Self-assembled Cationic Surfactant-based Electrolytes for Rechargeable Aqueous Zinc Metal Batteries

Surfactants possess unique properties in bulk solutions and at interfaces, naturally forming self-assembled structures. Herein, cetyltrimethylammonium trifluoroacetate (CTATFA) was incorporated into aqueous electrolytes as a cationic surfactant to enhance their ionic conductivity and electrochemical stability. The presence of CTATFA widened the electrochemical stability windows of both Li-based and Zn-based electrolytes. The Zn-based electrolyte exhibited high ionic conductivity and low viscosity in the bulk solution. In a Zn symmetric cell, the electrolyte containing 1 M Zn(TFA)2-0.5 M CTATFA demonstrated excellent Zn plating/stripping reversibility for over 800 h at 1 mAh cm−2 and 1 mA cm−2. A Zn-Cu cell with 1 M Zn(TFA)2-0.5 M CTATFA exhibited excellent reversibility, achieving over 300 plating/stripping cycles at 5 mA cm−2 and 5 mAh cm−2. The Zn/MnO2 cell using the Zn-based electrolyte also demonstrated a specific capacity of 105 mAh g−1 over 750 cycles at a current density of 0.5 A g−1. This study provides insight into the design of high-performance aqueous electrolytes based on the self-assembly and surface adsorption of cationic surfactants.