The electrochemical lithium insertion process has been studied in the family of monophosphate tungsten bronzes (PO2)(4) (WO3)(2m), where m = 7 and 8. Structural changes in the pristine oxides were followed as lithium insertion proceeded. Through potentiostatic intermittent technique the different processes which take place in the cathode during the discharge of the cell were analyzed. The nature of the bronzes Li-x(PO2)(4)(WO3)(2m) formed was determined by in situ X-ray diffraction experiments. These results have allowed establishing a correlation with the reversible/irreversible processes detected during the electrochemical lithium insertion. (c) 2007 Published by Elsevier Ltd.