Preparation Of The Lithium-ion Battery Cathode Materials For Lithium Iron Phosphate And Modified

Polyanions Olivine LiFePO4 is a promising cathode material for lithium-ion batteries. This material has many advantages compared with conventional cathode materials, it is environmentally benign, inexpensive, and thermally stable. In addition, LiFePO4 has a large theoretical capacity of 170 mAh/g. However, the intrinsic defects of poor electronic, ionic conductivity and low density have limited its mass application in industry. In order to enhance the electrochemistry capability of material, this paper studied the effects of solid phase synthesis conditions, coating carbon, doping with metal-ion, complex coating and doping on the frame and properties of LiFePO4. The structure, morphology, and electrochemical performance of materials were also studied by means of XRD, SEM, AC impedance and electrochemical techniques.LiFePO4 was synthesized by tow-step solid-state reaction used Li2CO3, FeC2O4·2H2O, (NH4)2HPO4 as raw materials. At first, this paper discussed the characteristics of materials synthesized at different synthesis conditions including different ball-milling medium, different ball-milling time, different synthesis times and different synthesis temperatures. When the materials were ball-milling at 6h in anhydrous ethanol and synthesized at 750℃for 24h, the outcome showed excellent performance. Its initial discharge capacity was 111.63 mAh/g.The effect of coating carbon on the electrochemical properties of result materials was studied. The improvement of capacity and cyclic stability by carbon coating are attributed to the electronic conductivity enhancement, larger specific surface area, and smaller particle size of LiFePO4/C composite material. We found that 5 wt% is the most appropriate ratio among different carbon coating quantities. Its initial discharge capacity was 136.1mAh/g.In this paper, a series of LiFe1-xMnxPO4, Li1-aMgaFePO4 and LiFe1-bMgbPO4 have been synthesized by the best condition. The results showed that low concentration of metal-ion advanced the capability of materials, and 0.20,0.02,0.02 were the best mole ratio respectively. Their initial discharge capacity were 130.2,138.59 and 143.5 mAh/g. The experiment also researched on coating 5 wt% carbon base on metal-ion doping. LiFe0.8Mn0.2PO4/C, Li0.98Mg0.02FePO4/C and LiFe0.98Mg0.02PO4/C initial discharge capacity were 132.08,143.03 and 149.32 mAh/g. And then the mass ratio capacity of samples corresponding increased and the electrochemistry capability of materials improved.