Structure And Electrochemical Properites Of Re(Sm, Yb, Eu) Doped Lithium Iron Phosphate Cathode Materials

LiFePO₄/C and its composites were prepared by the methods of high-temperaturesolid-phase reaction in this paper. The samples were modified by ball milling and dopingRE （M=Sm, Eu,Yb） metal ions. The synthesis process conditions were optimized throughthe thermal analysis of precursor by TG-DTA.The structure and grain size of samples werestudied by XRD, FE-SEM and EDS method. The electrochemical performances includingdischarge capacity, cycle stability and rate dischargeability were measured. Themicrostructure of LiFe_1-xM_xPO₄/C （M=Sm, Eu, Yb） composites were examined. It isshown that all the samples have the crystal structure of olivine. With increasing thesubstitution content, the particles of synthesized LiFe_1-xM_xPO₄/C are fine andhomogeneous in size. The doping of M （M=Sm, Eu, Yb） increases I111/I131and c.Electrochemical test of LiFe_1-xM_xPO₄/C （M=Sm, Eu, Yb） composites show that thedoping of M （M=Sm, Eu, Yb） can improve the electrochemical performance of the sample.The optimal doping content of RE metal is that x=0.08in the LiFe_1-xM_xPO₄/C samples toachieve high discharge capacity and good cycle performances. The samples with x=0.08delivers the discharge capacity of152.2,143.5,159.4mAh/g at20℃. EIS testdemonstrates that the doping of Sm can improve the dynamic performance, decreases thecharge transfer resistance Rctand increases the exchange current density i0greatly.The temperature effect indicate that the discharge capacity increase with the rise oftemperature in-20～40℃. The sample with x=0.08exhibits the largest discharge capacityand the best cycle stability at40℃.the cycle stability decreases drastically at60℃.