More on the reactivity of olivine LiFePO4 nano-particles with atmosphere at moderate temperature

The changes appearing for LiFePO4–C nano-composites exposed to atmosphere at 120 °C have been structurally and chemically examined by the use of TGA, XRD, XPS, Mössbauer, 7Li MAS NMR and electrochemical methods. The results conclude that a highly disordered phase resulting from the aging of LiFePO4 appears on the surface of the grains of the material, is assigned to a phosphate phase and can insert lithium around 2.6 V with poor reversibility. The essential role of water has been investigated and clearly demonstrated. Thus, the aging mechanism occurring in hot humid air is completely different from a simple oxidation as well as from the aging process observed above 150 °C and involves the incorporation of hydroxyl groups. In addition, Fe2O3 formation has not been observed for such an aging in mild conditions.