Recent advances in capacitive deionization: Ion storage and transport mechanisms

Capacitive deionization (CDI) is a promising low-energy electrochemical desalination technology. Its practical performance is primarily dictated by salt adsorption capacity, charge efficiency, and long-term stability, which are inherently rooted in the dynamics of ion storage and transport within porous electrodes. This review critically examines the two primary ion storage mechanisms—electrical double layer (EDL) formation and Faradaic reactions—and their complex interplay with ion transport kinetics. We highlight how transport bottlenecks can severely limit the realized performance of high-capacity materials, establishing storage-transport coupling as a central paradigm for performance optimization. Furthermore, we analyze how advanced multi-scale simulations—molecular dynamics (MD), density functional theory (DFT), and the lattice Boltzmann method (LBM)—bridge atomic-scale interactions, pore-scale transport, and macroscopic performance, revolutionizing mechanistic understanding. By synthesizing this coupled perspective with simulation-guided insights, we provide a roadmap for the rational design of next-generation CDI materials and architectures, steering the field toward higher efficiency, selectivity, and stability for complex water treatment applications.