Synthesis and electrochemical studies of novel ionic liquid based electrolytes

"Room temperature ionic liquids (RTILs) have received substantial interest as nonaqueous electrolytes in lithium ion- and metal-air batteries in recent years due to their low volatility, non-flammability, wide liquid range, and thermal stability characteristics. Towards developing a new generation of high specific energy lithium ion batteries, a series of imidazolium and pyrrolidinium based ionic liquids were synthesized and explored as nonaqueous electrolytes in lithium-, lithium ion-, and lithium-air batteries. Pyrrolidinium-TFSI based ionic liquids have wide electrochemical stability (5.7 - 6.2 V vs Li/Li+); however, they show limited thermal stabilities and lithium cell discharge characteristics. TFSI-based ionic liquids are thermally and electrochemically more stable when compared with their BF4-based analogues. A series of fluorinated ionic liquid electrolytes were synthesized and investigated for their use in lithium-air batteries. These ionic liquids have improved the diffusion coefficient and higher solubility of oxygen when compared with currently used nonaqueous electrolytes.Cathode materials, such as LiNi1/3Mn1/3Co1/3O2 and LiFePO4, were chemically delithiated using nitronium tetrafluoroborate (NO2BF4), or disodium peroxydisulfate (Na2S2O8>), to explore their effect on the oxidative degradation of the carbonate based electrolytes. Using fluoroethylene carbonate as the electrolyte additive, electrolyte degradation was monitored by 19F NMR spectroscopy. Formation of the solid electrolyte interface (SEI) on the delithiated cathode materials was probed using surface techniques, such as X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM)"--Abstract, page iii.