Three-Parameter Modeling of Nonlinear Capacity Fade for Lithium-Ion Batteries at Various Cycling Conditions

Existing methods for predicting the capacity fade of lithium ion batteries (LIBs) are typically limited to the description of cells under fixed charge/discharge (C/D) cycling conditions. The prediction requires a large amount of experimental data for various cycling environments to construct empirical equations or to obtain parameters in physical-based models. Based on the porous electrode theory, a semi-empirical model with three constant parameters is developed here. It is found that fading data at various temperatures collapse into a single curve on a newly proposed plot. This finding enables us to use a much smaller amount of cycle-life data to determine the values of these parameters, which sufficiently characterize the fading response under a broad range of cycling conditions. The prediction yielded from the model is confirmed by several scenarios with varying cycling conditions, such as temperature, depth of discharge, and C/D rate. A further prediction shows that different average C/D rates, which give rise to different cell-temperature histories, have a strong influence on the capacity degradation of an LIB. By introducing the average C/D rate, we analyze the capacity loss after 1500 cycles with the use of two types of charging protocols, from which two operational treatments are suggested.