New ether-functionalized pyrazolium ionic liquid electrolytes based on the bis(fluorosulfonyl)imide anion for lithium-ion batteries

Abstract

Four new ionic liquids (ILs) composed of ether-functionalized pyrazolium cations and the bis(fluorosulfonyl)imide (FSI) anion are prepared and characterized in this report. The physicochemical properties of these ILs, such as melting point, thermal stability, viscosity, conductivity and electrochemical stability, are systematically investigated. These four FSI-based ILs are all in the liquid state and their viscosities are lower than 40 mPa s at room temperature. The charge–discharge performances of Li/LiFePO₄ cells containing these IL electrolytes with 0.8 mol L⁻¹ LiFSI are also examined. Three electrolytes exhibit nice cycling stability at 0.1C, and the PZ2o2-2-FSI electrolyte shows excellent rate performance.