Impact of Local Separation on the Structural and Electrochemical Behaviors in Li₂MoO₃-LiCrO₂ Disordered Rock-Salt Cathode Material

Li-excess disordered rock-salt oxides have emerged as a promising group of cathode materials for Li-ion batteries. However, the real cation distribution and short-range order of various disordered oxides have not been fully determined, making it difficult to understand their actual structures and reaction processes. Here, Li_1.233Mo_0.467Cr_0.3O₂ (LMCO), as a cathode material that undergoes a unique in situ cation-disorder is investigated. Through synchrotron- and lab-based multiscale characterizations, it is observed that the as-prepared material has separate domains resembling Li₂MoO₃ and LiCrO₂ even in a single-phase bulk crystal structure. The Mo/Li-rich and Cr/Li-poor domains are maintained even after significant cation-disorder. The formation and dissociation of short Mo-Mo bonds along with a unique MoO₆ distortion in Mo/Li-rich domain of disordered LMCO leads to minimal lattice parameter changes during Mo redox reactions. This phenomenon is intensified when the structure becomes more disordered owing to the dissipation of anisotropy. In disordered LMCO, the Mo^4+/6+ redox is highly reversible, while Cr^3+/4+ redox is not. Finally, based on the local separation that induces different 0-TM diffusion abilities according to the different domains in disordered LMCO, the mechanisms of the domain-dependent kinetics, asymmetric Li⁺ diffusion, and linked hysteresis/degradation processes are explained.