Modulating entropic driving forces to promote high lithium mobility in solid organic electrolytes

As large-scale lithium-ion battery deployment accelerates, continued use of flammable organic electrolytes exacerbate issues associated with battery fires during operation and disposal. While ionic liquid-derived electrolytes promise safe, nonflammable alternatives to carbonate electrolytes, use of ionic liquids in batteries is hindered by poor lithium transport due to formation of long-lived lithium-anion complexes. We report the design and characterization of novel ionic liquid-inspired organic electrolytes that leverage unique self-assembly properties of molecular diamond templates, called “diamondoids.” Combining thermodynamic characterization, vibrational and magnetic spectroscopy, and single-crystal X-ray analysis, we determine that diamondoid-functionalized cations can facilitate formation of molecularly porous phases that resist restructuring upon dissolution of lithium salts. These electrolytes can suppress lithium-anion coordination, manifesting in substantially enhanced lithium-ion mobility in the organic ion matrix. Our results provide a new paradigm for enhancing lithium mobility in solid electrolytes by tuning entropic self-assembly to enhance organic cation-anion interactions, suppress lithium-anion coordination, and increase lithium mobility in solid electrolytes.