Lithium-conducting ionic melt electrolytes from oligomeric ethylene glycols: Synthesis and characterization

Commercial lithium ion cells consist of electrolytes that undergo salt concentration polarization which is acute upon high discharge currents. This type of polarization occurs as a result of the mobility of more than one ionic species in the presence of an electric field. One way to overcome it is by employing a material that would allow the mobility of one ionic species. This thesis will describe the synthesis and characterization of several fluorosulfonimide and fluorosulfonate based ionic liquids/melts as electrolytes having lithium as the only mobile ion. These materials were prepared by the nucleophilic addition reaction of a deprotonated polyether onto a perfluorovinyl ether group. Their transport, thermal and rheological properties were studied. Lithium ion cells consisting of LiCO2 cathode and Li4Ti 5O12 spinel anode were fabricated and the electrochemical cell performance of the novel electrolytes was investigated under different discharge rates. It was found that the addition of partially fluorinated polyether functionalized with fluorinated lithium imide salt into the cathode composition, and the addition of polyether solvating agent into the electrolyte contributed to improved cell performance in terms of capacity and delivered power.