Magnetic field assisted chemical reduction preparation of Co-B alloys as anode materials for alkaline secondary battery

摘要

In this work, we reported the magnetic field assisted preparation of amorphous Co-B alloy by reducing CoCl_2 with alkaline sodium borohydride (NaBH_4) in solution. The prepared Co-B alloy has been characterized by scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET) adsorption, energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and electrochemical measurements. It was found that the Co-B alloy prepared under an external magnetic field shows a large amount of nanowire-like structures. Meanwhile, its B content and specific surface area are 24 percent and 99.6 m2/g, respectively. On the contrary, the Co-B alloy prepared without the magnetic field exhibits many aggregates consisting of nanoparticles, and its B content and specific surface area are only 15.4 percent and 38.5 m2/g, respectively. Particularly, electrochemical measurements indicate that the Co-B alloy prepared under the magnetic field exhibits better high-rate dischargeability. At a high rate of 650mA/g, its initial discharge capacity and capacity retention after 100 cycles are 287mAh/g and 84 percent, respectively, significantly higher than that of Co-B alloy prepared without magnetic field. Even at a discharge rate as high as 6C (1800 mA/g), the Co-B alloy prepared under a magnetic field can still deliver a reversibly electrochemical capacity of 243 mAh/g, which can be attributed to its larger specific area, its enhanced B content and its nanowire structures.