Iron-carbon based materials as negative electrode for energy storage devices

The effect of various carbon nanofibers (CNF) on the electrochemical properties of iron/carbon (Fe/C) composite electrodes has been investigated to find a suitable carbon additive for iron-based battery anode. The structure and characteristics of carbon such as particle size, surface area strongly affected the cycling performance of Fe/C composite electrode. Different types of CNF structures (herringbone and tubular) have been investigated and tubular type exhibited higher discharge capacity. The x-ray energy dispersive spectroscopy (EDS) revealed that iron species are dispersed on carbon surface during cycling, which may improve the electrochemical properties of the Fe/C composite electrodes. The aggregation of iron species into large particles on the carbon surface via dissolution-deposition process during cycling increased the resistance of the Fe/C electrode. This phenomenon caused the reduced redox current and discharge capacity of electrode during cycling. The electrochemical active material type and their particle size also influenced the cycling performance of electrode. When Fe was replaced by Fe2O3, the Fe2O3/C composite electrode provided larger capacity than Fe/C composite electrode. The discharge capacity of nano-Fe2O3/tubular CNF composite electrode was larger than that of micro-Fe2O3/tubular CNF composite electrode.