Prelithiation Activates Fe₂(MoO₄)₃Cathode 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 Mg 2+ /Li + cell using a monoclinic or orthorhombic Fe 2 (MoO 4 ) 3 cathode, a Mg anode, and a simple (PhMgCl) 2 –AlCl 3 + LiCl electrolyte. Hastelloy-C alloy is proposed as a current collector of high-voltage cathode for the hybrid Mg 2+ /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 Mg 2+ /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 Fe 2 (MoO 4 ) 3 significantly enhances the cycling stability and reversibility.