The material stability of ramsdellite type Li2+xTi3O7 has been investigated from the view of the correlation between structural and electrochemical behaviors during Li insertion and extraction. The interfacial reaction of Li2+xTi3O7 is identified by using AC-impedance spectroscopy and various electrochemical measurements are carefully conducted to interpret each elemental reaction of the complicated interfacial reaction. The impedance spectra indicate three semi-circles in the frequency range from 1 MHz to 5 mHz which fit expectations well. Li insertion at the interface is explained by applying the adatom model that includes desolvation and absorption of lithium ions through electron transfer and lattice incorporation. (C) 2011 Elsevier Ltd. All rights reserved.