The Preparation And Modification Property Research Of LiFePO₄Lithiun Ion Battery Cathode Materials

Lithium iron phosphate （LiFePO₄） is regarded as a promising cathode material fornext-generation lithium ion battery, owning to its many merits, such as abundant resources, high theoreticalcapacity （170mAh/g）, suitable voltage plateau （3.4V）, environmental benign, little volume change （6.8%）during the process of charging and discharging, long cycle life, ideal thermal stability, etc. Despite theseadvantages, Its its large-scale application is limited due to low electronic conductivity and low Li+diffusioncoefficients on solid phase, low tap density, poor rate capability; poor low-temperature performance. Inorder to overcome these drawbacks, many efforts were made. The main contents are listed as follows:1. In order to improve the intrinsic electronic conductivity and diffusion coefficient of material,LiFePO₄/C was synthesized by template hydrothermal method using glucose and lithium phosphate ascarbon source and lithium source, respectively. The structure, morphology and electrochemicalperformance of LiFePO₄/C material were characterized. In addition, the low-temperature performances ofLiFePO₄/C were tested at different rate. The results show that the specific capacities of sample reach153.6mAh/g （0.1C） and111.2mAh/g （5C） at25oC, respectively. With the decrease of operation temperature, thespecific capacities of sample decreased to104.4mAh/g （0.1C） and70.3mAh/g （5C） at-20oC, respectively.At-20oC the specific capacity of sample reaches about68.0%（0.1C） and63.2%（5C） of that at roomtemperature.2. In order to further improve the rate discharge properties and low-temperature performance ofmaterial, LiFePO₄was modified by CuO and glucose.The influence of experimental conditions onCu-coated LiFePO₄/C is studied through characterizing the morphology and electrochemical performanceof the material. In addition, the low-temperature performances of Cu-coated LiFePO₄/C were carried out atdifferent rate. At25oC, the specific capacities of sample reach161.6mAh/g （0.1C） and121.1mAh/g （5C）,respectively. With the operation temperature decreased, the specific capacities of sample decreased to112.9mAh/g （0.1C） and84.6mAh/g （5C） at-20oC, respectively. The specific capacity of sample at-20oCreaches about70%of that at room temperature. 3. Fe₂O₃and FeC2O₄.2H₂O were used as iron source to synthesize LiFePO₄/C compound materials,and the rare-earth ions were adopted to improve its electrochemical properties. The morphology andelectrochemical properties of LiFePO₄/C synthesized using different iron source at-20oC were investigatedat different temperature and rate. At25oC, the specific capacities of LiFePO₄/C using Fe₂O₃andFeC2O₄.2H₂O as iron source reach139.6mAh/g,146.1mAh/g （0.1C）, and95.4mAh/g,108.8mAh/g （5C）,respectively. With the operation temperature decreased, the specific capacities of samples decreased to84.8mAh/g,99.8mAh/g （0.1C）, and66.7mAh/g,73.9mAh/g （5C） at-20oC, respectively.