Restraining O–O Dimerization for Highly Reversible Oxygen Redox in a Sodium-Ion Layered-Oxide Cathode

Abstract Activating the oxygen redox reaction in sodium-ion layered-oxide cathodes is a promising approach to elevate the energy density. However, oxygen-redox cathodes typically suffer from poor reversibility. O–O dimerization has been recognized as the underlying driver of irreversibility, but prevailing strategies have failed to fundamentally suppress it. Herein, O–O dimer formation was effectively inhibited through constructing a π-type conjugated ring within the Fe–O–Fe–O local structure. Such a unique ring architecture was achieved by introducing Sc3+ to strengthen Fe t2g–O 2p hybridization, thus enabling asymmetric Fe and O reductive coupling reactions and achieving highly reversible oxygen redox with significantly improved electrochemical kinetics. Consequently, Na0.67Fe0.3Sc0.1Mn0.6O2 delivers an impressive capacity of 192.3 mAh g–1 with 80.5% retention after 200 cycles at 4.5 V and maintains 82.2 mAh g–1 even at 10 C. The pouch full cell with a hard carbon anode exhibits a high energy density of 254.3 Wh kg–1. Restraining O–O dimerization establishes an insightful design principle for oxygen-loss-free layered-oxide cathodes.