Comparative Performance and Partial Load Cycling of Sodium‐Metal Chloride Battery Modules With Mixed‐Metal Fe,Zn and Ni,Fe Cells

ABSTRACT We present dynamic partial‐load cycling data for high‐temperature sodium–metal chloride battery modules employing nickel‐free cathodes based on iron and zink. The cathodes in these Ni‐free Na‐(Fe,Zn)Cl 2 cells achieve 39% metal utilization and a theoretical energy density of 129 Wh kg −1 at cell level, corresponding to 372 Wh kg −1 at electrode level. Ten‐cell modules incorporating this cathode were assembled and operated under realistic load conditions at 300°C. Dedicated characterization cycles enabled direct comparison with state‐of‐the‐art Ni,Fe cathodes (30% metal utilization, 145 Wh kg −1 at cell level, 398 Wh kg −1 at electrode level). Although the Na‐(Fe,Zn)Cl 2 modules exhibited lower peak power and current capability, they demonstrated competitive energy efficiency and stable cycling performance. Long‐term cycling was performed under dynamic partial‐load profiles simulating photovoltaic charging and household consumption. The protocol integrated a controlled cool‐down phase and intentional overcharge cycles to evaluate safety under failure conditions. Reliable operation was demonstrated for approximately four months, delivering an average discharge capacity of 17 Ah per cell over 87 cycles at charging rates of C/4–C/6 and discharging rates of C/6. These results confirm the viability of Ni‐free cathodes for high‐temperature Na‐metal chloride batteries, offering improved sustainability with acceptable rate‐performance trade‐offs for large‐scale stationary energy storage applications.