Hydrophilicity and Zincophilicity Coincorporated Zwitterionic Additives for High-Performance Zinc Metal Batteries

Despite the potential of Zn metal batteries (ZMBs) due to their low cost, environmental benefits, and favorable Zn²⁺/Zn redox potential, challenges such as low Zn utilization and parasitic reactions hinder their performance. These issues arise from the thermodynamic instability of the Zn anode and high-desolvation energy barriers. To overcome these challenges, this study investigates two zwitterionic compounds with hydrophilic and zincophilic functional groups, BES (N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid) and MES (2-(N-morpholino)ethanesulfonic acid), selecting BES as the optimal electrolyte additive. The zwitterionic effect of BES promotes Zn²⁺ dissociation, reduces concentration polarization, and enhances Zn²⁺ kinetics, forming a dynamic electric double layer (EDL) that guides uniform Zn deposition. As a result, Zn||Zn symmetric cells with BES demonstrate dendrite-free plating/stripping for over 3300 h at 1 mA cm^-2 and 2 mAh cm^-2. At a high current density (5 mA cm^-2) and a high areal capacity (10 mAh cm^-2), stable operation is achieved for over 450 h. Zn||ZnVO full cells show over 2700 cycles at 2 A g^-1 with 88% capacity retention. Zn||I₂ full cells cycle stably for over 30,000 cycles at 10 A g^-1 with negligible capacity decay, highlighting significant performance improvement of BES.