Probing ion coordination in polymer electrolytes with multinuclear NMR correlation spectroscopy

Solid polymer electrolytes (SPEs) are generally obtained by mixing an appropriate solvating polymer with alkali salt. Block copolymers based on poly(ethyleneoxide) (PEO) are suitable choices for SPEs because their polar ether moiety dissolves salts and their apolar component permits fine tuning of thermal and mechanical properties. However, the ionic properties of these materials depend greatly on the solvation state of the cation and the anion as well as the ion-pairing. In this paper, we present Heteronuclear Overhauser NMR Spectroscopy (HOESY) experiments for probing through-space proximity of the different components (cation–polymer, cation–anion, anion–polymer) within these melt electrolytes. The effect of the salt and the matrix is discussed as well as potential applications and limitations of this advanced structural tool.