Restraining Oxygen Loss and Suppressing Structural Distortion in a Newly Ti-Substituted Layered Oxide P2-Na_0.66Li_0.22Ti_0.15Mn_0.63O₂

Anionic redox reveals to be a promising strategy to effectively improve the energy density of layered metal oxide cathodes for sodium-ion batteries. However, lattice oxygen loss and derived structural distortion severely hinder its practical application. Herein, combined with anionic and cationic redox activities, we developed a layered structure P2-type Na0.66Li0.22Ti0.15Mn0.63O2 cathode, delivering an initial discharge capacity of 228 mAh g–1 and highly reversible structural evolution as well as improved cyclability. On the basis of comprehensive comparison with Ti-free P2-Na0.66Li0.22Mn0.78O2, both oxygen-related negative behaviors (irreversible O2 evolution and superoxo-related parasitic production) and Mn-related Jahn–Teller distortion have been effectively restrained by simultaneously suppressing both oxygen loss and the participation of Mn4+/Mn3+ redox. Not limited to discovering excess capacity derived from anionic oxidation up charging, our findings not only highlight an effective strategy to stabilize anionic and cationic redox activities but also pave the way for the further improvement of Na-deficient layered materials for high-energy sodium-ion batteries.