Date of Award

Spring 1-1-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Advisor

Sehee Lee

Second Advisor

Heather Platt

Third Advisor

Conrad Stoldt

Fourth Advisor

Ronggui Yang

Fifth Advisor

Wei Zhang

Abstract

Emergent technologies, such as electric vehicles and grid energy storage, are driving iterations of the lithium-ion battery (LIB) to exhibit enhanced safety and higher temperature capabilities. The commercial LIB based on organic liquid electrolytes presents a variety of safety concerns most notably flammability. Batteries encompassing inorganic solid electrolytes, known as solid-state batteries, have attracted significant attention in recent years due to resolution of overheating and thermal runaway, as well as lithium-ion conductivities matching liquids yet still maintaining a lithium transference number of unity. With commercial deployment rapidly approaching, solid-state research has been intensified to resolve many of the problems introduced once a liquid is replaced with a solid.

The most challenging problems presented in solid-state batteries are interfaces. These interfaces are present on a variety of length scales: between lithium and electrolyte, electrolyte and binder, active material and conductive additives, and within the active material itself. To mitigate many of the interfacing problems, a materials and/or engineering design approach is employed dependent upon the situation.

Fundamentals of electrolytic stability, particularly with Li10SiP2S12, against metallic lithium are explored including the effects of the decomposition layer on battery performance. Mixed conductors, such as tin and TiS2, are used for amplifying reaction area and simplifying charge transfer when interfacing with the active materials of silicon and FeS2, respectively. A new design approach is demonstrated on producing thin solid membranes utilizing a self-healing polymer to form an in-situ polymeric matrix for mechanical strength and enhanced conductance. The new membrane is demonstrated as a self-optimizing interface to suppress the formation of lithium metal dendrites. In the final chapter, the solid interfaces are taken advantage of to demonstrate a new phenomenon of charge storage that is only present in the solid-state - pseudocapacitance in disordered LiTiS2.

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