Studies of the Lifetime and Degradation of Li-Ion Cells

Abstract

High precision coulometry has been suggested as a technique to detect small differences in the coulombic efficiency (ratio of charge delivered to charge stored during a cycle) of cells in the early cycles that should correlate to cell lifetime. This thesis examines cells with different failure modes and shows how high precision coulometry can be used, in conjunction with other techniques, to reliably determine the relative performance of cells in experiments that last only a few weeks. It was shown that coulombic efficiency could be used to predict the long term performance of cells that show either gradual fade or very little fade until “roll-over” failure with different electrolyte additives. The effect of age on coulombic efficiency was also studied showing the increase in coulombic efficiency with time but the presence of charge slippage even later in a cells life that can eventually lead to cell failure.