Enhanced electrochemical properties of LiFePO4 cathode materials by Co and Zr multi-doping

Abstract

Nanostructured Co and Zr multi-doped Li1−xZrx/4Fe0.99Co0.01PO4 (x=0.005, 0.01, 0.015, 0.02) composites are synthesized via a conventional solid-state reaction route. The effects of Co and Zr multi-doping on the structure, morphology and electrochemical performance of LiFePO4 are systematically studied. It is clear that Co and Zr multi-doping maintains the olivine structure of LiFePO4 and significantly enhances its electrochemical performance. The multi-doped samples exhibited a high capacity and enhanced cycle stability as compared with the pristine LiFePO4 cathode material. All the multi-doped samples showed an initial discharge capacity of ~130mAhg−1 at 0.1C. The capacity fading rate decreased with the increase of Zr content, which can hold around 90% after 30cycles in the sample with x=0.02. The redox process was enhanced by Zr-doping, which showed the highest intensities of redox peaks in the sample with x=0.01. The related calculation verified that Zr and Co multi-doping could effectively decrease the charge transfer resistance and increase the lithium ion diffusion velocity of LiFePO4, especially the sample with x=0.01 had the smallest charge transfer resistance, largest exchange current density, and highest lithium-ion diffusion coefficient.