Further demonstration of improved performance from lead-acid batteries manufactured with bismuth-bearing high-purity lead

This investigation examines the cycle-life of valve-regulated lead-acid (VRLA) batteries which have been fabricated either with the manufacturer's own leady oxide (termed ‘factory oxide’) or with leady oxide prepared from Pasminco VRLA Refined™ lead (termed ‘VRLA Refined™ oxide’). VRLA Refined™ lead is a soft lead of high purity with a specified amount (0.05 wt.%) of bismuth. To provide a comparison of performance, benchmark tests are performed on batteries of equivalent design that have been supplied by two different manufacturers. Batteries made from factory oxide exhibit cycle-lives which exceed the minimum life specified by the Japanese Industrial Standard (JIS) test and by the International Electrotechnical Commission (IEC) test. Under the JIS procedure, the failure of both types of battery is due to expansion of the positive-plate material and subsequent extensive loss in connectivity between the constituent agglomerates of lead dioxide. By contrast, battery failure under the IEC procedure is caused by undercharging of the negative plates. The use of VRLA Refined™ oxide produces a marked improvement in battery cycle-life. Gains in performance from 675 to 800 cycles and from 510 to 675 cycles are obtained under JIS and IEC tests, respectively. It appears that the presence of bismuth at the specified level extends battery life by strengthening and increasing the connectivity in the positive-plate material (JIS test) or by raising the chargeability of negative plates (IEC test).