Crystal Structure and Lithium Diffusion Pathways of a Potential Positive Electrode Material for Lithium-Ion Batteries: Li2VIII(H0.5PO4)2.

A new potentially interesting material as a positive electrode for lithium-ion batteries, Li2VIII(H0.5PO4)2, was obtained by hydrothermal synthesis. Its crystal structure was solved thanks to single-crystal X-ray diffraction. This material is isostructural to Li2FeIII(PO4)(HPO4) and also closely related to Li2FeII(SO4)2. It can be described as a VO6 octahedron sharing corners with six PO4 tetrahedra to form a 3D framework. One oxygen atom of each phosphate group is unshared with a vanadium octahedron and as such linked to a hydrogen atom. The arrangement of these polyhedra generates large channels running along [100] in which lithium cations are located. The close structural relationship between Li2FeIII(PO4)(HPO4) and Li2FeII(SO4)2 allows one to investigate, by comparison, the effect of the hydrogen atoms lying on lithium diffusion pathways.