the hot air gradient curing is divided into three stages of heating, with a temperature range of 75℃-135℃. The total curing time is 4 minutes. During the curing process, the organic-inorganic covalent cross-linking reaction of the coating occurs, so that the modified coating forms a dense and stable covalent cross-linked network structure.

[0030] S7. The cured base film is introduced into a constant temperature roller pressing equipment for continuous hot pressing and shaping. The constant temperature roller pressing and shaping temperature is 90℃, the roller pressing line pressure is 1.0MPa, the roller pressing line speed is 1m / min, and the overall thickness deviation of the diaphragm after hot pressing is ≤0.25μm, the porosity deviation is ≤2.5%, and the diaphragm flatness is ≤0.3μm, thus stabilizing the pore structure, flatness, and dimensional stability of the diaphragm.

[0031] S8. The hot-pressed base film is cut to length using a high-precision laser cutting device. The laser cutting power is 60W, the cutting positioning accuracy is ≤0.08mm, and the cut edges are free of burrs, shrinkage cavities, and coating peeling. After cutting, the film is sent to a vacuum constant temperature aging device for aging treatment. The vacuum constant temperature aging temperature is 50℃, the vacuum degree is -0.08MPa, and the aging time is 36h. After completion, the target etched separator is obtained through performance testing.

[0032] Example 2 S1. A biaxially oriented polyolefin (PP / PE / PP) three-layer co-extruded polyolefin membrane was selected as the separator substrate. The total thickness of the membrane was 25 μm, the initial porosity was 42%, and the initial average pore size was 0.13 μm. A three-stage gradient cleaning process was adopted, consisting of alkaline degreasing solution spray cleaning, anhydrous ethanol immersion rinsing, and ultrapure water rinsing. The alkaline degreasing solution was a mixture of sodium hydroxide and anionic surfactant with a pH of 10.5. The total cleaning time for the three stages was 14 min, which removed oil, dust, and weak interfacial bonding layers from the surface of the substrate.

[0033] S2. The polyolefin base film that has completed gradient cleaning is sent to a vacuum drying equipment and dried using a constant temperature and pressure segmented heating mode. The vacuum drying temperature is 70℃, the equipment vacuum degree is -0.08MPa, and the drying time is 30min. The residual moisture inside and on the surface of the base film is removed. After drying, the moisture content inside the base film is less than 0.08%, and the base film is free from curling, deformation, and heat damage.

[0034] S3. The dried base film is introduced into a liquid phase etching device. A three-stage liquid phase etching process is performed using a composite oxidative chemical etching solution made of sulfuric acid, potassium permanganate, oxalic acid, and deionized water. The mass fraction of sulfuric acid is 21.5%, potassium permanganate is 3.25%, and oxalic acid is 1.65%. The three-stage liquid phase etching consists of pre-etching, main etching, and fine etching, with a total etching time of 135 seconds and an etching temperature of 45°C. Continuous stirring is maintained during the etching process to ensure uniform concentration of the etching solution. After etching, the base film is rinsed countercurrently with five stages of ultrapure water until the pH value of the base film surface reaches the neutral range.

[0035] S4. The washed base film is sent into the radio frequency plasma etching chamber. Under a vacuum atmosphere, a mixed gas source of oxygen, argon and nitrogen is used for vapor phase etching. The total gas flow rate is 160 sccm, the radio frequency plasma power is 325W, the vacuum degree of the etching chamber is 14Pa, and the vapor phase etching time is 195s. A multi-level microporous topology structure with uniform penetration is constructed on the surface and inside of the base film. After etching, the average pore size of the multi-level micropores on the surface of the base film is 0.225μm, and the pore uniformity deviation is less than 4%.

[0036] S5. Using a micro-gravure reverse coating equipment, a ternary electrolyte-resistant modified coating is simultaneously coated on both sides of the base film after plasma etching. The coating is a composite slurry of nano-alumina, PVDF-HFP copolymer, fluoroalkyl silane and conductive carbon dots. The coating thickness on one side is 5μm. The micro-gravure reverse coating speed is 4.5m / min. The coating surface density deviation is ≤0.2g / ㎡, and the coating thickness and surface density uniformity are precisely controlled.

[0037] S6. The coated base film is sent into a UV light and hot air coupled curing equipment for multi-stage gradient curing. The UV curing power is 425W, and the hot air gradient curing is divided into three stages of heating, with a temperature range of 75℃-135℃. The total curing time is 7 minutes. During the curing process, the organic-inorganic covalent cross-linking reaction of the coating occurs, so that the modified coating forms a dense and stable covalent cross-linked network structure.

[0038] S7. The cured base film is introduced into a constant temperature roller pressing equipment for continuous hot pressing and shaping. The constant temperature roller pressing and shaping temperature is 102℃, the roller pressing line pressure is 1.75MPa, the roller pressing line speed is 3m / min, and the overall thickness deviation of the diaphragm after hot pressing is ≤0.25μm, the porosity deviation is ≤2.5%, and the diaphragm flatness is ≤0.3μm, thus stabilizing the pore structure, flatness, and dimensional stability of the diaphragm.

[0039] S8. The hot-pressed base film is cut to length using a high-precision laser cutting device. The laser cutting power is 105W, the cutting positioning accuracy is ≤0.08mm, and the cut edges are free of burrs, shrinkage cavities, and coating peeling. After cutting, the film is sent to a vacuum constant temperature aging device for aging treatment. The vacuum constant temperature aging temperature is 57℃, the vacuum degree is -0.07MPa, and the aging time is 54h. After completion, the target etched separator is obtained through performance testing.

[0040] Example 3 S1. A biaxially oriented polyolefin (PP / PE / PP) three-layer co-extruded polyolefin membrane was selected as the membrane substrate. The total thickness of the membrane was 32 μm, the initial porosity was 52%, and the initial average pore size was 0.22 μm. A three-stage gradient cleaning process was adopted, consisting of alkaline degreasing solution spray cleaning, anhydrous ethanol immersion rinsing, and ultrapure water rinsing. The alkaline degreasing solution was a mixture of sodium hydroxide and anionic surfactant with a pH of 11.5. The total cleaning time for the three stages was 20 minutes to remove oil, dust, and weak interfacial bonding layers from the substrate surface.

[0041] S2. The polyolefin base film that has completed gradient cleaning is sent to a vacuum drying equipment and dried using a constant temperature and pressure segmented heating mode. The vacuum drying temperature is 80℃, the equipment vacuum degree is -0.07MPa, and the drying time is 40min. The residual moisture inside and on the surface of the base film is removed. After drying, the moisture content inside the base film is less than 0.08%, and the base film is free from curling, deformation, and heat damage.

[0042] S3. The dried base film is introduced into a liquid phase etching device. A three-stage liquid phase etching process is performed using a composite oxidative chemical etching solution made of sulfuric acid, potassium permanganate, oxalic acid, and deionized water. The sulfuric acid mass fraction is 28%, the potassium permanganate mass fraction is 4.5%, and the oxalic acid mass fraction is 2.5%. The three-stage liquid phase etching consists of pre-etching, main etching, and fine etching, with a total etching time of 210 seconds and an etching temperature of 55℃. Continuous stirring is maintained during the etching process to ensure uniform etching solution concentration. After etching, the base film is rinsed countercurrently with five stages of ultrapure water until the pH value of the base film surface reaches the neutral range.

[0043] S4. The washed base film is sent into the radio frequency plasma etching chamber. Under a vacuum atmosphere, a mixed gas source of oxygen, argon and nitrogen is used for vapor phase etching. The total gas flow rate is 220 sccm, the radio frequency plasma power is 450W, the vacuum degree of the etching chamber is 25Pa, and the vapor phase etching time is 270s. A multi-level microporous topology structure with uniform penetration is constructed on the surface and inside of the base film. After etching, the average pore size of the multi-level micropores on the surface of the base film is 0.35μm, and the pore uniformity deviation is less than 4%.

[0044] S5. Using a micro-gravure reverse coating equipment, a ternary electrolyte-resistant modified coating is simultaneously coated on both sides of the plasma-etched base film. The coating consists of a slurry of nano-alumina, PVDF-HFP copolymer, fluoroalkyl silane and conductive carbon dots. The coating thickness on one side is 6.5μm. The micro-gravure reverse coating speed is 7m / min. The coating surface density deviation is ≤0.2g / ㎡, and the coating thickness and surface density uniformity are precisely controlled.

[0045] S6. The coated base film is sent into a UV light and hot air coupled curing equipment for multi-stage gradient curing. The UV curing power is 600W, and the hot air gradient curing is divided into three stages of heating, with a temperature range of 75℃ to 135℃. The total curing time is 10 minutes. During the curing process, the organic and inorganic covalent cross-linking reaction of the coating occurs, so that the modified coating forms a dense and stable covalent cross-linked network structure.

[0046] S7. The cured base film is introduced into a constant temperature roller pressing equipment for continuous hot pressing and shaping. The constant temperature roller pressing and shaping temperature is 115℃, the roller pressing line pressure is 2.5MPa, the roller pressing line speed is 5m / min, the overall thickness deviation of the diaphragm after hot pressing is ≤0.25μm, the porosity deviation is ≤2.5%, the diaphragm flatness is ≤0.3μm, and the pore structure, flatness and dimensional stability of the diaphragm are stabilized.

[0047] S8. The hot-pressed base film is cut to length using a high-precision laser cutting device. The laser cutting power is 150W, the cutting positioning accuracy is ≤0.08mm, and the cut edges are free of burrs, shrinkage cavities, and coating peeling. After cutting, the film is sent to a vacuum constant temperature aging device for aging treatment. The vacuum constant temperature aging temperature is 65℃, the vacuum degree is -0.06MPa, and the aging time is 72h. After completion, the target etched separator is obtained through performance testing.

[0048] Comparative Example 1 S1. Select ordinary uniaxially stretched polyolefin monolayer film as the substrate. The total thickness of the substrate film is 25μm. It is rinsed with clean water for 5 minutes only. No three-stage gradient cleaning and degreasing treatment is performed. It is directly introduced into the subsequent process.

[0049] S2. The base film is air-dried at room temperature and pressure for 30 minutes without vacuum constant temperature drying, so that residual moisture inside the base film is not removed.

[0050] S3. A single liquid phase etching of 3% potassium permanganate solution was performed for 60 seconds at a temperature of 35°C. No three-stage fine etching or five-stage countercurrent rinsing was performed, and the etching parameters were not precisely controlled.

[0051] S4. No radio frequency plasma vapor phase etching is performed, the base film surface has no active groups grafted, and no multi-level microporous structure is constructed.

[0052] S5. A single PVDF coating is used for single-sided scraping, with a single-sided coating thickness of 5μm and a coating speed of 4.5m / min. No ternary corrosion-resistant composite coating is used, and there is no uniformity control.

[0053] S6. Only single hot air drying is used, the drying temperature is 100℃, the drying time is 7min, and no ultraviolet light and hot air coupled gradient curing is performed, and the coating has no dense cross-linked structure.

[0054] S7. Simple roller pressing at room temperature and pressure is adopted. The roller pressing pressure is 1.0MPa and the roller pressing speed is 3m / min. No constant temperature precision roller pressing is performed, and there is no control over size and porosity stability.

[0055] S8. Ordinary mechanical cutting is used, with a cutting accuracy of 0.5mm. No laser precision cutting or vacuum constant temperature aging treatment is performed to directly produce conventional diaphragms.

[0056] Table 1 Comparison of core preparation process parameters between Examples 1-3 and Comparative Example 1 Explanation of the table: This table precisely presents the core preparation process parameters of Examples 1-3 and Comparative Example 1. In Examples 1-3, parameters such as etching time, plasma power, and curing time increase with the base film thickness gradient, demonstrating precise adaptation of process parameters to substrate characteristics. The rolling and aging processes are subject to standardized numerical control. Comparative Example 1 lacks the core processes of plasma treatment and vacuum aging; the rolling is performed at room temperature without temperature control; and the etching and curing parameters lack fine-tuning. This table visually verifies the controllability and adaptability of the process parameters of this invention, quantitatively reflects the innovative points of the invention's process, provides accurate data reference for industrial production, and proves that parameter optimization is a core prerequisite for improving diaphragm performance.

[0057] Table 2 Comparison of Physicochemical Properties of the Membranes in Examples 1-3 and Comparative Example 1 Explanation of the table: This table uses quantitative data to illustrate the differences in the physicochemical properties of the separators. The tensile strength and interfacial adhesion of Examples 1-3 are significantly higher than those of Comparative Example 1, while thickness deviation, flatness, and pore uniformity deviation are all controlled at extremely low levels. Example 2, due to its optimal process parameters, achieves peak performance in all physicochemical properties, meeting the stringent standards for power battery separators. Comparative Example 1, lacking processes such as plasma grafting and coupling curing, exhibits weak adhesion between the coating and the base film, resulting in significantly reduced mechanical properties and extremely poor dimensional and pore uniformity. The data in this table confirms that the process of this invention can significantly improve the mechanical properties and dimensional stability of the separator, solving the industry problems of poor mechanical properties and low precision in traditional separators.

[0058] Table 3 Comparison of Electrolyte Corrosion Resistance Data between Examples 1-3 and Comparative Example 1 Explanation of the table: This table visually demonstrates the technical advantages of the separator of this invention through core corrosion resistance data. Examples 1-3 exhibit extremely low electrolyte corrosion rates, with a porosity retention rate approaching 99% after 480 hours of immersion. High-temperature shrinkage and coating peeling rates are both controlled at optimal levels, demonstrating outstanding electrolyte corrosion resistance. Comparative Example 1, lacking a ternary corrosion-resistant coating and a dense cross-linked structure, shows a corrosion rate more than five times that of Example 2, with significant coating peeling and complete failure of pore structure and dimensional stability. The data in this table fully validates that this invention, through composite etching, ternary coating, and coupled curing processes, can fundamentally improve the electrolyte corrosion resistance of the separator, providing core support for the long-cycle, high-safety operation of lithium-ion batteries.

[0059] refer to Figure 2 This bar chart visually reflects the differences in mechanical strength of separators prepared using different processes. Examples 1 to 3 utilize the multi-stage etching, coupling curing, and roll forming process of this invention, resulting in well-organized separator molecular chains, tight bonding between the coating and the substrate, and consistently high tensile strength. Example 2, with its optimal process parameters, achieves peak strength. Comparative Example 1 employs a traditional, simplified process lacking plasma activation and cross-linking curing, resulting in a loose internal structure of the base film and a significant decrease in mechanical properties. This chart directly verifies that the process of this invention can significantly improve the mechanical properties of the separator, meeting the structural stability requirements of power batteries under charging and discharging expansion and mechanical vibration conditions. It provides data support for ensuring the mechanical performance of high-end lithium-ion battery separators and demonstrates the role of process innovation in enhancing core product performance.

[0060] refer to Figure 3 This line graph illustrates the effect of plasma power on the uniformity of membrane pore size. At 0 W (the control group), no plasma treatment was performed, resulting in a highly inert substrate surface and extremely high pore size deviation due to uneven etching. As the power increases to the 200-450 W range, the plasma activates and etches the substrate surface, gradually unifying the pore arrangement and continuously reducing the deviation, reaching its optimal value at 325 W. Further increases in power lead to localized over-etching, causing a slight increase in pore size deviation. This demonstrates that moderate plasma treatment can optimize the micropore structure, solve the problem of uneven pore size in traditional membranes, and provide precise parameter data for industrial production, showcasing the value of refined process parameter control in improving membrane consistency.

[0061] refer to Figure 4This radar chart comprehensively compares the core performance of the optimal embodiment with that of traditional process samples. Example 2 achieves near-perfect scores across all dimensions, thanks to the synergistic effect of three-stage cleaning, composite etching, ternary coating, and coupled curing. The resulting separator exhibits high strength, high adhesion, high corrosion resistance, and high dimensional stability. Comparative Example 1, due to the lack of key process steps, shows lower overall performance, particularly weak corrosion resistance and interfacial adhesion. The chart visually demonstrates the comprehensive advantages of the separator of this invention, addressing the pain points of traditional separators such as poor electrolyte resistance, weak adhesion, and insufficient stability. It proves that this process can meet the requirements of power batteries and energy storage batteries for long lifespan, high safety, and wide temperature range of separators, possessing significant industrialization advantages.

[0062] refer to Figure 5 This scatter plot reveals the correlation between curing time and the corrosion resistance of the diaphragm. In the examples, the curing time was in the range of 4-10 minutes, during which the coating crosslinking gradually became sufficient, and the corrosion rate remained at a very low level. The crosslinking density was optimal at 7 minutes, and the corrosion rate was the lowest. Extending the curing time led to slight embrittlement of the coating and a slight increase in the corrosion rate. In the comparative example, single hot air curing was used. Although the time was the same, the crosslinking was insufficient, and the corrosion rate increased sharply. This distribution pattern confirms the necessity of UV-hot air coupled curing, indicating that moderate curing can form a dense corrosion-resistant network, effectively resisting electrolyte erosion, while avoiding the performance degradation caused by over-curing. This provides data support for optimizing process parameters and explains the core reason why the diaphragm of this invention maintains structural integrity even after long-term electrolyte immersion.

[0063] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for preparing an etched separator for lithium-ion batteries resistant to electrolyte corrosion, characterized in that, Includes the following steps: S1. Select a biaxially stretched multilayer co-extruded polyolefin base film as the separator substrate, and sequentially pass it through a three-stage gradient cleaning process: alkaline degreasing solution spray cleaning, anhydrous ethanol immersion rinsing, and ultrapure water rinsing. S2. The polyolefin-based film that has undergone gradient cleaning is sent into a vacuum drying equipment and dried using a constant temperature and pressure mode. S3. The dried base film is introduced into the liquid phase etching equipment and a three-stage liquid phase etching process is carried out using a composite oxidation chemical etching solution. After etching, the base film is rinsed with five-stage ultrapure water in a countercurrent manner until the pH value of the base film surface reaches the neutral range. S4. The washed base film is sent into the radio frequency plasma etching chamber and vapor phase etching is performed using a mixed gas source in a vacuum atmosphere to construct a through-and-uniform multi-level microporous topology on the surface and inside of the base film. S5. Using a micro-gravure reverse coating equipment, a ternary electrolyte corrosion-resistant modified coating is simultaneously coated on both the upper and lower surfaces of the base film after plasma etching. S6. The coated base film is sent into a UV light and hot air coupled curing equipment for multi-stage gradient curing treatment. S7. The cured base film is introduced into a constant temperature roller press for continuous hot pressing and shaping. S8. The hot-pressed base film is cut to length using a high-precision laser cutting device. After cutting, it is sent to a vacuum constant temperature aging device for aging treatment. After completion, the target etched diaphragm is obtained through performance testing.

2. The process for preparing an electrolyte-resistant etched separator for lithium-ion batteries according to claim 1, characterized in that, It also includes the directional oxidation pyrolysis etching reaction of polyolefin segments during the three-stage liquid phase etching process in S3.

3. The process for preparing an electrolyte-resistant etched separator for lithium-ion batteries according to claim 1, characterized in that, It also includes the grafting reaction of active hydroxyl groups and carboxyl groups that occurs during the vapor phase etching process in S4.

4. The process for preparing an electrolyte-resistant etched separator for lithium-ion batteries according to claim 1, characterized in that, The biaxially oriented multilayer co-extruded polyolefin base film in S1 has a PP / PE / PP three-layer composite structure with a total thickness of 18μm-32μm, an initial porosity of 32%-52%, and an initial average pore size of 0.04μm-0.22μm. The alkaline degreasing solution is a mixture of sodium hydroxide and anionic surfactant with a pH of 9.5-11.

5. The total time for the three-stage gradient cleaning is 8min-20min.

5. The process for preparing an electrolyte-resistant etched separator for lithium-ion batteries according to claim 1, characterized in that, The vacuum drying temperature in S2 is 60℃-80℃, the equipment vacuum degree is -0.09MPa to -0.07MPa, the drying time is 20min-40min, the drying process adopts a segmented heating mode, and the moisture content inside the base film is less than 0.08% after drying.

6. The process for preparing an electrolyte-resistant etched separator for lithium-ion batteries according to claim 1, characterized in that, The composite oxidation chemical etching solution in S3 is a mixture of sulfuric acid, potassium permanganate, oxalic acid and deionized water. The mass fraction of sulfuric acid is 15%-28%, the mass fraction of potassium permanganate is 2%-4.5%, and the mass fraction of oxalic acid is 0.8%-2.5%. The three-stage liquid phase etching consists of pre-etching, main etching and fine etching. The total etching time is 60s-210s, the etching temperature is 35℃-55℃, and the etching process is continuously stirred.

7. The process for preparing an electrolyte-resistant etched separator for lithium-ion batteries according to claim 1, characterized in that, In S4, the mixed gas source for radio frequency plasma etching is a mixture of oxygen, argon, and nitrogen in a certain proportion. The total gas flow rate is 100 sccm-220 sccm, the radio frequency plasma power is 200W-450W, the vacuum degree of the etching chamber is 3Pa-25Pa, and the gas phase etching time is 120s-270s.

8. The process for preparing an electrolyte-resistant etched separator for lithium-ion batteries according to claim 1, characterized in that, In S5, the ternary electrolyte corrosion-resistant modified coating is a slurry composed of nano-alumina, PVDF-HFP copolymer, fluoroalkyl silane, and conductive carbon dots. The single-sided coating thickness is 3.5μm-6.5μm, the microgravure reverse coating speed is 2m / min-7m / min, and the coating surface density deviation is ≤0.2g / ㎡. In S6, the UV curing power is 250W-600W, the hot air gradient curing is divided into three temperature stages, the temperature range is 75℃-135℃, the total curing time is 4min-10min, and the organic-inorganic covalent cross-linking reaction of the coating occurs during the curing process.

9. The process for preparing an electrolyte-resistant etched separator for lithium-ion batteries according to claim 1, characterized in that, The constant temperature roller pressing and shaping temperature in S7 is 90℃-115℃, the roller pressing line pressure is 1.0MPa-2.5MPa, and the roller pressing line speed is 1m / min-5m / min.

10. The process for preparing an electrolyte-resistant etched separator for lithium-ion batteries according to claim 1, characterized in that, The vacuum constant temperature aging temperature in S8 is 50℃-65℃, the vacuum degree is -0.08MPa to -0.06MPa, and the aging time is 36h-72h. After aging, the finished membrane is immersed in lithium salt electrolyte for 480h without swelling, delamination, coating peeling, or structural damage. The electrolyte corrosion rate is ≤0.006mg / h, the tensile strength is ≥110MPa, the interfacial bonding force is ≥6N / m, the porosity retention rate is ≥98.5%, and the dimensional shrinkage rate after high temperature cycling is ≤0.5%.

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