Superhalogens as building blocks of halogen-free electrolytes in lithium-ion batteries.

Most electrolytes currently used in Li-ion batteries contain halogens, which are toxic. In the search for halogen-free electrolytes, we studied the electronic structure of the current electrolytes using first-principles theory. The results showed that all current electrolytes are based on superhalogens, i.e., the vertical electron detachment energies of the moieties that make up the negative ions are larger than those of any halogen atom. Realizing that several superhalogens exist that do not contain a single halogen atom, we studied their potential as effective electrolytes by calculating not only the energy needed to remove a Li+ ion but also their affinity towards H2O. Several halogen-free electrolytes are identified among which Li(CB11H12) is shown to have the greatest potential.