| In recent years, solid-state electrolytes have been widely used to provide stable electrode/electrolyte interfaces for Li-metal batteries, and more importantly, they can greatly suppress the uneven dendritic growth of Li on the surface of the electrode during each subsequent discharge-recharge cycle. In this dissertation, I have studied a solid-state electrolyte consisting of a block copolymer/lithium salt mixture, polystyrene-b-polyethylene/lithium bis (trifluoromethane sulphone) imide (SEO/LiTFSI for short), primarily through depolarized light scattering (DPLS), to obtain information about the microstructure, such as the size and density of the micron-sized coherent ordered regions (i.e. "grains"), in SEO/LiTFSI mixtures with different concentrations and molecular weights at different temperatures.;We used an ellipsoidal grain model to fit the 2D intensity profile of DPLS patterns, which contains the information about grain structure (size and shape) in SEO/LiTFSI mixtures. We rebuilt existing instrumentation and modified algorithms providing a user-friendly interface that enables the automated extraction of grain structure information from DPLS patterns.;For low molecular weight mixtures (having accessible order-to-disorder transition temperatures), the grain structure evolution of the order-forming process during the disorder-to-order transition and the order-melting process in the order-to-disorder transition are monitored using DPLS measurements. For the first time, the thermodynamic and kinetic differences between a neat block copolymer and a block copolymer/salt binary mixture have been revealed by depolarized light scattering.;For high molecular weight mixtures (no accessible order-to-disorder transition temperatures), the grain structure in a heating-quenching cycle was studied by DPLS and small angle x-ray scattering to evaluate the effect of grain structure on conductivity. However, the results obtained from DPLS measurements appeared to contradict those obtained from SAXS measurements performed under identical thermal conditions. A hypothesis based on the existence of two populations of grains, growing at different rates, has been made to explain the apparently contradictory results. Both a theoretical simulation and further experimental work have been done to verify the hypothesis and some supportive results were found. The results of SAXS and in situ AC Impedance Spectroscopy indicate the ionic conductivity of high molecular weight mixture is inversely related to the grain size. |
