Studies on elechtrochemical behaviour of zinc-doped LiFePO4 for lithium battery positive electrode
The effects of zinc oxide doping on LiFePO4 have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic measurements. The XRD patterns demonstrate that the samples have the phase of LiFePO4 with an ordered olivine structure indexed to the orthorhombic Pmna space group. Also, XRD patterns show with the presence of LiZnPO4 phase for zinc oxide doped samples. The EIS results showed that the conductivity is enhanced by zinc oxide doping. The 2.5% ZnO-doped LiFePO4 demonstrated higher conductivity than the 1.5% ZnO and 5% ZnO-doped LiFePO4 or the un-doped sample. The CV curves show that 2.5% ZnO-doped LiFePO4 has higher electrochemical reactivity for lithium insertion and extraction than the un-doped material. The mean redox potential is E1/2 = 3.45 V vs. Li+/Li. The first discharge curve of the 2.5% ZnO-doped LiFePO4 shows a mainly flat voltage plateau over the 3.45–3.5 V range, indicating the lithium extraction and insertion reactions between LiFePO4 and FePO4. A specific discharge capacity of about 177 mAh g−1 was achieved, with little decrease during cycling.