Impact of Different Conductive Polymers on the Performance of the Sulfur Positive Electrode in Li–S Batteries

Abstract

Sulfurparticleswerecoatedwithconductivepolymerlayers bydielectricbarrierdischarge(DBD)plasmatechnologyunderatmospheric conditions(ambientpressureandlowtemperature).TheDBDplasma processisadryandsustainable(solvent-free,limitedenergyconsumption) techniquecompatiblewithupscaling.Differentconductivecoatedsulfur materialswereproducedandlabeledas“PEDOT-S”[poly(3,4-ethylene dioxythiophene-sulfur)],“PANI-S”(polyaniline-sulfur),“PTs-S”(polythiophene-sulfur),and“PPy-S”(polypyrrole-sulfur).Thecorresponding electricalconductivitiesweremeasuredat10−5,10−6,10−7,and10−8S/ cm,respectively.Theroleoftheconductivecoatingistoenhancethe electrochemicalperformanceofLi−Scellsbyimprovingtheelectronic conductivityofthesulfurparticlesandpreventingthewell-known polysulfideshuttlephenomenon.Avastrangeofcharacterizationmethods includingconductivityanalysis,X-raydiffraction,scanningelectron microscopy,X-rayphotoelectronspectroscopy,andcarbon-13NMR(nuclearmagneticresonancespectroscopy)wereusedto assessthechemicalcharacteristicsusingthedifferentconductivepolymer-coatedsulfurmaterials.Inthecoatedsulfursamples, fragmentationofaromaticringswasobserved,88%forthePTs-Sand42%forthePEDOT-S,whileitisverylimitedforthePANI-S. Suchaphenomenonhasneverbeenreportedintheliterature.Theuncoatedandcoatedsulfurpowderswereused(asactive material)inpositiveelectrodesofLi−Scellswitharelativelyhighsulfurloadingof∼4.5mg/cm2usingLiPAA(lithiumpolyacrylate) asan(aqueous)binder.Long-termgalvanostaticcyclingatC/10andmulti-C-ratetestsshowedthecapacityfadeandratecapability lossestobehighlymitigatedforcellscontainingconductivepolymer-coatedsulfurincomparisontocellsusingtheuncoatedsulfur. Kineticinvestigationsbycyclicvoltammetryandelectrochemicalimpedancespectroscopyanalysesundoubtedlyconfirmimproved electronandLi-iontransportwithintheelectrodescontainingconductivepolymer-coatedsulfur.Theelectrochemicalperformance canberankedasPEDOT-S>PANI-S>PTs-S>PPy-S>rawsulfur