A Multifunctional Zwitterion Electrolyte Additive for Highly Reversible Zinc Metal Anode

Although zinc metal anode is promising for zinc-ion batteries (ZIBs) owing to high energy density, its reversibility is significantly obstructed by uncontrolled dendrite growth and parasitic reactions. Optimizing electrolytes is a facile yet effective method to simultaneously address these issues. Herein, 2-(N-morpholino)ethanesulfonic acid (MES), a pH buffer as novel additive, is initially introduced into conventional ZnSO4 electrolyte to ensure a dendrite-free zinc anode surface, enabling a stable Zn/electrolyte interface, which is achieved by controlling the solvated sheath through H2O poor electric double layer (EDL) derived from zwitterionic groups. Moreover, this zwitterionic additive can balance localized H+ concentration of the electrolyte system, thus preventing parasitic reactions in damaging electrodes. DFT calculation proves that the MES additive has a strong affinity with Zn2+ and induces uniform deposition along (002) orientation. As a result, the Zn anode in MES-based electrolyte exhibits exceptional plating/stripping lifespan with 1600 h at 0.5 mA cm-2 (0.5 mAh cm-2) and 430 h at 5.0 mA cm-2 (5.0 mAh cm-2) while it maintains high coulombic efficiency of 99.8%. This work proposes an effective and facile approach for designing dendrite-free anode for future aqueous Zn-based storage devices. The Regulation of Electrode Interface and Solvation Structure via Additive. The MES additive plays multifunctional roles in realizing highly reversible Zn2+ plating/stripping behavior by pH buffering, water shielding, and uniforming Zn2+ reflux guided by anionic sulfated group.image

Automated summary

This study proposes a method to improve the reversibility of zinc-ion batteries by optimizing the electrolyte composition and using MES additive. The MES additive can protect the zinc electrode surface from dendrite growth and prevent parasitic reactions by buffering the pH of the electrolyte and controlling the solvation structure. Experimental results show that the zinc anode in the MES-based electrolyte exhibits exceptional plating/stripping lifespan and high coulombic efficiency.