Study On Modified LiFePO₄by Polydopamine As Cathode Materials For Lithium Ion Batteries

Lithium iron phosphate （LiFePO₄） is used as a positive material for lithium ion batteriesdue to its low cost, high theoretical specific capacity, high operating voltage and goodchemical stability as well as excellent cycle life and safety. It will be potential candidate tobe used as power batteries for electric vehicles and state grid. However, the low electronicconductivity and lithium ion diffusion rate have limited its practical applications.In this thesis, polydopamine had been introduced to the surface of LiFePO₄due to itsstrong adhesion. The structure and morphology were characterized by FT-IR, UV, XRD,TEM and FSEM. The charge-discharge cycling tests were also investigated.It was found that: LiFePO₄which was treated in0.1mg/mL of dopamine solution （pH=8.5） had better cycle performance. There were uniform coating layers on the surface ofLiFePO₄after treated in0.5mg/mL of dopamine solution （pH=8.5） and above. However,the electrochemical performance was not improved.The polydopamine coated LiFePO₄which was being sintered at700°C for2h in Ar/H₂（95/5） mixed gas atmosphere showed better initial discharge capacities at a current rate of0.2C.The composite LiFePO₄/Ag had an initial discharge capacity of136mAh/g at a currentof0.1C when the ratio of nano-silver was5wt.%. However, the coated LiFePO₄with nanosilver did not show better performance at60°C, which was caused probably by theinhomogenous coating of nano siliver.