LENGTH-SCALE-DEPENDENT STRESS RELIEF MECHANISMS IN HIGH PURITY INDIUM

Abstract

Lithium-ion batteries are widely used in portable electronics and electric vehicles. However, due to the presence of flammable liquid electrolytes, these devices fail catastrophically when the cell experiences a short circuit. One attractive solution to this problem is a solid-state battery. As the name implies, the flammable liquid electrolyte is replaced by a non-flammable solid-state electrolyte (SSE). The unexpected, yet frequently observed failure mechanism in these devices is the formation and growth of lithium dendrites originating at the interface between the lithium anode and the SSE. As the dendrites grow, device performance degrades. Once the dendrites completely penetrate the SSE, the device short circuits and fails. To better understand the deformation mechanisms controlling the stress concentrations thought to be the precursor to dendrite formation, this dissertation is focused on experimentally identifying the stress relaxation mechanisms operating in small, constrained volumes of high purity metals subjected to high homologous temperatures. To that end, high-purity indium is the model material examined here. Using nanoindentation and electron microscopy, the stress relaxation mechanisms controlling flow have been studied at length scales where the probability of finding dislocations is low. The significant finding is a unique, length-scale dependent competition for stress relief wherein indium, like lithium, is found to be capable of supporting 50 times the expected stress at indentation depths less than 600 nm. In conjunction, nanoindentation creep experiments have been performed within two distinctly different deformation regimes. An analytical model has been developed to rationalize the magnitude of the stress exponent based on the dominant deformation mechanism operating within each regime. Collectively, these results provide significant new insight into the stress relaxation mechanisms operating in small, constrained volumes of crystalline metals subjected to high homologous temperatures.