Role of the cathode and anode in heat generation of Li-ion cells as a function of state of charge

Thermal stability of Li-ion cells (from two different manufacturers, A and 13) and their cathodes and anodes were evaluated as a function of state of charge (SOC) using accelerating rate calorimetry (ARC). Cell A was rated at 750mAh and consisted of Sn-doped LiCoO2 cathode and meso-carbon micro-fiber (MCMF) anode. Cell B was rated at 790 mAh and was comprised of a cathode and an anode made of LiCoO2) and graphite. The electrolytes in cells A and B were mixtures of EC:EMC + 1MLiPF(6) and EC:EMC:DMC + 1MLiPF(6), respectively. ARC results indicated that between 50 and 125% SOC, the total heat generated by cell A is mostly dominated by self-heating of the cathode, while between 125 and 200% SOC the total heat generated by the cell was dominated by the anode. The total heat generated in cell B, however, was dominated by self-heating of the graphite anode, over the entire 50-200% SOC range. Also, the self-heating in cell B was higher than that for cell A. Heat generation of the LiCoO2 increases with increasing SOC, and the Sn-LiCoO2 heat generation reaches a maximum near 125% SOC. At low SOC, the temperature of the onset of chemical reaction (T-OSCR) for cell A was higher than that for the cell B. For both cells, at higher SOC, TOSCR decreased with a sharp drop between 100 and 150% SOC. Overall results show that cell A offers a higher thermal stability than cell B. Also, the ARC test is more suitable than differential scanning calorimetry for con-elation of cathode and anode heat generations to the thermal performance of full Li-ion cells. (C) 2004 Elsevier B.V. All rights reserved.