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

The high-rate discharge capability of the negative electrode in a Ni/MH battery is mainly determined by the charge transfer process at the interface between the NH alloy powder and the electrolyte, and the mass transfer process in the bulk MH alloy powder. In this study, the negative electrode was made from a Mm(0.95)Ti(0.05)Ni(3.85)Co(0.45)Mn(0.35)Al(0.35) alloy for the anodic polarization measurements. The charge transfer reaction reflects the capability of hydrogen to be adsorbed at the surface of MH alloy powders. The 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 the bulk MH alloy, based on the limiting current in the anodic polarization curves, 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.