Selective Ion Separation by Capacitive Deionization: A Comprehensive Review

Within the last decade, in addition to water desalination, capacitive deionization (CDI) has been used for the resource recovery and selective separation of target ions in multicomponent solutions. CDI is a new technology for selectively extracting valuable metal ions from solutions using an electric field and electrode materials. Unlike traditional adsorption methods, it raises attention for its environmentally friendly process and low cost, especially for extracting valuable elements. CDI technology has advanced significantly in desalination and selective element extraction due to a deep understanding of ion storage, electrode material structure–activity relationships, solvent effects, and reactor design. However, it still faces challenges like short electrode cycle life, poor reversible absorption/desorption, low charge utilization, and limited ion selectivity. In this review, we commence with an examination of the historical development of CDI technology, followed by a comprehensive summary of the fundamental operating principles of capacitors. We then evaluate the criteria for assessing capacitor performance and analyze the advantages and disadvantages associated with various capacitor materials. According to the review, we address the current challenges and obstacles encountered in the advancement of capacitor technology and offer constructive recommendations for its future development.