16th International Symposium on Metal-Hydrogen Systems, Guangzhou, China, 28 October - 02 November 2018, vol.1, no.1
Surface Modified Metal Hydrides as Negative Electrodes in NiMH Batteries
Cavit Eyovge1,2, Ezgi Onur Sahin1,2 and Tayfur Ozturk1,2
1Center 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  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.
 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), 9948-9953,2016