Cationic\nand Anionic Dual Redox Activity of MoS<sub>2</sub> for Electrochemical\nPotassium Storage

MoS<sub>2</sub> is\nregarded as one of the most promising\npotassium-ion\nbattery (PIB) anodes. Despite the great progress to enhance its electrochemical\nperformance, understanding of the electrochemical mechanism to store\nK-ions in MoS<sub>2</sub> remains unclear. This work reports that\nthe K storage process in MoS<sub>2</sub> follows a complex reaction\npathway involving the conversion reactions of Mo and S, showing both\ncationic redox activity of Mo and anionic redox activity of S. The\npresence of dual redox activity, characterized in-depth through synchrotron\nX-ray absorption, X-ray photoelectron, Raman, and UV–vis spectroscopies,\nreveals that the irreversible Mo oxidation during the depotassiation\nprocess directs the reaction pathway toward S oxidation, which leads\nto the occurrence of K–S electrochemistry in the (de)­potassiation\nprocess. Moreover, the dual reaction pathway can be adjusted by controlling\nthe discharge depth at different cycling stages of MoS<sub>2</sub>, realizing a long-term stable cycle life of MoS<sub>2</sub> as a\nPIB anode.