Enabling Stable Zn Anodes by Molecularly Engineering the Inner Helmholtz Plane with Amphiphilic Dibenzenesulfonimide Additive

Abstract

The notorious dendrite growth and hydrogen evolution reaction (HER) are considered as main barriers that hinder the stability of the Zn-metal anode. Herein, molecular engineering is conducted to optimize the inner Helmholtz plane with a trace of amphiphilic dibenzenesulfonimide (BBI) in an aqueous electrolyte. Both experimental and computational results reveal that the BBI^- binds strongly with Zn²⁺ to form {Zn(BBI)(H₂ O)₄ }⁺ in the electrical double layer and reduces the water supply to the Zn anode. During the electroplating process, {Zn(BBI)(H₂ O)₄ }⁺ is "compressed" to the Zn anode/electrolyte interface by Zn²⁺ flow, and accumulated and adsorbed on the surface of the Zn anode to form a dynamic water-poor inner Helmholtz plane to inhibit HER. Meanwhile, the{Zn(BBI)(H₂ O)₄ }⁺ on the Zn anode surface possesses an even distribution, delivering uniform Zn²⁺ flow for smooth deposition without Zn dendrite growth. Consequently, the stability of the Zn anode is largely improved with merely 0.02 M BBI^- to the common electrolyte of 1 M ZnSO₄ . The assembled Zn||Zn symmetric cell can be cycled for more than 1180 h at 5 mA cm^-2 and 5 mA h cm^-2 . Besides, the practicability in Zn||NaV₃ O₈ ·1.5 H₂ O full cell is evaluated, which suggests efficient storage even under a high mass loading of 12 mg cm^-2 .