A Perspective on Multiscale Electrodiffusion and Model Selection for Ion Transport in Energy-Storage Nanomaterials

Ion transport in energy storage nanomaterials is described with models that resolve different scales and different physical effects. Device models such as the Doyle-Fuller-Newman framework are well suited to cell voltage, concentration polarization, and electrode utilization, but they usually average local charge separation into effective transport and interface laws. Charge-resolved Poisson-Nernst-Planck, modified Poisson-Nernst-Planck, and Poisson-Fermi descriptions can instead resolve electric potential, ion partitioning, finite ion size, and space charge inside narrow pores and interphases. Molecular simulation gives solvation, adsorption, and interfacial structure, while pore-network and homogenized models connect local transport to electrode geometry. This Perspective compares these model families, states their limits, and explains how quantities should be passed from molecular and pore scales to electrode and device models. Representative examples are discussed for liquid-electrolyte batteries, all-solid-state batteries, and nanoporous supercapacitors. Two concise calculations are retained as model audits. The first tests whether a first-order finite-size approximation remains reliable when its leading correction is small by cancellation. The second tests when local electroneutrality becomes inaccurate in a charged pore and how steric crowding changes screening. These calculations are not new device predictions. The main contribution is a practical procedure that links model choice, cross-scale handoff, and validation with measurable quantities such as voltage, concentration profiles, impedance, interfacial resistance, capacitance, and charging time.