Structur And Properties Of LiFe_1-xCu_xPO₄for Lithium Iron Battery Cathode Materials

LiFePO₄/C was synthesized as the cathode material for lithium ion battery byhigh-temperature solid-phase reaction in this paper, and the samples were modified bydoping copper acetate and copper oxide as different copper sources, and the effect ofdifferent copper sources on LiFePO₄material structure and electrochemical performancewas studied.The LiFePO₄/C composite material precursor was tested by means ofthermogravimetric apparatus, and the temperature for synthesization was determinedaccording to TG-DTA curves. The reaction time was determined through currentcharge-discharge. The structure and electrochemical behavior of the materials areinvestigated using a wide range of techniques such as X-ray diffraction （XRD）, particlesize analysis, scanning electron microscope （SEM）, energy dispersive spectroscopy （EDS）,galvanostatic charge/discharge and electrochemical impedance spectroscopy （EIS）.The results show that doping a small amount of Cu²⁺ion have no effect on the crystalstructure of LiFePO₄, effectively reduce the grain size, improve the discharge capacity,and enhanced the cycling stability. The LiFePO₄/C composite material had betterelectrochemical properties in700℃at17h.The optimal doping of copper acetate metal is4%in the LiFe1-xCuxPO₄/C samplesto achieve good electrochemical performances with the maximum discharge capacity of154.2,113.7,98.6and85.4mAh g-1at rates of0.2C,0.5C,1C and2C, respectively. At0.2C rate, the initial discharge capacity reached to70.4,79.9,101.8,154.2,153.6and127.3mAh g-1at-20,-10,0,20,40and60℃, respectively.The optimal doping of copper oxide metal is3%in the LiFe1-xCuxPO₄/C samples toachieve good electrochemical performances with the maximum discharge capacity of150.4,130.7,118.5and93.6mAh g-1at rates of0.2C,0.5C,1C and2C, respectively. At0.2C rate, the initial discharge capacity reached to76.5,120.6,121.5,150.4,152.2and72.7mAh g-1at-20,-10,0,20,40and60℃, respectively. According to the results ofXRD and EDS, it is inferred that Cu²⁺ion occupies Fe²⁺ion site in LiFePO₄/C.