Surface Modification of MgNi by Perylene

Abstract

Amorphous MgNi was modified by ball milling with perylene and its effects on the charge/discharge capacity were examined by using a conventional two-electrode cell. It was found that both the ball milling time and perylene/MgNi ratio had great influence on the discharge capacity and cycle life of MgNi. Three types of effects were identified, depending on ball-milling conditions. One of them was the increase in the discharge capacity at the first cycle, the second type was the deceleration of the degradation of the discharge capacity with charge/discharge cycle, and the last type was the reduction in the charge/discharge capacity. Chemical states of modified surfaces were analyzed by Auger electron spectroscopy (AES) as well as ab-inito calculation. Both AES and ab-initio calculations indicated that carbon atoms can form bonding with both magnesium and nickel atoms, but bonding with magnesium atoms is most preferable. The change in the charge/discharge capacity is attributed to such kind of reactions, and the three distinct effects are ascribed to the presence of different MgNi-perylene composites, formed during the ball milling on the surface, resulting in the retardation or acceleration of Mg(OH)₂ formation on the electrode.