Fitting lifetime distributions to interval censored cyclic-aging data of lithium-ion batteries

In lifetime analysis of lithium-ion batteries, the failure of a battery is commonly defined as the time point at which the battery holds only a certain percentage of its initial storage capacity. Usually, lifetime experiments are carried out to record degradation up to a certain level, and thus do not offer an appropriate data base for fitting lifetime distributions to different end-of-life (EoL) criteria by means of residual capacity. However, for a second use of batteries, e.g. in a home energy storage system, lifetime modeling for long-term usage is of specific interest. Based on real data from long-term cyclic aging experiments with lithium-ion batteries, the fitting of three of the most popular lifetime distributions, namely Weibull, lognormal and inverse Gaussian distributions, is examined with respect to some particular EoL criteria. The impact of chosen lifetime distributions on confidence intervals (CIs) for the mean lifetime and certain quantiles is studied. Moreover, since data of capacity decline are commonly interval-censored, comparisons of resulting CIs under full and interval-censored information are made by means of simulations.