Strong Dipole Inner Salt Molecule as Interface Ion Bridge for Rechargeable Aqueous Zn-Anode Batteries

Abstract

Aqueous electrolyte additives are effective to improve the Zn anode performance, but their structural effect on electric double layer and Zn plating remains elusive. By comparing several additives with varied compositions and polarities, we reveal that the dipole moment plays an important role in modulating the electrode interface, while zincophilic functional groups are crucial to Zn stripping/plating kinetics. A strongly dipolar inner salt, L-α-glycerylphosphorylcholine, is screened as a favorable additive to stabilize the hydrophobic surface of the Zn anode and act as a Zn²⁺-migration bridge for fast desolvation. An aqueous 2 M ZnSO₄ electrolyte containing 75 mM L-α-glycerylphosphorylcholine results in the restriction of parasitic hydrogen evolution, zinc sulfation hydroxylation, and dendrite formation. Consequently, the Zn anodes achieve a high Coulombic efficiency of 99.8% in Zn||Cu cells at 1 mA cm^–2 and sustain 1800 h of cycling at 50% depth of discharge at 3 mA cm^–2. This study underscores the screening and mechanistic understanding of dipolar inner salt additives to formulate better aqueous electrolytes.