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Strategies to enhance ionic conductivities in solid electrolytes typically focus on the effects of modifying their crystal structures or of tuning mobile-ion stoichiometries. A less-explored approach is to modulate the chemical bonding interactions within a material to promote fast lithium-ion diffusion. Recently, the idea of a solid-electrolyte inductive effect has been proposed, whereby changes in bonding within the solid-electrolyte host framework modify the potential energy landscape for the mobile ions, resulting in an enhanced ionic conductivity. Direct evidence for a solid-electrolyte inductive effect, however, is lacking-in part because of the challenge of quantifying changes in local bonding interactions within a solid-electrolyte host framework. Here, we consider the evidence for a solid-electrolyte inductive effect in the archetypal superionic lithium-ion conductor Li10Ge1-xSnxP2S12. Substituting Ge for Sn weakens the {Ge,Sn}-S bonding interactions and increases the charge density associated with the S2- ions. This charge redistribution modifies the Li+ substructure causing Li+ ions to bind more strongly to the host framework S2- anions, which in turn modulates the Li+ ion potential energy surface, increasing local barriers for Li+ ion diffusion. Each of these effects is consistent with the predictions of the solid-electrolyte inductive effect model. Density functional theory calculations predict that this inductive effect occurs even in the absence of changes to the host framework geometry due to Ge → Sn substitution. These results provide direct evidence in support of a measurable solid-electrolyte inductive effect and demonstrate its application as a practical strategy for tuning ionic conductivities in superionic lithium-ion conductors.

International audience; Highly conductive solid electrolytes are fundamental for all solid-state batteries with low inner cell resistance. Such fast solid electrolytes are often found by systematic substitution experiments in which one atom is exchanged for another, and corresponding changes in ionic transport are monitored. With this strategy, compositions with the most promising transport properties can be identified fast and reliably. However, the substitution of one element does not only influence the crystal structure and diffusion channel size (static) but also the underlying bonding interactions and with it the vibrational properties of the lattice (dynamic). Since both static and dynamic properties influence the diffusion process, simple one-dimensional substitution series only provide limited insights to the importance of changes in the structure and lattice dynamics for the transport properties. To overcome these limitations, we make use of a two-dimensional substitution approach, investigating and comparing the four single-substitution series Na3P1-xSbxS4, Na3P1-xSbxSe4, Na3PS4-ySey, and Na3SbS4-ySey. Specifically, we find that the diffusion channel size represented by the distance between S/Se ions cannot explain the observed changes of activation barriers throughout the whole substitution system. Melting temperatures and the herein newly defined anharmonic bulk modulus-as descriptors for bonding interactions and corresponding lattice dynamics-correlate well with the activation barriers, highlighting the relevance of lattice softness for the ion transport in this class of fast ion conductors.

In recent years, ternary halides Li3MX6 (M = Y, Er, In; X = Cl, Br, I) have garnered attention assolid electrolytes due to their wide electrochemical stability window and favorable roomtemperatureconductivities. In this material class, the influences of iso- or aliovalentsubstitutions are so far rarely studied in-depth, despite this being a common tool for correlatingstructure and transport properties. In this work, we investigate the impact of Zr substitution onthe structure and ionic conductivity of Li3InCl6 (Li3-xIn1-xZrxCl6 with 0 ≤ x ≤ 0.5) using acombination of neutron diffraction, nuclear magnetic resonance and impedance spectroscopy.Analysis of high-resolution diffraction data shows the presence of an additional tetrahedrallycoordinated lithium position together with cation site-disorder, both of which have not beenreported previously for Li3InCl6. This Li+ position and cation disorder lead to the formation ofa three-dimensional lithium ion diffusion channel, instead of the expected two-dimensionaldiffusion. Upon Zr4+ substitution, the structure exhibits non-uniform volume changes alongwith an increasing number of vacancies, all of which lead to an increasing ionic conductivity inthis series of solid solutions

All-solid-state batteries (ASSBs) show great potential for providing high power and energy density with enhanced battery safety. While new solid electrolytes (SEs) have been developed with high enough ionic conductivities, SSBs with long operational life are still rarely reported. Therefore, on the way to high performance and long-life ASSBs, a better understanding of the complex degradation mechanisms, occurring at the electrode / electrolyte interfaces is pivotal. While the lithium metal / solid electrolyte interface is receiving considerable attention due to the quest for high energy density, the interface between the active material and solid electrolyte particles within the composite cathode is arguably the most difficult to solve and to study. In this work, multiple characterization methods are combined to better understand the processes that occur at the LiCoO2 cathode and the Li10GeP2S12 solid electrolyte interface. Indium and Li4Ti5O12 are used as anode materials to avoid the instability problems associated with Li metal anodes. Capacity fading and increased impedances are observed during longterm cycling. Post-mortem analysis with scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS), x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) show that electrochemically driven mechanical failure and degradation at the cathode / solid electrolyte interface contribute to the increase in internal resistance and the resulting capacity fading. These results suggest that the development of electrochemically more stable SEs and the engineering of cathode / SE interfaces are crucial for achieving reliable SSB performance.

Li7La3Zr2O12 (LLZO) and related compounds are considered as promising candidates for future all-solid-state Li-ion battery applications. Still, the processing of those materials into thin membranes with the right stoichiometry and crystal structure is difficult and laborious. The sensitivity of the Li-ion conductive garnets against moisture and the associated Li+/H+ cation exchange makes their processing even more difficult. Formulation of suitable polymer/ceramic hybrid solid state electrolytes could be a prosperous way to reach the future large scale production of solid state Li-ion batteries. In fact, solvent mediated and/or slurry based wet-processing of the LLZO, e.g., tape-casting, could result in irreversible Li-ion loss of the pristine material due to Li+/H+ cation exchange. The concomitant structural changes and loss in functionality in terms of Li-ion conductivity are the results of the above process. Therefore, in the present work a systematic study on the chemical stability and structural retention of Al-substituted LLZO in different solvents is reported. It was found that Li+/H+ exchange in LLZO occurs upon solvent immersion, and its magnitude is dependent on the availability of −OH functional groups of the solvent molecules. As a result, a larger degree of Li+/H+ exchange causes higher increase of the lattice parameter of the LLZO, determined by synchrotron diffraction analyses. The expansion of the cubic unit cell was ascertained, when Li+ was replaced by H+ in the host lattice, by ab initio computational studies. The application of the most common solvent as dispersion medium, i.e., high purity water, causes the most significant Li+/H+ exchange and, therefore, structural change, while acetonitrile was proven to be the best suitable solvent for wet postprocessing of LLZO. Finally, computational calculations suggested that the Li+/H+ exchange could result in diminished ionic, i.e., mixed Li+-H+, conductivity due to the insertion of protons with lower mobility than that of Li-ions.

Inspired by the promising thermoelectric properties of chalcopyrite-like quaternary chalcogenides, here we describe the synthesis and characterization of the solid solution Cu(2)Zn(1-x)Fe(x)GeSe(4). Upon substitution of Zn with the isoelectronic Fe, no charge carriers are introduced in these intrinsic semiconductors. However, a change in lattice parameters, expressed in an elongation of the c/a lattice parameter ratio with minimal change in unit cell volume, reveals the existence of a three-stage cation restructuring process of Cu, Zn, and Fe. The resulting local anisotropic structural disorder leads to phonon scattering not normally observed, resulting in an effective approach to reduce the lattice thermal conductivity in this class of materials.

The 18-electron ternary intermetallic systems TiNiSn and TiCoSb are promising for applications as high-temperature thermoelectrics and comprise earth-abundant, and relatively nontoxic elements. Heusler and half-Heusler compounds are usually prepared by conventional solid state methods involving arc-melting and annealing at high temperatures for an extended period of time. Here, we report an energy-saving preparation route using a domestic microwave oven, reducing the reaction time significantly from more than a week to one minute. A microwave susceptor material rapidly heats the elemental starting materials inside an evacuated quartz tube resulting in near single phase compounds. The initial preparation is followed by a densification step involving hot-pressing, which reduces the amount of secondary phases, as verified by synchrotron X-ray diffraction, leading to the desired half-Heusler compounds, demonstrating that hot-pressing should be treated as part of the preparative process. For TiNiSn, high thermoelectric power factors of 2 mW/mK^2 at temperatures in the 700 to 800 K range, and zT values of around 0.4 are found, with the microwave-prepared sample displaying somewhat superior properties to conventionally prepared half-Heuslers due to lower thermal conductivity. The TiCoSb sample shows a lower thermoelectric figure of merit when prepared using microwave methods because of a metallic second phase.