Material Science Forum Vol. 377 (2001) pp. 63-70 Journal of Metastable and Nanocrystalline Materials Vol. 11 (2001) pp. 63-70 © 2001 Trans Tech Publications, Switzerland Optimization of the Ball-milling parameters for the synthesis of Amorphous MgNi alloy used as negative electrode in Ni-MH batteries S. Ruggeri 1 , C. Lenain 1 , L. Roué 1 , H. Alamdari 2 , G. Liang 2 , J. Huot 2 and R. Schulz 2 1 INRS-Énergie et Matériaux, 1650 Boul. Lionel-Boulet, C.P. 1200, Varennes (Québec), Canada, J3X 1S2 2 Institut de Recherche d’Hydro-Québec 1800 Boul. Lionel-Boulet, C. P. 1000, Varennes (Québec), Canada, J3X 1S1 Keywords : nickel-metal hydride battery, hydrogen storage alloys, magnesium-based alloy, mechanical alloying. Abstract The optimization of the ball milling parameters resulted in the synthesis with a milling duration equal to 10 hours of amorphous MgNi having an initial discharge capacity over 520 mAh/g. Further milling results in a partial crystallization of amorphous MgNi into nanocrystalline MgNi 2 and Mg 2 Ni, which decreases significantly the electrode performance. This study also shows that it is possible to obtain an amorphous and electroactive material in large scale (1 kg of alloy per batch) using an industrial high-energy attritor. In addition, it was demonstrated that the carbon added at the beginning of the milling to avoid powder welding, in spite of its small proportion (1 wt.%), has a notable influence on the performance of the material. This study also confirms the major loss of activity during cycles. However, the partial substitution of Ti for Mg leads to a remarkable improvement of the cycle lifetime of the alloy. 1. INTRODUCTION It was recently found that some amorphous Mg-Ni alloys prepared by mechanical alloying can absorb and desorb electrochemically a much larger amount of hydrogen at room temperature than their polycrystalline counterparts. For example, the amorphous MgNi alloy has a maximum discharging capacity around 500 mAh/g (at a current density of 20 mA/g), which is ten times higher than that of the crystalline alloy [1]. In addition, they need no activation process unlike the conventional AB 5 -type and AB 2 -type hydrogen storage alloys. Nevertheless, the cycle lifetimes of Mg-based electrodes are insufficient and further improvements must be done. Although many studies have been done about MgNi-based alloys prepared by ball milling, little information is available for the optimization of the ball-milling parameters in order to obtain the best alloy in the shorter milling time. An economical study, performed by Hydro-Québec, demonstrated that the milling time must be shorter than 10 hours to consider the ball milling method as economically viable to synthesize metal hydrides in industrial scale. The purpose of this paper is to optimize the ball milling parameters in order to synthesize an amorphous MgNi alloy having the best first discharging capacity with the shortest ball milling duration. The synthesizes were accomplished by varying the type of milling machine (vibrator, attritor and planetary mill), the ball to powder weight ratio and the milling duration. In addition, the influence of the carbon added to the elemental powders was studied. The variation of these parameters allows the structure, the particle morphology and the charge/discharge capacity of the material to be modified.