Studies on electrochemical behaviour of zinc-doped LiFePO_4 for lithium battery positive electrode

摘要

The effects of zinc oxide doping on LiFePO_4 have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvano-static measurements. The XRD patterns demonstrate that the samples have the phase of LiFeP04 with an ordered olivine structure indexed to the orthorhombic Pmna space group. Also, XRD patterns show with the presence of LiZnPO_4 phase for zinc oxide doped samples. The EIS results showed that the conductivity is enhanced by zinc oxide doping. The 2.5 percent ZnO-doped LiFePO_4 demonstrated higher conductivity than the 1.5 percent ZnO and 5 percent ZnO-doped LiFePO_4 or the un-doped sample. The CV curves show that 2.5 percent ZnO-doped LiFePO_4 has higher electrochemical reactivity for lithium insertion and extraction than the un-doped material. The mean redox potential is E_(1/2) = 3.45 V vs. Li~+/Li. The first discharge curve of the 2.5 percent ZnO-doped LiFePO_4 shows a mainly flat voltage plateau over the 3.45-3.5 V range, indicating the lithium extraction and insertion reactions between LiFePO_4 and FePO_4. A specific discharge capacity of about 177 mAhg~(-1) was achieved, with little decrease during cycling.