Lithium intercalation into amorphous FePO 4 cathode in aqueous solutions

Abstract

Amorphous iron phosphate (FePO 4) was investigated as a cathode material for battery applications using aqueous (lithium hydroxide or potassium hydroxide) electrolytes. Phosphate-based cathode materials are of great interest in lithium batteries which use non-aqueous electrolytes. In order for these materials to be used as cathodes in aqueous electrolytes it is important to understand their reduction/oxidation mechanisms. Potentiostatic and galvanostatic techniques are used to study these mechanisms. X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) have been used to gain insight into the reduction/oxidation behavior of FePO 4 cathodes. Our results show that FePO 4 undergoes reversible Fe 3+/ 2+ processes of reduction and oxidation in LiOH electrolyte, while using KOH electrolyte this process is found to be irreversible. The lithium intercalation mechanism is identified for LiOH while in the case of KOH electrolyte H reacts to form FeOOH. The Zn|LiOH|FePO 4 battery provides a reversible capacity of 65 mAh/g. The results indicate the trigonal FePO 4 as an attractive host intercalation compound.