Establishing Ultralow Activation Energies for Lithium Transport in Garnet Electrolytes

Abstract

Garnet-type structured lithium ion conducting ceramics represent a promising alternative to liquidbased electrolytes for all-solid-state batteries. However, their performance is limited by their polycrystalline nature and the inherent inhomogeneous current distribution due to the different ion dynamics at grains, grain boundaries and interfaces. In this study we use a combination of electrochemical impedance spectroscopy, distribution of relaxation times analysis and solid state nuclear magnetic resonance (NMR), in order to understand the role that bulk, grain boundary and interfacial processes play in the ionic transport and electrochemical performance of garnet based cells.Variable temperature impedance analysis reveals the lowest activation energy for Li transport in the bulk of the garnet electrolyte (0.15 eV), consistent with pulsed field gradient NMR spectroscopy measurements (0.14 eV). We also show a decrease in grain boundary activation energy at temperatures below 0 °C , that is followed by the total conductivity, suggesting that the bottleneck to ionic transport resides in the grain boundaries. We reveal that the grain boundary activation energy is heavily affected by its composition that, in turn, is mainly affected by the segregation of dopants and Li. We suggest that by controlling the grain boundary composition, it would be possible to pave the

Li1.5La1.5MO6 (M = W6+, Te6+) as a new series of lithium-rich double perovskites for all-solid-state lithium-ion batteries

“…Subsequent improvement of conduction properties in novel oxide materials following their original report in the literature is often observed. For instance, benchmark Li-rich garnets oxides were originally reported to have ionic conductivities on the order of 10 −6 S cm −1 with activation energies in the 0.4-0.5 eV range, comparable with our novel Li 1.5 La 1.5 TeO 6 double perovskite, and improvements in the last decade have seen these values rise to above 10 −3 S cm −1 with activation energies below 0.2 eV [65][66][67] . The low local Li + activation energy below 0.2 eV and similar Li + diffusion coefficient obtained by µ + SR here for the Li 1.5 La 1.5 TeO 6 material is comparable to that of the LLZO benchmark garnet electrolyte probed by the same technique, where again pellet microstructure greatly impacts the macroscopic transport properties 21 .…”

X-ray pair distribution function analysis and electrical and electrochemical properties of cerium doped Li5La3Nb2O12 garnet solid-state electrolyte

“…[30][31][32][33] The ionic transport was reported to be limited by the grain boundaries, which are heavily affected by the segregation of dopants and Li. 34 Mechanical polishing, carbon annealing or acid treatment were reported to remove this unwanted surface layer. 35,36 Metal or non-metal coatings on garnet pellets, which consequently enables lithium alloying, have also been used to minimise the interfacial resistance between lithium metal and garnet, and to reduce the dendrite growth.…”

Suppressing void formation in all-solid-state batteries: the role of interfacial adhesion on alkali metal vacancy transport

“…For the LLZO family of materials it has been demonstrated that the intrinsic charge transfer resistance across the Li/LLZO interface is very small once contaminant layers have been removed. 17,19,20,21 Analogously, in the Na ''alumina system, the removal of hydroxyl and carbon contaminants through heat treatment in an inert atmosphere was found to lead to very small (<10 cm 2 ) interfacial Ω resistances with Na metal. 12 Improvement of the wetting between alkali metals and SSE surfaces has been achieved in several studies through the addition of a thin, metallic interlayer phase.…”