LiTi2(PO4)3 with NASICON-type structure as lithium-storage materials

LiTi2(PO4)3 with a Na+ superionic conductor (NASICON)-type structure is prepared by a two-step solid-state reaction. X-ray diffraction (XRD) confirms that the LiTi2(PO4)3 compound has a NASICON structure, i.e. rhombohedral (space group: R3c). It is found that lithium can be electrochemically inserted into the LiTi2(PO4)3 structure, with a maximum intake of 5.2 mol of lithium per mole of LiTi2(PO4)3 compound, and that [PO4] tetrahedra can participate in the redox reaction. This corresponds to a lithium-storage capacity of 360 mAh g−1. The kinetic parameters of lithium insertion in LiTi2(PO4)3 NASICON are determined by means of ac impedance technique. The charge-transfer resistance (RCT) and exchange current density (i0) are invariable regardless of the state of lithium insertion. This is associated with the unique structure characteristics of the NASICON skeleton. By contrast, the diffusion coefficient, DLi of lithium varies with the state of lithium insertion. The value of DLi is in the range 1.4×10−11 to 1.2×10−9 m2 s−1, which is much higher than for other intercalation materials.