Electrochemical investigation of SEI layer in the formation process of natural graphite anode in Li-ion battery

The solid electrolyte interphase (SEI) is a passivating film that is formed on the anode surface by electrolyte decomposition in a lithium ion battery. The proper understanding of the SEI formation process on the graphite anodes can create a wider view to overcome the challenges associated with these anodes, which lead to better cyclic performance. In this research, cyclic voltammetry, electrochemical impedance spectroscopy and cyclic charge/ discharge tests were used for graphite anode coin cell to obtain a perfect understanding of SEI formation process on the surface of graphite anode. The results of cyclic voltammetry test indicate that the large part of SEI layer is formed in the first cycle and the SEI will be stable by continued voltammetric cycles. The electrochemical impedance studies show that the charge transfer resistance (Rct) of graphite anode decreases from 122 Ω to 62.5 Ω after electrochemical cycles, which indicates the facility of the charge transfer process after the formation of the SEI layer. The results of cyclic charge/ discharge test also represent that the irreversible capacity of first cycle is consumed to form the SEI, and the reversibility has been sustained after the subsequent charge / discharge cycles.