Electrospun Na4Fe3(PO4)2(P2O7) nanofibers as free-standing cathodes for ultralong-life and high-rate sodium-ion batteries

The development of low-cost and long-lifespan cathode materials for sodium-ion batteries has been one of the key issues for the success of grid-scale energy storage. Na4Fe3(PO4)2P2O7 has received a great deal of attention due to its high theoretical capacity, good structural stability, and high abundance of resources. Herein, hierarchical carbon decorated Na4Fe3(PO4)2P2O7 nanofibers are designed and fabricated through a feasible electrospinning technique and subsequent pyrolysis. The free-standing Na4Fe3(PO4)2P2O7/C electrode exhibits good mechanical flexibility, together with high electronic conductivity and ultrafast Na+ migration in sodium-ion batteries, leading to high reversible capacity (118 mA h g−1 at 0.2 C), superior cycling stability (79.6% of capacity retention over 10,000 cycles at 10 C) and excellent rate performance (64 mA h g−1 at 20 C). The full cell assembled with Na4Fe3(PO4)2P2O7/C cathode and hard carbon anode, shows reversible capacity of 126.4 mA h g−1 with high working voltage of 2.9 V at 20 mA g−1. Such an effective concept of fabricating hierarchical carbon-decorated electrodes for SIBs is expected to accelerate the practical applications of high-rate flexible energy storage devices.