In Situ Growth of Iron Sulfide on Fast Charge Transfer V 2 C‐MXene for Superior Sodium Storage Anodes

Due to the upstream pressure of lithium resources, low‐cost sodium‐ion batteries (SIBs) have become the most potential candidates for energy storage systems in the new era. However, anode materials of SIBs have always been a major problem in their development. To address this, V 2 C/Fe 7 S 8 @C composites with hierarchical structures prepared via an in situ synthesis method are proposed here. The 2D V 2 C‐MXene as the growth substrate for Fe 7 S 8 greatly improves the rate capability of SIBs, and the carbon layer on the surface provides a guarantee for charge–discharge stability. Unexpectedly, the V 2 C/Fe 7 S 8 @C anode achieves satisfactory sodium storage capacity and exceptional rate performance (389.7 mAh g −1 at 5 A g −1 ). The sodium storage mechanism and origin of composites are thoroughly studied via ex situ characterization techniques and first‐principles calculations. Furthermore, the constructed sodium‐ion capacitor assembled with N‐doped porous carbon delivers excellent energy density (135 Wh kg −1 ) and power density (11 kW kg −1 ), showing certain practical value. This work provides an advanced system of sodium storage anode materials and broadens the possibility of MXene‐based materials in the energy storage.