Synthesis of LiFePO4 nanocrystals and their properties as cathodic material for lithium ion batteries

Abstract

The method of lithium iron phosphate (LiFePO4) synthesis in a melt mixture of choline chloride and diethylene glycol (DEG) at 230 ?C is proposed. Powders with lamellar morphology consisting of LiFePO4 crystals (size ~30 nm) with olivine structure were synthesized. The size of crystals increased to ~60 nm during the annealing process carried out to obtain a carbon coating on the grain surface of LiFePO4. The charge-discharge curves of the electrode prepared from these powders have a horizontal portion at the potential of 3.4 and 3.5 V, corresponding to the intercalation/deintercalation of lithium in the structure of olivine. The specific discharge capacity of the LiFePO4/C is 133 mA h g-1 for a discharge current of 0.1C. The dependence of the anodic (cathodic) voltammetric current peaks, Ip, on the potential scan rate indicates the diffusion nature of the lithiating step. For the anodic and cathodic processes the averaged diffusion coefficient values are 1.3?10-10 and 1.5?10-10 cm2 s-1, respectively.