Date of Award
Master of Science in Chemistry
FTIR and NMR spectroscopy were used to investigate the structure and composition of lithium ion solvation spheres of single salt electrolyte solutions composed of common lithium salts (LiTFSI, LiPF6, LiBF4, and LiClO4) dissolved in aprotic polar linear and cyclic carbonate solvents (propylene carbonate (PC), dimethyl carbonate (DMC)). The coordination of the carbonyl oxygen of the solvents to the lithium ion is observed by FTIR spectroscopy. Determination of relative percent coordination of PC and DMC was used to calculate solvent coordination numbers in a range from 2 to 7. Solvent coordination was also monitored with 13C NMR spectroscopy and agreement was found when comparing the two spectroscopic methods. Solvent coordination is dependent upon the magnitude of salt dissociation. LiTFSI, LiPF6, and LiClO4 dissociated to approximately the same degree, while LiBF4 had significantly less dissociation. Dissociation trends between salts were approximate under all solvent systems. The primary solvation sphere was determined to form contact ion pairs at low solvent to salt ratios (up to 4:1) and solvent separated ion pairs in dilute solutions up to (30:1). In dilute solutions, PC had preference over DMC for preferential solvation as expected by the magnitude of relative permittivity. This investigation was conducted in order to develop a fundamental understanding about the solution structure and aid as a tool for the ionic association evaluation of commonly used LIB electrolytes.
Chapman, Navid, "Spectroscopic Measurements of Ionic Associaition in Common Lithium Salts and Carbonate Electrolytes" (2016). Open Access Master's Theses. Paper 924.