Stabilization of zinc metal electrodes by solvation structure modulation of Zn(NTf2)2 electrolyte additives†

Abstract

Currently, aqueous Zn-ion batteries (ZIBs) are considered as one of the most promising sustainable energy storage devices. However, issues such as dendrite growth of Zn and the occurrence of side reactions constrain their development. This study addresses these challenges by introducing a novel electrolyte additive, Zn(NTf₂)₂, into 1 M ZnSO₄, resulting in enhanced specific capacity and improved cycling stability. The mechanism of Zn(NTf₂)₂ is investigated using techniques such as molecular dynamics simulations, molecular orbital theory analysis, X-ray photoelectron spectroscopy, and in situ deposition experiments. The additive Zn(NTf₂)₂ functions by altering the solvation structure of Zn²⁺, disrupting the hydrogen bonding network among water molecules and reducing the activity of water molecules, thereby suppressing side reactions and controlling dendrite growth. Consequently, the addition of Zn(NTf₂)₂ improves the dendrite growth problem, extends the cycle stability, and enhances the specific capacity of the battery. Zn symmetric cells with 3% Zn(NTf₂)₂ added can demonstrate stable cycling for more than 2000 h and the full cell with 3% Zn(NTf₂)₂ maintains a discharge capacity of around 100 mA h g⁻¹ after 160 cycles. This research provides a strategy for improving the electrochemical performance of aqueous Zn²⁺ batteries through electrolyte additives.