Suppressing staircase-like electrochemical profile induced by P O transition by solid-solution reaction with continuous structural evolution in layered Na-ion battery cathode

Layered P2-type sodium manganese oxide materials (NaxMnO2) attract substantial interest due to their low cost and high security. However, the staircase-like electrochemical profiles in P2-type NaxMnO2 caused by unfavorable phase transitions and layer gliding upon sodium extraction/re-insertion, particularly from P-type stacking to O-type stacking (e. g. P2 to O2 or OP4), are difficult to be eliminated. In this work, the staircase-like electrochemical profiles induced by PO transition are effectively suppressed in P’2-type Na2/3Mn0.8Ti0.2O2 by a solid-solution reaction with continuous structural evolution during the charge/discharge processes. P’2-Na2/3Mn0.8Ti0.2O2 exhibits smooth voltage profiles and delivers a high specific capacity of 153 mA h g−1 within 2.0–4.0 V. Structural characterizations indicate that P’2-Na2/3Mn0.8Ti0.2O2 undergoes a solid-solution reaction with continuous phase transition from P’2 phase to so-called “Z” phase, considered as an intergrowth of P-type stacking and O-type stacking in the layered lattice. The structural evolution mechanism described in this work provides a solution to suppress the staircase-like electrochemical profiles induced by PO transition in P2-type oxide cathode materials and a versatile strategy for boosting the performance of P2-type cathode materials.