Temperature-resistant battery diaphragm and application thereof in lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a temperature-resistant battery diaphragm and application thereof to a lithium ion battery. The diaphragm is composed of polyvinylidene fluoride, poly (lithium acrylate)-b-poly (vinyl perfluoro caprylate)-g-aluminum oxide, a pore-foaming agent and N, N-dimethylacetamide, a block polymer is grafted on the surface of aluminum oxide through an atom transfer radical polymerization (ATRP) technology, and the interface bonding force and dispersity of inorganic particles and a polymer matrix are effectively improved. The diaphragm has good dimensional stability and mechanical strength in a high-temperature environment, the risks of thermal shrinkage and battery short circuit can be remarkably reduced, and the safety and reliability of the lithium ion battery are improved. The preparation process disclosed by the invention is high in controllability, coordinates the physical performance and the ion conduction performance of the diaphragm, and is suitable for the manufacturing requirements of the high-performance lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a temperature-resistant battery separator and its application in lithium ion batteries. Background Art

[0002] With the rapid development of new energy vehicles and energy storage systems, lithium-ion batteries, as core energy storage devices, are facing increasingly stringent application environment requirements. Especially under high-temperature conditions, the performance stability of battery separators is directly related to the safety and reliability of the entire battery system. Traditional polyolefin separators, such as polypropylene (PP) and polyethylene (PE), although they have good chemical stability and mechanical strength at room temperature, their low melting point and glass transition temperature make them prone to thermal shrinkage and mechanical performance degradation in high-temperature environments.

[0003] The commercial separators currently on the market are mainly made of polyolefin materials through dry or wet processes. These separators will experience significant dimensional shrinkage when the temperature exceeds 120°C, resulting in an increased risk of internal short circuits in the battery. In order to improve the heat resistance of the separator, researchers have tried a variety of technical paths, including surface coating of ceramic particles, blending modification, and chemical cross-linking. However, these methods often have certain limitations: the surface coating method easily leads to insufficient bonding between the coating and the substrate, resulting in peeling under mechanical stress; although blending modification can improve temperature resistance, it often comes at the expense of the permeability and flexibility of the separator; the chemical cross-linking method may affect the electrochemical stability of the separator.

[0004] In recent years, polyvinylidene fluoride (PVDF) has garnered widespread attention in the lithium battery separator field due to its excellent temperature resistance and chemical stability. PVDF has a high melting point and glass transition temperature, maintaining stable physical and chemical properties over a wide temperature range. However, pure PVDF separators often suffer from low porosity and poor electrolyte wettability, limiting their application in high-performance lithium batteries.

[0005] To address these issues, the introduction of inorganic nanoparticles is considered an effective modification method. Alumina, a typical ceramic material, possesses excellent thermal stability and mechanical strength. However, its high surface energy can easily lead to particle agglomeration, impairing dispersion within the polymer matrix. Furthermore, the varying compatibility between the inorganic particles and the organic polymer matrix can lead to insufficient interfacial bonding, thus compromising the overall performance of the composite material.

[0006] The development of surface modification technology has provided new insights into addressing the dispersion and compatibility issues of inorganic particles. By grafting functional polymer chains onto the particle surface, the interface between the particle and the matrix can be optimized. In particular, the unique molecular structure of block polymers allows them to possess both hydrophobic and hydrophilic properties, making it possible to construct composite separators that combine mechanical strength with electrolyte compatibility.

[0007] Atom transfer radical polymerization (ATRP), a living, controlled polymerization method, enables precise control of polymer molecular weight and molecular weight distribution, and enables the design and synthesis of complex molecular structures. ATRP can be used to construct block polymers on the surface of aluminum oxide, enabling molecular-level interface design and providing a new technical approach for the development of high-performance, heat-resistant battery separators.

[0008] However, the existing technology still lacks in-depth research on the molecular design of block polymers on the surface of alumina, the influence of polymerization sequence on the final performance, and the composite mechanism with the polymer matrix, which limits the industrial application of this technology. Summary of the Invention

[0009] In view of this, the purpose of the present invention is to propose a temperature-resistant battery separator and its application in lithium-ion batteries, so as to solve the problem that the existing battery separator is prone to thermal shrinkage and deformation in high temperature environment, resulting in a significantly increased risk of battery short circuit failure.

[0010] Based on the above objectives, the present invention provides a heat-resistant battery separator, which is prepared from the following raw materials, by weight: 10-20 parts of polyvinylidene fluoride, 2-8 parts of poly(lithium acrylate)-b-poly(vinyl perfluorooctanoate)-g-alumina, 3-6 parts of a porogen, and 80-160 parts of N,N-dimethylacetamide.

[0011] Furthermore, the preparation method of the poly(lithium acrylate)-b-poly(vinyl perfluorooctanoate)-g-alumina comprises the following steps:

[0012] S1: Under nitrogen atmosphere, vinyl perfluorooctanoate was polymerized on ATRP initiator-grafted alumina to obtain poly(vinyl perfluorooctanoate)-g-alumina;

[0013] S2: Under nitrogen atmosphere, acrylic acid was polymerized on poly(vinyl perfluorooctanoate)-g-alumina to obtain poly(acrylic acid)-b-poly(vinyl perfluorooctanoate)-g-alumina.

[0014] S3: Adjust the pH of the poly(acrylic acid)-b-poly(vinyl perfluorooctanoate)-g-alumina aqueous solution to 7.3-7.8 with hydrated lithium hydroxide, centrifuge, and vacuum dry to obtain poly(lithium acrylate)-b-poly(vinyl perfluorooctanoate)-g-alumina.

[0015] Preferably, the ATRP initiator grafted alumina in step S1 is prepared by modifying alumina with a silane coupling agent KH-550 to obtain amino alumina, which is then reacted with bromoisobutyryl bromide.

[0016] Preferably, the average particle size of the aluminum oxide is 20-100 nm.

[0017] Preferably, the weight ratio of the aluminum oxide to the silane coupling agent KH-550 is 3:0.2-0.4.

[0018] Preferably, the weight ratio of the amino-alumina to bromoisobutyryl bromide is 3:0.18-0.3.

[0019] Preferably, in step S1, the weight ratio of ATRP initiator grafted alumina to vinyl perfluorooctanoate is 3:7.5-13.5.

[0020] Preferably, in step S2, the weight ratio of poly(vinyl perfluorooctanoate)-g-alumina to acrylic acid is 5:2.5-4.5.

[0021] Preferably, the porogen is polyethylene glycol.

[0022] Furthermore, the present invention provides a method for preparing a heat-resistant battery separator, comprising the following steps:

[0023] (1) Add polyvinylidene fluoride to N,N-dimethylacetamide, heat to 75-85°C, stir for 3-5 hours, then add poly(lithium acrylate)-b-poly(vinyl perfluorooctanoate)-g-alumina, ultrasonicate for 20-40 minutes, then add porogen, continue stirring for 1.5-2.5 hours, and vacuum degas to obtain a composite membrane solution;

[0024] (2) casting the composite film liquid onto a polyethylene terephthalate carrier film through a doctor blade coater, pre-curing, peeling, and performing a heat stretching treatment using a biaxial synchronous stretching device to obtain a stretched composite film;

[0025] (3) Immersing the stretched composite film in deionized water for extraction treatment, and then subjecting the extracted composite film to high-temperature shaping on a tension shaping machine to obtain a temperature-resistant battery separator.

[0026] The temperature of the high-temperature setting in step (3) is 178-182° C., the time is 25-35 min, and the tension is 145-155 N / m.

[0027] Furthermore, the present invention provides an application of a temperature-resistant battery separator for lithium-ion batteries.

[0028] The present invention significantly improves the comprehensive performance of the heat-resistant battery separator by constructing a block polymer with a specific structure on the surface of aluminum oxide, and has the following beneficial effects:

[0029] First, the present invention achieves an ordered arrangement of hydrophobic and hydrophilic microdomains through precise molecular design. In the block polymer grafted onto the alumina surface, strong intermolecular forces and physical entanglements form between the fluorinated segments and the polyvinylidene fluoride matrix, effectively enhancing the interfacial bonding strength between the inorganic particles and the polymer matrix, significantly improving the mechanical properties and structural stability of the separator.

[0030] Secondly, the amphiphilic molecular structure of the block polymer cleverly balances the mechanical strength of the separator with its electrolyte affinity. The hydrophobic nature of the fluorinated chain ensures good compatibility with the polyvinylidene fluoride matrix, while the hydrophilic nature of the lithium acrylate chain provides an excellent wetting interface for the electrolyte, optimizing ion transport channels.

[0031] Third, the preparation process of this invention enables precise control of the microporous structure. The selective dissolution of polyethylene glycol, a porogen, during the extraction process, combined with the orderly arrangement of the block polymer, forms a regular microporous network within the separator. The hydrophilic segments enriched on the pore surface provide an ideal channel environment for electrolyte penetration and ion transport.

[0032] Fourth, surface modification of the alumina particles effectively addresses the difficulty of dispersing inorganic fillers within the polymer matrix. Pretreatment with a silane coupling agent and grafting with an ATRP initiator achieves functional modification of the alumina surface, eliminating the tendency for particles to agglomerate and ensuring uniform microstructure of the composite membrane.

[0033] Fifth, the unique molecular structure of the block polymer imparts excellent thermal stability to the separator. The rigid molecular chains and high bond energy of the fluorinated segments effectively inhibit molecular chain motion in the polymer matrix at high temperatures, significantly reducing the thermal shrinkage of the separator and improving the safety performance of the battery in high-temperature environments.

[0034] Sixth, the preparation method of the present invention has good process controllability and reproducibility. The controllable activity of ATRP polymerization technology ensures precise control of the molecular weight and composition of the block polymer, while the optimization of the biaxial stretching process achieves the coordinated unification of the microstructure and macroscopic properties of the separator.

[0035] Seventh, the composite separator achieves an effective balance of air permeability while maintaining excellent heat resistance. The ordered arrangement of the block polymer and the synergistic effect of the porogen form a well-connected pore structure, ensuring rapid lithium ion transmission and meeting the application requirements of high-power density batteries.

[0036] Finally, the heat-resistant battery separator prepared by the present invention performs well in terms of electrolyte affinity. The effective interaction between the hydrophilic chain segments and the electrolyte solvent molecules significantly improves the electrolyte absorption and retention capacity of the separator, providing a strong guarantee for the long-term stable operation of the battery. DETAILED DESCRIPTION

[0037] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments.

[0038] Example 1:

[0039] (1) 3 g of alumina (average particle size 50 nm) was added to 100 g of anhydrous ethanol, ultrasonicated for 25 min, and then 0.2 g of silane coupling agent KH-550 was added. The temperature was raised to 58°C, stirred for 2 h, centrifuged, washed with anhydrous ethanol three times, and vacuum dried to obtain amino-alumina.

[0040] (2) Add 3 g of ammoniated alumina to 40 g of toluene and sonicate for 25 min. Then, add 0.18 g of bromoisobutyryl bromide and 0.12 g of triethylamine in an ice bath, stir for 1.5 h, warm to room temperature, stir for 8 h, centrifuge, wash three times with dichloromethane, and vacuum dry to obtain ATRP initiator-grafted alumina.

[0041] (3) Under nitrogen atmosphere, 3 g of ATRP initiator-grafted alumina was added to 80 g of methanol and ultrasonicated for 25 min. Then, 7.5 g of vinyl perfluorooctanoate, 0.07 g of copper bromide, 0.06 g of pentamethyldiethylenetriamine, and 0.06 g of L-ascorbic acid were added. The temperature was raised to 48°C and stirred for 10 h. The mixture was centrifuged, washed three times with methanol, and dried in vacuo to obtain poly(vinyl perfluorooctanoate)-g-alumina.

[0042] (4) Under nitrogen atmosphere, 5 g of poly(vinyl perfluorooctanoate)-g-alumina was added to 80 g of methanol and ultrasonicated for 25 min. Then, 2.5 g of acrylic acid, 0.1 g of copper bromide, 0.08 g of pentamethyldiethylenetriamine, and 0.08 g of L-ascorbic acid were added. The temperature was raised to 48°C, stirred for 6 h, centrifuged, washed three times with methanol, and vacuum dried to obtain poly(acrylic acid)-b-poly(vinyl perfluorooctanoate)-g-alumina.

[0043] (5) 5 g of poly(acrylic acid)-b-poly(vinyl perfluorooctanoate)-g-alumina was added to 80 g of deionized water, ultrasonicated for 30 min, and then the pH was adjusted to 7.3 with hydrated lithium hydroxide, centrifuged, and vacuum dried to obtain poly(lithium acrylate)-b-poly(vinyl perfluorooctanoate)-g-alumina;

[0044] (6) 10 g of polyvinylidene fluoride (brand Solef 1015) was added to 80 g of N,N-dimethylacetamide, heated to 75 °C, stirred for 3 h, and then 2 g of poly(lithium acrylate)-b-poly(vinyl perfluorooctanoate)-g-alumina was added. Ultrasonication was performed for 20 min, and then 3 g of polyethylene glycol (PEG-400) was added. Stirring was continued for 1.5 h, and finally degassing was performed at a vacuum degree of -0.08 MPa for 10 min to obtain a composite membrane solution.

[0045] (7) The composite film liquid was cast onto a polyethylene terephthalate carrier film using a doctor blade coater, with a doctor blade gap of 180 μm and a coating speed of 1.8 m / min. The cast composite film was pre-cured at 115° C. for 40 min, and the pre-cured composite film was peeled off from the polyethylene terephthalate carrier film and subjected to heat stretching treatment using a biaxial synchronous stretching device. The stretching temperature was set at 140° C., the longitudinal stretching ratio was 3.5:1, the transverse stretching ratio was 3.8:1, and the stretching speed was 50 mm / min to obtain a stretched composite film;

[0046] (8) The stretched composite membrane was immersed in deionized water for extraction treatment (the water bath volume was 15 times the membrane volume) at a temperature of 65°C for 5 hours to form a microporous structure. The extracted composite membrane was then subjected to high-temperature setting on a tension setting machine with a set temperature of 178°C, a holding time of 25 minutes, and a tension of 145 N / m to obtain a heat-resistant battery separator.

[0047] Example 2:

[0048] (1) 3 g of alumina (average particle size 50 nm) was added to 120 g of anhydrous ethanol, and ultrasonicated for 30 min. 0.3 g of silane coupling agent KH-550 was then added. The temperature was raised to 60°C, stirred for 3 h, centrifuged, washed three times with anhydrous ethanol, and vacuum dried to obtain amino-alumina.

[0049] (2) Add 3 g of ammoniated alumina to 60 g of toluene and sonicate for 30 min. Then, add 0.24 g of bromoisobutyryl bromide and 0.18 g of triethylamine in an ice bath, stir for 2 h, warm to room temperature, stir for 12 h, centrifuge, wash three times with dichloromethane, and vacuum dry to obtain ATRP initiator-grafted alumina.

[0050] (3) Under nitrogen atmosphere, 3 g of ATRP initiator-grafted alumina was added to 120 g of methanol and ultrasonicated for 30 min. Then, 10.5 g of vinyl perfluorooctanoate, 0.1 g of copper bromide, 0.08 g of pentamethyldiethylenetriamine, and 0.08 g of L-ascorbic acid were added. The temperature was raised to 50°C, stirred for 12 h, centrifuged, washed three times with methanol, and vacuum dried to obtain poly(vinyl perfluorooctanoate)-g-alumina.

[0051] (4) Under nitrogen atmosphere, 5 g of poly(vinyl perfluorooctanoate)-g-alumina was added to 100 g of methanol and ultrasonicated for 30 min. Then, 3.5 g of acrylic acid, 0.15 g of copper bromide, 0.12 g of pentamethyldiethylenetriamine, and 0.12 g of L-ascorbic acid were added. The temperature was raised to 50°C and stirred for 8 h. The mixture was centrifuged, washed with methanol three times, and vacuum dried to obtain poly(acrylic acid)-b-poly(vinyl perfluorooctanoate)-g-alumina.

[0052] (5) 5 g of poly(acrylic acid)-b-poly(vinyl perfluorooctanoate)-g-alumina was added to 100 g of deionized water, ultrasonicated for 30 min, and then the pH was adjusted to 7.5 with hydrated lithium hydroxide, centrifuged, and vacuum dried to obtain poly(lithium acrylate)-b-poly(vinyl perfluorooctanoate)-g-alumina;

[0053] (6) 15 g of polyvinylidene fluoride (brand Solef 1015) was added to 120 g of N,N-dimethylacetamide, heated to 80 °C, stirred for 4 h, then 5 g of poly(lithium acrylate)-b-poly(vinyl perfluorooctanoate)-g-alumina was added, ultrasonicated for 30 min, then 4.8 g of polyethylene glycol (PEG-400) was added, and stirring was continued for 2 h. Finally, degassing was carried out at a vacuum degree of -0.08 MPa for 15 min to obtain a composite membrane solution;

[0054] (7) The composite film liquid was cast onto a polyethylene terephthalate carrier film using a doctor blade coater, with a doctor blade gap of 200 μm and a coating speed of 2 m / min. The cast composite film was pre-cured at 120° C. for 45 min, and the pre-cured composite film was peeled off from the polyethylene terephthalate carrier film and subjected to heat stretching treatment using a biaxial synchronous stretching device. The stretching temperature was set at 140° C., the longitudinal stretching ratio was 3.5:1, the transverse stretching ratio was 3.8:1, and the stretching speed was 50 mm / min to obtain a stretched composite film.

[0055] (8) The stretched composite membrane was immersed in deionized water for extraction treatment (the water bath volume was 20 times the membrane volume) at a temperature of 70°C for 6 hours to form a microporous structure. The extracted composite membrane was then subjected to high-temperature shaping on a tension shaping machine with a set temperature of 180°C, a holding time of 30 minutes, and a tension of 150 N / m to obtain a heat-resistant battery separator.

[0056] Example 3:

[0057] (1) 3 g of alumina (average particle size 50 nm) was added to 140 g of anhydrous ethanol, and ultrasonicated for 35 min. 0.4 g of silane coupling agent KH-550 was then added. The temperature was raised to 62°C, stirred for 4 h, and centrifuged. The mixture was washed three times with anhydrous ethanol and dried in vacuo to obtain amino-alumina.

[0058] (2) 3 g of ammoniated alumina was added to 80 g of toluene and ultrasonicated for 35 min. 0.3 g of bromoisobutyryl bromide and 0.24 g of triethylamine were added under ice bath and stirred for 2.5 h. The mixture was then warmed to room temperature and stirred for 16 h. The mixture was centrifuged, washed with dichloromethane three times, and dried under vacuum to obtain ATRP initiator grafted alumina.

[0059] (3) Under nitrogen atmosphere, 3 g of ATRP initiator-grafted alumina was added to 150 g of methanol and ultrasonicated for 35 min. Then, 13.5 g of vinyl perfluorooctanoate, 0.13 g of copper bromide, 0.1 g of pentamethyldiethylenetriamine, and 0.1 g of L-ascorbic acid were added. The temperature was raised to 52°C, stirred for 14 h, centrifuged, washed three times with methanol, and vacuum dried to obtain poly(vinyl perfluorooctanoate)-g-alumina.

[0060] (4) Under nitrogen atmosphere, 5 g of poly(vinyl perfluorooctanoate)-g-alumina was added to 120 g of methanol and ultrasonicated for 35 min. Then, 4.5 g of acrylic acid, 0.2 g of copper bromide, 0.16 g of pentamethyldiethylenetriamine, and 0.16 g of L-ascorbic acid were added. The temperature was raised to 52°C, stirred for 10 h, centrifuged, washed three times with methanol, and vacuum dried to obtain poly(acrylic acid)-b-poly(vinyl perfluorooctanoate)-g-alumina.

[0061] (5) 5 g of poly(acrylic acid)-b-poly(vinyl perfluorooctanoate)-g-alumina was added to 120 g of deionized water, ultrasonicated for 30 min, and then the pH was adjusted to 7.8 with hydrated lithium hydroxide, centrifuged, and vacuum dried to obtain poly(lithium acrylate)-b-poly(vinyl perfluorooctanoate)-g-alumina;

[0062] (6) 20 g of polyvinylidene fluoride (brand Solef 1015) was added to 160 g of N,N-dimethylacetamide, heated to 85 °C, stirred for 5 h, then added 8 g of poly(lithium acrylate)-b-poly(vinyl perfluorooctanoate)-g-alumina, ultrasonicated for 40 min, then added 6 g of polyethylene glycol (PEG-400), continued stirring for 2.5 h, and finally degassed at -0.08 MPa vacuum for 20 min to obtain a composite membrane solution;

[0063] (7) The composite film liquid was cast onto a polyethylene terephthalate carrier film using a doctor blade coater, with a doctor blade gap of 220 μm and a coating speed of 2.2 m / min. The cast composite film was pre-cured at 125° C. for 50 min, and the pre-cured composite film was peeled off from the polyethylene terephthalate carrier film and subjected to heat stretching treatment using a biaxial synchronous stretching device. The stretching temperature was set at 140° C., the longitudinal stretching ratio was 3.5:1, the transverse stretching ratio was 3.8:1, and the stretching speed was 50 mm / min to obtain a stretched composite film;

[0064] (8) The stretched composite membrane was immersed in deionized water for extraction treatment (the water bath volume was 25 times the membrane volume) at a temperature of 75°C for 7 hours to form a microporous structure. The extracted composite membrane was then subjected to high-temperature setting on a tension setting machine with a set temperature of 182°C, a holding time of 35 minutes, and a tension of 155 N / m to obtain a heat-resistant battery separator.

[0065] Comparative Example 1:

[0066] The difference between Comparative Example 1 and Example 2 is that the ATRP initiator is grafted onto the surface of alumina to polymerize acrylic acid first and then vinyl perfluorooctanoate;

[0067] Comparative Example 2:

[0068] The difference between Comparative Example 2 and Example 2 is that only vinyl perfluorooctanoate is polymerized on the surface of the alumina grafted with the ATRP initiator;

[0069] Comparative Example 3:

[0070] The difference between Comparative Example 3 and Example 2 is that only acrylic acid is polymerized on the surface of the ATRP initiator-grafted alumina;

[0071] Comparative Example 4:

[0072] The difference between Comparative Example 4 and Example 2 is that the poly(lithium acrylate)-b-poly(vinyl perfluorooctanoate)-g-alumina in step (4) is replaced with alumina (average particle size 50 nm);

[0073] Performance testing:

[0074] Air permeability test: Referring to GB / T 36363-2018, a circular specimen with a diameter of 25 mm was cut and fixed in the test chamber of the air permeability tester. A pressure of 4.89 kPa was applied, and the time required for 100 mL of air to pass through the diaphragm was recorded. This was repeated five times, and the average value was taken to calculate the air permeability. The results are shown in Table 1.

[0075] Mechanical properties test: Referring to GB / T 1040.3-2006, the diaphragm was cut into dumbbell-shaped specimens (gauge length 50 mm, width 10 mm). The thickness was measured and the average value of 3 points was taken. A universal material testing machine (tensile speed 50 mm / min, temperature 25°C) was used to record the tensile strength (MPa) and elongation at break (%). The average value of 5 specimens in each group was taken. The results are shown in Table 1.

[0076] Thermal stability test: Refer to GB / T 7141-2008, cut a 100 mm × 100 mm specimen, mark the origin, place it in a 150°C oven for 1 hour, remove it, cool it to room temperature, and measure the shrinkage in the machine direction (MD) and transverse direction (TD).

[0077] Electrolyte affinity test: Refer to GB / T 36363-2018, weigh the dry sample, immerse it in the electrolyte (1MLiPF6 in EC:DMC=1:1v / v) at 25°C for 1 hour, remove it and drain it for 60 seconds, remove any residual droplets on the surface, weigh it, and calculate the liquid absorption rate.

[0078] Table 1 Performance test results

[0079]

[0080]

[0081] Data Analysis:

[0082] As can be seen from the data of Examples 1-3 in Table 1, the heat-resistant battery separator prepared by the present invention exhibits good comprehensive performance in terms of air permeability, mechanical properties, thermal stability and electrolyte affinity. This may be attributed to the unique molecular design of the block polymer on the surface of alumina, in which strong intermolecular forces and physical entanglements are formed between the poly(vinyl perfluorooctanoate) chain segment and the polyvinylidene fluoride molecular chain, thereby effectively improving the mechanical strength and thermal stability of the separator. At the same time, there is good compatibility and hydrogen bond interaction between the poly(lithium acrylate) chain segment and the polyethylene glycol, and this interaction is conducive to the formation of a uniform dispersion system during the film making process. During the extraction process, the dissolution of polyethylene glycol may form a regular microporous structure inside the separator, while the poly(lithium acrylate) chain segment enriched on the pore surface may provide a good wetting interface for the electrolyte, thereby significantly improving the liquid absorption performance of the separator. The amphiphilic molecular structure design of the block polymer may achieve an orderly arrangement of hydrophobic-hydrophilic microdomains, and this microstructure helps to optimize the formation of ion transport channels while maintaining good mechanical properties.

[0083] As can be seen from the data of Example 2 and Comparative Example 1 in Table 1, the two show obvious differences in various performance indicators, which is closely related to the polymerization sequence of the block polymer. The polymerization sequence of Comparative Example 1 may cause the fluorine segment to be wrapped in the outer layer, limiting its effective interaction with the polyvinylidene fluoride matrix, and may also affect the full contact of the poly (lithium acrylate) segment with polyethylene glycol. This molecular structure difference may further affect the dispersion state and interfacial compatibility of the block polymer in the matrix, thereby showing different effects in terms of mechanical properties, thermal stability and electrolyte affinity. The difference in the molecular chain arrangement of the block polymer and the surface chemical environment may be the fundamental reason leading to performance differences.

[0084] As can be seen from the data of Example 2 and Comparative Example 2 in Table 1, the performance difference between the two is mainly reflected in the electrolyte affinity, which may be closely related to the presence of hydrophilic segments in the molecular structure. The introduction of poly (lithium acrylate) segments in Example 2 may provide a large number of hydrophilic groups on the surface of the diaphragm pores, and these groups may form effective interactions with the polar solvent molecules in the electrolyte, thereby significantly improving the wetting and penetration ability of the electrolyte. The molecular structure of the fluorine-containing segment in Comparative Example 2 may cause the diaphragm surface to mainly exhibit hydrophobic properties. Although this property is conducive to compatibility with the polyvinylidene fluoride matrix, it may limit the effective wetting of the electrolyte.

[0085] The data from Example 2 and Comparative Example 3 in Table 1 show significant differences in mechanical properties and thermal stability between the two, likely due to the presence of fluorine segments and their interaction with the polyvinylidene fluoride matrix. The structure of Comparative Example 3, containing only hydrophilic segments, may lead to compatibility issues with the hydrophobic polyvinylidene fluoride matrix. This phase separation tendency may be exacerbated during heat treatment, leading to a significant increase in thermal shrinkage. In contrast, the block structure in Example 2 achieves a synergistic effect of hydrophobic and hydrophilic microdomains, ensuring good compatibility with the matrix while providing a hydrophilic interface required for electrolyte wetting.

[0086] The data from Example 2 and Comparative Example 4 in Table 1 show that alumina-grafted block polymers significantly improve diaphragm performance. The lithium polyacrylate phase in the block structure forms continuous hydrophilic channels after extraction, improving liquid absorption. The entanglement of the fluorine segments with the matrix enhances the interfacial bonding strength between the inorganic particles and the polymer. The agglomeration tendency of the unmodified alumina (Comparative Example 4) may lead to an increase in stress concentration points and a decrease in elongation at break. Furthermore, the lack of an organic coating on the surface prevents the particles from suppressing matrix shrinkage during high-temperature curing, significantly degrading their thermal stability.

[0087] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Within the scope of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

Claims

1. A heat-resistant battery separator, characterized in that: The invention is prepared from the following raw materials in parts by weight: 10-20 parts of polyvinylidene fluoride, 2-8 parts of poly(lithium acrylate)-b-poly(vinyl perfluorooctanoate)-g-alumina, 3-6 parts of a porogen, and 80-160 parts of N,N-dimethylacetamide; The preparation method of the poly(lithium acrylate)-b-poly(vinyl perfluorooctanoate)-g-alumina comprises the following steps: S1: Under nitrogen atmosphere, vinyl perfluorooctanoate was polymerized on ATRP initiator-grafted alumina to obtain poly(vinyl perfluorooctanoate)-g-alumina; S2: Under nitrogen atmosphere, acrylic acid was polymerized on poly(vinyl perfluorooctanoate)-g-alumina to obtain poly(acrylic acid)-b-poly(vinyl perfluorooctanoate)-g-alumina. S3: Adjust the pH of the poly(acrylic acid)-b-poly(vinyl perfluorooctanoate)-g-alumina aqueous solution to 7.3-7.8 with hydrated lithium hydroxide, centrifuge, and vacuum dry to obtain poly(lithium acrylate)-b-poly(vinyl perfluorooctanoate)-g-alumina.

2. The heat-resistant battery separator according to claim 1, characterized in that: In step S1, the ATRP initiator grafted alumina is prepared by modifying alumina with a silane coupling agent KH-550 to obtain amino alumina, which is then reacted with bromoisobutyryl bromide.

3. The heat-resistant battery separator according to claim 2, characterized in that: The average particle size of the aluminum oxide is 20-100 nm.

4. The heat-resistant battery separator according to claim 2, characterized in that: The weight ratio of the alumina to the silane coupling agent KH-550 is 3:0.2-0.4; the weight ratio of the amination alumina to bromoisobutyryl bromide is 3:0.18-0.

3.

5. The heat-resistant battery separator according to claim 1, characterized in that: In step S1, the weight ratio of the ATRP initiator grafted alumina to vinyl perfluorooctanoate is 3:7.5-13.

5.

6. The heat-resistant battery separator according to claim 1, characterized in that: In step S2, the weight ratio of poly(vinyl perfluorooctanoate)-g-alumina to acrylic acid is 5:2.5-4.

5.

7. The heat-resistant battery separator according to claim 1, characterized in that: The porogen is polyethylene glycol.

8. The heat-resistant battery separator according to claim 1, characterized in that: The preparation method of the heat-resistant battery separator comprises the following steps: (1) Add polyvinylidene fluoride to N,N-dimethylacetamide, heat to 75-85°C, stir for 3-5 hours, then add poly(lithium acrylate)-b-poly(vinyl perfluorooctanoate)-g-alumina, ultrasonicate for 20-40 minutes, then add porogen, continue stirring for 1.5-2.5 hours, and vacuum degas to obtain a composite membrane solution; (2) casting the composite film liquid onto a polyethylene terephthalate carrier film through a doctor blade coater, pre-curing, peeling, and performing a heat stretching treatment using a biaxial synchronous stretching device to obtain a stretched composite film; (3) Immersing the stretched composite film in deionized water for extraction treatment, and then subjecting the extracted composite film to high-temperature shaping on a tension shaping machine to obtain a temperature-resistant battery separator.

9. The heat-resistant battery separator according to claim 8, characterized in that: The temperature of the high-temperature setting in step (3) is 178-182° C., the time is 25-35 min, and the tension is 145-155 N / m.

10. An application of the heat-resistant battery separator according to any one of claims 1 to 9, characterized in that: For lithium-ion batteries.

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