Figure 6 . (a) Surface voltage as a function of surface charge density; and (b) the capacitance of nanoslit versus the surface charge density, predicted through the CDFT in comparison with the simulation reported by Górniak et al.59
By using the MDFT in combination with the critical structural orientation = 0.68, we first calculate the solvation diameters of ions in confined MeCN within the nanoslits with different pore widths. Here, the anion of BF4- is considered which is modeled as a LJ particle carrying one elementary charge. The LJ parameters are presented in the SI with the size of bare ion = 0.33 nm.Figure 7 (a) shows the dependence of the predicted solvation diameter versus the pore width of nanoslit,i.e ., . The solvation diameter varies along the pore width, displaying an oscillative decline when reducing the pore width.
By incorporating the ion solvation diameter into the solvation-diameter-dependent coarse-grained model, and assuming that the cation and anion have equal size, the capacitances of the nanoslits involving MeCN-based electrolyte with different pore widths are calculated through CDFT, as shown in Figure 7 (b) . Here, the bulk ion concentration = 1.50 M and the other system parameters are the same as those in Figure 5 . For comparison, the capacitances without considering ion desolvation are calculated as well, in which all parameters are the same except that a uniform ion size is adopted as = 0.73 nm corresponding to the solvation diameter of BF4- in bulk MeCN. Conventionally, the ion solvation diameter in bulk solution has been employed in theoretical calculation.60