Study on electrochemical properties of europium-doped LiFePO4 cathode material for lithium-ion battery
The olivine LiFePO4 cathode material is widely used in the field of electric vehicles and energy storage due to its multiple advantages,however,its low temperature and rate performance are limited by poor electrical conductivity and slug-gish lithium ions diffusion kinetics.Elemental doping is considered to be an effective strategy to improve the properties of cath-ode materials such as multiplicity and low temperature performance.Here,rare earth metal europium-doped LiFe1-xEuxPO4/C cathode materials were synthesized by solid-phase method,and the effects of europium doping on the morphology,structure,and electrochemical properties of LiFePO4 were investigated.The results showed that europium doping could improve the electrochemical properties of LiFePO4/C.The LiFe0.97Eu0.03PO4/C showed the best rate,low temperature and cycling perfor-mance,with its discharge capacity of 95.1 mA·h/g at high rate of 20C(57.7%enhancement compared with that of LiFePO4/C),discharge capacity of 81.5 mA·h/g(73.8%enhancement compared with that of LiFePO4/C)at low temperature of-20℃,and capacity retention rate of 96.43%(26.2%enhancement compared with that of LiFePO4/C)after 200 cycles at 1C.X-ray diffraction(XRD)and scanning electron microscopy(SEM)results showed that the europium doping could in-crease the cell volume of LiFePO4 and decrease the binding energy between Li and O atoms,which could improve the diffu-sion rate of lithium ions.Electrochemical alternating impedance(EIS)test results showed that LiFe0.97Eu0.03PO4/C exhibited the lowest charge transfer resistance,and the highest lithium ion diffusion coefficient that was two orders of magnitude higher than that of the undoped LiFePO4/C,which explained its excellent rate,low-temperature and cycling performance.
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