Effect of milling time on electrochemical properties of MmNi_3.9Co_0.45Mn_0.4 Al_0.25-CoB composite hydrogen storage alloy

MmNi_3.9Co_0.45Mn_0.4 Al_0.25-CoB composite alloy were prepared by ball-milled method. The structure, morphology and electrochemical properties were studied by using X-ray diffraction, scanning electron microscopy, charge and discharge testing, linear polarization measurement. The results showed that the diffraction peaks of the composite hydrogen storage alloy became broaden and the particle of the alloy tended to be amorphous with the increase of milling time. The average particle size decreased, the surface of the particles became rough and the distribution of the particle was homogeneous when the milling time increased. When the milling time reached 45 min, the cycling capacity retention rate, exchange current density, hydrogen diffusion coefficient of composite hydrogen storage alloy electrode were better than those of the other electrodes, leading to a significant improvement on electrochemical kinetic properties. But the alloy particle would become agglomeration and conglobation after the elongation of the milling time, resulting in a decrease of exchange current density.