Supercapacitors are becoming increasingly important in energy storage applications due to their high power density, long cycle life, and fast charging capabilities. However, to further enhance supercapacitor performance, a deeper understanding of the electric double layer (EDL) structure at the electrode-electrolyte interface is essential. This molecular dynamics (MD) study explores the structure and electrochemical behavior of 2 M 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide/dimethyl sulfoxide ([EMIM][NTf₂]/DMSO) electrolytes, with and without water impurities, confined within slit-shaped carbon micropores (widths: 0.7–1.9 nm; surface charge densities: 0 to ± 1.6 e/nm²). The findings reveal that water disrupts ion layering, reduces the counterion fraction near electrode surfaces, and alters hydrogen-bonding patterns. Disjoining pressure oscillates with pore width, with minor changes upon water addition. The disjoining pressure's parabolic dependence on surface charge matches reported data for [EMIM][NTf₂] in carbon electrodes. Water reduces disjoining pressure in moderately negative pores (σ = -0.2 to -0.8 e/nm²) but increases it in neutral and highly charged pores, reflecting hydration and adsorption changes. Calculated differential capacitance profiles exhibit camel-shaped curves, with an asymmetry between positive and negative potentials, consistent with experimental trends for [EMIM][NTf₂]/DMSO systems. The values align closely with those reported for carbon electrodes.
