In this work, we investigated the mechanism of K storage process in MoS2 using commercially available material and a combination of electrochemical, spectroscopic, structural, and morphological characterizations. We unrevealed the formation of metallic Mo and molecular S at the depotassiated state of MoS2, which is due to the irreversible oxidation of the metallic Mo formed at the potassiated state to Mo 4+ and the resulting oxidation of S 2-to S 0 . As a result, a dual reaction pathway enabled by Mo cationic redox activity and S anionic redox activity (i.e., K-S electrochemistry) directed the K storage process in MoS2. Moreover, the combined characterizations showed the effect of the dual reaction pathway on the PIB performance of MoS2, based on which we provided a solution of controlling discharge depth at different cycling stages, i.e., deep discharge at 0.001 V in the 1 st cycle and raising discharge depth to 0.2 V from the 2 nd cycle, to realize high cycling stability and rate capability. Using the solution, the MoS2 electrode was able to deliver a stable capacity retention of 84% after 500 cycles and capacities of 121 and 91 mAh g -1 at 1 and 2 A g -1 , respectively. To the best of our knowledge, this is the first comprehensive investigation on the K storage mechanism of MoS2. Unlike the mainstream study of MoS2 for PIBs, our investigation reveals interesting simultaneous cationic and anionic redox activity of the material, contributing new insights into design strategies to further enhance the PIB performance of MoS2, for instance, developing strategies to reduce the dissolution of polysulfides, integrate catalysts to enhance sulfur redox activity, and incorporate secondary component to regulate the distribution of Mo and S redox reaction products.