Polarization performance of a MH electrode at the interface between the MHalloy powder and electrolyte

The high-rate discharge capability of the negative electrode in a Ni/MH bat tery is mainly determined by the charge transfer process at the interface b etween the NH alloy powder and the electrolyte, and the mass transfer proce ss in the bulk MH alloy powder. In this study, the negative electrode was m ade from a Mm(0.95)Ti(0.05)Ni(3.85)Co(0.45)Mn(0.35)Al(0.35) alloy for the a nodic polarization measurements. The charge transfer reaction reflects the capability of hydrogen to be adsorbed at the surface of MH alloy powders. T he mass transfer process involves hydrogen diffusion in the bulk of the MH alloy. With increasing the number of charge/discharge cycles, the MH alloy powders microcrack into particles several-microns in diameter. The decrease in alloy particle size leads to an improvement in the high-rate discharge capability of the MH electrode. The diffusion coefficient of hydrogen in th e bulk MH alloy, based on the limiting current in the anodic polarization c urves, is 1.2x10(-11) cm(2)s(-1) at assuming a charge transfer coefficient a=0.5 and average particle radius of 5 mu m.