Electrochemical Properties of the ZrNiMnCrV Alloy Depending on Quantitative Phase Composition

The ZrNi_1.2Mn_0.5Cr_0.2V_0.1 alloy was qualified using isotherms of hydrogen desorption in a gas atmosphere, equilibrium curves of hydrogen desorption in a 30% KOH solution, and X-ray diffraction data. The equilibrium pressure of the ZrNi_1.2Mn_0.5Cr_0.2V_0.1 alloy in a gas atmosphere at 20°C that was equal to ~1 atm (101,325 Pa) indicated that the alloy could be used in Ni–MH batteries, and the equilibrium hydrogen desorption curve obtained by the electrochemical method indicated that insignificant self-discharge could occur. The alloy samples crystallized at different cooling rates showed different quantitative phase composition. Electrodes produced from the sample with a greater amount of the Zr₇Ni₁₀ phase activated faster and those with a greater amount of the C15 and C14 phases had higher maximum discharge capacity. After the electrodes were exposed to air for 14 days, the Zr₇Ni₁₀ phase decreased by 7 vol.% and the total content of the C15 and C14 phases increased by 7 vol.% in the sample with a greater amount of the Zr₇Ni₁₀ phase (~ 24 vol.%). No changes in quantitative phase composition were found in the sample with a smaller amount of the Zr₇Ni₁₀ phase (~12 vol.%). Electrodes prepared from the sample with a lower content of the Zr₇Ni₁₀ phase showed better cyclic stability both before and after a pause in the cycles. The loss of the maximum achieved discharge capacity of these electrodes for 100 cycles with a pause in the cycles for 14 days (after the 80^th cycle) and for 200 cycles with a pause in the cycles for 45 days (after the 150^th cycle) was only 2 and 16%, and that of the electrodes with a higher content of the Zr₇Ni₁₀ phase was 30 and 52%. Thus, the electrodes produced from the alloy sample that showed stable quantitative phase composition according to X-ray diffraction had better hydrogenation–dehydrogenation cyclic stability when exposed to air in powder form for 14 days. Taking into account some similarities in hydrogenation-dehydrogenation and exposure to air of the zirconium alloys (oxidation of alloy components, significant increase in nickel surface concentration, etc.), the better cyclic stability of the electrodes was logically assumed to be due to more stable quantitative phase composition of the surface. The relationship between the electrochemical properties of the ZrNi_1.2Mn_0.5Cr_0.2V_0.1 alloy and the cooling rate in crystallization (quantitative phase composition) allows the development of materials with predicted functional properties.