Investigation of a novel metal hydride electrode for Ni-MH batteries

The science and technology of a nickel metal hydride battery that stores hydrogen in the solid hydride phase has many advantages, including high energy density, high power, long life, tolerance to abuse, wide range of operating temperatures, quick-charge capability, and totally sealed and absolutely maintenance-free operation. The primary goal of metal hydride research for use in battery electrodes has been a cell capacity higher than that presently available with conventional Ni-Cd technology. A novel metal hydride consisting of Y, Zr, Mn, Fe, Co, V and Cr: Y(x)Z(1-x)Mn(m)Fe(n)Co(p)V(o)Cr(q) (m+n+o+p+q=2) is shown to give a higher electrochemical capacity. The electrochemical properties, such as electrode potential, reversible electrochemical capacity and diffusion coefficient as a function of state of charge in electrodes, are investigated in order to evaluate their suitability of the material as an electrode. The reversible electrochemical capacity of the electrode is found to be in excess of 450 mAh/g. Hydrogen concentration is estimated as r = n(H)/n(f.u.) = 3.5. The process that occurs in the electrode during charge and discharge has been studied by cyclic voltammogram (CV) experiments, carried out at different sweep rates. It is found that at low sweep rates, the hydrogen concentration on the surface increases due to longer polarization and approaches a value that favors a metal hydride formation. The diffusion coefficients are also evaluated with respect to state of charge.