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With the goal of finding new lithium solid electrolytes by a combined computational–experimental method, the exploration of the Li–Al–O–S phase field resulted in the discovery of a new sulfide Li3AlS3. The structure of the new phase was determined through an approach combining synchrotron X-ray and neutron diffraction with 6Li and 27Al magic-angle spinning nuclear magnetic resonance spectroscopy and revealed to be a highly ordered cationic polyhedral network within a sulfide anion hcp-type sublattice. The originality of the structure relies on the presence of Al2S6repeating dimer units consisting of two edge-shared Al tetrahedra. We find that, in this structure type consisting of alternating tetrahedral layers with Li-only polyhedra layers, the formation of these dimers is constrained by the Al/S ratio of 1/3. Moreover, by comparing this structure to similar phases such as Li5AlS4and Li4.4Al0.2Ge0.3S4((Al + Ge)/S = 1/4), we discovered that the AlS4dimers not only influence atomic displacements and Li polyhedral distortions but also determine the overall Li polyhedral arrangement within the hcplattice, leading to the presence of highly ordered vacancies in both the tetrahedral and Li-only layer. AC impedance measurements revealed a low lithium mobility, which is strongly impacted by the presence of ordered vacancies. Finally, a composition–structure–property relationship understanding was developed to explain the extent of lithium mobility in this structure type.

All-solid-state batteries (ASSBs) based on noncombustible solid electrolytes are promising candidates for safe and high energy storage systems, but it remains a challenge to prepare systems with stable interfaces between the various solid components that survive both the synthesis conditions and electrochemical cycling. We have investigated cathode mixtures based on a carbon-coated LiFePO4active material and Li3+xP1–xSixO4solid electrolyte for potential use in all-solid-state batteries. Half-cells were constructed by combining both compounds into pellets by spark plasma sintering (SPS). We report the fast and quantitative formation of two solid solutions (LiFePO4–Fe2SiO4and Li3PO4–Li2FeSiO4) for different compositions and ratios of the pristine compounds, as tracked by powder X-ray diffraction and solid-state nuclear magnetic resonance; X-ray absorption near-edge spectroscopy confirms the formation of iron silicates similar to Fe2SiO4. Scanning electron microscopy and energy dispersive X-ray spectroscopy reveal diffusion of iron cations up to 40 μm into the solid electrolyte even in the short processing times accessible by SPS. Electrochemical cycling of the SPS-treated cathode mixtures demonstrates a substantial decrease in capacity following the formation of the solid solutions during sintering. Consequently, all-solid-state batteries based on LiFePO4and Li3+xP1–xSixO4would necessitate iron ion blocking layers. More generally, this study highlights the importance of systematic studies on the fundamental reactions at the active material–solid electrolyte interfaces to enable the introduction of protective layers for commercially successful ASSBs.

The properties of mixed ionic–electronic conductors (MIECs) are most conveniently controlled through site-specific aliovalent substitution, yet few techniques can report directly on the local structure and defect chemistry underpinning changes in ionic and electronic conductivity. In this work, we perform high-resolution 17O (I= 5/2) solid-state NMR spectroscopy of La2–xSrxNiO4+δ, an MIEC and prospective solid oxide fuel cell (SOFC) cathode material, showing the sensitivity of 17O hyperfine (Fermi contact) shifts and quadrupolar coupling constants due to local structural changes arising from Sr substitution (x). Previously, we resolved resonances from three distinct oxygen sites (interstitial, axial, and equatorial) in the unsubstituted x= 0 material (Halat et al., J. Am. Chem. Soc.2016, 138, 11958). Here, substitution-induced changes in these three spectral features indirectly report on the ionic conductivity, local octahedral tilting, and electronic conductivity, respectively, of the (substituted) materials. In particular, the intensity of the 17O resonance arising from mobile interstitial defects decreases, and then disappears, at x= 0.5, consistent with reports of lower bulk ionic conductivity in Sr-substituted phases. Second, local distortions among the split axial oxygen sites diminish, even on modest incorporation of Sr (x< 0.1), which is also accompanied by faster spin–lattice (T1) relaxation of the interstitial 17O resonances, indicating increased mobility of the associated sites. Finally, the hyperfine shift of the equatorial oxygen resonance decreases due to conversion of Ni2+(d8) to Ni3+(d7) by charge compensation, a mechanism associated with improved electronic conductivity in the Sr-substituted phases. Valence and coordination changes of the Ni cations are further supported by Ni K-edge X-ray absorption near-edge structure (XANES) measurements, which show a decrease in the Jahn–Teller distortion of the Ni3+sites and a Ni coordination change consistent with the formation of oxygen vacancies. Ultimately, these insights into local atomic and electronic structure that rely on 17O solid-state NMR spectroscopy should prove relevant for a broad range of aliovalently substituted functional paramagnetic oxides.

Large-scale computations of nuclear magnetic resonance (NMR) shifts for extended paramagnetic solids (pNMR) are reported using the highly efficient Gaussian-augmented plane-wave implementation of the CP2K code. Combining hyperfine couplings obtained with hybrid functionals with g-tensors and orbital shieldings computed using gradient-corrected functionals, contact, pseudocontact, and orbital-shift contributions to pNMR shifts are accessible. Due to the efficient and highly parallel performance of CP2K, a wide variety of materials with large unit cells can be studied with extended Gaussian basis sets. Validation of various approaches for the different contributions to pNMR shifts is done first for molecules in a large supercell in comparison with typical quantum-chemical codes. This is then extended to a detailed study of g-tensors for extended solid transition-metal fluorides and for a series of complex lithium vanadium phosphates. Finally, lithium pNMR shifts are computed for Li3V2(PO4)3, for which detailed experimental data are available. This has allowed an in-depth study of different approaches (e.g., full periodic versus incremental cluster computations of g-tensors and different functionals and basis sets for hyperfine computations) as well as a thorough analysis of the different contributions to the pNMR shifts. This study paves the way for a more-widespread computational treatment of NMR shifts for paramagnetic materials.

Among the many different processes proposed for large-scale carbon capture and storage (CCS), high-temperature CO2looping has emerged as a favorable candidate due to the low theoretical energy penalties that can be achieved. Many different materials have been proposed for use in such a process, the process requiring fast CO2absorption reaction kinetics as well as being able to cycle the material for multiple cycles without loss of capacity. Lithium ternary oxide materials, and in particular Li2ZrO3, have displayed promising performance, but further modifications are needed to improve their rate of reaction with CO2. Previous studies have linked rates of lithium ionic conduction with CO2absorption in similar materials, and in this work we present work aimed at exploring the effect of aliovalent doping on the efficacy of Li2ZrO3as a CO2sorbent. Using a combination of X-ray powder diffraction, theoretical calculations, and solid-state nuclear magnetic resonance, we studied the impact of Nb, Ta, and Y doping on the structure, Li ionic motion, and CO2absorption properties of Li2ZrO3. These methods allowed us to characterize the theoretical and experimental doping limit into the pure material, suggesting that vacancies formed upon doping are not fully disordered but instead are correlated to the dopant atom positions, limiting the solubility range. Characterization of the lithium motion using variable-temperature solid-state nuclear magnetic resonance confirms that interstitial doping with Y retards the movement of Li ions in the structure, whereas vacancy doping with Nb or Ta results in a similar activation energy as observed for nominally pure Li2ZrO3. However, a marked reduction in the CO2absorption of the Nb- and Ta-doped samples suggests that doping also leads to a change in the carbonation equilibrium of Li2ZrO3, disfavoring the CO2absorption at the reaction temperature. This study shows that a complex mixture of structural, kinetic, and dynamic factors can influence the performance of Li-based materials for CCS and underscores the importance of balancing these different factors in order to optimize the process.

Ternary rare‐earth cobalt gallides RE4Co3Ga16(RE = Gd–Er, Y) have been prepared by arc‐melting of the elements followed by annealing at 800 °C. Single crystals of the Gd and Tb members were also grown in the presence of a Ga self‐flux. They extend the rare‐earth substitution possible in the Sm4Co3Ga16‐type structure (Pearson symbol tP23, space group P4/mmm, Z= 1), in which additional Co atoms enter as self‐interstitials into the parent RE2CoGa8structure. Structural refinements were carried out on single‐crystal (RE = Gd, Tb) and powder (RE = Dy, Ho, Er, Y) X‐ray diffraction data. Cell parameters lie in the ranges of a= 6.03–5.96 Å and c= 11.11–10.96 Å. Magnetic measurements on RE4Co3Ga16(RE = Gd, Tb, Dy) reveal that they order antiferromagnetically below TNof 19, 25, and 14 K, respectively; Y4Co3Ga16is Pauli paramagnetic. The electrical resistivity of Tb4Co3Ga16undergoes a transition coincident with the magnetic ordering temperature. Band structure calculations on Y4Co3Ga16indicate that the major bonding contributions arise from Co–Ga and Ga–Ga interactions, with the stuffing of interstitial Co atoms into octahedral sites of the parent Y2CoGa8structure, which provides additional Co–Ga bonding stabilization.