Aramid composite battery separator, method of making the same, and battery

Abstract

This invention relates to the field of battery technology, and proposes an aramid composite battery separator, its preparation method, and a battery thereof. An aramid composite battery separator includes a base film and a composite coating disposed on at least one surface of the base film; the composite coating includes aramid fibers and porous ceramics, with the aramid fibers and porous ceramics forming a three-dimensional interpenetrating network. This technical solution solves the problems of insufficient heat resistance and poor wettability in related technologies for composite battery separators.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to an aramid composite battery separator, its preparation method, and the battery thereof. Background Technology

[0002] Currently, polyolefin microporous membranes are still the mainstream type of lithium-ion battery separators. However, the inherent molecular structure of polyolefin materials determines that they have an insurmountable shortcoming in heat resistance. This shortcoming creates a prominent contradiction with the current industry demand for lithium-ion batteries to develop towards high energy density, high rate charge and discharge, high safety, and long cycle life.

[0003] To address the industry pain point of insufficient heat resistance in polyolefin-based separators, various separator modification technologies have been developed. Among them, coating the surface of the polyolefin-based membrane with a heat-resistant modified coating has become the mainstream modification solution in the industry. However, as lithium-ion batteries rapidly iterate towards higher energy density, higher rate capability, and higher safety, existing technologies still have the following problems: (1) The protection function is mainly passive heat resistance, which cannot take into account both high temperature dimensional stability and active thermal shutdown response capability. The core protection logic of existing aramid-ceramic composite coatings is to improve the high-temperature dimensional stability of the separator by leveraging the ultra-high heat resistance of para-aramid and the rigid framework of ceramic particles. Essentially, this is a passive heat protection method, which can only delay the process of separator thermal shrinkage and rupture, but cannot provide an active and precise safety response to abnormal temperature rises inside the battery. When a battery experiences abuse conditions such as overcharging, internal short circuits, compression, or puncture, the temperature of local hot spots can rise rapidly at a rate of tens of degrees Celsius per second. At this point, passive heat-resistant coatings alone cannot block lithium-ion cross-membrane transport. The main lithium insertion / extraction reaction and electrolyte decomposition side reaction inside the battery continue, and Joule heat and reaction heat accumulate, eventually exceeding the thermal runaway critical temperature, leading to serious safety accidents such as fires and explosions.

[0004] (2) The high-temperature active sealing mechanism has inherent defects, such as easy loss of core material and poor sealing effect, which cannot achieve stable and irreversible ion channel blocking; To endow diaphragms with active thermal response capabilities, existing technologies mostly employ polymer thermoplastic microspheres such as polyethylene wax and paraffin wax as responsive functional materials. Their core mechanism involves the overall melting of the polymer at high temperatures, with the molten material filling the microporous structure of the diaphragm and coating, attempting to block ion channels. However, extensive academic research and industrial validation have shown that this type of technology cannot achieve a stable and reliable self-sealing effect.

[0005] (3) Traditional ceramic particles have a single function and can only achieve inert rigid filling. They cannot form a synergistic effect with functional materials and it is difficult to achieve integrated design of structure and function. In existing aramid-ceramic composite coatings, ceramic particles are commonly used as inorganic fillers. Their core function is only to provide rigid skeleton support and suppress the high-temperature thermal shrinkage of the diaphragm. They are typical inert fillers with limited functions and cannot meet the multifunctional design requirements of intelligent responsive coatings, thus having many inherent limitations. Summary of the Invention

[0006] This invention proposes an aramid composite battery separator, its preparation method, and the battery thereof, to solve or alleviate at least one of the above-mentioned problems.

[0007] The technical solution of the present invention is as follows: The present invention proposes an aramid composite battery separator, comprising a base film and a composite coating disposed on at least one surface of the base film; the composite coating comprises aramid fibers and porous ceramics, wherein the aramid fibers and porous ceramics form a three-dimensional interpenetrating network.

[0008] Preferably, the pore size of the porous ceramic is 2~50nm.

[0009] Preferably, the diameter of the aramid fiber is 10~250nm, and the aspect ratio of the aramid fiber is >100.

[0010] Preferably, the porous ceramic surface is loaded with responsive microcapsules, wherein the core material of the responsive microcapsules is polyacrylonitrile and the wall material is polyacrylate.

[0011] Preferably, the mass ratio of the aramid fiber, the porous ceramic, and the responsive microcapsule is 1~3:8~12:0.5~1.5.

[0012] Preferably, the particle size of the responsive microcapsules is 300~800nm.

[0013] Preferably, the polyacrylate is composed of a first polyacrylate, a second polyacrylate, and a third polyacrylate, wherein the first polyacrylate, the second polyacrylate, and the third polyacrylate have different glass transition temperatures.

[0014] Preferably, the glass transition temperature of the first polyacrylate is >100°C, the glass transition temperature of the second polyacrylate is 0~100°C, and the glass transition temperature of the third polyacrylate is <0°C.

[0015] This invention also proposes a method for preparing an aramid composite battery separator, comprising the following steps: S1. Prepare responsive microcapsules by loading the responsive microcapsules onto the surface of porous ceramic to obtain porous ceramic@microcapsule composite particles; S2. Dissolve the aramid fibers and separate the phases to obtain an aramid fiber dispersion; S3. Add the porous ceramic@microcapsule composite particles to the aramid fiber dispersion, add a dispersant, and disperse to obtain a composite coating solution. S4. The composite coating liquid is coated on at least one surface of the base film, and after drying, the aramid composite battery separator is obtained.

[0016] The present invention also proposes a battery comprising the aramid composite battery separator described above or the aramid composite battery separator prepared by the preparation method described above.

[0017] The beneficial effects of this invention are as follows: In this invention, the composite coating utilizes a combination of porous ceramic particles and aramid fibers to construct a multi-level porous system, thereby enabling the membrane to possess comprehensive properties such as second-level wetting, efficient liquid retention, rapid mass transfer, and high-temperature sealing. Furthermore, the three-dimensional interpenetrating network structure, formed by the three-dimensional skeleton of the porous rigid ceramic particles and the cross-linked network of the flexible aramid fibers, achieves a comprehensive improvement in the coating's high rigidity, high strength, high flexibility, and high adhesion. Detailed Implementation

[0018] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will be described through embodiments.

[0020] As a key functional component of batteries, the separator is often made of polyolefin materials as the base membrane in existing technologies. However, this material has the defect of insufficient heat resistance. In order to solve the industry pain point of insufficient heat resistance of polyolefin-based separators, various separator modification technologies have been developed. Among them, aramid-ceramic composite coating technology can effectively solve the problem of insufficient heat resistance. However, with the rapid development of lithium-ion batteries, the defects of aramid-ceramic composite coating technology have become increasingly prominent.

[0021] On the one hand, the existing aramid-ceramic composite coating technology has the problem that its protective function is mainly passive heat resistance, and it cannot take into account both high-temperature dimensional stability and active thermal shutdown response capability. On the other hand, the high-temperature active sealing mechanism of aramid-ceramic composite coating technology has inherent defects: the molten core material of the responsive functional material is prone to migration and loss, the pore sealing efficiency is extremely low, the sealing of the responsive functional material is only physical stacking and filling, the sealing stability is poor, the responsive functional material cannot achieve a step decrease in ionic conductivity, and the active shutdown threshold is unclear. On the other hand, traditional ceramic particles have a single function and can only achieve inert rigid filling, which cannot form a synergistic effect with functional materials and makes it difficult to achieve integrated design of structure and function.

[0022] To address the three core deficiencies of the existing technologies, this invention aims to provide an aramid composite battery separator, its preparation method, and the battery itself. This invention introduces porous ceramics with high specific surface area and abundant pore structure as a multifunctional carrier, anchoring responsive microcapsules on the surface to achieve uniform dispersion of the responsive material in the coating. Simultaneously, during abnormal high-temperature heating, the capillary force of the porous ceramic channels actively draws in the core material released from the microcapsules. After curing, this core material forms a mechanically interlocked structure with the coating framework, thereby achieving a self-sealing function where the coating maintains high ionic conductivity at room temperature and actively decreases ionic conductivity by 2-3 orders of magnitude at a response temperature of 140-150℃. This, combined with the pore-closing function of the polyolefin base film, forms a dual-gradient protection mechanism where the base film first closes the pores, followed by the coating. This fundamentally solves the technical contradiction of the incompatibility between heat resistance and responsiveness in existing technologies, achieving a high degree of unity between separator structural and functional design.

[0023] A specific embodiment of the first aspect of the present invention provides an aramid composite battery separator, comprising a base film and a composite coating disposed on at least one surface of the base film; the composite coating comprises aramid fibers and porous ceramics, wherein the aramid fibers and porous ceramics form a three-dimensional interpenetrating network.

[0024] In this invention, the base membrane can be one or more of the following: a polyethylene monolayer microporous membrane, a polypropylene monolayer microporous membrane, and a polyethylene / polypropylene / polyethylene layer co-extruded composite microporous membrane. Preferably, it is a polyethylene monolayer microporous membrane. The thickness of the polyethylene membrane is 5~25μm, for example, any value from 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 22μm, and 25μm, or any range between any two values, preferably 12μm. The polyethylene monolayer microporous membrane undergoes melting deformation within a temperature range of approximately 130°C, spontaneously sealing its own microporous structure, blocking the transmembrane transport of lithium ions, achieving thermal shutdown protection of the battery, and providing basic overheat safety protection for the battery.

[0025] In one embodiment of the present invention, the porous ceramic particles have a particle size of 200-800 nm, a pore size of 2-50 nm, and a specific surface area of ​​50-300 m². 2 / g, the pore volume of the porous ceramic particles is 0.2~1.0cm³. 3 / g, the thermal stability of porous ceramic particles is ≥500℃.

[0026] In this invention, the porous ceramic particles can be one or more of porous alumina, porous boehmite, porous silica, porous titanium dioxide, and porous zirconium oxide. The particle size of the porous ceramic particles is 200~800nm, for example, any value or range between any two values ​​from 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, to 800nm. The pore size of the porous ceramic particles is 2~50nm, for example, 2nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, to 50nm. The specific surface area of ​​the porous ceramic particles is 50~300m². 2 / g, for example, could be 50m 2 / g, 100m 2 / g, 150m 2 / g、200m 2 / g、250m 2 / g、300m 2 The value of any point in / g and the range between any two points; the pore volume of the porous ceramic particles is 0.2~1.0 cm³. 3 / g, for example, could be 0.2cm 3 / g, 0.3cm 3 / g, 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1.0cm 3 Any point value in / g and the range between any two point values.

[0027] In this invention, the 2-50 nm mesoporous structure of porous ceramics generates extremely strong capillary adsorption force, enabling active adsorption of electrolyte within 2-3 seconds. The electrolyte wetting speed is 10-30 times faster than that of traditional dense ceramic coatings. The confinement effect of the mesopores firmly binds the electrolyte within the pores, forming a massive micro electrolyte reservoir. This significantly improves the coating's liquid absorption rate and liquid retention rate compared to traditional ceramics, overcoming the shortcomings of traditional dense ceramics, such as lack of pore structure, slow liquid absorption rate, and poor liquid retention capacity. Simultaneously, the fully wetted mesopores form a continuous liquid-phase ion conduction network, increasing the coating's ionic conductivity by 20%-30%. The ultra-fast wetting characteristic significantly shortens the settling time in the battery electrolyte filling process, greatly improving cell production efficiency and significantly reducing battery manufacturing costs.

[0028] In this invention, the porous ceramic has a high thermal decomposition temperature, which is much higher than that of aramid fiber and polyolefin materials. It can form a continuous thermal barrier in the coating, blocking the heat transfer of hot spots inside the battery and delaying the spread of thermal runaway. At the same time, it can significantly increase the thermal deformation temperature of the coating, so that the separator can maintain its complete structural morphology at high temperatures without melting or breaking, further expanding the safe operating temperature range of the separator.

[0029] In one embodiment of the present invention, the diameter of the aramid fiber is 10~250nm and the aspect ratio of the aramid fiber is >100.

[0030] In this invention, the aramid fiber is preferably poly(p-phenylene terephthalamide) fiber. The aramid fiber can provide a basic porous structure, ensuring ion conduction, improving electrolyte wettability, and forming a three-dimensional interpenetrating network with the porous ceramic. The abundant hydroxyl active sites on the surface of the porous ceramic can form hydrogen bonds with the amide groups on the aramid fiber molecular chain, and at the same time form strong interfacial bonding with the polar modified groups on the surface of the polyolefin base film, significantly improving the adhesion between the coating and the base film. This solves the industry pain points of poor compatibility between traditional dense ceramics and aramid matrix, easy powdering of coatings, and easy cracking.

[0031] In this invention, the diameter of the aramid fiber is 10~250nm, for example, it can be any point value or any range between any two points from 10nm, 20nm, 30nm, 50nm, 80nm, 100nm, 120nm, 150nm, 180nm, 200nm, 220nm, to 250nm. The three-dimensional network pores formed by the cross-linking and winding of the aramid fiber constitute a macroporous structure, which is completely connected with the mesoporous structure. At room temperature, it provides a low-resistance transmembrane transport main channel for lithium ions, and at the same time provides a rapid diffusion channel for electrolyte, so that the electrolyte can diffuse to various areas of the coating through the macropores within a few seconds, and then complete rapid adsorption and storage through the mesopores, realizing the synergistic wetting effect of overall rapid diffusion and local adsorption. At high temperature, as a secondary filling unit of the phase change core material, the excess core material can quickly fill the macroporous structure, realize the complete sealing of all pores of the coating, and form a synergy with the anchoring and sealing of the mesopores to ensure the thoroughness of the self-sealing effect. In traditional single-channel coatings, excessively small pore sizes lead to high ion transport resistance and poor rate performance; excessively large pore sizes result in weak electrolyte adsorption, poor electrolyte retention, and short cycle life. The multi-level pore structure of this invention balances electrolyte absorption and retention capacity with ion transport resistance, enabling the membrane to possess both excellent cycle life and rate performance, achieving a synergistic wetting effect of the multi-level pore structure.

[0032] In this invention, the aspect ratio of aramid fibers is >100. Aramid fibers with a high aspect ratio can form a continuous, flexible cross-linked network in the slurry system. Simultaneously, through particle size classification of porous ceramic particles, they are uniformly dispersed within the aramid fiber network, forming a three-dimensional structure with completely interpenetrating two phases. The high aspect ratio aramid fibers cross-link and wrap around the surface of the porous ceramic particles, filling the gaps in the rigid skeleton to form a continuous, flexible cross-linked network. This provides the coating with excellent flexibility, elongation at break, and interfacial adhesion, while firmly locking the porous ceramic particles within the network to prevent particle detachment. The rigid skeleton and flexible network interpenetrate and support each other. The rigid skeleton inhibits the high-temperature thermal shrinkage of the flexible aramid network, while the flexible network alleviates the internal stress of the rigid ceramic particles. This solves the problem of high brittleness and easy cracking in single ceramic coatings, enabling the coating to simultaneously possess ultra-high mechanical strength, excellent flexibility, extremely low winding curvature, and ultra-strong interfacial adhesion, thus solving the problem of powder shedding during rolling and winding processes.

[0033] In this invention, traditional aramid-ceramic coatings, due to their high ceramic particle content, generally suffer from brittleness, easy cracking, and poor adhesion to the base film. During high-speed coating, rolling, and cell winding processes, coating cracking and powder shedding are highly likely, resulting in low yield and making them unsuitable for high-speed mass production lines. The three-dimensional interpenetrating network structure of this invention fundamentally solves this problem, making it suitable for high-speed coating production lines with speeds ≥80m / min and achieving a high coating yield.

[0034] In this invention, the three-dimensional interpenetrating network structure allows for the controllable distribution of multi-level pores in the coating, ensuring the connectivity and uniformity of the pores. Simultaneously, it provides a stable space for the uniform dispersion of microcapsules, guaranteeing consistent thermal response performance across the entire separator. Excellent flexibility and interfacial adhesion ensure that the coating maintains structural integrity during long-term charge-discharge cycles, preventing cracking and detachment as the electrode expands and contracts. This avoids localized short circuits caused by coating damage and maintains excellent electrolyte retention capacity, significantly extending the battery's cycle life.

[0035] In one embodiment of the present invention, the surface of the porous ceramic is loaded with responsive microcapsules, the core material of which is polyacrylonitrile and the wall material is polyacrylate.

[0036] In this invention, porous ceramics, with their mesoporous structure and active adsorption sites on the surface, can uniformly anchor responsive microcapsules onto the surface through physical adsorption and spatial confinement effects. This solves the defects of traditional dense ceramics, such as insufficient specific surface area, inability to load functional materials, leading to easy aggregation, uneven distribution, and poor thermal response consistency of microcapsules in the coating. This improves the heat resistance and wettability of the composite battery separator. The mesoporous structure of the porous ceramics provides a dedicated space for the phase change core material released from the microcapsules. The capillary force of the pores enables the active absorption of the core material. After cooling and solidification, the core material forms a strong mechanical interlocking structure with the inner wall of the pores, solving the core problems of easy loss of molten core material, lack of anchoring, and unstable sealing effect in traditional technologies.

[0037] The porous ceramic particles overcome the limitations of traditional dense ceramic particles, which can only serve as rigid framework fillers. Porous ceramics possess an ultra-high specific surface area and abundant mesoporous structure, with numerous active adsorption sites on their surface. Through physical adsorption and spatial confinement effects, responsive microcapsules can be uniformly anchored onto the porous ceramic surface. This solves the problems of insufficient specific surface area in traditional dense ceramics, which cannot support functional materials, leading to microcapsule agglomeration, uneven distribution, and poor thermal response consistency in coatings. The porous ceramic particles retain the rigidity and high-temperature dimensional stability of inorganic ceramic materials. By constructing a three-dimensional rigid support network in the coating, the thermal shrinkage performance of the diaphragm can be improved, high-temperature thermal shrinkage of the polyolefin-based film can be suppressed, short circuits between positive and negative electrodes can be avoided, and heat-resistant protection can be achieved synergistically with the aramid system.

[0038] In one embodiment of the present invention, the particle size of the responsive microcapsules is 300~800 nm.

[0039] In this invention, the particle size of the responsive microcapsules is 300~800nm, for example, it can be any point value or the range between any two point values ​​from 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm.

[0040] In one embodiment of the present invention, the mass ratio of aramid fiber, porous ceramic and responsive microcapsule is 1~3:8~12:0.5~1.5.

[0041] In one embodiment of the present invention, the polyacrylate is composed of a first polyacrylate, a second polyacrylate, and a third polyacrylate, wherein the first polyacrylate, the second polyacrylate, and the third polyacrylate have different glass transition temperatures.

[0042] In one embodiment of the present invention, the glass transition temperature of the first polyacrylate is greater than that of the second polyacrylate and the third polyacrylate.

[0043] In one embodiment of the present invention, the glass transition temperature of the first polyacrylate is >100°C, the glass transition temperature of the second polyacrylate is 0~100°C, and the glass transition temperature of the third polyacrylate is <0°C.

[0044] In this invention, the first polyacrylate, the second polyacrylate, and the third polyacrylate are all produced by emulsion polymerization. Any other type of monomer that can achieve the glass transition temperature of this patent is within the scope of protection of this patent, and the polymerization monomers are not fixed.

[0045] In this invention, the raw materials of the responsive microcapsules include a first polyacrylate, a second polyacrylate, and a third polyacrylate with different glass transition temperatures, thereby constructing a full-temperature-range intelligent adhesive system that covers the entire temperature range, is heat-resistant and shrink-resistant, and achieves excellent high-temperature heat resistance and active adhesive thermal response capability.

[0046] In one embodiment of the present invention, the raw materials for the responsive microcapsules also include deionized water and sodium carboxymethyl cellulose.

[0047] In this invention, sodium carboxymethyl cellulose can also be lithium carboxymethyl cellulose or carboxymethyl cellulose.

[0048] A second aspect of the present invention provides a method for preparing an aramid composite battery separator, used to prepare the aramid composite battery separator provided in the first aspect of the present invention, comprising the following steps: S1. Porous ceramics with positive charge are obtained after surface modification of porous ceramics. Responsive microcapsules are obtained by spray drying. The responsive microcapsules are loaded onto the surface of the positively charged porous ceramics to obtain porous ceramic@microcapsule composite particles. In this invention, porous ceramic particles are dispersed in an aqueous solution containing a cationic polymer, stirred, centrifuged, washed, and dried to obtain positively charged porous ceramic particles. The concentration of the aqueous solution containing the cationic polymer is 0.5wt%~2wt%, for example, it can be any value from 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt% and any range between any two values, preferably 1wt%. The cationic polymer can be one or both of polyethyleneimine and polydiallyldimethylammonium chloride, preferably polyethyleneimine. The mass-to-volume ratio of porous ceramic particles to the aqueous solution containing the cationic polymer is 1g:10mL, and the dispersion is obtained by stirring for 2~4h, so that the surface of the ceramic particles is positively charged.

[0049] In this invention, deionized water, sodium carboxymethyl cellulose, and polyacrylonitrile are mixed evenly, emulsified once, and then polyacrylate is added. After a second emulsification, the mixture is spray-dried and granulated to obtain responsive microcapsules. The rotation speed of the first emulsification is 1000 r / min, and the emulsification time is 10 min. The rotation speed of the second emulsification is 2000 r / min, and the emulsification time is 30 min. The inlet air temperature of the spray dryer is 80℃, the outlet air temperature is 45℃, the spray dryer pressure is 1.0 MPa, and the spray dryer time is 3 h. The acrylate is composed of a first polyacrylate, a second polyacrylate, and a third polyacrylate. The mass ratio of deionized water, sodium carboxymethyl cellulose, polyacrylonitrile, the first polyacrylate, the second polyacrylate, and the third polyacrylate is 10:0.1~0.3:0.1~0.3:1~5:1~3:5~8; for example, it can be any point value or the range between any two point values ​​in 10:0.1:0.1:1:1:5, 10:0.2:0.2:3:2:6, 10:0.3:0.3:5:3:8.

[0050] In this invention, responsive microcapsules are dispersed in water, positively charged porous ceramic particles are added, and after stirring, the mixture is centrifuged, washed, and dried to obtain porous ceramic@microcapsule composite particles. The mass-to-volume ratio of responsive microcapsules to water is 1 g:50 mL, and the mass ratio of responsive microcapsules to porous ceramic particles is 1:5~20. For example, it can be any value or range between any two values ​​from 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, preferably 1:10. After stirring for 1~2 h, electrostatic adsorption is used to uniformly attach the microcapsules to the surface of the ceramic particles.

[0051] S2. Dissolve the aramid fibers and separate the phases to obtain an aramid fiber dispersion; In this invention, aramid fibers are dissolved in a mixed solution, stirred, and then a solvent is added for phase separation to obtain an aramid fiber dispersion. The mixed solution consists of an organic solvent and potassium hydroxide. The organic solvent can be one or more of dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone, preferably dimethyl sulfoxide. The mass concentration of potassium hydroxide in the mixed solution is 2 wt%, and the mass-volume ratio of aramid fibers to the mixed solution is 1 g:50 mL. The mixture is stirred at 70°C for 6 h. The solvent can be one or two of deionized water and ethanol, preferably deionized water, and the mass-volume ratio of aramid fibers to the solvent is 1 g:5 mL.

[0052] S3. Add porous ceramic@microcapsule composite particles to aramid fiber dispersion, add dispersant, and after dispersion, obtain composite coating liquid; In this invention, the mass ratio of porous ceramic@microcapsule composite particles to aramid fibers is 2:1, the dispersant can be one or more of polyvinylpyrrolidone, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and fatty alcohol polyoxyethylene ether, preferably polyvinylpyrrolidone, the mass ratio of aramid fibers to dispersant is 4:1, and the solid content of the composite coating liquid is 10wt%~30wt%.

[0053] S4. Coat the composite coating liquid onto at least one surface of the base film, and after drying, obtain the aramid composite battery separator.

[0054] In this invention, the coating method can be one of microgravure coating, spraying, dot coating or slot extrusion coating, preferably microgravure coating, in which the composite coating liquid is coated on one or both sides of the polyolefin membrane and dried at 60~80℃ to form a composite coating with a thickness of 1~5μm.

[0055] A specific embodiment of the third aspect of the present invention provides a battery, including an aramid composite battery separator provided by the specific embodiment of the first aspect of the present invention or an aramid composite battery separator prepared by the preparation method provided by the specific embodiment of the second aspect of the present invention.

[0056] The present invention will now be described in detail with reference to preferred embodiments and comparative examples. The preferred embodiments of the invention described below can be modified in various ways, and therefore the scope of the invention should not be construed as limited to the preferred embodiments described in detail below. Preferred embodiments are provided to help those skilled in the art to more readily understand the invention.

[0057] In the following examples and comparative examples, the aramid fiber is poly(p-phenylene terephthalamide) fiber with a length of 100 nm, an aspect ratio of 120, a number-average molecular weight of sodium carboxymethyl cellulose of 89,000 g / mol, a number-average molecular weight of polyacrylonitrile of 102,000 g / mol, and a weight-average molecular weight of polyethyleneimine of 100,000 g / mol. The preparation method of the first polyacrylate includes the following steps: methyl methacrylate, isobornyl methacrylate and acrylamide are mixed in a mass ratio of 1:1:1, and the mixture is emulsion polymerized under the condition of azobisisobutyramidine hydrochloride as an initiator to obtain the first polyacrylate. The amount of initiator is 0.5% of the total mass of methyl methacrylate, isobornyl methacrylate and acrylamide, and the number average molecular weight is 93200 g / mol. The preparation method of the second polyacrylate includes the following steps: methyl acrylate, methyl methacrylate and isobutyl methacrylate are mixed in a mass ratio of 1:1:1, and emulsion polymerization is carried out under the condition of azobisisobutyramidine hydrochloride as an initiator to obtain the second polyacrylate. The amount of initiator is 0.5% of the total mass of methyl acrylate, methyl methacrylate and isobutyl methacrylate; the number average molecular weight is 95000 g / mol. The preparation method of the third polyacrylate includes the following steps: n-propyl acrylate, isopropyl acrylate and isobutyl acrylate are mixed in a mass ratio of 1:1:1, and emulsion polymerization is carried out under the condition of azobisisobutyramidine hydrochloride as initiator to prepare the third polyacrylate. The amount of initiator is 0.5% of the total mass of n-propyl acrylate, isopropyl acrylate and isobutyl acrylate; the number average molecular weight is 83000 g / mol.

[0058] Example 1 A method for preparing an aramid composite battery separator includes the following steps: S1. Take 10g of porous boehmite particles (particle size 400nm, pore size 30nm, specific surface area 150m²) 2 / g, pore volume 0.5cm 3 / g) was dispersed in 100mL of an aqueous solution containing 1wt% polyethyleneimine, stirred for 3h, centrifuged and washed to obtain porous boehmite with a positively charged surface. Deionized water, sodium carboxymethyl cellulose and polyacrylonitrile were added to an emulsification vessel, and the emulsification rate was 1000r / min for 10min. Polyacrylate was then added, and the emulsification rate was 2000r / min for 30min to form a spray precursor liquid. The spray precursor liquid was spray dried and granulated to obtain responsive microcapsules. The inlet air temperature of the spray dryer was 80℃, the outlet air temperature of the spray dryer was 45℃, and the spray dryer pressure was... The spray drying time was 3 hours, the atomizer frequency was 300 Hz, and 1 g of responsive microcapsules were dispersed in 50 mL of deionized water. Porous boehmite with a positive surface charge was added, and the mixture was stirred for 1.5 hours. After centrifugation and drying, porous ceramic@microcapsule composite particles were obtained. The polyacrylate was composed of a first polyacrylate, a second polyacrylate, and a third polyacrylate. The mass ratio of deionized water, sodium carboxymethyl cellulose, polyacrylonitrile, and the first, second, and third polyacrylates was 10:0.2:0.2:1:1:5. S2. Dissolve 2g of aramid fiber in 100mL of dimethyl sulfoxide / potassium hydroxide (potassium hydroxide concentration 2wt%) system, stir at 70℃ for 6h, add 10mL of deionized water to obtain aramid fiber dispersion; S3. Add porous ceramic@microcapsule composite particles to aramid fiber dispersion, with a mass ratio of porous ceramic@microcapsule composite particles to aramid fiber of 2:1. Add 0.5g of polyvinylpyrrolidone and disperse evenly at high speed to obtain composite coating solution. S4. Using a micro-gravure coating method, the composite coating liquid is coated on one side of a 12μm thick PE separator and dried at 80℃ to form a 3μm thick composite coating, thus obtaining an aramid composite battery separator.

[0059] Example 2 The difference from Example 1 is that porous boehmite is replaced with an equal amount of porous alumina with a particle size of 500 nm and a specific surface area of ​​100 m². 2 / g, pore size 30nm, pore volume 0.5cm³ 3 / g.

[0060] Example 3 The difference between Example 3 and Example 1 is that the total amount of polyacrylate remains unchanged, and the polyacrylate is composed of a first polyacrylate, a second polyacrylate, and a third polyacrylate in a mass ratio of 5:3:8.

[0061] Example 4 The difference between Example 4 and Example 3 is that the total amount of polyacrylate remains unchanged, and the polyacrylate is composed of a first polyacrylate and a second polyacrylate in a mass ratio of 5:3.

[0062] Example 5 The difference between Example 5 and Example 3 is that the total amount of polyacrylate remains unchanged, and the polyacrylate is composed of a first polyacrylate and a third polyacrylate in a mass ratio of 5:8.

[0063] Example 6 The difference between Example 6 and Example 3 is that the polyacrylate is composed of a second polyacrylate and a third polyacrylate in a mass ratio of 3:8.

[0064] Example 7 The difference between Example 7 and Example 3 is that the polyacrylate is a first polyacrylate.

[0065] Example 8 The difference between Example 8 and Example 3 is that the polyacrylate is a second polyacrylate.

[0066] Example 9 The difference between Example 9 and Example 3 is that the polyacrylate is a third polyacrylate.

[0067] Example 10 The difference between Example 10 and Example 2 is that no response microcapsules were added in step S1.

[0068] Example 11 Compared with Example 2, the difference in Example 11 is that in step S1, the preparation process of porous ceramic@microcapsule composite particles is physical mixing, without loading.

[0069] Comparative Example 1 Compared with Example 2, Comparative Example 1 differs in that porous alumina is replaced with an equal amount of alumina with a particle size of 500 nm and a specific surface area of ​​12 m². 2 / g.

[0070] The following performance tests were conducted on the aramid composite battery separators of Examples 1-11 and Comparative Example 1: (1) Heat shrinkage: The longitudinal (MD) heat shrinkage performance and transverse (TD) heat shrinkage performance of the diaphragm sample at 200℃ for 1h were tested according to the test method specified in GB / T 36363-2018. (2) Liquid absorption rate and liquid retention rate: The diaphragm was cut into 50mm×50mm samples, and the weight of the samples before testing was recorded as m1; Liquid absorption rate test process: The weighed diaphragm is immersed in the electrolyte at 25°C for 30 minutes, then removed and placed on industrial wiping paper. After wiping the free electrolyte with industrial wiping paper, the weight is recorded as m2. Liquid retention rate test procedure: After weighing the sample and placing it at 25℃ for 1 hour, the liquid absorption rate is recorded as m3; Liquid absorption rate (%) = (m2-m1) / m1×100; Liquid retention rate (%) = (m3-m1) / m1×100; The electrolyte is a mixture of electrolyte and solvent. The electrolyte is lithium hexafluorophosphate, and the solvent is a mixture of ethylene carbonate and diethyl carbonate (volume ratio of ethylene carbonate to diethyl carbonate is 1:1). The concentration of the electrolyte in the electrolyte is 1 mol / L. (3) Wetting property: The formula for calculating wettability v is: v = h / t; In the formula, h is the wetting height (the height to which the electrolyte penetrates the membrane in the vertical direction), in mm; t is the wetting time, in min. The electrolyte is a mixture of electrolyte and solvent. The electrolyte is lithium hexafluorophosphate, and the solvent is a mixture of ethylene carbonate and diethyl carbonate (the volume ratio of ethylene carbonate to diethyl carbonate is 1:1). The concentration of the electrolyte in the electrolyte is 1 mol / L. (4) Ionic conductivity: Ionic conductivity was tested in accordance with GB / T 36363-2018 "Polyolefin separators for lithium-ion batteries", where the temperature was 40℃ and the relative humidity was 50%. (5) Static contact angle test: The test method is in GB / T 30693-2014 "Measurement of contact angle between plastic film and water", and the electrolyte is the same as that used for wettability test; (6) Electrode adhesion test: The electrode is either a positive electrode or a negative electrode. When the electrode is a positive electrode, the positive electrode adhesion is obtained, and when the electrode is a negative electrode, the negative electrode adhesion is obtained. Cold-pressed positive electrode bonding strength: The diaphragm size is 25×150mm, and the positive electrode size is 25×150mm; the cold press temperature is adjusted to the set value, and the pressure is 1000kg. The diaphragm and positive electrode are preheated for 1 second and then cold-pressed for 1 second using the cold press; the bonding strength of the cold-pressed positive electrode is tested using an electronic tensile testing machine. The diaphragm and positive electrode are peeled until the tensile distance of the electronic tensile testing machine is 50mm. The speed of the electronic tensile testing machine is 300mm / min, and the peel angle is 180°. The bonding strength of the cold-pressed positive electrode is calculated based on the peel force divided by the tensile distance of the electronic tensile testing machine. The peel force is the average value of the force collected by the electronic tensile testing machine during the peeling process of the diaphragm and positive electrode. The bonding strength of the cold-pressed positive electrode is calculated based on the data between 10 and 40mm, that is, the bonding strength of the cold-pressed positive electrode is calculated based on the peel force between 10 and 40mm divided by 30mm. The positive electrode is a ternary lithium nickel cobalt aluminum oxide with the chemical formula LiNi. 0.8 Co 0.15 Al 0.05 The O2 electrode and the negative electrode are carbon-based graphite electrodes (containing 91% carbon). Ten sets of tests were conducted and the average value was taken.

[0071] The test results are shown in Tables 1 and 2 below.

[0072] Table 1 Performance test results of Examples 1-11 and Comparative Example 1

[0073] Table 2 Performance test results of Examples 1-11 and Comparative Example 1

[0074] Comparing Example 1 with Comparative Example 1, it can be seen that when the ceramic particles are porous ceramics, they are no longer a single inorganic filler. Through their porous structure and high specific surface area, they not only improve the electrolyte wetting speed and liquid absorption rate, but also firmly lock the electrolyte in the pores, forming a highly efficient ion transport network, thereby improving the ion conductivity. The porous structure can also adsorb microcapsules, improving the heat resistance and wettability of the composite battery separator. The three-dimensional interpenetrating network structure formed by the porous ceramic particles and aramid fibers gives the separator both excellent adhesion and dimensional stability.

[0075] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An aramid composite battery separator, characterized in that, It includes a base film and a composite coating disposed on at least one surface of the base film; the composite coating includes aramid fibers and porous ceramics, the aramid fibers and porous ceramics forming a three-dimensional interpenetrating network.

2. The aramid composite battery separator according to claim 1, characterized in that, The porous ceramic has a pore size of 2~50nm.

3. The aramid composite battery separator according to claim 1, characterized in that, The diameter of the aramid fiber is 10~250nm, and the aspect ratio of the aramid fiber is >100.

4. The aramid composite battery separator according to claim 1, characterized in that, The porous ceramic surface is loaded with responsive microcapsules, the core material of which is polyacrylonitrile and the wall material is polyacrylate.

5. The aramid composite battery separator according to claim 1, characterized in that, The mass ratio of the aramid fiber, the porous ceramic, and the responsive microcapsule is 1~3:8~12:0.5~1.

5.

6. The aramid composite battery separator according to claim 4, characterized in that, The particle size of the responsive microcapsules is 300~800nm.

7. The aramid composite battery separator according to claim 4, characterized in that, The polyacrylate is composed of a first polyacrylate, a second polyacrylate, and a third polyacrylate, and the first polyacrylate, the second polyacrylate, and the third polyacrylate have different glass transition temperatures.

8. The aramid composite battery separator according to claim 7, characterized in that, The first polyacrylate has a glass transition temperature >100℃, the second polyacrylate has a glass transition temperature of 0~100℃, and the third polyacrylate has a glass transition temperature <0℃.

9. A method for preparing an aramid composite battery separator, used to prepare the aramid composite battery separator according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Prepare responsive microcapsules by loading the responsive microcapsules onto the surface of porous ceramic to obtain porous ceramic@microcapsule composite particles; S2. Dissolve the aramid fibers and separate the phases to obtain an aramid fiber dispersion; S3. Add the porous ceramic@microcapsule composite particles to the aramid fiber dispersion, add a dispersant, and disperse to obtain a composite coating solution. S4. The composite coating liquid is coated on at least one surface of the base film, and after drying, the aramid composite battery separator is obtained.

10. A battery, characterized in that, The aramid composite battery separator includes the aramid composite battery separator according to any one of claims 1 to 8 or the aramid composite battery separator prepared by the preparation method according to claim 9.

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