Identifying anionic redox activity within the related O3 and P2 type cathodes for sodium-ion battery.

As promising cathodes for Na-ion batteries (NIBs), layered transition metal (TM) oxides have attracted intense research activities due to high specific capacities, especially benefitting from the boosted capacity triggered by oxygen-related anionic redox reactions (ARRs). However, on the aspect of ARRs activity, the difference between typically O3 and P2-type structures has not been clearly clarified with the in-depth exploration. Herein, composed with similar composition, ARRs induced oxygen behaviors within O3-Na0.6Li0.2Fe0.4Ru0.4O2 and P2-Na0.6Li0.35Fe0.1Ru0.55O2 are systematically investigated by varying ex/in-situ spectroscopic characterizations. Conducted with lower charging cut-off voltage (4.0 V), P2-type cathode will be easier to trigger the reversible oxygen behaviors and delivers a larger capacity, better rate performance as well as stable cyclability, in contrast to the O3-type cathode. Moreover, within O3-type structure, increasing charging potential (beyond 4.3 V) would induce additional ani...