Nigel Peter Haigh

Understanding the mechanism by which bismuth improves lead-acid battery capacity

Abstract To elucidate the mechanism by which bismuth enhances the capacity of valve-regulated lead-acid (VRLA) batteries, model experiments are performed on pulverized positive electrodes produced either from leady oxide, which contains virtually no bismuth (termed ‘Bi-free oxide’), or from Pasminco VRLA Refined™ oxide, which is of high purity and contains a specified amount (0.05 wt.%) of bismuth. The electrodes are compressed under a range of pressures (1.4 to 60 kPa). Below 40 kPa, the presence of bismuth increases the initial capacity. At all pressures, bismuth enhances the rate at which the capacity develops during cycling. Reconnection of the separated agglomerates of lead dioxide is the key factor in restoring the capacity of the pulverized electrode. Electron micrographs reveal that there are two essential types of contact in the positive material: (i) ‘micro-contact’ between individual irregular-shaped or individual needle-like crystals, to form the agglomerates; (ii) ‘macro-contact’ between individual agglomerates, to form the skeleton of the positive mass. Bismuth encourages the growth of fine needle-like crystals on the surface of the agglomerates. These crystals spread out and inter-weld to form ‘bridges’ between the agglomerates and, thereby, consolidate the porous mass of the electrode. This influence of bismuth on morphology is considered to be responsible for the demonstrated improvements in capacity performance.

Capacity and cycle-life of batteries using bismuth-bearing oxide

Abstract An examination is made of the capacity performance of lead–acid positive electrodes which are prepared from bismuth (Bi)-bearing oxide. This oxide is produced from Pasminco VRLA Refined™ lead which contains 0.05 wt.% Bi. For comparison, benchmark tests are performed on electrodes made from oxide with virtually no bismuth (

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

Abstract This investigation examines the cycle-life of valve-regulated lead-acid (VRLA) batteries which have been fabricated either with the manufacturers 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).