Band Structure Engineering Promotes Anionic Redox Reversibility of Cobalt-Free Li-Rich Layered Oxides Cathodes.

Li-rich layered oxides cathodes (LLOs) have prevailed as the promising high-energy-density cathode materials due to their distinctive anionic redox chemistry. However, uncontrollable anionic redox process usually leads to structural deterioration and electrochemical degradation. Herein, a Mo/Cl co-doping strategy is proposed to regulate the relative position of energy band for modulating the anionic redox chemistry and strengthening the structural stability of Co-free Li1.16Mn0.56Ni0.28O2 cathodes. The incorporation of Mo with high d state orbit and Cl with low electronegativity can narrow the band energy gap between bonding and antibonding bands via increasing the filled lower-Hubbard band (LHB) and decreasing the non-bonding O 2p energy bands, promoting the anionic redox reversibility. In addition, strong covalent Mo─O and Mn─Cl bonding further increases the covalency of Mn─O band to further stabilize the O2 n- species and enhance the reversible distortion of MnO6 octahedron. The strengthening electronic conductivity, together with the epitaxial structure Li2MoO4 facilitates the fast Li+ kinetics. As a result, the dual doping material exhibits enhanced anionic redox reversibility and suppressed oxygen release with increased cyclic stability and excellent rate performance. This strategy provides some guidance to design high-energy-density LLOs with desirable anionic redox reversibility and stable crystal structure via band structure engineering.