Nanostructure of ZnCl 2 + LiCl Water-in-Bisalt Electrolytes and Their Anomalous Volumetric and Transport Properties

Abstract

Superconcentrated aqueous solutions of two salts, named “water-in-bisalt” electrolytes (WIBEs) are a subclass of the water-in-salt electrolytes (WISEs) with applications to different types of advanced aqueous batteries. Here, we have investigated the nanostructural, volumetric, and transport properties of highly concentrated ZnCl2 + LiCl WIBE with relevance for advanced aqueous Zn batteries. Nontrivial results have been observed for the molar volume and the viscosity of ZnCl2 (30 m) + LiCl (m) solutions, although they exhibit an almost ideal volumetric behavior. A strong conductivity/viscosity decoupling is observed when LiCl is added to the 30 m ZnCl2 solution, which is the signature of nanoscale heterogeneities that were revealed by small-angle neutron scattering analysis. The results complement previous Raman spectroscopy studies, indicating the presence of [ZnCl4−m m−2 ] ionic clusters, with a characteristic size around 3 Å, but also the existence of bicontinuous nanodomains that can be described by the Teubner−Streyl model, with characteristic distances around 7.8 Å−9.4 Å.