Preparation And Properties Of LiFePO₄/Graphene Lithium Ion Battery Cathode Material

In this paper, LiFePO₄ cathode materials were synthesized by a solvothermal approach using EtOH/H₂O as a co-solvent and oleic acid as a surfactant. LiFePO₄/GR（graphene） composite electrode materials were prepared by ball milling method. Effect of GR on microstructure and electrochemical performances of LiFePO₄/GR composite electrode materials have been investigated using X-ray diffraction（XRD）, scanning electron microscopy（SEM） and transmission electron microscopy（TEM）, electrochemical impedance spectroscopy（EIS） and cyclic voltammetry（CV） measurements.The microstructure of LiFePO₄/GRcomposite electrode materials were examined.The results show that all the samples have the crystal structure of olivine. The particles of synthesized LiFePO₄ are fine（ about 200 nm） and homogeneous in size for the sample prepared with 3% oleic acid. In addition, the ball-milling is an effective mathod to reduce the particle size of LiFePO₄ electrode materials, the particles of synthesized LiFePO₄/GR composite electrode materials are about 50 nm with 5% GR.The test results of electrochemical performance show that oleic acid can improve the discharge capacity of the electrode material and improve its dynamic performance. The maximum discharge capacity of the sample with 3% oleic acid is 123.6 mAh×g^-1, which is33.9% higher then that of sample without the addition of oleic acid(92.3 mAh×g^-1). The charge transfer resistance Rct is 632.4 Ω for the sample with 3% oleic acid, which is about59.16% lower nearly one-half than the sample without the addition of oleic acid. Coating GR by ball-milling could further improve the discharge capacity and cycle stability of LiFePO₄ electrode materials. The maximum discharge capacity is 163.6 mAh·g^-1 at 0.2 C,which is closed to the theoretical value. The capacity retention is abot 98.6% after 60 circles. In addition, the charge transfer resistance is reduced from 632.4 Ω to 345.3 Ω for the sample with 5% GR.