期刊
ENERGY STORAGE MATERIALS
卷 24, 期 -, 页码 220-228出版社
ELSEVIER
DOI: 10.1016/j.ensm.2019.08.017
关键词
Garnets; Single crystal; NMR; Dynamics; Conductivity
资金
- European Union's Horizon 2020 research and innovation programme [769929]
- Federal Ministry of Science, Research and Economy
- National Foundation for Research, Technology and Development (CD-Laboratory of Lithium Batteries: Ageing Effects, Technology and New Materials)
- DFG [WI3600, 2-1/4-1]
- FFG in the frame of the K-project 'safe battery'
- H2020 Societal Challenges Programme [769929] Funding Source: H2020 Societal Challenges Programme
Li7La3Zr2O12 (LLZO) garnet-type ceramics are considered as very promising candidates for solid electrolytes and have been extensively studied in the past few years. Several studies report on an increase in ionic conductivity by doping with ions, such as Al3+ and Ga3+, to stabilize the cubic modification of LLZO. Unfortunately, so far ion dynamics have mainly been studied using powdered samples. Such studies may suffer from chemical heterogeneities concerning Al distribution. Here, we took advantage of Al-stabilized LLZO single crystals to throw light on the elementary steps of ion hopping. We used Li-7 nuclear magnetic resonance (NMR) spin-lattice relaxation measurements and conductivity spectroscopy to probe dynamic parameters from both a microscopic and macroscopic point of view. At 293 K the total conductivity turned out to be 0.082 mS cm(-1), which is remarkably good for LLZO exhibiting an Al-content of only 0.37 wt%. Most importantly, Li-7 NMR spin-lock transients revealed two overlapping diffusion-induced processes. Overall, activation energies from spin-lock NMR excellently agree with that from conductivity measurements; both techniques yield values around 0.36 eV. The corresponding diffusion coefficients deduced from NMR and conductivity measurements almost coincide. The magnetic spin fluctuations sensed by NMR provide an in-depth look at the elementary jump processes, which can barely be revealed by macroscopic impedance spectroscopy providing average values. In particular, we were able to precisely measure the local hopping barrier (0.20 eV) characterizing forward-backward jumps between the sites 24d and 96h.
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