An ultra-high molecular weight polyethylene battery separator and a method of making the same

Abstract

The application discloses a kind of ultra-high molecular weight polyethylene battery separators and preparation method thereof, belong to battery separator field.The ultra-high molecular weight polyethylene battery separator includes the following mass parts of raw materials: ultra-high molecular weight polyethylene 100 parts, polyether block polyamide 10~20 parts, antioxidant 0.5~2 parts and migration accelerator 1~3 parts;The ultra-high molecular weight polyethylene battery separator is also modified treatment;Modified ultra-high molecular weight polyethylene battery separator double-sided surface is coated with boehmite.Polyether block polyamide under the action of migration accelerator, with the melting blending process of ultra-high molecular weight polyethylene, it will migrate to surface, can improve the wettability and ion transport efficiency of the obtained battery separator, and provide active site for in-situ growth of boehmite, by in-situ combination mode on the surface of the separator coating boehmite binding force is strong, boehmite is not easy to fall off, can improve the thermal stability and cycle capacity retention rate of separator.

Description

Technical Field

[0001] This invention relates to the field of battery separators, and in particular to an ultra-high molecular weight polyethylene battery separator and its preparation method. Background Technology

[0002] With the increasing energy consumption and growing environmental awareness, electrochemical power sources, as a new type of renewable and clean energy, are receiving more and more attention. Battery technology can achieve rapid energy storage and conversion, playing an important role in solving the problem of energy depletion. Among them, lead-acid batteries, as one of the most widely used energy storage devices, are widely used in various electronic devices and automotive fields due to their low cost and long cycle life.

[0003] The separator material, after absorbing the electrolyte, is assembled between the positive and negative electrodes of the battery, making it a crucial component. Its performance directly determines the battery's performance and safety. Battery separators can be categorized by structure into polyolefin separators, non-woven fabric separators, and inorganic composite separators. Among these, polyolefin separators, due to their excellent mechanical properties and chemical stability, are currently the most widely used separator material. They ensure a uniform distribution of electrolytes within the battery, improving its performance and safety.

[0004] In recent years, with the rapid development of new energy vehicles, the safety of power batteries has gradually received high attention, placing higher demands on the performance of separator materials. Ultra-high molecular weight polyethylene (UHMWPE) stands out as an advantageous battery separator due to its high molecular weight. UHMWPE battery separators exhibit superior wear resistance, impact resistance, chemical corrosion resistance, and mechanical properties compared to ordinary polyethylene and polypropylene battery separators. In particular, they readily gel at high temperatures, melting without collapsing, providing excellent safety protection against short circuits and explosions during overcharging or sudden temperature increases, making them more suitable for high-efficiency, high-power power batteries.

[0005] Ultra-high molecular weight polyethylene (UHMWPE) battery separators have excellent overall performance, but they still suffer from defects such as poor heat resistance and poor wettability with polar electrolytes. These defects cause the resulting battery separators to shrink and deform at high temperatures and become unevenly wetted with electrolytes, leading to a surge in the risk of short circuits in the resulting power batteries. The increased interface resistance directly limits their rate performance. Therefore, it is of great significance to obtain a high-strength UHMWPE battery separator with good wettability and thermal dimensional stability. Summary of the Invention

[0006] This invention provides an ultra-high molecular weight polyethylene (UHMWPE) battery separator and its preparation method, which can solve the problems of poor thermal stability and poor wettability of UHMWPE battery separators in the prior art.

[0007] In a first aspect, the present invention provides an ultra-high molecular weight polyethylene battery separator, comprising the following raw materials in parts by weight:

[0008] 100 parts of ultra-high molecular weight polyethylene;

[0009] 10-20 parts of polyether block polyamide;

[0010] Antioxidant 0.5 to 2 parts;

[0011] Migration promoter 1-3 parts;

[0012] The ultra-high molecular weight polyethylene (UHMWPE) battery separator has also undergone modification treatment; the modified UHMWPE battery separator is coated with boehmite on both sides.

[0013] Preferably, the boehmite coating amount is 3 to 5% of the mass of the ultra-high molecular weight polyethylene battery separator.

[0014] Preferably, the molecular weight of ultra-high molecular weight polyethylene is 500,000 to 1,500,000.

[0015] Preferably, the antioxidant includes one or more combinations of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl) phosphite, 2,6-di-tert-butyl-p-cresol, and octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

[0016] By adopting the above technical solution, polyether block polyamide is added during the production process of ultra-high molecular weight polyethylene (UHMWPE) battery separators. Since polyether block polyamide is a polar molecule containing polar functional groups, the large polarity difference between it and non-polar UHMWPE leads to high interfacial tension. This, in turn, promotes the migration of polyether block polyamide towards the gas-solid interface, i.e., the separator surface, during melt blending, thereby reducing the system's free energy. Furthermore, the low-viscosity polyether block polyamide forms a continuous phase during melt blending. Utilizing the viscosity difference and continuous network structure, and with the action of migration promoters, the polyether block polyamide can be promoted to migrate towards low-resistance surface regions, achieving efficient migration of the polyether block polyamide. Polar segments then travel along the network path to the separator surface.

[0017] By migrating polyether-blocked polyamide segments to the surface of the ultra-high molecular weight polyethylene (UHMWPE) battery separator, polar amide groups can be introduced onto the separator surface. This enhances the wettability between the UHMWPE battery separator and the electrolyte. The exposed amide groups can form hydrogen bonds or dipole interactions with the electrolyte, thereby significantly reducing the contact angle between the UHMWPE battery separator surface and the electrolyte. Furthermore, compared to traditional irradiation grafting modification methods for battery separators, this method does not damage the separator's structure, thus avoiding a decline in separator performance.

[0018] On the other hand, by improving the wettability between the separator and the electrolyte, the polyether block polyamide that migrates to the surface of the separator can form an electrolyte-friendly functional layer, thereby shortening the lithium-ion transport path, promoting the uniform diffusion of lithium ions at the interface, reducing the interfacial resistance of the separator, thereby improving the electrochemical performance of the separator, enhancing ion transport efficiency and improving rate performance.

[0019] Furthermore, the ultra-high molecular weight polyethylene (UHMWPE) battery separator of this invention has undergone modification treatment, with both surfaces coated with boehmite. Due to the migration of polyether block polyamide to the surface of the UHMWPE battery separator, a large number of active sites are provided for the bonding of the boehmite. After modification, the high melting point of the boehmite significantly inhibits the melting shrinkage of the UHMWPE battery separator at high temperatures, thereby preventing internal short circuits due to thermal runaway and greatly improving the thermal stability of the UHMWPE battery separator. The rigid coating layer formed by the boehmite helps suppress dendrite penetration and improves the capacity retention of the separator.

[0020] Furthermore, the surface of boehmite is rich in oxygen-containing functional groups such as hydroxyl groups, which can further enhance the affinity between the ultra-high molecular weight polyethylene battery separator and the electrolyte, enabling instantaneous spreading and penetration of the electrolyte. The synergistic migration of polyether block polyamide segments improves the electrolyte wettability of the separator.

[0021] Preferably, the modification treatment specifically includes the following steps:

[0022] Aluminum salts are dissolved in an alcohol solvent to obtain an aluminum ion solution; ultra-high molecular weight polyethylene battery separators are immersed in the aluminum ion solution for 1-2 hours, then removed and cleaned, and then immersed in an ammonia aqueous solution for 1-2 hours. Finally, they are washed and heat-treated to obtain the final product.

[0023] Preferably, the aluminum salt includes one or a combination of aluminum chloride, aluminum nitrate, and aluminum sulfate.

[0024] Preferably, the heat treatment temperature is 300–350°C.

[0025] More preferably, the alcohol solvent includes any one of ethanol, methanol, and isopropanol.

[0026] More preferably, the concentration of the aluminum ion solution is 0.2–0.4 mol / L.

[0027] More preferably, the concentration of the ammonia aqueous solution is 0.04–0.06 mol / L.

[0028] By adopting the above technical solution, aluminum salt is dissolved in an alcohol solvent to obtain an aluminum ion solution. The aluminum ions can undergo adsorption and complexation reactions with the polar groups of polyether block polyamide that migrate to the surface of the separator. The aluminum ions are then adsorbed and nucleated on the surface of the separator. After impregnation with an ammonia aqueous solution, the ions adsorbed on the surface of the separator undergo a hydrolysis reaction with the ammonia to form aluminum hydroxide. In an alkaline environment, the aluminum hydroxide further undergoes hydrolysis to form boehmite. Finally, heat treatment is performed to remove any adsorbed water that may be present in the boehmite, thereby uniformly coating the surface of the ultra-high molecular weight polyethylene battery separator with boehmite.

[0029] This invention utilizes migrated and exposed polar groups to grow boehmite in situ on the separator surface. Compared to conventional coating methods, this coating method exhibits stronger adhesion to the separator surface and avoids issues such as difficulty in controlling coating thickness, insufficient interaction with the separator, and easy powder shedding during charge-discharge cycles that occur during coating modification. Furthermore, the coating layer formed through in-situ growth is extremely thin, preventing an increase in battery internal resistance due to increased coating thickness.

[0030] The modified ultra-high molecular weight polyethylene battery separator obtained by this method has significantly improved heat resistance and stability. Moreover, the present invention selects boehmite as the modifying material for the battery separator. Compared with alumina or other inorganic particles, it has more oxygen-containing functional groups on its surface, which can synergistically enhance the wettability of the ultra-high molecular weight polyethylene battery separator with polyether block polyamide, thereby improving electrochemical performance.

[0031] Preferably, the migration promoter includes one or more combinations of erucamide, oleamide and stearamide.

[0032] By adopting the above technical solution, in the preparation process of ultra-high molecular weight polyethylene battery separator, polyether block polyamide has a tendency to migrate to the surface. However, due to the high molecular weight of polyethylene, there is a large diffusion resistance. Moreover, due to the large difference in polarity between the two, polyether block polyamide tends to form a dispersed phase rather than a continuous phase during melt blending, which will inhibit the surface migration process.

[0033] To address the aforementioned issues, the ultra-high molecular weight polyethylene battery separator of this invention also contains migration promoters, such as erucamide, a low molecular weight substance. On the one hand, it can penetrate into the gaps between ultra-high molecular weight polyethylene molecular chains, weakening inter-chain forces by utilizing steric hindrance, increasing the free volume of the polymer, and creating channels for polyether block polyamide. On the other hand, it can utilize its amphiphilic structural characteristics to reduce interfacial tension and promote the enrichment of polyether block polyamide on the separator surface.

[0034] Furthermore, due to the low molecular weight of the migration promoter, it is easy to migrate to the membrane surface, which can guide the directional migration of polyether block polyamide, thereby promoting the migration of polyether block polyamide to the surface, thereby increasing the surface polarity of the membrane, enhancing the wettability of the electrolyte, and providing active sites for the coating of boehmite.

[0035] Secondly, the present invention provides a method for preparing an ultra-high molecular weight polyethylene battery separator, characterized by comprising the following process steps:

[0036] S1. Weigh the raw materials according to the corresponding mass proportions and mix them to obtain a mixture;

[0037] S2. The mixture is melt-extruded, with white oil added during the melt-extruded process. After extrusion, it is cast and cooled by rollers to obtain a cast film.

[0038] S3. The cast film is sequentially stretched longitudinally, stretched laterally, extracted, heat-set and wound to obtain an ultra-high molecular weight polyethylene battery separator, which is then modified to obtain the final product.

[0039] Preferably, the melt extrusion temperature is 150–230°C; the cooling directional roller temperature is 10–50°C; the longitudinal stretching temperature is 90–120°C with a stretching ratio of 6–10 times; the transverse stretching temperature is 100–130°C with a stretching ratio of 6–12 times; and the heat setting temperature is 95–125°C.

[0040] More preferably, the mass ratio of white oil to ultra-high molecular weight polyethylene is (2-3):1.

[0041] More preferably, the extraction temperature is 5–20°C, and the extractant includes dichloromethane.

[0042] More preferably, the thickness of the ultra-high molecular weight polyethylene battery separator is 5–20 μm.

[0043] The beneficial effects of this invention are:

[0044] 1. The raw materials for an ultra-high molecular weight polyethylene battery separator provided by the present invention include ultra-high molecular weight polyethylene and polyether block polyamide. During the melt blending process, due to the large polarity difference between polyether block polyamide and ultra-high molecular weight polyethylene, the interfacial tension is large, which makes polyether block polyamide tend to migrate to the gas-solid interface, i.e., the separator surface. Under the action of the migration promoter, the polyether block polyamide can be promoted to migrate to the low resistance surface region during the separator preparation process, so as to achieve efficient migration of polyether block polyamide to the separator surface, and the polar chain segments reach the separator surface along the network path.

[0045] The migration of polyether-block polyamide to the surface of the battery separator can greatly improve the wettability between the separator and the electrolyte, shorten the lithium-ion transport path, promote the uniform diffusion of lithium ions at the interface, reduce internal resistance, and thus improve the electrochemical performance of the separator.

[0046] 2. The ultra-high molecular weight polyethylene battery separator of the present invention is also modified and coated with boehmite on both sides. By utilizing the polar groups exposed by the polyether block polyamide that migrates to the surface of the separator, the boehmite can grow in situ on the surface of the separator for coating. The rigid coating layer formed in this way has strong bonding force with the separator. Compared with traditional coating modification, there will be no phenomenon of inorganic particles falling off, which improves the cycle stability of the battery and can also enhance the thermal stability of the separator.

[0047] Furthermore, compared to ordinary inorganic particles, boehmite has more oxygen-containing functional groups on its surface, which can synergistically improve the wettability of the membrane with polyether block polyamide. Detailed Implementation

[0048] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0049] Example

[0050] Example 1: An ultra-high molecular weight polyethylene battery separator was prepared according to the following method:

[0051] S1. Weigh 100 parts of ultra-high molecular weight polyethylene (average molecular weight 1 million) and 15 parts of polyether block polyamide (density 1.02 g / cm³). 3 1 part pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 2 parts erucamide were mixed evenly to obtain a mixture.

[0052] S2. The mixture is melt-extruded, wherein the melt extrusion temperature is set to 180-220℃. During the melt extrusion process, white oil is added from the oil injection port of the extruder. The mass ratio of white oil to ultra-high molecular weight polyethylene is 2:1. After extrusion, a cast film is obtained by casting and cooling rollers, wherein the temperature of the cooling rollers is 35℃.

[0053] S3. The cast film is longitudinally stretched at 100℃ with a stretching ratio of 8 times; transversely stretched at 110℃ with a stretching ratio of 10 times; extracted with dichloromethane at 15℃; then heat-set at 110℃; and finally wound up to obtain an ultra-high molecular weight polyethylene battery separator. This separator then undergoes modification treatment, specifically including the following steps:

[0054] 9.2 g of aluminum chloride was dissolved in ethanol to prepare an aluminum ion solution with a concentration of 0.3 mol / L. 100 g of the ultra-high molecular weight polyethylene (UHMWPE) battery separator obtained above was immersed in the aluminum ion solution for 1 h, then removed and washed for 10 min, and then immersed in an aqueous ammonia solution with a concentration of 0.04 mol / L for 1 h. Finally, after washing, it was heat-treated at 300 °C for 2 h to obtain the final product. The boehmite coating amount was calculated to be 4.12% of the mass of the UHMWPE battery separator; the thickness of the UHMWPE battery separator was 10 μm.

[0055] Examples 2 and 3 describe an ultra-high molecular weight polyethylene (UHMWPE) battery separator, differing from Example 1 only in that the raw material ratio of the UHMWPE battery separator was adjusted, as shown in Table 1.

[0056] Table 1. Formulations for Examples 1 to 3

[0057]

[0058] The modification process of the ultra-high molecular weight polyethylene battery separator in Examples 2 and 3 is the same as that in Example 1.

[0059] Example 4, an ultra-high molecular weight polyethylene battery separator, differs from Example 1 only in that the modification treatment of the ultra-high molecular weight polyethylene battery separator specifically includes the following steps:

[0060] 7g of aluminum chloride was dissolved in ethanol to prepare an aluminum ion solution with a concentration of 0.1mol / L. 100g of the ultra-high molecular weight polyethylene battery separator prepared in Example 1 was immersed in the aluminum ion solution for 1 hour, then taken out and washed for 10 minutes, and then immersed in an aqueous ammonia solution with a concentration of 0.04mol / L for 1 hour. Finally, after washing, it was heat-treated at 300°C for 2 hours to obtain the final product. The boehmite coating amount was calculated to be 3.06% of the mass of the ultra-high molecular weight polyethylene battery separator.

[0061] Example 5, an ultra-high molecular weight polyethylene battery separator, differs from Example 1 only in that the modification treatment of the ultra-high molecular weight polyethylene battery separator specifically includes the following steps:

[0062] 11g of aluminum chloride was dissolved in ethanol to prepare an aluminum ion solution with a concentration of 0.4mol / L. 100g of the ultra-high molecular weight polyethylene battery separator prepared in Example 1 was immersed in the aluminum ion solution for 1 hour, then removed and washed for 10 minutes, and then immersed in an aqueous ammonia solution with a concentration of 0.04mol / L for 1 hour. After washing, it was heat-treated at 300°C for 2 hours to obtain the final product. The boehmite coating amount was calculated to be 4.95% of the mass of the ultra-high molecular weight polyethylene battery separator.

[0063] Example 6, an ultra-high molecular weight polyethylene battery separator, differs from Example 1 only in that the modification treatment of the ultra-high molecular weight polyethylene battery separator specifically includes the following steps:

[0064] 2.5g of aluminum chloride was dissolved in ethanol to prepare an aluminum ion solution with a concentration of 0.1mol / L. 100g of the ultra-high molecular weight polyethylene battery separator prepared in Example 1 was immersed in the aluminum ion solution for 1 hour, then removed and washed for 10 minutes, and then immersed in an aqueous ammonia solution with a concentration of 0.04mol / L for 1 hour. Finally, after washing, it was heat-treated at 300°C for 2 hours to obtain the final product. The boehmite coating amount was calculated to be 1.10% of the mass of the ultra-high molecular weight polyethylene battery separator.

[0065] Example 7, an ultra-high molecular weight polyethylene battery separator, differs from Example 1 only in that the modification treatment of the ultra-high molecular weight polyethylene battery separator specifically includes the following steps:

[0066] 16g of aluminum chloride was dissolved in ethanol to prepare an aluminum ion solution with a concentration of 0.4mol / L. 100g of the ultra-high molecular weight polyethylene battery separator prepared in Example 1 was immersed in the aluminum ion solution for 1 hour, then removed and washed for 10 minutes, and then immersed in an aqueous ammonia solution with a concentration of 0.04mol / L for 1 hour. After washing, it was heat-treated at 300°C for 2 hours to obtain the final product. The boehmite coating amount was calculated to be 7.05% of the mass of the ultra-high molecular weight polyethylene battery separator.

[0067] Comparative Example

[0068] Comparative Example 1, an ultra-high molecular weight polyethylene battery separator, differs from Example 1 only in that the amount of polyether block polyamide added is 5 parts.

[0069] Comparative Example 2, an ultra-high molecular weight polyethylene battery separator, differs from Example 1 only in that the amount of polyether block polyamide added is 25 parts.

[0070] Comparative Example 3, an ultra-high molecular weight polyethylene battery separator, differs from Example 1 only in that the amount of erucamide added is 0.5 parts.

[0071] Comparative Example 4, an ultra-high molecular weight polyethylene battery separator, differs from Example 1 only in that the amount of erucamide added is 4 parts.

[0072] Comparative Example 5 is an ultra-high molecular weight polyethylene battery separator, which differs from Example 1 only in that it does not contain erucamide.

[0073] Comparative Example 6, an ultra-high molecular weight polyethylene battery separator, differs from Example 1 only in that it does not contain polyether block polyamide.

[0074] Comparative Example 7, an ultra-high molecular weight polyethylene battery separator, differs from Example 1 only in that the modification treatment of the ultra-high molecular weight polyethylene battery separator specifically includes the following steps:

[0075] 9.2g of aluminum chloride was dissolved in ethanol to prepare an aluminum ion solution with a concentration of 0.3mol / L. 100g of the ultra-high molecular weight polyethylene battery separator obtained above was immersed in the aluminum ion solution for 1 hour. After washing, it was heat-treated at 300℃ for 2 hours to form sodium oxide on the surface of the ultra-high molecular weight polyethylene battery separator. Finally, the boehmite coating amount formed was calculated to be 4.03% of the mass of the ultra-high molecular weight polyethylene battery separator.

[0076] Comparative Example 8, an ultra-high molecular weight polyethylene battery separator, differs from Example 1 only in that the modification treatment of the ultra-high molecular weight polyethylene battery separator specifically includes the following steps:

[0077] Add 0.08g sodium polyacrylate and 4.2g boehmite (particle size 1-5μm) to deionized water and disperse at 1000r / min for 20min. Then add 0.4g polystyrene-butadiene emulsion as binder and disperse at 5000r / min for 40min to obtain boehmite slurry.

[0078] The obtained boehmite slurry was coated on both sides of an ultra-high molecular weight polyethylene battery separator, and then dried. The resulting coating thickness was 4 μm.

[0079] Comparative Example 9 is an ultra-high molecular weight polyethylene battery separator, which differs from Example 1 only in that the ultra-high molecular weight polyethylene battery separator is not modified and its surface is not coated with boehmite.

[0080] Performance testing

[0081] 1. Physical property tests of the diaphragm:

[0082] (1) Thermal stability test: Take the ultra-high molecular weight polyethylene battery separator obtained in the examples and comparative examples, and cut it into 10 pieces. A 10cm separator sample was placed in an oven and heated at 90℃ for 1 hour. After being removed and cooled, the transverse and longitudinal thermal shrinkage rates of the separator sample were tested to characterize the thermal stability of the ultra-high molecular weight polyethylene battery separator.

[0083] (2) Wetting test: The contact angle between the ultra-high molecular weight polyethylene battery separator and the electrolyte obtained in the examples and comparative examples was tested using a contact angle tester, wherein the electrolyte was dimethyl carbonate.

[0084] The results of the above experiments are shown in Table 2.

[0085] 2. Electrochemical performance test:

[0086] A lithium-ion battery was assembled using lithium iron phosphate as the positive electrode, lithium sheet as the negative electrode, lithium hexafluorophosphate as the solute, a 1:1 mass ratio of ethylene carbonate and dimethyl carbonate mixed solution as the solvent, and ultra-high molecular weight polyethylene battery separator obtained in the examples and comparative examples as the battery separator.

[0087] Then, after 100 charge-discharge cycles at 25℃ and 2C rate, the battery capacity retention rate was tested and calculated. The test results are shown in Table 3.

[0088] Table 2 Results of Physical Property Tests

[0089]

[0090] Table 3 Electrochemical performance test results

[0091]

[0092] Based on Tables 2 and 3, and in conjunction with Examples 1, 6, 7, and Comparative Example 9, it can be seen that the thermal shrinkage rate of Examples 6, 7, and 9 decreased, the contact angle increased, and the capacity retention rate decreased. This is because Examples 6, 7, and 9 adjusted the boehmite content on the surface of the modified ultra-high molecular weight polyethylene battery separator compared to Example 1. When the boehmite coating amount decreases, the thermal stability decreases accordingly, the cycle capacity retention rate decreases, and the number of polar groups on the separator surface decreases, leading to a decrease in wettability. In Comparative Example 9, the surface was not coated with boehmite, so the performance decrease was more pronounced. However, in Comparative Example 9, the contact angle was also within a relatively small range because the ultra-high molecular weight polyethylene battery separator obtained in Comparative Example 9 had migrating polyether-blocked polyamide segments on its surface. The exposed polar groups improved the wettability of the battery separator obtained in Comparative Example 9 compared to ordinary ultra-high molecular weight polyethylene battery separators. In Example 7, the increased boehmite coating amount affects the pore structure of the battery separator, and pore blockage leads to a significant decrease in capacity retention.

[0093] Based on Example 1 and Comparative Examples 1 to 6, it can be seen that the performance of Comparative Examples 1 to 6 is lower than that of Example 1. The reason for this may be that Comparative Examples 1 to 6 are adjustments to the dosage of polyether block polyamide and migration promoter in the ultra-high molecular weight polyethylene battery separator outside the specified range. When the content of polyether block polyamide is reduced or not added, the amount of polar substances migrating to the separator surface is reduced. On the one hand, this directly affects the wettability between the separator and the electrolyte, and on the other hand, it affects the bonding force between boehmite and the separator, resulting in a significant decrease in capacity retention and wettability. The reduction in the dosage of migration promoter also leads to a reduction in the amount of polyether block polyamide migrating to the separator surface, thereby causing a decrease in various performance characteristics. When the amount of polyether block polyamide increases, some polyether block polyamide migrates to the surface of the separator. However, due to excessive addition, the separator molecules also contain polyether block polyamide. Since polyether block polyamide and ultra-high molecular weight polyethylene have large polarity differences and poor compatibility, it will directly affect the performance of the obtained battery separator, leading to a decrease in performance. When the amount of migration promoter added is excessive, the migration promoter will also migrate to the surface, affecting the bonding force between boehmite and separator. During cycling, boehmite will fall off, resulting in a significant decrease in capacity retention.

[0094] Based on Examples 1, 7, and 8, it can be seen that the performance of Comparative Examples 7 and 8 is lower than that of Example 1. This may be because in Comparative Example 7, alumina was used to replace boehmite on the membrane surface. However, alumina contains fewer oxygen-containing groups, limiting its improvement in wettability, which in turn leads to a decrease in the electrochemical performance of the membrane. In Comparative Example 8, boehmite was coated onto the membrane surface using a coating modification method. This not only directly blocks the effect of the polyether block polyamide migrating to the surface, but also results in poor adhesion of the coating modification method, leading to a decrease in cycle capacity retention.

[0095] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A battery separator made of ultra-high molecular weight polyethylene, characterized in that, The raw materials include the following parts by weight: 100 parts of ultra-high molecular weight polyethylene; 10-20 parts of polyether block polyamide; Antioxidant 0.5 to 2 parts; Migration promoter 1-3 parts; The ultra-high molecular weight polyethylene battery separator has also undergone modification treatment; The modified ultra-high molecular weight polyethylene battery separator is coated with boehmite on both sides. The boehmite coating amount is 3-5% of the mass of the ultra-high molecular weight polyethylene battery separator; The modification process specifically includes the following steps: Aluminum salts are dissolved in an alcohol solvent to obtain an aluminum ion solution; ultra-high molecular weight polyethylene battery separators are immersed in the aluminum ion solution for 1-2 hours, then removed and cleaned, and then immersed in an ammonia aqueous solution for 1-2 hours. Finally, they are washed and heat-treated to obtain the final product.

2. The ultra-high molecular weight polyethylene battery separator according to claim 1, characterized in that, The aluminum salt includes one or more combinations of aluminum chloride, aluminum nitrate, and aluminum sulfate.

3. The ultra-high molecular weight polyethylene battery separator according to claim 1, characterized in that, The heat treatment temperature is 300–350°C.

4. The ultra-high molecular weight polyethylene battery separator according to claim 1, characterized in that, The molecular weight of the ultra-high molecular weight polyethylene is 500,000 to 1,500,000.

5. The ultra-high molecular weight polyethylene battery separator according to claim 1, characterized in that, The migration promoters include one or more combinations of erucamide, oleamide, and stearamide.

6. The ultra-high molecular weight polyethylene battery separator according to claim 1, characterized in that, The antioxidants include one or more of the following: pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butylphenyl) phosphite, 2,6-di-tert-butyl-p-cresol, and octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

7. A method for preparing an ultra-high molecular weight polyethylene (UHMWPE) battery separator, used to prepare the UHMWPE battery separator according to any one of claims 1 to 6, characterized in that, The process includes the following steps: S1. Weigh the raw materials according to the corresponding mass proportions and mix them to obtain a mixture; S2. The mixture is melt-extruded, with white oil added during the melt-extruded process. After extrusion, it is cast and cooled by rollers to obtain a cast film. S3. The cast film is sequentially stretched longitudinally, stretched laterally, extracted, heat-set and wound to obtain an ultra-high molecular weight polyethylene battery separator, which is then modified to obtain the final product.

8. The method for preparing the ultra-high molecular weight polyethylene battery separator according to claim 7, characterized in that, The melt extrusion temperature is 150–230°C; the cooling directional roller temperature is 10–50°C; the longitudinal stretching temperature is 90–120°C with a stretching ratio of 6–10 times; the transverse stretching temperature is 100–130°C with a stretching ratio of 6–12 times; and the heat setting temperature is 95–125°C.

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