To deepen our understanding of the ion association, several Cole-Cole plots were taken into consideration as shown in Figure . The presence of multiple depressed semicircles in the Cole-Cole permittivity and capacitance plots reveals complex dielectric behavior characterized by multiple relaxation processes and complex ionic environments within the EDL. On the other hand, the Nyquist admittance (Figure ) and Cole-Cole conductivity (Figure ) plots show single perfect semicircles, indicating a single relaxation time and validating the accuracy of our EDL capacitance calculation approach. However, the depressed semicircles in The influence of ion association on electrochemical data was further confirmed by Raman spectra, showing successive shifts of the sulfur-nitrogen-sulfur (S-N-S) bending band from ~744 cm⁻¹ (1 mol•kg⁻¹) to ~748 cm⁻¹ (20 mol•kg⁻¹) as illustrated in Figure . The LiTFSI salt crystal exhibits an S-N-S band at 751.6 cm⁻¹, as demonstrated in Figure . This shift results from significant changes in the hydration structure of Li + and TFSI -, forming various Li + -TFSI -clusters, such as the free anion (FA) at 738.6 cm⁻¹, the loose ion pair (LIP) at 743.9 cm⁻¹, the intimate ion pair (IIP) at 747.4 cm⁻¹, and the aggregate ion pair (AGP) at 749.1 cm⁻¹. These regions were deconvoluted to estimate the ion-pair contribution percentages based on their corresponding peak area to total area ratio. Peak fitting details along with error ranges are provided in Tables and . PFG-NMR shows the co-existence of these ion pairs to result in a dramatic decrease in the diffusivity of Li + and TFSI -. The self-ion diffusivity values listed in Tables and were used to obtain ion-pair (mutual) diffusivity values DLiTFSI in Table . This was achieved by applying the modified Darken's relationship for binary diffusivity, as proposed by Krachkovskiy et al. and summarized in Method S5. The ionic tortuosity of the water channels imposed by the ion pairs could be expressed as the ratio of diffusivity in the 1 mol•kg⁻¹ solution to that at any specific concentration between 5 and 20 mol•kg⁻¹. Figure and Table illustrate a notable monotonic increase in ionic tortuosity with respect to salt concentration, aligning with the observations reported by Han et al. Therefore, the polarizability of electrolyte solutions decreases with increasing salt concentration, resulting in a very low relative permittivity in Figure , as determined by Kim et al. using dielectric relaxation spectroscopy. These spatial phenomena result in a monotonic increase in the inner frictional constant ξ, calculated on the basis of Stokes' law in equation 2 and illustrated in Figure .