The Behavior of Oxygen Transport in Valve-Regulated Lead-Acid Batteries with Absorptive Glass Mat Separator

Center for Solar Energy and Hydrogen Research, D-89081 Ulm, GermanyIn the oxygen cycle of valve-regulated lead-acid~VRLA! batteries, there are two ways in which oxygen can move from thepositive to the negative plates, namely, either horizontally to penetrate the absorptive glass mat ~AGM! separator, and/or transportvertically via the gas space. It is found that the oxygen transport depends on the passageway with big void space in the AGMseparator and its rate is proportional to the oxygen partial pressure. The rate constant of vertical transport is about three ordershigher than that of horizontal transport because of the large void space between the AGM separator and plates. However, in thehorizontal direction, the area is very large and the transport path is very short. So the way and the rate of oxygen transport actuallydepend on the level of saturation in VRLA batteries. The horizontal transport is dominant when the saturation is less than 93%,while the vertical transport becomes dominant when it is higher than 93%. The experiments also indicate that with decreasingsaturation, the recombination of more oxygen at the negative plate may oxidize more active H