Rational Design of Na(Li<sub>1/3</sub> Mn<sub>2/3</sub> )O<sub>2</sub> Operated by Anionic Redox Reactions for Advanced Sodium-Ion Batteries.

Kim, Duho; Cho, Maenghyo; Cho, Kyeongjae · Adv Mater · 2017

basic_science · Level V

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Abstract

In an effort to develop high-energy-density cathodes for sodium-ion batteries (SIBs), low-cost, high capacity Na(Li<sub>1/3</sub> Mn<sub>2/3</sub> )O<sub>2</sub> is discovered, which utilizes the labile O 2p-electron for charge compensation during the intercalation process, inspired by Li<sub>2</sub> MnO<sub>3</sub> redox reactions. Na(Li<sub>1/3</sub> Mn<sub>2/3</sub> )O<sub>2</sub> 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 Li<sub>2</sub> MnO<sub>3</sub> . Using the anionic redox reaction (O<sup>2-</sup> /O<sup>-</sup> ), this Mn-oxide is predicted to show high redox potentials (≈4.2 V vs Na/Na<sup>+</sup> ) with high charge capacity (190 mAh g<sup>-1</sup> ). Predicted cathode performance is validated by experimental synthesis, characterization, and cyclic performance studies. Through a fundamental understanding of the redox reaction mechanism in Li<sub>2</sub> MnO<sub>3</sub> , Na(Li<sub>1/3</sub> Mn<sub>2/3</sub> )O<sub>2</sub> is designed as an example of a new class of promising cathode materials, Na(Li<sub>1/3</sub> M<sub>2/3</sub> )O<sub>2</sub> (M: transition metals featuring stabilized M<sup>4+</sup> ), for further advances in SIBs.