Effects of Li2CO3 as a secondary lithium source on the LiFePO4/C composites prepared via solid-state method

Li2CO3 was used as the secondary lithium source for the synthesis of LiFePO4/C composites via a solid-state reaction method by adopting Li3PO4 as the main lithium source. The main purpose of using Li2CO3 is to compensate for the partial lithium loss during the sintering while reducing the usage of excess Li3PO4. In this study, the effects of Li2CO3 amount on the phase, structural and electrochemical properties of LiFePO4/C material were systematically investigated. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), constant-current charge-discharge test and cyclic voltammetry (CV). The results showed that by adding an appropriate amount of Li2CO3, the impurities, e.g. Li3PO4, normally appearing in the final product, could be excluded. It was found that LiFePO4/C with Li2CO3 in 6% excess (vs. stoichiometric LiFePO4) exhibited the best electrochemical performance, which delivered initial discharge capacities of 141.7, 125.2, 119.9 and 108.9 mAh g(-1), respectively, at 0.5, 1, 2 and 5C rates. The capacity was reduced to 113.4 mAh g(-1) after 50 cycles at 2C rate, with capacity retention rate of 94.6%. (C) 2012 Elsevier Ltd. All rights reserved.