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

YQ Wang and XS Hao and Y Kang and MY Dong and Z Fang and Y Hu and HT Wang and XL Fan and YG Yan and ZZ Ye and XS Peng, JOURNAL OF MATERIALS CHEMISTRY A, 11, 1394-1402 (2023).

DOI: 10.1039/d2ta08244f

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.

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