A study on the electrode characteristics of Zr-based alloy surface-modified with Ti-based alloy by ball-milling process as an anode material for Ni-MH rechargeable batteries

摘要

In order to improve the kinetic properties of the Zr-based hydrogen storage alloy electrode, the ball-milling process is applied to the Zr-based alloy using the Ti-based alloy powder as a surface modifier. While the Zr-based alloy electrode is not fully activated before 50 cycles, the ball-milled Zr-based alloy electrode using Ti-based alloy as a surface modifier is fully activated within only four cycles. In order to analyze the strikingly improved kinetic characteristics after ball-milling, the microstructure of ball-milled alloy is examined by transmission (TEM), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). It is observed that there is a surface-alloying region at the contact points between the two alloy powders from the TEM bright-field image. Furthermore, the local quantitative analysis by EDS clearly reveals that the atomic concentration of the constituting elements in the surface-alloying region is gradually changed between the two alloy powders. From the above results, it is suggested that the high kinetic energy applied in the ball-milling process causes cold-welding or surface alloying at the points of impact where Zr-based alloy particles collide with Ti-based alloy particles by the action of steel balls at high speed. The SEM analysis demonstrates that the particle size is decreased as the ball-milling time increases, which implies an increase in the surface area of Zr-based alloy particles touching Ti-based alloy particles. Eventually, it can be suggested that Ti-alloy powder serves as a window for hydrogen to penetrate into the Zr-based alloy, which leads to easy absorption/desorption of hydrogen and also to improvement in the kinetic properties of the Zr-based alloy electrode at initial cycles.