With the increasing needs for creating new clean and sustainable energy sources to substitute traditional fossil fuel at present, lithium-ion... Show moreWith the increasing needs for creating new clean and sustainable energy sources to substitute traditional fossil fuel at present, lithium-ion batteries as one of the most promising energy storage devices have been shown much attention. As a necessary and important component in a battery system, electrolytes need to be expanded according to the cell's requirements for varied applications. Especially nowadays, researches for safe, environmentally friendly and cost effective battery electrolyte systems are very challenging and active all around the world. This dissertation describes three different approaches to achieve an improved electrolyte system for lithium-ion batteries. For solid polymer electrolytes (SPEs), three different plasticizers have been synthesized and incorporated into a conventional poly(ethylene oxide) (PEO)-based SPEs. The room temperature ionic conductivity was significantly improved by decreasing the glass transition temperature of the polymer matrix. One new poly(ethylene glycol)-grafted-polybutadiene was designed and synthesized. Different weight ratios of new co-polymer and PEO mixtures were studied for using as polymer host for SPEs. For liquid electrolytes, two different strategies have been investigated. One is that series of small molecular weight molecular liquids were designed and synthesized to improve the low temperature performance and safety of commonly used organic carbonates systems. Different concentrations of lithium bis-trifluoromethanesulfonimide (LiTFSI) solutions were studied to find the optimized combinations. A series of new zwitterionic liquids (ZILs) were also designed and synthesized as ionic liquid electrolytes. However, this type of electrolytes is too viscous to provide a satisfied ionic conductivity, thus 2-nitropropane as a co-solvent was used here to reduce the viscosity. Last, a series of novel diphosphate-based tetra lithium salts was synthesized and studied. Solartron electrochemical analyzer was used to test ionic conductivity, electrochemical window and lithium cation transference number. The technologies of thermal gravimetric analysis and differential scanning calorimetry were used to study thermal properties of electrolytes. Furthermore, some future plans of studies in lithium-ion battery electrolyte field were also discussed. Ph.D. in Chemistry, December 2014 Ph.D. in Chemistry, December 2014 Show less
