Preparation And Characterization Of LiFePO₄/3DG Composite By Hydrothermal Method

Olivine?LiFePO₄?has a great potential for development of lithium-ion battery cathode material due to its high theoretical specific capacity,high cyclability,high-temperature behavior,long cycling life,good safety performance,low cost,and being environmentally friendly,attracting extensively more and more attention by people.In this paper,the synthesis of lithium iron phosphate composite material was studied by hydrothermal-carbothermal reduction method and freeze drying by two different composite methods.Researches on the structure,morphology and electrochemical performances of the materials were carried out with XRD,SEM,Raman,EIS,CV curve and charge-discharge tests.The details are as follows:?1?A good spherical FePO₄?FP?precursor was prepared by controlling some factors such as the ratio of Fe source to P source,reaction temperature,duration time and pH.?2?The Optimum condition LiFePO₄/carbon composite was successfully synthesized by mixing by mixing a certain amount of Lithium acetate,10 wt%ascorbic acid and 10 wt%glucose as carbon source,the precursors were prepared at 350?for 4 h,and then calcined at 350?for 10 h.?3?The graphite oxide?GO?gel was synthesized from graphite powder using improved redox method,50 mL of aqueous solution of dispersed GO?4 mg/mL?was ultrasonicated, subsequent hydrothermal and freeze drying.finally,three dimensional porous graphene material was prepared.?4?In the FePO₄ precursor,LiFePO₄ material has excellent electrochemical performance by adding 5 wt%of the content of 3DG full grinding,carbothermic reduction of the system, 3DG-LiFePO₄/C composite delivers a first discharge specific capacity of 163.6 mAh/g at a rate of about 0.2 C.The prepared composite also exhibits an excellent cycling performance,with capacity remains 99.5%over 50 cycles.And the initial discharge specific capacity at different rates of 0.5 C,1 C,2 C,5 C,10 C are respectively 152.7 mAh/g,142.3 mAh/g,127.4 mAh/g,103.7 mAh/g,83.9 mAh/g,after 100 cycles at a rate of 1 C,the capacity of the material is still maintained at about 91.7%.?5?By controlling mass ratio of GO to FePO₄ was 1:5,the LiFePO₄/3DG/C composite materials with good electrochemical performance,such as the rate performance and cycle performance,which were synthesized by the uniform encapsulation of iron phosphate with three-dimensional graphene,were successfully prepared by carbothermic reduction.SEM image of the LiFePO₄/3DG composite shows clearly the spherical FePO₄ is well embedded in the aperture of 3DG and coated evenly.The first discharge specific capacity of the material was 165.1 mAh/g at a rate of 0.2 C,capacity remains 99.3%over 50 cycles and the initial discharge specific capacity at different rates of 0.5 C,1 C,2 C,5 C,10 C are respectively 153.8 mAh/g,144.7 mAh/g,130.4mAh/g,110.1 mAh/g,91.3 mAh/g,after 100 cycles at a rate of 1 C,the capacity of the material is still maintained at about 99.6%.