Role of ligands in the stability of BX and CBX (n = 5-10; X = H, F, CN) and their potential as building blocks of electrolytes in lithium ion batteries.

Stabilizing small multiply charged negative ions in the gas phase has been of considerable interest in recent years. BH is one of the most well-known dianions which is stable against auto-detachment of its second electron in the gas phase by 0.9 eV, whereas BH with n < 12 is unstable. Using density functional theory, we have examined systematically the role of ligands in stabilizing smaller mono- and di-anions of BX and CBX (n = 5-10; X = H, F, CN). We show that the stability of the negative ions of these complexes increases with the electron affinity of the ligand and B(CN) can even be stable against electron emission for n≥ 5. We also show that CB(CN) is stable against electron emission for n≥ 8, even though these moieties contain one electron more than needed to satisfy the Wade-Mingos rule. We have examined the potential of these stable negative ions as building blocks of electrolytes in Li-ion batteries. By calculating the binding energies between the CBX and Li, we find that some of these clusters may even outperform CBH as electrolytes in metal-ion batteries.