Study on water electrolysis mechanism of a lead-acid battery under idling stop system operational conditions

Water electrolysis behavior of a 12 V lead-acid battery for vehicles equipped with idling stop system under vehicle operational conditions is investigated. The behavior of water electrolysis during a microcycling test at 60°C is analyzed by means of in-situ gas analyses and electrochemical measurements. During charge phases under partial state of charge conditions, rates at which gas is released out of the battery container are always higher than those at the steady states during static overcharge conditions at the same voltage. The volume ratio of hydrogen to oxygen released during the charge under partial state of charge conditions is significantly different from 2, which is the stoichiometric ratio of water electrolysis products. This gas evolution behavior can be ascribed to the different potentials of each positive and negative electrode under the two different charge conditions. Reducing the difference between the potentials under the two conditions will be a key to reduce the water electrolysis during microcycling operations.