Modeling Ionic Liquid Based Electrolytes for Lithium Batteries

Abstract

Based on ever-growing societal demand for stable energy supply, recent times have witnessed an increasing emphasis on developing energy storage devices such as batteries with improved specific energy and specific power. Among the myriad energy-storage technologies, rechargeable lithium ion batteries are widely used as energy sources for a range of portable electronic devices because of their relatively high specific energy storage capabilities [1]. However, the highest energy storage capacity achieved by a state-of-the-art lithium ion battery is too low to meet current demands in larger applications such as in the automotive industry [1]. The limitation is due, in part, to the limited ionic conductivity of currently used organic electrolytes coupled with their volatility, electrochemical instability and flammability, which raises safety concerns. The development of new generation of lithium ion batteries with significantly improved energy storage would require the selection of novel electrolyte materials with improved performance without compromising on safety standards. In recent years, there has been growing interest in the development of room temperature ionic liquids because they have extremely low vapor pressure, are stable at high temperatures, are highly resistant to oxidation and reduction, possess high ionic conductivity and have tunable electrochemical properties. However, the ionic conductivity of ionic liquids doped with lithium salt is extremely sensitive to the molecular structure of the ions as well as the extent of coordination between neighboring ionic species. In an effort to understand how atomistic interactions determine transport properties of ionic liquids, in the current study, we simulated lithium salt doped pyrrolidinium based ionic liquids using fundamental atomistic simulations. Properties such as density and self-diffusion coefficients were determined from molecular dynamics simulations and compared to experimental data to validate our model. Our simulations indicate that the mobility of lithium ions is limited due to association with multiple salt anions.