Lithium-Ion Insertion Kinetics of Na-Doped LiFePO_4 as Cathode Materials for Lithium-Ion Batteries

摘要

Na-doped Li_(1-x)Na_XFePO_4(x = 0, 0.05, 0.1, and 0.2) materials were synthesized by a simple high-temperature solid-state method. The structure, morphology, and kinetic performances of the samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). XRD indicates that all samples are in accordance with the standard LiFePO_4 with olivine structure. SEM reveals that the particle size of all samples is about 1 to 2 μm. CV exhibits that Na doping obviously improves the reversibility and dynamic behaviors of lithium intercalation and dein-tercalation. EIS shows that Na doping decreases the charge transfer resistance of LiFePO_4 and improves the lithium diffusion coefficients. It can be concluded that Na doping results in lower electrode polarization and higher lithium-ion diffusion coefficient, which can effectively improve the kinetic performance of LiFePO_4.