Functional Ionic Liquid Based Electrolytes

Abstract

NOHMs Technologies is developing functional ionic liquid based hybrid electrolytes for high energy density, high voltage, and high power batteries for EV and military applications. The composition of electrolytes greatly affects the cell performance from rate capability, lithium cycling efficiency, and capacity retention at various temperatures to tolerance against electrical, mechanical and thermal abuses. Ionic liquids offer a host of attractive properties, including ultralow vapor pressure, high thermal stability, high ionic conductivity and wide electrochemical stability, which make them attractive as electrolytes. However, there are some physical property limitations that to-date has made them unattractive for lithium battery applications. High viscosity and the fraction of the ionic conductivity of the electrolyte arising from mobile lithium ions (i.e. the so-called lithium transference numbers) are typically low for these materials, which make cells assembled using ionic liquid electrolytes prone to large polarization during operation of the cell. These limitations can be easily overcome by blending ionic liquids with appropriate co-solvents. These hybrid electrolytes simultaneously overcome the poor thermal & electrochemical stability and safety problems that have plagued lithium battery electrolytes for years while still maintaining high conductivity. They provide a platform for engineering electrolytes with both chemical and interfacial tunability that beyond improving safety, expand the range of available battery form factors. During the presentation, we will show how the ionic liquid functionality affects the SEI formation on the graphite anode and high voltage stability. We intend to answer the following questions: 1) functional ionic liquid and co-solvent formulations to achieve a >4.5V electrolyte, 2) is the capacity fade dependent on the upper voltage cut-off, and 3) how the electrolyte formulations improve the capacity retention of at high voltages and elevated temperatures using 200 mAh pouch cells. Figure 1