Density functional theory study of selectivity of crown ethers to Li+ in spent lithium-ion batteries leaching solutions

It is a challenge to recover lithium from the leaching solution of spent lithium-ion batteries, and crown ethers are potential extractants due to their selectivity to alkali metal ions. The theoretical calculations for the selectivity of crown ethers with different structures to Li ions in aqueous solutions were carried out based on the density functional theory. The calculated results of geometries, binding energies, and thermodynamic parameters show that 15C5 has the strongest selectivity to Li ions in the three crown ethers of 12C4, 15C5, and 18C6. B15C5 has a smaller binding energy but more negative free energy than 15C5 when combined with Li+, leading to that the lithium ions in aqueous solutions will combine with B15C5 rather than 15C5. The exchange reactions between B15C5 and hydrated Li+, Co2+, and Ni2+ were analyzed and the results show that B15C5 is more likely to capture Li+ from the hydrated ions in an aqueous solution containing Li+, Co2+, and Ni2+. This study indicates that it is feasible to extract Li ions selectively using B15C5 as an extractant from the leaching solution of spent lithium-ion batteries.