Electrochemical Properties of Solid Zn/ZnCl ₂ Redox Anode for the Zn/ZnCl ₂ -Graphite Molten Salt Battery

Metal chloride-graphite molten salt batteries are promising for safe, low-cost energy storage at moderate temperatures (<200 °C). Here, we report a Zn/ZnCl2-graphite molten salt battery that integrates a solid-state Zn/ZnCl2 redox anode with a graphite cathode based on reversible Cn/Cn[AlCl4] intercalation chemistry. In an AlCl3/LiCl/NaCl molten salt electrolyte, the Zn/ZnCl2 redox couple exhibits a low equilibrium potential of 0.28 V versus Al/Al3+ and high reversibility. A ZnCl2 anode fabricated via dry-powder calendering delivers a specific capacity of 143 mAh g–1, while the full-cell achieves 95% capacity retention over 100 cycles at 140 °C. Mechanistic investigations reveal that ZnCl2 undergoes a solid-state conversion to metallic Zn accompanied by NaCl crystallization during reduction, whereas the cathodic process proceeds through reversible formation of graphite intercalation compounds. This work establishes a cost-effective medium-temperature battery chemistry and provides insights into solid-state metal chloride redox processes for scalable and intrinsically safe energy storage.