The Research Of New Method And Process For Synthesis Of LFP/C Composite Cathode Materials

Li Fe PO4(LFP) has been used as a cathode material of lithium-ion batteries in industry for years. Because of its excellent performance, it plays an important role in such as electric vehicles, portable mobile device power, energy storage power and other fields. The key reason making LFP popular is that it satisfies the people about battery safety. But in the process of industrial production, there lie some obstacles on the road to high-power battery. For example, the ammonium salt used as a raw material in high temperature solid state method results in the generation of ammonia in production process, which increases the cost of company handling exhaust gas, deteriorates the environment, and threatens the health of producers. Some inherent quality of the lithium iron phosphate also increases the difficulty of application in power battery, such as the low ionic conductivity, electronic conductivity and tap density.This paper explored the production processes and methods of synthesis of LFP/C, in which ammonia would not be generated in the production process. And some materials modifications were also used to improve the electrochemical properties of the battery. The key to avoid exhausting ammonia gas is removing ammonium salt from raw materials. Depending on the material formulation, my work optimized the process parameters in terms of sintering temperature, sintering time, and the amount of carbon coating. XRD, SEM were used to characterize the synthesized materials, and the electrochemical workstation and land tester were used to test the assembled battery.Experiment proved that sucrose was better as a carbon resource in synthesizing LFP/C with Fe PO4 and Li2CO3 as raw materials compared with the citric acid. And on this basis the optimal coating(4.21wt%) amount of carbon from sucrose was obtained by optimizing experiment. After the optimization of sintering schedule, 650 ℃and 10 hours were determined to be the optimal sintering condition, on which the specific capacity could reach up to 160 m Ahg-1 at 0.5C. lithium dihydrogen phosphate was also used as raw materials to synthesis the LFP/C. Different iron source were used to synthesize and offered different electrochemical performance respectively. 680 ℃and 10 h were considered as the optimal sintering condition when the LFP/Cwas synthesized with Li H2PO4 and Li2CO3 as raw materials. The coating methode were investigated for modification of the electrochemical property, and relatively good result was obtained when the LFP was coated by 3.5wt% sucrose-resouce and 1.5 wt% carbon nano tube(CNT). To midify the electrochemical property, lithium vanadium phosphate(LVP) was introduced to synthesize x Li Fe PO4-(1-x)Li3V2(PO4)3 composite material, and higher specific capacity and rate capacity were achieved when the value of x was 0.9 or 0.85. This composite material offered a up to 161.9 m Ahg-1 discharge specific capacity of the first cycle and performed good cycle performance.