Rational Design of Na4Fe3(PO4)2(P2O7) Nanoparticles Embedded in Graphene: Toward Fast Sodium Storage Through the Pseudocapacitive Effect

In this study, we design a sol–gel-based synthetic route to integrate the reduced graphene oxide (rGO) with carbon-coated Na4Fe3(PO4)2(P2O7) (NFPP). In this nanocomposite, the NFPP nanoparticles are wrapped with amorphous carbon (AC) coating, that are embedded in cross-linked reduced graphene oxide (rGO) networks. It is the first time to investigate the interaction between graphene and NFPP. Benefiting from the open and stable framework of NFPP with three-dimensional ion channels and the improved electronic conductivity and dispersity of NFPP@AC particles after rGO incorporation, the NFPP@AC/rGO composite enables ultrafast sodium storage in a wide temperature range (78 mAh g–1 at 20C and 30 °C, 42 mAh g–1 at 20C, and −15 °C), and stable long-term cycling, which are more than 50% higher than the corresponding discharge capacities of NFPP@AC. A kinetics analysis demonstrates that the strong pseudocapacitive effect induced by graphene is responsible for the improvements of capacity and high-rate capability. These results suggest that the NFPP@AC/rGO composite is a promising cathode material for high-rate, long-life, and low-cost sodium-ion batteries.