Charge–Discharge and Interfacial Propertiesof Ionic Liquid-Added Hybrid Electrolytes for Lithium–SulfurBatteries

摘要

Even though lithium–sulfur batteries possess higher theoretical capacity and energy density than conventional lithium-ion batteries, the challenging issues such as poor electronic conductivity of sulfur, dendrite formation and subsequent polysulfide shuttling, and the undesirable interfacial properties of the lithium metal anode with an electrolyte impede this system from commercialization. To circumvent the dissolution of lithium polysulfides and to improve the interfacial properties of the electrolyte with the lithium metal anode, numerous tactics have been employed. Therefore, in this work, hybrid electrolytes composed of room-temperature ionic liquids of different cations with the bis(trifluoromethanesulfonyl)imide (TFSI) anion and a nonaqueous liquid electrolyte [1 M LiTFSI in tetraethylene glycol dimethyl ether/1,3-dioxolane 1:1 (v/v)] have been prepared, and their physicoelectrochemical properties were thoroughly investigated. The lithium surface upon cycling was characterized by Raman, Fourier transform infrared, and X-ray photoelectron spectroscopy analyses. The dendrite and shuttle current measurements also indicated the formationof a stable solid electrolyte interphase and lower polysulfide shuttlingbetween the electrodes. Among the systems examined, the hybrid electrolytecomposed of 1-methyl-1-propylpyrrolidinium TFSI exhibited appreciablecharge–discharge characteristics, better interfacial propertieswith the lithium metal anode, and increased ionic conductivity whichwere attributed to the enhanced ion-pair interaction that is presentbetween the 1-methyl-1-propylpyrrolidinium cation and the TFSI anionin the electrolyte which was substantiated by Raman analysis.