Effects of temperature on the formation of graphite/LiCoO2 batteries

The effects of temperature on the formation of graphite/LiCoO2 batteries were studied using various electrochemical techniques, such as electrochemical impedance spectroscopy (EIS), cyclic voltammetry, and battery performance testing. Results showed that the coulombic efficiency of the first charge and discharge for batteries at 25 degrees C was higher than that at 50 degrees C. The batteries with different formation temperatures of 25 and 50 degrees C exhibited very similar cycling performance at 25 degrees C. The EIS of batteries at 25 degrees C was composed of two overlapped semicircles at high to medium frequency and a slope line at low frequency, while the EIS of batteries at 50 degrees C was composed of an inductive loop at very high frequency followed by two overlapped semicircles at high to medium frequency and a slope line at low frequency. The bulk resistance (R-b) of batteries at 50 degrees C was much larger than that at 25 degrees C. The resistance of solid electrolyte interface (R-SEI) and charge-transfer resistance (R-ct) of batteries at 50 degrees C, which were subjected to 50 cycles at 50 degrees C, were increased greatly, and the cycle performance of batteries became obviously worse with the increase in formation temperature. (c) 2008 The Electrochemical Society.