Aqueous Zn-ion batteries (AZIBs) have been recognized as promising energy storage devices due to their high theoretical energy density and cost-effectiveness. However, side reactions and Zn dendrite generation during cycling limit their practical application. Herein, ammonium acetate (CH 3 COONH 4 ) is selected as a trifunctional electrolyte additive to enhance the electrochemical performance of AZIBs. Research findings show that NH 4 + (oxygen ligand) and CH 3 COO -(hydrogenligand) with preferential adsorption on the Zn electrode surface can not only hinder Zn anode directly contact with active H 2 O, but also regulate the pH value of the electrolyte, thus suppressing the parasitic reactions. Additionally, the formed SEI is mainly consisted of Zn 5 (CO 3 ) 2 (OH) 6 with a high Zn 2+ transference number, which could achieve a dendrite-free Zn anode by homogenizing Zn deposition. Consequently, the Zn||Zn symmetric batteries with CH 3 COONH 4 -based electrolyte can operate steadily at an ultrahigh current density of 40 mA cm -2 with a cumulative capacity of 6880 mAh cm -2 , especially stable cycling at −10 °C. The assembled Zn||MnO 2 full cell and Zn||activated carbon capacitor also deliver prominent electrochemical reversibility. This work provides unique understanding of designing multi-functional electrolyte additive and promotes a long lifespan at ultrahigh current density for AZIBs.

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