Suppression mechanism of the self-discharge reaction in nickel-metal hydride batteries using a sulfonated polyolefin separator

The suppression mechanism of the self-discharge reaction in nickel-metal hydride batteries using a sulfonated polyolefin separator was investigated with sealed-type AA size cells. The experimental results indicate that a sulfonated polyolefin separator effectively suppresses the self-discharge reaction in nickel-metal hydride batteries by trapping nitrogen-containing redox shuttle substances. It is also found that a sulfonated polyolefin separator traps the shuttle substances as gaseous ammonia. In the experiment examining the influence of the amount of the shuttle substances on the self-discharge, the starting point of the self-discharge agreed well with the point at which the nitrogen adsorption capacity of a sulfonated polyolefin separator reached its maximum.