Enhancing Ionic Conductivity and Moisture Sensivity of Halide Solid-state Electrolytes via Cation and Anion Substitution — 16a — Farzaneh Bahmani¹, and Alevtina Smirnova^{1, 2} 

¹Materials Engineering and Science (MES) Program

²Department of Chemistry, Biology, and Health Sciences, South Dakota Mines, Rapid City, SD 

The remarkable safety and high energy density of solid-state batteries (SSBs) created significant advantages  in the development of next-generation energy storage. The properties of these batteries are highly dependent  on the characteristics of solid-state electrolytes (SSEs), making them a crucial material in the development  of such batteries. Following diverse principles of material design, lithium halide SSEs, particularly Li₃InCl₆,  open new opportunities in the development of SSBs due to their unique properties including broad  electrochemical stability window, high lithium-ion conductivity, and excellent deformability. Through a  mechano-thermal synthesis approach, Li₃InCl₆ demonstrates substantial ionic conductivity at room  temperature. We studied the temperature-dependent behavior of Li₃InCl₆ by using in-situ/operando  techniques such as XRD and XPS. However, its susceptibility to moisture poses a significant challenge for  practical implementation in SSBs. To overcome this limitation, this research is focused on a novel solution:  fluorine, and zirconium doping of Li₃InCl₆. Integrating zirconium and fluorine into the Li₃InCl₆ structure results in a substantial improvement in electrochemical performance. The Li_2.6In_0.6Zr_0.4Cl_5.9F_0.1 solid-state  electrolyte not only showcases heightened ionic conductivity but also demonstrates improved resistance to  moisture. The achieved ionic conductivity reaches approximately 1.43 mS cm^-1, marking a significant 4- fold increase compared to Li₃InCl₆. Noteworthy is the fact that, after 5 hours of exposure to air with 15%  humidity, the observed reduction in ionic conductivity for Li_2.6In_0.6Zr_0.4Cl_5.9F_0.1 is 27%, a notably lower  decrease compared to the 57% reduction seen in Li₃InCl₆. 

The efficacy of zirconium and fluorine doping provides a crucial advancement in the field of solid-state  electrolytes, promising a transformative impact on next-generation energy storage systems.

South Dakota School of Mines & Technology
Prof. Alevtina Smirnova