文摘
Nuclear Magnetic Resonance (NMR) has been shown to be a useful tool for the study of the structure [1–4] and dynamics [3, 5–11] of ionic conductors. While magic-angle spinning techniques are most often used for obtaining structural details, the dynamics of ion are usually explored by measuring spin-relaxation times [12]. Many of these NMR studies of ionically conducting materials have focused on lithium ion conductors. The reason is probably twofold: on the one hand, the huge interest in these materials for their application in solid state batteries due to the usually high lithium mobility; and on the other hand, the existence of two stables isotopes, 6Li and 7Li, with different magnetic dipole and electrical quadrupole moments, that allow studying these ionic conductors from two different views since different NMR interactions dominant for different probe nuclei [10, 11, 13, 14]. However, in many cases lithium NMR experiments are performed with the 7Li (I = 3/2) nucleus rather than 6Li (I = 1). This is because of the higher sensitivity of the former due to its higher natural abundance and gyromagnetic ratio, while 6Li experiments require enrichment of the samples. Incidentally a series of (6Li,7Li)2O-2.88B2O3 glasses had been studied for the Li isotope mass dependence of conductivity by Downing et al. [15], and data were explained by the Coupling Model [16]. Recently, NMR spectroscopy has been also shown to be useful to probe the structural changes that occur in battery electrode materials during electrochemical cycling [17]. While most of these studies have been performed ex situ, providing considerable insight into the structural and dynamical processes that occur in battery materials at different (previously achieved) states of charge, in situ NMR now provides a non-invasive means to study the electrochemically-induced structural changes that occur on cycling a lithium ion battery [18].