How to identify mechanism consistency for LFP/C batteries during accelerated calendar and cycling aging using the lognormal distribution

The accelerated aging test is a powerful tool to stress batteries and predict their performance. Although some test conditions cause the battery to age more rapidly, it may force other unexpected effects on how they age over time, leading to a misunderstanding of normal lifetime results. This paper explores the experimental stress intervals for commercial LFP/C batteries to ensure mechanistic consistency based on a 43-month calendar aging test and a 10-month cyclic aging test, taking the log-normal distribution as a time-to-failure statistical lifetime model. A comprehensive study is performed based on capacity measurements during calendar aging considering two stress factors (the temperature and the state-of-charge (SOC) level) and cycling aging considering three stress factors (the temperature, the SOC level, and the cycle-depth (CD) level). The permutation test using likelihood ratio (LR) is used to determine the consistency of parameter estimates. Based on the consistent acceleration factor principle, test conditions causing different lifetime behaviors can be pointed out. The ranking of different stress effects in the test range can be obtained. This method can be used as a reference to make reasonable test plans for detecting battery's performance, thereby, predicting their lifetime more accurately.