Study On Preparation And Modification Of LiFePO₄ Cathode Material

The olivine -type structure LiFePO4 cathode material is now widely considered as most development and application potential of the new generation of lithium -ion battery cathode materials. The LiFePO4 material have a lot of advantages,such as higher theoretical specific capacity ( about 170 mAh / g), more environmentally friendly, relatively good safety and thermal stability. However, limited by its own structure , the material also has low ionic conductivity and electronic conductivity, which ultimately limited its large-scale commercial applications.In this paper, LiFePO4 precursor was synthesized by sol - gel method using FeC12as iron source, powder materials prepared by the use of organic additives though two stage calcination method,The materials were characterized by XRD, SEM and other electrochemical test. The results show that the LiFePO4 synthesized by FeCl2 with the adding of Vc and lauric acid had the largest initial specific capacity of 131.69 mAh/g at 670 ?sintering temperature, and after 20 cycles the capacity retention is above 99%. But have a poor discharge performance after discharge rate raise to 1C, only 101.46mAh / g.At present, the electronically conductive of LiFePO4 have been greatly improved by the application and development of coating technology. Metal ion doping is considered to be the most direct and effective way to improve LiFePO4 material's ionic conductivity. Respectively doping V, Cr, Mn, we can find that ,For the V3+ doped LiFePO4 cathode material, 2% V3+doped LiFePO4 cathode material shows the best discharge and cycling performance. 0.1C and 1C at room temperature of the initial discharge capacity respectively over 133.19 mAh/g and 110.87 mAh/g, and after 20 cycles can still have a higher capacity retention rate; The 2% Cr ion doped LiFePO4 has the best 0.1 C discharge performance,the initial discharge capacity of 0.1C is 165.30mAh/g. but the 3% Cr ion doped LiFePO4 material has a better 1C discharge performance, the initial discharge capacity of 1C can reach 134.73 mAh / g, and have good cycle performance after 20 cycles to maintain 99 percent capacity; The 2% Mn2+ doped LiFePO4 material have the best 0.1C and 1C discharge capacity , were 151.25mA.h / g and 131.26 mAh / g. Also have excellent discharge performance after 20 cycles.