An Investigation of the Lead-Acid Negative Tafel Break

In the transition from antimonial to the lead-calcium alloy system in the U.S. stationary battery market, it was observed that the calcium suffers inherently wider voltage variation within a battery string than would be expected due to variability in cell purity levels. The opening discussion relates to the base for the Tafel presentation of electrode polarization behavior. The work of Willihnganz is reviewed in relation to the Tafel, particularly as positive float polarization levels affect corrosion life. The negative Tafel break is considered and its contribution to the bi-modal voltage distribution observed in calcium battery strings. The problem of insufficient positive polarization following start of float operation is discussed and depicted graphically. Experimental work conducted to discover the mechanisms at play in the float operation of the lead acid cell which cause the negative Tafel break are discussed. The discovery of the relationship between buoyancy and negative polarization from the beam cell experiment is considered. The experiments to operate the cell without the presence of the normal oxygen from the positive and the impact of this on negative tafel behavior are discussed. Based on the experimental data, the hypothesis for hydrogen shielding of the negative is reached and proven experimentally. Data characterizing tafel break behavior and its fundamental instability are discussed in light of the hydrogen shielding mechanism, resulting in the prediction of the observed bi-modal voltage distribution in full strings of batteries.