Abstract:With the continuous progress of science and technology and the enhancement of global awareness of environmental protection, the application of clean energy has become an inevitable trend of social development. Lithium iron phosphate battery has shown great application potential in the fields of new energy vehicles and energy storage systems due to its environmental friendliness, long life and high safety. In order to meet the growing demand for high-performance batteries, scientific research institutions and enterprises have invested resources to improve the energy density, charging speed and comprehensive performance of lithium iron phosphate batteries, thus broadening their application scenarios. The core of lithium iron phosphate battery is its cathode material, i.e., lithium iron phosphate (LiFePO4). Its high energy density, long cycle life and excellent thermal stability make it one of the current mainstream cathode materials. However, lithium iron phosphate material itself has some inherent structural defects, such as low electronic conductivity, poor electronic conductivity, low ion diffusion rate and insufficient tap density. These problems limit the high rate charge and discharge performance of the battery, especially at high current density. In order to solve the above problems, researchers have adopted a series of advanced functional modification technologies to improve the electrochemical performance of LiFePO4 materials. Among them, strategies such as material nanocrystallization, surface carbon coating, and element doping are particularly eye-catching. Nanocrystallization of material can significantly shorten the transmission path of lithium ions and electrons, improve the specific surface area of the material, and facilitate the full contact between the electrolyte and the active material, thereby improving the charge and discharge efficiency of the battery. The surface carbon coating can not only improve the conductivity of the material, but also effectively inhibit the agglomeration of particles during charging and discharging, and maintain the stability of the structure. Element doping is to introduce other elements to replace part of Li+, Fe2+ or O2- in LiFePO4 to improve the structure of the material and increase the diffusion rate and electrochemical activity of lithium ions. Specifically, lithium-site doping and iron-site doping are two more studied doping methods. Lithium site doping can improve the diffusion efficiency of lithium ions by increasing the migration channel of lithium ions or optimizing the occupation environment of lithium ions. Fe-site doping may optimize the electronic structure and promote the conduction of electrons by adjusting the ratio of Fe3+/Fe2+. These modification strategies aim to fundamentally solve the performance bottleneck of lithium iron phosphate materials and enhance their application potential in large-scale energy storage and fast charge-discharge scenarios. Based on this, spherical Fe3O4 was synthesized by solvothermal method as a precursor of lithium iron phosphate. The purity and crystallinity of the synthesized materials were confirmed by X-ray diffraction (XRD) analysis. High-quality crystallization is beneficial to improve the conductivity and electrochemical performance of the materials. Field emission scanning electron microscopy (SEM ) and transmission electron microscopy (TEM ) observations reveal the uniformity and dispersion of the precursor particles, which is crucial for the subsequent preparation of high-performance LiFePO4/C composites. X-ray photoelectron spectroscopy (XPS) further verified the correctness of the valence state of the element and the chemical composition of the material, ensuring the effective realization of the modification effect. Electrochemical performance tests show that the initial discharge specific capacity of LiFePO4/C material prepared by spherical Fe3O4 precursor synthesized by solvothermal method is as high as 155.2 mAh/g at 0.1 C rate, and the capacity retention rate is close to 100% after charge and discharge cycles at different rates, showing excellent rate performance and cycle stability. After 200 cycles at 1 C, the capacity retention rate is still as high as 99.2%. Even after 1 000 cycles, the capacity retention rate remains above 97.6%, which fully proves the effectiveness of the modification strategy. In the charge-discharge curve of the reversible specific capacity voltage diagram, the typical charge-discharge platform at 3.5/3.4 V further verifies the good electrochemical performance of the material, and also shows that the optimization of the precursor morphology significantly improves the performance of the final product. The microstructure analysis after electrochemical cycling shows that the agglomeration of LP-FePO4 and LP-B samples on the reaction surface is not significant, which provides the necessary channel space for the rapid diffusion of lithium ions and ensures the continuous output of high performance. The symmetry of the cyclic voltammetry curve reveals the high reversibility of the material during the charge and discharge process, which is a necessary characteristic for high-performance battery materials.