A Reversible Lithium Intercalation Process in an ReO[sub 3]-Type Structure PNb[sub 9]O[sub 25]

Among the large family of Wadsley-Roth-type phases, presents, as other shear structures such as and a peculiar arrangement of -type blocks connected through tetrahedra. The crystal structure was redetermined by combined Rietveld refinements of X-ray and neutron powder diffraction data, for the first time in the tetragonal space group I with and The electrochemical insertion of lithium into reaches a value of between 3.0 and 1.0 V vs. at a slow cycling rate. Within this voltage window, in situ X-ray diffraction reveals that the reversible intercalation of lithium occurs through three single- and two two-phase regions. The variation of the lattice parameters as a function of indicates a global change of associated with the reduction of to and then partly to At voltages lower than 1 V vs. extra irreversible phenomena, such as electrolyte and/or carbon reduction were identified but, remarkably, highly crystalline particles of remain unaltered when discharging the cell for prolonged time down to 0.02 V vs. The behavior of is very similar to that of but different to that of where irreversible reduction of to (in tetrahedral coordination) takes place.