An Ionic Liquid‐Based Gel Electrolyte: Formation Mechanism and Feasibility for Lithium Metal Batteries

Abstract

Abstract Quasi‐solid‐state electrolytes (QSSEs) based on ionic liquids are recognized as one of the frontrunners of electrolytes for ensuring the safety and high energy density of next‐generation lithium batteries. However, the incapacity of such systems to meet the performance demands of batteries is significantly subject to the properties of the electrolyte and the intricacies of related interfacial processes. Recently, we have designed a high‐performing pyrrolidinium bis(trifluoromethylsulfonyl)imide (Py14TFSI) based QSSE (Py‐Gel), with introducing LiBF4 and LiCl, which served as a system for probing the dynamic Li deposition mechanism. Herein, we focus on understanding the mechanisms of Py‐Gel formation and examining the chemistry and structure as well as the properties of the solid‐electrolyte interphases (SEIs) formed in the Py‐Gel and their influences on Li deposition. Spectroscopic characterizations suggest the existence of a cross‐linked structure in Py‐Gel, for which multiple intermolecular/intramolecular hydrogen bondings and ionic coulumbic interactions among Py cations, TFSI− anions, and Li salts are responsible. The Py‐Gel electrolyte exhibits exceptional electrical properties at room temperature. Different SEIs are prepared in the Py‐Gel via electrochemical protocols to elucidate that the synergy between a well‐featured electrolyte and an outstanding SEI is vital for stable cycling of Li metal anodes in such a QSSE.

Keywords

• quasi-solid-state electrolyte
• lithium metal deposition
• solid-electrolyte interphase
• ionic liquid