Tailoring electronic structure to enhance ammonium-ion storage properties of VO2 by molybdenum doping toward highly-efficient aqueous ammonium-ion battery

Abstract

Recently, the researches on ammonium-ion storage have gained widespread interest, and it is still a major problem and a popular research area to produce high-performance electrode materials for aqueous ammonium ion batteries (AAIBs). Herein, the electronic structure of tunnel-like vanadium dioxide (VO2) is tailored by molybdenum doping (denoted as VO2-Mo) to enhance ammonium-ion storage properties toward highly-efficient AAIBs. VO2-Mo with unique nanobelt structure is designed and synthesized by adjusting the content of Mo via a facile hydrothermal method. Density functional theory (DFT) simulations and experimental data both demonstrate that molybdenum atom in VO2 structure can improve mass transfer, speed up ion transport, and accelerate kinetic, showing boosted NH4+-storage properties. With 2 % Mo doping, at 0.1 A g−1, VO2-Mo exhibits a specific discharge capacity of around 370 mAh g−1, surpassing VO2 (232 mAh g−1) and the vanadium oxides-based materials that have been reported for NH4+-storage. Approximately 6000 successive charging and discharging cycles at 2 A g−1, it essentially maintains the specific capacity of 140 mAh g−1. Using VO2-Mo, polyaniline (PANI) and 1 M (NH4)2SO4 as the anode, cathode, and electrolyte, respectively, VO2-Mo//PANI full battery is further built, and at 0.2 A g−1, it reaches a specific discharge capacity of up to 232 mAh g−1, surpassing the performances of the most state-of-the-art AAIBs. At 89 W·kg−1, the VO2-Mo//PANI battery can achieve an energy density (E) up to 133 Wh·kg−1. This study provides new ideas for tailoring electrode materials with enhanced NH4+-storage for AAIBs.