Synthesis Of Lithium Iron Phosphate Cathode Material Under Vacuum And Its Properties

Lithium ion battery is widely used in practice and obtain great success in business.In this paper,LiFePO4/C materials were synthesized by vacuum sintering method.X-ray diffraction(XRD),scan electron microscope(SEM),electrochemical impedance spectroscopy(EIS)and constant current charge/discharge test were used to study the morphological characterization and electrochemical properties of the composites with different synthetic conditions.First,we compared the differences of LiFePO4/C composite materials prepared by the two-step high temperature solid-state sintering method under argon and vacuum conditions.The LiFePO4/C was synthesized by using Li2CO3,FeC2O4·2H2O,NH4H2PO4 as raw materials and sucrose as carbon source.Then,the optimum conditions for the synthesis of LiFePO4/C by changing the factors such as carbon source adding mode,pre-sintering time,and different carbon source coating were discussed.The experiment results showed that samples were prepared under vacuum condition have the smaller particles and more uniform,good rate and cycle performance.In addition,it can also reduce the consumption of protective gas and production costs.The performance of LiFePO4/C is better when the precursor was sintered at 350 ? for 5 h and heated to 650 ? for 6 h under vacuum condition.Its initial discharge capcity was 156.2 mAh g-1,at a discharge rate of 0.1 C,and the capacity retention rate was 98.9%after 100 cycles at a discharge rate of 1 C.In order to further reduce the energy consumption,the LiFePO4/C cathode materials were synthesized by one step high temperature solid-state sintering method under vacuum condition.The effects of sintering temperature,sintering time,and carbon coating on the properties of the LiFePO4/C composites were discussed.Then,the results demonstrated that the electrochemical performance of LiFePO4/C composites synthesized by heating at 650 ? for 6 h with carbon content of 7 wt%in vacuum condition is the best,and the discharge specific capacity is 154.5 mAh g-1 at a discharge rate of 0.2 C,the specific capacity was 123.6 mAh g-1 at a discharge rate of 1 C and a capacity retention rate of 98.3%after 100 cycles.The electrode materials are synthesized by high temperature solid-state sintering method.Because vacuum sintering furnace contains few oxygen,it's very hard to form surface oxidization problems.The combination of grain boundary will be more solid.Vacuum sintering method also has many advantages,such as low temperature sintering,short sintering time,low gas consumption and so on,so it has become an effective method of electrodes sintering method.