A porous alumina, a battery separator, a battery, and an electrical device

Abstract

The present invention provides a porous alumina and a battery separator, a battery, and an electrical device, and relates to the technical field of battery materials. The porous alumina is an alumina particle with a plurality of mesopores on the surface and / or inside of the particle; and the alumina particle is a quadrangular prism crystal with a thickness not less than 20% of the length of the bottom side; the cumulative particle size D50 of 50% of the particles on the small particle size side in the cumulative particle size distribution is 0.3~2μm; and the angle of repose of the porous alumina is 36.0°~38.5°. The present application also provides a battery separator, a battery, and an electrical device based on porous alumina. The porous alumina provided in the present application improves the problem that the surface flatness of the coating formed by the existing alumina and the heat shrinkage optimization of the separator are difficult to achieve at the same time.

Description

Technical Field

[0001] The present invention relates to the field of battery materials, and in particular to a porous alumina, a battery separator, a battery, and an electrical device. Background Art

[0002] In order to improve the mechanical properties, heat resistance, and breakdown voltage of a separator mainly composed of a polymer such as polyolefin, a ceramic coating containing ceramic particles is often formed on one or both sides of a polymer film (base film) in the prior art. As a common ceramic particle with high strength, good thermal stability, and chemical stability, alumina particles have become a preferred material for the ceramic particles in the ceramic coating.

[0003] The coating of the separator not only requires the strength, thermal stability, and chemical stability of the ceramic particles, but also has requirements for the self-fluidity of the ceramic particles and their supporting effect on the base film based on the heat shrinkage performance, surface flatness, etc. of the separator. However, alumina particles have a high affinity with water, and it is difficult to dry and disperse them. In order to meet the requirements of the dispersibility and self-fluidity of alumina, alumina particles with extremely excellent self-fluidity are often used as the coating ceramics of the separator in the prior art, but their supporting effect on the base film is poor, resulting in poor improvement of the heat shrinkage of the obtained separator; while alumina particles with poor self-fluidity are prone to poor dispersibility and poor uniformity of the formed coating, affecting the surface flatness of the separator. Summary of the Invention

[0004] The purpose of the present invention is to provide a porous alumina, the particles of which are mainly prismatic crystals with a thickness not less than 20% of the length of the bottom side length, and the angle of repose thereof is not higher than 38.5° and not lower than 36°, which can make the surface flatness of the coating formed based on the porous alumina better.

[0005] Another purpose of the present invention is to provide a battery separator.

[0006] Another purpose of the present invention is to provide a battery.

[0007] Another purpose of the present invention is to provide an electrical device.

[0008] In a first aspect, the present application provides a porous alumina, which is an alumina particle having a number of mesopores on the surface and / or inside of the particle; and the alumina particle is a prismatic crystal with a thickness not less than 20% of the length of the bottom side length; the cumulative particle size D50 of 50% of the particles on the small particle size side in the cumulative particle size distribution is 0.3 - 2 μm;

[0009] and the angle of repose of the porous alumina is 36.0° - 38.5°.

[0010] Further, in some embodiments of the present application, the angle of repose of the porous alumina is 38.1° to 38.5°; and / or

[0011] The maximum particle size D of the porous alumina max is not higher than 4 μm.

[0012] Further, in some embodiments of the present application, the particle size distribution of the porous alumina satisfies the following formula:

[0013] SPAN1 = D99 / D50 < 2.5;

[0014] SPAN2 = (D90 - D50) / D10 < 1.5.

[0015] Further, in some embodiments of the present application, the cumulative particle size D50 of 50% of the particles on the small particle size side in the cumulative particle size distribution of the porous alumina is 0.4 to 1.2 μm.

[0016] Further, in some embodiments of the present application, its particle size distribution satisfies the following formula:

[0017] SPAN1 = D99 / D50 < 2.0;

[0018] SPAN2 = (D90 - D50) / D10 < 1.2.

[0019] Further, in some embodiments of the present application, the maximum particle size D of the porous alumina max is not higher than 2 μm.

[0020] Further, in some embodiments of the present application, the BET specific surface area of the porous alumina is in the range of 5 to 50 m 2 / g;

[0021] and the apparent density of the porous alumina is 2 to 3 g / cm 3 .

[0022] Further, in some embodiments of the present application, the pore volume of the porous alumina is 0.01 - 0.4 cm 3 / g;

[0023] The particles in the porous alumina powder are at least one of θ phase, δ phase, γ phase, α phase or at least one of η phase, κ phase, χ phase, ρ phase.

[0024] In a second aspect, the present application further provides a battery separator, which includes a substrate and a coating formed on at least one side of the substrate, and the porous alumina described in the first aspect is distributed in the coating.

[0025] Further, in some embodiments of the present application, the thickness uniformity δ of the coating is not higher than 0.3;

[0026] The test method for the thickness uniformity is as follows:

[0027] Take 6 points on the surface array of the base film provided with the coating, and obtain the thickness S of the coating at each point n , where n is the number of the measured points taken, and the value is a natural number in the range of 1 to 6. Statistically calculate the average thickness S of the coating 均 and the square root value of the sum of the squares of the differences between the coatings measured at each point. The calculation formula is as follows:

[0028] δ = ((S 1 - S 均 )) 2 + ((S 2 - S 均 )) 2 ……((S 6 - S 均 )) 2 )) 1 / 2 .

[0029] Further, in some embodiments of the present application, the number of surface bumps of the coating is not higher than 1 / 100 cm2;

[0030] The test method for the number of bumps is as follows:

[0031] Tighten the base film provided with the coating and place it under light, and observe and count the number of black dots from the back.

[0032] Further, in some embodiments of the present application, the thickness of the coating in the battery separator is 1 to 5 μm, and the proportion of porous alumina in the coating is 90% to 99% by mass fraction.

[0033] Thirdly, the present application also provides a battery, including the battery separator described in the second aspect.

[0034] Fourthly, the present application also provides an electrical device, including the battery described in the third aspect.

[0035] The embodiments of the present application provide a porous alumina, an electronic diaphragm, a battery, and an electrical device. The angle of repose and morphology of the porous alumina are controlled within a specific range, so that the dispersion of the porous alumina in the formed coating is good, the flatness of the coating surface is better, the bumps on the coating surface are reduced, the damage to the battery caused by the bumps on the coating surface is avoided, and it is beneficial to improve the heat shrinkage of the diaphragm and the stability and reliability of the battery. In addition, a large number of mesopores are contained on the surface and inside of the alumina particles of the porous alumina provided by the present application, which can provide channels for ion conduction and reduce the unit surface density of the diaphragm; at the same time, its specific surface area is controlled to be at a relatively low level, avoiding the high water affinity due to the high surface area of the alumina particles, resulting in difficulty in reducing the water content to the required content, and thus introducing water molecules that are not conducive to its reliability into the battery. Description of the Drawings

[0036] Figure 1 It is an SEM image of the porous alumina provided by the present application. Detailed Embodiments

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0038] [Apparent density ρ1]

[0039] The apparent density ρ1 mentioned in the present application is the ratio of the mass of the material of the solid particles to the apparent volume, where the apparent volume is the sum of the solid volume of the solid particles, the volume of the closed pores, and the volume of the open pores, and it can be used to represent the proportion of the pore volume in the particles; when the difference between the apparent density of the particles and the theoretical density is higher, it means that the pore volume of the particles is higher; when the difference between the apparent density of the particles and the theoretical density is lower, it means that the pore volume of the particles is lower.

[0040] [Angle of repose]

[0041] The angle of repose mentioned in the present application refers to the maximum angle measured when the gravity and the friction between the particles reach equilibrium and the particles are in a static state when sliding on the free slope of the powder pile in the gravitational field, and it can be used to represent the self-fluidity of the particles. When the angle of repose of the particle accumulation state is larger, it means that the self-fluidity of the particles is worse; when the angle of repose of the particle accumulation state is smaller, it means that the self-fluidity of the particles is better.

[0042] The present application provides a porous alumina, such as Figure 1 shown, in the surface and / or interior of the porous alumina particles, there are several alumina particles with mesopores (2 - 50 nm); and the alumina particles are prismatic crystals with a thickness not less than 20% of the length of the bottom side length; and its particle size D50 is 0.3 - 2 μm.

[0043] Among them, D50 is the cumulative particle size of 50% of the particles on the small particle size side in the cumulative particle size distribution; D90 is the cumulative particle size of 90% of the particles on the small particle size side in the cumulative particle size distribution; D99 is the cumulative particle size of 99% of the particles on the small particle size side in the cumulative particle size distribution; D10 is the cumulative particle size of 10% of the particles on the small particle size side in the cumulative particle size distribution; Dmax is the cumulative particle size of 99.9% of the particles on the small particle size side in the cumulative particle size distribution.

[0044] In order to provide support for the base film and reduce the thermal shrinkage rate of the separator, it is required that the ceramic particles used for the separator coating are not prone to misalignment flow when coated on the base film, which is mainly manifested as poor self-fluidity of the ceramic particles. However, due to their poor dispersibility and fluidity, ceramic particles with poor self-fluidity are difficult to form a coating with good surface flatness on the surface of the base film. Thus, it is difficult to simultaneously achieve a reduction in the thermal shrinkage of the separator and good surface flatness and uniform distribution of ceramic particles in the coating. Based on this technical problem, the applicant found that when controlling the morphology of the alumina particles to be a prismatic crystal with a thickness not less than 20% of the length of the bottom side length and the angle of repose of the alumina particles within the range of 36° - 38.5°, the alumina particles in the coating formed by the alumina have good uniform distribution, the surface flatness of the coating is good, and the improvement of the thermal shrinkage of the separator is also excellent, which is beneficial to the optimization of the thermal performance, mechanical strength, and breakdown voltage of the separator, and is also beneficial to improving the reliability of the battery.

[0045] It should be noted that the statement in the present application that "the morphology of the alumina particles is a prismatic crystal with a thickness not less than 20% of the length of the bottom side length" should be understood as that the morphology of the alumina particles provided in the present application is mainly a prismatic crystal with a thickness not less than 20% of the length of the bottom side length, rather than each particle of the alumina particles being a prismatic crystal with a thickness not less than 20% of the length of the bottom side length. Exemplarily, the proportion of the prismatic crystals with a thickness not less than 20% of the length of the bottom side length in the porous alumina provided in the present application is not less than 60%, or not less than 70%, not less than 80%; preferably, the proportion of the prismatic crystals with a thickness not less than 20% of the length of the bottom side length in the porous alumina provided in the present application is not less than 90%, and more preferably not less than 95%.

[0046] In the present application, the proportion of alumina particles with other morphologies in the porous alumina needs to be controlled within 40%. In particular, the proportion of spherical or quasi-spherical alumina particles is preferably controlled within 5%, and the total amount of needle-shaped, rod-shaped or fiber-shaped alumina particles is preferably controlled within 2%. More preferably, the total amount of needle-shaped, rod-shaped or fiber-shaped alumina particles is controlled within 1%. This is beneficial to achieving the required dispersibility of the porous alumina and the surface flatness of the coating while maintaining the improvement of the heat shrinkage of the porous alumina for the separator.

[0047] More preferably, the ratio of the thickness (the length of the side in the Z-axis direction) to the length of the bottom side (the length of the longest side on the plane formed by the X-axis and the Y-axis) of the porous alumina provided in the present application is preferably 0.6 to 1.8, and more preferably 0.6 to 0.9 or 1.2 to 1.8. That is, it is more preferable that the proportion of particles with the ratio of the thickness to the length of the bottom side of the porous alumina provided in the present application falling within the range of 0.6 to 1.8 is larger. More preferably, it is more preferable that the proportion of particles with the ratio of the thickness to the length of the bottom side of the porous alumina provided in the present application falling within the range of 0.6 to 0.9 or 1.2 to 1.8 is larger.

[0048] In order to further improve the ionic conductivity of the separator, the alumina particles provided in the present application are porous alumina particles with a large number of mesopores on the surface and inside. They not only provide channels for ionic conduction, but also can reduce the areal density of the coating and make the separator lighter. At the same time, the applicant also found that when the pores on the surface and inside of the alumina particles provided in the present application are controlled within the size of mesopores (2 - 50 nm), it is also beneficial to control the self-flowability of the porous alumina provided in the present application. Preferably, the pores on the surface and inside of the alumina provided in the present application are controlled within the size of 8 - 30 nm, which is more preferable. It is not only beneficial to control the self-flowability of the porous alumina, but also more beneficial to the ionic conduction rate of lithium ions in the pores, making its ionic conductivity better, and to control the specific surface area of the porous alumina, reducing the amount of the binder for the coating entering the mesopores, reducing the amount of the binder used, and leaving space for the absorption and storage of the electrolyte.

[0049] The BET specific surface area of the porous alumina provided in the present application can be controlled within the range of 5 - 50 m 2 / g, which is beneficial to controlling the affinity of alumina for water molecules and reducing the hydroxyl content on the surface of alumina; and the apparent density of the porous alumina is 2 - 3 g / cm 3 , making the areal density of the coating smaller and the separator significantly lighter.

[0050] Preferably, the maximum particle size D of the porous alumina provided in the present application maxIt can also be controlled within a range not higher than 4 μm, which is more conducive to reducing the number of surface bumps of the separator coating and further optimizing the surface flatness of the coating.

[0051] In addition, the particle size distribution of the porous alumina provided by this application is preferably satisfied:

[0052] SPAN1 = D99 / D50 < 2.5;

[0053] SPAN2 = (D90 - D50) / D10 < 1.5.

[0054] The narrow particle size distribution of the porous alumina is more conducive to improving the uniformity of the distribution of the porous alumina in the coating and the surface flatness, and is also conducive to the retention of ion transport channels in the coating, and is more conducive to optimizing the ion conductivity of the separator.

[0055] In addition, the technical effect of the porous alumina provided by this application is more obvious in thin coatings with a coating thickness of less than 2 μm. When the porous alumina provided by this application is applied to a thin coating with a coating thickness rate not higher than 2 μm, the particle size D50 of the porous alumina is preferably 0.4 - 1.2 μm, the angle of repose is preferably 38.1° - 38.5°, and the maximum particle size D max is not higher than 2 μm. The surface flatness of the separator coating formed by the porous alumina within this range is better, and its optimization of the heat shrinkage of the separator is also more obvious. In addition, due to the thin coating thickness, the areal density of the separator formed based on this porous alumina is low and the weight reduction of the separator is more significant.

[0056] On this basis, the particle size distribution of the porous alumina provided by this application can also be further controlled within the range of SPAN1 = D99 / D50 < 2.0 and SPAN2 = (D90 - D50) / D10 < 1.2, which is more conducive to improving the surface flatness and optimizing the heat shrinkage rate of the separator coating.

[0057] In addition, the applicant also found that by further controlling the product of the cumulative particle size D50 of 50% of the particles on the small particle size side in the cumulative particle size distribution of the porous alumina provided by this application, the specific surface area BET, and the apparent density ρ of the porous alumina, the separator of the coating formed based on the alumina provided by this application can be further optimized, making it superior in both the surface hydroxyl content of the porous alumina particles and the areal density of the coating surface when applied in the separator coating. Among them, the product of the particle size D50 of the porous alumina, the specific surface area BET, and the apparent density ρ needs to satisfy the following formula:

[0058] 15 < D50 × BET × ρ < 75

[0059] When the product of the particle size D50, the specific surface area BET, and the apparent density ρ of the porous alumina provided in this application is controlled within this range, the surface hydroxyl content of the alumina can reach 5 per nm 2 Hereinafter, and when the formed coating diaphragm ensures the ionic conductivity, the unit surface density of the coating with a solid content (the content of alumina particles in the coating) of 93% can be reduced to 4 g / (m 2 ·μm) or less, and even the unit surface density of the formed coating can be reduced to within 2 g / (m 2 ·μm).

[0060] Preferably, the product of the particle size D50, the specific surface area BET, and the apparent density ρ of the porous alumina satisfies the following formula:

[0061] 20 < D50 × BET × ρ < 60

[0062] More preferably, for porous alumina particles within different particle size ranges, the product of the particle size D50, the specific surface area BET, and the apparent density ρ of the porous alumina within the corresponding range is more conducive to the optimization of its coating surface density, ionic conductivity, and coating performance. For example, when the particle size D50 of the porous alumina is 0.3 - 0.4 μm and its SPAN1 = D99 / D50 < 2.0, SPAN2 = (D90 - D50) / D10 < 1.2, when the value of D50 × BET × ρ is preferably within the range of 19 - 25, the surface uniformity value δ of its coating can be controlled within 0.2; and when the particle size D50 of the porous alumina is 0.8 - 1.0 and its SPAN1 = D99 / D50 < 2.2, SPAN2 = (D90 - D50) / D10 < 1.2, when the value of D50 × BET × ρ is preferably within the range of 48 - 55, the surface uniformity value δ of its coating can be controlled within 0.3.

[0063] The pore volume of the porous alumina provided in this application is 0.02 - 0.4 cm 3 / g, preferably 0.05 - 0.2 cm 3 / g.

[0064] In the porous alumina provided in this application, the particles in the porous alumina are at least one of α-alumina, θ-alumina, and δ-alumina. It is preferably free of γ-alumina, or the content of γ-alumina in the porous alumina provided in this application does not exceed 5% by mass fraction to improve the chemical stability of the porous alumina and reduce its activity.

[0065] In the porous alumina powder provided in this application, the particles in the porous alumina powder are at least one of θ-phase, δ-phase, γ-phase, α-phase or at least one of η-phase, κ-phase, χ-phase, ρ-phase.

[0066] It should be noted that when the porous alumina powder includes γ-phase alumina, in addition to the γ-phase alumina, it further includes at least one of δ-phase, η-phase, κ-phase, χ-phase, and ρ-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 5%, and more preferably not higher than 2%.

[0067] That is, the porous alumina powder provided in the present application can be any one of the pure phase of θ-alumina and the mixed-phase alumina with other phases, the pure phase of δ-alumina and the mixed-phase alumina with other phases, the pure phase of η-alumina and the mixed-phase alumina with other phases, the pure phase of κ-alumina and the mixed-phase alumina with other phases, the pure phase of χ-alumina and the mixed-phase alumina with other phases, the pure phase of ρ-alumina and the mixed-phase alumina with other phases, the mixed-phase alumina of γ-alumina and other phases, and the mixed-phase alumina of α-alumina and other phases. Preferably, the porous alumina powder is preferably the pure phase of θ-alumina and the mixed-phase alumina with other phases, the pure phase of δ-alumina and the mixed-phase alumina with other phases, the pure phase of η-alumina and the mixed-phase alumina with other phases, the pure phase of κ-alumina and the mixed-phase alumina with other phases, the pure phase of χ-alumina and the mixed-phase alumina with other phases, the pure phase of ρ-alumina and the mixed-phase alumina with other phases. Further, in order to improve the porous alumina provided in the present application, the content of γ-alumina in the porous alumina provided in the present application is preferably relatively low, such as less than 10% or less than 8%, to improve the chemical stability of the porous alumina and reduce the activity.

[0068] In some embodiments, the content of metal elements in the porous alumina powder is as follows: the content of metal elements in the porous alumina powder is: sodium ion content: 0 - 300 ppm; calcium ion content: 0 - 300 ppm; iron ion content: 0 - 200 ppm; silicon ion content: 0 - 300 ppm; cobalt ion content: 0 - 50 ppm; copper ion content: 0 - 50 ppm; zinc ion content: 0 - 50 ppm; lead ion content: 0 - 50 ppm; chromium ion content: 0 - 50 ppm; nickel ion content: 0 - 50 ppm; zirconium ion content: 0 - 3000 ppm; tin ion content: 0 - 50 ppm.

[0069] Even more preferably, the sum of the contents of metal elements in the porous alumina powder is not higher than 5000 ppm. More preferably, the sum of the contents of iron, cobalt, chromium, zinc, and nickel elements in the porous alumina powder is not higher than 500 ppm, so as to avoid side reactions between impurity elements and the electrolyte and the positive and negative electrodes during the charge and discharge process of the battery, increase the consumption of the electrolyte, generate gas, and cause a decrease in ionic conductivity, which is beneficial to reducing the damage of these impurities to the battery.

[0070] The sum of the contents of metal elements such as iron, cobalt, chromium, zinc, and nickel in the porous alumina provided by this application is relatively low. The reason may be that the porous alumina particles provided by this application are mainly single-crystal particles with a high degree of crystal particle integrity; and during the preparation process, the formation of its pores is not through granulation, but through the escape of water molecules in the crystal particles and the atomic displacement during the crystal phase change process; making it difficult for metal elements to be embedded in the porous alumina particles and attached to the surface of single-crystal particles, making it easier for other metal ions in ionic state to remain in the reaction system and be removed through cleaning or demagnetization and impurity removal means.

[0071] Preferably, the porous alumina provided by this application is directly prepared from raw materials and is not obtained by compounding and sorting a variety of porous alumina.

[0072] [Preparation method of porous alumina]

[0073] The porous alumina provided by this application can be obtained by using aluminum hydroxide or aluminum ions as crystal nuclei with seeds through hydrothermal reaction to control the growth of intermediates, and adjusting the pH value of the system after hydrothermal reaction and before drying, and then controlling the temperature curve of the calcination process in the presence of a barrier agent after drying and crushing to obtain porous alumina particles with a specific morphology, a specific particle size range, and a specific angle of repose.

[0074] In this preparation method, the seeds used are boehmite with a particle size not exceeding 80 nm. The crystallization water content of the obtained intermediate is preferably controlled to be 1 to 1.2. The purity of boehmite crystals in the intermediate is controlled to be above 99% through hydrothermal process and pH value adjustment process. And the particle size of the intermediate obtained by growth satisfies D50 of 0.3 to 2 μm, and its morphology is mainly a quadrangular prism crystal with a specific thickness not less than 20% of the length of the bottom side length.

[0075] For those skilled in the art to better understand and implement this application, the following also provides an example of the preparation method of the above-mentioned porous alumina as follows:

[0076] Preparation method:

[0077] Step (1): Provide aluminum hydroxide, seeds, and pure water. Mix aluminum hydroxide, additives, and pure water, grind for 30 min to 60 min, and immediately add seeds, mix and synchronously heat up to 60°C to 80°C, stir and react for 1 h to 3 h; then heat up to 150°C to 200°C, keep warm and react for 4 h to 48 h to obtain an intermediate; control the reaction pressure to be 1.4 to 3.7 MPa;

[0078] Step (2): Adjust the pH value of the system, and after pressure filtration, dry it by infrared microwave drying method to form an intermediate powder. At this time, control the free water content in the intermediate powder not higher than 0.2%, and the crystal water content not higher than 1.2 water molecules;

[0079] Step (3): Add a barrier agent, mix it evenly with the intermediate, and then calcine it at 600 °C - 1200 °C for 0.5 - 5 h. After air classification, porous alumina is obtained.

[0080] In the system formed by aluminum hydroxide, additives and pure water, the addition amount of the additive is 0.01 - 1% by mass fraction; the addition amount of aluminum hydroxide is 10 - 30% by mass fraction. The addition amount of the seed crystal is 0.01 - 0.2% of this system. It should be noted that the particle size of the seed crystal is not higher than 80 nm; when alcohol is added to the additive, the addition amount of alcohol is not less than 30% and not higher than 60% of the dispersant.

[0081] The alcohol used here can be one or more of common alcohol solvents such as ethanol, propanol, n-butanol, isobutanol, pentanol, isopentanol, etc.

[0082] Among them, after the intermediate is obtained, use organic acid to adjust the pH value of the intermediate slurry to 7.2 - 8.3, preferably 7.5 - 8.0, and dry it by infrared microwave drying. The drying method can also be spray drying. When spray drying is adopted, after spray drying and before calcination, there is also a dispersion process, using air classification or grinding means to disperse the dried particles into particles with a D50 particle size of 0.3 - 2 μm.

[0083] When infrared microwave drying is adopted, the dried intermediate powder does not need to be dispersed or broken, and can directly enter the calcination process, saving costs and improving the morphological integrity of the product. In addition, in order to achieve a good dispersion effect, when infrared microwave drying is adopted, first filter the slurry into a filter cake with a free water content not less than 65%, break it into small filter cakes, then irradiate it with infrared light to heat it to a temperature not less than 150 °C, process it for 8 - 15 min, then cool it down to 80 - 100 °C, heat it with microwave for 3 - 10 min, and then heat it with microwave to above 150 °C until the small filter cake automatically explodes into powder. Similarly, the water content of the intermediate powder formed by segmental drying using the infrared microwave drying process is low, and can reach a water content (free water) not higher than 0.2%. Moreover, in this process, the appearance morphology of the particles is not damaged due to grinding or ball milling, and the integrity is better. And because there is no high-temperature spray process and the process of automatic explosion into powder, the agglomeration of crystal particles in the obtained powder is lower, and the single-crystal dispersion of the product is better.

[0084] The crystal water content of the obtained intermediate, calculated by the number of crystal molecules, does not exceed 1.2 water molecules, preferably 1 - 1.2 crystal waters, and the morphology is mainly prismatic, and the particle size is mainly distributed in the range of 0.3 - 2 μm.

[0085] In step (3), 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, more preferably not lower than 50 °C and not higher than 100 °C. Exemplarily, the barrier agent can be ammonium bicarbonate, ammonium carbonate, ammonium nitrate, preferably ammonium carbonate; the dosage of the barrier agent is 0.01% - 0.1% by mass fraction of the dried intermediate powder obtained in step (2). The addition timing of the barrier agent can be in the drying stage or in the calcination stage. When it is added in the calcination stage, it can also reduce the adhesion of particles to the wall of the container used for calcination during the calcination process. The temperature curve of its calcination process is preferably: rapidly heating up to at least 300 °C at a heating rate of not less than 8 °C / min, reducing the heating rate (the heating rate is not higher than 2 °C / min) and then heating up to the holding temperature, and then holding and sintering for 0.5 h - 5 h to obtain the product, so as to promote the maintenance of the single crystal morphology of the particles of porous alumina and the control of pore size and pore volume.

[0086] In this preparation method, the inventors found that directly adjusting the acidity of the slurry after the reaction can promote the consistency of the crystal structure, particle size and pore size distribution of the product. The reason may be that directly adjusting the acidity after the reaction can inhibit the formation of aluminum trihydrate, making the obtained intermediate have higher purity and a large number of defects appear on the intermediate, providing a preferential guidance for the formation and development of subsequent pores.

[0087] In the second aspect, the present application also provides a battery separator, which includes a substrate and a coating formed on at least one side of the substrate, and the coating is distributed with the porous alumina described in the first aspect.

[0088] Among them, the thickness uniformity δ of the coating formed based on the above-mentioned porous alumina is not higher than 0.3.

[0089] Preferably, the number of surface bumps of the coating formed based on the above-mentioned porous alumina can also be as low as not higher than 1 / m 2, and its heat shrinkage can be reduced to within 2.2% in MD (transverse direction) and within 2.7% in TD (longitudinal direction). For porous alumina applicable to thin coatings (coating thickness within 2 μm), when its particle size is within 0.4 - 1.2 μm and Dmax is within 2 μm, SPAN1 ≤ 2, SPAN2 ≤ 1.2, and the angle of repose is within the range of 36° - 38.5°, the heat shrinkage of the coating formed based on this porous alumina can be optimized to below 1.9% in MD (transverse direction) and within 1.4% in TD (longitudinal direction), and at the same time, the thickness uniformity of its coating can be optimized to within 0.27. More preferably, when the porous alumina has a particle size within 0.4 - 0.8 μm and Dmax within 2 μm, SPAN1 ≤ 2, SPAN2 ≤ 1.2, and the angle of repose is within the range of 38.5° - 40.5°, the heat shrinkage of the coating formed based on this porous alumina can be optimized to below 1.2% in MD (transverse direction) and within 1.1% in TD (longitudinal direction), and at the same time, the thickness uniformity of its coating can be optimized to within 0.2.

[0090] Among them, the test method for the thickness uniformity is as follows:

[0091] Take 6 points on the surface array of the base film with the coating, and obtain the thickness S of the coating at each point n , where n is the serial number of the measured points taken, and the value is a natural number within the range of 1 - 6. Statistically calculate the average thickness S of the coating 均 and the square root value of the sum of the squares of the differences between the average thickness and the coating thickness measured at each point. Its calculation formula is:

[0092] δ = ((S 1 - S 均 ) 2 + (S 2 - S 均 ) 2 ... (S 6 - S 均 ) 2 ) 1 / 2 .

[0093] The thickness uniformity δ represents the standard variance of the coating thickness at each position on the separator compared to the average value, and it can be used to represent the thickness uniformity of the coating formed on the separator.

[0094] The test method for the number of convex points is as follows:

[0095] Tighten the base film with the coating and place it under light, observe from the back and count the number of black dots.

[0096] The number of bumps is tested based on the principle that powder agglomeration / large particles will cause light passing through to be blocked, showing as black dots. It can be used to represent the number of bumps on the coating surface. The more bumps there are, it not only indicates poor thickness uniformity of the coating, but also can indicate poor dispersion of alumina particles in the coating. A large number of bumps has an impact on the reliability of the battery.

[0097] Preferably, the thickness of the coating in the battery separator is 1-5 μm, and the proportion of porous alumina in the coating is 90%-99% by mass fraction.

[0098] In a third aspect, the present application also provides a battery, including the battery structural member described in the second aspect.

[0099] In a fourth aspect, the present application also provides an electrical device, including the battery described in the third aspect. The electrical device can be any electrical device that can use an ion battery, such as an electric vehicle, an aircraft, a vehicle, a mobile phone, a tablet computer, a handheld game console, a portable digital device (such as a digital camera), a smart home, a smart wearable (such as a smart bracelet, a smart watch, smart glasses), etc.

[0100] To facilitate those skilled in the art to understand the innovative points of the present application, the following provides some preferred embodiments in conjunction with the drawings to illustrate the above technical solutions.

[0101] Manufacture of Porous Alumina

[0102] Example 1

[0103] Step (1): Provide aluminum hydroxide, seeds, and pure water. Mix aluminum hydroxide and pure water, grind for 40 min, immediately add seeds, mix and simultaneously heat up to 65°C, stir and react for 2 h; then heat up to 170°C, keep the temperature for reaction for 10 h to obtain an intermediate; control the reaction pressure to be 2 MPa;

[0104] Step (2): Adjust the pH value of the system to 7.8, and filter the slurry into a filter cake with a free water content of not less than 65%. After breaking the filter cake into small pieces, irradiate and heat it with infrared light to a temperature of not less than 150°C, process for 10 min, then cool down to 80°C, heat-treat with microwave for 8 min, and then heat up with microwave to above 150°C until the small filter cake automatically explodes into powder;

[0105] Step (3): Add an ammonium carbonate blocking agent with a mass fraction of 0.05% based on 100% of the mass of alumina. After mixing evenly with the intermediate, quickly heat up to 300°C at a heating rate of 8°C / min, reduce the heating rate to 2°C / min and then heat up to 1100°C, then keep the temperature for sintering for 3 h. After airflow milling, obtain sample 1 of porous alumina.

[0106] Example 2

[0107] Step (1): Provide aluminum hydroxide, seed crystals, and pure water. Mix aluminum hydroxide and pure water, grind for 50 min, then immediately add the seed crystals, mix and simultaneously heat up to 65 °C, and stir and react for 2 h; then heat up to 170 °C and hold the reaction for 10 h to obtain an intermediate; control the reaction pressure to be 2 MPa;

[0108] Step (2): Adjust the pH value of the system to 7.8, filter the slurry into a filter cake with a free water content of not less than 65%, break it into small filter cakes, then irradiate with infrared light to heat to a temperature of not less than 150 °C, treat for 10 min, then cool down to 80 °C, treat with microwave heating for 8 min, and then use microwave heating to heat up to above 150 °C until the small filter cakes automatically burst into powder;

[0109] Step (3): Add an ammonium carbonate barrier agent with a mass fraction of 0.05% based on 100% of the mass of alumina, mix it evenly with the intermediate, quickly heat up to 300 °C at a heating rate of 8 °C / min, reduce the heating rate to 2 °C / min and then heat up to the holding temperature, then hold and sinter for 3 h, and after air jet milling, obtain sample 2 of porous alumina.

[0110] Example 3

[0111] Step (1): Provide aluminum hydroxide, seed crystals, and pure water. Mix aluminum hydroxide and pure water, grind for 50 min, then immediately add the seed crystals, mix and simultaneously heat up to 65 °C, and stir and react for 3 h; then heat up to 170 °C and hold the reaction for 15 h to obtain an intermediate; control the reaction pressure to be 2 MPa;

[0112] Step (2): Adjust the pH value of the system to 7.8, filter the slurry into a filter cake with a free water content of not less than 65%, break it into small filter cakes, then irradiate with infrared light to heat to a temperature of not less than 150 °C, treat for 10 min, then cool down to 80 °C, treat with microwave heating for 8 min, and then use microwave heating to heat up to above 150 °C until the small filter cakes automatically burst into powder;

[0113] Step (3): Add an ammonium carbonate barrier agent with a mass fraction of 0.03% based on 100% of the mass of alumina, mix it evenly with the intermediate, quickly heat up to 300 °C at a heating rate of 8 °C / min, reduce the heating rate to 2 °C / min and then heat up to the holding temperature, then hold and sinter for 3 h, and after air jet milling, obtain sample 3 of porous alumina.

[0114] Example 4

[0115] Step (1): Provide aluminum hydroxide, seed crystals, and pure water. Mix aluminum hydroxide and pure water, grind for 40 min, immediately add the seed crystals, mix and simultaneously heat up to 65 °C, stir and react for 3 h; then heat up to 170 °C, keep the temperature for reaction for 15 h to obtain an intermediate; control the reaction pressure to be 2 MPa;

[0116] Step (2): Adjust the pH value of the system to 7.8, filter the slurry into a filter cake with a free water content of not less than 65%, break it into small pieces of filter cake, then irradiate and heat it with infrared light to a temperature of not less than 150 °C, treat for 10 min, then cool down to 80 °C, heat-treat with microwave for 8 min, and then heat up with microwave to above 150 °C until the small filter cake automatically explodes into powder;

[0117] Step (3): Add an ammonium carbonate barrier agent with a mass fraction of 0.03% based on 100% of the mass of alumina, mix it evenly with the intermediate, quickly heat up to 300 °C at a heating rate of 8 °C / min, reduce the heating rate to 2 °C / min and then heat up to the holding temperature, then hold and sinter for 3 h, and after jet milling, obtain sample 4 of porous alumina.

[0118] Comparative Example 1

[0119] Compared with Example 1, in this comparative example, the mixing and grinding time of aluminum hydroxide and pure water is 30 min; the remaining steps are the same as those in Example 1 to obtain comparative sample 1.

[0120] Comparative Example 2

[0121] Compared with Example 2, in this comparative example, the mixing and grinding time of aluminum hydroxide and pure water is 35 min; the remaining steps are the same as those in Example 1 to obtain comparative sample 2.

[0122] Comparative Example 3

[0123] Compared with Example 3, in this comparative example, the mixing and grinding time of aluminum hydroxide and pure water is 35 min; the remaining steps are the same as those in Example 3 to obtain comparative sample 3.

[0124] Comparative Example 4

[0125] Compared with Example 4, in this comparative example, the mixing and grinding time of aluminum hydroxide and pure water is 30 min; the remaining steps are the same as those in Example 4 to obtain comparative sample 4.

[0126] [Testing of Porous Alumina]

[0127] Perform particle size distribution test, specific surface area test, apparent density test, angle of repose test, and morphology characterization on the obtained porous alumina. The specific testing methods are as follows:

[0128] 1. Particle size distribution test

[0129] Measured by Malvern 3000 laser particle size analyzer.

[0130] 2. Specific surface area measurement

[0131] Measured by Micromeritics specific surface area analyzer.

[0132] 3. Angle of repose measurement

[0133] Measured by powder property instrument.

[0134] 4. Morphology characterization

[0135] Characterized by SEM scanning electron microscope.

[0136] The test results are shown in Table 1.

[0137] Table 1

[0138]

[0139] The alumina particles obtained from the above examples and comparative examples were configured into slurries, and the formed slurries were respectively coated on the base films cut into pieces, and dried to obtain separator samples. Among them, the configuration of the slurry and the method of coating the slurry into a film are as follows:

[0140] (1) Take 350 g of porous alumina powder and 650 g of deionized water, stir and mix for 10 min;

[0141] (2) Add 10.5 g of dispersant SF8 and continue to stir for 10 min;

[0142] (3) Add 5.25 g of emulsifier lauryl alcohol polyoxyethylene ether and continue to stir for 10 min;

[0143] (4) Add 17.5 g of acrylic emulsion BM900-B and continue to stir for 30 min to obtain the coating slurry;

[0144] (5) Coat the slurry on the surface of the PE separator with an on-line rod coater, and place it in a blast drying oven at 40 °C for 10 min to obtain the separator with a coated layer.

[0145] Among them, the base film is a PE film with a thickness of 9 μm, purchased from Suzhou Jieli New Energy Materials Co., Ltd. The dispersant is SF8 purchased from San Nopco, Japan. The binder is BM900-B purchased from Zeon, Japan. Lauryl alcohol polyoxyethylene ether is purchased from Nantong Haian Chemical Industry.

[0146] Measure the viscosity of the above slurry, and weigh, measure the thickness, measure the heat shrinkage, measure the water content, detect the number of bumps of the separator, and calculate the thickness uniformity and coating surface density of the separator.

[0147] The specific test methods are as follows:

[0148] 1. Thickness uniformity

[0149] Cut the separator into a 20×50 cm separator. Take 6 points on the separator at equilateral triangles with a side length of 10 cm, and take three equilateral triangles at different positions on the separator. Considering non-production equipment coating, the thickness fluctuation is relatively large on both lateral sides of the coating. Therefore, only two points farther from the edge are selected in the transverse direction, for a total of 6 points. Statistically calculate the square root value δ of the sum of the squares of the differences between the data points and the mean point. The specific calculation formula is as follows:

[0150] δ = ((S 1 - S 均 ) 2 +(S 2 - S 均 ) 2 ……(S 6 - S 均 ) 2 ) 1 / 2

[0151] Among them, the thicknesses of the separator and the base film are measured using a German Mahr thickness tester.

[0152] 2. Measurement of heat shrinkage

[0153] Obtained by referring to the measurement in 6.6.2 of GB / T36363-2018.

[0154] 3. Measurement of water content

[0155] Use a Karl Fischer moisture meter to test the moisture content of the separator to obtain the water content.

[0156] 4. Viscosity measurement

[0157] Obtained by using an NJD-5 rotational viscometer.

[0158] 5. Detection of the number of bumps

[0159] Cut the separator into a 20×50 cm separator and place it under a light. Observe and count the number of black dots from the back.

[0160] The test results are shown in Table 2.

[0161] Table 2

[0162]

[0163] Among them, the measured values of the thickness of the coating for calculating the δ value are shown in Table 3:

[0164] Table 3

[0165]

[0166] As can be seen from the above table, the particle size D50 and the angle of repose of the porous alumina with a specific morphology provided by this solution can be controlled within the range of 36° to 38.5°. The alumina has a relatively high structural consistency, a uniform particle size distribution, relatively low apparent density and specific surface area, and relatively low viscosity of the formed slurry. The alumina has excellent dispersibility in the slurry and good fluidity of the slurry. The alumina particles in the separator coating formed by coating the slurry based on the porous alumina are also evenly distributed. The surface density of the separator coating is low, the thermal shrinkage rate is lower, and the thickness uniformity of the film surface is also significantly optimized; there are very few bumps on the film surface, almost none.

[0167] In addition, for thin coatings (coatings with a thickness not higher than 2 μm), when alumina with a narrower particle size distribution, a lower particle size D50, and an angle of repose within the range of 38.1° to 38.5° is used, the shrinkage rate of the formed coating for the separator is increased more significantly, and its apparent performance is also better.

[0168] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A porous alumina, characterized in that: The porous alumina is an alumina particle with a plurality of mesopores on the surface and / or inside of the particle; and the alumina particle is a quadrangular prism crystal with a thickness not less than 20% of the length of the bottom side; the cumulative particle size D50 of 50% of the particles on the small particle size side in the cumulative particle size distribution is 0.3-2 μm; and the pore size of the mesopore is 2-50 nm; The repose angle of the porous alumina is 36.0° to 38.5°; the maximum particle size D of the porous alumina is max Not higher than 4μm; The particle size distribution of the porous alumina satisfies the following formula: SPAN1=D99 / D50<2.5; SPAN2=(D90-D50) / D10<1.5; The specific surface area of ​​the porous alumina is 5 to 50 m 2 / g within this range; The apparent density of the porous alumina is 2-3 g / cm 3 .

2. The porous alumina according to claim 1, characterized in that: The repose angle of the porous alumina is 38.1° to 38.5°.

3. The porous alumina according to claim 1 or 2, characterized in that: The cumulative particle size D50 of 50% of particles on the small particle size side in the cumulative particle size distribution of the porous alumina is 0.4 to 1.2 μm.

4. The porous alumina according to claim 3, characterized in that: Its particle size distribution satisfies the following formula: SPAN1=D99 / D50<2.0; SPAN2=(D90-D50) / D10<1.

2.

5. The porous alumina according to claim 3, characterized in that: The maximum particle size D of porous alumina max Not higher than 2μm.

6. The porous alumina according to claim 1, characterized in that: The pore volume of the porous alumina is 0.01-0.4 cm 3 / g; The particles in the porous alumina powder 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.

7. A battery separator, characterized in that: The battery separator comprises a substrate and a coating formed on at least one side of the substrate, wherein the porous alumina according to any one of claims 1 to 6 is distributed in the coating.

8. The battery separator according to claim 7, characterized in that: The thickness uniformity δ of the coating is not higher than 0.3; The test method for thickness uniformity is: Take 6 points on the surface array of the base film with coating and obtain the thickness S of the coating at each point. n , where n is the number of the measurement point, which is a natural number in the range of 1 to 6. The average thickness S of the coating is calculated. 均 The square root of the sum of the squares of the coating differences measured at each point is calculated as follows: δ=((S1-S 均 ) 2 +(S2-S 均 ) 2 ……( S6-S 均 ) 2 ) 1 / 2 。 9. The battery separator according to claim 7, characterized in that: The number of convex points on the surface of the coating is not higher than 1 / 100cm 2 ; The testing method of the number of convex points is: The base film with the coating was stretched and placed under light, and the number of black spots was observed from the back side and counted.

10. The battery separator according to any one of claims 7 to 9, characterized in that: The coating thickness in the battery separator is 1-5 μm, and the proportion of porous aluminum oxide in the coating is 90%-99% by mass.

11. A battery, characterized in that: A battery separator comprising the battery separator according to any one of claims 7 to 10.

12. An electrical equipment, characterized in that: Comprising the battery of claim 11.

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