Lithium dynamics in molybdenum disulfide intercalation compounds studied by nuclear magnetic resonance

Abstract

Cluster architecture and lithium motion dynamics are investigated in nanocomposites formed by the intercalation of lithium and a dialkylamine (diethylamine, dibutylamine and dipentylamine) in molybdenum disulfide by means of 7 Li Nuclear Magnetic Resonance (NMR) technique. The present contribution illustrates the potential of the NMR techniques in the study of both the short range atomic structure and the local dynamics of ions in these intercalation compounds. Structural information is gained through measurements of the various interactions (such as dipolar and quadrupolar) that affect the lineshapes of the NMR spectra, while ion dynamics information is gained through the study of the effects that ionic motion has on the nuclear relaxation times, which are modulated by these interactions. The formation of lithium clusters in these nanocomposites is suggested by the Li-Li dipolar interaction strength calculated from the 7 Li NMR data. The lithium spin-lattice relaxation is mainly due to the interaction between the quadrupolar moment of the 7 Li nuclei and the fluctuating electric field gradient at the site of the nucleus, produced by the surrounding charge distribution. The relaxation mechanism is consistent with a fast exchange motion of lithium ions between the coordination sites within the aggregates.