Mechanically alloyed Mg-based alloys for Ni-MHx batteries

In the development of new hydrogen absorbing materials for metal hydride electrodes of rechargeable batteries, Ni-MHx, metastable Mg-Ni(Cu)- based compounds find currently special attention. They are fundamentally studied regarding their electrochemical (de-)hydrogenation reactivity (see here), the effect of hydrogen on phase stability and thermal phase transformation processes (link to Teresiak), but also under application-relevant battery-like conditions. Alloy powders with the composition Mg63Ni30Y7 were produced by means of mechanical alloying. The milling conditions have a significant effect on the alloy microstructure, morphology and thermal stability. Alloying in a planetary ball mill evolves a predominantly amorphous structure. A lowering of the milling temperature by cooling with liquid nitrogen triggers the amorphization process. Mechanical alloying in a shaker mill results in the formation of a main nanocrystalline phase (Mg2-xNi1-yYx+y) besides a small amorphous matrix. Electrodes made from shaker milled nanocrystalline alloy powders exhibit better hydriding properties than those made from predominantly amorphous powders, but a lower stability under free corrosion and oxidative conditions. The measured maximum discharge capacity of 247 mAh/g is higher than values reliably reported for mechanically alloyed Mg2Ni powder electrodes. The cycling stability of electrodes made from as-milled powders is limited by the corrosion stability.

 

 

Discharge behavior of electrodes from Mg-Ni-Y alloy powders in 6 M KOH (charge: -100 mA/g 10 h - discharge: 20 mA/g to –0,4 V)

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