Reaction behavior of LiFePO4 as a cathode material for rechargeable lithium batteries

We investigated the effect of cell temperature on the electrochemical reaction behavior of LiFePO4. We evaluated its electrochemical characteristics by using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Both the electron transfer activity and the lithium ion diffusion rate in the LiFePO4 electrode increased as we increased the operating temperature. The apparent activation energy for the lithium diffusion was more than twice that for charge transfer. This result supports the idea that the large discharge capacity of LiFePO4 at elevated temperatures is mainly caused by the high lithium diffusion rate in the LiFePO4 particles, which makes it possible to utilize more material near the center of the particles. We also evaluated the thermal stability of LiFePO4 by differential scanning calorimetry (DSC). Charged LiFePO4 in contact with an electrolyte solution exhibited no obvious endothermic or exothermic reaction below 340 degreesC. This means that LiFePO4 has higher thermal stability than such other cathode materials as LiCOO2, LiNiO2 and LiMn2O4. (C) 2002 Elsevier Science B.V. All rights reserved.