Preparation method of High-purity alumina powder and its application in lithium batteries

Alumina, a white amorphous powder, is an amphoteric oxide insoluble in water. High-purity alumina (purity ≥99.995%) features high melting point, high hardness, excellent catalytic performance, good thermal stability, excellent corrosion resistance, and outstanding photoelectric performance. It is widely used in semiconductor materials, fire-resistant and fireproof fields, ceramic fields, and LED fields. The continuous growth of scientific and technological innovation cannot do without the support of research funds.

Preparation method of high-purity alumina

In the 1980s, German researchers first produced high-purity alumina. Subsequently, various countries conducted in-depth research on its preparation process. In recent years, the preparation process of high-purity alumina in China has developed rapidly, gradually replacing imports. At the same time, a variety of new preparation processes have also been developed.

Improved Bayer process: Based on the traditional Bayer process for preparing alumina, the obtained sodium aluminate is first desilsified and then iron-removed. The product is hydrolyzed to obtain high-purity aluminum hydroxide. After high-temperature calcination, the powder is ground to obtain various high-purity alumina that meet customer requirements.

Aluminum alcohol hydrolysis method: Aluminum metal undergoes a chemical reaction with alcohol organic compounds, and under the action of a catalyst, organic alkoxides and hydrogen gas are generated. After distillation, high-purity aluminum hydroxide is obtained through hydrolysis reaction in a solvent. It is then calcined in a high-temperature environment to obtain alumina with a purity of over 99.9%. The higher the purity of organic alcohols, the less impurities are introduced in the process, both of which can reduce the difficulty of impurity removal in the subsequent processes.

Pyrolysis method of ammonium aluminium sulfate：First, sulfuric acid and aluminium hydroxide are neutralized to prepare aluminium sulfate solution. Then, under strictly controlled pH value and reaction temperature of the solution, ammonium sulfate is added and fully reacted to obtain ammonium aluminium sulfate. After multiple recrystallization refining to remove impurities, ammonium aluminium sulfate crystals are prepared. Finally, the ammonium aluminium sulfate crystals are calcined at high temperature to generate high-purity alumina products.

Pyrolysis method of ammonium aluminium carbonate：Ammonium bicarbonate and refined ammonium aluminium sulfate are synthesized in a certain proportion to generate ammonium basic aluminium carbonate. Then, high-purity ammonium basic aluminium carbonate is calcined at high temperature to produce high-purity alumina products.

High-purity aluminum activation hydrolysis method：Using a catalyst, the active aluminum powder foil (powder) and water are dissolved to form aluminum hydroxide, which is then calcined at 1450℃ to obtain high-purity alumina. Aluminum chloride gas-phase synthesis method: Under the action of a catalyst, aluminum chloride is gas-phase synthesized into AlOxCly(OH)z, and then high-purity alumina is obtained after sintering at 1400℃.

The Application of High-purity alumina in Lithium batteries

Lithium batteries are mainly composed of a positive electrode, a negative electrode, a separator, an electrolyte solution, etc.

Cathode material: Coating the surface of the electrode material with high-purity alumina can reduce the contact between the electrode material and acidic substances in the electrolyte, lower the acid corrosion of the electrode material, and is of great help in improving the structural stability of the cathode material. For instance, adding high-purity alumina to lithium manganate materials can enhance structural stability and address the issue of electrode capacity attenuation. Adding high-purity alumina to high-nickel materials can reduce the surface activity of the materials and improve their thermal stability. Adding high-purity alumina to lithium nickel-manganese oxide materials can enhance the discharge rate performance of the materials.

Anode material: Evenly coating high-purity alumina on the surface of the graphite anode can enhance the stability of the anode interface, reduce the loss of active lithium, and improve the charge retention capacity and cycle performance of lithium-ion batteries.

Battery separator: Currently, the base materials of lithium battery separators are mainly polyethylene and polypropylene. The melting point of polyolefins is relatively low. When the battery is charged or discharged at high power, local heat is released, which may lead to thermal runaway and subsequently cause battery explosion. The preparation of composite ceramic-coated lithium battery separators by using a uniform coating process of high-purity alumina can regulate the porosity of the separator, significantly enhancing the safety performance of lithium batteries, thus providing the possibility for high-energy density and safe and reliable charging and discharging of high-power lithium batteries. In addition, the mechanical strength of the diaphragm has also been significantly enhanced.

Solid electrolytes: High-purity alumina added to polymer solid electrolytes, such as polyethylene oxide (PEO) solid electrolytes, can enhance the conductivity and stability of polymers, reduce the crystallinity of polymers, and improve the chain movement capacity. When added to oxide solid electrolytes, such as garnet type Li7La3Zr2O12 (LLZO) solid electrolyte, it can enhance the electrical conductivity and capacity retention rate of the electrolyte.