Nano ceramic fiber coated polyolefin diaphragm and preparation method thereof, and metal ion battery and preparation method thereof

Abstract

The invention relates to the technical field of battery diaphragms, in particular to a nano ceramic fiber coated polyolefin diaphragm and a preparation method thereof as well as a metal ion battery and a preparation method thereof. The nano ceramic fiber coated polyolefin diaphragm comprises a polyolefin diaphragm and a nano ceramic fiber coating coated on at least one side of the polyolefin diaphragm, the average diameter of nano ceramic fibers in the nano ceramic fiber coating is 20-1000nm, the length-diameter ratio is 20-1000, the nano ceramic fibers are stacked on the surface of the polyolefin diaphragm to form a ceramic skeleton of a three-dimensional network structure, and the porosity is 40-80%. The invention provides a nano ceramic fiber and application thereof in the technical field of battery diaphragms, nano ceramic long fibers are mutually stacked to form a two-dimensional heat conduction network, and the two-dimensional network is mutually stacked to form a three-dimensional network structure; heat generated in the battery is quickly conducted to the outside of the battery through the two-dimensional plane direction network, so that heat accumulation in the battery is effectively relieved, and the risk of thermal runaway of the battery is reduced.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, and particularly to a nano-ceramic fiber coated polyolefin separator and its preparation method, and a metal-ion battery and its preparation method. Background Technology

[0002] Batteries, as a highly efficient and portable energy source, are widely used in modern electronic devices, electric vehicles, and energy storage. With the continuous development of battery technology, societal attention to their safety is constantly increasing. The separator, as one of the main battery materials, plays a crucial role in isolating the positive and negative electrodes, providing ion channels, and insulating electronic pathways. A high-safety separator can significantly improve battery thermal diffusion, promptly conducting heat away when the battery overheats and fails, effectively reducing battery fires caused by heat accumulation. However, currently, polyolefin separators on the market are mainly made of polypropylene (PP) and polyethylene (PE). The former has a rupture temperature of approximately 160-170°C, and the latter approximately 135-150°C, while the thermal runaway trigger temperature of a battery is as high as approximately 250°C. During battery heating, the PP and PE separators deform under high temperatures due to heat accumulation, failing to maintain their original structure and causing direct contact between the positive and negative electrodes, leading to a violent short circuit reaction and ultimately, battery combustion and fire, resulting in a safety accident.

[0003] To improve the safety performance of separators, current technology involves coating polyolefin separators with nano-ceramic powder. This enhances thermal stability, improves mechanical strength, improves electrolyte wettability, and optimizes interfacial properties, fundamentally reducing the risk of battery thermal runaway. However, existing ceramic separators still face the following bottlenecks: (1) The zero-dimensional ceramic particle stacked coating has a point-to-point contact and an in-plane thermal conductivity of only 0.3~0.8 W / (m·K). The heat diffusion efficiency is low, and local hot spots are prone to triggering membrane shrinkage, resulting in short circuit between positive and negative electrodes.

[0004] (2) The interface between the powder particles and the polyolefin membrane is a weak van der Waals force. When subjected to electrode pressure or winding tension, it is easy to crack and lose powder, which contaminates the electrolyte.

[0005] (3) Dense inorganic particles in the coating occupy the pores, reducing the electrolyte wetting channels, decreasing the liquid absorption rate and liquid retention, which leads to increased polarization in the later stages of battery cycling and faster battery capacity decay.

[0006] Therefore, research on structural improvements to the coating on the separator surface is of great strategic significance for promoting the development and safe application of modern battery technology. Summary of the Invention

[0007] This invention provides a functional powder ceramic separator with a two-dimensional thermally conductive network, high safety, and high liquid absorption. Its purpose is to propose a new approach of "ceramic powder fiberization – two-dimensional thermally conductive network – high thermal conductivity polyolefin separator" to improve the thermal conductivity of existing ceramic separators and reduce the risk of safety accidents caused by thermal runaway combustion of batteries due to internal heat accumulation.

[0008] To achieve the above objectives, the present invention provides a nano-ceramic fiber coated polyolefin separator, wherein the nano-ceramic fiber coated polyolefin separator comprises a polyolefin separator and a nano-ceramic fiber coating coated on at least one side of the polyolefin separator. The nano-ceramic fibers in the nano-ceramic fiber coating have a dendritic structure with an average diameter of 20-1000 nm and an aspect ratio of 20-1000, and are stacked on the surface of the polyolefin separator to form a three-dimensional network ceramic skeleton with a porosity of 40%-80%. The thickness of the nano-ceramic fiber coating is 0.5-4 μm, and the thickness of the polyolefin separator is 5-25 μm.

[0009] To improve the thermal conductivity, thermal stability, liquid absorption, and mechanical strength of current battery separators, this invention provides a nano-ceramic fiber and its application in battery separators.

[0010] Preferably, the nano-ceramic fiber comprises one or more of Al2O3, ZrO2, SiC, Si3N4, SiO2, AlN, or TiO2; and the polyolefin membrane is any one of polyethylene membrane, polypropylene membrane, or a composite membrane of PP and PE.

[0011] Under the same technical concept, the present invention also provides a method for preparing a polyolefin separator coated with nano-ceramic fibers, comprising the following steps: (1) Dissolve metal alkoxides or inorganic salts in a solvent, add a catalyst and heat in a water bath and stir magnetically to form a sol; add a spinning aid to the sol and concentrate it to obtain a spinnable gel, wherein the viscosity of the spinnable gel is 30~100 Pa·s. (2) The spinnable gel in step (1) is electrospun, and then dried and calcined to obtain nano-ceramic fibers; (3) The nano-ceramic fibers in step (2) are mixed evenly with solvent, binder and dispersant to obtain slurry, and the slurry is coated on polyolefin membrane and dried under vacuum to obtain nano-ceramic fiber coated polyolefin membrane.

[0012] Preferably, in step (1), the metal alkoxide includes one or more of the following: aluminum triisopropoxy, aluminum trisec-butoxy, titanium tetraethoxy, titanium tetraisopropoxy, zirconium tetrapropoxy, zirconium tetrabutoxy, tetraethyl orthosilicate, or methyl orthosilicate; the inorganic salt includes one or more of the following: aluminum nitrate nonahydrate, aluminum nitrate, aluminum chloride hexahydrate, zirconium oxychloride octahydrate, zirconium nitrate, sodium silicate, titanium chloride, or titanium sulfate; and the solvent includes one or more of the following: ethanol or deionized water.

[0013] Preferably, in step (1), the catalyst includes one or more of nitric acid, hydrochloric acid, acetylacetone or acetic acid; the spinning aid includes one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl butyral, cellulose diacetate, polyethylene glycol, lactic acid or acetic acid.

[0014] Preferably, in step (1), the water bath heating temperature is 40~100℃, the magnetic stirring speed is 200~400r / min, and the time is 2~15h; the concentration is rotary evaporation at a temperature of 40~100℃.

[0015] Preferably, in step (2), the electrospinning voltage is 10~30kV, the needle-collector distance during electrospinning is 10~25cm, the liquid supply rate is 0.5~3mL / h, and the collector rotation speed is 200~2000r / min; The drying temperature is 50~100℃, the calcination temperature is 600~1500℃, and the calcination holding time is 0.5~6h.

[0016] Preferably, in step (3), the solvent includes one or more of water, N-methylpyrrolidone, acetone or ethanol; the binder includes one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyvinylidene fluoride, polyacrylic acid or styrene-butadiene rubber; and the dispersant includes one or more of polyvinyl alcohol, sodium polyacrylate, lithium polyacrylate, fatty polyoxyethylene ether or polyvinylpyrrolidone.

[0017] Under the same technical concept, the present invention also provides a metal-ion battery, which includes a positive electrode, a negative electrode, an electrolyte, and the nano-ceramic fiber coated polyolefin separator, or a nano-ceramic fiber coated polyolefin separator prepared by the preparation method described above.

[0018] Under the same technical concept, the present invention also provides a method for preparing a metal-ion battery, the method comprising: sequentially stacking or winding a positive electrode, a nano-ceramic fiber coated polyolefin separator, and a negative electrode into a core, then injecting an electrolyte into the core and sealing it to obtain a metal-ion battery.

[0019] The above-described solution of the present invention has the following beneficial effects: (1) This invention provides a nano-ceramic fiber and applies it to the field of battery separator technology. The nano-ceramic long fibers are stacked to form a two-dimensional thermally conductive network, and the two-dimensional network is then stacked to form a three-dimensional network structure. The heat generated inside the battery can be quickly conducted to the outside of the battery through the two-dimensional planar network, which effectively alleviates the heat accumulation inside the battery and reduces the risk of battery thermal runaway.

[0020] (2) The high aspect ratio (average diameter 20~1000nm, aspect ratio 20~1000) nano-ceramic fibers prepared by the present invention achieve spatial interpenetration through random stacking. With their own high modulus and multi-point physical contact, they construct a cross-linked and strong "ceramic skeleton" and build a three-dimensional rigid network structure on the surface of the polyolefin membrane. This can effectively disperse external stress and suppress the deformation of the base membrane under stress. This "skeleton" effect significantly improves the puncture resistance and tensile modulus of the polyolefin membrane.

[0021] (3) This invention provides a nano-ceramic fiber and applies it to the field of battery separator technology. Due to the one-dimensional structure of the nano-ceramic fiber, its stacking on the polyolefin separator forms a large number of nano- to submicron-sized pores. The porosity depends on the fiber packing density. After coating the polyolefin separator, the porosity of the coating can reach 40% to 80%. Since the fibers are randomly stacked, the pores have an irregular three-dimensional interconnected structure. This structure effectively improves the liquid absorption capacity of the separator, thereby increasing the liquid retention capacity of the battery and giving the battery a longer cycle life.

[0022] (4) This invention provides a process for preparing nano-ceramic fibers by combining a sol-gel method with electrospinning. The sol-gel process ensures that the ceramic precursor is uniformly dispersed at the molecular level, forming a dense and uniform ceramic phase after sintering, avoiding local weaknesses and improving the overall structural strength. Furthermore, since metal alkoxides or inorganic salts are used as raw materials, and the solvent is non-polymer such as ethanol or water, the problem of ceramic fibers easily breaking into short fragments during sintering when polymers are used as raw materials can be solved. This process can prepare nano-ceramic fibers with controllable diameter, high density, and excellent one-dimensional thermal conductivity. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the preparation method of the nano-ceramic fiber coated polyolefin separator of the present invention; Figure 2 This is a SEM image of the nano-ceramic fibers prepared in Example 1 of this invention; Figure 3 This is a SEM image of the nano-ceramic fibers prepared in Example 2 of the present invention. Detailed Implementation

[0024] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0026] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a locking connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0027] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] Example 1 This embodiment illustrates the nano-ceramic fibers provided by the present invention and their application in battery separators. The preparation process is as follows: Figure 1 As shown.

[0029] (1) Preparation of nano-ceramic fibers: 21g of aluminum triisopropoxy, 5.5mL of 15mol / L nitric acid, and 56mL of anhydrous ethanol were reacted in a water bath at 60℃ with magnetic stirring at 300r / min for 8h to obtain a transparent sol. Then, 2.5g of polyvinylpyrrolidone was added and mixed, and the mixture was rotary evaporated at 50℃ to obtain a spinnable gel with a viscosity of 50Pa·s.

[0030] Nano-alumina ceramic fibers were obtained by setting the spinning voltage to 20kV, the distance between the needle tip and the collector to 16cm, the spinning solution flow rate to 1mL / h, and the collector rotation speed to 800r / min. The obtained ceramic fibers were dried at 80℃ for 6h, and then heated to 1000℃ at a rate of 3℃ / min and held for 3h to obtain nano-alumina ceramic fibers.

[0031] The SEM image of the nano-alumina ceramic fibers prepared in this embodiment is as follows: Figure 2 As shown.

[0032] (2) Preparation of nano-ceramic fiber coated diaphragm: Take 2.62g of nano-alumina ceramic fiber, 7g of N-methylpyrrolidone, 0.3g of polyvinylidene fluoride and 0.08g of polyvinylpyrrolidone and mix them. After stirring evenly, a coating slurry is obtained. The slurry is then coated onto both sides of a polyethylene membrane with a thickness of 20μm. The thickness of the single-layer nano-ceramic fiber coating is 2μm. After drying at 70℃ under a vacuum of -0.1MPa for 5 hours, a nano-ceramic fiber coated polyolefin membrane is obtained.

[0033] The nano-ceramic fibers in the nano-ceramic fiber coating of the polyolefin separator exhibit a dendritic structure, such as... Figure 2 As shown, the average diameter of the nano-ceramic fibers is 20~500nm, the aspect ratio is 20~500, and they are stacked on the surface of the polyolefin membrane to form a three-dimensional network ceramic skeleton with a porosity of 50%-80%.

[0034] Example 2 This embodiment illustrates the nano-ceramic fibers provided by the present invention and their application in battery separators.

[0035] (1) Preparation of nano-ceramic fibers: 21.5 g of aluminum trisec-butoxy, 5.5 g of urea, 85 mL of anhydrous ethanol, 2.6 mL of 12 mol / L acetylacetone and 3.5 g of polyvinylpyrrolidone were mixed and reacted with magnetic stirring at 300 r / min at 60 °C for 8 h to obtain a transparent sol. Then, the sol was rotary evaporated at 50 °C to obtain a spinnable gel with a viscosity of 50 Pa·s.

[0036] Nano-aluminum nitride ceramic fibers were obtained by setting the spinning voltage to 20kV, the distance between the needle tip and the collector to 16cm, the spinning solution flow rate to 1mL / h, and the collector rotation speed to 800r / min. The obtained ceramic fibers were dried at 80℃ for 6h, and then heated to 1000℃ at a rate of 3℃ / min and held for 3h to obtain nano-aluminum nitride ceramic fibers.

[0037] The SEM image of the nano-aluminum nitride ceramic fibers prepared in this embodiment is as follows: Figure 3 As shown.

[0038] (2) Preparation of nano-ceramic fiber coated diaphragm: Take 2.62g of nano-aluminum nitride ceramic fiber, 7g of N-methylpyrrolidone, 0.3g of polyvinylidene fluoride and 0.08g of polyvinylpyrrolidone and mix them. After stirring evenly, a coating slurry is obtained. The slurry is then coated onto both sides of a polyethylene membrane with a thickness of 20μm. The thickness of the single-layer nano-ceramic fiber coating is 2μm. After drying at 70℃ under a vacuum of -0.1MPa for 5 hours, a nano-aluminum nitride ceramic fiber coated membrane is obtained.

[0039] The nano-ceramic fibers in the nano-ceramic fiber coating of the polyolefin separator, which is coated with nano-aluminum nitride ceramic fibers, exhibit a dendritic structure, such as... Figure 3 As shown, the average diameter of the nano-ceramic fibers is 50~500nm, the aspect ratio is 50~500, and they are stacked on the surface of the polyolefin membrane to form a three-dimensional network ceramic skeleton with a porosity of 60%-80%.

[0040] Example 3 This embodiment illustrates the nano-ceramic fibers provided by the present invention and their application in battery separators.

[0041] (1) Preparation of nano-ceramic fibers: 20.5g of tetra-n-butoxyzirconium, 2.5g of tetraethyl orthosilicate, 87mL of anhydrous ethanol, 5.5mL of 12mol / L hydrochloric acid, and 3g of polyvinylpyrrolidone were mixed and reacted with magnetic stirring at 300r / min at 60℃ for 8h to obtain a transparent sol. Then, the sol was rotary evaporated at 50℃ to obtain a spinnable gel with a viscosity of 50Pa·s.

[0042] Nano-zirconia-silica composite ceramic fibers were obtained by setting the spinning voltage to 20kV, the distance between the needle tip and the collector to 16cm, the spinning solution flow rate to 1mL / h, and the collector rotation speed to 800r / min. The obtained ceramic fibers were dried at 80℃ for 6h, and then heated to 1000℃ at a rate of 3℃ / min and held for 3h to obtain nano-zirconia-silica composite ceramic fibers.

[0043] (2) Preparation of nano-ceramic fiber coated diaphragm: 2.62g of nano-zirconia-silica composite ceramic fiber, 7g of N-methylpyrrolidone, 0.3g of polyvinylidene fluoride and 0.08g of polyvinylpyrrolidone were mixed and stirred evenly to obtain a coating slurry. The slurry was then coated onto both sides of a polyethylene membrane with a thickness of 20μm, and the thickness of the single layer of nano-ceramic fiber coating was 2μm. After drying at 70℃ under a vacuum of -0.1MPa for 5 hours, a nano-zirconia-silica composite ceramic fiber coated membrane was obtained.

[0044] Example 4 This embodiment illustrates the nano-ceramic fibers provided by the present invention and their application in battery separators.

[0045] (1) Preparation of nano-ceramic fibers: 17.5g of tetraethoxytitanium, 4mL of deionized water, 91mL of anhydrous ethanol, 4g of glacial acetic acid and 3g of polyvinylpyrrolidone were mixed and reacted with magnetic stirring at 300r / min at 60℃ for 8h to obtain a transparent sol. Then, the sol was rotary evaporated at 50℃ to obtain a spinnable gel with a viscosity of 50Pa·s.

[0046] Nano-titanium oxide ceramic fibers were obtained by setting the spinning voltage to 20 kV, the distance between the needle tip and the collector to 16 cm, the spinning solution flow rate to 1 mL / h, and the collector rotation speed to 800 r / min. The obtained ceramic fibers were dried at 80 °C for 6 h, and then heated to 700 °C at a rate of 3 °C / min and held at that temperature for 3 h to obtain nano-titanium oxide ceramic fibers.

[0047] (2) Preparation of nano-ceramic fiber coated diaphragm: Take 2.62g of nano-titanium oxide ceramic fiber, 7g of N-methylpyrrolidone, 0.3g of polyvinylidene fluoride and 0.08g of polyvinylpyrrolidone and mix them. After stirring evenly, a coating slurry is obtained. The slurry is then coated onto both sides of a polyethylene membrane with a thickness of 20μm, and the thickness of the single layer of nano-ceramic fiber coating is 2μm. After drying at 70℃ under a vacuum of -0.1MPa for 5 hours, a nano-aluminum nitride ceramic fiber coated membrane is obtained.

[0048] Example 5 This embodiment illustrates the nano-ceramic fibers provided by the present invention and their application in battery separators.

[0049] (1) Preparation of nano-ceramic fibers: The preparation of nano-ceramic fibers is the same as in Example 1.

[0050] (2) Preparation of nano-ceramic fiber coated diaphragm: Take 2.62g of nano-alumina ceramic fiber, 7g of N-methylpyrrolidone, 0.3g of polyvinylidene fluoride and 0.08g of polyvinylpyrrolidone and mix them. After stirring evenly, a coating slurry is obtained. The slurry is then coated onto both sides of a polyethylene membrane with a thickness of 20μm, and the thickness of the single layer of nano-ceramic fiber coating is 3μm. After drying at 70℃ under a vacuum of -0.1MPa for 5 hours, a nano-alumina ceramic fiber coated membrane is obtained.

[0051] Example 6 This embodiment illustrates the nano-ceramic fibers provided by the present invention and their application in battery separators.

[0052] (1) Preparation of nano-ceramic fibers: The preparation of nano-ceramic fibers is the same as in Example 1.

[0053] (2) Preparation of nano-ceramic fiber coated diaphragm: Take 2.62g of nano-alumina ceramic fiber, 7g of N-methylpyrrolidone, 0.3g of polyvinylidene fluoride and 0.08g of polyvinylpyrrolidone and mix them. After stirring evenly, a coating slurry is obtained. The slurry is then coated onto both sides of a polyethylene membrane with a thickness of 20μm, and the thickness of the single layer of nano-ceramic fiber coating is 4μm. After drying at 70℃ under a vacuum of -0.1MPa for 5 hours, a nano-alumina ceramic fiber coated membrane is obtained.

[0054] Comparative Example 1 This comparative example is used to illustrate the reference ceramic diaphragm and its preparation method.

[0055] 2.62g of spherical alumina ceramic powder (D50=100nm, 99.9%), 7g of N-methylpyrrolidone, 0.3g of polyvinylidene fluoride and 0.08g of polyvinylpyrrolidone were mixed and stirred until uniform to obtain a coating slurry. The slurry was then coated onto both sides of a polyethylene membrane with a thickness of 20μm, and a single layer of nano-ceramic fiber coating with a thickness of 2μm was applied. The membrane was then dried at 70℃ under a vacuum of -0.1MPa for 5 hours to obtain a nano-spherical alumina ceramic coated membrane.

[0056] Comparative Example 2 This comparative example is used to illustrate the reference ceramic diaphragm and its preparation method. The polyethylene diaphragm used in this comparative example is exactly the same as that in Example 1, the only difference being that the polyethylene diaphragm used in this comparative example is not coated with slurry.

[0057] The performance of the ceramic membranes prepared in Examples 1-6 and Comparative Examples 1-2 was measured. Table 1 shows the final test comparison results.

[0058] Table 1

[0059] As shown in Table 1, comparing Example 1 and Comparative Example 1, it can be seen that using nano-ceramic fibers instead of nano-spherical ceramics as the coating material can significantly improve the thermal conductivity, heat shrinkage resistance, and liquid absorption performance of the ceramic separator. The low heat shrinkage rate demonstrates the separator's excellent resistance to deformation, indicating good mechanical properties to some extent. The high liquid absorption performance demonstrates the separator's large porosity, indicating that the three-dimensional rigid network structure formed by the nano-ceramic fibers provides abundant pores. One of the main reasons for battery cycle capacity decay is electrolyte consumption; if the separator can provide a large electrolyte absorption capacity in the initial stage, its cycle performance can be fundamentally improved. Comparing Examples 1-4, it can be seen that the separator with nano-aluminum nitride fibers as the coating material has the highest thermal conductivity, because aluminum nitride ceramics have the best intrinsic thermal conductivity among these four materials.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications 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.

Claims

1. A polyolefin separator coated with nano-ceramic fibers, characterized in that, The nano-ceramic fiber coated polyolefin separator comprises a polyolefin separator and a nano-ceramic fiber coating coated on at least one side of the polyolefin separator. The nano-ceramic fibers in the nano-ceramic fiber coating have a dendritic structure with an average diameter of 20-1000 nm and an aspect ratio of 20-1000. They are stacked on the surface of the polyolefin separator to form a three-dimensional network ceramic skeleton with a porosity of 40%-80%. The thickness of the nano-ceramic fiber coating is 0.5-4 μm, and the thickness of the polyolefin separator is 5-25 μm.

2. The nano-ceramic fiber coated polyolefin separator as described in claim 1, characterized in that, The nano-ceramic fibers are composed of one or more of Al2O3, ZrO2, SiC, Si3N4, SiO2, AlN, or TiO2; the polyolefin membrane is any one of polyethylene membrane, polypropylene membrane, or PP and PE composite membrane.

3. A method for preparing a polyolefin separator coated with nano-ceramic fibers, characterized in that, Includes the following steps: (1) Dissolve metal alkoxides or inorganic salts in a solvent, add a catalyst and heat in a water bath and stir magnetically to form a sol; add a spinning aid to the sol and concentrate it to obtain a spinnable gel, wherein the viscosity of the spinnable gel is 30~100 Pa·s. (2) The spinnable gel in step (1) is electrospun, and then dried and calcined to obtain nano-ceramic fibers; (3) The nano-ceramic fibers in step (2) are mixed evenly with solvent, binder and dispersant to obtain slurry, and the slurry is coated on polyolefin membrane and dried under vacuum to obtain nano-ceramic fiber coated polyolefin membrane.

4. The preparation method according to claim 3, characterized in that, In step (1), the metal alkoxide includes one or more of the following: aluminum triisopropoxy, aluminum trisec-butoxy, titanium tetraethoxy, titanium tetraisopropoxy, zirconium tetrapropoxy, zirconium tetrabutoxy, tetraethyl orthosilicate, or methyl orthosilicate; the inorganic salt includes one or more of the following: aluminum nitrate nonahydrate, aluminum nitrate, aluminum chloride hexahydrate, zirconium oxychloride octahydrate, zirconium nitrate, sodium silicate, titanium chloride, or titanium sulfate; and the solvent includes one or more of the following: ethanol or deionized water.

5. The preparation method according to claim 3, characterized in that, In step (1), the catalyst includes one or more of nitric acid, hydrochloric acid, acetylacetone or acetic acid; the spinning aid includes one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl butyral, cellulose diacetate, polyethylene glycol, lactic acid or acetic acid.

6. The preparation method according to claim 3, characterized in that, In step (1), the water bath heating temperature is 40~100℃, the magnetic stirring speed is 200~400r / min, and the time is 2~15h; the concentration is rotary evaporation at a temperature of 40~100℃.

7. The preparation method according to claim 3, characterized in that, In step (2), the electrospinning voltage is 10~30kV, the needle-collector distance is 10~25cm, the liquid supply rate is 0.5~3mL / h, and the collector rotation speed is 200~2000r / min. The drying temperature is 50~100℃, the calcination temperature is 600~1500℃, and the calcination holding time is 0.5~6h.

8. The preparation method according to claim 3, characterized in that, In step (3), the solvent includes one or more of water, N-methylpyrrolidone, acetone or ethanol; the binder includes one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyvinylidene fluoride, polyacrylic acid or styrene-butadiene rubber; and the dispersant includes one or more of polyvinyl alcohol, sodium polyacrylate, lithium polyacrylate, fatty polyoxyethylene ether or polyvinylpyrrolidone.

9. A metal-ion battery, characterized in that, The metal-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a nano-ceramic fiber coated polyolefin separator as described in any one of claims 1-2, or a nano-ceramic fiber coated polyolefin separator prepared by any one of claims 3-8.

10. A method for preparing a metal-ion battery as described in claim 9, characterized in that, The preparation method includes: sequentially stacking or winding a positive electrode, a polyolefin separator coated with nano-ceramic fibers, and a negative electrode into a core, then injecting electrolyte into the core and sealing it to obtain a metal-ion battery.

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