Synthesis Of The Lithium-ion Batteries Cathode Material LiFePO₄

With the development of mobile electronic equipments, the demand to high capacity of lithium ion batteries increases. Comparing with the anode of lithium ion battery, the cathode material obviously lags. To improve the performance of the cathode is a key method for lithium ions batteries. So far,the conventional cathode materials such as LiCoO2, LiNiO2 and LiMn2O4 etc. are the mainstream materials and they have different short comings not to meet the demand of the power battery.Olivine-struetured LiFePO4 is considered as a promising cathode material for lithium-ion batteries due to its advantages such as environmentally friendliness, abundant raw materials, inexpensive price and high safety. However, it suffers from low conductivity, poor rate Performance and low batch stability, which prevents it from commercial use. To improve the conductivity, electrochemical performances and batch stability of LiFePO4 material, the synthesis condition, morphology, metal doping, carbon coating and electrochemieal behavior of LiFePO4 as cathode materials were studied in detail in this dissertation.The study introduce iron oxalate as iron source for the first time, phosphoric acid and lithium hydroxide as the phosphorus sources and lithium source respectively, and use co-crystallization + mechanical alloying + high-temperature sintering to prepare LiFePO4. The crystalline structure, morphology, carbon contents and electrochemical performances were investigated by XRD, SEM, EDS, thermogravimetric analysis and electrochemical tests. The effects of synthesis time, temperature, the different amount of dispersant and mechanical alloying on electrochemical performances of LiFePO4 material were discussed. In this experiment, the optimized synthesis condition was obtained, the ration of Li/Fe was 1, the amount of carbon in precursor was 3.2%, the pre-sintering temperature was 350℃, the time of sintering was 5h. In high-energy ball milling, the ration of material/ball was 1:50, the rotating speed was 580r/min, the time of ball milling was 3h, the sintering temperature was 650℃, the sintering time was 8h in inert atmosphere. LiFePO4 synthesized by the above-mentioned process has good and pure crystal, and the diameter is between 50~100nm, the specific surface area is 28.9m2/g, has good degree of spherical particles, uniform particle size distribution.LiFePO4 was doped by Mn, Ti and Mg, and the Doped LiFePO4 exhibited the initial discharge capacity of 133.2mAh/g in 2.5~4.2V and at 0.1C rate, 102.2mAh/g at 1C rate, and retaining 99% after 50 cycles.