Manipulating hydrogen and coordination bond chemistry for reversible zinc metal anodes

Abstract

Aqueous zinc ion hybrid capacitors (ZHCs) are promising as electrochemical energy storage devices due to their safety and cost-effectiveness. However, the practical application of aqueous ZHCs is impeded by zinc dendrite growth and side reactions induced by H2O during long-term cycling. Herein, an organic small molecule, dimethyl sulfoxide (DMSO), is elaborately introduced into 2 M ZnSO4 electrolyte to simultaneously overcome these challenges. As convincingly evidenced by experimental and theoretical results, the DMSO reconstructs the Zn[(H2O)6]2+ structure and original hydrogen bond networks at the molecular level. By forming coordination bonds with Zn2+ and hydrogen bonds with H2O due to the stronger electron donating ability of oxygen in molecule, DMSO establishes a Zn2+ solvation shell structure that inhibits H2O decomposition and dendrite growth. As a proof of concept, the implementation of this hybrid electrolyte in a Zn||Cu asymmetrical cell results in a high Coulombic efficiency (CE) of over 99.8% for 568 cycles at a current density of 2 mA cm−2. Furthermore, the full cells using this hybrid electrolyte coupled with activated carbon (AC) cathode can operate for over 30,000 cycles. These results suggest that reconstructing the solvation structure and hydrogen bond networks guide the design of electrolytes for the development of high-performance aqueous ZHCs.