Confining Pyrrhotite Fe<sub>7</sub>S<sub>8</sub> in Carbon Nanotubes Covalently Bonded onto 3D Few‐Layer Graphene Boosts Potassium‐Ion Storage and Full‐Cell Applications
Kun Han, Fuqiang An, Qi Wan, Lidong Xing, Lei Wang, Qiang Liu, Wei Wang, Yongchang Liu, Ping Li, Xuanhui Qu
Abstract
Abstract The pyrrhotite Fe 7 S 8 with mixed Fe‐valence possesses high theoretical capacity, high conductivity, low discharge/charge voltage plateaus, and superior redox reversibility but suffers from structural degradation upon (de)potassiation process due to severe volume variations. Herein, to conquer this issue, a novel hierarchical architecture of confining nano‐Fe 7 S 8 in carbon nanotubes covalently bonded onto 3D few‐layer graphene (Fe 7 S 8 @CNT@3DFG) is designed for potassium storage. Notably, CNTs could successfully grow on the surface of 3DFG via a tip‐growth model under the catalytic effect of Fe 3 C. Such structure enables the hierarchical confinement of 0D nano‐Fe 7 S 8 to 1D CNTs and further 1D CNTs to 3DFG, effectively buffering the volume variations, prohibiting the agglomeration of Fe 7 S 8 nanograins, and boosting the ionic/electronic transportation through the stable and conductive CNTs‐grafted 3DFG framework. The as‐prepared Fe 7 S 8 @CNT@3DFG electrode delivers an exceptional rate capability (502 mAh g −1 at 50 mA g −1 with 277 mAh g −1 at 1000 mA g −1 ) and an excellent long‐term cyclic stability up to 1300 cycles. Besides, the in‐situ XRD and ex‐situ XPS/HRTEM results first elucidate the highly reversible potassium‐storage mechanism of Fe 7 S 8 . Furthermore, the designed potassium full‐cell employing Fe 7 S 8 @CNT@3DFG anode and potassium Prussian blue (KPB) cathode delivers a promising energy density of ≈ 120 Wh kg −1 , demonstrating great application prospects.