Observation of Li+ jumps in solid inorganic electrolytes over a broad dynamical range: A case study of the lithium phosphidosilicates Li8SiP4 and Li14SiP6

7Li NMR spectroscopy is known to be very sensitive to translational motion in solids and therefore highly suited for investigating temperature-dependent Li+ dynamics. A number of different NMR methods are available for choosing the dynamical range of the observed Li+ jump frequencies present in inorganic solid-state electrolytes. This includes 7Li spin-alignment echo NMR spectroscopy, static 7Li lineshape analysis, and 7Li spin-lattice relaxometry that can be used to detect Li+ jumps in the Hz, kHz, and MHz range, respectively. We introduce and discuss these NMR techniques with respect to their theoretical description and practical application to investigate the Li+ dynamics at different time scales for the two solid-state electrolytes Li8SiP4 and Li14SiP6. The data evaluation for all methods is discussed in detail, focusing on the determination of Li+ jump frequencies and activation energies for the investigated self-diffusion processes in a given structure

Effective Solid Electrolyte Interphase Formation on Lithium Metal Anodes by Mechanochemical Modification

Lithium metal batteries are gaining increasing attention due to their potential for significantly higher theoretical energy density than conventional lithium ion batteries. Here, we present a novel mechanochemical modification method for lithium metal anodes, involving roll-pressing the lithium metal foil in contact with ionic liquid-based solutions, enabling the formation of an artificial solid electrolyte interphase with favorable properties such as an improved lithium ion transport and, most importantly, the suppression of dendrite growth, allowing homogeneous electrodeposition/-dissolution using conventional and highly conductive room temperature alkyl carbonate-based electrolytes. As a result, stable cycling in symmetrical Li∥Li cells is achieved even at a high current density of 10 mA cm–2. Furthermore, the rate capability and the capacity retention in NMC∥Li cells are significantly improved

Exploring Aliovalent Substitutions in the Lithium Halide Superionic Conductor Li_{3– x}In_{1– x}Zr_xCl₆ (0 ≤ x ≤ 0.5)

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 solution

Correlating Structural Disorder to Li+Li^+ Ion Transport in Li4–xGe1–xSbxS4Li_{4–x}Ge_{1–x}Sb_xS_4 (0 ≤ x ≤ 0.2)

Strong compositional influences are known to affect the ionic transport within the thio-LISICON family, however, a deeper understanding of the resulting structure - transport correlations have up until now been lacking. Employing a combination of high-resolution neutron diffraction, impedance spectroscopy and nuclear magnetic resonance spectroscopy, together with bond valence site energy calculations and the maximum entropy method for determining the underlying Li+ scattering density distribution of a crystal structure, this work assesses the impact of the Li+ substructure and charge carrier density on the ionic transport within the Li4-xGe1-xSbxS4 substitution series. By incorporating Sb5+ into Li4GeS4, an anisometric expansion of the unit cell is observed. An additional Li+ position is found as soon as (SbS4)3− polyhedra are present, leading to a better local polyhedral connectivity and a higher disorder in the Li+ substructure. Here, we are able to relate structural disorder to an increase in configurational entropy, together with a two order-of-magnitude increase in ionic conductivity. This result reinforces the typically believed paradigm that structural disorder leads to improvements in ionic transport

Understanding Lithium-Ion Transport in Selenophosphate-Based Lithium Argyrodites and Their Limitations in Solid-State Batteries

To develop solid-state batteries with high power and energy densities, solid electrolytes with fast Li+ transport are required. Superionic lithium argyrodites have proven to be a versatile system, in which superior ionic conductivities can be achieved by elemental substitutions. Herein, we report the novel selenophosphate-based lithium argyrodites Li6–xPSe5–xBr1+x (0 ≤ x ≤ 0.2) exhibiting ionic conductivities up to 8.5 mS·cm–1 and uncover the origin of their fast Li+ transport. Rietveld refinement of neutron powder diffraction data reveals a better interconnection of the Li+ cages compared to the thiophosphate analogue Li6PS5Br, by the occupation of two additional Li+ sites, facilitating fast Li+ transport. Additionally, a larger unit cell volume, lattice softening, and higher structural disorder between halide and chalcogenide are unveiled. The application of Li5.85PSe4.85Br1.15 as the catholyte in In/LiIn|Li6PS5Br|LiNi0.83Co0.11Mn0.06O2:Li5.85PSe4.85Br1.15 solid-state batteries leads to severe degradation upon charging of the cell, revealing that selenophosphate-based lithium argyrodites are not suitable for applications in lithium nickel cobalt manganese oxide-based solid-state batteries from a performance perspective. This work further expands on the understanding of the structure–transport relationship in Li+ conducting argyrodites and re-emphasizes the necessity to consider chemical and electrochemical stability of solid electrolytes against the active materials when developing fast Li+ conductors

On the Discrepancy between Local and Average Structure in the Fast Na+Na^+ Ionic Conductor Na2.9Sb0.9W0.1S4Na_{2.9}Sb_{0.9}W_{0.1}S_{4}

Aliovalent substitution is a common strategy to improve the ionic conductivity of solid electrolytes for solid-state batteries. The substitution of SbS43– by WS42– in Na2.9Sb0.9W0.1S4 leads to a very high ionic conductivity of 41 mS cm–1 at room temperature. While pristine Na3SbS4 crystallizes in a tetragonal structure, the substituted Na2.9Sb0.9W0.1S4 crystallizes in a cubic phase at room temperature based on its X-ray diffractogram. Here, we show by performing pair distribution function analyses and static single-pulse 121Sb NMR experiments that the short-range order of Na2.9Sb0.9W0.1S4 remains tetragonal despite the change in the Bragg diffraction pattern. Temperature-dependent Raman spectroscopy revealed that changed lattice dynamics due to the increased disorder in the Na+ substructure leads to dynamic sampling causing the discrepancy in local and average structure. While showing no differences in the local structure, compared to pristine Na3SbS4, quasi-elastic neutron scattering and solid-state 23Na nuclear magnetic resonance measurements revealed drastically improved Na+ diffusivity and decreased activation energies for Na2.9Sb0.9W0.1S4. The obtained diffusion coefficients are in very good agreement with theoretical values and long-range transport measured by impedance spectroscopy. This work demonstrates the importance of studying the local structure of ionic conductors to fully understand their transport mechanisms, a prerequisite for the development of faster ionic conductors