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

Aqueous nonmetallic ion batteries have garnered significant interest due to their cost-effectiveness, environmental sustainability, and inherent safety features. Specifically, ammonium ion (NH₄⁺) 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 (VO₂) with a tunnel structure, which serves as a highly efficient NH₄⁺ (de)intercalation host material. Herein, a novel architecture, wherein carbon-coated VO₂ nanobelts (VO₂@C) with a core-shell structure are engineered to augment NH₄⁺ storage capabilities of VO₂. In detail, VO₂@C is synthesized via the glucose reduction of vanadium pentoxide under hydrothermal conditions. Experimental results manifest that the introduction of the carbon layer on VO₂ nanobelts can enhance mass transfer, ion transport and electrochemical kinetics, thereby culminating in the improved NH₄⁺ storage efficiency. VO₂@C core-shell composite exhibits a remarkable specific capacity of ∼300 mAh/g at 0.1 A/g, which is superior to that of VO₂ (∼238 mAh/g) and various other electrode materials used for NH₄⁺ storage. The NH₄⁺ storage mechanism can be elucidated by the reversible NH₄⁺ (de)intercalation within the tunnel of VO₂, facilitated by the dynamic formation and dissociation of hydrogen bonds. Furthermore, when integrated into a full battery with polyaniline (PANI) cathode, the VO₂@C//PANI full battery demonstrates robust electrochemical performances, including a specific capacity of ∼185 mAh·g^-1 at 0.2 A·g^-1, remarkable durability of 93 % retention after 1500 cycles, as well as high energy density of 58 Wh·kg^-1 at 5354 W·kg^-1. This work provides a pioneering approach to design and explore composite materials for efficient NH₄⁺ storage, offering significant implications for future battery technology enhancements.