Solid lithium ion conductors and thin films in hybrid electrolytes for next-generation batteries

Thesis (Ph. D.)--University of Rochester. Department of Chemical Engineering, 2020.
In promising next generation electrochemical cells for energy storage like Li-air and Li-sulfur, Li metal is the preferred anode to be used, mainly due to its high specific capacity (an order of magnitude higher than graphite). However, lithium poses, among others, two important concerns, namely its high reactivity and the dendritic structure formation during cycling, which compromises battery life and safety. In order to address these issues, solid electrolytes are proposed to replace conventional membranes and separators. The combination of a solid and a liquid electrolyte is a concept referred to as “hybrid electrolyte”. The liquid electrolyte facilitates ion transport and ensures good wetting of the electrode surfaces, while the solid electrolyte isolates the lithium anode from being exposed to the liquid environment and mechanically suppresses dendrite evolution, while still allowing for ionic transport. Several classes of solid electrolytes have been under investigation by the research community for hybrid electrolyte applications. These electrolytes can be in bulk format with thickness of several microns, or in thin film format with thicknesses varying from a few nanometers to a few microns. The liquid electrolyte can be either aqueous or aprotic, based on the compatibility with the other components of the battery. Some classes of solid electrolytes, like NASICON type are unstable against lithium metal, whereas others like Garnets, are very sensitive to the environment. To address chemical stability, thin film intercalation materials are also proposed to be used as protection layers at the interface between the solid electrolyte and the liquid electrolyte.Overall, in order to implement hybrid electrolytes in cells, the structural, chemical and electrochemical stability between the components needs to be ensured. In this thesis a variety of hybrid electrolyte combinations has been investigated, as well as the fabrication of protective coatings. Physical Vapor