We find that the primary factor influencing L ++ self and L -- self is the overall density of the electrolyte, where the latter is determined by the piston equilibration method described above. In Fig. , we overlay the electrolyte's self-diffusion coefficients and the inverse of the solution density as a function of slit height. We observe a very strong correlation between these quantities, with higher densities yielding lower self-diffusion coefficients of all species. The non-monotonic trend in water dynamics resulting from density/layering effects has been reported previously for both viscosity and diffusion coefficients based on classical force field-based simulations of pure water in graphene slit-pores, in which oscillations were observed based on whether the slit heights were commensurate or incommensurate with full, well-separated water layers. We observe that non-monotonic water transport also translates to very similar trends in sodium and chloride ion diffusion. To further demonstrate the importance of solution density in determining electrolyte diffusion, we have performed additional simulations for some of the slit heights in which the density is fixed at a constant value, rather than the equilibrium value obtained from the piston-based procedure. These systems will be subject to artificial pressure between the electrolyte and graphene sheets and thus may not correspond to experimentally relevant setups, but they allow us to more directly probe the role of density on electrolyte transport.