Electrochemical Characteristics of Co-Substituted α- and β-Li5AlO4 as High-Specific Capacity Positive Electrode Materials

Electric vehicles and hybrid electric vehicles require batteries with higher energy densities than conventional batteries. Anion redox-type active materials have been proposed as new high-capacity positive electrode materials for Li-ion batteries with high-energy densities. Co-substituted Li₅AlO₄ is a novel and promising high-capacity positive electrode material for Li-ion batteries. In this study, we investigated the influence of different synthesis conditions on the enhancement of the specific capacity. The material prepared via mechanical alloying of β-Li₅AlO₄ with LiCoO₂ at 300 rpm for 24 h exhibited a higher specific capacity than that prepared from α-Li₅AlO₄ and LiCoO₂. Co-substituted β-Li₅AlO₄ demonstrated a specific capacity of approximately 250 mA h g^-1. The specific capacity of Co-substituted α and β-Li₅AlO₄ increased with increasing Co content in the samples. According to X-ray absorption near edge structure measurements, the irreversible oxygen redox reaction and a reversible reaction involving the formation and consumption of peroxide were responsible for the charge compensation of Co-substituted β-Li₅AlO₄ and α-Li₅AlO₄, respectively.