Enhanced sodium storage performance of silk fibroin-derived hollow iron sulfide with potential window control

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.