Bryan D. McCloskey/ Venkatasubraman Viswanathan Proposal Number: 1604927/1604898
Of all battery chemistries currently being explored to power next-generation electric vehicles, metal-air (O2) couples possess some of the highest known theoretical specific energies and volumetric energy densities. In particular, the aprotic nonaqueous Li-O2 battery has recently received significant attention because of its superior specific energy. Yet many of the challenges facing Li-O2 battery development remain unsolved. One of these challenges involves understanding the link between electrolyte composition and the discharge/charge electrochemical processes. The proposed research will address the fundamental dependence of the Li-O2 electrochemistry mechanism on both cation and anion solvation, thereby providing a better understanding of how to improve the performance of high-energy nonaqueous Li-O2 and other metal-O2 batteries. If successful, Li-O2 batteries could advance and accelerate the adoption of electric vehicles for reduced emissions, improved efficiency, and domestic energy security. The PIs are committed to broad dissemination of their results. As such, they will develop online video modules to make publicly accessible the prospects of this exciting new area of energy storage. The online modules will be structured for simple incorporation into energy and electrochemical system courses, including those taught by the PIs. The PIs will also develop a broader and more engaging educational content on electrochemistry/batteries with a vision to run a massive online open course.
The overall objective of the proposed research is to elucidate the effect of ion solvation on the fundamental oxygen electrochemistry in nonaqueous electrolytes, with a particular emphasis on oxygen reduction in Li+-bearing electrolytes. Recent studies have identified the importance of electrolyte composition on both the ultimate oxygen reduction product formed and the mechanism by which it forms. For example, a 2 e- oxygen reduction to form lithium peroxide, Li2O2, is found to occur in nonaqueous Li-O2 batteries, whereas a 1 e- reduction process to form sodium superoxide, NaO2, occurs in Na-O2 batteries. Furthermore, the Li-O2 discharge mechanism was recently shown to be affected by a delicate interplay between anion and solvent selection, as the Lewis acidity and basicity of both components affected the lifetime of oxygen reduction intermediates in solution. The PIs used this knowledge to improve the discharge capacity (or usable energy) of a Li-O2 battery four-fold. However, the understanding of the complex role of electrolyte constituents (ions, additives, and solvents) on electrode reactions and ion solvation is not complete. This understanding potentially has far-reaching implications in many other electrochemical systems (e.g., CO2 reduction, Li-S batteries, and other metal-air batteries). The proposed research tasks will leverage unique experimental and theoretical capabilities developed by the PIs to study Li-O2 batteries, including Differential Electrochemical Mass Spectrometry (DEMS) to quantify Coulombic efficiency of batteries employing different electrolyte compositions, and nuclear magnetic resonance spectroscopy to probe cation and anion solvation in these electrolytes. The theoretical capabilities to describe non-equilibrium charge transport, and solution and surface electrochemistry, will be based on density functional theory calculations. Through a well-developed theoretical and experimental framework, the PIs will identify novel electrolyte compositions that can trigger solution electrochemistry, thereby improving discharge capacity while maintaining chemical stability. The PIs will then experimentally link ion solvation effects in the most promising electrolyte compositions to stability and capacity enhancements.
