Redox Behaviors in a Li-Excess Cation-Disordered Mn–Nb–O–F Rocksalt Cathode

Lithium-excess cation-disordered rocksalt oxides (DRXs) are a new class of high energy Li-ion cathode materials. A DRX cathode can deliver an exceptionally high capacity of >250 mA h g^–1, implying the participation of cationic transition metal and anionic oxygen redox in the electrochemistry. Understanding the roles of these distinct redox processes in the newly developed cathode is of critical importance for the further development of these materials. Herein, we synthesize a representative Mn redox-based fluorinated DRX material, Li_1.2Mn^0.625Nb_0.175O_1.95F_0.05 (LMNOF). Using a comprehensive suite of electroanalytical methods, we probe the cationic and anionic redox processes and their evolution upon cycling exclusively from an electrochemical point of view. This work sheds light on understanding the cationic and anionic redox reactions and their roles in the capacity loss for this high-capacity fluorinated DRX cathode, meanwhile showcases a thorough approach to studying the electrochemical properties of novel electrode materials using nondisruptive electroanalytical methods.