Electrochemical Stabilization of Self-Extinguishing Electrolyte Solutions with Trimethyl Phosphate by Adding Potassium Salts

A potassium salt, potassium bis(trifluoromethanesulfonyl)amide (KTFSA), with a weak Lewis acid in a self-extinguishing electrolyte solution containing trimethylphosphate (TMP) can improve the Coulombic efficiency of charge–discharge in lithium-ion batteries with graphite negative electrodes. 17 O nuclear magnetic resonance (NMR) analysis of electrolyte solutions with KTFSA indicated that weak Lewis acid K + decreased the strength of the EC–Li + interaction and improved the Coulombic efficiency. Furthermore, three X-ray analyses, X-ray diffraction (XRD), X-ray fluorescence (XRF), and X-ray photoelectron spectroscopy (XPS), clarified that the addition of KTFSA derived from the stabilization of the electrolyte solution by forming an effective protective film on the graphite surface had the greatest effect on the Coulombic efficiency.