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

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Fe/FeCl₂-Graphite molten salt batteries offer potential for large-scale energy storage due to their long lifespan, low operating temperature, and cost-effectiveness.
• Current limitations include the lack of scalable preparation methods and insufficient redox stability of the Fe/FeCl₂ electrode, hindering practical application.

Purpose of the Study:

• To develop a scalable and reliable preparation strategy for Fe/Fe²⁺ negative electrodes for Fe/FeCl₂-Graphite molten salt batteries.
• To address the redox stability issues of FeCl₂ as the active substance in these batteries.

Main Methods:

• Introduction of an electrochemical anodic electrolysis (EAE) strategy using an Al|AlCl₃/NaCl/LiCl|Fe system for Fe → Fe²⁺ conversion.
• Formation of a protective oxidized film on the electrode surface to prevent dissolution.
• Validation of the EAE strategy in galvanostatic and potentiostatic processes, and in capacity-expanded batteries.

Main Results:

• EAE-prepared Fe/Fe²⁺ electrodes demonstrated a stabilized capacity of 0.72 mAh/cm² after 7000 cycles with low polarization (∼29 mV).
• Potentiostatic EAE electrodes achieved 14 mAh after 1000 cycles with 85% retention and 98% Coulombic efficiency.
• Scalability demonstrated with capacity-expanded batteries reaching 155.1 mAh after 1000 cycles (94% retention) and a production rate of 68.6 m²/day.

Conclusions:

• The EAE strategy effectively enhances the redox stability and cycle life of Fe/Fe²⁺ electrodes for molten salt batteries.
• This method provides a scalable and reliable approach for preparing advanced negative electrodes.
• The successful assembly of a 0.42 Ah Fe/FeCl₂-Graphite battery paves the way for commercialization of this energy storage technology.