3D Framework Structure of a New Lithium Thiophosphate, LiTi2(PS4)3, as Lithium Insertion Hosts

The M2(PS4)3 (M = transition metal) structure has been investigated as a new open 3D-framework structure for electrode materials for lithium rechargeable batteries. One of these compounds, LiTi2(PS4)3, was synthesized from solid state reaction. From the single crystal X-ray diffraction analysis, it was observed that the LiTi2(PS4)3 crystallizes in the hexagonal space group P6cc (No. 184) with a = 19.8978 (4) A, c = 11.5198(3) A, and Z = 8. The resemblance of the powder X-ray diffraction pattern and the lattice parameters obtained from single crystal X-ray diffraction measurement indicates that the crystal structure is isomorphous with NaTi2(PS4K This structure is built of TiS6 octahedra linked by edges to PS4 tetrahedra and vice versa to build a 3D framework. Most attractively, very wide tunnels are obtained along the c-axis where lithium ions are mobile. Electrochemical insertion of lithium into LiTi2(PS4)3 was carried out. The initial structure of LiTi2(PS4)3 was changed with initial insertion of lithium, but ???7 Li per formula unit could be inserted in the modified structure without decomposition of the starting material. However, such a large capacity was not retained on cycling.