Oxalic acid-assisted preparation of LiFePO4/C cathode material for lithium-ion batteries

LiFePO4/C composite is synthesized by oxalic acid-assisted rheological phase method. Fe2O3 and LiH2PO4 are chosen as the starting materials, sucrose as carbon sources, and oxalic acid as the additive. The crystalline structure and morphology of the products are characterized by X-ray diffraction and field emission scanning electron microscopy. The charge-discharge kinetics of LiFePO4 electrode is investigated using cyclic voltammetry and electrochemical impedance spectroscopy. It is found that the introduction of appropriate amount of oxalic acid leads to smaller particle sizes, more homogeneous size distribution, and some Fe2P produced in the final products, resulting in reduced polarization, impedance, and improved Li+ ion diffusion coefficient. The best cell performance is delivered by the sample with R = 1.5 (R of the molar ratio of oxalic acid to LiH2PO4). Its discharge capacity is 154 mAh g(-1) at 0.2 C rate and 120 mAh g(-1) at 5.0 C rate. At the same time, it exhibits an excellent cycling stability; no obvious decrease even after 1,000 cycles at 1.0 C rate.