Proton-driven lithium separation using alkali-templated coordination cages

The extraction of lithium from natural deposits is energy intensive due to its coexistence with physiochemically similar alkali (Na⁺ and K⁺) and alkaline earth (Mg²⁺ and Ca²⁺) metal ions. Methods for the direct and specific extraction of lithium from salt mixtures are thus essential to ensure an adequate supply of this metal for the batteries needed to decarbonize the world economy. Here, we present the preparation of alkali-metal-templated coordination cages and their application to lithium extraction. Within the cage framework, protons alter the relative binding affinities of Li⁺ and similar metal ions: protons associate exclusively with Li⁺ in close proximity at the cage vertices, repelling other cations as a result of increased electrostatic repulsion, enhanced steric hindrance, and reduced availability of coordinating nitrogen atoms. We developed this proton-driven lithium recognition within coordination cages into a separation cycle capable of extracting Li⁺ from a mixture of salts that includes Na⁺, K⁺, Mg²⁺, and Ca²⁺.