A electrochemical cell having an non-aqueous electrolyte is provided. The properties of the electrolyte include high conductivity, high Coulombic efficiency, and an electrochemical window that can exceed 3.5 V vs. Mg/Mg.sup.+2. The use of the electrolyte promotes the electrochemical deposition and dissolution of Mg without the use of any Grignard reagents, other organometallic materials, tetraphenyl borate, or tetrachloroaluminate derived anions. Other Mg-containing electrolyte systems that are expected to be suitable for use in secondary batteries are also described.
STATEMENT REGARDING FEDERALLY FUNDED RESEARCH OR DEVELOPMENT
 This invention was made with government support under award number DE-AR0000062, awarded by Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy. The government has certain rights in the invention.