Preparation method of high-temperature-resistant slurry, battery diaphragm and battery

Abstract

The invention relates to the technical field of batteries, in particular to a preparation method of high-temperature-resistant slurry, a battery diaphragm and a battery. The preparation method of the high-temperature-resistant slurry comprises the following steps: 1, mixing inorganic particles, a surface modifier and an organic solvent, and grinding the mixed solution to obtain a uniformly dispersed dispersion solution; step 2, under the protection of nitrogen, dissolving aromatic diamine in the dispersion liquid, then adding aromatic dianhydride, and carrying out polymerization reaction to obtain a ceramic / polyamide acid composite resin solution; 3, performing spray drying on the ceramic / polyamide acid composite resin solution obtained in the step 2 to form particles, and performing imidization reaction at 200-500 DEG C in a nitrogen atmosphere to obtain polyimide / ceramic composite powder; and 4, mixing the polyimide / ceramic composite powder obtained in the step 3 with a binder and a solvent to obtain the high-temperature-resistant slurry. The high-temperature-resistant slurry disclosed by the invention has good high-temperature resistance and adhesion.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a method for preparing a high-temperature resistant slurry, a battery separator, and a battery. Background Technology

[0002] In the structure of lithium-ion batteries, the separator is a key component, primarily serving to isolate the positive and negative electrodes, prevent short circuits, and allow lithium ions to pass freely. Currently, commercially available lithium-ion batteries generally use polyolefin microporous membranes as separator materials. These materials offer good electrochemical stability, mechanical strength, and cost advantages, but their heat resistance is poor. Under extreme conditions such as overcharging, short circuits, high temperatures, or mechanical abuse, the separator is prone to thermal shrinkage or even melting, leading to direct contact between the positive and negative electrodes and causing serious safety issues such as internal short circuits, thermal runaway, and even fires and explosions.

[0003] To improve the thermal stability of separators, existing technologies typically coat their surfaces with a ceramic coating formed from ceramic particles. This coating significantly improves the separator's high-temperature resistance, suppresses thermal shrinkage, and enhances electrolyte wettability and ionic conductivity. However, due to the low surface energy and lack of active functional groups of the polyolefin substrate, the interfacial compatibility between the polyolefin substrate and the ceramic particles is poor, resulting in insufficient adhesion between the ceramic coating and the separator substrate. During battery manufacturing or long-term cycling, the ceramic coating is prone to detachment, cracking, or peeling, which not only reduces the thermal stability of the separator but may also introduce impurities, affecting battery performance and safety. Summary of the Invention

[0004] This invention provides a method for preparing a high-temperature resistant slurry, a battery separator, and a battery, solving the technical problem of insufficient adhesion between existing ceramic coatings and separator substrates.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for preparing a high-temperature resistant slurry, comprising the following preparation steps: Step 1: Mix the inorganic particles, surface modifier and organic solvent, and then grind the mixture to obtain a uniformly dispersed dispersion. Step 2: Under nitrogen protection, the aromatic diamine is dissolved in the dispersion prepared in Step 1, and then the aromatic dianhydride is added to carry out the polymerization reaction. After the reaction, a ceramic / polyamic acid composite resin solution is obtained. Step 3: The ceramic / polyamic acid composite resin solution from Step 2 is spray-dried into particles, and then subjected to an imidization reaction at 200℃~500℃ under a nitrogen atmosphere to obtain polyimide / ceramic composite powder. Step 4: Mix the polyimide / ceramic composite powder obtained in Step 3 with the binder and solvent to obtain a high-temperature resistant slurry.

[0006] In some embodiments, in step one, the inorganic particles include at least one of Al2O3, AlOOH, CaO2, CaCO3, Ca(OH)2, MgO2, Mg(OH)2, TiO2, BaSO4, Ba(OH)2, SiO2, ZrO2, BN, and SiC; the surface modifier is at least one of KH-550, KH-560, and KH-570; and the organic solvent includes at least one of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0007] In some embodiments, the inorganic particles have a particle size of 0.1-5 μm.

[0008] In some implementations, in step one, the mixture is first stirred at a stirring speed of 1000-2000 rpm for 20-60 minutes, and then ground with a sand mill for 0.2-5 hours.

[0009] In some embodiments, in step one, the mass ratio of inorganic particles, surfactant, and organic solvent is 50-60:1-5:35-49.

[0010] In some embodiments, in step two, the aromatic diamine includes at least one of ODA, PDA, and BAPP; the aromatic dianhydride includes at least one of PMDA, BPDA, ODPA, and 6FDA.

[0011] In some embodiments, the molar ratio of the aromatic diamine to the aromatic dianhydride is 0.5-1.5:1-2.

[0012] In some implementations, the reaction temperature in step two is 5-30°C.

[0013] The present invention also provides a battery separator, which includes a separator substrate and a high-temperature resistant coating disposed on the surface of the separator substrate. The high-temperature resistant coating is formed by coating the surface of the separator substrate with a high-temperature resistant slurry and curing it. The high-temperature resistant slurry is prepared by the above-described preparation method.

[0014] The present invention also provides a battery comprising the battery separator described above.

[0015] The beneficial effects of this invention are: This invention introduces a surface modifier onto the surface of inorganic particles and polymerizes it in situ in its dispersion to generate polyamic acid (PAA). This PAA is then imidized to form a polyimide-coated ceramic composite structure, enabling a strong chemical-physical bond between the inorganic ceramic and the organic polymer. Polyimide itself possesses excellent film-forming and adhesive properties, effectively enhancing the interfacial compatibility and adhesion between the coating and the polyolefin membrane substrate, thus avoiding the problems of easy peeling and cracking of traditional ceramic coatings.

[0016] Polyimide has an extremely high thermal decomposition temperature (typically >500℃) and a low coefficient of thermal expansion. When combined with inorganic particles, the resulting coating maintains structural integrity at high temperatures, effectively suppressing thermal shrinkage of the separator under high-temperature or abuse conditions, thereby significantly improving battery safety.

[0017] The polyimide molecular chain contains polar groups, which, combined with surface-modified inorganic particles, can synergistically enhance the coating's affinity for the electrolyte, facilitating the rapid migration of lithium ions. This, in turn, improves electrolyte wettability and ion transport performance, thereby enhancing the battery's rate performance and cycle stability.

[0018] This method employs a combination of spray drying and thermal imidization, resulting in composite powders with uniform particle size and good flowability. This facilitates subsequent mixing with binders to form stable slurries, making it suitable for existing coating processes and easy to scale up for mass production. Detailed Implementation

[0019] To make the objectives, technical solutions, and technical effects of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. The embodiments described below are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art in conjunction with the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed; where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0020] In the description of this invention, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0021] In the description of this invention, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can each be single or multiple.

[0022] It should be understood that the weights of the relevant components mentioned in the embodiments of this invention can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this invention is within the scope of this invention. Specifically, the weights mentioned in the embodiments of this invention can be well-known units of mass in the chemical industry, such as μg, mg, g, and kg.

[0023] Furthermore, unless the context explicitly uses it otherwise, the singular form of a word should be understood as including the plural form of that word. The terms "comprising" or "having" are intended to specify the presence of a feature, quantity, step, operation, element, part, or combination thereof, but are not intended to exclude the presence or possible addition of one or more other features, quantities, steps, operations, elements, parts, or combinations thereof.

[0024] The present invention provides a method for preparing a high-temperature resistant slurry, which includes the following preparation steps: Step 1: Mix the inorganic particles, surface modifier and organic solvent, and then grind the mixture to obtain a uniformly dispersed dispersion. Step 2: Under nitrogen protection, the aromatic diamine is dissolved in the dispersion prepared in Step 1, and then the aromatic dianhydride is added to carry out the polymerization reaction. After the reaction, a ceramic / polyamic acid composite resin solution is obtained. Step 3: The ceramic / polyamic acid composite resin solution from Step 2 is spray-dried into particles, and then subjected to an imidization reaction at 200~500℃ under a nitrogen atmosphere to obtain polyimide / ceramic composite powder. Step 4: Mix the polyimide / ceramic composite powder obtained in Step 3 with the binder and solvent to obtain a high-temperature resistant slurry.

[0025] This invention introduces a surface modifier onto the surface of inorganic particles and polymerizes it in situ in its dispersion to generate polyamic acid (PAA). This PAA is then imidized to form a polyimide-coated ceramic composite structure, enabling a strong chemical-physical bond between the inorganic ceramic and the organic polymer. Polyimide itself possesses excellent film-forming and adhesive properties, effectively enhancing the interfacial compatibility and adhesion between the coating and the polyolefin membrane substrate, thus avoiding the problems of easy peeling and cracking of traditional ceramic coatings.

[0026] Polyimide has an extremely high thermal decomposition temperature (typically >500℃) and a low coefficient of thermal expansion. When combined with inorganic particles, the resulting coating maintains structural integrity at high temperatures, effectively suppressing thermal shrinkage of the separator under high-temperature or abuse conditions, thereby significantly improving battery safety.

[0027] The polyimide molecular chain contains polar groups, which, combined with surface-modified inorganic particles, can synergistically enhance the coating's affinity for the electrolyte, facilitating the rapid migration of lithium ions. This, in turn, improves electrolyte wettability and ion transport performance, thereby enhancing the battery's rate performance and cycle stability.

[0028] This method employs a combination of spray drying and thermal imidization, resulting in composite powders with uniform particle size and good flowability. This facilitates subsequent mixing with binders to form stable slurries, making it suitable for existing coating processes and easy to scale up for mass production.

[0029] In some embodiments, in step one, the inorganic particles include at least one of Al2O3, AlOOH, CaO2, CaCO3, Ca(OH)2, MgO2, Mg(OH)2, TiO2, BaSO4, Ba(OH)2, SiO2, ZrO2, BN, and SiC; the surface modifier is at least one of KH-550, KH-560, and KH-570; and the organic solvent includes at least one of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0030] This invention specifies that the inorganic particles are at least one selected from Al2O3, AlOOH, CaO2, CaCO3, Ca(OH)2, MgO2, Mg(OH)2, TiO2, BaSO4, Ba(OH)2, SiO2, ZrO2, BN, and SiC. Among these, Al2O3 and SiO2 are low-cost and have mature processing methods, and are widely used to improve the heat resistance of separators; ZrO2 has higher mechanical strength and thermal stability; BN possesses excellent thermal conductivity and chemical inertness, which helps in heat dissipation and suppressing side reactions; and SiC combines high hardness, high thermal conductivity, and corrosion resistance. By selecting one or more combinations of the above inorganic particles, the thermal management, mechanical, and electrochemical properties of the coating can be flexibly adjusted according to the battery application scenario (such as high energy density, high power, or high safety requirements).

[0031] Preferably, the inorganic particles are a mixture of Al2O3, SiO2, and BN in a mass ratio of 1:1:0.5.

[0032] This invention combines Al2O3, SiO2, and BN in a ratio of 1:1:0.5, which retains the cost advantage and process maturity of Al2O3 / SiO2, while introducing the high thermal conductivity of BN. This allows the coating to simultaneously provide thermal insulation, thermal conductivity, and structural support, significantly delaying or preventing the thermal shrinkage and melting of the polyolefin separator, and greatly improving battery safety.

[0033] On the other hand, Al2O3 provides high hardness and rigidity support, while SiO2 particles are typically finer and smoother, filling voids and improving coating density. The BN lamellar structure offers a degree of lubricity and flexibility, mitigating stress concentration during drying or winding. By controlling the ratio of these three components within the aforementioned range, moderate flexibility can be introduced while maintaining high modulus. This prevents the coating from becoming brittle or peeling during battery manufacturing (such as rolling and winding) and long-term cycling, solving the problem of easy powdering and shedding of traditional single ceramic coatings and ensuring coating integrity and long-term stability.

[0034] Secondly, the composite ceramic and the PI matrix together form a porous and hydrophilic network structure, which not only improves the electrolyte absorption rate and liquid retention capacity, but also provides a continuous and low-resistance transport channel for lithium ions, thereby improving the battery rate performance and cycle life.

[0035] In summary, the composite ceramic system of Al2O3:SiO2:BN = 1:1:0.5, combined with surface modification, in-situ polyimide coating, and spray drying-imidization process, not only overcomes the functional limitations of single ceramics, but also achieves comprehensive performance breakthroughs in multiple dimensions such as high temperature resistance, mechanical integrity, interfacial adhesion, electrolyte compatibility, and process adaptability through the physicochemical synergy between components. This effectively solves the problems of easy peeling, insufficient thermal stability, and poor safety of existing ceramic coatings.

[0036] The surface modifier is limited to at least one of KH-550 (γ-aminopropyltriethoxysilane), KH-560 (γ-glycidoxypropyltrimethoxysilane), or KH-570 (γ-methacryloyloxypropyltrimethoxysilane), all of which are silane coupling agents containing different active functional groups. They can form a chemically bonded layer on the surface of inorganic particles, reacting with hydroxyl groups on one end of the ceramic surface and providing functional groups such as amino, epoxy, or methacryloyloxy groups on the other end. This results in strong interactions (such as hydrogen bonds, covalent bonds, or physical entanglement) with the polyamic acid / polyimide segments subsequently generated by polymerization, significantly improving the dispersion stability of the ceramic in organic solvents and promoting its interfacial bonding with the polyimide matrix, preventing agglomeration and phase separation.

[0037] Preferably, the surface modifier is composed of KH-550, KH-560 and KH-570 in a mass ratio of 1:1:2.

[0038] KH-550, KH-560, and KH-570 are three silane coupling agents, each carrying different active functional groups. When mixed in a 1:1:2 ratio, the coating simultaneously possesses excellent chemical grafting properties, cross-linking strengthening function, and flexible compatibility. In particular, the higher proportion of KH-570 helps alleviate the brittleness of rigid ceramic / PI systems, improves coating flexibility, and prevents cracking during separator winding or battery assembly.

[0039] The three silanes mentioned above, upon hydrolysis, can form siloxane (Si–O–M) covalent bonds on the surfaces of ceramics such as Al2O3, SiO2, and BN, effectively shielding high-energy sites on the particle surface. Furthermore, the different functional groups of these three surface modifiers impart differentiated polarities to the particle surface, avoiding the problem of excessive similarity aggregation between particles caused by the same modifier. The long alkyl chain of KH-570 provides steric hindrance, while the polar groups of KH-550 / KH-560 enhance the interaction with highly polar solvents such as DMF / NMP. The synergistic effect of these three modifiers facilitates the long-term stable and uniform dispersion of inorganic particles in organic solvents, preventing coarsening or sedimentation after grinding, providing a homogeneous reaction environment for subsequent in-situ polymerization, and ensuring complete coating of the ceramic by polyamic acid.

[0040] In step two, aromatic diamines and dianhydrides polymerize in situ in a ceramic dispersion to generate PAA. The amino group of KH-550 acts as an "initiation site" or "anchor point," guiding PAA chains to preferentially grow on the ceramic surface, forming a core-shell structure. The epoxy group of KH-560 can slowly react with trace amounts of water or carboxyl groups in the system at low temperatures, adjusting the local crosslinking density. KH-570 optimizes interfacial tension through a hydrophobic-hydrophilic balance, making the polymer more easily wettable on the ceramic surface. The combined action of these three modifiers facilitates the tight, continuous, and uniform coating of polyamic acid onto the surface of inorganic particles, forming a structurally complete PI / ceramic composite powder.

[0041] In summary, the composite surface modifier scheme using KH-550:KH-560:KH-570=1:1:2, through multifunctional group synergistic design, constructs a multifunctional interface layer on the surface of inorganic particles that combines reactivity, steric hindrance, and flexible compatibility. This not only significantly improves the dispersibility and coating integrity of ceramics in the polymerization system, but also fundamentally strengthens the inorganic-organic phase interface bonding. As a result, the final high-temperature resistant slurry and its coating are endowed with high adhesion, high thermal stability, good flexibility, and excellent electrochemical compatibility, effectively overcoming the technical bottlenecks of existing ceramic coatings such as easy peeling, high brittleness, and poor interfacial compatibility.

[0042] This invention limits the organic solvent to at least one of dimethylformamide (DMF), dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), or dimethyl sulfoxide (DMSO). These are all highly polar aprotic solvents, which can not only effectively dissolve aromatic diamines and dianhydride monomers, but also effectively disperse surface-modified inorganic particles. This ensures that the in-situ polymerization of polyamic acid is carried out in a homogeneous or quasi-homogeneous system, which is conducive to the formation of a uniform and fully coated ceramic / polyamic acid composite system, laying the foundation for obtaining high-performance composite powders in the future.

[0043] In some embodiments, the inorganic particles have a particle size of 0.1-5 μm.

[0044] When the particle size of inorganic particles is ≤5μm, sedimentation, agglomeration, or clogging of the coating die caused by large particles can be effectively avoided; when the particle size is ≥0.1μm, problems such as excessive surface energy, easy agglomeration, and dramatic increase in viscosity caused by excessively large specific surface area of ​​nano-sized particles are prevented. By limiting the inorganic particles to the above particle size range and treating them with surface modifiers, the resulting slurry has moderate viscosity, no hard agglomerates, and no sedimentation or stratification.

[0045] Preferably, the inorganic particles are composed of inorganic particles with different particle sizes.

[0046] Inorganic particles of different sizes can form a multi-level filling structure during the coating and drying process. Fine particles fill the gaps between medium and coarse particles, which helps to reduce the porosity of the coating and increase the ceramic content per unit volume, thereby enhancing the mechanical strength, wear resistance, and puncture resistance of the coating. At the same time, the dense structure more effectively blocks the contact between the positive and negative electrodes, providing a stronger physical barrier under thermal abuse conditions. This allows for improved safety protection and structural stability of the diaphragm without increasing the coating thickness.

[0047] If only a single fine particle is used, the coating, although dense, will have excessively small pores, which can hinder lithium-ion migration and increase the battery's internal resistance. If only coarse particles are used, the pores will be too large and unevenly distributed, reducing the thermal barrier effect and easily forming defect channels. A wide-distribution mixed particle size of 0.1-5μm can construct a gradient pore network in a dense matrix, achieving micron-level pores to ensure rapid ion transport, and nano / submicron-level pores to maintain a high specific surface area for electrolyte adsorption. This allows the coating to maintain high thermal stability while possessing excellent electrolyte absorption rate, electrolyte retention capacity, and low interfacial impedance, which is beneficial for improving battery rate performance and cycle life.

[0048] By using mixed inorganic particles with different particle sizes in the polyimide coating system, agglomeration caused by van der Waals forces between particles can be reduced, making it easier to obtain a uniform dispersion through sand milling, and giving the slurry suitable viscosity, good flowability and storage stability.

[0049] Coatings with single-particle sizes are prone to microcracks due to uneven shrinkage during drying or heat treatment. The multi-level particle size system of this invention, through a stress dispersion mechanism, allows localized thermal expansion or mechanical deformation to be synergistically buffered by particles of different sizes. This is particularly effective on flexible substrates with low surface energy and high thermal shrinkage, such as polyolefin separators (e.g., PE / PP). The flexible and dense composite coating can better adapt to substrate deformation without peeling. Therefore, using inorganic particles composed of a mixture of different particle sizes can significantly reduce the risk of cracking and peeling during battery manufacturing (e.g., rolling, winding) and long-term cycling, improving interfacial adhesion reliability.

[0050] In some implementations, in step one, the mixture is first stirred at a stirring speed of 1000-2000 rpm for 20-60 minutes, and then ground with a sand mill for 0.2-5 hours.

[0051] Inorganic particles, when dry, readily form hard agglomerates due to van der Waals forces or electrostatic forces. Initial high-speed stirring at 1000-2000 rpm can break up these soft agglomerates, allowing the surface modifier to fully contact the particle surface and initiating a hydrolysis-condensation reaction for initial coating. Subsequent sand milling, through high-energy mechanical shearing and the collision of the grinding media, effectively breaks up any remaining hard agglomerates, dispersing the particles to a primary particle size level. This facilitates obtaining agglomerate-free, highly stable ceramic dispersion, providing a homogeneous reaction environment for subsequent in-situ polymerization and preventing uneven polyamic acid coating or coating defects caused by particle aggregation.

[0052] In some embodiments, in step one, the mass ratio of inorganic particles, surfactant, and organic solvent is 50-60:1-5:35-49.

[0053] The inorganic particles account for 50-60 wt%, which is a high solids content system, ensuring that the final coating has sufficient inorganic phase content; High ceramic content can significantly improve the thermal dimensional stability, mechanical strength, and electrical insulation of the separator, effectively suppressing high-temperature shrinkage, enhancing the battery's puncture resistance, and preventing micro-short circuits. Simultaneously, in the polyimide-coated structure, a high ceramic ratio helps form a composite structure with ceramic as the framework and PI as the bonding network, balancing rigidity and toughness.

[0054] When the amount of surface modifier added is too low, it cannot completely cover the ceramic surface, and the residual hydrophilic hydroxyl groups can lead to agglomeration or poor compatibility with the polymer. When the amount of surface modifier added is too high, excess unreacted modifier may remain in the system as impurities, or interfere with PAA chain growth in subsequent polymerization, or even reduce slurry stability. By limiting the amount of surface modifier added within the above-mentioned ratio range, the modifier can be fully hydrolyzed and condensed on the ceramic surface, and can also provide an appropriate amount of active functional groups to participate in or promote the in-situ coating of polyamic acid, achieving efficient, economical and clean interface modification, enhancing non-organic compatibility, and avoiding the introduction of side reactions or impurities.

[0055] In summary, by limiting the mass ratio of ceramic:modifier:solvent = (50-60):(1-5):(35-49), the goals of high functionality, strong interfacial bonding and excellent process adaptability are achieved, which is beneficial to improving the thermal stability, adhesion and ionic conductivity of the slurry.

[0056] In some embodiments, in step two, the aromatic diamine includes at least one of ODA (4,4'-diaminodiphenyl ether), PDA (p-phenylenediamine), and BAPP (bisphenol A bis(4-aminophenyl) ether); the aromatic dianhydride includes at least one of PMDA (pyromellitic dianhydride), BPDA (3,3',4,4'-biphenyltetracarboxylic dianhydride), ODPA (4,4'-oxophthalic anhydride), and 6FDA (4,4'-(hexafluoroisopropylidene)phthalic anhydride).

[0057] The aromatic monomers mentioned above all contain rigid benzene ring structures. The polyimide backbone formed has high conjugation and strong intermolecular forces. The PI coating layer formed does not soften, melt, or shrink under extreme battery conditions (such as overcharge, short circuit, and high temperature), effectively supporting the ceramic skeleton and significantly improving the overall thermal stability of the separator.

[0058] Preferably, the aromatic diamine is composed of ODA, PDA, and BAPP in a mass ratio of 1:1:0.3; and the aromatic dianhydride is composed of PMDA, BPDA, and 6FDA in a mass ratio of 1:0.2:0.6.

[0059] By using the above-mentioned aromatic monomers for compounding, the resulting polyimide coating remains intact and crack-free after imidization at 300–500℃. It is both heat-resistant and has sufficient flexibility, which can closely adhere to the polyolefin membrane substrate and adapt to mechanical deformations such as winding and rolling, significantly reducing the risk of coating cracking or peeling.

[0060] The three diamines and three dianhydrides mentioned above are randomly copolymerized to form an irregular but functionally complementary copolymer PI structure, which avoids the decrease in wettability caused by crystallization. This results in a coating with high liquid absorption rate, high liquid retention and low interfacial impedance, which is conducive to the rapid migration of lithium ions and improves the rate performance and low temperature performance of the battery.

[0061] The two primary amine groups of PDA are highly reactive, preferentially co-reacting or hydrogen-bonding with surface modifiers during in-situ polymerization to achieve "chemical anchoring." ODA / BAPP provides spatial extensibility, making it easier for PAA chains to encapsulate inorganic particles of different sizes. The large-volume side groups of 6FDA can adjust the local crosslinking density, avoiding excessive density that leads to uneven coating. Therefore, using the above-mentioned aromatic monomers in a compounding process is beneficial for forming a continuous, dense, and strongly adhesive core-shell structure of polyimide on the ceramic surface, fundamentally solving the problem of inorganic-organic phase separation in traditional physically mixed coatings.

[0062] This technical solution achieves multi-objective synergistic optimization at the molecular level by precisely controlling the copolymerization composition of aromatic diamines (ODA:PDA:BAPP = 1:1:0.3) and aromatic dianhydrides (PMDA:BPDA:6FDA = 1:0.2:0.6), balancing rigidity and flexibility, polarity and free volume, and reactivity and processability. The resulting polyimide not only possesses excellent high-temperature resistance but also forms strong interfacial bonds with multi-scale inorganic particles (Al2O3 / SiO2 / BN), giving the coating excellent electrolyte compatibility.

[0063] In some embodiments, the molar ratio of the aromatic diamine to the aromatic dianhydride is 0.5-1.5:1-2.

[0064] By limiting the molar ratio of aromatic diamines and aromatic dianhydrides within the aforementioned range, the monomer concentration is sufficient to generate adequate PAA in situ on the surface of inorganic particles, forming a continuous and dense organic coating layer. If the monomer ratio is too low, the amount of PAA will be insufficient, failing to completely coat the high-solids-content ceramic, resulting in weak interfacial bonding; if the monomer ratio is too high, the system viscosity will increase sharply, affecting stirring and mass transfer, and may cause gelation or phase separation due to excessively high local concentrations.

[0065] In some implementations, the reaction temperature in step two is 5-30°C.

[0066] The reaction of aromatic diamines and aromatic dianhydrides in polar aprotic solvents (such as NMP and DMF) to form PAA is an exothermic reaction. If carried out at higher temperatures, the aromatic diamines are easily oxidized, and the PAA chains may branch or crosslink, or even prematurely cyclize to form insoluble polyimide microgels. Temperatures between 5 and 30°C significantly reduce the rate of side reactions, allowing the reaction to proceed mainly along a linear polycondensation pathway, resulting in PAA with high molecular weight, high solubility, and low defects.

[0067] At this temperature, the PAA chain growth rate is moderate, and the nucleation and growth process is more controllable, which is conducive to the formation of a dense and continuous core-shell structure. If the temperature is too high, PAA is rapidly generated and aggregated in the bulk solution, resulting in uneven ceramic coating and even the formation of a free polymer phase.

[0068] The present invention also provides a battery separator, which includes a separator substrate and a high-temperature resistant coating disposed on the surface of the separator substrate. The high-temperature resistant coating is formed by coating the surface of the separator substrate with a high-temperature resistant slurry and curing it. The high-temperature resistant slurry is prepared by the above-described preparation method.

[0069] The present invention also provides a battery comprising the battery separator described above.

[0070] To enable those skilled in the art to clearly understand the above-described implementation details and operations of the present invention, and to demonstrate the significant advancements in the performance of the embodiments of the present invention, the following examples illustrate the above technical solutions.

[0071] Example 1 A method for preparing a high-temperature resistant slurry, comprising the following preparation steps: Step 1: Mix the inorganic particles, surface modifier and organic solvent in a mass ratio of 55:3:42. First, stir the mixture at 1500 rpm for 40 minutes, and then grind the mixture in a sand mill for 2.5 hours to obtain a uniformly dispersed solution. Step 2: Under nitrogen protection, the aromatic diamine is dissolved in the dispersion prepared in Step 1, and then the aromatic dianhydride is added to carry out the polymerization reaction at a temperature of 20°C. After the reaction, a ceramic / polyamic acid composite resin solution is obtained. Step 3: The ceramic / polyamic acid composite resin solution from Step 2 is spray-dried into particles, and then subjected to an imidization reaction at 400°C under a nitrogen atmosphere to obtain polyimide / ceramic composite powder. Step 4: Mix the polyimide / ceramic composite powder obtained in Step 3 with PVDF binder and NMP solvent at a mass ratio of 50:10:90 to obtain a high-temperature resistant slurry.

[0072] In step one, the inorganic particles are a mixture of Al2O3, SiO2, and BN in a mass ratio of 1:1:0.5. The surface modifier is composed of KH-550, KH-560, and KH-570 in a mass ratio of 1:1:2. The organic solvent is dimethylformamide.

[0073] The inorganic particles are composed of inorganic particles with different particle sizes, which range from 0.1 to 5 μm.

[0074] In step two, the aromatic diamine is composed of ODA, PDA, and BAPP in a mass ratio of 1:1:0.3; the aromatic dianhydride is composed of PMDA, BPDA, and 6FDA in a mass ratio of 1:0.2:0.6.

[0075] The molar ratio of the aromatic diamine to the aromatic dianhydride is 1:1.

[0076] A battery separator includes a PE separator substrate and a high-temperature resistant coating disposed on the surface of the separator substrate. The high-temperature resistant coating is formed by coating the surface of the separator substrate with the high-temperature resistant slurry prepared above and curing it, and the coating thickness is 20 μm.

[0077] Example 2 A method for preparing a high-temperature resistant slurry, comprising the following preparation steps: Step 1: Mix Al2O3 inorganic particles, KH-550 surface modifier and dimethylacetamide organic solvent in a mass ratio of 55:3:42. First, stir the mixture at 1500 rpm for 40 minutes, and then grind the mixture in a sand mill for 2.5 hours to obtain a uniformly dispersed solution. Step 2: Under nitrogen protection, ODA is dissolved in the dispersion prepared in Step 1, and then PMDA is added to carry out a polymerization reaction at a reaction temperature of 5°C. After the reaction, a ceramic / polyamic acid composite resin solution is obtained. Step 3: The ceramic / polyamic acid composite resin solution from Step 2 is spray-dried into particles, and then subjected to an imidization reaction at 200°C under a nitrogen atmosphere to obtain polyimide / ceramic composite powder. Step 4: Mix the polyimide / ceramic composite powder obtained in Step 3 with PVDF binder and NMP solvent at a mass ratio of 50:10:90 to obtain a high-temperature resistant slurry.

[0078] The inorganic particles have a particle size of 0.1-5 μm and are composed of inorganic particles with different particle sizes.

[0079] The molar ratio of ODA to PMDA is 1:1.

[0080] A battery separator includes a PE separator substrate and a high-temperature resistant coating disposed on the surface of the separator substrate. The high-temperature resistant coating is formed by coating the separator substrate surface with the aforementioned high-temperature resistant slurry and curing it, with a coating thickness of 20 μm.

[0081] Example 3 A method for preparing a high-temperature resistant slurry, comprising the following preparation steps: Step 1: Mix SiO2 inorganic particles, KH-560 surface modifier and N-methylpyrrolidone organic solvent at a mass ratio of 50:1:35. First, stir the mixture at 1000 rpm for 60 min, and then grind the mixture in a sand mill for 0.2 h to obtain a uniformly dispersed solution. Step 2: Under nitrogen protection, PDA is dissolved in the dispersion prepared in Step 1, and then BPDA is added to carry out a polymerization reaction at a reaction temperature of 30°C. After the reaction, a ceramic / polyamic acid composite resin solution is obtained. Step 3: The ceramic / polyamic acid composite resin solution from Step 2 is spray-dried into particles, and then subjected to an imidization reaction at 300°C under a nitrogen atmosphere to obtain polyimide / ceramic composite powder. Step 4: Mix the polyimide / ceramic composite powder obtained in Step 3 with PVDF binder and NMP solvent at a mass ratio of 50:10:90 to obtain a high-temperature resistant slurry.

[0082] The inorganic particles have a particle size of 0.1-5 μm and are composed of inorganic particles with different particle sizes.

[0083] The molar ratio of the PDA to the BPDA is 1:1.

[0084] A battery separator includes a PE separator substrate and a high-temperature resistant coating disposed on the surface of the separator substrate. The high-temperature resistant coating is formed by coating the separator substrate surface with the aforementioned high-temperature resistant slurry and curing it, with a coating thickness of 20 μm.

[0085] Example 4 A method for preparing a high-temperature resistant slurry, comprising the following preparation steps: Step 1: Mix ZrO2 inorganic particles, KH-570 surface modifier and N-methylpyrrolidone organic solvent in a mass ratio of 60:5:49. First, stir the mixture at 2000 rpm for 20 minutes, and then grind the mixture in a sand mill for 5 hours to obtain a uniformly dispersed solution. Step 2: Under nitrogen protection, BAPP is dissolved in the dispersion prepared in Step 1, and then ODPA is added to carry out the polymerization reaction at a reaction temperature of 20°C. After the reaction, a ceramic / polyamic acid composite resin solution is obtained. Step 3: The ceramic / polyamic acid composite resin solution from Step 2 is spray-dried into particles, and then subjected to an imidization reaction at 500°C under a nitrogen atmosphere to obtain polyimide / ceramic composite powder. Step 4: Mix the polyimide / ceramic composite powder obtained in Step 3 with PVDF binder and NMP solvent at a mass ratio of 50:10:90 to obtain a high-temperature resistant slurry.

[0086] The inorganic particles have a particle size of 0.1-5 μm and are composed of inorganic particles with different particle sizes.

[0087] The molar ratio of the aromatic diamine to the aromatic dianhydride is 1:1.

[0088] A battery separator includes a PE separator substrate and a high-temperature resistant coating disposed on the surface of the separator substrate. The high-temperature resistant coating is formed by coating the surface of the separator substrate with a high-temperature resistant slurry and curing it, and the coating thickness is 20 μm.

[0089] Example 5 The difference between Example 5 and Example 1 is that the inorganic particles in Example 5 have a particle size of 3 μm.

[0090] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that no surface modifier is added in step one of Comparative Example 1, while the other preparation steps are the same as in Example 1.

[0091] Comparative Example 2 A method for preparing a high-temperature resistant slurry, comprising the following preparation steps: Step 1: Mix the inorganic particles, surface modifier, and organic solvent in a mass ratio of 55:3:42. Stir the mixture at 1500 rpm for 40 minutes, and then grind the mixture in a sand mill for 2.5 hours to obtain a uniformly dispersed dispersion. The specific components of the inorganic particles, surface modifier, and organic solvent are the same as in Example 1. Step 2: Add 20 parts by weight of polyimide, 10 parts by weight of PVDF binder and 50 parts by weight of NMP solvent to the dispersion from Step 1, and mix thoroughly to obtain a high-temperature resistant slurry.

[0092] The high-temperature resistant slurry prepared above is coated onto the surface of the PE separator substrate and cured to form a coating thickness of 20 μm, thus obtaining a battery separator.

[0093] Performance testing The battery separators prepared in Examples 1-5 and Comparative Examples 1-2 were subjected to mechanical properties, thermal shrinkage rate and battery performance tests, respectively. The test results are shown in Table 1.

[0094] Mechanical properties: The tensile properties of the diaphragm were determined using an electronic universal testing machine at a test temperature of 25℃; Heat shrinkage rate: Cut a 5cm×5cm diaphragm sample, measure the longitudinal (MD) and transverse (TD) dimensions before baking, and record them as L1 and H1 respectively. Then bake the diaphragm at 150℃ for 1h and 200℃ for 1h, and measure the MD and TD dimensions again, and record them as L2 and H2 respectively. The heat shrinkage rate of MD is (L1L2) / L1×100%, and the heat shrinkage rate of TD is (H1H2) / H1×100%. The higher value of the heat shrinkage rate of MD and TD is defined as the heat shrinkage rate of the diaphragm. Battery performance: The separator and positive electrode sheet (a positive electrode slurry is prepared by uniformly mixing lithium cobalt oxide, conductive acetylene black, and polyvinylidene fluoride in an N-methylpyrrolidone solvent at a mass ratio of 97:1:2, which is then coated onto aluminum foil, dried, cold-pressed, and slit to form the positive electrode sheet) and negative electrode sheet (a negative electrode slurry is prepared by uniformly mixing graphite, conductive carbon black SuperP, and styrene-butadiene rubber in deionized water at a mass ratio of 97:1:2, which is then coated onto copper foil, dried, cold-pressed, and slit to form the negative electrode sheet) are manufactured. A lithium-ion battery was assembled using a 1 mol / L lithium hexafluorophosphate electrolyte (prepared by dissolving lithium hexafluorophosphate LiPF6 in a mixed solvent consisting of ethylene carbonate EC, dimethyl carbonate DMC, and ethyl methyl carbonate EMC in a volume ratio of 1:1:1) in a conventional manner. The battery performance was then tested. Specifically, the battery was charged at 1C constant current and constant voltage to 4.35V, then discharged at 0.1C, left to rest for 10 minutes, and cycled 200 times. The capacity retention rate was recorded for each of the 200 cycles.

[0095] Table 1 Performance test results of the examples and comparative examples Results Analysis As shown in Table 1, among Examples 1-5, the membrane prepared in Example 1 has the best performance, indicating that Example 1 comprehensively improves the mechanical, thermal and electrochemical properties of the membrane through the synergistic effect of multi-scale inorganic particle mixing, composite coupling agent and in-situ PI coating.

[0096] Example 5 uses inorganic particles of a single size, which reduces particle packing density and causes uneven pore structure, resulting in decreased mechanical strength and thermal stability.

[0097] Comparative Example 1, without the addition of a surface modifier, showed a significant decrease in tensile strength, thermal shrinkage, and capacity retention. This indicates that the absence of a silane coupling agent leads to poor interfacial compatibility between the inorganic particles and the polyimide matrix, forming a weak interface. Under stress or high temperature, this interface is prone to debonding and microcrack propagation, resulting in a sharp drop in strength, increased thermal shrinkage, and accelerated capacity decay.

[0098] Comparative Example 2, which directly physically mixed PI and ceramic dispersion, resulted in the lowest tensile strength, the most severe thermal shrinkage, and the worst capacity retention. Because a chemically bonded ceramic / PI composite structure was not formed through in-situ polymerization, the two phases separated significantly through physical blending. PI could not effectively coat the inorganic particles, resulting in numerous interfacial voids and stress concentration points within the coating. This led to PI softening and ceramic slippage at high temperatures, causing the overall membrane structure to collapse, resulting in extremely poor thermal dimensional stability and decreased cycle performance.

[0099] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a high-temperature resistant slurry, characterized in that, The preparation steps include the following: Step 1: Mix the inorganic particles, surface modifier and organic solvent, and then grind the mixture to obtain a uniformly dispersed dispersion. Step 2: Under nitrogen protection, the aromatic diamine is dissolved in the dispersion prepared in Step 1, and then the aromatic dianhydride is added to carry out the polymerization reaction. After the reaction, a ceramic / polyamic acid composite resin solution is obtained. Step 3: The ceramic / polyamic acid composite resin solution from Step 2 is spray-dried into particles, and then subjected to an imidization reaction at 200℃~500℃ under a nitrogen atmosphere to obtain polyimide / ceramic composite powder. Step 4: Mix the polyimide / ceramic composite powder obtained in Step 3 with the binder and solvent to obtain a high-temperature resistant slurry.

2. The method for preparing the high-temperature resistant slurry according to claim 1, characterized in that, In step one, the inorganic particles include at least one of Al2O3, AlOOH, CaO2, CaCO3, Ca(OH)2, MgO2, Mg(OH)2, TiO2, BaSO4, Ba(OH)2, SiO2, ZrO2, BN, and SiC; the surface modifier is at least one of KH-550, KH-560, and KH-570; and the organic solvent includes at least one of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

3. The method for preparing the high-temperature resistant slurry according to claim 1, characterized in that, The inorganic particles have a particle size of 0.1-5 μm.

4. The method for preparing the high-temperature resistant slurry according to claim 1, characterized in that, In step one, the mixture is first stirred at a stirring speed of 1000-2000 rpm for 20-60 minutes, and then ground in a sand mill for 0.2-5 hours.

5. The method for preparing the high-temperature resistant slurry according to claim 1, characterized in that, In step one, the mass ratio of inorganic particles, surfactant and organic solvent is (50-60):(1-5):(35-49).

6. The method for preparing the high-temperature resistant slurry according to claim 1, characterized in that, In step two, the aromatic diamine includes at least one of ODA, PDA, and BAPP; the aromatic dianhydride includes at least one of PMDA, BPDA, ODPA, and 6FDA.

7. The method for preparing the high-temperature resistant slurry according to claim 1, characterized in that, The molar ratio of the aromatic diamine to the aromatic dianhydride is 0.5-1.5:1-2.

8. The method for preparing the high-temperature resistant slurry according to claim 1, characterized in that, The reaction temperature in step two is 5-30℃.

9. A battery separator, characterized in that, It includes a diaphragm substrate and a high-temperature resistant coating disposed on the surface of the diaphragm substrate. The high-temperature resistant coating is formed by coating the diaphragm substrate surface with a high-temperature resistant slurry and curing it. The high-temperature resistant slurry is prepared by any one of the preparation methods of claims 1-8.

10. A battery, characterized in that, Includes the battery separator as described in claim 9.

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