Crystal structures and electronic properties for the over-lithiated and Li-Ag substituted phases of Li9V3(P2O7)(3)(PO4)(2) insertion electrode system

摘要

For the Li6V3(P2O7)(3)(PO4)(2) insertion electrode system with a multiple-electron reaction, the over-lithiated phase LixV3(P2O7)(3)(PO4)(2) with 9 < x <= 10 and the Li Ag substituted phase Li9-yAgyV3 (P2O7)(3)(PO4)(2) with 0 < y <= 1 are synthesized, and their crystal structures and electronic properties are explored through measurements of X-ray diffraction with a four-circle diffractometer, electrochemistry, electrical resistivity, and magnetization. Both the structures are isomorphous to that of Li6V3(P2O7)(3)(PO4)(2) which has (VP2(2)O(7))(3)(P1O(4))(2) layers in the ab-plane built up of VO6 octahedra sharing corners with P1O(4) tetrahedra and P2(2)O(7) groups. In LixV3(P2O7)(3)(PO4)(2), the over-inserted Li4 ion surrounded by three oxygens in a planar triangular arrangement resides with a significantly large thermal parameter in the tunnels formed by the stacking of the layers and in between the octahedral Li1 sites, leading to a linear chain of Li ions with the distance 3.40 angstrom parallel to the direction of diffusion pathways. In Li9-yAgyV3(P2O7)(3)(PO4)(2), where the Li1 site is substituted by Ag, the reduction of the electron hopping and the electrostatic potential for V ions are revealed in comparison with those of unsubstituted parent, which may account for the increase of mean voltage in the Li ion battery. (C) 2014 Elsevier Inc. All rights reserved.