The Synthesis And Performance Modification Research Of LiFePO₄

Lithium-ion battery system has the advantage of high energy density and highpower density, it has been widely used in electric vehicles, mobile devices andmedical devices. The cathode materials occupy a lot of costs in lithium-ion battery,olivine LiFePO4attracts the most interests due to its excellent electrochemicalproperties, as well as its low cost, non-toxicity, excellent thermal stability andenvironment friendliness. However, the application of LiFePO4was limited by themain drawbacks of this material lie on its poor ionic and intrinsic electronicconductivity. So it is particularly important to improve electrochemical properties byimprove electrical conductivity and control particles size of LiFePO4.The crystalline structure, morphology and chemical composition of LiFePO4/Cparticles were characterized by X-ray diffraction and scanning electron microscopy.The objective is to know the morphology and particle size, to analyze the influencesof morphology and particle size on electrochemical performance. In this paper,electrochemical performance was characterized by constant-current charge–dischargetest technique, through the analysis of the electrochemical properties of variousmaterials, and find out the relations between the electrochemical properties andmorphology, particle size. The synthesis and character research methods oflithium-ion battery cathode materials LiFePO4as follows：(1) Lithium-ion battery cathode material LiFePO4/C was synthesized in atraditional way, and ethylene glycol was used as surfactant. In different calciningtemperatures(650℃，700℃，750℃), the effects of ethylene glycol on the crystalgrowth direction and particle morphology were discussed in this paper, the grains ofLiFePO4/C which synthesized with ethylene glycol-assisted present plate-typeaccumulation in700℃. The charge–discharge potential flats present smooth in different current density and the cycle ability is stable.(2) Lithium-ion battery cathode materials LiFe1-xNixPO4/C(x=0.05，0.1，0.15)wassynthesized in a route based on hydrothermal method and subsequent heat treatmentway. The grains size of LiFe1-xNixPO4/C is400to500nm. All the doped samples tookthe shape of edges and corners and had much smaller size. LiFe0.9Ni0.1PO4/C showsbetter reversibility and excellent electrochemical performance than the other materials,it exhibits high capacities of150mAh·g1at0.1C, its electricpotential differencebetween oxidation peak and reduction peak is lower at the scan rate of0.1mV/s,which showed that LiFe0.9Ni0.1PO4/C has better reversibility and higher electricalconductivity.