Fire-Retardant Pyrrolinium-Based Ionic Liquids As Electrolytes for Lithium Ion Batteries
The ILs are salts that remain as liquid at room temperature even if they are composed of ionic species, cations and anions. Due to the ionic nature in bonding, ILs show favorable physicochemical properties such as high ionic conductivity, non-volatility, and non-flammability as well as a wide liquid range and wide electrochemical stability window. Previously reported imidazolium-based ILs with low viscosity and high ionic conductivity have some defects such as decomposition of an acidic proton at the C-2 position. To overcome the decomposition imidazolium ring, we have studied saturated cyclic ammonium-based ILs based on pyrrolidinium or piperidinium, which showed more stable electrochemical behavior compared to the imidazolium-based ILs, but less favored physicochemical properties such as high viscosity and lower ionic conductivity.
In this work, some novel pyrrolinium-based ionic liquids have been prepared and studied as electrolytes for LIBs to address those problems. Introduction of a beneficial functional group such as an oxygen atom into the partially saturated pyrrolinium ring was expected to give some positive effects on both the electrochemical stability and the physicochemical properties. Therefore, several target ILs that were synthesized in the present study showed higher thermal stability than the combustible organic solvent such carbonates. We will present the thermal, physicochemical, and electrochemical properties of several pyrrolinium-based ionic liquids as electrolytes, which are compared to those of the conventional carbonate.
 Bull. Korean Chem. Soc., 2006, 27, 847