Unlocking the Capacity of Vanadium Oxide by Atomically Thin Graphene‐Analogous V2O5·nH2O in Aqueous Zinc‐Ion Batteries

Abstract Aqueous Zn‐ion batteries (AZIBs) are promising due to their high theoretical energy density and intrinsic safety, and the natural abundance of Zn. Since low voltage is an intrinsic shortage of AZIBs, achieving super‐high capacity of cathode materials is a vital way to realize high practical energy density, which however remains a huge challenge. Herein, the capacity increase of classical vanadium oxide cathode is predicted via designing atomic thickness of 2D structure to introduce abundant Zn 2+ storage sites based on density functional theory (DFT) calculation; then graphene‐analogous V 2 O 5 ·nH 2 O (GAVOH) with only few atomic layers is fabricated, realizing a record capacity of 714 mAh g −1 . Pseudocapacitive effect is unveiled to mainly contribute to the super‐high capacity due to the highly exposed GAVOH external surface. In situ Raman and synchrotron X‐ray techniques unambiguously uncover the Zn 2+ storage mechanism. Carbon nanotubes (CNTs) are further introduced to design GAVOH‐CNTs gel ink for large‐scale cathode fabrication. The hybrid cathode demonstrates ultra‐stable cycling and excellent rate capability and delivers a high energy density of 476 Wh kg −1 at 76 W kg −1 ; 228 Wh kg −1 is still retained at high mass loading of 10.2 mg cm −2 . This work provides inspiration for breaking the capacity limit of cathode in AZIBs.