Toward high-performance ionic liquid-based quasi-solid-state electrolytes: Tunable electrochemical properties by introducing suitable diluents

Superior to conventional liquid electrolytes, incombustible ionic liquids (ILs) with wide electrochemical stability windows show privilege to endow quasi-solid-state electrolyte (QSE) with benign interfacial contact with both metallic Li and high-voltage cathode, which bodes well for implementation of high-performance solid-state Li metal battery. But regardless of its merits, the inherent high-viscosity and frail interphase chemistry of IL towards cathodes still jeopardize ionic conductivity within QSE and even crossing the interface, and should be overcame. Herein, we creatively introduce N, N-Dimethyltrifluoroacetamide (FDMAC) into QSE fabrication, design a quasi-solid-state electrolyte (QSE-EF) by hybridizing FDMAC/EMImFSI-based IL mixture and nano-LLZTO@PVDF-HFP. This FDMAC with well compatibility to IL, significantly decreases the viscosity but without sacrificing noncombustible feature. With the aid of FDMAC, QSE-EF exhibits fast ion-conducting and high Li+ transference number. More importantly, FDMAC also contributes to tuning interphase chemistry, and therefore, the high compatibilities of both QSE-EF|Li and QSE-EF|NCM622 interfaces are fulfilled involving profitable CEI&SEI establishment. Consequently, the assembled NCM622|QSE-EF|Li cell delivers outstanding electrochemical behaviors even at 4.4 V high voltage. 1.0 Ah NCM811||Li pouch cell also shows satisfactory energy density (350 Wh center dot kg(-1)) with negligible capacity loss. This work provides a feasible strategy to circumvent inherent defect of ionic liquid in QSE, and emphasizes the importance of tuning compatible interfacial chemistry in further QSE design.