Abstract
Li6PS5I acts as a perfect model substance to study length scale-dependent diffusion parameters in an ordered matrix. It provides Li-rich cages which offer rapid but localized Li+ translational jump processes. As jumps between these cages are assumed to be much less frequent, long-range ion transport is sluggish, resulting in ionic conductivities in the order of 10–6 S cm–1 at room temperature. In contrast, the site disordered analogues Li6PS5X (X = Br, Cl) are known as fast ion conductors because structural disorder facilities intercage dynamics. As yet, the two extremely distinct jump processes in Li6PS5I have not been visualized separately. Here, we used a combination of 31P and 7Li NMR relaxation measurements to probe this bimodal dynamic behavior, that is, ultrafast intracage Li+ hopping and the much slower Li+intercage exchange process. While the first is to be characterized by an activation energy of ca. 0.2 eV as directly measured by 7Li NMR, the latter is best observed by 31P NMR and follows the Arrhenius law determined by 0.44 eV. This activation energy perfectly agrees with that seen by direct current conductivity spectroscopy being sensitive to long-range ion transport for which the intercage jumps are the rate limiting step. Moreover, quantitative agreement in terms of diffusion coefficients is also observed. The solid-state diffusion coefficient Dσ obtained from conductivity spectroscopy agrees very well with that from 31P NMR (DNMR ≈ 4.6 × 10–15 cm2 s–1). DNMR was directly extracted from the pronounced diffusion-controlled 31P NMR spin-lock spin–lattice relaxation peak appearing at 366 K.
Highlights
The search for powerful solid electrolytes that can be used in sustainable Li-ion and Na-ion energy storage systems has reached an unpreceded level today.[1−5] To identify and understand the origins behind fast ion transport in crystalline and amorphous solids, model substances are needed that allow the characterization of the distinct dynamic processes in detail, without any interfering effects from other diffusion processes taking place at the same time
We used a combination of 7Li and 31P nuclear magnetic resonance (NMR) spin−lattice relaxation techniques[24−28] to conclusively characterize this unique dynamic property in Li6PS5I
As we have shown earlier,[29,33] peak C, most likely, reflects rotational motions of the polyanions as it is unique to 31P and is not seen in 7Li NMR
Summary
The search for powerful solid electrolytes that can be used in sustainable Li-ion and Na-ion energy storage systems has reached an unpreceded level today.[1−5] To identify and understand the origins behind fast ion transport in crystalline and amorphous solids, model substances are needed that allow the characterization of the distinct dynamic processes in detail, without any interfering effects from other diffusion processes taking place at the same time.solLidi6PelSe5cItrboellyotnesg6s−t2o1 the well-known that is assumed group of argyrodite-type to host two dynamically distinct Li+ diffusion processes.[22,23] In the anion-orderedLi6PS5I, whose structure is depicted in Figure 1, Li-rich cages are present that provide the opportunity of rapid localized Li+ hopping processes.[22,23] Intercage jumps are, assumed to be much less frequent.[22,23] This assumption was used to explain the that shows poor long-range ion transport properties of ionic conductivities in the order of onlyL1i06−P6S5SI cm−1 at room temperature.[22]. The search for powerful solid electrolytes that can be used in sustainable Li-ion and Na-ion energy storage systems has reached an unpreceded level today.[1−5] To identify and understand the origins behind fast ion transport in crystalline and amorphous solids, model substances are needed that allow the characterization of the distinct dynamic processes in detail, without any interfering effects from other diffusion processes taking place at the same time. SolLidi6PelSe5cItrboellyotnesg6s−t2o1 the well-known that is assumed group of argyrodite-type to host two dynamically distinct Li+ diffusion processes.[22,23] In the anion-ordered. Li6PS5I, whose structure is depicted, Li-rich cages are present that provide the opportunity of rapid localized Li+ hopping processes.[22,23] Intercage jumps are, assumed to be much less frequent.[22,23] This assumption was used to explain the that shows poor long-range ion transport properties of ionic conductivities in the order of only. We used a combination of 7Li and 31P nuclear magnetic resonance (NMR) spin−lattice relaxation techniques[24−28] to conclusively characterize this unique dynamic property in Li6PS5I
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
