Chemical and electrochemical insertion of lithium into two allotropic varieties of NbPO5

The chemical and electrochemical insertions of lithium into alpha-NbPO5 (P4/n) and beta-NbPO5 (P2(1)/c) are compared. Both materials were evaluated as positive electrodes in lithium-type rechargeable batteries through galvanostatic, GITT, and PITT cycling modes within various voltage windows. They present distinct behaviors with regard to lithium insertion. beta-Li-x-NbPO5 rapidly and reversibly uptakes lithium leading to a sustained capacity of 90-120 mA(.)h/g (i.e., operating to the Nb5+/Nb4+ couple) for more than 100 cycles at similar to2 V vs Li+/Li. This reversibility was confirmed by in situ X-ray diffraction in the range 0 less than or equal to x less than or equal to 0.7 that additionally revealed a series of single- and two-phase insertion mechanisms. On the other hand, alpha-LixNbPO5 displays an insertion plateau at similar to1.7 V vs Li+/Li indicative of a two-phase process that was found to be poorly reversible. Both materials, when discharged at voltages lower than 1 V, present irreversible reactions with complete amorphization.