Solid state compounds with room temperature ionic conductivity larger than 1 mS/cm may compete with liquid electrolytes in rechargeable batteries. New class of fast ionic conductors was found as a by-product of hydrogen storage research in closo-borame materials. Very high conductivity of sodium reported in Na2B12H12 can compete with the best alumina based solid state conductors known for this metal. Further developments reveal borane based Na superionic conductors that are by orders of magnitude better than any known before. On the contrary this class of materials exhibit conductivity of lithium that is lower than sodium.
The origin of cation mobility in this class of materials still remains puzzled. We will present theoretical studies, based on DFT calculations, resolving the puzzle of superionic conductivity of closo-boranes. The relation between the superionic conductivity and the crystal structure and the composition of the anion sublattice will be presented in detail. Simple rules for design of stable and highly conductive boranes based on modification of the B12H122- anion sublattice will be shown with example of tuning the crystal structure with combinations of B12H122- and CB11H12- anions. The pitfalls of the theoretical description of these materials at high temperatures .
 Y. Sadikin, P. Schouwink, M. Brighi, Z. Lodziana, R. Cerny, Inorg. Chem. 2017, 56, 5006−5016.