The recent interest in the halide-based solid electrolytes Li<sub>3</sub>MX<sub>6</sub> (M = Y, Er, In; X = Cl, Br, I) shows these materials to be promising candidates for solid-state battery application, due to high ionic conductivity and large electrochemical stability window. However, almost nothing is known about the underlying lithium sub-structure within those compounds. Here, we investigate the lithium sub-structure of Li<sub>3</sub>YCl<sub>6</sub> and Li<sub>3</sub>YBr<sub>6</sub> using temperature-dependent neutron diffraction. We compare compounds prepared by classic solid-state syntheses with a mechanochemical synthesis to shed light on the influence of the synthetic approach on the reported yttrium disorder and the resulting surrounding lithium sub-structure. This work provides a better understanding of the strong differences in ionic transport depending on the synthesis procedure of Li<sub>3</sub>MX<sub>6</sub>.
The recent interest in the halide-based solid electrolytes Li<sub>3</sub>MX<sub>6</sub> (M = Y, Er, In; X = Cl, Br, I) shows these materials to be promising candidates for solid-state battery application, due to high ionic conductivity and large electrochemical stability window. However, almost nothing is known about the underlying lithium sub-structure within those compounds. Here, we investigate the lithium sub-structure of Li<sub>3</sub>YCl<sub>6</sub> and Li<sub>3</sub>YBr<sub>6</sub> using temperature-dependent neutron diffraction. We compare compounds prepared by classic solid-state syntheses with a mechanochemical synthesis to shed light on the influence of the synthetic approach on the reported yttrium disorder and the resulting surrounding lithium sub-structure. This work provides a better understanding of the strong differences in ionic transport depending on the synthesis procedure of Li<sub>3</sub>MX<sub>6</sub>.
Lithium ion conducting argyrodites are among the most studied solid electrolytes due to their high ionic conductivities. A major concern in a solid-state battery is the solid electrolyte stability. Here we present a systematic study on the influence of cationic and anionic substitution on the electrochemical stability of Li6PS5X, using step-wise cyclic voltammetry, optical band gap measurements, hard X-ray photoelectron spectroscopy along with first-principles calculations. We observe that going from Li6PS5Cl to Li6+xP1-xMxS5I (M = Si4+, Ge4+), the oxidative degradation does not change. Considering the chemical bonding shows that the valence band edges are mostly populated by non-bonding orbitals of the PS43- units or unbound sulfide anions and that simple substitutions in these sulfide-based solid electrolytes cannot improve oxidative stabilities. This work provides insights on the role of chemical bonding on the stability of superionic conductors and shows that alternative strategies are needed for long-term stable solid-state batteries.
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