A review of composite polymer electrolytes for solid-state lithium-sulfur batteries: Synthesis methods, optimal design, and critical challenges

Solid-state lithium-sulfur batteries (SSLSBs) offer superior cathode capacity and safety for the growing electronic equipment market. However, the low ionic conductivity and high interfacial impedance of single-phase solid electrolytes hinder their application. Composite polymer electrolytes (CPEs) enhance ionic conductivity and maintain single-phase electrolyte advantages, making them promising for SSLSBs. Herein, this review focuses on the application of CPEs in SSLSBs, with the goal of identifying discrepancies between current research advancements and practical demands, as well as providing a thorough explanation of the operational principles of SSLSBs constructed with CPEs and the mechanisms of lithium-ion transport. Methods for preparing various CPEs are also examined, including solution casting, electrospinning, in-situ polymerization, and their combinations, with the advantages and limitations of these methods in the production of CPEs for SSLSBs being highlighted. In addressing the challenges associated with SSLSBs, strategies for the suppression of lithium dendrites, the enhancement of interfacial contact with electrodes, and solutions to the shuttling effect caused by polysulfides are systematically described using different CPEs. Recent breakthroughs and achievements in understanding the interaction between CPEs and polysulfides at the molecular scale via calculation models are also discussed. More importantly, the potential of CPE systems and the design of efficient CPE structures for achieving room-temperature operable SSLSBs are presented. Finally, the development of CPEs and the challenges for their application in SSLSBs are summarized and prospected. These discussions and recommended strategies will provide more approaches for the commercial application of SSLSBs with excellent electrochemical performance in the future.