Dealloying Under Conditions of Significant Solid-State Mass Transport

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TECHNICAL SUMMARY:This research program examines the kinetics of dealloying and morphology evolution in alloy systems for which the solid-state mass transport processes of lattice and grain-boundary diffusion are significant at ambient temperature. The major control parameters in the work will be the alloy composition, grain size of the polycrystalline hosts, particle size in the particulate hosts and temperature. The electrochemical parameters to be varied include dissolution under conditions of fixed voltage (chronoamperometry) and fixed current (chronopotentiometry). This will allow for the separate determination of the dependence of morphology on the applied electrochemical potential and dealloying rate. In order to examine these issues a combined experimental and computational approach is used. The alloy systems under study are Li-Sn, Li-Pb and Li-Cd. These host metals and similar ones are currently being considered as anode reservoirs in future lithium-ion batteries and have been chosen for study since they represent variations in the host crystal structures, tetragonal, face-centered cubic and hexagonal close-packed, respectively, and have a rich history with abundant thermodynamic and kinetic data available. Electrochemical methods are used to produce the alloys, measure dealloying rates and determine associated solid-state mass transport rates. Dealloying morphologies are examined using focused ion-beam machining and scanning electron microscopy. Kinetic Monte Carlo simulations are used to model morphology evolution in dealloying as a function of the electrochemical potential and dealloying rate.NON-TECHNICAL SUMMARY:This research examines morphology evolution during dealloying of low melting point lithium alloys. Such alloys are currently being considered for use in advanced lithium-ion batteries in which the dealloying process corresponds to that occurring during discharge of these battery systems. The findings likely to emerge from this research will significantly impact research in energy storage and particularly the development of new materials for future batteries. As this country considers its energy options, it will need people with combined expertise in electrochemistry and materials science to address current and future energy technologies. The scope of research in this program will afford undergraduate and graduate students the opportunity for fundamental training in an integrated materials electrochemistry laboratory environment. More generally in the area of education and training, the PI will be developing a new undergraduate course in the "materials science of electrochemical energy storage and production," and the course together with all materials will be available for colleagues to use via the worldwide web.