LAUSR

In this study, we developed iron sulfide (Fe7S8) hollow mesocrystals (HMs) for sodium‐ion battery application using silk fibroin‐derived iron oxide (Fe2O3) via a simple sulfidation process. The Fe7S8 HM electrodes exhibited a high specific capacity of 654 mA h g−1 at the current density of 0.5 A g−1 over the potential window of 0.01 to 3 V during the first cycle. However, rapid capacity decay was observed during 200 cycles. Thus, to improve the cycling stability, we performed additional electrochemical measurements with a limited potential window of 0.4 to 3 V. The specific capacity of the Fe7S8 HM electrodes decreased slightly to 530 mA h g−1 over the potential window of 0.4 to 3 V. The Fe7S8 HM electrodes showed excellent cycle stability with 84% retention over 300 cycles. The Fe7S8 HMs exhibited excellent Na storage performance and sufficient void space, which effectively suppressed their large volume changes by the synergetic effect with the tuned voltage window.