Performance improvement of phenyl acetate as propylene carbonate-based electrolyte additive for lithium ion battery by fluorine-substituting

• Performance of PA as electrolyte additive of Li-ion battery is improved by F-substituting.
• 4-FPA is more effective than PA for forming SEI on graphite in PC-based electrolyte.
• 4-FPA improves cyclic stability of Li-ion battery using PC-based electrolyte.
• Incorporation of 4-FPA reduction products into SEI contributes to the improved performance.

Phenyl acetate (PA) is more stable and much cheaper than vinylene carbonate (VC), a commercial electrolyte additive for graphite anode of lithium ion battery, but its performance needs to be improved. In this paper, we report a new additive, 4-fluorophenyl acetate (4-FPA), which results from the fluorine-substituting of PA. The properties of the formed solid electrolyte interphase (SEI) by 4-FPA are investigated comparatively with PA by molecular energy level calculation, cyclic voltammetry, charge–discharge test, scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. It is found that the SEI formed by 4-FPA is more protective than PA, resulting in the improved cyclic stability of lithium ion battery: the capacity retention of LiFePO4/graphite cell after 90 cycles is 92% for 4-FPA but only 84% for PA. The fluorine in 4-FPA makes it more reducible than PA and the fluorine-containing reduction products of 4-FPA are incorporated into the SEI, which contributes to the improved performance.