Molecular Storage of Mg Ions with Vanadium Oxide Nanoclusters

Mg batteries have potential advantages in terms of safety, cost, and reliability over existing battery technologies, but their practical implementations are hindered by the lack of amenable high-voltage cathode materials. The development of cathode materials is complicated by limited understandings of the unique divalent Mg²⁺ ion electrochemistry and the interaction/transportation of Mg²⁺ ions with host materials. Here, it is shown that highly dispersed vanadium oxide (V₂O₅) nanoclusters supported on porous carbon frameworks are able to react with Mg²⁺ ions reversibly in electrolytes that are compatible with Mg metal, and exhibit high capacities and good reaction kinetics. They are able to deliver initial capacities exceeding 300 mAh g^-1 at 40 mA g^-1 in the voltage window of 0.5 to 2.8 V. The combined electron microscope, spectroscopy, and electrochemistry characterizations suggest a surface-controlled pseudocapacitive electrochemical reaction, and may be best described as a molecular energy storage mechanism. This work can provide a new approach of using the molecular mechanism for pseudocapacitive storage of Mg²⁺ for Mg batteries cathode materials.