Monitoring the Cation Coordination Sphere Using Hydrated Eutectic Electrolyte for Better Cyclic Stability and High Energy Density Zn-Ion Battery

Abstract

Aqueous rechargeable Zn-ion batteries (ZiBs) are receiving increasing attention worldwide owing to their inherent safety and cost effectiveness. However, ZiBs are still struggling with rapid performance degradation caused by poor Zn anode reversibility and cathode dissolution into aqueous electrolytes. Inspired by the knowledge of industrial-scale Zn electroplating, a cyanide functional group containing a succinonitrile (SN) neutral ligand-based hydrated eutectic electrolyte was used to mitigate these issues. The ligand-oriented SN partially replaced free water molecules from the Zn2+ ion primary solvation sheath, resulting in delayed oxidation and a smaller Zn2+ ion desolvation energy barrier which promoted uniform Zn nucleation. Moreover, the MoO3@Mn3O4 cathode and Zn anode-based ZiB in an eutectic hydrated electrolyte with a 10:10 molar ratio of ZnCl2 and SN exhibited an ∼2.3 V working potential window which delivered a maximum of ∼476 mAh g–1 specific capacity and ∼232.2 Wh kg–1 energy density at a 0.2 A g–1 current density. The fabricated device exhibited ∼79.56% specific capacity retention after 5000 cycles at a 10 A g–1 current density. The coinsertion/extraction of H+ and Zn2+ ions and the Zn deposition/dissolution mechanism of the optimized hydrated eutectic electrolyte-based ZiBs are investigated by ex situ physicochemical and electrochemical studies. Overall, this work provides a new path on exploring green electrolytes and layered-structure materials for the development of high-performance ZiBs.