<p>Lithium-sulfur (Li-S) batteries are promising candidates for high-energy-density storage but face challenges such as polysulfide-shuttling and safety concerns associated with liquid electrolytes. While solid-state electrolytes offer potential solutions, they often suffer from low ionic conductivity at room temperature and poor interfacial contact. In this work, we present a composite solid electrolyte (CSE) engineered using F127 triblock copolymer via a scalable solution-casting approach. F127 serves a triple role: its micelles template the assembly of PVDF-HFP to suppress crystallinity (reducing the relative crystallinity from 47.1% to 8.5%), promote the formation of an interpenetrating polymer network for mechanical robustness, and catalyze interfacial interactions to facilitate Li⁺ transport. This synergistic microstructure establishes multi-channel pathways for efficient ion conduction while improving electrode/electrolyte adhesion. The optimized CSE with 10 wt.% F127 (CSE10) achieves a room-temperature ionic conductivity of 6.9×10⁻⁴ S cm⁻¹—surpassing most reported PVDF-HFP-based CSEs—along with a tensile strength of 57.6 MPa, effectively resisting lithium dendrite penetration. When applied in solid-state Li-S cells, CSE10 delivers a high initial capacity of 1121 mAh g⁻¹ at 0.1C and exceptional cycling stability, retaining 639 mAh g⁻¹ after 100 cycles at 1C with a minimal decay rate of 0.07% per cycle. This study highlights the effectiveness of F127 as a multifunctional microstructure regulator in developing high-performance and safe solid-state Li-S batteries.</p>