Defensive and Ion Conductive Surface Layer Enables High Rate and Durable O3‐type NaNi1/3Fe1/3Mn1/3O2 Sodium‐Ion Battery Cathode

Abstract

AbstractNa‐based layered transition metal oxides with an O3‐type structure are considered promising cathodes for sodium‐ion batteries. However, rapid capacity fading, and poor rate performance caused by serious structural changes and interfacial degradation hamper their use. In this study, a NaPO3 surface modified O3‐type layered NaNi1/3Fe1/3Mn1/3O2 cathode is synthesized, with improved high‐voltage stability through protecting layer against acid attack, which is achieved by a solid‐gas reaction between the cathode particles and gaseous P2O5. The NaPO3 nanolayer on the surface effectively stabilizes the crystal structure by inhibiting surface parasitic reactions and increasing the observed average voltage. Superior cyclic stability is exhibited by the surface‐modified cathode (80.1% vs 63.6%) after 150 cycles at 1 C in the wide voltage range of 2.0 V–4.2 V (vs Na+/Na). Moreover, benefiting from the inherent ionic conduction of NaPO3, the surface‐modified cathode presents excellent rate capability (103 mAh g−1 vs 60 mAh g−1) at 10 C. The outcome of this study demonstrates a practically relevant approach to develop high rate and durable sodium‐ion battery technology.