Two synthesis routes for the production of LiFePO 4 particles were investigated in water at subcritical and supercritical conditions. Micron and nano-sized particles of LiFePO 4 were obtained via both routes, with nano-sized particles predominating when temperature was above the critical temperature of water. Our results suggest that synthesis in supercritical water is attractive for obtaining nanometer-sized crystalline particles of LiFePO 4 with a low degree of agglomeration. Electrochemical tests showed that this material exhibited improved capacity compared with LiFePO 4 prepared via other methods.