Modification Of Lithium Iron Phosphate Cathode Material Synthesized By Using A New Iron Source

Recent years,lithium iron phosphates used in lithium ion batteries exhibit many advantages for their high theoretical capacity,environment-friendly excellent cyclic stability and low cost.Lithium iron phosphates are considered one of the most promising cathode materials in the field of lithium ion batteries.However,lithium iron phosphates also possess many disadvantages,such as,its low density,poor electrical conductivity and bad diffusion performance of lithium ions.This dissertation synthesized lithium-rich lithium iron phosphate cathode materials by using a high temperature solid state method.The physicochemical properties of the as-prepared samples are measured by using many advanced techniques,such as XRD,charge-discharge test,cyclic voltammograms,A.C.impedance,SEM,FTIR and so on.The main research results are as following:1.The series of doped Ru lithium iron phosphates from a general tube furnace synthesized by the optimization of sintering temperature and sample composition.Among them,the sample with the theoretical composition of the Li1.04Fe0.96Rb0.038PO4/C synthesized at 770? exhibits the best electrochemical properties,which exhibits the capacities of 135.9,111.2,94.7,78.3 and 60.4mAh·g-1 at the 1st cycle,and 126.2,107.5,92.5,78.3 and 56.3mAh·g-1 at the 50th cycle,while discharged at the 2C,5C,10C,20C,50C rate,respectively.Its stored sample exhibits the capacities of 121.2mAh·g-1(at room temperature),149.2mAh·g-1(at 55?)and 89.9mAh·g-1(-22?),respectively.Doping rubidium ion improves high-rate discharge performance of lithium iron phosphates.2.The series of doped Ru lithium iron phosphates from an improved rolling furnace synthesized by the optimization of sintering temperature,heating rate,sintering atmosphere and volume ratio of N2 and CO.Among them,the sample with the theoretical composition of the Li1.04Fe0.96Rb0.038PO4/C synthesized at 600?(heating rate:1?/min,sintering atmosphere:N2 and CO volume ratio 1:0.06)exhibits the best electrochemical properties,which exhibits the capacities of 140.0,115.0,105.2 and 82.3mAh·g-1 at the 1st cycle,and 138.6,117.3,101.land 70.8mAh·g-1 at the 40th cycle,while discharged at the 2C,5C,10C,20C rate,respectively.Its stored sample exhibits the capacities of 131.9mAh·g-1(at room temperature),147.7mAh·g-1(at 55?)and 97.2mAh·g-1(-22?),respectively,after the sample stored for a year.Compared with tube furnace,the sample synthesized from improved rolling furnace exhibits better high-rate discharge performance,storage performance and high and low temperature properties.3.The series of doped lithium iron phosphates from an improved rolling furnace synthesized by doped different metal ions at 600 C(heating rate:1?/min?sintering atmosphere:N2 and CO volume ratio 1:0.06).The sample with the theoretical composition of the Li1.04Fe0.96La0.038PO4/C synthesized at 600?(heating rate:1?/min,sintering atmosphere:N2 and CO volume ratio 1:0.06)by the improved rolling kiln exhibits the best electrochemical properties,which exhibits the capacities of 131.9,118.3,105.1,87.5mAh·g-1 at the 1st cycle,and 143.0,117.7,105.5,75.0mAh·g-1 at the 50th cycle,while discharged at the 2C,5C,10C,20C rate,respectively.The sample exhibits the capacities of 157.5mAh·g-1(at 55?)and 103.7mAh·g-1(-22?),respectively.Doping titanium ion improves high-rate discharge performance and high and low temperature properties.