Anti-siting for stabilizing structure and modulating cationic/anionic redox reactions

The layered Mn-rich oxide cathode materials with oxygen redox activity are highly appealing in sodium-ion (Na-ion) batteries because of their high energy density and low cost. However, the applications of such materials are hindered by issues such as low Mn redox potential and irreversible phase transformation. Rational modulation of the ordering of the transition metal (TM) layer can inhibit the constraints and stabilize the anionic redox reactions. Herein we introduce stable Li/Mn anti-siting in the TM layer of P2-type Na_0.6Li_0.2Mn_0.8O₂ as a strategy to create abundant Mn sites and O sites that are inequivalent to the counterpart of each in the lattice, and thus to prompt the diverse Mn and O redox. The self-locking of the anti-siting energetically inhibits the P2-O2 phase transformation and the resultant structural degradations. In addition, such modulation activates more Mn in charge compensation at high potentials. As a result, this regulation increases the reversible capacity from 104.2 mAh g⁻¹ to 153.7 mAh g⁻¹ and enhances the cycling stability of Na_0.6Li_0.2Mn_0.8O₂. This anti-siting strategy offers a new solution to designing cathode materials with high structural stability and high energy density.