LiTFSI Stability in Water and Its Possible Use in Aqueous Lithium-Ion Batteries: pH Dependency, Electrochemical Window and Temperature Stability

Ion chromatography was used to investigate the stability of LiTFSI in water at various temperatures. The addition of HNO3, LiOH and HTFSI as pH adjustment measures was studied and the long-term stability of the electrolytes at different pH values stored at 60°C investigated. A minor degradation product was found upon the addition of HNO3 to the electrolyte and identified via electrospray ionization mass spectrometry. The compound was formed only in traces immediately after the acidification and the concentration is not increasing over time. Electrochemical stability window investigations, using two different methods, indicate the wide applicable potential range of the aqueous LiTFSI electrolyte, which, combined with the high stability of the TFSI anion vs. hydrolysis and elevated temperature, smoothens the path for a possible application in aqueous lithium-ion systems.