Effect of the carbon mesoporous structure on the transport properties of confined lithium chloride aqueous solutions

Abstract

Accurate determination of fluid dynamics in confined carbons with pore size distribution (PSD) ranging from micro to mesopores is a fundamental aspect for many relevant applications, such as lithium battery electrodes, supercapacitors, or fuel cells. Here we present a synthesis route that enables the preparation of carbons with tailored PSD, which are characterized by nitrogen adsorption methods and nuclear magnetic resonance (NMR). The combination of micro and mesopores is determined straightforwardly by the determination of confined water self-diffusion coefficients and longitudinal relaxation times. Employing 2D-NMR experiments pore interconnectivity was characterized, determining exchange rates for water between micropores, mesopores, and bulk solution. Furthermore, their functionality was tested in simple ion release experiments of a solution of LiCl carried out both by conductivity and NMR experiments. We found that the lithium release rate can be set by tailoring the connectivity between micro and mesopores. For samples with mesopores larger than 5 nm and a small content of micropores, ion mobility is mainly restricted by the material's porosity. On the other hand, tortuosity analysis reveals that carbon wall-ion interaction is the main factor of the sluggish diffusion in materials with a large fraction of micropores well connected to the mesopore network.