Rational Design of Na(Li1/3Mn2/3)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(Li_1/3Mn_2/3)O₂ is discovered, which utilizes the labile O 2p-electron for charge compensation during the intercalation process, inspired by Li₂MnO₃ redox reactions. Na(Li_1/3Mn_2/3)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 Li₂MnO₃. 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 Li₂MnO₃, Na(Li_1/3Mn_2/3)O₂ is designed as an example of a new class of promising cathode materials, Na(Li_1/3M_2/3)O₂ (M: transition metals featuring stabilized M⁴⁺), for further advances in SIBs.

Inspired by Li₂MnO₃ redox reactions, Na(Li_1/3Mn_2/3)O₂ operated by anionic redox reactions (labile lone-pair O) is rationally designed based on the site preference of Na in the Li sites of Li₂MnO₃ for high-energy-density cathodes. Na(Li_1/3Mn_2/3)O₂ shows high redox potentials (≈4.2 V vs Na/Na⁺) with high charge capacity (190 mAh g⁻¹), utilizing O²⁻/O⁻ anionic redox with the fixed Mn⁴⁺ during desodiation.

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