Enhanced electrochemical performance of LiFePO4 cathode with the addition of fluoroethylene carbonate in electrolyte

The effect of the fluoroethylene carbonate (FEC) addition in electrolyte on LiFePO4 cathode performance was investigated in low-temperature electrolyte LiPF6/EC/PC/EMC (0.14/0.18/0.68). Cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge tests were conducted in this work. In the presence of FEC, the polarization of LiFePO4 electrode decreased both at room and low temperatures. Meanwhile, the exchange current density increased. The rate capability of LiFePO4 electrode was greatly enhanced as well. The morphology of the solid electrolyte interphase (SEI) on LiFePO4 surface was modified with the addition of FEC as confirmed by scanning electron microscopy measurement. A compact film with small impedance was formed on LiFePO4 surface compared to the case of FEC-free. The compositions of the film were analyzed by X-ray photoelectron spectroscopic measurement. The contents of Li (x) PO (y) F (z) , LiF, and the carbonate species generated from solvents decomposition were reduced. The modified SEI promoted the migration of lithium ion through the electrode/electrolyte interphase and enhanced the electrochemical performance of the cathode.