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

Abstract V 3 O 7 ·H 2 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 µ m; 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 V 3 O 7 · H 2 O, V 2 O 5 nanobelts, and V 5 O 12 · 6H 2 O film. Zinc ion storage in V 3 O 7 ·H 2 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 V 3 O 7 · H 2 O to a stable hexagonal Zn 3 (VO 4 ) 2 (H 2 O) 2.93 phase, which is a new electrochemical route found in V 3 O 7 materials. This phase transition process provides new insight into the reactions of aqueous ZIBs.