Electrochemical performance of sol-gel synthesized LiFePO4 in lithium batteries

LiFePO4, Li0.98Mg0.01FePO4, and Li0.96Ti0.01FePO4 were synthesized via a sol-gel method using a variety of processing conditions. For comparison, LiFePO4 was also synthesized from iron acetate by a solid-state method. The electrochemical performance of these materials in lithium cells was evaluated and correlated to LiFePO4 powder morphology and residual carbon structure, as determined by Raman microprobe spectroscopy. For materials with mean agglomerate sizes below 20 mm, an association between structure and crystallinity of the residual carbon and improved utilization was observed. Addition of small amounts of organic compounds or polymers during processing results in carbon coatings with higher graphitization ratios and better electronic properties on the LiFePO4 samples and improves cell performance in some cases, even though total carbon contents remain low (<2%). In contrast, no performance enhancement was seen for samples doped with Mg or Ti. These results suggest that it should be possible to design high-power LiFePO4 electrodes without unduly compromising energy density by optimizing the carbon coating on the particles. (C) 2004 The Electrochemical Society.