Investigation and electrochemical analysis of SEI layer formation in natural graphite anode formation process in lithium-ion battery

The solid electrolyte interface (SEI) layer is a surface film formed by the decomposition of the electrolyte in a lithium-ion battery on the anode surface. A proper understanding of the SEI layer formation process in graphite anodes can provide a broader view of overcoming the challenges associated with these anodes, which will lead to better charge/discharge performance. In this research, cyclic voltammetry tests, electrochemical impedance spectroscopy and sequential charge/discharge tests have been used for cell to gain an accurate understanding of the SEI film formation process on the graphite anode surface. The results of the cyclic voltammetry test show that most of the SEI layer is formed in the first cycle and reaches stability with the continuation of the voltammetric cycles of the SEI layer. Also, the charge transfers resistance (Rct) has decreased from 123.5Ω to 27.96Ω after the electrochemical cycles, which indicates the facilitation of the charge transfer process after the formation of the SEI layer. The results of the consecutive charge/discharge test of anode graphite coin cell also show that the amount of non-reversible capacity in the first cycle is much higher than the amount of non-reversible capacity in subsequent cycles. This indicates the formation of a large part of the SEI layer in the first cycle. Considering that the SEI layer is almost stable after the second cycle, it can be said that the method of forming a lithium-ion cell with graphite anode can be done in two charge/discharge cycles.