Formation of amorphous LiCl aggregate regions in LiCl–Li2O–P2O5 fast ion conducting glasses studied by ac conductometry and 7Li MAS NMR

Fast Li+-ion conducting glasses of LiCl–Li2O–P2O5 system with different glass network structures were synthesized by a twin-roller quenching method. Ac conductometry and 7Li MAS NMR measurements were performed for the glasses in order to obtain the information about the microscopic structure and the ion conduction mechanism of the glasses. The activation energies of Li+-ion conduction for the glasses of (LiCl)x(LiPO3)1−x, (LiCl)x(Li1.4PO3.2)1−x and (LiCl)x(Li1.67PO3.33)1−x, in which LiPO3, Li1.4PO3.2 and Li1.67PO3.33 have different network structures of one dimensional chain, pentamer and trimer, respectively, were revealed to converge upon a certain value of 46 ± 2 kJ mol−1 in a high LiCl composition range near the glass-forming composition limit, independent of the glass network structures. 7Li MAS NMR spectra of the glasses showed a broad signal, and a linear dependence of the chemical shift on LiCl composition, x, was observed. The glasses with relatively high LiCl compositions exhibited a sharp signal besides the broad one in the spectra. The chemical shift of the sharp signal corresponded well with that estimated by extrapolating the linear relation between the chemical shift of the broad signal and the LiCl composition to the limit value of x = 1, and the sharp signal was assigned reasonably to the Li+ ions interacting only with Cl− ions. It was concluded from the results that amorphous LiCl aggregate regions were formed within the glasses in the high LiCl composition range, and that the Li+ ions included in the amorphous LiCl aggregates contributed mainly to the fast ion conduction of the glasses.