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

Abstract

To investigate the effect of matrix, counter ions and cycling conditions on the properties of mixed iron oxides, CaFe₂O₄, Li_0.5Ca_0.5(Fe_1.5Sn_0.5)O₄ and NaFeSnO₄ have been synthesized and their electrochemical performance studied. CaFe₂O₄ shows a reversible capacity of ~200 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. Li_0.5Ca_0.5(Fe_1.5Sn_0.5)O₄ gives a reversible capacity of ~450 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.