Stabilizing Oxygen Redox via Li Dopants Into P2‐Type Cathodes for High‐Voltage Sodium‐Ion Batteries

ABSTRACT Anionic redox offers a pathway to increase the energy density of layered cathodes for sodium‐ion batteries, yet it is often accompanied by structure and interface degradation. Here, we demonstrate that Li dopants as regulators for oxygen redox in P2‐Na 0.67 Ni 0.33 Mn 0.67 O 2 through tuning local coordination environments and charge compensation pathways. Li dopants enhance Ni redox activity while moderating transition metal‐oxygen (TM‐O) coupling at high voltages. The online electrochemical mass spectrometry with 18 O isotope labeling reveals that it suppresses the lattice oxygen participation in electrolyte decomposition and mitigates irreversible oxygen loss. As a result, the Li‐doped Na 0.67 Li 0.2 Ni 0.23 Mn 0.67 O 2 exhibits improved rate capability cycling stability, delivering an initial capacity of 116.6 mAh/g with 80% retention after 400 cycles at 1 C, compared to 27% for the undoped counterpart. This work highlights the importance of controlling reactive oxygen species and establishes a strategy to stabilize high‐voltage operation by decoupling oxygen redox from degradation pathways in sodium‐ion cathodes.