Rational Design of Na(Li1/3 Mn2/3 )O2 Operated by Anionic Redox Reactions for Advanced Sodium-Ion Batteries.

In an effort to develop high-energy-density cathodes for sodium-ion batteries (SIBs), low-cost, high capacity Na(Li1/3 Mn2/3 )O2 is discovered, which utilizes the labile O 2p-electron for charge compensation during the intercalation process, inspired by Li2 MnO3 redox reactions. Na(Li1/3 Mn2/3 )O2 is systematically designed by first-principles calculations considering the Li/Na mixing enthalpy based on the site preference of Na in the Li sites of Li2 MnO3 . Using the anionic redox reaction (O2- /O- ), this Mn-oxide is predicted to show high redox potentials (≈4.2 V vs Na/Na+ ) with high charge capacity (190 mAh g-1 ). Predicted cathode performance is validated by experimental synthesis, characterization, and cyclic performance studies. Through a fundamental understanding of the redox reaction mechanism in Li2 MnO3 , Na(Li1/3 Mn2/3 )O2 is designed as an example of a new class of promising cathode materials, Na(Li1/3 M2/3 )O2 (M: transition metals featuring stabilized M4+ ), for further advances in SIBs.