Supplementary Information (ESI) available: Schematic of a setup for polysulfide permeation tests; SEM image of the as-prepared carbon nanofiber paper electrode; BET surface area and pore volume of the un-activated versus CO2activated CNF paper; Molecular structures of the original Nafion and lithiated Nafion materials; Pictures of fresh and cycled Nafion membranes;The development of lithium-sulfur (Li-S) battery technology is experiencing a critical challenge due to the migration of the soluble polysulfide species from the cathode to the lithium-metal anode which results in poor cyclability of the cell. To overcome the above issue, use of lithium-ion conductive membranes instead of the traditional porous Celgard membrane as the separator/electrolyte is one of the promising approaches. In this study, a lithiated Nafion membrane is used as a cation-selective electrolyte for Li-S batteries to suppress the polysulfide diffusion. An advanced cathode structure containing a high-surface activated carbon nanofiber (AC-CNF) current collector filled with dissolved lithium polysulfides and a thin AC-CNF upper current collector is used to improve the sulfur utilization. The Li-S battery system with the lithiated Nafion membrane and the sandwich cathode exhibits significantly enhanced cyclability relative to the cells with the traditional liquid-electrolyte integrated porous separator.

A facile functional group developed on the polypropylene (PP) battery separator significantly suppresses the polysulfide-shuttle behavior in Li–S batteries.

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