Uncovering Required Molecular Properties for Interface Regulators and Modification Mechanisms for Zn Anode in Aqueous Batteries

Abstract

Inhomogeneous deposition and side reactions at Zn anode in aqueous batteries seriously limit the electrochemical performance. Electrolyte additives at low content are desired, and the uncovery of fundamental required molecular properties is necessary. Herein, systematic studies are carried out to reveal factors showing correlations with the interface regulation effect and stability of the Zn electrode, which presents a screening rule for electrolyte additives. Accordingly, a phosphoramide (PA) molecule stands out as a suitable interface regulator with only 0.1% addition. Further analysis demonstrates the transformation of Zn²⁺ solvation structures from water-dominated in the bulk electrolyte to PA and anion participation toward the Zn surface. The latter helps to homogenize Zn²⁺ flux, modulate desolvation paths, regulate deposition kinetics, and suppress side reactions, which ensures the uniform and dense plating of Zn. Even with the high depth of discharge/capacity of 52.2%/50 mAh cm⁻² and 92.4%/88.5 mAh cm⁻², symmetric Zn cells still reach 392 h and 140 h lifespans, respectively, superior to PA-free cells (fails before 2 cycles/cannot cycle). The 0.1% PA additive also enables stable cycling for full cells.