Solid Electrolytes: Extremely Fast Charge Carriers in Garnet-Type Li6La3ZrTaO12 Single Crystals

The development of all-solid-state electrochemical energy storage systems, such as lithium-ion batteries with solid electrolytes, requires stable, electronically insulating compounds with exceptionally high ionic conductivities. Considering ceramic oxides, garnet-type Li7La3Zr2O12 and derivatives, see Zr-exchanged Li6La3ZrTaO12 (LLZTO), have attracted great attention due to its high Li+ ionic conductivity of 10-3Scm-1 at ambient temperature. Despite numerous studies focussing on conductivities of powder samples, only few use time-domain NMR methods to probe Li ion diffusion parameters in single crystals. Here we report on temperature-variable NMR relaxometry measurements using both laboratory and spin-lock techniques to probe Li jump rates covering a dynamic time window spanning several decades. Both techniques revealed a consistent picture of correlated Li ion jump diffusion in the single crystal; the data perfectly mirror a modified BPP-type relaxation response being based on a Lorentzian-shaped relaxation function. The rates measured could be parameterized with a single set of diffusion parameters. Results from NMR are completely in line with ion transport parameters derived from conductivity spectroscopy.