Mg-Doped Na4Fe3(PO4)(2)(P2O7)/C Composite with Enhanced Intercalation Pseudocapacitance for Ultra-Stable and High-Rate Sodium-Ion Storage

Na4Fe3(PO4)(2)(P2O7) (NFPP) is considered as a promising cathode material for sodium-ion batteries (SIBs) due to its low cost, non-toxicity, and high structural stability, but its electrochemical performance is limited by the poor electronic conductivity. In this study, Mg-doped NFPP/C composites are presented as cathode materials for SIBs. Benefiting from the enhanced electrochemical kinetics and intercalation pseudocapacitance resulted from the Mg doping, the optimal Mg-doped NFPP/C composite (NFPP-Mg5%) delivers high rate performance (capacity of approximate to 40 mAh g(-1) at 20 A g(-1)) and ultra-long cycling life (14 000 cycles at 5 A g(-1) with capacity retention of 80.8%). Moreover, the in situ X-ray diffraction and other characterizations reveal that the sodium storage process of NFPP-Mg5% is dominated by the intercalation pseudocapacitive mechanism. In addition, the full SIB based on NFPP-Mg5% cathode and hard carbon anode exhibits the discharge capacity of approximate to 50 mAh g(-1) after 200 cycles at 500 mA g(-1). This study demonstrates the feasibility of improving the electrochemical performance of NFPP by doping strategy and presents a low-cost, ultra-stable, and high-rate cathode material for SIBs.