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-Na_0.67Ni_0.33Mn_0.67O₂ 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 Na_0.67Li_0.2Ni_0.23Mn_0.67O₂ 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.