Reducing Carbon in LiFePO4 / C Composite Electrodes to Maximize Specific Energy, Volumetric Energy, and Tap Density

TLDR: In this paper, three carbon-coated samples, one after the synthesis of pure LiFePO 4, one synthesized with sugar added before the heating steps, and one synthesised with sugar adding before heating and subsequently coated with carbon, were studied.

Abstract: Efforts were made to synthesize LiFePO 4 /C composites showing good rale capability and high energy density while attempting to minimize the amount of carbon in the composite. First, three carbon-coated samples, one coated with carbon after the synthesis of pure LiFePO 4 , one synthesized with sugar added before the heating steps, and one synthesized with sugar added before heating and subsequently coated with carbon, were studied. The resulting carbon contents for these samples arc 2.7, 3.5, and 6.2 wt %, respectively. Electrochemical tests showed that the latter two samples had comparable rate capabilities to the LiFePO 4 /C composite (15 wt % carbon) recently reported by Huang et al. We believe the synthesis of LiFePO 4 with sugar added before heating is the best method because it gives particles having uniform small size that are covered by carbon. Further studies of samples made by this method show that a very small percentage of carbon, even less than 1 wt %, causes a significant increase in rate capability, hut unfortunately, a dramatic decrease in tap density. To make LiFePO 4 /C composites having good rate capability, high energy density, and high tap density, the carbon content and method for coating carbon onto the LiFePO 4 particles must he given careful attention. However, based on the studies reported here, we are not certain that all desired parameters can he simultaneously achieved, and this may limit the usefulness of LiFePO 4 in some practical applications.