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.