Liquid electrolytes containing new tailored salts for sodium-ion batteries

Sodium 4,5-dicyano-2-(pentafluoroethyl)imidazolate (NaPDI) and 4,5-dicyano-2-(trifluoromethyl) imidazolate (NaTDI) were tested in order to find the optimal solvent mixture composition for possible application in sodium battery electrolytes. The chemical structure of the above imidazolate salts is based on the stable imidazolium ring architecture substituted with electrophilic groups via carbon atoms. It has been shown here that electrolytes with these new salts exhibit high conductivity at room temperature and excellent electrochemical stability up to 4.5 V vs. sodium metal. Moreover, both salts are not corrosive to Al foil. The high performance of the new electrolytes in sodium battery technology was also confirmed by compatibility tests carried out with NaxCoO2 cathode materials.