Synthesis And Electrochemical Property Study Of Lifepo₄ As Cathode Materials

The olivine-structured orthophosphate LiFePO₄ has become a highly promising cathode material for using in lithium ion batteries because of its high operating voltage (³.5V vs. Li/Li+) and large theoretical gravimetric capacity (¹70mAh·g^-1), as well as its low cost, non-toxicity and safety advantages. However, its low intrinsic conductivity is one impediment to the wider use of LiFePO₄. Corbon Coating has been used to overcome this obstacle, synthesize LiFePO₄/C composites showing good electrochemical performance while attempting to minimize the amount of carbon in the composite.In this thesis, LiFePO₄/C was prepared by solid-state reaction. The micro-structure,morphological characterization and electrochemical properties were investigated by TG-DTA,XRD,SEM,CV,EIS and galvanosatic charge-discharge. Technological conditions of this synthesis method were investigated systematically and optimized.In this thesis, the crystallinity of sample rising with the increasing temperature from 550⁷50℃,while the specific capacity is improving accordingly. The sample synthesized at 750℃have the optimal electrochemical performance for its reasonable particle size and narrow distribution.Based on our research, comparing the coating effect of different carbon content, the coating effect of amylum with 10wt% contents has the best electrochemical performance. The specific capacity is 135 mAh·g^-1 discharging with 0.2C current and rate capability of the carbon-coated materials is better than of uncoated. The specific capacity is nearly 120 mAh·g^-1 discharging at 1.0C current, which reaches to 70% theoretical capacity.