An analytical model for the CC-CV charge of Li-ion batteries with application to degradation analysis

While the constant current charge time (CCCT) and constant voltage charge time (CVCT) are increasingly used for the state of health (SOH) estimation of Li-ion batteries, their correlations with battery degradation are not investigated comprehensively. This paper develops an analytical model to quantify the chargeable capacity of a Li-ion battery under a CC-CV profile, in which CCCT and CVCT are identified as two uncoupled parameters. The model is verified using a battery dataset of cycling tests subjected to 19 different test conditions with different discharge currents, ambient temperatures, and rest times. The behaviors of CCCT and CVCT during battery degradation are studied in terms of chargeable capacity fade. A new health indicator, the CV-CC time ratio, is developed for degradation analysis. Two partial CC-CV cases are also considered in the studies: in one case, the partial CC-CV charge starts after different discharged depths, and in the other case, different fast charging policies are executed before the partial CC-CV charge.