Formation Mechanism and Dielectric Properties of Ultra-High-Voltage Anodic Al Foils Investigated by ReaxFF-MD and DFT

Understanding the atomic-scale formation of anodic oxide films is critical for Al electrolytic capacitors. The formation mechanism and dielectric properties of an ultra-high-voltage anodized Al foil were investigated by combining experiments, reactive molecular dynamics, and first-principles calculations. Results indicate that film growth is primarily governed by the (011) crystal plane, and the density of the oxide film increases with the applied electric field. The diffusion barrier of H atoms (0.54 eV) is significantly lower than that of O atoms (1.41 eV), suggesting the preferential formation of Al hydroxide oxide species on the surface. As the anodization voltage increases, the oxide undergoes phase evolution from AlOOH to γ-Al₂O₃ and finally to α-Al₂O₃. First-principles calculations reveal the dielectric constants of alumina, which are 7.96 for AlOOH, 21.80 for γ-Al₂O₃ (Paglia structure), and 10.24 for α-Al₂O₃. These findings provide a theoretical basis for optimizing the microstructure and dielectric performance of ultra-high-voltage anodized Al foils.