Cathodes Properties of Phospho-olivine for Lithium Secondary Batteries

Four types of orthorhombic olivine LiMPO_4 (M:Co, Fe, Ni, Mn) were investigated as high voltage cathode active materials for lithium secondary batteries. LiCoPO_4 exhibited the highest 4.8V discharge plateau of 100mAh/g vs. Li/Li^+ after initial charging to 5.1V and its energy density was comparable to that of layeredrocksalt LiCoO_2 (120mAh/g×4V=480mWh/g). In contrast, the open circuit voltage profile of LiFePO_4 was 160mAh/g on the 3V plateau. TG-DSC measurements showed that the thermal stability of charged Li_<1-x>CoPO_4 is better than that of fully-charged Li_<1-x>CoO_2. The chemical state of Co in LiCoPO_4 was also analyzed using HRXRF