Cathode performance of olivine-type LiFePO4 synthesized by chemical lithiation

Chemical lithiation with LiI in acetonitrile was performed for amorphous FePO4 synthesized from an equimolar aqueous suspension of iron powder and an aqueous solution of P2O5. An orthorhombic LiFePO4 olivine structure was obtained by annealing a chemically lithiated sample at 550 °C for 5 h in Ar atmosphere. The average particle size remained at approximately 250 nm even after annealing. The lithium content in the sample was quantitatively confirmed by Li atomic absorption analysis and 57Fe Mössbauer spectroscopy. While an amorphous FePO4/carbon composite cathode has a monotonously decreasing charge–discharge profile with a reversible capacity of more than 140 mAh g−1, the crystallized LiFePO4/carbon composite shows a 3.4 V plateau corresponding to a two-phase reaction. This means that the lithium in the chemically lithiated sample is electrochemically active. Both amorphous FePO4 and the chemically lithiated and annealed crystalline LiFePO4 cathode materials showed good cyclability (more than 140 mAh g−1 at the 40th cycle) and good discharge rate capability (more than 100 mAh g−1 at 5.0 mA cm−2). In addition, the fast-charge performance was found to be comparable to that with LiCoO2.