EFFECT OF PHOSPHORIC-ACID ON THE POSITIVE ELECTRODE IN THE LEAD-ACID-BATTERY .3. MECHANISM

Phosphoric acid added to battery electrolyte modifies the morphology of PbO2 corrosion films by reacting to produce Pb3(PO4)2 as an intermediate in the oxidation of Pb to PbO2. Because these modified PbO2 films resist reduction to PbSO4, battery failure from formation of a resistive PbSO4 film at the positive grid/active material interface is forestalled. Three new findings support this mechanism: (i) the identification of Pb3(PO4)2 in lead corrosion films, (ii) the predictions of a thermodynamic model of the Pb/H2SO4/H3PO4/H2O system, and (Hi) the measurement of sulfation rates of PbO2 films formed from Pb3(PO4)2 and PbHPO4. © 1979, The Electrochemical Society, Inc. All rights reserved.