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 exacerbates issues associated with battery fires
during operation and disposal. While ionic liquid-derived electrolytes
promise safe, nonflammable alternatives to carbonate electrolytes,
the use of ionic liquids in batteries is hindered by poor lithium
transport due to the 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 the 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.