Dual‐Doped Hematite Nanorod Arrays on Carbon Cloth as a Robust and Flexible Sodium Anode

Rechargeable batteries with flexibility can find tremendous applications in wearable and bendable electronics. One central mission for the advancement of such high‐performance batteries is the exploration of flexible anodes with electrochemical and mechanical robustness. Herein reported is a robust and flexible sodium‐ion anode based on self‐supported hematite nanoarray grown on carbon cloth. The ammonia treatment that results in dual doping of both nitrogen and low‐valent iron renders surface reactivity and electric conductivity to the material. The dual‐doped hematite arrays afford a robust activity for sodium storage, exhibiting reversible capacities of 895 and 382 mAh g−1 at current rates of 0.1 and 5 A g−1, respectively, or 615 and 356 mAh g−1 by removing the contribution of the substrate. They also sustain 85% of the initial capacity upon 200 cycles at 0.2 A g−1. To demonstrate the flexibility, full cells composed of a hematite array anode and Na3V2(PO4)3/C cathode are assembled. The cell is capable of affording an energy density of 201 Wh kg−1 and sustaining repeated bending without performance decay, demonstrating a significant potential in practical application.