Iron–tin oxides with CaFe2O4 structure as anodes for Li-ion batteries

To investigate the effect of matrix, counter ions and cycling conditions on the properties of mixed iron oxides, CaFe2O4, Li0.5Ca0.5(Fe1.5Sn0.5)O4 and NaFeSnO4 have been synthesized and their electrochemical performance studied. CaFe2O4 shows a reversible capacity of not, vert, similar200 mAh g−1 at 60 mA g−1 and 12–50 cycles in the range 0.005–3.0 V, but shows slight capacity fading when the upper voltage is reduced to 2.5 V. Li0.5Ca0.5(Fe1.5Sn0.5)O4 gives a reversible capacity of not, vert, similar450 mAh g−1 in the voltage range 0.005–3.0 V at a current density of 60 mA g−1 over 5–30 cycles and shows slight capacity-fading up to 50 cycles. NaFeSnO4 displays drastic capacity-fading on cycling to 3.0 V, but has very good cycling performance (310–340 mAh g−1 for to 4–110 cycles) on cycling between 0.005 and 1.0 V at 60 mA g−1. The mechanism of operation of the electrodes, as well as the beneficial effects of the presence of Ca ions and cycling up to a 3.0 V cut-off in the Ca-ferrites, are discussed.