Cationic and anionic dual redox activity of MoS2 for electrochemical potassium storage

MoS2 is receiving intensive attention in the research area of potassium-ion batteries (PIBs) and regarded as one of the most promising PIB anodes. Great progress has been made to enhance the electrochemical performance of MoS2, but understanding of the electrochemical mechanism to store K-ion in MoS2 remains unclear. This work reports that the K storage process in MoS2 follows a complex reaction pathway involving the conversion reactions of both Mo and S and as a result, the storage process shows 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 the irreversible Mo oxidation during the depotassiation process redirects the reaction pathway towards S oxidation, which leads to the progression of K-S electrochemistry in the (de)potassiation process. Moreover, the dual reaction pathway can be regulated by controlling the discharge depth at different cycling stages of MoS2, realizing a long-term stable cycle life of MoS2 as a PIB anode.