Corrosion resistance and cycling behaviour of pure lead gravity cast thick plate AGM VRLA reserve power batteries

Valve-regulated lead/acid (VRLA) batteries with absorptive glass mat (AGM) separators have been in use for over twenty years in different standby applications. These applications are increasingly varied, especially regarding environmental conditions like elevated temperature and frequent discharge. This paper describes how the use of pure lead in the positive grid of VRLA AGM reserve power products gives an improved combination of corrosion resistance and cyclability. This combination allows the use of VRLA AGM products in a wider range of applications. Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) experiments performed on samples of pure lead and lead-calcium-tin alloy give an indication of the superior corrosion resistance of pure lead but indicate a possible passivation issue in cycling. In addition to that, cycling experiments according to IEC 60896-21&22 standards and other custom specifications have been completed on VRLA AGM batteries with pure lead positive grids (pure lead product) and with lead-calcium-tin positive grids. These trials identified certain key parameters for the cyclability of pure lead products. Optimized design characteristics and recharge conditions must be defined in order to enhance the grid/active-material interface. Active mass must be formulated to avoid premature softening. Acid stratification must be limited as much as possible by selecting appropriate separator, saturation level and recharge conditions. It has also been identified that plate thickness is a very important factor because it impacts acid diffusion and hence influences the charge acceptance and recharge behaviour. When these characteristics are optimised pure lead products exhibit superior corrosion resistance whilst maintaining good cyclability.