Features of the electrochemical lithium insertion into monophosphate tungsten bronzes (PO2)4(WO3)2m (m=9 and 10)

Abstract Electrochemical lithium insertion into (PO 2 ) 4 (WO 3 ) 2 m , where m =9 and 10, has allowed the determination of several phases Li x (PO 2 ) 4 (WO 3 ) 2 m between 3.4 and 0.01 V vs Li + /Li 0 . After the first cycle the electrochemical system was unable to maintain the high specific capacity of the cells (∼540 Ah/kg) due to irreversible processes. Nevertheless at high voltage values, above 1.4 V vs Li + /Li 0 , the lithium insertion proceeded through a reversible mechanism. By means of X-ray diffraction experiments we have detected the nature of different phases Li x (PO 2 ) 4 (WO 3 ) 2 m formed and we have established a correlation with the reversible/irreversible processes detected during the electrochemical insertion.