Water Loss in Carbon-doped Lead–Acid Batteries at Elevated Temperatures
Recent research efforts have clearly demonstrated that different forms of carbon added to the negative active-material (NAM) improve dynamic charge-acceptance and cycleability of lead–acid batteries during partial state-of-charge cycling duty (automotive or energy-storage applications). Unfortunately, however, the additional carbon content can raise the level of water consumption and thereby have an adverse impact on lead-acid battery performance. The processes and phenomena leading to increased water loss in carbon-containing lead̶–acid batteries at elevated temperatures have been scarcely studied. For instance, the literature data are not consistent and do not provide fundamental understanding of the impact of carbon materials under steady-state overcharge. It is, therefore, essential to establish first-order correlations between microstructure (morphology) and electrochemical properties of negative plates containing different carbon additives, related to processes and phenomena of water decomposition at high operating temperatures.
This presentation reports a study in which different paste batches were prepared by varying the concentration of certain carbon materials, namely, carbon black, activated carbon, graphite. For comparison, control cells without carbon additives in NAM were assembled. The essential carbon material characteristics (e.g., surface area, porosity) were varied, one at a time. The flooded cells (2 V, 4.5 Ah) were subjected to constant-current or constant-voltage overcharge at 25oC, 40oC, 60oC. The overcharging current, negative plate potential, input Ah and cell weight were monitored. The Tafel dependences of cell gassing at different temperatures were plotted. The correlation between water loss (g; g Ah-1), overcharging current, temperature and NAM microstructural characteristics was established. The different carbon forms are found to exert distinct patterns of behaviour on water loss with temperature variation. It is also concluded that carbon materials may affect the water loss indirectly by releasing organic substances into the electrolyte. Surprisingly, during overcharge of NAM with carbon additives, besides the hydrogen evolution reaction, certain processes provoking dramatic NAM structure reorganization also take place. There are changes in lead crystal morphology and pore system characteristics that are strongly affected by the type and content of carbon additives, as well as by the temperature.
Associate Professor, PhD, Institute of Electrochemistry and Energy Systems - Bulgarian Academy of Sciences
Plamen Nikolov holds the position of Associate Professor in the Institute of Electrochemistry and Energy Systems at the Bulgarian Academy of Sciences. He has more 15 years of experience in the research and development of lead–acid batteries. The major part of Plamen’s studies is directed to improvement and optimization of the dynamic charge-acceptance and cycling performance of lead̶–acid batteries for a variety of applications through the use of carbon additives to the negative active-mass.