Ionic/electronic conducting characteristics of LiFePO4 cathode materials - The determining factors for high rate performance

Li+ ion diffusion coefficient of lithium iron phosphate (LiFePO4) cathode materials should not be measured by the standard method because there is no composition variation but the movement of the LiFePO4/FePO4 interface during Li insertion/extraction. A method to measure the intrinsic electronic and ionic conductivity of mixed conductive LiFePO4 was reported, for the first time, based on the conductivity measurements of mixed conductive solid electrolyte using blocking electrodes. The conductivities of the three LiFePO4 materials (mixed electronic/ionic conductor, electronic conductor, and ionic conductor), were measured using the proposed method, and the electronic and ionic conductivities were linked with their electrochemical reaction kinetics and rate capabilities. These LiFePO4 samples have the same X-ray diffraction crystal structure and similar particle size, but different rate performance due to the difference in the ionic/electronic conductivity. The rate performance of the mixed electronic/ionic conductive LiFePO4 is much higher than that of the electronic conductive LiFePO4 and the ionic conductive LiFePO4. (c) 2007 The Electrochemical Society.