Morphology engineering of electro-deposited iron oxides for aqueous rechargeable Ni/Fe battery applications

Abstract

Aqueous rechargeable Ni/Fe batteries possess potential advantages for large-scale energy storage applications due to their low cost, high safety and fast ion diffusions in electrolyte. However, the electrochemical performance of the iron-based anode is still far from ideal due to particle aggregations. Herein, we carry out the morphology engineering on the iron oxide active materials via a facile electrochemical method to improve its charge storage capability. The morphology transition from zero-dimensional particles to one-dimensional nanorods is realized by tuning the electrolyte composition, while subsequent annealing treatment results in further morphology modification into 3D interconnected nanoparticles (10–20 nm). The hierarchical structure allows facile ion and electron transfers, and the large surface provides various active sites for the charge storage conversion reaction. As a result, even at the high current density of 2 A g−1 (∼6C rate), the iron oxide electrode can still deliver a high specific capacity of 184 mAh g−1. At the same time, the morphology integrity and stability of the electrode leads to a good cycle life, with 87.5% capacity retained upon 5000 cycles. The Ni/Fe full cell assembled with the iron oxide anode and a Ni-Co double hydroxide cathode exhibits a good energy density of 82.3 Wh kg−1 at the power density of 3.3 kW kg−1. Our fundamental study would provide new insights for the electro-deposition of iron-based materials and endow new opportunities for the fabrication of high-performance iron-based electrodes for energy storage systems.