Improvement of the performance of the positive electrode in the lead/acid battery by addition of boric acid

A major disadvantage of the lead/acid battery is the decrease in voltage during operation which makes it unsuitable for systems sensitive to voltage fluctuations. Additives like BaSO4 or SrSO4, which are isomorphous to PbSO4, have been used to overcome this problem. Phosphoric acid and the various phosphates have long been used to improve the performance of the positive electrode of the battery. A beneficial effect of phosphoric acid is to inhibit the rate of the self-discharge reaction of the positive electrode in the lead/acid battery. However, adverse effects of phosphoric acid include capacity loss in the initial cycles, excessive mossing, especially at high H3PO4 concentrations, and poor low-temperature performance (decrease in the rate of PbSO4 oxidation). The effect of boric acid as an additive substituting for H3PO4 has been investigated using linear sweep voltammetry, constant potential and impedance measurements. The results show that boric acid markedly improves the kinetics of the PbO2/PbSO4 couple and removes the problems encountered during the usage of H3PO4.