A semi-empirical and multi-variable model for prediction of capacity loss in lithium-ion batteries: Considering cycling and performance time degradations

Abstract

The lifetime of a lithium-ion battery (LIB) is primarily influenced by several key factors including time (number of charge-discharge cycles and performance time), temperature, and current rate (C-rate). In this study, a semi-empirical model is employed to predict the lifetime of LIBs by incorporating these variables. Previous models mainly neglect the influence of performance time on LIB capacity loss. However, our analysis reveals that adding performance time parameter significantly improves the model's accuracy. Additionally, the present model investigates the relationship between the functions of the semi-empirical model and factors such as temperature and C-rate, thereby improving the precision of the model's predictions. The experiments are conducted at several temperatures (25, 35, and 45 °C), each subjected to three current rates of 0.5C, 1 C, and 1.5C to develop the models. The proposed model for estimating LIB capacity loss consists of two terms that account for the impacts of cycling and performance time. The optimization findings indicate that both temperature and current rate have an impact on the cycling term. However, the term of performance time has temperature functions. Validation tests of the model are conducted at 25 °C-0.8C and 45 °C-1.7C. There is a perfect agreement between the model results and the experimental data. Using this model, it is possible to predict the lifetime of LIB with a relative error of less than 2%. Furthermore, this error diminishes as the number of cycles increases. Moreover, the proposed model allows for a quantitative evaluation of the individual contributions of cycling or performance time to the total LIB capacity loss. The results reveal that when the LIB undergoes more cycles, the proportion of capacity loss ascribed to performance time increases, while the proportion assigned to cycling declines. This indicates that the electrochemical processes responsible for the gradual capacity loss, which have no relationship to cycling, happen more rapidly during the LIB's operation.