Charge/discharge Behavior of Triclinic LiTiOPO<sub>4</sub> Anode Materials for Lithium Secondary Batteries

Abstract

Triclinic LiTiOPO4 fine powders were synthesized via low-temperature thermal treatment. First, amorphous fine powders were prepared by mechanical milling (MM) treatment of a mixture of the starting materials (Li2CO3, TiO2, and P2O5) at room temperature. The mechanically milled amorphous powder formed a triclinic LiTiOPO4 crystal below 700°C in air. The mechanically milled powders before heat treatment barely worked as an active material at ca. 0.1 C rate in the potential range of 1.0 to 3.0 V versus Li/Li+ in lithium cells. On the other hand, the triclinic LiTiOPO4 compounds obtained by the crystallization of the mechanically milled amorphous powders at 700°C in air worked as anode materials in lithium cells. The triclinic LiTiOPO4 electrode materials exhibited capacities of around 100 mAh g−1. The average operation potential was around 1.7 V (vs. Li/Li+). The triclinic LiTiOPO4 pristine compound when used as an anode caused a phase transition into an orthorhombic compound during lithium insertion (charge process). The orthorhombic compound changed into a triclinic phase during lithium extraction (discharge process). The triclinic LiTiOPO4 electrodes exhibited a good cycle performance in the potential range of 1.0 to 3.0 V versus Li/Li+. It is suggested that the crystalline phase changes reversibly during charge/discharge.