Layered Iron Vanadate for High-Performance and Stable Cathode Material for Aqueous Manganese Batteries

Aqueous rechargeable metal batteries have gained significant attention because of the low cost, high capacity, and inherent safety offered by nonflammable water-based electrolytes. Among these, Mn-based systems are promising owing to their intrinsic stability, abundance, affordability, and high energy density. Despite these advantages, the development of suitable host structures for Mn storage remains underexplored. This study introduces layered iron vanadate, FeV₃O₉·1.1H₂O, as a new cathode material for aqueous Mn batteries, demonstrating exceptional performance. The cathode exhibits a reversible capacity of 306.9 mAh g^-1 at 0.25 A g^-1 and an excellent rate performance of 210.6 mAh g^-1 at 2 A g^-1. In addition, FeV₃O₉·1.1H₂O exhibits outstanding cycling stability, retaining 73.4% of its initial capacity after 3000 cycles at 3 A g^-¹, which is attributed to its low layered volume expansion. The underlying reaction mechanism is elucidated through spectroscopic and microscopic analyses. When integrated into the final Mn cell, the cathode system demonstrates superior performance compared to Zn batteries, underscoring its potential for next-generation aqueous battery systems. These findings advance the aqueous Mn battery technology, paving the way for safer, more cost-effective, and high-performance energy storage solutions.