Phase stability study of Li_1-xMnPO₄ (0≤x≤1) cathode for Li rechargeable battery

The phase stability of Li_1-xMnPO₄ (0≤x≤1) is investigated in this study for different Li compositions and temperatures by high temperature X-ray diffraction and electron microscopy. The map of stable phases is determined at temperature ranges between room temperature and 410°C. While pure LiMnPO₄ phase is stable at high temperature, partial phase transformation of MnPO₄ into Mn₂ P ₂O₇ is observed in delithiated phases above 210°C. Electron microscopy study also indicates the instability of the delithiated phase. The morphology of LiMnPO₄ is severely damaged upon delithiation. The instability of the delithiated phase and the phase transformation into Mn₂ P₂ O₇ may imply that safety concerns can be raised regarding the LiMnPO₄ cathode, unlike its Fe counterpart.