Magnesocene-Based Electrolytes: A New Class of Electrolytes for Magnesium Batteries.

Unlike ferrocene, bis(η5 -cyclopentadienyl)magnesium (magnesocene, MgCp2 ) is slightly dissociated in solvents, such as ethers, resulting in electrolyte solutions with low conductivity. MgCp2 /tetrahydrofuran solutions make possible reversible magnesium plating and stripping with low over-potentials for many cycles. The Mg deposits appear with a cauliflower-like morphology. IR and NMR spectroscopy confirm that the electrolyte is stable and not decomposed during prolonged cycling. The anodic stability limit is in the range of 1.5 V (at platinum) and 1.8 V versus Mg/Mg2+ (at stainless steel), which may be sufficient for low-voltage cathode materials. MgCp2 is a first example of a completely new class of halide-free electrolytes, which may open up a new research direction for future magnesium metal and magnesium-ion batteries.