Modern battery electrolytes: Ion-ion interactions in Li+/Na+ conductors from DFT calculations

Sodium-ion batteries, the sodium counterpart of the ubiquitous lithium-ion batteries, are currently being developed as a complementary technology to assure resource availability. As battery electrolytes tend to be one of the more limiting parts of any battery for both performance and life-length, chemical and physical data on sodium-ion battery electrolytes are important for rational development. Here the cation-anion interaction, a key property of any salt used in an electrolyte, of a number of salts is probed using numerous DFT methods via the ion-pair dissociation reaction: AlkAn reversible arrow Alk(+) + An(-), where An(-) is any anion and Alk(+) is Na+ or Li+, the latter used here for a straight-forward literature and methodology comparison. Furthermore, the applicability of different DFT functionals for these types of calculations is benchmarked vs. a robust higher accuracy method (G4MP2).