LixFeF6 (x = 2, 3, 4) battery materials: Structural, electronic and lithium diffusion properties

Schroeder M., Eames C., Tompsett D.A., Lieser G., Islam M.S.

Abstract

Lithium iron fluoride materials have attracted recent interest as cathode materials for lithium ion batteries. The electrochemical properties of the high energy density LixFeF6 (x = 2, 3, 4) materials have been evaluated using a combination of potential-based and DFT computational methods. Voltages of 6.1 V and 3.0 V are found for lithium intercalation from Li 2FeF6 to α-Li3FeF6 and α-Li3FeF6 to Li4FeF6 respectively. The calculated density of states indicate that Li 2FeF6 possesses metallic states that become strongly insulating after lithium intercalation to form α-Li3FeF 6. The large energy gain associated with this metal-insulator transition is likely to contribute to the associated large voltage of 6.1 V. Molecular dynamics simulations of lithium diffusion in α-Li 3FeF6 at typical battery operating temperatures indicate high lithium-ion mobility with low activation barriers. These results suggest the potential for good rate performance of lithium iron fluoride cathode materials. © 2013 the Owner Societies.