An investigation has been made of the effect of lignin and BaSO4 on the capacity and life of the negative plate. BaSO~ alone, lignin alone, and combinations of the two improved cycle life. Of the combinations tested, 0.5% BaSO4 and L0% lignin gave the greatest improvement on SAE cycle life tests. Lignin alone was as effective as the lignin-BaSO4 combination in highrate, low-temperature discharges. Lignin decreased the diameter Of the lead particles and passivated portions of the lead surface, so that lead sulfate crystal growth was away from the surface, leaving considerable open space in the mass of crystals at the end of discharge. Without lignin the lead particles were larger, more closely spaced, and lead sulfate grew solidly along the lead surfaces, so that there was little void space at the end of charge. Microscopic examination showed nothing to explain the beneficial effect of BaSO4.

Microscopic investigation of the effect of lignin and BaSO4 on the negative lead electrode showed that lignin was able to modify the lead crystal structure produced during the forming operation, in addition to its effect on the structure of the PbSO4 crystals formed on discharge. The effect of the lignin was to reduce the size and complexity of the dendritic lead crystals in the formed plate. The presence of BaSO4 had no appreciable effect on the microstructure of the formed plate.At low temperatures and at high discharge rates, the capacity of lead-acid batteries of the pasted plate type is usually controlled by the negative lead electrode. This limiting action is the result of increased polarization at the negative electrode which seriously limits reaction. Of the factors responsible for this polarization, the resistive component is the most serious in its effect. That is to say that low temperature increases the viscosity of the electrolyte, decreases diffusion, lowers conductivity, and otherwise increases the resistance to current flow and reaction at both electrodes. The process at the negative, in addition, produces highly resistive and passivating films of lead sulfate on the reacting lead electrode. Although lead sulfate is also produced on the lead dioxide electrode, the passivating effect in this case is less severe so that the reaction at this electrode can be faster than at the lead electrode.It has been found that certain substances, called expanders, can decrease the polarization and passivation at the negative electrode. Lamp black, barium sulfate, and certain lignin derivatives have been found to change but not entirely eliminate the limiting character of the negative electrode.Of these additives, barium sulfate and lampblack have been used almost as long a time as have pasted electrodes and there is now no means of determining if their first use was the result of fortuity or deliberate planning. Lignin, however, was deliberately used to restore desirable properties attributed to products leached from wood separators, as this need became * Electrochemical Society Active Member.

No abstract

Der Einfluß von Lignin allein, BaSO4 allein und der beiden Additive zusammen auf Kapazität und Lebensdauer der negativen Platte wird untersucht.

Durch Rasterelektronenmikroskopie wird der Einfluß von Addition auf die Struktur der während des Ladens′ gebildeten Pb‐Dendriten untersucht.