Understanding solid electrolyte interface film formation on graphite electrodes

Using ac impedance, we studied the formation process of solid electrolyte i nterface (SED film on graphite electrode during initial cycles. Results sho w that the SEI formation takes place through two major stages. The first st age takes place at voltages above 0.25 V (before lithiation of graphite), d uring which a loose and highly resistive film is formed. The second stage o ccurs at a narrow voltage range of 0.25-0.04 V, which proceeds simultaneous ly with lithiation of graphite electrode, In the second stage, a stable, co mpact, and highly conductive SEI film is produced. (C) 2001 The Electrochem ical Society.