Charging capability of positive and negative plates in valve-regulated lead-acid batteries produced with Bi-bearing oxide

Based on research conducted in a joint CSIRO-Pasminco research programme, Pasminco has recently proposed a new specification for soft lead to suit the increasing performance requirements regulated lead-acid (VRLA) batteries. In this specification, bismuth (Bi), which has been demonstrated as being beneficial, is increased to a level which produces significant improvements in battery performance. By contrast, other common impurities which are known to be harmful to VRLA batteries are restricted to very low levels. Bi-bearing oxide (either Barton-pot or ball-mill variety), as well as VRLA batteries, has been manufactured from this new soft lead by various battery companies. These VRLA batteries provide good capacity and service-life under deep-discharge or partial state-of-discharge cycling. In this study, the suitability of VRLA batteries using Bi-bearing oxide for float service is assessed in terms of the float current and the charging capability of the negative and the positive plates, particularly at elevated temperatures. Results show that the batteries do not suffer from `selective discharge´ of the negative or the positive plates during float charging at a constant voltage. The set voltage can be as low as 2.20 V, even when oxygen reduction (`recombination´) has become very efficient (i.e., 98%). Moreover, the float current delivered by the Bi-bearing batteries over a wide range of temperatures (20 to 55°C) is significantly lower than that from commercial VRLA products. To gain maximum performance, the negative-to-positive mass ratios in VRLA batteries should be selected to suit the requirements of a particular float application, such as those experienced in telecommunications and uninterruptible power supply systems