Effect of HF in LiPF ₆ Based Electrolytes on the Properties of Surface Passivation Films Formed on Graphite Electrodes in Li Secondary Batteries

ABSTRACT

The effect of hydrofluoric acid (HF) concentration in conventional LiPF ₆/EC+DEC electrolyte on the properties of solid electrolyte interphase (SEI) films formed on synthetic graphite electrode and the electrochemical performance were studied using x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), elemental analysis and electrochemical measurement. The morphology and composition of SEI are affected by a small amount of HF in the electrolyte. Higher F content in the SEI was observed when high HF electrolyte were used, although the irreversible capacities used for formation of SEI were nearly the same value. The cycleability of the synthetic graphite electrode was greatly improved when surface film contains larger amount of LiF.