Re-Evaluation of the Electrochemical Performance of Ketjen Black in Aqueous Zinc-Ion Batteries and Overcharge Effect.

Carbon additives, known for their high surface area and excellent electronic conductivity, are commonly employed in battery systems to enhance the electrochemical performance of active materials. Traditionally, however, these additives have been considered electrochemically inert, and their intrinsic properties have largely been overlooked. In this study, the electrochemical behavior of Ketjen black is systematically re-evaluated in aqueous zinc batteries by varying the electrolyte composition and the upper cutoff voltages. Under standard conditions, Ketjen Black EC600J (KB) exhibits typical electric double-layer capacitor behavior, with its capacitance dependent on the applied voltage range. Notably, when the batteries are overcharged, a new pair of redox peaks emerges at ≈1.2/1.4 V, accompanied by a significant increase in capacitance to ≈123 mAh g^-1 at a current density of 0.5 A g^-1. This overcharge-induced activation is attributed to a preliminary anion intercalation process. Subsequent analysis reveals the presence of a dual-ion intercalation mechanism. Furthermore, KB demonstrates robust cycling stability over 300 cycles in the modified electrolyte, with the specific capacity retaining ≈83 mAh g^-1.