Preserved Layered Structure Enables Stable Cyclic Performance of MoS2 upon Potassium Insertion

Transitional metal dichalcogenides represent one important type of anodes for emerging K-ion batteries. K ions are stored through both intercalation and conversion reactions, but the detailed phase transition is not clear. It is believed that deep potassiation would trigger the conversion reaction, which induces the fracture of particles and leads to fast capacity degradation. By utilizing MoS2 as a model material, the competition between intercalation and conversion is revealed, which shows a rate-dependent behavior. The crystal structure of several newly discovered intermediate phases including K0.5MoS2 and K1.0MoS2 is disclosed by complementary experimental and calculational approaches. It shows that intercalation takes place even discharge down to 0 V, differing from the cases in Li-ion and Na-ion batteries. The intercalated compound preserves the layered structure of MoS2, which avoids the structural collapse and maintains the integrity of the electrode for stable cyclic performance. This finding opens up a new opportunity in the exploration of high capacity anode among layered transitional metal dichalcogenide families. © 2019 American Chemical Society.