Kamphaus, Ethan Phillip (2021-03). Physical, Chemical, and Reactivity Behavior of Materials and Processes of Lithium Sulfur Batteries. Doctoral Dissertation.
Thesis
In the field of energy storage, there are many possible battery systems each with different chemistries and characteristics. The current gold standard battery of rechargeable battery technology is the lithium-ion battery due to the cycle life and energy storage capabilities. Though the lithium-ion battery's use has transformed many technologies and advanced electronics, there is a demand for higher performance battery systems. One such next generation battery technology is the lithium-sulfur battery. This technology offers a significant improvement over the theoretical characteristics of the lithium-ion battery (~5 times the specific energy). Given this massive improvement over the current lithium-ion battery, the lithium-sulfur battery has the potential to be a revolutionary technology allowing for long range electric vehicles (>300 miles in one charge) or push lithium battery technology into off-grid energy storage. However, the lithium-sulfur battery is not a practical and commercial battery system yet due to two major problems: The use of lithium metal and the polysulfide shuttle effect. In order to achieve a higher capacity, lithium metal is used as one of the electrodes which is challenging due to its high reactivity and formation of the passivating solid-electrolyte interphase layer. The polysulfide shuttle effect creates a cascade of performance issues throughout the battery due to the dissolution and subsequent mass transfer of sulfur reduction intermediates. These problems must be solved or addressed in order for the lithium-sulfur battery to become a practical technology. Currently, there is a lack of fundamental knowledge with regard to the structure and mechanisms of transport and reaction of polysulfide species. This is a major problem with attempting to design solutions to the mentioned problems because these fundamental processes must be known in order to make intelligent decisions in optimization and design. In this work, the fundamental structure, properties and processes of polysulfide species are investigated throughout the battery (both electrodes and the electrolyte) with computational chemistry methods. From the investigations of the nanoscale fundamentals of the polysulfide shuttle effect, different mitigation strategies are evaluated and design recommendations are made for SEI and electrolyte composition.
