A parts-per-million scale electrolyte additive for durable aqueous zinc batteries

Zinc-ion batteries have demonstrated promising potential for future energy storage, whereas drawbacks, including dendrite growth, hydrogen evolution reaction, and localized deposition, heavily hinder their development for practical applications. Herein, unlike elaborated structural design and electrolyte excogitation, we introduce an effective parts-per-million (ppm)-scale electrolyte additive, phosphonoglycolic acid (PPGA), to overcome the intrinsic issues of zinc negative electrode in mild acidic aqueous electrolytes. Profiting from absorbed PPGA on zinc surface and its beneficial interaction with hydrogen bonds of adjacent water molecules, stable symmetric stripping/plating of zinc in aqueous ZnSO₄ electrolyte at around 25 ^oC was achieved, procuring 362 and 350 days of operation at 1 mA cm^-2, 1 mAh cm^-2 and 10 mA cm^-2, 1 mAh cm^-2, respectively. As a proof-of-concept, an Ah-level Zn||Zn_0.25V₂O₅·nH₂O pouch cell examined the validity of PPGA and sustained 250 cycles at 0.2 A g^-1 and around 25 ^oC without capacity loss. The Zn||Br₂ redox flow battery demonstrated an operation of over 800 h at 40 mA cm^-2, 20 mAh cm^-2 with an average coulombic efficiency of 98%, which is attributed to restrained dendrite growth and side effects. This work is believed to open up new ways forward for knowledge of electrolyte additive engineering.