Assessing the Impact of Li⁺ Concentration and Stacking Faults in the Aliovalent-Substituted Ionic Conductor Li₃ScCl₆

Abstract

Halide electrolytes have gained interest due to their decent conductivities in the mS·cm^-1 range and wide electrochemical stability windows. The ionic transport can be influenced by changing the Li⁺ concentration in the structure. Due to the high cost of the rare-earth elements in the halide electrolytes, the substitution of lower-cost elements is favored. Based on the idea of changing the Li⁺ concentration and substituting with low-cost elements, the two substitution series Li_3-xSc_1-xZr_xCl₆ and Li_3+xSc_1-xMg_xCl₆ (0 ≤ x ≤ 0.3) are investigated in this work. Structural information was obtained by X-ray and neutron diffraction and combined with transport properties obtained by impedance spectroscopy. Two main transport influencing factors were found: The Li⁺ concentration and the c/a lattice parameter. The occupation of the Li⁺-only layers seems to affect the lattice parameter in the c-direction. However, the structural refinement was not straightforward as stacking faults appear in layered halide materials that complicate the refinements, and the substitution with Mg²⁺ seems to influence the extent of stacking fault formation. Overall, this work highlights the need to consider several factors in halide materials to correlate the structure-transport processes.