The effect of Gd on the microstructure and electrochemical properties of Mg-Ni-based alloys

The Mg-Ni-based alloys have been extensively investigated as negative electrode materials in Nickel-Metal Hydride (Ni-MH) batteries. In this work, two Mg-Ni-based samples (Mg71Ni29 and Mg72.6Ni25.3Gd1.1) were prepared by means of melting. The X-ray diffraction (XRD), scanning electron microscope (SEM), galvanostatic charging/ discharging and other electrochemical measurements were used for the investigation. The results show that the Mg71Ni29 and Mg72.6Ni25.3Gd1.1 alloys include the characteristic peaks of Mg2Ni and the less strong characteristic peaks of Mg and MgNi2 phases. The diffraction peak of the major phase Mg2Ni of the Mg72.6Ni25.3Gd1.1 alloy is shifted to a small angle and its unit cell volume increases. With the addition of Gd, the alloy electrodes exhibits better cycling stability. After 50 charge/ discharge cycles, the capacity retention rate of the alloy electrode increase from 16% (Mg71Ni29) to 22% (Mg72.6Ni25.3Gd1.1). However, the maximum discharge capacity of the alloy electrode decrease from 134.3 mAh/g (Mg71Ni29) to 91.9 mAh/g (Mg72.6Ni25.3Gd1.1). The Mg72.6Ni25.3Gd1.1 alloy possess lower limiting current density IL and exhibit relatively high corrosion resistance against the alkaline solution. After Gd doping, the charge transfer capacity of the Mg72.6Ni25.3Gd1.1 alloy surface is increased.