The Woodruff School

SUMMARY

Rechargeable batteries are at the heart of revolutionary innovations in technologies ranging from consumer electronics and electric vehicles to large-scale energy storage/conversion for intermittent renewable sources (wind, solar, etc.). All-solid-state batteries (ASBs) show great promise as next-generation energy storage architectures because of their enhanced safety and higher energy density compared to conventional batteries with flammable liquid electrolytes. However, solid electrolyte (SE) materials with good ionic conductivity and electrochemical stability are necessary for ASBs to be viable. Such SEs can be developed from rationally designed candidate materials, provided one has an in-depth understanding of ionic conduction behavior in solids and the governing structural parameters. In this dissertation, I present design strategies for several recently-developed lithium and sodium SE materials, discuss the characteristics/performance of these materials, and demonstrate the establishment of structure-property relationships in various material groups. First, a group of new Li ion conductors are designed through a joint computational and experimental study. Aided by first principles computation and in situ experimental methods, a group of oxide-based Li SEs with sphene structure and greatly improved ionic conductivities (from 10-8 to 10-5 S/cm) was identified and synthesized for the first time. Next, a series of sulfide-based Na SE materials is investigated. These materials originate from Na3SbS4 compound by iso-valent substitution and bill-mill processing. High resolution X-ray diffraction coupled with pair distribution function analysis shed light on their structural evolution during composition variation and synthesis. Lastly, a systematic investigation on Na4SnS4-based SE materials through alio-valent substitution is presented. The key underlying structural contributors for significantly improved conductivities are identified and discussed. In summary, this dissertation highlights the importance of understanding the structure-property relationship of SE materials to rationally tune material structure and composition for enhanced ionic conductivities. The material design methodologies in this work provide guidance for fast ion conductor development, which is relevant not only for the design of ASBs, but also for fuel cells, gas sensors, and other potential applications.

SUBJECT:	Ph.D. Dissertation Defense

BY:	Shan Xiong

TIME:	Wednesday, November 18, 2020, 3:00 p.m.

PLACE:	https://bluejeans.com/658642264, Online

TITLE:	Understanding Ionic Conduction in Solid Electrolytes for Lithium and Sodium Ion Batteries

COMMITTEE:	Dr. Hailong Chen, Chair (Mechanical Engineering) Dr. Meilin Liu (Materials Science and Engineering) Dr. Matthew McDowell (Mechanical Engineering) Dr. Angus Wilkinson (Chemistry and Biochemistry) Dr. Ting Zhu (Mechanical Engineering)

SUMMARY Rechargeable batteries are at the heart of revolutionary innovations in technologies ranging from consumer electronics and electric vehicles to large-scale energy storage/conversion for intermittent renewable sources (wind, solar, etc.). All-solid-state batteries (ASBs) show great promise as next-generation energy storage architectures because of their enhanced safety and higher energy density compared to conventional batteries with flammable liquid electrolytes. However, solid electrolyte (SE) materials with good ionic conductivity and electrochemical stability are necessary for ASBs to be viable. Such SEs can be developed from rationally designed candidate materials, provided one has an in-depth understanding of ionic conduction behavior in solids and the governing structural parameters. In this dissertation, I present design strategies for several recently-developed lithium and sodium SE materials, discuss the characteristics/performance of these materials, and demonstrate the establishment of structure-property relationships in various material groups. First, a group of new Li ion conductors are designed through a joint computational and experimental study. Aided by first principles computation and in situ experimental methods, a group of oxide-based Li SEs with sphene structure and greatly improved ionic conductivities (from 10-8 to 10-5 S/cm) was identified and synthesized for the first time. Next, a series of sulfide-based Na SE materials is investigated. These materials originate from Na3SbS4 compound by iso-valent substitution and bill-mill processing. High resolution X-ray diffraction coupled with pair distribution function analysis shed light on their structural evolution during composition variation and synthesis. Lastly, a systematic investigation on Na4SnS4-based SE materials through alio-valent substitution is presented. The key underlying structural contributors for significantly improved conductivities are identified and discussed. In summary, this dissertation highlights the importance of understanding the structure-property relationship of SE materials to rationally tune material structure and composition for enhanced ionic conductivities. The material design methodologies in this work provide guidance for fast ion conductor development, which is relevant not only for the design of ASBs, but also for fuel cells, gas sensors, and other potential applications.