Strontium-Enriched Barite for Enhanced PbSO₄ Nucleation in Lead-Acid Batteries

Barite (BaSO₄) crystals are an important additive in lead acid batteries due to their ability to promote the controlled nucleation and growth of anglesite (PbSO₄) during battery cycling. This is due to BaSO₄'s isostructural match with PbSO₄, which facilitates epitaxial nucleation. However, BaSO₄'s efficacy as a nucleation promoter is limited by lattice mismatches between the two phases of 1-5%. Here, strontium-enriched barite, (Ba,Sr)SO₄, is synthesized to produce a nucleating promoter that displays an improved lattice match with PbSO₄. Nucleation of PbSO₄ from Pb-rich sulfuric acid solutions on strontium-free and strontium-enriched barite (up to 17 mol% Sr) is investigated using in-situ atomic force microscopy and optical microscopy. At low strontium concentrations, PbSO₄ forms by the Stranski-Krastanov growth pathway (monolayer + island formation), with most nucleation occurring on edges and surface defects. At higher concentrations, the layer-by-layer growth mechanism known as Frank van-der-Merwe growth is observed, which allows for facile growth of continuous PbSO₄ films across the BaSO₄ surface. These films are successfully re-dissolved on exposure to Pb-free sulfuric acid. The results show that strontium incorporation fundamentally alters the mechanism of PbSO₄ nucleation on BaSO₄, and thus provides a potential avenue for creating improved nucleation promoters in lead-acid batteries.