Porous alumina powder applied to lithium ion battery and preparation method of porous alumina powder

Abstract

The invention relates to the technical field of battery materials, and particularly provides porous aluminum oxide powder applied to a lithium ion battery and a preparation method of the porous aluminum oxide powder. The porous alumina powder of the present application comprises: a porous alumina matrix, the aperture of which is gradually reduced from the surface to the center; the silane coupling agent modification layer covers at least part of the surface of the porous aluminum oxide matrix, and a silane coupling agent has a Si-O-Al bonded network structure; the fluorocarbon hydrophobic layer is coated on at least part of the surface of the silane coupling agent modification layer, and the fluorocarbon hydrophobic layer is of a perfluoroalkyl chain structure. According to the preparation method, the wettability, the interface stability and the moisture resistance of the electrolyte are synchronously improved through cooperation of a gradient aperture structure and silane-fluorocarbon double-layer modification.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a porous alumina powder used in lithium-ion batteries and a preparation method thereof. Background Art

[0002] With the widespread application of lithium-ion batteries in electric vehicles and energy storage, the market's requirements for battery performance are becoming increasingly stringent, requiring high safety and environmental adaptability while improving energy density and cycle life. Although porous alumina can improve electrolyte wettability as a battery separator coating or electrode additive, its traditional design has significant defects: uniform pore size structure makes it difficult to balance the wetting speed and ion transmission efficiency; side reactions caused by surface hydroxyl groups lead to pore blockage and interface degradation; and moisture absorption caused by high porosity further exacerbates battery performance degradation.

[0003] Therefore, it is urgent to develop a new type of porous alumina material to break through the bottleneck of battery performance and environmental adaptability. Summary of the invention

[0004] The present invention provides a porous alumina powder for lithium-ion batteries and a preparation method thereof. The gradient pore size structure cooperates with silane-fluorocarbon double-layer modification to simultaneously improve electrolyte wettability, interface stability and moisture resistance. The outer large pores accelerate electrolyte penetration, and the inner small pores maintain a high specific surface area, thereby achieving coordinated optimization of the wetting efficiency and the ion transport channel. The silane coupling agent and the fluorocarbon double-layer modification passivate the surface hydroxyl groups and inhibit side reactions, while utilizing the selective coating of the fluorocarbon hydrophobic layer to achieve compatibility between moisture resistance and pore patency, thereby breaking through the performance limitations of a single modification layer.

[0005] To achieve the first objective of the present invention, the present invention provides a porous alumina powder for lithium-ion batteries, the porous alumina powder comprising: a porous alumina substrate, the pore size of the porous alumina substrate gradually decreases from the surface to the center, wherein the surface pore size is 100-500nm, and the central area pore size is 5-50nm; a silane coupling agent modification layer, the silane coupling agent modification layer covers at least part of the surface of the porous alumina substrate, the silane coupling agent has a Si-O-Al bonding network structure; a fluorocarbon hydrophobic layer, the fluorocarbon hydrophobic layer is coated on at least part of the surface of the silane coupling agent modification layer, and the fluorocarbon hydrophobic layer is a perfluoroalkyl chain structure.

[0006] In any of the above technical solutions, the thickness of the porous alumina substrate is 10-200 μm; and / or the thickness of the silane coupling agent modified layer is 1-10 nm; and / or the thickness of the fluorocarbon hydrophobic layer is 2-50 nm.

[0007] In any of the above technical solutions, the porosity of the porous alumina powder is 60-80%; and / or the specific surface area of ​​the porous alumina powder is 50-200 m² / g.

[0008] To achieve the second purpose of the present invention, the present invention provides a method for preparing porous alumina powder for lithium ion batteries, which is used to prepare the porous alumina powder of any one of the above technical solutions, and the preparation method comprises: S100, preparing a precursor: dispersing an alumina precursor and a template in an ethanol solution to form a first sol; S200, preparing a porous alumina matrix: mixing the first sol with a pore-forming agent, spraying the mixture, and calcining the mixture in stages to obtain a porous alumina matrix; S300, preparing a silane coupling agent modified layer: plasma pretreatment of the porous alumina matrix, followed by vapor deposition of a silane coupling agent in an inert atmosphere to obtain a silane-modified alumina powder; S400, preparing a fluorocarbon hydrophobic layer: vapor deposition of fluorocarbon gas and annealing of the silane-modified alumina powder in an inert atmosphere to obtain a porous alumina powder.

[0009] In any of the above technical solutions, in step S100, the alumina precursor includes at least one of aluminum nitrate and aluminum isopropoxide; and / or the template is selected from at least one of hexadecyltrimethylammonium bromide, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, and poloxamer F127; and / or the mass ratio of the alumina precursor to the template is 1:(0.01-0.5); and / or the solid content of the first sol is 5-30wt%, and the pH value is 3-5; and / or the preparation conditions of the first sol include: stirring at 40-80°C for 2-24h.

[0010] In any of the above technical solutions, step S200 specifically includes: S201, mixing the first sol and the pore-forming agent in a mass ratio of 1: (0.1-1.5), stirring at a speed of 200-800rpm for 10-30min to obtain a second sol; S202, spray-drying the second sol through a centrifugal atomizer, controlling the inlet temperature to 180-220℃ and the outlet temperature to 80-120℃, to obtain porous alumina precursor particles; S203, calcining the porous alumina precursor particles in an air atmosphere in stages to obtain a porous alumina matrix; wherein the staged calcination treatment includes a first calcination treatment and a second calcination treatment; the first calcination treatment is heated to 300-400℃ at 2-5℃ / min and kept warm for 1-2h; the second calcination treatment is heated to 600-800℃ at 1-3℃ / min and kept warm for 2-4h.

[0011] In any of the above technical solutions, in step S201, the pore-forming agent includes at least one of polymethyl methacrylate microspheres, ammonium bicarbonate, and urea; and / or in step S202, the pressure of the spray drying process is 0.2-0.8 MPa.

[0012] In any of the above technical schemes, step S300 specifically includes: S301, subjecting the porous alumina substrate to plasma treatment in an oxygen-containing inert atmosphere at a pressure of 5-50Pa and a power of 20-100W for 5-30 minutes to obtain a surface-activated porous alumina substrate; S302, in an inert atmosphere, introducing silane coupling agent vapor into the surface-activated porous alumina substrate, controlling the temperature to 80-120°C, the pressure to 10-500Pa, and the deposition time to 0.5-3h to form alumina powder preliminarily modified with silane; S303, cooling the alumina powder preliminarily modified with silane to room temperature, and vacuum drying it at 80-150°C for 1-5h to obtain a silane-modified alumina powder.

[0013] In any of the above technical solutions, in step S301, the oxygen-containing inert atmosphere includes Ar / O2 gas, and the volume ratio of Ar to O2 gas is 4:1; in step S302, the silane coupling agent includes at least one of 3-aminopropyltriethoxysilane and 3-glycidyloxypropyltrimethoxysilane.

[0014] In any of the above technical solutions, in step S400, the fluorocarbon gas includes at least one of perfluorooctane, tetrafluoroethylene, and hexafluoropropylene; and / or the conditions for fluorocarbon gas vapor deposition include: a deposition temperature of 80-150°C, a pressure of 10-200 Pa, and a time of 0.5-2h; and / or the annealing treatment is carried out under an inert atmosphere, including heating to 150-250°C at a rate of 1-5°C / min and keeping warm for 0.5-3h.

[0015] After adopting the technical solution of the present invention, the technical effects that can be achieved are as follows: 1. The porous alumina matrix has a pore size gradient that gradually decreases from the surface to the center. Combined with high porosity and particle morphology, it can increase the specific surface area of ​​the material, allowing the electrolyte to quickly penetrate into the interior through the large pores on the surface. At the same time, the small pores in the center provide more active sites, promoting the uniform diffusion and efficient transmission of lithium ions, thereby enhancing the rate performance and cycle stability of the battery, and avoiding uneven wetting or decreased ion mobility caused by uniform pore size; 2. The silane coupling agent modified layer is firmly bonded to the alumina matrix through the Si-O-Al bonding network, passivating the surface hydroxyl groups and reducing corrosion; at the same time, its functional groups can participate in the formation of a stable SEI film, reduce the interface impedance and improve the interface bonding force; 3. The perfluoroalkyl chain is selectively coated on the outside of the silane layer through vapor deposition, isolating the intrusion of water while maintaining the pores unobstructed. The chemical inertness of the fluorocarbon layer further inhibits the side reaction of electrolyte decomposition, thereby improving the chemical stability of the material in the electrolyte and reducing electrode powdering and capacity attenuation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1This is a SEM image of the porous alumina of Example 1 of the present invention; Figure 2 TEM image of porous alumina of Example 1 of the present invention; Figure 3 This is a SEM image of the porous alumina substrate of Example 1 of the present invention; Figure 4 This is a graph showing the capacity retention of porous alumina according to Examples 1-3 of the present invention and Comparative Examples 1-3. DETAILED DESCRIPTION

[0017] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0018] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0019] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below.

[0020] With the widespread application of lithium-ion batteries in electric vehicles and energy storage, the market's requirements for battery performance are becoming increasingly stringent, requiring high safety and environmental adaptability while improving energy density and cycle life. Although porous alumina can improve electrolyte wettability as a battery separator coating or electrode additive, its traditional design has significant defects: uniform pore size structure makes it difficult to balance the wetting speed and ion transmission efficiency; side reactions caused by surface hydroxyl groups lead to pore blockage and interface degradation; and moisture absorption caused by high porosity further exacerbates battery performance degradation.

[0021] The existing technology cannot systematically solve the above contradictions through single pore size control or surface modification schemes, which has become a key bottleneck restricting the development of high-reliability batteries. Therefore, this embodiment provides a porous alumina powder for lithium-ion batteries and a preparation method thereof, which solves the above technical contradictions through the design of gradient pore size matrix + double-layer interface modification; the porous alumina powder includes: A porous alumina substrate, wherein the pore size of the porous alumina substrate gradually decreases from the surface to the center, wherein the surface pore size is 100-500 nm and the center area pore size is 5-50 nm; A silane coupling agent modified layer, wherein the silane coupling agent modified layer covers at least a portion of the surface of the porous alumina substrate, and the silane coupling agent has a Si-O-Al bonding network structure; The fluorocarbon hydrophobic layer is coated on at least a portion of the surface of the silane coupling agent modified layer, and the fluorocarbon hydrophobic layer is a perfluoroalkyl chain structure.

[0022] Preferably, the gradient pore structure cooperates with the silane-fluorocarbon double layer modification to simultaneously improve the electrolyte wettability, interface stability and moisture resistance. The large pores in the outer layer accelerate the electrolyte penetration, and the small pores in the inner layer maintain a high specific surface area, thereby achieving the coordinated optimization of the wetting efficiency and the ion transport channel. The silane coupling agent layer passivates the interface through Si-O-Al bonding, inhibits side reactions and enhances the electrode binding force. The fluorocarbon hydrophobic layer selectively coats the interface to achieve moisture resistance and corrosion resistance while maintaining unobstructed pores, thereby achieving the compatibility of moisture resistance and pore patency, breaking through the performance limitations of a single modification layer.

[0023] This embodiment provides a method for preparing porous alumina powder for lithium ion batteries, the preparation method comprising: S100, preparing a precursor: dispersing an aluminum oxide precursor and a template in an ethanol solution to form a first sol; S200, preparing a porous alumina matrix: mixing the first sol with a pore-forming agent, spraying the mixture, and performing staged calcination to obtain a porous alumina matrix; S300, preparing a silane coupling agent modified layer: performing plasma pretreatment on the porous alumina substrate, and then performing vapor deposition of a silane coupling agent under an inert atmosphere to obtain a silane-modified alumina powder; S400, preparing a fluorocarbon hydrophobic layer: subjecting the silane-modified alumina powder to fluorocarbon gas vapor deposition and annealing treatment under an inert atmosphere to obtain a porous alumina powder.

[0024] Preferably, in step S100, the chemical and physical foundation for the subsequent formation of a gradient pore size structure is laid by precursor selection, template regulation and sol preparation process optimization: the alumina precursor includes at least one of aluminum nitrate and aluminum isopropoxide; as an aluminum source, aluminum nitrate has a fast hydrolysis rate and low cost, while aluminum isopropoxide has high purity and good colloidal stability, and the two can be used alone or in combination to balance the reaction activity and product purity; the template is selected from at least one of hexadecyltrimethylammonium bromide, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, and poloxamer F127; the pore structure is regulated by self-assembly, hexadecyltrimethylammonium bromide guides micropores-mesopores, and polyethylene oxide guides micropores-mesopores. The triblock copolymer of alkyl-polypropylene oxide-polyethylene oxide forms mesopores-macropores, and cooperates with the subsequent pore-forming agent to realize the gradient pore size design; the mass ratio of the alumina precursor to the template is 1: (0.01-0.5), the solid content of the first sol is 5-30wt%, and the pH value is 3-5, which can control the sol viscosity and the template concentration, ensure the uniformity of the precursor particles during spray drying, avoid agglomeration or excessive agglomeration, and the acidic condition inhibits the rapid gelation of alumina; the preparation conditions of the first sol include: stirring at 40-80°C for 2-24h, stirring at medium temperature to promote the hydrolysis-condensation equilibrium of the aluminum source, form a stable sol, and provide a homogeneous reaction environment for the controllable growth of the gradient pore structure.

[0025] Furthermore, step S200 specifically includes: S201, mixing the first sol and the pore-forming agent in a mass ratio of 1:(0.1-1.5), stirring at a speed of 200-800 rpm for 10-30 min to obtain a second sol; S202, spray drying the second sol through a centrifugal atomizer, controlling the inlet temperature to 180-220° C. and the outlet temperature to 80-120° C., to obtain porous alumina precursor particles; S203, calcining the porous alumina precursor particles in an air atmosphere in stages to obtain a porous alumina matrix; The staged calcination treatment includes a first calcination treatment and a second calcination treatment; the first calcination treatment is heated to 300-400°C at 2-5°C / min and kept warm for 1-2h; the second calcination treatment is heated to 600-800°C at 1-3°C / min and kept warm for 2-4h.

[0026] Preferably, in step S201, the pore-forming agent includes at least one of polymethyl methacrylate, ammonium bicarbonate, and urea. The polymethyl methacrylate microspheres are used as templates to form macropores after decomposition, while the ammonium bicarbonate or urea decomposes to produce gas to form small pores. By mixing different pore-forming agents, graded pore formation can be achieved, and gradient pore formation can be achieved by utilizing the difference in their decomposition temperatures. Under medium-speed stirring, the pore-forming agent is ensured to be evenly dispersed to avoid agglomeration leading to uneven pore distribution, and to prevent the pore-forming agent from settling or sol-gelling.

[0027] Furthermore, in step S202, the pressure, inlet and outlet temperatures of spray drying will affect the morphology and pore structure of the precursor particles; the centrifugal atomizer breaks the sol into micron-sized droplets at a pressure of 0.2-0.8 MPa, so that its D50 particle size is 1-50 μm, the high temperature at the inlet quickly evaporates the solvent, and the low temperature at the outlet solidifies the particles to avoid cracking, so the inlet temperature is controlled to 180-220°C and the outlet temperature is 80-120°C to ensure uniform particle size, and the pore-forming agent is co-precipitated with the alumina precursor during the drying process to form a porous precursor particle prototype.

[0028] Furthermore, in step S203, step-by-step pore formation is performed through segmented calcination. The first calcination treatment is used to decompose low-temperature pore-forming agents such as ammonium bicarbonate / urea to form central small pores, while partially removing the template agent. The temperature is controlled to rise to 300-400°C at 2-5°C / min and kept warm for 1-2 hours. The second calcination treatment completely decomposes the polymethyl methacrylate microspheres and residual organic matter to generate surface macropores and densify the alumina matrix. The high-temperature stage promotes the transformation of alumina from amorphous to γ ​​phase, improves mechanical strength and thermal stability, and avoids pore structure collapse through segmented heating to ensure that the pore size decreases continuously from the surface to the inside. The low-temperature stage retains small pores, and the high-temperature stage forms large pores and strengthens the matrix to maintain good compressive strength. The segmented insulation completely decomposes organic matter, reduces carbon residues, and avoids battery side reactions.

[0029] That is to say, low-temperature pore-forming agents such as ammonium bicarbonate and urea decompose at low temperature during the first calcination treatment, releasing gas during decomposition, and the gas escapes from the inside of the material, thereby forming small pores inside the material, forming internal small pores, while the polymethyl methacrylate microspheres have not yet decomposed, maintaining the microsphere structure; during the second calcination treatment, the polymethyl methacrylate microspheres decompose at this high temperature, the carbon chain breaks and oxidizes, the template is removed, and large pores are formed; at the same time, the high temperature further sinters the alumina skeleton to stabilize the pore structure. And during calcination, there is a temperature gradient from the surface to the inside of the material. The surface area may reach the PMMA decomposition temperature first, while the inside is still mainly decomposed by ammonium bicarbonate, further strengthening the "large outside and small inside" stepped pore size distribution.

[0030] Preferably, step S300 specifically includes: S301, subjecting the porous alumina substrate to plasma treatment in an oxygen-containing inert atmosphere at a pressure of 5-50 Pa, with a power of 20-100 W for a time of 5-30 minutes, to obtain a surface-activated porous alumina substrate; S302, in an inert atmosphere, introducing silane coupling agent vapor into the surface-activated porous alumina substrate, controlling the temperature to 80-120° C., the pressure to 10-500 Pa, and the deposition time to 0.5-3 h, to form alumina powder preliminarily modified with silane; S303, cooling the aluminum oxide powder preliminarily modified with silane to room temperature, and vacuum drying it at 80-150° C. for 1-5 h to obtain aluminum oxide powder modified with silane.

[0031] For example, in step S301, the oxygen-containing inert atmosphere includes Ar / O2 gas, and the volume ratio of Ar to O2 gas is 4:1; the mixed gas is used to avoid excessive oxidation of pure O2 that causes increased surface roughness, and the plasma power of 20-100W and the time of 5-30min are used to accurately control the degree of surface activation. The high-energy particles in the plasma bombard and remove organic pollutants on the surface of aluminum oxide. At the same time, the surface hydroxyl density is increased through the oxidation effect of O2, providing active sites for the bonding of silane coupling agents; and the Ar / O2 mixed gas penetrates into the interior of the pores under low pressure to achieve uniform activation of the entire pore surface, avoiding uneven distribution of the subsequent modification layer.

[0032] For example, in step S302, the silane coupling agent includes at least one of 3-aminopropyltriethoxysilane and 3-glycidoxypropyltrimethoxysilane; the silane coupling agent forms a Si-O-Al bonding network on the activated surface through a hydrolysis condensation reaction, and the amino group or epoxy group of the silane coupling agent is introduced to provide a chemical anchor point with the electrolyte or electrode to enhance the interface compatibility; the silane vapor is caused to penetrate deep into the pores under low pressure and medium temperature to achieve full pore modification.

[0033] Furthermore, heating in a vacuum environment promotes dehydration and condensation between silane molecules to form a dense cross-linked network, while unreacted silane monomers and by-products are removed by suction to ensure the purity of the modified layer and avoid clogging of the pores by liquid residues.

[0034] Preferably, in step S400, the fluorocarbon gas includes at least one of perfluorooctane, tetrafluoroethylene, and hexafluoropropylene, and the fluorocarbon layer makes the aluminum oxide surface corrosion-resistant; the conditions for the vapor deposition of fluorocarbon gas include: a deposition temperature of 80-150°C, a pressure of 10-200Pa, and a time of 0.5-2h; the appropriate temperature promotes the physical adsorption and orientation arrangement of fluorocarbon molecules on the surface of the substrate, and the low pressure condition ensures that the fluorocarbon vapor penetrates into the pores to achieve full coverage of the outer surface of the silane layer, and the appropriate time can balance the deposition efficiency and layer thickness control to avoid excessive clogging of the pores; the annealing treatment is carried out in an inert atmosphere, including heating to 150-250°C at 1-5°C / min and keeping warm for 0.5-3h. The annealing treatment promotes the close stacking and orientation consistency of the perfluoroalkyl chains, achieves directional arrangement through intermolecular forces, reduces surface defects, and improves the thermal stability of the hydrophobic layer.

[0035] Specifically, the perfluorooctane of this embodiment has a fully fluorinated straight-chain alkane with high CF bond energy and strong chemical inertness. It can be physically adsorbed on the surface of the silane layer through van der Waals forces to form a fluorocarbon hydrophobic layer; that is, the silane layer mainly passivates the hydroxyl groups on the surface of aluminum oxide to improve the interface compatibility, and the fluorocarbon layer provides hydrophobicity through physical coating, and the two work together without chemical interference.

[0036] Example 1 This embodiment provides a method for preparing porous alumina powder for lithium ion batteries, the preparation method comprising: S100, preparing a precursor: dispersing aluminum nitrate and hexadecyltrimethylammonium bromide in an ethanol solution at a mass ratio of 1:0.3, stirring at 60° C. for 12 h to form a first sol; S201, mixing the first sol with polymethyl methacrylate microspheres and ammonium bicarbonate in a mass ratio of 1:1, and stirring at a speed of 600 rpm for 20 minutes to obtain a second sol; S202, spray drying the second sol through a centrifugal atomizer, controlling the inlet temperature to 200° C., the outlet temperature to 100° C., and the pressure to 0.6 MPa, to obtain porous alumina precursor particles; S203, calcining the porous alumina precursor particles in an air atmosphere in stages to obtain a porous alumina matrix, such as Figure 3 As shown; Wherein, the staged calcination process includes a first calcination process and a second calcination process; The first calcination treatment is to increase the temperature to 350°C at 3°C / min and keep the temperature for 1 hour; The second calcination treatment is carried out by heating the temperature to 700°C at a rate of 2°C / min and keeping the temperature for 3 hours; S301, subjecting the porous alumina substrate to plasma treatment for 20 min in a mixed inert gas having a volume ratio of Ar to O2 of 4:1 at a pressure of 30 Pa and a power of 80 W to obtain a surface-activated porous alumina substrate; S302, in an Ar atmosphere, introducing 3-aminopropyltriethoxysilane vapor into the surface-activated porous alumina substrate, controlling the temperature to 100° C., the pressure to 200 Pa, and the deposition time to 1 h, to form alumina powder preliminarily modified with silane; S303, cooling the aluminum oxide powder preliminarily modified with silane to room temperature, and vacuum drying at 100° C. for 3 h to obtain an aluminum oxide powder modified with silane; S400, preparation of fluorocarbon hydrophobic layer: Silane-modified alumina powder was subjected to perfluorooctane gas vapor deposition in an Ar atmosphere at a temperature of 100°C, a pressure of 100 Pa, and a time of 1 h. The annealing treatment was performed by heating the temperature to 200°C at a rate of 3°C / min and keeping the temperature for 1.5 h to obtain porous alumina powder. The SEM and TEM images are shown in FIG. Figure 1 , Figure 2 shown.

[0037] Example 2 This embodiment provides a method for preparing porous alumina powder for lithium ion batteries, the preparation method comprising: S100, preparing a precursor: dispersing aluminum isopropoxide and a triblock copolymer of polyethylene oxide-polypropylene oxide-polyethylene oxide in an ethanol solution at a mass ratio of 1:0.01, stirring at 40° C. for 24 hours to form a first sol; S201, mixing the first sol with polymethyl methacrylate microspheres and ammonium bicarbonate in a mass ratio of 1:0.5, and stirring at a speed of 200 rpm for 10 minutes to obtain a second sol; S202, spray drying the second sol through a centrifugal atomizer, controlling the inlet temperature to 180° C., the outlet temperature to 80° C., and the pressure to 0.2 MPa, to obtain porous alumina precursor particles; S203, calcining the porous alumina precursor particles in an air atmosphere in stages to obtain a porous alumina matrix; Wherein, the staged calcination process includes a first calcination process and a second calcination process; The first calcination treatment is to increase the temperature to 300°C at 2°C / min and keep the temperature for 2h; The second calcination treatment is carried out by heating the temperature to 600°C at a rate of 1°C / min and keeping the temperature for 4 hours; S301, subjecting the porous alumina substrate to plasma treatment for 30 min in a mixed inert gas having a volume ratio of Ar to O2 of 4:1 at a pressure of 5 Pa and a power of 20 W to obtain a surface-activated porous alumina substrate; S302, in an Ar atmosphere, introducing 3-glycidyloxypropyltrimethoxysilane vapor into the surface-activated porous alumina substrate, controlling the temperature to 80° C., the pressure to 10 Pa, and the deposition time to 0.5 h, to form alumina powder preliminarily modified with silane; S303, cooling the aluminum oxide powder preliminarily modified with silane to room temperature, and vacuum drying at 80° C. for 5 h to obtain an aluminum oxide powder modified with silane; S400, preparing a fluorocarbon hydrophobic layer: subjecting the silane-modified alumina powder to tetrafluoroethylene gas vapor deposition in an Ar atmosphere at a temperature of 80°C, a pressure of 10 Pa, and a time of 2 h, and annealing treatment by raising the temperature to 150°C at a rate of 1°C / min and keeping the temperature for 3 h to obtain a porous alumina powder.

[0038] Example 3 This embodiment provides a method for preparing porous alumina powder for lithium ion batteries, the preparation method comprising: S100, preparing a precursor: dispersing aluminum isopropoxide and poloxamer F127 in an ethanol solution at a mass ratio of 1:0.5 at 80° C. with stirring for 2 h to form a first sol; S201, mixing the first sol with polymethyl methacrylate microspheres and urea in a mass ratio of 1:1.5, and stirring at a speed of 800 rpm for 30 minutes to obtain a second sol; S202, spray drying the second sol through a centrifugal atomizer, controlling the inlet temperature to 220° C., the outlet temperature to 120° C., and the pressure to 0.8 MPa, to obtain porous alumina precursor particles; S203, calcining the porous alumina precursor particles in an air atmosphere in stages to obtain a porous alumina matrix; Wherein, the staged calcination process includes a first calcination process and a second calcination process; The first calcination treatment is to increase the temperature to 400°C at 5°C / min and keep the temperature for 1 hour; The second calcination treatment is carried out by heating the temperature to 800°C at a rate of 3°C / min and keeping the temperature for 2h; S301, subjecting the porous alumina substrate to plasma treatment for 5 min in a mixed inert gas having an Ar and O2 gas volume ratio of 4:1 at a pressure of 50 Pa and a power of 100 W to obtain a surface-activated porous alumina substrate; S302, in an Ar atmosphere, introducing 3-aminopropyltriethoxysilane vapor into the surface-activated porous alumina substrate, controlling the temperature to 120° C., the pressure to 500 Pa, and the deposition time to 0.5 h, to form alumina powder preliminarily modified with silane; S303, cooling the aluminum oxide powder preliminarily modified with silane to room temperature, and vacuum drying at 150° C. for 1 h to obtain an aluminum oxide powder modified with silane; S400, preparing a fluorocarbon hydrophobic layer: subjecting the silane-modified alumina powder to hexafluoropropylene gas vapor deposition in an Ar atmosphere at a temperature of 150° C., a pressure of 200 Pa, and a time of 0.5 h, and annealing treatment by raising the temperature to 250° C. at a rate of 5° C. / min and keeping the temperature for 0.5 h to obtain a porous alumina powder.

[0039] Comparative Example 1 This comparative example provides a porous alumina powder, which is purchased from outside.

[0040] Comparative Example 2 This comparative example provides a porous alumina, which includes, from the inside to the outside, an alumina substrate, a silane coupling agent modification layer, and the surface of the alumina substrate has a porous structure. The preparation method is the same as that of Example 1, except that there is no step S400.

[0041] Comparative Example 3 This comparative example provides a porous alumina, which includes, from the inside to the outside, an alumina substrate and a fluorocarbon hydrophobic layer. The surface of the alumina substrate has a porous structure. The preparation method is the same as that of Example 1, except that there is no step S300.

[0042]

Characterization test

[0043] Table 1

Performance test

[0044] Table 2 Combining Table 1 with Table 2, it can be obtained from Examples 1-3 and Comparative Example 1 that the pore size of the porous alumina matrix gradually decreases from the surface to the center, which can significantly shorten the electrolyte infiltration time; the high specific surface area and porosity can promote the rapid diffusion of lithium ions, and the cycle capacity retention rate is maintained at no less than 88%; According to Examples 1-3 and Comparative Examples 2-3, the silane layer improves the interfacial bonding strength through Si-O-Al bonding, and the fluorocarbon layer provides hydrophobicity, inhibits side reactions, and improves the cycle stability; the contact angle of Comparative Example 2 without a fluorocarbon layer is only 50°, the electrolyte infiltration is fast, but the capacity retention rate is low, indicating that the lack of a hydrophobic protective layer leads to aggravated side reactions; in Comparative Example 3 without a silane layer, the fluorocarbon layer directly coats alumina with a contact angle of 130°, but due to weak interface bonding, the cycle stability is lower than that of the embodiment, proving the necessity of silane coupling agent for interface optimization.

[0045] In the description of this specification, the description of the terms "one embodiment", "some embodiments", "specific embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0046] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A porous alumina powder for lithium ion batteries, characterized in that: The porous alumina powder comprises: A porous alumina substrate, wherein the pore size of the porous alumina substrate gradually decreases from the surface to the center, wherein the surface pore size is 100-500 nm and the central area pore size is 5-50 nm; A silane coupling agent modified layer, wherein the silane coupling agent modified layer covers at least a portion of the surface of the porous alumina substrate, and the silane coupling agent has a Si—O—Al bonding network structure; A fluorocarbon hydrophobic layer is coated on at least a portion of the surface of the silane coupling agent modified layer, and the fluorocarbon hydrophobic layer is a perfluoroalkyl chain structure.

2. The porous alumina powder according to claim 1, characterized in that The thickness of the porous alumina substrate is 10-200 μm; and / or The thickness of the silane coupling agent modified layer is 1-10 nm; and / or The thickness of the fluorocarbon hydrophobic layer is 2-50 nm.

3. The porous alumina powder according to claim 1, characterized in that: The porosity of the porous alumina powder is 60-80%; and / or The specific surface area of ​​the porous alumina powder is 50-200 m² / g.

4. A method for preparing porous alumina powder for lithium ion batteries, characterized in that: For preparing the porous alumina powder according to any one of claims 1 to 3, the preparation method comprises: S100, preparing a precursor: dispersing an aluminum oxide precursor and a template in an ethanol solution to form a first sol; S200, preparing a porous alumina matrix: mixing the first sol with a pore-forming agent, spraying the mixture, and performing staged calcination to obtain the porous alumina matrix; S300, preparing a silane coupling agent modified layer: performing plasma pretreatment on the porous alumina substrate, and then performing vapor deposition of a silane coupling agent under an inert atmosphere to obtain a silane-modified alumina powder; S400, preparing a fluorocarbon hydrophobic layer: subjecting the silane-modified alumina powder to fluorocarbon gas vapor deposition and annealing treatment under an inert atmosphere to obtain the porous alumina powder.

5. The preparation method according to claim 4, characterized in that: In step S100, The aluminum oxide precursor includes at least one of aluminum nitrate and aluminum isopropoxide; and / or The template agent is selected from at least one of cetyltrimethylammonium bromide, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, and poloxamer F127; and / or The mass ratio of the aluminum oxide precursor to the template is 1:(0.01-0.5); and / or The preparation conditions of the first sol include: stirring at 40-80° C. for 2-24 hours.

6. The preparation method according to claim 4, characterized in that: Step S200 specifically includes: S201, mixing the first sol and the pore-forming agent in a mass ratio of 1:(0.1-1.5), stirring at a speed of 200-800 rpm for 10-30 min to obtain a second sol; S202, spray drying the second sol through a centrifugal atomizer, controlling the inlet temperature to 180-220° C. and the outlet temperature to 80-120° C., to obtain porous alumina precursor particles; S203, calcining the porous alumina precursor particles in an air atmosphere in stages to obtain the porous alumina matrix; Wherein, the staged calcination process includes a first calcination process and a second calcination process; The first calcination treatment is to increase the temperature to 300-400°C at 2-5°C / min and keep the temperature for 1-2h; The second calcination treatment is carried out by heating the temperature to 600-800°C at a rate of 1-3°C / min and keeping the temperature for 2-4h.

7. The preparation method according to claim 6, characterized in that: In step S201, the pore-forming agent includes at least one of polymethyl methacrylate microspheres, ammonium bicarbonate, and urea; and / or In step S202, the pressure of the spray drying process is 0.2-0.8 MPa.

8. The preparation method according to claim 4, characterized in that: Step S300 specifically includes: S301, subjecting the porous alumina substrate to the plasma treatment for 5-30 min at a pressure of 5-50 Pa and a power of 20-100 W in an oxygen-containing inert atmosphere to obtain a surface-activated porous alumina substrate; S302, under an inert atmosphere, introducing the silane coupling agent vapor into the surface-activated porous alumina substrate, controlling the temperature to 80-120° C., the pressure to 10-500 Pa, and the deposition time to 0.5-3 h, to form alumina powder preliminarily modified with silane; S303, cooling the aluminum oxide powder preliminarily modified with silane to room temperature, and vacuum drying it at 80-150°C for 1-5h to obtain the aluminum oxide powder modified with silane.

9. The preparation method according to claim 8, characterized in that: In step S301, the oxygen-containing inert atmosphere includes Ar / O2 gas, and the volume ratio of Ar to O2 gas is 4:1; In step S302, the silane coupling agent includes at least one of 3-aminopropyltriethoxysilane and 3-glycidyloxypropyltrimethoxysilane.

10. The preparation method according to claim 4, characterized in that: In step S400, The fluorocarbon gas includes at least one of perfluorooctane, tetrafluoroethylene and hexafluoropropylene; and / or The conditions for the fluorocarbon gas vapor deposition include: a deposition temperature of 80-150° C., a pressure of 10-200 Pa, and a time of 0.5-2 h; and / or The annealing treatment is carried out in an inert atmosphere, including heating to 150-250° C. at 1-5° C. / min and keeping the temperature for 0.5-3 h.

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