Steering Three-Dimensional Li ₂ S Deposition via a Janus-Structured Separator with a Dual-Ion/Electron-Conducting Interfacial Mediator for Low-Temperature Lithium–Sulfur Batteries

Lithium-sulfur (Li-S) batteries face critical challenges from sluggish sulfur redox kinetics, polysulfide shuttle, and lithium dendrite growth. Herein, a Janus-structured separator featuring a miscible polystyrene/poly(methyl methacrylate) (PSA) gel buffer layer and a cathode-facing single-layer coating of ordered mesoporous carbon (s-OMC) is prepared as both charge-carrier transport vehicle and electron transfer mediator. The PSA layer endows dendrite-free lithium deposition and physically isolates the conductive s-OMC from the anode to prevent short circuits. Meanwhile, s-OMC with parallel aligned nanochannels enhances Li⁺ diffusivity and supplies abundant electrons to steer controlled three-dimensional Li₂S deposition. This dual-functional architecture effectively mitigates interfacial passivation and accelerates sulfur redox kinetics. Consequently, Li-S batteries based on the Janus-structured PP/PSA/s-OMC separator deliver exceptional electrochemical performances under practical conditions, including stable cycling at a high sulfur loading (5.3 mg cm⁻² or 5.43 mAh cm⁻²), outstanding rate capability (704 mAh g⁻¹ at 5 C), and remarkable low-temperature operation (922 mAh g⁻¹ at -20 °C).