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 Fe_<i>x</i>Co_1-<i>x</i>S₂ (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 (S₂)^2-. The Fe_0.5Co_0.5S₂ 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 Mg²⁺, contributing to the fast kinetics and the superior cycling stability of the Fe_0.5Co_0.5S₂. 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.