Multifunctional Amphoteric Additive Alanine Enables High-Performance Wide-pH Zn Metal Anodes

Abstract

Interfacial pH fluctuation is one of the primary reasons for issues related to Zn metal anodes. Herein, polar amphoteric alanine, as a multifunctional electrolyte additive, is designed to regulate the electric double layer (EDL) and solvation structure. Alanine with self-adaptation capability to pH can stabilize electrolyte pH. Due to more negative adsorption energy, alanine preferentially adsorbs on the Zn surface and repels water molecules within the EDL. Alanine-enriched EDL effectively shields the surface tips, homogenizes interfacial electric field distribution, and promotes preferential deposition of horizontal flaky Zn. Alanine-enriched EDL limits the contact between water and the Zn anode. Alanine additive decreases the quantity of water molecules in the Zn²⁺ solvation sheath and disrupts H-bond networks in the electrolyte. Consequently, a dense and textured Zn deposition is achieved. Corrosion and side reactions are suppressed. Cycling stability of symmetrical cells attains 2700 h at 3 mA cm⁻²/1 mAh cm⁻² and 2050 h at 5 mA cm⁻²/1 mAh cm⁻². Average coulombic efficiency reaches 99.8% over 4500 cycles at 5 mA cm⁻²/1 mAh cm⁻². Even within KOH alkaline electrolytes, alanine additive still improves the cycling lifespan of symmetrical cells to 100 h at 0.5 mA cm⁻²/0.5 mAh cm⁻².