Ionic Liquid-Tethered Hybrid Nanoparticle Electrolytes For Secondary Lithium Batteries

Abstract

Rechargeable lithium-based battery is one of the most promising battery candidates for high energy storage devices. Batteries containing lithium metal, eschewed the use of carbon supporting materials can lead to as much as a ten-fold improvement in anode storage capacity from 360 mAh g-1 to 3860 mAh g-1 and would open up opportunities for high energy un-lithiated cathode materials such as sulfur and oxygen, among others. Unfortunately, significant improvements in safe and stable battery performance are needed due to the non-uniform lithium deposition on the negative electrode. These uneven dendritic structures increase the potential risk of cell short-circuiting, energy fading or even fire hazards. Recent discoveries and advances have focused on electrolyte reconfigurations for the sake of suppressing or even eliminating dendrite formation. Of the various options, ionic liquids offer multiple synergetic properties that make them attractive electrolytes for extending lifetime and safety of LMBs. Their inherently low vapor pressure, non-flammability, good electrochemical stability in the presence of metallic lithium make ILs excellent choice in fail-safe LMBs. When anchored to metal oxide nanoparticle surface, it promotes the mechanical strength as well as maintaining the advantages of ILs. This dissertation researches ionic liquid-tethered hybrid nanoparticle electrolytes with several goals: improving room temperature ionic conductivity of the electrolytes while maintaining chemical and mechanical stabilities, improving lithium-ion transference number, and studying the dendritic lithium metal growth as a function of electrolyte properties. It is found that all types of IL electrolytes show improvements over the conventional electrolytes such as propylene carbonate in LiTFSI. It also found that untethered IL has comparable cell lifetime to tethered IL and piperidinium-based IL suppresses dendrite growth more efficiently than imidazolium-based IL. Later in this dissertation, we discussed the efforts of extending the cell lifetime beyond ionic 3 liquid platform. Chapter 7 and 8 evaluate the battery performance and cell lifetime by adding fluorine generating salt and by employing single ion conductor, respectively. 4