Method for preparing magnesium diboride nanoplatelets, magnesium diboride nanoplatelets, coating slurry, battery separator, battery, battery pack, and electric device

Abstract

The application provides a preparation method of magnesium diboride nanosheets, magnesium diboride nanosheets, coating slurry, a battery separator, a battery, a battery pack and an electric device, and particularly relates to the technical field of separator materials. The preparation method of the magnesium diboride nanosheets comprises the following steps: uniformly mixing magnesium diboride particles, water, tetrabutylammonium hydroxide (TBAH) and cetyltrimethylammonium bromide (CTAB) and ultrasonicating, and then performing solid-liquid separation after standing; taking supernatant, dialysis and freezing, and then performing freeze-drying to obtain the magnesium diboride nanosheets. The method does not require high temperature and high pressure or strong oxidation / reduction conditions, is simple to operate and has mild conditions, the obtained nanosheets have high specific surface area and good colloidal stability, and the processability of the magnesium diboride in a dispersion medium and the subsequent functional application potential are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of membrane material technology, and in particular to a method for preparing magnesium diboride nanosheets, magnesium diboride nanosheets, coating slurry, battery separator, battery, battery pack and electrical device. Background Technology

[0002] Lithium-ion batteries, as the mainstream electrochemical energy storage device, have been widely used in consumer electronics, new energy vehicles, and large-scale energy storage systems due to their high energy density, long cycle life, and good safety and reliability. Their core structure consists of a positive electrode, a negative electrode, a separator, and an electrolyte. The separator, as a key inner component for physically isolating the active materials of the positive and negative electrodes, has dual functions of "insulation and blocking" and "ion conduction": it must effectively prevent short circuits caused by direct contact between the positive and negative electrodes, and also provide a low-impedance, uniformly connected lithium-ion transport channel. Therefore, the physicochemical properties of the separator (such as thermal stability, mechanical strength, porosity, wettability, and interfacial bonding) directly restrict the battery's energy efficiency, cycle retention rate, and intrinsic safety level.

[0003] Currently, commercially available lithium-ion batteries generally use polyolefin microporous membranes, mainly including single-layer or multi-layer composite membranes of polypropylene (PP) and polyethylene (PE). These materials offer advantages such as low cost, mature pore-forming technology, and uniform pore size distribution, making them the mainstream choice in the industry. However, their inherent material properties also present significant application bottlenecks: 1. Insufficient thermal stability: PP has a melting point of about 165℃, while PE has a melting point of only about 135℃. Under conditions such as high-rate charging and discharging, long-term storage in high-temperature environments, or local abnormal temperature rise (such as overcharging or the initial stage of internal short circuit), the separator is prone to irreversible thermal shrinkage or even melting and collapse, which leads to the failure of physical isolation between the positive and negative electrodes, induces internal short circuit, and further aggravates the risk of thermal runaway. 2. Performance trade-offs in modification schemes: To improve heat resistance, the industry often uses inorganic ceramic particle coating modification. However, this strategy introduces new problems: the ceramic phase itself has extremely low ionic conductivity, and excessively thick coatings or high coverage will significantly increase lithium-ion migration resistance, raise the overall internal resistance of the battery, and deteriorate rate performance and low-temperature adaptability; the single-layer ceramic coating has weak interfacial bonding with the base film, and during long-term battery cycling, it is prone to coating cracking, peeling, or even pulverization under the repeated breathing-type volume expansion / contraction stress of the negative electrode, leading to the risk of thermal failure in the exposed base film area, weakening the long-term effectiveness and reliability of the modification.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing magnesium diboride nanosheets, magnesium diboride nanosheets, coating slurry, battery separator, battery, battery pack, and electrical device, aiming to solve at least one of the above-mentioned technical problems in the prior art.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: The first aspect of the present invention provides a method for preparing magnesium diboride nanosheets, wherein magnesium diboride particles, water, tetrabutylammonium hydroxide (TBAH) and hexadecyltrimethylammonium bromide (CTAB) are mixed and sonicated, and then separated into solid and liquid components after standing; the supernatant is dialyzed, frozen, and freeze-dried to obtain magnesium diboride nanosheets.

[0007] Furthermore, the particle size of the magnesium diboride particles is 0.8~1μm.

[0008] Preferably, the amount of water added is 30-40 wt% of the magnesium diboride particles.

[0009] Preferably, the amount of tetrabutylammonium hydroxide added is 3-4 wt% of the magnesium diboride particles.

[0010] Preferably, the amount of hexadecyltrimethylammonium bromide added is 0.3~0.4 wt% of the magnesium diboride particles.

[0011] Furthermore, the frequency of the ultrasound is 60~80KHz, and the duration is 60~120min.

[0012] Preferably, the settling time is 8 to 16 hours.

[0013] Preferably, the solid-liquid separation method includes centrifugation.

[0014] Preferably, the centrifugation speed is 6000~10000 rpm and the time is 10~30 min.

[0015] Furthermore, in the dialysis, deionized water is used as the dialysis medium.

[0016] Preferably, the dialysis time is 48-96 hours, and the dialysis medium is changed every 8-16 hours.

[0017] Preferably, the freezing temperature is -22 to -18°C.

[0018] Preferably, the freeze-drying temperature is -50 to -30°C and the time is 36 to 60 hours.

[0019] The second aspect of the present invention provides a magnesium diboride nanosheet, which is prepared by the preparation method described in the first aspect; wherein the thickness of the magnesium diboride nanosheet is 120~200 nm.

[0020] The third aspect of the present invention provides a coating slurry, comprising, by weight, 12-25 parts of magnesium diboride nanosheets, 3-8 parts of a functional polymer, 0.8-2 parts of an epoxy silane crosslinking agent, and 48-75 parts of a solvent; wherein the magnesium diboride nanosheets are the magnesium diboride nanosheets described in the second aspect.

[0021] Furthermore, the functional polymer includes at least one of lithium polyacrylate, polyacrylonitrile, polyvinylidene fluoride copolymer, and polyvinyl alcohol.

[0022] Preferably, the epoxy silane crosslinking agent comprises at least one of trimethylolpropane triglycidyl ether, γ-glycidyl etheroxysilylpropyl sesquioxane, and a trifunctional aziridine crosslinking agent.

[0023] Preferably, the solvent comprises water and / or N-methylpyrrolidone.

[0024] Furthermore, the coating slurry also includes 0-1 parts of dispersant and 0-0.5 parts of wetting agent.

[0025] Preferably, the dispersant comprises at least one of sodium polyacrylate, lithium polyacrylate, potassium polyacrylate, and ammonium polyacrylate.

[0026] Preferably, the wetting agent includes at least one of ether-based wetting agents, polyether-modified siloxanes, and acetylenic diol-based wetting agents.

[0027] A fourth aspect of the present invention provides a battery separator, comprising a base film and a coating on the surface of the base film; wherein the coating is obtained by coating, drying and curing the coating slurry described in the third aspect.

[0028] Furthermore, the thickness of the coating is 1~5μm.

[0029] Preferably, the drying and curing temperature is 70~90℃ and the time is 1~3h.

[0030] Preferably, the membrane is made of polyolefin.

[0031] Preferably, the thickness of the diaphragm is 9~25μm.

[0032] A fifth aspect of the present invention provides a battery including the aforementioned battery separator.

[0033] A sixth aspect of the present invention provides a battery pack including the battery.

[0034] A seventh aspect of the present invention provides an electrical device, including the battery or the battery pack described above.

[0035] Compared with the prior art, the present invention has at least the following beneficial effects: The preparation method provided by this invention involves mixing magnesium diboride particles with water, TBAH, and CTAB, followed by ultrasonic treatment. TBAH provides a strongly alkaline environment to weaken interlayer bonds, while CTAB's amphiphilic structure adsorbs onto the magnesium diboride surface and provides steric hindrance to stabilize the exfoliated nanosheets. After static separation and solid-liquid separation, a stable supernatant is obtained. This supernatant is then dialyzed to remove free surfactants and small molecule impurities, followed by freeze-drying to finally obtain magnesium diboride nanosheets with uniform morphology and controllable thickness. This method requires no high temperature, high pressure, or strong oxidation / reduction conditions, is simple to operate, and operates under mild conditions. The resulting nanosheets exhibit high specific surface area and good colloidal stability, significantly improving the processability and potential for subsequent functionalization of magnesium diboride in dispersion media.

[0036] The coating slurry provided by this invention uses magnesium diboride nanosheets as a functional filler, which, together with functional polymers, provides film-forming properties and mechanical support. During film formation, the epoxy silane crosslinking agent undergoes a condensation reaction with the polymer and the hydroxyl groups on the nanosheet surface, constructing a three-dimensional crosslinked network, significantly improving the coating's cohesive strength and interfacial adhesion. The solvent ensures the slurry has suitable solids content and rheological properties, meeting the requirements of the coating process. Due to its high thermal conductivity, high melting point, and intrinsic chemical inertness, the magnesium diboride nanosheets form continuous thermal / electrical pathways in the coating and prevent heat accumulation, effectively suppressing localized temperature rise. Its nanoscale two-dimensional morphology can also fill the micropores of the polymer matrix, enhancing density. The synergistic effect of the components results in a coating with excellent thermal stability, structural integrity, and process adaptability, suitable for applications with stringent safety and reliability requirements, such as heat-resistant modification of lithium battery separators.

[0037] Given the excellent high-temperature dimensional stability and thermal barrier capabilities of the aforementioned battery separator, thermal shrinkage and melt collapse under high-rate / high-temperature conditions are significantly suppressed; at the same time, it maintains low ion transport resistance, maintains high-rate performance and cycle life of batteries, battery packs and electrical devices, and improves the thermal safety redundancy and long-term service reliability of lithium batteries from the source. Attached Figure Description

[0038] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0039] Figure 1 Here is a scanning electron microscope image of the magnesium diboride nanosheets prepared in Example 1; Figure 2Transmission electron microscopy (TEM) image of magnesium diboride nanosheets prepared in Example 1; Figure 3 This is a schematic diagram of the battery pack provided by the present invention; Figure 4 This is a schematic diagram of the electrical device provided by the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0041] In the following, the terms “comprising,” “having,” and their cognates, which may be used in various embodiments of the invention, are intended only to indicate a particular feature, number, step, operation, element, component, or combination thereof, and should not be construed as excluding, firstly, the presence of one or more other features, numbers, steps, operations, elements, components, or combinations thereof, or adding the possibility of one or more features, numbers, steps, operations, elements, components, or combinations thereof.

[0042] The first aspect of the present invention provides a method for preparing magnesium diboride nanosheets, wherein magnesium diboride particles, water, tetrabutylammonium hydroxide (TBAH) and hexadecyltrimethylammonium bromide (CTAB) are mixed and sonicated, and then separated into solid and liquid components after standing; the supernatant is dialyzed, frozen, and freeze-dried to obtain magnesium diboride nanosheets.

[0043] The preparation method provided by this invention involves mixing magnesium diboride particles with water, TBAH, and CTAB, followed by ultrasonic treatment. TBAH provides a strongly alkaline environment to weaken interlayer bonds, while CTAB's amphiphilic structure adsorbs onto the magnesium diboride surface and provides steric hindrance to stabilize the exfoliated nanosheets. After static separation and solid-liquid separation, a stable supernatant is obtained. This supernatant is then dialyzed to remove free surfactants and small molecule impurities, followed by freeze-drying to finally obtain magnesium diboride nanosheets with uniform morphology and controllable thickness. This method requires no high temperature, high pressure, or strong oxidation / reduction conditions, is simple to operate, and operates under mild conditions. The resulting nanosheets exhibit high specific surface area and good colloidal stability, significantly improving the processability and potential for subsequent functionalization of magnesium diboride in dispersion media.

[0044] Furthermore, the particle size of the magnesium diboride particles is 0.8~1μm.

[0045] Preferably, the amount of water added is 30-40 wt% of the magnesium diboride particles, providing a suitable liquid phase environment that is sufficient to support the alkaline dissociation of TBAH and the formation of CTAB micelles, promoting the weakening of MgB2 interlayer bonds and surface adsorption stability, while avoiding excessive dilution that would lead to a decrease in ultrasonic exfoliation efficiency and an increase in energy consumption for subsequent dialysis / lyophilization. This falls within the optimized range that balances exfoliation efficiency, dispersion stability, and process economy.

[0046] Typically, but not limitingly, the amount of water added can be, for example, 30 wt%, 32 wt%, 34 wt%, 36 wt%, 38 wt%, or 40 wt% of the magnesium diboride particles, or any value in the range of 30 to 40 wt%.

[0047] Preferably, the amount of tetrabutylammonium hydroxide added is 3-4 wt% of the magnesium diboride particles, which can provide sufficiently strong alkalinity (OH-). - This weakens the Mg-B bonds between MgB2 layers while avoiding excessive side reactions; below 3 wt% results in insufficient peeling, low yield, and thick sheets; above 4 wt% can easily cause edge etching of nanosheets, structural damage, and subsequent pH mismatch in slurry, impairing the film-forming properties and interface stability of the coating.

[0048] Typically, but not limitingly, the amount of tetrabutylammonium hydroxide added can be, for example, 3 wt%, 3.2 wt%, 3.4 wt%, 3.6 wt%, 3.8 wt%, or 4 wt% of the magnesium diboride particles, or any value in the range of 3 to 4 wt%.

[0049] Preferably, the amount of hexadecyltrimethylammonium bromide added is 0.3~0.4 wt% of the magnesium diboride particles, which can provide just the right amount of amphiphilic adsorption and steric stabilization during the exfoliation process, effectively preventing nanosheet aggregation and maintaining the long-term dispersion of the colloid. If the amount is less than 0.3 wt%, the surface coverage is insufficient, leading to re-stabilization or sedimentation. If the amount is more than 0.4 wt%, excessive CTAB will form free micelles, which will interfere with dialysis purification, remain on the surface of the nanosheets and weaken their interfacial reaction activity with the polymer / crosslinking agent, and may degrade the ionic conductivity and thermal stability of the coating.

[0050] Typically, but not limitingly, the amount of hexadecyltrimethylammonium bromide added can be, for example, 0.3 wt%, 0.32 wt%, 0.34 wt%, 0.36 wt%, 0.38 wt%, or 0.4 wt% of the magnesium diboride particles, or any value in the range of 0.3 to 0.4 wt%.

[0051] Furthermore, the frequency of the ultrasound is 60~80KHz, and the duration is 60~120min.

[0052] Typical, but not limiting, ultrasound duration can be, for example, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, or 120 min, or any value within the range of 60 to 120 min.

[0053] Preferably, the settling time is 8 to 16 hours.

[0054] Typical, but not restrictive, resting time can be, for example, 8h, 10h, 12h, 14h or 16h, or any value within the range of 8 to 16h.

[0055] Preferably, the solid-liquid separation method includes centrifugation.

[0056] Preferably, the centrifugation speed is 6000~10000 rpm and the time is 10~30 min.

[0057] Typically, but not limitingly, the centrifugation speed can be, for example, 6000 rpm, 7000 rpm, 8000 rpm, 9000 rpm, or 10000 rpm, or any value within the range of 6000 to 10000 rpm; the centrifugation time can be, for example, 10 min, 15 min, 20 min, 25 min, or 30 min, or any value within the range of 10 to 30 min.

[0058] Furthermore, in the dialysis, deionized water is used as the dialysis medium to selectively remove free TBAH, CTAB and their degraded small molecule impurities, while avoiding the introduction of electrolytes such as metal ions that interfere with the surface charge stability of the nanosheets and the compatibility of the subsequent slurry, thus ensuring the purity of the magnesium diboride nanosheet dispersion and the interfacial reactivity.

[0059] Preferably, the dialysis time is 48-96 hours, and the dialysis medium is changed every 8-16 hours.

[0060] Typical, but not limiting, dialysis time can be, for example, 48h, 56h, 64h, 72h, 80h, 88h or 96h, or any value within the range of 48 to 96h; the interval for changing dialysis media can be, for example, 8h, 10h, 12h, 14h or 16h, or any value within the range of 8 to 16h.

[0061] Preferably, the freezing temperature is -22 to -18°C.

[0062] Typical, but not limiting, freezing temperatures can be, for example, -22°C, -21°C, -20°C, -19°C, or -18°C, or any value within the range of -22°C to -18°C.

[0063] Preferably, the freeze-drying temperature is -50 to -30°C and the time is 36 to 60 hours.

[0064] Typically, but not limitingly, the freeze-drying temperature can be, for example, -50°C, -45°C, -40°C, -35°C, or -30°C, or any value within the range of -50°C to -30°C; the freeze-drying time can be, for example, 36h, 42h, 48h, 54h, or 60h, or any value within the range of 36 to 60h.

[0065] Freezing is used to quickly solidify the nanosheet dispersion into a uniform ice crystal structure, fix the spatial distribution of the nanosheets, and prevent agglomeration. Then freeze-drying removes the ice phase directly under low temperature and low pressure, avoiding the stacking or structural collapse of nanosheets caused by the surface tension of the liquid phase, thus preserving its two-dimensional morphology, high specific surface area and colloidal redispersibility.

[0066] The second aspect of the present invention provides a magnesium diboride nanosheet, which is prepared by the preparation method described in the first aspect; wherein the thickness of the magnesium diboride nanosheet is 120~200 nm.

[0067] The third aspect of the present invention provides a coating slurry, comprising, by weight, 12-25 parts of magnesium diboride nanosheets, 3-8 parts of a functional polymer, 0.8-2 parts of an epoxy silane crosslinking agent, and 48-75 parts of a solvent; wherein the magnesium diboride nanosheets are the magnesium diboride nanosheets described in the second aspect.

[0068] The coating slurry provided by this invention uses magnesium diboride nanosheets as a functional filler, which, together with functional polymers, provides film-forming properties and mechanical support. During film formation, the epoxy silane crosslinking agent undergoes a condensation reaction with the polymer and the hydroxyl groups on the nanosheet surface, constructing a three-dimensional crosslinked network, significantly improving the coating's cohesive strength and interfacial adhesion. The solvent ensures the slurry has suitable solids content and rheological properties, meeting the requirements of the coating process. Due to its high thermal conductivity, high melting point, and intrinsic chemical inertness, the magnesium diboride nanosheets form continuous thermal / electrical pathways in the coating and prevent heat accumulation, effectively suppressing localized temperature rise. Its nanoscale two-dimensional morphology can also fill the micropores of the polymer matrix, enhancing density. The synergistic effect of the components results in a coating with excellent thermal stability, structural integrity, and process adaptability, suitable for applications with stringent safety and reliability requirements, such as heat-resistant modification of lithium battery separators.

[0069] Typically, but not limitingly, the magnesium diboride nanosheets in the coating slurry may be, for example, 12 parts, 15 parts, 18 parts, 21 parts, 23 parts, or 25 parts by weight, or any value within the range of 12 to 25 parts; the functional polymer may be, for example, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, or 8 parts, or any value within the range of 3 to 8 parts; the epoxy silane crosslinking agent may be, for example, 0.8 parts, 1.0 parts, 1.2 parts, 1.4 parts, 1.6 parts, 1.8 parts, or 2 parts, or any value within the range of 0.8 to 2 parts; the solvent may be, for example, 48 parts, 55 parts, 62 parts, 68 parts, 72 parts, or 75 parts, or any value within the range of 48 to 75 parts.

[0070] Furthermore, the functional polymer includes at least one of lithium polyacrylate, polyacrylonitrile, polyvinylidene fluoride copolymer, and polyvinyl alcohol.

[0071] Preferably, the epoxy silane crosslinking agent comprises at least one of trimethylolpropane triglycidyl ether, γ-glycidyl etheroxysilylpropyl sesquioxane, and a trifunctional aziridine crosslinking agent.

[0072] Preferably, the solvent comprises water and / or N-methylpyrrolidone.

[0073] Furthermore, the coating slurry also includes 0-1 parts of dispersant and 0-0.5 parts of wetting agent.

[0074] Typically, but not limitingly, the dispersant in the coating slurry can be, for example, 0 parts, 0.2 parts, 0.4 parts, 0.6 parts, 0.8 parts, or 1 part, or any value in the range of 0 to 1 part; the wetting agent can be, for example, 0 parts, 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, or 0.5 parts, or any value in the range of 0 to 0.5 parts.

[0075] Preferably, the dispersant comprises at least one of sodium polyacrylate, lithium polyacrylate, potassium polyacrylate, and ammonium polyacrylate.

[0076] Preferably, the wetting agent includes at least one of ether-based wetting agents, polyether-modified siloxanes, and acetylenic diol-based wetting agents.

[0077] A fourth aspect of the present invention provides a battery separator, comprising a base film and a coating on the surface of the base film; wherein the coating is obtained by coating, drying and curing the coating slurry described in the third aspect.

[0078] Furthermore, the thickness of the coating is 1~5μm.

[0079] Typically, but not limitingly, the thickness of the coating can be, for example, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm, or any value in the range of 1 to 5 μm; Preferably, the drying and curing temperature is 70~90℃ and the time is 1~3h.

[0080] Typical, but not limiting, drying and curing temperatures can be, for example, 70°C, 75°C, 80°C, 85°C, or 90°C, or any value within the range of 70°C to 90°C; drying and curing times can be, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours, or any value within the range of 1 to 3 hours. Preferably, the membrane is made of polyolefin.

[0081] Preferably, the thickness of the diaphragm is 9~25μm.

[0082] Typically, but not limitingly, the thickness of the diaphragm can be, for example, 9 μm, 12 μm, 15 μm, 18 μm, 21 μm or 25 μm, or any value in the range of 9 to 25 μm.

[0083] Given the excellent high-temperature dimensional stability and thermal barrier capabilities of the aforementioned battery separator, thermal shrinkage and melt collapse under high-rate / high-temperature conditions are significantly suppressed; at the same time, it maintains low ion transport resistance, maintains high-rate performance and cycle life of batteries, battery packs and electrical devices, and improves the thermal safety redundancy and long-term service reliability of lithium batteries from the source.

[0084] A fifth aspect of the present invention provides a battery including the aforementioned battery separator.

[0085] A sixth aspect of the present invention provides a battery pack including the battery.

[0086] In some implementations, batteries can be assembled into battery modules, and battery modules can be assembled into battery packs. The number of battery modules contained in a battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0087] Figure 3 An exemplary structure of a battery pack is shown. Figure 3 As shown, the battery pack includes a housing and multiple battery modules housed within the housing. The housing comprises a lower housing and an upper housing, with the upper housing covering the lower housing and together forming a closed space to accommodate the battery modules. The multiple battery modules can be arranged in any manner within the housing.

[0088] A seventh aspect of the present invention provides an electrical device, including the battery or the battery pack described above.

[0089] According to another aspect of the present invention, an electrical device is provided, comprising at least one of the aforementioned batteries or battery packs. The battery or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include mobile devices (typically mobile phones, laptops, etc.), electric vehicles (typically pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, or energy storage systems, etc.

[0090] Figure 4 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery can be used.

[0091] The present invention is further illustrated below with specific embodiments and comparative examples. However, it should be understood that these embodiments are merely for illustrative purposes and should not be construed as limiting the invention in any way. Unless otherwise specified, the raw materials used in the embodiments and comparative examples of the present invention were carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0092] Example 1 This embodiment provides a magnesium diboride nanosheet, and the specific preparation steps are as follows: 1. Take magnesium diboride particles with a purity of ≥99.5% as the starting material; place them in a planetary ball mill and ball mill them at 300 rpm for 3 hours under an argon protective atmosphere to obtain MgB2 micro powder with a more uniform particle size distribution (particle size of about 800 nm) for later use.

[0093] 2. Weigh the above MgB2 micro powder, deionized water, tetrabutylammonium hydroxide and hexadecyltrimethylammonium bromide in a mass ratio of 300:100:10:1; add each component to a beaker in sequence, stir magnetically for 10 minutes until initially mixed, then transfer to an ultrasonic cleaner and ultrasonically treat for 90 minutes at a frequency of 80kHz.

[0094] 3. After sonication, transfer the mixture to a stoppered glass container and let it stand at room temperature for 12 hours. Then, take the clear liquid from the top layer, transfer it to a centrifuge tube, and centrifuge it at 8000 rpm for 20 minutes in a high-speed refrigerated centrifuge. Discard the bottom precipitate and collect the supernatant.

[0095] 4. Place the supernatant into a dialysis bag, immerse it in sufficient deionized water, and dialyze at room temperature for 72 hours; change the deionized water every 12 hours during this period; after dialysis, remove the liquid from the dialysis bag to obtain the purified magnesium diboride nanosheet aqueous dispersion.

[0096] 5. The above dispersion was quickly placed in a -20℃ ultra-low temperature freezer for 12 hours to allow the system to solidify completely; then it was freeze-dried at -40℃ for 48 hours to obtain fluffy, gray-black magnesium diboride nanosheet powder with an average thickness of 120 nm.

[0097] Example 2 This embodiment provides a magnesium diboride nanosheet. Unlike Example 1, the mass ratio of MgB2 micropowder, deionized water, tetrabutylammonium hydroxide, and hexadecyltrimethylammonium bromide is 280:90:10:1; the ultrasonic cleaning frequency is 60 kHz; and the remaining steps are the same as in Example 1, and will not be repeated here. The average thickness of the prepared nanosheet is 200 nm.

[0098] Example 3 This embodiment provides a magnesium diboride nanosheet. The difference from Example 1 is that the mass ratio of MgB2 micro powder, deionized water, tetrabutylammonium hydroxide and hexadecyltrimethylammonium bromide is 300:100:8:1. The remaining steps are the same as in Example 1 and will not be repeated here.

[0099] Example 4 This embodiment provides a magnesium diboride nanosheet. The difference from Example 1 is that the mass ratio of MgB2 micro powder, deionized water, tetrabutylammonium hydroxide and hexadecyltrimethylammonium bromide is 300:100:9:1. The remaining steps are the same as in Example 1 and will not be repeated here.

[0100] Example 5 This embodiment provides a magnesium diboride nanosheet. The difference from Example 1 is that the mass ratio of MgB2 micro powder, deionized water, tetrabutylammonium hydroxide and hexadecyltrimethylammonium bromide is 300:100:12:1. The remaining steps are the same as in Example 1 and will not be repeated here.

[0101] Example 6 This embodiment provides a magnesium diboride nanosheet. The difference from Example 1 is that the mass ratio of MgB2 micro powder, deionized water, tetrabutylammonium hydroxide and hexadecyltrimethylammonium bromide is 300:100:15:1. The remaining steps are the same as in Example 1 and will not be repeated here.

[0102] Example 7 This embodiment provides a magnesium diboride nanosheet. The difference from Example 1 is that the mass ratio of MgB2 micro powder, deionized water, tetrabutylammonium hydroxide and hexadecyltrimethylammonium bromide is 300:100:10:0.8. The remaining steps are the same as in Example 1 and will not be repeated here.

[0103] Example 8 This embodiment provides a magnesium diboride nanosheet. The difference from Example 1 is that the mass ratio of MgB2 micro powder, deionized water, tetrabutylammonium hydroxide and hexadecyltrimethylammonium bromide is 300:100:10:0.9. The remaining steps are the same as in Example 1 and will not be repeated here.

[0104] Example 9 This embodiment provides a magnesium diboride nanosheet. The difference from Example 1 is that the mass ratio of MgB2 micro powder, deionized water, tetrabutylammonium hydroxide and hexadecyltrimethylammonium bromide is 300:100:10:1.2. The remaining steps are the same as in Example 1 and will not be repeated here.

[0105] Example 10 This embodiment provides a magnesium diboride nanosheet. The difference from Example 1 is that the mass ratio of MgB2 micro powder, deionized water, tetrabutylammonium hydroxide and hexadecyltrimethylammonium bromide is 300:100:10:1.5. The remaining steps are the same as in Example 1 and will not be repeated here.

[0106] Example 11 This embodiment provides a magnesium diboride nanosheet. Unlike Example 1, the dialysis in step 4 is omitted. The remaining steps are the same as in Example 1 and will not be repeated here.

[0107] Example 12 This embodiment provides a magnesium diboride nanosheet. Unlike embodiment 1, the pre-freezing process in step 5 is omitted and the freeze-drying is performed directly. The remaining steps are the same as in embodiment 1 and will not be described again here.

[0108] Comparative Example 1 This comparative example provides a magnesium diboride nanosheet. Unlike Example 1, tetrabutylammonium hydroxide is not used. The remaining steps are the same as in Example 1 and will not be repeated here.

[0109] Comparative Example 2 This comparative example provides a magnesium diboride nanosheet. Unlike Example 1, it does not use hexadecyltrimethylammonium bromide. The remaining steps are the same as in Example 1 and will not be repeated here.

[0110] Characterization Example 1 Scanning electron microscopy (SEM) was performed on the magnesium diboride nanosheets prepared in Example 1, and the resulting SEM images are shown below. Figure 1 As shown, from Figure 1 It can be seen that after processing, the raw material lumpy magnesium diboride is effectively exfoliated into a two-dimensional sheet structure. The overall sheet morphology of the product is regular, the transverse size of the sheet is uniform, and there are no large number of coarse unexfoliated particles remaining. The sample as a whole has no obvious agglomeration. The spatial steric hindrance provided by CTAB effectively inhibits the re-stacking of the sheets, with only a small amount of loose overlap. This confirms that this process can achieve uniform exfoliation of MgB2 and obtain highly dispersed two-dimensional nanosheets.

[0111] Characterization Example 2 Transmission electron microscopy (TEM) was performed on the magnesium diboride nanosheets prepared in Example 1, and the TEM images obtained are as follows: Figure 2 As shown, from Figure 2 It can be seen that the two-dimensional thin-layer properties of the material can be directly demonstrated; the nanosheets have clear edges and complete boundaries, without obvious damage or etching holes, proving that the system can peel off nanosheets with controllable thickness and complete morphology.

[0112] Application Example 1-12 These application examples provide a battery separator, and the specific preparation process is as follows: 1. Using 15 parts of magnesium diboride nanosheets obtained in Examples 1-12, 5 parts of lithium polyacrylate (PAA-Li, MW~5000, 10% solid content aqueous solution), 1 part of trimethylolpropane triglycidyl ether, 0.8 parts of sodium polyacrylate dispersant, and 60 parts of deionized water, the above raw materials were premixed at 700 rpm for 90 min. Finally, 0.3 parts of polyether-modified siloxane wetting agent were added, and the mixture was stirred at 500 rpm at room temperature for 2 h to obtain a uniform and stable coating slurry.

[0113] 2. Using Celgard 2400 PP separator as the base membrane, the coating slurry was applied by gravure coating. It was then dried and cured in a 75℃ oven to complete the crosslinking reaction, resulting in a coating thickness of 3μm, thus obtaining the battery separator.

[0114] Application Example 13 These application examples provide a battery separator. Unlike Application Example 1, it uses 23 parts of magnesium diboride nanosheets. The remaining steps are the same as in Application Example 1 and will not be repeated here.

[0115] Application Example 14 These application examples provide a battery separator. Unlike application example 1, lithium polyacrylate is omitted from the coating slurry. The remaining steps are the same as in application example 1 and will not be described again here.

[0116] Application Example 15 These application examples provide a battery separator. Unlike Application Example 1, the coating slurry omits trimethylolpropane triglycidyl ether. The remaining steps are the same as in Application Example 1 and will not be described again here.

[0117] Comparative Application Examples 1-2 These application examples provide a battery separator. Unlike Application Example 1, the magnesium diboride nanosheets are provided by Comparative Example 1 and Comparative Example 2, respectively. The remaining steps are the same as in Application Example 1 and will not be repeated here.

[0118] Comparative Application Example 3 This application example provides a battery separator. The difference from application example 1 is that magnesium diboride nanosheets are replaced with nano-alumina. The remaining steps are the same as in application example 1, and will not be repeated here.

[0119] Comparative Application Example 4 This application example provides a battery separator, specifically a Celgard 2400 type PP separator.

[0120] Test Example 1 The battery separators obtained from the application examples and comparative application examples were subjected to the following performance tests: The peel strength was tested using a universal testing machine; the air permeability of the diaphragm was tested using an air permeability tester; the ionic conductivity of the diaphragm was tested at room temperature using an electrochemical workstation via AC impedance spectroscopy, and its thermal stability and electrochemical cycling performance were also tested.

[0121] The diaphragm was subjected to performance tests for heat shrinkage rate and puncture strength, in accordance with GB / T 36363. 2018 Standard for Polyolefin Separators for Lithium-ion Batteries.

[0122] Electrochemical cycling performance was characterized by capacity retention. The test method was as follows: the separator was prepared into a lithium battery, and the lithium-ion battery was subjected to a stepped fast charge cycle test in the voltage range of 2.0-3.65V at 25℃. The capacity retention of the battery after 200 cycles was calculated.

[0123] The obtained data are summarized in Table 1.

[0124] Table 1

[0125] As shown in Table 1, the peel strength of the coating in Application Example 1 of this invention reaches a maximum of 58 N / m, which is 5.3 times that of the traditional alumina coating in Application Example 3 and 1.9-2.5 times that of the coatings without a three-dimensional network in Application Examples 14-15. The three-dimensional cross-linked network composed of two-dimensional nanosheets, functional polymers, and cross-linking agents can significantly improve the adhesion between the coating and the diaphragm, which helps to avoid the risk of coating peeling during charging and discharging, and further improves long-term cycle performance. The puncture data also indirectly confirms this. In terms of thermal shrinkage, the coating of this invention in Application Example 1, after heat treatment at 130℃ / 1h, has a lower MD (Mean Density). The thermal shrinkage rate of / TD is significantly lower than that of the traditional alumina coating in Comparative Application Example 3 and the polyolefin blank separator in Comparative Application Example 4. This solves the core safety hazards of polyolefin separators being prone to thermal shrinkage and melting collapse at high temperatures. It can avoid the failure of physical isolation between the positive and negative electrodes under abnormal temperature rise conditions such as battery overcharging and the initial stage of internal short circuit. From the cycle data, it can be corroborated by the data on air permeability and ionic conductivity. The conductive network of the coating under this invention can effectively improve ionic conductivity and improve the charge and discharge capacity of the battery under high rate conditions. The capacity retention rate after 200 fast charge cycles is also significantly better than that of the traditional alumina coating and the polyolefin blank separator.

[0126] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing magnesium diboride nanosheets, characterized in that, Magnesium diboride, water, tetrabutylammonium hydroxide, and hexadecyltrimethylammonium bromide were mixed and sonicated, and then separated into solid and liquid components after standing. The supernatant was dialyzed, frozen, and freeze-dried to obtain magnesium diboride nanosheets.

2. The preparation method according to claim 1, characterized in that, The magnesium diboride particles have a particle size of 0.8~1μm; Preferably, the amount of water added is 30-40 wt% of the magnesium diboride particles; Preferably, the amount of tetrabutylammonium hydroxide added is 3-4 wt% of the magnesium diboride particles; Preferably, the amount of hexadecyltrimethylammonium bromide added is 0.3~0.4 wt% of the magnesium diboride particles.

3. The preparation method according to claim 1 or 2, characterized in that, The frequency of the ultrasound is 60~80KHz, and the duration is 60~120min; Preferably, the settling time is 8-16 hours; Preferably, the solid-liquid separation method includes centrifugation; Preferably, the centrifugation speed is 6000~10000 rpm and the time is 10~30 min.

4. The preparation method according to claim 1 or 2, characterized in that, In the dialysis, deionized water is used as the dialysis medium; Preferably, the dialysis time is 48-96 hours, and the dialysis medium is changed every 8-16 hours; Preferably, the freezing temperature is -22 to -18°C; Preferably, the freeze-drying temperature is -50 to -30°C and the time is 36 to 60 hours.

5. A magnesium diboride nanosheet, characterized in that, It was prepared by the preparation method according to any one of claims 1 to 4; The thickness of the magnesium diboride nanosheets is 120~200nm.

6. A coating slurry, characterized in that, The composition, by weight, includes 12-25 parts magnesium diboride nanosheets, 3-8 parts functional polymer, 0.8-2 parts epoxy silane crosslinking agent, and 48-75 parts solvent; The magnesium diboride nanosheets described herein are those described in claim 5.

7. The coating slurry according to claim 6, characterized in that, The functional polymer includes at least one of lithium polyacrylate, polyacrylonitrile, polyvinylidene fluoride copolymer and polyvinyl alcohol; Preferably, the epoxy silane crosslinking agent comprises at least one of trimethylolpropane triglycidyl ether, γ-glycidyl etheroxysilylpropyl sesquioxane, and a trifunctional aziridine crosslinking agent; Preferably, the solvent comprises water and / or N-methylpyrrolidone.

8. The coating slurry according to claim 6, characterized in that, It also includes 0-1 parts of dispersant and 0-0.5 parts of wetting agent; Preferably, the dispersant comprises at least one of sodium polyacrylate, lithium polyacrylate, potassium polyacrylate, and ammonium polyacrylate; Preferably, the wetting agent includes at least one of ether-based wetting agents, polyether-modified siloxanes, and acetylenic diol-based wetting agents.

9. A battery separator, characterized in that, Includes a base film and a coating on the surface of the base film; The coating is obtained by applying, drying and curing the coating slurry according to any one of claims 6 to 8.

10. The battery separator according to claim 9, characterized in that, The thickness of the coating is 1~5μm; Preferably, the drying and curing temperature is 70~90℃ and the time is 1~3h; Preferably, the membrane is made of polyolefin; Preferably, the thickness of the diaphragm is 9~25μm.

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

12. A battery pack, characterized in that, Includes the battery as described in claim 11.

13. An electrical appliance, characterized in that, Includes the battery of claim 11 or the battery pack of claim 12.

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