Molecular Elucidation of Reaction Mechanisms in Aluminum & Lithium Metal Batteries by Solid-State NMR Spectroscopy and Electrochemical Methods

Author

Leo W. Gordon, CUNY City CollegeFollow

Date of Award

2023

Document Type

Dissertation

Department

Chemical Engineering

First Advisor

Robert J. Messinger

Keywords

Aluminum-organic batteries, aluminum-chalcogen batteries, ionic liquid electrolytes, Li-ion battery electrolytes, nuclear magnetic resonance spectroscopy, organic electrodes

Abstract

As society wrestles with the ever-growing climate consequences of burning fossil fuels, the increased demand for electric vehicles and renewable power generation mandates safe, sustainable, earth-abundant, low cost, and energy dense batteries. Different use cases will necessitate different types of batteries; for example, stationary storage systems prioritize minimal expense, whereas mobile applications like electric vehicles emphasize high energy densities. Aluminum and lithium metal batteries hold great promise for next-generation energy storage due to their large specific capacities (2980 mA h g^-1, and 3860 mA h g^-1, respectively). In particular, aluminum metal is low cost, has high earth crust abundance (8.23 wt.%), and is inherently safe, in addition to its mature mining, refinement, and recycling industries that minimize geopolitical constraints on its use. The rechargeable aluminum battery field is still emerging and thus only a small number of cathode materials have been successfully demonstrated, while fewer still have well understood charge storage mechanisms. In addition, the electrolytes needed to reversibly electrodeposit aluminum have (electro)chemical reactivity issues with many cathode materials and cell components. Organic molecules are attractive as electrode materials as they compliment key aluminum metal properties, such as sustainability, while their molecular structures are tunable to optimize performance. With fewer than 15 extant papers in the literature, however, their electronic and ionic charge storage mechanisms are not well understood. Aluminum-selenium batteries are another system of interest due to selenium’s large specific capacity (2036.5 mA h g^-1). However, in current literature, its full six-electron capacity has not reliably been accessed, due to the seemingly capricious nature of the selenium reduction reaction. Lithium metal batteries are energy dense but suffer from deleterious side reactions that affect cycle life; currently these issues are mitigated by high-cost fluorinated solvents. Herein, electrochemical reaction mechanisms and chemical processes were elucidated up from the molecular level in emerging aluminum and advanced lithium metal batteries via a combination of nuclear magnetic resonance (NMR) spectroscopy and electrochemical methods. NMR spectroscopy is a singularly powerful tool that enables nuclide-specific, atomic-scale characterization of local environments, dynamics, and interactions between nuclei. In aluminum-organic batteries, electronic and ionic charge storage mechanisms were revealed through solid-state NMR measurements, which demonstrated the electrochemical reduction of carbonyl active sites coupled with the coordination of charge-compensating aluminum-containing cations. The interplay between electrolyte speciation and ionic charge storage mechanisms were identified by NMR measurements, the results of which are further supported by quantum chemical calculations of possible structures and reaction pathways. In aluminum-selenium batteries, the occurrence of the selenium reduction reaction was linked to its intermediate-range structural order by solid-state NMR spectroscopy and X-ray diffraction, resulting in materials design principles for future aluminum-selenium batteries intending to use their full six-electron capacity. Commercial lithium battery electrolytes were modified by addition of P₂O₅, subsequently generating compounds beneficial for long life operation of lithium metal batteries. These molecules were identified and characterized by liquid-state NMR. More generally, advanced solid-state NMR methods, particularly dipolar-mediated and multiple-quantum experiments, were shown to be invaluable to elucidate electrochemical reaction mechanisms and chemical processes in battery materials and electrolytes.

Recommended Citation

Gordon, Leo W., "Molecular Elucidation of Reaction Mechanisms in Aluminum & Lithium Metal Batteries by Solid-State NMR Spectroscopy and Electrochemical Methods" (2023). CUNY Academic Works.
https://academicworks.cuny.edu/cc_etds_theses/1127