Rotary-type atomic layer deposition of aluminum oxide coating on micropowder for secondary battery anode applications

Atomic layer deposition (ALD) on powder materials is often limited to achieve uniform and conformal thin films because of the insufficient precursor adsorption by a very large surface area of powder materials. To minimize the amount of precursor consumed while securing the adsorption time of the precursor on the powder surface, we introduced a stop-valve mode during the precursor pulse step. Briefly, we investigated a rotary-type ALD system capable of coating Al₂O₃ thin films on 3D structures with diverse microparticle shapes, and optimized the operating parameters, which were found to be a stop valve time, trimethylaluminum pulse time, water vapor pulse time, and temperature of 20, 0.2, 0.2 s, and 150 °C, respectively, yielding an average growth rate of 1.3 Å/cycle and refractive index of 1.64. This method surpasses normal ALD in controlling Al₂O₃ thin film deposition on 3D substrates with high specific surface areas, as verified by surface and microscopic analyses. To demonstrate the effectiveness of the ALD process with stop valve mode, a comparative analysis of materials deposited versus those coated with normal ALD was carried out. Crucially, the capacity retention of Si alloy powder-based secondary battery anodes coated using ALD with the stop valve mode was approximately 24 % higher than bare anodes and 7 % higher than those coated with normal ALD.