Core-shell electrospun and doped LiFePO4/FeS/C composite fibers for Li-ion batteries

Abstract Core-shell olivine-type electrospun and doped LiFePO 4 /FeS/C composite fibers were synthesized via a single-step process employing an electrospinning method using LiOH·H 2 O, metal sul phates, H 3 PO 4 , citric acid, and polyvinylpyrrolidone (PVP) as the starting materials. Electron microscopy studies showed that the mean diameter of the core-shell composite fibers was about 280 ± 20 nm with a LiFePO 4 phase forming a core with a diameter of about 100 ± 20 nm and a carbon shell with a thickness of 80 ± 20 nm. An FeS phase was formed by a direct reduction of iron (II) sulfate (FeSO 4 ) that was evenly distributed within the core region of the composite fibers and further improved the electronic conductivity of the fibers. Na 1+ , Mg 2+ , and Al 3+ doping ions affected fiber morphology and electrochemical performance. All composite fibers showed excellent electrochemical performance. However, Al 3+ ions improved the electrochemical performance of the composite fibers to a significantly greater degree than Na 1+ and Mg 2+ doping ions, increasing the electronic and ionic conductivities of the material while maintaining their core-shell composite fiber characteristics.