Effect of particle size, surface area and conductivity of nano-carbon additives on deep discharge lead-acid battery

The effect of carbon nano- and micro-particle additives on performance of lead-acid battery (LAB) was studied by considering two different carbon blacks, both having low electrical conductivity. Full-scale 150 Ah flooded-electrolyte stationary batteries were prepared in a battery manufacturing unit and subjected to deep discharge cyclic conditions at depth-of-discharge (DOD) similar to 65%. We report that carbon particle size played a significant role in LAB performance. In comparison to nano-size, micron-scale particles demonstrated better results and this was completely in accordance with Pavlov's findings. Moreover, an improvement in LAB charging regime and its charge return percentage was observed by the inclusion of multi-walled carbon nanotubes (MWCNTs) in negative active material (NAM). Intriguingly, upon testing with 100 Ah deep discharge traction battery by replacing 0.075 wt% of micron additive with MWCNTs, the battery back-up time was increased by half an hour roughly (during C5 discharge with 100% DOD), while its charging time was reduced by 15-25 min, which seems to be significant. Such enhancement in LAB's charge-discharge efficacy can be attributed to high specific surface area and electrical conductivity of MWCNTs, which with its tubular morphology was helpful in establishing an effective conductive network within NAM. The microscopic analysis confirms the useful dispersion and structural stability of MWCNTs in NAM.