Exploring interfacial and nanoscale electrical effects in solid state ionic conductors for application in low temperature solid oxide fuel cells and solid state batteries

Abstract

High-performance solid-state energy storage and conversion devices are a vital technology component of the U.S. Department of Energy’s clean and renewable energy implementation strategy. Solid-state fuel cells are important technologies for efficient conversion of a wide variety of fuels to electricity, while development of solid-state batteries is critical for safe storage of electricity generated by clean technologies. Solid-state devices are pursued due to their inherent mechanical and chemical stability at high temperatures and under harsh conditions; ensuring long-lifetime, fuel flexibility and safe operation. However, large resistance to ionic transport in the solid state, especially at low operating temperatures, severely limits the performance of solid state devices. In this work, ionic transport properties at interfaces of solid-state electrolytes have been investigated as a route for developing high performance solid state energy conversion and storage devices. Interfacial effects including the space-charge effect, the strain effect, and the curvature effect alter ionic charge carrier mobility and/or concentration at interfaces in solid-state electrolytes, leading to dramatic changes in ionic conductivity. By harnessing these energetically-favorable effects at solid-state electrolyte interfaces and fabricating interface-rich electrolytes, the total conductivity of the solid electrolyte and performance of solid-state electrochemical devices can be greatly enhanced. Interfacial effects on oxygen, hydrogen and lithium ion transport in nanocrystalline bulk samples, heterostructured thin film samples, and powder samples at high pressure (35GPa) have been studied by structural and electrical characterization techniques. The work provides important insight into interfacial effects on ionic conductivity in solid-state electrolytes relevant to current solid-state fuel cell and battery development. The fundamental understanding of interfacial effects on ionic conductivity has been widened by this study and several conclusions from the work can be applied directly to enhance the performance of solid state energy conversion and storage devices.