Porous aluminum oxide powder for lithium-ion battery and preparation method therefor, battery separator, battery, and electric device

Abstract

Disclosed are a porous aluminum oxide powder for a lithium-ion battery and a preparation method therefor, a battery separator based on the porous aluminum oxide, a battery, and an electric device. The porous aluminum oxide powder comprises aluminum oxide particles having a tetragonal prism structure in an amount of not less than 50%, aluminum oxide particles having a spherical structure in an amount of not more than 1%, and aluminum oxide particles having an acicular structure and a flaky structure in an amount of not more than 5%. The ratio of the prism edge length to the length of the longer diagonal among bottom surface diagonals of each aluminum oxide particle having the tetragonal prism structure is 1:(0.5-5). The porous aluminum oxide is conducive to optimizing the electrolyte wettability of the polymer separator, so that the electrolyte diffusion radius of the separator is significantly increased.

Description

A porous alumina powder for lithium-ion batteries, its preparation method, battery separator, battery, and electrical equipment.

[0001] Cross-reference to related applications

[0002] This disclosure claims priority to Chinese Patent Application No. 2024115258679, filed on October 30, 2024, entitled "A porous alumina powder for lithium-ion batteries, a battery separator, a battery, and an electrical device", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of battery materials, and in particular to a porous alumina powder for lithium-ion batteries, a method for preparing the same, a battery separator, a battery, and electrical equipment. Background Technology

[0004] The main structures in a lithium-ion battery system are the negative electrode, the separator, and the positive electrode, as well as the electrolyte filling the space between the negative and positive electrodes. The charging process of a lithium-ion battery involves lithium ions being extracted from the positive electrode material, migrating through the separator and electrolyte to the surface of the negative electrode material, and inserting into the crystal structure of the negative electrode material. The discharging process involves lithium ions being extracted from the crystal structure of the negative electrode material, migrating through the electrolyte and separator to the surface of the positive electrode material, and embedding into the crystal structure of the positive electrode material.

[0005] Therefore, it is evident that the lithium-ion transport rate within the separator directly affects the battery's charge / discharge efficiency during charging and discharging. Currently, the separators in existing lithium-ion battery systems are primarily polymer separators. However, polymer separators, due to their high molecular weight polymers such as polyolefins, exhibit poor wettability with aqueous electrolytes and also suffer from poor heat resistance, thus failing to enhance the battery's electrochemical performance. To improve the heat resistance of polymer separators, those skilled in the art have proposed coating the separator surface with a ceramic coating. However, this ceramic coating reduces the lithium-ion conductivity of the separator and also affects the electrolyte's wettability, thereby impacting the separator's ionic conductivity. Furthermore, the poor electrolyte wettability caused by polymer separators is mainly due to the poor affinity between the polymer base film and the electrolyte. Therefore, current optimization of polymer separator wettability primarily focuses on optimizing the polymer base film, with little attention paid to optimizing the wettability of the separator through ceramic coatings. Summary of the Invention

[0006] The purpose of this disclosure is to provide a porous alumina powder for lithium-ion batteries, wherein the particle size of the porous alumina powder is beneficial for optimizing the electrolyte wettability of the polymer separator.

[0007] The purpose of this disclosure is also to provide a method for preparing porous alumina powder for lithium-ion batteries, so as to prepare porous alumina powder that can optimize the electrolyte wettability of polymer separators.

[0008] Another object of this disclosure is to provide a battery separator.

[0009] Another object of this disclosure is to provide a battery.

[0010] Another object of this disclosure is to provide an electrical appliance.

[0011] In a first aspect, this disclosure provides a porous alumina powder for lithium-ion batteries, wherein the particle size D50 of the porous alumina powder is 0.3–2 μm, and the specific surface area of ​​the porous alumina powder is 5–50 m². 2 / g; The porous alumina powder contains at least 50% alumina particles with a tetragonal prism morphology, at most 1% alumina particles with a spherical morphology, and at most 5% alumina particles with a needle-like or plate-like morphology.

[0012] The ratio of the edge length to the diagonal length of the base of the alumina particles with a tetragonal prism structure is 1:(0.5~5).

[0013] In optional embodiments, in some embodiments of this disclosure, the porous alumina powder includes at least 90% alumina particles with a tetragonal prism morphology.

[0014] And / or, the amount of alumina particles with a spherical morphology is at most 0.5%;

[0015] And / or, the amount of alumina particles with needle-like and lamellar structures is no more than 2%.

[0016] In optional embodiments, in some embodiments of this disclosure, the content of α-alumina in the porous alumina powder is not higher than 50%.

[0017] In optional embodiments, in some embodiments of this disclosure, the surface hydroxyl content of the porous alumina powder is 8 hydroxyl groups / nm. 2 the following;

[0018] And / or, the infrared spectrum of porous alumina powder at wavenumber 1600 cm⁻¹ -1 ~3700cm -1 Within the range, no part of it exceeds its baseline and has a width of 50cm. -1 The following are infrared peaks.

[0019] In optional embodiments, in some embodiments of this disclosure, the surface hydroxyl content of the porous alumina powder is 5 hydroxyl groups / nm. 2 the following;

[0020] And / or, the infrared spectrum of porous alumina powder at wavenumber 1600 cm⁻¹ -1 ~3700cm -1 Within the range, no part of the baseline is exceeded and the width is less than 100cm. -1 The following are infrared peaks.

[0021] In optional embodiments, in some examples of this disclosure, the particles in the porous alumina powder each include a plurality of pores, the pore diameter being 5–50 nm and the pore volume being 0.01–0.4 cm³. 3 / g; the specific surface area of ​​porous alumina powder is 5-50m². 2 / g.

[0022] In optional embodiments, in some embodiments of this disclosure, the pore diameter is 8–20 nm, and the pore volume is 0.05–0.2 cm³. 3 / g;

[0023] And / or, the specific surface area of ​​porous alumina powder is 6–20 m². 2 / g.

[0024] In optional embodiments, in some embodiments of this disclosure, the particles in the porous alumina powder are at least one of the θ phase, δ phase, γ phase, or at least one of the η phase, κ phase, χ phase, ρ phase.

[0025] In optional embodiments, in some embodiments of this disclosure, porous alumina powder is prepared directly without being compounded from multiple porous alumina powders.

[0026] Secondly, this disclosure also provides a method for preparing porous alumina powder for lithium-ion batteries in any of the above embodiments, comprising:

[0027] Aluminum hydroxide, alcohol, inorganic acid and water are mixed to obtain a precursor solution;

[0028] The precursor solution is mixed with organic acid and water, and the reaction is heated to obtain the intermediate.

[0029] The intermediate was calcined to obtain porous alumina powder.

[0030] In an optional embodiment, the mass ratio of aluminum hydroxide, alcohol, inorganic acid and water is 1:1:(0.1-0.3):(1-3);

[0031] And / or, the alcohol is selected from at least one of ethanol, propanol, n-butanol, isobutanol, pentanol, and isoamyl alcohol;

[0032] And / or, the inorganic acid is selected from at least one of nitric acid, sulfuric acid and hydrochloric acid.

[0033] In an optional embodiment, the heating reaction process in the preparation of the intermediate includes: first reacting at 60℃~80℃ for 1h~3h; then heating to 150℃~200℃ and reacting for 4h~48h, while controlling the reaction pressure at 1.4MPa~3.7MPa;

[0034] And / or, the mass ratio of the precursor solution to organic acid and water is 1:(0.12~0.2):(0.2~0.4), the mass ratio of inorganic acid to organic acid is controlled to be (0.16~0.5):1; and the mass ratio of alcohol to organic acid is (1.2~2.0):1;

[0035] And / or, the organic acid is selected from at least one of acetic acid, oxalic acid and citric acid.

[0036] In an optional embodiment, the intermediate is first washed, demagnetized, and dried, and then calcined.

[0037] And / or, control the calcination temperature to be 600℃~1200℃ and the calcination time to be 0.5h-5h;

[0038] And / or, after calcination, air jet milling is performed to obtain porous alumina powder.

[0039] In an optional embodiment, a barrier agent with a decomposition temperature not exceeding 450°C is added during the preparation of porous alumina powder from the intermediate.

[0040] In an optional implementation, the barrier agent is added during the drying or calcination stage;

[0041] And / or, the mass ratio of the dried intermediate powder to the barrier agent is 100:(0.01~0.1);

[0042] And / or, the barrier agent is selected from at least one of ammonium bicarbonate, ammonium carbonate and ammonium nitrate.

[0043] Thirdly, this disclosure also provides a battery separator, the battery separator comprising the porous alumina of the first aspect.

[0044] In an optional embodiment, the battery separator disclosed herein is a battery separator, which includes a substrate and a coating formed on at least one side of the substrate, wherein porous alumina is distributed in the coating.

[0045] The liquid absorption capacity of the battery separator is not less than 0.6 mL / g. Fourthly, this disclosure also provides a battery including the battery separator of the third aspect.

[0046] Fifthly, this disclosure also provides an electrical device, including the battery of the fourth aspect.

[0047] This disclosure provides a porous alumina, electronic components, batteries, and electrical devices. The porous alumina contains very few needle-like, plate-like, or spherical alumina particles, primarily consisting of tetragonal prism-structured alumina particles. The coating formed based on this alumina has fewer surface bumps and higher flatness, and its electrolyte wettability on the separator is significantly optimized. This not only results in a high diffusion rate of the electrolyte on the separator but also a larger diffusion radius, a significantly reduced dynamic contact angle, and a higher electrolyte adsorption rate. Furthermore, the specific surface area of ​​the porous alumina powder provided in this disclosure is lower than that of alumina powder with a high specific surface area but higher than that of conventional α-alumina powder. It exhibits superior stability and weak water adsorption, avoiding defects such as electrolyte consumption and ion transport channel blockage caused by difficulty in reducing the water content in the alumina powder or by increased activity and decreased stability due to water absorption during use.

[0048] The porous alumina powder disclosed herein also possesses stability and dispersibility. When applied to membrane coatings, it is beneficial for improving the thermal shrinkage performance and mechanical strength of the membrane. Furthermore, it can provide more ion transport channels for ion conduction, which is conducive to optimizing the performance of the battery membrane. Attached Figure Description

[0049] Figure 1 is an electron microscope image of the porous alumina prepared in Example 1 of this disclosure;

[0050] Figure 2 is an infrared spectrum of porous alumina provided in Embodiment 1 of this disclosure. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0052] Polymer separators, primarily composed of high-molecular-weight polymers, represent a major direction in the evolution and research of lithium-ion batteries. However, high-molecular-weight polymers exhibit poor wettability with aqueous electrolytes, hindering ion conduction within the separator and negatively impacting battery performance—a primary reason for the separator's influence on battery electrical performance. Since ceramic coatings, especially alumina coatings, are typically hydrophilic, and high-molecular-weight polymers are the main factor affecting separator wettability, current research on improving separator wettability mainly focuses on the polymer base film, with less research on the impact of ceramic coatings, or primarily on the modification of inorganic particles in ceramic coatings. However, hydrophilic modification of inorganic particles, such as alumina particles, can easily lead to increased water content, poor dispersibility, and reduced stability. Alumina, on the other hand, is commonly used in battery separator coatings, electrode material coatings, and other battery structural components in contact with the electrolyte, with one of its main advantages being its excellent chemical stability. Therefore, the applicant aims to provide porous alumina particles that improve and optimize membrane wettability without modifying the alumina.

[0053] To this end, the applicant has proposed an alumina powder in this disclosure, wherein the alumina particles are porous and the morphology of the particles is mainly tetragonal prism, with few or no alumina particles of other morphologies. That is, the applicant provides a porous alumina particle with a specific particle morphology within a specific particle size range (D50 is 0.3 to 2 μm, such as 0.3 μm, 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, etc.). It was unexpectedly discovered that the membrane coating formed by the alumina based on this feature has a particularly significant improvement in wettability for membranes with polymer substrates as the base film, providing a prerequisite for optimizing the electrical performance of the membrane.

[0054] The applicant believes that the reason may be that, based on the morphology and particle size of the alumina particles, when forming a coating, the alumina particles may tend to form a stacking pattern similar to "short-range ordered, long-range disordered". This is manifested in the large stacking angle of the porous alumina powder and the relatively uniform gap width between particles. Combined with the mesopores on the particles, a network of straight capillary channels and nanoscale capillary tunnels (mesoporous pores on the particle surface) are formed, which allows the electrolyte to quickly wet, diffuse, and conduct, promoting the wetting and diffusion of the electrolyte on the membrane surface.

[0055] The inventors discovered that when alumina, as an inorganic particle, is used in battery separators, the packing pattern of the alumina particles has a significant impact on the layer structure formed by the alumina particle packing. However, since the particle size of alumina powder is usually in the nanometer or micrometer range, it is impossible to subjectively control the packing pattern of the alumina. The inventors found that by controlling the morphology of the alumina particles, the packing pattern of the alumina particles can be controlled to a certain extent. The porous alumina powder proposed in this disclosure forms a layered structure in which the porous alumina particles tend to form a "short-range ordered, long-range disordered" stacking pattern. When applied to a diaphragm coating, it results in a coating with high surface smoothness and few or no protrusions, especially thin coatings (coatings with a thickness of less than 3 μm). The improvement in surface smoothness and protrusions helps reduce the safety and thermal shrinkage of the diaphragm, and also optimizes its mechanical strength. In addition to improving thermal shrinkage, mechanical strength, and stability, the optimization of the porous structure and stacking pattern of the particles improves the wettability of the diaphragm, which in turn facilitates the absorption and storage of electrolyte and increases ion transport channels.

[0056] The solution provided in this public disclosure is as follows:

[0057] The particle size D50 of the porous alumina powder is 0.3-2 μm; the porous alumina powder contains at least 50% alumina particles with a tetragonal prism structure, at most 1% alumina particles with a spherical structure, and at most 5% alumina particles with a needle-like or plate-like structure; the ratio of the edge length to the diagonal length of the base of the alumina particles with a tetragonal prism structure is 1:(0.5-5), such as 1:0.5, 1:1.0, 1:2.0, 1:3.0, 1:4.0, 1:5.0, etc.

[0058] In this disclosure, alumina particles with a tetrahedral prism structure refer to particles whose apparent morphology (ignoring the notches formed by the porous structure on their surface) is a prism structure enclosed by six rectangles or parallelograms (including two end faces and four side faces). The two end faces of the particle are rectangles or parallelograms, and the four side faces are perpendicular to the two end faces. The edge length is the length of the edge perpendicular to the end face on the side face of the alumina particle; the base diagonal length is the length of the longer of the two diagonals on the end face.

[0059] Preferably, the ratio of the edge length to the diagonal length of the base of the alumina particles with a tetragonal prism structure is 1:(1-3).

[0060] In this disclosure, alumina particles with a spherical structure refer to alumina particles with a spherical or near-spherical shape, such as alumina particles with a sphericity of not less than 95% or higher. Alumina particles with a needle-like structure refer to alumina particles with a conical, near-conical, rod-shaped, strip-shaped, or similar morphologies. Alumina particles with a plate-like structure refer to alumina particles with a plate-like or near-plate-like morphology, or a layered structure of multiple plate-like particles stacked together. In the single-layer structure of the plate-like or layered structure constituting the alumina particles, the ratio of the edge length to the side length of the end face is not less than 10, or even not less than 20, thus clearly exhibiting a plate-like structure where the edge height is much lower than the side length of the end face.

[0061] The alumina particles disclosed in this disclosure, when in a stacked state, exhibit an angle of repose of 38°–45° in their free-stacking state, which is significantly higher than that of spherical or near-spherical alumina particles of the same size (typically <15°). The applicant speculates that this may be due to the formation of a partially "short-range ordered, long-range disordered" stacking pattern during the stacking process, which greatly increases the contact area between particles, enhances friction, and thus increases the angle of repose of the powder. It should be noted that the "short-range ordered, long-range disordered" stacking pattern in this disclosure is not strictly short-range ordered, but rather refers to the tendency of adjacent particles on the same plane to contact each other in a parallel surface-to-surface contact manner, rather than a point-to-point contact manner.

[0062] When the porous alumina particles with a tetragonal prism structure provided in this disclosure are applied to diaphragm coatings, they tend to form a "short-range ordered, long-range disordered" stacking pattern. This increases the contact area between adjacent porous alumina particles and the contact area between the alumina particles and the substrate, and reduces slippage, which is beneficial for improving the thermal shrinkage and mechanical strength (puncture strength) properties of the diaphragm. The resulting coating has high surface smoothness. Furthermore, although the porous alumina particles provided in this disclosure have a relatively high angle of repose, their dispersion performance is good, and they are not prone to agglomeration. The resulting coating also has almost no bumps. This may be because although the alumina particles provided in this disclosure are porous, their specific surface area is not high, and the hydroxyl content on their surface is extremely low, resulting in low affinity for water. Therefore, the probability of agglomeration between particles due to water molecules adhering to their surfaces is low. Simultaneously, the porous structure of their surface reduces the actual contact area between adjacent particles, making them less prone to slippage, but the actual contact area between surfaces is much lower than that of non-porous particles, thus reducing the likelihood of agglomeration. Meanwhile, since the alumina particles provided in this disclosure are porous alumina particles, the mesopores on the alumina can provide channels for ion conduction, increasing ion conductivity. Furthermore, they may exhibit a unique nanocapillary tunneling effect, optimizing the absorption and diffusion of the electrolyte. Additionally, the gaps between the particles may form two-level capillary channels, enhancing electrolyte adsorption and diffusion, which is beneficial for optimizing liquid absorption and improving wettability. Moreover, due to its "long-range disordered" stacking structure, the resulting coating is more likely to exhibit isotropy, resulting in similar optimization of the longitudinal and transverse tensile strengths of the diaphragm under the same tensile conditions. Furthermore, due to its prism structure and "short-range ordered" stacking structure, it is less prone to overlapping in thin-coated layers, reducing the specific surface area loss of alumina particles caused by overlapping, and significantly decreasing the air permeability of the applied diaphragm. Moreover, the prism-structured alumina particles have a greater strength advantage than plate-like or needle-like alumina particles, and can reduce sharp protrusions in the formed coating, minimizing damage to the substrate and coating equipment.

[0063] Furthermore, the alumina powder provided in this disclosure consists of porous particles, each with several nanopores, which relatively increases its specific surface area, increases ion transport channels, and reduces the decrease in membrane permeability caused by the coating.

[0064] Preferably, the porous alumina powder contains at least 90% alumina particles with a tetragonal prism morphology, at most 0.5% alumina particles with a spherical morphology, and at most 2% alumina particles with needle-like and lamellar morphologies. More preferably, the porous alumina powder contains at least 99% alumina particles with a tetragonal prism morphology, and even approaches 100%.

[0065] The porous alumina powder provided in this disclosure has good morphological consistency of alumina particles, which is more conducive to forming a "short-range ordered, long-range disordered" stacking form. This is more conducive to reducing the internal stress of the coating, improving the smoothness and mechanical strength of the coating, and reducing the coating thickness of the diaphragm under the same coating performance.

[0066] Preferably, the porous alumina powder provided in this disclosure has a narrow particle size distribution, with a (D90-D10) / D50 value not exceeding 3, or even not exceeding 2. When applied to a separator coating, this results in a separator coating with higher smoothness and better uniformity. Simultaneously, it can shorten the ion transport path, improve ion conductivity, and optimize battery performance. More preferably, the porous alumina particles in the porous alumina powder provided in this disclosure are mainly alumina single crystals with a narrow particle size distribution and good morphological uniformity. When applied to a separator coating, this results in better coating uniformity and smoothness, which is beneficial for further reducing the separator coating thickness and density, and increasing the volumetric energy density of the battery while maintaining the same coating performance.

[0067] Preferably, the D50 of the porous alumina powder provided in this disclosure is 0.4 μm to 1 μm, more preferably 0.5 μm to 0.6 μm. Even more preferably, the ratio between the average diameter and the D50 particle size of the porous alumina powder provided in this disclosure is 0.9 to 1.1; the particle size distribution of the porous alumina powder provided in this disclosure is a normal distribution or infinitely close to a normal distribution.

[0068] It should be noted that, in this disclosure, D50 particle size refers to the particle size corresponding to a cumulative particle size distribution percentage of 50%, D90 refers to the particle size corresponding to a cumulative particle size distribution percentage of 90%, D10 refers to the particle size corresponding to a cumulative particle size distribution percentage of 10%, and the common diameter is the particle size corresponding to the particle size distribution frequency density being the maximum.

[0069] It's important to note that to ensure the chemical stability of alumina, the alumina particles used in the battery separator, which comes into contact with the electrolyte, generally should not have too high a specific surface area or be overly reactive. High specific surface area alumina particles can make water molecule removal difficult, leading to water introduction into the battery and consequently affecting battery life, performance, and safety. Conversely, highly reactive alumina particles are more likely to react with components in the electrolyte, causing electrolyte consumption and blockage of ion transport channels.

[0070] The porous alumina powder provided in this disclosure comprises particles with a plurality of pores, the pore diameter being 5–50 nm (e.g., 5 nm, 8 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, etc.), preferably 8–20 nm; the specific surface area is 5–50 m² / g.2 Within this range (e.g., 5m) 2 / g、6m 2 / g, 10m 2 / g, 15m 2 / g、20m 2 / g、30m 2 / g、40m 2 / g, 50m 2 / g, etc.), more preferably 6-40m 2 / g, more preferably 6-20m 2 / g.

[0071] The porous alumina powder disclosed herein mainly comprises alumina particles with a tetragonal prism structure, and in fact, its alumina particles are primarily alumina single crystals. The pores are formed on the surface and inside the single-crystal alumina particles, exhibiting good crystal stability and a relatively low specific surface area compared to powders with extremely high specific surface areas (e.g., 150 μm²). 2 Alumina particles with a specific surface area of ​​1 g or more are more likely to form alumina powder with lower water content during preparation. The water content of the alumina powder is also more stable during storage, and it is less prone to defects such as agglomeration and adhesion. In contrast, alumina powders with ultra-high specific surface area, especially nano- or submicron-sized alumina powders, often exhibit defects such as difficulty in water removal and rapid agglomeration due to their high hydrophilicity and specific surface area. However, the porous alumina powder provided in this disclosure does not have a low specific surface area, which can increase the specific surface area of ​​alumina, increase the space for absorbing and storing electrolyte, thus increasing its absorption capacity of electrolyte and the ion transport channels. At the same time, due to its relatively low specific surface area, it can simultaneously increase electrolyte absorption capacity and ion transport channels while also possessing water absorption and good dispersibility in slurries.

[0072] The porous alumina powder disclosed herein has a pore volume of 0.01-0.4 cm³. 3 / g (e.g., 0.01cm) 3 / g, 0.05cm 3 / g, 0.10cm 3 / g, 0.20cm 3 / g, 0.30cm 3 / g, 0.40cm 3 / g, etc., preferably 0.05-0.2cm 3 / g.

[0073] It should also be noted that when alumina powder comes into contact with water molecules for a long time, a slow hydration reaction occurs, resulting in the formation of highly viscous and highly active hydrated alumina. Therefore, low and stable water content in alumina powder is crucial for its application in batteries.

[0074] The porous alumina powder disclosed herein has a low water content, and testing revealed that its surface hydroxyl content is 8 per nm. 2 Below, and its infrared spectrum at wavenumber 1600 cm⁻¹ -1 ~3700cm -1 Within the range, no part of it exceeds its baseline and has a width of 50cm. -1 The following infrared peaks show that the water content is almost negligible. Furthermore, the inventors placed the prepared porous alumina powder in an air environment for 48 hours before testing its water content. They found that the porous alumina powder remained stable below 0.3%, indicating high stability and preventing rapid absorption of moisture from the air, thus avoiding clumping or agglomeration. This may be because the porous alumina particles in the disclosed porous alumina powder are mainly alumina single crystals. During the formation of alumina crystals and porous structures, a large number of aluminum atoms in the crystals are not exposed, making it difficult for them to combine with hydroxyl groups in water molecules. This reduces their water absorption capacity and improves their stability in the presence of water vapor. The applicant discovered that although a very small amount of hydroxyl groups were still present on the surface of the porous alumina powder, no vibrational peaks of hydroxyl groups were observed in its infrared spectrum. At the same time, the porous alumina exhibited unexpectedly excellent stability in water or water vapor and excellent dispersibility in slurry. Its viscosity and stability in water or aqueous solutions were unexpectedly optimized. This is beneficial for the application of porous alumina powder in battery components that come into contact with the electrolyte, such as separators.

[0075] Preferably, the surface hydroxyl content of the porous alumina powder is 5 hydroxyl groups / nm. 2 Below, and its infrared spectrum at wavenumber 1600 cm⁻¹ -1 ~3700cm -1 Within the range, no part of the baseline is exceeded and the width is less than 100cm. -1 The following infrared peaks are observed. More preferably, the surface hydroxyl content of the porous alumina powder is 3-5 hydroxyl groups / nm. 2 For example, it can be 3 / nm 2 4 / nm 2 5 per nm 2 wait.

[0076] The porous alumina powder provided in this disclosure contains particles that are at least one of the θ phase, δ phase, γ phase, and α phase, or at least one of the η phase, κ phase, χ phase, and ρ phase.

[0077] It should be noted that when the porous alumina powder includes γ-phase alumina, it also includes at least one of δ-phase, η-phase, κ-phase, χ-phase, and ρ-phase alumina in addition to γ-phase alumina; when the porous alumina powder includes α-phase alumina, the content of α-alumina in the porous alumina powder is not higher than 50%, and more preferably not higher than 20%.

[0078] Furthermore, in order to improve the porous alumina provided in this disclosure, the content of γ-alumina in the porous alumina provided in this disclosure is preferably low, such as less than 10% or less than 8%, so as to improve the chemical stability of the porous alumina and reduce its activity.

[0079] The total content of metallic elements such as iron, cobalt, chromium, zinc, and nickel in the porous alumina disclosed herein can reach less than 500 ppm. This is likely because the porous alumina particles provided herein are primarily single-crystal particles with high crystal integrity; and during the preparation process, the porosity is not formed through granulation, but rather through the escape of water molecules from the crystal particles and atomic displacement during phase changes. This makes it difficult for metallic elements to embed into the porous alumina particles or adhere to the surface of the single-crystal particles, allowing other ionic metal ions to remain more easily in the reaction system and be removed through cleaning, demagnetization, or impurity removal.

[0080] It should be noted that the porous alumina powder provided in this disclosure is obtained directly from raw materials without the process of compounding multiple porous alumina powders. Specifically, the porous alumina particles in the porous alumina powder provided in this disclosure are mainly tetragonal prism-shaped particles, with very few or no spherical / quasi-spherical, needle-shaped, or plate-shaped alumina particles. Furthermore, the particle size distribution of these porous alumina particles is narrow. These powder characteristics are not formed through screening, grading, or compounding, but are inherent to the morphology of the directly prepared product.

[0081] In order to enable those skilled in the art to better understand and implement this disclosure, the following provides a method for preparing the above-mentioned porous alumina powder.

[0082] Step (1): Provide aluminum hydroxide, alcohol, inorganic acid and pure water, mix them, and stir the mixture at a temperature of 60℃~80℃ (e.g., 60℃, 70℃, 80℃, etc.) for 30min-60min (e.g., 30min, 40min, 50min, 60min) to obtain a precursor solution; control the stirring speed to 30Hz~50Hz (e.g., 30Hz, 40Hz, 50Hz, etc.);

[0083] Step (2): Mix the precursor solution with organic acid and pure water, heat to 60℃~80℃ (e.g., 60℃, 70℃, 80℃, etc.), stir and react for 1h-3h (e.g., 1h, 2h, 3h, etc.); then heat to 150℃~200℃ (e.g., 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, etc.), keep the temperature for 4h~48h (e.g., 4h, 10h, 20h, 30h, 40h, 48h, etc.) to obtain the intermediate; control the reaction pressure to 1.4MPa~3.7MPa (e.g., 1.4MPa, 2.0MPa, 3.0MPa, 3.7MPa, etc.);

[0084] Step (3): Wash, demagnetize, dry, and then calcine at 600℃~1200℃ (e.g., 600℃, 800℃, 1000℃, 1200℃, etc.) for 0.5~5h (e.g., 0.5h, 1.0h, 3.0h, 5.0h, etc.). After air jet milling, porous alumina powder is obtained.

[0085] In step (3), a small amount of a barrier agent that can decompose into gas at a low temperature is added. The decomposition temperature of the barrier agent is not higher than 450°C, and more preferably not lower than 50°C and not higher than 100°C. For example, the barrier agent can be ammonium bicarbonate, ammonium carbonate, or ammonium nitrate, preferably ammonium carbonate. The amount of the barrier agent, by mass fraction, is 0.01% to 0.1% of the dry intermediate powder obtained in step (3). The barrier agent can be added during the drying stage or the calcination stage. When it is added during the calcination stage, it can also reduce the adhesion of particles to the container wall used for calcination during the calcination process.

[0086] Furthermore, the inventors discovered that controlling the morphology consistency of porous alumina powder is significantly related to the morphology and purity of the intermediate before calcination, the water content in the intermediate, and the temperature control during the calcination process. The intermediate before calcination also needs to be controlled to have a predominantly tetragonal prism structure with virtually no or no spherical or near-spherical particles. Preferably, the intermediate before calcination consists of single-crystal particles with a narrow particle size distribution and good morphological consistency. The inventors also unexpectedly discovered that the water content in the intermediate, by mass fraction, should not exceed 35%, preferably not less than 5%, and even more preferably not less than 16%. Within this range, the pore volume, pore size, and hydroxyl content of the resulting porous alumina particles can be controlled within the required range, and these porous alumina particles exhibit a wavenumber of 1600 cm⁻¹ in the infrared spectrum. -1 ~3700cm -1 Within the range, no part of it exceeds its baseline and has a width of 50cm. -1The following infrared peaks may be due to the control of the water of crystallization content, morphology, and calcination process in the intermediates during preparation. This allows oxygen atoms to be more easily exposed during the phase transition of aluminum and oxygen atoms in the resulting porous alumina crystals, while aluminum atoms are less exposed. This results in alumina particles that remain relatively stable even in environments containing water molecules. It should be noted that the "wavenumber 1600 cm⁻¹" mentioned here refers to... -1 ~3700cm -1 Within the range, no part of it exceeds its baseline and has a width of 50cm. -1 The following infrared peaks refer to those peaks that are distinct and have a transmittance of less than 98%.

[0087] In step (2), the reaction system obtained in step (1) is added to step (2). An alcohol and an inorganic acid (strong acid) are introduced into the reaction system in step (2), forming a pH buffer with the organic acid (weak acid) added in step (2). This maintains a significant acidity in the reaction system during the reaction, while the hydrogen ion content does not change significantly with the occurrence of the reaction, promoting the formation of intermediates and ensuring good consistency of the intermediates. In addition, the addition of alcohol introduces a certain amount of alkyl groups into the system. The presence of alcohol may replace hydroxyl groups, thereby affecting the deprotonation process, slowing down the reaction rate and the degree of reaction completion, promoting the dissolution of the generated aluminum hydroxide, further promoting the transport and transfer of metal oxygen ions, and regulating the nucleation and growth of intermediates. The intermediates formed by the above methods have better crystal size and crystal consistency. This may be because after the reaction rate is reduced, the dissolved aluminum hydroxide tends to nucleate heterogeneously and crystallize on the undissolved aluminum hydroxide. The aluminum nitrate in the precursor solution provides more metal aluminum ions, increasing the supersaturation of the system and increasing the nucleation driving force. Furthermore, the intermediate obtained by the above-mentioned preparation method has a high water of crystallization content. This may be because the complex formed by aluminum ions and citrate ions during the reaction inhibits the crystallization process, resulting in incomplete crystallization. Additionally, the entire reaction mainly involves the dissolution, transport, and dehydration crystallization of aluminum hydroxide. During crystallization, the anhydrous aluminum complex may compete with aluminum hydroxide for hydroxyl groups, occupying specific lattice sites, thereby inducing a large number of lattice distortions, oxygen vacancies, and aluminum interstitials. This leads to incomplete crystallization, reduced dehydration effect, and increased water of crystallization content, resulting in an intermediate with high water of crystallization content. These lattice defects and the release of water of crystallization during subsequent calcination cause the crystal structure to collapse, forming a porous structure. Furthermore, anions in the reaction system are adsorbed by cations during crystallization, which promotes or inhibits grain growth along specific directions or crystal faces, leading to anisotropic crystal growth. This may explain the specific morphology of the alumina particles.

[0088] In this preparation method, the mass ratio of aluminum hydroxide, alcohol, inorganic acid, and pure water is 1:1:(0.1-0.3):(1-3), such as 1:1:0.1:1, 1:1:0.2:2, 1:1:0.3:3, etc.; in step (2), the mass ratio of the precursor solution to organic acid and pure water is 1:(0.12-0.2):(0.2-0.4), such as 1:0.12:0. 2, 1:0.15:0.3, 1:0.20:0.4, etc.; wherein the mass ratio of inorganic acid to organic acid is controlled at (0.16~0.5):1, such as 0.16:1, 0.20:1, 0.30:1, 0.40:1, 0.50:1, etc.; the mass ratio of alcohol to organic acid is (1.2~2.0):1, such as 1.2:1, 1.5:1, 1.8:1, 2.0:1, etc.

[0089] Among them, alcohol can be one or more of the common alcohol solvents such as ethanol, propanol, n-butanol, isobutanol, pentanol, and isopentanol; inorganic acid can be one or more of the inorganic strong acid such as nitric acid, sulfuric acid, and hydrochloric acid; organic acid can be one or more of the organic weak acid such as acetic acid, oxalic acid, and citric acid.

[0090] Preferably, in step (3), the temperature curve of the calcination process is as follows: rapidly heat to at least 250°C at a heating rate of not less than 5°C / s, reduce the heating rate (heating rate not higher than 1°C / s) and then heat to the holding temperature, and then hold and sinter for 0.5 to 5 hours to obtain the product, so as to promote the maintenance of the single crystal morphology of porous alumina particles and the control of pore size and pore volume.

[0091] The preferred drying method is infrared microwave drying. When using infrared microwave drying, the dried intermediate powder does not need to be dispersed or crushed and can be directly entered into the calcination process, saving costs and improving the morphological integrity of the product. In addition, in order to achieve a good dispersion effect, when using infrared microwave drying, the demagnetized slurry is first pressure filtered into a filter cake with a free water content of not less than 60%, and then broken into small pieces. The filter cake is then heated to a temperature of not less than 150°C by infrared light irradiation for 8 to 15 minutes, then cooled to 80 to 100°C, and microwave-heated for 3 to 10 minutes. Finally, the temperature is raised to above 150°C by microwave heating until the small filter cakes automatically burst open into powder.

[0092] The intermediate powder formed by segmented drying using infrared microwave drying technology has a low water content, which can reach no more than 0.2% (free water). Moreover, the appearance of the particles is not damaged by grinding or ball milling during this process, resulting in better integrity. Furthermore, since it does not involve high-temperature spraying or automatic powdering, the resulting powder has a lower agglomeration of crystal particles and better single-crystal dispersion.

[0093] In this process, after the intermediate is obtained but before demagnetization, the pH of the intermediate slurry is adjusted to 7–8.5, preferably 7.5–8.0, using an organic acid. Then, demagnetization is performed, followed by drying. The drying method can be spray drying or infrared microwave drying. When spray drying is used, a dispersion step is included after spray drying and before calcination, using an air jet mill or grinding method to disperse the dried particles to a size of 0.2–5 μm.

[0094] The preferred drying method is infrared microwave drying. Similarly, when using infrared microwave drying, the dried intermediate powder does not need to be dispersed or crushed and can be directly entered into the calcination process, saving costs and improving the morphological integrity of the product. In addition, in order to achieve a good dispersion effect, when using infrared microwave drying, the demagnetized slurry is first filtered into a filter cake with a free water content of not less than 60%, and then broken into small pieces. The filter cake is then heated to a temperature of not less than 150°C by infrared light irradiation for 8 to 15 minutes, then cooled to 80 to 100°C, and microwave-heated for 3 to 10 minutes. Finally, the temperature is raised to above 150°C by microwave heating until the small filter cakes automatically burst open into powder. Similarly, the intermediate powder formed by segmented drying using infrared microwave drying technology has a low water content, which can reach no more than 0.2% (free water). Moreover, the appearance of the particles is not damaged by grinding or ball milling during this process, resulting in better integrity. Furthermore, since there is no high-temperature spraying process or automatic bursting into powder, the agglomeration of crystal particles in the obtained powder is lower, and the single crystal dispersion of the product is better.

[0095] The intermediate obtained by preparation also exhibits a water content of no more than 35% by mass fraction, preferably no less than 5%, and more preferably no less than 16%, and the morphology is mainly tetragonal prism, with the particle size mainly distributed in the range of 0.2 to 5 μm.

[0096] Similarly, in step (2), a small amount of a barrier agent that can decompose into gas at a lower temperature is added. The decomposition temperature of the barrier agent is not higher than 450°C, and more preferably not lower than 50°C and not higher than 100°C. For example, the barrier agent can be ammonium bicarbonate, ammonium carbonate, or ammonium nitrate, preferably ammonium carbonate. The amount of the barrier agent, in terms of mass fraction, is 0.01% to 0.1% of the dry intermediate powder obtained in step (2), such as 0.01%, 0.03%, 0.05%, 0.08%, 0.10%, etc. The barrier agent can be added during the drying stage or the calcination stage. When it is added during the calcination stage, it can also reduce the adhesion of particles to the container wall used for calcination during the calcination process. The preferred temperature curve for the calcination process is as follows: rapidly heat to at least 250°C at a heating rate of not less than 5°C / min, reduce the heating rate (heating rate not higher than 1°C / min), then heat to the holding temperature, and then hold and sinter for 0.5h to 5h to obtain the product, so as to promote the maintenance of the single crystal morphology of porous alumina particles and the control of pore size and pore volume.

[0097] In this preparation method, the inventors discovered that adjusting the acidity of the slurry directly after the reaction can promote the uniformity of the crystal structure and particle size of the product as well as the pore size distribution. The reason may be that adjusting the acidity directly after the reaction can dissolve aluminum hydroxide, resulting in a higher purity intermediate and a large number of defects on the intermediate, which provides biased guidance for the formation and development of subsequent pores.

[0098] Secondly, this disclosure also provides a battery separator, the battery separator comprising the porous alumina of the first aspect.

[0099] The battery separator can be a battery separator, which includes a substrate and a coating formed on at least one side of the substrate, wherein porous alumina is distributed in the coating; the liquid absorption performance of the battery separator is not less than 0.6 mL / g.

[0100] Thirdly, this disclosure also provides a battery, including the battery separator of the second aspect.

[0101] Fourthly, this disclosure also provides an electrical device, including the battery of the third aspect. The electrical device can be any electrical device that can use a lithium-ion solid-state battery, such as an electric vehicle, aircraft, spacecraft, mobile phone, tablet computer, handheld game console, portable digital device (e.g., digital camera), smart home device, smart wearable device (e.g., smart bracelet, smartwatch, smart glasses).

[0102] To facilitate understanding of the innovative aspects of this disclosure by those skilled in the art, some preferred embodiments are provided below in conjunction with the accompanying drawings to illustrate the above technical solutions.

[0103] Example 1

[0104] This embodiment provides a method for preparing porous alumina powder, including the following steps:

[0105] Aluminum hydroxide, n-butanol, nitric acid, and pure water were added to a reaction vessel in a mass ratio of 1:1:0.2:2. The temperature was controlled at 70℃, and the stirring speed was controlled at 45Hz. The reaction was carried out for 30 minutes. Aluminum nitrate, citric acid, and pure water were added to the reaction vessel in a mass ratio of 0.2:0.6:1 to aluminum hydroxide, with a filling volume of 60%. The vessel temperature was controlled at 70℃, and the stirring speed was controlled at 45Hz. The reaction was carried out for 2 hours. The temperature was increased at a rate of 5℃ / min, and the temperature was increased to 150℃ and held for 8 hours. The pressure was 2.12 MPa, and a slurry was obtained.

[0106] The slurry was washed with pure water and filtered to obtain an intermediate; the intermediate was then dispersed with pure water to form a slurry, which was demagnetized and spray-dried at 200-220°C to obtain spray particles; the spray particles were then milled with air jet mill to obtain intermediate particles with a particle size mainly distributed in the range of 0.2-5 μm.

[0107] By mass fraction, 0.01% ammonium carbonate was added to the intermediate particles, mixed evenly, and then heated to 1100℃ at a heating rate of 5℃ / min and held for 2 hours to obtain porous alumina powder.

[0108] Example 2

[0109] This embodiment also provides a method for preparing porous alumina powder. Compared with Example 1, in this embodiment, the mass ratio of aluminum nitrate, citric acid, and pure water to aluminum hydroxide is 0.15:0.45:1; the pressure in the reaction vessel is controlled at 2.21 MPa; and the remaining preparation steps are the same as in Example 1 to obtain porous alumina powder.

[0110] Example 3

[0111] This embodiment also provides a method for preparing porous alumina powder. Compared with Example 1, in this embodiment, aluminum nitrate, citric acid, and pure water are prepared in a mass ratio of 0.12:0.36:1 to aluminum hydroxide; the pressure in the reaction vessel is controlled at 2.25 MPa; and the remaining preparation steps are the same as in Example 1 to obtain porous alumina powder.

[0112] Example 4

[0113] This embodiment also provides a method for preparing porous alumina powder. Compared with Example 1, in this embodiment, the mass ratio of aluminum nitrate, citric acid, and pure water to aluminum hydroxide is 0.1:0.3:1; the pressure in the reaction vessel is controlled at 2.35 MPa; and the remaining preparation steps are the same as in Example 1 to obtain porous alumina powder.

[0114] Example 5

[0115] This embodiment also provides a method for preparing porous alumina powder. Compared with Example 1, in this embodiment, the mass ratio of aluminum nitrate, citric acid, and pure water to aluminum hydroxide is 0.05:0.15:1; the pressure in the reaction vessel is controlled at 2.42 MPa; and the remaining preparation steps are the same as in Example 1 to obtain porous alumina powder.

[0116] Example 6

[0117] This embodiment also provides a method for preparing porous alumina powder. Compared with Example 1, the temperature is raised to 180°C and held for 8 hours. The pressure in the reaction vessel is controlled at 3.50 MPa. The remaining preparation steps are the same as in Example 1, and porous alumina powder is obtained.

[0118] Example 7

[0119] This embodiment also provides a method for preparing porous alumina powder. Compared with Example 1, aluminum hydroxide, n-butanol, nitric acid, and pure water are mixed in a mass ratio of 1:0.2:0.2:2.8, and the pressure in the reaction vessel is controlled at 1.50 MPa. The remaining preparation steps are the same as in Example 1, and porous alumina powder is obtained.

[0120] Example 8

[0121] This embodiment also provides a method for preparing porous alumina powder. Compared with Example 1, after demagnetization, the slurry is hydraulically filtered to form a filter cake with a solid content of not less than 65%. The filter cake is broken into small pieces with a diameter of no more than 3 cm. Infrared light is then used to raise the temperature of the small filter cake pieces to 80°C. The infrared light is kept on throughout the drying process, with an infrared temperature of approximately 150°C. After drying for 10 minutes, infrared light is used again to raise the temperature of the small filter cake pieces to 100°C, causing the moisture inside the filter cake to gradually evaporate. After drying for 7 minutes, microwaves are used to raise the temperature of the small filter cake pieces to 150°C, causing the moisture inside and outside the material to evaporate to ≤0.2% and automatically burst open to present a powder state, resulting in intermediate particles with a particle size mainly distributed in the range of 0.2–5 μm. The remaining preparation steps are the same as in Example 1, yielding porous alumina powder.

[0122] Comparative Example 1

[0123] Compared to Example 1, in this comparative example, aluminum hydroxide, n-butanol, nitric acid, and pure water were added to a reactor in a mass ratio of 1:1:0.1:2. The temperature was controlled at 70°C, the stirring speed at 45Hz, and the reaction time was 30 min. Aluminum nitrate, citric acid, and pure water were added to the reactor in a mass ratio of 0.05:0.6:1 (to aluminum hydroxide), with a filling volume of 60%. The reactor temperature was controlled at 70°C, the stirring speed at 45Hz, and the reaction time was 2 h. The heating rate was 5°C / min, and the temperature was increased to 150°C and held for 8 h at a pressure of 2.33 MPa to obtain a slurry. The remaining steps were the same as in Example 1, resulting in a comparative sample.

[0124] Comparative Example 2

[0125] Compared to Example 1, in this comparative example, aluminum hydroxide, n-butanol, nitric acid, and pure water were added to a reactor in a mass ratio of 1:1:0.05:2. The temperature was controlled at 70°C, the stirring speed at 45Hz, and the reaction time was 30 min. Aluminum nitrate, citric acid, and pure water were added to the reactor in a mass ratio of 0.05:0.6:1 (to aluminum hydroxide), with a filling volume of 60%. The reactor temperature was controlled at 70°C, the stirring speed at 45Hz, and the reaction time was 2 h. The heating rate was 5°C / min, and the temperature was increased to 150°C and held for 8 h at a pressure of 2.23 MPa to obtain a slurry. The remaining steps were the same as in Example 1, resulting in a comparative sample.

[0126] Comparative Example 3

[0127] Compared to Example 1, in this comparative example, aluminum hydroxide, n-butanol, nitric acid, and pure water were added to a reactor in a mass ratio of 1:1:0.2:3. The temperature was controlled at 70°C, the stirring speed at 45Hz, and the reaction was carried out for 30 minutes with a filling volume of 60%. The reactor temperature was controlled at 70°C, the stirring speed at 45Hz, and the reaction was carried out for 2 hours. The heating rate was 5°C / min, and the temperature was increased to 150°C and held for 8 hours at a pressure of 2.10 MPa to obtain a slurry. The remaining steps were the same as in Example 1, resulting in a comparative sample.

[0128] Comparative Example 4

[0129] Compared to Example 1, ammonium carbonate was not added during the calcination process in this comparative example, while the remaining steps were the same as in Example 1, resulting in a comparative sample.

[0130] Comparative Example 5

[0131] Compared to Example 1, aluminum hydroxide, n-butanol, nitric acid, and pure water were added to the reaction vessel in a mass ratio of 1:1:0.2:2. The temperature was controlled at 70°C, the stirring speed at 45Hz, and the reaction was carried out for 30 minutes. Aluminum nitrate, nitric acid, and pure water were added to the reaction vessel in a mass ratio of 0.1:0.6:1 to aluminum hydroxide, with a filling volume of 60%. The vessel temperature was controlled at 70°C, the stirring speed at 45Hz, and the reaction was carried out for 2 hours. The heating rate was 5°C / min, and the temperature was increased to 150°C and held for 8 hours. The pressure was 2.12 MPa, and a slurry was obtained. The remaining steps were the same as in Example 1, resulting in a comparative sample.

[0132] test

[0133] 1. Particle size testing

[0134] The Mastersizer 3000 laser particle size analyzer was used for testing.

[0135] 2. Pore volume, specific surface area

[0136] The tests were conducted using a Micromeritics 3030 physical adsorption analyzer.

[0137] 3. Infrared Spectroscopy

[0138] Using Nicolet TM IS50 Fourier Transform Infrared Spectrometer.

[0139] 4. Surface hydroxyl content

[0140] The test was conducted using NaOH titration.

[0141] 5. Impurity content

[0142] The tests were conducted using a Thermo Scientific ICP inductively coupled plasma analyzer.

[0143] 6. Angle of repose

[0144] The test was conducted using an Aode-307 angle of repose tester.

[0145] 7. Particle size ratio

[0146] Scanning electron microscope (SEM) images of the product were taken. The number of particles N1 and the number of particles with a tetragonal prism structure N2 in the SEM images were counted. The proportion of particles with a tetragonal prism structure was calculated by the formula N2 / N1×100%.

[0147] 8. Electrolyte diffusion radius

[0148] On a concentric circular plane, a diaphragm coated with different alumina (a circular piece with a radius of 60 mm) is placed. Under the conditions of temperature 25℃, humidity 60RH, and atmospheric pressure 298.15K, 1 mL of electrolyte (DEC:EMC:DMC = 1:1:1, LIPF6 hexafluorophosphate, 1 mol / L) is rapidly added dropwise at the center of the circle. The radius of electrolyte diffusion is observed and measured after 1 min.

[0149] 9. Breathability rating: Tested using the American Gurley 4110N breathability tester.

[0150] 10. Contact angle and dynamic contact angle: The contact angle at 10s was tested using a SINDIN contact angle tester.

[0151] The porous alumina powders obtained in Examples 1-8 and the comparative samples obtained in Comparative Examples 1-5 were subjected to particle size, pore volume, pore size, hydroxyl content, impurity content and infrared spectroscopy tests, respectively. The test results are shown in Table 1.

[0152] Table 1

[0153] As can be seen from Table 1, the porous alumina particles provided in this disclosure have a lower hydroxyl content. Furthermore, the applicant conducted infrared spectroscopy analysis on the porous alumina particles prepared according to this disclosure, and the results are shown in Figure 2. The figure shows that the porous alumina particles provided in this disclosure exhibit lower hydroxyl content at a wavenumber of 1600 cm⁻¹. -1 ~3700cm -1 Within the range, no part of the baseline is exceeded and the width is less than 100cm. -1 As can be seen from the infrared peaks below, the porous alumina particles provided in this disclosure have a low affinity for water molecules, which is beneficial for optimizing the reliability of the batteries in which they are applied. Furthermore, the angle of repose of the porous alumina particles provided in this disclosure is controlled within the range of 38–45°. The inventors discovered during coating that when the angle of repose of the porous alumina particles provided in this disclosure is controlled within this range, the resulting coating exhibits good uniformity, and its thermal shrinkage and strength (puncture strength, tensile strength) are also improved, with the improvement being approximately 8%–15% higher than that of coating spherical alumina.

[0154] The applicant further investigated the porous alumina ceramic particles provided in this disclosure as a diaphragm coating, which exhibits excellent coating thickness uniformity, low surface protrusion rate, and large liquid injection capacity. Raw materials: Porous alumina provided in Examples 1-8; Porous alumina provided in Comparative Examples 1-5;

[0155] Conventional alumina powder, D50 = 0.4µm, D50 = 0.8µm, Suzhou Jinyi New Materials.

[0156] PE diaphragm, 9μm, Suzhou Jieli New Energy Materials Co., Ltd.

[0157] Dispersant SF8, from Sannopco, Japan.

[0158] Adhesive BM900-B, Zeon Japan.

[0159] Laureth polyoxyethylene ether, Nantong Haian Chemical.

[0160] Preparation of diaphragm samples:

[0161] Take 100g of alumina powder and 180g of deionized water, and mix for 10 minutes. Add 3g of dispersant SF8 and stir for 10 minutes. Add 1.75g ​​of emulsifier lauryl alcohol polyoxyethylene ether and stir for 10 minutes. Finally, add 5g of acrylic emulsion BM900-B and continue stirring for 30 minutes to obtain a ceramic slurry. Coat the surface of a PE diaphragm with the ceramic slurry on an online rod coater, and dry it in a forced-air oven at 40℃ for 10 minutes to obtain a coated diaphragm. The performance of the coated diaphragm is then tested, and the results are as follows.

[0162] Table 2

[0163] As shown in Table 2, the electrolyte diffusion radius of the membrane coating formed by the porous alumina provided in this disclosure is significantly improved. Under the condition of a consistent substrate, its electrolyte diffusion radius increases from the existing 13-15 mm to over 22 mm. This demonstrates that the specific morphology, particle size range, and porous structure of the alumina particles provided in this disclosure are beneficial for optimizing the electrolyte diffusion radius. Furthermore, the alumina coating provided in this disclosure also significantly improves the air permeability of the membrane.

[0164] The electrolyte dynamic contact angles of the membrane coatings formed by the porous alumina obtained in Example 1 and Comparative Examples 1-5 are shown in Table 3.

[0165] Table 3

[0166] In addition, the applicant also tested the dynamic and static electrolyte contact angles of the coatings formed by the alumina provided in Examples 1 and Comparative Examples 1-5, as well as conventional alumina. The test results are shown in Table 3. As can be seen from the table, although the static electrolyte contact angle (50s) of the coatings formed by the porous alumina obtained in the examples and comparative examples is not significantly different, the change in their dynamic contact angle is quite different. The dynamic contact angle of the porous alumina decreases more rapidly, which can achieve rapid absorption of electrolyte. The porous alumina provided in this disclosure not only shows a particularly rapid change in dynamic contact angle, but also has a lower static contact angle, which may be one of the reasons for its superior electrolyte diffusion radius.

[0167] Furthermore, based on the above-described method for preparing the diaphragm, diaphragms with coating thicknesses of 2 μm and 3 μm were prepared from the porous alumina and conventional alumina obtained in Example 1, respectively, according to the coating thickness. The liquid absorption rate, coating thickness uniformity, and surface bump characteristics were then tested. The test methods and results are as follows.

[0168] test

[0169] 1. Liquid absorption rate

[0170] The membranes with coating thicknesses of 2 μm and 3 μm obtained from the porous alumina coating of Example 1 (Example 1 and Example 2, respectively) and the membranes with coating thicknesses of 2 μm and 3 μm obtained from Comparative Example 1 (Comparative Example 1 and Comparative Example 2, respectively) were cut into several 20 mm × 50 mm rectangles, denoted as AT1, AT2... and AL1, AL2..., respectively, and weighed to obtain the membrane mass M1;

[0171] The membrane is completely immersed in the electrolyte and left for a period of time to ensure that the electrolyte is completely absorbed. Then the coated membrane is air-dried for 12-24 hours. The air-dried membrane is weighed to obtain the mass M2 of the membrane after immersion. The liquid absorption rate of multiple coated membranes is calculated and the average value is taken as the final liquid absorption rate of the coated membrane: (M2-M1) / (M1*ρelectrolyte).

[0172] 2. Thickness uniformity

[0173] A 20x50cm coated film was used, with three testing points each at the front, middle, and back, for a total of six points. The square root δ of the sum of the squares of the differences between each data point and the mean point was calculated. The smaller the δ value, the higher the film thickness uniformity. The specific formula is as follows:

[0174] 3. Test for the number of protrusions on the membrane surface

[0175] Place a 20×50cm coated film under a light, observe from the back and count the number of black dots.

[0176] The test results are shown in Table 4.

[0177] Table 4

[0178] Table 4 shows that the smaller the δ value, the better the thickness uniformity; the fewer the number of protrusions on the membrane surface, the smoother the ceramic diaphragm; and the higher the liquid absorption rate, the better the performance. Compared with conventional alumina, porous alumina diaphragm coating has the characteristics of good thickness uniformity, low surface protrusion rate, and large liquid injection capacity.

[0179] The above are merely specific embodiments of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims. Industrial applicability

[0180] The porous alumina powder disclosed herein contains very few needle-like, plate-like, or spherical alumina particles, with a predominance of tetragonal prism-structured alumina particles. The coating formed based on this alumina has fewer surface bumps and higher flatness, and its electrolyte wettability on the separator is significantly optimized. This not only results in a high electrolyte diffusion rate on the separator but also a larger diffusion radius, a significantly reduced dynamic contact angle, and a higher electrolyte adsorption rate. Applying this porous alumina powder to the coating of battery separators can improve the liquid absorption performance of the battery separator, demonstrating good industrial applicability.

Claims

1. A porous alumina powder for lithium-ion batteries, characterized in that, The porous alumina powder has a particle size D50 of 0.3–2 μm and a specific surface area of ​​5–50 m². 2 / g; The porous alumina powder contains at least 50% alumina particles with a tetragonal prism structure, at most 1% alumina particles with a spherical structure, and at most 5% alumina particles with a needle-like or plate-like structure. The ratio of the edge length to the diagonal length of the base of the alumina particles with a tetragonal prism structure is 1:(0.5~5).

2. The porous alumina powder for lithium-ion batteries according to claim 1, characterized in that, The porous alumina powder contains at least 90% alumina particles with a tetragonal prism morphology. And / or, the amount of alumina particles with a spherical morphology is at most 0.5%; And / or, the amount of alumina particles with needle-like and lamellar structures is no more than 2%.

3. The porous alumina powder for lithium-ion batteries according to any one of claims 1-2, characterized in that, The content of α-alumina in the porous alumina powder is not higher than 50%.

4. The porous alumina powder for lithium-ion batteries according to any one of claims 1-3, characterized in that, The porous alumina powder has a surface hydroxyl content of 8 hydroxyl groups / nm. 2 the following; And / or, the infrared spectrum of the porous alumina powder at wavenumber 1600 cm⁻¹ -1 ~3700cm -1 Within the range, no part of it exceeds its baseline and has a width of 50cm. -1 The following are infrared peaks.

5. The porous alumina powder for lithium-ion batteries according to claim 4, characterized in that, The porous alumina powder has a surface hydroxyl content of 5 hydroxyl groups / nm. 2 the following; And / or, the infrared spectrum of the porous alumina powder at wavenumber 1600 cm⁻¹ -1 ~3700cm -1 Within the range, no part of the baseline is exceeded and the width is less than 100cm. -1 The following are infrared peaks.

6. The porous alumina powder for lithium-ion batteries according to any one of claims 1 to 5, characterized in that, The porous alumina powder particles each contain several pores, with a pore size of 5–50 nm and a pore volume of 0.01–0.4 cm³. 3 / g.

7. The porous alumina powder for lithium-ion batteries according to claim 6, characterized in that, The pore diameter is 8–20 nm, and the pore volume is 0.05–0.2 cm³. 3 / g; And / or, the specific surface area of ​​the porous alumina powder is 6–20 m². 2 / g.

8. The porous alumina powder for lithium-ion batteries according to any one of claims 1-7, characterized in that, The particles in the porous alumina powder are at least one of the θ phase, δ phase, γ phase, or at least one of the η phase, κ phase, χ phase, ρ phase.

9. The porous alumina powder for lithium-ion batteries according to any one of claims 1-8, characterized in that, The porous alumina powder is prepared directly without being compounded from multiple porous alumina powders.

10. A method for preparing porous alumina powder for lithium-ion batteries according to any one of claims 1-9, characterized in that, include: Aluminum hydroxide, alcohol, inorganic acid and water are mixed to obtain a precursor solution; The precursor solution was mixed with organic acid and water, and the reaction was carried out at a heated temperature to obtain an intermediate. The intermediate was calcined to obtain porous alumina powder.

11. The preparation method according to claim 10, characterized in that, The mass ratio of aluminum hydroxide, alcohol, inorganic acid, and water is 1:1:(0.1-0.3):(1-3); And / or, the alcohol is selected from at least one of ethanol, propanol, n-butanol, isobutanol, pentanol, and isoamyl alcohol; And / or, the inorganic acid is selected from at least one of nitric acid, sulfuric acid and hydrochloric acid.

12. The preparation method according to claim 10 or 11, characterized in that, The heating reaction process in the preparation of the intermediate includes: first reacting at 60℃~80℃ for 1h~3h; then heating to 150℃~200℃ and reacting for 4h~48h, while controlling the reaction pressure at 1.4MPa~3.7MPa; And / or, the mass ratio of the precursor solution to organic acid and water is 1:(0.12~0.2):(0.2~0.4), the mass ratio of inorganic acid to organic acid is controlled to be (0.16~0.5):1; and the mass ratio of alcohol to organic acid is (1.2~2.0):1; And / or, the organic acid is selected from at least one of acetic acid, oxalic acid and citric acid.

13. The preparation method according to any one of claims 10-12, characterized in that, The intermediate is first washed, demagnetized, and dried, and then calcined. And / or, control the calcination temperature to be 600℃~1200℃ and the calcination time to be 0.5h-5h; And / or, after calcination, perform air jet milling to obtain porous alumina powder.

14. The preparation method according to claim 13, characterized in that, A barrier agent with a decomposition temperature not exceeding 450°C is added during the preparation of the porous alumina powder from the intermediate.

15. The preparation method according to claim 14, characterized in that, The barrier agent is added during the drying or calcination stage; And / or, the mass ratio of the dried intermediate powder to the barrier agent is 100:(0.01 to 0.1); And / or, the barrier agent is selected from at least one of ammonium bicarbonate, ammonium carbonate, and ammonium nitrate.

16. A battery separator, characterized in that, The battery separator includes a base film and a ceramic coating formed on at least one side of the base film, the ceramic coating including the porous alumina powder according to any one of claims 1 to 9; the base film is a polymer base film.

17. The battery separator according to claim 16, characterized in that, The battery separator has a liquid absorption capacity of not less than 0.6 mL / g; the electrolyte diffusion radius of the battery separator is not less than 20 mm, wherein the electrolyte ratio is: DEC:EMC:DMC = 1:1:1, LIPF6 hexafluorophosphate, 1 mol / L.

18. A battery, characterized in that, Includes the battery separator as described in claim 16 or 17.

19. An electrical appliance, characterized in that, Includes the battery as described in claim 18.

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