Stabilizing All-Solid-State Li–S Batteries by a Polysulfide-Repelling and Anode-Protecting Self-Segregated Trilayer Polymer Electrolyte

Rational management of lithium polysulfide (LiPS) transport is essential for stable, high-energy-density Li-S batteries. We introduce a freestanding, self-segregated trilayer polymer electrolyte (TLE) that forms two layers of nanometer-thin, ion-selective coatings at the cathode and anode interfaces by autonomous phase separation of two immiscible polymers while preserving a highly conductive bulk matrix. In Li-S cells, these coatings simultaneously repel dissolved LiPS at the sulfur cathode and stabilize lithium plating and stripping at the Li metal anode without sacrificing ion transport. Operando optical cell monitoring and theoretical modeling reveal that the dual-functional coatings are responsible for stable Li metal anode operation and effective shuttle suppression. The TLE enables an initial discharge capacity of 1369 mAh g^-1 (81.7% of theoretical) and maintains a stable capacity over 50 cycles at 0.2C. Fabricated by a single-step casting process, this scalable electrolyte membrane offers a practical route to durable, all-solid-state Li-S batteries.