Electrochemical Transport and Reaction in Polymer and Hybrid Electrolytes for Lithium Metal Batteries

Increasing the energy density of lithium-ion batteries requires, among other advances, electrolytes that are compatible with lithium metal and next-generation cathodes. Polymer electrolytes play an important role in this regard, but overcoming slow ion transport is a major challenge. Recent advancements in time-resolved infrared spectroscopy to characterize salt diffusion in polymer electrolytes will be reported as well as efforts to electrochemically measure transference number and electrochemical reaction kinetics in these electrolytes. In addition to our efforts in developing characterization techniques, we will report recent progress in solid electrolyte development. Hybrid electrolytes that combine fast ion transport of ceramic electrolytes and processability of polymer electrolytes are promising. This requires either 1) low binder contents that maximize ceramic transport pathways or 2) unity polymer transference number that takes advantage of transport in both phases. Our progress in both of these directions will be discussed, focusing on 1) free-standing sulfide solid electrolytes with small amounts of inert binder and 2) polymer blend electrolytes. Both exhibit single-ion conduction, which yields numerous transport and efficiency advantages. The effect of processing solvent on binder-containing sulfide electrolyte properties will be covered. State of the art in the polymer blend electrolytes will also be reviewed including recent advancements from our team using precision polyanions with polyether solvating polymer. This presentation will cover miscibility, conductivity, and transference numbers as a function of composition and temperature. Distinct differences between blends containing different anionic forms will be explained in the context of ion correlation. Important future directions for polymer blend and hybrid electrolytes will also be discussed.