Prelithiation Activates Fe2(MoO4)3 Cathode for Rechargeable Hybrid Mg2+/Li+ Batteries

The development of rechargeable Mg-based batteries with a high energy density is restricted by the high-voltage cathodes and the parasitic side reactions between the battery components and electrolytes operating at relatively high potentials. Here, we develop a hybrid Mg2+/Li+ cell using a monoclinic or orthorhombic Fe2(MoO4)3 cathode, a Mg anode, and a simple (PhMgCl)2–AlCl3 + LiCl electrolyte. Hastelloy-C alloy is proposed as a current collector of high-voltage cathode for the hybrid Mg2+/Li+ battery within a Swagelok-type cell. The application of the Hastelloy-C alloy current collector breaks the crucial bottleneck of incompatibility between the currently available current collectors and electrolytes. The hybrid cell features a low voltage polarization between the discharge and charge profiles, which is in favor of practical applications. On the other hand, because all Li+ ions are supplied by the electrolyte in a hybrid Mg2+/Li+ battery, a high Li+ concentration is required to operate at high capacities for the hybrid battery. We further show the first-hand evidence about the compensation of Li+ ions by simply soaking the cathode in the hybrid electrolyte. The prelithiation of Li+ ions into monoclinic Fe2(MoO4)3 significantly enhances the cycling stability and reversibility.