Confirming reversible Al³⁺ storage mechanism through intercalation of Al³⁺ into V₂O₅ nanowires in a rechargeable aluminum battery

As a new type of multi-electron transfer device, rechargeable aluminum batteries are promising post-lithium ion batteries owing to their high theoretical energy density. However, it is unknown whether Al³⁺ can be reversibly stored in the lattice of the host electrode material because of its small cation diameter and high valence state, thus trapping it tightly in lattice or defect sites. Here, we report the reversible storage of Al³⁺ in V₂O₅ nanowires. It is found that Al³⁺ intercalates into crystalized V₂O₅ nanowires in the first discharge. Meanwhile, this electrochemical intercalation leads to the reduction of V⁵⁺ and the formation of an amorphous layer on the edge of nanowires. In the subsequent cycling, a new phase forms along the nanowires’ edges and a two-phase transition reaction occurs. Our findings demonstrate clearly for the first time that it is possible that Al³⁺ can be inserted into the metal oxide and stored reversibly through intercalation and a phase-transition reaction, which is expected to inspire more comprehensive investigations for rechargeable aluminum batteries.