Electrochemical devices and processes for forming them include an anode having magnesium, a cathode, and an electrolyte in contact with the anode and the cathode. The electrolyte includes a carboranyl magnesium salt and a mixed ether solvent in which the carboranyl magnesium salt is dissolved. The mixed ether solvent includes a first ether solvent and a second ether solvent that is different from the first ether solvent.