Negligible Voltage Hysteresis with Strong Anionic Redox in Conventional Battery Electrode

Lattice oxygen redox reactions (ORR) offers opportunities for developing highcapacity batteries, however, suffers the notoriously high voltage hysteresis and low initial coulombic efficiency, which hinder its practical applications. Particularly, ORR was widely considered inherent to these kinetic issues. In this paper, unambiguous evidence of strong and reversible ORR is found in Na_2/3Ni_1/3Mn_2/3O₂, which displays negligible voltage hysteresis (0.1 V) and high initial coulombic efficiency with a highly stable electrochemical profile. Our independent and quantitative analysis of all the Ni, Mn and O states consistently interpret the redox mechanism of Na_2/3Ni_1/3Mn_2/3O₂, which reveals, for the first time, a conventional 3d transition-metal ORR system with facile kinetics and highly stable electrochemical profile that previously found only in cationic redox systems.