Mesocarbon microbeads (MCMB), soft carbon coated nature graphite (GDR), and soft carbon were investigated as the negative electrodes for spinel/carbon cells with the aim to understand the capacity loss mechanism of carbon/spinel cells at elevated temperatures. The high-temperature cycling performance of MCMB/spinel cell and GDR/spinel cell was improved by formatting the cells at 55 degrees C. In this case, a stable solid electrolyte interphase (SEI) was believed to form at 55 degrees C and hence protected the carbon electrodes from attack by the solvents and Mn2+. Particularly, the cycling performance of the cells was dramatically improved by limiting the upper cutoff voltage of the cells to 4.1 V. The poor performance of the cells cycled to 4.3 V was believed to be related to the extra electrochemical reactions of lithium removal from the lithium-rich manganese oxide spinel that occurs at about 4.5 V vs Li. The relationship between the accelerated capacity fade and extra electrochemical reaction of lithium-rich spinel is also discussed in this manuscript. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.2147073] All rights reserved.