Ionic Liquids (ILs) are organic salts comprised entirely of organic cations and organic/inorganic anions. ILs are recognized as “designer solvents”“ due to their composition and the endless combinations of anions and cations. ILs have various outstanding properties, such as negligible vapor pressure, excellent thermal and chemical stability, nonflammability, nonvolatility, etc. These unique attributes explains the interest in ILs, which has been growing since the 1930s, for a wide variety of applications, including gas/liquid separation, chemical reaction, lubrication and electrochemical devices. Even though there are many thousands of possible combinations of anions and cations for ILs design, the choice/selection of cations and anions commercialized in electrochemical devices is much less diverse due to strict industrial standards.
Most electrolytes currently in commercial use are volatile and flammable organic solvents, so safety is a serious concern that must be addressed. The focus of this thesis is to develop halogen-free ionic liquid electrolytes to overcome the drawbacks of conventional organic solvents used in lithium-ion batteries and to gain further insight into the influence of structure on physicochemical and electrochemical properties from both theoretical and practical perspectives. This thesis describes the effects of the experimental temperature, the structure of the cation and anion, and the concentration of lithium salt on the properties of ILs. More specifically, physicochemical property measurements cover density, viscosity and diffusivity, and electrochemical property investigation includes conductivity, electrochemical window, Walden plot behavior and ionicity. Understanding these effects can not only guide practical development of safer and more liable electrolytes for lithium-ion batteries, but also pave the way for future theoretical investigation of ILs as electrolytes for lithium-ion battery applications.