On Li-chelating additives to electrolytes for Li batteries

The relative affinity of several electrochemically stable bi- and polydentate organic ligands (containing ether, amino, carbonate or phosphonate moieties) to Li ion was estimated by ab initio calculations at the MP2/6-31G(d) level comparing their calculated binding energies (BEs). Polyether 12-crown-4 and a bisphosphonate, which is covalently locked in a cyclic "chelating" conformation, are stronger Li⁺ chelators than isosparteine and 1,2-methylenebisphosphonate (an open-chain compound). Organic biscarbonates are the weakest complexing agents among the ligands considered. Although BE values were calculated for the gas phase, the order of ligand complexation ability obtained is also considered relevant to solutions since the difference between the BEs for these three groups of ligands is significant. The same calculations that were performed for complexes of Li ion and different organic carbonate diesters (solvents usually used in Li-ion batteries) allowed singling out of conformationally locked bisphosphonates as new battery life-prolonging additives to carbonate electrolytes.