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

Electrochemical lithium insertion into (PO2)4(WO3)2m, where m=9 and 10, has allowed the determination of several phases Lix(PO2)4(WO3)2m between 3.4 and 0.01 V vs Li+/Li0. 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+/Li0, the lithium insertion proceeded through a reversible mechanism. By means of X-ray diffraction experiments we have detected the nature of different phases Lix(PO2)4(WO3)2m formed and we have established a correlation with the reversible/irreversible processes detected during the electrochemical insertion.