Influence of phosphoric acid on both the electrochemistry and the operating behaviour of the lead/acid system

Abstract The addition of phosphoric acid to the electrolyte or the positive active material of the lead/acid battery yields different results. For antimony-free batteries, the capacity is reduced but the lifetime is improved under deep-discharge service. Both effects at the positive electrode appear to originate from the same cause, namely, the crystal size of PbSO 4 is decreased considerably in the presence of phosphoric acid. The utilization of the positive active material is reduced because the resulting fine-grained PbSO 4 covers the PbO 2 . On the other hand, the PbSO 4 protects the corrosion layer against further discharge. The action of phosphoric acid is demonstrated through cyclic voltammetric, potential-step, impedance and microscopic investigations.