One-step hydrothermal synthesis of vanadium dioxide/carbon core-shell composite with improved ammonium ion storage for aqueous ammonium-ion battery.

Aqueous nonmetallic ion batteries have garnered significant interest due to their cost-effectiveness, environmental sustainability, and inherent safety features. Specifically, ammonium ion (NH) as a charge carrier has garnered more and more attention recently. However, one of the persistent challenges is enhancing the electrochemical properties of vanadium dioxide (VO) with a tunnel structure, which serves as a highly efficient NH (de)intercalation host material. Herein, a novel architecture, wherein carbon-coated VO nanobelts (VO@C) with a core-shell structure are engineered to augment NH storage capabilities of VO. In detail, VO@C is synthesized via the glucose reduction of vanadium pentoxide under hydrothermal conditions. Experimental results manifest that the introduction of the carbon layer on VO nanobelts can enhance mass transfer, ion transport and electrochemical kinetics, thereby culminating in the improved NH storage efficiency. VO@C core-shell composite exhibits a remarkable specific capacity of ∼300 mAh/g at 0.1 A/g, which is superior to that of VO (∼238 mAh/g) and various other electrode materials used for NH storage. The NH storage mechanism can be elucidated by the reversible NH (de)intercalation within the tunnel of VO, facilitated by the dynamic formation and dissociation of hydrogen bonds. Furthermore, when integrated into a full battery with polyaniline (PANI) cathode, the VO@C//PANI full battery demonstrates robust electrochemical performances, including a specific capacity of ∼185 mAh·g at 0.2 A·g, remarkable durability of 93 % retention after 1500 cycles, as well as high energy density of 58 Wh·kg at 5354 W·kg. This work provides a pioneering approach to design and explore composite materials for efficient NH storage, offering significant implications for future battery technology enhancements.