Preparation method of low-sodium ultrafine alumina for lithium battery diaphragm

Abstract

The application relates to the field of functional material preparation, in particular to a preparation method of low-sodium superfine aluminum oxide for lithium battery diaphragms; the preparation method comprises the following steps: carrying out a dissolution reaction on industrial aluminum hydroxide and a sodium hydroxide solution, then performing temperature reduction and filtration to obtain a sodium aluminate solution; adding heterogeneous seed crystals containing aluminum oxide into the sodium aluminate solution to perform seed crystal decomposition, then performing filtration and washing to obtain heterogeneous doped superfine aluminum hydroxide; performing beating on the heterogeneous doped superfine aluminum hydroxide and pure water, and performing a hydrothermal sodium removal reaction, then adding a surfactant to perform dispersion, and performing filtration and washing to obtain low-sodium-content aluminum oxide hydrate; calcining the low-sodium-content aluminum oxide hydrate to obtain low-sodium calcined aluminum oxide; performing grinding and scattering on the low-sodium calcined aluminum oxide, then performing electromagnetic iron removal and screening impurity removal to obtain low-sodium superfine aluminum oxide; the method can efficiently and at low cost prepare superfine aluminum oxide powder with small original crystal grain size, fine grain size and narrow distribution.

Description

Technical Field

[0001] This application relates to the field of functional material preparation technology, and in particular to a method for preparing low-sodium ultrafine alumina for lithium battery separators. Background Technology

[0002] Low-sodium ultrafine alumina possesses advantages such as thermal conductivity, insulation, corrosion resistance, good thermal stability, and high-temperature resistance. It is primarily used in the production of lithium-ion battery separator coatings, microcrystalline ceramics, foam ceramics, electronic packaging, and special light source devices. Due to the advantages of alumina in lithium-ion battery separator coatings, including long cycle life, high rate capability, and excellent thermal conductivity, as well as good liquid absorption and retention capabilities, it can block current when the current is too high and the temperature rises, preventing the negative electrode separator from melting due to excessive temperature and causing a short circuit risk. This improves the energy density and safety reliability of high-power lithium-ion batteries. However, alumina used in lithium-ion battery separators requires low levels of harmful impurities such as silicon, iron, sodium, and calcium. It also requires high product purity, fine particle size, and narrow particle size distribution to ensure sufficient membrane porosity for ion passage. Furthermore, the alumina must not contain large particles to avoid puncturing the separator. To ensure proper separator operation, the alumina needs a good morphology and structure with microspherical grains.

[0003] Currently, lithium-ion battery products for smartphones, tablets, laptops, and other digital devices require reduced separator thickness while ensuring safety, thereby increasing the battery's gravitational energy density. For power batteries used in new energy vehicles, electric bicycles, power tools, and energy storage power stations, safety performance is paramount. This necessitates further thinning of the separator while ensuring a long service life and the ability to withstand high rates and high power charging and discharging. Therefore, thinning of lithium-ion battery separators has become a trend. The thinner the separator coating, the finer the alumina particle size required for its preparation. Furthermore, the high demands on the electrical insulation, thermal conductivity, and permeability of the separator coating necessitate calcined alumina with even finer primary grain size, more regular morphology, and a suitable specific surface area.

[0004] Currently, the main production processes for low-sodium ultrafine alumina used in lithium-ion battery separators include ammonium aluminum carbonate pyrolysis, aluminum alkoxide hydrolysis, and alumina pretreatment calcination and grinding. Most of these processes use industrial alumina as the main raw material, first purifying it through pretreatment, and then calcining it at high temperatures in a tunnel kiln or shuttle kiln to prepare low-sodium ultrafine alumina. The resulting alumina has a relatively coarse primary crystal size, generally around 0.8 μm. Furthermore, because industrial alumina is a polymeric particle, uneven heating during calcination leads to inconsistent crystal size and poor morphological regularity, affecting product performance. In contrast, the ammonium aluminum carbonate pyrolysis and aluminum alkoxide hydrolysis methods for producing low-sodium ultrafine alumina are complex, inefficient, and costly.

[0005] Therefore, how to provide a method for preparing low-sodium ultrafine alumina for lithium-ion battery separators, so as to develop an efficient and low-cost ultrafine high-purity alumina preparation process and prepare ultrafine high-purity alumina powder for lithium-ion battery separators with fine primary crystals, fine particle size and narrow distribution, is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] This application provides a method for preparing low-sodium ultrafine alumina for lithium battery separators, in order to solve the technical problems of high preparation cost and coarse primary grain size of the prepared product in the prior art.

[0007] In a first aspect, this application provides a method for preparing low-sodium ultrafine alumina for lithium battery separators, the method comprising:

[0008] Industrial aluminum hydroxide is reacted with sodium hydroxide solution to undergo a dissolution reaction, followed by cooling and filtration to obtain sodium aluminate solution;

[0009] A heterogeneous seed crystal containing aluminum oxide was added to a sodium aluminate solution to decompose the seed crystal, followed by filtration and washing to obtain heterogeneous doped ultrafine aluminum hydroxide.

[0010] The heterogeneous doped ultrafine aluminum hydroxide and pure water were slurried and subjected to a hydrothermal desodiuming and impurity removal reaction. Then, a surfactant was added for dispersion, followed by filtration and washing to obtain alumina hydrate with low sodium content.

[0011] The low-sodium-content alumina hydrate is calcined to obtain low-sodium calcined alumina;

[0012] The low-sodium calcined alumina was ground and broken down, and then subjected to electromagnetic iron removal and sieving to remove impurities, in order to obtain low-sodium ultrafine alumina.

[0013] Optionally, the temperature of the dissolution reaction is 105℃~145℃, and the time of the dissolution reaction is 20min~120min.

[0014] Optionally, the heterogeneous seed crystals include ultrafine α-alumina powder or ultrafine boehmite.

[0015] Optionally, the average grain size of the heterogeneous seeds is <0.8 μm; and / or,

[0016] The seed coefficient of the heterogeneous seed crystal is 0.01 to 1.0.

[0017] Optionally, the initial temperature for seed decomposition is 55℃~85℃, the final decomposition temperature is ≥50℃, the decomposition time is 6h~48h, and the cooling rate is <0.5℃ / h.

[0018] Optionally, the temperature of the hydrothermal desodiuming reaction is 140℃~210℃, and the reaction time is 0.5h~8h; and / or,

[0019] The target solid content of the pulp is 50 g / L to 200 g / L.

[0020] Optionally, the surfactant includes at least one selected from stearic acid, polyvinyl alcohol, and polyethylene glycol; and / or,

[0021] The molecular weight of the polyvinyl alcohol is 4,000 to 10,000, and the molecular weight of the polyethylene glycol is 2,000 to 8,000.

[0022] Optionally, the amount of surfactant added is 0.1% to 2%.

[0023] Optionally, the calcination temperature is 1150℃~1250℃, and the calcination time is 0.5h~4h.

[0024] Optionally, the grinding and dispersing may be carried out by ball milling or sand milling, wherein the diameter of the grinding balls is 2mm to 20mm, and the ball-to-material ratio is 1:1 to 10:1; and / or,

[0025] The grinding and dispersing process includes wet grinding followed by spray drying and dispersing.

[0026] The technical solutions provided in this application have the following advantages compared with the prior art:

[0027] This application provides a method for preparing low-sodium ultrafine alumina for lithium-ion battery separators. First, aluminum hydroxide is dissolved in sodium hydroxide solution to obtain a sodium aluminate solution. Then, a heterogeneous seed crystal containing aluminum oxide is added for seed decomposition to obtain heterogeneous doped ultrafine alumina. This seed decomposition method ensures uniform mixing and close contact between the heterogeneous seed crystal and the ultrafine alumina precursor, thereby reducing the phase transition activation energy. Therefore, α-phase alumina nuclei can be rapidly precipitated at a lower temperature through low-temperature calcination, resulting in finer alumina crystals. The method involves reducing the size of the protocrystalline nuclei and simultaneously improving the α-phase conversion rate. Then, a hydrothermal desodiuming reaction is performed using pure water to remove sodium oxide impurities while completing the hydrothermal phase transformation process. After calcination, high-purity ultrafine alumina with low sodium content is obtained, resulting in ultrafine alumina powder with small protocrystalline particle size and narrow particle size distribution. Since this method only requires two major reactions—seed decomposition and hydrothermal desodiuming—the overall preparation process can achieve low-cost and high-efficiency preparation, while also obtaining ultrafine alumina powder with small protocrystalline particle size and narrow particle size distribution. Attached Figure Description

[0028] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0029] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 A schematic diagram of a method for preparing low-sodium ultrafine alumina for lithium battery separators provided in this application embodiment;

[0031] Figure 2 This is a schematic diagram of the actual industrial production process of low-sodium ultrafine alumina for lithium battery separators, provided as an embodiment of this application. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0034] The creative thinking behind this application is:

[0035] Currently, the main production processes for low-sodium ultrafine alumina used in lithium-ion battery separators include ammonium aluminum carbonate pyrolysis, aluminum alkoxide hydrolysis, and alumina pretreatment calcination, among others.

[0036] (1) Aluminum isopropoxide with a purity of 99.999% is prepared into a sol by heating and stirring with pure water and nitric acid, and then high-purity ultrafine alumina powder is obtained by high-temperature spray pyrolysis. The purity of the product can reach 99.995%, the particle size distribution is narrow, D100≤2.5μm, and the crystal form can be γ-Al2O3 or α-Al2O3.

[0037] (2) Alumina ultrafine powder is obtained by reacting elemental aluminum as aluminum source, anhydrous low-carbon alcohol as oxygen donor (solvent) and anhydrous low-carbon organic acid as precipitant. The wet precipitate is dried and calcined.

[0038] (3) A slurry was prepared using 4N α-alumina powder and solvent as raw materials, and a certain amount of surfactant was added. The slurry was then ground to the required particle size. High-purity ultrafine alumina powder with D50≤0.8μm and uniform particle size was obtained by spray drying and air jet milling.

[0039] (4) Metallic aluminum and carbon alcohol are subjected to an alcoholysis reaction, and after secondary purification, a hydrolysis reaction is carried out to obtain a high-purity hydrolysis product; the high-purity hydrolysis product is dried and calcined to obtain high-purity ultrafine alumina with a purity of 5N. The alumina for lithium battery separator coating prepared by the aluminum alkoxide method and the aluminum carbonate ammonium thermal method has high product purity and fine particle size, but the process is complex and the production cost is high.

[0040] Most of the above methods use metallic aluminum as raw material, reacting it with organic alcohols to obtain aluminum ol, which is then hydrolyzed to prepare low-sodium ultrafine alumina. This method is costly and carries significant safety risks. Alternatively, industrial alumina can be used as the main raw material. The raw material is first purified through pretreatment, and then calcined at high temperature in a tunnel kiln or shuttle kiln to prepare low-sodium ultrafine alumina. The resulting alumina has a relatively coarse primary crystal size, generally around 0.8 μm. In addition, because industrial alumina consists of agglomerated particles, uneven heating during calcination leads to inconsistent crystal size in the calcined alumina, and the product has poor morphological regularity, affecting its performance.

[0041] Alumina's chemical bonds are a transitional type between ionic and covalent bonds, and its melting point is as high as 2050℃. During the transition from the transition phase to the α phase, lattice reorganization occurs. Due to the large energy barrier required for the phase transition, a high calcination temperature is needed to overcome this barrier and initiate the phase transition. Simultaneously, at high temperatures, crystal growth is rapid, and abnormal grain growth occurs, making it difficult to prepare low-sodium ultrafine calcined alumina suitable for lithium-ion battery separators with high α-phase conversion rates. Although lowering the calcination temperature can suppress rapid grain growth, it is difficult to overcome the phase transition barrier, and the phase transition rate is slow, resulting in low α-phase conversion rates and making it unsuitable for lithium-ion battery separator coating production. While current preparation techniques involve uniformly mixing precursor powder and α-Al₂O₃ seeds to obtain a mixture, followed by microwave heating of the mixture to obtain ultrafine alumina, the heterogeneous nucleation effect of the seeds is difficult to effectively utilize because the seed and precursor are a solid-phase mixture, and the calcination of alumina is a mass transfer reaction occurring in the solid phase. In addition, in order to obtain fine-grained alumina, the calcination temperature was lowered. As a result, sodium oxide in the precursor was difficult to volatilize and be discharged, making it difficult to prepare low-sodium alumina by calcining industrial alumina powder at low temperature.

[0042] To meet the growing demand for thinner and lighter lithium-ion battery separator coatings and address the issues of high cost or coarse grain size in existing processes, it is crucial to develop an efficient and low-cost method for preparing ultrafine, high-purity alumina powder with fine grain size and narrow particle size distribution for lithium-ion battery separators. This application provides a method for preparing low-sodium ultrafine alumina for lithium-ion battery separators, which offers advantages such as low production cost, fine grain size, low content of harmful impurities, and high phase conversion rate, thus meeting the requirements for thinner and lighter lithium-ion battery separator coatings.

[0043] like Figure 1 As shown in the embodiment of this application, a method for preparing low-sodium ultrafine alumina for lithium battery separators is provided, the preparation method comprising:

[0044] S1. Industrial aluminum hydroxide is reacted with sodium hydroxide solution to undergo a dissolution reaction, followed by cooling and filtration to obtain sodium aluminate solution;

[0045] S2. Add aluminum oxide-containing heterogeneous seed crystals to sodium aluminate solution to decompose the seed crystals, then filter and wash to obtain heterogeneous doped ultrafine aluminum hydroxide;

[0046] S3. The heterogeneous doped ultrafine aluminum hydroxide and pure water are slurried and subjected to hydrothermal desodium removal and impurity removal reaction. Then, a surfactant is added for dispersion, and the mixture is filtered and washed to obtain alumina hydrate with low sodium content.

[0047] S4. Calcining the low-sodium-content alumina hydrate to obtain low-sodium calcined alumina;

[0048] S5. The low-sodium calcined alumina is ground and broken down, and then subjected to electromagnetic iron removal and sieving to remove impurities, in order to obtain low-sodium ultrafine alumina.

[0049] In this embodiment, the industrial aluminum hydroxide is preferably metallurgical grade aluminum hydroxide produced by alkaline process using gibbsite as raw material (alumina hydroxide produced by alkaline process using boehmite, diaspore or mixed type bauxite can also be used). The impurity content of the industrial aluminum hydroxide is: SiO2 content ≤ 0.007%, Fe2O3 content ≤ 0.007%, Na2O content ≤ 0.25%, and the lower the impurity content, the better.

[0050] The sodium hydroxide solution can be an industrial alkali solution with a concentration of about 48%, or a mixed solution with a concentration of about 50% prepared by mixing solid sodium hydroxide with pure water. Alternatively, it can be the mother liquor obtained after decomposing the sodium aluminate solution described in this application and then evaporating it. At the same time, the mother liquor can be supplemented with alkali as needed (such as the Bayer process in the prior art).

[0051] The dissolution apparatus used in the dissolution reaction is the pipeline dissolution apparatus or pressure cooker commonly used in alumina production.

[0052] Filtration can be carried out using alumina ceramic membranes or leaf filters.

[0053] In some optional embodiments, the temperature of the dissolution reaction is 105°C to 145°C, and the time of the dissolution reaction is 20 min to 120 min.

[0054] In this embodiment, by controlling the specific temperature and time of the dissolution reaction, the hydroxide ions in the sodium hydroxide solution can be used to fully dissolve the aluminum element in the aluminum hydroxide, resulting in a sodium aluminate solution with a suspended solids content ≤0.02 g / L, an Al2O3 concentration of 100 g / L to 160 g / L, and a caustic alkali Na2O concentration of 90 g / L to 160 g / L. K It ranges from 1.2 to 1.6.

[0055] The temperature for the dissolution reaction can be 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, or 145℃.

[0056] The dissolution reaction time can be 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, or 120 min.

[0057] In some alternative embodiments, the heterogeneous seed crystals include ultrafine α-alumina micro powder (also known as calcined alumina micro powder) or ultrafine boehmite.

[0058] In some alternative embodiments, the average grain size of the heterogeneous seeds is <0.8 μm; and / or,

[0059] The seed coefficient of the heterogeneous seed crystal is 0.01 to 1.0.

[0060] In the embodiments of this application, by controlling the specific average particle size and seed coefficient of heterogeneous crystal seeds, and by controlling the specific type of heterogeneous crystal seeds, the heterogeneous crystal seeds and the precursor can be uniformly mixed and in close contact. The heterogeneous crystal seeds can be used to reduce the phase transformation activation energy, so that α-phase alumina crystal nuclei can be rapidly precipitated at a lower temperature. This solves the technical problem that it is difficult to balance the calcination temperature with the fineness of the original crystal grains and the high α-phase conversion rate in traditional processes.

[0061] In some optional embodiments, the initial decomposition temperature of the seed crystal decomposition is 55℃~85℃, the final decomposition temperature of the seed crystal decomposition is ≥50℃, the decomposition time of the seed crystal decomposition is 6h~48h, and the cooling rate of the seed crystal decomposition is <0.5℃ / h.

[0062] In this embodiment, controlling the specific initial temperature, final decomposition temperature, and specific decomposition time of the seed crystal decomposition, as well as controlling the specific cooling rate of the seed crystal decomposition, is beneficial for obtaining aluminum hydroxide crystals with a complete crystal structure under conditions of higher initial temperature, longer seed crystal decomposition time, and slower cooling rate. At the same time, it can also reduce the intercrystalline alkali content of aluminum hydroxide. Thus, after subsequent filtration and washing, a heterogeneous doped ultrafine aluminum hydroxide product with Na2O content ≤0.20%, SiO2 content ≤0.007%, Fe2O3 content ≤0.007%, and average particle size of 0.2μm~4.0μm can be obtained.

[0063] In some optional embodiments, the hydrothermal desodiuming reaction is carried out at a temperature of 140°C to 210°C, and the reaction time is 0.5 h to 8 h; and / or,

[0064] The target solid content of the pulp is 50 g / L to 200 g / L.

[0065] In this embodiment of the application, by controlling the specific target solid content of the pulp during pulping, the content of sodium oxide impurities in the ultrafine aluminum hydroxide before the hydrothermal desodiumization reaction can be reduced, thereby reducing the sodium content in the alumina hydrate.

[0066] By controlling the specific temperature and time of the hydrothermal desodiumization reaction, the phase transition process of aluminum hydroxide to aluminum oxide can be completed using hydrothermal methods. At the same time, sodium oxide impurities in aluminum hydroxide can be removed by hydrothermal methods, and then aluminum oxide hydrate with a Na2O content ≤0.02% can be obtained through filtration and washing.

[0067] To ensure washing effectiveness, hot pure water with a temperature ≥40℃ can be used for washing here.

[0068] The temperature for this hydrothermal desodium reaction can be 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, or 210℃.

[0069] The hydrothermal desodiuming reaction can take 0.5 h, 1.0 h, 1.5 h, 2.0 h, 2.5 h, 3.0 h, 3.5 h, 4.0 h, 4.5 h, 5.0 h, 5.5 h, 6.0 h, 6.5 h, 7.0 h, 7.5 h, or even 8.0 h.

[0070] In some alternative embodiments, the surfactant includes at least one selected from stearic acid, polyvinyl alcohol, and polyethylene glycol; and / or,

[0071] The molecular weight of the polyvinyl alcohol is 4,000 to 10,000, and the molecular weight of the polyethylene glycol is 2,000 to 8,000.

[0072] In some optional embodiments, the amount of surfactant added is 0.1% to 2%.

[0073] In this embodiment, by controlling the specific type of surfactant, the specific molecular weight of the surfactant, and the specific amount of surfactant added, the alumina particles after hydrothermal desodiumization can be coated with a high molecular weight surfactant, so that the alumina can be uniformly dispersed in the solution, while the sodium oxide impurities dissolve in the solution, thereby ensuring the effect of hydrothermal desodiumization and facilitating subsequent filtration and washing to obtain alumina hydrate with low sodium content.

[0074] The molecular weight of the polyvinyl alcohol can be 4000, 5000, 6000, 7000, 8000, 9000, or 10000.

[0075] The molecular weight of the polyethylene glycol can be 2000, 3000, 4000, 5000, 6000, 7000, or 8000.

[0076] In some optional embodiments, the calcination temperature is 1150℃~1250℃, and the calcination time is 0.5h~4h.

[0077] In this embodiment, the specific temperature and time of calcination are controlled. Since a relatively low temperature is used for calcination, in some optional embodiments, the grinding and dispersing includes ball milling or sand milling, with the grinding balls having a diameter of 2mm to 20mm and the ball-to-material ratio being 1:1 to 10:1; and / or,

[0078] The grinding and dispersing process includes wet grinding followed by spray drying and dispersing.

[0079] In this embodiment of the application, by controlling the specific ball diameter and specific ball-to-material ratio of the grinding balls used for grinding and dispersing, the calcined low-sodium calcined alumina can be fully ground to obtain a low-sodium ultrafine alumina product that meets the expected particle size.

[0080] The diameter of the grinding ball can be 2mm, 5mm, 10mm, 15mm, or 20mm.

[0081] The ball-to-material ratio can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1.

[0082] Grinding and dispersing can be carried out using a ball mill or sand mill with an alumina ceramic liner; grinding and dispersing can also be carried out by wet grinding in a sand mill followed by spray drying.

[0083] The mesh size of the sieve used for sieving and removing impurities is 100 to 500 mesh.

[0084] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0085] Example 1

[0086] like Figure 2 As shown, 520g of a 48% sodium hydroxide solution (prepared using 96% chemically pure sodium hydroxide and pure water) was reacted with 340g of industrial aluminum hydroxide (dry basis) and 1100g of deionized water in a 5L hydrothermal reactor for dissolution at 145℃ for 0.5h. The industrial aluminum hydroxide used contained 0.006% SiO2, 0.006% Fe2O3, and 0.20% Na2O impurities. After dissolution, the solution was cooled and then filtered through a water-circulating vacuum filter to obtain a sodium aluminate solution.

[0087] 1.30 g of calcined alumina micropowder with an average particle size of 0.5 μm and an α-alumina phase content of 95% was added to the finely filtered sodium aluminate solution. Seed decomposition was carried out at 72 °C, with a final decomposition temperature of 68 °C and a decomposition time of 36 h. Afterward, vacuum filtration was performed, and the filter cake was washed twice with hot washing water until the pH value of the washing water was close to neutral. The resulting doped ultrafine aluminum hydroxide filter cake weighed approximately 170 g on a dry basis, with a particle size of 2.0 μm and a sodium oxide content of 0.17%.

[0088] The ultrafine aluminum hydroxide filter cake was mixed with 2.5L of pure water to form a slurry. The slurry was then subjected to a hydrothermal desodiumification reaction in a 5L hydrothermal reactor at a temperature of 180℃ for 2 hours. After cooling to 95℃, 3g of polyvinyl alcohol (6000g) was added to the reactor and stirred for 0.5 hours. The mixture was then filtered and washed with hot water at a rate twice the mass of the filter cake.

[0089] The washed filter cake was then placed in a sagger and calcined in a muffle furnace at 1200℃ for 3 hours. The resulting calcined alumina was then ground in a ball mill jar. The diameters of the zirconia grinding balls used were 10 mm and 5 mm, with a ball-to-material ratio of 10:1, and the grinding time was 8 hours. The resulting low-sodium ultrafine alumina powder product had a particle size distribution that met the requirements of D. 50 : 0.4μm, D 90 : 1.0μm, D 100 The particle size is 1.8 μm, and its SiO2 content is 0.007%, Fe2O3 content is 0.006%, Na2O content is 0.025%, and α phase content is 96.6%.

[0090] Example 2

[0091] 1720 kg of 48% sodium hydroxide solution (prepared using 96% chemically pure sodium hydroxide and pure water) was mixed with 1000 kg of industrial aluminum hydroxide (dry basis) and 1100 kg of deionized water at a concentration of 2 m³. 3 The leaching reaction was carried out in a hydrothermal reactor at a temperature of 145℃ for 0.5 hours. The industrial aluminum hydroxide used contained 0.006% SiO2, 0.006% Fe2O3, and 0.20% Na2O impurities. After leaching, the temperature was lowered to 95℃, and the leaching solution was then filtered through an alumina ceramic microfiltration membrane to obtain a sodium aluminate solution.

[0092] 120 kg of boehmite with an average particle size of 0.6 μm was added to the dissolved sodium aluminate solution, and seed decomposition was carried out at 72 °C. The final decomposition temperature was 68 °C, and the decomposition time was 36 h. After that, vacuum filtration was performed, and the filter cake was washed twice with hot washing water until the pH value of the washing water was close to neutral. The resulting doped ultrafine aluminum hydroxide filter cake weighed about 500 kg on a dry basis, with a particle size of 0.4 μm and a sodium oxide content of 0.17%.

[0093] The ultrafine aluminum hydroxide filter cake was mixed with 2.5m 3 Pure water was used to prepare a slurry, which was then poured into a 5m container. 3 The hydrothermal desodiuming reaction was carried out in a hydrothermal reactor at a temperature of 200℃ for 1 hour. After cooling to 95℃, 3 kg of polyvinyl alcohol with a molecular weight of 4000 was added to the reactor and stirred for 0.5 hours. The mixture was then filtered and washed with hot water at a rate twice the mass of the filter cake.

[0094] The washed filter cake was then placed in a sagger and calcined in a tunnel kiln at 1200℃ for 2 hours. The resulting calcined alumina was then ground in a ball mill. The diameter of the alumina grinding balls used was 10 mm, the ball-to-material ratio was 4:1, and the grinding time was 5 hours. The resulting low-sodium ultrafine alumina powder product had a particle size distribution that met the D... 50 : 0.3μm, D 90 : 0.8μm; D 100 The particle size is 1.5 μm, and its SiO2 content is 0.007%, Fe2O3 content is 0.006%, Na2O content is 0.020%, and α phase content is 97.0%.

[0095] Example 3

[0096] 1750 kg of 48% sodium hydroxide solution, 1000 kg of industrial aluminum hydroxide (dry basis), and 1100 kg of deionized water were mixed at a concentration of 2 m³. 3 The leaching reaction was carried out in a hydrothermal reactor at a temperature of 130℃ for 1.5 hours. The industrial aluminum hydroxide used contained 0.006% SiO2, 0.006% Fe2O3, and 0.20% Na2O impurities. After leaching, the temperature was lowered to 90℃, and the leaching solution was then filtered through an alumina ceramic nanofiltration membrane to obtain a sodium aluminate solution.

[0097] 100 kg of ultrafine alumina with an average particle size of 0.6 μm and 100 kg of boehmite with an average particle size of 0.7 μm were added to the dissolved sodium aluminate solution. Seed decomposition was carried out at 82 °C, with a final decomposition temperature of 65 °C and a decomposition time of 36 h. Afterward, vacuum filtration was performed, and the filter cake was washed twice with hot wash water until the pH value of the wash water was close to neutral. The resulting doped ultrafine aluminum hydroxide filter cake weighed approximately 700 kg on a dry basis, with a particle size of 0.3 μm and a sodium oxide content of 0.15%.

[0098] The ultrafine aluminum hydroxide filter cake was mixed with 2.5m 3 Pure water was used to prepare a slurry, which was then poured into a 5m container. 3 The hydrothermal desodiuming reaction was carried out in a hydrothermal reactor at a temperature of 140℃ for 8 hours. After cooling to 95℃, 10 kg of polyvinyl alcohol with a molecular weight of 10,000 was added to the reactor and stirred for 0.5 hours. The mixture was then filtered and washed with hot water at a rate twice the mass of the filter cake.

[0099] The washed filter cake was then placed in a sagger and calcined in a tunnel kiln at 1250℃ for 2 hours. The resulting calcined alumina was then ground in a ball mill. The diameter of the alumina grinding balls used was 10 mm, the ball-to-material ratio was 4:1, and the grinding time was 15 hours. The resulting low-sodium ultrafine alumina powder product had a particle size distribution that met the D... 50: 0.35μm, D 90 0.8μm, D 100 The particle size is 1.5 μm, and its SiO2 content is 0.007%, Fe2O3 content is 0.006%, Na2O content is 0.020%, and α phase content is 97.2%.

[0100] Example 4

[0101] 1700 kg of 48% sodium hydroxide solution, 1000 kg of industrial aluminum hydroxide (dry basis), and 1100 kg of deionized water were mixed at a concentration of 2 m³. 3 The leaching reaction was carried out in a hydrothermal reactor at a temperature of 135℃ for 1.5 hours. The industrial aluminum hydroxide used contained 0.006% SiO2, 0.006% Fe2O3, and 0.20% Na2O impurities. After leaching, the temperature was lowered to 85℃, and the leaching solution was then filtered using a leaf filter to obtain a sodium aluminate solution.

[0102] 100 kg of ultrafine alumina with an average particle size of 0.6 μm and 100 kg of boehmite with an average particle size of 0.6 μm were added to the dissolved sodium aluminate solution. Seed decomposition was carried out at 70 °C, with a final decomposition temperature of 65 °C and a decomposition time of 36 h. Afterward, vacuum filtration was performed, and the filter cake was washed twice with hot wash water until the pH value of the wash water was close to neutral. The resulting doped ultrafine aluminum hydroxide filter cake weighed approximately 600 kg on a dry basis, with a particle size of 0.3 μm and a sodium oxide content of 0.18%.

[0103] The ultrafine aluminum hydroxide filter cake was mixed with 2.5m 3 Pure water was used to prepare a slurry, which was then poured into a 5m container. 3 The hydrothermal desodiuming reaction was carried out in a hydrothermal reactor at a temperature of 210℃ for 1 hour. After cooling to 95℃, 12 kg of polyvinyl alcohol with a molecular weight of 8000 was added to the reactor and stirred for 0.5 hours. The mixture was then filtered and washed with hot water at a rate of twice the mass of the filter cake.

[0104] The washed filter cake was then placed in a sagger and calcined in a shuttle kiln at 1180℃ for 3 hours. The resulting calcined alumina was then ground in a sand mill to obtain a low-sodium ultrafine alumina powder product with a particle size distribution that meets the requirements of D. 50 0.3μm, D 90 : 1.0μm, D 100 The particle size is 2.0 μm, and its SiO2 content is 0.007%, Fe2O3 content is 0.006%, Na2O content is 0.020%, and α phase content is 96.5%.

[0105] Example 5

[0106] 1750 kg of 48% sodium hydroxide solution, 1000 kg of industrial aluminum hydroxide (dry basis), and 1100 kg of deionized water were mixed at a concentration of 2 m³. 3 The leaching reaction was carried out in a hydrothermal reactor at a temperature of 130℃ for 2 hours. The industrial aluminum hydroxide used contained 0.006% SiO2, 0.006% Fe2O3, and 0.20% Na2O impurities. After leaching, the temperature was lowered to 85℃, and the leaching solution was then filtered using a leaf filter to obtain a sodium aluminate solution.

[0107] 100 kg of ultrafine alumina with an average particle size of 0.6 μm and 100 kg of boehmite with an average particle size of 0.6 μm were added to the dissolved sodium aluminate solution. Seed decomposition was carried out at 70 °C, with a final decomposition temperature of 65 °C and a decomposition time of 36 h. Afterward, vacuum filtration was performed, and the filter cake was washed twice with hot wash water until the pH value of the wash water was close to neutral. The resulting doped ultrafine aluminum hydroxide filter cake weighed approximately 650 kg on a dry basis, with a particle size of 0.3 μm and a sodium oxide content of 0.18%.

[0108] The ultrafine aluminum hydroxide filter cake was mixed with 2.5m 3 Pure water was used to prepare a slurry, which was then poured into a 5m container. 3 The hydrothermal desodiuming reaction was carried out in a hydrothermal reactor at a temperature of 180℃ for 2.0 hours. After cooling to 95℃, 12 kg of stearic acid was added to the reactor and stirred for 0.5 hours. The mixture was then filtered and washed with hot water at a rate twice the mass of the filter cake.

[0109] The washed filter cake was then placed in a sagger and calcined in a tunnel kiln at 1150℃ for 4 hours. The resulting calcined alumina was then ground in a sand mill. The ground slurry was then subjected to electromagnetic iron removal to remove magnetic materials and a 200-mesh sieve to remove large particles. After spray drying, the dried and dispersed product yielded a low-sodium ultrafine alumina powder with a particle size distribution that met the D... 50 0.3μm, D 90 : 1.0μm, D 100 The particle size is 2.0 μm, and its SiO2 content is 0.007%, Fe2O3 content is 0.006%, Na2O content is 0.020%, and α phase content is 96.0%.

[0110] In summary, this application provides a method for preparing low-sodium ultrafine alumina for lithium-ion battery separators. By adding ultrafine α-Al₂O₃ micropowder (also known as calcined alumina micropowder) or boehmite as seed crystals during the decomposition process, and controlling the parameters of seed crystal decomposition, doped aluminum hydroxide micropowder is prepared. This ensures uniform mixing and close contact between the heterogeneous seed crystals and the precursor, which is more conducive to reducing the phase transition activation energy and rapidly precipitating α-phase alumina nuclei at a lower calcination temperature. This solves the technical problem of balancing calcination temperature with fine original grain size and high α-phase conversion rate in traditional processes. Through hydrothermal phase transformation, low-sodium alumina hydrate is obtained, solving the problems of difficult sodium removal during low-temperature calcination and the difficulty in producing low-sodium ultrafine alumina using ordinary industrial alumina or aluminum hydroxide.

[0111] One or more technical solutions in the embodiments of this application have at least the following technical effects or advantages:

[0112] (1) The embodiment of this application provides a method for preparing low-sodium ultrafine alumina for lithium battery separators. The resulting low-sodium ultrafine alumina product has the following characteristics: Na2O content < 0.03% (wt%), α-alumina content > 95%, iron oxide content < 0.01% (wt%), and silicon dioxide content < 0.01% (wt%). The overall particle size of the product is fine and narrowly distributed, and its particle size distribution satisfies D... 50 : 0.2μm~0.6μm, D 90 ≤1.5μm; D 100 ≤2.5μm.

[0113] (2) The method for preparing low-sodium ultrafine alumina for lithium battery separators provided in this application has the advantages of high production efficiency, low production cost, energy saving and environmental protection. The ultrafine alumina produced has small and uniform grains, low content of harmful impurities, high phase inversion rate and good performance, which can meet the requirements of thinner lithium battery separators.

[0114] (3) The present application provides a method for preparing low-sodium ultrafine alumina for lithium battery separators. The resulting low-sodium ultrafine alumina product can be used as a raw material for the production of lithium battery separator coatings, thin film alumina ceramic substrates, etc. At the same time, it can also provide an economical and environmentally friendly method for the production of low-sodium ultrafine alumina for ultrathin lithium battery separators and alumina ceramic substrates.

[0115] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0116] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the orientation shown in the accompanying drawings. Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to."

[0117] In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without necessarily requiring or implying any actual relationship or order between these entities or operations. In this document, "and / or" describes the association between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c," or "at least one of a, b, and c," can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0118] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing low-sodium ultrafine alumina for lithium battery separators, characterized in that, The preparation method includes: Industrial aluminum hydroxide is reacted with sodium hydroxide solution to undergo a dissolution reaction, followed by cooling and filtration to obtain a sodium aluminate solution. The dissolution reaction temperature is 105℃~145℃. The industrial aluminum hydroxide is metallurgical grade aluminum hydroxide produced by alkaline process using gibbsite-type bauxite as raw material. The impurity content of the industrial aluminum hydroxide is: SiO2 content ≤0.007%, Fe2O3 content ≤0.007%, Na2O content ≤0.25%. Heterogeneous seed crystals were added to a sodium aluminate solution for seed decomposition, followed by filtration and washing to obtain heterogeneous doped ultrafine aluminum hydroxide. The heterogeneous seed crystals were ultrafine α-alumina micro powders with an average particle size of <0.8 μm. The initial decomposition temperature of the seed crystals was 55℃~85℃, the final decomposition temperature was ≥50℃, the decomposition time was 6h~48h, the cooling rate was <0.5℃ / h, and the seed coefficient of the heterogeneous seed crystals was 0.01~1.

0. The heterogeneous doped ultrafine aluminum hydroxide was slurried with pure water and subjected to a hydrothermal desodiuming and impurity removal reaction. A surfactant was then added for dispersion, followed by filtration and washing to obtain alumina hydrate with low sodium content. The surfactant was at least one of stearic acid, polyvinyl alcohol, and polyethylene glycol, and the amount of surfactant added was 0.1%–2%. The molecular weight of the polyvinyl alcohol was 4000–10000, and the molecular weight of the polyethylene glycol was 2000–8000. The temperature of the hydrothermal desodiuming reaction was 140℃–210℃, and the reaction time was 0.5h–8h. The low-sodium-content alumina hydrate is calcined to obtain low-sodium calcined alumina, wherein the calcination temperature is 1150℃~1250℃; The low-sodium calcined alumina was ground and dispersed, then subjected to electromagnetic iron removal and sieving to remove impurities, yielding low-sodium ultrafine alumina. The low-sodium ultrafine alumina contained Na₂O < 0.03 wt%, α-alumina > 95%, iron oxide < 0.01 wt%, and silicon dioxide < 0.01 wt%; the particle size distribution met the D... 50 : 0.2μm~0.6μm, D 90 ≤1.5μm; D 100 ≤2.5μm.

2. The preparation method according to claim 1, characterized in that, The dissolution reaction takes 20 to 120 minutes.

3. The preparation method according to claim 1, characterized in that, The target solid content of the pulp is 50 g / L to 200 g / L.

4. The preparation method according to claim 1, characterized in that, The calcination time is 0.5h to 4h.

5. The preparation method according to claim 1, characterized in that, The grinding and dispersing process includes ball milling or sand milling, with the grinding balls having a diameter of 2mm to 20mm and the ball-to-material ratio being 1:1 to 10:1.

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