LiFePO4 and graphite electrodes with ionic liquids based on bis(fluorosulfonyl)imide (FSI)- for Li-ion batteries

Ambient-temperature ionic liquids (IL) based on bis(fluorosulfonyl)imide (FSI) as anion and 1-ethyl-3-methyleimidazolium (EMI) or N-methyl-N-propylpyrrolidinium (Py13) as cations have been investigated with natural graphite anode and LiFePO4 cathode in lithium cells. The electrochemical performance was compared to the conventional solvent EC/DEC with 1 M LiPF6 or 1 M LiFSI. The ionic liquid showed lower first coulombic efficiency (CE) at 80% compared to EC-DEC at 93%. The impedance spectroscopy measurements showed higher resistance of the diffusion part and it increases in the following order; EC-DEC-LiFSI