Experiment-Based Determination of the Optimized Current Level to Achieve Multiple Constant Current Charging for Lithium-Ion Batteries

Abstract

This study experimentally tested a multi-stage constant-current (CC) charging method for lithium-ion batteries controlled by the state-of-charge (SoC) discretization. The Taguchi method was used in the experiments to take three different charge performance objectives, including the charge time, charge efficiency and average cell surface temperature rise, into consideration at the same time to determine the most preferable one. Under the triple-objective optimization, with an equal discretized <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SoC</i> strategy, the three-stage CC (3SCC) protocol was found to yield much shorter charge time than the four- and five-stage CC protocols, while no significant differences were found in the charge efficiency and average cell surface temperature rise when the three CC protocols with different stages were employed. Thus, an additional performance objective, the energy loss, was used in a further investigation on the 3SCC protocol. In this investigation, a quad-objective problem was formed to determine whether the 3SCC protocol with unequally discretized <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SoC</i> intervals in each stage would produce better outcomes than the protocol with equally discretized <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SoC</i> intervals or vice versa. The results indicate that the 3SCC with the unequal <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SoC</i> discretization strategy reduces the energy loss by 1.82%, decreases the charge time by 4.27%, increases the charge efficiency by 0.32%, and lowers the average cell surface temperature rise by 12.5%, compared to the results yielded with the equal <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SoC</i> discretization in each stage.