Prospects for Improved Magnesocene-Based Magnesium Battery Electrolytes

Magnesium batteries are currently attracting a lot of interest as a next generation battery technology. One critical issue is to find a suitable electrolyte and herein we explore an electrolyte based on magnesocene (MgCp₂) in tetrahydrofuran (THF), aiming for low-voltage Mg batteries, with respect to: Mg plating characteristics, electrochemical stability windows, electrolyte speciation, and electrolyte decomposition reactions; both experimentally and computationally. Overall, the electrolyte does not seem to decompose on a Mg metal anode and most likely reduced solvation of Mg²⁺ by the Cp⁻ anion is important and species such as MgCp₂THF₂ may play an important role for Mg plating with small overpotential. The oxidation limit is largely determined by the Cp⁻ anion and density functional theory predicted oxidation reactions point to polymerized end-products to be possible. Furthermore, in silico substitution studies enable us to establish the prospects of some Cp⁻ anion derivatives to further improve the oxidative stability, but still the Mg²⁺ solvation must be monitored for ease of reduction and Mg plating.