Electrochemical characteristics and charge-discharge mechanisms of Co-substituted Li5AlO4 as a novel positive electrode material

Modern and future products such as electric vehicles and hybrid electric vehicles require batteries with higher energy densities than that of conventional batteries. Anion redox-type active materials are proposed as a new high-capacity positive electrode material for Li-ion batteries with high energy density. We developed Li5AlO4 as an anion redox-type active material with a higher stability than that of Co-substituted Li2O. Li5AlO4 was substituted with Co by mechanical alloying with LiCoO2 to enhance its conductivity and its reactivity as an oxide anion. Co-substituted Li5AlO4 showed a slightly higher electron conductivity and a remarkably higher oxide anion reactivity than the as-prepared Li5AlO4. From electrochemical analysis, it was shown that Co-substituted Li5AlO4 had a reversible capacity of approximately 140 mAh g−1, while the as-prepared Li5AlO4 had no reversible capacity. According to the atomic valence of Co and Al and the partial structure for Co-substituted Li5AlO4 during the first charge-discharge cycle, we found that the charge capacity of Co-substituted Li5AlO4 is derived from the oxidation of oxide anions, the formation of peroxide and superoxide, and the fact that the partial structure of Co-substituted Li5AlO4 remains unchanged. These results indicate that the charge-discharge reaction of Co-substituted Li5AlO4 proceeds reversibly. Co-substituted Li5AlO4 demonstrates a relatively high specific capacity and good reversibility during the charge-discharge process. •Co-substituted Li5AlO4 has a higher capacity than does Li5AlO4.•Li5AlO4 has a characteristic bonding state of oxygen, yielded by Co substitution.•The bonding state of oxygen varies during the charge-discharge process.