Epoxy-Ether Network Binder Empowers Ultra-High Sulfur Loading in Practical Lithium-Sulfur Batteries

Achieving high energy density and long-term cycling stability in lithium-sulfur (Li-S) batteries under practical conditions, namely high sulfur loading (≥ 5 mg cm^-2) and lean electrolyte content (E/S ratio < 5 µL mg^-1), remains a formidable challenge due to severe volume expansion, interfacial instability, and polysulfide shuttling. Herein, a rationally designed 3D cross-linked polyether binder (PTPO) is reported, synthesized via cationic copolymerization of glycerol triglycidyl ether (TEP) and 1,3-dioxolane (DOL). This multifunctional binder integrates high mechanical flexibility, superior interfacial adhesion, and strong chemical affinity toward lithium polysulfides through its abundant ether linkages and epoxy groups. The 3D polymer network not only accommodates the volumetric stress during cycling but also effectively suppresses the shuttle effect, thereby enhancing electrochemical stability. As a result, Li-S cells employing the PTPO binder deliver a high areal capacity of 7.62 mAh cm^-2 and a cell-level energy density of 301 Wh kg^-1 under an ultra-high sulfur loading of 11 mg cm^-2 and E/S ratio of 6.4 µL mg^-1. Notably, a proof-of-concept pouch cell achieves an initial capacity of 2.25 Ah, underscoring the practical viability of the PTPO binder. This work demonstrates a new design paradigm for functional polymer binders, offering an integrated solution for interfacial stabilization and performance enhancement in next-generation, high-energy-density Li-S batteries.