Nanocomposite Ionic Liquid Electrolytes for Li-Ion Batteries

Abstract

Ion-conducting polymer based membranes have been widely studied for several low temperature energy and environmental applications. One major problem with such polymer based membranes is their thermal stability, limiting the operating temperature of the devices. Room Temperature Ionic Liquids (RTILs) constitute an interesting class of compounds that is being investigated for many applications due to their high thermal and electrochemical stability and negligible vapor pressure. These electrolytes can be customized and tailored to achieve desired properties. Due to their intrinsic viscosity, RTILs present intermediate values of ionic conductivity at room temperature and extreme conductivities at higher temperatures. However at high temperatures, RTILs lose mechanical stability due to decrease in viscosity and it becomes an impossible task of forming stable membrane structures. It is thus necessary to provide essential mechanical stability to the RTILs by the use of an ion-permeable separator with comparable thermal and electrochemical stability. Herein, we design and develop RTILs based high temperature stable ion-permeable membrane using boron nanoparticles. Boron nanoparticles serve as fillers to increase the diffusion of RTIL while still being electrically insulating and mechanically robust. The ionic conductivity of thus formed composites has been assessed at temperatures ranging from room temperature to 150°C using Electrochemical Impedance Spectroscopy. Scanning electron micrographs of the composite also show no visible morphological changes indicating high thermal and mechanical stability. Thus, these RTILs based nanocomposite membranes could be an ideal candidate for high temperature application where ionic conductivity is of primary concern.