Effect of VC additive on MFA-based electrolyte in Li-ion batteries

Rapid capacity fading of a graphite electrode was obtained with LiPF ₆/MFA electrolyte due to poor properties of solid electrolyte interphase (SEI). Vinylene carbonate (VC) was therefore applied to the MFA-based electrolyte as an SEI modification additive. The effects of VC concentration on the electrochemical properties of the graphite/Li half-cell were investigated at 25 and 60 °C. At 25 °C, the graphite electrode in MFA + 1% VC-based electrolyte showed good capacity retention of 300 mA h g^-1 after 50 cycles, which was comparable with that in EC-DMC-based electrolyte; at 60 °C, the electrode in MFA + 3% VC-based electrolyte showed capacity retention of 240 mA h g^-1 after 50 cycles, which was much better than that in EC-DMC-based electrolyte. Overabundant VC additives showed negative effects because of the formation of too-thick and/or too-dense SEI. DSC measurements were carried out to study the thermal behavior of MFA-based electrolyte coexisting with lithiated graphite. VC-containing MFA-based electrolyte still showed much better thermal stability than EC-DMC-based electrolyte. TG-MS analysis was performed on delithiated graphite cycled in MFA-based electrolyte containing different VC concentrations to analyze VC's effect on SEI formation. In summary, VC-added MFA-based electrolyte was a promising electrolyte for the development of safer Li-ion batteries, especially at elevated temperature.