An assessment of alkali metal-O2 chemistry: perspectives and prospectives

Abstract

Alkali metal-O2 batteries (AOB) have emerged as a promising technology for energy storage due to their large discharge capacity compared to technologies such as lithium-ion batteries. In AOBs, the discharge process involves the formation of superoxides or peroxides, while charge involves oxygen evolution from discharge deposits. However, the discharge deposits are electronically insulating, requiring high overpotentials that can cause electrolyte degradation and limit battery cyclability. As a consequence, there has been significant interest in understanding battery chemistry to improve battery performance. Most studies have focused on battery cathodes, however, and the complexity of such systems makes it difficult to gain fundamental understanding of the system. In this work, several experimental frameworks are described to characterize alkali metal-O2 chemistry. First, an attempt to use field ionization to describe battery chemistry is described. Field ionization experiments can provide a controlled environment that can provide fundamental, semi-quantitative information about reactions such as intermediates, relative rates of formation, and location of active reaction sties. Other areas of fundamental research that can provide key information for AOBs and other technologies related to metal-O2 chemistry are defined. These include solvation characterization, parasitic chemistry studies, side product charge characterization, and catalyst exploration. In addition, a series of fundamental experiments are proposed to understand phenomena such as the initial stages of discharge and charge, electrolyte solvent reactions with discharge deposits, and spatial distribution of discharge products within discharge deposits. The concept of key states for battery chemistry characterization is described, where a key state is defined as a region where the charge/discharge curve changes behavior such as plateaus or inflection points. Finally, several case studies are presented to show the application of key states to describe battery phenomena such as cell death and transitions between stages of a charge/discharge profile.