EAGER: RUI: Elucidation of the AlCl4- and Al2Cl7- ions speciation, interactions and transport in electrolytes comprised of RTILs by Multi-Nuclear NMR techniques.

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Non-technical summary:Societal energy needs demand the expansion of current electrical energy storage systems capabilities. Lithium ion batteries have dominated the markets due in part to lithium's high gravimetric and volumetric capacities and have advanced the development of products like electric vehicles and smartphones. However, they are expensive and more suitable for portable and small-scale applications due to lithium's limited long-term utility. Additionally, lithium ion batteries can be a fire hazard, a problem which has caused restrictions in their application and transportation. To ensure the advancement of society, improvements in electrical energy storage systems are needed and the development of aluminum ion batteries is one approach. Aluminum metal is attractive because of its low cost, low flammability and high charge storage capacity. Aluminum ion batteries are cheaper and safer than lithium ion ones, and they can be used for large-scale storage applications as needed by renewables like wind and solar. Their wide-scale application is, however, impeded by a number of factors, including a lack of enhanced electrolytes. This project, funded by the Solid State and Materials Chemistry Program in NSF's Division of Materials Research, identifies electrolytes for aluminum ion batteries and investigates fundamental characteristics of ion transport that enable better performance in the future. The project incorporates educational programs for students of all levels and interests and involves students of all education levels in the research activities. The scientific broader impact of this project is to promote the advancement of science through enhancement of energy storage systems. This in turn advances the welfare of society through improvements in our living and environmental conditions. Technical summary: This project, funded by the Solid State and Materials Chemistry Program in NSF's Division of Materials Research, elucidates the fundamental ion-ion interactions and their effects on ion dynamics and transport in aluminum ion battery electrolytes, addressing a lack of fundamental understanding of the aluminum ions' solvation, their interactions and transport. Knowledge of all three is necessary for the optimization of the electrolytes and for advancing the development of aluminum ion batteries as alternative energy storage devices. Therefore, the PI and her group investigate the available free volume of all ions through measurements of multi-nuclear (protons, fluorine, aluminum and chlorine) magnetic resonance self-diffusion coefficients and spin-lattice relaxation times, both as a function of increasing hydrostatic pressure, and temperature. Special focus will be on the aluminum nucleus. The procedure involves working both in the fringe-magnetic field to determine the pressure dependent self-diffusion coefficients, and in the homogeneous field to determine the temperature dependencies of the focused parameters. Through these measurements the researchers gain knowledge of the effect of aprotic organic solvents on the aluminum ion dynamics, and produce the first successful application of the aluminum high-pressure nuclear magnetic resonance technique. The electrolytes of interest are room temperature ionic liquids with imidazolium and pyrrolidinium cations, fluorosulfonamide and chlorine anions, containing the aluminum chloride compound combined with organic aprotic additives such as cyclopentane and benzene, with molar ratios of AlCl3/RTIL in the acidic range. This research opens the door for direct determination of the mass transport of other non-lithium ions in electrolytes and broadcasts the capabilities of the much-underutilized fringe-field high-pressure nuclear magnetic resonance technique.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.