Abstract
Electrolyte-filled nanoporous electrodes with fast-charging capability are critical for advanced energy storage and iontronic devices. However, experiments and simulations consistently show that increasing electrode thickness degrades performance by limiting ion access to effective electrode/electrolyte interfaces, especially under fast-charging conditions. While often attributed to sluggish ion transport, the underlying mechanisms and the quantitative link between thickness and performance remain unclear due to complex pore structures and nanoconfined ion dynamics. Here, using multilayered graphene membranes as a model system, modified Poisson-Nernst-Planck simulations with experiments are combined to reveal how electrosorbed ions reshape local electrical and chemical potentials, particularly as the surface-to-volume ratio increases with reduced pore size. It is shown that electrosorbed ions substantially influence the scaling behavior of capacitance across electrode thicknesses, causing marked deviations from classical transmission line models as pores approach nanometric dimensions. Despite the complexity introduced by nanoconfinement, introducing a correction factor enables capacitance-scan rate relationships to collapse into a unified curve across various electrode architectures, allowing computationally efficient design of high-performance fast-charging electrochemical and iontronic devices. This work highlights the unique role of 2D nanomaterials as a versatile platform for bridging experiments and theory to address long-standing challenges in ion transport dynamics.