Ionophilicity and transport dynamics of concentrated electrolytes in sub-nanometre graphite confinement

Abstract

Nanoconfined electrolytes exhibit distinct structural and transport properties critical for emerging energy storage and nanofluidic technologies. Graphite nanochannels, with their atomically smooth surfaces and ionophilicity, serve as ideal model systems to explore ion-specific interactions under extreme confinement. To investigate the ionophilicity of graphite, we performed molecular dynamics simulations on four aqueous electrolytes—LiCl, LiTFSI, NaCl, and NaTFSI—confined within 0.89 nm graphite slit pores. For LiCl and LiTFSI, additional simulations across a wide range of concentrations up to the water-in-salt regime were conducted. In agreement with experiments, at low concentrations, the channels show a clear anion selectivity: TFSI⁻-based electrolytes exhibit strong ion enrichment within the channel, whereas Cl⁻-based systems display significantly weaker adsorption. This preference is, however, notably reduced at higher concentrations, where ionic distributions become more uniform regardless of anion type. These results are rationalized in terms of capillary pressure and liquid viscosity, which ultimately govern the channel ions uptake. Our findings provide molecular-level insights into how ion-specific interactions regulate transport dynamics in narrow graphite channels, offering guidance for designing efficient nanoconfined electrochemical systems.