In this paper, ethyl xanthate nickel (EXN) was used as nickel and sulfur sources to modify Fe3O4 powder nanoparticles dissolved in pyridine. After short heat treatments, the generated NiS nanoparticles were not only compactly and uniformly coated on the surface of Fe3O4 but also induced the decreased particle size of Fe3O4. The microstructure, morphology and particle size of the resulting NiS coated Fe3O4 particles were characterized X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Raman spectroscopy. The results showed that thickness of the NiS coating on Fe3O4 particles was about 6 nm. The NiS coated Fe3O4 particles were tested as positive materials for nickel-iron batteries and found to effectively inhibit the iron anode passivation and improve the efficiency of charge capacity. The NiS (1.5%) - Fe3O4 nano particles delivered a significant power density of 557.2 mA h g(-1) at a current density of 120 mA with a charging efficiency of 79.6%. Furthermore, discharge capacities of 550.2 and 436.8 mA h g(-1) were achieved respectively at 300 and 600 mA g(-1), with charging efficiencies reaching up 85.9% and 76.5% of the initial capacity after 100 cycles. (C) 2017 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.