NSF Award
2427263
Electrical energy storage is one of the most critical needs in power systems for a more sustainable future. Lithium–sulfur (Li-S) batteries are promising candidates because of their higher energy density and reduced cost due to the use of sulfur. However, a key limitation of the Li-S system is polysulfide shuttling. Shuttling occurs when polysulfide molecules from the cathode dissolve into the electrolyte and shuttle across the separator to react with the anode materials. This process is irreversible and leads to a rapidly fading capacity. This project addresses the fundamental shuttle effect of lithium polysulfides in lithium sulfur batteries with emphasis on developing surface engineered host materials for immobilizing lithium polysulfides and promoting their conversion. A series of surface engineered and shape-controlled cerium oxides will be developed and characterized to understand which structural features best limit polysulfide shutting. Such knowledge is critical for designing novel host materials and long-life energy storage systems, which will have a potentially immense impact on portable electronics, electric vehicles, and devices for intermittent renewable energy storage from solar and wind resources. The investigator will continue to support the outstanding recruitment, mentoring, and retention of minority students in STEM by providing unique research opportunities for undergraduates as early as their freshman year and with continuing scholarships to promote their retention.<br/><br/>The overall objective of this proposal is to elucidate the effect of surface engineered polar CeO2 addition as a host material via shape control (nanorods, nanocubes, and nanoctahedra with different exposed crystal planes: (110), (100) and (111)) and chemical etching treatment on the lithium polysulfides immobilization, catalytic conversion, and electrochemical performance in lithium-sulfur batteries. These findings will provide insight into a fundamental understanding of sulfur conversion chemistry and act as a guide for the future design and screening of new host materials toward achieving high sulfur loading/utilization in lithium-sulfur batteries. The investigators hypothesize that physical confinement and surface engineered polar CeO2 with distinct termination surface structures would effectively store and entrap sulfur species to prevent the dissolution and migration of intermediate lithium polysulfides avoiding the shuttle effect and capacity degradation during the electrochemical cycling. In addition, ex situ/in situ transmission electron microscopy and electron energy loss spectroscopy characterization techniques will be employed to achieve a deeper understanding of dynamic adsorption/desorption, liquid/solid and solid/solid interactions, and structural/compositional changes at the lithium polysulfides/CeO2 interface. New insights (quantitative dynamic atomic-level structural and chemical characterizations) into lithium polysulfides/CeO2 interfacial structures will provide powerful practical strategies to promote or suppress various kinds of interface phenomena. The obtained knowledge on battery chemistry of sulfur-oxide additive interaction promises long-life and high energy/power density lithium-sulfur batteries.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
