Thermal instability of Olivine-type LiMnPO4 cathodes

The remarkable thermal stability of LiFePO4 and its charged counterpart, FePO4, have been instrumental in its commercialization as a lithium-ion battery cathode material. Despite the similarity in composition and structure, and despite the high thermal stability of the parent compound, LiMnPO4, we find that the delithiated phase LiyMnPO4 (which contains a small amount of residual lithium), is relatively unstable and reactive toward a lithium-ion electrolyte. The onset temperature for heat evolution in the presence of 1 M LiPF6 in 1:1 ethylene carbonate/propylene carbonate is around 150 °C, and the total evolved heat is 884 J g−1, comparable to that produced under similar conditions by charged LiCoO2 electrodes.