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, V0.9Ti0.1 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 V0.9Ti0.1 electrode (to -0.7 V versus Hg/HgO), it is found that only the higher one of the two plateau pressure regions of the V0.9Ti0.1 electrodes is electrochemically useful for battery application. But the open-circuit potential change and thermal desorption spectra of the V0.9Ti0.1 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 V0.9Ti0.1 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. (C) 1998 Elsevier Science S.A.