The Influence of different types of nickel on he electrochemical characteristics of ZrNiMnCrV alloy

Abstract

The electrochemical characteristics (activation rate, cyclic stability, and ability to restore the discharge capacity and cyclic stability after a break in the cycle) possessed by three samples of the ZrNi_1.2Mn_0.5Cr_0.2V_0.1 alloy doped with cathode, cathode rolled, and electrolytic nickel were studied. The impurity content was determined by emission spectral analysis. There were almost no impurities (except for traces of magnesium and titanium) in cathode nickel. In cathode rolled nickel, the largest number of elements (traces of magnesium and aluminum, 0.1 wt.% titanium, 0.1 wt.% copper, 0.1 wt.% silicon, and 0.2 wt.% iron) was revealed. In electrolytic nickel, the largest amount of iron impurities (>1 wt.%) was found. The experiments were performed with electrodes both without and with carbonyl nickel powder additions (50 and 100% of the electrode weight) as a catalyst of the electrochemical reaction. The electrodes made from samples of this alloy doped with cathode and cathode rolled nickel showed similar electrochemical behavior, differing significantly from the behavior of the electrodes made from the sample with electrolytic nickel. Thus, these electrodes without nickel additions are activated at 30 °C for three cycles and reach a discharge capacity of 256 and 280 mA × h/g and those with doped electrolytic nickel for six cycles reach 242 mA × h /g. Nickel additions amounting to 50 and 100% of the electrode weight to the electrodes made from samples with cathode and cathode rolled nickel at 15 °C significantly accelerate the activation and have almost no effect on the activation at 30 °C because its proceeds very rapidly at this temperature (for three cycles). The ambiguous effect of catalytic additions in the case of electrodes made from the sample with electrolytic nickel both at 15 °C and at 30 °C (mainly accelerated activation) was revealed. Taking into account the results of emission spectral analysis, this is probably due to a relatively large amount of iron in the electrolytic nickel and, as a consequence, less stable surface. Depending on the experimental temperature and the presence of activating additions, the discharge capacity of the electrodes made from samples with cathode and cathode rolled nickel after a break in the cycle for five days either completely restored or slightly increased. The discharge capacity of the electrodes made from samples with electrolytic nickel significantly decreases for the electrode without catalytic additions and practically recovers in case of their presence. The electrodes from the samples doped with cathode and cathode rolled nickel are characterized by a constant rate of loss in the discharge capacity before and after a pause in the cycle both at 15 °C and at 30 °C (~0.7 mA × h/g per cycle) in contrast to the electrodes with electrolytic nickel, which is 1.14–1.3 mA × h/g per cycle, and after a pause in the cycle increases to 5.0 mA × h/g per cycle. The electrode made from the sample with cathode nickel and addition of 50% nickel powder in pressing, preliminary soaked in a 30% KOH solution for five days, after a pause in the cycle shows similar discharge capacity and better cyclic stability at 15 °C than the electrode at 30 °C.