Unexpected intercalation-dominated potassium storage in WS2 as a potassium-ion battery anode

Unexpected intercalation-dominated process is observed during K+ insertion in WS2 in a voltage range of 0.01-3.0 V. This is different from the previously reported two-dimensional (2D) transition metal dichalcogenides that undergo a conversion reaction in a low voltage range when used as anodes in potassium-ion batteries. Charge/discharge processes in the K and Na cells are studied in parallel to demonstrate the different ion storage mechanisms. The Na+ storage proceeds through intercalation and conversion reactions while the K+ storage is governed by an intercalation reaction. Owing to the reversible K+ intercalation in the van der Waals gaps, the WS2 anode exhibits a low decay rate of 0.07% per cycle, delivering a capacity of 103 mAh center dot g(-1) after 100 cycles at 100 mA center dot g-(1). It maintains 57% capacity at 800 mA center dot g(-1) and shows stable cyclability up to 400 cycles at 500 mA center dot g-(1). Kinetics study proves the facilitation of K+ transport is derived from the intercalation-dominated mechanism. Furthermore, the mechanism is verified by the density functional theory (DFT) calculations, showing that the progressive expansion of the interlayer space can account for the observed results.