Addressing Low E/S and N/P Ratio Challenges in Li-S Batteries with a Multifunctional Interlayer

Lithium-sulfur (Li-S) batteries are promising next-generation energy storage systems due to their high energy density and low cost of sulfur. However, their commercialization is hindered by the shuttle effect of soluble polysulfides and the poor rate capability, which are further exacerbated under practical conditions of low negative/positive (N/P) ratio and electrolyte/sulfur (E/S) ratio necessary for high-energy and cost-effective Li-S batteries. To address these challenges, we report the fabrication of a large-area (9.5 cm × 7.5 cm), ultrathin (90 nm), lightweight (0.05 mg cm^-2), and conductive PFSA/CNT/PEDOT:TCB (PCP) composite interlayer via the solution shearing technique coupled with Marangoni-flow-assisted film transfer, enabling uniform film formation and facile transfer of the interlayer onto a polypropylene (PP) separator. In addition to providing efficient electronic pathways, the PCP interlayer improves ionic conductivity and mitigates polysulfide shuttling through electrostatic repulsion and physical size exclusion, as validated by molecular dynamics (MD) simulations. These combined functionalities allow the PCP interlayer to overcome key challenges in Li-S batteries, leading to a 3 × 5 cm² pouch-type cell that delivers a high initial discharge capacity of 1086 mAh g^-1 over 68 cycles under practical conditions of E/S = 5 µL mg^-1 and N/P ratio = 1.3.