| Abstract
| - The chemical and electrochemical insertions of lithium into α-NbPO5 (P4/n) and β-NbPO5(P21/c) are compared. Both materials were evaluated as positive electrodes in lithium-typerechargeable batteries through galvanostatic, GITT, and PITT cycling modes within variousvoltage windows. They present distinct behaviors with regard to lithium insertion. β-LixNbPO5 rapidly and reversibly uptakes lithium leading to a sustained capacity of 90−120mA·h/g (i.e., operating to the Nb5+/Nb4+ couple) for more than 100 cycles at ∼2 V vs Li+/Li.This reversibility was confirmed by in situ X-ray diffraction in the range 0 ≤ x ≤ 0.7 thatadditionally revealed a series of single- and two-phase insertion mechanisms. On the otherhand, α-LixNbPO5 displays an insertion plateau at ∼1.7 V vs Li+/Li indicative of a two-phase process that was found to be poorly reversible. Both materials, when discharged atvoltages lower than 1 V, present irreversible reactions with complete amorphization.
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