Weakly Solvating Nonaqueous Electrolyte Enables Zn Anode with Long-term Stability and Ultra-low Overpotential

Abstract

Developing nonaqueous electrolytes for zinc-ion batteries (ZIBs) is increasingly considered a promising solution to address the crucial issues associated with aqueous electrolytes, including hydrogen evolution, side reactions, and dendritic growth. However, most organic solvents tend to form a double-toothed or multi-toothed Zn-O strong coordination structure with Zn²⁺ through the donor O atom, which significantly impedes the de-solvation kinetics and results in an undesired overpotential during Zn deposition. A promising strategy is employing nitrogenous solvents to construct a weakly solvated structure with Zn-N coordination and simultaneously permit a high proportion of anion entry into the solvation sheath. Inspired by this, a weakly solvating nonaqueous electrolyte is designed using methylimidazole (EMI) and Zn(TFSI)₂ as the solvent and salt, respectively, in which Zn(EMI)_4.99(TFSI)_1.01 is determined the most stable thermodynamic configuration. During the deposition process, the TFSI^– anion in the solvated sheath is preferentially reduced, resulting in forming a double-layer solid electrolyte interface (SEI) that is rich in ZnF₂, ZnS, and ZnN_x favorable inorganic components. As expected, the designed nonaqueous electrolyte offers a long-term stable Zn plating/stripping performance over 7900 h (∼ 11 months) and an ultra-low overpotential of 20 mV. The Zn||Cu asymmetric cell exhibits an average Coulombic efficiency as high as 99.43%, providing a novel insight and avenue for promising nonaqueous electrolyte design.