Due to its good safety performance, long cycle life and low cost, lithium ferrous phosphate is the preferred cathode material for power and energy storage lithium-ion batteries. It is mainly used in electric bicycles, electric motorcycles, electric vehicles, electric tools, etc. On the basis of fully understanding and analyzing the current preparation methods of LiFePO4, we proposed the idea of synthesizing LiFePO4 materials by solid-liquid method. Specifically, during the synthesis process, the spherical precursor iron phosphate or ammonium ferrous phosphate is used as a solid phase, and the lithium source (lithium hydroxide or lithium acetate) is used as a liquid phase. Chemical reactions are carried out at the solid-liquid interface to finally produce the target product spherical LiFePO4. For ferrous ammonium phosphate, the above process can also be called ion exchange, that is, lithium ions and ammonium ions are exchanged. This method organically combines the advantages of solid phase method and liquid phase method, and effectively overcomes their shortcomings. Compared with the solid-solid interface reaction, the solid-liquid interface reaction area is large and the reaction substances are in full contact. Preliminary experimental results show that the synthesized material has high purity, good batch properties, low reaction temperature and short time, and is energy-saving and environmentally friendly. Features: (1) The solid-liquid method has low sintering temperature and short time. It only needs to be heat treated at 700 ° C for 2 hours to obtain a LiFePO4 material with complete crystallinity. Battery tests show that the material has good electrochemical properties and has a specific discharge capacity at 0.1C.(After deducting about 2 wt % of carbon), it is close to the theoretical value of 170mAh/g, especially with good high current characteristics. The discharge capacity at 10C exceeds 120mAh/g and the discharge capacity at 24C exceeds 90mAh/g. This value is easy to obtain for large batteries of the 18650 class. However, the laboratory button battery we used remains at around room temperature even when discharged at high current, which fully reflects the complete crystallization of the material synthesized by the solid-liquid method. There are few unreacted impurities and the material has high electrochemical activity. (2)Another significant advantage of this method is that the batch performance of the material is good. There are almost no batch differences in multiple batches of kilogram samples prepared in the early stage, which is very important for mass production. (3)The method avoids the precursors of lithium dihydrogen phosphate and ferrous oxalate, but uses iron phosphate or ammonium ferrous phosphate as the precursor, which is not only easy to prepare, but also low in price. It is combined with a short-term energy-saving solid-liquid method to synthesize lithium ferrous phosphate materials, and truly achieves the goals of high performance and low cost for power and energy lithium ion batteries. Furthermore, by controlling the particle size and morphology of the precursor, lithium ferrous phosphate for different purposes, such as power-based and energy-based materials, can be obtained.