Irrespective of the anion size considered, the cations are seen to be primarily localized on the surface sites for all particle loadings (Figure ). This is a consequence of the strong electrostatic interactions between the cations and the grafted anions. In other words, the primary mechanism of cation diffusion in such nanoparticle-based single-ion conducting electrolytes is by transport along the surface sites. Based on this observation, the increase in D cat and conductivity with φ at low particle loadings can be understood as a consequence of the associated reduction of interparticle distance (SI, Section S5.1) and the corresponding increase of connectivity between the surface sites of neighboring particles. This proximity allows for the cations to more easily hop between the surface sites of neighboring particles and traverse larger distances per unit time. To understand the decrease in conductivity at higher particle volume fractions (Fig-