Lithium-Magnesium Hybrid Battery with Vanadium Oxychloride as Electrode Material

Metallic magnesium represents a promising solution for next generation electrochemical energy storage devices because of its dendrite-free electrodeposition, higher theoretical volumetric energy density, abundancy and safety compared to lithium technology. Nevertheless, Mg2+ is strongly polarized, which slows down its diffusion during discharging/charging. An electrochemical energy storage device containing a metallic Mg anode, a Li intercalation cathode and a Li/Mg-electrolyte can be regarded as a solution to circumvent the intrinsic drawbacks linked to both Li- and Mg-electrochemistry. In this contribution, we report on the performance of a VOCl/Mg cell containing a Li−Mg hybrid electrolyte. The cell delivered 195 mA h g−1 at 100 mA g−1 with a coulombic efficiency of 97.5%. At 200 mA g-1, after 150 cycles, 107 mA h g−1 was measured with 99.5% coulombic efficiency. At 500 mA g−1, after 800 cycles, the cell still produced 75 mA h g−1 with 99.8% coulombic efficiency. Lithium reacted with VOCl first via an intercalation reaction and then in a conversion reaction to LiCl and VO. The co-deposition of Li at the anode, Li−Mg alloy formation or contributions from side reactions could be ruled out.