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

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-Na0.67Ni0.33Mn0.67O2 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 18O isotope labeling reveals that it suppresses the lattice oxygen participation in electrolyte decomposition and mitigates irreversible oxygen loss. As a result, the Li-doped Na0.67Li0.2Ni0.23Mn0.67O2 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.