Electrochemical lithiation of Co2MnSi with a Heusler structure is investigated as a candidate negative electrode (anode) material for secondary lithium batteries. The electrode maintains a reversible discharge capacity of 112mAhg−1 for 50 cycles when cycled between 0.01 and 3V. It is proposed that the lithiation mechanism consists of two steps. Co2MnSi transforms to Heusler-type Li2MnSi during the first charge cycle and subsequent charge–discharge cycles involve the formation of a solid solution in Li x MnSi. The latter compound maintains its structural integrity throughout cycling to provide steady cycling behaviour. Magnetic measurements are also employed to substantiate further the structural changes during electrochemical cycling.