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.