Acid-treated multi-walled carbon nanotubes as additives for negative active materials to improve high-rate-partial-state-of-charge cycle-life of lead-acid batteries

In this work, a trace amount of acid-treated multi-walled carbon nanotubes (a-MWCNTs) is introduced into the negative active materials (NAMs) of a lead acid battery (LAB) by simply dispersing a-MWCNTs in the water, which is then added into the dry mixture of lead oxide powder, expanders and carbon black for lead paste preparation. The abundant oxygen-containing groups on the a-MWCNTs show significant influence on the chemical reactions happening during the curing process, leading to the improved properties of NAMs. Specifically, after formation, the NAMs containing 100 ppm a-MWCNTs display a spongy-like structure comprised of interconnected domino-like Pb slices, giving favorable porosity and electroactive surface area of the NAMs. Moreover, the quasi-rod structure of Pb slices provides the channels for fast electron transfer. These two features greatly accelerate the electrochemical reaction between Pb and PbSO4, and hence hinder the accumulation of PbSO4 crystals. As a result, the high-rate partial-state-of-charge (HRPSoC) cycle-life of the simulated cell constructed from the a-MWCNTs-containing negative plate achieves a HRPSoC cycle-life more than 1.5 times longer than the cell constructed when the negative plate contains only carbon black. Since our method is of great convenience and low-cost, it is expected to have a great feasibility in the LAB industry.