Performance of LiFePO4 as lithium battery cathode and comparison with manganese and vanadium oxides

LiFePO4 was synthesized by a high temperature method and high purity was confirmed by both powder X-ray diffraction and thermal analysis. It can deliver 136 Ah/kg, 80% of theoretical capacity at 1 mA/cm2 at high cathode load levels at room temperature; 100% capacity can be obtained by raising the temperature to 60 °C or reducing the discharge rate to 0.1 mA/cm2. The method of carbon addition/coating was not found to be critical, carbon black being as efficient as in situ formed carbon coatings. These materials suffer from a low volumetric energy density, which will seriously impact their possible application. Stabilized layered structures of manganese substituted nickel oxides, such as LiMn0.4Co0.2Ni0.4O2, show a behavior typical of a single phase intercalation reaction, and a reversible capacity of around 180 Ah/kg with an upper voltage cut-off of 4.3 V. Stabilized δ-structures of vanadium pentoxide show capacities approaching 300 Ah/kg, but with a median discharge potential of 2.6 V.