Preparation And Performance Modification Research Of LiFePO₄ For Cathode Material Of Lithium-ion Battery

LiFePO₄ is new generation cathode material of lithium-ion battery.It has high theoretical capacity,wide electrochemistry window,good heat stability,low cost and choiceness Performance for environment.It has potential for applying in kinds of power supply field.So it is very hopeful material as cathode materials for the future lithium-ion batteries material.We synthesize olive structure LiFePO₄ using in solid-state reaction,hydrothermal reaction,emulsification reaction and sol-carbothermal reduction method.Low electron conductivity and ion diffusivity with inhesion structure improve by C coated and doping metal ion.The structure,morphology and electrochemical performance of the samples were characterized by XRD,SEM,AC impedance,cyclic voltammetry and galvanostatic charge-discharge methods.The results show that emulsification reaction success synthesizes hexagonal-type phase FePO₄,but a few impurity phase appear in LiFePO₄ by using FePO₄ synthesized.There is perfect olive structure LiFePO₄ without any impurity phase by other methods.The sample synthesize by sol-carbothermal reduction method has the highest plateau capacity and capacity preserve ratio.Plateau capacity of hydrothermal reaction and capacity preserve ratio of emulsification reaction are the lowest respectively.Carbon coating can disperse particles of material,decrease impedance of electrode reaction and enhance reversibility.Material after carbon coating can in evidence increase the initial capacity and cycle performances,initial discharge capacity and capacity attenuation ratio aider 20 cycle are 147.9mAh/g,147.9mAh/g,147.9mAh/g and 3.0%,2.7%,2.4%respectively at 0.1C,0.2C,0.5C.Doping metal ion in crystal lattice show that:Samples doping a few Zn²⁺,Sr2⁺,Dy³⁺,Eu³⁺are not change crystal structure of LiFePO₄.The lattice parameters expand in different degree.Cycle performances are improved in evidence compared by original sample.The samples doping 1%Sr2⁺,Zn²⁺initial capacity increase to 139.9mAh/g and 130.4mAh/g respectively.But capacity wilt be decrease by more doping.The Sample doping 1%Dy³⁺has similar initial capacity(90.0mAh/g) compared by original sample.However,The Sample doping 1%Eu³⁺has lower initial capacity(60.1mAh/g)compared by original sample.Carbon coating the sample doping 1%Zn²⁺shows that:Discharge capacity are159.2mAh/g and 137.3mAh/g at 0.1C,0.5C respectively.Capacity attenuation ratio is no more than 5%after 200 cycle.