Study On The Performance Of LiFePO₄Synthesized By Hydrothermal Method

LiFe1-xMxPO4/C (M=Sm, Yb, Nd, Eu) used as cathode materials for lithium ionbattery were synthesized by hydrothermal method. The structure and morphology ofsamples were characterized by XRD, SEM and TEM method. Electrochemicalperformances were tested by galvanostatic charge/discharge, electrochemical impedancespectroscopy (EIS) and cyclic voltammetry (CV).XRD, SEM and TEM analyses reveal that all the samples exhibit a single phase ofLiFePO4with an olivine structure and space group of Pnma, while an appropriate amountof rare earth elements(M=Sm,Yb,Nd,Eu) doping causes change of the cell parameters andthe cell volumn, as well as the refining of particles. For example, doing Sm lead to thedecrease of a. While the value of a for the sample x=0.02is1.0324nm, which is obviouslysmaller than the value for a of the sample un-doped(1.0352nm); The particle size of thematerial x=0.02is about100nm, which is1/10times than that of the sample un-doped(1μm, approximately).Electrochemical performance tests show that rare earth elements doping can improvethe discharge capacity and cycle stability. Such as, sample of Sm doping amount of0.01,0.02,0.04,0.06have maximum discharge capacity of120.3mAh.g-1,154.4mAh.g-1,151.1mAh.g-1,148.4mAh.g-1, respectively, while the sample without Sm is101.0mAh.g-1. Especially for the sample x=0.02has a maximum discharge capacity of154.4mAh.g-1, which is about1.5times than that of the sample un-doped, and it has thedischarge capacity of142.8mAh.g-1and the capacity retention of92.5%after30cycles.EIS tests indicate that rare earth elements doping can decrease the value of Rct. Whenthe doping amount is0.02for those elements (Sm, Yb, Nd, Eu), the value of Rctaredecreased from815.2Ω to107.4Ω，110.1Ω，252.6Ω，169.5Ω, respectively.CVtests show that rare earth elements doping can improve the electrochemical reversibilityof LiFePO4/C as the cathode material of lithium-ion battery.