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

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.