Assessing the impact of an antisolvent-regulated ZnCl2 water-in-salt electrolyte on solvation structure: a multiscale computational validation for aqueous Zn-ion battery application

Abstract

This investigation delves into the profound alterations induced by methanol (MeOH) as an antisolvent in ZnCl₂ water-in-salt electrolyte (WiSE), specifically focusing on its influence on the solvation shell. Employing a comprehensive array of ex situ techniques and theoretical calculations, we scrutinize the chemical environment of solvated species. Remarkably, Raman and IR spectroscopy analysis unveiled a marked transformation in the solvation shell of the Zn²⁺ ion upon the addition of methanol, characterized by a discernible reduction in hydrogen bonding between H₂O–MeOH, correlating with methanol volume percentage. This observation is in good agreement with radial distribution function calculations. Consequently, the introduction of the antisolvent displayed discernible changes in ionic mobility and diffusion coefficients. Deeper insights into ion diffusivity and ionic mobility in the antisolvent-based electrolyte are gleaned through mean square displacement (MSD) and spatial distribution function (SDF) calculations. Moreover, the electrochemical ramifications of the modified electrolyte are substantiated by its application in investigating a Prussian blue analogue with rhombohedral structure (PBAR) in a half-cell. Notably, the PBAR demonstrates an augmented zinc storage capability and reversibility when utilized with 10 m ZnCl₂-WiSE-10% MeOH and exhibited a 17% improvement in specific capacity from 56 mA h g⁻¹ to 67 mA h g⁻¹. Furthermore, a full-cell aqueous zinc-ion battery comprising a PBAR as a cathode and Zn as an anode, integrated with 10 m ZnCl₂-WiSE-2% MeOH and operated at a high C-rate of 6C, exhibited exceptional reversibility, delivering high coulombic efficiency of >90% with better capacity retention. Thus, this exploration promises to furnish novel insight into the optimization of solvation structures, thereby bolstering the performance-cum-efficiency of aqueous zinc-based battery systems.