Advanced Integrated Fast-Charging Protocol for Lithium-Ion Batteries by Considering Degradation

In the modern electric vehicle industry, the fast charging of lithium-ion batteries is essential. Charging at a high C-rate minimizes the charging time; however, this results in degradation due to the rapid rise in the temperature and voltage. Therefore, we propose an advanced charging protocol that reflects degradation conditions by integrating multistage constant current-constant voltage and pulse protocols. The proposed protocol was efficiently evaluated using a high-fidelity lithium-ion battery model based on porous electrode theory. However, this model-based optimal protocol design has challenges regarding the expansion of the design space based on the increasing number of parameters and lack of information about the degradation conditions. A Bayesian optimization was applied to perform sample-efficient optimization without using a first-principles model and to incorporate the variability of battery cells into a stochastic prediction model. The charging protocol design guidelines identified in the naïve design space are used as prior knowledge to improve the efficiency of charging protocol design considering degradation. As a result, advanced protocols that suppress degradation and allow for minimized charging times compared to reference protocols (i.e., multistage constant current-constant voltage) are given as a Pareto front.