Novel insights into the impact of highly concentrated nanostructured carbon compounds on the positive active mass in a 2V AGM lead-acid battery

Lead–acid batteries (LABs) face persistent challenges, including lead-grid corrosion and sulfation, prompting ongoing research into performance improvements. One promising strategy involves the incorporation of nanostructured carbon materials into advanced electrodes. In this context, this paper evaluates three commercial carbon compounds (carbon black (CB), discrete carbon nanotubes (d-CNTs), and graphite), introduced into the positive plates during manufacturing at relatively high contents (0.4–1.6 wt.%PbO), focusing on their effects on battery capacity and water consumption (WC). C20 capacity tests showed that carbon-containing LABs delivered higher specific discharge capacity due to improved PAM utilization. In particular, adding graphite or d-CNTs at 1.6 wt.%PbO increased the specific discharge capacity by >5% compared with the standard (STD) cell. Accelerated WC analysis via electrolysis also indicated that carbon in the PAM—especially graphite at 1.6 wt.%PbO—substantially enhanced grid corrosion resistance and oxygen recombination. Post-test teardown analysis corroborated the SEM-observed microstructural changes in carbon-modified PAMs. Besides multiple PbO₂ polymorph crystallites, distinct PbSO₄ particle morphologies were detected in samples with carbon additives. Smaller PbSO₄ crystals were detected, particularly at high graphite and d-CNT loadings (1.6 wt.%PbO), instead of the larger agglomerates present on STD plate surfaces. These features promote better electrolyte diffusion and electronic exchange, thereby extending battery service life. XRD confirmed the reduced PbSO₄ content in cells with carbons, while cross-sectional SEM revealed well-defined, more homogeneous, and more compact corrosion layers compared with the STD.