3D framework structure of a new lithium thiophosphate, LiTi2(PS4)3, as lithium insertion hosts

The M-2(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) angstrom, c = 11.5198(3) angstrom, 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(PS4)(3). This structure is built of PS6 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 similar to 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.