Self-discharge mechanism of Vanadium–Titanium metal hydride electrodes for Ni–MH rechargeable battery

Abstract

In order to investigate the effect of the equilibrium hydrogen pressure (plateau pressure) of metal hydride (MH) alloys on self-discharge behavior, V 0.9Ti 0.1 alloys having multi-plateau pressures (low and high plateau pressures) have been used as working electrodes in a half cell. The thermal desorption experiment and open-circuit potential monitoring were conducted to observe the self-discharge behavior of the electrode. From the thermal desorption spectra of the fully charged and discharged V 0.9Ti 0.1 electrode (to −0.7 V versus Hg/HgO), it is found that only the higher one of the two plateau pressure regions of the V 0.9Ti 0.1 electrodes is electrochemically useful for battery application. But the open-circuit potential change and thermal desorption spectra of the V 0.9Ti 0.1 electrode after various open-circuit storage periods prove that the self-discharge behavior is attributed to the hydrogen desorption from the low plateau pressure (10 −8 atm) as well as the high plateau pressure (0.1 atm). Therefore, it is suggested that the self-discharge behavior of V 0.9Ti 0.1 electrodes can not be effectively suppressed by reducing the plateau pressure of alloys through alloy modification. In addition, the pressure–composition–isotherms ( P–C–T) of the low pressure region can be estimated by using the open-circuit potential corresponding to this region in Nernst's equation.