In Situ Growth of Iron Sulfide on Fast Charge Transfer V2 C-MXene for Superior Sodium Storage Anodes.

ABSTRACT

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, V2 C/Fe7 S8 @C composites with hierarchical structures prepared via an in situ synthesis method are proposed here. The 2D V2 C-MXene as the growth substrate for Fe7 S8  greatly improves the rate capability of SIBs, and the carbon layer on the surface provides a guarantee for charge-discharge stability. Unexpectedly, the V2 C/Fe7 S8 @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.