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.