Synthesis and Analysis of Ionic Liquid As Additive for Li-Ion Battery Electrolyte

Abstract

Lithium ion batteries are promising power sources for various applications such as portable electronics and electrical vehicles, due to their high specific energy density and long cycle life. As one key component of lithium ion battery, the electrolyte should allow lithium ion transport but prevent electron conduction. One big challenge of lithium ion battery is that the high voltage and high current in the charge process can cause self-decomposition of the electrolyte, leading to combustion of the battery. In order to solve the combustion problem in the fast charge process, new electrolyte materials with high ionic conductivity and good chemical stability are urgently needed.Ionic liquid is usually organic salt consisting of anion and cation with low vapor pressure, high boiling point, high ionic conductivity, large specific heat capacity, and non-flammable characteristics. Ionic liquid is aqueous at or near the room temperature. The features of ionic liquid such as the high heat resistance and wide liquid temperature range make it a promising electrolyte material for lithium ion battery.This project aims at tailoring the suitable structure of ionic liquid as the additive for lithium ion battery. Our ionic liquid is a designed composition of anion of TFSI as SEI forming additive and imidazole based cation. A two-step process has been developed for synthesizing ionic liquid. The physical and chemical properties of the ionic liquid were measured to evaluate the feasibility of applying ionic liquid to lithium ion battery.Both the density and the viscosity of the ionic liquid are measured at different temperatures. The density was found to decrease linearly with temperature in both single and binary system. The determined negative excess molar volume of ethyl acetate and ionic liquid system is relative to the interaction between different molecules. The viscosity of the analyzed electrolyte solvent was found to decrease linearly with increasing temperature. Arrhenius-like law was found to be able to fit the measured data well. The fitting parameters were able to predict viscosity at different temperature.The conductivity of the whole electrolyte system and compatibility with the active materials will be tested and discussed in the next study.