Doctor of Philosophy (PhD)
Nonaqueous electrolytes play an important role in electrochemical devices such as flip chip and lithium-air batteries. In this work, we examine ammonium-Cu, Sn and Li interactions in nonaqueous electrolytes to optimize the future flip chip flux and electrolyte additive of lithium-air battery. The activity of halogen-free carboxylic acid flux is considered one of the most important aspects in controlling flip chip joint quality recently. CuOx removal effectiveness of carboxylic acid solutions at Cu substrates using electrochemical methods at elevated temperatures from 100ºC to 180ºC is studied thoroughly by chronopotentiometry and gravimetric analysis. Carboxylic acid-based solutions with ethanolamine show oxide removal rates similar to hydrochloric acid solutions at temperatures above 140ºC. Sn (II) and Sn (IV) voltammetry shows Sn2+ and Sn4+ can form Sn-carboxylate complex and dissolve into the solution. XPS results indicate under high temperature (180 ºC) and relatively low pH (~2.50), carboxylic acid can clean the surface of Sn as well as halide acid. Equilibrium coefficients between the complexes are obtained and potential-pH diagrams for adipic acid and maleic acid in PEG are presented. Ammonium cations are known to interact with superoxides (O2-) or peroxides (O22-) and to affect the reversibility of lithium-air battery reactions. Here we study the reversibility of reduced oxygen in dimethyl sulfoxide using seven different ammonium cations. Results from cyclic voltammetry show superoxide selectivity and reversibility are generally improved with larger ammonium cations. XANES (X-ray adsorption near edge structure) analysis also shows the ammonium species influence selectivity in lithium-containing electrolytes including up to a ~10% increase in the formation of Li2O2. The nature of selectivity enhancement is believed to be associated with improving the stability of the O=O bond and possible mechanisms are proposed.
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Qu, Guoying, "Electrochemical Study of Ammonium Interaction with Au,Sn and Cu Electrodes in Nonaqueous Electrolytes" (2015). LSU Doctoral Dissertations. 3261.