(4bu) Electrochemically Active ZnO Formed in Rechargeable Zinc Alkaline Batteries: Mechanistic Insights for Improved Zinc Battery Performance

Rechargeable zinc alkaline batteries are attractive candidates for mid- to large-scale energy storage applications such as electric vehicles and grid energy storage because of their low cost, high energy density, environmental friendliness, and inherent safety. However, these batteries have not yet been commercialized on a large scale in part because of the limited cycle life of zinc metal (Zn) electrodes at high utilization. This stems in part from the buildup of zinc oxide (ZnO), which can increase resistance and lead to passivation and cell death. Despite decades of research on this ZnO discharge product, Zn battery researchers lack a complete understanding of its properties and its effects on performance. In this work, we show the ZnO that forms in Zn batteries is electrochemically active, changing its conductivity as a function of electrode potential. This is significant because ZnO in Zn batteries has traditionally been viewed as electrochemically inactive except for its conversion to zinc metal. This unique dynamic conductivity leads to complex behavior in Zn batteries, where ZnO either facilitates discharge of Zn electrodes or contributes to their failure depending on the electrode potential. This makes control tactics possible to improve Zn battery performance.

Operando impedance spectroscopy shows the ZnO that forms in Zn alkaline batteries changes its conductivity by over 1000x in an electrochemical window of only 0.6 V. Careful electrochemical measurements and quantitative solid-state magic angle spinning (MAS) ¹H single-pulse nuclear magnetic resonance (NMR) spectroscopy establish protons and electrons simultaneously insert into the electroactive ZnO at low electrode potentials, causing the increased conductivity. Additionally, operando UV-vis spectroscopy reveals ZnO changes its color and carrier concentration as a function of electrode potential. This electrochromic effect is facilitated by charged-impurity-assisted free carrier absorption. The link between color, conductivity, and electrode potential allows for improved control tactics to extend cycle life and increase utilization of Zn electrodes.

Additionally, variable discharge rate and additive tests reveal the electroactivity of ZnO that forms in Zn electrodes is closely tied to the rate of precipitation from the alkaline electrolyte, where faster precipitation forms more disordered ZnO with higher electroactivity. To gain insight into the crystallographic defects that enable this unique behavior, we utilized operando confocal Raman spectroscopy to characterize native defects in the ZnO. We also performed 2D ¹H{¹H} EXchange SpectroscopY (EXSY) and radio frequency driven recouping (RFDR) NMR experiments to better understand the nature of the proton defect environments. This work highlights the effects ZnO buildup have on Zn alkaline battery performance. These discoveries have the potential to aid in the development of improved additives, cycling protocols, and other control tactics to enable the widespread commercialization of low-cost rechargeable Zn alkaline batteries for future energy storage applications.

Research Interests

My interests lie broadly in improving state-of-the-art energy systems. In my PhD I have worked with (1) NASA to develop batteries for orbital and planetary surface missions with high energy density and long cycle life that operate in extreme conditions – primarily low temperatures – and (2) Sandia National Laboratories to increase the depth of discharge and extend the cycle life of zinc-alkaline batteries for commercial applications. In these projects, I performed extensive operando characterization to better understand fundamental electrochemical processes to ultimately improve battery performance. Though my research as a PhD student has been focused on batteries, I am interested in research in all areas of the rapidly growing and changing energy landscape.

Other Experience

I will begin an internship at the NASA Jet Propulsion Lab in September 2021. Work will focus on understanding how battery materials are affected by extreme temperatures and radiation exposure. This will inform the design of new materials to improve battery performance for orbital and planetary surface missions.

I completed an internship in 2018 at battery manufacturer Urban Electric Power where I tested commercial-scale zinc-manganese dioxide batteries under different cycling protocols and studied failure mechanisms. I analyzed electrochemical data and dissected and characterized electrodes to understand cause of failure and to develop better design and cycling protocol for improved performance.

Prior to my time as a PhD student, I worked as Lead Engineer at a construction consulting firm in New York City. Here, I consulted on the design of energy systems including building envelopes, mechanical systems, and lighting systems. After five years, I obtained licensure as a Professional Engineer, and I am currently licensed to practice in the State of New York.