Slow Li Exchange in a Li3N Single Crystal Measured by Li NMR Selective Quadrupole Satellite Inversion

Lithium nitride, Li3N, is one of the best Li conductors at room temperature. Unfortunately, its application as electrolyte in batteries is limited due to the low decomposition potential of only 0.45 V. Nevertheless, diffusion in Li3N was studied by many groups and various techniques (see [1-3] and references therein) which predestines it to act as a model system for the establishment of new techniques. Li3N crystallizes in a layered structure of the hexagonal space group P6/mmm [3,4] (see Fig. 1). There are two alternating types of layers, one with the stoichiometry Li2N, the other containing only Li. As a result, there are two different Li positions, Li(2) in the Li2N layer and Li(1) in the Li layer. Li diffusion in the Li2N layer (ab-plane, intralayer diffusion) is fast, while the Li diffusion parallel to the caxis is moderate. The mechanism of this interlayer diffusion process is directly associated with a Li exchange between the two Li positions (see Fig. 1) since the Li ions cannot jump from one Li(2) site to the other but transitionally reside on a Li(1) site [5]. This makes it possible to measure the interlayer diffusion process by exchange NMR techniques.