Argyrodite-type Li 6 PS 5 X (X = Cl, Br) compounds are considered to act as powerful ionic conductors in next-generation allsolid-state lithium batteries. In contrast to Li 6 PS 5 Br and Li 6 PS 5 Cl compounds showing ionic conductivities on the order of several mS cm −1 , the iodine compound Li 6 PS 5 I turned out to be a poor ionic conductor. This difference has been explained by anion site disorder in Li 6 PS 5 Br and Li 6 PS 5 Cl leading to facile through-going, that is, longrange ion transport. In the structurally ordered compound, Li 6 PS 5 I, long-range ion transport is, however, interrupted because the important intercage Li jump-diffusion pathway, enabling the ions to diffuse over long distances, is characterized by higher activation energy than that in the sibling compounds. Here, we introduced structural disorder in the iodide by soft mechanical treatment and took advantage of a high-energy planetary mill to prepare nanocrystalline Li 6 PS 5 I. A milling time of only 120 min turned out to be sufficient to boost ionic conductivity by 2 orders of magnitude, reaching σ total = 0.5 × 10 −3 S cm −1 . We followed this noticeable increase in ionic conductivity by broad-band conductivity spectroscopy and 7 Li nuclear magnetic relaxation. X-ray powder diffraction and high-resolution 6 Li, 31 P MAS NMR helped characterize structural changes and the extent of disorder introduced. Changes in attempt frequency, activation entropy, and charge carrier concentration seem to be responsible for this increase.

Ceramic electrolytes, characterized by a very high ionic conductivity as it is the case for Al-stabilized cubic Li 7 La 3 Zr 2 O 12 (Al:LLZO), are of utmost interest to develop next-generation batteries that can efficiently store electrical energy from renewable sources. If envisaged not as a solid electrolyte but as a protecting layer in lithium-metal batteries with liquid electrolytes, the ceramic should allow Li + to pass through but block out other species such as H + . Protons, for example, originating from the decomposition of electrolyte solvent molecules, will form detrimental LiH that severely affects the performance and lifetime of such batteries. Although Li-ion dynamics in Al:LLZO has been the topic of many studies, until today, little information is available about macroscopic proton diffusion in LLZO. Here, we used single-crystal X-ray diffraction to study the Li + /H + exchange rate in AL:LLZO over a period of about 3 years. Rietveld refinements reveal that H solely exchanges on the 96h site. The Li/H portion significantly changes from the anhydrous pristine sample to Li 4.21 :H 0.66 after 17 days of altering in humid air and finally to Li 2.55 :H 2.32 after 960 days. Considering the change of the Li/H portion and the probing depth of X-rays into Al:LLZO, we applied a spherical diffusion model to estimate the proton diffusion coefficient of D 0 ≈ 10 −17 m 2 s −1 . Such a proton diffusion coefficient value is sufficiently high to have significant impact on cell performance and safety if Al:LLZO is going to be used to protect the Li-metal anode from reaction with the liquid electrolyte. In particular, during Li plating, such a high H + penetration rate may accelerate the formation of LiH, giving rise to safety problems of these types of batteries.

Lithium-thiophosphates have attracted great attention as they offer a rich playground to develop tailor-made solid electrolytes for clean energy storage systems. Here, we used poorly conducting Li6PS5I, which can be converted into a fast ion conductor by high-energy ball-milling to understand the fundamental guidelines that enable the Li+ ions to quickly diffuse through a polarizable but distorted matrix. In stark contrast to well-crystalline Li6PS5I (10–6 S cm–1), the ionic conductivity of its defect-rich nanostructured analog touches almost the mS cm–1 regime. Most likely, this immense enhancement originates from site disorder and polyhedral distortions introduced during mechanical treatment. We used the spin probes 7Li and 31P to monitor nuclear spin relaxation that is directly induced by Li+ translational and/or PS4 3– rotational motions. Compared to the ordered form, 7Li spin–lattice relaxation (SLR) in nano-Li6PS5I reveals an additional ultrafast process that is governed by activation energy as low as 160 meV. Presumably, this new relaxation peak, appearing at T max = 281 K, reflects extremely rapid Li hopping processes with a jump rate in the order of 109 s–1 at T max. Thus, the thiophosphate transforms from a poor electrolyte with island-like local diffusivity to a fast ion conductor with 3D cross-linked diffusion routes enabling long-range transport. On the other hand, the original 31P nuclear magnetic resonance (NMR) SLR rate peak, pointing to an effective 31P-31P spin relaxation source in ordered Li6PS5I, is either absent for the distorted form or shifts toward much higher temperatures. Assuming the 31P NMR peak as being a result of PS4 3– rotational jump processes, NMR unveils that disorder significantly slows down anion dynamics. The latter finding might also have broader implications and sheds light on the vital question how rotational dynamics are to be manipulated to effectively enhance Li+ cation transport.

Understanding the origins of fast ion transport in solids is important to develop new ionic conductors for batteries and sensors. Nature offers a rich assortment of rather inspiring structures to elucidate these origins. In particular, layer-structured materials are prone to show facile Li + transport along their inner surfaces. Here, synthetic hectorite-type Li 0.5 [Mg 2.5 Li 0.5 ]Si 4 O 10 F 2 , being a phyllosilicate, served as a model substance to investigate Li + translational ion dynamics by both broadband conductivity spectroscopy and diffusion-induced 7 Li nuclear magnetic resonance (NMR) spin–lattice relaxation experiments. It turned out that conductivity spectroscopy, electric modulus data, and NMR are indeed able to detect a rapid 2D Li + exchange process governed by an activation energy as low as 0.35 eV. At room temperature, the bulk conductivity turned out to be in the order of 0.1 mS cm –1 . Thus, the silicate represents a promising starting point for further improvements by crystal chemical engineering. To the best of our knowledge, such a high Li + ionic conductivity has not been observed for any silicate yet.

The development of ceramic proton conductors is currently attracting great attention, as they might be useful to construct new energy storage systems. Li6La3ZrTaO12 (LLZTO) is known for its rapid Li+ diffusivity as has been directly revealed by 7Li NMR measurements. Exchanging parts of the highly mobile Li+ ions by protons through treatment of a single crystal in water or glacial acetic acid yields a mixed proton–lithium ionic conductor. Here, H+ proton diffusivity and Li+ diffusivity have separately been studied with element-specific 1H and 7Li NMR spectroscopy. While long-range 7Li diffusion is noticeably slowed in Li–H exchanged LLZTO, we directly observe rather high H+ diffusivity, which is, however, significantly slower than Li+ dynamics. With the help of spin–lattice relaxation measurements we were able to measure local (and long-range) energy barriers (0.20(1) eV vs 0.45(3) eV) as well as the self-diffusion coefficient D H of H+ dynamics (1.2 × 10–15 m2 s–1 at 125 °C). These encouraging results are assumed to open new directories in designing ceramics offering fast transport pathways for protons.