To improve the electrochemical properties of rare-earth-Mg-Ni-based hydrogen storage alloys,the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the alloys were studied.Nonsubstituted Ml_(0.80)Mg_(0.20)(Ni_(2.90)Co_(0.50)-Mn_(0.30)Al_(0.30))_x(x = 0.68,0.70,0.72,0.74,0.76) alloys and Cu-substituted Ml_(0.80)Mg_(0.20)(Ni_(2.90)Co_(0.50-y)Cu_yMn_(0.30)Al_(0.30))_(0.70)(y= 0,0.10,0.30,0.50)alloys were prepared by induction melting.Phase structure analysis shows that the nonsubstituted alloys consist of a LaNi_5 phase,a LaNi_3phase,and a minor La_2Ni_7 phase;in addition,in the case of Cu-substitution,the Nd_2Ni_7 phase appears and the LaNi_3 phase vanishes.Thermodynamic tests show that the enthalpy change in the dehydriding process decreases,indicating that hydride stability decreases with increasing stoichiometry and increasing Cu content.The maximum discharge capacity,kinetic properties,and cycling stability of the alloy electrodes all increase and then decrease with increasing stoichiometry or increasing Cu content.Furthermore,Cu substitution for Co ameliorates the discharge capacity,kinetics,and cycling stability of the alloy electrodes.
