Unlock the Potassium Storage Behavior of Single‐Phased Tungsten Selenide Nanorods via Large Cation Insertion

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-Kx WSe2 ) 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-Kx WSe2 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.