Study On Modified LiFePO₄ Cathode Materials For Li-ion Batteries

Because of the development of electronic equipment and electric mobile have new demands on lithium ion batteries for long cycling life and high theoretical capacity, depend on new energy resources and new material technology cathode material of lithium ion batteries continuously develops new direction.The developments of new cathode material with lower capital, high voltage, pollution-free and long cycling life already become primary research. LiFePO4 as the cathode material has the poformance of its high theoretical capacity (170mAh/g), appropriate voltage (about 3.5V), good stability both at room temperature and high temperature and being environmentally benign and inexpensive,that LiFePO4 has become the uppermost competitor at the cathode material. But the crystalloid configuration restricts LiFePO4 at low electronic conductivity and low lithium ion diffusivity, especially restricting its electrochemical reversibility, increasing the conductance of LiFePO4 is becoming the hotspot. In order to overcome these defaults, the researches focus the way both of carbon coating and ion doping.The cathode material LiFePO4 were obtained by solid-state reaction, and developing by ion doping and then coated carbon. LiFePO4 was characterized by XRD, SEM, TEM, CV analysis. We also studied the electrochemical properties of the product at different conditions.At the preparation by single species ion doping of LiFePO4, Zr ion and Nb ion dopants showed the best electrochemical properties. The both first discharge capacity of above-mentioned samples was over 120mAh/g with a current density of 0.1C.Excellent electrochemical reversibility and cycling stability have been achieved. Lithium iron phosphate contained diversified ion(Mn, Zr, Ni) dopants showed the best electrochemical properties. The first discharge capacity was 121.1mAh/g with a current density of 0.1C. The electrochemical reversibility and cycling stability were not bad.We used the carbon coating the ion doping samples for development which we mentioned. The carbon coating enhanced the discharge capacity, reduced the polarization of the material, tranquilized electrochemical properties and greatly increased the electrochemical properties of the cathode material.And the sample coated carbon which contained Mn, Zr, Ni ion had best performance .Its first discharge capacity was 159mAh/g with a current density of 0.1C. Its electrochemical reversibility was 120mAh/g with a current density of 0.5C.