Thermodynamics of Li-Crown Ether Interactions in Aqueous Solvent.

Lithium ion-based batteries are ubiquitous in modern technology due to applications in personal electronics and high-capacity storage for electric vehicles. Concerns about lithium supply and battery waste have prompted interest in lithium recycling methods. The crown ether 12-crown-4 has been studied for its abilities to form stable complexes with lithium ions (Li). In this paper, molecular dynamics simulations are applied to examine the binding properties of a 12-crown-4-Li system in aqueous solution. It was found that 12-crown-4 did not form stable complexes with Li in aqueous solution due to the binding geometry which was prone to interference by surrounding water molecules. In addition, the binding properties of sodium ions (Na) to 12-crown-4 are examined for comparison. Subsequently, calculations were performed with the crown ethers 15-crown-5 and 18-crown-6 to study their complexation with Li as well as Na. It was determined that binding was unfavorable for both types of ions for all three crown ethers tested, though 15-crown-5 and 18-crown-6 showed a marginally greater affinity for Li than 12-crown-4. Metastable minima present in the potential of mean force for Na render binding marginally more likely there. We discuss these results in the context of membrane-based applications of crown ethers for Li separations.