A graphene-coated aramid separator and a preparation method and application thereof

Abstract

The application relates to the technical field of battery separators, in particular to an aramid separator containing a graphene coating and a preparation method and application thereof, the preparation method being as follows: S1, scraping aramid slurry solution on a PE base film, then sequentially treating in a coagulation bath and water to form, and then drying to obtain an aramid base film; S2, coating a graphene composite slurry on the surface of the aramid base film, and then drying to obtain the aramid separator containing the graphene coating; the graphene composite slurry comprises polyvinylpyrrolidone, ethylene glycol, deionized water and graphene powder. The aramid separator containing the graphene coating is composed of an aramid base film and a graphene composite coating, the graphene composite coating is coated on the surface of the aramid base film, the separator is applied between positive and negative electrodes of a lithium battery as a separation component, smooth transmission of lithium ions is realized, growth of lithium dendrites is inhibited, short circuit of the positive and negative electrodes is prevented, and meanwhile, the thermal stability and cycle performance of the lithium battery are improved.

Description

Technical Field

[0001] This invention relates to an aramid separator with a graphene coating, its preparation method and application, belonging to the field of battery separator technology. Background Technology

[0002] Currently, commercially available lithium battery separators are mainly polyolefin separators (such as polypropylene (PP) and polyethylene (PE). However, these separators have significant technical bottlenecks: low mechanical strength (tensile strength is usually less than 10 MPa) and poor thermal stability. They are prone to thermal shrinkage or even melting at high temperatures, leading to direct contact between the positive and negative electrodes, causing internal short circuits, thermal runaway, and other safety hazards. The pore size is large and unevenly distributed, which cannot effectively suppress lithium dendrite growth. The puncture of lithium dendrites can easily cause separator damage, further exacerbating battery safety risks. At the same time, their electrolyte wettability is poor and their ionic conductivity is low, which seriously affects the cycle life and rate performance of the battery, making it difficult to meet the requirements of high safety and high energy density lithium batteries in fields such as new energy electric vehicles and large-scale energy storage.

[0003] To address the aforementioned issues, the industry commonly employs surface coating modification to optimize separators. Among these methods, aramid fibers, due to their extremely high mechanical strength, excellent thermal stability (decomposition temperature exceeding 500 °C), and good chemical stability, have become the preferred material for separator coating or substrates. The abundant amide groups (-CO-NH-) on the aramid molecular chain can bind with anions in the electrolyte, promoting lithium salt dissociation, improving lithium ion distribution, and thus inhibiting lithium dendrite growth. However, pure aramid separators or aramid-coated separators still suffer from insufficient ionic conductivity and high interfacial impedance, limiting their application in high-rate, high-energy-density lithium batteries.

[0004] Graphene, a two-dimensional nanomaterial with ultra-high specific surface area, excellent conductivity, and mechanical properties, can be composited with aramid fibers to form a coating. The high conductivity of graphene enhances the ionic conductivity of the separator, while the synergistic effect of the two materials further strengthens the separator's mechanical strength, thermal stability, and electrolyte wettability, inhibiting lithium dendrite growth. Although existing technologies include graphene-aramid composite separators, many suffer from problems such as weak adhesion between the coating and the substrate, easy coating detachment, complex preparation processes, high costs, or limited performance improvement. These advancements fail to simultaneously optimize safety and electrochemical performance, making it difficult to meet the demands of large-scale industrial applications. Therefore, developing a stable, easily prepared, and cost-effective aramid separator with a graphene coating, and clarifying its application in lithium-ion batteries, has become a key research focus in the field of lithium-ion battery separators. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing an aramid separator with a graphene coating, its preparation method, and its applications. A layered coating strategy is employed to spatially separate the aramid and graphene layers, achieving functional division and structural synergy. While retaining the heat-resistant and insulating properties of aramid and the high thermal conductivity of graphene, the mutual interference between the two in a single coating is effectively avoided. This solves the problems of poor thermal stability, insufficient mechanical strength, low ionic conductivity, and poor lithium dendrite suppression in traditional lithium battery separators. It achieves simultaneous improvements in lithium battery safety, cycle life, and rate performance, while simplifying the preparation process and reducing application costs, meeting the needs of large-scale industrial production and lithium battery use in various scenarios.

[0006] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing an aramid membrane with a graphene coating, wherein the preparation method is as follows: S1. Aramid slurry solution is coated onto a PE base film, and then the film is formed by coagulation bath and water treatment, and then dried to obtain an aramid base film. S2. After coating the surface of the aramid-based membrane with graphene composite slurry, the membrane is dried to obtain an aramid membrane with a graphene coating. The graphene composite slurry comprises polyvinylpyrrolidone, ethylene glycol, deionized water, and graphene powder.

[0007] Furthermore, the aramid slurry solution is a DMAC solution of poly(m-phenylene isophthalamide) with a mass concentration of 4%-6%.

[0008] Furthermore, the coagulation bath is a DMAC solution with a mass concentration of 35%-45%.

[0009] Further, in step S1, after coating the aramid slurry solution onto the PE base film, it is first immersed in a coagulation bath for 10-15 seconds, then immersed in water for 20-30 seconds, and dried at 50-60℃ to obtain the aramid base film.

[0010] Furthermore, in step S1, the coating thickness of the aramid slurry solution is 1.5-2.5 micrometers; in step S2, the coating thickness of the graphene composite slurry is 0.8-1.5 micrometers.

[0011] Further, by weight, the graphene composite slurry comprises 3-6 parts of polyvinylpyrrolidone, 23-25 ​​parts of ethylene glycol, 70-74 parts of deionized water, and 11-34 parts of graphene powder.

[0012] Furthermore, the preparation method of the graphene composite slurry is as follows: dissolve polyvinylpyrrolidone in a mixed solvent of ethylene glycol and deionized water, mix evenly to obtain a dispersion, and then add graphene powder to obtain the graphene composite slurry.

[0013] Furthermore, the polyvinylpyrrolidone is PVP-K30.

[0014] The present invention also discloses an aramid membrane with a graphene coating, wherein the aramid membrane is prepared according to the preparation method described in the present invention.

[0015] The present invention also discloses an application of an aramid separator with a graphene coating, wherein the aramid separator is used in a lithium battery.

[0016] The beneficial effects of this invention are: 1) Significantly Improved Safety Performance: In existing technologies, graphene runs through the entire single-layer coating. Uneven dispersion or excessive content can easily lead to the formation of a continuous conductive network, causing a decrease in the surface resistivity of the separator and resulting in micro-short circuits or even thermal runaway between the positive and negative electrodes. In this invention, the bottom layer of aramid is an electronic insulator. Its complete porous framework physically isolates the surface graphene from the base film and electrodes. Even if the surface graphene is locally conductive, it cannot form a through-circuit, fundamentally eliminating the risk of micro-short circuits. Simultaneously, under the coating shear force, the surface graphene sheets are aligned in parallel, forming a continuous planar thermally conductive network. When localized overheating occurs inside the battery, heat rapidly diffuses along the separator plane, preventing hotspot accumulation and subsequent thermal runaway chain reactions. The bottom layer of aramid is temperature resistant to >400℃ and maintains structural integrity even after the base film melts, providing high-temperature mechanical support for the separator.

[0017] 2) Significantly optimized electrochemical performance: The ultra-high specific surface area and excellent conductivity of graphene improve the ionic conductivity of the separator. The porous structure and polar characteristics of the graphene composite coating improve the wettability of the separator electrolyte, accelerate the lithium-ion transport rate, and reduce the battery interface impedance.

[0018] 3) Enhanced Interface and Cyclic Stability: The bonding between the aramid coating and the PE base film is mainly achieved through the following synergistic mechanism: During the DMAC solution immersion stage, the aramid molecular chains swell, increasing chain segment mobility and providing conditions for interpenetration; subsequently, during the phase transformation process of deionized water immersion, the exchange of solvent and non-solvent allows the aramid to solidify and form. During this process, the aramid molecular chains embed into the micropores or rough structures on the surface of the PE base film, forming mechanical anchoring. The graphene composite coating is firmly bonded to the aramid base film and is not easily detached. PVP-K30 is used as a dispersant in the graphene composite slurry. The carbonyl groups in its molecular chains form π-π interactions and hydrogen bonds with the graphene surface, effectively preventing graphene sheet aggregation; simultaneously, PVP forms hydrogen bonds with the amide groups on the aramid layer surface, enhancing the interlayer interface bonding strength. This separator can form a stable solid electrolyte interface film on the electrode surface, reducing electrolyte decomposition and lowering interfacial impedance. Lithium batteries using this separator can maintain a capacity retention of over 97% after 100 cycles at 1C rate.

[0019] These characteristics enable aramid separators with graphene coatings to have excellent practical performance in lithium batteries. They not only solve the technical pain points of traditional separators, but also take into account the cost and efficiency requirements of industrial production, providing a new solution for the development of high-safety, high-energy-density lithium batteries. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the preparation process of the aramid membrane with graphene coating described in this invention. Figure 2 SEM image of the aramid membrane with graphene coating prepared in Example 1; Figure 3 The graphs show the constant cycle test results of the graphene-coated aramid membrane (graphene-modified aramid membrane) prepared in Example 1 and the aramid membrane in Comparative Example 1. Figure 4 This is a comparison graph of the ionic conductivity of the aramid membrane with graphene coating (graphene-modified aramid membrane) prepared in Example 1 and the aramid membrane in Comparative Example 1. Detailed Implementation

[0021] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0023] like Figure 1 As shown, a method for preparing an aramid membrane with a graphene coating is described, wherein the preparation method is as follows: S1. Aramid slurry solution is coated onto a PE base film, and then the film is formed by coagulation bath and water treatment, and then dried to obtain an aramid base film. S2. After coating the surface of the aramid-based membrane with graphene composite slurry, the membrane is dried to obtain an aramid membrane with a graphene coating. The graphene composite slurry comprises polyvinylpyrrolidone, ethylene glycol, deionized water, and graphene powder.

[0024] Specifically, the aramid slurry solution is a DMAC solution of poly(m-phenylene isophthalamide) with a mass concentration of 4%-6%.

[0025] More specifically, the aramid sizing solution is prepared by diluting the aramid sizing (poly(m-phenylene isophthalamide) solution before meta-aramid spinning with DMAC to a concentration of 4%-6%, which is the aramid sizing solution. In this embodiment of the invention, the aramid sizing used is a meta-aramid sizing, with a solid content of 20% (solvent is DMAC), a viscosity of 550-750 Pa·s, and a pH value of 7.8-8.5.

[0026] Specifically, the coagulation bath is a DMAC solution with a mass concentration of 35%-45% (i.e., a solution of DMAC and water).

[0027] Specifically, in step S1, after coating the aramid slurry solution onto the PE base film, it is first immersed in a coagulation bath for 10-15 seconds, then immersed in water for 20-30 seconds, and dried at 50-60℃ to obtain the aramid base film.

[0028] Specifically, in step S1, the coating thickness of the aramid slurry solution is 1.5-2.5 micrometers; in step S2, the coating thickness of the graphene composite slurry is 0.8-1.5 micrometers.

[0029] Preferably, the ratio of the coating thickness of the aramid slurry solution to the coating thickness of the graphene composite slurry is (1.5-2.0):1.

[0030] This thickness ratio effectively separates the functions of electronic insulation and ion conduction. As an electronic insulator, the aramid layer, with a thickness at least 1.5 times that of the graphene layer, forms a continuous, defect-free insulating barrier, completely physically isolating the surface graphene coating from the PE base film and electrodes. Even if the graphene layer forms a conductive network locally, electrons cannot penetrate longitudinally to the base film or electrodes, fundamentally eliminating the micro-short-circuit risk present in traditional hybrid coating membranes. Simultaneously, with the aramid layer thickness not exceeding 2.0 times that of the graphene layer, the lithium-ion transport path is not significantly lengthened due to excessive aramid layer thickness, avoiding ion transport obstruction and allowing the increased ionic conductivity of the graphene layer to be fully utilized. Tests show that within this thickness ratio range, the membrane maintains high ionic conductivity while ensuring safe electronic insulation between the positive and negative electrodes. Furthermore, this thickness ratio provides excellent interfacial mechanical stability for the composite coating. Compared to graphene layers, aramid layers offer superior flexibility. When the aramid layer thickness is 1.5-2.0 times that of the graphene layer, it acts as an elastic buffer layer, effectively absorbing and dispersing interfacial stresses generated by the volume expansion and contraction of the graphene coating and electrodes during cycling. This prevents the graphene layer from cracking or peeling due to stress concentration, ensuring the structural integrity of the composite coating during long-cycle charge-discharge cycles, thus extending the lifespan of the separator in battery applications. Furthermore, this thickness ratio creates a deep safety barrier for both thermal conductivity and insulation. Under shear force, the graphene layers align parallel to the separator surface, forming a highly efficient planar thermally conductive network that rapidly diffuses localized hotspots along the separator plane, preventing heat accumulation at single points. The aramid layer, 1.5-2.0 times thicker than the graphene layer, plays a dual role in longitudinal thermal insulation and high-temperature structural support. On the one hand, it slows down the penetration rate of heat along the thickness direction; on the other hand, thanks to its temperature resistance exceeding 400℃, it can independently maintain the porous structure and physical integrity of the separator even under extreme high-temperature conditions where the underlying PE base film undergoes thermal shrinkage or even melting, preventing large-area direct contact between the positive and negative electrodes and thus interrupting the thermal runaway chain reaction. Finally, this thickness limit also solves the problem of excessive penetration of the dispersant PVP into the aramid layer in the graphene composite slurry, leading to pore blockage. When the aramid layer thickness is 1.5-2.0 times that of the graphene layer, the PVP molecular chains in the slurry mainly entangle and hydrogen bond anchor on the surface and shallow areas of the aramid layer during the coating process, forming a strong interlayer bond, without penetrating in large quantities into the depths of the aramid layer and blocking the core pores for ion transport. This achieves the optimal state of "firm anchoring in the shallow layer and unobstructed ion conduction in the deep layer" at the process level.

[0031] Specifically, by weight, the graphene composite slurry comprises 3-6 parts of polyvinylpyrrolidone, 23-25 ​​parts of ethylene glycol, 70-74 parts of deionized water, and 11-34 parts of graphene powder.

[0032] Specifically, the polyvinylpyrrolidone is PVP-K30.

[0033] More specifically, the mass ratio of PVP-K30 to graphene powder is 1:(2-7). This ratio is key to achieving synergistic optimization of uniform graphene dispersion, strong interlayer bonding, and unobstructed ion transport channels. When the mass ratio is within this range, the carbonyl groups on the PVP-K30 molecular chains can be fully adsorbed onto the graphene sheet surface through π-π interactions and hydrogen bonds, forming an effective steric hindrance layer. This overcomes the van der Waals forces between graphene sheets, ensuring that the graphene remains uniformly dispersed in the slurry and subsequent coatings, avoiding localized conductive concentrations or mechanical defects in the coating due to graphene agglomeration. Simultaneously, the PVP molecular chains adsorbed on the graphene surface retain a large number of free carbonyl sites, which can form a dense hydrogen bond network with the amide groups on the aramid film surface during coating, firmly anchoring the graphene coating to the aramid film and ensuring that the composite coating does not peel off during long-term cycling. More importantly, when the ratio of PVP to graphene is 1:(2-7), PVP can provide sufficient dispersion and bonding functions, and avoid excessively high concentrations of free PVP molecules in the slurry. Excessive free PVP not only increases slurry viscosity, leading to decreased coating uniformity, but also accumulates in the pores or openings of the aramid membrane after drying, blocking lithium-ion transport paths and weakening the membrane's ionic conductivity. Therefore, this mass ratio range is beneficial for balancing the three aspects of "sufficiently dispersing graphene, effectively bonding the aramid interface, and preventing free PVP from clogging pores."

[0034] More specifically, there is a synergistic relationship between the DMAC concentration in the coagulation bath and the amount of PVP-K30 in the graphene composite slurry. The DMAC concentration in the coagulation bath can regulate the pore size and porosity of the aramid-based membrane surface. PVP-K30, as a dispersant and interlayer binder for graphene, directly affects the adhesion of graphene and the pore structure on the membrane. The constrained surface pore structure restricts the permeation behavior of PVP-K30, and an appropriate amount of PVP-K30 ensures interfacial adhesion, ultimately achieving a precise, thin, firm, and non-clogging functional coating on the porous framework surface of the aramid membrane. The synergistic effect of the DMAC concentration in the coagulation bath and the amount of PVP-K30 in the graphene composite slurry ultimately achieves a balance between firm anchoring of graphene in the shallow layer of the membrane and unobstructed pores in the deeper layers.

[0035] Preferably, when the mass concentration of DMAC in the coagulation bath is ≥35% and <40%, the weight fraction of PVP-K30 in the graphene composite slurry is 3.0-4.5 parts; when the mass concentration of DMAC in the coagulation bath is ≥40% and ≤45%, the weight fraction of PVP-K30 in the graphene composite slurry is 4.6-6.0 parts. When the concentration in the coagulation bath is too low, the solvent-non-solvent exchange on the surface of the aramid membrane occurs more rapidly, resulting in a larger pore size on the surface of the aramid membrane. The high concentration of free PVP molecules and high osmotic pressure in the graphene composite slurry will exacerbate the infiltration into the depth of the membrane, leading to large-area blockage of the ion transport channels inside the aramid membrane by PVP, and a decrease in the ionic conductivity of the membrane. If the PVP content is low, although some PVP will still penetrate deep into the membrane, the total amount is limited, and the degree of pore blockage is relatively controllable. More importantly, a small amount of PVP can still play a basic role in dispersing graphene and providing interlayer adhesion on the surface, preventing the graphene coating from completely losing its bonding strength. Therefore, in passive situations where the coagulation bath concentration is low and the surface pore size is large, a lower PVP content should be chosen to minimize the amount penetrating deep into the membrane and reduce the risk of pore blockage to a minimum. When the coagulation bath concentration is high, a sufficient and uniform pregel layer will form on the surface of the aramid liquid membrane, guiding the subsequent phase transformation to form a porous structure with smaller surface pore size, moderate density, and uniform distribution. PVP macromolecules are sieved on the surface, forming a thin layer on the solid-phase framework. Increasing the amount of PVP will not aggravate deep pore blockage, but will form a more continuous hydrogen bond network on the surface, enhancing the adhesion to the graphene coating, while the pores remain open.

[0036] Specifically, the preparation method of the graphene composite slurry is as follows: polyvinylpyrrolidone is dissolved in a mixed solvent of ethylene glycol and deionized water, mixed evenly to obtain a dispersion, and then graphene powder is added to obtain the graphene composite slurry.

[0037] More specifically, the graphene powder in this embodiment of the invention is obtained by a self-made method, and the preparation method of the graphene powder is as follows: Weigh 5g of graphite powder and 5g of Na2SO4 and add them to a flask. Slowly add 200mL of H2SO4 and incubate in an ice bath (0℃) for 1 hour to form a graphite intercalation compound to widen the interlayer spacing. Slowly add 20g of KMnO4 at 200rpm and react in a water bath at 38℃ for 26 hours to oxidize the carbon-carbon double bonds on the graphene sheets. Then, slowly add 250mL of deionized water at 300rpm and react in a water bath at 84℃ for 15 minutes to further increase the interlayer spacing. After the reaction, pour the mixture into a beaker containing 500mL of deionized water and add 30% H2O2 dropwise until no bubbles are generated to reduce the residual oxidant and moderately reduce the over-oxidized functional groups. Wash with HCl 3-4 times to remove ions, then wash with deionized water until neutral to remove residual acid and salt. Place the obtained graphene oxide in a tube furnace and treat at 80℃ for 2 hours under argon protection to restore the sp(s) of graphene. 2 The conjugated structure ultimately yielded graphene powder.

[0038] An aramid membrane with a graphene coating, wherein the aramid membrane is prepared according to the preparation method described in this invention.

[0039] An application of an aramid separator with a graphene coating, wherein the aramid separator is used in a lithium battery.

[0040] Specifically, in this embodiment of the invention, when the aramid separator is applied to a lithium battery, the lithium battery is prepared as follows: the positive electrode material is NCM811. A lithium sheet is used as the negative electrode, and 811 graphite electrolyte is used. The batteries are assembled into CR2025 type button cells in a glove box. The assembled button cells are then left to stand for 12 hours.

[0041] Example 1

[0042] The preparation method of an aramid separator with graphene coating and a lithium battery is as follows: (1) Preparation of aramid-based film: The aramid slurry was diluted with DMAC to a solid content of 5%, stirred evenly, and the prepared aramid slurry solution was uniformly coated onto the PE base film (coating thickness of 2 micrometers). First, it was immersed in 40% DMAC solution for 10 seconds to promote the relaxation of aramid molecular chains. Then, it was immersed in water for 20 seconds to trigger the exchange of DMAC with water, which caused the aramid molecular chains to embed into the micropores or rough structures on the surface of the PE base film, forming mechanical anchoring. Finally, it was dried in an oven at 55 ℃. The aramid base film was then obtained.

[0043] (2) Preparation of graphene: Weigh 5g of graphite powder and 5g of Na2SO4 and add them to a flask. Slowly add 200mL of H2SO4 and incubate on ice for 1h to form a graphite intercalation compound to widen the interlayer spacing. Slowly add 20g of kMnO4 at 200rpm and react in a 38℃ water bath for 26h to oxidize the carbon-carbon double bonds on the graphene sheets. Then, slowly add 250mL of deionized water at 300rpm and react in an 84℃ water bath for 15min to further increase the interlayer spacing. After the reaction, pour the mixture into a beaker containing 500mL of deionized water and add 30% H2O2 dropwise until no bubbles are generated to reduce the residual oxidant and moderately reduce the over-oxidized functional groups. Wash with HCl 3-4 times to remove ions, and then wash with deionized water until neutral to remove residual acid and salt. The obtained graphene oxide was placed in a tube furnace and treated at 80 °C for 2 hours under argon protection to restore the sp2 conjugated structure of graphene.

[0044] (3) Preparation of graphene composite slurry: 5g of PVP-K30 (polyvinylpyrrolidone) was dissolved in a mixed solvent of 24g of ethylene glycol and 71g of deionized water and magnetically stirred at room temperature for 24h to prepare a dispersion with a mass fraction of 5%; then 11g of graphene powder was added to the dispersion and magnetically stirred at room temperature for another 24h to obtain a graphene composite slurry with uniform dispersion and good stability.

[0045] (4) Aramid membrane coating and drying: Graphene composite slurry is uniformly coated on the surface of the aramid base membrane (coating thickness is 1 micrometer). The PVP molecular chains in the slurry and the amide groups on the surface of the aramid base membrane form a preliminary interface bond through hydrogen bonds. At the same time, the graphene sheets in the slurry are uniformly distributed under the dispersion effect of PVP. A wet film is formed, first dried at room temperature and pressure, and then vacuum dried at ≤60 ℃ for ≥48h to remove the solvent, thus obtaining an aramid membrane with a graphene coating.

[0046] (5) Lithium battery preparation: The main material of the positive electrode is NCM811. The negative electrode uses lithium sheet, the electrolyte uses 811 graphite electrolyte, and the separator uses the separator prepared in this embodiment. In a glove box, the CR2025 type button cell power battery is assembled. The assembled button cell is left to stand for 12 hours.

[0047] Example 2

[0048] The preparation method of an aramid separator with graphene coating and a lithium battery is as follows: (1) Preparation of aramid-based film: The aramid slurry was diluted with DMAC to a solid content of 5%, stirred evenly, and the prepared aramid slurry solution was uniformly coated onto the PE base film (coating thickness of 2 micrometers). First, it was immersed in 40% DMAC solution for 10 seconds to promote the relaxation of aramid molecular chains. Then, it was immersed in water for 20 seconds to trigger the exchange of DMAC with water, which caused the aramid molecular chains to embed into the micropores or rough structures on the surface of the PE base film, forming mechanical anchoring. Finally, it was dried in an oven at 55 ℃. The aramid base film was then obtained.

[0049] (2) Preparation of graphene: Weigh 5g of graphite powder and 5g of Na2SO4 and add them to a flask. Slowly add 200mL of h2SO4 and incubate on ice for 1h to form a graphite intercalation compound to widen the interlayer spacing. Slowly add 20g of kMnO4 at 200rpm and react in a water bath at 38℃ for 26h to oxidize the carbon-carbon double bonds on the graphene sheets. Then, slowly add 250mL of deionized water at 300rpm and react in a water bath at 84℃ for 15min to further increase the interlayer spacing. After the reaction, pour the mixture into a beaker containing 500mL of deionized water and add 30% h2O2 dropwise until no bubbles are generated to reduce the residual oxidant and moderately reduce the over-oxidized functional groups. Wash with HCl 3-4 times to remove ions, and then wash with deionized water until neutral to remove residual acid and salt. The obtained graphene oxide was placed in a tube furnace and treated at 80 °C for 2 hours under argon protection to restore the sp2 conjugated structure of graphene.

[0050] (3) Preparation of graphene composite slurry: 5g of PVP-K30 (polyvinylpyrrolidone) was dissolved in a mixed solvent of 24g of ethylene glycol and 71g of deionized water and magnetically stirred at room temperature for 24h to prepare a dispersion with a mass fraction of 5%; then 22g of graphene powder was added to the dispersion and magnetically stirred at room temperature for another 24h to obtain a graphene composite slurry with uniform dispersion and good stability.

[0051] (4) Aramid membrane coating and drying: Graphene composite slurry is uniformly coated on the surface of the aramid base membrane (coating thickness is 1 micrometer). The PVP molecular chains in the slurry and the amide groups on the surface of the aramid base membrane form a preliminary interface bond through hydrogen bonds. At the same time, the graphene sheets in the slurry are uniformly distributed under the dispersion effect of PVP. A wet film is formed, first dried at room temperature and pressure, and then vacuum dried at ≤60 ℃ for ≥48h to remove the solvent, thus obtaining an aramid membrane with a graphene coating.

[0052] (5) Lithium battery preparation: The main positive electrode material is NCM811. Lithium foil is used as the negative electrode, 811 graphite electrolyte is used as the electrolyte, and the separator prepared in this embodiment is used. The CR2025 type button cell power battery is assembled in a glove box. The assembled button cell is left to stand for 12 hours.

[0053] Example 3

[0054] The preparation method of an aramid separator with graphene coating and a lithium battery is as follows: (1) Preparation of aramid-based film: The aramid slurry was diluted with DMAC to a solid content of 5%, stirred evenly, and the prepared aramid slurry solution was uniformly coated onto the PE base film (coating thickness of 2 micrometers). First, it was immersed in 40% DMAC solution for 10 seconds to promote the relaxation of aramid molecular chains. Then, it was immersed in water for 20 seconds to trigger the exchange of DMAC with water, which caused the aramid molecular chains to embed into the micropores or rough structures on the surface of the PE base film, forming mechanical anchoring. Finally, it was dried in an oven at 55 ℃. The aramid base film was then obtained.

[0055] (2) Preparation of graphene: Weigh 5g of graphite powder and 5g of Na2SO4 and add them to a 500mL three-necked flask. Slowly add 200mL of h2SO4 and incubate on ice for 1h to form a graphite intercalation compound to widen the interlayer spacing. Slowly add 20g of kMnO4 at 200rpm and react in a 38℃ water bath for 26h to oxidize the carbon-carbon double bonds on the graphene sheets. Then, slowly add 250mL of deionized water at 300rpm and react in an 84℃ water bath for 15min to further increase the interlayer spacing. After the reaction, pour the mixture into a beaker containing 500mL of deionized water and add 30% h2O2 dropwise until no bubbles are generated to reduce the residual oxidant and moderately reduce the over-oxidized functional groups. Wash with HCl 3-4 times to remove ions, and then wash with deionized water until neutral to remove residual acid and salt. The obtained graphene oxide was placed in a tube furnace and treated at 80 °C for 2 hours under argon protection to restore the sp2 conjugated structure of graphene.

[0056] (3) Preparation of graphene composite slurry: 5g of PVP-K30 (polyvinylpyrrolidone) was dissolved in a mixed solvent of 24g of ethylene glycol and 71g of deionized water and magnetically stirred at room temperature for 24h to prepare a dispersion with a mass fraction of 5%; then 33g of graphene powder was added to the dispersion and magnetically stirred at room temperature for another 24h to obtain a graphene composite slurry with uniform dispersion and good stability.

[0057] (4) Aramid membrane coating and drying: Graphene composite slurry is uniformly coated on the surface of the aramid base membrane (coating thickness is 1 micrometer). The PVP molecular chains in the slurry and the amide groups on the surface of the aramid base membrane form a preliminary interface bond through hydrogen bonds. At the same time, the graphene sheets in the slurry are uniformly distributed under the dispersion effect of PVP. A wet film is formed, first dried at room temperature and pressure, and then vacuum dried at ≤60 ℃ for ≥48h to remove the solvent, thus obtaining an aramid membrane with a graphene coating.

[0058] (5) Lithium battery preparation: The main positive electrode material is NCM811. Lithium foil is used as the negative electrode, 811 graphite electrolyte is used as the electrolyte, and the separator prepared in this embodiment is used. The CR2025 type button cell power battery is assembled in a glove box. The assembled button cell is left to stand for 12 hours.

[0059] Example 4

[0060] The preparation method of an aramid separator with graphene coating and a lithium battery is as follows: (1) Preparation of aramid-based film: The aramid slurry was diluted with DMAC to a solid content of 4%, stirred evenly, and the prepared aramid slurry solution was uniformly coated onto the PE base film (coating thickness of 1.5 micrometers). First, it was immersed in 45% DMAC solution for 15 seconds to promote the relaxation of aramid molecular chains. Then, it was immersed in water for 30 seconds to trigger the exchange of DMAC with water, which caused the aramid molecular chains to embed into the micropores or rough structures on the surface of the PE base film, forming mechanical anchoring. Finally, it was dried in an oven at 55 ℃. The aramid base film was then obtained.

[0061] (2) Preparation of graphene: Same as in Example 1.

[0062] (3) Preparation of graphene composite slurry: 6g of PVP-K30 (polyvinylpyrrolidone) was dissolved in a mixed solvent of 24g of ethylene glycol and 70g of deionized water and magnetically stirred at room temperature for 24h to prepare a dispersion; then 12g of graphene powder was added to the dispersion and magnetically stirred at room temperature for another 24h to obtain a graphene composite slurry with uniform dispersion and good stability.

[0063] (4) Aramid membrane coating and drying: Graphene composite slurry is uniformly coated onto the surface of the aramid base membrane (coating thickness is 0.8 micrometers). The PVP molecular chains in the slurry and the amide groups on the surface of the aramid base membrane form a preliminary interfacial bond through hydrogen bonds. At the same time, the graphene sheets in the slurry are uniformly distributed under the dispersion effect of PVP. A wet film is formed, first dried at room temperature and pressure, and then vacuum dried at ≤60 ℃ for ≥48h to remove the solvent, thus obtaining an aramid membrane with a graphene coating.

[0064] (5) Lithium battery preparation: Same as in Example 1.

[0065] Example 5

[0066] The preparation method of an aramid separator with graphene coating and a lithium battery is as follows: (1) Preparation of aramid-based film: The aramid slurry was diluted with DMAC to a solid content of 6%, stirred evenly, and the prepared aramid slurry solution was uniformly coated onto the PE base film (coating thickness of 2.5 micrometers). First, it was immersed in a 35% DMAC solution for 10 seconds to promote the relaxation of aramid molecular chains. Then, it was immersed in water for 20 seconds to trigger the exchange of DMAC with water, which caused the aramid molecular chains to embed into the micropores or rough structures on the surface of the PE base film, forming mechanical anchoring. Finally, it was dried in an oven at 55 ℃. The aramid-based film was then obtained.

[0067] (2) Preparation of graphene: Same as in Example 1.

[0068] (3) Preparation of graphene composite slurry: 3g of PVP-K30 (polyvinylpyrrolidone) was dissolved in a mixed solvent of 23g of ethylene glycol and 74g of deionized water and magnetically stirred at room temperature for 24h to prepare a dispersion; then 20g of graphene powder was added to the dispersion and magnetically stirred at room temperature for another 24h to obtain a graphene composite slurry with uniform dispersion and good stability.

[0069] (4) Aramid membrane coating and drying: Graphene composite slurry is uniformly coated on the surface of the aramid base membrane (coating thickness is 1.5 micrometers). The PVP molecular chains in the slurry and the amide groups on the surface of the aramid base membrane form a preliminary interface bond through hydrogen bonds. At the same time, the graphene sheets in the slurry are uniformly distributed under the dispersion effect of PVP. A wet film is formed, first dried at room temperature and pressure, and then vacuum dried at ≤60 ℃ for ≥48h to remove the solvent, thus obtaining an aramid membrane with a graphene coating.

[0070] (5) Lithium battery preparation: Same as in Example 1.

[0071] Comparative Example 1 An aramid separator and lithium battery were prepared using the same method as in Example 1, except that no graphene composite slurry was coated in this Comparative Example 1. The specific preparation method is as follows: (1) Preparation of aramid-based membrane: The aramid slurry was diluted with DMAC to a solid content of 5%, stirred evenly, and the prepared aramid slurry solution was uniformly coated onto the PE base membrane (coating thickness of 2 micrometers). First, it was immersed in a 40% DMAC solution for 10 seconds to promote the relaxation of aramid molecular chains. Then, it was immersed in water for 20 seconds to trigger the exchange of DMAC with water, which caused the aramid molecular chains to embed into the micropores or rough structures on the surface of the PE base membrane, forming mechanical anchoring. Finally, it was dried in an oven at 55 ℃. The aramid membrane was then obtained.

[0072] (1) Lithium battery preparation: Same as in Example 1.

[0073] Comparative Example 2 The preparation of an aramid separator with a graphene coating and a lithium battery follows the same method as in Example 1, except that PVP-K30 was not added in Comparative Example 2. The specific preparation method is as follows: (1) Preparation of aramid-based film: Same as in Example 1.

[0074] (2) Preparation of graphene: Same as in Example 1.

[0075] (3) Preparation of graphene composite slurry: Mix 24g of ethylene glycol and 71g of deionized water, add 11g of graphene powder, and stir magnetically at room temperature for 24h to obtain graphene composite slurry.

[0076] (4) Aramid diaphragm coating and drying: Same as in Example 1.

[0077] (5) Lithium battery preparation: Same as in Example 1.

[0078] Comparative Example 3 The preparation of an aramid separator with a graphene coating and a lithium battery follows the same method as in Example 1, except that the amount of PVP-K30 added is increased in Comparative Example 3. The specific preparation method is as follows: (1) Preparation of aramid-based film: Same as in Example 1.

[0079] (2) Preparation of graphene: Same as in Example 1.

[0080] (3) Preparation of graphene composite slurry: 10g of PVP-K30 (polyvinylpyrrolidone) was dissolved in a mixed solvent of 24g of ethylene glycol and 71g of deionized water, and the mixture was magnetically stirred at room temperature for 24h to prepare a dispersion with a mass fraction of 5%; then 11g of graphene powder was added to the dispersion, and the mixture was magnetically stirred at room temperature for another 24h to obtain graphene composite slurry.

[0081] (4) Aramid diaphragm coating and drying: Same as in Example 1.

[0082] (5) Lithium battery preparation: Same as in Example 1.

[0083] Comparative Example 4 The preparation of an aramid separator with a graphene coating and a lithium battery follows the same method as in Example 1, except that a coagulation bath was not used in Comparative Example 4. The specific preparation method is as follows: (1) Preparation of aramid base film: dilute the aramid slurry with DMAC to 5% solid content, stir evenly, and uniformly coat the prepared aramid slurry solution onto the PE base film (coating thickness is 2 micrometers), immerse in water for 20s, and finally dry in an oven at 55 ℃ to obtain the aramid base film.

[0084] (2) Preparation of graphene: Same as in Example 1.

[0085] (3) Preparation of graphene composite slurry: Same as in Example 1.

[0086] (4) Aramid diaphragm coating and drying: Same as in Example 1.

[0087] (5) Lithium battery preparation: Same as in Example 1.

[0088] Comparative Example 5 The preparation of an aramid separator with a graphene coating and a lithium battery follows the same method as in Example 1, except that the concentration of the coagulation bath is increased in Comparative Example 5. The specific preparation method is as follows: (1) Preparation of aramid-based film: The aramid slurry was diluted with DMAC to a solid content of 5%, stirred evenly, and the prepared aramid slurry solution was uniformly coated onto the PE base film (coating thickness of 2 micrometers). First, it was immersed in 60% DMAC solution for 10 seconds to promote the relaxation of aramid molecular chains. Then, it was immersed in water for 20 seconds to trigger the exchange of DMAC with water, which caused the aramid molecular chains to embed into the micropores or rough structures on the surface of the PE base film, forming mechanical anchoring. Finally, it was dried in an oven at 55 ℃. The aramid base film was then obtained.

[0089] (2) Preparation of graphene: Same as in Example 1.

[0090] (3) Preparation of graphene composite slurry: Same as in Example 1.

[0091] (4) Aramid diaphragm coating and drying: Same as in Example 1.

[0092] (5) Lithium battery preparation: Same as in Example 1.

[0093] Comparative Example 6 The preparation of an aramid separator with a graphene coating and a lithium battery follows the same method as in Example 1, except that the coating thickness ratio of the aramid slurry solution to the graphene composite slurry in Comparative Example 6 is 1:1. The specific preparation method is as follows: The preparation method of an aramid separator with graphene coating and a lithium battery is as follows: (1) Preparation of aramid-based film: The aramid slurry was diluted with DMAC to a solid content of 5%, stirred evenly, and the prepared aramid slurry solution was evenly coated onto the PE base film (coating thickness of 1.5 micrometers). The film was first immersed in 40% DMAC solution for 10 seconds, then immersed in water for 20 seconds, and finally dried in an oven at 55 ℃. The aramid-based film was then obtained.

[0094] (2) Preparation of graphene: Same as in Example 1.

[0095] (3) Preparation of graphene composite slurry: Same as in Example 1.

[0096] (4) Aramid membrane coating and drying: Graphene composite slurry is uniformly coated on the surface of aramid base membrane (coating thickness is 1.5 micrometers) to form a wet film. It is first dried at room temperature and pressure, and then vacuum dried at ≤60 ℃ for ≥48h to remove the solvent and obtain an aramid membrane with graphene coating.

[0097] (5) Lithium battery preparation: Same as in Example 1.

[0098] Comparative Example 7 The preparation of an aramid separator with a graphene coating and a lithium battery follows the same method as in Example 1, except that the mass ratio of PVP-K30 to graphene powder in Comparative Example 7 is 1:11. The specific preparation method is as follows: (1) Preparation of aramid-based film: The aramid slurry was diluted with DMAC to a solid content of 5%, stirred evenly, and the prepared aramid slurry solution was evenly coated onto the PE base film (coating thickness of 2.0 micrometers). It was first immersed in 35% DMAC solution for 10 seconds, then immersed in water for 20 seconds, and finally dried in an oven at 55 ℃. The aramid-based film can then be obtained.

[0099] (2) Preparation of graphene: Same as in Example 1.

[0100] (3) Preparation of graphene composite slurry: 3g of PVP-K30 (polyvinylpyrrolidone) was dissolved in a mixed solvent of 24g of ethylene glycol and 71g of deionized water and magnetically stirred at room temperature for 24h to prepare a dispersion with a mass fraction of 5%; then 33g of graphene powder was added to the dispersion and magnetically stirred at room temperature for another 24h to obtain graphene composite slurry.

[0101] (4) Aramid diaphragm coating and drying: Same as in Example 1.

[0102] (5) Lithium battery preparation: Same as in Example 1.

[0103] Comparative Example 8 The preparation of an aramid separator with a graphene coating and a lithium battery follows the same method as in Example 1, except that the mass concentration of DMAC in the coagulation bath in Comparative Example 8 is 35%, and the weight fraction of PVP-K30 is 6.0 parts. The specific preparation method is as follows: (1) Preparation of aramid-based film: The aramid slurry was diluted with DMAC to a solid content of 5%, stirred evenly, and the prepared aramid slurry solution was evenly coated onto the PE base film (coating thickness of 2 micrometers). The film was first immersed in 35% DMAC solution for 10 seconds, then immersed in water for 20 seconds, and finally dried in an oven at 55 ℃. The aramid-based film can then be obtained.

[0104] (2) Preparation of graphene: Same as in Example 1.

[0105] (3) Preparation of graphene composite slurry: 6.0g of PVP-K30 (polyvinylpyrrolidone) was dissolved in a mixed solvent of 24g of ethylene glycol and 71g of deionized water and magnetically stirred at room temperature for 24h to prepare a dispersion with a mass fraction of 5%; then 11g of graphene powder was added to the dispersion and magnetically stirred at room temperature for another 24h to obtain graphene composite slurry.

[0106] (4) Aramid diaphragm coating and drying: Same as in Example 1.

[0107] (5) Lithium battery preparation: Same as in Example 1.

[0108] Comparative Example 9 The preparation of an aramid separator with a graphene coating and a lithium battery follows the same method as in Example 1, except that the mass concentration of DMAC in the coagulation bath in Comparative Example 9 is 45%, and the weight fraction of PVP-K30 is 3.0 parts. The specific preparation method is as follows: (1) Preparation of aramid-based film: The aramid slurry was diluted with DMAC to a solid content of 5%, stirred evenly, and the prepared aramid slurry solution was evenly coated onto the PE base film (coating thickness of 2 micrometers). The film was first immersed in 45% DMAC solution for 10 seconds, then immersed in water for 20 seconds, and finally dried in an oven at 55 ℃. The aramid-based film can then be obtained.

[0109] (2) Preparation of graphene: Same as in Example 1.

[0110] (3) Preparation of graphene composite slurry: 3.0g of PVP-K30 (polyvinylpyrrolidone) was dissolved in a mixed solvent of 24g of ethylene glycol and 71g of deionized water and magnetically stirred at room temperature for 24h to prepare a dispersion with a mass fraction of 5%; then 11g of graphene powder was added to the dispersion and magnetically stirred at room temperature for another 24h to obtain graphene composite slurry.

[0111] (4) Aramid diaphragm coating and drying: Same as in Example 1.

[0112] (5) Lithium battery preparation: Same as in Example 1.

[0113] Comparative Example 10 The preparation of an aramid separator with a graphene coating and a lithium battery follows the same method as in Example 1, except that the polyvinylpyrrolidone used in Comparative Example 10 is PVP-K15. The specific preparation method is as follows: (1) Preparation of aramid-based film: Same as in Example 1.

[0114] (2) Preparation of graphene: Same as in Example 1.

[0115] (3) Preparation of graphene composite slurry: 5g of PVP-K15 (polyvinylpyrrolidone) was dissolved in a mixed solvent of 24g of ethylene glycol and 71g of deionized water and magnetically stirred at room temperature for 24h to prepare a dispersion with a mass fraction of 5%; then 11g of graphene powder was added to the dispersion and magnetically stirred at room temperature for another 24h to obtain graphene composite slurry.

[0116] (4) Aramid diaphragm coating and drying: Same as in Example 1.

[0117] (5) Lithium battery preparation: Same as in Example 1.

[0118] Comparative Example 11 In Comparative Example 11, graphene and PVP-K30 were directly added to the aramid slurry solution for one-step coating. The specific preparation method is as follows: (1) Preparation of graphene: Same as in Example 1.

[0119] (2) Aramid membrane coating and drying: The aramid slurry was diluted with DMAC to a solid content of 5%, and graphene and PVP-K30 were added (wherein, the mass content of graphene in the composite solution is 2.5%, and the mass content of PVP-K30 in the composite solution is 1.2%). The mixture was stirred evenly, and the prepared composite solution was uniformly coated onto the PE base film (coating thickness is 3 micrometers). The film was first immersed in 40% DMAC solution for 10 seconds, then immersed in water for 20 seconds, and finally placed in an oven at 55 ℃ for vacuum drying to obtain an aramid membrane with graphene coating.

[0120] (3) Lithium battery preparation: Same as in Example 1.

[0121] The separators and lithium batteries prepared in the above embodiments and comparative examples were subjected to performance tests, and the test methods involved were as follows: (1) Heat shrinkage rate test: The diaphragm was heat-treated in ovens at 130℃, 150℃, and 180℃ for 30 minutes to study the dimensional changes of the diaphragm before and after heat treatment.

[0122] (2) Electrochemical performance testing: Ionic conductivity was determined using AC impedance spectroscopy. A coin cell (SS / separator / SS) was assembled by placing the membrane material between two stainless steel electrodes (SS), and the test was performed using a CHI760E with a frequency range of 0.01-10. 6 For an AC signal amplitude of 5mV, the ionic conductivity σ is calculated as follows: σ = d / (Rb × S).

[0123] Where d is the thickness of the diaphragm (μm), the bulk resistance Rb (Ω) of the diaphragm can be obtained from the intersection of the real and imaginary axes of the corresponding EIS spectrum, and S represents the effective contact area between the diaphragm and the electrode (cm²). 2 ).

[0124] (3) Air permeability test: Air permeability refers to the time required for a specific amount of air to pass through a membrane of a specific area under a specific pressure, and is expressed by the Gurley value. An air permeability tester (4110N, Gurley) is used to determine the time it takes for air to pass through a membrane sample under conditions of 100cc of gas, a certain pressure, and a certain area. (Gurley value (unit: s / 100cc) represents the time required for 100mL of air to pass through a membrane sample with an area of ​​1 square inch under a constant pressure difference of 1.22kPa).

[0125] (4) Cyclic performance test: The battery's long-cycle performance test setup was as follows: First, two cycles were performed in a constant current charge-constant voltage charge-constant current discharge mode at a current density of 0.1C. Then, cycles were performed in the same charge-discharge mode at 1C, and the battery's capacity retention rate was measured after 100 cycles.

[0126] (4) Puncture strength: Cut the diaphragm into strips measuring 10cm × 20cm. Place the strips flat in the testing instrument and clamp them with a special clamp. Once ready, turn on the testing instrument and move the needle at a speed of 10mm / min. The strength value at which the needle punctures the diaphragm is the puncture strength of the diaphragm.

[0127] The specific test results are shown in Table 1 below.

[0128] Table 1 Performance Test Results

[0129] The data above shows that Examples 1-5 are aramid separators prepared using the method of this invention. These graphene-coated aramid separators exhibit excellent thermal stability, mechanical strength, ionic conductivity, and lithium dendrite suppression. When applied to lithium batteries, they can significantly improve battery safety and electrochemical performance. Furthermore, the preparation process is simple, cost-effective, and widely adaptable, showing broad development prospects in new energy power batteries, energy storage batteries, and other fields. Figure 2 The SEM images show that the membrane surface prepared by the method of the present invention exhibits a porous morphology, which provides abundant transport channels for lithium ions, and the porous structure enhances the wettability and retention capacity of the electrolyte.

[0130] Comparison of experimental results between Comparative Example 1 and Example 1, and Figure 3 , Figure 4 As can be seen, compared with aramid-coated membranes, the graphene-coated aramid membrane of this invention exhibits better cycling stability and capacity retention at the same cycle number, with a capacity retention of over 97% after 100 cycles at a 1c rate. Furthermore, the graphene-coated aramid membrane of this invention demonstrates superior ionic conductivity, increasing to 0.602 mS / cm.

[0131] A comparison of the experimental results from Comparative Example 2 and Example 1 shows that without the addition of PVP-K30, the graphene sheets agglomerated severely due to van der Waals forces, failing to disperse evenly in the slurry and coating. This resulted in localized concentration of conductive material and significant mechanical defects in the coating. Furthermore, the lack of hydrogen bond anchoring points between the graphene coating and the aramid film surface significantly weakened the interfacial bonding, making the coating prone to peeling off during cycling and resulting in a marked decrease in the membrane's cycling stability.

[0132] A comparison of the experimental results from Comparative Example 3 and Example 1 shows that increasing the amount of PVP-K30 results in an excessively high concentration of free PVP molecules in the slurry. After coating, a large amount of PVP penetrates deep into the pores of the aramid membrane or accumulates at the pore openings, blocking the lithium-ion transport pathways and significantly reducing the membrane's ionic conductivity. Simultaneously, excessive PVP increases the slurry viscosity and reduces coating uniformity, negatively impacting the dispersion of graphene and the overall coating quality.

[0133] A comparison of the experimental results of Comparative Example 4 and Example 1 shows that if the aramid liquid film is directly immersed in the coagulation bath without its own coagulation bath, a violent solvent-non-solvent exchange occurs on the surface, resulting in instantaneous solidification and the formation of a dense skin layer with uneven pore size distribution and poor permeability. This not only increases the ion transport resistance of the membrane itself but also prevents subsequent PVP molecules from forming a uniform anchor on the surface, reduces the adhesion of the graphene coating, and hinders the internal pores from fully utilizing their ion conduction function due to structural defects.

[0134] A comparison of the experimental results from Comparative Example 5 and Example 1 shows that if the concentration of the coagulation bath is increased beyond the limits defined in this invention, the DMAC concentration difference between the coagulation bath and the subsequent water coagulation bath increases dramatically. When the aramid liquid membrane is transferred from a high-concentration coagulation bath to a pure water coagulation bath, the driving force for solvent-non-solvent exchange between the two baths is significantly enhanced, and the phase transformation process is too violent, resulting in a large number of irregular finger-like macropores and even penetrating defects inside the aramid membrane. Although the surface skin is thick, its structure is loose and contains microcracks. This non-ideal pore structure not only reduces the mechanical strength and ion selectivity of the membrane, but also causes uneven penetration of the subsequently coated PVP and graphene slurry along the defects, damaging the coating integrity, reducing interfacial adhesion, and ultimately leading to a deterioration in the overall performance of the membrane.

[0135] A comparison of the experimental results from Comparative Example 6 and Example 1 shows that if the coating thickness ratio of the aramid slurry solution to the graphene composite slurry is 1:1 (not conforming to (1.5-2.0):1), then the aramid layer thickness is slightly insufficient compared to the graphene composite slurry thickness. This affects the formation of a continuous, defect-free electronic insulating barrier, and the conductive network of the surface graphene may partially penetrate into the base film or electrode, posing a certain risk of micro-short circuits. Simultaneously, an excessively thin aramid layer reduces its ability to act as an elastic buffer layer, and stress concentration during cycling can easily lead to cracking or peeling of the graphene layer, resulting in a slight decrease in interface stability.

[0136] A comparison of the experimental results from Comparative Example 7 and Example 1 shows that if the mass ratio of PVP-K30 to graphene powder is 1:11 (which does not meet the requirement of 1:(2-7)), the PVP content cannot adequately cover the graphene sheets with steric hindrance, resulting in decreased dispersibility of graphene in the slurry. Simultaneously, the PVP molecular chains adsorbed on the graphene surface have too few free carbonyl sites, leading to low hydrogen bond density between the coating and the aramid film, reduced interfacial adhesion, and easy detachment of the graphene coating during cycling, thus decreasing the long-term cycling stability of the membrane.

[0137] A comparison of the experimental results of Comparative Example 8 and Example 1 shows that if the mass concentration of DMAC in the coagulation bath is 35% and the weight of PVP-K30 is 6.0 parts (which does not meet the requirement that "when the mass concentration of DMAC in the coagulation bath is ≥35% and <40%, the weight of PVP-K30 in the graphene composite slurry is 3.0-4.5 parts"), then a mismatch of "low concentration coagulation bath - high PVP dosage" is formed. Under a 35% coagulation bath, the pore size of the aramid membrane surface is relatively small, and 6.0 parts of PVP makes the free PVP concentration and osmotic pressure in the slurry relatively high. PVP will penetrate into the depth of the aramid membrane and accumulate, resulting in the blockage of ion transport channels. The ionic conductivity of the separator is reduced, and the rate performance of the battery is also reduced.

[0138] A comparison of the experimental results of Comparative Example 9 and Example 1 shows that if the mass concentration of DMAC in the coagulation bath is 45% and the weight fraction of PVP-K30 is 3.0 parts (which does not meet the requirement that "when the mass concentration of DMAC in the coagulation bath is ≥40% and ≤45%, the weight fraction of PVP-K30 in the graphene composite slurry is 4.6-6.0 parts"), then a mismatch of "high concentration coagulation bath - low PVP dosage" is formed. Under a 45% coagulation bath, the pore size of the aramid membrane surface is small and dense. Although PVP is intercepted on the surface, the total amount of 3.0 parts is insufficient to form a sufficiently continuous hydrogen bond network between graphene and aramid. This reduces the interfacial adhesion of the coating, making it prone to peeling and detachment during cycling, thus affecting the final cycle performance of the battery.

[0139] A comparison of the experimental results of Comparative Example 10 and Example 1 shows that if the molecular weight of the polyvinylpyrrolidone used is too low, the steric hindrance effect is insufficient, resulting in poor graphene dispersion; if the molecular weight is too high, the slurry viscosity is too high, the coating uniformity decreases, and it is more likely to form a film and clog pores on the aramid membrane surface. The molecular weight range of PVP-K30 used in this invention can take into account the comprehensive requirements of dispersion, adhesion, and anti-clogging, which is more conducive to obtaining a membrane with excellent overall performance.

[0140] A comparison of the experimental results of Comparative Example 11 and Example 1 shows that if graphene and PVP-K30 are directly added to the aramid slurry solution and coated in a one-step process, the graphene and aramid are mixed in the same coating, making it impossible to achieve the functional separation design of this invention. Graphene runs through the entire coating, and if there is uneven dispersion in some areas, a continuous conductive network is formed, posing a risk of micro-short circuits. Furthermore, after aramid and graphene are mixed, the insulating and heat-resistant framework function of aramid and the planar thermal conductivity function of graphene cannot be separately utilized, resulting in the loss of the thermo-electric synergistic effect. The aramid separator with graphene coating described in this invention consists of an aramid base film and a graphene composite coating. The graphene composite coating is coated on the surface of the aramid base film. This separator is applied between the positive and negative electrodes of a lithium battery as a separating component, enabling smooth lithium ion transport, inhibiting lithium dendrite growth, preventing short circuits between the positive and negative electrodes, and simultaneously improving the thermal stability and cycle performance of the lithium battery.

[0141] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0142] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing an aramid membrane with a graphene coating, characterized in that, The preparation method is as follows: S1. Aramid slurry solution is coated onto a PE base film, and then the film is formed by coagulation bath and water treatment, and then dried to obtain an aramid base film. S2. After coating the surface of the aramid-based membrane with graphene composite slurry, the membrane is dried to obtain an aramid membrane with a graphene coating. The graphene composite slurry comprises polyvinylpyrrolidone, ethylene glycol, deionized water, and graphene powder; The graphene composite slurry comprises, by weight, 3-6 parts polyvinylpyrrolidone, 23-25 ​​parts ethylene glycol, 70-74 parts deionized water, and 11-34 parts graphene powder; the polyvinylpyrrolidone is PVP-K30. The mass ratio of PVP-K30 to graphene powder is 1:(2-7). The coagulation bath is a DMAC solution with a mass concentration of 35%-45%; When the mass concentration of DMAC in the coagulation bath is ≥35% and <40%, the weight fraction of PVP-K30 in the graphene composite slurry is 3.0-4.5 parts; when the mass concentration of DMAC in the coagulation bath is ≥40% and ≤45%, the weight fraction of PVP-K30 in the graphene composite slurry is 4.6-6.0 parts. The ratio of the coating thickness of the aramid slurry solution to the coating thickness of the graphene composite slurry is (1.5-2.0):

1.

2. The method for preparing an aramid membrane with a graphene coating according to claim 1, characterized in that, The aramid slurry solution is a DMAC solution of poly(m-phenylene isophthalamide) with a mass concentration of 4%-6%.

3. The method for preparing an aramid membrane with a graphene coating according to claim 1, characterized in that, In step S1, after coating the aramid slurry solution onto the PE base film, it is first immersed in a coagulation bath for 10-15 seconds, then immersed in water for 20-30 seconds, and dried at 50-60℃ to obtain the aramid base film.

4. The method for preparing an aramid membrane with a graphene coating according to claim 1, characterized in that, In step S1, the coating thickness of the aramid slurry solution is 1.5-2.5 micrometers; in step S2, the coating thickness of the graphene composite slurry is 0.8-1.5 micrometers.

5. The method for preparing an aramid membrane with a graphene coating according to claim 1, characterized in that, The graphene composite slurry is prepared by dissolving polyvinylpyrrolidone in a mixed solvent of ethylene glycol and deionized water, mixing them evenly to obtain a dispersion, and then adding graphene powder to obtain the graphene composite slurry.

6. An aramid separator with a graphene coating, characterized in that, The aramid membrane is prepared according to the preparation method described in any one of claims 1-5.

7. An application of the aramid membrane with a graphene coating according to claim 6, characterized in that, The aramid separator is used in lithium batteries.

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