| Abstract Scope |
As an alternative to Li-based technology for grid storage, Na-ion batteries made of earth-abundant elements have attracted substantial interest. Na storage materials with a layered structure undergo reversible phase transformations upon Na intercalation due to complex interatomic interactions. However, large desodiation often leads to an unclarified, irreversible phase transformation at high voltage, hindering the full use of transition metal (TM) redox. In this talk, how TM selection affects the stability of desodiated sodium TM oxides will be discussed, and recent findings on a quaternary TM system including Ti and Fe will be underlined. A highly-desodiated phase that exhibits peculiar oxygen stacking to afford alternating octahedral and prismatic Na layers, namely OP2 stacking, will be demonstrated. The formation of OP2 is rationalized by distortion-tolerant Ti and Jahn-Teller-active Fe. This new phase participates in redox reaction reversibly, fundamentally distinct from inactive high-voltage phases in many Na-ion cathodes. |