Electrochemical Behavior of LiFePO[sub 4]∕C Cathode Material for Rechargeable Lithium Batteries

Abstract

Electrochemical behavior of cathode material synthesized by ballmilling technique from a mixture of Fe powder, , , and sucrose was studied in half-cells using lithium metal as anode. The prepared cathode material exhibits excellent rate capability with initial discharge capacities of (1 C), (2 C), (3 C), and (5 C), respectively. Good cycling performance under 2 C charge-discharge rate could be obtained at room temperature with a discharge capacity of for 300 cycles. Impedance spectroscopy was applied to investigate the material behavior during the 2 C rate charge–discharge cycling. It is found that the Nyquist plots of the cycled lithium cell at discharged state are comprised of one or two semicircles in high-to-medium frequency range followed by an inclined line in low-frequency range. The first semicircle at higher frequency shows close relationship with the cycling performance of the lithium cell. Thus, it may be used to predict the cycle life of the cathode. Through a combined X-ray diffraction (XRD) analysis and scanning electron microscope observation on the cathode upon the 2 C rate cycling, we correlated the observed capacity fading after 300 cycles at 2 C charge-discharge rate with the particle cracking and the increase of particle contact resistance. No significant phase change of was observed even after 800 cycles according to the XRD patterns.