Optimization of multi-stage constant currents fast charging protocol with negative pulses considering Lithium plating, stripping, and heat generation rates for Lithium-ion batteries

Multi-stage Constant Current (MCC) is a widely used Fast Charging (FC) protocol that decreases its current amplitude to minimize degradation. Lithium Plating is the most popular degradation effect considered when designing fast charging protocols because of its high degradation rate and growth of dendrites, potentially leading to thermal runaway. Anode potential is popularly considered as lithium plating onset indicator; however, it is insufficient because of continuously varying electrochemical mechanisms under different operating conditions. This study proposes a real-time optimized MCC protocol with negative pulses (O-MCC + NP) to minimize charging time, considering degradation and heat generation. The proposed O-MCC + NP provides a double protection mechanism by not only suppressing the reaction of lithium plating but also promoting reaction of lithium stripping, thereby significantly enhancing battery safety. Based on a validated reduced-order electrochemical-thermal life model, the charging and negative pulse current amplitudes are optimized using two separate Nonlinear Model Predictive Control algorithms under constrained lithium plating overpotential and anode concentration gradients to prevent lithium plating. Pulse frequency is determined experimentally, reducing heat generation associated with diffusion resistance by Distribution of Relaxation Time (DRT) analysis. The proposed charging protocol is experimentally tested in a battery-in-the-loop system, showing a 16 % reduction in charging time and a 37 % reduction in capacity fade compared with those by the conventional MCC protocol by preventing lithium plating and promoting lithium stripping simultaneously.