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.

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The aim of this work was to study failure and stabilization mechanisms of Li-graphite electrodes. As model electrolyte systems, tetrahydrofuran (THF), propylene carbonate (PC), THF containing water contamination, and THF/PC solutions were used. A variety of electrode behavior can be observed in these solutions including reversible intercalation at high capacity, cyclability with deteriorating capacity, and in cases of dry THF and PC solutions, disability of Li intercalation. Chronopotentiometry, chronoamperometry, cyclic voltammetry impedance spectroscopy, electron microscopy, in situ and ex situ XRD, and surface sensitive FTIR spectroscopy were used in order to understand the reasons for the stability or failure of Li-graphite intercalation anodes. In PC and dry THF, massive solvent reduction occurs with a relatively low degree of electrode passivation. These processes change the electrode's morphology and electrically isolate carbon particles. At low concentration of water (>40 ppm) and PC (optimum 1 M) in THF, the surface chemistry of graphite differs considerably from that in dry THF or PC solutions. Passivating surface films are formed and provide a protective envelope for the electrode. Their structure and mechanism of formation, as well as the correlation between the surface chemistry, 3D structure, morphology, and the electrochemical behavior of the electrodes in solution, are discussed.

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