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[摘要]：Garnet-like structures containing lithium are of interest for applications in lithium ion batteries because of their inherent lithium ion conductivity and stability against chemical reaction with Li. Here, a series of materials, with parent composition LaLi(0.5)Fe(0.2)O(2.09), are synthesized using solid-state chemistry, and characterized, in terms of their structure, using a combination of powder X-ray diffraction (PXRD), (7)Li, and (139)La solid-state NMR, which reveal disorder on the Li and Fe sites in the lattice. The (7)Li spectra comprise a set of peaks that are distinguished based on their T(1) relaxation properties, as a diamagnetic set and a paramagnetic set of peaks. The (139)La spectra include two La environments, one well-defined, with a C(Q) of 56 MHz +/- 1 MHz and asymmetry parameter, eta of 0.05 +/- 0.05, and a second, which experiences a range of local environments, because of the Li/Fe substitution, and has a C(Q) of 29 MHz +/- 2 MHz, and eta of 0.6 +/- 0.1. The dynamics within the materials were characterized using impedance spectroscopy, and trends were correlated with the lithium content and structural features. The best conductivity was determined for the parent material, LaLi(0.5)Fe(0.2)O(2.09), after sintering at 850 degrees C. The complex (7)Li and (139)La NMR spectra, interpreted together with (PXRD) data, indicate that the increasing concentration of lithium in the material populates an iron site with excess lithium, in a range of possible local environments, which appears to decrease the total ionic and electronic conductivity. |
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