Inefficiency of the oxygen cycle and parameters on which it depends [VRLA batteries]

On cycling of VRLA batteries, the charge voltage is limited to 2.50-2.53 V/cell. This leads to intense oxygen evolution. When absorptive glass mat (AGM) is used as separator, the transport of oxygen is impeded and it is not possible for the whole amount of O₂ evolved at the positive plate to reach the negative plate and recombine to water there. Hence, the oxygen cycle is inefficient. Through measuring the gas leaving the battery cells it is possible to determine the inefficiency of the oxygen cycle (OC). The present paper reports the authors´ finding that there is an upper limit of the efficiency of the OC in VRLA batteries of the AGM type. The degree of polarization of these batteries is determined by the transport of oxygen through the AGM separator. With increase in temperature the inefficiency of the OC increases, especially at temperatures higher than 40°C. On cycling of VRLA batteries, the AGM separator undergoes certain structural changes, which impair the efficiency of the oxygen cycle