Optimizing Kinetics of Anionic Redox Reaction in Cathode Material by Distinct 4d Transition-metal Substitution

Abstract Anionic redox reactions (ARR) offer significant opportunities for developing high-energy-density batteries. However, suffering from the sluggish anionic kinetics, the concept meets serious challenges on practical application. Recently, the interplay between cationic and anionic redox processes on kinetics is revealed and the mixed cationic/anionic redox process shows faster kinetics. In this work, we further find that stronger TM(4d)–O(2p) (e. g. Ru–O) hybridization improves the kinetics of independent ARR. The redox reactions of Na2/3Mg1/3Mn1/2Ru1/6O2 (NMMR) and their evolution of Ru, Mn, and O during charging and discharging is studied in detail. The O and TM redox process in initial cycle are distinguished. Then, the different influence on kinetics in ARR and TM redox stages by Ru substitution is unraveled. The significantly improved Na+ diffusion coefficient in NMMR indicates stronger TM(4d)–O(2p) (Ru–O) hybridization does optimize the kinetics of ARR.