Unlock the potassium storage behaviour 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, we first investigate the energy-storage behaviour and decisively associate them with the capacity-degradation of the promising layer-structured WSe 2 from an integrated chemical and physical point of view. Then, a single-phased WSe 2 with pre-intercalated high K content (SP-K x WSe 2 ) is designed to overcome the capacity-degradation issue fundamentally. Theoretical calculations clarify the beneficial effect of K-ions inside the interlayer of WSe 2 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 WSe 2 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-K x WSe 2 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. This article is protected by copyright. All rights reserved.