Joint Cationic and Anionic Redox Chemistry for Advanced Mg Batteries.

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 FeCoS (0 ≤ ≤ 1) was specially designed, in which S 3p electrons pour into the d bands of Fe and Co, generating redox-active dimerized (S). The FeCoS 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, contributing to the fast kinetics and the superior cycling stability of the FeCoS. 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.