Prototype systems for rechargeable magnesium batteries

The thermodynamic properties of magnesium make it a natural choice for use as an anode material in rechargeable batteries, because it may provide a co nsiderably higher energy density than the commonly used lead-acid and nicke l-cadmium systems. Moreover, in contrast to lead and cadmium, magnesium is inexpensive, environmentally friendly and safe to handle. But the developme nt of Mg batteries has been hindered by two problems. First, owing to the c hemical activity of Mg, only solutions that neither donate nor accept proto ns are suitable as electrolytes; but most of these solutions allow the grow th of passivating surface films, which inhibit any electrochemical reaction (1-3). Second, the choice of cathode materials has been limited by the diff iculty of intercalating Mg ions in many hosts(4). Following previous studie s of the electrochemistry of Mg electrodes in various non-aqueous solutions (1,5), and of a variety of intercalation electrodes(6,7), we have now devel oped rechargeable Mg battery systems that show promise for applications. Th e systems comprise electrolyte solutions based on Mg organohaloaluminate sa lts, and MgxMo3S4 cathodes, into which Mg ions can be intercalated reversib ly, and with relatively fast kinetics. We expect that further improvements in the energy density will make these batteries a viable alternative to exi sting systems.