Exploring Aliovalent Substitutions in the Lithium Halide Superionic Conductor Li3-xIn1-xZrxCl6 (0 ≤ X ≤ 0.5)

Abstract

<p>In recent years, ternary halides Li<sub>3</sub><i>MX</i><sub>6</sub> (<i>M</i> = Y, Er, In; <i>X</i> = Cl, Br, I) have garnered attention as solid electrolytes due to their wide electrochemical stability window and favorable room-temperature conductivities. In this material class, the influences of iso- or aliovalent substitutions are so far rarely studied in-depth, despite this being a common tool for correlating structure and transport properties. In this work, we investigate the impact of Zr substitution on the structure and ionic conductivity of Li<sub>3</sub>InCl<sub>6</sub> (Li<sub>3-<i>x</i></sub>In<sub>1-<i>x</i></sub>Zr<i><sub>x</sub></i>Cl<sub>6</sub> with 0 ≤ <i>x</i> ≤ 0.5) using a combination of neutron diffraction, nuclear magnetic resonance and impedance spectroscopy. Analysis of high-resolution diffraction data shows the presence of an additional tetrahedrally coordinated lithium position together with cation site-disorder, both of which have not been reported previously for Li<sub>3</sub>InCl<sub>6</sub>. This Li<sup>+</sup> position and cation disorder lead to the formation of a three-dimensional lithium ion diffusion channel, instead of the expected two-dimensional diffusion. Upon Zr<sup>4+</sup> substitution, the structure exhibits non-uniform volume changes along with an increasing number of vacancies, all of which lead to an increasing ionic conductivity in this series of solid solutions.</p>

Electrochemically Stable Li3–xIn1–xHfxCl6 Halide Solid Electrolytes for All-Solid-State Batteries

“…This is similar to the results reported for Li 3−x In 1−x Zr x Cl 6 . 21 Although the crystal structure of Li 3 InCl 6 has been confirmed previously, 18,21,31 in the present study, obtaining accurate concentrations of Hf in the subcation lattice was necessary. As shown in Figures 2b and S2 2c, the G(r) values for r < 30 Å show a similar trend as those for pristine Li 3 InCl 6 , indicating that In/Hf site disorder is not the main factor for ionic conductivity.…”

“…However, Li + does not readily cross the (001) lattice plane for 3D migration through the c-direction owing to In 3+ /Hf 4+ acting as blocking defects. 21 3D migration through the cdirection is also not favorable for Li + transport from an energy point of view. The migration energy barrier required to cross is lower for Li 2.7 In 0.7 Hf 0.3 Cl 6 compared to that for Li 3 InCl 6 .…”

Investigation of Structure, Ionic Conductivity, and Electrochemical Stability of Halogen Substitution in Solid-State Ion Conductor Li3YBrxCl6–x

“…No tetrahedral sites were necessary for a physically consistent refinement as reported in isostructural chlorides. 27,28 Despite that the tetrahedral voids are not occupied on average, they are still available as interstitial sites for the diffusion pathways.…”

Synthetic control of structure and conduction properties in Na–Y–Zr–Cl solid electrolytes

“…13,16,18,23 These conductivities can be further improved through iso-and aliovalent substitution on the halide or metal site. [6][7][8]15,18,19,21,[24][25][26][27] While none of the halides have been shown to be stable against a metal anode, chlorides and uorides are stable at potentials >4 V as their highly electronegative anions resist oxidation, enabling stable long-term cycling even when tested against (uncoated) oxide cathodes. 11 Finally, scalable solution-based synthesis methods that can yield >100 g of material per batch have been reported for many A 3 MX 6 chemistries.…”