Room temperature ionic liquids (IL), a class of materials consisting of ions and remain liquid at room temperatures, have shown promises as electrolytes in various applications, such as energy storage devices and sensors. Their unique characteristics (wide liquidus range, low volatility, good thermal and electrochemical stability, etc.) broaden the operating temperature window on both high and low ends. Moreover, the strategy of incorporating other solvents, ILs, and salts is broadly applied for enhancements on both physical and electrochemical properties. The versatile designs and highly tunable properties have made IL based systems potential candidates as electrolytes for the molecular electronic transducer (MET) seismometer to conduct seismology studies under harsh environments, especially low temperatures. In this work, we present an IL-organic solvents-salt system specifically designed for MET seismometer operations at ultra-low temperatures. We discovered that the two organic solvents can form hydrogen bonds with the imidazolium cation, which effectively weakened the coulombic attractions between cations and anions, as evidenced by NMR spectrums. Furthermore, the optimized molecular interactions were achieved at a designed ratio, where neither organic solvent caused undesired crystallization and melting behaviors. The developed electrolyte system exhibited a glass transition temperature (T<sub>g</sub>) at -119 degree Celsius with no other phase transitions observed. Additionally, significant improvements in fluidity and ionic conductivity were confirmed over a broad temperature range (25 to -75 degree Celsius), especially at low temperatures in comparison to the previously developed aqueous based system. The electrochemical stability of the electrolyte will be investigated to ensure its compatibility with the sensing mechanism. Discoveries of the presented work may benefit MET seismometer operations, and also inspire developments of other low-temperature IL based electrolyte systems.

Development of low-temperature ionic liquid-organic solvents-salt electrolyte systems for MET seismometer

2019 Spring National Meeting

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