An ab initio study of the Li-ion battery cathode material Li2FeSiO4

A density functional theory (DFT) calculation is reported for the novel Li-ion battery cathode material lithium iron silicate (Li2FeSiO4) and for three possible Li arrangements in the delithiated structure (LiFeSiO4). Relevant battery-related properties have been derived: average voltage (2.77 V vs. Li/Li+), energy density (1200 Wh/l) and specific energy (440 Wh/kg). Lattice constants and atomic fractional coordinates are also given for each case. The calculated values are in good agreement with recent experimental values (A. Nytén, A. Abouimrane, M. Armand, T. Gustafsson, J.O. Thomas, Electrochem. Commun., 7 (2005) 156). Voltages were calculated (again vs. Li/Li+) for the three different Li arrangements in LiFeSiO4; these differed by 0.22 V – a difference which could perhaps be related to the experimentally observed 0.30 V drop in voltage between the first and subsequent charge cycles.