Joint Cationic and Anionic Redox Chemistry for Advanced Mg Batteries.

Mao, Minglei; Tong, Yuxin; Zhang, Qinghua; Hu, Yong-Sheng; Li, Hong; Huang, Xuejie; Chen, Liquan; Gu, Lin et al. · Nano Lett · 2020

basic_science · Level V

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Abstract

Lack of appropriate cathodes severely restrains the development of high-energy Mg batteries. In this work, we proposed joint cationic and anionic redox chemistry of transition-metal (TM) sulfides as the most promising way out. A series of solid-solution pyrite Fe<sub><i>x</i></sub>Co<sub>1-<i>x</i></sub>S<sub>2</sub> (0 ≤ <i>x</i> ≤ 1) was specially designed, in which S 3p electrons pour into the d bands of Fe and Co, generating redox-active dimerized (S<sub>2</sub>)<sup>2-</sup>. The Fe<sub>0.5</sub>Co<sub>0.5</sub>S<sub>2</sub> sample is highlighted to deliver a high specific energy of 240 Wh/kg at room temperature involving both cationic (Fe and Co) and anionic (S) redox. The highly delocalized electronic clouds in pyrite structures comfortably accommodate the charge of Mg<sup>2+</sup>, contributing to the fast kinetics and the superior cycling stability of the Fe<sub>0.5</sub>Co<sub>0.5</sub>S<sub>2</sub>. It is anticipated that the joint cationic and anionic redox chemistry proposed in this work would be the ultimate answer for designing high-energy cathodes for advanced Mg batteries.