LAUSR

Metal chalcogenide anodes with a layered structure have been regarded as potential K‐based electrochemical energy storage devices with high energy density for large‐scale energy storage applications. However, their development is impeded by the slow K‐ion transport kinetics and poor structural stability. In this work, the energy‐storage behavior is investigated first and decisively associated them with the capacity‐degradation of the promising layer‐structured WSe2 from an integrated chemical and physical point of view. Then, a single‐phased WSe2 with pre‐intercalated high K content (SP‐KxWSe2) is designed to overcome the capacity‐degradation issue fundamentally. Theoretical calculations clarify the beneficial effect of K‐ions inside the interlayer of WSe2 on boosting its electrochemical performance, including increasing the electronic conductivity, promoting the K‐ion diffusivity, and improving the structural stability. The novel design enables the K‐ions pre‐intercalated WSe2 anode material to exhibit a high reversible specific capacity of 211 mAh g−1 at 5 A g−1 and superior cycling stability (89.3% capacity retention after 5000 cycles at 1 A g−1). Especially, the K‐ion hybrid capacitor, assembled from the anode of SP‐KxWSe2 and the cathode of porous activated carbon, delivers superior energy‐density up to 175 Wh kg−1, high power‐density as well as exceptional cycling stability.