The Preparation And Modification Research Of Lithium Ion Battery Cathode Material LiFePO₄

In recent years, with the rapid development of industrialization, all industries have badly demand of energy, and the demand for energy is more and more tending to be low carbon, energy conservation and environmental protection. Lithium ion batteries is a new type of green energy battery, with high working voltage, high energy density, repeated charge-discharge and no memory effect, the advantages of long service life, small self-discharge, environment friendly, have received continuous attention of researchers; while lithium ion battery cathode material is an important part in lithium ion batteries, the study of the cathode materials is also very common. Olivine structure of lithium iron phosphate(LiFePO4) with wide raw material sources, the hygroscopicity, non-toxic, environmentally friendly, high theoretical specific capacity(~ 170 mAh/g) and moderate working voltage(~3.45 V vs. Li+/Li) advantages is becoming the most potential of lithium ion battery cathode material.Firstly, with Fe2O3 as ferric source, acetylene black and glucose as carbon source and reducing agent, using carbon thermal reduction method to prepare the LiFePO4/C cathode material. The structure and electrochemical properties of the prepared materials are investigated with X-ray diffraction, scanning electron microscopy, Raman spectra, galvanostatic charge and discharge. The results indicated that when the mixing ratio of glucose and acetylene black is 1:1, the LiFePO4/C cathode material shows the optimal performance and under the condition of 0.1C ratio, the discharge specific capacity is 152.5mAh/g.Then, doping different content of K in the site of Li, preparing Li1-xKxFePO4(x=0,0.01,0.02,0.03,0.04)cathode material; doping different content of Mn in the site of Fe, preparing LiFe1-yMnyPO4(y=0,0.01,0.03,0.05,0.07)cathode material. The structure and electrochemical properties of the prepared materials are investigated with X-ray diffraction, scanning electron microscopy, Raman spectra, galvanostatic charge and discharge. The results indicated that when x = 0.03, cathode material has the optimal performance and under the condition of 1C ratio, the discharge specific capacity is 124.3mAh/g; when y = 0.03, cathode material has the optimal performance and under the condition of 1C ratio, the discharge specific capacity is 129.9mAh/g.Finally, using the Li0.97K0.03FePO4 and graphene as source material, and to obtained Li0.97K0.03FePO4/graphene cathode material. The structure and electrochemical properties of the prepared materials are investigated with X-ray diffraction, scanning electron microscopy, X-ray photoelectron, Raman spectra, galvanostatic charge and discharge. The results indicated that after the addition of graphene, the Li0.97K0.03FePO4/C cathode material shows the better performance, and under the condition of 1C ratio, the discharge specific capacity of Li0.97K0.03FePO4/C/graphene cathode material is 90.55mAh/g.