Quantifying the Ionic Conductivity of Redox Active Zinc Slurry Electrodes Using Electrochemical Impedance Spectroscopy

Slurry electrodes have gained traction in various electrochemical systems such as electrochemical flow capacitors, flow batteries, primary Zn-MnO 2 batteries and rechargeable Zn batteries. Such electrodes are formed by suspending solid active particles in a high viscosity gel. Devices with slurry electrodes are used because they offer high volumetric capacity, high surface area and reduced complexities in manufacturing and recycling. However, charge conduction in slurry electrodes is complex, in many cases relying on both the ionic and electronic conductivity, with charge being carried through the electrolyte (as ions) and by the particles (as electrons). The dynamics of charge conduction are influenced by the nature of the suspended particles, additives, concentration of the supporting electrolyte and underlying reaction mechanisms. This is particularly evident in Zn-MnO 2 alkaline batteries where the performance of the slurred zinc anode is limited by the ionic conductivity of Zinc slurry, which is several orders of magnitude lower than the electronic conductivity of the slurry. This causes the reacting front to begin at the anode-separator interface, leading to passivation of the anode, incomplete discharge and increased gassing. Therefore, it is important to increase the value of the ionic conductivity. But, due to the complex charge transport mechanism, the ionic and electronic conductivities are ultimately coupled [1]. As such, the literature does not have an established method that is able to independently determine the effective ionic and electronic conductivities when integrated into the slurry. In this study, a novel methodology is reported to quantify ionic conductivity of slurried anode electrodes, with the primary focus being the Zn anode in primary Zn-MnO2 batteries. This innovative approach aims to provide a deeper understanding of the complex interconnection between electronic and ionic conductivities of the Zinc slurry – and allows the effects of several variables to be quantified. This work can contribute not only to advancing the fundamental understanding and application of Zn-MnO 2 alkaline batteries, but also might pave the way for significant improvements in the performance and reliability of a wide array of applications. References 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-MnO 2 Alkaline Battery Gassing with Operando Visualization and Pressure Cells”, J. Electrochem. Soc., 165 (2018) A2528-A2535