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

Abstract

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.