Mobility of Li cations in X zeolites studied by solid-state NMR spectroscopy

Li-6 and Li-7 MAS NMR spectra of the dehydrated zeolites LiX-1.0 [(SiAlO4)(96)Li-96] and LiX-1.25 [(Si106Al86O384)Li-86] contain three peaks belonging to cations in the crystallographic sites SI', SII, and SIII. Li-7 MAS NMR spectra recorded at variable temperature show that the SIII cations are mobile at temperatures above 233 K in case of LiX-1.0, and above 273 K in case of LiX-1.25. The mobility of the SIII cations causes a shorter T-1 for SIII in comparison to the non-mobile six-ring cations of LiX-1.0 at 293 K. An activation energy of 13 kJ mol(-1) was determined for the SIII cations in the temperature range of T = 233-313 K. We predict that the Li ion conductivity of zeolite LiX-1.0 will be higher than the Li ion conductivity of any zeolite reported up to date. (C) 1999 Published by Elsevier Science B.V. All rights reserved.