BATTERY PERFORMANCE ENHANCEMENT WITH ADDITIONS OF BISMUTH

Automotive and valve-regulated batteries (VRBs) of typical commercial design have been constructed using positive and negative plates produc ed from leady oxide that is doped with 0.06 wt.% bismuth. The doping i s performed by adding bismuth (III) oxide powder during the paste-mixi ng stage. Both battery designs have been subjected to endurance tests (automotive batteries: JIS cycle-life test; VRBs: repetitive 3-h disch arge) in parallel with batteries that are similar in all respects but do not contain bismuth. A strategy and necessary hardware have been de veloped to measure the gassing properties of the VRBs during both char ge and discharge. The procedure involves monitoring the internal press ure with high-precision pressure transducers. For automotive batteries , doping with bismuth produces no significant differences in JIS cycle life. By contrast, both the endurance and the capacity of VRBs are fo und to be enhanced by the presence of bismuth. Furthermore, bismuth re duces the build-up in gas pressure (mainly oxygen) in VRBs during cons tant-current charging. These results suggest that future specification s for leady oxide should include a minimum - rather than a maximum - b ismuth content. In this respect, although studies performed to date sh ow that significant advantages can be achieved with 0.06 wt.% bismuth in the active material, the optimum bismuth level has yet to be establ ished.