Na2FePO4F/Biocarbon Nanocomposite Hollow Microspheres Derived from Biological Cell Template as High-Performance Cathode Material for Sodium-Ion Batteries

We have successfully synthesized Na2FePO4F/biocarbon nanocomposite hollow microspheres from Fe-III precursor as cathodes for sodium-ion batteries through self-assembly of yeast cell biotemplate and sol-gel technology. The carbon coating on the nanoparticle surface with a mesoporous structure enhances electron diffusion into Na2FePO4F crystal particles. The improved electrochemical performance of Na2FePO4F/biocarbon nanocomposites is attributed to the larger electrode-electrolyte contact area and more active sites for Na+ on the surface of hollow microspheres compared with those of Na2FePO4F/C. The Na2FePO4F/biocarbon nanocomposite exhibits a high initial discharge capacity of 114.3 mAh g(-1) at 0.1 C, long-cycle stability with a capacity retention of 74.3 % after 500 cycles at 5 C, and excellent rate capability (70.2 mAh g(-1) at 5 C) compared with Na2FePO4F/C. This novel nanocomposite hollow microsphere structure is suitable for improving the property of other cathode materials for high-power batteries.