Stability of LiFePO4 in water and consequence on the Li battery behaviour

The stability of LiFePO₄ in water was investigated. Changes upon exposure to water can have several important implications for storage conditions of LiFePO₄, aqueous processing of LiFePO₄-based composite electrodes, and eventually for utilisation in aqueous lithium batteries. A Li₃PO₄ layer of a few nanometers thick was characterised at the LiFePO₄ grains surface after immersion in water, accompanied by an increase of Fe^III percentage in the grains. For first charge–discharge cycles in a lithium battery, no effect was observed on electrochemical performances for a sample of LiFePO₄ immersed for 24 h at a concentration of 50 g L⁻¹ without any pH modification. To limit the aging of LiFePO₄ during aqueous electrode processing, it is advised to reduce the immersion duration, to concentrate the LiFePO₄ suspensions, and not to modify the pH. In addition, since immersion in water mimics an accelerated exposure to air humidity, LiFePO₄ should be stored in a dry atmosphere. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.