Anodic Electrolysis Strategy Enabled Fe/FeCl₂ Electrode for Scalable Fe/FeCl₂-Graphite Molten Salt Battery

The Fe/FeCl 2 -Graphite molten salt battery is a promising technology for large-scale energy storage, offering a long lifespan, a low operating temperature (<200 °C), and cost efficiency. However, its practical applications are hindered by the lack of a scalable preparation approach and insufficient redox stability in the Fe/FeCl 2 electrode. Our study introduces an electrochemical anodic electrolysis (EAE) strategy, employing the anodic process (Fe → Fe 2+ ) in an Al|AlCl 3 /NaCl/LiCl|Fe electrolysis system for the Fe/Fe 2+ negative electrode in the Fe/FeCl 2 -Graphite battery. The EAE strategy forms an oxidized film, preventing incipient dissolution in the electrolyte and addressing redox stability issues with FeCl 2 as the active substance. The Fe/Fe 2+ negative electrode prepared by the EAE strategy exhibits a stabilized capacity of 0.72 mAh/cm 2 after 7000 cycles at 5 mA/cm 2, with a lower polarization level (∼29 mV) compared to FeCl 2 as the active component. The flexibility of the EAE strategy is validated in both galvanostatic and potentiostatic processes, with a discharge capacity of 14 mAh after 1000 cycles, a capacity retention rate of 85%, and a Coulombic efficiency of 98% in the potentiostatic anodic electrolysis Fe/Fe 2+ electrode. The scalability and reliability of the EAE strategy are further demonstrated in capacity-expanded Fe/FeCl 2 -Graphite batteries, reaching a discharge capacity of 155.1 mAh after 1000 cycles at 130 mA, with a capacity retention rate of 94%. For the first time, we showcased an EAE approach capable of producing Fe/Fe 2+ electrodes at a rate of about 68.6 m 2 per day. Additionally, we successfully assembled an Fe/FeCl 2 -Graphite battery at about a 0.42 ampere-hour level, paving the way for the scalable application of Fe/FeCl 2 -Graphite batteries.