LiPF₆/methyl difluoroacetate electrolyte with vinylene carbonate additive for Li-ion batteries

A methyl difluoroacetate (MFA)-based LiPF₆ solution was applied as an electrolyte to improve the thermal stability of Li-ion batteries. The addition of vinylene carbonate (VC) improved the electrochemical characteristics of the electrolyte significantly, and satisfactory reversible capacity and cycling performance were obtained with a graphite negative electrode. The thermal stability of the electrolytes was investigated with DSC. Regardless of whether or not VC was used, the electrolyte exothermically decomposed at a temperature higher than 450 °C. The thermal behavior of a mixture of lithiated graphite and VC-added electrolyte was also studied in detail. The ratio between the electrolyte and the electrode was a dominant factor in the heat generation of the mixture. A sharp exothermic peak at about 330 °C was observed when the electrode was superabundant, but the heat value was much smaller than that obtained with 1 mol dm^-3 LiPF₆/EC-DMC electrolyte under the same conditions. When the electrolyte was superabundant, a mild exothermic decomposition of the electrolyte became the dominant reaction in the mixture. X-ray photoelectron spectroscopic analysis was carried out on delithiated graphite electrodes to study the effect of VC additive on solid electrolyte interphase (SEI) modification. VC-added MFA-based electrolyte was considered to be a good candidate for developing safer Li-ion batteries.