Hydrothermal synthesis of lithium iron phosphate

LiFePO4 is a potential cathode candidate for the next generation of secondary lithium batteries. The LiFePO4 was synthesized by a hydrothermal process. Phase-pure material was obtained and the critical synthesis parameters were determined. Iron disorder onto the lithium sites can be eliminated by using temperatures in excess of 175 °C; above this temperature the crystalline unit cell was essentially identical to that of the high temperature material, with a volume of 291.3 ± 0.2 Å3. The use of a soluble reductant, such as sugar or ascorbic acid, was found to minimize the oxidation of the iron to ferric. The electronic conductivity was enhanced by the deposition of carbon from the sugar, or by the addition of carbon nanotubes to the hydrothermal reactor. The electrochemical behavior of this material showed more than 90% lithium removal on charge and complete capacity retention over 50 cycles.