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Hard carbon has emerged as an attractive anode material for sodium ion batteries (NIBs) because of its low cost, high initial coulombic efficiency, high specific capacity, and steady cycling performance. Based on combined molecular dynamics (MD) simulation and density functional theory (DFT) calculations, we present an atomistic description of the electrolyte-electrode interaction of sodium hexafluorophosphate (NaPF6) in mixed ethylene (EC) and dimethyl carbonate (DMC) electrolyte inside nanoporous carbon electrode. We investigate the microstructure of electrolyte in carbon nanopores with an average pore size of 8.9 Å and a specific surface area of 1794 m2g-1 at 0 V and 2 V to gain molecular insight into electrolyte behavior such as solvent packing, preferential adsorption sites, and solvation structure. Our simulation suggests good accessibility of carbon nanopores by electrolyte molecules upon charging. At 2 V, Na+ is desolvated and intercalates into highly confined carbon structures as a result of the strong interaction between Na+ and charged carbon atoms while PF6 - occupies weakly confined carbon nanostructures by forming ion pairs with Na+. Also, we examined the various levels of confinement of electrolyte components using a degree of confinement (DoC) analysis, and present the effects of confinement on electrolyte properties. Our calculations show a 29 % reduction in Na+ adsorption distance for a nanoporous structure compared to a planar structure of carbon, and the preferential adsorption of Na+ at a hydrogen-terminated edge of porous carbon with an adsorption energy of -0.27 eV compared to a basal site with a higher adsorption energy of 0.02 eV. Finally, an investigation of the solvation sheath structure as a function of DoC shows decreased solvation shell, shortened adsorption distances, and increased counter-charge with increasing DoC.

Sodium-ion batteries (NIBs) are in the spotlight as highly promising energy storage applications due to the low cost and wide availability of Na sources. To date, computational studies of Na storage and transport in carbon electrodes have been carried out without considering the realistic structural and dynamic properties of a carbon anode - electrolyte, which could be critical to battery performance. Using combined molecular dynamics (MD) simulation and density functional theory (DFT) calculations, we describe the behavior of a Na-based electrolyte, consisting of sodium hexafluorophosphate (NaPF6), ethylene carbonate (EC), and dimethyl carbonate (DMC), near the confined structures of nanoporous carbon electrodes. In our simulation, nanoporous carbons with an average pore size of 8.9 Å were first generated using the Mimetic porous carbon model by quench MD simulation. We also adopted the constant potential method (CPM) to model the electrode carbon to account for the fluctuation of the local charges that are characteristic of realistic battery systems. We investigated the distribution of electrolyte molecules and their microstructures at 0 V and 2 V potentials to provide molecular insights on properties such as solvent packing, degree of confinement (DoC), preferential adsorption sites, and solvation sheath structure. Under the influence of applied potential, we report a good wettability of the electrode by electrolyte molecules as a result of the interconnectivity of nanopores, with the accumulation of electrolyte compounds at the electrode/electrolyte interface as they diffuse into the nanopores. Also, Na+ intercalates into highly confined carbon structures while PF6 - occupies weakly confined carbon nanostructures by forming ion pairs with Na+. We show that nanoporous carbon structures reduce the adsorption distance of Na+ by ~29 % compared to planar electrodes and consequently identify a hydrogen-terminated edge of porous carbon as a preferential adsorption site for Na+ of favorable adsorption energy of -0.27 eV compared to the adsorption energy of 0.02 eV for Na+ insertion onto a basal surface. Finally, an investigation of the solvation sheath structure as a function of DoC shows decreased solvation shell, shortened adsorption distances, and increased counter-charge with increasing DoC.