Synthesis and electrochemical properties of TiNb (PO4)3 cathode materials for lithium secondary batteries

Hexagonal TiNb(PO4)3, a host framework structure, has been synthesized at various temperatures ranging from 200 to 1300 °C and systematically characterized. An optimum synthesis temperature of 1200 °C has been found to be suitable for a cathode material for lithium secondary batteries. The samples synthesized at 1100 and 1200 °C have shown fewer undesirable reaction products than the samples synthesized at 1000 or 1300 °C. Titanium niobium phosphate (TiNb(PO4)3), without any lithium in its structure, was used as a cathode for a lithium secondary battery and intercalation of lithium into the vacant sites of the sample was achieved electrochemically. Of the TiNb(PO4)3 samples studied (1100, 1200 and 1300 °C), the sample synthesized at 1200 °C exhibits a better capacity of 147 mAh/g with a relatively high voltage. The discharge potential of this sample was found to be 2.3 V vs. lithium. In order to maximize cycle life and deliverable capacity, a safe voltage limit for this material has been determined.