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.