Haining Liu 1,2, Ijaz Haider Naqvi 3, Fajia Li 1, Chengliang Liu 4, Neda Shafiei 2, Yulong Li 2,5, and Michael Pecht 2
1 School of Mechanical Engineering, University of Jinan, Jinan, 250022, China
2 Center for Advanced Life Cycle Engineering (CALCE), University of Maryland, College Park, MD 20742, USA
3 Department of Electrical Engineering, Lahore University of Management Sciences (LUMS), Lahore 54792, Pakistan
4 School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China
5 Key Lab for Robot & Welding Automation of Jiangxi Province, Mechanical & Electrical Engineering School, Nanchang University, Nanchang, 330031, China
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.