Lithium ion complexation kinetics by cyclic and acyclic polyethers

Abstract

Results of the ultrasonic absorption relaxation and nuclear magnetic resonance studies of the kinetics of alkali metal cation complexation by macrocyclic ligands in a variety of nonaqueous solvents are reviewed. The effects of a competition between low permittivity solvent molecules, anions, and neutral macrocycles for the first coordination sphere of the lithium cation are clearly evident. The utility of the Eigen-Winkler reaction mechanism for describing the ultrasonic absorption results is pointed out. When the same ultrasonic techniques are used to explore the kinetics of lithium ion complexation by acyclic polyethers such as poly(ethylene oxide) in acetonitrile a striking insight emerges: The complexation kinetics reflect a localized cation-polyether interaction that is independent of the length of the polyether chain as one proceeds from triglyme to a poly(ethylene oxide) of 15,000 average molar weight. Extension of this result to similar lithium ion complexation kinetic studies in neat liquid poly(ethylene oxides) is discussed and possible applications of the results in developing an understanding of polymeric electrolytes in lithium batteries is outlined. © 1990 De Gruyter