Thermal Stabilities of Delithiated Olivine MPO[subscript 4] (M=Fe,Mn) Cathodes investigated using First Principles Calculations

Abstract

We present an analysis of the thermal reduction of delithiated LiMnPO[subscript 4] and LiFePO[subscript 4] based on the quarternary phase diagrams as calculated from first principles. Our results confirm the recent experimental findings that MnPO[subscript 4] decomposes at a much lower temperature than FePO[subscript 4], thereby potentially posing larger safety issues for LiMnPO[subscript 4] cathodes. We find that while substantial oxygen is released as MnPO[subscript 4] reduces to Mn[subscript 2]P[subscript 2]O[subscript 7], the mixed valence phases that form in the decomposition process of FePO[subscript 4] limit the amount of oxygen evolved.