Influence of annealing temperature on the structure and electrochemical performance of the Fe3O4 anode material for alkaline secondary batteries

• Fe3O4 polyhedrons were successfully synthesized via a facile route.
• Annealing temperature plays a vital role in the performance improvement of Fe3O4.
• The Fe3O4 polyhedrons exhibit attractive rate capability and cycle stability.
• The enhanced property mainly results from the unique polyhedron microstructures.

High-performance Fe3O4 polyhedrons as alkaline secondary battery anode materials have successfully been synthesized using a facile co-precipitation method with a subsequent annealing treatment at 700 °C for 1 h. The physical and electrochemical properties of the Fe3O4 samples annealed at different temperatures are investigated. It has been discovered that the annealing temperature plays a vital role in improving the physical and electrochemical performances of the Fe3O4 materials. The results also indicate that the Fe3O4 sample annealed at 700 °C performs better (faster activation rate, higher specific discharge capacity, better high-rate ability and cycle stability) than the samples annealed at other temperatures. The specific discharge capacity of the 700 °C-annealed Fe3O4 reaches 604.2mAh g-1 at a current density of 120 mA g-1 with a charging efficiency of 83.9%. Moreover, discharge capacities of 587.6, 539.5 and 500.1 mAh g-1 are achieved at 240, 600 and 1200 mA g-1, respectively, exhibiting remarkable high-rate discharge capability. This performance improvement may be attributable to better reaction reversibility, lower charge transfer impedance and better inhibiting effect on hydrogen evolution reaction of the material. We believe that this Fe3O4 polyhedron is a promising candidate as the anode material for high-performance alkaline secondary batteries.