To exceed the demands of current hybrid, plug-in hybrid and electric vehicles, new battery systems with high energy density are required. Magnesium (Mg) is an attractive alternative to current lithium-ion technologies because of the transfer of 2 electrons per magnesium-ion, higher volumetric capacity of magnesium metal compared to lithium metal, and greater natural abundance. However, to realize complete magnesium battery, cathodes capable of reversible Mg2+ reactions are required. Recently, we proposed α-MnO2 as a candidate for Mg batteries because of a large initial discharge capacity of 280 mAh/g. However, the capacity faded to 70 mAh/g by the 10th cycle. We observed that instead of following the typical insertion reaction as with Li+, magnesiation occurs through a conversion pathway to form an amorphous (Mg, Mn)O product. Through TEM and soft-XAS, we determined that magnesiation is partially reversible through the amorphous layer. From these results, we were encouraged to pursue amorphous materials as an avenue for magnesium battery cathodes. In Figure 1, we show the potential of amorphous V2O5-P2O5 cathodes for magnesium batteries through cyclic voltammetry. In a non-aqueous, full-cell system with a magnesium metal anode, we have observed a capacity of 164 mAh/g with good capacity retention. Importantly, we have identified the meta-stable phase which gives the amorphous V2O5-P2O5 system improved electrochemical properties over the bulk, crystalline V2O5. Mg batteries have great potential as a post Li-ion technology, but finding a viable cathode material is vital to realizing a practical system. The V2O5-P2O5 system shows excellent potential as a cathode material, and provides us with an alternative, promising path for a complete magnesium battery.

Amorphous cathodes for magnesium batteries: The V2O5:P2O5 system

249th National Meeting (2015)

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