Cholinium Cations Enable Highly Compact and Dendrite‐Free Zn Metal Anodes in Aqueous Electrolytes

Abstract Metallic Zn is believed to be an ideal anode for aqueous batteries, but its reversibility is deteriorated by noncompact and dendritic Zn deposition along with interfacial parasitic reactions. Herein, it is reported that introducing cholinium (Ch + ) cations into aqueous electrolytes enables a spatially compact, non‐dendritic, and corrosion‐free Zn electrode even at high areal capacity (5.0 and 10.0 mAh cm –2 ) using a pressure‐free electrolytic cell. This strategy is applicable to various Zn‐salt‐based aqueous electrolytes (e.g., 1 M ZnSO 4 , Zn(CH 3 COO) 2 , and ZnCl 2 ). It is found that bulky Ch + cations create a “leveling effect” to homogenize Zn deposition and render an H 2 O poor electrical double layer near Zn by favorably absorbing on the Zn surface. Moreover, Ch + cations with –OH group disrupt the original H‐bonded network of water to reduce H 2 O‐induced side reactions and promote the Zn 2+ de‐solvation by forming H‐bond with H 2 O. As a result, the Zn electrode in the optimized 1 M ZnSO 4 with 4 M Ch + electrolyte manifests remarkable electrochemical performances involving high Coulombic efficiency of 99.6% in Zn//Cu cell and prolonged cycling stability over 2000 h in Zn//Zn cell (1.0 mA cm –2 , 1.0 mAh cm –2 ). This work provides a new strategy for the design of compact and dendrite‐free Zn battery chemistry.