Solid-State Lithium-Ion Superionic Electrolytes with Reduced Moisture Sensitivity

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 Li 3 InCl 6 , 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, Li 3 InCl 6 demonstrates substantial ionic conductivity at room temperature. We studied the temperature-dependent behavior of Li 3 InCl 6 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: hafnium doping of Li 3 InCl 6 . Integrating hafnium into the Li 3 InCl 6 structure results in a substantial improvement in electrochemical performance. The Li 2.6 In 0.6 Hf 0.4 Cl 6 solid-state electrolyte not only showcases heightened ionic conductivity but also demonstrates improved resistance to moisture. The achieved ionic conductivity reaches approximately 1 mS cm -1 , marking a significant 3.5-fold increase compared to Li 3 InCl 6 . Noteworthy is the fact that, after 5 hours of exposure to air with 15% humidity, the observed reduction in ionic conductivity for Li 2.6 In 0.6 Hf 0.4 Cl 6 is 37%, a notably lower decrease compared to the 57% reduction seen in Li 3 InCl 6 . The efficacy of hafnium doping provides a crucial advancement in the field of solid-state electrolytes, promising a transformative impact on next-generation energy storage systems.