Exploring Fe redox enabled by kinetically stabilized interphase for rechargeable aluminum batteries

Screening cathode material from view of metal redox center has been proven useful in battery research. Fe redox is extensively utilized due to multiple valence and low cost. However, the utilization of Fe redox in rechargeable aluminum batteries is much unclear and the mechanism is insufficient for further effort. Herein, we unravel the Fe redox mechanisms involving 3-electron transfer with high theory energy densities when coupled with Al anode (637 Wh kg⁻¹ for Fe²⁺/Fe⁰ in a deposition/dissolution reaction, 881 Wh kg⁻¹ for Fe³⁺/Fe²⁺ in a molecular redox, 1518 Wh kg⁻¹ in total). To solve the detrimental Fe²⁺ dissolution during battery cycle, we tune the interphase easily by current density based on electrochemical model that interprets the connection between reaction kinetics and interphase. It is found that Fe²⁺ dissolution, despite the thermodynamic trend, will be blocked at critical current density (kinetic driven force) and channel into the condensation as a kinetically stabilized interphase. The battery can realize a high areal capacity at 0.74 mAh cm⁻² with high Coulombic efficiency of 99% since the initial cycle. This work will navigate low-cost cathode materials employing Fe redox, and as well highlight the mechanism understanding of interphase in aluminum batteries.