Anion‐Regulated Electric Double Layer and Progressive Nucleation Enable Uniform and Nanoscale Zn Deposition for Aqueous Zinc‐Ion Batteries

Abstract

AbstractAqueous zinc‐ion batteries have been regarded as safe and cheap energy storage devices. However, severe zinc dendrite growth and water decomposition limit the sustainability of aqueous zinc‐ion batteries. Herein, sodium‐difluoro(oxalato)borate (NaDFOB) is introduced into ZnSO4 electrolyte to modify the electric double layer (EDL) and the nucleation mechanism. Electrochemical tests and density functional theory calculations reveal that DFOB− adsorbs on the zinc electrode to form a water‐poor EDL, effectively suppressing side reactions. Notably, a detailed investigation of zinc deposition demonstrates that the adsorbed DFOB− ions induce progressive nucleation, resulting in nanoscale zinc nuclei and uniform zinc growth. Additionally, the adsorbed DFOB− ions decompose into a solid electrolyte interphase, further protecting the zinc electrode. Consequently, the Zn/Zn symmetric cell using ZnSO4/NaDFOB electrolyte can cycle for over 500 h at 5 mA cm−2 to reach a capacity of 10 mAh cm−2, while a Zn/Cu half cell maintains an average Coulombic efficiency of 99.3% over 400 cycles. A high capacity retention of 93.0% with a capacity of 250 mAh g−1 at 0.2 A g−1 is achieved in the ZnSO4/NaDFOB electrolyte in full cell cycling. These findings highlight the impact of anion‐modified EDL and progressive nucleation on achieving highly uniform zinc deposition.