Reduced Graphene Oxide/Few-Walled Carbon Nanotube Composite Films for Shuttle Suppression in Lithium-Sulfur...

Lithium-sulfur (Li-S) batteries offer high theoretical energy density but are critically limited by the dissolution and migration of soluble polysulfide intermediates, leading to capacity fading and poor cycling stability. In this work, free-standing reduced graphene oxide/few-walled carbon nanotube (rGO@FWCNT) composite membranes are investigated as functional films for Li-S cells, with emphasis on the role of interfacial chemistry. FWCNTs provide mechanical robustness and efficient electronic percolation, while rGO introduces tunable surface functionality and morphology. The composite films exhibit a highly wrinkled, lamellar architecture composed of partially stacked rGO sheets interconnected by a three-dimensional nanotube network, favoring electrolyte infiltration and ionic transport. Despite a decrease in intrinsic rGO conductivity with increasing functionalization, highly functionalized rGO@FWCNT membranes significantly enhance apparent Li⁺ diffusion through surface-assisted diffusion mechanisms mediated by oxygen-containing functional groups. In parallel, these membranes effectively confine soluble polysulfides near the cathode region, suppressing their migration while acting as electrochemically active extensions of the sulfur cathode. As a result, internal resistance, ohmic polarization, and charge-transfer resistance associated with sulfur redox reactions are substantially reduced. Among the investigated systems, the highly functionalized rGO300@FWCNT membrane (24.3 wt % O) delivers the best electrochemical performance, achieving a discharge capacity of 1143 mAh g^-1 at C/10 along with enhanced rate capability and cycling stability. These results highlight the importance of rational interfacial design in functional membranes for advanced Li-S batteries.