Aging mechanism in Li ion cells and calendar life predictions

In this work, the long term calendar life of lithium ion cells for satellite and standby applications has been studied in experiments where the capacity evolution is tracked as a function of storage temperature. Cells containing 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 negative electrode and the data were fit to a model which involved a rate-determining step governed by electronic conductivity of the solid electrolyte interphase (SEI) layer, following Arrhenius’ law as a function of temperature. When nickel-based positives are used, a “lithium reserve” exists on the negative and this property enhances the calendar life for long life applications.