Study Of Lithium Iron Phosphates As Cathode Material For Power Lithium-ion Battery

With the rapid development of power battery and energy storage battery industry, the higher requirements of lithium ion battery on safety and cycle performance have been put forward. Compared with other conventional cathode materials, lithium iron phosphate material has high safety and long cycle performance. Therefore, lithium iron phosphate material becomes the preferred cathode material of power and energy storage lithium ion battery, and has aroused widespread attention and research. However, lithium iron phosphate material still exist problems including high temperature cycle capacity fading, low electronic conductivity and lithium ion diffusivity and so on, which would hinder the lithium iron phosphate material and battery further development and application.In this thesis, aims to improve the electrochemical performance of lithium iron phosphate material and battery. The repair coating, multi-doping and high temperature formation method has been adopted, respectively. Specific research includes the following three parts:(1) For the high temperature cycle capacity fading of olivine-type LiFePO4/C material, the AlPO4nanoparticles have been adopted to repair coating LiFePO4/C selectively. From the result of experiments, the AlPO4repair coating could reduce the Fe2+dissolved from LiFePO4/C material in the LiPF6electrolyte system, could improve the high temperature cycle performance of LiFePO4/C material, and have no adverse effects and damage to the safety of LiFePO4/C material.(2) For the low electronic conductivity and lithium ion diffusivity of olivine-type LiFePO4material, the LiFePO4/C have been prepared by carbothermal reduction method, and co-doped with Ti+Mn elements in Li-site and Fe-site. From the result of experiments, the synergy of Ti+Mn co-doping could improve the electronic conductivity and lithium ion diffusivity of LiFePO4/C material, could improve the rate performance, cycling performance and so on.(3) For the SEI quality would influence the electrochemical performance of lithium ion battery, the lithium iron phosphate battery has been activated with high temperature formation process. From the result of experiments, the high temperature formation could improve the thermal stability of graphite anode SEI film, could improve the high temperature cycle performance of lithium iron phosphate battery, and have no adverse effects to the room temperature cycle performance of battery.