Tuning [VO6] Octahedron of Ammonium Vanadates via F Incorporation for High-Performance Aqueous Zinc Ion Batteries.

The electrochemical properties of vanadium-based materials as cathode materials for aqueous zinc ion batteries are still restricted by low conductivity, sluggish reaction kinetics, and poor structural stability. Herein, the [VO6] octahedron, as the basic unit of vanadium-oxide layer of ammonium vanadates (NH4V4O10, denoted as NVO), is incorporated by F atoms to regulate the coordinated environment of vanadium. Density functional theory (DFT) calculations and experimental results show that both physicochemical and electrochemical properties of NVO are improved by F-doping. The enhanced electronic conductivity accelerates the electron transfer and the expanded interlayer spacing expedites the diffusion kinetics of zinc ions. As a result, the F-doped NVO (F-NVO) electrode shows a high discharge capacity (465 mAh g-1 at 0.1 A g-1), good rate capability (260 mAh g-1 at 5 A g-1), and long-term cycling stability (88% capacity retention over 2000 cycles at 4 A g-1). The reaction kinetics and energy storage mechanism of F-NVO are further validated by in situ and ex situ characterizations.