Effects of methanol contaminant in electrolyte on performance of graphite electrodes for Li-ion batteries studied via electrochemical impedance spectroscopy

Abstract

Electrochemical performance of graphite electrode cycled vs. Li in 1 mol/L LiPF6-EC/DEC/DMC (1: 1: 1, volume ratio) electrolyte solution, which contains different concentrations of methanol, was investigated by cyclic voltammetry and electrochemical impedance spectroscopy( EIS) in the process of first lithiation. It was demonstrated that methanol contaminant caused the deterioration of the electrochemical performance of graphite electrodes, which depends markedly on the concentration of methanol. Based on the experimental results and analysis, a mechanism of the deterioration of the electrochemical performance of graphite electrode caused by methanol contaminant was proposed. The methanol was reduced to lithium methoxide, that deposited on graphite electrode surface to form initial SEI ( solid electrolyte interphase) near 2.0 V, which resulted in ethylene carbonate excess decomposition and poor passive ability of the SEI ultimately formed.