Ionic Pathways in Li13Si4 investigated by 6Li and 7Li solid state NMR experiments

Abstract Local environments and dynamics of lithium ions in the binary lithium silicide Li 13 Si 4 have been studied by 6 Li MAS-NMR, 7 Li spin-lattice relaxation time and site-resolved 7 Li 2D exchange NMR measurements as a function of mixing time. Variable temperature experiments result in distinct differences in activation energies characterizing the transfer rates between the different lithium sites. Based on this information, a comprehensive picture of the preferred ionic transfer pathways in this silicide has been developed. With respect to local mobility, the results of the present study suggests the ordering Li6/Li7>Li5>Li1>Li4 >Li2/Li3. Mobility within the z =0.5 plane is distinctly higher than within the z =0 plane, and the ionic transfer between the planes is most facile via Li1/Li5 exchange. The lithium ionic mobility can be rationalized on the basis of the type of the coordinating silicide anions and the lithium-lithium distances within the structure. Lithium ions strongly interacting with the isolated Si 4− anions have distinctly lower mobility than those the coordination of which is dominated by Si 2 6− dumbbells.