Li‐Rich Mn–Mg Layered Oxide as a Novel Ni‐/Co‐Free Cathode

Abstract Although Li 2 MnO 3 exhibits high capacity via anionic oxygen redox, it suffers from rapid capacity decay owing to structural disordering accompanying irreversible Mn migration and O 2 release. To promote the reversibility of the anionic redox reaction, Li 1.8 Mg 0.3 Mn 0.9 O 3 as a novel cathode material, prepared by partially substituting Li + and Mn 4+ of Li 2 MnO 3 with the redox‐inactive Mg 2+ as a structural stabilizer is proposed. Li 1.8 Mg 0.3 Mn 0.9 O 3 delivers a high specific capacity and energy density of ≈310 mAh g −1 and ≈915 Wh kg −1 , respectively. In particular, the power‐capability and cycle performance of Li 1.8 Mg 0.3 Mn 0.9 O 3 greatly surpass those of Li 2 MnO 3 . Through first‐principles calculations and various experiments, it is revealed that Mg substitution effectively suppresses the Mn migration by stabilizing Mn cations in the original sites at the charged state. The energetically stabilized layered structure disfavors the distortion of the MnO 6 octahedra, which induces the oxygen dimer (OO) formation through the metal–oxygen decoordination, thus mitigating oxygen release.