Seaweed-derived synthesis of Na3.12Fe2.44(P2O7)2/r-GO aerogels as air stable cathode materials for sodium-ion batteries

Due to the high theoretical capacity and open frameworks, the low-cost sodium iron pyrophosphate Na3.12Fe2.44(P2O7)2 has become a promising candidate for cathode materials of the sodium ion batteries (SIBs). However, NFPO is very sensitive to moisture and CO2, which causes serious surface oxidation reaction and results in degraded high-rate charge/discharge performance and cyclic stability. Herein, we developed a seaweed-derived synthesis strategy to prepare air stable NFPO/r-GO aerogels by using sodium alginate (SA) and reduced graphene oxide (r-GO) as precursors. X-ray photoelectron spectroscopy (XPS) proved that there were no residual Na species on the surface of prepared NFPO/r-GO aerogels and no any oxidized impurities after exposing in air for 100 days. When evaluating the NFPO/r-GO aerogels as cathode materials for SIBs, the sample exhibits excellent reversible capacity of 116.1 mAh g−1 at 0.1 C, 88.82% capacity retention after 5000 cycles and superior rate capacity of 72.3 mAh g−1 at 20 C. The superior electrochemical performances are mainly attributed the delicate structure, which can not only increase the electronic conductivity, but also improve air stability of NFPO by suppressing surface side reactions with moisture and CO2.