Enhancing Cycle Stability via Discharge Voltage Regulation in Li–S Batteries: Impact of the Lower Cutoff Voltage on Electrochemical Stability

Abstract

The lithium–sulfur (Li–S) battery emerges as a candidate for next-generation batteries owing to its superior energy density and cost-effectiveness. Despite these advantages, the longevity of Li–S batteries remains a complex challenge. The shuttle effect has been identified as a principal factor contributing to degradation, prompting extensive research aimed at mitigating its impact. Recent studies, however, have unveiled that the presence of Li2S exerts a significant influence on the kinetics and stability of the electrochemical reaction. Although lower cutoff voltage directly controls the formation of Li2S, its relationship between lower cut-off voltage and Li2S formation has not been investigated so far. In this study, we regulated the discharge voltage and revealed the relationship between lower cutoff voltage and electrochemical stability. A low lower cut-off voltage increased Li2S formation and the first discharge capacity but reduced Li2S transformation to sulfur, as confirmed by the high overpotential and low charge capacity. Furthermore, repeated cycles at a high discharge exhibited severe capacity loss and deteriorated Coulombic efficiency. By contrast, a high lower cut-off voltage cell exhibited enhanced capacity retention with a low overpotential owing to the inhibition of Li2S formation. Thus, this study provides insights into controlling Li2S formation, which is critical to stabilizing the electrochemical reaction and enhancing the cycle stability of Li–S batteries.