Lithium aluminium titanium phosphate (LATP) belongs to one of the most promising solid electrolytes.Besides sufficiently high electrochemical stability, its use in lithium-based all-solid-state batteries crucially depends on the ionic transport properties. While many impedance studies can be found in literature that report on overall ion conductivities, a discrimination of bulk and grain boundary electrical responses via conductivity spectroscopy has rarely been reported so far. Here, we took advantage of impedance measurements that were carried out at low temperatures to separate bulk contributions from the grain boundary responses. It turned out that bulk ion conductivity is by at least three orders of magnitude higher than ion transport across the grain boundary regions. At temperatures well below ambient long-range Li ion dynamics is governed by activation energies ranging from 0.26 to 0.29 eV depending on the sintering conditions. As an example, at temperatures as low as 173 K, the bulk ion conductivity, measured in N 2 inert gas atmosphere, is in the order of 8.1 Â 10 À6 S cm À1 . Extrapolating this value to room temperature yields ca. 3.4 Â 10 À3 S cm À1 at 293 K. Interestingly, exposing the dense pellets to air atmosphere over a long period of time causes a significant decrease of bulk ion transport.This process can be reversed if the phosphate is calcined at elevated temperatures again.
Lithium-containing thiophosphates represent promising ceramic electrolytes for all-solid-state batteries. The underlying principles that cause high Li + diffusivity are, however, still incompletely understood. Here, β-Li 3 PS 4 served as a model compound to test the recently presented hypothesis that a channel-like Li + diffusion pathway influences ionic transport in its 3D network of the LiS 4 , LiS 6 , and PS 4 polyhedra. We looked at the temperature dependence of diffusion-induced 7 Li nuclear spin−lattice relaxation rates to check whether they reveal any diagnostic differences as compared to the nuclear spin response frequently found for isotropic (3D) diffusion. Indeed, distinct anomalies show up that can be understood if we consider the influence of lowdimensional diffusion. Hence, even for isotropic materials without clearly recognizable 1D or 2D diffusion pathways, such as layered or channel-structured materials, structurally hidden dimensionality effects might help explain high ionic conductivities and refine the design principles currently discussed. In the present case, such rapid pathways assist the ions to move through the crystal structure.
The realization of green and economically friendly energy storage systems needs materials with outstanding properties. Future batteries based on Na as an abundant element take advantage of non-flammable ceramic electrolytes with very high conductivities. Na3Zr2(SiO4)2PO4-type superionic conductors are expected to pave the way for inherently safe and sustainable all-solid-state batteries. So far, only little information has been extracted from spectroscopic measurements to clarify the origins of fast ionic hopping on the atomic length scale. Here we combined broadband conductivity spectroscopy and nuclear magnetic resonance (NMR) relaxation to study Na ion dynamics from the µm to the angstrom length scale. Spin-lattice relaxation NMR revealed a very fast Na ion exchange process in Na3.4Sc0.4Zr1.6(SiO4)2PO4 that is characterized by an unprecedentedly high self-diffusion coefficient of 9 × 10−12 m2s−1 at −10 °C. Thus, well below ambient temperature the Na ions have access to elementary diffusion processes with a mean residence time τNMR of only 2 ns. The underlying asymmetric diffusion-induced NMR rate peak and the corresponding conductivity isotherms measured in the MHz range reveal correlated ionic motion. Obviously, local but extremely rapid Na+ jumps, involving especially the transition sites in Sc-NZSP, trigger long-range ion transport and push ionic conductivity up to 2 mS/cm at room temperature.
Amorphous self-assembled titania nanotube layers are fabricated by anodization in ethylene glycol based baths. The nanotubes having diameters between 70-130 nm and lengths between 4.5-17 μm are assembled in Na-ion test cells. Their sodium insertion properties and electrochemical behavior with respect to sodium insertion is studied by galvanostatic cycling with potential limitation and cyclic voltammetry. It is found that these materials are very resilient to cycling, some being able to withstand more than 300 cycles without significant loss of capacity. The mechanism of electrochemical storage of Na(+) in the investigated titania nanotubes is found to present significant particularities and differences from a classical insertion reaction. It appears that the interfacial region between titania and the liquid electrolyte is hosting the majority of Na(+) ions and that this interfacial layer has a pseudocapacitive behavior. Also, for the first time, the chemical diffusion coefficients of Na(+) into the amorphous titania nanotubes is determined at various electrode potentials. The low values of diffusion coefficients, ranging between 4 × 10(-20) to 1 × 10(-21) cm(2)/s, support the interfacial Na(+) storage mechanism.
Ceramics with nm-sized dimensions are widely used in various applications such as batteries, fuel cells or sensors. Their oftentimes superior electrochemical properties as well as their capabilities to easily conduct ions are, however, not completely understood. Depending on the method chosen to prepare the materials, nanostructured ceramics may be equipped with a large area fraction of interfacial regions that exhibit structural disorder. Elucidating the relationship between microscopic disorder and ion dynamics as well as electrochemical performance is necessary to develop new functionalized materials. Here, we highlight some of the very recent studies on ion transport and electrochemical properties of nanostructured ceramics. Emphasis is put on TiO
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The realization of green and economically friendly energy storage systems needs materials with outstanding properties. Future batteries based on Na as an abundant element take advantage of non-flammable ceramic electrolytes with very high conductivities. Na 3 Zr 2 (SiO 4 ) 2 PO 4 -type superionic conductors are expected to pave the way for inherently safe and sustainable all-solid-state batteries. So far, only little information has been extracted from spectroscopic measurements to clarify the origins of fast ionic hopping on the atomic length scale. Here we combined broadband conductivity spectroscopy and nuclear magnetic resonance (NMR) relaxation to study Na ion dynamics from the µm to the angstrom length scale. Spin-lattice relaxation NMR revealed a very fast Na ion exchange process in Na 3.4 Sc 0.4 Zr 1.6 (SiO 4 ) 2 PO 4 that is characterized by an unprecedentedly high self-diffusion coefficient of 9 × 10 −12 m 2 s −1 at −10 °C. Thus, well below ambient temperature the Na ions have access to elementary diffusion processes with a mean residence time τ NMR of only 2 ns. The underlying asymmetric diffusioninduced NMR rate peak and the corresponding conductivity isotherms measured in the MHz range reveal correlated ionic motion. Obviously, local but extremely rapid Na + jumps, involving especially the transition sites in Sc-NZSP, trigger long-range ion transport and push ionic conductivity up to 2 mS/cm at room temperature.
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