Effect of lanthanum and yttrium doped LiFePO4 cathodes on electrochemical performance of lithium-ion battery

The low Li+ diffusivity and electronic conductivity of LiFePO4 (LFP) cathode materials seriously hinder the application in lithium-ion batteries (LIBs) at high-rate. To break these limits, we synthesized the La3+ or/and Y3+-doped LiFePO4 cathode materials with 2-3 nm thick carbon layer prepared using ascorbic acid by hydrothermal method. The material structure was analyzed and characterized by Fourier transform infrared spectroscopy (FT-IR), x-ray spectroscopy (XRD), x-ray photoelectron spectroscopy (XPS), Raman spectroscopy (Raman), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical performance of the materials was studied by electrochemical workstation and battery tester. It was found that the La3+ and Y3+ co-doped LiFePO4 (La·Y-LFP/C) reached a high specific capacity of 160.56 mAh g−1 at 0.2C and still had a specific capacity of 138.27 mAh g−1 after 100 cycles at 5C. The Li+ diffusivity (DLi+) of La·Y-LFP/C was 3.68 × 10–13 cm2 s−1. It was believed that doping La3+ or/and Y3+ can enlarge the lattice of LiFePO4 to widen the migration path for Li+, and help to reduce the electrostatic binding of surrounding atoms to Li+. The calculation results of band gap and state density further confirmed that doping of La3+ or/and Y3+ increased the charge carrier concentration of the material to achieve better Li+ diffusivity and electron conductivity of LiFePO4. Therefore, the La3+ and Y3+ co-doped LiFePO4 cathode material has a good application prospect in high-power LIBs with outstanding electrochemical performance.