Na4Fe3(PO4)2P2O7/C nanospheres as low-cost, high-performance cathode material for sodium-ion batteries

Sodium-ion battery is regarded as a promising power source for large-scale energy storage systems. However, the development of sodium-ion batteries is hindered by the lack of applicable cathode materials with low cost and long cycle life. Here, we report a successful synthesis of Na4Fe3(PO4)2P2O7/C nanospheres with tunable particle size and carbon coating thickness by a template approach. The as-prepared Na4Fe3(PO4)2P2O7/C nanospheres deliver a high discharge capacity of 128.5 mAh g−1 (near to the theoretical capacity: 129 mAh g−1) at 0.2C, with capacity retention of 63.5% at 10 C after 4000 cycles. Particularly, a high reversible capacity of 79 mAh g−1 is exhibited at an ultrahigh current rate of 100 C (charge/discharge in 36s). The excellent performances result from the shortened Na+ ion diffusion length within the nanospheres (∼30 nm) and highly conductive pathways for electrons in the carbon coating layers (∼3 nm). Owing to their low cost, long lifespan and outstanding rate capability, we believe that the Na4Fe3(PO4)2P2O7/C nanospheres are considerable competitive to other cathode materials for application in stationary sodium-ion batteries.