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

Abstract

The development of all-solid-state electrochemical energy storage systems, such as lithiumion batteries with solid electrolytes, requires stable, electronically insulating compounds with exceptionally high ionic conductivities. Considering oxides, garnet-type Li7La3Zr2O12 and derivatives, see Zr-exchanged Li6La3ZrTaO12 (LLZTO), have attracted great attention because of its high Li + ionic conductivity of up to 1 mS · cm −1 . Despite numerous studies focusing on conductivities of powder samples, only a few use time-domain NMR methods to probe Li ion diffusion parameters in single crystals. Here we report, for the first time, on temperature-variable 7 Li NMR relaxometry measurements using both laboratory and spin-lock techniques to probe Li jump rates in monocrystalline Li-bearing garnets. Timedomain NMR offers the possibility to study Li ion dynamics on both the short-range and long-range length scale. The techniques applied yield a fully consistent picture of correlated Li ion jump diffusion in LLZTO; 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. Dynamic information about the elementary jump processes, such as jump rates and activation energies, were extracted from complete diffusion-induced rate peaks that are obtained when the relaxation rate is plotted vs inverse temperature. Results from NMR are completely in line with ion transport parameters derived from conductivity spectroscopy. Acknowledgement. We thank our colleagues at the University of Hannover and the TU Graz for valuable discussions. Financial support by the Deutsche Forschungsgemeinschaft

High Ionic Conductor Member of Garnet‐Type Oxide Li6.5La3Zr1.5Ta0.5O12

“…The result of this time shows a diffusion coefficient faster than the previous result. Actually, lithium ion conductivity by AC impedance measurement is also 1.27×10 −3 S cm −1 , which is higher than the value reported (3×10 −4 S cm −1 ) . We believe that it depends on the degree of tantalum substitution and because the distance between Li and Li is shorter than previously reported as the amount of Li in the crystal structure is more disordered.…”

“…In the future, we think that it is necessary to measure with a rod without crushing the single crystal. On the other hand, the diffusion coefficient of L 6 La 3 ZrTaO 12 using a single crystal before was 10 −14 m 2 s −1 . The result of this time shows a diffusion coefficient faster than the previous result.…”

“…Oxide solid electrolytes are further classified into glass, glass‐ceramic, and crystalline types. Crystalline solid electrolytes include LISICON, perovskite, β‐alumina with Na + /Li + ion exchange, and garnet types . Li 7– x La 3 Zr 2– x Nb x O 12 , and Li 7– x La 3 Zr 2– x Ta x O 12 ,,,, in which part of Li 7 La 3 Zr 2 O 12 ,, is substituted with niobium or tantalum, has high lithium ion conductivity and a wide potential window.…”

“…Previously, we reported for the first time that single crystals of garnet type solid electrolyte can be grown by the floating zone (FZ) method which is one of melting methods . Recently, a report showed single‐crystal growth of Li 6 La 3 ZrTaO 12 by the Czochralski method and demonstrated NMR measurement of a single crystal . It has been reported that in the polycrystalline body of the tantalum substitution product, the lithium ion conductivity is the highest when the tantalum substitution amount is 0.5 .…”

Lithium‐Battery Anode Gains Additional Functionality for Neuromorphic Computing through Metal–Insulator Phase Separation

“…Li‐ion intercalation oxides are an attractive new class of functional materials for memristive devices . Relative to valence change memories, Li‐ion intercalation oxides have at least 2 orders of magnitude larger diffusivities (10 −9 –10 −11 cm 2 s −1 ) . Additionally, a metal–insulator transition (MIT) can be easily and drastically tuned by changing the Li content of the material.…”