The thermodynamic properties of magnesium make it a natural choice for use as an anode
material in rechargeable batteries, because it may provide a considerably higher energy
density than the commonly used lead-acid and nickel-cadmium systems. Moreover, in
contrast to lead and cadmium, magnesium is inexpensive, environmentally friendly and
safe to handle. But the development of Mg batteries has been hindered by two problems.
First, owing to the chemical activity of Mg, only solutions that neither donate nor
accept protons are suitable as electrolytes; but most of these solutions allow the
growth of passivating surface films, which inhibit any electrochemical reaction. Second,
the choice of cathode materials has been limited by the difficulty of intercalating
Mg ions in many hosts. Following previous studies of the electrochemistry of Mg electrodes
in various non-aqueous solutions, and of a variety of intercalation electrodes, we
have now developed rechargeable Mg battery systems that show promise for applications.
The systems comprise electrolyte solutions based on Mg organohaloaluminate salts,
and Mg(x)Mo3S4 cathodes, into which Mg ions can be intercalated reversibly, and with
relatively fast kinetics. We expect that further improvements in the energy density
will make these batteries a viable alternative to existing systems.