Mg ions intercalated with V 3 O 7 ·H 2 O to construct ultrastable cathode materials for aqueous zinc-ion batteries.

V 3 O 7 ·H 2 O (VO) stands out as a highly promising cathode material for aqueous zinc-ion batteries (AZIB). However, due to the instability of the VO structure and the limited ion transport rate, achieving the required specific capacity and extended cycling lifespan has been challenging. To tackle this issue, we synthesized Mg-ion intercalated VO (MgVO) using a straightforward hydrothermal method. Introducing Mg 2+ as an interlayer support enhanced the flexibility of MgVO within the confined layer space, stabilized its lamellar structure, and expanded the VO layer spacing. The AZIB employing the MgVO cathode demonstrated a high specific capacity of 382.7 mA h g -1 at a current density of 0.1 A g -1 and showed excellent cycling stability. The robust structural stability of MgVO suggests promising applications for large-scale energy storage, while the Mg 2+ intercalation strategy presents a novel approach for exploring other potential cathode materials.