Probing the Potential of Halogen-Free Superhalogen Anions As Effective Electrolytes of Li-ion Batteries: a Theoretical Prospect from Combined Ab Initio and DFT Studies

The potential of 23 superhalogen anions of halogen-free structures as high-performance electrolytes of Li-ion batteries is theoretically explored here. According to high-level ab initio results at the CCSD(T) level, eight candidates, obeying the Wade-Mingos rule, should be capable of forming electrolytes, which are better than the currently used commercial products. When comparing different methods, MP2 was found to be in good agreement with CCSD(T) in the calculation of ΔELi+ and ΔEH2O, which are parameters describing the performance of potential electrolytes. Thus, MP2 represents a good choice for such calculations, particularly for large potential electrolyte systems wherein CCSD(T) calculations are actually impractical. The five functionals selected here (ωB97XD, B2GP-PLYP, B2K-PLYP, B2T-PLYP and B3LYP) are also capable of reproducing the variational trends of the relative values of different structures at the CCSD(T) level. However, the actual DFT values of ΔELi+ are usually different from those of CCSD(T) by more than 1 eV. These significant deviations may be a problem when accurate ΔELi+ values are required.