V-Ti alloy is very attractive for anode material of Ni/MH secondary battery because of its large hydrogen storage capacity. However, for being incapable of discharging in KOH electrolyte the alloy has not been used for anode material.
V-Ti alloy was mechanically alloyed with Ni by ball-milling process to have a catalytic effect of hydrogen absorption/desorption in KOH electrolyte. The discharge capacity of the electrodes was increased up to the peak value and then decreased with ball-milling conditions, ball-milling time and Ni content. The optimum ball-milling condition was ball-milling with 10wt% Ni for 30min. In ball-milling process, increasing of ball-milling time led to not only alloy with Ni effectively, but also decrease the interstitial site of hydrogen storage in the V-Ti alloy. So, it is needed to develop effective surface alloying process without increasing ball-milling time.
Flake-type Ni was very active material to have much strain which was formed by ball-milling process, and then we expected that ball-milling with flake-type Ni was more effective than with sphere-type Ni. In case of using flake-type Ni, the optimum ball-milling condition was ball-milling with 10wt% flake-type Ni for 20min. Ball-milling time of this condition was decreased, then the loss of interstitial site of hydrogen storage was decreased. The maximum discharge capacity was 439mAh/g, it was the highest discharge capacity.
The cyclic durability of V-Ti alloy is very poor because of the formation of Ti-oxide in the surface of V-Ti alloy. But V-Ti surface-modified alloy by ball-milling had good cycle life because of Ni-enrich region in the surface of V-Ti alloy. So, we believe that the formation of Ti-oxide of V-Ti alloy was suppressed by surface-alloying with Ni.
