Wet Milling And Electric Dip Process On The Hydrogen Storage Alloy

A new way of preparing hydrogen storage alloy powder was studied in this paper, which combines the method of wet milling and surface modification. X-ray diffraction (XRD), Scaning Electronic Microscope (SEM), Electrochemical Impedance Spectroscopy(EIS), Energy Disperse Spectroscopy(EDS) and Electrochemical Properties Test Set were employed to analyze the effect of wet milling and surface modification on the electrochemical performances(discharge capacity, high-rate discharge capability, and cycle life), microstructure and kinetic characteristics of the alloys treated in different liquid medium. The effect of electric soaking on electrochemical properties of hydrogen storage alloy was also studied in this paper.(1) The discharge capacities of hydrogen storage alloys after treatment in Na₂H₂PO₂ medium are improved. Especially, the discharge capacities of the alloy treated by 0.8mol/L NaH₂PO₂ in 50% ethanol medium reaches 309.857mAh/g. The activation and cycle life of alloy treated by KBH4 medium are improved also, the activation number of the alloy treated in 0.08mol/L KBH4 is three.(2) XRD shows that Al₂O₃ peak appears in the diagram of the alloy after treatment of wet milling, and the micro-aberrance of alloy treated in KOH medium is increased, which results in the broaden of diffraction peaks, however, the FWHM of the alloy treated by KBH₄ medium is less than the alloy treated by KOH medium. The crystal lattice parameters a₀ value is enlarged and crystal lattice C₀ and c₀/a₀ are reduced, compared to the bare alloy, and crystal lattice volume of the hydrogen storage alloy treated by KOH medium are reduced, which is in contrasted with the alloy treated by KBH4 medium. SEM shows that the surface of the treated alloy is full of crack, and the figure of the particles are very irregular. The alloy treated by KBH4 shows that the spongy and multihole surface exists, and the particle size are identical, which is in contrast with other conditions. EDS shows that the surface of the alloy after treatment is rich of Al and Ni element.EIS shows that because the oxygen content of surface at the alloy isincreased after wet milling, the polarization resistance increases, and the speed of electrode reaction is controlled by the electrochemical activation process.(3) The FWHM of the alloy after electric soaking decreases, and the component and phase structure of the alloy becomes more homogeneous, the discharge capacity of the treated alloy reduces, and the discharge voltage and activation of the alloy are improved.