Improving the rate and low-temperature performance of LiFePO4 by tailoring the form of carbon coating from amorphous to graphene-like

A solid-state reaction process with poly(vinyl alcohol) as the carbon source is developed to synthesize LiFePO4-based active powders with or without modification assistance of a small amount of Li3V2(PO4)(3). The samples are analyzed by X-ray diffraction, scanning/transmission electron microscopy, and Raman spectroscopy. It is found that, in addition to the minor effect of a lattice doping in LiFePO4 by substituting a tiny fraction of Fe2+ ions with V3+ ions, the change in the form of carbon coating on the surface of LiFePO4 plays a more important role to improve the electrochemical properties. The carbon changes partially from sp(3) to sp(2) hybridization and thus causes the significant rise in electronic conductivity in the Li3V2(PO4)(3)-modified LiFePO4 samples. Compared with the carbon-coated baseline LiFePO4, the composite material 0.9LiFePO(4)center dot 0.1Li(3)V(2)(PO4)(3) shows totally different carbon morphology and much better electrochemical properties. It delivers specific capacities of 143.6 mAh g(-1) at 10 C rate and 119.2 mAh g(-1) at 20 C rate, respectively. Even at the low temperature of -20 A degrees C, it delivers a specific capacity of 118.4 mAh g(-1) at 0.2 C.