Influence of cycling on the nature of the positive active mass of lead/acid batteries and effect of CaSO4 on the behaviour of the positive plates

Through cycling of tubular powder electrodes filled with positive active mass (PAM) powder obtained from positive SLI plates with purelead grids, it has been established that during cycling PAM loses its ability to restore its skeleton structure. X-ray diffraction investigations have shown that the crystallinity of PAM increases on cycling. This is probably the reason for the loss of PAMʹs ability to restore its skeleton structure. This ability is influenced by some metal ions called binders. The results of the present investigation indicate that Sn+ i ions do not act as binders in contrast to Ca+ i ions, which have a notable binder action. They facilitate the rebuilding process of the disintegrated PAM structure during discharge and, thus, improve the cycle life of positive plates with pure-lead grids. This effect of Ca+ i ions is most pronounced when the positive paste contains 0.8% of CaSO4.. Besides, Ca+ i ions reduce the crystallinity of PAM particles and, hence, their proportion of gel (hydrated) zones increases. This yields a flexible skeleton structure of PAM. The effect of Ca+ i ions on the properties of PAM is explained by the phenomena that occur in the gel/crystal structure of the PAM as a result of the electrochemical, chemical and crystallization processes.