Butylene sulfite as a film-forming additive to propylene carbonate-based electrolytes for lithium ion batteries

Butylene sulfite (BS) has been synthesized and the BS-based electrolytes containing different lithium salt are evaluated with differential scanning calorimetry (DSC) and alternating current impedance spectroscopy. These electrolytes exhibit high thermal stability and good electrochemical properties. BS has been investigated as a new film-forming additive to propylene carbonate (PC)-based electrolytes for use in lithium ion batteries. Even in small additive amounts (5 vol.%) BS can effectively suppress the co-intercalation of PC with solvation lithium ion into graphite. The formation of a stable passivating film on the graphite surface is believed to be the reason for the improved cell performance. The LUMO energy and the total energy of the sulfite molecules are higher than that of the carbonate ones. It is clearly indicated that the sulfite molecules can easily accept electrons and bears a high reaction activity. The lithium-oxy-sulfite film (Li₂SO₃ and ROSO₂Li) resulting from the reductive decomposition of BS is studied by the density functional theory (DFT) calculations. In addition, the PC-BS electrolytes are characterized by a high oxidation stability allowing the cycling of a LiMn_1.99Ce_0.01O₄ and LiFePO₄-C cathodes with good reversibility.