Antimony in lead/antimony alloys is known to have a beneficial influence on tile capacity and cycle life of lead-acid battery positive plates. The present work shows that Sb3O93- ions formed on oxidation of PbSb alloys improve the capacity of the Pb/PbO2 electrode. Whilst SbOSO4- ions have an adverse effect and passivate this electrode, A mechanism of the influence of these ions is proposed based on the gel-crystal concept for the structure of PbO2. The paper also discusses the effect of PbSO4 formed at the grid/PAM interface on the capacity. It has been established that the major part of the PbSO4 crystals are oxidized to PbO2 within a few cycles. There still remain a certain number of PbSO4 crystals which border narrow pores and are oxidized at a very slow rate, thus preserving their influence even after 10 discharge-charge cycles. It has also been found that the higher the density of PAM the stronger the adverse effect of PbSO4 in the grid/PAM interface on the capacity. All these phenomena are related to the PCL effect and methods to suppress them are proposed.