There is great interest in scaling up Li-ion batteries for use in electric vehicles, requiring cheap and safe cathodes. Recently, silicate-based cathodes have been described, especially Li2FeSiO4. It has been shown that Li may be removed and reinserted in a reversible manner associated with oxidation and reduction of Fe. Silicon and iron are highly abundant making this sustainable, cheap and safe Recently we studied several Li2FeSiO4 samples prepared at different temperatures, which revealed the existence of at least 3 polymorphs. Given the promising performance of Li2FeSiO4, and the potential of Li2Fe1-xMnxSiO4 to deliver capacities up to 280mAhg-1 it is important to determine the phase stability ranges as a function of temperature. Accordingly we wish to study the structures, for Li2FeSiO4, Li2MnSiO4 and Li2Fe0.5Mn0.5SiO4 as a function of temperature from 25 oC to 1000 oC.