pH-responsive graphene oxide subnanochannels for sustainable lithium recovery from spent lithium ion battery

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Abstract
The rapid advancement of electric vehicles is expected to significantly increase the production volume of spent lithium-ion batteries. Separation of lithium from complex spent battery leaching solution is crucial for critical metal recovery and the sustainability of the circular economy. However, achieving precise separation between Li+ and competing multivalent ions remains a challenge due to their similar hydrated radii. In this study, an EDTA-functionalized graphene oxide membrane that exhibits pH-responsive properties and ultrahigh selectivity for monovalent and divalent ions was constructed. The EDTA ligands anchored within the nanochannels demonstrate pH-dependent coordination chemistry: under neutral or alkaline conditions, deprotonated EDTA binds strongly to multivalent cations, effectively gating the channels and facilitating preferential Li+ permeation. Conversely, under acidic conditions, the protonation of the carboxyl groups in EDTA weakens its binding to divalent ions. This results in a Li + /M 2+ selectivity of 300 under neutral or alkaline conditions, surpassing previously reported membranes. Additionally, through electrodialysis, a Li 2 CO 3 product with a purity of 98.5% was obtained. Furthermore, using quartz crystal microbalance, we decoupled the contributions of partitioning and diffusion energy barriers to the overall transport energy barrier, revealing that precise ion separation is achieved by modulating the diffusion barrier through pH-responsive coordination. This work provides mechanistic insights for the design of membranes with high ion selectivity and demonstrates the potential for sustainable lithium recovery from spent batteries.
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