Synthesis And Electrochemical Performances Of LiFePO₄/C For Lithium-Ion Battery Cathode Material

Olive-structured LiFePO₄ is a new kind of cathode material for lithium-ion battery. It has a relatively large theoretical capacity of 170mAh/g. This material is cheap and environmentally friendly, thermally stable in the fully charged state. In this paper, we introduce a novel, low cost and easy-controlled method to synthesize pure LiFePO₄ by using H₃PO₄ to replace NH₄H₂PO₄. In this study, high purity LiFePO₄ cathode material was synthesized through a combination of both solid-state reaction and solution methods. The micro-structures and morphologies of these materials were investigated by XRD, SEM observations. The electrochemical performances have been evaluated by galvanostatic charge-discharge and cyclic voltammetry (CV). The effects of the synthesis parameters on the physico-electrochemical properties of carbon-coated LiFePO₄ have been discussed in detail.Carbon- coating method can effectively control the growing of particle size of LiFePO₄ and fine powder can be obtained. Small particles of carbon tightly wrap the sample LiFePO₄, which can reduce the reaction resisitance of electrode and improve the electrochemical performance. Comparing the doping effect of different carbon resource including lactose, glucose, sucrose and solubility amylum, the results indicate that the coating effect of lactose with 7.5% contents is the best. The specific capacity is 146.9mAh/g discharging with 0.2C current.LiFePO₄ as cathode material is sintered by high temperature solid-reaction method. The particle size of sample minishes with the rising temperature from 550℃to 700℃, while the specific capacity is accordingly increasing. When the tempreture reaches 800℃, the powder becomes reunited and the capacity decreases immediately. The samples sintered at 700℃have the optimal electrochemical performance for its reasonable particle size and narrow distribution.The electrochemical performances of LiFePO₄ by Fe₂O₃,Fe(OH)₃,FeCrO₄,and Fe₃O₄ solid state reaction are discussed. The results show that the electrochemical performances of LiFePO₄ prepared by Fe₂O₃ have a better capacity and cycle performance. The capacity has 146.9mAh/g at a current density of 0.3mA/cm².LiFePO₄ doped with TiO₂,Cu(CH₃COO)₂,ZrO₂ was synthesized by solid state reaction. The result indicates that the Zr doped take from electrochemical performances of LiFePO₄, but Cu and Ti doped show better electrochemical performances. The circle performance and high-rate property of sample are improved accordingly.In this paper, we introduce a novel method to synthesize pure LiFePO₄ by using H₃PO₄ to replace a part of NH₄H₂PO₄. High purity LiFePO₄ cathode material was synthesized through a combination of both solid-state reaction and solution method. The products with starting materials H₃PO₄,NH₄H₂PO₄ in a stoichiometric molar ratio 2:8 possessed excellent electrochemical performance. The capacity has 156.3mAh/g at a current density of 0.3mA/cm². The crystalline structure, granularity and morphology of particles of the sample are investigated by X-ray diffraction (XRD), particle diameter measure system, scanning electron microscope (SEM).