Electrochemical hydrogen storage behaviors of as-milled Mg-Ti-Ni-Co-Al-based alloys applied to Ni-MH battery

In the study, the hydrogen storing materials Mg-Ni-based Mg50-xTixNi45Al3Co2 (x = 0,1, 2, 3, 4) + 50 wt% Ni (named Mg50-xTixNi45Al3Co2 (x = 0-4) + 50Ni) with nanocrystalline and amorphous structures were fabricated by the method of mechanical milling and designed for the negative electrode of Ni-MH batteries. The investigation aims at researching the function of Ti dosage on the electrochemical hydrogen storing characteristics and microstructure of the experimental specimens. The analysis of X-ray diffraction profiles and Scanning Electron Microscope images determines that the experiment specimens contain the major phase Mg2Ni and the minor phase MgNi2. The observation of TEM images reveals a fact that the specimens after ball-milling treatment consist of the nanocrystal and amorphism structures. The electrochemical tests show that as for the samples after ball-milling treatment, the discharge capacities of them gain the utmost value at the first circulate without activation treatment, and the increase of Ti dosage brings on an evident rise in the specimens' discharge capacity and cycle stability. Concretely, as the Ti content alters from 0 to 4, the discharge capacities of the as-milled (20 h) sample increase from 405.0 to 519.4 mAh/g and capacity retention rate of 100th circulate (S-100= C-100/C-max) augments from 45% to 72%. What's more, a series of measurements, such as the high rate discharge ability (HRD), the electrochemical impedance spectrum (EIS) as well as Tafel polarization curves etc. show that the electrochemical kinetics performances of as-milled specimens in this experiment have a trend of increasing first and then decreasing with the addition of Ti element. (C) 2020 Elsevier Ltd. All rights reserved.