A multi-closed-loop constant-current constant-strain fast charging strategy for lithium-ion batteries

Abstract

Fast charging is considered the key technology of electric vehicles. Battery expansion is critical during the charging process, reflecting the battery's state and performance. However, most of the current research has ignored the expansion of the battery during charging, which will increase the capacity and performance loss during charging. Therefore, a constant-current constant-strain (CC-CS) charging strategy with multiple closed-loop control is proposed in this paper. The proposed strategy adds a strain control loop to the traditional constant-current constant-voltage (CC-CV) charging strategy. The strain control loop can realize real-time strain control by adjusting the charging current, eliminating the need for complex models. In the study, the CC-CS strategy achieved fast charging of 0 to 80 % SOC in 10.2 min with a cycle life of more than 500 cycles. Compared to the CC-CV charging strategy, the CC-CS strategy reduces the charging time by 6.7 % and the capacity loss by 36.24 % at the same expansion strain limit. Under the same charging speed, the CC-CS strategy reduces the expansion strain by 8.9 % and the capacity loss by 53.96 %. In summary, the proposed CC-CS charging strategy can improve the charging speed and reduce capacity loss, which shows the superiority of this strategy.