Structural Design Principle of Rocksalt Oxides for Li-Excess Cathode Materials

Li-excess oxide cathodes have received increasing attention due to their high capacity derived from accumulated cation and anion redox activity. However, Li-excess layered oxides suffer from capacity and voltage decay due to the irreversible phase transition, while cation-disordered cathodes also have the problems of poor cycling stability and rate capability. The rocksalt oxides with a layered-disordered coexistence nanostructure can combine the advantages of both phases such as the inherent high capacity of Li-excess oxides, good rate capability of the layered phase, and structural stability resulting from the intergrown disordered phase. Herein, for rational design, we developed a descriptor by correlating the ionic radius and electronic configuration to predict layered, cation-disordered, and coexistent structures of Li-excess cathode materials. Accordingly, we experimentally synthesized Li_1.2Ni_0.4Mn_0.2Nb_0.2O₂ oxide with a coexistent structure in which the layered and disordered phases are well combined in the nanoscale region, achieving a high capacity (312 mAh g^-1) with good cycling stability and rate capability. The design principle with composition predicting structure provides a valuable strategy in controllably designing and preparing Li-excess cathode materials.