Synthesis by Electrospinning and Electrochemical Properties of Na2Fe2(SO4)3 Nanofibers as a Cathode Material for Sodium-Ion Batteries

Alluaudite-type Na2+2xFe2−x (SO4)3 is a promising cathode material for sodium-ion batteries because of its high voltage, low cost, and feasible synthesis at low temperature. However, it has a low ionic conductivity (1 × 10−7 S/cm) and electrical conductivity (2 × 10−9 S/cm). In this study, we improved the ionic conductivity by using electrospinning to activate ion diffusion. We also improved the electrical conductivity by using poly(vinylpyrrolidone) to form a carbon coating. Scanning electron microscopy revealed that the synthesized material consisted of nanofibers with sizes of approximately 400–800 nm. The surface area was measured by using atomic force microscopy. An X-ray Diffraction analysis was carried out to determine the structure of the Na2Fe2(SO4)3 nanofibers. Additionally, the initial charge-discharge capacities of Na2Fe2(SO4)3 were found to be 22.27 mAh/g and 19.39 mAh/g, respectively, at a current density of 0.1 C-rate.