Enhanced ion conductivity of “water-in-salt” electrolytes by nanochannel membranes

Abstract

Understanding ion transport in electrolytes is fundamentally significant in nanofluidic, energy, and environmental sciences. Enhanced ion transport is widely observed in dilute electrolytes confined in nanochannels but is not well understood in concentrated electrolytes, including “water-in-salt” (WIS) systems. Herein, we report an unusually enhanced ion transport of WIS electrolytes in two-dimensional nanochannel membranes. Compared to in bulk solution, 21 M lithium electrolyte showed quadrupled ionic conductivity in confined graphene oxide (GO) nanochannels. Pulsed-field gradient nuclear magnetic resonance and modeling revealed a functional group-induced stratification mechanism for this faster transport, where a free anion layer moves between two continuous water-cation layers. As-fabricated lithium-ion batteries with GO nanochannel-confined electrolyte showed improved capacity and capacity retention at near 100% coulombic efficiency. Our work provides an insight into the ion transport mechanism in nanoconfined concentrated electrolytes and new strategies for designing high-performance and safe electrolytes for aqueous batteries and other energy and environmental devices.