Nanostructured Carbon-Enhanced Positive Active Mass for Absorbent Glass Mat 2 V Lead Acid Batteries: Toward Improved Active Material Utilization, Extended Cyclability, and Reduced Water Loss

This article investigates the effects of three commercial carbon compounds—graphite, carbon black (CB), and carbon nanotubes (d-CNT)—on positive active material (PAM) utilization, cycling performance, and water consumption (WC) in 2 V absorbent glass mat lead–acid batteries (LABs). After an initial screening of these materials based on their physicochemical properties—such as surface area, porosity, degree of graphitization, conductivity, and contact angle (wettability)—the carbon additives were incorporated into positive electrodes during manufacturing and tested in cells with a 1+/2− configuration. Both C20 and cold cranking tests revealed a significant increase in the specific discharge capacity of LABs containing d-CNT and graphite. Furthermore, LABs incorporating d-CNT or graphite exhibited an enhanced cyclability over other samples during the 50% depth-of-discharge test, also demonstrating a greater capacity to accept a larger charge during initial recharge. WC analysis, conducted in accordance with EN 50 342-1:2016−11 protocol, revealed reduced water loss, particularly in LABs with d-CNT, due to the increased recombination rate of hydrogen and oxygen resulting from electrolyte water electrolysis. Postmortem physicochemical analysis of the positive plates confirms these results. The CB-containing PAM exhibited the highest PbSO4 content, with scanning electron microscopy revealing larger PbSO4 crystallites on its surface. In contrast, graphite- and d-CNT-based samples showed smaller PbSO4 particles randomly distributed over the PAM surface, whereas in the STD PAM, PbO2 polymorphs covered larger PbSO4 crystallites.