A Synergistic Binder with Stress-Resilient and Polysulfide Adsorption to Enhance the Cycle Stability of Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) are regarded as a promising high-density energy storage system due to their high theoretical capacity (1675 mA h g–1) and energy density (2500 W h kg–1). However, the commercialization of LSBs has been impeded by the shuttle effect of intermediate lithium polysulfides (LiPSs) and the significant volume expansion of sulfur species during the discharge process. These disadvantages result in rapid capacity decay and the irreversible loss of active material, ultimately leading to the short cycle life of the LSBs. In this study, we propose a synergistic polyurethane-polyethylenimine (PEP) binder designed to provide exceptional stress resilience and strong chemical interactions with LiPSs, addressing the critical challenges of the shuttle effect and electrode instability in sulfur cathodes of LSBs. The excellent stress resilience of the PEP binder accommodates the stress generated during the volume expansion of sulfur species over repeated cycling conditions, leading to stabilizing the sulfur cathode surface and preserving Li-ion (Li+) transfer pathways. Furthermore, the abundant polar groups in PEP, including ether, urethane, and amine groups, facilitate Li+ transport while effectively interacting with soluble LiPSs to suppress the shuttling behavior. Consequently, the cell with the PEP binder demonstrated favorable LiPSs conversion, superior electrochemical performances, and improved redox reaction kinetics compared to those with poly(vinylidene fluoride) (PVDF) and epoxy-terminated polyurethane (PUE) binders. This research offers a strategic methodology for designing a multifunctional polymer binder to develop high-performance LSBs.