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

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. (C) 2014 Elsevier B.V. All rights reserved.