Pushing the theoretical capacity limits of iron oxide anodes: capacity rise of γ-Fe2O3 nanoparticles in lithium-ion batteries

Abstract

Nanoparticles (NPs) of γ-Fe₂O₃ are successfully prepared via facile hydrolysis of a complex iron iodide precursor with subsequent oxidation under mild conditions. When evaluated as an anode material in lithium ion half-cells, electrodes made with γ-Fe₂O₃ NPs exhibit excellent rate capabilities with high capacities and good coulombic efficiencies. Electrodes of γ-Fe₂O₃ NPs initially deliver capacities of 1100 mA h g⁻¹ at 100 mA g⁻¹ current density and 980 mA h g⁻¹ at 1000 mA g⁻¹. Following an activation step of the electrodes, the capacities increase by up to ∼300 mA h g⁻¹ while coulombic efficiencies also improve slightly. At a high current density of 4000 mA g⁻¹, a stable capacity of 770 mA h g⁻¹ is achieved. In this study, dQ/dv plots are employed to graphically illustrate the capacity breakdown of each cycle into intercalation, conversion, and extra capacity regions. Upon prolonged cycling, the extra capacity region expands to yield higher capacities; this phenomenon has been attributed to both pulverization-induced particle size reduction and high-rate lithiation-induced activation processes. This study concludes that γ-Fe₂O₃ NPs could serve as a promising anode material with comparable results to widely studied α-Fe₂O₃ and Fe₃O₄ NPs.