(735a) Understanding the behavior of Zinc slurries in Zn-MnO2 Alkaline Batteries

Zn-MnO₂ batteries have dominated the primary battery market for several decades. Even though these batteries are well developed and provide reliable power at low cost, the performance of Zn-MnO₂ batteries is limited by the Zinc Anode due to corrosion, passivation, and decreased Zinc utilization. The Zinc anode is comprised of 60-80 wt.% Zinc powder, 20-40 wt.% KOH gelled electrolyte, and <1 wt.% of surfactants. Despite its high mass fraction, the volume fraction of Zinc is typically low, which leads to poor particle-to-particle contact. To conduct electrons, the complex charge-conducting mechanisms have been proposed that rely on the movement of charge both within and between the particles [1], which leads to slurry ionic conductivity being several orders of magnitude lower than the electronic conductivity. This results in a mass transport-limited reaction front that migrates radially inwards from the anode-separator interface towards the center of the current collector, leading to passivation of the anode, incomplete discharge, and increased gassing. In addition to this, corrosion is another challenge encountered in the Zinc anode where highly alkaline gelled electrolyte (pH ~15) leads to significant hydrogen evolution on the Zinc particle interface.

In this study, a novel methodology is reported to quantify the contributions of the ionic and electronic conductivity in the discharge and corrosion of Zn slurry anodes. Through this new understanding, challenges in passivation and corrosion can possibly be mitigated by optimizing the composition of the slurry including Zinc weight percent, KOH concentration, and surfactant type and amount of surfactant and analyzing their behaviors using various electrochemical techniques in ex-situ and in-situ cells. The results of the presented work aim to provide new design principles for the study and utilization of slurry-based anodes for primary Zn batteries and beyond.

References

1. Faegh, T. Omasta, M. Hull, S. Ferrin, S. Shrestha, J. Lechman, D. Bolintineanu, M. Zuraw and W.E. Mustain, “Understanding the Dynamics of Primary Zn-MnO2 Alkaline Battery Gassing with Operando Visualization and Pressure Cells”, J. Electrochem. Soc., 165 (2018) A2528-A2535