Electrochemically Induced Phase Transition in V₃O₇ · H₂O Nanobelts/Reduced Graphene Oxide Composites for Aqueous Zinc‐Ion Batteries

Abstract

V₃ O₇ ·H₂ O nanobelts/reduced graphene oxide (rGO) composites (weight ratio: 86%/14%) are synthesized by a microwave approach with a high yield (85%) through controlling pH with acids. The growth mechanisms of the highly crystalline nanobelts (average diameter: 25 nm; length: ≈20 µm; oriented along the [101] direction) have been thoroughly investigated, with the governing role of the acid upon the morphology and oxidation state of vanadium disclosed. When used as the ZIB cathode, the composite can deliver a high specific capacity of 410.7 and 385.7 mAh g^-1 at the current density of 0.5 and 4 A g^-1 , respectively, with a high retention of the capacity of 93%. The capacity of the composite is greater than those of V₃ O₇ · H₂ O, V₂ O₅ nanobelts, and V₅ O₁₂ · 6H₂ O film. Zinc ion storage in V₃ O₇ ·H₂ O/rGO is mainly a pseudocapacitive behavior rather than ion diffusion. The presence of rGO enables outstanding cycling stability of up to 1000 cycles with a capacity retention of 99.6%. Extended cycling shows a gradual phase transition, that is, from the original orthorhombic V₃ O₇ · H₂ O to a stable hexagonal Zn₃ (VO₄ )₂ (H₂ O)_2.93 phase, which is a new electrochemical route found in V₃ O₇ materials. This phase transition process provides new insight into the reactions of aqueous ZIBs.