A porous alumina powder for use in lithium ion batteries and a preparation method therefor

Abstract

The present invention relates to the technical field of battery materials, and specifically provides a porous alumina powder for use in lithium-ion batteries and a preparation method thereof; the porous alumina powder of the present application includes: a porous alumina matrix with pore diameters gradually decreasing from the surface to the center; a silane coupling agent modification layer that covers at least part of the surface of the porous alumina matrix, and the silane coupling agent has a Si-O-Al bonding network structure; a fluorocarbon hydrophobic layer that coats at least part of the surface of the silane coupling agent modification layer, and the fluorocarbon hydrophobic layer is a perfluoroalkyl chain structure. The present application synergistically modifies the gradient pore structure with a double layer of silane-fluorocarbon to simultaneously improve the electrolyte wettability, interface stability, and moisture resistance.

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 object of the present invention, the present invention provides a method for preparing porous alumina powder for use in lithium-ion batteries, for preparing the porous alumina powder of any one of the above technical solutions. The preparation method includes: S100, preparing a precursor: dispersing an alumina precursor and a templating agent in an ethanol solution to form a first sol; S200, preparing a porous alumina matrix: mixing the first sol with a pore-forming agent, followed by spray treatment and segmented calcination treatment to obtain a porous alumina matrix; S300, preparing a silane coupling agent modification layer: performing plasma pretreatment on the porous alumina matrix, and then performing silane coupling agent vapor deposition in an inert atmosphere to obtain silane-modified alumina powder; S400, preparing a fluorocarbon hydrophobic layer: performing fluorocarbon gas vapor deposition and annealing treatment on the silane-modified alumina powder in an inert atmosphere to obtain 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 templating agent is selected from at least one of cetyltrimethylammonium bromide, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer, and poloxamer F127; and / or the mass ratio of the alumina precursor to the templating agent is 1:(0.01 - 0.5); and / or the solid content of the first sol is 5 - 30 wt% and the pH value is 3 - 5; and / or the preparation conditions of the first sol include: stirring at 40 - 80 °C for 2 - 24 h.

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

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

[0012] In any of the above technical solutions, 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 and a power of 20-100 W for 5-30 minutes to obtain a surface-activated porous alumina substrate; S302. Introducing silane coupling agent vapor into the surface-activated porous alumina substrate under an inert atmosphere, controlling the temperature at 80-120 °C, the pressure at 10-500 Pa, and the deposition time at 0.5-3 h to form alumina powder preliminarily modified with silane; S303. After cooling the alumina powder preliminarily modified with silane to room temperature, drying it under vacuum at 80-150 °C for 1-5 h to obtain alumina powder modified with silane.

[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 is 4:1; in step S302, the silane coupling agent includes at least one of 3-aminopropyltriethoxysilane and 3-glycidoxypropyltrimethoxysilane.

[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 the vapor deposition of the fluorocarbon gas include: the deposition temperature is 80-150 °C, the pressure is 10-200 Pa, and the time is 0.5-2 h; and / or the annealing treatment is carried out in an inert atmosphere, including heating to 150-250 °C at a rate of 1-5 °C / min and holding for 0.5-3 h.

[0015] After adopting the technical solution of the present invention, the achievable technical effects are as follows:

[0016] 1. The porous alumina substrate has a pore size gradient that gradually decreases from the surface to the center. Combining the high porosity and particle morphology can increase the specific surface area of the material, enabling the electrolyte to quickly penetrate through the large surface pores to the interior. At the same time, the small center pores 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 a decrease in ion mobility caused by a uniform pore size.

[0017] 2. The silane coupling agent modification layer is firmly bonded to the alumina substrate 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, reducing the interfacial impedance and improving the interfacial bonding force.

[0018] 3. The perfluoroalkyl chain selectively coats the outside of the silane layer through vapor deposition, isolating the intrusion of moisture while maintaining the pore channels unobstructed. Moreover, the chemical inertness of the fluorocarbon layer further inhibits the side reaction of electrolyte decomposition, thereby enhancing the chemical stability of the material in the electrolyte and reducing electrode pulverization and capacity attenuation. Description of the Drawings

[0019] Figure 1 SEM image of the porous alumina of Example 1 of the present invention;

[0020] Figure 2 TEM image of the porous alumina of Example 1 of the present invention;

[0021] Figure 3 SEM image of the porous alumina matrix of Example 1 of the present invention;

[0022] Figure 4 Capacity retention rate graph of the porous alumina of Examples 1-3 and Comparative Examples 1-3 of the present invention. Detailed implementation manners

[0023] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

[0024] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0025] In order to make the above-mentioned objects, features and advantages of this aspect more obvious and understandable, the specific embodiments of this aspect will be described in detail below.

[0026] With the wide application of lithium-ion batteries in the fields of electric vehicles and energy storage, the market's requirements for battery performance are becoming increasingly stringent. While improving the energy density and cycle life, high safety and environmental adaptability need to be taken into account. As a battery separator coating or electrode additive, porous alumina can improve the electrolyte wettability, but its traditional design has significant defects: the uniform pore size structure is difficult to balance the wetting speed and ion transport efficiency; side reactions caused by surface hydroxyl groups lead to pore blockage and interface deterioration; the moisture absorption problem caused by high porosity further exacerbates the battery performance decay.

[0027] The prior art cannot systematically solve the above contradictions through a single pore size regulation or surface modification scheme, which has become the key bottleneck restricting the development of high-reliability batteries. Therefore, this embodiment provides a porous alumina powder for lithium-ion batteries and its preparation method, which solves the above technical contradictions through the design of a gradient pore size matrix + double-layer interface modification; the porous alumina powder includes:

[0028] A porous alumina matrix, the pore size of the porous alumina matrix gradually decreases from the surface to the center, where the surface pore size is 100 - 500 nm and the pore size in the central region is 5 - 50 nm;

[0029] A silane coupling agent modification layer, the silane coupling agent modification layer covers at least part of the surface of the porous alumina matrix, and the silane coupling agent has a Si - O - Al bonding network structure;

[0030] A fluorocarbon hydrophobic layer, the fluorocarbon hydrophobic layer coats at least part of the surface of the silane coupling agent modification layer, and the fluorocarbon hydrophobic layer is a perfluoroalkyl chain structure.

[0031] Preferably, the gradient pore size 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, realizing the synergistic optimization of the wetting efficiency and the ion transport channels; the silane coupling agent layer passivates the interface through Si - O - Al bonding, inhibits side reactions and enhances the electrode binding force; the selective coating of the fluorocarbon hydrophobic layer realizes moisture resistance and corrosion resistance while keeping the pores unobstructed, achieving the compatibility of moisture resistance and pore unobstructedness, and breaking through the performance limitations of a single modification layer.

[0032] This embodiment provides a preparation method of porous alumina powder applied to a lithium - ion battery. The preparation method includes:

[0033] S100. Prepare a precursor: Disperse an alumina precursor and a template agent in an ethanol solution to form a first sol;

[0034] S200. Prepare a porous alumina matrix: After mixing the first sol and a pore - forming agent, perform spray treatment and segmented calcination treatment to obtain a porous alumina matrix;

[0035] S300. Prepare a silane coupling agent modification layer: Perform plasma pretreatment on the porous alumina matrix, and then carry out silane coupling agent vapor deposition in an inert atmosphere to obtain silane - modified alumina powder;

[0036] S400. Prepare a fluorocarbon hydrophobic layer: Carry out fluorocarbon gas vapor deposition and annealing treatment on the silane - modified alumina powder in an inert atmosphere to obtain porous alumina powder.

[0037] 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.

[0038] Furthermore, step S200 specifically includes:

[0039] 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;

[0040] 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;

[0041] S203, calcining the porous alumina precursor particles in an air atmosphere in stages to obtain a porous alumina matrix;

[0042] 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.

[0043] Preferably, in step S201, the pore former includes at least one of polymethyl methacrylate, ammonium bicarbonate, and urea. The polymethyl methacrylate microspheres serve as templates and will form macropores after decomposition, while ammonium bicarbonate or urea decomposes to produce gas and form micropores. By mixing different pore formers, hierarchical pore formation can be achieved, and gradient pore formation can be realized by utilizing the difference in their decomposition temperatures. Under medium-speed stirring, ensure the uniform dispersion of the pore former to avoid uneven pore distribution caused by agglomeration and prevent the sedimentation or sol-gelation of the pore former.

[0044] 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, with its D50 particle size being 1 - 50 μm. The high inlet temperature rapidly evaporates the solvent, and the low outlet temperature solidifies the particles to avoid cracking. Therefore, control the inlet temperature at 180 - 220 °C and the outlet temperature at 80 - 120 °C to ensure uniform particle size, and during the drying process, the pore former and the alumina precursor co-precipitate to form the prototype of porous precursor particles.

[0045] Even further, in step S203, stepped pore formation is carried out by staged calcination. The first calcination treatment is used to decompose low-temperature pore formers such as ammonium bicarbonate / urea, form central micropores, and at the same time partially remove the templating agent. Control the heating rate to 2 - 5 °C / min to 300 - 400 °C and hold for 1 - 2 h. The second calcination treatment completely decomposes the polymethyl methacrylate microspheres and residual organic matter, generates surface macropores, and densifies the alumina matrix. The high-temperature section promotes the transformation of alumina from amorphous to γ-phase, improving the mechanical strength and thermal stability. By staged heating, avoid the collapse of the pore structure and ensure that the pore diameter continuously decreases from the surface to the inside. The low-temperature section retains the micropores, and the high-temperature section forms macropores and strengthens the matrix, enabling it to maintain good compressive strength. Staged holding completely decomposes the organic matter, reduces carbon residue, and avoids side reactions in the battery.

[0046] That is to say, low-temperature pore formers such as ammonium bicarbonate and urea decompose at low temperature during the first calcination treatment. When decomposing, they release gas, and the gas escapes from the inside of the material, thus forming micropores inside the material, forming internal micropores. At this time, the polymethyl methacrylate microspheres have not decomposed and maintain the microsphere structure. When the second calcination treatment is carried out, the polymethyl methacrylate microspheres decompose at this high temperature, the carbon chains break and oxidize, and the template is removed to form macropores. At the same time, the high temperature further sinters the alumina skeleton and stabilizes 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 dominated by the decomposition of ammonium bicarbonate, further strengthening the "large outside and small inside" stepped pore size distribution.

[0047] Preferably, step S300 specifically includes:

[0048] S301. Subject 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 and a time of 5 - 30 minutes to obtain a surface-activated porous alumina substrate;

[0049] S302. Under an inert atmosphere, introduce the vapor of a silane coupling agent into the surface-activated porous alumina substrate, control the temperature at 80 - 120 °C, the pressure at 10 - 500 Pa, and the deposition time at 0.5 - 3 h to form alumina powder with a preliminary silane modification;

[0050] S303. After cooling the alumina powder with a preliminary silane modification to room temperature, conduct vacuum drying at 80 - 150 °C for 1 - 5 h to obtain alumina powder with a silane modification.

[0051] For example, in step S301, the oxygen-containing inert atmosphere includes Ar / O₂ gas, and the volume ratio of Ar to O₂ is 4:1; the mixed gas is used to avoid excessive oxidation by pure O₂, which may lead to an increase in surface roughness. The plasma power of 20 - 100 W and the time of 5 - 30 min precisely control the degree of surface activation. The high-energy particles in the plasma bombard and remove the organic pollutants on the alumina surface. At the same time, the oxidation effect of O₂ increases the surface hydroxyl density, providing active sites for the bonding of the silane coupling agent; and the Ar / O₂ mixed gas penetrates into the internal pores under low pressure to achieve uniform activation of the entire pore surface, avoiding uneven distribution of the subsequent modification layer.

[0052] 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 through hydrolysis and condensation reactions on the activated surface, providing chemical anchor points with the electrolyte or electrode by introducing the amino group or epoxy group of the silane coupling agent to enhance the interfacial compatibility; under low pressure and medium temperature, the silane vapor is promoted to penetrate deep into the pores to achieve modification of the entire pore.

[0053] Furthermore, under a vacuum environment, the temperature is increased to promote dehydration and condensation between silane molecules to form a dense cross-linked network. At the same time, the unreacted silane monomers and by-products are sucked out to ensure the purity of the modification layer and avoid blockage of the pores caused by liquid-phase residues.

[0054] Preferably, in step S400, the fluorocarbon gas includes at least one of perfluorooctane, tetrafluoroethylene, and hexafluoropropylene. The fluorocarbon layer renders the surface of alumina corrosion-resistant. The conditions for chemical vapor deposition of the fluorocarbon gas include: deposition temperature of 80 - 150 °C, pressure of 10 - 200 Pa, and time of 0.5 - 2 h. The appropriate temperature promotes the physical adsorption and orientation arrangement of fluorocarbon molecules on the surface of the substrate. The low-pressure condition ensures the penetration of fluorocarbon vapor into the pores, achieving full coverage of the outer surface of the silane layer. The appropriate time can balance the deposition efficiency and layer thickness control, avoiding blockage of the pores due to excessive thickness. The annealing treatment is carried out in an inert atmosphere, including heating to 150 - 250 °C at a rate of 1 - 5 °C / min and holding for 0.5 - 3 h. The annealing treatment promotes the close packing and orientation consistency of perfluoroalkyl chains, achieving directional arrangement through intermolecular forces, reducing surface defects, and enhancing the thermal stability of the hydrophobic layer.

[0055] Specifically, the perfluorooctane in this embodiment has a fully fluorinated straight-chain alkane with a high C-F bond energy and strong chemical inertness, and can be physically adsorbed on the surface of the silane layer through van der Waals forces to form a fluorocarbon hydrophobic layer. That is to say, the silane layer mainly passivates the hydroxyl groups on the surface of alumina to improve the interfacial compatibility. The fluorocarbon layer provides hydrophobicity through physical coating, and the two work synergistically without chemical interference.

[0056] Example 1

[0057] This embodiment provides a preparation method for porous alumina powder applied to lithium-ion batteries. The preparation method includes:

[0058] S100. Prepare a precursor: Mix aluminum nitrate and cetyltrimethylammonium bromide at a mass ratio of 1:0.3, and stir for 12 h at 60 °C to disperse in an ethanol solution to form a first sol;

[0059] S201. Mix the first sol with polymethyl methacrylate microspheres and ammonium bicarbonate at a mass ratio of 1:1, and stir at a rotation speed of 600 rpm for 20 min to obtain a second sol;

[0060] S202. Perform spray drying treatment on the second sol through a centrifugal atomizer, controlling the inlet temperature at 200 °C, the outlet temperature at 100 °C, and the pressure at 0.6 MPa to obtain porous alumina precursor particles;

[0061] S203. Perform staged calcination treatment on the porous alumina precursor particles in an air atmosphere to obtain a porous alumina matrix, as Figure 3 shown;

[0062] Among them, the staged calcination treatment includes a first calcination treatment and a second calcination treatment;

[0063] The first calcination treatment is heated to 350 °C at a rate of 3 °C / min and held for 1 h;

[0064] The second calcination treatment is heated to 700 °C at a rate of 2 °C / min and held for 3 h;

[0065] S301. The porous alumina substrate is subjected to plasma treatment in a mixed inert gas with a volume ratio of Ar to O2 of 4:1 at a pressure of 30 Pa and a power of 80 W for 20 min to obtain a surface-activated porous alumina substrate;

[0066] S302. In an Ar atmosphere, 3-aminopropyltriethoxysilane vapor is introduced into the surface-activated porous alumina substrate, the temperature is controlled at 100 °C, the pressure is 200 Pa, and the deposition time is 1 h to form alumina powder with a preliminary silane modification;

[0067] S303. After the alumina powder with a preliminary silane modification is cooled to room temperature, it is vacuum-dried at 100 °C for 3 h to obtain alumina powder with a silane modification;

[0068] S400. Prepare a fluorocarbon hydrophobic layer: The alumina powder with a silane modification is subjected to gas-phase deposition of perfluorooctane gas in an Ar atmosphere at a temperature of 100 °C, a pressure of 100 Pa, and a time of 1 h. The annealing treatment is heated to 200 °C at a rate of 3 °C / min and held for 1.5 h to obtain porous alumina powder. The SEM image and TEM image are as Figure 1 、 Figure 2 shown.

[0069] Example 2

[0070] This example provides a preparation method of porous alumina powder applied to a lithium-ion battery. The preparation method includes:

[0071] S100. Prepare a precursor: Aluminum isopropoxide and a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer are mixed at a mass ratio of 1:0.01 and stirred at 40 °C for 24 h and dispersed in an ethanol solution to form a first sol;

[0072] S201. The first sol is mixed with polymethyl methacrylate microspheres and ammonium bicarbonate at a mass ratio of 1:0.5 and stirred at a rotation speed of 200 rpm for 10 min to obtain a second sol;

[0073] S202. The second sol is subjected to spray drying treatment through a centrifugal atomizer, and the inlet temperature is controlled at 180 °C, the outlet temperature is 80 °C, and the pressure is 0.2 MPa to obtain porous alumina precursor particles;

[0074] S203. The porous alumina precursor particles are subjected to a segmented calcination treatment in an air atmosphere to obtain a porous alumina substrate;

[0075] Among them, the segmented calcination treatment includes a first calcination treatment and a second calcination treatment;

[0076] The first calcination treatment is heated to 300 °C at a rate of 2 °C / min and held for 2 h;

[0077] The second calcination treatment is heated to 600 °C at a rate of 1 °C / min and held for 4 h;

[0078] S301. Plasma-treat a porous alumina substrate in a mixed inert gas with a volume ratio of Ar to O2 of 4:1 at a pressure of 5 Pa and a power of 20 W for 30 min to obtain a surface-activated porous alumina substrate;

[0079] S302. In an Ar atmosphere, introduce 3-glycidoxypropyltrimethoxysilane vapor into the surface-activated porous alumina substrate, control the temperature at 80 °C, the pressure at 10 Pa, and the deposition time at 0.5 h to form preliminarily silane-modified alumina powder;

[0080] S303. After cooling the preliminarily silane-modified alumina powder to room temperature, vacuum-dry it at 80 °C for 5 h to obtain silane-modified alumina powder;

[0081] S400. Prepare a fluorocarbon hydrophobic layer: Perform chemical vapor deposition of tetrafluoroethylene gas on the silane-modified alumina powder in an Ar atmosphere at a temperature of 80 °C, a pressure of 10 Pa, and a time of 2 h. For the annealing treatment, heat it to 150 °C at a rate of 1 °C / min and hold for 3 h to obtain porous alumina powder.

[0082] Example 3

[0083] This example provides a method for preparing porous alumina powder applied to a lithium-ion battery. The preparation method includes:

[0084] S100. Prepare a precursor: Mix aluminum isopropoxide and poloxamer F127 at a mass ratio of 1:0.5, and stir and disperse them in an ethanol solution at 80 °C for 2 h to form a first sol;

[0085] S201. Mix the first sol with polymethyl methacrylate microspheres and urea at a mass ratio of 1:1.5, and stir at a speed of 800 rpm for 30 min to obtain a second sol;

[0086] S202. Spray-dry the second sol through a centrifugal atomizer, control the inlet temperature at 220 °C, the outlet temperature at 120 °C, and the pressure at 0.8 MPa to obtain porous alumina precursor particles;

[0087] S203. Subject the porous alumina precursor particles to a staged calcination treatment in an air atmosphere to obtain a porous alumina substrate;

[0088] Among them, the segmented calcination treatment includes a first calcination treatment and a second calcination treatment;

[0089] The first calcination treatment is heated to 400 °C at a rate of 5 °C / min and held for 1 h;

[0090] The second calcination treatment is heated to 800 °C at a rate of 3 °C / min and held for 2 h;

[0091] S301. Plasma-treat a porous alumina substrate in a mixed inert gas with a volume ratio of Ar to O2 of 4:1 at a pressure of 50 Pa and a power of 100 W for 5 min to obtain a surface-activated porous alumina substrate;

[0092] S302. In an Ar atmosphere, introduce 3-aminopropyltriethoxysilane vapor into the surface-activated porous alumina substrate, control the temperature at 120 °C, the pressure at 500 Pa, and the deposition time at 0.5 h to form alumina powder with a preliminary silane modification;

[0093] S303. After cooling the alumina powder with a preliminary silane modification to room temperature, vacuum-dry it at 150 °C for 1 h to obtain alumina powder with a silane modification;

[0094] S400. Prepare a fluorocarbon hydrophobic layer: Perform vapor deposition of hexafluoropropylene gas on the alumina powder with a silane modification in an Ar atmosphere at a temperature of 150 °C, a pressure of 200 Pa, and a time of 0.5 h. For the annealing treatment, heat it to 250 °C at a rate of 5 °C / min and hold for 0.5 h to obtain porous alumina powder.

[0095] Comparative Example 1

[0096] This comparative example provides a kind of porous alumina powder, which is obtained by outsourcing.

[0097] Comparative Example 2

[0098] This comparative example provides a kind of porous alumina, which sequentially includes from the inside to the outside: an alumina substrate, a silane coupling agent modification layer. The surface of the alumina substrate has a porous structure, and its preparation method is the same as that of Example 1, except that step S400 is absent.

[0099] Comparative Example 3

[0100] This comparative example provides a kind of porous alumina, which sequentially includes from the inside to the outside: an alumina substrate, a fluorocarbon hydrophobic layer. The surface of the alumina substrate has a porous structure, and its preparation method is the same as that of Example 1, except that step S300 is absent.

[0101]

Characterization and Testing

[0102] The pore size and porosity of the porous alumina substrates in Examples 1-3 and Comparative Examples 1-3 were measured by mercury intrusion porosimetry. Mercury liquid was injected into the porous alumina precursor particles, and the intrusion volume of mercury at different pressures was recorded. The results are shown in Table 1.

[0103] The results of the thickness of the porous alumina in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0104]

[0105] Table 1

[0106]

Performance Test

[0107] The electrolyte wetting time, 100-week cycle capacity retention rate, and contact angle of the porous alumina in Examples 1-3 and Comparative Examples 1-3 were tested. The results are shown in Table 2, and the 100-week cycle capacity retention rate graph is as Figure 4 shown.

[0108]

[0109] Table 2

[0110] Combining Table 1 and Table 2, from Examples 1-3 and Comparative Example 1, it can be seen that the pore size of the porous alumina substrate gradually decreases from the surface to the center, which can significantly shorten the electrolyte wetting time; the high specific surface area and porosity can promote the rapid diffusion of lithium ions, and the cycle capacity retention rate is not less than 88%;

[0111] From Examples 1-3 and Comparative Examples 2-3, it can be obtained that the silane layer improves the interfacial bonding force through Si-O-Al bonding, and the fluorocarbon layer provides hydrophobicity, inhibits side reactions, and improves cycle stability; in Comparative Example 2 without a fluorocarbon layer, the contact angle is only 50°, and the electrolyte wets quickly, but the capacity retention rate is low, indicating that the lack of a hydrophobic protection layer leads to an increase in side reactions; in Comparative Example 3 without a silane layer, the contact angle of the fluorocarbon layer directly coated on alumina is 130°, but due to weak interfacial bonding, the cycle stability is lower than that of the examples, proving the necessity of silane coupling agent for interface optimization.

[0112] In the description of this specification, the descriptions of terms such as "one embodiment", "some embodiments", "specific embodiments", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or instance. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0113] 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 stepwise 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 silane coupling agent vapor deposition 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.

Images