On the Thermal Stability of Olivine Cathode Materials for Lithium-Ion Batteries

The thermal stability of pristine and electrochemically delithiated LiMPO 4 (Carbon coated-LiMnPO 4 , Carbon coated-LiMn 0.8 Fe 0.2 PO 4 , and Carbon coated-LiFePO 4 ), LiCoO 2 and LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) composite electrodes with LiPF 6 solutions in ethylene carbonate (EC)/dimethyl carbonate (DMC) and EC/propylene carbonate (PC), was investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis, coupled with mass spectrometry. The thermal reactions products were measured by XRD and electron microscopy. The LiFePO 4 and LiMnPO 4 cathode materials were found to have comparable thermal stability in their pristine and fully delithiated states. The onset temperatures of the thermal reactions are lower in EC/DMC than in EC/PC solutions but the specific heat evolution of all the thermal reactions are higher with EC-PC solutions. No evidence was found that delithiated LiMnPO 4 or Li[MnFe]PO 4 have lower thermal stability than delithiated LiFePO 4 . The thermal reactivity of the layered LiCoO 2 and LiNi 0.8 Co 0.15 Al 0.05 O 2 cathode materials was found to be comparable to that of the LiMPO 4 materials. Oxygen release was detected from the layered compounds upon their heating around 200°C.