Chemical lithiation route to size-controllable LiFePO4/C nanocomposite

Abstract

Chemical lithiation of amorphous FePO4 with LiI in acetonitrile is performed to form amorphous LiFePO4. The amorphous FePO4·2H2O precursor is synthesized by co-precipitation method from equimolar aqueous solutions of FeSO4·7H2O and NH4H2PO4, using H2O2 (hydrogen peroxide) as the oxidizing agent. The nanocrystalline LiFePO4/C is obtained by annealing the amorphous LiFePO4 and in situ carbon coating with sucrose in a reducing atmosphere. The particle size of FePO4·2H2O precursor decreases with increasing reaction temperature. The final LiFePO4/C products completely maintain the shape and size of the precursor even after annealing at 700 °C for 2 h. The excellent electrochemical properties of these nanocrystalline LiFePO4/C composites suggest that to decrease the particle size of LiFePO4 is very effective in enhancing the rate capability and cycle performance. The specific discharge capacities of LiFePO4/C obtained from the FePO4·2H2O precursor synthesized at 75 °C are 151.8 and 133.5 mAh g−1 at 0.1 and 1 C rates, with a low capacity fading of about 0.075 % per cycle over 50 cycles at 0.5 C rate.