High Rate Performance of Ti Doped LiFePO4 Cathodes for Lithium Ion Battery

Abstract

A Li-ion battery cathode with target stoichiometry LiTi0.08Fe0.92PO4 was prepared by doping excess amount of Ti4+ into the olivine structure using solid-state reaction at 700 °C. X-ray diffraction (XRD) results of the prepared sample confirmed the presence of a major olivine phase in addition to few impurity phases including the ion-conducting NASICON-type Li3Fe2(PO)4 and Li2TiFe(PO4)3 phases. Further, the calculated lattice parameter values appear to confirm Ti-doping in LiFePO4. Electron microscopy and particle distribution studies revealed a slight increase in the average particle-sizes in addition to fragmented particles and the presence of surface carbon coating on the sample particles. EDX mapping studies revealed a fair distribution of Ti4+ ions in the prepared sample. When examined as a cathode in a non-aqueous lithium cell at room temperature, LiTi0.08Fe0.92PO4 delivered high specific capacities and good capacity retentions (≤ 2% capacity loss after 50 cycles). Besides, the cathode delivered impressive rate capabilities as specific capacities of 160 and 110 mAhg-1 at 0.1 and 11.4 C, respectively, were retained. Although the average particle-size was slightly higher, the presence of ion-conducting NASICON-type species appear to contribute to the enhanced electrical conductivity and hence to the cathode performance of LiTi0.08Fe0.92PO4.