Enhanced cycle performance of Ultrabatteries by a surface-treated-coke coating

Lead-acid batteries and Ultrabatteries suffer from hard sulfation due to the high-rate partial state-of-charge (HRPSoC) cycling that occurs in practical applications. In this work, we use low-cost and highly abundant coke as the coating material on Pb negative electrodes in ultracells. The effects of the surface treatments of the coke prior to coating are investigated in terms of the electrochemical properties of the resulting cells. The coke is subjected to KOH activation, followed by surface treatments of either mild oxidation (MO) or H₂O₂ treatment, resulting in the increase in its specific surface area and porosity. Additionally, oxygen-containing functional groups, such as -hydroxyl, -carbonyl, and -carboxyl groups, are formed on the surfaces of the coke, which appear to hinder the parasitic hydrogen evolution reaction that occurs during charging. The full-cell tests demonstrate that coating of the KOH-MO-treated coke on the Pb electrodes results in the improvement of the charge acceptances and HRPSoC cycling stabilities over 10⁴ cycles for these cells. This is due to the improved charge delocalization that hinders the occurrence of severe sulfation during repeated cycles.