Aging mechanism in Li ion cells and calendar life predictions

In this work, the long term calendar Life of lithium ion cells for satellit e and standby applications has been studied in experiments where the capaci ty evolution is tracked as a function of storage temperature. Cells contain ing either LiCoO2 and LiNixMyO2 positives coupled with a graphite negative were float charged at 3.8 or 3.9 V. This study focused on losses at the neg ative electrode and the data were fit to a model which involved a rate-dete rmining step governed by electronic conductivity of the solid electrolyte i nterphase (SEI) layer, following Arrhenius' law as a function of temperatur e. When nickel-based positives are used, a "lithium reserve" exists on the negative and this property enhances the calendar life for long life applica tions. (C) 2001 Elsevier Science B.V. All rights reserved.