Unraveling the Design Principles of Crystallographic Orientation for Ultralong, 8500 Cycled Fe-Ion Battery

Rechargeable aqueous Fe-ion batteries using Fe anodes is very promising in stationary grid-scale energy storage but suffer from hydrogen evolution (HER) and Fe corrosion. Herein, we present new insights on the design principle of crystallographic orientation of the metallic Fe anode for long lifespan, sustainable Fe-ion batteries. Guided by a density functional theory simulation on optimal surface energy and adsorption energy, we obtained highly [110] oriented Fe by annealing the commercial Fe foil at 1000°C in Ar/H₂ atmosphere. The [110] oriented Fe foil with the maximum exposure of (110) plane shows the significantly decreased lattice defect, residual stress, and grain boundary density. Consequently, side reactions including HER and by-product formation were well suppressed with enhanced Fe-ion diffusion and charge transfer kinetics. Significantly, 8540 cycle-lifespan at 5.0 A g^-1 with 99.3% capacity retention was achieved in the full battery, which is not only very prominent in aqueous Fe²⁺ ion battery systems, but also surpasses most of aqueous Zn²⁺, Mg²⁺ ion batteries recently reported. Our findings demonstrate that uniform epitaxial Fe²⁺ electrodeposition along the surface of preferred oriented Fe anode is an effective strategy to address the troublesome HER and corrosion issues in the aqueous battery using low-cost, industrial Fe element.