Non-technical Abstract: Within a Li-ion battery, the electrolyte facilitates the conduction of Li ions between the two electrodes (cathode and anode) that store energy. Better solid state electrolytes will enable the development of safer batteries with improved lifetimes, and have the potential to completely eliminate the flammability and toxicity associated with current organic electrolyte technologies for Li-ion batteries. This project will lead to the discovery of better solid state electrolytes both by evaluating new candidate compounds and by carrying out fundamental studies to better understand how Li ions diffuse through solid electrolytes. This work will be supported by diffraction studies at national user facilities that will allow the accurate determination of the crystal structure of solid electrolytes at the atomic scale, allowing the mechanism of ionic motion to be understood. This project will additionally support the training of young researchers in advanced structural characterization methods through a national summer school on structural analysis to be offered every year. The integration of solid state electrolytes into next-generation Li-ion batteries has the potential to completely eliminate battery fires, to extend the range and reduce the cost of electric vehicles, and to facilitate the integration of renewable energy sources into the electrical grid by providing low-cost load leveling.
In the last 50 years, only about half a dozen structural families of superionic conductors for Li and Na ions have been discovered. A major goal of this proposal is the identification of new superionic conductors, an aim which will be supported by fundamental studies to identify and control the structural features that most directly influence the ionic conductivity. The development of improved solid state superionic conductors that can replace the organic liquid electrolytes (which are responsible for major flammability, toxicity, and lifetime issues) in current Li-ion battery systems will lead to safer batteries with improved lifetimes. Fundamental studies will be carried out to understand and optimize the conductivity of ions at room temperature within a special CUBICON ceramic host whose cubic symmetry allows ions to be transported equally well in all directions, unlike most other alternative systems. First, chemical syntheses (solid state and ion exchange) will be carried out to prepare a variety of single-phase CUBICON materials of known and novel compositions. Next, X-ray and neutron diffraction studies will be carried out to accurately locate the positions of atoms (enabling both qualitative estimates and quantitative calculations of the strength of bonding and mobility of ions). New in situ methods will be applied to determine ion exchange mechanisms relevant to their synthesis. Finally, physical properties measurements will be done to assess the ionic and electronic conductivity of these materials, and to identify design rules than can be used to prepare CUBICON materials with optimal properties.
