How sulfur-containing additives stabilize Electrode/Electrolyte interface of high voltage Graphite/LiCoO2 battery

Film-forming additives have been studied as one of efficient choices to improve battery performance. However, the relationship among film-forming additives, interphase film and battery performance remain mysterious. A comparative study was conducted on the effects of four sulfur-containing cyclic additives, sulfolane (Sul), 1,2-Ethylene Sulfite (ES), 1,3-Propane sultone (PS), and 1,3,2-Dioxathiolan-2,2-oxide (DTD), on the properties of interphase film. Through time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) detection, an “effective interfacial functional group (EIFG)”, sulfonate (−O-SO₂-), was discovered in the electrode/electrolyte interphase (EEI) film of cells containing PS or DTD added electrolytes. It can stabilize the interphase and inhibit the continued decomposition of the electrolyte, thereby improving the electrochemical performance of 4.48 V graphite/LiCoO₂ full-cell and 4.55 V Li/LiCoO₂ half-cell. The capacity retention of the full-cell after 200 cycles exceeds 87 %, and that of half-cell after 300 cycles is nearly 90 %. Based on differential electrochemical mass spectra (DEMS), XPS detection during formation process and theoretical calculation results, it can be revealed that the similar EIFG-containing components can be obtained through different reaction pathways even with additives containing different functional groups. This provides an important basis for the design of new additives/electrolytes.