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

The Fe/FeCl₂-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/FeCl₂ electrode. Our study introduces an electrochemical anodic electrolysis (EAE) strategy, employing the anodic process (Fe → Fe²⁺) in an Al|AlCl₃/NaCl/LiCl|Fe electrolysis system for the Fe/Fe²⁺ negative electrode in the Fe/FeCl₂-Graphite battery. The EAE strategy forms an oxidized film, preventing incipient dissolution in the electrolyte and addressing redox stability issues with FeCl₂ as the active substance. The Fe/Fe²⁺ negative electrode prepared by the EAE strategy exhibits a stabilized capacity of 0.72 mAh/cm² after 7000 cycles at 5 mA/cm², with a lower polarization level (∼29 mV) compared to FeCl₂ 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/Fe²⁺ electrode. The scalability and reliability of the EAE strategy are further demonstrated in capacity-expanded Fe/FeCl₂-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/Fe²⁺ electrodes at a rate of about 68.6 m² per day. Additionally, we successfully assembled an Fe/FeCl₂-Graphite battery at about a 0.42 ampere-hour level, paving the way for the scalable application of Fe/FeCl₂-Graphite batteries.