Selective Lithium separation from Li/Co/Ni mixtures using optimized flow-electrode capacitive deionization

The increasing need for lithium has heightened its significance as a crucial resource in numerous sectors, particularly in realms of portable electronics, electric vehicles (EVs), and large-scale energy storage systems. However, the finite availability of lithium resources and environmental concerns associated with its extraction underscore the significance of developing an efficient recycling method. In this study, we explored the potential of recovering lithium from waste battery leachate using an emerging technology known as flow-electrode capacitive deionization (FCDI). Unlike traditional capacitive deionization (CDI), FCDI offers continuous desalination capabilities, making it particularly suitable for recycling industries. While FCDI exhibits promise in recovering waste battery leachate, its inherent lack of selectivity presents a challenge. To address this issue, we tried to tune its selectivity towards lithium by employing a layer-by-layer deposition method to modify a cation exchange membrane (CEM) with poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) functional multilayers. This strategic modification of CEM was performed by alternatively depositing positively charged PAH and negatively charged PSS multilayers, which switched an innate divalent cation preference of CEM into a monovalent cation preference based on differences in ion sizes and charge densities. The membrane was used to treat a synthetic leachate mixture from wasted batteries, with a molar ratio of 30 mM:44 mM:4 mM for Li:Co:Ni, demonstrating a Li selectivity of 12.88 over Co and Ni with an exceptionally low energy consumption of 0.57 Wh/molLi. We believe our approach can lead to new technologies that address shortcomings of existing lithium recycling method and expand the application not only to lithium recycling, but also to future lithium production technologies and removal of specific ions such as for toxin removal. [Display omitted] •Selective and continuous separation of Li from Li/Co/Ni mixture was realized.•PAH/PSS functionalized membrane changes affinity from divalent to monovalent cations.•Li selectivity reached 12.88 with a low energy consumption of 0.57 Wh/molLi.•Li selectivity is improved by modifying FCDI operational conditions.•Li is successfully separated from synthetic lithium-ion-battery leachate by FCDI system.