A multifunctional fire-retardant gel electrolyte to enable Li-S batteries with higher Li-ion conductivity and effectively inhibited shuttling of polysulfides

A main huddle against the practical application of lithium-sulfur battery lies in serious safety concerns due to liquid organic electrolyte, shuttling of polysulfides and formation of lithium dendrites. Herein, we have devised an asymmetric and structurally stable gel electrolyte system to enable high ionic conductivity, flame-retardancy, and effective blockage of shuttling. Such a multi-functional gel electrolyte utilizes an electro-spun network of interwoven nano-fibers of poly vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) as structural scaffolds, with SiO2-polyvinyl alcohol (SiO2@PVA) suspension being loaded at one surface by blade coating. Such asymmetrically coated PVDF-HFP membranes are highly wettable that is essential to thorough gelling, with its well-connected porous channels to enable outstanding ionic conductivity above the limit by conventional Celgard separator, to accommodate huge volumetric changes over redox reactions, to shield polysulfides and fend off lithium dendrites. Ultimately, application of the gel electrolyte to a model Li-S cell with cathode containing 90% S delivered high initial capacity of 1439 mA h g−1 at 0.1C and a remarkable cycling stability over 300 cycles at 1C. The current gel electrolyte is expected to provide a valuable means for developing safe low-cost and durable Li–S batteries of practical importance.