In Situ Transmission Electron Microscopy and Density Functional Theory Calculation on the Potassiation of MoS ₂ Nanosheets

Two-dimensional layered MoS 2 has been considered the most promising anode material for potassium-ion batteries (PIBs) due to its relatively large interlayer spacing and high theoretical specific capacity. Despite extensive research on their electrochemical performance, reaction mechanisms, structural changes, and kinetic behavior during potassiation processes are still unknown or controversial. Here, in situ transmission electron microscopy was used to track the migration of potassium ions in the layered structure of MoS 2 nanosheets in real time at the atomic scale. These results reveal that the potassiation process proceeds in a region-by-region manner, namely, a multistep intercalation reaction initiated from the outer region to the adjacent inner region. Meanwhile, the local stress induced by the insertion of potassium ions results in structural distortion, deformation, and dislocation formation. Additionally, the potassiation behaviors of MoS 2 nanosheets only involve intercalation, and the final product is identified as K x MoS 2, which is quite different from the mechanisms of lithiation and sodiation. Meanwhile, density functional theory calculations verified that less electrovalent K–S bonds inhibit the occurrence of the conversion reaction, favoring maintenance of the MoS 2 layered structure. This work provides valuable insights into the potassiation mechanisms of MoS 2 and guides the design of high-performance anodes for PIBs.