In summary, we carried out a mechanistic study on the K storage process in MoS2 and revealed that Mo and S conversion reactions took place simultaneously during (de)potassiation. The process utilized the cationic redox activity of Mo and anionic redox activity of S simultaneously, which, to the best of our knowledge, was reported for the first time regarding the use of MoS2 as an anode material for PIBs. Furthermore, we demonstrated the importance of controlling discharge depth in enabling the advantages of dual redox activity. A balance needs to be taken into consideration between maximizing the dual redox activity and minimizing the structural deterioration of MoS2 and the dissolution of polysulfides. To this end, we showed that it is beneficial to deep discharge to 0.001 V in the initial cycle and raise the discharge depth to 0.2 V from the 2 nd cycle onwards, which enhances capacity retention, cycling stability and rate capability compared to consistent deep discharge to 0.001 V. This work does not follow mainstream approaches driven by pursing the high capacity of MoS2 but takes a deep dive into the underlying electrochemical mechanism of the K storage in MoS2.