Anion-Regulated Lithium Isotope Separation with Crown Ethers Via Tuning Coordination Environments

Efficient separation of lithium isotopes (6Li and 7Li) is critical for sustainable nuclear energy. The crown ether system exhibits outstanding lithium isotope separation performance, with the anion exerting a significant influence; however, the molecular-level mechanism of action of anions and how this affects the separation process remain unclear. This limits the design of higher performance separation systems. Through combining 6Li/7Li separation experiments, 7Li NMR spectroscopy, and quantum chemical calculations, this work makes it clear that anions control the separation factor by changing the Li+ coordination microenvironment. Through manipulation of hydration and crown ether encapsulation, charge-delocalized anions provide a coordinating environment around Li+ that balances the bond strengths inside a crown-ether container. This balance of the bonding state improves the thermodynamic driving force for the 6Li/7Li exchange between the aqueous and organic phases and substantially increases the separation coefficient. This study provides an efficient screening method for lithium isotope separation and offers theoretical guidance for designing and optimizing more efficient lithium isotope separation systems.