Is it possible to prepare olivine-type LiFeSiO4?: A joint computational and experimental investigation

Silicates LiMSiO4 are potential positive electrode materials for lithium ion batteries. In this work we analyse from first principles calculations the relative stability of possible LiFeSiO4-polymorphs within four structural types. Olivine-LiFeSiO4 is predicted to be more stable than the LiFeSiO4 prepared by delithiation of Li2FeSiO4; the latter being the only LiFeSiO4 compound reported so far. Attempts to prepare olivine-LiFeSiO4 from a mixture of reactants at ambient pressure (600–1100 °C) resulted in a mixture of quartz-SiO2, Li2SiO3, LiFe5O8 and LiFeSi2O6 phases. Conducting the reaction under HP conditions (40 kbar) leads to the formation of LiFeSi2O6 as a majority phase, regardless the nature of the reactants/precursors. First principles calculations indicate that the preparation of the olivine-LiFeSiO4 is thermodynamically hindered due to the competition with the more stable LiFeSi2O6 pyroxene, in the range of pressure/temperature investigated.