Lanthanum-doped LiFePO₄ cathode materials for lithium ion battery by citric acid-assisted carbothermal reduction method using acid-washed iron red as raw material

To realize the high value–added utilization of acid-washed iron red, in this paper, acid-washed iron red is used as raw material. Aiming at the problem of low conductivity of iron-based lithium ion batteries (LIBs) LiFePO₄/C materials, different metal ions are doped in the iron position, and the microstructure and electrochemical properties of the obtained material are systematically studied. Here, LiFePO₄/C is synthesized through simple carbothermal reduction method using acid-washed iron red as the iron source. On this basis, La (1%, 2%, 3%) doping modification is carried out. Then doped modification is performed on this basis, preferably 2% La-doped LiFePO₄/C materials. The XRD patterns show that the diffraction peaks of the samples prepared at all doping amounts can be perfectly matched with the standard card (PDF # 40–1499), and there is no impurity peak, all of which are pure phases. According to the refined data, it is clear that minor amount of La has successfully replaced the position of Fe and incorporated into the lattice. Electrochemical tests show that LiFe_0.98La_0.02PO₄/C has the highest charge and discharge capacity of 146.5/138.2 mAh·g⁻¹ in the first cycle at 0.5C, and the reversible specific capacity of 136.5 mAh·g⁻¹ remains after 50 cycles. Furthermore, the first-principles calculations more strongly confirm that La doping can significantly improve the defects of low electronic conductivity of LiFePO₄.