Cationic and Anionic Dual Redox Activity of MoS2 for Electrochemical Potassium Storage.

MoS₂ is regarded as one of the most promising potassium-ion battery (PIB) anodes. Despite the great progress to enhance its electrochemical performance, understanding of the electrochemical mechanism to store K-ions in MoS₂ remains unclear. This work reports that the K storage process in MoS₂ follows a complex reaction pathway involving the conversion reactions of Mo and S, showing both cationic redox activity of Mo and anionic redox activity of S. The presence of dual redox activity, characterized in-depth through synchrotron X-ray absorption, X-ray photoelectron, Raman, and UV-vis spectroscopies, reveals that the irreversible Mo oxidation during the depotassiation process directs the reaction pathway toward S oxidation, which leads to the occurrence of K-S electrochemistry in the (de)potassiation process. Moreover, the dual reaction pathway can be adjusted by controlling the discharge depth at different cycling stages of MoS₂, realizing a long-term stable cycle life of MoS₂ as a PIB anode.