Effects of Double Anionic Substitution on Li–Ion Conductivity in Hexagonal LiBH4–LiI–LiBr Solid Solution

This study introduces promising candidates for Li-based solid-state electrolytes. By substitution of BH4- ions with I- and Br-, the hexagonal structure of LiBH4 has been stabilized at room temperature, thereby enhancing Li-ion conductivity. The structural characterization of samples in the LiBH4-LiI-LiBr system was conducted using X-ray diffraction along with infrared spectroscopy. Various compositions were explored, and a preliminary evaluation of the pseudoternary phase diagram was performed. The impact of dual anionic substitution on the Li-ion conduction properties of LiBH4 was investigated using electrochemical impedance spectroscopy and cyclic voltammetry. Halogenation enabled the operation of the ternary solid solution as fast ionic conductors in solid-state electrolytes below 120 °C, suggesting potential applications for Li-ion solid-state batteries. Collected data revealed a significant effect of the amount of added LiI and LiBr, indicating an influence of ionic radius on lattice expansion of the hexagonal phase of LiBH4, suggesting a relationship to the Li-ion conductivity.