There is great interest in scaling up Li-ion batteries for use in electric vehicles, requiring cheap and safe cathodes. Li2FeSiO4 shows promising performance as a cathode but has limited capacity since only 1 lithium may be removed and reinserted. The Li2(Fe,Mn)SiO4 solid solution is of particular interest as both DFT calculations and preliminary studies indicate that with appropriate cut-off voltage this system can deliver a reversible capacity of 200mAhg−1 (compared with 120mAhg-1 for Li2FeSiO4) and at least partially exploiting the change of oxidation state Mn(II) to Mn(IV). We wish to determine the detailed structure, including Li positions, for several Li2(Fe,Mn)SiO4 phases as a function of electrochemical cycling. In order to optimise these potentially important materials it is vital to understand the processes which occur on cycling, particularly phase changes.