Influence of iron phosphate on the performance of lithium iron phosphate as cathodic materials in rechargeable lithium batteries

Iron phosphate (FePO₄·2H₂O) has emerged as the mainstream process for the synthesis of lithium iron phosphate (LiFePO₄), whereas FePO₄·2H₂O produced by different processes also has a great influence on the performance of LiFePO₄. In this paper, FePO₄·2H₂O was produced by two different processes, in which FeSO₄ ferrous and Fe(NO₃)₃·9H₂O ferric were used, respectively. After dehydration under the same conditions, a carbon-coated lithium iron phosphate (LiFePO₄/C) cathode material was synthesized by a high-temperature solid phase method. The results demonstrated that FePO₄·2H₂O contained different impurities due to different raw materials, which led to different particle sizes, specific surface areas, microscopic morphology, and crystal structures. The difference of FePO₄·2H₂O eventually resulted in the difference of LiFePO₄/C cathode materials in micro-morphology and crystal structure, which affected the electrochemical performance. Under the premise of comprehensively considering the cost and quality of FePO₄·2H₂O, improving the purity of FePO₄·2H₂O is an important method to improve the electrochemical performance of LiFePO₄/C cathode materials. Simultaneously, it is also expected to provide theoretical guidance for the preparation of lower-cost and better-quality LiFePO₄/C cathode materials.