Unveiling the Descriptor of Parasitic Reactions of Zinc Anode: A Comparative Study of Trace Pyridinesulfonic Acid‐Based Additives in Aqueous Electrolyte

Abstract Understanding and controlling parasitic reactions on the Zn metal anode (ZMA) surface is essential to enhance the energy capabilities of aqueous zinc‐ion batteries (ZIBs). However, the accurate regulation scheme is often obscured due to the lack of fundamental understanding concerning the ZMA/electrolyte interface. Herein, the descriptor of interfacial parasitic reactions is revealed through a systematic comparative study of three model trace adsorption‐type pyridinesulfonic acid‐based additives with structural variations. Using in situ spectroscopies coupled with density functional theory calculations, direct spectroscopic evidence of interfacial H 2 O evolution during Zn 2+ deposition process is obtained. It is proposed that, beyond the traditional cognitions, the distance between solvated Zn(H 2 O) 6 2+ and ZMA surface highly dictates the stability of ZMAs. Consequently, the trace 3‐Pyridinesulfonic acid with most effective capacity to drive solvated Zn(H 2 O) 6 2+ away from the ZMA surface, enables a robust cycle life over 420 h for the Zn||Zn symmetric cell at 10 mA cm −2 /10 mAh cm −2 (depth of discharge of 45%), a high Coulombic efficiency of 99.78% and an extended cycling life of 1500 cycles for the Zn//NH 4 V 4 O 10 full battery. The work sheds light on the underlying mechanism of parasitic reactions on ZMA surface and provides fundamental insights into the design of trace additives for better ZIBs.