Diffusion-induced 7Li NMR relaxation of layer-structured tin disulphide — Li diffusion along the buried interfaces in Li0.17SnS2

Abstract

7Li NMR relaxation has been used to study lithium-ion diffusion in layer-structured SnS2. Keeping the Li intercalation degree in LixSnS2 below x=0.49, the Li ions preferentially occupy sites in the van der Waals gap between the SnS2 sheets. In contrast to conventional NMR spin-lattice relaxation (SLR) rate measurements in the laboratory frame of reference, which are sensitive to rather fast Li exchange processes, with the help of spin-locking SLR NMR slower Li motions were extracted from characteristic diffusion-induced rate peaks. The latter contain information on both Li+ activation energies Ea and Li ion jump rates τ−1 characterizing the elementary steps of Li+ hopping. Our results point to two different diffusion processes (Ea(I)=0.38eV; Ea(II)=0.28eV), a slower and a faster one, observable directly after chemical Li insertion. Interestingly, the diffusion behaviour irreversibly changes when the sample has been exposed to temperatures as high as 573K. Diffusion-induced NMR rates and corresponding line shapes are discussed with respect to an inhomogenous distribution of Li ions in SnS2, which seems to be present directly after Li intercalation.