J.W. Gallaway
Northeastern University,
United States
Keywords: batteries electrochemistry
Summary:
The growing demands on the power grid require development of cost-effective, safe battery technologies. While lithium-ion batteries dominate current markets, their flammable organic electrolytes pose significant safety challenges for large-scale deployment. Aqueous electrolyte batteries offer a compelling alternative with inherently safer operation, lower material costs, and simplified manufacturing. However, these face a critical technical barrier, which is the narrow electrochemical stability window of water, which limits achievable voltage and energy density. A possible solution leverages high-capacity two-electron conversion reactions to compensate for reduced voltage, which could provide commercially-viable energy density in an aqueous platform. However, there is a fundamental instability challenge of conversion cathodes, which is managing transient intermediate species that form during the two-electron transfer process. In some systems, these intermediates are a possible source of degradation, leading to inactive or resistive materials that can build up and cause failure of the cell. In this talk we will discuss conversion reactions for aqueous batteries and address the impact of intermediate species on electrode stability during long term cycling. This stability is tied not only to chemical structures and reactivity, but also evolution of the material morphologies and microstructures developed in the electrodes over long cycle life. An example cathode that will be discussed is the rechargeable alkaline MnO2 electrode, which cycles with the reaction given below.