Surface Modified Metal Hydrides as Negative
Electrodes in NiMH BatteriesCavit Eyovge1,2, Ezgi Onur Sahin1,2
and Tayfur Ozturk1,21Center for Energy Materials and
Storage Devices, Middle East Technical University, Ankara 2Dept. of Metallurgical and
Materials Engineering, Middle East Technical University, Ankara There is a renewed interest in NiMH
batteries with improved energy densities that could approach those of Li-ion
batteries. Efforts to improve the energy density concentrates on alternative
anode as well as cathode materials. For anode, AB2 and Mg based alloys are
candidates with potentials that go beyond the capacity achieved with rare-earth
based AB5 compounds. In a recent study [1] we have shown an AB2 alloy which is
sluggish in its activation could readily be activated when it was surface
modified with hot-alkaline treatment. The treatment resulting in fine porous
surface rich in Ni not only activates the alloy but it also increases the
discharge capacity by a significant amount. This was attributed to positive
effect of porous surface where hydrogen evolution was made difficult by the
associated stabilizing effect. For Mg based alloys, we have investigated A2B7
alloy where the amount of Mg is quite low and an amorphous Mg50Ni50 alloy. Here
rather than modifying the powders, the electrode itself was modified by nafion
coating. The electrodes were tested both in bare and coated form with a notable
difference in discharge capacity. Nafion coating increased maximum attainable
discharge capacity in both alloys up to 150%. Electrochemical impedance
spectroscopy measurements showed that the charge transfer resistance increases
with increased coating. The role of nafion coating in developing Mg based
negative electrode materials is discussed.
[1] Tan
S., Shen Y., Sahin E. O., Noréus D., Ozturk T., "Activation behavior of an
AB2 type metal hydride alloy for NiMH batteries" International Journal of
Hydrogen Energy 41 (23), 9948-9953,201