Oxygen-ion displacement regulation for designing high-performance P2-type Na-based layered oxide cathode

The practical application of P2-type sodium cathodes is restricted by intrinsic Na + /vacancy ordering and unstable cathode-electrolyte interphases (CEI). While conventional inactive-element doping improves stability, it typically sacrifices specific capacity. Addressing these challenges, we demonstrate that trace Bi doping simultaneously boosts specific capacity, cycling life, and rate performance, effectively circumventing the classic capacity-stability trade-off. The concurrent improvement primarily originates from Bi-induced structural modulation, which we quantitatively characterize through a newly proposed oxygen-ion displacement rate ( δ O ) descriptor. Through doping control, we successfully synthesized two P2-type materials with significantly distinct δ O values (∼38.07 % vs. ∼31.58 %), demonstrating the critical role of δ O in governing electrochemical performance. The material with ultra-low δ O has suppressed Na + /vacancy ordering due to its weak Na-O correlations. Additionally, its strong TM-O correlations effectively inhibit TM (transition metals) dissolution, construct a stable CEI, and alleviate the lattice strain. Consequently, this material exhibits delivers a 23.1 % enhancement in specific capacity, exceptional cycling stability (72.9 % capacity retention after 1000 cycles), and remarkable rate performance by achieving a 51.1 % capacity within just 34 s. This work introduces a pioneering perspective based on oxygen-ion displacement for designing high-performance oxide cathode materials.