Superior electrochemical properties of α-Fe₂O₃ nanofibers with a porous core/dense shell structure formed from iron acetylacetonate-polyvinylpyrrolidone composite fibers

Porous core/dense shell α-Fe₂O₃ nanofibers were prepared by heat-treating electrospun gel nanofibers containing iron acetylacetonate-polyvinylpyrrolidone at 500 °C. Diffusion of Fe to the outer part of the nanofibers during the heating process results in a polyvinylpyrrolidone (PVP)-rich interior. Combustion of phase separated nanofibers produces α-Fe₂O₃ nanofibers with a porous core/dense shell structure. The nanofiber shell thickness and core diameter are 26 and 130 nm, respectively. The initial discharge and charge capacities of the α-Fe₂O₃ nanofibers at a current density of 1000 mA g^-1 are 1392 and 1112 mA h g^-1, respectively; the discharge capacities for the 2nd and 100th cycles are 1149 and 1225 mA h g^-1, respectively. The stable reversible discharge capacities of the nanofibers decreased from 1198 to 1061 mA h g^-1 as the current density increased from 500 to 3000 mA g^-1.