Next-generation supramolecular strategies for selective lithium ion-pair recognition and extraction: Receptor design, cooperative binding mechanisms, and functional materials

초록

Lithium extraction from increasingly dilute and compositionally complex resources, including natural brines, seawater, geothermal fluids, and spent battery electrolytes, has become a critical challenge for sustainable energy storage and resource recovery. Conventional lithium separation technologies often suffer from limited selectivity, high energy consumption, and reduced efficiency in the presence of competing ions such as Na+, K+, Ca2+, and Mg2+. Supramolecular ion-pair recognition has emerged as a promising strategy to overcome these limitations by enabling the cooperative and simultaneous recognition of lithium ions and their accompanying counter-anions. This systematic review critically compares the evolution of lithium-selective supramolecular receptors, from early monotopic hosts to modern macrocyclic, Schiff-base, ether, polypodal, ditopic, and heteroditopic architectures, identifying receptor preorganization, cavity geometry, binding-site complementarity, and cation-anion cooperativity as the principal design features governing selective lithium ion-pair recognition. Particular attention is given to experimentally validated ion-pair receptors that demonstrate simultaneous Li+-anion binding through spectroscopic, thermodynamic, structural, or computational evidence, while clearly distinguishing these systems from materials that exhibit only Li+-selective adsorption, transport, or size-sieving behaviour. The review quantitatively compares receptor performance using association constants, extraction efficiencies, separation factors, membrane selectivities, adsorption capacities, and operational stability, while critically evaluating the influence of solvent environment, competing-ion composition, and counter-anion-induced receptor conformational adaptation on lithium recognition. Integration of supramolecular receptors into membranes, metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and polymeric platforms is assessed with respect to scalability, receptor stability, receptor leaching, pore blockage, coordination-site poisoning, fouling resistance, recyclability, and long-term operation under realistic extraction conditions. Finally, challenges associated with receptor synthesis complexity, reagent toxicity, sustainability, and the absence of standardised selectivity evaluation protocols are discussed, and the need for a unified framework for assessing lithium selectivity under different experimental conditions is highlighted. By identifying current limitations, comparing receptor architectures, and establishing emerging design principles, this review provides a rigorous framework for developing next-generation supramolecular systems capable of efficient, selective, and economically viable lithium extraction from complex resources.

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