Impact of LiFePO4/C composites porosity on their electrochemical performance

Fe(III) citrate was used as a source for synthesis of microsized porous LiFePO4/C particles. All samples, prepared either by solid-state or by sol-gel techniques, are phase-pure triphylite phases, which, however, have different morphology highly influenced by the type of synthesis and synthesis parameters. Their common feature is porosity due to thermal decomposition of citrate anion. The impact of particle porosity on the electrochemical behavior is discussed in terms of qualitative results obtained from scanning electron microscopy (SEM) micrographs and in terms of quantitative results obtained from N-2 adsorption isotherms. The best electrochemical behavior (above 140 mAh/g at C/2 rate during continuous cycling) was obtained with composites prepared at a relatively high heating rate (above 5 K/min). This suggests that interlaced pores were formed inside particles. A strong correlation between the electrochemical results and the heating rate was observed, which could easily be explained based on SEM micrographs and on some trends found in porosity measurements. The latter reveal the main difference between samples prepared by solid-state and by sol-gel techniques. (c) 2005 The Electrochemical Society.