Production of hollow and porous Fe2O3 from industrial mill scale and its potential for large-scale electrochemical energy storage applications

Abstract

Mill scale, which is a waste product from the steel industry, abundantly available and comprising a mixture of iron oxides, has been converted into hollow and porous Fe₂O₃ micro-rods using a facile and scalable chemical treatment. The Fe₂O₃ morphology and structure was characterised by a range of electron microscopy and other techniques, and then sprayed into large area electrodes that were investigated for electrochemical supercapacitor and lithium ion battery applications. The Fe₂O₃ supercapacitor electrode delivered a specific capacitance of 346 F g⁻¹ at 2 mV s⁻¹ with 88% capacitance retention after 5000 cycles, while the battery electrode delivered an initial reversible specific capacity of 953 mA h g⁻¹ at 0.1C, reducing to 933 mA h g⁻¹ after 100 cycles and to 673 mA h g⁻¹ at 5C. The Fe₂O₃ electrodes had similar or superior performance to more costly, small batches of laboratory synthesised Fe₂O₃ in both supercapacitor and battery applications, which was ascribed to the hollow and porous structure that facilitated ion mobility throughout the electrodes, a high surface area and excellent strain accommodation during lithiation and de-lithiation.