INFLUENCE OF PHOSPHORIC-ACID ON BOTH THE ELECTROCHEMISTRY AND THE OPERATING BEHAVIOR OF THE LEAD ACID SYSTEM

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 PbSO4 is decreased considerably in the presence of phosphoric acid. The utilization of the positive active material is reduced because of the resulting fine-grained PbSO4 covers the PbO2. On the other hand, the PbSO4 protects the corrosion layer against further discharge. The action of phosphoric acid is demonstrated through cyclic voltammetric, potential-step, impedance and microscopic investigations.