MOLECULAR SIMULATION OF IONIC LIQUIDS: EFFECTS OF SOLVATION, HUMIDIFICATION, AND CONFINEMENT

Abstract

Ionic liquids are organic salts that exist in the liquid state near ambient conditions. They exhibit remarkable physical properties, including low vapor pressure and high thermal, chemical, and electrochemical stability, and application-specific tunability. They hold great potential for a number of applications across several industries, such as electrochemical energy storage, cellulose processing, and separations. This dissertation primarily focuses on their use in electrochemical capacitors, or supercapacitors. These are energy storage devices that store energy by physical adsorption of ions at charged interfaces with no chemical reactions. As a result, they exhibit great power density and lower energy density than batteries - the storage and delivery of energy is much quicker, but the amount of stored energy is lower. Supercapacitors are used in niche applications, such as regenerative braking in automobiles, but need to exhibit higher energy and power density to become achieve broader adoption. This dissertation explores some potential means by which the performance of supercapacitors can be increased. One proposed technique is dissolving ionic liquids in organic solvents, by which ion mobility is greatly enhanced and, as a result, power density increased. Fundamental connections between solvent properties and ionic liquid structure and dynamics, however, are not well-understood. We have employed a computational screening study to consider 400 mixtures of ionic liquids in organic solvents. Trends between solvent properties, mixture properties, and their effects on energy storage applications, are discussed. The focus of this talk will be the solvent study, however other topics, including the use of porous carbons and novel 2-D materials and the effects of humidity and nanoconfinement will briefly be discussed.