Rechargeable hydrogen batteries using rare-earth-based hydrogen storage alloys

Hydrogen storage characteristics of Ti–Zr–Cr–V alloys

Hydrogen storage for off-grid power supply

Extensive work has been carried out on utilizing MmNi 5 -based alloys (Mm, mischmetal) as a low cost negative battery electrode. The replacement of nickel by cobalt was effective in improving cycle lifetime but caused a decrease in capacity and high rate capability. The replacement of lanthanum by large amounts of cerium of neodymium gave the alloy a satisfactory cycle lifetime with small amounts of cobalt present and without impairing the high rate capability. The alloy MmNi 3.5 Co 0.7 Al 0.8 was selected consistent with the above requirements. Induction-melting tests showed that the surface region with a columnar structure had a longer cycle lifetime than the inner region with an equiaxed structure. Annealing treatment also caused a decrese in the cycle lifetime. It was considered that alloys with smaller crystal grains had a longer cycle lifetime because the protective surface layer on the grain would remain effective after pulverization. The deviation from stoichiometric composition to the nickel-rich side or the Mm-rich side also caused a decrease in cycle lifetime, accompanied by the precipitation of nickel or Mm on the grain boundaries. It was concluded that the surface layer of the crystal grain played a very important role in preventing capacity decay.

Rare-earth-based alloy electrodes for a nickel-metal hydride battery

R&d on metal hydride materials and Ni-MH batteries in Japan

In order to reduce the large hysteresis effect in MmNi hydrides (Mm  misch metal) we studied the hydrogen absorption-desorption characteristics of multicomponent alloys such as MmNi5−xAl(Mn)y−zMz and MmNi5−xAl(Mn)yM2 (M = Co, Cr, Cu, Nb, Ti, V, Zr; x = 0.3 − 0.5; y = 0.3 − 0.5; z = 0.05 − 0.1). The substitution or addition of the element M eliminates the large hysteresis effect that occurs during an absorption-desorption cycle. The hysteresis factor (equal to In( P a P d )) for MmNi4.7Al0.3M0.1 hydrides decreased for additives M in the following order: Zr > Co > Cr > Ti,V > Cu. Investigations of the effects of cycling showed that spalling occurred more rapidly for MmNi4.5Mn0.5 than for MmNi4.5Mn0.5Zr0.005 and MmNi4.5Mn0.5Zr0.1.

S. Kawai

Papers

Hydrogen absorption-desorption characteristics of MmNiAlM and MmNiMnM alloys (Mm misch metal)