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Li oxide garnets are among the most promising candidates for solid-state electrolytes in novel Li ion and Li metal based battery concepts. Cubic Li7La3Zr2O12 stabilized by a partial substitution of Zr4+ by Bi5+ has not been the focus of research yet, despite the fact that Bi5+ would be a cost-effective alternative to other stabilizing cations such as Nb5+ and Ta5+. In this study, Li7–xLa3Zr2–xBixO12 (x = 0.10, 0.20, ..., 1.00) was prepared by a low-temperature solid-state synthesis route. The samples have been characterized by a rich portfolio of techniques, including scanning electron microscopy, X-ray powder diffraction, neutron powder diffraction, Raman spectroscopy, and 7Li NMR spectroscopy. Pure-phase cubic garnet samples were obtained for x ≥ 0.20. The introduction of Bi5+ leads to an increase in the unit-cell parameters. Samples are sensitive to air, which causes the formation of LiOH and Li2CO3 and the protonation of the garnet phase, leading to a further increase in the unit-cell parameters. The incorporation of Bi5+ on the octahedral 16a site was confirmed by Raman spectroscopy. 7Li NMR spectroscopy shows that fast Li ion dynamics are only observed for samples with high Bi5+ contents., The cubic modification of Li7La3Zr2O12 can be stabilized by a by a partial substitution of Zr4+ by Bi5+. The incorporation of Bi5+ leads to an increase in the unit-cell parameters. Samples prepared by a low-temperature preparation route are sensitive to CO2 and H2O from air, causing a protonation of the garnet phase. 7Li NMR spectroscopy shows that fast translational Li ion dynamics are only observed for samples with high Bi5+ contents.

© 2018 American Chemical Society. The interface stability versus Li represents a major challenge in the development of next-generation all-solid-state batteries (ASSB), which take advantage of the inherently safe ceramic electrolytes. Cubic Li7La3Zr2O12garnets represent the most promising electrolytes for this technology. The high interfacial impedance versus Li is, however, still a bottleneck toward future devices. Herein, we studied the electrochemical performance of Fe3+-stabilized Li7La3Zr2O12(LLZO:Fe) versus Li metal and found a very high total conductivity of 1.1 mS cm-1at room temperature but a very high area specific resistance of 1 k cm2. After removing the Li metal electrode we observe a black surface coloration at the interface, which clearly indicates interfacial degradation. Raman- and nanosecond laser-induced breakdown spectroscopy reveals, thereafter, the formation of a 130 μm thick tetragonal LLZO interlayer and a significant Li deficiency of about 1-2 formula units toward the interface. This shows that cubic LLZO:Fe is not stable versus Li metal by forming a thick tetragonal LLZO interlayer causing high interfacial impedance.

In many cases nanocrystalline materials, prepared through high-energy ball milling, reveal enhanced ion dynamics when compared to the situation in the coarse-grained analogues. This effect, which has particularly been seen for lithium alumosilicates, has been ascribed to structural disorder, i.e., the introduction of defect sites during mechanical treatment. Much less is, however, known about ion transport in nanostructured amorphous materials, e.g., nanoglassy compounds, which are regarded as a new class of functional materials. Following earlier studies on nanoglassy lithium alumosilicates and borates, here we studied ion dynamics in nanoglassy petalite LiAlSi4O10. While conductivity spectroscopy unequivocally reveals that long-range ion dynamics in nanoglassy LiAlSi4O10 decreases upon milling, local dynamics, sensed by 7 Li nuclear magnetic resonance (NMR) spin-lattice relaxation, points to enhanced Li ion mobility compared to the non-treated glass. Most likely, as for nanocrystalline ceramics also for nanoglassy samples a heterogeneous structure, consisting of bulk and interfacial regions, is formed. For LiAlSi4O10 these interfacial regions, characterized by a higher degree of free volume, might act as hosts for spins experiencing fast longitudinal NMR relaxation. Obviously, these regions do not form a through-going network, which would allow the ions to move over long distances as quickly as in the unmilled glass.

© 2016 American Chemical Society. Several "Beyond Li-Ion Battery" concepts such as all solid-state batteries and hybrid liquid/solid systems envision the use of a solid electrolyte to protect Li-metal anodes. These configurations are very attractive due to the possibility of exceptionally high energy densities and high (dis)charge rates, but they are far from being realized practically due to a number of issues including high interfacial resistance and difficulties associated with fabrication. One of the most promising solid electrolyte systems for these applications is Al or Ga stabilized Li7La3Zr2O12(LLZO) based on high ionic conductivities and apparent stability against reduction by Li metal. Nevertheless, the fabrication of dense LLZO membranes with high ionic conductivity and low interfacial resistances remains challenging; it definitely requires a better understanding of the structural and electrochemical properties. In this study, the phase transition from garnet (Ia3Ì...d, No. 230) to "non-garnet" (I4Ì...3d, No. 220) space group as a function of composition and the different sintering behavior of Ga and Al stabilized LLZO are identified as important factors in determining the electrochemical properties. The phase transition was located at an Al:Ga substitution ratio of 0.05:0.15 and is accompanied by a significant lowering of the activation energy for Li-ion transport to 0.26 eV. The phase transition combined with microstructural changes concomitant with an increase of the Ga/Al ratio continuously improves the Li-ion conductivity from 2.6 × 10-4S cm-1to 1.2 × 10-3S cm-1, which is close to the calculated maximum for garnet-type materials. The increase in Ga content is also associated with better densification and smaller grains and is accompanied by a change in the area specific resistance (ASR) from 78 to 24 Ω cm2, the lowest reported value for LLZO so far. These results illustrate that understanding the structure-properties relationships in this class of materials allows practical obstacles to its utilization to be readily overcome.

Several “Beyond Li-Ion Battery” concepts such as all solid-state batteries and hybrid liquid/solid systems envision the use of a solid electrolyte to protect Li-metal anodes. These configurations are very attractive due to the possibility of exceptionally high energy densities and high (dis)charge rates, but they are far from being realized practically due to a number of issues including high interfacial resistance and difficulties associated with fabrication. One of the most promising solid electrolyte systems for these applications is Al or Ga stabilized Li7La3Zr2O12 (LLZO) based on high ionic conductivities and apparent stability against reduction by Li metal. Nevertheless, the fabrication of dense LLZO membranes with high ionic conductivity and low interfacial resistances remains challenging; it definitely requires a better understanding of the structural and electrochemical properties. In this study, the phase transition from garnet (Ia3̅d, No. 230) to “non-garnet” (I4̅3d, No. 220) space group as a function of composition and the different sintering behavior of Ga and Al stabilized LLZO are identified as important factors in determining the electrochemical properties. The phase transition was located at an Al:Ga substitution ratio of 0.05:0.15 and is accompanied by a significant lowering of the activation energy for Li-ion transport to 0.26 eV. The phase transition combined with microstructural changes concomitant with an increase of the Ga/Al ratio continuously improves the Li-ion conductivity from 2.6 × 10–4 S cm–1 to 1.2 × 10–3 S cm–1, which is close to the calculated maximum for garnet-type materials. The increase in Ga content is also associated with better densification and smaller grains and is accompanied by a change in the area specific resistance (ASR) from 78 to 24 Ω cm2, the lowest reported value for LLZO so far. These results illustrate that understanding the structure–properties relationships in this class of materials allows practical obstacles to its utilization to be readily overcome.

Zinc aluminate (ZnAl2O4) nanoparticles with an average size of about 10 nm are synthesized via one-step mechanochemical processing of the ZnO : g-Al2O3 stoichiometric mixture at ambient temperature. The mechanochemically induced formation of the phase is followed by XRD and 27Al MAS NMR. Highresolution TEM studies reveal a non-uniform nanostructure of mechanosynthesized aluminate consisting of ordered grains surrounded or separated by disordered surface and interfacial regions. Due to the capability of 27Al MAS NMR to probe the local environment of the Al cations, valuable insights into the short-range structure of ZnAl2O4 on the °Angstr¨om length scale are provided. It is demonstrated that the as-prepared aluminate possesses a partly inverse spinel structure with a far-from equilibrium arrangement of cations and distorted polyhedra, which are spatially confined to the surface and interfacial regions with a volume fraction of ca. 50% and a thickness of ca. 1 nm. The response of the nanostructured ZnAl2O4 to subsequent thermal treatment is further investigated. It turned out that the thermally induced grain growth is accompanied by a release of microstrain, by a shrinkage of the lattice parameter, as well as by a variation in the oxygen parameter and metal–oxygen bond lengths. Evidence is given of the thermally induced redistribution of cations approaching their equilibrium positions. Upon heating above 1100 K, mechanosynthesized ZnAl2O4 relaxes towards a structural state that is similar to the bulk one.

The present work focuses on channel-structured Li0.7Nb3S4, where, among others, the question of the dimensionality of the diffusion pathway arises.