Modulating Entropic Driving Forces to Promote High Lithium Mobility in Solid Organic Electrolytes

Abstract

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.

Linking Electric Double Layer Formation to Electrocatalytic Activity

“…Ionic liquids are widely studied model systems for exploring electric double layer formation (Figure ). ,,− As neat liquid salts often exceed 4 M in ion concentration, ionic liquids provide opportunities to study double layer formation in highly correlated electrolytes. , Ionic liquids also have many technologically advantageous properties, , such as tunable molecular structures, high electrochemical stability, and negligible volatility. As such, ionic liquids have been broadly applied as electrolyte additives within the electrocatalysis community to control electrochemical reaction rates and selectivity. ,,− …”

Electrostatic Correlations Lead to High Capacitance in Zwitterion-Containing Thin Films

“…The usefulness of ILs in devices such as batteries and fuel cells is, however, limited by the competing migration rate of the component ions under an applied electric field. − The high ionic conductivity of ILs can also be detrimental in organic electrochemical transistors, often causing slower than desired switching speeds due to their intercalation into the semiconductor. − Zwitterions, in which the cationic and anionic functional groups are covalently bound, are molecules with zero net charge, making them promising alternatives to ILs. Their tethered structure allows the rotational reorientation of molecules under an applied electric field, avoiding its translational motion and allowing the mobility of only the target ions. ,,− So far, zwitterions have primarily been investigated as additives to other electrolytes in batteries, but their application as a whole electrolyte is gradually increasing. , Zwitterions have also been used as highly polar dopants and functional coatings to affect the molecular orientation in liquid crystals to facilitate low driving voltage and large contrast smart windows for flexible wearable devices. , More broadly, zwitterions have been extensively studied for applications such as surfactants, surface coatings, and catalysts − and typically pose a significantly lower risk to aquatic species compared to their IL counterparts …”