Self-discharge mechanism of vanadium-titanium metal hydride electrodesfor Ni-MH rechargeable battery

In order to investigate the effect of the equilibrium hydrogen pressure (plateau pressure) of metal hydride (MH) alloys on self-discharge behavior, V₀₉Ti₀₁ alloys having multi-plateau pressures (the low and high plateau pressure) have been used as working electrodes in a half cell. A thermal desorption experiment and open-circuit potential monitoring were conducted to observe the self-discharge behavior of the electrodes. From the thermal desorption spectra of fully charged and discharged V₀₉Ti₀₁ electrodes (to-0.7 V vs. Hg/ HgO), it was found that only the high plateau pressure region from V₀₉Ti₀₁ electrodes is electrochemically useful in battery application. However, the open-circuit potential change and thermal desorption spectra of V₀₉Ti₀₁ electrodes after various open-circuit storage periods prove that self-discharge behavior is caused by hydrogen desorption from the low plateau pressure region (10^-8 atm) as well as the high plateau pressure region (0.1 atm). Therefore, it is suggested that the self-discharge behavior of V₀₉Ti₀₁ electrodes cannot be suppressed effectively by reduction of 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.