MnO₂|Mg(Ac)₂|V₆O_13-x: An Aqueous Full Cell for High-Performance Magnesium-Ion Storage

The promise of low cost and high energy density is driving growing attention toward aqueous magnesium-ion batteries (AMIBs) for energy storage applications. Aqueous electrolytes offer advantages such as high safety compared to organic counterparts. However, Mg metal anodes are unstable in aqueous electrolytes, limiting their application. Vanadium oxide is a promising intercalation anode material due to its high theoretical capacity from multi-electron redox reactions, but low conductivity and sluggish redox kinetics remain challenges. This study demonstrates that oxygen-deficient V₆O_13-x functions as an efficient AMIB anode. Oxygen defect engineering accelerates Mg²⁺ and charge transfer, enhancing electrochemical activity. V₆O_13-x shows exceptional rate performances of 298.2 and 155.7 mAh g^-1 at 1.0 and 5.0 A g^-1, as well as the excellent cycle performances of 123.1 mAh g^-1 after 1,500 cycles at 5.0 A g^-1 with a capacity retention of 85%. Our V₆O_13-x is particularly outstanding among the reported anodes in aqueous battery systems. When coupled with MnO₂ cathode, a magnesium ion full cell (MnO₂|Mg(Ac)₂|V₆O_13-x) was assembled, which delivers a reversible capacity of 159.2 mAh g^-1 at 0.2 A g^-1 and can be stabilized for up to 3,000 cycles at 2.0 A g^-1. This work presents a novel route to high-performance AMIBs.