Li ion transport in an intercalated polymer electrolyte

Abstract

Lithium ions solvated by polyethylene-oxide (PEO) have been confined by intercalation within the galleries of an insulating, inorganic layered solid CdPS₃. The dc conductivity of this confined polymer electrolyte Cd_0.75PS₃Li_0.5(PEO) displays a distinct change in the mechanism of conduction with temperature, exhibiting a crossover from an Arrhenius temperature dependence at low temperatures to an non-Arrhenius, Vogel-Tamman-Fulcher behavior at higher temperatures. We use ²H, ⁷Li, and ¹³C nuclear magnetic resonance (NMR) in combination with infrared spectroscopy to probe Li ion mobility as well as segmental motion of the intercalated PEO. Within the galleries of Cd_0.75PS₃Li_0.5(PEO) both rigid and mobile fractions of the intercalated polymer are present with the equilibrium fraction of the mobile species increasing with temperature. The ⁷Li (I = 3/2) NMR of the confined polymer electrolyte exhibits an unusual behavior-the appearance of quadrupolar satellites at high temperatures where the conductivity values are appreciable. The results signify the solvation of Li ions by mobile segments of the intercalated PEO. Further proof of this association is seen in the ¹³C NMR as well as infrared spectra, both of which show evidence of the complexation of Li ions by ether linkages of the interlamellar PEO at high temperature and the absence of such an association at lower temperature when polymer motion is absent.