Electrochemical-Conditioning-Free and Water-Resistant Hybrid AlCl3 /MgCl2 /Mg(TFSI)2 Electrolytes for Rechargeable Magnesium Batteries.

Rechargeable magnesium batteries are a promising alternative to Li-based energy storage because of their abundant and inexpensive components. The high sensitivity and reactivity of the organic Mg2+ electrolyte makes their development challenging. Herein, we develop a new hybrid electrolyte, based on three simple inorganic salts of MgCl2 , AlCl3 , and Mg(TFSI)2 . The electrolyte exhibits unprecedented electrochemical performance for reversible deposition and stripping of Mg, with Coulombic efficiency up to 97 %, overpotential down to 0.10 V, good stability especially for aluminum and stainless-steel current collectors. It maintained its activity even after introducing 2000 ppm water and it could be prepared from impure chemicals. A full cell with the hybrid electrolyte and Mg foil as anode, Mo6 S8 as cathode gave a specific capacity of 98 mAh g-1 and maintained 94 % capacity after 100 cycles at a rate of 0.20 C, indicating the good compatibility of the hybrid electrolyte.