Hierarchical two-atom-layered WSe2/C ultrathin crumpled nanosheets assemblies: Engineering the interlayer spacing boosts potassium-ion storage

Abstract Nonaqueous potassium-ion batteries (KIBs) represent a potential low-cost and source-abundant alternative to lithium-ion batteries (LIBs). The critical challenge of the electrode materials for KIBs mainly lies in the structural degradation and slow kinetics caused by the large-size K ions. Herein, we report the engineering of interlayer spacing of two-atom-layered WSe2/C ultrathin crumpled nanosheet assemblies (denoted as WSNC) to achieve optimal electrochemical performance as an anode for KIBs via an oleylamine-assisted solvothermal strategy. Individual crumpled nanosheets with two atomic layer thickness are hierarchically assembled to curb the agglomeration, enhance the cycling stability and the resistance to mechanical stress. Notably, the expanded interlayer spacing (from 0.651 to 0.755 nm) of WSe2 can provide more active sites, reduce its volume expansion and accelerate ion diffusion during the intercalation/deintercalation of K ions, thus increasing the specific capacity and simultaneously boosting the structural stability and reaction kinetics. Besides, the nitrogen-doped carbon coating can further improve the electronic conductivity of WSe2 and strengthen the structural stability. Further in-situ characterizations and density functional theory (DFT) computations indicate that the WSNC shows reverisible intercalation/deintercalation and conversion mechanism, as well as a low diffusion barriers and slight volume change during the intercalation of K ions. As expected, WSNC delivers a high capacity of 384 mAh g−1 over 200 cycles at 0.1 A g−1, superior rate capability, and excellent cycling stability up to 500 cycles at high rates.