Effect of iron‑phosphorus ratio on the structure and electrochemical performance of non-stoichiometric carbon-coated LiFePO4 cathode materials

In this paper, non-stoichiometric LiFe x PO 4 /C (x = 0.965, 0.97, 0.975, 0.98) was prepared by high-temperature solid-phase method combined with spray drying. The effects of regulating Fe/P ratio on the crystal structure, morphology and electrochemical properties of LiFePO 4 cathode materials were studied. The structure and morphology of the synthesized materials were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the Fe/P ratio has a great influence on the lattice parameters, micro-stress and degree of antisite defects of LiFePO 4 in structure; it also affects the particle size and carbon layer quality in morphology. Therefore, among the four stoichiometric ratios in the experiment, LiFe 0.97 PO 4 /C has the most stable crystal structure and the best carbon layer quality, and exhibits the best electrochemical performance, with a discharge capacity of 159.23 mAh/g at a 0.1C rate, a discharge capacity of 122 mAh/g at a 5C rate, and a maximum lithium ion diffusion coefficient of 1.22 × 10 −14 cm 2 s −1 . • Fe/P ratio affects lattice parameters and Li/Fe antisite defect levels in LiFe x PO 4 /C. • Fe content affects the particle size, the carbon layer uniformity and graphitization. • Optimal composition (x = 0.97) delivers best electrochemical performance and Li + diffusion.