Spinel MnV ₂ O ₄ Nanospheres Fabricated via Ultrasonic Spraying as Novel Anodes for Aqueous Ammonium‐Ion Batteries

ABSTRACT

Aqueous ammonium‐ion batteries (AAIBs) have attracted considerable attention for large‐scale energy storage applications because of their safety and sustainability. However, their further development has been hindered by the lack of electrode materials with high conductivity, rapid ammonium‐ion diffusion kinetics, and structural stability. In this study, two spinel‐phase manganese vanadate samples were synthesized using the evaporation–crystallization and ultrasonic spray methods. The ultrasonically sprayed manganese vanadate exhibited smaller particle sizes, more uniform nanospheres, and enhanced structural stability compared with the crystallized sample. These optimized structural features significantly improved the ammonium‐ion storage performance, delivering higher capacities and better cycling stability. The reversible ammonium‐ion storage mechanism of spinel manganese vanadate was systematically investigated. During electrochemical cycling, reversible ammonium ion insertion/extraction was coupled with the redox reactions of the manganese and vanadium species. Meanwhile, ammonium ions formed reversible interactions with lattice oxygen through hydrogen bonding, accompanied by slight and recoverable variations in the lattice spacing and particle size. Furthermore, the manganese trioxide//manganese vanadate full batteries achieved a maximum energy density of 104 Wh·kg ⁻¹ and a peak power density of 1313.5 W·kg ⁻¹ , demonstrating the feasibility of manganese vanadate as an anode material for AAIBs. This study revealed the relationship among synthetic regulation, structural evolution, and electrochemical performance, providing insights into the design of advanced ammonium‐ion storage materials.