Enhancing Specific Energy and Cycling Stability of High-temperature Na-zncl₂ Batteries with Foam-based Electrodes

Sodium-zinc chloride (Na-ZnCl2) batteries offer a sustainable alternative to sodium-nickel chloride (Na-NiCl2) batteries but face challenges with low specific energy and cycle life. This study evaluates two electrode designs: conventional particle-based Zn/NaCl granules and newly developed foam-based Zn/NaCl electrodes. Particle-based electrodes, with 30% Zn utilization, cycled in tubular cells with a mass loading of 1.13 g cm(-2) and an areal capacity of 150 mAh cm(-2), achieve a specific energy of 231 Wh kg(-)(1) on electrode composite level at 15 mA cm(-)(2) but suffer from degradation in voltage efficiency due to Zn agglomeration. To address this, foam-based Zn/NaCl electrodes are developed, enhancing Zn utilization to 66%. Cycled in planar Na-ZnCl2 cells, these foam-based electrodes achieve over 200 mAh cm(-2) areal capacity at a mass loading of 1.04 g cm(-2), providing a specific energy of 336 Wh kg(-)(1) at 15 mA cm(-)(2) with stable voltage profiles. The foam-based design stabilizes the electrode microstructure, delivering a high cumulative discharge capacity of 5.4 Ah cm(-)(2) with stable voltage efficiency. These results represent the highest mass loadings and areal capacities reported for sodium metal chloride cells to date, demonstrating their potential for enabling cost-effective Na-ZnCl2 batteries for stationary energy storage applications.